Quantitative trait analysis of polymorphisms in two bilirubin metabolism enzymes to physiologic bilirubin levels in Chinese newborns

Influence of UGT1A1 Genetic Variants on Free Bilirubin Levels in Japanese Newborns: A Preliminary Study

BACKGROUND

Free bilirubin (Bf) is a better marker than total serum bilirubin (TSB) for predicting bilirubin encephalopathy (BE). To date, two UGT1A1 genetic variants (rs4148323 and rs3064744) have been associated with neonatal hyperbilirubinemia; however, the direct association between UGT1A1 variants and Bf levels in newborns has not been elucidated.

METHODS

We retrospectively analyzed the clinical data of 484 infants, including the genotype data of two UGT1A1 genetic variants. We divided the infants into a high Bf group (Bf ≥ 1.0 µg/dL, n = 77) and a non-high Bf group (Bf < 1.0 µg/dL, n = 407), based on the peak Bf values. Logistic regression analysis was performed to calculate the odds ratios (ORs) for each variant allele compared to wild-type alleles.

RESULTS

The frequencies of the A allele in rs4148323 and (TA)₇ allele in rs3064744 in the high Bf group (29% and 4%, respectively) were significantly different from those in the non-high Bf group (16% and 12%, respectively). In logistic regression analysis, for rs4148323, the A allele was significantly associated with an increased risk of hyper-free bilirubinemia over the G allele (adjusted OR: 1.80, 95% confidence interval [CI]: 1.19-2.72, p < 0.01). However, for rs3064744, the (TA)₇ allele was significantly associated with a decreased risk of hyper-free bilirubinemia over the (TA)₆ allele (adjusted OR: 0.42, 95% CI: 0.18-0.95, p = 0.04).

CONCLUSIONS

This study is the first to show that the A allele in rs4148323 is a risk factor and that the (TA)₇ allele in rs3064744 is a protective factor for developing hyper-free bilirubinemia in Japanese newborns.

Ensemble learning for the early prediction of neonatal jaundice with genetic features

BACKGROUND

Neonatal jaundice may cause severe neurological damage if poorly evaluated and diagnosed when high bilirubin occurs. The study explored how to effectively integrate high-dimensional genetic features into predicting neonatal jaundice.

METHODS

This study recruited 984 neonates from the Suzhou Municipal Central Hospital in China, and applied an ensemble learning approach to enhance the prediction of high-dimensional genetic features and clinical risk factors (CRF) for physiological neonatal jaundice of full-term newborns within 1-week after birth. Further, sigmoid recalibration was applied for validating the reliability of our methods.

RESULTS

The maximum accuracy of prediction reached 79.5% Area Under Curve (AUC) by CRF and could be marginally improved by 3.5% by including genetic variant (GV). Feature importance illustrated that 36 GVs contributed 55.5% in predicting neonatal jaundice in terms of gain from splits. Further analysis revealed that the main contribution of GV was to reduce the false-positive rate, i.e., to increase the specificity in the prediction.

CONCLUSIONS

Our study shed light on the theoretical and practical value of GV in the prediction of neonatal jaundice.

Association between HO‑1 gene promoter polymorphisms and diseases (Review)

Heme oxygenase‑1 (HO‑1) is an inducible cytoprotective enzyme that degrades heme into free iron, carbon monoxide and biliverdin, which is then rapidly converted into bilirubin. These degradation products serve an important role in the regulation of inflammation, oxidative stress and apoptosis. While the expression level of HO‑1 is typically low in most cells, it may be highly expressed when induced by a variety of stimulating factors, a process that contributes to the regulation of cell homeostasis. In the 5'‑non‑coding region of the HO‑1 gene, there are two polymorphic sites, namely the (GT)n dinucleotide and T(‑413)A single nucleotide polymorphism sites, which regulate the transcriptional activity of HO‑1. These polymorphisms have been shown to be closely associated with the occurrence and progression of numerous diseases, including cardiovascular, pulmonary, liver and kidney, various types of cancer and viral diseases. The present article reviews the progress that has been made in research on the association between the two types of polymorphisms and these diseases, which is expected to provide novel strategies for the diagnosis, treatment and prognosis of various diseases.

