Curr Hepatology Rep DOI 10.1007/s11901-014-0229-3

FATTY LIVER DISEASE (SA HARRISON AND J GEORGE, SECTION EDITORS)

Role of Insulin Resistance and Diabetes in the Pathogenesis and Treatment of Nonalcoholic Fatty Liver Disease Paola Portillo & Sahzene Yavuz & Fernando Bril & Kenneth Cusi

# Springer Science+Business Media New York 2014

Abstract Nonalcoholic fatty liver disease (NAFLD) is now a frequent cause of consultation for hepatologists and other health care providers. To a significant extent, this is because the metabolic abnormalities associated with obesity and type 2 diabetes mellitus (T2DM) promote liver disease and are more prevalent than ever before. Clinicians must be aware that insulin resistance and hyperglycemia are believed to worsen the natural history of NAFLD, fueling inflammation, hepatocyte injury (ballooning) and fibrosis. End-stage liver disease and hepatocellular carcinoma (HCC) develop more often in this setting. Interventions that reverse insulin resistance and hyperglycemia, may halt or ameliorate the disease process. Therefore, a comprehensive approach is needed for the successful management of these patients that addresses both, the liver-specific and the associated metabolic conditions. This review focuses on the mechanisms by which insulin resistance, and both lipo- and glucotoxicity, are believed to contribute to the development of NAFLD, and on the treatments tested in obese patients with T2DM and NAFLD, as a means to assist practitioners managing these complex patients.

Keywords Fatty liver . Nonalcoholic fatty liver disease (NAFLD) . Steatosis . Nonalcoholic steatohepatitis (NASH) . Treatment . Type 2 diabetes mellitus . Obesity . Insulin resistance . Hyperglycemia . Lipotoxicity . Glucotoxicity . Pioglitazone, Vitamin E . Obeticholic acid . Metformin . Exenatide . Liraglutide P. Portillo : S. Yavuz : F. Bril : K. Cusi (*) Division of Endocrinology, Diabetes and Metabolism, University of Florida, 1600 SW Archer Road, room H-2, Gainesville, FL 32610, USA e-mail: [email protected] S. Yavuz : K. Cusi Malcom Randall VAMC, Gainesville, FL, USA

Introduction Nonalcoholic fatty liver disease (NAFLD) has become the most common chronic liver disorder of adults worldwide [1•]. The diagnosis is based on evidence of hepatic steatosis, either by imaging or by histology, and absence of secondary causes for hepatic triglyceride accumulation (such as alcohol abuse, medications, genetic diseases, other). Histologically, the disease is divided into nonalcoholic fatty liver (NAFL), when hepatic steatosis is not associated with evidence of hepatocellular injury (hepatocyte ballooning), or as NASH, when associated with hepatic steatosis, inflammation and ballooning, with or without fibrosis [2••]. At a time when obesity is reaching epidemic proportions, it is not surprising that the vast majority of patients with NAFLD have metabolic risk factors such as insulin resistance, dyslipidemia, hypertension or diabetes mellitus, and that cardiovascular disease (CVD) is the most common cause of mortality in this population [3••, 4••]. The true prevalence of NAFLD remains unknown because most of the epidemiological information is based upon diagnostic tools with low sensitivity, such as plasma aminotransferase levels (AST/ALT). Moreover, few studies have focused on obese patients, or those with diabetes. In the most comprehensive studies to date, the prevalence of NAFLD in the general population has been estimated to be between 34 % [5] to 46 % [6••]. A caveat is that these population studies originated from tertiary care centers that could have inevitably biased the sample, and perhaps to some extent, enriched with obese and diabetic patients. By liver magnetic resonance and spectroscopy (MRS), it is estimated that more than 60 % of obese non-diabetic patients have NAFLD [5], consistent with our own experience over the past 10 years [7•, 8, 9, 10••]. In patients with diabetes, studies using liver ultrasound from Brazil [11], Italy [12], India [13], and South Korea [14] have estimated that ~70 % of patients have NAFLD. In our experience systematically using MRS to screen patients over the

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past 10 years, ≥80 % of patients with T2DM have hepatic steatosis (in many cases confirmed with a liver biopsy). Liver biopsy is considered the gold standard but has certain limitations, depending on sample size, right versus left liver lobe and the number of independent readings of the liver biopsy samples [2••, 15, 16]. Studies focusing on patients with T2DM with liver histology are of limited value given their small sample size, but taken collectively, the estimated prevalence of NASH has been reported to range between 63–87 %, and that of any fibrosis at 22–60 % [17]. In our hands, in a predominantly obese population, the prevalence of NASH has been ~50 % in patients with T2DM and NAFLD. The high prevalence of NASH in T2DM has major clinical implications because several studies have now reported that NASH is associated with a shorter lifespan [2••, 4••], and the presence of diabetes appears to worsen the natural history of the disease (see below). For instance, in a 13-year longitudinal study of patients with NASH by Ekstedt et al. [16], the survival of patients with NASH was significantly reduced not only from liver-related causes, including end-stage liver disease (5.4 %) and HCC (2.3 %), but also from increased cardiovascular events, consistent with a large body of literature reviewed elsewhere [2••, 4••, 18].

Prevalence of Insulin Resistance and Diabetes in NAFLD Insulin resistance is almost universal in patients with NAFLD, and the disease is (rather simplistically) frequently quoted as the “hepatic manifestation of the metabolic syndrome”. However, this would be strictly correct if insulin resistance is accepted as the universal underlying mechanism for the metabolic syndrome (or as we would prefer to label it, the “insulin resistance syndrome”), although this remains controversial. Moreover, there are many definitions of the insulin resistance syndrome (from ATPIII, WHO, AACE, EASD, other) and patients classified as meeting the more commonly used ATPIII criteria (prediabetes, dyslipidemia, and/or central obesity) many times have NAFLD without meeting such a definition. For instance, NASH may develop in non-obese subjects without the “metabolic syndrome” [19], but typically such patients have adipose tissue (as well as muscle and liver) insulin resistance. Finally, as discussed below, there is also controversy as to whether hepatic steatosis and NASH develop secondary to peripheral insulin resistance, or intrinsic hepatic signaling defects may be the initiating event, rather than a consequence, of altered whole body insulin action [20]. T2DM is a common comorbidity among patients with NAFLD but estimates of the prevalence of prediabetes (defined as either a fasting plasma glucose [FPG] between 100125 mg/dl, HbA1c between 5.7-6.4 % or a 2-hour plasma glucose between 140-199 mg/dl during an oral glucose tolerance test [OGTT]) and T2DM (defined as either a FPG

≥126 mg/dl, HbA1c between ≥6.5 % or a 2-hour plasma glucose between ≥200 mg/dl during an OGTT) in patients with NAFLD are uncertain. The prevalence of abnormal glucose metabolism in patients with NAFLD has been reported to be in the range of ~10 to ~30 % when only based on selfreporting or a fasting plasma glucose level [21]. However, when more systematic screening is performed with an OGTT, the gold-standard for the diagnosis of diabetes, several studies have reported much higher rates [3••]. Recently, Ortiz-Lopez et al. [22] found, when screening 118 obese patients for diabetes with an OGTT, that having NAFLD was associated with severe insulin resistance and a three-fold increase in the rate of prediabetes and T2DM compared to healthy controls without NAFLD well matched for obesity. It is also important to highlight that the presence of NAFLD often precedes and appears to promote the development of T2DM. Recently, Sung at al [21], reported in a prospective 5-year study in 11,091 patients that only 0.7 % of individuals without a baseline fatty liver developed T2DM compared to 4 % of individuals with hepatic steatosis on liver ultrasound. Even after adjustment for multiple variables including baseline glucose concentration, the hazard ratio (HR) for developing T2DM was two-fold higher in individuals with baseline fatty liver. In another recent study in 38,291 Korean non-diabetic subjects followed for 5.1 years, the HR for diabetes depending on the severity of NAFLD ranged between 2.0 (mild NAFLD) to 4.7 (moderate-severe NAFLD) after applying multivariate-adjusted models [23]. Similar results have been reported in other large longitudinal studies [18]. Taken together, these findings suggest that a diagnosis of fatty liver should prompt screening for T2DM (at least with a HbA1c), specially in patients at high-risk of developing diabetes (obese, with features of the metabolic syndrome or with a family history of T2DM), although a fatty liver may be even more predictive in non-obese subjects [18].

