The protective effects of the thromboxane synthetase inhibitor Dazmegrel on nephrotoxicity in cyclosporine-treated rats.

Renal vasoconstriction has been implicated as a major contributing factor for the nephrotoxic effects of cyclosporine. In an attempt to assess the relative contribution of thromboxane (Tx), the effects of coadministering CsA with the selective Tx synthetase inhibitor, Dazmegrel (DAZ) (Pfizer, Inc.), were determined. Rats were treated orally with 50 mg/kg of DAZ plus 50 mg/kg of CsA and various indicators of nephrotoxicity and efficacy were assessed. Animals treated with CsA + DAZ had a normalization of renal TxB2 synthesis as compared with animals treated with CsA alone (160 vs. 338 pg/ml). Kidney proximal tubule damage following CsA treatment alone was also reduced in animals coadministered DAZ, as indicated by reduced urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG) (9.7 vs. 14.1 U/g creatinine) and by histological examination of kidney sections. However, DAZ did not affect blood levels of CsA nor its efficacious activity in a model of experimental allergic encephalomyelitis (EAE). These studies suggest a major role of elevated thromboxane production in the acute nephrotoxic effects of CsA and demonstrate a reduction in this toxicity by DAZ without altering CsA's efficacious activity.

In vitro and in vivo uptake of azithromycin (CP-62,993) by phagocytic cells: possible mechanism of delivery and release at sites of infection.

Azithromycin, a novel azalide antibiotic, concentrated in human and mouse polymorphonuclear leukocytes (PMNs), murine peritoneal macrophages, and mouse and rat alveolar macrophages, attaining intracellular concentrations up to 226 times the external concentration in vitro. In murine peritoneal macrophages, azithromycin achieved concentration gradients (internal to external) up to 26 times higher than erythromycin. The cellular uptake of azithromycin was dependent on temperature, viability, and pH and was decreased by 2,4-dinitrophenol. Azithromycin did not decrease phagocyte-mediated bactericidal activity or affect PMN or macrophage oxidative burst activity (H2O2 release or Nitro Blue Tetrazolium reduction, respectively). Azithromycin remained in cells for several hours, even after extracellular drug was removed. However, its release was significantly enhanced by phagocytosis of Staphylococcus aureus (82 versus 23% by 1.5 h). In vivo, 0.05 micrograms of azithromycin was found in peritoneal fluids of mice 20 h after oral treatment with a dose of 50 mg/kg. Following caseinate-induced PMN infiltration, there was a sixfold increase in peritoneal cavity azithromycin to 0.32 micrograms, most of which was intracellular. Therefore, the uptake, transport, and later release of azithromycin by these cells demonstrate that phagocytes may deliver active drug to sites of infection.

Generation of enhanced macrophage-mediated antibacterial resistance in animals responding to tumor allografts.

Enhanced systemic antibacterial resistance was acquired by ACF1 (H-2ad) and B6D2F1 (H-2bd) mice bearing allogenetic BP-3 (H-2b) and SA-1 (H-2a) footpad tumors, respectively. This effect was dose dependent, in that the implantation of greater numbers of tumor cells produced larger tumors and higher levels of nonspecific resistance. Although the rejection of the tumor was T-cell dependent, the generation of nonspecific resistance was not. Thus, T-cell-deficient mice bearing progressively growing tumor allografts generated significant levels of antibacterial resistance. Two mechanisms were found to be involved in the generation of nonspecific resistance: (i) an acquired radioresistant mechanism responsible for initially destroying a large proportion of injected bacteria and (ii) an acquired radiosensitive mechanism responsible for destroying a significant number of bacteria after 24 h.

Immunologic consequences of antibiotic-induced abridgement of bacterial infection: effect on generation and loss of protective T cells and level of immunologic memory.

Ampicillin was employed in mice to determine the effect of rapidly abridging bacterial infection on the generation of T cell-mediated antibacterial immunity. It was found that antibiotic-induced abridgement of infection with Listeria monocytogenes had a pronounced effect on the generation of splenic T cells capable of adoptively immunizing normal recipients against a Listeria challenge infection. Ampicillin given at the time of maximum bacterial growth at 24 hr caused a striking reduction in the number of protective T cells produced at the time of peak response on day 6. Although the greatest effect was caused by giving ampicillin early in infection, a significant reduction in peak T cell production occurred even when Ampicillin was given as late as day 5. On the other hand, the effect of abridging infection at the onset of decay of the anti-Listeria response was to cause protective T cells to be lost from the spleen at a much faster rate. These results clearly show that regardless of any immunoregulatory mechanism involved, the duration of generation, and the onset and duration of decay of the anti-Listeria response are determined by the number of replicating Listeria in the tissues. Moreover, Ampicillin-induced abridgement of infection, either before or at the time of peak primary response, resulted in the expression of greatly reduced levels of immunologic memory at a later time. This indicates that memory cells are generated throughout the entire course of the primary anti-Listeria response, including the period of its decay.

Increased toxicity of endotoxin for tumor-bearing mice and mice responding to bacterial pathogens: macrophage activation as a common denominator.

Mice bearing the syngeneic SA-1 sarcoma or treated with live Mycobacterium bovis BCG or Formalin-killed Corynebacterium parvum acquired a greatly increased susceptibility to the lethal effects of endotoxin. In all three experimental models, the acquisition of increased sensitivity to endotoxin was concordant with the generation of a systemically activated macrophage system.

Suppressive effect of bacterial endotoxin on the expression of cell-mediated anti-Listeria immunity.

Intravenous injection of bacterial endotoxin into mice at any time during ongoing infection with Listeria monocytogenes resulted in a markedly increased multiplication of this organism in the liver and spleen. Experiments designed to investigate the basis of this infection-enhancing effect revealed that endotoxin was also capable of inhibiting the expression of adoptive T-cell-mediated anti-Listeria immunity if given to normal recipient mice up to 48 h before they were infused with protective T-cells. On the other hand, endotoxin had only a marginal effect on the expression of adoptive immunity if given to donor mice before their spleen cells were harvested for adoptive transfer. Taken together, these results indicate that endotoxin probably interferes with the antibacterial function of macrophages rather than with mediator lymphocytes. The additional finding that the infection-enhancing action of endotoxin could be greatly reduced by making mice "tolerant" to endotoxin suggests that the acquisition of tolerance to this effect of endotoxin may be an important adaptive mechanism in acquired resistance to infection with gram-negative bacteria.