Studies On The Antioxidative Properties Of Chitosan, Glucosamine And Thiazolidine Derivatives

Free radicals are constantly produced mostly as reactive oxygen species in aerobic cells. In physiological conditions, free radicals are removed by enzymic and nonenzymic antioxidant defenses including enzyme and antioxidant molecules. Once there is excessive generation of free radicals because of metabolism of exogenous toxins and/or impairment of endogenous antioxidants, oxidative stress occurs. Numerous evidences suggest that oxidative stress is closely related to pathological changes. So much interest focus on antioxidants investigation. Reduced glutathione plays critical roles in antioxidant defense. The homeostasis of GSH is very important in many pathological conditions. The most important and efficient way for GSH restoration is L-cysteine administration. But L-cysteine is toxic at functional concentration and is easily oxidized. The traditional prodrug design proved to be effective in stimulating GSH biosynthesis, counteracting oxidative stress with reduced toxicity. L-cysteine and aldoses can form thiazolidine derivatives through cyclo-condensation. Thiazolidine derivatives can be used as the precursor of L-cysteine, which can liberate L-cysteine and the sugars by non-enzymic hydrolysis. Their biological and pharmacological functions have been extensively studied.Chito-oligosaccarides (COS) can be prepared by deacetylation and enzymic hydrolysis of chitin, the second most abundant polymer in nature. The application of COS in pharmaceutical, food and other fields have been extensively studied because of good biocompatibility, degradation, non-toxicity and easy-absorbability. In recent years, studies have shown that COS and its derivatives have antioxidative activities both in vivo and in vitro. But further research needs to be done to better illustrate its antioxidant activity and mechanism. In this study, glucosamine (GlcNH₂) and N-acetyl-glucosamine (GlcNAc) was condensed with L-cysteine to form novel thiazolidine derivatives. The physical characteristics such as melting point, optical activity, IR spectrometer and ¹H-NMR were conducted. Based on the characterization of two previously reported thiazolidinederivatives, the results show that GlcNH2Cys and GlcNAcCys were 2-substituted-thiazolidine- 4(R)-carboxylic acids.In our study, the antioxidant of chitosan, GlcNH2, GlcNAc, and their thiazolidine derivatives were investigated in vitro and in vivo. Antioxidant activity such as free radical scavenging ability, reducing power, chelating effects and protective effects against oxidative damage to biomoleculars such as lipid, deoxyribose and protein were evaluated using in vitro hydroxyl radical generating system. The antioxidative, hepato-protective effects of COS and its derivatives on carbon tetrachloride/APAP-induced liver toxicity in mice and the possible mechanisms involved in their protection were also illustrated. UV radiation damage in closely related oxidative stress and protection of GlcNAcCys against UV radiation induced lipid and DNA damage in mitochondria and nuclei were studied to further apply GlcNAcCys as UV protector.Our data indicate that GlcNHa, GlcNI^Cys have strong in vitro antioxidative property. They can scavenge directly reactive free radicals like hydroxyl radical and superoxide anion, protect macromolecules including deoxyribose, protein and lipid against oxidative damage induced by hydroxyl radical. Pretreatment with COS and its derivatives (1.5 g/kg body weight per day) for 12 consecutive days before CCU challenge showed hepato-protective effects. Serum alanine and aspartate aminotransferase activities were effectively decreased. Hepatic malondialdehyde formation was inhibited and sulfhydryl contents, total antioxidant capabilities were restored. Liver metallothionein concentration was also significantly induced by pretreatment of COS and its derivatives. Genotoxicity as reflected by DNA fragmentation, however, was not mitigated by pretreatment of COS and its derivatives. APAP metabolism can cause severe GSH depletion, oxidative stress and subsequent liver toxicity. Thiazolidine derivatives administration (800 mg/kg body weight) 30 min after APAP challenge provide efficient protection as manifested by decreased serum enzyme activities, elevated sulfhydryl levels and total antioxidative capabilities and decreased malondialdehyde contents in liver. GlcNAcCys exhibit UV radiation protection function as it can inhibit lipid peroxidation in mitochondria and nuclei if pre-incubated toUV radiation.In conclusion, our results suggested that COS, glucosamine and thiazolidine derivatives have excellent in vitro and in vivo antioxidant properties. They promise to be candidates in oxidative stress-involved pathological conditions. Our work provide theoretical for further application of chitosan in biological, medical and nutritional fields.