Triglycerides as a risk factor for coronary artery disease

Development and Validation of an Enzymatic Method for Total Cholesterol Analysis Using Whole Blood Spot

BACKGROUND

High serum cholesterol represents a risk factor for cardiovascular disease. This study aims to quantify total cholesterol in dried blood spot (DBS) by direct enzymatic method.

METHODS

Three hundred seventeen blood samples with serum cholesterol level ranging from 81 to 337 mg/dl were collected. DBS were manually prepared, cholesterol was extracted using methanol and analyzed by a manual enzymatic method. DBS cholesterol method was validated for imprecision and extraction efficacy. DBS cholesterol values were correlated (training test) with serum values measured by automated enzymatic method (reference method). The obtained correlation was used for predicting serum cholesterol from DBS analysis of a new sample group (validation test, n = 58).

RESULTS

Within-day and between-day coefficient of variation (CV%) were lower than 7.69 and 6.32, respectively. Residual cholesterol in DBS after extraction was 16%. DBS cholesterol and serum cholesterol showed a linear correlation (slope = 0.5217; r = 0.9139) and a bias of -28%. Furthermore, DBS cholesterol values of validation test (n = 58), converted using the training test correlation, were not statistically different compared to the corresponding plasma values (P = 0.9487), and the comparison by Passing and Bablok showed a linear regression with a slope of 1.068 (r = 0.611) and a bias of -0.22%.

CONCLUSIONS

The results show that this enzymatic method is suitable to analyze cholesterol in DBS and it could be automated and used for population screening of total blood cholesterol.

Identification of molecular species of oxidized triglyceride in plasma and its distribution in lipoproteins

The role of triglycerides carried in the triglyceride-rich lipoproteins (TRL) in the progression of atherosclerosis is uncertain. Identification of oxidized triglycerides and its possible association with atherosclerosis were largely ignored. Here we applied mass spectrometric approach to detect and identify triglyceride hydroperoxides (TGOOH) in human plasma and lipoproteins.

EDTA plasma was collected from healthy human volunteers (n=9) after 14–16 h of fasting. Very low-density lipoprotein (VLDL)

We identified 11 molecular species of TGOOH in either plasma or VLDL and IDL, of which TGOOH-18:1/18:2/16:0, TGOOH-18:1/18:1/16:0, TGOOH-16:0/18:2/16:0, TGOOH-18:1/18:1/18:1, and TGOOH-16:0/20:4/16:0 were most dominant. These TGOOH molecules are carried by TRL but not by LDL and HDL. Mean concentration of TGOOH in plasma, VLDL and IDL were, respectively, 56.1±25.6, 349.8±253.6 and 512.5±173.2 μmol/mol of triglycerides.

This is the first report to identify several molecular species of oxidized triglycerides in TRL. Presence of oxidized triglyceride may contribute to the atherogenicity of TRL. Further work is needed to elucidate the association of the oxidized triglyceride in atherosclerosis.

The effects of treatment on lipoprotein subfractions evaluated by polyacrylamide gel electrophoresis in patients with autoimmune hypothyroidism and hyperthyroidism

BACKGROUND

Atherogenic dyslipoproteinemia is one of the most important risk factor for atherosclerotic changes development. Hypothyroidism is one of the most common causes of secondary dyslipidemias which results from reduced LDL clearance and therefore raised levels of LDL and apoB. Association between small dense LDL (sdLDL) presentation and thyroid status has been examinated using polyacrylamide gel electrophoresis for lipoprotein subfractions evaluation.

METHODS

40 patients with diagnosed autoimmune hypothyroidism and 30 patients with autoimmune hyperthyroidism were treated with thyroxine replacement or thyreo-suppressive treatment. In both groups lipid profiles, LDL subractions, apolipoproteins (apoA1, apoB), apoA1/apoB ratio and atherogenic index of plazma (AIP) were examined before treatment and in state of euthyreosis.

RESULTS

Thyroxine replacement therapy significantly reduced levels of total cholesterol (TC), LDL, triglycerides (TG) and also decreased levels of sdLDL (8,55±11,671 vs 0,83±1,693mg/dl; p<0,001), apoB and AIP. For estimation of atherogenic lipoprotein profile existence an AIP evaluation seems to be better than apoB measurement because of the more evident relationship with sdLDL (r=0,538; p<0,01). Thyreo-suppressive therapy significantly increased levels of TC, LDL, TG and apoB. The sdLDL was not found in hyperthyroid patients.

CONCLUSIONS

Atherogenic lipoprotein profile was present in 52.5% of hypothyroid subjects, which is higher prevalence than in normal, age-related population. Substitution treatment leads to an improvement of the lipid levels, TG, apoB, AIP and LDL subclasses. It significantly changed the presentation of sdLDL - we noticed shift to large, less atherogenic LDL particles. Significantly positive correlation between sdLDL and TAG; sdLDL and VLDL alerts to hypertriglyceridemia as a major cardiovascular risk factor.

Pharmacological evaluation of the efficacy of Dysoxylum binectariferum stem bark and its active constituent rohitukine in regulation of dyslipidemia in rats

The antidyslipidemic effect of the ethanolic extract of Dysoxylum binectariferum stem bark and its major active constituent rohitukine was evaluated in a high fat diet (HFD)-fed dyslipidemic rat model. Chronic feeding of ethanolic extract (200 mg/kg) in HFD-fed rats showed significant lipid lowering activity. The bioassay guided fractionation of ethanolic extract resulted in the identification of known alkaloid rohitukine as major active constituent. Rohitukine (50 mg/kg) significantly decreased the plasma levels of total cholesterol (24 %), phospholipids (25 %), triglycerides (27 %), very low density lipoprotein (27 %) and low density lipoprotein (32 %) accompanied with an increase in high density lipoprotein (21 %). The present study demonstrated that ethanolic extract of Dysoxylum binectariferum stem bark and its major constituent rohitukine both have antidyslipidemic as well as antioxidant potentials. The antidyslipidemic activity of rohitukine can be correlated to its effect on enzymes involved in lipid metabolism.

