The
immunosuppressant cyclosporin A (CsA) has been shown to exert potent
neuroprotective effects, possibly via the inhibition of
calcineurin and
mitochondrial permeability transition pore formation. Here, we investigated the neuroprotective profile of a novel derivative of CsA,
FR901459, by evaluating its effects against in vitro mitochondrial damage and in vivo brain damage in transient global or focal
cerebral ischemia models, in comparison with those of CsA. Efficacy of
calcineurin inhibition was estimated from its immunosuppressive effect on the mixed lymphocyte reaction. Results showed that the immunosuppressive effect of
FR901459 was approximately 7-fold less potent than that of CsA. In contrast,
FR901459 suppressed Ca(2+)-induced mitochondrial swelling measured in isolated liver mitochondria with greater potency than CsA. Further,
FR901459 showed approximately 30-fold greater neuroprotective potency than CsA against neuronal cell damage induced by
thapsigargin in SH-SY5Y cells. In a transient global
cerebral ischemia model in gerbils,
FR901459 showed the dose-dependent suppression of neuronal cell death, while
FR901459 was less efficacious than CsA. In a rat transient focal
ischemia model,
FR901459 tended to reduce brain damage on both
intravenous injection as well as
intracerebroventricular infusion, but with less efficacy than CsA which significantly reduced the damage. These findings suggest that
FR901459 exerts a potent
neuroprotective effect by inhibiting mitochondrial damage in vitro, but that in in vivo
transient cerebral ischemia, its immunosuppressive component which possibly acts via the inhibition of
calcineurin may play a more important role in attenuating brain damage than its inhibitory effect against mitochondrial damage.