Efficacy and safety of ezetimibe 40 mg vs. ezetimibe 10 mg in the treatment of patients with homozygous sitosterolaemia

OBJECTIVE

To assess the effect of ezetimibe (EZE) 40 mg/day on non-cholesterol sterol plasma concentrations in patients with homozygous sitosterolaemia (HoS).

METHODS

This was a multi-centre, randomised, double-blind, placebo-controlled parallel group study. Twenty-seven patients (> or = 18 years) with HoS and plasma sitosterol levels > 5 mg/dl who had been taking EZE 10 mg/day for > or = 6 months prior to enrolment received open-label EZE 10 mg/day for the duration of the study and were randomised 1 : 1 to blinded EZE 30 mg/day (4 x EZE 10 mg tablets; n = 13) or placebo (1 x EZE 10 mg tablet and 3 x matching placebo tablets; n = 14) for 26 weeks. Patients were permitted to remain on other ongoing treatments (e.g. bile salt-binding resin, statin and/or low sterol diet). End-points included median per cent between-group changes from baseline in plasma sitosterol, campesterol, lathosterol, low-density lipoprotein (LDL) sterols, LDL cholesterol (LDL-C) measured by gas-liquid chromatography, and Achilles tendon thickness size measured radiographically.

RESULTS

Ezetimibe 40 mg/day resulted in median per cent changes from baseline in plasma sitosterol levels of 3.3% vs. -10% in the EZE 10 mg/day group, in plasma campesterol of -0.5% vs. -9.7% in the EZE 10 mg/day group, and in plasma lathosterol of 0.8% vs. 1.1% in the EZE 10 mg/day group (p = ns for all between-group differences). Median per cent changes in the EZE 40 mg/day and EZE 10 mg/day groups, respectively, were 1.3% and 0% for LDL sterols and 2.5% and 4.4% for LDL-C (p = ns for both between-group differences). At study end-point, Achilles tendon thickness remained unchanged in the EZE 40 mg/day group and increased slightly in the EZE 10 mg/day group (2.2%), yielding a non-significant between-group difference of -2.2%. EZE 40 mg/day was generally well tolerated.

CONCLUSIONS

In patients with HoS, treatment with EZE 40 mg/day for 26 weeks was no more effective at reducing plasma plant sterol concentrations vs. EZE 10 mg/day. EZE 40 mg/day had a safety and tolerability profile similar to EZE 10 mg/day.

Normal cognition and behavior in a Smith-Lemli-Opitz syndrome patient who presented with Hirschsprung disease

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive disorder of cholesterol biosynthesis. It is caused by mutations in the gene encoding the enzyme 7-dehydrocholesterol Delta7-reductase (DHCR7), which catalyzes the final step in cholesterol biosynthesis, usually resulting in cholesterol deficiency. We report a 3.5-year-old girl who has cognition in the low average range and normal behavior, but in whom molecular studies identified two missense mutations in DHCR7: V326L and F284L. She was born at term following an uncomplicated pregnancy and delivery, and presented at 12 days of age with poor feeding, abdominal distention, and jaundice. Colonic biopsy was consistent with Hirschsprung disease. On physical examination she had mild ptosis, a long philtrum, mild micrognathia, a short, upturned nose, and subtle 2,3 syndactyly. Her 7-dehydrocholesterol (7-DHC) level was markedly elevated at 8.7 mg/dl (normal 0.10 +/- 0.05), and her cholesterol level was normal at 61 mg/dl (normal for newborn period 50-80 mg/dl). Karyotype analysis was normal, 46,XX. Breast milk feeding was initiated and continued for 18 months. Cholesterol supplementation was implemented at 100 mg/kg/day at 3 months, which resulted in increased cholesterol levels and reduced dehydrocholesterol levels. Neuropsychological testing has shown functioning in the low average range, between the 14th and 18th centiles when compared to peers. This is markedly higher than most children with SLOS. She has no behavioral problems. MRI and MRS testing of the brain revealed no structural abnormalities. This is in contrast to a recently reported case by Prasad et al. [2002: Am J Med Genet 108:64-68] with a mild phenotype, behavioral problems, and abnormal MRI, who is compound heterozygote for both a null and missense mutation. Our case suggests that patients with severe feeding disorders with or without Hirschprung disease and postnatal onset microcephaly may warrant screening for SLOS.

Ezetimibe effectively reduces plasma plant sterols in patients with sitosterolemia

BACKGROUND

Sitosterolemia is a recessively inherited disorder that results from mutations in either ABCG5 or G8 proteins, with hyperabsorption of dietary sterols and decreased hepatic excretion of plant sterols and cholesterol. As a consequence of markedly elevated plasma and tissue sitosterol and campesterol levels, premature atherosclerosis develops.

METHODS AND RESULTS

In this multicenter, double-blind, randomized, placebo-controlled study, we examined whether treatment with ezetimibe, an inhibitor of cholesterol absorption, reduces plant sterol levels in patients with sitosterolemia. After a 3-week placebo run-in, 37 patients were randomized to receive placebo (n=7) or ezetimibe 10 mg/d (n=30) for 8 weeks. Sitosterol concentrations decreased by 21% (P<0.001) in patients treated with ezetimibe compared with a nonsignificant 4% rise in those on placebo (between-group P<0.001). The reduction in sitosterol from baseline was progressive, with further decline observed at each subsequent biweekly visit. Campesterol also progressively declined, with a mean decrease after 8 weeks of 24% with ezetimibe and a mean increase of 3% with placebo treatment (between-group P<0.001). Reductions in plant sterol concentrations were similar irrespective of whether patients were undergoing concomitant treatment with resin or statin. Reductions in total sterols and apolipoprotein B were also observed. Ezetimibe was well tolerated, with no serious treatment-related adverse events or discontinuations due to adverse events being reported.

CONCLUSIONS

Ezetimibe produced significant and progressive reductions in plasma plant sterol concentrations in patients with sitosterolemia, consistent with the hypothesis that ezetimibe inhibits the intestinal absorption of plant sterols as well as cholesterol, leading to reductions in plasma concentrations.

Two novel mutations in the sterol 27-hydroxylase gene causing cerebrotendinous xanthomatosis

Cerebrotendinous xanthomatosis (CTX) is a rare recessive autosomal disease caused by mutations of the sterol 27-hydroxylase gene. Clinically, CTX is characterized by tendon xanthomas, cataracts and progressive neurological deficits. Because of the disruption of the 27-hydroxylase activity, CTX patients have elevated plasma levels of cholestanol, a by-product of abnormal bile acid synthesis. The present authors describe a female patient with CTX. The proband in this study presented with elevated cholestanol levels, markedly reduced mitochondrial 27-hydroxylase activity and altered bile acid composition. The 27-hydroxylase gene was analysed for mutations by polymerase chain reaction amplification of the exons and the splice-junction regions of the gene. The proband was found to be a compound heterozygote for two different mutations which have not been previously described: (1) a G --> A transition at nucleotide 455 that is responsible for converting a glycine to a glutamic acid residue at amino acid position 112 (G112E); and (2) a five-nucleotide deletion in exon 5 (from nucleotide 965 to 969) that is responsible for a shift in the reading frame and the insertion of a premature codon at position 296, and consequently, the synthesis of a truncated protein lacking the heme-binding and andrenodoxin-binding domains. Long-term (18-year) treatment of the proband with chenodeoxycholic acid (750 mg day-1) has been effective in preventing any progression of the disease.

Developmental sensitivity of associative learning to cholesterol synthesis inhibitors

Patients with Smith-Lemli-Opitz syndrome, a genetic disorder associated with severe mental retardation, are unable to convert 7-dehydrocholesterol to cholesterol. Treatment of rats with agents that block cholesterol synthesis produces a sterol profile reminiscent of Smith-Lemli-Opitz patients i.e., low levels of cholesterol accompanied by the appearance of its immediate precursor 7-dehydrocholesterol. In previous work, chronic inhibition of cholesterol synthesis in just-weaned rats impaired acquisition of the classically conditioned eyeblink response. The present study had two primary goals--(1) to determine whether the learning impairment depended on the age in which treatment was initiated; and (2) to determine whether the deficit was associative or due to performance factors. Consistent with earlier work, acquisition of the eyeblink conditioned response was impaired when the 30-day treatment was initiated on postnatal day (PND) 21. Reactivity to acoustic stimuli and to eyelid stimulation were normal, suggesting that the learning impairment was associative in nature. The learning impairment was transitory; acquisition was normal when evaluated 30 days after the cessation of treatment. When treatment was initiated 30 days after weaning (PND 51), acquisition of the eyeblink response was normal. However, brain sterols of young adult rats were less affected than those of just-weaned rats. Thus, there is a developmental sensitivity to cholesterol synthesis blocking agents both in terms of their effects on brain sterols and new motor learning.

