title: Concentration-dependent bimodal effect of specific 18 kDa translocator protein (TSPO) ligands on cell death processes induced by ammonium chloride: potential implications for neuropathological effects due to hyperammonemia.
abstract: The role of the 18-kDa Translocator Protein (TSPO) in cell death induced by NH4Cl (1-50 mM) for 24-72 hours to human glioblastoma U118MG cells was investigated. Cell death was already observed after 48 hours of treatment with NH4Cl at 5 mM. Dose and time-responses curves indicated that 15 mM of NH4Cl applied for 72 hours was the optimal condition for our viability assays. For example, 72 hours of 15 mM of NH4Cl caused a 50.3% increase in propidium iodide uptake, and lactate dehydrogenase release was 41.2% of the positive control, indicating significant increases in cell death. Furthermore, compared to vehicle control, these experimental conditions resulted in a significant decrease of 44.9% of the mitochondrial activity, a 62.3% increase in incidence of collapse of mitochondrial membrane potential, and an increase of 49.0% of cardiolipin peroxidation. In addition, a significant 4.3 fold increase in the maximal binding capacity (Bmax) of TSPO was found in NH4Cl-exposed cells. Surprisingly, western blot analysis and real-time PCR did not demonstrate changes in TSPO expression. We also found that neither NH4Cl nor glutamine (a metabolic product of enhanced NH4Cl levels) inhibited binding of the TSPO ligand [(3)H]PK 11195. Interestingly, we observed a bimodal effect of the TSPO ligands PK 11195, Ro5-4864, and FGIN-1-27 on the toxicity of NH4Cl; such that 1-100 nM concentrations of TSPO ligands were protective, while concentrations above 1 μM enhanced NH4Cl-induced cell death processes. In conclusion, TSPO takes part in a bimodal way in the lethal effects induced by NH4Cl in glial type cells.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Caballero
authors.forename: Leo
authors.initials: L
authors.lastname: Veenman
authors.forename: Julia
authors.initials: J
authors.lastname: Bode
authors.forename: Svetlana
authors.initials: S
authors.lastname: Leschiner
authors.affiliation: Rappaport Family Institute for Research in the Medical Sciences, Technion-Israel Institute of Technology, Department of Molecular Pharmacology, Ephron Street, P.O. Box 9649, Bat-Galim, Haifa 31096, Israel;. mgavish@techunix.technion.ac.il.
authors.forename: Moshe
authors.initials: M
authors.lastname: Gavish
mesh_terms: D000643:Ammonium Chloride / Q000633:toxicity*; D001570:Benzodiazepinones / Q000494:pharmacology; D002308:Cardiolipins / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects* / Q000502:physiology*; D045744:Cell Line, Tumor; D048430:Cell Shape; D004305:Dose-Response Relationship, Drug; D018682:GABA Agents / Q000494:pharmacology; D005973:Glutamine / Q000378:metabolism; D006801:Humans; D022124:Hyperammonemia / Q000139:chemically induced / Q000188:drug therapy / Q000503:physiopathology*; D007210:Indoleacetic Acids / Q000494:pharmacology; D007546:Isoquinolines / Q000378:metabolism / Q000494:pharmacology; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008024:Ligands; D015227:Lipid Peroxidation / Q000187:drug effects; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects / Q000502:physiology; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology; D018696:Neuroprotective Agents / Q000494:pharmacology; D011419:Propidium / Q000737:chemistry; D018079:Receptors, GABA / Q000378:metabolism*
chemical_list: D001570:Benzodiazepinones; D002308:Cardiolipins; D018682:GABA Agents; D007210:Indoleacetic Acids; D007546:Isoquinolines; D008024:Ligands; D018696:Neuroprotective Agents; D018079:Receptors, GABA; C499229:TSPO protein, human; D000643:Ammonium Chloride; D005973:Glutamine; C081306:N,N-di-n-hexyl-2-(4-fluorophenyl)indole-3-acetamide; C028513:4'-chlorodiazepam; D011419:Propidium; D007770:L-Lactate Dehydrogenase; C037850:PK 11195