Carnitine improves lipid anomalies in haemodialysis patients

Mitigating the pro-oxidant state and melanogenesis of Retinitis pigmentosa: by counteracting mitochondrial dysfunction

Retinitis pigmentosa (RP) is a group of mitochondrial diseases characterized by progressive degeneration of rods and cones leading to retinal loss of light sensitivity and, consequently, to blindness. To date, no cure is available according to the clinical literature. As a disease associated with pigmentation-related, pro-oxidant state, and mitochondrial dysfunction, RP may be viewed at the crossroads of different pathogenetic pathways involved in adverse health outcomes, where mitochondria play a preeminent role. RP has been investigated in a number of experimental and clinical studies aimed at delaying retinal hyperpigmentation by means of a number of natural and synthetic antioxidants, as well as mitochondrial cofactors, also termed mitochondrial nutrients (MNs), such as alpha-lipoic acid, coenzyme Q10 and carnitine. One should consider that each MN plays distinct-and indispensable-roles in mitochondrial function. Thus, a logical choice would imply the administration of MN combinations, instead of individual MNs, as performed in previous studies, and with limited, if any, positive outcomes. A rational study design aimed at comparing the protective effects of MNs, separately or in combinations, and in association with other antioxidants, might foresee the utilization of animal RP models. The results should verify a comparative optimization in preventing or effectively contrasting retinal oxidative stress in mouse RP models and, in prospect, in human RP cases.

Evaluation of Carnitine Levels According to the Peritoneal Equilibration Test in Patients on Continuous Ambulatory Peritoneal Dialysis

The evidence of carnitine abnormal metabolism in patients on continuous ambulatory peritoneal dialysis (CAPO) is unclear, and previous studies have reported conflicting results.

The total (TC), free (FC), and acylated (AC) carnitines were estimated in blood and dialysate, as well as the AC/FC ratio, in 29 patients on CAPO, grouped into high (H-Abs) and low (L-Abs) absorbers, according to the results of the peritoneal equilibration test (fast PE-test).

Ourdata demonstrated that patients with higher peritoneal transport rates, which was the H-Abs group, males and females, showed a better carnitine metabolic status compared to the L-Abs group. Although the H-Abs group lost significantly more free carnitine than the L-Abs group, the AC/FC ratio of the H-Abs group remained within normal range.

All the patients in our study showed abnormally high triglyceride (TAG) levels and an abnormally high total cholesterol/HOL cholesterol ratio. In particular, the patients In the L-Abs group showed significantly higher TAG levels and total cholesterol/HOL cholesterol ratios than the H-Abs group. Those patients who have been on CAPO for more than 2 years showed significantly abnormally higher AC/FC ratios than those with shorter periods on CAPO treatment. In patients with AC/FC ratio greater than 0.4, the supplementation of L-carnitine may have a beneficial effect on their carnitine and lipid metabolism.

Factors Affecting Plasma Free Fatty Acids Rise during Hemodialysis

We studied the mechanisms responsible for causing acute changes in plasma lipids during hemodialysis. Dialysis decreased plasma triglycerides to the same extent as when heparin was given without dialysis. Cholesterol increased in proportion to hemoconcentration. Plasma free fatty acids (FFA) levels were also increased, but more so than with heparin alone. Glucose and acetate did not play a role, nor did carnitine loss, and hemofiltration elicited similar effects. The rise in plasma FFA is therefore likely to be caused by other as yet unknown mechanism.

Correlation between Plasma Carnitine, Muscle Carnitine and Glycogen Levels in Maintenance Hemodialysis Patients

Chronic hemodialysis (HD) may lead to losses of carnitine from plasma and muscle. Plasma carnitine does not reflect the body content of carnitine. The purpose of this study was the evaluation of total and free plasma and muscle carnitine concentrations (TPC, FPC, TMC, FMC), muscle glycogen and the relationship between plasma and tissue carnitine content and the basic indices of lipid metabolism in HD patients. The studies were conducted in two groups: the first one consisted of 37 HD patients (19 F, 18 M), the second one served as the control and was composed of 29 (10 F, 19 M) patients with healthy kidneys. Tissue specimens in HD patients were taken during surgery on arterio-venous fistula from brachioradial muscle. Carnitine and glycogen measurements were performed using enzymatic methods according to Cederblad and Huijng respectively. Total cholesterol (CH), HDL-CH, and triglycerides were assayed by enzymatic commercial test system (Boehringer-Mannheim, Germany). To summarise, we found the following phenomena in our HD patients in comparison with the controls: 1) In plasma: similar TPC but decreased FPC levels and FPC/TPC ratio which may suggest free carnitine deficiency. 2) In muscle: significantly lower TMC and FMC levels but normal FMC/TMC ratio. 3) Negative correlation between TMC and FMC levels and duration of dialysis treatment. 4) No correlation between plasma and muscle carnitine concentration. 5) Significantly higher concentration of muscle glycogen which could be explained by the changes in the structure of muscle fibres in HD patients and/or lower physical activity. 6) A positive correlation between FPC/APC or FPC/TPC ratio and HDL-CH in HD patients which may suggest that an appropriate proportion between free and acylcarnitines may influence HDL-CH levels in that population. (Int J Artif Organs 2000; 23: 90–6)

Levocarnitine and Dialysis: A Review

Among the various metabolic abnormalities documented in dialysis patients are abnormalities related to the metabolism of fatty acids. Aberrant fatty-acid metabolism has been associated with the promotion of free-radical production, insulin resistance, and cellular apoptosis. These processes have been identified as important contributors to the morbidity experienced by dialysis patients. There is evidence that levocarnitine supplementation can modify the deleterious effects of defective fatty-acid metabolism. Patients receiving hemodialysis and, to a lesser degree, peritoneal dialysis have been shown to be carnitine deficient, as manifested by reduced levels of plasma free carnitine and an increase in the acyl:free carnitine ratio. Cardiac and skeletal muscles are particularly dependent on fatty-acid metabolism for the generation of energy. A number of clinical abnormalities have been correlated with a low plasma carnitine status in dialysis patients. Clinical trials have examined the efficacy of levocarnitine therapy in a number of conditions common in dialysis patients, including skeletal-muscle weakness and fatigue, cardiomyopathy, dialysis-related hypotension, hyperlipidemia, and anemia poorly responsive to recombinant human erythropoietin therapy (rHuEPO). This review examines the evidence for carnitine deficiency in patients requiring dialysis, and documents the results of relevant clinical trials of levocarnitine therapy in this population. Consensus recommendations by expert panels are summarized and contrasted with present guidelines for access to levocarnitine therapy by dialysis patients.

