Antibiotic dosing in the 'at risk' critically ill patient: Linking pathophysiology with pharmacokinetics/pharmacodynamics in sepsis and trauma patients

Background

Critical illness, mediated by trauma or sepsis, can lead to physiological changes that alter the pharmacokinetics of antibiotics and may result in sub-therapeutic concentrations at the sites of infection. The first aim of this project is to identify the clinical characteristics of critically ill patients with significant trauma that have been recently admitted to ICU that may predict the dosing requirements for the antibiotic, cefazolin. The second aim of this is to identify the clinical characteristics of critically ill patients with sepsis that may predict the dosing requirements for the combination antibiotic, piperacillin-tazobactam.

Methods/Design

This is an observational pharmacokinetic study of patients with trauma (cefazolin) or with sepsis (piperacillin-tazobactam). Participants will have samples from blood and urine, collected at different intervals. Patients will also have a microdialysis catheter inserted into subcutaneous tissue to measure interstitial fluid penetration of the antibiotic. Participants will be administered sinistrin, indocyanine green and sodium bromide as well as have cardiac output monitoring performed and tetrapolar bioimpedance to determine physiological changes resulting from pathology. Analysis of samples will be performed using validated liquid chromatography tandem mass-spectrometry. Pharmacokinetic analysis will be performed using non-linear mixed effects modeling to determine individual and population pharmacokinetic parameters of antibiotics.

Discussion

The study will describe cefazolin and piperacillin-tazobactam concentrations in plasma and the interstitial fluid of tissues in trauma and sepsis patients respectively. The results of this study will guide clinicians to effectively dose these antibiotics in order to maximize the concentration of antibiotics in the interstitial fluid of tissues.     

The relation between cartilage biomarkers (C2C,C1,2C,CS846, and CPII) and the long-term outcome of rheumatoid arthritis patients within the CAMERA trial

Introduction  

The aim of this study was to investigate whether serum biomarker levels of C2C, C1,2C, CS846, and CPII can predict the long-term course of disease activity and radiographic progression early in the disease course of rheumatoid arthritis (RA).     

Apical location of ferroportin 1 in airway epithelia and its role in iron detoxification in the lung

Ferroportin 1 (FPN1; aka MTP1, IREG1, and SLC40A1), which was originally identified as a basolateral iron transporter crucial for nutritional iron absorption in the intestine, is expressed in airway epithelia and upregulated when these cells are exposed to iron. Using immunofluorescence labeling and confocal microscopic imaging techniques, we demonstrate that in human and rodent lungs, FPN1 localizes subcellularly to the apical but not basolateral membrane of the airway epithelial cells. The role of airway epithelial cells in iron mobilization in the lung was studied in an in vitro model of the polarized airway epithelium. Normal human bronchial epithelial cells, grown on membrane supports until differentiated, were exposed to iron, and the efficiency and direction of iron transportation were studied. We found that these cells can efficiently take up iron across the apical but not basolateral surface in a concentration-dependent manner. Most of the iron taken up by the cells is then released into the medium within 8 h in the form of less reactive protein-bound complexes including ferritin and transferrin. Interestingly, iron release also occurred across the apical but not basolateral membrane. Our findings indicate that FPN1, depending on its subcellular location, could have distinct functions in iron homeostasis in different cells and tissues. Although it is responsible for exporting nutrient iron from enterocytes to the circulation in the intestine, it could play a role in iron detoxification in airway epithelial cells in the lung.     

TNF, IFN-gamma, and endotoxin increase expression of DMT1 in bronchial epithelial cells

Regulation of the metal transport protein divalent metal transporter-1 (DMT1) may contribute to the uptake and detoxification of iron by cells resident in the respiratory tract. Inflammation has been associated with an increased availability of this metal resulting in an oxidative stress. Because proinflammatory cytokines and LPS have been demonstrated to affect an elevated expression of DMT1 in a macrophage cell line, we tested the hypothesis that tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma, and LPS increase DMT1 expression in airway epithelial cells. We used RT-PCR to detect mRNA for both -IRE DMT1 and +IRE DMT1 in BEAS-2B cells. Treatment with TNF-alpha, IFN-gamma, or LPS increased both forms. Western blot analysis also demonstrated an increase in the expression of both isoforms of DMT1 after these treatments. Twenty-four hours after exposure of an animal model to TNF-alpha, IFN-gamma, or LPS, a significant increase in pulmonary expression of -IRE DMT1 was seen by immunohistochemistry; the level of +IRE DMT1 was too low in the lung to be visualized using this methodology. Finally, iron transport into BEAS-2B cells was increased after inclusion of TNF-alpha, IFN-gamma, or LPS in the media. We conclude that proinflammatory cytokines and LPS increase mRNA and protein expression of DMT1 in airway cells in vitro and in vivo. Furthermore, both -IRE and +IRE isoforms are elevated after exposures. Increased expression of this protein appears to be included in a coordinated response of the cell and tissue where the function might be to diminish availability of metal.     

