Retinopathy of prematurity and bilirubin

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.

Incidence and risk factors of retinopathy of prematurity in three neonatal intensive care units in Palestine

BACKGROUND

Severe Retinopathy of Prematurity (ROP) is a serious vasoproliferative disorder that can affect extremely premature infants. It continues to be one of the most important preventable causes of blindness in children. Our study is aimed at finding the incidence of ROP and its association with some risk factors in Palestine.

METHODS

From the 1st of January 2016 to 31st December 2016, a total number of 115 infants who met the criteria for ROP screening in three neonatal intensive care units were included in the study. The medical records of infants were reviewed retrospectively and multiple factors that may be associated with the development of ROP were collected manually.

RESULTS

The incidence of ROP and severe type 1 ROP that require treatment was 23.5 and 11.3% respectively. After conducting univariate analysis of risk factors, statistically significant risk factors affecting the development of ROP in our study were: low gestational age, low birth weight, type of multiple gestation, the presence of affected sibling, low level of Hemoglobin at birth, respiratory distress syndrome, low Hemoglobin level, blood transfusion and days on oxygen supplements with either mechanical, non-mechanical methods or both combined. High bilirubin levels were found as a protective factor against the development of ROP. However, when a multivariate analysis was performed, only low gestational age, total days on oxygen supplement and high bilirubin levels were significant regarding the development of ROP.

CONCLUSION

The incidence of ROP is considered a relatively low percentage compared to neighboring countries that have higher levels of human development index. Statistically significant risk factors need to be considered when clinicians deal with premature infants.

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.

Systemic regulation of bilirubin homeostasis: Potential benefits of hyperbilirubinemia

Neurotoxic bilirubin is the end product of heme catabolism in mammals. Bilirubin is solely conjugated by uridine diphospho-glucuronosyltransferase 1A1, which is a membrane-bound enzyme that catalyzes the transfer of glucuronic acid. Due to low function of hepatic and intestinal uridine diphospho-glucuronosyltransferase 1A1 during the neonatal period, human neonates develop mild to severe physiological hyperbilirubinemia. Accumulation of bilirubin in the brain leads to the onset of irreversible brain damage, termed kernicterus. Breastfeeding is one of the most significant factors that increase the risk of developing kernicterus in infants. Why does this most natural way of feeding increase the risk of brain damage or even death? This question leads to the hypothesis that breast milk-induced hyperbilirubinemia might bring certain benefits that outweigh those risks. While bilirubin is neurotoxic and cytotoxic, this compound is also a potent antioxidant. There are studies showing improved clinical conditions in patients with hyperbilirubinemia. Accumulating evidence also shows that genetic polymorphisms linked to hyperbilirubinemia are beneficial against various diseases. In this review article, we first introduce the production, metabolism, and transport of bilirubin. We then discuss the potential benefits of neonatal and adult hyperbilirubinemia. Finally, epigenetic factors as well as metabolomic information associated with hyperbilirubinemia are described. This review article advances the understanding of the physiological importance of the paradoxical compound bilirubin. (Hepatology 2018;67:1609-1619).

Does bilirubin protect against developing diabetes mellitus?

After 25 years of evaluating bilirubin as a possible protective agent in neonatal and cardiovascular disease, interest has moved on to a exploring a possible protective role in diabetes mellitus (DM). This review finds conflicting prospective data for a protective relationship though there are retrospective, case-controlled data, that can only show association, which is not causality. Only prospective studies can show causality. Also, it would appear that the underlying biochemical assumptions do not readily translate from the animal to the human setting. Given that many factors impact on circulating bilirubin levels, it is not surprising that a clear-cut answer is not available; the jury is still out. Any relationship between DM and bilirubin might relate to intermediates in bilirubin metabolism, including relationships involving the genes for the enzymes participating in those steps. Nevertheless, the pursuit of bilirubin in disease causation is opening new avenues for research and if it is established that serum bilirubin can predict risks, much will have been achieved. The answer may have to come from molecular genetic analyses.

Preservation solution supplemented with biliverdin prevents lung cold ischaemia/reperfusion injury

OBJECTIVES

Biliverdin (BV), one of the byproducts of heme catalysis through the heme oxygenase system, is a known scavenger of the reactive oxygen species. We hypothesized that adding BV to the perfusate and cold storage solution could protect rat lung grafts from oxidative injuries via its antioxidant efficacies.

