Lipoprotein abnormalities in hypertriglyceridemia: significance in atherosclerosis

The association between lipid parameters and obesity in university students

BACKGROUND

Abdominal obesity is associated with high plasma triglyceride and with low plasma high-density lipoprotein cholesterol levels.

AIM AND METHODS

Objective of the study was to find an association between plasma lipid and lipoprotein levels and anthropometric parameters in abdominal obesity in Slovakian university students. Lipid profile and anthropometric parameters of obesity were studied in a sample of 419 probands, including 137 men and 282 women.

RESULTS

Males had higher values of non-high-density lipoprotein cholesterol (non-HDL-C), low-density lipoprotein cholesterol (LDL-C), triglycerides (TG) and very low-density lipoprotein cholesterol (VLDL-C) than females, but these differences were not significant. Females had significantly (P < 0.05) higher TC and HDL-C (P < 0.001) than males. In comparison, all anthropometric parameters in the males were significantly (P < 0.001) higher than in the females. A positive correlation between non-HDL-C, TG, VLDL-C and anthropometric parameters (BMI, WC, WHR, WHtR) was found at P < 0.001. LDL was positively correlated with BMI, WCF, WHtR and TC with BMI, WHtR at P < 0.001. We also observed a correlation between TC-WCF and LDL-WHR at P < 0.01. A negative correlation was found between HDL and all monitored anthropometric parameters at P < 0.001. On the other hand, no correlation between TC and WHR was detected.

CONCLUSION

This study shows an association between plasma lipid and lipoprotein levels and anthropometric parameters in abdominal obesity in young people, predominantly university students.

Fat depots, free fatty acids, and dyslipidemia

Body fat deposition and excess free fatty acid (FFA) metabolism contribute to dyslipidemia and the adverse health consequences of obesity. Individuals with upper body obesity have impaired functioning of adipocytes, the primary fatty acid storage site. Excess visceral fat is strongly associated with impaired suppression of FFA release in response to insulin, as well as with hypertriglyceridemia and low concentrations of high density lipoprotein (HDL) cholesterol. High FFA concentrations can induce insulin resistance in muscle and liver. Furthermore, failure of hyperinsulinemia to normally suppress FFA is associated with impaired carbohydrate oxidation and muscle glucose storage, reduced hepatic insulin clearance and elevated triglycerides. Understanding the impact of body fat distribution on FFA metabolism and dyslipidemia is critical for determining the link between overweight and obesity and cardiovascular disease risk. In the current review, we will explore the relationship between adipose tissue, body fat depots, and FFA metabolism.

Relationship between apolipoproteins and the alteration of HDL subclasses in hyperlipidemic subjects

BACKGROUND

To elucidate the relationship between the apolipoproteins, especially apoA-I and the alteration of HDL subclasses in hyperlipidemic, HTC and HTG subjects.

METHODS

ApoA-I contents of plasma HDL subclasses were quantitated by two-dimensional gel electrophoresis coupled with immunodetection in 233 normolipidemic subjects and 312 hyperlipidemic subjects (132 HTC and 180 HTG subjects). Making use of the mean +/-1 SD of apoA-I levels, we further subdivided normolipidemic, hyperlipidemic, HTC and HTG subjects into 3 subgroups, respectively.

RESULTS

Subjects in the middle and low apoA-I subgroups had decreased HDL-C and apoA-I while increased TG, apoB100, apoCII, apoCIII and apoE concentrations. With the reduction of apoA-I concentrations, the apoA-I contents of all HDL subclasses decreased successively and significantly. The relative percentage of small-sized HDL increased significantly while those of large-sized HDL(2a), HDL(2b) decreased significantly in hyperlipidemic, especially in HTG group. Multiple liner regression result revealed that apoA-I was positively and significantly correlated with all HDL subclasses and apoA-I level influenced the distribution of HDL subclasses powerfully in hyperlipidemic subjects.

CONCLUSIONS

Both the rate and efficiency of RCT might be weakened more seriously in hyperlipidemic, especially in HTG subjects with low apoA-I levels. ApoA-I level might be a powerful factor correlated with the distributions of HDL subclasses.

Mechanisms of HDL lowering in insulin resistant, hypertriglyceridemic states: the combined effect of HDL triglyceride enrichment and elevated hepatic lipase activity

Hypertriglyceridemia, low plasma concentrations of high density lipoproteins (HDL) and qualitative changes in low density lipoproteins (LDL) comprise the typical dyslipidemia of insulin resistant states and type 2 diabetes. Although isolated low plasma HDL-cholesterol (HDL-c) and apolipoprotein A-I (apo A-I, the major apolipoprotein component of HDL) can occur in the absence of hypertriglyceridemia or any other features of insulin resistance, the majority of cases in which HDL-c is low are closely linked with other clinical features of insulin resistance and hypertriglyceridemia. We and others have postulated that triglyceride enrichment of HDL particles secondary to enhanced CETP-mediated exchange of triglycerides and cholesteryl ester between HDL and triglyceride-rich lipoproteins, combined with the lipolytic action of hepatic lipase (HL), are driving forces in the reduction of plasma HDL-c and apoA-I plasma concentrations. The present review focuses on these metabolic alterations in insulin resistant states and their important contributions to the reduction of HDL-c and HDL-apoA-I plasma concentrations.

Dietary restriction reduces atherosclerosis and oxidative stress in the aorta of apolipoprotein E-deficient mice

Dietary restriction (DR) has been shown to inhibit almost all the age-related diseases, e.g. cardiomyopathy and cancers, in rodents. However, there is little information for the effect of DR on atherosclerosis. In the present study, we examined the effect of DR on the development of atherosclerosis in mice homozygous knockout for apolipoprotein E gene (ApoE(-/-)). The ApoE(-/-) mice were fed either ad libitum (AL) or 60% of the diet consumed by the mice fed AL. Atherosclerotic lesions in the proximal aorta of these mice were measured. Our results showed that ApoE(-/-) mice fed the calorie-restricted diet had smaller and relatively early stages of atherosclerotic lesions (e.g. foam cells and free lipids) when compared to ApoE(-/-) mice fed AL, who developed more advanced lesions (e.g. fibrous caps and acellular areas). In addition, ApoE(-/-) mice fed the calorie-restricted diet showed a significant decrease in the level of lipid hydroperoxides and the production of superoxide and hydrogen peroxide in the aorta as compared to ApoE(-/-) mice fed AL. These observations suggest that reduction of oxidative stress in the arterial wall may contribute to the anti-atherogenic effect of DR in ApoE(-/-) mice.

