L-carnitine supplementation in humans. The effects on physical performance

Nutrition Supplements to Stimulate Lipolysis: A Review in Relation to Endurance Exercise Capacity

Athletes make great efforts to increase their endurance capacity in many ways. Using nutrition supplements for stimulating lipolysis is one such strategy to improve endurance performance. These supplements contain certain ingredients that affect fat metabolism; furthermore, in combination with endurance training, they tend to have additive effects. A large body of scientific evidence shows that nutrition supplements increase fat metabolism; however, the usefulness of lipolytic supplements as ergogenic functional foods remains controversial. The present review will describe the effectiveness of lipolytic supplements in fat metabolism and as an ergogenic aid for increasing endurance exercise capacity. There are a number of lipolytic supplements available on the market, but this review focuses on natural ingredients such as caffeine, green tea extract, L-carnitine, Garcinia cambogia (hydroxycitric acid), capsaicin, ginseng, taurine, silk peptides and octacosanol, all of which have shown scientific evidence of enhancing fat metabolism associated with improving endurance performance. We excluded some other supplements owing to lack of data on fat metabolism or endurance capacity. Based on the data in this review, we suggest that a caffeine and green tea extract improves endurance performance and enhances fat oxidation. Regarding other supplements, the data on their practical implications needs to be gathered, especially for athletes.

Effects of amino acid derivatives on physical, mental, and physiological activities

Nutritional ergogenic aids have been in use for a long time to enhance exercise and sports performance. Dietary components that exhibit ergogenic activity are numerous and their consumption is common and popular among athletes. They often come under scrutiny by legal authorities for their claimed benefits and safety concerns. Amino acid derivatives are propagated as being effective aids to enhance physical and mental performance in many ways, even though studies have pointed out that individuals who are deficient are more likely to benefit from dietary supplementation of amino acid derivatives than normal humans. In this review, some of the most common and widely used amino acids derivatives in sports and athletics namely creatine, tyrosine, carnitine, HMB, and taurine have been discussed for their effects on exercise performance, mental activity as well as body strength and composition. Creatine, carnitine, HMB, and taurine are reported to delay the onset of fatigue, improve exercise performance, and body strength. HMB helps in increasing fat-free mass and reduce exercise induced muscle injury. Taurine has been found to reduce oxidative stress during exercise and also act as an antihypertensive agent. Although, studies have not been able to find any favorable effect of tyrosine administration on exercise performance, it has been proved to be very effective in fighting stress, improving mood and cognitive performance particularly in sleep-deprived subjects. While available data from published studies and findings are equivocal about the efficacy of creatine, tyrosine, and HMB, more comprehensive researches on carnitine and taurine are necessary to provide evidence for the theoretical basis of their ergogenic role in nutritional modification and supplementation.

The influence of chronic L-carnitine supplementation on the formation of preneoplastic and atherosclerotic lesions in the colon and aorta of male F344 rats

L-Carnitine, a key component of fatty acid oxidation, is nowadays being extensively used as a nutritional supplement with allegedly "fat burning" and performance-enhancing properties, although to date there are no conclusive data supporting these claims. Furthermore, there is an inverse relationship between exogenous supplementation and bioavailability, i.e., fairly high oral doses are not fully absorbed and thus a significant amount of carnitine remains in the gut. Human and rat enterobacteria can degrade unabsorbed L-carnitine to trimethylamine or trimethylamine-N-oxide, which, under certain conditions, may be transformed to the known carcinogen N-nitrosodimethylamine. Recent findings indicate that trimethylamine-N-oxide might also be involved in the development of atherosclerotic lesions. We therefore investigated whether a 1-year administration of different L-carnitine concentrations (0, 1, 2 and 5 g/l) via drinking water leads to an increased incidence of preneoplastic lesions (so-called aberrant crypt foci) in the colon of Fischer 344 rats as well as to the appearance of atherosclerotic lesions in the aorta of these animals. No significant difference between the test groups regarding the formation of lesions in the colon and aorta of the rats was observed, suggesting that, under the given experimental conditions, L-carnitine up to a concentration of 5 g/l in the drinking water does not have adverse effects on the gastrointestinal and vascular system of Fischer 344 rats.

Manual therapy ameliorates delayed-onset muscle soreness and alters muscle metabolites in rats

Delayed-onset muscle soreness (DOMS) can be induced by lengthening contraction (LC); it can be characterized by tenderness and movement-related pain in the exercised muscle. Manual therapy (MT), including compression of exercised muscles, is widely used as physical rehabilitation to reduce pain and promote functional recovery. Although MT is beneficial for reducing musculoskeletal pain (i.e. DOMS), the physiological mechanisms of MT remain unclear. In the present study, we first developed an animal model of MT in DOMS; LC was applied to the rat gastrocnemius muscle under anesthesia, which induced mechanical hyperalgesia 2–4 days after LC. MT (manual compression) ameliorated mechanical hyperalgesia. Then, we used capillary electrophoresis time-of-flight mass spectroscopy (CE-TOFMS) to investigate early effects of MT on the metabolite profiles of the muscle experiencing DOMS. The rats were divided into the following three groups; (1) normal controls, (2) rats with LC application (LC group), and (3) rats undergoing MT after LC (LC + MT group). According to the CE-TOFMS analysis, a total of 171 metabolites were detected among the three groups, and 19 of these metabolites were significant among the groups. Furthermore, the concentrations of eight metabolites, including branched-chain amino acids, carnitine, and malic acid, were significantly different between the LC + MT and LC groups. The results suggest that MT significantly altered metabolite profiles in DOMS. According to our findings and previous data regarding metabolites in mitochondrial metabolism, the ameliorative effects of MT might be mediated partly through alterations in metabolites associated with mitochondrial respiration.

