Standardized bench method for evaluating the efficacy of phototherapy devices

AIM

As phototherapy (PT) devices employ a variety of broadband light sources, we developed and tested a standardized bench method for evaluating the efficacy of some devices.

METHODS

To evaluate efficacy, we quantified the in vitro photodegradation rate (expressed as t1/2) of unconjugated bilirubin in solution at 37 degrees C during exposure to a given light source at its mean delivered irradiance to the 2D body surface area (BSA) of newborn models. Reproducibility (between-day variation) of the method was determined at irradiance levels from 10 to 70 microW/cm2/nm on three different days.

RESULTS

Between-day t1/2 measurements had coefficients of variation from 3% to 10%. When t1/2 values were normalized to the exposable 2D horizontal BSA, halogen lamp devices, without and with fiberoptics, were least effective (t1/2=60-108 min and 100-126 min for preterm and term models, respectively). Fluorescent tube devices had t1/2=19-78 min and 25-78 min, for preterm and term models, respectively. Light-emitting diode (LED)-based devices yielded the shortest t1/2 values (16-24 min) for preterm and term newborn models.

CONCLUSIONS

We demonstrated the applicability of the method through the determination of the efficacy of several commercially available PT devices. This standardized method is reproducible and effectively evaluates the relative in vitro efficacy of various devices and may guide further in vitro and in vivo evaluations of devices.

Oxidative stress and proinflammatory cytokine levels are increased in premature neonates of preeclamptic mothers with HELLP syndrome

BACKGROUND

Respiratory distress syndrome (RDS) incidence is increased in infants of preeclamptic mothers with hemolysis, elevated liver enzymes, low platelets (HELLP) syndrome. RDS and HELLP syndrome have been associated with oxidative stress and inflammatory processes.

OBJECTIVES

We hypothesize that end-tidal carbon monoxide corrected for inhaled CO (ETCOc), malondialdehyde (MDA) (markers of oxidative stress) and proinflammatory cytokine (IL-6, IL-8) production are higher in infants of preeclamptic mothers with HELLP syndrome than in those of preeclamptic mothers without HELLP syndrome.

METHODS

Prospective study of 36 infants of preeclamptic mothers (GA <32 weeks) admitted to the Neonatal Intensive Care Unit. ETCOc was measured at 0-12, 48-72 and 168 h postnatally using the CO-Stattrade mark End-Tidal Breath Analyzer. Simultaneously, blood was sampled for MDA, IL-8 and IL-6.

RESULTS

At 0-12 h, ETCOc, MDA and IL-8 values (median[range]) were significantly higher in HELLP infants than in infants from preeclamptic mothers without HELLP (ETCOc 2.2 [1.5-3.9] vs. 1.8 [0.5-2.9] ppm; MDA 2.3 [1.3-4.1] vs. 1.5 [0.4-3.1] mumol/l; IL-8 145 [24-606] vs. 62 [26-397] pg/ml; all p <0.05). MDA remained significantly higher during the first 168 h of life (2.3 [0.8-5.8] vs. 1.1 [0.8-3.7] mumol/l, p = 0.02).

CONCLUSION

Oxidative stress and proinflammatory cytokine levels are increased in infants of preeclamptic mothers with HELLP syndrome. These processes may cause inactivation of surfactant explaining the increased RDS incidence in these infants.

Regulation of maternal and fetal hemodynamics by heme oxygenase in mice

Heme oxygenase (HMOX) regulates vascular tone and blood pressure through the production of carbon monoxide (CO), a vasodilator derived from the heme degradation pathway. During pregnancy, the maternal circulation undergoes significant adaptations to accommodate the hemodynamic demands of the developing fetus. Our objective was to investigate the role of HMOX on maternal and fetal hemodynamics during pregnancy in a mouse model. We measured and compared maternal tissue and placental HMOX activity and endogenous CO production, represented by excreted CO and carboxyhemoglobin levels, during pregnancy (Embryonic Days 12.5-15.5) to nonpregnant controls. Micro-ultrasound was used to monitor maternal abdominal aorta diameters as well as blood flow velocities and diameters of fetal umbilical arteries. Tin mesoporphyrin, a potent HMOX inhibitor, was used to inhibit HMOX activity. Changes in maternal vascular tone were monitored by tail cuff blood pressure measurements. Effects of HMOX inhibition on placental structures were assessed by histology. We showed that maternal tissue and placental HMOX activity and CO production were significantly elevated during pregnancy. When HMOX in the placenta was inhibited, maternal and fetal hemodynamics underwent significant changes, with maternal blood pressures increasing. We concluded that increases in maternal tissue and placental HMOX activity contribute to the regulation of peripheral vascular resistance and therefore are important for the maintenance of normal maternal vascular tone and fetal hemodynamic functions during pregnancy.

