A prospective study of triglyceride level, low-density lipoprotein particle diameter, and risk of myocardial infarction

Improved metabolic control reduces the number of postprandial apolipoprotein B-48-containing particles in type 2 diabetes

Postprandial lipoproteins are raised in diabetes and there is increasing evidence for the atherogenicity of the chylomicron remnant. Increased postprandial cholesteryl ester transfer has also been demonstrated in diabetes and may contribute to the atherogenic lipoprotein profile. The present study examined the effect of improving metabolic control on postprandial lipoproteins in 13 Type 2 diabetic patients. Blood was taken fasting and at 2-h intervals following a high fat, 1100 kcal meal. Patients were brought into good control by intensified dietary advice and oral hyperglycaemic agents or insulin if blood glucose failed to respond. Fasting and postprandial cholesteryl ester transfer protein (CETP) and lecithin:cholesteryl acyltransferase (LCAT) were determined in six patients. Lipoproteins were isolated by sequential ultracentrifugation. Chylomicron and very low density lipoprotein (VLDL) apolipoprotein B-48 and apolipoprotein B-100 were isolated by polyacrylamide gradient gel electrophoresis and quantified by densitometric scanning. CETP and LCAT were determined by an endogenous method which determined cholesterol esterification and transfer between the patients' lipoproteins. There was a significant reduction in postprandial chylomicron apo B-48 (P<0.005), apo B-100 (P<0.0005) and chylomicron cholesterol (P<0.001) following improved diabetic control. The chylomicron lipid/apo B ratio increased with improved control (P<0.01). Postprandial CETP and LCAT were significantly reduced in good control (P<0.01 and P<0.05, respectively) and there were significant changes in HDL composition. The study shows that improvement in metabolic control in Type 2 diabetic patients leads to a reduction in postprandial chylomicron particles and less transfer of cholesterol to apo B-containing lipoproteins.

Acute hyperinsulinemia and very-low-density and low-density lipoprotein subfractions in obese subjects

BACKGROUND

The influence of hyperinsulinemia on concentrations of lipoprotein subfractions in obese, nondiabetic persons has not been clarified.

OBJECTIVE

We analyzed VLDL and LDL subfractions before and after a euglycemic, hyperinsulinemic clamp.

DESIGN

Lipoprotein subfractions were isolated from plasma samples obtained in the basal state and after a 4-h clamp from obese patients, obese patients with type 2 diabetes, and nonobese control subjects.

RESULTS

Hyperinsulinemia tended to reduce concentrations (&xmacr;: 20%) of large, triacylglycerol-rich VLDL(1) in obese patients but had a minor effect on VLDL(2) and VLDL(3). Placing obese patients into insulin-sensitive and insulin-resistant subgroups revealed distinct effects of the degree of insulin sensitivity on VLDL. VLDL(1) concentrations decreased by a mean of 38% (P < 0.05) in insulin-sensitive patients after the clamp, similar to but less marked than the decrease observed in control subjects (&xmacr;: 62%; P < 0.01). VLDL(1) concentrations did not change significantly after the clamp in insulin-resistant patients (and patients with type 2 diabetes), whereas VLDL(3) concentrations decreased in both groups, in contrast with the changes seen in the insulin-sensitive patients and control subjects. Acute hyperinsulinemia modified the LDL subfraction profile toward a greater prevalence of small, dense LDLs in insulin-resistant patients and patients with type 2 diabetes.

CONCLUSIONS

Insulin resistance appears to be the primary determinant of the modifications to VLDL subfraction concentrations. Our results suggest a continuum of impaired insulin action on VLDL, ranging from that in healthy persons to that in patients with type 2 diabetes, in which obese patients occupy a transition state. Insulin resistance may also play a role in detrimental modifications to the LDL profile by allowing the development of hypertriglyceridemia.

Resistance vessel endothelial function in healthy humans during transient postprandial hypertriglyceridemia

A single high-fat meal transiently impairs conduit vessel endothelial function. We tested the hypothesis that transient moderate hypertriglyceridemia by consumption of a high-fat meal impairs forearm resistance vessel endothelial function. Fifteen healthy persons consumed isocaloric high- and low-fat meals (900 calories, 50 and 4 g of fat, respectively) on 2 separate days. Endothelial function in forearm resistance vessels was assessed using blood flow responses to local intra-arterial infusion of nitroprusside, acetylcholine, bradykinin, and verapamil from 1 to 3 hours after the meal. Serum triglycerides increased from 112 +/- 15 mg/dl preprandially to 165 +/- 20 mg/dl 4 hours after the high-fat meal, which was a significantly larger increase than levels after the low-fat meal (p = 0.01). Total cholesterol, high-density lipoprotein, low-density lipoprotein, and very low density lipoprotein (VLDL) cholesterol concentrations did not change. There was no difference between high- and low-fat meals in vasodilation to the endothelium-dependent agents acetylcholine (low fat, 337 +/- 47%; high fat, 356 +/- 88%; p = 0.81) and bradykinin (low fat, 312 +/- 39%; high fat, 403 +/- 111%; p = 0.28), or to the endothelium-independent vasodilators nitroprusside (low fat, 313 +/- 27%; high fat, 355 +/- 42%; p = 0.31) and verapamil (low fat, 292 +/- 48%; high fat, 299 +/- 36%; p = 0.18). Thus, transient hypertriglyceridemia due to a high-fat meal does not impair resistance vessel endothelial function. These data contrast with previous studies in conduit vessels that showed substantial endothelial dysfunction. Therefore, although high-fat intake may contribute to large artery atherosclerosis, it probably does not predispose to hypertension or ischemia through resistance vessel dysfunction. The results suggest that the mechanism by which triglyceride-rich lipoproteins impair endothelial function in conduit vessels is not operative in resistance vessels.

Hypertriglyceridemia and low high-density lipoprotein: risks for coronary artery disease?

Elevated total cholesterol and LDL cholesterol have been well established as risk factors for coronary heart disease (CHD). Several large clinical trials have demonstrated that lipid lowering decreases the incidence and mortality that results from CHD. However, a high percentage of subjects in these studies did not receive benefit from LDL lowering. Many experts believe that other lipid disorders may play a significant role in the atherogenic process, including elevated triglyceride levels alone or in association with a low level of HDL. Do elevated triglyceride levels pose an increased risk for CHD? This article describes the research done evaluating this question, as well as the influences of lifestyle changes and pharmacologic interventions on these dyslipidemias.

Effect of long-chain n-3 polyunsaturated fatty acids on fasting and postprandial triacylglycerol metabolism

Elevated plasma triacylglycerol concentrations have been associated with increased risk of coronary heart disease (CHD). In the past, the epidemiologic evidence about the causal role of triacylglycerols in CHD has not been well regarded, but recent prospective evidence shows that nonfasting plasma triacylglycerol concentration is a strong and independent predictor of future myocardial infarction. Elevated plasma triacylglycerol concentrations are associated with other CHD risk factors, namely reduced HDL-cholesterol concentrations and a preponderance of highly atherogenic, small, dense LDL particles. Plasma triacylglycerol concentrations increase after the ingestion of a fat-containing meal, and elevated postprandial triacylglycerolemia leads to a series of metabolic reactions that reduce HDL-cholesterol concentrations and promote the formation of small, dense LDL particles. The magnitude of the postprandial response is largely determined by fasting plasma triacylglycerol concentrations. Metabolism of plasma triacylglycerols also influences postprandial factor VII activation and the postprandial lipemic responsiveness to dietary cholesterol. Therefore, dietary factors that improve fasting plasma triacylglycerol concentrations must have a role in a healthy diet. Eicosapentaenoic and docosahexaenoic acids are n-3 polyunsaturated fatty acids (PUFAs) in fish oil that effectively reduce plasma triacylglycerol concentrations. Because n-3 PUFAs are effective at low doses (1 g n-3 PUFA/d), they provide a realistic option for the optimization of plasma triacylglycerol metabolism.

Lipoprotein subpopulation distributions in lean, obese, and type 2 diabetic women: a comparison of African and white Americans

OBJECTIVE

Abnormal subpopulation distributions of plasma lipoproteins have been reported in white American (WA) women with obesity and type 2 diabetes that explain part of the elevated rate of cardiovascular disease in these patients. This study examined if these perturbations also occur in obese and diabetic African American (AA) women and compared the lipoprotein profiles with WA counterparts.

RESEARCH METHODS AND PROCEDURES

We determined the lipoprotein subpopulation distribution in the plasma of 51 lean women (29 WA, 22 AA, body mass index [BMI] < 30), 50 obese women (27 WA, 23 AA, BMI > 30), and 43 obese women with type 2 diabetes (27 WA, 16 AA), by nuclear magnetic resonance spectroscopy.

RESULTS

AA diabetic women, like WA diabetic women, had a larger average very low density lipoprotein (VLDL) size, elevated levels of small low density lipoprotein cholesterol (LDL-C), and lower levels of small high density lipoprotein cholesterol (HDL-C), when compared to lean controls (p<0.05). These differences were accompanied by higher VLDL-triglycerides (TG) and LDL-C in WA (p<0.05), but not in AA. Although the effects of obesity and diabetes on lipoprotein subpopulation were fairly similar for AA and WA, some racial differences, particularly with respect to HDL, were observed.

