Utilization of dietary precursors for carnitine synthesis in human adults

Carnitine promotes recovery from oxidative stress and extends lifespan in C. elegans

Carnitine is required for transporting fatty acids into the mitochondria for β-oxidation. Carnitine has been used as an energy supplement but the roles in improving health and delaying aging remain unclear. Here we show in C. elegans that L-carnitine improves recovery from oxidative stress and extends lifespan. L-carnitine promotes recovery from oxidative stress induced by paraquat or juglone and improves mobility and survival in response to H₂O₂ and human amyloid (Aβ) toxicity. L-carnitine also alleviates the oxidative stress during aging, resulting in moderate but significant lifespan extension, which was dependent on SKN-1 and DAF-16. Long-lived worms with germline loss (glp-1) or reduced insulin receptor activity (daf-2) recover from aging-associated oxidative stress faster than wild-type controls and their long lifespans were not further increased by L-carnitine. A new gene, T08B1.1, aligned to a known carnitine transporter OCTN1 in humans, is required for L-carnitine uptake in C. elegans. T08B1.1 expression is elevated in daf-2 and glp-1 mutants and its knockdown prevents L-carnitine from improving oxidative stress recovery and prolonging lifespan. Together, our study suggests an important role of L-carnitine in oxidative stress recovery that might be important for healthy aging in humans.

L-Carnitine as a Diet Supplement in Patients With Type II Diabetes

Introduction: L-Carnitine is a very important component of the human body which is involved in cardiac function and generally in the proper functioning of the muscular system. Also, it contributes to the proper use of glucose by the cell, thereby improving the regulation of glucose metabolism of the diabetic patient and preventing complications such as fatigue, insomnia, and mental activity. In this paper we would like to show the therapeutic effect of L-carnitine on type II diabetic patients after 2 g/day oral administration of L-carnitine.

Methods: In this study 181 Greek patients, 84 men and 97 women, aged 50-65 years, Type II diabetics, were administered L-carnitine for six months. All of them were euglycemic, under the proposed treatment, with no diabetic complications or cardiovascular problems. They were under the Mediterranean diet trying to keep their body mass index (BMI) constant. They were neither smokers nor alcohol drinkers. They were administered 2 g/day L-carnitine, orally, once daily for six months, on an empty stomach. The blood tests included fasting glucose, glycated hemoglobin (HBA1c), total cholesterol, and triglycerides and they were performed before, three months after, and six months after the treatment initiation. We also evaluated their tiredness, insomnia, and mental activity at these time points; the participants were given forms to fill out (regarding the distance they are able to brisk walk thrice/week, the duration of their calm uninterrupted sleep and their performance in a cognitive screening test, respectively) and based on the results of their answers, they were allocated to graded groups and scale analysis was performed in each one of them.

Results: Fasting glucose mean decrease was 17.51 after three months of medication (p<0.05); the decrease though noted after six months was not statistically significant. HbA1c showed a statistically significant mean decrease in both three- and six-month milestones (0.335, p<0.05 and 0.623, p<0.05 respectively). Changes noted in cholesterol levels were not statistically significant. Triglyceride measurements showed a significant decrease; -15.38 after three months (p<0.05) and -31.39 after six months of treatment (p<0.05). Finally, significant changes were found in both time periods for tiredness (three months: -0.49, p<0.05, six months: -0.88, p<0.05), insomnia (three months: -0.49, p<0.05, six months: -0.88, p<0.05), and mental activity (three months: +0.25, p<0.05, six months: +0.89, p<0.05).

Conclusion: L-Carnitine could be a valuable dietary supplement in patients with type II diabetes who follow a Mediterranean diet and are under recommended treatment. Research in this field though is at an early stage and more studies should be performed.

Effects of Exercise Training on Renal Carnitine Biosynthesis and Uptake in the High-Fat and High-Sugar-Fed Mouse

(1) Background: Diet-induced obesity inhibits hepatic carnitine biosynthesis. Herein, the effects of high-fat (HF) and high-sugar (HFHS) feeding and exercise training (ET) on renal carnitine biosynthesis and uptake were determined. (2) Methods: Male C57BL/6J mice were assigned to the following groups: lean control (standard chow), HFHS diet, and HFHS diet with ET. ET consisted of 150 min of treadmill running per week for 12 weeks. Protein levels of γ-butyrobetaine hydroxylase (γ-BBH) and organic cation transporter-2 (OCTN2) were measured as markers of biosynthesis and uptake, respectively. (3) Results: HFHS feeding induced an obese diabetic state with accompanying hypocarnitinemia, reflected by decreased free carnitine levels in plasma and kidney. This hypocarnitinemia was associated with decreased γ-BBH (~30%) and increased OCTN2 levels (~50%). ET failed to improve the obesity and hyperglycemia, but improved insulin levels and prevented the hypocarnitinemia. ET increased protein levels of γ-BBH, whereas levels of OCTN2 were decreased. Peroxisome proliferator-activated receptor-alpha content was not changed by the HFHS diet or ET. (4) Conclusions: Our results indicate that ET prevents the hypocarnitinemia induced by HFHS feeding by increasing carnitine biosynthesis in kidney. Increased expression of OCTN2 with HFHS feeding suggests that renal uptake was stimulated to prevent carnitine loss.

Maternal Plasma l-Carnitine Reduction During Pregnancy Is Mainly Attributed to OCTN2-Mediated Placental Uptake and Does Not Result in Maternal Hepatic Fatty Acid β-Oxidation Decline

l-Carnitine (l-Car) plays a crucial role in fatty acid β-oxidation. However, the plasma l-Car concentration in women markedly declines during pregnancy, but the underlying mechanism and its consequences on maternal hepatic β-oxidation have not yet been clarified. Our results showed that the plasma l-Car level in mice at gestation day (GD) 18 was significantly lower than that in nonpregnant mice, and the mean fetal-to-maternal plasma l-Car ratio in GD 18 mice was 3.0. Carnitine/organic cation transporter 2 (OCTN2) was highly expressed in mouse and human placenta and upregulated as gestation proceeds in human placenta, whereas expressions of carnitine transporter (CT) 1, CT2, and amino acid transporter B^0,+ were extremely low. Further study revealed that renal peroxisome proliferator-activated receptor α (PPARα) and OCTN2 were downregulated and the renal l-Car level was reduced, whereas the urinary excretion of l-Car was lower in late pregnant mice than in nonpregnant mice. Meanwhile, progesterone (pregnancy-related hormone) downregulated the expression of renal OCTN2 via PPARα-mediated pathway, and inhibited the activity of OCTN2, but estradiol, corticosterone, and cortisol did not. Unexpectedly, the maternal hepatic level of l-Car and β-hydroxybutyrate (an indicator of mitochondrial β-oxidation), and mRNA levels of several enzymes involved in fatty acid β-oxidation in GD 18 mice were higher than that in nonpregnant mice. In conclusion, OCTN2 mediated l-Car transfer across the placenta played a major role in maternal plasma l-Car reduction during pregnancy, which did not subsequently result in maternal hepatic fatty acid β-oxidation decrease.

