Association between serum substance P levels and mortality in patients with severe sepsis

BACKGROUND

Substance P (SP) is a peptide of the tachykinins family involved in the inflammatory response. Circulating SP levels have been assessed in septic patients in 2 previous studies with a small number of subjects (61 and 42 patients, respectively), and there were no significant differences in SP levels at the moment of sepsis diagnosis between surviving and nonsurviving patients. The main goal of this study was to determine a possible relationship between serum SP levels and patient outcome in the largest cohort of severe septic patients analyzed so far.

METHODS

We performed an observational, prospective, multicenter study in 6 Spanish intensive care units. Serum SP levels were measured at the moment of severe sepsis diagnosis in 238 patients. The end point of the study was 30-day mortality.

RESULTS

We found that surviving septic patients (n = 153) showed higher serum SP levels than did nonsurvivors (n = 85). Multiple logistic regression analysis showed that serum SP levels higher than 350 pg/mL were associated with survival at 30 days (odds ratio, 0.43; 95% confidence interval, 0.24-0.77; P = .005) after controlling for serum lactic acid levels and Sepsis-related Organ Failure Assessment score.

CONCLUSIONS

The major new finding of our study was that serum SP levels were associated with mortality in severe septic patients.

Serum substance P levels are associated with severity and mortality in patients with severe traumatic brain injury

INTRODUCTION

Substance P (SP) is a member of the tachykinin family of neuropeptides, which are widely distributed throughout the central nervous system (CNS) and actively involved in inflammatory processes. SP is released early following acute injury to the CNS, promoting a neurogenic inflammatory response characterized by an increase in the permeability of the blood-brain barrier and the development of vasogenic edema. High levels of SP could lead to an exacerbated inflammatory response that could be fatal for patients with traumatic brain injury (TBI). Thus, the main goal of the present study was to determine whether serum SP levels are associated with injury severity and mortality in patients with severe TBI.

METHODS

This multicenter, observational, prospective study was carried out in six Spanish intensive care units and included patients with Glasgow Coma Scale (GCS) scores ≤ 8. Patients with an Injury Severity Score ≥ 10 in non-cranial aspects were excluded. Blood samples were collected on day 1 of TBI to measure serum SP levels. The endpoint was 30-day mortality.

RESULTS

We found higher serum SP levels (P = 0.002) in non-surviving patients (n = 27) than in surviving patients (n = 73). The area under the curve for serum SP levels with regard to predicting 30-day mortality was 0.70 (95% confidence interval (CI), 0.60 to 0.79; P < 0.001). Survival analysis showed that patients with serum SP levels >299 pg/ml had higher 30-day mortality than patients with lower levels (hazard ratio = 3.7; 95% CI, 1.75 to 7.94; P < 0.001). Multiple binomial logistic regression analysis showed that serum SP levels >299 pg/ml were associated with 30-day mortality when we controlled for APACHE II score and Marshall computed tomography lesion classification (odds ratio (OR) = 5.97; 95% CI, 1.432 to 24.851; P = 0.01) and for GCS score and age (OR = 5.71; 95% CI, 1.461 to 22.280; P = 0.01). We found a negative association between serum SP levels and GCS score (Spearman's ρ = -0.22; P = 0.03).

CONCLUSIONS

We report, for the first time to our knowledge, that serum SP levels were associated with injury severity and mortality in patients with severe TBI. These results open the possibility that SP antagonists may be useful in the treatment of patients with severe TBI.

Tachykinins and their receptors: contributions to physiological control and the mechanisms of disease