(TA)n UGT 1A1 promoter polymorphism: a crucial factor in the pathophysiology of jaundice in G-6-PD deficient neonates

Increased heme catabolism has been reported in glucose-6-phosphate dehydrogenase (G-6-PD)-normal neonates who were also homozygous for (TA)7/(TA)7 (UGT1A1*28) uridine diphosphoglucuronate-glucuronosyltransferase 1A1 (UGT) promoter polymorphism (Gilbert syndrome). As G-6-PD deficiency is associated with increased hemolysis, we hypothesized that in G-6-PD-deficient neonates who also have the (TA)7/(TA)7 UGT promoter genotype, steady-state hemolysis would be even further increased. Male G-6-PD-deficient neonates were sampled for plasma total bilirubin (PTB), blood carboxyhemoglobin corrected for inhaled carbon monoxide in ambient air (COHbc) (an index of heme catabolism), and UGT (TA)n promoter genotype determination and compared with previously published G-6-PD-normal neonates. Although COHbc values were higher in the G-6-PD-deficient than in the G-6-PD-normal cohorts (0.97 +/- 0.32% of total Hb (tHb) versus 0.76 +/- 0.19% of tHb, p < 0.001), PTB values were similar (9.2 +/- 3.4 mg/dL versus 8.9 +/- 3.0 mg/dL, respectively, p = 0.3). Within the G-6-PD-deficient group, although COHbc values were alike between the three UGT promoter genotypes, PTB was higher in the (TA)7/(TA)7 homozygotes (11.1 +/- 4.0 mg/dL) compared with (TA)6/(TA)7 heterozygotes (9.1 +/- 3.2 mg/dL, p = 0.03) and wild-type (TA)6/(TA)6 homozygotes (8.8 +/- 3.4 mg/dL, p = 0.02). In the steady state, similar rates of hemolysis, but increased PTB in the G-6-PD- deficient, (TA)7/(TA)7 homozygotes, imply that (TA)7/(TA)7, homozygosity is central to increased PTB.

Heme oxygenase-1 stabilizes the blood-spinal cord barrier and limits oxidative stress and white matter damage in the acutely injured murine spinal cord

We hypothesized that heme oxygenase (HO)-1, the inducible form of HO, represents an important defense against early oxidative injury in the traumatized spinal cord by stabilizing the blood-spinal cord barrier and limiting the infiltration of leukocytes. To test this hypothesis, we first examined the immunoexpression of HO-1 and compared barrier permeability and leukocyte infiltration in spinal cord-injured HO-1-deficient (+/-) and wild-type (WT, +/+) mice. Heme oxygenase was expressed in both endothelial cells and glia of the injured cord. Barrier disruption to luciferase and infiltration of neutrophils were significantly greater in the HO-1+/- than WT mice at 24 h postinjury (P<or=0.019 and =0.049, respectively). We next examined by Western immunoblots the generation of 4-hydroxynoneal (HNE) and malondialdehyde (MDA), major products of lipid peroxidation, in the injured epicenter. There was a significant increase in 10 kDa HNE- and MDA-modified proteins in the HO-1+/- as compared with WT mice (P=0.037 and 0.043, respectively). Finally, we compared the degradation of myelin basic protein (MBP), an indicator of white matter damage, in the HO-1+/- and WT mice by Western immunoblots. There was significantly greater degradation of MBP in the HO-1+/- compared with WT mice (P=0.049). Together, these findings show that HO-1 modulates oxidative stress and white matter injury in the acutely injured spinal cord. This modulation may be partially attributed to the ability of HO-1 to stabilize the blood-spinal cord barrier and limit neutrophil infiltration.

Effects of sample dilution, peroxidase concentration, and chloride ion on the measurement of unbound bilirubin in premature newborns

OBJECTIVES

To assess the effects of sample dilution, peroxidase concentration, and chloride ion (Cl(-)) on plasma unbound bilirubin (B(f)) measurements made using a commercial peroxidase methodology (UB Analyzer) in a study population of ill, premature newborns.

DESIGN AND METHODS

B(f) was measured with a UB Analyzer in 74 samples at the standard 42-fold sample dilution and compared with B(f) measured at a 2-fold sample dilution using a FloPro Analyzer. B(f) was measured at two peroxidase concentrations to determine whether the peroxidase steady state B(f) (B(fss)) measurements were significantly less than the equilibrium B(f) (B(feq)), in which case it was necessary to calculate B(feq) from the two B(fss) measurements. B(f) was also measured before and after adding 100 mmol/L Cl(-) to the UB Analyzer assay buffer.

RESULTS

B(feq) at the 42-fold dilution was nearly 10-fold less than but it correlated significantly with B(feq) at the 2-fold dilution (mean 8.2+/-5.2 nmol/L versus 73.5+/-70 nmol/L, respectively, p<0.0001; correlation r=0.6). The two UB Analyzer B(fss) measurements were significantly less than B(feq) in 42 of 74 (57%) samples, and Cl(-) increased B(feq) in 66 of 74 (89%) samples by a mean of 82+/-67%.

