Neonatal hyperbilirubinemia in Japanese neonates: analysis of the heme oxygenase-1 gene and fetal hemoglobin composition in cord blood

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.

Two Faces of Heme Catabolic Pathway in Newborns: A Potential Role of Bilirubin and Carbon Monoxide in Neonatal Inflammatory Diseases

In an infant's body, all the systems undergo significant changes in order to adapt to the new, extrauterine environment and challenges which it poses. Fragile homeostasis can be easily disrupted as the defensive mechanisms are yet imperfect. The activity of antioxidant enzymes, i.e., superoxide dismutase, catalase, and glutathione peroxidase, is low; therefore, neonates are especially vulnerable to oxidative stress. Free radical burden significantly contributes to neonatal illnesses such as sepsis, retinopathy of premature, necrotizing enterocolitis, bronchopulmonary dysplasia, or leukomalacia. However, newborns have an important ally-an inducible heme oxygenase-1 (HO-1) which expression rises rapidly in response to stress stimuli. HO-1 activity leads to production of carbon monoxide (CO), free iron ion, and biliverdin; the latter is promptly reduced to bilirubin. Although CO and bilirubin used to be considered noxious by-products, new interesting properties of those compounds are being revealed. Bilirubin proved to be an efficient free radicals scavenger and modulator of immune responses. CO affects a vast range of processes such as vasodilatation, platelet aggregation, and inflammatory reactions. Recently, developed nanoparticles consisting of PEGylated bilirubin as well as several kinds of molecules releasing CO have been successfully tested on animal models of inflammatory diseases. This paper focuses on the role of heme metabolites and their potential utility in prevention and treatment of neonatal diseases.

Association between genetic polymorphism of heme oxygenase 1 promoter and neonatal hyperbilirubinemia: a meta-analysis

Objective: The association between a (GT)_n dinucleotide length polymorphism in the promoter region of heme oxygenase 1 (HMOX1) and the risk of neonatal hyperbilirubinemia remains controversial. This meta-analysis was, therefore, performed with aims to examine the correlation between the HMOX1 (GT)_n repeat length polymorphism and neonatal hyperbilirubinemia susceptibility.Materials and methods: We searched the databases including PubMed, Embase, Cochrane Library, China national knowledge infrastructure (CNKI), and Wanfang Data, with all reviewed studies published before 28 June 2018. After the evaluation of quality, we used RevMan to perform the meta-analyses. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to assess the effect of HMOX1 gene promoter polymorphisms on the risk of neonatal hyperbilirubinemia.Results: Seven studies, involving 584 patients with neonatal hyperbilirubinemia and 1655 controls, were included. A statistically significant association was found between the HMOX1 (GT)_n repeat length polymorphism and risk of neonatal hyperbilirubinemia under the allele (allele S vs. allele L: OR = 1.81, 95% CI = 1.22-2.67, p = .003), recessive (genotype SS vs. genotypes LS + LL: OR = 1.38, 95% CI = 1.02-1.86, p = .04), dominant (genotypes SS + LS vs. LL: OR = 1.37, 95% CI = 1.01-1.76, p = .01), and homozygous genetic models (genotype SS vs. genotype LL: OR = 1.47, 95% CI = 1.02-2.11, p = .003), but not under the heterozygous genetic model. Interestingly, subgroup analysis revealed that the cutoffs of the S allele < 25 showed significant associations in any of the five genetic models (allele S vs. allele L: OR = 2.26, 95% CI = 1.68-3.05, p < .00001; genotype SS vs. genotypes LS + LL: OR = 2.56, 95% CI = 1.41-4.65, p = .002; genotypes SS + LS vs. genotype LL: OR = 1.82, 95% CI = 1.28-2.59, p = .0009; genotype SS vs. genotype LL: OR = 3.09, 95% CI = 1.50-6.36, p = .002; genotype LS vs. genotype LL: OR = 1.64, 95% CI = 1.11-2.42, p = .01); however, this association was not observed in the cutoffs of the S allele ≥25.Conclusion: The results of this study indicate that there is a significant association between the HMOX1 (GT)_n repeat length polymorphism and susceptibility to neonatal hyperbilirubinemia. Newborns carrying shorter (GT)_n repeats in the HMOX1 gene promoter may have a higher risk of neonatal hyperbilirubinemia.

