Plasma and urinary levels of carnitine in different experimental models of hyperammonemia and the effect of sodium benzoate treatment

Effects of L-carnitine in patients with hepatic encephalopathy

AIM

To evaluate the influence of L-carnitine on mental conditions and ammonia effects on patients with hepatic encephalopathy (HE).

METHODS

One hundred and fifty patients (10 patients with alcoholism, 41 patients with hepatitis virus B infection, 78 patients with hepatitis C virus infection, 21 patients with cryptogenetic cirrhosis) meeting the inclusion criteria were randomized into group A receiving a 90-d treatment with L-carnitine (2 g twice a day) or into group B receiving placebo in double blind.

RESULTS

At the end of the study period, a significant decrease in NH4 fasting serum levels was found in patients with hepatic encephalopathy (P<0.05) after the treatment with levocarnitine (LC). Significant differences were also found between symbol digit modalities test and block design in patients with hepatic encephalopathy (P<0.05).

CONCLUSION

Results of our study suggest an important protective effect of L-carnitine against ammonia-precipitated encephalopathy in cirrhotic patients.

Carnitine metabolism in chronic liver disease

The liver is a central organ for carnitine metabolism and for the distribution of carnitine to the body. It is therefore not surprising that carnitine metabolism is impaired in patients and experimental animals with certain types of chronic liver disease. In this review, the changes in carnitine metabolism associated with chronic liver disease and the role of carnitine as a therapeutic agent in some of these conditions are discussed.

Benzoate therapy and carnitine deficiency in non-ketotic hyperglycinemia

Five patients presenting with non-ketotic hyperglycinemia in the neonatal period were treated with sodium benzoate to normalize plasma glycine levels. This therapy resulted in seizure reduction and a marked increase in wakefulness. Plasma carnitine deficiency was noted in three of four patients tested, and benzoylcarnitine was identified in plasma, urine, and CSF. Treatment with L-carnitine normalized plasma free carnitine. L-carnitine showed a tendency to increase the glycine conjugation of benzoate. An episode of coma and increased seizures in one patient was associated with a toxic level of benzoate, probably due to insufficient mobilization of glycine for conjugation. High dose benzoate therapy improved the quality of life of surviving patients. Close monitoring of glycine, benzoate and carnitine levels is advised.

Tissue acylcarnitine and acyl-coenzyme A profiles in chronically hyperammonemic mice treated with sodium benzoate and supplementary L-carnitine

The aim of the present study, was to establish the hepatic profile of acyl-coenzyme A (acyl-CoA) in relation to the hepatic profile of acylcarnitines in chronically hyperammonemic spf mice (hereditary deficiency in ornithine transcarbamylase) treated with sodium benzoate alone or in combination with L-carnitine. The muscular profile of the acylcarnitines and the stability of sarcolemma were also assessed in the same mice. Following administration of sodium benzoate, we observed decreases in hepatic total and free coenzyme A and in acetyl-CoA, which was accompanied by an increase in hepatic acyl-CoA. This treatment also resulted in increased free carnitine, decreased total carnitine, and decreased short and medium chain acylcarnitines in the liver. Increases in plasma creatine kinase levels, muscular free, total, and in short and medium chain acylcarnitines were also observed in this treatment group. In mice receiving a combination of sodium benzoate and L-carnitine, increases in free and total coenzyme A, acetyl-CoA and in free, total and esterified hepatic carnitines were observed. In this treatment group, the plasma level of creatine kinase was found to be reduced, while the free muscular carnitine was increased. Our results indicate that sodium benzoate is implicated in the decrease of total hepatic coenzyme A, through either an inhibition of CoA synthesis or activation of its degradation. The distribution of hepatic coenzyme-A and of hepatic and muscular carnitine (free or esterified) is altered following administration of sodium benzoate which results in a further destabilization of the sarcolemma induced by hyperammonemia. Supplemental treatment with L-carnitine was shown to have a positive effect by increasing hepatic coenzyme A and carnitine levels and restoring the stability of the sarcolemma caused by the treatment of sodium benzoate alone.

