L-histidine but not D-histidine attenuates brain edema following cryogenic injury in rats.

Oxygen free radicals have been implicated in the genesis of traumatic brain injury and brain edema (BE). Recent studies have suggested that hydroxyl radical can initiate lipid peroxidation, thus producing lipid-free radicals that may become important sources of singlet oxygen. L-histidine, a singlet oxygen scavenger, potentially can be used to treat BE. In this study we investigated the effects of L-histidine and D-histidine on BE following cryogenic injury in rats. Male Wistar rats were anaesthetized with chloral hydrate. Vasogenic BE was produced by a cortical freezing lesion. Generation of singlet oxygen from photoactivation of rose bengal was studied by electron spin resonance (ESR). Animals were separated into four groups: sham rats (n = 5), saline-treated rats (n = 10), L-histidine treated rats (n = 6) and D-histidine treated rats (n = 7). Each agent (100 mg/kg) was administered intravenously at 30 minutes before lesion production. Animals were sacrificed at 24 hours after lesion production and the brain water content was determined by the dry-wet weight method. L-histidine had no effect on rectal and brain temperature. Election Spin Resonance studies demonstrated that L-histidine is a singlet oxygen scavenger. L-histidine but not D-histidine significantly attenuated BE following cryogenic injury (p < 0.05). In conclusion, L-histidine is useful in the treatment of traumatic BE.