Deuterium uptake and plasma cholesterol precursor levels correspond as methods for measurement of endogenous cholesterol synthesis in hypercholesterolemic women

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.

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.

Genetic deletion of Abcc6 disturbs cholesterol homeostasis in mice

Genetic studies link adenosine triphosphate-binding cassette transporter C6 (ABCC6) mutations to pseudoxanthoma elasticum (PXE). ABCC6 sequence variations are correlated with altered HDL cholesterol levels and an elevated risk of coronary artery diseases. However, the role of ABCC6 in cholesterol homeostasis is not widely known. Here, we report reduced serum cholesterol and phytosterol levels in Abcc6-deficient mice, indicating an impaired sterol absorption. Ratios of cholesterol precursors to cholesterol were increased, confirmed by upregulation of hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase (Hmgcr) expression, suggesting activation of cholesterol biosynthesis in Abcc6-/- mice. We found that cholesterol depletion was accompanied by a substantial decrease in HDL cholesterol mediated by lowered ApoA-I and ApoA-II protein levels and not by inhibited lecithin-cholesterol transferase activity. Additionally, higher proprotein convertase subtilisin/kexin type 9 (Pcsk9) serum levels in Abcc6-/- mice and PXE patients and elevated ApoB level in knockout mice were observed, suggesting a potentially altered very low-density lipoprotein synthesis. Our results underline the role of Abcc6 in cholesterol homeostasis and indicate impaired cholesterol metabolism as an important pathomechanism involved in PXE manifestation.

Exploring the effect of vitamin D3 supplementation on surrogate biomarkers of cholesterol absorption and endogenous synthesis in patients with type 2 diabetes-randomized controlled trial

BACKGROUND

Inverse associations have been reported between serum 25-hydroxyvitamin D [25(OH)D] and circulating cholesterol concentrations in observational studies. Postulated mechanisms include reduced bioavailability of intestinal cholesterol and alterations in endogenous cholesterol synthesis.

OBJECTIVE

To explore the effect of daily supplementation with 4000 IU/d vitamin D3 for 24 wk on surrogate biomarkers of cholesterol absorption (campesterol and β-sitosterol) and endogenous synthesis (lathosterol and desmosterol).

METHODS

Ancillary study of The Vitamin D for Established Type 2 Diabetes (DDM2) trial. Patients with established type 2 diabetes (N = 127, 25-75 y, BMI 23-42 kg/m2) were randomly assigned to receive either 4000 IU vitamin D3 or placebo daily for 24 wk. Of participants without changes in cholesterol-lowering medications (n = 114), plasma surrogate cholesterol absorption and endogenous synthesis biomarker concentrations were measured and merged with available measures of serum LDL cholesterol and HDL cholesterol concentrations.

RESULTS

At week 24, vitamin D3 supplementation significantly increased 25(OH)D concentrations (+21.5 ± 13.4 ng/mL) but not insulin secretion rates (primary outcome of the parent study) as reported previously. In this ancillary study there was no significant effect of vitamin D3 supplementation on serum cholesterol profile or surrogate biomarkers of cholesterol absorption and endogenous synthesis. Compared with participants not treated with cholesterol-lowering medications, those who were treated exhibited a greater reduction in plasma campesterol concentrations in the vitamin D3 but not placebo group (P-interaction = 0.011). Analyzing the data on the basis of cholesterol absorption status (hypo- versus hyperabsorbers) or cholesterol synthesis status (hypo- versus hypersynthesizers) did not alter these results.

CONCLUSIONS

Vitamin D3 supplementation for 24 wk had no significant effect on surrogate biomarkers of cholesterol absorption or endogenous synthesis, consistent with the lack of effect on serum cholesterol profile. Vitamin D3 supplementation resulted in greater reduction in campesterol concentrations in participants not using compared with those using cholesterol-lowering medications. Further studies are required.This trial was registered at clinicaltrials.gov as NCT01736865.

Dysregulated Brain Cholesterol Metabolism Is Linked to Neuroinflammation in Huntington's Disease

Huntington's disease is an autosomal-dominant, neurodegenerative disorder caused by a CAG repeat expansion in exon-1 of the huntingtin gene. Alterations in cholesterol metabolism and distribution have been reported in Huntington's disease, including abnormal interactions between mutant huntingtin and sterol regulatory element-binding proteins, decreased levels of apolipoprotein E/cholesterol/low-density lipoprotein receptor complexes, and alterations in the synthesis of ATP-binding cassette transporter A1. Plasma levels of 24S-hydroxycholestrol, a key intermediary in cholesterol metabolism and a possible marker in neurodegenerative diseases, decreased proportionally to the degree of caudate nucleus atrophy. The interaction of mutant huntingtin with sterol regulatory element-binding proteins is of particular interest given that sterol regulatory element-binding proteins play a dual role: They take part in lipid and cholesterol metabolism, but also in the inflammatory response that induces immune cell migration as well as toxic effects, particularly in astrocytes. This work summarizes current evidence on the metabolic and immune implications of sterol regulatory element-binding protein dysregulation in Huntington's disease, highlighting the potential use of drugs that modulate these alterations. © 2020 International Parkinson and Movement Disorder Society.

Diurnal Variation of Markers for Cholesterol Synthesis, Cholesterol Absorption, and Bile Acid Synthesis: A Systematic Review and the Bispebjerg Study of Diurnal Variations

Human studies have shown diurnal rhythms of cholesterol and bile acid synthesis, but a better understanding of the role of the circadian system in cholesterol homeostasis is needed for the development of targeted interventions to improve metabolic health. Therefore, we performed a systematic literature search on the diurnal rhythms of cholesterol synthesis and absorption markers and of bile acid synthesis markers. We also examined the diurnal rhythms of the cholesterol synthesis markers lathosterol and desmosterol, and of the cholesterol absorption markers cholestanol, campesterol, and sitosterol in serum samples from the Bispebjerg study. These samples were collected every three hours over a 24-h period in healthy males (n = 24) who consumed low-fat meals. The systematic search identified sixteen papers that had examined the diurnal rhythms of the cholesterol synthesis markers lathosterol (n = 3), mevalonate (n = 9), squalene (n = 2), or the bile acid synthesis marker 7α-hydroxy-4-cholesten-3-one (C4) (n = 4). Results showed that lathosterol, mevalonate, and squalene had a diurnal rhythm with nocturnal peaks, while C4 had a diurnal rhythm with daytime peaks. Furthermore, cosinor analyses of the serum samples showed a significant diurnal rhythm for lathosterol (cosinor p < 0.001), but not for desmosterol, campesterol, sitosterol, and cholestanol (cosinor p > 0.05). In conclusion, cholesterol synthesis and bile acid synthesis have a diurnal rhythm, though no evidence for a diurnal rhythm of cholesterol absorption was found under highly standardised conditions. More work is needed to further explore the influence of external factors on the diurnal rhythms regulating cholesterol homeostasis.

