Development of a model based on body composition to predict drug kinetics-1 evaluation in healthy volunteers.

A kinetic model for widely used drugs, based on body composition analysis, was developed and evaluated in young and elderly healthy individuals. Body composition was studied by body impedance analysis (BIA). Antipyrine, amlodipine, digoxin and tobramycin kinetics, liver microsomal activity enzyme (lidocaine/MEGX test), and appropriate clinical and laboratory tests were carried out. Major variables (V(d), AUC, t(1/2), C(max), Cl) for these drugs were calculated, and the possible relationships with the other clinical and biochemical data were analyzed by the Pearson's moment correlation, forecasting models being then obtained by a multiple linear regression method. Major kinetic parameters, particularly for the mixed elimination drugs (liver/renal), i.e. digoxin and amlodipine, proved to be well correlated to data collected during the study, in particular with body structure parameters. Results were less satisfactory in the case of the mainly renally handled tobramycin. Mathematical models to forecast the kinetic behaviors of the three chosen drugs, using readily accessible data, showed both in the young and the elder, as well as in the whole examined population, very satisfactory correlations in the case of digoxin (R(2) ranging from 0.89 to 0.85) and amlodipine (R(2) between 0.81 and 0.91), less satisfactory (with a wide range of R(2), from 0.65 to 0.94), in the case of tobramycin.

Development of a model based on body composition to predict drug kinetics; II. Application of the model to the use of digoxin in elderlies.

The applicability of a kinetic model for the prediction of steady-state blood levels, based on body composition as assessed by bioelectric impedance analysis (BIA), was applied to a population of elderly patients, candidates for digoxin therapy. Elderlies, all >70 years of age, underwent standard laboratory and clinical evaluation but no further characterization of liver or renal function. These 72 patients were given 0.125 mg digoxin for 5 days, in order to reach steady-state levels. Treatment was then interrupted and samples were collected 2 and 48 h after the last administration. Plasma digoxin levels were determined both by the immunochemical method with TDX and according to the BIA method described in the accompanying paper. Plasma levels calculated and measured in 2 h samples did not differ statistically, but levels were about 15% higher in the directly measured samples. There was a similar underestimation, i.e. about 15%, for the 48 h calculated levels. However, only approximately 5% of the levels were outside of the 95% confidence intervals as determined from the directly measured levels. These findings indicate that digoxin levels, calculated based on a BIA evaluation, may be sufficiently reliable, in the majority of patients, to allow direct determination of the more appropriate doses of digoxin.

Effects of yoghurt enriched with plant sterols on serum lipids in patients with moderate hypercholesterolaemia.

The objective of the present study was to assess the effect of consumption of a yoghurt-based drink enriched with 1-2 g plant sterols/d on serum lipids, transaminases, vitamins and hormone status in patients with primary moderate hypercholesterolaemia. Thirty patients were randomly assigned to one of two treatment groups: a low-fat low-lactose yoghurt-based drink enriched with 1 g plant sterol extracted from soyabean/d v. a low-fat low-lactose yoghurt, for a period of 4 weeks. After a 2-week wash-out period, patients were crossed over for an additional 4-week period. Second, after a 4-week wash-out period, eleven patients were treated with 2 g plant sterols/d in a second open part of the study for a period of 8 weeks. The yoghurt enriched with plant sterols significantly reduced, in a dose-dependent manner, serum total cholesterol and LDL-cholesterol levels and LDL-cholesterol:HDL-cholesterol (P<0.001), whereas no changes were observed in HDL-cholesterol and triacylglycerol levels, either in the first or the second part of the study. There were only slight, not statistically significant, differences in serum transaminase, vitamin and hormone levels. To conclude, a low-fat yoghurt-based drink moderately enriched with plant sterols may lower total cholesterol and LDL-cholesterol effectively in patients with primary moderate hypercholesterolaemia.

Statins enhance arachidonic acid synthesis in hypercholesterolemic patients.

