Entry of roxithromycin (RU 965), imipenem, cefotaxime, trimethoprim, and metronidazole into human polymorphonuclear leukocytes

Dual β-lactams for the treatment of Mycobacterium abscessus: a review of the evidence and a call to act against an antibiotic nightmare

Mycobacterium abscessus complex is a group of rapidly growing non-tuberculous mycobacteria (NTM), increasingly emerging as opportunistic pathogens. Current treatment options for these microorganisms are limited and associated with a high rate of treatment failure, toxicity and recurrence. In search of new therapeutic strategies, interest has grown in dual β-lactam (DBL) therapy, as research recently discovered that M. abscessus cell wall synthesis is mainly regulated by two types of enzymes (d,d-transpeptidases and l,d-transpeptidases) differently susceptible to inhibition by distinct β-lactams. In vitro studies testing several DBL combinations have shown synergy in extracellular broth cultures as well as in the intracellular setting: cefoxitin/imipenem, ceftaroline/imipenem, ceftazidime/ceftaroline and ceftazidime/imipenem. The addition of specific β-lactamase inhibitors (BLIs) targeting M. abscessus β-lactamase did not significantly enhance the activity of DBL combinations. However, in vivo data are lacking. We reviewed the literature on DBL/DBL-BLI-based therapies for M. abscessus infections to raise greater attention on this promising yet overlooked treatment option and to guide future preclinical and clinical studies.

Measurement of Accumulation of Antibiotics to Staphylococcus aureus in Phagosomes of Live Macrophages

Staphylococcus aureus (S. aureus) has evolved the ability to persist after uptake into host immune cells. This intracellular niche enables S. aureus to potentially escape host immune responses and survive the lethal actions of antibiotics. While the elevated tolerance of S. aureus to small-molecule antibiotics is likely to be multifactorial, we pose that there may be contributions related to permeation of antibiotics into phagocytic vacuoles, which would require translocation across two mammalian bilayers. To empirically test this, we adapted our recently developed permeability assay to determine the accumulation of FDA-approved antibiotics into phagocytic vacuoles of live macrophages. Bioorthogonal reactive handles were metabolically anchored within the surface of S. aureus, and complementary tags were chemically added to antibiotics. Following phagocytosis of tagged S. aureus cells, we were able to specifically analyze the arrival of antibiotics within the phagosomes of infected macrophages. Our findings enabled the determination of permeability differences between extra- and intracellular S. aureus, thus providing a roadmap to dissect the contribution of antibiotic permeability to intracellular pathogens.

Measurement of Accumulation of Antibiotics to Staphylococcus aureus in Phagosomes of Live Macrophages

Staphylococcus aureus ( S. aureus ) has evolved the ability to persist after uptake into host immune cells. This intracellular niche enables S. aureus to potentially escape host immune responses and survive the lethal actions of antibiotics. While the elevated tolerance of S. aureus to small-molecule antibiotics is likely to be multifactorial, we pose that there may be contributions related to permeation of antibiotics into phagocytic vacuoles, which would require translocation across two mammalian bilayers. To empirically test this, we adapted our recently developed permeability assay to determine the accumulation of FDA-approved antibiotics into phagocytic vacuoles of live macrophages. Bioorthogonal reactive handles were metabolically anchored within the surface of S. aureus, and complementary tags were chemically added to antibiotics. Following phagocytosis of tagged S. aureus cells, we were able to specifically analyze the arrival of antibiotics within the phagosomes of infected macrophages. Our findings enabled the determination of permeability differences between extra- and intracellular S. aureus , thus providing a roadmap to dissect the contribution of antibiotic permeability to intracellular pathogens.

Intergenerational and biological effects of roxithromycin and polystyrene microplastics to Daphnia magna

The influence of microplastics (MPs) on transgenerational effects of pharmaceuticals are drawing growing attention, however, whether aged process will alter the carrier effects of MPs were unknown. In this study, the intergenerational toxicity of single and combined exposure of polystyrene microplastics (PS-MPs) and roxithromycin (ROX) were investigated at the environmentally related concentrations, using Daphina magna as test organism. In the presence of UV-aged PS-MPs, the survival of D. magna for maternal generation (F0) at ROX concentration of 0.1 and 10 µg/L were increased by 20% and 40%, respectively. Meanwhile, the inhibition effects of ROX on the number of offspring and intrinsic rate of natural increase were obviously moderated. All these reproductive toxicity of ROX and PS-MPs in the first offspring (F1) were further aggravated both for the single and combined exposure. And the adverse effects disappeared much easier for the single exposure compared to the co-exposure through subsequent recovery. The combined exposure resulted in the change of inhibition of ROX on the swimming velocity and acceleration of D. magna into induction, while the feeding behavior kept inhibited. The AChE activity was distinctly increased by 1.61-3.25 times for the single and combined treatments, and the induction level of UV-aged MPs was higher than that of original MPs. Oxidative stress of the single exposure of ROX and original PS-MPs was observed with obvious induction of T-AOC and SOD activity, while the significant increase of MDA content was observed for the co-exposure. Among all indicators, the biochemical biomarkers and time of first brood were attributed to a class among all indicators, indicating that the time of first brood might be the most sensitive reproductive toxicity index. These results illustrated that both maternal impacts and offspring quality need to be considered for assessment of interaction of emerging contaminants.

In vitro antibiotic activity against intraosteoblastic Staphylococcus aureus: a narrative review of the literature

Staphylococcus aureus – a major aetiological agent of bone and joint infection (BJI) – is associated with a high risk of relapse and chronicity, in part due to its ability to invade and persist in non-professional phagocytic bone cells such as osteoblasts. This intracellular reservoir protects S. aureus from the action of the immune system and most antibiotics. To date, the choice of antimicrobial strategies for BJI treatment mostly relies on standard susceptibility testing, bone penetration of antibiotics and their ‘antibiofilm’ activity. Despite the role of intracellular persistent S. aureus in the development of chronic infection, the ability of antibiotics to target the S. aureus intraosteoblastic reservoir is not considered in therapeutic choices but might represent a key determinant of treatment outcome. This review provides an overview of the intracellular pharmacokinetics of antistaphylococcal drugs used in the treatment of BJI and of their ability to target intraosteoblastic S. aureus. Thirteen studies focusing on the intraosteoblastic activity of antibiotics against S. aureus were reviewed, all relying on in vitro models of osteoblast infection. Despite varying incubation times, multiplicities of infection, bacterial strains, and the types of infected cell lines, rifamycins and fluoroquinolones remain the two most potent antimicrobial classes for intraosteoblastic S. aureus eradication, consistent with clinical data showing a superiority of this combination therapy in S. aureus orthopaedic device-related infections.

Intracellular Penetration and Effects of Antibiotics on Staphylococcus aureus Inside Human Neutrophils: A Comprehensive Review

Neutrophils are important assets in defense against invading bacteria like staphylococci. However, (dysfunctioning) neutrophils can also serve as reservoir for pathogens that are able to survive inside the cellular environment. Staphylococcus aureus is a notorious facultative intracellular pathogen. Most vulnerable for neutrophil dysfunction and intracellular infection are immune-deficient patients or, as has recently been described, severely injured patients. These dysfunctional neutrophils can become hide-out spots or “Trojan horses” for S. aureus. This location offers protection to bacteria from most antibiotics and allows transportation of bacteria throughout the body inside moving neutrophils. When neutrophils die, these bacteria are released at different locations. In this review, we therefore focus on the capacity of several groups of antibiotics to enter human neutrophils, kill intracellular S. aureus and affect neutrophil function. We provide an overview of intracellular capacity of available antibiotics to aid in clinical decision making. In conclusion, quinolones, rifamycins and sulfamethoxazole-trimethoprim seem very effective against intracellular S. aureus in human neutrophils. Oxazolidinones, macrolides and lincosamides also exert intracellular antibiotic activity. Despite that the reviewed data are predominantly of in vitro origin, these findings should be taken into account when intracellular infection is suspected, as can be the case in severely injured patients.

Evaluation of the intracellular activity of drugs against Mycobacterium abscessus using a THP-1 macrophage model

We evaluated the antimicrobial effectiveness against M. abscessus in a THP-1 cell line model. No intracellular activity was observed when using amikacin or imipenem. A bacteriostatic effect was observed for cefoxitin, clarithromycin and azithromycin. Tigecycline showed the best antibacterial effect by decreasing the intracellular growth up to bactericidal level.

