Progress and perspectives in plant sterol and plant stanol research

Current evidence indicates that foods with added plant sterols or stanols can lower serum levels of low-density lipoprotein cholesterol. This review summarizes the recent findings and deliberations of 31 experts in the field who participated in a scientific meeting in Winnipeg, Canada, on the health effects of plant sterols and stanols. Participants discussed issues including, but not limited to, the health benefits of plant sterols and stanols beyond cholesterol lowering, the role of plant sterols and stanols as adjuncts to diet and drugs, and the challenges involved in measuring plant sterols and stanols in biological samples. Variations in interindividual responses to plant sterols and stanols, as well as the personalization of lipid-lowering therapies, were addressed. Finally, the clinical aspects and treatment of sitosterolemia were reviewed. Although plant sterols and stanols continue to offer an efficacious and convenient dietary approach to cholesterol management, long-term clinical trials investigating the endpoints of cardiovascular disease are still lacking.

First international descriptive and interventional survey for cholesterol and non-cholesterol sterol determination by gas- and liquid-chromatography-Urgent need for harmonisation of analytical methods

Serum concentrations of lathosterol, the plant sterols campesterol and sitosterol and the cholesterol metabolite 5α-cholestanol are widely used as surrogate markers of cholesterol synthesis and absorption, respectively. Increasing numbers of laboratories utilize a broad spectrum of well-established and recently developed methods for the determination of cholesterol and non-cholesterol sterols (NCS). In order to evaluate the quality of these measurements and to identify possible sources of analytical errors our group initiated the first international survey for cholesterol and NCS. The cholesterol and NCS survey was structured as a two-part survey which took place in the years 2013 and 2014. The first survey part was designed as descriptive, providing information about the variation of reported results from different laboratories. A set of two lyophilized pooled sera (A and B) was sent to twenty laboratories specialized in chromatographic lipid analysis. The different sterols were quantified either by gas chromatography-flame ionization detection, gas chromatography- or liquid chromatography-mass selective detection. The participants were requested to determine cholesterol and NCS concentrations in the provided samples as part of their normal laboratory routine. The second part was designed as interventional survey. Twenty-two laboratories agreed to participate and received again two different lyophilized pooled sera (C and D). In contrast to the first international survey, each participant received standard stock solutions with defined concentrations of cholesterol and NCS. The participants were requested to use diluted calibration solutions from the provided standard stock solutions for quantification of cholesterol and NCS. In both surveys, each laboratory used its own internal standard (5α-cholestane, epicoprostanol or deuterium labelled sterols). Main outcome of the survey was, that unacceptably high interlaboratory variations for cholesterol and NCS concentrations are reported, even when the individual laboratories used the same calibration material. We discuss different sources of errors and recommend all laboratories analysing cholesterol and NCS to participate in regular quality control programs.

Low dose chloroquine decreases insulin resistance in human metabolic syndrome but does not reduce carotid intima-media thickness

BACKGROUND

Metabolic syndrome, an obesity-related condition associated with insulin resistance and low-grade inflammation, leads to diabetes, cardiovascular diseases, cancer, osteoarthritis, and other disorders. Optimal therapy is unknown. The antimalarial drug chloroquine activates the kinase ataxia telangiectasia mutated (ATM), improves metabolic syndrome and reduces atherosclerosis in mice. To translate this observation to humans, we conducted two clinical trials of chloroquine in people with the metabolic syndrome.

METHODS

Eligibility included adults with at least 3 criteria of metabolic syndrome but who did not have diabetes. Subjects were studied in the setting of a single academic health center. The specific hypothesis: chloroquine improves insulin sensitivity and decreases atherosclerosis. In Trial 1, the intervention was chloroquine dose escalations in 3-week intervals followed by hyperinsulinemic euglycemic clamps. Trial 2 was a parallel design randomized clinical trial, and the intervention was chloroquine, 80 mg/day, or placebo for 1 year. The primary outcomes were clamp determined-insulin sensitivity for Trial 1, and carotid intima-media thickness (CIMT) for Trial 2. For Trial 2, subjects were allocated based on a randomization sequence using a protocol in blocks of 8. Participants, care givers, and those assessing outcomes were blinded to group assignment.

RESULTS

For Trial 1, 25 patients were studied. Chloroquine increased hepatic insulin sensitivity without affecting glucose disposal, and improved serum lipids. For Trial 2, 116 patients were randomized, 59 to chloroquine (56 analyzed) and 57 to placebo (51 analyzed). Chloroquine had no effect on CIMT or carotid contrast enhancement by MRI, a pre-specified secondary outcome. The pre-specified secondary outcomes of blood pressure, lipids, and activation of JNK (a stress kinase implicated in diabetes and atherosclerosis) were decreased by chloroquine. Adverse events were similar between groups.

CONCLUSIONS

These findings suggest that low dose chloroquine, which improves the metabolic syndrome through ATM-dependent mechanisms in mice, modestly improves components of the metabolic syndrome in humans but is unlikely to be clinically useful in this setting.Trial registration ClinicalTrials.gov (NCT00455325, NCT00455403), both posted 03 April 2007.

Vitamin D3 supplementation decreases a unique circulating monocyte cholesterol pool in patients with type 2 diabetes

Cross-sectional studies indicate consistent associations between low 25(OH)D concentration and increased risk of cardiovascular disease (CVD), but results of randomized control trials (RCTs) are mixed. However, the majority of the RCTs do not focus on type 2 diabetics, potentially obscuring the effects of vitamin D in this population. In vitro 1,25(OH)₂D₃ downregulates macrophage cholesterol deposition, but the in vivo effects are unknown. To explore potential mechanisms of the effects of vitamin D on CVD risk in patients with type 2 diabetes, we isolated monocytes in a subset of 26 patients from our RCT of diabetics with baseline serum 25(OH)D <25ng/mL randomized to vitamin D₃ 4000 IU/day or placebo for 4 months. Upon enrollment, the mean 25(OH)D level was 17ng/mL, which increased to 36ng/mL after vitamin D and remained unchanged in the placebo group. Before randomization, groups demonstrated similar mean hemoglobin A1c and plasma lipids levels, none of which was significantly altered by vitamin D supplementation. Moreover, assessment of oxidized LDL uptake in monocytes cultured in the patient's own serum before vs. after treatment resulted in >50% reduction in the vitamin D group with no change in the placebo group. This was mediated through suppression of endoplasmic reticulum stress and scavenger receptor CD36 protein expression. The reduction in monocyte cholesterol uptake was reflected in a 19% decrease in total monocyte cholesterol content. Interestingly, cross-sectional analysis of circulating monocytes from vitamin D-deficient vs. sufficient diabetic patients revealed 8-fold higher cholesteryl ester content, confirming the capacity of these monocytes to uptake and carry cholesterol in the circulation. This study identifies a unique circulating cholesterol pool within monocytes that is modulated by vitamin D and has the potential to contribute to CVD in type 2 diabetes.

Endogenous Cholesterol Excretion Is Negatively Associated With Carotid Intima-Media Thickness in Humans

OBJECTIVE

Epidemiological studies strongly suggest that lipid factors independent of low-density lipoprotein cholesterol contribute significantly to cardiovascular disease risk. Because circulating lipoproteins comprise only a small fraction of total body cholesterol, the mobilization and excretion of cholesterol from plasma and tissue pools may be an important determinant of cardiovascular disease risk. Our hypothesis is that fecal excretion of endogenous cholesterol is protective against atherosclerosis.

APPROACH AND RESULTS

Cholesterol metabolism and carotid intima-media thickness were quantitated in 86 nondiabetic adults. Plasma cholesterol was labeled by intravenous infusion of cholesterol-d₇ solubilized in a lipid emulsion and dietary cholesterol by cholesterol-d₅ and the nonabsorbable stool marker sitostanol-d₄. Plasma and stool samples were collected while subjects consumed a cholesterol- and phytosterol-controlled metabolic kitchen diet and were analyzed by mass spectrometry. Carotid intima-media thickness was negatively correlated with fecal excretion of endogenous cholesterol (r=-0.426; P<0.0001), total cholesterol (r=-0.472; P≤0.0001), and daily percent excretion of cholesterol from the rapidly mixing cholesterol pool (r=-0.343; P=0.0012) and was positively correlated with percent cholesterol absorption (r=+0.279; P=0.0092). In a linear regression model controlling for age, sex, systolic blood pressure, hemoglobin A1c, low-density lipoprotein, high-density lipoprotein cholesterol, and statin drug use, fecal excretion of endogenous cholesterol remained significant (P=0.0008).

CONCLUSIONS

Excretion of endogenous cholesterol is strongly, independently, and negatively associated with carotid intima-media thickness. The reverse cholesterol transport pathway comprising the intestine and the rapidly mixing plasma, and tissue cholesterol pool could be an unrecognized determinant of cardiovascular disease risk not reflected in circulating lipoproteins. Further work is needed to relate measures of reverse cholesterol transport to atherosclerotic disease.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01603758.