DISCUSSION

The atherogenic perturbations in lipoprotein profiles of obese AA women, particularly those with diabetes, were relatively similar to those found in WA women and may be contributing to the increased rate of cardiovascular disease (CVD) in AA with obesity and diabetes. The parameters of subpopulation distribution may provide better markers for CVD than lipid concentrations alone, particularly in AA women. Furthermore, subtle racial differences in lipoprotein profiles suggest that race-specific criteria may be needed to screen patients for CVD.

Fibrates, dyslipoproteinaemia and cardiovascular disease

Recent epidemiological data have reaffirmed that elevated plasma triglyceride and low HDL-cholesterol levels are important risk factors for atherosclerotic vascular disease. The rationale for the clinical use of fibric acid derivatives, which are designed to correct this metabolic nexus, is now on firmer ground. The mechanism of action of fibrates on lipoprotein metabolism has recently been elucidated at the molecular level and involves the activation of peroxisome proliferator-activated receptor-alpha 1 in the liver, with the net effect of improving the plasma transport rates of several lipoproteins. Other potential anti-atherothrombotic effects include the inhibition of coagulation and enhancement of fibrinolysis, as well as the inhibition of inflammatory mediators involved in atherogenesis. These consequences probably underpin the favourable effects of fibrates seen in recent angiographic and clinical trials. Two important clinical trials on the effect of gemfibrozil (Veterans Administration-HDL-Cholesterol Intervention Trial) and bezafibrate (Bezafibrate Infarction Prevention Study) have recently been completed in subjects with elevated triglyceride, low HDL and normal or near-normal LDL-cholesterol levels. The results testify to the efficacy of these agents in decreasing the incidence of cardiovascular events, particularly in patients with multiple risk factors and plasma triglyceride levels of over 2.2 mmol/l. The findings of these trials are compared with the statin-based Air Force/Texas Coronary Atherosclerosis Prevention Study, with a recommendation that future studies in appropriately selected patients should examine the synergistic effect of the fibrate/statin combination. The absolute risk reduction in the incidence of coronary events in the Veterans Administration-HDL-Cholesterol Intervention Trial compares favourably with the statin trials. The therapeutic aspects of the efficacy and safety of fibrates are reviewed. Besides primary mixed hyperlipidaemias, particular indications for the clinical use of fibrates include type 2 diabetes, the metabolic syndrome and renal insufficiency. The St Mary's, Ealing, Northwick Park Diabetes Cardiovascular Disease Prevention Study has suggested that fibrates may decrease the incidence of coronary events in type 2 diabetes, but this hypothesis will be more extensively tested in the Diabetes Atherosclerosis Intervention Study, Fenofibrate in Event Lowering in Diabetes Study and Lipids in Diabetes Study projects. Although significant new knowledge has accrued over the past few years concerning the fundamental and clinical aspects of fibrates, the success of these agents in clinical practice depends on the availability of methods for assessing cardiovascular risk as well as on treatment guidelines, which as presently designed and recommended may be inaccurate and suboptimal.

Estrogen improves acetylcholine-induced but not metabolic vasodilation in biological males

We have previously shown that chronic estrogen therapy improves endothelium-dependent vasodilation in the resistance vessels of biological males. Whether this is nitric oxide (NO) mediated and whether estrogen improves metabolic vasodilation is unknown. Resting forearm blood flow (FBF), ACh-induced vasodilation, and functional hyperemic blood flow (exercise) were assessed before and after the inhibition of NO with N(G)-monomethyl-L-arginine (L-NMMA) in 15 male-to-female transsexuals prescribed estrogen and in 14 age-matched males. Resting FBF was similar in the two groups and was similarly (P = 0.44) but significantly reduced by 48% after infusion of L-NMMA (P < 0.0001). The ACh dose-response relationship was shifted upward and to the left in the transsexual compared with the male group (P < 0.01). After the inhibition of NO, however, the difference in the ACh dose-response curve between the two groups was abolished (P = 0.15). Peak functional hyperemic blood flow was similar for the two groups (P = 0.94). L-NMMA produced a significant (P < 0.01) but similar (P = 0.64) reduction in peak hyperemia in the two groups. The volume of blood repaid to the forearm 1 and 5 min after exercise was also reduced by L-NMMA (P < 0.0001); however, there were no differences between the two groups. This suggests that ACh-mediated NO-dependent vasodilation may be more sensitive to the effects of chronic estrogen than exercise-induced vasodilation. Long-term estrogen does not appear to improve exercise-induced metabolic vasodilation in biological males, despite the fact that NO contributes to this process.

Prevention of coronary heart disease. Part I. Primary prevention

The first concern in primary prevention is the physician's belief that primary prevention is important for all adults and that intervention can significantly affect risk. Given the coronary plaque burden over many years and the importance of the development of healthy lifestyles early in adulthood to decrease coronary plaque burden, there are excellent reasons to begin prevention even with young adults. At the very least, a patient seen for any reason should provide a smoking history, have knowledge of the presence of early CHD in first-degree relatives and measurements of blood pressure, height, and weight, provide evidence for a cholesterol level within 5 years (after age 20 according to NCEP guidelines or in middle age according to ACP guidelines), and be given an assessment of glucose tolerance or diabetes. Information about alcohol intake and physical activity status are also of some importance. Other than height, weight, and blood pressure, during the physical examination, the physician should initially assess the strength of pulses in the lower extremities, evidence for carotid or femoral bruits, and eyegrounds for retinal arterial changes, and the skin and subcutaneous tissue should be examined for xanthomas and the eyes should be examined for corneal arcus and xanthelesma. These elements should be part of any initial examination by a primary care physician and are not extraordinary. In addition to lipid and blood sugar analyses, other evaluations may include blood urea nitrogen and creatinine and electrolytes in patients with hypertension or diabetes or in patients who are on antihypertensive agents. It may be prudent to obtain an ECG for patients who are older than 40 years. The elements mentioned above are the elements of the history, physical examination, and laboratory examination in subjects without a past history of CHD and with no clinical evidence for CHD. Primary prevention management begins with a discussion of risk factors with the patient. The key interventions aim at the lowering of blood pressure to at least less than 140/90 mm Hg, the complete cessation of smoking, the lowering of lipid levels to less than 130 mg/dL, the lowering of triglycerides to less than 200 mg/dL (or, some would argue, < 150 mg/dL), and the attempt to keep HDL cholesterol above 35 mg/dL (more than 40 to 45 mg/dL is a better goal) with the use of lifestyle modification. For patients with diabetes, strict control of glucose levels is essential to minimize disease of the microvasculature and possibly to minimize progressive renal disease. There are several lifestyle modifications for lipids. For patients with elevated LDL cholesterol, modifications include a less than 30% fat calorie diet and less than 300 mg of cholesterol intake daily, with fat calories approximately equally distributed among saturated fats, polyunsaturated fats, and monounsaturated fats (1/3, 1/3, 1/3; rule of 3s). The assistance of a dietician is extremely helpful in this regard. For patients with a low HDL cholesterol, weight reduction (for overweight patients) by calorie control and increased physical activity and smoking cessation will have some modest effect. For patients with elevated triglycerides, a diet similar to that for lowering of LDL cholesterol with the addition of stricter calorie limitation, avoidance of refined sugars, increase in complex carbohydrates, and avoidance of alcohol will be helpful. A decrease in the percent of fat calories to 20% to 25% will be of assistance to those patients with particularly high triglycerides. The treatment of underlying conditions such as diabetes mellitus, hypothyroidism, liver disease, and some renal conditions may also significantly modify high triglycerides. For patients with hypertension, limitation of sodium to 2 gm/d (6 gm sodium chloride), limitation of alcohol to 1 to 2 drinks a day, increased physical activity, and weight reduction are the key lifestyle modifications. (ABSTRACT TRUNCATED)

Low density lipoprotein (LDL) binding affinity for the LDL receptor in hyperlipoproteinemia

We measured the binding affinity of low density lipoprotein (LDL) for the LDL receptor in patients with various types of hyperlipoproteinemia and investigated the effects of LDL lipid composition and particle size on receptor affinity. LDL (1.019 < d < 1.063) was isolated by sequential ultracentrifugation from the serum of normolipidemic controls and patients with hyperlipoproteinemia. Patients with type IIa hyperlipoproteinemia had LDL with a similar receptor affinity to that of normal LDL. However, patients with hypertriglyceridemia (type IIb and type IV hyperlipoproteinemia) had LDL with a low receptor affinity, and the degree of the reduction in affinity paralleled the severity of the hypertriglyceridemia. The LDL of hypertriglyceridemic patients was rich in protein and triglycerides, had a low content of cholesterol and phospholipids, and was smaller than normal, thus resembling the atherogenic lipoprotein known as small, dense LDL. These abnormalities were observed even in patients with mild hypertriglyceridemia regardless of their serum cholesterol levels. The degree of alteration in LDL lipid composition and particle size was strongly associated with the reduction of LDL receptor affinity. We also examined the effects of two lipid-lowering agents (bezafibrate and probucol) on the characteristics of LDL. LDL receptor affinity was only improved when the lipid composition and particle size were normalized by drug therapy. Although it has been reported that decreased cholesteryl ester transfer protein (CETP) activity results in the formation of small LDL, plasma CETP activity was normal in the hyperlipoproteinemic patients and the normalization of LDL characteristics by drug therapy was not accompanied by an increase of CETP activity. Our results suggested that an abnormal lipid composition and/or small particle size might cause a decrease in the receptor affinity of LDL. These structural and functional abnormalities were reversed by drug therapy, underlining the importance of treating hypertriglyceridemia for the prevention of atherosclerosis.

