A new study from NYU Abu Dhabi shows that exposure to arsenic — a common compound present naturally in the Earth’s crust that is lethal to those exposed to high levels — causes fatty liver disease in zebrafish exposed to lower levels over a longer period. The findings are supported by another study from researchers at Emory University (USA) that showed arsenic exposure in humans is associated with fatty liver in the American population.
Fatty liver disease, the most common liver disease in the world, is defined by fat accumulation in cells in the liver. This makes the liver vulnerable to other forms of injury, promoting progression to more advanced liver diseases such as cancer or cirrhosis.
Researchers hypothesize that the disease can be caused or accelerated by a combination of factors, such as genetics, dietary habits, and lifestyle choices, which determines who gets the disease and who doesn’t. The study brings to light the role environmental toxicants can play in this cocktail of factors.
Look to the Ground For Answers
Arsenic, along with other environmental toxicants, such as lead, nickel, and zinc, is present in the Earth’s bedrock and soil in varying concentrations throughout the globe. It makes its way into groundwater systems and is usually filtered out according to global safety standards before being deemed safe for public consumption.
“A lot of the toxicants that we all are exposed to are not from any human activity at all— they’re just part of the bedrock, which then makes its way into our drinking water,” said Kirsten Sadler Edepli, associate professor of biology at NYU Abu Dhabi and senior investigator on this study.
Sadler’s research team found that arsenic alone was capable of causing fatty liver disease in zebrafish and “almost all the fish ended up getting sick after four or five days of exposure,” she said.
Did You Know?
We have a lot in common with zebrafish; 84 percent of human genes, that are linked to diseases contracted by humans, have a counterpart in zebrafish, which makes the fish ideal research subjects for these very diseases.
Common genetics aside, zebrafish embryos are transparent and develop outside the mother’s body in water, which makes it easy for biologists to have an unobstructed view of the early stages of development. Hundreds of offspring are reproduced at weekly intervals and the embryos grow rapidly: most organs appear within 36 hours of fertilization. This is very useful as the effects of toxicants introduced in the developmental stages can be observed in less than a week.
While obesity and diabetes are common risk factors for people to develop the disease, there’s a gap in knowledge to explain why seemingly healthy individuals are contracting it.
According to Sadler, most public health research in this area focuses on nutrition and activity levels. But she emphasizes “this isn’t enough” because “we should also be looking into the environmental factors they are being exposed to.”
The study also makes the alarming discovery that combining low doses of arsenic with low doses of alcohol causes severe liver disease in zebrafish, indicating that low levels of a toxicant that has no effect on its own can join forces with low levels of other toxicants to cause liver disease.
“It would be interesting to do an epidemiological study, which is studying the whole population, and see if exposure to environmental toxicants — maybe it's arsenic or something else — could explain the obesity and diabetes epidemic we are experiencing now particularly here in the Gulf,” said Sadler.
The research was led by Kathryn Bambino, a postdoctoral research fellow with the Sadler Edepli Lab and Icahn School of Medicine at Mount Sinai in New York, and was recently published in Disease Models and Mechanisms, an international online biomedical research journal. This study was supported by a grant from the National Institute of Health (USA).