CONCLUSIONS

B(fss) measured by the UB Analyzer at the standard 42-fold sample dilution using assay buffer without Cl(-) and a single peroxidase concentration is significantly less than the B(feq) in undiluted plasma. Accurate B(f) measurements can be made only in minimally diluted serum or plasma.

Concentration of carbon monoxide (CO) in postmortem human tissues: effect of environmental CO exposure

We studied how carbon monoxide (CO) is distributed within the human body through quantitation of CO concentrations in postmortem tissue samples from fatalities including possible CO exposure. Stored, frozen tissues were diced, sonicated in water, and 0.01-8.0 mg wet weight (ww) tissues were incubated with sulfosalicylic acid in CO-purged, septum-sealed vials. CO released into the headspace was quantitated by reduction gas chromatography. Mean tissue CO concentrations (pmol/mg ww) from subjects diagnosed to have no known CO exposure (control, N=14), died from fire (N=13), and CO asphyxiation (N=7), respectively, were: adipose (2;13;9), brain (3;13;65), muscle (15;97;297), heart (30;99;371), kidney (22;432;709, lung (54;690;2638), spleen (73;1366;3548), and blood (162;2238;5070). Carboxyhemoglobin concentrations were 1.4%, 25.2%, and 69.1% of total hemoglobin, respectively. We conclude that measurements of CO concentration in a variety of tissues can be used as markers for the degree of exogenous CO exposure and the identification of possible causes of death.

Expression and regulation of heme oxygenase isozymes in the developing mouse cortex

Heme oxygenase (HO), the rate-limiting enzyme in heme degradation, plays a role in neonatal jaundice. Understanding the regulation of the developmental expression patterns of the two HO isozymes, HO-1 and HO-2, is essential for targeting HO to control pathologic jaundice, and uncovering the fundamental role that they play in mammalian development. Here we characterized the ontogeny of HO-1 and HO-2 expression in the developing mouse cortex by in vivo bioluminescence imaging, quantitative RT-PCR, and Western blot. HO-2, the predominant isoform in the adult cortex, was relatively stable throughout all ages. HO-1 was observed to be progressively down-regulated in an age-related manner. HO-1 expression in the adult cortex was also the lowest among the eight adult tissues analyzed. Because there is a 283-bp CpG island region in the HO-1 promoter, we hypothesized that methylation of the island is responsible for the age-related HO-1 down-regulation in the cortex. Methylation status was assessed using regular and quantitative methylation-specific PCR and the CpG island was found to be hypomethylated at all ages. Therefore, we conclude that HO-1 gene expression in the cortex is developmentally-regulated and that methylation of the HO-1 CpG island is not associated with the down-regulation of the gene.

Determination of in vivo carbon monoxide production in laboratory animals via exhaled air

INTRODUCTION

In vitro assays play an important role in the understanding of the heme oxygenase (HO)/carbon monoxide (CO) pathway. However, because physiological roles for the products of this pathway are hypothesized, it is becoming increasingly important to perform in vivo studies. Since CO production is primarily mediated by HO and is excreted mainly by the lungs, measurements of total body CO excretion (VeCO) via the breath allow continuous, noninvasive monitoring of heme degradation and CO and bilirubin production. Here, we describe a modified flow-through method for the collection and quantitation of CO from small laboratory animals.

METHODS

Mice and rats were studied in gas-tight chambers supplied with a continuous flow of CO-free air. CO in the exhaust air was measured by gas chromatography with a reduction gas analyzer. After establishing baseline VeCO levels, animals were administered various xenobiotics known to alter HO activity and further monitored for changes in CO production for up to 12 h without observable distress.

RESULTS

Administration of heme (substrate for HO) resulted in reproducible increases in CO production; whereas, prior administration of zinc protoporphyrin (ZnPP, HO inhibitor) or cobalt protoporphyrin (CoPP, HO inducer) resulted in respective dose-dependent decreases and increases in the heme-induced CO production.

DISCUSSION

We have demonstrated that this noninvasive method of CO quantitation reliably estimates heme degradation with sensitivity to distinguish between different types of HO-manipulating xenobiotics in a dose-dependant manner in both mouse and rat models. Furthermore, VeCO measurements allow nearly real-time determinations of CO and bilirubin formation, which helps to illustrate the time course of drug action.

End-tidal carbon monoxide measurements in infant respiratory distress syndrome

BACKGROUND

RDS involving inflammatory and oxidative processes may lead to increased production of carbon monoxide (CO).

AIM

The relationship between end-tidal CO, corrected for inhaled CO (ETCOc), and RDS severity was investigated in preterm infants as well as the value of early ETCOc measurements to predict chronic lung disease.

