D.W. Erkelens

Impaired chylomicron remnant clearance in familial combined hyperlipidemia.

Postprandial chylomicron remnant clearance was studied in six patients with familial combined hyperlipidemia (FCH) and seven control subjects by using an oral retinyl palmitate (RP) fat-loading test. The chylomicron remnant clearance (Sf < 1,000 fraction), expressed as the area under the RP curve (AUC-RP), was delayed in FCH subjects (65.05 +/- 12.84 hours x [mg/L]) compared with control subjects (25.1 +/- 5.4 hours x [mg/L]; p = 0.01). Postprandial lipoprotein particle size and composition in the Sf > 1,000 fraction were different between FCH and control subjects as analyzed by molecular-sieve chromatography. Fasting high density lipoprotein cholesterol was lower in FCH patients (0.54 +/- 0.09 mmol/L) than in control subjects (0.89 +/- 0.05 mmol/L; p < 0.01). Mean plasma postheparin lipoprotein lipase and hepatic lipase activities were similar between FCH patients (94 +/- 25 and 427 +/- 57 milliunits/mL, respectively) and control subjects (126 +/- 16 and 362 +/- 33 milliunits/mL, respectively). In FCH, a 54% reduction (p < 0.05) of plasma triglycerides to 2.63 +/- 0.41 mmol/L by drug treatment resulted in an enhanced, but not normalized, clearance of chylomicron remnants (39.4 +/- 6.0 hours x [mg/L]). Univariate regression analysis revealed that in FCH subjects the changes in fasting plasma apolipoprotein C-III concentrations after therapy were significantly associated with the changes in chylomicron remnant AUC-RP (r = 0.87; p = 0.02). Delayed elimination of atherogenic chylomicron remnants may contribute to the increased risk of premature atherosclerosis in FCH.

Triglyceride-rich lipoproteins in non-insulin-dependent diabetes mellitus: post-prandial metabolism and relation to premature atherosclerosis.

Non‐insulin‐dependent diabetes mellitus is frequently associated with premature atherosclerosis. Abnormalities in lipid and lipoprotein metabolism contribute to the increased risk of coronary heart disease. One of the most common lipid abnormalities in non‐insulin‐dependent diabetes mellitus is hypertriglyceridaemia. In the present paper, the authors review the metabolism of triglyceride‐rich lipoproteins, with special emphasis on the post‐prandial state. Several studies have demonstrated that levels of atherogenic post‐prandial lipoproteins are increased in patients with non‐insulin‐dependent diabetes mellitus. An increased supply of glucose and free fatty acids contributes to overproduction of very low‐density lipoproteins, increasing the burden of triglyceride‐rich lipoproteins on the common lipolytic pathway at the level of lipoprotein lipase. Low lipoprotein lipase activity and increased amounts of lipolysis‐inhibiting free fatty acids further impair lipolysis of post‐prandial lipoproteins. The clearance of atherogenic remnants is also delayed in non‐insulin‐dependent diabetes mellitus. There is evidence that a relative hepatic removal defect exists, secondary to impaired remnant‐receptor interaction and increased competition with very low density lipoprotein remnants. Correction of the increased post‐prandial lipaemia in non‐insulin‐dependent diabetes mellitus is advisable, as it may contribute to attenuation of the risk on premature atherosclerosis. When dietary measures and hypoglycaemic agents have failed to achieve acceptable lipid levels, lipid‐lowering drugs should be advised. Fibric acids and hydroxymethylglutaryl coenzyme A (HMG CoA) reductase inhibitors are the drugs of choice.

