[The impaired glucose tolerance in the pathogenesis of dyslipidemia]

It is well known that hyperlipidemia is often present in patient with impaired glucose tolerance, obesity and/or hypertension. All of these are risk factors for coronary artery disease (CAD). The coexistence of these risk factors markedly increase the likelihood of CAD. Recently, it has been reported that the impaired glucose tolerance and insulin resistence are associated with the increased proinsulin, which is linked to the risk of CAD. We review that the impaired glucose tolerance is an important factor causing dyslipidemia. The characteristic of dyslipidemia associated with the impaired glucose tolerance include hypertriglyceridemia, high level of VLDL and low level of HDL cholesterol. They also associate with accumulation of remnant lipoproteins and appearance of small dense LDL. In addition, we pointed out that the increased number of risk factors is associated with elevated insulin and proinsulin level.

[Obesity and insulin resistance syndrome]

Obesity is commonly associated with insulin resistance. The etiology of insulin resistance syndrome such as syndrome X or deadly quartet is not clear. We have proposed visceral fat syndrome, in which fat accumulation is predominant in the intra-abdominal cavity, frequently accompanied by disorders of glucose and lipid metabolism, and also hypertension. Excess free fatty acid of the portal circulation may cause the enhancement of lipid synthesis and gluconeogenesis as well as insulin resistance, resulting in hyperlipidemia, glucose intolerance and hypertension and finally atherosclerosis. Enhanced production of PAI-1 by increased visceral fat may be partly responsible for the development of cardiovascular disease in patient with visceral fat assmulation.

Effect of combination therapy with lipid-reducing drugs in patients with coronary heart disease and "normal" cholesterol levels. A randomized, placebo-controlled trial. Harvard Atherosclerosis Reversibility Project (HARP) Study Group

BACKGROUND

Combination drug therapy has been shown to decrease cholesterol levels in hyperlipidemic patients. However, its efficacy has not been well studied in patients previously considered to be normolipidemic, many of whom are now candidates for this therapy.

OBJECTIVE

To determine the efficacy and tolerability of multidrug therapy designed to improve low-density lipoprotein (LDL) and high-density lipoprotein (HDL) cholesterol levels in patients with coronary heart disease and average lipid levels.

DESIGN

Randomized, placebo-controlled, 2.5-year trial comparing patients receiving usual care with patients receiving stepped-care drug therapy.

INTERVENTION

Stepped-care therapy (pravastatin, nicotinic acid, cholestyramine, and gemfibrozil) to decrease total cholesterol levels to less than 4.1 mmol/L (160 mg/dL) and the ratio of LDL cholesterol to HDL cholesterol to less than 2.0.

SETTING

2 academic, urban, tertiary care hospitals.

PATIENTS

91 patients (80 men and 11 women) with coronary heart disease, a mean age of 60 years, total cholesterol levels less than 6.4 mmol/L (250 mg/dL) at baseline, and ratios of total cholesterol to HDL cholesterol greater than 4.0 at baseline.

MEASUREMENTS

Fasting serum lipoprotein profile, fasting apolipoprotein levels, and frequency of adverse effects. Patients were assessed every 6 weeks during drug titration and every 3 months thereafter.

RESULTS

Mean lipid levels at baseline were as follows: total cholesterol, 5.5 mmol/L (214 mg/dL); LDL cholesterol, 3.6 mmol/L (140 mg/dL); HDL cholesterol, 1.1 mmol/L (42 mg/dL); and triglycerides, 1.8 mmol/L (159 mg/dL). With pravastatin, changes in levels from baseline were -22% for total cholesterol, -32% for LDL cholesterol +8% for HDL cholesterol, and -15% for triglycerides (P < 0.001 for all comparisons). With the addition of 1.5 g of nicotinic acid, additional changes were -6% for total cholesterol (P < 0.002). -11% for LDL cholesterol, +8% for HDL cholesterol, and -10% for triglycerides (P < 0.001 for all comparisons). With 2.25 to 3 g of nicotinic acid, these changes were -7% for total cholesterol (P = 0.007), -14% for LDL cholesterol (P < 0.001), +6% for HDL cholesterol (P = 0.02), and -13% for triglycerides (P = 0.03). With cholestyramine, total cholesterol and LDL cholesterol levels were unchanged compared with the previous step; the change in HDL cholesterol level was -8% (P = 0.03); and the change in triglyceride level was +46% (P < 0.001). With gemfibrozil, total cholesterol level was unchanged; the additional change in LDL cholesterol level was +12% (P = 0.09); the change in HDL cholesterol level was +12% (P = 0.03); and the change in triglyceride level was -37% (P < 0.001). Apolipoprotein B levels decreased by 25% overall (P < 0.001); lipoprotein(a) levels did not change significantly. Adverse effects were primarily attributable to nicotinic acid or cholestyramine. In 18 of the 35 patients (50%) whose baseline LDL cholesterol levels were greater than 3.35 mmol/L (130 mg/dL), pravastatin decreased LDL cholesterol levels to 2.6 mmol/L (100 mg/dL) or less by 6 weeks; 70% of patients needed combination therapy to reach this National Cholesterol Education Program goal during the 2.5 years of the study. Adding nicotinic acid to pravastatin produced LDL cholesterol levels of 2.6 mmol/L or less in 15 more of these 35 patients, so that 94% (n = 33) of the patients receiving these two drugs reached this goal.

