Simultaneous determination of mevalonate and 7 alpha-hydroxycholesterol in human plasma by gas chromatography-mass spectrometry as indices of cholesterol and bile acid biosynthesis

Measurement of HMG CoA reductase activity in different human cell lines by ultra-performance liquid chromatography tandem mass spectrometry

Hydroxymethylglutaryl coenzyme A reductase (HMGCR) catalyzes the rate limiting step in cholesterol biosynthesis converting HMG-CoA into mevalonic acid (MVA), which equilibrates with mevalonic acid lactone (MVL) under neutral pH conditions. We developed a fast, sensitive, and efficient method to determine HMGCR activity in human cell lines measuring MVL levels by ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). Convenient prepared samples containing MVL-D7 as an internal standard were injected, separated, and eluted from an ACQUITY HSS PFP column. Measurement of MVL was performed by electrospray ionization mass spectrometry with multiple reaction monitoring. Calibration curves were linear and reproducible in the range of 0.15-165 μg/l (r>0.99). Lower limit of quantification was 0.12 μg/l. Intra- and interassay imprecision were <1.3% and <2.9%, respectively. HMGCR enzymatic activity measurements of cells cultivated under different cell culture conditions (with 10% FCS, with 10% lipoprotein-deficient serum and under serum starvation) revealed the applicability of this test system for various experimental settings. This efficient UPLC-MS/MS assay permits rapid and high sensitive determination of HMGCR enzyme activity, tracing potential alterations in cholesterol biosynthesis.

An ultrasensitive enzymatic method for measuring mevalonic acid in serum

We have developed a simple, precise, and ultrasensitive enzymatic method for measuring serum mevalonic acid (MVA) concentration, which is thought to be a good indicator of the in vivo cholesterol biosynthesis rate. This assay is based on an enzyme cycling reaction and makes use of HMG-CoA reductase (HMGR), thio-NAD, NADH, and CoA. MVA participates in the HMGR cycling reaction, and its level is measured based on the production of thio-NADH, which is determined from the change in absorbance at 405 nm. To achieve high specificity, we used mevalonate kinase (MVK) in addition to HMGR. Only substrates able to participate in both the HMGR cycling reaction and the MVK reaction are measured as MVA. The detection limit for MVA is 0.4 ng/ml (2.7 nmol/l), and the calibration curve for MVA is linear up to 44 ng/ml (300 nmol/l). Regression analysis with 40 serum samples showed the accuracy of quantifying MVA with this enzymatic assay to be comparable to that using LC-MS/MS (correlation: y = 0.83x + 0.24; r = 0.97). This procedure is simple, precise, and robust. It is also rapid and has a high throughput, making it potentially useful for clinical applications.

Highly sensitive and specific analysis of sterol profiles in biological samples by HPLC-ESI-MS/MS

High-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) is a powerful method for the microanalysis of compounds in biological samples. Compared with gas chromatography-mass spectrometry (GC-MS), this method is more broadly applicable to various compounds and usually does not require a derivatization step before analysis. However, when neutral sterols are analyzed, the sensitivities of usual HPLC-MS/MS method are not superior to those of GC-MS because the sterols are relatively resistant to ionization. In this review, we introduce the recent development of HPLC-MS/MS analysis for the quantification of non-cholesterol sterols. By adding an effective derivatization step to the conventional procedure, sterol analysis by HPLC-MS/MS surpassed that obtained by GC-MS in sensitivity. In addition, sufficient specificity of this method was achieved by selected reaction monitoring (SRM) and thorough chromatographic separation of each sterol.

Increase of serum cholesterol levels by heat-moisture-treated high-amylose cornstarch in rats fed a high-cholesterol diet

The effects of four cornstarches containing various contents of resistant starch on serum and liver cholesterol levels in rats fed a high-cholesterol diet were investigated. Male Sprague Dawley rats (aged 4 weeks) were divided into four groups (n = 7) and fed high-cholesterol diets containing 15% of cornstarch (CS), heat-moisture-treated CS (HCS), high-amylose CS (HA), or heat-moisture-treated HA (HHA) for 21 days. The results showed that the serum and hepatic level of total cholesterol, LDL-cholesterol, and triglyceride in rats of the HHA group and their arteriosclerosis index were significantly higher, suggesting that HHA increases the risk of arteriosclerosis under a high-cholesterol dietary condition. No significant between-group differences were noted in the levels of plasma mevalonic acid and hepatic HMG-CoA reductase mRNA, whereas fecal cholesterol excretion was significantly higher in the HHA group, indicating that the elevation of the serum and liver cholesterol levels was not due to the promotion of liver cholesterol synthesis and cholesterol absorption in the intestine.

Determination of key intermediates in cholesterol and bile acid biosynthesis by stable isotope dilution mass spectrometry

For more than a decade, we have developed stable isotope dilution mass spectrometry methods to quantify key intermediates in cholesterol and bile acid biosynthesis, mevalonate and oxysterols, respectively. The methods are more sensitive and reproducible than conventional radioisotope (RI), gas-chromatography (GC) or high-performance liquid chromatography (HPLC) methods, so that they are applicable not only to samples from experimental animals but also to small amounts of human specimens. In this paper, we review the development of stable isotope dilution mass spectrometry for quantifying mevalonate and oxysterols in biological materials, and demonstrate the usefulness of this technique.

Highly sensitive assay of HMG-CoA reductase activity by LC-ESI-MS/MS

We have developed a new sensitive and specific nonradioisotope assay method to measure the activity of HMG-CoA reductase, the rate-controlling enzyme in the cholesterol biosynthetic pathway. This method was based upon a stable isotope dilution technique by liquid chromatography-tandem mass spectrometry using electrospray ionization in positive mode. Mevalonic acid, the product of HMG-CoA reductase, was converted to mevalonolactone (MVL) in an incubation mixture, extracted by a salting-out procedure, derivatized into the mevalonyl-(2-pyrrolidin-1-yl-ethyl)-amide, and then purified using a disposable silica cartridge. The resulting mevalonylamide was quantified by selected reaction monitoring using the positive electrospray ionization mode. The detection limit of this mevalonylamide was found to be 240 amol (signal-to-noise ratio=3), approximately 833 times more sensitive than that of MVL measured by a conventional radioisotope (RI) method (200 fmol). The variances between sample preparations and between measurements by this method were analyzed by one-way layout and calculated to be 3.2% and 1.8%, respectively. The recovery experiments were performed using incubation mixtures spiked with 0.77-2.31 nmol MVL/mg protein and were validated by a polynomial equation. These results showed that the estimated concentration within a 95% confidence limit was 0.47+/-0.07 nmol/mg protein, which coincided completely with the observed X0 nmol/mg protein with a mean recovery of 94.6%. This method made it possible to measure HMG-CoA reductase activity with a high degree of reproducibility and reliability, and especially with sensitivity superior to that of the conventional RI method.

