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

Dietary Lipids, Gut Microbiota, and Their Metabolites: Insights from Recent Studies

Dietary lipid intake can influence the gut microbiota (GM) and their metabolites, such as short-chain fatty acids (SCFA) and bile acids, which are key mediators of health. The objective is to examine how dietary lipids' quantity and quality influence the GM and metabolite profiles. A literature review of 33 studies in animals and humans was performed on the effects of saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids (PUFAs), trans-fatty acids (TFAs), and sterols on GM composition and gut-derived metabolites. The results show that diets rich in MUFAs, n-3 PUFAs, and short-chain FAs have the potential to enhance beneficial bacteria and metabolites. In addition, trans-palmitoleic acid, conjugated linoleic acid, and phytosterols may also have potentially beneficial effects on GM, but more research is needed. Medium-chain FAs and n-6 PUFAs have variable effects on the GM. Conversely, intakes of high-fat diets, long-chain SFAs, industrial TFAs, and cholesterol disrupt GM balance. In conclusion, animal studies clearly demonstrate that dietary fats influence the GM and related metabolites. Yet, human studies are limited. Therefore, well-designed human studies that consider the whole diet and baseline health status are needed to better understand the effects of dietary lipids on GM.

Unique sterol metabolite shifts in inflammatory bowel disease and primary sclerosing cholangitis

Inflammatory bowel disease (IBD) triggers chronic intestinal inflammation and is linked to primary sclerosing cholangitis (PSC). Cholesterol homeostasis, tightly regulated under normal conditions, becomes disrupted in both inflammation and chronic liver disease. We analyzed fecal and serum levels of cholesterol synthesis precursors, oxysterols, and phytosterols in 87 patients with IBD (81 for serum analysis) including patients with Crohn's disease (CD) and ulcerative colitis (UC), 11 patients with PSC, 21 patients with PSC-IBD (18 for serum analysis), and 16 healthy controls (17 for serum analysis). Cholesterol was analysed by flow injection analysis on a high-resolution hybrid quadrupole-Orbitrap mass spectrometer and further serum sterols and all fecal sterols were analysed by a gas chromatograph mass spectrometer. Serum levels of lanosterol, 7-dehydrocholesterol, 7-beta-hydroxycholesterol, 27-hydroxycholesterol, and the plant sterols campesterol, stigmasterol, and sitosterol were similar across control and patient groups. Notably, serum lathosterol was elevated in CD patients compared to those with UC, PSC, PSC-IBD, and healthy controls. All other serum and fecal sterols showed no differences between CD and UC. Cholesterol synthesis precursors in serum, serum cholesterol levels, and both serum and fecal plant sterol levels decreased with increasing IBD severity. Consequently, serum cholesterol, campesterol, sitosterol, and fecal 5-beta sitostanol and 5-alpha sitostanol were negatively correlated with C-reactive protein and fecal calprotectin. The conversion of cholesterol to coprostanol in feces was impaired in IBD, PSC, and PSC-IBD, independent of bowel inflammation severity or liver disease extent. Patients with PSC, and to a lesser extent PSC-IBD, had elevated serum plant sterol levels, positively correlating with liver disease markers. In conclusion, in patients with IBD, cholesterol biosynthetic precursors, serum cholesterol levels, and fecal plant sterols decrease with intestinal inflammation. An inverse association of serum plant sterols with intestinal inflammation was observed in patients with IBD and a direct association of serum phytosterols with liver injury in patients with PSC. The conversion of fecal cholesterol to coprostanol was impaired in all patient cohorts. IBD and PSC alter serum sterol levels differently, whereas changes in fecal sterols are not disease specific and are moderate.

Reversal of insulin resistance in people with obesity by lifestyle-induced weight loss does not impact the proportion of circulating 12α-hydroxylated bile acids

AIM

Bile acids (BAs) are implicated in the pathogenesis of several metabolic syndrome-related diseases, including insulin resistance (IR) and type 2 diabetes (T2D). It has been reported that IR and T2D are associated with an increased ratio of 12α/non-12α-hydroxylated BAs in the circulating BA pool. It is, however, unknown whether the improvement of insulin sensitivity inversely affects BA composition in humans. Therefore, we assessed whether lifestyle-induced weight loss induces changes in BA metabolism in people with obesity, with or without T2D, and if these changes are associated with metabolic parameters.