Multicenter performance evaluation of a second generation cortisol assay

Background:

Untreated disorders of the adrenocortical system, such as Cushing’s or Addison’s disease, can be fatal, and accurate quantification of a patient’s cortisol levels is vital for diagnosis. The objective of this study was to assess the analytical performance of a new fully-automated Elecsys® Cortisol II assay (second generation) to measure cortisol levels in serum and saliva.

Methods:

Four European investigational sites assessed the intermediate precision and reproducibility of the Cortisol II assay (Roche Diagnostics) under routine conditions. Method comparisons of the Cortisol II assay vs. liquid chromatography-tandem mass spectrometry (LC-MS/MS), the gold standard for cortisol measurement, were performed. Cortisol reference ranges from three US sites were determined using samples from self-reported healthy individuals.

Results:

The coefficients of variation (CVs) for repeatability, intermediate precision, and reproducibility for serum samples were ≤2.6%, ≤5.8%, and ≤9.5%, respectively, and for saliva were ≤4.4% and ≤10.9%, and ≤11.4%, respectively. Agreement between the Cortisol II assay and LC-MS/MS in serum samples was close, with a slope of 1.02 and an intercept of 4.473 nmol/L. Reference range samples were collected from healthy individuals (n=300) and serum morning cortisol concentrations (5–95th percentile) were 166.1–507 nmol/L and afternoon concentrations were 73.8–291 nmol/L. Morning, afternoon, and midnight saliva concentrations (95th percentile) were 20.3, 6.94, and 7.56 nmol/L, respectively.

Conclusions:

The Cortisol II assay had good precision over the entire measuring range and had excellent agreement with LC-MS/MS. This test was found suitable for routine diagnostic application and will be valuable for the diagnosis of adrenocortical diseases.

Ezetimibe Increases Endogenous Cholesterol Excretion in Humans

OBJECTIVE

Ezetimibe improves cardiovascular outcomes when added to optimum statin treatment. It lowers low-density lipoprotein cholesterol and percent intestinal cholesterol absorption, but the exact cardioprotective mechanism is unknown. We tested the hypothesis that the dominant effect of ezetimibe is to increase the reverse transport of cholesterol from rapidly mixing endogenous cholesterol pool into the stool.

APPROACH AND RESULTS

In a randomized, placebo-controlled, double-blind parallel trial in 24 healthy subjects with low-density lipoprotein cholesterol 100 to 200 mg/dL, we measured cholesterol metabolism before and after a 6-week treatment period with ezetimibe 10 mg/d or placebo. Plasma cholesterol was labeled by intravenous infusion of cholesterol-d₇ in a lipid emulsion and dietary cholesterol with cholesterol-d₅ and sitostanol-d₄ solubilized in oil. Plasma and stool samples collected during a cholesterol- and phytosterol-controlled metabolic kitchen diet were analyzed by mass spectrometry. Ezetimibe reduced intestinal cholesterol absorption efficiency 30±4.3% (SE, P<0.0001) and low-density lipoprotein cholesterol 19.8±1.9% (P=0.0001). Body cholesterol pool size was unchanged, but fecal endogenous cholesterol excretion increased 66.6±12.2% (P<0.0001) and percent cholesterol excretion from body pools into the stool increased 74.7±14.3% (P<0.0001), whereas plasma cholesterol turnover rose 26.2±3.6% (P=0.0096). Fecal bile acids were unchanged.

CONCLUSIONS

Ezetimibe increased the efficiency of reverse cholesterol transport from rapidly mixing plasma and tissue pools into the stool. Further work is needed to examine the potential relation of reverse cholesterol transport and whole body cholesterol metabolism to coronary events and the treatment of atherosclerosis.

CLINICAL TRIALS REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01603758.

Multicenter evaluation of analytical characteristics of the Elecsys® Periostin immunoassay

OBJECTIVE

The multifunctional cytokine IL-13 is thought to play a central role in Type 2 inflammation in asthma. Serum periostin has been explored as a candidate biomarker for evaluating IL-13 activity in the airway. We describe the technical performance characteristics of a novel, fully automated immunoassay for the determination of periostin in serum.

DESIGN AND METHODS

Limit of blank [LoB], limit of detection [LoD] and limit of quantitation [LoQ], linearity, precision and reproducibility across sites and lots were evaluated according to Clinical and Laboratory Standards Institute guidelines. Interferences and sample stability were also investigated.

RESULTS

The pre-specified values for LoB (2ng/mL), LoD (4ng/mL) and LoQ (10ng/mL) were met. The assay was linear throughout the measuring range (10-160ng/mL) with recoveries within ±10% of target at concentrations >30ng/mL and within ±3ng/mL at concentrations ≤30ng/mL. Recovered periostin concentrations were also within ±10% of target in presence of 43 potentially interfering substances and drugs. Samples were stable across various storage conditions and durations (24h at room temperature, 7days at 4°C, 12weeks at -20°C, and 3 freeze/thaw cycles). Repeatability experiments resulted in CVs across samples and controls ranging from 0.9-1.5%. Intermediate precision was 1.2-1.7% and reproducibility including 3 testing sites and 3 reagent lots was 1.7-3.1%. The final assay correlates to the assay version used in previous clinical trials (Pearson's r=0.998, bias at 50ng/mL=1.2%).

CONCLUSION

The performance evaluation of the Elecsys^® Periostin immunoassay including a multicenter precision analysis demonstrated that the assay is suitable for measuring serum periostin at clinically important concentrations around 50ng/mL.

Altered Cholesterol Metabolism and Hypocholesterolemia in Patients with Single Ventricle following Fontan Palliation

OBJECTIVE

To assess whether an abnormality in cholesterol absorption or synthesis may be associated with hypocholesterolemia in patients with single ventricle anatomy following Fontan palliation.

STUDY DESIGN

This is a cross-sectional study of 21 patients with hypocholesterolemia following Fontan procedure and age/sex-matched healthy controls, with median age of 13.4 (IQR 10.6-16.1) years. Laboratory values of several biomarkers, including phytosterols and 5-α-cholestanol (for cholesterol absorption) and lathosterol (for cholesterol biosynthesis), as well as cholesterol levels, inflammatory markers, and indices of liver function were compared between patients following Fontan procedure and controls.

RESULTS

The Fontan cohort had significantly lower total cholesterol (mean 117 ± SD 13.9, vs 128 ± 19.2 mg/dL, P = .03) and free cholesterol (35.5 ± 4.5 vs 39.2 ± 5.4 mg/dL, P = .02) compared with control patients. There was an increase in normalized 5-α-cholestanol (1.51 ± 0.6 vs 1.14 ± 0.37 μg/mL, P = .02), and a significantly lower lathosterol/5-α-cholestanol ratio (0.70 ± 0.38 vs 1.11 ± 0.76, P = .04). There was a strong correlation (r = 0.78, P < .0001) between lathosterol and cholesterol levels in the Fontan cohort, not seen in controls (r = 0.47, P = .04). The Fontan cohort also had significantly higher C-reactive protein, transaminases, total bilirubin, and gamma-glutamyl transferase levels.

CONCLUSIONS

Patients with hypocholesterolemia following Fontan procedure have evidence of increased cholesterol absorption and decreased cholesterol synthesis. As cholesterol absorption efficiency is a regulated process, this finding suggests an upregulation of cholesterol absorption as a result of decreased cholesterol production. In the setting of elevated liver indices and possible inflammation, this finding supports a growing body of data suggesting development of liver disease in patients receiving Fontan.

Technical performance of a novel, fully automated electrochemiluminescence immunoassay for the quantitation of β-amyloid (1-42) in human cerebrospinal fluid

INTRODUCTION

Available assays for quantitation of the Alzheimer's disease (AD) biomarker amyloid-beta 1-42 (Aβ [1-42]) in cerebrospinal fluid demonstrate significant variability and lack of standardization to reference measurement procedures (RMPs). We report analytical performance data for the novel Elecsys β-amyloid (1-42) assay (Roche Diagnostics).

METHODS

Lot-to-lot comparability was tested using method comparison. Performance parameters were measured according to Clinical & Laboratory Standards Institute (CLSI) guidelines. The assay was standardized to a Joint Committee for Traceability in Laboratory Medicine (JCTLM) approved RMP.

RESULTS

Limit of quantitation was <11.28 pg/mL, and the assay was linear throughout the measuring range (200-1700 pg/mL). Excellent lot-to-lot comparability was observed (correlation coefficients [Pearson's r] >0.995; bias in medical decision area <2%). Repeatability coefficients of variation (CVs) were 1.0%-1.6%, intermediate CVs were 1.9%-4.0%, and intermodule CVs were 1.1%-3.9%. Estimated total reproducibility was 2.0%-5.1%. Correlation with the RMP was good (Pearson's r, 0.93).