Mechanisms of the Macrolide-Induced Inhibition of Superoxide Generation by Neutrophils

The effect of macrolides on the superoxide (O2 (-)) production by neutrophils was studied. Resting neutrophils become primed by lipopolysaccharide (LPS) or N-formyl-methionyl-leucyl-phenylalanine (fMLP), and primed neutrophils generate O2 (-) in response to fMLP or adhesion, respectively. Both LPS-primed fMLP-stimulated O2 (-) generation by macrolide-treated neutrophils and adhesion-stimulated O2 (-) generation by macrolide-treated fMLP-primed neutrophils were inhibited. Macrolide inhibition of O2 (-) generation was dependent on serum or pH. Serum could be substituted by NaHCO3. The intensity of inhibition was azithromycin = roxithromycin > clarithromycin > erythromycin, in that order. Non-antimicrobial derivatives of erythromycin, that is, EM703 and EM900, inhibited O2 (-) generation at pH 7.4. NH4Cl abolished the activity of azithromycin (AZ) only when added to neutrophils with AZ but not after incubation with AZ, suggesting that NH4Cl prevented the influx of AZ. AZ did not affect the expression of alkaline phosphatase, CD11b, and cytochrome b558 in both resting and LPS-primed neutrophils. These results suggested that macrolides did not affect granule mobilization but inhibited O2 (-) generation selectively.

Killing of Staphylococcus aureus in murine macrophages by chloroquine used alone and in combination with ciprofloxacin or azithromycin

This study aimed to determine any alteration in the killing of Staphylococcus aureus in murine peritoneal macrophages when chloroquine (CQ) is used alone compared with when it is used in combination with ciprofloxacin (CIP) or azithromycin (AZM). The study also aimed to find out the implication of reactive oxygen species (ROS) production and cytokine release in the intracellular killing of S. aureus in macrophages. We present here data obtained with a model of S. aureus-infected mouse peritoneal macrophages in which the intracellular growth of the bacteria and the influence of antibiotics was monitored for 30, 60, and 90 minutes in the presence or absence of CQ along with the production of ROS and alteration in levels of antioxidant enzymes and cytokines. It was observed that S. aureus-triggered cytokine response was regulated when macrophages were co-cultured with CQ and AZM as compared with CQ stimulation only. It can be suggested that action of AZM in mediating bacterial killing is enhanced by the presence of CQ, indicating enhanced uptake of AZM during early infection that may be essential for bacteria killing by AZM. Reduction of oxidative stress burden on the S. aureus-infected macrophages may pave the way for better killing of internalized S. aureus by CQ plus ciprofloxacin (CIP) or CQ plus AZM. Based on these observations, one may speculate that in an inflammatory milieu, CQ loaded with AZM elicits a stronger proinflammatory response by increasing the intracellular uptake of AZM or CIP, thus enabling the immune system to mount a more robust and prolonged response against intracellular pathogens.

Identification of an outer membrane lipoprotein involved in nasopharyngeal colonization by Moraxella catarrhalis in an animal model

Colonization of the human nasopharynx by Moraxella catarrhalis is presumed to involve attachment of this bacterium to the mucosa. DNA microarray analysis was used to determine whether attachment of M. catarrhalis to human bronchial epithelial (HBE) cells in vitro affected gene expression in this bacterium. Attachment affected expression of at least 454 different genes, with 163 being upregulated and 291 being downregulated. Among the upregulated genes was one (ORF113) previously annotated as encoding a protein with some similarity to outer membrane protein A (OmpA). The protein encoded by ORF113 was predicted to have a signal peptidase II cleavage site, and globomycin inhibition experiments confirmed that this protein was indeed a lipoprotein. The ORF113 protein also contained a predicted peptidoglycan-binding domain in its C-terminal half. The use of mutant and recombinant M. catarrhalis strains confirmed that the ORF113 protein was present in outer membrane preparations, and this protein was also shown to be at least partially exposed on the bacterial cell surface. A mutant unable to produce the ORF113 protein showed little or no change in its growth rate in vitro, in its ability to attach to HBE cells in vitro, or in its autoagglutination characteristics, but it did exhibit a reduced ability to survive in the chinchilla nasopharynx. This is the first report of a lipoprotein essential to the ability of M. catarrhalis to persist in an animal model.

Azithromycin suppresses proliferation, interleukin production and mitogen-activated protein kinases in human peripheral-blood mononuclear cells stimulated with bacterial superantigen

Objectives

Macrolide antibiotics are used for the treatment of immunological disorders such as psoriasis. However, few studies have investigated the immunoregulatory efficacy of macrolides in bacterial superantigen-stimulated immune cells.

Methods

The suppressive efficacies of azithromycin, clarithromycin, roxithromycin and prednisolone were evaluated in vitro against the concanavalin A- or toxic shock syndrome toxin 1 (TSST-1)-induced proliferation of peripheral-blood mononuclear cells (PBMCs) obtained from nine healthy subjects. The concentrations of six cytokines in a PBMC-culture medium were measured using bead-array procedures followed by flow cytometry. Cellular c-jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) activity were measured using cell-based ELISA procedures.

Key findings

Azithromycin, clarithromycin and roxithromycin inhibited the proliferation of both the concanavalin A- and superantigen-stimulated PBMCs dose-dependently. The effect of azithromycin was the strongest, with IC50 values of less than 5 µg/ml. Furthermore, the suppressive efficacy of prednisolone against concanavalin A- or TSST-1-stimulated PBMCs was significantly promoted in combination with 5 µg/ml azithromycin (P < 0.002). The concentrations of TNF-α, interleukin (IL)-2, −4, −5 and −10 in the supernatant of concanavalin A- or TSST-1-stimulated PBMCs cultured for 72 h decreased by 65–98% in the presence of 5 µg/ml azithromycin. The stimulation of PBMCs with concanavalin A or TSST-1 increased cellular JNK and ERK activity, and 5 µg/ml azithromycin significantly attenuated the increased activity of JNK in the TSST-1-stimulated cells and ERK in the concanavalin A- and TSST-1-stimulated PBMCs, respectively (P < 0.05).

Conclusions

Azithromycin suppresses mitogen- or superantigen-induced proliferation of PBMCs by possibly inhibiting both cellular JNK and ERK activity.

Meropenem: effects on human leukocyte functions and interleukin release

Modifications of the immune response have been reported for a number of antimicrobial agents following both in vivo and in vitro experiments. Present results were obtained from in vitro incubated human polymorphonuclear cells (PMN) and monocytes treated with meropenem, a novel carbapenem antibiotic. Only the highest concentrations of meropenem (50-200 microg/ml) significantly reduced the phagocytic activity and unstimulated superoxide release of neutrophils after 1 h of incubation. Moreover meropenem (100 and 200 microg/ml) reduced PMA-stimulated superoxide release by PMN after 1 h of incubation. Only the highest concentration used (200 microg/ml) was found to reduce significantly superoxide release by PMA-unstimulated and -stimulated PMN incubated for 2 h. Meropenem did not affect some of the PMN functions studied (killing of Candida albicans, chemotaxis and glucose consumption) over a broad range of concentrations (5, 10, 20, 50, 100, 200 microg/ml). The leukocyte viability did not change even at the highest antibiotic concentration used, as showed by the trypan blue exclusion test. The LPS-induced release of IL-1alpha, IL-6 and IL-8 from isolated monocytes was not impaired by meropenem (100 and 200 microg/ml), that significantly reduced TNFalpha stimulated by LPS, after 4 h of incubation. In conclusion our data suggest that therapeutically relevant concentrations (5-20 microg/ml) of meropenem did not modify substantially the viability and the functions of human leukocytes.

