Drug control of reverse cholesterol transport.

Reverse cholesterol transport identifies a series of metabolic events resulting in the transport of excess cholesterol from peripheral tissues to the liver. High-density lipoproteins (HDL) are the vehicle of cholesterol in this reverse transport, a function believed to explain the inverse correlation between plasma HDL levels and atherosclerosis. An attempt to stimulate, by the use of drugs, this transport process may hold promise in the prevention and treatment of arterial disease. Among the agents affecting lipoprotein metabolism, only probucol exerts significant effects on reverse cholesterol transport, by stimulating the activity of the cholesteryl ester transfer protein and, consequently, altering HDL subfraction composition/distribution. Another approach to the stimulation of reverse cholesterol transport consists of raising plasma HDL levels; studies in animals, either by exogenous supplementation or by endogenous overexpression, have shown a consistent benefit in terms of atherosclerosis regression and/or non-progression. Thus, it is time to consider different future treatments of atherosclerosis, combining the classical lipid-lowering treatments with innovative methods to promote cholesterol removal from the arterial wall.

Microsomal enzyme inducers raise plasma high-density lipoprotein cholesterol levels in healthy control subjects but not in patients with primary hypoalphalipoproteinemia.

In this study we compared the ability of phenytoin, a microsomal enzyme inducer, to raise plasma high-density lipoprotein (HDL) levels in normolipidemic subjects and patients with primary hypoalphalipoproteinemia. In healthy control subjects, phenytoin caused a dose-dependent increase of plasma HDL, HDL2, and HDL3 cholesterol levels, up to 40% to 50%. Minor changes were recorded in the plasma concentrations of apolipoprotein (apo) A-I and apo A-II; the plasma level of the cholesteryl ester transfer protein (CETP) decreased by 42%. In contrast, none of the patients with hypoalphalipoproteinemia had changes in plasma HDL, HDL2, or HDL3 cholesterol, apo A-I, apo A-II, or CETP levels. These findings indicate that microsomal enzyme inducers are unsuitable to increase plasma HDL levels in high-risk patients with primary hypoalphalipoproteinemia, and they disclose a new mechanism, that is, decreased CETP-mediated transfer of cholesterol out of HDL, for the HDL-raising effect of microsomal enzyme inducers in healthy individuals.

Plasma triglycerides and lipoprotein(a): inverse relationship in a hyperlipidemic Italian population.

The relationship between plasma lipoprotein(a) (Lp(a)) levels and other clinical/biochemical variables was investigated in 1200 consecutive hyperlipidemic patients. Plasma Lp(a) concentrations were measured by a sandwich-ELISA method, while the patients were either on diet or diet plus lipid-lowering drugs; 38% of them had a plasma Lp(a) level > 30 mg/dl. The median plasma Lp(a) concentration and the frequency of Lp(a) > 30 mg/dl were significantly lower in individuals with severe hypertriglyceridemia vs. hypercholesterolemics (HC) or mixed hyperlipidemics (M-HLP), but similar to normolipidemic healthy controls. Patients with isolated moderate hypertriglyceridemia had Lp(a) levels intermediate between HC and M-HLP subjects. The in vitro addition of triglyceride-rich lipoproteins to normotriglyceridemic plasma did not affect the Lp(a) measurement. Plasma Lp(a) concentrations in the whole hyperlipidemic population correlated negatively with triglycerides and positively with total cholesterol, HDL-cholesterol and age, being unrelated to either body mass index or lipid-lowering treatment. In HC patients, the presence of tendon xanthomas was associated with twofold higher Lp(a) levels. These findings argue for a regulatory role of triglycerides on plasma Lp(a) levels in hyperlipidemic patients.

Injury produces early rise in lipoprotein lipase activity in rabbit aorta.

The mechanisms following intimal injury predisposing towards atherosclerotic changes have not been fully elucidated. We speculated that a local increase in the enzyme lipoprotein lipase (LPL) might explain a higher susceptibility of the damaged intima to lipid accretion, and so we investigated the effect of balloon endothelial denudation on LPL activity and cholesterol content (LPLa and Cholc, respectively), in aortas from normolipidemic male New Zealand white rabbits. Arteries were obtained from injured and control animals after 2, 6, 8 and 10 weeks to evaluate the shortest period after de-endothelialization necessary to detect LPLa changes. Injury resulted in a 4-fold LPLa rise (P < 0.01), as early as 2 weeks, and the enzymatic activity remained increased throughout the study period. A mild but significant 22% Cholc increase (P < 0.03) was found after 2 weeks of injury, even in this normolipidemic rabbit model. We conclude that physical damage to the intima markedly and soon increases LPLa. This finding might account for the higher lipid accumulation by injured vessels, providing additional support to the hypothesis of LPL as an atherogenic mediator.

