Pterostilbene induces cell cycle arrest and apoptosis in MOLT4 human leukemia cells.

Pterostilbene, a polyphenolic compound present in grapes and other fruits, has been demonstrated to inhibit growth and induce apoptosis and autophagy in some cancer cell types. We found that pterostilbene at the IC(90) concentration of 44 µM inhibited proliferation and induced apoptosis in MOLT4 human leukemia cells. Treatment with pterostilbene resulted in a transient accumulation of cells in the G(0)/G(1)-cell cycle phase followed by the S-phase arrest. Pterostilbene-induced apoptotic death of MOLT4 cells was mediated by caspase-3 activation and was accompanied by the disruption of mitochondrial membrane potential, phosphatidylserine externalization and internucleosomal DNA fragmentation. Our results suggest that pterostilbene could serve as a potential additional chemotherapeutic agent for the treatment of leukemia.

Feedback inhibition of cholesterol biosynthesis by dietary cholesterol in experimental chronic renal failure.

OBJECTIVE: Enhanced liver cholesterol synthesis is present in experimental chronic renal failure (CRF), even though cholesterol concentrations in blood and liver are increased, suggesting that CRF results in disturbed cholesterolegenesis feedback regulation. DESIGN: This study sought to elucidate whether dietary cholesterol exerts inhibitory effects on liver cholesterologenesis in CRF rats. METHODS: Male Wistar rats were used. Experimental CRF was achieved by a 5/6 nephrectomy model. Cholesterologenesis was measured (1) in vivo by tritiated water incorporation into cholesterol, and (2) in vitro (using liver slices) by [(14)C]-acetate and [(3)H]-mevalonate incorporation into cholesterol. In addition, the mRNA abundance of 3-hydroxy-3-methylglutaryl-CoA reductase, a rate-limiting enzyme in cholesterologenesis pathway, as well as its activity, was determined. Finally, the mRNA level of liver sterol regulatory element-binding protein-2, a nuclear transcription factor engaged in intracellular cholesterol homeostasis, was measured. RESULTS: Experimental CRF was associated with significantly increased concentrations of serum and liver cholesterol. In vitro and in vivo cholesterologenesis was enhanced in CRF rats. A cholesterol-enriched diet resulted in a significant decrease in (1) in vivo and in vitro cholesterol synthesis, (2) 3-hydroxy-3-methylglutaryl-CoA reductase gene expression, and (3) the level of liver sterol regulatory element-binding protein-2 mRNA in CRF rats. CONCLUSIONS: Despite elevated plasma and liver cholesterol concentrations, cholesterologenesis is increased in CRF rats. It is, however, inhibited by dietary cholesterol. These results suggest that a feedback inhibition of cholesterologenesis by dietary cholesterol is preserved in experimental CRF.

Increased gene expression of liver SREBP-2 in experimental chronic renal failure.

Sterol regulatory element-binding protein-2 (SREBP-2) is a transcription factor regarded as the main regulator of cholesterol homeostasis. Therefore, increased level of SREBP-2 could be responsible for hypercholesterolemia, which is observed in experimental chronic renal failure (CRF). This study was designed primary to evaluate the impact of experimental CRF (5/6 nephrectomy model) on rat liver SREBP-2 gene expression. In CRF rats, a twofold increase in SREBP-2 mRNA level, as well as in mature SREBP-2 protein abundance was found, when compared to control animals. It was associated with enhanced activity and mRNA abundance of liver HMG-CoA reductase, a rate-limiting enzyme for cholesterol biosynthesis. A twofold increase in liver cholesterologenesis rate was also noted. We conclude that experimental CRF is associated with increased liver SREBP-2 gene expression. This is probably the cause for enhanced HMG-CoA reductase gene expression and, consequently, for increase in liver cholesterol synthesis in CRF rats. Despite increased SREBP-2 gene expression we found LDL-receptor mRNA level to be lower than in controls, suggesting SREBP-2 independent mechanisms of LDL-receptor transcriptional regulation in CRF rats. Enhanced cholesterol synthesis and decreased LDL-receptor mRNA level are probably responsible for an almost fourfold increase in serum cholesterol concentration in CRF rats.

Does resveratrol prevent free radical-induced acute pancreatitis?