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.

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.

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.

Increased cholesterol absorption rather than synthesis is involved in boosted protease inhibitor-associated hypercholesterolaemia

OBJECTIVE

The aim of this study was to compare the differential effects of first-line efavirenz (EFV)-based vs. boosted lopinavir-based antiretroviral regimens on cholesterol metabolism.

DESIGN

Multicentre, open-label, randomized clinical trial.

METHODS

Forty-nine naive HIV-infected patients were randomized (1 : 1) to receive either ritonavir-boosted lopinavir (LPV/r) or EFV both in combination with tenofovir and emtricitabine (ClinicalTrials.gov: NCT00759070). Lipid profile and serum phytosterols and cholesterol precursors were determined at baseline and after 16 weeks.

RESULTS

After 16 weeks of intervention, total and non-HDL cholesterol as well as triglyceride levels significantly increased in the LPV/r-group (+1.0 ± 0.8; +0.8 ± 0.7 and +0.8 ± 1.5 mmol/l, respectively), but not in the EFV-group (+0.4 ± 0.7; +0.4 ± 0.6 and 0.2 ± 0.5 mmol/l, respectively). Markers of cholesterol absorption (campesterol-to-cholesterol and sitosterol-to-cholesterol ratios) significantly increased in the LPV/r-group, but not in the EFV-group, whereas there were no changes in either group of the lathosterol-to-cholesterol ratio, a marker of cholesterol synthesis.

CONCLUSION

Treatment with an LPV/r-based therapy increased total cholesterol relative to EFV-based therapy. Our data suggest that absorption rather than synthesis is the mechanism involved in LPV/r-associated increased total cholesterol.

Bile acid synthesis precursors in subjects with genetic hypercholesterolemia negative for LDLR/APOB/PCSK9/APOE mutations. Association with lipids and carotid atherosclerosis

Some oxysterols are precursors of bile acid synthesis and play an important role in cholesterol homeostasis. However, if they are involved in the pathogeny of genetic hypercholesterolemia has not been previously explored. We have studied non-cholesterol sterol markers of cholesterol synthesis (lanosterol and desmosterol) and oxysterols (7α-hydroxy-4-cholesten-3-one, 24S-hydroxycholesterol and 27-hydroxycholesterol) in 200 affected subjects with primary hypercholesterolemia of genetic origin, negative for mutations in LDLR, APOB, PCSK9 and APOE genes (non-FH GH) and 100 normolipemic controls. All studied oxysterols and cholesterol synthesis markers were significantly higher in affected subjects than controls (P<0.001). Ratios of oxysterols to total cholesterol were higher in non-FH GH than in controls, although only 24S-hydroxycholesterol showed statistical significance (P<0.001). Cholesterol synthesis markers had a positive correlation with BMI, triglycerides, cholesterol and apoB in control population. However, these correlations disappeared in non-FH GH with the exception of a weak positive correlation for non-HDL cholesterol and apoB. The same pattern was observed for oxysterols with high positive correlation in controls and absence of correlation for non-FH GH, except non-HDL cholesterol for 24S-hydroxycholesterol and 27-hydroxycholesterol and apoB for 27-hydroxycholesterol. All non-cholesterol sterols had positive correlation among them in patients and in controls. A total of 65 (32.5%) and 35 (17.5%) affected subjects presented values of oxysterols ratios to total cholesterol above the 95th percentile of the normal distribution (24S-hydroxycholesterol and 27-hydroxycholesterol, respectively). Those patients with the highest levels of 24S-hydroxycholesterol associated an increase in the carotid intima media thickness. These results suggest that bile acid metabolism is affected in some patients with primary hypercholesterolemia of genetic origin, negative for mutations in the candidate genes, and may confer a higher cardiovascular risk. Our results confirm that cholesterol synthesis overproduction is a primary defect in non-HF GH and suggest that subjects with non-FH GH show high levels of oxysterols in response to hepatic overproduction of cholesterol.

Complex effects of inhibiting hepatic apolipoprotein B100 synthesis in humans

Mipomersen is a 20mer antisense oligonucleotide (ASO) that inhibits apolipoprotein B (apoB) synthesis; its low-density lipoprotein (LDL)-lowering effects should therefore result from reduced secretion of very-low-density lipoprotein (VLDL). We enrolled 17 healthy volunteers who received placebo injections weekly for 3 weeks followed by mipomersen weekly for 7 to 9 weeks. Stable isotopes were used after each treatment to determine fractional catabolic rates and production rates of apoB in VLDL, IDL (intermediate-density lipoprotein), and LDL, and of triglycerides in VLDL. Mipomersen significantly reduced apoB in VLDL, IDL, and LDL, which was associated with increases in fractional catabolic rates of VLDL and LDL apoB and reductions in production rates of IDL and LDL apoB. Unexpectedly, the production rates of VLDL apoB and VLDL triglycerides were unaffected. Small interfering RNA-mediated knockdown of apoB expression in human liver cells demonstrated preservation of apoB secretion across a range of apoB synthesis. Titrated ASO knockdown of apoB mRNA in chow-fed mice preserved both apoB and triglyceride secretion. In contrast, titrated ASO knockdown of apoB mRNA in high-fat-fed mice resulted in stepwise reductions in both apoB and triglyceride secretion. Mipomersen lowered all apoB lipoproteins without reducing the production rate of either VLDL apoB or triglyceride. Our human data are consistent with long-standing models of posttranscriptional and posttranslational regulation of apoB secretion and are supported by in vitro and in vivo experiments. Targeting apoB synthesis may lower levels of apoB lipoproteins without necessarily reducing VLDL secretion, thereby lowering the risk of steatosis associated with this therapeutic strategy.

Trans fatty acids and cholesterol levels: An evidence map of the available science

High intakes of industrial trans fatty acids (iTFA) increase circulating low density lipoprotein cholesterol (LDL-C) levels, which has implicated iTFA in coronary heart disease (CHD) risk. Published data on iTFA and LDL-C, however, represent higher intake levels than the U.S. population currently consume. This study used state-of-the-art evidence mapping approaches to characterize the full body of literature on LDL-C and iTFA at low intake levels. A total of 32 independent clinical trials that included at least one intervention or control group with iTFA at ≤3%en were found. Findings indicated that a wide range of oils and interventions were used, limiting the ability to determine an isolated effect of iTFA intake. Few data points were found for iTFA at <3%en, with the majority of low-level exposures actually representing control group interventions containing non-partially hydrogenated (PHO) oils. Further, it appears that few dose-response data points are available to assess the relationship of low levels of iTFA, particularly from PHO exposure, and LDL-C. Therefore, limited evidence is available to determine the effect of iTFA at current consumption levels on CHD risk.