DISCUSSION

The Elecsys β-amyloid (1-42) assay has high analytical performance that may improve biomarker-based AD diagnosis.

Deletion of macrophage Vitamin D receptor promotes insulin resistance and monocyte cholesterol transport to accelerate atherosclerosis in mice

Intense effort has been devoted to understanding predisposition to chronic systemic inflammation because it contributes to cardiometabolic disease. We demonstrate that deletion of the macrophage vitamin D receptor (VDR) in mice (KODMAC) is sufficient to induce insulin resistance by promoting M2 macrophage accumulation in the liver as well as increasing cytokine secretion and hepatic glucose production. Moreover, VDR deletion increases atherosclerosis by enabling lipid-laden M2 monocytes to adhere, migrate, and carry cholesterol into the atherosclerotic plaque and by increasing macrophage cholesterol uptake and esterification. Increased foam cell formation results from lack of VDR-SERCA2b interaction, causing SERCA dysfunction, activation of ER stress-CaMKII-JNKp-PPARγ signaling, and induction of the scavenger receptors CD36 and SR-A1. Bone marrow transplant of VDR-expressing cells into KODMAC mice improved insulin sensitivity, suppressed atherosclerosis, and decreased foam cell formation. The immunomodulatory effects of vitamin D in macrophages are thus critical in diet-induced insulin resistance and atherosclerosis in mice.

Preparation of intravenous cholesterol tracer using current good manufacturing practices

Studies of human reverse cholesterol transport require intravenous infusion of cholesterol tracers. Because insoluble lipids may pose risk and because it is desirable to have consistent doses of defined composition available over many months, we investigated the manufacture of cholesterol tracer under current good manufacturing practice (CGMP) conditions appropriate for phase 1 investigation. Cholesterol tracer was prepared by sterile admixture of unlabeled cholesterol or cholesterol-d7 in ethanol with 20% Intralipid(®). The resulting material was filtered through a 1.2 micron particulate filter, stored at 4°C, and tested at time 0, 1.5, 3, 6, and 9 months for sterility, pyrogenicity, autoxidation, and particle size and aggregation. The limiting factor for stability was a rise in thiobarbituric acid-reacting substances of 9.6-fold over 9 months (P < 0.01). The emulsion was stable with the Z-average intensity-weighted mean droplet diameter remaining at 60 nm over 23 months. The zeta potential (a measure of negative surface charge protecting from aggregation) was unchanged at -36.2. Rapid cholesterol pool size was 25.3 ± 1.3 g. Intravenous cholesterol tracer was stable at 4°C for 9 months postproduction. CGMP manufacturing methods can be achieved in the academic setting and need to be considered for critical components of future metabolic studies.

Plasma biomarker of dietary phytosterol intake

Background

Dietary phytosterols, plant sterols structurally similar to cholesterol, reduce intestinal cholesterol absorption and have many other potentially beneficial biological effects in humans. Due to limited information on phytosterol levels in foods, however, it is difficult to quantify habitual dietary phytosterol intake (DPI). Therefore, we sought to identify a plasma biomarker of DPI.

Methods and Findings

Data were analyzed from two feeding studies with a total of 38 subjects during 94 dietary periods. DPI was carefully controlled at low, intermediate, and high levels. Plasma levels of phytosterols and cholesterol metabolites were assessed at the end of each diet period. Based on simple ordinary least squares regression analysis, the best biomarker for DPI was the ratio of plasma campesterol to the endogenous cholesterol metabolite 5-α-cholestanol (R² = 0.785, P < 0.0001). Plasma campesterol and 5-α-cholestanol levels varied greatly among subjects at the same DPI level, but were positively correlated at each DPI level in both studies (r > 0.600; P < 0.01).

Conclusion

The ratio of plasma campesterol to the coordinately regulated endogenous cholesterol metabolite 5-α-cholestanol is a biomarker of dietary phytosterol intake. Conversely, plasma phytosterol levels alone are not ideal biomarkers of DPI because they are confounded by large inter-individual variation in absorption and turnover of non-cholesterol sterols. Further work is needed to assess the relation between non-cholesterol sterol metabolism and associated cholesterol transport in the genesis of coronary heart disease.

Plasma sterol evidence for decreased absorption and increased synthesis of cholesterol in insulin resistance and obesity

BACKGROUND

The rise in LDL with egg feeding in lean insulin-sensitive (LIS) participants is 2- and 3-fold greater than in lean insulin-resistant (LIR) and obese insulin-resistant (OIR) participants, respectively.

OBJECTIVE

We determined whether differences in cholesterol absorption, synthesis, or both could be responsible for these differences by measuring plasma sterols as indexes of cholesterol absorption and endogenous synthesis.

DESIGN

Plasma sterols were measured by gas chromatography-mass spectrometry in a random subset of 34 LIS, 37 LIR, and 37 OIR participants defined by the insulin sensitivity index (S(I)) and by BMI criteria selected from a parent group of 197 participants. Cholestanol and plant sterols provide a measure of cholesterol absorption, and lathosterol provides a measure of cholesterol synthesis.

RESULTS

The mean (±SD) ratio of plasma total absorption biomarker sterols to cholesterol was 4.48 ± 1.74 in LIS, 3.25 ± 1.06 in LIR, and 2.82 ± 1.08 in OIR participants. After adjustment for age and sex, the relations of the absorption sterol-cholesterol ratios were as follows: LIS > OIR (P < 0.001), LIS > LIR (P < 0.001), and LIR > OIR (P = 0.11). Lathosterol-cholesterol ratios were 0.71 ± 0.32 in the LIS participants, 0.95 ± 0.47 in the LIR participants, and 1.29 ± 0.55 in the OIR participants. After adjustment for age and sex, the relations of lathosterol-cholesterol ratios were as follows: LIS < OIR (P < 0.001), LIS < LIR (P = 0.03), and LIR < OIR (P = 0.002). Total sterol concentrations were positively associated with S(I) and negatively associated with obesity, whereas lathosterol correlations were the opposite.

CONCLUSIONS

Cholesterol absorption was highest in the LIS participants, whereas cholesterol synthesis was highest in the LIR and OIR participants. Therapeutic diets for hyperlipidemia should emphasize low-cholesterol diets in LIS persons and weight loss to improve S(I) and to decrease cholesterol overproduction in LIR and OIR persons.

Combined effects of ezetimibe and phytosterols on cholesterol metabolism: a randomized, controlled feeding study in humans

BACKGROUND

Both ezetimibe and phytosterols inhibit cholesterol absorption. We tested the hypothesis that the combination of ezetimibe and phytosterols is more effective than ezetimibe alone in altering cholesterol metabolism.

METHODS AND RESULTS

Twenty-one mildly hypercholesterolemic subjects completed a randomized, double-blind, placebo-controlled, triple-crossover study. Each subject received a phytosterol-controlled diet plus (1) ezetimibe placebo+phytosterol placebo, (2) 10 mg/d ezetimibe+phytosterol placebo, and (3) 10 mg/d ezetimibe+2.5 g phytosterols for 3 weeks each. All meals were prepared in a metabolic kitchen. Primary outcomes were intestinal cholesterol absorption, fecal cholesterol excretion, and low-density lipoprotein cholesterol levels. The combined treatment resulted in significantly lower intestinal cholesterol absorption (598 mg/d; 95% confidence interval [CI], 368 to 828) relative to control (2161 mg/d; 95% CI, 1112 to 3209) and ezetimibe alone (1054 mg/d; 95% CI, 546 to 1561; both P<0.0001). Fecal cholesterol excretion was significantly greater (P<0.0001) with combined treatment (962 mg/d; 95% CI, 757 to 1168) relative to control (505 mg/d; 95% CI, 386 to 625) and ezetimibe alone (794 mg/d; 95% CI, 615 to 973). Plasma low-density lipoprotein cholesterol values during treatment with control, ezetimibe alone, and ezetimibe+phytosterols averaged 129 mg/dL (95% CI, 116 to 142), 108 mg/dL (95% CI, 97 to 119), and 101 mg/dL (95% CI, 90 to 112; (P<0.0001 relative to control).

CONCLUSION

The addition of phytosterols to ezetimibe significantly enhanced the effects of ezetimibe on whole-body cholesterol metabolism and plasma low-density lipoprotein cholesterol. The large cumulative action of combined dietary and pharmacological treatment on cholesterol metabolism emphasizes the potential importance of dietary phytosterols as adjunctive therapy for the treatment of hypercholesterolemia.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00863265.

