Effects of L-carnitine and its acetate and propionate esters on the molecular dynamics of human erythrocyte membrane

Salivary metabolites as potential predictive biomarkers for lung surgery complications: a retrospective cross-sectional study

PURPOSE

Saliva is often used as a tool for identifying systemic diseases because of the noninvasive nature of its collection. Moreover, salivary metabolites can be potential predictive factors for postoperative survival. We conducted the present study to establish whether salivary metabolites can function as predictive biomarkers for lung surgery complications.

METHODS

Unstimulated salivary samples were collected from 412 patients before lung surgery. Salivary metabolites were analyzed comprehensively by capillary electrophoresis mass spectrometry. Clinical data with the discriminatory ability of biomarkers were assessed to predict lung surgery complications using multivariate logistic regression analysis. The primary endpoint was the risk factors for postoperative complications of Clavien-Dindo grade ≥ III.

RESULTS

Postoperative complications of Clavien-Dindo grade ≥ III developed in 36 patients (8.7%). There was no postoperative 30-day mortality. Male sex (odds ratio [OR], 3.852; 95% confidence interval CI 1.455-10.199; p = 0.007) and salivary gamma-butyrobetaine (OR, 0.809; 95% CI 0.694-0.943; p = 0.007) were identified as significant risk factors for postoperative complications of Clavien-Dindo grade ≥ III.

CONCLUSION

Salivary metabolites are potential noninvasive biomarkers for predicting postoperative complications of lung surgery.

Nocturnal Leg Cramping Caused by Carnitine Deficiency Due to Long-Term Pivalate Antibiotics Administration in a Patient With Chronic Kidney Disease

Carnitine deficiency is a known cause of leg cramps and is sometimes observed in patients taking certain medications such as pivalate-containing antibiotics. A 69-year-old Japanese woman presented with a progression of painful involuntary nocturnal leg cramping. She had been taking cefcapene-pivoxil for six months. Serum-free carnitine (FC) and acylcarnitine levels were decreased. Then, carnitine deficiency due to long-term pivalate-containing antibiotics administration was diagnosed. After initiating oral L-carnitine treatment, her symptoms improved. It should be aware of carnitine deficiency if a patient taking pivalate-containing antibiotics presents with leg cramping.

Dietary L-Carnitine Affects Leukocyte Count and Function in Dairy Cows Around Parturition

In early lactation, an energy deficit leading to a negative energy balance (NEB) is associated with increased susceptibility to disease and has been shown to be an important factor during transition in dairy cows. L-carnitine as a key factor in the mitochondrial transport of fatty acids and subsequently for β-oxidation and energy release is known to modulate mitochondrial biogenesis and thus influence metabolism and immune system. In the current study, we characterized hematological changes around parturition and investigated the potential effects of dietary L-carnitine supplementation on immune cell functions. For this approach, dairy cows were assigned either to a control (CON, n = 30) or an L-carnitine group [CAR, n = 29, 25 g rumen-protected L-carnitine per cow and day (d)]. Blood samples were taken from d 42 ante partum (ap) until d 110 post-partum (pp), with special focus and frequent sampling from 0.5 to72 h post-calving to clarify the impact of L-carnitine supplementation on leukocyte count, formation of reactive oxygen species (ROS) in polymorphonuclear cells (PMN) and peripheral mononuclear cells (PBMC) and their phagocytosis activity. Blood cortisol concentration and the capacity of PBMC proliferation was also investigated. All populations of leukocytes were changed during the peripartal period, especially granulocytes showed a characteristic increase up to 4 h pp. L-carnitine supplementation resulted in increased levels of eosinophils which was particularly pronounced one day before to 4 h pp, indicating a possible enhanced support for tissue repair and recovery. Non-supplemented cows showed a higher phagocytic activity in PBMC as well as a higher phagocytic capacity of PMN during the most demanding period around parturition, which may relate to a decrease in plasma levels of non-esterified fatty acids reported previously. L-carnitine, on the other hand, led to an increased efficiency to form ROS in stimulated PMN. Finally, a short period around calving proved to be a sensitive period in which L-carnitine administration was effective.

