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Preparation of Gallic Acid-Chitosan Complex (Eco-Brown) and Its Application for Adsorption of Mutagens and Carcinogens Hee-Kyung Jeon1, Youn-Jung Kim2 & Jae-Chun Ryu2 1 Busan Development Institute, #273-20 Yangjung-2dong Busanjin-gu, Busan 614-052, Korea 2 Cellular and Molecular Toxicology Laboratory, Korea Institute of Science and Technology (KIST), #39-1 Hawolgok-dong Sungbuk-gu, Seoul 136-791, Korea Correspondence and requests for materials should be addressed to J.-C. Ryu ([email protected])

Accepted 13 July 2009

Abstract Gallic acid was reported to suppress the mutagenicity and to inhibit the metabolic activation. Chitosan is a unique polysaccharide derived from chitin and is utlized as adsorbents of organic trace pollutants in environmental water sample. In this study, we have found that chitosan was suitable as a solid support to carry gallic acid. And it was examined that gallic acid could form an insoluble material when mixed with chitosan, and the solid chitosan-gallic acid complex (eco-brown) thus prepared could efficiently trap polycyclic mutagenic compounds. The adsorption of the test compounds was observed using UV/Visible spectrometry. The order of extent of removal by ecobrown was B[a]P (96.1%)¤QC (83.0%)¤2-AA (80.3%) ¤2-AF (30.3%)¤PhIP (29.6%). From these results, eco-brown may be expected as a useful adsorber for several polycyclic mutagens and carcinogens. Keywords: Gallic acid-chitosan complex, Adsorption, Polycyclic mutagens, Carcinogens

mutagenicity of aflatoxin B1 in the Ames test1. It was shown that gallic acid inhibits the metabolic activation. Naphthol and several naturally occurring naphthoquinones are inhibitors of the metabolism of benzo[a]pyrene (B[a]P), and as a result they can suppress the mutagenicity of B[a]P in the Salmonella assay2. Chitosan (poly(1 4)2-amino-2-deoxy-β-D-glucan, Figure 1C) is a unique polysaccharide derived from chitin (poly(1 4)2-acetamide-2-deoxy-β-D-glucan, Figure 1B), a main constituent of crustacean shell. Several attempts have been made to use this biopolymer in biomedical field, for example, the development of hemodialysis membranes, artificial skin, drug targeting and other applications3. This biodegradable and biocompatible chitosan may be used in substituting or regenerating the blood/tissue interfaces4. Also, chitosan was used in water treatment, photographic emulsions and improving the dye ability of synthetic fiber and fabrics. Chitin and chitosan, which are animal dietary fibers, are also utilized as adsorbents of organic trace pollutants in environmental water sample5. Therefore, we have selected that chitosan is suitable as a solid support to carry gallic acid. Previously, we reported the preparation and adsorption activity for several potent mutagens and carcinogens and heavy metals of chitosan-phthalocyanine complex (eco-blue)6,7 and potent mutagens and carcinogens of folic acidchitosan complex (eco-yellow)8. In this study, we established the process of preparation of the gallic acid-chitosan complex (eco-brown) and evaluated the usefulness of eco-brown for the adsorption of the mutagenic and carcinogenic compounds having polycyclic structures.

Results Introduction Gallic acid (CAS 149-91-7, Figure 1A) was obtained by alkaline or acid hydrolysis of the tannins from nutgalls and by enzymatic hydrolysis using spent broths from penicillium glaucum or aspergillus niger which contain tannase. It was used as photographic developer, in tanning, in dyeing, and formerly as astringent or styptic. Gallic acid was also reported to suppress the

Preparation of Gallic Acid-Chitosan Complex (Eco-Brown) To a solution of chitosan (2 g) in distilled water (190 mL) was added 1 N HCl (ca. 10 mL) with continuous mechanical stirring of the solution, to adjust the pH to 3. Due to its low solubility in neutral water, gallic acid (3.76 g) was dissolved in 30 mL of 0.5 N NaOH (alkalic status). After complete dissolution, the distilled

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Table 1. Adsorption of polycyclic mutagens to eco-brown.

