Genetic (primary) forms of hypertriglyceridemia

Hypertriglyceridemia and Recurrent Pancreatitis following Splenectomy

Hyperlipoproteinemia represents a constellation of clinical syndromes that frequently includes hypertriglyceridemia. Because of the degree of elevation in the triglyceride levels frequently seen in these syndromes, they are associated with complications not generally observed among those patients with essential hypertriglyceridemia, including as in this case report, recurrent pancreatitis. Here, we present a case of a patient with hyperlipoproteinemia who developed acute worsening of his hypertriglyceridemia and onset of acute panceatitis that became recurrent following elective splenectomy for suspected lymphoma. In particular, we discuss the dietary management of hypertriglyceridemia which significantly reduced the number of episodes of acute pancreatitis in this patient.

Overexpression of apolipoprotein CIII increases and CETP reverses diet-induced obesity in transgenic mice

OBJECTIVE

We recently described that hypertriglyceridemic apolipoprotein (apo) CIII transgenic mice show increased whole body metabolic rate. In this study, we used these apo CIII-expressing mice, combined or not with the expression of the natural promoter-driven CETP gene, to test the hypothesis that both proteins modulate diet-induced obesity.

MEASUREMENTS AND RESULTS

Mice expressing apo CIII, CIII/CETP, CETP and nontransgenic (NonTg) mice were maintained on a high-fat diet (14% fat by weight) during 20 weeks after weaning. At the end of this period, all groups exhibited the expected lipemic phenotype. Fasting glucose levels were neither affected by the high-fat diet nor by the distinct genotypes. However, apo CIII mice showed significantly higher glycemia ( approximately 35%) and lower insulin levels ( approximately 45%) in the fed state, compared with the NonTg mice. The apo CIII mice presented significantly increased body weight, lipid content of the carcass ( approximately 25%), visceral adipose tissue mass (about twofold) and adipocyte size ( approximately 25%) compared with the CETP and NonTg mice. The CETP expression in the apo CIII background normalized the subcutaneous adipose depot and visceral adipocyte size to the levels of NonTg mice. Plasma leptin levels were lower in CETP groups (25-50%) and higher in the apo CIII mice. Similar core body temperature in all groups and similar liver mitochondrial resting respiration rates in CIII and NonTg mice indicate no differences in basal energy expenditure rates among these mice fed a high-fat diet.

CONCLUSION

The elevation of plasma apo CIII levels aggravates diet-induced obesity and the expression of physiological levels of circulating CETP reverses this adipogenic effect, indicating a novel role for CETP in modulating adiposity.

Accumulation of apoE-enriched triglyceride-rich lipoproteins in patients with coronary artery disease

Triglycerides (TGs) are vehicled by multiple particles with different abilities to promote atherosclerosis. Among plasma TG-rich lipoproteins (TRLs), subspecies may or may not contain apolipoprotein E (apoE) molecules: in this study, we evaluated the relative contribution of apoE-rich and apoE-poor TRLs to coronary atherosclerosis. We selected a group of males with premature coronary artery disease (CAD) without any of the classical nonlipid risk factors and/or high plasma lipid levels and evaluated the plasma concentration of TRL subspecies in comparison with healthy controls. Patients with CAD and controls had total cholesterol and TG levels within the normal range (despite slightly, even if significantly, higher TG levels in patients with CAD) and low-density lipoprotein cholesterol levels near optimal values. Nevertheless, patients with CAD had significantly lower high-density lipoprotein cholesterol, smaller low-density lipoprotein peak particle size, and a reduced HDL2b subfraction than controls. In addition, we observed higher concentrations of total TRL in patients with CAD together with a selective increase in apoE-rich particles. All these data were confirmed after correction for TG levels. We also investigated which parameters were associated with the spread of coronary atherosclerosis. Subjects with a single-vessel disease had selectively lower levels of apoE-rich fractions than patients with a multivessel disease. This was confirmed by multivariate analysis. Patients with a premature CAD free of nonlipid conventional risk factors, despite not having elevated lipid levels, show several lipoprotein abnormalities. Besides known atherogenic alterations, the accumulation of apoE-rich TRL subfractions may represent an additive factor that can potentially promote and initiate the atherosclerotic process.

