Bilirubin levels and severe retinopathy of prematurity in infants with estimated gestational ages of 23 to 26 weeks

Hyperbilirubinemia and retinopathy of prematurity: a retrospective cohort study

Retinopathy of prematurity (ROP) is a vasoproliferative retinal disease in preterm infants. Oxidative stress plays a key role in the pathogenesis of ROP. Due to its antioxidant effects, bilirubin has been proposed to be protective against ROP. This study explored the association between hyperbilirubinemia and ROP. We analyzed a 10-year cohort from a neonatal intensive care unit in Milan, Italy, including 1606 infants born under 32 weeks and/or < 1500 g. Data from 1606 infants meeting specific inclusion criteria were reviewed. Eighty infants were excluded due to lack of data, 1526 were deemed eligible for analysis, and 1269 had hyperbilirubinemia requiring phototherapy. There was a higher incidence of ROP among infants with hyperbilirubinemia (13.8%) versus those without (7.8%, p<0.01). Infants with any ROP, non-severe or severe ROP, were exposed to hyperbilirubinemia for a significantly higher number of days compared with those without ROP. Each additional day of exposure increases the risk of developing any ROP by 5%, non-severe ROP by 4%, and severe ROP by 6%. However, this correlation was not observed in infants with gestational age less than 27 weeks and/or body weight less than 1000 g.    Conclusion: Our data show that hyperbilirubinemia requiring phototherapy is associated with an increased risk of developing ROP. However, severe hyperbilirubinemia and ROP share many of their risk factors. Therefore, rather than being a risk factor itself, hyperbilirubinemia may be a surrogate for other risk factors for ROP.    Clinical Trial Registration: NCT05806684. What is Known: • The development of retinopathy of prematurity (ROP) is influenced by several critical risk factors, including low gestational age, low birth weight, supplemental oxygen use, and increased oxidative stress. • In vitro, unconjugated bilirubin is an effective scavenger of harmful oxygen species and a reducing agent, highlighting its potential protective role against oxidative stress. What is New: • Hyperbilirubinemia requiring phototherapy was associated with an increased risk of developing ROP, but this association was not observed in the most vulnerable population of extremely preterm infants. • Every additional day of phototherapy for hyperbilirubinemia increases the risk of ROP by 5% for any ROP, 4% for non-severe ROP, and 6% for severe ROP.

The incidence and risk factors associated with the retinopathy of prematurity in a tertiary hospital using 10-year retrospective data

BACKGROUND

The study aimed to examine the incidence and risk factors associated with retinopathy of prematurity at Phramongkutklao Hospital.

METHODS

A retrospective review was conducted on the medical records of premature infants screened for retinopathy of prematurity between January 2011 and December 2021. The screening examination was performed on infants who met the screening criteria, and retinopathy of prematurity was diagnosed according to the International Classification of Retinopathy of Prematurity. Maternal, obstetric, neonatal, and medical data were retrieved. Logistic regression analysis was used to identify the risk factors associated with retinopathy of prematurity.

RESULTS

A total of 403 premature infants were screened. The mean ± SD birth weight and gestational ages were 1,538 ± 543 grams and 31 ± 3 weeks, respectively. The incidence of any retinopathy of prematurity and stages 2 and 3 were 13.6%, 3.5%, and 10.1%, respectively. Multiple logistic regression analysis demonstrated that gestational age (adjusted odds ratio = 1.98, 95% CI:1.15-3.39), low birth weight (adjusted odds ratio = 0.99, 95% CI: 0.99-1.00), and phototherapy (adjusted odds ratio = 0.41, 95% CI: 0.17-1.00) were significant factors associated with the development of retinopathy of prematurity, after controlling for other confounding factors.

CONCLUSIONS

The incidence of total retinopathy of prematurity cases in this population was 13.6%. Overall, retinopathy of prematurity cases classified as stage 2 equated to 3.5% and stage 3 to 4.1%. Our data suggest that factors associated with retinopathy of prematurity consist of birth weight, gestational age, and phototherapy.

Potential Role of Bilirubin in Preventing Retinopathy of Prematurity

BACKGROUND

One of the most common problems in preterm neonates is retinopathy of prematurity (ROP). It has been shown antioxidants may be effective in preventing the development and progression of ROP. Considering the antioxidant properties of bilirubin, we decided to investigate the bilirubin level in neonates with ROP and compare it with healthy neonates.

