Effects of green tea catechin on hepatic microsomal phospholipase A2 activities and changes of hepatic phospholipid species in streptozotocin-induced diabetic rats

Protective role of Phyllanthusfraternus in alloxan-induced diabetes in rats

BACKGROUND

Phyllanthusfraternus is a pantropical weed of family phyllanthaceae, mainly found in northeast India. It has been used in the folklore medicine of Manipur tribe for treating type 2 diabetes.

OBJECTIVE

The present study was commenced to evaluate the anti-diabetic and renoprotective potential of P.fraternus (aerial parts) in alloxan-induced diabetes in rats.

MATERIALS AND METHODS

Alloxan (130 mg/kg, ip) was used for the induction of diabetes in adult male wistar rats. Animals with blood glucose level greater than 280 mg/dL were treated once daily for 14 days with various test extracts. The biochemical parameters were measured from serum on the 15th day post-treatment. Necropsy samples harvested from pancreas and kidneys were examined for histopathological changes in these organs.

RESULTS

Alloxan-induced diabetes not only caused significant increases in blood glucose, triglycerides, total cholesterol, creatinine and urea levels, but also provoked high oxidative stress in pancreas and kidneys. Profound morphological injuries were observed in islets of Langerhans and kidneys of diabetic animals. Administration of methanol extract (200 and 400 mg/kg) and mother liquor (200 and 400 mg/kg) ameliorate the elevated levels of blood glucose, triglycerides, total cholesterol as well as other biochemical parameters, but highest reduction in blood glucose concentration was observed with the largest dose of ethyl acetate fraction (400 mg/kg) of P.fraternus. Histopathological examination of pancreas and kidneys also exhibited greater protection by treatment with acetate fraction (400 mg/kg). The HPLC analysis showed the presence of four polyphenols such as catechin, gallic acid, caffeic acid and ellagic acid in ethyl acetate fraction of P. fraternus during HPLC analysis.

CONCLUSION

The results suggest that polyphenols present in P.fraternus may be responsible for the anti-diabetic and renoprotective activity in rats. Such protective effects of could be mediated through flavonol-induced anti-oxidant and anti-inflammatory activities in the pancreas and kidneys.

Metabolomics evaluation of the effects of green tea extract on acetaminophen-induced hepatotoxicity in mice

Green tea has been purported to have beneficial health effects including protective effects against oxidative stress. Acetaminophen (APAP) is a widely used analgesic drug that can cause acute liver injury in overdose situations. These studies explored the effects of green tea extract (GTE) on APAP-induced hepatotoxicity in liver tissue extracts using ultra performance liquid chromatography/quadrupole time-of-flight mass spectrometry and nuclear magnetic resonance spectroscopy. Mice were orally administered GTE, APAP or GTE and APAP under three scenarios. APAP alone caused a high degree of hepatocyte necrosis associated with increases in serum transaminases and alterations in multiple metabolic pathways. The time of GTE oral administration relative to APAP either protected against or potentiated the APAP-induced hepatotoxicity. Dose dependent decreases in histopathology scores and serum transaminases were noted when GTE was administered prior to APAP; whereas, the opposite occurred when GTE was administered after APAP. Similarly, metabolites altered by APAP alone were less changed when GTE was given prior to APAP. Significantly altered pathways included fatty acid metabolism, glycerophospholipid metabolism, glutathione metabolism, and energy pathways. These studies demonstrate the complex interaction between GTE and APAP and the need to employ novel analytical strategies to understand the effects of dietary supplements on pharmaceutical compounds.

Beneficial effects of green tea: a literature review

The health benefits of green tea for a wide variety of ailments, including different types of cancer, heart disease, and liver disease, were reported. Many of these beneficial effects of green tea are related to its catechin, particularly (-)-epigallocatechin-3-gallate, content. There is evidence from in vitro and animal studies on the underlying mechanisms of green tea catechins and their biological actions. There are also human studies on using green tea catechins to treat metabolic syndrome, such as obesity, type II diabetes, and cardiovascular risk factors.Long-term consumption of tea catechins could be beneficial against high-fat diet-induced obesity and type II diabetes and could reduce the risk of coronary disease. Further research that conforms to international standards should be performed to monitor the pharmacological and clinical effects of green tea and to elucidate its mechanisms of action.