Protective effect of L-carnitine on myocardial injury in rats with heatstroke

PURPOSE

To investigate the protective effect of L-carnitine on myocardial injury in rats with heatstroke.

METHODS

orty-eight rats were randomly divided into control, heatstroke and 25, 50 and 100 mg/kg L-carnitine groups. The last three groups were treated with 25, 50 and 100 mg/kg L-carnitine, respectively, for seven successive days. Then, except for the control group, the other four groups were transferred into the environment with ambient temperature of (39.5 ± 0.4 °C) and relative humidity of (13.5 ± 2.1%) for 2 h. The core temperature (Tc), mean arterial pressure (MAP), heart rate (HR) and serum and myocardial indexes were detected.

RESULTS

Compared with the heatstroke group, in the 100 mg/kg L-carnitine group, the Tc was significantly decreased, the MAP and HR were significantly increased, the serum creatine kinase, lactate dehydrogenase, alkaline phosphatase, aspartate aminotransferase, tumor necrosis factor α and interleukin 1β levels were significantly decreased, the myocardial superoxide dismutase and glutathione peroxidase levels were significantly increased, the myocardial malondialdehyde level was significantly decreased and the cardiomyocyte apoptosis index and myocardial caspase-3 protein expression level were remarkably decreased (p < 0.05).

CONCLUSIONS

The L-carnitine pretreatment can alleviate the myocardial injury in heatstroke rats through reducing the inflammatory response, oxidative stress and cardiomyocyte apoptosis.

Effects of Dietary L-Carnitine Supplementation on Platelets and Erythrogram of Dairy Cows with Special Emphasis on Parturition

During late gestation and early lactation, many proliferative processes and metabolic adaptions are involved in homeorhesis. An adjusted supply of oxygen is a precondition for an optimized cellular energy metabolism whereby erythrocytes play a central role. Endogenous L-carnitine modulates the mitochondrial fatty acid utilization for generating adenosine triphosphate (ATP). As it might be insufficient around calving due to increased need, L-carnitine supplementation is frequently recommended. Thus, the present study addressed the interplay between the red hemogram, platelets, oxidative stress indices, and L-carnitine supplementation of dairy cows around calving. German Holstein cows were assigned to a control (n = 30) and an L-carnitine group (n = 29, 25 g of rumen-protected L-carnitine per cow and per day), and blood samples were taken from day 42 ante partum (ap) until day 110 postpartum (pp), with a higher sampling frequency during the first three days pp. The time courses of the erythrogram parameters reflected the physiological adaptations to the oxygen need without being influenced by L-carnitine supplementation. Erythrocytic antioxidative enzymatic defence paralleled the relative development of polycythemia ap, while non-enzymatic total plasma antioxidative capacity continuously increased pp. In contrast to erythrocytes, the platelet counts of the L-carnitine supplemented cows varied at significantly higher levels. This can be interpreted as a result of a membrane-stabilizing effect of L-carnitine.

Effects of L-Carnitine Supplementation in Patients Receiving Hemodialysis or Peritoneal Dialysis

L-carnitine is an important factor in fatty acid metabolism, and carnitine deficiency is common in dialysis patients. This study evaluated whether L-carnitine supplementation improved muscle spasm, cardiac function, and renal anemia in dialysis patients. Eighty Japanese outpatients (62 hemodialysis (HD) patients and 18 peritoneal dialysis (PD) patients) received oral L-carnitine (600 mg/day) for 12 months; the HD patients further received intravenous L-carnitine injections (1000 mg three times/week) for 12 months, amounting to 24 months of treatment. Muscle spasm incidence was assessed using a questionnaire, and cardiac function was assessed using echocardiography. Baseline free carnitine concentrations were relatively low in patients who underwent dialysis for >4 years. Total carnitine serum concentration, free carnitine, and acylcarnitine significantly increased after oral L-carnitine treatment for 12 months, and after intravenous L-carnitine injection. There was no significant improvement in muscle spasms, although decreased muscle cramping after L-carnitine treatment was reported by 31% of patients who had undergone HD for >4 years. Hemoglobin concentrations increased significantly at 12 and 24 months in the HD group. Therefore, L-carnitine may be effective for reducing muscle cramping and improving hemoglobin levels in dialysis patients, especially those who have been undergoing dialysis for >4 years.

