The Effect of Moxonidine on Plasma Lipid Profile and on LDL Subclass
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Journal of Human Hypertension (1999) 13, 781–785 1999 Stockton Press. All rights reserved 0950-9240/99 $15.00 http://www.stockton-press.co.uk/jhh ORIGINAL ARTICLE The effect of moxonidine on plasma lipid profile and on LDL subclass distribution MS Elisaf, C Petris, E Bairaktari, S-A Karabina, C Tzallas, A Tselepis and KC Siamopoulos Department of Internal Medicine, University of Ioannina Medical School, Greece Moxonidine is a new antihypertensive agent whose cant decrease in both systolic and diastolic blood ,mechanism of action appears to involve specific stimu- pressure (from 147 ؎ 10 to 131 ؎ 11 mm Hg, P Ͻ 0.001 ,lation of imidazoline receptors resulting in an inhibition and from 98 ؎ 4.5 to 86 ؎ 5 mm Hg, P Ͻ 0.001 of the activity of the central and peripheral sympathetic respectively). No significant change in plasma lipid pro- nervous system. The drug seems to behave neutrally file was observed after moxonidine administration. with respect to plasma lipid parameters. However, there Additionally, no change in the susceptibility of LDL sub- are no data on the effects of moxonidine on the low- classes to copper-induced oxidative modification was density lipoprotein (LDL) subclass pattern or on the LDL noticed. Finally, drug therapy was not followed by any oxidation susceptibility, both of which are known to play change in either LDL phenotype or in mass and compo- a prominent role in the pathogenesis of atherosclerosis. sition of the three LDL subfractions. We conclude, that Thus, we undertook the present study to examine the unlike other antihypertensive drugs, such as beta-block- influence of moxonidine on the LDL subspecies profile ers which may predispose to expression of a relatively and their susceptibility to copper-induced oxidative atherogenic lipoprotein subclass pattern, moxonidine modification in 20 hypertensive patients (11 men, 9 does not affect either plasma lipid parameters or lipo- women) aged 38–61 years. Moxonidine administered at protein composition. a dose of 0.4 mg daily for 8 weeks produced a signifi- Keywords: moxonidine; plasma lipid profile; LDL oxidation susceptibility; LDL subclass pattern; sympathetic nervous system Introduction pheral vascular resistance. Moreover, the reduced sympathetic drive results in lower concentrations of It is well known that some antihypertensive agents, catecholamines and renin.10,11 Randomised com- especially diuretics in high dosage and beta-block- parative studies have shown that the efficacy of ers, have unfavourable effects on plasma lipids, moxonidine as monotherapy is similar to that of including elevation of triglycerides and total choles- other antihypertensive drugs.12 In clinical studies terol and reduction of high-density lipoprotein chol- moxonidine has been found to behave neutrally 1–4 esterol (HDL-C). Additionally, it has been shown with respect to plasma lipid parameters.12–14 How- that beta-blocker use may predispose to expression ever, there are no data on the effects of moxonidine of a relatively atherogenic lipoprotein subclass pro- on the LDL subclass pattern or on the LDL oxidation file, as it is associated with a predominance of susceptibility, both of which are known to play a smaller, denser, low-density lipoprotein (LDL) par- 5,6 prominent role in the pathogenesis of atheroscler- ticles and less HDL mass. Since an overview of all osis. Thus, we undertook the present study to exam- hypertension trials has shown that antihypertensive ine the influence of moxonidine on the LDL sub- treatment does lead to a less than expected species profile and their susceptibility to copper- reduction in coronary heart disease (CHD) event induced oxidative modification in patients with 7,8 rates, it is tempting to suggest that the adverse idiopathic hypertension. effects of the study drugs on lipid metabolism may have offset the potential benefit of blood pressure Materials and methods (BP) reduction. The selective imidazoline-I1-recep- tor agonists, a recently introduced class of antihy- Twenty patients (11 male, 9 female) aged 38–61 pertensive agents, offers an innovative therapeutic years with mild/moderate arterial hypertension approach to the treatment of hypertension.9 Moxoni- were studied. No patient had clinical or biochemical dine, the first drug of this class, stimulates imidazo- evidence of diabetes mellitus, thyroid, hepatic, or line I receptors in the medulla, thereby reducing renal disease. Additionally, none of them was taking central sympathetic drive and attenuating peri- any lipid lowering drugs or any other medication known to affect lipid metabolism, including hor- monal therapy. Individuals known to ingest more Correspondence: Dr Moses S Elisaf, Associate Professor of Medi- cine, Department of Internal Medicine, University of Ioannina, than two alcoholic drinks or to take vitamin sup- Medical School, GR 451 10 Ioannina, Greece plements were excluded from the study. To avoid