Bile acid synthesis. Metabolism of 3 beta-hydroxy-5-cholenoic acid in the hamster

Bioconversion of 3beta-hydroxy-5-cholenoic acid into chenodeoxycholic acid by rat brain enzyme systems

We have previously demonstrated that the rat brain contains three unconjugated bile acids, and chenodeoxycholic acid (CDCA) is the most abundantly present in a tight protein binding form. The ratio of CDCA to the other acids in rat brain tissue was significantly higher than the ratio in the peripheral blood, indicating a contribution from either a specific uptake mechanism or a biosynthetic pathway for CDCA in rat brain. In this study, we have demonstrated the existence of an enzymatic activity that converts 3beta-hydroxy-5-cholenoic acid into CDCA in rat brain tissue. To distinguish marked compounds from endogenous related compounds, 18O-labeled 3beta-hydroxy-5-cholenoic acid, 3beta,7alpha-dihydroxy-5-cholenoic acid, and 7alpha-hydroxy-3-oxo-4-cholenoic acid were synthesized as substrates for in vitro incubation studies. The results clearly suggest that 3beta-hydroxy-5-cholenoic acid was converted to 3beta,7alpha-dihydroxy-5-cholenoic acid by microsomal enzymes. The 7alpha-hydroxy-3-oxo-4-cholenoic acid was produced from 3beta,7alpha-dihydroxy-5-cholenoic acid by the action of microsomal enzymes, and Delta4-3-oxo acid was converted to CDCA by cytosolic enzymes. These findings indicate the presence of an enzymatic activity that converts 3beta-hydroxy-5-cholenoic acid into CDCA in rat brain tissue. Furthermore, this synthetic pathway for CDCA may relate to the function of 24S-hydroxycholesterol, which plays an important role in cholesterol homeostasis in the body.

Metabolism of 3 beta-hydroxycholest-5-en-26-oic acid in hamsters

Metabolism of 26-hydroxycholesterol to 3 beta-hydroxychol-5-en-24-oic acid and other C24-bile acids has been expected to occur by way of 3 beta-hydroxycholest-5-en-26-oic acid in studies in vitro. 3 beta-Hydroxycholest-5-en-26-oic acid was infused intravenously into bile fistula hamsters and the following C24-bile acids were identified: 3 beta-hydroxychol-5-en-24-oic acid, lithocholic acid, chenodeoxycholic acid, and a small amount of cholic acid.

Cholesterol autoxidation 1981-1986

Literature published between 1980 and 1986 dealing broadly with the topic of cholesterol autoxidation is reviewed. The review builds on the detailed 1981 monographic treatment of the topic by the author and covers new items of chemistry, analysis, and metabolism.

26-Hydroxycholesterol disulfate: metabolism and excretion in the normal neonate

Deuterated 26-hydroxycholesterol disulfate has been given in a tracer amount to neonates to evaluate the pool size, metabolism and excretion of the endogenously occurring compound in meconium. In a group of 5 normal neonates excretion of endogenous 26-hydroxycholesterol during the initial 72 h of life ranged from 327 to 1096 micrograms. Recovery of administered isotope during the same period was 66-98%. Only trace amounts of 26-hydroxycholesterol were recovered in urine. The findings indicate that relative to bile acid pool size, the normal neonate has a small intestinal pool of 26-hydroxycholesterol which, for the most part, is rapidly excreted and does not contribute significantly to bile acid synthesis. The techniques developed during the course of the study provide an approach to non invasive metabolic studies that give insights on the normal transition from fetal to neonatal life.

