Serum 27-hydroxycholesterol in patients with primary biliary cirrhosis suggests alteration of cholesterol catabolism to bile acids via the acidic pathway

PCSK9 ablation attenuates Aβ pathology, neuroinflammation and cognitive dysfunctions in 5XFAD mice

BACKGROUND

Increasing evidence highlights the importance of novel players in Alzheimer's disease (AD) pathophysiology, including alterations of lipid metabolism and neuroinflammation. Indeed, a potential involvement of Proprotein convertase subtilisin/kexin type 9 (PCSK9) in AD has been recently postulated. Here, we first investigated the effects of PCSK9 on neuroinflammation in vitro. Then, we examined the impact of a genetic ablation of PCSK9 on cognitive performance in a severe mouse model of AD. Finally, in the same animals we evaluated the effect of PCSK9 loss on Aβ pathology, neuroinflammation, and brain lipids.

METHODS

For in vitro studies, U373 human astrocytoma cells were treated with Aβ fibrils and human recombinant PCSK9. mRNA expression of the proinflammatory cytokines and inflammasome-related genes were evaluated by q-PCR, while MCP-1 secretion was measured by ELISA. For in vivo studies, the cognitive performance of a newly generated mouse line - obtained by crossing 5XFADHet with PCSK9KO mice - was tested by the Morris water maze test. After sacrifice, immunohistochemical analyses were performed to evaluate Aβ plaque deposition, distribution and composition, BACE1 immunoreactivity, as well as microglia and astrocyte reactivity. Cholesterol and hydroxysterols levels in mouse brains were quantified by fluorometric and LC-MS/MS analyses, respectively. Statistical comparisons were performed according to one- or two-way ANOVA, two-way repeated measure ANOVA or Chi-square test.

RESULTS

In vitro, PCSK9 significantly increased IL6, IL1B and TNFΑ mRNA levels in Aβ fibrils-treated U373 cells, without influencing inflammasome gene expression, except for an increase in NLRC4 mRNA levels. In vivo, PCSK9 ablation in 5XFAD mice significantly improved the performance at the Morris water maze test; these changes were accompanied by a reduced corticohippocampal Aβ burden without affecting plaque spatial/regional distribution and composition or global BACE1 expression. Furthermore, PCSK9 loss in 5XFAD mice induced decreased microgliosis and astrocyte reactivity in several brain regions. Conversely, knocking out PCSK9 had minimal impact on brain cholesterol and hydroxysterol levels.

CONCLUSIONS

In vitro studies showed a pro-inflammatory effect of PCSK9. Consistently, in vivo data indicated a protective role of PCSK9 ablation against cognitive impairments, associated with improved Aβ pathology and attenuated neuroinflammation in a severe mouse model of AD. PCSK9 may thus be considered a novel pharmacological target for the treatment of AD.

A Japanese prospective multicenter study of urinary oxysterols in biliary atresia

Diagnosis of biliary atresia (BA) can involve uncertainties. In the present prospective multicenter study, we considered whether urinary oxysterols represent a useful marker for diagnosis of BA in Japanese children. Subjects under 6 months old at 7 pediatric centers in Japan were prospectively enrolled, including patients with cholestasis and healthy controls (HC) without liver disease. Patients with cholestasis constituted 2 groups representing BA patients and others with cholestasis from other causes (non-BA). We quantitatively analyzed 7 oxysterols including 4β-, 20(S)-, 22(S)-, 22(R)-, 24(S)-, 25-, and 27-hydroxycholesterol by liquid chromatography/electrospray ionization-tandem mass spectrometry. Enrolled subjects included 14 with BA (median age 68 days; range 26-170) and 10 non-BA cholestatic controls (59; 14-162), as well as 10 HC (57; 25-120). Total urinary oxysterols were significantly greater in BA (median, 153.0 μmol/mol creatinine; range 24.1-486.7; P < 0.001) and non-BA (36.2; 5.8-411.3; P < 0.05) than in HC (2.7; 0.8-7.6). In patients with BA, urinary 27-hydroxycholesterol (3.61; 0.42-11.09; P < 0.01) was significantly greater than in non-BA (0.71; 0-5.62). In receiver operating characteristic (ROC) curve analysis for distinguishing BA from non-BA, the area under the ROC curve for urinary 27-hydroxycholesterol was 0.83. In conclusion, this first report of urinary oxysterol analysis in patients with BA indicated that 27-hydroxycholesterol may be a useful marker for distinguishing BA from other causes of neonatal cholestasis.

