Tissue carnitine deficiency due to dietary lysine dificiency: triglyceride accumulation and concomitant impairment in fatty acid oxidation

L-lysine dietary supplementation for childhood and adolescent growth: Promises and precautions

BACKGROUND

L-lysine (lysine) is an essential amino acid that plays a vital role in human nutrition. It serves as a key component in protein synthesis and fulfills critical roles in various physiological activities. For decades, lysine supplements have been extensively used to promote the growth and development of children, particularly in developing countries where cereal-based diets are everyday staples.

AIM OF THE REVIEW

This review aims to provide an overview of the overall effectiveness of lysine supplements concerning the growth of children and adolescents. Additionally, it addresses the potential precautions that should be considered when using lysine supplements in this context.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Receiving lysine oral supplements and lysine-fortified cereal diets were observed to enhance nitrogen retention and improve anthropometric measurements such as height, weight, Z-scores, body mass index, and skinfold thickness. Furthermore, lysine positively influenced the children's developmental quotient and various serological biochemical parameters, such as hormones, immunological indicators, proteins, bone metabolic indicators, and red blood cell parameters. These supplements are generally considered clinically safe, with no reported toxicity where the related side effects are limited to subjective gastrointestinal tract symptoms. It is essential to be cautious about excessive intake of lysine, as it can lead to an imbalance of amino acids, thereby potentially suppressing its intended benefits. When used with appropriate precautions, lysine can serve as a safe supplement with promising benefits for the growth of children and adolescents. Nevertheless, further contemporary research studies on lysine supplementation would be insightful and valuable in better understanding its optimal use, potential benefits, and safety in promoting growth.

Messages from the Small Intestine Carried by Extracellular Vesicles in Prediabetes: A Proteomic Portrait

Extracellular vesicles (EVs) mediate communication in physiological and pathological conditions. In the pathogenesis of type 2 diabetes, inter-organ communication plays an important role in its progress and metabolic surgery leads to its remission. Moreover, gut dysbiosis is emerging as a diabetogenic factor. However, it remains unclear how the gut senses metabolic alterations and whether this is transmitted to other tissues via EVs. Using a diet-induced prediabetic mouse model, we observed that protein packaging in gut-derived EVs (GDE), specifically the small intestine, is altered in prediabetes. Proteins related to lipid metabolism and to oxidative stress management were more abundant in prediabetic GDE compared to healthy controls. On the other hand, proteins related to glycolytic activity, as well as those responsible for the degradation of polyubiquitinated composites, were depleted in prediabetic GDE. Together, our findings show that protein packaging in GDE is markedly modified during prediabetes pathogenesis, thus suggesting that prediabetic alterations in the small intestine are translated into modified GDE proteomes, which are dispersed into the circulation where they can interact with and influence the metabolic status of other tissues. This study highlights the importance of the small intestine as a tissue that propagates prediabetic metabolic dysfunction throughout the body and the importance of GDE as the messengers. Data are available via ProteomeXchange with identifier PXD028338.

Is Ambient Weather a Risk Factor for Acute Encephalopathy Outbreaks in Children in Muzaffarpur, Bihar, India? Insight from a 9-Year Analysis

OBJECTIVES

Despite periodic outbreaks, the causes and risk factors of acute encephalitis syndrome (AES) in children of Muzaffarpur, Bihar, India, remain unknown. We explored the correlation between AES caseload and the climate parameters.

METHODS

Data for 1318 hospitalized children with AES during 2012-20 were used. The correlation between AES cases and daily climate parameters (temperature, sunshine, rainfall, humidity and wind speed) for the previous 24, 48 and 72 h were examined using Pearson's and Spearman's rank-order correlation and Poisson regression or negative binomial regression analyses.

RESULTS

Most (91.8%) of the AES cases occurred during the summer season (May-July months), especially June month. Pearson's and Spearman's rank-order correlation analyses revealed that AES caseload had positive correlations with maximum (r = 0.275, ρ = 0.293) and minimum (r = 0.306, ρ = 0.306) temperatures during past 24 h and heat index (r = 0.325, ρ = 0.325) and negative correlation with humidity (r = -0.222, ρ = -0.222) and rainfall (r = -0.183, ρ = -0.183) (all p < 0.05). The correlation was consistent for the climate parameters for the past 24, 48 and 72 h. Regression analysis also documented a significant association of AES cases with daily maximum (β: 0.32-0.36) and minimum (β: 0.53-0.62) temperatures and heat index (β: 0.92-1.03) over past 24, 48 and 72 h (all p < 0.01). The number of AES cases exponentially increased when the daily maximum and minimum temperatures crossed 40°C and 31°C, respectively.

