Novel mechanisms of metformin-induced vasorelaxation of mesenteric arterioles via endothelium-dependent hyperpolarization to treat murine colitis.

RESEARCH PURPOSE: Metformin, an FDA-approved medication for type 2 diabetes mellitus (T2DM), has been previously reported to have anti-colitis effects via anti-inflammatory, antioxidant, and gut microbiota modulation. However, the precise mechanisms of metformin-induced vasorelaxation in intestinal resistance vessels in health and ulcerative colitis (UC), remain largely unknown.

MATERIALS AND

METHODS

Mulvany-style wire myograph was used to determine metformin-induced vasorelaxation of human submucosal arterioles and mesenteric arterioles from wild-type C57BL/6 mice and transient receptor potential vanilloid 4 knockout mice (TRPV4 KO mice). Ca2+ imaging and patch clamp were applied in human umbilical vein endothelial cells (HUVEC). DSS-induced mouse UC model was used to examine the role of metformin-induced vasorelaxation in its anti-colitis effects.

RESULTS

Metformin-induced vasorelaxation of human and mouse mesenteric arterioles through endothelium-dependent hyperpolarization (EDH) predominantly. Metformin induced endoplasmic reticulum (ER)/Ca2+ release via PLC/IP3/IP3R pathway in HUVEC. Metformin also promoted Ca2+ influx and membrane currents via store-operated Ca2+ entry (SOCE) and TRPV4 channels. Metformin/EDH-mediated vasorelaxation almost remained intact in colitis while acetylcholine (ACh)/EDH-mediated vasorelaxation was almost impaired totally. Importantly, metformin/EDH-mediated vasorelaxation could rescue the impaired ACh/EDH-mediated vasorelaxation and ameliorate the destructive colitis mucosae.

CONCLUSIONS

Metformin/EDH-mediated vasorelaxation protects intestinal mucosae against colitis by rescuing the impaired ACh-induced vasorelaxation to recover mucosal hemoperfusion. We reveal an innovative action mode and underlying mechanisms of metformin on microvascular activities in health and colitis. Our data strongly suggest that metformin could be repurposed as a safe and effective medication to prevent/treat colitis, especially as a choice of drug for patients suffering from T2DM and UC.