Internal exposure of rats to benzidine derived from orally administered benzidine-based dyes after intestinal azo...

Area of Science:

• Toxicology
• Microbiology
• Pharmacology

Background:

• Benzidine-based dyes are widely used industrial chemicals.
• The metabolic fate and potential toxicity of these dyes are not fully understood.
• The intestinal flora's role in xenobiotic metabolism is a significant area of research.

Purpose of the Study:

• To investigate the role of rat intestinal flora in the azo reduction of benzidine-based dyes.
• To determine if the reduction products are absorbed and excreted as mutagens.
• To establish the intestinal flora's contribution to the biotoxification of these dyes.

Main Methods:

• In vitro anaerobic incubation of direct black 38, direct blue 6, and direct brown 95 with caecal bacteria.
• Measurement of benzidine formation.
• In vivo studies using Wistar rats (conventional and germ-free) with oral administration of dyes, followed by urine mutagenicity testing.

Main Results:

• Benzidine was formed from direct black 38, direct blue 6, and direct brown 95 during anaerobic incubation with caecal bacteria.
• Benzidine showed significantly better absorption from the intestinal tract compared to the parent dyes.
• Oral administration of direct black 38 or direct brown 95 to Wistar rats led to urinary excretion of mutagens, which was absent in germ-free rats.

Conclusions:

• The intestinal flora is essential for the azo reduction of benzidine-based dyes.
• This reduction leads to the formation of benzidine, which is absorbed and excreted as a mutagen.
• Intestinal flora-mediated reduction is the critical initial step in the biotoxification of benzidine-based dyes.