pH dependence of neutrophil-endothelial cell adhesion and adhesion molecule expression

Immune Cell Migration to Cancer

Immune cell migration is required for the development of an effective and robust immune response. This elegant process is regulated by both cellular and environmental factors, with variables such as immune cell state, anatomical location, and disease state that govern differences in migration patterns. In all cases, a major factor is the expression of cell surface receptors and their cognate ligands. Rapid adaptation to environmental conditions partly depends on intrinsic cellular immune factors that affect a cell's ability to adjust to new environment. In this review, we discuss both myeloid and lymphoid cells and outline key determinants that govern immune cell migration, including molecules required for immune cell adhesion, modes of migration, chemotaxis, and specific chemokine signaling. Furthermore, we summarize tumor-specific elements that contribute to immune cell trafficking to cancer, while also exploring microenvironment factors that can alter these cellular dynamics within the tumor in both a pro and antitumor fashion. Specifically, we highlight the importance of the secretome in these later aspects. This review considers a myriad of factors that impact immune cell trajectory in cancer. We aim to highlight the immunotherapeutic targets that can be harnessed to achieve controlled immune trafficking to and within tumors.

Effects of permissive hypercapnia on intraoperative cerebral oxygenation and early postoperative cognitive function in older patients with non-acute fragile brain function undergoing laparoscopic colorectal surgery: protocol study

BACKGROUND

Perioperative brain protection in older patients has been the focus of research recently; meanwhile, exploring the relationship between regional cerebral oxygen saturation (rSO2) and brain function in the perioperative period has been an emerging and challenging area-the difficulties related to the real-time monitoring of rSO2 and the choice of feasible interventions. As an advanced instrument for intraoperative rSO2 monitoring, the clinical application of near-infrared spectrum (NIRS) cerebral oxygen monitoring has gradually increased in popularity and is being recognized for its beneficial clinical outcomes in patients undergoing cardiac and noncardiac surgery. In addition, although sufficient evidence to support this hypothesis is still lacking, the effect of permissive hypercapnia (PHC) on rSO2 has expanded from basic research to clinical exploration. Therefore, monitoring intraoperative rSO2 in older patients with NIRS technology and exploring possible interventions that may change rSO2 and even improve postoperative cognitive performance is significant and clinically valuable.

METHODS

This study is a single-center randomized controlled trial (RCT). 76 older patients are enrolled as subjects. Patients who meet the screening criteria will be randomly assigned 1:1 to the control and intervention groups. PHC-based mechanical ventilation will be regarded as an intervention. The primary outcome is the absolute change in the percent change in rSO2 from baseline to the completion of surgery in the intervention and control groups. Secondary outcomes mainly include observations of intraoperative cerebral oxygenation and metabolism, markers of brain injury, and assessments of patients' cognitive function using scale through postoperative follow-up.

DISCUSSION

The findings of this RCT will reveal the effect of PHC on intraoperative rSO2 in older patients with nonacute fragile brain function (NFBF) and the approximate trends over time, and differences in postoperative cognitive function outcomes. We anticipate that the trial results will inform clinical policy decision-makers in clinical practice, enhance the management of intraoperative cerebral oxygen monitoring in older patients with comorbid NFBF, and provide guidance for clinical brain protection and improved postoperative cognitive function outcomes.

TRIAL REGISTRATION

ChiCTR, ChiCTR2200062093, Registered 9/15/2022.

Acid-Sensing Ion Channels: Expression and Function in Resident and Infiltrating Immune Cells in the Central Nervous System

Peripheral and central immune cells are critical for fighting disease, but they can also play a pivotal role in the onset and/or progression of a variety of neurological conditions that affect the central nervous system (CNS). Tissue acidosis is often present in CNS pathologies such as multiple sclerosis, epileptic seizures, and depression, and local pH is also reduced during periods of ischemia following stroke, traumatic brain injury, and spinal cord injury. These pathological increases in extracellular acidity can activate a class of proton-gated channels known as acid-sensing ion channels (ASICs). ASICs have been primarily studied due to their ubiquitous expression throughout the nervous system, but it is less well recognized that they are also found in various types of immune cells. In this review, we explore what is currently known about the expression of ASICs in both peripheral and CNS-resident immune cells, and how channel activation during pathological tissue acidosis may lead to altered immune cell function that in turn modulates inflammatory pathology in the CNS. We identify gaps in the literature where ASICs and immune cell function has not been characterized, such as neurotrauma. Knowledge of the contribution of ASICs to immune cell function in neuropathology will be critical for determining whether the therapeutic benefits of ASIC inhibition might be due in part to an effect on immune cells.

Effects of hypercapnia in sepsis: A scoping review of clinical and pre-clinical data

BACKGROUND

Perform a scoping review of (1) pre-clinical studies testing the physiological effects of higher PaCO2 levels in the setting of sepsis models and (2) clinical investigations testing the effects of hypercapnia on clinical outcomes in mechanically ventilated patients with sepsis.

METHODS

We performed a search of CENTRAL, PUBMED, CINAHL, and EMBASE. Study inclusion criteria for pre-clinical studies were: (1) bacterial sepsis model (2) measurement of PaCO2 , and (3) comparison of outcome measure between different PaCO2 levels. Inclusion criteria for clinical studies were: (1) diagnosis of sepsis, (2) receiving invasive mechanical ventilation, (3) measurement of PaCO2 , and (4) comparison of outcomes between different PaCO2 levels. We performed a qualitative analysis to collate and summarize the physiological and clinical effects of hypercapnia according to the recommended methodology from the Cochrane Handbook.

RESULTS

Fifteen pre-clinical and nine clinical studies were included. Among pre-clinical studies, the individual studies found higher PaCO2 augments tissue blood flow and oxygenation, and attenuates inflammation and lung injury; however, all pre-clinical studies were found to have some degree of risk of bias. Six of the nine clinical studies were deemed to be good quality. Among clinical studies hypercapnia was associated with increased cerebral perfusion and oxygenation; however, there were conflicting results testing the association between hypercapnia and mortality.

CONCLUSION

While individual pre-clinical studies identified potential mechanisms by which changes in PaCO2 levels could affect pathophysiology in sepsis, there is a paucity of clinical data as to the optimal PaCO2 range, demonstrating a need for future research.

REGISTRATION

PROSPERO number CRD42018086703.

GPR4 signaling is essential for the promotion of acid-mediated angiogenic capacity of endothelial progenitor cells by activating STAT3/VEGFA pathway in patients with coronary artery disease

BACKGROUND

Patients with coronary artery disease (CAD) are characterized by a decline in vascular regeneration, which is related to the dysfunction of endothelial progenitor cells (EPCs). G-protein-coupled receptor 4 (GPR4) is a proton-sensing G-protein-coupled receptor (GPCR) that contributes to neovascularization in acidic microenvironments. However, the role of GPR4 in regulating the angiogenic capacity of EPCs from CAD patients in response to acidity generated in ischemic tissue remains completely unclear.

METHODS

The angiogenic capacity of EPCs collected from CAD patients and healthy subjects was evaluated in different pH environments. The GPR4 function of regulating EPC-mediated angiogenesis was analyzed both in vitro and in vivo. The downstream mechanisms were further investigated by genetic overexpression and inhibition.