CONCLUSIONS

The climate parameters, especially temperature appears to be a risk factor for AES in children. The definite aetiological role of heat for AES in children needs further exploration.

Alteration of serum amino acid profiles by dietary adenine supplementation inhibits fatty liver development in rats

Studies on animal models have demonstrated that feeding a low-arginine diet inhibits triacylglycerol (TAG) secretion from the liver, resulting in marked fatty liver development in rats. Here, we first showed that culturing hepatocytes in the medium mimicking the serum amino acid profile of low-arginine diet-fed rats induced TAG accumulation in the cells, indicating that the specific amino acid profile caused TAG accumulation in hepatocytes. Dietary adenine supplementation completely recovered hepatic TAG secretion and abolished hepatic TAG accumulation in rats. A comprehensive non-linear analysis revealed that inhibition of hepatic TAG accumulation by dietary adenine supplementation could be predicted using only serum amino acid concentration data. Comparison of serum amino acid concentrations indicated that histidine, methionine, and branched-chain amino acid (BCAA) concentrations were altered by adenine supplementation. Furthermore, when the serum amino acid profiles of low-arginine diet-fed rats were altered by modifying methionine or BCAA concentrations in their diets, their hepatic TAG accumulation was abolished. Altogether, these results suggest that an increase in methionine and BCAA levels in the serum in response to dietary arginine deficiency is a key causative factor for hepatic TAG accumulation, and dietary adenine supplementation could disrupt this phenomenon by altering serum amino acid profiles.

Effect of L-carnitine on health-related quality of life in patients with liver cirrhosis

L-carnitine (4-N-trimethylammonium-3-hydroxybutyric acid) is the physiologically active form of carnitine and is a natural compound that has been shown to exhibit antioxidant activity. L-carnitine is used as a supplementary treatment in patients with cirrhosis with hepatic encephalopathy, hyperammonemia or muscle cramps. In the present study, the effect of L-carnitine supplementation on health-related quality of life in 30 patients with cirrhosis was prospectively examined. L-carnitine (1,800 mg/day) was administered orally for 6 months. To assess the effects of L-carnitine on chronic fatigue, patients filled out a self-report questionnaire regarding their physical and mental health. The levels of total and free carnitine, and acylcarnitine were found to be significantly higher 1, 3 and 6 months after therapy initiation compared with before treatment. Serum albumin levels were significantly increased 3 and 6 months after initiation of therapy. L-carnitine supplementation significantly increased the BAP/d-ROM ratio, a marker of antioxidant status in patients with cirrhosis. Changes in serum carnitine concentrations were positively correlated with changes in serum albumin levels (R²=0.369; P=0.012), but not with changes in serum ammonia levels (R²= 0.005; P=0.78). Total and mental health scores improved significantly, and physical scores improved marginally 3 and 6 months after initiation of L-carnitine. These findings may be attributed to the enhanced serum albumin levels and oxidative stress rather than the reduced serum ammonia levels. Based on these results, it is suggested that L-carnitine can potentially alleviate chronic fatigue, along with the increased BAP/d-ROM ratio, which were involved in increased oxidative stress in patients with cirrhosis. The specific mechanisms by which L-carnitine ameliorates chronic fatigue is not fully understood and requires further investigation.

Differential correlation network analysis identified novel metabolomics signatures for non-responders to total joint replacement in primary osteoarthritis patients

INTRODUCTION

Up to one third of total joint replacement patients (TJR) experience poor surgical outcome.

OBJECTIVES

To identify metabolomic signatures for non-responders to TJR in primary osteoarthritis (OA) patients.

METHODS

A newly developed differential correlation network analysis method was applied to our previously published metabolomic dataset to identify metabolomic network signatures for non-responders to TJR.

RESULTS

Differential correlation networks involving 12 metabolites and 23 metabolites were identified for pain non-responders and function non-responders, respectively.

CONCLUSION

The differential networks suggest that inflammation, muscle breakdown, wound healing, and metabolic syndrome may all play roles in TJR response, warranting further investigation.

