Cholesterol absorption, elimination, and synthesis related to LDL kinetics during varying fat intake in men with different apoprotein E phenotypes

Cholesterol absorption, fecal elimination, and synthesis and low density lipoprotein (LDL) metabolism were measured in 29 middle-aged men while on their normal diet and a diet low in fat and cholesterol, and the obtained values were related to apoprotein (apo) E phenotypes. Basal cholesterol absorption efficiency was positively related to production rate (PR) for LDL apo B and negatively to cholesterol synthesis (measured by fecal steroids and dietary cholesterol), which in turn was negatively associated with the LDL level and positively with the fractional removal (FCR) of LDL apo B. The apo E subscript (e.g., E2/2 = 1, E2/3 = 2, etc.) was positively associated with cholesterol absorption and the LDL apo B and cholesterol levels and negatively with cholesterol synthesis and FCR for LDL apo B. Effective bile acid and cholesterol synthesis, fecal elimination of cholesterol, removal of LDL apo B, and low cholesterol absorption characterized men with the epsilon 2 allele. Reduction of dietary fat and cholesterol intakes lowered LDL cholesterol levels and cholesterol absorption but increased cholesterol synthesis proportionally to the apo E subscript; the FCR and PR for LDL apo B were significantly increased and decreased, respectively. The decrease in absorption was related to enhanced removal of LDL apo B and synthesis of cholesterol. During the modified diet, cholesterol metabolism was poorly related to LDL, apo E phenotypes, and LDL apo B kinetics. A positive correlation of cholesterol absorption with dietary fat intake in combined studies suggests that a dietary fat reduction-associated decrease in LDL cholesterol is at least partly caused by reduced cholesterol absorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholesterol absorption and synthesis related to low density lipoprotein metabolism during varying cholesterol intake in men with different apoE phenotypes

The aim of the present study was, first, to investigate whether cholesterol (C) absorption, enhanced by cholesterol feeding, was related to synthesis of cholesterol, serum level of low density lipoprotein (LDL)-C, and receptor activity for LDL apolipoprotein (apo) B in healthy men. Secondly, we were interested in whether apolipoprotein E (apoE) phenotypes contributed to cholesterol and LDL apoB metabolism under these conditions. We studied 29 home-living men aged 55 +/- 1 (mean +/- SE) years on a low-fat, low cholesterol (208 +/- 13 mg/day) diet followed by a low-fat high cholesterol (878 +/- 38 mg/day) diet during 5 weeks. Cholesterol feeding increased total cholesterol, LDL-C, high density lipoprotein (HDL)-C, and LDL apoB levels from 10% to 13% (P less than 0.05) and bile acid production and cholesterol turnover by 16% (P less than 0.05), decreased the fractional catabolic rate (FCR) for LDL apoB by 10% (P less than 0.05) and cholesterol absorption efficiency by 8% (P less than 0.05), while cholesterol synthesis only tended to decrease. During the cholesterol feeding, LDL-C was positively related to apoB production rate and cholesterol absorption efficiency (P less than 0.05), and negatively related to bile acid and cholesterol synthesis (P less than 0.05) and FCR for LDL apoB, which, in turn, was negatively related to cholesterol absorption efficiency and positively to bile acid synthesis. ApoE phenotype was positively related to TC, LDL-C, and LDL apoB levels and negatively to FCR for LDL apoB. The increase of the LDL-C level by the high cholesterol intake was positively correlated with LDL-C on high cholesterol diet and apoE phenotypes, so that the increase was 7% in apoE2 (ns), 11% in apoE3 (P less than 0.05), and 18% in apoE4 (P less than 0.05); the increase of bile acid synthesis was significant only in subjects with apoE2. Moreover, the increase of LDL-C was positively related to the absolute amount of dietary cholesterol absorbed and negatively to FCR for LDL apoB. The findings suggest that the higher the LDL-C level, the higher is the absorption efficiency of cholesterol and production of LDL apoB, and the lower is the removal of LDL apoB and synthesis of both bile acids and cholesterol, and the more frequently the subjects had epsilon 4 allele. The nonresponsiveness to dietary cholesterol was dependent on low LDL-C level, apoE2 phenotype, and effective bile acid synthesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Persistence of abnormalities in metabolism of apolipoproteins B-100 and A-I after weight reduction in patients with primary hypertriglyceridemia