RESULTS

Acidic environment prestimulation significantly enhanced the angiogenic capacity of EPCs from the non-CAD group both in vivo and in vitro, while the same treatment yielded the opposite result in the CAD group. Among the four canonical proton-sensing GPCRs, GPR4 displays the highest expression in EPCs. The expression of GRP4 was markedly lower in EPCs from CAD patients than in EPCs from non-CAD individuals independent of acid stimulation. The siRNA-mediated knockdown of GPR4 with subsequent decreased phosphorylation of STAT3 mimicked the impaired function of EPCs from CAD patients at pH 6.4 but not at pH 7.4. Elevating GPR4 expression restored the neovessel formation mediated by EPCs from CAD patients in an acidic environment by activating STAT3/VEGFA signaling. Moreover, the beneficial impact of GPR4 upregulation on EPC-mediated angiogenic capacity was abrogated by blockade of the STAT3/VEGFA signaling pathway.

CONCLUSIONS

Our present study demonstrated for the first time that loss of GPR4 is responsible for the decline in proton sensing and angiogenic capacity of EPCs from CAD patients. Augmentation of GPR4 expression promotes the neovessel formation of EPCs by activating STAT3/VEGF signaling. This finding implicates GPR4 as a potential therapeutic target for CAD characterized by impaired neovascularization in ischemic tissues.

Studying Neutrophil Function in vitro: Cell Models and Environmental Factors

Neutrophils are the most abundant immune cell type in the blood and constitute the first line of defense against invading pathogens. Despite their important role in many diseases, they are challenging to study due to their short life span and the inability to cryopreserve or expand them in vitro. Thus, research into neutrophils has to rely on cells freshly isolated from peripheral blood of human donors, introducing donor-dependent variation in the experimental data. To counteract these problems, researchers tried to develop adequate cell models, such as cell lines. For those functional studies that cannot rely on cell models, a standardization of protocols regarding neutrophil purification and culturing could be a solution. In this review, we provide an overview of the most commonly used models for neutrophil function (HL-60, PLB-985, NB4, Kasumi-1 and induced pluripotent stem cells). In addition, we describe the effects of glucose concentration, pH, oxygen tension and temperature on neutrophil function.

Swine hemorrhagic shock model and pathophysiological changes in a desert dry-heat environment

BACKGROUND

This study aimed to establish a traumatic hemorrhagic shock (THS) model in swine and examine pathophysiological characteristics in a dry-heat environment.

METHODS

Forty domestic Landrace piglets were randomly assigned to four study groups: normal temperature non-shock (NS), normal temperature THS (NTHS), desert dry-heat non-shock (DS), and desert dry-hot THS (DTHS) groups. The groups were exposed to either normal temperature (25°C) or dry heat (40.5°C) for 3 h. To induce THS, anesthetized piglets in the NTHS and DTHS groups were subjected to liver trauma and hypovolemic shock until death, and piglets in the NS and DS groups were euthanized at 11 h and 4 h, respectively. Body temperature, blood gas, cytokine production, and organ function were assessed before and after environmental exposure at 0 h and at every 30 min after shock to death. Hemodynamics was measured post exposure and post-shock at 0 h and at every 30 min after shock to death.

RESULTS

Survival, body temperature, oxygen delivery, oxygen consumption, and cardiac output were significantly different for traumatic hemorrhagic shock in the dry-heat groups compared to those in the normal temperature groups. Lactic acid and IL-6 had a marked increase at 0.5 h, followed by a progressive and rapid increase in the DTHS group.

CONCLUSIONS

Our findings suggest that the combined action of a dry-heat environment and THS leads to higher oxygen metabolism, poorer hemodynamic stability, and earlier and more severe inflammatory response with higher mortality.

Evaluation of cell metabolic adaptation in wound and tumour by Fluorescence Lifetime Imaging Microscopy

Acidic pH occurs in acute wounds progressing to healing as consequence of a cell metabolic adaptation in response to injury-induced tissue hypoperfusion. In tumours, high metabolic rate leads to acidosis affecting cancer progression. Acidic pH affects activities of remodelling cells in vitro. The pH measurement predicts healing in pathological wounds and success of surgical treatment of burns and chronic ulcers. However, current methods are limited to skin surface or based on detection of fluorescence intensity of specific sensitive probes that suffer of microenvironment factors. Herein, we ascertained relevance in vivo of cell metabolic adaptation in skin repair by interfering with anaerobic glycolysis. Moreover, a custom-designed skin imaging chamber, 2-Photon microscopy (2PM), fluorescence lifetime imaging (FLIM) and data mapping analyses were used to correlate maps of glycolytic activity in vivo as measurement of NADH intrinsic lifetime with areas of hypoxia and acidification in models of skin injury and cancer. The method was challenged by measuring the NADH profile by interfering with anaerobic glycolysis and oxidative phosphorylation in the mitochondrial respiratory chain. Therefore, intravital NADH FLIM represents a tool for investigating cell metabolic adaptation occurring in wounds, as well as the relationship between cell metabolism and cancer.

Acid-base alterations in ESRD and effects of hemodialysis

Acid-base alterations in patients with kidney failure and on hemodialysis (HD) treatment contribute to (1) intradialytic hypercapnia and hypoxia, (2) hemodynamic instability and cardiac arrhythmia, (3) systemic inflammation, and (4) a number of associated electrolyte alterations including potentiating effects of hypokalemia, hypocalcemia and, chronically, soft-tissue and vascular calcification, imparting poor prognosis and mortality. This paper discusses acid-base regulation and pathogenesis of dysregulation in patients with kidney failure. Major organ and systemic effects of acid-base perturbations with a specific focus on kidney failure patients on HD are emphasized, and potential mitigating strategies proposed. The high rate of HD-related complications, specifically those that can be accounted for by rapid and steep acid-base perturbations imposed by HD treatment, attests to the pressing need for investigations to establish a better dialysis regimen.

pH-Dependent Interactions in Dimers Govern the Mechanics and Structure of von Willebrand Factor

Von Willebrand factor (VWF) is a multimeric plasma glycoprotein that is activated for hemostasis by increased hydrodynamic forces at sites of vascular injury. Here, we present data from atomic force microscopy-based single-molecule force measurements, atomic force microscopy imaging, and small-angle x-ray scattering to show that the structure and mechanics of VWF are governed by multiple pH-dependent interactions with opposite trends within dimeric subunits. In particular, the recently discovered strong intermonomer interaction, which induces a firmly closed conformation of dimers and crucially involves the D4 domain, was observed with highest frequency at pH 7.4, but was essentially absent at pH values below 6.8. However, below pH 6.8, the ratio of compact dimers increased with decreasing pH, in line with a previous transmission electron microscopy study. These findings indicated that the compactness of dimers at pH values below 6.8 is promoted by other interactions that possess low mechanical resistance compared with the strong intermonomer interaction. By investigating deletion constructs, we found that compactness under acidic conditions is primarily mediated by the D4 domain, i.e., remarkably by the same domain that also mediates the strong intermonomer interaction. As our data suggest that VWF has the highest mechanical resistance at physiological pH, local deviations from physiological pH (e.g., at sites of vascular injury) may represent a means to enhance VWF's hemostatic activity where needed.

Cancer acidity: An ultimate frontier of tumor immune escape and a novel target of immunomodulation

The link between cancer metabolism and immunosuppression, inflammation and immune escape has generated major interest in investigating the effects of low pH on tumor immunity. Indeed, microenvironmental acidity may differentially impact on diverse components of tumor immune surveillance, eventually contributing to immune escape and cancer progression. Although the molecular pathways underlying acidity-related immune dysfunctions are just emerging, initial evidence indicates that antitumor effectors such as T and NK cells tend to lose their function and undergo a state of mostly reversible anergy followed by apoptosis, when exposed to low pH environment. At opposite, immunosuppressive components such as myeloid cells and regulatory T cells are engaged by tumor acidity to sustain tumor growth while blocking antitumor immune responses. Local acidity could also profoundly influence bioactivity and distribution of antibodies, thus potentially interfering with the clinical efficacy of therapeutic antibodies including immune checkpoint inhibitors. Hence tumor acidity is a central regulator of cancer immunity that orchestrates both local and systemic immunosuppression and that may offer a broad panel of therapeutic targets. This review outlines the fundamental pathways of acidity-driven immune dysfunctions and sheds light on the potential strategies that could be envisaged to potentiate immune-mediated tumor control in cancer patients.