Effects of Dietary Supplementation of L-Carnitine and Excess Lysine-Methionine on Growth Performance, Carcass Characteristics, and Immunity Markers of Broiler Chicken

L-carnitine as well as lysine and methionine are amino acids of important nutritional and nutraceutical interest and are used in nutritional strategies as diet supplements to improve feed quality characteristics in animals and broiler chicken in particular. This study investigated the effect of different levels of L-carnitine and extra levels of lysine-methionine on growth performance, carcass characteristics, and some immune system markers. Two hundred seventy male Ross 308 broilers were a fed control diet (C) and eight different diets supplemented with an excess of amino acids. In the experimental diets, identified as D1, D2, D3, D4, D5, D6, D7, and D8, extra L-carnitine, lysine, and methionine were added in excess with respect to the American National Research Council (NRC) recommendations: L-carnitine equal to NRC (D1); control diet supplemented with lysine at 30% in excess of NRC, methionine at 30% in excess of NRC, and L-carnitine equal to NRC (D2); control diet supplemented with lysine equal to NRC, methionine equal to NRC, and L-carnitine at 15% in excess of NRC (D3); control diet supplemented control diet supplemented with lysine at 15% in excess of NRC, methionine at 15% in excess of NRC, and L-carnitine at 15% in excess of NRC (D4); control diet supplemented lysine at 30% in excess of NRC, methionine at 30% in excess of NRC, and L-carnitine at 15% in excess of NRC (D5); control diet supplemented with lysine equal to NRC recommendations, methionine equal to NRC recommendations, and L-carnitine at 75% in excess of NRC (D6); control diet supplemented with lysine at 15% in excess of NRC, methionine at 15% in excess of NRC, and L-carnitine at 75% in excess of NRC (D7); and control diet supplemented with lysine at 30% in excess of NRC, methionine at 30% in excess of NRC, and L-carnitine at 75% in excess of NRC (D8). During the starter and growth phases, feed intake was not affected by dietary treatment (p > 0.05). By contrast, body weight and FCR were both affected (p < 0.001) during the starter period. During the finisher phase, feed consumption was affected (p < 0.05) by dietary treatment. Feed intake of broilers fed on C, D3, D6, and D7 were statistically similar (p > 0.05) (1851.90, 1862.00, 1945.10, and 1872.80 g/pen/day, respectively) and were higher (p < 0.05) than 1564.40 g/pen/day (D5). With the exception of drumsticks, neck, back thoracic vertebrae, and proventriculus weights, economical carcass segments were not affected (p > 0.05) by the dietary supplementation of amino acids. Duodenum and ileum weights and lengths decreased with amino acid supplementation (p < 0.05). IgT and IgG titers against Sheep Red Blood Cells (SRBC) for both primary and secondary responses were not affected by dietary treatments (p > 0.05). Dietary amino acids supplementation did not affect IgM titer after the secondary challenge (p > 0.05) and had a significant effect (p < 0.05) on serum antibody titers in broilers vaccinated against Newcastle disease (NCD) and Gumboro ‘s disease at the 27th and 30th days, respectively.

Importance of Serum Amino Acid Profile for Induction of Hepatic Steatosis under Protein Malnutrition

We previously reported that a low-protein diet caused animals to develop fatty liver containing a high level of triglycerides (TG), similar to the human nutritional disorder “kwashiorkor”. To investigate the underlying mechanisms, we cultured hepatocytes in amino acid-sufficient or deficient medium. Surprisingly, the intracellular TG level was increased by amino acid deficiency without addition of any lipids or hormones, accompanied by enhanced lipid synthesis, indicating that hepatocytes themselves monitored the extracellular amino acid concentrations to induce lipid accumulation in a cell-autonomous manner. We then confirmed that a low-amino acid diet also resulted in the development of fatty liver, and supplementation of the low-amino acid diet with glutamic acid to compensate the loss of nitrogen source did not completely suppress the hepatic TG accumulation. Only a dietary arginine or threonine deficiency was sufficient to induce hepatic TG accumulation. However, supplementation of a low-amino acid diet with arginine or threonine failed to reverse it. In silico analysis succeeded in predicting liver TG level from the serum amino acid profile. Based on these results, we conclude that dietary amino acid composition dynamically affects the serum amino acid profile, which is sensed by hepatocytes and lipid synthesis was activated cell-autonomously, leading to hepatic steatosis.

Environmental Enteric Dysfunction is Associated with Carnitine Deficiency and Altered Fatty Acid Oxidation

BACKGROUND

Environmental enteric dysfunction (EED), a condition characterized by small intestine inflammation and abnormal gut permeability, is widespread in children in developing countries and a major cause of growth failure. The pathophysiology of EED remains poorly understood.

METHODS

We measured serum metabolites using liquid chromatography-tandem mass spectrometry in 400 children, aged 12-59months, from rural Malawi. Gut permeability was assessed by the dual-sugar absorption test.