Evaluation of immunosuppression induced by metronidazole in Balb/c mice and human peripheral blood lymphocytes

The immunomodulatory effect of metronidazole (MTZ), a nitroimidazole drug used as an antiprotozoal and antibacterial agent, was investigated using Balb/c mice and human peripheral blood lymphocytes. For in vivo studies, mice were divided into six groups, six animals per group, group I received vehicle alone while the other groups (II-VI) received intraperitoneal injections of MTZ (14, 28, 42, 57, and 114 mg/kg) respectively. For in vitro studies different concentrations of MTZ (5, 10, 50, and 200 microg/ml) were used. MTZ showed a significant decrease in the percentage of circulating neutrophils and monocytes and an increase in the percentage of circulating lymphocytes. The relative weights of spleen as well as the relative body weight gain also decreased. Detectable changes were seen in the histology of spleen and thymus. Splenic plaque-forming cells (PFC), hemagglutination (HA) titer to sheep red blood cells (SRBC), spleenocytes and human peripheral blood lymphocytes proliferation (MLR) were markedly suppressed by MTZ treatment as compared to control group. MTZ also induced a significant decrease in delayed-type hypersensitivity (DTH) reaction, phagocytic activity (assessed by phagocytic capacity and phagocytic index) as well as TNF-alpha secretion by peritoneal macrophages. These observations indicate that MTZ significantly induced immunosuppression in mice and in human peripheral blood lymphocytes.

Delivery systems to increase the selectivity of antibiotics in phagocytic cells

Many infectious diseases are caused by facultative organisms that are able to survive in phagocytic cells. The intracellular location of these microorganisms protects them from the host defence systems and from some antibiotics with poor penetration into phagocytic cells. One strategy used to improve the penetration of antibiotics into phagocytic cells is the use of carrier systems that deliver these drugs directly to the target cell. Delivery systems such as liposomes, micro/nanoparticles, lipid systems, conjugates, and biological carriers such as erythrocyte ghosts may contribute to increasing the therapeutic efficacy of antibiotics and antifungal agents in the treatment of infections caused by intracellular microorganisms. The main objective of this review is to analyze recent advances and current perspectives in the use of antibiotic delivery systems in the treatment of intracellular infections such as mycobacterial infections, brucellosis, salmonellosis, listeriosis, fungal infections, visceral leishmaniasis, and HIV.

Enhanced Escherichia coli adherence and invasion in Crohn's disease and colon cancer

BACKGROUND & AIMS

Altered mucosal glycosylation in inflammatory bowel disease and colon cancer could affect mucosal bacterial adherence. This study aimed to quantify and characterize mucosa-associated and intramucosal bacteria, particularly Escherichia coli, in these conditions.

METHODS

Mucosa-associated bacteria were isolated, after dithiothreitol mucolysis, from biopsy samples obtained at colonoscopy (Crohn's disease, n = 14 patients; ulcerative colitis, n = 21; noninflamed controls, n = 24) and at surgical resection (colon cancer, n = 21). Intramucosal bacteria were grown after gentamicin treatment followed by hypotonic lysis.

RESULTS

Mucosa-associated and intramucosal bacteria were cultured more commonly in Crohn's disease (79%, P = 0.03; and 71%, P < 0.01, respectively), but not ulcerative colitis (38% and 48%), than in noninflamed controls (42% and 29%) and were commonly cultured from colon cancers (71% and 57%). Mucosa-associated E. coli, which accounted for 53% of isolates, were more common in Crohn's disease (6/14; 43%) than in noninflamed controls (4/24, 17%), as also were intramucosal E. coli: Crohn's disease, 29%; controls, 9%. E. coli expressed hemagglutinins in 39% of Crohn's cases and 38% of cancers but only 4% of controls, and this correlated (P = 0.01) with adherence to the I407 and HT29 cell lines. Invasion was cell-line dependent. E. coli, including nonadherent isolates, induced interleukin-8 release from the cell lines. E. coli adhesins showed no blood group specificity, excepting 1 cancer isolate (HM44) with specificity for the Thomsen-Friedenreich antigen, but they could be blocked by soluble plantain fiber.

CONCLUSIONS

These studies support a central role for mucosally adherent bacteria in the pathogenesis of Crohn's disease and colon cancer. Soluble plant fibers that inhibit their adherence have therapeutic potential.

Macrolide antibiotics inhibit prostaglandin E2 synthesis and mRNA expression of prostaglandin synthetic enzymes in human leukocytes

We investigated the action of macrolide antibiotics, which are considered to have anti-inflammatory activity, on lipopolysaccharide (LPS)-stimulated prostaglandin (PG) E2 synthesis and the expression of mRNAs for cytosolic phospholipase A2 (cPLA2), cyclooxygenase (COX)-1, and COX-2 in human leukocytes. The production of LPS-stimulated PGE2 was significantly increased in peripheral polymorphonuclear leukocytes (PMNLs) and in mononuclear leukocytes (MNLs). Amounts of mRNAs for COX-2 and cPLA2, but not for COX-1, were enhanced by LPS in PMNLs and MNLs. The LPS-enhanced PGE2 synthesis and the expression of cPLA2 and COX-2 mRNAs were inhibited by clarithromycin, azithromycin and dexamethasone in PMNLs and MNLs. The mRNA expression of COX-1 in PMNLs was decreased by clarithromycin and azithromycin. Macrolide antibiotics inhibited PGE2 synthesis in human leukocytes by suppressing cPLA2, COX-1, and COX-2 mRNA expression. These data indicate one mechanism of macrolide anti-inflammatory activity.

Propionibacterium acnes-induced IL-8 production may be mediated by NF-kappaB activation in human monocytes

Propionibacterium acnes (P. acnes) causes an inflammatory acne that is characterized by massive neutrophilic infiltration. IL-8 is thought to play an important role in the pathophysiology of P. acnes, although the mechanisms by which P. acnes up-regulates the release of IL-8, a neutrophilic chemokine, from target cells is not well understood. In this study, we investigated the mechanisms through which heat-killed P. acnes induces IL-8 production in THP-1 cells (a human monocytic cell line). We found that P. acnes is able to directly induce IL-8 production and IL-8 mRNA expression in human monocytic cells in a dose- and time-dependent manner through a mechanism requiring transcription factor NF-kappaB activation. Additionally, P. acnes-induced IL-8 secretion was inhibited by roxithromycin, a macrolide antibiotic, and its inhibitory effect seemed to be partially associated with the inhibition of P. acnes-induced NF-kappaB activation. This is the first study to show that NF-kappaB activation is involved in the IL-8 production of monocytic cells stimulated by P. acnes.

Characteristics and mechanisms of azithromycin accumulation and efflux in human polymorphonuclear leukocytes

Azithromycin achieves prolonged, high tissue concentrations in spite of low serum levels and obviously must be active at tissue sites of infection to be effective. These unique features prompted us to evaluate the interactions of azithromycin and human polymorphonuclear leukocytes (PMN). Uptake of radiolabeled antibiotic by PMN was determined by a velocity-gradient centrifugation technique and expressed as the ratio of cellular to extracellular drug concentration (C/E). Azithromycin was massively accumulated by human PMN (C/E=387.2 at 2 h). Uptake was not influenced by inhibitors of cellular metabolism, but phagocytosis slightly inhibited the entry of azithromycin into PMN. After removal of extracellular drug, the release (efflux) of azithromycin from PMN was extremely slow. Agents which neutralize lysosomal pH, preventing protonation and trapping of azithromycin, markedly increased antibiotic efflux. Active concentration and prolonged retention of azithromycin by phagocytic cells should allow delivery and subsequent release of accumulated drug at sites of infection.

Cellular uptake of two fluoroketolides, HMR 3562 and HMR 3787, by human polymorphonuclear neutrophils in vitro

We analyzed the cellular accumulation of two new fluoroketolides, HMR 3562 and HMR 3787, by human polymorphonuclear neutrophils (PMN) in vitro. Both compounds were rapidly taken up by PMN, with a cellular-to-extracellular concentration ratio (C/E) of about 141 (HMR 3562) and 117 (HMR 3787) at 5 min, and this was followed by a plateau at 60 to 180 min, with a C/E of >300 at 180 min. Both ketolides were mainly located in PMN granules (about 75%) and egressed slowly from loaded cells (about 40% at 60 min), owing to avid reuptake. Uptake was moderately sensitive to external pH, and activation energy was also moderate (about 70 kJ/mol). As with other macrolides and ketolides, the existence of an active transport system was suggested by (i) the strong interindividual variability in uptake kinetics, suggesting variability in the number or activity of a transport protein; (ii) the saturation kinetics characteristic of a carrier-mediated transport system (V(max), about 2,300 ng/2.5 x 10(6) PMN/5 min; K(m), about 50 microg/ml); (iii) the inhibitory effects of Ni(2+) (a blocker of the Na+-Ca(2+) exchanger), phorbol myristate acetate (a protein kinase C activator), and H89 (a protein kinase A inhibitor). Although these two ketolides are more related to HMR 3647 (telithromycin), it is interesting that the presence of a fluoride gave these molecules a cellular pharmacokinetics more like those of HMR 3004 than those of HMR 3647. The macrolide transport system has not been yet elucidated, but our data confirm that, despite variations in chemical structure, all erythromycin A derivatives share a transmembrane transport system.