BACKGROUND AND AIM: It has been shown that statins enhance arachidonic acid biosynthesis from linoleic acid in vitro, and there is also evidence that statin-treated patients have high plasma and cellular arachidonic acid levels. The aim of this study was to investigate the possible effects of statins on the desaturating steps of arachidonic acid biosynthesis in patients. METHODS AND RESULTS: Plasma polyunsaturated fatty acids (percentages and concentrations), total cholesterol, LDL-cholesterol and triglycerides were measured in three groups of hypercholesterolemic patients before and after treatment with statins or fibrates for about three years, or before and after four months on a low-fat diet. As expected, there was a significant reduction in plasma total cholesterol (-23%) and LDL-cholesterol (-27%) levels in the statin group, and a significant reduction in triglycerides (-29%) and some decrease in total cholesterol (-12%) in the fibrate group; no change was observed in the control group. The selective increase in plasma arachidonic acid levels (in terms of absolute concentration and as a percentage of total fatty acids) was of the same order as the reduction in cholesterol, and the selective increase in the product/precursor ratios for delta 5 desaturation in the statin group indicated that this key step in arachidonic acid synthesis is affected. CONCLUSIONS: Our data show that an increase in arachidonic acid synthesis due to enhanced delta 5 desaturation is a major effect of statin treatment, and has the same order of magnitude as the reduction in plasma cholesterol levels.

Efficacy and tolerability of fluvastatin extended-release delivery system: a pooled analysis.

BACKGROUND: At high doses, the pharmacokinetics of fluvastatin immediate-release (IR) are nonlinear, possibly due to saturation of hepatic uptake. Fluvastatin delivery to the liver in a slower but sustained fashion would be expected to avoid hepatic saturation without elevating systemic drug levels. OBJECTIVE: This pooled analysis compared the efficacy and tolerability of extended-release (XL) 80-mg and IR 40-mg formulations of fluvastatin in lowering low-density lipoprotein cholesterol (LDL-C) and triglyceride (TG) levels and raising high-density lipoprotein cholesterol (HDL-C) levels in patients with hypercholesterolemia. METHODS: Data were pooled from 3 double-blind, randomized, active-controlled, multicenter, parallel-group studies that compared changes in lipid and apolipoprotein levels with fluvastatin XL 80 mg at bedtime (HS) with changes in fluvastatin IR 40 mg HS or BID in patients aged > or =18 years with primary hypercholesterolemia (consistently elevated LDL-C level [> or =160 mg/dL] and plasma TG levels < or =400 mg/dL). The primary efficacy variable was percent change in LDL-C from baseline. RESULTS: The pooled analysis provided an intent-to-treat efficacy study population of 1674 patients. At 4 weeks, fluvastatin XL 80 mg HS reduced LDL-C levels by a mean of 36.3% (median 38%), significantly greater than a mean reduction of 25.9% (median 27%) seen with fluvastatin IR 40 mg HS, and an incremental additional mean reduction in LDL-C of 10.4% (P < 0.001). At 4 and 24 weeks, fluvastatin XL 80 mg HS provided an LDL-C reduction equivalent to fluvastatin IR 40 mg BID (P < 0.001 for noninferiority). Significant, dose-related changes in HDL-C, LDL-C:HDL-C ratio, total cholesterol, TG, and apolipoprotein A-I and apolipoprotein B levels also occurred. Mean HDL-C level increased by 8.7% and median TG level decreased by 19% with fluvastatin XL 80 mg HS (P < 0.001 and P < 0.05 vs fluvastatin IR 40 mg HS, respectively). Maximum mean increases in HDL-C level (21%) and median decreases in TG level (31%) with fluvastatin XL 80 mg HS occurred in patients with type IIb dyslipidemia and the highest baseline TG. Adverse events were mild, with similar frequency in all treatment groups. CONCLUSIONS: Once-daily administration of fluvastatin XL 80 mg provides enhanced efficacy with an additional 10.4% reduction in LDL-C levels compared with fluvastatin IR 40 mg HS, and superior increases in HDL-C levels, particularly in patients with elevated TG levels (P < 0.05 vs fluvastatin IR 40 mg HS). Fluvastatin XL 80 mg HS has a good tolerability profile and is effective as starting and maintenance lipid-lowering treatment in patients with type II hypercholesterolemia.

Very low intakes of N-3 fatty acids incorporated into bovine milk reduce plasma triacylglycerol and increase HDL-cholesterol concentrations in healthy subjects.

