Tight binding of clarithromycin, its 14-(R)-hydroxy metabolite, and erythromycin to Helicobacter pylori ribosomes

Abstract

Clarithromycin is a recently approved macrolide with improved pharmacokinetics, antibacterial activity, and efficacy in treating bacterial infections including those caused by Helicobacter pylori, an agent implicated in various forms of gastric disease. We successfully isolated ribosomes from H. pylorz and present the results of a study of their interaction with macrolides. Kinetic data were obtained by using '4C-labeled macrolides to probe the ribosomal binding site. Clarithromycin, its parent compound erythromycin, and its 14-(R)-hydroxy metabolite all bound tightly to H. pylori ribosomes. Kd values were in the range of 2 x 10-10 M, which is the tightest binding interaction observed to date for a macrolide-ribosome complex. This tight binding was due to very slow dissociation rate constants of 7.07 x 10", 6.83 x 10-4, and 16.6 x 10-4 min-' for clarithromycin, erythromycin, and 14-hydroxyclarithromycin, respectively, giving half-times of dissociation ranging from 7 to 16 h, the slowest yet measured for a macrolide-ribosome complex. These dissociation rate constants are 2 orders of magnitude slower than the dissociation rate constants of macrolides from other gram-negative ribosomes.[14C]clarithromycin was bound stoichiometrically to 50S ribosomal subunits following incubation with 70S ribosomes and subsequent separation of the 30S and 50S subunits by sucrose density gradient centrifugation. These data predict that the lower MIC of clarithromycin compared with that of erythromycin for H. pylori is likely due to a faster rate of intracellular accumulation, possibly because of increased hydrophobicity.

Clarithromycin Resistance and 23S rRNA Mutations in Helicobacter pylori

“…Clarithromycin is a recently approved 14-membered macrolide with increased stability in acid and improved pharmacokinetics, including the appearance of a microbiologically active metabolite in humans. Clarithromycin possesses broad-spectrum antimicrobial activity, inhibiting a range of gram-positive and gram-negative organisms, some anaerobes, and atypical pathogens, in many cases with greater in vitro activity than erythromycin [7]. Clarithromycin is a semi-synthetic macrolide antibiotic.…”

Macrolide Resistance Conferred by Base Substitutions in 23S rRNA

“…The preferred treatment for aggressive infections is a drug combination including the erythromycin derivative clarithromycin (Fig. 1), which has improved acid stability and uptake properties compared to erythromycin (57). H. pylori is susceptible to many antibiotics in vitro, although treatment in vivo is less trivial as the stomach is a difficult environment in which to carrying out successful antimicrobial therapy (58).…”

In Vitro Antibacterial Activity of Acyl-Lysyl Oligomers againstHelicobacter pylori

“…Clarithromycin, like other macrolides, binds to the 50S subunit of bacterial ribosomes, thus inhibiting translocation of tRNA during translation. Binding of clarithromycin to H. pylori ribosomes has been shown to be very strong and is irreversible (27). Finally, metronidazole is a 5-nitroimidazole drug whose mode of action is mediated by nitro metabolites, such as the radical anion (NO 2 ⅐ Ϫ ) and perhaps nitroso (RNO) and hydroxylamine (RNHOH) derivatives (39).…”