Diurnal triglyceride profiles: a novel approach to study triglyceride changes

Fasting plasma triglycerides (TG) show a high intra-individual variability, and therefore, repeated measurements and alternative methodology are necessary when studying TG metabolism. In search for novel approaches to study TG changes, we evaluated the feasibility of determining ambulatory capillary TG. In addition, well-known characteristics (e.g. gender differences) of TG metabolism in healthy subjects were determined. In 18 subjects with a wide range of fasting plasma TG, the results of standardised oral fat loading tests (50 g m(-2)) were compared to their diurnal capillary TG profiles, measured on 3 different days, six times each day in an out-patient clinic setting. The diurnal TG-profile was calculated as area under the capillary TG curve (TGc-AUC) and as incremental area (dTGc-AUC). Clearance of plasma TG after the acute oral fat load correlated well with the diurnal TGc-AUC (r=0.77; P<0.01). In addition, hypertriglyceridemic subjects (plasma TG >2.0 mmol l(-1)) had a higher diurnal triglyceridemia (49.83+/-15.37 h mmol l(-1)) as well as a higher response of plasma TG to the oral fat load (42.10+/-15.37 h mmol l(-1)), than the subjects with normal fasting plasma TG (29.83+/-11.75 h mmol l(-1) (P<0.05) and 20.75+/-5.89 h mmol l(-1) (P<0.01), respectively). In an observational study, 106 volunteers (54 females and 52 males) measured capillary triglycerides. Food intake was recorded and fasting blood was drawn once at the start of the study. Body composition was assessed by anthropometric parameters and body-impedance. Repeated measurements of diurnal triglyceridemia tended to be less variable than fasting capillary triglycerides (mean coefficients of variation 15.1% (range: 0.60-45.9%) and 24.9% (range: 1.44-72.7%), respectively; P=0.09) for the whole group and in males (18.6% (0.60-45.9%) and 24.0% (1.4-58.2%), respectively; P=0.07). The mean diurnal TGc-AUC and dTGc-AUC were lower in females (16.50+/-4.85 and 1.82+/-3.46 h mmol l(-1), respectively) than in males (23.44+/-6.50 and 6.93+/-4.67 h mmol l(-1); P<0.001 for each). The total daily energy intake was lower in females (8911+/-1905 kJ) than in males (11042+/-2604 kJ, P<0.001) because of a lower intake of all nutrients. In females, estrogen status determined significantly the capillary TG profiles. Stepwise multiple regression analysis for females and males, with TGc-AUC as the dependent variable, showed that the best predictors were fasting capillary TG, gender, systolic blood pressure and mean daily energy intake, explaining 72% of the variation. Incremental triglyceridemia was best described by gender, mean daily protein intake and systolic blood pressure, explaining 42% of the variation. Diurnal capillary TG profiles may be used to estimate the total daily load of potential atherogenic particles to which individuals are subjected during the day without the need for metabolic ward studies.

A proposal to redefine familial combined hyperlipidaemia -- third workshop on FCHL held in Barcelona from 3 to 5 May 2001, during the scientific sessions of the European Society for Clinical Investigation.