METHODS

Orthotopic left lung transplantation was performed in a syngenic Lewis-to-Lewis rat combination under 100% oxygen. Grafts were preserved in low-potassium dextran (LPD; Perfadex) at 4°C for 6 h with or without supplementation of 1 or 10 μM of BV into LPD.

RESULTS

Prolonged cold storage and reperfusion resulted in a considerable deterioration of graft functions associated with massive apoptosis in the grafts after reperfusion. The untreated grafts exhibited the early up-regulations of mRNA for inflammatory mediators and an increase in a marker of lipid peroxidation, showing oxidative injuries. Although BV supplementation of LPD at a lower concentration (1 μM) did not improve the graft gas exchange, the grafts treated with BV (10 μM) showed a significant improvement of oxygenation and less inflammatory responses as well as reduced lipid peroxidation and apoptosis. Although the rapid activations of mitogen-activated protein kinases (MAPKs) were seen 30 min after reperfusion in the grafts stored in control LPD, BV treatment significantly reduced phosphorylated-MAPK protein expression.

CONCLUSIONS

This study demonstrates that the exposure of the lung grafts to BV during cold storage can impart potent cytoprotective effects to lung cold ischaemia/reperfusion injury and significantly improve the lung graft function following extended cold preservation and transplantation by the mechanism of a reduction in oxidative injury and following inflammatory events.

Total serum bilirubin levels during the first 2 days of life and subsequent neonatal morbidity in very low birth weight infants: a retrospective review

To determine the relationship between total serum bilirubin (TSB) during the first 2 days of life and subsequent neonatal morbidity in very low birth weight (VLBW, less than 1500 g) infants. We performed a prospective study of 582 VLBW infants born between July 1, 2005 and December 31, 2009. TSB was measured in umbilical cord blood (UCB), at 24 and 48 h after birth. Demographic and clinical characteristics of infants in hospital were recorded. The interaction between TSB variables during the first 48 h of life and subsequent neonatal morbidity were assessed in logistic regression analyses adjusted for multiple risk factors. It was found that TSB in UCB was in a negative correlation with occurrence of respiratory distress syndrome (RDS) [OR 0.626, 95% confidence interval (95% CI): 0.446-0.879, p = 0.007], and there was also a negative correlation between TSB in UCB and occurrence of intraventricular hemorrhage (IVH) [OR 0.695, 95% CI 0.826-0.981, p = 0.020]. However, TSB in UCB positively correlated with hyperbilirubinemia [OR 2.471, 95% CI 1.326-3.551, p = 0.012], and TSB at 24 h after birth was also in a positive correlation with early onset sepsis (EOS) [OR 1.299, 95% CI 1.067-1.582, p = 0.011]. VLBW infants with low TSB levels in UCB were more likely to develop RDS and IVH, and those with low TSB levels in UCB were less likely to develop hyperbilirubinemia. Infants with high TSB levels at 24 h after birth were more likely to develop EOS. The protective effect of raised TSB in UCB with respect to RDS and IVH warrants further investigation.

Application of heme oxygenase-1, carbon monoxide and biliverdin for the prevention of intestinal ischemia/reperfusion injury

Intestinal ischemia/reperfusion (I/R) injury occurs frequently in a variety of clinical settings, including mesenteric artery occlusion, abdominal aneurism surgery, trauma, shock, and small intestinal transplantation, and is associated with substantial morbidity and mortality. Although the exact mechanisms involved in the pathogenesis of intestinal I/R injury have not been fully elucidated, it is generally believed that polymorphonuclear neutrophils, pro-inflammatory cytokines, and mediators generated in the setting of oxidative stress, such as reactive oxygen species (ROS), play important roles. Heme oxygenase (HO) is the rate-limiting enzyme that catalyzes the degradation of heme into equimolar quantities of biliverdin and carbon monoxide (CO), while the central iron is released. An inducible form of HO (HO-1), biliverdin, and CO, have been shown to possess generalized endogenous anti-inflammatory activities and provide protection against intestinal I/R injury. Further, recent observations have demonstrated that exogenous HO-1 expression, as well as exogenously administered CO and biliverdin, have potent cytoprotective effects on intestinal I/R injury as well. Here, we summarize the currently available data regarding the role of the HO system in the prevention intestinal I/R injury.

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.

