Kadiyala Babu Dakshayani

Prevention by melatonin of hepatocarcinogenesis in rats injected with N-nitrosodiethylamine

Abstract:  N‐nitrosodiethylamine (NDEA) is a potent carcinogenic agent that induces liver cancer. To evaluate the chemopreventive function of melatonin in this experimental model, Wistar male rats received a single i.p. injection of NDEA or vehicle followed by weekly s.c. injections of carbon tetrachloride or vehicle for 6 weeks. Melatonin (5 mg/kg body weight) or its vehicle (0.5 mL saline) was given i.p. on a daily basis 2 hr before lights off for 20 wk. At the end of this period the rats were killed and liver and blood samples were taken for histological and biochemical studies. As markers for liver function, the activity of aspartate transaminase (AST) and alanine transaminase (ALT) and the levels of α‐fetoprotein were measured in serum. To assess lipid peroxidation and the antioxidant status in liver and blood, the levels of thiobarbituric acid reactive substances (TBARS) and of reduced glutathione (GSH) were measured. The activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione S‐transferase (GST) was assessed in liver and erythrocyte fraction of NDEA‐treated rats. NDEA administration inhibited body weight, macro‐ and microscopically detectable liver tumors and increased levels of plasma AST, ALT and α‐fetoprotein. NDEA treatment decreased liver TBARS levels and CAT and SOD activities and increased liver GSH levels and GST and GPx activities. Plasma TBARS were augmented, while plasma GSH levels and the activities of erythrocyte CAT, SOD, GST and GPx decreased, in NDEA‐treated rats. Melatonin administration significantly curtailed tumor development and counteracted all the biochemical effects.

Effects of α-ketoglutarate on antioxidants and lipid peroxidation products in rats treated with ammonium acetate

The effects of alpha-ketoglutarate (alpha-KG) on hyperammonemia induced by ammonium acetate were studied biochemically in experimental rats. The levels of circulatory urea and non-protein nitrogen increased significantly in rats treated with ammonium acetate and decreased significantly in rats treated with alpha-KG and ammonium acetate. In liver and kidney tissues, similar patterns of alterations across groups were observed in the levels of thiobarbituric acid-reactive substances and lipid profile variables (free fatty acids, triacylglycerols, phospholipids, and cholesterol). Further, enzymatic (superoxide dismutase, catalase, and glutathione peroxidase) and non-enzymatic (reduced glutathione) antioxidants in both tissues decreased significantly in rats treated with ammonium acetate and increased significantly in rats treated with alpha-KG and ammonium acetate. The biochemical alterations during alpha-KG treatment might have been due to 1) the detoxification of excess ammonia, 2) participation in the non-enzymatic oxidative decarboxylation during hydrogen peroxide decomposition, and 3) enhancement of the proper metabolism of fats that could suppress oxygen radical generation and thus prevent lipid peroxidative damages in rats.

24-Hour rhythms in oxidative stress during hepatocarcinogenesis in rats: effect of melatonin or α-ketoglutarate

Abstract To compare the effects of α-ketoglutarate (α-KG) and melatonin on 24-h rhythmicity of oxidative stress in N-nitrosodiethylamine (NDEA)-injected Wistar male rats, melatonin (5 mg/kg i.p.) or α-KG (2 g/kg through an intragastric tube) was given daily for 20 weeks. In blood collected at 6 time points during a 24-h period, serum activity of aspartate transaminase (AST) and alanine transaminase (ALT) and the levels of α-fetoprotein (α-FP) were measured as markers of liver function. To assess lipid peroxidation and the antioxidant status, plasma levels of thiobarbituric acid reactive substances (TBARS) and of reduced glutathione (GSH) were measured, together with the activity of erythrocyte superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione S-transferase (GST). NDEA augmented mesor and amplitude of rhythms in AST and ALT activity and plasma α-FP levels and mesor values of plasma TBARS, while decreasing mesor values of plasma GSH and erythrocyte SOD, CAT, GPx and GST. Acrophases were delayed by NDEA in all cases except for α-FP rhythm, which became phase-advanced. Co-administration of melatonin or α-KG partially counteracted the effects of NDEA. Melatonin decreased mesor of plasma TBARS and augmented mesor of SOD activity. The results indicate that melatonin and α-KG are effective in protecting from NDEA-induced perturbation of 24-h rhythms in oxidative stress. Melatonin augmented antioxidant defense in rats.

