4.P.231 Metabolism of triglyceride-rich lipoproteins determines occurrence of atherogenic LDL phenotype

Thursday 9 October 1997.• Posters Triglyceride-rich lipoproteins

344

asymptomatic patients with hyperlipoproteinemia . The population was divided into deciles of TG (TG levels 30-4100 mg/dL) . Results reported in figures 1 and 2 show that both FVIIc (%) and PAI-1 (ng/mL) levels increase linearly with TG levels (p = 0 .0001) . We conclude that the relationships between TG levels and FVIIc as well as PAI-1 are continuous without threshold value .

4 .R229

Characteristics of dyslipidemia in intermittent claudication patients

D .D. Cilla, T. Wang, W.P. Forbes, K. Nakajima. Otsuka America Pharmaceutical, Inc., Rockville, Maryland, USA Intermittent claudication (IC) is the most common symptom of occlusive arterial disease of the extremities, a form of peripheral arterial disease (PAD) . Cigarette smoking, diabetes, hypertension, low HDL-C, high LDL-C and plasma triglycerides (TG) are thought to be important risk factors for PAD . The role of triglyceride-rich lipoprotein (TRL) remnants in PAD has not been studied . However, previous studies have shown that TRL remnants, including Remnant-Like Particles-Cholesterol (RLP-C), are elevated in patients with coronary artery disease and are likely to be atherogenic according to their biological characteristics . The objectives of this study were to evaluate the relationship between RLP-C and PAD, and compare the significance of other lipids and lipoproteins in the development of PAD in the United Sates . IC patients over 40 years old (n = 303) had significantly higher serum RLP-C and total TG levels than non-IC controls of the same age range (n = 336) . HDL-C levels were significantly lower in IC patients . There was no statistical difference between the two groups in serum total cholesterol (CHOL) and LDL-C levels . Lipid and lipoprotein levels in the table are in mg/dL. RLP-C Median 25%tile 75%tile

CHOL

TG

LDL-C

HDL-C

IC

CON

IC

CON

IC

CON

IC

CON

IC

CON

8 .5 6 .2 12.4

6.4 5.2 9.0

180 120 240

113 80 163

213 189 244

208 184 231 0.086

135 116 159

133

39 33 47

47 38 57

110 155

<0 .001 <0 .001 0 .091 <0 .001 ` by Mann-Whitney U test This is the first study to evaluate the relationship between remnant lipoproteins and PAD . Our study suggests that TRL and their remnants (RLP) as well as HDL may play an important role in the pathogenesis of PAD . Px

4 .P.230

Pseudo-hypertriglyceridemia in four kindreds with benign hyperglycerolemia

I . Cortella, C . Gabelli, A . Burlina l , S . Martini, L. Previato, S . Donazzan, G . Baggio, G . Crepaldi . Dept. of Int. Med. ; 1 Dept. of Pediatrics, University of Padua, Italy Four unrelated male subjects from Northern Italy with severe hypertriglyceridemia (HTG) refractory to dietary and farmacologic treatment were referred to our Lipid Clinic . Subsequently a fifth patient (SD), brother of SS, was found with the same lipid abnormality . Age and lipid values (mg/dl) of the five subjects were as follow : SS SD CC FL CL

Age 8 2 .5 8

62 70

TC

TG

246 185 149 160 209

517 488 387 540 644

VLDL-TG n .d. n .d. 86 115 99

HDL-C 55 46 59 63 88

Triglyceride (TG) values were determined by GPO-PAP colorimetric method which measures free glycerol after enzymatic hydrolysis of plasma TG . In spite of the severe HTG all patients had clear serum, normal lipoprotein electrophoresis pattern and, where measured, normal VLDL-TG levels ; moreover high TG values in > 1 .21 g/ml density fraction were observed in patient CC suggesting high levels of free plasma glycerol . Determination of free glycerol by gas chromatography/mass spectrometry revealed in all subjects extremely elevated levels in plasma (out of scale) and values ranging from 12 to 118 mol/mol of creatinine in urine (normal values <0 .2) confirming the diagnosis of hyperglycerolemia . All patients were free from symptoms and signs specific for muscolar dystrophy or adrenal hypoplasia indicating the presence of isolated glycerol kinase deficiency . In conclusion, if HTG unresponsive to treatment is found, diagnosis of benign hyperglycerolemia should be considered . The simple evaluation of serum aspect and of the lipoprotein electrophoretic pattern may be helpfull in the diagnosis before more sofisticated analyses.