Exploring the Limits of Cell Adhesion under Shear Stress within Physiological Conditions and beyond on a Chip

Cell adhesion processes are of ubiquitous importance for biomedical applications such as optimization of implant materials. Here, not only physiological conditions such as temperature or pH, but also topographical structures play crucial roles, as inflammatory reactions after surgery can diminish osseointegration. In this study, we systematically investigate cell adhesion under static, dynamic and physiologically relevant conditions employing a lab-on-a-chip system. We screen adhesion of the bone osteosarcoma cell line SaOs-2 on a titanium implant material for pH and temperature values in the physiological range and beyond, to explore the limits of cell adhesion, e.g., for feverish and acidic conditions. A detailed study of different surface roughness R_q gives insight into the correlation between the cells’ abilities to adhere and withstand shear flow and the topography of the substrates, finding a local optimum at R_q = 22 nm. We use shear stress induced by acoustic streaming to determine a measure for the ability of cell adhesion under an external force for various conditions. We find an optimum of cell adhesion for T = 37 °C and pH = 7.4 with decreasing cell adhesion outside the physiological range, especially for high T and low pH. We find constant detachment rates in the physiological regime, but this behavior tends to collapse at the limits of 41 °C and pH 4.

The choice of dialysate bicarbonate: do different concentrations make a difference?

Metabolic acidosis is a common complication of chronic kidney disease; it is typically caused by the accumulation of sulfate, phosphorus, and organic anions. Metabolic acidosis is correlated with several adverse outcomes, such as morbidity, hospitalization, and mortality. Thus, correction of metabolic acidosis is fundamental for the adequate management of many systemic complications of chronic kidney disease. In patients undergoing hemodialysis, acid-base homeostasis depends on many factors including the following: net acid production, amount of alkali given by the dialysate bath, duration of the interdialytic period, and residual diuresis, if any. Recent literature data suggest that the development of metabolic alkalosis after dialysis may contribute to adverse clinical outcomes. Our review is focused on the potential effects of different dialysate bicarbonate concentrations on hard outcomes such as mortality. Unfortunately, no randomized studies exist about this issue. Acid-base equilibrium is a complex and vital system whose regulation is impaired in chronic kidney disease. We await further studies to assess the extent to which acid-base status is a major determinant of overall survival in patients undergoing hemodialysis. For the present, the clinician should understand that target values for predialysis serum bicarbonate concentration have been established primarily based on observational studies and expert opinion. Based on this, we should keep the predialysis serum bicarbonate level at least at 22 mmol/l. Furthermore, a specific focus should be addressed by the attending nephrologist to the clinical and nutritional status of the major outliers on both the acid and alkaline sides of the curve.

Effect of extracellular pH on selectin adhesion: theory and experiment

Selectins mediate circulatory leukocyte trafficking to sites of inflammation and trauma, and the extracellular microenvironments at these sites often become acidic. In this study, we investigated the influence of slightly acidic pH on the binding dynamics of selectins (P-, L-, and E-selectin) to P-selectin glycoprotein ligand-1 (PSGL-1) via computational modeling (molecular dynamics) and experimental rolling assays under shear in vitro. The P-selectin/PSGL-1 binding is strengthened at acidic pH, as evidenced by the formation of a new hydrogen bond (seen computationally) and the observed decrease in the rolling velocities of model cells. In the case of L-selectin/PSGL-1 binding dynamics, the binding strength and frequency increase at acidic pH, as indicated by the greater cell-rolling flux of neutrophils and slower rolling velocities of L-selectin-coated microspheres, respectively. The cell flux is most likely due to an increased population of L-selectin in the high-affinity conformation as pH decreases, whereas the velocities are due to increased L-selectin/PSGL-1 contacts. In contrast to P- and L-selectin, the E-selectin/PSGL-1 binding does not exhibit significant changes at acidic pH levels, as shown both experimentally and computationally.

Regulation of inflammation by extracellular acidification and proton-sensing GPCRs

Under ischemic and inflammatory circumstances, such as allergic airway asthma, rheumatoid arthritis, atherosclerosis, and tumors, extracellular acidification occurs due to the stimulation of anaerobic glycolysis. An acidic microenvironment has been shown to modulate pro-inflammatory or anti-inflammatory responses, including cyclooxygenase-2 (COX-2) expression, prostaglandin synthesis, and cytokine expression, in a variety of cell types, and thereby to exacerbate or ameliorate inflammation. However, molecular mechanisms underlying extracellular acidic pH-induced actions have not been fully understood. Recent studies have shown that ovarian cancer G protein-coupled receptor 1 (OGR1)-family G protein-coupled receptors (GPCRs) can sense extracellular pH or protons, which in turn stimulates intracellular signaling pathways and subsequent diverse cellular responses. In the present review, I discuss extracellular acidic pH-induced inflammatory responses and related responses in inflammatory cells, such as macrophages and neutrophils, and non-inflammatory cells, such as smooth muscle cells and endothelial cells, focusing especially on proton-sensing GPCRs.

An acidic microenvironment increases NK cell killing of Cryptococcus neoformans and Cryptococcus gattii by enhancing perforin degranulation

Cryptococcus gattii and Cryptococcus neoformans are encapsulated yeasts that can produce a solid tumor-like mass or cryptococcoma. Analogous to malignant tumors, the microenvironment deep within a cryptococcoma is acidic, which presents unique challenges to host defense. Analogous to malignant cells, NK cells kill Cryptococcus. Thus, as in tumor defense, NK cells must kill yeast cells across a gradient from physiologic pH to less than 6 in the center of the cryptococcoma. As acidic pH inhibits anti-tumor activities of NK cells, we sought to determine if there was a similar reduction in the anticryptococcal activity of NK cells. Surprisingly, we found that both primary human NK cells and the human NK cell line, YT, have preserved or even enhanced killing of Cryptococcus in acidic, compared to physiological, pH. Studies to explore the mechanism of enhanced killing revealed that acidic pH does not increase the effector to target ratio, binding of cytolytic cells to Cryptococcus, or the active perforin content in effector cells. By contrast, perforin degranulation was greater at acidic pH, and increased degranulation was preceded by enhanced ERK1/2 phosphorylation, which is essential for killing. Moreover, using a replication defective ras1 knockout strain of Cryptococcus increased degranulation occurred during more rapid replication of the organisms. Finally, NK cells were found intimately associated with C. gattii within the cryptococcoma of a fatal infection. These results suggest that NK cells have amplified signaling, degranulation, and greater killing at low pH and when the organisms are replicating quickly, which would help maintain microbicidal host defense despite an acidic microenvironment.

Immune responses that protect from infection must occur in a variety of unique and potentially hostile environments. Within these environments, acidosis causes profound affects on protective responses. Low pH can occur in focal tumor-like infections, such as in a cryptococcoma produced by the fungal pathogen Cryptococcus. Similarly, low pH occurs in focal malignant tumors. It follows that Cryptococcus and malignant cells can both be killed by NK cells, which provide an important mechanism of host defense. Thus, we asked whether low pH, which impairs tumor killing, might also affect NK cell killing of Cryptococcus. Surprisingly, despite impaired tumor killing, NK cells possess enhanced killing of Cryptococcus at low pH. The mechanism involved a gain in intracellular signal transduction that led to enhanced perforin degranulation. This led us to examine NK cells in persistent cryptococcoma of a fatal brain infection and lung. We found that NK cells associate with Cryptococcus within the cryptococcoma, but perforin is reduced. These studies suggest NK cell cytotoxicity need not be impaired at low pH, and that enhanced signal transduction and degranulation at low pH might be used to enhance host defense.

