Kazuo Hatano

Evidence for the involvement of GABAA receptor blockade in convulsions induced by cephalosporins

There is accumulating evidence that most beta-lactam antibiotics (i.e., cephalosporins and penicillins) have some degree of convulsive activity, both in laboratory animals as well as in clinical settings. The proposed mechanism is suppression of inhibitory postsynaptic responses, mainly mediated by gamma-amino butyric acid (GABA)(A)-receptors (GABA(A)-R). However, comprehensive studies on the convulsive activities of various beta-lactam antibiotics in vivo and in vitro have not been performed. We have therefore examined the convulsive activities of seven different cephalosporins using both in vivo and in vitro models: intracerebroventricular (ICV) administration in mouse; [(3)H]muscimol binding assay (BA) in mouse brain synaptosome; and inhibition of recombinant mouse alpha1beta2gamma2s GABA(A)-Rs in Xenopus oocyte (GR). The rank orders of convulsive activities in mouse (cefazolin>cefoselis>cefotiam>cefpirome>cefepime>ceftazidime>cefozopran) correlated with those of inhibitory potencies on [(3)H]muscimol binding and GABA-induced currents of GABA(A)-R in vitro, with correlation coefficients of ICV:GR, ICV:BA and BA:GR of 0.882, 0.821 and 0.832, respectively. In contrast, none of the antibiotics had affinities for N-methyl-D-aspartate (NMDA) receptors nor facilitatory actions on NMDA receptor-mediated current in oocytes. These results clearly demonstrate that the mechanism of cephalosporin-induced convulsions is mediated predominantly through the inhibition of GABA(A)-R function and not through NMDA receptor modulation.

In Vitro and In Vivo Activities of a New Cephalosporin, FR264205, against Pseudomonas aeruginosa

ABSTRACT FR264205 is a novel parenteral 3′-aminopyrazolium cephalosporin. This study evaluated the in vitro and in vivo activities of FR264205 against Pseudomonas aeruginosa. The MIC of FR264205 at which 90% of 193 clinical isolates of P. aeruginosa were inhibited was 1 μg/ml, 8- to 16-fold lower than those of ceftazidime (CAZ), imipenem (IPM), and ciprofloxacin (CIP). FR264205 also exhibited this level of activity against CAZ-, IPM-, and CIP-resistant P. aeruginosa. The reduction in the susceptibility of FR264205 by AmpC β-lactamase was lower than that of CAZ, indicating a relatively high stability of FR264205 against AmpC β-lactamase, the main resistance mechanism for cephalosporins. Neither expression of efflux pumps nor deficiency of OprD decreased the activity of FR264205. No spontaneous resistance mutants were selected in the presence of FR264205, and the reduction in susceptibility to FR264205 was lower than that to CAZ, IPM, and CIP after serial passage, suggesting that FR264205 has a low propensity for selecting resistance. In murine pulmonary, urinary tract, and burn wound models of infection caused by P. aeruginosa, the efficacy of FR264205 was superior or comparable to those of CAZ and IPM. These results indicate that FR264205 should have good potential as an antibacterial agent for P. aeruginosa.

Efficacy of FK463, a New Lipopeptide Antifungal Agent, in Mouse Models of Pulmonary Aspergillosis

ABSTRACT The efficacy of FK463, a novel water-soluble lipopeptide, was evaluated in mouse models of pulmonary aspergillosis and was compared with that of amphotericin B (AMPH-B). In the pulmonary aspergillosis models induced by intranasal inoculation, FK463 exhibited good efficacy, with 50% effective doses in the range of 0.26 to 0.51 mg/kg of body weight; these values were comparable to those of AMPH-B. In anAspergillus target organ assay with immunosuppressed mice, under conditions of constant plasma levels of FK463, using a subcutaneously implanted osmotic pressure pump, a significant reduction in viable fungal cells was observed at plasma FK463 levels of 0.55 to 0.80 μg/ml or higher. We conclude that FK463 is highly effective in the treatment of pulmonary aspergillosis in this animal model. These results indicate that FK463 may be a potent parenterally administered antifungal agent for pulmonary aspergillosis.