METHODS

This case-control study was performed on VLBW neonates admitted to the NICU of Ghaem Hospital in Mashhad between 2014 and 2020 for a Jaundice evaluation. Complete neonate's characteristics, maternal history and laboratory results were collected in a questionnaire. Then the neonates were examined for ROP by a fellowship of the retina of an ophthalmologist at 32 weeks or four weeks after birth. The highest bilirubin levels during their hospitalization were also recorded.

RESULTS

Of 427 neonates examined, 121 (37.7%) had a normal eye examination, and 266 (62.3%) had ROP. The mean weight, gestational age and bilirubin were 1455.8 ± 431.4 grams, 31.6 ± 2.3 weeks and 8.8 ± 2.4 mg/dl, respectively. There was a significant difference between controls and neonates with ROP with regard to birth weight, duration of intermittent positive pressure ventilation (IPPV), duration of oxygen therapy, first and fifth minute Apgar scores, the maximum level of bilirubin and gestational age (P < 0.05). It was observed that the maximum level of bilirubin was lower in neonates with higher stages of ROP.

CONCLUSION

According to the results of this study, higher levels of bilirubin in neonates may be a protective factor against ROP. Moreover, increased levels of bilirubin are associated with reduced severity of ROP. Therefore, prophylaxis phototherapy in premature infants may need to be reconsidered.

Spectral-domain OCT changes in retina and optic nerve in children with hypoxic-ischaemic encephalopathy

Purpose

To evaluate the effect of neonatal hypoxic–ischaemic injury on the retina and the optic nerve and to correlate ocular damage with systemic parameters, laboratory tests, neurological imaging and therapeutic hypothermia at birth.

Methods

Forty-one children with hypoxic–ischaemic encephalopathy (HIE) at birth (9.09 ± 3.78 years) and a control group of 38 healthy subjects (9.57 ± 3.47 years) were enrolled in a cohort study. The HIE population was divided into three subgroups, based on the degree of encephalopathy according to Sarnat score and the treatment with therapeutic hypothermia (TH): Sarnat score I not treated with hypothermia, Sarnat score II-III treated with TH and Sarnat score II-III not subjected to TH. Total macular thickness, individual retinal layers and peripapillary nerve fibre layer thickness were measured with spectral-domain optical coherence tomography. Clinical data of perinatal period of HIE children were collected: APGAR score, pH and base excess of funiculus blood at birth, apnoea duration, brain ultrasound, cerebral MRI ischaemic lesions and blood chemistry tests.

Results

Children with Sarnat score I did not show a reduction of peripapillary nerve fibres and ganglion cell layer compared to the control group (p = 0.387, p = 0.316). Peripapillary nerve fibre layer was 109.06 ± 7.79 μm in children with Sarnat score II-III treated with TH, 108.31 ± 7.83 μm in subjects with Sarnat score II-III not subjected to TH and 114.27 ± 6.81 μm in the control group (p = 0.028, p = 0.007). Ganglion cell layer was thinner in children with Sarnat score II-III treated with TH (50.31 ± 5.13 μm) compared to the control group (54.04 ± 2.81 μm) (p = 0.01). Inner retinal layers damage correlated with C-reactive protein and lactate dehydrogenase increase, while higher levels of total bilirubin were protective against retinal impairment (p < 0.05). Cerebral oedema was related to peripapillary nerve fibre layer damage (p = 0.046).

Conclusions

Thickness reduction of inner retinal layer and peripapillary nerve fibre impairment was related to encephalopathy severity. Ocular damage was associated with inflammation and cerebral oedema following hypoxic–ischaemic damage.

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.

Retinopathy of prematurity: a review of risk factors and their clinical significance

Retinopathy of prematurity (ROP) is a retinal vasoproliferative disease that affects premature infants. Despite improvements in neonatal care and management guidelines, ROP remains a leading cause of childhood blindness worldwide. Current screening guidelines are primarily based on two risk factors: birth weight and gestational age; however, many investigators have suggested other risk factors, including maternal factors, prenatal and perinatal factors, demographics, medical interventions, comorbidities of prematurity, nutrition, and genetic factors. We review the existing literature addressing various possible ROP risk factors. Although there have been contradictory reports, and the risk may vary between different populations, understanding ROP risk factors is essential to develop predictive models, to gain insights into pathophysiology of retinal vascular diseases and diseases of prematurity, and to determine future directions in management of and research in ROP.