OCTN: A Small Transporter Subfamily with Great Relevance to Human Pathophysiology, Drug Discovery, and Diagnostics

OCTN is a small subfamily of membrane transport proteins that belongs to the larger SLC22 family. Two of the three members of the subfamily, namely, OCTN2 and OCTN1, are present in humans. OCTN2 plays a crucial role in the absorption of carnitine from diet and in its distribution to tissues, as demonstrated by the occurrence of severe pathologies caused by malfunctioning or altered expression of this transporter. These findings suggest avoiding a strict vegetarian diet during pregnancy and in childhood. Other roles of OCTN2 are related to the traffic of carnitine derivatives in many tissues. The role of OCTN1 is still unclear, despite the identification of some substrates such as ergothioneine, acetylcholine, and choline. Plausibly, the transporter acts on the control of inflammation and oxidative stress, even though knockout mice do not display phenotypes. A clear role of both transporters has been revealed in drug interaction and delivery. The polyspecificity of the OCTNs is at the base of the interactions with drugs. Interestingly, OCTN2 has been recently exploited in the prodrug approach and in diagnostics. A promising application derives from the localization of OCTN2 in exosomes that represent a noninvasive diagnostic tool.

Biosynthesis of the Essential Fatty Acid Oxidation Cofactor Carnitine Is Stimulated in Heart and Liver after a Single Bout of Exercise in Mice

We determined whether one single bout of exercise stimulates carnitine biosynthesis and carnitine uptake in liver and heart. Free carnitine (FC) in plasma was assayed using acetyltransferase and [14C]acetyl-CoA in Swiss Webster mice after 1 hour of moderate-intensity treadmill running or 4 hours and 8 hours into recovery. Liver and heart were removed under the same conditions for measurement of carnitine biosynthesis enzymes (liver butyrobetaine hydroxylase, γ-BBH; heart trimethyllysine dioxygenase, TMLD), organic cation transporter-2 (OCTN2, carnitine transporter), and liver peroxisome proliferator-activated receptor-alpha (PPARα, transcription factor for γ-BBH and OCTN2 synthesis). In exercised mice, FC levels in plasma decreased while heart and liver OCTN2 protein expressed increased, reflecting active uptake of FC. During recovery, the rise in FC to control levels was associated with increased liver γ-BBH expression. Protein expression of PPARα was stimulated in liver after exercise and during recovery. Interestingly, heart TMLD protein was also detected after exercise. Acute exercise stimulates carnitine uptake in liver and heart. The rapid return of FC levels in plasma after exercise indicates carnitine biosynthesis by liver is stimulated to establish carnitine homeostasis. Our results suggest that exercise may benefit patients with carnitine deficiency syndromes.

Clinical Features of Carnitine Deficiency Secondary to Pivalate-Conjugated Antibiotic Therapy

OBJECTIVE

To examine the clinical features and risk factors of secondary carnitine deficiency due to long-term use of pivalate-conjugated antibiotics (PCAs).

STUDY DESIGN

We retrospectively investigated the age, clinical manifestations, PCA administration period, and background of 22 patients who showed a decrease in free carnitine (C0; ≤20 μmol/L) concomitant with an increase in pivaloyl carnitine (detected as C5-acylcarnitine) on acylcarnitine analysis with tandem mass spectrometry. Administration of PCAs was confirmed in all cases.

RESULTS

The patients ranged in age from 2 months to 42 years (median, 1 year, 11 months). One patient was aged <1 year, 10 patients were aged 1 year, 1 patient was aged 2 years, and 10 patients were aged ≥3 years. Nine patients had known underlying disease. Fourteen patients developed acute encephalopathy, 13 with accompanying hypoglycemia. Four patients presented with hypoglycemia without signs of encephalopathy. C0 values ranged from 0.25 to 19.66 μmol/L (median, 1.31 μmol/L); C5-acylcarnitine values, from 0.43 to 11.92 μmol/L (median, 3.23 μmol/L). There was no correlation between the PCA administration period and C0 level. Ten patients developed the symptoms after PCA administration for ≥14 days, whereas 6 patients showed symptoms after PCA administration for <14 days.

CONCLUSION

Carnitine deficiency resulting from PCA treatment was most frequently observed in 1-year-old infants. Most patients manifested acute encephalopathy and/or hypoglycemia. Some patients developed carnitine deficiency after PCA administration for <14 days.

Dioxygenases of Carnitine Biosynthesis: 6-N-Trimethyllysine and γ-Butyrobetaine Hydroxylases

This chapter describes the state of knowledge of the two 2-oxoglutarate-dependent dioxygenases of carnitine biosynthesis: 6-N-trimethyllysine hydroxylase and γ-butyrobetaine hydroxylase. Both enzymes have been extensively investigated as carnitine plays an important role in fatty acid metabolism in animals and some other life forms. Carnitine metabolism is introduced followed by a comprehensive review of the properties of the two carnitine biosynthesis dioxygenases including their purification, kinetic and biophysical characterization, regulation and roles in metabolism.

Pharmacological doses of niacin stimulate the expression of genes involved in carnitine uptake and biosynthesis and improve the carnitine status of obese Zucker rats

Background

Activation of peroxisome proliferator-activated receptor (PPAR)α and PPARδ causes an elevation of tissue carnitine concentrations through induction of genes involved in carnitine uptake [novel organic cation transporter 2, (OCTN2)], and carnitine biosynthesis [γ-butyrobetaine dioxygenase (BBD), 4-N-trimethyl-aminobutyraldehyde dehydrogenase (TMABA-DH)]. Recent studies showed that administration of the plasma lipid-lowering drug niacin causes activation of PPARα and/or PPARδ in tissues of obese Zucker rats, which have a compromised carnitine status and an impaired fatty acid oxidation capacity. Thus, we hypothesized that niacin administration to obese Zucker rats is also able to improve the diminished carnitine status of obese Zucker rats through PPAR-mediated stimulation of genes involved in carnitine uptake and biosynthesis.