Impact of Diabetes in the Natural History of NAFLD It is difficult to separate insulin resistance from T2DM, but both factors clearly play a role in the natural history of NAFLD in this setting. Several studies have described the association between these entities and NAFLD, and the topic has been the subject of in-depth reviews [18, 24, 25]. Patients with T2DM have an increased risk of developing NASH, and both fibrosis and cirrhosis occur more often [24, 26–28]. Some studies have reported that as many as 55 to 66 % of patients with NAFLD had advanced fibrosis when diabetes and obesity were present, and that cirrhosis may develop without clinical evidence of liver disease and even normal plasma aminotransferases [29–31]. In the Nonalcoholic Steatohepatitis Clinical Research Network –

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NASH CRN – patients with definite NASH, or fibrosis, were much more likely to have diabetes [32, 33]. Two recent longitudinal studies, by Pais et al. [34••] and Stepanova et al. [35], have recently confirmed that diabetes is the single most important risk factor of future poor prognosis in patients with NASH. There has also been considerable interest on the underlying mechanisms for diabetes increasing by two- to four-fold the odds of developing cirrhosis and HCC [36]. However, the risk of HCC appears limited to NASH patients largely with cirrhosis [36]. The 10-year mortality from cirrhosis in NASH is on the magnitude of 20 % [37]. How hyperglycemia, insulin resistance or other factors may promote worse liver disease, and ultimately HCC, remains unclear. However, clinicians must be aware that diabetes and its associated metabolic defects, as summarized below, considerably increase the risk of liver-related mortality in patients with NASH and an aggressive treatment approach in this population is warranted.

abnormalities [42]. A number of defects in mitochondrial function have been described in vivo [43••, 44, 45] and in humans [46, 47, 48••] in NAFLD/NASH, also in support of the notion of intrinsic hepatocyte abnormalities, but this cannot be truly dissected from acquired (secondary) defects. It should be noted that hepatocyte triglyceride accumulation by itself does not promote insulin resistance. Differently than in diet-induced obesity, induction of hepatic steatosis in several unique mice models (i.e., overexpression of hepatic TG synthesis, inhibition of hepatic VLDL secretion or βoxidation) is not associated with insulin resistance (reviewed in [3••]). Subjects with familial hypobetalipoproteinemia have a fatty liver but normal hepatic and muscle insulin sensitivity [49]. In summary, except for specific KO animal models (which may or may not truly apply to human disease) or rare genetic syndromes [49], it is not possible to clinically isolate NAFLD from insulin resistance. This makes it difficult to establish the precise relationship between these two entities and to fully understand their role in the pathogenesis of NAFLD.

Role of Metabolic Factors in the Development of NAFLD Adipose Tissue Insulin Resistance and “Lipotoxicity” Multiple mechanisms are involved in the pathogenesis of NAFLD. Given the focused nature of this review, we will touch only on the metabolic factors known to play an important role in the development of the disease (insulin resistance, lipo- and glucotoxicity, and other closely related metabolic insults), and refer the reader to a comprehensive review on the many current mechanisms causing NAFLD and NASH [4••]. Insulin Resistance in NAFLD: Cause or Consequence? Extensive experimental and clinical evidence supports the close relationship between insulin resistance and NAFLD [20, 38, 39]. However, there is still considerable debate on whether hepatic steatosis causes or promotes systemic insulin resistance, or vice-versa [20, 40], with evidence for as well as against each hypothesis. A “liver-centric” view would suggest that hepatic triglyceride accumulation, in the setting of obesity and the “insulin resistance” syndrome, impairs insulin’s ability to suppress hepatic glucose production (HGP). This would stimulate insulin secretion aimed at maintaining HGP and the plasma glucose concentration within the normal range. According to this view, the resulting chronic hyperinsulinemia could promote the subsequent development of systemic insulin resistance, as shown experimentally in humans [41]. However, this does not rule out the possibility that intrinsic defects of skeletal muscle insulin signaling in obesity or T2DM may result in systemic insulin resistance, chronic hyperinsulinemia and promotion of hepatic steatosis. Studies in hyperphagic, obese rats in which reduced hepatic mitochondrial function precedes hepatic steatosis, being followed by systemic insulin resistance, suggest a role for early liver

A more “adipocyte-centric” view would propose that systemic insulin resistance could be secondary to increased fatty acid turnover, ectopic lipid deposition in insulin-sensitive tissues, stimulation of hepatic lipogenesis in combination with altered mitochondrial fatty acid oxidation and/or hepatic VLDL secretion, and whole body defects in energy expenditure. A spectrum of defects at multiple levels, largely shown in a number of animal models but also in clinical experiments, demonstrate that the delicate liver metabolic balance can be tilted toward hepatic fat accumulation by any of the above [3••, 4••, 39, 50]. Chronic overfeeding leads to hypertrophy and relative hypoxia of adipocytes, macrophage infiltration, and triggers local and systemic inflammation. When chronically exposed to an excessive supply of FFA, either from endogenous or exogenous sources, hepatocytes accumulate multiple toxic lipid intermediates (diacylglycerols, ceramides, acylcarnitines, other), with activation of inflammatory pathways and endoplasmic reticulum stress, mitochondrial dysfunction (as mentioned earlier), and generation of reactive oxygen species. This is associated with an inability of the mitochondria to increase oxidation in proportion to the increased fatty acid supply [43••, 44] generating a state of hepatic “metabolic inflexibility” where mitochondrial function is chronically “on” and unable to further increase oxidation upon demand, as recently also shown in patients with NAFLD [48••]. Taken together, these factors lead to hepatocyte necroinflammation, and ultimately, activation of a liver fibrotic response and risk of end-stage liver disease. A large body of experimental and clinical data reviewed elsewhere [3••, 39, 50] supports the notion that hepatic (and

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skeletal muscle) insulin resistance could result from excess fatty acid flux to the liver from dysfunctional adipose tissue, so typical of obesity and T2DM. For instance, a low-dose intravenous lipid infusion can, within only 48 hours, cause muscle and liver insulin resistance in healthy non-obese subjects [51, 52], and metabolically healthy obese (MHO) individuals are usually insulin-sensitive and do not develop NAFLD [8, 53]. The genetic fabric for this can also be seen in insulin-sensitive young obese co-twins that do not differ from their lean co-twin in liver fat, plasma lipids, blood pressure, systemic inflammation or adipose tissue transcriptomics [54•]. Of note, defects in insulin sensitivity may develop early-on and be very subtle. For instance, when Bril et al. [55] recently compared presumably insulin-sensitive patients with NAFLD to well-matched controls without NAFLD using detailed glucose turnover measurements, patients with steatosis already had mild insulin resistance in adipose tissue, as well as in skeletal muscle. When Lomonaco et al. [8] compared 207 well-matched subjects with and without NAFLD, hepatic steatosis metabolic parameters, liver aminotransferases, hepatic insulin resistance, and liver fibrosis (but not necroinflammation) deteriorated as quartiles of adipose tissue insulin resistance progressed from the least to the more severe. Obese MHO patients had none of the above. Future work on the metabolic and molecular defects of early stages of obesity may help develop better strategies to prevent NAFLD in high-risk patients. Role of Hyperinsulinemia in NAFLD It has been known for some time now that adaptation to insulin resistance is associated with increased insulin secretion, but much less consideration has been given to the role of chronic hyperinsulinemia in NAFLD and NASH. Understanding the role of hyperinsulinemia is important as it is associated with the development of T2DM and cardiovascular disease (CVD) [56], as well as hepatocellular carcinoma [57], together, leading causes of morbidity and mortality in p a t i e n t s w i t h N A S H . E x p e r i m e n t a l l y, c h r o n i c hyperinsulinemia in healthy subjects may induce peripheral (primarily muscle) insulin resistance [41]. At a molecular level, hyperinsulinemia promotes the transcriptional upregulation of genes that control hepatic de novo lipogenesis and VLDL secretion [40, 45, 50, 58, 59], among them sterol regulatory element binding protein 1-c (SREBP1c), via stimulation of the mTOR complex. Unfortunately, studies examining the contribution of impaired insulin clearance in T2DM have been inconsistent, some [60, 61], but not all [62], reporting it to be impaired. In a recent study, Bril et al. [10••] reported on insulin secretion and clearance in 208 patients in the first study examining patients with biopsy-proven NASH. Impaired insulin clearance, rather than hypersecretion of insulin, appeared to be the

