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The mechanism by which chronic treatment with HIV (human immunodeficiency virus)-1 protease inhibitors leads to a deterioration of glucose metabolism appears to involve insulin resistance, and may also involve impaired insulin secretion. Here we investigated the long-term effects of HIV-1 protease inhibitors on glucose-stimulated insulin secretion from beta cells and explored whether altered insulin secretion might be related to altered insulin signaling. INS-1 cells were incubated for 48 h with different concentrations of amprenavir, indinavir, nelfinavir, ritonavir or saquinavir, stimulated with 20 mM d-glucose, and insulin determined in the supernatant. To evaluate insulin signaling, cells were stimulated with 100 nM insulin for 2 min, and insulin-receptor substrate (IRS)-1, -2 and Akt phosphorylation determined. Incubation for 48 h with ritonavir, nelfinavir and saquinavir resulted in impaired glucose-induced insulin secretion at 2.5, 5 and 5 μM respectively, whereas amprenavir or indinavir had no effects even at 20 and 100 μM respectively. The impaired insulin secretion by ritonavir, nelfinavir and saquinavir was associated with decreased insulin-stimulated IRS-2 phosphorylation, and, for nelfinavir and saquinavir, with decreased insulin-stimulated IRS-1 and Thr³⁰⁸-Akt phosphorylation. No such effects on signaling were observed with amprenavir or indinavir. In conclusion, certain HIV-1 protease inhibitors, such as ritonavir, nelfinavir and saquinavir, not only induce peripheral insulin resistance, but also impair glucose-stimulated insulin secretion from beta cells. With respect to the long-term effect on beta-cell function there appear to be differences between the protease inhibitors that may be clinically relevant. Finally, these effects on insulin secretion after a 48 h incubation with protease inhibitor were associated with a reduction of the insulin-stimulated phosphorylation of insulin signaling parameters, particularly IRS-2, suggesting that protease inhibitor-induced alterations in the insulin signaling pathway may contribute to the impaired beta-cell function.

Leptin is an important adipocytokine whose main regulative effects on energy metabolism are exerted via activation of signalling pathways in the central nervous system. Another important regulator of energy homeostasis is insulin. The role of direct autocrine leptin effects on adipose tissue and crosstalk with insulin, in particular in the thermogenically active brown adipose tissue, remains unclear. In the present study, we have investigated leptin secretion and interaction with insulin in highly insulin-responsive immortalised mouse brown adipocytes. Leptin was secreted in a differentiation-dependent manner, and acute leptin treatment of mature adipocytes dose- and time-dependently stimulated phosphorylation of STAT3 and MAP kinase. Interestingly, acute pretreatment of fully differentiated brown adipocytes with leptin (100 nM) significantly diminished insulin-induced glucose uptake by approximately 25%. This inhibitory effect was time-dependent and maximal after 60 min of leptin prestimulation. Furthermore, it correlated with a 35% reduction in insulin-stimulated insulin receptor kinase activity after acute leptin pretreatment. Insulin-induced insulin receptor substrate-1 tyrosine phosphorylation and binding to the regulatory subunit p85 of phosphatidylinositol 3-kinase (PI 3-kinase) were diminished by approximately 60% and 40%, respectively. Taken together, this study has demonstrated strong differentiation-dependent leptin secretion in brown adipocytes and PI 3-kinase-mediated negative autocrine effects of this hormone on insulin action. Direct peripheral leptin-insulin crosstalk may play an important role in the regulation of energy homeostasis.

Obesity is associated with chronic inflammation. Pro-inflammatory adipokines may promote metabolic disorders and cardiovascular morbidity. However, the key mechanisms leading to obesity-related inflammation are poorly understood. The corticosteroid metabolism in adipose tissue plays a crucial role in the pathogenesis of the metabolic syndrome. Both the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR) mediate corticosteroid action in adipose tissue. The significance of the interplay of these receptors in mediating an inflammatory adipokine response is virtually unexplored. In the present study, we investigated the differential roles of the GR and MR in controlling the key adipose tissue functions including inflammatory adipokine expression and adipogenesis using selective stimulation with receptor agonists, acute receptor knockdown via RNA interference and newly generated knockout adipose cell lines. Selective GR stimulation of white adipocytes with dexamethasone inhibited the expression of interleukin 6 (IL6), monocyte chemoattractant protein-1 (MCP1 or CCL2 as listed in the MGI Database), tumour necrosis factor-α, chemerin and leptin. By contrast, selective MR stimulation with aldosterone promoted the expression of IL6, plasminogen activator inhibitor 1, chemerin and leptin. Furthermore, in the presence of an acute GR knockdown as well as in GR knockout adipocytes, corticosterone increased the gene expression of the pro-inflammatory adipokines IL6 and MCP1. Whereas GR knockout adipocytes displayed a mildly impaired adipogenesis during early differentiation, MR knockout cells completely failed to accumulate lipids. Taken together, our data demonstrate a critical role for the balance between gluco- and mineralocorticoid action in determining adipocyte responses implicated in obesity-associated inflammation and cardiovascular complications.