Macrophage 3-hydroxy-3-methylglutaryl coenzyme a reductase activity in sitosterolemia: effects of increased cellular cholesterol and sitosterol concentrations

Sitosterolemia is a rare, recessively inherited disease characterized clinically by accelerated atherosclerosis and xanthomas and biochemically by hyperabsorption and retention of sitosterol and other plant sterols in tissues. Decreased cholesterol biosynthesis and inhibition of 3-hydroxy-3-methylgluratyl coenzyme A (HMG-CoA) reductase and other enzymes in the biosynthetic pathway have been associated with enhanced low-density lipoprotein (LDL) receptor function. We examined the effects of cholesterol and sitosterol on sterol concentrations and composition and HMG-CoA reductase activity in monocyte-derived macrophages (MDM) from 12 control and 3 homozygous sitosterolemic subjects. The cells were cultured up to 7 days in media devoid of plant sterols, but containing increasing amounts of serum cholesterol. Before culture, MDM from the homozygous sitosterolemic subjects contained 22% more total sterols than cells from control subjects. Plant sterols and stanols represented 15.6% of MDM total sterols in sitosterolemic cells, but only 3.8% in control cells. After 7 days of culture in 10% delipidated serum (DLS) (20 microg/mL cholesterol, no sitosterol), all plant sterols were eliminated so that cells from both phenotypes contained only cholesterol. When DLS was replaced with fetal bovine serum (FBS) (300 micromL cholesterol), with and without addition of 200 microg/mL LDL, cholesterol levels in MDM from sitosterolemic subjects increased 108% (P <.05) compared with a 65% increase (P <.04) in control MDM cultured similarly. MDM HMG-CoA reductase activity from the 3 sitosterolemic subjects, which was significantly lower than controls at baseline (24 +/- 3 v 60 +/- 10 pmol/mg/min, P <.05), was not downregulated by increased cellular cholesterol levels, as observed in control cells. Control MDM were also cultured in medium that contained 10% DLS and was supplemented with 100 microg/mL cholesterol or sitosterol dissolved in ethanol or the ethanol vehicle alone. In contrast to cellular cholesterol accumulation, which significantly downregulated HMG-CoA reductase activity (-53%, P <.05), the increase in cellular sitosterol up to 25.1% of total sterols did not change MDM HMG-CoA reductase activity. Evidence of a normal HMG-CoA reductase protein in sitosterolemic cells, which was not derepressed upon removal of cellular sitosterol, and the failure of cellular sitosterol to inhibit normal HMG-CoA reductase activity argue against feedback inhibition by sitosterol as a mechanism for low reductase activity in this disease. The larger accumulation of sterols and inadequate downregulation of HMG-CoA reductase in MDM may be mechanisms for foam cell formation and explain, in part, the increased risk of atherosclerosis in sitosterolemia.

7-Dehydrocholesterol-dependent proteolysis of HMG-CoA reductase suppresses sterol biosynthesis in a mouse model of Smith-Lemli-Opitz/RSH syndrome

Smith-Lemli-Opitz/RSH syndrome (SLOS), a relatively common birth-defect mental-retardation syndrome, is caused by mutations in DHCR7, whose product catalyzes an obligate step in cholesterol biosynthesis, the conversion of 7-dehydrocholesterol to cholesterol. A null mutation in the murine Dhcr7 causes an identical biochemical defect to that seen in SLOS, including markedly reduced tissue cholesterol and total sterol levels, and 30- to 40-fold elevated concentrations of 7-dehydrocholesterol. Prenatal lethality was not noted, but newborn homozygotes breathed with difficulty, did not suckle, and died soon after birth with immature lungs, enlarged bladders, and, frequently, cleft palates. Despite reduced sterol concentrations in Dhcr7(-/-) mice, mRNA levels for 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate-controlling enzyme for sterol biosynthesis, the LDL receptor, and SREBP-2 appeared neither elevated nor repressed. In contrast to mRNA, protein levels and activities of HMG-CoA reductase were markedly reduced. Consistent with this finding, 7-dehydrocholesterol accelerates proteolysis of HMG-CoA reductase while sparing other key proteins. These results demonstrate that in mice without Dhcr7 activity, accumulated 7-dehydrocholesterol suppresses sterol biosynthesis posttranslationally. This effect might exacerbate abnormal development in SLOS by increasing the fetal cholesterol deficiency.

Side chain hydroxylations in bile acid biosynthesis catalyzed by CYP3A are markedly up-regulated in Cyp27-/- mice but not in cerebrotendinous xanthomatosis

The accumulation of various 25-hydroxylated C(27)-bile alcohols in blood and their excretion in urine are characteristic features of cerebrotendinous xanthomatosis (CTX) a recessively inherited inborn error of bile acid synthesis caused by mutations in the mitochondrial sterol 27-hydroxylase (CYP27) gene. These bile alcohols may be intermediates in the alternative cholic acid side chain cleavage pathway. The present study was undertaken to identify enzymes and reactions responsible for the formation of these bile alcohols and to explain why Cyp27(-/-) mice do not show CTX-related abnormalities. Microsomal activities of 5beta-cholestane-3alpha,7alpha,12alpha-triol 25- and 26-hydroxylases, 5beta-cholestane-3alpha,7alpha,12alpha,25-tetrol 23R-, 24S-, and 27-hydroxylases and testosterone 6beta-hydroxylase, a marker enzyme for CYP3A, in Cyp27(-/-) mice livers were markedly up-regulated (5.5-, 3.5-, 6.5-, 7.5-, 2.9-, and 5.4-fold, respectively). In contrast, these enzyme activities were not increased in CTX. The activities of 5beta-cholestane-3alpha,7alpha,12alpha-triol 25- and 26-hydroxylases and 5beta-cholestane-3alpha,7alpha,12alpha,25-tetrol 23R-, 24R-, 24S-, and 27-hydroxylases were strongly correlated with the activities of testosterone 6beta-hydroxylase in control human liver microsomes from eight unrelated donors. Troleandomycin, a specific inhibitor of CYP3A, markedly suppressed these microsomal side chain hydroxylations in both mouse and human livers in a dose-dependent manner. In addition, experiments using recombinant overexpressed human CYP3A4 confirmed that these microsomal side chain hydroxylations were catalyzed by a single enzyme, CYP3A4. The results demonstrate that microsomal 25- and 26-hydroxylations of 5beta-cholestane-3alpha,7alpha,12alpha-triol and microsomal 23R-, 24R-, 24S-, and 27-hydroxylations of 5beta-cholestane-3alpha,7alpha,12alpha,25-tetrol are mainly catalyzed by CYP3A in both mice and humans. Unlike Cyp27(-/-) mice, CYP3A activity was not up-regulated despite marked accumulation of 5beta-cholestane-3alpha,7alpha,12alpha-triol in CTX.

Plant stanol fatty acid esters inhibit cholesterol absorption and hepatic hydroxymethyl glutaryl coenzyme A reductase activity to reduce plasma levels in rabbits

The aim of this study was to study the inhibitory effect of dietary stanols (campestanol and sitostanol) fatty acid esters (SE) on intestinal cholesterol absorption. New Zealand white rabbits were fed regular chow alone or enriched with 0.2% cholesterol, 0.33% SE + cholesterol, 0.66% SE + cholesterol, 1.2% SE + cholesterol, 2.4% SE + cholesterol, and 1.2% SE alone. After 2 weeks, plasma cholesterol levels increased 3.6 times in the cholesterol group and did not decrease after addition of 0.33% or 0.66% SE to the cholesterol-enriched diets. However, after addition of 1.2% SE to the cholesterol diet, plasma cholesterol concentration decreased 50% (P <.001), but it did not decrease further after doubling of SE to 2.4%. Percent cholesterol absorption measured by the plasma dual-isotope ratio method was 73.0% +/- 8.1 % in the cholesterol group, which was similar to untreated baseline control. The percent absorption of cholesterol did not decrease significantly after addition of 0.33% or 0.66% SE to the cholesterol diet but decreased 43.8% (P <.001) in the 1.2% SE + cholesterol group, a finding similar to those in rabbits fed 1.2% SE alone. Increasing SE to 2.4% in the cholesterol diet did not further decrease absorption. Hepatic hydroxymethyl glutaryl coenzyme A (HMG-CoA) reductase activity reflecting cholesterol synthesis and low-density lipoprotein receptor-mediated binding unexpectedly decreased 67% (P <.01) and 57% (P <.05) in rabbits fed 1.2% SE alone. Increasing dietary SE intake to 1.2% reduced cholesterol absorption and plasma levels. Dietary SE intake below 1.2% was ineffective and above 2.4% did not further decrease percent absorption or plasma cholesterol levels. These results support the hypothesis that dietary SEs competitively displace cholesterol from intestinal micelles to reduce cholesterol absorption and decrease plasma cholesterol levels.

Cholecystectomy prevents expansion of the bile acid pool and inhibition of cholesterol 7alpha-hydroxylase in rabbits fed cholesterol

To study the effect of cholecystectomy on the regulation of classic and alternative bile acid syntheses, gallbladder-intact (n = 20) and cholecystectomized (n = 20) New Zealand White rabbits were fed either chow or chow with 2% cholesterol (3 g/day). After 10 days, bile fistulas were constructed in half of each rabbit group to recover and measure the bile acid pool and biliary bile acid flux. After cholesterol feeding, the bile acid pool size increased from 268 +/- 55 to 444 +/- 77 mg (P < 0.01) with a 2-fold rise in the biliary bile acid flux in intact rabbits but did not expand the bile acid pool (270 +/- 77 vs. 276 +/- 62 mg), nor did the biliary bile acid flux increase in cholecystectomized rabbits. Ileal apical sodium-dependent bile acid transporter protein increased 46% from 93 +/- 6 to 136 +/- 23 units/mg (P < 0.01) in the intact rabbits but did not change in cholecystectomized rabbits (104 +/- 14 vs. 99 +/- 19 units/mg) after cholesterol feeding. Cholesterol 7alpha-hydroxylase activity was inhibited 59% (P < 0.001) while cholesterol 27-hydroxylase activity rose 83% (P < 0.05) after cholesterol feeding in the intact rabbits but neither enzyme activity changed significantly in cholesterol-fed cholecystectomized rabbits. Fecal bile acid outputs reflecting bile acid synthesis increased significantly in the intact but not in the cholecystectomized rabbits fed cholesterol. Removal of the gallbladder prevented expansion of the bile acid pool after cholesterol feeding as seen in intact rabbits because ileal bile acid transport did not increase. As a result, cholesterol 7alpha-hydroxylase was not inhibited.

