Novel combined UGT1A1 mutations in Crigler Najjar Syndrome type I

Genetic variation features of neonatal hyperbilirubinemia caused by inherited diseases

BACKGROUND

Genetic factors play an important role in neonatal hyperbilirubinemia (NH) caused by genetic diseases.

AIM

To explore the characteristics of genetic mutations associated with NH and analyze the correlation with genetic diseases.

METHODS

This was a retrospective cohort study. One hundred and five newborn patients diagnosed with NH caused by genetic diseases were enrolled in this study between September 2020 and June 2023 at the Second Affiliated Hospital of Xiamen Medical College. A 24-gene panel was used for gene sequencing to analyze gene mutations in patients. The data were analyzed via Statistical Package for the Social Sciences 20.0 software.

RESULTS

Seventeen frequently mutated genes were found in the 105 patients. Uridine 5'-diphospho-glucuronosyltransferase 1A1 (UGT1A1) variants were identified among the 68 cases of neonatal Gilbert syndrome. In patients with sodium taurocholate cotransporting polypeptide deficiency, the primary mutation identified was Na+/taurocholate cotransporting polypeptide Ntcp (SLC10A1). Adenosine triphosphatase 7B (ATP7B) mutations primarily occur in patients with hepatolenticular degeneration (Wilson's disease). In addition, we found that UGT1A1 and glucose-6-phosphate dehydrogenase mutations were more common in the high-risk group than in the low-risk group, whereas mutations in SLC10A1, ATP7B, and heterozygous 851del4 mutation were more common in the low-risk group.

CONCLUSION

Genetic mutations are associated with NH and significantly increase the risk of disease in affected newborns.

Ozone induced multigenerational glucose and lipid metabolism disorders in Drosophila

Ozone (O3), a persistent pollutant, poses a significant health threat. However, research on its multigenerational toxicity remains limited. Leveraging the Drosophila model with its short lifespan and advanced genetic tools, we explored the effects of O3 exposure across three generations of fruit flies. The findings revealed that O3 disrupted motility, body weight, stress resistance, and oxidative stress in three generations of flies, with varying effects observed among them. Transcriptome analysis highlighted the disruption of glucose metabolism-related pathways, encompassing gluconeogenesis/glycolysis, galactose metabolism, and carbon metabolism. Hub genes were identified, and RT-qPCR results indicated that O3 decreased their transcription levels. Comparative analysis of their human orthologs was conducted using Comparative Toxicogenomics Database (CTD) and DisGeNET databases. These genes are linked to various metabolic diseases, including diabetes, hypoglycemia, and obesity. The trehalose content was reduced in F0 generation flies but increased in F1-F2 generations after O3 exposure. While the trehalase and glucose levels were decreased across F0-F2 generations. TAG synthesis-related genes were significantly upregulated in F0 generation flies but downregulated in F1-F2 generations. The expression patterns of lipolysis-related genes varied among the three generations of flies. Food intake was increased in F0 generation flies but decreased in F1-F2 generations. Moreover, TAG content was significantly elevated in F0 generation flies by O3 exposure, while it was reduced in F2 generation flies. These differential effects of O3 across three generations of flies suggest a metabolic reprogramming aimed at mitigating the damage caused by O3 to flies. The study affirms the viability of employing the Drosophila model to investigate the mechanisms underlying O3-induced glucose and lipid metabolism disorders while emphasizing the importance of studying the long-term health effects of O3 exposure. Moreover, this research highlights the Drosophila model as a viable tool for investigating the multigenerational effects of pollutants, particularly atmospheric pollutants.

Molecular biology of glucose-6-phosphate dehydrogenase and UDP-glucuronosyltransferase 1A1 in the development of neonatal unconjugated hyperbilirubinemia

