Triglycerides and atherogenic lipoproteins: rationale for lipid management

Diagnosis, prevention, and intervention for the metabolic syndrome

The term metabolic syndrome refers to a virulent and lethal group of atherosclerotic risk factors, including dyslipidemia, insulin resistance, obesity, and hypertension. This syndrome affects some 47 million people in the United States, placing them at increased risk for coronary artery disease (CAD). Particularly prominent as a risk factor for development of heart disease is central obesity. Immediate treatment of the metabolic syndrome is essential because these patients quickly develop diabetes, CAD, and stroke. Treatment is a multifactorial process and includes diet, exercise, and pharmacologic therapy. The latter consists of statins, fibrates, angiotensin-converting enzyme inhibitors, and thiazolidinediones, all of which can decrease the risk and incidence of CAD.

Comparative effects of simvastatin and atorvastatin in hypercholesterolemic patients with characteristics of metabolic syndrome

BACKGROUND

Hypercholesterolemic patients with metabolic syndrome (MS) are at high risk for coronary heart disease. The National Cholesterol Education Program (NCEP) Adult Treatment Panel III (ATP III) guidelines provide the option of aggressively lowering low-density lipoprotein cholesterol (LDL-C) in hypercholesterolemic patients with MS.

OBJECTIVE

The lipid-modifying efficacy of simvastatin and atorvastatin in hypercholesterolemic patients with MS as defined by NCEP ATP III was assessed.

METHODS

A post hoc subgroup analysis was performed on data from a 36-week, multicenter (54 sites worldwide), randomized, double-blind, parallel-group, dose-escalation (forced-titration) study designed to assess the effects of simvastatin (40-80 mg) and atorvastatin (20-80 mg) on high-density lipoprotein cholesterol (HDL-C) and apolipoprotein (apo) A-I levels in patients with LDL-C > or = 160 mg/dL. Patients were classified as having MS if they met >/=3 of the following criteria: (1) triglyceride (TG) level > or =150 mg/dL; (2) HDL-C <40 mg/dL (men) or <50 mg/dL (women); (3) secondary diagnosis of type 2 diabetes mellitus and/or taking antidiabetic medication and/or fasting serum glucose (FSG) level > or =110 mg/dL; (4) secondary diagnosis of hypertension and/or taking antihypertensive medication and/or systolic blood pressure (SBP)/diastolic blood pressure (DBP) > or =130/ > or =85 mm Hg; and (5) body mass index (BMI) > or =30 kg/m(2) (surrogate for waist circumference).

RESULTS

Of 808 evaluable patients, 212 (26.2%) were classified as having MS at baseline. Compared with the non-MS subgroup, MS patients were slightly older and more likely to be female. They also had higher BMI, SBP/DBP, FSG, and TG levels, and lower HDL-C and apo A-I levels than non-MS patients. The simvastatin group contained 99 patients; the atorvastatin group, 113 patients. Both drugs produced large reductions in total cholesterol, LDL-C, non-HDL-C, TG, and apo B, with atorvastatin producing slightly greater reductions in TG. However, simvastatin consistently produced larger increases in HDL-C and apo A-I than atorvastatin, especially at higher doses. After 36 weeks of treatment, 47.7% and 48.5% in the simvastatin and atorvastatin groups, respectively, no longer met > or =3 of the MS criteria.

CONCLUSIONS

In hypercholesterolemic patients with characteristics of MS, simvastatin and atorvastatin had comparable beneficial effects on apo B-containing atherogenic lipids and lipoproteins, and MS status was effectively modified by both drugs. However, although atorvastatin produced slightly larger decreases in TG, simvastatin produced larger increases in HDL-C.

Triacylglycerol biosynthesis in yeast

Triacylglycerol (TAG) is the major storage component for fatty acids, and thus for energy, in eukaryotic cells. In this mini-review, we describe recent progress that has been made with the yeast Saccharomyces cerevisiae in understanding formation of TAG and its cell biological role. Formation of TAG involves the synthesis of phosphatidic acid (PA) and diacylglycerol (DAG), two key intermediates of lipid metabolism. De novo formation of PA in yeast as in other types of cells can occur either through the glycerol-3-phosphate- or dihydroxyacetone phosphate-pathways-each named after its respective precursor. PA, formed in two steps of acylation, is converted to DAG by phosphatidate phosphatase. Acylation of DAG to yield TAG is catalyzed mainly by the two yeast proteins Dga1p and Lro1p, which utilize acyl-CoA or phosphatidylcholine, respectively, as acyl donors. In addition, minor alternative routes of DAG acylation appear to exist. Endoplasmic reticulum and lipid particles (LP), the TAG storage compartment in yeast, are the major sites of TAG synthesis. The interplay of these organelles, formation of LP, and enzymatic properties of enzymes catalyzing the synthesis of PA, DAG, and TAG in yeast are discussed in this communication.