MATERIALS AND METHODS

Individual BAs and C4 were quantified by ultra-high-performance liquid chromatography-tandem mass spectrometry in plasma samples collected from two cohorts of people with obesity (OB) and with T2D and obesity (T2D), before and after a lifestyle intervention.

RESULTS

Lifestyle-induced weight loss improved glycaemic control in both cohorts, with plasma BA concentrations not affected by the lifestyle interventions. The ratio of 12α/non-12α-hydroxylated BAs remained unchanged in OB (p = .178) and even slightly increased upon intervention in T2D (p = .0147). Plasma C4 levels were unaffected in OB participants (p = .20) but significantly reduced in T2D after intervention (p = .0003). There were no significant correlations between the ratio of 12α/non-12α-hydroxylated BAs and glucose, insulin, or homeostatic model assessment-IR, nor in plasma triglycerides, low-density lipoprotein cholesterol, lipoprotein (a) in the T2D cohort.

CONCLUSIONS

Lifestyle-induced weight loss did improve glycaemic control but did not affect BA concentrations. Improvements in insulin sensitivity were not associated with changes in BA parameters in people with obesity, with or without T2D.

The effect of hydroxychloroquine on cholesterol synthesis depends on the profile of cholesterol metabolism. A controlled clinical study

Background and aims

Hydroxychloroquine (HCQ) has a variable effect on cholesterol synthesis. To clarify this, we assessed the effect of HCQ on the cholesterol-synthesis pathway in individuals with low and high cholesterol absorption efficiency.

Method

A total of 53 acute myocardial infarction patients with a constant statin dose randomized to receive HCQ or placebo for six months in a double-blind manner, were classified further into low (n = 26) and high (n = 27) cholesterol absorbers based on the median baseline serum cholestanol level. Serum lipids and biomarkers of cholesterol synthesis (squalene, lanosterol, zymostenol, desmosterol, and lathosterol) and absorption efficiency (sitosterol and cholestanol), were measured at baseline and one-, six-, and 12-month follow-up visits.

Results

In low cholesterol absorbers, serum cholesterol concentration and cholesterol synthesis and absorption biomarkers did not differ between the HCQ and placebo groups. At one month, high cholesterol absorbers with HCQ had lower serum cholesterol concentration and serum lanosterol to cholesterol ratio in comparison to the placebo group (HCQ 3.18 ± 0.62 vs. placebo 3.71 ± 0.65, p = 0.042, and HCQ 10.4 ± 2.55 vs. placebo 13.1 ± 2.36, p = 0.008, respectively). At 12 months, serum desmosterol to cholesterol ratio was lower in HCQ users (HCQ 47.1 ± 7.08 vs. placebo 59.0 ± 13.1, p = 0.011).

Conclusions

HCQ affects the cholesterol-synthesis pathway in high cholesterol absorbers. It reduces serum lanosterol and desmosterol ratios and consequently serum cholesterol concentration possibly by inhibiting the activity of lanosterol synthase as described earlier in vitro studies.

Trial registration

ClinicalTrials.gov Identifier: NCT02648464.

Serum Low Density Lipoprotein Cholesterol Concentration Is Not Dependent on Cholesterol Synthesis and Absorption in Healthy Humans

