New chemiluminescent substrates of paraoxonase 1 with improved specificity: synthesis and properties

Paraoxonase 1 (PON1) is an important hydrolase, and the enzyme activity decreases in patients with liver disease, diabetes, coronary heart disease, etc. Phenyl acetate and organophosphates are usually employed as substrates for serum PON1 activity assay. However, phenyl acetate for arylesterase activity assay exhibits disadvantage of high background. According to properties of PON1, four new chemiluminescent acridinium esters were designed, prepared through three steps, and characterized with (1)H NMR and mass spectrometry (MS) data, and their properties as PON1 substrates were investigated. The hydrolyses of the four compounds catalyzed by recombinant human PON1 (rhPON1) (or serum) followed first-order kinetics within 22 min. The PON1 activator (NaCl, 0.10 mol L(-1)) could boost the rhPON1-mediated and serum-mediated hydrolyses of the acridinium esters to 2.01 ~ 2.26 folds, but 1.0 mol L(-1) NaCl decreased the serum arylesterase activity. RhPON1 showed selectivity over other serum esterases such as lipase, acetylcholinesterase, and esterase D more than 300 folds. By using ethylene diamine tetraacetic acid (EDTA) inhibitor, the specificities of the four substrates toward serum PON1 were determined as 78.3 ~ 92.9%, which is improved than that of the model compound 9-(4-chloro-phenoxycarbonyl)-10-methylacridinium ester triflate. Due to low toxicity, high specificity, and sensitivity of the substrates, they are useful for serum PON1 activity assay.