METHODS

78 infants (30 no RDS, 32 moderate RDS, 16 severe RDS) were included. ETCOc was measured using the CO-Stat End Tidal Breath Analyzer.

RESULTS

ETCOc was significantly higher in RDS compared to no RDS during the first week (p<0.05). Severity of RDS was the most significant independent variable in a stepwise regression model related to ETCOc (F-test: 18.17). Negative predictive value of early (within first 12 h of life) ETCOc measurement (<2.5 ppm) for development of chronic lung disease was excellent (100%).

CONCLUSION

During severe RDS, inflammation may contribute to increased lipid peroxidation leading to increased local CO production in the lung, indicated by increased ETCOc. Early ETCOc determinations may be helpful to exclude occurrence of chronic lung disease.

Respiratory distress syndrome-associated inflammation is related to early but not late peri/intraventricular hemorrhage in preterm infants

OBJECTIVE

To investigate whether or not peri/intraventricular hemorrhages (PIVHs) occurring in the first 12 hours of life (early PIVHs) are related to respiratory distress syndrome (RDS)-associated inflammatory factors in contrast to PIVHs developing after 12 hours of life (late PIVHs).

STUDY DESIGN

Blood samples obtained at 0 to 12 hours, 48 to 72 hours, and 168 hours of life were evaluated for determination of the proinflammatory cytokines interleukin (IL)-8 and IL-6, tumor necrosis factor (TNF)-alpha, and malondialdehyde (MDA) as measures of lipid peroxidation. Simultaneously, cranial ultrasonography was performed in 114 neonates under 32 weeks gestational age.

RESULTS

Out of the total study group of 114 neonates, 67 (59%) had RDS. Early PIVH occurred in 16 neonates, 14 of whom (88%) had RDS. Late PIVHs occurred in 12 neonates. Neonates with RDS had higher IL-8 and IL-6 levels at 0 to 12 hours (P < .0001; < .0001) and at 48 to 72 hours (P < .001; < .01) than those without RDS. Neonates with early PIVH had higher IL-8 (P < .02), IL-6 (P < .02), and MDA (P < .01) levels at 0 to 12 hours than those with late PIVH or no PIVH. Those with early PIVH had higher IL-8 levels at 48 to 72 hours than those without PIVH (P < .02). Multiple linear regression revealed an association between RDS/early PIVH and IL-8, IL-6, and MDA levels.

CONCLUSIONS

An RDS-associated increase in proinflammatory cytokine and MDA levels was associated with early PIVHs, but not with late PIVHs, suggesting a different etiopathogenesis in early versus late PIVHs.

Management of hyperbilirubinemia and prevention of kernicterus in 20 patients with Crigler-Najjar disease

We summarize the treatment of 20 patients with Crigler-Najjar disease (CND) managed at one center from 1989 to 2005 (200 patient-years). Diagnosis was confirmed by sequencing the UGTA1A gene. Nineteen patients had a severe (type 1) phenotype. Major treatment goals were to maintain the bilirubin to albumin concentration ratio at <0.5 in neonates and <0.7 in older children and adults, to avoid drugs known to displace bilirubin from albumin, and to manage temporary exacerbations of hyperbilirubinemia caused by illness or gallstones. A variety of phototherapy systems provided high irradiance over a large body surface. Mean total bilirubin for the group was 16+/-5 mg/dl and increased with age by approximately 0.8 mg/dl per year. The molar ratio of bilirubin to albumin ranged from 0.17 to 0.75 (mean: 0.44). The overall non-surgical hospitalization rate was 0.12 hospitalizations per patient per year; one-half of these were for neonatal hyperbilirubinemia and the remainder were for infectious illnesses. Ten patients (50%) underwent elective laproscopic cholecystectomy for cholelithiasis. No patient required invasive bilirubin removal or developed bilirubin-induced neurological damage under our care. Visual acuity and color discrimination did not differ between CND patients and age-matched sibling controls. Four patients treated with orthotopic liver transplantation were effectively cured of CND, although one suffered significant transplant-related complications.Conclusions. While patients await liver transplantation for CND, hyperbilirubinemia can be managed safely and effectively to prevent kernicterus. Lessons learned from CND can be applied to screening and therapy of non-hemolytic jaundice in otherwise healthy newborns.