Familial combined hyperlipidaemia (FCHL) was described in 1973 by three separate groups as a common familial disorder characterized by multiple lipoprotein phenotypes and an increased risk of premature coronary artery disease [1– 3]. No metabolic explanation was offered for the variable lipid phenotypes and opinion differed as to whether this was likely to be a monogenic or polygenic disorder. In 1986, the first FCHL workshop was held in Seattle and at that meeting an elevated plasma apolipoprotein B (apoB) was added to the list of characteristics. However, it was not made an essential feature, nor was any change to the fundamental approach to phenotypic classification suggested, notwithstanding that complexity of diagnosis severely limits clinical application and comparison of research results [4]. In 1998, investigators met in Helsinki for the second FCHL workshop and heard of the newest efforts to identify the genetic and metabolic bases for FCHL. All of the analyses were presented within the context of the original diagnostic approach. At the most recent meeting of the European Society for Clinical Investigation in Barcelona, the third workshop on FCHL was organized by Dr J. Ribalta (Reus, Spain) and Dr M. Castro Cabezas (Utrecht, the Netherlands) to reconsider this most common, but least well characterized, familial atherogenic dyslipoproteinaemia. Our objective became to search for the most important pathophysiological features. From the outset, as outlined by Professor M-R. Taskinen (Helsinki, Finland) , the two most well-documented features are increased very low-density lipoprotein (VLDL) secretion and impaired clearance of postprandial lipoproteins [5,6]. The increased VLDL2 secretion results in hypertriglyceridaemia and an elevated plasma apoB. Long residence time of VLDL1 particles favour the formation of small dense low-density lipoprotein (LDL). Based on this, we considered the hypothesis that the phenotype of FCHL might not be multiple but unitary – namely, hypertriglyceridaemic (hyperTg) hyperapoB. If so, FCHL phenotype could be defined more simply and consistently as follows. The phenotype of hyperTg hyperapoB would have to be present in more than one family member and at least one individual in the family must have premature symptomatic coronary artery disease. Other genetic disorders and secondary causes of dyslipidaemia, including type 1 and type 2 diabetes would, of course, have to be excluded [4,5]. It was emphasized that such a change only represents an evolution in diagnosis based on the advances in knowledge and technology that have occurred since the disorder was Mike Rosenbloom Laboratory for Cardiovascular Research, McGill University Health Centre, McGill University, Montreal, Quebec, Canada (A. D. Sniderman); Departments of Internal Medicine and Endocrinology, University Medical Centre, Utrecht, the Netherlands (M. Castro Cabezas, D. W. Erkelens); Unitat de Recerca de Lípids i Arteriosclerosi, Facultat de Medicina, Hospital Universitari de Sant Joan, Universitat Rovira i Virgili, Reus, Spain (J. Ribalta, L. Masana); Servicio de Endocrinología, Departamento de Medicina, Universidad de Valencia, Valencia, Spain (R. Carmena, J. T. Real); Departments of Medicine and Endocrinology, Academic Hospital, 6202 AZ Maastricht, the Netherlands (T. W. A. de Bruin); Department General Internal Medicine 541, UMC Nijmegen, the Netherlands (J. de Graaf); Division of Cardiovascular Genetics, Department of Medicine, Royal Free and University College Medical School, London WC1E 6JJ, UK (S. E. Humphries, P. J. Talmud); Department of Medicine, University of Helsinki, Helsinki, Finland (M. R. Taskinen).

Delayed chylomicron remnant clearance in subjects with heterozygous familial hypercholesterolaemia

Castro Cabezas M, De Bruin TWA, Westerveld HE, Meijer E, Erkelens DW (Departments of Internal Medicine and Endocrinology, University Hospital Utrecht and University Hospital Maastricht, The Netherlands). Delayed chylomicron remnant clearance in subjects with heterozygous familial hypercholesterolaemia. J Intern Med 1998; 244: 299–307.

Gender differences in diurnal triglyceridemia in lean and overweight subjects

AIMS: Increased fasting and postprandial triglyceridemia is one of the cardiovascular risk factors for patients with insulin resistance. Since triglyceride (TG) metabolism largely depends on gender, we have investigated diurnal TG changes in patients with and without overweight, focusing on gender differences.METHODS: Twenty-two males and 22 females with overweight (mean body mass index (BMI) 28.0±2.3 kg/m2) measured capillary TG concentrations at six fixed time points on three different days. Diurnal TG profiles were calculated as area under the capillary TG curves (TGc-AUCs). The control group consisted of 24 males and 21 females who were not overweight (mean BMI 22.4±1.5 kg/m2). Biochemical and anthropometric parameters associated with insulin resistance were measured.RESULTS: Lean males and lean females had comparable fasting insulin levels (6.9±2.6 and 8.1±4.7 mU/l, respectively), but females had a more favorable fasting lipoprotein profile when compared to males. Diurnal TG profiles were lower in lean females than in lean males (16.9±4.3 vs 20.3±5.7 mMh, respectively, P<0.05). Overweight males and females had comparable fasting insulin levels (10.3±3.4 and 12.1±4.9 mU/l, respectively), which were higher than in lean subjects. Overweight females also had a more favorable fasting lipoprotein profile compared to overweight males. Diurnal TG profiles were similar in overweight females and overweight males (31.1±15.6 and 32.9±13.2 mMh, respectively). Stepwise multiple regression analysis showed that in both males and females, waist circumference was the strongest determinant of diurnal TG profiles when fasting TG concentrations were excluded from the model (R 2=0.49 for males and R 2=0.33 for females). These results suggest that overweight resulted in a ‘male diurnal TG profile’ in females due to abdominal fat accumulation.CONCLUSION: Insulin resistance in overweight subjects partly mitigates the gender differences of fasting and postprandial TG metabolism. The significant positive association between diurnal triglyceridemia and waist circumference supports the view that especially abdominal fat associated with insulin resistance enhances postprandial lipemia.