Diet composition and the metabolic syndrome: what is the optimal fat intake?

Two cholesterol-raising fatty acids in the diet, saturated fatty acids and trans fatty acids, increase the serum low-density lipoprotein cholesterol concentration. This fact justifies the recommendation of a reduced intake of cholesterol-raising fatty acids. Emerging data suggest that diets higher in unsaturated fatty acids, particularly monounsaturated fatty acids, have several advantages over high-carbohydrate intakes. This advantage appears to hold, particularly for populations having a high prevalence of insulin resistance, such as the US population. If the US public were to modify its eating habits in the direction of better weight control and more exercise, higher intakes of carbohydrate might be better tolerated. At the same time, the experience with the Mediterranean population reveals that in healthier populations, diets relatively high in unsaturated fatty acids are well tolerated and are associated with a low prevalence of both coronary heart disease and type 2 diabetes.

Comparing the effects of five different statins on the HDL subpopulation profiles of coronary heart disease patients

We compared the effects of five different statins (atorvastatin, simvastatin, pravastatin, lovastatin, and fluvastatin) on the lipid, lipoprotein, and apolipoprotein (apo) A-I-containing high-density lipoprotein (HDL) subpopulation profiles of 86 coronary heart disease (CHD) patients. Patients with established CHD, and low density lipoprotein (LDL) cholesterol (C)>130 mg/dl, and triglyceride (TG)<400 mg/dl, were treated with atorvastatin 20, 40, and 80 mg/day and one of the other four statins at 20, 40, and when available 80 mg/day in increasing doses (4 weeks of each dose) in a randomized crossover fashion. There was an 8-week placebo controlled washout period between different drug treatments. All five statins on each dose resulted in significant reductions in total- and LDL-C compared to placebo treatment. There were also decreases in plasma TG and increases in HDL-C and apoA-I concentrations, but not all treatments changed these parameters significantly. Each statin except fluvastatin improved the HDL subpopulation profile by increasing the concentrations of the large, cholesterol-rich, LpA-I alpha-1 and prealpha-1 HDL subpopulations. CHD patients have significantly lower concentration of the large, LpA-I alpha-1 HDL particles compared to controls. Our data indicate that statins which are the most effective in lowering LDL-C and TG are also the most effective agents in modifying the HDL subpopulation profile in CHD patients towards the patterns found in healthy individuals. The order of efficacy of statins in increasing alpha-1 HDL subpopulation was: atorvastatin, simvastatin, pravastatin, lovastatin and fluvastatin.

New cholesterol guidelines, new treatment challenges

Coronary heart disease (CHD) is the largest single killer of Americans. Epidemiologic trials have indicted low-density lipoprotein cholesterol (LDL) as directly correlating with CHD events, and clinical trials confirmed that lipid-lowering therapy decreases the risk of CHD events. The literature also indicates that only about 18% of these patients are treated to their goal LDL levels. New guidelines from the National Cholesterol Education Program extend the LDL-lowering recommendations, add a new non-high-density lipoprotein cholesterol (non-HDL) goal for patients with hypertriglyceridemia, and increase the number of drug-eligible patients from about 15 to 36 million. Most of those who are eligible for lipid-altering drug therapy have the highest CHD risk and require the most aggressive treatment to achieve goals. This presents a challenge to clinicians: how best to achieve LDL and non-HDL goals. Statins are the most effective agents for lowering LDL and one of the most effective for lowering non-HDL. This efficacy and the ability to reduce CHD risk were well documented in a number of randomized clinical trials. When statin monotherapy fails to achieve goals, a bile acid resin, niacin, or both may be added to lower LDL further, or a fibrate, niacin, or fish oils may be added to lower non-HDL further. Drugs are under development that may enhance our ability to reach LDL and non-HDL goals. Included are a group of so-called super statins, rosuvastatin and pitavastatin; agents that interfere with cholesterol or bile acid transport in the gut, such as ezetimibe; and dual peroxisome proliferator-activated receptor agonists that have both fibrate and thiazolidinedione-like effects.