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.

CYP7A1-rs3808607 and APOE isoform associate with LDL cholesterol lowering after plant sterol consumption in a randomized clinical trial

BACKGROUND

The benefits of plant sterols (PSs) for cholesterol lowering are hampered by large heterogeneity across individuals, potentially because of genetic polymorphisms.

OBJECTIVE

We investigated the impact of candidate genetic variations on cholesterol response to PSs in a trial that recruited individuals with high or low endogenous cholesterol synthesis, estimated by lathosterol to cholesterol (L:C) ratio.

DESIGN

Mildly hypercholesterolemic adults preselected as possessing either high endogenous cholesterol synthesis (n = 24; mean ± SEM: L:C ratio = 2.03 ± 0.39 μmol/mmol) or low endogenous cholesterol synthesis (n = 39; mean ± SEM: L:C ratio = 0.99 ± 0.28 μmol/mmol) consumed 2 g PS/d or a placebo for 28 d by using a dual-center, single-blind, randomized crossover design. Cholesterol synthesis and change in cholesterol absorption were measured with stable isotopic tracers. Candidate single-nucleotide polymorphisms and apolipoprotein E (APOE) isoform were assessed by TaqMan genotyping assay.

RESULTS

The cholesterol fractional synthesis rate was higher (P < 0.001) in participants with high endogenous cholesterol synthesis (mean ± SEM: placebo: 9.16% ± 0.47%; PSs: 9.74% ± 0.47%) than in participants with low endogenous cholesterol synthesis (mean ± SEM placebo: 5.72% ± 0.43%; PS: 7.10% ± 0.43%). Low-density lipoprotein (LDL) cholesterol lowering in response to PSs was associated with individuals' genotypes. Cholesterol 7 alpha-hydroxylase (CYP7A1-rs3808607) T/T homozygotes showed no LDL cholesterol lowering (mean ± SEM: -0.05 ± 0.07 mmol/L, P = 0.9999, n = 20), whereas the presence of the G-allele associated with LDL cholesterol response in a dose-dependent fashion (mean ± SEM G/T: -0.22 ± 0.06 mmol/L, P = 0.0006, n = 35; G/G: -0.46 ± 0.12 mmol/L, P = 0.0009, n = 8). Similarly, APOE ɛ3 carriers (mean ± SEM: -0.13 ± 0.05 mmol/L, P = 0.0370, n = 40) responded less than APOE ɛ4 carriers (mean ± SEM: -0.31 ± 0.07 mmol/L, P < 0.0001, n = 23). Moreover, genoset CYP7A1-rs3808607 T/T/APOE ɛ3 was associated with nonresponsiveness (mean ± SEM: +0.09 ± 0.08 mmol/L, P = 0.9999, n = 14). rs5882 in cholesteryl ester transfer protein (CETP) and rs4148217 in ATP-binding cassette subfamily G member 8 (ABCG8) did not associate with LDL cholesterol lowering. Cholesterol absorption decreased as a result of PS consumption, but this decrease was not related to circulating LDL cholesterol concentrations, cholesterol synthesis phenotype, or genotypes.

CONCLUSION

CYP7A1-rs3808607 and APOE isoform are associated with the extent of reduction in circulating LDL cholesterol in response to PS consumption and could serve as potential predictive genetic markers to identify individuals who would derive maximum LDL cholesterol lowering with PS consumption. The trial was registered at clinicaltrials.gov as NCT01131832.

Identification and metabolic profiling of patients with lysosomal acid lipase deficiency

BACKGROUND

Lysosomal acid lipase (LAL), encoded by the LIPA gene, catalyzes the intracellular hydrolysis of cholesteryl esters and triglycerides in hepatocytes and macrophages. LIPA defects cause accumulation of these lipids in lysosomes. LAL deficiency (LAL D) presents and progresses as a continuum with dyslipidemia, hepatomegaly, and liver fibrosis.

OBJECTIVE

To improve the understanding of the genetic basis of LAL D, an underappreciated cause of dyslipidemia and cirrhosis, we studied DNA samples from patients with various phenotypes of dyslipidemia.

METHODS

Participants (N = 1357) were identified by lipid profiles and screened for the common disease causing LIPA exon 8 skipping splice-site mutation (c.894G>A; p.Ser275_Gln298del; rs116928232).

RESULTS

Six patients were heterozygous for this variant. Complete LIPA sequencing revealed a patient, subsequently confirmed to have LAL D, with a heterozygous frameshift mutation involving deletion of exon 4 (p.Gly77Valfs*17 c.230-106_c.428+541del). A family study revealed a sister with the same genotype and phenotype. Genetic, clinical, and lipoprotein profiles of these sisters plus 6 additional family members are reported. Profiles of 2 other LAL D patients monitored for 2 decades are presented. Cholesterol homeostasis was studied to investigate rates of cholesterol synthesis and absorption in 4 LAL D patients. High-density lipoprotein (HDL) subspecies were also analyzed.

CONCLUSIONS

We used this LIPA sequencing strategy (detection of the relatively common exon 8 variant followed by complete gene sequencing to identify additional mutations) as a means to further elucidate the genetic basis of LAL D among individuals with a suggestive clinical phenotype.

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.

Effects of ezetimibe on cholesterol metabolism in HIV-infected patients with protease inhibitor-associated dyslipidemia: a single-arm intervention trial

Background

The effects of ezetimibe on cholesterol metabolism in HIV-infected patients receiving boosted protease inhibitors have not been thoroughly assessed. The aim of this study was to assess cholesterol homeostasis in patients with PI associated dyslipidemia and its relationship with the response to treatment with the cholesterol-absorption inhibitor ezetimibe.

Methods

Fifteen patients with ritonavir-boosted PI-containig therapy and LDL-cholesterol > 3.36 mmol/L (>130 mg/dL) were assessed at baseline and after an 8-week course of ezetimibe 10 mg/d. Serum non-cholesterol sterols were measured at each visit as markers of cholesterol synthesis and absorption. Total-, LDL-, and HDL-cholesterol triglycerides, apolipoproteins A1 and B, high sensitivity C-reactive protein, CD4 cells and HIV-1 RNA were also measured.