Introduction. Pharmacological reduction of cholesterol (C) synthesis and C absorption lowers serum low-density lipoprotein C (LDL-C) concentrations. We questioned whether high baseline C synthesis or C absorption translates into high serum LDL-C concentrations or if there was no connection. Therefore, we studied the association between serum LDL-C and C synthesis or C absorption in healthy subjects. Methods. Three published data sets of young subjects on different diets (study 1), mildly hypercholesterolemic subjects without cardiovascular disease (study 2) and healthy controls of the Framingham study (study 3) were used. The three study populations varied in sex, age, and weight. C synthesis and C fractional absorption rate (FAR) were measured with fecal sterol balance and stable isotope techniques (studies 1 and 2). Additionally, serum lathosterol and campesterol concentrations corrected for the serum total C concentration (R_lathosterol and R_campesterol) were used as markers for hepatic C synthesis and C FAR, respectively (studies 1−3). Linear regression analysis was applied to evaluate associations between LDL-C, C synthesis, and C absorption. Results. Seventy-three, 37, and 175 subjects were included in studies 1, 2, and 3, respectively. No statistically significant associations were found between LDL-C and the measured C synthesis and C FAR, nor for R_lathosterol and R_campesterol in any of the study groups. This lack of associations was confirmed by comparing the male subjects of studies 1 and 2. Study 1 subjects had a 50% lower serum LDL-C than the study 2 subjects (p < 0.01), but not a lower C synthesis, C FAR, R-lathosterol, or R_campesterol. Conclusions. Under physiological conditions, C synthesis and C FAR are not major determinants of circulating serum LDL-C concentrations in healthy subjects. The results need to be confirmed in large-scale studies in healthy subjects and patients at risk for cardiovascular disease.

Genetic variation and intestinal cholesterol absorption in humans: A systematic review and a gene network analysis

Intestinal cholesterol absorption varies widely between individuals, which may translate into differences in responsiveness to cholesterol-lowering drugs or diets. Therefore, understanding the importance of genetic variation on cholesterol absorption rates and the complex intestinal cholesterol network is important. Based on a systematic review, genetic variants in seven genes (ABCG5, ABCG8, ABO, APOE, MTTP, NPC1L1, and LDLR) were identified that were associated with intestinal cholesterol absorption. No clear associations were found for variants in APOA4, APOB, CETP, CYP7A1, HMGCR, SCARB1, SLCO1B1, and SREBF1. The seven genes were used to construct an intestinal cholesterol absorption network. Finally, a network with fifteen additional genes (APOA1, APOA4, APOB, APOC2, APOC3, CETP, HSPG2, LCAT, LDLRAP1, LIPC, LRP1, OLR1, P4HB, SAR1B, and SDC1) was generated. The constructed network shows that cholesterol absorption is complex. Further studies are needed to validate and improve this network, which may ultimately lead to a better understanding of the wide inter-individual variability in intestinal cholesterol absorption and the development of personalized interventions.

Plasma lathosterol measures rates of cholesterol synthesis and efficiency of dietary phytosterols in reducing the plasma cholesterol concentration

OBJECTIVES

Because the plasma campesterol/cholesterol ratio does not differ between groups that absorb different amounts of cholesterol, the authors investigated whether the plasma Phytosterols (PS) relate to the body's cholesterol synthesis rate measured as non-cholesterol sterol precursors (lathosterol).

METHOD

The authors studied 38 non-obese volunteers (58±12 years; Low-Density Lipoprotein Cholesterol ‒ LDL-C ≥ 130 mg/dL) randomly assigned to consume 400 mL/day of soy milk (Control phase) or soy milk + PS (1.6 g/day) for four weeks in a double-blind, cross-over study. PS and lathosterol were measured in plasma by gas chromatography coupled to mass spectrophotometry.

RESULTS

PS treatment reduced plasma total cholesterol concentration (-5.5%, p < 0.001), LDL-C (-7.6%, p < 0.001), triglycerides (-13.6%, p < 0.0085), and apolipoprotein B (apo B) (-6.3%, p < 0.008), without changing high density lipoprotein cholesterol (HDL-C concentration), but plasma lathosterol, campesterol and sitosterol expressed per plasma cholesterol increased.

CONCLUSIONS

The lathosterol-to-cholesterol plasma ratio predicted the plasma cholesterol response to PS feeding. The highest plasma lathosterol concentration during the control phase was associated with a lack of response of plasma cholesterol during the PS treatment period. Consequently, cholesterol synthesis in non-responders to dietary PS being elevated in the control phase indicates these cases resist to further synthesis rise, whereas responders to dietary PS, having in the control phase synthesis values lower than non-responders, expand synthesis on alimentary PS. Responders absorb more PS than non-responders, likely resulting from responders delivering into the intestinal lumen less endogenous cholesterol than non-responders do, thus facilitating greater intestinal absorption of PS shown as increased plasma PS concentration.

