PubMed Health⌕ Search

Biomedical subjects

Jon F Watchko

Publications and source records attributed to Jon F Watchko.

17 recordsLinked to original sources
PubMed2006

Calculated in vivo free bilirubin levels in the central nervous system of Gunn rat pups.

In vitro studies suggest a free bilirubin (B(F)) concentration in the range of 71-770 nmol/L can induce neurotoxicity. In vivo data regarding central nervous system (CNS) B(F) levels have not been determined. We calculated in vivo CNS B(F) levels in Gunn rat pups (15-19 d old; heterozygous nonjaundiced Gunn rats (J/j) and homozygous jaundiced Gunn rats (j/j); saline or sulfadimethoxine treated) based on 1) total brain bilirubin (TBB) content, 2) brain albumin level, 3) CNS bilirubin binding capacity attributable to brain albumin determined using an ultrafiltration technique, and 4) published Gunn rat albumin-bilirubin binding constants (k). Gunn rat brain bilirubin binding capacity was approximately 22 x 10(-3) micromol/g, of which two thirds was accounted for by brain albumin. Using a Gunn rat pup in vivo, k of 9.2 L/micromol, calculated CNS B(F) levels ranged from 72 to 112 nmol/L [95% confidence interval (CI)] in saline and from 59 to 156 nmol/L (95% CI) in sulfadimethoxine-treated J/j pups. These animals demonstrated no neurobehavioral abnormalities and normal cerebellar weight. Calculated CNS B(F) levels were severalfold higher (p < 0.001) in saline (95% CI: 556-1110 nmol/L) and sulfadimethoxine-treated (95% CI: 3461-8985 nmol/L) j/j pups; the former evidenced reduced cerebellar weight; the latter both reduced cerebellar weight and acute neurobehavioral abnormalities. We conclude that calculated CNS B(F) values in j/j pups are substantially higher than those in J/j animals. Given the absence of CNS abnormalities in J/j pups, the presence of such in j/j animals, and the CNS B(F) levels in these groups, we speculate that the CNS B(F) neurotoxicity threshold in vivo is subsumed within the range (71-770 nmol/L) reported in vitro.

Albumins↗
PubMed2006

Sex-specific regional brain bilirubin content in hyperbilirubinemic Gunn rat pups.

BACKGROUND: The hyperbilirubinemic j/j Gunn rat is frequently used to study the effects of neonatal hyperbilirubinemia on the developing central nervous system (CNS). Despite evidence that the cerebellar region and males are predisposed to bilirubin-induced brain injury in this animal model, there are limited regional and no sex-specific brain bilirubin content data. OBJECTIVE/METHODS: To characterize and contrast the regional (cortex, brainstem, cerebellum) and sex-specific CNS bilirubin contents of hyperbilirubinemic j/j Gunn rat pups and their age-matched (15-19 days) nonjaundiced J/j counterparts. Pups were injected 24 h prior to sacrifice with sulfadimethoxine (200 mg/kg i.p.) to enhance the CNS bilirubin content. RESULTS: The CNS bilirubin contents in each region and total serum bilirubin levels were significantly greater in jaundiced j/j pups versus nonjaundiced J/j pups. Within the sulfadimethoxine-treated male j/j cohort, the mean brain bilirubin content was highest in the cerebellum (18.9 +/- 7.8 microg/g), intermediate in the brainstem (10.7 +/- 8.0 microg/g), and lowest in the cortex (4.7 +/- 3.0 microg/g) (F = 11.31, p < 0.001 by ANOVA), and the cerebellar bilirubin level was significantly higher than in the littermate-matched sulfadimthoxine-treated j/j female pups (p < 0.02). The serum albumin levels were not different between j/j male and j/j female pups. CONCLUSIONS: We conclude that the brain bilirubin content of hyperbilirubinemic j/j Gunn rat pups is greater than in nonjaundiced J/j pups and varies as a function of CNS region and sex. We speculate that the higher cerebellar bilirubin content may preferentially predispose male j/j Gunn rat pups to bilirubin-induced neurotoxicity.

Animals↗
PubMed2006

Hyperbilirubinemia and bilirubin toxicity in the late preterm infant.

