Quantitation of apolipoprotein A-I of human plasma high density lipoprotein

Apolipoprotein A-I, elevated in trauma patients, inhibits platelet activation and decreases clot strength

Apolipoprotein A-I (ApoA-I) is elevated in the plasma of a subgroup of trauma patients with systemic hyperfibrinolysis. We hypothesize that apoA-I inhibits platelet activation and clot formation. The effects of apoA-I on human platelet activation and clot formation were assessed by whole blood thrombelastography (TEG), platelet aggregometry, P-selectin surface expression, microfluidic adhesion, and Akt phosphorylation. Mouse models of carotid artery thrombosis and pulmonary embolism were used to assess the effects of apoA-I in vivo. The ApoA-1 receptor was investigated with transgenic mice knockouts (KO) for the scavenger receptor class B member 1 (SR-BI). Compared to controls, exogenous human apoA-I inhibited arachidonic acid and collagen-mediated human and mouse platelet aggregation, decreased P-selectin surface expression and Akt activation, resulting in diminished clot strength and increased clot lysis by TEG. ApoA-I also decreased platelet aggregate size formed on a collagen surface under flow. In vivo, apoA-I delayed vessel occlusion in an arterial thrombosis model and conferred a survival advantage in a pulmonary embolism model. SR-BI KO mice significantly reduced apoA-I inhibition of platelet aggregation versus wild-type platelets. Exogenous human apoA-I inhibits platelet activation, decreases clot strength and stability, and protects mice from arterial and venous thrombosis via the SR-BI receptor.

Supplementation of Rumen-Protected Glucose Increased the Risk of Disturbance of Hepatic Metabolism in Early Postpartum Holstein Cows

The dual stress of reduced feed intake and increased milk yield in dairy cows early postpartum results in a negative energy balance. Rumen-protected glucose (RPG) has been reported to replenish energy, increase milk yield, and improve gut health. However, early postpartum cows often develop an insulin resistance, implying that RPG may not be well utilized and increased milk production may increase the liver’s fat oxidization burden. This study aimed to investigate the effects of RPG on the hepatic oxidative/antioxidative status and protein profile. Starting 7 d before expected calving, six pairs of cows were supplemented with rumen-protected glucose (RPG, n = 6) or with an equal amount of rumen-protecting coating fat (CON, n = 6). Liver samples were obtained from 10 cows 14 d after calving (d 14). Concentration of malondialdehyde and activity of glutathione peroxidase were increased and the activities of catalase and superoxide dismutase tended to increase in the livers of the RPG cows compared to the CON cows. The revised quantitative insulin sensitivity check index (RQUICKI) was decreased by RPG, but triacylglycerol concentration in liver was increased by RPG supplementation. The overall profiles of hepatic proteins were similar between CON and RPG. A partial least square regression was conducted to identify the proteins associated with liver lipidosis, oxidative stress, and antioxidative capacity. The top twenty proteins, according to their variable importance value, were selected for metabolic pathway enrichment analysis. Eighteen enriched KEGG pathways were identified, including metabolism, the citrate cycle, propanoate metabolism, the peroxisome, and type II diabetes mellitus. Our study showed that RPG supplementation reduced insulin sensitivity but increased the liver triglyceride concentration and the oxidative stress in early postpartum cows. Liver proteins related to lipidosis, oxidative stress, and antioxidative capacity, were positively associated with the glutamine metabolism, citric acid cycle, peroxisome, and type II diabetes pathways, which may indicate an increased risk of liver metabolic disorders caused by RPG supplementation in early postpartum cows.

Plasma apolipoproteins and physical and cognitive health in very old individuals

Apolipoproteins play a crucial role in lipid metabolism with implications in cardiovascular disease, obesity, diabetes, Alzheimer's disease, and longevity. We quantified 7 apolipoproteins in plasma in 1067 individuals aged 56-105 using immunoassays and explored relationships with APOE polymorphism ε2/3/4, vascular health, frailty, and cognition. ApoA1, ApoA2, ApoB, ApoC3, ApoE, ApoH, and ApoJ decreased from mid-life, although ApoE and ApoJ had U-shaped trends. Centenarians had the highest ApoE levels and the lowest frequency of APOE ε4 allele relative to younger groups. Apolipoprotein levels trended lower in APOE ε4 homozygotes and heterozygotes compared with noncarriers, with ApoE and ApoJ being significantly lower. Levels of all apolipoproteins except ApoH were higher in females. Sex- and age-related differences were apparent in the association of apolipoproteins with cognitive performance, as only women had significant negative associations of ApoB, ApoE, ApoH, and ApoJ in mid-life, whereas associations at older age were nonsignificant or positive. Our findings suggest levels of some apolipoproteins, especially ApoE, are associated with lifespan and cognitive function in exceptionally long-lived individuals.

Heritabilities of Apolipoprotein and Lipid Levels in Three Countries

This study investigated the influence of genes and environment on the variation of apolipoprotein and lipid levels, which are important intermediate phenotypes in the pathways toward cardiovascular disease. Heritability estimates are presented, including those for apolipoprotein E and AII levels which have rarely been reported before. We studied twin samples from the Netherlands (two cohorts;n= 160 pairs, aged 13–22 andn= 204 pairs, aged 34–62), Australia (n= 1362 pairs, aged 28–92) and Sweden (n= 302 pairs, aged 42–88). The variation of apolipoprotein and lipid levels depended largely on the influences of additive genetic factors in each twin sample. There was no significant evidence for the influence of common environment. No sex differences in heritability estimates for any phenotype in any of the samples were observed. Heritabilities ranged from 0.48–0.87, with most heritabilities exceeding 0.60. The heritability estimates in the Dutch samples were significantly higher than in the Australian sample. The heritabilities for the Swedish were intermediate to the Dutch and the Australian samples and not significantly different from the heritabilities in these other two samples. Although sample specific effects are present, we have shown that genes play a major role in determining the variance of apolipoprotein and lipid levels in four independent twin samples from three different countries.

Apolipoprotein M expression increases the size of nascent pre beta HDL formed by ATP binding cassette transporter A1

Apolipoprotein M (apoM) is a novel apolipoprotein that is reportedly necessary for pre beta HDL formation; however, its detailed function remains unknown. We investigated the biogenesis and properties of apoM and its effects on the initial steps of nascent pre beta HDL assembly by ABCA1 in HEK293 cells. Transiently transfected apoM was localized primarily in the endomembrane compartment. Pulse-chase analyses demonstrated that apoM is inefficiently secreted, relative to human serum albumin, and that approximately 50% remains membrane-associated after extraction with sodium carbonate, pH 11.5. To investigate the role of apoM in nascent pre beta HDL formation, ABCA1-expressing or control cells, transfected with empty vector, apoM, or C-terminal epitope-tagged apoM (apoM-C-FLAG), were incubated with (125)I-apoA-I for 24 h. Conditioned media were harvested and fractionated by fast-protein liquid chromatography (FPLC) to monitor HDL particle size. Pre beta HDL particles were formed effectively in the absence of apoM expression; however, increased apoM expression stimulated the formation of larger-sized nascent pre beta HDLs. Immunoprecipitation with anti-apoA-I antibody followed by apoM Western blot analysis revealed that little secreted apoM was physically associated with pre beta HDL. Our results suggest that apoM is an atypical secretory protein that is not necessary for ABCA1-dependent pre beta HDL formation but does stimulate the formation of larger-sized pre beta HDL. We propose that apoM may function catalytically at an intracellular site to transfer lipid onto pre beta HDL during or after their formation by ABCA1.