The Negative Relationship between Bilirubin Level and Diabetic Retinopathy: A Meta-Analysis

Objectives

Findings on the relationship between total bilirubin level (TBL) and diabetic retinopathy (DR) are inconsistent. Thus, we carried out a meta-analysis to investigate the relationship between TBL and the risk of DR.

Methods

Relevant studies were selected from six databases up to 31 May 2016 using a search strategy. The relevant data were extracted from the included studies according to the inclusion and exclusion criteria, and the mean value with standard errors or odds ratio (OR) with 95% confidence intervals (CIs) were calculated. We compared TBL in patients with DR with that in patients with diabetes but without retinopathy (NDR), and analyzed the dose-response relationship between TBL and the risk of DR.

Results

Twenty-four studies were selected in this meta-analysis. Twenty studies were included to calculate the pooled SMD, and the results showed that TBL in the DR group was lower than that in the NDR group (SMD: –0.52, 95% CI: –0.67, –0.38). Nine studies were included to calculate the pooled ORs, and the results showed that there was a significant negative relationship between TBL and the risk of DR (OR: 0.19, 95% CI: 0.14, 0.25). Six studies were included to investigate the dose-response relationship between TBL and the risk of DR, and we found a nonlinear relationship between TBL and the risk of DR. The results of our meta-analysis were found to be reliable using subgroup and sensitivity analyses.

Conclusions

The results of our meta-analysis indicate that higher TBL may be protective against DR in subjects with diabetes, and TBL could be used as a biomarker to predict the risk of DR.

One-year experience in the retinopathy of prematurity: frequency and risk factors, short-term results and follow-up

AIM

As a result of the increase in premature births and the advances in neonatal intensive care, retinopathy of prematurity (ROP) remains one of the most important causes of childhood blindness worldwide. The main factors in the development of ROP are gestational age, birth weight and oxygen therapy. ROP continues to gain importance due to the increasing survival rates of more immature babies.

METHODS

Between January 2007 and October 2008, 203 premature infants treated at the Neonatal Intensive Care Unit (NNICU) were prospectively enrolled and the relationship between known risk factors and the occurance of ROP was studied.

RESULTS

ROP in various stages developed in 86 cases (42.4%). Statistically significant correlations were found between the development of ROP and birth weight (P<0.0001) gestational age (P<0.0001), oxygen treatment and its duration (P<0.0001 and P=0.002), mechanical ventilation (MV) and its duration (P=0,0001 and P=0.0001), apnea (P=0.001), intraventricular hemorrhage (IVH) (P=0.046), sepsis (P=0.0001), use of erythropoietin (EPO) (P=0.003), the number of blood transfusions and frequency (P=0.0001 and P=0.0001), surfactant application (P=0.0001), the presence of patent ductus arteriosus (PDA) (P=0.001) or bronchopulmonary dysplasia (BPD) (P=0.0001). No significant correlations were found between the occurance of ROP and maternal pre-eclampsia (P=0.293), multiple pregnancy (P=0.218), or hyperbilirubinemia (P=0.494). Severity of ROP was related significantly with birth weight (P=0.0001), but no significant correlation between severity of ROP and gestational age was present.

CONCLUSION

Early description and reduction of the risk factors related with the occurance of ROP with the help of routine screening programs may warrant the prevention of visual loss, however early ophthalmic diagnosis and treatment are still mandatory to provide better visual rehabilitation.

Total serum bilirubin level in umbilical cord blood and respiratory distress syndrome in very low birth weight infants

AIMS

To explore the association between total serum bilirubin (TSB) level in umbilical cord blood (UCB) and the occurrence and/or severity of respiratory distress syndrome (RDS) in very low birth weight (VLBW) infants.

METHODS

We performed a prospective study of 579 VLBW infants. The mean TSB level in UCB (1.8 mg/dL) was used to divide the cohort into two groups: neonates with levels <1.8 mg/dL and those with levels >1.8 mg/dL. Demographic and clinical characteristics of the 2 groups, including diagnosis of RDS, need for ventilation, peak fraction of inspired oxygen (FiO2), oxygenation index (OI), and duration of respiratory support, were compared.

RESULTS

Three hundred and twenty-four infants were included in the low-TSB group and 255 infants were included in the high-TSB group. RDS was less frequent in the high TSB group than in the low one (46.3% vs. 56.6%, P=0.01). A negative association between TSB level in UCB and the occurrence of RDS [odds ratio (OR)=0.620; 95% confidence interval (CI) 0.440-0.873, P=0.006] was observed. However, lower TSB in UCB was not associated with the maximum FiO2, OI, or duration of mechanical ventilation.