RKIP: much more than Raf kinase inhibitory protein

From its discovery as a phosphatidylethanolamine-binding protein in bovine brain to its designation as a physiological inhibitor of Raf kinase protein, RKIP has emerged as a critical molecule for maintaining subdued, well-orchestrated cellular responses to stimuli. The disruption of RKIP in a wide range of pathologies, including cancer, Alzheimer's disease, and pancreatitis, makes it an exciting target for individualized therapy and disease-specific interventions. This review attempts to highlight recent advances in the RKIP field underscoring its potential role as a master modulator of many pivotal intracellular signaling cascades that control cellular growth, motility, apoptosis, genomic integrity, and therapeutic resistance. Specific biological and functional niches are highlighted to focus future research towards an enhanced understanding of the multiple roles of RKIP in health and disease.

Identification of macrophage genes responsive to extracellular acidification

OBJECTIVE

A low pH microenvironment is a characteristic feature of inflammation loci and affects the functions of immune cells. In this study, we investigated the effect of extracellular acidification on macrophage gene expression.

METHODS

RAW264.7 macrophages were incubated in neutral (pH 7.4) or acidic (pH 6.8) medium for 4 h. Global mRNA expression levels were determined using Affymetrix genechips.

RESULTS

The mRNA expressions of 353 macrophage genes were significantly modified after incubation in acidic medium; 193 were up-regulated and 160 down-regulated. Differentially regulated genes were grouped into 13 classes based on the functions of the corresponding protein products. Pathway analysis revealed that differentially expressed genes are enriched in pathways related to inflammation and immune responses. Quantitative real-time PCR analysis confirmed that the expressions of CXCL10, CXCL14, IL-18, IL-4RA, ABCA1, CCL4, IL-7R, CXCR4, TLR7, and CCL3 mRNAs were regulated by extracellular acidification.

CONCLUSION

The results of this study provide insights into the effects of acidic extracellular environments on macrophage gene expression.

Sabiporide improves cardiovascular function, decreases the inflammatory response and reduces mortality in acute metabolic acidosis in pigs

INTRODUCTION

Acute metabolic acidosis impairs cardiovascular function and increases the mortality of critically ill patients. However, the precise mechanism(s) underlying these effects remain unclear. We hypothesized that targeting pH-regulatory protein, Na(+)/H(+) exchanger (NHE1) could be a novel approach for the treatment of acute metabolic acidosis. The aim of the present study was to examine the impact of a novel NHE1 inhibitor, sabiporide, on cardiovascular function, blood oxygen transportation, and inflammatory response in an experimental model of metabolic acidosis produced by hemorrhage-induced hypovolemia followed by an infusion of lactic acid.

METHODS AND RESULTS

Anesthetized pigs were subjected to hypovolemia for 30 minutes. The animals then received a bolus infusion of sabiporide (3 mg/kg) or vehicle, followed by an infusion of lactic acid for 2 hours. The animals were continuously monitored for additional 3 hours. Hypovolemia followed by a lactic acid infusion resulted in a severe metabolic acidosis with blood pH falling to 6.8. In association with production of the acidemia, there was an excessive increase in pulmonary artery pressure (PAP) and pulmonary vascular resistance (PVR). Treatment with sabiporide significantly attenuated the increase in PAP by 38% and PVR by 67%, as well as significantly improved cardiac output by 51%. Sabiporide treatment also improved mixed venous blood oxygen saturation (55% in sabiporide group vs. 28% in control group), and improved systemic blood oxygen delivery by 36%. In addition, sabiporide treatment reduced plasma levels of TNF-α (by 33%), IL-6 (by 63%), troponin-I (by 54%), ALT (by 34%), AST (by 35%), and urea (by 40%).

CONCLUSION

These findings support the possible beneficial effects of sabiporide in the treatment of acute metabolic acidosis and could have implications for the treatment of metabolic acidosis in man.

Extracellular low pH modulates phosphatidylserine-dependent phagocytosis in macrophages by increasing stabilin-1 expression

Microenvironmental acidosis is a common feature of inflammatory loci, in which clearance of apoptotic cells is necessary for the resolution of inflammation. Although it is known that a low pH environment affects immune function, its effect on apoptotic cell clearance by macrophages has not been fully investigated. Here, we show that treatment of macrophages with low pH medium resulted in increased expression of stabilin-1 out of several receptors, which are known to be involved in PS-dependent removal of apoptotic cells. Reporter assays showed that the -120/-1 region of the mouse stabilin-1 promoter was a low pH-responsive region and provided evidence that extracellular low pH mediated transcriptional activation of stabilin-1 via Ets-2. Furthermore, extracellular low pH activated JNK, thereby inducing translocation of Ets-2 into the nucleus. When macrophages were preincubated with low pH medium, phagocytosis of phosphatidylserine-exposed red blood cells and phosphatidylserine-coated beads by macrophages was enhanced. Blockade of stabilin-1 in macrophages abolished the enhancement of phagocytic activity by low pH. Thus, our results demonstrate that a low pH microenvironment up-regulates stabilin-1 expression in macrophages, thereby modulating the phagocytic capacity of macrophages, and suggest roles for stabilin-1 and Ets-2 in the maintenance of tissue homeostasis by the immune system.

Comparative effects of verapamil, nicardipine, and nitroglycerin on myocardial ischemia/reperfusion injury

The aim of this experiment was to establish whether verapamil, nicardipine, and nitroglycerin have (1) infarct size-limiting effects and (2) antiarrhythmic effects in in vivo rabbit hearts during ischemia/reperfusion. Rabbits received regional ischemia by 30 min of left anterior descending coronary artery occlusion followed by 3 hours of reperfusion under ketamine and xylazine anesthesia. The animals were randomly assigned to the following 4 treatment groups: a control group, a verapamil group, a nicardipine group, and a nitroglycerin group. A continuous infusion of verapamil, nicardipine, or nitroglycerin was initiated 5 min prior to ischemia. Infarct size/area at risk decreased in verapamil, and nitroglycerin. The incidence of ischemia-induced arrhythmia decreased in nicardipine, verapamil and nitroglycerin. The incidence of reperfusion-induced arrhythmias decreased in verapamil and nitroglycerin. From the present experimental results, verapamil and nitroglycerin rather than nicardipine did afford significant protection to the heart subjected to ischemia and reperfusion in a rabbit model.

The low viability of human CD34+ cells under acidic conditions is improved by exposure to thrombopoietin, stem cell factor, interleukin-3, or increased cyclic adenosine monophosphate levels

BACKGROUND

Transplanted hematopoietic progenitor cells (CD34+) have shown great promise in regenerative medicine. However, the therapeutic potential of transplanted cells is limited by their poor viability. It is well known that the microenvironment in which progenitors reside substantially affects their behavior. Because extracellular acidosis is a common feature of injured tissues or the tumor microenvironment and is a critical regulator of cell survival and activation, we evaluated the impact of acidosis on CD34+ cell biology.

STUDY DESIGN AND METHODS

Apoptosis was evaluated by fluorescence microscopy and binding of annexin V, hypodiploid cells, Bcl-xL expression, active caspase-3, and mitochondrial membrane potential was determined by flow cytometry. Colony-forming units were studied by clonogenic assays, and cell cycle was evaluated by flow cytometry.