Late preterm gestation is an important risk factor for the development of severe neonatal hyperbilirubinemia and kernicterus. An exaggerated hepatic immaturity contributes to the greater prevalence, severity, and duration of neonatal jaundice in late preterm infants. Breast milk feeding is almost uniformly present and large for gestational age status, male sex, and G6PD deficiency are over-represented among that cohort of late preterm infants with kernicterus. Attention to screening measures for jaundice in the newborn nursery, the provision of lactation support, parental education, timely postdischarge follow-up, and appropriate treatment when clinically indicated should help to reduce the risk of late preterm neonates developing severe neonatal jaundice or kernicterus.

Breast Feeding↗
PubMed2006

Kernicterus and the molecular mechanisms of bilirubin-induced CNS injury in newborns.

Kernicterus is a devastating, chronic disabling neurological disorder whose central nervous system (CNS) sequelae reflect both a predilection of bilirubin toxicity for neurons (rather than glial cells) and the regional topography of bilirubin-induced neuronal injury that is characterized by prominent basal ganglia, cochlear, and oculomotor nuclei involvement. The molecular pathogenesis of bilirubin-induced neuronal cell injury, although incompletely understood, likely reflects the untoward effects of hazardous unconjugated bilirubin concentrations on plasma, mitochondrial, and/or endoplasmic reticulum (ER) membranes. These membrane perturbations, in turn, might lead to the genesis of neuronal excitotoxicity, mitochondrial energy failure, or increased intracellular calcium concentration [Ca2+]i. These three phenomena are likely to be linked spatially and temporally in the pathogenesis of bilirubin-induced neuronal injury. Downstream events triggered by increased [Ca2+]i may include, among others, the activation of proteolytic enzymes, apoptotic pathways, and/or necrosis, the individual occurrence of which is likely a function of the degree and duration of bilirubin exposure. A recent study demonstrates the activation of mitogen-activated protein kinase signal transduction pathways by bilirubin heralding a degree of complexity regarding the molecular mechanism(s) of bilirubin-induced neurotoxicity not previously appreciated. There remains, however, a paucity of data regarding specific effects of bilirubin on intracellular signaling and cell death pathways, particularly in vivo. An enhanced understanding of the molecular pathogenesis of bilirubin-induced neuronal injury will lead to the identification of potential novel interventional strategies to protect the CNS against kernicterus.

Apoptosis↗
PubMed2005

Vigintiphobia revisited.

In this review the historical tenets and evidence-based clinical research in support of a bilirubin exchange threshold of >20 mg/dL for the healthy term neonate are revisited. In addition, a hypothesis is ventured that recent cases of kernicterus are related in part to changes in population factors coupled with genetic predispositions that have unmasked an unappreciated potential for marked neonatal hyperbilirubinemia.

Anemia, Hemolytic↗
PubMed2003

Administration of drugs known to inhibit P-glycoprotein increases brain bilirubin and alters the regional distribution of bilirubin in rat brain.

P-glycoprotein (P-gp) is an ATP-dependent integral plasma membrane efflux pump, expressed in abundance in brain capillary endothelial cells and astrocytes. P-gp contributes to the blood-brain barrier in limiting the influx and retention of a variety of lipophilic compounds, including unconjugated bilirubin. Several drugs block P-gp function and thereby enhance intracellular accumulation of P-gp substrates. In this study we proposed that pretreatment with drugs known to inhibit P-gp function in clinically relevant doses would alter the uptake of bilirubin in the brain of 32- to 36-d-old rats. In the first arm of the study, the animals received pretreatment with an i.v. infusion of either propanolol, erythromycin, verapamil, ceftriaxone, rifampin, or saline, 10 min before an i.v. bolus of 50 mg/kg bilirubin was given. Except for the erythromycin-treated rats, all treatment groups had significantly higher brain-to-serum bilirubin ratios than control animals (p < 0.05, Welch's t test). In the second arm of the study, treatment with either ceftriaxone or rifampin or saline i.v. preceded a 50 mg/kg i.v. bolus of radioactive bilirubin. Analysis of seven different brain regions by scintillation counting showed that the distribution patterns differed significantly between the study groups (p < 0.001, ANOVA), however, not in accordance with a kernicteric staining pattern. Because of limited knowledge of expression and function of P-gp and other membrane transport proteins in the newborn, the implications of this study remain to be seen. We speculate that drugs known to inhibit P-gp function may increase the risk of bilirubin encephalopathy in the hyperbilirubinemic infant.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2003

Regulation of FasL/Fas in human trophoblasts: possible implications for chorioamnionitis.

