Serum lathosterol concentration is an indicator of whole-body cholesterol synthesis in humans

The Diagnostic Use of the Plasma Quantification of 24S-Hydroxycholesterol and Other Oxysterols in Neurodegenerative Disease

Cholesterol regulates fluidity and structure of cellular membranes. The brain is involved in signal transduction, synaptogenesis, and membrane trafficking. An impairment of its metabolism was observed in different neurodegenerative diseases, such as Multiple Sclerosis, Alzheimer, and Huntington diseases. Because of the blood-brain barrier, cholesterol cannot be uptaken from the circulation and all the cholesterol is locally synthetized. The excess cholesterol in neurons is converted into 24S-hydroxycholesterol (24OHC) by the cholesterol 24-hydroxylase (CYP46A1). The plasmatic concentration of 24OHC results in the balance between cerebral production and liver elimination. It is related to the number of metabolically active neurons in the brain. Several factors that affect the brain cholesterol turnover and the liver elimination of oxysterols, the genetic background, nutrition, and lifestyle habits were found to significantly affect plasma levels of 24OHC. Reduced levels of 24OHC were found related to the loss of metabolically active cells and the degree of brain atrophy. The dysfunction of the blood-brain barrier, inflammation, and increased cholesterol turnover might overlap with this progressive reduction giving temporary increased levels of 24OHC.The study of plasma 24OHC is likely to offer an insight into brain cholesterol turnover with a limited diagnostic power.

Long-term administration of intravenous Trappsol® Cyclo™ (HP-β-CD) results in clinical benefits and stabilization or slowing of disease progression in patients with Niemann-Pick disease type C1: Results of an international 48-week Phase I/II trial

Background

Niemann-Pick disease type C (NPC) is a rare, fatal, pan-ethnic, autosomal recessive lysosomal storage disease characterized by progressive major organ failure and neurodegeneration. Preclinical studies confirmed a critical role of systemically administered hydroxypropyl-β-cyclodextrin (HP-β-CD; Trappsol® Cyclo™) in cholesterol metabolism and homeostasis in peripheral tissues of the body, including the liver, and in the central nervous system (CNS). Herein, the pharmacokinetics (PK), safety, and efficacy of HP-β-CD, and biomarkers of NPC were assessed in pediatric and adult patients with NPC1.

Methods

This was a multicenter, Phase I/II, randomized, double-blind, parallel-group, 48-week study (ClinicalTrials.gov identifier NCT02912793) to compare the PK of three different single intravenous (IV) doses of HP-β-CD in pediatric and adult patients with NPC1 and to evaluate the efficacy and tolerability of three different dosages of HP-β-CD in patients with NPC1 after long-term treatment. Twelve patients aged at least 2 years (2-39 years of age) with a confirmed diagnosis of NPC1 were randomized to receive one of three IV doses of HP-β-CD (1500 mg/kg, 2000 mg/kg, or 2500 mg/kg) every 2 weeks for 48 weeks. All patients received HP-β-CD; there was no placebo or other control. PK testing of plasma and cerebrospinal fluid (CSF) was at set times after the first infusion. Pharmacodynamic assessments included biomarkers of cholesterol metabolism (synthesis and breakdown products), N-palmitoyl-O-phosphocholineserine (PPCS), and specific biomarkers of CSF neurodegeneration (including total Tau), CNS inflammation (glial fibrillary acidic protein [GFAP] and tumor necrosis factor α [TNFα]), CNS cholesterol metabolism (24S-hydroxycholesterol) and inflammatory markers. Efficacy measures included clinical disease severity, neurologic symptoms, and clinical impressions of improvement. Safety assessment included physical examination, vital signs, clinical safety laboratory assessment and adverse events (AEs).

Results

Nine patients completed the study, 2 in the 1500 mg/kg group, 4 in the 2000 mg/kg group and 3 in the 2500 mg/kg group. Three patients (all in the 1500 mg/kg group) discontinued the study because of either physician decision/site Principal Investigator (PI) discretion, withdrawal by subject/patient/parent/guardian, or other non-safety reasons. In 5 patients who underwent serial lumbar punctures, HP-β-CD was detected in the CSF. Of the 9 patients who completed the study, 8 (88.9%) improved in at least two domains of the 17-Domain Niemann-Pick disease Type C-Clinical Severity Scale (17D-NPC-CSS), and 6 of these patients improved in at least one domain viewed by patients and their caregivers to be key to quality of life, namely, speech, swallow, fine and gross motor skills, and cognition. Of the 9 patients who completed the study, 7 were viewed by their treating physicians as having improved to some degree at the end of the study, and 2 remained stable; both outcomes are highly relevant in a progressive neurodegenerative disease. Some patients and families reported improvement in quality of life.All three doses of HP-β-CD were well tolerated overall, with most treatment-emergent adverse events transient, mild-to-moderate in nature, and considered by the site PIs to be not related to study drug.

Interpretation

This 48-week trial is the longest to date to evaluate the safety, tolerability, and efficacy across multiple clinical endpoints of IV administration of Trappsol® Cyclo™ (HP-β-CD) in NPC1 patients. In pediatric and adult patients with NPC, Trappsol® Cyclo™ IV improved clinical signs and symptoms and was generally well tolerated. The findings presented here demonstrate a favorable benefit-risk profile and support the global pivotal trial now underway to evaluate the long-term treatment benefits and the potential of Trappsol® Cyclo™ as a disease-modifying treatment in this patient population.

Effects of Heat-Moisture-Treated High-Amylose Rice Flour on Body Weight, Lipid Metabolism, and Gut Microbiome Composition in Obese Rats

The rising prevalence of lifestyle diseases, such as type 2 diabetes, cardiovascular diseases, and metabolic syndrome, has increased the need for effective dietary interventions. This study aimed to evaluate the effects of heat-moisture-treated high-amylose rice (HA-HMT) on body weight, lipid metabolism, and gut microbiome composition in a rat model of obesity. Starch digestibility-specifically, resistant starch-has been shown to provide various health benefits, including improved metabolic health and gut microbiome composition. We employed a sequential approach: firstly, utilizing diet-induced obesity rat models fed with HMT-processed and HMT-non-processed low- or high-amylose rice to investigate the potential of amylose content or HMT to alter phenotypic characteristics and lipid metabolism; and secondly, using the optimal rice flour identified in the previous step to explore the underlying mechanisms. Our findings indicate that heat-moisture treatment, rather than the level of the amylose content of the rice, contributes to the observed anti-obesity and cholesterol-lowering effects. We identified candidate genes contributing to the cholesterol-regulating potential and demonstrated that HMT rice flour could influence the gut microbiome, particularly the Ruminococcus taxa. This study provides valuable insights into the health benefits of HA-HMT rice and supports its potential as a functional food ingredient in the management of obesity and cholesterol-related disorders.

Phenotype-genotype correlation in aldosterone-producing adenomas characterized by intracellular cholesterol metabolism

Aldosterone-producing adenoma (APA) is histologically composed of clear and compact tumor cells. KCNJ5- mutated APAs were reported to be associated with higher plasma aldosterone concentration and more abundant clear tumor cells containing lipid droplets than non-KCNJ5- mutated APAs. However, the association among cholesterol uptake and/or synthesis, cellular morphology and genotypes has remained unknown. Therefore, in order to explore these differences, 52 APA cases (KCNJ5 mt: n = 33, non-KCNJ5 mt: n = 19; ATP1A1: n = 3, ATP2B3: n = 3, CACNA1D: n = 5, CTNNB1: n = 1, tumors without any mutation above: n = 7), zona glomerulosa (ZG) tissue adjacent to APA and 10 non-pathological adrenal glands (NAs) were examined for quantitative histopathological analysis of tumor morphology and immunohistochemical analysis of cholesterol receptors (SR-B1, LDL-R), cholesterol metabolic enzymes (ACAT1, ACAT2, HSL, DHCR24, StAR), and the enzymes required for steroid synthesis (CYP11A1, CYP17A, 3βHSD, CYP11B1, CYP11B2). Gas chromatography-mass spectrometry (GC-MS) analysis was further performed to profile cholesterol precursors and metabolites in 21 APA cases (KCNJ5 mt: n = 16, non-KCNJ5 mt: n = 5) and 14 adrenal cortex of adjacent adrenal tissues. Results demonstrated that both SR-B1 and DHCR24 were significantly lower in the ZG than in fasciculata or reticularis of NAs but LDL-R was not significantly different among them in immunohistochemical analysis. SR-B1 and DHCR24 were both significantly higher in APAs than in ZG tissue adjacent to APA. In GC-MS analysis, most cholesterol precursors and metabolites, except for lanosterol, and their metabolic ratios (= concentration of cholesterol/ precursor) were higher in APAs than in the adjacent adrenal cortex tissue. LDL-R, ACAT1/2, HSL, DHCR24 were all significantly lower in clear than in compact tumor cells of APA. LDL-R was significantly lower and cholesterol/lanosterol ratio was significantly higher in KCNJ5- mutated than non-KCNJ5- mutated APAs. We demonstrated SR-B1 mediated selective uptake of cholesterol ester and de novo cholesterol synthesis were both enhanced in APAs. In addition, cholesterol uptake and metabolism were different between clear and compact tumor cells. KCNJ5- mutated APAs were predominantly composed of clear tumor cells containing abundant cholesteryl ester but less activated LDL-R mediated uptake and increased de novo synthesis. Those findings above indicated their more pronounced functional deviation from the normal ZG cells in terms of their steroidogenic and intracellular cholesterol metabolism.

