Phenoxybenzamine is neuroprotective in a rat model of severe traumatic brain injury.

Phenoxybenzamine (PBZ) is an FDA approved α-1 adrenergic receptor antagonist that is currently used to treat symptoms of pheochromocytoma. However, it has not been studied as a neuroprotective agent for traumatic brain injury (TBI). While screening neuroprotective candidates, we found that phenoxybenzamine reduced neuronal death in rat hippocampal slice cultures following exposure to oxygen glucose deprivation (OGD). Using this system, we found that phenoxybenzamine reduced neuronal death over a broad dose range (0.1 µM-1 mM) and provided efficacy when delivered up to 16 h post-OGD. We further tested phenoxybenzamine in the rat lateral fluid percussion model of TBI. When administered 8 h after TBI, phenoxybenzamine improved neurological severity scoring and foot fault assessments. At 25 days post injury, phenoxybenzamine treated TBI animals also showed a significant improvement in both learning and memory compared to saline treated controls. We further examined gene expression changes within the cortex following TBI. At 32 h post-TBI phenoxybenzamine treated animals had significantly lower expression of pro-inflammatory signaling proteins CCL2, IL1ß, and MyD88, suggesting that phenoxybenzamine may exert a neuroprotective effect by reducing neuroinflammation after TBI. These data suggest that phenonxybenzamine may have application in the treatment of TBI.

Administration of low dose methamphetamine 12 h after a severe traumatic brain injury prevents neurological dysfunction and cognitive impairment in rats.

We recently published data that showed low dose of methamphetamine is neuroprotective when delivered 3 h after a severe traumatic brain injury (TBI). In the current study, we further characterized the neuroprotective potential of methamphetamine by determining the lowest effective dose, maximum therapeutic window, pharmacokinetic profile and gene expression changes associated with treatment. Graded doses of methamphetamine were administered to rats beginning 8 h after severe TBI. We assessed neuroprotection based on neurological severity scores, foot fault assessments, cognitive performance in the Morris water maze, and histopathology. We defined 0.250 mg/kg/h as the lowest effective dose and treatment at 12 h as the therapeutic window following severe TBI. We examined gene expression changes following TBI and methamphetamine treatment to further define the potential molecular mechanisms of neuroprotection and determined that methamphetamine significantly reduced the expression of key pro-inflammatory signals. Pharmacokinetic analysis revealed that a 24-hour intravenous infusion of methamphetamine at a dose of 0.500 mg/kg/h produced a plasma Cmax value of 25.9 ng/ml and a total exposure of 544 ng/ml over a 32 hour time frame. This represents almost half the 24-hour total exposure predicted for a daily oral dose of 25mg in a 70 kg adult human. Thus, we have demonstrated that methamphetamine is neuroprotective when delivered up to 12 h after injury at doses that are compatible with current FDA approved levels.

Treatment with low-dose methamphetamine improves behavioral and cognitive function after severe traumatic brain injury.

BACKGROUND: Methamphetamine increases the release and blocks the reuptake of dopamine. The moderate activation of dopamine receptors may elicit neuroprotective effects. We have recently demonstrated that low doses of methamphetamine reduce neuronal loss after ischemic injury. On the basis of this finding, we hypothesized that methamphetamine could also prevent neuronal loss and improve functional behavior after severe traumatic brain injury (TBI). METHODS: The rat lateral fluid percussion injury model was used to generate severe TBI. Three hours after injury, animals were treated with saline or methamphetamine. Neurological severity scores and foot fault assessments were used to determine whether treatment enhanced recovery after injury. The potential for methamphetamine treatment to improve cognitive function was assessed using the Morris water maze. Forty-eight hours after injury, paraffin-embedded brain sections were TUNEL stained to measure apoptotic cell death. Sections were also stained with antibody to doublecortin to quantify immature neurons within the dentate gyrus. RESULTS: Treatment with low-dose methamphetamine significantly reduced both behavioral and cognitive dysfunction after severe TBI. Methamphetamine-treated animals scored significantly lower on neurological severity scores and had significantly less foot faults after TBI compared with saline-treated control rats. Furthermore, methamphetamine treatment restored learning and memory function to near normal ability after TBI. At 48 hours after injury, apoptotic cell death within the hippocampus was significantly reduced, and the presence of immature neurons was significantly increased in methamphetamine-treated rats compared with saline-treated controls. CONCLUSION: Treatment with low-dose methamphetamine after severe TBI elicits a robust neuroprotective response resulting in significant improvements in behavioral and cognitive functions.

Low dose methamphetamine mediates neuroprotection through a PI3K-AKT pathway.

High doses of methamphetamine induce the excessive release of dopamine resulting in neurotoxicity. However, moderate activation of dopamine receptors can promote neuroprotection. Therefore, we used in vitro and in vivo models of stroke to test the hypothesis that low doses of methamphetamine could induce neuroprotection. We demonstrate that methamphetamine does induce a robust, dose-dependent, neuroprotective response in rat organotypic hippocampal slice cultures exposed to oxygen-glucose deprivation (OGD). A similar dose dependant neuroprotective effect was observed in rats that received an embolic middle cerebral artery occlusion (MCAO). Significant improvements in behavioral outcomes were observed in rats when methamphetamine administration delayed for up to 12 h after MCAO. Methamphetamine-mediated neuroprotection was significantly reduced in slice cultures by the addition of D1 and D2 dopamine receptor antagonist. Treatment of slice cultures with methamphetamine resulted in the dopamine-mediated activation of AKT in a PI3K dependant manner. A similar increase in phosphorylated AKT was observed in the striatum, cortex and hippocampus of methamphetamine treated rats following MCAO. Methamphetamine-mediated neuroprotection was lost in rats when PI3K activity was blocked by wortmannin. Finally, methamphetamine treatment decreased both cleaved caspase 3 levels in slice cultures following OGD and TUNEL staining within the striatum and cortex in rats following transient MCAO. These data indicate that methamphetamine can mediate neuroprotection through activation of a dopamine/PI3K/AKT-signaling pathway.