Reduced high density lipoproteins as a risk factor after acute myocardial infarction

In a group of normocholesterolemic, non-diabetic middle-aged males surviving an acute myocardial infarction for 4 +/- 2 years (mean +/- SD), we have previously described a low apolipoprotein A-I and a deficient fibrinolytic activity as two major characteristics. In the present study we have followed morbidity and mortality risk factors for five years in these males. Mortality was 40% in a hypertensive group and 16% in a normotensive group. In the normotensive group mortality was related to reinfarction. Furthermore, patients with a poor prognosis in the normotensive group had lower high density lipoprotein (HDL) cholesterol and lower apolipoprotein A-I concentration in plasma than patients with a good prognosis. Unexpectedly, in the hypertensive group death was related to a low (p less than 0.05) cortisol concentration in urine. It is concluded that a low HDL level may be a bad prognostic sign in males who have sustained an acute myocardial infarction and show no evidence of other risk factors, such as diabetes, hypercholesterolemia or hypertension.

High density lipoprotein composition versus heredity for acute myocardial infarction in middle-aged males

The levels of high density lipoprotein (HDL) cholesterol and apolipoprotein AI (Apo AI) were determined in 299 men, 48 years of age. We found a significant negative correlation between HDL cholesterol and serum triglyceride concentrations and a significant correlation between serum triglyceride concentration and the Apo AI/HDL cholesterol ratio. A history of acute myocardial infarction (AMI) was significantly more common than expected among the fathers of men with a low HDL cholesterol level. We also found a relationship between AMI among fathers and high Apo AI level in sons, although this relationship was not as strong as that between AMI among fathers and low HDL cholesterol in sons. No significant relationship was found between AMI among mothers and HDL cholesterol or Apo AI in sons.

Elevation of high-density lipoprotein in epileptic patients treated with phenytoin

Previous observations have shown that serum alpha (high-density) lipoprotein (HDL) cholesterol is increased by some agents which also act as liver microsomal inducers. Against this background we measured the serum HDL and other lipoprotein and apolipoprotein A levels in 28 epileptic patients who received phenytoin as the only medication. In comparison with healthy controls of similar age and sex, the phenytoin users had significantly higher HDL cholesterol (p less than 0.001) and apolipoprotein A-I (p less than 0.01) levels. Highest values of both parameters were found in patients whose serum phenytoin concentration was within the therapeutic range. HDL cholesterol levels were above the control mean +2 S.D. in 43% of the phenytoin users. Hypertriglyceridemia was more common among male phenytoin users than in control males (33 vs. 16%). It is suggested that phenytoin increases the secretion of nascent HDL particles (and probably also that of VLDL) by the liver and that this could be associated with the induction of hepatic microsomes. Since HDL is inversely reversely related to risk of coronary heart disease, the observed increase of this lipoprotein may be an example of a beneficial side-effect of a drug.

Reference distributions for apolipoproteins AI and B and B/AI ratios: comparison of a large cohort to the world's literature

Limiting the clinical utility of apolipoproteins AI (apo AI) and B (apo B) and the apo B/AI ratios until the last decade has been the lack of satisfactory methods for quantifying serum levels and credible reference materials. Great technological strides have been made in the last few years. The remaining barrier to more relevant and cost-effective use of serum protein data for diagnosis and prognosis has been the availability of widely recognized reliable reference intervals from birth to old age for both males and females. A total of 82 publications reporting reference intervals have been identified that meet most of the same inclusion criteria used in our prior six studies. These have been analyzed statistically and compared to similar studies, i.e., sufficient number, listed subject criteria, method, and reference material, in general terms. Published smaller studies with constrained age ranges, agree on average with our large series of life-long reference intervals that range from less than one year to over 80 years. This study was performed to assess the degree of agreement between smaller reference interval studies to our large population analysis. This meta-analysis provides support and reassurance that many of the smaller reference intervals published previously fall within reasonable limits of out large population.

A brief history of lipid and lipoprotein measurements and their contribution to clinical chemistry

The study of modern lipid chemistry began in the 17th and 18th centuries with early observations by Robert Boyle, Poulletier de la Salle, Antoine François de Fourcroy and others. The 19th century chemist, Chevreul, identified several fatty acids, suggested the name 'cholesterine' for the fatty substance in gallstones, coined the word 'glycerine', and showed that fats were comprised of glycerol and fatty acids. The 20th century brought many advances in the understanding of lipoprotein structure and function, and explored relationships between lipoproteins and disease states. The development of the ultracentrifuge and other lipoprotein separation techniques, and reagents for accurate, standardized quantitative measurement have steadily increased our understanding of the important role of lipoprotein metabolism in both healthy and disease states.

Modulating effect of the A-278C promoter polymorphism in the cholesterol 7alpha-hydroxylase gene on serum lipid levels in normolipidaemic and hypertriglyceridaemic individuals

The rate-limiting enzyme in the conversion of cholesterol into bile acids is cholesterol 7alpha-hydroxylase (CYP7A1). An A to C substitution 278 bp upstream in the promoter of the CYP7A1 gene was found to be associated with variations in serum lipid levels in normolipidaemic populations. In the present study, we investigated the involvement of this polymorphism in four different lipid disorders: hypertriglyceridaemia (HTG), combined hyperlipidaemia (CH), familial dysbetalipoproteinaemia (FD) and familial hypercholesterolaemia (FH). In a normolipidaemic male population, homozygous for the apoE3 isoform, an association was found between the AA genotype and higher levels of serum triglycerides (AA: +34%, P = 0.036). In HTG patients, the AA genotype was associated with significantly higher concentrations of total cholesterol (+23%, P = 0.005). There was a tendency towards increased levels of serum triglycerides (+39%, P = 0.06), VLDL-triglycerides (+48%, P = 0.053) and VLDL-cholesterol (+35%, P = 0.059). No significant associations were found between serum lipid levels and the CYP7A1 polymorphism in patients with CH, FD and FH. Our results show that the A-278C polymorphism in the CYP7A1 gene has an effect on triglyceride levels in normolipidaemic males and on cholesterol levels in patients with hypertriglyceridaemia..

Influence of apoA-I and apoE on the formation of serum amyloid A-containing lipoproteins in vivo and in vitro

Serum amyloid A (SAA) circulates bound to HDL3 during the acute-phase response (APR), and recent evidence suggests that elevated levels of SAA may be a risk factor for cardiovascular disease. In this study, SAA-HDL was produced in vivo during the APR and without the APR by injection of an adenoviral vector expressing human SAA-1. SAA-HDL was also produced in vitro by incubating mouse HDL with recombinant mouse SAA and by SAA-expressing cultured hepatoma cells. Whether produced in vivo or in vitro, SAA-HDL floated at a density corresponding to that of human HDL3 (d 1.12 g/ml) separate from other apolipoproteins, including apolipoprotein A-I (apoA-I; d 1.10 g/ml) when either apoA-I or apolipoprotein E (apoE) was present. In the absence of both apoA-I and apoE, SAA was found in VLDL and LDL, with low levels in the HDL and the lipid-poor fractions suggesting that other HDL apolipoproteins are incapable of facilitating the formation of SAA-HDL. We conclude that SAA does not exist in plasma as a lipid-free protein. In the presence of HDL-associated apoA-I or apoE, SAA circulates as SAA-HDL with a density corresponding to that of human HDL3. In the absence of both apoA-I and apoE, SAA-HDL is not formed and SAA associates with any available lipoprotein.

