Identification and inheritance of inbred hamster N-acetyltransferase isozymes in peripheral blood

Area of Science:

• Pharmacogenetics
• Biochemistry
• Genetics

Background:

• N-acetyltransferase (NAT) enzymes are critical for metabolizing various xenobiotics, including drugs and environmental toxins.
• Individual differences in NAT activity, known as acetylator phenotypes (rapid vs. slow), significantly impact drug efficacy and toxicity.
• Understanding the genetic basis of NAT activity is essential for personalized medicine and predicting drug responses.

Purpose of the Study:

• To investigate the inheritance pattern of acetyl CoA-dependent p-aminobenzoic acid and p-aminosalicylic acid N-acetyltransferase (NAT) activity in a hamster model.
• To determine the primary blood cell type expressing NAT activity and its relationship with acetylator genotype.
• To elucidate the genetic mechanism controlling NAT activity through segregation analysis in hamster progeny.

Main Methods:

• Acetylator genotype-dependent NAT activity was measured in peripheral blood and blood cells of inbred rapid (RR) and slow (rr) acetylator hamsters and their F1, F2, and backcross generations.
• NAT activity was localized to specific blood cell fractions, primarily erythrocytes.
• Segregation analysis of NAT activity levels in progeny was performed to assess Mendelian inheritance patterns. Partial purification of NAT was achieved using ion-exchange chromatography.

Main Results:

• NAT activity was predominantly found in erythrocytes and was directly correlated with acetylator genotype: highest in RR, intermediate in heterozygous (Rr), and lowest in rr hamsters.
• F1 progeny exhibited unimodal NAT activity between parental levels. F2 progeny segregated into low, intermediate, and high activity modes consistent with a 1:2:1 ratio.
• Backcross progeny also showed segregation patterns consistent with Mendelian inheritance, supporting a single autosomal locus with two codominant alleles. Two NAT isozymes were identified, both showing genotype-dependent expression.

Conclusions:

• Blood NAT activity in hamsters is controlled by a single autosomal genetic locus with two codominant alleles, exhibiting simple Mendelian inheritance.
• The expression levels of NAT activity are directly influenced by the acetylator genotype, with distinct isozymes contributing to the observed phenotype.
• These findings provide a foundational understanding of the genetic regulation of NAT activity, relevant for pharmacogenetic studies and drug metabolism research.