RESULTS

Exposure of CD34+ cells to low pH (7.0-6.5) caused intracellular acidification, decreased cell proliferation, and triggered apoptosis via the mitochondrial pathway. Whereas exposure to thrombopoietin (TPO), stem cell factor (SCF), interleukin (IL)-3 or increases in cyclic adenosine monophosphate (cAMP) levels prevented CD34+ cell death induced by acidic conditions, granulocyte-macrophage-colony-stimulating factor, FMS-like tyrosine kinase 3-ligand, erythropoietin, and vascular endothelial growth factor had no effect. Despite their cytoprotective effect, CD34+ cell expansion triggered by TPO, SCF, or IL-3 was significantly impaired at low pH. However, a cocktail of these three cytokines synergistically supported proliferation, cell cycle progression, and colony formation.

DISCUSSION

Our findings indicate that an acidic milieu is deleterious for CD34+ cells and that a combination of certain cytokines and cAMP donors may improve cell viability and function. These data may be useful to develop new therapeutic strategies or to optimize protocols for regenerative medicine.

Heme oxygenase-1 does not mediate the effects of extracellular acidosis on vascular smooth muscle cell proliferation, migration, and susceptibility to apoptosis

BACKGROUND

Unbalanced vascular smooth muscle cell (VSMC) proliferation, migration, and apoptosis contribute to vascular disorders such as atherosclerosis, restenosis, and pulmonary hypertension. The effect of extracellular acidosis (EA) on VSMC homeostasis is incompletely understood but we previously reported that EA increases heme oxygenase-1 (HO-1) expression in VSMCs. Since HO-1 regulates VSMC proliferation and apoptosis we sought to define the role of HO-1 in VSMC responses to EA.

METHODS

Mouse aortic smooth muscle cells (MASMCs) were isolated from wild-type and HO-1-null mice. Cell proliferation and migration assays were done in a physiologic pH (7.4) or EA (pH 6.8). VSMC apoptosis in response to hydrogen peroxide was assessed by JC-1 staining, caspase-3 cleavage, annexin V, and Hoechst staining.

RESULTS

Wild-type MASMCs showed decreased proliferation and migration at pH 6.8 compared to pH 7.4. This observation was also true in HO-1-null MASMCs. Although wild-type and HO-1-null cells showed differences in the mode and kinetics of cell death, both genotypes exhibited increased susceptibility to hydrogen peroxide-induced apoptosis at pH 6.8 compared to 7.4.

CONCLUSIONS

EA inhibits VSMC proliferation and migration and increases susceptibility to oxidant-induced apoptosis. These effects of acidosis on VSMC homeostasis are independent of HO-1.

Acidic extracellular pH promotes activation of integrin α(v)β(3)

Acidic extracellular pH is characteristic of the cell microenvironment in several important physiological and pathological contexts. Although it is well established that acidic extracellular pH can have profound effects on processes such as cell adhesion and migration, the underlying molecular mechanisms are largely unknown. Integrin receptors physically connect cells to the extracellular matrix, and are thus likely to modulate cell responses to extracellular conditions. Here, we examine the role of acidic extracellular pH in regulating activation of integrin α_vβ₃. Through computational molecular dynamics simulations, we find that acidic extracellular pH promotes opening of the α_vβ₃ headpiece, indicating that acidic pH can thereby facilitate integrin activation. This prediction is consistent with our flow cytometry and atomic force microscope-mediated force spectroscopy assays of integrin α_vβ₃ on live cells, which both demonstrate that acidic pH promotes activation at the intact cell surface. Finally, quantification of cell morphology and migration measurements shows that acidic extracellular pH affects cell behavior in a manner that is consistent with increased integrin activation. Taken together, these computational and experimental results suggest a new and complementary mechanism of integrin activation regulation, with associated implications for cell adhesion and migration in regions of altered pH that are relevant to wound healing and cancer.

Role of HIF-1alpha in proton-mediated CXCR4 down-regulation in endothelial cells

AIMS

Acidification is associated with a variety of pathological and physiological conditions. In the present study, we aimed at investigating whether acidic pH may regulate endothelial cell (EC) functions via the chemokine receptor CXCR4, a key modulator of EC biological activities.

METHODS AND RESULTS

Exposure of ECs to acidic pH reversibly inhibited mRNA and protein CXCR4 expression, CXCL12/stromal cell-derived factor (SDF)-1-driven EC chemotaxis in vitro, and CXCR4 expression and activation in vivo in a mouse model. Further, CXCR4 signalling impaired acidosis-induced rescue from apoptosis in ECs. The inhibition of CXCR4 expression occurred transcriptionally and was hypoxia-inducible factor (HIF)-1alpha-dependent as demonstrated by both HIF-1alpha and HIF-1alpha dominant negative overexpression, by HIF-1alpha silencing, and by targeted mutation of the -29 to -25 hypoxia response element (HRE) in the -357/-59 CXCR4 promoter fragment. Moreover, chromatin immunoprecipitation (ChIP) analysis showed endogenous HIF-1alpha binding to the CXCR4 promoter that was enhanced by acidification.

CONCLUSION

The results of the present study identify CXCR4 as a key player in the EC response to acidic pH and show, for the first time, that HRE may function not only as an effector of hypoxia, but also as an acidosis response element, and raise the possibility that this may constitute a more general mechanism of transcriptional regulation at acidic pH.

Effects of hypercapnia with and without acidosis on hypoxic pulmonary vasoconstriction

Acute respiratory disorders and permissive hypercapnic strategy may lead to alveolar hypoxia and hypercapnic acidosis. However, the effects of hypercapnia with or without acidosis on hypoxic pulmonary vasoconstriction (HPV) and oxygen diffusion capacity of the lung are controversial. We investigated the effects of hypercapnic acidosis and hypercapnia with normal pH (pH corrected with sodium bicarbonate) on HPV, capillary permeability, gas exchange, and ventilation-perfusion matching in the isolated ventilated-perfused rabbit lung. No alteration in vascular tone was noted during normoxic hypercapnia with or without acidosis compared with normoxic normocapnia. Hypercapnia with normal pH resulted in a transient increase in HPV during the course of consecutive ventilation maneuvers, whereas hypercapnic acidosis increased HPV over time. Hypercapnic acidosis decreased exhaled NO during hypoxia more than hypercapnia with normal pH and normocapnia, whereas intravascular NO release was unchanged. However, inhibition of NO synthesis by nitro-L-arginine (L-NNA) resulted in a loss of the increased HPV caused by hypercapnic acidosis but not that caused by hypercapnia with normal pH. Furthermore, capillary permeability increased during hypoxic hypercapnia with normal pH but not hypoxic hypercapnic acidosis. This effect was NO-dependent because it disappeared during L-NNA administration. Ventilation-perfusion matching and arterial PO2 were improved according to the strength of HPV in hypercapnia compared with normocapnia during Tween nebulization-induced lung injury. In conclusion, the increased HPV during hypercapnic acidosis is beneficial to lung gas exchange by improving ventilation-perfusion matching and preserving the capillary barrier function. These effects seem to be linked to NO-mediated pathways.