Serum paraoxonase: effect of the apolipoprotein composition of HDL and the acute phase response

Genetic variations of paraoxonase (PON) correlate with HDL cholesterol and apolipoprotein A-I (apoA-I), suggesting antiatherogenic properties. Atherosclerosis occurs naturally in humans and rabbits but not in mice. We compared variations of PON arylesterase activity (PON AEase, phenylacetate substrate) in humans, rabbits, and mice. In humans and rabbits, >95% of PON AEase is HDL associated. In mice, about 30% of PON AEase is lipid poor. In the absence of apoA-I in mice, total PON AEase is reduced and >60% is lipid poor. PON AEase level and distribution is restored in apoA-I-/- mice injected with adenoviruses encoding human apoA-I and in transgenic mice expressing human apoA-I at a steady-state level. Thus, while apoA-I is not required for the HDL association of PON AEase, induced variations in apoA-I correlate with changes in HDL-associated, but not lipid-poor, PON AEase. PON AEase associates only with apoA-I- or apoE-containing HDL but not VLDL. In the absence of both apoA-I and apoE, PON AEase is all-lipid-poor. PON AEase is displaced from HDL by ultracentrifugation and following incubation with serum amyloid A. Variations in the PON distribution between HDL and lipid-poor fractions may have important consequences in its antioxidant activity and in atherogenesis.

Evidence for genetic factors explaining the association between birth weight and low-density lipoprotein cholesterol and possible intrauterine factors influencing the association between birth weight and high-density lipoprotein cholesterol: analysis in twins

Recent studies have demonstrated an association between low weight at birth and an atherogenic lipid profile in later life. To examine the influences of intrauterine and genetic factors, we investigated 53 dizygotic and 61 monozygotic adolescent twin pairs. Regression analysis demonstrated that low birth weight was associated with high levels of total cholesterol, low-density lipoprotein (LDL) cholesterol and apolipoprotein B (-0.17 mmol/liter per kg, P = 0.07; -0.18 mmol/liter per kg, P = 0.04; and -0.07 g/liter per kg, P = 0.02, respectively) and with low levels of high-density lipoprotein (HDL) cholesterol (+0.04 mmol/liter per kg, P = 0.1), after adjustment for age, sex, and body mass index. Intrapair differences in birth weight were significantly associated with differences in total cholesterol, LDL cholesterol, and apolipoprotein B in dizygotic twins after adjustment for differences in current body mass index (-0.49 mmol/liter per kg, P = 0.02; -0.51 mmol/liter per kg, P = 0.01; and -0.10 g/liter per kg, P = 0.04, respectively), demonstrating that the larger the difference in birth weight, the higher these risk factors in the twin with the lower birth weight, compared with the cotwin with the higher birth weight. In monozygotic twins, however, the associations between intrapair differences in birth weight and differences in total cholesterol, LDL cholesterol, and apolipoprotein B were in the opposite direction (+0.32 mmol/liter per kg, P = 0.03; +0.23 mmol/liter per kg, P = 0.08; and +0.06 g/liter per kg, P = 0.04, respectively). The association between intrapair differences in birth weight and differences in HDL cholesterol was not significant in dizygotic twins (+0.04 mmol/liter per kg, P = 0.6) and of borderline significance in monozygotic twins (+0.11 mmol/liter per kg, P = 0.05). These data suggest that genetic factors account for the association of low birth weight with high levels of total cholesterol, LDL cholesterol, and apolipoprotein B, whereas intrauterine factors possibly play a role in the association between birth weight and HDL cholesterol.

Apolipoprotein B and AI distributions in the United States, 1988–1991: results of the National Health and Nutrition Examination Survey III (NHANES III)

Serum apolipoproteins (apo) B and AI were measured in a probability sample of the noninstitutionalized US civilian population, ages ≥4 years, which included non-Hispanic whites, non-Hispanic blacks, and Mexican-Americans. Apo B concentrations were the same in males and females, lower in black males than in other males, low in childhood (∼0.80 g/L) and increasing to ∼1.2 g/L in adults, and higher in younger women on hormones. Apo AI was higher in females than males, higher in blacks than in others, remained constant from childhood to adulthood (∼1.35 g/L) in males, but increased with age (∼1.30 g/L to ∼1.55 g/L) in females, and was higher in women taking hormones. These are the first national probability estimates of apo B and apo AI in the US and are referable to the WHO-IFCC First International Reference Materials for apo AI and B.

Lipoprotein compositional abnormalities in type I diabetes: effect of improved glycaemic control

Major lipoprotein mass and composition were assessed in 45 subjects with insulin dependent diabetes mellitus (IDDM), before and after 2 months of intensive insulin therapy (IIT) and in 40 healthy control subjects. As compared to the control group, diabetic subjects at baseline had higher low density lipoprotein (LDL) and lower high density lipoprotein (HDL) masses. Expressing each lipoprotein constituent as a percent of total lipoprotein mass, very low density lipoprotein (VLDL) of diabetic patients was enriched in cholesterol and phospholipid and depleted in triglyceride and protein; IDL had higher triglyceride and phospholipid and lower cholesterol and protein proportion; LDL was depleted in protein and enriched in triglyceride; HDL was depleted in protein and enriched in triglyceride, cholesterol and phospholipid. After 2 months of IIT, HbA1c fell from 10.3 +/- 2 to 7.5 +/- 2% (P < 0.0001) and so did VLDL mass, which was lower than in control subjects. In addition, LDL and HDL masses, as well as triglyceride and cholesterol proportion in IDL particles normalized. The other compositional abnormalities improved without complete normalization. Thus, intensive insulin therapy in IDDM subjects brought quantitative lipoprotein alterations to normal even subnormal range, while most of the composition abnormalities improved without reaching complete normalization.

Genetic analysis of sex and generation differences in plasma lipid, lipoprotein, and apolipoprotein levels in adolescent twins and their parents

In a sample of Dutch families consisting of parents aged 35-65 years and their twin offspring aged 14-21 years, a significant difference between generations was observed in phenotypic variances and in genetic heritabilities for plasma levels of total cholesterol, triglycerides, high density lipoprotein (HDL) and low density lipoprotein (LDL) cholesterol, and apolipoproteins (apo) A1, A2, B, and E. For all traits parents were more variable than their offspring. This increase in phenotypic variance was best explained by a genetic model in which individual specific environmental variance increased with increasing age. Genetic variance was the same across generations for nearly all traits except triglycerides and apoE, for which a decrease in genetic variance was observed. This model led to large intergenerational differences in genetic heritabilities. Heritabilities for children were between 65 and 87%, while heritabilities for their parents were between 10 and 50%. No evidence was found for effects of a shared family environment.