Eight normolipidaemic volunteers, habitual partial skim milk drinkers and non-eaters of fish during the study, were given 500 ml day(-1) of partial skim milk for 1 month; they were then switched to 500 ml day(-1) of a novel commercially available milk preparation, supplying 400 mg of N-3 fatty acids-of which 300 mg were EPA+DHA-and 15 mg vitamin E, for 6 weeks. No changes in plasma lipid parameters were observed after the first run-in month; at 3 and 6 weeks on the N-3-rich milk, marked increments of plasma EPA (44 and 31%, respectively) and DHA (13 and 31%, respectively) were observed. Triacylglycerol (TG) concentrations decreased by 19% and high-density lipoprotein (HDL) concentrations increased by 19% at 6 weeks; plasma vitamin E rose by 21% while the susceptibility of plasma to oxidation was unaffected. Correlations were found between plasma EPA or DHA and TG, cholesterol, and HDL. In conclusion, the intake of a milk preparation providing low amounts of EPA+DHA to healthy individuals led to marked increases of N-3 fatty acids and vitamin E in plasma and in associated favourable changes in HDL and TG.

Omacor in familial combined hyperlipidemia: effects on lipids and low density lipoprotein subclasses.

Elevations of plasma cholesterol and/or triglycerides, and the prevalence of small, dense LDL particles remarkably increase coronary risk in patients with familial combined hyperlipidemia (FCHL). A total of 14 FCHL patients were studied, to investigate the ability of Omacor, a drug containing the n-3 fatty acids eicosapentaenoic and docosahexaenoic acid (EPA and DHA), to favorably correct plasma lipid/lipoprotein levels and LDL particle distribution. The patients received four capsules daily of Omacor (providing 3.4 g EPA+DHA per day) or placebo for 8 weeks in a randomized, double-blind, cross-over study. Omacor significantly lowered plasma triglycerides and VLDL-cholesterol levels, by 27 and 18%, respectively. Total cholesterol did not change but LDL-cholesterol and apolipoprotein B (apoB) concentrations increased by 21 and 6%. As expected, LDL particles were small (diameter=24.9+/-0.3 nm) and apoB-rich (LDL-cholesterol/apoB ratio=1.27+/-0.26) in the selected subjects. After Omacor treatment LDL became enriched in cholesterol (LDL-cholesterol/apoB ratio=1.40+/-0.17), mainly cholesteryl esters, indicating accumulation in plasma of more buoyant and core enriched LDL particles. Indeed, the separation of LDL subclasses by rate zonal ultracentrifugation showed an increase of the plasma concentration of IDL and of the more buoyant, fast floating LDL-1 and LDL-2 subclasses after Omacor, with a parallel decrease in the concentration of the denser, slow floating LDL-3 subclass. However, the average LDL size did not change after Omacor (25.0+/-0.3 nm). The resistance of the small LDL pattern to drug-induced modifications implies that a maximal lipid-lowering effect must be achieved to reduce coronary risk in FCHL patients.

Effects of gemfibrozil on insulin sensitivity and on haemostatic variables in hypertriglyceridemic patients.

In order to assess the efficacy of gemfibrozil on lipid and haemostatic parameters in patients with plurimetabolic syndrome, a multicenter double-blind placebo controlled, parallel study was carried out in 56 patients with primary hypertriglyceridemia and glucose intolerance. These patients had elevated PAI activity and antigen and t-PA antigen levels at rest and after venous occlusion. Gemfibrozil reduced plasma triglyceride levels (P<0.001), whereas it increased free fatty acids (P<0.05) and high density lipoprotein cholesterol levels (P<0.05). In those patients reaching normalization of plasma triglyceride levels (triglyceride reduction > or =50%) (n=15), insulin levels (P<0.05) as well as the insulin resistance index were reduced by gemfibrozil treatment, suggesting an improvement of the insulin resistance index in this patient subgroup. Gemfibrozil treatment did not affect plasma fibrinolysis or fibrinogen levels, despite marked reduction of plasma triglycerides and improvement of the insulin sensitivity associated with triglyceride normalization.

L-carnitine reduces plasma lipoprotein(a) levels in patients with hyper Lp(a).