OBJECTIVE: The purpose of this study was to examine protective and antioxidative effect of stilbene derivatives, resveratrol and diethylstilbestrol, in experimental acute pancreatitis (EAP). METHODS: EAP was induced in male Wistar rats by retrograde injection of tert-butyl hydroperoxide (ButOOH) solution, a well-known prooxidant agent, into the common bile pancreatic duct. After a 3-hour observation, the animals were killed. Blood samples were collected. Each pancreas was removed and weighed. Tissue samples were taken for microscopic studies. The carbonyl and sulfhydryl (SH) group levels were estimated in the homogenate. RESULTS: Examination using light microscopy revealed morphologic changes in pancreata removed from EAP rats, namely focal edema, acinar cell vacuolization, and focal necrosis of pancreatic acini. The electron microscopic analysis also showed changes in their subcellular structures: dilated cisternae of the rough endoplasmic reticulum, swollen mitochondria, and "debris" of mitochondrial cristae. These changes corresponded with higher activities of serum amylase and tissue carbonyl groups levels and decreased SH group level compared with controls. Changes in pancreata were much less pronounced in the rats that received resveratrol or diethylstilbestrol for 8 days prior to ButOOH injection. CONCLUSION: Stilbene derivatives prevent pancreatic cells from structural changes during ButOOH-induced acute pancreatitis.

Contribution of increased HMG-CoA reductase gene expression to hypercholesterolemia in experimental chronic renal failure.

The aim of the present study was to examine hypothesis that the enhanced cholesterologenesis, found in rats with experimental chronic renal failure (CRF) resulted from the increased gene expression of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase--the rate limiting enzyme in the cholesterologenesis pathway, responsible for mevalonate synthesis. Wistar rats were used and experimental CRF was achieved by 5/6 nephrectomy model. We examined: (a) the changes in the rat liver microsomal HMG-CoA reductase activity, (b) the rat liver HMG-CoA reductase mRNA abundance in various times of day. Obtained data indicates that the increased activity of HMG-CoA reductase in the liver of rats with experimental CRF parallel enhanced mRNA level and suggests that enhanced cholesterol biosynthesis, observed in experimental CRF is at least in part due to the increased HMG-CoA reductase gene expression. The results also indicate that the physiological diurnal rhythm of HMG-CoA reductase activity is preserved in the course of experimental CRF.

[Pathomechanism of hyperlipoproteinemia in chronic renal failure]. / Patomechanizm hiperlipoproteinemii w przewleklej niewydolnosci nerek.

Lipid disorders are one of the known metabolic changes associated with chronic renal failure (CRF) [1, 2]. They are present as: hypertriglyceridemia--existed in 60% of CRF patients and hypercholesterolemia observed in 20-30% of people with this syndrome. These disorders, what was shown also in our own studies, are existing in different intensity in patients treated with maintenance haemodialysis [3], peritoneal dialysis [4] and after renal transplantation as well [5]. Mechanism of hypertriglyceridemia, despite over thirty years of studies, is still not finally elucidated. The opinion that it is a result of impaired triglyceride removal (due to decreased activities of both lipoprotein and hepatic lipases) is well documented, however the role of lipogenesis in its development is obscure [6, 7]. The reports concerning this problem contain contradictory data. In our studies performed several years ago we have shown that lipogenesis rate in white adipose tissue of uremic rats is significantly augmented [8, 9, 10] due to activation of free fatty acid synthase. Therefore, recently we paid once again our attention on the activity of this lipogenesis rate limiting enzyme responsible for the long term regulation. We measured its activity, protein abundance and mRNA level in liver and epididymal white adipose tissue of rats with surgically induced renal failure (two-stage subtotal nephrectomy). The results support the thesis that lipogenesis takes a part in a hypertriglyceridemia found in renal failure. There have been observed a significant increase in plasma triglyceride and VLDL concentrations in uremic animals and it was associated with the increase of FAS activity, FAS protein abundance and FAS mRNA. The results were similar in both studied tissues. Moreover, there have been also observed the increased activities of malic enzyme, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. All these enzymes participate in NADPH production, which is a necessary substrate for fatty acid biosynthesis [11, 12, 13]. Concluding, it appears that the rise in plasma triglyceride and VLDL concentrations observed in CRF rats is not only the result of increased liver and white adipose tissue lipogenesis rate. One has to remember, that these date are strictly original and enabling to elucidation further pathogenesis of hyperlipidemia in CRF. In the second set of experiments performed also in rats with experimentally induced CRF we have found that hypercholesterolemia observed in those animals is dependent on the significant activation of cholesterol synthase, induced by increased production of this enzyme (increment of protein abundance and synthase mRNA [14, 15]. Simultaneously, we have performed original studies on the diurnal rhythm of cholesterologenesis, showing that activity of this process is significantly augmented during whole twenty four hours [15]. Summarizing, one have to underline that our observations have important impact to the elucidation of lipid disturbances pathomechanism. Nevertheless further studies are necessary to establish how experimental data are corresponding with human pathology.