FINDINGS

80.7% of children had EED. Of 677 serum metabolites measured, 21 were negatively associated and 56 were positively associated with gut permeability, using a false discovery rate approach (q<0.05, p<0.0095). Increased gut permeability was associated with elevated acylcarnitines, deoxycarnitine, fatty acid β-oxidation intermediates, fatty acid ω-oxidation products, odd-chain fatty acids, trimethylamine-N-oxide, cystathionine, and homocitrulline, and with lower citrulline, ornithine, polyphenol metabolites, hippurate, tryptophan, and indolelactate.

INTERPRETATION

EED is a syndrome characterized by secondary carnitine deficiency, abnormal fatty acid oxidation, alterations in polyphenol and amino acid metabolites, and metabolic dysregulation of sulfur amino acids, tryptophan, and the urea cycle. Future studies are needed to corroborate the presence of secondary carnitine deficiency among children with EED and to understand how these metabolic derangements may negatively affect the growth and development of young children.

Global Metabolomic Identification of Long-Term Dose-Dependent Urinary Biomarkers in Nonhuman Primates Exposed to Ionizing Radiation

Due to concerns surrounding potential large-scale radiological events, there is a need to determine robust radiation signatures for the rapid identification of exposed individuals, which can then be used to guide the development of compact field deployable instruments to assess individual dose. Metabolomics provides a technology to process easily accessible biofluids and determine rigorous quantitative radiation biomarkers with mass spectrometry (MS) platforms. While multiple studies have utilized murine models to determine radiation biomarkers, limited studies have profiled nonhuman primate (NHP) metabolic radiation signatures. In addition, these studies have concentrated on short-term biomarkers (i.e., <72 h). The current study addresses the need for biomarkers beyond 72 h using a NHP model. Urine samples were collected at 7 days postirradiation (2, 4, 6, 7 and 10 Gy) and processed with ultra-performance liquid chromatography (UPLC) quadrupole time-of-flight (QTOF) MS, acquiring global metabolomic radiation signatures. Multivariate data analysis revealed clear separation between control and irradiated groups. Thirteen biomarkers exhibiting a dose response were validated with tandem MS. There was significantly higher excretion of l-carnitine, l-acetylcarnitine, xanthine and xanthosine in males versus females. Metabolites validated in this study suggest perturbation of several pathways including fatty acid β oxidation, tryptophan metabolism, purine catabolism, taurine metabolism and steroid hormone biosynthesis. In this novel study we detected long-term biomarkers in a NHP model after exposure to radiation and demonstrate differences between sexes using UPLC-QTOF-MS-based metabolomics technology.

Effect of lysine, vitamin B(6), and carnitine supplementation on the lipid profile of male patients with hypertriglyceridemia: a 12-week, open-label, randomized, placebo-controlled trial

BACKGROUND

Fat metabolism is known to be altered in hypertriglyceridemia. Fat oxidation requires carnitine, which can be obtained either from the diet (animal or dairy products) or through synthesis in the body using both lysine and vitamin B(6).

OBJECTIVE

The goal of this study was to investigate the effect of lysine, vitamin B(6), and carnitine supplementation on both glycemia and the lipid profiles, specifically triglyceride (TG) levels, in men with hypertriglyceridemia.

METHODS

This 12-week, randomized, placebo-controlled clinical trial was conducted at a Lebanese medical center. A total of 85 hypertriglyceridemic (TG> 150 mg/dL) male patients were randomized to 1 of 5 groups and given supplements of lysine (1 g/d), vitamin B(6) (50 mg/d), lysine (1 g/d) + vitamin B(6) (50 mg/d), carnitine (1 g/d), or placebo for 12 weeks. The lipid profile (TG, total cholesterol, LDL-C, and HDL-C) and fasting plasma glucose levels were assessed at baseline and at 6 and 12 weeks.

RESULTS

Adults (∼50 years) Lebanese males from a low socioeconomic status in Beirut were given the appropriate supplements. Vitamin B(6) supplementation was associated with a significant reduction in total cholesterol and HDL-C of ∼10%. In addition, plasma TG was reduced by 36.6 mg/dL at 6 weeks, whereas levels in the placebo group increased by 18 mg/dL; this difference failed to reach statistical significance. No major changes in the lipid profile were observed in the lysine and carnitine groups or when lysine was added to vitamin B(6).

CONCLUSION

Vitamin B(6) supplementation in these male patients with hypertriglyceridemia reduced plasma total cholesterol and HDL-C concentrations.

