Pollutants in fish may inhibit our natural defence system

Environmental pollutants found in fish may obstruct the human body's natural defence system to expel harmful toxins, a new study has warned.

This information should be used to better assess the human health risks from eating contaminated seafood, according to researchers at the University of California - San Diego.

A protein found in cells of nearly all plants and animals, called P-gp, acts as the cell's bouncer by expelling foreign chemicals from the body.

P-gp is well known for its ability to transport therapeutic drugs out of cancer cells and, in some cases, rendering these cells resistant to multiple drugs at once.

To determine how effective P-gp is at ridding cells of industrial and agricultural pollutants found in seafood, collectively known as persistent organic pollutants (POPs), the research team conducted a biochemical analysis of P-gp proteins from humans and mice against POPs.

The scientists focused on POPs most commonly found in human blood and urine, and also detected in the muscle tissues of wild-caught yellow-fin tuna. The pollutants included older "legacy" compounds such as the pesticide DDT as well as newer industrial chemicals, such as flame retardants.

The researchers discovered that all 10 pollutants interfered with the ability of P-gp to protect cells.

The study was also the first to show how one of the 10 pollutants, PBDE-100, commonly used as a flame retardant in upholstery foam and plastics, binds to the transporter protein.

The POP binds to the protein in a similar way as chemotherapeutics and other drugs, but instead of being transported out of the cell, the bound POP ultimately inhibits the protein's ability to perform its defence function.

"When we eat contaminated fish, we could be reducing the effectiveness of this critical defence system in our bodies," said Amro Hamdoun, an associate professor at Scripps Institution of Oceanography, and lead author of the study.

The researchers point out that newborns and fish larvae are two of the most vulnerable populations. Newborns are particularly vulnerable since they are exposed to high concentrations of POPs in breast milk, and have low amounts of the protective P-gp protein.

Fish larvae may be at increased risk since the accumulation of pollutants may slow down the animal's defence system to combat other marine pollutants, such as oil hydrocarbons encountered at oil spill sites.

"We show that these inhibitors are found in the fish we eat," said Scripps postdoctoral researcher Sascha Nicklisch.

The researchers suggest that environmental chemicals should be tested to determine if they impede the effectiveness of the body's natural defence system to expel these, and other foreign chemicals. The study was published in the journal Science Advances.