Dhanapal Sakthisekaran

The Vascular Endothelium and Human Diseases

Alterations of endothelial cells and the vasculature play a central role in the pathogenesis of a broad spectrum of the most dreadful of human diseases, as endothelial cells have the key function of participating in the maintenance of patent and functional capillaries. The endothelium is directly involved in peripheral vascular disease, stroke, heart disease, diabetes, insulin resistance, chronic kidney failure, tumor growth, metastasis, venous thrombosis, and severe viral infectious diseases. Dysfunction of the vascular endothelium is thus a hallmark of human diseases. In this review the main endothelial abnormalities found in various human diseases such as cancer, diabetes mellitus, atherosclerosis, and viral infections are addressed.

Role of human organic anion transporter 4 in the transport of ochratoxin A.

The purpose of this study was to investigate the characteristics of ochratoxin A (OTA) transport by multispecific human organic anion transporter 4 (hOAT4) using mouse proximal tubule cells stably transfected with hOAT4 (S(2) hOAT4). Immunohistochemical analysis revealed that hOAT4 protein was localized to the apical side of the proximal tubule. S(2) hOAT4 expressed hOAT4 protein in the apical side as well as basolateral side and the cells were cultured on the plastic dish for experiments. S(2) hOAT4 exhibited a time- and concentration-dependent, and a saturable increase in OTA uptake, with an apparent K(m) value of 22.9+/-2.44 microM. The OTA uptakes were inhibited by several substrates for the OATs. Probenecid, piroxicam, octanoate and citrinin inhibited OTA uptake by hOAT4 in a competitive manner (K(i)=44.4-336.4 microM), with the following order of potency: probenecid > piroxicam > octanoate >citrinin. The efflux of OTA by S(2) hOAT4 was higher than that by mock. Addition of OTA resulted in slight decrease in viability of S(2) hOAT4 compared with mock. These results indicate that hOAT4 mediates the high-affinity transport of OTA on the apical side of the proximal tubule, whereas the transport characteristics of OTA are distinct from those by basolateral OATs.

Protective role of Apigenin on the status of lipid peroxidation and antioxidant defense against hepatocarcinogenesis in Wistar albino rats.

Apigenin, a dietary plant derived flavone subclass of flavonoid is expected to play a role in cancer chemoprevention and cancer chemotherapy. Here we designed our experiment to establish whether treatment of apigenin (25 mg/kg body weight) for 14 consecutive days to (N-nitrosodiethylamine) DEN induced (200 mg/kg body weight; by single ip. injection) and phenobarbital promoted (0.05% through drinking water for 14 successive weeks) rats provide protection against the oxidative stress caused by the carcinogen. The level of lipid peroxidation (LPO) markedly increased in carcinogen administered animals, which was brought back to near normal by apigenin treatment. In contrast the activities/levels of the antioxidant status both in liver and kidney were decreased in carcinogen administered animals, which was recouped back to near normal upon apigenin administration. From our findings we concluded that apigenin prevents LPO and protects antioxidant system in DEN induced and phenobarbital promoted hepatocellular carcinogenesis.

Antitumour activity of crocetin in accordance to tumor incidence, antioxidant status, drug metabolizing enzymes and histopathological studies

Lung cancer is the leading cause of cancer related mortality worldwide. Crocetin, saffron plant derivative known to play a role in cancer chemoprevention. In the present study the effects of crocetin was tested against lung cancer-bearing mice in both pre-initiation and post-initiation periods. Healthy male Swiss albino mice (6–8 weeks old) were used throughout the study. Experiment was designed with the treatment regimen of crocetin [20 mg/kg body weight dissolved in dimethyl sulphoxide (DMSO)] for 4 weeks before (pre-initiation) and from 12th week after Benzo(a) pyrene B(a)p (50 mg/kg body weight) induced lung carcinoma(post-initation). The level of lipid peroxidation (LPO) and marker enzymes markedly increased in carcinogen administered animals, which was brought back to near normal by crocetin treatment. The activities of the enzymic antioxidants and glutathione metabolizing enzymes were decreased in B(a)p induced animals and increased upon drug treatment. Crocetin profoundly reverted back the pathological changes observed in cancerous animals. From the results crocetin proves to scavenge free radical and plays an important role in cellular function. Tumor incidence and histopathological studies proves crocetin is a potent antitumour agent.