Role of carnitine in disease

Carnitine is a conditionally essential nutrient that plays a vital role in energy production and fatty acid metabolism. Vegetarians possess a greater bioavailability than meat eaters. Distinct deficiencies arise either from genetic mutation of carnitine transporters or in association with other disorders such as liver or kidney disease. Carnitine deficiency occurs in aberrations of carnitine regulation in disorders such as diabetes, sepsis, cardiomyopathy, malnutrition, cirrhosis, endocrine disorders and with aging. Nutritional supplementation of L-carnitine, the biologically active form of carnitine, is ameliorative for uremic patients, and can improve nerve conduction, neuropathic pain and immune function in diabetes patients while it is life-saving for patients suffering primary carnitine deficiency. Clinical application of carnitine holds much promise in a range of neural disorders such as Alzheimer's disease, hepatic encephalopathy and other painful neuropathies. Topical application in dry eye offers osmoprotection and modulates immune and inflammatory responses. Carnitine has been recognized as a nutritional supplement in cardiovascular disease and there is increasing evidence that carnitine supplementation may be beneficial in treating obesity, improving glucose intolerance and total energy expenditure.

L-carnitine treatment reduces steatosis in patients with chronic hepatitis C treated with alpha-interferon and ribavirin

BACKGROUND

Hepatic steatosis is a common presentation in patients with chronic hepatitis C. Interferon alpha exerts both antiviral and immunomodulating actions, and influences on lipid metabolism. The aim of our study was to test whether L-carnitine reduces steatosis in patients treated with interferon and ribavirin.

PATIENTS AND METHODS

A total of 70 patients were randomly assigned to receive either leucocyte IFN alpha at a dose of 3 MIU thrice a week plus 1,000 mg ribavirin per day for 12 months (group A) or IFN alpha and ribavirin at the same dose plus 2 g carnitine per day (group B).

RESULTS

Comparison of the two treatments showed significant differences between the mean values of the following parameters at the end of the treatment: ALT -68 vs -95 IU/ml (P < 0.05), total cholesterol 0.08 vs -0.91 mmol/l (P < 0.05) and triglycerides +0.25 vs -20 mmol/l (P < 0.05); and at the follow-up: AST -35 vs -65 IU/ml (P < 0.05) and ALT -55 vs -84 IU/ml (P < 0.05). All values were lower in group B (IFN + Ribavirin + Carnitine) than in group A (IFN plus Ribavirin). When comparing those patients treated with IFN + ribavirin with those treated with IFN plus ribavirin plus carnitine, the response at the end of the treatment was 48% vs 56%, and the sustained response 39% vs 46%, respectively.

CONCLUSIONS

Combined treatment with L: -carnitine, ribavirin and IFN alpha resulted in greater antihyperlipidaemic effects and than with ribavirin and IFN alpha alone. The results of this study suggest that L: -carnitine may have a role among the reduction of steatosis strategies in patients with hepatitis C treated with IFN alpha and ribavirin.

Effects of L-carnitine supplementation of diets differing in energy levels on performance, abdominal fat content, and yield and composition of edible meat of broilers

Responses to supplemental dietaryl-carnitine of broilers fed on diets with different levels of metabolizable energy (ME) were investigated using growth performance and some carcass measurements. Three isonitrogenous diets containing 13.5, 12.8 or 12.2 MJ ME/kg were formulated, with or without supplementall-carnitine (50mg/kg) and fedad libitumfrom 18 to 53 d of age. Supplementall-carnitine increased body-weight gain (BWG) and improved feed conversion (FC) during the first 2 weeks of study. FC was also improved during the fourth week of the experiment. Weights of breast yield and thigh meat yield were significantly increased, whereas quantity and percentage of abdominal fat were reduced by supplementall-carnitine. A significant interaction between supplemental dietaryl-carnitine and dietary energy level was noted for BWG and FC during the second week of study.

L-Carnitine Stimulates Lipolysis via Induction of the Lipolytic Gene Expression and Suppression of the Adipogenic Gene Expression in 3T3-L1 Adipocytes

We investigated the lipolytic effects of L-carnitine in 3T3-L1 adipocytes. L-carnitine at 10-S100 nM suppressed lipid accumulation. The release of glycerol and free fatty acid into the medium was significantly increased by 1.5- and 1.7- fold, respectively, by the addition of 100 nM L-carnitine compared with the control (P < .05). The mRNA levels of hormone-sensitive lipase, carnitine palmitoyltransferase I-a, and acyl-coenzyme A oxidase, all of which participate in lipid catabolism, were increased in the presence of 100 nM L-carnitine by 2.8-, 2.2-, and 1.6-fold, respectively (P < .05). However, the expression of peroxisome proliferator-activated receptor-gamma and adipose-specific fatty acid-binding protein, which are involved in adipogenesis, were down-regulated by L-carnitine in 3T3-L1 adipocytes (P < .05). These results suggest an anti-obesity action of L-carnitine. L-carnitine may modulate lipid metabolism by stimulation of lipolysis and beta-oxidation accompanied by corresponding changes in gene expression and suppression of adipogenic gene expression.

