Phagomimetic action of antibiotics: Revisited. How do antibiotics know where to go?

Phagocytic cells know exactly where an infection is by following chemotactic signals. The phagocytosis of bacteria results in a 'respiratory burst' in which superoxide radicals are released. We have previously compared the release of reactive oxygen species (ROS) by antibiotics, during electron transfer reactions, to this event. Antibiotics in their normal bacterial environment, and ROS, are both increasingly implicated in purposeful signalling functions, rather than their more widely known roles in bacterial killing and molecular damage. Here, we extend our comparison between antibiotics and phagocytic cells to propose that antibiotics actively accumulate at a site of pathogen infection or tumour growth. A common link being virulent cellular growth. When this occurs, new proteins are secreted, aberrant iron acquisition takes place, and lipocalins are released. Each provide a mechanism by which antibiotics can bind, and be retained, at an active site of pathogen infection or tumour growth.

Plasma S100A8/A9 heterodimer is an early prognostic marker of acute kidney injury associated with cardiac surgery.

AIM: We investigated whether plasma levels of the inflammation marker S100A8/A9, could predict acute kidney injury (AKI) onset in patients undergoing cardiac surgery necessitating cardiopulmonary bypass (CPB). PATIENTS & METHODS: Plasma levels of S100A8/A9 and other neutrophil cytosolic proteins were measured in 39 patients pre- and immediately post-CPB. RESULTS: All markers increased significantly post-CPB with S100A8/A9, S100A12 and myeloperoxidase levels significantly higher in patients who developed AKI within 7 days. S100A8/A9 had good prognostic utility for AKI, with an area under the receiver operating characteristic curve of 0.81 (95% CI: 0.676-0.949) and a cut-off value of 10.6 µg/ml (85.7% sensitivity and 75% specificity) irrespective of age. CONCLUSION: Plasma S100A8/A9 levels immediately after cardiac surgery, can predict onset of AKI, irrespective of age.

Development of a novel UHPLC-MS/MS-based platform to quantify amines, amino acids and methylarginines for applications in human disease phenotyping.

Amine quantification is an important strategy in patient stratification and personalised medicine. This is because amines, including amino acids and methylarginines impact on many homeostatic processes. One important pathway regulated by amine levels is nitric oxide synthase (NOS). NOS is regulated by levels of (i) the substrate, arginine, (ii) amino acids which cycle with arginine and (iii) methylarginine inhibitors of NOS. However, biomarker research in this area is hindered by the lack of a unified analytical platform. Thus, the development of a common metabolomics platform, where a wide range of amino acids and methylarginines can be measured constitutes an important unmet need. Here we report a novel high-throughput ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) platform where ≈40 amine analytes, including arginine and methylarginines can be detected and quantified on a molar basis, in a single sample of human plasma. To validate the platform and to generate biomarkers, human plasma from a well-defined cohort of patients before and after coronary artery bypass surgery, who developed systemic inflammatory response syndrome (SIRS), were analysed. Bypass surgery with SIRS significantly altered 26 amine analytes, including arginine and ADMA. Consequently, pathway analysis revealed significant changes in a range of pathways including those associated with NOS.

The Hepcidin/Ferroportin axis modulates proliferation of pulmonary artery smooth muscle cells.

Studies were undertaken to examine any role for the hepcidin/ferroportin axis in proliferative responses of human pulmonary artery smooth muscle cells (hPASMCs). Entirely novel findings have demonstrated the presence of ferroportin in hPASMCs. Hepcidin treatment caused increased proliferation of these cells most likely by binding ferroportin resulting in internalisation and cellular iron retention. Cellular iron content increased with hepcidin treatment. Stabilisation of ferroportin expression and activity via intervention with the therapeutic monoclonal antibody LY2928057 reversed proliferation and cellular iron accumulation. Additionally, IL-6 treatment was found to enhance proliferation and iron accumulation in hPASMCs; intervention with LY2928057 prevented this response. IL-6 was also found to increase hepcidin transcription and release from hPASMCs suggesting a potential autocrine response. Hepcidin or IL-6 mediated iron accumulation contributes to proliferation in hPASMCs; ferroportin mediated cellular iron excretion limits proliferation. Haemoglobin also caused proliferation of hPASMCs; in other novel findings, CD163, the haemoglobin/haptoglobin receptor, was found on these cells and offers a means for cellular uptake of iron via haemoglobin. Il-6 was also found to modulate CD163 on these cells. These data contribute to a better understanding of how disrupted iron homeostasis may induce vascular remodelling, such as in pulmonary arterial hypertension.