Obesity commonly accompanies hypertriglyceridemia, and weight reduction is widely recommended for treatment of elevated triglyceride levels. To determine whether weight reduction will normalize lipoprotein metabolism in overweight, hypertriglyceridemic patients, 10 such male patients underwent weight loss until their body weights were within the desirable range. After reestablishment of a steady state in body weight at the lower level, measurements were made of plasma lipid, lipoprotein, and apolipoprotein levels and the kinetics of low density lipoprotein (LDL) apolipoprotein B-100 (apo B) and apolipoprotein A-I (apo A-I). The patients lost an average of 10.6 +/- 2.1 kg (mean +/- SEM). Plasma triglyceride concentrations fell from 431 +/- 42 mg/dl to 248 +/- 27 mg/dl (p less than 0.001), whereas concentrations of total cholesterol, LDL cholesterol, total apo B, and high density lipoprotein (HDL) cholesterol were unchanged after weight loss. On average, the fractional catabolic rates (FCRs) for LDL were much higher in the patients after weight loss than in 16 normal control subjects (0.55 +/- 0.06 versus 0.31 +/- 0.06 pool/day), and input rates for LDL also were higher for hypertriglyceridemic patients after weight loss (22.2 +/- 2.4 versus 12.8 +/- 2.3 mg/kg.day). Compared with 20 normal control subjects, hypertriglyceridemic patients after weight reduction had persistent low HDL cholesterol levels (32 +/- 2 versus 54 +/- 3 mg/dl) as well as low apo A-I levels (99 +/- 5 versus 122 +/- 4 mg/dl).(ABSTRACT TRUNCATED AT 250 WORDS)

Non-cholesterol sterols, absorption and synthesis of cholesterol and apolipoprotein A-I kinetics in a Finnish lecithin-cholesterol acyltransferase deficient family

We describe the first Finnish LCAT-deficient family with two affected, one questionably affected and one healthy family member. The affected family members presented stomatocytes in the peripheral blood, exhibited low serum levels of total, LDL and HDL cholesterol, triglycerides, phospholipids and apolipoprotein A-I and especially A-II. Apolipoprotein A-I catabolism was accelerated to moderately high and very high levels in the two affected subjects. Cholesterol esterification percentage was low in all lipoprotein fractions. The intestinal cholesterol absorption efficiency and cholesterol and bile acid synthesis were within normal limits. The esterification percentage of demethylated cholesterol precursor sterols, cholestanol and plant sterols resembled mostly that of cholesterol, while those of VLDL and LDL methostenols, precursor sterols esterified by acyl-CoA:cholesterol acyltransferase (ACAT), suggested normal ACAT activity. In HDL all sterols were poorly esterified. The observations on stomatocytes, normal absorption and synthesis of cholesterol and bile acids, abnormal kinetics of apolipoprotein A-I, evidence of normal ACAT activity and abnormal esterification of non-cholesterol sterols are findings presented for the first time in LCAT deficiency.