Dietary fish as a major component of a weight-loss diet: effect on serum lipids, glucose, and insulin metabolism in overweight hypertensive subjects

BACKGROUND

Obesity in hypertensive patients is associated with dyslipidemia and insulin resistance, both of which are improved by weight control. n-3 Fatty acids have diverse effects on mechanisms underlying atherosclerosis, including a decrease in serum triacylglycerols and an increase in HDL(2) cholesterol.

OBJECTIVE

The objective was to examine whether dietary fish enhances the effects of weight loss on serum lipids, glucose, and insulin in 69 overweight, treated hypertensive patients.

DESIGN

Overweight patients being treated for hypertension were randomly assigned to either a daily fish meal (3.65 g n-3 fatty acids), a weight-loss regimen, the 2 regimens combined, or a control group for 16 wk.

RESULTS

Sixty-three subjects completed the study. Weight decreased by a mean (+/-SEM) of 5.6 +/- 0.8 kg with energy restriction. Weight loss decreased fasting insulin (P = 0.003) and the area under the curve for insulin (P = 0.003) and glucose (P = 0.047) during an oral-glucose-tolerance test. The greatest decrease occurred in the fish + weight-loss group. There was no independent effect of fish on glucose or insulin. Fish increased HDL(2) cholesterol (P = 0.004) and decreased HDL(3) cholesterol (P = 0.026) without altering total, LDL, or HDL cholesterol. Weight loss had no effect on these variables. Fasting triacylglycerols fell significantly with fish consumption (29%) and weight loss (26%). The fish + weight-loss group showed the greatest improvement in lipids: triacylglycerols decreased by 38% (P < 0.001) and HDL(2) cholesterol increased by 24% (P = 0.04) compared with the control group.

CONCLUSIONS

Incorporating a daily fish meal into a weight-loss regimen was more effective than either measure alone at improving glucose-insulin metabolism and dyslipidemia. Cardiovascular risk is likely to be substantially reduced in overweight hypertensive patients with a weight-loss program incorporating fish meals rich in n-3 fatty acids.

LDL size and risk of coronary heart disease in elderly men and women

A predominance of small, dense, low density lipoprotein (LDL) particles has consistently been associated with coronary heart disease (CHD) in young and middle-aged subjects in cross-sectional studies. Recently, 3 prospective, case-control studies showed that decreased LDL size is a predictor of CHD in middle-aged subjects. However, it is not known whether decreased LDL size is mainly associated with premature CHD or whether it continues to play a role in CHD risk at older ages also. We performed a prospective, nested case-control study in 86 subjects (58 nondiabetic and 28 type 2 diabetic) aged 65 to 74 years who were free of myocardial infarction at baseline and who then had a myocardial infarction or CHD death during a 3.5-year follow-up (cases) and in 172 controls matched for sex and diabetes status but who remained free of CHD during follow-up. LDL particle size determined by gradient gel electrophoresis (268.2+/-0.9 versus 268.5+/-0.7 A, P=0.782) and the proportion of subjects with LDL subclass phenotype B (20.9 versus 21. 5, P=0.914) were similar among cases and controls. Furthermore, diastolic blood pressure, total cholesterol, high density lipoprotein cholesterol, triglycerides, apolipoprotein A(1), fasting glucose, fasting insulin, waist-to-hip ratio, and body mass index were not associated with CHD risk. However, smoking and increased systolic blood pressure, apolipoprotein B levels, and the total cholesterol-high density lipoprotein cholesterol ratio were significant predictors of CHD events both in univariate and multivariate analyses. Our findings indicate that LDL size is not a predictor of CHD events in elderly white subjects after controlling for diabetes status.

Independent effects of Apo E phenotype and plasma triglyceride on lipoprotein particle sizes in the fasting and postprandial states

LDL particle sizes and Apo E phenotypes were determined in 212 subjects of whom 51 had angina. LDL diameter was significantly less in subjects with an epsilon2 allele (24.76+/-0.08 vs 24.94+/-0.02 nm, P=0.02), and this was evident for both E2/E3 (24.77+/-0.09 nm) and E2/E4 (24.69+/-0.08 nm) phenotypes. Although there was a negative relation between LDL diameter and plasma triglyceride, the effect of apo E2 was still evident with adjustment for triglyceride. In multiple regression analysis, the significant determinants of LDL diameter were gender (with females having larger particles than males), body mass index, and the presence (or absence) of E2. HDL particle sizes and compositions were determined on fasting samples and, additionally, 5 and 8 hours after a fat-rich meal for 48 coronary heart disease cases and 49 control subjects. Fasting HDL particle sizes were not related to the presence of E2 but were significantly smaller for subjects possessing an epsilon4 allele (8. 09+/-0.08 vs 8.39+/-0.05 nm, P=0.003) and were negatively related to plasma triglyceride. However, the effect of E4 persisted after adjustment for triglyceride. In a multiple regression analysis, the only significant determinant of fasting HDL diameter was the presence (or absence) of E4 with fasting plasma triglyceride just failing to reach significance (P=0.06). There was a postprandial increase in HDL diameter that was less marked in subjects with coronary heart disease. The postprandial increase in HDL diameter was of sufficient magnitude to result in size reclassification of HDL particles. The influence of E4 was also evident at both postprandial time points. Compositional analysis demonstrated that the increase in HDL diameters postprandially could be attributed to triglyceride enrichment, with an accompanying fall in cholesterol ester content. Phospholipid changes postprandially were biphasic with an initial fall followed by a rise in concentration. The increase in triglyceride content was significantly less in those subjects with angina despite an equivalent rise in plasma triglyceride. The present study demonstrates significant, but different, effects of variation in apo E phenotype on the particle sizes of both HDL and LDL. Such effects were still evident with adjustment for differences in plasma triglyceride and suggests that variation in apo E phenotype exerts effects on lipoprotein particle sizes by mechanisms additional to those dependent on change in plasma triglyceride.

LDL particle size distribution is associated with carotid intima-media thickness in healthy 50-year-old men

Results of cross-sectional and prospective studies have suggested that small, dense low-density lipoprotein (LDL) particles predispose to coronary heart disease. We investigated the relationships between plasma concentrations of LDL subfractions and intima-media thickness (IMT) of the common carotid artery (CCA), quantified by B-mode ultrasound, in 94 healthy, 50-year-old men, all of whom were homozygous for the apolipoprotein E3 allele. A novel 3% to 7.5% polyacrylamide gradient gel was developed to provide separation of LDL subfractions with high resolution, as was a procedure to quantify plasma concentrations of these LDL subspecies. The LDL particle size distribution pattern obtained by the gradient gel electrophoresis procedure was in good agreement with the one obtained by a well-established, single-spin density gradient ultracentrifugation technique. LDL-II (particle size, 23.5 to 25.0 nm) was the most abundant subfraction, and its plasma concentration correlated closely with the total LDL cholesterol concentration (r=0. 61, P<0.001) but not with CCA IMT (r=-0.13, NS). In contrast, the plasma concentration of the predominant small, dense LDL particle subfraction (LDL-III; particle size, 22.5 to 23.5 nm) correlated strongly with CCA IMT (r=0.42, P<0.001). In multivariate analysis, the plasma concentration of the LDL-III subfraction contributed significantly to the variation in CCA IMT (R(2)=0.19). When plasma triglycerides and LDL cholesterol were forced into the multivariate model, 10% of the variation in CCA IMT was still accounted for by the LDL-III subfraction. In summary, use of a novel and sensitive gradient gel electrophoresis method for evaluation of LDL heterogeneity provided the basis for demonstrating an independent relation between the plasma concentration of small LDL and IMT of the CCA in healthy, middle-aged men.

Bromocriptine improves glycaemic control and serum lipid profile in obese Type 2 diabetic subjects: a new approach in the treatment of diabetes

Bromocriptine, a potent dopamine D(2) receptor agonist, has been shown to reduce insulin resistance, glucose intolerance and hyperlipidaemia in both numerous animal studies and in Phase II studies. Bromocriptine has been used worldwide for over 20 years to treat Parkinson's disease, macroprolactinoma and other disorders; it has been found to be generally safe. We therefore investigated the possible beneficial effects of Ergoset(R) (Ergo Science Corp.), a new quick release formulation of bromocriptine, on glycaemic control and serum lipid profile in obese Type 2 diabetic subjects in two large Phase III studies. A large, randomised, double-blind placebo-controlled study was conducted in which Ergoset was given once daily at 8 am. (4.8 mg maximum dose) for 24 weeks as adjunctive therapy to sulphonylurea (485 subjects) to obese Type 2 diabetics held on a weight- maintaining diet. Treatment efficacy parameters included change from baseline in glycated haemoglobin A(1c) (HbA(1c)), fasting and post-prandial serum glucose, insulin, triglyceride and free fatty acid levels. Baseline glycated haemoglobin, fasting glucose, insulin, triglyceride and free fatty acid levels did not differ between treatment groups. and on average were 9.4 +/- 0.05%, 222 +/- 2 mg/dl, 24 +/- 1 µU/ml, 248 +/- 11 mg/dl, and 850 +/- 32 µEq/l, respectively. A similarly designed study of Ergoset as monotherapy in Type 2 diabetics (154 subjects) with similar baseline clinical characteristics was conducted. Addition of Ergoset treatment to sulphonylurea reduced percent glycated HbA(1c) by 0.55 (P < 0.0001) (approximately 1.0 for responders, 65% of population), fasting and post-prandial glucose by 23 and 26 mg/dl (P < 0.0002), fasting and post-prandial triglycerides by 72 and 63 mg/dl (P < 0.005) and fasting and post-prandial free fatty acids by 150 and 165 µEq/l (P < 0.05), relative to placebo. Twelve percent of all Ergoset subjects, compared to 3% of placebo subjects, withdrew from the study due to adverse events. The most common events causing withdrawal were nausea, dizziness, asthenia, and rhinitis (representing 4.5, 3.3, 2.0, and 0.8% of the total Ergoset populations, respectively). The incidence of serious adverse events did not differ between Ergoset- (3.4%) and placebo- (4.3%) treated subjects. Ergoset as monotherapy also improved glycaemic control (0.56 HbA(1c) decrease relative to placebo after 24 weeks of treatment; P < 0.02). Once daily Ergoset treatment improves glycaemic control and serum lipid profile and is well-tolerated in obese Type 2 diabetics.

