Competitive profiling for enzyme inhibitors using chemical probes.

Enzyme inhibitors are central tools for chemical biology. In this chapter we will discuss the application of chemical probes for competitive profiling of inhibitors of the quinolone biosynthesis enzyme PqsD of Pseudomonas aeruginosa. The human pathogen P. aeruginosa produces a large diversity of 2-alkyl-4(1H)-quinolones and their derivatives as metabolites with major roles in quorum sensing, virulence, and interspecies competition. PqsD is a central enzyme in the biosynthesis of all of these quinolones and hence an interesting target for inhibitor discovery. Activity-based probes with an electrophilic warhead bind covalently to active site nucleophiles like cysteine or serine. An α-chloroacetamide probe with terminal alkyne tag allowed to selectively label the active site cysteine of PqsD and was demonstrated to be a useful tool for inhibitor discovery using competition experiments. Potent inhibitors bind to the active site and thereby prevent labeling of the enzyme by the probe. Labeling intensity is quantified on polyacrylamide gels by the fluorescence of a reporter tag appended by bioorthogonal click chemistry. The competitive inhibitor profiling strategy has many advantages over traditional screening approaches and is applicable in vitro as well as in live cells. Here we describe the synthesis of an activity-based probe and provide our detailed protocols for target enzyme labeling as well as its application for the screening for potent enzyme inhibitors of PqsD by a competitive profiling strategy.

Comparación entre ciprofloxacina y antibióticos de otros grupos farmacológicos para el tratamiento de infecciones del tracto urinario / Comparison between ciprofloxacine and antibiotics of other pharmacological groups for urinary tract infection treatment / Comparação entre a ciprofloxacina e outros antibióticos grupos farmacológicos para o tratamento de infecções do tracto urinário

ResumenIntroducción. Las infecciones de tracto urinario son un tema común en los servicios de consulta externa y emergencias de los centros de salud. El uso inadecuado e irracional de antibióticos puede favorecer la aparición de cepas resistentes y limitar la capacidad de respuesta de estos fármacos. Este artículo busca revisar el uso de quinolonas (específicamente ciprofloxacina) con antibióticos de otros grupos farmacológicos y comparar efectividad y resistencia bacteriana.Método. A partir de la metodología que señala la práctica clínica basada en la evidencia para las revisiones rápidas, se estableció una pregunta clínica a la que se le procuró responder mediante la búsqueda de investigaciones primarias en bases de datos electrónicas como MEDLINE, PubMed, Cochrane Library Plus y el Journal of Infection.Resultado. Según el tipo de bacteria y cepa analizada, hay presencia de resistencia a diversos antibióticos. Las infecciones de origen comunitario han sido tratadas con betalactámicos, nitrofurantoína, trimetoprimsulfametoxasol y fluoroquinolonas (especialmente ciprofloxacina).Conclusión. No se determinó si las quinolonas son más efectivas que los antibióticos que pertenecen a otros grupos farmacológicos

AbstractIntroduction. Urinary tract infections are a common reason of consultation in medical practical in ambulatory and emergency rooms in centers of health. The inadequate and irrational use of antibiotics can favor the appearance of resistant bacterial strain and limit the capacity of response of these medicines. This article seeks to review the use of quinolones (specifically ciprofloxacine) with antibiotics of other pharmacological groups and to compare efficiency and bacterial resistance.Method.From the methodology that indicates the clinical practice based on the evidence for the rapid reviews, there was established a clinical question to which response was tried to give by means of the search of primary investigations in electronic databases like MEDLINE, PubMed, Cochrane Library Plus and the Journal of Infection.Result. According to the type of bacterium and analyzed bacterial strain there is presence of resistance to diverse antibiotics. The infections of community origin have been treated by beta-lactamics, nitrofurantoine, trimetoprimsulfametoxasol and fluoroquinolones (specially ciprofloxacine).Conclusion. It was not possible to determine if the quinolonas are more effective than the antibiotics that belong to other pharmacological groups.

