A selective decrease in the xenobiotic metabolizing activity of rat lungs by nitrogen dioxide exposures.

Area of Science:

• Environmental Toxicology
• Biochemistry
• Respiratory System Research

Background:

• Nitrogen dioxide (NO2) is a common air pollutant with known respiratory effects.
• Xenobiotic metabolism in the lungs plays a crucial role in detoxifying foreign compounds.
• Understanding the impact of NO2 on lung metabolic enzymes is vital for assessing health risks.

Purpose of the Study:

• To investigate the dose-effect relationship between nitrogen dioxide (NO2) exposure and xenobiotic metabolizing activity in rat lung microsomes.
• To determine which specific metabolic enzymes are most sensitive to NO2 exposure.

Main Methods:

• Male Wistar rats were exposed to varying concentrations of NO2 (1.2 to 15 ppm) for 1 or 2 weeks.
• Lung microsomal proteins and enzyme activities (cytochrome P-450, cytochrome b5, reductase activities, coumarin hydroxylase, 7-ethoxycoumarin O-deethylase, benzo[a]pyrene hydroxylase, benzphetamine N-demethylase) were measured.

Main Results:

• Lung cytochrome P-450 levels decreased significantly at higher NO2 concentrations (10-15 ppm) and showed a tendency to decrease at 6-10 ppm.
• Coumarin hydroxylase and 7-ethoxycoumarin O-deethylase activities were most sensitive, showing dose-dependent reductions even at low NO2 levels (≥1.2 ppm).
• Other measured enzymes like cytochrome b5 and reductase activities showed increases with prolonged NO2 exposure (6-10 ppm).

Conclusions:

• Nitrogen dioxide exposure, particularly at concentrations above 1.2 ppm, causes a consistent and preferential reduction in specific lung xenobiotic metabolizing enzyme activities.
• Lung cytochrome P-450 is preferentially decreased by higher NO2 concentrations.
• These findings highlight the potential for NO2 to impair the lung's ability to metabolize foreign compounds, with implications for respiratory health.