BACKGROUND AND AIMS: Elevated Lp(a) levels are a significant cardiovascular risk factor, particularly for young individuals and for subjects with concomitant high LDL cholesterol. Increased Lp(a) is believed to be linked to an enhanced production of the lipoprotein, controlled by genetic factors; it can be reduced by agents such as nicotinic acid, lowering free fatty acid inflow to the liver. METHODS AND RESULTS: L-carnitine, a natural compound stimulating fatty acid oxidation at the mitochondrial level, was tested in a double blind study in 36 subjects with Lp(a) levels ranging between 40-80 mg/dL, in most with concomitant LDL cholesterol and triglyceride elevations. L-carnitine (2 g/day) significantly reduced Lp(a) levels (-7.7% vs baseline and -11.7% vs placebo treatment), the reduction being more dramatic in the subjects with the more marked elevations. In particular, in the L-carnitine group, 14 out of 18 subjects (77.8%) had a significant reduction of Lp(a) vs only 7 out of 18 (38.9%) in the placebo group (chi 2 = 4.11, p = 0.0452). In a significant number of subjects the reduction of Lp(a) resulted in a return of this major cardiovascular risk parameter to the normal range. CONCLUSIONS: L-carnitine offers a potentially useful therapeutic agent for atherogenic conditions characterized by high Lp(a) levels, also in view of the excellent tolerability and essential lack of major side effects.

Effect of plasma cholesterol reduction by pravastatin on the functional properties of forearm arteries in hypercholesterolemic patients.

BACKGROUND AND AIM: Since functional properties in the vasculature of hypercholesterolemic subjects are impaired, a six-month pravastatin treatment (20 mg/die) was tested in an open design, on the impaired unstimulated forearm arterial compliance (Un-FAC(AUC)) of 14 asymptomatic type IIa familial hypercholesterolemic patients. In order to evaluate whether FAC(AUC) changes might be related to the extent of cholesterol reduction achieved, this evaluation was carried out in five severely hypercholesterolemic patients, undergoing LDL-apheresis. METHODS AND RESULTS: Arterial functional properties, i.e. FAC(AUC) responses to glyceryl trinitrate (GTN-FAC(AUC)) and acetylcholine (ACh-FAC(AUC), four patients) and the effects on rest and peak forearm blood flow and vascular resistance were evaluated on the non-dominant arm using plethysmographic methods, that also allow the direct assessment of the non-linear "compliance-blood pressure" curve. Selective LDL-apheresis was performed by using a dextran-sulphate column. Pravastatin effectively lowered plasma total (-16%, p = 0.002) and LDL cholesterol levels (-22%, p = 0.006 vs baseline). Rest and peak flow, basal and post ischemic vascular resistance were not affected as well as Un-FAC(AUC) and GTN-FAC(AUC). However, in the four hypercholesterolemic patients undergoing ACh infusion, there was an improvement in the ACh-FAC(AUC) of borderline statistical significativity (p = 0.056). LDL-apheresis reduced plasma total and LDL cholesterol levels by 55% and 59%, without affecting blood pressure. In this series of five patients Un-FAC(AUC) increased, the Un-FAC(AUC) rise being inversely related to the absolute reduction of plasma total (r = 0.92, p < 0.05) and LDL cholesterol (r = 0.89, p < 0.05) levels. CONCLUSIONS: In hypercholesterolemic patients a short-term hypocholesterolemic treatment with pravastatin, although able to improve the lipid profile, cannot alter significantly blood flow, vascular resistance, Un-FAC(AUC) and GTN-FAC(AUC). A possible selective improvement in the ACh-receptor-activated signal transduction pathway has been observed and the importance of a drastic reduction of cholesterol concentrations in order to affect the Un-FAC(AUC) is suggested.

Double-blind study of the addition of high-protein soya milk v. cows' milk to the diet of patients with severe hypercholesterolaemia and resistance to or intolerance of statins.

Total substitution of soyabean protein for animal protein in the diet has been repeatedly shown to lower plasma cholesterol levels in hypercholesterolaemic individuals. A new, highly palatable, high-protein soya drink may allow replacement of a significant percentage of animal protein in the diet. The soya drink was given, within a crossover design v. a cows' milk preparation of similar composition and taste, to twenty-one severely hypercholesterolaemic patients (mean baseline plasma cholesterol 8.74 mmol/l) with a history of resistance to or intolerance of statin treatment. Each dietary supplement was given for 4 weeks, with a 4-week interval between treatments, Plasma lipid levels were monitored every 2 weeks during each dietary sequence. The concomitant dietary treatment, which had been followed for a long time by all patients, was carefully monitored throughout the study. The soya supplementation reduced plasma total cholesterol level by 6.5%, when given first, and by 7.4% when given after cows' milk. When given first, cows' milk resulted in a small, non-significant reduction of plasma cholesterol level (-3.9%), and when given after soya, it changed total plasma cholesterol to a minimal extent (-1.6%). Changes in total and LDL-cholesterol levels after 2 and 4 weeks of soya v. cows' milk treatment were, thus, respectively -6.1, -7.0 and -6.2, -7.8% (both P < 0.05). These first data from a double-blind study confirm a significant cholesterol-lowering effect of soyabean protein, even when only partly replacing animal protein in the diet, in individuals with extreme plasma cholesterol elevations.

