Corticosteroid suppresses urea-cycle-related gene expressions in ornithine transcarbamylase deficiency

Abstract

Background: Ornithine transcarbamylase deficiency (OTCD) is most common among urea cycle disorders (UCDs), defined by defects in enzymes associated with ureagenesis. Corticosteroid administration to UCD patients, including OTCD patients, is suggested to be avoided, as it may induce life-threatening hyperammonemia. The mechanism has been considered nitrogen overload due to the catabolic effect of corticosteroids; however, the pathophysiological process is unclear.

Methods: To elucidate the mechanism of hyperammonemia induced by corticosteroid administration in OTCD patients, we analyzed a mouse model by administering corticosteroids to OTC^spf-ash mice deficient in the OTC gene. Dexamethasone (DEX; 20 mg/kg) was administered to the OTC^spf-ash and wild-type (WT) mice at 0 and 24 h, and the serum ammonia concentrations, the levels of the hepatic metabolites, and the gene expressions related with ammonia metabolism in the livers and muscles were analyzed.

Results: The ammonia levels in Otc^spf-ash mice that were administered DEX tended to increase at 24 h and increased significantly at 48 h. The metabolomic analysis showed that the levels of citrulline, arginine, and ornithine did not differ significantly between Otc^spf-ash mice that were administered DEX and normal saline; however, the level of aspartate was increased drastically in Otc^spf-ash mice owing to DEX administration (P < 0.01). Among the enzymes associated with the urea cycle, mRNA expressions of carbamoyl-phosphate synthase 1, ornithine transcarbamylase, arginosuccinate synthase 1, and arginosuccinate lyase in the livers were significantly downregulated by DEX administration in both the Otc^spf-ash and WT mice (P < 0.01). Among the enzymes associated with catabolism, mRNA expression of Muscle RING-finger protein-1 in the muscles was significantly upregulated in the muscles of WT mice by DEX administration (P < 0.05).

Conclusions: We elucidated that corticosteroid administration induced hyperammonemia in Otc^spf-ash mice by not only muscle catabolism but also suppressing urea-cycle-related gene expressions. Since the urea cycle intermediate amino acids, such as arginine, might not be effective because of the suppressed expression of urea-cycle-related genes by corticosteroid administration, we should consider an early intervention by renal replacement therapy in cases of UCD patients induced by corticosteroids to avoid brain injuries or fatal outcomes.

Keywords: Corticosteroid; Hyperammonemia; Late-onset ornithine transcarbamylase deficiency; Ornithine transcarbamylase deficiency; Urea cycle disorder.

Fig. 1

The time-course of serum ammonia levels. The blood samples were collected at 0, 24, and 48 h after the first DEX administration. Ammonia levels at 24 h after DEX administration were increased in the Otc^spf−ash-DEX group (P < 0.05; vs. dex-matched controls, P = 0.06; vs. genotype-matched controls). Ammonia levels at 48 h after DEX administration were further increased in the Otc^spf−ash-DEX group (P = 0.06; vs. dex-matched controls, P < 0.05; vs. genotype-matched controls). Data are expressed as the mean ± SD. WT-NS and WT-DEX, n = 3/group; Otc^spf−ash- NS and Otc^spf−ash-DEX, n = 5/group. ^†P < 0.05; vs. dex-matched controls, *P < 0.05; vs. genotype-matched controls. NS; normal saline, DEX; dexamethasone

Fig. 2

The levels of hepatic metabolites from WT and Otc^spf−ash mice that were administered DEX or NS. a Heat map analysis of metabolomics. It was generated by coloring the values of all data across their respective ranges. The color red indicates that the relative content of metabolites is high, while green indicates that they are low. The brightness of each color corresponds to the magnitude of the difference between the observed value and the average value. b The amounts of urea-cycle-related metabolites in WT and Otc^spf−ash mice, normalized to those in WT-NS were presented as mean ± SD. ∗ p < 0.05 and ∗ ∗p < 0.01. ASS1, arginosuccinate synthase 1; ASL, arginosuccinate lyase; ARG1, arginase 1; ORNT1, mitochondrial ornithine transporter 1; OTC, ornithine transcarbamylase; CPS1, carbamoyl-phosphate synthase 1. NS; normal saline, DEX; dexamethasone

Fig. 3

The urea-cycle-related gene expression levels in WT and Otc^spf−ash mice administered DEX or NS. Quantitative RT-PCR analysis of the urea-cycle-related genes. The gene expression levels normalized to those of WT-NS and were presented as mean ± SE. ∗p < 0.05 and ∗∗p < 0.01. SLC25A13, Solute Carrier Family 25 Member 13; ASS1, arginosuccinate synthase 1; ASL, arginosuccinate lyase; ARG1, arginase 1; ORNT1, mitochondrial ornithine transporter 1; OTC, ornithine transcarbamylase; CPS1, carbamoyl-phosphate synthase 1; NAGS, N-acetylglutamate synthetase. NS; normal saline, DEX; dexamethasone

Fig. 4

The gene expression levels related with catabolism and anabolism in WT and Otc^spf−ash muscles administered DEX or NS. a Quantitative RT-PCR analysis of the anabolism-related genes. b Quantitative RT-PCR analysis of the catabolism-related genes. c Quantitative RT-PCR analysis of the autophagy-related genes. The gene expression levels normalized to those of WT-NS and were presented as mean ± SE. ∗p < 0.05 and ∗ ∗p < 0.01. PI3K, phosphatidylinositol-3 kinase; mTOR, mammalian target of rapamycin; 4E-BP1, Eukaryotic translation initiation factor 4E-binding protein 1; eIF4E, eukaryotic translation initiation factor 4E; Rps6kb1, Ribosomal Protein S6 Kinase B1; FOXO1, forkhead box protein O1; KLF15, Kruppel Like Factor 15; MuRF-1, Muscle RING-finger protein-1; ULK1, Unc-51 Like Autophagy Activating Kinase 1; ATG, Autophagy related. NS; normal saline, DEX; dexamethasone