Interactions of Oxysterols with Atherosclerosis Biomarkers in Subjects with Moderate Hypercholesterolemia and Effects of a Nutraceutical Combination (Bifidobacterium longum BB536, Red Yeast Rice Extract) (Randomized, Double-Blind, Placebo-Controlled Study)

Background: Oxysterol relationship with cardiovascular (CV) risk factors is poorly explored, especially in moderately hypercholesterolaemic subjects. Moreover, the impact of nutraceuticals controlling hypercholesterolaemia on plasma levels of 24-, 25- and 27-hydroxycholesterol (24-OHC, 25-OHC, 27-OHC) is unknown. Methods: Subjects (n = 33; 18–70 years) with moderate hypercholesterolaemia (low-density lipoprotein cholesterol (LDL-C:): 130–200 mg/dL), in primary CV prevention as well as low CV risk were studied cross-sectionally. Moreover, they were evaluated after treatment with a nutraceutical combination (Bifidobacterium longum BB536, red yeast rice extract (10 mg/dose monacolin K)), following a double-blind, randomized, placebo-controlled design. We evaluated 24-OHC, 25-OHC and 27-OHC levels by gas chromatography/mass spectrometry analysis. Results: 24-OHC and 25-OHC were significantly correlated, 24-OHC was correlated with apoB. 27-OHC and 27-OHC/total cholesterol (TC) were higher in men (median 209 ng/mL and 77 ng/mg, respectively) vs. women (median 168 ng/mL and 56 ng/mg, respectively); 27-OHC/TC was significantly correlated with abdominal circumference, visceral fat and, negatively, with high-density lipoprotein cholesterol (HDL-C). Triglycerides were significantly correlated with 24-OHC, 25-OHC and 27-OHC and with 24-OHC/TC and 25-OHC/TC. After intervention, 27-OHC levels were significantly reduced by 10.4% in the nutraceutical group Levels of 24-OHC, 24-OHC/TC, 25-OHC, 25-OHC/TC and 27-OHC/TC were unchanged. Conclusions: In this study, conducted in moderate hypercholesterolemic subjects, we observed novel relationships between 24-OHC, 25-OHC and 27-OHC and CV risk biomarkers. In addition, no adverse changes of OHC levels upon nutraceutical treatment were found.

Nutraceutical approach for the management of cardiovascular risk - a combination containing the probiotic Bifidobacterium longum BB536 and red yeast rice extract: results from a randomized, double-blind, placebo-controlled study

BACKGROUND

Probiotics incorporated into dairy products have been shown to reduce total (TC) and LDL cholesterolemia (LDL-C) in subjects with moderate hypercholesterolemia. More specifically, probiotics with high biliary salt hydrolase activity, e.g. Bifidobacterium longum BB536, may decrease TC and LDL-C by lowering intestinal cholesterol reabsorption and, combined with other nutraceuticals, may be useful to manage hypercholesterolemia in subjects with low cardiovascular (CV) risk. This study was conducted to evaluate the efficacy and safety of a nutraceutical combination containing Bifidobacterium longum BB536, red yeast rice (RYR) extract (10 mg/day monacolin K), niacin, coenzyme Q10 (Lactoflorene Colesterolo®). The end-points were changes of lipid CV risk markers (LDL-C, TC, non-HDL-cholesterol (HDL-C), triglycerides (TG), apolipoprotein B (ApoB), HDL-C, apolipoprotein AI (ApoAI), lipoprotein(a) (Lp(a), proprotein convertase subtilisin/kexin type 9 (PCSK9)), and of markers of cholesterol synthesis/absorption.