Utility of dried blood spots for measurement of cholesterol and triglycerides in a surveillance study

BACKGROUND

Developing countries are facing a rise in noncommunicable diseases (NCD), which is a cause for concern. The World Health Organization has recommended a stepwise approach for NCD risk factor surveillance. Screening for risk factors in remote populations is difficult due to lack of resources and technical expertise, including standardized laboratory facilities. The collection of samples on filter paper for the assessment of risk factors circumvents the need for blood processing, storage, and shipment at ultralow temperatures.

METHOD

Samples were collected on 3-mm Whatman filter paper from one industry (National Thermal Power Corporation) located in the periphery of Delhi as part of a surveillance carried out in industries from different parts of India. Total cholesterol was measured in serum and dried blood by the cholesterol oxidase/p-aminophenazone method and triglycerides by the glycerophosphate oxidase-peroxidase/aminophenazone method. Values obtained by the two methods were compared using Pearson correlation, and Bland-Altman plots were prepared to assess bias.

RESULTS

The correlation coefficient "r" was 0.78 for cholesterol and 0.94 for triglycerides between dried blood spots and serum. Bland-Altman plots suggest that differences in values obtained by the two methods were within two standard deviations for most of the samples.

CONCLUSIONS

Blood samples dried on filter paper can be a successful option for population screening in remote areas, provided preanalytical variations arising due to the method of blood spot preparation and storage are well controlled.

Cardiometabolic risk factors assessed by a finger stick dried blood spot method

BACKGROUND

Cardiovascular and metabolic risk factors are gaining attention as potential indicators for intervention in the prevention and treatment of cardiovascular disease (CVD) and type 2 diabetes mellitus (T2DM). Blood spot technology offers an efficient, convenient method to measure these risk factors in an at-risk population. Simple and convenient methods to assess cardiometabolic risk factors will allow clinicians to formulate treatment strategies for effective prevention and management of these conditions.

METHOD

Insulin and high sensitivity C-reactive protein (hs-CRP) were measured in dried blood spot and corresponding serum samples using conventional commercial serum kits based on a direct sandwich ELISA technique. The triglyceride assay involved enzymatic hydrolysis of triglycerides by lipase to glycerol and free fatty acids. The glycerol produced was then measured by coupled enzyme reactions. Blood spot assays were modified from previously published methods to give improved accuracy and turnaround time.

RESULTS

Blood spot levels correlated well with serum levels of hs-CRP (r = 0.99), triglycerides (fasting, r = 0.95; nonfasting, r = 0.94), and insulin (fasting, r = 0.93; nonfasting, r = 0.97).

CONCLUSION

Blood spot testing for insulin, hs-CRP, and triglycerides may be helpful in the cardiometabolic screening or monitoring of patients at risk of developing CVD, T2DM, or metabolic syndrome.

Influence of aging and menopause on postprandial lipoprotein responses in healthy adult women

AIM

To analyze the influence of menopause and age on postprandial lipoprotein responses in healthy adult women.

METHOD

Twenty-seven healthy young and middle-aged pre- and postmenopausal female volunteers aged 21-53 y were enrolled. They ingested OFTT cream(Jomo, Takasaki, Japan). Fasting and postprandial blood samples were obtained for up to 6 h, and serum concentrations of lipoproteins were analyzed.

RESULTS

In the postprandial phase, serum triglycerides(TG), remnant-like particle(RLP)-TG(RLP-TG), RLP-cholesterol(RLP-C), and TG-rich lipoprotein-TG(TRL-TG)concentrations in all groups peaked after 2 h. After 4 h, the TG, RLP-C, RLP-TG and TRL-TG concentrations in the young women returned to the fasting concentrations. However, at 6 h, these parameters in the pre- and postmenopausal women had barely returned to the fasting concentrations.

CONCLUSION

The present results suggest that:(1)the magnitude of postprandial TG concentrations is dependent on age, but not on menopause;(2)clearance of remnant lipoproteins is delayed with age in pre- and postmenopausal women compared to young women, and(3)menopause is associated with an increase of RLP-C, but may not influence LDL particle size.

Asian plantain (Plantago asiatica) essential oils suppress 3-hydroxy-3-methyl-glutaryl-co-enzyme A reductase expression in vitro and in vivo and show hypocholesterolaemic properties in mice

Asian plantain (Plantago asiatica) essential oil (PAEO) contains multiple bioactive compounds, but its potential effects on lipid metabolism have not been examined. PAEO was found to be mostly composed of oxygenated monoterpenes, with linalool as the major component (82.5 %, w/w), measured using GC-MS. Incubation of 0-200 microg PAEO/ml with HepG2 cells for 24 h resulted in no significant toxicity. Incubation with 0.2 mg PAEO/ml altered the expression of LDL receptor (+83 %; P < 0.05) and 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase ( - 37 %; P < 0.05), as assessed using RT-PCR. LDL oxidation was markedly inhibited by PAEO treatment due to the prevalence of linalool compounds in PAEO. Oral administration of PAEO for 3 weeks in C57BL/6 mice significantly reduced plasma total cholesterol and TAG concentrations by 29 and 46 %, respectively. The mRNA (+58 %; P < 0.05), but not protein, levels of the LDL receptor were significantly higher, whereas both mRNA and protein levels of HMG-CoA reductase were significantly lower ( - 46 and - 11 %, respectively; P < 0.05) in the liver of PAEO-fed than of control mice. The mRNA levels of CYP7A1 were marginally reduced in HepG2 cells, but not in mouse liver after PAEO treatment. Thus, PAEO may have hypocholesterolaemic effects by altering the expression of HMG-CoA reductase. Reduced TAG and oxidised LDL may provide additional cardiovascular protective benefits.