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.

Products of heme oxygenase and their potential therapeutic applications

Heme oxygenase 1 (HO-1) is induced in response to cellular stress and is responsible for converting the prooxidant heme molecule into equimolar quantities of biliverdin (BV), carbon monoxide (CO), and iron. BV is then converted to bilirubin (BR) by the enzyme biliverdin reductase. Experimental evidence suggests that induction of the HO system is an important endogenous mechanism for cytoprotection and that the downstream products of heme degradation, CO, BR, and BV, may mediate these powerful beneficial effects. These molecules, which were once considered to be toxic metabolic waste products, have recently been shown to have dose-dependent vasodilatory, antioxidant, and anti-inflammatory properties that are particularly desirable for tissue protection during organ transplantation. In fact, recent work has demonstrated that administration of exogenous CO, BR, or BV may offer a simple, inexpensive method to substitute for the cytoprotective effects of HO-1 in a variety of clinically applicable models. This review will attempt to summarize the relevant biochemical and cytoprotective properties of CO, BR, and BV, and will discuss emerging studies involving the therapeutic applications of these molecules in the kidney and other organ systems.

Biliverdin reductase: a major physiologic cytoprotectant

Bilirubin, an abundant pigment that causes jaundice, has long lacked any clear physiologic role. It arises from enzymatic reduction by biliverdin reductase of biliverdin, a product of heme oxygenase activity. Bilirubin is a potent antioxidant that we show can protect cells from a 10,000-fold excess of H2O2. We report that bilirubin is a major physiologic antioxidant cytoprotectant. Thus, cellular depletion of bilirubin by RNA interference markedly augments tissue levels of reactive oxygen species and causes apoptotic cell death. Depletion of glutathione, generally regarded as a physiologic antioxidant cytoprotectant, elicits lesser increases in reactive oxygen species and cell death. The potent physiologic antioxidant actions of bilirubin reflect an amplification cycle whereby bilirubin, acting as an antioxidant, is itself oxidized to biliverdin and then recycled by biliverdin reductase back to bilirubin. This redox cycle may constitute the principal physiologic function of bilirubin.

Neural roles for heme oxygenase: contrasts to nitric oxide synthase

The heme oxygenase (HO) and nitric oxide (NO) synthase (NOS) systems display notable similarities as well as differences. HO and NOS are both oxidative enzymes using NADPH as an electron donor. The constitutive forms of the enzyme are differentially activated, with calcium entry stimulating NOS by binding to calmodulin, whereas calcium entry activates protein kinase C to phosphorylate and activate HO2. Although both NO and carbon monoxide (CO) stimulate soluble guanylyl cyclase to form cGMP, NO also S-nitrosylates selected protein targets. Both involve constitutive and inducible biosynthetic enzymes. However, functions of the inducible forms are virtual opposites. Macrophage-inducible NOS generates NO to kill other cells, whereas HO1 generates bilirubin to exert antioxidant cytoprotective effects and also provides cytoprotection by facilitating iron extrusion from cells. The neuronal form of HO, HO2, is also cytoprotective. Normally, neural NO in the brain seems to exert some sort of behavioral inhibition. However, excess release of NO in response to glutamate's N-methyl-d-aspartate receptor activation leads to stroke damage. On the other hand, massive neuronal firing during a stroke presumably activates HO2, leading to neuroprotective actions of bilirubin. Loss of this neuroprotection after HO inhibition by mutant forms of amyloid precursor protein may mediate neurotoxicity in Familial Alzheimer's Disease. NO and CO both appear to be neurotransmitters in the brain and peripheral autonomic nervous system. They also are physiologic endothelial-derived relaxing factors for blood vessels. In the gastrointestinal pathway, NO and CO appear to function as coneurotransmitters, both stimulating soluble guanylyl cyclase to cause smooth muscle relaxation.

