A redox-based chemical delivery system that enhances estradiol distribution to the brain: disposition studies in the rat.

The disposition of a chemical delivery system for estradiol (E2-CDS) which is based on a redox dihydropyridine-pyridinium salt conversion was investigated in rats. Tissue and plasma concentrations of E2-CDS and the oxidized metabolite (E2-Q+) were evaluated at times ranging from 1 to 14 days after intravenous administration of E2-CDS formulated as a modified cyclodextrin inclusion complex. While E2-CDS levels were below HPLC assay detection limits for all samples by 1 day postdosing, E2-Q+ was readily quantified. The calculated half-life of E2-Q+ was longest in brain tissue, significantly shorter in heart, lung, and kidney tissues, and shortest in plasma. There was a linear relationship between administered E2-CDS dose and oxidized metabolite measured in brain as well as in other tissues collected 24 hr after drug administration. Coadministration of high doses of a similarly oxidizable dihydropyridine, 1-methyl-1,4-dihydronicotinamide (NMN), in a dimethylsulfoxide (DMSO) vehicle decreased E2-Q+ measured in brain and other tissues without significantly affecting the relative patterns of distribution in these tissues. Brain tissue E2Q+ levels were not detected after dosing with the oxidized metabolite.