Glycosidic bond cleavage is not required for phytosteryl glycoside-induced reduction of cholesterol absorption in mice

Phytosteryl glycosides occur in natural foods but little is known about their metabolism and bioactivity. Purified acylated steryl glycosides (ASG) were compared with phytosteryl esters (PSE) in mice. Animals on a phytosterol-free diet received ASG or PSE by gavage in purified soybean oil along with tracers cholesterol-d(7) and sitostanol-d(4). In a three-day fecal recovery study, ASG reduced cholesterol absorption efficiency by 45 ± 6% compared with 40 ± 6% observed with PSE. Four hours after gavage, plasma and liver cholesterol-d(7) levels were reduced 86% or more when ASG was present. Liver total phytosterols were unchanged after ASG administration but were significantly increased after PSE. After ASG treatment both ASG and deacylated steryl glycosides (SG) were found in the gut mucosa and lumen. ASG was quantitatively recovered from stool samples as SG. These results demonstrate that ASG reduces cholesterol absorption in mice as efficiently as PSE while having little systemic absorption itself. Cleavage of the glycosidic linkage is not required for biological activity of ASG. Phytosteryl glycosides should be included in measurements of bioactive phytosterols.

The effects of phytosterols present in natural food matrices on cholesterol metabolism and LDL-cholesterol: a controlled feeding trial

BACKGROUND/OBJECTIVES

Extrinsic phytosterols supplemented to the diet reduce intestinal cholesterol absorption and plasma low-density lipoprotein (LDL)-cholesterol. However, little is known about their effects on cholesterol metabolism when given in native, unpurified form and in amounts achievable in the diet. The objective of this investigation was to test the hypothesis that intrinsic phytosterols present in unmodified foods alter whole-body cholesterol metabolism.

SUBJECTS/METHODS

In all, 20 out of 24 subjects completed a randomized, crossover feeding trial wherein all meals were provided by a metabolic kitchen. Each subject consumed two diets for 4 weeks each. The diets differed in phytosterol content (phytosterol-poor diet, 126 mg phytosterols/2000 kcal; phytosterol-abundant diet, 449 mg phytosterols/2000 kcal), but were otherwise matched for nutrient content. Cholesterol absorption and excretion were determined by gas chromatography/mass spectrometry after oral administration of stable isotopic tracers.

RESULTS

The phytosterol-abundant diet resulted in lower cholesterol absorption (54.2±2.2% (95% confidence interval 50.5%, 57.9%) vs 73.2±1.3% (69.5%, 76.9%), P<0.0001) and 79% higher fecal cholesterol excretion (1322±112 (1083.2, 1483.3) vs 739±97 mg/day (530.1, 930.2), P<0.0001) relative to the phytosterol-poor diet. Plasma lathosterol/cholesterol ratio rose by 82% (from 0.71±0.11 (0.41, 0.96) to 1.29±0.14 μg/mg (0.98, 1.53), P<0.0001). LDL-cholesterol was similar between diets.

CONCLUSIONS

Intrinsic phytosterols at levels present in a healthy diet are biologically active and have large effects on whole-body cholesterol metabolism not reflected in circulating LDL. More work is needed to assess the effects of phytosterol-mediated fecal cholesterol excretion on coronary heart disease risk in humans.

Phytostanol tablets reduce human LDL-cholesterol

The feasibility of using solid dosage forms containing stanol lecithin to lower human LDL-cholesterol was investigated. The particle size distribution of a coarse aqueous dispersion of a stanol lecithin mixture was determined at various weight ratios of the components. At a stanol-to-lecithin weight ratio of 1.00–1.50, dispersions could be spray dried and the solid reconstituted with water to produce a particle size distribution that was similar to that of the aqueous dispersion from which it was derived. Two solid dosage forms containing this spray-dried stanol lecithin preparation had different disintegration times — tablets less than 10 min and capsules greater than 45 min. Each delivery system was then tested for LDL-cholesterol reduction activity in a placebo-controlled, double-blind clinical trial containing a total of 52 subjects. After a six-week treatment period, the group that received rapidly disintegrating stanol lecithin tablets (1.26g stanols daily) experienced a decrease in both LDL-cholesterol and the ratio of LDL-cholesterol to HDL-cholesterol by 10.4% (P=0.01) and 11.5% (P=0.03), respectively, relative to placebo. On the other hand, with slowly disintegrating capsules (1.01 g daily) there was no statistically significant difference in any lipid parameter between the active group and placebo group. Taken together, these studies demonstrate that for maximum LDL-cholesterol reduction activity the stanol lecithin formulation must be delivered in a rapidly dispersible form to reach the site of cholesterol absorption.

Dose effects of dietary phytosterols on cholesterol metabolism: a controlled feeding study

BACKGROUND

Phytosterol supplementation of 2 g/d is recommended by the National Cholesterol Education Program to reduce LDL cholesterol. However, the effects of different intakes of phytosterol on cholesterol metabolism are uncertain.

OBJECTIVE

We evaluated the effects of 3 phytosterol intakes on whole-body cholesterol metabolism.

DESIGN

In this placebo-controlled, crossover feeding trial, 18 adults received a phytosterol-deficient diet (50 mg phytosterols/2000 kcal) plus beverages supplemented with 0, 400, or 2000 mg phytosterols/d for 4 wk each, in random order. All meals were prepared in a metabolic kitchen; breakfast and dinner on weekdays were eaten on site. Primary outcomes were fecal cholesterol excretion and intestinal cholesterol absorption measured with stable-isotope tracers and serum lipoprotein concentrations.

RESULTS

Phytosterol intakes (diet plus supplements) averaged 59, 459, and 2059 mg/d during the 3 diet periods. Relative to the 59-mg diet, the 459- and 2059-mg phytosterol intakes significantly (P < 0.01) increased total fecal cholesterol excretion (36 +/- 6% and 74 +/- 10%, respectively) and biliary cholesterol excretion (38 +/- 7% and 77 +/- 12%, respectively) and reduced percentage intestinal cholesterol absorption (-10 +/- 1% and -25 +/- 3%, respectively). Serum LDL cholesterol declined significantly only with the highest phytosterol dose (-8.9 +/- 2.3%); a trend was observed with the 459-mg/d dose (-5.0 +/- 2.1%; P = 0.077).

CONCLUSIONS

Dietary phytosterols in moderate and high doses favorably alter whole-body cholesterol metabolism in a dose-dependent manner. A moderate phytosterol intake (459 mg/d) can be obtained in a healthy diet without supplementation. This trial was registered at clinicaltrials.gov as NCT00860054.

Phytosterol-deficient and high-phytosterol diets developed for controlled feeding studies

Phytosterols reduce cholesterol absorption and low-density lipoprotein cholesterol concentrations, but the quantity and physiological significance of phytosterols in common diets are generally unknown because nutrient databases do not contain comprehensive phytosterol data. The primary aim of this study was to design prototype phytosterol-deficient and high-phytosterol diets for use in controlled feeding studies of the influence of phytosterols on health. A second aim was to quantify the phytosterol content of these prototype diets and three other diets consumed in the United States. This study was conducted from June 2001 to September 2008 and involved designing, preparing, and then analyzing five different diets: an experimental phytosterol-deficient control diet, a relatively high-phytosterol diet based on the Dietary Approaches to Stop Hypertension diet, American Heart Association diet, Atkins lifetime maintenance plan, and a vegan diet. A single day of meals for each diet was homogenized and the resulting composites were analyzed for free, esterified, and glycosylated phytosterols by gas chromatography. Independent samples t tests were used to compare the diets' total phytosterol content. The total phytosterol content of the experimental phytosterol-deficient diet was 64 mg/2,000 kcal, with progressively larger quantities in Atkins, American Heart Association, vegan, and the high-phytosterol Dietary Approaches to Stop Hypertension diet (163, 340, 445, and 500 mg/2,000 kcal, respectively). Glycosylated phytosterols, which are often excluded from phytosterol analyses, comprised 15.9%+/-5.9% of total phytosterols. In summary, phytosterol-deficient and high-phytosterol diets that conform to recommended macronutrient guidelines and are palatable can now be used in controlled feeding studies.

Phytosterol glycosides reduce cholesterol absorption in humans

Dietary phytosterols inhibit intestinal cholesterol absorption and regulate whole body cholesterol excretion and balance. However, they are biochemically heterogeneous and a portion is glycosylated in some foods with unknown effects on biological activity. We tested the hypothesis that phytosterol glycosides reduce cholesterol absorption in humans. Phytosterol glycosides were extracted and purified from soy lecithin in a novel two-step process. Cholesterol absorption was measured in a series of three single-meal tests given at intervals of 2 wk to each of 11 healthy subjects. In a randomized crossover design, participants received approximately 300 mg of added phytosterols in the form of phytosterol glycosides or phytosterol esters, or placebo in a test breakfast also containing 30 mg cholesterol-d7. Cholesterol absorption was estimated by mass spectrometry of plasma cholesterol-d7 enrichment 4-5 days after each test. Compared with the placebo test, phytosterol glycosides reduced cholesterol absorption by 37.6+/-4.8% (P<0.0001) and phytosterol esters 30.6+/-3.9% (P=0.0001). These results suggest that natural phytosterol glycosides purified from lecithin are bioactive in humans and should be included in methods of phytosterol analysis and tables of food phytosterol content.