METHODS

A 12-week randomized, parallel, double-blind, placebo-controlled study. Thirty-three subjects (18-70 years) in primary CV prevention and low CV risk (SCORE: 0-1% in 24 and 2-4% in 9 subjects; LDL-C: 130-200 mg/dL) were randomly allocated to either nutraceutical (N = 16) or placebo (N = 17).

RESULTS

Twelve-week treatment with the nutraceutical combination, compared to placebo, significantly reduced TC (- 16.7%), LDL-C (- 25.7%), non-HDL-C (- 24%) (all p < 0.0001), apoB (- 17%, p = 0.003). TG, HDL-C, apoAI, Lp(a), PCSK9 were unchanged. Lathosterol:TC ratio was significantly reduced by the nutraceutical combination, while campesterol:TC ratio and sitosterol:TC ratio did not change, suggesting reduction of synthesis without increased absorption of cholesterol. No adverse effects and a 97% compliance were observed.

CONCLUSIONS

A 12-week treatment with a nutraceutical combination containing the probiotic Bifidobacterium longum BB536 and RYR extract significantly improved the atherogenic lipid profile and was well tolerated by low CV risk subjects.

TRIAL REGISTRATION

NCT02689934 .

Non-Cholesterol Sterol Concentrations as Biomarkers for Cholesterol Absorption and Synthesis in Different Metabolic Disorders: A Systematic Review

Non-cholesterol sterols are validated biomarkers for intestinal cholesterol absorption and endogenous cholesterol synthesis. However, their use in metabolic disturbances has not been systematically explored. Therefore, we conducted a systematic review to provide an overview of non-cholesterol sterols as markers for cholesterol metabolism in different metabolic disorders. Potentially relevant studies were retrieved by a systematic search of three databases in July 2018 and ninety-four human studies were included. Cholesterol-standardized levels of campesterol, sitosterol and cholestanol were collected to reflect cholesterol absorption and those of lathosterol and desmosterol to reflect cholesterol synthesis. Their use as biomarkers was examined in the following metabolic disorders: overweight/obesity (n = 16), diabetes mellitus (n = 15), metabolic syndrome (n = 5), hyperlipidemia (n = 11), cardiovascular disease (n = 17), and diseases related to intestine (n = 16), liver (n = 22) or kidney (n = 2). In general, markers for cholesterol absorption and synthesis displayed reciprocal patterns, showing that cholesterol metabolism is tightly regulated by the interplay of intestinal absorption and endogenous synthesis. Distinctive patterns for cholesterol absorption or cholesterol synthesis could be identified, suggesting that metabolic disorders can be classified as 'cholesterol absorbers or cholesterol synthesizers'. Future studies should be performed to confirm or refute these findings and to examine whether this information can be used for targeted (dietary) interventions.

Lipoprotein-X fifty years after its original discovery

AIMS

To review the formation, catabolism, and the possible atherogenic properties of Lp-X.

DATA SYNTHESIS

The conversion of cholesterol to bile acids is regulated by several mechanisms including cholesterol 7 alpha hydroxylase, fibroblast growth factor 19, and farnesoid X receptors. During cholestasis these mechanisms are altered and there is an accumulation of bile acids and cholesterol in plasma. The hypercholesterolemia observed in cholestasis is due to the presence of an anomalous lipoprotein called lipoprotein-X (Lp-X). Lp-X is a lipoprotein rich in phospholipid and free cholesterol present in plasma of patients with cholestasis and, with some variations, in patients with lecithin-cholesterol-acyl-transferase deficiency (LCAT), and after lipid infusion. Lp-X is formed from a bile lipoprotein moving to the blood vessels where it incorporates small quantities of triglycerides, apo-C and esterified cholesterol and becomes a "mature" Lp-X. The activity of the phosphatidilcholine canalicular transporter Mdr2 P-glycoprotein (homologous to the human ABCB4) is essential for LpX appearance, since its suppression abolishes Lp-X formation. However, the concentration of Lp-X in plasma is determined also by the degree of the cholestasis, the residual liver function, and the LCAT deficiency. The Lp-X catabolism seems to be mediated by the reticuloendothelial system and possibly the kidney.

