Differing effects of cholesterol and taurocholate on steady state hepatic HMG-CoA reductase and cholesterol 7 alpha-hydroxylase activities and mRNA levels in the rat

We investigated the effects of cholesterol, cholestyramine, and taurocholate feeding on steady state specific activities and mRNA levels of hepatic 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase and cholesterol 7 alpha-hydroxylase in the rat. Interruption of the enterohepatic circulation of bile acids (cholestyramine feeding) increased total HMG-CoA reductase activity 5-fold. Cholesterol and taurocholate administration suppressed total microsomal HMG-CoA reductase activities 87% and 65%, respectively. HMG-CoA reductase mRNA levels increased 3-fold with cholestyramine, did not decrease significantly with cholesterol feeding, but were markedly decreased after taurocholate treatment. Cholesterol 7 alpha-hydroxylase activity increased 4-fold with cholestyramine and 29% during cholesterol feeding, but decreased 64% with taurocholate. Cholesterol 7 alpha-hydroxylase mRNA levels rose 150% and 50% with cholestyramine and cholesterol feeding, respectively, but decreased 73% with taurocholate. The administration of cholesterol together with taurocholate prevented the decline in cholesterol 7 alpha-hydroxylase mRNA levels, but inhibition of enzyme activity persisted (-76%). Hepatic microsomal cholesterol concentrations increased 2-fold with cholesterol feeding but did not change with taurocholate or cholestyramine treatment. These results demonstrate that mRNA levels of HMG-CoA reductase are controlled by the hepatic taurocholate flux, whereas mRNA levels of cholesterol 7 alpha-hydroxylase are controlled by the cholesterol substrate supply. These end products, cholesterol and bile acids, exert post-transcriptional regulation on HMG-CoA reductase and cholesterol 7 alpha-hydroxylase, respectively.

Sitosterolemia

Sitosterolemia is a rare inherited lipid storage disease characterized chemically by the accumulation of plant sterols and 5 alpha-saturated stanols in plasma and tissues. Very low cholesterol synthesis due to a deficiency of HMG-CoA reductase associated with increased intestinal plant sterol absorption and slow hepatic sterol removal are major biochemical features. Because cholesterol synthesis cannot up-regulate, bile acid malabsorption mobilizes body sterols for bile acid synthesis and dramatically lowers plasma and monocyte sterol concentrations and may halt the progression of the atherosclerotic process.

Lithotripsy plus ursodiol is superior to ursodiol alone for cholesterol gallstones

The safety and efficacy of gallbladder extracorporeal shock-wave lithotripsy combined with 600 mg/day ursodiol were examined in 85 patients with radiolucent gallstones, 15 with lightly calcified gallstones, and 12 with radiolucent stones pretreated for greater than or equal to 2 months with 600 mg/day ursodiol. Results were compared with those of a well-matched lithotripsy-eligible group of 32 subjects treated with ursodiol alone (no lithotripsy). Pretreatment with ursodiol significantly improved while gallstone calcification interfered with fragmentation. Small gallstone size and number also aided fragmentation. Biliary lithotripsy plus ursodiol increased efficacy twofold compared with ursodiol therapy alone (47% vs. 22% of subjects gallstone free; P less than 0.02). Gallstones did not disappear in any subject with calcified gallstones (P less than 0.001) vs. lithotripsy). Product-limit analysis showed that the efficacy for gallstone dissolution increases in the following order: ursodiol alone, lithotripsy-ursodiol, lithotripsy-ursodiol pretreated with ursodiol (P less than 0.02, pairwise). Similar mean gallstone-dissolution rate constants (stone size divided by time to disappear) of stone fragments and whole gallstones during ursodiol therapy suggest that most fragments disappear by dissolution not expulsion. This finding explains why fragmentation appears to be the key predictor of disappearance and even partial fragmentation accelerates gallstone clearance.

