Studies on the Mechanism of the Epileptiform Activity Induced by U18666A. II. Concentration, Half‐Life and Distribution of Radiolabeled U18666A in the Brain

Abstract

The concentration, half-life, and distribution in brain of U18666A, a drug that can drastically alter cerebral lipids and induce a chronic epileptiform state, was determined following both acute and chronic drug administration. U18666A specifically labeled with tritium was prepared by custom synthesis. Brain levels of 1 x 10(-6)M and higher were reached soon after giving an acute 10-mg/kg dose (i.p. or s.c.) of U18666A containing 7-3H-U18666A of known specific activity. A steady state concentration of 1 to 2 x 10(-6)M was reached with chronic injection of 10 mg/kg every 4th day, a treatment schedule that results in altered brain lipids and induction of epilepsy if begun soon after birth. The disappearance of U18666A from both brain and serum was described by two similar biexponential processes, a brief rapid clearance (t1/2 = 10 h) and a sustained and much slower one (t1/2 = 65 h). Brain levels of the drug were about 10 times higher than serum at all times examined. Few differences were seen in the regional distribution of radiolabeled drug in brain as determined by both direct analysis and by autoradiographic examination; but the drug did concentrate in lipid-rich subcellular fractions. For example, the synaptosome and myelin fractions each contained about 25-35% of both the total 3H-labeled drug and total lipid in whole brain. The lipid composition of these fractions was drastically altered in treated animals. In conclusion, the chronic epileptiform state induced by U18666A does not appear to involve localization of the drug in a specific brain region or particular cell type. Rather, the condition could involve localization of the drug in lipid-rich membranes and marked changes in the composition of these membranes.

Prevention of Prion Propagation by Dehydrocholesterol Reductase Inhibitors in Cultured Cells and a Therapeutic Trial in Mice

“…Since the turn-over of cholesterol in the adult brain is very slow, 24) the inhibitory effect of AY-9944 and U18666A on DHCR7 and DHCR24 could have been negligible in terms of overall changes in the brain's sterol composition in such a metabolically static state. Alternatively, although U18666A and AY-9944 injected via an intraperitoneal route delivered rapidly into the brains of young animals, 16,17) the delivery of the drugs into the brain of adult animals might have been less efficient.…”

“…The synthesis of cholesterol in mammals proceeds along two paths after the synthesis of lanosterol; the Kandutsch-Russell pathway in which 7-dehydrocholesterol is the immediate precursor of cholesterol, and the Bloch pathway in which desmosterol is the immediate precursor (Chart 1). In the present study, we show that AY-9944 (1,4-bis-[2-chlorobenzylaminomethyl]-cyclohexane; CAS # 366-93-8), an inhibitor of 7-dehydrocholesterol reductase (DHCR7, Chart 1), 15,16) and U18666A (3-b-[2-diethylaminoethoxy]-androstenone; CAS # 3039-71-2), an inhibitor of 24-dehydrocholesterol reductase (DHCR24, Chart 1), 15,17) prevent the propagation of PrP Sc in ScN2a cells. Furthermore, we have evaluated the efficacies of U18666A and AY-9944 in vivo.…”

Direct perturbation of lens membrane structure may contribute to cataracts caused by U18666A, an oxidosqualene cyclase inhibitor

“…U18666A was estimated earlier to be present at 2-3 M in whole lenses of treated rats (39). However, this whole lens concentration most likely greatly underestimates the con- centration of drug achieved in lens membranes, because U18666A concentrates in lipid-rich membranes (47) and membrane lipids occupy only ‫%6.0ف‬ of the total mass of the rat lens (33). Furthermore, the regional distribution of U18666A in the lens is unknown; it might be restricted to the epithelium and superficial cortex, which occupy less than 10% of the lens's total volume.…”

“…Our cells were not lipid laden. Because U18666A appears to concentrate in lipid-rich subcellular structures (47), U18666A may largely partition into macrophage lipids, thereby decreasing the drug's toxicity. Adequate drug levels may remain in the cytosol to inhibit cholesterol trafficking.…”

Aromatase/Seladin-1 Interactions in Human Neuronal Cell Culture, the Hippocampus of Healthy Rats and Transgenic Alzheimer’s Disease Mice

“…Cells were centrifuged at 14,000 g for 20 min at 4°C in a microcentrifuge. Protein contents of the supernatants were detected spectrophotometrically by Lowry protein assay (Bio-Rad Laboratories, Hercules, CA, USA) [37]. Cell lysates were stored at –80°C until the Western blot experiments could be performed.…”