Differences in the relation of obesity to serum triacylglycerol and VLDL subclass concentrations between black and white children: the Bogalusa Heart Study

BACKGROUND

Obese children and adults, particularly those with abdominal obesity, have an elevated serum triacylglycerol concentration. Furthermore, triacylglycerol concentrations are generally higher in whites than in blacks, and the relation of obesity to triacylglycerol concentrations may be stronger in whites. However, there is little information on the relation of obesity to the metabolically distinct subclasses of VLDL in children.

OBJECTIVE

The objective was to examine possible differences between blacks (n = 367) and whites (n = 549) in mean concentrations of triacylglycerols, in mean concentrations of small and large VLDL, and in the relation of waist circumference to concentrations of triacylglycerol and VLDL subclasses.

DESIGN

We measured VLDL subclass concentrations and assessed the relation of various obesity indexes to triacylglycerols in a cross-sectional study of 10- to 17-y-olds.

RESULTS

The mean triacylglycerol concentration was 0.3 mmol/L (25 mg/dL) higher in white than in black children, primarily because of a 0.2-mmol/L (140%) difference in mean concentrations of large VLDL. In contrast, the mean concentrations of small VLDL differed by only 0.05 mmol/L (29%). In addition, the relations of waist girth to concentrations of triacylglycerol and large VLDL were 2- to 6-fold stronger among white children than among black children. Although white children had higher concentrations of large VLDL than did black children, this difference increased from 0.1 to 0.4 mmol/L across quintiles of waist circumference. Waist circumference was not significantly related to concentrations of small VLDL.

CONCLUSION

These contrasting associations with obesity, which differ between white and black children, suggest that information on VLDL subclasses could provide additional information on the risk of obesity-related ischemic heart disease.

The DGA1 gene determines a second triglyceride synthetic pathway in yeast

Diacylglycerol esterification provides an excellent target for the pharmacological reduction of triglyceride accumulation in several human disease states. We have used Saccharomyces cerevisiae as a model system to study this critical component of triglyceride synthesis. Recent studies of an oleaginous fungus, Mortierella ramanniana, identified a new family of enzymes with in vitro acyl-CoA:diacylglycerol acyltransferase activity. We show here that DGA1, the sole member of this gene family in yeast, has a physiological role in triglyceride synthesis. Metabolic labeling of DGA1 deletion strains with triglyceride precursors detected significant reductions in triglyceride synthesis. Triglyceride synthesis was virtually abolished in four different growth conditions when DGA1 was deleted in concert with LRO1, an enzyme that esterifies diacylglycerol from a phospholipid acyl donor. The relative contributions of the two enzymes depended on growth conditions. The residual synthesis was lost when ARE2, encoding an acyl-CoA:sterol acyltransferase, was deleted. In vitro microsomal assays verified that DGA1 and ARE2 mediate acyl-CoA:diacylglycerol acyltransferase reactions. Three enzymes can thus account for diacylglycerol esterification in yeast. Yeast strains deficient in both diacylglycerol and sterol esterification showed only a slight growth defect indicating that neutral lipid synthesis is dispensable under common laboratory conditions.

The effects of lipid-lowering therapy on low-density lipoprotein auto-antibodies: relationship with low-density lipoprotein oxidation and plasma total antioxidant status

BACKGROUND

Oxidized low-density lipoprotein (Ox-LDL) is believed to play an important role in the progression of atherosclerosis. Oxidative modification of low-density lipoprotein (LDL) is a prerequisite for rapid accumulation of LDL in macrophages and for the formation of foam cells. Because of high antioxidant levels in plasma, LDL oxidation is suggested to occur mainly in the subendothelial space of the arterial wall, where there is the concomitant presence of large amounts of reactive oxygen species generated by endothelial cells and activated leukocytes. After Ox-LDL formation, antibodies against this form of LDL may occur. Auto-antibodies against Ox-LDL (AuAb-Ox-LDL) show directly in in-vivo LDL oxidation. Many studies have indicated that the amount of antibodies in serum is positively correlated to the rate of progression of atherosclerotic plaques.