CONCLUSIONS

Lp-X might be considered a defense mechanism against the toxic effect of free cholesterol in cholestasis. The frequency of cardiovascular events in patients affected by primary biliary cholangitis, in whom the Lp-X is present in high concentration, are not increased. Further studies could now clarify the remaining open questions on the role of Lp-X in the dyslipidemia of cholestasis.

Low-density lipoprotein oxidation biomarkers in human health and disease and effects of bioactive compounds

Based on the significance of oxidized low-density lipoprotein (LDL) in health and disease, this review focuses on human studies addressing oxidation of LDL, including three lines of biomarkers, (i) ex vivo LDL resistance to oxidation, a "challenge test" model, (ii) circulating oxidized LDL, indicating the "current in vivo status", and (iii) autoantibodies against oxidized LDL as fingerprints of an immune response to oxidized LDL, along with circulating oxysterols and 4-hydroxynonenal as biomarkers of lipid peroxidation. Lipid peroxidation and oxidized LDL are hallmarks in the development of various metabolic, cardiovascular and other diseases. Changes further occur across life stages from infancy to older age as well as in athletes and smokers. Given their responsiveness to targeted nutritional interventions, markers of LDL oxidation have been employed in a rapidly growing number of human studies for more than 2 decades. There is growing interest in foods, which, besides providing energy and nutrients, exert beneficial effects on human health, such as protection of DNA, proteins and lipids from oxidative damage. Any health claim, however, needs to be substantiated by supportive evidence derived from human studies, using reliable biomarkers to demonstrate such beneficial effects. A large body of evidence has accumulated, demonstrating protection of LDL from oxidation by bioactive food compounds, including vitamins, other micronutrients and secondary plant ingredients, which will facilitate the selection of oxidation biomarkers for future human intervention studies and health claim support.

Evaluation of cholesterol metabolism in cerebrotendinous xanthomatosis

BACKGROUND

Cerebrotendinous xanthomatosis (CTX) is a treatable bile acid disorder caused by mutations of CYP27A1. The pathogenesis of neurological damage has not been completely explained. Oral chenodeoxycholic acid (CDCA) can lead to clinical stabilization, but in a subgroup of patients the disease progresses despite treatment. In the present study, we aimed at clarifying cholesterol metabolism abnormalities and their response to CDCA treatment, in order to identify reliable diagnostic and prognostic markers and understand if differences exist between stable patients and those with neurological progression.

METHODS

We enrolled 19 untreated CTX patients and assessed serum profile of bile acids intermediates, oxysterols, cholesterol, lathosterol, and plant sterols. Then we performed a long-term follow up during CDCA therapy, and compared biochemical data with neurological outcome.

RESULTS

We observed increase of cholestanol, 7α-hydroxy-4-cholesten-3-one (7αC4), lathosterol, and plant sterols, whereas 27-hydroxycholesterol (27-OHC) was extremely low or absent. CDCA treatment at a daily dose of 750 mg normalized all biochemical parameters except for 7αC4 which persisted slightly higher than normal in most patients, and 27-OHC which was not modified by therapy. Biochemical evaluation did not reveal significant differences between stable and worsening patients.

DISCUSSION

Cholestanol and 7αC4 represent important markers for CTX diagnosis and monitoring of therapy. Treatment with CDCA should aim at normalizing serum 7αC4 as well as cholestanol, since 7αC4 better mirrors 7α-hydroxylation rate and is thought to be correlated with cholestanol accumulation in the brain. Assessment of serum 27-OHC is a very good tool for biochemical diagnosis at any stage of disease. Lathosterol and plant sterols should be considered as additional markers for diagnosis and monitoring of therapy. Further studies including long-term assessment of bile acid intermediates in cerebrospinal fluid are needed in patients who show clinical progression despite treatment.

