Transmission pathways and mediators as the basis for clinical pharmacology of pain.

INTRODUCTION: Mediators in pain transmission are the targets of a multitude of different analgesic pharmaceuticals. This review explores the most significant mediators of pain transmission as well as the pharmaceuticals that act on them. Areas covered: The review explores many of the key mediators of pain transmission. In doing so, this review uncovers important areas for further research. It also highlights agents with potential for producing novel analgesics, probes important interactions between pain transmission pathways that could contribute to synergistic analgesia, and emphasizes transmission factors that participate in transforming acute injury into chronic pain. Expert commentary: This review examines current pain research, particularly in the context of identifying novel analgesics, highlighting interactions between analgesic transmission pathways, and discussing factors that may contribute to the development of chronic pain after an acute injury.

Pain transduction: a pharmacologic perspective.

INTRODUCTION: Pain represents a necessary physiological function yet remains a significant pathological process in humans across the world. The transduction of a nociceptive stimulus refers to the processes that turn a noxious stimulus into a transmissible neurological signal. This involves a number of ion channels that facilitate the conversion of nociceptive stimulus into and electrical signal. AREAS COVERED: An understanding of nociceptive physiology complements a discussion of analgesic pharmacology. Therefore, the two are presented together. In this review article, a critical evaluation is provided on research findings relating to both the physiology and pharmacology of relevant acid-sensing ion channels (ASICs), transient receptor potential (TRP) cation channels, and voltage-gated sodium (Nav) channels. Expert commentary: Despite significant steps toward identifying new and more effective modalities to treat pain, there remain many avenues of inquiry related to pain transduction. The activity of ASICs in nociception has been demonstrated but the physiology is not fully understood. A number of medications appear to interact with ASICs but no research has demonstrated pain-relieving clinical utility. Direct antagonism of TRPV1 channels is not in practice due to concerning side effects. However, work in this area is ongoing. Additional research in the of TRPA1, TRPV3, and TRPM8 may yield useful results. Local anesthetics are widely used. However, the risk for systemic effects limits the maximal safe dosage. Selective Nav antagonists have been identified that lack systemic effects.

Arterial Catheterization and Infection: Toll-like Receptors in Defense against Microorganisms and Therapeutic Implications.

Radial artery catheterization has become a preferred route over femoral artery catheterization, in order to monitor the blood pressure of hemodynamically unstable patients or for repeated sampling of arterial blood gases. While the incidence of catheter-related infection is lower in the radial artery than the femoral artery, infection remains a major issue that requires attention. In this review of the literature, we discuss infectious complications of radial artery catheterization, with a focus on various risk factors and establishing the most common causative agents. We also critically review the role of the innate immune system involving Toll-like receptors (TLRs) in host-defense, with the goal of establishing a common pathway used by the innate immune system via TLRs to combat the pathogens that most commonly cause infection in radial artery catheterization. If this pathway can be therapeutically manipulated to preemptively attack pathogenic agents, immunomodulation may be an option in reducing the incidence of infection in this procedure.

Therapeutic Basis of Clinical Pain Modulation.

Pain is a hallmark of almost all bodily ailments and can be modulated by agents, including analgesics and anesthetics that suppress pain signals in the central nervous system. Defects in the modulatory systems, including the endogenous pain-inhibitory pathways, are a major factor in the initiation and chronicity of pain. Thus, pain modulation is particularly applicable to the practice of medicine. This review summarizes the existing literature on pain modulation. Here, we critically reviewed the literature from PubMed on pain modulation published primarily within the past 5 years in high impact journals. Specifically, we have discussed important anatomical landmarks of pain modulation and outlined the endogenous networks and underlying mechanisms of clinically relevant pain modulatory methods. The Gate Control Theory is briefly presented with discussion on the capacity of pain modulation to cause both hyper- and hypoalgesia. An emphasis has been given to highlight key areas in pain research that, because of unanswered questions or therapeutic potential, merit additional scientific scrutiny. The information presented in this paper would be helpful in developing novel therapies, metrics, and interventions for improved patient management.

Effect of sedative-hypnotics, anesthetics and analgesics on sleep architecture in obstructive sleep apnea.