The effect of D,L-carnitine supplementation on muscle metabolism, neuropathy, cardiac and hepatic function in hemodialysis patients. A pilot study

Three patients on regular hemodialysis treatment were perorally supplemented with D.L-carnitine, 900 mg/d, during four weeks. Before treatment, muscle carnitine concentrations were low and the patients showed signs of hypometabolism in skeletal muscle, cardiomyopathy, impaired hepatic function and a moderate hyperlipoproteinemia. After treatment, the skeletal muscle metabolism normalized. The results further indicate improvement of the cardiac and hepatic function and of the neuropathy on the sensory side. No improvement was found, however, in plasma lipoprotein pattern or in variables reflecting plasma lipid transport (lipoprotein lipase activity and intravenous fat tolerance).

The use of levo-carnitine in children with renal disease: a review and a call for future studies

Carnitine is an amino acid derivative that has a key role in the regulation of fatty acid metabolism and ATP formation. Carnitine deficiency has been described in various conditions, including chronic kidney disease (CKD) and end stage renal disease (ESRD). The deficiency of this micronutrient is postulated to lead to adverse effects across multiple organ systems. There is a paucity of information on carnitine deficiency and its effects in the pediatric CKD and ESRD populations. Currently, there is no evidence supporting the routine use of carnitine supplementation in children with ESRD. In this article, we review the pathophysiology, pharmacokinetics and the potential effects of levo-carnitine supplementation with a focus on the pediatric CKD and ESRD populations. Finally, potential future directions of research are discussed.

The effect of oral L-carnitine supplementation on the lipid profiles of hyperlipidaemic children

AIM

To investigate the carnitine status and the effect of carnitine supplementation on serum lipid profiles in children with hyperlipoproteinaemia, a clinical open trial was conducted at Hacettepe University Ihsan Dogramaci Children's Hospital, Section of Nutrition and Metabolism.

METHODS

Patients were given carnitine at a dose of 100 mg/kg/d for 12 wk. Blood samples for the determination of lipid profile and carnitine levels and urine samples for carnitine levels were obtained on admission, at week 4 and week 12 of the study period.

RESULTS

A total of 41 children were enrolled in the study: 20 patients had type II heterozygotes, eight patients had type II homozygotes, three patients had type III, six patients had type V and four patients had secondary hyperlipidaemias. Serum and urine carnitine levels were within normal limits on admission. No significant correlations were found between serum carnitine levels and serum lipid profiles. Serum HDL and apolipoprotein A-I decreased significantly during the 12 wk of intervention in type II heterozygotes. In type II homozygotes, total cholesterol and LDL levels at weeks 4 and 12 increased significantly compared to initial levels. No significant change was noted for lipid parameters in hyperlipoproteinaemia type V.

CONCLUSION

The results of this trial demonstrated that carnitine supplementation was of no benefit for children with hyperlipidaemias, especially in primary hyperlipoproteinaemia type II heterozygotes, homozygotes and type V.

Carnitine supplementation improves apolipoprotein B levels in pediatric peritoneal dialysis patients

There have been conflicting reports concerning the effect of carnitine supplementation on lipid metabolism in patients on peritoneal dialysis (PD). We investigated several parameters of lipid metabolism in pediatric PD patients supplemented with carnitine. The study included 20 patients receiving PD (treatment group) aged 2-18 years and a matched healthy control group. In the treatment group, baseline triglyceride, total cholesterol, low-density lipoprotein cholesterol, very low-density lipoprotein cholesterol, and apolipoprotein B levels were higher than in the control group. High-density lipoprotein cholesterol, free fatty acid, phospholipids, and apolipoprotein A-I levels were not different from those in the control group. The baseline plasma free carnitine level was lower and acyl-carnitine level was higher in the treatment group. No difference was found between the groups with respect to plasma total carnitine levels. Oral l-carnitine supplementation (50 mg/kg per day for 30 days) led to a significant decrease (from a baseline value of 146.6+/-51.8 mg/dl to 63.6+/-22.2 mg/dl, P<0.001) in apolipoprotein B levels, and no significant change in the other lipid parameters of the treatment group. Oral l-carnitine supplementation does not ameliorate the lipid profile in pediatric PD patients, but it causes a significant decrease in apolipoprotein B levels. Hence, carnitine supplementation may be recommended for decreasing apolipoprotein B levels in this patient population.

Effect of L-carnitine supplementation on red blood cells deformability in hemodialysis patients

Anemia is a serious problem in hemodialysis patients, the main cause of which is erythropoietin deficiency. After the discovery of recombinant human erythropoietin (rHuEpo) at the end of the last decade, the hematological profile of hemodialysis patients improved significantly but at considerable expense. The deformability of red blood cells (RBC) influences their microcirculation and tissue oxygen delivery along with their life span. We investigated the deformabilty of RBCs in 15 hemodialysis patients before and after three months on L-carnitine supplementation (30 mg/Kg body wt/dialysis session). We excluded from the study all patients who received blood transfusions three months before or during the study, patients who had hemorrhagic episodes, those with hyperparathyroidism or infections, and any who required surgical intervention during the study. The serum iron, folic acid and vitamin B-12 levels were kept normal during the duration of the study. The erythropoietin dose taken before the beginning of L-cartnitine supplementation was not changed. The deformability of RBCs before and after dialysis, prior to and following three months on L-carnitine was determined and compared to the deformability of RBCs from a control group. Hematocrit levels were measured before entry into the study and every month for three months. We found that the deformability of RBCs before the dialysis session was significantly greater than that found in the control group (t-test, p < 0.00001), and that there was a further increase after the end of the dialysis session. Three months following L-carnitine supplementation, we found a significant reduction of RBCs deformability (paired t-test, p < 0.004), and a significant increase in the hematocrit (ANOVA, p < 0.0001). We concluded that abnormalities in the deformability of RBCs improved after L-carnitine and that this was responsible for the increase in the hematocrit. This may allow a substantial reduction in rHuEpo dose.