Glycocholic acid and glycodeoxycholic acid but not glycoursocholic acid inhibit bile acid synthesis in the rabbit

Feedback regulation of derepressed hepatic bile acid biosynthesis was studied individually with glycocholic, glycodeoxycholic, and glycoursocholic acids by infusion into bile acid-depleted rabbits. Construction of a bile fistula drained the endogenous bile acid pool (90% glycodeoxycholic acid, 10% glycocholic acid) within 24 hours and elicited maximal bile acid synthesis after about 72 hours, at which time glycocholic acid became the only biliary bile acid (greater than 98%). Replacement of the bile acid pool with glycocholic acid or glycodeoxycholic acid at a rate equivalent to the hepatic endogenous bile acid flux inhibited endogenous biosynthesis by 40%. In contrast, glycoursocholic acid, the 7 beta-hydroxy epimer of glycocholic acid, failed to suppress synthesis. Hepatic bile acid depletion increased hydroxymethyglutary coenzyme A (HMG-CoA) reductase activity fourfold and cholesterol 7 alpha-hydroxylase activity threefold, which were reduced 48% and 51%, respectively, from their maximum levels during replacement with glycocholic acid. Glycodeoxycholic acid infusion depressed cholesterol 7 alpha-hydroxylase activity by 59% without reducing HMG-CoA reductase activity significantly. There was no significant change in the activity of either enzyme during glycoursocholic acid infusion. Biliary cholesterol and cholestanol secretion declined 13% and 53%, respectively, during glycocholic acid infusion, were not affected by glycodeoxycholic acid infusion, but increased 19% and 43%, respectively, during glycoursocholic acid infusion. These results show that in rabbits the feedback regulation of hepatic bile acid synthesis depends on the hepatic flux of the normally present endogenous bile acids glycocholic acid and glycodeoxycholic acid but does not respond to the 7 beta-hydroxy glycoursocholic acid. Glycocholic acid inhibits both HMG-CoA reductase and cholesterol 7 alpha-hydroxylase while glycodeoxycholic acid affects primarily cholesterol 7 alpha-hydroxylase. Thus, the regulation of bile acid synthesis may be mediated by both the availability of cholesterol substrate and the activity of the rate-determining enzyme for bile acid synthesis.

Increased sitosterol absorption is offset by rapid elimination to prevent accumulation in heterozygotes with sitosterolemia

Using plasma isotope-kinetic methods, we measured the absorption and turnover rates of cholesterol and sitosterol (24-ethylcholesterol) in two obligate heterozygotes (parents) and their homozygous daughter with sitosterolemia with xanthomatosis. Diets contained approximately 500 mg/day cholesterol and 100 mg/day sitosterol. In the homozygote, plasma cholesterol and apolipoprotein B concentrations were slightly higher, but sitosterol levels were 22 and 58 times higher than in her heterozygous parents. Cholesterol absorption was at the high end of the normal range in both heterozygotes (59% and 84%) and in the homozygote (62%) (value in the control subject 48%). In contrast, cholesterol synthesis was severely depressed in the homozygote (28% and 26% as great as in the heterozygotes and the control, respectively). Sitosterol absorption in the homozygote (34%) was 2.3 and 2.0 times greater than in the heterozygotes and 6.8 times greater than in the control. The sitosterol turnover rate, calculated independently by mathematical analysis of specific-activity decay curves, amounted to 15 and 24 mg/day in the heterozygotes compared with 27 mg/day in the homozygote and 7.9 +/- 2.3 mg/day in five control subjects. However, the total body sitosterol pool was 15 and 10.3 times larger in the homozygote (4,080 mg) than in her heterozygous parents because of extremely slow removal. The average sitosterol elimination constant in the heterozygotes (KA = 0.11 day-1) was 10 times that in the homozygote (KA = 0.01 day-1) but 35% less than that in the controls (KA = 0.17 day-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Stereoselective synthesis of (24R and 24S) 5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,25-pentols and (25R and 25S) 5 beta-cholestane-3 alpha,7 alpha,12 alpha,25,26-pentols using a modified osmium-catalyzed Sharpless asymmetric dihydroxylation process

Described herein are the stereoselective syntheses of the (24R, 24S) and (25R, 25S) isomers of 5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,25-pentols and 5 beta-cholestane-3 alpha,7 alpha,12 alpha,25,26-pentols by using a modified osmium-catalyzed Sharpless asymmetric dihydroxylation process. Also presented herein are the results of lanthanide-induced CD Cotton effect measurements and 1H- and 13C-nuclear magnetic resonance studies of (24R, 24S) and (25R, 25S)-5 beta-cholestanepentols and their derivatives. These compounds were required to study the biosynthesis of cholic acid from cholesterol.