Systemic effects of orally-administered zinc and tin (IV) metalloporphyrins on heme oxygenase expression in mice

Some metalloporphyrins (Mps) inhibit heme oxygenase (HO), the rate-limiting enzyme in the production of bilirubin, and are potential compounds for the treatment of neonatal jaundice. We studied the safety and efficacy of Mps following oral administration. Adult HO-1-luc reporter mice were administered 30 micromol/kg body weight of tin mesoporphyrin (SnMP), zinc bis glycol deuteroporphyrin (ZnBG), or zinc protoporphyrin (ZnPP), or vehicle by oral gavage. Bilirubin production was measured as total body carbon monoxide (CO) excretion (VeCO). HO activity was quantitated via CO measurements by gas chromatography. HO-1 protein was determined by Western blot. HO-1 transcription levels were assessed by in vivo bioluminescence imaging. A significant 28% decrease in bilirubin production occurred within 3 h of SnMP treatment and persisted beyond 48 h. Bilirubin production decreased 15% and 9% by 3 h after administration of ZnBG and ZnPP, respectively, but returned to baseline within 48 h. Maximal inhibition of liver, spleen, and intestine HO activity was seen at 3 h with inhibitory effects decreasing in the order: SnMP > or = ZnBG > or = ZnPP. After SnMP treatment, HO-1 transcription increased 5.7-fold after 24 h. Furthermore, liver and spleen HO-1 protein significantly increased 3.7- and 2.0-fold, respectively, after 24 h. HO-1 transcription and protein were not affected in ZnBG- or ZnPP-treated mice. We conclude that the three Mps are absorbed at different rates in the mouse and affect bilirubin production and HO-1 expression in a tissue- and time-dependent manner.

Selectivity of imidazole-dioxolane compounds for in vitro inhibition of microsomal haem oxygenase isoforms

Haem oxygenases (HO) are involved in the catalytic breakdown of haem to generate carbon monoxide (CO), iron and biliverdin. It is widely accepted that products of haem catabolism are involved in biological signaling in many physiological processes. Conclusions to most studies in this field have gained support from the judicious use of synthetic metalloporphyrins such as chromium mesoporphyrin (CrMP) to selectively inhibit HO. However, metalloporphyrins have also been found to inhibit other haem-dependent enzymes, such as nitric oxide synthase (NOS), cytochromes P-450 (CYPs) and soluble guanylyl cyclase (sGC), induce the expression of HO-1 or exhibit varied toxic effects. To obviate some of these problems, we have been examining non-porphyrin HO inhibitors and the present study describes imidazole-dioxolane compounds with high selectivity for inhibition of HO-1 (rat spleen microsomes) compared to HO-2 (rat brain microsomes) in vitro. (2R,4R)-2-[2-(4-chlorophenyl)ethyl]-2-[(1H-imidazol-1-yl)methyl]-4-methyl-1,3-dioxolane hydrochloride) was identified as the most selective inhibitor with a concentration of 0.6 microM inhibiting HO-1(inducible) by 50% compared with 394 microM for HO-2 (constitutive). These compounds were found to have no effects on the catalytic activities of rat brain NOS and lung sGC, but were potent inhibitors of microsomal CYP2E1 and CYP3A1/3A2 activities. In conclusion, we have identified imidazole-dioxolanes that are able to inhibit microsomal HO in vitro with high selectivity for HO-1 compared to HO-2, and little or no effect on the activities of neuronal NOS and sGC. These molecules could be used to facilitate studies on the elucidation of physiological roles of HO/CO in biological systems.

Transcutaneous bilirubinometry: a noninvasive tool for studying newborn jaundiced rats before and after exposure to light

The homozygous Gunn rat is the most frequently used animal model for the study of neonatal jaundice. We evaluated the applicability of noninvasive transcutaneous bilirubin (TcB) measurements as an index of serum total bilirubin (STB) levels in neonatal rats by comparison to invasive STB measurements. TcB measurements were made during the first 96 h of life with the Model 101 Minolta/Air-Shields Jaundice Meter (JM) and SpectRx BiliCheck System (BC). Measurements with both devices displayed parallel TcB profiles, rapidly rising within 24 h, increasing during the next 6 h, then leveling off after 30 h. Linear regressions for the JM (n = 60) were as follows: STB (mg/dL) = 0.79 (JM) - 0.01 (units, r = 0.95, head); STB (mg/dL) = 0.82 (JM) + 1.51 (units, r = 0.95, upper back); and STB (mg/dL) = 0.74 (JM) + 1.60 (units, r = 0.91, lower back). Mean bias +/- imprecision were as follows: -0.02 +/- 3.99 mg/dL, -0.01 +/- 3.90, and 0.01 +/- 4.28 at the head, upper back, and lower back, respectively. For the BC, only lower back measurements were taken, and the regression was as follows: STB (mg/dL) = 0.77 (BC) + 1.65 mg/dL, (r = 0.93, n = 29) with a mean bias +/- imprecision of -1.08 +/- 3.08 mg/dL. When pups were exposed to light, correlations remained strong but intercepts increased. These results demonstrate that noninvasive TcB measurements correlate highly with STB in the Gunn rat during the first 96 h of life and after exposure to light. We conclude that JM measurements at the head and BC at the lower back reflect STB most reliably and consistently. Thus, in addition to being a useful tool for evaluating jaundice in human neonates, TcB methodology can be used successfully for the noninvasive monitoring of jaundice in neonatal Gunn rats pre- and postlight exposure.

