Decrease in the metabolic activating capacities of arylamines in livers bearing hyperplastic nodules: association...

Area of Science:

• Biochemistry
• Hepatology
• Toxicology

Background:

• Carcinogenic arylamines require metabolic activation by hepatic enzymes for their toxic effects.
• Pre-neoplastic or hyperplastic nodules in the liver can alter the expression and activity of key metabolic enzymes, including cytochrome P-450 (CYP) isozymes.

Purpose of the Study:

• To investigate the mechanism behind altered carcinogenic arylamine-activating capacities in livers with pre-neoplastic nodules induced by the Solt-Farber protocol.
• To correlate these changes with alterations in specific hepatic cytochrome P-450 isozymes.

Main Methods:

• Salmonella mutagenesis assay using specific arylamines (2-amino-3-methylimidazo[4,5-f]quinoline, 2-aminofluorene, 2-amino-6-methyldipyrido-[1,2-a:3',2'-d]imidazole).
• Western blot analysis using specific antibodies to quantify hepatic levels of various CYP450 isozymes (P-450-male, P-450b, P-448-H, P-450(6 beta-1), P-450e).
• Measurement of testosterone hydroxylation (16 alpha-, 2 alpha-, and 6 beta-hydroxylations) as an indicator of CYP activity.

Main Results:

• Microsomes from nodule-bearing livers showed significantly lower activation of tested arylamines compared to controls.
• Hepatic contents of P-450-male and P-450b were decreased in nodule-bearing livers (to 63% and 35% of controls, respectively).
• No significant decrease was observed in P-448-H, P-450(6 beta-1), or P-450e levels. Testosterone 16 alpha- and 2 alpha-hydroxylations were reduced, correlating with P-450-male decrease.

Conclusions:

• The selective decrease in hepatic P-450-male content is a primary factor responsible for the reduced metabolic activation of carcinogenic arylamines in livers with hyperplastic nodules.
• These findings highlight the role of specific CYP isozyme alterations in modulating the metabolic activation of carcinogens during liver pre-neoplasia.