DESIGN AND METHODS

In this study the effect of lipid-lowering therapy on the levels of AuAb-Ox-LDL in patients with dyslipidemia was determined using atorvastatin (10 mg/day), and the relationship between the antibodies and plasma total antioxidant status (TAS) and LDL oxidation capacity was also investigated. Serum levels of AuAb-Ox-LDL, lipids, lipoproteins, TAS and susceptibility of LDL to oxidation were determined using lag time in 44 patients with dyslipidemia (29 with hypercholesterolemia and 15 with mixed-type hyperlipidemia).

RESULTS

After lipid-lowering therapy, serum levels of AuAb-Ox-LDL were found to be significantly decreased, by 18.7%, while lag time and plasma TAS were increased (31.3% and 7.6% respectively) in patients with dyslipidemia. The percentage change in lag time was found to be negatively correlated to the percentage change in AuAb-Ox-LDL (r = -0.31, P < 0.05). The percentage change in lag time also showed a positive correlation with the percentage change in TAS (r = 0.58, P < 0.01). AuAb-Ox-LDL levels decreased by 21.7% in patients with hypercholesterolemia and by 12.6% in patients with mixed-type hyperlipidemia. Also AuAb-Ox-LDL levels in patients with hypercholesterolemia were higher than in those with mixed-type hyperlipidemia (367 +/- 294 compared with 300 +/- 176 mU/l).

CONCLUSION

It was concluded that lipid-lowering therapy may contribute to the reduction in levels of AuAb-Ox-LDL and the increase in the antioxidant capacity of plasma LDL and TAS. It was also suggested that the measurement of antibodies against Ox-LDL during lipid-lowering therapy may be used as an important marker for representing in-vivo LDL oxidation and atherosclerotic processes.

Effects of short-term feeding of a highly palatable diet on vascular reactivity in rats

BACKGROUND

Numerous studies have shown that long-term consumption of high-fat, high-energy diet results in obesity, which in turn, leads to cardiovascular disorders. However, there is little or no data on the acute effects of a highly palatable diet on vascular function.

MATERIAL AND METHODS

In this study we aimed to evaluate the changes in metabolic and vascular reactivity in Wistar rats fed a palatable diet for 2 days.

RESULTS

Two-days feeding of rats with a palatable diet did not effect body weight, fat-pad mass or gastrocnemius muscles weights. Nor there were any changes in plasma glucose, insulin or leptin levels. However, compared with chow-fed rats, palatable diet-fed rats had significantly raised plasma free fatty acids and triglycerides levels (for both, P < 0.01). Compared with chow-fed animals, vasorelaxation responses to carbamylcholine and sodium nitroprusside were significantly attenuated in palatable diet-fed rats (for both, P < 0.01). However, there were no differences in histamine-induced vasorelaxation between chow-fed and palatable diet-fed rats.

CONCLUSION

These data indicates that diet-induced endothelium-dependent and -independent vascular dysfunction occurs long before obesity develops.

An apolipoprotein influencing triglycerides in humans and mice revealed by comparative sequencing

Comparison of genomic DNA sequences from human and mouse revealed a new apolipoprotein (APO) gene (APOAV) located proximal to the well-characterized APOAI/CIII/AIV gene cluster on human 11q23. Mice expressing a human APOAV transgene showed a decrease in plasma triglyceride concentrations to one-third of those in control mice; conversely, knockout mice lacking Apoav had four times as much plasma triglycerides as controls. In humans, single nucleotide polymorphisms (SNPs) across the APOAV locus were found to be significantly associated with plasma triglyceride levels in two independent studies. These findings indicate that APOAV is an important determinant of plasma triglyceride levels, a major risk factor for coronary artery disease.

Choose beverages and foods to moderate your intake of sugars: the 2000 dietary guidelines for Americans--what's all the fuss about?

As part of the 2000 Dietary Guidelines for Americans, the public is advised to choose beverages and foods to moderate their intake of sugars. The term sugars is conventionally used to describe the mono- and disaccharides. However, the Dietary Guidelines for Americans distinguish between added sugars and other sources of carbohydrates. The concept of added sugars provides consumers with useful information, especially if they are trying to limit excessive use of caloric sweeteners. Added sugars are defined as sugars that are eaten separately at the table or used as ingredients in processed or prepared foods. Consumption of added sugars has increased steadily as documented by both food supply data and nationwide food consumption survey data. The largest source of added sugars in the U.S. diet is nondiet soft drinks, accounting for one third of total intake. Diets high in sugars have been associated with various health problems, including dental caries, dyslipidemias, obesity, bone loss and fractures, and poor diet quality. Research gaps are identified.