Hyperinsulinemia is closely related to low urinary clearance of D-chiro-inositol in men with a wide range of insulin sensitivity

We have previously shown that women with polycystic ovary syndrome (PCOS) have increased urinary clearance of D-chiro-inositol (uCl(DCI)), which was positively associated with hyperinsulinemia. The objective of this study was thus to determine if such relationship also exists in men with a large range of insulin sensitivity and levels. A cross-sectional study was performed on 11 brothers of women with PCOS and 21 control men. In this study, brothers served as a model of insulin resistance. We assessed uCl(DCI), urinary clearance of myo-inositol, and insulin levels with a standard 75-g oral glucose tolerance test, a 2-hour euglycemic-hyperinsulinemic clamp, and a 24-hour urine collection. Our results showed in all men together that low uCl(DCI) was strongly associated (P < .001) with hyperinsulinemia, for which uCl(DCI) was a significant predictor independent of other classic factors. Brothers were heavier than controls (P = .02), with increased glucose-stimulated glucose (P < .001) and insulin levels (P < .001) and reduced insulin sensitivity (P = .001). In this group, plasma DCI was increased by 3-fold (P = .02), with a 3-fold decrease in the uCl(DCI) to urinary clearance of myo-inositol ratio, which was almost significant (P = .07). Low uCl(DCI) is strongly associated with hyperinsulinemia in all men, and brothers of PCOS women who are more insulin resistant display increased plasma DCI and borderline decreased uCl(DCI). Thus, compensatory hyperinsulinemia might suppress renal clearance of DCI to increase plasma DCI levels and partially compensate for insulin resistance by improving DCI availability in men. The apparent discrepancy with PCOS women might be explained by higher insulin levels in men as compared with women and requires confirmation.

Human sodium/inositol cotransporter 2 (SMIT2) transports inositols but not glucose in L6 cells

To characterize the function of the sodium/inositol symporter SMIT2 in skeletal muscle, human SMIT2 cDNA was transfected into L6 myoblasts using pcDNA3.1 expression vector. Compared with the pcDNA3.1 vector only transfection, this overexpression increased the uptake of [(3)H]D-chiro-inositol (DCI) by 159-fold. [(3)H]myo-Inositol uptake increased by 37-fold. In contrast, [(14)C]D-glucose, [(14)C]2-deoxy-D-glucose, or [(14)C]3-O-methyl-D-glucose uptake remained unchanged in the presence of either 0, 5.5, or 25 mM unlabeled glucose. The K(m) of DCI and myo-inositol for DCI uptake was 111.0 and 158.0 microM, respectively, whereas glucose competed for DCI uptake with a K(i) of 6.1 mM. Insulin treatment of non-transfected L6 cells (2 microM for 24 h) increased [(3)H]DCI specific uptake 18-fold. DCI transport is up regulated by insulin and competitively inhibited by millimolar levels of glucose. Therefore, expression and/or function of SMIT2, a high affinity transporter specific for DCI and myo-inositol, may be reduced in diabetes mellitus, insulin resistance and polycystic ovary syndrome causing the abnormal DCI metabolism observed in these conditions.

Relationships between urinary inositol excretions and whole-body glucose tolerance and skeletal muscle insulin receptor phosphorylation

This study assessed the relationships of urinary D-chiro-inositol and myo-inositol excretions to indices of whole-body glucose tolerance and total content and tyrosine phosphorylation of the insulin receptor (activation) in skeletal muscle of older nondiabetic subjects. Fifteen adults (age, 65 +/- 8 years; body mass index, 27.9 +/- 3.3 kg/m(2) [mean +/- SD]) completed duplicate assessments of oral (75-g oral glucose tolerance test [OGTT]) and intravenous (300 mg/kg body weight intravenous glucose tolerance test) glucose tolerance challenges and 24-hour urinary D-chiro-inositol and myo-inositol excretions. Skeletal muscle (vastus lateralis) biopsies were obtained at minute 60 of the OGTTs. Subjects with higher urinary D-chiro-inositol excretion had higher insulin (rho = 0.51, P < or = .05) and C-peptide (rho = 0.56, P < or = .05) area under the curves, and lower insulin sensitivity index (rho = -0.60, P < or = .05) during the intravenous glucose tolerance test. The urinary myo- to D-chiro-inositol ratio was also inversely related to insulin area under the curve (rho = -0.59, P < or = .05). Urinary D-chiro-inositol (rho = -0.60, P < or = .05) and myo-inositol (rho = -0.60, P < or = .05) were inversely related to tyrosine phosphorylation of the insulin receptor (phosphotyrosine 1162/1163), but not total content of the insulin receptor during the OGTT. The apparent relationships were modestly weakened when adjustments were made for sex. These findings support previous research linking higher urinary D-chiro-inositol excretion with a progressive decline in whole-body glucose tolerance. This is the first report to link higher urinary D-chiro-inositol excretion to a blunted activation of skeletal muscle insulin receptor signaling in older nondiabetic subjects.

Insulin-stimulated release of D-chiro-inositol-containing inositolphosphoglycan mediator correlates with insulin sensitivity in women with polycystic ovary syndrome

Some actions of insulin are mediated by inositolphosphoglycan (IPG) mediators. Deficient release of a putative D-chiro-inositol-containing (DCI) IPG mediator may contribute to insulin resistance in women with polycystic ovary syndrome (PCOS). Previously, we demonstrated that oral DCI supplementation improved ovulation and metabolic parameters in women with PCOS. However, whether oral DCI mediates an increase in the release of the DCI-IPG mediator and an improvement in insulin sensitivity in women with PCOS is unknown. We conducted a randomized controlled trial of DCI supplementation vs placebo in 11 women with PCOS who were assessed at 2 time points 6 weeks apart. Plasma DCI, DCI-IPG release during oral glucose tolerance test (AUC(DCI-IPG)), and insulin sensitivity (S(i)) by frequently sampled intravenous glucose tolerance test were assessed at baseline and end of study. The study was terminated early because of a sudden unavailability of the study drug. However, in all subjects without regard to treatment assignment, there was a positive correlation between the change in AUC(DCI-IPG)/AUC(insulin) ratio and the change in S(i) during the 6-week period (r = 0.69, P = .02), which remained significant after adjustment for body mass index (P = .022) and after further adjustment for body mass index and treatment allocation (P = .0261). This suggests that, in women with PCOS, increased glucose-stimulated DCI-IPG release is significantly correlated with improved insulin sensitivity. The significant relationship between DCI-IPG release and insulin sensitivity suggests that the DCI-IPG mediator may be a target for therapeutic interventions in PCOS.

Greek hyperinsulinemic women, with or without polycystic ovary syndrome, display altered inositols metabolism

BACKGROUND We have shown that American women with polycystic ovary syndrome (PCOS) have decreased glucose-stimulated release of a putative mediator of insulin action, D-chiro-inositol (DCI)-containing inositolphosphoglycan (DCI-IPG), and increased urinary clearance of DCI (uCl(DCI)), which was associated with hyperinsulinemia.

METHODS

DCI levels and the release of insulin and DCI-IPG during an oral glucose tolerance test (AUCs) were assessed in 27 Greek PCOS and 10 normal Greek women.

RESULTS

PCOS women were heavier than controls (BMI = 28.4 versus 23.7 kg/m(2), P = 0.05) with higher waist-to-hip ratios (WHR = 0.78 versus 0.71, P = 0.009) and increased free testosterone (P = 0.048) and AUC(insulin) (P = 0.04). In PCOS women, incremental AUC(DCI-IPG) was significantly decreased by 59% (2158 versus 5276%.min, P = 0.01), even after correction for BMI and WHR. Finally, increased uCl(DCI) (r = 0.35, P = 0.04) and decreased AUC(DCI-IPG) (r = 0.46, P = 0.004) were significantly associated with hyperinsulinemia in all women together, even after correction for BMI and WHR (Ps = 0.02 and 0.007), and regardless of PCOS status.

CONCLUSIONS

Greek women, with or without PCOS, display increased uCl(DCI) and decreased AUC(DCI-IPG) in association with higher insulin levels but independent of adiposity. Increased clearance of inositols might reduce tissue availability of DCI and decrease the release of DCI-IPG mediator, which could contribute to insulin resistance and compensatory hyperinsulinemia in Greek women, as previously described in American women.

Regulation of cholesterol absorption by phytosterols

Phytosterols are chemical homologs of cholesterol that are found in most plant foods and are particularly abundant in vegetable oils and whole grains. They interfere with the micellar solubilization of cholesterol in the intestine and reduce the efficiency of cholesterol absorption. The net absorption of phytosterols themselves is very small and most clinical studies suggest that consumption is safe. Phytosterols naturally present in foods appear to be bioactive, but many commercial phytosterol supplements are comprised of purified crystals with limited bioavailability. Proper formulation to improve bioavailability is critical for phytosterol supplements. Phytosterols appear to be quantitatively as important to cholesterol lowering as reducing saturated fat consumption, and they provide an additional tool for regulation of circulating cholesterol through lifestyle changes.