Carnitine Requires Choline to Exert Physiological Effects in Saccharomyces cerevisiae

L-Carnitine is a key metabolite in the energy metabolism of eukaryotic cells, functioning as a shuttling molecule for activated acyl-residues between cellular compartments. In higher eukaryotes this function is essential, and defects in carnitine metabolism has severe effects on fatty acid and carbon metabolism. Carnitine supplementation has been associated with an array of mostly beneficial impacts in higher eukaryotic cells, including stress protection and regulation of redox metabolism in diseased cells. Some of these phenotypes have no obvious link to the carnitine shuttle, and suggest that carnitine has as yet unknown shuttle-independent functions. The existence of shuttle-independent functions has also been suggested in Saccharomyces cerevisiae, including a beneficial effect during hydrogen peroxide stress and a detrimental impact when carnitine is co-supplemented with the reducing agent dithiothreitol (DTT). Here we used these two distinct yeast phenotypes to screen for potential genetic factors that suppress the shuttle independent physiological effects of carnitine. Two deletion strains, Δcho2 and Δopi3, coding for enzymes that catalyze the sequential conversion of phosphatidylethanolamine to phosphatidylcholine were identified for suppressing the phenotypic effects of carnitine. Additional characterisation indicated that the suppression cannot be explained by differences in phospholipid homeostasis. The phenotypes could be reinstated by addition of extracellular choline, but show that the requirement for choline is not based on some overlapping function or the structural similarities of the two molecules. This is the first study to suggest a molecular link between a specific metabolite and carnitine-dependent, but shuttle-independent phenotypes in eukaryotes.

l-carnitine as a Potential Additive in Blood Storage Solutions: A Study on Erythrocytes

Erythrocytes undergo various changes during storage (storage lesion) that in turn reduces their functioning and survival. Oxidative stress plays a major role in the storage lesion and antioxidants can be used to combat this stress. This study elucidates the effects of l-carnitine (LC) on erythrocytes of stored blood. Blood was obtained from male Wistar rats and stored (4 °C) for 20 days in CPDA-1 (citrate phosphate dextrose adenine) solution. Samples were divided into-(i) controls (ii) LC 10 (l-carnitine at a concentration of 10 mM) (iii) LC 30 (l-carnitine at a concentration of 30 mM) and (iv) LC 60 (l-carnitine at a concentration of 60 mM). Every fifth day, the biomarkers (haemoglobin, hemolysis, antioxidant enzymes, lipid peroxidation and protein oxidation products) were analysed in erythrocytes. Hemoglobin and protein sulfhydryls were insignificant during storage indicative of the maintenance of hemoglobin and sulfhydryls in all groups. Superoxide dismutase and malondialdehyde levels increased initially and decreased towards the end of storage. The levels of catalase and glutathione peroxidase were lower in experimentals than controls during storage. l-carnitine assisted the enzymes by scavenging the reactive oxygen species produced. Hemolysis increased in all groups with storage, elucidating that l-carnitine could not completely protect lipids and proteins from oxidative stress. Hence, this study opens up new avenues of using l-carnitine as a component of storage solutions with combinations of antioxidants in order to maintain efficacy of erythrocytes.

Pharmacological effects and clinical applications of propionyl-L-carnitine

Propionyl-L-carnitine (PLC) is a naturally occurring derivative of carnitine that plays an important role in the metabolism of both carbohydrates and lipids, leading to an increase of ATP generation. PLC, however, is not only a metabolic drug; it is also a potent antiradical agent and thus may protect tissues from oxidative damage. PLC has been demonstrated to exert a protective effect in different models of both cardiac and endothelial dysfunction, to prevent the progression of atherosclerosis, and, more recently, to improve some of the cardiometabolic alterations that frequently accompany insulin resistance. As a result, most of the clinical trials conducted in humans highlight PLC as a potential treatment option in cardiovascular diseases such as peripheral arterial disease, chronic heart failure, or stable angina, especially when type 2 diabetes mellitus or hyperglycemia (i.e., patients on hemodialysis) are also present. The aim of this review is to summarize the pharmacological effects and possible therapeutic applications of PLC, including the most recent findings to date.