Methods

To test this hypothesis, we used plasma, muscle and liver samples from a recent experiment with obese Zucker rats, which were fed either a niacin-adequate diet (30 mg niacin/kg diet) or a diet with a pharmacological niacin dose (780 mg niacin/kg diet), and determined concentrations of carnitine in tissues and mRNA and protein levels of genes critical for carnitine homeostasis (OCTN2, BBD, TMABA-DH). Statistical data analysis of all data was done by one-way ANOVA, and Fisher’s multiple range test.

Results

Rats of the obese niacin group had higher concentrations of total carnitine in plasma, skeletal muscle and liver, higher mRNA and protein levels of OCTN2, BBD, and TMABA-DH in the liver and higher mRNA and protein levels of OCTN2 in skeletal muscle than those of the obese control group (P < 0.05), whereas rats of the obese control group had lower concentrations of total carnitine in plasma and skeletal muscle than lean rats (P < 0.05).

Conclusion

The results show for the first time that niacin administration stimulates the expression of genes involved in carnitine uptake and biosynthesis and improves the diminished carnitine status of obese Zucker rats. We assume that the induction of genes involved in carnitine uptake and biosynthesis by niacin administration is mediated by PPAR-activation.

Primary carnitine deficiency and pivalic acid exposure causing encephalopathy and fatal cardiac events

BACKGROUND

Several episodes of sudden death among young Faroese individuals have been associated with primary carnitine deficiency (PCD). Patients suffering from PCD have low carnitine levels and can present with metabolic and/or cardiac complications. Pivalic acid exposure decreases carnitine levels. The purpose of this study was to investigate and describe the association and pathophysiology of exposure to antibiotics containing pivalic acid and severe neurological and cardiac complications in six identified subjects suffering from PCD.

METHODS AND MATERIALS

Six cases of PCD were identified and studied through medical records and family interview. Stored biomaterial was analyzed for mutations causing PCD.

RESULTS

Five patients (two children, three adults) died suddenly while one adult patient survived sudden cardiac arrest. Lethal cardiac arrhythmia was documented in five patients, while one patient was not monitored at time of death, but had signs of cardiac arrhythmia a few days earlier. All patients suffered encephalopathy before cardiac arrhythmia. Autopsy showed severe hepatic steatosis and signs of cerebral edema in four out of five. One subject had a dilated heart. All patients were homozygous for the c.95A>G (p.N32S) mutation in SLC22A5 causing PCD. All patients had been treated with antibiotics containing pivalic acid prior to the episode.

CONCLUSION

Exposure to antibiotics containing pivalic acid was associated with encephalopathy and progression to lethal cardiac arrhythmia in patients suffering from PCD.

Carnitine and acylcarnitines: pharmacokinetic, pharmacological and clinical aspects

L-Carnitine (levocarnitine) is a naturally occurring compound found in all mammalian species. The most important biological function of L-carnitine is in the transport of fatty acids into the mitochondria for subsequent β-oxidation, a process which results in the esterification of L-carnitine to form acylcarnitine derivatives. As such, the endogenous carnitine pool is comprised of L-carnitine and various short-, medium- and long-chain acylcarnitines. The physiological importance of L-carnitine and its obligatory role in the mitochondrial metabolism of fatty acids has been clearly established; however, more recently, additional functions of the carnitine system have been described, including the removal of excess acyl groups from the body and the modulation of intracellular coenzyme A (CoA) homeostasis. In light of this, acylcarnitines cannot simply be considered by-products of the enzymatic carnitine transfer system, but provide indirect evidence of altered mitochondrial metabolism. Consequently, examination of the contribution of L-carnitine and acylcarnitines to the endogenous carnitine pool (i.e. carnitine pool composition) is critical in order to adequately characterize metabolic status. The concentrations of L-carnitine and its esters are maintained within relatively narrow limits for normal biological functioning in their pivotal roles in fatty acid oxidation and maintenance of free CoA availability. The homeostasis of carnitine is multifaceted with concentrations achieved and maintained by a combination of oral absorption, de novo biosynthesis, carrier-mediated distribution into tissues and extensive, but saturable, renal tubular reabsorption. Various disorders of carnitine insufficiency have been described but ultimately all result in impaired entry of fatty acids into the mitochondria and consequently disturbed lipid oxidation. Given the sensitivity of acylcarnitine concentrations and the relative carnitine pool composition in reflecting the intramitochondrial acyl-CoA to free CoA ratio (and, hence, any disturbances in mitochondrial metabolism), the relative contribution of L-carnitine and acylcarnitines within the total carnitine pool is therefore considered critical in the identification of mitochondria dysfunction. Although there is considerable research in the literature focused on disorders of carnitine insufficiency, relatively few have examined relative carnitine pool composition in these conditions; consequently, the complexity of these disorders may not be fully understood. Similarly, although important studies have been conducted establishing the pharmacokinetics of exogenous carnitine and short-chain carnitine esters in healthy volunteers, few studies have examined carnitine pharmacokinetics in patient groups. Furthermore, the impact of L-carnitine administration on the kinetics of acylcarnitines has not been established. Given the importance of L-carnitine as well as acylcarnitines in maintaining normal mitochondrial function, this review seeks to examine previous research associated with the homeostasis and pharmacokinetics of L-carnitine and its esters, and highlight potential areas of future research.

Regulation of Genes Involved in Carnitine Homeostasis by PPARα across Different Species (Rat, Mouse, Pig, Cattle, Chicken, and Human)

Recent studies in rodents convincingly demonstrated that PPARα is a key regulator of genes involved in carnitine homeostasis, which serves as a reasonable explanation for the phenomenon that energy deprivation and fibrate treatment, both of which cause activation of hepatic PPARα, causes a strong increase of hepatic carnitine concentration in rats. The present paper aimed to comprehensively analyse available data from genetic and animal studies with mice, rats, pigs, cows, and laying hens and from human studies in order to compare the regulation of genes involved in carnitine homeostasis by PPARα across different species. Overall, our comparative analysis indicates that the role of PPARα as a regulator of carnitine homeostasis is well conserved across different species. However, despite demonstrating a well-conserved role of PPARα as a key regulator of carnitine homeostasis in general, our comprehensive analysis shows that this assumption particularly applies to the regulation by PPARα of carnitine uptake which is obviously highly conserved across species, whereas regulation by PPARα of carnitine biosynthesis appears less well conserved across species.

Role of carnitine in the regulation of glucose homeostasis and insulin sensitivity: evidence from in vivo and in vitro studies with carnitine supplementation and carnitine deficiency

BACKGROUND

Although carnitine is best known for its role in the import of long-chain fatty acids (acyl groups) into the mitochondrial matrix for subsequent β-oxidation, carnitine is also necessary for the efflux of acyl groups out of the mitochondria. Since intracellular accumulation of acyl-CoA derivatives has been implicated in the development of insulin resistance, carnitine supplementation has gained attention as a tool for the treatment of insulin resistance. More recent studies even point toward a causative role for carnitine insufficiency in developing insulin resistance during states of chronic metabolic stress, such as obesity, which can be reversed by carnitine supplementation.