CONCLUSIONS

To reach current goals for LDL cholesterol levels, most normolipidemic patients with coronary heart disease in this study needed combination therapy. Pravastatin with nicotinic acid and pravastatin with gemfibrozil are well-tolerated combinations that can maintain target LDL cholesterol levels, decrease triglyceride levels, and increase HDL cholesterol levels. Adding resin to these combinations produced no further benefit.

Dyslipidaemia in polycystic ovarian syndrome: different groups, different aetiologies?

The objective was to study the pathophysiology of the dyslipidaemia in polycystic ovarian syndrome (PCOS) patients, and to determine how it is related to hyperinsulinaemia, hyperandrogenism and dehydroepiandrosterone sulphate (DHEA-S) concentrations. The lipoprotein lipid profile, anthropometric measurements, endocrine profile and the presence of insulin resistance were evaluated in 31 PCOS patients and 20 age-matched healthy women, who served as controls. PCOS patients had higher fasting insulin concentrations, higher body mass indexes (BMI) and were hyperlipidaemic, with higher total cholesterol, low density lipoprotein (LDL) and triglyceride (TG) concentrations. There were no relationships between plasma lipids and anthropometric variables in the patient group as a whole. Insulin-resistant (IR) and non-IR (NIR) PCOS patients were then evaluated separately. Obesity with marked hyperandrogenism were the predominant features in patients with IR. NIR patients were not obese and had significantly less hyperandrogenism. The adrenal androgen DHEA-S was at the upper limit of its normal range in both groups. However, both PCOS subgroups exhibited similar significant abnormalities in terms of their lipid parameters. Insulin and DHEA-S concentrations were positively correlated with total cholesterol, LDL and TG, and negatively correlated with high density lipoprotein, in IR patients. In NIR subjects, insulin was not correlated with any of the lipids and DHEA-S was negatively related to cholesterol and LDL. Anthropometric variables were related to lipids in only the NIR patients. Thus PCOS subjects as a group exhibit dyslipidaemia, characterized by increased total cholesterol, LDL and TG concentrations. When divided into IR and NIR subjects, there were no differences in the degree of lipid abnormalities, despite significant variations in the BMI and androgen status. Thus, in PCOS subjects, dyslipidaemia may occur irrespective of insulin resistance. Insulin and DHEA-S concentrations were positively correlated with an atherogenic lipid profile in the IR group only. As distinct from syndrome X when IR was present, dyslipidaemia was not related to body weight or the waist:hip ratio. In the NIR group there was no relationship between lipids and insulin; DHEA-S, on the other hand, was negatively related to cholesterol and LDL concentrations. Thus, dyslipidaemia in PCOS patients may occur irrespective of insulin resistance, and may have different metabolic aetiologies depending on DHEA-S metabolism. It remains to be seen whether the two types of PCOS are associated with different risks for ischaemic heart disease.

Lipid lowering therapy and military aviators

This article discusses the role of the newer lipid lowering agents (statins and fibrates) for the treatment of hyperlipidemias in military aviators. Special emphasis will be on long-term safety and the effects of these drugs on CNS functions pertinent to aviators. We propose that these new lipid lowering agents, such as hydrophilic statins and newer fibrates are reasonably safe in aviators with restricted flying duties, subject to long-term surveillance by a specialist.