Validation of the LC-MS/MS method for the quantification of mevalonic acid in human plasma and determination of the matrix effect

A simple, specific, and sufficiently sensitive liquid chromatography-tandem mass spectrometry (negative-ion electrospray ionization) methodology to determine mevalonic acid (MVA) in human plasma is described, and its application to the analysis of rat plasma MVA levels after rosuvastatin administration is demonstrated. The method was validated over the linearity range of 0.5-50.0 ng/ml (r(2) > 0.99) using deuterated MVA as an internal standard. The lower limit of quantification was 0.5 ng/ml. The assay procedure involved the isolation of MVA from plasma samples using solid-phase extraction. Chromatographic separation was achieved on a HyPurity Advance column with a mobile phase consisting of ammonium formate buffer (10 mM, pH 8.0) and acetonitrile (70:30, v/v). Excellent precision and accuracy were observed. MVA and deuterated mevalonolactone were stable in water and plasma under different storage and processing conditions. The recovery observed was low, which was attributable to a significant matrix effect. A significant decrease (30-40%; P < 0.05) was observed in rat plasma MVA levels after rosuvastatin administration.

Metabolomics: building on a century of biochemistry to guide human health

Medical diagnosis and treatment efficacy will improve significantly when a more personalized system for health assessment is implemented. This system will require diagnostics that provide sufficiently detailed information about the metabolic status of individuals such that assay results will be able to guide food, drug and lifestyle choices to maintain or improve distinct aspects of health without compromising others. Achieving this goal will use the new science of metabolomics - comprehensive metabolic profiling of individuals linked to the biological understanding of human integrative metabolism. Candidate technologies to accomplish this goal are largely available, yet they have not been brought into practice for this purpose. Metabolomic technologies must be sufficiently rapid, accurate and affordable to be routinely accessible to both healthy and acutely ill individuals. The use of metabolomic data to predict the health trajectories of individuals will require bioinformatic tools and quantitative reference databases. These databases containing metabolite profiles from the population must be built, stored and indexed according to metabolic and health status. Building and annotating these databases with the knowledge to predict how a specific metabolic pattern from an individual can be adjusted with diet, drugs and lifestyle to improve health represents a logical application of the biochemistry knowledge that the life sciences have produced over the past 100 years.

Analysis of acyl CoA ester intermediates of the mevalonate pathway in Saccharomyces cerevisiae

The mevalonate pathway plays an important role in providing the cell with a number of essential precursors for the synthesis of biomass constituents. With respect to their chemical structure, the metabolites of this pathway can be divided into two groups: acyl esters [acetoacetyl CoA, acetyl CoA, hydroxymethylglutaryl (HMG) CoA] and phosphorylated metabolites (isopentenyl pyrophosphate, dimethylallyl pyrophosphate, geranyl pyrophosphate, farnesyl pyrophosphate). In this study, we developed a method for the precise analysis of the intracellular concentration of acetoacetyl CoA, acetyl CoA and HMG CoA; and we used this method for quantification of these metabolites in Saccharomyces cerevisiae, both during batch growth on glucose and on galactose and in glucose-limited chemostat cultures operated at three different dilution rates. The level of the metabolites changed depending on the growth phase/specific growth rate and the carbon source, in a way which indicated that the synthesis of acetoacetyl CoA and HMG CoA is subject to glucose repression. In the glucose batch, acetyl CoA accumulated during the growth on glucose and, just after glucose depletion, HMG CoA and acetoacetyl CoA started to accumulate during the growth on ethanol. In the galactose batch, HMG CoA accumulated during the growth on galactose and a high level was maintained into the ethanol growth phase; and the levels of acetyl CoA and HMG CoA were more than two-fold higher in the galactose batch than in the glucose batch.

Significance of plasma 7alpha-hydroxy-4-cholesten-3-one and 27-hydroxycholesterol concentrations as markers for hepatic bile acid synthesis in cholesterol-fed rabbits

Plasma 7alpha-hydroxy-4-cholesten-3-one has been used as an index of hepatic bile acid synthesis. The aim of the current study was to ascertain whether the level of this oxysterol reflects hepatic cholesterol 7alpha-hydroxylase activity when plasma cholesterol concentrations are markedly changed. In addition, the relationship of hepatic sterol 27-hydroxylase activity with plasma concentrations of 27-hydroxycholesterol and 3beta-hydroxy-5-cholestenoic acid was studied. We used New Zealand white rabbits fed 2% cholesterol for 5 or 10 days and/or constructed bile fistula. Feeding cholesterol markedly increased and bile drainage reduced plasma cholesterol concentrations. Initially, in these models there was no correlation between plasma 7alpha-hydroxy-4-cholesten-3-one concentrations and hepatic cholesterol 7alpha-hydroxylase activities (r = -0.24, n = 10). Cholesterol feeding was associated with downregulated 7alpha-hydroxylase activities, while plasma 7alpha-hydroxy-4-cholesten-3-one concentrations were elevated in the presence of increased plasma cholesterol levels. However, this discrepancy was overcome and significant correlation was observed (r = 0.73, P <.05, n = 10) by expressing 7alpha-hydroxy-4-cholesten-3-one levels relative to cholesterol. In contrast, hepatic sterol 27-hydroxylase activities were not significantly correlated with plasma absolute (r = 0.23, difference not significant [NS], n = 10) nor cholesterol-related levels of 27-hydroxycholesterol (r = -0.13, NS, n = 10), or 3beta-hydroxy-5-cholestenoic acid concentrations (r = 0.30, NS, n = 10). In conclusion, plasma 7alpha-hydroxy-4-cholesten-3-one concentrations reflected hepatic cholesterol 7alpha-hydroxylase activities when the sterol levels were adjusted to plasma cholesterol concentrations in rabbits with hypercholesterolemia. The results suggest that plasma 7alpha-hydroxy-4-cholesten-3-one relative to cholesterol is a better marker for hepatic cholesterol 7alpha-hydroxylase activity than the absolute concentration when hypercholesterolemia is present. In contrast, 27-hydroxycholesterol and 3beta-hydroxy-5-cholestenoic acid levels in plasma did not reflect hepatic sterol 27-hydroxylase activities even if the levels were adjusted to plasma cholesterol concentrations.