The effects of acute L-carnitine supplementation on endurance performance of athletes

This study examined the effect of acute L-carnitine loading on the endurance performance of footballers. Measurements were performed on 26 candidate professional footballers who volunteered to take part in the study. Athletes were given a glass of fruit juice 1 hour before applying L-carnitine with the double-blind method. Then, 12 participants were given 3 g of L-carnitine (LK-3) and the remaining 14 were given 4 g (LK-4). Athletes began the exercise test at a running speed of 8 km·h and then continued at 10 km·h. The speed was increased 1 km·h every 3 minutes, and the test continued until the subject chose to quit. Heart rate was registered using a portable telemetric heart rate monitor during the test. Blood samples were taken from the earlobes of the footballers both before the test and before the speed increase (during the 1-minute interval), and the lactate (La) concentration was measured electroenzymatically. The test was repeated after 1 week as a group of placebos (P-3 and P-4). The result showed that the running speeds corresponding to specific La concentrations were increased, and La and heart rate responses to the running speeds were decreased in both supplemented groups compared with placebos (p ≤ 0.05). A significant reduction in heart rate was found in LK-4 and P-4 (p ≤ 0.05). When the Borg responses to the running speeds were analyzed, a significant difference was found in both supplemented groups (p ≤ 0.05). The results show that 3 or 4 g of L-carnitine taken before physical exercise prolonged exhaustion.

The effects of L-carnitine on some hematological parameters in rats fed a cholesterol-rich diet

We evaluated the effects of L-carnitine on the hematological characteristics of rats fed a cholesterol-rich diet. Healthy male Wistar Albino rats were assigned to four equal groups. During the 40 day experiment, group 1 was fed standard rat pellets, group 2 was fed standard rat pellets containing 7.5 % cholesterol powder, group 3 was fed standard rat pellets and water that contained 75 mg/l L-carnitine, and group 4 was fed standard rat pellets that contained 7.5% cholesterol and water that contained 75 mg/l L-carnitine. Blood samples were analyzed for red (RBC) and white (WBC) blood cells, hemoglobin, hematocrit, granulocytes, lymphocytes, monocytes, mean cell volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC) using an automated cell counter. The RBC count in the group that received the 7.5% cholesterol diet was decreased significantly compared to the other groups. The hematocrit of the cholesterol group was lower than for the L-carnitine + cholesterol and L-carnitine groups. The MCV in the cholesterol group was significantly higher than the control group. The MCH in the cholesterol group was higher than for the other groups. There was no significant difference among the groups with regard to hemoglobin, MCHC, WBCs and leukocyte types. L-carnitine appears to have beneficial effects on erythrocyte stability, erythropoiesis and hyperlipidemia.

Effect of L-carnitine therapy on patients in maintenance hemodialysis: a systematic review and meta-analysis

BACKGROUND

L-Carnitine has been used as adjuvant therapy in hemodialysis (HD) patients for many years. However, there is controversy whether L-carnitine supplementation is beneficial. Therefore we performed a meta-analysis of randomized controlled trials (RCTs) to assess the effect of L-carnitine on HD patients.

METHODS

RCTs of L-carnitine versus placebo for HD patients were searched from Medline, EMBASE and the Cochrane Central Register of Controlled Trials. We screened relevant studies according to predefined inclusion and exclusion criteria, and performed meta-analyses using Revman 5.1 software.

RESULTS

Meta-analysis showed L-carnitine could not increase the total score of 36-item Short-Form Health Survey Questionnaire (SF-36) (SMD 0.76, 95 % CI -0.13 to 1.65, P = 0.09), and L-carnitine therapy did not improve serum C-reactive protein (SMD -0.37, 95 % CI -0.88 to 0.14, P = 0.16), oxidized low-density lipoprotein (SMD 0.04, 95 % CI -0.43 to 0.50, P = 0.87), albumin (SMD 0.25, 95 % CI -0.31 to 0.81, P = 0.38;), hemoglobin (SMD 0.23, 95 % CI -0.23 to 0.68, P = 0.33), cholesterol (SMD -0.24, 95 % CI -0.71 to 0.24, P = 0.33), triglycerides (SMD 0.02, 95 % CI -0.4 to 0.44, P = 0.91) or parathyroid hormone (SMD 0.21, 95 % CI -0.35 to 0.76, P = 0.46) levels.

CONCLUSIONS

There is no evidence that L-carnitine can improve the inflammation, oxidative stress, nutrition, anemia, dyslipidemia, hyperparathyroidism status or quality of life in HD patients. However, given methodological limitations and lack of hard endpoints, high-quality, long-term randomized trials are required to fully elucidate the clinical value of L-carnitine administration in hemodialysis patients.

Análise do potencial mutagênico dos esteroides anabólicos androgênicos (EAA) e da l-carnitina mediante o teste do micronúcleo em eritrócitos policromáticos