OH

(A) HO

Mutagen

Abs.

OH O

OH

(B)

O HOCH2

C

NH

HO

CH3

O HO

O

H

O n

O

(C)

NH

C

CH3 CH2OH

HOCH2

NH2

HO O O

HO

O O

HO

NH2

H n

Mean (%) SD Eco-brown Chitosan

Compounds with 3 or more fused rings B[a]P 230 nm 5 96.1 2-AA 260 nm 3 80.3 2-AF 282 nm 3 30.3 NH 348 nm 3 22.4 MS 301 nm 3 14.3 Trp-p-1 264 nm 3 10.8 IQ 265 nm 3 10.5 Trp-p-2 264 nm 3 5.3 9-AA 260 nm 3 2.8 Compounds with 2 rings QC 255 nm PhIP 271 nm

O HO

No. of rings in the molecular structure

2 2

2.2 1.9 0.5 3.2 0.7 0.7 0.7 0.7 0.4

19.0 22.7 29.2 14.6 10.6 4.4 11.6 6.4 2.1

83.0 4.0 29.6 2.2

3.1 0.7 0.6 2.7 1.0 1.2 0.6 0.7 0.5

85.7 2.8 37.0 2.0

9-Aminoacridine (9-AA), 2-Aminoanthracene (2-AA), 2-Aminofluorene (2-AF), Benzo[a]pyrene (B[a]P), 2-Amino-3-methyl-3H-imidazo[4,5-f ]quinoline (IQ), 2-Amino-1-methyl-6-phenylimidazo[4,5b]pyridine (PhIP), 3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole acetate (Trp-p-1), 3-Amino-1-methyl-5H-pyrido[4,3-b]indole acetate (Trp-p-2), 8-Methoxypsoralen (MS), Norharmane (NH), Quercetin (QC)

CH2OH

Figure 1. Structure of (A) gallic acid, (B) chitin and (C) chitosan.

Table 2. Elution of polycyclic mutagens to eco-brown. Mutagen

Abs.

No. of rings in the molecular structure

Mean (%)

SD

Eco-brown Chitosan

water (170 mL) was added to it with stirring. 1 M EDAC (1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride) was prepared by dissolving 3.84 g of EDAC in 20 mL of distilled water and incubated for 30 min before use. Gallic acid (0.1 M) was mixed with the solution of chitosan and added 0.5 N of NaOH to adjust the pH to 6. After than 1 M EDAC was added to the solution and gently swirled in the reaction flask for 12 hr. The resulting precipitate was collected by centrifuging at 3,000 rpm for 10 min. The precipitate was washed with 10% NaCl (300 mL, twice), water (300 mL, twice), methanol (300 mL, 4 times), water (500 mL, twice), 0.05 N NaOH (300 mL, twice) and water repeatedly until the washing became colorless. Finally, it was washed methanol and diethyl ether, dried in a desiccator and ground into powder. The yields were 2.0 0.5 g (mean SD, 6 experiments). This material is hereafter referred to as ‘ecobrown’.

9-Aminoacridine (9-AA), 2-Aminoanthracene (2-AA), 2-Aminofluorene (2-AF), Benzo[a]pyrene (B[a]P), 2-Amino-3-methyl-3H-imidazo[4,5-f ]quinoline (IQ), 2-Amino-1-methyl-6-phenylimidazo[4,5b]pyridine (PhIP), 3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole acetate (Trp-p-1), 3-Amino-1-methyl-5H-pyrido[4,3-b]indole acetate (Trp-p-2), 8-Methoxypsoralen (MS), Norharmane (NH), Quercetin (QC)

Adsorption of Polycyclic Mutagenic Compounds to Eco-Brown By mixing chitosan and gallic acid, each in an aqueous solution, an insoluble brown precipitate was formed. When suspended in water, the dry powdery ecobrown did not precipitate, but floated. In order to

‘wet’ the material, a treatment with 5% Na2SO4 was found to be effective. The adsorption was achieved simply by a batch process, shaking the mutagen solution with the eco-brown added. These adsorption took place in neutral aqueous solutions. According to Ari-