Personal Metabolomics as a Next Generation Nutritional Assessment

Nutrition research is in the process of addressing a series of questions related to the future of diet and health. Are all humans the same with respect to their response to diet? If not, humans must be fed differently according to the differences in their genetics and metabolic needs. Are those differences self-evident to the individual or their care-givers? If not, methods must be developed to measure the basis of differences between humans. Are the current sets of diagnostic biomarkers for disease appropriate and sufficient to distinguish the appropriate diets of humans for optimal metabolic health? If not, metabolites must be measured such that the differences in human metabolism are resolvable before they become diseased. Will a small subset of metabolic markers provide an indication of intended and unintended effects of diets that relate to overall metabolism? If not, comprehensive metabolic analyses (metabolomics) must be put in place to ensure that all aspects of health are accurately assessed. Inappropriate dietary choices are accelerating the development of chronic metabolic disease and threatening to overwhelm public health's ability to manage them. Nutrition and food sciences will need to collaborate with other scientific disciplines to develop and implement metabolic assessment technologies and to assemble annotated databases of metabolite profiles in humans, thus building the knowledge needed to link metabolism to diet and health. Biochemical and physiological research must be guided to define the mechanisms by which diet interacts with metabolism in different individuals. Integrating metabolism with the genetic and dietary variables that affect health is the role of nutrition sciences. Integrating personal nutritional value with food's other key values of safety, quality, comfort, delight, convenience and affordability is the role of food science. It is time for these two fields to address a common problem, metabolic health, with coordinated solutions.

Origin of oxysterols in hepatic bile of patients with biliary infection

OBJECTIVES

Oxysterols are ubiquitous in the body and are potential cytotoxic agents in addition to being metabolic regulators. Although bile contains high concentrations of cholesterol, oxysterol concentrations in bile and the effect of infection on oxysterol levels have not been measured, nor has their origin been studied. The purpose of this study was to determine if infection of the biliary tract was associated with increased concentrations of oxysterols in the bile and, if so, which oxysterols showed a significant change.

METHODS

Hepatic bile was obtained from eight patients with biliary tract disease by means of a naso-biliary catheter. Oxysterols were extracted and purified by solid-phase extraction, derivatized and measured by gas chromatography-mass spectrometry.

RESULTS

The following were quantified in hepatic bile: 7-alpha-hydroxycholesterol, 7-beta-hydroxycholesterol, cholestan-3-beta,5-alpha,6-beta-triol, 25-hydroxycholesterol, 26-hydroxycholesterol, 7-ketocholesterol, and 7-alpha-hydroxy-4-cholesten-3-one. Total oxysterols in hepatic bile ranged from 0.133 mumol/L to 7.748 mumol/L (1.47 +/- 2.55 mumol/L). Levels of 7-alpha-hydroxycholesterol and 7-beta-hydroxycholesterol were increased in infected bile (14.2 +/- 15.1 x 10(-3)% of cholesterol vs 1.9 +/- 0.5 x 10(-3)% of cholesterol, p < 0.05, and 22.0 +/- 25.0 x 10(-3)% of cholesterol vs 1.6 +/- 1.2 x 10(-3)% of cholesterol, p < 0.05, respectively). Serum C-reactive protein levels correlated positively with biliary levels of 7-alpha-hydroxycholesterol (R = 0.948), 7-beta-hydroxycholesterol (R = 0.976), cholestan-3-beta,5-alpha,6-beta-triol (R = 0.823), 7-alpha-hydroxy-4-cholesten-3-one (R = 0.846,) and 7-ketocholesterol (R = 0.973). Different oxysterols were found in gallstones, chiefly 3-keto-cholest-4-ene (624 +/- 316 parts per million [ppm] of dry weight), 3-keto-cholesta-4,6-diene (240 +/- 329 ppm) and 7-keto-cholesterol (77 +/- 81 ppm). Incubation of human leukocytes with model bile in the presence of bacterial lipopolysaccharide resulted in changes in sterol composition, including increases in oxysterols. We have identified and quantified oxysterols from uninfected and infected human hepatic bile and from gallstones and gallbladder bile. Biliary infection may be involved in the biogenesis of oxysterols in bile through the production of reactive oxygen species from activated leukocytes.

Validation and application of an assay for the determination of mevalonic acid in human plasma by liquid chromatography tandem mass spectrometry

The validation of a method for the determination of mevalonic acid (MVA; after conversion to the lactone, MVAL) in human plasma, using high-performance liquid chromatography with tandem mass spectrometry (HPLC-MS-MS), is reported. MVAL and deuterated internal standard were extracted from human plasma samples using automated solid-phase extraction. Analysis was conducted by column-switching, reversed-phase LC-MS-MS, using two hyper-cross-linked styrene-divinylbenzene copolymer sorbent reversed-phase columns. An assay range of 0.2-35 ng/ml and a lower limit of quantitation (LLOQ) of 0.2 ng/ml were achieved with acceptable accuracy and precision. MVA was stable in plasma under a variety of storage conditions.

Determination of mevalonic acid in human urine as mevalonic acid lactone by gas chromatography-mass spectrometry

Mevalonic acid in urine is converted to its lactone form by incubation overnight at acidic pH, extracted and analysed by GC-MS. The lower limit of quantitation of 7.5 ng/ml provides adequate sensitivity to measure changes in urinary excretion of MVA following administration of drugs which affect cholesterol synthesis. The assay is linear up to 300 ng/ml and has acceptable precision (<15%) and accuracy (<+/-20%) across the calibration range.