Determination of genetic scores to estimate disturbances in circulating lipid profile biomarkers of adolescents: A preliminary report

OBJECTIVE

The aim of this study was to develop genetic scores based on single-nucleotide polymorphisms (SNPs) related to lipid metabolism and evaluate whether they used to estimate disturbances in the circulating lipid profile biomarkers of adolescents.

METHODS

In a preliminary cross-sectional approach, 113 Brazilian adolescents (10-19 y of age) with cardiovascular disease risk factors were evaluated. Genetic scores from 20 SNPs related to lipid metabolism were calculated by codifying each of them as the rescaled sum of risk allele frequencies. All scores were distributed in classes between 0 (absence of risk alleles) and 10 (presence of all risk alleles) to evaluate the additive effect of risk alleles on the lipid profile outcomes in the same interval. Multiple linear regression analyses were performed to evaluate the association between each score and blood lipid profile biomarkers.

RESULTS

Significant associations between genetic scores and unfavorable outcomes in all evaluated lipid profile biomarkers were found. The mean ± SD of the genetic scores for the circulating lipid profile biomarkers in the 0 to 10 scale were 4.4 ± 2 for triacylglycerol, 5.3 ± 1.5 for total cholesterol, 5.6 ± 1.2 for high-density lipoprotein cholesterol, 4.9 ± 1.6 for low-density lipoprotein cholesterol, and 3.6 ± 1.9 for minimally modified low-density lipoprotein cholesterol. For each point obtained in each genetic score, a mean increase ± SE of 15.8 ± 4.2 mg/dL in triacylglycerol (P = 0.0001), 5.3 ± 1.7 mg/dL in total cholesterol (P = 0.0032), 4.8 ± 1.3 mg/dL in low-density lipoprotein cholesterol (P = 0.0003), and 1.1 ± 0.3 U/L in minimally modified low-density lipoprotein cholesterol (P = 0.0020) and a mean decrease of 3.7 ± 0.7 mg/dL in high-density lipoprotein cholesterol (P < 0.0001) concentrations were obtained.

CONCLUSION

The calculated genetic scores could be used to estimate disturbances in circulating lipid profile biomarkers of adolescents and be applied in clinical practice to better target interventions to reduce cardiovascular disease risk throughout life.

Lumacaftor/ivacaftor improves liver cholesterol metabolism but does not influence hypocholesterolemia in patients with cystic fibrosis

BACKGROUND

Cystic fibrosis (CF) patients have reduced intestinal absorption of sterols and, despite enhanced endogenous synthesis, low plasma cholesterol. Lumacaftor/ivacaftor CFTR protein modulator therapy is used to improve the clinical outcome of CF patients homozygous for F508del mutation (homo-deltaF508). Aim of the study is to evaluate the cholesterol metabolism and hepatobiliary injury/function in adult homo-deltaF508 patients, before and after lumacaftor/ivacaftor treatment. Baseline parameters in homo-deltaF508 patients were compared to those in CF patients compound heterozygous for F508del mutation and another severe mutation (hetero-deltaF508).

METHODS

Cholesterol metabolism was evaluated measuring plasma phytosterols and cholestanol, as intestinal absorption markers, and lathosterol, as liver biosynthesis marker. We quantified serum vitamin E, as nutritional marker. We evaluated liver injury by aspartate aminotransferase (AST) and alanine transaminase (ALT), biliary injury by γ-glutamyltransferase (γGT) and AP, and the liver function by bilirubin and albumin.

RESULTS

Before the treatment, homo-deltaF508 patients (n = 20) had significantly lower cholesterol and vitamin E compared to hetero-deltaF508 (n = 20). Lumacaftor/ivacaftor treatment caused: 1) further reduction of cholesterol; 2) lathosterol reduction, suggesting a normalization of endogenous synthesis; 3) cholestanol and vitamin E increment, indicating an improvement of lipid digestion/absorption. Vitamin E difference (after-before treatment) was positively associated to treatment months. Alkaline phosphatase was also reduced.