Results

Ezetimibe treatment was well tolerated in all patients and resulted in significant reductions in total cholesterol (-11.4%, p = .002), LDL-cholesterol (-20.4%, p = .003), non-HDL-cholesterol (-13.4%, p = .002) and apolipoprotein B (-9.1%, p = .021).

Treatment with ezetimibe was associated with decreased cholesterol absorption markers (campesterol-to-cholesterol ratio -43.0%, p = .001; sitosterol-to-cholesterol ratio -41.9%, p = .001) and increased synthesis markers (lathosterol-to-cholesterol ratio 53.2%, p = .005). Baseline absorption or synthesis markers were unrelated to the response to treatment. CD4 cell count and plasma HIV-1 RNA remained unchanged.

Conclusions

The level of cholesterol absorption or synthesis does not appear to be a major determinant of the responsiveness to ezetimibe in patients on ritonavir-boosted PI-containing therapy.

Trial registration

EudraCT: 2006-006156-36

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2334-14-497) contains supplementary material, which is available to authorized users.

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.

Methodological considerations for the harmonization of non-cholesterol sterol bio-analysis

Non-cholesterol sterols (NCS) are used as surrogate markers of cholesterol metabolism which can be measured from a single blood sample. Cholesterol precursors are used as markers of endogenous cholesterol synthesis and plant sterols are used as markers of cholesterol absorption. However, most aspects of NCS analysis show wide variability among researchers within the area of biomedical research. This variability in methodology is a significant contributor to variation between reported NCS values and hampers the confidence in comparing NCS values across different research groups, as well as the ability to conduct meta-analyses. This paper summarizes the considerations and conclusions of a workshop where academic and industrial experts met to discuss NCS measurement. Highlighted is why each step in the analysis of NCS merits critical consideration, with the hopes of moving toward more standardized and comparable NCS analysis methodologies. Alkaline hydrolysis and liquid-liquid extraction of NCS followed by parallel detection on GC-FID and GC-MS is proposed as an ideal methodology for the bio-analysis of NCS. Furthermore the importance of cross-comparison or round robin testing between various groups who measure NCS is critical to the standardization of NCS measurement.

Study of cholesterol metabolism in Huntington's disease

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by an abnormal expansion of a CAG repeat in the huntingtin gene. Neurodegeneration of striatum and cortex with a severe atrophy at MRI are common findings in HD. The expression of genes involved in the cholesterol biosynthetic pathway such as HMG-CoA reductase and the levels of cholesterol, lanosterol, lathosterol and 24S-hydroxycholesterol are reduced in the brain, striatum and cortex in several HD mouse models. Mutant huntingtin affects the maturation and translocation of SREBP and cannot up-regulate LXR. There is a lower synthesis and transport of cholesterol from astrocytes to neurons via ApoE. In primary oligodendrocytes, mutant huntingtin inhibits the regulatory effect of PGC1α on cholesterol metabolism and the expression of Myelin Basic Protein. In humans the decrease of plasma 24S-hydroxycholesterol follows disease progression proportionally to motor and neuropsychiatric dysfunctions and MRI brain atrophy. Huntingtin seems to play a regulatory role in lipid metabolism. Dysregulation of PGC1α and mitochondrial dysfunction may reduce synthesis of Acetyl-CoA and ATP contributing to the cerebral and whole body impairment of cholesterol metabolism.

De novo lipogenesis and cholesterol synthesis in humans with long-standing type 1 diabetes are comparable to non-diabetic individuals

BACKGROUND

Synthesis of lipid species, including fatty acids (FA) and cholesterol, can contribute to pathological disease. The purpose of this study was to investigate FA and cholesterol synthesis in individuals with type 1 diabetes, a group at elevated risk for vascular disease, using stable isotope analysis.

METHODS

Individuals with type 1 diabetes (n = 9) and age-, sex-, and BMI-matched non-diabetic subjects (n = 9) were recruited. On testing day, meals were provided to standardize food intake and elicit typical feeding responses. Blood samples were analyzed at fasting (0 and 24 h) and postprandial (2, 4, 6, and 8 hours after breakfast) time points. FA was isolated from VLDL to estimate hepatic FA synthesis, whereas free cholesterol (FC) and cholesteryl ester (CE) was isolated from plasma and VLDL to estimate whole-body and hepatic cholesterol synthesis, respectively. Lipid synthesis was measured using deuterium incorporation and isotope ratio mass spectrometry.

RESULTS

Fasting total hepatic lipogenesis (3.91 ± 0.90% vs. 5.30 ± 1.22%; P = 0.41) was not significantly different between diabetic and control groups, respectively, nor was synthesis of myristic (28.60 ± 4.90% vs. 26.66 ± 4.57%; P = 0.76), palmitic (12.52 ± 2.75% vs. 13.71 ± 2.64%; P = 0.65), palmitoleic (3.86 ± 0.91% vs. 4.80 ± 1.22%; P = 0.65), stearic (5.55 ± 1.04% vs. 6.96 ± 0.97%; P = 0.29), and oleic acid (1.45 ± 0.28% vs. 2.10 ± 0.51%; P = 0.21). Postprandial lipogenesis was also not different between groups (P = 0.38). Similarly, fasting synthesis of whole-body FC (8.2 ± 1.3% vs. 7.3 ± 0.8%/day; P = 0.88) and CE (1.9 ± 0.4% vs. 2.0 ± 0.3%/day; P = 0.96) and hepatic FC (8.2 ± 2.0% vs. 8.1 ± 0.8%/day; P = 0.72) was not significantly different between diabetic and control subjects.

CONCLUSIONS

Despite long-standing disease, lipogenesis and cholesterol synthesis was not different in individuals with type 1 diabetes compared to healthy non-diabetic humans.

Impact of buttermilk consumption on plasma lipids and surrogate markers of cholesterol homeostasis in men and women

BACKGROUND AND AIMS

Sphingolipids (SL) are important components of the milk fat globule membrane (MFGM) found in buttermilk. While studies in animal models suggest that dietary SL may have cholesterol-lowering properties, data in human are lacking. The aim of this study was to investigate the impact of buttermilk consumption on plasma lipids and surrogate markers of cholesterol (C) homeostasis in humans.