Alterations in the main steps of reverse cholesterol transport in male patients with primary hypertriglyceridemia and low HDL-cholesterol levels

Hypertriglyceridemia is a complex pathological entity strongly connected to low HDL-C levels but controversially related to the risk of coronary artery disease. In this study, we evaluated the main steps of the antiatherogenic pathway called reverse cholesterol transport in a group of patients with primary hypertriglyceridemia and low HDL-C levels in comparison to normotriglyceridemic subjects with or without hypoalphalipoproteinemia. In patients with primary hypertriglyceridemia, low HDL-C levels were accompanied by decreased apo A-I and apo A-II concentrations. These reductions were manifested by a selective reduction in LpA-I:A-II particles. In addition, apo C-III Lp non B was found to be elevated and HDL lipid percentage composition showed a triglyceride enrichment and cholesterol depletion. The capacity of serum samples from hypertriglyceridemic patients to promote cellular cholesterol efflux was reduced, as evidenced by using two different cellular models, Fu5AH and J774 cells. This impaired cholesterol efflux promotion was also corroborated by incubations of isolated HDL fractions with Fu5AH cells. Lecithin:cholesterol acyltransferase (LCAT) activity, the driving force of reverse cholesterol transport, showed a tendency towards lower values in hypertriglyceridemic patients, but this difference was not statistically significant. Additionally, cholesteryl ester transfer protein (CETP) activity was increased in this group of patients. Therefore, hypertriglyceridemia was found to induce quantitative and qualitative alterations in HDL and its subclasses and, consequently, in some steps of reverse cholesterol transport. The abnormalities found in this antiatherogenic pathway and its promoters could constitute a possible connection between hypertriglyceridemia and atherosclerosis.

Atherosclerosis in a dog with diabetes mellitus

A seven-year-old male Pomeranian with unstable insulin-dependent diabetes mellitus developed atherosclerosis. Hyperlipidaemia, consisting of hypertriglyceridaemia and hypercholesterolaemia, was diagnosed concurrently with the onset of lipid-laden aqueous humour. Serum lipoprotein analysis was characterised by the presence of chylomicrons, an increase in the very low density lipoprotein fraction, with a broad very low density lipoprotein-low density lipoprotein band, and a reduced high density lipoprotein fraction. The dog developed ketoacidosis one year later and died. At postmortem examination, atherosclerotic plaques were observed in the terminal aorta and in medium-sized arteries, including the coronary arteries, renal and arcuate arteries, and arteries of the brain. Mineralised plaques or complicated plaques were not observed. The absence of clinical signs of organ ischaemia was thought to be associated with the absence of thrombosis and/or complete occlusion of all vessels examined. Signs of chronic organ hypoxia, although considered likely owing to the severe vessel lumen reduction, were restricted to only a low voltage QRS complex on the electrocardiogram.

HDL metabolism in hypertriglyceridemic states: an overview

Reduced plasma high-density lipoprotein (HDL) cholesterol levels have been recognized as a highly significant independent risk factor for atherosclerotic cardiovascular disease. HDL levels are also inversely related to plasma triglyceride levels and there is a dynamic interaction between HDL and triglyceride (TG) rich lipoproteins in vivo. The mechanisms underlying the lowering of HDL in hypertriglyceridemic states have not been fully elucidated, but there is evidence to suggest that triglyceride enrichment of HDL, a common metabolic consequence of hypertriglyceridemia, may play an important role in this process. There is accumulating evidence to suggest that the primary mechanisms leading to reduced plasma HDL cholesterol levels and HDL particle number in hypertriglyceridemic states may be due to any one or a combination of the following possibilities: (1) small HDL particles, which are the product of the intravascular lipolysis of triglyceride-enriched HDL, may be cleared more rapidly from the circulation, (2) triglyceride-enriched HDL may be intrinsically more unstable in the circulation, with apo A-I loosely bound, (3) the lipolytic process itself of triglyceride-enriched HDL may lower HDL particle number by causing apo A-I to be shed from the HDL particles and cleared from the circulation, (4) a dysfunctional lipoprotein lipase or reduced LPL activity may contribute to the lowering of HDL levels by reducing the availability of surface constituents of triglyceride-rich lipoproteins that are necessary for the formation of nascent HDL particles. This review summarizes the evidence that triglyceride-enrichment of HDL is an important factor determining the rate at which HDL is catabolized, a mechanism which could explain, at least in part, the reduced plasma HDL cholesterol levels and particle number frequently observed in hypertriglyceridemic states.

Lipoprotein response to a National Cholesterol Education Program step II diet with and without energy restriction

This study examined the efficacy of a National Cholesterol Education Program (NCEP) step II diet (25% fat with < 7% saturated fat [SFA]) with and without moderate energy restriction. We tested the hypothesis that moderate energy restriction would improve the lipid profile resulting from an isoweight NCEP step II diet. Twenty hypercholesterolemic subjets (10 men and 10 postmenopausal women) consumed the following three controlled diets, each of 4 weeks' duration, as outpatients: (1) high-fat, high-saturated-fat diet to establish baseline lipids and isoweight energy requirements, (2) NCEP step II diet at isoweight energy, and (3) NCEP step II diet with an energy level 15% less than isoweight. The NCEP step II diet at isoweight energy reduced total cholesterol (TC) by 4% (P = .015), high-density lipoprotein cholesterol (HDL-c) by 13% (P < .0001), and HDL2-c by 40% (P < .0001). The TC:HDL-c ratio increased from 4.9 to 5.5 (P < .0001) and was increased in 19 of 20 subjects. Apolipoprotein B (apo B)-containing lipoproteins changed reciprocally: low-density lipoprotein cholesterol (LDL-c) decreased 4% (P = .008) and very-low-density lipoprotein cholesterol (VLDL-c) increased 29% (P < .0001). Apo B levels did not change. Compared with the NCEP isoweight diet the NCEP hypocaloric diet significantly reduced VLDL-c (-9%, P = .014) and apo B (-5%, P = .015). There was an additional reduction in TC (-4%, P = .073) and LDL-c (-4%, P = .126) with no change in HDL-c (P = .807). These data indicate that a NCEP step II diet with energy restriction produces a more desirable lipoprotein response than a NCEP step II isoweight diet. Neither NCEP step II diet improved the TC:HDL-c ratio.