Effects of Ornithine α-Ketoglutarate on Circulatory Antioxidants and Lipid Peroxidation Products in Ammonium Acetate Treated Rats

The effects of ornithine α-ketoglutarate (OKG) on ammonium acetate induced hepatotoxicity were studied biochemically in rats. The levels of urea, nonprotein nitrogen, and thiobarbituric acid reactive substances were significantly increased in ammonium acetate treated rats; these levels were significantly decreased in rats treated with ammonium acetate and OKG. Similar patterns of alterations were observed in the levels of free fatty acids, triglycerides, and phospholipids. Furthermore, nonenzymatic antioxidants (vitamins C and E) were significantly decreased in ammonium acetate treated rats, when compared with control rats, and increased in OKG and ammonium acetate treated rats. The biochemical alterations during OKG treatment could be (1) by detoxifying excess ammonia; (2) by participating in nonenzymatic oxidative decarboxylation in the hydrogen peroxide decomposition process, and (3) by enhancing the proper metabolism of fats which could suppress oxygen radical generation and thus prevent the lipid peroxidative damages in rats.

Metabolic normalization of α-ketoglutarate against N-nitrosodiethylamine-induced hepatocarcinogenesis in rats

Chemoprevention of cancer is one of the reliable approaches to control the incidence of cancer. In the present study, we investigated the chemopreventive role of α‐ketoglutarate (α‐KG) during N‐nitrosodiethylamine (NDEA)‐induced hepatocarcinogenesis. The activities of serum aspartate and alanine transaminases were found to be significantly higher in NDEA + CCl4‐treated animals when compared with control animals. Administration of α‐KG restored the activities of transaminases to near normal range. The levels of lipid peroxides, thiobarbituric acid reactive substances were decreased in the liver tissue of NDEA + CCl4‐treated animals when compared with control animals. α‐KG reversed the lipid peroxide levels to near normal range. Levels of antioxidants, reduced glutathione and activities of its dependent enzymes, glutathione peroxidase and glutathione‐S‐transferase were found to be significantly higher in liver tissue of NDEA + CCl4‐treated animals when compared with control animals. α‐KG administration positively modulated the antioxidant levels to near normal range. In conclusion, it can be suggested that α‐KG exerts chemopreventive role which may attributable to its ability to positively modulate the transaminase activities and oxidant–antioxidant imbalance during hepatocarcinogenesis.

Effect Of Melatonin On N-Nitrosodiethylamine-Induced Hepatocarcinogenesis In Rats With Reference To Biochemical Circadian Rhythms

ABSTRACT Tumors and tumor-bearing hosts exhibit markedly altered circadian rhythms, which serve as markers in the early diagnosis and prognosis of cancer. Our study presents the effect of melatonin on circadian rhythms of lipid peroxides and antioxidants in N-nitrosodiethylamine (NDEA)-induced hepatocarcinogenesis. The circadian rhythm characteristics (acrophase, amplitude, and mesor) of thiobarbituric acid reactive substances (TBARS), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and reduced glutathione (GSH) were markedly altered in NDEA-treated rats. Melatonin administration caused a significant increase in the amplitude and mesor values of antioxidants and a significant decrease in the mesor values of TBARS. Further delays in acrophase in NDEA-treated rats were reversed by melatonin administration. In conclusion, melatonin may exert its chemopreventive effect by its role as an antioxidant as well as by altering the circadian rhythm characteristics.