High-protein diets in hyperlipidemia: effect of wheat gluten on serum lipids, uric acid, and renal function

BACKGROUND

The metabolic effects of diets high in vegetable protein have not been assessed despite much recent interest in the effect of soy proteins in reducing serum cholesterol.

OBJECTIVE

We assessed the metabolic effects of diets high in vegetable protein (specifically, wheat gluten) on serum lipids, uric acid concentrations, and renal function.

DESIGN

Twenty hyperlipidemic men and women consumed isoenergetic test (high-protein) and control metabolic diets for 1 mo in a randomized crossover design. In the high-protein diet, 11% of the total dietary energy from starch in the control bread was replaced by vegetable protein (wheat gluten), resulting in 27% of total energy from protein compared with 16% in the control diet. In other respects, the 2 diets were identical.

RESULTS

Compared with the control, the high-protein diet resulted in lower serum concentrations of triacylglycerol (by 19.2 +/- 5.6%; P = 0.003), uric acid (by 12.7 +/- 2.0%; P < 0.001), and creatinine (by 2.5 +/- 1.1%; P = 0.035) and higher serum concentrations of urea (by 42.2 +/- 5.8%; P < 0.001) and a higher 24-h urinary urea output (by 99.2 +/- 17.2%; P < 0.001). No significant differences were detected in total or HDL cholesterol or in the renal clearance of creatinine. LDL oxidation, assessed as the ratio of conjugated dienes to LDL cholesterol in the LDL fraction, was lower with the high-protein diet (by 10.6 +/- 3.6%; P = 0.009).

CONCLUSIONS

High intakes of vegetable protein from gluten may have beneficial effects on cardiovascular disease risk by reducing oxidized LDL, serum triacylglycerol, and uric acid. Further studies are required to assess the longer-term effects on renal function.

Improving compliance in your dyslipidemic patient: an evidence-based approach

PURPOSE

To synthesize the evidence from landmark clinical studies of lipid-lowering pharmacotherapy and nurse management of hyperlipidemia, discuss issues related to nonadherence, and proposes strategies for achieving long-term cholesterol control.

DATA SOURCES

All publications of lipid-lowering clinical trials related to pharmacotherapy for dyslipidemias were accessed from a thorough Medline Search and reviewed by two nurse experts.

CONCLUSIONS

Randomized controlled studies provide compelling evidence that reduction of blood cholesterol with pharmacotherapy reduces both first and subsequent coronary events. Nonetheless, inadequate provider and patient adherence to guidelines for lipid lowering remains prevalent. Studies show that nurses provide safe and effective care for patients with abnormal lipids.

IMPLICATIONS

This article assists nurse practitioners in playing an active role in the implementation of the National Cholesterol Education Program Adult Treatment Panel III Report to be released in Spring 2001, where a strong emphasis will be placed on multidisciplinary approaches and adherence.

Water-soluble organosulfur compounds of garlic inhibit fatty acid and triglyceride syntheses in cultured rat hepatocytes

The putative hypolipidemic effect of garlic remains controversial. To gain further insight into the effect of garlic on lipid metabolism, the present study determined the inhibitory effects of water-soluble organosulfur compounds present in garlic on triglyceride (TG) and fatty acid synthesis in cultured rat hepatocytes. When incubated at 0.05 to 4.0 mmol/L with cultured hepatocytes, S-allyl cysteine (SAC) and S-propyl cysteine (SPC) decreased [2-14C]acetate incorporation into triglyceride in a concentration-dependent fashion achieving a maximal inhibition at 4.0 mmol/L of 43 and 51%, respectively. The rate of [2-14C]acetate incorporation into phosphlipids was depressed to a similar extent by SAC and SPC. SPC, SAC, S-ethyl cysteine (SEC), and gamma-glutamyl-S-methyl cysteine decreased [2-14C]acetate incorporation into fatty acid synthesis by 81, 59, 35, and 40%, respectively, at 2.0-4.0 mmol/L concentrations. Alliin, gamma-glutamyl-S-allyl cysteine, gamma-glutamyl-S-propyl cysteine S-allyl-N-acetyl cysteine, S-allylsulfonyl alanine, and S-methyl cysteine had no effect on fatty acid synthesis. The activities of lipogenic enzymes, fatty acid synthase (FAS), and glucose-6-phosphate dehydrogenase (G6PDH) were measured in cultured hepatocytes treated with the inhibitors. The activity of FAS in cells treated with 4.0 mmol/L SAC and SPC, respectively, was 32 and 27% lower than that of nontreated cells. Neither SAC nor SPC affected G6PDH activity. The results indicate that SAC, SEC, and SPC inhibit lipid biosynthesis in cultured rat hepatocytes, and further suggest that these S-alk(en)yl cysteines of garlic impair triglyceride synthesis in part due to decreased de novo fatty acid synthesis resulting from inhibition on FAS. Whether tissue concentrations of active garlic components can achieve levels required to inhibit TG synthesis in vivo warrants further investigation.

