The Antidiabetic Drug Metformin Stimulates Glycolytic Lactate Production in Cultured Primary Rat Astrocytes

Abstract

Metformin is the most frequently used drug for the treatment of type 2 diabetes in humans. However, only little is known about effects of metformin on brain metabolism. To investigate potential metabolic consequences of an exposure of brain cells to metformin, we incubated rat astrocyte-rich primary cultures with this compound. Metformin in concentrations of up to 30 mM did not acutely compromise the viability of astrocytes, but caused a time- and concentration-dependent increase in cellular glucose consumption and lactate production. For acute incubations in the hour range, the presence of 10 mM metformin doubled the glycolytic flux, while already 1 mM metformin doubled glycolytic flux during incubation for 24 h. In addition to metformin, also other guanidino compounds increased astrocytic lactate production. After 4 h of incubation, half-maximal stimulation of glycolysis was observed for metformin, guanidine and phenformin at concentrations of around 3 mM, 3 mM and 30 µM, respectively. The acute stimulation of glycolytic lactate production by metformin was persistent after removal of extracellular metformin and was also observed, if glucose was absent from the incubation medium or replaced by other hexoses. The metformin-induced stimulation of glycolytic flux was not prevented by compound C, an inhibitor of AMP-dependent protein kinase, nor was it additive to the stimulation of glycolytic flux caused by respiratory chain inhibitors. These data demonstrate that the antidiabetic drug metformin has the potential to strongly activate glycolytic lactate production in brain astrocytes.

The antidiabetic drug metformin decreases mitochondrial respiration and tricarboxylic acid cycle activity in cultured primary rat astrocytes

“…C). These results obtained in astrocyte cultures on 5‐cm dishes confirm literature data reported for astrocytes that had been incubated with or without metformin in 24‐well cell culture dishes (Westhaus et al, ) with another medium‐to‐cell ratio.…”

“…Therefore, it appears unlikely that the accelerated glycolytic flux in metformin‐treated astrocytes is causing the observed decline in TCA cycle activity but, rather, that the metformin‐induced alteration in mitochondrial metabolism is likely to cause the acceleration of glycolytic flux. This is consistent with a stimulation of PDH by trichloroacetate (Schmidt et al, ), which did not modulate the metformin‐induced stimulation of glycolytic flux (Westhaus et al, ). In addition, at least for isolated muscle tissue from metformin‐treated mice, PDH expression and activity were not changed, nor was citrate synthase activity (Kristensen et al, ).…”

“…Furthermore, this study recommends a dose-efficiency study to measure the plasma metformin concentration that corresponds to the therapeutic metformin concentration (Kajbaf et al, 2016). However, it should also be mentioned here that during longer incubations of cultured astrocytes for 24 hr, already the presence of 1 mM metformin is sufficient to double glycolytic lactate production (Westhaus et al, 2017).…”

“…that had been incubated with or without metformin in 24-well cell culture dishes (Westhaus et al, 2017) with another medium-to-cell ratio.…”

“…Recent studies on cultured astrocytes have demonstrated that metformin augments the formation of ketone bodies (Takahashi et al, 2014) and reduces ammonia-induced release of thrombospondin 1 (Jayakumar et al, 2014). In addition, metformin has been reported to increase glycolytic flux in cultured rat and mouse astrocytes (Allaman et al, 2015;Westhaus et al, 2017). For various peripheral cell lines and for isolated mitochondria, it has been reported that metformin lowers tricarboxylic acid (TCA) cycle activity and mitochondrial respiration (Fendt et al, 2013;Andrzejewski et al, 2014;Bridges et al, 2014).…”