METHODS AND RESULTS

Men and women (n = 34) with serum LDL-C <5.0 mmol/L at screening (mean LDL-C = 3.8 mmol/L) were recruited in this double-blinded randomized crossover placebo controlled study. Their diets were supplemented with 45 g/d of buttermilk and with 45 g/d of a macro/micronutrient matched placebo (4 weeks each in random order). Serum lipid concentrations and surrogate markers of cholesterol homeostasis were measured post diet and compared using mixed models for repeated measures. Consumption of buttermilk led to reduction in serum cholesterol (-3.1%, P = 0.019), LDL-C (-3.1%, P = 0.057) and triacylglycerol (-10.7%, P = 0.007). Buttermilk consumption increased plasma lathosterol concentrations (+12.1%, P = 0.001), but multiple regression analysis indicated that variations in β-sitosterol concentrations (P = 0.002) were the only significant predictor of the LDL-C response to buttermilk consumption.

CONCLUSION

Buttermilk consumption may be associated with reduced cholesterol concentrations in men and women, primarily through inhibition of intestinal absorption of cholesterol.

REGISTRATION NUMBER

This trial is registered at clinicaltrials.gov as NCT01248026.

Ezetimibe and bile acid sequestrants: impact on lipoprotein metabolism and beyond

PURPOSE OF REVIEW

Several lines of evidence indicate that the enterocyte plays a pivotal role in cholesterol homeostasis. The development of the selective inhibitor of cholesterol absorption ezetimibe and bile acid sequestrants (BAS) interrupting the enterohepatic circulation of bile salts has expanded the options for preventing and treating cardiovascular disease. We discuss here a selection of recently published studies that evaluated the effects of ezetimibe and BAS on lipoprotein metabolism.

RECENT FINDINGS

Although significant progress has been made in recent years in elucidating the impacts of ezetimibe and BAS on lipoprotein metabolism, underlying mechanisms are not completely understood. Important new insights have been provided by using in-vivo kinetic studies of apolipoproteins labelled with a stable isotope. Other reports indicated that ezetimibe and BAS modulate the expression of several key genes involved in intestinal lipoprotein metabolism. Many of these effects have been related to the local effects of ezetimibe and BAS on intestinal cholesterol homeostasis.

SUMMARY

A substantial effort is being made by researchers to fully understand the mechanisms by which ezetimibe and BAS improve lipid profile. The efficacy of combination therapy of statins with ezetimibe or BAS for the prevention of cardiovascular disease remains to be confirmed in clinical endpoint studies.

Sex-specific differences in the predictive value of cholesterol homeostasis markers and 10-year cardiovascular disease event rate in Framingham Offspring Study participants

BACKGROUND

Available data are inconsistent regarding factors influencing plasma cholesterol homeostasis marker concentrations and their value in predicting subsequent cardiovascular disease (CVD) events.

METHODS AND RESULTS

To address this issue, the relationship between markers of cholesterol absorption (campesterol, sitosterol, cholestanol) and synthesis (squalene, desmosterol, lathosterol) and 10-year CVD incidence was assessed in Framingham Offspring Study participants (cycle 6) who were without CVD at baseline and not taking lipid-lowering medications (N=2616). The primary end point was "hard" coronary heart disease (HCHD; coronary death and myocardial infarction), and the secondary end point was full CVD (HCHD plus stroke, coronary insufficiency, angina pectoris, peripheral artery disease, and congestive heart failure). In cross-sectional analysis, significant differences by sex, age, body mass index, blood pressure, and smoking status were observed. In both women and men, lower cholesterol absorption was associated with higher triglyceride and lower high-density lipoprotein (HDL) cholesterol concentrations, whereas lower cholesterol synthesis was associated with higher low-density lipoprotein (LDL) cholesterol concentrations (P for trend <0.05). In women only, lower cholesterol synthesis and absorption were associated with higher non-HDL cholesterol concentrations. Using Cox proportional hazards model adjusting for standard CVD risk factors, squalene concentrations were associated with lower HCHD in women (hazard ratio=0.70 [0.5 to 0.9]). In contrast, squalene (hazard ratio=1.40 [1.1 to 1.8]) concentrations were associated with higher HCHD in men (P<0.0001 for interaction). The cholesterol absorption markers were not predictive of HCHD or full CVD in either women or men.

CONCLUSIONS

These data suggest significant sex differences in the 10-year prognostic value of cholesterol synthesis markers and HCHD, specifically coronary death and incidence of myocardial infarction.

CLINICAL TRIAL REGISTRATION

URL:http://ClinicalTrials.gov. Unique identifier: NCT00074464.

Plasma plant sterols serve as poor markers of cholesterol absorption in man

The validation of the use of plasma plant sterols as a marker of cholesterol absorption is frail. Nevertheless, plant sterol concentrations are routinely used to describe treatment-induced changes in cholesterol absorption. Their use has also been advocated as a clinical tool to tailor cholesterol-lowering therapy. Prior to wider implementation, however, the validity of plant sterols as absorption markers needs solid evaluation. Therefore, we compared plasma plant sterol concentrations to gold-standard stable isotope-determined cholesterol absorption. Plasma campesterol/TC concentrations (camp/TC) were measured in a population of 175 mildly hypercholesterolemic individuals (age: 59.7 ± 5.6 years; BMI: 25.5 ± 2.9 kg/m(2); LDL-C: 4.01 ± 0.56 mmol/l). We compared cholesterol absorption according to the plasma dual-isotope method in subjects with the highest camp/TC concentrations (N = 41, camp/TC: 2.14 ± 0.68 μg/mg) and the lowest camp/TC concentrations (N = 39, camp/TC: 0.97 ± 0.22 μg/mg). Fractional cholesterol absorption did not differ between the groups (24 ± 12% versus 25 ± 16%, P = 0.60), nor was it associated with plasma camp/TC concentrations in the total population of 80 individuals (β = 0.13; P = 0.30, adjusted for BMI and plasma triglycerides). Our findings do not support a relation between plasma plant sterol concentrations and true cholesterol absorption and, therefore, do not favor the use of these sterols as markers of cholesterol absorption. This bears direct consequences for the interpretation of earlier studies, as well as for future studies targeting intestinal regulation of cholesterol metabolism.

24S-hydroxycholesterol in plasma: a marker of cholesterol turnover in neurodegenerative diseases

Brain cholesterol is mainly involved in the cell membrane structure, in signal transduction, neurotransmitter release, synaptogenesis and membrane trafficking. Impairment of brain cholesterol metabolism was described in neurodegenerative diseases, such as Multiple Sclerosis, Alzheimer and Huntington Diseases. Since the blood-brain barrier efficiently prevents cholesterol uptake from the circulation into the brain, de novo synthesis is responsible for almost all cholesterol present there. Cholesterol is converted into 24S-hydroxycholesterol (24OHC) by cholesterol 24-hydroxylase (CYP46A1) expressed in neural cells. Plasma concentration of 24OHC depends upon the balance between cerebral production and hepatic elimination and is related to the number of metabolically active neurons in the brain. Factors affecting brain cholesterol turnover and liver elimination of oxysterols, together with the metabolism of plasma lipoproteins, genetic background, nutrition and lifestyle habits were found to significantly affect its plasma levels. Either increased or decreased plasma 24OHC concentrations were described in patients with neurodegenerative diseases. A group of evidence suggests that reduced levels of 24OHC are related to the loss of metabolically active cells and the degree of brain atrophy. Inflammation, dysfunction of BBB, increased cholesterol turnover might counteract this tendency resulting in increased levels or, in some cases, in unsignificant changes. The study of plasma 24OHC is likely to offer an insight about brain cholesterol turnover with a limited diagnostic power.