Insomnia affects the levels of plasma bilirubin and protein metabolism: an observational study and GWGEIS in UK Biobank cohort

STUDY OBJECTIVES

We aim to explore the mechanism of relationship between insomnia and liver metabolism by examining the gene × insomnia interactions.

METHODS

Individual level genotypic and phenotypic data were obtained from the UK Biobank cohort. Regression analysis was first conducted to test the association of insomnia with plasma total bilirubin (TBil; n = 186,793), direct bilirubin (DBil; n = 159,854) and total protein (TP; n = 171,574) in UK Biobank cohort. Second, genome-wide gene-environment interaction study (GWGEIS) was conducted by PLINK 2.0, and FUMA platform was used to identify enriched pathway terms.

RESULTS

In UK Biobank cohort, we found that TP (P < 2.00 × 10^-16), DBil (P = 1.72 × 10^-3) and TBil (P = 3.38 × 10^-5) were significantly associated with insomnia. GWGEIS of both DBil and TBil observed significant G × INSOMNIA effects between insomnia and UDP Glucuronosyltransferase Family 1 (rs6431558, P = 6.26 × 10^-11) gene. GWGEIS of TP also detected several significant genes interacting with insomnia, such as KLF15, (rs70940816, P = 6.77 × 10^-10) and DOK7, (rs2344205, P = 1.37 × 10^-9). Multiple gene ontology (GO) terms were identified for bilirubin, such as GO_URONIC_ACID_METABOLIC_PROCESS (adjusted P = 4.15 × 10^-26).

CONCLUSION

Our study results suggested negative associations between insomnia and DBil and TBil; and a positive association between insomnia and TP.

A UGT1A1 variant is associated with serum total bilirubin levels, which are causal for hypertension in African-ancestry individuals

Serum bilirubin is associated with several clinical outcomes, including hypertension, type 2 diabetes (T2D), and drug metabolism. Here, we describe findings from our genome-wide association studies (GWAS) of serum (TBIL) using a generalized linear mixed model in West Africans (n = 1127), with adjustment for age, sex, body mass index, T2D, significant principal components of population structure, and cryptic relatedness. Genome-wide conditional analysis and CAVIARBF were used to fine map significant loci. The causal effect of TBIL on hypertension was assessed by Mendelian randomization (MR) using the GWAS findings as instrumental variables (IVs) in African Americans (n = 3,067). The SNP rs887829 (UGT1A1) was significantly associated with TBIL levels (effect allele (T) frequency = 0.49, β (SE) = 0.59 (0.04), p = 9.13 × 10^-54). Genome-wide conditional analysis and regional fine mapping pointed to rs887829 as a possible causal variant with a posterior inclusion probability of 0.99. The T allele of rs887829 is associated with lower hepatic expression of UGT1A1. Using rs887829 as an IV, two-stage least-squares MR showed a causal effect of bilirubin on hypertension (β = -0.76, 95% CI [-1.52, -0.01], p = 0.0459). Our finding confirms that UGT1A1 influences bilirubin levels. Notably, lower TBIL is causally associated with the increased risk of hypertension.

UGT1A1 mutation association with increased bilirubin levels and severity of unconjugated hyperbilirubinemia in ABO incompatible newborns of China

BACKGROUND

Neonatal hyperbilirubinemia causing jaundice is common in East Asian population. Uridine diphosphate glucuronosyltransferase isoenzyme (UGT1A1) glucuronidates bilirubin and converts the toxic form of bilirubin to its nontoxic form.

METHOD

A retrospective study was conducted to review clinical information of ABO hemolysis neonates (ABO HDN) admitted to the Department of Neonatology, referred for neonatal hyperbilirubinemia, in a large general hospital of southern China from 2011 to 2017. Variation status of UGT1A1 was determined by direct sequencing or genotype assays.