Interference of antibacterial agents with phagocyte functions: immunomodulation or "immuno-fairy tales"?

Professional phagocytes (polymorphonuclear neutrophils and monocytes/macrophages) are a main component of the immune system. These cells are involved in both host defenses and various pathological settings characterized by excessive inflammation. Accordingly, they are key targets for immunomodulatory drugs, among which antibacterial agents are promising candidates. The basic and historical concepts of immunomodulation will first be briefly reviewed. Phagocyte complexity will then be unravelled (at least in terms of what we know about the origin, subsets, ambivalent roles, functional capacities, and transductional pathways of this cell and how to explore them). The core subject of this review will be the many possible interactions between antibacterial agents and phagocytes, classified according to demonstrated or potential clinical relevance (e.g., neutropenia, intracellular accumulation, and modulation of bacterial virulence). A detailed review of direct in vitro effects will be provided for the various antibacterial drug families, followed by a discussion of the clinical relevance of these effects in two particular settings: immune deficiency and inflammatory diseases. The prophylactic and therapeutic use of immunomodulatory antibiotics will be considered before conclusions are drawn about the emerging (optimistic) vision of future therapeutic prospects to deal with largely unknown new diseases and new pathogens by using new agents, new techniques, and a better understanding of the phagocyte in particular and the immune system in general.

Interference of antibacterial agents with phagocyte functions: immunomodulation or "immuno-fairy tales"?

Professional phagocytes (polymorphonuclear neutrophils and monocytes/macrophages) are a main component of the immune system. These cells are involved in both host defenses and various pathological settings characterized by excessive inflammation. Accordingly, they are key targets for immunomodulatory drugs, among which antibacterial agents are promising candidates. The basic and historical concepts of immunomodulation will first be briefly reviewed. Phagocyte complexity will then be unravelled (at least in terms of what we know about the origin, subsets, ambivalent roles, functional capacities, and transductional pathways of this cell and how to explore them). The core subject of this review will be the many possible interactions between antibacterial agents and phagocytes, classified according to demonstrated or potential clinical relevance (e.g., neutropenia, intracellular accumulation, and modulation of bacterial virulence). A detailed review of direct in vitro effects will be provided for the various antibacterial drug families, followed by a discussion of the clinical relevance of these effects in two particular settings: immune deficiency and inflammatory diseases. The prophylactic and therapeutic use of immunomodulatory antibiotics will be considered before conclusions are drawn about the emerging (optimistic) vision of future therapeutic prospects to deal with largely unknown new diseases and new pathogens by using new agents, new techniques, and a better understanding of the phagocyte in particular and the immune system in general.

Intracellular accumulation, subcellular distribution, and efflux of tilmicosin in bovine mammary, blood, and lung cells

Tilmicosin is a semisynthetic macrolide antibiotic currently approved for veterinary use in cattle and swine to combat respiratory disease. Because the concentrations of tilmicosin are generally low in bovine serum, the interaction of tilmicosin with three types of bovine phagocytes (monocyte-macrophages, macrophages, and neutrophils from blood, lungs, and mammary gland, respectively) and mammary gland epithelial cells was evaluated to provide an understanding of potential clinical efficacy. After incubation with radiolabeled tilmicosin, uptake was determined and expressed as the ratio of the intracellular to the extracellular drug concentration. Accumulation of tilmicosin at 4 h of incubation by the alveolar macrophages (Cc/Ce 193) was 4 to 13 times more than that observed in monocyte-macrophages (Cc/Ce 43), neutrophils, (Cc/Ce 13), or mammary epithelial cells (Cc/Ce 20). Subcellular distribution showed that 70 to 80% of tilmicosin was localized in the lysosomes. Uptake in mammary gland cells was dependent on cell viability, temperature, and pH, but was not influenced by metabolic inhibitors or anaerobiosis. However, lipopolysaccharide exposure increased tilmicosin uptake by the bovine mammary macrophages and epithelial cells. When neutrophils and epithelial cells were incubated in the presence of tilmicosin and extracellular tilmicosin was then removed, 40% of the intracellular tilmicosin remained cell associated after 4 h of incubation (i.e., 60% effluxed), but only 25% remained in macrophages. These in vitro interactions of tilmicosin with bovine phagocytes and epithelial cells suggest an integral role in effecting clinical efficacy.

Pharmacokinetics and pharmacodynamics of the nitroimidazole antimicrobials

Metronidazole, the prototype nitroimidazole antimicrobial, was originally introduced to treat Trichomonas vaginalis, but is now used for the treatment of anaerobic and protozoal infections. The nitroimidazoles are bactericidal through toxic metabolites which cause DNA strand breakage. Resistance, both clinical and microbiological, has been described only rarely. Metronidazole given orally is absorbed almost completely, with bioavailability > 90% for tablets; absorption is unaffected by infection. Rectal and intravaginal absorption are 67 to 82%, and 20 to 56%, of the dose, respectively. Metronidazole is distributed widely and has low protein binding (< 20%). The volume of distribution at steady state in adults is 0.51 to 1.1 L/kg. Metronidazole reaches 60 to 100% of plasma concentrations in most tissues studied, including the central nervous system, but does not reach high concentrations in placental tissue. Metronidazole is extensively metabolised by the liver to 5 metabolites. The hydroxy metabolite has biological activity of 30 to 65% and a longer elimination half-life than the parent compound. The majority of metronidazole and its metabolites are excreted in urine and faeces, with less than 12% excreted unchanged in urine. The pharmacokinetics of metronidazole are unaffected by acute or chronic renal failure, haemodialysis, continuous ambulatory peritoneal dialysis, age, pregnancy or enteric disease. Renal dysfunction reduces the elimination of metronidazole metabolites; however, no toxicity has been documented and dosage alterations are unnecessary. Liver disease leads to a decreased clearance of metronidazole and dosage reduction is recommended. Recent pharmacodynamic studies of metronidazole have demonstrated activity for 12 to 24 hours after administration of metronidazole 1 g. The post-antibiotic effect of metronidazole extends beyond 3 hours after the concentration falls below the minimum inhibitory concentration (MIC). The concentration-dependent bactericidal activity, prolonged half-life and sustained activity in plasma support the clinical evaluation of higher doses of metronidazole given less frequently. Metronidazole-containing regimens for Helicobacter pylori in combination with proton pump inhibitors demonstrate higher success rates than antimicrobial regimens alone. The pharmacokinetics of metronidazole in gastric fluid appear contradictory to these results, since omeprazole reduces peak drug concentration and area under the concentration-time curve for metronidazole and its hydroxy metabolite; however, concentrations remain above the MIC. Other members of this class include tinidazole, ornidazole and secnidazole. They are also well absorbed and distributed after oral administration. Their only distinguishing features are prolonged half-lives compared with metronidazole. The choice of nitroimidazole may be influenced by the longer administration intervals possible with other members of this class; however, metronidazole remains the predominant antimicrobial for anaerobic and protozoal infections.