Metabolic consequences of mitochondrial coenzyme A deficiency in patients with PANK2 mutations

Pantothenate kinase-associated neurodegeneration (PKAN) is a rare, inborn error of metabolism characterized by iron accumulation in the basal ganglia and by the presence of dystonia, dysarthria, and retinal degeneration. Mutations in pantothenate kinase 2 (PANK2), the rate-limiting enzyme in mitochondrial coenzyme A biosynthesis, represent the most common genetic cause of this disorder. How mutations in this core metabolic enzyme give rise to such a broad clinical spectrum of pathology remains a mystery. To systematically explore its pathogenesis, we performed global metabolic profiling on plasma from a cohort of 14 genetically defined patients and 18 controls. Notably, lactate is elevated in PKAN patients, suggesting dysfunctional mitochondrial metabolism. As predicted, but never previously reported, pantothenate levels are higher in patients with premature stop mutations in PANK2. Global metabolic profiling and follow-up studies in patient-derived fibroblasts also reveal defects in bile acid conjugation and lipid metabolism, pathways that require coenzyme A. These findings raise a novel therapeutic hypothesis, namely, that dietary fats and bile acid supplements may hold potential as disease-modifying interventions. Our study illustrates the value of metabolic profiling as a tool for systematically exploring the biochemical basis of inherited metabolic diseases.

Tamm-Horsfall protein 1 macrophage lipid accumulation unaffected by fatty acid double-bond geometric or positional configuration

Dietary fatty acid type alters atherosclerotic lesion progression and macrophage lipid accumulation. Incompletely elucidated are the mechanisms by which fatty acids differing in double-bond geometric or positional configuration alter arterial lipid accumulation. The objective of this study was to evaluate the suitability of using Tamm-Horsfall protein 1 (THP-1) macrophages as a model for human monocytes/macrophages to address this issue. Our hypothesis was that THP-1 macrophages pretreated with ω-3 polyunsaturated fatty acids (PUFA) or fatty acid containing a cis double bond would accumulate less lipid, particularly cholesteryl ester, compared with ω-6 polyunsaturated fatty acids or a fatty acid containing a trans double bond, respectively. THP-1 monocytes were differentiated into macrophages and then incubated with fatty acids for 48 hours. There was an increase in intracellular lipid in response to all the fatty acids assessed, and by response was similar among the fatty acids. The increase in lipid accumulation was contributed to triglyceride and to a lesser extent cholesterol, primarily free cholesterol. These data suggest that free fatty acids bound to bovine serum albumin, regardless of double-bond geometric or positional configuration, induce triglyceride accumulation but had only a modest effect on cholesterol accumulation in THP-1 macrophages. The cells appeared to respond similarly to the assessed fatty acids in terms of amount and type of lipid accumulated. Hence, the THP-1 cell line was not appropriate to test the hypotheses of interest.

Atorvastatin increases intestinal expression of NPC1L1 in hyperlipidemic men

Inhibition of cholesterol synthesis by 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CoAR) inhibitors has been associated with an increase in intestinal cholesterol absorption. This study examined how HMG-CoAR inhibition by atorvastatin modulates expression of key genes involved in intestinal cholesterol metabolism. A crossover study was conducted in which 22 hyperlipidemic men received atorvastatin, 40 mg/day, or placebo, each for 12 weeks. Gene expression was assessed by real-time PCR using duodenal biopsy samples obtained at the end of each phase of treatment. Treatment with atorvastatin was associated with a 76% reduction in lathosterol and significant increases in sitosterol (70%). Atorvastatin significantly increased intestinal mRNA levels of HMG-CoAR (59%), LDL receptor (LDLR) (52%), PCSK9 (187%), SREBP-2 (44%), and HNF-4α (13%). Furthermore, atorvastatin significantly increased intestinal mRNA levels of NPC1L1 by 19% and decreased mRNA levels of both ABCG5 and ABCG8 by 14%. Positive correlations were observed between changes in SREBP-2 and HNF-4α expression and concurrent changes in the intestinal mRNA levels of HMG-CoAR, LDLR, and NPC1L1. These results indicate that HMG-CoAR inhibition with atorvastatin stimulates the intestinal expression of NPC1L1, LDLR, and PCSK9; increases cholesterol absorption; and reduces expression of ABCG5/8; these effects are most likely mediated by upregulation of the transcription factors SREBP-2 and HNF-4α.

Impact of dietary fat type within the context of altered cholesterol homeostasis on cholesterol and lipoprotein metabolism in the F1B hamster

Cholesterol status and dietary fat alter several metabolic pathways reflected in lipoprotein profiles. To assess plasma lipoprotein response and mechanisms by which cholesterol and dietary fat type regulate expression of genes involved in lipoprotein metabolism, we developed an experimental model system using F1B hamsters fed diets (12 weeks) enriched in 10% (wt/wt) coconut, olive, or safflower oil with either high cholesterol (0.1%; cholesterol supplemented) or low cholesterol coupled with cholesterol-lowering drugs 10 days before killing (0.01% cholesterol, 0.15% lovastatin, 2% cholestyramine; cholesterol depleted). Irrespective of dietary fat, cholesterol depletion, relative to supplementation, resulted in lower plasma non-high-density lipoprotein (non-HDL) and HDL cholesterol, and triglyceride concentrations (all Ps < .05). In the liver, these differences were associated with higher sterol regulatory element binding protein-2, low-density lipoprotein receptor, 3-hydroxy-3-methylglutaryl coenzyme A reductase, and 7α-hydroxylase messenger RNA (mRNA) levels; higher scavenger receptor B1 and apolipoprotein A-I mRNA and protein levels; lower apolipoprotein E protein levels; and in intestine, modestly lower sterol transporters adenosine triphosphate-binding cassette (ABC) A1, ABCG5, and ABCG8 mRNA levels. Irrespective of cholesterol status, coconut oil, relative to olive and safflower oils, resulted in higher non-HDL cholesterol and triglyceride concentrations (both Ps < .05) and modestly higher sterol regulatory element binding protein-2 mRNA levels. These data suggest that, in F1B hamsters, differences in plasma lipoprotein profiles in response to cholesterol depletion are associated with changes in the expression of genes involved in cholesterol metabolism, whereas the effect of dietary fat type on gene expression was modest, which limits the usefulness of the experimental animal model.