Hyodeoxycholic acid efficiently suppresses atherosclerosis formation and plasma cholesterol levels in mice

We examined the effect of hyodeoxycholic acid (HDCA) on plasma cholesterol levels and atherosclerosis in mice. In wild-type C57BL/6 mice, feeding increasing amounts of HDCA resulted in i) progressive decrease in dietary cholesterol absorption, ii) increased concentrations of HDCA in the gallbladder bile, iii) decreased liver cholesterol content, iv) increased liver cholesterol synthesis, and v) increased plasma concentrations of HDCA. In C57BL/6 LDL-receptor knockouts (LDLR-KO) the addition of HDCA to chow and a 0.5% cholesterol diet decreased their total plasma cholesterol levels by 21% and 62%, respectively, because of a decrease in VLDL and LDL cholesterol. Turnover studies showed that HDCA has no effect on VLDL removal from plasma. Furthermore, the addition of HDCA to chow- and 0.5% cholesterol-fed LDLR-KO mice decreased the aortic root atherosclerosis lesion area by 50% and 80%, respectively. Finally, we tested the effect of HDCA on intestinal tumor formation. Feeding C57BL/6 ApcMin mice with HDCA did not affect the number of tumors but decreased the tumor volume in these animals. These results suggest that HDCA might have beneficial effects in the treatment of increased plasma cholesterol levels and atherosclerosis.

Hepatic cholesterol and bile acid synthesis, low-density lipoprotein receptor function, and plasma and fecal sterol levels in mice: effects of apolipoprotein E deficiency and probucol or phytosterol treatment

We compared hepatic cholesterol metabolism in apolipoprotein (apo) E-knockout (KO) mice with their wild-type counterparts. We also investigated the effects of treatment with phytosterols or probucol on the activity of hepatic 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase (cholesterol synthesis), cholesterol 7 alpha-hydroxylase and sterol 27-hydroxylase (bile acid synthesis), and low-density lipoprotein (LDL) receptor function in this animal model of atherogenesis. These findings were then related to treatment-induced changes in plasma, hepatic, and fecal sterol concentrations. Mouse liver membranes have binding sites similar to LDL receptors; the receptor-mediated binding represents 80% of total binding and is LDL concentration-dependent. These binding sites have higher affinity for apo E-containing particles than apo B only-containing particles. Deletion of apo E gene was associated with several-fold increases in plasma cholesterol levels, 1.5-fold increase in hepatic cholesterol concentrations, 50% decrease in HMG-CoA reductase activity, 30% increase in cholesterol 7 alpha-hydroxylase and 25% decrease in LDL receptor function. Treatment of apo E-KO mice with either probucol or phytosterols significantly reduced plasma cholesterol levels. Phytosterols significantly increased the activity of hepatic HMG-CoA reductase, and probucol significantly increased cholesterol 7 alpha-hydroxylase activity. Neither treatment significantly altered hepatic LDL receptor function. Phytosterols, but not probucol, significantly increased fecal sterol excretion and decreased hepatic cholesterol concentrations. Plasma cholesterol lowering effects of phytosterols and probucol are due to different mechanisms: stimulation of cholesterol catabolism via increased bile acid synthesis by probucol and decreased cholesterol absorption by phytosterols. In the absence of apo E, hepatic LDL receptors could not be upregulated and did not contribute to the cholesterol lowering effects of either agent.

Differences in hepatic levels of intermediates in bile acid biosynthesis between Cyp27(-/-) mice and CTX

Cerebrotendinous xanthomatosis (CTX) is a rare, recessively inherited lipid storage disease characterized by a markedly reduced production of chenodeoxycholic acid and an increased formation of 25-hydroxylated bile alcohols and cholestanol. Patients with this disease are known to have mutations in the sterol 27-hydroxylase (Cyp27) gene. However, one study showed that mice with a disrupted Cyp27 gene did not have any CTX-related clinical or biochemical abnormalities. To explore the reason, hepatic cholesterol, cholestanol, and 12 intermediates in bile acid biosynthetic pathways were quantified in 10 Cyp27(-/-) and 7 Cyp27(+/+) mice, two CTX patients (untreated and treated with chenodeoxycholic acid), and four human control subjects by high resolution gas chromatography-mass spectrometry. Mitochondrial 27-hydroxycholesterol and 5beta-cholestane-3alpha,7alpha,12alpha,27-tetrol were virtually absent in both Cyp27(-/-) mice and CTX patients. In Cyp27(-/-) mice, microsomal concentrations of intermediates in the early bile acid biosynthetic pathway (7alpha-hydroxycholesterol, 7alpha-hydroxy-4-cholesten-3-one, 7alpha,12alpha-dihydroxy-4-cholesten-3-one, and 5beta-cholestane-3alpha,7alpha,12alpha-triol), 25-hydroxylated bile alcohols (5beta-cholestane-3alpha,7alpha,12alpha,25-tetrol, 5beta-cholestane-3alpha,7alpha,12alpha,23R,25-pentol, and 5beta-cholestane-3alpha,7alpha,12alpha,24R, 25-pentol), and cholestanol were all significantly elevated compared with those in Cyp27(+/+) mice, although the levels were lower than those in untreated CTX patients. The intermediate levels in early bile acid biosynthesis were more elevated in male (16;-86% of CTX) than in female Cyp27(-/-) mice (7-30% of CTX). In contrast, 25-hydroxylated bile alcohol concentrations were not significantly different between male and female Cyp27(-/-) mice and were considerably lower (less than 14%) than those in CTX patients.These results suggest that 1) in Cyp27(-/-) mice, especially in females, classic bile acid biosynthesis via 7alpha-hydroxycholesterol is not stimulated as much as in CTX patients; and 2) formed 25-hydroxylated bile alcohols are more efficiently metabolized in Cyp27(-/-) mice than in CTX patients.

Fine-mapping, mutation analyses, and structural mapping of cerebrotendinous xanthomatosis in U.S. pedigrees

Cerebrotendinous xanthomatosis (CTX) is a rare autosomal recessive disorder of bile acid biosynthesis. Clinically, CTX patients present with tendon xanthomas, juvenile cataracts, and progressive neurological dysfunction and can be diagnosed by the detection of elevated plasma cholestanol levels. CTX is caused by mutations affecting the sterol 27-hydroxylase gene (CYP27 ). CTX has been identified in a number of populations, but seems to have a higher prevalence in the Japanese, Sephardic Jewish, and Italian populations. We have assembled 12 previously unreported pedigrees from the United States. The CYP27 locus had been previously mapped to chromosome 2q33-qter. We performed linkage analyses and found no evidence of genetic heterogeneity. All CTX patients showed segregation with the CYP27 locus, and haplotype analysis and recombinant events allowed us to precisely map CYP27 to chromosome 2q35, between markers D2S1371 and D2S424. Twenty-three mutations were identified from 13 probands analyzed thus far; 11 were compound heterozygotes and 2 had homozygous mutations. Of these, five are novel mutations [Trp100Stop, Pro408Ser, Gln428Stop, a 10-base pair (bp) deletion in exon 1, and a 2-bp deletion in exon 6 of the CYP27 gene]. Three-dimensional structural modeling of sterol 27-hydroxylase showed that, while the majority of the missense mutations disrupt the heme-binding and adrenodoxin-binding domains critical for enzyme activity, two missense mutations (Arg94Trp/Gln and Lys226Arg) are clearly located outside these sites and may identify a potential substrate-binding or other protein contact site.

Mechanisms for cholesterol homeostasis in rat jejunal mucosa: effects of cholesterol, sitosterol, and lovastatin

The effects of feeding cholesterol, sitosterol, and lovastatin on cholesterol absorption, biosynthesis, esterification, and LDL receptor function were examined in the rat jejunal mucosa. Cholesterol absorption was measured by the dual-isotope plasma ratio method; the rate-limiting enzyme of cholesterol biosynthesis, 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, was measured as total and expressed enzyme activities (in the absence and presence of a phosphatase inhibitor, NaF, respectively); mucosal total and esterified cholesterol concentrations were determined by gas-liquid chromatography; LDL receptor function was assayed as receptor-mediated binding of (125)I-labeled LDL to mucosal membranes. Feeding 2% sitosterol or 0.04% lovastatin for 1 week significantly (P < 0.01) decreased the amounts of cholesterol absorbed per day (-85% and -63%, respectively). In contrast, feeding 2% cholesterol for 1 week increased the amounts of absorbed cholesterol 27-fold, even though the percent absorption significantly decreased. With all three treatments, there was a coordinate regulation of total HMG-CoA reductase activity and receptor-mediated LDL binding. Cholesterol feeding downregulated both total jejunal HMG-CoA reductase activity (P < 0.05) and receptor-mediated LDL binding (P < 0.01), whereas lovastatin- and sitosterol-supplemented diets significantly upregulated both of these parameters. In the control, cholesterol-fed, and sitosterol-fed animals, about half of the total jejunal HMG-CoA reductase activity was expressed (in functional dephosphorylated form). However, in the lovastatin-treated rats with 4-fold stimulation of HMG-CoA reductase, only 23% of the total enzyme activity was expressed. Changes in total HMG-CoA reductase activity and receptor-mediated LDL binding in all tested groups occurred with no change in total concentrations of mucosal cholesterol, and only cholesterol-fed animals had increased mucosal esterified cholesterol concentrations. Thus, in response to various fluxes of dietary or newly formed cholesterol, HMG-CoA reductase and receptor-mediated LDL binding are coordinately regulated to maintain constant cellular cholesterol concentrations in the jejunum.