Carbapenems and monobactams: imipenem, meropenem, and aztreonam

Imipenem and meropenem, members of the carbapenem class of beta-lactam antibiotics, are among the most broadly active antibiotics available for systemic use in humans. They are active against streptococci, methicillin-sensitive staphylococci, Neisseria, Haemophilus, anaerobes, and the common aerobic gram-negative nosocomial pathogens including Pseudomonas. Resistance to imipenem and meropenem may emerge during treatment of P. aeruginosa infections, as has occurred with other beta-lactam agents; Stenotrophomonas maltophilia is typically resistant to both imipenem and meropenem. Like the penicillins, the carbapenems have inhibitory activity against enterococci. In general, the in vitro activity of imipenem against aerobic gram-positive cocci is somewhat greater than that of meropenem, whereas the in vitro activity of meropenem against aerobic gram-negative bacilli is somewhat greater than that of imipenem. Daily dosages may range from 0.5 to 1 g every 6 to 8 hours in patients with normal renal function; the daily dose of meropenem, however, can be safely increased to 6 g. Infusion-related nausea and vomiting, as well as seizures, which have been the main toxic effects of imipenem, occur no more frequently during treatment with meropenem than during treatment with other beta-lactam antibiotics. The carbapenems should be considered for treatment of mixed bacterial infections and aerobic gram-negative bacteria that are not susceptible to other beta-lactam agents. Indiscriminate use of these drugs will promote resistance to them. Aztreonam, the first marketed monobactam, has activity against most aerobic gram-negative bacilli including P. aeruginosa. The drug is not nephrotoxic, is weakly immunogenic, and has not been associated with disorders of coagulation. Aztreonam may be administered intramuscularly or intravenously; the primary route of elimination is urinary excretion. In patients with normal renal function, the recommended dosing interval is every 8 hours. Patients with renal impairment require dosage adjustment. Aztreonam is used primarily as an alternative to aminoglycosides and for the treatment of aerobic gram-negative infections. It is often used in combination therapy for mixed aerobic and anaerobic infections. Approved indications for its use include infections of the urinary tract or lower respiratory tract, intra-abdominal and gynecologic infections, septicemia, and cutaneous infections caused by susceptible organisms. Concurrent initial therapy with other antimicrobial agents is recommended before the causative organism has been determined in patients who are seriously ill or at risk for gram-positive or anaerobic infection.

A comparative investigation of the restorative effects of roxithromycin on neutrophil activities

The effects of roxithromycin, a macrolide antibiotic, on neutrophil activities were investigated in six seriously handicapped patients with severe mental retardation. Neutrophil activities were evaluated by flow cytometry using a heparinized blood analysis method. All six patients showed decreased levels of neutrophil phagocytosis, intracellular killing, and CD11b expression. Treatment with roxithromycin in vitro selectively restored the decreased phagocytic and bactericidal activities of neutrophils in these patients. There was no significant restorative effect with cefaclor, ofloxacin, or aztreonam. These results suggest the need to consider therapeutic effects of antibiotics on neutrophil functions in patients at increased risk for bacterial infections due to decreased neutrophil activities.

Intracellular accumulation, subcellular distribution, and efflux of tilmicosin in chicken phagocytes

Tilmicosin is a semi-synthetic macrolide antibiotic, currently approved for veterinary use in cattle and swine respiratory disease, and is in development for use in poultry mycoplasma air sacculitis. In order to provide an understanding of clinical efficacy, the in vitro interaction of tilmicosin with three types of chicken phagocytes (MQ-NCSU macrophages, monocyte-macrophages, and heterophils) was evaluated. After incubation with radiolabeled tilmicosin, uptake was determined and expressed as the ratio of the cellular (Cc) to the extracellular (Ce) drug concentration (Cc:Ce). Tilmicosin was avidly accumulated by heterophils (Cc: Ce 138 at 4 h incubation vs 32 and 66, respectively, in MQ-NCSU and monocyte-macrophages) with 61 to 88% localized in the lysosomes. Uptake was dependent on cell viability, temperature, and pH, but was not influenced by metabolic inhibitors. However, phagocytosis of Pasteurella multocida and lipopolysaccharide exposure increased tilmicosin uptake by the chicken phagocytes. Upon removal of extracellular tilmicosin, 50% of the intracellular tilmicosin was effluxed within the first 30 min, but after 4 h of incubation in antibiotic-free medium, 30% remained cell-associated. Opsonized P. multocida significantly enhanced the release of tilmicosin from all three types of chicken phagocytes. Tilmicosin uptake was observed to increase lysosomal enzyme (acid phosphatase, lysozyme, avidin, and beta-glucuronidase) production. Finally, neutrophils were shown to transport and efflux bioactive tilmicosin in a test system measuring both neutrophil chemotaxis under agarose and a bioassay measuring inhibition of bacterial growth in the presence of antibiotic in agar. These in vitro observations of cellular pharmacology suggest a complex interaction between phagocytes and tilmicosin that contribute to clinical efficacy.

Intracellular accumulation, subcellular distribution and efflux of tilmicosin in swine phagocytes

Tilmicosin is a semi-synthetic macrolide antibiotic, currently approved for veterinary use in cattle and swine respiratory disease. As the concentrations of tilmicosin are generally low in swine lung tissue, the interaction of tilmicosin with three types of swine phagocytes (monocyte-macrophages, alveolar macrophages, and neutrophils) was evaluated to provide an understanding of clinical efficacy. After incubation with radiolabelled tilmicosin, uptake was determined and expressed as the ratio of the intracellular (Ci) to the extracellular (Ce) drug concentration (Ci/Ce). Tilmicosin was avidly accumulated by the swine phagocytes (Ci/Ce 48-69 at 4 h incubation) with 51 to 85% localized in the lysosomes. Uptake was dependent on cell viability, temperature and pH, but was not influenced by the metabolic inhibitors, sodium cyanide or potassium fluoride. However, lipopolysaccharide (LPS) exposure increased tilmicosin uptake by the swine phagocytes. In neutrophils, upon removal of extracellular tilmicosin, 60% of the intracellular tilmicosin was effluxed within the first 30 min, but after 4 h of incubation in drug-free medium, 25% remained cell-associated. In contrast, after 4 h of incubation in drug-free medium, 60% and 45% of tilmicosin remained cell-associated, within alveolar macrophages and monocyte-derived macrophages, respectively. Tilmicosin uptake was observed to increase lysosomal enzyme (acid phosphatase, lysozyme and beta-glucuronidase) production. Finally, neutrophils were shown to transport and efflux bioactive tilmicosin in a test system measuring both neutrophil chemotaxis under agarose and a bioassay measuring inhibition of bacterial growth in the presence of antibiotic in agar. These in vitro interactions of tilmicosin with swine phagocytes suggest an integral role in effecting clinical efficacy.

Interactions between HMR 3647, a new ketolide, and human polymorphonuclear neutrophils

HMR 3647, a new ketolide, is active upon intracellular pathogens. We previously demonstrated that HMR 3004 (RU 64004), another ketolide, is highly concentrated by human polymorphonuclear neutrophils (PMNs). This prompted us to evaluate whether the presence of a 3-keto group instead of an L-cladinose, a neutral sugar characteristic of erythromycin A derivatives, confers peculiar pharmacokinetic properties with regard to cellular accumulation and efflux. After incubation with the radiolabelled drug, HMR 3647 uptake was determined by a velocity gradient centrifugation technique. HMR 3647 was avidly concentrated by PMNs, without saturation, over a 3-h incubation period, with cellular-to-extracellular concentration ratios of 31 +/- 4.2 at 5 min and up to 348 +/- 27.1 at 180 min. About 60% of HMR 3647 was located in the granular compartment; less than 6% was associated with the membranes. HMR 3647 gradually egressed from loaded cells placed in drug-free medium. Uptake was dependent on environmental temperature (activation energy, 128 +/- 9. 4 kJ/mol) but not on extracellular pH. HMR 3647 displayed Michaelis-Menten saturation kinetics with a mean Vmax of 2315 ng/2.5 x 10(6) PMNs/5 min and a mean Km of 117 mg/liter (144 microM). As already observed with erythromycin A-derived macrolides, extracellular Ca2+ was necessary for optimal uptake of HMR 3647. Interestingly, verapamil increased the uptake of HMR 3647 at 5 min, but this was followed by gradual inhibition at later incubation times, a phenomenon probably related to stimulation of drug efflux. The impact of intracellular accumulation of HMR 3647 on PMN functions was also investigated. In contrast to other erythromycin A derivatives, HMR 3647 only weakly triggered granule exocytosis, but it inhibited superoxide anion production in a time- and concentration-dependent manner, with concentrations which inhibited 50% of control response of 55 (67 microM) (5 min) and 30 (36 microM) (30 min) mg/liter for formyl-methionyl-leucyl-phenylalanine stimulation and 117 (143 microM) (5 min) and 44 (54 microM) (30 min) mg/liter for phorbol myristate acetate stimulation.

