The nickel and cobalt present in many industrial working environments and consumer products. They are two of the leading causes of allergic contact dermatitis, which is a typical delayed(type IV) hypersensitivity reaction. However, the mechanism by which nickel and cobalt causes this pathology is not well known. The nickel and cobalt induced contact dermatitis is mediated primarily through macrophages. This mechanism is similar to the autotoxicity procedure for NO. Therefore, this study was designed to examine whether the metals could modulate NO production and how the metals may affect ATP production and cell viability. In summary, the purpose of this study was to elucidate the role of NO in the nickel and cobalt induced cytotoxicity.

This study is based on observations of cultures of RAW 264.7 cells which are originated from a tumor of Balb/c mouse that was induced by Abelson murine leukemia virus. RAW 264.7 cells were treated with either Ni, Co, Ni plus Co, or Nmonomethyl-L- arginine(NMLA) for 24-72 h. The cytotoxicity of the nickel and cobalt was measured by cell viability and NO2-, and mitochondrial function was evaluated by adenosine triphosphate(ATP) production in RAW 264.7 cells. In addition, the morphology of cells was observed using an inverted microsope.

The NO2- synthesis of RAW 264.7 cells increased with increasing concentrations of Ni and Co up to 50 microM after 24 and 48 h of exposure to Ni and Co but then decreased if the concentration was greater than 50 microM and the time period was greater than 48 h. However, the viability of cells was decreased by Ni and Co exposure in a dose and time dependent manner. Therefore, 50 microM Ni or Co and 48 h of treatment were used in this study. A complete inhibition of NO2- synthesis by Ni or/and Co occurred when iNOS inhibitor, NMLA, were pretreated prior to addition of Ni or/and Co, whereas Ni or/and Co induced decrease of synthesis of ATP and viability completely recovered when NMLA were pretreated prior to addition of Ni or/and Co. Ni or/and Co(50 microM) induced the characteristic morphological features of cytotoxicity which is characterized by a shrinkage of cytoplasm and irregular shape of the cells, but the pretreatment of NMLA resulted in a recovered morphological change of the cells to their normal appearance.

These results suggest that NO plays an important role in the pathogenesis of the cytotoxicity of nickel and cobalt, and nickel and cobalt may exert their toxicities by means of modulation of NO production. The results from this study may facilitate further understanding the role of NO on nickel and cobalt induced immune and inflammatory processes.