Influence of mild to moderately elevated triglycerides on low density lipoprotein subfraction concentration and composition in healthy men with low high density lipoprotein cholesterol levels

Epidemiologic studies have shown that a dyslipoproteinemia with low concentrations of high density lipoprotein (HDL) cholesterol and elevated serum triglycerides (TG) is associated with a particularly high incidence of coronary artery disease. This lipid profile is associated with increased concentrations of small, dense low density lipoprotein (LDL) particles. To evaluate the role of mild to moderately elevated TG on the LDL subfraction profile in patients with low HDL cholesterol, concentration and composition of six LDL subfractions was determined by density gradient ultracentrifugation in 41 healthy men (31+/-9 years, body mass index (BMI) 25.1+/-3.9 kg/m2) with equally low HDL cholesterol levels < 0.91 mmol/l but different TG levels: TG < 1.13 mmol/l, n = 16; TG = 1.13-2.26 mmol/l, n = 13: TG = 2.26-3.39 mmol/l, n = 12. Those men with moderately elevated TG levels between 2.26 and 3.39 mmol/l had significantly higher concentrations of very low density lipoprotein (VLDL), intermediate low density lipoprotein (IDL), and small, dense LDL apoB and cholesterol than men with TG < 1.13 mmol/l. With increasing serum TG, the TG content per particle also increased in VLDL, IDL as well as total LDL particles while the cholesterol and phospholipid (PL) content decreased in VLDL and IDL, but not in LDL particles. LDL subfraction analysis revealed that only large, more buoyant LDL particles (d < 1.044 g/ml) but not the smaller, more dense LDL, were enriched in TG. Small, dense LDL particles were depleted of free cholesterol (FC) and PL. This study has shown that in men with low HDL cholesterol levels mild to moderately elevated serum TG strongly suggest the presence of other metabolic cardiovascular risk factors and in particular of a more atherogenic LDL subfraction profile of increased concentration of small, dense LDL particles that are depleted in surface lipids.

Glucose phosphorylation is essential for the turnover of neutral lipid and the second stage assembly of triacylglycerol-rich ApoB-containing lipoproteins in primary hepatocyte cultures

Primary hepatocytes cultured in a medium supplemented with amino acids and lipogenic substrates responded to increased extracellular glucose by increasing the secretion of VLDL apoB. This effect was accompanied by an increased secretion of VLDL triacylglycerol (TAG) derived from endogenous stores. Glucose also stimulated intracellular TAG mobilization via the TAG lipolysis/esterification cycle. All these effects were abolished in the presence of mannoheptulose (MH), an inhibitor of glucose phosphorylation. Glucose also gave rise to a modest (50% to 60%) increase in the incorporation of 35S methionine into newly synthesized apoB (P<0.05) and to a doubling of newly-synthesized apoB secretion as VLDL (P<0. 05). The magnitude of these effects was similar for apoB-48 and for apoB-100. MH inhibited apoB-48 and apoB-100 synthesis and VLDL secretion at all glucose concentrations. The effects of glucose and MH on the secretion of newly-synthesized apoB-48 or apoB-100 as small dense particles were less pronounced. Glucose had no effects on the posttranslational degradation of newly-synthesized apoB-100 or apoB-48. However, this process was significantly enhanced by MH. The results suggest that glucose stimulates TAG synthesis, turnover, and output as VLDL. These effects are associated with an increased VLDL output of apoB mediated mainly by an increase in the net synthesis of both apoB-48 and apoB-100. All these changes are prevented by interference with glucose phosphorylation. Output of small, dense, apoB-containing particles is relatively unaffected by the glucose and MH-induced changes in TAG synthesis and lipolysis, an observation which suggests that only the bulk lipid addition step of VLDL assembly is affected by changes in glucose metabolism.

Fractional removal rate of fat emulsion (K2) remains to be low in APOE3/3 phenotype subjects with serum triglyceride level above 180mg/dl

The relation between fractional catabolic rate (K2) of an intravenously injected fat emulsion, Intralipid, and the level of serum triglyceride (TG) was evaluated to cast light on TG-rich lipoprotein metabolism in 182 subjects who were homozygotes for the most common form of apoE3/3. Both normolipidemic individuals and primary hyperlipidemic patients were included. To assess the influence of variation in the apoE phenotype on fat emulsion metabolism, 25 subjects with the apoE 4/3 phenotype and 21 with apoE 3/2 phenotype were also evaluated. In the apoE 3/3 subjects, K2 decreased with increasing TG level up to 180mg/dl, but above 180mg/dl, K2 remained at a constant level. This TG value was therefore concluded to be a cut off beyond which the TG-dependent decrease in K2 disappeared. No apparent correlation between K2 and serum TG was observed in subjects with apoE 4/3 or 3/2 phenotypes. In subjects with TG above 180mg/dl, presumably both accelerated synthesis and limited removal are involved in the development of their hypertriglyceridemia. Since K2 demonstrated little change with increase of TG over 180mg/dl in apoE 3/3 subjects, we concluded that the capacity to catabolize fat emulsion reaches a kinetic saturation. The TG value of 180mg/dl may be a physiological significance. The relation between K2 and TG was specific in apoE 3/3, as it was not observed in subjects having apoE 4/3 or 3/2 phenotypes.

VLDL compositional changes and plasma levels of triglycerides and high density lipoprotein

VLDL chemical composition is related to plasma levels of triglycerides and HDL-cholesterol. We evaluated patients with primary hypertriglyceridemia with or without hypoalphalipoproteinemia and subjects with normotriglyceridemia with hypoalphalipoproteinemia. The pattern observed in all the groups was an enrichment in the triglyceride content of VLDL and in apo B-VLDL. Compared to controls, LpC-III:B levels were higher in hypertriglyceridemic patients with low or normal HDL-cholesterol levels (7.3 +/- 0.6 vs. 14.9 +/- 1.8 and 12.3 +/- 2.8 mg/dl; P < 0.005 and P < 0.01, respectively) and LpE:B concentration was only increased in patients with hypertriglyceridemia and normal HDL-cholesterol levels (3.1 +/- 0.5 vs. 6.3 +/- 1.0 mg/dl; P < 0.01). The activity of the cholesteryl ester transfer protein was higher in hypertriglyceridemic patients with low HDL-cholesterol levels than in controls (380 +/- 25 vs. 262 +/- 14% cholesteryl esters/ml.h; P < 0.001). The most atypical VLDL particle was found in patients who combined an accumulation of VLDL particles and a reduction in HDL-cholesterol concentration. These two parameters represent both ends of the cholesteryl ester-triglyceride transfer, a crucial factor for VLDL chemical composition and HDL levels.