Pulmonary Arterial Hypertension: Iron Matters.

The interplay between iron and oxygen is longstanding and central to all aerobic life. Tight regulation of these interactions including homeostatic regulation of iron utilization ensures safe usage of this limited resource. However, when control is lost adverse events can ensue, which are known to contribute to an array of disease processes. Recently, associations between disrupted iron homeostasis and pulmonary artery hypertension (PAH) have been described with the suggestion that there is a contributory link with disease. This review provides a background for iron regulation in humans, describes PAH classifications, and discusses emerging literature, which suggests a role for disrupted iron homeostatic control in various sub-types of PAH, including a role for decompartmentalization of hemoglobin. Finally, the potential for therapeutic options to restore iron homeostatic balance in PAH are discussed.

Modified criteria for the systemic inflammatory response syndrome improves their utility following cardiac surgery.

BACKGROUND: Debate remains regarding whether the systemic inflammatory response syndrome (SIRS) identifies patients with clinically important inflammation. Defining criteria may be disproportionately sensitive and lack specificity. We investigated the incidence and evolution of SIRS in a homogenous population (following cardiac surgery) over 7 days to establish the relationship between SIRS and outcome, modeling alternative permutations of the criteria to increase their discriminatory power for mortality, length of stay, and organ dysfunction. METHODS: We conducted a retrospective analysis of prospectively collected data from a cardiothoracic ICU. Consecutive patients requiring ICU admission for the first time after cardiac surgery (N = 2,764) admitted over a 41-month period were studied. RESULTS: Concurrently, 96.2% of patients met the standard two criterion definition for SIRS within 24 h of ICU admission. Their mortality was 2.78%. By contrast, three or four criteria were more discriminatory of patients with higher mortality (4.21% and 10.2%, respectively). A test dataset suggested that meeting two criteria for at least 6 consecutive h may be the best model. This had a positive and negative predictive value of 7% and 99.5%, respectively, in a validation dataset. It performed well at predicting organ dysfunction and prolonged ICU admission. CONCLUSIONS: The concept of SIRS remains valid following cardiac surgery. With suitable modification, its specificity can be improved significantly. We propose that meeting two or more defining criteria for 6 h could be used to define better populations with more difficult clinical courses following cardiac surgery. This group may merit a different clinical approach.

Methemoglobin-induced signaling and chemokine responses in human alveolar epithelial cells.

Diffuse alveolar hemorrhage is characterized by the presence of red blood cells and free hemoglobin in the alveoli and complicates a number of serious medical and surgical lung conditions including the pulmonary vasculitides and acute respiratory distress syndrome. In this study we investigated the hypothesis that exposure of human alveolar epithelial cells to hemoglobin and its breakdown products regulates chemokine release via iron- and oxidant-mediated activation of the transcription factor NF-κB. Methemoglobin alone stimulated the release of IL-8 and MCP-1 from A549 cells via activation of the NF-κB pathway; additionally, IL-8 required ERK activation and MCP-1 required JNK activation. Neither antioxidants nor iron chelators and knockdown of ferritin heavy and light chains affected these responses, indicating that iron and reactive oxygen species are not involved in the response of alveolar epithelial cells to methemoglobin. Incubation of primary cultures of human alveolar type 2 cells with methemoglobin resulted in a similar pattern of chemokine release and signaling pathway activation. In summary, we have shown for the first time that methemoglobin induced chemokine release from human lung epithelial cells independent of iron- and redox-mediated signaling involving the activation of the NF-κB and MAPK pathways. Decompartmentalization of hemoglobin may be a significant proinflammatory stimulus in a variety of lung diseases.

Association between preoperative plasma sRAGE levels and recovery from cardiac surgery.