Cholesterol metabolism after bariatric surgery in grade 3 obesity: differences between malabsorptive and restrictive procedures

OBJECTIVE

Malabsorptive bariatric surgery (biliopancreatic diversion and biliointestinal bypass [BIBP]) reduces serum cholesterol levels more than restrictive surgery (adjustable gastric banding [AGB]), and this is thought to be due to greater weight loss. Our aim was to evaluate the changes of cholesterol metabolism induced by malabsorptive and restrictive surgery independent of weight loss.

RESEARCH DESIGN AND METHODS

In a nonrandomized, self-selected, unblinded, active-comparator, bicenter, 6-month study, glucose metabolism (blood glucose and serum insulin levels and homeostasis model assessment of insulin resistance [HOMA-IR] index) and cholesterol metabolism (absorption: serum campesterol and sitosterol levels; synthesis: serum lathosterol levels; catabolism: rate of appearance and serum concentrations of serum 7-α- and serum 27-OH-cholesterol after infusions of deuterated 7-α- and 27-OH-cholesterol in sequence) were assessed in grade 3 obesity subjects undergoing BIBP (n = 10) and AGB (n = 10). Evaluations were performed before and 6 months after surgery.

RESULTS

Subjects had similar values at baseline. Weight loss was similar in the two groups of subjects, and blood glucose, insulin levels, HOMA-IR, and triglycerides decreased in a similar way. In contrast, serum cholesterol, LDL cholesterol, non-HDL cholesterol, serum sitosterol, and campesterol levels decreased and lathosterol levels increased only in BIBP subjects, not in AGB subjects. A significant increase in 7-α-OH-cholesterol occurred only with BIBP; serum 27-OH-cholesterol decreased in both groups.

CONCLUSIONS

Malabsorptive surgery specifically affects cholesterol levels, independent of weight loss and independent of glucose metabolism and insulin resistance. Decreased sterol absorption leads to decreased cholesterol and LDL cholesterol levels, accompanied by enhanced cholesterol synthesis and enhanced cholesterol catabolism. Compared with AGB, BIBP provides greater cholesterol lowering.

Effects of bile duct ligation and cholic acid treatment on fatty liver in two rat models of non-alcoholic fatty liver disease

BACKGROUND

Non-alcoholic fatty liver disease, one of the most prevalent liver disorders in Western countries, is characterized by hepatic accumulation of triglycerides. Bile acids have long been known to affect triglyceride homeostasis through a not completely understood mechanism.

AIM

To analyse the effects of two different manipulations of bile acid circulation on non-alcoholic fatty liver disease.

METHODS

Two animal models of non-alcoholic fatty liver disease were developed by either feeding rats with a choline deficient or with a high fat diet. After 4 weeks, rats were randomized to undergo either bile duct ligation, sham operation or cholic acid administration.

RESULTS

During cholestasis there was an increased CYP7A1 expression, the rate limiting enzyme in bile acid synthesis, and a reduction of hepatic concentration of oxysterols, ligands of the liver X receptors. Target genes of the liver X receptors, involved in fatty acid and triglyceride synthesis, were down-regulated in association with decreased hepatic triglyceride content and improvement of fatty liver. Administration of cholic acid, ligand of farnesoid X receptor, also had a beneficial effect on fatty liver in rats on choline deficient diet.

CONCLUSION

These results indicate that pharmacological approaches increasing the expression of CYP7A1 or stimulating farnesoid X receptor pathway could represent a promising treatment for non-alcoholic fatty liver disease.

Increased appearance rate of 27-hydroxycholesterol in vivo in hypercholesterolemia: a possible compensatory mechanism

BACKGROUND AND AIMS

The first step in the alternative pathway of bile acid biosynthesis is the 27-hydroxylation of cholesterol, which takes place both in liver and extrahepatic tissues. This pathway is believed to play a role in peripheral cholesterol degradation. Aim of this study was to investigate the impact of hyperlipidemia on 27-hydroxycholesterol appearance rate, and to assess the effects induced by treatment with statins.