Cisplatin induced nephrotoxicity and the modulating effect of glutathione ester

The objective of this study was to assess the therapeutic advantage of glutathione ester along with cisplatin. Comparisons were made with renal reduced glutathione, enzymatic antioxidants, and lipid peroxidation levels. Cisplatin caused differential toxic effects on renal antioxidants and lipid peroxidation. However administration of glutathione ester modulates the toxic effects of cisplatin observed in renal antioxidants and lipid peroxidation. The finding that glutathione ester co-administration along with cisplatin is more effective and advantageous in protecting against the nephrotoxicity of cisplatin when it was given alone.

Naringenin reduces tumor size and weight lost in N-methyl-N′-nitro-N-nitrosoguanidine–induced gastric carcinogenesis in rats

Carcinoma of the stomach is reportedly the second most common cancerous condition affecting the general population. Administration of antioxidants is reported to effectively alleviate the risk of gastric carcinoma. Therefore, we assessed the protective role of naringenin, an antioxidant and naturally occurring citrus flavanone, on gastric carcinogenesis induced by MNNG (200 mg/kg body weight) and S-NaCl (1 mL per rat) in Wistar rats (obtained from the Central Animal House Facility, University of Madras, Taramani Campus, Chennai, India). The animals were divided into 5 groups, and the effects of naringenin on simultaneous and posttreated stages of MNNG were tested. Cancer risk was analyzed along with their antioxidant status. The LPO levels in the experimental groups were assessed as an index of oxidative milieu. Altered redox status was subsequently investigated by assaying the superoxide and hydroxyl radicals, the enzymatic antioxidants (SOD, CAT, GPx), and the nonenzymatic antioxidants viz reduced GSH, vitamin C, and vitamin E. In the presence of MNNG, cancer incidence and LPO levels were significantly increased, whereas enzymatic (SOD, CAT, and GPx) and nonenzymatic antioxidant activities (GSH, Vitamins C, and E) were decreased in the treated rats compared with control rats. Administration of naringenin to gastric carcinoma-induced rats largely up-regulated the redox status to decrease the risk of cancer. We conclude that up-regulation of antioxidants by naringenin treatment might be responsible for the anticancer effect in gastric carcinoma.

Apigenin inhibits oxidative stress‐induced macromolecular damage in N‐nitrosodiethylamine (NDEA)‐induced hepatocellular carcinogenesis in Wistar albino rats

Apigenin (4′,5,7‐trihydroxyflavone), a flavone subclass of flavonoid widely distributed in many herbs, fruits, and vegetables is a substantial component of the human diet and has been shown to possess a variety of biological activities including tumor growth inhibition and chemoprevention. Recent studies in several biological systems have shown that apigenin induces tumor growth inhibition, cell cycle arrest, and apoptosis. Free radical‐induced degradation of polyunsaturated fatty acid results in electrophilic products and causes severe oxidative stress. Oxidative stress induced by free radicals, nonoxidizing species, electrophiles, and associated DNA damages have been frequently coupled with carcinogenesis. In the present study, the protective role of apigenin was examined against the oxidative stress caused by N‐nitrosodiethylamine (NDEA) and phenobarbital (PB) in Wistar albino rats. Oxidative stress was measured in terms of lipid peroxidation (LPO) and protein carbonyl formation. Oxidative stress‐induced DNA damage was measured by single cell gel electrophoresis (comet assay). Apigenin exhibited its antioxidant defense against NDEA‐induced oxidative stress. We have observed minimal levels of LPO and DNA damage in apigenin‐treated hepatoma bearing animals. Based on the results, we suggest that apigenin may be developed as a promising chemotherapeutic agent against the development of chemical carcinogenesis.

Oral supplementation of piperine leads to altered phase II enzymes and reduced DNA damage and DNA-protein cross links in Benzo(a)pyrene induced experimental lung carcinogenesis.