METHODS

The present review provides an overview about data from both animal and human studies reporting effects of either carnitine supplementation or carnitine deficiency on parameters of glucose homeostasis and insulin sensitivity in order to establish the less well-recognized role of carnitine in regulating glucose homeostasis.

RESULTS

Carnitine supplementation studies in both humans and animals demonstrate an improvement of glucose tolerance, in particular during insulin-resistant states. In contrast, less consistent results are available from animal studies investigating the association between carnitine deficiency and glucose intolerance. The majority of studies dealing with this question could either find no association or even reported that carnitine deficiency lowers blood glucose and improves insulin sensitivity.

CONCLUSIONS

In view of the abovementioned beneficial effect of carnitine supplementation on glucose tolerance during insulin-resistant states, carnitine supplementation might be an effective tool for improvement of glucose utilization in obese type 2 diabetic patients. However, further studies are necessary to explain the conflicting observations from studies dealing with carnitine deficiency.

Low availability of carnitine precursors as a possible reason for the diminished plasma carnitine concentrations in pregnant women

BACKGROUND

It has been shown that plasma carnitine concentrations decrease markedly during gestation. A recent study performed with a low number of subjects suggested that this effect could be due to a low iron status which leads to an impairment of carnitine synthesis. The present study aimed to confirm this finding in a greater number of subjects. It was moreover intended to find out whether low carnitine concentrations during pregnancy could be due to a reduced availability of precursors of carnitine synthesis, namely trimethyllysine (TML) and gamma-butyrobetaine (BB).

METHODS

Blood samples of 79 healthy pregnant women collected at delivery were used for this study.

RESULTS

There was only a weak, non-significant (P > 0.05), correlation between plasma concentration of ferritin and those of free and total carnitine. There was no correlation between other parameters of iron status (plasma iron concentration, hemoglobin, MCV, MCH) and plasma concentration of free and total carnitine. There were, however, significant (P < 0.05) positive correlations between concentrations of TML and BB and those of free and total carnitine in plasma.

CONCLUSIONS

The results of this study suggest that an insufficient iron status is not the reason for low plasma carnitine concentrations observed in pregnant women. It is rather indicated that low plasma carnitine concentrations are caused by a low availability of precursors for carnitine synthesis during gestation.

Orlistat and L-carnitine compared to orlistat alone on insulin resistance in obese diabetic patients

Our study wants to evaluate the effects of one year treatment with orlistat plus L-carnitine compared to orlistat alone on body weight, glycemic and lipid control, and insulin resistance state in type 2 diabetic patients. Two hundred and fifty-eight patients with uncontrolled type 2 diabetes mellitus (T2DM) [glycated hemoglobin (HbA(1c)) > 8.0%] in therapy with different oral hypoglycemic agents or insulin were enrolled in this study and randomised to take orlistat 120 mg three times a day plus L-carnitine 2 g one time a day or orlistat 120 mg three times a day. We evaluated at baseline, and after 3, 6, 9, and 12 months these parameters: body weight, body mass index (BMI), HbA(1c), fasting plasma glucose (FPG), post-prandial plasma glucose (PPG), fasting plasma insulin (FPI), homeostasis model assessment insulin resistance index (HOMA-IR), total cholesterol (TC), low density lipoprotein-cholesterol (LDL-C), high density lipoprotein-cholesterol (HDL-C), triglycerides (Tg), retinol binding protein-4 (RBP-4), resistin, visfatin, high sensitivity-C reactive protein (Hs-CRP). We observed a faster, and better decrease of body weight, HbA(1c), FPG, PPG, LDL-C, HOMA-IR with orlistat plus L-carnitine compared to orlistat. A faster improvement of TC, Tg, FPI, resistin, RBP-4, visfatin, and Hs-CRP was reached with orlistat plus L-carnitine compared to orlistat. We can safely conclude that the association of orlistat plus L-carnitine was better than orlistat in improving body weight, glycemic and lipid profile, insulin resistance, and inflammatory parameters and no significant adverse events were recorded.

Sibutramine and L-carnitine compared to sibutramine alone on insulin resistance in diabetic patients

OBJECTIVE

To evaluate the effects of one year of treatment with sibutramine plus L-carnitine compared to sibutramine on body weight, glycemic control, and insulin resistance state in type 2 diabetic patients.

METHODS

Two hundred and fifty-four patients with uncontrolled type 2 diabetes mellitus (T2DM) [glycated hemoglobin (HbA(1c)) >8.0%] in therapy with different oral hypoglycemic agents or insulin were enrolled in this study and randomised to take sibutramine 10 mg plus L-carnitine 2 g or sibutramine 10 mg in monotherapy. We evaluated at baseline, and after 3, 6, 9, and 12 months these parameters: body weight, body mass index (BMI), glycated hemoglobin (HbA(1c)), fasting plasma glucose (FPG), post-prandial plasma glucose (PPG), fasting plasma insulin (FPI), homeostasis model assessment insulin resistance index (HOMA-IR), total cholesterol (TC), low density lipoprotein-cholesterol (LDL-C), high density lipoprotein-cholesterol (HDL-C), triglycerides (Tg), retinol binding protein-4 (RBP-4), resistin, visfatin, high sensitivity-C reactive protein (Hs-CRP).

RESULTS

There was a decrease in body weight, BMI, HbA(1c), FPI, HOMA-IR, and RBP-4 in both groups, even when the values obtained with sibutramine plus L-carnitine were lower than the values obtained in sibutramine group. There was a faster decrease of FPG, PPG, TC, LDL-C, resistin and Hs-CRP with sibutramine plus L-carnitine even when no differences between the two groups were obtained. Furthermore, only sibutramine plus L-carnitine improved Tg, and visfatin.

CONCLUSION

Sibutramine plus L-carnitine gave a faster improvement of lipid profile, insulin resistance parameters, glycemic control, and body weight compared to sibutramine.