main driver of hyperinsulinemia in this population. Both, hepatic and peripheral, insulin clearance were abnormal. Decreased hepatic insulin clearance developed even with mild steatosis and had no correlation with the severity of hepatocyte necrosis, inflammation and fibrosis. Taken together, blunting the lipogenic and atherogenic potential of insulin by reversal of chronic hyperinsulinemia may be important in the management of these patients. Decreased Adiponectin Secretion Adiponectin is the most abundant and adipose-specific adipokine, and exerts a myriad of beneficial metabolic effects that span from reversal of insulin resistance to many other antidiabetic and antiatherosclerotic effects [63]. Its release is generally down-regulated under conditions associated with insulin resistance such as obesity, NAFLD, polycystic ovary syndrome, T2DM, and even in healthy non-obese subjects with a family history of T2DM [3••]. The adipokine sensitizes hepatocytes to the effects of insulin, suppresses the expression of the glucose-6-phosphatase (one of the main regulators of gluconeogenesis) and increases the phosphorylation of the insulin receptor, as well as the downstream insulin-signaling steps. Impaired plasma adiponectin levels are typically associated with hepatic and systemic insulin resistance [64]. Administration of adiponectin to steatotic mice dramatically increases hepatic fatty acid oxidation and can completely reverse hepatomegaly, steatosis and inflammation [65]. Adiponectin reverses the impaired mitochondrial respiratory chain activity associated with hepatic steatosis in animal models of NAFLD (reviewed in [63]). Therefore, low levels of adiponectin appear to be a permissive risk factor for the development of NAFLD and ectopic fat accumulation, being typically low in these patients, even when matched for adiposity [66]. A number of studies suggest that decreased adiponectin contributes to the development of steatohepatitis and fibrosis by altering lipid metabolism and hepatocyte, Kupffer cell and stellate cell biology [64]. At least in part, the beneficial effects of pioglitazone therapy in patients with NASH may be related to their ability to increase plasma adiponectin concentration and this may happen as soon as 12 weeks after initiating treatment [66]. Hyperglycemia and Glucotoxicity It is well established that prolonged exposure to elevated glucose concentrations can have toxic effects on a broad spectrum of cells, such as endothelial cells, retinal pericytes, messangial cells in the renal glomerulus, neurons, pancreatic β-cells and many others, with glucose-sensing pathways that may translate into pro-apoptotic signals [67]. Hyperglycemia is a major risk factor for the development of microvascular complications, but it remains unclear whether the combination

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of diabetes and NAFLD worsens outcomes. Only a few crosssectional studies have looked at microvascular complications in relation to NAFLD. However, there is some suggestion, that in both type 1 diabetes mellitus (T1DM) and in T2DM, the presence of NAFLD may increase the risk of chronic renal disease [18]. At the level of the liver, hyperglycemia can cause oxidative stress by several mechanisms. Glucose may induce apoptosis in liver cells through increased oxidative stress related to the formation of hydrogen peroxide and hydroxyl radicals that cause hepatocyte lipid peroxidation [68]. The mitochondrial membrane, rich in lipids, is very vulnerable to lipid perioxidation-derived products like malondialdehyde. Advanced glycosylation end-products (AGEs), also called glycotoxins, play an important role in the development of micro-and macrovascular complications in diabetes [69]. They are the final reaction products of protein with sugars produced through a Maillard reaction. Their interaction with cell surface receptor (RAGE) is associated with the development of inflammation. Both Kupffer and hepatic stellate cells have RAGE receptors [70]. Hyogo et al. [71], reported that livers of NASH patients stained positively for glyceraldehydederived AGE and that their plasma levels were significantly higher in patients with steatohepatitis compared to those with simple steatosis or healthy controls. There is also reported an inverse correlation with plasma adiponectin. Kimura et al. [72], described in a small trial that atorvastatin decreased plasma AGEs and improved liver histology (NAFLD activity score: NAS) in patients with NASH, at least in part, due to this mechanism. However, this must be taken with caution as statins rarely have been reported to improve necroinflammation in patients with NASH (reviewed in [73•]). Fructose is a simple carbohydrate found in fruits, but in modern diets fructose corn syrup is abundant in processed foods and in the form of soft drinks. Growing evidence points to the harmful effects on metabolism of high chronic consumption of this type of sugar. More recently, there has been an increasing concern for fructose as an important cause for the development of NAFLD [74]. High fructose-based diets promote de novo lipogenesis and activate inflammatory pathways (i.e., c-jun N-terminal kinase [JUN]-signaling pathway) that can induce hepatocyte apoptosis. Recently, the importance of the cell surface glucose and fructose transporter GLUT8 (Slc2A8), highly expressed in liver and other oxidative tissues, was demonstrated in mice manipulated to lack GLUT8 and having diminished fructose uptake, de novo lipogenesis and hepatic steatosis [75]. Ouyang and Diehl [76] reported that patients with biopsy-proven NAFLD had a two- to three-fold higher consumption of fructose compared to well-matched controls. They also found increased fructokinase gene expression, an essential enzyme for fatty acid synthase, a key lipogenic enzyme. Abdelmalek et al. [77] also reported a modest correlation between higher fibrosis stages and weekly fructose intake in patients with NASH.

However, most studies examining the role of fructose have been small, of short duration (≤4 weeks), and of overall poor quality. Chiu et al. [78], performed a meta-analysis from 13 trials involving 260 healthy subjects and found no effect of fructose in isocaloric-diet trials, but a positive effect for fructose to induce NAFLD and increase plasma ALT in studies with hypercaloric fructose-based diets. The authors interpreted this data relating the effect more closely to excess energy than fructose itself. Clearly more work is needed in this area to understand the role of fructose in NAFLD. The molecular mechanisms by which hyperglycemia may worsen hepatic insulin resistance in NAFLD or exacerbate steatohepatitis have not been carefully examined. However, the activation of glucose-6-phosphatase (G6Pase), a key enzyme of endogenous glucose production, is a well-established defect in diabetes. Hyperglycemia appears to induce the production of reactive oxygen species (ROS) and, in parallel, induce G6pc promoter activity. This was abolished in the presence of small interfering RNA that targeted either the hypoxia-inducible factor (HIF)-1α or the CREB-binding protein (CBP) [79]. An experimental elevation of glucose increases the interaction of HIF-1α with CBP and the recruitment of HIF-1α to the G6pc promoter, exacerbating hepatic glucose production and hyperglycemia. Glucose also regulates the transcription of many genes encoding important lipogenic/glycolytic pathways, such as the transcription factor carbohydrate responsive element-binding protein (ChREBP) [80]. Glucose can contribute to lipotoxicity by stimulating ChREBP and increasing the activity of liver-pyruvate kinase (L-PK) [59]. This enzyme is fundamental for the conversion of pyruvate to citrate in the mitochondria, in order to then be transported to the cytosol to feed fatty acid synthesis. In contrast, at the clinical level, we have not found that modest hyperglycemia in patients with T2DM (i.e., HbA1c between ~6.5 % to ~8.0 %) frankly worsens histopathology in patients with NASH [22], in contrast to the clear role that insulin resistance, obesity or the presence of diabetes per se play. Also, there is very limited clinical data that good glycemic control per se (independent of changes in insulin resistance, exercise or weight loss interventions) improves liver histology in patients with steatohepatitis, as detailed below. Treatment Given the brief nature of this review, we refer the reader to recent in-depth reviews examining the many pharmacological agents that have been studied in patients with NAFLD/NASH [2••, 81•, 82•]. We focus here on pharmacological agents that have been tested (or are undergoing testing) to reverse insulin resistance and/or hyperglycemia. Table 1 summarizes the most relevant information. At the present time, other than pioglitazone and obeticholic acid (OCA) (see below), only

Curr Hepatology Rep Table 1 Effect of antidiabetic medications during RCTs in patients with prediabetes or T2DM Treatment

Mechanism of action

AST/ALT

Steatosis by US/CT

Liver fat by MRS

Liver histology

Metformin [82•, 84] Pioglitazone [95, 96] Exenatide [102, 107] Insulin# [115] Canagliflozin [111]

Insulin-sensitzer PPARγ agonist GLP-1 agonist Replacement Inhibits renal glucose reabsortion