Received 10 January 1999; accepted 25 February 1999 any possible effects of diet on the susceptibility of Effect of moxonidine on LDL subclass distribution MS Elisaf et al 782 the LDL subfractions to oxidation, all subjects were dation is divided into three consecutive phases, lag advised to avoid altering their dietary habits phase, propagation phase and decomposition phase. throughout the study. The lag time, the maximal rate of conjugated dienes After a wash-out period of at least 4 weeks for the formation, and the total amount of dienes formed patients on antihypertensive drugs, moxonidine was were calculated as previously described.16 The rela- given at a dose of 0.4 mg/day for 8 weeks. Before tive electrophoretic mobility (REM) of the oxidised and after treatment BP was measured by a calibrated subfractions was determined by agarose gel electro- sphygmomanometer as triplicate measurements phoresis on agarose gels [Lipo + Lp(a), Sebia]. after the patients had been sitting for 5 min. In addition to BP measurements, pulse rate was Analytical methods recorded and venous blood was obtained after a 14 h overnight fast for the determination of plasma Total plasma cholesterol and triglyceride levels lipid parameters. were measured by enzymatic colorimetric assays Subfractionation of LDL with density gradient using an RA 1000 analyser (Technicon Instruments, ultracentrifugation was performed and the suscepti- NY, USA). HDL-cholesterol levels were also deter- bility of LDL subclasses to copper-induced oxidative mined by the same method after precipitation of modification was tested. apoB-containing lipoproteins with magnesium-dex- tran sulphate. LDL-cholesterol levels were calcu- lated using the Friedewald formula.17 Plasma lipo- Subfractionation of low-density lipoprotein protein (a) [Lp(a)] levels were measured in duplicate Venous blood samples were collected from over- using a monoclonal anti-Lp(a) antibody technique night fasting donors in tubes containing 0.001% by the enzyme immunoassay Macra Lp(a) (Terumo Na2EDTA. Immediately after collection of plasma, Medical Corporation Diagnostic Division, Elkton, 1.3 mM EDTA and 50 g/ml of gentamicin were MD, USA). The lower limit of detectability was added and plasma was stored at 4°C in order to pre- 0.8 mg/dL. Plasma apoAl and apoB were measured vent metal cation catalysed lipoprotein oxidation by immunonephelometry with the aid of a Beckman and microbial growth. Within 24 h from its collec- array analyser (Beckman Instruments, CA, USA). tion, plasma was submitted to density gradient ultra- The cholesterol, phospholipid and triglyceride con- centrifugation in a Beckman ultracentrifuge at tent of each lipoprotein subfraction was determined 40 000 rpm, 14°C for 24 h, using a Beckman SW41 enzymatically using the BioMerieux kits. The pro- Ti rotor as previously described.15 Construction of a tein content of the gradient fractions and lipoprotein discontinuous density gradient at ambient tempera- subfractions was determined by the BCA method. ture was initiated by pumping 3 ml of plasma into Lipoprotein mass in each subfraction was calculated the bottom of the tube. The density of the plasma as the sum of the concentrations of the individual was raised to 1.10 g/ml by dissolution of 0.42 g KBr. components (cholesterol, triglyceride, phospholipid The plasma was then successively overlayered by and protein) and allowed the determination of the four solutions of decreasing density (2 ml of d = percent chemical composition.16 1.065 g/ml, 3 ml of d = 1.035 g/ml, 3 ml of d = 1.019 g/ml and 1.0 ml of d = 1.006 g/ml). After ultra- Statistical analysis centrifugation, 30 fractions of 400 l were collected by successive aspiration with a precision pipette Data were expressed as mean ± s.d., except for Lp(a), from the meniscus downwards. All fractions were which was expressed in terms of median and range. analysed for their protein content. Subsequently, Statistical analysis was performed using paired or equal volumes of specific gradient fractions corre- unpaired Student’s t-test or Wilcoxon signed-rank sponding to d = 1.030–1.034 g/ml, d = 1.034– test. A P value of less than 0.05 was considered to 1.041 g/ml and d = 1.041–1.048 g/ml were pooled to be significant. constitute the LDL1, LDL2 and LDL3 subfractions, respectively. Results Moxonidine produced a significant decrease in both Oxidation of low-density lipoprotein subfractions systolic and diastolic BP (from 147 ± 10 to 131 ± 11 Before oxidation, LDL subfractions were dialysed to mm Hg, P Ͻ 0.001, and from 98 ± 4.5 to 86 ± 5 remove EDTA against two changes of a 200-fold vol- mm Hg, P Ͻ 0.001, respectively) while no significant ume of 10 mM phosphate buffered saline solution change in heart rate was noticed. As shown in Table (PBS), pH 7.4 for 24 h at 4°C in the dark. From the 1, drug administration was not followed by any dialysed LDL subfractions, a volume of 1 ml con- significant change in plasma lipid parameters. taining 100 g protein/ml PBS was oxidised in the presence of CuSO ,5M final concentration.