ResumoIntrodução. As infecções do trato urinário são um tema comum nos serviços de consulta externa e emergências dos centros de saúde. O uso inadequado e irracional de antibióticos pode favorecer o aparecimento de cepas resistentes e limitar a capacidade de resposta destes medicamentos. Este artigo busca revisar o uso de quinolonas (especificamente ciprofloxacina) com antibióticos de outros grupos farmacológicos e comparar efetividade e resistência bacteriana.Método. A partir da metodologia que aponta a prática clínica baseada na evidência para as revisões rápidas, se estabeleceu uma pergunta clínica que se procurou responder mediante pesquisas primárias em bases de dados eletrônicas como MEDLINE, PubMed, Cochrane Library Plus e o Journal of Infection.Resultado. Segundo o tipo de bactéria e cepa analisada, há presença de resistência a diversos antibióticos. As infecções de origem comunitária tem sido tratadas com betalactâmicos, nitrofurantoína, trimetoprimsulfametoxasol e fluoroquinolonas (especialmente ciprofloxacina).Conclusão. Não se determinou se as quinolonas são mais eficazes que os antibióticos que pertencem a outros grupos farmacológicos

Antagonistic effects of indoloquinazoline alkaloids on antimycobacterial activity of evocarpine.

AIMS: The interaction of quinolone and indoloquinazoline alkaloids concerning their antimycobacterial activity was studied. METHODS AND RESULTS: The antimycobacterial and modulating activity of evodiamine (1), rutaecarpine (2) and evocarpine (3) was tested on mycobacteria including three multidrug-resistant (MDR) clinical isolates of Mycobacterium tuberculosis. Antagonistic effects were concluded from fractional inhibitory concentration (FICI) values. Interaction energies of the compounds were calculated using GLUE docking module implemented in GRID. 1 and 2 exhibited weak inhibition of rapidly growing mycobacteria, however, 1 was active against Myco. tuberculosis H37Rv (MIC = 10 mg l(-1) ) while 2 was inactive. Both 1 and 2 showed a marked antagonistic effect on the susceptibility of different mycobacterial strains to 3 giving FICI values between 5 and 9. The interaction energies between compounds 1 and 2 with compound 3 suggested the possibility of complex formation in solution. CONCLUSIONS: Indoloquinazoline alkaloids markedly reduce the antimycobacterial effect of the quinolone alkaloid evocarpine. Complex formation may play a role in the attenuation of its antimycobacterial activity. SIGNIFICANCE AND IMPACT OF THE STUDY: This study gives a striking example of antagonism between compounds present in the same plant extract which should be considered in natural product based screening projects.

Use of propranolol blockade to explore the pharmacology of GSK961081, a bi-functional bronchodilator, in healthy volunteers: results from two randomized trials.

PURPOSE: The objective of this study was to explore the pharmacology of GSK961081, a bi-functional bronchodilator, in healthy volunteers. METHODS: Two randomized, double-blind, placebo-controlled studies were conducted. Following optimization of the propranolol dosing regimen (study 1), we conducted a five-period crossover study (study 2) in which subjects received the following treatments: dry powder inhaler (DPI) GSK961081 400 µg + oral placebo, DPI GSK961081 1,200 µg + oral placebo, DPI GSK961081 400 µg + oral propranolol 80 mg, DPI GSK961081 1,200 µg + oral propranolol 80 mg and DPI and oral placebo. GSK961081 (or inhaled placebo) was dosed at 0 h. Propranolol (or oral placebo) was dosed at -8, -2, 4, 10, and 16 h. The primary endpoint for both studies was bronchodilation, measured by specific airway conductance (sGaw), which was assessed at 0, 1, 4, 7, 12, 22, and 24 h in study 2. Tolerability and pharmacokinetics were secondary endpoints. RESULTS: Studies 1 and 2 enrolled 18 and 23 subjects, respectively. In study 2, bronchodilation was seen for 24 h following GSK961081 400 and 1,200 µg. In the presence of ß2 blockade, GSK961081 1,200 µg demonstrated bronchodilation in the first 4 h after dosing (treatment difference from placebo at 1 h: 1.206; 90% confidence interval [CI] 1.126-1.292; and at 4 h: 1.124; 90% CI 1.078-1.173) but not at 7 h onwards. In the presence of ß2 blockade, GSK961081 400 µg demonstrated bronchodilation in the first 1 h after dosing (treatment difference from placebo: 1.193; 90% CI 1.117-1.274), but not at 4 h onwards. Adverse events were reported for 21 (study 1) and 15 subjects (study 2); none were serious, and there were no deaths. CONCLUSION: The duration of bronchodilation as a result of receiving the muscarinic antagonist component alone was shorter than that from the muscarinic antagonist ß2 agonist combination. Removing the ß2 agonist component may underestimate the contribution of the muscarinic antagonist component to the bronchodilation of the combination.

