Chemical pollution and the cocktail effect: a path towards toxicological testing without animal experiments

Here's an image showing mitochondria in pink: these are the lungs and "energy plants" that enable cells (in green, with their nuclei in blue) to breathe, live and perform their functions.

Abdel Aouacheria, University of Montpellier

In healthy cells on the left, mitochondria are rather long and interconnected, like a road network seen from the sky; whereas in stressed and damaged cells on the right, their network is shattered into a constellation of solitary mitochondria, which produce less energy and will eventually precipitate the cells down the path to suicide.

Mitochondria are a good barometer of the health of our cells, with the architecture of their networks even varying in tissues from diseased individuals. Thanks to real-timeconfocal imaging, using high-content imaging robots in particular, we can reveal in less than a second the contours of a living cell, its nucleus and unique "organelles" (elements of a cell that perform specific functions, such as mitochondria), in order to study the effects of different pollutants on cells and their health.

Rapid imaging of mitochondria as an environmental health "early warning system

Air, water and food contamination, soil and noise pollution: measuring the impact of environmental risks on the health of organisms and ecosystems is no easy task.

The images generated by the imaging platforms are computer-processed to provide valuable information on the effects of the many pollutants that surround us.

It's a step forward in deciphering the "exposome", a concept introduced by British scientist Christopher Paul Wild in 2005 and defined as the totality of exposures to which an individual is subjected throughout his or her life (from conception to death).

Pollution outside (air, water, soil) and inside (home, office, car) not only has a negative impact on our health (with the onset of chronic illnesses) and that of ecosystems (with an unprecedented drop in biodiversity and agricultural yields), but also a huge socio-economic cost.

One in six deaths is attributable to it every year, three times more than AIDS, tuberculosis and malaria combined. Moreover, we are constantly evolving in a "chemosphere" (a mixture of substances) whose risks are very poorly understood: epidemiologists and toxicologists have only been able to assess the toxicity of a tiny fraction of the 350,000 chemicals registered since the 1960s in the main national and regional chemical inventories (for production and commercial use).

The health and ecological impact of these compounds, which are likely to jeopardize the integrity of the Earth system, remains poorly characterized when studied separately. What's more, their potential "cocktail effects" (the effects resulting from exposure to several substances at the same time, which are sometimes more deleterious than "simple" exposure) are almost never tested, for lack of ad hoc technologies.

How can we translate the reality of these multiple exposures at the cellular level of an organism?

A new generation of non-animal toxicological tests

This is where mitochondria come into their own. Fragmentation of mitochondria and the mitochondrial network is an early reflection of their loss of functionality, and thus a marker of environmental danger.

The principle of the method consists in painting (with vital dyes) the mitochondria and other constituents of cells cultivated in vitro. The latter are primary human cells, or cell lines, of various tissue origins (skin, lung, kidney, intestine, for example), which will be exposed to toxic substances found in our environment, such as pesticides or fine particles. There's no need to sacrifice an animal for each experiment.

Using software, a battery of parameters is calculated from confocal microscopy images: mitochondrial size, circularity and degree of connectivity are just some of the hundred or so possible descriptors that can be used to highlight the deleterious effect of toxic substances, alone or in combination (cocktail effect).

The aim is to link molecular initiating events, such as exposure to these chemicals, with harmfulness or toxicity, at different biological scales, from cells, tissues and organs to individuals. If mitochondria connect toxicities and alterations expressed at the microscopic scale (cells) and adverse effects and pathologies observed at the tissue scale, the uncertainty concerns the extrapolation of toxicological data obtained in vitro to possible effects on organisms and ecosystems.

Ultimately, this system could also be used to identify ingredients capable of protecting or restoring the "mitochondriomes" (the mitochondria) of cells exposed to pollutants.

Abdel Aouacheria, Biologist, CNRS research fellow, specialist in cell life and death, University of Montpellier

This article is republished from The Conversation under a Creative Commons license. Read theoriginal article.