Enhanced oxidative susceptibility and reduced antioxidant content of metabolic precursors of small, dense low-density lipoproteins

PURPOSE

Elevated plasma concentrations of low-density lipoproteins (LDL) increase risk for coronary heart disease. However, lipoprotein profiles rich in small, dense LDL particles confer greater risk than those that mainly consist of large, buoyant LDL. This may be due, in part, to the greater oxidative susceptibility of small, dense LDL. In the current studies, we tested whether differences in the oxidative behavior of buoyant and dense LDL arise from differences in their immediate metabolic precursors, intermediate-density lipoproteins.

SUBJECTS AND METHODS

We compared the properties of intermediate-density lipoproteins and buoyant and dense LDL subfractions in 9 subjects with the large, buoyant LDL phenotype versus 6 with the small, dense LDL phenotype. Oxidative susceptibility was evaluated based on conjugated diene formation and parinaric acid oxidation induced by copper. Antioxidants (ubiquinol-10 and alpha-tocopherol) were measured by high-performance liquid chromatography.

RESULTS

Oxidative susceptibility was increased and antioxidant concentrations were decreased with increasing lipoprotein density (intermediate intermediate-density lipoproteins to buoyant LDL to dense LDL). Intermediate-density lipoproteins from subjects with the small, dense LDL phenotype had a greater oxidative susceptibility (by the parinaric acid test) and lower antioxidant concentrations than corresponding particles from subjects with the large, buoyant LDL phenotype.

CONCLUSIONS

Differences in oxidative susceptibility between large, buoyant and small, dense LDL particles are apparent in their lipoprotein precursors. These results suggest that lipoprotein oxidative susceptibility may be metabolically programmed and that intermediate-density lipoproteins may contribute to the increased risk associated with the small, dense LDL phenotype.

MR imaging of the salivary glands in sicca syndrome: comparison of lipid profiles and imaging in patients with hyperlipidemia and patients with Sjögren's syndrome

OBJECTIVE

We correlated abnormalities on MR imaging with the plasma lipid profiles of patients with hyperlipidemia and symptoms of sicca syndrome.

SUBJECTS AND METHODS

MR imaging features of the salivary glands, salivary function, immunologic abnormalities, and plasma lipid profiles were analyzed in 24 patients with hyperlipidemia and symptoms of sicca syndrome and compared with those of 50 patients with Sjögren's syndrome.

RESULTS

Swelling of the parotid gland, impaired salivary flow, or both were observed in 20 (83%) of 24 patients with hyperlipidemia and symptoms of sicca syndrome. MR imaging findings included an enlarged parotid gland replaced with extensive lipid infiltration, whereas sialography of the parotid gland revealed normal findings. Immunologic studies and analyses of the labial glands of the mouth revealed distinctive features in patients with Sjögren's syndrome. Importantly, elevated levels of plasma triglyceride correlated with parotid gland swelling, and increased cholesterol levels significantly affected salivary flow.

CONCLUSION

Our findings suggest a distinct entity of sicca syndrome in patients with hyperlipidemia compared with patients with Sjögren's syndrome. Characteristic MR imaging findings of salivary glands in patients with hyperlipidemia included extensive lipid infiltration and gland enlargement.