The perioperative care of obstructive sleep apnea (OSA) patients is currently receiving much attention due to an increased risk for complications. It is established that postoperative changes in sleep architecture occur and this may have pathophysiological implications for OSA patients. Upper airway muscle activity decreases during rapid eye movement sleep (REMS). Severe OSA patients exhibit exaggerated chemoreceptor-driven ventilation during non-rapid eye movement sleep (NREMS), which leads to central and obstructive apnea. This article critically reviewed the literature relevant to preoperative screening for OSA, prevalence of OSA in surgical populations and changes in postoperative sleep architecture relevant to OSA patients. In particular, we addressed three questions in regard to the effects of sedative-hypnotics, anesthetics and analgesics on sleep architecture, the underlying mechanisms and the relevance to OSA. Indeed, these classes of drugs alter sleep architecture, which likely significantly contributes to abnormal postoperative sleep architecture, exacerbation of OSA and postoperative complications.

Development of a TaqMan multiplex PCR assay for detection of plasmid-mediated ampC ß-lactamase genes.

A multiplex, real-time TaqMan assay was designed to identify clinical isolates carrying plasmid-mediated ampC genes. The specificity and sensitivity of this assay were 100% when testing characterized AmpC/non-AmpC-producing isolates and randomly selected clinical isolates. This is a rapid assay that can be performed in a clinical microbiology laboratory.

Levofloxacin/imipenem prevents the emergence of high-level resistance among Pseudomonas aeruginosa strains already lacking susceptibility to one or both drugs.

OBJECTIVES: Previous studies have demonstrated that a combination of levofloxacin with imipenem could prevent the emergence of resistance during the treatment of susceptible Pseudomonas aeruginosa isolates in a two-compartment pharmacodynamic model of infection. In this study, the efficacy of levofloxacin/imipenem was further evaluated against a panel of characterized P. aeruginosa strains that lacked susceptibility to one or both drugs in the combination. METHODS: Five P. aeruginosa strains with characterized resistance mechanisms were evaluated. Log-phase cultures were inoculated into the peripheral compartment of the in vitro pharmacokinetic model and treated using simulated doses of 750 mg levofloxacin (dosed every 24 h) and 250 mg or 1 g doses of imipenem (dosed every 12 h). Peak levels were adjusted for protein binding. Pharmacodynamic interactions were evaluated by measuring the changes in viable counts over 30 h. To evaluate the emergence of resistance, samples removed at 30 h were plated onto agar containing the drug at 4x MIC, and potential mutants were evaluated for changes in susceptibility. RESULTS: Against strains overexpressing MexAB-OprM, MexCD-OprJ and MexEF-OprN efflux pumps, levofloxacin/imipenem prevented the emergence of resistance and achieved a 5 log total kill of one strain and eradication of two strains. Levofloxacin/imipenem also eradicated an imipenem-resistant strain lacking OprD. Although the combination initially killed 6-7 logs of a dual-resistant strain lacking OprD and overexpressing MexXY, it could not prevent the emergence of resistance when the 250 mg dose of imipenem was simulated in the combination. However, when the 1 g dose of imipenem was simulated with the combination, resistance was suppressed. CONCLUSIONS: These data suggest that levofloxacin/imipenem may be an effective combination for preventing the emergence of resistance among P. aeruginosa, even with strains already lacking susceptibility to one or both drugs in the combination. Clinical evaluation of this combination is warranted.

Promoter sequences necessary for high-level expression of the plasmid-associated ampC beta-lactamase gene blaMIR-1.