Identification and characterization of solvent-filled channels in human ferrochelatase

Ferrochelatase catalyzes the formation of protoheme from two potentially cytotoxic products, iron and protoporphyrin IX. While much is known from structural and kinetic studies on human ferrochelatase of the dynamic nature of the enzyme during catalysis and the binding of protoporphyrin IX and heme, little is known about how metal is delivered to the active site and how chelation occurs. Analysis of all ferrochelatase structures available to date reveals the existence of several solvent-filled channels that originate at the protein surface and continue to the active site. These channels have been proposed to provide a route for substrate entry, water entry, and proton exit during the catalytic cycle. To begin to understand the functions of these channels, we investigated in vitro and in vivo a number of variants that line these solvent-filled channels. Data presented herein support the role of one of these channels, which originates at the surface residue H240, in the delivery of iron to the active site. Structural studies of the arginyl variant of the conserved residue F337, which resides at the back of the active site pocket, suggest that it not only regulates the opening and closing of active site channels but also plays a role in regulating the enzyme mechanism. These data provide insight into the movement of the substrate and water into and out of the active site and how this movement is coordinated with the reaction mechanism.     

Mosquito-bite infection of humanized mice with chikungunya virus produces systemic disease with long-term effects

Chikungunya virus (CHIKV) is an emerging, mosquito-borne alphavirus responsible for acute to chronic arthralgias and neuropathies. Although it originated in central Africa, recent reports of disease have come from many parts of the world, including the Americas. While limiting human CHIKV cases through mosquito control has been used, it has not been entirely successful. There are currently no licensed vaccines or treatments specific for CHIKV disease, thus more work is needed to develop effective countermeasures. Current animal research on CHIKV is often not representative of human disease. Most models use CHIKV needle inoculation via unnatural routes to create immediate viremia and localized clinical signs; these methods neglect the natural route of transmission (the mosquito vector bite) and the associated human immune response. Since mosquito saliva has been shown to have a profound effect on viral pathogenesis, we evaluated a novel model of infection that included the natural vector, Aedes species mosquitoes, transmitting CHIKV to mice containing components of the human immune system. Humanized mice infected by 3–6 mosquito bites showed signs of systemic infection, with demonstrable viremia (by qRT-PCR and immunofluorescent antibody assay), mild to moderate clinical signs (by observation, histology, and immunohistochemistry), and immune responses consistent with human infection (by flow cytometry and IgM ELISA). This model should give a better understanding of human CHIKV disease and allow for more realistic evaluations of mechanisms of pathogenesis, prophylaxis, and treatments.     

Effect of temperature on seed production in the invasive grass Glyceria maxima (Hartm.) Holmb. (Poaceae) in South Africa

Temperature is one of the main factors that determine sexual reproduction in terrestrial and emergent aquatic plant species. The effect of temperature on sexual reproduction and seed production of Glyceria maxima (Hartm.) Holmb. in the southern hemisphere is unknown. Glyceria maxima collections in February 2010 at three isolated infestations in KwaZulu-Natal failed to yield a single seed, only empty panicles. Laboratory experiments showed that vernalisation had no consistent effect on seed production. Field- and laboratory-grown plants produced seeds in the 2010/2011 season, because of having sufficient time at optimum temperatures required for seed production (1 491 and 1 585 hours, respectively), compared to a shorter period (1 352 hours) of suitable temperatures during the 2009/2010 growing season. An inadequate period of optimum temperatures (15–25°C) during seed production resulted in the lack of seeds in the field in the 2009/2010 growing season. This study showed that temperature and duration of exposure thereto during the seed-production period play vital roles in G. maxima sexual reproduction.