Influence of worksite environmental tobacco smoke on serum lipoprotein profiles of female nonsmokers

The purpose of this study was to examine the influence of environmental tobacco smoke (ETS) in the workplace on high-density lipoprotein cholesterol (HDL-C), HDL-C subfractions, and apolipoprotein (apo) A-I and apo B in female workers. Premenopausal women free from factors known to influence HDL-C (cigarette smoking, vigorous physical exercise, etc) who were not taking oral contraceptives, were moderate consumers of alcohol, caffeine, and dietary fat, and were between the ages of 21 and 50 years participated in one of two groups: (1) nonsmokers who had never smoked cigarettes and were generally free from ETS exposure (nonsmokers), and (2) nonsmokers who had never smoked but were subjected to concentrated doses of ETS at least 6 hours per day, 4 days per week, for at least 6 consecutive months (ETS-exposed). A third group consisting of current cigarette smokers who smoked a minimum of 20 cigarettes per day for at least the past 5 consecutive years served as smoking control (smokers). Subjects were matched by group as closely as possible with regard to criteria that can influence blood lipoprotein levels. Participants were solicited from taverns and restaurants where they were employed. It was hypothesized that individuals chronically exposed to ETS would demonstrate unfavorable lipoprotein profiles. Results showed that HDL-C, HDL2, and apo A-I were significantly (P < .05) depressed for ETS-exposed and smokers as compared with nonsmokers. Values for ETS-exposed were not different from those for smokers. Total cholesterol, triglycerides, HDL3, and apo B did not differ among the three groups. It was concluded that excessive exposure to ETS in female workers can have deleterious effects on HDL-C, HDL2, and apo A-I in nonsmokers that are similar to effects observed in cigarette smokers. It is possible that these effects increase coronary artery disease (CAD) risk.

Determinants of severity of coronary artery disease in Australian men and women

BACKGROUND

Factors predicting the occurrence of premature coronary artery disease (CAD) may not be quantitatively the same as those predicting CAD severity, particularly in women, in whom there have been few studies.

METHODS AND RESULTS

To determine factors predictive of severity of CAD and of angina pectoris, we documented atherogenic variables and the extent of CAD at angiography in 594 consecutively studied men and women aged 65 years or less. Severity was assessed from the number of involved major coronary arteries with significant (> 50%) luminal obstructions and from a coronary disease severity score. We related severity to quantitative and categorical atherogenic variables and assessed severity of angina (no angina, stable angina, or unstable angina) at the time of study in the same way. There were eight variables independently predictive of severity: in descending order of relative importance, male gender, diabetes, smoking dose, ratio of total cholesterol to high-density lipoprotein cholesterol (TC/HDL-C), lipoprotein(a) [Lp(a)], age, positive family history, and hypertension. These correctly classified 43.3% of patients into no-, one-, two-, and three-vessel disease categories and accounted for 25.8% of variance of severity. Among 246 patients not taking lipid-lowering or beta-blocking drugs, these variables (in slightly different order) correctly classified 49.2% of patients and accounted for 36% of the variance. Among men (n = 427), seven significant variables correctly classified 39.3% of patients compared with 54.5% in women (n = 167). For those not taking the above drugs, these proportions were 49.4% and 65.4%, respectively. Among the quantitative variables, total smoking dose was the most predictive independent variable irrespective of current or ex-smoking habit and was more predictive in women than in men; of the lipid variables, high TC/HDL-C (or low HDL-C) and high Lp(a) were consistently highly predictive for all patients and in the subgroup analyses. Patients with unstable angina had higher coronary severity scores and Lp(a) levels and were more likely to have diabetes, hypertension, or a positive family history.

CONCLUSIONS

We conclude that the quantitative variables most relevant to severity of premature CAD and to its prevention in Australian men and women are total amount of lifetime smoking, TC/HDL-C (or HDL-C), and Lp(a) and that patients with unstable versus stable angina usually have more severe disease and higher Lp(a).

Determinants of plasma cholesterol responsiveness to diet

Plasma cholesterol change, or 'responsiveness', to dietary saturated fat modification has long been acknowledged. The present study sought to determine the specific, predicted response of each cholesterol subfraction to known dietary manipulations. Two metabolically controlled diets, one with a low polyunsaturated:saturated fat (low P:S) ratio, and one with a high P:S ratio were fed in a crossover design to sixty-seven normolipidaemic subjects pooled from six foregoing metabolic studies. A series of statistical analyses was performed to identify the lipids and subfractions independently affected by the diet crossover. Multivariate analysis of variance revealed that the changes in total cholesterol (delta TC), low-density-lipoprotein-cholesterol (delta LDL-C), and high-density-lipoprotein-cholesterol (delta HDL-C) were the only statistically significant diet-specific 'responsive' lipids. Multiple regression was performed to identify the independent predictors of delta TC, delta LDL-C and delta HDL-C. It was found that age (years), extent of change in dietary saturated fat, and baseline LDL-C (mg/l) levels determine LDL-C change, while extent of change in saturated and polyunsaturated fat, and baseline HDL-C (mg/l) levels can predict HDL-C change. A series of equations to predict lipoprotein responsiveness to diet are derived for potential use in clinical practice.

Relationship of apolipoprotein E phenotypes to hypocholesterolemia

PURPOSE

Persons with total cholesterol (TC) levels less than 130 mg/dL (less than 3.26 mmol/L) make up less than 1% of a healthy population. Causes of hypocholesterolemia include a diet very low in cholesterol and saturated fat, disease, genetic factors (including low apolipoprotein B-100 [apo B-100] and the apo E allele), and drug therapy. The purpose of this study was to determine the causes of hypocholesterolemia in a healthy Kaiser Foundation Health Plan (KFHP) population.

PATIENTS AND METHODS

We conducted a dietary and health survey of 201 healthy hypocholesterolemic adults (range: 2.04 to 3.88 mmol/L [79 to 150 mg/dL]) and 200 matched control subjects with TC levels in the middle quintile of the population (range: 5.0 to 5.61 mmol/L [194 to 217 mg/dL]) who had routine health screening from 1983 through 1985. We did apo E phenotyping studies and lipid and apo A-1 and B-100 measurements in a subgroup of 45 hypocholesterolemic subjects (mean TC level: 3.26 mmol/L [126 mg/dL]) and in a comparison group of 49 unmatched volunteers (mean TC level: 5.04 +/- 0.75 mmol/L [195 +/- 29 mg/dL]).

RESULTS

We found no differences in dietary intake or clinically significant medical illness between hypocholesterolemic and control subjects. In the hypocholesterolemic subgroup, we found an increased frequency of the apo E2 allele (epsilon 2) and a decreased frequency of the apo E4 allele (epsilon 4); the frequencies of the epsilon 2, epsilon 3, and epsilon 4 alleles were 33.3%, 63.3%, and 3.3%, respectively. The corresponding apo E allele frequencies in the comparison subgroup were 8.2%, 73.5%, and 18.4%, similar to those previously reported for the general population and significantly different from those found in the hypocholesterolemic subgroup (p < 0.0001). One hypocholesterolemic subject (a 46th patient) had a mutation in the apo B gene that resulted in the synthesis of a truncated species of apo B (apo B-46).

CONCLUSION

Our study indicates that hypocholesterolemia in our KFHP urban population is usually not caused by diet or disease. Biochemical factors, including the increased frequency of the apo E-2 phenotype and the decreased frequency of the apo E-4 phenotype, are more important.

