Editor's note: This article on the Duke University Marine Biomedical Sciences Center (MBC) is the fourth in a series that appears intermittently in NIEHS News. The series highlights the activities of Environmental Health Sciences and Marine and Freshwater Biomedical Sciences Centers. The first article in the series appeared in volume 101, number 7.
The mission of the Duke University Marine Biomedical Sciences Center (MBC) is to use marine or freshwater organisms in research and training in the area of environmental health and to develop nonmammalian models and innovative methods for toxicological research. Its primary objective is to increase scientific and public understanding of the molecular mechanisms that underlie adverse environmental effects. The MBC acts as a bridge between the marine science community, the diverse programs of the School of the Environment at Duke University, and the clinical and research arms of the Duke University Medical School community.
Environmental pollution is a problem of increasing concern, one that is tightly linked to increases in world population. Human activities may be perturbing global weather patterns. The mental processes that make us creative and rational human beings can be impaired by toxic metals. We view with alarm the sores and cancers on fish taken from our lakes and oceans, sensing that their diseases forecast our own. There is a heavy reliance on pesticides, and DDT levels in our lakes and streams are rising. The programs at the Marine Biomedical Center (MBC) at Duke University play a role in solving such environmental problems.
Barnacles beware. Research on G-proteins in barnacles may give rise to nontoxic marine paints.
Through its visiting scholar program, feasibility studies, thematic research, and outreach efforts, the MBC encourages research on mechanisms of toxicity. Understanding the complexities of these mechanisms requires knowledge of events that occur at the cellular or molecular level. Marine and freshwater organisms offer many simple and highly appropriate model systems that complement studies on vertebrates. Research using the sea urchin embryos, for example, have taught us about human growth and development. Millions of eggs are generated by a single female sea urchin during spawning, which occurs two or three times a year. The life and further development of the sea urchin is critically dependent on the integrity of the membrane that separates it from its external environment. Studies of sea urchin development have significantly advanced knowledge of how membranes are structured, how they allow access to some substances, exclude others, and the role they play in promoting or inhibiting growth and cellular differentiation. Scientists are also learning more about the way the cell membrane recognizes and responds to chemicals, knowledge that will enhance the ability to deliver medicines and target specific cells for treatment.
A Matter of Choice
Interactive multidisciplinary studies are the hallmark of MBC programs. Through interdisciplinary studies, it has been discovered that some of the metals previously regarded as inert are highly toxic, carcinogenic, or teratogenic in specific circumstances. Studies on the mechanism of toxicity of heavy metals, activated oxygen species, and free radicals are being pursued by MBC. Alternative animal models and new materials are being developed to better explore and prevent toxic environmental effects. The environmental effects of detergents is another area of study at MBC. In terms of molecular toxicity, detergents are not all alike. Although equal in cleaning efficiency, they vary widely in their effect on membrane structure and function. Studies of the relationship between detergent structure and environmental toxicity are in progress.
Interdisciplinary Research
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Walls of wonder. Membranes of sea urchin embryos may hold answers to human development. |
Metal perturbation of development. David McClay studies the mechanisms of cellular differentiation and pattern formation, using sea urchin embryos as a model system. These researchers have recently discovered that nickel can cause developmental abnormalities. The effect of nickel is very specific. If embryos are treated with submillimolar concentrations of nickel during a specific time window, the embryos fail to establish normal dorsal and ventral axes. Most structures normally found in the "dorsal territory" fail to develop in the nickel-treated embryos. This finding has allowed McClay and colleagues to define several signals that operate during development and to explore the factors that influence cellular differentiation and commitment. McClay and colleagues are conducting an MBC-sponsored feasibility study to further clarify the effects of nickel.
