Toxicity, uptake, and subcellular distribution in rat hepatocytes of roxithromycin, a new semisynthetic macrolide, and erythromycin base

Abstract

Rat hepatocytes were used to study the toxicity of a new semisynthetic macrolide, roxithromycin, in comparison with erythromycin base and erythromycin estolate. Roxithromycin caused lactate dehydrogenase leakage close to that of erythromycin estolate and higher than erythromycin base after 21 h of exposure to the drugs. This effect was, at least in part, explained by the higher uptake: roxithromycin was two to three times more concentrated by liver cells than erythromycin base. For both roxithromycin and erythromycin base, the uptake depended on time, temperature, and extracellular antibiotic concentration. The accumulated macrolides egressed rapidly when cells were incubated in antibiotic-free medium. No uptake and no loss of accumulated drugs were observed at 4C. After accumulation by hepatocytes, roxithromycin and erythromycin base underwent similar subcellular distribution, mostly concentrating in cytosol and lysosomes. The small amount accumulated in the other particulate fractions followed the order mitochondria >> nuclei > microsomes. Roxithromycin, however, was less concentrated than erythromycin base in the microsomes.Erythromycin base and its derivatives are macrolide antibiotics widely used for the treatment of respiratory tract infections and are a useful alternative to penicillin in allergic patients (18). However, they have two major limitations: erythromycin base is inactivated by gastric juice and erythromycin estolate, though more gastro-resistant, may produce hepatic injury in patients (10) and in experimental models (7,8,27,28). A new semisynthetic macrolide, roxithromycin (formerly RU 28965), recently synthesized by Roussel Uclaf (Paris, France) and which is an ether oxime derivative of erythromycin (14) (Fig. 1), was reported to have similar antibacterial activity (1, 14, 24) but more favorable pharmacokinetic properties than erythromycin base (20,26).Cultured rat hepatocytes, which are known to show a good correlation between the in vitro and in vivo toxicities of macrolides (7,8,27,28), were used to evaluate the hepatotoxicity of the new antibiotic in comparison with the two analogs inducing mild (erythromycin base) and severe (erythromycin estolate) hepatic damage. The results presented in this study show that roxithromycin causes lactate dehydrogenase leakage higher than erythromycin base and close to that of erythromycin estolate, although it does not possess a surface-active component like lauryl sulfate, which seems to be the main cause of erythromycin estolate hepatotoxicity (8).Erythromycin and its derivatives have been described to be concentrated intracellularly by eucaryotic cells to different degrees (13), so different uptake of roxithromycin and erythromycin base by hepatocytes might explain their different toxicities for liver cells. To gain an insight into the mechanism of the different hepatotoxicities of the two macrolides, the uptake and subcellular distribution of roxi-* Corresponding author.

Enteral Exsorption of Acetaminophen after Intravenous Injection in Rats: Influence of Activated Charcoal on This Clearance Path

“…The difference was even higher at later stages. In the collection period 60 -90 min., the bile concentration was about 800 mg/l while plasma concentration corresponded to 12.5 mg/l in accordance with the well-known ability of the liver cells to concentrate xenobiotics (metabolites) in the sinusoidal space [15].…”

Influence on Mitochondria and Cytotoxicity of Different Antibiotics Administered in High Concentrations on Primary Human Osteoblasts and Cell Lines

“…Macrolides and clindamycin like linezolid and chloramphenicol inhibit bacterial protein synthesis by binding the bacterial 50S ribosomal subunit and might inhibit mitochondrial protein synthesis as well, although this has not been shown directly so far (39). The impairment of mitochondrial energetics could also be caused by direct interaction with mitochondrial membranes, because at least macrolides are known to interact directly with phospholipids (35,47) and macrolides as well as clindamycin are accumulated intracellularly (22,48). The increase in lactate production caused by the fluoroquinolones was only marginal, because it was superposed with direct toxic effects in higher concentrations.…”

Role of extracellular calcium in in vitro uptake and intraphagocytic location of macrolides

“…A likely mechanism for their intracellular accumulation involves the weakly basic nature of macrolides and the possibility of trapping by protonation within acidic cellular compartments, lysosomes, and polymorphonuclear neutrophil (PMN) granules (9,36). This hypothesis has been verified in phagocytic and nonphagocytic human and animal cells (6,9,45,50,51). The possibility that the intragranular location alters the correct functioning of this cellular compartment (exocytosis, phagolysosomal fusion) has been little explored (1,8,30).…”

“…We used regression analysis to determine the concentrations inhibiting 50% of macrolide uptake at 5 min (IC 50 ) of Ni 2ϩ , which were 2 mM dirithromycin (three to seven experiments; r ϭ 0.964; P Ͻ 0.001) and 1.6 mM roxithromycin (two to five experiments; r ϭ 0.917; P Ͻ 0.001). Approximation of the IC 50 , which is poorly active in this system (K i , 1.25 mM), was also assessed. Mg 2ϩ (up to 5 mM) did not inhibit macrolide uptake over a 60-min incubation period.…”