Influence of l-carnitine on metabolism and performance of sows

In recent years, l-carnitine has been used increasingly as a supplement in livestock animals. The present review gives an overview of the effects of dietary l-carnitine supplementation on the reproductive performance of sows. Results concerning the effect of l-carnitine supplementation during pregnancy on litter sizes are controversial. There are some studies reporting an increased number of piglets born alive per litter, while others could not find such an effect. In contrast, most studies performed show consistently that l-carnitine supplementation to a sow diet low in native carnitine during gestation increases piglet and litter weights at birth and enhances growth of litters during the suckling period. Biochemical mechanisms underlying the favourable effect of carnitine on intra-uterine growth have not been fully elucidated. There is, however, some evidence that carnitine influences the insulin-like growth factor-axis in sows and leads to greater placentae, which in turn improves intra-uterine nutrition, and stimulates oxidation of glucose in the fetuses. These effects may, at least in part, be responsible for higher birth weights of piglets. The stimulating effect of carnitine on growth of the litters might be due to an improved suckling behaviour of piglets born to l-carnitine-supplemented sows, causing the sows' milk production to rise. In conclusion, recent studies have clearly shown that dietary l-carnitine supplementation increases the reproductive performance of sows. These findings suggest that endogenous de novo synthesis of carnitine is insufficient to meet the metabolic requirement of sows during gestation.

A moderate excess of dietary lysine lowers plasma and tissue carnitine concentrations in pigs

This study was performed to investigate whether dietary lysine concentration influences the carnitine status of pigs. Therefore, an experiment with twenty young pigs with an average body weight of 21 kg was performed which were fed either a control diet (9.7 g lysine/kg) or a diet with a moderate excess of lysine (16.8 g lysine/kg). Concentrations of all the other amino acids did not differ between the diets. Pigs fed the high-lysine diet had lower concentrations of free and total carnitine in plasma, liver, kidney and skeletal muscle than control pigs (P<0.05). Pigs fed the high-lysine diet moreover had an increased concentration of trimethyllysine (TML), a reduced mRNA abundance of TML dioxygenase and reduced concentrations of gamma-butyrobetaine (BB) in muscle, indicating that the conversion of TML into BB in muscle was impaired. Concentrations of BB, the metabolic precursor of carnitine, in plasma, liver and kidney were also reduced in pigs fed the high-lysine diet while the activity of BB dioxygenase in kidney was not different and that in liver was even increased compared to control pigs (P<0.05). In conclusion, this study shows that a moderate dietary excess of lysine lowers plasma and tissue carnitine concentrations in pigs. Reduced concentrations of BB in liver and kidney suggest that the depressed carnitine status was likely caused by a decreased rate of carnitine synthesis due to a diminished availability of carnitine precursor, probably mainly as a result of an impaired BB formation in muscle.

Breeder hen dietary L-carnitine affects progeny carcase traits

(1) Ross 308 broiler breeder hens were given diets containing 0 or 25 mg L-carnitine/kg from 21 weeks of age. (2) Hens were inseminated with semen from Ross broiler breeder males and subsequent growth performance and carcase traits, of progeny obtained from hatches at 30, 35 and 37 weeks of age, were evaluated. (3) Progeny were hatched in a common facility and separated by gender. Experimental treatments employed for the 30-, 35- and 37-week hatches, respectively, were: hen diet and progeny gender (16 replications with two subplots); hen diet, progeny diet (0 and 50 mg L-carnitine/kg of diet) and progeny gender (16 replications with 4 subplots); and hen diet and progeny diet (high and low density; 16 replications with two subplots). (4) Females had lower growth rate and less breast meat, but greater proportions of carcase fat and breast meat than males. Growth performance measurements of progeny were not affected by hen L-carnitine, but hen L-carnitine decreased abdominal fat in progeny. Increasing diet density in the chick diets increased growth and carcase weights. Hen and progeny dietary L-carnitine interacted to increase male mortality. However, dietary hen L-carnitine decreased carcase fat and increased breast meat in progeny fed on high nutrient density diets. (5) In conclusion, L-carnitine in the diet of hens affected carcase traits of their progeny.

Carnitine in type 2 diabetes

Carnitine, the L-beta-hydroxy-gamma-N-trimethylaminobutyric acid, is synthesized primarily in the liver and kidneys from lysine and methionine. Carnitine covers an important role in lipid metabolism, acting as an obligatory cofactor for beta-oxidation of fatty acids by facilitating the transport of long-chain fatty acids across the mitochondrial membrane as acylcarnitine esters. Furthermore, since carnitine behaves as a shuttle for acetyl groups from inside to outside the mitochondrial membrane, it covers also a key role in glucose metabolism and assists in fuel-sensing. A reduction of the fatty acid transport inside the mitochondria results in the cytosolic accumulation of triglycerides, which is implicated in the pathogenesis of insulin resistance. Acute hypercarnitinemia stimulates nonoxidative glucose disposal during euglycemic hyperinsulinemic clamp in healthy volunteers. Similar results were obtained in type 2 diabetic patients. The above findings were confirmed in healthy volunteers using the minimal modeling of glucose kinetics. The total end-clamp glucose tissue uptake was significantly increased by the administration of doses of acetyl-L-carnitine (ALC) from 3.8 to 5.2 mg/kg/min, without a significant dose-response effect. In conclusion, both L-carnitine and ALC are effective in improving insulin-mediated glucose disposal either in healthy subjects or in type 2 diabetic patients. Two possible mechanisms might be invoked in the metabolic effect of carnitine and its derivative: the first is a regulation of acetyl and acyl cellular trafficking for correctly meeting the energy demand; the second is a control action in the synthesis of key glycolytic and gluconeogenic enzymes.

Metabolic, antioxidant, nutraceutical, probiotic, and herbal therapies relating to the management of hepatobiliary disorders

Many nutraceuticals, conditionally essential nutrients, and botanical extracts have been proposed as useful in the management of liver disease. The most studied of these are addressed in terms of proposed mechanisms of action, benefits, hazards, and safe dosing recommendations allowed by current information. While this is an area of soft science, it is important to keep an open and tolerant mind, considering that many major treatment discoveries were in fact serendipitous accidents.

History of L-carnitine: implications for renal disease

L-carnitine (LC) plays an essential metabolic role that consists in transferring the long chain fatty acids (LCFAs) through the mitochondrial barrier, thus allowing their energy-yielding oxidation. Other functions of LC are protection of membrane structures, stabilizing a physiologic coenzyme-A (CoA)-sulfate hydrate/acetyl-CoA ratio, and reduction of lactate production. On the other hand, numerous observations have stressed the carnitine ability of influencing, in several ways, the control mechanisms of the vital cell cycle. Much evidence suggests that apoptosis activated by palmitate or stearate addition to cultured cells is correlated with de novo ceramide synthesis. Investigations in vitro strongly support that LC is able to inhibit the death planned, most likely by preventing sphingomyelin breakdown and consequent ceramide synthesis; this effect seems to be specific for acidic sphingomyelinase. The reduction of ceramide generation and the increase in the serum levels of insulin-like growth factor (IGF)-1, could represent 2 important mechanisms underlying the observed antiapoptotic effects of acetyl-LC. Primary carnitine deficiency is an uncommon inherited disorder, related to functional anomalies in a specific organic cation/carnitine transporter (hOCTN2). These conditions have been classified as either systemic or myopathic. Secondary forms also are recognized. These are present in patients with renal tubular disorders, in which excretion of carnitine may be excessive, and in patients on hemodialysis. A lack of carnitine in hemodialysis patients is caused by insufficient carnitine synthesis and particularly by the loss through dialytic membranes, leading, in some patients, to carnitine depletion with a relative increase in esterified forms. Many studies have shown that LC supplementation leads to improvements in several complications seen in uremic patients, including cardiac complications, impaired exercise and functional capacities, muscle symptoms, increased symptomatic intradialytic hypotension, and erythropoietin-resistant anemia, normalizing the reduced carnitine palmitoyl transferase activity in red cells.