Detergent toxicity. Celia Bonaventura and colleagues investigate the effects of various detergents on marine organisms. Results obtained to date show that oil consumption by a marine bacterium, Achromobacter, can be enhanced by adding detergent, probably as a result of increased bioavailability of the oil. At high levels, detergents can prevent bacterial growth by causing membrane disruption. The desirable levels of detergents to use in promoting oil consumption by bacteria vary widely depending on the nature of the detergent.
Although detergents are known to be acutely toxic to most aquatic organisms, little is known about their toxic effects at the cellular and molecular levels. Donovan Bodishbaugh, a doctoral candidate in the Integrated Toxicology Program at MBC, is studying mechanistic aspects of detergent toxicity. In fish, the primary target tissue of detergents is believed to be the gill. Toxicity is being investigated both in vivo and in an in vitro fish-gill model to better understand toxic mechanisms and structure-activity relationships of this diverse group of industrial chemicals. Results to date suggest that in fish and other aquatic animals impaired osmoregulation is an important toxic mechanism for detergents.
Cancers in clams and human health. Results of a feasibility study conducted by Rebecca Van Beneden have led to long-term NIH support for exploration of the links between cancers in clams and humans. Studies by Van Beneden and collaborators showed, for the first time, oncogene activation in a bivalve system. The increased incidence of cancers in clams and increased ovarian tumors in neighboring human populations suggests a common cause, possibly the exposure of both clams and humans to agrichemicals.
Cancer susceptibility in fish. Richard Di Giulio and collaborators are researching the mechanisms of aromatic hydrocarbon metabolism and cancer production, using the channel catfish and the brown bullhead catfish. These two fish share many physiological features and can live in the same environment, yet they show pronounced differences in cancer incidence when exposed to the same environmental pollutants. Microsomes of the bullhead catfish generate sixfold greater reactive oxygen species upon incubation with quinones than microsomes of the channel catfish and the brown bullhead catfish. It appears that the toxicity and mutagenicity of quinones and related environmental pollutants is due largely to their redox cycling and subsequent generation of toxic oxygen species.
Nitric oxide involvement in learning and memory. Using the octopus as an animal model, David Robertson and colleagues have made exciting discoveries that show nitric oxide has a significant role in learning and memory. They found that inhibition of nitric oxide synthase (NOS) prevents tactile learning in the octopus. Animals injected intramuscularly with an NOS inhibitor failed to learn a standard tactile discrimination task that control animals were able to learn. Additional experiments showed that the animals could learn again after the NOS inhibitor had dissipated. This report is the first of such findings in an invertebrate.
Engineered hemoglobins. Joseph Bonaventura leads a research project aimed at biomedical applications of structurally distinct hemoglobins, "sculpted" by site-directed mutagenesis to perform a variety of functions. One aspect of work with engineered hemoglobins concerns possible cancer therapy based on increased oxygen delivery to tumors. Mark Dewhirst, a specialist in hyperthermia and radiation oncology, along with Bonaventura and other MBC participants, is studying ways hemoglobins engineered to act like fish hemoglobins may facilitate oxygen delivery to tumors by changing pH and temperature sensitivity.
Nontoxic antifouling coatings. MBC participants are seeking alternatives to toxic metals to protect submerged surfaces from the adverse effects of biological growth (fouling). Dan Rittschof receives research support from the Office of Naval Research and from paint companies, who share a keen interest in eliminating potent metallic and organic toxicants from marine paints. Most antifouling coatings contain slow-release toxicants, either organotins or copper compounds. Increasingly, these coatings are being banned. Rittschof and colleagues are finding natural products that can be economically used as alternatives.
Progress is also being made in defining the systems that trigger larval settlement, an essential part of the fouling process. A collaborative effort between Anthony Clare, Stephen Liggett, and Ronald Thomas involves potential G-protein-coupled receptors of barnacles. The G-protein-coupled receptors, which have important roles in humans, may be significant in triggering barnacle settlement. Results of these studies suggest that paints can be made that block the barnacle settlement system.