Evaluation of methods for the determination of cholesterol absorption and synthesis in humans

Cardiovascular disease risk and its associated complications correlate positively with circulating cholesterol levels. Plasma cholesterol levels are maintained by reciprocally related endogenous cholesterol synthesis and cholesterol absorption from dietary and biliary sources. Numerous in vivo clinical methods exist to quantify the absorption and synthesis of cholesterol in humans. This review summarizes these different methods available to study cholesterol absorption and synthesis, highlighting each method's strengths and weaknesses, as well as their applicability in different types of trials.

Familial combined hyperlipidemia is associated with alterations in the cholesterol synthesis pathway

OBJECTIVE

Familial combined hyperlipidemia (FCH) is a common familial lipid disorder characterized by increases in plasma total cholesterol, triglyceride, and apolipoprotein B-100 levels. In light of prior metabolic and genetic research, our purpose was to ascertain whether FCH cases had significant abnormalities of plasma markers of cholesterol synthesis and absorption as compared to unaffected kindred members.

METHODS AND RESULTS

Plasma levels of squalene, desmosterol, and lathosterol (cholesterol synthesis markers) and campesterol, sitosterol, and cholestanol (cholesterol absorption markers) were measured by gas-liquid chromatography in 103 FCH patients and 240 normolipidemic relatives (NLR). Squalene, desmosterol, and lathosterol levels were 6% (0.078), 31%, (P<0.001) and 51% (P<0.001) higher in FCH as compared to NLR, and these differences were especially pronounced in women. An interaction with obesity was also noted for a subset of these markers. We did not observe any apparent differences for the cholesterol absorption markers among FCH patients and NLR.

CONCLUSIONS

Our data indicate that both men and women with FCH have alterations in the cholesterol synthesis pathway, resulting in 51% higher levels of lathosterol (and additionally desmosterol in women). Plasma levels of the cholesterol precursor sterol squalene were only slightly increased (6%), suggesting enhanced conversion of squalene to lathosterol in this disorder.

Alterations in cholesterol absorption/synthesis markers characterize Framingham offspring study participants with CHD

Data is limited on measures influencing cholesterol homeostasis in subjects at high risk of developing cardiovascular disease (CVD) relative to established risk factors. To address this, we quantified circulating indicators of cholesterol homeostasis (plasma phytosterols and cholesterol precursor concentrations as surrogate measures of cholesterol absorption and synthesis, respectively) in Framingham Offspring Study Cycle-6 participants diagnosed with established CVD and/or >or=50% carotid stenosis not taking lipid lowering medication (cases, N = 155) and matched controls (N = 414). Cases and controls had similar plasma LDL-cholesterol; HDL-cholesterol was significantly lower in males, while triglyceride concentrations were significantly higher in female cases relative to their respective controls. Cholesterol absorption markers were significantly higher (229 +/- 7 vs. 196 +/- 4, 169 +/- 6 vs. 149 +/- 3 and 144 +/- 5 vs. 135 +/- 3 for campesterol, sitosterol, and cholestanol, respectively), whereas cholesterol synthesis markers were significantly lower (116 +/- 4 vs. 138 +/- 3, 73 +/- 3 vs. 75 +/- 2 for lathosterol and desmosterol, respectively) in cases compared with controls, irrespective of sex. After controlling for standard risk factors, campesterol (2.47 [1.71-3.56]; P < 0.0001), sitosterol (1.86 [1.38-2.50]; P < 0.0001), cholestanol (1.57 [1.09-2.27]; P = 0.02), desmosterol (0.59 [0.42-0.84]; P = 0.003), and lathosterol (0.58 [0.43-0.77]; P = 0.0002) were significantly associated with CVD (odds ratio [95% confidence interval]). These data suggest that impaired cholesterol homeostasis, reflected by lower synthesis and higher absorption marker concentrations, are highly significant independent predictors of prevalent CVD in this study population.

Effects of ezetimibe and simvastatin on apolipoprotein B metabolism in males with mixed hyperlipidemia

Sixteen hyperlipidemic men were enrolled in a randomized, placebo-controlled, double-blind, cross-over study to evaluate the effect of ezetimibe 10 mg and simvastatin 40 mg, coadministered and alone, on the in vivo kinetics of apolipoprotein (apo) B-48 and B-100 in humans. Subjects underwent a primed-constant infusion of a stable isotope in the fed state. The coadministration of simvastatin and ezetimibe significantly reduced plasma concentrations of cholesterol (-43.0%), LDL-C (-53.6%), and triglycerides (-44.0%). Triglyceride-rich lipoproteins (TRL) apoB-48 pool size (PS) was significantly decreased (-48.9%) following combination therapy mainly through a significant reduction in TRL apoB-48 production rate (PR) (-38.0%). The fractional catabolic rate (FCR) of VLDL and LDL apoB-100 were significantly increased with all treatment modalities compared with placebo, leading to a significant reduction in the PS of these fractions. We also observed a positive correlation between changes in TRL apoB-48 PS and changes in TRL apoB-48 PR (r = 0.85; P < 0.0001) with combination therapy. Our results indicate that treatment with simvastatin plus ezetimibe is effective in reducing plasma TRL apoB-48 levels and that this effect is most likely mediated by a reduction in the intestinal secretion of TRL apoB-48. Our study also indicated that the reduction in LDL-C concentration following combination therapy is mainly driven by an increase in FCR of apoB-100 containing lipoproteins.

Single nucleotide polymorphisms in ABCG5 and ABCG8 are associated with changes in cholesterol metabolism during weight loss

The purpose of this study was to examine whether changes in cholesterol metabolism after weight loss were affected by single nucleotide polymorphisms (SNPs) in ABCG5 and ABCG8 genes. Thirty-five hypercholesterolemic women lost 11.7 +/- 2.5 kg (P < 0.001). Cholesterol kinetics were assessed using stable isotope techniques. TaqMan PCR was used to detect SNPs in ABCG5/G8. Homozygous Q604E variants in ABCG5 had larger (P < 0.05) reductions in cholesterol absorption and greater increases (P < 0.05) in synthesis in contrast to heterozygous and homozygous wild-type carriers. Heterozygous C54Y carriers had smaller declines (P = 0.047) in synthesis compared with homozygous variant individuals. The presence of at least one Y54 variant was associated with higher (P = 0.042) post-weight-loss synthesis compared with carriers of the C54 genotype. The direction of the results is consistent with cross-sectional studies on the effects of Q604E and C54Y polymorphisms on plasma cholesterol. SNPs in ABCG5/G8 were found to be associated with the response of cholesterol metabolism to weight loss. The evidence for associations between SNPs in ABCG5/G8 and various parameters of cholesterol metabolism indicates the potential effectiveness of establishing genetic screening tools to determine optimal lipid-lowering treatment routes for individuals during weight reduction.