CONCLUSIONS

These data suggest an effect of lumacaftor/ivacaftor on cholesterol metabolism and enterohepatic flux in CF patients. However, lumacaftor/ivacaftor does not promote the increase of cholesterol serum concentration that on the contrary declines. Further studies are needed to research the real mechanism causing this reduction.

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.

Comparison of phytosterol intake from FFQ with repeated 24-h dietary recalls of the Adventist Health Study-2 calibration sub-study

We evaluated the performance of an FFQ in estimating phytosterol intake against multiple 24-h dietary recalls (24HDR) using data from 1011 participants of the calibration sub-study of the Adventist Health Study-2 (AHS-2) cohort. Dietary assessments of phytosterol intake included a self-administered FFQ and six 24HDR and plasma sterols. Plasma sterols were determined using the GLC flame ionisation method. Validation of energy-adjusted phytosterol intake from the FFQ with 24HDR was conducted by calculating crude, unadjusted, partial and de-attenuated correlation coefficients (r) and cross-classification by race. On average, total phytosterol intake from the FFQ was 439·6 mg/d in blacks and 417·9 mg/d in whites. From the 24HDR, these were 295·6 mg/d in blacks and 351·4 mg/d in whites. Intake estimates of β-sitosterol, stigmasterol, other plant sterols and total phytosterols from the FFQ had moderate to strong correlations with estimates from 24HDR (r 0·41-0·73). Correlations were slightly higher in whites (r 0·42-0·73) than in blacks (r 0·41-0·67). FFQ estimates were poorly correlated with plasma sterols as well as 24HDR v. plasma sterols. We conclude that the AHS-2 FFQ provided reasonable estimates of phytosterol intake and may be used in future studies relating phytosterol intake and disease outcomes.

The Effect of Proprotein Convertase Subtilisin/Kexin Type 9 Inhibition on Sterol Absorption Markers in a Cohort of Real-World Patients

Background:

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is expressed in multiple tissues, including the small intestine. The effect of PCSK9 inhibition on cholesterol absorption is not known.

Objectives:

Measure serum cholesterol absorption markers before and after initiation of PCSK9 inhibitors.

Methods:

Single-center retrospective cohort of patients administered evolocumab and alirocumab between July 2015 and January 2017. Paired t tests were used to compare mean serum cholesterol marker concentrations, and ratios to total cholesterol, before and after PCSK9 inhibitor initiation. Analyses were repeated for those taking and not taking statins and taking or not taking ezetimibe at both initiation and follow-up, for each PCSK9 inhibitor, and based on follow-up time (<60, 60-120, and >120 days).

Results:

There were 62 possible participants, 34 were excluded for lack of data or unknown PCSK9 inhibitor initiation date. Average follow-up was 92.5 days. Mean campesterol (before 3.14 μg/mL, 95% CI: 2.79-4.38 μg/mL; after 2.09 μg/mL, 95% CI: 1.87-2.31 μg/mL; P < .0001), sitosterol (before 2.46 μg/mL, 95% CI: 2.23-2.70 μg/mL; after 1.62 μg/mL, 95% CI: 1.48-1.75 μg/mL; P < .0001), and cholestanol (before 3.25 μg/mL, 95% CI: 3.04-3.47 μg/mL; after 2.08 μg/mL, 95% CI: 1.96-2.21 μg/mL; P < .0001) all significantly decreased at follow-up. There was no significant change in absorption marker to total cholesterol ratios. Findings were not influenced by statin or ezetimibe use or nonuse, which PCSK9 inhibitor was prescribed, or time to follow-up.

Conclusion:

Proprotein convertase subtilisin/kexin type 9 inhibition was associated with decreased cholesterol absorption markers.

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.