Carnitine and antioxidants levels in patients with rheumatoid arthritis

Rheumatoid arthritis (RA) is a heterogeneous disorder with a spectrum of clinical severity ranging from mild arthritis to a crippling joint disease with involvement of internal organs. Carnitine is essential for muscle energy production and is required for the transport of long chain fatty acids and the acyl coenzyme A derivatives across the inner mitochondrial membrane. The levels of malondialdehyde (MDA), an index of lipid peroxidation, and the antioxidants copper-zinc superoxide dismutase (CuZnSOD), glutathione (GSH), ceruloplasmin (CP), catalase (CAT), and carnitine were assessed in 42 patients with RA and 24 control subjects. While plasma carnitine and erythrocyte CuZnSOD levels were significantly lower in the patients with RA compared with the control group (p<0.01 and p<0.001, respectively), the CAT level was not different from controls (p>0.05). Plasma MDA, CP, and erythrocyte GSH levels were significantly higher than in the control group (p<0.001, p<0.001 and p<0.01, respectively). MDA levels showed a positive correlation with CP and GSH levels (r=0.716, p<0.001 and r=0.492, p<0.01, respectively). However, MDA, GSH, and CP demonstrated a negative correlation with carnitine (r=-0.719, p<0.001; r=-0.559, p<0.01, and r=-0.635, p<0.001, respectively) in the patient group but not in controls. There was also a significant positive correlation between CP and GSH levels (r=0.561, p<0.01). However, neither CuZnSOD nor CAT levels demonstrated correlation withcarnitine, MDA, GSH, or CP levels. It was interesting that CAT activity was not altered and CuZnSOD activity decreased when compared with the control group. These results suggest that while CP, MDA and GSH levels increased, carnitine and CuZnSOD levels decreased, but CAT activity was unchanged.

Carnitine and its derivatives in cardiovascular disease

Carnitine and its derivative propionyl-L-carnitine are endogenous cofactors which enhance carbohydrate metabolism and reduce the intracellular buildup of toxic metabolites in ischemic conditions. The carnitines have been, and are being used in a spectrum of diseases including multiple cardiovascular conditions. These include angina, acute myocardial infarction, postmyocardial infarction, congestive heart failure, peripheral vascular disease, dyslipidemia, and diabetes. Most published data on carnitine, propionyl-L-carnitine, and other carnitine congeners are favorable but the clinical trials have been relatively small. In currently used doses, these substances are virtually devoid of significant side effects.

Lipid-lowering therapy in patients with renal disease

A growing number of clinical trials have examined the effects of different lipid lowering strategies in patients with renal disease. We carried out a meta-analysis to compare and contrast the relative efficacy of various antilipemic therapies in different renal disease settings. Studies that investigated one or more therapies designed to lower serum lipids were combined using weighted multiple linear regression. The analysis adjusted treatment effects for differences in baseline lipid levels and possible placebo effects. The results showed that antilipemic therapies generally had similar effects on lipids in different renal disease settings. In nephrotic syndrome the greatest and most consistent reductions in low density lipoprotein cholesterol (LDL) were seen with 3-hydroxy-3-methylglutaryl co-enzyme A (HMG-CoA) reductase inhibitors (regression coefficient with 95% confidence interval in mg/dl = -63, -79 to -46). Similar results were seen for LDL in renal transplant (-51, -57 to -45), renal insufficiency (-62, -82 to -42), hemodialysis (-65, -80 to -50) and continuous ambulatory peritoneal dialysis (CAPD) patients (-84, -104 to -64). Fibric acid analogues had less effect on LDL, but caused greater reductions in triglycerides: -132, -178 to -87, in nephrotic syndrome; -69, -93 to -45 in transplant: -107, -169 to -45 in renal insufficiency; -72, -120 to -24 in hemodialysis; and -96, -162 to -30 in CAPD. In general, the effects of diet and other therapies were less consistent. Despite possible limitations of this meta-analysis, the results provide a useful framework for choosing antilipemic therapy, and point to areas for future long-term studies examining the safety and efficacy of lipid lowering strategies in patients with renal disease.

Propionyl-L-carnitine prevents the progression of atherosclerotic lesions in aged hyperlipemic rabbits

We have characterized the extent and the phenotype of total and proliferating cell population of aortic plaques in aged rabbits receiving a long-term low-dose cholesterol hyperlipemic diet, which represents an experimental model of atherosclerosis. For nine months, rabbits received the hypercholesterolemic diet alone or in addition to a treatment with propionyl-L-carnitine (PLC), a derivative of carnitine, an intramitochondrial carrier of fatty acids present in most cell types. We observed that, in both PLC-treated and control hyperlipemic rabbits, the ratio between proliferating macrophage-derived and smooth muscle cells was 2:1. PLC in addition to the hypercholesterolemic diet induced a marked lowering of plasma triglycerides, very low density lipoprotein (VLDL) and intermediate density lipoprotein (IDL) triglycerides, while plasma cholesterol was slightly and transiently reduced. Moreover, PLC-treated hyperlipemic rabbits exhibited a reduction of plaque thickness and extent, a slight but significant reduction of the percentage of macrophage-derived cells as compared to control hyperlipemic animals and a reduction of the number of both proliferating macrophage- and smooth muscle cell-derived foam cells. Finally, both proliferating and non-proliferating plaque cells expressed large amounts of macrophage colony-stimulating factor protein, in particular macrophage-derived foam cells. These results indicate that a modification of plasma lipemic pattern obtained by a long-term oral administration of PLC was associated with a decrease of plaque cell proliferation and severity of aortic atherosclerotic lesions.

Long-term effects of Aroclor 1254 (PCBs) on plasma lipid and carnitine concentrations in rhesus monkey

Sixty-seven female rhesus monkeys (Macaca mulatta) were orally dosed daily for 152 weeks with 0, 5, 20, 40, and 80 micrograms Aroclor 1254 (PCB)/kg body wt. Blood polychlorinated biphenyl (PCB) concentrations were highly positively correlated (r = 0.92, P < 0.001) with doses of PCB administered. A comprehensive analysis of plasma lipids/lipoproteins revealed a PCB-associated increase in plasma triglycerides and decreases in plasma total cholesterol, high-density lipoprotein cholesterol (HDL-chol), very-low plus low-density lipoprotein cholesterol (VLDL+LDL-chol), and total carnitine (which is involved in fatty acid metabolism). All of the lipid/lipoprotein changes were significantly (P < or = 0.05) correlated with blood PCB concentration. These data, obtained after 152 weeks of continuous daily exposure of a primate model to PCB support a causal relationship between plasma lipid changes and PCB intake. Previously, causality has been refuted on the premise that the commonly observed elevation of triglycerides with increasing concentration of blood PCB is a reflection, not of PCB dose, but of the partitioning of PCB between tissues (adipose) and blood in proportion to the blood lipid present. The mechanism of the plasma lipid changes was not investigated in this study but the altered lipid/lipoprotein pattern is discussed with respect to known cardiovascular risk profiles.