Characterization of a Multigene-Encoded Sodium/Hydrogen Antiporter (Sha) from Pseudomonas aeruginosa: Its Involvement in Pathogenesis

Sha (also known as Mrp/Mnh/Pha) is a Na+/H+ antiporter encoded by a cluster of six or seven genes that probably form a multisubunit transport complex. The Sha system is important for the homeostasis of H+, Na+, and other monovalent cations and plays a critical role in various functions, including alkaliphily, sporulation, and symbiosis. Here, we characterized the sha homologue genes from the opportunistic pathogen Pseudomonas aeruginosa, which exist as a cluster of six genes (PA1054 to PA1059). The gene cluster PA1054 to PA1059, but not the cluster with a deletion of PA1054, complemented a growth defect in the presence of 0.2 M NaCl and a defect in Na+/H+ antiport activity of the Escherichia coli TO114 mutant lacking the three major Na+/H+ antiporters, indicating that genes PA1054 to PA1059 are responsible for Na+/H+ antiport activity. We disrupted PA1054 (a shaA homologue gene) and determined its effect on Na+ tolerance during growth, Na+ efflux, and pathogenicity in mice. Disruption of PA1054 resulted in severe Na+ sensitivity during growth and decreased Na+ efflux activity. In mice, the deletion mutant of PA1054 also exhibited an attenuated virulence in systemic, pulmonary, and urinary tract infections and also a decrease in colonization of the infected organs. From these results, we conclude that the genes PA1054 to PA1059 encode a Na+/H+ antiporter that is largely responsible for Na+ extrusion in P. aeruginosa and has a role in the infection of the pathogen. We propose to designate PA1054 to PA1059 as the sha (sodium hydrogen antiporter) genes, shaABCDEFG.

Killing Activity of Micafungin against Aspergillus fumigatus Hyphae Assessed by Specific Fluorescent Staining for Cell Viability

ABSTRACT We studied the anti-Aspergillus activity of micafungin by using two fluorescent dyes to detect cell viability. Micafungin induced flattened hyphae, caused by the bursting of cells, which had lost their viability. Micafungin has killing activity against actively growing hyphae, even though it is not fungicidal against the whole burden of Aspergillus fumigatus.

Synthesis and SAR of novel parenteral anti-pseudomonal cephalosporins: discovery of FR264205.

We describe herein the synthesis and biological evaluation of a series of novel cephalosporins with potent activity against Pseudomonas aeruginosa. Introduction of various amino groups to the 4-position of a 3-amino-2-methylpyrazole cephalosporin 3-side chain resulted in enhanced MIC values against multiple Pseudomonas aeruginosa strains and ultimately led to the discovery of FR264205 (15) with excellent anti-bacterial activity and weak convulsion effect by direct intracerebroventricular injection assay.

Simulation of Human Plasma Levels of β-Lactams in Mice by Multiple Dosing and the Relationship between the Therapeutic Efficacy and Pharmacodynamic Parameters

A mathematical multiple dosing model was designed so that human plasma concentration-versus-time curves of beta-lactams are reproduced in mouse plasma. The pharmacokinetic parameters of FK037, a new injective cephalosporin, in volunteers and in the mice model were 6,966 and 6,894 ml, respectively, for Vc, 2.592 and 2.698/h for alpha, 0.2875 and 0.3027/h for beta, and 0.9079 and 1.0506 for K21. Therefore, real pharmacokinetics of humans were reproduced in mice by this method. The 8-hour therapeutic efficacy (the decrease of the viable counts in the lung) against pneumonia with Staphylococcus aureus and Pseudomonas aeruginosa in mice was well correlated with the time above MIC value, but not with AUC, Cmax or AUC above MIC. These results indicate that this model was valuable to evaluate the beta-lactam antibiotics for predicting their clinical efficacy and that the time above MIC is an important factor in selecting beta-lactam agents and determining dosage in pulmonary infection.

