ABSTRACT
Over the last few years, studies have suggested that oxidative stress plays a role in the regulation of hematopoietic cell homeostasis. In particular, the effects of hydrogen peroxide (H2O2) range from hematopoietic cell proliferation to cell death, depending on its concentration in the intracellular milieu. In this work, we evaluated the effects of an oxidative environment on normal and leukemic hematopoietic cells by stimulating normal human (umbilical cord blood) and murine (bone marrow) hematopoietic cells, as well as human myeloid leukemic cells (HL-60 lineage), upon H2O2 stimulus. Total cell populations and primitive subsets were evaluated for each cell type. H2O2 stimulus induces HL-60 cell death, whereas the viability of human and murine normal cells was not affected. The effects of H2O2 stimulus on hematopoietic stem/progenitor cell subsets were examined and the normal primitive cells were found to be unaffected; however, the percentage of leukemic stem cells (LSC) increased in response to H2O2, while clonogenic ability of these cells to generate myeloid clones was inhibited. In addition, H2O2 stimulus caused a decrease in the levels of p-AKT in HL-60 cells, which most likely mediates the observed decrease of viability. In summary, we found that at low concentrations, H2O2 preferentially affects both the LSC subset and total HL-60 cells without damage normal cells.
ABSTRACT
O ATP media uma vastidão de efeitos por ação dos receptores purinérgicos P2 expressados em muitos tecidos(Mackenzie e cols.,1999; Harden e cols., 1995). Existem dois diferentes mecanismos de sinalização e as estruturas moleculares determinada por sequenciamento dos receptores P2 forma a base para classificação destes receptores purinérgicos em duas maiores famílias: P2X e a família P2Y. (Burnstock e Kennedy, 1985). Estas duas famílias de receptores purinérgicos P2 tem sido divididas em um grande número de subtipos (P2X1 - P2X7 e P2Y1 - P2Y11) baseado no perfil farmacológico de respostas para agonista e na estrutura destes receptores (Bumstock,1996). Estimulação de receptores P2 rápidamente eleva concentração de cálcio citosólico (intracelular é de 100nM enquanto a concentração extracelular é de 1300nM), por influxo via canal cátion iônico (P2X, receptor ionotrópico)ou por liberação de cálcio dos estoques intracelulares, subsequente à ativação de fosfolipase C por proteína G (P2Y, receptor metabotrópico) com produção de IP3 (inositol trisfosfato ) e abertura dos canais de cálcio dos IP3 localizados no reticulo endoplasmático (Mackenzie, col.,1999) (au)