Heme oxygenase-2 acts to prevent neuronal death in brain cultures and following transient cerebral ischemia

Heme oxygenase (HO) cleaves the heme ring to form biliverdin, which is rapidly reduced to bilirubin, carbon monoxide, and iron. HO1, the first form of the enzyme discovered, is an inducible protein, concentrated in tissues that are exposed to degrading red blood cells and stimulated by hemolysis and numerous other toxic perturbations to eliminate potentially toxic heme. By contrast, HO2 is constitutive and most highly concentrated in neural tissues. Carbon monoxide, formed from HO2, is a putative neurotransmitter in the brain and peripheral autonomic nervous system. HO1 regulates the efflux of potentially toxic iron from cells, as iron efflux is deficient in mice with targeted deletion of HO1 (HO1(-/-)), and transfection of HO1 facilitates iron efflux. Bilirubin appears to be a physiologic neuroprotectant. Activation of HO2 by phorbol esters, that stimulate protein kinase C to phosphorylate HO2, augments production of bilirubin which protects brain cultures from oxidative stress. Bilirubin itself in nanomolar concentrations is neuroprotective, while HO2 deletion (HO2(-/-)) leads to increased neurotoxicity in brain cultures and increased neural damage following transient cerebral ischemia in intact mice. Mechanisms whereby HO2 provides neuroprotection have not been clarified including whether protection is primarily associated with apoptotic or necrotic cell death. Moreover, the generality of neurotoxic stimuli influenced by HO2 has been unclear. We now demonstrate increased neuronal death in cerebellar granule cultures of HO2(-/-) mice with a selective augmentation of apoptotic death. We also demonstrate that HO2 transfection rescues apoptotic death. In intact mice, we show an increased incidence of apoptotic morphology in the penumbra area surrounding the infarct core in HO2(-/-) mice undergoing transient focal ischemia.

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

Oxidative injury may contribute to the development of retinopathy of prematurity (ROP), and bilirubin may be a physiologically important antioxidant. Therefore we evaluated the relationship of ROP to bilirubin levels in 157 infants born at 23 to 26 weeks estimated gestational age. We found no definite association between bilirubin levels and severe ROP.

Bilirubin, formed by activation of heme oxygenase-2, protects neurons against oxidative stress injury

Heme oxygenase (HO) catalyzes the conversion of heme to carbon monoxide, iron, and biliverdin, which is immediately reduced to bilirubin (BR). Two HO active isozymes exist: HO1, an inducible heat shock protein, and HO2, which is constitutive and highly concentrated in neurons. We demonstrate a neuroprotective role for BR formed from HO2. Neurotoxicity elicited by hydrogen peroxide in hippocampal and cortical neuronal cultures is prevented by the phorbol ester, phorbol 12-myristate 13-acetate (PMA) via stimulation of protein kinase C. We observe phosphorylation of HO2 through the protein kinase C pathway with enhancement of HO2 catalytic activity and accumulation of BR in neuronal cultures. The neuroprotective effects of PMA are prevented by the HO inhibitor tin protoporphyrin IX and in cultures from mice with deletion of HO2 gene. Moreover, BR, an antioxidant, is neuroprotective at nanomolar concentrations.

An elevated level of copper zinc superoxide dismutase fails to prevent oxygen induced retinopathy in mice

BACKGROUND

To determine whether a higher level of copper zinc superoxide dismutase (CuZnSOD) can reduce the severity of oxygen induced retinopathy (OIR) in a mouse model.

METHODS

CuZnSOD transgenic mice with a threefold increase in CuZnSOD activity and control non-transgenic mice were exposed to 90% oxygen for 12 hours a day during the first 5 days of life. After oxygen treatment, all mice were reared in room air for 10 days. Another group of transgenic and non-transgenic mice were kept in room air for 15 days and served as control groups for the oxygen effect. At day 15, all mice were killed and perfused with India ink. The retinas were flat mounted on slides and examined with a light microscope.

RESULTS

There was a statistically significant increase in the incidence of OIR in mice exposed to high levels of oxygen, whether or not they were transgenic. However, there was no statistically significant difference in the severity of OIR between oxygen treated transgenic and non-transgenic mice.

CONCLUSION

A threefold higher CuZnSOD activity does not protect against OIR in mice. This is an unexpected finding, since oxygen radicals are considered a major factor causing OIR, and increased CuZnSOD activity has reduced oxygen radical induced damage in several neuronal and non-neuronal systems. The possibility of a damaging role for other radicals not affected by CuZnSOD cannot be excluded.