Optimization of anti-virulence PqsR antagonists regarding aqueous solubility and biological properties resulting in new insights in structure-activity relationships.

Increasing antibiotic resistance urgently requires novel therapeutic options to combat bacterial infections. The anti-virulence therapy selectively intervening with pathogenicity without affecting bacterial viability is such a strategy to overcome resistance. We consider the virulence regulator PqsR as an attractive target in the human pathogen Pseudomonas aeruginosa, and recently discovered the first PqsR antagonists, which, however, suffered from poor aqueous solubility. In this work, the antagonists were structurally modified to become more soluble, and their structure-activity as well as structure-property relationships were studied. A novel promising compound with improved solubility and enhanced anti-virulence activity was discovered (IC50: 3.8 µM, pyocyanin). Our findings emphasize the crucial role of substituents at the 3-position and the carbonyl group at the 4-position for ligand-receptor interactions, and illuminate the way for further optimization of PqsR antagonists as anti-virulence agents.

Antagonism of the adenosine A2A receptor attenuates akathisia-like behavior induced with MP-10 or aripiprazole in a novel non-human primate model.

Akathisia is a subset of the larger antipsychotic side effect profile known as extrapyramidal syndrome (EPS). It is associated with antipsychotic treatment and is characterized as a feeling of inner restlessness that results in a compulsion to move. There are currently no primate models available to assess drug-induced akathisia; the present research was designed to address this shortcoming. We developed a novel rating scale based on both the Barnes Akathisia Rating Scale (BARS) and the Hillside Akathisia Scale (HAS) to measure the objective, observable incidence of antipsychotic-induced akathisia-like behavior in Cebus apella non-human primates (NHPs). To induce akathisia, we administered the atypical antipsychotic aripiprazole (1 mg/kg) or the selective phosphodiesterase 10A (PDE10A) inhibitor MP-10 (1-3 mg/kg). Treatment with both compounds produced significantly greater akathisia scores on the rating scale than vehicle treatment. Characteristic behaviors observed included vocalizations, stereotypies, teeth grinding, restless limb movements, and hyperlocomotion. Adenosine A2A receptor antagonists have previously been shown to be effective in blocking antipsychotic-induced EPS in primates. The selective A2A receptor antagonist, SCH 412348 (10-30 mg/kg), effectively reduced or reversed akathisia-like behavior induced by both aripiprazole and MP-10. This work represents the first NHP measurement scale of akathisia and demonstrates that NHPs are responsive to akathisia-inducing agents. As such, it provides a useful tool for the preclinical assessment of putative antipsychotics. In addition, these results provide further evidence of the utility of A2A receptor antagonists for the treatment of antipsychotic-induced movement disorders.

QapR (PA5506) represses an operon that negatively affects the Pseudomonas quinolone signal in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a Gram-negative, opportunistic pathogen that can cause disease in varied sites within the human body and is a significant source of morbidity and mortality in those afflicted with cystic fibrosis. P. aeruginosa is able to coordinate group behaviors, such as virulence factor production, through the process of cell-to-cell signaling. There are three intercellular signaling systems employed by P. aeruginosa, and one of these systems utilizes the small molecule 2-heptyl-3-hydroxy-4-quinolone (Pseudomonas quinolone signal [PQS]). PQS is required for virulence in multiple infection models and has been found in the lungs of cystic fibrosis patients colonized by P. aeruginosa. In this study, we have identified an RpiR family transcriptional regulator, QapR, which is an autoregulatory repressor. We found that mutation of qapR caused overexpression of the qapR operon. We characterized the qapR operon to show that it contains genes qapR, PA5507, PA5508, and PA5509 and that QapR directly controls the transcription of these genes in a negative manner. We also show that derepression of this operon greatly reduces PQS concentration in P. aeruginosa. Our results suggest that qapR affects PQS concentration by repressing an enzymatic pathway that acts on PQS or a PQS precursor to lower the PQS concentration. We believe that this operon comprises a novel mechanism to regulate PQS concentration in P. aeruginosa.