Analysis of Carnitine Biosynthesis Metabolites in Urine by HPLC–Electrospray Tandem Mass Spectrometry

Background: We developed a method to determine the urinary concentrations of metabolites in the synthetic pathway for carnitine from N6-trimethyllysine and applied this method to determine their excretion in control individuals. In addition, we investigated whether newborns are capable of carnitine synthesis from deuterium-labeled N6-trimethyllysine.

Methods: Urine samples were first derivatized with methyl chloroformate. Subsequently, the analytes were separated by ion-pair, reversed-phase HPLC and detected online by electrospray tandem mass spectrometry. Stable-isotope-labeled reference compounds were used as internal standards.

Results: The method quantified all carnitine biosynthesis metabolites except 4-N-trimethylaminobutyraldehyde. Detection limits were 0.05–0.1 μmol/L. The interassay imprecision (CV) for urine samples with added compounds was 6–12%. The intraassay imprecision (CV) was 1–5% (3–10 μmol/L). Recoveries were 94–106% at 10–20 μmol/L and 98–103% at 100–200 μmol/L. The mean (SD) excretions of N6-trimethyllysine and 3-hydroxy-N6-trimethyllysine were 2.8 (0.8) and 0.45 (0.15) mmol/mol creatinine, respectively. γ-Butyrobetaine and carnitine excretions were more variable with values of 0.27 (0.21) and 15 (12) mmol/mol creatinine, respectively. After oral administration of deuterium-labeled N6-trimethyllysine, all urines of newborns contained deuterium-labeled N6-trimethyllysine, 3-hydroxy-N6-trimethyllysine, γ-butyrobetaine, and carnitine.

Conclusions: HPLC in combination with electrospray ionization tandem mass spectrometry allows rapid determination of urinary carnitine biosynthesis metabolites. Newborns can synthesize carnitine from exogenous N6-trimethyllysine, albeit at a low rate.

Carnitine biosynthesis in mammals

Carnitine is indispensable for energy metabolism, since it enables activated fatty acids to enter the mitochondria, where they are broken down via beta-oxidation. Carnitine is probably present in all animal species, and in numerous micro-organisms and plants. In mammals, carnitine homoeostasis is maintained by endogenous synthesis, absorption from dietary sources and efficient tubular reabsorption by the kidney. This review aims to cover the current knowledge of the enzymological, molecular, metabolic and regulatory aspects of mammalian carnitine biosynthesis, with an emphasis on the human and rat.

Carnitine biosynthesis in mammals

Carnitine is indispensable for energy metabolism, since it enables activated fatty acids to enter the mitochondria, where they are broken down via beta-oxidation. Carnitine is probably present in all animal species, and in numerous micro-organisms and plants. In mammals, carnitine homoeostasis is maintained by endogenous synthesis, absorption from dietary sources and efficient tubular reabsorption by the kidney. This review aims to cover the current knowledge of the enzymological, molecular, metabolic and regulatory aspects of mammalian carnitine biosynthesis, with an emphasis on the human and rat.

Role of intrapartum hypoxia in carnitine nutritional status during the early neonatal period

We analyze markers of carnitine insufficiency and deficiency, lysine (LYS) and methionine (MET), in 39 neonates with intrapartum hypoxia (selection criteria: umbilical artery pH <7.20, lactate >1.8 mmol/l and PaO2 <25 mm Hg), and in 35 healthy newborn infants (control group) in the early neonatal period (1-7 days of life). Free (FC), total (TC) carnitine and acylcarnitines (AC=short-chain+long-chain acylcarnitines) were measured using a radioisotopic micromethod; LYS and MET were determined by high-pressure liquid chromatography. AC and TC plasma concentrations and AC/FC ratio were higher while FC/TC ratio was lower in the hypoxic neonates than in the control group. Hypoxic newborn infants (59%) presented "carnitine deficiency" (FC/TC <0.7) and 60% of them "carnitine insufficiency" (AC/FC ratio >0.4) vs. 31% and 28%, respectively, for the neonates of the control group (p<0.05). In the healthy neonates group, MET correlated with FC/TC and the AC/FC ratio. FC, TC, AC, AC/FC and umbilical artery pH (pHua) were inversely correlated. FC/TC and MET correlated with pHua. We conclude that: (1) an important percentage of newborn infants with intrapartum hypoxia suffer carnitine deficiency and carnitine insufficiency in the early neonatal period, related to MET plasma levels; (2) the carnitine deficiency or insufficiency in the neonate is determined by the degree of intrapartum acidosis.

Dietary betaine modifies hepatic metabolism but not renal injury in rat polycystic kidney disease

We undertook a morphometric and proton nuclear magnetic resonance ((1)H-NMR) study to test the hypothesis that 1% dietary betaine supplementation would ameliorate renal disease in the heterozygous Han:SPRD-cy rat, a model of polycystic kidney disease (PKD) and progressive chronic renal failure. After 8 wk of pair feeding, betaine had no effect on renal cystic change, renal interstitial fibrosis, serum creatinine, serum cholesterol, or serum triglycerides. (1)H-NMR spectroscopy of renal tissue revealed no change in renal osmolytes, including betaine, or renal content of other organic anions in response to diet. (1)H-NMR spectroscopy of hepatic tissue performed to explore the metabolic fate of ingested betaine revealed that heterozygous animals fed the control diet had elevated hepatic levels of gluconeogenic amino acids, increased beta-hydroxybutyrate, and increased levels of some citric acid cycle metabolites compared with animals without renal disease. Betaine supplementation eliminated these changes. Chronic renal failure in the Han:SPRD-cy rat is associated with disturbances of hepatic metabolism that can be corrected with betaine therapy, suggesting the presence of a reversible methylation defect in this form of chronic renal failure.

