Canadian scientists have found that methylmercury directly affect vision by accumulating in the retinal photoreceptors, i.e. the cells that respond to light in our eyes.
More than one billion people worldwide rely on fish as an important source of animal protein, states the United Nations Food and Agriculture Organization. And while fish provide slightly over 7 per cent of animal protein in North America, in Asia they represent about 23 per cent of consumption.
Humans consume low levels of methylmercury by eating fish and seafood. Methylmercury compounds specifically target the central nervous system, and among the many effects of their exposure are visual disturbances.The new study:
Visual disturbances related to mercury intoxication were previously
thought to be solely due to methylmercury-induced damage to the brain
visual cortex. However, after combining powerful synchrotron X-rays and
methylmercury-poisoned zebrafish larvae, scientists have found that
methylmercury may also directly affect vision by accumulating in the
retinal photoreceptors, i.e. the cells that respond to light in our
Dr. Gosia Korbas, BioXAS staff scientist at the Canadian Light
Source (CLS), says the results of this experiment show quite clearly
that methylmercury localizes in the part of the photoreceptor cell
called the outer segment, where the visual pigments that absorb light
This cross-section of a zebrafish eye shows the localization of mercury in the outer segments of photoreceptor cells.
Credit: Malgorzata Korbas, Barry Lai, Stefan Vogt, Sophie-Charlotte
Gleber, Chithra Karunakaran, Ingrid J. Pickering, Patrick H. Krone, and
Graham N. George.)
"There are many reports of people affected by methylmercury claiming a constricted field of vision or abnormal colour vision," said Korbas. "Now we know that one of the reasons for their symptoms may be that methylmercury directly targets photoreceptors in the retina."
Korbas and the team of researchers from the University of Saskatchewan including Profs. Graham George, Patrick Krone and Ingrid Pickering conducted their experiments using three X-ray fluorescence imaging beamlines (2-ID-D, 2-ID-E and 20-ID-B) at the Advanced Photon Source, Argonne National Laboratory near Chicago, US, as well as the scanning X-ray transmission beamline (STXM) at the Canadian Light Source in Saskatoon, Canada.
After exposing zebrafish larvae to methylmercury chloride in water, the team was able to obtain high-resolution maps of elemental distributions, and pinpoint the localization of mercury in the outer segments of photoreceptor cells in both the retina and pineal gland of zebrafish specimens. The results of the research were published in ACS Chemical Biology under the title “Methylmercury Targets Photoreceptor Outer Segments”.
Korbas said zebrafish are an excellent model for investigating the mechanisms of heavy metal toxicity in developing vertebrates. One of the reasons for that is their high degree of correlation with mammals. Recent studies have demonstrated that about 70 per cent of protein-coding human genes have their counterparts in zebrafish, and 84 per cent of genes linked to human diseases can be found in zebrafish.
“Researchers are studying the potential effects of low level chronic exposure to methylmercury, which is of global concern due to methylmercury presence in fish, but the message that I want to get across is that such exposures may negatively affect vision. Our study clearly shows that we need more research into the direct effects of methylmercury on the eye,” Korbas concluded.
Source: Adapted from Canadian Light Source, Inc. The cited new study
Malgorzata Korbas, Barry Lai, Stefan Vogt, Sophie-Charlotte Gleber, Chithra Karunakaran, Ingrid J. Pickering, Patrick H. Krone, Graham N. George, Methylmercury Targets Photoreceptor Outer Segments
, ACS Chem. Biol., 2013, DOI: 10.1021/cb4004805 Related studies
Myriam Fillion, Mélanie Lemire, Aline Philibert, Benoît Frenette, Hope Alberta Weiler, Jason Robert Deguire, Jean Remy Davée Guimarães, Fabrice Larribe, Fernando Barbosa Jr, Donna Mergler, Toxic risks and nutritional benefits of traditional diet on near visual contrast sensitivity and color vision in the Brazilian Amazon
, NeuroToxicology, 37 (2013) 173–181. doi: 10.1016/j.neuro.2013.04.010
Malgorzata Korbas, Tracy C. MacDonald, Ingrid J. Pickering, Graham N. George, Patrick H. Krone, Chemical Form Matters: Differential Accumulation of Mercury Following Inorganic and Organic Mercury Exposures in Zebrafish Larvae
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last time modified: September 12, 2013