Propionyl-L-carnitine in Leriche-Fontaine stage II peripheral arterial obstructive disease

Peripheral arterial obstructive disease (PAOD) of the lower limbs affects 5% of the adult population. Uncontrolled arteriopathy is established due to a microcirculatory deficit, which may be present despite a good Winsor index and which leads to exhaustion of the functional microcirculatory reserve. The target of this study was to examine possible improvements in microvascular and tissue homeostasis by the administration of propionyl-L-carnitine (PLC). A total of 26 patients were enrolled in this study, aged 65 +/- 15 years; two males were diagnosed at stage IIA and 17 males and seven females at stage IIB PAOD. The main criterion of inclusion was the worsening of walking distance during the last month. In this study the duration of therapy was 33 days. PLC was administered in three flasks, each containing 300 mg in 250 cc saline by continuous infusion. The following parameters were measured before and after treatment: pain-free and maximum walking distance (measured on a treadmill at 3.2 km/hr with a gradient of 12%), recovery time from pain after maximum walking distance, ankle-brachial index by means of the Doppler apparatus, and evaluation of the microcirculation using capillaroscopy. The results showed that therapy with PLC was effective at restoring activity of skeletal muscle in ischemic conditions. In particular, capillaroscopy showed improvement in the angioarchitecture in the microcirculation fields, expressed as increased numbers of visible capillaries and diminution in the time of loss of sodium fluorescein marker. The clinical data showed increased walking distance and diminished time to recover from pain, and the clinical improvement correlated with improved microcirculatory function. From these preliminary data has emerged an indication of therapy with PLC for chronic obstructive arteriopathy of the lower limbs at stage II. Further studies with higher numbers of patients and more controlled variables are planned.

Cellular properties of human erythrocytes preserved in saline-adenine-glucose-mannitol in the presence of L-carnitine

L-Carnitine (LC) in the preservation medium during storage of red blood cells (RBC) can improve the mean 24-hr percent recovery in vivo and increase RBC life-span after reinfusion. The purpose of the study was to investigate the differences in the biochemical properties of RBCs stored in the presence or absence of LC, and the cell-age related responses to storage conditions and to LC. RBC concentrates in saline-adenine-glucose-mannitol (SAG-M) were stored in the presence or absence of 5 mM LC at 4 degrees C for up to 8 weeks. RBC subpopulations of different densities were prepared by centrifugation on Stractan density gradient. Cells were sampled at 0, 3, 6, and 8 weeks, and hematological and cellular properties analyzed (MCV, MCHC, 4.1a/4.1b ratio as a cell age parameter, intracellular Na(+) and K(+)). After 6 weeks, MCV of RBC stored in the presence of LC was lower than that of controls (6 weeks MCV: controls 95.4 +/- 1.8 fl; LC 91.5 +/- 2.0 fl; n = 6; P < 0.005). This was due to swelling of control cells, and affected mainly older RBCs. LC appeared to reduce or retard cell swelling. Among the osmotically active substances whose changes during storage could contribute to cell swelling, only intracellular Na(+) and K(+) differed between stored control RBCs and LC-treated cells. LC reduces the swelling of older cells during storage at 4 degrees C in SAG-M, possibly by acting on the permeability of cell membrane to monovalent cations.

L-carnitine ameliorates abnormal vulnerability of steatotic rat livers to cold ischemic preservation

BACKGROUND

Up to 30% of all livers retrieved for organ transplantation exhibit steatotic transformations. Chronic organ-donor shortage has led to the acceptance of these organs for transplantation, although a higher risk of graft nonfunction is associated with the preservation of steatotic livers.

METHODS

A dietary steatosis was induced in Wistar rats by fasting them for 2 days and feeding them with a fat-free diet. Fatty livers (n=14) were retrieved and flushed with 60 mL of histidine, tryptophane, alpha-ketoglutarate (HTK) solution. In half of the experiments, L-carnitine (5 mM) was added to the HTK. Functional integrity of the livers was evaluated by isolated reperfusion with KHB in a recirculating system at 37 degrees C for 45 minutes.

