Ryan Woodman1, Warren Lockette. 1. Department of Clinical Investigations, Naval Medical Center, San Diego, 34800 Bob Wilson Drive, Mail Code KCA, San Diego, CA 92134, USA.
Abstract
OBJECTIVE: Circulating catecholamines and adrenal steroids are significantly increased following traumatic brain injury, and elevations in plasma catecholamines and cortisol portend a poor outcome. We hypothesize that an increase in the generation of reactive oxygen species from the synthesis of adrenal steroids and catecholamines is responsible for neuronal injury following traumatic brain injury. As a first step in testing this hypothesis, we sought to determine whether or not inhibition of catecholamine synthesis would decrease neuronal damage. METHODS AND RESULTS: Using PC12 cells as a model of catecholamine synthesizing neurons, and serum deprivation as a method to induce neuronal damage, we show (1) adrenal corticosteroids increase reactive oxygen species formation and apoptosis induced by serum deprivation; (2) the inhibitor of catecholamine synthesis, alpha-methyltyrosine, reduces reactive oxygen species formation and apoptosis in PC12 cells; and (3) that acetazolamide, chlorthalidone, and the neurosteroid, allopregnanolone, which inhibits chloride transport, protect PC12 cells from apoptosis. CONCLUSIONS: It may be possible to protect catecholaminergic neurons from reactive oxygen species-induced apoptotic death by not only blocking catecholamine synthesis, but also, by inhibiting carbonic anhydrase-dependent chloride/bicarbonate exchange with acetazolamide or chlorthalidone. These agents may prove salutary in reducing cell death in patients with traumatic brain injury or stroke.
OBJECTIVE: Circulating catecholamines and adrenal steroids are significantly increased following traumatic brain injury, and elevations in plasma catecholamines and cortisol portend a poor outcome. We hypothesize that an increase in the generation of reactive oxygen species from the synthesis of adrenal steroids and catecholamines is responsible for neuronal injury following traumatic brain injury. As a first step in testing this hypothesis, we sought to determine whether or not inhibition of catecholamine synthesis would decrease neuronal damage. METHODS AND RESULTS: Using PC12 cells as a model of catecholamine synthesizing neurons, and serum deprivation as a method to induce neuronal damage, we show (1) adrenal corticosteroids increase reactive oxygen species formation and apoptosis induced by serum deprivation; (2) the inhibitor of catecholamine synthesis, alpha-methyltyrosine, reduces reactive oxygen species formation and apoptosis in PC12 cells; and (3) that acetazolamide, chlorthalidone, and the neurosteroid, allopregnanolone, which inhibits chloride transport, protect PC12 cells from apoptosis. CONCLUSIONS: It may be possible to protect catecholaminergic neurons from reactive oxygen species-induced apoptotic death by not only blocking catecholamine synthesis, but also, by inhibiting carbonic anhydrase-dependent chloride/bicarbonate exchange with acetazolamide or chlorthalidone. These agents may prove salutary in reducing cell death in patients with traumatic brain injury or stroke.