High mercury levels attributed to particular cell types in mammalian brains

Exposure to mercury (Hg) is extremely neurotoxic in most chemical forms. Even scientists who study mercury compounds are at risk due to their potential exposure to Hg. Famous physicist Michael Faraday suffered from mercury poisoning from prolonged exposure to mercury vapor, leading him to to interrupt his research at the age of 49 due to the deterioration of his health. Another example is that of laboratory chemist Karen Wetterhahn, who was killed by dimethylmercury poisoning after a few drops escaped from a pipette and fell on one of her latex-gloved hands.

Many studies have focused on Hg exposure and effects, particularly in marine and marine creatures. It is well known that people should limit the consumption of certain fish, such as tuna, due to the presence of mercury. However, the question arises: can mercury ions reach the brains of land animals?

Dr. Yulia Pushkar, a professor of physics and astronomy at Purdue University’s College of Science, was initially skeptical. She has maintained a brain imaging program since 2008 at Purdue University. His group, with expertise in sample preparation, measurements and data analysis, is sought after by researchers in the United States and around the world, including those in Japan and more recently Australia.

Pushkar’s research group was tasked with checking the presence of Hg in the brains of mongooses collected from the island of Okinawa. Surprisingly, brain scans revealed the presence of mercury in these invasive animals. The research group refined the scans, reaching a resolution of a few tens of nanometers to observe affected brain cells. Their collaborative results were recently published in Environmental Chemistry Letters.

The mystery of how mercury gets into the mongoose’s brain remains unsolved. Possible sources include the water they drink, the bird eggs they consume, exposure to minerals, or even the air they breathe. One thing is very clear, however: this is a very bad sign.

“Hg is very toxic at low concentrations, because it can bind to and affect the function of essential biomolecules,” explains Pushkar. “The effectiveness of detoxification will depend on the constant absorption and binding inside the detected accumulations and the potential leakage of these if the brain cells die. At present, there is no way known to safely dissolve these aggregates from tissues and there are no reports of reversal of Hg poisoning. neuronal system. The main approach we should all take is to avoid all exposure, in particularly chronic exposures as in the case of Faraday.

“I was skeptical that mercury could be detected. Usually, neurotoxic elements, even if they enter the brain, are present in extremely low concentrations,” says Pushkar. “We took these specimens to the Advanced Photon Source at Argonne National Laboratory, where the brains were exposed to intense X-rays. Defying my skepticism, the Hg signal was present.”

By analyzing brain samples, researchers began to trace areas of the brain that appeared to have higher Hg content. After three years of study and five trips to two national synchrotron facilities (Advanced Photon Source at Argonne National Laboratory and NSLS-II at Brookhaven National Laboratory), researchers can now report that particular brain cells: cells of the choroid plexus (forming the blood barrier to the cerebrospinal fluid) and astrocytes in the subventricular zone contain puncta rich in Hg (size of approximately 0.5 to 2 microns).

Pushkar’s team of researchers believe these cells help filter Hg from blood and brain tissue and store it with the help of another element, selenium (Se). It remains to be discovered which particular biological molecules containing Hg bind Hg.

Pushkar’s team for this publication consisted of Pavani Devabathini and Gabriel Bury (both graduate students) and Darrell Fischer, then an undergraduate (now at Harvard Graduate School). The data was collected by the entire team and analyzed by Devabathini and Fischer. Once the data was analyzed, the entire team contributed to the writing of the publication.

This discovery is important for environmental monitoring of terrestrial animals and provides new tools for tracing Hg in brain cells, which could impact human health and safety.

“Human activities result in the emission of 2,000 tonnes of mercury compounds per year and we don’t really understand where all this neurotoxic mercury ends up,” says Pushkar. “So far, most studies have focused on marine biota (fish and whales), but apparently terrestrial species are also affected. We expect the human brain to respond to Hg in the same way via interactions with choroid plexus cells and astrocytes. However, we do not know whether the human brain has sufficient Se-containing biomolecules to bind Hg.”