Aberrations of ammonia metabolism in ornithine carbamoyltransferase-deficient spf-ash mice and their prevention by treatment with urea cycle intermediate amino acids and an ornithine aminotransferase inactivator

Abstract

Sparse fur with abnormal skin and hair (spf-ash) mice are deficient in ornithine carbamoyltransferase (OCT) activity, but their OCT protein is kinetically normal. We administered ammonium chloride to spf-ash mice, in order to analyze ammonia metabolism and to find a rationale for the therapy of OCT deficiency. Ammonia concentration in the liver of spf-ash mice increased to a level much higher than in the control. Ammonium chloride injection caused an increase in ornithine (Orn) 5 min after injection and an increase in the sum of Orn, citrulline (Cit) and arginine (Arg) for at least 15 min in the liver of control mice, but no increase in Orn, Cit and Arg in the liver of spf-ash mice. Treatment of spf-ash mice with Arg 5-20 min prior to the injection of ammonium chloride kept the hepatic ammonia concentration at a level comparable to that without the load. A significant reciprocal relationship between ammonia and Orn concentrations in the liver of spf-ash mice 5 min after an ammonium chloride load with or without Arg strongly suggests that ammonia disposal is dependent on the supply of Orn. In spf-ash mice loaded with tryptone as a nitrogen source, Arg supplementation showed a dramatic decrease in urinary orotic acid excretion in a dose-dependent manner. Similar effects were observed with Cit and Orn at the same dose, and a long-lasting effect with an ornithine aminotransferase inactivator, 5-(fluoromethyl)ornithine, at a much lower dose. The rate of urea formation in liver perfused with ammonium chloride was lower in spf-ash mice than in controls, but with the addition of Orn to the medium it increased to a similar level in control and spf-ash mice. These results indicate that OCT is not saturated with Orn in vivo under physiological conditions and that the administration or enrichment of the urea cycle intermediate amino acids enhances the OCT reaction so that the ammonia metabolism of OCT-deficient spf-ash mice is at least partially normalized.

Treatment of a citrin‐deficient patient at the early stage of adult‐onset type II citrullinaemia with arginine and sodium pyruvate

“…This report is the first to show that Na-Pyr in combination with arginine is effective in treating CTLN2. Arginine may facilitate ammonia detoxification via the activities of mitochondrial urea cycle enzymes (Awrich et al 1975;Li et al 1999), although its precise mechanism of action in CTLN2 is unknown. Exogenously supplied pyruvate can not only reduce the lactate/pyruvate ratio and hence the cytosolic NADH/NAD + ratio in the liver, which relieves the inhibition of glycolysis and activates ureagenesis by supplying cytosolic oxaloacetate and aspartate, but also may act as an energy source (Moriyama et al 2006;Tanaka et al 2007).…”

Slc25a13-Knockout Mice Harbor Metabolic Deficits but Fail To Display Hallmarks of Adult-Onset Type II Citrullinemia

“…Mice were maintained on standard laboratory chow (Prolab RMH 1000) and analyzed at 8, 26, and 52 weeks of age. Eight-to 12-week-old mice were also subjected to ammonium chloride (NH 4 Cl) injection (0.2 M solution; administered at 2 mmol per kg of body weight) as previously described (22). Sodium chloride (NaCl) injection (0.2 M solution; administered at 2 mmol per kg of body weight) was used as a control.…”

“…The freeze-clamped livers of 10-to 18-week-old mice were pulverized in liquid nitrogen, and the solute was extracted with 3% sulfosalicylic acid. The ammonia levels in the extracts were analyzed by flow injection (46) as described by Li et al (22). The amino acid concentrations in the extracts were determined with a model 835 amino acid analyzer (Hitachi, Tokyo, Japan).…”

Interaction between murinespf-ashmutation and genetic background yields different metabolic phenotypes

“…Ornithine entry rate should not be affected, at least directly, by the reduction in OTC activity due to the spf-ash mutation. Ornithine has been shown in mice to be the first UCI to increase in the liver after a sudden nitrogen load, expanding the amount of intermediates and supporting the need for ammonia detoxification through urea synthesis (17). Similarly, in sheep, the portal infusion of ammonia increased the extraction rate of ornithine, but not of the other UCI (24).…”