Hypertriglyceridemia increases mitochondrial resting respiration and susceptibility to permeability transition

High plasma level of triglycerides (TGs) is a common feature in atherosclerosis, obesity, diabetes, alcoholism, stress, and infection. Since mitochondria have been implicated in cell death under a variety of metabolic disorders, we examined liver mitochondrial functions in hypertriglyceridemic transgenic mice. Hypertriglyceridemia increased resting respiration and predisposed to mitochondrial permeability transition (MPT). Ciprofibrate therapy reduced plasma TG levels, normalized respiration, and prevented MPT. The higher resting respiration in transgenic mitochondria remained in the presence of the adenine nucleotide carrier inhibitor, carboxyatractyloside, bovine serum albumin, and the uncoupling proteins (UCPs) inhibitor, GDP. UCP2 content was similar in both control and transgenic mitochondria. We propose that faster resting respiration represents a regulated adaptation to oxidize excess free fatty acid in the transgenic mice.

Diagnostic pitfalls during therapy for extreme hypertriglyceridaemia

We report the case of a 34-year-old man with extreme hypertriglyceridaemia (276.6 mmol/l) that was corrected by diet and triple-drug therapy. No primary defect could be found despite an intensive biochemical and genetic evaluation. Early in the time course of triglyceride-lowering therapy, the composition and concentration of different lipoprotein species changed markedly. His lipoprotein profile mimicked type III hyperlipidaemia, then familial hypercholesterolaemia, and finally hyperalphalipoproteinaemia. The increase in LDL cholesterol and apolipoprotein B was paralleled by a sixfold increase in lipoprotein(a). We conclude that these different forms of hypercholesterolaemia disappear solely with a continuation of the triglyceride-lowering therapy.

Influences on the quality of published drug studies

To practice evidence-based medicine, physicians need data on the clinical effectiveness, toxicity, convenience, and cost of new drugs compared with available alternatives. We give examples of published drug studies that are defective, sometimes because pharmaceutical industry funding has affected their content and quality. We make recommendations on how to avoid these defects.

Effects of VLDL, chylomicrons, and chylomicron remnants on platelet aggregability

Although influences of cholesterol-rich lipoproteins on platelet aggregation are well established, the knowledge of interactions between triglyceride-rich lipoproteins and platelets, in particular in the postprandial state, is limited and controversial. The in-vitro effects of these lipoproteins from hypertriglyceridemic subjects on the aggregation behavior of platelets from normolipemic donors were investigated with two whole-blood methods. VLDL and chylomicrons, but not chylomicron remnants, in concentrations comparable to concentrations occurring after a fatty meal, reduced platelet aggregation in a dose-dependent manner in particle counting. Impedance aggregometry failed to monitor these effects. We conclude, that triglyceride-rich lipoproteins inhibit platelet aggregation in vitro. They may, therefore, not be linked to the acute onset of myocardial infarction.

Hypertriglyceridemia during late pregnancy is associated with the formation of small dense low-density lipoproteins and the presence of large buoyant high-density lipoproteins

Late pregnancy is a unique metabolic state where there are transient increases in the concentrations of plasma triglyceride (TG), cholesterol, and apolipoprotein (apo) B. Despite the hypertriglyceridemic environment, we recently reported that there is an unusual shift in high-density lipoprotein (HDL) subclass distribution from smaller HDL subclasses to the largest, most buoyant HDL2b subclass. In the present investigation, we determined whether the subclasses of low-density lipoprotein (LDL) also change during this transient hyperlipidemic state and whether such changes were associated with plasma TG and apolipoprotein concentrations. Thirty-six Hispanic subjects at 35 to 36 weeks' gestation and at 6 weeks' postpartum were studied. At 35 to 36 weeks of gestation, plasma concentrations of TG, cholesterol, and apo B were increased (218 +/- 62, 234 +/- 48, and 130 +/- 35 mg/dL, respectively) over levels at 6 weeks' postpartum (112 +/- 69, 197 +/- 36, and 97 +/- 25 mg/dL respectively). However, lipoprotein(a) [Lp(a)] concentrations were not changed during pregnancy compared with postpartum. LDL subclass patterns (A, B, or I) were determined by nondenaturing polyacrylamide gradient gel electrophoresis in our group of 36 pregnant women. During late pregnancy, 97% of subjects were categorized as LDL subclass patterns B or I, indicating that small, dense LDL particles predominated. This predominance of small, dense LDL was associated with plasma TG concentration, where there was a significant inverse relationship (r = -.45, P < .01) between the LDL peak particle diameter and plasma TG concentration. In an apparent anomaly, there were significant increases in the concentrations of HDL cholesterol (HDL-C) and HDL2 mass, even though small, dense LDL particles predominated.(ABSTRACT TRUNCATED AT 250 WORDS)

