Pharmacokinetics and lung distribution of macrolide antibiotics in sepsis model rats.

Recent studies have shown azithromycin-specific clinical efficacy against macrolide-resistant strains of Streptococcus pneumoniae, despite the low susceptibility of the bacteria in vitro. This discrepancy complicates dosing and selection for treatment of macrolide-resistant strains. Although phagocyte delivery of azithromycin to inflamed tissues is considered a possible factor for clinical efficacy, there is a lack of sufficient evidence, and other pharmacokinetic factors under systemic inflammation may contribute.The concentrations of azithromycin, clarithromycin and erythromycin in the plasma and buffy coat were determined in normal and sepsis model rats. Furthermore, we compared the transport of the drug into the lung.The levels of all three macrolides in the buffy coat were higher than the levels in the plasma, and lower leukocyte counts in plasma were observed in septic rats, suggesting accumulation of the drugs per leukocyte was increased. The concentrations in the lung tissue of septic rats at each sampling time were the same as those in normal rats, and azithromycin-specific long-term stasis in the lung was evident.These results suggest that both the phagocyte delivery and the stasis of azithromycin in the lung could contribute to its clinical efficacy in treating infections caused by macrolide-resistant strains.

The yeast Arf-GAP Glo3p is required for the endocytic recycling of cell surface proteins.

Small GTP-binding proteins of the Ras superfamily play diverse roles in intracellular trafficking. Among them, the Rab, Arf, and Rho families function in successive steps of vesicle transport, in forming vesicles from donor membranes, directing vesicle trafficking toward target membranes and docking vesicles onto target membranes. These proteins act as molecular switches that are controlled by a cycle of GTP binding and hydrolysis regulated by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). In this study we explored the role of GAPs in the regulation of the endocytic pathway using fluorescently labeled yeast mating pheromone α-factor. Among 25 non-essential GAP mutants, we found that deletion of the GLO3 gene, encoding Arf-GAP protein, caused defective internalization of fluorescently labeled α-factor. Quantitative analysis revealed that glo3Δ cells show defective α-factor binding to the cell surface. Interestingly, Ste2p, the α-factor receptor, was mis-localized from the plasma membrane to the vacuole in glo3Δ cells. Domain deletion mutants of Glo3p revealed that a GAP-independent function, as well as the GAP activity, of Glo3p is important for both α-factor binding and Ste2p localization at the cell surface. Additionally, we found that deletion of the GLO3 gene affects the size and number of Arf1p-residing Golgi compartments and causes a defect in transport from the TGN to the plasma membrane. Furthermore, we demonstrated that glo3Δ cells were defective in the late endosome-to-TGN transport pathway, but not in the early endosome-to-TGN transport pathway. These findings suggest novel roles for Arf-GAP Glo3p in endocytic recycling of cell surface proteins.