High Throughput Screening Methods to Assess Pollutants Effects: A Relevant Technique?

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Bioenergetics for management and conservation is a section of the Evolutionary dynamics and management application course at University of Pau and Pays de l’Adour (Anglet, France). In this course, 2nd

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High Throughput Screening Methods to Assess Pollutants Effects: A Relevant Technique?by Alexandre Bijaye and Melody Fernandez

Published by Charlotte Recapet the March 12, 2019 on 7:43 PM

The purpose of the paper written by Miller et al. in 2016 is to assess the effectiveness of HTS (High Throughput Screening) techniques to predict the effects of metal nanoparticles on a population of Isochrysis Galbana, a common species of phytoplankton. 

High Throughout Screening is one of the newest techniques used in toxicology and which is planned to be implemented in biological and chemical sciences in the near future. Their technology is based on the analyzes of chemical compounds to be conducted in a short time. The affinity of biological structures which is related to the toxicity to be defined. 

In this article, we’ll focus on nanoparticles: Engineered nanoparticles (ENPs) are actually an emerging form of metal contamination. These particles are widely used in biochemistry, engineering,… Four elements are studied in this paper: Ag, ZnO, CeO2 and CuO. The studied concentrations of each compound chosen were known to affect phytoplankton populations.


Silver nanoparticules (T. Theivasanthi/Wikimedia)

The results showing a decline of the photosynthetic activity (PSII) are compared to the HTS tests results. DEBtox models are energycally and toxycodynamically balanced modelling techniques (DEBtox and TD) and are here used to evaluate the impact of ENPs.

First, the decline in photosynthetic activity is a good predictor. Phytoplankton are vulnerable to pollution, particularly because of their aptitude to accumulate contaminants. As a result, such a bioaccumulation can impact food webs integrity.

Isochrysis Galbana populations were cultured at 20°C in sterile seawater (at 34 per thousand of salinity). In these conditions, HTS techniques measured cellular lesions responding to a toxic agent, permitting here to measure the potential impacts of ENPs on organisms. 

Four HTS tests were undertaken (based on the mitochondrial membrane potential, ROS occurence, (3) cellular efflux pump action and cell membranes permeability). These tests are based on fluorescence and cell health. The impact of metallic nanoparticles was also measured. However, the results obtained were not consistent enough to highlight responses to ENP exposure:

Non-HTS tests were performed by the measurement of the impact on photosynthetic efficiency. The metal concentrations were measured using the graphite furnace atomic absorption.

Fluorescence kinetics of chlorophyll was also measured with an amplitude modulated pulsed fluorometer. Then the maximum fluorescence yield was computed using WinControl Software. This  the maximum fluorescence variation is assumed to be a measurement of the potential quantum yield of the PSII.

A clear decrease in the performance of the PSII was observed for all the ENP’s:

  1. A greater decrease was observed for ZnO
  2. Also, a notable decrease was measured for CuO, at low concentrations
  3. Finally, the presence CeO and Ag decreased the performances as well even though the decrease was the smoothest.

According to the authors, these results linked with the different dissolution rates that are specific to each compound. In this direction, Zn has a high dissolution rate, CuO and Ag dissolve very slowly and CeO has an undetectable dissolution rate. 

As a conclusion by the authors, HTS methods can not be used to measure the impacts of metal particles because of their poor predictive power. So far, traditional ecotoxicological methods must be used.

With such results in mind, we also agree on this statement: the four tests led by the authors all brought different conclusions. As HTS methods rely on the affinity of biological structures which is often related to toxicity to be defined, the presence of cellular compensatory mechanisms could have masked cellular responses to ENPs expositions.

In conclusion, although HTS methods offer promising opportunities in the biological sciences (such as ecotoxicology), there are need for further investigation in this area before these techniques can be commonly adopted and used.

Cited study: Miller, Robert J., et al. (2016) Photosynthetic efficiency predicts toxic effects of metal nanomaterials in phytoplankton, Aquatic toxicology 183, 85-93.

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