Decreased carnitine biosynthesis in rats with secondary biliary cirrhosis

Carnitine biosynthesis was investigated in rats with secondary biliary cirrhosis induced by bile duct ligation (BDL) for 4 weeks (n = 5) and in pair-fed, sham-operated control rats (n = 4). Control rats were pair-fed to BDL rats, and all rats were fed an artificial diet with negligible contents of carnitine, butyrobetaine, or trimethyllysine. Biosynthesis of carnitine and its precursors was determined by measuring their excretion in urine and accumulation in the body of the animals. Four weeks after BDL, total carnitine content was increased by 33% in livers from BDL rats when compared with control rats, but was unchanged in skeletal muscle and whole carcass. The plasma total carnitine concentration averaged 29.0 +/- 4.1 vs. 46.4 +/- 7.3 micromol/L in BDL rats and control rats, respectively. Urinary total carnitine excretion was reduced by 56% in BDL rats as compared with control rats. Carnitine biosynthesis was significantly decreased in BDL rats (0.45 +/- 0.19 vs. 0.93 +/- 0.08 micromol/100 g body weight/d in BDL and control rats, respectively). The tissue content of free and protein-linked trimethyllysine, a carnitine precursor, and trimethyllysine plasma concentrations were not different between BDL and control rats. However, urinary trimethyllysine excretion was increased 5-fold in BDL rats and approximated glomerular filtration. In contrast, urinary excretion of butyrobetaine, the direct carnitine precursor, was decreased by 40% in BDL rats as compared with control rats. Trimethyllysine biosynthesis was not different, but butyrobetaine biosynthesis was decreased by 51% in BDL as compared with control rats. In conclusion, carnitine biosynthesis is decreased in BDL rats as a result of a defect in the conversion of trimethyllysine to butyrobetaine.

Carnitine transport into muscular cells. Inhibition of transport and cell growth by mildronate

Carnitine is involved in the transfer of fatty acids across mitochondrial membranes. Carnitine is found in dairy and meat products, but is also biosynthesized from lysine and methionine via a process that, in rat, takes place essentially in the liver. After intestinal absorption or hepatic biosynthesis, carnitine is transferred to organs whose metabolism is dependent on fatty acid oxidation, such as heart and skeletal muscle. In skeletal muscle, carnitine concentration was found to be 50 times higher than in the plasma, implicating an active transport system for carnitine. In this study, we characterized this transport in isolated rat myotubes, established mouse C2C12 myoblastic cells, and rat myotube plasma membranes and found that it was Na(+)-dependent and partly inhibited by a Na(+)/K(+) ATPase inhibitor. L-carnitine analogues such as D-carnitine and gamma-butyrobetaine interfere with this system as does acyl carnitine. Among these inhibitors, the most potent was mildronate (3-(2,2,2-trimethylhydrazinium)propionate), known as a gamma-butyrobetaine hydroxylase inhibitor. It also induced a marked decrease in carnitine transport into muscle cells. Removal of carnitine or treatment with mildronate induced growth inhibition of cultured C2C12 myoblastic cells. These data suggest that myoblast growth and/or differentiation is dependent upon the presence of carnitine.

Effect of sports activity on carnitine metabolism. Measurement of free carnitine, gamma-butyrobetaine and acylcarnitines by tandem mass spectrometry

The effects of sports activity on carnitine metabolism were studied using mass spectrometry. Serum levels of free carnitine, acylcarnitines (acetylcarnitine, propionylcarnitine, C4-, C5- and C8-acylcarnitine) and gamma-butyrobetaine, a carnitine precursor, were determined by tandem mass spectrometry in liquid secondary ion mass ionization mode. The coefficients of variation at three different concentrations were 2.8-7.9% for gamma-butyrobetaine, and 1.2 to approximately 6.7% for free carnitine. The recoveries added to serum were 109.1% for gamma-butyrobetaine, 89.3% for free carnitine. Sports activity caused increased serum levels of gamma-butyrobetaine, acetylcarnitine, C4- and C8-acylcarnitines and decreased serum levels of free carnitine. This method requires a small amount of sample volume (20 microl of serum) and short total instrumental time for the analysis (1 h for preparation, 2 min per sample for mass spectrometric analysis). Therefore, this method can be applied to study carnitine metabolism under various conditions that affect fatty acid oxidation.

Effect of long-term valproic acid administration on the efficiency of carnitine reabsorption in humans

To elucidate the etiology of valproic acid-induced carnitine deficiency, we tested the hypothesis that long-term valproic acid administration decreases the rate of carnitine reabsorption. Thirteen healthy men participated in a 34-day protocol in which carnitine clearance was measured before and after 28 days of valproic acid administration. During valproic acid administration (days 6 to 33), plasma free and total carnitine concentrations decreased (18% and 12%, respectively, P<.05) by 16 days, but returned to pretreatment concentrations by 28 days. From day 14 to day 30, the rate of free carnitine excretion was 50% lower than at baseline (day 4, P<.05). Free and total carnitine clearance, indexed to the glomerular filtration rate, was lower after valproic acid administration (P<.01). Contrary to our hypothesis, after 28 days of valproic acid administration, the rate of carnitine reabsorption was enhanced independent of the glomerular filtration rate and filtered load. Changes in the plasma concentration, rate of excretion, and clearance were specific for carnitine and were not generalized in magnitude or direction to the other amino acids. We conclude that the kidney adapts to conserve carnitine during valproic acid administration and therefore does not cause valproic acid-induced carnitine depletion in adults.

Carnitine metabolism and its regulation in microorganisms and mammals

In procaryotes, L-carnitine may be used as both a carbon and nitrogen source for aerobic growth, or the carbon chain may be used selectively following cleavage trimethylamine. Under anaerobic conditions and in the absence of preferred substrates, some bacteria use carnitine, via crotonobetaine, as an electron acceptor. Formation of trimethylamine and lambda-butyrobetaine (from reduction of crotonobetaine) from L-carnitine by enteric bacteria has been demonstrated in rats and humans. Carnitine is not degraded by enzymes of eukaryotic origin. In higher organisms, carnitine has specific functions in intermediary metabolism. Concentrations of carnitine and its esters in cells of eukaryotes are rigorously maintained to provide optimal function. Carnitine homeostasis in mammals is preserved by a modest rate of endogenous synthesis, absorption from dietary sources, efficient reabsorption, and mechanisms present in most tissues that establish and maintain substantial concentration gradients between intracellular and extracellular carnitine pools.