Low-density lipoprotein composition and oxidability in atherosclerotic cardiovascular disease

OBJECTIVES

To characterize low-density lipoprotein (LDL) chemical composition and oxidability in normolipidemic and dyslipidemic patients with atherosclerotic cardiovascular disease, as compared with matched control subjects. To evaluate LDL susceptibility to oxidation, we determined the cutoff points of thiobarbituric reactive substances (TBARS) in LDL after oxidative stress, as well as its resistance to oxidation.

DESIGN AND METHODS

LDL (density 1.019-1.063 g/mL) of 24 men with atherosclerotic cardiovascular disease (12 normolipidemic and 12 dyslipidemic patients) and 18 age-matched healthy control men. LDL chemical composition was determined and apo B/cholesterol ratio was calculated. TBARS in native LDL and after 60 and 120 min of LDL oxidation with copper were measured. The conjugated diene production kinetics during LDL incubation with copper were also studied, lag time being an oxidation resistance marker. Cutoff points for the positivity criterion of apoB/cholesterol ratio in LDL and TBARS in native and oxidized LDL were evaluated using the receiver operator characteristic (ROC) graphic method.

RESULTS

LDL were triglyceride-enriched, the apoB/cholesterol ratio being higher in patients than in controls, without differences between normolipidemic and dyslipidemic subgroups. We have established the following cutoff values to differentiate between patients and controls: 0.43 mg/mg for the apo B/cholesterol ratio in LDL; 3.0 nmol malondialdehyde/mg protein for TBARS in native LDL; 22 and 80 nmol malondialdehyde/mg protein after 60- and 120-min postoxidative stress, respectively. We did not find differences in the conjugated diene production kinetics between patients and controls.

CONCLUSIONS

The enrichment in triglycerides and the high apoB/ cholesterol ratio suggest the presence of an abnormal LDL particle in normolipidemic and dyslipidemic patients. This LDL particle was more susceptible to oxidation. In the ROC analysis, the TBARS plot at 120 min exhibited greater accuracy and better performance than the other LDL oxidability markers.

Selective recruitment of ApoB-48 for the assembly of VLDL in rat triacylglycerol-enriched hepatocytes

Primary rat hepatocyte cultures were enriched in cellular triacylglycerol (TAG) by exposure to extracellular oleate for 3 days. Control cells were cultured for the same time without oleate. The large increase in TAG secretion into the medium of TAG-enriched cells during the final 24 hours (225 +/- 30 versus 40 +/- 10 micrograms/mg cell protein [control cells], P < .01) was not accompanied by a similar change in apolipoprotein B (apoB) secretion (4.22 +/- 0.94 versus 3.72 +/- 0.75 micrograms/mg per 24 hours, respectively). Instead, TAG-enriched cells recruited a larger proportion of apoB for the synthesis of very low density lipoprotein (VLDL), the secretion of which was substantially higher under these circumstances (1.46 +/- 0.39 versus 0.34 +/- 0.06 microgram apoB per milligram cell protein per 24 hours, P < .05). The increase in VLDL assembly was accompanied by a selective 2.5-fold increase (P < .05) in the specific recruitment of apoB-48. There was no significant increase in the amount of apoB-100, which appeared in the VLDL fraction when cells were enriched with TAG. Under these circumstances there was an increase in net cellular synthesis of apoB-48 (5524 +/- 667 versus 2505 +/- 598 disintegrations per minute per milligram protein per hour, P < .05). The net cellular synthesis of apoB-100 was unchanged compared with that observed in control cell cultures (1548 +/- 237 versus 2000 +/- 897 dpm/ mg per hour, respectively). A large proportion of the total secreted apoB was associated with small particles of density higher than VLDL, even when VLDL output was maximally stimulated, suggesting that apoB was oversecreted and in excess of the cells' requirement to transport TAG.

Compositions of very low density lipoprotein subfractions from patients with polydisperse low density lipoproteins

In some hyperlipidemic patients, low density lipoprotein (LDL) shows several peaks (polydisperse) on polyacrylamide gel disc electrophoreses, though LDL usually shows a single peak (monodisperse). In order to clarify the relationship between the LDL polydispersion and VLDL heterogeneity, LDL and VLDL were prepared from hyperlipidemic patients sera with mono- and polydisperse LDL by sequential ultracentrifugation and fractionated by gradient ultracentrifugation and their compositions were analyzed. Polydisperse LDL was rich in triacylglycerol (TG) and poor in esterified cholesterol (CE) as compared with monodisperse LDL and consisted of the lowest and the medium density subfractions when the LDL was separated into six subfractions. The monodisperse LDL was composed of a single major subfraction of a medium density. VLDL from the patients with polydisperse LDL was relatively rich in the dense and poor in the buoyant subfractions as compared with that from the patients with monodisperse LDL. The subfractions in the former contained more CE and less TG than the corresponding subfractions in the latter. There were no significant differences in the apolipoprotein compositions between those VLDLs. The results suggest that polydisperse LDL might be originated from VLDL that differs in particle sizes, densities and compositions from ordinary VLDL.

