Central nervous system demyelinating diseases and increased release of cholesterol into the urinary system of rats.

The question of what happens to cholesterol in the adult central nervous system during its slow turnover has been addressed using rats with brain and spinal cord labeled with [4-14C]cholesterol upon intracerebral injection of labeled cholesterol into rats at 10-12 days of age. At six months after injection, 14C was found only in the brain and spinal cord and was slowly released via the rat's urine. When labeled rats were given demyelinating agents (triethyl tin chloride, hexachlorophene, sodium cyanide) and when experimental allergic encephalomyelitis was induced, a measurable increase in urinary 14C label above control levels was found. It was concluded that there is a direct relationship between the experimental demyelination induced and the increased release of cholesterol metabolites into urine. The study suggests that a clinical method could be developed to determine the rate of central nervous system demyelination by measuring the amount of urinary cholesterol metabolites.

Unusual urinary cholesterol metabolites following intracerebral injection of [4-14C]cholesterol into rats: I. The minor 14C-metabolite.

[4-14C]Cholesterol injected intracerebrally into 10-12-day-old rats becomes localized largely in central nervous system myelin. If sufficient 14C is injected, myelin cholesterol remains labeled for the rest of the rats' lives. In the course of the slow myelin cholesterol turnover that ensues, a unique series of cholesterol metabolites is excreted exclusively in the rats' urine. There is reason to believe that the metabolites are formed in the central nervous system before entering the urine. This manuscript describes separation of the 2 urinary 14C-labeled metabolic types and isolation and identification of the minor 14C-labeled material which consists of cholesterol and 2 other sterols bound covalently to short-chain peptides. The minor sterols have been tentatively identified as 24- and 26-hydroxycholesterol. The sterol-peptide combinations have been isolated from human male urine, also.

Metabolism of cholesteryl palmitate by rat brain in vitro; formation of cholesterol epoxides and cholestane-3beta,5alpha,6beta-triol.

Incubation of [4-(14)C]cholesteryl palmitate with the 12,000 g supernatant fraction of adult rat brain fortified with an NADPH-generating system and beta-mercaptoethylamine resulted in formation (2-5%) of more polar metabolites characterized as a mixture of cholesterol-5,6-epoxides. Under extended incubation conditions, cholestane-3beta-5alpha-6beta-triol was isolated as the major end product of the incubations. Free [4-(14)C]cholesterol incubated under similar conditions was not oxidized, whereas oxidation of [4-(14)C]cholesteryl palmitate appeared to be dependent upon hydrolysis of the ester by the rat brain microsomal subcellular fraction. Elimination of the NADPH-generating system or the addition of EDTA to the incubation mixture inhibited epoxide formation, suggesting that the products are derived from an NADPH-dependent enzymatic lipoperoxidation mechanism. The in vitro conversion of [4-(14)C]cholesterol-5alpha,6alpha-epoxide to cholestane-3beta,5alpha,6beta-triol was also demonstrated in rat brain subcellular fractions in the absence of added cofactors.

Conversion of sodium lithocholate-24-(14)C to other products by guinea pig brain.

Intracerebral injection of sodium lithocholate into guinea pig showed that this steroid can be converted into other acidic products by the brain, in vivo. One of the products has been identified as 3-keto-5ß-cholanoic acid.