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.

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.

Association of HMOX1 gene promoter polymorphisms with hyperbilirubinemia in the early neonatal period

BACKGROUND

Heme oxygenase (HO) is the rate-limiting enzyme in the heme degradation pathway that produces bilirubin. The promoter region of human heme oxygenase-1 (HMOX1) contains a polymorphic (GT)n repeat that can regulate gene expression. Here, we investigated the association of (GT)n repeat length in the HMOX1 promoter region with neonatal hyperbilirubinemia in a population of Japanese term neonates.

METHODS

Using polymerase chain reaction and fragment analysis, we determined the number of (GT)n repeats in 149 Japanese neonates. To omit the effects of the G71R mutation in uridine diphosphoglucuronosyltransferase on hyperbilirubinemia, we excluded 41 neonates with the G71R mutation. As a result, 25 neonates with hyperbilirubinemia and 83 non-hyperbilirubinemic controls were included in this prospective case-control study. Allele and genotype frequencies of (GT)n repeats in the HMOX1 gene were compared between hyperbilirubinemic and non-hyperbilirubinemic control neonates.

RESULTS

The prevalence of short alleles (< 22 (GT)n repeats) was significantly higher in hyperbilirubinemic than in control neonates (18% vs 7%, P = 0.015). Hyperbilirubinemia was more frequent in homozygous or heterozygous short allele carriers than control neonates (28% vs 11%, respectively, P = 0.03). Possession of short alleles was significantly associated with the development of neonatal hyperbilirubinemia (OR, 3.1; 95%CI: 1.03-9.53).

CONCLUSIONS

Infants carrying short alleles (< 22 (GT)n repeats) in the HMOX1 gene promoter region appear to be at a higher risk for developing neonatal hyperbilirubinemia.

Genetic polymorphisms of heme-oxygenase 1 (HO-1) may impact on acute kidney injury, bronchopulmonary dysplasia, and mortality in premature infants

BACKGROUND

Heme oxygenase 1 (HO1) catalyzes heme degradation, and offers protection for several organs, including the kidney. Genetic polymorphisms of HO-1 are associated with poor clinical outcomes in several populations.

METHODS

POPULATION

We prospectively enrolled 117 premature infants (birth weight ≤1,200 g or postgestational age ≤31 wk) and evaluated two DNA genetic variants proximal to the promoter region of HO-1 (GT(n) repeats, and -413T>A SNP). We evaluated how these polymorphisms affect two clinical outcomes: (i) Acute Kidney Injury (AKI)-rise in serum creatinine (SCr) ≥ 0.3 mg/dl or ≥ 150-200% from lowest previous value, (ii) the composite of mortality and bronchopulmonary dysplasia (BPD) defined as receipt of oxygen at 36 wk postmenstrual age.

RESULTS

AKI occurred in 34/117 (29%) of neonates; 12/117 (10%) died; 29/105 (28%) survivors had BPD. Neonates with TT genotype at 413T>A before the HO-1 promoter had higher rates of AKI (P < 0.05). There was no difference in number of GT(n) repeats and clinical outcomes.

CONCLUSION

We did not find an association between the GT(n) tandem repeat of HO-1 and AKI nor BPD/mortality. However, infants with TT genotype of the 413T>A genetic alteration had lower incidence of AKI. Further studies using larger cohorts are needed to better understand these relationships.