The role of hypertriglyceridemia in atherosclerosis

Atherosclerosis is a chronic disease associated with accumulation of lipids in lesions along blood vessels, leading to the occlusion of blood flow. Much of the focus has been on the role of low-density lipoprotein (LDL), and of oxidatively modified LDL, in the initiation and progression of this disease. LDL is in fact a metabolic end-product of the triglyceride-rich lipoproteins (ie, very-low density lipoproteins). Over the years, univariate analyses have implicated triglycerides as a contributor in atherosclerosis. However, depending on the studies, the significance of this relationship is either reduced or nullified when other co-variates are taken into account. This review summarizes more recent data that support the role of triglyceride-rich lipoproteins in the atherosclerotic process, both in the fasted as well as in the postprandial state.

Use of filter paper stored dried blood for measurement of triglycerides

Adaptation of assays on dried blood has advantages of ease of collection, transportation, minimal invasiveness and requirement of small volume. A method for extraction and estimation of triglyceride from blood spots dried on filter paper (Whatman no. 3) has been developed. A single dried blood spot containing 10 muL blood was used. Triglyceride was efficiently extracted in methanol from blood dried on filter paper by incubation at 37 degrees C for two hours with gentle shaking. For the estimation, a commercially available enzymatic method was used. Blood spot assays showed mean intra and inter assay coefficient of variance of 6.0% and 7.4% respectively. A comparison of paired whole blood spots and plasma samples (n = 75, day 0) gave an intraclass correlation of 0.96. The recovery was 99.6%. The dried blood triglyceride concentrations were stable for one month when the filter discs were stored at room temperature (16-28 degrees C). Storage of filters at 4 degrees C extended the stability and triglycerides could be quantitatively recovered after 3 months of storage.

Mechanism of highly active anti-retroviral therapy-induced hyperlipidemia in HIV-infected individuals

The use of highly active anti-retroviral therapy (HAART) is associated with long-term adverse metabolic events including lipodystrophy, dyslipidemia, and insulin resistance. The purpose of the present study was to prospectively examine the mechanism of HAART-induced hyperlipidemia in HIV-seropositive, HAART-naive men prior to the development of frank lipodystrophy. Patient's (n = 13) weight, BMI, lean mass, and percent fat mass, waist circumference did not change after 8 weeks of treatment with HAART. Plasma FFA concentration was already elevated in HAART-naive patients compared to healthy, untreated, HIV negative control individuals and was further increased after 8 weeks of HAART in the former. Insulin-mediated suppression of plasma FFA concentrations was impaired both prior to and following introduction of HAART, compared to healthy, matched controls. VLDL-apoB and VLDL-TG concentrations rose significantly from normal levels after HAART. Compared to healthy control subjects, VLDL fractional catabolic rate and clearance in HIV-seropositive individuals was reduced by approximately 40%, a defect that was not corrected after HAART. The increase in VLDL after HAART was explained by an increase of VLDL-apoB and VLDL-TG secretion towards normal while the impaired VLDL clearance remained unchanged. We conclude that elevation of circulating VLDL early in the course of HAART is caused by the combination of impaired VLDL clearance already present in HAART-naive HIV-seropositive patients and HAART-mediated increase in VLDL secretion. These changes occur concomitantly with an elevation of plasma free fatty acids but before significant change in body composition.

Impact of kidney transplantation on the progression of cardiovascular disease

Kidney transplantation, of all the treatment modalities for end-stage renal disease, affords the greatest potential for prolonged survival and improved quality of life. Great strides in immunosuppressant therapy have improved graft survival and forced clinicians to consider other health-care needs of kidney transplant recipients. Chief among these needs is the prevention and treatment of cardiovascular disease. Cardiovascular disease is the most common cause of death among patients with a working renal allograft. Because therapies for primary and secondary prevention are successful in the general population, transplant clinicians are increasingly focused on preventing or limiting the progression of cardiovascular disease. Initiation of aggressive management of conventional atherosclerotic risk factors and uremia-related risk factors, ideally during the early stages of chronic kidney disease (CKD) or after kidney transplantation, and efforts to delay the progression of kidney disease will hopefully reduce the cardiovascular burden in transplant recipients.

Pharmacology and therapeutics of ezetimibe (SCH 58235), a cholesterol-absorption inhibitor

BACKGROUND

Ezetimibe is the first of a new class of antihyperlipidemic agents, the cholesterol-absorption inhibitors. It is indicated for monotherapy or in combination with 3-hydroxy-3-methylglutaryl coenzyme A-reductase inhibitors (statins) in patients with primary hypercholesterolemia, in combination with simvastatin or atorvastatin in patients with homozygous familial hypercholesterolemia, and as monotherapy in patients with homozygous familial sitosterolemia.

OBJECTIVE

This article reviews available data on the clinical pharmacology, clinical efficacy, and tolerability of ezetimibe.

METHODS

A literature review was conducted using the search terms ezetimibe and SCH 58235 to identify articles and abstracts indexed in MEDLINE and the Iowa Drug Information Service from 1966 to February 2003. The reference lists of the identified articles were reviewed for additional publications.

RESULTS

In adults, ezetimibe 10 mg PO given once daily has been reported to reduce intestinal cholesterol absorption by 54% from baseline in association with a compensatory increase in endogenous cholesterol synthesis. Within 2 weeks of its initiation, ezetimibe monotherapy produced a 17% to 20% reduction from baseline in low-density lipoprotein cholesterol (LDL-C); in combination with statins, ezetimibe produced a reduction in LDL-C of up to 40% over the same period. Based on studies performed to date, ezetimibe appears to be well tolerated, with a safety profile similar to that of placebo. Because ezetimibe is eliminated primarily by glucuronidation and not by cytochrome P450 (CYP) oxidation, it is subject to minimal drug interactions involving the CYP enzyme system.

CONCLUSIONS

Ezetimibe is an option for monotherapy in patients with mild hypercholesterolemia or in those requiring adjunctive drug therapy for reduction of LDL-C levels. It may be useful in patients at risk for adverse events (eg, liver toxicity, myopathy) from other hypocholesterolemic agents. Additive LDL-C-lowering effects of ezetimibe may allow use of lower doses of conventional agents (eg, statins, fibric acid derivatives, niacin) to achieve an equivalent effect, thereby reducing the potential for adverse events and drug interactions. However, because trials have lasted no longer than 12 weeks, the long-term effect of ezetimibe on cardiovascular morbidity and mortality remains to be determined.

