Levels of Prebeta-1 High-Density Lipoprotein Are a Strong Independent Positive Risk Factor for Coronary Heart Disease and Myocardial Infarction: A Meta-Analysis

Background We previously showed that levels of prebeta-1 high-density lipoprotein (HDL), the principal acceptor of cholesterol effluxed from cells, including artery wall macrophages, are positively associated with coronary heart disease (CHD) and myocardial infarction (MI) risk. Methods and Results In a multiethnic follow-up cohort of 1249 individuals from University of California-San Francisco clinics, we determined the degree to which prebeta-1 HDL levels, both absolute and percentage of apolipoprotein AI, are associated with CHD and history of MI. Independent, strong, positive associations were found. Meta-analysis revealed for the absolute prebeta-1 HDL for the top tertile versus the lowest, unadjusted odds ratios of 1.90 (95% CI, 1.40-2.58) for CHD and 1.79 (95% CI, 1.35-2.36) for MI. For CHD, adjusting for established risk factors, the top versus bottom tertiles, quintiles, and deciles yielded sizable odds ratios of 2.37 (95% CI, 1.74-3.25, P<0.001), 3.20 (95% CI, 2.07-4.94, P<0.001), and 4.00 (95% CI, 2.11-7.58, P<0.001), respectively. Men and women were analyzed separately in a combined data set of 2507 individuals. The odds ratios for CHD and MI risk were similar. Higher levels of prebeta-1 HDL were associated with all 5 metabolic syndrome features. Addition of prebeta-1 HDL to these 5 features resulted in significant improvements in risk-prediction models. Conclusions Analysis of 2507 subjects showed conclusively that levels of prebeta-1 HDL are strongly associated with a history of CHD or MI, independently of traditional risk factors. Addition of prebeta-1 HDL can significantly improve clinical assessment of risk of CHD and MI.

Levels of prebeta-1 high-density lipoprotein are elevated in 3 phenotypes of dyslipidemia

BACKGROUND

Prebeta-1 high-density lipoprotein (HDL) is a small subspecies of HDL that functions as the HDL quantum particle and is the principal acceptor of cholesterol effluxed from macrophages through the ATP-binding cassette transporter, ABCA1. High levels of prebeta-1 HDL are associated with increased risk of structural coronary artery disease and myocardial infarction.

OBJECTIVE

We aimed to compare prebeta-1 HDL levels in normal subjects and in 3 phenotypes of dyslipidemia.

METHODS

We studied 2435 individuals (1388 women; 1047 men). Of these, 2018 were not taking lipid-lowering medication when enrolled: 392 were normolipidemic controls; 713 had elevated levels of low-density lipoprotein cholesterol; 623 had combined hyperlipidemia; and 290 had hypertriglyceridemia.

RESULTS

Relative to controls, prebeta-1 HDL levels were increased in all 3 dyslipidemic phenotypes, particularly the combined and hypertriglyceridemia groups. This increase possibly reflects increased acceptor capacity of apolipoprotein B-100 containing lipoproteins for entropically driven transfer of cholesteryl esters from HDL via cholesteryl ester transfer protein. Multiple regression analysis revealed that the main predictor variables significantly associated with prebeta-1 HDL levels were apolipoprotein A-I (apoA-1) (β = 0.500), triglyceride (β = 0.285), HDL-C (β = -0.237), and age (β = -0.169). There was an interaction between apoA-1 and sex (female vs male; β = -0.110). Among postmenopausal women, estrogenized subjects had a similar level of prebeta-1 HDL compared to those not receiving estrogens.

CONCLUSIONS

Prebeta-1 HDL levels are elevated in the 3 most common types of hyperlipidemia and are most strongly influenced by the levels of apoA-1, triglyceride, and HDL-C.

Identification and metabolic profiling of patients with lysosomal acid lipase deficiency

BACKGROUND

Lysosomal acid lipase (LAL), encoded by the LIPA gene, catalyzes the intracellular hydrolysis of cholesteryl esters and triglycerides in hepatocytes and macrophages. LIPA defects cause accumulation of these lipids in lysosomes. LAL deficiency (LAL D) presents and progresses as a continuum with dyslipidemia, hepatomegaly, and liver fibrosis.

OBJECTIVE

To improve the understanding of the genetic basis of LAL D, an underappreciated cause of dyslipidemia and cirrhosis, we studied DNA samples from patients with various phenotypes of dyslipidemia.

METHODS

Participants (N = 1357) were identified by lipid profiles and screened for the common disease causing LIPA exon 8 skipping splice-site mutation (c.894G>A; p.Ser275_Gln298del; rs116928232).

RESULTS

Six patients were heterozygous for this variant. Complete LIPA sequencing revealed a patient, subsequently confirmed to have LAL D, with a heterozygous frameshift mutation involving deletion of exon 4 (p.Gly77Valfs*17 c.230-106_c.428+541del). A family study revealed a sister with the same genotype and phenotype. Genetic, clinical, and lipoprotein profiles of these sisters plus 6 additional family members are reported. Profiles of 2 other LAL D patients monitored for 2 decades are presented. Cholesterol homeostasis was studied to investigate rates of cholesterol synthesis and absorption in 4 LAL D patients. High-density lipoprotein (HDL) subspecies were also analyzed.

CONCLUSIONS

We used this LIPA sequencing strategy (detection of the relatively common exon 8 variant followed by complete gene sequencing to identify additional mutations) as a means to further elucidate the genetic basis of LAL D among individuals with a suggestive clinical phenotype.

Evidence that an HMGA1 gene variant associates with type 2 diabetes, body mass index, and high-density lipoprotein cholesterol in a Hispanic-American population

BACKGROUND

High-mobility group AT-hook 1 (HMGA1) is an important regulator of the insulin receptor gene. We have previously shown in three populations of white European ancestry that the HMGA1 gene variant rs146052672 (also designated IVS5-13insC) is associated with type 2 diabetes mellitus (T2DM). The aim of this study was to measure the frequency of this variant and to determine the degree of the association with T2DM and other features of the metabolic syndrome in a replication cohort of Hispanic Americans.