Synthesis of 3 alpha, 7 alpha-dihydroxy-5 beta-cholestan-26-oic acid from 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestan-26-oic acid: configuration in the bile of Alligator mississippiensis

Synthesis of 25R- and 25S-diastereoisomers of 3 alpha,7 alpha-dihydroxy-5 beta-cholestan-26-oic acid from 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestan-26-oic acid is described. The 25S-diastereoisomer of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestan- 26-oic acid was obtained by vigorous hydrolysis of the bile of Alligator mississippiensis followed by repeated crystallization of the hydrolysate, and the 25R-diastereoisomer was isolated by hydrolysis of the bile salts in bile of A mississippiensis with rat feces. Acetylation of the 25R- or 25S-diastereoisomer of methyl 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestan-26-oic acid under controlled conditions yielded the corresponding 3 alpha,7 alpha-diacetate in approximately 70% yield. The diacetate was quantitatively oxidized to methyl 3 alpha,7 alpha-diacetoxy-12-oxo-5 beta-cholestan-26-oate, which was converted into the 12-tosylhydrazone in approximately 58% yield. Reduction of the tosylhydrazone with sodium borohydride in acetic acid yielded the 25R- or the 25S-diastereoisomer of 3 alpha,7 alpha-dihydroxy-5 beta-cholestan-26-oic acid as the major product. Purification via column chromatography yielded the pure diastereoisomers in approximately 25% overall yield. The two diastereoisomers were resolved on thin-layer chromatography and high-performance liquid chromatography. When the bile of A mississippiensis was hydrolyzed with rat fecal bacteria, the 3 alpha,7 alpha-dihydroxy-5 beta-cholestan-26-oic acid isolated via chromatographic purification was shown to be the 25R-diastereoisomer.

Metabolism of ursocholic acid in humans: conversion of ursocholic acid to deoxycholic acid

To study the metabolism of ursocholic acid, control subjects were injected with radiolabeled cholic and ursocholic acids before and after 1 wk of 900 mg/day oral ursocholic acid. Daily samples of bile were obtained, and biliary bile acids were extracted and purified to determine bile acid kinetics. During ursocholic acid therapy ursocholic acid became the principal bile acid (35% +/- 3% of total bile acids, mean +/- S.E.M.), and the percentage of biliary cholic and chenodeoxycholic acids decreased (p less than 0.05). Cholic acid production fell from 190 +/- 15 mg/day to 135 +/- 20 mg/day (p = 0.078). The total bile acid pool was increased twofold (p less than 0.05), whereas the deoxycholic acid pool was enlarged from 440 +/- 170 mg to 1,175 +/- 90 mg (p less than 0.02). As much as 28% of the fed ursocholic acid was excreted in the urine, 85% as the free acid and 15% as the glycine conjugate. During treatment, ursocholic acid became the source for 69% +/- 11% of biliary deoxycholic acid. The time course of the deoxycholic acid specific activity was modeled as a single pool precursor-product system with a variable time delay for the C-7-dehydroxylation of cholic and ursocholic acids (mean delay 0.86 +/- 0.11 days, p less than 0.001 vs. zero delay). Most of this delay probably arises from a slow process of bacterial C-7-dehydroxylation within the colon. These results demonstrate that during ursocholic acid therapy the synthesis of primary bile acids continues whereas the formation of secondary bile acids is greatly increased.