Prevalence and geographical distribution of major LDL receptor gene rearrangements in Finland

In order to determine the prevalence of major rearrangements of the low density lipoprotein (LDL) receptor gene in Finland, DNA samples of 199 unrelated Finnish patients with the heterozygous form of familial hypercholesterolaemia (FH) were examined by Southern blot analysis. The FH-Helsinki mutation, characterized by a 9.5-kb deletion in the 3'-end of the LDL receptor gene, was found in 75 (38%) of the patients. The prevalence of this mutation ranged from 26-58% in different areas of Finland. A striking exception was the North Karelia region, where only one out of 26 (4%) FH patients was found to carry the FH-Helsinki allele. Two patients were found to carry other types of large nucleotide rearrangements of the LDL receptor gene. One mutation was a 7.5-kb deletion eliminating exons 7 to 10, and the other was a 13-kb deletion covering exons 11 to 16 of the LDL receptor gene. Serum lipoprotein levels were very similar in each category of mutation, i.e. in patients with the FH-Helsinki gene, those with the two other types of deletion, and the remaining patients with as yet unknown types of LDL receptor gene defects. These results show that, even in genetically uniform populations, FH may be heterogeneous at the DNA level. DNA techniques enable an unequivocal diagnosis for almost 40% of the Finnish patients with the heterozygous form of FH.

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.

Evaluation of a method for study of kinetics of autologous apolipoprotein A-I

Apolipoprotein A-I (apoA-I) participates in transport of plasma cholesterol. Concentrations of apoA-I depend on the balance between production and fractional clearance. To elucidate factors influencing apoA-I levels, accurate estimates of apoA-I turnover rates may be valuable. We describe a method for isolation of autologous apoA-I and its use in turnover studies. Free apoA-I was isolated from high density lipoproteins (HDL) by treatment with guanidine hydrochloride. This free apoA-I was radioiodinated with 131I and injected into eleven subjects simultaneously with HDL labeled with 125I. Plasma die-away curves of free apoA-I (131I) and HDL apoA-I (125I) were compared; fractional clearance rates averaged 0.256 +/- 0.019 (SEM) and 0.254 +/- 0.017 pools/day, respectively. Although slight differences between the two die-away curves were noted for some of the patients, the differences were relatively small; for the group as a whole, average fractional catabolic rates were not significantly different. Thus, by isolation of autologous apoA-I under the conditions described, free apoA-I seemingly provides a valid method for estimating apoA-I turnover.

Hypolipidemic effect and mechanism of ketoconazole without and with cholestyramine in familial hypercholesterolemia

The hypocholesterolemic and metabolic effects of ketoconazole (400 mg/d) alone (inhibits cholesterol synthesis at 14 alpha-demethylation of lanosterol) and in combination with cholestyramine (12 g/d), were studied in nine women with xanthomatous familial hypercholesterolemia (FH). In addition to serum lipoprotein levels, cholesterol precursors, fecal steroids, and cholesterol absorption were measured before and during the drug treatments. Serum total and low-density lipoprotein (LDL)-cholesterol were reduced by 19% and 22% with ketoconazole; the respective changes were 16% and 21% for cholestyramine, and 31% and 41% for the combined ketoconazole and cholestyramine treatment. Serum triglycerides, very-low-density lipoprotein (VLDL)-and high-density lipoprotein (HDL)-cholesterol levels were unchanged. Accumulation of cholesterol precursors in serum suggested that ketoconazole inhibited cholesterol synthesis at delta 8-sterol levels. Serum and fecal lanosterols were increased up to 20-fold and were interrelated. Their maximal serum level was 1.3 mg/DL and the lanosterol contents were negatively related to the serum cholesterol levels. The intestinal absorption and total intestinal fluxes of cholesterol were reduced by 27% and 29%. Cholesterol and bile acid synthesis were decreased by ketoconazole only when combined with cholestyramine. The synthesis of chenodeoxycholic acid was deeply hindered by ketoconazole. Thus, ketoconazole efficiently lowers serum total and LDL-cholesterol levels in FH patients, probably by inhibiting cholesterol synthesis and absorption. Effective biliary and fecal outputs of cholesterol precursors prevent their excessive increase in serum.(ABSTRACT TRUNCATED AT 250 WORDS)

Phagocyte function in familial hypercholesterolaemia: peripheral blood monocytes exposed to lipopolysaccharide show increased tumour necrosis factor production