METHODS

This was a retrospective cohort study of well-characterized Hispanic-American participants analyzed in the Genomic Resource in Atherosclerosis (GRA) (Cardiovascular Research Institute, University of California, San Francisco). A total of 1144 individuals were studied, 320 of whom had T2DM. We examined associations of the rs146052672 SNP with T2DM, plasma lipids, lipoproteins, and body mass index (BMI).

RESULTS

In this Hispanic-American cohort, the HMGA1 rs146052672 minor allele (C-insertion) frequency (MAF) was 21.4% with a carrier frequency of 37.4%, considerably higher than we previously observed among GRA white Europeans (MAF 3.1%). The prevalence of the IVS5-13insC variant was significantly higher in those with T2DM compared to controls [42.2% vs. 35.5%; odds ratio (OR) 1.44 95% confidence interval (CI) 1.09-1.90, P=0.011). The variant was also associated with BMI (positively, P=0.045) and plasma high-density lipoprotein cholesterol (HDL-C) (negatively, P=0.047).

CONCLUSIONS

As we saw previously among white Europeans, a functional HMGA1 variant was associated with T2DM in individuals of Hispanic-American ethnicity and was present at a much higher frequency.

Relation of increased prebeta-1 high-density lipoprotein levels to risk of coronary heart disease

Preβ-1 high-density lipoprotein (HDL) plays a key role in reverse cholesterol transport by promoting cholesterol efflux. Our aims were (1) to test previous associations between preβ-1 HDL and coronary heart disease (CHD) and (2) to investigate whether preβ-1 HDL levels also are associated with risk of myocardial infarction (MI). Plasma preβ-1 HDL was measured by an ultrafiltration-isotope dilution technique in 1,255 subjects recruited from the University of California-San Francisco Lipid and Cardiovascular Clinics and collaborating cardiologists. Preβ-1 HDL was significantly and positively associated with CHD and MI even after adjustment for established risk factors. Inclusion of preβ-1 HDL in a multivariable model for CHD led to a modest improvement in reclassification of subjects (net reclassification index 0.15, p = 0.01; integrated discrimination improvement 0.003, p = 0.2). In contrast, incorporation of preβ-1 HDL into a risk model of MI alone significantly improved reclassification of subjects (net reclassification index 0.21, p = 0.008; integrated discrimination improvement 0.01, p = 0.02), suggesting that preβ-1 HDL has more discriminatory power for MI than for CHD in our study population. In conclusion, these results confirm previous associations between preβ-1 HDL and CHD in a large well-characterized clinical cohort. Also, this is the first study in which preβ-1 HDL was identified as a novel and independent predictor of MI above and beyond traditional CHD risk factors.

An apolipoprotein A-V gene SNP is associated with marked hypertriglyceridemia among Asian-American patients

Apolipoprotein A-V (apoA-V) is an important regulator of plasma levels of triglyceride (TG) in mice. In humans, APOA5 genetic variation is associated with TG in several populations. In this study, we determined the effects of the p.185Gly>Cys (c.553G>T; rs2075291) polymorphism on plasma TG levels in subjects of Chinese ancestry living in the United States and in a group of non-Chinese Asian ancestry. The frequency of the less common cysteine allele was 4-fold higher (15.1% vs. 3.7%) in Chinese high-TG subjects compared with a low-TG group (Chi-square = 20.2; P < 0.0001), corresponding with a 4.45 times higher risk of hypertriglyceridemia (95% confidence interval, 2.18-9.07; P < 0.001). These results were replicated in the non-Chinese Asians. Heterozygosity was associated, in the high-TG group, with a doubling of TG (P < 0.001), mainly VLDL TG (P = 0.014). All eleven TT homozygotes had severe hypertriglyceridemia, with mean TG of 2,292 +/- 447 mg/dl. Compared with controls, carriers of the T allele had lower postheparin lipoprotein lipase activity but not hepatic lipase activity. In Asian populations, this common polymorphism can lead to profound adverse effects on lipoprotein profiles, with homozygosity accounting for a significant number of cases of severe hypertriglyceridemia. This specific apoA-V variant has a pronounced effect on TG metabolism, the mechanism of which remains to be elucidated.

Variations in human HM74 (GPR109B) and HM74A (GPR109A) niacin receptors

HM74 (GPR109B) and the highly homologous gene, HM74A (GPR109A) code for Gi-G protein-coupled orphan receptors that recently have been discovered to be involved in the metabolic effects of niacin. The B vitamin niacin is an important agent used in the treatment of dyslipidemias, but its use is limited by side effects. The novel role of the adjacent HM74 and HM74A genes in the metabolism of niacin may provide new targets for drug development. Human genetic variations in HM74 and HM74A have been reported but have not been studied in detail. These variations may play a role in the response to agents targeting receptors coded by these genes. Here we show that many of the nonsynonymous SNPs listed in public databases for HM74 and HM74A are artifacts resulting from extensive homology between these two genes. This may be representative of a neglected phenomenon in reporting sequences of highly homologous genes. We provide primer sequences that permit selective amplification of the complete coding regions of HM74 and HM74A. Using these primers, we show that subsequent sequencing of HM74 and HM74A reveals a novel and unique variation in the HM74A gene. Haplotype analysis suggests four SNPs can define the five major haplotypes that lie within a single haplotype block encompassing these two genes.

