Low dose intravenous minocycline is neuroprotective after middle cerebral artery occlusion-reperfusion in rats

Abstract

Background: Minocycline, a semi-synthetic tetracycline antibiotic, is an effective neuroprotective agent in animal models of cerebral ischemia when given in high doses intraperitoneally. The aim of this study was to determine if minocycline was effective at reducing infarct size in a Temporary Middle Cerebral Artery Occlusion model (TMCAO) when given at lower intravenous (IV) doses that correspond to human clinical exposure regimens.

Methods: Rats underwent 90 minutes of TMCAO. Minocycline or saline placebo was administered IV starting at 4, 5, or 6 hours post TMCAO. Infarct volume and neurofunctional tests were carried out at 24 hr after TMCAO using 2,3,5-triphenyltetrazolium chloride (TTC) brain staining and Neurological Score evaluation. Pharmacokinetic studies and hemodynamic monitoring were performed on minocycline-treated rats.

Results: Minocycline at doses of 3 mg/kg and 10 mg/kg IV was effective at reducing infarct size when administered at 4 hours post TMCAO. At doses of 3 mg/kg, minocycline reduced infarct size by 42% while 10 mg/kg reduced infarct size by 56%. Minocycline at a dose of 10 mg/kg significantly reduced infarct size at 5 hours by 40% and the 3 mg/kg dose significantly reduced infarct size by 34%. With a 6 hour time window there was a non-significant trend in infarct reduction. There was a significant difference in neurological scores favoring minocycline in both the 3 mg/kg and 10 mg/kg doses at 4 hours and at the 10 mg/kg dose at 5 hours. Minocycline did not significantly affect hemodynamic and physiological variables. A 3 mg/kg IV dose of minocycline resulted in serum levels similar to that achieved in humans after a standard 200 mg dose.

Conclusions: The neuroprotective action of minocycline at clinically suitable dosing regimens and at a therapeutic time window of at least 4-5 hours merits consideration of phase I trials in humans in view of developing this drug for treatment of stroke.

Figures

Figure 1

Serum Levels of Minocycline. A linear relationship was observed between peak concentration and dose over the dose range studied (r = 0.998).

Figure 2

Effects of MC IV dosing on infarct size at 24 hr after 90 min TMCAO. The post hoc tests for the proportion infarct size showed that within the 4-hour administration time, the 3 mg/kg (p = 0.0001) and 10 mg/kg (p = 0.0001) minocycline groups had significantly lower mean proportion infarct size than the saline group. At the 5-hour administration time, the 3 mg/kg (p = 0.0010) and 10 mg/kg (p = 0.0002) minocycline groups had significantly lower mean proportion infarct size than the saline group. There were no statistically significant differences in the proportion infarct size between treatment groups at the 6-hour administration time window * the number atop the bar figure was the animal numbers of that group.

Figure 3

Effects of MC IV dosing on neurofunction at 24 hr after 90 min TMCAO. For the neurological score a statistically significant interaction between treatment group and administration time was detected. Within the 4-hour time window, the saline group had significantly higher neurological scores than the 3 mg/kg (p = 0.0001) and 10 mg/kg (p = 0.0001) minocycline groups. Within the 5-hour time window, the saline group had significantly higher neurological scores than the 10 mg/kg minocycline group (p = 0.0003), but the 3 mg/kg minocycline group was not statistically different (p = 0.0669). There were no statistically significant differences in neurological scores at the 6-hour administration window. * the number atop the bar figure was the animal numbers of that group.