Phytosterols, cholesterol absorption and healthy diets

The purpose of this review is to outline the emerging role of dietary phytosterols in human health. Dietary saturated fat, cholesterol and fiber are currently emphasized in the reduction of low-density lipoprotein cholesterol levels. However, other dietary components such as phytosterols may have equivalent or even larger effects on circulating cholesterol and need further study with respect to the potential for coronary heart disease risk reduction. Phytosterol effects were not considered in classic fat-exchange clinical trials and may account for some of the differences attributed to the food fats studied. Phytosterols reduce cholesterol absorption while being poorly absorbed themselves and the effects can be studied in human subjects in single-meal tests using stable isotopic tracers. Because phytosterols are insoluble and biologically inactive when purified, careful attention needs to be given to ensuring that commercial supplement products are rendered bioavailable by dissolution in fat or by emulsification. Recent work shows that phytosterols in natural food matrices are also bioactive. The retention of phytosterols during food manufacturing and the use of foods with high phytosterol content may constitute an alternative to the use of supplements.

Rapid transient absorption and biliary secretion of enantiomeric cholesterol in hamsters

To probe the pathway and specificity of cholesterol absorption, the synthetic enantiomer of cholesterol (ent-cholesterol) and cholesterol were labeled with deuterium, gavaged into hamsters, and measured by negative ion mass spectrometry. Initial uptake of both tracers into the intestinal mucosa at 30 min was similar but cholesterol was temporarily retained there, whereas mucosal ent-cholesterol declined rapidly with concomitantly increased enrichment in both the systemic circulation and the gut lumen. In a 3 day fecal recovery study, ent-cholesterol was quantitatively recovered in the stool, whereas cholesterol absorption was 53.2%. ent-Cholesterol given by intracardiac injection was selectively secreted into bile, and the ratio of ent-cholesterol to cholesterol tracers in the gut lumen increased down the length of the small bowel, with the largest value being found in stool. ent-Cholesterol is efficiently taken up by the intestinal mucosa and undergoes transient enterohepatic recirculation, but it is quantitatively eliminated over 3 days as a result of selective secretion into bile and selective enrichment within the lumen of the intestine. These findings suggest that cholesterol absorption is structurally specific and likely to be mediated by enantiospecific cellular proteins.

A targeted apoB38.9 mutation in mice is associated with reduced hepatic cholesterol synthesis and enhanced lipid peroxidation

Familial hypobetalipoproteinemia (FHBL) due to truncation-specifying mutations of apolipoprotein B (apoB), which impair hepatic lipid export in very low-density lipoprotein (VLDL) particles, is associated with fatty liver. In an FHBL-like mouse with the apoB38.9 mutation, fatty liver develops despite reduced hepatic fatty acid synthesis. However, hepatic cholesterol contents in apoB38.9 mice are normal. We found that cholesterogenic enzymes (3-hydroxy-3-methylglutaryl-coenzyme A reductase, sterol-C5-desaturase, and 7-dehydrocholesterol reductase) were consistently downregulated in two separate expression-profiling experiments using a total of 19 mice (n = 7 each for apob(+/+) and apob(+/38.9), and n = 5 for apob(38.9/38.9)) and Affymetrix Mu74Av2 GeneChip microarrays. Results were confirmed by real-time PCR. Cholesterol synthesis rates in cultured hepatocytes were reduced by 35% and 25% in apob(38.9/38.9) and apob(+/38.9), respectively, vs. apob(+/+). Hepatic triglycerides and lipid peroxides, the latter measured by thiobarbituric acid-reactive substances (TBARS) assay, were significantly elevated in apob(+/38.9) (117%) and apob(38.9/38.9) (132%) vs. apob(+/+) (100%), as were mRNA expression of the microsomal lipid peroxidizing enzymes Cyp4A10 and Cyp4A14. Hepatic lipid peroxide levels were positively correlated with triglyceride contents (r = 0.601, P = 0.0065). Thus the fatty liver due to a VLDL secretion defect is associated with insufficient adaptation to triglyceride accumulation and with increased lipid peroxidation. In contrast, apoB38.9 mice effectively maintain cholesterol homeostasis in the liver, at least in part, by reducing hepatic cholesterol synthesis.

Effect of plant stanol tablets on low-density lipoprotein cholesterol lowering in patients on statin drugs

The objective of this study was to show that plant sterols in tablet form provide additional low-density lipoprotein (LDL) cholesterol lowering for patients on statin therapy. Dispersible phytosterol tablets were tested in a double-blind, placebo-controlled, parallel clinical trial. Twenty-six patients who were following the American Heart Association Heart Healthy Diet and on long-term statin therapy were studied for 9 weeks. After 3 weeks of placebo treatment, the subjects were randomized to receive either 1.8 g of soy stanols or placebo for 6 weeks in addition to their usual statin regimen. Stanol tablets reduced LDL cholesterol 9.1% (p = 0.007) or 12.2 mg/dl. Total cholesterol was reduced by 12.9 mg/dl (p = 0.03). A strong inverse correlation (r(s) = -0.82, p = 0.0007) was found between the baseline LDL cholesterol and the percent change in LDL cholesterol observed after stanol treatment. The additional LDL cholesterol lowering with stanol/lecithin tablets provided a potential adjunctive therapy for patients who have not reached their target LDL cholesterol goal during statin therapy.

Altered D-chiro-inositol urinary clearance in women with polycystic ovary syndrome

OBJECTIVE

Evidence suggests that some actions of insulin are effected by inositolphosphoglycan (IPG) mediators. We hypothesize that a deficiency in D-chiro-inositol (DCI) and/or a DCI-containing IPG (DCI-IPG) may contribute to insulin resistance in humans.

RESEARCH DESIGN AND METHODS

To assess this possibility in polycystic ovary syndrome (PCOS), we determined insulin sensitivity (Si by frequently sampled intravenous glucose tolerance test), plasma and urinary DCI and myo-inositol (MYO) levels (by gas chromatography/mass spectrometry), and the release of insulin and DCI-IPG during the oral glucose tolerance test (area under the curve [AUC]) in 23 women with PCOS and 26 normal women.

RESULTS

Women with PCOS were heavier than control subjects (P = 0.002 for BMI), but also had decreased Si (P < 0.001) and increased AUC(insulin) (P < 0.001) compared with normal women, even when corrected for BMI. The urinary clearance of DCI (uCl(DCI)) was increased almost sixfold in PCOS compared with normal women (P = 0.001), but not MYO clearance (P = 0.10). uCl(DCI) correlated inversely with Si when all women were analyzed together (n = 49, r = -0.50, P < 0.001) and was one of the three best independent parameters predicting Si. Finally, the ratio of AUC(DCI-IPG) to AUC(insulin) was decreased threefold in women with PCOS (P < 0.001).

CONCLUSIONS

uCl(DCI) is inversely correlated with insulin sensitivity in women and is a strong independent predictor of insulin resistance in multivariate models. PCOS, which is characterized by insulin resistance, is associated with a selective increase in uCl(DCI) and impaired DCI-IPG release in response to insulin. These findings are consistent with a defect in tissue availability or utilization of DCI in PCOS that may contribute to the insulin resistance of the syndrome.

Reduced intestinal fat absorptive capacity but enhanced susceptibility to diet-induced fatty liver in mice heterozygous for ApoB38.9 truncation

Fatty liver is prevalent in apolipoprotein B (apoB)-defective familial hypobetalipoproteinemia (FHBL). Similar to humans, mouse models of FHBL produced by gene targeting (apob(+/38.9)) manifest low plasma cholesterol and increased hepatic triglycerides (TG) even on a chow diet due to impaired hepatic VLDL-TG secretive capacity. Because apoB truncations shorter than apoB48 are expressed in the intestine, we examined whether FHBL mice may have limited capacity for intestinal dietary TG absorption. In addition, we investigated whether FHBL mice are more susceptible to diet-induced hepatic TG accumulation. Fat absorption capacity was impaired in apoB38.9 mice in a gene dose-dependent manner. Relative fractional fat absorption coefficients for apob(+/+), apob(+/38.9), and apob(38.9/38.9) were 1.00, 0.96, and 0.71, respectively. To raise hepatic TG, we fed high-fat (HF) and low-fat (LF) pellets. Hepatic TG level was observed in rank order: HF > LF > chow. On both LF and HF, liver TG level was higher in the apob(+/38.9) than in apob(+/+). Hepatic TG secretion remained impaired in the apob(+/38.9) on the HF diet. Thus the FHBL mice are more susceptible to diet-induced fatty liver despite relatively reduced intestinal TG absorption capacity on a HF diet.

