Nickel chloride generates cytotoxic ROS that cause oxidative damage in human erythrocytes

Nickel is a heavy metal that is regarded as a possible hazard to living organisms due to its toxicity and carcinogenicity. Nickel chloride (NiCl₂), an inorganic divalent Ni compound, has been shown to cause oxidative stress in cells by altering the redox equilibrium. We have investigated the effect of NiCl₂ on isolated human erythrocytes under in vitro condition.

Isolated erythrocytes were treated with different concentrations of NiCl₂ (25-500 µM) for 24 h at 37 ºC. Hemolysates were prepared and several biochemical parameters were analyzed in them.

Treatment of erythrocytes with NiCl₂ enhanced the intracellular generation of reactive oxygen species (ROS). A significant increase in hydrogen peroxide levels and oxidation of proteins and lipids was also seen. This was accompanied by a reduction in levels of nitric oxide, glutathione, free amino groups and total sulfhydryl groups. NiCl₂ treatment impaired both enzymatic and non-enzymatic defense systems, resulting in lowered antioxidant capacity and diminished ability of cells to quench free radicals and reduce metal ions. NiCl₂ exposure also had an inhibitory effect on the activity of enzymes involved in pathways of glucose metabolism (glycolytic and pentose phosphate shunt pathways). Increased level of methemoglobin, which is inactive in oxygen transport, was also seen. The rate of heme breakdown increased resulting in the release of free iron. Exposure to NiCl₂ led to considerable cell lysis, indicating damage to the erythrocyte membrane. This was supported by the inhibition of membrane bound enzymes and increase in the osmotic fragility of NiCl₂ treated cells. NiCl₂ treatment caused severe morphological alterations with the conversion of normal discocytes to echinocytes. All changes were seen in a NiCl₂ concentration-dependent manner.

NiCl₂ generates cytotoxic ROS in human erythrocytes which cause oxidative damage that can decrease the oxygen carrying capacity of blood and also lead to anemia.