Potential roles of ROR-alpha in cardiovascular endocrinology

Atherosclerosis is a chronic disease of the arteries whose development involves a local inflammatory response characterized by the activation of different cells such as macrophages, T-lymphocytes, smooth muscle cells (SMCs) and endothelial cells (ECs). This review will summarize recent evidence for a modulatory role of the nuclear receptor ROR-alpha in cardiovascular disease.

Hyperlipidaemia in patients with HIV-1 infection receiving highly active antiretroviral therapy: epidemiology, pathogenesis, clinical course and management

A wide range of abnormalities of lipid metabolism have been recently described in HIV-infected patients receiving a protease inhibitor (PI)-based highly active antiretroviral therapy, including hypertriglyceridaemia and hypercholesterolaemia. The increase of plasma lipid concentrations may involve up to 70-80% of HIV-positive subjects treated with a PI-containing regimen and are frequently (but not always) associated with the fat redistribution or the lipodystrophy syndrome. Multiple pathogenetic mechanisms by which antiretroviral agents lead to dyslipidaemia have been hypothesized, but they are still controversial. The potential clinicopathological consequences of HIV-associated hyperlipidaemia are not completely known, but several anecdotal observations report an increased risk of premature coronary artery diseases in young HIV-positive individuals receiving PIs, besides peripheral atherosclerosis and acute pancreatitis. A limited-to-significant improvement of increased triglyceride and cholesterol plasma levels was described in patients who replaced PIs with nevirapine, efavirenz or abacavir, but the risks of long-term toxicity and virological relapse of this treatment switching are not completely defined. A hypolipidaemic diet and regular physical exercise may act favorably on dyslipidaemia, but pharmacological therapy becomes necessary when hyperlipidaemia is severe or persists for a long time. The choice of hypolipidaemic drugs is problematic because of potential pharmacological interactions with antiretroviral compounds and other antimicrobial agents, associated with an increased risk of toxicity and intolerance. Statins are considered the first-line therapy for the PI-related hypercholesterolaemia, while fibrates are the cornerstone of drug therapy when predominant hypertriglyceridaemia is of concern.

Common Variants in the Lipoprotein Lipase Gene in Brazil: Association with Lipids and Angiographically Assessed Coronary Atherosclerosis

Lipoprotein lipase is the rate-limiting enzyme in the lipolysis of plasma triglyceride-rich lipoproteins. We studied six variants (T-93G, D9N, N291S, PvuII, HindIII and S447X) in the lipoprotein lipase (LPL) gene in 309 non-diabetic patients with angiographically assessed coronary artery disease and in 197 controls in a southern Brazilian population of European descent. The HindIII H-allele was associated with lower triglycerides (p < 0.01) and higher high-density lipoprotein cholesterol (p = 0.03) levels, and the S447X mutation was associated with lower triglyceride levels (p < 0.01) in males, but not females. No other significant lipid associations were observed. Haplotypes were derived from these two sites (HindIII/S447X), and carriers of H-S and H-X haplotypes showed lower triglycerides (p < 0.01) and increased high-density lipoprotein cholesterol (p = 0.01) levels when compared to the H+S haplotype in males. In this gender, the H-X haplotype was associated with a protective effect (OR = 0.36, 95%CI = 0.13-0.97) for significant disease (> or = 60% of luminal coronary stenosis), even controlling for other classical risk factors.

Squalene synthase inhibitors suppress triglyceride biosynthesis through the farnesol pathway in rat hepatocytes

We recently demonstrated that squalene synthase (SQS) inhibitors reduce plasma triglyceride through an LDL receptor-independent mechanism in Watanabe heritable hyperlipidemic rabbits (Hiyoshi et al. 2001. Eur. J. Pharmacol. 431: 345-352). The present study deals with the mechanism of the inhibition of triglyceride biosynthesis by the SQS inhibitors ER-27856 and RPR-107393 in rat primary cultured hepatocytes. Atorvastatin, an HMG-CoA reductase inhibitor, had no effect on triglyceride biosynthesis, but reversed the inhibitory effect of the SQS inhibitors. A squalene epoxidase inhibitor, NB-598, affected neither triglyceride biosynthesis nor its inhibition by ER-27856 and RPR-107393. The reduction of triglyceride biosynthesis by ER-27856 and RPR-107393 was potentiated by mevalonolactone supplementation. Treatment of hepatocytes with farnesol and its derivatives reduced triglyceride biosynthesis. In addition, we found that ER-27856 and RPR-107393 significantly reduced the incorporation of [1-(14)C]acetic acid into oleic acid, but not the incorporation of [1-(14)C]oleic acid into triglyceride. Though ER-27856 and RPR-107393 increased mitochondrial fatty acid beta-oxidation, the inhibition of beta-oxidation by RS-etomoxir had little effect on their inhibition of triglyceride biosynthesis. These results suggest that SQS inhibitors reduce triglyceride biosynthesis by suppressing fatty acid biosynthesis via an increase in intracellular farnesol and its derivatives.

Tibolone versus four estrogen replacement therapy protocols and plasma lipid levels in postmenopausal women

OBJECTIVES

To compare tibolone therapy with four different estrogen replacement therapy protocols, with regard to the effects on plasma lipid profiles.

METHODS

The plasma lipid levels of 178 postmenopausal women in five different therapy groups were compared with each other as well as their baseline levels with 6-month intervals during 2-year follow-up. Student's t-test, paired t-test and Pearson correlation analysis were utilized for statistical analysis.

