Abstract
Cyclosporin A (CsA) has been shown to be neuroprotective in mature animal models of traumatic brain injury (TBI), but its effects on immature animal models of TBI are unknown. In mature animal models, CsA inhibits the opening of the mitochondrial permeability transition pore (MPTP), thereby maintaining mitochondrial homeostasis following injury by inhibiting calcium influx and preserving mitochondrial membrane potential. The aim of the present study was to evaluate CsA's ability to preserve mitochondrial bioenergetic function following TBI (as measured by mitochondrial respiration and cerebral microdialysis), in two immature models (focal and diffuse), and in two different species (rat and piglet). Three groups were studied: injured+CsA, injured+saline vehicle, and uninjured shams. In addition, we evaluated CsA's effects on cerebral hemodynamics as measured by a novel thermal diffusion probe. The results demonstrate that post-injury administration of CsA ameliorates mitochondrial dysfunction, preserves cerebral blood flow (CBF), and limits neuropathology in immature animals 24 h post-TBI. Mitochondria were isolated 24 h after controlled cortical impact (CCI) in rats and rapid non-impact rotational injury (RNR) in piglets, and CsA ameliorated cerebral bioenergetic crisis with preservation of the respiratory control ratio (RCR) to sham levels. Results were more dramatic in RNR piglets than in CCI rats. In piglets, CsA also preserved lactate pyruvate ratios (LPR), as measured by cerebral microdialysis and CBF at sham levels 24 h after injury, in contrast to the significant alterations seen in injured piglets compared to shams (p<0.01). The administration of CsA to piglets following RNR promoted a 42% decrease in injured brain volume (p<0.01). We conclude that CsA exhibits significant neuroprotective activity in immature models of focal and diffuse TBI, and has exciting translational potential as a therapeutic agent for neuroprotection in children.