Hypertriglyceridemia and lowered apolipoprotein C-II/C-III ratio in uremia: effect of a fibric acid, clinofibrate

We examined the effects of a fibric acid, clinofibrate, on lipoprotein metabolism in 12 hyperlipidemic patients with uremia treated on continuous ambulatory peritoneal dialysis during a 24 week treatment. Daily dose of clinofibrate was 200 mg for the initial four weeks, 400 mg for the second four weeks, and 600 mg for the subsequent 16 weeks. Serum and very-low density lipoprotein (VLDL) triglyceride were decreased by 36% and 48%, respectively. Neither total cholesterol nor apolipoprotein B changed significantly, whereas cholesterol was decreased in VLDL and increased in low (LDL) and high density lipoprotein (HDL) fractions. Post-heparin plasma lipoprotein lipase (LPL) before treatment was not lower than the normal value, and we found no change in LPL activity following clinofibrate. Hepatic triglyceride lipase also did not change. Apolipoprotein (apo) C-II/C-III ratio was low as compared to the normal value before treatment, and the ratio was increased by 38% after the treatment. Decrease in VLDL triglyceride was associated with increase in apo C-II/C-III ratio in all the cases. Abnormal enrichment with triglyceride of LDL and HDL fractions was improved by clinofibrate. Although one patient had a transient and asymptomatic elevation of serum creatine phosphokinase, no patient had muscle pain. There was no accumulation of the drug in the 24 week trial. These results suggest that clinofibrate is an effective and safe approach to the management of dyslipidemia in CAPD patients.

Multicenter trial of L-carnitine in maintenance hemodialysis patients. I. Carnitine concentrations and lipid effects

Previous studies have reported conflicting results of carnitine supplementation on plasma lipids in patients with chronic renal failure. We therefore performed a four center, double-blind placebo controlled trial to evaluate the effects of post-hemodialysis intravenous injection of L-carnitine in ESRD patients on maintenance hemodialysis. Thirty-eight patients received up to six months of L-carnitine infusions (20 mg/kg) post-dialysis and 44 patients received placebo infusions. In both groups of patients, baseline pre-dialysis plasma and red blood cell total carnitine levels were normal, but pre-dialysis plasma-free carnitine concentrations and free/total ratios were subnormal, and plasma acyl levels were elevated. Post-dialysis plasma free and total carnitine concentrations were also subnormal. Plasma and red blood cell total carnitine levels rose eightfold in carnitine recipients, but were unchanged from baseline in those receiving placebo. There were no significant changes observed in plasma triglycerides, HDL-cholesterol or other lipoprotein parameters in either the carnitine or placebo treated groups. We conclude that carnitine metabolism is altered in uremia. Furthermore, in a randomly-selected hemodialysis population, L-carnitine injection at the dose of 20 mg/kg results in significant increases in blood (and perhaps tissue) carnitine levels, but this is not associated with any major effects on lipid profiles.

Valproate, carnitine metabolism, and biochemical indicators of liver function. Collaborative Group for the Study of Epilepsy

The effects of valproate (VPA) on carnitine and lipid metabolism and on liver function were assessed in 213 age- and sex-matched outpatients from five centers, with the following distribution: VPA monotherapy, 54; VPA polytherapy, 55; other monotherapies, 51; and untreated, 53. Mean total and free carnitine levels were significantly lower in patients with polytherapy; acylcarnitine was significantly higher for VPA monotherapy and the ratio of acyl- to free carnitine was significantly higher in all patients receiving VPA. Ammonia, uric acid, and bilirubin were the only tests selectively impaired with VPA. A significant correlation was found between serum ammonia and VPA dosage. Glucose, beta-lipoproteins, triglycerides, acetacetate, and beta-hydroxybutyrate were unchanged in the four groups. Sex and age appeared to interact with total and free carnitine values. Adverse drug reactions were apparently unrelated to carnitine metabolism impairment. Only a few patients had abnormal carnitine values. Our data support the assumption that carnitine deficiency and abnormal liver function due to VPA are mostly subclinical events.

Kinetics of intravenously administered carnitine in haemodialysed children

The pharmacokinetics of low-dose bolus L-carnitine (5 mg kg-1 body wt) in five haemodialysed children were investigated. Kinetic variables were obtained by applying a two-compartment open model. The elimination half-life was very short, 2.43 +/- 0.35 h, despite the reduced plasma clearance of 41.2 +/- 5.7 ml min-1, compared with healthy adults. The apparent volume of distribution, 0.27 +/- 0.07 1 kg-1 body wt, corresponds well to the size of the extracellular space. The kinetic behaviour of intravenously supplied carnitine may assist in future evaluations of the therapeutic application of this drug in uraemic children.

Oral carnitine therapy in children with cystinosis and renal Fanconi syndrome

11 children with either cystinosis or Lowe's syndrome had a reduced content of plasma and muscle carnitine due to renal Fanconi syndrome. After treatment with oral L-carnitine, 100 mg/kg per d divided every 6 h, plasma carnitine concentrations became normal in all subjects within 2 d. Initial plasma free fatty acid concentrations, inversely related to free carnitine concentrations, were reduced after 7-20 mo of carnitine therapy. Muscle lipid accumulation, which varied directly with duration of carnitine deficiency (r = 0.73), improved significantly in three of seven rebiopsied patients after carnitine therapy. One Lowe's syndrome patient achieved a normal muscle carnitine level after therapy. Muscle carnitine levels remained low in all cystinosis patients, even though cystinotic muscle cells in culture took up L-[3H]carnitine normally. The half-life of plasma carnitine for cystinotic children given a single oral dose approximated 6.3 h; 14% of ingested L-carnitine was excreted within 24 h. Studies in a uremic patient with cystinosis showed that her plasma carnitine was in equilibrium with some larger compartment and may have been maintained by release of carnitine from the muscle during dialysis. Because oral L-carnitine corrects plasma carnitine deficiency, lowers plasma free fatty acid concentrations, and reverses muscle lipid accumulation in some patients, its use as therapy in renal Fanconi syndrome should be considered. However, its efficacy in restoring muscle carnitine to normal, and the optimal dosage regimen, have yet to be determined.