Unusual serum bile acid pattern in children with the syndrome of hepatic ductular hypoplasia

Fasting bile acids in serum of eight children with the syndrome of hepatic ductular hypoplasia were analyzed by gas chromatography. The children did not receive any kind of treatment during the month before the analysis. Serum concentrations of total bile acids ranged from 110.8-303.7 mumol/1. The predominant bile acids were chenodeoxycholic and cholic acids accounting for 62.8-86.5% of the total. The ratio of cholic acid to chenodeoxycholic acid ranged between 0.43 and 1.11. Monohydroxylated bile acids were found in increased amounts in all patients (5.1-23.9%), 3 beta-hydroxy-5-cholenoic acid being the major monohydroxylated bile acid (3.1-17.1%). Other unusual bile acids such as ursodeoxycholic acid and 12-oxo-3 alpha, 7 alpha-dihydroxy-5 beta-cholanoic acid (7.3-14.9%) were also detected. Neither 3 beta-hydroxy-5-cholenoic nor lithocholic acid levels were statistically correlated to cholic or chenodeoxycholic acids. However, a statistically significant correlation between total bile acid levels and 12-oxo-3 alpha, 7 alpha-dihydroxy-5 beta-cholanoic acid levels was found. These findings are interesting as far as the origin of the unusual bile acids found in this cholestatic syndrome is concerned. The large amounts of 3 beta-hydroxy-5-cholenoic acid measured in children with the syndrome of hepatic ductular hypoplasia could indicate the existence of an alternative fetal pathway of bile acid synthesis.

Rapid synthesis of 26-hydroxycholesterol from mevalonic acid in the Syrian hamster

Using isotope-ratio mass spectrometry, newly synthesized 26-hydroxycholesterol and its derivative, 3 beta-hydroxy-5-cholenoic acid, were detected in the liver and bile of animals within 2 h following intravenous administration of [5-13C]mevalonic acid. The findings indicate that 26-hydroxycholesterol merits further consideration as an in vivo modulator of HMG-CoA reductase activity.

Changes of the pattern of biliary bile acids during isolated rat liver perfusion

In spite of the extensive use of isolated perfused liver systems for bile acid related studies, the composition of biliary bile acids during liver perfusion is not well known. Using recently developed bioluminescence assays for 3 alpha-OH-, 7 alpha-OH-, and 12 alpha-OH- bile acids we studied the hydroxylation pattern of bile acids in bile during 90 minutes perfusion of isolated rat liver without added bile acid load. At the beginning 7 alpha-hydroxylated bile acids comprised more than 50% of total bile acids from male livers and more than 90% from female livers, this percentage declined rapidly during the first 40-50 minutes of perfusion to values between 10 and 20%. 12 alpha-hydroxylated bile acids comprised between 15 and 30% of the total at beginning of the perfusion and decreased to about 10% after 40 minutes. Sex differences as well as the influence of the duration of perfusion should be considered when the isolated perfused rat liver is used for bile acid related studies.

Chenodeoxycholic acid synthesis in the hamster: a metabolic pathway via 3 beta, 7 alpha-dihydroxy-5-cholen-24-oic acid

The quantitative significance of the metabolism of 3 beta, 7 alpha-dihydroxy-5-cholen-24-oic acid to chenodeoxycholic acid was evaluated in the hamster. A precursor-product relationship was established in this species by the finding that intravenous administration to an animal previously given cholesterol-4-14C caused a significant reduction in the specific activity of chenodeoxycholic acid. Administration of 12.9 mumole of the precursor was followed by a 10-fold increase in chenodeoxycholic acid excretion although the predominant excretory pathway was via biliary excretion as a monosulfate. The data indicate that synthesis of bile acid from cholesterol via the intermediate 3 beta, 7 alpha-dihydroxy-5-cholen-24-oic acid can be a quantitatively important pathway.

Cholest-5-ene-3 beta, 26-diol: synthesis and biomedical use of a deuterated compound

To further studies of the metabolism of 26-hydroxycholesterol in fetal and neonatal life, a deuterated compound was prepared from kryptogenin by Clemmensen reduction. The spectra of the deuterated 26-hydroxycholesterol showed that five to nine deuterium atoms were incorporated per 26-hydroxycholesterol molecule, with the maximum incorporation of eight deuterium atoms. The deuterated compound was recovered unchanged from the feces of a child following oral administration. Comparison of the ratio of deuterated to protium compound indicated the presence of an endogenous pool of 26-hydroxycholesterol. Parenteral administration of the compound to a hamster indicated metabolism to deuterated chenodeoxycholic acid. The compound is useful as an isotope tracer for studies of the endogenous metabolism of 26-hydroxycholesterol.