One-year treatment with ethyl esters of n-3 fatty acids in patients with hypertriglyceridemia and glucose intolerance: reduced triglyceridemia, total cholesterol and increased HDL-C without glycemic alterations.

n-3 Fatty acids in the form of ethyl esters (EE) allow lower daily doses and improved compliance. Administration of n-3 fatty acids to patients with glucose intolerance has led to controversial findings, some studies indicating worsening of the disorder, others no effect, or an improvement. A total of 935 patients with hypertriglyceridemia, associated with additional cardiovascular risk factors, i.e. glucose intolerance, NIDDM and/or arterial hypertension were entered a double blind (DB) protocol lasting 6 months with n-3 EE versus placebo, followed by a further 6 months of open study (n = 868) on 2 g a day of n-3 EE. At the end of the DB period, triglyceridemia in the total group was reduced significantly more by n-3 EE, without alterations in glycemic parameters. In the 6 months open follow up, patients on n-3 EE with type IIB hyperlipoproteinemia showed a significant reduction of total cholesterol, both in cases with (-4.15% vs. the 6 month levels) and without NIDDM (-3.8%). HDL-cholesterol had an overall mean rise of 7.4%, maximal in type IV patients with (+9.1%) and without (+10.1%) NIDDM. No alterations in glycemic parameters were detected in treated patients. Administration of n-3 EE to patients with hypertriglyceridemia associated with NIDDM or impaired glucose tolerance appears safe and effective.

Direct effects of statins on the vascular wall.

The beneficial effects of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) on coronary events have generally been attributed to their hypocholesterolemic properties. Mevalonate and other intermediates of cholesterol synthesis (isoprenoids) are necessary for cell proliferation and other important cell functions; thus effects other than cholesterol reduction may help to explain the antiatherosclerotic properties of statins. Recently we provided in vitro and in vivo evidence of decreased smooth-muscle cell (SMC) proliferation and migration by fluvastatin and simvastatin, but not by pravastatin, independent of plasma cholesterol reduction. The ability of fluvastatin to interfere with arterial SMC proliferation at therapeutic concentrations (0.1-1 microM) prompted us to investigate the pharmacologic activity of sera from 10 patients treated with fluvastatin, 40 mg once daily, on the proliferation of cultured human arterial myocytes. Pravastatin, 40 mg once daily, displays a lipid-lowering activity similar to that of fluvastatin without affecting SMC proliferation and was investigated as a control for assessing this non-lipid-related effect of fluvastatin. Fluvastatin and pravastatin, given for 6 days to patients with type IIa hypercholesterolemia, resulted in a similar decrease in low-density-lipoprotein (LDL) cholesterol. However, the addition of 15% whole-blood sera from patients treated with fluvastatin to the culture medium resulted in a 43% inhibition of cholesterol synthesis in SMCs (p < 0.01) that mirrored the pharmacokinetic profile of fluvastatin. When SMC proliferation was investigated, a significant inhibition of cell growth (-30%; p < 0.01) was detected with sera obtained 6 h after the last dose. No effect on SMC proliferation or cholesterol biosynthesis was observed when sera from patients treated with pravastatin were evaluated. These results suggest that statins exert a direct antiproliferative effect on the arterial wall, beyond their effects on plasma lipids, which could prevent significant cardiovascular disease.

Platelet alpha 2-adrenergic receptors in hypercholesterolemia: relationship between binding studies and epinephrine-induced platelet aggregation.