Effects of L-carnitine on sodium transport in erythrocytes from dialyzed uremic patients

Red blood cell (RBC) sodium transport systems were studied by cation flux methodology, measuring both the ouabain-sensitive Na-K pump and the ouabain-insensitive Na-K cotransport (CoT), as well as the Na-lithium (Li) countertransport (CTT), in eight patients on chronic hemodialysis and a control group of eight normal individuals. Intracellular sodium content and passive Na permeability were also determined. The effect of L-carnitine on RBC sodium transport in the uremic group was evaluated by supplementation with oral (1 g/day) and i.v. (1 g post-hemodialysis) L-carnitine for 60 days. Mean Na efflux through the ouabain-sensitive Na-K pump was 30.7% lower in uremic patients than in controls (3.49 +/- 1.52 vs. 5.04 +/- 0.72 mmol/liter RBCxhr; P less than 0.025). Intracellular Na content was higher in uremic patients (11.57 +/- 3.38 vs. 8.86 +/- 0.88 mEq/liter RBC; P less than 0.05), but no differences were found in Na-K CoT, Na-Li CTT or passive Na permeability. L-carnitine treatment increased the ouabain-sensitive Na efflux in uremic patients (4.76 +/- 1.6 vs. 3.49 +/- 1.52 mmol/liter RBCxhr; P less than 0.05), with no change in CoT, CTT, intracellular Na content or passive Na permeability. We conclude that L-carnitine deficiency may play a major role in uremic Na-K pump disfunction.

The influence of diet and carnitine supplementation on plasma carnitine, cholesterol and triglyceride in WHHL (Watanabe-heritable hyperlipidemic), Netherland dwarf and New Zealand rabbits (Oryctolagus cuniculus)

1. Plasma carnitine levels in the spontaneously (endogenously) hyperlipidemic Watanabe (WHHL) rabbit are approximately 2-fold higher (P less than 0.001) than in normal rabbits of the New Zealand (NZ) or Netherland Dwarf (NDw) breeds. 2. Plasma carnitine levels in WHHL (44 +/- 3 nmol/ml) can be approximated in NZ and NDw which are rendered exogenously hyperlipidemic by supplementation of the stock chow diet with cholesterol and peanut oil. 3. The induction of endogenous hyperlipidemia in NZ by feeding a sucrose casein rich diet results in a biphasic response of plasma carnitine (elevation followed by normalization). 4. Plasma carnitine in WHHL is readily elevated by supplemental L-carnitine and the elevation is associated with a reduction in plasma triglyceride which shows differences in individual response time; plasma cholesterol is unaffected by supplemental L-carnitine.

Lipid lowering treatment with bezafibrate in patients on chronic haemodialysis: pharmacokinetics and effects

Hyperlipidaemia may contribute to the high rate of cardiovascular complications in patients on chronic haemodialysis (CHD). However, possibilities of lipid lowering therapy in CHD are still limited. The applicability of bezafibrate (BF), a recently developed clofibrate analogue, was investigated in patients on CHD with triglyceride and/or total cholesterol levels above 300 mg/dl. The lipid lowering effect was studied in a placebo-controlled trial over 6 months in 19 patients. Long-term effect was followed in six patients over a mean period of 29 months. Elimination half-life and mean therapeutic serum concentration were calculated by 72-h BF serum profiles, obtained after the first drug administration of a single 200-mg dose and during steady state after 12 weeks of treatment. Elimination half-lives were 17 h at start and 22 h after 12 weeks compared with 2 h in subjects with normal renal function. Dose reduction to 200 mg every 3rd day was necessary and resulted in a mean therapeutic serum concentration of 3.4 mg/l, which was similar to 3.0 mg/l of normal subjects, who received the dose optimal for lowering of lipids (200 mg 3 X/day). The protein-bound serum fraction of BF was decreased to 8% in CHD patients, compared with 95% found in normal subjects. BF therapy resulted in a marked reduction of serum triglycerides from 478 mg/dl by 31% and total cholesterol levels from 311 mg/dl by 19% as well as beta-Lp-cholesterol from 178 mg/dl by 17%, whereas the initially low alpha-Lp-cholesterol increased significantly from 18.3 mg/dl by 58%.(ABSTRACT TRUNCATED AT 250 WORDS)

Carnitine deficiency in haemodialysed patients

Free carnitine, acylcarnitine and total carnitine concentrations have been determined in the sera of chronic renal insufficiency patients undergoing regular haemodialysis treatment and in those of healthy controls. The most striking difference was found to be the high proportion of acylated carnitine (23.4 mumol/l) in the haemodialysed patients. Free carnitine and acylcarnitine levels were not completely restored between successive dialysis treatments, making levels measured immediately before the third weekly sessions significantly lower than those measured before the first session (p less than 0.01). In patients monitored throughout 25 wk of treatment, there was an exponential decay of both total serum carnitine levels (Spearman's r = -0.993, p less than 0.001) and free carnitine levels (Spearman's r = -0.972, p less than 0.001). It is suggested that in the absence of exogenous supplies of carnitine, endogenous synthesis is unable to make up for losses due to dialysis treatment, and that carnitine deficiency consequently ensues.

Carnitine status, plasma lipid profiles, and exercise capacity of dialysis patients: effects of a submaximal exercise program

Carnitine status, blood lipid profiles, and exercise capacity were evaluated in a combined group of hemodialysis (N = 4) and continuous ambulatory peritoneal dialysis (N = 6) patients before and after an 8-week submaximal exercise program. Maximal aerobic capacity (VO2max) was only 18.5 +/- 5.9 (mean +/- SD) mL O2/kg/min, well below the expected 30 to 35 mL O2/kg/min for age-matched sedentary controls. Plasma short-chain acylated carnitine levels, which were two to three times normal values, were reduced after the exercise program, but the long-chain acylcarnitines were significantly reduced during acute exercise. Muscle biopsies of the vastus lateralis were performed at rest in five patients prior to and after the 8-week exercise program. Total carnitine in skeletal muscle was 3.09 (.076 SD) mumol/g ww, with only 11.3% acylated prior to the exercise program, which was much lower than the 4.25 +/- 1.27 mumol/g ww, with 28.5% acylated in a group of healthy athletic subjects (N = 28). Muscle free carnitine concentrations decreased significantly following the 8-week training period, with only a slight reduction in total carnitine. The percent of acylated carnitine was therefore significantly increased (P less than 0.05) from 11.3% to 25.2% after the experimental period. Pretraining carnitine palmitoyl transferase activity at rest was 0.57 +/- 0.28 nmol palmitoyl carnitine formed/5 min/mg mitochondrial protein, which was not changed by exercise training v 1.80 +/- 0.51 nmol/5 min/mg protein in 28 healthy normals (P less than 0.001). Free fatty acid concentrations were reduced significantly during acute exercise as a result of the exercise training program whereas other plasma lipids were not altered. (ABSTRACT TRUNCATED AT 250 WORDS)