RESULT

Sixty-nine ABO HDNs were included into the final analysis. UGT1A1 c.211 G > A mutation (UGT1A1*6, p.Arg71Gly, rs4148323) was significantly associated with the increased bilirubin level in ABO HDNs, after adjusted by age, sex and feeding method (P = 0.019 for TBIL, P = 0.02 for IBIL). Moreover, heterozygous and/or homozygous UGT1A1 mutations in the coding sequence region were significantly associated with the increased risk of developing hazardous hyperbilirubinemia (as defined by TSB > 427 umol/L) as compared those with a normal UGT1A1 genotype (OR_adj = 9.16, 95%CI 1.99-42.08, P = 0.002) in the study cohort.

CONCLUSION

UGT1A1 variant in coding region is actively involved in the pathogenesis of ABO hemolysis related neonatal hyperbilirubinemia. Genetic assessment of UGT1A1 may be useful for clinical diagnosis of neonatal unconjugated hyperbilirubinemia.

The Role of Heme Oxygenase-1 Promoter Polymorphisms in Perinatal Disease

Heme oxygenase (HO) is the rate-limiting enzyme in the heme catabolic pathway, which degrades heme into equimolar amounts of carbon monoxide, free iron, and biliverdin. Its inducible isoform, HO-1, has multiple protective functions, including immune modulation and pregnancy maintenance, showing dynamic alteration during perinatal periods. As its contribution to the development of perinatal complications is speculated, two functional polymorphisms of the HMOX1 gene, (GT)_n repeat polymorphism (rs3074372) and A(-413)T single nucleotide polymorphism (SNP) (rs2071746), were studied for their association with perinatal diseases. We systematically reviewed published evidence on HMOX1 polymorphisms in perinatal diseases and clarified their possible significant contribution to neonatal jaundice development, presumably due to their direct effect of inducing HO enzymatic activity in the bilirubin-producing pathway. However, the role of these polymorphisms seems limited for other perinatal complications such as bronchopulmonary dysplasia. We speculate that this is because the antioxidant or anti-inflammatory effect is not directly mediated by HO but by its byproducts, resulting in a milder effect. For better understanding, subtyping each morbidity by the level of exposure to causative environmental factors, simultaneous analysis of both polymorphisms, and the unified definition of short and long alleles in (GT)_n repeats based on transcriptional capacity should be further investigated.

The relationship between hyperbilirubinemia and the promoter region and first exon of UGT1A1 gene polymorphisms in Vietnamese newborns

BACKGROUND

To investigate the relationship between unexplained indirect hyperbilirubinemia of Vietnamese newborns and the polymorphism of the promoter TATA box and exon 1 of bilirubin uridine diphosphate glucuronosyltransferase (UGT1A1) gene.

METHODS

A total of 149 neonates were divided into the hyperbilirubinemia group (n = 99) and control group (n = 50). The gene polymorphisms of UGT1A1 gene in the two groups were detected by PCR and direct sequencing, which revealed the relationship between UGT1A1 polymorphism with neonatal hyperbilirubinemia of neonates. The types of UGT1A1 polymorphism in the hyperbilirubinemia group and the peak total serum bilirubin (PSB) levels with different genotypes were observed.

RESULTS

(1) (TA)7 insertion mutation, 211G>A, 189C>T, 190G>A, 378C>T and 686C>A were detected. (2) The allele frequency of 211G>A allele mutation was significantly different between the two groups (p < 0.05). (3) Logistic regression analysis showed that homozygosity and heterozygosity of 211G>A were both significantly associated with neonatal hyperbilirubinemia. (4) In the hyperbilirubinemia group, the peak total serum bilirubin level of 211G>A homozygous neonates was higher than that of the wild-type neonates (p < 0.05).

CONCLUSIONS

We noted that there was an association between neonates with unexplained indirect hyperbilirubinemia in Vietnam and the polymorphism of UGT1A1c.211G>A. In addition, the homozygous 211G>A polymorphism was related to the degree of hyperbilirubinemia.

IMPACT

Our article provided data on UGT1A1 polymorphism distribution in the Vietnamese population, which have not been reported yet. Our findings revealed that mutations in UGT1A1 gene are risk factors for unexplained hyperbilirubinemia in Vietnamese neonates. Our article will strengthen the cognition of neonatal jaundice at the genetic level in the pediatric field in Vietnam.