Metals and bioremediation. Metals and chelation effects may prove to have an important role in environmental management and environmental bioremediation. Richard Barber and other oceanographers are considering recent data that suggest oceanic phytoplankton growth can be increased by increasing iron availability. The complexation of iron with organic or inorganic materials is an important factor in iron bioavailability. From another perspective, studies in the laboratory of Alvin Crumbliss have drawn attention to the use of iron by microbes in the soil and in our bodies. Iron is acquired by microbial organisms by the excretion of iron-specific complexing agents known as siderophores. Crumbliss and colleagues have studied the kinetics and mechanisms of ligand-exchange reactions with iron complexes that are relevant to microbial iron transport. They have shown that metallic environmental pollutants such as aluminum can interfere with normal iron transport processes.
The MBC director, Celia Bonaventura, invites inquiries regarding the projects described above, potential animal models, or other aspects of the MBC. For more information or to receive the Center's newsletter, ENVIRONS, write to MBC, Duke University School of the Environment Marine Laboratory, 135 Duke Marine Lab Road, Beaufort, NC 28516-9721.
The Duke University
Marine Biomedical Center
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Overlooking North Carolina's Crystal Coast, the Marine and Freshwater Biomedical Sciences Center (MBC) is located on Pivers Island, adjacent to historic Beaufort. The MBC was founded in 1978 through a competitive grant provided by the NIEHS. Administrative offices and research facilities are housed within the Duke University School of the Environment Marine Laboratory.
MISSION
The mission of the MBC is to promote the use of marine and freshwater organisms in research and training in environmental health and to develop nonmammalian models and other innovative methods for toxicological research.
OBJECTIVES
The MBC's primary objective is to understand the mechanisms that underlie adverse environmental health effects. MBC programs promote research and communication in the areas of toxicology of metals and free radicals, developmental toxicology and carcinogenesis, and environmental toxicology and chemistry.
SUPPORT
Funding support is provided in the areas of technical assistance, feasibility grants, visiting scholars; meetings, seminars, and workshops; and equipment and facilities. |
Cyanide Exposure May Affect the Brain
Moderate, chronic exposure to cyanide, a commonly used industrial compound, may cause cellular damage and lesions to the brain, characteristic of what might be seen in Parkinson's disease, animal studies supported by the NIEHS reveal. Cyanide is regularly used in the metal-processing industry. It is also present in cigarettes, as well as in the pits of apples, peaches, and apricots, but it is thought that the amounts of cyanide in these substances are generally too low to cause harm.
However, some industrial workers are typically exposed to cyanide on a regular, sustained basis, and some experts suspect this could alter brain function. Evidence from early animal studies suggest it may cause a loss of key brain chemicals.
Gary Isom and colleagues at Purdue University treated mice with moderate doses of cyanide twice a day for a week. Sixteen hours after the last dose was given, various measures of brain chemicals, blood, and behavior were taken and compared to the same measures in control mice. The researchers found that dopamine levels were significantly depleted in the treated mice due to a loss of brain cells. In some parts of the brain, dopamine levels declined by as much as 41%. Such changes did not occur in the controls.
Dopamine is a neurotransmitter that helps regulate movement. Accordingly, mice treated with cyanide for longer periods of time experienced noticeable motor control deficits, such as incoordination. These effects were not seen in mice only briefly exposed to the agent.
The mobility impairment seen in the cyanide-treated mice mimics, in part, some symptoms seen in Parkinson's disease, leading the researchers to speculate that chronic exposure to elevated levels of cyanide may be a health hazard.
Validation of Alternative Methods
The NIEHS has established an ad hoc committee of staff from federal agencies that generate or use toxicity data for regulatory decisions. The committee will join the NIEHS in meeting the directive of the NIH Revitalization Act of 1993 to establish criteria for the validation and regulatory acceptance of alternative testing methods and to recommend a process through which scientifically validated alternative methods can be accepted for regulatory use. The panel has been designated the Interagency Coordinating Committee on the Validation of Alternative Methods, or ICCVAM.