Pleiotropic genetic effects on LDL size, plasma triglyceride, and HDL cholesterol in families

The interrelationships among low density lipoprotein (LDL) particle size, plasma triglyceride (TG), and high density lipoprotein cholesterol (HDL-C) are well established and may involve underlying genetic influences. This study evaluated common genetic effects on LDL size, TG, and HDL-C by using data from 85 kindreds participating in the Genetic Epidemiology of Hypertriglyceridemia (GET) Study. A multivariate, maximum likelihood-based approach to quantitative genetic analysis was used to estimate the additive effects of shared genes and shared, unmeasured nongenetic factors on variation in LDL size and in plasma levels of TG and HDL-C. A significant (P<0.001) proportion of the variance in each trait was attributable to the additive effects of genes. Maximum-likelihood estimates of heritability were 0.34 for LDL size, 0.41 for TG, and 0.54 for HDL-C. Significant (P<0.001) additive genetic correlations (rho(G)), indicative of the shared additive effects of genes on pairs of traits, were estimated between all 3 trait pairs: for LDL size and TG rho(G)=-0.87, for LDL size and HDL-C rho(G)=0.65, and for HDL-C and TG rho(G)=-0.54. A similar pattern of significant environmental correlations between the 3 trait pairs was also observed. These results suggest that a large proportion of the well-documented correlations in LDL size, TG, and HDL-C are likely attributable to the influence of the same gene(s) in these families. That is, the gene(s) that may contribute to decreases in LDL size also contribute significantly to higher plasma levels of TG and lower plasma levels of HDL-C. These relationships may be useful in identifying genes responsible for the associations between these phenotypes and susceptibility to cardiovascular disease in these families.

Purple grape juice improves endothelial function and reduces the susceptibility of LDL cholesterol to oxidation in patients with coronary artery disease

BACKGROUND

In vitro, the flavonoid components of red wine and purple grape juice are powerful antioxidants that induce endothelium-dependent vasodilation of vascular rings derived from rat aortas and human coronary arteries. Although improved endothelial function and inhibition of LDL oxidation may be potential mechanisms by which red wine and flavonoids reduce cardiovascular risk, the in vivo effects of grape products on endothelial function and LDL oxidation have not been investigated. This study assessed the effects of ingesting purple grape juice on endothelial function and LDL susceptibility to oxidation in patients with coronary artery disease (CAD).

METHODS AND RESULTS

Fifteen adults with angiographically documented CAD ingested 7.7+/-1.2 mL. kg(-1). d(-1) of purple grape juice for 14 days. Flow-mediated vasodilation (FMD) was measured using high-resolution brachial artery ultrasonography. Susceptibility of LDL particles to oxidation was determined from the rate of conjugated diene formation after exposure to copper chloride. At baseline, FMD was impaired (2.2+/-2. 9%). After ingestion of grape juice, FMD increased to 6.4+/-4.7% (P=0.003). In a linear regression model that included age, artery diameter, lipid values, and use of lipid-lowering and antioxidant therapies, the effect of grape juice on FMD remained significant (mean change 4.2+/-4.4%, P<0.001). After ingestion of grape juice, lag time increased by 34.5% (P=0.015).

CONCLUSIONS

Short-term ingestion of purple grape juice improves FMD and reduces LDL susceptibility to oxidation in CAD patients. Improved endothelium-dependent vasodilation and prevention of LDL oxidation are potential mechanisms by which flavonoids in purple grape products may prevent cardiovascular events, independent of alcohol content.

Potential new cardiovascular risk factors: left ventricular hypertrophy, homocysteine, lipoprotein(a), triglycerides, oxidative stress, and fibrinogen

The 1996 Bethesda Conference acknowledged left ventricular hypertrophy, hyperhomocysteinemia, lipoprotein(a) excess, hypertriglyceridemia, oxidative stress, and hyperfibrinogenemia as possible new cardiac risk factors. This review summarizes the current literature that supports these conditions as cardiac risk factors. Left ventricular hypertrophy is an independent risk factor for vascular disease. Improvement or progression of left ventricular hypertrophy influences subsequent cardiovascular complications. Clinical trials are under way to assess the potential benefit of decreasing homocysteine levels. The role of lipoprotein(a) excess in vascular disease is controversial. The atherogenic potential of lipoprotein(a) seems to be neutralized by effective reduction of low-density lipoprotein cholesterol levels. Increasing evidence supports an independent role of hypertriglyceridemia in cardiovascular disease and a possible clinical benefit from decreasing triglyceride levels. Among antioxidant micronutrients, supplementation with vitamin E has been shown to be beneficial in primary and secondary prevention studies. Data supporting the use of other antioxidants are much weaker. Preliminary evidence suggests that reducing fibrinogen levels in patients with high baseline levels and coronary disease may be beneficial. Despite the potential relation between new risk factors and cardiovascular disease, routine clinical application of these conditions as cardiovascular risk factors would be premature. Evidence is needed that these conditions extend prognostic ability beyond conventional risk factors and that modification of these conditions can reduce the risk for cardiovascular events.

Identification and treatment of hypertriglyceridemia as a risk factor for coronary heart disease

Recent publications, including new population-based studies and a meta-analysis of prospective, population-based studies, provide strong evidence for an elevated triglyceride level as an independent risk factor for coronary heart disease. Pathophysiologic relationships between elevated triglyceride levels and both reduced high-density lipoprotein levels and an increase in the proportion of low density lipoproteins that are small and dense support the epidemiologic data, and suggest that an elevated triglyceride level should constitute a target for lipid-lowering therapy. There are no clear recommendations for management of patients with hypertriglyceridemia available in the current treatment guidelines. Treatment options include life-style measures and, if drug therapy is required, nicotinic acid, fibrates, more potent 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins), or combination therapy with statin plus fibrate or nicotinic acid.

LDL size in African Americans, Hispanics, and non-Hispanic whites : the insulin resistance atherosclerosis study

The prevalence of cardiovascular disease (CVD) and atherosclerosis varies among several minority ethnic groups in the United States. Recently, small, dense low density lipoprotein (LDL) particle size has been recognized as a risk factor for CVD. We examined LDL size as a possible explanation for differences in CVD rates in 1571 subjects from the Insulin Resistance Atherosclerosis Study (IRAS), a multiethnic study of insulin resistance and cardiovascular risk factors. LDL size (A) was significantly different by ethnic group (African Americans 262.1+/-0.6, Hispanics 257.6+/-0.6, and non-Hispanic whites 259.2+/-0.4, P<0.001). Ethnic differences in LDL size continued to be statistically significant after adjustment for upper body adiposity, insulin resistance, and glucose tolerance status. However, after further adjustment for other cardiovascular risk factors, especially ethnic differences in triglyceride and high density lipoprotein (HDL) cholesterol levels, the ethnic differences in LDL size were markedly attenuated and in general no longer statistically significant. The relation of triglyceride, HDL cholesterol, insulin resistance, and adiposity to LDL size in each ethnic group was similar. LDL size differs by ethnic group, which is independent of obesity or insulin resistance. These ethnic differences appear to be due to ethnic variations in dyslipidemia (especially differences in triglyceride levels); ethnic differences in LDL size are not consistent with previously reported ethnic dissimilarities in CVD or atherosclerosis.

Elevated serum triglyceride levels and long-term mortality in patients with coronary heart disease: the Bezafibrate Infarction Prevention (BIP) Registry

BACKGROUND

The association between elevated blood triglyceride levels and subsequent mortality risk in patients with established coronary heart disease (CHD) has been investigated rarely. The aim of the present study was to investigate this association.