Urinary mevalonate excretion rate in type 2 diabetes: role of metabolic control

An increased cholesterogenesis has been described in obese dyslipidemic type 2 diabetic patients and in a small number of patients with poor glucose control. So far, it is not clear if increased cholesterogenesis in type 2 diabetes is related to the degree of glycemic control or depends on the commonly associated dyslipidemia or both. Therefore, the aim of the present study was to investigate the relationships among cholesterogenesis and degree of metabolic control in a group of non-obese normolipidemic type 2 diabetic patients. Fifty four (25 men and 29 postmenopausal women) non-obese type 2 diabetic patients with cholesterol and triglyceride plasma levels, respectively, below 6.40 and 2.85 mmol/l and 20 normal subjects matched for age and sex were studied. Endogenous cholesterol synthesis was evaluated by the determination of 24-h urinary mevalonate excretion (MVA). In the diabetic group the mean glycated hemoglobin was 8.47+/-2.2% (range 4.6-14.6%), the mean total cholesterol, triglycerides, HDL and LDL cholesterol were, respectively, 4.86+/-0.7, 1.64+/-0.5, 1.19+/-0.3 and 2.87+/-0.7 mmol/l. The mean 24-h MVA urine excretion rates were 1.41+/-0.3 micromol/24 h in control subjects and 1.66+/-0.7 micromol/24 h in diabetics (P=0.05). In diabetics, urinary mevalonate excretion was significantly correlated with glycated hemoglobin concentrations (HbA(1c)) (r=0.65; P=0.0001) and body mass index (BMI) (r=0.33; P=0.009). In the multivariate analysis both HbA(1c) and BMI were independent predictors of urinary mevalonate. These data demonstrate that lower the degree of blood glucose control, higher is the whole body cholesterol production even in the absence of overt dyslipidemia. In conclusion, the relationship between mevalonate excretion rate and glycated hemoglobin gives further weight to the importance of intensive blood-glucose control in diabetic disease and adds a new element to the list of potentially atherogenic factors strictly related to hyperglycemia in type 2 diabetic patients.

Determinants of Variable Response to Statin Treatment in Patients With Refractory Familial Hypercholesterolemia

Abstract —Interindividual variability in low density lipoprotein (LDL) cholesterol (LDL-C) response during treatment with statins is well documented but poorly understood. To investigate potential metabolic and genetic determinants of statin responsiveness, 19 patients with refractory heterozygous familial hypercholesterolemia were sequentially treated with placebo, atorvastatin (10 mg/d), bile acid sequestrant, and the 2 combined, each for 4 weeks. Levels of LDL-C, mevalonic acid (MVA), 7-α-OH-4-cholesten-3-one, and leukocyte LDL receptor and hydroxymethylglutaryl coenzyme A reductase mRNA were determined after each treatment period. Atorvastatin (10 mg/d) reduced LDL-C by an overall mean of 32.5%. Above-average responders (ΔLDL-C −39.5%) had higher basal MVA levels (34.4±6.1 μmol/L) than did below-average responders (ΔLDL-C −23.6%, P <0.02; basal MVA 26.3±6.1 μmol/L, P <0.01). Fewer good responders compared with the poor responders had an apolipoprotein E4 allele (3 of 11 versus 6 of 8, respectively; P <0.05). There were no baseline differences between them in 7-α-OH-4-cholesten-3-one, hydroxymethylglutaryl coenzyme A reductase mRNA, or LDL receptor mRNA, but the latter increased in the good responders on combination therapy ( P <0.05). Severe mutations were not more common in poor than in good responders. We conclude that poor responders to statins have a low basal rate of cholesterol synthesis that may be secondary to a genetically determined increase in cholesterol absorption, possibly mediated by apolipoprotein E4. If so, statin responsiveness could be enhanced by reducing dietary cholesterol intake or inhibiting absorption.

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.

Effect of inhibiting HMG-CoA reductase on 7 alpha-hydroxy-4-cholesten-3-one, a marker of bile acid synthesis: contrasting findings in patients with and without prior up-regulation of the latter pathway

BACKGROUND

Atorvastatin is a potent inhibitor of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase, but its effect on bile acid synthesis is unknown. The objectives of the study were to determine the effect of atorvastatin on bile acid synthesis in patients in whom this process had not been or had been previously up-regulated by pharmacological or surgical means.

MATERIALS AND METHODS

Four patients with heterozygous familial hypercholesterolaemia (FH) and partial ileal bypass (PIB) and 19 FH heterozygotes without PIB were treated with placebo, atorvastatin 10 mg and atorvastatin 40 mg daily, each regimen for 4 weeks. The non-PIB group was subsequently treated with bile acid (BA) sequestrant 8-16 g daily followed by co-administration of atorvastatin 10 mg, each for 4 weeks. Plasma 7 alpha-hydroxy-4-cholesten-3-one (7 alpha-HCO), a well-validated marker of BA synthesis was measured using high-performance liquid chromatography with UV detection.

RESULTS

The plasma 7 alpha-HCO concentration was tenfold higher with placebo in the PIB than in the non-PIB group (418.5 ng mL-1 vs. 39.6 ng mL-1 p = 0.0001). Levels decreased in PIB patients treated with atorvastatin 10 mg and 40 mg daily (350.1 ng mL-1 and 174.0 ng mL-1, P = 0.007 respectively) but did not change significantly in the non-PIB group (44.7 ng mL-1 and 28.3 ng mL-1 respectively). Administration of BA sequestrant to non-PIB patients increased 7 alpha-HCO to 197.4 ng mL-1; this decreased to 106.0 ng mL-1 during co-administration of atorvastatin 10 mg daily (P = 0.0001).

CONCLUSION

Atorvastatin decreases the rate of BA synthesis only if the latter is up-regulated by PIB or BA sequestrants, presumably by limiting the supply of newly synthesized free cholesterol.

