Grantee Research Project Results
2000 Progress Report: Increased Vulnerability of Neonates to Naphthalene and Its Derivatives
EPA Grant Number: R827442Title: Increased Vulnerability of Neonates to Naphthalene and Its Derivatives
Investigators: Fanucchi, Michelle V.
Institution: University of California - Davis
EPA Project Officer: Aja, Hayley
Project Period: October 1, 1999 through September 30, 2002
Project Period Covered by this Report: October 1, 1999 through September 30, 2000
Project Amount: $374,543
RFA: Children's Vulnerability to Toxic Substances in the Environment (1999) RFA Text | Recipients Lists
Research Category: Children's Health , Human Health
Objective:
The overall objective of this project is to identify the factors critical to establishing whether children need greater protection from environmental contaminants that produce lung toxicity in adults. Currently in the United States, children grow up in urban environments with high potential for exposure to a large number of toxic compounds derived from both industrial and military sources. Many of these compounds require metabolic activation to generate cytotoxic and carcinogenic derivatives. Current standards for acceptable levels of these contaminants in the environment are based on assessments of risk to the adult population. Little information is available regarding the relative susceptibility of children to these compounds. This project focuses on one of the cell types in pulmonary airways, the Clara cell. The Clara cell is a progenitor cell and is the pulmonary cell most likely to be affected by bioactivated toxicants. The Clara cell continues to develop and differentiate during the postnatal period. How do exposures to environmental contaminants during this period of development affect the Clara cell? Is it more susceptible to toxicant injury than a fully differentiated Clara cell of an adult? And, if so, what are the critical factors that create the increased susceptibility? This project is designed to answer these questions using two species (mice and rats) and four different environmental toxicants (naphthalene, 1-nitronaphthalene, 2-methylnaphthalene, and 2-isopropylnaphthalene). This project addresses the following issues: (1) is the increased susceptibility of Clara cells in neonates chemical- and/or species-specific? (2) is the increase in injury in the immature Clara cell due to a difference in the balance of activation and deactivation enzymes in favor of the activation pathways? (3) is the increase in injury to immature Clara cells due to a decreased ability to regulate glutathione pools?Progress Summary:
To date, we have finished the in vivo portion of the dose-response studies establishing the level of vulnerability of neonatal mice and rats to pulmonary injury from naphthalene and 1-nitronaphthalene as compared to adult mice and rats. Adult and 7-day old male Swiss Webster mice and Sprague Dawley rats were injected intraperitoneally with 0, 12.5, 25, 50 or 100 mg/kg naphthalene or 1-nitronaphthalene in corn oil and killed 24 hours post-treatment. Lungs were evaluated by high-resolution light microscopy. In adult mice, a few vacuolated and swollen cells were detected in bronchioles after 50 mg/kg naphthalene while in neonatal mice, vacuolated and swollen cells were detected after 25 mg/kg naphthalene. Injury progressed in a dose-dependent fashion for both ages. In both adult and neonatal rats, there was no detectable injury following any dose of naphthalene. Injury was detected in adult mice after 100 mg/kg 1-nitronaphthalene and in neonatal mice after 12.5 mg/kg 1-nitronaphthalene. No neonatal mice at other doses survived to the 24h time-point. A few vacuolated cells were detected in both bronchi and bronchioles after 25 mg/kg 1-nitronaphthalene in adult rats. In neonatal rats, vacuolated and exfoliated cells were detected in bronchi after 12.5 mg/kg 1-nitronaphthalene. This injury also progressed in a dose-dependent manner. To summarize, the order of sensitivity (greatest to least) for naphthalene is: 7D mice >> adult mice >> 7D rats = adult rats; and for 1-nitronaphthalene: 7D mice >> 7D rats > adult rats >> adult mice. We conclude that neonatal susceptibility to environmental pollutants is species and chemical specific, but cannot be reliably predicted based on adult susceptibility.We are in the process of defining the potential of differentiating Clara cells of neonatal airway epithelium to bioactivate naphthalene and 1-nitronaphthalene as compared to the bioactivation potential of differentiated Clara cells in the adult lung. We are evaluating the metabolism of 1-nitronaphthalene in specific airway compartments (trachea, lobar bronchus, major daughter airways, minor daughter airways, terminal bronchioles, and parenchyma). The isolated airways are incubated with 0.5 mM 1-nitronaphthalene for two hours and metabolites are evaluated by HPLC. This work is in progress, and so far we have detected metabolism in airways from both adult and neonatal rats. Preliminary data suggests that 1-nitronaphthalene metabolism is lower in neonatal rats than in adult rats.
We have finished the distribution and site-specific expression of glutathione in the neonatal mouse airways as compared to the adult airways. Adult, 14- and 7-day-old male mice were injected intraperitoneally with 0, 25 or 100 mg/kg NA in corn oil to initiate Clara cell injury and killed at 1, 2 3 or 6 hours post-treatment. Airway epithelium was evaluated for GSH content at specific airway generations (1, 9, 14-15, and 20-22) using quantitative epifluorescent imaging microscopy and HPLC. Adult and neonatal animals contained similar baseline levels of GSH in all airway generations studied except in generation 9 where 7-day-old mice had significantly more GSH. Treatment with NA resulted in an airway-specific decrease in the amount of GSH present in all ages. In adults and 14-day-old mice, the greatest decrease was observed in airway generations 20-22. In 7-day-old mice, the greatest decrease was seen in airway generation 1. We conclude that differentiating Clara cells of neonatal mice do not modulate cellular GSH pools in response to NA treatment in the same manner as differentiated Clara cells in adults and that this difference may play a role in the heightened sensitivity of differentiating Clara cells to NA injury.
Future Activities:
In the next year, we will initiate the dose-response studies with 2-methylnaphthalene and 2-isopropylnaphthalene in the neonatal and adult mice and rats. We also will expand upon the metabolic studies that were begun in the first year to determine the exact 1-nitronaphthalene metabolites formed in the neonatal and adult mice and rats. We also will begin to evaluate the expression of glutathione in neonatal and adult rat airways.Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 10 publications | 5 publications in selected types | All 5 journal articles |
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Fanucchi MV, Buckpitt AR, Murphy ME, Storms DH, Hammock BD, Plopper CG. Development of phase II xenobiotic metabolizing enzymes in differentiating murine Clara cells. Toxicology and Applied Pharmacology 2000;168(3):253-267. |
R827442 (2000) R827442 (Final) |
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Plopper CG, Fanucchi MV. Do urban environmental pollutants exacerbate childhood lung diseases? Environmental Health Perspectives 2000;108(6):A252-A253. |
R827442 (2000) R827442 (Final) |
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Supplemental Keywords:
chemicals, histology, pathology, biochemistry., RFA, Health, Scientific Discipline, Toxics, Toxicology, Environmental Chemistry, Genetics, Health Risk Assessment, HAPS, Susceptibility/Sensitive Population/Genetic Susceptibility, Biochemistry, Children's Health, genetic susceptability, Pathology, glutathione pools, health effects, neonates, sensitive populations, cytochrome P450, infants, vulnerability, health risks, second hand smoke, Naphthalene, airway disease, gene-environment interaction, respiratory problems, exposure, air pollution, high resolution histopathology, children, childhood respiratory disease, children's vulnerablity, lung dysfunction, susceptibility, high performance liquid chromatography, cigarette smoke, bioactivated environmental toxicants, biomedical research, exposure assessmentProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.