Inhibition of urea synthesis by 4-pentenoic acid

The effect of L-carnitine supplementation in 4 pentenoic acid treated rats

The effects of prolonged administration (7 days) of 4 pentenoic acid (4PA, 20 mg/kg/day) or 4PA (20 mg/kg/day) with L-carnitine (200 mg/kg/day) on carnitine metabolism and morphological changes of liver mitochondria were assessed in rats. 4PA-treated rats showed hyperammonemia, decreased levels of blood glucose, free fatty acids and beta-OH-butyrate, and of free carnitine in serum, muscle and liver, increased excretion of acylcarnitine in urine, and enlarged mitochondria with microvesicular steatosis, when compared to saline-injected control rats, respectively. 4PA plus L-carnitine rats showed decreased levels of blood ammonia and increased levels of beta-OH-butyrate, compared to the 4PA group. On the other hand, the levels of free carnitine in serum and liver in rats treated with both 4PA and L-carnitine were increased, when compared to controls. The ratio of acylcarnitine to free carnitine excreted in urine in 4PA-treated rats was higher than that in either the control or 4PA plus L-carnitine group. The liver mitochondria in the 4PA plus L-carnitine group were the same as in the controls. The results suggested that the abnormal biochemical and morphological findings due to only 4PA may be relieved with L-carnitine supplementation.

Effects of organic acids on the synthesis of citrulline by intact rat liver mitochondria

Citrulline synthesis, mostly regulated at the carbamoyl-phosphate synthase I (EC 6.3.4.16) step by the intramitochondrial concentration of ATP and/or N-acetylglutamate is tested with four organic acids: propionate, alpha-ketobutyrate, dipropyl-acetate and 4-pentenoate. In the presence of 10 mM succinate, as the oxidizable substrate, citrullinogenesis was only inhibited by propionate and 4-pentenoate. With 10 mM L-glutamate, a significant inhibition was observed with the four acids. After the addition of ATP and N-acetylglutamate to uncoupled mitochondria, no inhibition could be demonstrated with dipropylacetate and 4-pentenoate. However, a slight inhibition remained with propionate and alpha-ketobutyrate. When mitochondria were incubated with 10 mM L-glutamate, ATP decreased with propionate, dipropylacetate and 4-pentenoate. Under the same conditions, N-acetylglutamate synthesis was strongly inhibited by each organic acid. The decrease of N-acetylglutamate synthesis was related to the constant diminution of intramitochondrial acetyl-coenzyme A (CoA) and to the increase of propionyl-CoA with propionate and alpha-ketobutyrate. Acetyl-CoA and propionyl-CoA are respectively substrate and competitive inhibitor of the N-acetylglutamate synthase (EC 2.3.1.1). Each acid displayed its optimum inhibition at concentrations between 1 and 2 mM. At these acid concentrations, mitochondria had the lowest acetyl-CoA content and the highest propionyl-CoA content.

Inhibition of urea synthesis by pent-4-enoate associated with decrease in N-acetyl-L-glutamate concentration in isolated rat hepatocytes

Pent-4-enoate at 0.1 to 1.0 mM strongly inhibited urea synthesis in isolated rat hepatocytes. Pent-4-enoate at the same concentrations markedly decreased concentrations of N-acetyl-L-glutamate, an essential activator of carbamoyl-phosphate synthase-I (EC 2.7.2.5), and the decrease was well in parallel with the inhibition of urea synthesis by pent-4-enoate. This compound also lowered cellular concentrations of acetyl-CoA, a substrate of acetylglutamate synthase (EC 2.3.1.1). Pent-4-enoate in a dose of 1 mM did not significantly affect cellular concentrations of ATP, and had no direct effect on acetylglutamate synthase activity. These results suggest that the inhibition of urea synthesis by pent-4-enoate is due to decrease in N-acetyl-L-glutamate concentration and that the decrease is probably brought about by decreased rate of its synthesis due to the lowered concentration of cellular acetyl-CoA.

Urinary organic acid profiles of Reye's syndrome patients

The status of mitochondrial functioning in Reye's syndrome was assessed by comparing organic acid profiles from nine pathological urines with those from normal urines. It was found that Reye's syndrome urines have a normal content of succinic, oxaloacetic, aconitic, and citric acids suggesting that the enzymes of the acid cycle are functional. Elevated pyruvate and depressed alpha-ketoglutarate levels were observed. Abnormal urinary constituents detected were salicylic and adipic acids. Presence of the latter indicates that the enzymes of fatty acid beta-oxidation are functional.

Effect of pent-4-enoic acid, propionic acid and other short-chain fatty acids on citrulline synthesis in rat liver mitochondria

19 The effect of pent-4-enoic acid, propionic acid and several other short-chain fatty acids on citrulline synthesis in rat liver mitochondria was studied. 2.Pent-4-enoate at 1 mM inhibited mitochondrial citulline synthesis by about 80-90%. It is concluded that pent-4-enoate inhibits citrulline synthesis by interfering with some aspect of mitochondrial energy metabolism. This results in impairment of mitochondrial ornithine uptake or depletion of mitochondrial ATP, which, in turn, impairs carbamoyl phosphate synthesis or both. Evidence in support of this conclusion includes: pent-4-enoate has no effect on citrulline synthesis supported by succinate or exogenous ATP; pent-4-enoate lowers the medium plus mitochondrial ATP concentration; finally, when glutamate is the oxidizable substrate, pent-4-enoate decreases the carbamoyl phosphate concentration in mitochondria incubated without ornithine to minimize citrulline synthesis and impairs the mitochondrial uptake of ornithine, but it has neither effect when succinate is the oxidizable substrate. 4. Propionate, butyrate and crotonate also inhibit mitochondrial citrulline synthesis, but much less than pent-4-enoate. 5. Acetate, pentanoate, pent-2-enoate, hexanoate, octanoate, isovalerate, tiglylate and alpha-methylbutyrate have little or no effect on mitochondrial citrulline synthesis.