METHODS AND RESULTS

Seven patients with familial hypercholesterolemia and eight patients with familial combined hyperlipidemia underwent determination of 27-hydroxylation rates in vivo by i.v. infusion of deuterated 27-hydroxycholesterol. Isotope enrichment was assayed by gas chromatography-mass spectrometry, allowing to calculate 27-hydroxycholesterol appearance rates. Six normocholesterolemic subjects were regarded as controls. In some hypercholesterolemic patients the infusions were repeated during treatment with atorvastatin or rosuvastatin. Hydroxylation rates were higher in hypercholesterolemic patients (8.7 ± 2.5 mg/h; controls, 3.4 ± 2.0 mg/h; combined hyperlipidemia, 4.4 ± 1.6 mg/h; mean ± SD, P < 0.01 vs both). After statin treatment, both plasma cholesterol levels and hydroxylation rates dropped by nearly 50%. No difference was detectable between the two statins. A linear correlation was shown between plasma cholesterol and 27-hydroxylation rates.

CONCLUSION

Hypercholesterolemia associates with increased 27-hydroxycholesterol appearance rates, which decrease during hypocholesterolemic treatment. The correlation with cholesterol levels supports the view that 27-hydroxylation may act as a compensatory mechanism in a condition of larger plasma cholesterol pool. A regulatory role for hepatic and extrahepatic nuclear receptors seems reasonable. These data prompt novel pharmacological approaches for the management of hypercholesterolemia and the prevention of atherosclerosis.

The use of stable and radioactive sterol tracers as a tool to investigate cholesterol degradation to bile acids in humans in vivo

Alterations of cholesterol homeostasis represent important risk factors for atherosclerosis and cardiovascular disease. Different clinical-experimental approaches have been devised to study the metabolism of cholesterol and particularly the synthesis of bile acids, its main catabolic products. Most evidence in humans has derived from studies utilizing the administration of labeled sterols; these have several advantages over in vitro assay of enzyme activity and expression, requiring an invasive procedure such as a liver biopsy, or the determination of fecal sterols, which is cumbersome and not commonly available. Pioneering evidence with administration of radioactive sterol derivatives has allowed to characterize the alterations of cholesterol metabolism and degradation in different situations, including spontaneous disease conditions, aging, and drug treatment. Along with the classical isotope dilution methodology, other approaches were proposed, among which isotope release following radioactive substrate administration. More recently, stable isotope studies have allowed to overcome radioactivity exposure. Isotope enrichment studies during tracer infusion has allowed to characterize changes in the degradation of cholesterol via the "classical" and the "alternative" pathways of bile acid synthesis. Evidence brought by tracer studies in vivo, summarized here, provides an exceptional tool for the investigation of sterol metabolism, and integrate the studies in vitro on human tissue.

Oxysterols in bile acid metabolism

Increasing body of evidence is available indicating that oxysterols are more much than intermediates of metabolic pathways. Oxysterols play a role in the regulation of cholesterol synthesis, transport and efflux. A scavenger effect of cholesterol 27-hydroxylase on elevated serum cholesterol levels is well demonstrated. Bile acid synthesis occurs through two main pathways, the classic and the alternative ones. Since plasma concentrations of 27-hydroxycholesterol were clearly shown to reflect its production rate the alternative pathway of bile acid synthesis can be easily explored. Conversely this was not true for 7α-hydroxycholesterol and also the direct evaluation of the classic pathway by kinetic studies is more difficult since the rate of plasma appearance during continuous infusion of deuterated isotopomers may not exactly measure its production rate. Hepatic cholesterol 7alpha-hydroxylase activity is absent during fetal life in humans and upregulates after birth. Both the classic and alternative pathways become mature after the age of 4 years. It has been clearly demonstrated that in patients with liver disease the classic pathway is impaired while the alternative one is preserved. Conversely, in obese patients, preliminary data suggest an increase of the production rate of 27-hydroxycholesterol, a possible mechanism to counteract the increase of atherosclerotic risk.

