Some fish have adapted to survive high levels of pollution, but these adaptations may lead to other effects in the fish population, according to Nishad Jayasundara, Ph.D., winner of the 2015 Karen Wetterhahn Award, in a Nov. 28 lecture at NIEHS.
“My work is at the nexus of ecological and human health,” said Jayasundara, who also presented at the 2015 Superfund Research Program (SRP) Annual Meeting. “The goal is to learn about mechanisms of toxicity by focusing on organisms that have evolved adaptations to resist the harmful effects of various pollutants.”
Each year, the SRP Karen Wetterhahn Award winner receives support to give a lecture at NIEHS and meet with senior staff. Jayasundara, a postdoctoral fellow at Duke University, provided an overview of his work, including recent findings and next steps in his research.
Uncovering mechanisms involved in adaptation
Under the guidance of Duke SRP Center project leader Richard Di Giulio, Ph.D., Jayasundara studies killifish in the Elizabeth River, near the Atlantic Wood Industries Superfund site in Portsmouth, Virginia.
Through decades of long-term exposure, these fish have become resistant to polycyclic aromatic hydrocarbons (PAHs), chemical pollutants resulting from various activities, including incomplete fuel combustion. He pairs studies on wild fish with laboratory studies in zebrafish, a model organism, to better understand the mechanisms involved in the changes that allowed the killifish to adapt to a heavily polluted river.
Jayasundara integrates his understanding of fish physiology with other approaches, such as genomics and transcriptomics, which is the study of all messenger RNA molecules in a cell. He studies how the fish respond to stressors and changes in their biological processes that occur as they develop resistance to the toxic effects of pollution.
His is specifically studying potential metabolic consequences of rapid adaptation. He found that at some river temperatures, fish from the Elizabeth River had the capacity for aerobic activity comparable to wild fish. However, he observed a significantly reduced capacity at a higher temperature of approximately 93 degrees Fahrenheit, a typical summer temperature. Jayasundara developed a high-throughput method that uses the oxygen consumption rate in whole fish hearts as a way to measure the fish’s aerobic capacity.
“Although fish in the Elizabeth River have the capacity to adapt to a contaminated environment, it comes at a cost, such as reduced capacity for aerobic activity in higher temperatures,” said Jayasundara. “We are investigating how the aryl hydrocarbon receptor [AHR], a protein involved in regulating a number of biological responses, may play a role in this process, by both mediating PAH toxicity and regulating mitochondrial function.”
Emphasis on chemical mixtures
Jayasundara performed other studies to determine how AHR is involved in PAH toxicity and adaptive responses to PAH mixtures. In zebrafish exposed to PAHs, he observed cardiac effects that were dependent on AHR and mediated, at least in part, through changes in calcium levels. He saw this effect from exposure to a mixture of the PAHs fluoranthene and benzo(a)pyrene, but not from exposure to each PAH alone.
“To truly understand the environmental impacts, it is extremely important to consider chemical mixtures when studying the mechanisms of toxicity, instead of only looking at individual chemical components,” Jayasundara said.
Creating research and training opportunities
“Nishad is not only dedicated to environmental health research, he also has a passion for mentoring students and creating opportunities for others,” said SRP Director Bill Suk, Ph.D., who introduced Jayasundara.
A native of Sri Lanka, Jayasundara is taking his expertise back to his native country. He is setting up a zebrafish research facility in Sri Lanka to investigate the potential toxicity of chemical mixtures in the region. He hopes zebrafish, which are native to South Asia, will help him begin to understand how dramatic changes in the environment in Sri Lanka and rest of the region may be affecting the ecosystem and human health. Jayasundara also co-founded SL2College, a platform to help students in Sri Lanka access information about applying for higher education opportunities abroad.
Jayasundara N, Van Tiem Garner L, Meyer JN, Erwin KN, Di Giulio RT. 2014. AHR2-Mediated transcriptomic responses underlying the synergistic cardiac developmental toxicity of PAHs. Toxicol Sci 143(2):469−481.
Jayasundara N, Kozal JS, Arnold MC, Chan SS, Di Giulio RT. 2015. High-throughput tissue bioenergetics analysis reveals identical metabolic allometric scaling for teleost hearts and whole organisms. PLoS One 10(9):e0137710.
(Sara Mishamandani Amolegbe is a research and communication specialist for MDB Inc., a contractor for the NIEHS Division of Extramural Research and Training.)