From Dietary Cholesterol to Blood Cholesterol, Physiological Lipid Fluxes, and Cholesterol Homeostasis

Dietary cholesterol (C) is a major contributor to the endogenous C pool, and it affects the serum concentration of total C, particularly the low-density lipoprotein cholesterol (LDL-C). A high serum concentration of LDL-C is associated with an increased risk for atherosclerosis and cardiovascular diseases. This concentration is dependent on hepatic C metabolism creating a balance between C input (absorption and synthesis) and C elimination (conversion to bile acids and fecal excretion). The daily C absorption rate is determined by dietary C intake, biliary C secretion, direct trans-intestinal C excretion (TICE), and the fractional C absorption rate. Hepatic C metabolism coordinates C fluxes entering the liver via chylomicron remnants (CMR), LDL, high-density lipoproteins (HDL), hepatic C synthesis, and those leaving the liver via very low-density lipoproteins (VLDL), biliary secretion, and bile acid synthesis. The knowns and the unknowns of this C homeostasis are discussed.

Exposure to environmental contaminants is associated with altered hepatic lipid metabolism in non-alcoholic fatty liver disease

BACKGROUND & AIMS

Recent experimental models and epidemiological studies suggest that specific environmental contaminants (ECs) contribute to the initiation and pathology of non-alcoholic fatty liver disease (NAFLD). However, the underlying mechanisms linking EC exposure with NAFLD remain poorly understood and there is no data on their impact on the human liver metabolome. Herein, we hypothesized that exposure to ECs, particularly perfluorinated alkyl substances (PFAS), impacts liver metabolism, specifically bile acid metabolism.

METHODS

In a well-characterized human NAFLD cohort of 105 individuals, we investigated the effects of EC exposure on liver metabolism. We characterized the liver (via biopsy) and circulating metabolomes using 4 mass spectrometry-based analytical platforms, and measured PFAS and other ECs in serum. We subsequently compared these results with an exposure study in a PPARa-humanized mouse model.

RESULTS

PFAS exposure appears associated with perturbation of key hepatic metabolic pathways previously found altered in NAFLD, particularly those related to bile acid and lipid metabolism. We identified stronger associations between the liver metabolome, chemical exposure and NAFLD-associated clinical variables (liver fat content, HOMA-IR), in females than males. Specifically, we observed PFAS-associated upregulation of bile acids, triacylglycerols and ceramides, and association between chemical exposure and dysregulated glucose metabolism in females. The murine exposure study further corroborated our findings, vis-à-vis a sex-specific association between PFAS exposure and NAFLD-associated lipid changes.

CONCLUSIONS

Females may be more sensitive to the harmful impacts of PFAS. Lipid-related changes subsequent to PFAS exposure may be secondary to the interplay between PFAS and bile acid metabolism.

LAY SUMMARY

There is increasing evidence that specific environmental contaminants, such as perfluorinated alkyl substances (PFAS), contribute to the progression of non-alcoholic fatty liver disease (NAFLD). However, it is poorly understood how these chemicals impact human liver metabolism. Here we show that human exposure to PFAS impacts metabolic processes associated with NAFLD, and that the effect is different in females and males.

Associations between Circulating Markers of Cholesterol Homeostasis and Macrovascular Events among Patients Undergoing Hemodialysis

Current strategies targeting serum cholesterol bring limited benefits to mortality and macrovascular events prevention among hemodialysis patients. Direct measurements and analysis on circulating markers of cholesterol homeostasis could be promising solutions to this bottleneck. We prospectively enrolled 90 maintenance hemodialysis patients and 9 healthy controls in 2019 for 1 year. We measured circulating desmosterol and lathosterol as markers for cholesterol synthesis and campesterol and sitosterol for cholesterol absorption. At baseline, hemodialysis patients showed higher levels of campesterol (p = 0.023) compared to healthy controls. During follow-up, we identified 14 (15.4%) patients who experienced macrovascular events. Comparisons of cholesterol homeostasis markers between cohorts with and without macrovascular events showed no significant differences in markers of cholesterol synthesis or absorption. Using logistic regression analysis, the odds ratio was not statistically significant for the prediction of macrovascular events after full-adjusting for age, sex, diabetes, serum albumin, cholesterol, and triglyceride. We concluded that hemodialysis patients demonstrated higher level of cholesterols absorption, indicated by circulating campesterol compared to healthy subjects. Markers for cholesterol homeostasis were not significantly associated with macrovascular events during a 1-year follow-up. Our results shed light on the novel therapeutic target of modulating cholesterol absorption in HD patients.

A case of ezetimibe-effective hypercholesterolemia with a novel heterozygous variant in ABCG5

Sitosterolemia is caused by homozygous or compound heterozygous gene mutations in either ATP-binding cassette subfamily G member 5 (ABCG5) or 8 (ABCG8). Since ABCG5 and ABCG8 play pivotal roles in the excretion of neutral sterols into feces and bile, patients with sitosterolemia present elevated levels of serum plant sterols and in some cases also hypercholesterolemia. A 48-year-old woman was referred to our hospital for hypercholesterolemia. She had been misdiagnosed with familial hypercholesterolemia at the age of 20 and her serum low-density lipoprotein cholesterol (LDL-C) levels had remained about 200-300 mg/dL at the former clinic. Although the treatment of hydroxymethylglutaryl-CoA (HMG-CoA) reductase inhibitors was ineffective, her serum LDL-C levels were normalized by ezetimibe, a cholesterol transporter inhibitor. We noticed that her serum sitosterol and campesterol levels were relatively high. Targeted analysis sequencing identified a novel heterozygous ABCG5 variant (c.203A>T; p.Ile68Asn) in the patient, whereas no mutations were found in low-density lipoprotein receptor (LDLR), proprotein convertase subtilisin/kexin type 9 (PCSK9), or Niemann-Pick C1-like intracellular cholesterol transporter 1 (NPC1L1). While sitosterolemia is a rare disease, a recent study has reported that the incidence of loss-of-function mutation in the ABCG5 or ABCG8 gene is higher than we thought at 1 in 220 individuals. The present case suggests that serum plant sterol levels should be examined and ezetimibe treatment should be considered in patients with hypercholesterolemia who are resistant to HMG-CoA reductase inhibitors.

Plasma Non-cholesterol Sterols as Markers of Cholesterol Synthesis and Intestinal Absorption: A Critical Review

Plasma concentrations of phytosterols and non-cholesterol sterol precursors of cholesterol synthesis have been used as markers of intestinal cholesterol absorption and synthesis in inherited and secondary dyslipidemias and in population-based investigations to evaluate the risk for cardiovascular disease, respectively. The method aims at replacing initial research procedures such as the use of stable isotopes associated with fecal steroid balance, which are limited by the high cost and tedious procedures. However, we show in this review that numerous results obtained with serum sterol measurements are contradictory. In this regard, the following points are discussed: 1) how phytosterols relate to atherosclerosis considering that defects in biliary output or in the transport of phytosterols from the intestinal mucosa back into the intestinal lumen provide increased content of phytosterols and other sterols in plasma and tissues, thus not allowing to conclude that their presence in arteries and atheromas represents the etiology of atherosclerosis; 2) serum non-cholesterol sterols as markers of cholesterol synthesis and absorption, such as cholestanol, present discrepant results, rendering them often inadequate to identify cases of coronary artery disease as well as alterations in the whole body cholesterol metabolism; 3) such methods of measurement of cholesterol metabolism are confounded by factors like diabetes mellitus, body weight and other pathologies including considerable hereditary hyperlipidemias biological variabilities that influence the efficiency of synthesis and intestinal absorption of cholesterol.

Serum phytosterols associate with T helper 1 cytokine concentration in pregnant women

The dietary phytosterols have been demonstrated to modulate CD4+ T-cell polarization in cells, animals, and humans. However, T helper (Th)1/Th2 dichotomy has rarely been correlated with phytosterols during pregnancy. The present study investigated associations between the serum cytokines and serum phytosterols in 100 pregnant women at 34- to 37-week gestation and their offspring. The results showed that serum concentrations of interferon (IFN)-γ, tumor necrosis factor (TNF)-α, and total Th1 cytokines were positively associated with serum β-sitosterol level, adjusting for age, BMI, and serum cholesterol. Serum IFN-γ and total Th1 cytokine concentrations positively correlated with total phytosterol concentration, controlling age, BMI, and serum cholesterol. Moreover, none of the cytokines measured correlated with phytosterol concentration in the newborns. Our results show that serum Th1 cytokine concentrations, but not Th2 levels, are positively associated with serum phytosterols in pregnant women. These findings implicate that phytosterols modulate Th1/Th2 balance by inducing Th1 secretions in pregnant women.