Chorioamnionitis is a common cause of premature birth and is associated with significant morbidity and mortality in the mother and infant. Preterm birth shares similarities with rejection of the fetal allograft, which is characterized by increased apoptosis of placental trophoblasts. We hypothesized that there is increased trophoblast apoptosis in chorioamnionitis and that this increased apoptosis is mediated by the Fas ligand (FasL)/Fas pathway. To test our hypothesis, we examined placental villous tissues from patients with chorioamnionitis and used the TUNEL assay to demonstrate enhanced trophoblast apoptosis in patients with chorioamnionitis. When the same samples were stained for Fas, there was increased trophoblast Fas expression in patients with chorioamnionitis. To define the mechanisms responsible for this increase in trophoblast apoptosis, we cultured villous explants from uncomplicated term placentas with proinflammatory cytokines and demonstrated a marked increase in trophoblast apoptosis. By blocking FasL, we reduced tumor necrosis factor alpha-induced and interferon gamma-induced apoptosis. These data suggest that chorioamnionitis is associated with increased trophoblast apoptosis and enhanced trophoblast Fas expression. As a complement to our in vivo study, we demonstrated that cytokine-induced trophoblast apoptosis is mediated in part by the FasL/Fas pathway, suggesting that cytokines promote sensitivity to Fas-mediated apoptosis. These mechanisms may be important in perpetuating inflammation in the placental microenvironment and may contribute to the pathogenesis of chorioamnionitis.

Adult↗
PubMed2003

IUGR alters postnatal rat skeletal muscle peroxisome proliferator-activated receptor-gamma coactivator-1 gene expression in a fiber specific manner.

Uteroplacental insufficiency and subsequent intrauterine growth retardation (IUGR) increase the risk of insulin resistance in humans and rats. Aberrant skeletal muscle lipid metabolism contributes to the pathogenesis of insulin resistance. Peroxisome proliferator-activated receptor-gamma co-activator-1 (PGC-1) is a transcriptional co-activator that affects gene expression of key lipid metabolizing enzymes such as carnitine palmitoyl-transferase I (mCPTI). Because gene expression of lipid metabolizing enzymes is altered in IUGR postnatal skeletal muscle, and we hypothesized that PGC-1 expression would be similarly affected. To prove this hypothesis, bilateral uterine artery ligation and sham surgery were used to produce IUGR and control rats respectively. Western Blotting demonstrated that PGC-1 hind limb skeletal muscle protein levels were increased in perinatal and postnatal IUGR rats. Conventional RT-PCR demonstrated that PGC-1 mRNA levels were similarly increased in perinatal hind limb skeletal muscle and juvenile extensor digitorum longus (EDL), but were decreased in juvenile soleus. Because a gender specific trend was noted in PGC-1 mRNA levels, real time RT-PCR was used for further differentiation. Real time RT-PCR revealed that changes in postnatal skeletal muscle PGC-1 expression were more marked in male IUGR rats versus female IUGR rats. Down stream targets of PGC-1 followed a similar pattern of expression. We conclude that PGC-1 expression is altered in rat IUGR skeletal muscle and speculate that it contributes to the pathogenesis of insulin resistance in the IUGR rat.

Female↗
PubMed2002

Effect of injecting primary myoblasts versus putative muscle-derived stem cells on mass and force generation in mdx mice.

