Acute and delayed effects of prolonged exercise on concentration and composition of LDL subfractions and VLDL

Tuesday II October 1994: Poster Abstracts Metabolism

The RP and SQ data in VLDL support the hypothesis that aging is probably associated with delayed postprandial clearance of remnant particles, although a contribution of reduced intestinal function to the extensive delay in teaching postprandial peak values in the elderly is not excluded. 11131 w,

Lowering of LDL-cholesterol by inhibition of cholesterol absorption and synthesis in hypercholesterolemic type II diabetes Vanhanen H, Miettinen TA, 2nd Dept. of Med., Cbtiv.

of Helsinki, Helsinki, Finland

NIDDM is associated with accelerated atherosclerosis and hyperlipidemia in this disease needs to be treated more effectively than in non-NIDDM subjects. We studied the efficacy of inhibiting cholesterol (C) absorption by sitostanol (3 g/day) ester (S; dissolved in rapeseed oil margarine) and neomycin (N; 1.5 g/day), and C synthesis by pravastatin (P; 40 mg/day) alone and in combination, in eight middle-aged NIDDM men on oral antidiabetic treatment. The study consisted of six 7-week periods, during which the subjects consumed 9 g t.i.d. of the margarine without (control = M) and with S. The study was carried out doubleblinded for the periods on M, MS, MP, IMPS, MN and MNS and with cross-sectional design. Lipoproteins were separated by ultracentrifugation, C absorption was studied with the oral doubleisotope method and quantitation of serum plant sterols and C synthesis with sterol balance technique and serum cholesterol precursor sterol levels. LDL-C was decreased from the M value of 4.2 + 0.1 mmobl (mean + SE) to 3.5 + 0.1 (P < 0.05) during MS, to 2.4 * 0.2 during MP (P < 0.05). to 2.2 + 0.2 during MPS (P < O.OS), to 3.0 + 0.2 during MN (PC 0.05) and to 2.6 + 0.2 during MNS (P < 0.05). HDL-C was significantly decreased only during MN and MNS. C absorption efficiency was significantly decreased from M 25 + 3% by 71% during MS and by 29% during MPS; during MP it increased back to the M level. The serum campesteroVC proportion was decreased significantly by 46%,26%, 28% and 50% during MS, MPS, MN and MNS, respectively and unchanged during MP. Cholesterol synthesis and/or the serum lathosterol proportion decreased during MP and MPS, and increased during MS, MN and MNS. Thus, C absorption may be inhibited mom by S than by N, yet LDL-C may be increased more by N, the combination of the two having an additive effect. However, N also reduces HDL-C. The combination of inhibiting both C absorption and synthesis exhibits the most powerful LDL-C lowering. Serum level, absorption and synthesis of cholesterol during lone-term Dravastatin treatment in FH and no&I-I subTjects _ Yanhanen, Miettinen TA, 2nd Dept. of Med., Cbziv.of Helsinki,

11141

FIN-00290 Helsinki, Finland

We have analyzed serum cholesterol, cholesterol precursor sterols, and intestinal cholesterol metabolism with cholesterol balance and absorption techniques in 12 familial hypercholesterolemic (FH) patients, six with ileal bypass (IBP) before and 1, 6 and 36 months after pravastatin (P) treatment, increasing the dose from 40 to 80 mg/day for the last 24 months. In addition, 9 hypercholesterolemic (non-FH) subjects were treated with 40 mg/day of P and 9 non-FH subjects with placebo for 3 months in a doubleblind placebo control design. In the FH study serum cholesterol, mainly LDL-C, was reduced by 30% with 40 mg/day and significantly more (P < 0.05) by 80 mg/day of P (final decrease 40%). The levels of serum cholesterot precursors were significantly reduced by up to 40% at 40 mg/day and insignificantly further at 80 mg/day. In the FH subjects cholesterol absorption efficiency gradually decreased

121

from 51% by an insignificant 10% at 1 month, 33% at 6 months (P-c 0.05) with P 40 mg/day and insignificantly further during 80 mg/day at 36 months, both without and with IBP (P < 0.05 for

both). The respective serum plant sterol and cholestanol values were decreased, and fecal elimination of cholesterol was reduced by up to 40% (P < 0.05). In the non-FH study a placebo-related reduction of serum cholesterol was 22%, that of serum cholesterol precursor sterols 278, but elimination of fecal sterols only tended to be reduced and cholesterol absorption efficiency was unchanged. Thus, pravastatin inhibited cholesterol absorption efficiency in FH both without and with ileal bypass, but in non-FH absorption is unaffected. Fish Eye Disease: structural and metabolic abnormalities of high density lipoproteins m, Elkhalil L, Majd 2, Bakir R, Poulain P, Lacroix B, Duhal N, Fruchart JC, Dept. of Res. on Atherosclerosis, SERLIA and

11151

INSERM U325, Inst. Pasteur de Lille, I, rue du Professeur Calmette, 59019 Lille Cedex, France