CONCLUSIONS

VLBW infants with low TSB levels in UCB were more likely to develop RDS. However, in conjunction with surfactant replacement therapy, no correlation was found between TSB levels in UCB and the severity of RDS. The negative association between high TSB in UCB and RDS warrants further investigation.

High serum bilirubin levels and diabetic retinopathy: the Hisayama Study

PURPOSE

To assess the association between serum total bilirubin levels and diabetic retinopathy prevalence in participants of the Hisayama Study who had diabetes and impaired glucose metabolism.

DESIGN

Population-based, cross-sectional study.

PARTICIPANTS

Of 3119 participants of the Hisayama Study Eye Examinations in 2007, Japan, 1672 aged ≥40 years with either diabetes or impaired glucose metabolism (defined by a 75-g oral glucose tolerance test) were enrolled in the present study.

METHODS

Diabetic retinopathy was assessed via ophthalmic examination after pupil dilatation. The presence and the severity of diabetic retinopathy were determined by grading of color fundus photographs using the modified Airlie House classification system. Association of diabetic retinopathy with serum bilirubin quartiles was assessed using logistic regression model adjusting for age and known risk factors for diabetic retinopathy.

MAIN OUTCOME MEASURES

Prevalent diabetic retinopathy.

RESULTS

Diabetic retinopathy was present in 70 of 1672 (4.2%) participants. The prevalence of diabetic retinopathy in persons with the highest bilirubin quartile (≥0.9 mg/dL) was 2.7%, compared with the prevalence of 3.4%, 5.1%, and 5.1% in those with the first (<0.6 mg/dL), second (0.6-0.69 mg/dL), and third quartiles (0.7-0.89 mg/dL). After adjusting for factors known to be associated with diabetic retinopathy, the prevalence was significantly lower among persons with the highest bilirubin quartile compared with those with the lowest quartile (odds ratio [OR], 0.25; 95% confidence interval [CI], 0.09-0.72) or compared with those in the 3 lower quartiles (OR, 0.25; 95% CI, 0.11-0.58).

CONCLUSIONS

Elevated serum bilirubin levels may be protective against diabetic retinopathy among persons with either diabetes or impaired glucose metabolism, independent of known risk factors for diabetic retinopathy.

Possible roles of bilirubin and breast milk in protection against retinopathy of prematurity

AIM

To explore the association of serum bilirubin level and breast milk feeding with retinopathy of prematurity (ROP) in preterm infants.

METHODS

We conducted a case-control study to examine the independent and combined effects of serum bilirubin and breast milk feeding on ROP risk in infants <32 weeks gestation or with birth weight <1500 g. Cases (66 infants with ROP) were matched with controls (66 infants without ROP) based on factors known to affect ROP risk.

RESULTS

When analysed using the paired t-test, the peak bilirubin levels were lower in ROP cases than in controls (mean 7.2 vs. 7.9 mg/dL; p = 0.045). Using conditional logistic regression, we found a negative association between highest serum bilirubin level and risk of ROP (OR = 0.82 per 1-mg/dL change in bilirubin; p = 0.06). There was no significant association between breast milk feeding and risk of ROP.

CONCLUSION

Bilirubin may help to protect preterm infants against ROP.

Oxygen as a neonatal health hazard: call for détente in clinical practice

Education in oxygenation and in how oxygen is given to newborns needs to increase. Treatment with oxygen should no longer be considered proverbial and customary, regardless of our 'past experience' or consensus recommendations in clinical guidelines, since oxygen may lead to acute or chronic health effects.

CONCLUSION

Inappropriate oxygen use is a neonatal health hazard associated with aging, DNA damage and cancer, retinopathy of prematurity, injury to the developing brain, infection and others. Neonatal exposure to pure O2, even if brief, or to pulse oximetry >95% when breathing supplemental O2 must be avoided as much as possible.

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.

Kernicterus: still a concern

The presence of yellow staining and damage to the brain caused by unconjugated bilirubin was first described by Hervieux in 1847. Kernicterus, the technical term used to describe the intense yellow staining in the basal ganglia of the brain, was first used by Schmorl in 1903. Perhaps as many as 60 percent of all babies born each year in the U.S. are diagnosed with clinical jaundice. Kernicterus is a preventable brain injury caused by severe jaundice, yet it remains a threat today. Because of this, anyone caring for newborns must be aware of the risks and treatment for hyperbilirubinemia and the sequelae of this seemingly benign entity.

