Review for 10.1186/s12876-022-02213-0 (2022)

Title: Corticosteroid suppresses urea-cycle-related gene expressions in ornithine
transcarbamylase deficiency
Version: 1 Date: 05 Dec 2021
Reviewer's report:
Imoto K. et al report on two male patients with late-onset OTC deficiency who developed an
episode of hyperammonemia that was triggered by exposure to corticosteroid preparations. The
authors found that the magnitude of hyperammonemia in their own and previously reported
patients who developed hyperammonemic episodes after exposure to corticosteroid preparations
was greater than those induced by infectious disease or protein overload.
To clarify mechanism of corticosteroid-induced hyperammonemic decompensation, they
undertook dexamethasone (DEX) challenging tests using wild type (WT) and Otcspf-ash mice,
and found that DEX administration induced significant hyperammonemia in Otcspf-ash mice,
but not in WT mice or sham Otcspf-ash mice that received saline. They then performed
metabolomic analysis using livers of these mice and found that aspartate concentration was
increased while fumarate decreased in Otcspf-ash mice by DEX treatment, which lead the
authors to hypothesize that DEX reduced mRNA expression levels of urea cycle enzymes and
ORNT1. Actually, the DEX treatment generally reduced mRNA expression levels of these
enzymes, irrespective of genotype of mice. Among them, intriguingly, expression level of ARG1
mRNA was significantly decreased in Otcspf-ash mice, as compared to WT mice.
The reviewer finds that this study presents information that is not only useful in management
of patients with UCD but also in understanding the molecular mechanism of adaptive
characteristics of the urea cycle enzymes and related proteins. However, several points remain
to be addressed before this article can be published.
Major points
#1  N-acetylglutamate synthetase (NAGS) and mitochondrial aspartate-glutamate carrier
(SLC25A13) are also rate-limiting determinants of ureagenesis. The reviewer suggests
expression levels of mRNA of these two proteins are also studied. Alternatively, the authors
may discuss possible changes in the gene expressions of these proteins induced by DEX.
#2  P14, line 1  The authors refer to metabolites in the liver of the patients. Nevertheless, the
data presented in the relevant figures illustrate metabolites in liver of mice.
#3  P15, top line  ARG1 mRNA expression level is apparently lower in Otcspf-ash mice than in
WT mice, regardless of presence or absence of the dexamethasone challenge. Some explanatory
comments on this phenomenon would be made preferably.
#4  P18, line 14  The authors’ inference that arginine may not work appropriately in
hyperammonemic event in OTCD patients that is induced by corticosteroid administration
is reasonable. Nonetheless, it is recommended to replenish arginine to maintain its plasma
concentration in a physiological range, which is often reduced in OTCD patients, because
insufficient NO synthesis due to arginine deficiency is a crucial part of the OTCD
pathophysiology.
Minor points
#5  P2, line 7  “common” or something similar appears more descriptive than “popular” in this
context.
#6  P18, line 12.  “Ornitine” should be spelled “ornithine”.
#7  Figures 5b and 5c could be replaced by concise descriptions in the text.
#8  Table, top line  What kind of corticosteroid preparation did this patient (Ref. 7) receive?