The following is a fish story. No, not the big one that got away. This is about the role fish play in helping scientists at Oregon State University understand how substances in the environment and in the foods we eat affect our health. It's a story about cancer, pollution, growing old, chemical weapons-and how fish are providing scientists with insights into these complex issues.
The fish and the scientists are part of the OSU Marine/Freshwater Biomedical Sciences Center, one of five such centers in the United States that use aquatic models-fish-to investigate human health problems.
Consider the rainbow trout, Onchoryhncus mykiss, a finned wonder at the heart of research on the connection between diet and cancer at the center. The center's off-campus Aquatic Core Facility east of Corvallis houses a trout hatchery.
"The particular rainbow we use, the Shasta strain, is extremely sensitive to many compounds in the environment, including those that cause cancer. And they can be more like humans in a few ways than mammals used in research," said George Bailey, an OSU food scientist who is the center's director.
A major emphasis in cancer research at the center has been on foods we eat that may prevent or inhibit the cancer process. To understand the center's research on cancer, you have to know about aflatoxin, a potent cancer-causing substance found in molds that grow on improperly stored grains and nuts. Aflatoxin causes liver tumors within a few months in rainbow trout and has been found to cause cancer in the liver, kidneys and lungs of rats, dogs, pigs and cattle. It is considered to be a likely cause of liver cancer in humans who eat aflatoxin-contaminated food.
"In the United States, storage of grains and nuts is controlled to reduce the occurrence of aflatoxins. But in developing countries, you find a high rate of liver cancer among populations that regularly eat moldy corn and peanuts," Bailey said.
Research at the center has identified compounds in vegetables that inhibit the development of cancer in rainbow trout exposed to aflatoxin. One of those compounds, indole-3-carbinol, held peril as well as promise.
"Indole-3-carbinol was very protective when given to trout before or during the time they were exposed to aflatoxin. But in trout that already had cancer, it actually promoted the growth and spread of existing tumors," Bailey said.
Recently, Bailey and two colleagues-Jerry Hendricks, a pathologist, and Dave Williams, a biochemist-demonstrated that a derivative of chlorophyll, the common green plant pigment, prevented cancer from forming in trout that had been exposed to aflatoxin. The researchers theorized that the interaction between chlorophyll and aflatoxin in the stomach blocked the uptake of aflatoxin in the tissue.
Moreover, unlike indole-3-carbinol, chlorophyll did not affect pre-existing cancer in the trout. "This finding raises the possibility that chlorophyll might be promising for use in humans," Bailey said.
Last summer, Bailey and his colleagues got a chance to find out. In a cooperative project with Johns Hopkins University, where similar research was conducted with rats, they began clinical trials in China's Qidong Province. Moldy corn and grain is a regular part of the diet in the province and there is a high rate of liver cancer among the population.
If the Chinese trial provides positive results, Bailey sees it leading to a cheap and practical way of reducing liver cancer in developing countries. And even though aflatoxin exposure is not a significant concern in the United States, the outcome of this research may have benefits here. The same mechanism will work for some cancer-causing agents in addition to aflatoxins, Bailey explained. For example, carcinogens in charcoal-broiled meat.
"We may need to eat a lot more spinach with our hamburgers," Bailey said.
A note of caution. Few of the plant compounds investigated so far have been shown to cause remission of existing cancer. "The compounds in vegetables, called phytochemicals because they come from plants, are best at stopping cancer before it starts," said Jerry Hendricks, center researcher and director of the Aquatic Core Facility.
OSU's Marine/Freshwater Biomedical Sciences Center evolved out of research that led to the discovery of aflatoxin. In 1962, a die-off occurred among hatchery trout in the Northwest and turkeys in England. Russell Sinnhuber, now a retired OSU professor of food science and technology, determined that the trout had liver cancer and traced the cause to moldy cottonseed meal in trout feed. In England, scientists traced the cause of liver tumors in the turkeys to moldy peanut meal.
Aflatoxin was isolated from fungi on the cottonseed and peanut meal. Sinnhuber fed aflatoxin to his trout and told a newspaper reporter at the time, "Aflatoxin is so potent that less than 1 part per billion can cause cancer in a rainbow." Sinnhuber realized that the trout's extreme sensitivity to aflatoxin made it an excellent model for cancer research.
Construction of the hatchery that is now the Aquatic Core Facility began in 1965. It is the only trout hatchery in the world devoted to research on cancer and owes its uniqueness to an aquifer that supplies an abundance of pure, cold water. "Trout require a lot of clean water, which you don't find in many places outside the Willamette Valley. You couldn't have a facility like this in, say, New York or Seattle," Bailey said.
Sinnhuber went on to develop a method to measure levels of aflatoxin in human foods as well as animal feed. The method is still widely used-for instance, in a 1989 outbreak of aflatoxin in corn in the Midwest and to verify the reliability of a procedure used in the Southwest to eliminate aflatoxin in dairy cow feed.