We studied functions of polymorphonuclear leucocytes (PMN) and monocytes from peripheral blood of subjects with familial hypercholesterolaemia (FH). FH monocytes exposed to Escherichia coli lipopolysaccharide (LPS) in 10% human AB serum generated tumour necrosis factor (TNF) significantly more than did control monocytes. After lowering of serum low-density lipoprotein (LDL) levels by drug treatment, FH monocytes exposed to LPS in the absence of exogenous lipoproteins generated significantly more TNF than did control monocytes. These findings suggest that increased TNF production is not affected by hypolipidaemic treatment and may not derive from differences between uptake of exogenous LDL by FH monocytes and control cells. Chemotaxis, chemokinesis, and random migration of both FH PMN and FH monocytes were normal, as determined by agarose assay and membrane filter assay. FH PMN showed increased luminol-enhanced chemiluminescence in response to 2.5 x 10(-8) M, but not to 2.5 x 10(-6) M, N-formyl-methionyl-leucyl-phenylalanine, and not to serum-treated zymosan or to phorbol myristate acetate. Luminol- and lucigenin-enhanced chemiluminescence responses of FH monocytes were normal. In summary, the major aberration found in the present study was that FH monocytes stimulated with LPS show enhanced production of TNF. The possibility that exaggerated TNF production contributes to an early development of atherosclerotic lesions in FH subjects warrants further studies.

Apolipoprotein E phenotype and cholesterol metabolism in familial hypercholesterolemia

Serum lipids, lipoproteins, cholesterol absorption and parameters of cholesterol metabolism were related to apolipoprotein E phenotypes in 38 patients with familial xanthomatous hypercholesterolemia. Serum lipids and lipoproteins were similar in 2 most frequent apo E phenotypes E 3/3 and E 4/3. Coronary artery disease was not related to the apo E phenotypes. Cholesterol absorption efficiency was significantly lower in the apo E 3/3 patients than in the apo E 4/3 group. A high serum level of cholesterol precursor lathosterol, a high lathosterol/sitosterol ratio and sterol balance data suggest that cholesterol synthesis may be slightly higher in the apo E 3/3 than E 4/3 group. The findings indicate that the genetically determined apo E polymorphism contributes to cholesterol absorption efficiency in FH patients, but serum total and lipoprotein cholesterol levels are poorly related to apo E isoforms.

Use of hospital care and hospital case-fatality of myocardial infarction during three years' follow-up in Finland

The epidemiology and use of hospital care of myocardial infarction was studied at the population level with routinely collected hospital discharge data of the whole country during a three-year follow-up. The study population was a one-year-cohort of 13,520 patients with an acute myocardial infarction in 1981 in Finland. The incidence figures were comparable with the previous data attained from expensive and laborious special registries or population studies. With the possibility of record linkage and follow-up we could get information on the use of hospital care of these patients. We conclude that routinely collected hospital discharge data in Finland give information valuable for epidemiological studies, for the planning of health services and for the evaluation of hospital care.

Genetic polymorphism of the apolipoprotein B gene locus influences serum LDL cholesterol level in familial hypercholesterolemia

An XbaI restriction fragment length polymorphism (RFLP) within the coding region of the apolipoprotein B (apoB) gene has been found to be associated with serum cholesterol and triglyceride levels in several populations. Mutations in another genetic locus, the low density lipoprotein (LDL) receptor gene, give rise to familial hypercholesterolemia (FH), a disease characterized by hypercholesterolemia, tendon xanthomas and atherosclerosis. We determined the XbaI genotypes and serum lipoprotein levels of 120 unrelated patients with the heterozygous form of FH. A non-parametric analysis of variance showed a significant association between elevated serum total cholesterol concentration (P less than 0.05), serum LDL-cholesterol concentration (P less than 0.025) and the presence of the XbaI restriction site (X2 allele). Thus, patients homozygous for the presence of the XbaI restriction site (genotype X2X2, n = 28) had on average a 14% higher serum total cholesterol level and a 21% higher serum LDL-cholesterol level than those homozygous for the absence of this site (genotype X1X1, n = 29); patients heterozygous for the XbaI restriction site (genotype X1X2, n = 63) had intermediate serum total and LDL-cholesterol levels. No significant differences were seen in serum triglyceride or high-density lipoprotein (HDL)-cholesterol values between these patient groups. These data demonstrate that genetic polymorphism of the principal ligand for the LDL receptor, apoB, may contribute to serum cholesterol regulation, even in patients with grossly distorted cholesterol homeostasis.