Transintestinal Cholesterol Transport Is Active in Mice and Humans and Controls Ezetimibe-Induced Fecal Neutral Sterol Excretion

Except for conversion to bile salts, there is no major cholesterol degradation pathway in mammals. Efficient excretion from the body is therefore a crucial element in cholesterol homeostasis. Yet, the existence and importance of cholesterol degradation pathways in humans is a matter of debate. We quantified cholesterol fluxes in 15 male volunteers using a cholesterol balance approach. Ten participants repeated the protocol after 4 weeks of treatment with ezetimibe, an inhibitor of intestinal and biliary cholesterol absorption. Under basal conditions, about 65% of daily fecal neutral sterol excretion was bile derived, with the remainder being contributed by direct transintestinal cholesterol excretion (TICE). Surprisingly, ezetimibe induced a 4-fold increase in cholesterol elimination via TICE. Mouse studies revealed that most of ezetimibe-induced TICE flux is mediated by the cholesterol transporter Abcg5/Abcg8. In conclusion, TICE is active in humans and may serve as a novel target to stimulate cholesterol elimination in patients at risk for cardiovascular disease.

Measurement of Intestinal and Peripheral Cholesterol Fluxes by a Dual-Tracer Balance Method

Long-term elevated plasma cholesterol levels put individuals at risk for developing atherosclerosis. Plasma cholesterol levels are determined by the balance between cholesterol input and output fluxes. Here we describe in detail the methodology to determine the different cholesterol fluxes in mice. The percentage of absorbed cholesterol is calculated from a stable isotope-based double-label method. Cholesterol synthesis is calculated from MIDA after ¹³ C-acetate enrichment. Cholesterol is removed from the body via the feces. The fecal excretion route is either biliary or non-biliary. The non-biliary route is dominated by trans-intestinal cholesterol efflux, or TICE. Biliary excretion of cholesterol is measured by collecting bile. Non-biliary excretion is calculated by computational modeling. In this article, we describe methods and procedures to measure and calculate dietary intake of cholesterol, fractional cholesterol absorption, fecal neutral sterol output, biliary cholesterol excretion, TICE, cholesterol synthesis, peripheral fluxes, and whole-body cholesterol balance. © 2016 by John Wiley & Sons, Inc.

Recent progress in the development of small-molecule glucagon receptor antagonists

The endocrine hormone glucagon stimulates hepatic glucose output via its action at the glucagon receptor (GCGr) in the liver. In the diabetic state, dysregulation of glucagon secretion contributes to abnormally elevated hepatic glucose output. The inhibition of glucagon-induced hepatic glucose output via antagonism of the GCGr using small-molecule ligands is a promising mechanism for improving glycemic control in the diabetic state. Clinical data evaluating the therapeutic potential of small-molecule GCGr antagonists is currently emerging. Recently disclosed clinical data demonstrates the potential efficacy and possible therapeutic limitations of small-molecule GCGr antagonists. Recent pre-clinical work on the development of GCGr antagonists is also summarized.

"Add-on" effect of phytosterols-enriched fermented milk on lipids and markers of cholesterol metabolism in statin-treated elderly patients

The effect of plant sterol (PS) enriched matrices on lipid profile has been evaluated in statin-treated individuals, with LDL-C concentrations between 3.35mmol/L and 4.90mmol/L, but studies in the elderly are scarce. In this study the additional effect of a low-fat PS-enriched fermented milk (PS-FM) on cholesterol metabolism markers and serum lipids was evaluated in the elderly on stable statin therapy with baseline LDL-C<3.35mmol/L. Thirty-five individuals (88.6% women; 81±8years old; BMI 29.9±6.0kg/m(2)), living in elderly nursing care facilities were placed on a daily intake of 2g PS-FM for 6weeks, in addition to their statin monotherapy. A fasting blood sample was collected at baseline (t0), after 2 consecutive periods of 3weeks intake (t1 and t2), and after 6weeks of washout (t3), for the analysis of serum lipid profile and cholesterol synthesis (lathosterol, desmosterol) and absorption (sitosterol, campesterol and cholestanol) markers. PS-FM consumption led to a LDL-C reduction of 0.15mmol/L (t1) and 0.27mmol/L (t2) from baseline (P<0.05). Serum campesterol and sitosterol (P<0.001) increased (t0-t1; t0-t2), reflecting PS intake and contributing to the inhibition of cholesterol intestinal absorption, leading to a decrease in cholestanol-to-cholesterol ratio. There was a reciprocal homeostatic rise of serum cholesterol precursors, desmosterol and lathosterol (P<0.001) from baseline, based on the up-regulation of the opposing pathway. Statin-treated elderly individuals, with baseline LDL-C<3.35mmol/L, may still have therapeutic benefit from strategies that reduce cholesterol absorption, such as 2g/day PS-FM.

