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The toxic effects of metallic nanoparticles and rare earth elements on the mitochondrial oscillator

Author(s): Francois Gagne* and Hanana H, PhD

Mitochondria display non-linear oscillation in NAD(P)H levels as a result of the delicate balance between NAD(P)H production during glycolysis and oxidation during the electron transport chain step. The purpose of this study was to examine the effects of selected elements on the mitochondrial oscillator in freshwater mussels Dreissena bugensis. Freshly isolated mitochondria were treated by increasing concentrations of zinc oxide nanoparticles (nZnO), erbium (Er) and lutetium (Lu) for 40 min, and the oscillations in NAD(P) H levels were measured using fluorescence spectroscopy. Under normal conditions, NAD(P)H levels oscillate with a period of 2 min (frequency 0.25) and an initial oxidation rate of NAD(P)H) during the first 20 min which stopped for the remainder of the exposure period. Exposure to the selected elements first showed that the NAD(P)H oxidation rate progressed well for over 20 min and the rate was significantly increased for nZnO (0.64 μg/L), Er (12 mg/L) and Lu (16 mg/L). The oscillatory behaviour of NAD(P)H levels (fluorescence data) were examined using Fourier transformation, which revealed that these elements reduced the amplitudes at the normal frequency in a dose-dependent manner, with signals appearing at lower frequency. The decrease in amplitudes at the normal frequency occurred at concentrations 5-10 times less than those that significantly increased the rate of NAD(P)H oxidation. Moreover, the lower frequencies were out of phase with those of the controls, which suggests the appearance of emerging toxic frequency. Oscillations in NAD(P)H could be altered by contaminants and could thus constitute a novel and sensitive biomarker of ecotoxicity.

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