RESULTS

Addition of L-carnitine to the HTK promoted a significant reduction of the enzyme leakage from the livers upon reperfusion. Release of alanine-aminotransferase was reduced to one third (127+/-22 vs. 423+/-61 U/L), and the loss of glutamate dehydrogenase in the perfusate could be reduced significantly (42+/-7 vs. 542+/-134 U/L) when compared with livers stored without additional medication. Morphologic corroboration of these data was obtained by electron microscopy. Although normal appearance of liver mitochondria was preserved at the end of the cold ischemic storage, reperfusion of cold-stored fatty livers entailed massive alterations and frequent destruction of hepatic mitochondria. However, these morphologic impairments were remarkably mitigated in the carnitine-treated group.

CONCLUSIONS

L-carnitine represents a feasible metabolic adjunct for a safe and more successful preservation of ischemia-reperfusion-sensitive steatotic livers.

L-carnitine treatment of anemia

Recombinant human erythropoietin (rHuEPO) and iron supplementation have had a profoundly positive impact on the anemia of patients with chronic kidney disease. However, a significant number of patients remain hyporesponsive to rHuEPO, with hemoglobin values less than target levels. A suboptimal response to rHuEPO is associated with complications that can reduce quality of life and increase morbidity, mortality, and costs. There are a number of other metabolic derangements associated with uremia that can impact on the production and survival of red blood cells. Dialysis-related carnitine disorder is a functional metabolic deficiency, common in chronic dialysis patients, that can have a negative impact on erythrocyte production and survival. This article reviews the role of L-carnitine in the pathogenesis and adjunctive treatment of anemia associated with kidney failure. After a comprehensive database search, primary and secondary reports were analyzed. Laboratory studies examining the influence of carnitine on red blood cell function and clinical trials of L-carnitine in dialysis patients support the use of L-carnitine in the setting of rHuEPO hyporesponsiveness. Consensus groups, including the National Kidney Foundation-Kidney Disease Outcome Quality Initiative (K/DOQI), consider the use of L-carnitine for hyporesponsive rHuEPO-dependent anemia a promising application of this therapy, recommending an empiric trial of L-carnitine in these patients.

Propionyl-L-carnitine prevents renal function deterioration due to ischemia/reperfusion

BACKGROUND

Ischemia-reperfusion injury after organ transplantation is a major cause of delayed graft function. Prevention of post-transplant ischemia acute renal failure is still elusive.

METHODS

The present study was designed to examine whether propionyl-l-carnitine, an acyl derivative of carnitine involved in fatty acid oxidation pathway and adenosine 5'-triphosphate (ATP) generation of mitochondria, prevented renal function deterioration and structural injury induced by ischemia-reperfusion in an ex vivo rat model of isolated perfused kidney (IPK) preparation and in vivo in a model of syngeneic kidney transplantation.

RESULTS

In the model of ischemia (20 or 40 min)/reperfusion (90 or 70 min) in IPK, untreated kidneys showed a marked reduction of glomerular filtration rate (GFR) and renal perfusate flow (RPF) as compared to baseline, when perfusion was established by restoring effective perfusion pressure to 100 mm Hg. Exposure of kidneys to propionyl-l-carnitine before establishing the ischemia insult to tissue, largely prevented renal function impairment. Pre-exposure of ischemic kidneys to propionyl-l-carnitine largely reduced the percent of lactate dehydrogenase (LDH), a cell injury marker, released into the perfusate after reperfusion as compared to untreated ischemic kidneys. Histologic findings showed very mild post-ischemic lesions in kidneys exposed to propionyl-l-carnitine as compared to untreated ischemic kidneys. Immunohistochemical detection of 4-hydroxynonenal protein adduct, a major product of lipid peroxidation, was very low in kidney infused with propionyl-l-carnitine and exposed to ischemia/reperfusion as compared to untreated ischemic kidneys. ATP levels were not affected by propionyl-l-carnitine treatment. Renal function of kidneys exposed for four hours to cold Belzer UW solution added with propionyl-l-carnitine and transplanted to binephrectomized recipients was largely preserved as compared to untreated ischemic grafts. Propionyl-l-carnitine almost completely prevented polymorphonuclear cell graft infiltration and reduced tubular injury at 16 hours post-transplant.