Of mice and men: murine bile acids explain species differences in the regulation of bile acid and cholesterol metabolism

Compared with humans, rodents have higher synthesis of cholesterol and bile acids (BAs) and faster clearance and lower levels of serum LDL-cholesterol. Paradoxically, they increase BA synthesis in response to bile duct ligation (BDL). Another difference is the production of hydrophilic 6-hydroxylated muricholic acids (MCAs), which may antagonize the activation of FXRs, in rodents versus humans. We hypothesized that the presence of MCAs is key for many of these metabolic differences between mice and humans. We thus studied the effects of genetic deletion of the Cyp2c70 gene, previously proposed to control MCA formation. Compared with WT animals, KO mice created using the CRISPR/Cas9 system completely lacked MCAs, and displayed >50% reductions in BA and cholesterol synthesis and hepatic LDL receptors, leading to a marked increase in serum LDL-cholesterol. The doubling of BA synthesis following BDL in WT animals was abolished in KO mice, despite extinguished intestinal fibroblast growth factor (Fgf)15 expression in both groups. Accumulation of cholesterol-enriched particles ("Lp-X") in serum was almost eliminated in KO mice. Livers of KO mice were increased 18% in weight, and serum markers of liver function indicated liver damage. The human-like phenotype of BA metabolism in KO mice could not be fully explained by the activation of FXR-mediated changes. In conclusion, the presence of MCAs is critical for many of the known metabolic differences between mice and humans. The Cyp2c70-KO mouse should be useful in studies exploring potential therapeutic targets for human disease.

Overeating Saturated Fat Promotes Fatty Liver and Ceramides Compared With Polyunsaturated Fat: A Randomized Trial

CONTEXT

Saturated fatty acid (SFA) vs polyunsaturated fatty acid (PUFA) may promote nonalcoholic fatty liver disease by yet unclear mechanisms.

OBJECTIVE

To investigate if overeating SFA- and PUFA-enriched diets lead to differential liver fat accumulation in overweight and obese humans.

DESIGN

Double-blind randomized trial (LIPOGAIN-2). Overfeeding SFA vs PUFA for 8 weeks, followed by 4 weeks of caloric restriction.

SETTING

General community.

PARTICIPANTS

Men and women who are overweight or have obesity (n = 61).

INTERVENTION

Muffins, high in either palm (SFA) or sunflower oil (PUFA), were added to the habitual diet.

MAIN OUTCOME MEASURES

Lean tissue mass (not reported here). Secondary and exploratory outcomes included liver and ectopic fat depots.

RESULTS

By design, body weight gain was similar in SFA (2.31 ± 1.38 kg) and PUFA (2.01 ± 1.90 kg) groups, P = 0.50. SFA markedly induced liver fat content (50% relative increase) along with liver enzymes and atherogenic serum lipids. In contrast, despite similar weight gain, PUFA did not increase liver fat or liver enzymes or cause any adverse effects on blood lipids. SFA had no differential effect on the accumulation of visceral fat, pancreas fat, or total body fat compared with PUFA. SFA consistently increased, whereas PUFA reduced circulating ceramides, changes that were moderately associated with liver fat changes and proposed markers of hepatic lipogenesis. The adverse metabolic effects of SFA were reversed by calorie restriction.

CONCLUSIONS

SFA markedly induces liver fat and serum ceramides, whereas dietary PUFA prevents liver fat accumulation and reduces ceramides and hyperlipidemia during excess energy intake and weight gain in overweight individuals.

Serum noncholesterol sterols in Alzheimer's disease: the Helsinki Businessmen Study

Cerebral cholesterol metabolism is perturbed in late-onset Alzheimer's disease (AD), but whether also the extracerebral cholesterol metabolism is perturbed is not known. Thus, we studied whole-body cholesterol synthesis and absorption with serum noncholesterol sterols in men without AD (n = 114) or with (n = 18) "pure" AD (no concomitant atherosclerotic cardiovascular disease) in a long-term cohort (the Helsinki Businessmen Study) of home-dwelling older men without lipid-lowering drugs and on their habitual home diet. Serum lipids did not differ between AD and controls, but age was higher (78 ± 1 vs 74 ± 0.3 years, mean ± standard error, P < 0.001), age-adjusted plasma glucose concentration was lower (4.8 ± 0.3 vs 5.7 ± 0.1 mmol/L, P = 0.011), and APOE ε4 allele and frailty were more frequent in AD than in controls. Of the age and frailty-adjusted serum noncholesterol sterols desmosterol and lathosterol ratios to cholesterol reflecting cholesterol synthesis were lower in AD than in controls (eg, lathosterol 114 ± 12 vs 137 ± 5 10² µmol/mmol cholesterol, P = 0.004). Cholestanol ratio to cholesterol was higher in AD than in controls suggesting increased cholesterol absorption. lathosterol/sitosteroll ratio reflecting cholesterol metabolism was lower in AD than in controls (0.95 ± 0.28 vs 1.52 ± 0.11 10² µmol/mmol cholesterol, P = 0.027). In AD, plasma glucose correlated negatively with cholesterol synthesis, whereas in controls the correlation was positive. In conclusion, extracerebral cholesterol metabolism was altered in AD. This finding along with the low plasma glucose concentration and its paradoxical interaction with cholesterol synthesis opens new perspectives in the regulation of cholesterol metabolism and glucose homeostasis in AD.

Mechanisms that minimize retinal impact of apolipoprotein E absence

Apolipoprotein E (APOE) is a component of lipid-transporting particles and a recognition ligand for receptors, which bind these particles. The APOE isoform ε2 is a risk factor for age-related macular degeneration; nevertheless, APOE absence in humans and mice does not significantly affect the retina. We found that retinal cholesterol biosynthesis and the levels of retinal cholesterol were increased in Apoe^-/- mice, whereas cholesterol elimination by metabolism was decreased. No focal cholesterol deposits were observed in the Apoe^-/- retina. Retinal proteomics identified the most abundant cholesterol-related proteins in WT mice and revealed that, of these cholesterol-related proteins, only APOA4 had increased expression in the Apoe^-/- retina. In addition, there were changes in retinal abundance of proteins involved in proinflammatory and antiinflammatory responses, cellular cytoskeleton maintenance, vesicular traffic, and retinal iron homeostasis. The data obtained indicate that when APOE is absent, particles containing APOA1, APOA4, and APOJ still transport cholesterol in the intraretinal space, but these particles are not taken up by retinal cells. Therefore, cholesterol biosynthesis inside retinal cells increase, whereas metabolism to oxysterols decreases to prevent cells from cholesterol depletion. These and other compensatory changes underlie only a minor retinal phenotype in Apoe^-/- mice.

Paradox of hypercholesterolaemia in highly trained, keto-adapted athletes

Objective

A growing number of ultra-endurance athletes have switched to a very low-carbohydrate/high-fat eating pattern. We compared markers of cholesterol and the lipoprotein profile in a group of elite ultra-runners consuming a high-carbohydrate (HC) or low-carbohydrate (LC) diet.

Methods

Fasting blood was obtained from competitive male ultra-endurance runners habitually consuming a very low-carbohydrate (LC; n=10) or high-carbohydrate (HC; n=10) diet to determine blood cholesterol profile, lipoprotein particle distribution and sterol biomarkers of cholesterol balance.

Results

Plasma total cholesterol, low-density lipoprotein (LDL-C) and high-density lipoprotein (HDL-C) cholesterol were all significantly greater (p<0.000) in the LC group (65%, 83% and 60%, respectively). There were also significant differences in lipoprotein particle distribution as evidenced by a greater size and concentration of large HDL and LDL particles, and total LDL particle concentration was significantly greater in the LC group, but they had significantly fewer small LDL particles.

Conclusion

Ultra-endurance athletes habitually consuming a very low-carbohydrate/high-fat diet for over a year showed unique cholesterol profiles characterised by consistently higher plasma LDL-C and HDL-C, less small LDL particles, and lipoprotein profiles consistent with higher insulin sensitivity. There may be a functional purpose to the expansion of the circulating cholesterol pool to meet the heightened demand for lipid transport in highly trained, keto-adapted athletes.

Genetic polymorphism of sterol transporters in children with future gallstones

BACKGROUND & AIMS

Gallstone disease is related to hypersecretion of cholesterol in bile, and low serum phytosterol levels. We examined how genetic polymorphisms of sterol transporters affect childhood cholesterol metabolism trait predicting adult gallstone disease.

PATIENTS AND METHODS

In retrospective controlled study, we determined D19H polymorphism of ABCG8 gene, genetic variation at Niemann-Pick C1-like 1 (NPC1L1) gene locus (rs41279633, rs17655652, rs2072183, rs217434 and rs2073548), and serum cholesterol, noncholesterol sterols and lipids in children affected by gallstones decades later (n = 66) and controls (n = 126).

RESULTS

In childhood, phytosterols were lower (9.7%-23.4%) in carriers of risk allele 19H compared to 19D homozygotes. Lowest campesterol/cholesterol tertile consisted of 1.9-times more future gallstone subjects, and 3.7-times more 19H carriers than highest one. Campesterol/cholesterol-ratio was highest in 19D homozygote controls, but ∼11% lower in gallstone 19D homozygotes and ∼25% lower among gallstone and control carriers of 19H. Gallstone subjects with alleles CC of rs41279633 and TT of rs217434 of NPC1L1 had ∼18% lower campesterol/cholesterol-ratio compared to mutation carriers.

