Multi-walled carbon nanotubes decrease lactate dehydrogenase activity in enzymatic reaction

The oxidation of 1, 4-nicotinamide adenine dinucleotide (NADH) to β-nicotinamide adenine dinucleotide (NAD+) coupled with converting of pyruvic acid (PA) to lactate catalyzed by lactate dehydrogenase (LDH), NADH + PA + H+ ⇌LDH NAD+ + Lactate, was widely adopted to quantify the cell's death, membrane infiltration and proliferation induced by potential toxins. The differential pulse voltammetry (DPV) cathodic signal of NAD+ at a hanging mercury drop electrode (HMDE) showed LDH activity decreased with the elevating dosages of and the pre-contact time (tc) with multi-walled carbon nanotubes (MWCNTs). Comparison of kinetic rate constant of above enzymatic reaction (ER) was able to sensitively assay the adverse influence of MWCNTs. Toxic concentration of altering relative LDH activity by 50% (TC50) of MWCNTs was derived to be 40 mg/L. TC50 values indicated a decrease toxicity order Al (III) > MWCNTs > nano-Al13 > 50 nm-Al2O3 ≥ 1000 nm-Al2O3. The negatively charged surfaces of these nanoparticles (NPs) might be a main cause for the decrement of LDH activity. This decrement was capable to result in the underestimation of the toxicity of NPs in classic LDH assays. This observation would highlight to settle down contradictory medium dependent toxicity of MWCNTs among the literature.

► Comparison of kinetic rate constant of above enzymatic reaction (ER) was able to sensitively assay the adverse influence of MWCNTs. ► Toxic concentration of altering relative LDH activity by 50% (TC50) of MWCNTs was derived to be 40 mg/L. ► Negative charge on the surfaces of NPs is a main cause to decrease LDH activity.