Effects of pravastatin on apolipoprotein-specific high density lipoprotein subpopulations and low density lipoprotein subclass phenotypes in patients with primary hypercholesterolemia

The HMG-CoA reductase inhibitor class of cholesterol-lowering agents reduces very low density lipoproteins (VLDL) and low density lipoproteins (LDL) and slightly increases high density lipoproteins (HDL). However, the effects of these agents on subclasses within the LDL and HDL fractions are not well understood. We have employed an HMG-CoA reductase inhibitor, pravastatin, to determine if LDL subclass phenotypes, as determined by gradient gel electrophoresis, and HDL particles containing both apolipoprotein (apo) A-I and A-II, Lp(AI w AII), and those containing apo A-I but not A-II, Lp(AI w/o AII) are affected by pravastatin (10 mg daily). Twenty-four subjects with LDL-cholesterol (LDL-C) > 160 mg/dl, triglyceride (TG) < 350 mg/dl and no recent myocardial infarction or secondary causes of hypercholesterolemia were enrolled. Compared with an age- and sex-matched normolipidemic reference group (controls), the hypercholesterolemic subjects had reduced levels of Lp(AI w/o AII) and increased levels of Lp(AI w AII) at baseline. In addition, both of their HDL subpopulations had significantly more small (7.0-8.2 nm) particles (P < 0.02 and 0.0001) but significantly fewer large (9.2-11.2 nm) particles (P < 0.002 and 0.0001). Pravastatin induced statistically significant (P < 0.001) reductions in plasma total C (15%), LDL-C (18%), and apo B (16%). While apo A-I and A-II levels increased 5% (P < 0.001) and 6% (P < 0.05), respectively, concentration, composition, and size abnormalities in Lp(AI w AII) and Lp(AI w/o AII) persisted. Lp(a), apo E and cholesteryl ester transfer protein (CETP) levels also did not change. Although changes in LDL subclass phenotypes were observed, all changes involved the intermediate phenotype, and no significant changes in LDL peak particle diameter were seen in either group. Interrelationships between CETP, LDL subclass phenotypes and HDL subpopulations were also seen.

CONCLUSIONS

Although pravastatin decreased plasma apo B and LDL lipid concentrations, no major changes were seen in LDL subclass phenotypes or HDL subpopulations even in the presence of abnormalities associated with arteriosclerosis. Similarly, CETP, which is believed to play a role in HDL and LDL particle size distribution, did not change with pravastatin treatment. Further research is needed to determine the pathophysiological basis of abnormal HDL and LDL subclasses in hypercholesterolemia and explore methods of rectifying the abnormalities.

Lipoprotein heterogeneity in end-stage renal disease

Fifteen patients on chronic maintenance hemodialysis without any additional known cause for dyslipidemia were arbitrarily divided into two groups based on fasting plasma triglyceride levels. The hypertriglyceridemic patients (plasma triglyceride levels above 170 mg/dl, N = 7) also had decreased high density lipoprotein (HDL) cholesterol levels and decreased post-heparin plasma lipoprotein lipase activity compared to the normotriglyceridemic patients (N = 8). All lipoprotein fractions collected by density gradient ultracentrifugation were triglyceride-enriched in the hypertriglyceridemic patients. Both groups of patients had elevated intermediate density lipoprotein levels, heterogeneity in the distribution of low density lipoproteins (LDL) and apoprotein-specific HDL subpopulations, and abnormalities in the size and composition of both LDL and HDL. The described alterations tended to be more marked in hypertriglyceridemic patients and are not detected by the usual laboratory evaluation of lipoproteins. These lipoprotein abnormalities have been shown to be atherogenic in patients without renal disease and are likely to contribute to the high prevalence of premature atherosclerosis in end-stage renal disease.

Characterization of apolipoprotein A-I- and A-II-containing lipoproteins in a new case of high density lipoprotein deficiency resembling Tangier disease and their effects on intracellular cholesterol efflux

A 48-yr-old Caucasian female of central European origin (subject IM) with low plasma cholesterol and normal plasma triglyceride (TG) had extremely low apo A-I (6 mg/dl), A-II (5 mg/dl), and HDL cholesterol (2 mg/dl) levels. She had most of the clinical symptoms typically associated with Tangier disease, including early corneal opacities, yellow-streaked tonsils, hepatomegaly, and variable degrees of peripheral neuropathy, but had no splenomegaly. She had a myocardial infarction at age 46. Since HDL are postulated to be involved in the transport of excess cholesterol from peripheral tissues to the liver for degradation, and the ability of an HDL particle to promote cellular cholesterol efflux appears to be related to its density, size, and apo A-I and A-II contents, we isolated and characterized the HDL particles of this patient and all her first degree relatives (mother, a brother, and two children). The plasma A-I, A-II, and HDL cholesterol levels of all five relatives were either normal or high. Using anti-A-I and anti-A-II immunosorbents, we found three populations of particles in IM: one contained both apo A-I and A-II, Lp(AI w AII); one contained apo A-I but no A-II, Lp(AI w/o AII); and the third (an unusual one) contained apo A-II but no A-I, Lp(AII). Two-thirds of her plasma A-I and A-II existed in separate HDL particles, i.e., in Lp(AI w/o AII) and Lp(AII), respectively. Only Lp(AI w AII) and Lp(AI w/o AII) were present in the plasma of the relatives. All three populations of the patient's HDL particles had a normal core/surface lipid ratio, but the cores were enriched with TG. The apo A-I-containing particles, however, were considerably smaller and contained much less lipid than Lp(AII). Despite these unusual physicochemical characteristics, the apo A-I-containing particles and Lp(AII) were effective suppressors of intracellular cholesterol esterification in cholesterol-loaded human skin fibroblast. The patient's plasma apo D and lecithin cholesterol acyltransferase levels were reduced, with an increased proportion located in non-HDL plasma fractions. These findings are discussed in light of Tangier disease and other known HDL-deficiency cases, and the role of HDL in the maintenance of cell cholesterol homeostasis.

The acute-phase response and associated lipoprotein abnormalities accompanying lymphoma

Lipoprotein abnormalities seen in patients with inflammatory diseases are thought to develop secondary to circulating cytokines and the accompanying acute-phase response. Patient's with lymphoma may develop similar lipoprotein abnormalities but the mechanism is unclear. We report a patient with B-cell lymphoma who presented with an HDL cholesterol level of 3 mg dl-1, an ApoA level of 17.4 mg dl-1, elevated triglyceride level (272 mg dl-1) and an elevated ApoB level of 156 mg dl-1. Density gradient analysis of the patient's lipoproteins demonstrated a virtual absence of an identifiable HDL particle. Serum amyloid A and C-reactive protein were also elevated. All of the lipoprotein abnormalities resolved with chemotherapy and resolution of the acute-phase response. The acute-phase response may be associated with striking lipoprotein abnormalities in a subset of patients with lymphoma. Lymphoma should be included in the differential diagnosis of patients with hypertriglyceridaemia and low HDL cholesterol.