INTRODUÇÃO: Os esteroides anabólicos androgênicos são usados por pessoas que desejam aumentar sua massa muscular para obter um melhor desempenho nos esportes ou melhorar a aparência física. Os EAA são derivados sintéticos da testosterona, capazes de promover a hipertrofia das fibras musculares, aumentando a síntese proteica intracelular. A L-carnitina é um suplemento alimentar empregado para aumentar a produção energética por meio da oxidação de ácidos graxos. Embora haja trabalhos mostrando as propriedades fisiológicas dessas drogas, há poucos estudos sobre o potencial mutagênico das mesmas. OBJETIVOS: Este trabalho avaliou a clastogenicidade e genotoxicidade do decanoato de nandrolona, decanoato de testosterona e da L-carnitina, em diferentes tratamentos, através do teste do micronúcleo em eritrócitos policromáticos de ratos Wistar. MÉTODOS: Os animais foram submetidos a diferentes concentrações e associações de EAA. O controle positivo recebeu ciclofosfamida 50 mg/kg através de injeção intraperitoneal e o controle negativo, 1 ml de soro fisiológico por gavagem. Os ratos foram sacrificados após 36 horas da última aplicação, tendo seus fêmures removidos e a medula óssea extraída. O material foi homogeneizado e centrifugado. O botão de células foi pipetado e transferido para as lâminas, que foram coradas com Giemsa. Foram contados 1.000 eritrócitos policromáticos por animal, observando a frequência de micronúcleos. RESULTADOS: Foi realizado o teste de Kruskal-Wallis, com nível de significância de 5%, que demostrou que o decanoato de nandrolona - três doses de 0,2 mg/kg e 0,6 mg/kg, oito doses de 7,5 mg/kg, L-carnitina - sete doses de 0,4 ml/250g e 1,5 ml/250g, decanoato de testosterona - 28 doses de 0,075 mg/kg, decanoato de nandrolona - oito doses de 7,5 mg/kg associado a L-carnitina 1 ml e decanoato de nandrolona - oito doses de 7,5 mg/kg associado à decanoato de testosterona - oito doses de 7,5 mg/kg apresentaram potencial mutagênico. CONCLUSÃO: Os tratamentos revelaram-se clastogênicos, não sendo indicado como recurso ergogênico.

A suplementação de L-carnitina não promove alterações na taxa metabólica de repouso e na utilização dos substratos energéticos em indivíduos ativos

OBJETIVO: Avaliar o efeito da suplementação de L-carnitina, por 30 dias, sobre a taxa metabólica de repouso (TMR) e oxidação de ácidos graxos livres (AGL), em repouso e exercício. SUJEITOS E MÉTODOS: Vinte e um voluntários ativos (40 a 58 anos) com sobrepeso foram randomizados em dois grupos: suplementado (GS; N = 11; 1,8 g/dia de L-carnitina) e placebo (GP; N = 10; maltodextrina). Foi feita avaliação da ingestão calórica, antropometria, determinação da TMR, VO2máx, quociente respiratório e AGL plasmáticos. RESULTADOS: Não houve diferença significativa na ingestão (-244,66 vs. -126,00 kcal/dia), composição corporal (-0,07 vs. -0,17 kg/m²), TMR (0,06 vs. -0,02 kcal/ dia), quociente respiratório em repouso (3,69 vs. -1,01) e exercício (0,01 vs. -0,01) e VO2máx (0,50 vs. 1,25 mL/kg/min) para o grupo GS em relação ao GP. Houve aumento dos AGL em repouso no GP (0,27), porém sem diferenças no exercício para os grupos. CONCLUSÃO: Não houve efeito da L-carnitina em nenhuma das variáveis analisadas no estudo.

L-carnitine modulates blood platelet oxidative stress

The oxidative stress induced by acute exertion may interfere with blood platelet activation. The beneficial effect of L-carnitine (gamma-trimethylamino-beta-hydroxybutyric acid) on oxidative stress in blood platelets has not been fully investigated; however, different studies indicate that this compound modulates platelet functions. The aim of our study was to assess the effects of L-carnitine on platelet activation and oxidative/nitrative protein damage (determined by the levels of protein carbonyl groups, thiol groups, and 3-nitrotyrosine residues) in resting blood platelets or platelets treated with peroxynitrite (ONOO(-), a strong physiological oxidant) in vitro. We also investigated the effects of L-carnitine on the level of platelet glutathione and on the formation of superoxide anion radicals O2(-*), lipid peroxidation measured by thiobarbituric acid reactive substances (TBARS) in blood platelets stimulated by thrombin (a strong physiological agonist), and platelet aggregation induced by adenosine diphosphate (a strong physiological stimulator). We have observed that carnitine decreases platelet activation (measured by platelet aggregation, the generation of O2(-*), and TBARS production). Moreover, our results in vitro demonstrate that carnitine may protect against oxidation of thiol groups induced by ONOO(-). Thus, carnitine may have some protectory effects against oxidative changes induced in blood platelets.

The role of nutritional supplements and feeding strategies in equine athletic performance

In human and animal nutrition, much interest has been focused on the potential role of dietary supplements in promoting health, athletic performance and disease mitigation. Supplements may include essential nutrients provided in amounts greater than required to prevent a deficiency state, or substances purported to have a role in metabolism or tissue function but that are not recognized as an essential nutrient. This review aims to provide the rationale and scientific evidence for use (or not) of some of the supplements marketed for use in horses, with emphasis on supplements purported to directly boost performance, such as creatine, carnitine and branched-chain amino acids. It also discusses the so-called ‘joint supplements’ (or slow-acting, disease-modifying osteoarthritis agents), such as glucosamine and chondroitin sulphate. The effects of selected feeding strategies on performance, including fat supplementation, are also examined. It is concluded that although the use of nutritional supplements is commonly alleged to boost performance or health in horses, for most, if not all, of these supplements there is little or no scientific evidence of efficacy.

Exercise and functional foods

Appropriate nutrition is an essential prerequisite for effective improvement of athletic performance, conditioning, recovery from fatigue after exercise, and avoidance of injury. Nutritional supplements containing carbohydrates, proteins, vitamins, and minerals have been widely used in various sporting fields to provide a boost to the recommended daily allowance. In addition, several natural food components have been found to show physiological effects, and some of them are considered to be useful for promoting exercise performance or for prevention of injury. However, these foods should only be used when there is clear scientific evidence and with understanding of the physiological changes caused by exercise. This article describes various "functional foods" that have been reported to be effective for improving exercise performance or health promotion, along with the relevant physiological changes that occur during exercise.

