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

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 role of hepatic and renal functions in the development of retinopathy of prematurity: Is proteinuria a new risk factor?

PURPOSE

To investigate the association of hepatic and renal parameters with the development of retinopathy of prematurity (ROP) in premature infants with a gestational age ≤ 32 weeks.

METHODS

Medical records of 240 preterm infants were reviewed retrospectively, 85 of them were grouped as type 1, type 2 ROP, and control group. The 4th week hepatic and renal function test results of the groups, on the day of their first ROP examinations, were compared for the risk of development of ROP and the development of type 1 ROP.

RESULTS

In this study, 12, 35, and 38 infants were enrolled in the type 1, type 2 ROP, and control group, respectively. The average gestational age and birth weight were higher; however, the duration of oxygen treatment was lower in the control group (p < 0.001). The blood glucose level was significantly higher in the type 1 ROP group than in the other groups (p = 0.023). The mean of total serum bilirubin of the type 1 ROP group was significantly lower than those of the type 2 ROP and control group (p = 0.032). Proteinuria was present in 85.7% of preterms with treatment-requiring ROP and proteinuria increased the risk of ROP by 3.9 times (OR with 95% CI 3.9 (1.19-12.75), p = 0.042).

CONCLUSION

We found significantly higher blood glucose and lower total bilirubin level in the type 1 ROP group. Moreover, our findings suggest that proteinuria may not be only a comorbidity factor but also related to a higher frequency of ROP and type 1 ROP in preterm infants.

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.

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.

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.

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.

Potential protective effects of bilirubin following the treatment of neonatal hypoxic-ischemic encephalopathy with hypothermia therapy

Background: Therapeutic hypothermia (TH) is the standard therapy for hypoxic-ischemic encephalopathy (HIE) and is associated with a wide range of physiological changes. Objective: We re-evaluated the effects of HIE and TH on bilirubin measurements following HIE in a center involved in the China cooling randomized controlled trial (RCT). Methods: Serial serum bilirubin concentrations measured during the first week of life were compared among the HIE + NT (normothermia) group, HIE + TH treatment group and control group (without HIE). Survivors of HIE were followed and assessed at approximately 2 years of age, and the results were correlated with peak bilirubin levels during the first week of life. Results: One hundred and thirty-eight infants were available for analysis. Significantly lower bilirubin levels were recorded in the HIE + NT group than in the controls (P<0.05). Significant differences were not observed among the patients in the HIE + NT group (mild to severe) or between the HIE + TH group and the HIE + NT group at any time point (P>0.05). The peak serum bilirubin concentrations recorded at 96 h of age showed a good correlation with the results of the Bayley Scales of Infant and Toddler Development, third edition (BSID-III) (P=0.02). Conclusion: Bilirubin potentially exerts a neuroprotective effect during the first week of life, and low temperature does not affect the possible antioxidant function of bilirubin during TH following HIE.

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.

17β-estradiol ameliorates oxygen-induced retinopathy in the early hyperoxic phase

Retinopathy of prematurity (ROP) is a major and leading cause of blindness in premature infants. It has been realized that early treatment for ROP is important. However, all the early treatments of ROP are focusing on peripheral retinal ablation which does not surmount the limit of extinguishing retinal neovascularization and protecting the retinas of children with ROP from the injury of ablation. In this study, we investigated the morphological changes of retina and oxidative stress alterations in the early phase of oxygen-induced retinopathy (OIR) and tested the effects of 17β-estradiol (17β-E2), a nonselective estrogen receptor (ER) agonist, on early phase OIR development. We found that large central capillary-free areas were induced in the retinas of pups exposed to hyperoxia on postnatal day 9 (P9), whereas vascularization was almost complete in the retinas of pups exposed to normoxia at the same age. The concentrations of malondiadehyde (MDA), an end-product of oxidative stress, and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, a major enzyme producing free radicals, as well as the activity of NADPH oxidase were significantly elevated in the retinas of pups exposed to hyperoxia on P9 and postnatal day 13 (P13) compared to those in age matched pups exposed to normoxia. Treatment with 17β-E2 decreased not only the percentage of the central capillary-free area to total retina area but also the concentrations of MDA and NADPH oxidase as well as the activity of NADPH oxidase in a dose-dependent manner in pups exposed to hyperoxia on p9 and P13. The concentration of VEGF was significantly decreased on P9 but increased on P14 in the retinas of pups exposed to hyperoxia, whereas it was significantly elevated on P9 but decreased on P14 in the retinas of pups treated with 17β-E2. The effect of 17β-E2 could be reversed by the co-treatment with ICI182780, a high affinity estrogen receptor antagonist, which suggested that 17β-E2 might exert its effect on early hyperoxic phase of OIR through estrogen receptor. Our results suggest that treatment with antioxidant drugs at early hyperoxic phase of ROP even before the appearance of retinal neovascularization may be more effective than their application to ROP at late phase, which may abolish the deleterious factors that contribute to retinal neovascularization and promote retinal blood vessels to develop healthily.