Identification of the ZAK-MKK4-JNK-TGFß signaling pathway as a molecular target for novel synthetic iminoquinone anticancer compound BA-TPQ.

Identification and validation of molecular targets are considered as key elements in new drug discovery and development. We have recently demonstrated that a novel synthetic iminoquinone analog, termed [7-(benzylamino)- 1,3,4,8-tetrahydropyrrolo [4,3, 2-de]quinolin-8(1H)-one] (BA-TPQ), has significant anti-breast cancer activity both in vitro and in vivo, but the underlying molecular mechanisms are not fully understood. Herein, we report the molecular studies for BA-TPQ's effects on JNK and its upstream and downstream signaling pathways. The compound up-regulates the JNK protein levels by increasing its phosphorylation and decreasing its polyubiquitination-mediated degradation. It activates ZAK at the MAPKKK level and MKK4 at the MAPKK level. It also up-regulates the TGFß2 mRNA level, which can be abolished by the JNK-specific inhibitor SP600125, but not TGFß pathway-specific inhibitor SD-208, indicating that both JNK and TGFß signaling pathways are activated by BA-TPQ and that the JNK pathway activation precedes TGFß activation. The pro-apoptotic and anti-growth effects of BA-TPQ are significantly blocked by both the JNK and TGFß pathway inhibitors. In addition, BA-TPQ activates the ZAK-MKK4-JNK pathway in MCF7 cells, but not normal MCF10A cells, demonstrating its cancer-specific activities. In conclusion, our results demonstrate that BA-TPQ activates the ZAK-MKK4-JNK-TGFß signaling cascade as a molecular target for its anticancer activity.

Targeting late SV40 factor: is the achilles heel of hepatocarcinogenesis revealed?

Hepatocellular carcinoma (HCC) is a dreadful cancer and a major cause of death among patients with chronic liver disease and cirrhosis. The apparent alterations in a diversity of intracellular pathways found in HCC has set the rational for developing molecular-directed drugs that simultaneously inhibit multiple pathways, such as the multi-kinase inhibitor Sorafenib. However, recently this concept has been challenged by showing that HCC is heavily dependent on a single oncogene designated late SV-40 factor (LSF), a transcription factor that is over-expressed in liver cancer cells and that its expression is strongly correlated with tumor grade and aggressiveness. Furthermore, using an intensive screening for drugs that inhibit LSF activity, Grant et al have found a molecule designated factor quinolinone inhibitor 1 that can specifically block the ability of LSF to bind its target promoters, resulting in a massive death of HCC cells both in vitro and in vivo. The innovative findings of HCC representing "oncogene addiction" to LSF and the ability of a single molecule to block the activity of this oncogene resulting in tumor abolishment are encouraging and provide us with the hope that the "Achilles heel" of HCC has been found.

Bicyclic compounds repress membrane vesicle production and Pseudomonas quinolone signal synthesis in Pseudomonas aeruginosa.

Pseudomonas aeruginosa secretes membrane vesicles (MVs) that deliver several virulence factors as a cargo. We found that indole and its derivative compounds, including 4-hydroxyindole, 5-hydroxyindole, 6-hydroxyindole and isatin, repress MV production significantly. These compounds also repressed the synthesis of Pseudomonas quinolone signal (PQS), which is one of the quorum-sensing signals that upregulate virulence gene expression and positively control MV production. Moreover, we showed that other bicyclic compounds, including 1-naphthol, 2-naphthol, 2,3-dihydroxynaphthalene, 1-aminonaphthalene and 8-quinolinol, significantly repress MV production and PQS synthesis. In conclusion, we provide new information about the chemical structures that inhibit P. aeruginosa virulence.