CONCLUSIONS

Risk trait of cholesterol metabolism (low phytosterols) in childhood favouring cholesterol gallstone disease later in adulthood is influenced by risk variant 19H of ABCG8 and obviously also other factors. NPC1L1 variants have minor influence on noncholesterol sterols.

Noncholesterol Sterols as Surrogate Markers in Patients with Severe Alcoholic Hepatitis

Severe alcoholic hepatitis (AH) is a life-threatening condition lacking good serologic markers to tailor treatment and predict recovery. We examined the cholesterol metabolism in severe AH to explore prognostic markers and evaluate the profile of cholesterol precursors, cholestanol and phytosterols, in this context. We assessed serum cholesterol, cholesterol precursors, cholestanol, phytosterols, and biochemical markers in 24 patients with severe AH treated with prednisolone and randomized to ciprofloxacin in the ratio 1:1. Response to prednisolone was assessed with the Lille model. Evaluations were made between responders and nonresponders to corticosteroid treatment and during follow-up for 180 days. The findings were compared with those from patients with primary sclerosing cholangitis (PSC) (n = 156) and healthy individuals (n = 124). Responders to prednisolone had ~56-60% higher (p-value 0.032-0.044) serum ratios to cholesterol of phytosterols, while the lathosterol/campesterol ratio was ~76% (p = 0.031) lower compared to nonresponders. Stigmasterol/cholesterol predicted response to corticosteroid therapy. Surrogate markers of cholesterol synthesis (lathosterol and desmosterol) inversely reflected those of absorption (cholestanol and phytosterols) in PSC and controls (r-range -0.247 to -0.559, p < 0.01 for all), contrary to AH patients, among whom this reciprocal regulation was partially recovered on day 90 (lathosterol: r-range -0.733 to -0.952, p < 0.05 for all). AH patients had ~26% lower lathosterol/cholesterol, but 1.13-3.87-fold higher cholestanol/cholesterol and sitosterol/cholesterol compared to control groups (p < 0.05 for all). Median ferritin concentration at baseline was ~37% lower (p = 0.011) among the responders. Cholesterol precursors and phytosterols have a disease-specific profile in AH. Phytosterols and ferritin may serve as surrogate markers for short-term response.

Cholesterol metabolism in humans: a review of methods and comparison of results

PURPOSE OF REVIEW

Cholesterol metabolism has been the object of intense investigation for decades. This review focuses on classical and novel methods assessing in vivo cholesterol metabolism in humans. Two factors have fueled cholesterol metabolism studies in the last few years: the renewed interest in the study of reverse cholesterol transport (RCT) as an atheroprotective mechanism and the importance of the gut microbiome in affecting cholesterol metabolism.

RECENT FINDINGS

Recent applications of these methods have spanned from the assessment of the effect on cholesterol synthesis, absorption or excretion of drugs (such as ezetimibe, PCSK9 inhibitors and plant sterols) and the gut microbiome to the more complex assessment of transintestinal cholesterol excretion (TICE) and RCT.

SUMMARY

These methods continue to be a valuable tool to answer novel questions and investigate the complexity of in-vivo cholesterol metabolism.

The value of surrogate markers to monitor cholesterol absorption, synthesis and bioconversion to bile acids under lipid lowering therapies

INTRODUCTION

Regulation of cholesterol (Chol) homeostasis is controlled by three main fluxes, i.e. intestinal absorption, de novo synthesis (ChS) and catabolism, predominantly as bile acid synthesis (BAS). High serum total Chol and LDL-Chol concentrations in particular are considered risk factors and markers for the development of atherosclerosis. Pharmaceutical treatments to lower serum Chol have focused on reducing absorption or ChS and increasing BAS. Monitoring of these three parameters is complex involving isotope techniques, cholesterol balance experiments and advanced mass spectrometry based analysis methods. Surrogate markers were explored that require only one single fasting blood sample collection. These markers were validated in specific, mostly physiological conditions and during statin treatment to inhibit ChS. They were also applied under cholesterol absorption restriction, but were not validated in this condition. We retrospectively evaluated the use of serum campesterol (Camp), sitosterol (Sit) and cholestanol (Cholol) as markers for cholesterol absorption, lathosterol (Lath) as marker for ChS and 7α-hydroxycholesterol (7α-OH-Ch) and 27-hydroxycholesterol (27-OH-Ch) as markers for BAS under conditions of Chol absorption restriction. Additionally, their values were corrected for Chol concentration (R_sterol or oxysterols).

METHODS

Thirty-seven healthy male omnivore subjects were studied under treatments with placebo (PLAC), ezetimibe (EZE) to inhibit cholesterol absorption, simvastatin (SIMVA) to reduce cholesterol synthesis and a combination of both (EZE+SIMVA). Results were compared to those obtained in 18 pure vegetarian subjects (vegans) whose dietary Chol intake is extremely low. Relative or fractional Chol absorption (FrChA) was measured with the continuous feeding stable isotope procedure, ChS and BAS with the cholesterol balance method. The daily Chol intake (DICh) was inventoried and the daily Chol absorption (DACh) calculated.

RESULTS

Monitoring cholesterol absorption, R_Camp, R_Sit and R_Cholol responded sensitively to changes in FrChA. R_Camp correlated well with FrChA in all omnivore treatment groups and in the vegan group. R_Camp confirmed reduced FrChA under EZE treatment and reduced DACh in the vegan subjects. R_Sit and R_Cholol did not accurately reflect FrChA or DACh in all situations. Monitoring endogenous cholesterol synthesis, R_Lath correlated with ChS in the vegan group, but in none of the omnivore treatment groups. R_Lath confirmed increased ChS under EZE treatment and was reduced under SIMVA treatment, while ChS was not. An increased ChS under EZE+SIMVA treatment could not be confirmed with R_Lath. R_Lath responded very insensitively to a change in ChS. Monitoring BAS, R_7α-OH-Ch but not R_27-OH-Ch correlated with BAS during PLAC, EZE and SIMVA treatments. In line with BAS, R_7α-OH-Ch did not differ in any of the omnivore treatment groups. R_7α-OH-Ch responded insensitively to a change in BAS.

CONCLUSIONS

Under Chol absorption restriction, serum R_Camp is a sensitive and valid marker to monitor FrChA in a population with a normal DICh. Also, major changes in DACh can be detected in vegans. Serum R_Lath does not reflect ChS measured with the cholesterol balance method during EZE treatment. This result initiates the question whether the measured ChS reflects pure de novo synthesis. Serum R_7α-OH-Ch appears to be a valid but insensitive marker for BAS.

Acute caloric restriction counteracts hepatic bile acid and cholesterol deficiency in morbid obesity

BACKGROUND

Bile acid (BA) synthesis is regulated by BA signalling in the liver and by fibroblast growth factor 19 (FGF19), synthesized and released from the intestine. In morbid obesity, faecal excretion and hepatic synthesis of BAs and cholesterol are strongly induced and caloric restriction reduces their faecal excretion considerably. We hypothesized that the high intestinal food mass in morbidly obese subjects promotes faecal excretion of BAs and cholesterol, thereby creating a shortage of both BAs and cholesterol in the liver.

METHODS

Ten morbidly obese women (BMI 42 ± 2.6 kg m^-2 ) were monitored on days 0, 3, 7, 14 and 28 after beginning a low-calorie diet (800-1100 kcal day^-1 ). Serum was collected and liver size and fat content determined. Synthesis of BAs and cholesterol was evaluated from serum markers, and the serum levels of lipoproteins, BAs, proprotein convertase subtilisin/kexin type 9 (PCSK9), insulin, glucose and FGF19 were monitored. Fifty-four nonobese women (BMI <25 kg m^-2 ) served as controls.

RESULTS

At baseline, synthesis of both BAs and cholesterol and serum levels of BAs and PCSK9 were elevated in the obese group compared to controls. Already after 3 days on a low-calorie diet, BA and cholesterol synthesis and serum BA and PCSK9 levels normalized, whereas LDL cholesterol increased. FGF19 and triglyceride levels were unchanged, and liver volume was reduced by 10%.

CONCLUSIONS

The results suggest that hepatic BAs and cholesterol are deficient in morbid obesity. Caloric restriction rapidly counteracts these deficiencies, normalizing BA and cholesterol synthesis and circulating PCSK9 levels, indicating that overproduction of cholesterol in enlarged peripheral tissues cannot explain this phenotype. We propose that excessive food intake promotes faecal loss of BAs and cholesterol contributing to their hepatic deficiencies.

Effects of PCSK9 Inhibition With Alirocumab on Lipoprotein Metabolism in Healthy Humans

Supplemental Digital Content is available in the text.

Background:

Alirocumab, a monoclonal antibody to proprotein convertase subtilisin/kexin type 9 (PCSK9), lowers plasma low-density lipoprotein (LDL) cholesterol and apolipoprotein B100 (apoB). Although studies in mice and cells have identified increased hepatic LDL receptors as the basis for LDL lowering by PCSK9 inhibitors, there have been no human studies characterizing the effects of PCSK9 inhibitors on lipoprotein metabolism. In particular, it is not known whether inhibition of PCSK9 has any effects on very low-density lipoprotein or intermediate-density lipoprotein (IDL) metabolism. Inhibition of PCSK9 also results in reductions of plasma lipoprotein (a) levels. The regulation of plasma Lp(a) levels, including the role of LDL receptors in the clearance of Lp(a), is poorly defined, and no mechanistic studies of the Lp(a) lowering by alirocumab in humans have been published to date.

