Quantitative assessment of the binding of acetaminophen metabolites to mouse liver microsomal phospholipid

Phospholipids were quantitatively extracted from microsomes and separated by an h.p.l.c. gradient system with a solvent mixture of n-hexane/n-propanol/water/acetic acid. In a model reaction using horseradish peroxidase/H2O2 in order to activate acetaminophen and inactivated microsomes as target, a covalent binding of 10 nmol drug metabolite per mg microsomal lipid was found. In isolated intact microsomes from methylcholanthrene-pretreated male albino mice, a binding of 0.1 nmol acetaminophen metabolite per mg phospholipid was determined while the binding of metabolites to protein amounted to 3 nmol/mg. The results demonstrate that in mouse liver microsomes metabolizing acetaminophen, about one out of 10(4) phospholipid molecules is modified.