Effects of green tea catechin on polymorphonuclear leukocyte 5'-lipoxygenase activity, leukotriene B4 synthesis, and renal damage in diabetic rats

The purpose of this study was to investigate the effects of green tea catechin on polymorphonuclear leukocyte 5'-lipoxygenase activity, leukotriene B4 synthesis, and renal damage in diabetic rats. Male Sprague-Dawley rats weighing 100 +/- 10 g were randomly assigned to 1 normal group and 3 diabetic groups given a catechin-free diet (DM-0C group), 0.25% catechin diet (DM-0.25C group), or 0.5% catechin diet (DM-0.5C group), respectively. 5'-Lipoxygenase activity in the polymorphonuclear leukocytes significantly increased by 54% in the DM-0C group compared to the normal group, while the level in the DM-0.5C group remained the same as in the normal group. The leukotriene B4 content in the polymorphonuclear leukocytes increased 55% in the DM-0C group compared to the normal group, whereas the DM-0.25C and DM-0.5C groups exhibited the same level as the normal group. The superoxide radical content in the kidney microsomes increased 116% in the DM-0C group when compared to the normal group, yet decreased 29% in the DM-0.25C group and 50% in the DM-0.5C group compared to DM-0C group. The lipofuscin content was 197 and 136% higher in the DM-0C and DM-025C groups, respectively, than in the normal group, whereas the DM-0.5C group exhibited the same content as in the normal group. The carbonyl value increased 118% in the DM-0C group compared to the normal group, and the DM-0.25C and DM-0.5C groups were not significantly different from the DM-0C group. Accordingly, these results indicate that dietary catechin inhibited the generation of superoxide radicals, oxidized protein, and lipid peroxide in the kidney of streptozotocin-induced diabetic rats. Furthermore, green tea catechin supplementation in diabetic rats also appeared to inhibit the production of leukotriene B4 based on regulating the activity of 5'-lipoxygenase, thereby potentially reducing renal oxidative damage and inflammatory reactions.

Green tea catechin improves microsomal phospholipase A2 activity and the arachidonic acid cascade system in the kidney of diabetic rats

The purpose of this study was to investigate the effects of green tea catechin on the microsomal phospholipase A2 activity and arachidonic acid cascade in the kidneys of streptozotocin-induced diabetic rats. Sprague-Dawley male rats weighing 100 +/- 10 g were assigned randomly to one normal and three streptozotocin-induced diabetic groups. The diabetic groups were the DM-0C group (n = 10), fed a catechin-free diet, the DM-0.25C group (n = 10), fed a 0.25 g catechin per 100 g diet, and the DM-0.5C group (n = 10), fed a 0.5 g catechin per 100 g diet. The kidney microsomal phospholipase A2 activity was higher in the diabetic groups than in the normal group, while it was lower in the DM-0.25C and DM-0.5C groups than in the DM-OC group. The percentage of phosphatidylcholine hydrolysed in the kidney microsomes was not significantly different between any of the four groups. The percentage of phosphatidylethanolamine hydrolysed in the kidney microsomes was progressively higher in the DM-0.5C, DM-0.25C and DM-OC groups, respectively, compared to the normal group. The formation of thromboxane A2 was significantly higher while the formation of prostacyclin was lower in kidney microsomes of the streptozotocin-induced diabetic groups compared with the normal group, but this condition was improved by catechin supplementation. Kidney microsomal vitamin E concentrations were progressively lower in the DM-0.5C, DM-0.25C, and DM-0C groups, respectively, compared to the normal group. The kidney thiobarbituric acid reactive substance (TBARS) contents became higher in the DM-0C and DM-0.25C groups as compared with the normal group, whereas the DM-0.5C group did not differ from the normal group. Kidney function appears to be improved by green tea catechin supplementation due to its antithrombus action, which in turn controls the arachidonic acid cascade system.