The tachykinins, exemplified by substance P, are one of the most intensively studied neuropeptide families. They comprise a series of structurally related peptides that derive from alternate processing of three Tac genes and are expressed throughout the nervous and immune systems. Tachykinins interact with three neurokinin G protein-coupled receptors. The signaling, trafficking, and regulation of neurokinin receptors have also been topics of intense study. Tachykinins participate in important physiological processes in the nervous, immune, gastrointestinal, respiratory, urogenital, and dermal systems, including inflammation, nociception, smooth muscle contractility, epithelial secretion, and proliferation. They contribute to multiple diseases processes, including acute and chronic inflammation and pain, fibrosis, affective and addictive disorders, functional disorders of the intestine and urinary bladder, infection, and cancer. Neurokinin receptor antagonists are selective, potent, and show efficacy in models of disease. In clinical trials there is a singular success: neurokinin 1 receptor antagonists to treat nausea and vomiting. New information about the involvement of tachykinins in infection, fibrosis, and pruritus justifies further trials. A deeper understanding of disease mechanisms is required for the development of more predictive experimental models, and for the design and interpretation of clinical trials. Knowledge of neurokinin receptor structure, and the development of targeting strategies to disrupt disease-relevant subcellular signaling of neurokinin receptors, may refine the next generation of neurokinin receptor antagonists.

Ventilation-induced lung injury

Mechanical ventilation (MV) is, by definition, the application of external forces to the lungs. Depending on their magnitude, these forces can cause a continuum of pathophysiological alterations ranging from the stimulation of inflammation to the disruption of cell-cell contacts and cell membranes. These side effects of MV are particularly relevant for patients with inhomogeneously injured lungs such as in acute lung injury (ALI). These patients require supraphysiological ventilation pressures to guarantee even the most modest gas exchange. In this situation, ventilation causes additional strain by overdistension of the yet non-injured region, and additional stress that forms because of the interdependence between intact and atelectatic areas. Cells are equipped with elaborate mechanotransduction machineries that respond to strain and stress by the activation of inflammation and repair mechanisms. Inflammation is the fundamental response of the host to external assaults, be they of mechanical or of microbial origin and can, if excessive, injure the parenchymal tissue leading to ALI. Here, we will discuss the forces generated by MV and how they may injure the lungs mechanically and through inflammation. We will give an overview of the mechanotransduction and how it leads to inflammation and review studies demonstrating that ventilator-induced lung injury can be prevented by blocking pathways of mechanotransduction or inflammation.

Neurokinin-1 receptor antagonists for chemotherapy-induced nausea and vomiting: a systematic review

BACKGROUND

The addition of neurokinin-1 receptor (NK1R) antagonists to antiemetic regimens has substantially reduced chemotherapy-induced nausea and vomiting (CINV). We sought to systematically review the overall impact of NK1R antagonists on CINV prevention.

METHODS

We systematically searched the MEDLINE, EMBASE, and CENTRAL databases, and meeting proceedings for randomized controlled trials (RCTs) that evaluated NK1R antagonists plus standard antiemetic therapy for CINV prevention. Complete response (CR) to therapy was defined as the absence of emesis and the absence of rescue therapy. The endpoints were defined as CR in the overall phase (during the first 120 hours of chemotherapy), CR in the acute phase (first 24 hours), and the delayed phase (24-120 hours) after chemotherapy, nausea, and toxicity. Subgroup analyses evaluated the type of NK1R antagonist used, the emetogenic potential of the chemotherapy regimen, and prolonged use of 5-HT3 (serotonin) receptor antagonists, a class of standard antiemetic agents. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using a random-effects model. Statistical tests for heterogeneity were one-sided; statistical tests for effect estimates and publication bias were two-sided.

RESULTS

Seventeen trials (8740 patients) were included in this analysis. NK1R antagonists increased the CR rate in the overall phase from 54% to 72% (OR = 0.51, 95% CI = 0.46 to 0.57, P < .001). CR and nausea were improved in all phases and subgroups. The expected side effects from NK1R antagonists did not statistically significantly differ from previous reports; however, this analysis suggests that the incidence of severe infection increased from 2% to 6% in the NK1R antagonist group (three RCTs with a total of 1480 patients; OR = 3.10; 95% CI = 1.69 to 5.67, P < .001).

CONCLUSIONS

NK1R antagonists increased CINV control in the acute, delayed, and overall phases. They are effective for both moderately and highly emetogenic chemotherapy regimens. Their use might be associated with increased infection rates; however, additional appraisal of specific data from RCTs is needed.

