Poster only 3rd Metabolic Diseases; Breakthrough Discoveries in Diabetes & Obesity 2022

Effect of a protein kinase C epsilon inhibitor on insulin signalling in lipid-treated HepG2 hepatocytes and glucose intolerance in fat-fed mice (#74)

Miguel L Agoncillo 1 2 , Zhongmin Gao 1 , Harmannus C De Kraker 3 , Stanton F McHardy 3 , Robert O Messing 4 , Carsten Schmitz-Peiffer 1 5 6
  1. Garvan Institute of Medical Research, Darlinghurst, NSW, Australia
  2. Center for Diabetes, Obesity and Endocrinology, Westmead Institute of Medical Research, Sydney, NSW, Australia
  3. Department of Chemistry, Center For Innovative Drug Discovery, University of Texas San Antonio, San Antonio, Texas, USA
  4. Department of Neuroscience, University of Texas at Austin, Austin, Texas, USA
  5. School of Life and Environmental Sciences, University of Sydney, Sydney, NSW, Australia
  6. St Vincent's Clinical School, University of New South Wales, Sydney, NSW, Australia

Aims: Protein kinase C epsilon (PKCε) has been shown to play a causative role in the generation of glucose intolerance and insulin resistance. Tissue-specific deletion of PKCε indicates multiple sites of action, further validating the kinase as a potential target for the treatment of T2D. Here, we examined the effects of a recently-developed PKCε inhibitor (CIDD-0150612) on insulin signalling in palmitate-treated HepG2 hepatocytes and also acute and long-term effects on glucose homeostasis in fat-fed mice.

Methods: HepG2 cells were treated for 18 h with 500 µM palmitate and 10 µM CIDD-0150612, and stimulated with 30 nM insulin for 10 min after a 2 h serum-free period. Mice were fed a high-fat diet for 8 weeks and treated with CIDD-0150612 (40 mg/kg ip eod) in the final 2 weeks.

Results: In contrast to reports that PKCε mediates inhibitory threonine phosphorylation of the insulin receptor (IR), CIDD-0150612 had no effect on insulin-stimulated IR tyrosine phosphorylation in lipid-treated hepatocytes, nor on downstream IRS-1 tyrosine phosphorylation. However, the inhibitor promoted Akt phosphorylation in a highly insulin-dependent manner, and reversed the 40% inhibition of insulin-stimulated Akt phosphorylation by palmitate (P<0.01). Fat-fed mice treated with CIDD-0150612 had reduced body fat (14.6 vs 20.2%, P<0.01) and body weight (25.4 vs 28.3 g, P<0.001) compared to vehicle-treated littermates. Mice treated acutely with CIDD-0150612 exhibited elevated fasting blood glucose (15.7 vs 10.0 mM, P<0.05). However, mice subjected to glucose tolerance tests 24h after the last inhibitor dose had lower fasting glucose (8.6 vs 10.3 mM, P<0.05), improved glucose tolerance  (AUC 1162 vs 1626 mM.min, P<0.001) and lower insulin excursions (AUC 49 vs 88 ng/ml.min, P<0.05).

Conclusions: The PKCε inhibitor CIDD-0150612 had beneficial effects on insulin signalling, fat mass and glucose homeostasis. Because certain effects were not previously observed in studies of PKCε-deficient mice, off-target effects may be partly responsible.