Heme regulation in traumatic brain injury: relevance to the adult and developing brain

Intracranial bleeding is one of the most prominent aspects in the clinical diagnosis and prognosis of traumatic brain injury (TBI). Substantial amounts of blood products, such as heme, are released because of traumatic subarachnoid hemorrhages, intraparenchymal contusions, and hematomas. Despite this, surprisingly few studies have directly addressed the role of blood products, in particular heme, in the setting of TBI. Heme is degraded by heme oxygenase (HO) into three highly bioactive products: iron, bilirubin, and carbon monoxide. The HO isozymes, in particular HO-1 and HO-2, exhibit significantly different expression patterns and appear to have specific roles after injury. Developmentally, differences between the adult and immature brain have implications for endogenous protection from oxidative stress. The aim of this paper is to review recent advances in the understanding of heme regulation and metabolism after brain injury and its specific relevance to the developing brain. These findings suggest novel clinical therapeutic options for further translational study.

Determination of carbon monoxide (CO) in rodent tissue: Effect of heme administration and environmental CO exposure

Carbon monoxide (CO), produced endogenously during heme degradation, is considered a messenger molecule in vascular and neurologic tissues. To study this role, it is important to determine CO concentration in target tissues pre- and post-perturbations. Here, we describe a sensitive and reproducible method, which is linear and accurate, and provide some examples of its application for quantitation of CO concentrations in tissues pre- and post-perturbations. Tissues from adult rats and mice were sonicated (20% w/w), and volumes representing 0.04-8 mg fresh weight (FW) were incubated at 0 degrees C for 30 min with sulfosalicylic acid. CO liberated into the headspace was quantitated by gas chromatography. Tissue CO concentrations (mean+/-SD, pmol CO/mg FW) were as follows: blood (47+/-10, 45+/-5), muscle (4+/-4, 10+/-1), kidney (5+/-2, 7+/-2), heart (6+/-3, 6+/-1), spleen (11+/-3, 6+/-1), liver (4+/-1, 5+/-1), intestine (2+/-1, 4+/-2), lung (2+/-1, 3+/-1), testes (1+/-1, 2+/-1), and brain (2+/-1, 2+/-0) in untreated rat (n=3) and mouse (n=5), respectively. Between the rat and the mouse, only CO concentrations in the muscle and spleen were significantly different (p0.05). Endogenous CO generation, after administration of heme arginate to mice (n=3), increased CO concentrations by 0-43 pmol/mg FW. Exposure of mice (n=3) to 500 ppm CO for 30 min yielded significantly elevated CO concentrations by 4-2603 pmol/mg FW in all tissues over the native state. While blood had the highest CO concentration for all conditions, muscle, kidney, heart, spleen, and liver, all rich in hemoglobin and/or other CO-binding hemoproteins, also contained substantial CO concentrations. Intestine, lung, testes, and brain contained the lowest CO concentrations.

Neonatal bilirubin production-conjugation imbalance: effect of glucose-6-phosphate dehydrogenase deficiency and borderline prematurity

OBJECTIVE

To evaluate relations between production and conjugation of bilirubin in the pathophysiology of jaundice in glucose-6-phosophate dehydrogenase (G6PD) deficient neonates.

METHODS

Term and borderline premature (35-37 weeks gestational age), healthy, male, G6PD deficient neonates were studied close to the beginning of the 3rd day. Blood carboxyhaemogobin corrected for inspired CO (COHbc; an index of bilirubin production) and serum total conjugated bilirubin (TCB; a reflection of bilirubin conjugation) were measured in simultaneously drawn blood samples by gas chromatography and reverse phase high performance liquid chromatography respectively. A bilirubin production-conjugation index comprising COHbc/TCB was determined; a high index reflects imbalance between the bilirubin production and conjugation processes. COHbc and TCB individually and the production-conjugation index were studied in relation to serum total bilirubin (STB) concentration.

RESULTS

Fifty one G6PD deficient neonates were sampled at 51 (8) hours. COHbc values did not correlate with STB (r=0.22, p=0.15). TCB did correlate inversely with STB (r=-0.42, p=0.004), and there was a positive correlation between the production-conjugation index and STB (r=0.45, p=0.002). The production-conjugation index (median (interquartile range)) was higher in the premature (n=8) than term neonates (2.31 (2.12-3.08) v 1.05 (0.53-1.81), p=0.003). This difference was the result of changes in TCB.

CONCLUSIONS

The data show that jaundice in G6PD deficient neonates is the result of an imbalance between production and conjugation of bilirubin with a tendency for inefficient bilirubin conjugation over increased haemolysis in its pathogenesis. Borderline premature infants are at special risk of bilirubin production-conjugation imbalance.