Association of neonatal hyperbilirubinemia in breast-fed infants with UGT1A1 or SLCOs polymorphisms

Neonates have physiologically increased bilirubin production and immature bilirubin metabolism, and present hyperbilirubinemia in association with genetic and or epigenetic factors. We previously reported that maximal body weight loss (inadequate feeding) is an independent risk factor for the development of hyperbilirubinemia in breast-fed Japanese neonates, and the UGT1A1 211G>A genotype becomes a risk factor under conditions of inadequate feeding. We extended the study to the association of other genetic factors, the UGT1A1 (TA)7 and solute-carrier organic anion transporters (SLCOs) polymorphisms with neonatal hyperbilirubinemia. We enrolled 401 full-term Japanese infants who were exclusively breastfeeding and classified them into two groups based on the degree of maximal body weight loss. We analyzed the clinical characteristics and UGT1A1 and SLCOs genotypes. Statistical analysis revealed that maximal body weight loss is the only independent risk factor for the development of neonatal hyperbilirubinemia. UGT1A1, SLCO1B1 and SLCO1B3 polymorphisms become risk factors in neonates showing 10% or greater body weight loss during the neonatal period. Inadequate feeding may increase the bilirubin burden and cause apparent hyperbilirubinemia in neonates, who have a polymorphic change in the genes involved in the transport and/or metabolism of bilirubin.

HMOX1 gene promoter polymorphism is not associated with coronary artery disease in Koreans

Background

The heme oxygenase-1 gene (HMOX1) promoter polymorphisms modulate its transcription in response to oxidative stress. This study screened for HMOX1 polymorphisms and investigated the association between HMOX1 polymorphisms and coronary artery disease (CAD) in the Korean population.

Methods

The study population consisted of patients with CAD with obstructive lesions (n=110), CAD with minimal or no lesions (n=40), and controls (n=107). Thirty-nine patients with CAD with obstructive lesions underwent follow-up coronary angiography after six months for the presence of restenosis. The 5'-flanking region containing (GT)n repeats of the HMOX1 gene was analyzed by PCR.

Results

The numbers of (GT)n repeats in the HMOX1 promoter showed a bimodal distribution. The alleles were divided into two subclasses, S25 and L25, depending on whether there were less than or equal to and more than 25 (GT)n repeats, respectively. The allele and genotype frequencies among groups were statistically not different. More subjects in the S25-carrier group had the low risk levels of high sensitivity C-reactive protein (hsCRP) for the CAD than those in the non-S25 carrier group (P=0.034). Multivariate logistic regression analysis revealed that the genotypes of (GT)n repeats were not related to CAD status. The restenosis group in the coronary angiography follow-up did not show any significant difference in HMOX1 genotype frequency.

Conclusions

The HMOX1 genotypes were not found to be associated with CAD, but the short allele carrier group contained more individuals with hsCRP values reflecting low risk of cardiovascular disease in the Korean population.

Heme oxygenase-1 promoter polymorphisms and neonatal jaundice

BACKGROUND

Heme oxygenase (HO) is the initial, rate-limiting enzyme in the conversion of heme to bilirubin. Dinucleotide (GT)n repeat length in the promoter region of the encoding gene modulates transcription: shorter alleles, in contrast with longer allele counterparts, are associated with greater gene expression and should result in increased heme catabolism.

OBJECTIVE

We compared the rates of heme catabolism and plasma total bilirubin (TB) between HO-1 promoter genotypes of varying (GT)n repeat lengths in glucose-6-phosphate dehydrogenase (G6PD)-normal and -deficient neonates.

METHODS

HO-1 promoter length was determined from genomic DNA from previous studies by size discrimination of fluorescently-labeled PCR products with capillary electrophoresis. Sizing was confirmed by sequencing homozygote samples. Alleles were categorized as: short (≤24 GT repeats), medium (25-33 GT repeats), and long (≥34 GT repeats). Previously determined values for blood carboxyhemoglobin, corrected for inspired carbon monoxide (COHbc), and TB were used to determine the rate of heme catabolism and 3rd day TB values for each HO-1 promoter length genotype, respectively. G6PD Mediterranean was determined by PCR analysis.