Properties of triglyceride-rich and cholesterol-rich lipoproteins in the remnant-like particle fraction of human blood plasma

An immunoassay procedure that quantifies remnant-like particle (RLP) cholesterol in human blood plasma has shown considerable promise as a clinically applicable risk marker for atherosclerotic disease. The lipoproteins included in this assay include not only certain TG-rich lipoproteins [all particles containing apolipoprotein B-48 (apoB-48) and a fraction of those containing apoB-100] but also a very small proportion of plasma cholesterol-rich lipoproteins. The TG-rich lipoprotein component of RLP has been partially characterized, but relatively little is known about the component cholesterol-rich lipoproteins. We have further characterized the properties of the TG-rich component that is included in RLP in which about 25% of the particles contain apoB-48 and the remainder apoB-100. We show that the cholesterol-rich component is comprised mainly of beta-migrating LDLs that contain predominantly apoB-100. ApoE found in the LDL fraction of RLP resides on pre-beta lipoproteins that lack apoA-I as well as apoB. The TG-rich component of RLP is responsible for increased RLP-cholesterol concentrations associated with hypertriglyceridemia. By contrast, the cholesterol-rich component is a major contributor to plasma RLP-cholesterol in individuals with low plasma TG. Our results suggest that particle heterogeneity in the RLP fraction is likely to affect the ability of RLP-cholesterol concentration to predict atherosclerotic risk. RLP-cholesterol concentrations in individuals with low plasma TG may not have the same clinical significance as they do in those with hypertriglyceridemia.

Elevated baseline triglyceride levels modulate effects of HMGCoA reductase inhibitors on plasma lipoproteins

BACKGROUND

The response in levels of very-low-density (VLDL) and low-density (LDL) lipoproteins varies substantially among hyperlipidemic patients during treatment with HMGCoA reductase inhibitors. Apolipoprotein E genotype and gender are known to contribute to the regulation of steady state levels of plasma lipoproteins. This study explores the effect of these and other potential determinants of the response of VLDL and LDL to treatment with reductase inhibitors.

METHODS

Using mixed linear statistical models, the response of lipoprotein lipid values was studied in 142 hyperlipidemic individuals who were treated with reductase inhibitors. Patients received one or more of the following drugs individually for a total of 623 treatment observations: lovastatin, pravastatin, simvastatin, or atorvastatin. For evaluation of the effects of treatment in the aggregate, actual doses were expressed as equivalent doses of atorvastatin, using factors based on random assignment comparisons in 16 reported studies. The analysis factors considered were apolipoprotein E genotype, baseline average triglycerides >170 mg/dL (vs less), and gender.

RESULTS

Presence of an apo epsilon4 allele was associated with a trend toward greater reduction of triglyceride levels and a diminished ability of the reductase inhibitors to reduce LDL cholesterol levels. Gender had only minimal effect on the response of either LDL cholesterol or triglycerides. However, the effect of elevated baseline triglycerides on the response of both triglycerides and LDL cholesterol was striking and was exerted in opposite directions. The triglyceride-lowering effect of reductase inhibitors was greater in patients with initial triglyceride levels above 170 mg/dL (P=0.0001). The effect was even greater in patients with initial triglyceride levels over 250 mg/dL (P=0.015). Conversely, for LDL cholesterol levels, elevated baseline triglycerides were associated with a significantly decreased response to the drugs (P=0.0015).

CONCLUSIONS

These findings indicate that baseline triglyceride levels are an important predictor of response of plasma lipoproteins to HMGCoA reductase inhibitors, perhaps reflecting fundamental differences in mechanism underlying the hyperlipidemic phenotype.

Risk factors for stroke and type of stroke in persons with isolated systolic hypertension. Systolic Hypertension in the Elderly Program Cooperative Research Group

BACKGROUND AND PURPOSE

We sought to determine risk factors for stroke and stroke type in persons with isolated systolic hypertension (ISH).

METHODS

We performed proportional hazards analyses of data from the Systolic Hypertension in the Elderly Program, a double-blind, randomized, placebo-controlled trial of 4736 persons aged > or =60 years with ISH (systolic blood pressure, 160 to 219 mm Hg; diastolic blood pressure, <90 mm Hg). One treatment group received chlorthalidone (12.5 to 25 mg/d) with step-up to atenolol (25.0 to 50.0 mg/d) or reserpine (0.05 to 0.10 mg/d), if needed. The other treatment group received matching placebo. The main outcome measures were stroke, stroke or transient ischemic attack [TIA], and stroke types: ischemic (including lacunar, atherosclerotic, and embolic) and hemorrhagic.

RESULTS

During an average follow-up of 4.5 years, 384 strokes or TIAs and 262 strokes (including 217 ischemic, 66 lacunar, 26 atherosclerotic, and 25 embolic strokes) were documented. In multivariate analyses, placebo treatment, older age, smoking, history of diabetes, higher systolic blood pressure, lower HDL cholesterol, and ECG abnormality were significantly associated (P<0.05) with increased incidence of stroke or TIA, stroke, or ischemic stroke. Greater lacunar stroke risk was significantly related to placebo treatment, older age, history of diabetes (relative risk [RR] = 3.03; 95% confidence interval [CI], 1.70 to 5.40), and smoking (RR = 3.04; 95% CI, 1.73 to 5.37). Greater atherosclerotic and embolic stroke risk were significantly related to presence of carotid bruit (RR = 5.75; 95% CI, 2.50 to 13.24) and older age (RR = 1.65 per 5 years; 95% CI, 1.25 to 2.18), respectively.

CONCLUSIONS

In older persons with ISH, history of diabetes and smoking are important risk factors for lacunar stroke, whereas carotid bruit and age are important risk factors for atherosclerotic and embolic stroke, respectively.