Peripheral atherosclerosis in familial hypercholesterolaemia

Unlike coronary artery disease, peripheral atherosclerosis is considered to be infrequent in heterozygous familial hypercholesterolaemia. The authors studied 20 consecutive asymptomatic familial hypercholesterolaemic patients and an age- and sex-matched control group of consecutive normolipidaemic and asymptomatic patients admitted to the hospital for elective non-vascular surgery. The patients and the controls were studied non-invasively by measuring the ankle-arm systolic blood pressure ratio at rest. Peripheral atherosclerosis was common in this study population in contrast to the control group: an abnormal (less than 0.97) pressure ratio was found in 13 patients (65%) in the study group but in only one person in the control group. Eight out of 20 patients had coronary artery disease, and seven of them had an asymptomatic concomitant peripheral artery disease. Neither the classical risk factors, i.e. age, smoking, obesity, hypertension and glucose intolerance, nor serum lipid or lipoprotein status or the parameters of cholesterol metabolism correlated with peripheral atherosclerosis. It is concluded that atherosclerosis in familial hypercholesterolaemia is a multilevel disease that frequently affects also the peripheral arteries.

Absorption and metabolism of cholesterol in familial hypercholesterolaemia

1. The present study investigated the role of intestinal cholesterol absorption in the regulation of cholesterol metabolism and serum lipoprotein levels in 22 patients with heterozygous familial hypercholesterolaemia on low to normal cholesterol intake. 2. The results showed that the higher the dietary cholesterol absorption, the lower was the overall synthesis of cholesterol. Efficient cholesterol absorption actually reduced the elimination of cholesterol as faecal neutral sterols but not consistently as bile acids. 3. In multifactorial analysis, body mass index and dietary plant sterols were negatively associated with cholesterol absorption, but were unrelated to cholesterol synthesis. 4. Fractional cholesterol absorption was related only to the serum very-low-density triacylglycerol level. It was not associated with the total or low-density lipoprotein cholesterol levels. On the other hand, cholesterol synthesis was significantly associated with the serum concentrations of very-low-density lipoprotein and intermediate-density lipoprotein cholesterol and triacylglycerols, and with those of low-density lipoprotein triacylglycerols. 5. In conclusion, dietary cholesterol absorption is an essential regulator of cholesterol homoeostasis in familial hypercholesterolaemia, even in patients on low cholesterol intake.

Effects of acipimox and cholestyramine on serum lipoproteins, non-cholesterol sterols and cholesterol absorption and elimination

The hypolipidaemic and metabolic effects of cholestyramine combined with acipimox or placebo have been evaluated in a double-blind ninety-day study in 18 patients with xanthomatous familial hypercholesterolaemia. Serum LDL-cholesterol was reduced by 35% in the cholestyramine group and 39% in the acipimoxcholestyramine group. The latter treatment increased the HDL-cholesterol level. Serum VLDL-cholesterol and triglyceride concentrations were unchanged. Cholesterol absorption efficiency was significantly reduced, and bile acid synthesis and faecal cholesterol elimination in both groups were increased. The metabolic changes were similar in the two treatment groups, but the increase in faecal neutral sterol excretion was significant only when acipimox was added. The serum cholesterol precursor sterol contents were similarly increased during the two treatments, indicating enhancement of endogenous cholesterol synthesis. The decrease in cholesterol absorption and the increase in neutral sterol excretion were more pronounced in subjects with greater than 30% than in those with less than 30% reduction in LDL-cholesterol. The changes in serum total and LDL-cholesterol levels and cholesterol metabolism were not related to apoE phenotype, but the increase in HDL-cholesterol was higher in E4 then in E3 subjects.

