Copper Ions Reduced Toxicity of Sodium Azide and Lipopolysaccharide on Cultured Cerebellar Granule Neurons

Abstract

Introduction. Copper ions (Cu2+) are structural elements of proteins such as cytochrome с oxidase (Complex IV), an enzyme that catalyzes the final step of electron transfer to oxygen during oxidative phosphorylation in the mitochondria. With Cu2+ homeostasis being of utmost importance, its disturbances in the central nervous system are involved in the mechanisms of many neurodegenerative and other brain disorders. This study aimed to assess the effects of non-toxic copper ion levels on death of cerebellar granule neurons associated with lipopolysaccharide (LPS; in vitro inflammation model) or azide sodium (NaN3; cytochrome с oxidase inhibitor). Materials and methods. LPS (10 μg/mL) or NaN3 (250 μM) was added on day 7 to 8 to the culture medium with rat cerebellar cells for 24 hours in vitro. Nitrite concentrations were measured in the culture medium by Griess assay; absorbance was recorded with a spectrophotometer at 540 nm, and morphologically intact cells were counted as survived neurons. Results. Added to the culture medium, LPS or NaN3 reduced neuron survival to 15 ± 2% or 20 ± 3% vs. control, respectively. Cu2+ (0.5 to 5.0 μM) increased neuron survival in a dose-dependent manner to 78 ± 4% with toxic levels of LPS and to 86 ± 6% with NaN3 with 5 μM Cu2+. The concentration of nitrites in the control culture medium was 2.0 ± 0.2 μM. Added to the cell cultures, LPS increased the concentration of nitrites to 8.5 ± 0.5 μM. Cu2+ 5 μM did not show any significant effects on nitrite accumulation in the culture medium. Conclusions. We showed that copper ions can exert protective effects on neurons against LPS-induced or NaN3-induced toxicity. This protection is likely to be associated rather with Cu2+ interaction with Complex IV of the electron transfer chain in the mitochondria than with inhibition of NO production. Effects of Cu2+ on apoptosis pathway proteins also cannot be ruled out.

Keywords

• neurons
• copper ions
• sodium azide
• nitrogen oxide