Fish Eye Disease (FED) in humans is characterized by comeal opacities and markedly decreased plasma concentrations of HDLC and apo A-I, while no tendency to precocious atherosclerosis is present. To elucidate this paradox, the structure and the in vivo metabolism of HDL were determined in a 53-year-old woman with a FED syndrome associated with a markedly decreased LCAT activity in HDL due to a mutation of the LCAT gene (Arg158 -+ Cys). HDL isolated by ultracentrifugation were enriched in unesterified cholesterol and phosphohpids at the expense of cholesteryl esters and proteins. The apolipoprotein content showed an enrichment in apo E and apo A-IV while apo A-I was dramatically reduced. SDS-PAGE and immunoblotting using specific antibodies showed that the apo E was free or covalently bound to apo A-II. These particles analyzed by native gradient gel electrophoresis were small lipoproteins whose size was similar to the smallest fraction of normal HDL3. To assess the metabolism of HDL apolipoproteins, in vivo apolipoprotein kinetic studies were. performed using endogenous labeling techniques in the patient with FED and in three control subjects. Ail subjects were administered D+abeled leucine by primed constant infusion for up to 10 h. The fractional synthetic rates of apo A-I and apo A-II in the patient were 0.674 and 0.594/day, clearly higher than in controls, 0.225 & 0.043 and 0.151 k O.OOl/day for apo A-I and apo A-II respectively. The apo A-I and apo A-II production rates in the patient with FED were normal, 11.32 and 2.62 mg/kg/day respectively, cf. those of normal subjects 11.53 + 1.21 and 2.56 f m&g/day. These data established that hypoalphabpoproteinemia in this case of FED was caused by marked hypercatabolism of apo A-I and apo A-II. This hypercatabolism could be the consequence of the structural abnormalities of HDL due to the selective LCAT deficiency. Acute and delayed effects of prolonged exercise on concentration and composition of LDL subfractions and VLDL Baums&rk MW, Frey I, Berg A, Center of Int. Med., D-79106

11161

Freiburg. Germany

To investigate the effects of a single episode of prolonged exercise on lipoprotein concentration and composition, 13 healthy endurance-trained men were examined before and after (1 h, 20 h) a cross-country run (30 km, time 130 * 7.4 mitt). The data show that following acute exercise, serum TG levels are reduced (36%) as a consequence of a reduced number (31%) of VLDL particles. Small changes of VLDL composition were observed. In contrast

Atherosclerosis X, Montreal, October I994

Tuesday 1 I October 1994: Poster Abstracts Metabolism

122

to this, acute exercise did not induce significant changes in the average concentration of specific LDL subfractions. Changes in dense LDL (d > 1.044) concentration, however, were significantly correlated to changes in serum TG; a reduction in dense LDL occurred in subjects with large reductions in serum TG. In addition, LDL composition changed significantly with exercise. Immediately (1 h) after exercise the TG content of all LDL subfractions was reduced. These reductions were significant in large (d = 1.006-1.037 g ml-‘) and small LDL (1.044-1.063 g ml-‘), It can be concluded that acute exercise primarily alters the composition of LDL subfractions while their concentration mmains stable. If large reductions in serum TG are induced a concomitant reduction in dense LDL is observed.

11171LDL subfraction metabolism in young healthy males Q&&M,,!, Packard CJ, Griffin BA, Gaw A, Shepherd J, Dept. of Pathological Biochemistry, Glasgow Royal Infirmary, UK

The object of this study was to investigate the metabolism of LDL subfractions in three young healthy males (mean cholesterol 4.55 mmol/l and TG 0.67 mmol/l). LDL-I (d = 1.025-1.034 g/ml), LDL-II (d = 1.034-1.044 g/ml) and LDL-III (d = 1.0441.060 g/ml) were prepared by density gradient ultracentrifugation. Mean concentrations of LDL-I. LDL-II and LDLIII were 55. 159 and 48 mg lipoprotein/100 ml plasma respectively, with LDL-II being the predominant species in each individual. The subjects underwent two turnovers; on the first occasion the tracers were (I-125) LDL-I and (I-131) LDL-III and on the second (I-131) LDL-II and (I-125) LDL-III. Following injection, the radioactivity in plasma, LDL-I, LDL-II, LDL-III and urine was measured over 2 weeks. Multicompartmental modeling using the SAMM program was used to build a model and generate kinetic constants. All LDL subfractions were subject to direct catabolism from plasma at various fractional catabolic rates (LDL-I, 0.17; LDL-II, 0.39 and LDL-III, 0.69 pools/day). LDL-I was converted to LDLII and to some extent LDL-III. When LDL-II was the tracer some was transferred to LDL-III with very little conversion to large LDL-I. When LDLIII was injected it quickly disappeared over the first 4 days, due to fast catabolism and also transfer to LDL-II. None of the radiolabeled LDL-II or LDL-III appeared in LDL-I. Fractional transfer rates between the LDL subfractions were calculated as LDL-I to -II (0.17) pools/day, LDL-II to -1 (O.Ol), LDL-II to -111(0.22) and LDLIII to -II (0.19). These preliminary data suggest that the LDL subfractions are metabolically related in a delipidation scheme, whereby large LDL-I is converted to LDL-II to small dense LDL-III, with LDL-II and LDLIII existing in a dynamic equilibrium. In conclusion, the inter-relationships among the LDL subfractions appear complex and their catabolism is not simply related to density. 11181