Serum noncholesterol sterols related to cholesterol metabolism in familial hypercholesterolemia

Serum cholesterol precursor levels and plant sterol were related to parameters of cholesterol metabolism in 22 patients with heterozygous familial hypercholesterolemia. The serum levels of cholesterol precursor sterols were inversely related to fractional absorption of dietary cholesterol and subsequently positively to overall cholesterol synthesis. The serum plant sterol levels, on the contrary, were significantly associated with fractional cholesterol absorption and negatively with overall cholesterol synthesis. These results were confirmed also with multivariate analyses. Fecal lanosterol, a cholesterol precursor, was related positively to cholesterol synthesis measured by sterol balance and serum precursors and negatively to serum plant sterols. The serum precursor and plant sterol levels were inversely significantly related to each other, indicating that the higher cholesterol absorption efficiency the higher are the serum plant sterol levels and the lower the precursor sterol contents and the overall cholesterol synthesis.

A longitudinal study of cholesterol metabolism in familial hypercholesterolemia

Sterol balance studies were performed in 11 patients with familial hypercholesterolemia before and after a 15-year follow-up exactly under the same conditions to evaluate whether ageing exerts any changes on serum lipids and cholesterol metabolism. No significant intraindividual variation could be observed in serum lipids, bile acid and cholesterol synthesis and cholesterol excretion as neutral sterols and no age-related association could be observed in these parameters.

Identification of a deletion in the LDL receptor gene. A Finnish type of mutation

A cDNA probe for the low density lipoprotein (LDL) receptor gene was used to screen DNA samples from 52 unrelated Finnish patients with the heterozygous form of familial hypercholesterolemia (FH) and 51 healthy controls. Southern blot analysis using the restriction enzyme PvuII revealed an abnormal 11 kb (kilo base-pair) restriction fragment in 16 (31%) of the patients but none of the controls. A more detailed restriction enzyme analysis of the DNA from patients revealed a mutation which apparently is due to an 8 kb deletion extending from intron 15 to exon 18 of the LDL receptor gene. Co-segregation of FH with the mutated gene was demonstrated in three families. These data are consistent with a 'founder gene effect' and support the assumption that recombinant DNA methods may have great impact on the diagnostics of FH in genetically homogeneous populations.

Mortality and cholesterol metabolism in familial hypercholesterolemia. Long-term follow-up of 96 patients

The aim of this prospective study was to explore the association of different prognostic factors including parameters of cholesterol metabolism with coronary morbidity and mortality in a study group of 96 patients who were heterozygous for familial hypercholesterolemia. During a 15-year follow-up period, 27% of the patients (44% of the men and 10% of the women, p less than 0.01) died from coronary disease, and an additional 4% died of noncoronary causes. Of the baseline characteristics, male gender, previous myocardial infarction, and smoking were the classical risk factors significantly associated with poor cardiac prognosis. In addition, a low bile acid synthesis predicted enhanced coronary mortality both in univariate and multivariate analysis, and in men bile acid synthesis was significantly correlated with cardiac mortality. Further analysis indicated that also in subjects without baseline myocardial infarction, low bile acid, cholesterol synthesis, or both predicted increased risk of coronary events. In multivariate analysis, male gender, previous myocardial infarction, and low bile acid synthesis at baseline explained 5%, 15%, and 5% (25%), respectively, of the variability of survival. Age, serum total cholesterol, and triglyceride values were unrelated to survival.