Plasma levels of mevalonate and 7alpha-hydroxy-4-cholesten-3-one in chronic liver disease

BACKGROUND AND AIMS

Cholesterol levels in blood tend to be preserved despite hepatic impairment, in contrast to albumin levels and other markers of liver function in patients with liver cirrhosis (LC). We reported previously that the levels of plasma mevalonate (MVA) and 7alpha-hydroxy-4-cholesten-3-one (7alpha3one) closely reflect hepatic synthetic rates of cholesterol and bile acids. The aim of this study was to examine the association between hepatic cholesterogenesis and bile acid synthesis in hepatocellular impairment using these indices.

METHODS

The plasma indices were measured in patients with LC (n = 38) or chronic hepatitis (CH; n = 11) and in normal controls (n = 22). The severity of LC was assessed by the Child-Pugh score.

RESULTS

There were no significant differences in plasma MVA levels between CH, LC and control groups. However, plasma 7alpha3one levels were significantly lower in LC than in CH and control groups (P< 0.01). While MVA levels did not correlate with the Child-Pugh score, there was a significant correlation between 7alpha3one level and Child-Pugh score (P< 0.005). The plasma 7alpha3one level in controls correlated positively with MVA levels (P< 0.01); however, there was no significant correlation between these indices in CH and LC.

CONCLUSION

In chronic liver disease, there was a tendency for hepatic cholesterogenesis to be sustained in the face of hepatocellular impairment, while bile acid synthesis declined in parallel with the severity of impairment.

Determination of 7alpha-hydroxycholesterol in dog plasma by high-performance liquid chromatography with fluorescence detection

A new method was developed for the determination of 7alpha-hydroxycholesterol (7-HC) in dog plasma by means of high-performance liquid chromatography (HPLC) with fluorescence detection. 7-HC extracted with organic solvent from plasma was purified with Bond Elut 2OH and converted to a sensitive fluorescent derivative containing double coumarin groups at the C-3 and C-7 positions of the steroid nucleus with 7-methoxycoumarin-3-carbonyl azide. After removal of the excess reagent with Bond Elut NH2, the 7-HC derivative was separated by reverse-phase HPLC method. The detection limit of the authentic 7-HC-3,7-coumarin derivative was 4 pg (S/N = 5), approximately four times less than that of the 7-HC-3-anthroyl derivative yielded by reaction of 7-HC with 1-anthroylcyanide. The newly developed method was used to investigate the effects of consecutive oral administrations of cholestyramine (CA) on 7-HC levels in dog plasma. The plasma 7-HC levels of the CA-treated group were two times greater than those of the control group.

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.

Cholesterol synthesis is increased in mixed hyperlipidaemia

We showed previously that hypertriglyceridaemia, but not hypercholesterolaemia, is correlated with increases in cholesterol synthesis and apolipoprotein B secretion in patients with secondary hypertriglyceridaemia. The aim of the present study was to compare the rate of cholesterol synthesis, using fasting plasma mevalonic acid (MVA) as an index, in patients with primary mixed hyperlipidaemia (type IIb phenotype, n=45) and primary hypercholesterolaemia (type IIa phenotype, n=92). LDL cholesterol was significantly higher in types IIa (6.38+/-0.18 mmol/l) and IIb (5.89+/-0.25 mmol/l) compared to 40 normolipidaemic controls (2. 99+/-0.1 mmol/l, P<0.0001), whereas serum triglyceride was higher in type IIb (2.62 (range 2.2-3.0) mmol/l) than type IIa (1.22 (range 0. 85-1.60) mmol/l, P<0.001) and controls (0.90 (range 0.68-1.24) mmol/l, P<0.001). Similarly, MVA was higher in type IIb (7.0+/-0.46 ng/ml) than IIa (5.6+/-0.23 ng/ml, P<0.0) and controls (5.6+/-0.36 ng/ml, P<0.05). Plasma MVA correlated positively with serum triglyceride (r=0.22, P=0.004) and negatively with LDL cholesterol (r=-0.21, P=0.014). These results are in accordance with previous observations that VLDL-apolipoprotein B secretion and cholesterol synthesis are linked and demonstrate that the latter is increased in mixed hyperlipidaemia.

Enzyme immunoassay of urinary mevalonic acid and its clinical application

We have developed an enzyme immunoassay for mevalonic acid (MVA), using a specific monoclonal antibody. The intra- and interassay coefficients of variation calculated on two urine samples were 3.3% and 3.4%, respectively, in the intraassay precision test and 3.5% and 6.9% in the interassay evaluation. Pravastatin, a 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor, was administered to nine healthy men, and in all cases, their MVA excretion rates then decreased. The more MVA that was excreted in the urine before the pravastatin administration, the greater a reduction of MVA excretion was observed. The daily MVA excretions in healthy men (n = 120) and women (n = 105) were 2.32 μmol/day (SD, 0.82 μmol/day) and 1.85 μmol/day (SD, 0.47 μmol/day), respectively. In streptozotocin-induced diabetic rats (n = 14), the plasma cholesterol concentrations and MVA excretion rates were increased, and a positive correlation was observed between the plasma cholesterol and the urinary MVA concentrations.

Use of cholesterol precursors to assess changes in cholesterol synthesis under non-steady-state conditions

BACKGROUND

Quantification of plasma levels of an early and late intermediate on the cholesterol pathway, mevalonic acid (MVA) and lathosterol respectively, provides a useful method of estimating cholesterol synthesis in humans. The aim of this study was to assess further their roles as indices of cholesterol synthesis under non-steady-state conditions.

METHODS

The short-term effects of pharmacological inhibition of 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase on both variables were determined in four normolipidaemic subjects during and after treatment with simvastatin 20 mg daily. Plasma MVA was measured using gas chromatography-mass spectrometry, and lathosterol using gas chromatography.

RESULTS

A single dose of 20 mg of simvastatin decreased plasma MVA after 2 h and decreased the lathosterol-cholesterol (L/C) ratio after 4 h. Treatment with simvastatin 20 mg daily for 9 days decreased both variables by approximately 50%, the nadir of plasma MVA occurring on the second day and of the L/C ratio on the fifth day, and resulted in a 39% reduction in low-density lipoprotein (LDL)-cholesterol. After discontinuing simvastatin, there were rebounds in plasma MVA and the L/C ratio to above basal levels but not in LDL cholesterol or apolipoprotein B (apoB), the latter continuing to decrease for a further 2 days.