Little is known about mechanisms involved in high-level expression of plasmid-associated ampC genes. The sequence for bla(MIR-1) has been elucidated, and the gene is not inducible. Although the sequence for the promoter (prA) that drives expression of Enterobacter cloacae chromosomal ampC is present upstream of bla(MIR-1), high-level expression from bla(MIR-1) is directed from a hybrid promoter (prB) located further upstream of prA. The purpose of this study was to determine the influence of each promoter on bla(MIR-1) expression and beta-lactam resistance. RNA expression by deletion clones with both promoters was measured and compared to that by clones in which -35 and/or -10 elements of prA and/or prB were altered. Primer extension revealed two start sites for bla(MIR-1) transcription. Expression of bla(MIR-1) in clones with both promoters was 171-fold higher than that in clones carrying only prA. In addition, bla(MIR-1) expression from prA increased 11-fold in the presence of the prB -10 element compared to expression driven from prA alone. Ceftazidime and cefotaxime MICs increased 42- and 64-fold, respectively, for the clone expressing bla(MIR-1) from both promoters compared to expression from prA alone. The upstream promoter prB of bla(MIR-1) is solely responsible for high-level expression required for cefotaxime and ceftazidime resistance. These data suggest that resistance to extended-spectrum cephalosporins mediated by noninducible plasmid-associated ampC genes requires the formation of novel promoter elements that are capable of increasing ampC expression.

Plasmid-encoded functions compensate for the biological cost of AmpC overexpression in a clinical isolate of Salmonella typhimurium.

OBJECTIVES: In a previous study with a Salmonella typhimurium strain containing cloned ampC-ampR from Enterobacter cloacae, it was suggested that ampC expression must be kept at low levels by AmpR to maintain normal growth and virulent phenotype. The purpose of this study was to determine whether findings obtained with a laboratory model can be extended to a virulent clinical isolate of S. typhimurium expressing the plasmid-encoded bla(CMY-7). METHODS: Disc induction assays were carried out to investigate inducibility of bla(CMY-7). Primer extension and sequence analyses were carried out to map the transcriptional start site of bla(CMY-7) and determine the relative expression. Growth and invasion potential of Salmonella strains were monitored by optical density, viable counts and cell invasion assays. RESULTS: Sequence analysis confirmed the absence of ampR upstream of bla(CMY-7) therefore confirming the negative results observed using the disc induction assay. Primer extension analysis mapped the start site of bla(CMY-7) transcription within an ISEcp1-like element. The relative expression of bla(CMY-7) was approximately 965-fold higher than the expression of a wild-type Citrobacter freundii chromosomal ampC and approximately 4.1-fold higher than ampC expression from a derepressed mutant of C. freundii. Growth and the capacity to invade mammalian cells were not compromised for either the clinical isolate or the S. typhimurium transconjugant containing bla(CMY-7). However, a Salmonella transformant containing bla(CMY-7) exhibited a compromised phenotype with respect to growth and invasion of mammalian cells. CONCLUSION: These findings indicate that the biological cost of high-level AmpC production can be compensated by plasmid-encoded factors and not by regulating ampC expression.

Association between handling of pet treats and infection with Salmonella enterica serotype newport expressing the AmpC beta-lactamase, CMY-2.

Resistance to the extended-spectrum cephalosporins can occur in Salmonella species via the production of extended-spectrum and AmpC beta-lactamases. We describe human infections with Salmonella enterica serotype Newport phage type 14 strains resistant to ceftazidime (CAZ) and cefoxitin (FOX) related to the handling of pet treats containing dried beef. These strains were isolated from five patients in Calgary, Alberta, Canada, during 2002 and were compared to a strain cultured from a commercial pet treat present at the property of one of the patients. The strains were resistant to FOX, CAZ, cefpodoxime, ampicillin, and chloramphenicol; intermediate resistant to ceftriaxone and cefotaxime; and sensitive to the aminoglycosides, ciprofloxacin, cefepime, and imipenem. Isoelectric focusing, multiplex PCR, and sequencing of the amplicons showed that all strains produced the plasmid-encoded AmpC beta-lactamase, CMY-2. Restriction analysis of plasmid DNA following transformation demonstrated that bla(CMY-2) was encoded on an approximately 140-kb plasmid. Pulsed-field gel electrophoresis showed the human and pet treat Salmonella strains to be highly related. This study is the first to implicate the transfer of multidrug-resistant Salmonella species through the handling of commercial pet treats containing animal products. In addition to documenting the first cases of human infection caused by CMY-2-producing S. enterica serotype Newport strains in Canada, this study illustrates the necessity of rapid and accurate laboratory-based surveillance in the identification of novel types of antimicrobial resistance.

Factors influencing gene expression and resistance for Gram-negative organisms expressing plasmid-encoded ampC genes of Enterobacter origin.