Marked neointimal lipoprotein lipase increase in distinct models of proclivity to atherosclerosis: a feature independent of endothelial layer integrity.

Lipoprotein lipase (LPL) in the arterial wall has been proposed to enhance the retention of apoB-containing lipoproteins, an early event in atherosclerosis. As the neointima is considered the primary site of lipid accumulation in atherogenesis, the arterial expression and location of LPL was investigated in distinct experimental models of neointimal formation in normolipidemic rabbits and rats. Neointima elicited by balloon aortic denudation or raised beneath an anatomically intact endothelial layer by placing a silastic collar around the common carotid artery, both showed a striking LPL immunostaining that mostly co-localized with neointimal smooth muscle cells. Besides, increased LPL protein and mRNA in deendothelialized aortas was demonstrated by Western and Northern blot analysis, respectively, suggesting an enhanced expression of LPL in injured arteries. It was concluded that LPL is increased in neointima developed in either denuded vessels or arteries with a preserved endothelium, a finding which suggests that LPL abundance may be an attribute of the neointima, whatever the stimulus that promotes its formation. On the basis of former evidence concerning the role of LPL in lipid retention, this study provides a possible explanation for the injury-induced vessel susceptibility to atherosclerosis, and the particular proneness of the neointimal layer to lipid accretion.

Mechanisms of high-density lipoprotein reduction after probucol treatment: changes in plasma cholesterol esterification/transfer and lipase activities.

Probucol treatment results in a significant reduction of plasma high-density lipoprotein (HDL) levels. Since the remodeling of HDL within the plasma compartment is a crucial determinant of HDL levels, the activities of several factors participating in the process, ie, lecithin:cholesterol acyltransferase (LCAT), cholesteryl ester transfer protein (CETP), and lipoprotein and hepatic lipases (LPL, HL), were evaluated in 15 hypercholesterolemic patients treated with probucol (1 g/d) for 8 weeks. Drug treatment was associated with significant reductions of HDL cholesterol ([HDL-C] -32%), HDL2-C (-65%), HDL3-C (-22%), apolipoprotein (apo)A-I (-27%), and apo A-II (-11%) levels and with the accumulation of small HDL in plasma. CETP activity increased by 48%, with minor changes in LCAT (-7%), LPL (+4%), and HL (-7%) activities. By linear regression analysis, CETP activity correlated inversely with HDL-C, HDL2-C, and apo A-I levels (r = -.63, -.52, and -.73, respectively) and with HDL particle size. In multivariate analysis, CETP activity was the strongest predictor of HDL-C levels, apo A-I levels, and HDL particle size. The hypothetical mechanism of probucol is a stimulation of CETP activity, resulting in the formation of triglyceride (TG)-enriched HDL. These are acted on by HL, leading to the accumulation of small HDL in plasma.

[Repeatability of insulin sensitivity estimation using the Minimal Model and comparison with a modified short low-dose insulin tolerance test]. / Reproducibilidad de la cuantificación de la sensibilidad a la acción insulínica con el modelo mínimo y comparación con un test de tolerancia a bajas dosis de insulina.

Hyperinsulinemia and insulin-resistance are metabolic disturbances associated with obesity, essential hypertension, hypertriglyceridemia, glucose intolerance, overt non-insulin dependent diabetes mellitus, polymetabolic syndrome and atherosclerotic disease. The assessment of in vivo insulin sensitivity (SAI in vivo) changes achieved by life style modifications or drug interventions require a reproducible technique. To evaluate the day-to-day intra-individual repeatability of SAI-in vivo, we determined the variation in the SI index (calculated from the Minimal Model of Bergman modified by insulin or MMins) in 11 subjects with a wide range of insulin-resistance. SI (first study) varied from 0.82 to 8.48 x 10(-4) min-1/microU.mL (4.43 +/- 2.85 x 10(-4) min-1/microU.mL mean +/- SD) and highly correlated with SI (second study) (r = 0.89; p = 0.0002). The average interday coefficient of variation was 20.9 +/- 13.9% and was similar in subjects with low or high SI values. We also measured SAI in vivo by assessing the rate of serum glucose decline induced by human cristalline insulin 0.025 U/kg IV dose after a 12-14 hours fasting period (a modified Bonora's method or BBD) in 11 subjects. No subject presented biochemical or symptomatic hypoglycemia. SAI in vivo values determined by BBD varied from 21 a 234 mumol/ml/min (134 +/- 64.8 mumol/ml/min, mean +/- SD). We found a highly significant correlation between SI values obtained from MMins and SAI in vivo assessed by the BBD (r = 0.89, p = 0.0002). Our results suggest that the Mmins is a fairly reproducible procedure and that a BBD is an acceptable option to quantify SAI in vivo, mainly when a fast-execution practice is necessary or cost restrictions are required.