Genetic disorders of carnitine metabolism and their nutritional management

Carnitine functions as a substrate for a family of enzymes, carnitine acyltransferases, involved in acyl-coenzyme A metabolism and as a carrier for long-chain fatty acids into mitochondria. Carnitine biosynthesis and/or dietary carnitine fulfill the body's requirement for carnitine. To date, a genetic disorder of carnitine biosynthesis has not been described. A genetic defect in the high-affinity plasma membrane carnitine-carrier(in) leads to renal carnitine wasting and primary carnitine deficiency. Myopathic carnitine deficiency could be due to an increase in efflux moderated by the carnitine-carrier(out). Defects in the carnitine transport system for fatty acids in mitochondria have been described and are being examined at the molecular and pathophysiological levels. the nutritional management of these disorders includes a high-carbohydrate, low-fat diet and avoidance of those events that promote fatty acid oxidation, such as fasting, prolonged exercise, and cold. Large-dose carnitine treatment is effective in systemic carnitine deficiency.

Vitamin C depletion is associated with alterations in blood histamine and plasma free carnitine in adults

OBJECTIVE

The purpose of this study was to determine whether carnitine metabolism or histamine degradation would be useful parameters for investigating the optimal requirement for vitamin C.

METHODS

Twenty-two non-scorbutic subjects with subnormal vitamin C status (plasma vitamin C < 28 mumol/L) were placed on a metabolic diet low in vitamin C for 3 weeks and repleted with graded doses of vitamin C: 10, 30 and 60 mg vitamin C daily (group 1) or 10,125 and 250 mg vitamin C daily (group 2) for weeks 1, 2 and 3, respectively. Fasting blood samples were collected weekly and analyzed for plasma vitamin C, plasma free carnitine and blood histamine.

RESULTS

Group 1 subjects remained in a subnormal vitamin C state throughout the 3-week study, and blood histamine and plasma free carnitine were not impacted by the experimental treatment. Plasma vitamin C in group 2 subjects rose significantly during the study, and these subjects finished the study with an ample vitamin C status indicative of vitamin C intakes above the recommended dietary allowance. Both blood histamine and plasma free carnitine were inversely related to vitamin C status in group 2 subjects.

CONCLUSIONS

These data indicate that blood histamine and plasma free carnitine are altered in individuals with subnormal, non-scorbutic vitamin C status and provide evidence that metabolic changes independent of collagen metabolism occur prior to the manifestation of scurvy. Thus utilizing scurvy as an end-point to determine vitamin C requirements may not provide adequate vitamin C to promote optimal health and well-being.

Generation of hydroxytrimethyllysine from trimethyllysine limits the carnitine biosynthesis in premature infants

epsilon-N-Trimethyl-L-lysine (TML) was given orally for 1 day to two groups of premature infants. There was no change in the output or plasma levels of carnitine at a dose of 100 mumol/day; however, the urinary TML increased 17-fold. In the second group, administration of 1 mmol TML increased the plasma levels and urinary output of carnitine; the output of TML increased 62-fold. During a search of the metabolites of carnitine biosynthesis by 1H NMR analysis of urine, only one new resonance (corresponding to the TML) could be identified in both groups. Fast atom bombardment mass spectrometry (FAB-MS) analysis of urine samples indicated an increase in TML in the treated patients; no changes were found in the relative abundance of any other precursors. These data show that a significant limitation of the conversion of hydroxy-TML to carnitine is not likely; rather, the conversion of TML to hydroxy-TML is regulatory in neonatal carnitine biosynthesis.

The ability of guinea pigs to synthesize carnitine at a normal rate from epsilon-N-trimethyllysine or gamma-butyrobetaine in vivo is not compromised by experimental vitamin C deficiency

Experimental vitamin C deficiency in guinea pigs is associated with low carnitine concentrations in blood and some tissues. Ascorbic acid is a cofactor for two enzymes in the pathway of carnitine biosynthesis. The effect of experimental vitamin C deficiency on the ability of guinea pigs to synthesize carnitine was in animals fed a vitamin C-deficient diet for 28 days. On days 19 to 28, supplements (0.5 mmol.kg body weight-1.d-1) of the carnitine precursors epsilon-N-trimethyllysine or gamma-butyrobetaine were administered orally. Ascorbate-supplemented, ascorbate-deficient, and pair-fed (to ascorbate-deficient) animals showed an increase in the rate of carnitine biosynthesis (as estimated from measured rates of carnitine excretion) of 32 to 40 mumol.kg body weight-1.d-1 following supplementation with epsilon-N-trimethyllysine. Likewise, animals in each experimental group showed an increase in the rate of carnitine biosynthesis of 41 to 50 mumol.kg body weight-1.d-1 after supplementation with gamma-butyrobetaine. These results indicate that scorbutic guinea pigs are able to synthesize carnitine at a normal or above-normal rate. For guinea pigs not given a carnitine precursor supplement, rates of free and total carnitine excretion for ascorbate-deficient (but not pair-fed) animals were threefold higher than for ascorbate-supplemented animals during days 19 to 28 of the feeding regimen. Thus, carnitine depletion in vitamin C deficiency likely is due to excessive urinary excretion of carnitine and not to a decreased rate of carnitine biosynthesis.

[Effects of L-carnitine in poultry]

Because of the well established function of carnitine possible effects of carnitine were studied in poultry. In trial I it was investigated if carnitine and its precursors (lysine, methionine) reduce the formation of abdominal fat in broilers. Chickens (10 groups of 10 chickens each) were fed different diets (control, lysine and methionine in excess and deficient, respectively, with or without 5% fat supplement, L-carnitine and DL-carnitine supplement, respectively). Performance (body weight gain, feed conversion), amount of abdominal fat and carnitine concentration in blood, muscles (M. sartorius, M. pectoralis superficialis, cardiac), liver and kidney were determined. Performance and abdominal fat were influenced by dietary fat, lysine and methionine as expected and were not altered by carnitine. Excess and deficiency of lysine and methionine did not influence, fat supplement reduced and carnitine supplementation significantly increased tissue concentration of carnitine. In trial II it was studied if supplementation of a commercial layers' ration with either 500 mg L-carnitine or 500 mg nicotinic acid or both per kg reduces the cholesterol concentration in yolk. Influence on body weight, feed intake, laying performance, serum and yolk cholesterol concentration could not be observed, but yolk concentration of carnitine was significantly increased in supplemented groups. Trial III should clarify if the L-carnitine content in broiler parent stock ration influences hatchability. Four groups of 1350 hens each were fed a commercial all-mash supplemented with 0, 20, 50 and 100 mg L-carnitine, respectively. Hatching rate was increased from 83% to 87% and from 82.4% to 85.3% in groups supplemented with 50 and 100 mg L-carnitine, respectively, and in randomly sampled eggs of these groups carnitine concentration in yolk was higher.