Differential effect of extracellular acidosis on the release and dispersal of soluble and membrane proteins secreted from the Weibel-Palade body

Proteins secreted from Weibel-Palade bodies (WPBs) play important roles in regulating inflammatory and hemostatic responses. Inflammation is associated with the extracellular acidification of tissues and blood, conditions that can alter the behavior of secreted proteins. The effect of extracellular pH (pH(o)) on the release of von Willebrand factor (VWF), the VWF-propolypeptide (Proregion), interleukin-8, eotaxin-3, P-selectin, and CD63 from WPBs was investigated using biochemical approaches and by direct optical analysis of individual WPB fusion events in human endothelial cells expressing green or red fluorescent fusions of these different cargo proteins. Between pH(o) 7.4 and 7.0, ionomycin-evoked WPB exocytosis was characterized by the adhesion of VWF to the cell surface and the formation of long filamentous strands. The rapid dispersal of Proregion, interleukin-8, and eotaxin-3 into solution, and of P-selectin and CD63 into the plasma membrane, was unaltered over this pH(o) range. At pH(o) 6.8 or lower, Proregion remained associated with VWF, in many cases WPB failed to collapse fully and VWF failed to form filamentous strands. At pH(o) 6.5 dispersal of interleukin-8, eotaxin-3, and the membrane protein CD63 remained unaltered compared with that at pH(o) 7.4; however, P-selectin dispersal into the plasma membrane was significantly slowed. Thus, extracellular acidification to levels of pH(o) 6.8 or lower significantly alters the behavior of secreted VWF, Proregion, and P-selectin while rapid release of the small pro-inflammatory mediators IL-8 and eotaxin-3 is essentially unaltered. Together, these data suggest that WPB exocytosis during extracellular acidosis may favor the control of inflammatory processes.

Permissive hypercapnia

Mechanical ventilation using high tidal volume (VT) and transpulmonary pressure can damage the lung, causing ventilator-induced lung injury. Permissive hypercapnia, a ventilatory strategy for acute respiratory failure in which the lungs are ventilated with a low inspiratory volume and pressure, has been accepted progressively in critical care for adult, pediatric, and neonatal patients requiring mechanical ventilation and is one of the central components of current protective ventilatory strategies.

MSC response to pH levels found in degenerating intervertebral discs

Painful degenerative disc disease is a major health problem and for successful tissue regeneration, MSCs must endure and thrive in a harsh disc microenvironment that includes matrix acidity as a critical factor. MSCs were isolated from bone marrow of Sprague-Dawley rats from two different age groups (<1 month, n=6 and 4-5 months, n=6) and cultured under four different pH conditions representative of the healthy, mildly or severely degenerated intervertebral disc (pH 7.4, 7.1, 6.8, and 6.5) for 5 days. Acidity caused an inhibition of aggrecan, collagen-1, and TIMP-3 expression, as well as a decrease in proliferation and viability and was associated with a change in cell morphology. Ageing had generally minor effects but young MSCs maintained greater mRNA expression levels. As acidic pH levels are typical of increasingly degenerated discs, our findings demonstrate the importance of early interventions and predifferentiation when planning to use MSCs for reparative treatments.

Impact of buffering hypercapnic acidosis on cell wounding in ventilator-injured rat lungs

We measured the effects of raising perfusate pH on ventilator-induced cell wounding and repair in ex vivo mechanically ventilated hypercapnic rat lungs. Lungs were randomized to one of three perfusate groups: 1) unbuffered hypercapnic acidosis, 2) bicarbonate-buffered hypercapnia, or 3) tris-hydroxymethyl aminomethane (THAM)-buffered hypercapnia. The membrane-impermeant label propidium iodide was added to the perfusate either during or after injurious ventilation providing a means to subsequently identify transiently wounded and permanently wounded cells in optical sections of subpleural alveoli. Normalizing perfusate pH in hypercapnic preparations attenuated ventilator-induced cell injury, particularly in THAM-buffered preparations. This was observed despite greater amounts of edema and impaired lung mechanics compared with other treatment groups. Protective effects of buffering of hypercapnic acidosis on injury and repair were subsequently confirmed in a cell scratch model. We conclude that buffering of hypercapnic acidosis attenuates plasma cell injury induced by mechanical hyperinflation.

Inhibition of Na+/H+ exchanger enhances low pH-induced L-selectin shedding and beta2-integrin surface expression in human neutrophils

Ischemia-reperfusion injury is a common pathological occurrence causing tissue damage in heart attack and stroke. Entrapment of neutrophils in the vasculature during ischemic events has been implicated in this process. In this study, we examine the effects that lactacidosis and consequent reductions in intracellular pH (pH(i)) have on surface expression of adhesion molecules on neutrophils. When human neutrophils were exposed to pH 6 lactate, there was a marked decrease in surface L-selectin (CD62L) levels, and the decrease was significantly enhanced by inclusion of Na(+)/H(+) exchanger (NHE) inhibitor 5-(N,N-hexamethylene)amiloride (HMA). Similar effects were observed when pH(i) was reduced while maintaining normal extracellular pH, by using an NH(4)Cl prepulse followed by washes and incubation in pH 7.4 buffer containing NHE inhibitors [HMA, cariporide, or 5-(N,N-dimethyl)amiloride (DMA)]. The amount of L-selectin shedding induced by different concentrations of NH(4)Cl in the prepulse correlated with the level of intracellular acidification with an apparent pK of 6.3. In contrast, beta(2)-integrin (CD11b and CD18) was only slightly upregulated in the low-pH(i) condition and was enhanced by NHE inhibition to a much lesser extent. L-selectin shedding was prevented by treating human neutrophils with inhibitors of extracellular metalloproteases (RO-31-9790 and KD-IX-73-4) or with inhibitors of intracellular signaling via p38 MAP kinase (SB-203580 and SB-239063), implying a transmembrane effect of pH(i). Taken together, these data suggest that the ability of NHE inhibitors such as HMA to reduce ischemia-reperfusion injury may be related to the nearly complete removal of L-selectin from the neutrophil surface.

Modulatory effects of hypercapnia on in vitro and in vivo pulmonary endothelial-neutrophil adhesive responses during inflammation

Reducing tidal volume as a part of a protective ventilation strategy may result in hypercapnia. In this study, we focused on the influence of hypercapnia on endothelial-neutrophil responses in models of inflammatory-stimulated human pulmonary microvascular endothelial cells (HMVEC) and in an animal model of lipopolysaccharide (LPS)-induced acute lung injury. Neutrophil adhesion and adhesion molecules expression and nuclear factor-kappaB (NF-kappaB) were analyzed in TNF-alpha and LPS-treated HMVEC exposed to either eucapnia or hypercapnia. In the in vivo limb, bronchoalveolar lavage fluid cell counts and differentials, adhesion molecule and chemokine expression were assessed in LPS-treated rabbits ventilated with either low tidal volume ventilation and eucapnia or hypercapnia. In both the in vitro and in vivo models, hypercapnia significantly increased neutrophil adhesion and adhesion molecule expression compared to eucapnia. Activity of NF-kappaB was significantly enhanced by hypercapnia in the in vitro experiments. IL-8 expression was greatest both in vitro and in vivo under conditions of hypercapnia and concomitant inflammation. CD11a expression was greatest in isolated human neutrophils exposed to hypercapnia+LPS. Our results demonstrate that endothelial-neutrophil responses per measurement of fundamental molecules of adhesion are significantly increased during hypercapnia and that hypercapnia mimics conditions of eucapnia+inflammation.

Lung injury after in vivo reperfusion: outcome at 27 hours after reperfusion

BACKGROUND

Although short-term findings after lung reperfusion have been extensively reported, in vivo animal studies have not described outcome beyond the immediate time period. Therefore, the authors evaluated lung injury 27 h after reperfusion. They also investigated whether attenuation of lung injury with the A3 adenosine receptor agonist MRS3558 was sustained beyond the immediate time period.

METHODS

In intact-chest, spontaneously breathing cats in which the left lower lung lobe was isolated and subjected to 2 h of ischemia and 3 h of reperfusion, MRS3558 was administered before reperfusion. Animals were killed 3 or 27 h after reperfusion.