4 .P.231

Metabolism of triglyceride-rich lipoproteins determines occurrence of atherogenic LDL phenotype

Th . Demant, C.J. Packard, J .P. Stewart, D. Bedford, G. Schwertfeger, A . Bedyneck, D. Seidel, J. Shepherd. Institute of Biochemistry, Glasgow Royal Infirmary, University NHS Trust, UK; Institut fir Klinische Chemie, Universitktsklinikum Grojihadern, LMUMiinchen, Germany We studied the in-vivo metabolism of apolipoprotein B-containing lipoproteins in order to define metabolic determinants for the occurrence of different LDL phenotypes which are believed to be of different atherogenic potential . In 20 men with plasma triglyceride 60-210 mg/dl and cholesterol 145-270 mg/dl the LDL phenotype was determined by gradient gel electrophoresis as either phenotype A (> 26 nm, n = 9), phenotype I (25-26 run, n = 5) or phenotype B (<25 run, n = 6) . The metabolism of VLDLI (Sf 60-400), VLDL2 (Sf 20-60) . IDL (Sf 12-20) and LDL (Sf 0-12) apo, B was followed using a tracer injection of tri-deuterated leucine . Generally, the LDL apo B fractional catabolic rate (FCR) was inversely related to plasma triglyceride and positively related to the percent of direct apo B production in the IDLJLDL density range (p = 0.002 and p = 0.001) . Subjects with a predominance of LDL phenotype A were distinguished from those with the phenotype B as follows : LDL-Phenotype : VLDLI-delipidation(pootsld) VLDL2-delipidation (poolsld) VLDL2 production (mgld) IDLLDL product. (% of total) LDL-FCR (poolsld)

A

B

16.3 7 .2 8 .1 4.0 142 315 26.0 11 .0 0 .53 0 .33

p 0.010 0.001 0.029

0.022 0.026

In conclusion, rates of apo B secretion and delipidation have a major impact on the occurrence of LDL phenotypes which differ in metabolic qualities and atherogenicity .

4 . P 232

Possible competition between VLDL and LDL for the binding to LDL receptor at hypertriglyceridemia - an in vitro estimate

A .D . Dergunov, V. Yakushkin, E. Smirnova, V. Tsibulski, S . Visvikis l , G . Siest l . National Research Centre for Preventive Medicine, Moscow, Russia; 'Centre de Medecine Preventive, Nancy, France The efficiencies of VLDL and LDL binding to the LDL receptor (LDLR) in vitro were compared by solid-phase assay free of steric hindrance observed in cell binding [Chappell et al 1993 J . Biol. Chem. 268 : 25487-25493 .] . VLDL and LDL particles were isolated from plasma of patients with low (<200 mg/dl), intermediate and high (>300 mg/dl) triglyceride (TG) content ; the mean values of plasma cholesterol content were in the range of 226-266 mg/dl for these groups . The maximal number of binding sites did not change for both type of particles and between groups . The mean value of dissociation constant for VLDL binding Kd(VLDL) (2 .0 rg apoB/mI) was 4 .2-fold lower compared to that for LDL binding . Direct involvement of apoE into VLDL binding was confirmed by the inhibition of the process by antibodies to apoE . A comparison of the groups with low and high TG content revealed a significant (p < 0 .05) 1 .9-fold decrease of Kd(VLDL) values and a significant 2.2-fold increase of Kd(LDL) values . Based on these data, VLDL concentrations corresponding to 50% inhibition of LDL binding in an assumption of the competition of both ligands for LDLR (IC50) were calculated in terms of LDL cholesterol mass ; the mean values of IC50 decreased from 106 to 41 mg/dl when plasma TG content exceeded 200 mg/dl . Some peculiarities of protein-protein and protein-lipid interactions in VLDL and LDL particles in these groups were visualised by protein cross-linking and and fluorescence study. The possible competition of VLDL with LDL for the catabolism site(s) in vivo, while plasma TG increasing, could "buffer" the atherogenic action of TG-rich lipoproteins .

4 P.233

The uptake of chylomicron remnants and their effects on endothelial cell function in the perfused rat aorta

D .J . Grieve, M .A. Avella, J . Elliott, K .M. Botham . Dept. of Veterinary Basic Sciences, Royal Veterinary College, London, England Although endothelial cell function is known to be modulated by endogenous lipoproteins, little is known about the influence of chylomicron remnants (CMRs) . The aim of this study was to investigate the effects of perfusing the isolated rat aorta with CMRs on endothelial function, and to compare them with the effects observed in freshly isolated vessel rings . An in vitro system for perfusion of the rat aorta was developed using a perfusate consisting of 33% bovine serum replacement and 67% Krebs-Henseleit solution (KHS) . The

11th International Symposium on Atherosclerosis, Paris, October 1997