CONCLUSIONS

These data indicate that propionyl-l-carnitine is of value in preventing decline of renal function that occurs during ischemia-reperfusion. The beneficial effect of propionyl-l-carnitine possibly relates to lowering lipid peroxidation and free radical generation that eventually results in the preservation of tubular cell structure. The efficacy of propionyl-l-carnitine to modulate ischemia-reperfusion injury in these models opens new perspectives for preventing post-transplant delayed graft function.

Effects of L-carnitine on leukocyte function and viability in hemodialysis patients: A double-blind randomized trial

Excess morbidity and mortality among long-term hemodialysis patients because of infectious complications is partly caused by an impairment of cellular immune defense. We hypothesized this impairment is related to an abnormal carnitine metabolism also present in these patients. In a double-blind, randomized, placebo-controlled trial, we investigated the effect of L-carnitine on phagocytic function and viability of blood leukocytes in 17 patients undergoing maintenance hemodialysis. After an observation period of 1 month, the patients received either 10 mg/kg of L-carnitine or placebo intravenously at the end of each hemodialysis session over a period of 4 months. Leukocyte oxidative metabolism was measured by means of luminol-enhanced chemiluminescence and superoxide generation after stimulation with Staphylococcus aureus or phorbol myristate acetate. Killing capacity and phagocytosis of radiolabeled staphylococci were determined. A lactate dehydrogenase (LDH) release test was applied to assess cell viability. We were unable to show an effect of L-carnitine on phagocytic function and viability in vivo. Several clinical parameters were observed during the trial. No statistically significant differences concerning dialysis-related morbidity, anemia, or reduction of blood urea nitrogen and creatinine levels were detected. Additionally, we tested the effect of L-carnitine on phagocytic function after in vitro incubation of blood leukocytes, which also showed no changes. LDH release was decreased, indicating an improved viability of these cells. The latter results were found after in vitro incubation of cells, but could not be confirmed in vivo. In summary, we could not show beneficial effects of L-carnitine administration in hemodialysis patients for the dosage and duration of treatment stated, either on phagocytic function and viability or on the clinical and biochemical parameters observed.

The effect of chronic L-carnitine treatment on blood pressure and plasma lipids in spontaneously hypertensive rats

The effect of chronic L-carnitine treatment on blood pressure and plasma lipids was studied in spontaneously hypertensive rats (SHR). L-Carnitine treatment for 6 weeks lowered significantly both the systolic and mean arterial pressure of SHR but its influence on diastolic and pulse pressure was only modest. L-Carnitine did not influence the relative heart and kidney weight of SHR. However, L-carnitine completely abolished the age-dependent rise of plasma total cholesterol, triglycerides and uric acid seen in untreated SHR. On the other hand, L-carnitine treatment had no significant effects on blood pressure, relative organ weight and plasma lipids in normotensive Wistar-Kyoto rats. Our results suggest that L-carnitine might prevent some cardiovascular alterations by its influence on lipid metabolism.

Effects of propionyl-L-carnitine and insulin on the electroretinogram, nerve conduction and nerve blood flow in rats with streptozotocin-induced diabetes

The effect of an analogue of L-carnitine, propionyl-L-carnitine, on the electroretinogram, motor nerve conduction velocity and nerve blood flow was determined in rats with streptozotocin-induced diabetes, and was compared with the effects of insulin alone or combined therapy. Oral administration of propionyl-L-carnitine (3 g/kg daily for 4 weeks) significantly increased caudal nerve motor conduction velocity and sciatic nerve blood flow in diabetic rats. There were no differences in the effects of insulin (8-10 U daily for 4 weeks), propionyl-L-carnitine and combined therapy. Although propionyl-L-carnitine significantly shortened the peak latency of the electroretinogram b-wave in diabetic rats, its effect was far weaker than that of insulin or combined therapy, with combined therapy producing the greatest improvement. These effects of propionyl-L-carnitine were accompanied by a decrease of serum lipid levels, an increase of the sciatic nerve carnitine content, and no changes of the tissue (nerve and retinal) sorbitol and myo-inositol concentrations. In contrast, insulin significantly reduced the tissue sorbitol content and markedly increased myo-inositol. These findings suggest that propionyl-L-carnitine may improve diabetic neuropathy and retinopathy without influencing the polyol pathway, and that this beneficial effect may be mediated through the amelioration of microcirculation and tissue carnitine content, thus probably increasing fatty acid oxidation.