Entry of sanfetrinem into human polymorphonuclear granulocytes and its cell-associated activity against intracellular, penicillin-resistant Streptococcus pneumoniae

The entry of antibiotics into phagocytes is necessary for activity against intracellular pathogens. The ability of sanfetrinem, the first member of a new class of antibiotics, to penetrate human polymorphonuclear granulocytes and its consequences upon subsequent phagocytosis and killing of ingested penicillin-resistant Streptococcus pneumoniae have been evaluated. Sanfetrinem penetrated into human polymorphonuclear leukocytes (PMNs) at all concentrations tested, with cellular concentration/extracellular concentration ratios of 6.6 to 5.03 and 4.21 when sanfetrinem was used at 0.25 to 0.5 and 1 microgram/ml, respectively, within 30 min of incubation. The uptake was complete within 5 min and was not energy dependent, since it was not affected by cell viability, environmental temperature, or the addition of a metabolic inhibitor. At a concentration of one-half the MIC, sanfetrinem significantly enhanced human PMN phagocytosis and increased intracellular bactericidal activity against penicillin-resistant S. pneumoniae. Following preexposure of PMNs to a concentration of one-half the MIC of sanfetrinem, there was a significant increase in both phagocytosis and killing compared with that for the controls, indicating the ability of sanfetrinem to interact with biological membranes and remain active within PMNs. Preexposure of streptococci to sanfetrinem made penicillin-resistant S. pneumoniae more susceptible to the bactericidal mechanisms of human PMNs than untreated organisms.

Metronidazole. A therapeutic review and update

The nitroimidazole antibiotic metronidazole has a limited spectrum of activity that encompasses various protozoans and most Gram-negative and Gram-positive anaerobic bacteria. Metronidazole has activity against protozoans like Entamoeba histolytica, Giardia lamblia and Trichomonas vaginalis, for which the drug was first approved as an effective treatment. Anaerobic bacteria which are typically sensitive are primarily Gram-negative anaerobes belonging to the Bacteroides and Fusobacterium spp. Gram-positive anaerobes such as peptostreptococci and Clostridia spp. are likely to test sensitive to metronidazole, but resistant isolates are probably encountered with greater frequency than with the Gram-negative anaerobes. Gardnerella vaginalis is a pleomorphic Gram-variable bacterial bacillus that is also susceptible to metronidazole. Helicobacter pylori has been strongly associated with gastritis and duodenal ulcers. Classic regimens for eradicating this pathogen have included metronidazole, usually with acid suppression medication plus bismuth and amoxicillin. The activity of metronidazole against anaerobic bowel flora has been used for prophylaxis and treatment of patients with Crohn's disease who might develop an infectious complication. Treatment of Clostridium difficile-induced pseudomembraneous colitis has usually been with oral metronidazole or vancomycin, but the lower cost and similar efficacy of metronidazole, coupled with the increased concern about imprudent use of vancomycin leading to increased resistance in enterococci, have made metronidazole the preferred agent here. Metronidazole has played an important role in anaerobic-related infections. Advantages to using metronidazole are the percentage of sensitive Gram-negative anaerobes, its availability as oral and intravenous dosage forms, its rapid bacterial killing, its good tissue penetration, its considerably lower chance of inducing C. difficile colitis, and expense. Metronidazole has notable effectiveness in treating anaerobic brain abscesses. Metronidazole is a cost-effective agent due to its low acquisition cost, its pharmacokinetics and pharmacodynamics, an acceptable adverse effect profile, and its undiminished antimicrobial activity. While its role as part of a therapeutic regimen for treating mixed aerobic/anaerobic infections has been reduced by newer, more expensive combination therapies, these new combinations have not been shown to have any therapeutic advantage over metronidazole. Although the use of metronidazole on a global scale has been curtailed by newer agents for various infections, metronidazole still has a role for these and other therapeutic uses. Many clinicians still consider metronidazole to be the 'gold standard' antibiotic against which all other antibiotics with anaerobic activity should be compared.

Cellular accumulation of the new ketolide RU 64004 by human neutrophils: comparison with that of azithromycin and roxithromycin

We analyzed the uptake of RU 64004 by human neutrophils (polymorphonuclear leukocytes [PMNs]) relative to those of azithromycin and roxithromycin. RU 64004 was strongly and rapidly accumulated by PMNs, with a cellular concentration/extracellular concentration ratio (C/E) of greater than 200 in the first 5 min, and this was followed by a plateau at 120 to 180 min, with a C/E of 461 +/- 14.8 (10 experiments) at 180 min. RU 64004 uptake was moderately sensitive to external pH, and activation energy was also moderate (63 +/- 3.8 kJ/mol). RU 64004 was mainly located in PMN granules (about 70%) and egressed slowly from loaded cells, owing to avid reuptake. The possibility that PMN uptake of RU 64004 and other macrolides occurs through a carrier-mediated system was suggested by three key results. First, there existed a strong interindividual variability in uptake kinetics, suggesting variability in the numbers or activity of a transport protein. Second, macrolide uptake displayed saturation kinetics characteristic of that of a carrier-mediated transport system: RU 64004 had the highest Vmax value (3,846 ng/2.5 x 10(6) PMNs/5 min) and the lowest Km value (about 28 microM), indicating a high affinity for the transporter. Third, as observed previously with other erythromycin A derivatives, Ni2+ (a blocker of the Na+/Ca2+ exchanger which mediates Ca2+ influx in resting neutrophils) impaired RU 64004 uptake by PMNs, with a 50% inhibitory concentration of about 3.5 mM. In addition, we found that an active process is also involved in macrolide efflux, because verapamil significantly potentiated the release of all three macrolides tested. This effect of verapamil does not seem to be related to an inhibition of Ca2+ influx, because neither EGTA [ethylene glycol-bis (beta-aminoethyl ether)-N,N',N'-tetraacetic acid] nor Ni2+ modified macrolide efflux. The nature and characteristics of the entry- and efflux-mediating carrier systems are under investigation.

Penetration of brodimoprim into human neutrophils and intracellular activity

The entry of an antibiotic into phagocytes is a prerequisite for its intracellular bioactivity against susceptible facultative or obligatory intracellular microorganisms. Brodimoprim is a dimethoxybenzylpyrimidine that has recently entered into clinical use, and its uptake into and elimination from human polymorphonuclear neutrophils (PMNs), together with its effects on normal phagocytic and antimicrobial mechanisms, have been investigated. Brodimoprim uptake by PMNs was determined by a velocity-gradient centrifugation technique under various experimental conditions and was expressed as the ratio of the intracellular to the extracellular drug concentration (C/E) in comparison with the C/E of trimethoprim, which was used as a control drug. After incubation with 7.5 micrograms of brodimoprim per ml, PMNs accumulated brodimoprim (C/E, 74.43 +/- 12.35 at 30 min) more avidly than trimethoprim (C/E, 20.97 +/- 6.61 at 30 min). The cellular uptake of brodimoprim was not affected by temperature, 2,4-dinitrophenol, or potassium fluoride and was increased with an increase in the pH of the medium. It was reduced in formaldehyde-killed PMNs. The efflux of brodimoprim was very rapid (46% after 5 min). The liposolubility of brodimoprim was about three times that of trimethoprim, as was the uptake. Therefore, a possible passive transmembrane diffusion mechanism might be proposed. Brodimoprim did not decrease either phagocytosis or phagocyte-mediated bactericidal activity, nor did it affect oxidative burst activity, as investigated by luminol-amplified chemiluminescence. On the basis of the pharmacokinetic data for brodimoprim, the concentration of 7.5 micrograms/ml was chosen as the highest concentration attainable in serum by oral therapy, and at this concentration of brodimoprim, the amount of drug that penetrated into PMNs was able to maintain its antimicrobial activity without interfering with the functions of the PMNs.