Rationale for use of non-high-density lipoprotein cholesterol rather than low-density lipoprotein cholesterol as a tool for lipoprotein cholesterol screening and assessment of risk and therapy

The plasma level of low-density lipoprotein (LDL) cholesterol is the "gold standard" for estimating the lipoprotein-related risk for complications of atherosclerotic vascular disease. LDL cholesterol concentrations are commonly estimated by the Friedewald formula that requires only the measurement (after overnight fasting) of plasma cholesterol and triglycerides along with high-density lipoprotein (HDL) cholesterol. This value, however, is not in fact a true estimate of LDL cholesterol but rather of LDL cholesterol along with variable, usually smaller, amounts of intermediate-density lipoprotein (IDL) cholesterol and lipoprotein(a). Estimation of LDL cholesterol levels by the Friedewald formula becomes progressively less accurate as plasma triglyceride concentrations increase, and the formula is generally considered inapplicable when triglyceride levels exceed 400 mg/dL. We believe that a very simple measurement-non-HDL cholesterol (serum cholesterol minus HDL cholesterol)-has considerable potential as a screening tool for identifying dyslipoproteinemias, for risk assessment, and for assessing the results of hypolipidemic therapy. Unlike the estimation of LDL cholesterol levels by the Friedewald formula, the estimation of non-HDL cholesterol concentrations requires no assumptions about the relation of very-low-density (VLDL) cholesterol levels to plasma triglyceride concentrations. This method includes all of the cholesterol present in lipoprotein particles now considered to be potentially atherogenic [VLDL, IDL, LDL, and lipoprotein(a)]. This article provides examples of the utility of non-HDL cholesterol concentrations in clinical medicine.

Effect of diuretic-based antihypertensive treatment on cardiovascular disease risk in older diabetic patients with isolated systolic hypertension. Systolic Hypertension in the Elderly Program Cooperative Research Group

OBJECTIVE

To assess the effect of low-dose, diuretic-based antihypertensive treatment on major cardiovascular disease (CVD) event rates in older, non-insulin-treated diabetic patients with isolated systolic hypertension (ISH), compared with nondiabetic patients.

DESIGN

Double-blind, randomized, placebo-controlled trial: the Systolic Hypertension in the Elderly Program (SHEP).

SETTING

Multiple clinical and support centers in the United States.

PARTICIPANTS

A total of 4736 men and women aged 60 years and older at baseline with ISH (systolic blood pressure [BP], > or = 160 mm Hg; diastolic BP, <90 mm Hg) at baseline, 583 non-insulin-dependent diabetic patients and 4149 nondiabetic patients (4 additional patients not so classifiable were randomized but not included in these analyses). Diabetes mellitus defined as physician diagnosis, taking oral hypoglycemic drugs, fasting glucose level of 7.8 mmol/L or more (> or = 140 mg/dL), or any combination of these characteristics.

INTERVENTION

The active treatment group received a low dose of chlorthalidone (12.5-25.0 mg/d) with a step-up to atenolol (25.0-50.0 mg/d) or reserpine (0.05-0.10 mg/d) if needed. The placebo group received placebo and any active antihypertensive drugs prescribed by patient's private physician for persistently high BP.

MAIN OUTCOME MEASURES

The 5-year rates of major CVD events, nonfatal plus fatal stroke, nonfatal myocardial infarction (MI) and fatal coronary heart disease (CHD), major CHD events, and all-cause mortality.

RESULTS

The SHEP antihypertensive drug regimen lowered BP of both diabetic and nondiabetic patients, with few adverse effects. For both diabetic and nondiabetic patients, all outcome rates were lower for participants randomized to the active treatment group than for those randomized to the placebo group. Thus, 5-year major CVD rate was lower by 34% for active treatment compared with placebo, both for diabetic patients (95% confidence interval [CI], 6%-54%) and nondiabetic patients (95% CI, 21%-45%). Absolute risk reduction with active treatment compared with placebo was twice as great for diabetic vs nondiabetic patients (101/1000 vs 51/1000 randomized participants at the 5-year follow-up), reflecting the higher risk of diabetic patients.

CONCLUSION

Low-dose diuretic-based (chlorthalidone) treatment is effective in preventing major CVD events, cerebral and cardiac, in both non-insulin-treated diabetic and nondiabetic older patients with ISH.

Effect of diuretic-based antihypertensive treatment on cardiovascular disease risk in older diabetic patients with isolated systolic hypertension. Systolic Hypertension in the Elderly Program Cooperative Research Group

OBJECTIVE

To assess the effect of low-dose, diuretic-based antihypertensive treatment on major cardiovascular disease (CVD) event rates in older, non-insulin-treated diabetic patients with isolated systolic hypertension (ISH), compared with nondiabetic patients.

DESIGN

Double-blind, randomized, placebo-controlled trial: the Systolic Hypertension in the Elderly Program (SHEP).

SETTING

Multiple clinical and support centers in the United States.

PARTICIPANTS

A total of 4736 men and women aged 60 years and older at baseline with ISH (systolic blood pressure [BP], > or = 160 mm Hg; diastolic BP, <90 mm Hg) at baseline, 583 non-insulin-dependent diabetic patients and 4149 nondiabetic patients (4 additional patients not so classifiable were randomized but not included in these analyses). Diabetes mellitus defined as physician diagnosis, taking oral hypoglycemic drugs, fasting glucose level of 7.8 mmol/L or more (> or = 140 mg/dL), or any combination of these characteristics.

INTERVENTION

The active treatment group received a low dose of chlorthalidone (12.5-25.0 mg/d) with a step-up to atenolol (25.0-50.0 mg/d) or reserpine (0.05-0.10 mg/d) if needed. The placebo group received placebo and any active antihypertensive drugs prescribed by patient's private physician for persistently high BP.

MAIN OUTCOME MEASURES

The 5-year rates of major CVD events, nonfatal plus fatal stroke, nonfatal myocardial infarction (MI) and fatal coronary heart disease (CHD), major CHD events, and all-cause mortality.

RESULTS

The SHEP antihypertensive drug regimen lowered BP of both diabetic and nondiabetic patients, with few adverse effects. For both diabetic and nondiabetic patients, all outcome rates were lower for participants randomized to the active treatment group than for those randomized to the placebo group. Thus, 5-year major CVD rate was lower by 34% for active treatment compared with placebo, both for diabetic patients (95% confidence interval [CI], 6%-54%) and nondiabetic patients (95% CI, 21%-45%). Absolute risk reduction with active treatment compared with placebo was twice as great for diabetic vs nondiabetic patients (101/1000 vs 51/1000 randomized participants at the 5-year follow-up), reflecting the higher risk of diabetic patients.