Carnitine: an overview of its role in preventive medicine

Carnitine (beta-hydroxy-gamma-N-trimethylaminobutyric acid) is required for transport of long-chain fatty acids into the inner mitochondrial compartment for beta-oxidation. Widely distributed in foods from animal, but not plant, sources, carnitine is also synthesized endogenously from two essential amino acids, lysine and methionine. Human skeletal and cardiac muscles contain relatively high carnitine concentrations which they receive from the plasma, since they are incapable of carnitine biosynthesis themselves. Since the discovery of a primary genetic carnitine deficiency syndrome in 1973, carnitine has become the subject of extensive research. It is now recognized that carnitine deficiency may also occur secondary to genetic disorders of intermediary metabolism as well as to a variety of clinical disorders, including renal disease treated by hemodialysis, the renal Fanconi syndrome, cirrhosis, untreated diabetes mellitus, malnutrition, Reye's syndrome, and certain disorders of the endocrine, neuromuscular, and reproductive systems. Administration of the anticonvulsant valproic acid and total parenteral nutrition may also induce hypocarnitinemia. In many instances, the physiological implications of secondary carnitine deficiency have not been resolved. However, evidence for a specific carnitine requirement for the newborn, especially if preterm, is accumulating. Moreover, carnitine administration may have a favorable effect on some forms of hyperlipoproteinemia. Carnitine, now recognized as a conditionally essential nutrient, is a significant factor in preventive medicine.

Potential role of carnitine in patients with renal insufficiency

Carnitine metabolism is altered in renal insufficiency and influenced by the treatment modalities. Chronically uremic patients with end-stage renal disease under conservative therapy, hemodialysis, or peritoneal dialysis show low, normal, or elevated serum levels of TC and a distorted pattern of FC, SCAC, and LCAC. HD induces a marked depletion of FC, while predialytic elevated SCAC and LCAC are in the normal range at the end of dialysis treatment. All carnitine fractions rapidly return to predialysis levels 6 h after HD due to a transport of carnitine from muscle stores to plasma pool. Muscle carnitine content is elevated in chronic uremic patients under conservative therapy. Normal or decreased levels are observed in patients on long-term HD treatment. In addition, weekly losses of carnitine in patients undergoing HD or peritoneal dialysis do not exceed urinary carnitine excretion of CO. Supplementation with currently recommended doses (1-2 g L-carnitine i.v. at the end of each HD) is followed by a marked rise in plasma carnitine levels, suggesting limited carnitine utilization in uremia. Therefore, lower carnitine doses and modified application regimens should be considered to avoid exaggerated plasma levels of carnitine and carnitine esters. Furthermore, carnitine application has been reported to show beneficial, worsening, or no effect on the deranged lipid metabolism of the uremic patients. In patients undergoing CAPD or IPD predominantly normal serum carnitine levels have been reported. On the other hand, SCAC and LCAC esters are markedly elevated in these patients. After kidney transplantation the pattern of carnitine fractions is fully normalized in patients with plasma creatinine less than or equal to 120 mumol/l.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma lipoproteins, liver function and glucose metabolism in haemodialysis patients: lack of effect of L-carnitine supplementation

The effects of L-carnitine administration (2 g i.v. three times weekly for 6 weeks) were studied in a double blind trial comprising 2 X 14 patients on regular haemodialysis treatment. The initial plasma carnitine concentrations were normal in the male, but slightly lowered in the female participants and rose more than ten-fold in the patients receiving active treatment. The majority (15/28) of patients had moderate hypertriglyceridaemia, whereas plasma HDL cholesterol levels were normal. Activities of hepatic and lipoprotein lipase were decreased and fat tolerance impaired. The S-triiodothyronine and/or thyroxine levels were subnormal in 11 patients. Four patients had fasting hyperinsulinemia, and 6 demonstrated abnormal B-glucose patterns after a peroral glucose load. The galactose elimination rate demonstrated moderately impaired hepatocyte function in four patients. No effects of carnitine treatment on any of the variables could be detected.

The short term effects of bezafibrate on the hypertriglyceridaemia of moderate to severe uraemia

Hypertriglyceridaemia, an atherogenic risk factor, is a well recognised complication of uraemia, and is present in the earliest stages of the disease. Bezafibrate is an effective hypolipidaemic agent, and its effect in moderate to severe uraemia is documented in this study. Significant reductions in serum triglyceride and cholesterol have been achieved after 1 month's therapy with a reduced dosage of bezafibrate. A reduction in the hyperinsulinaemia was also seen, but no change in the fractional removal rate of injected lipid emulsion (K2) was observed. An accelerated decline in some patients' renal function was observed, which was partially reversed on cessation of treatment. Reversible elevations in the serum creatinine phosphokinase were also seen, but no patient exhibited the myositis-like syndrome associated with clofibrate.

Effects of fish oil rich in eicosapentaenoic acid on serum lipid in hyperlipidemic hemodialysis patients

The incidence of atherosclerosis in hemodialysis (HD) patients is very high. Major risk factors are aging, lipid metabolism disturbances, high blood pressure, and smoking. High blood pressure and hypertriglyceridemia, which is atherogenic in the presence of smoking, are encountered very often in HD patients. The effects of eicosapentaenoic acid (EPA) on plasma lipids and blood pressure were studied for the first time in HD patients by the administration of capsules containing fish oil rich in EPA, which is known to lower serum lipid concentration and blood pressure. We treated 12 hyperlipidemic patients (3 of type IIa, 3 of type IIb, and 6 of type IV; 3 males, 9 females; 31 to 70 years of age; 4 to 90 months on HD) with 24 capsules (1.6 g EPA and 1.0 g docosahexaenoic acid) per day for 13 weeks. Serum triglycerides, total cholesterol, and phospholipid decreased significantly after capsule administration. The ratio of EPA to arachidonic acid in serum increased significantly. There was a small but statistically significant decrease in platelet count. Diastolic blood pressure decreased at the end of the experiment. These effects of fish oil are considered favorable for the prevention of atherosclerosis and its subsequent diseases.