Compounds with 3 or more fused rings B[a]P 230 nm 5 ND 2-AA 260 nm 3 12.1 1.9 2-AF 282 nm 3 2.4 1.5 NH 348 nm 3 ND MS 301 nm 3 11.4 9.9 Trp-p-1 264 nm 3 37.9 0.3 IQ 265 nm 3 32.2 4.7 Trp-p-2 264 nm 3 93.2 7.5 9-AA 260 nm 3 32.8 0.1 Compounds with 2 rings QC 255 nm PhIP 271 nm

2 2

5.9 7.9

0.2 11.2

28.0 14.9 5.4 2.0 2.7 22.7 7.8 9.1 23.2

3.0 2.4 1.2 2.3 1.9 1.2 4.5 1.4 2.3

0.4 0.8 3.8 6.6

Adsorption of Mutagens using Gallic Acid-chitosan Complex

(A)

(B)

(C)

129

(D)

NH2 NH2

NH2

N

(E)

(F)

(G)

(H) CH3

NH2 N N

N CH3 O

O

O

N H

OCH3

N

(I)

(J)

N H

N

NH2 CH3

(K) OH OH

CH3 CH3

N N H

HO

O

N NH2

N

N

OH

NH2 OH

O

Figure 2. Structures of polycyclic mutagens (A) 2-AA, (B) 9-AA, (C) 2-AF, (D) B[a]P, (E) IQ, (F) MS, (G) NH, (H) Trp-p-1, (I) Trp-p-2, (J) PhIP, (K) QC.

moto-Kobayashi et al. method, contents of adsorption were determined by UV/Visible spectrophotometry at maximum absorbance of compounds9. The adsorption of various mutagens to eco-brown was measured and the results were given in Table 1. The order of extent of removal by eco-brown was B[a]P¤quercetin (QC)¤2-aminoanthracene (2-AA) ¤2-aminofluorene (2AF)¤2-amino-1-methyl-6phenylimidazo[4,5-b]pyridine (PhIP). For the 11 compounds having 2 or more fused rings, extensive adsorptions were observed. The highest adsorption level tested in this study was determined for B[a]P (96.1%). Although these compounds showed non-specific adsorption to chitosan, these adsorptions of other compounds except for QC, PhIP, 2-amino-3-methyl-3Himidazo[4,5-f ]quinoline (IQ) and 3-amino-1-methyl5H-pyrido[4,3-b]indole acetate (Trp-p-2) were significantly smaller than those to eco-brown.

Elution of Test Compounds from Eco-Brown Whether the adsorbed compounds were able to elute by treatment with phosphate buffer was tested. Table 2 shows the results of experiments in which the elution was compared between eco-brown and chitosan of equal masses.

The extents of elution to eco-brown were greater than chitosan except for B[a]P, 2-AA, 2-AF and norharmane (NH). Most of the compounds were eluted from the eco-brown with phosphate buffer. Thus, it appears that these mutagens can be released into the buffer, even though once adsorbed to eco-brown.

Discussion Many organic polycyclic compounds have mutagenic and carcinogenic properties. They are found in the environmental and also in protein-rich foods (e.g. meat and fish) as a result of their thermal treatment10. In general, PhIP is quantitatively most important in beef and fish while IQ is usually only a minor constituent11. IQ, however, warrants special attention since it is among the most potent mutagenic and carcinogenic heterocyclic amines12. We present structures of polycyclic mutagens used in this study (Figure 2). Gallic acid used in this study, is known as potently antimutagenic against various polycyclic mutagens and interested as dietary inhibitors of mutagenesis. Also chitosan was selected because it is suitable as a solid support to carry gallic acid. In the previous stu-

