Transcriptional regulation of lipid metabolism by fatty acids: a key determinant of pancreatic β-cell function

BACKGROUND: Optimal pancreatic β-cell function is essential for the regulation of glucose homeostasis in both humans and animals and its impairment leads to the development of diabetes. Type 2 diabetes is a polygenic disease aggravated by environmental factors such as low physical activity or a hypercaloric high-fat diet. RESULTS: Free fatty acids represent an important factor linking excess fat mass to type 2 diabetes. Several studies have shown that chronically elevated free fatty acids have a negative effect on β-cell function leading to elevated insulin secretion basally but with an impaired response to glucose. The transcription factors PPARα, PPARγ and SREBP-1c respond to changing fat concentrations in tissues, thereby coordinating the genomic response to altered metabolic conditions to promote either fat storage or catabolism. These transcription factors have been identified in β-cells and it appears that each may exert influence on β-cell function in health and disease. CONCLUSION: The role of the PPARs and SREBP-1c as potential mediators of lipotoxicity is an emerging area of interest

Effects of lipopolysaccharide-induced septic shock on rat isolated kidney, possible role of nitric oxide and protein kinase C pathways

Objective(s): Pathophysiology of sepsis-associated renal failure (one of the most common cause of death in intensive care units) had not been fully determined. The effect of nitric oxide and protein kinase C (PKC) pathways in isolated kidney of Lipopolysaccharide-treated (LPS) rats were investigated in this study. Materials and Methods: Vascular responsiveness to phenylephrine and acetylcholine in the presence and absence of a potent PKC inhibitor (chelerythrine) and nonspecific NO inhibitor (L-NAME) as well as responses to acetylcholine and sodium nitroprusside (SNP) were examined.Results: LPS (10 mg/kg, IP) treatment resulted in a lower systemic pressure and reduction of responses to vasoconstrictor and vasodilator agents (PConclusion: Present study highlighted that five hours of intraperitoneal endotoxin injection is adequate to reduce renal basal perfusion pressure. These results also suggest that PKC inhibition may have a beneficial role in vascular hyporesponsiveness induced by LPS. Although our study partly elaborated on the effects of LPS on isolated renal vascular responses to vasoactive agents, further studies are required to explain how LPS exerts its renal vascular effects

Expression of PPARα modifies fatty acid effects on insulin secretion in uncoupling protein-2 knockout mice

AIMS/HYPOTHESIS: In uncoupling protein-2 (UCP2) knockout (KO) mice, protection of beta cells from fatty acid exposure is dependent upon transcriptional events mediated by peroxisome proliferator-activated receptor-α (PPARα). METHODS: PPARα expression was reduced in isolated islets from UCP2KO and wild-type (WT) mice with siRNA for PPARα (siPPARα) overnight. Some islets were also cultured with oleic or palmitic acid, then glucose stimulated insulin secretion (GSIS) was measured. Expression of genes was examined by quantitative RT-PCR or immunoblotting. PPARα activation was assessed by oligonucleotide consensus sequence binding. RESULTS: siPPARα treatment reduced PPARα protein expression in KO and WT islets by >85%. In siPPARα-treated UCP2KO islets, PA but not OA treatment significantly decreased the insulin response to 16.5 mM glucose. In WT islets, siPPARα treatment did not modify GSIS in PA and OA exposed groups. In WT islets, PA treatment significantly increased UCP2 mRNA and protein expression. Both PA and OA treatment significantly increased PPARα expression in UCP2KO and WT islets but OA treatment augmented PPARα protein expression only in UCP2KO islets (p < 0.05). PA treatment induced carnitine palmitoyltransferase I, acyl CoA oxidase and malonyl CoA decarboxylase mRNA in UCP2KO islets. CONCLUSION: These data show that the negative effect of saturated fatty acid on GSIS is mediated by PPARα/UCP2. Knockout of UCP2 protects beta-cells from PA exposure. However, in the absence of both UCP2 and PPARα even a short exposure (24 h) to PA significantly impairs GSIS

Uncoupling protein-2 increases nitric oxide production and TNFAIP3 pathway activation in pancreatic islets

Mutations in the uncoupling protein 2 (Ucp2) gene are linked to type-2 diabetes. Here, a potential mechanism by which lack of UCP2 is cytoprotective in pancreatic β-cells was investigated. Nitric oxide (NO) production was elevated in Ucp2−/− islets. Proliferation (cyclin D2, Ccnd2) and anti-apoptosis (Tnfaip3) genes had increased expression in Ucp2−/− islets, whereas the mRNA of pro-apoptosis genes (Jun, Myc) was reduced. TNFAIP3 cellular localization was detected in both α- and β-cells of Ucp2−/− islets but in neither α- nor β-cells of UCP2+/+ islets, where it was detected in pancreatic polypeptide-expressing cells. TNFAIP3 distribution was not markedly altered 14 days after streptozotocin treatment. Basal apoptosis was attenuated in Ucp2−/− β-cells, while the nuclear factor κB (NF-κB) pathway was transactivated after islet isolation. Ucp2+/+ and Ucp2−/− islets were treated with cytokines for 24 h. Cytokines did not increase NF-κB transactivation or apoptosis in Ucp2−/− islets and TNFAIP3 was more strongly induced in Ucp2−/− islets. Inhibition of NO production strongly reduced NF-κB activation and apoptosis. These data show that null expression of Ucp2 induces transactivation of NF-κB in isolated islets, possibly due to NO-dependent up-regulation of inhibitor of κB kinase β activity. NF-κB transactivation appears to result in altered expression of genes that enhance a pro-survival phenotype basally and when β-cells are exposed to cytokines. TNFAIP3 is of particular interest because of its ability to regulate NF-κB signaling pathways

