title: 1,25-Dihydroxyvitamin D3 increases the toxicity of hydrogen peroxide in the human monocytic line U937: the role of calcium and heat shock.
abstract: 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) increases synthesis of heat shock proteins in monocytes and U937 cells and protects these cells from thermal injury. We examined whether 1,25-(OH)2D3 would also modulate the susceptibility of U937 cells to H2O2-induced oxidative stress. Cell viability was assessed by trypan blue exclusion and [3H]thymidine incorporation into DNA. Prior incubation for 24 h with 1,25-(OH)2D3 (25 pM or higher) unexpectedly increased H2O2 toxicity. Since cellular Ca2+ may be a mediator of cell injury we investigated effects of altering extracellular Ca2+ ([Ca2+]e) on 1,25-(OH)2D3-enhanced H2O2 toxicity as well as effects of 1,25-(OH)2D3 and H2O2 on cytosolic free Ca2+ concentration ([Ca2+]f). Basal [Ca2+]f in medium containing 1.5 mM Ca as determined by fura-2 fluorescence was higher in 1,25-(OH)2D3-pretreated cells than control cells (137 versus 112 nM, P less than 0.005). H2O2 induced a rapid increase in [Ca2+]f (to greater than 300 nM) in both 1,25-(OH)2D3-treated and control cells, which was prevented by a reduction in [Ca2+]e to less than basal [Ca2+]f. The 1,25(OH)2D3-induced increase in H2O2 toxicity was also prevented by preincubation with 1,25-(OH)2D3 in Ca2+-free medium or by exposing the cells to H2O2 in the presence of EGTA. Preexposure of cells to 45 degrees C for 20 min, 4 h earlier, partially prevented the toxic effects of H2O2 particularly in 1,25-(OH)2D3-treated cells, even in the presence of physiological levels of [Ca2+]e. Thus 1,25-(OH)2D3 potentiates H2O2-induced injury probably by increasing cellular Ca2+ stores. The 1,25-(OH)2D3-induced amplification of the heat shock response likely represents a mechanism for counteracting the Ca2+-associated enhanced susceptibility to oxidative injury due to 1,25-(OH)2D3.
authors.affiliation: Department of Medicine, Harvard Medical School, Boston, Massachusetts.
authors.forename: B S
authors.initials: BS
authors.lastname: Polla
authors.forename: J V
authors.initials: JV
authors.lastname: Bonventre
authors.forename: S M
authors.initials: SM
authors.lastname: Krane
mesh_terms: D002117:Calcitriol / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D006360:Heat-Shock Proteins / Q000096:biosynthesis; D006358:Hot Temperature; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D009000:Monocytes / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D010084:Oxidation-Reduction
chemical_list: D006360:Heat-Shock Proteins; D006861:Hydrogen Peroxide; D002117:Calcitriol; D002118:Calcium