↓ ↓ ↓ ↔ ↓^

↓ ↓ Unknown Unknown Unknown

No data ↓ ↓ ↓ No data

Unchanged Improved Unknown Unknown Unknown

#

No RCT currently available in patients with NAFLD

^In patients without a diagnosis of NAFLD by imaging techniques

vitamin E has proven to be clearly effective in adults with NASH, but it has not been studied in a RCT in patients with T2DM [83]. Dietary Interventions in Obese Patients with T2DM and NAFLD Lifestyle intervention is a fundamental aspect for the comprehensive management of patients with insulin resistance or T2DM. A number of clinical trials have demonstrated the impact of weight loss in NAFLD (recently reviewed in [4••, 81•, 84]), but few have focused on patients with T2DM [85, 86]. Among these, Lazo et al. [86] conducted a 12-month dietary and exercise intervention study in 102 obese middleaged patients with T2DM. The control group received only general nutrition and exercise information during group sessions. The intensive lifestyle intervention arm lost more weight (-8.5 vs. -0.05 %; p<0.01) and 50.8 % of patients had a decrease in hepatic steatosis, compared to 22.8 % of the control group (p=0.04). Glycemic control was also better in the intensive lifestyle group (A1C: -0.7 % vs. -0.2 %; p= 0.04). Underscoring the importance of weight loss to the reduction in hepatic steatosis, both variables were closely correlated. Reversal of steatosis was especially significant when weight loss was greater than 10 %. Exercise, either aerobic or resistance training, can also significantly ameliorate insulin resistance, hyperglycemia and hepatic steatosis in patients with T2DM, as reported by Bacchi et al. [87••]. The investigators randomized 31 sedentary adults with T2DM and NAFLD to either aerobic exercise or resistance training for 4 months. After training, mean plasma glucose, insulin resistance and hepatic fat content, all decreased to a comparable degree with both training approaches (-32.8 % vs. -25.9 %, respectively; NS between groups, both p<0.001 vs. baseline). The impact of lifestyle intervention on liver histology has been best examined by Promrat et al. [88] in a 48-week randomized control trial (RCT) in obese diabetic and nondiabetic patients with biopsy-proven NASH. Intensive lifestyle intervention led to an average weight loss of 9.3 % (versus 0.2 % in the control group, p=0.003) compared to a

control group that received only basic education on diet and exercise. This was associated with significant histological (NAS) improvement in 72 % of patients (versus 30 % in controls, p=0.03). Improvement in NAS correlated with the degree of weight reduction (r=0.497, P=0.007), especially in those with a weight loss ≥7 %. Both diabetics and nondiabetics appeared to receive similar benefit. Recently, Eckard et al. [89], using different combinations of diet and exercise, confirmed the beneficial effects of lifestyle intervention in insulin-resistant, obese patients with NASH, although weight loss was overall modest. In summary, weight loss achieved through lifestyle intervention leads to improvements in liver histology in NASH.

Pharmacological Agents that Induce Weight-loss Lifestyle intervention alone aimed at significant and sustainable weight loss (≥5 %) is difficult to achieve, so there is increasing interest in pharmacological agents that may help achieve and maintain weight loss. Of the weight-loss agents available in the United States, only orlistat (Xenical®) has been tested in RCTs in NAFLD. It is a potent pancreatic lipase inhibitor that decreases fat absorption. Zelber-Sagi et al. [90] reported a modest decrease in aminotransferases levels and hepatic steatosis, while Harrison et al. [91] found a reduction in steatosis and inflammation if weight loss was ≥9 %, but in neither study was mean weight loss or histological changes statistically different compared from placebo. Two new weight-loss agents await testing in insulinresistant, obese patients with NAFLD/NASH: Lorcaserin (Belviq®), a selective serotonin 2C receptor agonist with anorexigenic effects through the activation of the neuronal propiomelanocortin system, and the sympathomimetic amine phentermine combined with the antiepileptic topiramateextended release (Qsymia®) [92]. In a recent meta-analysis, the proportion of patients achieving at least 5 % of total body weight loss was between 37 to 47 % for lorcaserin, and 67 to 70 % for phentermine plus topiramate-extended release (at maximal doses).

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Metformin The intracellular target(s) of the insulin-sensitizer metformin have long been debated and involve AMP-activated protein kinase (AMPK)-dependent and independent (largely mitochondrial) pathways [93]. Since first suggested to be beneficial in a small group of patients (n=20) with steatohepatitis [94], it has been possibly the most tested pharmacological agent for patients with NAFLD/NASH. However, it is now clear from a number of RCTs that the biguanide has minimal effects on necroinflammation and fibrosis in NASH [2••, 3••, 82•, 84], and its use is not recommended to this end. Pioglitazone The thiazolinediones (TZD) are ligands for the nuclear receptor peroxisome proliferator-activated receptor ϒ (PPAR ϒ), a transcriptor factor that regulates a broad spectrum of pathways involving intermediary metabolism, adipocyte differentiation and systemic inflammation [3••]. Pioglitazone reverses liver, skeletal muscle, and adipose tissue insulin resistance. The TZD was the first agent proven in a RCT to improve liver histology (hepatic steatosis, inflammation, and ballooning) in patients with NASH [95]. These results have been expanded in a recent 18-month RCT of pioglitazone treatment versus placebo in 101 patients with prediabetes or T2DM and biopsyproven NASH [96]. Pioglitazone therapy resulted in a marked improvement in steatosis, inflammation and ballooning (all p <0.001 versus placebo), and to some extent, hepatic fibrosis. These effects have persisted in patients who continued treatment for up to 3 years. As reviewed elsewhere [97], potential side effects of pioglitazone include weight gain, an increase in the risk of osteoporosis (primarily in females) and bladder cancer (especially in males), and water retention with development of congestive heart failure in patients with unrecognized diastolic dysfunction. However, pioglitazone has also been reported to reduce the risk of certain types of cancers (liver, breast) [98••, 99] and decrease the rate of cardiovascular events in patients with T2DM [100]. Incretin-mimetics Glucagon-like peptide-1 (GLP-1) is an incretin hormone secreted by L-cells of the small intestine in response to food ingestion [101]. The peptide has multiple aspects that make it attractive for use in obese patients with T2DM: it stimulates insulin secretion, inhibits excessive postprandial glucagon release, promotes satiety, and induces weight loss. It is believed that incretin-mimetics hold potential in NAFLD from the combination of weight loss, improved glycemic control and potential effects on hepatic GLP-1 receptors [3••]. Reduction of hepatic steatosis through direct GLP-1mediated signaling pathways has been reported in animal

models [102, 103], although this remains highly controversial [101]. In humans, data is limited to case reports [104] or small, uncontrolled series where results were inconclusive [105]. In a pilot study, we observed that twice-daily exenatide improved liver steatosis in well-controlled patients with T2DM [106]. Liraglutide is another GLP-1 analogue that significantly improves glycosylated hemoglobin concentrations according to a series of large RCTs from the Liraglutide Efficacy and Action in Diabetes (LEAD) pivotal trials. An analysis of those studies in relation to hepatic endpoints has been recently published [107]. Using individual patient data, the authors combined results from six phase-III RCTs of 26-week duration. Out of 4442 patients, 50.8 % patients had an abnormal ALT at baseline (mean ALT 34 IU/L in females; 47 IU/L in males). Liraglutide 1.8 mg (maximal dose) significantly reduced ALT in these patients vs. placebo (-8.20 vs. -5.01 IU/L; p=0.003) in a dose-dependent manner with no significant differences versus placebo at lower doses of the drug. Of note, the positive effect observed on ALT vanished after adjusting for liraglutide's reduction in weight and HbA1c. In the LEAD-2 sub-study that included CT-measurements of hepatic steatosis, liraglutide at 1.8 mg showed a trend toward improving hepatic triglyceride content versus placebo (p=0.07). Once again, the difference became nonsignificant when correcting for changes in weight and HbA1c. In summary, while liraglutide may improve liver aminotransferase levels in patients with T2DM, the effect appears largely attributable to weight loss and improved glycemic control. Results from a RCT with liver histology as the primary endpoint will soon provide a definite answer as to the role of liraglutide in patients with NASH [108].

Inhibitors of Sodium Glucose Co-transporters (SGLTs) The sodium-glucose cotransporter (SGLT) 2 plays an important role in renal glucose reabsorption and inhibitors are a new class of oral agents representing a novel strategy for the control of hyperglycemia in T2DM [109, 110]. The SGLT2 is located in the proximal segment of the renal proximal tubule, and is responsible for nearly 90 % of active renal glucose reabsorption. Plasma glucose levels decreased with SGLT2 inhibitors as the threshold for glucosuria is reduced and urinary glucose excretion increases, resulting in a mild osmotic diuresis and net caloric loss. While they have not been carefully tested in patients with T2DM and NAFLD, there is some suggestion that they may decrease hepatic fat accumulation. For instance, improved glycemic control and modest weight loss after 52 weeks of treatment with canagliflozin is associated with a mild reduction in plasma ALT levels [111]. However, this was not observed after dapagliflozin treatment in a recent study [112].