RESULTS

Neither COHbc nor TB values were significantly different between various HO-1 promoter genotypes for either G6PD-normal or -deficient neonates.

CONCLUSIONS

In the steady state, HO-1 promoter genotypes, based on the length of (GT)n repeats, do not modulate heme catabolism or 3rd day TB values in either G6PD-normal or -deficient neonates.

Heme oxygenase-1 gene variants and hyperbilirubinemia risk in North Indian newborns

Heme oxygenase-1 (HO-1) is a rate-limiting enzyme in bilirubin metabolism, and its genetic variant may modulate hyperbilirubinemia risk in neonates. The aim of the present study was to assess the association between heme oxygenase-1 gene variants and hyperbilirubinemia risk in Indian newborns. In a prospective case-control study, we analyzed (GT)n repeats and g.-413A>T variant of HO-1 gene and UGT1A1 gene variants in 100 case newborns with total serum bilirubin (TSB) levels exceeding 95th percentile and 100 control newborns with TSB levels below 75th percentile on the hour-specific bilirubin nomogram of the American Academy of Pediatrics. Study population consisted of term (37-41 weeks) and late preterm (34-36 weeks) newborns during the first 2 weeks of age. In our analysis, the (GT)n allele was highly polymorphic, ranging in number from 15 to 40. The incidence of short (GT)n allele (≤ 20) was significantly higher in neonates with hyperbilirubinemia than in controls. Although g.-413A>T variant was widely prevalent in the study population, no difference was noted in its prevalence between cases and controls. Short (GT)n repeats of HO-1 gene, c.211G>A variant of UGT1A1 gene, and excessive weight loss were independent risk factors for neonatal hyperbilirubinemia. In the presence of two or more risk factors, the odds of developing neonatal hyperbilirubinemia were high. Shorter (GT)n genotype in the promoter region of HO-1 gene is significantly associated with hyperbilirubinemia risk in Indian newborns. This genotype may interact with other genetic and clinical risk factors to further potentiate hyperbilirubinemia risk in newborns.

Neonatal hyperbilirubinemia and Gly71Arg mutation of UGT1A1 gene: a Chinese case-control study followed by systematic review of existing evidence

AIM

To determine whether the UDP-glucuronosyltransferase 1A1 gene (UGT1A1) Gly71Arg (211G>A) mutation is associated with neonatal hyperbilirubinemia.

METHODS

The study consisted of two parts. The case-control study included 112 hyperbilirubinemic infants and 105 control subjects from the Fifth People's Hospital of Shenzhen. Polymerase chain reaction, restriction fragment length polymorphisms and agarose gel electrophoresis techniques were used to detect the UGT1A1 211G>A mutation. Meta-analyses was performed to assess the association between neonatal hyperbilirubinemia and UGT1A1 211G>A.

RESULTS

Our case-control study revealed that the likelihood of developing neonatal hyperbilirubinemia was 2.65 times higher in the infants with the A allele in the UGT1A1 211G>A than in the infants with the G allele (95% CI, 1.60-4.39). Meta-analyses (including data from our study) revealed that UGT1A1 211G>A is associated with an increased risk of neonatal hyperbilirubinemia [odds ratio (OR), 2.37; 95% CI, 2.05-2.74]. In the subgroup analyses based on ethnicity, significantly elevated risks were found in Asian populations (OR, 2.45; 95% CI, 2.10-2.84), but no significant associations were present in Caucasian populations (OR, 1.54; 95% CI, 0.87-2.75).

CONCLUSION

  The UGT1A1 211G>A mutation is associated with neonatal hyperbilirubinemia in Asians, but not in Caucasians.