Combined hyperlipidemia in transgenic mice overexpressing human apolipoprotein Cl

We have generated transgenic mice over-expressing human apolipoprotein CI (apo CI) using the native gene joined to the downstream 154-bp liver-specific enhancer that we defined for apo E. Human apo CI (HuCI)-transgenic mice showed elevation of plasma triglycerides (mg/dl) compared to controls in both the fasted (211 +/- 81 vs 123 +/- 52, P = 0.0001) and fed (265 +/- 105 vs 146 +/- 68, P < 0.0001) states. Unlike the human apo CII (HuCII)- and apo CIII (HuCIII)-transgenic mouse models of hypertriglyceridemia, plasma cholesterol was disproportionately elevated (95 +/- 23 vs 73 +/- 23, P = 0.002, fasted and 90 +/- 24 vs 61 +/- 14, P < 0.0001, fed). Lipoprotein fractionation showed increased VLDL and IDL + LDL with an increased cholesterol/triglyceride ratio (0.114 vs 0.065, P = 0.02, in VLDL). The VLDL apo E/apo B ratio was decreased 3.4-fold (P = 0.05) and apo CII and apo CIII decreased in proportion to apo E. Triglyceride and apo B production rates were normal, but clearance rates of VLDL triglycerides and postlipolysis lipoprotein "remnants" were significantly slowed. Plasma apo B was significantly elevated. Unlike HuCII- and HuCIII-transgenic mice, VLDL from HuCI transgenic mice bound heparin-Sepharose, a model for cell-surface glycosaminoglycans, normally. In summary, apo CI overexpression is associated with decreased particulate uptake of apo B-containing lipoproteins, leading to increased levels of several potentially atherogenic species, including cholesterol-enriched VLDL, IDL, and LDL.

ACTH lowers serum lipids in steroid-treated hyperlipemic patients with kidney disease

The mechanisms behind secondary hyperlipidemia in patients with various chronic inflammatory diseases are not known in detail. We have recently demonstrated that ACTH exerts strong hypolipidemic effects in healthy volunteers. To test the clinical relevance of this finding, we administrated ACTH during three weeks to nine hyperlipidemic steroid-treated patients with kidney disease. Before administration of ACTH 1-24, plasma ACTH concentrations were low. Treatment with ACTH led to 20 to 50% reductions in serum concentrations of triglycerides, cholesterol, LDL cholesterol and Apo B as well as of Lp(a). HDL cholesterol and Apo A1 concentrations increased by 10 to 25%. HL activity in postheparin plasma decreased by about 40% and LPL activity, which was initially low, increased by about 140%. The effects of ACTH were similar in kidney transplant recipients and in patients with inflammatory kidney disease. Our results indicate that hyperlipidemia in steroid treated patients with kidney disease may at least partly be due to iatrogenic ACTH deficiency.

Estrogen increases low-density lipoprotein receptor-independent catabolism of apolipoprotein B in hyperlipidemic rabbits

Estrogen has been reported to increase the catabolism of low-density lipoprotein (LDL) apolipoprotein (apo) B by increasing LDL receptor activity. To determine the effect of estrogen on LDL receptor-independent pathways, paired turnover studies of native LDL and chemically modified LDL (methyl-LDL) were performed before and during estrogen administration in female New Zealand rabbits consuming a diet containing 0.5% (wt/wt) cholesterol. Rabbits were matched by plasma cholesterol concentration and assigned randomly to receive estrogen (estradiol cypionate 0.5 mg/kg/wk) or placebo. The residence time of both the native LDL apo B tracer and the methyl-LDL apo B tracer in plasma was decreased by estrogen but not by placebo. Multicompartmental modeling of the paired, double-labeled turnover studies indicated that an increase in fractional catabolic rate (FCR) of the fast-turnover pool, a kinetically distinct LDL subpopulation in plasma, accounted for the observed decrease in residence time in plasma for both tracers. These data support the hypothesis that, in addition to any effect on the LDL receptor, estrogen promotes the activity of LDL receptor-independent pathways.

Post-transplant hyperlipidemia: mechanisms and management

Hyperlipidemia is common after renal transplantation. In recent years, much progress has been made in understanding the causes and treatment of lipid abnormalities in renal transplant patients. Recently, short-term studies have shown that newer antilipemic agents appear to be safe and effective in treating hyperlipidemia in this population. Despite the absence of large, controlled clinical trials examining the effect of lipid-lowering strategies on cardiovascular disease and chronic renal allograft rejection, therapy appears to be warranted in renal transplant patients with an atherogenic lipid profile and multiple risk factors.

