Induction and inactivation of cytochrome P-450 by macrolide antibiotics

Macrolide antibiotics, which are N-demethylated, may generate a metabolite which binds to cytochrome P-450 (P-450) forming a metabolic-intermediate (MI) complex. The complex inhibits further P-450 activity and is spectrally detectable at 456 nm. Compounds which form complexes also induce hepatic P-450. Among seven macrolide antibiotics tested, troleandomycin was the most potent inducer and MI complex former of rat hepatic P-450. After four days of troleandomycin (500 mg/kg/day; i.g.), hepatic P-450 was tripled with 65% sequestered as a MI complex. The P-450 subpopulations induced and complexed by troleandomycin eluted in fractions I and II after DEAE cellulose column chromatography. SDS polyacrylamide gel electrophoresis revealed two unique subpopulations in troleandomycin-induced microsomes not found in uninduced or phenobarbital-induced (PB) microsomes. Their apparent molecular weights were 52,000 and 58,000 daltons. Troleandomycin induced ethylmorphine N-demethylase activity more than p-nitroanisole O-demethylase activity, whereas phenobarbital induced both equally. The induced P-450 subpopulations and MI complex were persistent in vivo; four days after the cessation of drug treatment, 38% of total P-450 was complexed and the associated mixed-function oxidase (MFO) activities still inhibited. By several criteria, the nitrogenous macrolide antibiotics constitute a new class of MI complex-forming substrates. Formation of MI complex requires an induced state of P-450. The quantity of complex formed in liver is much more than that from the amines, SKF 525-A or norbenzphetamine. No macrolide antibiotic MI complex was formed in lung microsomes. The quantity of MI complex formed from macrolide antibiotics differed among PB animals; rat liver formed more MI complex from troleandomycin than rabbit liver, yet both animals formed complex from erythromycin to equivalent extents. The troleandomycin MI complex was stable to changes in pH, temperature and ionic strength during solubilization. The complex was not stable in the presence of potassium ferricyanide or high oxygen tension. Troleandomycin induces select subpopulations of P-450 and subsequently, during metabolism, forms a MI complex. The persistence of elevated hepatic P-450 and MI complex in vivo and the consequent alterations in MFO activities suggests exercising caution when troleandomycin is administered concommitantly with other therapeutic agents whose metabolism is P-450 dependent.