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

We compared the uptakes and intracellular locations of four 14-membered-ring macrolides (roxithromycin, dirithromycin, erythromycin, and erythromycylamine) in human polymorphonuclear neutrophils (PMNs) in vitro. Intracellular location was assessed by cell fractionation and uptake kinetics in cytoplasts (granule-poor PMNs). Trapping of dirithromycin within PMN granules (up to 80% at 30 min) was significantly more marked than the intracellular trapping of the other drugs (erythromycylamine, 45% +/- 5.1%; erythromycin, 42% +/- 3.7%; roxithromycin, 35% +/- 3.0%). A new finding was that, in the absence of extracellular calcium, the uptakes of all of the macrolides by PMNs and cytoplasts were significantly impaired, by about 50% (PMN) and 90% (cytoplasts). Furthermore, inorganic Ca2+ channel blockers inhibited macrolide uptake in a concentration-dependent manner, with 50% inhibitory concentrations of 1.6 to 2.0 mM and 29 to 35 microM, respectively, for Ni2+ and La3+. The intracellular distributions of the drugs were unchanged in the presence of Ni2+ and La3+ and in Ca(2+)-free medium supplemented with ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. The organic Ca2+ channel blocker nifedipine had no effect on macrolide uptake, whereas verapamil inhibited it in a time- and concentration-dependent manner. These data show the importance of extracellular Ca2+ in macrolide uptake by phagocytes and suggest a link with Ca2+ channels or a Ca2+ channel-operated mechanism.

Influence of pentoxifylline and its derivatives on antibiotic uptake and superoxide generation by human phagocytic cells

Pentoxifylline modulates multiple activities of stimulated polymorphonuclear neutrophils (PMNs), including the respiratory burst response and membrane transport of certain substances (e.g., nucleosides). We found that several weakly basic antibiotics are highly concentrated by human PMNs and that these drugs also inhibit the respiratory burst response (by a mechanism different from that of pentoxifylline). Since both pentoxifylline and antibiotics will be administered to some patients with serious infections, we have evaluated several types of interactions between these drugs and human PMNs and have attempted to identify the mechanisms that produce alterations in cellular function. Roxithromycin, dirithromycin, and clindamycin were avidly concentrated by PMNs. Pentoxifylline and two derivatives (HWA-448 [torbafylline] and HWA-138 [albifylline]) increased the uptake of these antibiotics by PMNs, both in the resting state and during phagocytosis. Pentoxifylline, HWA-448, HWA-138, and the highly concentrated antibiotics each exerted an inhibitory effect on the stimulated respiratory burst response in PMNs. The combination of both pentoxifylline and a modulatory antibiotic (roxithromycin or clindamycin) inhibited superoxide production to a greater extent than either agent alone. This additive effect might be expected, since pentoxifylline and the modulatory antibiotics influence the respiratory burst activation pathway at different sites. The ability of pentoxifylline to augment the entry of antibiotics into neutrophils has important therapeutic implications. The consequences of this phenomenon might include improved intracellular bactericidal activity as well as efficient antibiotic delivery and release at sites of infection.

Antibiotic effects on phagocyte chemiluminescence in vitro

Phagocytes are an essential defence against infection. Since drugs which affect their function may alter the outcome of infections, we have studied the effect of nine antibiotics on phagocyte function in vitro. The effects of antibiotics on the respiratory burst function of phagocytes from healthy adult donors were investigated using lucigenin-enhanced chemiluminescence in response to serum-opsonised zymosan. Aminoglycosides showed dose-dependent suppression of polymorphonuclear leucocyte chemiluminescence, except streptomycin which caused enhancement. Erythromycin caused profound suppression of chemiluminescence from both polymorphonuclear leucocytes and monocytes. Benzylpenicillin and the cephalosporins caused variable suppression of phagocyte chemiluminescence: cefotaxime increased monocyte chemiluminescence in some experiments. None of the drugs produced suppression at clinically relevant plasma concentrations, but erythromycin and some other drugs are preferentially concentrated in phagocytes to levels which suppress their oxidative metabolism in vitro. It is therefore possible that some antibiotics alter phagocyte function: ex vivo studies of phagocyte function in patients taking antibiotics would be valuable.

Intracellular activity of azithromycin against bacterial enteric pathogens

Azithromycin, a new azalide antibiotic, is active in vitro against a variety of enteric bacterial pathogens. Since it is concentrated inside human neutrophils and other cells, it might be particularly useful in the treatment of infections caused by enteropathogens that invade host tissues. The intracellular activity of azithromycin against several enteric pathogens that had been phagocytosed by neutrophils was determined. Azithromycin was effective in reducing the intracellular viabilities of almost all strains tested, including representative strains of Salmonella, Shigella, and enteroinvasive, enteropathogenic, enterotoxigenic, and enterohemorrhagic Escherichia coli. Erythromycin was also effective in this model system, although azithromycin was generally more effective than erythromycin against strains of invasive enteric pathogens. Cefotaxime reduced intracellular bacterial viability to a lesser extent than either azithromycin or erythromycin. The presence of neutrophils did not significantly affect the activity of azithromycin in this system. Azithromycin may be a useful agent for the treatment of bacterial diarrhea, and clinical trials should be considered.

Roxithromycin. An update of its antimicrobial activity, pharmacokinetic properties and therapeutic use

Roxithromycin is a derivative of the macrolide antibacterial erythromycin with in vitro antibacterial activity resembling that of the parent compound. The drug has activity against some Staphylococcus spp., many Streptococcus spp., Moraxella (Branhamella) catarrhalis, Mycoplasma pneumoniae, Legionella pneumophila and Chlamydia trachomatis as well as many less common organisms. Measured using recently proposed guidelines, roxithromycin has in vitro activity against Haemophilus influenzae. In comparison with that of its parent compound, the pharmacokinetic profile of roxithromycin is characterised by high plasma, tissue and body fluid concentrations and a long half-life permitting an extended dosage interval. Roxithromycin has proven clinical efficacy in upper and lower respiratory infections, skin and soft tissue infections, urogenital infections and orodental infections, and appears to be as effective as more established treatments including erythromycin, amoxicillin/clavulanic acid and cefaclor. The drug has also shown promise in a variety of more specialised indications including opportunistic infections in human immunodeficiency virus (HIV)-positive patients and as part of a Helicobacter pylori eradication regimen. Roxithromycin is very well tolerated with an overall incidence of adverse events of approximately 4%. Thus, roxithromycin is an attractive therapeutic alternative in its established indications, especially when the option of once-daily administration is considered.

Interactions of dirithromycin with human polymorphonuclear leukocytes

Dirithromycin, a new macrolide antibiotic, achieves prolonged, high levels in tissue. We previously demonstrated that certain macrolides are highly concentrated within phagocytic cells. This background information prompted us to evaluate the interactions of dirithromycin and human polymorphonuclear leukocytes (PMNs). After incubation with radiolabeled dirithromycin, antibiotic uptake by PMNs was determined by a velocity-gradient centrifugation technique and was expressed as the ratio of the cellular to the extracellular drug concentration (C/E). Dirithromycin was avidly accumulated by PMNs (C/E, 5 at 15 min, 10 at 30 min, 19 at 1 h, and 35 at 2 h). Uptake was dependent on cell viability, physiologic environmental temperature, and pH (optimum 8.6), but was not influenced by potential competitive inhibitors of membrane transport. Incubation with sodium cyanide caused an increase in dirithromycin accumulation by PMNs. Ingestion of microbial particles (mimicking in vivo infection) modestly inhibited the entry of dirithromycin into PMNs. After removal of extracellular drug, the efflux (release) of dirithromycin from PMNs was slow; only 10% was released within the first 30 min. This prolonged retention of dirithromycin within phagocytic cells might allow delivery and release of accumulated drug at sites of infection. The impact of intraphagocytic dirithromycin on cellular function was also evaluated. In a manner similar to that of other highly concentrated, weakly basic antibiotics, dirithromycin inhibited the respiratory burst response (superoxide production) in stimulated PMNs. The presence of dirithromycin slightly increased the intraphagocytic killing of Staphylococcus aureus in human PMNs. These interactions of dirithromycin with phagocytic cells may promote the extraphagocytic, and possibly the intraphagocytic, killing of infecting organisms.