Hypocarnitinemia in lysinuric protein intolerance

Carnitine deficiency in lysinuric protein intolerance (LPI) has been reported only in a single case. We describe hypocarnitinemia in a 11 year-old male patient with LPI and relate its development to intake, biosynthesis, and uptake of carnitine.

Enhancement of activities relative to fatty acid oxidation in the liver of rats depleted of L-carnitine by D-carnitine and a gamma-butyrobetaine hydroxylase inhibitor

This study was designed to examine whether the depletion of L-carnitine may induce compensatory mechanisms allowing higher fatty acid oxidative activities in liver, particularly with regard to mitochondrial carnitine palmitoyltransferase I activity and peroxisomal fatty acid oxidation. Wistar rats received D-carnitine for 2 days and 3-(2,2,2,-trimethylhydrazinium)propionate (mildronate), a noncompetitive inhibitor of gamma-butyrobetaine hydroxylase, for 10 days. They were starved for 20 hr before being sacrificed. A dramatic reduction in carnitine concentration was observed in heart, skeletal muscles and kidneys, and to a lesser extent, in liver. Triacylglycerol content was found to be significantly more elevated on a gram liver and whole liver basis as well as per mL of blood (but to a lesser extent), while similar concentrations of ketone bodies were found in the blood of D-carnitine/mildronate-treated and control rats. In liver mitochondria, the specific activities of acyl-CoA synthetase and carnitine palmitoyltransferase I were enhanced by the treatment, while peroxisomal fatty acid oxidation was higher per gram of tissue. It is suggested that there may be an enhancement of cellular acyl-CoA concentration, a signal leading to increased liver fatty acid oxidation in acute carnitine deficiency.

Wheat gluten-based diet retarded ethanol metabolism by altering alcohol dehydrogenase and not carnitine status in adult rats

The objective of this study was to determine the effect of a lysine-deficient diet on carnitine status in adult rats and subsequently on ethanol metabolism. Adult male rats were fed either the AIN-76 diet (NS), the AIN-76 diet with wheat gluten (WG) replacing casein, the WG diet plus 0.8% L-lysine (LS), or the LS diet plus 0.5% L-carnitine (CS) for 30 days. On the 31st day the rats were given an oral dose of ethanol and blood-ethanol concentrations (BEC) were monitored for the next 8 hours. One week later the rats were given a second dose of ethanol and urine was collected until killed, 3 hours post-ethanol administration (PEA). Besides growth retardation and hypoproteinemia, BEC were significantly elevated in the WG group compared to the other group at hours 3-8 PEA. There were no significant differences in BEC between the LS and CS groups; however, their BEC were significantly higher than that of the NS group. The BEC were inversely related to liver alcohol dehydrogenase (ADH) activities which were significantly lower in WG, LS and CS groups than in the NS group. Plasma, liver and urine carnitine values were significantly higher in the CS group than in the NS, WG and LS groups, wherein the values were similar. It is concluded that the WG diet reduced ADH activity and attenuated ethanol metabolism without significantly altering blood, liver and urinary carnitines in the adult rat.

Experimental carnitine depletion in rats

We studied tissue carnitine concentrations after long-term peroral feeding with carnitine-free parenteral nutrient solutions in rats. Group I (n = 22) was fed perorally for 6 weeks with the carnitine free experimental diet. The control group (group II, n = 22) was pair-fed a standard laboratory pellet diet containing carnitine 60 nmol/g. The carnitine free experimental diet caused approximately 50% depletion of carnitine in serum, muscle, and liver while the concentrations in the pair-fed rats were normal. The free and total carnitine concentrations in serum were 25.5 +/- 7.8 and 32.9 +/- 9.3 micromol/l (group I), and 69.3 +/- 13.7 and 84.1 +/- 16.5 micromol/l (group II, p < 0.001), in muscle 2.1 +/- 0.3 and 2.3 +/- 0.4 micromol/g dry weight (group I), and 3.8 +/- 0.6 and 4.3 +/- 0.8 micromol/g dry weight (group II, p < 0.001), and in liver 0.5 +/- 0.1 and 0.6 +/- 0.1 micromol/g dry weight (group I), and 1.2 +/- 0.1 and 1.3 +/- 0.1 micromol/g dry weight (group II p < 0.001). Daily supplementation of the experimental liquid diet with I-carnitine caused normal tissue carnitine concentrations, indicating the exclusion of dietary carnitine as the cause of carnitine depletion. We conclude that in rats carnitine depletion in serum, muscle, and liver can be induced by prolonged peroral feeding with carnitine free diet.