RESULTS

HDL cholesterol levels increased significantly from baseline in groups using oral estrogen (P<0.05) but a slight non-significant decrease was seen in tibolone therapy (P>0.05). LDL cholesterol levels significantly decreased at the end of the second year in oral estrogen and tibolone users (P<0.05). Triglyceride levels increased non-significantly with estrogen therapy (P>0.05), whilst decreased significantly in the tibolone group (P<0.05).

CONCLUSION

Tibolone may be a good alternative to estrogen replacement therapy in postmenopausal women, as it has beneficial effects on LDL cholesterol and triglyceride levels, which play important role in atherosclerosis.

Abnormal lipid concentrations in cystic fibrosis

BACKGROUND

Concentrations of cholesterol and triacylglycerol are commonly believed to be low in persons with cystic fibrosis and thus not of concern.

OBJECTIVE

The goal was to determine whether concentrations of cholesterol and triacylglycerol are related to glucose tolerance or nutritional status in patients with cystic fibrosis.

DESIGN

Fasting lipid profiles were measured in 192 patients ( +/- SD age: 21 +/- 11 y) in conjunction with an oral-glucose-tolerance test.

RESULTS

Cystic fibrosis patients in all age groups had higher triacylglycerol (1.51 +/- 0.95 mmol/L) and lower cholesterol (3.57 +/- 0.96 mmol/L) concentrations than US population means. Thirty patients (16%) had hypertriglyceridemia (3.22 +/- 1.22 mmol/L), and 8 patients (4%) had elevated cholesterol (6.05 +/- 1.32 mmol/L). In most cases, hypertriglyceridemia was isolated; only 3 subjects had elevation of both cholesterol and triacylglycerol. Lipid concentrations were not related to body mass index, weight, glucose tolerance, the areas under the curve for glucose or insulin, or glycated hemoglobin. Lipid concentrations also did not correlate with cystic fibrosis genotype, use of systemic steroids, blood pressure, liver enzymes, C-reactive protein, or pulmonary function.

CONCLUSIONS

Isolated hypertriglyceridemia appears to be common in cystic fibrosis, whereas cholesterol concentrations are generally low. Hypertriglyceridemia may be related to chronic low-grade inflammation or to a dietary macronutrient imbalance with excessive simple carbohydrate absorption relative to fat absorption. Whether it is associated with a risk of cardiovascular disease in this population is uncertain, but the clinical significance of triacylglycerol elevation may become important as survival improves.

Dietary restriction initiated in late adulthood can reverse age-related alterations of protein and protein metabolism

Many reports have been published on the effects of lifelong dietary restriction (DR) on a variety of parameters such as life span, carcinogenesis, immunosenescence, memory function, and oxidative stress. There is, however, limited available information on the effect of late onset DR that might have potential application to intervene in human aging. We have investigated the effect of DR initiated late in life on protein and protein degradation. Two months of DR in 23.5-month-old mice significantly reduced heat-labile altered proteins in the liver, kidney, and brain. DR reversed the age-associated increase in the half-life of proteins, suggesting that the dwelling time of the proteins is reduced in DR animals. In accordance with this observation, the activity of proteasome, which is suggested to be responsible for degradation of altered proteins, was found increased in the liver of rats 30 months of age subjected to 3.5 months of DR. Thus, DR can increase turnover of proteins, thereby possibly attenuating potentially harmful consequences by altered proteins. Likewise, DR in old rats reduced carbonylated proteins in liver mitochondria, although the effect was not observed in cytosolic proteins. Fasting induced apoA-IV synthesis in the liver of young mice for efficient mobilization of stored tissue fats, while it occurred only marginally in the old. DR for 2 months from 23 months of age partially restored inducibility of this protein, suggesting the beneficial effect of DR. Taking all these findings together, it is conceivable that DR conducted in old age can be beneficial not only to retard age-related functional decline but also to restore functional activity in young rodents. Interestingly, recent evidence that involves DNA array gene expression analysis supports the findings on the age-related decrease in protein turnover and its reversion by late-onset DR.

Perspectives: A Practical Approach to the Dietary Treatment of Hypertriglyceridemia

Reducing high plasma triglyceride (TG) levels is an important step in the treatment and prevention of coronary artery disease. The rise in plasma TGs seen after subjects consume low-fat, high-carbohydrate diets for a period of time may be due to the simple form of carbohydrate provided and/or prevention of weight loss in these studies. Ad libitum low-fat, high-carbohydrate intake often results in weight loss and decreases in plasma TGs. Replacing dietary carbohydrate with monounsaturated fat lowers serum TG levels and maintains serum high-density lipoprotein levels but fails to result in weight loss. Low-fat, high-complex carbohydrate intake reduces incidence rates of coronary artery disease. On the basis of the evidence, a low-fat, high-complex carbohydrate diet combined with limited alcohol and sugar intake is recommended for the treatment of hypertriglyceridemia. (c)2001 CHF, Inc.

Squalene synthase inhibitors reduce plasma triglyceride through a low-density lipoprotein receptor-independent mechanism

Inhibitors of squalene synthase are considered to be candidate drugs to reduce both plasma cholesterol and triglyceride. However, little is known about the mechanism of squalene synthase inhibitor-specific effect on plasma triglyceride. In this study, we confirmed the triglyceride-lowering effect of ER-27856, a potent squalene synthase inhibitor prodrug, in rhesus monkeys. To determine the role of low-density lipoprotein (LDL) receptor in the triglyceride-lowering effect of squalene synthase inhibitors, we intravenously administered ER-28448, the active form of ER-27856, to Watanabe heritable hyperlipidemic (WHHL) rabbits for 4 days. In heterozygotes, ER-28448 reduced plasma cholesterol and triglyceride by 52% and 37%, respectively. In homozygous rabbits, in contrast, ER-28448 lowered plasma triglyceride by 40% but did not lower plasma cholesterol. Orally administered ER-27856 reduced plasma triglyceride in homozygous animals but atorvastatin and bezafibrate did not. In hepatocytes isolated from homozygous WHHL rabbits, squalene synthase inhibitors but not atorvastatin reduced triglyceride biosynthesis. These data demonstrate that squalene synthase inhibitors reduced plasma triglyceride through an LDL receptor-independent mechanism, which was distinct from that of the triglyceride-lowering action of atorvastatin or bezafibrate. The reduction of hepatic triglyceride biosynthesis may play an important role in the hypotrigyceridemic action of squalene synthase inhibitors.

