Gallic acid protects RINm5F β-cells from glucolipotoxicity by its antiapoptotic and insulin-secretagogue actions

Abstract

Gallic acid is claimed to possess antioxidant, antiinflammatory and cytoprotective effects. Since pancreatic islets from Type 2 diabetic patients have functional defects, it was hypothesized that glucolipotoxicity might induce apoptosis in β-cells and gallic acid could offer protection. To test this, RINm5F β-cells were exposed to high glucose (25 μM) or palmitate (500 μM) or a combination of both for 24 h in the presence and absence of gallic acid. Cells subjected to glucolipotoxicity in the absence and presence of gallic acid were assessed for DNA damage by comet assay. Apoptosis was inferred by caspase-3 protein expression and caspase-3 activity and changes in Bcl-2 mRNA. RT-PCR was used to analyse PDX-1, insulin and UCP-2 mRNA expression in RINm5F β-cells and insulin levels were quantified from the cell culture supernatant. NFκB signal was studied by EMSA, immunofluorescence and Western blot analysis. While RINm5F β-cells subjected to glucolipotoxicity exhibited increased DNA damage, apoptotic markers and NFκB signals, all these apoptotic perturbations were resisted by gallic acid. Gallic acid dose-dependently increased insulin secretion in RINm5F β-cells and upregulated mRNA of PDX-1 and insulin. It is suggested that the insulin-secretagogue and transcriptional regulatory action of gallic acid is a newly identified mechanism in our study.