Methods:

Eighteen (10 F, 8 mol/L) participants completed a placebo-controlled, 2-period study. They received 2 doses of placebo, 2 weeks apart, followed by 5 doses of 150 mg of alirocumab, 2 weeks apart. At the end of each period, fractional clearance rates (FCRs) and production rates (PRs) of apoB and apo(a) were determined. In 10 participants, postprandial triglycerides and apoB48 levels were measured.

Results:

Alirocumab reduced ultracentrifugally isolated LDL-C by 55.1%, LDL-apoB by 56.3%, and plasma Lp(a) by 18.7%. The fall in LDL-apoB was caused by an 80.4% increase in LDL-apoB FCR and a 23.9% reduction in LDL-apoB PR. The latter was due to a 46.1% increase in IDL-apoB FCR coupled with a 27.2% decrease in conversion of IDL to LDL. The FCR of apo(a) tended to increase (24.6%) without any change in apo(a) PR. Alirocumab had no effects on FCRs or PRs of very low-density lipoproteins-apoB and very low-density lipoproteins triglycerides or on postprandial plasma triglycerides or apoB48 concentrations.

Conclusions:

Alirocumab decreased LDL-C and LDL-apoB by increasing IDL- and LDL-apoB FCRs and decreasing LDL-apoB PR. These results are consistent with increases in LDL receptors available to clear IDL and LDL from blood during PCSK9 inhibition. The increase in apo(a) FCR during alirocumab treatment suggests that increased LDL receptors may also play a role in the reduction of plasma Lp(a).

Clinical Trial Registration:

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01959971.

Early and brain region-specific decrease of de novo cholesterol biosynthesis in Huntington's disease: A cross-validation study in Q175 knock-in mice

Cholesterol precursors and cholesterol levels are reduced in brain regions of Huntington's disease (HD) mice. Here we quantified the rate of in vivo de novo cholesterol biosynthesis in the HD brain. Samples from different brain regions and blood of the heterozygous knock-in mouse model carrying 175 CAG repeats (Q175) at different phenotypic stages were processed independently by two research units to quantify cholesterol synthesis rate by ²H₂O labeling and measure the concentrations of lathosterol, cholesterol and its brain-specific cholesterol catabolite 24-hydroxy-cholesterol (24OHC) by isotope dilution mass spectrometry. The daily synthesis rate of cholesterol and the corresponding concentration of lathosterol were significantly reduced in the striatum of heterozygous Q175 mice early in the disease course. We also report that the decrease in lathosterol was inversely correlated with CAG-size at symptomatic stage, as observed in striatal samples from an allelic series of HD mice. There was also a significant correlation between the fractional synthesis rates of total cholesterol and 24OHC in brain of wild-type (WT) and Q175 mice, supporting the evidence that plasma 24OHC may reflect cholesterol synthesis in the adult brain. This comprehensive analysis demonstrates consistent cholesterol biosynthesis defects in HD mouse models and suggests that plasma 24OHC may serve as a biomarker of brain cholesterol metabolism.

Cholesterol metabolism in cardiac sarcoidosis

BACKGROUND AND AIMS

Patients with cardiac sarcoidosis (CS) suffer from myocardial inflammation, but atherosclerosis is not infrequent in these patients. However, the classical atherosclerotic risk factors, such as perturbed serum lipids and whole-body cholesterol metabolism, remain unravelled in CS.

METHODS

We assessed serum non-cholesterol sterols, biomarkers of whole-body cholesterol synthesis and cholesterol absorption efficiency, with gas-liquid chromatography in 39 patients with histologically verified CS and in an age-adjusted random population sample (n = 124).

RESULTS

CS was inactive or responding to treatment in all patients. Concentrations of serum, LDL, and HDL cholesterol and serum triglycerides were similar in CS patients and in control subjects. Cholesterol absorption markers were higher in CS patients than in controls (eg serum campesterol to cholesterol ratio in CS 246 ± 18 vs in controls 190 ± 8 10(2) x μmol/mmol of cholesterol, p = 0.001). Cholesterol synthesis markers were lower in CS patients than in controls (eg serum lathosterol to cholesterol ratio in CS 102 ± 8 vs in controls 195 ± 5 10(2) x μmol/mmol of cholesterol, p = 0.000). In CS patients, cholesterol absorption markers significantly correlated with plasma prohormone brain natriuretic peptide (proBNP), a marker of hemodynamic load.

CONCLUSION

High cholesterol absorption efficiency, which is suggested to be atherogenic, characterized the metabolic profile of cholesterol in CS patients. The association between cholesterol absorption efficiency and plasma proBNP concentration, which suggests a link between inflammation, cholesterol homeostasis, and hemodynamic load, warrants further studies in order to confirm this finding and to reveal the underlying mechanisms.

CYP46A1, the rate-limiting enzyme for cholesterol degradation, is neuroprotective in Huntington's disease

Huntington’s disease is an autosomal dominant neurodegenerative disease caused by abnormal polyglutamine expansion in huntingtin (Exp-HTT) leading to degeneration of striatal neurons. Altered brain cholesterol homeostasis has been implicated in Huntington’s disease, with increased accumulation of cholesterol in striatal neurons yet reduced levels of cholesterol metabolic precursors. To elucidate these two seemingly opposing dysregulations, we investigated the expression of cholesterol 24-hydroxylase (CYP46A1), the neuronal-specific and rate-limiting enzyme for cholesterol conversion to 24S-hydroxycholesterol (24S-OHC). CYP46A1 protein levels were decreased in the putamen, but not cerebral cortex samples, of post-mortem Huntington’s disease patients when compared to controls. Cyp46A1 mRNA and CYP46A1 protein levels were also decreased in the striatum of the R6/2 Huntington’s disease mouse model and in ST hdh Q111 cell lines. In vivo , in a wild-type context, knocking down CYP46A1 expression in the striatum, via an adeno-associated virus-mediated delivery of selective shCYP46A1, reproduced the Huntington’s disease phenotype, with spontaneous striatal neuron degeneration and motor deficits, as assessed by rotarod. In vitro , CYP46A1 restoration protected ST hdh Q111 and Exp-HTT-expressing striatal neurons in culture from cell death. In the R6/2 Huntington’s disease mouse model, adeno-associated virus-mediated delivery of CYP46A1 into the striatum decreased neuronal atrophy, decreased the number, intensity level and size of Exp-HTT aggregates and improved motor deficits, as assessed by rotarod and clasping behavioural tests. Adeno-associated virus-CYP46A1 infection in R6/2 mice also restored levels of cholesterol and lanosterol and increased levels of desmosterol. In vitro , lanosterol and desmosterol were found to protect striatal neurons expressing Exp-HTT from death. We conclude that restoring CYP46A1 activity in the striatum promises a new therapeutic approach in Huntington’s disease.

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.

Dysregulation of distal cholesterol biosynthesis in association with relapse and advanced disease in CHC genotype 2 and 3 treated with sofosbuvir and ribavirin

BACKGROUND & AIMS

Hepatitis C virus (HCV) modulates host lipid metabolism for its replication and lifecycle. Our aims were to assess changes in the serum lipid and distal (post-squalene) cholesterol biosynthesis metabolite profile of HCV genotypes (GT) 2 and 3 patients treated with sofosbuvir+ribavirin.

METHODS

Serum samples [baseline, treatment week 12, 4weeks post-treatment] were analyzed for apolipoproteins B and E (apoB/E), total cholesterol, HDL, LDL, and 11 post-squalene sterol metabolites using a GC/MS platform.

RESULTS

We selected 127 patients (GT2 n=50, GT3 n=77), 50% cirrhotic patients, and 42% who experienced a virological relapse. At baseline, GT3 patients had lower level of serum lipids, apoB/E, 7-dehydrocholesterol, desmosterol, lathosterol, compared to GT2 (p<0.006). Baseline lathosterol was lower in relapsers with cirrhosis compared to cirrhotic patients with SVR (p=0.003). From baseline to treatment week 12, serum lipids, apoB/E, and key sterol pathway metabolites (7-dehydrocholesterol, desmosterol, lathosterol, lanosterol) increased in GT3. In contrast, in GT2 patients, apoB/E and dihydrolanosterol decreased with viral suppression (p<0.025). At follow-up week 4, cirrhotic SVR patients showed substantially greater increases in apoB and total sterols compared to cirrhotic relapsers regardless of HCV genotype. After adjustment for genotype and gender, baseline lathosterol was independently associated with virologic response (p=0.04).

CONCLUSION

HCV GT3 is associated with reduced circulation of lipids involved in the distal cholesterol biosynthesis pathway, resulting in relative hypocholesterolemia. HCV suppression during sofosbuvir+ribavirin restores distal sterol metabolites indicating viral interference with de novo lipogenesis or selective retention by hepatocytes.