Synthesis of 3 alpha,6 beta,7 alpha,12 beta- and 3 alpha,6 beta,7 beta,12 beta-tetrahydroxy-5 beta-cholanoic acids

Chemical synthesis of 3 alpha,6 beta,7 alpha,12 beta- and 3 alpha,6 beta,7 beta,12 beta-tetrahydroxy-5 beta-cholan-24-oic acids is described. 3 alpha,12 beta-Dihydroxy-5 beta-chol-6-en-24-oic acid used as the starting material in the synthesis was prepared via oxidation of 3 alpha,12 alpha-dihydroxy-5 beta-chol-6-en-24-oic acid 3-hemisuccinate at C-12 followed by reduction with potassium/tertiary amyl alcohol. alpha-Epoxidation of the ester diacetate of 3 alpha,12 beta-dihydroxy-5 beta-chol-6-en-24-oic acid with m-chloroperbenzoic acid followed by cleavage of the epoxide with acetic acid and alkaline hydrolysis yielded 3 alpha,6 beta,7 alpha,12 beta-tetrahydroxy-5 beta-cholan-24-oic acid (overall yield 25%). N-Methylmorpholine-N-oxide-catalyzed osmium tetroxide oxidation of the ester diacetate of 3 alpha,12 beta-dihydroxy-5 beta-chol-6-en-24-oic acid followed by alkaline hydrolysis yielded 3 alpha,6 beta,7 beta,12 beta-tetrahydroxy-5 beta-cholan-24-oic acid (overall yield 33%). The structures of the synthesized bile acids were confirmed from their proto nuclear magnetic resonance and mass spectral fragmentation patterns.

Regulation of cholesterol biosynthesis in sitosterolemia: effects of lovastatin, cholestyramine, and dietary sterol restriction

We investigated the effects of lovastatin, cholestyramine, and dietary sterol restriction on cholesterol synthesis and low density lipoprotein receptor function in freshly isolated mononuclear leukocytes from two unrelated sitosterolemic families. Total plasma sterol concentrations were elevated in the two homozygous sitosterolemic subjects (343 and 301 vs. 185 mg/dl in controls) and contained increased amounts of plant sterols and 5 alpha-saturated stanols (20% and 8% vs. less than 1% in controls), but were not significantly different from controls in the two heterozygous subjects. The rates of conversion of acetate to cholesterol by mononuclear leukocytes were subnormal in all homozygous and heterozygous subjects and correlated with markedly reduced microsomal 3-hydroxy-3-methylglutaryl co-enzyme A (HMG-CoA) reductase activity. In the two homozygous subjects, cholestyramine treatment decreased plasma sterols 29% and 35%, and yet was associated with a paradoxical decline in mononuclear leukocyte HMG-CoA reductase activity. In contrast, plasma sterol concentrations decreased 14% and 5%, and mononuclear leukocyte HMG-CoA reductase activities increased 13% and 46% in three control and one heterozygous subjects treated with cholestyramine, respectively. Plasma sterol concentrations in the homozygous subjects unexpectedly failed to decline during treatment with lovastatin or a low sterol diet. In distinction, plasma sterol concentrations in three control and one heterozygous subjects dropped 28% and 31%, respectively, during treatment with lovastatin. Both cholestyramine and low dietary sterols stimulated low density lipoprotein receptor function. These results demonstrate a marked abnormality in cholesterol homeostasis in patients with homozygous sitosterolemia with xanthomatosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Ursodeoxycholic acid for the treatment of primary sclerosing cholangitis: a 30-month pilot study