Third generation antipsychotic drugs: partial agonism or receptor functional selectivity?

Functional selectivity is the term that describes drugs that cause markedly different signaling through a single receptor (e.g., full agonist at one pathway and antagonist at a second). It has been widely recognized recently that this phenomenon impacts the understanding of mechanism of action of some drugs, and has relevance to drug discovery. One of the clinical areas where this mechanism has particular importance is in the treatment of schizophrenia. Antipsychotic drugs have been grouped according to both pattern of clinical action and mechanism of action. The original antipsychotic drugs such as chlorpromazine and haloperidol have been called typical or first generation. They cause both antipsychotic actions and many side effects (extrapyramidal and endocrine) that are ascribed to their high affinity dopamine D(2) receptor antagonism. Drugs such as clozapine, olanzapine, risperidone and others were then developed that avoided the neurological side effects (atypical or second generation antipsychotics). These compounds are divided mechanistically into those that are high affinity D(2) and 5-HT(2A) antagonists, and those that also bind with modest affinity to D(2), 5-HT(2A), and many other neuroreceptors. There is one approved third generation drug, aripiprazole, whose actions have been ascribed alternately to either D(2) partial agonism or D(2) functional selectivity. Although partial agonism has been the more widely accepted mechanism, the available data are inconsistent with this mechanism. Conversely, the D(2) functional selectivity hypothesis can accommodate all current data for aripiprazole, and also impacts on discovery compounds that are not pure D(2) antagonists.

Precautions for use and adverse effects of vesnarinone: potential mechanisms and future therapies.

This article reviews the precautions and adverse effects associated with vesnarinone use, and the potential mechanisms responsible for these complications as well as suggested treatment strategies. Vesnarinone, a quinolinone derivative, improves the haemodynamics and quality of life in patients with congestive heart failure (CHF); however, it is associated with the adverse effects of increased sudden cardiac death and neutropenia. These adverse effects have limited the application of vesnarinone to the general population but perhaps with continued research into vesnarinone-induced neutropenia and advances in arrhythmia management, the risk/ benefit ratio of vesnarinone may become favourable. For now, the use of vesnarinone should be limited to patients with CHF who have demonstrated a poor response to other cardiac medications and devices. These patients should be closely monitored for both cardiac and non-cardiac adverse effects.

R115777 induces Ras-independent apoptosis of myeloma cells via multiple intrinsic pathways.

Ras activation is frequently observed in multiple myeloma either by mutation or through interleukin-6 receptor signaling. Recently, drugs designed to inhibit Ras have shown promise in preclinical myeloma models and in clinical trials. In this report, we characterize the pathways by which the clinically tested farnesyl transferase inhibitor (FTI) R115777 induces apoptosis in multiple myeloma cells. Contrary to the proposed mechanistic action of FTIs, we found that R115777 induces cell death despite Ras prenylation implying participation of Ras-independent mechanism(s). Apoptosis proceeded via an intrinsic cascade and was associated with an increase in the expression and activity of Bax. Bax activation correlated with a loss of mitochondrial membrane integrity and activation of the endoplasmic reticulum (ER) stress response. These pathways activate caspase-9 and consistent with this, cell death was prevented by caspase-9 blockade. Interestingly, cells overexpressing Bcl-X(L) remained partially sensitive to R115777 despite suppression of mitochondrial membrane dysfunction and ER-related stress. Taken together, these results indicate that R115777 induces apoptosis in a Ras-independent fashion via multiple intrinsic pathways.

Influence of albendazole on the disposition kinetics and milk antimicrobial equivalent activity of enrofloxacin in lactating goats.