CONCLUSION

Low-dose diuretic-based (chlorthalidone) treatment is effective in preventing major CVD events, cerebral and cardiac, in both non-insulin-treated diabetic and nondiabetic older patients with ISH.

Serum lipids and incidence of coronary heart disease. Findings from the Systolic Hypertension in the Elderly Program (SHEP)

BACKGROUND

The association of serum lipids with coronary heart disease has been studied extensively in middle-aged men and, to a lesser extent, in similar women. Less well defined are lipid variables predictive of CHD in individuals of age > or = 60 years.

METHODS AND RESULTS

The Systolic Hypertension in the Elderly Program recruited 4736 persons (mean age, 72 years; 14% were black; and 43% were men). Mean systolic and diastolic blood pressures were 170 and 77 mm Hg, respectively. Baseline mean total cholesterol was 6.11 mmol/L (236 mg/dL); HDL cholesterol, 1.39 mmol/L (54 mg/dL); and non-HDL cholesterol, 4.72 mmol/L (182 mg/dL). Triglyceride levels were 1.62 mmol/L (144 mg/dL) for fasting participants and 1.78 mmol/L for the total group. LDL cholesterol, estimated in fasting samples with triglycerides of < 4.52 mmol/L, averaged 3.98 mmol/L (154 mg/dL). Mean follow-up was 4.5 years. In multivariate Cox regression analyses, baseline total, non-HDL, and LDL cholesterol levels and the ratios of total, non-HDL, and LDL to HDL cholesterol were significantly related to CHD incidence. HDL cholesterol and triglycerides were not significant in these analyses. In fasting participants with triglyceride levels of < 4.52 mmol/L, a 1.03 mmol/L (40 mg/dL) higher baseline total, non-HDL, or LDL cholesterol was associated with a 30% to 35% higher CHD event rate.

CONCLUSIONS

The results of this study support the concept that serum lipids are CHD risk factors in older Americans.

Coronary heart disease risk factors in men and women aged 60 years and older: findings from the Systolic Hypertension in the Elderly Program

BACKGROUND

Coronary heart disease (CHD) is the most common cause of death in men and women aged 60 years and older. Although a number of studies support the concept that CHD risk factors that have been defined in younger adults are significantly associated with CHD events in older adults, others do not support this thesis, and further definition of the risk-factor concept in older adults is required.

METHODS AND RESULTS

The Systolic Hypertension in the Elderly Program recruited 4736 persons (mean age, 72 years); 14% were black, and 43% were men. Mean systolic and diastolic blood pressures were 170 and 77 mm Hg, respectively. About 13% of participants were current smokers; 10% had a history of diabetes; 5%, a prior myocardial infarction; 5% angina pectoris; 2.3%, intermittent claudication; and 7%, a carotid bruit. Mean total cholesterol value was 6.11 mmol/L. Mean follow-up was 4.5 years. In multivariate Cox regression analyses for CHD, variables that were significant were baseline total cholesterol value, smoking, history of diabetes, presence of carotid bruit, and treatment group in the trial. Active treatment yielded a 27% reduction in CHD risk. For each 1.03 mmol/L increase in total cholesterol value, there was an increase in risk of about 20%. Current smokers had a 73% increase, diabetics a 121% increase, and those with carotid bruit a 113% increase in CHD risk.

CONCLUSIONS

The results of this study support the concept that CHD risk factors are important in older men and women with isolated systolic hypertension.

Extremely low doses of heparin release lipase activity into the plasma and can thereby cause artifactual elevations in the serum-free thyroxine concentration as measured by equilibrium dialysis

Heparin can cause an artifactual elevation in the concentration of unbound (free) thyroxine (T4) in the plasma, particularly when measured by equilibrium dialysis. The lipase released into the plasma by heparin acts on substrate (triglycerides; TG) in the plasma in vitro to release nonesterified (free) fatty acids (FFA), which, in high concentrations, inhibit the binding of T4 to its plasma binding proteins. This artifact occurs only in the presence of sufficient substrate (serum TG greater than approximately 180 mg/dL), and is most pronounced in methods requiring long incubation times. We observed this artifact in a patient receiving intralipid and subcutaneous (sc) heparin. Plasma-free T4, when measured by equilibrium dialysis, was elevated, but was normalized when the in vitro generation of FFA during equilibrium dialysis was prevented by prior treatment of the sample with protamine to inhibit lipoprotein lipase and with an antibody to hepatic triglyceride lipase. This observation caused us to investigate formally whether heparin, at standard sc doses or at iv doses even lower than those that are commonly used to flush iv lines (100-300 U), could also cause this artifact. We gave increasing doses of heparin at weekly intervals to each of three normal volunteers and measured FFA generation in their plasma (supplemented with 250 mg/dL triglycerides) under conditions simulating equilibrium dialysis. We found that, indeed, iv doses of heparin as low as 0.08 U/kg (5.6 U in a 70-kg subject) as well as a standard dose of sc heparin (5000 U) could release significant lipase activity into the plasma and, in the setting of sufficient substrate, cause enough in vitro generation of FFA to artifactually increase the serum-free T4 concentration when measured by equilibrium dialysis. These results indicate that equilibrium dialysis may not always be the best method for assessing serum-free T4 concentrations in hospitalized patients, and should be taken into account when interpreting previous studies demonstrating inhibitors of T4-serum protein binding in sera from hospitalized patients.