It is well established that the injection of normal myoblasts or of muscle-derived stem cells (MDSCs) into the muscle of dystrophin-deficient mdx mice results in the incorporation of a number of donor myoblasts into the host muscle. However, the effect of the injected exogenous cells on mdx muscle mass and functional capacity has not been evaluated. This study evaluates the mass and functional capacity of the extensor digitorum longus (EDL) muscles of adult, male mdx mice that received intramuscular injections of primary myoblasts or of MDSCs (isolated by a preplating technique; Qu, Z., Balkir, L., van Deutekom, J.C., Robbins, P.D., Pruchnic, R., and Huard, J., J. Cell Biol. 1998;142:1257-1267) derived from normal mice. Evaluations were made 9 weeks after cell transplantation. Uninjected mdx EDL muscles have a mass 50% greater than that of age-matched C57BL/10J (normal) EDL muscles. Injections of either primary myoblasts or MDSCs have no effect on the mass of mdx EDL muscles. EDL muscles of mdx mice generate 43% more absolute twitch tension and 43% less specific tetanic tension then do EDL muscles of C57BL/10J mice. However, the absolute tetanic and specific twitch tension of mdx and C57BL/10J EDL muscles are similar. Injection of either primary myoblasts or MDSCs has no effect on the absolute or specific twitch and tetanic tensions of mdx muscle. Approximately 25% of the myofibers in mdx EDL muscles that received primary myoblasts react positively with antibody to dystrophin. There is no significant difference in the number of dystrophin-positive myofibers when MDSCs are injected. Regardless of the source of donor cells, dystrophin is limited to short distances (60-900 microm) along the length of the myofibers. This may, in part, explain the failure of cellular therapy to alter the contractile properties of murine dystrophic muscle.

Animals↗
PubMed2002

Understanding neonatal hyperbilirubinaemia in the era of genomics.

The genomics revolution offers novel approaches to scientific investigation. Application of genomics technologies including microarray gene chips will provide a more complete picture of biological phenomena and help define the genetic contribution to disease by monitoring changes in expression across thousands of genes in physiological and clinical contexts. We briefly summarize identified genetic components that contribute to the genesis of neonatal hyperbilirubinaemia with a focus on inborn errors of hepatic bilirubin conjugation and discuss the potential use of microarray gene expression profiling technology to enhance our understanding of the pathogenesis of hyperbilirubinaemic neuronal cell injury. Expanded study using the tools of genomics will shed insights into the genetics of newborn jaundice and the pathogenesis of hyperbilirubinaemic encephalopathy.

Bilirubin↗
PubMed2002

Functional characteristics of dystrophic skeletal muscle: insights from animal models.

Muscular dystrophies are a clinically and genetically heterogeneous group of disorders that show myofiber degeneration and regeneration. Identification of animal models of muscular dystrophy has been instrumental in research on the pathogenesis, pathophysiology, and treatment of these disorders. We review our understanding of the functional status of dystrophic skeletal muscle from selected animal models with a focus on 1) the mdx mouse model of Duchenne muscular dystrophy, 2) the Bio 14.6 delta-sarcoglycan-deficient hamster model of limb-girdle muscular dystrophy, and 3) transgenic null mutant murine lines of sarcoglycan (alpha, beta, delta, and gamma) deficiencies. Although biochemical data from these models suggest that the dystrophin-sarcoglycan-dystroglycan-laminin network is critical for structural integrity of the myofiber plasma membrane, emerging studies of muscle physiology suggest a more complex picture, with specific functional deficits varying considerably from muscle to muscle and model to model. It is likely that changes in muscle structure and function, downstream of the specific, primary biochemical deficiency, may alter muscle contractile properties.

Animals↗
PubMed2002

P-glycoprotein expression in mouse brain increases with maturation.

The mdr1a isoform of P-glycoprotein (Pgp) is an integral plasma membrane efflux pump expressed in adult brain capillary endothelial cells and astrocytes of the blood-brain barrier. We determined the developmental pattern of Pgp expression in brain tissue at embryonic day 16 (E16), day of life 0 (D0), day of life 7 (D7), day of life 21 (D21), and adults (Ad). The relative expression of Pgp mRNA and protein was indexed as a percent (mean +/- SEM) of D0 levels. Pgp mRNA levels increased significantly (p < 0.01) with maturation (E16: 75 +/- 8%; D21: 303 +/- 37%, and Ad: 1,160 +/- 120%). Similarly, Pgp protein expression was observed at E16 and increased significantly (p < 0.01) during development (E16: 52 +/- 8%; D7: 187 +/- 23%; D21: 440 +/- 48%, and Ad: 441 +/- 56%). This developmental pattern of enhanced blood-brain barrier Pgp expression with maturation was confirmed by immunohistochemistry. We conclude that (i) Pgp expression in mouse brain is limited during late embryogenesis and the newborn period; (ii) Pgp expression increases markedly with postnatal maturation, and (iii) by D21 brain Pgp protein expression approximates adult levels.

ATP Binding Cassette Transporter, Subfamily B, Mem↗