Research at the center has also addressed issues other than the human diet. For example, the center contributed to a 1991 study of dioxin contamination and fish health in the Willamette River. "This study influenced subsequent waterway management decisions related to point source pollution and water discharge permits," Bailey said.
More recent research by Dave Williams found that a product touted for its health benefits may actually be a threat. Dehydroepiandrosterone is hardly a household word, but under its more commonly known name, DHEA, this steroid hormone is widely sold as a dietary supplement. Advocates claim that it slows the aging process, prevents cancer and Alzheimer's disease, elevates mood, increases energy and heightens sexual desire.
Whether DHEA can do those things, it is a proven promoter of liver tumors and cancer, Williams explained. Experiments with rats were dismissed by some because the process by which DHEA causes tumors in rats does not apply to humans.
However, in experiments with trout, Williams found that DHEA, when fed for only a few months, caused liver cancer at 20-fold lower doses than in rats. Furthermore, the mechanism by which DHEA causes liver cancer in trout is relevant to humans, which led Williams to conclude that the potential benefits of DHEA can be overshadowed by an unacceptable risk.
"If you're over 60 years old and taking, say, 10 to 25 milligrams a day, the risk is probably minimal," said Williams. "My real concern is with people under age 60 who may be tempted to take higher doses over a number of years. With long-term exposure, the risk of liver damage and cancer is significantly higher. And in all cases, people should take DHEA only under the supervision of a medical doctor and have their liver function checked regularly."
Xeno-or foreign-estrogens are another source of environmental concern. These estrogens are not naturally present in the environment. Rather, they come from such unlikely sources as birth control pills. Excreted in the urine, estrogen passes unaffected through the sewage purification process directly into streams.
Xenoestrogens are one of a group of chemicals, referred to as endocrine disrupters, that mimic or interfere with the actions of hormones and impair normal growth, development and reproduction. Endocrine disrupters include pesticides, such as DDT; industrial chemicals, such as PCBs; drugs, such as DES; and contaminants, such as dioxins.
These chemicals have been linked with several disturbing phenomena, including:
-A worldwide decline in the quality of sperm among human males during the last 30 years.
-An increase in breast cancer in women associated with PCB residues.
- Birth defects and reproductive failures in alligators in Florida, and trout and cormorants in the Great Lakes.
Concern about these and similar incidents led to federal legislation requiring a listing of chemicals that interfere with the endocrine system in humans and wildlife. The center became involved with endocrine disrupters because many chemicals that create tumors in trout also affect the endocrine system. In addition, trout are extremely sensitive to xenoestrogens in the environment, said Williams, whose research on these substances is in its early stages.
With the arrival of Phil McFadden in 1990, the OSU center branched into another area of environmental concern-neurotoxins, or substances that damage the nervous system. One substance under investigation, Sarin, a nerve gas linked to health problems of Gulf War veterans, is stored-and awaiting disposal-at the Umatilla Army Depot.
The movement of nutrients in nerve cells, or neurons, holds the key to understanding how nerve gases and other environmental chemicals affect the nervous system. "Nerve cells are very long. For instance, one will stretch from the backbone to the fingertips. If it is not properly nourished, the tips of the nerve cell will starve," said McFadden, a member of the OSU Department of Biochemistry and Biophysics.
Nutrients travel slowly in nerve cells, he explained, taking a week to travel from the shoulder to the fingertip. Any interruption of the nutrient flow, such as by a compound in the environment, damages or destroys the nerve.
To study the flow of nutrients, McFadden turned to fish as a model system that is similar to humans. He has perfected a technique that involves rapid color changes in fish cells. "Color materials move through these fish cells in the same way that nutrients are transported through human nerve cells," McFadden said.
Rather than trout, McFadden uses warm water species-jewel cichlids, bluegills, sunfish, crappie-in his research. The scales of warm water fish survive for weeks in a petri dish with little care and specimens can be sent through the mail, making them convenient for field testing.
Nerve gas agents have a dramatic effect on fish cells, says McFadden. The Army's decision to destroy the chemical weapons at the Oregon depot has generated controversy and opposition. Although the ultimate fate of the nerve gas at Umatilla won't be decided solely in terms of science, the center's research capability can provide objective, reliable information to aid in the decision.
"The decision to destroy them needs to be as rational as possible and based on knowledge of the effects these nerve agents have on the environment," McFadden said.
Such real world applications of research have been an essential feature of the center since it began. For scientists, whose main aim is the pursuit of knowledge and whose work often remains obscure, these practical outcomes are a satisfying bonus, an unsought reward, like a composer whose symphony gets a public performance.
For the broader public, which enjoys the immediate benefits, the center's fish story is one of amazing connections between seemingly unrelated things. Trout, moldy cottonseed, cancer, a burst of color across a fish scale, harmful substances in the environment. It is a story about sickness and health, about life and death, and one just beginning to unfold.