Curr Hepatology Rep

Obeticholic Acid It is known that farnesoid X receptors (FXRs) play an important role in the regulation of bile acid synthesis and hepatic glucose metabolism [113]. The FXR ligand obeticholic acid (OCA) is a semisynthetic derivative of the bile acid chenodeoxycholic acid. In a short-term proof-of-concept study [114•], treatment with OCA improved insulin sensitivity and reduced markers of liver inflammation and fibrosis in patients with T2DM. Recently, 72 weeks of treatment with OCA (25 mg/day) was reported to lead to significant histological improvement compared to placebo in a large multicenter RCT in patients with NASH (FLINT trial; Intercept Pharmaceuticals press release Jan. 9, 2014)

create the “perfect storm” for the development of hepatic triglyceride accumulation and steatohepatitis. However, intrinsic, genetically-determined hepatic insulin signaling defects may also play a role in the development of NASH and the impairment of peripheral insulin action. Clinicians must be aware that insulin resistance and hyperglycemia may negatively impact the natural history of steatohepatitis, and accelerate progression to more advanced liver disease, and even HCC. Better control of these factors, with the combination of lifestyle intervention and a rapidly expanding list of pharmacological agents, will likely lead to improved long-term outcomes. The clinician must view NAFLD within its unique metabolic context, integrating current knowledge about these conditions into a comprehensive treatment plan for the successful management of these complex patients.

Insulin Therapy Insulin may inhibit excessive adipocyte lipolysis characteristic of insulin resistant-states, such as obesity, and ameliorate hyperglycemia in T2DM. Taken together, these metabolic effects may reduce substrate flux to the liver (FFA and glucose), and help control aberrant hepatic lipogenesis and steatosis. However, the data on the role of insulin in NAFLD or NASH is very limited. Juurinen et al. [115], reported that optimizing glycemic control with basal insulin therapy for 7 months in patients with T2DM led to a modest decrease in liver triglyceride content (from 17 to 14 %, p<0.05) and improved hepatic insulin sensitivity, with the changes in both variables being closely correlated. Having more severe steatosis at baseline was associated with more severe insulin resistance and the need for larger insulin doses. Cusi et al. (unpublished) treated 30 middle-aged patients with T2DM with bedtime insulin detemir for 3 months, followed by premeal insulin aspart for another 3 months. Improvement in HbA1c (from 9.0 % to 6.7 %; p<0.001) led to a significant ~50 % reduction in liver fat measured by MRS by 3 months (to ~12.0 %, p<0.01), but with no further reduction by 6 months. In conclusion, good glycemic control in patients with T2DM reduces hepatic steatosis, although its impact on hepatocyte necroinflammation remains to be carefully studied. In a small study from Japan [116], about a third of patients with T2DM who were switched from oral diabetic agents to insulin therapy had an improvement of liver fibrosis. However, glycemic control also improved, being more strongly associated with the change in liver fibrosis than with the use of insulin.

Conclusion The metabolic abnormalities of obesity and T2DM, characterized primarily by insulin resistance/hyperinsulinemia, hyperglycemia, lipotoxicity and low plasma adiponectin levels,

Acknowledgments This work was supported by the American Diabetes Association (to K. C.) and a VA Merit Award (1 I01 CX000167-01; to K. C.). Compliance with Ethics Guidelines Conflict of Interest Paola Portillo-Sanchez, Sahzene Yavuz, Fernando Bril and Kenneth Cusi declare no conflicts of interest. Human and Animal Rights and Informed Consent This article does not contain any studies with human or animal subjects performed by any of the authors.

References Papers of particular interest, published recently, have been highlighted as: • Of importance •• Of major importance 1.• Loomba R, Sanyal AJ. The global NAFLD epidemic. Nat Rev Gastroenterol Hepatol. 2013;10:686–90. 2.•• Chalasani N, Younossi Z, Lavine JE, Diehl AM, Brunt EM, Cusi K, et al. The diagnosis and management of non-alcoholic fatty liver disease: practice Guideline by the American Association for the Study of Liver Diseases, American College of Gastroenterology, and the American Gastroenterological Association. Hepatology. 2012;55:2005–23. Recent guidelines elicited on the management of NAFLD are must-read for clinicians taking care of these patients. 3.•• Cusi K. Role of obesity and lipotoxicity in the development of nonalcoholic steatohepatitis: pathophysiology and clinical implications. Gastroenterology. 2012;142:711–25. e716. A comprehensive review on the mechanisms by which obesity predisoses to NAFLD, including how NAFLD relates to dyslipidemia, T2DM and cardiovascular disease. The review also elaborates on treatments, in particular on the role of pioglitazone, for this condition. 4.•• Torres DM, Williams CD, Harrison SA. Features, diagnosis, and treatment of nonalcoholic fatty liver disease. Clin Gastroenterol Hepatol. 2012;10:837–58. A must-read state-of-the-art review on the epidemiology, pathogenesis and treatment to NAFLD.

Curr Hepatology Rep 5.

Browning JD, Szczepaniak LS, Dobbins R, Nuremberg P, Horton JD, Cohen JC, et al. Prevalence of hepatic steatosis in an urban population in the United States: impact of ethnicity. Hepatology. 2004;40:1387–95. 6.•• Williams CD, Stengel J, Asike MI, Torres DM, Shaw J, Contreras M, et al. Prevalence of nonalcoholic fatty liver disease and nonalcoholic steatohepatitis among a largely middle-aged population utilizing ultrasound and liver biopsy: a prospective study. Gastroenterology. 2011;140:124–31. The best ultrasound-based screening study assessing the prevalence of NAFLD and NASH. 7.• Lomonaco R, Ortiz-Lopez C, Orsak B, Finch J, Webb A, Bril F, et al. Role of ethnicity in overweight and obese patients with nonalcoholic steatohepatitis. Hepatology. 2011;54:837–45. The first study that carefully matched Hispanic and Caucasian patients for adiposity by dual X-ray absorptiometry in order to carefully examine the role of ethnicity without this confounding factor. 8. Lomonaco R, Ortiz-Lopez C, Orsak B, Webb A, Hardies J, Darland C, et al. Effect of adipose tissue insulin resistance on metabolic parameters and liver histology in obese patients with nonalcoholic fatty liver disease. Hepatology. 2012;55:1389–97. 9. Ortiz-Lopez C, Lomonaco R, Orsak B, Finch J, Chang Z, Kochunov VG, et al. Prevalence of prediabetes and diabetes and metabolic profile of patients with nonalcoholic fatty liver disease (NAFLD). Diabetes Care. 2012;35:873–8. 10.•• Bril F, Lomonaco R, Orsak B, Ortiz-Lopez C, Webb A, Tio F, Hecht J, Cusi K. Relationship between disease severity, hyperinsulinemia and impaired insulin clearance in patients with nonalcoholic steatohepatitis (NASH). Hepatology. 2014. doi:10. 1002/hep.26988. Novel study that examines the etiology of hyperinsulinemia in NAFLD and the role of steatohepatitis and fibrosis in the developemnt of impaired insulin clearance at the level of the liver and peripheral tissues. 11. Leite NC, Salles GF, Araujo AL, Villela-Nogueira CA, Cardoso CR. Prevalence and associated factors of non-alcoholic fatty liver disease in patients with type-2 diabetes mellitus. Liver Int. 2009;29:113–9. 12. Targher G, Bertolini L, Padovani R, Rodella S, Tessari R, Zenari L, et al. Prevalence of nonalcoholic fatty liver disease and its association with cardiovascular disease among type 2 diabetic patients. Diabetes Care. 2007;30:1212–8. 13. Prashanth M, Ganesh HK, Vima MV, John M, Bandgar T, Joshi SR, et al. Prevalence of nonalcoholic fatty liver disease in patients with type 2 diabetes mellitus. J Assoc Phys India. 2009;57:205–10. 14. Kim S-KK, Choi YJ, Huh BW, Park SW, Lee EJ, Cho Y-W, et al. Non-alcoholic fatty liver disease is associated with increased carotid intima-media thickness only in type 2 diabetic subjects with insulin resistance. J Clin Endocrinol Metab. 2014. doi:10. 1210/jc.2013-4133. 15. Rockey DC, Caldwell SH, Goodman ZD, Nelson RC, Smith AD. Liver biopsy. Hepatology. 2009;49:1017–44. 16. Vuppalanchi R, Unalp A, Van Natta ML, Cummings OW, Sandrasegaran KE, Hameed T, et al. Effects of liver biopsy sample length and number of readings on sampling variability in nonalcoholic Fatty liver disease. Clin Gastroenterol Hepatol. 2009;7: 481–6. 17. Doycheva I, Patel N, Peterson M, Loomba R. Prognostic implication of liver histology in patients with nonalcoholic fatty liver disease in diabetes. J Diabetes Complicat. 2013;27:293–300. 18. Bril F, Cusi K. Nonalcoholic fatty liver disease in type 2 diabetes mellitus: Current controversies and future directions. Diabetes Care. 2014; (in press). 19. Bugianesi E, Gastaldelli A, Vanni E, Ganbino R, Cassader M, Baldi S, et al. Insulin resistance in non-diabetic patients with nonalcoholic fatty liver disease: sites and mechanisms. Diabetologia. 2005;48:634–42.