Glucose-6-phosphate dehydrogenase (G6PD) deficiency and variants of the UDP-glucuronosyltransferase 1A1 (UGT1A1) gene are the most common genetic causes of neonatal unconjugated hyperbilirubinemia (NUH). In this review, we searched PubMed for articles on the genetic causes of NUH published before December 31, 2022, and analyzed the data. On the basis of the results, we reached eight conclusions: (1) 37 mutations of the G6PD gene are associated with NUH; (2) the clinical manifestation of G6PD deficiency depends not only on ethnicity but also on the molecular mechanisms underlying the deficiency (and thus its severity); (3) of mutations in the UGT1A1 gene, homozygous c.-53A(TA)6TAA > A(TA)7TAA is the main cause of NUH in Caucasians and Africans, whereas homozygous c.211G > A is the main genetic cause of NUH in East Asians; (4) in Indonesian neonates, homozygous c.-3279T > G is the most common cause of NUH development, and neither c.-53 A(TA)6TAA > A(TA)7TAA nor c.211G > A causes it; (5) in breast-fed East Asian neonates, the TA7 repeat variant of the UGT1A1 gene protects against the development of NUH; (6) G6PD deficiency combined with homozygous c.211G > A variation of the UGT1A1 gene increases the risk of severe NUH; (7) in Pakistani and Caucasian patients with Crigler-Najjar syndrome type 2 (CN-2), point mutations of the UGT1A1 gene are widely distributed and frequently occur with variation at nucleotide -53, whereas in Asian patients with CN-2, compound homozygous variations in the coding region are frequently observed; and (8) records of G6PD deficiency and UGT1A1 variation status for a neonate offer useful pharmacogenomic information that can aid long-term care. These results indicate that timely diagnosis of NUH through molecular tests is crucial and that early initiation of treatment for the neonates and educational programs for their parents improves outcomes.

Human UDP-glucuronosyltransferase 1As catalyze aristolochic acid D O-glucuronidation to form a lesser nephrotoxic glucuronide

ETHNOPHARMACOLOGICAL RELEVANCE

Aristolochic acids (AAs) are naturally occurring nitro phenanthrene carboxylic acids primarily found in plants of the Aristolochiaceae family. Aristolochic acid D (AAD) is a major constituent in the roots and rhizomes of the Chinese herb Xixin (the roots and rhizomes of Asarum heterotropoides F. Schmidt), which is a key material for preparing a suite of marketed Chinese medicines. Structurally, AAD is nearly identical to the nephrotoxic aristolochic acid I (AAI), with an additional phenolic group at the C-6 site. Although the nephrotoxicity and metabolic pathways of AAI have been well-investigated, the metabolic pathway(s) of AAD in humans and the influence of AAD metabolism on its nephrotoxicity has not been investigated yet.

AIM OF THE STUDY

To identify the major metabolites of AAD in human tissues and to characterize AAD O-glucuronidation kinetics in different enzyme sources, as well as to explore the influence of AAD O-glucuronidation on its nephrotoxicity.

MATERIALS AND METHODS

The O-glucuronide of AAD was biosynthesized and its chemical structure was fully characterized by both 1H-NMR and 13C-NMR. Reaction phenotyping assays, chemical inhibition assays, and enzyme kinetics analyses were conducted to assess the crucial enzymes involved in AAD O-glucuronidation in humans. Docking simulations were performed to mimic the catalytic conformations of AAD in human UDP-glucuronosyltransferases (UGTs), while the predicted binding energies and distances between the deprotonated C-6 phenolic group of AAD and the glucuronyl moiety of UDPGA in each tested human UGT isoenzyme were measured. The mitochondrial membrane potentials (MMP) and reactive oxygen species (ROS) levels in HK-2 cells treated with either AAI, or AAD, or AAD O-glucuronide were tested, to elucidate the impact of O-glucuronidation on the nephrotoxicity of AAD.

RESULTS

AAD could be rapidly metabolized in human liver and intestinal microsomes (HLM and HIM, respectively) to form a mono-glucuronide, which was purified and fully characterized as AAD-6-O-β-D-glucuronide (AADG) by NMR. UGT1A1 was the predominant enzyme responsible for AAD-6-O-glucuronidation, while UGT1A9 contributed to a lesser extent. AAD-6-O-glucuronidation in HLM, HIM, UGT1A1 and UGT1A9 followed Michaelis-Menten kinetics, with the Km values of 4.27 μM, 9.05 μM, 3.87 μM, and 7.00 μM, respectively. Docking simulations suggested that AAD was accessible to the catalytic cavity of UGT1A1 or UGT1A9 and formed catalytic conformations. Further investigations showed that both AAI and AAD could trigger the elevated intracellular ROS levels and induce mitochondrial dysfunction and in HK-2 cells, but AADG was hardly to trigger ROS accumulation and mitochondrial dysfunction.

CONCLUSION

Collectively, UGT1A-catalyzed AAD 6-O-glucuronidation represents a crucial detoxification pathway of this naturally occurring AAI analogs in humans, which is very different from that of AAI.