Anti-diabetic activity of green tea polyphenols and their role in reducing oxidative stress in experimental diabetes

An aqueous solution of green tea polyphenols (GTP) was found to inhibit lipid peroxidation (LP), scavenge hydroxyl and superoxide radicals in vitro. Concentration needed for 50% inhibition of superoxide, hydroxyl and LP radicals were 10, 52.5 and 136 micro g/ml, respectively. Administration of GTP (500 mg/kg b.wt.) to normal rats increased glucose tolerance significantly (P<0.005) at 60 min. GTP was also found to reduce serum glucose level in alloxan diabetic rats significantly at a dose level of 100 mg/kg b.wt. Continued daily administration (15 days) of the extract 50, 100 mg/kg b.wt. produced 29 and 44% reduction in the elevated serum glucose level produced by alloxan administration. Elevated hepatic and renal enzymes produced by alloxan were found to be reduced (P<0.001) by GTP. The serum LP levels which was increased by alloxan and was reduced by significantly (P<0.001) by the administration of 100 mg/kg b.wt. of GTP. Decreased liver glycogen, after alloxan administration showed a significant (P<0.001) increase after GTP treatment. GTP treated group showed increased antioxidant potential as seen from improvements in superoxide dismutase and glutathione levels. However catalase, LP and glutathione peroxidase levels were unchanged. These results indicate that alterations in the glucose utilizing system and oxidation status in rats increased by alloxan were partially reversed by the administration of the glutamate pyruvate transaminase.

Hepatobiliary scintigraphy for evaluating the hepatotoxic effect of halothane and the protective effect of catechin in comparison with histo-chemical analysis of liver tissue

Halothane and its metabolites cause liver damage by decreasing liver blood flow and generating free-radical species. Catechin suppresses lipid peroxidation and increases enzyme activity, therefore it seems to be capable of protecting liver parenchyma against the direct toxic effect of halothane. The aim of this study was to investigate the role of hepatobiliary scintigraphy in detecting liver damage after halothane anaesthesia and the protective effect of catechin in comparison with histo-chemical analysis. Thirty rabbits, divided into three groups (A, controls; B, halothane; and C, catechin+halothane), were investigated. In group A no anaesthesia was administered. Group B only received halothane, while group C was pretreated with catechin and halothane anaesthesia was administered for 2 h. Dynamic scintigrams were taken for 60 min after injecting 99mTc-mebrofenin, and the time of peak uptake (TPU) and the time for half of the activity to clear from the liver (T(1/2)) were calculated. Rabbits were killed, and malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT) levels were measured in hepatic tissue. The TPU and T(1/2) values of group A is significantly lower than in groups B and C (P<0.0002 and P<0.0002, respectively, for TPU; and P<0.0002 and P<0.0003, respectively, for T(1/2)). The TPU and T(1/2) values of group B were significantly higher than in group C (P<0.0003 and P<0.0003, respectively). The hepatic MDA level of group A was significantly lower than in groups B and C (P<0.0002 and P<0.0002, respectively). SOD, GSH-Px and CAT levels of group A were significantly higher than in groups B and C (P<0.0002, P<0.0001 and P<0.003, respectively, for group A vs group B; and P<0.0005, P<0.0002 and P<0.03, respectively, for group A vs group C). The MDA level of group B was significantly higher than that in group C (P<0.0002). SOD, GSH-Px and CAT levels of group B were significantly lower than in group C (P<0.0002, P<0.0002 and P<0.003, respectively). According to these results, we suggest that catechin protects liver parenchyma against the toxic effect of halothane and its metabolites, and that, compared to invasive histo-chemical analysis, hepatobiliary scintigraphy is a useful and alternative non-invasive method for detecting the protective effect of catechin on liver parenchyma after halothane anaesthesia.

Prostaglandylinositol cyclic phosphate (cPIP): a novel second messenger of insulin action. Comparative analysis of two kinds of "insulin mediators"

Insulin induces a broad spectrum of effects over a wide time interval. It also stimulates the phosphorylation of some cellular proteins, while decreasing the state of phosphorylation of others. These observations indicate the presence of different, but not necessarily mutually exclusive, pathways of insulin action. One well-known pathway represents a phosphorylation cascade initiated by the tyrosine kinase activity of the insulin receptor followed by involvement of different MAP-kinases. Another pathway suggests the existence of low molecular weight insulin mediators whose synthesis and/or release is initiated by insulin. Comparable analysis of two kinds of insulin mediators, namely inositolphosphoglycans and prostaglandylinositol cyclic phosphate (cPIP), has been carried out. It has been shown that the expression of a number of enzymes, such as phospholipase A(2), phospholipase C, cyclo-oxygenase and IRS-1-like enzyme, could regulate the biosynthesis of cPIP in both normal and diabetes-related conditions. Data on the activity of a key enzyme of cPIP biosynthesis termed cPIP synthase (IRS-1-like enzyme) in various monkey tissues before and twice during an euglycemic hyperinsulinemic clamp have been presented. It has been concluded that in vivo insulin increases cPIP synthase activity in both liver and subcutaneous adipose tissue of lean normal monkeys. It has been also suggested that abnormal production of cPIP could be related to several pathologies including glucocorticoid-induced insulin resistance and diabetic embryopathy. Further studies on cPIP and other types of insulin mediators are necessary to aid our understanding of insulin action.

