Calculated In Vivo Free Bilirubin Levels in the Central Nervous System of Gunn Rat Pups

Daood, Monica J.; Watchko, Jon F.

doi:10.1203/01.pdr.0000219561.07550.04

Cited by 27 publications

(31 citation statements)

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“…Calculated in vivo CNS B F levels were in the range of 221 to 2044 nM in saline and 2743 to 10 080 nM in sulfadimethoxinetreated hyperbilirubinemic j/j pups (95% CI), depending on which k value was used in the calculation. Importantly, and in stark contrast to asymptomatic neurologically intact non-jaundiced heterozygous J/j pups, the hyperbilirubinemic homozygous j/j animals universally showed low cerebellar weights indicative of bilirubin-induced cerebellar hypoplasia, 4 or in the case of sulfadimethoxine-treated j/j pups, acute neurobehavioral abnormalities (for example, ataxia, lethargy, failure of locomotion and feeding difficulty) as well, often followed by death consistent with severe neurotoxic injury during the 24 h postsulfadimethoxine injection period. 4 There are no reports of calculated CNS B F concentrations in human neonates.…”

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confidence: 93%

“…Importantly, and in stark contrast to asymptomatic neurologically intact non-jaundiced heterozygous J/j pups, the hyperbilirubinemic homozygous j/j animals universally showed low cerebellar weights indicative of bilirubin-induced cerebellar hypoplasia, 4 or in the case of sulfadimethoxine-treated j/j pups, acute neurobehavioral abnormalities (for example, ataxia, lethargy, failure of locomotion and feeding difficulty) as well, often followed by death consistent with severe neurotoxic injury during the 24 h postsulfadimethoxine injection period. 4 There are no reports of calculated CNS B F concentrations in human neonates. Studies on total brain bilirubin content in humans with kernicterus are limited to that of Claireaux et al, 22 who extracted diazo reacting (unconjugated) bilirubin equivalent to 2 mg per 100 g (36 mM) in 'nuclear' tissue (densely stained affected brainstem nuclei) and 0.5 mg per 100 g (9 mM) in the 'remainder' of the brain.…”

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confidence: 93%

“…3,23,[31][32][33][34] Among other factors, k varies as a function of sample dilution, albumin concentration, albumin species and the study medium including the presence of competing compounds. 3,23,[31][32][33][34] In this regard, the very low albumin concentration (3 mM) in the CNS of Gunn rat pups 4 relative to that in serum would be predicted to significantly increase the apparent bilirubin-albumin binding constant k (relative to serum) 33 and result in a lower calculated CNS B F than that reported using serum k values. 4 However, this effect is most likely countered, even offset, by the greatly decreased number of bilirubin-binding sites associated with the markedly lower CNS albumin concentration.…”

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confidence: 95%

“…Recently, Daood and Watchko 4 calculated central nervous system (CNS) B F levels in Gunn rat pups during peak postnatal hyperbilirubinemia (day of life 15 to 19) 5,6 and correlated those levels with the cerebellar weights and neurobehavioral status of the pups. 4 The Gunn rat 7 offers an excellent model to explore this relationship in vivo, as it spontaneously develops newborn jaundice and differs from other models that rely on artificially induced hyperbilirubinemia. 8,9 It is also less subject to the problems of bilirubin aggregation [10][11][12][13] that potentially plague in vitro studies.…”

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confidence: 99%

“…Sulfadimethoxine was used to displace bilirubin from albumin in hyperbilirubinemic j/j Gunn rat pups increasing their brain bilirubin content, risk of acute bilirubin-induced brain injury (kernicterus) and prevalence of overt neurobehavioral abnormalities. 4,6,[15][16][17][18][19][20] Saline (nonsulfadimethoxine)-treated hyperbilirubinemic j/j pups show no obvious neurobehavioral abnormalities but extensive neuronal degeneration of Purkinje cells in the cerebellar roof nuclei 16 and resultant cerebellar hypoplasia. 4,16 Non-jaundiced heterozygous J/j pups show normal neurobehavior and postnatal cerebellar weights whether treated with sulfadimethoxine or not, that is, no evidence of acute or chronic bilirubin-induced brain injury.…”

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confidence: 99%

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Calculated free bilirubin levels and neurotoxicity

2009

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Although most bilirubin in the circulation is bound to albumin, a relatively small fraction remains unbound. The concentration of this 'free' bilirubin (B F ) is believed to dictate the biologic effects of bilirubin in jaundiced newborns, including its neurotoxicity. The threshold at which B F produces changes in cellular function culminating in permanent cell injury and cell death has been the subject of considerable debate. The objective of this study was to compare calculated central nervous system (CNS) B F levels in Gunn rat pups during (i) peak postnatal hyperbilirubinemia and (ii) sulfadimethoxine-induced acute bilirubin encephalopathy (ABE) previously reported from our laboratory with those predicted in human neonates with peak total serum bilirubin (TSB) levels of 35 mg per 100 ml (599 mmol l À1 ), a clinical cohort that often evidence moderate-to-severe adverse post-icteric neurodevelopmental sequelae. Homozygous j/j Gunn rat pups with neonatal hyperbilirubinemia due to a deficiency of the bilirubin conjugating enzyme uridine-diphosphate-glucuronosyl transferase 1A1 were studied along with non-jaundiced littermate heterozygous J/j controls. Sulfadimethoxine was used to displace bilirubin from albumin in hyperbilirubinemic j/j Gunn rat pups to increase their brain bilirubin content and induce ABE. Calculated Gunn rat CNS B F levels were determined as a function of genotype, sulfadimethoxine exposure and albumin-bilirubin binding constant. These data were compared with the human CNS B F predicted from the calculated serum B F in human neonates with a TSB of 35 mg per 100 ml as a function of albumin-bilirubin binding constant, albumin concentration and the assumption that at this hazardous bilirubin level there may be rapid equilibration of B F between serum and brain. There was a large gap between the upper limit of the calculated CNS B F 95% confidence interval (CI) range in non-jaundiced J/j pups (for example, 112 nM at k ¼ 9.2 l mmol À1 ) and the lower limit seen in the saline-treated hyperbilirubinemic j/j pups (556 nM at k ¼ 9.2 l mmol À1 ) as well as between the upper limit in saline-treated hyperbilirubinemic j/j pups (1110 nM at k ¼ 9.2 l mmol À1 ) and the lower limit seen in sulfadimethoxine-treated jaundiced j/j littermates (3461 nM at k ¼ 9.2 l mmol À1 ). There was considerable overlap and remarkable similarity between the predicted human CNS B F values at a TSB of 35 mg per 100 ml for a range of reported human serum bilirubin-albumin binding constants and albumin concentrations, and those calculated for saline-treated hyperbilirubinemic j/j Gunn rat pups. This exercise yielded strikingly similar apparent calculated neurotoxic B F levels for Gunn rat pups and human neonates rather than orders of magnitude differences that might have been predicted at the outset and add to a growing literature aimed at defining clinically germane neurotoxic B F thresholds.

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confidence: 93%

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confidence: 93%