Hyperbilirubinemia results in reduced oxidative injury in neonatal Gunn rats exposed to hyperoxia

Bilirubin is a potent antioxidant in vitro. To determine whether bilirubin also is an antioxidant in vivo, we studied markers of oxidative injury in the Gunn rat model exposed to hyperoxia. Homozygous jaundiced males were mated with heterozygous nonjaundiced females to obtain both jaundiced and nonjaundiced pups within a litter. Once delivered, the pups and their mother were placed in air (21% O2) or hyperoxia (> 95% O2) for 3 d. Both jaundiced and nonjaundiced pups were removed from the chambers daily. Animals were sacrificed and blood was drawn for determination of serum bilirubin, blood thiobarbituric acid-reactive substances (TBARS) by fluorescence assay, serum hydroperoxides, and serum protein oxidation. Tissues (liver, lung, and brain) were assayed for lipid peroxides (TBARS, conjugated dienes [CD], loss of polyunsaturated fatty acid content [PUFA]). We also measured a wide range of serum antioxidants including superoxide dismutase, catalase, glutathione, vitamins A, C, and E, and uric acid. Blood TBARS were significantly decreased in the jaundiced pups compared to the nonjaundiced pups on day 3 of hyperoxia, and blood TBARS were inversely correlated to serum bilirubin on day 3 of hyperoxia (R2 +/- .89). Similar decreases in serum lipid hydroperoxides and serum protein carbonyl content were detected in the jaundiced pups as compared to their nonjaundiced littermates. Other serum antioxidants were not increased in jaundiced animals compared to nonjaundiced animals. Relative lung weight was lower in jaundiced pups exposed to hyperoxia compared to similarly exposed nonjaundiced pups, suggesting a reduction in hyperoxia-induced lung edema. We detected no significant effects of bilirubin on parameters of lipid peroxidation in solid tissues. We conclude that serum bilirubin protects against serum oxidative damage in the first days of life in neonatal Gunn rats exposed to hyperoxia. We speculate that bilirubin is a functionally important transitional antioxidant in the circulation of human neonates and that it may be involved in modulation of injury due to hyperoxia.

Evaluation of bilirubin as possible protective factor in the prevention of retinopathy of prematurity

Retinopathy of prematurity (ROP) appears to be a multifactorial disease, the prevention of which is probably impossible even with the most accurate methods of blood-gas monitoring and oxygen restrictions. The oxidative processes and consequent formation of free radicals are probably influenced by the availability of various antioxidants in the immature retina. Bilirubin, the end product of haem catabolism, has recently been regarded as a potential physiological antioxidant. In order to test the suggestion as to the possible effect of bilirubin in reducing the incidence of ROP a retrospective study was undertaken of the medical records of 151 neonates born between 1984 to 1988 who weighed less than 1500 g. Of these, 78 had various degrees of ROP, whereas 73 had no ROP and served as a control group. The daily mean bilirubin values were analysed in accordance with gestational age and birth weight as well as the severity of ROP, and the results were compared with those obtained for the control group. The results showed no correlation between bilirubin levels and severity of ROP in all subgroups of gestational age and birth weight. These findings indicate that there is no apparent protective effect of bilirubin on the development of ROP.

Variation of initial serum bilirubin rise in newborn infants with type of illness

Hyperbilirubinaemia in newborn infants is generally regarded as a problem, and bilirubin itself as toxic metabolic waste, but the high frequency in newborn infants suggests that the excess of neonatal bilirubin may have a positive function. To investigate the hypothesis that bilirubin has a role as a free-radical scavenger, the rate of rise in serum bilirubin in the first few days of life was measured in 44 infants with five illnesses thought to enhance free-radical production and in 58 control infants. The infants were selected from 2700 consecutive births by exclusion of those with factors known to affect bilirubin metabolism, including enteral feeding. The control infants were those who seemed to be ill and received treatment, including restriction of enteral feeds, but in whom no illness, or disorders not related to free-radical production, were found. The mean serum bilirubin rise was significantly lower in the combined illness group than in the control group (36.1 [95% Cl 26.9-45.3] vs 66.7 [55.9-77.5] mumol.l-1.day-1; p less than 0.0001). In subgroup analyses the mean rises in infants with circulatory failure, neonatal depression/asphyxia, aspiration syndromes, and proven sepsis were significantly lower than in controls matched for gestational age and birthweight, but rises in infants with respiratory distress and their matched controls did not differ. These findings are consistent with the hypothesis that bilirubin is consumed in vivo as an antioxidant. Such consumption may operate in vivo in addition to the standard pathways for bilirubin metabolism (production, isomerisation, and excretion).