Regulatory function of glucose and insulin on high-density lipoprotein cholesterol in normolipidemic subjects

A decreased plasma concentration of high-density lipoprotein (HDL) cholesterol is associated with a higher incidence of coronary artery disease in populations. Therefore, there is intense investigation into the mechanisms responsible for the regulation of HDL cholesterol concentration in plasma. Insulin has a potent effect on HDL cholesterol, but it is unclear whether this is mediated by the primary effect insulin has on plasma triglycerides (TG). In this study, the question of the relationship between glucose, insulin, and HDL cholesterol has been addressed by investigating a cohort of nondiabetic normolipidemic men living in the Venice, Italy, area. One hundred twenty-eight men aged 30 to 69 years were initially recruited. The following parameters were measured: fasting plasma cholesterol, TG, HDL cholesterol, glucose, and insulin. One hundred seventeen of these subjects underwent an oral glucose tolerance test (OGTT), and the glucose and insulin responses were assessed. The final statistical analysis was performed on 98 nondiabetic individuals with plasma lipid levels within the 75th percentile for cholesterol and TG concentrations of the general population of the same age. The insulin response was a positive independent variable for plasma TG (P < .005) and HDL cholesterol (P < .005). On the other hand, HDL cholesterol was negatively associated with plasma TG. This relationship remained significant (P < .0001) also after controlling for age, body mass index (BMI), and glucose- and insulin-related measurements. Consistent with these results, both a stepwise variable selection analysis and a stratification analysis of the data indicated that the plasma TG concentration is the major determinant of HDL cholesterol level.(ABSTRACT TRUNCATED AT 250 WORDS)

Cutaneous blood flow abnormalities in hypertriglyceridemia

An accelerated atherosclerosis, in particular of the coronary arteries, was documented in hypertriglyceridemia. The objective of the present study was to assess the cutaneous dynamic blood flow in hypertriglyceridemia, utilizing the optical noninvasive method of laser Doppler flowmetry. The cutaneous blood flow on the forearms was measured during the postischemic reactive hyperemia test in treated and non-treated patients with hypertriglyceridemia and healthy control subjects. The subjects were 32 patients with hypertriglyceridemia--15 untreated and 17 following 6-9 months of bezafibrate treatment--and 27 healthy control subjects. In untreated patients with hypertriglyceridemia, the peak flow was significantly lower than in both the treated group (p < 0.005) and control group (p < 0.02). Similarly, the area under the response-time curve of the untreated patients with hypertriglyceridemia was smaller (p < 0.01 and p < 0.05, respectively). These parameters were similar in the treated group and the control group. The reaction was faster in the treated group, as compared to the other two groups (p < 0.001). The control group exhibited a longer time to decay than the treated group (p < 0.01). Postischemic reactive hyperemia tests in patients with hypertriglyceridemia reveal cutaneous microcirculatory changes in the forearm. These changes may arise from several mechanisms, including functional abnormalities of the endothelium or vascular smooth muscle, or structural changes in the blood vessels that limit vasodilatation. These changes are reversible, and corrected when reducing the triglyceride levels, but other abnormalities are then present, suggesting a permanent damage. These dynamic measurements of cutaneous blood flow are sensitive indicators of atherogenesis, and can be employed for the evaluation of microvascular involvement and follow-up of patients with hypertriglyceridemia.

Influence of apolipoprotein H polymorphism on levels of triglycerides

Human apolipoprotein H (apo H) displays a genetically determined structural polymorphism: three alleles (H*1, H*2 and H*3) on chromosome 17 code for the six phenotypes (three homozygotes and three heterozygotes). The effect of apolipoprotein polymorphism on individual variations in plasma lipoprotein levels has been underscored in recent years. Since apo H is involved in metabolism of triglycerides (Tg), its phenotype could affect Tg levels. This paper reports an investigation of apo H phenotypes in a sample of 217 subjects of the Italian population by means of isoelectrofocussing followed by immunoblotting. The levels of the main lipid parameters were evaluated in relation to phenotype and other influential factors. Analysis of covariance disclosed a significant association between Tg levels (log transformed) and phenotype (F = 8.27, P = 0.004). Comparison of Tg levels between bearers of the two most frequent phenotypes (H2/2 and H3/2) divided by sex and age classes revealed significantly higher levels in male H3/2 heterozygotes (P = 0.0053) and in H3/2 subjects aged less than 50 (P = 0.0095). Our data support the view that there is an association between hypertriglyceridaemia and apo H polymorphism, especially with the H*3 allele.

The association of waist/hip ratio with diabetes complications in an adult IDDM population

Cross-sectional data from the Epidemiology of Diabetes Complications Study were used to examine the relationships between waist to hip circumference ratio (WHR) and the presence of diabetes complications in IDDM adults ages 18-45 years (N = 586). Significantly higher WHRs were observed among both genders with proliferative retinopathy or peripheral vascular disease and only among males with either neuropathy or nephropathy compared to those free of these complications. Logistic regression to determine the strength of association between WHR and each complication demonstrated that although WHR was significantly related to each complication (except nephropathy among females), WHR was only independently related to neuropathy in males and PVD in females in the final model when hypertension, LDL- and HDL-cholesterol and fibrinogen were included. These findings suggest that WHR acts as a marker of risk for diabetes complications mainly through an influence on other complication risk factors.

Hypoalphalipoproteinemia: postprandial response of subjects with preprandial normotriglyceridemia and hypertriglyceridemia to various diets

The effect of a single oral fat meal (60 g fat/m2 body surface area) enriched in either saturated (SFA) or polyunsaturated ([PUFA] omega-6 or omega-3) fatty acids on postprandial lipoprotein levels was studied in four men with primary hypoalphalipoproteinemia (HP) and in four age- and sex-matched controls. Vitamin A was included in the meal to label intestinally derived triglyceride-rich particles (TRP) with retinyl palmitate (RP). The HP subjects were either mildly hypertriglyceridemic (group A) or normotriglyceridemic (group B) and were phenotyped for post-heparin lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) activities and apolipoprotein (apo) E isoforms. Postprandial total plasma triglyceride (TG), high-density lipoprotein (HDL) cholesterol, and RP and TG concentrations in the chylomicron (Sf > 1,000) and nonchylomicron (Sf > 1,000) fractions were evaluated for 24 hours after the meal. At each time point, HDL composition and size and apolipoprotein distributions were also measured. Following the SFA meal, HP subjects had maximal plasma TG levels at 8 hours (4 hours in controls) with a slow return to baseline levels at 12 to 24 hours (8 to 12 hours for controls). In contrast, after the omega-6 meal plasma TG levels decreased in group A subjects, while group B subjects and controls showed only a small increase. The results after the omega-6 meal were intermediate between the SFA and the omega-3 meal. When compared with group B, subjects in group A showed higher levels of RP-associated TRP, slower clearance rates, 30% to 50% lower fasting LPL activity, and 1.5-fold to twofold higher fasting plasma apo C-III levels. The major preprandial HDL subclass in HP subjects was HDL3, which showed a relative decrease in cholesterol esters (CE) and an increase in TG levels following the SFA meal. After the omega-3 meal, HDL of group A subjects showed a decrease in TG, a reciprocal increase in CE, and either no changes or minor changes in phospholipid (PL) and free-cholesterol (FC) levels. The results show that HP subjects with mild preprandial hypertriglyceridemia respond to a single fat meal differently than subjects with normotriglyceridemia, and that this difference is the result of HP in addition to other factors such as low LPL and HTGL activities, high plasma apo C-III levels, and apo E2 phenotype.

