14-Day Nose-Only Inhalation Toxicity and Haber's Rule Study of NNK in Sprague-Dawley Rats

Area of Science:

• Toxicology
• Environmental Health
• Carcinogenesis

Background:

• 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a major tobacco-specific nitrosamine linked to lung cancer.
• Limited data exist on the repeated inhalation toxicity of NNK, crucial for understanding smoking-related risks.

Purpose of the Study:

• To assess the subacute inhalation toxicity of NNK in Sprague Dawley rats.
• To determine the lowest-observed-adverse-effect level (LOAEL) for NNK inhalation.
• To investigate the applicability of Haber's Rule to NNK inhalation toxicity.

Main Methods:

• Rats were exposed via nose-only inhalation to NNK aerosol (0.03-1.65 mg/L) for 1 hour/day for 14 days.
• Toxicity endpoints included clinical pathology, histopathology, biomarker analysis (NNK, NNAL, DNA adducts), and genotoxicity.
• Haber's Rule was assessed by comparing 1-hour and 4-hour daily exposure durations.

Main Results:

• NNK exposure induced significant adverse effects, with nasal non-neoplastic histopathological lesions being the most sensitive endpoint.
• The LOAEL was determined to be 0.8 mg/kg BW/day (0.03 mg/L air) for both sexes.
• Longer exposure durations (4 hours) at lower NNK concentrations resulted in greater toxicity than shorter durations (1 hour) at higher concentrations, consistent with Haber's Rule.

Conclusions:

• Subacute NNK inhalation causes significant toxicity, primarily affecting the nasal passages.
• Nasal lesions represent a sensitive indicator of NNK-induced toxicity.
• Exposure duration is a critical factor in NNK inhalation toxicity, with longer exposures leading to more severe effects.