20.

21.

22.

23.

24.

25. 26.

27.

28. 29. 30.

31.

32.

33.

34.••

35.

36.

37.

38.

Vanni E, Bugianesi E, Kotronen A, De Minicis S, Yki-Jarvinen H, Svegliati-Baroni G. From the metabolic syndrome to NAFLD or vice versa? Dig Liver Dis. 2010;42(5):320–30. Sung KC, Kim SH. Interrelationship between fatty liver and insulin resistance in the development of type 2 diabetes. J Clin Endocrinol Metab. 2011;96(4):1093–7. Ortiz-Lopez C, Lomonaco R, Orsak B, Finch J, Hardies J, Tio F, et al. Impact of glucose tolerance status on insulin sensitivity and disease severity in patients with NAFLD. Diabetes. 2012;61 suppl 1:A1761. Chang Y, Jung HS, Yun KE, Cho J, Cho YK, Ryu S. Cohort study of non-alcoholic fatty liver disease, NAFLD fibrosis score, and the risk of incident diabetes in a Korean population. Amer J Gastroenterol. 2013;108:1861–8. Williams KH, Shackel NA, Gorrell MD, McLennan SV, Twigg SM. Diabetes and nonalcoholic fatty liver disease: a pathogenic duo. Endocr Rev. 2013;34:84–129. Harrison SA. Liver disease in patients with diabetes mellitus. J Clin Gastroenterol. 2006;40:68–76. Adams LA, Waters OR, Knuiman MW, Elliott RR, Olynyk JK. NAFLD as a risk factor for the development of diabetes and the metabolic syndrome: an eleven-year follow-up study. Am J Gastroenterol. 2009;104:861–7. Gupte P, Amarapurkar D, Agal S, Baijal R, Kulshrestha P, Pramanik S, et al. Hafeezunnisa: Non-alcoholic steatohepatitis in type 2 diabetes mellitus. J Gastroenterol Hepatol. 2004;19:854–8. El-Serag HB. Hepatocellular carcinoma: recent trends in the United States. Gastroenterology. 2004;127(5 Suppl 1):S27–34. Angulo P. GI Epidemiology: nonalcoholic fatty liver disease. Aliment Pharmacol Ther. 2007;25:883–9. Leite NC, Villela-Nogueira CA, Pannain VL, Bottino AC, Rezende GF, Cardoso CR, et al. Histopathological stages of nonalcoholic fatty liver disease in type 2 diabetes: prevalences and correlated factors. Liver Int. 2011;31:700–6. Fracanzani AL, Valenti L, Bugianesi E, Andreoletti M, Colli A, Vanni E, et al. Risk of severe liver disease in nonalcoholic fatty liver disease with normal aminotransferase levels: a role for insulin resistance and diabetes. Hepatology. 2008;48:792–8. Loomba R, Abraham M, Unalp A, Wilson L, Lavine J, Doo E, et al. Association between diabetes, family history of diabetes, and risk of nonalcoholic steatohepatitis and fibrosis. Hepatology. 2012;56:943–51. Neuschwander-Tetri BA, Clark JM, Bass NM, Van Natta ML, Unalp-Arida A, Tonascia J, et al. Clinical, laboratory and histological associations in adults with nonalcoholic fatty liver disease. Hepatology. 2010;52:913–24. Pais R, Charlotte F, Fedchuk L, Bedossa P, Lebray P, Poynard T, et al. A systematic review of follow-up biopsies reveals disease progression in patients with non-alcoholic fatty liver. J Hepatol. 2013;59:550–6. Excellent prospective on the impact of risk factors such as obesity and T2DM in the progression of NASH. Stepanova M, Rafiq N, Makhlouf H, Agrawal R, Kaur I, Younoszai Z, et al. Predictors of all-cause mortality and liverrelated mortality in patients with non-alcoholic fatty liver disease (NAFLD). Dig Dis Sci. 2013;58:3017–23. White DL, Kanwal F, El-Serag HB. Association between nonalcoholic fatty liver disease and risk for hepatocellular cancer, based on systematic review. Clin Gastroenterol Hepatol. 2012;10:1342– 59. e1342. Bhala N, Angulo P, van der Poorten D, Lee E, Hui JM, Saracco G, et al. The natural history of nonalcoholic fatty liver disease with advanced fibrosis or cirrhosis: an international collaborative study. Hepatology. 2011;54:1208–16. Gaggini M, Morelli M, Buzzigoli E, DeFronzo RA, Bugianesi E, Gastaldelli A. Non-alcoholic fatty liver disease

Curr Hepatology Rep

39.

40.

41.

42.

43.••

44.

45.

46.

47.

48.••

49.

50.

51.

52.

53.

54.•

(NAFLD) and its connection with insulin resistance, dyslipidemia, atherosclerosis and coronary heart disease. Nutrients. 2013;5:1544–60. Birkenfeld AL, Shulman GI. Nonalcoholic fatty liver disease, hepatic insulin resistance, and type 2 diabetes. Hepatology. 2014;59:713–23. Fabbrini E, Sullivan S, Klein S. Obesity and nonalcoholic fatty liver disease: biochemical, metabolic, and clinical implications. Hepatology. 2010;51:679–89. Iozzo P, Pratipanawatr T, Pijl H, Vogt C, Kumar V, Pipek R, et al. Physiological hyperinsulinemia impairs insulin-stimulated glycogen synthase activity and glycogen synthesis. Am J Physiol. 2001;280:E712–9. Rector RS, Thyfault JP, Uptergrove GM, Morris EM, Naples SP, Borengasser SJ, et al. Mitochondrial dysfunction precedes insulin resistance and hepatic steatosis and contributes to the natural history of non-alcoholic fatty liver disease in an obese rodent model. J Hepatol. 2010;52:727–36. Satapati S, Sunny NE, Kucejova B, Fu X, He TT, Mendez-Lucas A, et al. Elevated TCA cycle function in the pathology of dietinduced hepatic insulin resistance and fatty liver. J Lipid Res. 2012;53:1080–92. Novel animal study on the role of mitochondrial dysfunction in the pathogenesis of hepatic steatosis. Wang SY, Kamat A, Pergola P, Swamy A, Tio F, Cusi K. Metabolic factors in the development of hepatic steatosis and altered mitochondrial gene expression in vivo. Metabolism. 2011;60:1090–9. Begriche K, Massart J, Robin MA, Bonnet F, Fromenty B. Mitochondrial adaptations and dysfunctions in nonalcoholic fatty liver disease. Hepatology. 2013;58:1497–507. Szendroedi J, Chmelik M, Schmid AI, Nowotny P, Brehm A, Krssak M, et al. Abnormal hepatic energy homeostasis in type 2 diabetes. Hepatology. 2009;50:1079–86. Schmid AI, Szendroedi J, Chmelik M, Krssak M, Moser E, Roden M. Liver ATP synthesis is lower and relates to insulin sensitivity in patients with type 2 diabetes. Diabetes Care. 2011;34:448–53. Sunny NE, Parks EJ, Browning JD, Burgess SC. Excessive hepatic mitochondrial TCA cycle and gluconeogenesis in humans with nonalcoholic fatty liver disease. Cell Metab. 2011;14:804– 10. Landmark study in humans offering strong evidence on the role of mitochondrial dysfunction, TCA cycle and gluconeogenesis in the pathogenesis of hepatic steatosis. Amaro A, Fabbrini E, Kars M, Yue P, Schechtman K, Schonfeld G, et al. Dissociation between intrahepatic triglyceride content and insulin resistance in familial hypobetalipoproteinemia. Gastroenterology. 2010;139:149–53. Neuschwander-Tetri BA. Hepatic lipotoxicity and the pathogenesis of nonalcoholic steatohepatitis: the central role of nontriglyceride fatty acid metabolites. Hepatology. 2010;52:774– 88. Kashyap S, Belfort R, Gastaldelli A, Pratipanawatr T, Berria R, Pratipanawatr W, et al. A sustained increase in plasma free fatty acids impairs insulin secretion in nondiabetic subjects genetically predisposed to develop type 2 diabetes. Diabetes. 2003;52:2461– 74. Kashyap S, Belfort R, Berria R, Suraamornkul S, Pratipranawatr T, Finlayson J, et al. Discordant effects of a chronic physiological increase in plasma FFA on insulin signaling in healthy subjects with or without a family history of type 2 diabetes. Am J Physiol. 2004;287:E537–46. Kantartzis K, Schick F, Haring HU, Stefan N. Environmental and genetic determinants of fatty liver in humans. Dig Dis. 2010;28: 169–78. Naukkarinen J, Heinonen S, Hakkarainen A, Lundbom J, Vuolteenaho K, Saarinen L, et al. Characterising metabolically healthy obesity in weight-discordant monozygotic twins.