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William S. Stokes |
In addition to the NIEHS, twelve other federal research and regulatory agencies have been invited to participate, including ATSDR, FDA, NIOSH and OSHA. The first meeting of the committee was in September, and it is anticipated that the group will meet monthly until completion of guidelines and recommendations on alternative methods.
William Stokes, a veterinarian on the NIEHS staff assigned to the alternative methods effort, noted that alternative methods, models, and approaches reduce the total number of animals required, incorporate refinements which result in the lessening of pain and distress to animals, and replace animals with nonanimal systems or replace one animal species with another, particularly if the substituted species is nonmammalian or invertebrate. "The vast majority of proposed new testing methods, both animal and nonanimal, usually involve some aspect of refinement, reduction, or replacement," Stokes said.
The committee's objective will be to develop uniform processes and criteria that will encourage the development of improved testing methods that will generate data more useful for risk assessment--lead to the scientific evaluation/validation of new alternative test methods, and increase the likelihood of regulatory acceptance of scientifically valid alternative test methods.
Mechanism-based Toxicology
Researchers, regulators, and legislators will come together to look at issues and implications of using mechanism-based toxicology in cancer risk assessment at a workshop sponsored by the National Toxicology Program. The workshop, titled "Mechanism-based Toxicology in Cancer Risk Assessment: Implications for Research, Regulation, and Legislation" will be held January 11-13 in Chapel Hill, North Carolina.
Emerging tools and insights into the carcinogenic process provided by molecular biology offer great promise in complementing and improving traditional approaches in toxicity testing and in strengthening the scientific foundation on which risk assessments are based. The workshop goals are to assess the scientific foundation for using mechanism-based risk toxicology to address critical issues in risk assessment, to identify and propose solutions to the regulatory problems which may emerge from the use of mechanistic toxicology, and to determine the applicability of mechanism-based toxicology and risk assessment to current legislative issues.The members of the plenary session, "Defining Scientific, Regulatory, and Legislative Issues," will be: Kenneth Olden, director,NTP and NIEHS; Lynn Goldman, assistant director, EPA; Bernard Schwetz, director, NCTR,FDA; Mark Schaefer, assistant director for environment, OSTP; Richard Jackson, director, NCEH, CDC; Linda Rosenstock, director, NIOSH; George Lucier, director, ETP, NIEHS; Carl Barrett, director, ECP, NIEHS; and Ray Tennant, ECP, NIEHS. The following five discussion groups will be presented:
* Mechanism-based toxicology for screening chemicals and for setting priorities for carcinogen testing: Linda Birnbaum, U.S. EPA, Marilyn Wind, U.S. Consumer Product Safety Commission, co-chairs. The focus of this discussion group will be on strategies developing rational approaches for identifying agents that should be further evaluated and testing classes of chemicals that share common structural or biological properties. Alternative or flexible designs of bioassays to test hypothesis that will impact on our understanding of the hazards of a series of chemicals/compounds are an important aspect of this discussion group. Included are alternative test systems, human epidemiological studies, and ecotoxicological studies. Short-term, mechanistic-based approaches to testing mixtures of chemicals are also relevant.
* Mechanism-based toxicology in carcinogen hazard identification: Hiroshi Yamasaki, International Agency for Research on Cancer, William Farland U.S. EPA, co-chairs. Strategies for identifying or predicting chemicals reasonably anticipated to be carcinogenic to humans in the absence of two-year rodent bioassay results will be addressed. The type and extent of data necessary (for example, structure activity, genotoxicity, receptor-mediated effects, and other biological activities) to predict and classify a chemical as potentially hazardous will be discussed. The intent is to identify potential carcinogens on the basis of mechanisms to provide strong evidence predicting a negative response. The extent to which this information can be used for setting priorities for further studies and for regulatory actions is a key point for discussion.