CONCLUSION

These results suggest that simvastatin rapidly down-regulates cholesterol synthesis, which is then up-regulated when the drug is withdrawn.

Apolipoprotein E genotype and cholesterogenesis in polygenic hypercholesterolemia

We studied 22 normal-weight patients with polygenic hypercholesterolemia (PH), of which 11 (two males and nine females) had the apolipoprotein (apo) E3/4 genotype and 11 (one male and 10 females) the E3/3 genotype. The two groups were comparable for age, body mass index, total and low-density lipoprotein (LDL) cholesterol levels. The diagnosis of PH was made on the basis of clinical assessment, the criteria being type IIa hypercholesterolemia without tendon xanthomas and/or family history and clinical criteria indicative of familial hypercholesterolemia and/or familial combined hyperlipidemia. To avoid the influence of the habitual individual diet on cholesterogenesis, daily urinary mevalonic acid (MVA) excretion, an index of whole-body cholesterol synthesis, was evaluated in the steady-state condition while patients were on a low-fat, low-cholesterol diet for at least 3 months. Urinary MVA excretion rates were 2.52 +/- 0.8 micromol/24 h in E3/4 patients, significantly higher (P < .001) than in E3/3 patients (1.38 +/- 0.6 micromol/24 h). This is the first evidence of a higher rate of cholesterogenesis in PH patients carrying the epsilon4 allele versus the epsilon3 allele under a standardized lipid-lowering diet. We conclude that the higher rate of cholesterogenesis in PH patients with the epsilon4 allele might partly explain the interindividual differences in response to treatment with cholesterol synthesis inhibitors such as statins.

Upregulation of cholesterol synthesis after acute reduction of low density lipoprotein by apheresis in normocholesterolaemic subjects: evidence for a threshold effect

The influence of low density lipoproteins (LDL) in the plasma on the regulation of cholesterol biosynthesis is not clear. We studied the changes in plasma mevalonic acid (MVA) concentration and the lathosterol/cholesterol (L/C) ratio, which are well established indices of whole body cholesterol synthesis, in four normocholesterolaemic subjects after each had undergone LDL apheresis on two occasions. LDL apheresis of 75% of the calculated plasma volume reduced LDL-cholesterol by 44% to 1.5 +/- 0.2 mmol/l without changing plasma MVA levels or L/C ratios. Apheresis of 125% of the calculated plasma volume decreased plasma LDL-cholesterol by 69% to 0.9 +/- 0.2 mmol/l, with significant increases in plasma MVA and L/C ratio on the day after the procedure. These results imply that LDL-cholesterol is an integral part of the sterol regulatory pool and suggest that plasma levels cannot be lowered below 1-1.4 mmol/l in normal subjects without upregulating cholesterol biosynthesis.

Short-term effects of 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor on cholesterol and bile acid synthesis in humans

Competitive inhibitors of 3-hydroxy-3-methylglutaryl-CoA reductase improve hypercholesterolemia. However, reports about the effects of these agents on bile acid synthesis, the metabolic pathway of cholesterol, are conflicting. We studied the short-term effect on one of these agents, pravastatin, on bile acid synthesis. Six male volunteers were given 40 mg of pravastatin. Plasma mevalonate level (which reflects cholesterol synthesis) and 7 alpha-hydroxy-4-cholesten-3-one level (which reflects bile acid synthesis) were measured every 2 h for 8 h. These plasma levels were compared to those of the same volunteers without pravastatin. Plasma mevalonate level after 2 h was lower than control (3.0 +/- 1.1 ng/mL vs. 6.7 +/- 2.5, mean +/- SD; P < 0.05). This decrease continued for 8 h (2.5 +/- 0.8 vs. 5.2 +/- 1.5; P < 0.05). On the other hand, plasma 7 alpha-hydroxy-4-cholesten-3-one level did not change until after 6 h; then at 8 h it was lower than control (15.7 +/- 11.8 ng/mL vs. 24.7 +/- 16.9; P < 0.05). According to three-way layout analysis of variance, mevalonate level was influenced by both pravastatin treatment (P < 0.01) and time-course (P < 0.01). On the other hand, the 7 alpha-hydroxy-4-cholesten-3-one level was affected by both individual difference (P < 0.01) and time course (P < 0.01), but pravastatin treatment did not influence this compound. This indicates that bile acid synthesis was influenced by pravastatin, although cholesterol synthesis was inhibited. The short-term inhibition of cholesterol synthesis did not affect bile acid synthesis.

A sensitive and selective method for the determination of mevalonic acid in dog plasma by gas chromatography/negative ion chemical ionization-mass spectrometry

A sensitive and selective method has been developed for the determination of mevalonic acid (MVA), a cholesterol biosynthetic precursor, in dog plasma using solid-phase extraction in combination with gas chromatography/negative ion chemical ionization-mass spectrometry (GC/NICI-MS). MVA extracted from plasma with a phenylboronic acid-bonded phase cartridge was converted to its pentafluorobenzyl (PFB) ester-cyclic boronate derivative to produce a carboxyltate anion [M-PFB]- in the NlCl mode. PFB ester boronate derivatives of MVA and its internal standard, d3-mevalonolactone, were monitored in the selected ion mode at m/z 213 and 216, respectively. The precision and accuracy of within-run and between-run assays were within 8%. This method was used to follow the diurnal variation of MVA levels in plasma of fasted and fed dogs. The diurnal variations of plasma MVA levels observed between the two groups were similar to those reported previously for human and rat plasma.

