Effect of Metformin on Mitophagy in Newly Diagnosed patients with T2DM: A Randomized, Placebo-Controlled Study

Shipra Bhansali 1, Anil Bhansali 2, Veena Dhawan 1*

1 Department of Experimental Medicine and Biotechnology, Postgraduate Institute of Medical Education and Research (PGIMER), Chandigarh, INDIA
2 Department of Endocrinology, Postgraduate Institute of Medical Education and Research (PGIMER), Chandigarh, INDIA



ABSTRACT

Background and Aims: Besides insulin deficiency and insulin resistance, patients with T2DM exhibit abnormalities in cell reparative processes including autophagy and mitophagy (selective autophagy of mitochondria). Metformin is widely prescribed as a first-line drug in the management of T2DM. It is a potent insulin sensitizer and exerts its pleiotropic effects via AMPK, however, it’s effect on mitophagy remains unexplored. Hence, the present study aims to elucidate the effect of metformin on mitophagy in newly diagnosed patients with T2DM (NDT2DM).

Methods: Forty five drug-naïve NDT2DM patients with a duration of diabetes < 6 months and HbA1c levels of 7-8% (53-63.9 mmol/mol) were randomized into 3 groups:  Group-I received metformin at a dose of 2g/day in divided doses, Group-II received voglibose at a dose of 0.3 mg thrice/day, and Group-III received placebo at a dose of 2g/day (n=15 each), along with lifestyle modifications to achieve a target HbA1C level ≤ 6.5% (47.5 mmol/mol). Voglibose was used as an active comparator to eliminate the effect of glucotoxicity on mitophagy, with respect to metformin. Anthropometry, parameters of glucose-insulin homeostasis were assessed at baseline and 12 weeks of treatment. In addition, mitochondrial oxidative stress indices, translational expression studies of mitophagy-related genes (PINK1, PARKIN, MFN2, NIX, LC3-II, and LAMP-2) and transmission electron microscopic (TEM) studies were performed in peripheral blood mononuclear cells (PBMCs).

Results: On intra-group comparison, both metformin and voglibose treatment resulted in a significant decrease in anthropometric measurements including weight, BMI, and waist circumference (WC), FPG, 2hPG, HbA1C and HOMA-IR levels in the study participants at 3 months of follow-up (p< 0.05). Placebo-treated study subjects showed a significant decrease in weight, BMI, WC, 2hPG and HOMA-IR levels (p< 0.05). Inter-group comparison among the metformin, voglibose and placebo-treated groups demonstrated non-significant alterations in all the anthropometric parameters. However, there was a significant decrease in FPG, 2hPG and HbA1c levels with the use of metformin and voglibose as compared to placebo treatment (p< 0.05). Further, a significant decrease in the mitochondrial oxidative stress indices was observed in both metformin and voglibose-treated study subjects (p< 0.05), but not in the placebo group after 3 months of treatment. Moreover, metformin monotherapy caused a significant up-regulation in the protein expression of mitophagy markers, accompanied with a significant decline in damaged mitochondria as shown by TEM studies (p< 0.05). However, voglibose did not show any effect on mitophagy as well as mitochondrial damage. Further, placebo-treated subjects showed no significant alterations in mitophagy, while, the mitochondrial damage was significantly increased at 3 months.

Discussion and Conclusion: Delta (Δ) change in weight was comparable among all the study subjects at the completion of the study, indicating that both metformin and voglibose are neutral on weight homeostasis. Further, both metformin and voglibose treatment showed a similar efficacy towards the reduction in plasma glucose, HbA1c levels, and mitochondrial stress indices, but only metformin treatment resulted in a significant increase in mitophagy. These observations suggest that both these drugs could reduce mitochondrial stress levels due to a decrease in the glucotoxicity, though, the mitochondrial damage was decreased only with metformin treatment. This may be attributed to the extended effect of metformin, besides its insulin sensitizing role, on the clearance of defunct mitochondria by the process of mitophagy, whereas, voglibose treatment did not exert any significant effect on mitophagy, indicating that metformin regulates mitophagy independent of reduction in glucotoxicity in patients with NDT2DM.

Effect of metformin on mitophagy in newly diagnosed patients with T2DM: a randomized, placebo-controlled study