Dyslipidemia in diabetes mellitus

Patients with diabetes mellitus have a higher rate of mortality than the general population. This higher mortality may be attributed mainly to cardiovascular disease. A high prevalence of dyslipidemia in diabetics can be one of the reasons for this. The most commonly recognized lipid abnormality in non-insulin-dependent diabetics (NIDDM) is hypertriglyceridemia, which is known to be an independent risk factor for coronary heart disease in diabetics. Hypertriglyceridemia can be produced by two mechanisms, increased synthesis of very-low-density lipoprotein (VLDL) triglyceride and removal defect of plasma triglyceride. It has been a matter of debate whether insulin always stimulates hepatic VLDL secretion but it is generally accepted that insulin deficiency results in an impairment of plasma triglyceride clearance. Considerable attention has recently been focused on the atherogenecity of postprandial hyperlipidemia, remnant lipoproteins, small, dense LDL, lipoprotein (a) [Lp(a)] and isolated hypo-alphalipoproteinemia in NIDDM subjects. Several reports suggested that these atherogenic lipoprotein abnormalities are present in NIDDMs even if they are apparently normolipidemic. Association of visceral fat obesity, insulin resistance and nephropathy may aggravate the atherogenic lipoprotein profile. Therefore, we propose here that plasma lipid levels of diabetic subjects must be more strictly controlled than for the non-diabetic population in order to avoid an increased risk for coronary heart disease. If they are obese or associated with insulin resistance or nephropathy, these conditions should be carefully controlled.

Comparative pharmacokinetics of theophylline in rabbits and in humans with hyperlipidemia

The study was carried out on male rabbits divided into two groups: a control and an experimental one, fed on a high-fat diet. Humans were also ascribed into two groups: control and those affected with primary, mixed form of hyperlipidemia. The animals and humans were given theophylline intravenously as a single dose. Blood was sampled after 5, 10, 15, 30 and 45 min and 1, 2, 4, 6, 8, 12 and 24 h following theophylline administration. FPIA method was used to determine blood serum concentrations of theophylline. Considerable alterations of theophylline pharmacokinetics in humans suffering from mixed form of hyperlipidemia were observed. Marked decrease in area under the concentration-time curve (AUC), diminished volume of distribution, increased total body clearance, and shortened elimination half-life were observed. On the contrary, in rabbits with alimentary induced lipid metabolism disturbances t1/2 of theophylline was practically unchanged and AUC only slightly increased.

IN CONCLUSION

(1) hyperlipidemia affects the pharmacokinetics of theophylline in human beings, (2) rabbit model with dietetary induced lipid metabolic disturbances is not a suitable subject for estimation of pharmacokinetics of xanthine derivatives.

Lipoprotein metabolism in renal replacement therapy: a review

Lipoprotein disorders are considered an important cause for the high cardiovascular morbidity and mortality in patients with end-stage renal disease and following renal transplantation. This article reviews the disease-associated changes of lipids and lipoproteins in these patients and, where known, the underlying causes and mechanisms. Further, we discuss the perturbed lipoprotein system in relation to the cardiovascular risk of patients on renal replacement therapy. Patients treated by hemodialysis are often hypertriglyceridemic with increased very low density lipoprotein (VLDL) levels and a type IV Frederickson pattern of hyperlipidemia. Total and LDL cholesterol concentrations are usually normal or subnormal. Treatment of end-stage renal disease by peritoneal dialysis results in increased total, VLDL and LDL cholesterol concentrations. Both treatment modalities are accompanied by a decrease of high density lipoprotein (HDL) cholesterol and apolipoprotein AI, whereas lipoprotein(a) [Lp(a)] concentrations are significantly elevated in both groups. Following renal transplantation a high incidence of hypercholesterolemia and hypertrigylceridemia is observed, which is attributed, at least in part, to the immunosuppressive therapy. Most patients normalize HDL cholesterol values and Lp(a) decreases to pre-disease plasma concentrations. Several studies have described elevated levels of cholesterol, triglycerides and Lp(a) in patients with cardiovascular complications during different phases of renal replacement therapy, which indicates a predictive (causative) role of these parameters for atherosclerotic diseases.

