Poster Abstract #11: Brain Microdialysate and Plasma Concentrations of Inosine During Intravenous Inosine Infusion in Conscious Rats

Background and Objective Inosine is an endogenous purine nucleoside with neuroprotective and nerve regenerative properties. The literature suggests that inosine can cross the blood–brain barrier (BBB) after parental administration, but no direct measurements of CNS interstitial inosine levels have been reported. The objectives of this study were to measure the interstitial levels of inosine in the brain during intravenous infusion of inosine. Methods Inosine was administered in aqueous bicarbonate buffer (pH 9.2) by intravenous infusion over 2 hours to two groups of male Sprague-Dawley rats ( n = 3 per group). One group received nominal dose rates of 0 (vehicle), 100, and 300 mg/kg/h, and the other received nominal dose rates of 0, 500, and 700 mg/kg/h. Each infusion was separated by a 2-day washout period. A microdialysis probe was inserted into the medial prefrontal cortex. Samples of CNS microdialysate and arterial blood samples were taken before the dose and at 20, 40, 60, 80, 100, and 120 minutes during inosine infusion. Microdialysate and plasma inosine concentrations were measured using an LC/MS/MS assay. Results Plasma inosine concentrations were dose-dependently increased with maximal values up to 5.0, 7.2, 26, 45, and 146 μg/mL after inosine doses of 0, 100, 300, 500, and 700 mg/kg/h, respectively. Basal microdialysate inosine concentrations were highly variable (0.138–1.40 ng/mL) within and between animals, and were therefore expressed as percent of the mean of two baseline values taken within 40 minutes before each infusion. No differences in microdialysate inosine percent increases were reliably seen between inosine doses of 0 (90% to 175%), 100 (113% to 146%), and 300 (96% to 116%) mg/kg/h. However, maximal increases of 526% to 632% and 574% to 653% were seen within 45 minutes after inosine doses of 500 and 700 mg/kg/h, respectively, and increases remained well above baseline for the remainder of these infusions. Conclusions Intravenous infusion of inosine at doses of 500 or 700 mg/kg/h resulted in maximal inosine increases in the brain microdialysates from the rat medial prefrontal cortex of approximately 600% above predose levels. These data suggest that intravenous infusion of inosine could be a viable alternative to more invasive administrations to treat CNS disorders such as stroke, spinal cord injury, and traumatic brain injury. Conducted by Bioanalytical Systems, Inc., for Alseres Pharmaceuticals.