Effect of propionylcarnitine on changes in endothelial function and plasma levels of adhesion molecules induced by acute exercise in patients with intermittent claudication

In patients with intermittent claudication, treadmill exercise may cause acute deterioration of endothelial function and increase in plasma concentrations of adhesion molecules. The authors evaluated the efficacy of intravenously administered propionylcarnitine (PLC)in preventing these phenomena. Thirty-six claudicants with postexercise decrease in brachial artery flow-mediated dilation (FMD)were randomized to either placebo or PLC (600 mg as a single bolus followed by 1 mg/kg/min for 60 minutes).In the 18 patients randomized to placebo, FMD markedly decreased with exercise before (from 6.8 +/-0.4% to 4.0 +/-0.4%; p < 0.001) and after treatment (from 6.5 +/-0.4% to 4.4 +/-0.5%; p < 0.001). By contrast, in the PLC group, FMD significantly decreased with exercise before treatment (from 8.0 +/-0.7% to 4.4 +/-0.4%; p < 0.001), but not after active drug administration (from 7.1 +/-0.7% to 6.0 +/-0.6%; p = 0.067). The difference between treatments was not significant (p = 0.099; ANOVA). However, in the PLC group, the authors found that the greater the exercise-induced deterioration in endothelial function before treatment, the greater the capacity of PLC to prevent a postexercise decrease in FMD (r = -0.50, p = 0.034). Accordingly, they analyzed data in the 19 patients with a baseline exercise-induced decrease in FMD >or=45% (ie, the median FMD reduction in the entire group of 36 patients), and found that the exercise-induced FMD decrease was less after PLC than after placebo (p = 0.046, ANOVA). In the same subgroup, the exercise-induced increase in plasma concentrations of soluble vascular cell adhesion molecule-1 (sVCAM-1) was significantly higher before than after treatment in patients randomized to PLC (23.4 +/-5% vs 15.3 +/-7%, p = 0.007). In conclusion, in patients with intermittent claudication suffering from a greater endothelial derangement after treadmill, PLC administration provided a protective effect against deterioration of FMD and increase of sVCAM-1 induced by exercise.

Aplicações clínicas da suplementação de L-carnitina

A carnitina, uma amina quaternária (3-hidroxi-4-N-trimetilamino-butirato), é sintetizada no organismo (fígado, rins e cérebro) a partir de dois aminoácidos essenciais: lisina e metionina, exigindo para sua síntese a presença de ferro, ácido ascórbico, niacina e vitamina B6. Tem função fundamental na geração de energia pela célula, pois age nas reações transferidoras de ácidos graxos livres do citosol para mitocôndrias, facilitando sua oxidação e geração de adenosina Trifosfato. A concentração orgânica de carnitina é resultado de processos metabólicos - como ingestão, biossíntese, transporte dentro e fora dos tecidos e excreção - que, quando alterados em função de diversas doenças, levam a um estado carencial de carnitina com prejuízos relacionados ao metabolismo de lipídeos. A suplementação de L-carnitina pode aumentar o fluxo sangüíneo aos músculos devido também ao seu efeito vasodilatador e antioxidante, reduzindo algumas complicações de doenças isquêmicas, como a doença arterial coronariana, e as conseqüências da neuropatia diabética. Por esse motivo, o objetivo do presente trabalho foi descrever possíveis benefícios da suplementação de carnitina nos indivíduos com necessidades especiais e susceptíveis a carências de carnitina, como os portadores de doenças renais, neuropatia diabética, síndrome da imunodefeciência adquirida e doenças cardiovasculares.

Supplementation of L-carnitine in athletes: does it make sense?

Studies in athletes have shown that carnitine supplementation may foster exercise performance. As reported in the majority of studies, an increase in maximal oxygen consumption and a lowering of the respiratory quotient indicate that dietary carnitine has the potential to stimulate lipid metabolism. Treatment with L-carnitine also has been shown to induce a significant postexercise decrease in plasma lactate, which is formed and used continuously under fully aerobic conditions. Data from preliminary studies have indicated that L-carnitine supplementation can attenuate the deleterious effects of hypoxic training and speed up recovery from exercise stress. Recent data have indicated that L-carnitine plays a decisive role in the prevention of cellular damage and favorably affects recovery from exercise stress. Uptake of L-carnitine by blood cells may induce at least three mechanisms: 1) stimulation of hematopoiesis, 2) a dose-dependent inhibition of collagen-induced platelet aggregation, and 3) the prevention of programmed cell death in immune cells. As recently shown, carnitine has direct effects in regulation of gene expression (i.e., carnitine-acyltransferases) and may also exert effects via modulating intracellular fatty acid concentration. Thus there is evidence for a beneficial effect of L-carnitine supplementation in training, competition, and recovery from strenuous exercise and in regenerative athletics.

Does exercise training interfere with the effects of L-carnitine supplementation?

OBJECTIVE

We investigated the effect of L-carnitine supplementation on carnitine content in muscle fiber, glucose, and fatty acid metabolism and on performance in trained rats.

METHODS

Male Wistar rats received a daily dose of 28 mg/kg, intragastrically, during the last 4 wk of a 6-wk moderate-intensity training program. The contents of carnitine and coenzyme A were evaluated in muscle fiber and its capacity to metabolize labeled glucose, oleate, and pyruvate. The ergogenic effect of the amine was assessed by the evaluation of time until exhaustion in an exercise session. The results were analyzed by analysis of variance and Tukey's post hoc test, and significance was set at P < 0.05.