Familial ligand-defective apolipoprotein B. Identification of a new mutation that decreases LDL receptor binding affinity

Detection of new ligand-defective mutations of apolipoprotein B (apoB) will enable identification of sequences involved in binding to the LDL receptor. Genomic DNA from patients attending a lipid clinic was screened by single-strand conformation polymorphism analysis for novel mutations in the putative LDL receptor-binding domain of apoB-100. A 46-yr-old woman of Celtic and Native American ancestry with primary hypercholesterolemia (total cholesterol [TC] 343 mg/dl; LDL cholesterol [LDL-C] 241 mg/dl) and pronounced peripheral vascular disease was found to be heterozygous for a novel Arg3531-->Cys mutation, caused by a C-->T transition at nucleotide 10800. One unrelated 59-yr-old man of Italian ancestry was found with the same mutation after screening 1,560 individuals. He had coronary heart disease, a TC of 310 mg/dl, and an LDL-C of 212 mg/dl. A total of eight individuals were found with the defect in the families of the two patients. They had an age- and sex-adjusted TC of 240 +/- 14 mg/dl and LDL-C of 169 +/- 10 mg/dl. This compares with eight unaffected family members with age- and sex-adjusted TC of 185 +/- 12 mg/dl and LDL-C of 124 +/- 12 mg/dl. In a dual-label fibroblast binding assay, LDL from the eight subjects with the mutation had an affinity for the LDL receptor that was 63% that of control LDL. LDL from eight unaffected family members had an affinity of 91%. By way of comparison, LDL from six patients heterozygous for the Arg3500-->Gln mutation had an affinity of 36%. The percentage mass ratio of the defective Cys3531 LDL to normal LDL was 59:41, as determined using the mAb MB19 and dynamic laser light scattering. Thus, the defective LDL had accumulated in the plasma of these patients. Using this mass ratio, it was calculated that the defective Cys3531 LDL particles bound with 27% of normal affinity. Deduced haplotypes using 10 apoB gene markers showed the Arg3531-->Cys alleles to be different in the two kindreds and indicates that the mutations arose independently. The Arg3531-->Cys mutation is the second reported cause of familial ligand-defective apoB.

Effects of dietary cholesterol and fat saturation on plasma lipoproteins in an ethnically diverse population of healthy young men

The individual effects of dietary cholesterol and fat saturation on plasma lipoprotein concentrations were determined in an ethnically diverse population of normolipidemic young men (52 Caucasian, 32 non-Caucasian). The experimental diets contained approximately 200 or 600 mg/d of cholesterol, 36-38% of calories as fat, and high or low proportions of saturated and polyunsaturated fat (polyunsaturated/saturated fat ratio approximately 0.8 vs 0.3). At the lower cholesterol intake, the high saturated fat diet had only a modest effect on LDL cholesterol in Caucasians (+ 6 mg/dl-1) and none in non-Caucasians. 600 mg cholesterol with high saturated fat led to a substantial mean increase in LDL cholesterol, which was significantly greater in Caucasian than in non-Caucasian subjects (+ 31 mg/dl vs 16 mg/dl, P < 0.005). 600 mg cholesterol with increased polyunsaturated fat gave a mean LDL increase of 16 mg/dl, lower than found when the same high cholesterol intake was coupled with increased saturated fat. Variation in cholesterol rather than the proportions of saturated and polyunsaturated fat had the most influence on LDL-cholesterol levels. Among non-Caucasians it was the only significant factor.

Conformational differences in human apolipoprotein B-100 among subspecies of low density lipoproteins (LDL). Association of altered proteolytic accessibility with decreased receptor binding of LDL subspecies from hypertriglyceridemic subjects

We asked at what point in the metabolic cascade of very low density lipoproteins (VLDL) to low density lipoproteins (LDL) the accessibility of proteolytic cleavage sites in B-100 changes, and we evaluated the effect of hypertriglyceridemia on the proteolytic accessibility, secondary structure, and receptor-binding affinity of B-100 in LDL subspecies of varying density. Limited proteolysis with Staphylococcus aureus V8 protease and cathepsin D identified the density (about 1.033 g/ml) between two LDL subspecies, designated LDL-1 and -2, as the transition point during VLDL metabolism of both normolipidemic (N-) and hypertriglyceridemic (HTG-) subjects at which accessibility to protease attack changed in three peptide regions of B-100. Hypertriglyceridemia greatly altered proteolytic accessibility of B-100 in the denser LDL subspecies. Specifically, B-100 in HTG-LDL exposed more cleavage sites than in N-LDL, including two novel sites, approximately 120 and approximately 130 kDa from the NH2 terminus in the small and dense subspecies (designated LDL-4, -4.5 or -5, d = 1.048-1.062 g/ml). Analysis of circular dichroic spectra indicated no difference in helical content between B-100 in N- and HTG-LDL but showed a greater content of beta-structure in HTG-LDL. Binding affinity for the LDL receptor of human fibroblasts decreased markedly with increasing density among HTG-LDL subspecies (by approximately 50% for LDL-4.5 or -5). We conclude that the changes in proteolytic accessibility observed between LDL-1 and -2 and in LDL-4, -4.5, or -5 indicate significant differences in local conformation of B-100 at specific peptide regions. The association of exposure of more cleavage sites, especially novel sites in the NH2-terminal regions, with greatly decreased receptor-binding affinity in LDL-4.5 or -5 suggests that altered local conformation in B-100 apart from the putative receptor-binding domain might affect interaction with the receptor.

Comparative effects of lovastatin and niacin in primary hypercholesterolemia. A prospective trial

BACKGROUND

Niacin and lovastatin are both effective drugs for the treatment of hypercholesterolemia and are among the drugs of first choice recommended by the adult treatment panel. To date, however, no studies have directly compared the lipoprotein-modifying effects and safety of lovastatin and niacin across their usual dosage range in patients with primary hypercholesterolemia.