TRPV1 deletion enhances local inflammation and accelerates the onset of systemic inflammatory response syndrome

The transient receptor potential vanilloid 1 (TRPV1) is primarily localized to sensory nerve fibers and is associated with the stimulation of pain and inflammation. TRPV1 knockout (TRPV1KO) mice show enhanced LPS-induced sepsis compared with wild type (WT). This implies that TRPV1 may have a key modulatory role in increasing the beneficial and reducing the harmful components in sepsis. We investigated immune and inflammatory mechanisms in a cecal ligation and puncture (CLP) model of sepsis over 24 h. CLP TRPV1KO mice exhibited significant hypothermia, hypotension, and organ dysfunction compared with CLP WT mice. Analysis of the inflammatory responses at the site of initial infection (peritoneal cavity) revealed that CLP TRPV1KO mice exhibited: 1) decreased mononuclear cell integrity associated with apoptosis, 2) decreased macrophage tachykinin NK(1)-dependent phagocytosis, 3) substantially decreased levels of nitrite (indicative of NO) and reactive oxygen species, 4) increased cytokine levels, and 5) decreased bacteria clearance when compared with CLP WT mice. Therefore, TRPV1 deletion is associated with impaired macrophage-associated defense mechanisms. Thus, TRPV1 acts to protect against the damaging impact of sepsis and may influence the transition from local to a systemic inflammatory state.

Recurrent recruitment manoeuvres improve lung mechanics and minimize lung injury during mechanical ventilation of healthy mice

INTRODUCTION

Mechanical ventilation (MV) of mice is increasingly required in experimental studies, but the conditions that allow stable ventilation of mice over several hours have not yet been fully defined. In addition, most previous studies documented vital parameters and lung mechanics only incompletely. The aim of the present study was to establish experimental conditions that keep these parameters within their physiological range over a period of 6 h. For this purpose, we also examined the effects of frequent short recruitment manoeuvres (RM) in healthy mice.

METHODS

Mice were ventilated at low tidal volume V(T) = 8 mL/kg or high tidal volume V(T) = 16 mL/kg and a positive end-expiratory pressure (PEEP) of 2 or 6 cm H(2)O. RM were performed every 5 min, 60 min or not at all. Lung mechanics were followed by the forced oscillation technique. Blood pressure (BP), electrocardiogram (ECG), heart frequency (HF), oxygen saturation and body temperature were monitored. Blood gases, neutrophil-recruitment, microvascular permeability and pro-inflammatory cytokines in bronchoalveolar lavage (BAL) and blood serum as well as histopathology of the lung were examined.

RESULTS

MV with repetitive RM every 5 min resulted in stable respiratory mechanics. Ventilation without RM worsened lung mechanics due to alveolar collapse, leading to impaired gas exchange. HF and BP were affected by anaesthesia, but not by ventilation. Microvascular permeability was highest in atelectatic lungs, whereas neutrophil-recruitment and structural changes were strongest in lungs ventilated with high tidal volume. The cytokines IL-6 and KC, but neither TNF nor IP-10, were elevated in the BAL and serum of all ventilated mice and were reduced by recurrent RM. Lung mechanics, oxygenation and pulmonary inflammation were improved by increased PEEP.

CONCLUSIONS

Recurrent RM maintain lung mechanics in their physiological range during low tidal volume ventilation of healthy mice by preventing atelectasis and reduce the development of pulmonary inflammation.

Common variants of the neuropeptide expressing tachykinin genes and susceptibility to asthma: a case-control study

Since tachykinins appear to be involved in the pathogenesis of allergic asthma, we investigated a possible association between 28 single nucleotide polymorphisms of the tachykinin genes TAC1, TAC3 and TAC4, and asthma susceptibility. A case-control study was conducted on 102 patients and 100 healthy subjects from the Canary Islands (Spain). A significant association with asthma was observed for two SNPs: rs2291855 in the TAC3 gene conferring asthma protection (Odds ratio [OR]: 0.46; 95% Confidence Interval [CI]: 0.22-0.97; P=0.038), and rs4794068 in the TAC4 gene associated with an increased risk for asthma (OR: 1.94; 95% CI: 1.06-3.54; P=0.03). The present study represents a preliminary step in elucidating the association between tachykinin gene polymorphisms and asthma susceptibility.

