Substrate selectivity of mouse N-acetyltransferases 1, 2, and 3 expressed in COS-1 cells

Area of Science:

• Pharmacogenetics and Drug Metabolism
• Enzymology
• Toxicology

Background:

• Human N-acetyltransferases (NAT1 and NAT2) are crucial for metabolizing various drugs and carcinogens.
• Polymorphisms in human NAT genes influence disease treatment and cancer risk.
• Mice are used as models for human NAT polymorphisms, but their NAT isoenzyme selectivity requires clarification.

Purpose of the Study:

• To determine the substrate selectivity of mouse N-acetyltransferase isoenzymes (Nat1, Nat2, and Nat3).
• To evaluate the functional analogy between mouse and human NAT enzymes.
• To aid in understanding the role of NAT polymorphisms in disease and cancer risk using mouse models.

Main Methods:

• Expression of mouse Nat1*, Nat2*8, and Nat3* in COS-1 cells.
• Evaluation of substrate selectivity using common N-acetyltransferase substrates, including isoniazid, sulfamethazine, p-aminobenzoic acid, 5-aminosalicylic acid, and 2-aminofluorene.
• Assay of catalytic activity for each mouse NAT isoenzyme with the selected substrates.

Main Results:

• Mouse Nat2 exhibited significantly higher catalytic activity (20- to 5.4-fold) for p-aminobenzoic acid, 5-aminosalicylic acid, and 2-aminofluorene compared to Nat1.
• Isoniazid N-acetylation was exclusively catalyzed by mouse Nat1.
• Mouse Nat3 showed limited activity, primarily towards 5-aminosalicylic acid, and mouse Nat2 selectively acetylated the endogenous substrate p-aminobenzoylglutamate.

Conclusions:

• Mouse Nat2 demonstrates broad substrate selectivity for common NAT substrates, analogous to human NAT1.
• The distinct substrate profiles of mouse NAT isoenzymes are important for their use as models in pharmacogenetics and toxicology.
• These findings enhance the understanding of species-specific differences in N-acetylation relevant to drug response and cancer risk.