Low plasma carnitine in patients on prolonged total parenteral nutrition: association with low plasma lysine

Plasma carnitine levels were determined in 17 patients maintained on long-term total parenteral nutrition (TPN) for a mean (+/- SEM) period of 69 +/- 11 months (range 12-196). All had severe malabsorption and were dependent on intravenous feeding. Plasma carnitine was determined by a modified Cederblad enzymatic method. Mean plasma carnitine was significantly below the mean normal for females (p less than 0.02) and borderline low for males (p = 0.07). In six patients the levels were below the low normal range, and in five others they were at the lowest levels of normal. Of the six patients with normal levels, three had elevated serum creatinine, indicating renal dysfunction which may by itself elevate plasma carnitine. In 10 patients the plasma levels of lysine (a carnitine precursor) were determined and found to be lower than normal (p less than 0.05). Plasma carnitine levels correlated positively with serum albumin (r = 0.62, p less than 0.05), and negatively with serum alkaline phosphatase (r = -0.64, p less than 0.05). Thus, patients maintained on long-term TPN may have low plasma carnitine, which could represent carnitine deficiency. The low plasma carnitine may be related to a deficiency of the carnitine precursor lysine. Further studies are required to determine the significance of the low plasma carnitine and whether carnitine supplementation should be required in long-term TPN.

Liver function in protein-energy malnutrition measured by cinnamic acid tolerance and benzoic acid tolerance: effect of carnitine supplementation

1. Rats fed on a protein-depleted diet for 8 weeks were repleted for 5 weeks on high-protein (HP), high-protein + 20 g DL-carnitine/kg (HP + C), or low-protein + 20 g DL-carnitine/kg (LP + C) diets. At 4 and 8 weeks of depletion, and 1 and 5 weeks of repletion, rats from each treatment group were given a benzoic acid tolerance test (BATT) or a cinnamic acid tolerance test (CATT) as a measure of liver function. 2. BATT and CATT measured the molar percentage of a test dose (1 mmol/kg body-weight) of benzoic acid or cinnamic acid excreted in the urine as hippuric acid within 24 h. Liver weight, liver lipid levels, and carnitine concentration in plasma and liver were also measured following liver-function testing. 3. BATT and CATT were severely impaired in protein-depleted rats, but returned rapidly to control levels following protein refeeding. Correlations of BATT and CATT with liver lipid concentration were high (r -0.49 and -0.62 respectively), and both tests show promise as clinical tests for liver function in protein-energy malnutrition. 4. Carnitine supplementation was required to return liver carnitine concentration of protein-depleted rats to control levels during repletion, but was not associated with accelerated reduction in liver fat concentration in protein-repleted rats.

Carnitine: an overview of its role in preventive medicine

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

14CO2 production is no adequate measure of [14C]fatty acid oxidation

Palmitate oxidation was comparatively assayed in various cell-free and cellular systems by 14CO2 production and by the sum of 14CO2 and 14C-labeled acid-soluble products. The 14CO2 production rate was dependent on incubation time and amount of tissue in contrast to the total oxidation rate. The 14CO2 contribution to the oxidation rate of [1-14C]palmitate varied with homogenates from 1% with rat liver to 28% with rat kidney and amounted to only 2-4% with human muscles. With cellular systems the 14CO2 contribution varied between 20% in human fibroblasts and 70% in rat muscles and myocytes. Addition of cofactors increased the oxidation rate, but decreased the 14CO2 contribution. Various conditions appeared also to influence to a different extent the 14CO2 production and the total oxidation rate with rat tissue homogenates and with rat muscle mitochondria. Incorporation of radioactivity from [1-14C]palmitate into protein was not detectable in cell-free systems and only 2-3% of the sum of 14CO2 and 14C-labeled acid-soluble products in cellular systems. Assay of 14CO2 and 14C-labeled acid-soluble products is a much more accurate and sensitive estimation of fatty acid oxidation than assay of only 14CO2.