Vitamin E improves microsomal phospholipase A2 activity and the arachidonic acid cascade in kidney of diabetic rats

The purpose of the present study was to investigate the effects of vitamin E on microsomal phospholipase A2 activity and the arachidonic acid cascade in the kidneys of streptozotocin (STZ)-induced diabetic rats. Sprague-Dawley male rats weighing 100 +/- 10 g were randomly assigned to one normal and three STZ-induced diabetic groups. The diabetic groups were fed a vitamin E-free diet (the DM-0E group), 40 mg vitamin E/kg diet (the DM-40E group) or a 400 mg vitamin E/kg diet (the DM-400E group). The kidney vitamin E concentrations were 59 and 49% lower in the DM-0E and DM-40E groups, respectively, than in the normal group. The kidney thiobarbituric acid reactive substance concentrations in the DM-0E, DM-40E and DM-400E groups were 119, 84 and 33% greater, respectively, than that in the normal group. The concentration in the DM-400E group was 39% lower than that in the DM-0E group. The phospholipase A2 (PLA2) activity in the kidney microsomes of the DM-0E-40E and DM-400E groups were 88, 58 and 35% greater, respectively, than that in the normal group. The activity in the DM-400E group was 28% lower than that in the DM-0E group and 16% lower than that in the DM-40E group. The differences in the phospholipids in the kidney microsomes included reductions in the phosphatidylcholine and phosphatidylethanolamine compositions. Phosphatidylethanolamine hydrolysis in the kidney microsomes of the DM-0E and DM-40E groups were 84 and 64%, which did not differ from the DM-400E group. The formation of thromboxane A2 (TXA2) in the kidney microsomes was 137 and 70% greater in the DM-0E and DM-40E groups, respectively, than in the normal group. TXA2 formation did not differ between the DM-400E and normal groups. The formation of prostacyclin in the kidney microsomes was 60 and 44% lower in the DM-0E and DM-40E groups, respectively, than in the normal group, whereas the DM-400E group did not differ from that in the normal group. The ratio of prostacyclin to TXA2 was 82 and 65% lower than normal in the DM-0E and DM-40E groups, respectively. Kidney function appears to be improved by vitamin E supplementation due to its antithrombus action, which in turn controls the arachidonic acid cascade system.

Ethyl docosahexaenoate-associated decrease in fetal brain lipid peroxide production is mediated by activation of prostanoid and nitric oxide pathways

Previously we have shown that intraamniotic administration of ethyl docosahexaenoate (Et-DHA) to pregnant rats resulted in decreased lipid peroxidation in the fetal brain, under a variety of conditions (S. Glozman, P. Green, E. Yavin, J. Neurochem. 70 (1998) 2482-2491). In the present study we examine the potential mechanisms to explain this effect. This was done by a pharmacological approach, utilizing brain slice preparations from Et-DHA treated or control rats in the presence of various agents and examining the formation of products in the tissue slices or incubation medium. Et-DHA treated brains produced 2-3-fold more prostanoids (PN) than control brains, indicating cyclooxygenase (COX) activation. Indomethacin at 50 microM inhibited PN formation and also abolished Et-DHA induced decrease in lipid peroxides, as evident by the levels of thiobarbituric acid reactive substances (TBARS) released in the medium. The phospholipase A2 inhibitors quinacrine and p-bromophenacyl bromide added at 0.1 mM concentration each to either slices from controls or Et-DHA treated fetal brains, decreased TBARS production. Et-DHA treated brains released 2.2-fold more nitric oxide (NO) than control brains and NO synthase (NOS) inhibitors abolished this effect. Increasing the concentration of NO by the addition of an NO donor greatly decreased the concentration of the TBARS in the medium. These results suggest that at least some of the effect of Et-DHA on decreased lipid peroxidation may be explained by a shift of oxygen species utilization via enzymatically regulated, therefore metabolically controlled, COX and NOS activities.