Overexpression of carbamoyl-phosphate synthase 1 significantly improves ureagenesis of human liver HepaRG cells only when cultured under shaking conditions

Expression and function of the urea cycle in widely-used hepatic cellular models

The group of rare metabolic defects termed urea cycle disorders (UCDs) occur within the ammonia elimination pathway and lead to significant neurocognitive sequelae for patients surviving decompensation episodes. Besides orthotopic liver transplantation, curative options are lacking for UCDs, with dietary management being the gold clinical standard. Novel therapeutic approaches are essential for UCDs; however, such effort presupposes preclinical testing in cellular models that effectively capture disease manifestation. Several cellular and animal models exist and aim to recapitulate the broad phenotypic spectrum of UCDs; however, the majority of those lack extensive molecular and biochemical characterization. The development of cellular models is emerging since animal models are extremely time and cost consuming, and subject to ethical considerations, including the 3R principle that endorses animal welfare over unchecked preclinical testing. The aim of this study was to compare the extent of expression and functionality of the urea cycle in two commercial hepatoma-derived cell lines, induced pluripotent stem cell hepatocytes (iPSC-Heps), primary human hepatocytes (PHHs) and human liver cell preparations. Using immunoblotting, immunocytochemistry, and stable isotope tracing of the urea cycle metabolites, we identified that the hepatoma-derived, 2-week differentiated HepaRG cells are urea cycle proficient and behave as cellular alternatives to PHHs. Furthermore, HepaRG cells were superior to iPSC-Heps, which are known to exhibit batch-to-batch variabilities in terms of hepatic maturity and enzyme expression. Finally, HepG2 cells lack the urea cycle enzymes ornithine transcarbamylase and arginase 1, the transporter ORNT1, which limits their suitability as model for the study of UCDs.

Elevated expression of histone deacetylase HDAC8 suppresses arginine-proline metabolism in necrotizing enterocolitis

Epigenetic alterations are especially important in necrotizing enterocolitis (NEC). Here, we reported that histone deacetylase 8 (HDAC8) plays a previously unknown role in modulating arginine metabolism via acetylation of histone 3 lysine 9 (acetyl-H3K9) regulation during the pathogenesis of NEC. We found that HDAC8 was upregulated in humans and mice intestinal samples with NEC, while selective inhibition of HDAC8 expression ameliorated NEC. HDAC8 regulates enzymes involved in the metabolic conversion of proline to arginine (PRODH, PRODH2, OAT, and OTC) and arginine to ornithine (ARG1). The results showed that H3K9ac signal in the PRODH/PRODH2 promoter region was mediated by HDAC8. Additionally, the decreased concentration of butyric acid was strongly correlated with elevated HDAC8 levels and circulating arginine, which may result from an unbalanced Firmicutes/Bacteroidetes ratio. These results reveal previously underappreciated roles of microbial metabolites and HDAC8 to coordinate the arginine metabolism during NEC development.

Maternal pyrimidine nucleoside supplementation regulates fatty acid, amino acid and glucose metabolism of offspring

Pyrimidine nucleosides (PN) are abundant in mammalian milk and mainly involved in glycogen deposition and lipid metabolism. To investigate the effects of maternal supplementation with pyrimidine nucleoside on glucose, fatty acids (FAs), and amino acids (AAs) metabolism in neonatal piglets. Forty pregnant sows were randomly assigned into the control (CON) group (fed a basal diet, n = 20) or the PN group (fed a basal diet supplemented with PN at 150 g/t, n = 20). Litter size, born alive and birth litter weight were recorded. The serum and placenta of sows, and jejunum and liver of neonatal piglets were sampled. The results indicated that supplementing sow diets with PN decreased birth mortality and increased the birth weight of piglets (P < 0.05). In addition, neonates from sows supplemented with PN had higher glucose levels in serum and liver compared with the CON group (P < 0.05). Moreover, maternal PN supplementation regulated the ratio of saturated FAs and polyunsaturated FAs, and AAs content in serum and liver of piglets (P < 0.05). Furthermore, an up-regulation of mRNA expression of genes related to glucose and AA transport were observed in the neonatal jejunum from the PN group (P < 0.05). Additionally, hepatic protein expressions of phosphorylated hormone-sensitive lipase (P-HSL), HSL, sterol regulatory element-binding transcription factor 1c (SREBP-1c), and phosphorylated protein kinase B (P-AKT) was higher in the piglets from the PN group than the CON group (P < 0.05). Together, maternal PN supplementation may regulate nutrient metabolism of neonatal piglets by modulating the gene expression of glucose and AA transporters in placenta and jejunum, and the gene and protein expression of key enzymes related to lipid metabolism in liver of neonatal piglets, which may improve the reproductive performance of sows.