The effect of dietary lysine levels on growth and metabolism of rainbow trout (Salmo gairdneri)

Groups of rainbow trout (Salmo gairdneri; mean weight 5 g) were given diets containing 10, 12, 14, 17, 21, 24 and 26 g lysine/kg diet for 12 weeks. By analysis of the growth values the dietary requirement of lysine in this experiment was found to be 19 g/kg diet. A similar requirement value was obtained from a dose-response curve of expired 14CO2 (following an intraperitoneal injection of L-[U-14C]lysine) v. dietary lysine concentration. Liver concentrations of total lipid and carnitine and activities of lysine-alpha-ketoglutarate reductase (saccharopine dehydrogenase (NADP+, lysine-forming), EC 1.5.1.8) in the liver were not significantly different in fish from the different dietary treatments. Hepatosomatic index, however, was higher in those fish given low levels of dietary lysine.

Effects of dietary carnitine on myocardial palmitate oxidation in the aging rat

Aging is associated with decreases in myocardial fatty acid oxidation and carnitine concentration. The purpose of this study was to investigate the effects of dietary carnitine manipulation on myocardial palmitate oxidation and carnitine content in young adult and middle-aged rats. Rats were fed either a carnitine-free or a carnitine-supplemented diet for nine weeks and killed at ages 6.5 and 18 months. Myocardial carnitine content was unaffected by age or diet. However, in 18 months rats fed a carnitine-free diet, myocardial palmitate oxidation was 77% higher, carnitine palmitoyltransferase activity 39% higher, and lipid droplet volume density 55% higher compared to 18 month rats fed a carnitine-supplemented diet. In 6.5 month rats, dietary carnitine had no effect on these variables. These results indicate that dietary carnitine restriction increases myocardial fatty acid metabolism in middle-aged but not in young adult rats.

Carnitine deficiency with hyperbilirubinemia, generalized skeletal muscle weakness and reactive hypoglycemia in a patient on long-term total parenteral nutrition: treatment with intravenous L-carnitine

Low levels of plasma carnitine and reduced urinary carnitine excretion with persistently elevated plasma bilirubin levels, reactive hypoglycemia and generalized skeletal muscle weakness are described in a patient requiring long-term total parenteral nutrition (TPN). Intravenous administration of L-carnitine at 400 mg/day for 7 days and subsequently a maintenance dose of 60 mg/day corrected the plasma carnitine deficiency and reactive hypoglycemia and was associated with a return to normal plasma bilirubin levels and a restoration of skeletal muscle strength.

Effects of feeding lysine-deficient diet on the metabolism of lipids in various tissues of rats

32 weanling male albino rats were divided into 4 groups to study the effects of lysine-deficient wheat diet (AW) and AW supplemented with either 0.4% lysine (LW) or 0.2% carnitine (CW) as compared to casein diet on metabolism of lipids in various tissues. LW, CW and casein diet groups were pair-fed with AW group. Changes in total lipids, lipid components, individual fatty acids, mitochondrial content in liver, heart, skeletal muscles, lungs and adipose tissue were determined after 8 weeks of feeding. AW diet resulted in accumulation of lipids (mainly acylglycerols) in heart, liver, skeletal muscles and depletion in adipose tissue. The LW and CW diets reversed the effects of AW diet, the CW being more effective than LW diet. The LW and CW diets increased the relative proportion of C 14:0, C 16:0, C 16:1 and decreased that of C18:1, C18:2; C18:3 fatty acids which were decreased and increased respectively, on the AW and casein diets. The fatty acids composition of adipose tissue was the same in all the groups. The AW diet increased the relative proportions of C 14:0, C 20:4 and decreased that of C 16:0, C 16:1, C 18:3 fatty acids in the lungs. Supplemented AW diet decreased the relative proportions of the former group and increased that of the later group including C 18:1 fatty acid also. The mitochondrial content of liver, heart, skeletal muscles and lungs was decreased on AW and reversed on LW and CW diets.

Dietary ascorbic acid and muscle carnitine (beta-OH-gamma-(trimethylamino) butyric acid) in guinea-pigs

Tissue ascorbic acid (AA) contents of approximately 12 and 100% saturation respectively were produced in two groups of guinea-pigs. The 'low-AA' group had a significantly lower muscle carnitine concentrations than the 'high-AA' group. There was no concomitant emergence of the symptoms customarily regarded as characteristic of hypovitaminosis C. It is concluded that muscle carnitine (beta-OH-gamma-(trimethyl-amino)butyric acid) is a highly-sensitive indicator of tissue AA contents; this could account for the lassitude and fatique reported to precede the emergence of frank scurvy in man.