* Mechanism-based toxicology for determining dose-response relationships for chemical effects and low-dose extrapolation: Michael Gallo, Robert Wood Johnson Medical School and Rutgers University, James W. Stratton, California Environmental Protection Agency, co-chairs. This group will discuss the use of mechanistically important endpoints other than tumor formation for determining dose-response relationships and low-dose extrapolation and the impact of this approach to risk assessment. Experimental and mathematical approaches to dose-effect relationships and the data necessary to predict tumor responses from mechanistic-based endpoints within the framework of multistage models need to be addressed. Of particular interest is the development of credible strategies for low-dose risk estimates.
* Mechanism-based toxicology for species extrapolation: Joseph Contrera, U.S. Food and Drug Administration, James Swenberg, Department of Environmental Sciences and Engineering, University of North Carolina at Chapel Hill, co-chairs. This group will discuss how to use mechanistic information for species extrapolation. Given that mechanisms of action are never completely understood, how can current advances in mechanisms of action of chemicals be used to predict responses in different species for different classes of chemicals? What chemical classes are currently understood sufficiently to allow this analysis? Additional classes that need to be studied, multiple mechanisms, and general strategies to direct necessary research to support mechanistic arguments will be discussed.
* Mechanism-based toxicology to determine distributions of risk: Carol Henry, U.S. Department of Energy, John Davis Groopman, Johns Hopkins University, co-chairs. Individuals vary greatly in their responses to chemically induced toxicity. Given this fact, current risk assessment methods assume that the most susceptible rodent represents the most susceptible human. This public health-based assumption can overestimate or underestimate risks to humans. Given the recent advances in identifying the basis of genetic susceptibilities for chemicals in humans and rodents as well as age and gender-dependent differences, how can we design experiments to determine the distribution of risks among different populations? Another topic for the group will be the use of mechanistic approaches to more accurately determine exposure so that genetic/environment interactions can be assessed more accurately.
Kenneth Olden, director of the NTP and the NIEHS, said, "Key to the success of the workshop will be the inclusion of the needs, views and issues of federal and state regulatory agencies, industry, labor, environmental organizations, legislators, the broader scientific community, and the public." He noted that discussion groups will be asked to develop recommendations and to identify areas of concensus, disagreement, knowledge gaps, and how to most efficiently address those gaps.
The workshop will be open to the public on a space-available basis, and a public comment session will provide the opportunity for additional views and comments. For registration and additional information, contact Sandy Lange, NTP Liaison Office, NIEHS, PO Box 12233, Research Triangle Park, NC 27709; (919) 541-0530, FAX (919) 541-0295.
Rall Returns to NIEHS
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David P. Rall |
"Prevention is not very exciting," said David P. Rall at the beginning of a presentation on his first return to the NIEHS since retiring in 1990 after 19 years as director. "You don't get any kudos from your patients whom you've protected from sure death. You don't even know whom you've helped. But prevention of disease is a task that ultimately must be done."
Rall delivered his invited lecture, "The Importance of Animal Testing in Safety Evaluation," as the first visiting scientist for the Duke/UNC/NIEHS Clinical Training Program, part of a larger collaborative effort launched in 1993 to develop a world-class clinical center for environmental health sciences research. The visiting scientist program will bring five internationally recognized environmental health scientists to the collaborating institutions each year.
In his presentation, Rall dismissed arguments of those in the field of comparative risk assessment, and others, who say that disease prevention is too expensive. "I think we can find holes in these arguments, judging from past work by these authors," he said. Early in his career, Rall was among the researchers developing cures for childhood leukemia at the National Cancer Institute. "These treatments cost hundreds of thousands of dollars; the illnesses and the treatment cause untold pain and suffering for patients. And the likelihood that patients will encounter cancer in later years is increased. Far better to prevent the disease in the first place. Preventing exposures is really the way to go, yet it's really very difficult. You use predictive toxicology to identify those compounds which are present but which can be removed from the environment."