Hyperabsorption and retention of campestanol in a sitosterolemic homozygote: comparison with her mother and three control subjects

We measured the percent absorption, turnover, and distribution of campestanol (24-methyl-5alpha-cholestan-3beta-ol) in a sitosterolemic homozygote, her obligate heterozygous mother, and three healthy human control subjects. For reasons relating to sterol hyperabsorption, the homozygote consumed a diet low in plant sterols that contained campestanol at about 2 mg/day. The heterozygote and three control subjects were fed a diet supplemented with a spread that contained campestanol at 540 mg/day and sitostanol (24-ethyl-5alpha-cholestan-3beta-ol) at 1.9 g/day as fatty acid esters. Plasma campestanol concentrations determined by capillary gas-liquid chromatography were 0.72 +/- 0.03 mg/dl in the homozygote, 0.09 +/- 0.04 mg/dl in the heterozygote, and 0.05 +/- 0.03 mg/dl for the control mean. After simultaneous pulse labeling with [3alpha-(3)H]campestanol intravenously and [23-(14)C]campestanol orally, the maximum percent absorption measured by the plasma dual-isotope ratio method as a single time point was 80% in the homozygote, 14.3% in the heterozygote, and 5.5 +/- 4.3% as the mean for three control subjects. Turnover (pool size) values estimated by mathematical analysis of the specific activity versus time [3alpha-(3)H]campestanol decay curves were as follows: 261 mg in the homozygote, 27.3 mg in the heterozygote, and 12.8 +/- 7.6 mg in the three control subjects (homogygote vs. controls, P < 0.001). The calculated production rate (mg/24 h) equivalent to actual absorption in the presence of dietary sterols and stanols was 0.67 mg/day or 31% of intake in the homozygote, 2.1 mg/day or 0.3% of intake in the heterozygote, and 0.7 +/- 0.3 mg/day or 0.1% of intake in the three control subjects. However, the excretion constant from pool A (K(A)) was prolonged markedly in the homozygote, but was 100 times more rapid in the heterozygote and three control subjects.Thus, campestanol, like other noncholesterol sterols, is hyperabsorbed and retained in sitosterolemic homozygotes. However, campestanol absorption was only slightly increased in the sitosterolemic heterozygote and removal was as rapid as in control subjects.

Tuberous xanthomas in sitosterolemia

Sitosterolemia is an autosomal recessive lipid disorder in which plasma plant sterol levels are extremely elevated and cholesterol levels are often elevated but may be normal. Clinically sitosterolemia is characterized by xanthomas, premature vascular disease, and arthritis. Adolescent boys and girls with sitosterolemia are susceptible to fatal cardiac events. Dermatologists may have a vital role in the diagnosis of this rare but serious condition because early detection and treatment are important in preventing the associated atherosclerotic heart disease. We present a 7-year-old girl with sitosterolemia and tuberous xanthomas.

Regulation of cholesterol biosynthetic pathway in patients with the Smith-Lemli-Opitz syndrome

The Smith-Lemli-Opitz syndrome (SLOS) is a recessively inherited birth disorder caused by a defect in 7-dehydrocholesterol (3beta-hydroxysteroid) delta7-reductase, the final enzyme in cholesterol biosynthesis. To investigate in vivo regulation of the cholesterol biosynthetic pathway in SLOS, we measured hepatic microsomal sterol concentrations and activities of several key enzymes in the pathway, including HMG-CoA synthase, HMG-CoA reductase, squalene synthase and 7-dehydrocholesterol delta7-reductase in liver specimens from a patient with SLOS and 11 controls. Hepatic microsomal 7-dehydrocholesterol delta7-reductase activity in the patient was less than 1% of the control mean, and decreased cholesterol concentration and markedly increased 7- and 8-dehydrocholesterol concentrations were observed in the patient's microsomes. HMG-CoA synthase and squalene synthase activities in the patient were upregulated to 149% and 532%, respectively, while the activity of HMG-CoA reductase, the rate-limiting enzyme in the pathway, was reduced to 39% of the control mean. Downregulation of HMG-CoA reductase activity in SLOS was supported by measuring plasma levels of mevalonic acid, the immediate product of HMG-CoA reductase. The levels in SLOS patients (n = 9) were significantly low compared with age-matched controls (n = 8) (12+/-2 vs 28 + 6nmol/L, p < 0.05). These results suggest that in most SLOS patients in vivo HMG-CoA reductase is not stimulated in spite of blocked cholesterol biosynthetic pathway and reduced plasma and hepatic cholesterol concentrations.

Abnormal hepatic sinusoidal bile acid transport in an Amish kindred is not linked to FIC1 and is improved by ursodiol

BACKGROUND & AIMS

The mechanism for abnormal hepatic bile acid transport was investigated in an 18-month-old Amish boy who presented with pruritus, poor growth, and severe bleeding episodes. Serum bilirubin, gamma-glutamyltranspeptidase, and cholesterol levels were normal, but prothrombin time and partial thromboplastin time were prolonged and bone alkaline phosphatase level was elevated.

METHODS AND RESULTS

Cholic acid plus chenodeoxycholic acid levels measured by capillary gas-chromatography were 32 times higher than control in serum (34.7 vs. 1.1+/-0.4 microg/dL) but were not detected in liver and were reduced in gallbladder bile. Treatment with ursodiol, a more hydrophilic bile acid, improved pruritus, produced 37% weight gain, and after 2 years reduced serum primary bile acid concentrations about 85%, while accounting for 71% of serum and 24% of biliary bile acid conjugates. On ursodiol therapy, hepatic bile acid synthesis was enhanced 2-fold compared with controls, and microscopy revealed chronic hepatitis without cholestasis. Three younger sisters with elevated serum bile acids responded positively to ursodiol. Microsatellite markers for the FIC1 (gene for Byler's disease) region in these 4 children were inconsistent with linkage to FIC1.

CONCLUSIONS

Conjugated cholic acid and chenodeoxycholic acid were synthesized in the liver and secreted into bile but could not reenter the liver from portal blood and accumulated in serum. In contrast, unconjugated ursodiol entered the liver and was conjugated and secreted into bile. Thus, the enterohepatic circulation of all conjugated bile acids was interrupted at the hepatic sinusoidal basolateral membrane. Unconjugated ursodiol bypassed the hepatic uptake block to enlarge the biliary and intestinal bile acid pools. A mutation in FIC1 recognized among the Amish and linkage of the disorder to FIC1 were excluded.

Spectrum of Delta(7)-dehydrocholesterol reductase mutations in patients with the Smith-Lemli-Opitz (RSH) syndrome

The Smith-Lemli-Opitz syndrome (SLOS; also known as the RSH syndrome) is an autosomal recessive genetic disorder, leading to characteristic multi-organ developmental abnormalities, dysmorphic facies, limb malformations and mental retardation. Mutations in the gene for Delta(7)-dehydrocholesterol reductase (Delta(7)-reductase), which catalyzes the last step in cholesterol biosynthesis, cause the disease. We screened 32 patients with SLOS, 28 from the USA and four from Sweden. Twenty-two different nucleotide changes, predicted to be disease-causing mutations, were identified; 20 missense mutations, one nonsense mutation and one splice-site mutation involving the exon 9 acceptor site (IVS8 -1G-->C) were detected. All probands were heterozygous for mutations. Twelve of these mutations have not been reported previously, including missense mutations L148R, F168I, D175H, P179L, P243R, F284L, N287K, F302L, R404S, Y462H, R469P and one nonsense mutation W37X [corrected]. Coupled with previously reported mutations, these findings bring the total of different Delta(7)-reductase mutations to 36. These are distributed throughout the coding sequence of the Delta(7)-reductase gene except exons 3 and 5, with a clustering in exon 9. Three mutations account for 54% of those observed in our cohort, the splice acceptor site mutation IVS8 -1G-->C (22/64 alleles, 34%), T93M (8/64, 12.5%) and V326L (5/64, 7.8%). Severity of SLOS was negatively correlated with both plasma cholesterol and relative plasma cholesterol, but not with 7-dehydrocholesterol, the immediate precursor, confirming previous observations. However, no correlation was observed between mutations and phenotype, suggesting that the degree of severity may be affected by other factors. We estimate that between 33 and 42% of the variation in the SLOS severity score is accounted for by variation in plasma cholesterol. Thus, factors other than plasma cholesterol are additionally involved in determining severity.

Blocking cholesterol synthesis impairs acquisition of the classically conditioned eyeblink response

Smith-Lemli-Opitz (SLO) syndrome is a congenital disorder characterized by severe mental retardation. Patients with SLO lack 7-dehydrocholesterol (7 dH) reductase, which catalyzes the last step of cholesterol synthesis. Administration of an agent that blocks 7 dH cholesterol reductase, BM 15.766 (BM), leads to a biochemical profile which resembles that of SLO patients, i.e., lower plasma, liver, and brain cholesterol levels accompanied by the appearance of the precursors 7 dH and 8 dH cholesterol. In this article we address the functional consequences of chronic BM treatment on new motor learning by assessing acquisition of the classically conditioned eyeblink response. Just-weaned rats were fed BM by gavage for four months, with half of these rats given exogenous cholesterol during the last two months of BM treatment. Acquisition of the eyeblink response was impaired in BM-treated rats. Impaired acquisition of the eyeblink response was not accompanied by alterations in responsiveness to either the conditioned or unconditioned stimulus. Exogenous cholesterol, a clinically relevant countertreatment, failed to correct for the learning impairment produced by BM treatment. Chronic treatment with a cholesterol synthesis-blocking agent impaired associative learning in just-weaned rats.