Molecular Physiology and Pathophysiology of Bilirubin Handling by the Blood, Liver, Intestine, and Brain in the Newborn

Bilirubin is the end product of heme catabolism formed during a process that involves oxidation-reduction reactions and conserves iron body stores. Unconjugated hyperbilirubinemia is common in newborn infants, but rare later in life. The basic physiology of bilirubin metabolism, such as production, transport, and excretion, has been well described. However, in the neonate, numerous variables related to nutrition, ethnicity, and genetic variants at several metabolic steps may be superimposed on the normal physiological hyperbilirubinemia that occurs in the first week of life and results in bilirubin levels that may be toxic to the brain. Bilirubin exists in several isomeric forms that differ in their polarities and is considered a physiologically important antioxidant. Here we review the chemistry of the bilirubin molecule and its metabolism in the body with a particular focus on the processes that impact the newborn infant, and how differences relative to older children and adults contribute to the risk of developing both acute and long-term neurological sequelae in the newborn infant. The final section deals with the interplay between the brain and bilirubin and its entry, clearance, and accumulation. We conclude with a discussion of the current state of knowledge regarding the mechanism(s) of bilirubin neurotoxicity.

Uridine 5'-diphospho-glucronosyltrasferase: Its role in pharmacogenomics and human disease

Biotransformation is an enzyme-catalyzed process in which the body converts endogenous compounds, xenobiotics and toxic substances into harmless or easily excreted metabolites. The biotransformation reactions are classified as phase I and II reactions. Uridine 5'-diphospho (UDP)-glucuronosyltransferases (UGTs) are a superfamily of phase II enzymes which have roles in the conjugation of xenobiotics or endogenous compounds, including drugs and bilirubin, with glucuronic acid to make them easier to excrete. The method the human body uses to achieve glucuronidation may be affected by a large interindividual variation due to changes in the sequences of the genes encoding these enzymes. In the last five years, the study of the genetic variants of the UGTs at a molecular level has become important due to its association with several diseases and the ability to predict adverse events due to drug metabolism. In the present review, the structure and the prominent genetic variants of the UGT1A subfamily and their metabolic and clinical implications are described.

Heme oxygenase-1 genetic variants and the conundrum of hyperbilirubinemia in African-American newborns

BACKGROUND

African-American (AA) infants are known to have, overall, lower bilirubin levels than infants of other ethnicities during their birth hospitalization. However, they are known to have a higher incidence of severe hyperbilirubinemia and are over represented in the US Kernicterus Registry. Heme oxygenase-1 (HO) is the rate limiting enzyme in heme metabolism leading to the equimolar production of bilirubin, carbon monoxide (CO) and free iron (Fe). Short (S) (GT)n repeats (<25) in the promoter region of the gene encoding the inducible HO-1 isozyme augment its expression, while long (L) repeats (>33) lead to an attenuation, modulating the production of bilirubin and CO. The impact of HO-1 promoter polymorphisms on bilirubin levels has not been well studied in (AA) infants.

OBJECTIVE

The objectives of this study were to compare the distribution of (GT)n repeat lengths in the HO-1 promoter region in a cohort of AA infants to those found in other ethnicities and to evaluate the contribution of this polymorphism to the degree of hyperbilirubinemia and the level of COHbc in this cohort.

METHODS

We prospectively studied a cohort of term AA infants with O+ mothers. Per hospital routine, infants' blood type, Rh status, direct antiglobulin test (DAT), and total bilirubin (TB) levels were checked prior to discharge. After parental consent, blood was collected for DNA extraction and carboxyhemoglobin (COHbc) measurements at the same time as the infants' newborn screen. An infant's TB percentile risk based on the Bhutani nomogram was used to determine need for phototherapy or follow-up. (GT)n repeat length in the HO-1 promoter was determined for each allele using PCR after DNA extraction from dried bloodspots. Size of allele lengths were typed as short (S, <25), medium (M, 25-33) or long (L, >33).