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.

Cholesterol metabolism and serum non-cholesterol sterols: summary of 13 plant stanol ester interventions

Background

The efficacy and safety of plant stanols added to food products as serum cholesterol lowering agents have been demonstrated convincingly, but their effects on cholesterol metabolism and on serum non-cholesterol sterols is less evaluated. The aim of this study was to assess the validity of serum non-cholesterol sterols and squalene as bioindices of cholesterol synthesis and absorption, and to examine how the individual serum non-cholesterol sterols respond to consumption of plant stanols.

Methods

We collected all randomized, controlled plant stanol ester (STAEST) interventions in which serum cholestanol, plant sterols campesterol and sitosterol, and at least two serum cholesterol precursors had been analysed. According to these criteria, there was a total of 13 studies (total 868 subjects without lipid-lowering medication; plant stanol doses varied from 0.8 to 8.8 g/d added in esterified form; the duration of the studies varied from 4 to 52 weeks). Serum non-cholesterol sterols were assayed with gas–liquid chromatography, cholesterol synthesis with the sterol balance technique, and fractional cholesterol absorption with the dual continuous isotope feeding method.

Results

The results demonstrated that during the control and the STAEST periods, the serum plant sterol/cholesterol- and the cholestanol/cholesterol-ratios reflected fractional cholesterol absorption, and the precursor sterol/cholesterol-ratios reflected cholesterol synthesis. Plant sterol levels were dose-dependently reduced by STAEST so that 2 g of plant stanols reduced serum campesterol/cholesterol-ratio on average by 32%. Serum cholestanol/cholesterol-ratio was reduced less frequently than those of the plant sterols by STAEST, and the cholesterol precursor sterol ratios did not change consistently in the individual studies emphasizing the importance of monitoring more than one surrogate serum marker.

Conclusions

Serum non-cholesterol sterols are valid markers of cholesterol absorption and synthesis even during cholesterol absorption inhibition with STAEST. Serum plant sterol concentrations decrease dose-dependently in response to plant stanols suggesting that the higher the plant stanol dose, the more cholesterol absorption is inhibited and the greater the reduction in LDL cholesterol level is that can be achieved.

Trial registration

Clinical Trials Register # NCT00698256 [Eur J Nutr 2010, 49:111-117]

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.

Association between cholesterol synthesis/absorption markers and effects of cholesterol lowering by atorvastatin among patients with high risk of coronary heart disease

No indices are currently available to facilitate clinicians to identify patients who need either statin monotherapy or statin-ezetimibe combined treatment. We aimed to investigate whether cholesterol synthesis and absorption markers can predict the cholesterol-lowering response to statin. Total 306 statin-naïve patients with high risk of coronary heart disease (CHD) were treated with atorvastatin 20 mg/day for 1 month. Cholesterol synthesis and absorption markers and LDL cholesterol (LDL-C) levels were measured before and after treatment. Atorvastatin decreased LDL-C by 36.8% (range: decrease of 74.5% to increase of 31.9%). Baseline cholesterol synthesis marker lathosterol and cholesterol absorption marker campesterol codetermined the effect of atorvastatin treatment. The effect of cholesterol lowering by atorvastatin was significantly associated with baseline lathosterol levels but modified bidirectionally by baseline campesterol levels. In patients with the highest baseline campesterol levels, atorvastatin treatment decreased cholesterol absorption by 46.1%, which enhanced the effect of LDL-C lowering. Atorvastatin treatment increased cholesterol absorption by 52.3% in those with the lowest baseline campesterol levels, which attenuated the effect of LDL-C reduction. Especially those with the highest lathosterol but the lowest campesterol levels at baseline had significantly less LDL-C reduction than those with the same baseline lathosterol levels but the highest campesterol levels (27.3% versus 42.4%, P = 0.002). These results suggest that combined patterns of cholesterol synthesis/absorption markers, rather than each single marker, are potential predictors of the LDL-C-lowering effects of atorvastatin in high-risk CHD patients.