Plasma mevalonate concentrations in uremic patients

Mevalonic acid (mevalonate or MVA), is an obligate precursor in the biosynthetic pathway of cholesterol. It is partially metabolized by the kidneys and its plasma concentrations are an index of endogenous cholesterol synthesis. The aim of the present study was to evaluate plasma MVA concentrations in uremic patients with different degrees of chronic renal failure (CRF; group A), and the effects of a single hemodialysis treatment on plasma MVA in a group of patients with end-stage renal disease (ESRD; group B). CRF patients exhibited a higher mean basal mevalonate concentration (13.3 +/- 6.5 ng/ml) than control subjects (4.68 +/- 1.32 ng/ml; P < 0.001). A statistically significant direct correlation was evident in CRF patients between mevalonate and creatinine plasma levels (r = 0.86; P < 0.001). A single hemodialysis treatment was associated with a significant reduction of plasma mevalonate concentrations four hours after the hemodialysis session (-57%; P < 0.001) and an increase up to the basal values 24 hours after the end of the treatment. In conclusion, our results demonstrated: (i) higher plasma MVA concentrations in patients with decreased renal function; (ii) a direct relationship between plasma MVA levels and the degree of kidney failure as expressed by creatinine plasma concentrations; and (iii) a clear cut reduction of elevated plasma MVA levels after a single hemodialysis treatment.

Relationship between the serum concentration of 7 alpha-hydroxycholesterol and fecal bile acid excretion in humans

BACKGROUND

Serum levels of 7 alpha-hydroxycholesterol have been shown to reflect the activity of cholesterol 7 alpha-hydroxylase, the key enzyme of bite acid synthesis in the liver, but a comparison with direct measurements of bile acid synthesis rates has never been performed.

METHODS

7 alpha-Hydroxycholesterol was measured by gas-liquid chromatography/mass spectrometry and bile acid synthesis by the fecal balance method in 35 subjects.

RESULTS

A significant correlation was found between 7 alpha-hydroxycholesterol concentration in serum and bile acid synthesis (r = 0.863, p < 0.001). Serum levels of 7 alpha-hydroxycholesterol in 20 patients treated with a 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor did not differ from levels obtained in healthy volunteers (78 +/- 7 ng/ml versus 63 +/- 5 ng/ml; NS). Treatment with fenofibrate reduced 7 alpha-hydroxycholesterol concentrations in six patients from 107 +/- 47 ng/ml to 61 +/- 12 ng/ml (p < 0.05).

CONCLUSIONS

We conclude that the concentration of 7 alpha-hydroxycholesterol in serum is an indicator of bile acid synthesis and that serum levels of 7 alpha-hydroxycholesterol are not affected in patients treated with HMG-CoA reductase inhibitors but are affected in those treated with fenofibrate.

Review of progress in sterol oxidations: 1987-1995

Material dealing with the chemistry, biochemistry, and biological activities of oxysterols is reviewed for the period 1987-1995. Particular attention is paid to the presence of oxysterols in tissues and foods and to their physiological relevance.

Plasma mevalonic acid, an index of cholesterol synthesis in vivo, and responsiveness to HMG-CoA reductase inhibitors in familial hypercholesterolaemia

Fasting plasma mevalonic acid (MVA), an indicator of in vivo cholesterol synthesis, was measured in 35 patients with familial hypercholesterolaemia (FH) of whom 7 were treated with pravastatin 10-40 mg/day, 7 with simvastatin 10-40 mg/day and 21 with atorvastatin 80 mg/day. Reductions in low density lipoprotein (LDL) cholesterol and MVA on maximal dose therapy differed significantly between the three drugs: 34.7%, 42.9% and 54.0% (P = 0.0001), and 31.6%, 48.9% and 58.8% (P = 0.004), respectively. Patients on atorvastatin were subdivided according to whether their reduction in LDL cholesterol on treatment was above or below the mean percentage change for the whole group. Basal values of LDL cholesterol did not differ significantly, but above average responders had a significantly higher mean pre-treatment level of MVA (6.2 +/- 0.60 vs. 4.3 +/- 0.61 ng/ml, P < 0.05) than below average responders. When all three drug groups were pooled above average responders showed a significantly greater absolute decrease in MVA on treatment than below average responders (3.85 +/- 0.48 vs. 2.33 +/- 0.40 ng/ml, P < 0.05). However, there was no significant correlation between the magnitude of the decreases in LDL cholesterol and MVA. These findings suggest that FH patients who responded well to statins had a higher basal level of plasma MVA, i.e. a higher rate of cholesterol synthesis, which was more susceptible to pharmacological inhibition. The more marked cholesterol lowering effect of atorvastatin 80 mg/day presumably reflects, at least in part, its ability to inhibit HMG-CoA reductase to a greater extent than maximal recommended doses of pravastatin and simvastatin of 40 mg/day.

Measurement of mevalonic acid in human urine by bench top gas chromatography-mass spectrometry

Urinary excretion of mevalonate was reported to be correlated with endogenous cholesterol biosynthesis. A method is described whereby mevalonate (MVA) concentration in urine is determined by bench top gas chromatography-mass spectrometry after extraction as mevalonalactone (MVL) and conversion to mevalonolactone mono-TMS derivative. Within- and between-assay coefficients of variation were 4.02% and 8%, respectively. The mean concentration of MVA in 24-h urine collections from ten normolipidemic urinary subjects was 203 +/- 49.6 ng/ml (range: 44-576 ng/ml). Administration of 40 mg of Pravastatin (an HMG-CoA reductase inhibitor) significantly decreased (approximately 50%) the night concentration of MVA in five healthy volunteers. This assay could be useful for investigation of endogenous cholesterol synthesis rate in various dyslipidemias and in response to drug treatment.

Primary dual defect of cholesterol and bile acid metabolism in liver of patients with intrahepatic calculi

BACKGROUND/AIMS

Intrahepatic calculi, which are characterized by cholesterol-rich pigment stones, are highly prevalent in East Asia. Their pathogenesis remains unknown. To elucidate the etiological factors underlying the formation of cholesterol-supersaturated bile, which leads to the formation of cholesterol-rich pigment stones cholesterol and bile acid de novo syntheses in the liver were studied.

METHODS

Liver specimens were assayed for the catalytic activities and steady-state messenger RNA levels of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase and cholesterol 7 alpha-hydroxylase.