RESULTS

In our model, carnitine supplementation increased time until exhaustion (14.0%), similar to that observed for trained rats, but the effect was even greater (30.3% increase) in the supplemented and trained rats. Carnitine supplementation increased oleate decarboxylation (17% for sedentary rats and 119% for trained rats) and decreased glucose (29.7% and 45% for sedentary and trained rats, respectively) and [2-(14)C ]-pyruvate (45.9% and 61% for sedentary and trained rats, respectively) decarboxylation. The flux of [1-(14)C]-pyruvate through the Krebs cycle increased by 32% and 70% for supplemented sedentary and trained rats, respectively. The training protocol also increased [1-(14)C]-pyruvate decarboxylation by 32%. The cytosolic content of free, long-chain, and short-chain acyl-carnitine increased in the soleus muscle obtained from supplemented sedentary rats by 28%, 117%, and 16%, respectively, and 99%, 205%, and 32% for the muscle from supplemented trained rats.

CONCLUSIONS

This study showed that carnitine supplementation increases fatty acid oxidation in skeletal muscle by a mechanism that includes increasing total carnitine content in soleus muscle mitochondria and the total content of acyl-carnitine. The most interesting finding was that the effect of supplementation was even greater in trained rats that had received 3-wk supplementation of carnitine.

Metabolic functions of L-carnitine and its effects as feed additive in horses. A review

L-carnitine, a betaine derivative of beta-hydroxybutyrate, is found in virtually all cells of higher animals and also in some microorganisms and plants. In animals it is synthesized almost exclusively in the liver. Two essential amino acids, i.e., lysine and methionine serve as primary substrates for its biosynthesis. Also required for its synthesis are sufficient amounts of vitamin B6, nicotinic acids, vitamin C and folate. The first discovered ergogenic function of L-carnitine is the transfer of activated long-chain fatty acids across the inner mitochondrial membrane into the mitochondrial matrix. For this transfer acyl-CoA esters are transesterified to form acylcarnitine esters. Thus, in carnitine deficiency fat oxidation and energy production from fatty acids are markedly impaired. Skeletal muscles constitute the main reservoir of carnitine in the body and have a carnitine concentration at least 200 times higher than blood plasma. Uptake of carnitine by skeletal muscles takes place by an active transport mechanism which transports L-carnitine into muscles probably in the form of an exchange process with gamma-butyrobetain. In young animals including foals, the capacity for biosynthesis of carnitine is not yet fully developed and apparently cannot meet the requirements of sucking animals. Sucking animals depend therefore on an extra supply of carnitine which is usually provided with milk. Additionally, young animals including foals possess a lower concentration of carnitine in blood plasma than adult animals. Besides its role as carrier of activated acyl groups, L-carnitine functions as a buffer for acetyl groups which may be present in excess in different tissues during ketosis and hypoxic muscular activity. Other functions of L-carnitine are protection of membrane structures, stabilizing of a physiologic CoA-SH/acetyl-CoA ratio and reduction of lactate production. Animal's derived feeds are rich in L-carnitine whereas plants contain usually very little or no carnitine. Carnitine is absorbed from the small intestine by active and passive transport mechanisms. From the increase in renal excretion of L-carnitine after oral supplementations of 10 g/d to horses it has been concluded that the efficiency of absorption of L-carnitine is rather low (about 5 to 10% of the supplied dose). A further decrease in fractional carnitine absorption was observed when the oral dose of carnitine was increased. L-carnitine is virtually not degraded in the body and renal excretion of carnitine is comparatively small under normal conditions. The concentration of L-carnitine in blood plasma of horses varies markedly between animals and between different days. In addition, circadian changes in carnitine concentration in plasma have been reported. Peak concentrations were found during late afternoon, being up to 30% higher than those in the morning. In breeding mares the carnitine concentration in blood plasma declines with onset of lactation. In resting skeletal muscles about 90% of the total carnitine content is present as free carnitine with the remaining part being available as carnitine esters. With increasing exercise intensity a continuing greater proportion of free carnitine (up to 80%) is converted into carnitine esters, mainly into acetylcarnitine. This shift from free to acetylcarnitine is readily reversed within about 30 min after termination of exercise. It appears that acute exercise does not have a marked effect on the content of total carnitine in skeletal muscle whereas training seems to elevate its total concentration in the middle gluteal muscle of 3 to 6 year old horses and to reduce variation of its concentration compared to age-matched untrained horses. Oral supplementations of 5 to 50 g of L-carnitine per day to horses elevated the carnitine concentration in blood plasma to about twice its basal concentration. No clear relationship existed, however, between the orally administered dose of carnitine and the increase of L-carni

Inhibition of platelet-activating factor synthesis in human neutrophils and platelets by propionyl-L-carnitine

Propionyl-L-carnitine (PrC) has been shown to exert beneficial effects in the treatment of myocardial and peripheral ischemia in man. These conditions are associated with the activation of circulating neutrophils and platelets. To determine whether PrC could affect the synthesis of lipid mediators known to influence neutrophil and platelet functions, we explored the effects of PrC on the synthesis of platelet-activating factor (PAF) and arachidonic acid (AA) metabolites. Preincubation (90 min) of human neutrophils with PrC (0.1-100 microM) inhibited the synthesis of PAF and of a PAF analog (1-alkyl-1'enyl-2-acetyl-sn-glycero-3-phosphoethanolamine: AEGPE) induced in vitro by the calcium ionophore A23187. In contrast, concentrations of PrC up to 100 microM did not influence the uptake of exogenous AA or the A23187-induced release of AA and eicosanoids from neutrophils in vitro. PrC (1 microM) also inhibited PAF synthesis from human platelets stimulated in vitro with thrombin, but had no effect on thrombin-induced aggregation. Oral administration of PrC (2 g/day for two weeks) to five normal volunteers resulted in a significant inhibition of PAF and AEGPE synthesis by neutrophils stimulated with A23187 ex vivo, with no effect on AA or eicosanoid release. These data indicate that PrC selectively inhibits in vitro and ex vivo PAF synthesis from human neutrophils and platelets without influencing AA metabolism or eicosanoid release. This effect of PrC might represent an additional mechanism by which this molecule can exert protective effects in tissue ischemia and in other inflammatory diseases associated with neutrophil and platelet activation.

