AABRE: NETWORKING IN PUERTO RICO

PR-AABRE Researcher: Silvina Fioressi, Ph.D., Department of Chemistry and Physics, University of Turabo

Cluster: Molecular Medicine

Collaborator: Nicholas Geacintov, Ph.D. (NYU)

Mentor: Rafael Arce, Ph.D. (UPR, Río Piedras Campus)

Project Title: Photochemistry and Bioactivity of Polycyclic Aromatic Hydrocarbons Adsorbed on Model Surfaces

Benzo [e] Pyrene

Benzo [a] Pyrene

UNLIKE OTHER RESEARCHERS who focus their research on treating or curing illnesses, chemistry professor Silvina Fioressi wants to prevent diseases—such as lung cancer—caused by airborne pollutants. By studying how the potential carcinogens polycyclic aromatic hydrocarbons PAHs) and nitro-polycyclic aromatic hydrocarbons (nitro-PAHs) react with sunlight and oxygen in the laboratory, she replicates what could happen to PAHs and nitro-PAHs once they are released into the atmosphere.

PAHs are formed when fossil fuels or organic material are burned in oxygen-deficient conditions. People are exposed to PAHs when they breathe ambient air or when they ingest PAHs in food and water. When airborne, PAHs undergo photochemical reactions and combine with nitrogen oxides, which could cause them to become carcinogenic or become more carcinogenic. And when PAHs are exposed to oxygen in the atmosphere, they can become harmful, even when nontoxic upon release.

The results of this study may one day affect EPA regulations for acceptable PAH levels.

“There are literally hundreds of PAHs. Each one reacts differently in the atmosphere. For example, a PAH exposed to nitrogen oxide might produce ten new products. Some PAHs have already been studied. We’re studying the PAH Benzo[a]pyrene, which is toxic, and the PAH Benzo[e]pyrene, which is nontoxic. They include exactly the same elements and the same number of elements but have different chemical alignments.

“Nobody studies the nontoxic PAHs because they are not harmful, but once exposed to conditions in the atmosphere their products have the potential to become very toxic.”

In the first year of this study, literally hundreds of reactions of the PAHs to atmospheric conditions were studied, and the researchers constructed a map of the reactions. Next the researchers will isolate and identify the products, which may take upwards of two years. They will use UV visible spectroscopy, fluorescence, laser flash photolysis, and electron spin resonance as tools to help them identify the products, some of which may turn out to be newly discovered compounds. Then the researchers will need to generate enough of the products to test for toxicity using the Ames Salmonella typhimurium assay. This test uses a histidine-dependent Salmonella strain. In the absence of an external histidine source, the cell cannot grow to form colonies, but if a mutation takes place, the cell can produce its own histidine and grow normally. If a Salmonella culture is incubated with a mutagenic compound, for example, some PAHs and nitro-PAHs, the colonies will increase. The assay is a rapid, reliable, and economical method for screening compounds of potential genetic activity at the nucleotide level. It can be used in the evaluation of toxic substances, and there is a good correlation between mutagenicity in Salmonella and carcinogenicity in mammals.

The last step of this project is writing up the results. “Then, of course, we publish the results of our research and hope that they affect environmental policy. We’re studying causes rather than the cure to contribute to the prevention of diseases.”

sfioressi@mail.suagm.edu

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