We investigated the effects of once-daily oral administration of 10 mg/kg ursodeoxycholic acid (generic name, ursodiol) on elevated serum enzyme activities, bilirubin, cholesterol, bile acids and symptoms in patients with primary sclerosing cholangitis. A 30-mo, open-label, pilot trial was designed to cover four periods: (a) 3 mo of pretreatment observation (period 1), (b) 6 mo on ursodiol (period 2), (c) 3 mo withdrawal of treatment (period 3) and (d) 18 mo of extended retreatment (period 4). Diagnosis was confirmed by cholangiography and liver biopsy specimens. We enrolled 12 patients with persistently elevated pretreatment alkaline phosphatase and gamma-glutamyltransferase levels (at least twice the upper limit of normal), and observed them for a median of 37 mo. Significant reductions in serum total cholesterol levels and in serum enzyme activities indicating cholestasis and hepatocellular injury occurred during ursodiol treatment in both treatment periods 2 and 4 and relapsed with treatment interruption in period 3. Elevated serum bilirubin and symptoms of disabling fatigue, pruritus and diarrhea were improved by ursodiol. Improvements have continued after 2 yr of treatment in 10 patients (1 patient had a transplantation after he relapsed on withdrawal of ursodiol therapy; another died of postoperative complications of colon resection for carcinoma). No other cases of clinical deterioration were observed in the retreatment period. The longer term reductions of alkaline phosphatase, transaminases, bilirubin and cholesterol after 2 yr of treatment were even greater than the initial reductions after 6 mo of treatment. These results justify initiation of larger, controlled clinical trials, with serial morphological evaluations of the liver and biliary tree.

Sonographic gallstone patterns are of value in predicting the outcome of biliary lithotripsy

The purpose of our study was to determine whether the qualitative features of gallstones, as expressed by their sonographic image, are related to the degree of fragmentation by shock-wave lithotripsy and the rate of stone clearance. The sonographic stone images of 73 patients with 1-3 uncalcified gallstones, followed for at least 1 yr after extracorporeal shock-wave lithotripsy, were analyzed and categorized by three independent observers into two distinct groups: type I--crescent to disc shape with gradual attenuation of echoes, and type II--rim-shape with abrupt shadowing. The degree of fragmentation and rate of stone clearance were significantly greater for type I stones than for type II stones. For all subjects, 1 yr after lithotripsy, 56% (27/48) of type I stones and 12% (3/25) of type II stones had cleared completely (p less than 0.0005). The clearance rate for solitary type I stones was 63% (20/32) versus 14% (2/14) for type II stones (p less than 0.005). Our observations suggest that sonographic analysis of stone patterns might help in predicting success, and contribute to greater cost-effectiveness of biliary extracorporeal shock-wave lithotripsy.

Stereospecific synthesis and two-dimensional 1H-NMR investigation of isoursocholic acid

This report describes the chemical synthesis of isoursocholic acid (3 beta, 7 beta, 12 alpha-trihydroxy-5 beta-cholanoic acid) from its corresponding 3 alpha-analog. The method consists of refluxing a mixture of ursocholic acid, triphenylphosphine, and diethyl azodicarboxylate in benzene solution with an acid such as formic acid. The sterically pure ester (3 beta-formate) so formed after saponification with LiOH-aqueous methanol then allowed an easy access to the epimer of the starting acid. Large scale preparative separation and purification of the final product and synthetic intermediates were accomplished by flash column chromatography of their methyl ester derivatives. Structural assignment of the isourscholic acid molecule was confirmed by complete analysis of proton NMR spectra using 2-D NMR correlation experiments which rigorously established the (3 beta/3 alpha) and (7 beta/7 alpha) hydroxyl configurations in the isoursocholic and ursocholic acids. It is suggested that the isoursocholic acid will be useful as a reference compound and as a substrate in studies dealing with the hepatic inversion of the 3 beta-hydroxy group.

The use of microwave oven for the rapid hydrolysis of bile acid methyl esters

An efficient and convenient procedure for the hydrolysis of bile acid methyl esters is described. This is achieved by the addition of aqueous lithium hydroxide in methanol/dioxane/tetrahydrofuran (or dimethylformamide) in the microwave oven. Under these conditions the formates as well as the acetate derivatives prepared under microwave irradiation conditions were also hydrolyzed, and the desired bile acids were isolated in 86-94% yield. All these reactions were completed in the microwave oven within 45-60 s.