Dyslipidemia in renal disease

In summary, dyslipidemia is a common feature of various renal syndromes. Whether this perturbed lipid metabolism results in accelerated atherosclerosis and increased cerebrovascular and cardiovascular morbidity and mortality remains a subject of inquiry. Also undefined is the role of dyslipidemia in the progression of renal injury. The malnutrition that becomes a dominant morbid feature in patients on maintenance renal replacement therapy provides a caveat against aggressive intervention for modest hyperlipidemia once dialysis is instituted. Individualized assessment of end organ atherosclerotic disease and cardiovascular risk factors should form the basis for modification of the treatment plan (ie, pharmacological intervention) should nonpharmacological means prove ineffective.

Dyslipidaemia and hyperlipidaemia following renal transplantation

The lipid metabolism of 93 patients with renal transplantation was prospectively studied. It was characterized by the serum levels of cholesterol, HDL, LDL, triglyceride, apolipoprotein Al, Apo B and lipoprotein (a) as well as by lipid electrophoresis. In addition to the examination of lipid concentrations, the authors looked for correlations with other metabolic changes, immunosuppressive treatment and the changes of body weight and hypertension following transplantation. Their conclusion is that hyperlipidaemic and dyslipidaemic changes, as reflected by the levels of total cholesterol, LDL and Apo B, are more considerable in women than in men. The levels of pre-beta and beta lipoprotein were not significantly lower in men than in women. With the passing of time after transplantation and with the reduction of the doses of cyclosporine and corticosteroids, the values of hypertension, hyperlipidaemia and dyslipidaemia decreased. According to the follow-up results, the lipid values measured in the winter and autumn months are higher than those found in the summer. The importance of early and follow-up examinations and of the reduction of pathological metabolic alterations is emphasized.

Hyperlipidaemia in renal transplant patients

OBJECTIVES

The aim of study was to assess the prevalence and severity of hyperlipidaemia in renal transplant patients in a Nordic country.

DESIGN

Multicentre, cross-sectional study.

SETTING

Outpatients and ward inpatients registered from 23 hospitals covering all regions of the country.

SUBJECTS

Renal transplant patients with a functioning graft were registered: 406 patients in all; that is, 43% of the national renal transplant population. All patients used prednisolone, 71% used cyclosporine, either with (51%) or without (20%) azathioprine. Total cholesterol values from general population were obtained from a national survey.

MAIN OUTCOME MEASURES

Blood lipids and their relation to clinical parameters.

RESULTS

Total cholesterol was significantly higher in transplant patients than in the general population for both genders and all age groups (P < 0.01). Female patients had higher total cholesterol (mean +/- SD: 7.49 +/- 1.61 mmol L(-1)) than males (7.01 +/- 1.55 mmol L(-1); P < 0.001), and also higher HDL cholesterol (1.55 +/- 0.43 vs. males: 1.32 +/- 0.46 mmol L(-1); P < 0.001). Triglycerides were equally elevated in both genders, and 33% had values above 2.2 mmol L(-1). Reduced creatinine clearance, a high body-mass index, female gender, hypertension, and coronary artery disease were independently associated with higher total cholesterol. Beta blockers were associated with lower HDL cholesterol and higher triglycerides, and diuretics with higher triglycerides. Blood lipid levels were not associated with cyclosporine immunosuppression.

CONCLUSION

Hyperlipidaemia is prevalent after renal transplantation, and is associated with impaired graft function, hypertension, and with the use of beta blockers and diuretics, but not with the use of cyclosporine.

Lipid status in a population of Spanish schoolchildren

We assessed lipid status in a population of 181 schoolchildren and adolescents divided into three age groups: 6-7 years (n = 60), 10-12 years (n = 61) and 13-15 years (n = 60). All subjects were from the Mediterranean coastal area of Vélez-Málaga in southern Spain. Nutrient intakes and biochemical parameters related with lipid status [total cholesterol (TC), HDL-chol, LDL-chol, VLDL-chol and triglycerides (TG)] were measured. Boys and girls aged 6-7 years had the same plasma concentrations of TC and TG; these concentrations were slightly higher than the mean values for age and sex found in earlier studies in Spanish populations. The high TC values were due mainly to increased concentrations of LDL-chol. This age group also had the largest percentage of members (26.6% boys, 36.6% girls) with plasma TC above 200 mg/dl. Of the groups aged 10-12 years, more girls than boys had abnormally high plasma cholesterol (16.1 vs 10%), HDL-chol (6.5 vs 0%) and TG concentrations (6.5 vs 0%). However, more adolescent boys than adolescent girls (aged 13-15 years) had abnormally low plasma concentrations of HDL-chol (10 vs 3.3%).