Fetal demise with Smith-Lemli-Opitz syndrome confirmed by tissue sterol analysis and the absence of measurable 7-dehydrocholesterol Delta(7)-reductase activity in chorionic villi

Smith-Lemli-Opitz syndrome (SLOS), an autosomal recessive condition with multiple malformations, mental retardation, and growth failure, results from markedly reduced activity of the final enzyme in the cholesterol biosynthetic pathway, 7-dehydrocholesterol Delta(7)-reductase (DHCR7). We diagnosed SLOS in a fetus following intrauterine demise at 32 weeks' gestation. Chorionic villus (CV) sampling had been performed at 30 weeks because oligohydramnios and atrioventricular septal defect were noted on fetal ultrasound. On fetal post-mortem examination, a midline U-shaped soft palate cleft, micrognathia, postaxial polydactyly of the fingers with single transverse palmar creases bilaterally, and cutaneous syndactyly of toes two-three bilaterally suggested SLOS. We hypothesized that SLOS could be confirmed by analysis of tissue sterols despite extensive autolysis, and by measurement of enzyme activity in CV cells. Measurement of DHCR7 activity in CV cells was undertaken using ergosterol as a substrate. CV cells were unable to convert any ergosterol to brassicasterol after a 72 h incubation period while control CV cells reduced 12.6-71.8% of ergosterol to brassciasterol in a 72 h period. SLOS was confirmed by measurement of elevated 7-dehydrocholesterol (7-DHC) in the CV cells. Measurements of sterols were made in multiple fetal tissues. All tissues analysed showed elevated 7-DHC with markedly increased 7-DHC/cholesterol ratios.

Regulation of 25- and 27-hydroxylation side chain cleavage pathways for cholic acid biosynthesis in humans, rabbits, and mice. Assay of enzyme activities by high-resolution gas chromatography;-mass spectrometry

In classic cholic acid biosynthesis, a series of ring modifications of cholesterol precede side chain cleavage and yield 5beta-cholestane-3alpha, 7alpha, 12alpha-triol. Side chain reactions of the triol then proceed either by the mitochondrial 27-hydroxylation pathway or by the microsomal 25-hydroxylation pathway. We have developed specific and precise assay methods to measure the activities of key enzymes in both pathways, 5beta-cholestane-3alpha, 7alpha, 12alpha-triol 25- and 27-hydroxylases and 5beta-cholestane-3alpha, 7alpha, 12alpha, 25-tetrol 23R-, 24R-, 24S- and 27-hydroxylases. The extracts from either the mitochondrial or microsomal incubation mixtures were purified by means of a disposable silica cartridge column, derivatized into trimethylsilyl ethers, and quantified by gas chromatography;-mass spectrometry with selected-ion monitoring in a high resolution mode. Compared with the addition of substrates in acetone, those in 2-hydroxypropyl-beta-cyclodextrin increased mitochondrial triol 27-hydroxylase activity 132% but decreased activities of the enzymes in microsomal 25-hydroxylation pathway (triol 25-hydroxylase and 5beta-cholestane-3alpha, 7alpha, 12alpha, 25-tetrol 23R-, 24R-, 24S- and 27-hydroxylases) 13;-60% in human liver. The enzyme activities in both pathways were generally 2- to 4-times higher in mouse and rabbit livers compared with human liver. In all species, microsomal triol 25-hydroxylase activities were 4- to 11-times larger than mitochondrial triol 27-hydroxylase activities but the activities of tetrol 24S-hydroxylase were similar to triol 27-hydroxylase activities in our assay conditions. The regulation of both pathways in rabbit liver was studied after bile acid synthesis was perturbed. Cholesterol feeding up-regulated enzyme activities involved in both 25- (64;-142%) and 27- (77%) hydroxylation pathways, while bile drainage up-regulated only the enzymes in the 25-hydroxylation pathway (178;-371%). Using these new assays, we demonstrated that the 25- and 27-hydroxylation pathways for cholic acid biosynthesis are more active in mouse and rabbit than human livers and are separately regulated in rabbit liver.

Detection of a common mutation in the RSH or Smith-Lemli-Opitz syndrome by a PCR-RFLP assay: IVS8-G-->C is found in over sixty percent of US propositi

The RSH or Smith-Lemli-Opitz syndrome (SLOS) is a relatively common autosomal recessive disorder of cholesterol biosynthesis resulting from a deficiency of the enzyme 7-dehydrocholesterol delta7-reductase (7-DHCR). Mutations in 7-DHCR gene cause SLOS. Among these, a G-->C transversion in the splice acceptor site of exon 9 (IVS8-1G-->C) was suspected to be a frequent mutation, having been detected in about 18% of SLOS patients so far. This mutation results in the elimination of a AlwN1 restriction endonuclease site. We report a simple PCR-RFLP assay to detect the IVS8-1G-->C mutation. Using this method, we identified the IVS8-1G-->C mutation in 21 of 33 SLOS propositi. This mutation was detected in one of 90 normal adult Caucasian Americans; but not among 121 Africans from Sierra Leone, 120 Caucasians from Finland, 95 Chinese or 103 Japanese adults. The results of this study provide further evidence that IVS8-1G-->C transversion is a very common mutation in SLOS patients from the US and that the carrier rate in US caucasians may be high. The simple PCR-RFLP assay developed makes identification of this mutation convenient for diagnosis and for carrier detection.

3-Hydroxy-3-methylglutaryl-coenzyme A reductase activity is inhibited by cholesterol and up-regulated by sitosterol in sitosterolemic fibroblasts

Sitosterolemia is an inherited recessive disease characterized by abnormally increased plasma and tissue plant sterol concentrations. Patients hyperabsorb sitosterol. In addition, hepatic, ileal, and mononuclear leukocyte 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate-controlling enzyme in the cholesterol biosynthetic pathway, is markedly suppressed in this disease. It is still controversial whether the down-regulation is due to accumulated sitosterol, but the effect of sitosterol on HMG-CoA reductase activity has not been studied in sitosterolemic tissues. To investigate whether sitosterol inhibits HMG-CoA reductase activity in sitosterolemia, we measured the enzyme activities in liver and cultured skin flbroblasts from patients. Hepatic HMG-CoA reductase activities in patients were decreased 76% (P < .05) as compared with results in control subjects. In contrast, HMG-CoA reductase activities in sitosterolemic fibroblasts were not decreased as compared with results in control fibroblasts, and the activities in all cells were up-regulated similarly when they were exposed to delipidated medium. Because the cultured sitosterolemic fibroblasts contained only trace amounts of plant sterols, we added 20 microg/mL sitosterol directly to the cell medium. Raising the intracellular sitosterol concentration to 7% of cellular cholesterol level increased HMG-CoA reductase activity 23% (P < .05), while the addition of the same amount of cholesterol to the cells reduced the activity 46% (P < .05). Thus, when sitosterolemic skin fibroblasts were used, it was possible to distinguish between the effects of cholesterol and those of sitosterol on the activity of HMG-CoA reductase. These results suggest that reduced HMG-CoA reductase activity in this disease is caused by secondary effects of unknown regulator(s) other than sitosterol.

Ileal bile acid transport regulates bile acid pool, synthesis, and plasma cholesterol levels differently in cholesterol-fed rats and rabbits

We investigated the effect of ileal bile acid transport on the regulation of classic and alternative bile acid synthesis in cholesterol-fed rats and rabbits. Bile acid pool sizes, fecal bile acid outputs (synthesis rates), and the activities of cholesterol 7alpha-hydroxylase (classic bile acid synthesis) and cholesterol 27-hydroxylase (alternative bile acid synthesis) were related to ileal bile acid transporter expression (ileal apical sodium-dependent bile acid transporter, ASBT). Plasma cholesterol levels rose 2.1-times in rats (98 +/- 19 mg/dl) and 31-times (986 +/- 188 mg/dl) in rabbits. The bile acid pool size remained constant (55 +/- 17 mg vs. 61 +/- 18 mg) in rats but doubled (254 +/- 46 to 533 +/- 53 mg) in rabbits. ASBT protein expression did not change in rats but rose 31% (P < 0.05) in rabbits. Fecal bile acid outputs that reflected bile acid synthesis increased 2- and 2.4-times (P < 0.05) in cholesterol-fed rats and rabbits, respectively. Cholesterol 7alpha-hydroxylase activity rose 33% (24 +/- 2.4 vs. 18 +/- 1.6 pmol/mg/min, P < 0.01) and mRNA levels increased 50% (P < 0.01) in rats but decreased 68% and 79%, respectively, in cholesterol-fed rabbits. Cholesterol 27-hydroxylase activity remained unchanged in rats but rose 62% (P < 0.05) in rabbits. Classic bile acid synthesis (cholesterol 7alpha-hydroxylase) was inhibited in rabbits because an enlarged bile acid pool developed from enhanced ileal bile acid transport. In contrast, in rats, cholesterol 7alpha-hydroxylase was stimulated but the bile acid pool did not enlarge because ASBT did not change. Therefore, although bile acid synthesis was increased via different pathways in rats and rabbits, enhanced ileal bile acid transport was critical for enlarging the bile acid pool size that exerted feedback regulation on cholesterol 7alpha-hydroxylase in rabbits.