Free carnitine and acetyl carnitine plasma levels and their relationship with body muscular mass in athletes

The purpose of the present study was to investigate the relationship between plasma carnitine concentration and body composition variation in relation to muscular and fat masses since there is no experimentally proved correlation between plasma carnitine and body masses. We used bioelectric impedance analysis (BIA), to determine body composition and to have a complete physical fitness evaluation. The post-absorptive plasma free carnitine and acetyl carnitine plasma levels, body composition as Fat-Free Mass (FFM) and Fat Mass (FM) in kg, as well as in percent of body mass, were analysed in 33 healthy subjects. A significant negative correlation was found between plasma acetyl carnitine and FFM in weight (kg) as well as in percent of body mass (respectively p < 0.0001; p < 0.01); a significant positive correlation was found only between FM in percent and plasma acetyl carnitine (p < 0.01). The observed negative correlation between plasma acetyl carnitine and muscular mass variation might reflect an oxidative metabolic muscle improvement in relation to muscular fat free mass increment and might be evidence that muscle metabolism change is in relation to plasma acetyl carnitine concentration.

The role of carnitine and carnitine supplementation during exercise in man and in individuals with special needs

Carnitine is critical for normal skeletal muscle bioenergetics. Carnitine has a dual role as it is required for long-chain fatty acid oxidation, and also shuttles accumulated acyl groups out of the mitochondria. Muscle requires optimization of both of these metabolic processes during peak exercise performance. Theoretically, carnitine availability may become limiting for either fatty acid oxidation or the removal of acyl-CoAs during exercise. Despite the theoretical basis for carnitine supplementation in otherwise healthy persons to improve exercise performance, clinical data have not demonstrated consistent benefits of carnitine administration. Additionally, most of the anticipated metabolic effects of carnitine supplementation have not been observed in healthy persons. The failure to demonstrate clinical efficacy of carnitine may reflect the complex pharmacokinetics and pharmacodynamics of carnitine supplementation, the challenges of clinical trial design for performance endpoints, or the adequacy of endogenous carnitine content to meet even extreme metabolic demands in the healthy state. In patients with end stage renal disease there is evidence of impaired cellular metabolism, the accumulation of metabolic intermediates and increased carnitine demands to support acylcarnitine production. Years of nutritional changes and dialysis therapy may also lower skeletal muscle carnitine content in these patients. Preliminary data have demonstrated beneficial effects of carnitine supplementation to improve muscle function and exercise capacity in these patients. Peripheral arterial disease (PAD) is also associated with altered muscle metabolic function and endogenous acylcarnitine accumulation. Therapy with either carnitine or propionylcarnitine has been shown to increase claudication-limited exercise capacity in patients with PAD. Further clinical research is needed to define the optimal use of carnitine and acylcarnitines as therapeutic modalities to improve exercise performance in disease states, and any potential benefit in healthy individuals.

Nitric oxide deficiency, leukocyte activation, and resultant ischemia are crucial to the pathogenesis of diabetic retinopathy/neuropathy--preventive potential of antioxidants, essential fatty acids, chromium, ginkgolides, and pentoxifylline

Impaired microcirculatory perfusion appears to be crucial to the pathogenesis of both neuropathy and retinopathy in diabetics. This in turn reflects a hyperglycemically mediated perturbation of vascular endothelial function that entails overactivation of protein kinase C, reduced availability of nitric oxide, increased production of superoxide and endothelin, impaired insulin function, diminished synthesis of prostacyclin/PGE1, and increased activation and endothelial adherence of leukocytes. These dysfunctions may be addressed with a supplementation program that includes high-dose antioxidants, fish oil, gamma-linolenic acid, chromium, arginine, carnitine, and ginkgolides. Pharmaceuticals likely to be of benefit in this regard include pentoxifylline, probucol, replacement estrogens, and inhibitors of angiotensin converting enzyme and aldose reductase.

The reduction of heat production in exercising pigeons after L-carnitine supplementation

Four groups (CS,CR,PS,PR) of nine trained male racing pigeons were deprived of feed for 1 d and then subjected to a respiration chamber test in order to study the effect of oral 1-carnitine supplementation on the energy metabolism during flight. One week before, groups CS and CR were orally supplemented with 90 mg of 1-carnitine daily, whereas PS and PR were given a placebo. Groups CS and PS underwent flight simulation by electrostimulation of the breast muscles. Flight simulation increased heat production, kept respiratory quotient from decreasing, decreased thyroxine levels, and increased weight loss. L-Carnitine decreased the rise in heat production during electrostimulation but did not influence respiratory quotient, weight loss, or thyroid hormones. L-Carnitine supplementation in pigeons improves fatty acid combustion efficiency during heavy exercise.

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.