RESULTS

When compared with 3 h of reperfusion, at 27 h the left lower lobe showed reduced apoptosis and no change in inflammation, but increased edema. Increased edema of the nonischemic right lung and hypoxemia were observed at 27 h after left lower lobe reperfusion. Increases in phosphorylated p38 levels were found at 3 h of reperfusion compared with control lung, with further increases at 27 h. The attenuation of injury observed with MRS3558 treatment at 3 h of reperfusion was sustained at 27 h.

CONCLUSIONS

Lung edema may worsen hours after the immediate postreperfusion period, even though lung apoptosis and inflammation are reduced or show no change, respectively. This was associated with further increases in phosphorylated p38 levels. The nonischemic lung may also be affected, suggesting a systemic response to reperfusion. In addition, early attenuation of injury is beneficial beyond the immediate period after reperfusion. Treatment aimed at inhibiting p38 activation, such as A3 receptor activation, should be further studied to explore its potential long-term beneficial effect.

Acute hypercapnia improves indices of tissue oxygenation more than dobutamine in septic shock

RATIONALE

Hypercapnia has similar hemodynamic effects to those of a dobutamine infusion and may have relevance in the management of septic shock.

OBJECTIVES

To compare the effects induced by hypercapnia with those of dobutamine in a clinically relevant model of septic shock.

METHODS

Fecal peritonitis was induced in 21 anesthetized, invasively monitored, mechanically ventilated female sheep. A combination of Ringer's lactate and 6% hydroxyethyl starch solution was titrated to maintain constant cardiac filling throughout the experiments. Two hours after feces spillage, animals were randomized to one of three groups (each, n = 7): (1) hypercapnia: carbon dioxide given to maintain partial pressure of carbon dioxide between 55 and 65 mm Hg throughout the experiment; (2) dobutamine: dobutamine infused intravenously (7 microg/kg/min); (3) control: no treatment. In the dobutamine and control groups, the partial pressure of carbon dioxide was kept between 35 and 45 mm Hg. All animals were monitored until spontaneous death.

MEASUREMENTS AND MAIN RESULTS

The animals in the hypercapnia group had significantly lower arterial pH than the other two groups (P < 0.05). Hypercapnic and dobutamine-treated animals developed significantly higher heart rate, cardiac index, and oxygen delivery, and lower lactate concentrations than control animals (P < 0.05). Hypercapnic animals had lower post mortem lung wet/dry ratio than the control animals (P < 0.05). The alveolar-arterial oxygen partial pressure difference and shunt fraction were significantly lower in hypercapnic animals than in the other groups (P < 0.05).

CONCLUSIONS

In this clinically relevant ovine model of septic shock, hypercapnia had similar effects to dobutamine on hemodynamic variables and lactic acidosis. Hypercapnia improved tissue oxygenation and reduced lung edema formation more than dobutamine administration.

The sodium/hydrogen exchanger: a possible mediator of immunity

Immune cells such as macrophages and neutrophils provide the first line of defence of the immune system using phagocytosis, cytokine and chemokine synthesis and release, as well as Reactive Oxygen Species (ROS) generation. Many of these functions are positively coupled with cytoplasmic pH (pHi) and/or phagosomal pH (pHp) modification; an increase in pHi represents an important signal for cytokine and chemokine release, whereas a decrease in pHp can induce an efficient antigen presentation. However, the relationship between pHi and ROS generation is not well understood. In immune cells two main transport systems have been shown to regulate pHi: the Na+/H+ Exchanger (NHE) and the plasmalemmal V-type H+ ATPase. NHE is a family of proteins which exchange Na+ for H+ according to their concentration gradients in an electroneutral manner. The exchanger also plays a key role in several other cellular functions including proliferation, differentiation, apoptosis, migration, and cytoskeletal organization. Since not much is known on the relationship between NHE and immunity, this review outlines the contribution of NHE to different aspects of innate and adaptive immune responses such as phagosomal acidification, NADPH oxidase activation and ROS generation, cytokine and chemokine release as well as T cell apoptosis. The possibility that several pro-inflammatory diseases may be modulated by NHE activity is evaluated.

A surgically induced hypoxic environment causes changes in the metastatic behaviour of tumours in vitro

The use of laparoscopic techniques for curative resections of malignant tumours has been under scrutiny. The potential benefits to the patient in the form of earlier recovery and less immune paresis are countered by the reports of increased tumour recurrence. The biological sequelae of the hypoxic laparoscopic environment on tumour cells is unknown. Components of the metastatic cascade were evaluated under in vitro laparoscopic conditions using a human colonic adenocarcinoma cell line (SW1222). Exposure to the laparoscopic gases carbon dioxide and helium for 4 h, comparable to the duration of a laparoscopic colorectal resection, had no effect on cell viability. A cellular hypoxic insult was demonstrated by the induction of hypoxia inducible factor 1alpha (HIF-1alpha). Exposure also resulted in significant reduction in homotypic adhesion as well as to a variety of extracellular matrix components. These effects were recoverable under re-oxygenation. The changes were reflected at the molecular level by significant down regulation of adhesion molecules known to be involved in tumour progression (E-cadherin, CD44 and beta1 sub-unit). Modulation of adherence has significant implications for laparoscopic oncological surgery, demonstrating that tumours become potentially more friable and easier to disseminate in surgeons who are less experienced or where instrumentation is sub-optimal.

Is hypercapnea a predictor of better survival in the patients who underwent mechanical ventilation for chronic obstructive pulmonary disease (COPD)?

BACKGROUND

There are contradictory reports concerning hypercapnia as a predictor of a better outcome in COPD. This study examined the clinical implications of hypercapnea in COPD patients (M:F = 59:19) who required mechanical ventilation.

METHODS

The clinical parameters at the time of MICU admission, the total ventilation time, the APACHE II score and the pulmonary function testing were retrospectively analyzed between the survivors and nonsurvivors.

RESULTS

Univariate analysis showed that compared with the nonsurvivors, the survivors had lower AaDO2 values (59.8 +/- 53.5 vs. 105.0 +/- 73.3 mmHg, p=0.000), higher PaCO2 values (64.9 +/- 16.0 vs. 48.9 +/- 17.8 mmHg, p=0.000), lower APACHE II scores (19.0 +/- 3.8 vs. 24.1 +/- 5.1, p=0.002), the more frequent application of initial noninvasive positive pressure ventilation (44.0 vs. 14.3%, p=0.008), and a lower combined rate of septic shock (4.0 vs. 39.3%, p=0.000). Multivariate analysis revealed that a lower PaCO2 (OR: 0.94, p=0.008), the presence of septic shock (OR: 10.16, p=0.011), a higher APACHE II score (OR: 1.22, p=0.040) and a longer ventilation time (OR: 1.002, p=0.041) were the risk factors for mortality. A lower PaCO2 was also verified as the predictor. for mortality by multivariate analysis when excluding septic shock.

CONCLUSIONS

Hypercapnia at admission is thought to be an independent predictor of better survival for the COPD patients who require mechanical ventilation.

Hypercapnic acidosis and mortality in acute lung injury*

OBJECTIVE

We tested the hypothesis that hypercapnic acidosis is associated with reduced mortality rate in patients with acute lung injury independent of changes in mechanical ventilation.

DESIGN

Secondary analysis of randomized clinical trial data using hypothesis-driven multivariate logistic regression.

SETTING

Randomized, multiple-center trial (n = 861) comparing 12 mL/kg to 6 mL/kg predicted body weight tidal volumes previously published by the National Institutes of Health Acute Respiratory Distress Syndrome (ARDS) Network.