A controlled study of maternal serum concentrations of lipoproteins in pregnancy-induced hypertension

Seventeen women with pregnancy-induced hypertension (PIH) and 17 controls with uncomplicated pregnancy who were matched for maternal and gestational age were investigated for lipid concentrations in whole serum and lipoprotein fractions. The triglyceride level in the low-density lipoprotein fraction was higher in PIH patients than in controls (P < 0.03). The differences between values of other parameters did not attain the level of statistical significance, although the tendency of the results was consistent with findings reported in other studies. The differences observed were small and the data exhibited wide variation. Therefore, it appears unlikely that serum lipid and lipoprotein concentrations could gain major clinical importance as diagnostic parameters in PIH.

U-73482: a novel ACAT inhibitor that elevates HDL-cholesterol, lowers plasma triglyceride and facilitates hepatic cholesterol mobilization in the rat

U-73482, a novel acylCoA:cholesterol acyltransferase (ACAT) inhibitor with systemic activity, has been evaluated for its effects on a variety of lipid metabolic parameters in the rat. The compound inhibits ACAT in vitro in cultured Fu5AH rat hepatoma cells and demonstrates systemic activity through inhibition of hepatic ACAT in rats receiving the drug orally. U-73482 also lowers plasma triglycerides at 40 mg/kg per day in the rat and elevates high density lipoprotein cholesterol (HDL-chol) in a dose-related fashion over the range of daily intakes of 0-40 mg/kg in the rat. Elevations in HDL-chol are followed by elevations in total plasma cholesterol in normal rats but the compound exerts hypocholesterolemic activity in cholesterol-fed rats and promotes clearance of stored hepatic sterol in rats pretreated with a hypercholesterolemic diet and then changed over to normal chow. The triglyceride-lowering and HDL-chol elevating effects of U-73482 coupled with its ability to promote tissue sterol clearance and block the hypercholesterolemic effects of dietary cholesterol in animals, suggests that the compound has potential as a therapeutic agent for treatment of lipid disorders in man.

Influence of early diabetic nephropathy on very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL), and low density lipoprotein (LDL) composition

The procedure of discontinuous gradient ultracentrifugation (DGU) was used to characterize the influence of early diabetic nephropathy on the composition of very low density lipoprotein (VLDL, flotation density 60-400 Svedberg (Sf) units), low density lipoprotein (LDL, flotation density 0-12 Sf) and subfractions of intermediate density lipoprotein (IDL1 and IDL2, 20-60 and 12-20 Sf, respectively). Forty-six subjects with type 1 (insulin-dependent) diabetes and serum creatinine, less than 140 mumol/l were studied, of whom 23 consistently had normal rates of albumin excretion (AER less than 15 micrograms/min), and 23 had persistent albuminuria (AER 20.0-960.6 micrograms/min). The two groups were similar with respect to total serum lipids, glycaemic control, age and body mass. The composition (lipid, protein and phospholipid) and mass of VLDL, LDL and IDL2 was not appreciably altered by early nephropathy, but free and total cholesterol concentration in IDL1 (Sf 20-60) was increased (total cholesterol 0.68 (0.09) (mean (SE)) vs. 0.47 (0.07) mmol/l, and free cholesterol 0.27 (0.04) vs. 0.17 (0.03) mmol/l, both P less than 0.05). The explanation of these findings was probably an accumulation in the circulation of the remnants of chylomicron metabolism and/or intermediates in the conversion from VLDL to IDL1. In addition, there was a decrease in serum high density lipoprotein (HDL) cholesterol in early nephropathy (1.27 (0.06) vs. 1.38 (0.10) mmol/l, P less than 0.05), due to a decrease in the HDL2 cholesterol subfraction (P less than 0.05). These findings may in part explain the increased risk of premature atherosclerosis associated with the development of albuminuria.

Impact of dietary fatty acid supplementation on renal injury in obese Zucker rats

We previously reported that renal injury in hyperlipidemic, obese Zucker rats was associated with a relative deficiency of tissue polyunsaturated fatty acids (PUFA). In the present study 10-week-old obese Zucker rats were pair fed regular chow or chow containing either 20% sunflower oil rich in n-6 PUFA, fish oil rich in n-3 PUFA, coconut oil medium-chain saturated fatty acid, or beef tallow long-chain saturated fatty acid. At 34 weeks of age there were comparable reductions in albuminuria, mesangial matrix expansion, and glomerulosclerosis in the fish oil and sunflower oil groups. While both fish oil and sunflower oil reduced serum triglycerides, and improved the composition of triglyceride-enriched lipoproteins, only fish oil decreased serum cholesterol. The effect of the dietary fatty acid supplementation on fatty acid profiles were similar in isolated glomeruli and cortical tissue. In general, the amelioration in injury in the fish oil and sunflower oil fed rats was most closely linked to glomerular levels of PUFA, either n-6 or n-3. These data suggest that hyperlipidemia and abnormalities in tissue FA are closely linked, and that dietary supplementation with PUFA may ameliorate chronic, progressive renal injury.