Threshold retinopathy at threshold of viability: the EpiBel study

AIM

To describe incidence, co-morbidity characteristics, and risk factors associated with threshold retinopathy of prematurity (ROP) in survivors with a gestational age (GA) of < or =26 weeks at birth.

METHODS

Retrospective analysis of perinatal data of all inborn survivors in all perinatal centres of Belgium in the period 1999-2000 (EpiBel cohort) believed to be between 22 and 26 weeks GA at time of delivery. Data on survivors who did and survivors who did not develop threshold ROP were compared (chi(2), Mann-Whitney U) and logistic regression was performed.

RESULTS

Of 303 admitted infants 175 (58%) were discharged alive. Incidence of major retinopathy (> or =stage 3) and of threshold ROP was 25.5% and 19.8% in survivors. Associated central nervous abnormalities were documented in six (17%) and associated chronic lung disease in 19 (54%) threshold ROP infants. Threshold ROP without additional morbidity characteristics at discharge was documented in 14 (40%) infants. Besides often reported risk factors, renal insufficiency (creatinaemia>1.5 mg/dl) was a risk factor to develop threshold ROP (p<0.0015) (chi(2)). Days of respiratory support (OR 1.02; 95% CI 1.002 to 1.039), number of transfusions (OR 1.118; 95% CI 1.030 to 1.214), and renal insufficiency (OR 3.31; 95% CI 1.344 to 8.196) remained independent risk factors to develop threshold ROP in this cohort in a stepwise logistic regression model (MedCalc).

CONCLUSIONS

Incidence of threshold ROP is high at the limits of viability. Renal insufficiency is a risk factor to develop threshold ROP in this cohort.

Role of redox in fetal development and neonatal diseases

In the cell, reducing and oxidizing molecules modulate the redox state. In embryonic and fetal growth, increased oxidative stress may be detrimental, but an oxidized state can also be beneficial. This is because redox may also affect key transcription factors that can alter gene expression during development. In addition, redox may impact on placentation and amniotic membrane integrity during pregnancy. Lastly, diseases of prematurity, such as necrotizing enterocolitis, retinopathy of prematurity, and chronic lung disease, may be modulated by redox in the premature. Because antioxidant therapies have not necessarily modified the outcome of these diseases, some debate exists as to this. Nonetheless, sufficient evidence suggests a role for redox throughout embryonic, fetal, and postnatal development. This evidence will be explored here.

Treatment of jaundice in low birthweight infants

Exchange transfusion and phototherapy remain the staples of intervention for the jaundiced newborn. Clinical management of the jaundiced low birthweight infant is discussed.

Does elevated peak bilirubin protect from retinopathy of prematurity in very low birthweight infants

OBJECTIVE

Bilirubin is a potent in vitro antioxidant. Despite repeated study, its in vivo significance has yet to be defined. Bilirubin is universally elevated in very low birthweight (VLBW) infants. Retinopathy of prematurity (ROP) is a disease thought to be associated with exposure to oxygen free radicals in VLBW infants. The objective of this study was to determine whether there was an association between peak bilirubin levels and ROP.

METHODS

The risk for ROP, stages III and IV was measured as a function of increasing peak bilirubin levels in VLBW infants admitted to the neonatal ICU. A similar analysis was performed on a subgroup of VLBW infants with prolonged (> or =28 days) oxygen requirement. The relation between peak bilirubin level and the duration of oxygen requirement was tested by logistic regression analysis. All analyses were conducted after controlling for birthweight and presence of intraventricular hemorrhage (IVH).

RESULTS

There was an increased risk for ROP, stages III and IV (OR 1.187; 95% CI 1.013 to 1.390; p=0.034) with elevated peak serum bilirubin levels in the entire population. Duration of oxygen requirement was not related to peak bilirubin (p>0.1). In the subgroup of infants with prolonged oxygen requirement (> or =28 days), there was no association between peak serum bilirubin levels and ROP III and IV (p>0.1); however, there was an association with further increased duration of oxygen requirement (p=0.034).

CONCLUSION

Elevated peak bilirubin does not protect from and may be a risk for ROP in VLBW infants.