PATIENTS

Acute lung injury patients enrolled in a randomized, multiple-center trial (n = 861).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The adjusted odds ratio and 95% confidence intervals (CI) for 28-day mortality rate associated with hypercapnic acidosis defined as day 1 pH <7.35 and Pa(CO2) >45 mm Hg were 0.14 (95% CI 0.03-0.70, p = .016) in the 12 mL/kg predicted body weight tidal volume group and 1.18 (95% CI 0.59-2.35, p = .639) in the 6 mL/kg predicted body weight tidal volume group. Other definitions of hypercapnic acidosis spanning a range of magnitudes suggest a dose-response association between hypercapnic acidosis and 28-day mortality in the 12 mL/kg predicted body weight tidal volume group. None of our definitions of hypercapnic acidosis were associated with reduction in 28-day mortality in the 6 mL/kg predicted body weight tidal volume group.

CONCLUSIONS

Hypercapnic acidosis was associated with reduced 28-day mortality in the 12 mL/kg predicted body weight tidal volume group after controlling for comorbidities and severity of lung injury. These results are consistent with a protective effect of hypercapnic acidosis against ventilator-associated lung injury that was not found when the further ongoing injury was reduced by 6 mL/kg predicted body weight tidal volumes.

Proton-sensing and lysolipid-sensitive G-protein-coupled receptors: A novel type of multi-functional receptors

OGR1, GPR4, G2A, and TDAG8 share 40% to 50% homology with each other and seem to form a family of GPCRs. They have been described as receptors for lipid molecules such as sphingosylphosphorylcholine, lysophosphatidylcholine, and psychosine. Recent studies, however, have revealed that these receptors also sense extracellular protons or pH through histidine residues of receptors and stimulate a variety of intracellular signaling pathways through several species of hetero-trimeric G-proteins, including G(s), G(i), G(q), and G(12/13). Thus, this family of GPCR seems to recognize both lipid molecules and protons as ligands. Although our knowledge of proton-sensing and lysolipid-sensitive GPCRs is preliminary, the receptor levels and ligand levels especially protons are both sensitively modulated in response to a variety of microenvironmental changes. These results suggest a multiple role of proton-sensing GPCRs in a variety of physiological and pathophysiological states.

Hypercapnic acidosis impairs plasma membrane wound resealing in ventilator-injured lungs

The objective of this study was to assess the effects of hypercapnic acidosis on lung cell injury and repair by confocal microscopy in a model of ventilator-induced lung injury. Three groups of normocapnic, hypocapnic, and hypercapnic rat lungs were perfused ex vivo, either during or after injurious ventilation, with a solution containing the membrane-impermeant label propidium iodide. In lungs labeled during injurious ventilation, propidium iodide fluorescence identifies all cells with plasma membrane wounds, both permanent and transient, whereas in lungs labeled after injurious ventilation propidium iodide fluorescence identifies only cells with permanent plasma membrane wounds. Hypercapnia minimized the adverse effects of high-volume ventilation on vascular barrier function, whereas hypocapnia had the opposite effect. Despite CO2-dependent differences in lung mechanics and edema the number of injured subpleural cells per alveolus was similar in the three groups (0.48 +/- 0.34 versus 0.51 +/- 0.19 versus 0.43 +/- 0.20 for hypocapnia, normocapnia, and hypercapnia, respectively). However, compared with normocapnia the probability of wound repair was significantly reduced in hypercapnic lungs (63 versus 38%; p < 0.02). This finding was subsequently confirmed in alveolar epithelial cell scratch models. The potential relevance of these observations for lung inflammation and remodeling after mechanical injury is discussed.

Hypercapnia via reduced rate and tidal volume contributes to lipopolysaccharide-induced lung injury

Appreciating that CO2 modifies the chemical reactivity of nitric oxide (NO)-derived inflammatory oxidants, we investigated whether hypercapnia would modulate pulmonary inflammatory responses. Rabbits (n = 72) were ventilated with approximately 7-ml/kg tidal volume for 6 hours. Animals were randomized to one of the following conditions: eucapnia (Pa(CO2) at approximately 35-40 mm Hg), eucapnia + lipopolysaccharide (LPS), eucapnia + LPS + inhaled NO (iNO delivered at approximately 20 ppm), hypercapnia (Pa(CO2) at approximately 60 mm Hg), hypercapnia + LPS, and hypercapnia + LPS + iNO. The hypercapnia + LPS groups compared with groups exposed to eucapnia + LPS displayed significantly increased bronchoalveolar lavage fluid protein concentrations (p < 0.05), lung wet-to-dry ratios (p < 0.05), bronchoalveolar lavage fluid cell counts (p < 0.05), and lung histologic alterations consistent with greater injury. Furthermore, expression of inducible nitric oxide synthase (p < 0.05), tissue myeloperoxidase content (p < 0.05), and formation of lung protein 3-nitrotyrosine derivatives (p < 0.05) was greatest under conditions of hypercapnia + LPS. Groups exposed to hypercapnic conditions without LPS did not manifest these changes. The inhalation of iNO attenuated selected indices of lung injury. We conclude that hypercapnia induced by means of reduced rate and tidal volume amplifies pulmonary inflammatory responses.

Bench-to-bedside review: Permissive hypercapnia

Current protective lung ventilation strategies commonly involve hypercapnia. This approach has resulted in an increase in the clinical acceptability of elevated carbon dioxide tension, with hypoventilation and hypercapnia 'permitted' in order to avoid the deleterious effects of high lung stretch. Advances in our understanding of the biology of hypercapnia have prompted consideration of the potential for hypercapnia to play an active role in the pathogenesis of inflammation and tissue injury. In fact, hypercapnia may protect against lung and systemic organ injury independently of ventilator strategy. However, there are no clinical data evaluating the direct effects of hypercapnia per se in acute lung injury. This article reviews the current clinical status of permissive hypercapnia, discusses insights gained to date from basic scientific studies of hypercapnia and acidosis, identifies key unresolved concerns regarding hypercapnia, and considers the potential clinical implications for the management of patients with acute lung injury.

Estrogen replacement treatment in diabetic ovariectomized female rats potentiates postischemic leukocyte adhesion in cerebral venules

BACKGROUND AND PURPOSE

Chronic 17beta-estradiol (E2) replacement therapy in ovariectomized (OVX) female rats reduces leukocyte adhesion and brain damage after transient forebrain ischemia. Recently, we found that E2 treatment in diabetic OVX females was associated with enhanced postischemic neuropathology. We tested the hypothesis that in chronically hyperglycemic diabetic OVX females, chronic E2 replacement potentiates post-transient forebrain ischemia leukocyte adhesion.

METHODS

Pial venules were observed through closed cranial windows. Adherence of rhodamine 6G-tagged leukocytes was monitored before and 10 hours after transient forebrain ischemia (20 minutes right common carotid artery occlusion plus hemorrhagic hypotension) in intact, untreated OVX and E2-treated OVX females rendered diabetic via streptozotocin. Leukocyte adhesion was quantitated as the percentage venular area occupied by adherent leukocytes.

RESULTS

At 2 hours after transient forebrain ischemia, a similar low level of leukocyte adhesion was seen in the 3 groups (<3% of the venular area). Starting at approximately 4 hours after ischemia, leukocyte adhesion in the E2-treated OVX females rose to significantly higher levels compared with the other groups. Relative to the 2-hour value, the level of adhesion at 10 hours was 12.5-fold, 4-fold, and 5-fold greater in the E2-treated OVX, OVX, and intact groups, respectively. Leukocyte extravasation (beginning after 6 hours of reperfusion) was observed in a majority (64%) of the E2-treated animals, with limited or no extravasation seen in the intact or OVX groups.

CONCLUSIONS

These results suggest that factors associated with diabetes and chronic hyperglycemia convert E2 from a counterinflammatory to a proinflammatory substance in an ischemic setting.