2,3-Oxidosqualene inhibitors: a novel approach for lipid-lowering agents ’ Mtiller P2, Woitun E2, Eisele Bl, ‘Dept. of Biochemis-

TV try, Dept. of Chemistry, Dr. Karl Thomae GmbH, 88397 Biberach, Germany

Within the cholesterol biosynthesis cascade the enzyme 2,3oxidosqualene cyclase [EC 5.4.99.71 (OSC) is of special interest because of its dual function: cyclization of monoepoxysqualene to lanosterol and diepoxysqualene to oxylanosterol. The significance of this enzyme for intracellular cholesterol homeostasis was further explored with a potent, specific inhibitor (BIBX 79). In Hep G2 cells the effects of BIBX 79 on cholesterol biosynthesis, OSC and HMG-CoA reductase activities were. studied. BIBX 79 is a potent inhibitor of sterol biosynthesis in HepG2 cells (IC5o 4 X 10eg mol/l).

No other enzyme within the cholesterol biosynthesis cascade was inhibited, as was evidenced by HPLC detection. Squalene cyclase was inhibited either directly or after 16 h of incubation, the ICso values being 9 x lo-’ mol/l and 3 x lO-‘O mol/l, respectively. In contrast to simvastatin no direct interaction with HMG-CoA reductase was observed. However, when cells were incubated for longer periods with simvastatin HMG-CoA mductase activity was increased up to 180%. With BIBX 79 a downregulation of this enzyme activity was observed in concentrations where squalene cyclase was partially inhibited @lo-’ < lo6 molll), whereas total inhibition of squalene cyclase resulted in an elevation of HMG-CoA teductase activity. This feedback loon is mediated via oxysterols. Because diepoxysqualene is preferentially- cvclized bv the OSC. with OSC inhibitors both an inhibitorv, _ as well as a regulatory effect on cholesterol biosynthesis can be achieved. It is concluded that OSC plays a crucial role in the regulation of intracellular cholesterol homeostasis. OSC inhibitors offer therefore an intelligent approach to novel lipid-lowering agents. Endogenous steroid hormones, visceral obesity and plasma lipoprotein levels in men Tchemof, Labtie F, Btlanger A, Bouchard C, Prud’homme D, Moorjani S, Lupien PJ, Despms JP, Lipid Res. Centre and MRC 11191

group in Molecular Endocrinology, CHUL Res. Centre and Physical Activity Sciences Lab., 2705 Laurier blvd, Ste-Foy, Canada GI V 4G2

It is well established that visceral obesity in men is associated with reduced plasma HDL-C levels, and with increased plasma apo B and TG concentrations. Steroid hormone concentrations are also associated with variations in plasma lipid and lipoprotein levels. Previous observations by our group revealed negative relationships between plasma testosterone (T), adrenal Cl9 steroids, sex hormone binding globulin (SHBG) concentrations and levels of total and abdominal adipose tissue (AT) in men. In this study, we have investigated the relative contribution of visceral AT accumulation measured by computed tomography (CT) and of endogenous steroid hormone levels to the variation of plasma lipoprotein levels in a sample of 78 men. Serum concentrations of T, androst-5-ene-3/3,17/J-diol(A’-DIOL) and androstenedione (A4DIONE) as well as SHBG were determined. Serum A5-DIOL levels correlated significantly with HDb-C (r = 0.33; P < 0.005) and TG concentrations (r = -0.26; P < 0.05). SHBG levels were also positively correlated with HDb-C (r = 0.40; P < 0.001) and negatively correlated with TG concentrations (r = -0.31; P < 0.01) whereas A5-DIOL, T and SHBG were negatively correlated with apo B levels (-0.29 < r 5 -0.43; 0.05 > P < 0.0001). Multivariate analyses revealed that SHBG, A5-DIOL and visceral AT area (measured by CT) all contributed to the variance in plasma lipoprotein concentrations (explaining 17-288 of the variance). Therefore, the concomitant elevation of visceral AT noted in men with reduced T, adrenal Cl9 steroid and SHBG concentrations does not fully explain the dyslipidemic state observed in abdominal obesity. In conclusion, both steroids and visceral AT are independently associated with variation in plasma lipoprotein levels in men. m

Direct correlation between in vivo cholesterol synthesis and hepatic secretion of apolipoprotein B-100 in normolipidemic subjects Naoumova RP+, Cummings MH*, Thompson GR+,

Pi-Dept. of Med., Univ. of Western Australia, Perth, WA 6000;

*Dept. of Endocrinology and Chemical Pathol,, St. Thomas’ Hospital (VMDS), London SE1 7EH; %RC Lipoprotein Team, Hammersmith Hospital, London WI2 OHS, UK

The hepatic secretion of apolipoprotein B-100 (apo B) is an im-

Atherosclerosis X, Montreal, October 1994