Lack of relationship in humans of the parameters of body cholesterol metabolism with plasma levels of subfractions of HDL or LDL, or with apoE isoform phenotype

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.

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.

Efficiency of intestinal cholesterol absorption in humans is not related to apoE phenotype

The present study investigated the role of apolipoprotein E (apoE) phenotype on intestinal cholesterol absorption and cholesterol synthesis. Studies were carried out in eight subjects homozygous for the apoE4 and 12 subjects homozygous for the E2 allele (six normocholesterolemic volunteers and six patients with type III hyperlipoproteinemia). Cholesterol absorption did not differ between the three groups of subjects and averaged 38 +/- 2% (mean +/- SEM) in normolipemic E2/2, 37 +/- 4% in type III hyperlipemic E2/2, and 41 +/- 3% in E4/4 subjects, respectively. Dietary intake of fat and cholesterol had no influence on cholesterol absorption efficiency. A positive correlation between efficiency of cholesterol absorption and the ratio of campesterol to cholesterol in plasma, an indirect marker for cholesterol absorption, was observed after combining the results of the three groups (r = 0.504; P < 0.02). Bile acid and total cholesterol synthesis were also not affected by the different apoE alleles, but the well-known relationship between body weight and cholesterol synthesis was noticed (r = 0.574; P < 0.01). Thus, the present study provides evidence that the efficiency of intestinal absorption and synthesis of cholesterol in humans are not related to the apoE phenotype.

Response of cholesterol synthesis to cholesterol feeding in men with different apolipoprotein E genotypes

To investigate the influence of dietary cholesterol level and apolipoprotein (apo) E polymorphism on cholesterol synthesis, seven apo E2/- and six apo E4/- normolipidemic subjects consumed self-selected diets containing low cholesterol ([LC] 250 mg/d) and high cholesterol ([HC] 800 mg/d) levels for approximately 20 days. On day 20, subjects were given 0.7 g deuterium oxide (D2O)/kg body water followed by maintenance doses. Cholesterol synthesis was measured as the uptake rate of D into plasma free cholesterol over 24 hours. Serum total cholesterol levels were higher (P < .05) in the apo E4/- versus apo E2/- group over both dietary periods. No influence of dietary cholesterol content on serum levels was observed, nor was there an effect of apo E genotype or dietary cholesterol level on cholesterogenesis. However, a genotype-independent association was observed between both cholesterogenesis (P < .001) and the increase in cholesterogenesis (P = .05) with the change in serum total cholesterol level subsequent to high-cholesterol feeding. These findings suggest that (1) apo E genotype is not associated with cholesterol synthesis rate in subjects on self-selected diets, and (2) hyporesponders to a dietary cholesterol challenge display higher synthetic rates than hyperresponders. The observation of lower cholesterol synthesis in individuals with the largest increases in serum cholesterol level after a dietary cholesterol challenge suggests a passive rather than dominant role of cholesterol synthesis in regulating serum levels.

Serum low density lipoprotein cholesterol level and cholesterol absorption efficiency are influenced by apolipoprotein B and E polymorphism and by the FH-Helsinki mutation of the low density lipoprotein receptor gene in familial hypercholesterolemia

The aim of the present study was to evaluate the effect of variation of different gene loci separately and in concert on lipid metabolism in heterozygous familial hypercholesterolemia (FH). We assayed a unique low density lipoprotein (LDL) receptor gene defect (designated as FH-Helsinki), the XbaI polymorphism of the apolipoprotein (apo) B, phenotypes of the apo E, and determined the levels of serum lipoproteins, the efficiency of cholesterol absorption, and the values for several parameters of cholesterol metabolism in 51 unrelated patients with heterozygous FH. The genetic parameters were distributed independently of each other. Gender distribution and the prevalence of coronary artery disease were similar in the different apo E phenotypes, in the apo B genotypes, and in patients with and without the FH-Helsinki mutation. However, the FH-Helsinki mutation was associated with an increased body mass index. Serum LDL cholesterol was significantly elevated in patients with the FH-Helsinki mutation and the apo B X2 allele. Apo E phenotypes were not related to serum lipids per se, but the highest serum LDL cholesterol levels were measured in patients with the FH-Helsinki gene, apo E4 phenotype, and at least one X2 allele. Patients with the FH-Helsinki mutation and apo E4 phenotype had the highest cholesterol absorption efficiency. Cholesterol absorption was not related to serum lipids or lipoproteins, but LDL cholesterol was most elevated in patients with the most efficient cholesterol absorption. We conclude that in FH, diverse genetic factors exert individual and additive influences on serum LDL cholesterol levels.

Plasma levels of lathosterol and phytosterols in relation to age, sex, anthropometric parameters, plasma lipids, and apolipoprotein E phenotype, in 160 Dutch families

In this study, the relation of plasma levels of lathosterol (an indicator of whole body cholesterol synthesis) and plant sterols (indicator of cholesterol absorption) with age, sex, weight, height, plasma lipids, and lipoproteins, and with apolipoprotein (apo) E phenotype, was investigated in a group of 160 nuclear families consisting of twins living with their parents. Lathosterol was higher in fathers than in mothers, but not different between boys and girls. In each of these four groups, there was a strong correlation with plasma and low-density lipoprotein (LDL)-cholesterol and -triglyceride, as well as with body weight, but not with height or high-density lipoprotein (HDL)-cholesterol. In adults, lathosterol was inversely correlated with plant sterols. Lathosterol was higher in children with E4/3 phenotype than in those with E3/3 or E3/2; in adults, lathosterol did not differ among the various E phenotypes. The plasma levels of the two plant sterols, campesterol and beta-sitosterol, were highly correlated with each other, and also with plasma or LDL-cholesterol, in each of the four groups. Plant sterols were higher in adults or children with E4/3 phenotype as compared with those with other phenotypes. In multivariate analysis (performed separately for two groups of adults and children) plasma cholesterol, plasma plant sterols, plasma triglycerides, and weight were found to make significant contributions to the variation of lathosterol in all groups, and E phenotype and sex only in one group, while age did not contribute in any group.(ABSTRACT TRUNCATED AT 250 WORDS)