METHODS AND RESULTS

We evaluated mortality over a mean follow-up time of 5. 1 years among 9033 male and 2499 female CHD patients who were screened for participation in the Bezafibrate Infarction Prevention (BIP) Study. A stepwise increase in mortality with increasing serum triglyceride levels was observed in patients with desirable or elevated serum total cholesterol levels and in patients with either desirable or abnormally low HDL cholesterol levels. Multivariate adjustment for factors other than HDL cholesterol yielded a slightly increased adjusted mortality risk with a 1-natural-log-unit elevation of triglyceride levels in men (hazard ratio [HR] 1.14, 95% CI 1.00 to 1.30) and women (HR 1.37, 95% CI 1.04 to 1.88). Excess covariate-adjusted risk was noted among patients with elevated total and LDL cholesterol and in women with HDL cholesterol levels >45 mg/dL. After additional adjustment for HDL cholesterol, the risk of mortality with a 1-natural-log-unit elevation of triglycerides declined in men (HR 1.09, 95% CI 0.94 to 1.26) and in women (HR 1.10, 95% CI 0.80 to 1.50). A trend for increased mortality risk remained in patients with elevated total and LDL cholesterol and in women with HDL cholesterol >45 mg/dL.

CONCLUSIONS

Elevated triglyceride levels were associated with a small, independent increased mortality risk in CHD patients. This risk may be increased among subgroups of patients with elevated total cholesterol and LDL cholesterol levels.

Acute changes in serum lipids and lipoprotein subclasses in triathletes as assessed by proton nuclear magnetic resonance spectroscopy

Exercise is associated with changes in lipids that may protect against coronary heart disease (CHD). In this study of 28 triathletes, we analyzed acute changes in serum lipid and lipoprotein concentrations after completion of the 1995 World Championship Hawaii Ironman Triathlon. With standard laboratory assays, we demonstrate significant decreases in total cholesterol, VLDL cholesterol, ApoB100, and Lp(a). Total HDL cholesterol increased significantly immediately after the race. With a novel proton NMR spectroscopy assay, we demonstrate that smaller diameter LDL particles, corresponding to small, dense LDL, declined by 62%. Moreover, larger HDL subclasses, whose levels are inversely associated with CHD, increased significantly by 11%. Smaller HDL subclasses, which have been directly associated with CHD in some studies, acutely decreased by 16%. Therefore, exercise not only acutely induces changes in lipoprotein concentrations among the standard species in a manner that favorably affects CHD risk, but also induces favorable changes in specific lipoprotein subclass size distribution that also may alter CHD risk independently of the total lipoprotein serum concentration.

Long-chain n-3 polyunsaturated fatty acids and triacylglycerol metabolism in the postprandial state

Elevated plasma triacylglycerol (TG; triglyceride) concentrations, especially in the postprandial state, have been associated with an increased risk of coronary heart disease (CHD). Postprandial lipemia represents a complex series of reactions which occur following the ingestion of a meal containing fat and is associated with a number of adverse metabolic events including the production of atherogenic chylomicron remnants, the formation of the highly atherogenic small dense low density lipoprotein particles, a reduction in the concentration of the cardioprotective high density lipoprotein fraction and the activation of coagulation factor VII. Fish oils are a rich source of the long-chain n-3 polyunsaturated fatty acids (PUFA), eicosapentaenoic acid and docosahexaenoic acid. Long chain n-3 PUFA are effective hypotriglyceridemic agents, lowering both fasting and postprandial TG concentrations. There is a large body of evidence which shows that n-3 PUFA reduces plasma TG concentrations through reduced endogenous very low density lipoprotein production. This in turn may account for the reduced postprandial lipemic response following n-3 PUFA supplementation. However, this does not preclude a contribution of enhanced chylomicron clearance, which may be mediated through altered chylomicron size, structure or chemical composition, or altered lipoprotein lipase metabolism in terms of enzyme concentration, activity, or affinity for chylomicrons. However the precise biochemical nature of this effect remains to be established. The reduction of postprandial plasma TG concentrations by n-3 PUFA may partly explain why n-3 PUFA intake is inversely related to CHD mortality.

The fatty acid distribution in low density lipoprotein in diabetes

Atherosclerosis is commonly found in diabetes. There is an association between small dense low density lipoprotein (LDL) phenotype, which is more prevalent in the diabetic state, and atherosclerosis. Small dense LDL is more easily oxidised and it is possible that fatty acid compositional changes, particularly an increase in polyunsaturated fatty acids, could underlie this association. However, there is little information about fatty acids in the different LDL phenotypes in the literature. This study examined LDL subfraction composition in 18 non-insulin-dependent diabetic (NIDDM) patients and 11 control subjects. LDL was isolated and fractionated into LDL 1, 2 and 3 by density gradient ultracentrifugation. NIDDM patients had significantly more fatty acids in all LDL subfractions than control subjects (P<0.01). Palmitic and linoleic acid were significantly greater in all subfractions in the diabetic patients compared to control subjects (P<0.01) and palmitoleic and oleic acids were also greater in LDL1 and LDL2 in diabetic patients (P<0.01). We conclude that in NIDDM fatty acids are increased in all LDL subfractions and this may be the reason for the increased atherosclerosis in diabetes irrespective of phenotype.

Small, dense low-density lipoprotein subclass pattern B: issues for the clinician

A large portion of coronary artery disease (CAD) can be attributed to disorders of lipoprotein metabolism. However, these disorders are a complex interaction of genetic susceptibility and environmental interaction. The most common disorder of lipoprotein metabolism contributing to CAD is the Small, Dense Low-Density Lipoprotein Pattern B disorder, also known as the Atherogenic Lipoprotein Profile (ALP), which consists of multiple metabolic disorders. This disorder is an independent risk factor for CAD and in patients with established CAD, identifies a subgroup with a twofold greater rate of arteriographic progression compared with CAD patients without this disorder. Treatment of the disorder is specific to lifestyle and some pharmacologic agents. The most effective treatments are often the least expensive.

Diagnosis, prediction, and natural course of HIV-1 protease-inhibitor-associated lipodystrophy, hyperlipidaemia, and diabetes mellitus: a cohort study

BACKGROUND

The prevalence and severity of lipodystrophy syndrome with long-term therapy for HIV-1 infection that includes a protease inhibitor is unknown. We studied the natural course of the syndrome to develop diagnostic criteria and identifying markers that predict its severity.

METHODS

We assessed 113 patients who were receiving HIV-1 protease inhibitors (mean 21 months) and 45 HIV-1-infected patients (28 with follow-up) never treated with a protease inhibitor. Lipodystrophy was assessed by questionnaire (including patients' rating of severity), physical examination, and dual-energy x-ray absorptiometry. Body composition and fasting lipid and glycaemic variables were compared with data obtained 8 months previously. Oral glucose tolerance was investigated.

FINDINGS

There was 98% concordance between patients' reports of the presence or absence of lipodystrophy (reported by 83% of protease-inhibitor recipients and 4% of treatment-naïve patients; p=0.0001) and physical examination. Patients' ratings of lipodystrophy were significantly associated with declining total body fat (p=0.02). Lower body fat was independently associated with longer duration of protease-inhibitor therapy and lower bodyweight before therapy, and more severe lipodystrophy was associated with higher previous (p < 0.03) and current (p < or = 0.01) triglyceride and C-peptide concentrations, and less peripheral and greater central fat (p=0.005 and 0.09, respectively). Body fat declined a mean 1.2 kg over 8 months in protease-inhibitor recipients (p=0.05). The prevalence of hyperlipidaemia remained stable over time (74% of treated patients vs 28% of naïve patients; p=0.0001). Impaired glucose tolerance occurred in 16% of protease-inhibitor recipients and diabetes mellitus in 7%; in all but three patients these abnormalities were detected on 2 h post-glucose load values.

INTERPRETATION

Diagnosis and rating severity of lipodystrophy is aided by the combination of physical examination, patient's rating, and measurement of body fat, fasting triglycerides, and C-peptide. Weight before therapy, fasting triglyceride, and C-peptide concentrations early in therapy, and therapy duration seem to predict lipodystrophy severity. Lipodystrophy was common and progressive after almost 2 years of protease inhibitor therapy, but was not usually severe. Hyperlipidaemia and impaired glucose tolerance were also common.

Role of fibrates in the management of hypertriglyceridemia

Elevated plasma triglyceride levels are increasingly recognized as a risk factor for cardiovascular disease. Fibric acid derivatives (fibrates) substantially decrease triglyceride levels and have been demonstrated to decrease clinical cardiovascular events in some trials. Ongoing research will elucidate the molecular mechanisms by which fibrates modify lipoprotein metabolism, clarify their use in combination with 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins), and determine their role in the prevention of cardiovascular events.

Epidemiology of hypertriglyceridemia and cardiovascular disease

Epidemiologic studies provide increasing evidence that hypertriglyceridemia is a risk factor for cardiovascular disease. A meta-analysis of 17 population-based studies of triglyceride levels and cardiovascular disease identified a 76% increase in cardiovascular disease risk in women and a 31% increase in men associated with a 1 mmol/L increase in triglyceride levels. Additional epidemiologic studies have shown that plasma triglyceride levels and low-density lipoprotein particle size predict subsequent coronary artery disease. Taken together, the existing epidemiologic data may help identify a group of patients who may benefit from interventions aimed at decreasing triglyceride levels associated with an increased risk of cardiovascular disease.

Familial predisposition and susceptibility to the effect of other risk factors for myocardial infarction

STUDY OBJECTIVES

To assess if familial predisposition to myocardial infarction (MI) is an indicator of increased susceptibility to the effect of other established risk factors. The study assessed whether a family history of MI modifies the effect of arterial blood pressure, plasma cholesterol, high and low density lipoprotein cholesterol, % triglycerides, diabetes mellitus, body mass index, height, smoking habits, alcohol intake, physical activity level, and educational level on the incidence of MI.