Green tea ingestion greatly reduces plasma concentrations of nadolol in healthy subjects.

This study aimed to evaluate the effects of green tea on the pharmacokinetics and pharmacodynamics of the ß-blocker nadolol. Ten healthy volunteers received a single oral dose of 30 mg nadolol with green tea or water after repeated consumption of green tea (700 ml/day) or water for 14 days. Catechin concentrations in green tea and plasma were determined. Green tea markedly decreased the maximum plasma concentration (C(max)) and area under the plasma concentration-time curve (AUC(0-48)) of nadolol by 85.3% and 85.0%, respectively (P < 0.01), without altering renal clearance of nadolol. The effects of nadolol on systolic blood pressure were significantly reduced by green tea. [(3)H]-Nadolol uptake assays in human embryonic kidney 293 cells stably expressing the organic anion-transporting polypeptides OATP1A2 and OATP2B1 revealed that nadolol is a substrate of OATP1A2 (Michaelis constant (K(m)) = 84.3 µmol/l) but not of OATP2B1. Moreover, green tea significantly inhibited OATP1A2-mediated nadolol uptake (half-maximal inhibitory concentration, IC(50) = 1.36%). These results suggest that green tea reduces plasma concentrations of nadolol possibly in part by inhibition of OATP1A2-mediated uptake of nadolol in the intestine.

Effects of smoking regular or light cigarettes on brachial artery flow-mediated dilation.

BACKGROUND AND PURPOSE: To compare the effects of regular cigarettes (RCs) and light cigarettes (LCs) on brachial artery flow-mediated dilation (FMD) and sublingual glyceryl trinitrate-induced dilation (GTN), markers of endothelial dependant and independent function, respectively. METHODS: 206 subjects (age 51.5 ± 12.8 yr, 122 men) had their smoking habits recorded and FMD and GTN measured by B-mode ultrasound. Cigarettes were categorized as RCs or LCs according to their content of tar, nicotine and CO. The chronic effect was assessed in current smokers of RCs (n = 85) or LCs (n = 53) and in never smokers (NS; n = 68). The acute effect was assessed in current smokers by measuring FMD before and 10-min after smoking a single regular (n = 29) or light (n = 51) cigarette. RESULTS: FMD was significantly lower in consumers of RCs (6.26%, 95% C.I. 5.58, 6.94) or LCs (5.59%, 95% C.I. 4.74, 6.45) compared to NS (8.68%, 95% C.I. 7.92, 9.44) (both P < 0.0001), but did not differ (P > 0.05) when compared to each other. GTN was similar in the three groups. Analyses adjusted for clinical confounders and for markers involved in oxidative stress, arginine/nitric oxide pathway, and inflammation provided identical results. Smoking a single cigarette, either regular or light, reduced FMD (-0.88% and -1.17%, respectively, both P < 0.05), without significant difference between cigarette type. RCs and LCs produced analogous chronic and acute effects when FMD was calculated with respect to the last 60 s of the low-flow phase (FMD60s). CONCLUSIONS: LCs impair endothelial-dependant vasodilation as much as RCs. Thus, smoking LCs cannot be considered an alternative to the only safe choice of a complete and permanent smoking cessation.

The metabolic syndrome predicts carotid intima-media thickness no better than the sum of individual risk factors in a lipid clinic population.

OBJECTIVE: To assess whether the diagnosis 'metabolic syndrome' (MS) predicts the degree of subclinical atherosclerosis better than its component parts or the total number of vascular risk factors (VRFs) in patients attending a lipid clinic. METHODS: Carotid intima-media thickness (C-IMT) was measured by B-mode ultrasound in 1804 patients (56+/-13 years; 52% women). To investigate whether the increased subclinical carotid atherosclerosis often ascribed to MS may be explained by a real interaction between the components or simply by a sum of VRFs, observed C-IMTs were compared with those predicted by the sum of individual components. Values for C-IMT of MS patients were also compared with those of controls matched for number of VRFs or for SCORE predicted risk (SPR). RESULTS: Carotid IMT values were significantly higher in patients with MS (n=362) than in those not so diagnosed (IMT(mean), 1.07+/-0.37 vs. 0.95+/-0.33; IMT(max), 1.98+/-0.93mm vs. 1.67+/-0.82mm, both p<0.0001), but were not higher than those predicted by the sum of individual risk factors. The linear regression lines of the correlations between C-IMT and total number of VRFs overlapped in patients with and without MS. In patients with and without MS matched for age, sex and total number of VRFs, or matched for age, sex and SPR the C-IMT differences disappeared. CONCLUSIONS: In patients attending a lipid clinic, 'metabolic syndrome' appears not to correlate with C-IMT to a greater extent than what is expected from its component parts or from the patient's total number of VRFs.