Comparative studies on the influence of different fibrates on serum lipoproteins in endogenous hyperlipoproteinaemia

Two trials have been performed in the same patients with hyperlipoproteinaemia Types IIb (12 cases), III (6 cases) and IV (11 cases). In the first study the lipid-lowering properties of bezafibrate, fenofibrate, gemfibrozil, etofibrate and etofylline clofibrate were compared and in a separate trial the influence of combined treatment with gemfibrozil plus colestipol and bezafibrate plus probucol on lipoproteins were investigated. The mean percentage lipid-lowering effect of each fibrate on serum and VLDL fraction was significant in the Types IIb, III and IV patients, but there were significant differences between the fibrates. In general, gemfibrozil and bezafibrate decreased plasma lipid levels more than etofibrate and etofylline clofibrate in Type IIb patients. In Type IV cases gemfibrozil and bezafibrate were significantly potent in reducing the triglyceride level than fenofibrate, etofibrate or etofylline clofibrate. All the fibrates produced an increase in HDL cholesterol, but there were significant differences between them were in the Type IV patients. The influence of fibrates on the LDL fraction was much more variable. In hyperlipoproteinaemia Type IIb, a decrease in both LDL cholesterol and LDL apolipoprotein B was observed. In Type III and IV patients, however, an increase in LDL concentration occurred. The addition of colestipol to gemfibrozil therapy led to a further decrease in total cholesterol, LDL cholesterol and LDL apolipoprotein B in Type IIb patients. In patients with hyperlipoproteinaemia Types III and IV colestipol prevented the increase in LDL concentration after treatment with gemfibrozil alone. The effect of probucol on LDL cholesterol was comparable to that of colestipol. Combined treatment with gemfibrozil and colestipol caused an increase in HDL cholesterol concentration in contrast to combined treatment with bezafibrate and probucol.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipoprotein and hepatic lipase activity and high-density lipoprotein subclasses after cardiac transplantation

Atherosclerosis is the leading obstacle to long-term survival in cardiac transplant patients. Increases in plasma triglycerides and lipoprotein cholesterol levels occur after transplantation that may contribute to transplant atherosclerosis. The etiology of this increase is unclear. We investigated the interaction of immunosuppressive medications with plasma triglycerides, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, the HDL subclasses HDL2 and HDL3 cholesterol, and hepatic and lipoprotein lipase activity in 72 consecutive cardiac transplant patients compared to 51 healthy control subjects. In the transplantation group, greater concentrations of plasma triglyceride (80%, p less than 0.001), LDL cholesterol (16%, p less than 0.005) and hepatic lipase activity (100%, p less than 0.001) were noted, whereas lipoprotein lipase activity was noted to be significantly lower (124%, p less than 0.001). No difference was detected in HDL, HDL2, or HDL3 cholesterol. Cyclosporine dose was significantly associated with hepatic lipase activity (r = 0.33, p less than 0.02) and inversely associated with lipoprotein lipase activity (r = -0.28, p less than 0.05). Lipoprotein lipase activity after transplantation correlated inversely with triglycerides (r = -0.36, p less than 0.002) and positively with HDL cholesterol (r = 0.23, p less than 0.05) and HDL2 cholesterol (r = 0.29, p less than 0.05). Hepatic lipase activity correlated inversely with LDL cholesterol (r = -0.21, p less than 0.08). In multiple regression analysis, cyclosporine dose was the major source of variation in hepatic lipase activity.

Insulin resistance and hypertension

The author has reviewed the development of the concept that insulin resistance is related not only to the hypertensive state but potentially to the initiation and maintenance of high blood pressure. Potential sequelae of insulin resistance and hyperinsulinemia, as they apply to atherogenesis, are also discussed. The impact of present antihypertensive pharmacologic therapy on insulin resistance is addressed, as are future directions in pharmacologic and nonpharmacologic management of hypertension. In addition, the author speculates on possible mechanisms leading to insulin resistance in hypertension.

Regional distribution of body fat, plasma lipoproteins, and cardiovascular disease

Several epidemiological studies have reported that the regional distribution of body fat is a significant and independent risk factor for cardiovascular disease (CVD) and related mortality. Although these associations are well established, the causal mechanisms are not fully understood. Numerous studies have, however, shown that specific topographic features of adipose tissue are associated with metabolic complications that are considered as risk factors for CVD such as insulin resistance, hyperinsulinemia, glucose intolerance and type II diabetes mellitus, hypertension, and changes in the concentration of plasma lipids and lipoproteins. The present article summarizes the evidence on the metabolic correlates of body fat distribution. Potential mechanisms for the association between body fat distribution, metabolic complications, and CVD are reviewed, with an emphasis on plasma lipoprotein levels and plasma lipid transport. From the evidence available, it seems likely that subjects with visceral obesity represent the subgroup of obese individuals with the highest risk for CVD. Although body fat distribution is now considered as a more significant risk factor for CVD and related death rate than obesity per se, further research is clearly needed to identify the determinants of body fat distribution and the causal mechanisms involved in the metabolic alterations. It appears certain, however, that an altered plasma lipid transport is a significant component of the relation between body fat distribution and CVD.

Correlates of plasma very-low-density lipoprotein concentration and composition in premenopausal women

Potential correlates of plasma very-low-density lipoprotein (VLDL) concentration and composition were studied in a sample of 75 premenopausal women. Fasting plasma free fatty acid (FFA) levels, as well as plasma glucose and insulin levels in the fasting state and during an oral glucose tolerance test, displayed significant positive correlations with plasma triglyceride (TG) and VLDL-TG levels (P less than .005). Plasma post-heparin lipoprotein lipase (LPL) activity, measured in a subsample of 31 women from the original sample, was negatively correlated with plasma TG, VLDL-cholesterol (CHOL), VLDL-TG, and VLDL-apolipoprotein (apo) B concentrations (.005 greater than P less than .05). Multivariate analyses showed that, after LPL was considered, the insulin area was the only other metabolic variable studied that was significantly correlated with VLDL-apo B concentration, whereas fasting FFA levels were significantly correlated with plasma TG and VLDL-TG levels. ANOVA revealed that plasma VLDL-CHOL, VLDL-TG, and VLDL-apo B levels were not associated with the glucose area, but were significantly associated with the insulin area (P less than .005). When the effect of insulin area was controlled for, the plasma FFA levels did not contribute significantly to the variance in VLDL-CHOL and VLDL-apo B, but showed an independent effect on VLDL-TG levels (P less than .05). Finally, stepwise multiple regression analyses indicated that once the variance explained by plasma LPL activity and by the insulin area was considered, no other metabolic variable could account for the variation in VLDL-CHOL and VLDL-apo B levels, whereas fasting FFA levels explained a further 5% of the VLDL-TG variance and one third of the variance observed in the VLDL-TG/apo B ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Postprandial lipemia and lipoprotein lipase in the rabbit are modified by olive and coconut oil