RESULTS

One hundred eighty infants were studied for a total of 360 separate alleles. 12.2% (44/360) of alleles were S which was significantly less than all other ethnicities reviewed. Carboxyhemoglobin (COHbc) levels and bilirubin percentiles were higher among infants who had at least one S allele when compared to those who had at least one L allele in the cohort as a whole: COHbc 0.92 ± 0.35 vs. 0.85 ± 0.37; p = 0.28 and Bilirubin percentile 48.6 ± 34.0 vs. 44.9 ± 31.6; p = 0.51. This relationship remained when only those infants who were DAT neg were examined: COHbc 0.81 ± 0.26 vs. 0.74 ± 0.21; p = 0.11 and Bilirubin percentile 43.6 ± 29.9 vs. 37.5 ± 28.7; p = 0.28.

CONCLUSIONS

The presence of L alleles of this variant is significantly greater among infants who are either African or of African descent. There was a trend toward lower COHbc levels among infants with at least one L allele as opposed to at least one S allele, although this did not have a statistically significant impact on TB risk percentile.

Heme oxygenase-1 promoter polymorphisms: do they modulate neonatal hyperbilirubinemia?

The role of genetic factors in the modulation of serum bilirubin levels and the pathophysiology of neonatal hyperbilirubinemia is being increasingly recognized. Heme oxygenase-1 (HO-1) is the rate-limiting enzyme by which heme is catabolized to biliverdin and thence to bilirubin, with the simultaneous release of equimolar quantities of ferrous iron (Fe³⁺) and carbon monoxide. Polymorphisms of the HO-1 gene promoter may modulate transcriptional activity, thereby augmenting or attenuating HO-1 expression with resultant modulation of the production of bilirubin. Few studies have related these polymorphisms to neonatal bilirubin metabolism and have reported conflicting results. In this clinical review, we surveyed the role of HO-1 gene promoter polymorphisms in the control of bilirubin production and further considered their role, if any, in the pathophysiology of neonatal hyperbilirubinemia.

Influence of UDP-Glucuronosyltransferase Polymorphisms on Stable Warfarin Doses in Patients with Mechanical Cardiac Valves

AIM

This study aimed to evaluate the effect of uridine diphosphate (UDP)-glucuronosyltransferase (UGT) polymorphisms on warfarin dosing requirements in patients with mechanical cardiac valves.

METHODS

A total of 191 patients with stable warfarin doses from the EAST Group of Warfarin were included in this study. The influence of genetic polymorphisms on stable warfarin doses was investigated by genotyping 6 single nucleotide polymorphisms (SNPs): vitamin K epoxide reductase complex 1 (VKORC1) rs9934438, cytochrome P450 (CYP) 2C9 rs1057910, CYP4F2 rs2108622, and UGT1A1 (rs887829, rs4148323, and rs4124874). An additional subgroup analysis was carried out using patients with wild-type homozygote carriers of CYP2C9.

RESULTS

One UGT1A1 SNP of rs887829 (C>T) exhibited significant association with stable warfarin doses in the study population and subgroup. Patients with the T allele in UGT1A1 rs887829 (CT or TT) required higher doses than those with the CC genotype in the study population (6.3 ± 2.4 mg vs. 5.2 ± 1.6 mg, P = 0.003). Similarly, in the subpopulation of AA carriers in the CYP2C9 gene, patients with the T allele required significantly higher doses of warfarin than those with other genotypes of rs887829 (6.5 ± 2.4 vs. 5.3 ± 1.5 mg, P = 0.002). Approximately 45.1% of overall interindividual variability in warfarin dose requirement was explained by the multivariate regression model. VKORC1, CYP2C9, UGT1A1 rs887829, age, and CYP4F2 accounted for 28.2%, 6.6%, 5.5%, 3.0%, and 1.8% of the variability, respectively.

CONCLUSION

Our results suggest that UGT1A1 could be a determinant of stable warfarin doses.

Risk assessment of gene variants for neonatal hyperbilirubinemia in Taiwan

Background

Hyperbilirubinemia is a common disorder during neonatal period in Taiwan. Gene variants may play an important role in the development of neonatal hyperbilirubinemia. The current study investigated the association between neonatal hyperbilirubinemia and common gene variants involving the production and metabolism of bilirubin.