Reconstituted high-density lipoprotein can elevate plasma alanine aminotransferase by transient depletion of hepatic cholesterol: role of the phospholipid component

Human apolipoprotein A-I preparations reconstituted with phospholipids (reconstituted high-density lipoprotein [HDL]) have been used in a large number of animal and human studies to investigate the physiological role of apolipoprotein A-I. Several of these studies observed that intravenous infusion of reconstituted HDL might cause transient elevations in plasma levels of hepatic enzymes. Here we describe the mechanism of this enzyme release. Observations from several animal models and in vitro studies suggest that the extent of hepatic transaminase release (alanine aminotransferase [ALT]) correlates with the movement of hepatic cholesterol into the blood after infusion. Both the amount of ALT release and cholesterol movement were dependent on the amount and type of phospholipid present in the reconstituted HDL. As cholesterol is known to dissolve readily in phospholipid, an HDL preparation was loaded with cholesterol before infusion into rats to assess the role of diffusion of cholesterol out of the liver and into the reconstituted HDL. Cholesterol-loaded HDL failed to withdraw cholesterol from tissues and subsequently failed to cause ALT release. To investigate further the role of cholesterol diffusion, we employed mice deficient in SR-BI, a transporter that facilitates spontaneous movement of cholesterol between cell membranes and HDL. These mice showed substantially lower movement of cholesterol into the blood and markedly lower ALT release. We conclude that initial depletion of hepatic cholesterol initiates transient ALT release in response to infusion of reconstituted HDL. This effect may be controlled by appropriate choice of the type and amount of phospholipid in reconstituted HDL. Copyright © 2015 John Wiley & Sons, Ltd.

Evidence for altered cholesterol metabolism in Huntington's disease post mortem brain tissue

AIMS

Cholesterol plays an essential role in membrane structure and function, being especially important in the brain. Alteration of brain cholesterol synthesis and metabolism has been demonstrated in several Huntington's disease (HD) mouse and cell models; however, less is known about these alterations in human tissue. This study aimed to identify alterations to cholesterol synthetic and metabolic pathways in human HD brain tissue.

METHODS

A broad range of cholesterol synthetic precursors, metabolites and oxidation products were measured by gas chromatography-tandem mass spectrometry in five regions of human post mortem HD brain and compared with age- and sex-matched control tissues. The level of enzymes that regulate cholesterol homeostasis, cholesterol 24-hydroxylase and delta(24)-sterol reductase were investigated by Western blotting and qPCR in putamen.

RESULTS

The most significant changes were localized to the putamen, where a 60% decrease in 24(S)-hydroxycholesterol, 30% increase in cholesterol and 100-200% increase in synthetic precursors (lathosterol, zymosterol and desmosterol) was detected. The enzymes cholesterol 24-hydroxylase and delta(24)-sterol reductase were also significantly decreased in HD putamen as compared with control tissues. Free radical-generated cholesterol oxidation products 7-keto cholesterol and 7β-hydroxycholesterol were also increased by 50-70% in HD putamen.

CONCLUSION

Human HD brain has significantly decreased cholesterol metabolism and disrupted cholesterol homeostasis. Our data also indicate that lipid oxidative stress accompanies HD pathology.

Cholesterol Biosynthesis and Trafficking in Cortisol-Producing Lesions of the Adrenal Cortex

CONTEXT

Cortisol-producing adenomas (CPAs), primary pigmented nodular adrenocortical disease (PPNAD), and primary macronodular adrenocortical hyperplasia (PMAH) cause ACTH-independent Cushing syndrome (CS). Investigation of their pathogenesis has demonstrated their integral link to the cAMP-dependent protein kinase signaling pathway.

OBJECTIVE

The aim of this study was to identify differences in cholesterol biosynthesis among different CS-causing adrenocortical tumors. Because of the concomitant associations of cAMP levels with cholesterol and with steroid biosynthesis, we hypothesized that benign cortisol-producing tumors would display aberration of these pathways.

DESIGN AND SETTING

Twenty-three patients with CPA, PPNAD, or PMAH who underwent adrenalectomy for CS were included in the study. Preoperative biochemical analyses were performed, and excised adrenal tissues were studied.

MAIN OUTCOME MEASURES

Serum, urinary hormone levels, serum lipid profiles, and anthropometric data were obtained preoperatively. Adrenal tissues were analyzed for total protein, cholesterol, and neutral sterol content by mass spectrometry and expression of HMGCR, LDLR, ABCA1, DHCR24, and STAR genes.

RESULTS

There were differences in cholesterol content and markers of cholesterol biosynthesis and metabolism that distinguished CPAs from PMAH and PPNAD; cholesterol, lathosterol, and lathosterol/cholesterol ratio were significantly higher in CPAs. ABCA1 mRNA was lower among CPAs compared to tissues from bilateral adrenocortical hyperplasia (PMAH and PPNAD), and mRNA expression of LDL-R, DCHR24, and HMGCR tended to be higher in CPA tumor tissues.

CONCLUSION

CPAs displayed characteristics of "cholesterol-starved" tissues when compared to PPNAD and PMAH and appeared to have increased intrinsic cholesterol production and uptake from the periphery, as well as decreased cholesterol efflux. This has implications for a potential new way of treating these tumors.

Understanding the cholesterol metabolism-perturbing effects of docosahexaenoic acid by gas chromatography-mass spectrometry targeted metabonomic profiling

PURPOSE

Over the past few decades, docosahexaenoic acid (DHA) has gained special attention for management of cholesterol-associated metabolic disorders and neurodegenerative diseases such as Alzheimer's disease (AD) owing to its neuroprotective, anti-inflammatory and hypolipidemic properties. Several epidemiological studies have reported the effect of DHA in reducing the risk of developing AD by lowering cholesterol. Hypercholesterolemia is a pro-amyloidogenic factor influencing the enzymatic processing of amyloid-β precursor protein (AβPP) to toxic β-amyloid. However, the mechanism by which DHA modulates the cholesterol pathway has not been established. Thus, the objective of this study was to investigate the mechanism of regulation of cholesterol metabolism by DHA in an AβPP₆₉₅ overexpressing AD cell model.

METHODS

A gas chromatography/mass spectrometry method was developed and validated for the targeted profiling of 11 cholesterol metabolites in DHA-treated Chinese hamster ovary wild-type (CHO-wt) and AβPP₆₉₅ overexpressing (CHO-AβPP₆₉₅) cells. The differential metabolite profiles between DHA- and vehicle-treated groups were further analyzed using fold change values of the ratio of concentration of metabolites in CHO-AβPP₆₉₅ to CHO-wt cells. Effect of DHA on key rate-limiting enzymatic activities within the cholesterol pathway was established using biochemical assays.

RESULTS

Our results showed that DHA reduced the levels of key cholesterol anabolites and catabolites in CHO-AβPP₆₉₅ cells as compared to CHO-wt cells. Further enzymatic studies revealed that the cholesterol-lowering effect of DHA was mediated by regulating HMG-CoA reductase and squalene epoxidase enzyme activities.

CONCLUSION

We demonstrate for the first time the dual effects of DHA in inhibiting HMG-CoA reductase and squalene epoxidase and modulating the sterol biosynthesis axis of the cholesterol pathway in AβPP₆₉₅ overexpressing AD. Our novel findings underscore the potential of DHA as a multi-target hypocholesterolemic agent for the prophylaxis of AD and other cholesterol-associated diseases.

Potential role of milk fat globule membrane in modulating plasma lipoproteins, gene expression, and cholesterol metabolism in humans: a randomized study

BACKGROUND

Butter is rich in saturated fat [saturated fatty acids (SFAs)] and can increase plasma low density lipoprotein (LDL) cholesterol, which is a major risk factor for cardiovascular disease. However, compared with other dairy foods, butter is low in milk fat globule membrane (MFGM) content, which encloses the fat. We hypothesized that different dairy foods may have distinct effects on plasma lipids because of a varying content of MFGM.

OBJECTIVE

We aimed to investigate whether the effects of milk fat on plasma lipids and cardiometabolic risk markers are modulated by the MFGM content.

DESIGN

The study was an 8-wk, single-blind, randomized, controlled isocaloric trial with 2 parallel groups including overweight men and women (n = 57 randomly assigned). For the intervention, subjects consumed 40 g milk fat/d as either whipping cream (MFGM diet) or butter oil (control diet). Intervention foods were matched for total fat, protein, carbohydrates, and calcium. Subjects were discouraged from consuming any other dairy products during the study. Plasma markers of cholesterol absorption and hepatic cholesterol metabolism were assessed together with global gene-expression analyses in peripheral blood mononuclear cells.

RESULTS

As expected, the control diet increased plasma lipids, whereas the MFGM diet did not [total cholesterol (±SD): +0.30 ± 0.49 compared with -0.04 ± 0.49 mmol/L, respectively (P = 0.024); LDL cholesterol: +0.36 ± 0.50 compared with +0.04 ± 0.36 mmol/L, respectively (P = 0.024); apolipoprotein B:apolipoprotein A-I ratio: +0.03 ± 0.09 compared with -0.05 ± 0.10 mmol/L, respectively (P = 0.007); and non-HDL cholesterol: +0.24 ± 0.49 compared with -0.14 ± 0.51 mmol/L, respectively (P = 0.013)]. HDL-cholesterol, triglyceride, sitosterol, lathosterol, campesterol, and proprotein convertase subtilisin/kexin type 9 plasma concentrations and fatty acid compositions did not differ between groups. Nineteen genes were differentially regulated between groups, and these genes were mostly correlated with lipid changes.