Fat metabolism following an intravenous bolus dose of a fat emulsion and carnitine

Intravenous fat tolerance tests were performed with (carboxyl-14C)-triolein labelled Intralipid in four normal subjects with and without L-carnitine administration, 20 and 25 mg/kg body weight. The pharmacokinetics of L-carnitine was studied simultaneously with measurements of variables reflecting fat metabolism during 4 h. 3-OH-butyrate concentration in plasma was higher in all subjects when carnitine was given. No effect of carnitine was found in elimination of the exogenous triglycerides, the 14CO2 activity in expired air, concentration and specific radioactivity of non- esterified fatty acids or glucose in plasma. The data suggest that carnitine may slightly increase fatty acid oxidation in normal subjects provided that increase of 3-OH-butyrate concentration in plasma is the most sensitive variable reflecting fatty acid oxidation of the variables applied in this study.

Improvement of myocardial function in diabetic rats after treatment with L-carnitine

The effects of L-carnitine administration on the severity of diabetes were investigated. Serum glucose, free fatty acids (FFA), triglycerides, and ketones from diabetic and normal rats injected for 2 weeks with 3 g/kg/d of either L-carnitine or saline were assayed. Hearts were analyzed for carnitine and long-chain acyl coenzyme A. L-carnitine treatment to diabetic rats significantly reduced serum glucose, FFA, triglycerides, and ketones. In nondiabetic rats, carnitine increased serum ketones while FFA and triglycerides were decreased. L-carnitine treatment to diabetic rats prevented a decrease in myocardial total carnitine content. Long-chain acyl carnitine increased while long-chain acyl coenzyme A decreased. In another experiment, L-carnitine administration (750 mg/kg/d for 14 days) significantly improved the recovery of cardiac output after 60, 90, and 120 minutes of ischemia in diabetic perfused hearts. These results suggest that L-carnitine therapy may reduce the severity of diabetes mellitus and improve myocardial performance.

Rationales for micronutrient supplementation in diabetes

Available evidence--some well-documented, some only preliminary--suggests that properly-designed nutritional insurance supplementation may have particular value in diabetes. Comprehensive micronutrient supplementation providing ample doses of antioxidants, yeast-chromium, magnesium, zinc, pyridoxine, gamma-linolenic acid, and carnitine, may aid glucose tolerance, stimulate immune defenses, and promote wound healing, while reducing the risk and severity of some of the secondary complications of diabetes.

An inverse relationship between plasma carnitine and triglycerides in selected Macaca arctoides and Macaca nemistrina fed a low-fat chow diet

Plasma carnitine and triglycerides were measured in five male Macaca arctoides and one female Macaca nemistrina during the course of feeding a low-fat (5.2% w/w), high carbohydrate diet and a high-fat (15.9% w/w), low carbohydrate diet. For each individual monkey, an inverse relationship was observed between plasma carnitine and triglyceride levels when the low-fat diet was fed but not when the high-fat diet was fed. The mechanism of the different responses to diet was not investigated but may be related to the primary source of the plasma triglycerides (i.e. endogenous origin or exogenous origin) or to differing hormonal effects. A close coupling between carnitine and triglyceride metabolism may be part of a sensitive homeostatic control mechanism that responds to endogenously-synthesized triglyceride.

Heat inhibition of in vitro lipolysis and 14C ibuprofen protein binding in plasma from heparinized uraemic subjects

Protein binding determination in post heparin plasma samples is complicated by the continued post heparin lipase activity, in vitro, during the binding analysis. The decomposition of lipoproteins and accumulation of nonesterified fatty acids (NEFA) results in artifically elevated free fractions of many drugs. This artefact is particularly accentuated in haemodialysis patients who are frequently hypertriglyceridaemic and receive large doses of heparin. Rapid heat treatment (60 degrees for 15 min) of plasma from heparinized uraemic subjects is shown to inhibit the in vitro lipolysis occurring during 2 hours of equilibrium dialysis at 37 degrees (ED). Mean NEFA concentrations in heat treated plasma after ED (means = 400 +/- 141 mumol/L) were not different (p greater than 0.05, n = 9) from the baseline values in fresh plasma (means 351 +/- 117 mumol/L) but were considerably less (p less than 0.005) than NEFA levels in untreated plasma after ED (means = 1025 +/- 523 mumol/L). The degree of in vitro lipolysis inhibition (92 +/- 6.6%) was very much greater than using the chemical inhibitors phenyl methyl sulphonyl fluoride, EDTA, Triton X100 or protamine sulphate. Heat treatment at 60 degrees for 15 min increased the percentage of free 14C ibuprofen in 3.5% isolated human serum albumin from 0.34% to 0.62%. Reduced binding as a result of heat treatment was not observed however in whole plasma. The percentage free ibuprofen in heat treated, whole plasma from both heparinized and non heparinized subjects (means = 1.22 +/- 0.19; n = 29) was not different (p greater than 0.05) from the percentage free determined in plasma from a non heparinized group (means = 1.16 +/- 0.23; n = 15). In contrast the % free ibuprofen in untreated plasma from heparinized subjects was markedly higher (means = 1.56 +/- 0.41; n = 24; p less than 0.05). There was a strong correlation between % free ibuprofen and plasma NEFA concentration (r = 0.8; p less than 0.005; n = 68). The heat treatment of plasma for 15 min at 60 degrees is proposed as an effective means of controlling heparin induced lipolysis in vitro and may be valuable in overcoming the post heparin binding artefact.

Carnitine and carnitine esters in plasma and adipose tissue of chronic uremic patients undergoing hemodialysis

Carnitine concentrations were measured in the plasma and adipose tissue of seven chronically uremic and hyperlipidemic patients undergoing hemodialysis. Plasma levels of carnitine had dropped by the end of dialysis. The clearance of free carnitine was greater than that of acylcarnitine. Fasting plasma free carnitine, long-chain acylcarnitine, D-beta-hydroxybutyrate and free fatty acid concentrations were normal but short-chain acylcarnitine values were elevated. In adipose tissue, total carnitine concentrations were normal but long-chain acylcarnitine concentrations were increased. These findings may indicate a hypermetabolic state in which the acute removal of carnitine during hemodialysis may lead to a critical shortage of this substance.

