Endothelial Cell-Targeted Deletion of PPARγ Blocks Rosiglitazone-Induced Plasma Volume Expansion and Vascular Remodeling in Adipose Tissue.

Thiazolidinediones (TZDs) are peroxisome proliferator-activated receptor γ (PPARγ) agonists that represent an effective class of insulin-sensitizing agents; however, clinical use is associated with weight gain and peripheral edema. To elucidate the role of PPARγ expression in endothelial cells (ECs) in these side effects, EC-targeted PPARγ knockout (Pparg ΔEC) mice were placed on a high-fat diet to promote PPARγ agonist-induced plasma volume expansion, and then treated with the TZD rosiglitazone. Compared with Pparg-floxed wild-type control (Pparg f/f) mice, Pparg ΔEC treated with rosiglitazone are resistant to an increase in extracellular fluid, water content in epididymal and inguinal white adipose tissue, and plasma volume expansion. Interestingly, histologic assessment confirmed significant rosiglitazone-mediated capillary dilation within white adipose tissue of Pparg f/f mice, but not Pparg ΔEC mice. Analysis of ECs isolated from untreated mice in both strains suggested the involvement of changes in endothelial junction formation. Specifically, compared with cells from Pparg f/f mice, Pparg ΔEC cells had a 15-fold increase in focal adhesion kinase, critically important in EC focal adhesions, and >3-fold significant increase in vascular endothelial cadherin, the main component of focal adhesions. Together, these results indicate that rosiglitazone has direct effects on the endothelium via PPARγ activation and point toward a critical role for PPARγ in ECs during rosiglitazone-mediated plasma volume expansion.

Effects of small interfering RNA-mediated hepatic glucagon receptor inhibition on lipid metabolism in db/db mice.

Hepatic glucose overproduction is a major characteristic of type 2 diabetes. Because glucagon is a key regulator for glucose homeostasis, antagonizing the glucagon receptor (GCGR) is a possible therapeutic strategy for the treatment of diabetes mellitus. To study the effect of hepatic GCGR inhibition on the regulation of lipid metabolism, we generated siRNA-mediated GCGR knockdown (si-GCGR) in the db/db mouse. The hepatic knockdown of GCGR markedly reduced plasma glucose levels; however, total plasma cholesterol was increased. The detailed lipid analysis showed an increase in the LDL fraction, and no change in VLDL HDL fractions. Further studies showed that the increase in LDL was the result of over-expression of hepatic lipogenic genes and elevated de novo lipid synthesis. Inhibition of hepatic glucagon signaling via siRNA-mediated GCGR knockdown had an effect on both glucose and lipid metabolism in db/db mice.

A novel selective peroxisome proliferator-activator receptor-gamma modulator-SPPARgammaM5 improves insulin sensitivity with diminished adverse cardiovascular effects.

The use of the thiazolidinedione insulin sensitizers rosiglitazone and pioglitazone for the treatment of type 2 diabetes mellitus in recent years has proven to be effective in helping patients resume normal glycemic control. However, their use is often associated with undesirable side effects including peripheral edema, congestive heart failure and weight gain. Here, we report the identification and characterization of a novel selective PPARgamma modulator, SPPARgammaM5 ((2S)-2-(2-chloro-5-{[3-(4-chlorophenoxy)-2-methyl-6-(trifluoromethoxy)-1H-indol-1-yl]methyl} phenoxy)propionic acid), which has notable insulin sensitizing properties and a superior tolerability profile to that of rosiglitazone. SPPARgammaM5 is a potent ligand of human PPARgamma with high selectivity versus PPARalpha or PPARdelta in receptor competitive binding assays. In cell-based transcriptional activation assays, SPPARgammaM5 was a potent partial agonist of human PPARgamma in comparison to the PPARgamma full agonist rosiglitazone. Compared to rosiglitazone or the PPARgamma full agonist COOH (2-(2-(4-phenoxy-2-propylphenoxy)ethyl)indole-5-acetic acid), SPPARgammaM5 induced an attenuated PPARgamma-regulated gene expression profile in fully differentiated 3T3-L1 adipocytes and white adipose tissue of chronically treated db/db mice. SPPARgammaM5 treatment also reduced the insulin resistance index by homeostasis model assessment (HOMA), suggesting an improvement in insulin resistance in these db/db mice. Treatment of obese Zucker rats with either rosiglitazone or SPPARgammaM5 resulted in an improvement in selected parameters that serve as surrogate indicators of insulin resistance and hyperlipidemia. However, unlike rosiglitazone, SPPARgammaM5 did not cause significant fluid retention or cardiac hypertrophy in these rats. Thus, compounds such as SPPARgammaM5 may offer beneficial effects on glycemic control with significantly attenuated adverse effects.