Cellular mechanisms by which lipoic acid confers protection during the early stages of cerebral ischemia: A possible role for calcium

Abstract

Lipoic acid (LA) is a naturally occurring compound and dietary supplement with powerful antioxidant properties. Although LA is neuroprotective in models of stroke, little is known about the cellular mechanisms by which it confers protection during the early stages of ischemia. Here, using a rat model of permanent middle cerebral artery occlusion (MCAO), we demonstrated that administration of LA 30min prior to stroke, reduces infarct volume in a dose dependent manner. Whole-cell patch clamp techniques in rat brain slices were used to determine if LA causes any electrophysiological alterations in either healthy neurons or neurons exposed to oxygen and glucose deprivation (OGD). In healthy neurons, LA (0.005mg/ml and 0.05mg/ml) did not significantly change resting membrane potential, threshold or frequency of action potentials or synaptic transmission, as determined by amplitude of excitatory post synaptic currents (EPSCs). Similarly, in neurons exposed to OGD, LA did not alter the time course to loss of EPSCs. However, there was a significant delay the onset of anoxic depolarization as well as in the time course of the depolarization. Next, intracellular calcium (Ca2+) levels were monitored in isolated neurons using fura-2. Pretreatment with 0.005mg/ml and 0.05mg/ml LA for 30min and 6h did not significantly alter resting Ca2+ levels or Ca2+ response to glutamate (250μM). However, pretreatment with 0.5mg/ml LA for 6h significantly increased resting Ca2+ levels and significantly decreased the Ca2+ response to glutamate. In summary, these findings suggest that LA does not affect neuronal physiology under normal conditions, but can protect cells from an ischemic event.