CONCLUSIONS

In contrast to milk fat without MFGM, milk fat enclosed by MFGM does not impair the lipoprotein profile. The mechanism is not clear although suppressed gene expression by MFGM correlated inversely with plasma lipids. The food matrix should be considered when evaluating cardiovascular aspects of different dairy foods. This trial was registered at clinicaltrials.gov as NCT01767077.

Relation of cholesterol metabolism to pediatric gallstone disease: a retrospective controlled study

Background

Cholesterol metabolism may be involved in pediatric gallstone disease. We aimed to reveal cholesterol metabolites and phytosterols and their relation to stone composition of sterols in children having black pigment and cholesterol stones.

Methods

We performed retrospective controlled clinical study, in which we examined parameters of cholesterol metabolism and liver function values in serum (n = 28) and gallstones (n = 46) of consecutively cholecystectomized children. Serum values of age-, body mass index- and sex-matched children (n = 82) and adult gallstones (n = 187) served as controls.

Results

Surrogate markers of cholesterol synthesis in serum (squalene/cholesterol, cholestenol/cholesterol and lathosterol/cholesterol) were 26–52 % higher in both stone subclasses compared to controls (p < 0.05 for all). Respectively, cholestanol/cholesterol and plant sterols campesterol/cholesterol and sitosterol/cholesterol (cholesterol absorption markers) had decreasing order in serum: black pigment stone group > controls > cholesterol stone group (p < 0.05 for all). In black pigment stone group, stone cholestanol/cholesterol was associated with serum bile acids (r = 0.620, p = 0.018). In cholesterol stone group, surrogate markers of cholesterol synthesis in serum (e.g., lathosterol/cholesterol) inversely reflected those of absorption (r-range -0.633–-0.706, p-range 0.036–0.015). In cholesterol stone group, serum and stone lathosterol/cholesterol and cholestanol/cholesterol were positively interrelated (r-range 0.727–0.847, p < 0.05 for both).

Conclusions

Gallstone subclasses shared enhanced cholesterol synthesis. Cholesterol stone children were low cholesterol absorbers with intact homeostasis of cholesterol metabolism. Black pigment stone group was characterized by deteriorated cholesterol metabolism, and accumulation of cholestanol, campesterol and sitosterol in serum and stones suggesting their participation in pathogenesis.

Anagliptin decreases serum lathosterol level in patients with type 2 diabetes: a pilot study

OBJECTIVE

The mechanism responsible for the lipid-lowering effect of dipeptidyl peptidase-4 (DPP-4) inhibitors remains unknown in humans. We evaluated the effect of anagliptin on serum lipid profiles, including cholesterol synthesis and absorption markers, in Japanese patients with type 2 diabetes.

METHODS

Thirty patients with type 2 diabetes (20 - 70 years old, low-density lipoprotein cholesterol (LDL-C) level over 120 mg/dl, and no history of treatment with antidiabetic or antihyperlipidemic drugs) were enrolled. One hundred milligrams of anagliptin were administered twice a day for a month.

RESULTS

After treatment of anagliptin, the LDL-C and total cholesterol (TC) levels did not decrease overall, but the TC level decreased significantly in 28 patients whose HbA1c levels decreased. Lathosterol decreased significantly, whereas no changes in campesterol, sitosterol or cholestanol were observed.

CONCLUSION

These results of our study show no significant change in LDL-C, a tendency of decrease in TC and non-high-density lipoprotein cholesterol (non-HDL-C) after treatment of anagliptin for 1 month. Anagliptin therapy decreased the cholesterol synthesis marker lathosterol without changing cholesterol absorption markers.

Anacetrapib lowers LDL by increasing ApoB clearance in mildly hypercholesterolemic subjects

BACKGROUND

Individuals treated with the cholesteryl ester transfer protein (CETP) inhibitor anacetrapib exhibit a reduction in both LDL cholesterol and apolipoprotein B (ApoB) in response to monotherapy or combination therapy with a statin. It is not clear how anacetrapib exerts these effects; therefore, the goal of this study was to determine the kinetic mechanism responsible for the reduction in LDL and ApoB in response to anacetrapib.

METHODS

We performed a trial of the effects of anacetrapib on ApoB kinetics. Mildly hypercholesterolemic subjects were randomized to background treatment of either placebo (n = 10) or 20 mg atorvastatin (ATV) (n = 29) for 4 weeks. All subjects then added 100 mg anacetrapib to background treatment for 8 weeks. Following each study period, subjects underwent a metabolic study to determine the LDL-ApoB-100 and proprotein convertase subtilisin/kexin type 9 (PCSK9) production rate (PR) and fractional catabolic rate (FCR).

RESULTS

Anacetrapib markedly reduced the LDL-ApoB-100 pool size (PS) in both the placebo and ATV groups. These changes in PS resulted from substantial increases in LDL-ApoB-100 FCRs in both groups. Anacetrapib had no effect on LDL-ApoB-100 PRs in either treatment group. Moreover, there were no changes in the PCSK9 PS, FCR, or PR in either group. Anacetrapib treatment was associated with considerable increases in the LDL triglyceride/cholesterol ratio and LDL size by NMR.

CONCLUSION

These data indicate that anacetrapib, given alone or in combination with a statin, reduces LDL-ApoB-100 levels by increasing the rate of ApoB-100 fractional clearance.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00990808.

FUNDING

Merck & Co. Inc., Kenilworth, New Jersey, USA. Additional support for instrumentation was obtained from the National Center for Advancing Translational Sciences (UL1TR000003 and UL1TR000040).

Serum sterol profiling reveals increased cholesterol biosynthesis in childhood obesity

Quantitative sterol profiling in obese children and their clinical implications have not been fully investigated. The aim of study was to evaluate the metabolic changes in serum cholesterol and its precursors and metabolites, and their associations with clinical characteristics of childhood obesity. A total of 253 children aged 6-14 years (72 obese, 39 overweight, and 72 normal controls; 147 girls and 106 boys) were recruited. Anthropometric indices, body composition, and fasting total lipid profiles were determined. Serum concentrations of 20 sterols, as their free fraction, were analyzed through gas chromatography-mass spectrometry-based metabolite profiling. There were no significant differences in total- and LDL-cholesterols between groups. Serum levels of the main cholesterol precursors, lanosterol (P<0.02) and lathosterol (P<0.0001), were significantly higher in obese children. In addition, they showed positive correlations with waist to hip ratio, body fat percent, and body fat mass. The metabolic ratios of lanosterol and lathosterol to cholesterol were also elevated (P<0.01 both), indicating the up-regulation of cholesterol biosynthesis with childhood obesity. In contrast, the absorption of plant sterols tended to show a compensatory decrease in obese children. Strong correlations between free cholesterol and total- and LDL-cholesterols were observed (r>0.760, P<0.001), while there was no correlation with HDL-cholesterols. The levels of total cholesteryl ester were closely associated with triglyceride (r=0.763, P<0.001). Quantitative results indicate that childhood obesity may increase cholesterol synthesis while maintaining overall cholesterol homeostasis.

Lathosterol-to-cholesterol ratio in serum predicts cholesterol-lowering response to plant sterol consumption in a dual-center, randomized, single-blind placebo-controlled trial

BACKGROUND

Benefits of plant sterols (PS) for cholesterol lowering are compromised by large variability in efficacy across individuals. High fractional cholesterol synthesis measured by deuterium incorporation has been associated with nonresponse to PS consumption; however, prospective studies that show this association have yet to be conducted.

OBJECTIVE

The goal was to test whether the lathosterol-to-cholesterol ratio (L:C ratio), a surrogate marker of endogenous cholesterol synthesis, serves as an a priori predictor of cholesterol lowering in response to PS consumption.

DESIGN

Sixty-three mildly hypercholesterolemic adults who were preselected as possessing either high endogenous cholesterol synthesis [HS; n = 24; L:C = 2.03 ± 0.39 μmol/mmol (mean ± SD)] or low endogenous cholesterol synthesis (LS; n = 39; L:C = 0.99 ± 0.28 μmol/mmol) on the basis of baseline L:C consumed 2 g PS/d or a placebo for 28 d with the use of a dual-center, single-blind, randomized crossover design. Plasma lipid and noncholesterol sterol concentrations were measured at the end of each phase.

RESULTS

PS consumption lowered total cholesterol (TC; -0.25 ± 0.05 mmol/L; P < 0.0001) and LDL cholesterol (-0.17 ± 0.04 mmol/L; P < 0.0001) overall. Specifically, LS individuals responded to PS treatment with a reduction in TC (-0.40 ± 0.07 mmol/L; P < 0.0001) and LDL cholesterol (-0.29 ± 0.05 mmol/L; P = 0.0002), whereas HS individuals failed to show cholesterol lowering (TC: -0.09 ± 0.09 mmol/L; P = 0.2843; LDL cholesterol: -0.05 ± 0.07 mmol/L; P = 0.4917). The odds of LS participants responding to PS consumption with cholesterol lowering better than the mean cholesterol lowering in all participants were 4.25 (95% CI: 1.242, 14.556; P = 0.0211) for TC and 3.36 (95% CI: 1.112, 10.161; P = 0.0317) for LDL cholesterol, which was higher than for HS participants.