The biochemistry and toxicology of benzoic acid metabolism and its relationship to the elimination of waste nitrogen

Detoxification of sodium benzoate by elimination as a conjugate with glycine, a nonessential amino acid, provides a pathway for the disposal of waste nitrogen. Since 1979, sodium benzoate has been widely used in the therapeutic regimen to combat ammonia toxicity in patients born with genetic defects in the urea cycle. Although the clinical use of benzoate is associated with improved outcome, the search for biochemical evidence in support of the rationale for benzoate therapy has produced conflicting results. This review begins with an historical account leading to elucidation of the biochemistry of benzoate detoxification and early work indicating the potential utility of the pathway for elimination of waste nitrogen. An introduction to contemporary efforts at employing benzoate to treat hyperammonemia is followed by a detailed review of studies on benzoate metabolism and resultant toxic interactions with other major metabolic pathways. With this background, the several metabolic routes by which benzoate is thought to promote the disposal of waste nitrogen are then examined, followed by a consideration of alternative mechanisms by which benzoate might combat ammonia toxicity.

Effect of L-carnitine on cerebral and hepatic energy metabolites in congenitally hyperammonemic sparse-fur mice and its role during benzoate therapy

Sparse-fur (spf) mutant mice with X-linked ornithine transcarbamylase deficiency were used to study the effect of L-carnitine on energy metabolites in congenital hyperammonemia. L-Carnitine was used at doses of 2, 4, 8, or 16 mmol/kg body weight (BW), and levels of ammonia, glutamine, glutamate, and some intermediates of energy metabolism were measured in brain and liver of spf/Y mice. Cerebral and hepatic levels of ammonia were decreased with 4 mmol L-carnitine (P < .001), whereas other doses did not seem to have any effect on this metabolite. Cerebral levels of glutamine were decreased following administration of L-carnitine at doses of up to 4 mmol/kg BW, whereas hepatic glutamine levels remained unaltered at all doses of L-carnitine. Both cerebral and hepatic levels of pyruvate, lactate, and alpha-ketoglutarate were decreased at doses of up to 8 mmol L-carnitine/kg BW. L-Carnitine treatment elevated adenosine triphosphate (ATP), free coenzyme A (CoA), and acetyl CoA levels in both brain and liver of spf/Y mice. Cytosolic and mitochondrial redox ratios of spf/Y mice, which were altered by congenital chronic hyperammonemia, were partially corrected by L-carnitine administration. L-Carnitine supplementation to spf/Y mice during sodium benzoate therapy also restored the availability of free CoA and ATP, thus counteracting the adverse effects of higher doses of sodium benzoate. These changes in free CoA and acetyl CoA levels could be due to the deinhibition of pantothenate kinase and stimulation of fatty acid oxidation by L-carnitine.(ABSTRACT TRUNCATED AT 250 WORDS)

Dose-dependent pharmacokinetics of benzoic acid following oral administration of sodium benzoate to humans

Plasma concentration-time data for benzoic and hippuric acids and urinary excretion-time data for hippuric acid were analyzed simultaneously after oral doses of 40, 80 or 160 mg/kg sodium benzoate administered at least one week apart to 6 healthy subjects. The mean AUCs of benzoic acid after the doses of 80 and 160 mg/kg of sodium benzoate were 3.7- and 12.0-times greater, respectively, than after 40 mg/kg. However, the mean AUC of hippuric acid was roughly proportional to the benzoate doses. The observed data were explained by a one-compartment model with first-order rate absorption and Michaelis-Menten elimination of benzoic acid, together with a one-compartment model with first-order elimination for hippuric acid. Although the maximum rate of biotransformation of benzoic acid to hippuric acid varied between 17.2 and 28.8 mg.kg-1.h-1 among the six individuals, the mean value (23.0 mg.kg-1.h-1) was fairly close to that provided by daily maximum dose (0.5 g.kg-1.day-1) recommended in the treatment of hyperammonaemia in patients with inborn errors of ureagenesis. The individual maximum rate of metabolism can be estimated from the urinary excretion rate of hippuric acid 1.5 to 3 h after the single oral dose of 80 to 160 mg.kg-1 sodium benzoate. The justification of this concept requires further studies in patients with inborn errors of urea synthesis.