Delayed and Exaggerated Postprandial Complement Component 3 Response in Familial Combined Hyperlipidemia

Very low density lipoprotein overproduction is the major metabolic characteristic in familial combined hyperlipidemia (FCHL). Peripheral handling of free fatty acids (FFAs) in vitro may be impaired in FCHL by decreased action of acylation-stimulating protein (ASP), which is identical to the immunologically inactive complement component 3a (C3adesArg). Because decreased FFA uptake by impaired complement component 3 (C3) response (as the precursor for ASP) may result in enhanced FFA flux to the liver in FCHL, we have evaluated postprandial C3 changes in vivo in FCHL patients. Accordingly, 10 untreated FCHL patients and 10 matched control subjects underwent an oral fat loading test. Fasting plasma C3 and ASP levels were higher in FCHL patients (1.33±0.09 g/L and 70.53±4.37 mmol/L, respectively) than in control subjects (0.91±0.03 g/L and 43.21±8.96 mmol/L, respectively;P =0.01 and P <0.05). In control subjects, C3 concentrations increased significantly after 4 hours (to 1.03±0.04 g/L). In FCHL, plasma C3 was unchanged after 4 hours. The earliest postprandial C3 rise in FCHL patients occurred after 8 hours (1.64±0.12 g/L). The maximal apolipoprotein B-48 concentration was reached after 6 hours in FCHL patients and control subjects. Postprandial FFA and hydroxybutyric acid (as a marker of hepatic FFA oxidation) were significantly higher in FCHL patients than in control subjects, and the early postprandial C3 rise was negatively correlated with the postprandial FFA and hydroxybutyric acid concentrations. The present data suggest an impaired postprandial plasma C3 response in FCHL patients, most likely as a result of a delayed response by C3, as the precursor for the biologically active ASP, acting on FFA metabolism. Therefore, an impaired postprandial C3 response may be associated with impaired peripheral postprandial FFA uptake and, consequently, lead to increased hepatic FFA flux and very low density lipoprotein overproduction.

Diurnal triglyceride profiles in healthy normolipidemic male subjects are associated to insulin sensitivity, body composition and diet

Elevated fasting and postprandial triglycerides (TG) are established risk factors for Coronary Heart Disease (CHD). Usually, fasting plasma TG are measured, although TG are mainly produced in a postprandial state. Our objective was to investigate diurnal TG profiles using serial capillary TG measurements, in normolipidemic healthy males.

Postprandial apolipoprotein B100 and B48 metabolism in familial combined hyperlipidaemia before and after reduction of fasting plasma triglycerides.

