Title

Insulin-Secretagogue and Anti-Apoptotic Effects of Gallic Acid Against Gluco-Lipotoxicity in RINm5F Cells.

Authors

Balasubramanyam, Muthuswamy; Sameer, Mahmood Z.; Mohan, Viswanathan

Abstract

Gallic acid is a polyphenolic flavonoid claimed to possess antioxidant, anti-inflammatory, and cytoprotective effects. Since pancreatic islets from Type 2 diabetic patients have functional defects imposed by sub-clinical inflammation and oxidative stress, we hypothesized that gluco-lipotoxicity might induce apoptosis in pancreatic beta cells and gallic acid could offer protection against this. To test this, RINm5F cells were treated with high glucose, palmitate or both (gluco-lipotoxicity) for 24 hrs in the absence and presence of gallic acid and assayed for various tests. The cell viability and proliferation rate were assessed using Methyl Thiazol Tetrazolium bromide (MTT) dye and thymidine uptake, respectively. DNA damage was measured by comet assay. Apoptosis was inferred by caspase-3 activity, TUNEL staining and changes in Bcl-2 mRNA expression. RT-PCR was used to analyse PDX-1 and Insulin mRNA expression and insulin levels were quantified from the cell culture supernatant. While RINm5F cells subjected to gluco-lipotoxicity exhibited decreased cell viability, increased DNA damage and caspase-3 activity, all these apoptotic markers were significantly decreased in the presence of gallic acid. Additionally, cells treated with gallic acid showed increased mRNA expression of Bcl-2, an anti-apoptotic signal. Gallic acid dose- dependently increased insulin secretion in RINm5F cells. Insulin secretory defect inducted by gluco-lipotoxicity was also reversed by gallic acid. Cells treated with gallic acid also showed upregulation of mRNA levels of PDX-1 and insulin genes. In addition, cells exposed to gallic acid exhibited increased Ca[sup 2 ] influx and transient depolarization, the two mandatory signals that promote insulin secretion. Gallic acid appears to resist glucolipotoxicity in RINm5F cells acting on multiple cellular sites and promote insulin secretion.

Subjects

INSULIN; GALLIC acid; TYPE 2 diabetes; CELLS; MESSENGER RNA

Publication

Diabetes, 2007, Vol 56, pA687

ISSN

0012-1797

Publication type

Academic Journal