Substance P receptor blockade decreases stretch-induced lung cytokines and lung injury in rats

Overdistension of lung tissue during mechanical ventilation causes cytokine release, which may be facilitated by the autonomic nervous system. We used mechanical ventilation to cause lung injury in rats, and studied how cervical section of the vagus nerve, or substance P (SP) antagonism, affected the injury. The effects of 40 or 25 cmH(2)O high airway pressure injurious ventilation (HV(40) and HV(25)) were studied and compared with low airway pressure ventilation (LV) and spontaneous breathing (controls). Lung mechanics, lung weight, gas exchange, lung myeloperoxidase activity, lung concentrations of interleukin (IL)-1 beta and IL-6, and amounts of lung SP were measured. Control rats were intact, others were bivagotomized, and in some animals we administered the neurokinin-1 (NK-1) receptor blocking agent SR140333. We first determined the durations of HV(40) and HV(25) that induced the same levels of lung injury and increased lung contents of IL-1 beta and IL-6. They were 90 min and 120 min, respectively. Both HV(40) and HV(25) increased lung SP, IL-1 beta and IL-6 levels, these effects being markedly reduced by NK-1 receptor blockade. Bivagotomy reduced to a lesser extent the HV(40)- and HV(25)-induced increases in SP but significantly reduced cytokine production. Neither vagotomy nor NK-1 receptor blockade prevented HV(40)-induced lung injury but, in the HV(25) group, they made it possible to maintain lung injury indices close to those measured in the LV group. This study suggests that both neuronal and extra-neuronal SP might be involved in ventilator-induced lung inflammation and injury. NK-1 receptor blockade could be a pharmacological tool to minimize some adverse effects of mechanical ventilation.

Differential roles of JNK in ConA/GalN and ConA-induced liver injury in mice

Tumor necrosis factor-alpha-mediated liver injury can be induced by several different means; however, the signaling events and mechanisms of cell death are likely different. We investigated the mechanism of both apoptotic and necrotic hepatocyte cell death as well as the role of c-Jun NH2-terminal kinase (JNK) in the ConA and ConA/D-galactosamine (GalN) models of murine liver injury. ConA alone induced primarily necrotic cell death with no caspase activation, whereas ConA/GalN induced apoptosis in addition to necrotic cell death. The bi-modal death pattern in the ConA/GalN model was confirmed by the use of transgenic mice expressing a dominant-negative form of Fas-associated death domain in which the mice were resistant to apoptotic but not necrotic cell death. JNK1 and, more significantly, JNK2 participated in the induction of hepatocyte apoptosis in response to ConA/GalN. Deletion of JNK led to the stabilization of FLIP L, reduced caspase-8 activation, decreased Bid cleavage, and inhibition of the mitochondrial apoptosis pathway. In contrast, JNK did not participate in necrotic death induced by ConA either alone or in combination with GalN. As such, JNK-deficient mice remained susceptible to necrotic liver injury in both model systems. Thus, ConA and ConA/GalN mouse models induce liver injury with different mechanisms of cell death, and JNK contributes to apoptotic but not necrotic cell death. These findings further elucidate the specific pathways involved in tumor necrosis factor-alpha-mediated liver injury.

Neuroimmune crosstalk in asthma: dual role of the neurotrophin receptor p75NTR

BACKGROUND

Neurotrophins have been implicated in the pathogenesis of asthma because of their ability to induce airway inflammation and to promote hyperreactivity of sensory neurons, which reflects an important mechanism in the pathogenesis of airway hyperreactivity. Neurotrophins use a dual-receptor system consisting of Trk-receptor tyrosine kinases and the structurally unrelated p75NTR. Previous studies revealed an important role of p75NTR in the pathogenesis of allergic asthma.

OBJECTIVES

The aim of the study was to investigate the precise mechanisms of neurotrophins in neuroimmune interaction, which can lead to both airway inflammation and sensory nerve hyperreactivity in vivo.

METHODS

Mice selectively expressing p75NTR in immune cells or nerves, respectively, were generated. After sensitization and allergen provocation, hyperreactivity of sensory nerves was tested in response to capsaicin. Airway inflammation was analyzed on the basis of differential cell counts and cytokine levels in bronchoalveolar lavage fluids.