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dies, chitosan was clearly demonstrated that it can be used as an effective coagulating agent for organic compounds, as a chelating polymer for binding toxic heavy metals13 and as an adsorption medium for dyes and small concentrations of phenols present in various industrial wastewaters. Accordingly, gallic acid and chitosan as its solid support formed potent synthetic product and it was expected to remove efficiently of mutagenic compounds having polycyclic fused rings. For the mutagenic compounds having 3 or more fused rings, the extent of removal by eco-brown was higher than it by non-specific chitosan. These results suggest that gallic acid in eco-brown can complex with aromatic polycyclic compounds having planar surfaces of 3 fused-ring areas. However, in the case of 2-ring compounds tested, the extent of removal by eco-brown was lower than it by non-specific chitosan. These 2-ring compounds against those with a 3-ring system particularly have a planar surface area. QC would have the planar surface area having the resonating character of the dihydroxyphenyl ring with the benzopyran portion. PhIP, also would have the resonating character of the phenyl ring with the imidazopyridine portion. In addition, to test the strength of adsorption of ecobrown, the elution assay of eco-brown was carried out. Most of test compounds adsorbed by eco-brown were not remained to adsorbed form. Although once adsorbed to eco-brown, these compounds can be readily released into aquatic media. From these results, the eco-brown may be expected to be a valuable adsorbent for several polycyclic mutagens and carcinogens but still need to make improvement of the efficiency as adsorbent.

Methods Chemicals Chitosan (poly(1 4)2-amino-2-deoxy-β-D-glucan) used in this experiment was products of Jakwang Co. (Korea). Gallic acid (3,4,5-trihydroxybenzoic acid) and EDAC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride) were obtained from Sigma-Aldrich Inc. (St. Louis, MO, USA). Gallic acid was colorless to pale yellow crystals and light sensitive. The purity of it was found to be¤99%. 9-Aminoacridine (9-AA), 2-aminoanthracene (2-AA), 2-aminofluorene (2-AF) and benzo[a]pyrene (B[a]P) were purchased from Sigma-Aldrich Inc. (St. Louis, MO, USA). 2Amino-3-methyl-3H-imidazo[4,5-f]quinoline (IQ), 8methoxypsoralen (MS), norharmane (NH), 2-amino1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), quercetin (QC), 3-amino-1,4-dimethyl-5H-pyrido[4,3-

b]indole acetate (Trp-p-1) and 3-amino-1-methyl-5Hpyrido[4,3-b]indole acetate (Trp-p-2) were obtained from ICN biomedicals Inc. (Aurora Ohio, USA). All other reagents were of the highest quality available.

Procedure for Adsorption of Test Compounds to Eco-Brown The eco-brown (10 mg) was soaked in 5% Na2SO4 (5 mL) by shaking at 37 C for 30 min for the purpose of wetting. The mixture was centrifuged at 3,000 rpm for 5 min and the supernatant was discarded. 0.1 mM Mutagen (2 mL; 0.2 μmol) in 20 mM Na phosphate-20 mM KCl buffer, pH 7, was added to the precipitate and the mixture was shaken vigorously at room temperature for 10 min. The mixture was centrifuged (3,000 rpm, 10 min) and the compound in the supernatant was quantified spectrophotometrically (UV/Vis spectrophotometer, Varian co.). For B[a]P, due to its extremely low solubility in water, a stock solution (50 mM) was prepared by dissolving B[a]P in ethanol-Tween 80 (2 : 1). The adsorption was done in 2.5 mM Na-phosphate-2.5 mM KCl at pH 7. For measuring non-specific adsorptions to chitosan, as controls, the same treatments were done using raw chitosan at an equivalent amount. All these adsorptions were done in duplicate, and the data reported here are the average values of these measurements. Procedure for Elution of Test Compounds from Eco-Brown After the adsorption test, eco-brown was washed with water, the mixture was centrifuged and the supernatant was removed. Elution of mutagen from the precipitate with a 20 mM Na phosphate-KCl buffer (2 mL) was done for 10 min with shaking, as in the adsorption experiments. The amount of a mutagen found in supernatant obtained upon centrifugation of the mixture represents the degree of elution.

Acknowledgements This subject is supported by the Korea Research Foundation grants from Korea Ministry of Environment as “The Eco-technopia 21 project” and KIST Core-Competence Program Technology to Ryu, J. C. of the Republic of Korea.

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Adsorption of Mutagens using Gallic Acid-chitosan Complex

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