Melatonin and minocycline for combinatorial therapy to improve functional and histopathological deficits following traumatic brain injury

Abstract

The biochemical sequelae that follow traumatic brain injury (TBI) are numerous and affect many different brain functions at different points of time as the secondary cascades progress. The complexity of the resulting pathophysiology is such that a singular therapeutic intervention may not provide adequate benefit and a combination of drugs targeting different pathways may be needed. Two of the most widely studied injury mechanisms are oxidative stress and inflammation. Numerous studies have suggested that pharmacological agents targeting either of these pathways may produce an improvement in histological and functional outcome measures. We hypothesized that combining melatonin, a potent antioxidant, with minocycline, a bacteriostatic agent that also inhibit microglia, would provide better neuroprotection than either agent used alone. To test this hypothesis, we subjected anesthetized adult male rats to a 1.5mm controlled cortical impact and administered melatonin or vehicle in the acute post-injury period followed by daily minocycline or vehicle injections beginning the following day in a 2×2 study design. The animals were allowed to recover for 5 days before undergoing Morris water maze (MWM) testing to assess cognitive functioning following injury. There was no significant difference in MWM performance between the vehicle, melatonin, minocycline, or combination treatments. Following sacrifice and histological examination for neuroprotection, we did not observe a significant difference between the groups in the amount of cortical tissue that was spared nor was there a significant difference in [(3)H]-PK11195 binding, a marker for activated microglia. These results suggest that neither drug has therapeutic efficacy, however dosing and/or administration issues may have played a role.

FIGURE 1

Experimental design.

FIGURE 2

Average escape latency travelled during the acquisition phase of the MWM following a 1.5 mm CCI for animals treated with MEL, MIN, or MEL+MIN. Acquisition data for VEH, MEL 5mg/kg, MIN 40 mg/kg, and MEL+MIN treated animals beginning on the sixth experimental day (5 days following a 1.5 mm injury). No significant treatment effects were seen in the acquisition phase of this task. Data represented as mean ± SD.

FIGURE 3

Cortical tissue spared nine days following a 1.5 mm CCI to rats administered MEL, MIN, or MEL+MIN. Cortical tissue sparing effect of VEH, MEL 5 mg/kg, MIN 40 mg/kg, and MEL+MIN at 14 days following a 1.5 mm CCI. ANOVA results did not detect a significant treatment effect. Data represented as mean ± SD.