Abstract Hepatic VLDL overproduction in familial combined hyperlipidaemia (FCH) may delay the clearance of atherogenic apolipoprotein (apo) B containing particles. We investigated if normalization of fasting plasma triglycerides (TG) by hypolipidaemic treatment results in improved metabolism of apo B48 and apo B100 in six male subjects with FCH and compared them to six normolipidaemic controls. The FCH patients were studied before (TG, 5·2±1·2 mmoll‐1; mean ± SEM) and after therapy (TG, 2·1±0·3 mmoll‐1) with either simvastatin (n= 4) or combined therapy with gemfibrozil (n= 2). The post‐prandial changes of apo B100 and apo B48 were studied after a single oral fat meal (24h; 50 gram fatm‐2). Changes in triglyceride rich particles (TRP; d < 1·006 gml‐1) and remnant fractions (REM; d: 1·006–1·019g ml‐1) of apo B were quantitated by scanning silverstained SDS‐PAGE (4–15%). Apo B48 in fasting TRP in untreated and treated FCH was 15% and 14% of total apo B, and 6% in controls (P < 0·05). In controls, postprandial B48 increased maximally at 4h by 81% in TRP and by 137% in REM compared to baseline. In treated FCH, the post‐prandial apo B48 pattern normalized in TRP compared to the untreated state. Postprandial apo B100 in controls decreased in TRP and REM by 33% and 18% (P < 0·05). In untreated and treated FCH, postprandial apo B100 remained unchanged vs. baseline in TRP and in REM suggesting hypersecretion of VLDL. The elimination of B100—assessed as area under the curve—in TRP (32·5±3·6 au.h; mean±SEM) and REM fractions (33·2±3·1 au.h), improved significantly after treatment (21·0±2·8 and 20·4±3·3 au.h, respectively). The apo B48 clearance in TRP fractions was improved after treatment (4·3±1·4 au.h vs. 2·9±1·2 au.h; P= 0·06), but not in REM fractions (2·8±1·0 au.h vs. 1·8±0·5 au.h; NS). In conclusion, in FCH subjects with apo B100 hypersecretion and increased fasting plasma apo B48 levels, reduction of fasting plasma TG improved, but did not normalize, TRP apo B48 and B100 metabolism. However, therapy normalized postprandial apo B100 remnant metabolism. Impaired postprandial apo B metabolism may be instrumental in the development of premature atherosclerosis in FCH subjects.

High Dose of Simvastatin Normalizes Postprandial Remnant-Like Particle Response in Patients With Heterozygous Familial Hypercholesterolemia

Familial hypercholesterolemia (FH) and disturbances in postprandial lipoprotein metabolism are both associated with premature atherosclerosis. The effect of &bgr;-hydroxy-&bgr;-methylglutaryl coenzyme A reductase inhibitors on plasma cholesterol levels in patients with FH is well established; however, it is not known whether postprandial lipoproteins are also influenced. In this case-controlled intervention study, we investigated the effects of high-dose simvastatin on postprandial lipoproteins. We used a new method to analyze remnant lipoproteins based on the immunoseparation principle (remnant-like particle cholesterol [RLP-C] assay) and the well-established measurement of retinyl ester (RE) analysis in plasma and in the Svedberg flotation unit (Sf)<1000 fraction. Seven heterozygous FH patients and 7 control subjects matched for sex, age, body mass index, triglycerides, and apolipoprotein E genotype were enrolled in the study. An oral vitamin A (RE) fat-loading test was performed at baseline in both groups and after 3 months of high-dose simvastatin (80 mg/d) treatment in the FH patients. Before treatment, FH patients had significantly higher fasting and postprandial concentrations of lipoprotein remnants (plasma RLP-C 42±19 mg/dL and area under the RLP-C curve 415±82 mg · L−1 · h−1, respectively) than did control subjects (7±3 mg/dL and 101±35 mg · L −1 · h−1, respectively;P <0.05), suggesting a delayed clearance of chylomicron remnant particles in the FH patients. Treatment with simvastatin significantly reduced fasting and postprandial remnant lipoprotein cholesterol concentrations (13±3 mg/dL and 136±53 mg · L −1 · h−1, respectively;P <0.05 for both). Postprandial RE in the Sf<1000 fraction, not total RE in plasma, was also significantly higher in FH patients than in control subjects (24±10 versus 6.3±5.9 mg · L −1 · h−1, P <0.05), but treatment with simvastatin did not result in improvement of the postprandial RE response, either in the Sf<1000 fraction or in plasma. It is concluded that heterozygous FH patients have increased fasting and postprandial remnant lipoprotein concentrations. Treatment with simvastatin significantly reduced the fasting and postprandial RLP-C concentrations but did not result in improved postprandial RE response.