RESULTS

Allergic mice selectively expressing p75NTR in immune cells showed normal inflammation but no sensory nerve hyperreactivity, whereas mice selectively expressing p75NTR in nerve cells had a diminished inflammation and a distinct sensory nerve hyperreactivity.

CONCLUSION

Our data indicate that p75NTR plays a dual role by promoting hyperreactivity of sensory nerves and airway inflammation. Additionally, our study provides experimental evidence that development of sensory nerve hyperreactivity depends on an established airway inflammation in asthma. In contrast, development of airway inflammation seems to be independent from sensory nerve hyperreactivity.

CLINICAL IMPLICATIONS

Because of its dual function, antagonization of p75NTR-mediated signals might be a novel approach in asthma therapy.

‘Sensing’ autoimmunity in type 1 diabetes

Type 1 diabetes (T1D) results from autoimmune-mediated loss of insulin-producing beta-cells. Recent findings suggest that the events controlling T1D development are not only immunological, but also neuronal in nature. In the non-obese diabetic (NOD) mouse model of T1D, a mutant sensory neuron channel, TRPV1, initiates chronic, progressive beta-cell stress, inducing islet cell inflammation. This novel mechanism of organ-specific damage requires a permissive, autoimmune-prone host, but ascribes tissue specificity to the local secretory dysfunction of sensory afferent neurons. In NOD mice, normalizing this neuronal function by administration of the neurotransmitter substance P clears islet cell inflammation, reduces insulin resistance and restores normoglycemia. Here, we discuss this neuro-immuno-endocrine model, its implications and the involvement of sensory neurons in other autoimmune disorders. These developments might provide novel neuronal-based therapeutic interventions, particularly in diabetes.

Neurokinin-1 receptor antagonist treatment protects mice against lung injury in polymicrobial sepsis

Earlier work from our laboratory has suggested a role for the neuropeptide substance P (SP) in inducing lung injury in sepsis. In that study, mice lacking the preprotachykinin-A gene, which encodes for SP, were protected against lung injury in sepsis. To further substantiate the role of SP in sepsis and to study its mechanism, we have evaluated the effect of SR140333, a SP receptor antagonist, on lung injury in sepsis, which was induced in male Swiss mice by cecal ligation and puncture (CLP). Sham-operated animals received the same surgical procedure, except CLP. Vehicle or SR140333 (1 mg/kg, s.c.) was administered to CLP mice 30 min before or 1 h after the CLP. Eight hours after surgery, lung tissue was collected and analyzed for myeloperoxidase (MPO) activity, chemokines, cytokines, and adhesion molecules. The CLP procedure alone caused a significant increase in the lung levels of MIP-2, MCP-1, IL-1beta, IL-6, ICAM-1, E- and P-selectin, and MPO activity when compared with sham-operated mice. SR140333 injected 30 min before or 1 h after CLP significantly attenuated the increased lung MPO activity and levels of MIP-2, MCP-1, IL-1beta, IL-6, ICAM-1, and E- and P-selectin compared with CLP-operated mice injected with the vehicle. Histological evaluation of the lung sections further supported the beneficial effect of SR140333 on lung inflammation. Therefore, SP receptor antagonism can be a potential therapeutic target in polymicrobial sepsis, and this effect is brought about via reduction in leukocyte recruitment.

Preprotachykinin-A Gene Products Are Key Mediators of Lung Injury in Polymicrobial Sepsis

Preprotachykinin-A (PPT-A) gene products substance P and neurokinin-A have been shown to play an important role in neurogenic inflammation. To investigate the role of PPT-A gene products in lung injury in sepsis, polymicrobial sepsis was induced by cecal ligation and puncture in PPT-A gene-deficient mice (PPT-A(-/-)) and the wild-type control mice (PPT-A(+/+)). PPT-A gene deletion significantly protected against mortality, delayed the onset of lethality, and improved the long-term survival following cecal ligation and puncture-induced sepsis. PPT-A(-/-) mice also had significantly attenuated inflammation and damage in the lungs. The data suggest that deletion of the PPT-A gene may have contributed to the disruption in recruitment of inflammatory cells resulting in protection against tissue damage, as in these mice the sepsis-associated increase in chemokine levels is significantly attenuated.