Dose-response effects of different plant sterol sources in fat spreads on serum lipids and C-reactive protein and on the kinetic behavior of serum plant sterols

OBJECTIVE

To test the dose-response effect on low-density lipoprotein cholesterol (LDL-c) of plant sterols (PS) from different sources in a low-fat spread.

METHODS

Dose responses of soybean oil (BO), tall oil (TO) and a mix of tall oil and rapeseed oil (TO/RP) as fatty acid esters were tested in a parallel design in free-living subjects recruited from the general community who had elevated cholesterol concentrations. Subjects received either control for 6 weeks or 1.6 g PS per day for 3 weeks, then 3.0 g/day for 3 weeks.

RESULTS

LDL-c was lowered significantly by consumption of 1.6 g/day of PS (-10.4%, range -7.3 to -11.4%). Increasing the dose to 3.0 g/day modestly reduced LDL-c concentrations further to -14.7%. TO, containing 78% sitosterol, produced an increase in serum sitosterol of 6.5 nmol/ml, while BO, containing only 27% campesterol, produced an increase in serum campesterol of 9.5 nmol/ml in 6 weeks. After PS withdrawal, serum sterols declined by 50% within 2 weeks.

CONCLUSION

Different PS sources were equally effective in lowering serum LDL-c concentrations. The decrease in absolute concentrations of LDL-c was dependent on the baseline concentrations.

Very long chain fatty acids (policosanols) and phytosterols affect plasma lipid levels and cholesterol biosynthesis in hamsters

The aim of the current study was to examine the effects of very long chain fatty acids (VLCFA) alone at 2 dietary levels, or in combination of VLCFA at the lower level with lecithin (LT) or phytosterols (PS), on lipid profiles and cholesterol biosynthesis in hamsters. Seventy-five male Golden Syrian hamsters, weighing 100 to 120 g, were fed a regular rodent chow for 2 weeks before being randomly assigned into 5 groups of 15 animals each fed semisynthetic diets for 4 weeks. Group 1 was given a control diet that contained 0.25% cholesterol and 5% fat with a polyunsaturated to saturated fatty acids ratio of 0.4. Groups 2 to 5 were fed the control diet and given 25 mg/kg BW per day of VLCFA (Licowax) (VLCFA25), 50 mg/kg BW per day of VLCFA (VLCFA50), 25 mg/kg BW per day of VLCFA+1000 mg/kg BW per day of LT (VLCFA25/LT), and 25 mg/kg BW per day of VLCFA+1000 mg/kg BW per day of PS (Cholestatin, VLCFA25/PS), respectively. Results showed that HDL-cholesterol (HDL-C) levels were not changed by VLCFA25, although increased by VLCFA50 (P<.05) relative to control. Total cholesterol (T-C) and non-HDL-C levels were not affected by VLCFA25 and VLCFA50 as compared with control. VLCFA25/LT had higher (P<.02) T-C and HDL-C levels than any other treatments and increased (P<.05) liver weight relative to control. In contrast, VLCFA25/PS reduced T-C (P=.0004) and non-HDL-C (P=.007) without effect on HDL-C levels compared with control. Triglyceride levels were not affected by any treatment. Cholesterol biosynthesis rate was higher (P<.05) in animals fed VLCFA25 and VLCFA50 than those fed control or VLCFA25/LT or VLCFA25/PS. Results suggest that PSs can decrease total and non-HDL-C cholesterol, whereas VLCFA may increase HDL-C in hamsters.

Impact of simvastatin, niacin, and/or antioxidants on cholesterol metabolism in CAD patients with low HDL

The HDL Atherosclerosis Treatment Study (HATS) demonstrated a clinical benefit in coronary artery disease patients with low HDL cholesterol (HDL-C) levels treated with simvastatin and niacin (S-N) or S-N plus antioxidants (S-N+A) compared with antioxidants alone or placebo. Angiographically documented stenosis regressed in the S-N group but progressed in all other groups. To assess the mechanism(s) responsible for these observations, surrogate markers of cholesterol absorption and synthesis were measured in a subset of 123 HATS participants at 24 months (on treatment) and at 38 months (off treatment). Treatment with S-N reduced desmosterol and lathosterol levels (cholesterol synthesis indicators) 46% and 36% (P < 0.05), respectively, and elevated campesterol and beta-sitosterol levels (cholesterol absorption indicators) 70% and 59% (P < 0.05), respectively, relative to placebo and antioxidant but not S-N+A. Treatment with antioxidants alone had no significant effect. Combining S-N with antioxidants reduced desmosterol and lathosterol by 37% and 31%, and elevated campesterol and beta-sitosterol levels by 54% and 46%, but differences did not attain significance. Mean change in percent stenosis was positively associated with a percent change in lathosterol (r = 0.26, P < 0.005) and negatively associated with a percent change in beta-sitosterol (r = -0.21, P < 0.01). These data suggest that changes in stenosis were attributable, in part, to changes in cholesterol metabolism.

Isotopomer spectral analysis of intermediates of cholesterol synthesis in human subjects and hepatic cells

Steroid intermediates of the cholesterol synthesis pathway are characterized by rapid turnover rates relative to cholesterol due to their small pool size. Because the small pools will label rapidly, these intermediates may provide valuable information about the incorporation of isotopes in de novo synthesis of cholesterol and related compounds. The labeling of cholesterol synthesis intermediates from [1-(13)C]acetate was investigated in human subjects and in liver cell models by means of isotopomer spectral analysis (ISA). In human subjects, infusing [1-(13)C]acetate into the duodenum for 12 h demonstrated that approximately 50% of the plasma lathosterol pool was derived from de novo synthesis during this interval. The lipogenic acetyl-CoA precursor pool enrichment reached a constant value within 3 h of the start of the infusion. In vitro studies indicated that liver cell models decrease de novo lathosterol synthesis when cholesterol synthesis is inhibited by statins or cholesterol-containing serum. We propose a new calculation to increase the accuracy and precision of cholesterol synthesis estimates in vivo combining the ISA of lathosterol and cholesterol.