Succinate ameliorates mitochondrial oxygen consumption of metformin-intoxicated human platelets

Introduction

Metformin intoxication inhibits mitochondrial complex I and oxygen consumption (VO₂). Succinate bypasses complex I by donating electrons to complex II. The aim of this study was to clarify whether succinate ameliorates mitochondrial VO₂ of metformin-intoxicated human platelets.

Methods

Platelet-rich-plasma was incubated for 72 hours with metformin at a final concentration of 0 mg/l (control), 1.66 mg/l (therapeutic dose) or 166 mg/l (toxic dose). Platelet VO₂ was then measured with a Clark-type electrode, in the presence of glutamate plus malate (complex I electron donors) (final concentration: 20 mmol/l for both) or succinate (complex II electron donor) (30 mmol/l), before and after adding cyanide (40 mmol/l). Mitochondrial (cyanide-sensitive) and extra-mitochondrial (cyanide-insensitive) VO₂ were corrected for platelet count.

Results

The main results, from four preliminary experiments, are shown in Figure 1. In the presence of glutamate plus malate, only platelets incubated with a high dose of metformin had a mitochondrial VO₂ significantly lower than controls. In the presence of succinate, mitochondrial VO₂ of controls did not change significantly whereas that of platelets incubated with metformin did. The effect of succinate tended to become larger as the dose of metformin was increased from 0 up to 166 mg/l (0.3 ± 0.2 vs. 0.6 ± 0.3 vs. 1.0 ± 0.3 nmol/minute*10⁶ cells) (P = 0.068).Even so, mitochondrial VO₂ of platelets incubated with.the highest dose of metformin did not return to the levels of controls. Extra-mitochondrial VO₂ was always the same.

Figure 1

Mitochondrial oxygen use of human platelets incubated with metformin.

Conclusion

Succinate ameliorates (but does not return to normal) mitochondrial VO₂ of human platelets incubated with a toxic dose of metformin.