Nutrition for improved sports performance. Current issues on ergogenic aids

Several nutritional modifications have been used by athletes to improve performance. Recent attention has focused on high fat diets, branched-chain amino acids, creatine, carnitine, bicarbonate and phosphate loading, and caffeine. Of these, only caffeine, which is present in food but has no known nutritional value, appears on the list of substances banned by the International Olympic Committee (IOC). While there is a theoretical basis for each of these diet manipulations to enhance performance, there are insufficient data to state unequivocally that high fat diets, branched-chain amino acids, carnitine or phosphate loading are effective. Caffeine has been found to enhance endurance performance, while creatine and bicarbonate loading were generally found to benefit short term strenuous exercise. Acute ingestion of these diet manipulations appears safe, although some, like caffeine and bicarbonate, can cause gastrointestinal disturbances or other problems in certain individuals. Long term use of high fat diets may have negative consequences on health. The safety of long term use of these diet manipulations has not been established.

Effects of L-carnitine supplementation on physical performance and energy metabolism of endurance-trained athletes: a double-blind crossover field study

A double-blind crossover field study was performed to investigate the effects of acute L-carnitine supplementation on metabolism and performance of endurance-trained athletes during and after a marathon run. Seven male subjects were given supplements of 2 g L-carnitine 2 h before the start of a marathon run and again after 20 km of the run. The plasma concentration of metabolites and hormones was analysed 1 h before, immediately after and 1 h after the run, as well as the next morning after the run. In addition, the respiratory exchange ratio (R) was determined before and at the end of the run, and a submaximal performance test was completed on a treadmill the morning after the run. The administration of L-carnitine was associated with a significant increase in the plasma concentration of all analysed carnitine fractions (i.e. free carnitine, short-chain acylcarnitine, long-chain acylcarnitine, total acid soluble carnitine, total carnitine) but caused no significant change in marathon running time, in R, in the plasma concentrations of carbohydrate metabolites (glucose, lactate, pyruvate), of fat metabolites (free fatty acids, glycerol, beta-hydroxybutyrate), of hormones (insulin, glucagon, cortisol), and of enzyme activities (creatine kinase, lactate dehydrogenase). Moreover, there was no difference in the result of the submaximal performance test the morning after the run. In conclusion, acute administration of L-carnitine did not affect the metabolism or improve the physical performance of the endurance-trained athletes during the run and did not alter their recovery.

Fish oil and other nutritional adjuvants for treatment of congestive heart failure

Published clinical research, as well as various theoretical considerations, suggest that supplemental intakes of the 'metavitamins' taurine, coenzyme Q10, and L-carnitine, as well as of the minerals magnesium, potassium, and chromium, may be of therapeutic benefit in congestive heart failure. High intakes of fish oil may likewise be beneficial in this syndrome. Fish oil may decrease cardiac afterload by an antivasopressor action and by reducing blood viscosity, may reduce arrhythmic risk despite supporting the heart's beta-adrenergic responsiveness, may decrease fibrotic cardiac remodeling by impeding the action of angiotensin II and, in patients with coronary disease, may reduce the risk of atherothrombotic ischemic complications. Since the measures recommended here are nutritional and carry little if any toxic risk, there is no reason why their joint application should not be studied as a comprehensive nutritional therapy for congestive heart failure.

The prediction of power and efficiency during near-maximal rowing

The relationship between power and gross efficiency during near-maximal rowing, and physiological measures of strength, power, aerobic and anaerobic capacities and United State Rowing Association (USRA) performance tests (independent variables) was investigated among collegiate male rowers. Criterion measures of rowing power and gross efficiency were measured in a moving-water rowing tank, using an oar instrumented with strain gauges to assess force and a potentiometer to assess oar position. Bivariate correlation analysis (n = 28) indicated no relationship between the independent variables and rowing gross efficiency (P > 0.05). Rowing power [mean (SD) 483.4 (34.75) W] was significantly related to inboard leg extension strength (IL strength, r = 0.63), outboard leg extension strength (r = 0.45), combined leg extension strength (r = 0.45), and time to complete the USRA 2000-m simulated rowing race (r = -0.52; P <0.05). Stepwise regression using resampling cross-validation of 15 random samples (21 subjects per sample selected from a total group of 28 intercollegiate oarsmen) indicated that predictors of rowing power were IL strength and blood lactate following a peak oxygen uptake rowing test with significant multiple correlations of R 0.61 to 0.86 (P <0.05). The standard error of estimate (SEM) ranged from 18.1 to 29.9 W, or 5.3 (0.77) percent of the criterion value. Cross-validation with a hold-out group (seven subjects per sample) was performed for each equation and correlations ranged from R = 0.14 to 0.97 (SEM = 8.0 to 38.9 W). In conclusion, data from the present study suggest that to increase rowing power, training should emphasize leg strength and anaerobic training to decrease the level of lactate accumulated during rowing.

Inhibition of citrate lyase may aid aerobic endurance

Owing to a substantial increase in glucose uptake by working muscle, glucose homeostasis during sustained aerobic exercise requires a severalfold increase in hepatic glucose output. As exercise continues and liver glycogen declines, an increasing proportion of this elevated glucose output must be provided by gluconeogenesis. Increased gluconeogenic efficiency in trained individuals is a key adaptation promoting increased endurance, since failure of hepatic glucose output to keep pace with muscle uptake rapidly leads to hypoglycaemia and exhaustion. Pre-administration of (-)-hydroxycitrate, a potent inhibitor of citrate lyase found in fruits of the genus Garcinia, may aid endurance during post-absorptive aerobic exercise by promoting gluconeogenesis. Carnitine and bioactive chromium may potentiate this benefit. The utility of this technique may be greatest in exercise regimens designed to promote weight loss.

Nutritional ergogenics in athletics

Nutritional ergogenic aids may be theorized to improve performance in athletics in a variety of ways, primarily by enhancing energy efficiency, energy control or energy production. Athletes have utilized almost every nutrient possible, ranging from amino acids to zinc, as well as numerous purported nutritional substances, such as ginseng, in attempts to enhance physical performance. This review focuses primarily on nutritional ergogenic aids thought to enhance performance by favourably affecting energy metabolism. Although most purported nutritional ergogenic aids have not been shown to enhance physical performance in well-trained, well-nourished athletes, some reliable scientific data support an ergogenic efficacy of several substances, including caffeine, creatine and sodium bicarbonate, but additional research is needed to evaluate their potential for enhancing performance in specific athletics events.