55.

56.

57.

58.

59.

60.

61.

62.

63. 64.

65.

66.

67. 68.

69. 70.

71.

72.

Diabetologia. 2014;57:167–76. Interesting study examining the genetic basis on NAFLD in monozygotic twins. Bril F, Lomonaco R, Portillo-Sanchez P, Orsak B, Maximos M, Finch J, Webb A, Cusi K. Does Nonalcoholic Fatty Liver Disease (NAFLD) Develop in Insulin Sensitive Patients? Diabetes. 2014 (accepted abstract 1804-P). Weyer C, Hanson RL, Tataranni PA, Bogardus C, Pratley RE. A high fasting plasma insulin concentration predicts type 2 diabetes independent of insulin resistance: evidence for a pathogenic role of relative hyperinsulinemia. Diabetes. 2000;49:2094–101. Balkau B, Kahn HS, Courbon D, Eschwege E, Ducimetiere P. Paris Prospective S: Hyperinsulinemia predicts fatal liver cancer but is inversely associated with fatal cancer at some other sites: the Paris Prospective Study. Diabetes Care. 2001;24:843–9. Lambert JE, Ramos-Roman MA, Browning JD, Parks EJ. Increased de novo lipogenesis is a distinct characteristic of individuals with nonalcoholic fatty liver disease. Gastroenterology. 2014;146:726–35. Postic C, Girard J. Contribution of de novo fatty acid synthesis to hepatic steatosis and insulin resistance: lessons from genetically engineered mice. J Clin Invest. 2008;118:829–38. Kotronen A, Juurinen L, Tiikkainen M, Vehkavaara S, YkiJarvinen H. Increased liver fat, impaired insulin clearance, and hepatic and adipose tissue insulin resistance in type 2 diabetes. Gastroenterology. 2008;135:122–30. Arslanian SA, Saad R, Lewy V, Danadian K, Janosky J. Hyperinsulinemia in African-American children: decreased insulin clearance and increased insulin secretion and its relationship to insulin sensitivity. Diabetes. 2002;51:3014–9. Gastaldelli A, Cusi K, Pettiti M, Hardies J, Miyazaki Y, Berria R, et al. Relationship between hepatic/visceral fat and hepatic insulin resistance in nondiabetic and type 2 diabetic subjects. Gastroenterology. 2007;133:496–506. Ye R, Scherer PE. Adiponectin, driver or passenger on the road to insulin sensitivity? Mol Metab. 2013;2:133–41. Polyzos SA, Kountouras J, Zavos C, Tsiaousi E. The role of adiponectin in the pathogenesis and treatment of non-alcoholic fatty liver disease. Diabetes Obes Metab. 2010;12:365–83. Xu A, Wang Y, Keshaw H, Xu L, Lam K, Cooper G. The fatderived hormone adiponectin alleviates alcoholic and nonalcoholic fatty liver diseases in mice. J Clin Invest. 2003;112:91–100. Gastaldelli A, Harrison S, Belfort-Aguiar R, Hardies J, Balas B, Schenker S, et al. Pioglitazone in the treatment of NASH: the role of adiponectin. Aliment Pharmacol Ther. 2010;32:769–75. Poitout V, Robertson RP. Glucolipotoxicity: fuel excess and betacell dysfunction. Endocr Rev. 2008;29:351–66. Shams ME, Al-Gayyar MM, Barakat EA. Type 2 Diabetes Mellitus-Induced Hyperglycemia in Patients with NAFLD and Normal LFTs: Relationship to lipid profile, oxidative stress and pro-Inflammatory cytokines. Sci Pharm. 2011;79: 623–34. Brownlee M. The pathobiology of diabetic complications: a unifying mechanism. Diabetes. 2005;54:1615–25. Leung C, Herath CB, Jia Z, Goodwin M, Mak KY, Watt MJ, et al. Dietary glycotoxins exacerbate progression of experimental fatty liver disease. J Hepatol. 2014;60:832–8. Hyogo H, Yamagishi S, Iwamoto K, Arihiro K, Takeuchi M, Sato T, et al. Elevated levels of serum advanced glycation end products in patients with non-alcoholic steatohepatitis. J Gastroenterol Hepatol. 2007;22:1112–9. Kimura Y, Hyogo H, Yamagishi S, Takeuchi M, Ishitobi T, Nabeshima Y, et al. Atorvastatin decreases serum levels of advanced glycation endproducts (AGEs) in nonalcoholic steatohepatitis (NASH) patients with dyslipidemia: clinical usefulness of AGEs as a biomarker for the attenuation of NASH. J Gastroenterol. 2010;45:750–7.

Curr Hepatology Rep 73.• Bril F, Lomonaco R, Cusi K. The challenge of managing dyslipidemia in patients with nonalcoholic fatty liver disease. Clin Lipidol. 2012;7:471–81. Comprehensive review on the role of dyslipidemia and impact of lipid-lowering agents in NAFLD and NASH. 74. Nseir W, Nassar F, Assy N. Soft drinks consumption and nonalcoholic fatty liver disease. World J Gastroenterol. 2010;16:2579– 88. 75. Debosch BJ, Chen Z, Saben JL, Finck BN, Moley KH. Glucose Transporter 8 (GLUT8) mediates fructose-induced de novo lipogenesis and macrosteatosis. J Biol Chem. 2014. doi:10.1074/JBC. M113.527002. 76. Ouyang X, Cirillo P, Sautin Y, McCall S, Bruchette JL, Diehl AM, et al. Fructose consumption as a risk factor for non-alcoholic fatty liver disease. J Hepatol. 2008;48:993–9. 77. Abdelmalek MF, Suzuki A, Guy C, Unalp-Arida A, Colvin R, Johnson RJ, et al. Increased fructose consumption is associated with fibrosis severity in patients with nonalcoholic fatty liver disease. Hepatology. 2010;51:1961–71. 78. Chiu S, Sievenpiper JL, de Souza RJ, Cozma AI, Mirrahimi A, Carleton AJ, Ha V, Di Buono M, Jenkins AL, Leiter LA et al. Effect of fructose on markers of non-alcoholic fatty liver disease (NAFLD): a systematic review and meta-analysis of controlled feeding trials. Eur J Clin Nutr. 2014. doi:10.1038/ejcn.2014.8. 79. Gautier-Stein A, Soty M, Chilloux J, Zitoun C, Rajas F, Mithieux G. Glucotoxicity induces glucose-6-phosphatase catalytic unit expression by acting on the interaction of HIF-1alpha with CREB-binding protein. Diabetes. 2012;61:2451–60. 80. Meugnier E, Rome S, Vidal H. Regulation of gene expression by glucose. Curr Opin Clin Nutr Metab Care. 2007;10:518–22. 81.• Lomonaco R, Sunny NE, Bril F, Cusi K. Nonalcoholic fatty liver disease: current issues and novel treatment approaches. Drugs. 2013;73:1–14. Comprehensive review on the role of lifestyle changes and current and novel treatments for patients with NAFLD/NASH. 82.• Corrado R, Torres D, Harrison S. Review of treatment options for nonalcoholic fatty liver disease. Med Clin N Am. 2014;98:55–72. In-depth review on the role of treatment modalities in patients with NASH. 83. Sanyal AJ, Chalasani N, Kowdley KV, McCullough A, Diehl AM, Bass NM, et al. Pioglitazone, vitamin E, or placebo for nonalcoholic steatohepatitis. N Engl J Med. 2010;362:1675–85. 84. Musso G, Cassader M, Rosina F, Gambino R. Impact of current treatments on liver disease, glucose metabolism and cardiovascular risk in non-alcoholic fatty liver disease (NAFLD): a systematic review and meta-analysis of randomised trials. Diabetologia. 2012;55:885–904. 85. Tamura Y, Tanaka Y, Sato F, Choi JB, Watada H, Niwa M, et al. Effects of diet and exercise on muscle and liver intracellular lipid contents and insulin sensitivity in type 2 diabetic patients. J Clin Endocrinol Metab. 2005;90:3191–6. 86. Lazo M, Solga SF, Horska A, Bonekamp S, Diehl AM, Brancati FL, et al. Effect of a 12-month intensive lifestyle intervention on hepatic steatosis in adults with type 2 diabetes. Diabetes Care. 2010;33:2156–63. 87.•• Bacchi E, Negri C, Targher G, Faccioli N, Lanza M, Zoppini G, et al. Both resistance training and aerobic training reduce hepatic fat content in type 2 diabetic subjects with NAFLD (The RAED2 randomized trial). Hepatology. 2013;58:1287–95. Well-designed controlled study comparing aerobic vs. resistance exercise for the treatment of NAFLD. 88. Promrat K, Kleiner DE, Niemeier HM, Jackvony E, Kearns M, Wands JR, et al. Randomized controlled trial testing the effects of weight loss on nonalcoholic steatohepatitis. Hepatology. 2010;51:121–9. 89. Eckard C, Cole R, Lockwood J, Torres DM, Williams CD, Shaw JC, et al. Prospective histopathologic evaluation of lifestyle modification in nonalcoholic fatty liver disease: a randomized trial. Ther Adv Gastroenterol. 2013;6:249–59.