Protein transfer between A-I-containing lipoprotein subpopulations: evidence of non-transferable A-I in particles with A-II

Transfer of apolipoproteins (apo) between the two subpopulations of apo A-I-containing lipoproteins in human plasma: those with A-II [Lp(AI w AII)] and those without [Lp(AI w/o AII)], were studied by observing the transfer of 125I-apo from a radiolabeled subpopulation to an unlabeled subpopulation in vitro. When Lp(AI w AII) was directly radioiodinated, 50.3 +/- 7.4 and 19.5 +/- 7.7% (n = 6) of the total radioactivity was associated with A-I and A-II, respectively. In radioiodinated Lp(AI w/o AII), 71.5 +/- 6.8% (n = 6) of the total radioactivity was A-I-associated. Time-course studies showed that, while some radiolabeled proteins transferred from one population of HDL particles to another within minutes, at least several hours were necessary for transfer to approach equilibrium. Incubation of the subpopulations at equal A-I mass resulted in the transfer of 51.8 +/- 5.0% (n = 4) of total radioactivity from [125I]Lp(AI w/o AII) to Lp(AI w AII) at 37 degrees C in 24 h. The specific activity (S.A.) of A-I in the two subpopulations after incubation was nearly identical. Under similar incubation conditions, only 13.4 +/- 4.6% (n = 4) of total radioactivity was transferred from [125I]Lp(AI w AII) to Lp(AI w/o AII). The S.A. of A-I after incubation was 2-fold higher in particles with A-II than in particles without A-II. These phenomena were also observed with iodinated high-density lipoproteins (HDL) isolated by ultracentrifugation and subsequently subfractionated by immunoaffinity chromatography. However, when Lp(AI w AII) radiolabeled by in vitro exchange with free [125I]A-I was incubated with unlabeled Lp(AI w/o AII), the S.A. of A-I in particles with and without A-II differed by only 18% after incubation. These data are consistent with the following: (1) in both populations of HDL particles, some radiolabeled proteins transferred rapidly (minutes or less), while others transferred slowly (hours); (2) when Lp(AI w AII) and Lp(AI w/o AII) were directly iodinated, all labeled A-I in particles without A-II were transferable, but some labeled AI in particles with A-II were not; (3) when Lp(AI w AII) were labeled by in vitro exchange with [125I]A-I, considerably more labeled A-I were transferable. These observations suggest the presence of non-transferable A-I in Lp(AI w AII).

Replacement of dietary fat with palm oil: effect on human serum lipids, lipoproteins and apolipoproteins

Thirty-eight male volunteers participated in a double-blind cross-over trial evaluating the effect of replacing the usual sources of saturated fat in the Dutch diet (animal fats and hydrogenated oils) by palm oil, which is virtually free of cholesterol and trans-fatty acids, on serum lipids, lipoproteins and apolipoproteins. Maximum (about 70%) replacement had no significant effect on serum total cholesterol or most lipoprotein fractions, but resulted in an 11% increase in serum high-density-lipoprotein (HDL)2-cholesterol relative to the control (P2 = 0.01). The palm-oil diet also caused an 8% decrease in low-density-lipoprotein (LDL):HDL2 + HDL3-cholesterol ratio (P2 = 0.02) as well as a 9% decrease in triacylglycerols in the low-density-lipoprotein fractions (P2 = 0.01). Palm oil consumption resulted in a 4% increase in serum apolipoprotein AI (P2 = 0.008) and a 4% decrease in apolipoprotein B (P2 = 0.01) relative to the control diet; the B:AI apolipoprotein ratio was decreased by 8% (P2 < 0.0001). These results were not significantly affected by the different lipoprotein E phenotypes of the volunteers. Although the observed differences were relatively modest, the present study, nonetheless, indicates that dietary palm oil, when replacing a major part of the normal fat content in a Dutch diet, may slightly reduce the lipoprotein- and apolipoprotein-associated cardiovascular risk profiles.

Interaction between high-density lipoprotein subpopulations in apo B-free and abetalipoproteinemic plasma

Two populations of high-density lipoprotein (HDL) particles exist in human plasma. Both contain apolipoprotein (apo) A-I, but only one contains apo A-II: Lp(AI w AII) and Lp(AI w/o AII). To study the extent of interaction between these particles, apo B-free plasma prepared by the selective removal of apo B-containing lipoproteins (LpB) from the plasma of three normolipidemic (NL) subjects and whole plasma from two patients with abetalipoproteinemia (ABL) were incubated at 37 degrees C for 24 h. Apo B-free plasma samples were used to avoid lipid-exchange between HDL and LpB. Lp(AI w AII) and Lp(AI w/o AII) were isolated from each apo B-free plasma sample before and after incubation and their protein and lipid contents quantified. Before incubation, ABL plasma had reduced levels of Lp(AI w AII) and Lp(AI w/o AII), (40% and 70% of normals, respectively). Compared to the HDL of apo B-free NL plasma, ABL HDL had higher relative contents of free cholesterol, phospholipid and total lipid, and contained more particles with apparent hydrated Stokes diameter in the 9.2-17.0 nm region. These differences were particularly pronounced in particles without apo A-II. Despite their differences, the total cholesterol contents of Lp(AI w AII) increased, while that of Lp(AI w/o AII) decreased in all five plasma samples and the amount of apo A-I in Lp(AI w AII) increased by 6-8 mg/dl in four during the incubation. These compositional changes were accompanied by a relative reduction of particles in the 7.0-8.2 nm Stokes diameter size region and an increase of particles in the 9.2-11.2 nm region. These data are consistent with intravascular modulation between HDL particles with and without apo A-II. The observed increase in apo A-II-associated cholesterol and apo A-I, could involve either the transfer of cholesterol and apo A-I from particles without apo A-II to those with A-II, or the transfer of apo A-II from Lp(AI w AII) to Lp(AI w/o AII). The exact mechanism and direction of the transfer remain to be determined.

Relation between insulinemia, body mass index, and lipoprotein composition in healthy, nondiabetic men and women

Altered lipoprotein composition may be a better predictor of cardiovascular disease than modestly increased serum lipid concentrations, although possible interactions between lipoprotein composition, obesity, and insulinemia have not been fully elucidated. Therefore, we investigated the association between different measures of insulinemia and lipoproteins in 297 healthy Caucasian men (body mass index [BMI] less than 27 in 233, greater than 27 [obese] in 64) and 295 healthy Caucasian women (BMI less than 25 in 198, greater than 25 [obese] in 97). Associations observed in both obese and nonobese men and women were between increasing tertiles of most insulin measures and serum triglyceride concentrations (p = 0.079-0.004) and the ratio of low density lipoprotein to high density lipoprotein cholesterol (p = 0.094-0.008). Graded reductions in the high density lipoprotein cholesterol to apolipoprotein A-I ratio were also recorded in obese women, with increasing tertiles of fasting (p = 0.014-0.007) and postglucose load (p = 0.001) serum insulin levels, after correcting for BMI and triglyceride concentrations. Less marked graded increases in the triglyceride to apolipoprotein B ratios were recorded in obese women with increasing tertiles of fasting (p = 0.001-0.006) and postglucose challenge (p = 0.081) insulinemic measures. In men with normal or slightly elevated cholesterol levels (fasting serum cholesterol less than 6.5 mmol/l), hyperapobetalipoproteinemia was recorded with increasing tertiles of insulinemia (p = 0.006, correcting for BMI and triglyceride concentrations), as well as in subjects with hypertriglyceridemia (fasting serum triglycerides greater than 1.70 mmol/l) (p = 0.004, correcting for BMI and age). Hyperinsulinemia and insulin resistance are associated with altered lipoprotein composition in obese women, presumably reflecting a complex interplay between sex hormones, body mass, and insulin action. Insulin resistance appears to be more associated with apolipoprotein B concentrations in men. The hyperinsulinemic nondiabetic subject may be at increased risk of cardiovascular disease because of altered concentrations of apolipoprotein concentrations and lipoprotein composition.