DESIGN

Prospective population based cohort study of cardiovascular risk and risk factors with follow up of MI by record linkage with the Cause of Death Register and The National Hospital Discharge Register until 1994.

SETTING

The Copenhagen Centre for Prospective Population Studies, where data from three Danish studies are integrated.

PARTICIPANTS

Subjects were 24,664 people aged 20-93, examined between 1976 and 1987.

MAIN RESULTS

A total of 1763 new cases of MI occurred during 293,559 person years of observation. All risk factors, including family history of MI reported by 4012 subjects, were, as expected, associated with incidence of MI. With a few inconsistent exceptions we found no significant interactions between family history of MI and cardiovascular risk factors in their effect on MI.

CONCLUSIONS

The familial predisposition to MI does not consistently modify the effect of other risk factors on the risk of MI. However, subjects with a family history of MI may still be regarded as an appropriate target group for screening for cardiovascular risk and intervention against other risk factors.

Evidence for a new pathophysiological mechanism for coronary artery disease regression: hepatic lipase-mediated changes in LDL density

BACKGROUND

Small, dense LDL particles are associated with coronary artery disease (CAD) and predict angiographic changes in response to lipid-lowering therapy. Intensive lipid-lowering therapy in the Familial Atherosclerosis Treatment Study (FATS) resulted in significant improvement in CAD. This study examines the relationship among LDL density, hepatic lipase (HL), and CAD progression, identifying a new biological mechanism for the favorable effects of lipid-altering therapy.

METHODS AND RESULTS

Eighty-eight of the subjects in FATS with documented coronary disease, apolipoprotein B levels >/=125 mg/dL, and family history of CAD were selected for this study. They were randomly assigned to receive lovastatin (40 mg/d) and colestipol (30 g/d), niacin (4 g/d) and colestipol, or conventional therapy with placebo alone or with colestipol in those with elevated LDL cholesterol levels. Plasma hepatic lipase (HL), lipoprotein lipase, and LDL density were measured when subjects were and were not receiving lipid-lowering therapy. LDL buoyancy increased with lovastatin-colestipol therapy (7.7%; P<0.01) and niacin-colestipol therapy (10.3%; P<0.01), whereas HL decreased in both groups (-14% [P<0.01] and -17% [P<0.01] with lovastatin-colestipol and niacin-colestipol, respectively). Changes in LDL buoyancy and HL activity were associated with changes in disease severity (P<0.001). In a multivariate analysis, an increase in LDL buoyancy was most strongly associated with CAD regression, accounting for 37% of the variance of change in coronary stenosis (P<0.01), followed by reduction in apolipoprotein Bl (5% of variance; P<0.05).

CONCLUSIONS

These studies support the hypothesis that therapy-associated changes in HL alter LDL density, which favorably influences CAD progression. This is a new and potentially clinically relevant mechanism linking lipid-altering therapy to CAD improvement.

A genome search identifies major quantitative trait loci on human chromosomes 3 and 4 that influence cholesterol concentrations in small LDL particles

Small, dense LDL particles are associated with increased risk of cardiovascular disease. To identify the genes that influence LDL size variation, we performed a genome-wide screen for cholesterol concentrations in 4 LDL size fractions. Samples from 470 members of randomly ascertained families were typed for 331 microsatellite markers spaced at approximately 15 cM intervals. Plasma LDLs were resolved by using nondenaturing gradient gel electrophoresis into 4 fraction sizes (LDL-1, 26.4 to 29.0 nm; LDL-2, 25.5 to 26.4 nm; LDL-3, 24.2 to 25.5 nm; and LDL-4, 21.0 to 24.2 nm) and cholesterol concentrations were estimated by staining with Sudan Black B. Linkage analyses used variance component methods that exploited all of the genotypic and phenotypic information in the large extended pedigrees. In multipoint linkage analyses with quantitative trait loci for the 4 fraction sizes, only LDL-3, a fraction containing small LDL particles, gave peak multipoint log10 odds in favor of linkage (LOD) scores that exceeded 3.0, a nominal criterion for evidence of significant linkage. The highest LOD scores for LDL-3 were found on chromosomes 3 (LOD=4.1), 4 (LOD=4.1), and 6 (LOD=2.9). In oligogenic analyses, the 2-locus LOD score (for chromosomes 3 and 4) increased significantly (P=0.0012) to 6.1, but including the third locus on chromosome 6 did not significantly improve the LOD score (P=0.064). Thus, we have localized 2 major quantitative trait loci that influence variation in cholesterol concentrations of small LDL particles. The 2 quantitative trait loci on chromosomes 3 and 4 are located in regions that contain the genes for apoD and the large subunit of the microsomal triglyceride transfer protein, respectively.

A very low-fat diet is not associated with improved lipoprotein profiles in men with a predominance of large, low-density lipoproteins

BACKGROUND

We found previously that men with a predominance of large LDL particles (phenotype A) consuming high-fat diets (40-46% fat) show less lipoprotein benefits of low-fat diets (20-24% fat) than do men with a high-risk lipoprotein profile characterized by a predominance of small LDL (phenotype B). Furthermore, one-third of men with phenotype A consuming a high-fat diet converted to phenotype B with a low-fat diet.

OBJECTIVE

We investigated effects of further reduction in dietary fat in men with persistence of LDL subclass phenotype A during both high- and low-fat diets.

DESIGN

Thirty-eight men who had shown phenotype A after 4-6 wk of both high- and low-fat diets consumed for 10 d a 10%-fat diet (2.7% saturates) with replacement of fat with carbohydrate and no change in cholesterol content or ratio of polyunsaturates to saturates.

RESULTS

In 26 men, phenotype A persisted (stable A group) whereas 12 converted to phenotype B (change group). LDL cholesterol did not differ from previous values for 20-24%-fat diets in either group, whereas in the change group there were higher concentrations of triacylglycerol and apolipoprotein B; greater mass of HDL, large LDL-I, small LDL-III and LDL-IV, and HDL3; lower concentrations of HDL cholesterol, apolipoprotein A-I; and lower mass of large LDL-I and HDL2.

CONCLUSIONS

There is no apparent lipoprotein benefit of reduction in dietary fat from 20-24% to 10% in men with large LDL particles: LDL-cholesterol concentration was not reduced, and in a subset of subjects there was a shift to small LDL along with increased triacylglycerol and reduced HDL-cholesterol concentrations.

Low-density lipoprotein particle size is inversely related to plasminogen activator inhibitor-1 levels. The Insulin Resistance Atherosclerosis Study

High levels of plasminogen activator inhibitor-1 (PAI-1) and preponderance of small dense low-density lipoproteins (LDL) have both been associated with atherosclerotic disease and with the insulin resistance syndrome (IRS). In vitro studies have shown a stimulatory effect of various lipoproteins on PAI-1 release from different cells, including endothelial cells and adipocytes. The authors sought to investigate the relation of PAI-1 to LDL particle size in a large tri-ethnic population (n=1549) across different states of glucose tolerance. LDL size was determined by gradient gel electrophoresis, and PAI-1 was measured by a 2-site immunoassay, sensitive to free PAI-1. PAI-1 was inversely related to LDL size in the overall population (r=-0.21, P<0.0001), independent of gender and ethnicity. However, the authors found a significant interaction with glucose tolerance status (P=0.035). In univariate analysis, the association between PAI-1 and LDL size was most pronounced in subjects with normal glucose tolerance (NGT, r=-0.22, P<0.0001) and weaker in impaired glucose tolerance (IGT, r=-0.12, P=0.03) and type-2 diabetes (r=-0.10, P=0.02). After adjustment for demographic variables and metabolic variables known to influence PAI-1 levels (triglyceride and insulin sensitivity), a significant inverse relation of LDL size to PAI-1 levels was only present in NGT (P=0. 023). In subjects with IGT or overt diabetes, who usually have elevated PAI-1 levels, additional factors other than LDL size seem to contribute more importantly to PAI-1 levels. The demonstrated inverse relation of LDL size and PAI-1 levels provides one possible explanation for the atherogeneity of small dense LDL particles.

Lipoprotein atherogenicity: an overview of current mechanisms

Raised serum cholesterol does not adequately explain the increased risk of CHD within populations or the relationship between diet and CHD. Nevertheless, the principal transport vehicle of cholesterol in the circulation, LDL, must still be regarded as the most atherogenic lipoprotein species, but not because of its contribution to serum cholesterol. The atherogenic potential of LDL in the majority of individuals arises from an increase in the number of small dense LDL particles and not from its cholesterol content per se. There is now a wealth of evidence from cross-sectional and prospective studies to show that LDL particle size is significantly associated with CHD and predictive of increased coronary risk. Moreover, there are a number of credible mechanisms to link small dense LDL with the atherogenic process. The rate of influx of serum lipoproteins into the arterial wall is a function of particle size, and will thus be more rapid for small dense LDL. Components of the extracellular tissue matrix in the intima, most notably proteoglycans, selectively bind small dense LDL with high affinity, sequestering this lipoprotein in a pro-oxidative environment. The oxidation of LDL promotes the final deposition of cholesterol in the arterial wall, and numerous studies have shown small dense LDL to be more susceptible to oxidative modification than its larger and lighter counterparts. An increase in the number of small dense LDL particles may originate from a defect in the metabolism of triacylglycerol-rich lipoproteins. One mechanism may involve the overproduction and increased residence time of large triacylglycerol-rich VLDL in the postprandial phase, a situation thought to arise through pathways of insulin resistance.