CONCLUSIONS

The L:C ratio predicts the extent of reduction in circulating TC and LDL cholesterol in response to PS consumption. Cholesterol synthesis assessment may thus have a use in identifying responders and nonresponders to PS therapy.

The combination of ezetimibe and ursodiol promotes fecal sterol excretion and reveals a G5G8-independent pathway for cholesterol elimination

Previous studies suggest an interdependent relationship between liver and intestine for cholesterol elimination from the body. We hypothesized that a combination of ursodiol (Urso) and ezetimibe (EZ) could increase biliary secretion and reduce cholesterol reabsorption, respectively, to promote cholesterol excretion. Treatment with Urso increased hepatic ABCG5 ABCG8 (G5G8) protein and both biliary and fecal sterols in a dose-dependent manner. To determine whether the drug combination (Urso-EZ) further increased cholesterol excretion, mice were treated with Urso alone or in combination with two doses of EZ. EZ produced an additive and dose-dependent increase in fecal neutral sterol (FNS) elimination in the presence of Urso. Finally, we sequentially treated wide-type and G5G8-deficient mice with Urso and Urso-EZ to determine the extent to which these effects were G5G8 dependent. Although biliary and FNS were invariably lower in G5G8 KO mice, the relative increase in FNS following treatment with Urso alone or the Urso-EZ combination was not affected by genotype. In conclusion, Urso increases G5G8, biliary cholesterol secretion, and FNS and acts additively with EZ to promote fecal sterol excretion. However, the stimulatory effect of these agents was not G5G8 dependent.

Role of dietary fats in modulating cardiometabolic risk during moderate weight gain: a randomized double-blind overfeeding trial (LIPOGAIN study)

BACKGROUND

Whether the type of dietary fat could alter cardiometabolic responses to a hypercaloric diet is unknown. In addition, subclinical cardiometabolic consequences of moderate weight gain require further study.

METHODS AND RESULTS

In a 7-week, double-blind, parallel-group, randomized controlled trial, 39 healthy, lean individuals (mean age of 27±4) consumed muffins (51% of energy [%E] from fat and 44%E refined carbohydrates) providing 750 kcal/day added to their habitual diets. All muffins had identical contents, except for type of fat; sunflower oil rich in polyunsaturated fatty acids (PUFA diet) or palm oil rich in saturated fatty acids (SFA diet). Despite comparable weight gain in the 2 groups, total: high-density lipoprotein (HDL) cholesterol, low-density lipoprotein:HDL cholesterol, and apolipoprotein B:AI ratios decreased during the PUFA versus the SFA diet (-0.37±0.59 versus +0.07±0.29, -0.31±0.49 versus +0.05±0.28, and -0.07±0.11 versus +0.01±0.07, P=0.003, P=0.007, and P=0.01 for between-group differences), whereas no significant differences were observed for other cardiometabolic risk markers. In the whole group (ie, independently of fat type), body weight increased (+2.2%, P<0.001) together with increased plasma proinsulin (+21%, P=0.007), insulin (+17%, P=0.003), proprotein convertase subtilisin/kexin type 9, (+9%, P=0.008) fibroblast growth factor-21 (+31%, P=0.04), endothelial markers vascular cell adhesion molecule-1, intercellular adhesion molecule-1, and E-selectin (+9, +5, and +10%, respectively, P<0.01 for all), whereas nonesterified fatty acids decreased (-28%, P=0.001).

CONCLUSIONS

Excess energy from PUFA versus SFA reduces atherogenic lipoproteins. Modest weight gain in young individuals induces hyperproinsulinemia and increases biomarkers of endothelial dysfunction, effects that may be partly outweighed by the lipid-lowering effects of PUFA.

CLINICAL TRIAL REGISTRATION URL

http://ClinicalTrials.gov. Unique identifier: NCT01427140.

Pathways of cholesterol homeostasis in mouse retina responsive to dietary and pharmacologic treatments

Effects of serum cholesterol on cholesterol content in the retina are currently unknown. It is also unclear how cholesterol levels are controlled in the retina. High-cholesterol diet and oral administrations of simvastatin were used to modulate serum cholesterol in mice. These treatments only modestly affected cholesterol content in the retina and had no significant effect on retinal expression of the major cholesterol- and vision-related genes; the sterol-regulatory element binding protein pathway of transcriptional regulation does not seem to be operative in the retina under the experimental conditions used. Evidence is obtained that posttranslational mechanisms play a role in the control of retinal cholesterol. Retinal genes were only upregulated by oral administrations of TO901317 activating liver X receptors. Three of the upregulated genes could be of particular importance (apoD, Idol, and Rpe65) and have not yet been considered in the context of cholesterol homeostasis in the retina. Collectively, the data obtained identify specific features of retinal cholesterol maintenance and suggest additional therapies for age-related macular degeneration, a blinding disease characterized by cholesterol and lipid accumulations in chorioretinal tissues.

Thyroid hormone reduces PCSK9 and stimulates bile acid synthesis in humans

Reduced plasma LDL-cholesterol is a hallmark of hyperthyroidism and is caused by transcriptional stimulation of LDL receptors in the liver. Here, we investigated whether thyroid hormone (TH) actions involve other mechanisms that may also account for the reduction in LDL-cholesterol, including effects on proprotein convertase subtilisin/kexin type 9 (PCSK9) and bile acid synthesis. Twenty hyperthyroid patients were studied before and after clinical normalization, and the responses to hyperthyroidism were compared with those in 14 healthy individuals after 14 days of treatment with the liver-selective TH analog eprotirome. Both hyperthyroidism and eprotirome treatment reduced circulating PCSK9, lipoprotein cholesterol, apoB and AI, and lipoprotein(a), while cholesterol synthesis was stable. Hyperthyroidism, but not eprotirome treatment, markedly increased bile acid synthesis and reduced fibroblast growth factor (FGF) 19 and dietary cholesterol absorption. Eprotirome treatment, but not hyperthyroidism, reduced plasma triglycerides. Neither hyperthyroidism nor eprotirome treatment altered insulin, glucose, or FGF21 levels. TH reduces circulating PSCK9, thereby likely contributing to lower plasma LDL-cholesterol in hyperthyroidism. TH also stimulates bile acid synthesis, although this response is not critical for its LDL-lowering effect.

Clinical utility of serum markers of cholesterol absorption and synthesis

PURPOSE OF REVIEW

The serum noncholesterol sterols are widely used today in clinical lipid research as surrogate markers of cholesterol absorption and synthesis. Their applicability and some aspects related to their analysis, use, and interpretations are discussed.

RECENT FINDINGS

The serum markers of cholesterol metabolism have been carefully validated in several populations and during different interventions. If the homeostasis between cholesterol absorption and synthesis is lost, the markers cannot be used as surrogates. The markers have been applied in large population and cohort studies to find out how cholesterol metabolism is related to coronary artery disease. Most of the large studies suggested that increased levels of the markers of cholesterol absorption may conceivably be a risk factor for coronary artery disease.

SUMMARY

Results even from large population studies vary from population to population. The large number of factors, which interfere with cholesterol metabolism, such as age, sex, BMI, diet, health status, medication, and genetic background, and differences in the analysis methods of the serum markers should be taken into consideration when interpreting the data.

Metabolomics approach reveals effects of antihypertensives and lipid-lowering drugs on the human metabolism

The mechanism of antihypertensive and lipid-lowering drugs on the human organism is still not fully understood. New insights on the drugs’ action can be provided by a metabolomics-driven approach, which offers a detailed view of the physiological state of an organism. Here, we report a metabolome-wide association study with 295 metabolites in human serum from 1,762 participants of the KORA F4 (Cooperative Health Research in the Region of Augsburg) study population. Our intent was to find variations of metabolite concentrations related to the intake of various drug classes and—based on the associations found—to generate new hypotheses about on-target as well as off-target effects of these drugs. In total, we found 41 significant associations for the drug classes investigated: For beta-blockers (11 associations), angiotensin-converting enzyme (ACE) inhibitors (four assoc.), diuretics (seven assoc.), statins (ten assoc.), and fibrates (nine assoc.) the top hits were pyroglutamine, phenylalanylphenylalanine, pseudouridine, 1-arachidonoylglycerophosphocholine, and 2-hydroxyisobutyrate, respectively. For beta-blockers we observed significant associations with metabolite concentrations that are indicative of drug side-effects, such as increased serotonin and decreased free fatty acid levels. Intake of ACE inhibitors and statins associated with metabolites that provide insight into the action of the drug itself on its target, such as an association of ACE inhibitors with des-Arg(9)-bradykinin and aspartylphenylalanine, a substrate and a product of the drug-inhibited ACE. The intake of statins which reduce blood cholesterol levels, resulted in changes in the concentration of metabolites of the biosynthesis as well as of the degradation of cholesterol. Fibrates showed the strongest association with 2-hydroxyisobutyrate which might be a breakdown product of fenofibrate and, thus, a possible marker for the degradation of this drug in the human organism. The analysis of diuretics showed a heterogeneous picture that is difficult to interpret. Taken together, our results provide a basis for a deeper functional understanding of the action and side-effects of antihypertensive and lipid-lowering drugs in the general population.