Abstract
<title>Abstract</title> <p>Fluorescent compounds are sensitive and convenient research tools in biological sciences. We observed that fluorescent 8-hydroxy-N1,N3,N6-trimethoxy-N1,N3,N6-trimethylpyrene-1,3,6-trisulfonamide (F-pyrene) is transported quickly into cells and visualized as green fluorescent color. During incubation, its green fluorescence emission was changed into blue emission in a fraction of human HepG2 liver cells, which was hypothesized to result from phase II drug metabolism into the respective glucuronide and sulfate conjugates, both of which show blue rather than green luminescence. The glucuronidation and sulfonation rates of F-pyrene were determined in human liver and intestine microsomes and cytosol, respectively, and for recombinant UDP-glucuronosyltransferase and sulfotransferase enzymes. Human microsomal glucuronidation rates were 5.10 ± 0.14 nmol/(s*g prot) and 2.9 ± 0.46 nmol/(s*g prot) in the liver and intestine, respectively. The cytosolic sulfonation rates were 0.063 ± 0.026 nmol/(s*g prot) and 0.199 ± 0.007 nmol/(s*g prot) in the human liver and intestine, respectively. The more active enzymes in F-pyrene glucuronidation were UGT1A1, 1A3, 1A7, 1A8, 1A9, and 1A10, while in sulfonation the more active enzymes were SULT1A1, 1A2, 1E1 and 2A1. Enzyme kinetics of all UGTs as well as the SULTs 1A1, 1A2, and 1E1 enzymes obeyed substrate inhibition kinetics, only SULT2A1 obeyed Michaelis-Menten kinetics. It is concluded that F-pyrene is a new, sensitive and versatile probe substrate for human UGT and SULT enzymes which can be used both in visualization of transport and conjugation metabolism, in cell cultures and other experimental models.</p>