BACKGROUND: The receptor for advanced glycation end products (RAGE) is an inflammation-perpetuating receptor, and soluble RAGE (sRAGE) is a marker of cellular RAGE expression. This study investigated whether raised plasma levels prior to surgery of sRAGE or S100A8/A9 (a RAGE ligand) were associated with longer duration of hospital care in patients undergoing cardiac surgery necessitating cardiopulmonary bypass. METHODS: Patients (n = 130) undergoing elective cardiac surgery were enrolled prospectively. Plasma sRAGE and S100A8/A9 concentrations were measured before and 2 h after surgery. RESULTS: Preoperative plasma sRAGE increased significantly (P < 0.0001) from 1.06 ng/mL (IQR, 0.72-1.76) to 1.93 ng/mL (IQR, 1.14-2.63) 2 h postoperatively. Plasma S100A8/9 was also significantly (P < 0.0001) higher 2 h postoperatively (2.37 µ g/mL, IQR, 1.81-3.05) compared to pre-operative levels (0.41 µ g/mL, IQR, 0.2-0.65). Preoperative sRAGE, but not S100A8/A9, was positively and significantly correlated with duration of critical illness (r = 0.3, P = 0.0007) and length of hospital stay (LOS; r = 0.31, P < 0.0005). Multivariate binary logistic regression showed preoperative sRAGE to be, statistically, an independent predictor of greater than median duration of critical illness (odds ratio 16.6, P = 0.014) and to be, statistically, the strongest independent predictor of hospital LOS. CONCLUSION: Higher preoperative plasma sRAGE levels were associated with prolonged duration of care in adults undergoing cardiac surgery requiring cardiopulmonary bypass.

Biomarkers of lung injury after one-lung ventilation for lung resection.

BACKGROUND AND OBJECTIVE: Acute lung injury contributes to the mortality of patients after lung resection and one-lung ventilation (OLV). The objective of this study was to characterise the effect of lung resection and OLV on proposed biomarkers of lung injury in exhaled breath condensate (EBC) and plasma. METHODS: In adults undergoing lung resection, EBC was collected before and at 30-min intervals during OLV. Inflammatory mediators were assayed in plasma samples taken preoperatively, immediately postoperatively and 24 h postoperatively. RESULTS: EBC pH decreased from 6.51 ± 0.43 preoperatively, to 6.17 ± 0.78 and 6.09 ± 0.83 at 30 and 60 min, respectively (mean ± SD, P = 0.034, n = 20). Plasma concentrations of the receptor for advanced glycation end-products, von Willebrand factor and interleukin-6 increased comparing preoperative and postoperative samples (all P < 0.001, n = 30). By contrast, levels of Krebs von den Lungen-6 and surfactant protein-D decreased (P < 0.001, n=30), and correlated inversely with the extent of lung resected. CONCLUSIONS: Lung resection and OLV was associated with a rapid reduction in EBC pH and differential changes in plasma biomarkers of lung injury. Further investigation of EBC pH as a marker of ventilator-induced lung injury is warranted.

Variation in iron homeostasis genes between patients with ARDS and healthy control subjects.

BACKGROUND: Abnormal plasma and lung iron mobilization is associated with the onset and progression of ARDS and is detectable in specific at-risk populations. Patients with ARDS also have pronounced oxidative and nitrosative stress that can be catalyzed and thereby aggravated by the bioavailability of redox active iron. ARDS of pulmonary and extrapulmonary origin may differ pathophysiologically and require different ventilatory strategies. Evidence suggests that genetic predisposition is relevant to the pathogenesis of ARDS. We therefore explored the hypothesis that polymorphisms from a panel of genes encoding iron-metabolizing proteins determine susceptibility to ARDS. METHODS: Retrospective case-control study conducted at the adult ICUs of two university hospitals. Patients with ARDS (n = 122) and healthy control subjects (n = 193) were genotyped. Sequence-specific primer polymerase chain reaction was used to genotype selected biallelic single-nucleotide polymorphisms. An audit of the patient database was conducted, and 104 of the 122 ARDS patients were eligible for the final data analysis. RESULTS: Preliminary analysis indicated differences between ARDS and healthy control subjects in the incidence of polymorphism of the gene encoding ferritin light chain. Subgroup analysis indicated the prevalence of ferritin light-chain gene -3381GG homozygotes was increased in patients with ARDS of extrapulmonary origin compared to healthy control subjects. Secondly, a common haplotype in the heme oxygenase 2 gene was reduced in patients with ARDS compared to healthy control subjects and was more evident in those with ARDS of direct or pulmonary etiology. CONCLUSIONS: These results provide preliminary evidence to suggest a distinction in the genetic background of the subpopulations studied, inferring that the ferritin light-chain gene genotype confers susceptibility to ARDS, while the heme oxygenase 2 haplotype is protective against the onset of the syndrome. Such data support further previous findings that suggest abnormalities in iron handling resulting in redox imbalance are implicated in the pathogenesis of ARDS.