Prevention of coronary artery disease

The magnitude of cardiovascular disease is enormous. When the risk factors that predispose a patient to heart disease are recognized early and the appropriate intervention is instituted, the incidence of morbidity and mortality from coronary heart disease can be reduced. Lifestyle modification and the judicious use of medications can improve the complications of heart disease and prevent its onset.

A lecithin cholesterol acyltransferase-like gene mediates diacylglycerol esterification in yeast

The terminal step in triglyceride biosynthesis is the esterification of diacylglycerol. To study this reaction in the model eukaryote, Saccharomyces cerevisiae, we investigated five candidate genes with sequence conservation to mammalian acyltransferases. Four of these genes are similar to the recently identified acyl-CoA diacylglycerol acyltransferase and, when deleted, resulted in little or no decrease in triglyceride synthesis as measured by incorporation of radiolabeled oleate or glycerol. By contrast, deletion of LRO1, a homolog of human lecithin cholesterol acyltransferase, resulted in a dramatic reduction in triglyceride synthesis, whereas overexpression of LRO1 yielded a significant increase in triglyceride production. In vitro microsomal assays determined that Lro1 mediated the esterification of diacylglycerol using phosphatidylcholine as the acyl donor. The residual triglyceride biosynthesis that persists in the LRO1 deletion strain is mainly acyl-CoA-dependent and mediated by a gene that is structurally distinct from the previously identified mammalian diacylglycerol acyltransferase. These mechanisms may also exist in mammalian cells.

Diabetic dyslipidaemia

Dyslipidaemia is an important component of the metabolic syndrome observed in patients with type 2 diabetes, and is characterized by moderate hypertriglyceridaemia and low levels of high-density lipoprotein (HDL) cholesterol concentrations. Dyslipidaemia contributes to increased vascular risk and is therefore a good target for therapeutic intervention in the form of glycaemic control, lifestyle measures and hypolipidaemic drugs. It is proposed that lipid abnormalities in type 2 diabetes are secondary consequences of insulin resistance. Any approach that lowers insulin resistance would be anticipated to have a beneficial effect on dyslipidaemia, but in many cases patients with type 2 diabetes fail to achieve normal lipidaemia through diet, exercise and glycaemic control. Subgroup analyses of major clinical trials suggests that lipid-lowering therapy reduces CHD risk in patients with diabetes, but trials performed specifically in populations of patients with diabetes are ongoing. Until then, patients with type 2 diabetes who have established CHD or high individual risk already warrant aggressive lipid-lowering pharmacotherapy. In the author's view, when ongoing studies are complete it is likely that most patients with type 2 diabetes will be prescribed lipid-lowering drugs.

Spontaneous combined hyperlipidemia, coronary heart disease and decreased survival in Dahl salt-sensitive hypertensive rats transgenic for human cholesteryl ester transfer protein

The acceleration of atherosclerosis by polygenic (essential) hypertension is well-characterized in humans; however, the lack of an animal model that simulates human disease hinders the elucidation of pathogenic mechanisms. We report here a transgenic atherosclerosis-polygenic hypertension model in Dahl salt-sensitive hypertensive rats that overexpress the human cholesteryl ester transfer protein (Tg[hCETP]DS). Male Tg[hCETP]DS rats fed regular rat chow showed age-dependent severe combined hyperlipidemia, atherosclerotic lesions, myocardial infarctions and decreased survival. These findings differ from various mouse atherosclerosis models, demonstrating the necessity of complex disease modeling in different species. The data demonstrate that cholesteryl ester transfer protein can be proatherogenic. The interaction of polygenic hypertension and hyperlipidemia in the pathogenesis of atherosclerosis in Tg[hCETP]DS rats substantiates epidemiological observations in humans.

Understanding coronary heart disease as a consequence of defective regulation of apolipoprotein B metabolism

Further understanding of the causative link between plasma lipids and coronary heart disease will come from a deeper appreciation of the impact of lipoprotein heterogeneity on the processes of atherosclerosis and thrombosis. It is now widely appreciated that remnants of triglyceride-rich lipoproteins, IDL and specific LDL subfractions may have a role in atherogenesis disproportionate to the plasma concentrations of these species. Elucidation of the factors that control the distribution of subfractions within the spectrum of apolipoprotein B-containing lipoproteins is underway but far from complete. Important influences are the rate and nature of lipoproteins secreted from the liver, the extent of remodelling by lipid exchange and lipolysis in the circulation and the affinity of the various particles for cell surface receptors.