Atorvastatin does not improve liver biochemistries or Mayo Risk Score in primary biliary cirrhosis

Statin treatment reduces hypercholesterolemia and may be anti-inflammatory. Case reports noted decreased alkaline phosphatase and histological improvement following statin treatment in primary biliary cirrhosis. The objective of this study was to assess the long-term effects of statin treatment in primary biliary cirrhosis. A retrospective analysis compared clinical and biochemical data from 15 hypercholesterolemic individuals with primary biliary cirrhosis who were treated long-term with atorvastatin with an age and gender matched, primary biliary cirrhosis control group. A significant decrease in total cholesterol and low-density lipoprotein (LDL)-cholesterol (p < or = 0.002) was observed throughout atorvastatin treatment (median time 2.5 years). LDL-cholesterol levels in the control group were not significantly changed after 2 years (p > 0.050). No significant changes were noted in alanine aminotransferase (ALT), alkaline phosphatase, total bilirubin and Mayo Risk Score in either group (p > 0.05). Long-term atorvastatin treatment reduced LDL-cholesterol in primary biliary cirrhosis, but there was no evidence of any anti-inflammatory effect.

Changes in classic and alternative pathways of bile acid synthesis in chronic liver disease

BACKGROUND

Cholesterol elimination occurs through bile acid synthesis that starts within the liver from 7alpha-hydroxylation or in extrahepatic tissues from 27-hydroxylation. This study was aimed at investigating in vivo these two pathways in patients with chronic liver disease.

METHODS

Serum concentrations of 7alpha- and 27-hydroxycholesterol were measured in 54 patients (29 with primary biliary cirrhosis and 25 with chronic hepatitis C) and 18 controls. The rate of oxysterol plasma appearance was calculated after intravenous infusions of deuterated 7alpha- and 27-hydroxycholesterol in patients (n=8) and control subjects (n=8) who gave consent. The expression of sterol 27-hydroxylase was evaluated in macrophages isolated from 20 subjects.

RESULTS

In patients with liver disease, the rate of plasma appearance of 7alpha-hydroxycholesterol was significantly reduced (1.44+/-0.96 vs. 2.75+/-1.43 mg/hour, p=0.03), the degree of reduction being related with the severity of the disease (p=0.01) whereas that of 27-hydroxycholesterol was unaffected. The rate of plasma appearance of 27-hydroxycholesterol was significantly related to its serum concentrations (r=0.54, p=0.03) and to its release from cultured macrophages ( r=0.85, p=0.03).

CONCLUSIONS

In liver disease 7alpha-hydroxylation of cholesterol seems to be impaired while 27-hydroxylation is unaffected. Serum concentrations of 27-hydroxycholesterol are useful to obtain information on the activity of this alternative pathway.

Biliary lipids, cholesterol and bile synthesis: different adaptive mechanisms to dietary cholesterol in lean and obese subjects

BACKGROUND

Increased biliary cholesterol secretion together with elevated cholesterol synthesis may predispose obese subjects to cholesterol gallstone formation.

AIM

To investigate whether processing of dietary cholesterol is altered in obesity, we enrolled eight lean and seven obese subjects in a double-blind crossover study.

METHODS

Cholesterol consumption was 300 mg/day on low and 1300 mg/day on high cholesterol diet. After 3 weeks on either diet, hepatic bile was collected to determine biliary lipid secretion, and bile salt composition by high-performance liquid chromatography and cholesterol saturation index was calculated. Cholesterol synthesis was measured employing mass isotopomer distribution analysis. Bile acid synthesis via neutral and acidic pathway was assessed by serum levels of 7alpha-hydroxy-4-cholesten-3-one and 27-hydroxycholesterol.

RESULTS

Cholesterol synthesis was increased in obese compared with lean and feedback inhibited only in obese. On low cholesterol diet, cholesterol secretion was doubled in obese but bile acid composition and synthesis was similar between the two groups. After high cholesterol diet, cholesterol saturation index and bile secretion were unchanged. In contrast to obese, lean increased bile acid synthesis only via the acidic pathway.

CONCLUSIONS

Dietary cholesterol appears to preferentially induce bile acid synthesis via the acidic pathway in lean, whereas cholesterol synthesis was inhibited in obese. Thus, stable cholesterol saturation index may be achieved by different mechanisms.