Exploring the genetic architecture of neonatal hyperbilirubinemia

The potential for genetic variation to modulate neonatal hyperbilirubinemia risk is increasingly being recognized. In particular, polymorphisms across three genes involved in bilirubin production and metabolism [glucose-6-phosphate dehydrogenase (G6PD), uridine diphosphate glucuronosyl transferase 1A1 (UGT1A1), and solute carrier organic anion transporter polypeptide 1B1 (SLCO1B1)] may interact with each other and/or environmental contributors to produce significant hyperbilirubinemia. Variant gene co-expression including compound and synergistic heterozygosity enhances hyperbilirubinemia risk, contributing to the etiologic heterogeneity and complex nature of neonatal jaundice.

Prolonged unconjugated hyperbilirubinaemia associated with the haem oxygenase-1 gene promoter polymorphism

AIM

To elucidate the genetic factors causing hyperbilirubinaemia in prolonged jaundice of the newborns, we investigated whether the HO-1 gene promoter polymorphism is a cause in unexplained pathological or prolonged jaundice.

METHODS

Three groups were defined: healthy newborns with no clinical jaundice, newborns hospitalized for jaundice without any identifiable pathological cause and newborns with prolonged jaundice associated with breast milk. Genomic DNA was extracted from the white blood cells and the promoter region of the HO-1 gene was amplified using PCR and their allelic repeats were determined.

RESULTS

We did not detect any significant difference in the allele frequencies between the healthy newborns and the newborns whose serum total bilirubin levels were >12.9 mg/dL. However, the patients with short (<24 GT) dinucleotide repeat in the HO-1 gene promoter on either allele had significantly higher prolonged unconjugated hyperbilirubinaemia than the healthy newborns. There was no significant difference between the groups 2 and 3.

CONCLUSION

The results indicate that polymorphism of HO-1 gene promoter region can be an underlying cause of the prolonged unconjugated hyperbilirubinaemia associated with breast milk. In this patient population, short repeat alleles of the HO-1 gene promoter polymorphism were associated with prolonged jaundice.

HO-1 polymorphism as a genetic determinant behind the malaria resistance afforded by haemolytic disorders

Malaria affects thousands of people around the world representing a critical issue regarding health policies in tropical countries. Similarly, also haemolytic diseases such as sickle cell disease and thalassemias are a concern in different parts of the globe. It is well established that haemolytic diseases, such as sickle cell disease (SCD) and thalassemias, represent a resistance factor to malaria, which explains the high frequencies of such genetic variants in malaria endemic areas. In this context, it has been shown that the rate limiting enzyme heme oxygenase I (HO-1), responsible for the catabolism of the free heme in the body, is an important resistance factor in malaria and is also important in the physiopathology of haemolytic diseases. Here, we suggest that allelic variants of HO-1, which display significant differences in terms of protein expression, have been selected in endemic malaria areas since the HO-1 enzyme can enhance the protection against malaria conferred by haemolytic diseases This protection apply mainly in what concerns protection against severe malaria forms. Therefore, HO-1 genotyping would be fundamental to determine resistance of a given individual to lethal forms of malaria as well as to common clinical complications typical to haemolytic diseases and would be helpful in the establishment of public health politics.

Hypoxia and heme oxygenases: oxygen sensing and regulation of expression

Heme is an essential molecule for life, as it is involved in sensing and using oxygen. Heme must be synthesized and degraded within an individual nucleated cell. Physiologic heme degradation is catalyzed by two functional isozymes of heme oxygenase, heme oxygenase-1 (HO-1) and HO-2, yielding carbon monoxide, iron, and biliverdin, an immediate precursor to bilirubin. HO-1 is an inducible enzyme, but the expression level of HO-2 is maintained in a narrow range. Characteristically, human HO-1 contains no Cys residue, whereas human HO-2 contains three Cys residues, each of which might be involved in heme binding. These features suggest separate physiologic roles of HO-1 and HO-2. Recent studies have shown that the expression levels of HO-1 and HO-2 are reduced under hypoxia, depending on the cell types. Moreover, we have proposed HO-2 as a potential O(2) sensor, because HO-2-deficient mice show hypoxemia and a blunted hypoxic ventilatory response with normal hypercapnic ventilatory response. HO-2-deficient mice also show hypertrophy of the pulmonary venous myocardium and enlargement of the carotid body. These morphometric changes are attributable to chronic hypoxemia. Here, we update the understanding of the regulation of HO-1 and HO-2 expression and summarize the regulatory role of HO-2 in the intercellular communication.