Phototherapy and Photo-Oxidation in Premature Neonates

OBJECTIVE

The potential for photo-oxidation during phototherapy in premature neonates was assessed by measuring parameters reflective of photo-oxidation.

METHODS

Blood was sampled from premature neonates prior to, and after 4 and 24 h of phototherapy, respectively. Total plasma bilirubin (TPB), blood carboxyhemoglobin corrected for inspired carbon monoxide (COHbc) (a sensitive index of heme catabolism), blood thiobarbituric acid reacting substances (TBARS) (a measure of lipid peroxidation), and plasma protein carbonyls (representative of protein oxidation) were determined. Study measurements were compared with baseline values both for the entire study group, and also individually for subgroups < and > or = 1.5 kg birthweight, respectively. The percentage difference (%delta) between baseline and the 24-hour measurement was calculated for each parameter.

RESULTS

Forty-one premature neonates (mean [+/- SD] gestational age 30.5 +/- 2.7 weeks and birthweight 1,499 +/- 448 g) were studied. Mean TPB values decreased from a baseline of 9.1 +/- 2.3 to one of 7.2 +/- 2.8 mg/dl, p < 0.01, during the first 24 h of phototherapy. For the entire patient sample, neither COHbc, TBARS or protein carbonyl values increased significantly over baseline measurements: COHbc: 0.90 +/- 0.26% vs. 0.92 +/- 0.32%; TBARS: 19.0 +/- 5.6 vs. 18.0 +/- 4.5 nmol/ml, and protein carbonyls 7.73 +/- 3.78 vs. 7.63 +/- 3.56 U/ml (baseline and 24-hour samples only are shown in the abstract). Similarly, for the entire group, %delta (mean, interquartile range) were not significantly different between COHbc [-3.77 (-15.89-17.65)%], TBARS [-7.47 (-17.37-7.38)%], and protein carbonyls [-1.47 (-28.51-43.48)%], respectively. For subgroup analysis of neonates < or > or = 1.5 kg birthweight, respectively, no significant increases in COHbc, TBARS or protein carbonyls were documented. A significant increase in %delta for COHbc in the <1.5 kg birthweight subgroup compared with those > or =1.5 kg, possibly indicative of hemolysis, was not matched by similar changes in %delta for TBARS or protein carbonyls, and may therefore not be a result of photo-oxidation.

CONCLUSIONS

Except for changes in %delta in COHbc alone and in the smallest babies only, overall, short term phototherapy in premature infants was effective in reducing TPB concentrations without associated evidence reflective of photo-oxidation.

Is carbon monoxide-mediated cyclic guanosine monophosphate production responsible for low blood pressure in neonatal respiratory distress syndrome?

Infant respiratory distress syndrome (RDS) involves inflammatory processes, causing an increased expression of inducible heme oxygenase with subsequent production of carbon monoxide (CO). We hypothesized that increased production of CO during RDS might be responsible for increased plasma levels of vasodilatory cGMP and, consequently, low blood pressure observed in infants with RDS. Fifty-two infants (no-RDS, n = 21; RDS, n = 31), consecutively admitted to the neonatal intensive care unit (NICU) between January and October 2003 were included. Hemoglobin-bound carbon monoxide (COHb), plasma cGMP, plasma nitric oxide (NOx), and bilirubin were determined at 0-12, 48-72, and at 168 h postnatally, with simultaneous registration of arterial blood pressure. Infants with RDS had higher levels of cGMP and COHb compared with no-RDS infants (RDS vs. no-RDS: cGMP ranging from 76 to 101 vs. 58 to 82 nmol/l; COHb ranging from 1.2 to 1.4 vs. 0.9 to 1.0%). Highest values were reached at 48-72 h [RDS vs. no-RDS mean (SD): cGMP 100 (39) vs. 82 (25) nmol/l (P < 0.001); COHb 1.38 (0.46) vs. 0.91 (0.26)% (P < 0.0001)]. Arterial blood pressure was lower and more blood pressure support was needed in RDS infants at that point of time [RDS vs. no-RDS mean (SD): mean arterial blood pressure 33 (6) vs. 42 (5) mmHg (P < 0.05)]. NOx was not different between groups and did not vary with time. Multiple linear regression analysis showed a significant correlation between cGMP and COHb, suggesting a causal relationship. Mean arterial blood pressure appeared to be primarily correlated to cGMP levels (P < 0.001). We conclude that a CO-mediated increase in cGMP causes systemic vasodilation with a consequent lower blood pressure and increased need for blood pressure support in preterm infants with RDS.

