Effect of carnitine on decrease of branched chain amino acids and glutamine in serum of septic rats

L-carnitine: Searching for New Therapeutic Strategy for Sepsis Management

In this review, we discussed the biological targets of carnitine, its effects on immune function, and how L-carnitine supplementation may help critically ill patients. L-carnitine is a potent antioxidant. L-carnitine depletion has been observed in prolonged intensive care unit (ICU) stays, while L-carnitine supplementation has beneficial effects in health promotion and regulation of immunity. It is essential for the uptake of fatty acids into mitochondria. By inhibiting the ubiquitin-proteasome system, down-regulation of apelin receptor in cardiac tissue, and reducing β-oxidation of fatty acid, carnitine may decrease vasopressor requirement in septic shock and improve clinical outcomes of this group of patients. We also have an overview of animal and clinical studies that have been recruited for evaluating the beneficial effects of L-carnitine in the management of sepsis/ septic shock. Additional clinical data are required to evaluate the optimal daily dose and duration of L-carnitine supplementation.

Effects on the Human Body of a Dietary Supplement Containing L-Carnitine and Garcinia cambogia Extract: A Study using Double-blind Tests

The effect of a dietary supplement with L-carnitine (600 mg/day) and Garcinia cambogia extract (500 mg/day as hydroxycitric acid) as main ingredients was studied in 35 healthy volunteers {48.3 ± 6.9 years, body mass index (BMI): 26.3 ± 1.7} in a double-blind test (18 subjects in the Test Group and 17 in the Control Group). The yearly examination includes the standard yearly medical tests done in Japan, tests for assessing hormonal age, and a survey for assessing physical and mental fitness of the subjects, called the Anti-Aging QOL Common Questionnaire (AAQol). Use of this supplement significantly improved the level of lipid peroxides (−12.8%) in the blood as well as physical symptoms such as “tired eyes,” “blurry eyes,” “muscle pain/stiffness,” “early satiety,” “epigastralgia,” “dizziness,” “arthralgia” and “easily breaking into a sweat.” The Control Group showed a significantly favorable improvement rate, especially for “dizziness.” On the other hand, groups of subjects using the test compounds saw a significant rise in total cholesterol (4.5%), fasting blood sugar (4.1%) and HbA1c (3.4%). Our findings suggest that the consumption of the supplement can reduce the oxidative damage; however, the effect on QOL was equivocal. Garcinia cambogia extract did not show dietary efficacy.

Intermediate metabolism in association with the amino acid profile during the third trimester of normal pregnancy and diet-controlled gestational diabetes

OBJECTIVE

The aim of this study was to investigate the levels of fasting maternal plasma amino acids in normal pregnant women and compare them with those in gestational diabetes controlled by diet only. We also wished to delineate the alterations occurring in intermediate metabolic pathways in gestational diabetes.

STUDY DESIGN

Forty-six (64.7%) pregnant women with uncomplicated pregnancy (NP group) and 25 (35.2%) women with gestational diabetes mellitus (GDM group) at 30-33 weeks of gestation participated in the study. Fasting maternal plasma carnitine (total, free, and acyl-carnitine), beta-hydroxybutyrate, free fatty acids, glycosylated hemoglobin, and 21 amino acids were assayed.

RESULTS

Fasting carnitine esters exhibited lower levels in the GDM group (P = .03). Higher levels of fasting beta-hydroxybutyrate and free fatty acids (P < .001 and .02, respectively) were observed in the GDM group. Of the 21 amino acids, only methionine, glycine, alanine, citrulline, and ornithine levels were found at significantly higher levels in the NP group (P = .03, P < .001, P = .01, P < .001, and P < .001, respectively).

CONCLUSION

In gestational diabetes, ketogenic amino acids and the branched-chain amino acid isoleucine are released at low rates from skeletal muscle and are mostly catabolized in the liver rather than in peripheral tissues. In contrast, in normal pregnancy proteinolysis is enhanced, and the ketogenic amino acids along with branched-chain amino acids are catabolized in both the liver and peripheral tissues. As a result, ketogenic amino acids are fully oxidized and gluconeogenesis becomes more efficient, whereas urea cycle operates at a higher rate.