Synthesis and antihypertensive activity of new 1,4-dihydropyridines

2343-2347A series of 1,4-dihydropyridines bearing dimethylamino 2a-f or 1H-imidazol-1-yl 3a-f side chain in the 2 position have been synthesized from unsubstituted ones 1a-f and tested for antihypertensive activity in desoxycorticosterone acetate (DOCA)-induced hypertensive rats. All the compounds have been found to be less active than nifedipine

Effects of 4-(2-Alkylthio-1-benzyl-5-imidazolyl)-Dihydropyridines on the Isolated Rat Colon and Right Atrium Contractility

Abstract Objectives In order to provide a pharmacological profile for some newly synthesized dihydropyridines, we investigated their effects on the isolated rat colon segments and the isolated rat atrium contractility. The tested compounds include alkyl ester analogues of nifedipine, in which the ortho-nitrophenyl group at position 4 is replaced by 2-alkylthio-1-benzyl-5-imidazolyl substituent, and nifedipine as a positive control substance. Materials and Methods Isolated rat colon and atrial tissues were prepared. Rat colon was contracted with 80 mM KCl, and maximum response was recorded (100%). After washing tissue with Krebs solution it was preincubated with different concentrations of test compounds and again KCl was added and percent change in contraction was calculated. Spontaneous contractions and its frequency for colon and atrium before and after addition of test compounds were also recorded and percent change was calculated. Nifedipine (10 -8 -10 -5 M) was used as positive control at all experiments. Results The compounds showed similar effects to that of nifedipine on the isolated rat colon. The potency of these analogues with concentration range 10 -5 to 10 -4 M was compared to potency of nifedipine which was effective at 10 -8 to 10 -5 M (P&lt;0.01). However, unlike nifedipine, the test compounds exerted significant positive inotropic effect on the isolated rat atrium (P &lt; 0.01). Our observations suggest that these analogues of nifedipine selectively enhance contractility of heart muscle while causing relaxation of intestinal smooth muscle. Conclusion These compounds may serve as valuable probes to develop novel dihydropyridines with dual smooth muscle relaxant effect and positive inotropic action

Different effects of L-arginine on morphine tolerance in sham and ovariectomized female mice*

Objective: The roles of gonadal hormones and nitric oxide (NO) on the analgesic effects of morphine, tolerance to morphine, and their interactions have been widely investigated. In the present study, the effect of L-arginine (an NO precursor) on morphine tolerance in sham and ovariectomized (OVX) female mice was investigated. Methods: Forty mice were divided into sham and OVX groups. On the first day, a hot plate test ((55±0.2) °C; cut-off 30 s) was carried out as a base record 15 min before injection of morphine (10 mg/kg, subcutaneously (s.c.)) and was repeated every 15 min after injection. The sham group was then divided into two subgroups: sham-tolerance-L-arginine (Sham-Tol-LA) and sham-tolerance-saline (Sham-Tol-Sal) which received either L-arginine 50 mg/kg (intraperitoneally (i.p.)) or saline 10 ml/kg (i.p.), respectively, three times in a day for three consecutive days. Morphine tolerance was induced in animals by injecting 30 mg/kg morphine (s.c.) three times/day for three days. This treatment was also used for OVX subgroups. On the fifth day, the hot plate test was repeated. The analgesic effect of morphine was calculated as the maximal percent effect (MPE). The results were compared using repeated measure analysis of variance (ANOVA). Results: There was no significant difference in MPE between the OVX and sham groups. The MPEs in both the Sham-Tol-Sal and OVX-Tol-Sal groups were lower than those in both the sham and OVX groups (P<0.01). The MPE in the OVX-Tol-Sal group was greater than that in the Sham-Tol-Sal group (P<0.01). The MPE in the Sham-Tol-LA group was higher than that in the Sham-Tol-Sal group (P<0.01). However, there was no significant difference between the Sham-Tol-LA and sham groups or between the OVX-Tol-LA and OVX-Tol-Sal groups. Conclusions: The results of the present study showed that repeated administration of morphine causes tolerance to the analgesic effect of morphine. L-Arginine could prevent tolerance to morphine but its effect was different in the presence of ovarian hormones