90.

91.

92. 93.

94.

95.

96.

97.

98.••

99.

100.

101. 102.

103.

104.

105.

106.

107.

Zelber-Sagi S, Kessler A, Brazowsky E, Webb M, Lurie Y, Santo M, et al. A double-blind randomized placebo-controlled trial of orlistat for the treatment of nonalcoholic fatty liver disease. Clin Gastroenterol Hepatol. 2006;4:639–44. Harrison S, Brunt E, Fecht W, N-T BA. Orlistat for overweight subjects with nonalcoholic steatohepatitis (NASH): a randomized prospective trial. Hepatology. 2009;49:80–6. Yanovski SZ, Yanovski JA. Long-term drug treatment for obesity: a systematic and clinical review. JAMA. 2014;311:74–86. Rena G, Pearson ER, Sakamoto K. Molecular mechanism of action of metformin: old or new insights? Diabetologia. 2013;56:1898–906. Marchesini G, Brizi M, Bianchi G, Tomassetti S, Zoli M, Melchionda N. Metformin in non-alcoholic steatohepatitis. Lancet. 2001;358:893–4. Belfort R, Harrison SA, Brown K, Darland C, Finch J, Hardies J, et al. A placebo-controlled trial of pioglitazone in subjects with nonalcoholic steatohepatitis. N Engl J Med. 2006;355:2297–307. Cusi K, Orsak B, Lomonaco R, Bril F, Ortiz-Lopez C, Hecht J, Webb A, Tio F, Darland CM, Hardies J. Extended treatment with pioglitazone improves liver histology in patients with prediabetes or type 2 diabetes mellitus and NASH. Hepatology. 2013; 58(Supplement 1):Abstract #82. Yau H, Rivera K, Lomonaco R, Cusi K. The future of thiazolidinedione therapy in the management of type 2 diabetes mellitus. Curr Diabetes Rep. 2013;13:329–41. Chang CH, Lin JW, Wu LC, Lai MS, Chuang LM, Chan KA. Association of thiazolidinediones with liver cancer and colorectal cancer in type 2 diabetes mellitus. Hepatology. 2012;55:1462–72. Large epidemiological study on the impact of thiazolidinedione treatment and risk of cancer. Monami M, Dicembrini I, Mannucci E. Thiazolidinediones and cancer: results of a meta-analysis of randomized clinical trials. Acta Diabetol. 2014;51:91–101. Lincoff AM, Wolski K, Nicholls SJ, Nissen SE. Pioglitazone and risk of cardiovascular events in patients with type 2 diabetes mellitus: a meta-analysis of randomized trials. JAMA. 2007;298: 1180–8. Mells JE, Anania FA. The role of gastrointestinal hormones in hepatic lipid metabolism. Semin Liver Dis. 2013;33:343–57. Sathyanarayana P, Jogi M, Muthupilla R, Ramkumar K, Samson S, Bajaj M. Effects of combined exenatide and pioglitazone therapy on hepatic fat content in type 2 diabetes. Obesity. 2011;19: 2310–5. Gupta NA, Mells J, Dunham RM, Grakoui A, Handy J, Saxena NK, et al. Glucagon-like peptide-1 receptor is present on human hepatocytes and has a direct role in decreasing hepatic steatosis in vitro by modulating elements of the insulin signaling pathway. Hepatology. 2010;51:1584–92. Tushuizen ME, Bunck MC, Pouwels PJ, van Waesberghe JH, Diamant M, Heine RJ. Incretin mimetics as a novel therapeutic option for hepatic steatosis. Liver Int Off J Int Study Liver. 2006;26:1015–7. Kenny PR, Brady DE, Torres DM, Ragozzino L, Chalasani N, Harrison SA. Exenatide in the treatment of diabetic patients with non-alcoholic steatohepatitis: a case series. Amer J Gastroenterol. 2010;105:2707–9. Mendoza CA, Mathew M, Chen J, Diaz N, Kaminski-Grant R, Darland C, et al. Exenatide promotes weight loss and improves insulin secretion, subclinical inflammation, and hepatic steatosis when replaced for premeal insulin in T2DM patients. Diabetes. 2009;58:A135. Armstrong MJ, Houlihan DD, Rowe IA, Clausen WH, Elbrond B, Gough SC, et al. Safety and efficacy of liraglutide in patients with type 2 diabetes and elevated liver enzymes: individual patient data

Curr Hepatology Rep

108.

109.

110.

111.

112.

meta-analysis of the LEAD program. Aliment Pharmacol Ther. 2013;37:234–42. Armstrong MJ, Barton D, Gaunt P, Hull D, Guo K, Stocken D, et al. Liraglutide efficacy and action in non-alcoholic steatohepatitis (LEAN): study protocol for a phase II multicentre, double-blinded, randomised, controlled trial. BMJ Open. 2013;3:e003995. doi:10. 1136/bmjopen-2013-003995. Abdul-Ghani MA, DeFronzo RA. Dapagliflozin for the treatment of type 2 diabetes. Expert Opin Pharmacother. 2013;14: 1695–703. Toderika Y, Ferguson N. Canagliflozin: a new class of antidiabetic agent targeting the sodium-glucose cotransporter. Cardiol Rev. 2014;22:97–104. Lavalle-Gonzalez FJ, Januszewicz A, Davidson J, Tong C, Qiu R, Canovatchel W, et al. Efficacy and safety of canagliflozin compared with placebo and sitagliptin in patients with type 2 diabetes on background metformin monotherapy: a randomised trial. Diabetologia. 2013;56:2582–92. List JF, Woo V, Morales E, Tang W, Fiedorek FT. Sodium-glucose cotransport inhibition with dapagliflozin in type 2 diabetes. Diabetes Care. 2009;32:650–7.

113.

Berrabah W, Aumercier P, Gheeraert C, Dehondt H, Bouchaert E, Alexandre J, Ploton M, Mazuy C, Caron S, Tailleux A et al. The glucose sensing O-GlcNacylation pathway regulates the nuclear bile acid receptor FXR. Hepatology. 2013. doi:10.1002/hep. 26710. 114.• Mudaliar S, Henry RR, Sanyal AJ, Morrow L, Marschall HU, Kipnes M, et al. Efficacy and safety of the farnesoid X receptor agonist obeticholic acid in patients with type 2 diabetes and nonalcoholic fatty liver disease. Gastroenterology. 2013;145: 574–82. e571. This study examines the effect of this novel agent on insulin sensitivity and other metabolic variables in patients with NAFLD. 115. Juurinen L, Tiikkainen M, Hakkinen AM, Hakkarainen A, YkiJarvinen H. Effects of insulin therapy on liver fat content and hepatic insulin sensitivity in patients with type 2 diabetes. Amer J Physiol. 2007;292:E829–35. 116. Hamaguchi E, Takamura T, Sakurai M, Mizukoshi E, Zen Y, Takeshita Y, et al. Histological course of nonalcoholic fatty liver disease in Japanese patients: tight glycemic control, rather than weight reduction, ameliorates liver fibrosis. Diabetes Care. 2010;33:284–6.