Comparative regulation of hepatic sterol 27-hydroxylase and cholesterol 7alpha-hydroxylase activities in the rat, guinea pig, and rabbit: effects of cholesterol and bile acids

The regulation of the classic and alternative bile acid synthetic pathways by key hepatic enzyme activities (microsomal cholesterol 7alpha-hydroxylase and mitochondrial sterol 27-hydroxylase, respectively) was examined in bile acid depletion and replacement and cholesterol-feeding experiments with rats, guinea pigs, and rabbits. The bile acid pool was depleted by creating a bile fistula (BF) and collecting bile for 2 to 5 days, and it was replaced by intraduodenal infusion of the major biliary bile acids (taurocholic acid [TCA], glycochenodeoxycholic acid [GCDCA], and glycocholic acid [GCA] in the rat, guinea pig, and rabbit, respectively) at rates equivalent to the measured hepatic flux of the bile acids. To study the effects of cholesterol, the animals were fed for 7 days on a basal diet with and without 2% cholesterol. Cholesterol 7alpha-hydroxylase and sterol 27-hydroxylase activities, measured by isotope incorporation assays, were related to bile acid output and composition and hepatic cholesterol concentrations. Intraduodenal infusion of bile acids increased the output of the tested bile acids, but did not significantly change hepatic cholesterol concentrations and had no effect on sterol 27-hydroxylase activity. Neither bile acid depletion nor replacement affected sterol 27-hydroxylase activity when three different substrates (cholesterol, 5beta-cholestane-3alpha,7alpha-diol, and 5beta-cholestane-3alpha,7alpha,12alpha-triol) were tested. In contrast, feeding 2% cholesterol increased hepatic cholesterol concentrations in rats, guinea pigs, and rabbits threefold, twofold, and eightfold, respectively, and increased hepatic mitochondrial sterol 27-hydroxylase activity (conversion of cholesterol to 27-hydroxycholesterol) in all three animal models. The stimulation and feedback inhibition of cholesterol 7alpha-hydroxylase activity by bile acid depletion and replacement were observed in all three animal models, whereas the effect of cholesterol feeding was species-dependent (cholesterol 7alpha-hydroxylase activity increased in the rat, did not change in the guinea pig, and was inhibited in the rabbit). Thus, in contrast to sterol 27-hydroxylase, which was upregulated by cholesterol but not affected by bile acid depletion and replacement in all three animal models, cholesterol 7alpha-hydroxylase activity was controlled consistently and inversely by the hepatic flux of bile acids, but was species-dependent in its response to a 1-week feeding with 2% cholesterol.

A convenient synthesis of dinorbile acids: oxidative hydrolysis of norbile acid nitriles

We report a convenient method for the synthesis of dinorbile acids (23,24-dinor-5beta-cholan-22-oic acids, pregnane-20-carboxylic acids) in fair to good yields from norbile acid nitriles in one step by oxidative hydrolysis with oxygen in the presence of potassium-t-butoxide. The method results in stepwise overall removal of two carbon atoms in bile acid side chains in two steps. Dinorbile acids corresponding to several common bile acids have been prepared and their structures confirmed by spectroscopic methods. This simple method for synthesis of dinorbile acids may facilitate their study metabolically.

Bile acid synthesis in the Smith-Lemli-Opitz syndrome: effects of dehydrocholesterols on cholesterol 7alpha-hydroxylase and 27-hydroxylase activities in rat liver

The Smith-Lemli-Opitz syndrome (SLOS) is a congenital birth defect syndrome caused by a deficiency of 3beta-hydroxysterol Delta(7)-reductase, the final enzyme in the cholesterol biosynthetic pathway. The patients have reduced plasma and tissue cholesterol concentrations with the accumulation of 7-dehydrocholesterol and 8-dehydrocholesterol. Bile acid synthesis is reduced and unnatural cholenoic and cholestenoic acids have been identified in some SLOS patients. To explore the mechanism of the abnormal bile acid production, the activities of key enzymes in classic and alternative bile acid biosynthetic pathways (microsomal cholesterol 7alpha-hydroxylase and mitochondrial sterol 27-hydroxylase) were measured in liver biopsy specimens from two mildly affected SLOS patients. The effects of 7- and 8-dehydrocholesterols on these two enzyme activities were studied by using liver from SLOS model rats that were treated with the Delta(7)-reductase inhibitor (BM15.766) for 4 months and were comparable with more severe SLOS phenotype in plasma and hepatic sterol compositions. In the SLOS patients, cholesterol 7alpha-hydroxylase and sterol 27-hydroxylase were not defective. In BM15.766-treated rats, both enzyme activities were lower than those in control rats and they were competitively inhibited by 7- and 8-dehydrocholesterols. Rat microsomal cholesterol 7alpha-hydroxylase did not transform 7-dehydrocholesterol or 8-dehydrocholesterol into 7alpha-hydroxylated sterols. In contrast, rat mitochondrial sterol 27-hydroxylase catalyzed 27-hydroxylation of 7- and 8-dehydrocholesterols, which were partially converted to 3beta-hydroxycholestadienoic acids. Addition of microsomes to the mitochondrial 27-hydroxylase assay mixture reduced 27-hydroxydehydrocholesterol concentrations, which suggested that 27-hydroxydehydrocholesterols were further metabolized by microsomal enzymes. These results suggest that reduced normal bile acid production is characteristic of severe SLOS phenotype and is caused not only by depletion of hepatic cholesterol but also by competitive inhibition of cholesterol 7alpha-hydroxylase and sterol 27-hydroxylase activities by accumulated 7- and 8-dehydrocholesterols. Unnatural bile acids are synthesized mainly by the alternative pathway via mitochondrial sterol 27-hydroxylase in SLOS.

Highly simplified method for gas-liquid chromatographic quantitation of bile acids and sterols in human stool

A simple method for the gas-liquid chromatographic quantitation of human fecal bile acids and sterols is described where bile acids are subjected to n-butyl ester derivatization, without prior isolation from the stool, followed by trimethylsilylation of the sterols and bile acids. Under these conditions, bile acid derivatives are well resolved from each other and from the trimethylsilyl ether derivatives of fecal sterols and no overlap occurs. The method was shown to be highly reproducible and recoveries were similar to those obtained with other methods used for fecal bile acid analysis. Application of the method for bile acid and sterol analysis in human stool is described.

Antenatal therapy of Smith-Lemli-Opitz syndrome

OBJECTIVES

Smith-Lemli-Opitz syndrome (SLOS) is a recessively inherited disorder caused by an inborn error of cholesterol metabolism that results in deficiency of cholesterol and accumulation of the cholesterol precursor, 7-dehydrocholesterol (DHC) and its epimer, 8-DHC. Affected patients present with congenital anomalies, growth restriction, and mental retardation. Postnatal treatment with cholesterol supplementation has been shown to improve plasma sterol levels and has resulted in improved growth and development in many patients. We hypothesized that prenatal supplementation of cholesterol could potentially arrest some of the adverse consequences of cholesterol deficiency at an earlier stage of development.

METHODS

SLOS was diagnosed in the third trimester in a fetus initially identified by sonography with intrauterine growth restriction and ambiguous genitalia and confirmed by elevated levels of 7- and 8-DHC in amniotic fluid. Antenatal supplementation of cholesterol was provided by fetal intravenous and intraperitoneal transfusions of fresh frozen plasma (cholesterol level = 219 mg/dl).

RESULTS

The in utero transfusions resulted in increased levels of fetal cholesterol, as measured in blood samples obtained by cordocentesis. In addition, fetal red cell mean corpuscular volume rose, which further indicated that the exogenous cholesterol was incorporated into the fetal erythrocytes.

CONCLUSIONS

Antenatal treatment of SLOS by cholesterol supplementation is feasible and results in improvement in fetal plasma cholesterol levels and fetal red cell volume. SLOS may be added to the growing list of human genetic disorders for which prenatal diagnosis is available and therapeutic intervention may be possible.

Anomalous enantioselectivity in the sharpless asymmetric dihydroxylation reaction of 24-nor-5beta-cholest-23-ene-3alpha,7alpha,12alpha-triol: synthesis of substrates for studies of cholesterol side-chain oxidation

Recently we described a block in bile acid synthesis in cerebrotendinous xanthomatosis (CTX), a lipid storage disease related to an inborn error of bile acid metabolism. In this disease a defect in hepatic microsomal (24S) hydroxylation blocks the transformation of 5beta-cholestane-3alpha,7alpha,12alpha,25-tetrol into (24S) 5beta-cholestane-3alpha,7alpha,12alpha,24,25- pentol and cholic acid. Mitochondrial cholesterol 27-hydroxylation has also been reported to be abnormal in CTX subjects, but the relative importance of the enzymatic defect in this alternative microsomal pathway (namely, the 24S hydroxylation of 5beta-cholestane-3alpha,7alpha, 12alpha,25-tetrol relative to the abnormality in mitochondrial 27-hydroxylase) has not been established in CTX. To delineate the sequence of side-chain hydroxylations and the enzymatic block in bile acid synthesis, we synthesized the (23R and 23S) 24-nor-5beta-cholestane-3alpha,7alpha, 12alpha,23,25-pentols utilizing a modified Sharpless asymmetric dihydroxylation reaction on 24-nor-5beta-cholest-23-ene-3alpha, 7alpha, 12alpha-triol, a C26 analog of the naturally occurring C27 bile alcohol, 5beta-cholest-24-ene-3alpha,7alpha,12alpha-triol . Stereospecific conversion of the unsaturated 24-nor triol to the corresponding chiral compounds (23R and 23S), 24-nor-5beta-cholestane-3alpha,7alpha,12alpha,23 ,25-pentols, was quantitative. However, conversion of the unsaturated 24-nor triol to the chiral nor-pentols had absolute stereochemistry opposite to the products predicted by the Sharpless steric model. The absolute configurations and enantiomeric excess of the C26 nor-pentols and the C27 pentols (synthesized from 5beta-cholest-24-ene-3alpha,7alpha,12alpha-triol for comparison) were confirmed by nuclear magnetic resonance and lanthanide-induced circular dichroism Cotton effect measurements. These results may contribute to a better understanding of the role of the 24S-hydroxylation vs. 27-hydroxylation step in cholic acid biosynthesis.