Pinitol supplementation does not affect insulin-mediated glucose metabolism and muscle insulin receptor content and phosphorylation in older humans

This study assessed the effect of oral pinitol supplementation on oral and intravenous glucose tolerances and on skeletal muscle insulin receptor content and phosphorylation in older people. Fifteen people (6 men, 9 women; age 66 +/- 8 y; BMI 27.9 +/- 3.3 kg/m(2); hemoglobin A1c 5.39 +/- 0.46%, mean +/- SD) completed a 7-wk protocol. Subjects were randomly assigned to groups that during wk 2-7 consumed twice daily either a non-nutritive beverage (Placebo group, n = 8) or the same beverage with 1000 mg pinitol dissolved into it (Pinitol group, n = 7, total dose = 2000 mg pinitol/d). Testing was done at wk 1 and wk 7. In the Pinitol group with supplementation, 24-h urinary pinitol excretion increased 17-fold. The fasting concentrations of glucose, insulin, and C-peptide, and the 180-min area under the curve for these compounds, in response to oral (75 g) and intravenous (300 mg/kg) glucose tolerance challenges, were unchanged from wk 1 to wk 7 and were not influenced by pinitol. Also, pinitol did not affect indices of hepatic and whole-body insulin sensitivity from the oral glucose tolerance test and indices of insulin sensitivity, acute insulin response to glucose, and glucose effectiveness from the intravenous glucose tolerance test, estimated using minimal modeling. Pinitol did not differentially affect total insulin receptor content and insulin receptor phosphotyrosine 1158 and insulin receptor phosphotyrosine 1162/1163 activation in vastus lateralis samples taken during an oral-glucose-induced hyperglycemic and hyperinsulinemic state. These data suggest that pinitol supplementation does not influence whole-body insulin-mediated glucose metabolism and muscle insulin receptor content and phosphorylation in nondiabetic, older people.

Resistive Training and Chromium Picolinate: Effects on Inositols and Liver and Kidney Functions in Older Adults

This study assessed the effects of resistive training (RT) with or without chromium picolinate (Cr-pic) supplementation on the 24-h urinary excretions of myo-inositol, D-chiro-inositol, and pinitol, as well as clinical indices of kidney and liver functions. Thirty-two nondiabetic subjects, age 62 ± 4 y, performed RT twice weekly for 12 wk and consumed either 924 μg Cr/d as Cr-pic (n = 17) or a placebo (n = 15). Whole-body strength increased in all subjects by 20% and urinary chromium excretion increased 47-fold in the Cr-pic group. Urinary myo-inositol, D-chiro-inositol, and pinitol were not changed with RT or influenced by Cr-pic. Serum indices of kidney and liver functions were within clinically normal ranges at baseline and the end of the study. These results suggest that RT did not influence the urinary excretions of inositols. High dose Cr-pic did not influence the urinary excretion of inositols and the selected indices of kidney and liver functions in conjunction with RT

Phytosterols and cholesterol metabolism

PURPOSE OF REVIEW

Phytosterols are plant sterols structurally similar to cholesterol that act in the intestine to lower cholesterol absorption. Because they have very low systemic absorption and are already present in healthy diets, increasing the intake of phytosterols may be a practical way to reduce coronary heart disease with minimum risk.

RECENT FINDINGS

Phytosterols displace cholesterol from intestinal micelles, reducing the pool of absorbable cholesterol, but they are also rapidly taken up by enterocytes and increase expression of the adenosine triphosphate-binding cassette A1 sterol transporter. Phytosterol esters dissolved in food fat reduce LDL-cholesterol by 10% at a maximum effective dose of 2 g/day. However, this work probably understates the true effectiveness of phytosterols because it does not account for those naturally present in baseline diets. Single meal studies show that phytosterols in intact foods are bioactive at doses as low as 150 mg. The potential effectiveness of phytosterols has been improved in several ways. Individuals most likely to respond have been identified as having high cholesterol absorption and low cholesterol biosynthesis. Phytosterols can be emulsified with lecithin and delivered in non-fat or low-fat foods and beverages, and the amount of fat in fat-based preparations can be reduced substantially with the retention of bioactivity.

SUMMARY

Phytosterols effectively reduce LDL-cholesterol when given as supplements, and the smaller amounts in natural foods also appear to be important. Future work will focus on the better delivery of phytosterols in natural foods and supplements and on further defining the mechanisms of action.

Inhibition of cholesterol absorption by phytosterol-replete wheat germ compared with phytosterol-depleted wheat germ

BACKGROUND

Low-fat vegetable foods contain phytosterols, but it is not known whether they are in biologically active forms or whether their concentrations are high enough to reduce cholesterol absorption and favorably affect lipid metabolism.

OBJECTIVE

The objective was to establish whether the selective removal of phytosterols from wheat germ would increase the cholesterol absorption measured from test meals composed of wheat germ muffins.

DESIGN

Wheat germ, which has a high content of phytosterols relative to total fat, was chosen as a low-fat test food. Cholesterol absorption was measured 3 times in 10 subjects. Each test meal was a muffin containing 30 mg heptadeuterated cholesterol tracer and, in random order, 80 g original wheat germ containing 328 mg phytosterols, wheat germ from which phytosterols had been selectively extracted, or extracted wheat germ reconstituted with purified phytosterols. Changes in cholesterol absorption were monitored by the measurement of tracer enrichment of plasma cholesterol 4 and 5 d after each meal with the use of negative ion mass spectrometry.

RESULTS

Tracer enrichment of plasma cholesterol was 42.8% higher after consumption of phytosterol-free wheat germ than after that of the original wheat germ (0.415 +/- 0.035 compared with 0.291 +/- 0.024 micro mol tracer/mmol cholesterol; P < 0.01). Tracer enrichment of plasma cholesterol was not significantly different between the wheat germ with extracted-and-reconstituted phytosterol (0.305 +/- 0.022 micro mol tracer/mmol cholesterol) and the original wheat germ.

CONCLUSION

The efficiency of cholesterol absorption from test meals was substantially lower after consumption of original wheat germ than after consumption of phytosterol-free wheat germ, which suggests that endogenous phytosterols in wheat germ and possibly in other low-fat vegetable foods may have important effects on cholesterol absorption and metabolism that are independent of major nutrients.

Fat-free foods supplemented with soy stanol-lecithin powder reduce cholesterol absorption and LDL cholesterol

OBJECTIVE

The objective of this work was to show that fat-free, lecithin-formulated soy stanols lower cholesterol absorption and serum LDL cholesterol.

DESIGN

Reduction in cholesterol absorption was measured in paired single-meal tests with or without formulated soy stanols (acute test), and changes in serum lipids were investigated in a 10-week, randomized, double-blind parallel trial in which formulated stanols or lecithin vehicle were given three times daily for the last 4 weeks (chronic test).

SUBJECTS/SETTING

Forty-five normal or mildly hypercholesterolemic subjects were recruited for both studies. The 21 subjects (16 female, 5 male; mean age 32.5 years) in the absorption studies had the following mean lipid values: LDL cholesterol, 2.79 mmol/L and total cholesterol, 4.73 mmol/L. For the lipid reduction, 24 subjects (16 female, 8 male; mean age 50.6 years) were enrolled with mean LDL cholesterol and total cholesterol of 3.72 mmol/L and 5.66 mmol/L, respectively.

INTERVENTION

Reduction in cholesterol absorption was measured using a lemonade beverage or egg whites that contained 625 mg stanols. Throughout the chronic study, subjects followed the American Heart Association Step I diet. During the 4-week treatment phase, subjects consumed daily a lemonade-flavored beverage containing either placebo or formulated soy stanols (1.9 g).

MAIN OUTCOME MEASURES

Inhibition of cholesterol absorption was determined from the difference in plasma deuterated cholesterol enrichment after a test meal containing stanol-lecithin and one with lecithin vehicle only. In the chronic study, the primary endpoints were changes in LDL and total cholesterol.

STATISTICAL ANALYSES PERFORMED

Paired or unpaired t tests were used to determine statistical significance.

RESULTS

Stanol-lecithin reduced cholesterol absorption by 32.1% (P=.0045, n=10) and by 38.2% (P=.0022, n=11) when delivered in a lemonade-flavored beverage and in egg whites, respectively. Reduction in cholesterol absorption was strongly related to the initial level of absorbed cholesterol tracer in serum (r(s)=-0.739). Stanol-lecithin given in a beverage reduced total serum cholesterol by 10.1% (P=.0019, n=24) and LDL cholesterol by 14.3% (P=.0016, n=24).

APPLICATIONS/CONCLUSIONS

Powdered soy stanol-lecithin lowers cholesterol absorption and LDL cholesterol when consumed in fat-free foods.

