Search

In the rat, a single subcutaneous injection of sodium dichromate (20 mg/kg) causes acute renal injury and significant polyuria, proteinuria, and glycosuria (peaking 2–3 days after treatment, and returning to normal by day 5) without any changes in the plasma levels of protein, glucose, and glycated haemoglobin. Surprisingly, the percentage levels of glycated plasma total proteins and albumin (assayed by boronate affinity chromatography) transiently and significantly decrease during recovery from proteinuria (days 4 and 10 after treatment) and were found in the normal range of values by day 18. These changes are concomitant with a significant increase in the percentage level of glycated albumin in urine. Constancy of total plasma protein and the temporal pattern of levels of glycation suggest that changes in the percentage values of glycated proteins are secondary to a transient selective loss of glycated plasma proteins in urine. [ABSTRACT FROM AUTHOR]

Metabolic syndrome is a proatherosclerotic condition clustering cardiovascular risk factors, including glucose and lipid profile alterations. The pathophysiological mechanisms favoring atherosclerotic inflammation in the metabolic syndrome remain elusive. Here, we investigated the potential role of the antilipolytic drug acipimox on neutrophil- and monocyte-mediated inflammation in the metabolic syndrome. Acipimox (500 mg) was orally administered to metabolic syndrome patients (n = 11) or healthy controls (n = 8). Serum and plasma was collected before acipimox administration (time 0) as well as 2-5 h afterward to assess metabolic and hematologic parameters. In vitro, the effects of the incubation with metabolic syndrome serum were assessed on human neutrophi I and monocyte migration toward the proatherosclerotic chemokine CCL3. Two to five hours after acipimox administration, a significant reduction in circulating levels of insulin and nonesterified fatty acid (NEFA) was shown in metabolic syndrome patients. At time o and 2 h after acipimox administration, metabolic syndrome serum increased neutrophil migration to CCL3 compared with healthy controls. No effect was shown in human monocytes. At these time points, serum-induced neutrophil migration positively correlated with serum levels of insulin and NEFA. Metabolic syndrome serum or recombinant insulin did not upregulate CCR5 expression on neutrophil surface membrane, but it increased intracellular JNK1/2 phosphorylation. Insulin immunodepletion blocked serum-induced neutrophil migration and associated JNKI/2 phosphorylation. Although mRNA expression of acipimox receptor (GPRIO9) was shown in human neutrophils, 5-500 μM acipimox did not affect insulin-induced neutrophil migration. In conclusion, results suggest that acipimox inhibited neutrophil proatherosclerotic functions in the metabolic syndrome through the reduction in circulating levels of insulin. [ABSTRACT FROM AUTHOR]

Vitamin E deficiency increases expression of the CD36 scavenger receptor, suggesting specific molecular mechanisms and signaling pathways modulated by α-tocopherol. We show here that α-tocopherol down-regulated CD36 expression (mRNA and protein) in oxidized low density lipoprotein (oxLDL)-stimulated THP-1 monocytes, but not in unstimulated cells. Furthermore, α-tocopherol treatment of monocytes led to reduction of fluorescent oxLDL-3,3′-dioctadecyloxacarbocyanine perchlorate binding and uptake. Protein kinase C (PKC) appears not to be involved because neither activation of PKC by phorbol 12-myristate 13-acetate nor inhibition by PKC412 was affected by α-tocopherol. However, α-tocopherol could partially prevent CD36 induction after stimulation with a specific agonist of peroxisome proliferator-activated receptor-γ (PPARγ; troglitazone), indicating that this pathway is susceptible to α-tocopherol action. Phosphorylation of protein kinase B (PKB) at Set473 was increased by oxLDL, and α-tocopherol could prevent this event. Expression of PKB stimulated the CD36 promoter as well as a PPARγ element-driven reporter gene, whereas an inactive PKB mutant had no effect. Moreover, coexpression of PPARγ and PKB led to additive induction of CD36 expression. Altogether, our results support the existence of PKB/PPARγ signaling pathways that mediate CD36 expression in response to oxLDL. The activation of CD36 expression by PKB suggests that both lipid biosynthesis and fatty acid uptake are stimulated by PKB. [ABSTRACT FROM AUTHOR]

In an effort to better understand the phenomenon of lipotoxicity in human beta-cells, we evaluated the effects of 48-h preculture with 1.0 or 2.0 mmol/l free fatty acid (FFA) (2:1 oleate to palmitate) on the function and survival of isolated human islets and investigated some of the possible mechanisms. Compared with control islets, triglyceride content was significantly increased and insulin content and glucose-stimulated insulin release were significantly reduced in islets precultured with increased FFA concentrations. These changes were accompanied by a significant reduction of glucose utilization and oxidation. By cell death detection techniques, it was observed that exposure to FFAs induced a significant increase of the amount of dead cells. Electron microscopy showed the involvement of beta-cells, with morphological appearance compatible with the presence of apoptotic phenomena. FFA-induced islet cell death was blocked by inhibition of upstream caspases and partially prevented by inhibiton of ceramide synthesis or serine protease activity, whereas inhibition of nitric oxide synthesis had no effect. RT-PCR studies revealed no major change of iNOS and Bax mRNA expression and a marked decrease of Bcl-2 mRNA expression in the islets cultured with FFA. Thus, prolonged exposure to FFAs has cytostatic and pro-apoptotic effects on human pancreatic beta-cells. The cytostatic action is likely to be due to the FFA-induced reduction of intraislet glucose metabolism, and the proapoptotic effects are mostly caspase mediated, partially dependent on ceramide pathway, and possibly Bcl-2 regulated. [ABSTRACT FROM AUTHOR]

Type 2 (non-insulin-dependent) diabetes results from decreased insulin action in peripheral target tissues (insulin resistance) and impaired pancreatic beta-cell function. These defects reflect both genetic components and environmental risk factors. Recently, the common Gly(972)-->Arg amino acid polymorphism of insulin receptor substrate 1 (Arg(972) IRS-1) has been associated with human type 2 diabetes. In this study, we report on some functional and morphological properties of isolated human islets carrying the Arg(972) IRS-1 polymorphism. Insulin content was lower in variant than control islets (94 +/- 47 vs. 133 +/- 56 microU/islet; P < 0.05). Stepwise glucose increase (1.7 to 16.7 mmol/l) significantly potentiated insulin secretion from control islets, but not Arg(972) IRS-1 islets, with the latter also showing a relatively lower response to glyburide and a significantly higher response to arginine. Proinsulin release mirrored insulin secretion, and the insulin-to-proinsulin ratio in response to arginine was significantly lower from Arg(972) IRS-1 islets than from control islets. Glucose utilization and oxidation did not differ in variant and wild-type islets at both low and high glucose levels. Electron microscopy showed that Arg(972) IRS-1 beta-cells had a severalfold greater number of immature secretory granules and a lower number of mature granules than control beta-cells. In conclusion, Arg(972) IRS-1 islets have reduced insulin content, impaired insulin secretion, and a lower amount of mature secretory granules. These alterations may account for the increased predisposition to type 2 diabetes in individuals carrying the Gly(972)-->Arg amino acid polymorphism of IRS-1. [ABSTRACT FROM AUTHOR]