Abstract
Plastics pervade our environment and potentially release important quantities of plastic nanoparticles (NPs) from degradation in the environment. The purpose of this study was to examine the crowding effects of polystyrene NPs on lactate dehydrogenase (LDH) in vitro and following exposure to Hydra attenuata. First, LDH activity was measured in vitro in the presence of filamentous (F-)actin and NPs (50 and 100 nm diameter) to determine changes in viscosity and the fractal kinetics of LDH. The fractal dimension (fD) was also determined using the rescaled range analysis procedure. Secondly, these changes were examined in hydra exposed to NPs for 96h to concentrations of NPs. The data revealed that the addition of F-actin increased the rate of LDH at low substrate (pyruvate) concentrations compared to LDH alone with a gradual decrease in the rate with the addition of pyruvate, which is characteristic of the fractal behavior of enzymes in crowded environments. The addition of 50 and 100 nm NPs also produced these changes, which suggest that NPs could change the space properties of the LDH reaction. The fD was reduced to 0.85 and 0.91 with 50 and 100 nm NPs compared to 1.093 with LDH alone. Decrease in the fD was related with increased amplitudes and frequency in viscosity waves in the reaction media. Exposure of hydra to NPs confirmed the increase in LDH activity and the fD was significantly correlated with LDH activity (r = −0.5). Correction of LDH activity (residuals) still revealed an increase in LDH activity in hydra suggesting increased anaerobic metabolism by NPs. In conclusion, the presence of NPs in the intracellular space decreased the fD, which could influence LDH activity in organisms exposed to NPs.
Highlights
The contamination of the aquatic environment by plastic waste represents one of the major pollution problems of the 21st century [1]
The fractal dimension (fD) revealed that the dimension of the lactate dehydrogenase (LDH) reaction significantly decreased with the addition of F-actin, for 50 and 100 nm NPs suggesting that the space-filling capacity of the reaction media was reduced by these colloids and influenced the LDH reaction rate
This study examined the biophysical properties of polystyrene nanoparticles towards LDH activity
Summary
The contamination of the aquatic environment by plastic waste represents one of the major pollution problems of the 21st century [1]. The degradation of plastic waste has the potential to release staggering amounts of NPs in the environment. The toxic properties of plastic NPs will differ from larger microplastic debris given their capacity to permeate tissues but cells as well [3]. The persistence and long-term effects of plastic NPs in cells are largely misunderstood at the present time. Plastic NPs are interesting case to examine the crowding effects of the intracellular space given their chemical stability/“inertness”. NP toxicity is initiated by the release of potentially toxic molecules, but by the size/shape, surface area properties (reactivity) and vector effects i.e., the transport of chemicals by NPs [4]. The distribution of plastic NPs in ecosystems is largely unknown owing to the lack of methods to detect particles. Plastic NPs could already contaminate our water bodies, pass biological barriers and find their way at the subcellular level [5]
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