A minimally invasive technique for the evaluation of the regulatory steps of the two major pathways of bile acid synthesis

BACKGROUND

Bile acid synthesis accounts for more than 95% of total cholesterol catabolism per day. We have developed a minimally invasive technique in humans that quantifies the rates of plasma appearance of 7alpha- and 27-hydroxycholesterol, representing the first steps of the "classical" and "alternative" pathways of bile acid synthesis, respectively.

METHODS

For this purpose, during the intravenous infusion of synthetic deuterated isotopomers of 7alpha-hydroxycholesterol and 27-hydroxycholesterol plasma samples are collected and analysed by a GC-MS based method that allows to quantify the exogenous/natural isotopomer ratio of the two sterols. From this data, the rates of plasma appearance of 7alpha- and 27-hydroxycholesterol are calculated.

RESULTS

In a group of healthy individuals steady state kinetics are obtained during a 2 h period yielding mean values of 2.0+/-0.8 and 3.7+/-0.6 mg/h for 7alpha- and 27-hydroxycholesterol, respectively. The data are consistent with findings using older techniques that require studies over several days.

CONCLUSION

Considering that at steady state of the exogenous/natural isotopomer ratio the plasma appearance of the two regulatory hydroxysterols are related to the rate of bile acid synthesis via the "classical" and the "alternative" pathways, respectively, the proposed method could be used to evaluate the immediate effects of different diets and drugs and other determinants on cholesterol catabolism.

Altered levels of plasma 24S- and 27-hydroxycholesterol in demented patients

Alterations in brain cholesterol metabolism and reduced 24S-hydroxycholesterol plasma levels have been described in Alzheimer's disease (AD) and vascular dementia (VD). We hypothesize that changes in peripheral cholesterol metabolism, such as alterations in the plasma levels of 27-hydroxycholesterol, might also be involved. Plasma levels of 24S-hydroxycholesterol and 27-hydroxycholesterol in patients suffering from dementing disorders such as AD, VD, and mild cognitive impairment (MCI) were compared to those in age- and cholesterol matched non-demented and depressed subjects. Cholesterol corrected concentrations of plasma 24S-hydroxycholesterol and 27-hydroxycholesterol were significantly reduced in patients with dementing disorders compared to non-demented subjects and depressed patients. A strong positive correlation between plasma 24S-hydroxycholesterol and 27-hydroxycholesterol levels was observed. The ratios of plasma 24S-hydroxycholesterol to 27-hydroxycholesterol were higher in patients with dementing disorders compared to non-demented subjects. Our results support the observation, that cholesterol metabolism is altered in dementing disorders, indicated by different plasma concentrations of brain specific and peripherally produced oxysterols.

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.

Kinetics and plasma concentrations of 26-hydroxycholesterol in baboons

26-Hydroxycholesterol (26OHC), a major oxysterol in human blood, is believed to play an important role in reverse cholesterol transport, bile acid formation, and regulation of various cellular processes. Using isotope dilution mass spectrometry, we measured plasma 26OHC concentrations in baboons fed either a high cholesterol/saturated fat (HC-SF) or normal chow diet. Plasma 26OHC levels in baboons were comparable to those reported for humans and were positively correlated with plasma cholesterol concentrations. Animals on the HC-SF diet had significantly higher 26OHC levels (0.274+/-0.058 microM, mean+/-S.D.) than those on the chow diet (0.156+/-0.046 microM). In separate experiments, [(3)H]26OHC was injected into four tethered baboons, and multiple blood samples drawn over a 1-h period were analyzed for [(3)H]26OHC and 26OHC. Fitting the specific radioactivity data to a two-pool compartmental model indicated a rapidly turning over plasma compartment (t(1/2) 2.9-6.0 min) and a second compartment with slow turnover (t(1/2) 76-333 min). The calculated 26OHC production rate was 2.5 micromol/kg body weight/day. Assuming all 26OHC is converted to bile acids, the 26OHC production rate corresponds to about 10% of total bile acid production in adult baboons. These results indicate that rapid turnover of plasma 26OHC at submicromolar concentrations could significantly contribute to bile acid synthesis.