Neuroprotective efficacy of FR901459, a novel derivative of cyclosporin A, in in vitro mitochondrial damage and in vivo transient cerebral ischemia models.

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.

A novel potent radical scavenger, 8-(4-fluorophenyl)-2-((2E)-3-phenyl-2-propenoyl)-1,2,3,4-tetrahydropyrazolo[5,1-c] [1,2,4]triazine (FR210575), prevents neuronal cell death in cultured primary neurons and attenuates brain injury after focal ischemia in rats.

Reactive oxygen species (ROS) play a vital role in brain damage after cerebral ischemia-reperfusion injury, and ROS scavengers have been shown to exert neuroprotective effects against ischemic brain injury. We have recently identified 8-(4-fluorophenyl)-2-((2E)-3-phenyl-2-propenoyl)-1,2,3,4-tetrahydropyrazolo[5,1-c][1,2,4]triazine (FR210575) as a novel, powerful free-radical scavenger. In the present study, the neuroprotective efficacy of FR210575 was evaluated in two neuronal death models in vitro as well as rat focal cerebral ischemia models in vivo. In the first model, primary cortical cultures were exposed to a high oxygen atmosphere (50% O2) for 48 h to induce cell death with apoptotic features. Treatment with FR210575 (10-7-10-5 M) significantly inhibited neuronal death. The second model used a growth-factor withdrawal paradigm. Withdrawal of TIP (transferrin, insulin, putrescine and progesterone)-supplemented medium induced apoptotic cell death after 2 days, but treatment with FR210575 exhibited dramatic protection against neuronal death. In two models of cerebral ischemia [photothrombotic occlusion of middle cerebral artery (MCA) for transient model and by permanent MCA occlusion for permanent model], rats received 3-h intravenous infusion (1-10 mg/kg/3 h) of FR210575, with brain damage determined 24 h later. FR210575 (3.2 mg/kg/3 h) significantly reduced the volume of focal damage in the cortex by 36% in the transient model and also reduced the size of ischemic brain damage in the permanent model. These findings indicate that the powerful radical scavenger FR210575 has potent neuroprotective activity and that FR210575 could be an attractive candidate for the treatment of stroke or other neurodegenerative disorders.