Leucine-induced activation of translational initiation is partly regulated by the branched-chain alpha-keto acid dehydrogenase complex in C2C12 cells

Branched-chain amino acid leucine has been shown to activate the translational regulators through the mammalian target of rapamycin. However, the leucine's effects are self-limiting because leucine promotes its own disposal by an oxidative pathway. The irreversible and rate-limiting step in the leucine oxidation pathway is catalyzed by the branched-chain alpha-keto acid dehydrogenase (BCKDH) complex. The complex contains E1 (alpha2beta2), E2, and E3 subunits, and its activity is abolished by phosphorylation of the E1alpha subunit by BCKDH kinase. The relationship between the activity of BCKDH complex and leucine-mediated activation of the protein translation was investigated using the technique of RNA interference. The activity of BCKDH complex in C2C12 cell was modulated by transfection of small interfering RNA (siRNA) for BCKDH E2 subunit or BCKDH kinase. Transfection of siRNAs decreased the mRNA expression and protein amount of corresponding gene. Suppression of either E2 subunit or kinase produced opposite effects on the cell proliferation and the activation of translational regulators by leucine. Suppression of BCKDH kinase for 48h resulted in decreasing cell proliferation. In contrast, E2 suppression led to increased amount of total cellular protein. The phosphorylation of p70 S6 kinase by leucine was increased in E2-siRNA transfected C2C12 cells, whereas the leucine's effect was diminished in kinase-siRNA transfected cells. These results suggest that the activation of the translational regulators by leucine was partly regulated by the activity of BCKDH complex.

Branched-chain amino acid-enriched nutritional support in surgical and cancer patients

Prolonged surgical stress and advanced malignant disease lead to systemic catabolism characterized by depletion of muscle protein and oxidation of skeletal muscle BCAA. BCAA oxidation provides energy for muscle and other organs and is the precursor for amino acid synthesis to replenish alanine and glutamine depleted in catabolic states. Persistent excessive catabolism leads to skeletal muscle wasting, negative nitrogen balance, and immune compromise. BCAAs, especially leucine, stimulate protein synthesis, inhibit proteolysis (in cell culture models and in animals), and promote glutamine synthesis. A number of small and diverse clinical trials studied the effects of BCAA-enriched nutritional support in moderately to severely stressed surgical and cancer patients. The findings of these clinical trials have been inconsistent; some show improved nitrogen balance, increased skeletal muscle protein synthesis, and reduced skeletal muscle catabolism whereas others show no significant improvement. The value of these trials is compromised by small sample size, heterogeneous patients, poor study design, varying degrees of metabolic stress, and inappropriate endpoints. More recent trials that evaluate clinical outcomes in hepatocellular carcinoma patients show promising results; in addition to improving metabolic parameters, BCAA-enriched oral supplementation improved morbidity and quality of life in patients undergoing major liver resection and chemo-embolization. In summary, the role of BCAAs in the nutritional support of stressed surgical and cancer patients remains to be clearly defined, despite their potential beneficial biological properties.

Mechanisms responsible for regulation of branched-chain amino acid catabolism

The branched-chain amino acids (BCAAs) are essential amino acids and therefore must be continuously available for protein synthesis. However, BCAAs are toxic at high concentrations as evidenced by maple syrup urine disease (MSUD), which explains why animals have such an efficient oxidative mechanism for their disposal. Nevertheless, it is clear that leucine is special among the BCAAs. Leucine promotes global protein synthesis by signaling an increase in translation, promotes insulin release, and inhibits autophagic protein degradation. However, leucine's effects are self-limiting because leucine promotes its own disposal by an oxidative pathway, thereby terminating its positive effects on body protein accretion. A strong case can therefore be made that the proper leucine concentration in the various compartments of the body is critically important for maintaining body protein levels beyond simply the need of this essential amino acid for protein synthesis. The goal of the work of this laboratory is to establish the importance of regulation of the branched chain alpha-ketoacid dehydrogenase complex (BCKDC) to growth and maintenance of body protein. We hypothesize that proper regulation of the activity state of BCKDC by way of its kinase (BDK) and its phosphatase (BDP) is critically important for body growth, tissue repair, and maintenance of body protein. We believe that growth and protection of body protein during illness and stress will be improved by therapeutic control of BCKDC activity. We also believe that it is possible that the negative effects of some drugs (PPAR alpha ligands) and dietary supplements (medium chain fatty acids) on growth and body protein maintenance can be countered by therapeutic control of BCDKC activity.

Branched-chain amino acids

The branched-chain amino acids (BCAA), isoleucine, leucine and valine, are unique in that they are principally metabolized extrahepatically in the skeletal muscle. This observation led to the investigation of these nutrients in a number of clinical scenarios. By far the most intensively studied applications for BCAA have been in patients with liver failure and/or patients in catabolic disease states. However, the resulting studies have not demonstrated a clear clinical benefit for BCAA nutritional supplements. In patients with liver failure, the BCAA did improve nitrogen retention and protein synthesis, but their effect on patient outcome was less clear. Similarly, in critically ill septic patients, BCAA did not improve either survival or morbidity. The BCAA are important nutrients, and it seems that any specific benefits associated with their use will be based upon a greater understanding of the underlying cellular biology. Potential areas of further research may include the combination of BCAA supplements with other anabolic factors (e.g. growth hormone) in managing patients with catabolic disease states.