Poison in the fish inhibits cell guards

Organic pollutants block important protective function of the body against chemicals

In fish whole cocktails can be contained from organic pollutants. They are especially enriched in high-fat predatory fish. © Comstock / thinkstock
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Fish with side effects: Organic pollutants contained in food fish can block an important protective function of our body. As researchers discovered, the environmental toxins inhibit the protein that is normally supposed to protect cells against such chemicals. Worrying: Nine out of ten organic pollutants found in tuna show this effect, as the scientists in the journal Science Advances report.

The sins of our past, but also the present catch us: long-lived organic pollutants are not only found in our soils and waters, they have long been enriched in the food chain. As a result, polar bears, marine mammals and fish are already heavily burdened.

Protein as cell guardian

A little-studied effect of long-lived organic pollutants (POPs) has now been detailed by Sascha Nicklisch of the University of California at San Diego and his colleagues. They investigated how these environmental toxins affect a specific protective mechanism of our cells. This consists of a protein in our cell membranes, the P-glycoprotein (P-gp), which acts as a kind of doorkeeper.

"This protein, on the one hand, limits the penetration of foreign chemicals into the cells and the body and, on the other hand, ensures that they are quickly excreted or degraded, " the researchers explain. Earlier observations, however, aroused the suspicion that organic pollutants, including polychlorinated biphenyls (PCBs), DDT, some insecticides and flame retardants based on polybrominated diphenyl ethers (PBDE), circumvent this cell guard.

The P-glycoprotein in the cell membrane serves as a "doorkeeper": it keeps chemicals out there and promotes their excretion. © public domain

Environmental toxins block the guardian

For their study, the researchers first tested the effect of ten common organic pollutants on the Wächter protein in cell cultures. It turned out that instead of reacting to the presence of these potentially harmful chemicals and becoming active, the T rh ter protein remained inactive. display

The reason was an analysis of the molecular processes: it turned out that the pollutants bind to the protein in such a way that they block any further action. Ironically, the molecule that is supposed to protect our cells against the ingress of harmful chemicals is thus put out of operation. "Given the almost ubiquitous spread of these P-gp pollutants, this raises the question of how much we are exposed to them, " say the researchers.

Inhibitors are in the fish

To find out, the scientists first ascertained how much the yellowfin tuna's meat is burdened with the ten most common organic pollutants. "We focused on this fish because it is one of the most consumed fish in the world, " explain Nicklisch and his colleagues.

Proportion of the various organic pollutants found in tuna. Nicklisch et al. / Science Advances

It showed: Nine of the ten previously tested organic pollutants were found in tuna meat in some high concentrations of up to 12 micromoles. "If we eat contaminated fish, we might be wary of the effectiveness of our body's critical protective system, " says study leader Amro Hamdoun of the University of California.

The fatter, the more

Worrying too: the pollutants accumulate mainly in fatty tissues, so other, more greasy fish might be even more polluted. "Our values ​​are remarkable, considering that we have analyzed only lean meat and not greasy parts or fish that could be enriched with even higher levels, " the researchers emphasize.

And there is one more thing to add: "Some heavily polluted fish carry more than one poison and that means an even greater threat, " explains Jacob James of the Waitt Foundation. Because the organic pollutants are combined, the inhibitory effect on the P-glycoprotein can be significantly strengthened, as laboratory tests showed.

Danger for infants?

The consequences of this burden could be felt especially by infants. Because if the mother eats contaminated fish or is exposed to these poisons on the environment, they get into the breast milk, as studies show. "In the process, high POP values ​​can be achieved", the researchers say.

The problem with this is that "newborns in the first few months of life already have only limited activity of these protective proteins, " explain Nicklisch and his colleagues. If this protective function is additionally inhibited by the POPs, this could have health consequences. "We are the only species that can affect whole food chains and habitats, " says James. "That's why we need to be more responsible with potentially harmful environmental chemicals." (Science Advances, 2016; doi: 10.1126 / sciadv.1600001)

(University of California - San Diego, 18.04.2016 - NPO)