Methods

This prospective study enrolled 444 healthy infants born in the Chang Gung Memorial Hospital at Taipei from 2013–2015. Hyperbilirubinemia was defined as a total bilirubin ≥ 15 mg/dL. A log-binomial model was used to assess the risk of gene variants.

Results

The most common genetic variant was short heme oxygenase (HO)-1 promoter GT-allele (<24 repeats) (39.4 %), followed by GA at nt388 in hepatic solute carrier organic anion transporter 1B1 (SLCO1B1) (31.1 %), GA at nt211 in UDP-glucuronosyltransferase 1A1 (UGT1A1) (29.3 %), ABO incompatibility (16.2 %), alpha thalassemia (5.0 %), and G6PD deficiency (3.2 %). The log-binomial analysis demonstrated greater risks of hyperbilirubinemia in infants with GA at nt211 in UGT1A1 (RR = 1.548; 95 % CI = 1.096–2.187), short HO-1 promoter GT-repeat (RR = 2.185; 95 % CI = 1.527–3.125), and G6PD deficiency (RR = 1.985; 95 % CI = 1.010–3.901). The other gene variants – including blood type, alpha thalassemia, and SLCO1B1 – carried no significant risk.

Conclusions

G6PD deficiency, short HO-1 promoter GT-repeat and GA at nt211 in UGT1A1 are risk factors of neonatal hyperbilirubinemia. The data provide clinical evidence to explain the high incidence of neonatal hyperbilirubinemia in Taiwan.

Role of pharmacogenetics on deferasirox AUC and efficacy

AIM

We evaluated deferasirox pharmacokinetic according to SNPs in genes involved in its metabolism and elimination. Moreover, we defined a plasma area under the curve cut-off value predicting therapy response.

PATIENTS & METHODS

Allelic discrimination was performed by real-time PCR. Drug plasma concentrations were measured by a high performance liquid chromatography system coupled with an ultraviolet method.

RESULTS

Pharmacokinetic parameters were significantly influenced by UGT1A1 rs887829C>T, UGT1A3 rs1983023C>T and rs3806596A>G SNPs. Area under the curve cut-off values of 360 μg/ml/h for efficacy were here defined and 250 μg/ml/h for nonresponse was reported. UGT1A3 rs3806596GG and ABCG2 rs13120400CC genotypes were factors able to predict efficacy, whereas UGT1A3 rs3806596GG was a nonresponse predictor.

CONCLUSION

These data show how screening patient's genetic profile may help clinicians to optimize iron chelation therapy with deferasirox.

Multiple Genetic Modifiers of Bilirubin Metabolism Involvement in Significant Neonatal Hyperbilirubinemia in Patients of Chinese Descent

The potential for genetic variation to modulate neonatal hyperbilirubinemia risk is increasingly being recognized. A case-control study was designed to assess comprehensive contributions of the multiple genetic modifiers of bilirubin metabolism on significant neonatal hyperbilirubinemia in Chinese descendents. Eleven common mutations and polymorphisms across five bilirubin metabolism genes, namely those encoding UGT1A1, HMOX1, BLVRA, SLCO1B1 and SLCO1B3, were determined using the high resolution melt (HRM) assay or PCR-capillary electrophoresis analysis. A total of 129 hyperbilirubinemic infants and 108 control subjects were evaluated. Breastfeeding and the presence of the minor A allele of rs4148323 (UGTA*6) were correlated with an increased risk of hyperbilirubinemia (OR=2.17, P=0.02 for breastfeeding; OR=9.776, P=0.000 for UGTA*6 homozygote; OR=3.151, P=0.000 for UGTA*6 heterozygote); whereas, increasing gestational age and the presence of –TA₇ repeat variant of UGT1A1 decreased the risk (OR=0.721, P=0.003 for gestational age; OR=0.313, P=0.002 for heterozygote TA₆/TA₇). In addition, the SLCO1B1 and SLCO1B3 polymorphisms also contributed to an increased risk of hyperbilirubinemia. This detailed analysis revealed the impact of multiple genetic modifiers on neonatal hyperbilirubinemia. This may support the use of genetic tests for clinical risk assessment. Furthermore, the established HRM assay can serve as an effective method for large-scale investigation.