Suppression of FoxO1 activity by long-chain fatty acyl analogs.

OBJECTIVE: Overactivity of the Forkhead transcription factor FoxO1 promotes diabetic hyperglycemia, dyslipidemia, and acute-phase response, whereas suppression of FoxO1 activity by insulin may alleviate diabetes. The reported efficacy of long-chain fatty acyl (LCFA) analogs of the MEDICA series in activating AMP-activated protein kinase (AMPK) and in treating animal models of diabesity may indicate suppression of FoxO1 activity. RESEARCH DESIGN AND METHODS: The insulin-sensitizing and anti-inflammatory efficacy of a MEDICA analog has been verified in guinea pig and in human C-reactive protein (hCRP) transgenic mice, respectively. Suppression of FoxO1 transcriptional activity has been verified in the context of FoxO1- and STAT3-responsive genes and compared with suppression of FoxO1 activity by insulin and metformin. RESULTS: Treatment with MEDICA analog resulted in total body sensitization to insulin, suppression of lipopolysaccharide-induced hCRP and interleukin-6-induced acute phase reactants and robust decrease in FoxO1 transcriptional activity and in coactivation of STAT3. Suppression of FoxO1 activity was accounted for by its nuclear export by MEDICA-activated AMPK, complemented by inhibition of nuclear FoxO1 transcriptional activity by MEDICA-induced C/EBPß isoforms. Similarly, insulin treatment resulted in nuclear exclusion of FoxO1 and further suppression of its nuclear activity by insulin-induced C/EBPß isoforms. In contrast, FoxO1 suppression by metformin was essentially accounted for by its nuclear export by metformin-activated AMPK. CONCLUSIONS: Suppression of FoxO1 activity by MEDICA analogs may partly account for their antidiabetic anti-inflammatory efficacy. FoxO1 suppression by LCFA analogs may provide a molecular rational for the beneficial efficacy of carbohydrate-restricted ketogenic diets in treating diabetes.

AMPK activation by long chain fatty acyl analogs.

The antidiabetic efficacy of first-line insulin sensitizers (e.g., metformin, glitazones) is accounted for by activation of AMP-activated protein kinase (AMPK). Long chain fatty acids (LCFA) activate AMPK, but their putative antidiabetic efficacy is masked by their beta-oxidized or esterified lipid products. Substituted alpha,omega-dicarboxylic acids of 14-18 carbon atoms in length (MEDICA analogs) are not metabolized beyond their acyl-CoA thioesters, and may therefore simulate AMPK activation by LCFA while avoiding LCFA turnover into beta-oxidized or esterified lipid products. MEDICA analogs are shown here to activate AMPK and some of its downstream targets in vivo, in cultured cells and in a cell-free system consisting of the (alpha(1)beta(1)gamma(1))AMPK recombinant and LKB1-MO25-STRAD (AMPK-kinase) recombinant proteins. AMPK activation by MEDICA is accompanied by normalizing the hyperglycemia-hyperinsulinemia of diabetic db/db mice in vivo with suppression of hepatic glucose production in cultured liver cells. Activation of AMPK by MEDICA or LCFA is accounted for by (a) decreased intracellular ATP/AMP ratio and energy charge by the free acid, (b) activation of LKB1 phosphorylation of AMPK(Thr172) by the acyl-CoA thioester. The two activation modes are complementary since LKB1/AMPK activation by the CoA-thioester is fully evident under conditions of excess AMP. MEDICA analogs may expand the arsenal of AMPK activators used for treating diabetes type 2.