Protease-activated receptor-2 activation induces acute lung inflammation by neuropeptide-dependent mechanisms

Protease-activated receptors (PARs) and tachykinin-immunoreactive fibers are located in the lung as sentries to respond to a variety of pathological stimuli. The effects of PAR activation on the lung have not been adequately studied. We report on the effects of instilling PAR-activating peptides (PAR-APs, including PAR1-, PAR2-, and PAR4-AP) into the lungs of ventilated or spontaneously breathing mice. PAR2-AP, but not PAR1-AP or PAR4-AP, caused a sharp increase in lung endothelial and epithelial permeability to protein, extravascular lung water, and airway tone. No responses to PAR2-AP were detected in PAR2 knockout mice. In bronchoalveolar lavage, PAR2 activation caused 8- and 5-fold increase in MIP-2 and substance P levels, respectively, and a 12-fold increase in the number of neutrophils. Ablation of sensory neurons (by capsaicin) markedly decreased the PAR2-mediated airway constriction, and virtually abolished PAR2-mediated pulmonary inflammation and edema, as did blockade of NK1 or NK2 receptors. Thus, PAR2 activation in the lung induces airway constriction, lung inflammation, and protein-rich pulmonary edema. These effects were either partly or completely neuropeptide dependent, suggesting that PAR2 can cause lung inflammation by a neurogenic mechanism.

Without nerves, immunology remains incomplete -in vivo veritas

Interest in the interactions between nervous and immune systems involved in both pathological and homeostatic mechanisms of host defence has prompted studies of neuroendocrine immune modulation and cytokine involvement in neuropathologies. In this review we concentrate on a distinct area of homeostatic control of both normal and abnormal host defence activity involving the network of peripheral c-fibre nerve fibres. These nerve fibres have long been recognized by dermatologists and gastroenterologists as key players in abnormal inflammatory processes, such as dermatitis and eczema. However, the involvement of nerves can all too easily be regarded as that of isolated elements in a local phenomenon. On the contrary, it is becoming increasingly clear that neural monitoring of host defence activities takes place, and that involvement of central/spinal mechanisms are crucial in the co-ordination of the adaptive response to host challenge. We describe studies demonstrating neural control of host defence and use the specific examples of bone marrow haemopoiesis and contact sensitivity to highlight the role of direct nerve fibre connections in these activities. We propose a host monitoring system that requires interaction between specialized immune cells and nerve fibres distributed throughout the body and that gives rise to both neural and immune memories of prior challenge. While immunological mechanisms alone may be sufficient for local responsiveness to subsequent challenge, data are discussed that implicate the neural memory in co-ordination of host defence across the body, at distinct sites not served by the same nerve fibres, consistent with central nervous mediation.

5-Lipoxygenase deficiency prevents respiratory failure during ventilator-induced lung injury

RATIONALE

Mechanical ventilation with high VT (HVT) progressively leads to lung injury and decreased efficiency of gas exchange. Hypoxic pulmonary vasoconstriction (HPV) directs blood flow to well-ventilated lung regions, preserving systemic oxygenation during pulmonary injury. Recent experimental studies have revealed an important role for leukotriene (LT) biosynthesis by 5-lipoxygenase (5LO) in the impairment of HPV by endotoxin.

OBJECTIVES

To investigate whether or not impairment of HPV contributes to the hypoxemia associated with HVT and to evaluate the role of LTs in ventilator-induced lung injury.

METHODS

We studied wild-type and 5LO-deficient mice ventilated for up to 10 hours with low VT (LVT) or HVT.

RESULTS

In wild-type mice, HVT, but not LVT, increased pulmonary vascular permeability and edema formation, impaired systemic oxygenation, and reduced survival. HPV, as reflected by the increase in left pulmonary vascular resistance induced by left mainstem bronchus occlusion, was markedly impaired in animals ventilated with HVT. HVT ventilation increased bronchoalveolar lavage levels of LTs and neutrophils. In 5LO-deficient mice, the HVT-induced increase of pulmonary vascular permeability and worsening of respiratory mechanics were markedly attenuated, systemic oxygenation was preserved, and survival increased. Moreover, in 5LO-deficient mice, HVT ventilation did not impair the ability of left mainstem bronchus occlusion to increase left pulmonary vascular resistance. Administration of MK886, a 5LO-activity inhibitor, or MK571, a selective cysteinyl-LT(1) receptor antagonist, largely prevented ventilator-induced lung injury.