BACKGROUND: Platelets isolated from patients with hypercholesterolemia are more sensitive in vitro to various aggregating agents, including epinephrine, than those isolated from normocholesterolemic subjects. Increased platelet reactivity is one mechanism that may explain the enhanced risk of thromboembolism in hypercholesterolemia. This study assessed whether platelet hyperreactivity to epinephrine in hypercholesterolemia is associated with higher alpha 2-adrenergic receptor density or affinity for epinephrine. METHODS: Platelet aggregation and binding studies, with use of [3H]yohimbine as ligand, were performed on platelets isolated from 30 patients with type IIa hypercholesterolemia and 23 control subjects. RESULTS: Platelet aggregation in response to epinephrine was significantly higher in patients with hypercholesterolemia than in control subjects. A statistically significantly higher alpha 2-adrenergic receptor density was observed in a subgroup of 13 patients with hypercholesterolemia than in 13 sex- and age-matched control subjects (280 +/- 61 and 230 +/- 49 fmol/mg protein respectively; p < 0.03), but no difference was observed in receptor affinity for the ligand. In these subgroups plasma total and levels of low-density lipoprotein (LDL) cholesterol were inversely correlated with platelet aggregation but directly correlated with platelet receptor density. CONCLUSION: Platelet alpha 2-adrenergic receptor density is increased in hypercholesterolemia and directly correlates with plasma total and levels of LDL cholesterol, providing at least a partial explanation for the enhanced platelet response to epinephrine that is observed in hypercholesterolemia.

Cholesterol synthesis inhibitors do not reduce Lp(a) levels in normocholesterolemic patients.

Experimental and clinical data suggest that activation of the LDL receptors by the use of HMG CoA reductase inhibitors, in the presence of normal plasma cholesterol levels, may result in a reduction of Lp(a) concentrations. This hypothesis has been tested in an open study on seven subjects with normal cholesterolemia but marked elevations of Lp(a) levels, three of whom received pravastatin and four simvastatin at standard therapeutic doses. While the two drugs caused the expected reduction of plasma total and LDL cholesterol levels, no significant changes in Lp(a) were noted. This study contradicts a prior clinical finding and suggests that HMG CoA reductase inhibitors are unlikely to reduce plasma Lp(a) levels even in the absence of hypercholesterolemia.

Iron-ovotransferrin preparation does not interfere with ciprofloxacin absorption.

Iron supplements can interfere with the bioavailability of a number of drugs, including thyroxine, tetracycline derivatives, penicillamine, methyldopa, levodopa, carbidopa, ciprofloxacin, and the newer fluoroquinolones. A new iron formulation was tested in which iron ions are bound to ovotransferrin, a protein that shares more than an 80% similarity with the sequence of human transferrin and apparently is less likely than the commonly used iron salts to reduce drug absorption. Ciprofloxacin was taken as a model drug, of wide use and restricted range of therapeutic levels, and its absorption was evaluated after the administration of the iron-ovotransferrin complex versus an iron-gluconate formulation in healthy volunteers. At variance with the iron gluconate formulation, which led to a reduction of about 50% of peak serum ciprofloxacin levels (Cmax; 1.0 +/- 0.2 versus 2.4 +/- 0.3 micrograms/ml; p < 0.01) and of the area under the serum concentration-time curve from time 0 to infinity [AUC(0 - infinity); 10.1 +/- 1.1 versus 18.3 +/- 1.0 mg.L-1.hr; p < 0.01], the iron-ovotransferrin complex caused only modest, non significant changes in absorption with a minimal reduction of the AUC[0 - infinity) (17.3 +/- 1.0 versus 18.3 +/- 1.0 mg.L-1.hr; difference not significant) and a nonsignificant decrease in the Cmax (2.2 +/- 0.3 versus 2.4 +/- 0.3 microgram/ml; difference not significant). Iron was also well absorbed from the formulation in the presence of a fatty meal. The very common drug interactions with oral iron preparations can be effectively prevented by the use of the iron-ovotransferrin complex interacting to a minimal extent with a sensitive drug with a reduced margin of efficacy, such as ciprofloxacin.

Measurement of ionized magnesium with AVL 988/4 electrolyte analyzer: preliminary analytical and clinical results.