Rall presented data illustrating that only a small percentage of cosmetics, food additives, pesticides, and other chemicals have been adequately studied for their health effects and that of those studied and found to have health effects in animals, less than half have been regulated. He noted that these figures contradict the insistence by some that "mouse hysteria" causes regulators to ban everything based on limited evidence from animal studies. He stated that only recently has EPA begun to move again, after many years, on regulating chemicals based on animal studies, and he asserted that few if any chemicals have been studied under TOSCA (Toxic Substances Control Act), which was legislation supposed to require industry to do toxicology testing on its own products before they were released into the environment. "The real problem is that most chemicals haven't been studied," he said.
Rall said that animal studies must serve as a primary tool of prevention. Epidemiology studies, while valuable, often provide information, "25 years too late," although molecular biologists are improving epidemiology and making it a better predictive tool. Use of chemical structures to predict toxicity (structure activity) is getting better, but it is still not useful for finding the first chemical of a particular type to cause toxicity. Short-term tests such as the Ames test are extremely valuable but provide limited information. Rall suggested that studies could be improved by beginning dosing of rats and mice earlier, increasing the length of studies so that animals could be followed for around 30 months. "Very young rats are much more sensitive," he said.
Among challenges for the future, Rall noted that combination toxicity--looking at the synergisms between environmental agents--is "frightfully difficult and horribly expensive, but simply has to be done." He also singled out the problem of mercury in freshwater lakes and streams and its subsequent appearance in game and food fish; in some instances, this mercury may come from power plants burning coal that contains mercury. Another emerging issue, according to Rall, is the discovery of the health effects of fine particulates, a previously or underestimated component of air pollution.
Topping-out Ceremony Marks Construction Milestone
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Onward and upward. A topping out ceremony in which a tree and an American flag were placed at the highest point of construction marked the latest milestone in the new "F" module. |
When 100 or so construction workers came down off the concrete frame of the four-story laboratory tower that will eventually be the NIEHS "F" module and magnetic resonance imaging facility, at lunch time on a beautiful August day, there was more than the usual bag lunch and thermos awaiting them. On the porch of the construction site trailer offices, a podium and chairs had been set up. After a brief explanation of the "topping-out ceremony," a pine tree and American flag were placed at the highest point on the building under construction, denoting that the concrete and steel frame of the building is complete. Final completion of the module and attached magnetic resonance imaging facility is scheduled for July 1996. William P. Lefebvre, master of ceremonies for the event and project manager for Marshall Contractors Inc., general contractors for the project, explained that the pine tree was not a cut tree usually used in these ceremonies, but a live tree that will later be planted near the module, at the request of NIEHS chief of the Facilities Engineering Branch Thomas Bedick, to reflect the environmental mission of the Institute.
The topping-out itself was followed by remarks by five invited speakers. Kenneth Olden, NIEHS director, especially acknowledged the assistance of the N.C. congressional delegation, and especially Congressmen David Price, Tim Valentine, and former Senator Terry Sanford for making the construction of the new module possible. "Without their commitment, dedication and support, this facility would not be a reality," Olden said
Bedick said that although the concrete and steel are in place, the great challenge lies ahead to make the structure, "look, feel, and act like a building." Alan Sparn, vice president of operations for Marshall, noted the outstanding safety record the contractor has earned during the course of this project.
James Roberson, president of the Research Triangle Foundation that serves as landlord for Research Triangle Park, commented that NIEHS, along with IBM, as newly arrived tenants in 1965, provided institutional anchors for Research Triangle Park, which now boasts more than 14 million square feet of office, laboratory, and other work space. South Gate Jones, of the Durham Chamber of Commerce, noted that high ratings of this area by Fortune and Money magazines, among others, should make it easier to recruit scientists to work in the new building.
Last Update: June 4, 1998