PPARS, metabolic disease and atherosclerosis

PPAR-alpha belongs to the family of nuclear receptors. Activated PPAR-alpha stimulates the expression of genes involved in fatty acid and lipoprotein metabolism. PPAR-alpha activators, such as the normolipidaemic fibric acids, decrease triglyceride concentrations by increasing the expression of lipoprotein lipase and decreasing apo C-III concentration. Furthermore, they increase HDL-cholesterol by increasing the expression of apo A-I and apo A-II. PPAR-alpha activation by fibric acids improves insulin sensibility, and decreases thrombosis and vascular inflammation. PPAR-alpha activators (gemfibrozil) decrease the risk of coronary heart disease in patients with normal LDL-cholesterol and low HDL-cholesterol (VA-HIT) and they slow the progression of premature coronary atherosclerosis (BECAIT) (bezafibrate), particularly in patients with type 2 diabetes (DAIS) (fenofibrate).

Cyclic nucleotides in platelets of genetically hypertriglyceridemic and hypertensive rats. Thrombin and nitric oxide responses are unrelated to plasma triglyceride levels

Prague hereditary hypertriglyceridemic (HTG) rats constitute a genetic model of hypertension associated with hyperlipidemia and insulin resistance. Various cell alterations, including changes in membrane dynamics, ion transport, and decreased platelet responses to thrombin have been observed in this strain. As hypertriglyceridemia appears to be associated with reduced endothelium-dependent vasodilation and platelet aggregation, we examined whether triglycerides could modulate cell responsiveness through changes in cyclic nucleotides in platelets of HTG rats. From the age of 6 weeks, these hypertensive animals were subjected for 10 weeks to interventions that modified circulating triglycerides levels (2.17+/-0.09 mmol/l), leading to their reduction (gemfibrozil treatment, 0.87+/-0.05 mmol/l) or elevation (high fructose intake, 3.23+/-0.07 mmol/l). Basal cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) contents were 15% and 48% lower in isolated platelets of HTG rats than in those of Lewis controls. cAMP level was further reduced in HTG rats subjected to high fructose intake. Irrespective of their plasma triglyceride levels, the thrombin-induced increase in platelet cGMP levels present in Lewis rats was absent in platelets of HTG rats. In contrast, no strain- or treatment-related differences were observed in the magnitude or kinetics of cGMP response to exogenous nitric oxide (NO). NO-induced cGMP and cAMP changes were associated in an opposite manner with trimethylamino-diphenylhexatriene (TMA-DPH) anisotropy, a biophysical parameter that reflects the microviscosity of the outer part of the cell membrane. Our results indicate that the attenuation of platelet responsiveness to thrombin in HTG rats represents a strain difference that cannot merely be due to a difference in plasma triglyceride levels. Platelet hyporesponsiveness to agonists such as thrombin in HTG rats cannot be explained by a change in levels of inhibitory cyclic nucleotides, since they were actually found to be low and not high.

Orlistat inhibits dietary cholesterol absorption

OBJECTIVE

Orlistat decreases the absorption of dietary triglycerides by inhibiting intestinal lipases. Orlistat therapy is associated with a greater decline in plasma low-density lipoprotein-cholesterol concentrations than that expected from weight loss alone. Therefore, we evaluated the effect of orlistat treatment on dietary cholesterol absorption as a possible mechanism for the independent effect of orlistat on plasma cholesterol concentration.

RESEARCH METHODS AND PROCEDURES

Cholesterol absorption from a standardized meal, containing 72 mg of cholesterol, was determined in 18 subjects with class II abdominal obesity (BMI, 35.0 to 39.9 kg/m(2)) by simultaneous administration of intravenous ([(2)H(6)] cholesterol) and oral ([(2)H(5)] cholesterol) cholesterol tracers. In protocol 1 (n = 9), cholesterol absorption was determined on two different occasions, 10 to 20 days apart, to assess the reproducibility of the tracer method. In protocol 2 (n = 9), cholesterol absorption was determined with and without orlistat therapy in a prospective, randomized, crossover design to assess the effect of orlistat on cholesterol absorption.

RESULTS

In protocol 1, cholesterol absorption from the test meal was the same on both occasions (53 +/- 5% and 51 +/- 5%). In protocol 2, orlistat treatment caused a 25% reduction in cholesterol absorption, from 59 +/- 6% to 44 +/- 5% (p < 0.01).

DISCUSSION

These data demonstrate that orlistat inhibits dietary cholesterol absorption, which may have beneficial effects on lipoprotein metabolism in obese subjects that are independent of weight loss itself.

Use of niacin in the prevention and management of hyperlipidemia

Niacin is an inexpensive drug useful in treating various forms of hyperlipidemia. Cardiac doses of niacin are effective in lowering serum triglyceride, low density lipoprotein, and lipoprotein-a levels and in elevating high density lipoprotein levels. Adverse reactions to niacin are varied and dose-dependent and range from annoying cutaneous flushing to hepatic toxicity. Patients advised to use the drug should be carefully screened and monitored. This paper reviews the pathologic and pharmacologic basis for niacin as an antilipemic agent. The biochemical and physiologic effects of the drug and its mechanisms of action are discussed. Emphasis is placed on the importance of aggressive management of serum lipids and the therapeutic uses of niacin. The use of niacin in primary and secondary prevention of heart disease is stressed. A patient education guide is included.