No clinical correlation between bilirubin levels and severity of retinopathy of prematurity

PURPOSE

To evaluate the hypothesis that bilirubin has a protective effect against the development of severe retinopathy of prematurity (ROP).

METHODS

An assessment of 76 infants born at 24 and 25 weeks' gestation and admitted to the level III neonatal intensive care unit at Saitama Children's Medical Center was made. Indirect ophthalmoscopy fundus examinations were performed on all infants to identify the degree and progression to threshold ROP. We analyzed the daily bilirubin levels and grouped the patients according to the severity of ROP based on the infant's worst ROP examination. The first group was comprised of infants with less than stage 3 ROP and infants with stage 3 ROP. The second group was infants with less than prethreshold ROP or prethreshold ROP, and infants with threshold ROP. Next, we divided the infants into 3 groups: less than prethreshold ROP, prethreshold ROP, and threshold ROP. The daily changes in serum bilirubin concentrations during the first 14 days of life were determined for each infant. Three groups (less than prethreshold ROP, prethreshold ROP, and threshold ROP) were comparable as to their basic data, clinical characteristics, and treatments.

RESULTS

ROP was found in 76 infants. There were no statistical differences in the clinical characteristics and treatments, excluding the duration of phototherapy, among the 3 groups. During the first 14 days of age, there were no significant differences in the daily mean bilirubin concentrations according to the groups separated by severity of ROP.

CONCLUSION

These results indicate that there is no distinct protective effect of bilirubin on the development of severe ROP.

Retinopathy of prematurity: causation

The incidence of ROP is birth weight dependent and restricting therapeutic oxygen levels has dramatically reduced the incidence of ROP in infants of birth weight >1000 g. However, the incidence of ROP has remained high in very low birth weight (VLBW) infants and this appears to be related to these babies being more ill. Several risk factors have been identified in this group, however oxygen variability, rather than high levels, has been correlated with severity of disease in recent clinical and animal studies. Difficulties in defining 'normal' oxygen in this group has meant the optimal range of oxygen therapy has not yet been defined. Clinical studies are now underway using even lower oxygen therapy ranges. The impact this may have on ROP, neurological and respiratory outcomes will require further study.

Formation of propentdyopents and biliverdin, oxidized metabolites of bilirubin, in infants receiving oxygen therapy

BACKGROUND

Bilirubin has antioxidative effects. When bilirubin reacts with reactive oxygen species, oxidized metabolites of bilirubin are formed, such as biliverdin and propentdyopents. A decrease in serum bilirubin concentration and an increase in serum and urinary oxidized metabolites of bilirubin may indicate the protective action of bilirubin against reactive oxygen species.

METHODS

In the in vitro study, we measured the oxidative products of bilirubin formed through the action of O2- by the xanthine-xanthine oxidase system, either as free bilirubin or bilirubin-human serum albumin complex. In the clinical investigation, serum concentrations of (ZZ)-bilirubin (4Z, 15Z-bilirubin), the subfraction and biliverdin, and urinary propentdyopent absorption, were measured in blood and urine samples, respectively, collected from 30 5-day-old neonates with birth weights of 1500-3624 g who had been hospitalized at the Ehime Prefectural Hospital and who had not undergone phototherapy.

RESULTS

In the in vitro study, a significant formation of propentdyopents was observed in aqueous solution. A statistically significant correlation was found between serum (ZZ)-bilirubin concentration and serum biliverdin concentration (r = 0.82, P < 0.0001), but not between serum (ZZ)-bilirubin concentration and urinary propentdyopent absorption. Serum (ZZ)- and serum (ZE)-bilirubin and biliverdin concentrations, and urinary propentdyopent absorption were compared between the groups with and without oxygen therapy. No significant differences were found in serum (ZZ)-bilirubin, serum (ZE)-bilirubin and biliverdin concentration, urinary propentdyopent absorption, serum biliverdin/serum (ZZ)-bilirubin, or urinary propentdyopent absorption/serum (ZZ)-bilirubin. Neither a decrease in serum bilirubin concentration nor an increase in serum biliverdin concentration and urinary propentdyopent absorption after oxygen therapy were demonstrated in the present study.

CONCLUSIONS

In the in vitro study, we demonstrated for the first time that propentdyopents were produced from (ZZ)-bilirubin by the xanthine-xanthine oxidase system but biliverdin was not. In the in vivo study, serum biliverdin concentration and urinary propentdyopent absorption seem to have a different relationship to serum (ZZ)-bilirubin concentration in sick and early neonates.