Phototherapy: current methods and future directions

Phototherapy is the most common therapeutic intervention used for the treatment of hyperbilirubinemia. Although it has become a mainstay since its introduction in 1958, a better understanding of the photobiology of bilirubin, characteristics of the phototherapy devices, the efficacy and safety considerations of phototherapy applications, and improvements in spectroradiometers and phototherapy devices are necessary for more predictable and improved clinical practices and outcomes. A step forward in instituting consistent, uniform, and effective use of phototherapy is the recent American Academy of Pediatrics clinical guideline on the management of hyperbilirubinemia in the newborn infant 35 or more weeks of gestation, which outlines a clinical strategy for the diagnosis of hyperbilirubinemia and contains direct recommendations for the application of phototherapy. This article reviews the parameters that determine the efficacy of phototherapy, briefly discusses current devices and methods used to deliver phototherapy, and speculates on future directions and studies that are still needed to complement our presently incomplete knowledge of the facets of this common mode of therapy.

NICHD Conference on Kernicterus: Research on Prevention of Bilirubin-Induced Brain Injury and Kernicterus: Bench-to-Bedside--Diagnostic Methods and Prevention and Treatment Strategies

In July 2003, the National Institute of Child Health and Human Development (NICHD) organized a consensus conference, where a group of experts were invited to review and discuss the current state of knowledge regarding neonatal hyperbilirubinemia and identify areas in which where future research should be directed. This paper summarizes the presentations addressing the current methodologies for direct and noninvasive assessments of serum total bilirubin concentrations as well as prevention and treatment strategies for the management of neonatal hyperbilirubinemia.

Transcutaneous bilirubin measurements and serum total bilirubin levels in indigenous African infants

OBJECTIVE

The objective of this study was to determine whether transcutaneous bilirubin (TcB) measurements correlate with serum total bilirubin (STB) levels in indigenous, darkly pigmented African newborns with varying degrees of skin pigmentation, some of which had developed kernicterus.

METHODS

Jaundiced infants who were < or =2 weeks of age and admitted to Baptist Medical Center-Eku (Eku; n = 29) and Jos University Teaching Hospital (Jos; n = 98) in Nigeria were studied. TcB measurements using the BiliChek were made simultaneously with blood sampling for STB measurements by spectrophotometry before phototherapy.

RESULTS

Using linear regression analysis, we found that measurements of TcB correlated well with those of STB with r values of.90 and.88 for Eku and Jos, respectively. Mean bias and imprecision of TcB measurements as compared with STB measurements for the total population was 0.5 +/- 7.6 mg/dL using the method of Bland and Altman. At STB > or 12 mg/dL, correlation (r =.84) and bias and imprecision (-1.2 +/- 8.6 mg/dL) of measurements were only slightly poorer. Furthermore, when infants were grouped by degree of skin pigmentation, correlations of TcB and STB measurements remained strong.

CONCLUSIONS

From these results, we can conclude that TcB measurements are a useful and reliable index for estimating STB levels in pigmented neonates, including those with hyperbilirubinemia and kernicterus. In the absence of reliable STB measurements, the relatively simple and noninvasive TcB measurements can be an important adjunct in directing phototherapy and exchange transfusions, thereby preventing bilirubin-induced morbidity and mortality in low-technology clinical environments.

Effects of metalloporphyrins on heme oxygenase-1 transcription: correlative cell culture assays guide in vivo imaging

Heme oxygenase (HO) is the rate-limiting step in the heme degradation pathway and is a potential target for the control, or prevention, of pathologic jaundice in neonates. Metalloporphyrins (Mps), a diverse set of synthetic derivatives of heme, can competitively inhibit the HO enzymes. However, certain Mps are phototoxic and some increase transcription of HO-1, the inducible HO isozyme. Therefore, effective development of this class of compounds as therapeutics for treating pathologic jaundice will require rapid and integrated biological screens to identify the most efficacious and safe Mps. To study the safety of these compounds, we assessed their cytotoxic effects and measured luciferase activity by bioluminescent imaging (BLI) as an index of HO-1 transcription, first in live cell cultures and then in living transgenic reporter mice. A total of 12 Mps were first evaluated in the correlative cell culture assay. Based on results from this study, 2 Mps, zinc protoporphyrin (ZnPP) and zinc bis glycol porphyrin (ZnBG), were selected for further studies in the live animal model. In vitro BLI showed ZnPP to be a strong inducer of HO-1 transcription in comparison to ZnBG, which showed minimal induction. Cytotoxicity studies revealed that ZnPP was phototoxic, whereas ZnBG had no effect on cell viability. In vivo BLI showed that both ZnPP and ZnBG had minimal effects on the levels of HO-1 transcription in the animals. Furthermore, serum enzyme assays indicated that neither caused detectable liver toxicity. These findings, and especially those with ZnBG, support the use of selected Mps as therapies for pathologic jaundice. Coupling the high throughput advantage of cell culture with the capability of imaging for whole-body temporal analyses could accelerate and refine the preclinical phases of drug development. Thus, this study serves as a model for understanding the effects of specific compounds in relation to defined targets using an integrated approach.