Kinetic compartmental analysis of carnitine metabolism in the dog

This study was undertaken to quantitate the dynamic parameters of carnitine metabolism in the dog. Six mongrel dogs were given intravenous injections of L-[methyl-3H]carnitine and the specific radioactivity of carnitine was followed in plasma and urine for 19-28 days. The data were analyzed by kinetic compartmental analysis. A three-compartment, open-system model [(a) extracellular fluid, (b) cardiac and skeletal muscle, (c) other tissues, particularly liver and kidney] was adopted and kinetic parameters (carnitine flux, pool sizes, kinetic constants) were derived. In four of six dogs the size of the muscle carnitine pool obtained by kinetic compartmental analysis agreed (+/- 5%) with estimates based on measurement of carnitine concentrations in different muscles. In three of six dogs carnitine excretion rates derived from kinetic compartmental analysis agreed (+/- 9%) with experimentally measured values, but in three dogs the rates by kinetic compartmental analysis were significantly higher than the corresponding rates measured directly. Appropriate chromatographic analyses revealed no radioactive metabolites in muscle or urine of any of the dogs. Turnover times for carnitine were (mean +/- SEM): 0.44 +/- 0.05 h for extracellular fluid, 232 +/- 22 h for muscle, and 7.9 +/- 1.1 h for other tissues. The estimated flux of carnitine in muscle was 210 pmol/min/g of tissue. Whole-body turnover time for carnitine was 62.9 +/- 5.6 days (mean +/- SEM). Estimated carnitine biosynthesis ranged from 2.9 to 28 mumol/kg body wt/day. Results of this study indicate that kinetic compartmental analysis may be applicable to study of human carnitine metabolism.

The effect of diet on plasma carnitine, triglyceride, cholesterol and arterial carnitine levels in cynomolgus monkeys

Plasma carnitine, cholesterol, and triglycerides were measured over a 13-week period in male cynomolgus monkeys (M. fascicularis) that were fed a control diet (Purina Monkey Chow, n = 5) and a semisynthetic hypercholesterolemic diet (n = 15). Plasma cholesterol levels rose from 100 +/- 5 to 743 +/- 50 mg/dl in the cholesterol-fed group during the 13-week period but remained below 133 +/- 13 mg/dl in the control group. Plasma triglyceride levels tended to be lower in the cholesterol-fed group, particularly at 4 week (28 +/- 3 vs 42 +/- 7 mg/dl, P less than 0.05). Plasma carnitine levels rose from 43 +/- 4 to 53 +/- 5 nmol/ml within two weeks in the cholesterol-fed group and remained above control values for the duration of the study. Carnitine levels were significantly higher in the carotid arteries of cholesterol-fed animals relative to control (224 +/- 25 vs 109 +/- 15 pmol/mm in situ length, P less than 0.01). Higher mean values of carnitine were also found in iliac, subclavian, and coronary arteries of cholesterol-fed animals but not in femoral arteries.

Effect of dialysis on serum carnitine, free fatty acids, and triglyceride levels in man and the rat

Serum free carnitine, free fatty acid and triglyceride values were followed in patients with end-stage renal disease on maintenance dialysis therapy. During dialysis a decrease in serum carnitine was documented. Whereas the elevated triglyceride concentration remained constant, there was a sharp rise in free fatty acids during the dialysis procedure. This pattern occurred whether patients were subjected to hemodialysis or intermittent peritoneal dialysis. Peritoneal dialysis was performed in a rat model and produced results similar to those observed in human subjects. Furthermore, it could be demonstrated that peritoneal dialysis initiated the hypertriglyceridemia in the otherwise normal animal within a short time period. Whereas the abnormalities observed in carnitine and fatty acid metabolism may or may not be causally related in rat or man, they both seem to result from dialysis therapy.

[Fat and renal failure--therapeutic aspects]

There is current debate as to whether or not the hyperlipidaemia seen in patients (1) with chronic renal insufficiency, (2) on regular dialysis treatment and (3) after successful renal transplantation should be specifically treated. The reduced HDL cholesterol fraction suggests that the risk of cardiovascular complications may be increased. Therapeutic possibilities include increased physical exercise and a reduction of carbohydrate intake. If these measures fail, then treatment with clofibrate or bezafibrate should be considered. The recommended dosage of clofibrate is 1.0-1.5 g/week (with CPK-control), and of bezafibrate is 400-500 mg/week in patients with chronic renal insufficiency (creatinin-clearance below 20 ml/min). In patients on regular dialysis treatment plasma lipids are reduced by adding carnitine. Most investigators believe that a specific therapy of the hypercholesterolaemia and hypertriglyceridaemia of patients with nephrotic syndrome is not necessary since the disturbances in fat metabolism are associated with an increased levels of HDL-cholesterol. With remission of the nephrotic syndrome an improvement of the hyperlipoproteinaemia is observed. If patients with acute renal failure are under parenteral nutrition fat infusion is recommended once per week to avoid a deficiency of essential fatty acids which is augmented by daily dialysis therapy.

[Alterations of fat metabolism in renal disease - pathogenetic mechanisms (author's transl)]

Hypertriglyceridaemia is often observed in patients (1) with chronic renal insufficiency, (2) on haemodialysis and (3) after successful renal transplantation. HDL cholesterol is reduced in all three groups of patients and plasma cholesterol is elevated after renal transplantation. In these three patient groups type IV hyperlipoproteinaemia is found most frequently and after renal transplantation there is a relative increase in the incidence of type II hyperlipoproteinaemia. The role of glucagon resistance and carnitine deficiency in the alteration of fat metabolism seen in patients with chronic renal failure and patients on haemodialysis is discussed. Other factors which may influence fat metabolism in uraemia include calcium and vitamin D status as well as beta adrenergic receptor blocking agents and diuretics. Steroid therapy may be one cause of the hypercholesterolaemia and hypertriglyceridaemia seen after renal transplantation. PHLP lipase activity is reduced in all three groups of patients. In nephrotic syndrome, if hypercholesterolaemia occurs, the HDL cholesterol fraction is increased and thus the cardiovascular risk may be lower than in the three patient group mentioned above.

Regulation of high density lipoprotein levels

Current concepts of the structure and metabolism of high density lipoproteins are presented and factors that influence their levels in human beings are surveyed.