Biomonitoring of aromatic amines. III: Hemoglobin binding of benzidine and some benzidine congeners

Area of Science:

• Toxicology
• Biochemistry
• Analytical Chemistry

Background:

• Benzidine and its congeners are known human carcinogens.
• Understanding their metabolic pathways and biological interactions is crucial for risk assessment.
• Hemoglobin adducts serve as biomarkers of exposure to certain chemicals.

Purpose of the Study:

• To investigate the covalent binding of benzidine and its congeners to hemoglobin in rats.
• To identify the metabolites formed and understand the metabolic pathways involved.
• To evaluate the potential of hemoglobin adduct analysis for biomonitoring of exposure.

Main Methods:

• Oral administration of benzidine, its congeners, and an azo dye (Direct Red 28) to Wistar rats.
• Alkaline hydrolysis of hemoglobin to release arylamine adducts.
• High-performance liquid chromatography (HPLC) with electrochemical detection for arylamine analysis.

Main Results:

• Benzidine formed three hemoglobin adducts, with monoacetylbenzidine being the major product, indicating 4-nitroso-4'-N-acetylaminobiphenyl as the primary reactive metabolite.
• A novel metabolic pathway involving 4-aminobiphenyl formation from benzidine was identified.
• Other benzidine congeners showed varying adduct profiles, and 3,3',5,5'-tetramethylbenzidine did not form detectable adducts.
• Administration of Direct Red 28 led to benzidine-typical adducts, confirming bioactivation and increased 4-aminobiphenyl formation.

Conclusions:

• Analysis of hemoglobin adducts provides insights into the metabolic activation and bioactivation of benzidine and related compounds.
• The formation of 4-aminobiphenyl from benzidine represents a previously unrecognized metabolic pathway.
• Hemoglobin adduct analysis is a promising tool for biomonitoring of occupational and environmental exposure to carcinogenic arylamines.