Inhibitory activity of fractions of Senna nigricans toward protein tyrosine phosphatase 1B and dipeptidyl peptidase IV

Abstract

Protein tyrosine phosphatase (PTP) 1B and dipeptidyl peptidase (DPP) IV are important in down regulation and secretion of insulin, respectively. While PTP 1B regulates insulin binding to its receptor, DPP IV hydrolyses incretin, which is an important regulator of postprandial insulin secretion. The study evaluated the in vitro inhibitory effect of different fractions of Senna nigricans against PTP IB and DPP IV and the results were compared with standard inhibitors, sumarin and P32/98. The methanolic extract was further fractionated using Soxhlet apparatus and then the most potent fraction eluted through column on silica gel. The result indicated that the methanolic fraction had the highest inhibition percentage of 56.43±3.98 against PTP 1B. The inhibition of PTP 1B by methanolic fraction was significantly (P<0.05) higher than that of the standard inhibitor, sumarin. The PTP 1B inhibition by ethyl acetate fraction (31.34±5.40%) was not significantly (P>0.05) different from that of sumarin, while hexane fraction had the inhibition of 19.03±4.24% which was significantly (P<0.05) decreased as compared with sumarin.  The result of DPP IV inhibition indicated that the methanolic, hexane and ethyl acetate fractions were not significantly different, but all the fractions were significantly less active than the standard inhibitor, P32/98 which recorded 63.1±4.67% inhibition of DPP IV. Because of S. nigricans as sources of PTP 1B inhibitors most especially and to some extent DPP IV inhibitors, the plant may be a potential source for the discovery of lead compounds as PTP 1B and DPP IV inhibitors to treat type 2 diabetes mellitus. Key words: Protein tyrosine phosphatase, dipeptidyl peptidase, inhibitors, Senna nigricans.