Phytosterols in human nutrition

Phytosterols are cholesterol-like molecules found in all plant foods, with the highest concentrations occurring in vegetable oils. They are absorbed only in trace amounts but inhibit the absorption of intestinal cholesterol including recirculating endogenous biliary cholesterol, a key step in cholesterol elimination. Natural dietary intake varies from about 167-437 mg/day. Attempts to measure biological effects in feeding studies have been impeded by limited solubility in both water and fat. Esterification of phytosterols with long-chain fatty acids increases fat solubility by 10-fold and allows delivery of several grams daily in fatty foods such as margarine. A dose of 2 g/day as the ester reduces low density lipoprotein cholesterol by 10%, and little difference is observed between Delta(5)-sterols and 5alpha-reduced sterols (stanols). Phytosterols can also be dispersed in water after emulsification with lecithin and reduce cholesterol absorption when added to nonfat foods. In contrast to these supplementation studies, much less is known about the effect of low phytosterol levels in the natural diet. However, reduction of cholesterol absorption can be measured at a dose of only 150 mg during otherwise sterol-free test meals, suggesting that natural food phytosterols may be clinically important. Current literature suggests that phytosterols are safe when added to the diet, and measured absorption and plasma levels are very small. Increasing the aggregate amount of phytosterols consumed in a variety of foods may be an important way of reducing population cholesterol levels and preventing coronary heart disease.

Effects of trace components of dietary fat on cholesterol metabolism: phytosterols, oxysterols, and squalene

The effect of dietary fats on serum cholesterol is widely assumed to be due solely to the fatty acids and cholesterol they contain. Phytosterols, sterol oxidation products, and sterol precursors such as squalene, however, are often present in dietary fats. Little is known of the physiology of these substances in natural foods and most published diet studies do not consider them at all. Supplementation of the diet with high-dose phytosterols is now recommended for prevention of heart disease, but both recent and old data strongly suggest that the lower levels of phytosterols naturally present in vegetable fats may also reduce cholesterol absorption and serum cholesterol substantially. Moreover, unmeasured phytosterols may confound otherwise well-controlled diet studies because there is an inverse correlation between phytosterol and saturated fatty acid content of vegetable fats. Sterol oxidation products, many of which are found in foods, are potent regulators of lipoprotein and cholesterol transport pathways in vitro. Squalene is a phytosterol precursor abundant in olive oil that is at least partly absorbed and then quantitatively converted to cholesterol. The effects of dietary triglyceride-derived fatty acids have not been experimentally separated from the effects of trace fat components in most clinical studies. A better understanding of the activity of sterol-related dietary components is needed to reduce variability in diet studies, accurately assess the effects of dietary fatty acids and to maximize the effectiveness of dietary treatment for hypercholesterolemia.

Phytosterols that are naturally present in commercial corn oil significantly reduce cholesterol absorption in humans

BACKGROUND

Although supplementing the diet with large quantities of phytosterols reduces cholesterol absorption and LDL-cholesterol concentrations, very little is known about the smaller amounts of phytosterols present naturally in food. Vegetable oils are the richest dietary source of phytosterols; corn oil contains 0.77% phytosterols by weight.

OBJECTIVE

We tested the hypothesis that removing phytosterols from corn oil would increase cholesterol absorption when measured in single-meal tests containing corn oil as a source of fat.

DESIGN

Free and esterified phytosterols were removed from corn oil on a kilogram scale by a new technique of competitive saturation adsorption to silica. Healthy subjects with a mean (+/-SEM) serum cholesterol concentration of 5.10 +/- 0.18 mmol/L received an otherwise sterol-free test breakfast on 2 occasions 2 wk apart that contained 35 mg hexadeuterated cholesterol and 30-35 g of a corn oil preparation. The plasma enrichment of tracer was measured by negative ion mass spectrometry.

RESULTS

Cholesterol absorption was 38.0 +/- 10.2% higher after consumption of the sterol-free corn oil than after consumption of commercial corn oil with an identical fatty acid content (P = 0.005; n = 10). When corn oil phytosterols were added back to sterol-free corn oil at a concentration of 150 mg/test meal, cholesterol absorption was reduced by 12.1 +/- 3.7% (P = 0.03; n = 5) and by 27.9 +/- 9.1% (P = 0.01; n = 10) after inclusion of 300 mg phytosterols.

CONCLUSIONS

Phytosterols comprising < 1% of commercial corn oil substantially reduced cholesterol absorption and may account for part of the cholesterol-lowering activity of corn oil previously attributed solely to unsaturated fatty acids.

Gastrointestinal absorption and plasma kinetics of soy Delta(5)-phytosterols and phytostanols in humans

Our objective was to measure the systemic absorption of lecithin-emulsified Delta(5)-phytosterols and phytostanols during test meals by use of dual stable isotopic tracers. Ten healthy subjects underwent two single-meal absorption tests in random order 2 wk apart, one with intravenous dideuterated Delta(5)-phytosterols and oral pentadeuterated Delta(5)-phytosterols and the other with the corresponding labeled stanols. The oral-to-intravenous tracer ratio in plasma, a reflection of absorption, was measured by a sensitive negative ion mass spectroscopic technique and became constant after 2 days. Absorption from 600 mg of Delta(5)-soy sterols given with a standard test breakfast was 0.512 +/- 0.038% for sitosterol and 1.89 +/- 0.27% for campesterol. The absorption from 600 mg of soy stanols was 0.0441 +/- 0.004% for sitostanol and 0.155 +/- 0.017% for campestanol. Reduction of the double bond at position 5 decreased absorption by 90%. Plasma t(1/2) for stanols was significantly shorter than that for Delta(5)-sterols. We conclude that the efficiency of phytosterol absorption is lower than what was reported previously and is critically dependent on the structure of both sterol nucleus and side chain.

Cholesterol absorption

Cholesterol absorption is a key regulatory point in human lipid metabolism because it determines the amount of endogenous biliary as well as dietary cholesterol that is retained, thereby influencing whole body cholesterol balance. Plant sterols (phytosterols) and the drug ezetimibe reduce cholesterol absorption and low-density lipoprotein cholesterol in clinical trials, complementing the statin drugs, which inhibit cholesterol biosynthesis. The mechanism of cholesterol absorption is not completely known but involves the genes ABC1, ABCG5, and ABCG8, which are members of the ATP-binding cassette protein family and appear to remove unwanted cholesterol and phytosterols from the enterocyte. ABC1 is upregulated by the liver X (LXR) and retinoid X (RXR) nuclear receptors. Acylcholesterol acytransferase-2 is an intestinal enzyme that esterifies absorbed cholesterol and increases cholesterol absorption when dietary intake is high. New clinical treatments based on better understanding of absorption physiology are likely to substantially improve clinical cholesterol management in the future.

Enantiospecificity of cholesterol function in vivo

The importance of the absolute configuration of cholesterol for its function in vivo is unknown. To directly test this question in vivo, we synthesized the enantiomer of cholesterol (ent-cholesterol) and tested its ability to substitute for natural cholesterol (nat-cholesterol) in the growth, viability, and behavior of Caenorhabditis elegans, a cholesterol auxotroph. First-generation animals grown on ent-cholesterol were viable with only mild behavioral defects. However, ent-cholesterol produced 100% lethality/arrest of their second generation progeny. Isotopically labeled ent-cholesterol incorporated into animals, indicating that its lethality was not secondary to cholesterol starvation. When mixed with nat-cholesterol, ent-cholesterol was not inert; rather, it antagonized the activity of nat-cholesterol. These results demonstrate for the first time that the absolute configuration of cholesterol, not just its physical properties, is essential for its functions in vivo.

Orlistat inhibits dietary cholesterol absorption

OBJECTIVE

Orlistat decreases the absorption of dietary triglycerides by inhibiting intestinal lipases. Orlistat therapy is associated with a greater decline in plasma low-density lipoprotein-cholesterol concentrations than that expected from weight loss alone. Therefore, we evaluated the effect of orlistat treatment on dietary cholesterol absorption as a possible mechanism for the independent effect of orlistat on plasma cholesterol concentration.

RESEARCH METHODS AND PROCEDURES

Cholesterol absorption from a standardized meal, containing 72 mg of cholesterol, was determined in 18 subjects with class II abdominal obesity (BMI, 35.0 to 39.9 kg/m(2)) by simultaneous administration of intravenous ([(2)H(6)] cholesterol) and oral ([(2)H(5)] cholesterol) cholesterol tracers. In protocol 1 (n = 9), cholesterol absorption was determined on two different occasions, 10 to 20 days apart, to assess the reproducibility of the tracer method. In protocol 2 (n = 9), cholesterol absorption was determined with and without orlistat therapy in a prospective, randomized, crossover design to assess the effect of orlistat on cholesterol absorption.

RESULTS

In protocol 1, cholesterol absorption from the test meal was the same on both occasions (53 +/- 5% and 51 +/- 5%). In protocol 2, orlistat treatment caused a 25% reduction in cholesterol absorption, from 59 +/- 6% to 44 +/- 5% (p < 0.01).

DISCUSSION

These data demonstrate that orlistat inhibits dietary cholesterol absorption, which may have beneficial effects on lipoprotein metabolism in obese subjects that are independent of weight loss itself.