In recent years, considerable emphasis has been focused on identifying new chemopreventive agents, which could be useful for the human population. Piperine is a pure, pungent alkaloid constituent of black and long peppers (piper nigrum and piper longum), which is a most common spice used throughout the world. In the present study, we examined the protective role of piperine during experimental lung carcinogenesis with reference to its effect on DNA damage and detoxification enzyme system. The activities of detoxifying enzymes such as glutathione transferase (GST), quinone reductase (QR) and UDP-glucuronosyl transferase (UDP-GT) were found to be decreased while the hydrogen peroxide level was increased in the lung cancer bearing animals. Supplementation of piperine (50 mg/kg bwt) enhanced the detoxification enzymes and reduced DNA damage as determined by single cell electrophoresis. Furthermore, the DNA-Protein cross links which was found to be high in lung cancer bearing animals was also modulated upon supplementation with piperine. Our present results explain the understanding of unique association between anti-peroxidative effect of piperine and ultimately the capability of piperine to prevent cancer. (Mol Cell Biochem 268: 141–147, 2005)

Chemopreventive effect of piperine on mitochondrial TCA cycle and phase-I and glutathione-metabolizing enzymes in benzo(a)pyrene induced lung carcinogenesis in Swiss albino mice

Piperine is a major component of black (Piper nigrum Linn) and long pepper (Piper longum Linn) used widely in various systems of traditional medicine. We have evaluated the effect of piperine on mitochondrial tricarboxylic acid cycle and phase I and glutathione-metabolizing enzymes in Benzo(a)pyrene induced experimental lung carcinogenesis in swiss albino mice. Lung cancer bearing mice showed a significant decrease in the activities of mitochondrial enzymes-isocitrate dehydrogenase (ICDH), -ketoglutarate dehydrogenase (KDH), succinate dehydrogenase (SDH), malate dehydrogenase (MDH) and significantly increased NADPH-Cytochorome reductase (NADPH-C reductase), cytochrome P450 (cyt-p450) and cytochrome b5(cyt-b5). The activities of glutathione-metabolizing enzymes glutathione peroxidase(GPx), glutathione reductase (GR) and glucose-6-phospho dehydrogenase(G6PDH) were significantly lowered in lung-cancer bearing mice when compared with control mice. Piperine supplementation to tumour-induced animals significantly lowered the phase-I enzymes (NADPH-C reductase, cyt-p450 and cyt-b5)) and there was a rise in glutathione-metabolizing enzymes (GPx, GR and G6PDH), which indicated an antitumour and anti-cancer effect. Comparison of normal control mice and mice administered piperine only as drug control showed no significant variations in enzyme activities. Piprine administration to benzo(a)pyrene induced animals significantly increased the activities of mitochondrial enzymes, thereby suggesting its role in mitochondrial energy production.

Cytoprotective effect of mangiferin on benzo(a)pyrene-induced lung carcinogenesis in swiss albino mice.

Antioxidants are one of the key players in tumourigenesis, and several natural and synthetic antioxidants have been shown to have anticancer effects. In the present investigation, the efficacy of mangiferin on the antioxidant status of benzo(a)pyrene-induced lung carcinogenesis in Swiss albino mice was assessed. The animals were divided into five groups. The animals in groups I and V were normal control and mangiferin control, respectively. Groups II, III and IV were administered with benzo(a)pyrene (50 mg/kg body weight, orally) for 4 weeks (twice a week) to induced lung carcinogenesis. Starting 1 week prior to benzo(a)pyrene administration, group III animals were treated with mangiferin (100 mg/kg body weight) in the diet for 18 weeks; 12 weeks after benzo(a)pyrene administration, group III animals were treated with mangiferin that continued until the end of the experiment period (18 weeks). At the end of the experiment period, the reactive oxygen species, glutathione and the activities of antioxidant enzymes were assessed in both lung and liver tissues. The levels of glutathione, superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, vitamin E and vitamin C were decreased in group II animals. However, in the mangiferin + benzo(a)pyrene-treated groups III and IV, the levels of GSH and the activities of antioxidant enzymes in both lung and liver were improved when compared with benzo(a)pyrene-induced group II animals. In addition, the finding that mangiferin decreased reactive oxygen species levels and enhanced antioxidant status suggests that this polyphenol might also be of value in the prevention of benzo(a)pyrene-induced lung carcinogenesis.