Bile acid abnormalities in cholestatic liver diseases

There is ample reason to believe that UDCA is the drug of choice in cholestatic liver diseases. It is possible that UDCA has to be administered for prolonged periods to see appreciable reversal in liver damage. Nevertheless, the amelioration of symptoms and improvement in nutrition of patients are equally important. Disabling symptoms such as pruritus are often brought under control, and quality of life improves. Clearly the goal for UDCA therapy is to slow the rate of disease progression, lessen the mortality risk, and improve the quality of life in patients. It is possible that a combination therapy would be more beneficial than UDCA alone. Initial results of administering UDCA with colchicine have shown no improvement in liver histology; however, administration of UDCA together with a strong anti-inflammatory drugs may be helpful to halt immune destruction of liver cells.

Campestanol (24-methyl-5alpha-cholestan-3beta-ol) absorption and distribution in New Zealand White rabbits: effect of dietary sitostanol

Campestanol (24-methyl-5alpha-cholestan-3beta-ol) is a naturally occurring plant stanol, structurally similar to cholesterol (5-cholesten-3beta-ol) and widely distributed in vegetable oils consumed in human diets. We measured the absorption and turnover of campestanol by the plasma dual-isotope ratio method and mathematical analysis of specific activity versus time decay curves after simultaneous oral and intravenous pulse-labeling with [3alpha-3H]- and [23-14C]-labeled campestanol, respectively, in New Zealand White (NZW) rabbits: six fed chow and six fed chow with 125 mg/d campestanol and 175 mg/d sitostanol (24-ethyl-5alpha-cholestan-3beta-ol). Plasma concentrations increased insignificantly from 0.08+/-0.01 to 0.09+/-0.01 mg/dL with dietary stanols. The percent campestanol absorption measured by the plasma dual-isotope ratio method after the rabbits were fasted for 6 hours yielded the percent absorption in the absence of competing intestinal sterols and stanols and declined insignificantly from 11.6%+/-3.5% in controls to 8.1%+/-3.7% in the treated rabbit groups. In contrast, the turnover, which measured actual absorption averaged over 24 hours, increased from 0.12+/-0.05 to 0.37+/-0.05 mg/d (P < .05) with campestanol and sitostanol added to the diet. However, the actual percent absorption declined from 3% to 0.3% of dietary intake with the campestanol and sitostanol-enriched diet. Campestanol pool sizes, although remaining small, increased slightly from 1.1+/-0.4 to 2.5+/-1.5 mg. The removal constant (KA) from pool A (MA) did not change significantly with added dietary campestanol and sitostanol (KA= -0.040+/-0.005 v -0.037+/-0.007 d(-1)). The results demonstrate small campestanol plasma concentrations and body pools even when the rabbits consumed substantial amounts because (1) intestinal absorption was limited and (2) was further reduced by competing dietary sitostanol, and (3) campestanol was removed rapidly from the body. Thus, campestanol, which shares the same basic structure and intestinal absorption pathway with cholesterol, does not accumulate when fed, and may be incorporated into the diet to block cholesterol absorption.

Gas chromatography of bile acids

Bile acids, the end products of cholesterol metabolism in the liver, are of vital importance in the tissue distribution of cholesterol. Abnormalities in cholesterol biosynthesis or metabolism are often reflected in the proportions, concentrations and conjugation of bile acids in various tissues and determination of bile acids in these tissues is important in the diagnosis of hepatobiliary diseases. Several methods for quantitative determination of bile acids in biological fluids are known and have been reviewed. In this review, we have discussed the gas-chromatographic method for determination of bile acids with special reference to bile acid quantitation in plasma, bile, urine and stool.

Increasing dietary cholesterol induces different regulation of classic and alternative bile acid synthesis

We investigated the effect of increasing dietary cholesterol on bile acid pool sizes and the regulation of the two bile acid synthetic pathways (classic, via cholesterol 7alpha-hydroxylase, and alternative, via sterol 27-hydroxylase) in New Zealand white rabbits fed 3 g cholesterol/per day for up to 15 days. Feeding cholesterol for one day increased hepatic cholesterol 75% and cholesterol 7alpha-hydroxylase activity 1.6 times without significant change of bile acid pool size or sterol 27-hydroxylase activity. After three days of cholesterol feeding, the bile acid pool size increased 83% (P < 0.01), and further feeding produced 10%-20% increments, whereas cholesterol 7alpha-hydroxylase activity declined progressively to 60% below baseline. In contrast, sterol 27-hydroxylase activity rose 58% after three days of cholesterol feeding and remained elevated with continued intake. Bile drainage depleted the bile acid pool and stimulated downregulated cholesterol 7alpha-hydroxylase activity but did not affect sterol 27-hydroxylase activity. Thus, increasing hepatic cholesterol does not directly inhibit cholesterol 7alpha-hydroxylase and initially favors enzyme induction, whereas increased bile acid pool is the most powerful inhibitor of cholesterol 7alpha-hydroxylase. Sterol 27-hydroxylase is insensitive to the bile acid flux but is upregulated by increasing hepatic cholesterol.

Cholesterol and oxygenated cholesterol concentrations are markedly elevated in peripheral tissue but not in brain from mice with the Niemann-Pick type C phenotype

Niemann-Pick disease type C (NP-C) is a rare genetic disorder characterized by progressive neurodegeneration, frequent developmental delay and early death. Tissues of affected individuals accumulate large quantities of free cholesterol in lysosomes. Because cytotoxic oxygenated derivatives of cholesterol are known to form readily when cholesterol concentrations are elevated, we searched for these compounds in liver, kidney, spleen and brain from mice with the NP-C phenotype. In order of abundance, we identified 7 alpha- and 7 beta-hydroxycholesterol, 5 alpha, 6 alpha-epoxycholestan-3 beta-ol, 4 beta-hydroxycholesterol, cholest-4-en-3 beta, 7 alpha-diol and cholest-4-en-3 beta, 6 beta-diol in most tissue samples. Cholesterol concentrations in affected mice were increased 3-fold in kidney and 7- to 8-fold in spleen and liver compared to controls (all p < 0.001) but were unchanged in brain. Although oxysterol levels were markedly elevated in nonbrain tissue, the oxysterol and cholesterol concentrations increased proportionally so that oxysterols expressed as percentage of total sterols were the same for all animals (0.34 +/- 0.19% averaged over all organs in affected animals vs 0.40 +/- 0.42% in control mice). In contrast to peripheral tissue, we could not detect any increase in either absolute or relative oxysterol levels in the brains of affected and control mice (49 +/- 61 vs 53 +/- 43 micrograms/g wet weight and 0.45 +/- 0.52 vs 0.47 +/- 0.37%, respectively). Thus, brain sterols are normal in NP-C mice and it is unlikely that an accumulation of cytotoxic oxygenated derivatives of cholesterol could account for the progressive neuropathology seen in the disease.

Regulation of rat hepatic 3beta-hydroxysterol delta7-reductase: substrate specificity, competitive and non-competitive inhibition, and phosphorylation/dephosphorylation

The mechanism for the catalytic reduction of the double bond at C-7, 8 in 7-dehydrocholesterol by 3beta-hydroxysterol Delta7-reductase was investigated by testing structurally related sterols as substrates and potential inhibitors. The hepatic smooth endoplasmic reticulum was identified as the site of enzyme activity. All putative substrates contained 27 carbons, but differed from 7-dehydrocholesterol by the addition of either an ethyl substituent at C-24 (7-dehydrositosterol), a double bond at C-22 with a methyl substituent at C-24 (ergosterol), epimerization of the hydroxyl from the 3beta- to 3alpha-configuration (7-dehydroepicholesterol), or a saturated double bond at C-5,6 (lathosterol). Two non-steroidal compounds that inhibit 3beta-hydroxysterol Delta7-reductase in vivo (AY 9944 and BM 15.766) were also tested. Ergosterol, 7-dehydrositosterol, and 7-dehydroepicholesterol were reduced at C-7, 8 to form brassicasterol, sitosterol, and epicholesterol, respectively, but 75% less efficiently than 7-dehydrocholesterol. Increasing concentrations of these sterols competitively inhibited 3beta-hydroxysterol Delta7-reductase activity. The double bond at C-7,8 in lathosterol was not reduced. AY 9944 and BM 15.766 inhibited 3beta-hydroxysterol Delta7-reductase activity non-competitively. 3beta-Hydroxysterol-Delta7-reductase activity declined after microsomes were exposed to alkaline phosphatase, and enzyme activity was increased by phosphorylation with Mg2+, and ATP. These results demonstrate that the reduction of the double bond at C-7,8 requires binding of the enzyme protein with the B-ring of the sterol substrate that contains a double bond at C-5,6. The reaction is hindered by substituents located on the apolar side-chain and epimerization of the hydroxyl group in ring A to a 3alpha-configuration. 3beta-Hydroxysterol Delta7-reductase exists in two forms: an active phosphorylated form and an inactive dephosphorylated form.

Accurate detection of Smith-Lemli-Opitz syndrome carriers by measurement of the rate of reduction of the ergosterol C-7 double bond in cultured skin fibroblasts

The activity of ergosterol delta 7-reductase (3 beta-hydroxysteroid delta 7-reductase) was measured in cultured skin fibroblasts from 7 controls, 10 Smith-Lemli-Opitz syndrome (SLOS) patients, and 10 parents (obligate carriers). The fibroblasts were exposed to delipidated medium supplemented with lovastatin for 24 h and the enzyme activity was determined by incubating cell-free homogenate with ergosterol (ergosta-5,7,22-trien-3 beta-ol) and measuring the mass of brassicasterol (ergosta-5,22-dien-3 beta-ol) formed by gas chromatography-mass spectrometry with selected-ion monitoring. In carriers, the activity was significantly lower than in controls (22 +/- 2 vs 65 +/- 10 pmol/min per mg protein, p < 0.0005), and no overlap was observed. The mean activity in carriers' fibroblasts was more than 100 times higher than in patients' cells (0.2 pmol/min per mg protein). The use of ergosterol avoids the many problems caused by the instability and lack of availability of radiolabelled 7-dehydrocholesterol. The present method makes it possible to discriminate SLOS carriers from both controls and patients using a commercially available substrate and common analytical equipment.