The exon 3-retaining and the exon 3-deleted forms of the growth hormone-binding protein (GHBP) in human serum are regulated differently

Recently, two isoforms of the growth hormone-binding protein (GHBP), which is identical with the extracellular domain of the growth hormone receptor (GHR), have been described. One isoform contains the exon 3 (E3+GHBP) and one excludes the exon 3 (E3-GHBP). The distribution of both isoforms in peripheral blood and their functional relevance is so far unknown. To study the molecular distribution of both species we have analysed sera of 141 subjects with average weight, overweight and obesity by newly developed immunoassays. The relationship between the different molecular forms of GHBP and specific parameters of body composition as well as risk factors of metabolic disturbances, were then examined. The extracellular domain of the exon 3-retaining and -deleted isoforms of the GHR are released as E3+GHBP and E3-GHBP into the peripheral circulation. Furthermore, both molecular species do not show any correlation to each other (r = 0.67) and their relative proportion in blood is gender-dependent with a higher E3-GHBP proportion in females (P < 0.01). E3+GHBP appears to have a considerably stronger correlation to indicators (BMI, fat mass, waist circumference) and metabolic risk factors (fasting insulin, uric acid, triglycerides, apolipoprotein B, diastolic blood pressure) of adiposity than E3-GHBP, indicating differences in their functional significance. The availability of assays for the determination of GHBP isoforms may be very important for the study of the GH receptor and its soluble extracellular domain, GHBP.

Preventing, stopping, or reversing coronary artery disease--triglyceride-rich lipoproteins and associated lipoprotein and metabolic abnormalities: the need for recognition and treatment

A substantial number of treated patients with or at high risk for coronary artery disease continue to have fatal and nonfatal coronary artery events in spite of significant reduction of elevated levels of low-density lipoprotein cholesterol. Other lipoprotein abnormalities besides an elevated level of low-density lipoprotein cholesterol contribute to risk of coronary artery disease and coronary artery events, and the predominant abnormalities that appear to explain much of this continued risk are an elevated serum triglyceride level and a low level of high-density lipoprotein cholesterol. Most patients with coronary artery disease have a mixed dyslipidemia with hypertriglyceridemia, which is associated and metabolically intertwined with other atherogenic risk factors, including the presence of triglyceride-rich lipoprotein remnants, low levels of high-density lipoprotein cholesterol, small, dense, low-density lipoprotein particles, postprandial hyperlipidemia, and a prothrombotic state. Aggressive treatment of these patients needs to focus on these other lipoprotein abnormalities as much as on low-density lipoprotein cholesterol. Combination drug therapy will usually be required. Reliable assessment of risk of coronary artery disease from lipoprotein measurements and response to therapy requires inclusion of all atherogenic lipoproteins in laboratory measurements and treatment protocols. At present this may be best accomplished by use of non-high-density lipoprotein cholesterol (total cholesterol minus high-density lipoprotein cholesterol) calculated from standard laboratory lipoprotein values. Ultimately, a more comprehensive assessment of coronary artery disease risk and appropriate therapy may include measurement of lipoprotein subclass distribution including determination of low-density lipoprotein particle concentration and sizes of the various lipoprotein particles.

Current, new and future treatments in dyslipidaemia and atherosclerosis

The new therapeutic options available to clinicians treating dyslipidaemia in the last decade have enabled effective treatment for many patients. The development of the HMG-CoA reductase inhibitors (statins) have been a major advance in that they possess multiple pharmacological effects (pleiotropic effects) resulting in potent reductions of low density lipoproteins (LDL) and prevention of the atherosclerotic process. More recently, the newer fibric acid derivatives have also reduced LDL to levels comparable to those achieved with statins, have reduced triglycerides, and gemfibrozil has been shown to increase high density lipoprotein (HDL) levels. Nicotinic acid has been made tolerable with sustained-release formulations, and is still considered an excellent choice in elevating HDL cholesterol and is potentially effective in reducing lipoprotein(a) [Lp(a)] levels, an emerging risk factor for coronary heart disease (CHD). Furthermore, recent studies have reported positive lipid-lowering effects from estrogen and/or progestogen in postmenopausal women but there are still conflicting reports on the use of these agents in dyslipidaemia and in females at risk for CHD. In addition to lowering lipid levels, these antihyperlipidaemic agents may have directly or indirectly targeted thrombogenic, fibrinolytic and atherosclerotic processes which may have been unaccounted for in their overall success in clinical trials. Although LDL cholesterol is still the major target for therapy, it is likely that over the next several years other lipid/lipoprotein and nonlipid parameters will become more generally accepted targets for specific therapeutic interventions. Some important emerging lipid/lipoprotein parameters that have been associated with CHD include elevated triglyceride, oxidised LDL cholesterol and Lp(a) levels, and low HDL levels. The nonlipid parameters include elevated homocysteine and fibrinogen, and decreased endothelial-derived nitric oxide production. Among the new investigational agents are inhibitors of squalene synthetase, acylCoA: cholesterol acyltransferase, cholesteryl ester transfer protein, monocyte-macrophages and LDL cholesterol oxidation. Future applications may include thyromimetic therapy, cholesterol vaccination, somatic gene therapy, and recombinant proteins, in particular, apolipoproteins A-I and E. Non-LDL-related targets such as peroxisome proliferator-activating receptors, matrix metalloproteinases and scavenger receptor class B type I may also have clinical significance in the treatment of atherosclerosis in the near future. Before lipid-lowering therapy, dietary and lifestyle modification is and should be the first therapeutic intervention in the management of dyslipidaemia. Although current recommendations from the US and Europe are slightly different, adherence to these recommendations is essential to lower the risk of atherosclerotic vascular disease, more specifically CHD. New guidelines that are expected in the near future will encompass global opinions from the expert scientific community addressing the issue of target LDL goal (aggressive versus moderate lowering) and the application of therapy for newer emerging CHD risk factors.