Dose-related increase of HDL-cholesterol levels after N-acetylcysteine in man.

Changes in plasma lipid-lipoprotein levels were evaluated in 10 hyperlipidemic patients during treatment with progressive doses (from 1200 mg day-1 to 3600 mg day-1) of N-acetylcysteine (NAC). Plasma total cholesterol and triglyceride levels, as well as those of lipoprotein (a) did not change to an appreciable extent, even with the highest dosage. However, the HDL-cholesterol levels showed a significant, dose-related rise, the mean absolute increase, with the highest NAC dose, being of approximately 10 mg dl-1 (16.2%). The rise of HDL-cholesterol was independent of changes in other lipid-lipoprotein parameters, suggesting a possible direct effect of NAC on the HDL system.

Common carotid intima-media thickness measurement. A method to improve accuracy and precision.

BACKGROUND AND PURPOSE: High-resolution ultrasonographic imaging is a noninvasive method that allows estimation of the thickness of the intima-media complex in human carotid arteries. The determination of intima-media thickness involves several steps, each of which may introduce an error that influences the reproducibility of the method. In the present study, apart from the general reproducibility of the determination of intima-media thickness, the error introduced by each step was evaluated. METHODS: B-mode scans were performed on 14 randomly selected patients. The common carotid arteries were examined in anterior, lateral, and posterior planes, with a standard methodology and by a new method, making use of external reference points. RESULTS: The error in general reproducibility in determination of the subject's mean intima-media thickness was 5.9%. This parameter was also evaluated in a paired manner after dividing the whole artery into sectors; with this protocol, the percent error in general reproducibility was 15%. The main source of variability in the evaluation of common carotid intima-media thickness was found to lie in the operator's subjectivity in the choice of the carotid sector to be processed (percent error, 10.27%). A method was therefore designed that used external reference points, resulting in reduction of this error by 38.2%. CONCLUSIONS: While the mean intima-media thickness might be considered a reproducible parameter to evaluate differences between populations exposed to diverse risk factors, evolutional or therapy-induced changes in the individual may be better monitored on defined carotid sectors. This may be achieved with a high reproducibility by use of the proposed method based on external reference points.

Tolerability of fibric acids. Comparative data and biochemical bases.

Fibric acids are an established class of drugs for the treatment of hyperlipoproteinaemias. Although they have been in use for 30 years or longer, some doubts remain as to their relative tolerability, both as a class and as single agents. Some side effects, e.g. lithogenicity, may be related to their mode of action, while others, e.g. the acute muscular syndrome, may be linked to the spatial conformation of the molecule. These disadvantages should, however, be weighed against the additional, potentially therapeutic properties shown by these compounds. In particular, effects on maturity onset diabetes and hyperuricaemia, as well as a very interesting fibrinolytic potential, have been described for some of them. A painstaking comparative analysis of the major literature data pertaining to the clinical toxicological profile of these agents allow to conclude that, while belonging to a chemical class, fibric acids show dramatic differences from one another, in terms of side effects and of additional pharmacodynamic activities. Moreover, in the case of lithogenicity for example, considerable differences exist between normo- and hyperlipidaemic subjects. Overall, newer molecules of more sophisticated design have a significantly improved tolerability profile vs the old clofibrate.

Determination of bezafibrate, ciprofibrate and fenofibric acid in human plasma by high-performance liquid chromatography.

A selective high-performance liquid chromatographic method to assess either bezafibrate, ciprofibrate or fenofibric acid plasma levels is described. Drugs are extracted with diethyl ether, after acidification with HCL. An isocratic acetonitrile 0.02 M H3PO4 (55:45) mobile phase, a C18 microns) column and UV detection are used. The LOQ found was 0.25 microgram/ml for the three fibrates. Intra- and inter-assay accuracy ranges were 90-107% and 82-111%: 96-115% and 94-107%: 94-114% and 94-126% for bezafibrate, ciprofibrate and fenofibric acid, respectively. Intra- and inter-assay precision (C.V.% ranges) were 1.72-3.06% and 2.66-7.67%: 1.88-4.64% and 0.62-2.99%: 1.26-4.69% and 3.56-7.17% for the three fibrates studied. Its sensitivity, accuracy and precision make it a useful tool for monitoring plasma levels of these drugs in a clinical setting and for research purposes.