Double-blind comparison of bezafibrate versus placebo in male volunteers with hyperlipoproteinemia

The efficacy and safety of bezafibrate were evaluated in 83 patients with type IIa, IIb, or IV hyperlipoproteinemia. Following a 12- to 14-week placebo period on a coronary-prudent diet (Period 1), patients were assigned randomly to receive either bezafibrate 600 mg/day or placebo, plus diet in a double-blind, 12-week treatment period (Period 2). The return of lipid and lipoprotein levels toward baseline was evaluated in a subsequent 8-week period on placebo plus diet (Period 3). In patients with type IIa hyperlipoproteinemia, bezafibrate significantly lowered total (14.6%, P less than 0.001) and LDL-cholesterol (16.4%, P less than 0.001) and total (29.9%, P less than 0.001) and VLDL-triglyceride (44.0%, P less than 0.001) and significantly increased HDL cholesterol (9.5%, P less than 0.001). In patients with type IIb, bezafibrate had a qualitatively similar effect to that seen in type IIa on each of these lipoproteins, but the sample size was too small for statistical evaluation. In patients with type IV, bezafibrate lowered total (48.3%, P less than 0.01) and VLDL-triglyceride (57.7%, P less than 0.001) and VLDL-cholesterol (56.8%, P less than 0.001) and increased HDL-cholesterol (16.6%, P less than 0.05). All values returned toward baseline during Period 3. Only two bezafibrate patients experienced adverse events that were considered definitely treatment related; one was dropped from the study because of elevations in SGOT and SGPT, 1.5- and 4-times the upper limit of normal, respectively. For other laboratory parameters, trends upward or downward were small and of doubtful clinical significance. Bezafibrate appears to be effective and safe for modifying lipid and lipoprotein levels in patients with types IIa, IIb and IV hyperlipoproteinemia.

Levels of lipids, lipoproteins, and apolipoproteins in a defined population

As part of a large cross-sectional investigation--the Rochester Family Heart Study--plasma levels of lipids, lipoproteins, and apolipoproteins were measured in a sample from the general population of male and female subjects who ranged in age from 5 to 90 years. Polyclonal radioimmunoassays developed at the Mayo Clinic were used for measurement of apolipoproteins A-I, A-II, C-II, C-III, and E, whereas a monoclonal enzyme-linked immunosorbent assay was used for apolipoprotein B. On the basis of 984 subjects who reported that they were fasting, were not pregnant, had never smoked, and were taking no medications thought to influence lipid levels, we determined age- and gender-specific percentiles for plasma levels of cholesterol, triglycerides, high-density lipoprotein cholesterol, and six apolipoproteins. These percentiles will facilitate identification of persons who are in the highest and lowest percentiles for their age and gender. The levels of the apolipoproteins varied for both age and gender. This is the first study to provide a reference sample for plasma levels of these apolipoproteins for male and female subjects 5 to 90 years of age selected from the general population.

Effects of polymorphisms in apolipoproteins E, A-IV, and H on quantitative traits related to risk for cardiovascular disease

The impact of the common alleles at structural loci coding for apolipoprotein (apos) A-IV, E, and H on 12 quantitative risk factors for cardiovascular disease (apos A-I, A-II, B, C-II, C-III, and E; total cholesterol; triglycerides; high density lipoprotein cholesterol; systolic blood pressure; diastolic blood pressure; and red blood cell sodium-lithium countertransport) was estimated in 453 unrelated individuals (227 men and 226 women) aged 26-63 years from the Rochester Family Heart Study, who were not using medications affecting lipid levels or blood pressure. Each risk factor was adjusted for concomitants (assay date, age, age, squared, height, weight and smoking status) before the genotypic effects on mean levels and variances were estimated. Allele frequencies were the same in men and women and were similar to those observed in other studies of US Caucasians. There were very different gender-specific estimates of the relative contribution of concomitants, measured genetic effects, and residual unexplained effects to the interindividual variation of particular traits. Allelic variation in apo E had effects on the greatest number of traits, namely apo E, apo B, apo C-II, and total cholesterol. An effect on triglycerides was dependent on the inclusion of hypertriglyceridemic subjects. Allelic effects of apo A-IV and apo H were much less than those estimated for the apo E polymorphism. A possible role for apo H in high density lipoprotein metabolism is suggested. This study indicates that variation in many genes may influence variation in a particular trait and that a particular gene may have pleiotropic effects on several traits.

Butyrate stimulates the secretion of apolipoprotein (apo) A-I and apo B100 by the human hepatoma cell line Hep G2. Induction of apo A-I mRNA with no change of apo B100 mRNA

Addition of sodium butyrate to the culture medium of the human hepatoma cell line Hep G2 resulted in a time- and dose-dependent increase in the secretion of apolipoprotein A-I (apo A-I) and apolipoprotein B100 (apo B100). After a 24 h preincubation period, a 2.4- and 2.2-fold increase in the secretion of apo A-I and apo B100 respectively was obtained during the next 24 h in the presence of 2 mM-sodium butyrate. Secretion of albumin, fibrinogen or [35S]methionine-labelled newly synthesized proteins was unaffected or only marginally affected, indicating that the effect of butyrate on apo A-I and apo B100 is not part of a general effect on protein synthesis and secretion. In structure-function studies, butyrate was found to be the most potent inducer among various straight-chain carboxylic acids. Hydroxylated, aminated and otherwise modified butyrate derivatives were inactive. The enhanced accumulation of apo A-I and apo B100 in the culture medium could not be explained by changes in the uptake and degradation of the synthesized apolipoproteins or by alterations in the secretion of possible intracellular pools. In addition, [35S]methionine incorporation studies indicated that synthesis and/or secretion of newly synthesized apo A-I and apo B100 is enhanced in the presence of butyrate. The apo A-I mRNA level was increased 2.3-fold upon treatment with 2 mM-butyrate for 48 h, suggesting regulation at (post-)transcriptional level. In contrast, no change in the level of apo B100 mRNA in butyrate-treated cells was observed, indicating regulation at translational or co- or post-translational level. We propose that the effect of butyrate on the secretion of apo A-I and apo B100 by Hep G2 results from two different regulatory mechanisms.

A prospective study of cholesterol, apolipoproteins, and the risk of myocardial infarction

BACKGROUND

The independent contributions of subfractions of high-density lipoprotein (HDL) cholesterol (HDL2 and HDL3) and apolipoproteins in predicting the risk of myocardial infarction are unclear. Prospective data are sparse, but HDL2 is widely believed to be a more important predictor than HDL3.

METHODS

Blood samples were collected at base line from 14,916 men (ages, 40 to 84 years) who were participants in the Physicians' Health Study. After five years of follow-up, plasma samples from 246 men with new myocardial infarction (case subjects) were analyzed together with specimens from 246 men matched to them for age and smoking status who had not had a myocardial infarction.