CONCLUSIONS

These results indicate that LTs play a central role in the lung injury and impaired oxygenation induced by HVT ventilation.

Massive brain injury enhances lung damage in an isolated lung model of ventilator-induced lung injury

OBJECTIVE

To assess the influence of massive brain injury on pulmonary susceptibility to injury attending subsequent mechanical or ischemia/reperfusion stress.

DESIGN

Prospective experimental study.

SETTING

Animal research laboratory.

SUBJECTS

Twenty-four anesthetized New Zealand White rabbits randomized to control (n = 12) or induced brain injury (n = 12) group.

INTERVENTIONS

After randomization, brain injury was induced by inflation of an intracranial balloon-tipped catheter, and animals were ventilated with a tidal volume of 10 mL/kg and zero end-expiratory pressure for 120 mins. Following heart-lung block extraction, isolated and perfused lungs were subjected to injurious ventilation with peak airway pressure 30 cm H2O and positive end-expiratory pressure 5 cm H2O for 30 mins.

MEASUREMENTS AND MAIN RESULTS

No difference was observed between groups in gas exchange, lung mechanics, or hemodynamics during the 2-hr in vivo period following induction of brain injury. However, after 30 mins of ex vivo injurious mechanical ventilation, lungs from the brain injury group showed greater change in ultrafiltration coefficient, weight gain, and alveolar hemorrhage (all p < .05).

CONCLUSIONS

Massive brain injury might increase lung vulnerability to subsequent injurious mechanical or ischemia-reperfusion insults, thereby increasing the risk of clinical posttransplant graft failure.

Tachykinins and tachykinin receptors: a growing family

The peptides of the tachykinin family are widely distributed within the mammalian peripheral and central nervous systems and play a well-recognized role as excitatory neurotransmitters. Currently, the concept that tachykinins act exclusively as neuropeptides is being challenged, since the best known members of the family, substance P, neurokinin A and neurokinin B, are also present in non-neuronal cells and in non-innervated tissues. Moreover, the recently cloned mammalian tachykinins hemokinin-1 and endokinins are primarily expressed in non-neuronal cells, suggesting a widespread distribution and important role for these peptides as intercellular signaling molecules. The biological actions of tachykinins are mediated through three types of receptors denoted NK(1), NK(2) and NK(3) that belong to the family of G protein-coupled receptors. The identification of additional tachykinins has reopened the debate of whether more tachykinin receptors exist. In this review, we summarize the current knowledge of tachykinins and their receptors.

Phosphoinositide 3-OH kinase inhibition prevents ventilation-induced lung cell activation

In acute respiratory distress syndrome patients, protective ventilation strategies reduce mortality and proinflammatory mediator levels. It has been suggested that some of the side effects of mechanical ventilation are caused by the excessive release of mediators capable of causing pulmonary inflammation and tissue destruction (biotrauma). Selective inhibition of this process might be used to minimize the side effects of artificial mechanical ventilation. This study was designed to identify the cell types and specific signaling mechanisms that are activated by ventilation with increased pressure/volume (overventilation). In isolated perfused mouse lungs, overventilation caused nuclear translocation of nuclear factor-kappaB (NF-kappaB) and enhanced expression of interleukin-6 mRNA in alveolar macrophages and alveolar epithelial type II cells. The phosphoinositide 3-OH kinase inhibitor Ly294002 prevented nuclear translocation of NF-kappaB and the subsequent release of interleukin-6 and macrophage inflammatory protein-2alpha in overventilated but not in endotoxic lungs. Similar results were obtained in rats in vivo, where Ly294002 prevented NF-kappaB activation by overventilation but not by endotoxin. These findings show that alveolar macrophages and alveolar epithelial type II cells contribute to the ventilation-induced release of proinflammatory mediators and that selective inhibition of this process is possible without inhibiting the activation of NF-kappaB by endotoxin.