Effects of biguanides on mitochondrial permeability transition pore opening in intact brain cells

Mitochondrial permeability transition pore (MPTP) is thought to be involved in ischemia/reperfusion- -induced cell death in various organs, including the brain. Thus, inhibition of MPTP is considered as a target for neuroprotection. A biguanide compound metformin has been found to exert neuroprotective effects possibly involving modulation of mitochondrial functions. The aim of this study was to investigate the effects of various biguanide compounds - metformin, phenformin, imeglimin on ionomycin-induced MPTP opening in intact brain cells. Cultures of isolated rat neuronal and astrocytic cells were pre-treated with biguanides and were loaded with calcein-AM and CoCl2. Then ionomycin was added allowing entry of excess Ca2+ into cells and triggering MPTP opening which was observed as subsequent loss of mitochondrial calcein fluorescence measured with fluorescence microscope. We found that in neurons 2-3 mM metformin protected against ionomicin-induced MPTP opening. Phenformin exerted partial protective effect at 50 μM and at 100 μM concentration fully prevented MPTP opening. Imeglimin exerted partial protection at 1 μM and completely blocked MPTP opening at 10 μM concentration. In astrocytes, 2-3 mM metformin, 1-10 μM imeglimin and 50-100 μM phenformin partially suppressed ionomycin-induced MPTP opening. Our data suggest that metformin, phenformin and imeglimin prevent MPTP opening in intact neurons and astrocytes.