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.

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.

Protective effect of bilirubin in ischemia-reperfusion injury in the rat intestine

BACKGROUND

Although bilirubin, which crosses the blood-brain barrier, can cause irreversible brain damage, it also possesses antioxidant properties that may be protective against oxidative stress. Intestinal ischemia-reperfusion (IR) injury results in cell destruction, mediated via the generation of reactive oxygen species. Although increased serum bilirubin is correlated with increased antioxidant potential in the face of hyperoxia, evidence of bilirubin-associated protective effect against IR injury remains nonspecific. We therefore sought to investigate whether hyperbilirubinemia would be protective against IR injury to the intestine.

METHODS

Young adult rats were randomly assigned to one of three groups: 1) IR/control (n = 12); 2) IR/hyperbilirubinemia (n = 10), in which IR was generated while the rats were treated with a continuous infusion of bilirubin; and 3) hyperbilirubinemia controls (n = 10). Blood and intestinal tissue samples were obtained to determine serial thiobarbituric acid reducing substances (index of lipid peroxidation) and for xanthine oxidase/xanthine dehydrogenase and glutathione/glutathione disulfide ratios. Intestinal histopathology was graded from 1 (normal) to 4 (severe necrotic lesions).

RESULTS

Histopathologic scoring and circulating and tissue thiobarbituric acid reducing substances were highest in the IR/control animals compared with either the IR/hyperbilirubinemics or the controls. All of these are consistent with the most severe injury in this group. Xanthine oxidase/xanthine dehydrogenase ratios were not significantly different among the groups.

CONCLUSION

Hyperbilirubinemia ameliorates the extent of intestinal IR injury in our model and appears to act as an antioxidant. This study supports the concept that bilirubin possesses some beneficial properties in vivo, although no direct clinical conclusions can be drawn from these data.

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.

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.

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.

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.

Retinopathy of prematurity and bilirubin--no clinical evidence for a beneficial role of bilirubin as a physiological anti-oxidant

The prevention of retinopathy of prematurity (ROP) remains a persistent problem. A previous report has focused on the possible protective effect of bilirubin on the development of ROP. These results still await clinical confirmation by other research groups. Therefore, we undertook a retrospective clinical study trying to confirm this attractive hypothesis. Twelve premature newborns under 32 weeks of gestation with ROP stage 3-4 were matched for gestational age with 12 infants without ROP. Data were collected about the infant's characteristics, medical illnesses, ventilatory settings and treatments. The total serum bilirubin concentrations between the 1st and 8th postnatal day were also gathered. The two matched groups were comparable as to their basic data, clinical characteristics and treatment, except for a slight, but significant longer duration of phototherapy for group ROP 0 (mean, 50.2 h; SD 48,6 vs 31.6 h; SD 42.7 in ROP 3-4; P = 0.02). No statistical difference relative to bilirubin was found between the two groups, neither when expressed as daily mean concentrations, nor as area under the curve (AUC) (mean, ROP 0: 17876.7; SD 6077.3 vs 18888.4; SD 55552.7 in ROP 3-4; P = 0.404) or AUC/h (mean, ROP 0: 135.1; SD 36.3 vs 144.1; SD 23.2 in ROP 3-4; P = 0.515). Our findings do not confirm the hypothesis of a clinically measurable, beneficial role of bilirubin on the development of ROP.