Lacking deoxygenation-linked interaction between cytoplasmic domain of band 3 and HbF from fetal red blood cells

AIM

Several of the red blood cell's metabolic and membrane functions display dependence on haemoglobin oxygenation. In adult human red cells, the increased glycolytic rate at low O2 tension results from binding of deoxygenated HbA at negatively charged, N-terminal, cytoplasmic domain of the membrane protein band 3, which liberates glycolytic enzymes from this site. This study aims to investigate the role of fetal HbF (that has lower anion-binding capacity than HbA) in fetal red cells (that are subjected to low O2 tensions), and to elucidate possible linkage (e.g. via the major red cell membrane organising centre, band 3) between the individual oxygenation-linked reactions encountered in red cells.

METHODS

The interaction between band 3 and Hb is analysed in terms of the effects, measured under different conditions, of a 10-mer peptide that corresponds to the N-terminus of human band 3 protein, on the oxygenation reaction of HbF and HbA, isolated from umbilical chord red cells.

RESULTS

Contrasting with the unequivocal interaction of the peptide with HbA that with fetal HbF is weak, and annihilated in the presence of autochthonous red cell O2 affinity modulators (chloride and organic phosphates).

CONCLUSION

The data indicate that HbF does not function as a transducer mediating O2 dependence of glycolysis in fetal red cells, in accordance with the different O2 and metabolic profiles compared to those in HbA-bearing adult red cells. In conjunction with the previously discovered O2 dependence of K+ transport in HbF-rich fetal cells, they moreover argue against linkage between different, physiologically relevant, O2-dependent red cell functions.

Reduced expression of heme oxygenase-1 in patients with coronary atherosclerosis

Heme oxigenase-1 (HO-1) is known to be an inducible cytoprotective enzyme that copes with oxidative stress. However, changes in HO-1 expression and their association with human diseases have not been studied. To test the hypothesis that the capacity to upregulate HO-1 in response to oxidative stress is an intrinsic marker for susceptibility to coronary atherosclerosis, we assessed stimulation-induced change in HO-1 expression in blood cells in 110 patients who underwent coronary angiography, comparing the results with the extent of coronary atherosclerosis and (GT)(n) repeat polymorphism in the HO-1 gene promoter region, which is believed to affect the gene expression level. The extent of coronary atherosclerosis was assessed by coronary score. Mononuclear cells were incubated with 10 micromol/l hemin or vehicle for 4 h to maximally stimulate HO-1 expression, then the HO-1 expression level was determined by real-time polymerase chain reaction (PCR). The difference between the HO-1 mRNA levels of hemin- and vehicle-treated cells (DeltaHO-1 mRNA) was taken as an index of the capacity to upregulate HO-1 mRNA. The coefficient of variance of DeltaHO-1 mRNA was 7.2%. Consistent with previous studies, DeltaHO-1 mRNA was significantly lower in patients carrying a long (GT)(n) repeat. DeltaHO-1 mRNA negatively and significantly correlated with the coronary score (r(2)=0.50, p<0.01). In conclusion, the capacity to upregulate HO-1 expression may be determined, at least in part, by genetics, and reduced ability to induce HO-1 may be involved in the mechanism of coronary atherosclerosis.

Heme oxygenase-1 gene promoter polymorphism is associated with risk of gastric adenocarcinoma and lymphovascular tumor invasion

PURPOSE

Heme oxygenase-1 (HO-1) gene, which encodes an oxidative response protein, plays a role in cytoprotection. A (GT)n dinucleotide repeat in HO-1 promoter is polymorphic and modulates the transcriptional activity of the gene. A HO-1 gene promoter polymorphism was reported to be associated with the risks of lung adenocarcinoma and oral squamous cancer. In this study, the correlation between the HO-1 gene promoter polymorphism and the clinicopathological characteristics, along with the risk of gastric cancer, was analyzed.