Pathogenesis of the systemic inflammatory syndrome and acute lung injury: role of iron mobilization and decompartmentalization.

Changes in iron homeostatic responses routinely accompany infectious or proinflammatory insults. The systemic inflammatory response syndrome (SIRS) and the development of acute lung injury (ALI) feature pronounced systemic and lung-specific alterations in iron/heme mobilization and decompartmentalization; such responses may be of pathological significance for both the onset and progression of acute inflammation. The potential for excessive iron-catalyzed oxidative stress, altered proinflammatory redox signaling, and provision of iron as a microbial growth factor represent obvious adverse aspects of altered in vivo iron handling. The release of hemoglobin during hemolytic disease or surgical procedures such as those utilizing cardiopulmonary bypass procedures further impacts on iron mobilization, turnover, and storage with associated implications. Genetic predisposition may ultimately determine the extent to which SIRS and related syndromes develop in response to such changes. The design of specific therapeutic interventions based on endogenous stratagems to limit adverse aspects of altered iron handling may prove of therapeutic benefit for the treatment of SIRS and ALI.

Persistently low plasma thioredoxin is associated with meningococcal septic shock in children.

OBJECTIVE: To compare plasma levels of thioredoxin (Trx), TNF-alpha and IL-1 beta in children during the acute phase of meningococcal septic shock (MSS) and in convalescence. DESIGN AND SETTING: Retrospective, observational study in the paediatric intensive care unit of a postgraduate teaching hospital. PATIENTS: Thirty-five children requiring intensive care for meningococcal sepsis; paired convalescent samples from 30 survivors (median interval between samples 62 days); 25 healthy control children. MEASUREMENTS AND RESULTS: Plasma Trx levels were significantly lower in the children with MSS, both during the acute illness (5.5 ng/ml, IQR 1.4-11.4) and in convalescence (2.5 ng/ml, IQR 0.4-6.9) than controls (18.8 ng/ml, IQR 7.9-25.0). Levels of IL-1 beta and TNF-alpha were higher in patients with acute MSS (30.3 pg/ml, IQR 3.6-63.6, and 145.9 pg/ml, IQR 31.8-278.1 respectively) than controls (3.7 pg/ml, IQR 0-36.9, and 23.8 pg/ml, IQR 0-124.3, respectively). Levels fell in convalescence (3.7 pg/ml, IQR 0-25.5, 3.7 pg/ml, IQR 0-304.8, respectively). Plasma Trx was higher in non-survivors, albeit a small group (n=5), than in survivors (n=30). Trx, IL-1 beta, and TNF-alpha levels were not correlated with predicted mortality as assessed by the paediatric risk of mortality (PRISM) score. CONCLUSIONS: Children with MSS exhibit persistently low plasma levels of Trx during acute illness and in convalescence.

Redox regulation of neutrophil apoptosis and the systemic inflammatory response syndrome.

SIRS (systemic inflammatory response syndrome) may result from a wide variety of non-infective insults. Surgery is a recognized cause of SIRS, the onset of which can have adverse prognostic significance. Neutrophil activation is a key histopathological feature of SIRS, and neutrophil clearance through programmed cell death or apoptosis is an essential step in its resolution. Increasingly, it is recognized that ROS (reactive oxygen species), such as those generated by activated neutrophils during cardiac surgery, may have a regulatory role, influencing neutrophil lifespan and thus inflammation. In this review, we discuss the continuing importance of SIRS as a herald of inflammation and the role of neutrophil longevity in the resolution of inflammation, and we consider recent evidence for the regulation of neutrophil apoptosis by ROS.

