Effect of NXY-059 on secondary mitochondrial dysfunction after transient focal ischemia; comparison with cyclosporin A.

The free radical trapping agents NXY-059 and alpha-phenyl-N-tert.-butylnitrone (PBN) markedly reduce infarct volume, even when given 1 or 3 h after the start of recirculation, following 2 h of middle cerebral artery (MCA) occlusion in rats. Their anti-ischemic effects are shared by the two immunosuppressants cyclosporin A (CsA) and FK506. Interestingly, CsA causes an additional reduction in infarct volume when given after only 5 min of recirculation, possibly reflecting blockade of a mitochondrial permeability transition (MPT) pore. PBN, CsA and FK506 are known to ameliorate the secondary dysfunction of mitochondrial function, as assessed in vitro, which occurs during the first 4-6 h of recirculation. The present experiments were undertaken to assess whether NXY-059 reduces tissue damage by acting directly on mitochondrial membranes, and provided that this is the case, if blockade of an MPT is involved. The results were compared to those of CsA, which thus served as a reference compound. NXY-059 was given i.v. after 5 min and 1 h, and CsA after 5 min of recirculation. Both NXY-059 and CsA reduced infarct volumes to about 30% of control, prevented the secondary decline in mitochondrial respiratory function during recirculation, and reduced the mitochondrial release of cytochrome c after 6 and 24 h of recirculation. However, NXY-059 failed to block the effect of Ca(2+) on mitochondrial swelling in vitro, as CsA did. Furthermore, NXY-059, given after 5 min of recirculation, did not reproduce the effects of CsA. The results thus suggest that NXY-059 exerts its effects on mitochondria by indirect mechanisms.