Inhibition of methemoglobin and metmyoglobin reduction by cobalt

Acute exposure to cobalt induces transient methemoglobinuria in rats

We observed transient excretion of dark-brown urine after acute exposure to cobalt in rats and investigated the mechanism of it. We injected cobalt into rats s.c. at a dose of 15 mg/kg and collected urine, peripheral blood, and organ samples at the indicated times after injection. Biochemical and histopathological examinations of these samples were conducted. Obvious macroscopic and biochemical methemoglobinuria was observed just after injection of cobalt, but the level of urinary methemoglobin decreased gradually, almost disappearing by 24 h. The levels of cobalt in peripheral blood and urine showed a very similar pattern to that of methemoglobinuria. Neither anemia nor bilirubinemia was observed, indicating no extrarenal intravascular hemolysis. Pathological examination of the kidneys revealed that the glomerular capillaries were filled with red blood cells at 1 h after injection. Electron microscopy showed deformed red blood cells in the glomerular capillaries and condensed hemoglobin in Bowman's capsule that passed through the basement membrane. There were no trends toward increases in plasma levels of creatinine or blood urea nitrogen. These results indicate that exposure to cobalt induces transient methemoglobinuria through the lysis of red blood cells and oxidation of iron in hemoglobin at the glomerular capillaries without causing renal dysfunction.

Application of a hepatocyte-erythrocyte coincubation system to studies of cyanide antidotal mechanisms

A coincubation system composed of hepatocytes in primary monolayer culture and erythrocytes suspended in the culture medium was developed and used as a model for investigations of mechanisms of cyanide antidote action at the cellular level. Hepatocyte ATP was used as the cytotoxicity indicator. Treatment of rat hepatocytes in the coincubation system with KCN (1.0 mM) for 10 min at 37 degrees C selectively reduced hepatocyte ATP levels to 33 +/- 15% of control (no KCN added) levels. 4-dimethylaminophenol (DMAP), cobalt(II) chloride, sodium nitrite, sodium thiosulfate, or a combination of the last two antidotes added to the KCN-containing medium significantly reversed ATP depression and the response was concentration dependent. The relative effectiveness, on a molar basis, was estimated to be DMAP greater than CoCl2 much greater than NaNO2 congruent to Na2S2O3. NaNO2 and DMAP induced methemoglobin formation in the absence of cyanide and cyanmethemoglobin formation in its presence; erythrocytes were required in the medium for effectiveness. CoCl2 produced neither cyanmethemoglobin nor thiocyanate in appreciable quantities nor required erythrocytes for antagonism. Na2S2O3 converted cyanide to thiocyanate and reversed ATP depression without erythrocytes in the medium. The addition of erythrocytes increased these rates significantly and to a greater extent than albumin. The overall results are consistent with previously proposed modes of action for these antidotes. However, the enhancement in cyanide metabolism and ATP recovery with Na2S2O3 and erythrocytes in the system was unexpected and raises the possibility that erythrocytes may contribute to cyanide disposition and antagonism in vivo when this antidote is administered.