Exhaled breath condensate detects markers of pulmonary inflammation after cardiothoracic surgery.

Cardiac surgery using cardiopulmonary by-pass and, to a greater extent, lung resection, causes acute lung injury that is usually subclinical. Analysis of mediators in exhaled breath condensate is a promising means of monitoring inflammation in a variety of airway diseases but the contribution of the airway lining fluid from the lower respiratory tract is uncertain. We compared the analysis of markers of lung injury in exhaled breath condensate and bronchoalveolar lavage in endotracheally intubated patients before and after coronary artery bypass graft surgery with cardiopulmonary bypass and lobectomy. The neutrophil count and leukotriene B4 concentration in bronchoalveolar lavage fluid rose after coronary artery bypass graft surgery (p < 0.05), but there was no significant change in leukotriene B4, hydrogen peroxide, or hydrogen ion concentrations in exhaled breath condensate. By contrast, after lobectomy, the concentration in exhaled breath condensate of leukotriene B4, hydrogen peroxide and hydrogen ions rose significantly (p < 0.05). Exhaled breath condensate is a safe, noninvasive method of sampling the milieu of the distal lung and is sufficiently sensitive to detect markers of inflammation and oxidative stress in patients after lobectomy, but not after the milder insult associated with cardiac surgery.

Antioxidant protection against iron in children with meningococcal sepsis.

OBJECTIVE: To assess antioxidant protection against iron-catalyzed reactive oxygen species in meningococcal sepsis and to establish whether severity of illness is related to deficiencies in these antioxidant systems. DESIGN: Prospective, controlled study. SETTING: Pediatric intensive care unit of a postgraduate teaching hospital. PATIENTS: Twenty children aged 6 months to 15 yrs (median, 5 yrs) with meningococcal septic shock were studied. Paired convalescent samples taken 8-10 wks after discharge were available in nine children. INTERVENTIONS: Routine management for meningococcal sepsis. MEASUREMENTS AND MAIN RESULTS: Patients were classified for disease severity using the Glasgow Meningococcal Septicaemia Prognostic Score. Paired acute and convalescent samples were compared. Transferrin level (1.77 +/- 0.08 g/L) and total iron-binding capacity (46.2 +/- 2.0 microM) were significantly decreased in acute patients compared with paired convalescent samples (2.85 +/- 0.10 g/L and 74.4 +/- 2.5 microM, respectively; p <.0001). The iron saturation of transferrin was significantly increased in acute disease (36.9% +/- 2.5%) compared with convalescence (18.8% +/- 1.5%; p =.0003). Iron-binding antioxidant protection was not significantly different in acute (81.4% +/- 1.7%) and paired convalescent samples (85.6% +/- 2.5%; p =.54). However, patients with more severe meningococcal septicemia (GMSPS, >10; n = 12) had significantly diminished protection (77.5% +/- 2.4%) compared with less severe disease (87.1% +/- 1.6%; p =.0028), and there was a significant correlation between disease severity and iron-binding antioxidant protection (R =.48; p =.00067) in acute disease. Paired ceruloplasmin levels were available in six patients and were decreased in acute disease (0.29 +/- 0.02 g/L) compared with convalescence (0.40 +/- 0.04 g/L), although not statistically significant (p =.076). However, there was a significant correlation between plasma ceruloplasmin and disease severity (Pearson product moment correlation, p =.038) in the acute patients. Iron-oxidizing antioxidant assays were performed in four paired samples and were diminished in acute patients (53.3 +/- 4.4%) compared with convalescence (67.8 +/- 3.2%; p =.015). Acute samples demonstrated a significant relationship between iron-oxidizing antioxidant protection and both disease severity (r =.30; p =.012) and plasma ceruloplasmin levels (r =.48; p =.00067). CONCLUSIONS: Children with meningococcal septicemia exhibit abnormal plasma iron chemistry and decreased protection against iron-catalyzed oxidative damage. Such deficiencies correlate with disease severity.