Reduction of free fatty acids may ameliorate risk factors associated with abdominal obesity

Experimental data as well as logical considerations suggest that the increased cardiovascular risk associated with abdominal obesity is mediated primarily by increased levels and flux of free fatty acids. Practical strategies for decreasing free fatty acid levels and/or flux may include: a very-low-fat, low-glycemic-index diet; promotion of insulin sensitivity (via exercise training, chromium, soluble fiber or drugs); anti-lipolytic agents; and stimulation of hepatic lipid oxidation with hydroxycitrate, carnitine and possibly fish omega-3s. Fortunately, many of these measures should also promote a leaner physique. Thus, even when abdominal obesity cannot be corrected, it may prove feasible to mitigate its dangers.

Urinary carnitine excretion in patients with heart failure

To evaluate the fatty acid metabolism in heart failure, the semiquantitative analysis of urinary free carnitine and acylcarnitine was made by fast atom bombardment mass spectrometry (FABMS) in 22 patients (mean age 67.3 years) with heart failure and 19 age-matched healthy controls (average age 60.4 years). Urinary excretion of free carnitine was 0.20 +/- 0.118 ratio/mg creatinine in the healthy controls and 1.32 +/- 1.170 ratio/mg creatinine in the patients with heart failure. The latter value was significantly higher (p < 0.01). Patients with heart failure were classified into two groups according to the urinary free carnitine concentration. One was the high excretion group (2.19 +/- 0.102 ratio/mg creatinine, 12 cases) and the other was the low excretion group (0.37 +/- 0.212 ratio/mg creatinine, 10 cases). In the high excretion group, urinary acetylcarnitine was also increased, but no significant abnormalities were observed in the urinary organic acid profile. In the high group, 1 patient was classified as NYHA class III and 11 as NYHA class IV. Four patients died in the hospital. In the low excretion group, five patients were classified as NYHA class III and five as NYHA class IV. Only one patient died in the hospital. In the high group, patients with severe and prolonged heart failure tended to maintain higher values of urinary free carnitine. We could not find any abnormalities in fatty acid metabolism in patients with heart failure, but it is suspected that the patients who excrete large amounts of free carnitine into the urine, namely the patients with severe heart failure, have some possibility of carnitine deficiency.

Promotion of hepatic lipid oxidation and gluconeogenesis as a strategy for appetite control

There is considerable evidence that hepatic vagal afferents monitor the availability of liver glycogen and glucose metabolites, and that this mechanism participates in appetite regulation. Thus, promotion of gluconeogenesis and liver glycogen storage may enhance satiety. Hepatic lipid oxidation drives gluconeogenesis by positive allosteric modulation of pyruvate carboxylase and fructodiphosphatase. The rate-limiting enzyme for hepatic lipid oxidation, carnitine acyltransferase I, is activated by exogenous carnitine, and inhibited by malonyl coA. The lipogenesis inhibitor (-)-hydroxycitrate--a natural fruit acid found in the Brindall berry--can decrease production of malonyl coA in hepatocytes by potent inhibition of citrate lyase; many studies demonstrate that (-)-hydroxycitrate can reduce body fat accumulation in growing rats, owing in large part to a reduction in appetite. Joint administration of (-)-hydroxycitrate and carnitine should therefore promote hepatic lipid oxidation, gluconeogenesis, and satiety. Thermogenic effects as well as a reduction of the respiratory quotient can also be predicted. If this technique proves clinically useful in weight management, it could be used in conjunction with chromium picolinate and soluble fiber supplements, which appear to aid hunger control at the level of the hypothalamus and terminal ileum, respectively.

Carnitine improves peripheral glucose disposal in non-insulin-dependent diabetic patients

To investigate the effects of carnitine on insulin sensitivity in non-insulin-dependent diabetes, insulin-mediated glucose disposal was measured in nine diabetic patients (age 54 +/- 3 years, BMI 27 +/- 1 kg/mq) during a primed (3 mmol) constant (1.7 mumol/min) intravenous infusion of carnitine. In control experiments, the same patients received saline instead of carnitine. Plasma glucose concentration was maintained constant at the level of 100 mg/dl during both studies while plasma insulin was raised to a plateau of 60 microU/ml. Despite similar insulin levels, whole-body glucose utilization was higher with carnitine (4.05 +/- 0.37 mg/kg/min) than saline infusion (3.52 +/- 0.36). Blood lactate concentrations were similar in the basal state and decreased significantly during carnitine infusion (P less than 0.05-0.005), whereas it remained substantially unchanged during saline infusion. Plasma FFA decreased to a similar level (0.1 mmol/l) in both studies. We conclude that an acute carnitine administration is able to improve insulin sensitivity in NIDDM patients. The lactate data suggest that this effect may at least in part be mediated by carnitine activation of pyruvate dehydrogenase.

Muscle lipofuscin content and satellite cell volume is increased after high altitude exposure in humans

Muscle ultrastructural changes during a typical expedition to the Himalayas were analyzed by taking muscle biopsies from seven climbers before and after their sojourn at high altitude (over 5000 m for 8 weeks). M. vastus lateralis samples were analyzed morphometrically from electron micrographs. A quantitative evaluation was made of lipofuscin, satellite cells and myonuclei. Significant increases of the volume densities of lipofuscin (+ 235%) and satellite cells (+ 215%) were observed.