Selective reduction of oxo bile acids: synthesis of 3 beta-, 7 beta-, and 12 beta-hydroxy bile acids

Preparation of some biologically important keto bile acids is described. Advantage is taken of the preferential ketalization of 3-oxo group in bile acids over 7- and 12-oxo groups for the selective reduction of these keto groups. The method was found to be specially useful for preparation of 7 beta-, 12 alpha, and 12 beta-[3H]-3-oxo bile acids. Improved methods are also described for the preparation of epimers of naturally occurring bile acids at C-3, C-7, and C-12. 3 beta-Hydroxy bile acids (iso-bile acids) were prepared with the use of diethylazodicarboxylate/triphenylphosphine/formic acid. Iso-bile acids were obtained in excellent yields (80-95%) except during synthesis of isoursodeoxycholic acid (yield, 50%). Isoursodeoxycholic acid was, however, prepared in very good yield via epimerization of 3 alpha-hydroxyl group in 7-oxolithocholic acid followed by stereoselective reduction of 7-oxo group. A highly efficient method for the reduction of 7-oxo and 12-oxo groups was developed. Thus, 7-oxolithocholic acid and 7-oxoisolithocholic acid on reduction with potassium/tertiary amyl alcohol yielded ursodeoxycholic acid and isoursodeoxycholic acid in yields of 96% and 94%, respectively, while reduction of 7-oxodeoxycholic acid resulted in ursocholic acid in 93% yield. In a similar manner, reduction of 12-oxolithocholic acid and 12-oxochenodeoxycholic acid yielded 3 alpha, 12 beta-dihydroxy-5 beta-cholanoic acid (lagodeoxycholic acid; 92% yield) and 3 alpha, 7 alpha, 12 beta-trihydroxy-5 beta-cholanoic acid (lagocholic acid, 86% yield).

High-performance liquid chromatographic separation of bile acids and bile alcohols diastereoisomeric at C-25

The high-performance liquid chromatographic separation of the 25R and 25S diastereoisomers of the bile alcohols 5 beta-cholestane-3 alpha,7 alpha,26-triol and 5 beta-cholestane-3 alpha,7 alpha, 12 alpha, 26-tetrol and the bile acids, 3 alpha,7 alpha-dihydroxy-5 beta-cholestane-26-oic acid and 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestane-26-oic acid is described. A Radial-Pak microBondapak C18 reversed-phase cartridge was used for the separations and elutions were carried out with acetonitrile-water-methanol-acetic acid mixtures. All eight diastereoisomeric compounds showed baseline separation when up to 200 micrograms of the isomeric mixtures were injected into the column and the method can be used for isolation of pure diastereoisomers of these bile acids and bile alcohols.

Treatment of cholesterol gallstones with litholytic bile acids

Cholesterol gallstone disease is reversible and can be treated medically with either CDCA or UDCA. Both bile acids correct the hepatic metabolic defect that is responsible for hypersecretion of cholesterol into the bile, and both desaturate the bile. UDCA is preferred because it is more effective, desaturate the bile to a greater extent than CDCA, and eliminates cholesterol as stable liquid crystalline dispersions. UDCA is virtually free of side effects and does not produce toxicity. Symptoms are relieved rapidly, and the quality of life improves. Dietary restrictions can be relaxed as the stones dissolve.

Regulation of cholesterol 7 alpha-hydroxylase by hepatic 7 alpha-hydroxylated bile acid flux and newly synthesized cholesterol supply