High-level expression of AmpC beta-lactamases results in organisms resistant to multiple beta-lactam antibiotics. The mechanism of chromosomally mediated AmpC resistance has been elucidated, however the mechanism(s) driving plasmid-encoded AmpC resistance are unknown. Studies were designed to identify factors which influence expression of plasmid-encoded ampC genes and correlate these factors with resistance. As the model system, ampC genes of Enterobacter origin were used to determine how gene copy number, genetic background and genetic organization influenced resistance phenotypes. To this end, gene expression from the plasmid-encoded inducible blaACT-1 and non-inducible blaMIR-1 were compared with chromosomal ampC gene expression from both wild-type (WT) and derepressed Enterobacter cloacae isolates. RNA levels within the original clinical isolates were examined using primer extension analysis, whereas a new PCR strategy was developed to examine gene copy number. These data revealed that blaACT-1 and blaMIR-1 constitutive expression was 33- and 95-fold higher than WT expression, whereas copy numbers of the plasmid-encoded genes were 2 and 12, respectively. Differences in promoters and transcriptional starts for the respective plasmid-encoded genes were noted and contribute to increases observed in overall expression. Finally, beta-lactam MICs were increased two- to 16-fold when blaACT-1 was expressed in Escherichia coli AmpD- strains compared with E. coli AmpD+ strains. In conclusion, high-level expression of plasmid-encoded ampC genes requires interplay between multiple factors including genetic organization, promoter modifications, genetic background, and to some extent gene copy number. In addition, clinical laboratories need to be aware that genetic backgrounds of inducible plasmid-encoded genes can dramatically influence MICs for organisms not normally associated with derepressed phenotypes.

Occurrence of newer beta-lactamases in Klebsiella pneumoniae isolates from 24 U.S. hospitals.

Despite the discovery of novel beta-lactamases such as extended-spectrum beta-lactamases (ESBLs), imported AmpC, and carbapenem-hydrolyzing beta-lactamases at least a decade ago, there remains a low level of awareness of their importance and how to detect them. There is a need to increase the levels of awareness of clinical laboratories about the detection of newer beta-lactamases. Therefore, a study was conducted in 2000 to investigate the occurrence of these beta-lactamases in Klebsiella pneumoniae isolates at 24 U.S. medical centers. To enhance the likelihood of detecting imported AmpC and carbapenem-hydrolyzing beta-lactamases, participating laboratories were permitted to include archived strains (1996 to 2000) that were intermediate or resistant to either cefoxitin or imipenem. The beta-lactamase production of 408 isolates positive by screening of 1,123 isolates was investigated by ESBL phenotypic confirmation tests; and for AmpC and carbapenem-hydrolyzing beta-lactamases, three-dimensional tests, isoelectric focusing, beta-lactamase inhibitor studies, spectrophotometric assays, induction assays, and molecular tests were used. ESBL-producing isolates were detected at 18 of the 24 sites (75%), imported AmpC-producing isolates were detected at 10 sites (42%), inducible imported AmpC-producing isolates were detected at 3 sites (12.5%), and a molecular class A carbapenem-hydrolyzing enzyme was detected at 1 site (4%). No class B or D carbapenem-hydrolyzing enzymes were detected. ESBLs and imported AmpC beta-lactamases were detected at a significant number of sites, indicating widespread penetration of these enzymes into U.S. medical institutions. Because these enzymes may significantly affect therapeutic outcomes, it is vital that clinical laboratories be aware of them and be able to detect their occurrence.

The ACT-1 plasmid-encoded AmpC beta-lactamase is inducible: detection in a complex beta-lactamase background.

The purpose of this study was to identify the genetic organization and inducibility of bla(ACT-1) in a clinical isolate of Klebsiella pneumoniae possessing at least five different beta-lactamases. The genetic organization of the bla(ACT-1)/ampR region is identical to those of inducible chromosomal ampC genes. RNA analysis using primer extension demonstrated a five-fold increase in bla(ACT-1) transcript production on exposure to cefoxitin. These findings are significant because induction was detected in a complicated beta-lactamase background. In addition, this report is the first to describe an inducible plasmid-encoded AmpC beta-lactamase of Enterobacter cloacae origin.