MUSC student pioneers lipidomics research in catfish

By Janie Thomas

What do South African crocodiles, sharp-toothed catfish, and humans have in common? They are all, in a sense, exposed to the same effluvia. A research project spearheaded by Theresa Cantu, a doctoral candidate in the Department of Biomedical Sciences at the Medical University of South Carolina (MUSC), aims to collect fat, plasma, and liver samples from fifty to sixty sharp-toothed catfish in her upcoming trip to South Africa. These samples will be brought back to Charleston to form new methods in the lab so that in future collection trips to South Africa the animals will not have to be sacrificed to obtain the samples. Cantu specializes in physiology and pathophysiological processes associated with environmental health.

They need samples from the abundant species of sharp-toothed catfish because the catfish are acting as a sentinel species for the crocodiles living in the same river as the fish. In 2008, more than two hundred crocodiles mysteriously died in the Letaba and Olifants Rivers in Kruger National Park in South Africa. In the subsequent years, crocodiles continued to die, leaving the local and scientific community puzzled. It was found that the crocodiles were suffering from pansteatitis, a disease found only in animals, usually in domesticated cats and agriculture, and is characterized by inflammation of the fat tissue. The crocodiles’ fat was hardening into rubber-like thickness and stripping the animals of the ability to walk. In consequence, these animals died for lack of the ability to physically bring themselves to their food sources.

The presence of this disease in a wild population, specifically a top predator, is alarming. And this isn’t the first time there has been a dramatic die-off of reptiles because of similar health conditions. Several years ago in India, many gharials, a sister species to the crocodile, died because of severe inflammation of the joint tissue, leading to the same problem ultimately killing the South African crocodiles: the inability to get to food. While humans do not contract pansteatitis, they can develop panniculitis, which is the inflammation of the subcutaneous tissue. At the same time as the crocodile die-off, the fish in the rivers were dying, too. This worries Cantu and her team because the people in the community subsist on the river for food (fish), drinking water, bathing, and water to clean. If there is something in the water toxic enough to kill crocodiles and multiple fish species, it is likely that humans are in danger as well.

Researchers are trying to understand the mysterious cause of death and determine if the dangerous toxin or mutation is zoonotic or transmissible to humans. Cantu’s mentor, Louis Guillette, Jr. Ph.D., Director of the Marine Biomedicine & Environmental Sciences Center at MUSC, always says, “If it’s not healthy for the animals, it’s not healthy for the humans.” This statement is the backbone of why they are racing against the clock of the unknown to figure out this mystery before it’s too late for the people.

Cantu is the recipient of one of this year’s trainee travel grants from the MUSC Center for Global Health. This money will assist in funding the trip to South Africa this summer, allowing Cantu and her team to retrieve samples. Sample collection is essential for the success of the project. The tests run on these samples are so sensitive that the scientists need to be present at every step of sample collection so they can take note of any special circumstances (for example, improper storing techniques or impure sample retrieval techniques) present at collection and transportation and document everything. “We have had samples from previous years sent to us, but they weren’t all the same species,” recounted Cantu. “They weren’t all collected in a certain area, and the data sheets weren’t matching up. It was hard to take that interpretation and do something with it to find meaningful results.”

At this point, Cantu cannot predict the kind of results she and her team will find from this trip to “the rainbow nation”, but they are excited to be the first group working on this particular aspect of environment-crocodile-catfish-human interaction. “While we don’t know if these situations or even inflammations are connected in some way, the point we can take from these seemingly similar situations is that die-offs in these polluted areas mean that something strange is happening environmentally,” explained Cantu. “This is why we are using sentinel species; because we don’t want this to get to the point that people are eating these fish or bathing in the water, and then later down the road, dealing with mysterious health problems or even death.” “Crocodiles are a sentinel species for a reason,” Cantu remarked. They are very similar to humans in some regards – in the way they eat, hunt, and they are not migratory; they are always going to live in the same environment. These crocodiles, therefore, create a good model to show how the environment affects health.”Though the early samples were not exactly what the team needed for their project, they were not lacking in benefit. Cantu and her team were able to show proof of concept in their assays because no one had ever produced lipidomics (a mapping out of the fat tissue in an animal) in a wild species before. They plan to create assays of the fat, plasma, and liver of these fish with the National Institutes of Standards and Technology, the oldest government-run physical science laboratory, so they can be used across species, not just on humans and mice samples.

Janie Thomas is an intern in MUSC Center for Global Health