Entry of lomefloxacin and temafloxacin into human neutrophils, peritoneal macrophages, and tissue culture cells

The uptake of lomefloxacin (difluoroquinolone) and temafloxacin (trifluoroquinolone) by human polymorphonuclear leukocytes (PMNs), peritoneal macrophages (PM phis), and two tissue culture cells (McCoy and Vero) was measured by a fluorometric assay. Both antimicrobials reached high intracellular concentrations in PMNs [cellular to extracellular ratio (C/E) greater than 4], in PM phis (C/E greater than 3) and lower in tissue culture cells (C/E greater than 1) at an extracellular concentration of 5 mg/L. Lomefloxacin uptake by PMNs was more rapid than that of temafloxacin. Entry of both quinolones into PMNs was environmental temperature-dependent, but not affected by cell viability. Ingestion of opsonized Staphylococcus aureus did not affect the ability of PMNs to concentrate these antimicrobials. Ingestion of opsonized zymosan or stimulation with phorbol myristate acetate significantly increased the PMN association of both quinolones, this effect being particularly marked with temafloxacin. It is concluded that both lomefloxacin and temafloxacin are markedly concentrated within human phagocytes and tissue culture cells, although this phenomenon is not dependent on the degree of fluorination of the molecule.

Clindamycin, erythromycin, and roxithromycin inhibit the proinflammatory interactions of Pseudomonas aeruginosa pigments with human neutrophils in vitro

The Pseudomonas aeruginosa-derived phenazine pigments pyocyanin and 1-hydroxyphenazine (1-hp) prime human neutrophils for enhanced, stimulus-activated release of superoxide and myeloperoxidase (MPO), respectively. In the present study, the modulatory potentials of the antimicrobial agents clindamycin, erythromycin, and roxithromycin (10 and 20 micrograms/ml) on the prooxidative interactions of pyocyanin and 1-hp (12.5 microM) with human neutrophils have been investigated. Clindamycin, erythromycin, and especially roxithromycin caused dose-related inhibition of the generation of superoxide by both untreated and pyocyanin-treated neutrophils during activation with either the synthetic chemotactic tripeptide N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) or the calcium ionophore A23187. The antimicrobial agents also inhibited the generation of reactive oxidants by the MPO-H2O2-halide system during activation of both untreated and 1-hp-treated neutrophils by FMLP. These effects appeared to be due to drug-related interference with membrane-associated oxidative metabolism, since none of the antimicrobial agents inhibited the release of MPO by activated neutrophils, nor did they possess oxidant-scavenging properties. These data demonstrate that clindamycin, erythromycin, and especially roxithromycin antagonize the proinflammatory interactions of pyocyanin and 1-hp with neutrophils and indicate a possible therapeutic role for these antimicrobial agents in the prevention of tissue damage in diseases characterized by P. aeruginosa infection.

In vitro and in vivo intraleukocytic accumulation of azithromycin (CP-62, 993) and its influence on ex vivo leukocyte chemiluminescence

The accumulation of azithromycin in phagocytic cells was studied both in vitro by using a radiolabelled drug and a bioassay and in vivo for 12 volunteers receiving 1.5 g (total dose) orally within 3 days. In vitro, neutrophils and unfractionated blood leukocytes accumulated azithromycin up to 160-fold the extracellular concentration within 1 h at 37 degrees C but less than 3-fold at 4 degrees C. Dead cells accumulated up to 30-fold azithromycin, whereas NaF-treated cells accumulated up to 60-fold arithromycin. The mean efflux from preloaded cells was at most 31.0% +/- 10.6% (standard error of the mean) of the cell-associated concentration within 4 h of incubation at 37 degrees C in drug-free buffer. In vivo, the azithromycin concentration was 45.2 +/- 6.1 mg/liter of intracellular fluid at 2 h after the third dose and 36.6 +/- 8.3 mg/liter at 1 week thereafter. The corresponding concentrations in serum were 0.2 +/- 0.1 (2 h) and less than 0.05 (1 week). The luminol-enhanced chemiluminescence response induced by phorbol myristate acetate, opsonized zymosan, and two opsonized strains of Haemophilus influenzae (a type b capsulated strain and a noncapsulated strain) was also studied ex vivo by using the blood leukocytes from the 12 test volunteers and 4 control volunteers at 2 and 6 h after the third oral dose of azithromycin and at 2, 4, and 7 days thereafter. Azithromycin did not influence this response despite high levels of cellular accumulation.

Imipenem

Imipenem is the first of a new class of beta-lactam antibiotics, the carbapenems, to be released for clinical use. It has the broadest antibacterial activity of all antibiotics available for systemic use in humans. It is active against streptococci, methicillin-sensitive staphylococci, Neisseria, Haemophilus, anaerobes, and the common aerobic gram-negative nosocomial pathogens including Pseudomonas. Resistance to imipenem may emerge during treatment of P. aeruginosa infections, as has occurred with other beta-lactam agents; P. maltophilia and P. cepacia are typically resistant to it. Like the penicillins, imipenem has inhibitory activity against enterococci. Daily doses may range from 500 mg to 1 g, every 6 to 8 hours, in patients with normal renal function. The principal toxic effects have been nausea and vomiting, which occur during intravenous infusion, and seizures, which develop in 1 to 3% of treated patients and are likely to occur in the setting of renal insufficiency and underlying disease of the central nervous system. Imipenem should be considered for treatment of mixed bacterial infections and treatment of resistant aerobic gram-negative bacteria that are not susceptible to other beta-lactam agents. In addition to provoking unnecessary toxicity, indiscriminate use of this agent will promote dissemination of resistance against it.

Failure of beta-lactam antibiotics and marked efficacy of fluoroquinolones in treatment of murine Yersinia pseudotuberculosis infection

The treatment of yersiniosis by beta-lactams is questionable considering the proven failure of newer beta-lactams for treating murine Yersinia enterocolitica infection. Another modality of experimental treatment was performed with a virulent strain of Y. pseudotuberculosis (nonproducer of beta-lactamase) highly susceptible (in terms of MICs) to amoxicillin, cefotaxime, ceftriaxone, imipenem, doxycycline, gentamicin, and ofloxacin. The in vivo comparative efficacy of these drugs was evaluated in a standardized and reproducible mouse model of systemic infection. Each single antibiotic was injected intravenously once, at 30 h after intravenous inoculation of the infective strain, and then repeatedly (at 30, 52, and 76 h postinfection). In vivo results were measured by counting the viable bacteria recovered from the whole spleens of mice sacrificed at selected times. Cefotaxime, even at high doses (250 mg/kg of body weight), was totally ineffective. Amoxicillin and imipenem at high doses (200 and 100 mg/kg, respectively) and ceftriaxone at usual doses (20 mg/kg) were active only in stopping bacterial proliferation to a more or less slight degree. Ceftriaxone was able to reduce viable counts in the spleen only at high doses (200 mg/kg), as were gentamicin (20 mg/kg) and doxycycline (125 mg/kg). Ofloxacin at the low dose of 5 mg/kg was demonstrated to be very effective by the very significant decrease observed in bacterial numbers from 10(6) to 10(3) CFU per spleen. The pharmacological parameters do not in themselves explain all the discrepancies between the in vitro and in vivo activities of beta-lactams on yersiniae. No emergence of beta-lactam-resistant organisms, which could explain the failure of beta-lactams, was detected. Thus, their use should be delayed in the therapy of human yersinosis until further investigations are carried out. The fluoroquinolone appeared more active and rapid than reference drugs in the treatment of murine yersinosis, which confirms initial clinical results.

The effect of trimethoprim on sodium transport across the frog skin epithelium

Trimethoprim, a dihydrofolate reductase inhibitor, is used as a therapeutical agent in combination with sulfamethoxazole. Studies of the interaction of trimethoprim with membrane transport are rare. This paper presents a study of the effect of trimethoprim on the short-circuit current (Isc) and on the transepithelial total conductance (Gt) of the isolated frog skin. We found a fast drop (less than 1 min) of Isc (50%) and Gt (30%) after the addition of the drug to the outside medium (mucosa). A dose-response curve of the effect of the drug has shown that trimethoprim has no effect for concentrations below 0.01 mM and reaches a half-maximum inhibition at 0.5 mM. Trimethoprim induces a decrease in the sodium radioactive tracer fluxes that parallel the decrease of the observed Isc. It induces a hyperpolarization of the mucosal barrier in the same way that amiloride does. A comparative study of the effect of trimethoprim and amiloride has shown that trimethoprim acts on the amiloride-sensitive sodium channels of the mucosal barrier and behaves as a competitive inhibitor of amiloride with a dissociation constant KTRIM of 53 x 10(-5) M while KAMIL = 46 x 10(-8) M.