Feeding a 14% coconut oil/0.5% cholesterol (CNO/chol) diet to rabbits resulted in plasma triglycerides that were, on average, 15 times higher than basal levels. Plasma triglycerides in rabbits fed a 14% olive oil/0.5% cholesterol (OO/chol) diet were significantly below baseline levels. Differences in postprandial triglyceride response and postheparin plasma lipoprotein lipase activity (LPL) in various feeding conditions were studied to determine the mechanism of the hypertriglyceridemia. Postprandial triglyceride responses after the first high fat/cholesterol meal were more prolonged in CNO/chol rabbits than in OO/chol rabbits; postprandial triglyceride responses after chronic CNO/chol feeding were significantly greater compared to OO/chol rabbits. When long-term CNO/chol rabbits were given one OO/chol or corn oil/chol meal, postprandial triglyceride peaks were greatly diminished, suggesting that these unsaturated fat meals may alter triglyceride clearance capacity. LPL activity was 400% higher than basal levels in chronically fed OO/chol rabbits but changed very little in chronically fed CNO/chol rabbits. Twenty-four hours after a single OO/chol meal was fed to chow-fed rabbits, LPL doubled; one CNO/chol meal was associated with only a 40% increase. Feeding a single OO/chol or corn oil/chol meal to chronically fed CNO/chol rabbits resulted in a 30% to 50% increase in LPL by 24 hours. Thus, the hypertriglyceridemia in CNO/chol rabbits may result in part from a decreased clearance capacity due to a lack of increase in LPL activity, while increased LPL may be partially responsible for the hypotriglyceridemia observed in OO/chol feeding. Aortic cholesterol was substantially higher in CNO/chol rabbits. Triglyceride was approximately eight times greater in livers from CNO/chol-fed rabbits than in those fed OO/chol, but liver cholesterol was only about one-third as much as that in OO/chol rabbits.

Enhanced net mass transfer of HDL cholesteryl esters to Apo B-containing lipoproteins in patients with peripheral vascular disease

In vitro net mass transfer of HDL cholesteryl ester to apolipoprotein (Apo) B-containing lipoproteins (HDL-CET) was found to be nearly twofold higher in plasma from 35 male patients with peripheral vascular disease compared to the values of 27 age- and sex-matched healthy controls (P less than 0.001). Differences in HDL-CET were predominantly observed between normolipidemic patients and controls, and were also demonstrable in pairs of patients and controls with similar HDL cholesterol, VLDL + LDL cholesterol, and triglyceride concentrations. Within the control group, higher HDL-CET was found in individuals with enhanced triglyceride or VLDL + LDL cholesterol levels. This dependence was not observed in the patient group. Consequently, enhanced HDL-CET in the patients seems to be independent of plasma lipid levels.

Improved method for enzymic determination of cholesterol in lipoproteins separated by electrophoresis on thin layer agarose gels

The cholesterol of lipoproteins, separated electrophoretically on thin layer agarose films, is visualised and quantitated by incubating the gels in an enzymic reagent containing cholesterol esterase and cholesterol dehydrogenase. The individual fractions are quantitated by scanning densitometry. No sample pretreatment is necessary. All major fractions are detected readily. The accuracy of the determination is similar to that of ultracentrifugation. On average, imprecision is 3.1% for beta-, 7.0% for pre beta-, and 4.8% for alpha-lipoprotein cholesterol. Concentration and colour development are linear up to 8 mmol/l cholesterol in a given lipoprotein fraction. The results from the direct enzymic procedure for beta-, pre beta- and alpha-lipoprotein cholesterol are compared with those from quantitative lipoprotein electrophoresis after precipitation with phosphotungstic acid and bivalent cations and with those from different precipitation methods using dextran sulphate and polyethylene glycol. The new method has several advantages: high specificity; lack of dependence on the actual composition of the lipoproteins; lack of interference from coprecipitated proteins in the gel, e.g. fibrinogen or paraproteins; and insensitivity to lipolysis and high free fatty acid concentrations caused by heparin application or ageing of the specimen (at least for alpha-lipoprotein cholesterol quantitation). In its convenience and simplicity of operation, and the simple calculation of results, the method is similar to standard protein electrophoresis. The proposed method is therefore suggested as a standard method for elucidating lipoprotein disorders.

Lipoprotein composition changes induced by fenofibrate in dysbetalipoproteinemia type III

Fenofibrate (300 mg daily) was given to 9 subjects (7 men, 2 women) with dysbetalipoproteinemia type III. The treatment brought about important plasma level reductions in cholesterol (-35%), triglycerides (-56%), VLDL-cholesterol (-63%) and VLDL-triglycerides (-59%). The VLDL-C/TG ratio, which was 0.40 before treatment, was 0.30 after 4 weeks of fenofibrate, still suggestive of type III. LDL-C, when measured by conventional methods, was unchanged but isolation of the IDL (1.006-1.019 g/ml) fraction from the 1.006 g/ml infranatant revealed that true LDL-C levels actually increased in 6 individuals while IDL-C decreased considerably. The total HDL-C increase was mostly due to a 33% HDL3-C change. Apolipoprotein levels were considerably modified, notably apo B, C-III and E which were decreased, as well as the lipoprotein particles containing combinations of these apolipoproteins, namely LpE:B and LpC-III:B. Apo A-I was slightly modified as LpA-I: A-II particle levels increased and LpA-I decreased. There were marked compositional modifications of apo B-containing lipoproteins which corresponded to changes of the whole lipoprotein profile. Some abnormal classes of lipoproteins (e.g., beta-VLDL, dense LDL), characteristic of this disease, tended to disappear and were in some cases replaced by material of different size and density.

A specific method for the direct determination of lipoprotein cholesterol in electrophoretic patterns

Lipoproteins are separated electrophoretically and cholesterol is visualised with an enzymic reagent specific for cholesterol in which the gels are incubated. Quantitation of the individual fractions is accomplished by scanning densitometry. No sample pretreatment is necessary. All major fractions are detected readily. Accuracy agrees favorably with results from the ultracentrifugation. On the average, imprecision is 3.1% for beta-, 6.9% for prebeta-, and 5.2% for alpha-lipoprotein cholesterol. Concentration and color development are linear up to 8 mmol/l cholesterol in a given lipoprotein fraction. The results of the direct enzymic procedure for beta-, prebeta- and alpha-lipoprotein cholesterol are compared to the quantitative lipoprotein electrophoresis after precipitation with phosphotungstic acid and bivalent cations.