Mapping a gene involved in regulating dietary cholesterol absorption. The sitosterolemia locus is found at chromosome 2p21

The molecular mechanisms regulating the amount of dietary cholesterol retained in the body as well as the body's ability to selectively exclude other dietary sterols are poorly understood. Studies of the rare autosomal recessively inherited disease sitosterolemia (OMIM 210250) may shed some light on these processes. Patients suffering from this disease appear to hyperabsorb both cholesterol and plant sterols from the intestine. Additionally, there is failure of the liver's ability to preferentially and rapidly excrete these non-cholesterol sterols into bile. Consequently, people who suffer from this disease have very elevated plasma plant sterol levels and develop tendon and tuberous xanthomas, accelerated atherosclerosis, and premature coronary artery disease. Identification of this gene defect may therefore throw light on regulation of net dietary cholesterol absorption and lead to an advancement in the management of this important cardiovascular risk factor. By studying 10 well-characterized families with this disorder, we have localized the genetic defect to chromosome 2p21, between microsatellite markers D2S1788 and D2S1352 (maximum lodscore 4.49, theta = 0.0).

Relationship between biliary and serum bile acids and response to ursodeoxycholic acid in patients with primary biliary cirrhosis

OBJECTIVE

Ursodeoxycholic acid (UDCA) improves liver biochemistries and enriches the bile with UDCA in patients with primary biliary cirrhosis. The aim of this study was to determine whether the degree of enrichment of bile correlated with that of serum and whether either of these measures correlated with improvement in measures of liver disease.

METHODS

In a randomized study, biliary and serum bile acid analyses were performed at entry and after 2 yr of UDCA or placebo.

RESULTS

The percentage of ursodeoxycholic acid in bile increased by 42% in the UDCA group (n = 61) compared with 8% in the placebo group (n = 57) (p < 0.0001). Measurement of serum bile acids in 32 patients (18 ursodeoxycholic acid, 14 placebo) indicated that at 2 yr, ursodeoxycholic acid comprised 65% of serum bile acids in the treated group and 7% in the placebo group. Agreement between bile and serum was fair (r = 0.75, p < or = 0.00002) because in some patients, plasma but not biliary bile acids were enriched with UDCA. Changes in biliary ursodeoxycholic acid correlated significantly but weakly with the changes in serum alkaline phosphatase, AST, bilirubin, and in Mayo risk score. Correlations between changes in serum bile acid composition and biochemical measures of disease activity were even weaker.

CONCLUSION

The measurement of biliary bile acids is superior to that of serum bile acids for assessing the compliance and changes in the circulating bile acids in patients receiving ursodeoxycholic acid for the treatment of primary biliary cirrhosis. Furthermore, measures to further increase the proportion of ursodeoxycholic acid in circulating bile acids should be explored.

Biliary cholesterol excretion: a novel mechanism that regulates dietary cholesterol absorption

The regulation of dietary cholesterol absorption was examined in C57BL/6 and transgenic mice with liver overexpression of the scavenger receptor BI (SR-BI Tg). In C57BL/6 animals, feeding 0.02 to 1% (wt/wt) dietary cholesterol resulted in a dose-dependent decrease in the percentage of dietary cholesterol absorbed. A plot of total daily mass of dietary cholesterol absorbed versus the percentage by weight of cholesterol in the diet yielded a curve suggesting a saturable process with a Km of 0.4% (wt/wt) and a Vmax of 0.65 mg cholesterol/g body weight per day. Dietary cholesterol suppressed hepatic 3-hydroxy-3-methylglutaryl CoA reductase activity, stimulated cholesterol 7alpha-hydroxylase activity, and enhanced fecal excretion of bile acids, but none of these changes correlated with the percentage of dietary cholesterol absorption. Dietary cholesterol also caused an increase in biliary cholesterol concentration, and in this case the concentration of biliary cholesterol was strongly and inversely correlated with the percentage dietary cholesterol absorption (r = -0.63, P < 0.0001). Biliary cholesterol concentration was also directly correlated with daily cholesterol intake, dietary cholesterol mass absorption, and liver cholesterol ester content. Transgene-induced overexpression of SR-BI resulted in a stimulation of excretion of cholesterol into the bile and suppressed percentage dietary cholesterol absorption. Furthermore, biliary cholesterol levels in SR-BI Tg mice were strongly and inversely correlated with the percentage of dietary cholesterol absorbed (r = -0.99, P < 0.0008). In summary, these results suggest that the excretion of cholesterol into the bile plays an important role in regulating the percentage absorption of dietary cholesterol.

Regulation of classic and alternative bile acid synthesis in hypercholesterolemic rabbits: effects of cholesterol feeding and bile acid depletion

The effect of cholesterol feeding (3 g/day) on bile acid synthesis was examined in 10 New Zealand white rabbits (NZW), 8 Watanabe heterozygous and 10 homozygous rabbits with partial and complete deficiencies of LDL receptors. After 10 days of cholesterol feeding, bile fistulas were constructed and bile acid pool sizes were measured. Cholesterol feeding increased plasma and hepatic cholesterol levels in all rabbit groups. Baseline bile acid pool sizes were smaller (P < 0.01) in heterozygotes (139 +/- 3 mg) and homozygotes (124 +/- 30 mg) than NZW rabbits (254 +/- 44 mg). After feeding cholesterol, bile acid pool sizes doubled with increased cholic acid synthesis in NZW and, to a lesser extent, in Watanabe heterozygous rabbits but not in homozygotes. Baseline cholesterol 7alpha-hydroxylase activity in NZW and heterozygotes declined 69% and 53% (P < 0.001), respectively, after cholesterol feeding. Sterol 27-hydroxylase activity reflecting alternative bile acid synthesis increased 66% (P < 0.01) in NZW and 37% in Watanabe heterozygotes but not in homozygotes after feeding cholesterol. Bile fistula drainage stimulated cholesterol 7alpha-hydroxylase activity but not sterol 27-hydroxylase activity in all three rabbit groups. These results demonstrated that dietary cholesterol increased hepatic sterol 27-hydroxylase activity and alternative bile acid synthesis to expand the bile acid pool and inhibited cholesterol 7alpha-hydroxylase in NZW and in Watanabe heterozygous rabbits but not in homozygotes with absent hepatic LDL receptor function. Thus, in rabbits, sterol 27-hydroxylase is up-regulated by the increased hepatic cholesterol that enters the liver via LDL receptors whereas cholesterol 7alpha-hydroxylase is controlled by the circulating hepatic bile acid flux.

Synthesis and intestinal metabolism of ursodeoxycholic acid conjugate with an antiinflammatory agent, 5-aminosalicylic acid

5-Aminosalicylic acid conjugate of ursodeoxycholic acid was synthesized in above 90% yield by adding a basic solution of 5-aminosalicylic acid into the mixed anhydride formed with ursodeoxycholic acid and ethyl chloroformate. The 5-aminosalicylic acid conjugate of ursodeoxycholic acid was poorly secreted into the bile and was deconjugated with cholylglycine hydrolase and Clostridium perfringens, that deconjugate naturally occurring glycine and taurine conjugates of bile acids. However, ursodeoxycholic acid 5-aminosalicylic acid conjugate was not absorbed from the duodenum but was concentrated in the colon where it was partially hydrolyzed by the intestinal bacteria to ursodeoxycholic acid and 5-aminosalicylic acid. We believe that this unique conjugation of ursodeoxycholic acid with 5-aminosalicylic acid may facilitate the transport of both 5-aminosalicylic acid and ursodeoxycholic acid to the colon and may be useful for the treatment of colonic inflammatory bowel diseases, ulcerative colitis and Crohn's disease.

Fetal Smith-Lemli-Opitz syndrome can be detected accurately and reliably by measuring amniotic fluid dehydrocholesterols

The Smith-Lemli-Opitz syndrome, characterized by limb, face and organ abnormalities, and mental retardation, is caused by an inherited block in the step of cholesterol biosynthesis in which the delta 7 double bond of 7-dehydrocholesterol is reduced. It is diagnosed by the presence of markedly elevated levels of 7-dehydrocholesterol and 8-dehydrocholesterol in plasma and tissue. We measured amniotic fluid sterols in 15 pregnancies in 13 women who had previously carried an affected fetus. Cholesterol, 7-dehydrocholesterol and 8-dehydrocholesterol concentrations averaged 18 +/- 3, 9.8 +/- 2.9 and 5.0 +/- 1.7 micrograms/ml, respectively, in seven pregnancies with an affected fetus or child. In contrast, these levels were 19 +/- 3, 0.05 +/- 0.01 and < 0.005 micrograms/ml, respectively, in eight increased-risk pregnancies with normal outcomes and 16 +/- 2, 0.07 +/- 0.01 and < 0.005 micrograms/ml in normal controls. 7-dehydrocholesterol concentrations, 2.2-26 and 0.05-0.10 micrograms/ml in pregnancies with an affected and unaffected fetus, respectively, did not overlap. Thus, abnormally elevated amniotic fluid dehydrocholesterol concentrations are an accurate predictor of fetal Smith-Lemli-Opitz syndrome. A false-positive or a false-negative result is highly unlikely.