METHODS

The efficacy and safety of lovastatin and niacin were compared in a controlled, randomized, open-label study of 26 weeks' duration that was conducted at five lipid clinics. One hundred thirty-six patients with primary hypercholesterolemia participated in the study. Entry criteria were a low-density lipoprotein (LDL) cholesterol level greater than 4.37 mmol/L (160 mg/dL) with coronary heart disease and/or more than two coronary heart disease risk factors or an LDL cholesterol level greater than 5.19 mmol/L (190 mg/dL) in patients without coronary heart disease or less than two coronary heart disease risk factors. The study consisted of a 4-week diet run-in period after which eligible patients were randomly assigned to receive treatment with either lovastatin (20 mg/d) or niacin (1.5 g/d) for 10 weeks. On the basis of the LDL cholesterol response and patient tolerance, the doses were sequentially increased to 40 and 80 mg/d of lovastatin or 3 and 4.5 g/d of niacin after 10 and 18 weeks of treatment, respectively.

RESULTS

In the two patient groups, 66% of patients treated with lovastatin and 54% of patients treated with niacin underwent full dosage titration. At all time points, lovastatin was significantly (P < .01) more effective than niacin in reducing LDL cholesterol levels (26% vs 5% at week 10, 28% vs 16% at week 18, and 32% vs 23% at week 26), whereas niacin was more effective (P < .01) in increasing high-density lipoprotein cholesterol levels (6% vs 20% at week 10, 8% vs 29% at week 18, and 7% vs 33% at week 26). Niacin reduced Lp(a) lipoprotein levels by 35% at week 26, whereas lovastatin had no effect. Cutaneous flushing was the most common side effect during treatment with niacin.

CONCLUSIONS

Lovastatin and niacin both exerted favorable dose-dependent changes on the concentrations of plasma lipids and lipoproteins. Lovastatin was more effective in reducing LDL cholesterol concentrations, whereas niacin was more effective in increasing high-density lipoprotein cholesterol concentrations and reducing the Lp(a) lipoprotein level. Lovastatin was better tolerated than niacin, in large part because of the common cutaneous side effects of niacin.

Molecular cloning and characteristics of a new apolipoprotein C-II mutant identified in three unrelated individuals with hypercholesterolemia and hypertriglyceridemia

A new rare mutant form of apolipoprotein C-II (apoC-II), designated apoC-IISF, was identified in three unrelated hyperlipidemic patients. The first was a Caucasian male with a total cholesterol (TC) of 313 mg/dl and total triglyceride (TG) of 282 mg/dl, the second an African-American female (TC 345 mg/dl, TG 203 mg/dl) and the third, an African-American male (TC 345 mg/dl, TG 1000 mg/dl). Each subject was found to be heterozygous for a G to A substitution in the codon for residue 38, resulting in a Lys for Glu exchange. This accounts for the increased pl value of 5.3. The third patient, in addition to apoC-IISF, had apoC-II2, another charge variant. This was determined by DNA sequencing, confirming the Gln for Lys change at residue 55 previously predicted by analysis of peptide fragments in this laboratory. Similar Michaelis constants of activation and activation energies were observed when the ability of apoC-IISF to activate lipoprotein lipase was compared to normal apoC-II. This indicates that major changes in charge around residue 38 lack effect on the activation properties. The variant may be altered in some other property, such as lipid binding, but since the distribution of apoC-IISF revealed no simple co-inheritance with lipid levels, it is unclear to what extent it plays a role in the observed hyperlipidemia. The presence of other factors acting together with the variant may predispose to elevated lipid levels.

Mechanism of the heparin-induced increase in the concentration of free thyroxine in plasma

The iv administration of heparin causes an increase in the plasma free T4 concentration, as determined by equilibrium dialysis. The mechanism and physiological consequences of this action of heparin are unknown. To explore the possibility that the heparin-induced increase in plasma free T4 is an in vitro artifact due to generation of FFA during equilibrium dialysis, we studied plasma samples from 10 subjects treated with iv heparin. In plasma from 4 of these subjects, free T4 concentrations measured by equilibrium dialysis did not increase above baseline values after heparin administration. In incubations performed in parallel with the equilibrium dialysis measurements, FFA concentrations in these plasma samples were found to increase, but in no subject did they exceed 2.5 meq/L after incubation. In contrast, in plasma from the other 6 subjects treated with heparin, free T4 concentrations rose markedly (by 130-520%) above baseline values after heparin administration. In all of these postheparin plasma samples, FFA concentrations were less than 2.8 meq/L before incubation, but rose during incubation by 80-270% to more than 3.8 meq/L. Treatment of these plasma samples with protamine to inhibit lipoprotein lipase and with specific antiserum to inhibit hepatic triglyceride lipase before equilibrium dialysis or incubation prevented, in parallel, the heparin-induced increases in FFA and free T4 concentrations. From these findings we conclude that the heparin-induced increase in free T4 is usually an in vitro artifact, and that most subjects receiving heparin have a normal plasma free T4 concentration in vivo. We also conclude that this in vitro artifact may account for many of the findings that led to the postulate of an inhibitor of T4 binding to plasma and intracellular proteins in heparin-treated patients and perhaps in patients with nonthyroid illness as well.

Lovastatin (mevinolin) in the treatment of heterozygous familial hypercholesterolemia. A multicenter study

STUDY OBJECTIVE

To evaluate the efficacy and tolerability of lovastatin under controlled conditions in heterozygous familial hypercholesterolemia.

DESIGN

Randomized, double-blind, placebo-controlled, multicenter trial.

SETTING

Five lipid clinics with a central laboratory and coordinating center.

PATIENTS

101 adult patients with heterozygous familial hypercholesterolemia.

INTERVENTIONS

Patients were on a lipid-lowering diet throughout the study. After a 4-week placebo baseline period, patients were randomized to five equal treatment groups. Each group received a different sequence of placebo or lovastatin 5 to 40 mg twice daily or 20 to 40 mg once daily in the evening, during three consecutive 6-week periods.

