dizocilpine-maleate and Kernicterus

Bilirubin encephalopathy or kernicterus is a potentially serious complication of neonatal hyperbilirubinemia. The mechanism of bilirubin-induced neurotoxicity is not known. Many neurological insults are mediated through NMDA receptor activation.. We assessed the effect of the NMDA channel antagonist, MK-801 on bilirubin neurotoxicity in vivo and in vitro.. Bilirubin toxicity in vitro was assessed using trypan blue staining. Sulfadimethoxine injected (i.p.) jaundiced Gunn rat pups exhibit many neurological sequelae observed in human hyperbilirubinemia. Brainstem auditory-evoked potentials (BAEPs), a noninvasive sensitive tool to assess auditory dysfunction due to bilirubin neurotoxicity, were used to assess neuroprotection with MK-801 (i.p.) in vivo.. In primary cultures of hippocampal neurons, 20 min exposure to 64:32 microM bilirubin:human serum albumin reduced the cell viability by approximately 50% ten hours later. MK-801 treatment did not protect the cells. MK-801 pretreatment doses ranging from 0.1-4.0 mg/kg did not protect against BAEP abnormalities in Gunn rat pups 6 h after sulfadimethoxine injection.. Our findings suggest that bilirubin neurotoxicity is not mediated through NMDA receptor activation.

Topics: Animals; Animals, Newborn; Anti-Infective Agents; Bilirubin; Cell Survival; Disease Models, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Evoked Potentials, Auditory, Brain Stem; Hyperbilirubinemia; Jaundice; Kernicterus; Neurons; Neuroprotective Agents; Rats; Rats, Gunn; Receptors, N-Methyl-D-Aspartate; Sulfadimethoxine

Unconjugated bilirubin (UCB) induces both apoptosis and necrosis in neurons. To investigate the role of caspases and excitotoxicity in UCB-induced cell death, we exposed NT2-N neurons to 5 microM UCB (a concentration known to induce apoptosis) or 2 microM staurosporine (positive apoptosis control) and investigated the effects of treatments with the specific caspase-3 inhibitor, zDEVD.FMK (20 and 100 microM), or the general caspase inhibitor, zVAD.FMK (20 and 100 microM), and/or the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 (10 microM) during a 24- or 48-h exposure. UCB increased caspase-3 activity 2.3-fold after 6 h. Despite this, treatment with zDEVD.FMK did not prevent cell death. zVAD.FMK enhanced neuronal survival by reducing apoptotic nuclear fragmentation, while MK-801 enhanced survival by reducing apoptotic nuclear condensation; both without affecting the MTT assays. Combined treatment reduced both apoptotic morphologies (without affecting necrosis), and this effect was also reflected in the MTT assays [corrected] We conclude that NMDA receptor-mediated pathways and caspase-mediated pathways are involved in UCB-induced cell death in human NT2-N neurons. Concomitant inhibition of both pathways results in synergistic protection.

Topics: Amino Acid Chloromethyl Ketones; Apoptosis; Bilirubin; Caspase 3; Caspase Inhibitors; Cysteine Proteinase Inhibitors; Dizocilpine Maleate; DNA Fragmentation; Drug Synergism; Enzyme Activation; Humans; Kernicterus; Neurons; Receptors, N-Methyl-D-Aspartate; Tumor Cells, Cultured

Severe hyperbilirubinemia in neonates with prematurity and/or systemic illnesses such as hemolytic disease, acidosis, and hypoxemia enhances their risk for developing cerebral palsy, paralysis of ocular upgaze, and deafness. This neurologic syndrome has been associated with selective neuronal vulnerability in the basal ganglia, certain brainstem nuclei, and Purkinje cells. However, the mechanism by which bilirubin damages neurons remains unclear. In these studies, we found that intracerebral injection of N-methyl-D-aspartate (NMDA), an excitotoxic analogue of glutamate, caused greater injury in jaundiced 7-day-old Gunn (jj) rat pups than in nonjaundiced heterozygous (Nj) littermate controls. NMDA injection caused even greater injury when protein-bound bilirubin was displaced with the sulfonamide drug sulfadimethoxine in jaundiced homozygous pups. In additional experiments, the acute signs of bilirubin-mediated neuronal injury, induced in homozygous (jj) Gunn rats by treatment with sulfonamide, were reduced by concurrent treatment with the NMDA-type glutamate channel antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohept-5,10-imine (MK-801, dizocilpine). The results suggest that bilirubin may cause encephalopathy and neuronal injury, at least in part, through an NMDA receptor-mediated excitotoxic mechanism. This conclusion is consistent with clinical observations that bilirubin encephalopathy is synergistically worsened by hypoxemia, which also shares an excitotoxic mechanism of neuronal injury.

Topics: Animals; Apoptosis; Bilirubin; Brain Damage, Chronic; Disease Models, Animal; Dizocilpine Maleate; Drug Synergism; Excitatory Amino Acid Antagonists; Genotype; Glucuronosyltransferase; Injections; Kernicterus; N-Methylaspartate; Neurotoxins; Purkinje Cells; Rats; Rats, Gunn; Receptors, Glutamate; Sulfadimethoxine