Novel Carbapenem Antibiotics for Parenteral and Oral Applications: In Vitro and In Vivo Activities of 2-Aryl Carbapenems and Their Pharmacokinetics in Laboratory Animals

ABSTRACT SM-295291 and SM-369926 are new parenteral 2-aryl carbapenems with strong activity against major causative pathogens of community-acquired infections such as methicillin-susceptible Staphylococcus aureus, Streptococcus pneumoniae (including penicillin-resistant strains), Streptococcus pyogenes, Enterococcus faecalis, Klebsiella pneumoniae, Moraxella catarrhalis, Haemophilus influenzae (including β-lactamase-negative ampicillin-resistant strains), and Neisseria gonorrhoeae (including ciprofloxacin-resistant strains), with MIC90s of ≤1 μg/ml. Unlike tebipenem (MIC50, 8 μg/ml), SM-295291 and SM-369926 had no activity against hospital pathogens such as Pseudomonas aeruginosa (MIC50, ≥128 μg/ml). The bactericidal activities of SM-295291 and SM-369926 against penicillin-resistant S. pneumoniae and β-lactamase-negative ampicillin-resistant H. influenzae were equal or superior to that of tebipenem and greater than that of cefditoren. The therapeutic efficacies of intravenous administrations of SM-295291 and SM-369926 against experimentally induced infections in mice caused by penicillin-resistant S. pneumoniae and β-lactamase-negative ampicillin-resistant H. influenzae were equal or superior to that of tebipenem and greater than that of cefditoren, respectively, reflecting their in vitro activities. SM-295291 and SM-369926 showed intravenous pharmacokinetics similar to those of meropenem in terms of half-life in monkeys (0.4 h) and were stable against human dehydropeptidase I. SM-368589 and SM-375769, which are medoxomil esters of SM-295291 and SM-369926, respectively, showed good oral bioavailability in rats, dogs, and monkeys (4.2 to 62.3%). Thus, 2-aryl carbapenems are promising candidates that show an ideal broad spectrum for the treatment of community-acquired infections, including infections caused by penicillin-resistant S. pneumoniae and β-lactamase-negative ampicillin-resistant H. influenzae, have low selective pressure on antipseudomonal carbapenem-resistant nosocomial pathogens, and allow parenteral, oral, and switch therapies.

In Vitro Antibacterial Activity of FK041, a New Orally Active Cephalosporin.

The in vitro activity of FK041, a new orally active cephem antibiotic, against a wide variety of clinical isolates of bacteria was investigated and compared with those of cefdinir (CFDN) and cefditoren (CDTR). FK041 exhibited broad spectrum activity against reference strains of Gram-positive and Gram-negative aerobes and anaerobes. FK041 was active against clinical isolates of Gram-positive organisms except Enterococcus faecalis with MIC90s less than 1.56 microg/ml. FK041 was more active than CFDN and CDTR against Staphylococcus aureus, Staphylococcus epidermidis, and Streptococcus agalactiae and was comparable to CFDN and CDTR against Streptococcus pyogenes and Streptococcus pneumoniae. FK041 had no activity against methicillin-resistant staphylococci, like CFDN and CDTR. FK041 showed moderate activity against penicillin-resistant S. pneumoniae with an MIC range of 0.05 approximately 3.13 microg/ml, and was superior to CFDN but inferior to CDTR. Against clinical isolates of many Gram-negative organisms such as Neisseria gonorrhoeae, Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis, FK041 had good activity comparable or superior to those of CFDN and CDTR. However, it was inferior to CDTR in activity against Moraxella catarrhalis, Haemophilus influenzae, Morganella morganii, and Serratia marcescens, and was inactive against Pseudomonas aeruginosa. With FK041 a small difference between MIC and MBC against S. aureus, E. coli, K. pneumoniae, and H. influenzae was found, indicating that its action is bactericidal against these species. FK041 was stable to group 2beta-lactamase hydrolysis but was unstable to group 1beta-lactamase hydrolysis. The stability of FK041 to these enzymes was similar to those of CFDN and CDTR. FK041 showed high affinity for the main penicillin-binding proteins (PBPs) of S. aureus (PBP 3, 2, and 1) and E. coli (PBP 3, 4, lbs, 2, and 1a).

In vitro antimicrobial activity of telavancin against methicillin-resistant Staphylococcus aureus clinical isolates from Japan (2006).

In vitro antimicrobial activity of telavancin, a rapidly bactericidal lipoglycopeptide, was evaluated against 1500 strains of MRSA recently isolated in Japan. Telavancin had potent activity, with MIC values that ranged from 0.12 μg/ml to 0.5 μg/ml and a MIC90 value of 0.5 μg/ml. The MIC90s of vancomycin and linezolid were 1.0μg/ml and 2 μg/ml, respectively. No vancomycin intermediate resistant or vancomycin-resistant MRSAs were detected in this surveillance study.