MEASUREMENTS AND MAIN RESULTS

The mean reductions in total plasma cholesterol and low-density lipoprotein cholesterol across the dosage ranges were 14% to 34% and 17% to 39%, respectively (p compared with zero and placebo less than 0.01). High-density lipoprotein cholesterol and apolipoproteins AI and AII rose slightly. Apolipoprotein B fell substantially at the higher dosage levels (-23% at 40 mg twice daily, p less than 0.01), indicating a reduction in the concentration of circulating low-density lipoprotein particles. Maximum response was achieved in 4 to 6 weeks. Twice-daily dosing was slightly more efficient than once-daily dosing. Of those patients receiving 40 mg twice a day, 89% had a fall in low-density lipoprotein cholesterol of at least 20%, and 61% had a fall of at least 40%. Adverse effects attributable to lovastatin were minimal, and no patient was withdrawn from the study.

CONCLUSION

Lovastatin was well tolerated and effective in the treatment of familial hypercholesterolemia.

Serum lipids and lipoproteins after myocardial infarction: associations with cardiovascular mortality and experience in the Aspirin Myocardial Infarction Study

Serum cholesterol and triglyceride levels were measured at baseline in 4021 men and 503 women (myocardial infarction survivors) participating in the Aspirin Myocardial Infarction Study (AMIS). A cohort of participants (1824 men and 226 women) had, in addition, a determination of high-density lipoprotein (HDL) cholesterol and an estimate of low-density lipoprotein (LDL) cholesterol. In comparison with values obtained for normal Americans by the Lipid Research Clinics Prevalence Study Group, AMIS participants had higher serum cholesterol, higher serum triglyceride, higher LDL cholesterol, and lower HDL cholesterol levels. These values were the most disparate in the women and younger men. The serum total cholesterol, the ratio of LDL to HDL cholesterol, and the serum triglyceride level were significantly related (p less than 0.05) to the 3-year cardiovascular mortality rate for men less than 55 years of age (univariate relationships). For men older than 55 years, these relationships were not statistically significant. After adjustment for multiple risk factors, serum cholesterol and the ratio of LDL to HDL cholesterol remained significant risk factors for cardiovascular death and the combined incidence of cardiovascular death or nonfatal myocardial infarction in men less than age 55 years.

Effect of free fatty acids on the concentration of free thyroxine in human serum: the role of albumin

The concentration of FFA in normal human plasma in vivo generally ranges between 0.2 and 0.7 meq/liter; slightly higher concentrations have occasionally been reported in patients who are seriously ill. To determine whether such FFA concentrations may increase the concentration of free T4 in serum, we added increasing amounts of oleic acid to pooled normal human serum (with known FFA content) and measured free T4 by equilibrium dialysis. Total FFA up to 3 meq/liter in normal serum, representing an FFA to albumin molar ratio of about 5:1, had little or no effect on the free T4 concentration, while higher FFA concentrations progressively increased free T4. This same molar ratio of FFA to albumin had to be exceeded to cause a significant increase in the free T4 concentration in diluted serum and in serum from patients with nonthyroid illness. Serum from which more than 95% of the albumin had been removed by chromatography with Affi-Gel blue was much more sensitive to the effects of FFA on free T4. This enhanced sensitivity was reversed by readdition of albumin to the serum, and the addition of albumin to normal serum resulted in diminished effects of FFA on free T4. These results indicate the following: physiological concentrations of FFA do not significantly increase the free T4 concentration in normal human serum; when FFA reach supraphysiological concentrations in serum (in vitro) and the higher affinity FFA-binding sites on albumin become saturated (apparently at an FFA to albumin molar ratio of approximately 5:1), the excess FFA interact with other serum proteins, including thyroid hormone-binding globulin, and thereby increase the free T4 concentration; the concentration of albumin (or other FFA binders) must be considered when evaluating the observed effects of FFA. To explore the relevance of these findings to the hypothesis that FFA may inhibit the binding of T4 to plasma proteins in patients with nonthyroid illness, we measured plasma FFA concentrations in 11 severely ill patients hospitalized in the intensive care unit. We found a mean plasma FFA concentration of 0.45 +/- 0.11 (+/- SEM) mEq/liter and a mean serum albumin concentration of 2.39 +/- 0.29 g/dl in these patients. Their mean plasma FFA to albumin molar ratio was 1.53 +/- 0.41. Since the FFA to albumin molar ratio must exceed about approximately 5:1 before a significant increase in the serum free T4 concentration occurs, these results suggest that FFA do not commonly influence the circulating free T4 concentration in vivo, even in severely ill patients.

Ichthyosis and neutral lipid storage disease

Four members of a consanguineous middle eastern family had a lipid storage disease characterized by congenital ichthyosiform erythroderma, neurosensory deafness, cataracts, mild myopathy, and leukocyte vacuoles. These patients are similar to several others recently reported and represent a unique disorder of lipid metabolism. The clinical and biochemical manifestations of this lipid storage disease are reviewed. Evidence is presented that the disorder is inherited as an autosomal recessive trait, and that heterozygotes may be detected by the presence of vacuoles within circulating eosinophils.

Purification of canine post-heparin hepatic lipase

A method for the purification of canine hepatic lipase from post-heparin hepatic venous blood plasma was developed and found applicable to mixed venous post-heparin plasma. The method employs sequential (NH4)2SO4 fractionation, heparin-Sepharose chromatography at pH 8.8 and, finally, adsorption to antiserum prepared against dog pre-heparin plasma. The lipase was purified 10,000-fold. The specific activity assayed with Intralipid as substrate was 840 mumol free fatty acid h-1 . mg-1. Enzyme recovery was 20%. Upon electrophoresis of the purified lipase in polyacrylamide gel containing SDS, a major protein-staining band with an apparent molecular weight of 60,000 was consistently found. This component accounted for 85-90% of the protein applied to the gel, and by amino acid analysis appeared to be distinct from canine antithrombin III, a protein thought to contaminate hepatic lipase purified by earlier methods.