EXPERIMENTAL DESIGN

We examined the genotypic frequencies of (GT)n repeats in 183 gastric cancer patients and 250 control subjects by PCR-based genotyping and DNA sequencing. The length polymorphisms of (GT)n repeats were classified into short (S) component (n <or= 25), medium (M) component (26 <or= n <or= 30) and long (L) component (n >or= 31). The distribution of S, M and L components in patient and control groups were evaluated to determine the correlation with susceptibility and clinicopathological characteristics of gastric adenocarcinoma.

RESULTS

Higher frequencies of L-allele, L-allele carrier (S/L, M/L, L/L) and S/L genotype were found in gastric cancer patients. The frequencies of M-allele, M-allele carrier (M/M, M/L, M/S) and M/M genotype were significantly lower in patients with gastric cancer than controls. Furthermore, the frequency of lymphovascular tumor invasion was significantly lower in M-allele carriers compared to non-M-allele carriers (S/S, S/L, L/L) (p = 0.009).

CONCLUSIONS

These findings suggest that the long (GT)n repeat of HO-1 gene promoter was associated with a higher frequency of gastric adenocarcinoma, and the medium (GT)n repeat might possess protective effect against gastric adenocarcinoma with a lower frequency of lymphovascular invasion in tumors.

Marked hyperbilirubinemia associated with the heme oxygenase-1 gene promoter microsatellite polymorphism in a boy with autoimmune hemolytic anemia

Mild hyperbilirubinemia is a clinical feature of hemolysis. Here we describe a boy with marked elevation of serum bilirubin values (maximum: 70 mg/dL) during an acute episode of autoimmune hemolytic anemia, which returned to within the reference range after clinical improvement. The boy was a homozygous carrier of short alleles of the heme oxygenase-1 (HO-1) gene GT dinucleotide-repeat promoter polymorphism, which is associated with increased activity and inducibility of the heme-degrading enzyme HO-1, which catalyzes the production of bilirubin. In addition, heterozygosity of the uridine 5'-diphosphate-glucuronosyl-transferase 1A1 promoter polymorphism that is linked with Gilbert syndrome was found in this patient. Because bilirubin production plays a critical role during the neonatal period, the HO-1 promoter polymorphism may be an important genetic factor for the clinical outcome of neonatal hyperbilirubinemia.

The Heme Catabolic Pathway and its Protective Effects on Oxidative Stress‐Mediated Diseases

Bilirubin, the principal bile pigment, is the end product of heme catabolism. For many years, bilirubin was thought to have no physiological function other than that of a waste product of heme catabolism--useless at best and toxic at worst. Although hyperbilirubinemia in neonates has been shown to be neurotoxic, studies performed during the past decade have found that bilirubin has a number of new and interesting biochemical and biological properties. In addition, there is now a strong body of evidence suggesting that bilirubin may have a beneficial role in preventing oxidative changes in a number of diseases including atherosclerosis and cancer, as well as a number of inflammatory, autoimmune, and degenerative diseases. The results also suggest that activation of the heme oxygenase and heme catabolic pathway may have beneficiary effects on disease prevention either through the action of bilirubin or in conjunction with bilirubin. If so, it may be possible to therapeutically induce heme oxygenase, increase bilirubin concentrations, and lower the risk of oxidative stress-related diseases.