Efficacy and safety of a combination of fluvastatin and bezafibrate in patients with mixed hyperlipidaemia (FACT study)

Preliminary data suggest that fluvastatin may be safely combined with fibrates. The Fluvastatin Alone and in Combination Treatment Study examined the effects on plasma lipids and safety of a combination of fluvastatin and bezafibrate in patients with coronary artery disease and mixed hyperlipidaemia. A total of 333 patients were randomly allocated in this multicentre double-blind trial to receive 40 mg fluvastatin alone (n=80), 400 mg bezafibrate (n=86), 20 mg fluvastatin+400 mg bezafibrate (n=85) or 40 mg fluvastatin+400 mg bezafibrate (n=82) for 24 weeks. Low-density lipoprotein (LDL)-cholesterol decreased >20% in all fluvastatin-containing regimens, with significantly greater decreases compared with bezafibrate alone (P<0.001). Bezafibrate alone and fluvastatin+bezafibrate combinations resulted in greater increases in high-density lipoprotein (HDL)-cholesterol and decreases in triglycerides compared with fluvastatin alone (P<0.001). Fluvastatin (40 mg)+bezafibrate was the most effective for all lipid parameters with a decrease from baseline at endpoint in LDL-cholesterol of 24%, a decrease in triglycerides of 38% and an increase in HDL-cholesterol of 22%. All treatments were well tolerated with no increase in adverse events for combination therapy versus monotherapy, or between combination regimens. No clinically relevant liver (aspartate aminotransferase [ASAT] or alanine aminotransferase [ALAT]) greater than three times the upper limit of normal) or muscular (creatine phosphokinase (CPK) greater than four times the upper limit of normal) laboratory abnormalities were reported. This large study shows 40 mg fluvastatin in combination with 400 mg bezafibrate to be highly effective and superior to either drug given as monotherapy in mixed hyperlipidaemia, and to be safe and well tolerated.

Carbohydrate-induced hypertriacylglycerolemia: historical perspective and review of biological mechanisms

Current trends in health promotion emphasize the importance of reducing dietary fat intake. However, as dietary fat is reduced, the dietary carbohydrate content typically rises and the desired reduction in plasma cholesterol concentrations is frequently accompanied by an elevation of plasma triacylglycerol. We review the phenomenon of carbohydrate-induced hypertriacylglycerolemia, the health effects of which are among the most controversial and important issues in public health nutrition today. We first focus on how seminal observations made in the late 1950s and early 1960s became the basis for subsequent important research questions and areas of scientific study. The second focus of this paper is on the current knowledge of biological mechanisms that contribute to carbohydrate-induced hypertriacylglycerolemia. The clinical rationale behind mechanistic studies is this: if carbohydrate-induced hypertriacylglycerolemia shares a metabolic basis with endogenous hypertriacylglycerolemia (that observed in subjects consuming high-fat diets), then a similar atherogenic risk may be more likely than if the underlying metabolic mechanisms differ. The third focus of the paper is on both the positive metabolic changes that occur when high-carbohydrate diets are consumed and the potentially negative health effects of such diets. The review concludes with a summary of some important research questions that remain to be addressed. These issues include the level of dietary carbohydrate that induces carbohydrate-induced hypertriacylglycerolemia, whether the phenomenon is transient or can be avoided, whether de novo lipogenesis contributes to the phenomenon, and what magnitude of triacylglycerol elevation represents an increase in disease risk.

Peroxisome proliferator-activated receptor-alpha activators regulate genes governing lipoprotein metabolism, vascular inflammation and atherosclerosis

The peroxisome proliferator-activated receptors (PPARs) [alpha, delta (beta) and gamma] form a subfamily of the nuclear receptor gene family. All PPARs are, albeit to different extents, activated by fatty acids and derivatives; PPAR-alpha binds the hypolipidemic fibrates whereas antidiabetic glitazones are ligands for PPAR-gamma. PPAR-alpha activation mediates pleiotropic effects such as stimulation of lipid oxidation, alteration in lipoprotein metabolism and inhibition of vascular inflammation. PPAR-alpha activators increase hepatic uptake and the esterification of free fatty acids by stimulating the fatty acid transport protein and acyl-CoA synthetase expression. In skeletal muscle and heart, PPAR-alpha increases mitochondrial free fatty acid uptake and the resulting free fatty acid oxidation through stimulating the muscle-type carnitine palmitoyltransferase-I. The effect of fibrates on the metabolism of triglyceride-rich lipoproteins is due to a PPAR-alpha dependent stimulation of lipoprotein lipase and an inhibition of apolipoprotein C-III expressions, whereas the increase in plasma HDL cholesterol depends on an overexpression of apolipoprotein A-I and apolipoprotein A-II. PPARs are also expressed in atherosclerotic lesions. PPAR-alpha is present in endothelial and smooth muscle cells, monocytes and monocyte-derived macrophages. It inhibits inducible nitric oxide synthase in macrophages and prevents the IL-1-induced expression of IL-6 and cyclooxygenase-2, as well as thrombin-induced endothelin-1 expression, as a result of a negative transcriptional regulation of the nuclear factor-kappa B and activator protein-1 signalling pathways. PPAR activation also induces apoptosis in human monocyte-derived macrophages most likely through inhibition of nuclear factor-kappa B activity. Therefore, the pleiotropic effects of PPAR-alpha activators on the plasma lipid profile and vascular wall inflammation certainly participate in the inhibition of atherosclerosis development observed in angiographically documented intervention trials with fibrates.

Hypertriglyceridemia: changes in the plasma lipoproteins associated with an increased risk of cardiovascular disease

There is a growing body of evidence from epidemiologic, clinical, and laboratory data that indicates that elevated triglyceride levels are an independent risk factor for cardiovascular disease. Identification and quantification of atherogenic lipoproteins in patients with hypertriglyceridemia are important steps in the prevention of cardiovascular disease. Increased levels of apoC-III, apoC-I, or apoA-II on the apoB-containing lipoproteins may alter lipoprotein metabolism and result in the accumulation of atherogenic remnants. Hypertriglyceridemic patients at risk for cardiovascular disease often develop a lipoprotein profile characterized by elevated triglyceride, dense LDL, and low HDL cholesterol. Understanding that each of these factors contributes separately to the patient's risk of cardiovascular disease can help physicians provide patients with more effective risk-reduction programs for cardiovascular disease.