Therapeutic management of triglycerides: an international perspective

Current recommendations from various international expert committees generally concur in their definitions of borderline and high triglyceride levels, with small but important differences between recommendations in the definition of normal levels. However, population-based data on triglyceride levels are poorly developed in most countries, making difficult any international comparisons of prevalences of hypertriglyceridemia using the new definitions. However, it is probable that there should be considerable differences in the prevalence of hypertriglyceridemia, probably due to a mixture of genetic and environmental influences. The management of hypertriglyceridemia must continue to emphasize the detection and correction of secondary causes, even though the specific secondary causes may vary between countries. Dietary and exercise interventions must deal with local customs and resources, including striking international differences in alcohol consumption. Pharmacologic therapies will likely increase in use if they follow the trends in countries with available data. Although various drugs are available, nicotinic acid and fibric acid derivatives remain the drugs of choice. Considerably more research is needed to describe these international differences in etiology, prevalence and management practices of hypertriglyceridemia.

The triglyceride connection in atherosclerosis

OBJECTIVE

To examine the proposed mechanism of triglyceride-induced atherogenesis, to address the controversy surrounding serum triglycerides as a coronary heart disease (CHD) risk factor, and to recommend an appropriate therapeutic approach to hypertriglyceridemia.

DATA SOURCES

Studies, review articles, and editorials published since 1976. A MEDLINE search of English-language literature was conducted using the terms triglyceride and hypertriglyceridemia.

STUDY SELECTION

Studies, review articles, and editorials were selected for detailed review if they addressed the pathogenesis of triglyceride-induced atherosclerosis, the controversy associated with elevated serum triglyceride as a CHD risk factor, and hypertriglyceridemia treatment options.

DATA EXTRACTION

Data were reviewed that described the atherogenicity of chylomicron and very low-density lipoprotein (VLDL) remnants, the inverse relationship that exists between high-density lipoprotein (HDL) and serum triglyceride, the hypertriglyceridemia treatment controversy, and the treatment options of diet, exercise, weight control, alcohol restriction, and medication.

DATA SYNTHESIS

Hypertriglyceridemia is a well-known risk factor for pancreatitis. However, its role in atherogenesis is less well defined. Several proposed connections appear to exist between hypertriglyceridemia and atherosclerosis, including the inverse correlation between triglycerides and HDL, the presumed atherogenicity of triglyceride-rich lipoprotein remnant particles, the potential resultant increase in the serum concentration and atherogenicity of low-density lipoprotein (LDL), and the proposed interaction between serum triglyceride and the fibrinolytic/coagulation system. Clinical trials addressing this issue offer mixed results that are subject to interpretation. Diet, exercise, weight control, alcohol restriction, and certain lipid-lowering medications are effective at reducing serum triglyceride.

CONCLUSIONS

Hypertriglyceridemia is a theoretical risk factor for CHD because of the increased production of atherogenic chylomicron and VLDL remnants, the inverse relationship present between serum triglyceride and HDL, the possible resultant increase in LDL attributable to remnant-reduced hepatic LDL-receptors as well as the formation of more dense and, therefore, more atherogenic LDL, and to the interaction between serum triglyceride and the fibrinolytic/coagulation system. However, most clinical trials that have found hypertriglyceridemia to be a risk factor for CHD do not include other CHD risk factors in their analyses. Therapeutic intervention to lower serum triglyceride with diet, exercise, and/or drugs is definitely recommended in the treatment and/or prevention of pancreatitis; however, the role of triglyceride-lowering to reduce CHD risk remains controversial.