RESULTS

The activity of HMG-CoA reductase, consistent with the messenger RNA level, was significantly higher in 13 patients with intrahepatic grown pigment stones (11.2 +/- 1.3 pmol.min-1.mg protein-1 [mean +/- SEM; P < 0.0001] for affected hepatic lobes and 13.4 +/- 1.7 [P < 0.0001] for unaffected ones [P < 0.0001]) than in 19 control subjects (6.4 +/- 0.4) and in 29 patients with gallbladder cholesterol stones (2.1 +/- 0.1). On the other hand, the activity of 7 alpha-hydroxylase, consistent with the messenger RNA level, was significantly lower in patients with intrahepatic brown pigment stones (2.8 +/- 0.5 pmol.min-1.mg protein-1 [P < 0.0001] for affected lobes and 2.6 +/- 0.5 [P < 0.0001] for unaffected ones) than in control subjects (6.0 +/- 0.6) and in patients with cholesterol stones (5.1 +/- 0.5).

CONCLUSIONS

In intrahepatic calculi, the formation of supersaturated bile and cholesterol-rich pigment stones may be attributed to the primary dual defect of up-regulated cholesterogenesis and down-regulated bile acid synthesis in the liver.

Determination of urinary mevalonic acid using isotope dilution technique

A simplified and highly accurate, stable isotope dilution method using gas chromatograph/mass spectrometry (GC/MS) with deuterated (2H7) or (2H7) or (2H3)mevalonic acid (MVA) as internal standard was developed for the measurement of MVA in urine samples. MVA was converted to its lactone (MVL) and transferred with the total water of the sample (100 microliters) to a mixture of acetone/methyl t-butyl ether (MTBE). This solution was concentrated and dried by azeotropic removal of MTBE/water in special vessels (used for volume reduction under partial reflux for solutions containing volatile compounds). After producing MVA by adding NaOH followed by azeotropic drying, MVA was converted to its tris-t-butyldimethylsilyl (tri-TBDMS) derivative. GC/MS selected ion monitoring measurements at m/z 317, m/z 320 and m/z 324 were performed in the electron impact ionization (EI) mode. Overall recoveries of about 70% were obtained as shown by following the procedure with (14C)MVL, (2H7)- and (2H3)MVL as external and/or internal standards. Six replicate analyses of one urine sample revealed a coefficient of variation of 3.3%. Based on this experience we developed two other methods. The second method was based on a fluid/fluid extraction and the third one on an extraction with total water transfer. Both methods are combined with azeotropic drying and showed improved precision, handling and speed.

Determination of 7 alpha-hydroxy-4-cholesten-3-one level in plasma using isotope-dilution mass spectrometry and monitoring its circadian rhythm in human as an index of bile acid biosynthesis

A highly sensitive and specific method has been developed for determination of the level of 7 alpha-hydroxy-4-cholesten-3-one in plasma. This method is based on a stable isotope-dilution technique by gas chromatography-selected-ion monitoring mass spectrometry. 7 alpha-Hydroxy-4-cholesten-3-one was extracted from plasma by saltingout extraction, and then purified by serial solid-phase extractions. The extract was treated with O-methylhydroxyl-amine hydrochloride and then dimethylethylsilylated. The resulting methyloxime-dimethylethylsilyl ether derivative was quantified by gas chromatography-selected-ion monitoring mass spectrometry with a high-resolution mode. The plasma levels of 7 alpha-hydroxy-4-cholesten-3-one were correlated with the cholesterol 7 alpha-hydroxylase activity to a higher degree than those of any other form of 7 alpha-hydroxycholesterol (r = 0.84, n = 16, p < 0.0001). The present method was applied to monitor the circadian rhythm of 7 alpha-hydroxy-4-cholesten-3-one levels in human plasma. It was concluded that the plasma level of 7 alpha-hydroxy-4-cholesten-3-one is a useful index for the monitoring of bile acid biosynthesis in the human liver.

Simple and sensitive quantitation method for mevalonic acid in plasma using gas chromatography/mass spectrometry

The combination of gas chromatography and mass spectrometry using a polar capillary column and isobutane chemical ionization made it possible to determine mevalonic acid (MVA) as the lactone at subnanogram levels using 1 mL of plasma. The pretreatment procedure consisted of only three steps, namely lactonization, washing with chloroform and liquid/liquid extraction. This simple, rapid and sensitive method, having good precision and accuracy, is useful for evaluating the change of plasma MVA, which is well correlated with whole-body cholesterol biosynthesis.

Alterations of bile acid composition in gallstones, bile, and liver of patients with hepatolithiasis, and their etiological significance

A detailed comparison was made of the bile acid composition in gallstones (brown pigment stones) and paired bile and liver from both affected and unaffected lobes by gallstones, which were taken at operation from 16 patients with hepatolithiasis, with the aim of elucidating whether stone formation is derived from possible local disturbances limited to intrahepatic bile ducts. Brown pigment stones in the intrahepatic bile ducts, most of which were accompanied by bile with high cholesterol saturation, had significantly more cholesterol, and less calcium bilirubinate and bile acid than those found in the extrahepatic bile ducts. Intrahepatic gallstones had significantly lower amounts of secondary and unconjugated bile acids, the bile acids modified by bacterial intervention, than extrahepatic stones. Bile specimens from both affected and unaffected lobes showed significantly increased molar percentages of cholesterol and decreased percentages of bile acids than bile from controls. In contrast, liver specimens from both lobes showed significantly higher concentrations of total bile acids. Secondary bile acids were present in a much lower proportion in bile and liver from both lobes than in bile and liver from controls. On the other hand, unconjugated bile acids were present in a much higher proportion in bile and liver from patients and only in negligible amounts in bile from controls. Furthermore, the plasma levels of mevalonate and those of 7 alpha-hydroxy-4-cholestene-3-one were found to be significantly higher and lower in patients than in controls, respectively, indicating that in hepatolithiasis cholesterol synthesis might increase and bile acid synthesis might decrease in the liver. These findings suggested that alterations of bile acid composition in gallstones, bile, and liver of patients with hepatolithiasis may be attributed to not only secondary changes resulting from local disturbances limited to intrahepatic bile ducts but also possible primary alterations of hepatocyte metabolism, such as bile acid conjugation and primary defects in cholesterol and bile acid synthesis.