Neonatal hyperbilirubinemia and the bilirubin uridine diphosphate-glucuronosyltransferase gene: the common -3263T > G mutation of phenobarbital response enhancer module is not associated with the neonatal hyperbilirubinemia in Japanese

BACKGROUND

Neonatal hyperbilirubinemia is frequent and severe in Japanese newborns. Previously, it has been reported that half of the Japanese neonates with severe hyperbilirubinemia carried the 211G > A (p.G71R) mutation of the bilirubin uridine diphosphate-glucuronosyltransferase (UGT1A1) gene causing Gilbert syndrome. Recently, it was reported that the -3263T > G mutation in the phenobarbital response enhancer module in UGT1A1 was associated with the majority of cases of Gilbert syndrome. The gene frequency of the -3263T > G mutation was determined and the relation with neonatal hyperbilirubinemia in Japanese was studied.

METHODS

UGT1A1 in 119 neonates born at Yamagata University Hospital, Yamagata, Japan, and 26 subjects who had undergone phototherapy due to severe hyperbilirubinemia at four other hospitals were studied. The gene frequency of -3263T > G mutation in Japanese, Korean, Chinese and German healthy adult controls was also determined. Hyperbilirubinemia was assessed with a Jaundice Meter and UGT1A1 was analyzed by sequence determination or restriction enzyme method.

RESULTS

The gene frequency of the -3263T > G mutation was 0.26 in Japanese subjects and was similar to the prevalence in Korean, Chinese and German populations. However, there was no significant increase in the gene frequency of the mutation in the neonates who required phototherapy for hyperbilirubinemia compared to that in the neonates without severe hyperbilirubinemia. In addition, neonates with or without the mutation did not show a significant change in the level of bilirubin and the mutation also did not show a synergic effect with the 211G > A mutation on the level of bilirubin.

CONCLUSION

The -3263T > G mutation is not likely to be associated with the neonatal hyperbilirubinemia in Japanese.

The role of heme oxygenase-1 promoter polymorphisms in human disease

Heme oxygenase (HO) seems to be a novel protective factor with potent anti-inflammatory, anti-oxidant, and anti-proliferative effects. HO-1, the inducible isoform, is expressed in various tissues and is upregulated by multiple stimuli. However, humans differ quantitatively in their ability to mount an HO-1 response, modulated by two potentially functional polymorphisms in the HO-1 gene promoter region. From several studies it seems that the ability of a patient with certain genotypes to respond strongly in terms of upregulating HO-1 may be an important endogenous protective factor. In the present article we systematically review the hitherto published evidence that promoter polymorphisms in the HO-1 gene exert functional importance by influencing the level of HO-1 expression in different organ systems.

The heme oxygenase dilemma in cellular homeostasis: new insights for the feedback regulation of heme catabolism

Heme must be synthesized and degraded within an individual nucleated cell. Heme degradation is catalyzed by the two isozymes of heme oxygenase, heme oxygenase-1 (HO-1) and HO-2, eventually yielding biliverdin/bilirubin, CO, and iron. These products possess important physiological roles but are potentially toxic to cells. Characteristically, human HO-1 contains no Cys residues, whereas HO-2 contains the potential heme-binding motifs of the Cys-Pro dipeptide. Expression of HO-1 is inducible or repressible, depending on cell types or cellular microenvironments, but expression levels of HO-2 are fairly constant. Thus, the main regulation of heme catabolism is a problem of the balance between induction and repression of HO-1. Notably, HO-1 expression is induced by heme in all mammalian cells examined, but is repressed by hypoxia in certain types of cultured human cells. The recent discovery of Bach1 as a heme-regulated and hypoxia-inducible repressor for transcription of the HO-1 gene has provided a missing link in the feedback control of heme catabolism. On the other hand, the human HO-1 gene promoter contains the (GT)n repeat polymorphism and a single nucleotide polymorphism (-427A --> T), both of which may contribute to fine-tuning of the transcription. Importantly, long (GT)n alleles are associated with susceptibility to smoking-induced emphysema or coronary artery disease, but may provide with resistance to cerebral malaria. The latter finding suggests a novel therapeutic strategy with inhibitors of HO-1 for the treatment of cerebral malaria. We discuss the potential regulatory role of Bach1 and HO-2 in heme catabolism and update the understanding of the regulation of HO-1 expression.