Dietary carbohydrates and triacylglycerol metabolism

There is a growing body of scientific evidence which demonstrates that plasma triacylglycerol (TAG) concentration, especially in the postprandial state, is an important risk factor in relation to the development of CHD. Postprandial hypertriacylglycerolaemia is associated with a number of adverse metabolic risk factors, including the preponderance of small dense LDL, low HDL-cholesterol concentrations and elevated factor VII activity. Traditionally, a low-fat high-carbohydrate diet was used to prevent CHD because it effectively reduces plasma cholesterol concentrations, but this dietary regimen increases plasma TAG concentrations and reduces HDL-cholesterol concentrations. There is substantial epidemiological evidence which demonstrates that high plasma TAG and low plasma HDL concentrations are associated with an increased risk of CHD. Thus, there is reason for concern that the adverse effects of low-fat high-carbohydrate diets on TAG and HDL may counteract or negate the beneficial effect of reducing LDL-cholesterol concentrations. Although there have been no prospective studies to investigate whether reduced fat intake has an adverse effect on CHD, there is strong epidemiological evidence that reducing total fat intake is not protective against CHD. On the other hand, high-fat diets predispose to obesity, and central obesity adversely affects TAG metabolism. There is substantial evidence that in free-living situations low-fat high-carbohydrate diets lead to weight loss, which in turn will correct insulin resistance and plasma TAG metabolism. Clearly there is a need for prospective studies to resolve the issue as to whether low-fat high-carbohydrate diets play an adverse or beneficial role in relation to the development of CHD.

Linkage of low-density lipoprotein size to the lipoprotein lipase gene in heterozygous lipoprotein lipase deficiency

Small low-density lipoprotein (LDL) particles are a genetically influenced coronary disease risk factor. Lipoprotein lipase (LpL) is a rate-limiting enzyme in the formation of LDL particles. The current study examined genetic linkage of LDL particle size to the LpL gene in five families with structural mutations in the LpL gene. LDL particle size was smaller among the heterozygous subjects, compared with controls. Among heterozygous subjects, 44% were classified as affected by LDL subclass phenotype B, compared with 8% of normal family members. Plasma triglyceride levels were significantly higher, and high-density lipoprotein cholesterol (HDL-C) levels were lower, in heterozygous subjects, compared with normal subjects, after age and sex adjustment. A highly significant LOD score of 6.24 at straight theta=0 was obtained for linkage of LDL particle size to the LpL gene, after adjustment of LDL particle size for within-genotype variance resulting from triglyceride and HDL-C. Failure to adjust for this variance led to only a modest positive LOD score of 1.54 at straight theta=0. Classifying small LDL particles as a qualitative trait (LDL subclass phenotype B) provided only suggestive evidence for linkage to the LpL gene (LOD=1. 65 at straight theta=0). Thus, use of the quantitative trait adjusted for within-genotype variance, resulting from physiologic covariates, was crucial for detection of significant evidence of linkage in this study. These results indicate that heterozygous LpL deficiency may be one cause of small LDL particles and may provide a potential mechanism for the increase in coronary disease seen in heterozygous LpL deficiency. This study also demonstrates a successful strategy of genotypic specific adjustment of complex traits in mapping a quantitative trait locus.

Treating patients with hypertriglyceridaemia saves lives: triglyceride revisited

The statin trials in secondary and primary prevention have shown that lowering LDL cholesterol produces a reduction in coronary event rates of around 35%. The most common dyslipidaemia in MI survivors is mixed hyperlipidaemia rather than hypercholesterolaemia. New evidence from VA-HIT and BIPS suggests that relatively low levels of triglyceride may be associated with a significant increase in coronary risk. In patients with established coronary disease, treatment with a fibrate that lowers triglyceride and raises HDL cholesterol, but which has little effect on LDL cholesterol, slows the rate of progression of coronary lesions. In hypertriglyceridaemic patients who have survived an MI or who have angina pectoris, fibrate treatment reduced the incidence of fatal and non-fatal MI by 40% (p = 0.03) (BIPS). In patients with coronary artery disease, who have low levels of HDL, fibrate treatment reduced the incidence of fatal and non-fatal MI by 22% (p = 0.006) (VA-HIT). These patients represent around 25% of the post-MI population. Work in progress will shortly define the effect of fibrate treatment on coronary event rate in patients with peripheral vascular disease and Type 2 diabetes.

Diabetic dyslipidemia

Usual risk factors for coronary artery disease account for only 25-50% of increased atherosclerotic risk in diabetes mellitus. Other obvious risk factors are hyperglycemia and dyslipidemia. However, hyperglycemia is a very late stage in the sequence of events from insulin resistance to frank diabetes, whereas lipoprotein abnormalities are manifested during the largely asymptomatic diabetic prodrome and contribute substantially to the increased risk of macrovascular disease. The insulin-resistant diabetes course affects virtually all lipids and lipoproteins. Chylomicron and very-low-density lipoprotein (VLDL) remnants accumulate, and triglycerides enrich high-density lipoprotein (HDL) and low-density lipoprotein (LDL), leading to high levels of potentially atherogenic particles and low levels of HDL cholesterol. Hyperglycemia eventually impairs removal of triglyceride-rich lipoproteins, the accumulation of which accentuates hypertriglyceridemia. As triglycerides increase-still within the so-called normal range-abnormalities in HDL and LDL became more apparent. Thus, when triglycerides are >200 mg/dL, LDL particles are small and dense (when they are <90 mg/dL, the particles are of the large, buoyant variety). The atherogenicity of small, dense LDL particles is attributed to their increased susceptibility to oxidation, but in many patients they may be a marker for insulin resistance or the presence of atherogenic VLDL. Hypertriglyceridemia is associated with atherosclerosis because (1) it is a marker for insulin resistance and atherogenic metabolic abnormalities; and (2) the small size of triglyceride-enriched lipoproteins enables them to infiltrate the blood vessel wall where they are oxidized, bind to receptors on macrophages, and ingested, leading to the development of the atherosclerotic lesion. Various studies (primary prevention with gemfibrozil: Helsinki Heart Study; secondary prevention with simvastatin and pravastatin: Scandinavian Simvastatin Survival Study [4S] and Cholesterol and Recurrent Events [CARE], respectively) have demonstrated that lipid-lowering therapy in type 2 diabetes is effective in decreasing the number of cardiac events. Risk reduction was 22% to 50% (statins) and approximately 65% (fibrate) relative to placebo. It was also noted (in 4S and CARE) that the risk of major coronary events in untreated diabetic patients was 1.5-1.7-fold greater than in untreated nondiabetic patients. Although gemfibrozil (fibric acid derivative) is more effective in decreasing triglycerides and increasing HDL cholesterol in diabetic patients than the statins, it does not change and may even increase LDL-cholesterol levels (fenofibrate may be an exception, decreasing LDL cholesterol by 20-25% in some studies). However, gemfibrozil does increase LDL particle size. Nevertheless, the statins are the current lipid-lowering drugs of choice because the change in LDL-cholesterol-to-HDL-cholesterol ratio is better than with gemfibrozil. Moreover, the diabetic patient may be more likely to benefit from statin therapy than the nondiabetic patient. It should be noted that, in theory, nicotinic acid can correct or improve all lipid or lipoprotein abnormalities in patients with type 2 diabetes. Unfortunately, it is relatively contraindicated because it causes insulin resistance and may precipitate or aggravate hyperglycemia (in addition to its other well-known side effects such as flushing, gastric irritation, development of hepatotoxicity, and hyperuricemia). It is unknown at present whether newer formulations such as once-daily Niaspan may be better tolerated in diabetes. In any case, most patients with type 2 diabetes have risk factors for coronary artery disease and qualify for aggressive LDL cholesterol-lowering therapy. At the same time, it is presently unknown whether improved glycemic control decreases coronary artery disease risk in such patients.

The atherogenic significance of an elevated plasma triglyceride level

The importance of hypertriglyceridemia as an independent predictor of coronary artery disease (CAD) remains unsettled. Hypertriglyceridemia, with or without associated hypercholesterolemia, occurs more frequently in premature CAD subjects than does hypercholesterolemia alone. With univariate analysis, most studies show a positive correlation between plasma triglyceride (TG) level and risk for CAD, but with multivariate analysis plasma TG level is no longer an independent risk factor except in women and diabetics. Prospective studies have shown that subjects with a high LDL/HDL cholesterol ratio and a high plasma TG level have the highest risk for CAD. Hypertriglyceridemia signifies the presence of excess triglyceride-rich lipoproteins (TRL), including chylomicrons, VLDL, and their remnants. The question then becomes one of whether TRL are directly or indirectly involved in atherogenesis. TRL were thought to be too big to infiltrate the arterial wall, and histopathological studies have shown cholesterol but not triglyceride accumulation in the atherosclerotic plaque. However, there was a recent demonstration of undegraded VLDL and IDL in atherosclerotic plaques. Larger TRL may undergo hydrolysis on the arterial surface to become smaller particles before entry into the intima. Possible cellular pathways for the uptake of TRL by macrophages have been described. The smaller TRL (Sf 20-60), including postprandial chylomicron remnants, are believed to be the most atherogenic of all TRL particles. Because large amounts of TRL are produced in the postprandial period, atherogenesis involving TRL may be primarily a postprandial phenomenon. Once in the intima, TG may undergo hydrolysis, releasing free fatty acids and mono- and diacyl glycerol, accounting for the dearth of TG in atherosclerotic lesions. Particle for particle, VLDL delivers five times as much cholesterol as LDL does to the macrophage.

