Case series
The clinical courses and blood tests of the two late-onset OTCD patients who received corticosteroids are summarized in Fig. 1.
Case 1
A 44-year-old previously healthy Japanese man was admitted to a local hospital owing to hyperammonemia and disorientation after prednisolone treatment for sudden hearing loss. Although he recovered naturally, the cause was not clear. One year after this admission, he was admitted again to this hospital because of Meniere’s disease. There was neither a family history of metabolic disease, liver disease, nor evidence of alcohol use. Prednisolone was administered per os at a dose of 60 mg/day for Meniere’s disease. However, he suffered from disorientation, and his blood test revealed hyperammonemia (110 μg/dL) 5 days later. The following day, his consciousness level rapidly worsened, the serum ammonia level increased to 286 μg/dL, and he was transferred to our hospital for further evaluation and treatment. On arrival at our hospital, his serum ammonia concentration rose to 784 μg/dL, and a head CT scan revealed cerebral edema. Since his neurological deterioration resulted in a coma, we started mechanical ventilation and high-flow continuous hemodiafiltration combined with L-arginine, lactulose, and rifaximin administration. The serum ammonia level was reduced by these treatments and became normal 5 days later. His consciousness level also improved gradually, and he regained consciousness within the next few days. He was discharged from our hospital and returned to his previously active life while maintaining a low-protein diet. His repeated serum ammonia level was 50–60 μg/dL. As the drastic increase in serum ammonia is not typical of hepatic hyperammonemia, UCDs were indicated as the most likely cause of impaired consciousness. After obtaining the patient’s informed consent, we performed a genomic analysis of the OTC gene, and Arg40His (c.119G > A) in exon 2 of the OTC gene was identified.
Case 2
A 30-year-old previously healthy Japanese man was admitted because of disorientation to our hospital. His uncle and cousin died of OTCD, and another cousin was diagnosed with OTCD. There was neither a history of liver disease nor evidence of alcohol use. One week before admission, he began receiving 30 mg/day of oral prednisolone for bronchial asthma. On admission, his serum ammonia level was 423 μg/dL. We administered L-arginine at first. However, L-arginine treatment did not improve his consciousness level, and the CT scan revealed cerebral edema. We started continuous hemodiafiltration immediately to remove ammonia rapidly from his circulation. His serum ammonia level was normalized, and he regained consciousness 24 h later. He was discharged from our hospital with no neurological sequelae. A few months later, the condition of the patient was good during a follow-up visit, and his serum ammonia level was 30 μg/dL. He was diagnosed with OTC deficiency thanks to a combination of his history, clinical presentation, amino acid analysis, and orotic aciduria; however, the genomic analysis was not performed owing to lack of the agreement. The patient returned to his previously active life while maintaining a low-protein diet.
Although we saved these two patients by multimodal treatments, the mechanism of acute hyperammonemia in OTCD with corticosteroids is unclear. To better understand and manage these patients, we undertook an experimental model of corticosteroid-associated acute hyperammonemia by administering corticosteroids to Otcspf-ash mice, a mouse model of OTCD.
Dexamethasone induced hyperammonemia in Otcspf-ash mice
To evaluate the effects of DEX administration (20 mg/kg/body) on ammonia metabolism, the serum ammonia levels of the mice were measured at 0, 24, and 48 h after DEX administration. The ammonia levels in Otcspf-ash mice were similar to those of WT mice at 0 h (103.2 ± 8.3 and 99.6 ± 10.8 μg/dL, P = 0.80; Fig. 2). The ammonia levels in Otcspf-ash mice that were administered DEX were rapidly elevated at 24 h (WT-normal saline (NS) 123.3 ± 10.8 μg/dL vs. WT-DEX 119.3 ± 31.1 μg/dL, P = 0.86, WT-DEX 119.3 ± 31.1 μg/dL vs. Otcspf-ash-DEX 299.8 ± 130.6 μg/dL, P < 0.05, Otcspf-ash-NS 150.8 ± 25.4 μg/dL vs. Otcspf-ash-DEX 299.8 ± 130.6 μg/dL, P = 0.06; Fig. 2). Further elevations in the ammonia levels in Otcspf-ash mice that were administered DEX were observed at 48 h (WT-NS 130.0 ± 12.5 μg/dL vs. WT-DEX 135.0 ± 21.7 μg/dL, P = 0.75, WT-DEX 135.0 ± 21.7 μg/dL vs. Otcspf-ash-DEX 561.0 ± 357.7 μg/dL, P = 0.06, Otcspf-ash-NS 144.8 ± 35.6 μg/dL vs. Otcspf-ash-DEX 561.0 ± 357.7 μg/dL, P < 0.05; Fig. 2).
Metabolomic analysis and the association with urea-cycle-related gene expression
Next, we analyzed the levels of the metabolites extracted from the livers of the patients (Fig. 3, Fig. 4a, Fig. 4b). The heat maps of metabolites other than the urea-cycle-related metabolites showed no significant changes (Fig. 4a). OTC deficiency resulted in a decrease in citrulline and ornithine in comparison to the Otcspf-ash-NS mice and the WT-NS mice (P < 0.05, Fig. 4b). The levels of citrulline, ornithine, and arginine did not differ significantly between Otcspf-ash-DEX and Otcspf-ash-NS. The levels of citrulline and ornithine did not differ significantly between WT-DEX and WT-NS, whereas DEX administration increased arginine in WT mice. DEX administration resulted in a decrease in fumarate and an increase in N-acetyl ornithine in Otcspf-ash mice. DEX administration also increased aspartate in Otcspf-ash mice but decreased aspartate in the WT mice. Glutamine tended to increase in WT mice by DEX administration (P = 0.12), although L-glutamine did not increase in Otcspf-ash mice by DEX administration (Fig. S1a).
Quantitative PCR analysis of urea-cycle-related genes
We examined urea-cycle-related gene expression levels of the WT and Otcspf-ash livers (Fig. 5(a)), since it was considered that the cause of the increase in aspartate and the decrease in fumarate may be the change in urea-cycle-related gene expression. OTC deficiency significantly decreased the gene expressions of ornithine transcarbamylase (OTC) and arginase 1 (ARG1) in Otcspf-ash-NS mice compared to WT-NS mice (Fig. 5a and 5b). DEX administration significantly decreased the gene expressions of carbamoyl-phosphate synthase 1 (CPS1), OTC, arginosuccinate synthase 1 (ASS1), and arginosuccinate lyase (ASL) in both WT and Otcspf-ash mice (Fig. 5a and 5c). DEX administration significantly decreased ARG1 gene expression in WT mice but not in Otcspf-ash mice and did not affect mitochondrial ornithine transporter 1 (ORNT1) expression in either WT or Otcspf-ash mice (Fig. 5a and 5c). The mRNA expression of glutamine synthetase (GS) was not increased in Otcspf-ash and WT mice after the administration of DEX (Fig. S1b).