title: Immunomodulatory and immunotoxic effects of bilirubin: molecular mechanisms.
abstract: The immunomodulatory and immunotoxic effects of purified UCB have not been evaluated previously at clinically relevant UCB concentrations and UCB:BSA ratios. To delineate the molecular mechanism of UCB-induced immunomodulation, immune cells were exposed to clinically relevant concentrations of UCB. It inhibited LPS-induced B cell proliferation and cytokine production from splenic macrophages. UCB (≥25 μM) was toxic to unfractionated splenocytes, splenic T cells, B cells, macrophages, LPS-stimulated CD19(+) B cells, human PBMCs, and RBCs. Purified UCB also was found to be toxic to splenocytes and human PBMCs. UCB induced necrosis and apoptosis in splenocytes. UCB activated the extrinsic and intrinsic pathways of apoptosis, as reflected by the markers, such as CD95, caspase-8, Bax, MMP, cytoplasmic Ca(+2), caspase-3, and DNA fragmentation. UCB depleted GSH and activated p38MAPK. NAC, caspase inhibitors, and p38MAPK inhibitor attenuated the UCB-induced apoptosis. In vivo administration of ≥25 mg/kbw UCB induced atrophy of spleen, depletion of bone marrow cells, and leukopenia and decreased lymphocyte count and the T and B cell response to mitogens. UCB administration to mice led to induction of oxidative stress, activation of p38MAPK, and cell death in splenocytes. These parameters were attenuated by the injection of NAC and the p38MAPK inhibitor. Our results demonstrate for the first time that clinically relevant concentrations of UCB induce apoptosis and necrosis in immune cells by depleting cellular GSH. These findings should prove useful in understanding the immunosuppression associated with hyperbilirubinemia.
authors.affiliation: Radiation Biology and Health Sciences Division, Bhabha Atomic Research Centre, Trombay, Mumbai, India.
authors.forename: Nazir M
authors.initials: NM
authors.lastname: Khan
authors.forename: T B
authors.initials: TB
authors.lastname: Poduval
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001402:B-Lymphocytes / Q000187:drug effects / Q000473:pathology; D001663:Bilirubin / Q000276:immunology / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism; D053938:DNA Fragmentation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007155:Immunologic Factors / Q000276:immunology / Q000494:pharmacology*; D056747:Immunomodulation; D008262:Macrophage Activation / Q000187:drug effects; D008264:Macrophages / Q000187:drug effects / Q000473:pathology; D008297:Male; D051379:Mice; D015398:Signal Transduction / Q000187:drug effects; D013601:T-Lymphocytes / Q000276:immunology; D051028:bcl-2-Associated X Protein / Q000378:metabolism; D019014:fas Receptor / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases
chemical_list: D004791:Enzyme Inhibitors; D007155:Immunologic Factors; D051028:bcl-2-Associated X Protein; D019014:fas Receptor; D048051:p38 Mitogen-Activated Protein Kinases; D053181:Caspase 8; D001663:Bilirubin; D002118:Calcium