Did grandma give you heart disease? The new battle against coronary artery disease

Atherosclerosis/coronary artery disease (CAD) is largely a result of genetically linked dyslipidemias that can often be identified in clinical practice. Expression of these genetic traits is highly individual and can be affected by environmental factors such as diet and exercise. By understanding the heterogeneity of CAD, it becomes clear that all patients cannot be optimally managed with the same therapeutic regimen. Whereas elevated low-density lipoprotein (LDL) cholesterol is strongly correlated with CAD risk, reduction of LDL cholesterol alone is not an adequate strategy in many cases. Patients with the small, dense LDL of the atherogenic lipoprotein profile (pattern B) experience a 3-fold increased risk of CAD, and pattern B is also correlated with the development of type 2 diabetes. Likewise, elevated lipoprotein(a) increases atherosclerotic risk, particularly in the presence of other risk factors, and is predictive of CAD risk in both women and men. Recent data show that the routine lipid profile--total cholesterol, triglycerides, LDL cholesterol, and high-density lipoprotein (HDL) cholesterol--does not detect the most common inherited dyslipidemias. Newer, more sophisticated tests, such as gradient gel electrophoresis, can detect disease-relevant lipidemic details, e.g., LDL subclass pattern, LDL particle diameter, and LDL subregions. Although these testing procedures are more expensive, their cost must be weighed against the potential lifelong cost of sometimes expensive drug treatment that may be avoided based on the results of such tests. Thus, by attending to the implications of family history, the interactions of genetic, metabolic, and environmental factors, and utilizing more targeted testing procedures, physicians can match the patient's disorder with specifically effective therapy while maintaining a cost-effective approach to disease management.

Measurement of LDL particle size in whole plasma and serum by high performance gel-filtration chromatography using a fluorescent lipid probe

We have recently described a technique for measuring LDL size by high performance gel-filtration chromatography (HPGC) with UV detection (Scheffer et al., Clin Chem 1997;43:1904–12). A drawback of this method is the necessity of LDL isolation before chromatography. We now describe a modification of this method based on selective detection of lipoproteins by postcolumn labeling with parinaric acid, a fluorescent lipid probe. Measuring the size of isolated LDL by HPGC in 56 subjects, we obtained diameters of 25.72 ± 0.60 nm with UV detection and of 25.74 ± 0.58 nm with fluorescence detection. The modified method is suitable for LDL size measurement in whole plasma or serum. LDL sizes measured in whole plasma correlated strongly with the respective values in isolated LDL (r = 0.976) but were on average 0.18 nm larger (P &lt; 0.001). CVs for within- and between-series imprecision were &lt;0.25%. The present method requires only 5 μL plasma or serum without sample preparation and is suitable for the unattended analysis of large series of samples.

Atorvastatin in the treatment of primary hypercholesterolemia and mixed dyslipidemias

OBJECTIVE

To review the efficacy and safety of atorvastatin in the treatment of dyslipidemias.

DATA SOURCES

A MEDLINE search (January 1960-April 1998), Current Contents search, additional references listed in articles, and unpublished data obtained from the manufacturer were used to identify data from scientific literature. Studies evaluating atorvastatin (i.e., abstracts, clinical trials, proceedings, data on file with the manufacturer) were considered for inclusion.

STUDY SELECTION

English-language literature was reviewed to evaluate the pharmacology, pharmacokinetics, therapeutic use, and adverse effects of atorvastatin. Additional relevant citations were used in the introductory material and discussion.

DATA EXTRACTION

Open and controlled animal and human clinical studies published in the English-language literature were reviewed and evaluated. Clinical trials selected for inclusion were limited to those in human subjects and included data from animals if human data were not available.

DATA SYNTHESIS

Atorvastatin is a recent hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor for the treatment of primary hypercholesterolemia, mixed dyslipidemias, and homozygous familial hypercholesterolemia. In patients who have not met the low-density lipoprotein cholesterol (LDL-C) goal as recommended by the National Cholesterol Education Program Adult Treatment Panel II guidelines, atorvastatin 10-80 mg/d may be used as monotherapy or as an adjunct to other lipid-lowering agents and dietary modifications. In placebo-controlled clinical trials, atorvastatin 10-80 mg/d lowered LDL-C by 35-61% and triglyceride (TG) concentrations by 14-45%. In comparative trials, atorvastatin 10-80 mg/d showed a greater reduction of serum total cholesterol (TC), LDL-C, TG concentrations, and apolipoprotein B-100 (apo B) compared with pravastatin, simvastatin, or lovastatin. In comparison, currently available HMG-CoA reductase inhibitors (lovastatin, simvastatin, pravastatin, fluvastatin, cerivastatin) lower LDL-C concentrations by approximately 20-40% and TG concentrations by approximately 10-30%. In pooled placebo-controlled clinical trials of up to a duration of 52 weeks, atorvastatin in dosages up to 80 mg/d appeared to be well tolerated. The most common adverse effect of atorvastatin was gastrointestinal upset. The incidence of elevated serum hepatic transaminases may be greater at higher dosages of atorvastatin. The risk of myopathy and/or rhabdomyolysis is increased when an HMG-CoA reductase inhibitor is taken concomitantly with cyclosporine, gemfibrozil, niacin, erythromycin, or azole antifungals.

CONCLUSIONS

Atorvastatin appears to reduce TC, LDL-C, TG concentrations, and apo B to a greater extent than do currently available HMG-CoA reductase inhibitors. Atorvastatin may be preferred in patients requiring greater than a 30% reduction in LDL-C or in patients with both elevated LDL-C and TG concentrations, which may obviate the need for combination lipid-lowering therapy. Adverse effects of atorvastatin appear to be similar to those of other HMG-CoA reductase inhibitors and should be routinely monitored. Long-term safety data (> 1 y) on atorvastatin compared with other HMG-CoA reductase inhibitors are still needed. Cost-effectiveness studies comparing atorvastatin with other HMG-CoA reductase inhibitors remain a subject for further investigation. Published clinical studies evaluating the impact of atorvastatin on cardiovascular morbidity and mortality are still needed. Additionally, clinical studies evaluating the impact of lipid-lowering therapy in a larger number of women, the elderly (> 70 y), and patients with diabetes for treatment of primary and secondary prevention of coronary heart disease are needed.

Elevated LDL triglyceride concentrations in subjects heterozygous for the hepatic lipase S267F variant

Although naturally occurring loss-of-function mutations in human hepatic lipase (HL) have been described, the biochemical phenotype of heterozygous HL deficiency remains ill defined. This may be due to the relatively small numbers of heterozygous adult carriers of HL mutations in index kindreds. We have identified several new heterozygotes for the catalytically inactive, nonsecreted HL variant S267F in the kindred that was originally ascertained because of hypertriglyceridemia due to the mutant, secreted, circulating apolipoprotein (apo) CII variant apo CII-T. Pairwise comparisons with family controls showed that only the plasma low density lipoprotein triglycerides (LDL TGs) were higher in 11 simple heterozygotes for HL S267F (P=0.002). In contrast, both plasma total TGs and LDL TGs were significantly higher in 12 simple heterozygotes for apo CII-T than in family-matched control subjects (P=0.005 and 0.009, respectively). These findings suggest that the TG content of LDL is increased by heterozygosity for 2 different mutations that affect different proteins involved in lipolysis. However, the mechanisms underlying this compositional change in LDL appear to be different for the 2 mutations, because the total TGs are also elevated in subjects heterozygous for apo CII-T but not in subjects heterozygous for HL S267F.

Epidemiologic aspects of lipid abnormalities

Existing cholesterol guidelines aimed at preventing cardiovascular disease emphasize the role of total cholesterol (TC) and low-density lipoprotein (LDL) cholesterol in lipid management decisions, with a subsidiary role for high-density lipoprotein (HDL) cholesterol in guiding treatment and little role for triglycerides. In this article, epidemiologic evidence is reviewed relating to the independent value of lipid factors in prediction of cardiovascular disease risk, including TC, LDL cholesterol, HDL cholesterol, very-low-density lipoprotein (VLDL) cholesterol and triglycerides, LDL particle size ("pattern B"), and the TC/HDL-cholesterol ratio. Several observations are highlighted. Triglycerides appear to be an independent risk factor in specific populations. Postprandial triglycerides may be superior to fasting triglycerides as a predictor of risk. LDL particle size does not have independent predictive value after adjustment for triglycerides. Particular emphasis is placed on the observation that the single most predictive lipid factor is the TC/HDL-cholesterol ratio, which implicitly incorporates information on both LDL and triglycerides in the numerator. This is the best predictor both of outcome and of treatment benefit, and its predictive value appears to be maintained into older age. It is concluded that increasing emphasis should be placed on the TC/HDL cholesterol ratio in epidemiologic analyses and in monitoring patients on therapy for dyslipidemia.