The pharmacokinetics of single intravenous and intramuscular administrations and milk antimicrobial equivalent activity of enrofloxacin at a dose of 5 mg per kilogram body weight were studied in clinically healthy lactating goats which were either not treated or had received 7.5 mg per kilogram body weight of albendazole orally. The concentrations of enrofloxacin in serum and milk were determined using microbiological assay. Following intravenous injection, enrofloxacin antimicrobial equivalent activity versus time data in serum was described by a two-compartmental open model. Albendazole treatment significantly decreased the elimination half-life (t(1/2beta)) (P>or=0.05) and the mean residence time (MRT) (P>or=0.05), whereas, the rate of enrofloxacin return to central compartment from peripheral tissue (K(21)) was significantly increased (P>or=0.01). In contrast, the volumes of distribution V(d(area)) and V(d(SS)) were significantly decreased (P>or=0.01 and P>or=0.05, respectively) in albendazole-treated goats. After intramuscular injection, enrofloxacin was rapidly absorbed in control and albendazole-treated lactating goats with absorption half-lives (t(1/2ab)) 0.43 and 0.39 h, respectively. The mean peaks of serum concentration (C(max)) were 0.68 and 0.65 mcg ml(-1) attained at (t(max)) 1.08 and 1.12 h, before and after albendazole dosing, respectively. The elimination half-life (t(1/2el)) and (MRT) following intramuscular injections were also shorter in the albendazole-treated lactating goats. The systemic bioavailability of enrofloxacin was significantly decreased from 110.16 to 84.38% in albendazole-treated lactating goats. Concomitant administration of albendazole with enrofloxacin resulted in significant alterations in the disposition kinetic of enrofloxacin and significant decrease in enrofloxacin concentrations in milk. Consequently, the interaction between albendazole and enrofloxacin could be of clinical significance and may require monitoring and adjustment of enrofloxacin dosage.

Induction of cyclooxygenase-2 in rat gastric mucosa by rebamipide, a mucoprotective agent.

Recent studies indicate an expression of mitogen-inducible cyclooxygenase (COX-2) in gastric mucosa. Rebamipide, a mucoprotective agent enhances prostaglandin (PG) synthesis. The present study was designed to clarify the mechanism for rebamipide-induced mucosal protection. Male Sprague-Dawley rats were administered 5, 15, or 50 mg/kg/day rebamipide for 14 days. The expression of constitutive cyclooxygenase (COX-1) and COX-2 in gastric mucosa was determined using Western blot analysis. Another series of rats was used to examine 1) the levels of PGE(2) in stomach with and without pretreatment with a COX-2 inhibitor; 2) the protective action of rebamipide against gastric damage caused by 0.6 N HCl; and 3) the effects of a COX-2 inhibitor on rebamipide-induced gastric mucosal protection. COX-2 expression was enhanced, whereas COX-1 expression did not change significantly in the gastric mucosa of rats after treatment with rebamipide. The gastric mucosal PGE(2) was higher in the rebamipide groups than in the vehicle-treated group. Rebamipide also suppressed gastric damage induced by HCl in a dose-dependent manner. A COX-2 inhibitor blocked the rebamipide-induced increase in mucosal PGE(2), and mucosal protection induced by rebamipide. The results indicate that rebamipide induces COX-2 expression, increases PGE(2) levels, and enhances gastric mucosal defense in a COX-2-dependent manner. Thus, COX-2 has an important role in the effects of rebamipide on gastric mucosal protection.

Cyclic adenosine monophosphate inhibits quinolone alkaloid evocarpine-induced apoptosis via activation of protein kinase A in human leukaemic HL-60 cells.

Evocarpine, an isoquinolone alkaloid isolated from the fruit of Evodia rutaecarpa, was found to induce apoptotic cell death in promyelocytic leukaemia HL-60 cells in dose- and time-dependent manners. We investigated the involvement of protein kinase A during the evocarpine-induced apoptotic cell death. Evocarpine-induced apoptosis was markedly inhibited by treatment of the cells with dibutyryl-cyclic adenosine monophosphate. Similar results were obtained with other commonly used cyclic adenosine monophosphate analogues, chlorophenylthio-cyclic adenosine monophosphate and the intracellular cyclic adenosine monophosphate-elevating agent, forskolin. In contrast, pretreatment of HL-60 cells with KT5720, an inhibitor of cyclic adenosine monophosphate-dependent protein kinase A, abrogated the protective effects of cyclic adenosine monophosphate analogues and forskolin on evocrpine-induced apoptosis. These findings suggest that cyclic adenosine monophosphate-dependent activation of protein kinase A plays a crucial role in protecting HL-60 cells from the evocarpine-induced apoptotic cell death.

