Cleavage of obestatin by DPP-IV and inhibition of incretin effect on MIN 6 cells

Obestatin is a poorly characterized peptide secreted from gastrointestinal tract (GIT) and pancreatic islet. It is a 23-amino acid amidated peptide hormone formed through posttranscriptional processing of ghrelin gene. Some studies suggest that obestatin plays an important role in gluco-regulation.These features of obestatin are similar to glucagon-like peptide-1 (GLP-1), which is also synthesized and secreted from GIT and formed through the posttranslational processing of proglucagon gene.Active form of GLP-1 potentiates insulin secretion mainly in presence of food or glucose stimuli (incretin effect), but it is inactivated by the cleavage of dipeptidyl peptidase-IV (DPPIV) enzyme. Obestatin was evaluated on MIN6 mouse pancreatic β-cells for incretin effect and survival. Cleavage and inactivation of obestatin by DPP-IV was confirmed by mass spectrometric analysis. Comparisons were made with standard GLP-1.In response to the incubation with external obestatin, endogenous secretion of obestatin was diminished, DPP-IV enzyme was found to be inhibitory on incretin effect. Mass spectrometric analysis of the incubated mixture of obestatin and DPP-IV revealed cleavage of obestatin .XTT assay and media concentration of DNA revealed positive influence of obestatin on MIN6 cells survival or proliferation. We conclude that obestatin exert incretin effect and positively influence survival of pancreatic cells similar to GLP-1.Obestatin was also found to be cleaved by DPP-IV enzyme at amidated C-terminal.