Effect of propionyl-L-carnitine treatment on membrane phospholipid fatty acid turnover in diabetic rat erythrocytes

In this work we have examined the effect of the oral administration of propionyl-L-carnitine (PLC) on the membrane phospholipid fatty acid turnover of erythrocytes from streptozotocin-induced diabetic rats. A statistically significant reduction in radioactive palmitate, oleate, and linoleate, but not arachidonate, incorporation into membrane phosphatidylcholine (PC) of diabetic rat erythrocytes with respect to control animals was found. Changes in radioactive fatty acid incorporation were also found in diabetic red cell phosphatidylethanolamine (PE), though they were not statistically significant. Oral propionyl-L-carnitine (PLC) treatment of diabetic rats partially restored the ability of intact red cells to reacylate membrane PC with palmitate and oleate, and reacylation with linoleate was fully restored. The analysis of the membrane phospholipid fatty acid composition revealed a consistent increase of linoleate levels in diabetic rat red cells, a modest decrease of palmitate, oleate and arachidonate. The phospholipid fatty acid composition of diabetic red blood cells was not affected by the PLC treatment. Lysophosphatidylcholine acyl-CoA transferase (LAT) specific activity measured with either palmitoyl-CoA or oleyl-CoA was significantly reduced in diabetic erythrocyte membranes in comparison to controls. In addition, LAT kinetic parameters of diabetic erythrocytes were altered. The reduced LAT activity could be partially corrected by PLC treatment of diabetic rats. Our data suggest that the impaired erythrocyte membrane physiological expression induced by the diabetic disease may be attenuated by the beneficial activity of PLC on the red cell membrane phospholipid fatty acid turnover.

Carnitine palmitoyl transferase-I activity in the aging mouse heart

We investigated the influence of age on carnitine palmitoyl transferase-I (CPT-I, EC 2.3.1.21) activity in the mouse heart. There was an age-associated decrease in CPT-I activity from 2 to 26 months (P = 0.006). We studied the effect of oxygen-derived radicals on CPT-I activity. Mitochondria from 2-month-old mouse hearts exposed to different concentrations of hydrogen peroxide (H2O2) showed a dose-related decrease in CPT-I activity (P < 0.002). To determine the possible reversibility of the age change in CPT-I activity, we studied the effect of oral administration of propionyl-L-carnitine (PLC). Oral pretreatment of middle-aged (18-month-old) mice with PLC resulted in a 37% increase of basal CPT-I activity (P < 0.05) compared to age-matched untreated animals, and restored it to a level similar to that of 2-month-old mice. Pretreatment of senescent (26-month-old) mice with PLC, however, showed no significant change in basal CPT-I activity. It is possible that the age-related decrease in CPT-I activity may result from an in vivo accumulation of oxygen-derived radical damage. It appears that the age change in CPT-I activity in 18- but not in the 26-month-old mice is reversible with PLC.

Sites of action of carnitine and its derivatives on the cardiovascular system: interactions with membranes

Carnitine plays an essential role in the regulation of long-chain fatty acid metabolism in skeletal and cardiac muscle, a process that is mediated by well-characterized enzymatic mechanisms. Here, Irving Fritz and Edoardo Arrigoni-Martelli review the evidence that carnitine and its O-acyl derivatives also influence membrane fluidity, ion channel functions, smooth muscle contractility, membrane stability and cardiac functions. The authors present the view that direct interactions of carnitine derivatives with cell membranes are independent of reactions catalysed by carnitine acyltransferases. They propose that the novel actions discussed are implicated in the mechanisms by which carnitine and its derivatives protect perfused hearts subjected to ischaemia or to oxidative stress, and help people suffering from certain types of myocardial ischaemia or peripheral arterial disease.