Anti-Angiogenic miR-222, miR-195, and miR-21a Plasma Levels in T1DM Are Improved by Metformin Therapy, Thus Elucidating Its Cardioprotective Effect: The MERIT Study

Type 1 diabetes (T1DM) is associated with increased cardiovascular disease (CVD) and reduced life expectancy. We thus hypothesized that anti-angiogenic miRs are increased in T1DM, and the cardioprotective effect of metformin is mediated via reducing those miRs. In an open label, case-controlled study, 23 T1DM patients without CVD were treated with metformin for eight weeks (TG), matched with nine T1DM patients on standard treatment (SG) and 23 controls (CG). Plasma miR-222, miR-195, miR-21a and miR-126 were assayed by real-time RT-qPCR. The results were correlated with: endothelial function (RHI), circulating endothelial progenitor cells (cEPCs) (vascular repair marker, CD45(dim)CD34(+)VEGFR2(+) cells) and circulating endothelial cells (cECs) (vascular injury marker, CD45(dim)CD34(+)CD133(-)CD144(+) cells). miR-222, miR-195 and miR-21a were higher in T1DM than CG; p = 0.009, p < 0.0001, p = 0.0001, respectively. There was an inverse correlation between logmiR-222 and logRHI (p < 0.05) and a direct correlation between logmiR-222 and logCD34(+) (p < 0.05) in TG. Metformin reduced miR-222, miR-195 and miR-21a levels in TG; p = 0.007, p = 0.002 p = 0.0012, respectively. miRs remained unchanged in SG. miR-126 was similar in all groups. There was a positive association between changes in logmiR-222 and logcECs after metformin in TG (p < 0.05). Anti-angiogenic miRs are increased in T1DM. Metformin has cardioprotective effects through downregulating miR-222, miR-195 and miR-21a, beyond improving glycemic control.