A novel effect of rebamipide: generation of [Ca(2+)](i) oscillations through activation of CCK(1) receptors in rat pancreatic acinar cells.

The protective effect of 2-(4-chlorobenzoylamino)-3-[2(1H)-quinolinon-4-yl]-propionic acid (rebamipide) on gastric mucosa is well established. Here we demonstrate that rebamipide acts on pancreatic acinar cells to generate oscillations of intracellular Ca(2+) concentration ([Ca(2+)](i)) through the activation of cholecystokinin subtype 1 (CCK(1)) receptors. At concentrations higher than 5 microM, rebamipide induced [Ca(2+)](i) oscillations in individual fura-2-loaded pancreatic acinar cells. The frequency of oscillations increased with increasing concentrations of rebamipide, while the latency between stimulation of cells and initiation of [Ca(2+)](i) oscillations decreased with increasing concentration. The [Ca(2+)](i) oscillations evoked by rebamipide were inhibited by the CCK(1) receptor antagonist L-364,718 but not by atropine or the CCK(2) receptor antagonist L-365,260 indicating that rebamipide is a nonpeptide CCK(1) receptor agonist.

Characterization of fluoroquinolone-induced Achilles tendon toxicity in rats: comparison of toxicities of 10 fluoroquinolones and effects of anti-inflammatory compounds.

Fluoroquinolone antibacterial agents have been reported to induce tendon lesions in juvenile rats. In the present study, we characterized fluoroquinolone-induced Achilles tendon lesions by comparing the effects of 10 fluoroquinolones and examining the potential of one of these antimicrobial agents, pefloxacin, to induce tendon lesions when coadministered with one of nine anti-inflammatory compounds. Among the 10 fluoroquinolones tested, fleroxacin and pefloxacin were the most toxic, inducing lesions at a dose of 100 mg/kg of body weight or more, while lomefloxacin, levofloxacin, and ofloxacin or sparfloxacin and enoxacin induced lesions at 300 mg/kg or more and 900 mg/kg, respectively. In contrast, norfloxacin, ciprofloxacin, and tosufloxacin had no effect even at the high dose of 900 mg/kg. The severity of the Achilles tendon lesions appeared to correlate with the structure of the substituent at the seventh position. Furthermore, pefloxacin-induced tendon lesions were inhibited by coadministration with dexamethasone and N-nitro-L-arginine methyl ester. Phenidone (1-phenyl-3-pyrazolidinone) and 2-(12-hydroxydodeca-5,10-diynyl)3,5,6-trimethyl-1,4-benzoqui none (AA861) also decreased the incidence of tendon lesions. In contrast, catalase, dimethyl sulfoxide, indomethacin, pyrilamine, and cimetidine did not modify these tendon lesions. These results suggest that nitric oxide and 5-lipoxigenase products partly mediate fluoroquinolone-induced tendon lesions.

Possible involvement of nitric oxide in the quinolone-induced tendon lesions in rats.

Quinolone antibacterial agents have been reported to induce adverse effects on the tendon and the musculoskeletal system in humans. We have previously demonstrated that Achilles tendon lesions could be induced in juvenile rats by a single oral administration of quinolones at high doses with simultaneous induction of lesions in the muscle, synovial membrane and articular cartilage. In the present investigation, we examined the involvement of nitric oxide (NO) in pefloxacin (PFLX)-induced lesions of the Achilles tendon in juvenile rats. The incidence of lesions was diminished markedly by co-administration of a potent NO synthase inhibitor, N-nitro-L-arginine methyl ester (L-NAME). Further, the urinary nitrate/nitrite excretion was decreased significantly by 4 h after administration, unchanged between 4 and 8 h, and significantly increased in the 8- to 24-h samples in the PFLX group, as compared to the control group. In contrast, the serum concentration of nitrate/nitrite was significantly higher in the PFLX group 4 h after administration, but there was no difference from controls was observed at 8 and 24 h. These results suggest that NO is involved in the induction of Achilles tendon lesions in juvenile rats by pefloxacin (PFLX) and may be similar to the tendon disorder of humans receiving quinolones.