Metformin decreases bacterial trimethylamine production and trimethylamine N-oxide levels in db/db mice

Janis Kuka,Eduards Sevostjanovs,Melita Videja,Maija Dambrova,Marina Makrecka-Kuka,Janis Liepins,Solveiga Grinberga,Edgars Liepinsh,Karlis Vilks

doi:10.1038/s41598-020-71470-4

Abstract

The current study aimed to explore whether metformin, the most widely prescribed oral medication for the treatment of type 2 diabetes, alters plasma levels of cardiometabolic disease-related metabolite trimethylamine N-oxide (TMAO) in db/db mice with type 2 diabetes. TMAO plasma concentration was up to 13.2-fold higher in db/db mice when compared to control mice, while in db/db mice fed choline-enriched diet, that mimics meat and dairy product intake, TMAO plasma level was increased 16.8-times. Metformin (250 mg/kg/day) significantly decreased TMAO concentration by up to twofold in both standard and choline-supplemented diet-fed db/db mice plasma. In vitro, metformin significantly decreased the bacterial production rate of trimethylamine (TMA), the precursor of TMAO, from choline up to 3.25-fold in K. pneumoniae and up to 26-fold in P. Mirabilis, while significantly slowing the growth of P. Mirabilis only. Metformin did not affect the expression of genes encoding subunits of bacterial choline-TMA-lyase microcompartment, the activity of the enzyme itself and choline uptake, suggesting that more complex regulation beyond the choline-TMA-lyase is present. To conclude, the TMAO decreasing effect of metformin could be an additional mechanism behind the clinically observed cardiovascular benefits of the drug.

Highlights

The current study aimed to explore whether metformin, the most widely prescribed oral medication for the treatment of type 2 diabetes, alters plasma levels of cardiometabolic disease-related metabolite trimethylamine N-oxide (TMAO) in db/db mice with type 2 diabetes
It was shown that the expression of TMAO producing enzyme flavin-containing monooxygenase 3 (FMO3) is suppressed by insulin[7]; subsequently, it was shown that FMO3 knockout mice are protected from the development of hyperglycaemia, hyperlipidaemia and atherosclerosis due to the suppression of FOXO1, a transcription factor that is the main target of insulin signalling
Because TMA and subsequent TMAO production depend on diet, we evaluated whether metformin treatment can affect chronic and acute dietary choline load-induced increases in TMAO levels

Summary

Introduction

The current study aimed to explore whether metformin, the most widely prescribed oral medication for the treatment of type 2 diabetes, alters plasma levels of cardiometabolic disease-related metabolite trimethylamine N-oxide (TMAO) in db/db mice with type 2 diabetes. Metformin significantly decreased the bacterial production rate of trimethylamine (TMA), the precursor of TMAO, from choline up to 3.25-fold in K. pneumoniae and up to 26-fold in P. Since TMA and subsequently TMAO are mostly formed from dietary tertiary amines, mainly from choline and carnitine/ butyrobetaine[4,17,18], additional experiments were performed to evaluate the efficacy of metformin in db/db mice under increased choline load to mimic high meat and dairy product (rich in choline, carnitine and other tertiary amines/their derivatives) intake as in typical Western diet. Klebsiella pneumoniae was chosen because it can produce TMA from all the main precursors—choline (via CutC/D (choline-TMA-lyase complex)) and carnitine/butyrobetaine (via CntA/B (Carnitine monooxygenase complex)), while Proteus mirabilis was chosen because it has just CutC/D and can produce TMA only from choline[19,20]

Methods

Results

Conclusion