Insulin-mimetic and anti-inflammatory potential of a vanadyl-Schiff base complex for its application against diabetes

Abstract

Insulin signalling causes the translocation of glucose transporter 4 (GLUT4) to the plasma membrane to facilitate cellular glucose uptake. Numerous observations indicate that the prime cause of type 2 diabetes mellitus (T2DM) is inflammation, the occurrence of which increases in obese individuals. Inflammatory mediators induce an insulin-resistance (IR) state where impaired insulin signalling fails to promote the glucose transporters for intracellular uptake of glucose. Hence compounds, which possess insulin-mimetic and anti-inflammatory potentials, may be effective in the treatment of obesity-induced IR during T2DM. Previous studies showed that vanadium oxo complexes possess insulin-mimetic activities whereas the tryptamine moiety offers anti-inflammatory potential. Hence a vanadyl-Schiff base complex (VOTP) consisting of the tryptamine moiety was synthesized by condensation of pyridoxal hydrochloride and tryptamine and its subsequent complexation with VOSO₄. HEK-293 cells, expressing a GLUT4-myc-GFP fusion protein, were treated with VOTP and GLUT4 translocation was quantified by total internal reflection fluorescence (TIRF) microscopy. Results indicated that VOTP could efficiently act as an insulin-mimetic substance. A high-content cell based assay using quantum dot–antibody conjugates showed that VOTP restored insulin signaling during IR by the inactivation of c-Jun N-terminal kinase-1 (JNK-1) and subsequent phosphorylation and activation of the tyrosine moiety of insulin receptor substrate (IRS). Also, high levels of phosphorylated Forkhead box O1 (FOXO) indicated low levels of gluconeogenesis. Hence VOTP has insulin-mimetic and anti-inflammatory potentials. Moreover, VOTP is highly effective at nanomolar treatment ranges, thus evades the toxicity issues. Collectively, these findings encourage us for future use of this compound as a potential anti-diabetic agent.