Only free magnesium has biological activity: technology for measuring the ionized fraction of magnesium is now available via ion-selective electrodes. We have evaluated an instrument (AVL 988/4) which determines ionized magnesium (cMg2+) with an ion-selective electrode based on the ionophore ETH 7025. The selectivity of the electrode is adequate for the ions normally present in plasma, except for calcium: the interference is automatically corrected by simultaneous measurements of calcium with compensation for the calcium interference to the magnesium signal. We have first verified possible interference caused by sampling procedures: known silicon interference has been avoided by use of glass tubes (BD Vacutainer with no additive, code 7626); heparin interference has been measured and found significant above 20 UI.mL-1 of plasma. Instrument evaluation according to NCCLS protocol gives the following imprecision results on 20 replicated analyses: cMg2+ (mmol.L-1) 1.29, 0.76, 0.23, CVs% (within-run) 0.67, 0.67, 3.00 and CVs% (between-run) 4.06, 3.91, 5.89 respectively. Linearity (in the range 0.23-1.60 mmol.L-1) was: measured cMg2+ = 0.981.(calculated cMg2+) + 0.009 mmol/L; r = 0.999. In healthy adults (n = 103) cMg2+ was in the range 0.46-0.74 mmol.L-1 (with a mean of 0.60 mmol/L and normal distribution). These values represent 57% to 84% of serum total magnesium concentration (TMg) (mean 71%). pH dependence of cMg2+ is present, usually to a lower extent with respect to cCa2+, but it seems different in patients with real or in vitro provoked acidosis and in hemodialyzed patients. Citrate interference on ionized magnesium measurements was found both in vitro and in vivo, whilst that due to lactate was demonstrated only in vitro. On a wide range of cMg2+ (n = 100), a good correlation is obtained both with TMg and ultrafiltrable Mg (UFMg): cMg2+ = 0.723.TMg + 0.008 mmol.L-1, r = 0.978; cMg2+ = 0.912.UFMg + 0.10 mmol.L-1, r = 0.968, respectively. The ionized magnesium in ultrafiltrate was found 25% lower than that in serum. The lifespan of the electrode, evaluated on the basis of both time from installation and on number of measured samples, was estimated longer than 4 months and able to analyze more than 1500 samples, whichever comes first. The four electrodes we used during 18 months behaved all the same way. The correlation between measurements performed in whole blood (WB-cMg2+) and in the corresponding serum (S-cMg2+) was excellent: WB-cMg2+ = 0.954.S-cMg2+ +0.02 mmol.L-1; r = 0.998; n = 60.

Triglycerides are major determinants of cholesterol esterification/transfer and HDL remodeling in human plasma.

Lecithin:cholesterol acyltransferase (LCAT) and cholesteryl ester transfer protein (CETP) are responsible for the esterification of cell-derived cholesterol and for the transfer of newly synthesized cholesteryl esters (CE) from HDL to apoB-containing lipoproteins in human plasma. LCAT and CETP are also crucial factors in HDL remodeling, a process by which HDL particles with a high capacity for cell cholesterol uptake are generated in plasma. In the present study, cholesterol esterification and transfer were evaluated in 60 patients with isolated hypercholesterolemia (HC, n = 20) and isolated (HTG, n = 20) or mixed hypertriglyceridemia (MHTG, n = 20) and in 20 normolipidemic healthy individuals (NL). Cholesterol esterification rate (CER) and net CE transfer rate (CETR) were measured in whole plasma. LCAT and CETP concentrations were determined by specific immunoassays. HDL remodeling was analyzed by monitoring changes in HDL particle size distribution during incubation of whole plasma at 37 degrees C. Mean CER and CETR were 48% and 73% higher, respectively, in hypertriglyceridemic (HTG + MHTG) versus normotriglyceridemic individuals. HDL remodeling was also significantly accelerated in plasma from hypertriglyceridemic patients. Strong positive correlations were found in the total sample between plasma and VLDL triglyceride levels and CER (r = .722 and r = .642, respectively), CETR (r = .510 and r = .491, respectively), and HDL remodeling (r = .625 and r = .620, respectively). No differences in plasma LCAT and CETP concentrations were found among the various groups except for a tendency toward higher CETP levels in hypercholesterolemic patients (+51% in MHTG and +20% in HC) versus control subjects (NL). By stepwise regression analysis, VLDL triglyceride level was the sole significant predictor of CER and CETR and contributed significantly together with baseline HDL particle distribution to HDL remodeling. These results indicate that plasma triglyceride level is a major factor in the regulation of cholesterol esterification/transfer and HDL remodeling in human plasma, whereas LCAT/CETP concentrations play a minor role in the modulation of reverse cholesterol transport.