We measured hepatic cholesterol 7 alpha-hydroxylase activity, mass, and catalytic efficiency (activity/unit mass) in bile fistula rats infused intraduodenally with taurocholate and its 7 beta-hydroxy epimer, tauroursocholate, with or without mevalonolactone to supply newly synthesized cholesterol. Enzyme activity was measured by an isotope incorporation assay and enzyme mass by densitometric scanning of immunoblots using rabbit anti-rat liver cholesterol 7 alpha-hydroxylase antisera. Cholesterol 7 alpha-hydroxylase activity increased 6-fold, enzyme mass 34%, and catalytic efficiency 5-fold after interruption of the enterohepatic circulation for 48 h. When taurocholate was infused to the bile acid-depleted animals at a rate equivalent to the hepatic bile acid flux (27 mumol/100-g rat/h), cholesterol 7 alpha-hydroxylase activity and enzyme mass declined 60 and 61%, respectively. Tauroursocholate did not significantly decrease cholesterol 7 alpha-hydroxylase activity, mass and catalytic efficiency. The administration of mevalonolactone, which is converted to cholesterol, modestly increased cholesterol 7 alpha-hydroxylase activity and enzyme mass in the bile acid-depleted rats. However, when taurocholate was infused together with mevalonolactone, cholesterol 7 alpha-hydroxylase activity and catalytic efficiency were markedly depressed while enzyme mass did not change as compared with bile acid-depleted rats. These results show that (a) hepatic bile acid depletion increases bile acid synthesis mainly by activating cholesterol 7 alpha-hydroxylase with only a small rise in enzyme mass, (b) replacement with taurocholate for 24 h decreases both cholesterol 7 alpha-hydroxylase activity and mass proportionally, (c) when cholesterol is available (mevalonolactone supplementation), the infusion of taurocholate results in the formation of a catalytically less active cholesterol 7 alpha-hydroxylase, and (d) tauroursocholate, the 7 beta-hydroxy epimer of taurocholate, does not inhibit cholesterol 7 alpha-hydroxylase. Thus, bile acid synthesis is modulated by the catalytic efficiency and mass of cholesterol 7 alpha-hydroxylase. The enterohepatic flux of 7 alpha-hydroxylated bile acids and the formation of hepatic cholesterol apparently control cholesterol 7 alpha-hydroxylase by different mechanisms.

Cerebrotendinous xanthomatosis as a multisystem disease mimicking premature ageing

The authors report the clinical findings in 10 Italian cases of cerebrotendinous xanthomatosis (CTX). In addition to the classical neurological manifestations, the presence of psychiatric symptoms and osteopenia is stressed. Chronic treatment with chenodeoxycholic acid resulted in decreased plasma cholestanol levels and improvement of some central and peripheral neurophysiological parameters including EEG, VEP, SEP and conduction velocities. Due to the presence of cataracts, ischemic heart disease, premature atherosclerosis, mental deterioration and osteoporosis, usually found in old age, CTX can be considered a useful model of premature ageing.

Biochemical abnormalities in cerebrotendinous xanthomatosis

Cerebrotendinous xanthomatosis (CTX) is a rare recessive inherited lipid storage disease that was first described by Van Bogaert. Although the principal clinical presentation affects the nervous system with dementia, spinal cord paresis, cerebellar ataxia and peripheral neuropathy, the liver is is the organ where the major biochemical abnormalities are expressed. The following sections deal with the pathogenesis and treatment of the biochemical problems in CTX.

Response to diet and cholestyramine in a patient with sitosterolemia

In this report, an 11-year-old boy with diffuse tendinous and tuberous xanthomatosis and a plasma sterol concentration of 555 mg/dL, consisting primarily of cholesterol, is described. Three months after changing from an unrestricted diet to a cholesterol-lowering diet, his plasma sterol concentration decreased to 221 mg/dL. Because of the degree and rapidity of his response to diet, sitosterolemia was suspected. According to results of capillary gas-liquid chromatography of his plasma sterols, there was a sitosterol concentration of 31.3 mg/dL (normal less than 1.0 mg/dL), establishing the diagnosis of sitosterolemia. Addition of cholestyramine therapy (8 g/d) to a low sterol diet further lowered his plasma sterol concentration to 173 mg/dL and led to complete regression of all tuberous xanthomata. Tendinous xanthomata regressed at a slower rate. These findings show that the diagnosis of sitosterolemia should be suspected in severely hypercholesterolemic children (total cholesterol greater than 400 mg/dL) whose plasma cholesterol level is highly responsive to dietary manipulation. The rapid and sustained lowering of plasma cholesterol and regression of xanthomata after treatment with diet and cholestyramine suggest that sitosterolemia is a treatable cause of premature atherosclerosis.