RESULTS

The levels of total cholesterol and apolipoprotein B-100 were significantly associated with an increased risk of myocardial infarction (data on levels of low-density lipoprotein cholesterol were unavailable). Both HDL cholesterol and HDL2 levels were associated with a substantially decreased risk of myocardial infarction, but the HDL3 level was the strongest predictor; the relative risk was 0.3 (95 percent confidence interval, 0.2 to 0.6) for those in the fifth of the group with the highest HDL3 levels, as compared with the fifth with the lowest levels. The benefit of a higher HDL cholesterol level was most pronounced among those with lower total cholesterol levels. Levels of apolipoprotein A-I and apolipoprotein A-II were also associated with decreased risk. However, the levels of HDL subfractions and apolipoproteins did not add significantly to the value of a multivariate model that included the ratio of total to HDL cholesterol in predicting myocardial infarction, whereas that ratio remained a significant independent predictor of risk. After adjustment for other risk factors, a change of one unit in the ratio of total to HDL cholesterol was associated with a 53 percent change in risk (95 percent confidence interval, 26 percent to 85 percent).

CONCLUSIONS

This study underscores the importance of HDL cholesterol in predicting the risk of myocardial infarction and demonstrates protective effects of both the HDL3 and HDL2 subfractions of HDL cholesterol. We found little or no predictive value for the levels of apolipoproteins A-I, A-II, and B or HDL subfractions after conventional risk factors and the ratio of total to HDL cholesterol were considered.

Quantitation of serum apolipoprotein A-I, A-II, B, C-II, C-III and E in healthy Japanese by turbidimetric immunoassay: reference values, and age- and sex-related differences

Serum apolipoproteins (Apo) A-I, A-II, B, C-II, C-III and E were determined in healthy Japanese subjects (male 1,603, female 1,800, aged 4-95 yr) by the turbidimetric immunoassay, with six kinds of automated instruments, and the commercial reagent kits with standards. There was a high degree of interlaboratory comparability of analytical values among the 15 participating laboratories. The reference values were calculated for adult males and females (male 677, female 467, aged 21-60 yr). Apo A-I and E levels were significantly higher and Apo C-II and C-III were significantly lower in females than in males. Furthermore, serum Apo A-I and A-II tended to decrease, and Apo B to increase with age. Apo C-II, C-III and E tended to decrease after 60 yr of age.

Supplemental growth hormone alters body composition, muscle protein metabolism and serum lipids in fit adults: characterization of dose-dependent and response-recovery effects

Using double-blind, placebo-controlled procedures, the effects of low and high therapeutic dosages of methionyl-human growth hormone (met-hGH) on body composition, muscle protein metabolism and serum lipids were studied in 7 fit adults without growth hormone (GH) deficiency. Dose-dependent changes in body composition were observed that in part appeared to be influenced by a response-recovery effect, as measured by responses factored according to the duration of washout between exposure to the low and high dosages of met-hGH (6 weeks vs. 12 weeks vs. 18 weeks). Increases in fat-free weight were accompanied by an increase in skeletal muscle protein metabolism. Basal levels of cholesterol were inversely related to peak levels of GH in response to exercise stimulation and IGF-I, while GH supplementation lowered levels of total cholesterol and high- and low-density lipoproteins. A dose-dependent effect occurred for total cholesterol, and the percent change in cholesterol was related to the percent change in insulin-like growth factor I (IGF-I). Endogenous levels of GH were attenuated in response to stimulation and IGF-I levels were increased after treatment with GH, but no dose-dependent changes were observed. We conclude that met-hGH alters body composition and muscle protein metabolism, and decreases stored and circulating lipids in fit adults with a pre-existing supranormal body composition. The physiological profile of the person was not as important as the treatment conditions in determining the somatic and physiological response outcomes.

High density lipoprotein turnover in patients with hypertension

Although hyperinsulinemia and decreased high density lipoprotein cholesterol concentration can occur in patients with hypertension, there is no information available concerning the dynamic state of high density lipoprotein metabolism. To address this issue, we quantified high density lipoprotein turnover in 12 patients with mild hypertension and 11 matched subjects with normal blood pressure. Patients with high blood pressure had lower high density lipoprotein cholesterol concentrations. Fractional catabolic rates of 125I-apolipoprotein AI (apoAI)/high density lipoprotein were faster in patients with hypertension (0.36 +/- 0.02 versus 0.26 +/- 0.02 l/day, p less than 0.001). Total synthetic rates of apoAI were also significantly greater in patients with high blood pressure (17.4 +/- 1.1 versus 13.2 +/- 0.6 mg/kg/day, p less than 0.001). Although significant correlation was observed between blood pressure and fractional catabolic rate of 125I-apoAI/high density lipoprotein in the experimental population (r = 0.52, p less than 0.01), no relation was found when patients with normal blood pressure or hypertension were considered separately. However, a highly significant positive correlation was found between 125I-apoAI/high density lipoprotein fractional catabolic rate and insulin concentration in the entire population (r = 0.72, p less than 0.001). In conclusion, the patients with mild hypertension studied were hyperinsulinemic, had a faster fractional catabolic rate of 125I-apoAI/high density lipoprotein, and a lower high density lipoprotein-cholesterol concentration. It is suggested that the changes seen in high density lipoprotein-cholesterol concentration and 125I-apoAI/high density lipoprotein fractional catabolic rates were secondary to the hyperinsulinemia and not due to the high blood pressure per se.

A comparative study of atherosclerosis and osteopenia in elderly and young hemodialysis patients

The effects of aging on atherosclerosis and osteopenia in hemodialysis patients were investigated. Eighty patients on maintenance hemodialysis were subdivided according to age into old (greater than or equal to 65 years old, N = 40) and young (less than 65 years old, N = 40). Biochemical, radiologic, and biophysical studies were performed in each patient to assess the degree of atherosclerosis and osteopenia. Compared to age-matched controls, patients in the old group exhibited a significantly higher aortic pulse wave velocity (PWV), and old female patients had a significantly lower bone mineral content/bone width (BMC/W). Elderly patients also had a significantly higher aortic PWV and higher grade of aortic calcification as assessed radiologically; in contrast, the BMC/W was lower. Concerning sex differences, elderly male patients had the highest average grade of aortic calcification, the lowest serum Pi, [Ca] x [Pi], and immunoreactive parathyroid hormone concentrations, while elderly female patients had the lowest BMC/W and highest incidence of osteopenia. These observations suggest that elderly male hemodialysis patients are more prone to develop atherosclerosis and elderly female hemodialysis patients to develop advanced osteopenia.

Relation of serum testosterone levels to high density lipoprotein cholesterol and other characteristics in men

Although levels of high density lipoprotein (HDL) cholesterol in males decrease during adolescence and after treatment with testosterone derivatives, several studies have reported that levels of HDL cholesterol are positively associated with endogenous levels of testosterone in men. This association was further examined using data collected during 1985 and 1986 from 3,562 white and 500 black men who ranged in age from 31 to 45 years. Black men had higher mean levels of both HDL cholesterol (8 mg/dl) and total testosterone (33 ng/dl) than white men, and positive associations were observed between testosterone and HDL cholesterol levels (r = 0.22, whites; r = 0.26, blacks). In addition, levels of testosterone were related positively to alcohol consumption and cigarette smoking and negatively to age, Quetelet index, and use of beta-blockers. We used stratification and regression analyses to determine if any of these characteristics could account for the positive association between levels of HDL cholesterol and total testosterone. Although controlling for most factors had little influence, adjusting for Quetelet index reduced the strength of the association between levels of testosterone and HDL cholesterol by approximately 30%. These findings suggest that the positive association between levels of testosterone and HDL cholesterol may not be causal. Multivariable analyses that control for obesity and other potentially confounding characteristics should be used in studies that assess the relation of testosterone levels to coronary heart disease.