Role of Endothelium/Nitric Oxide and Cyclic AMP in Isoproterenol Potentiation of 17ß-Estradiol-Mediated Vasorelaxation

Background: Calcitonin gene-related peptide (CGRP) is known to have an extremely potent and prolonged vasodilator effect on the coronary arteries. Studies have shown that CGRP increased coronary blood flow and alleviated reperfusion injury in vitro. It is still unknown, however, whether exogenous CGRP has a protective effect on the reperfusion heart associated with cardiopulmonary bypass (CPB). Methods: An in vivo porcine model of CPB was established. Twenty pigs, 10 controls and 10 CGRP used animals (CGRP group), were performed a median sternotomy followed by a standard CPB. All the hearts were arrested for 45 minutes. In the CGRP group, 1mg/kg CGRP was added into the cardioplegia, and another 1mg/kg was reperfused just before the aortic cross-clamp was removed. In both groups, myocardial microvascular perfusion, coronary arterial microvessel diameter and microvessel blood flow were detected by a laser doppler flowmeter and a contact microscope with TV monitor on five consecutive time perioperatively. Result: Myocardial microvascular perfusion was significantly higher and coronary arterial microvessel diameter was larger in the CGRP group on every point of time of reperfusion compared to those in the control group. In the CGRP group, microvessel blood flow also improved significantly than that in the control group during reperfusion. Conclusion: CGRP improves myocardial microcirculation during cardiac ischemia-reperfusion associated with CPB and could become a new, potent myocardial protector.     

Lymphoproliferative disorder early after cardiac transplantation

In cardiac transplantation, extremely potent immunosuppressive agents are used, which leave the host vulnerable to a variety of infections and malignancies. Among the malignancies, lymphoproliferative disorders are the most common.¹ Most cases of posttransplant lymphoproliferative disorders have been described in patients who have undergone several months of immunosuppression. ^2,3 This report describes our experience with patients who developed lymphoproliferative disorder within 3 months of heart transplantation.     

Cancer may be a pathway to cell survival under persistent hypoxia and elevated ROS: A model for solid‐cancer initiation and early development

A number of proposals have been made in the past century regarding what may drive sporadic cancers to initiate and develop. Yet the problem remains largely unsolved as none of the proposals have been widely accepted as cancer‐initiation drivers. We propose here a driver model for the initiation and early development of solid cancers associated with inflammation‐induced chronic hypoxia and reactive oxygen species (ROS) accumulation. The model consists of five key elements: (i)human cells tend to have a substantial gap between ATP demand and supply during chronic hypoxia, which would inevitably lead to increased uptake of glucose and accumulation of its metabolites; (ii) the accumulation of these metabolites will cast mounting pressure on the cells and ultimately result in the production and export of hyaluronic acid; (iii) the exported hyaluronic acid will be degraded into fragments of various sizes, serving as tissue‐repair signals, including signals for cell proliferation, cell survival and angiogenesis, which lead to the initial proliferation of the underlying cells; (iv) cell division provides an exit for the accumulated glucose metabolites using them towards macromolecular synthesis for the new cell, and hence alleviate the pressure from the metabolite accumulation; and (v) this process continues as long as the hypoxic condition persists. In tandem, genetic mutations may be selected to make cell divisions and hence survival more sustainable and efficient, also increasingly more uncontrollable. This model also applies to some hereditary cancers as their key mutations, such as BRCA for breast cancer, generally lead to increased ROS and ultimately to repression of mitochondrial activities and up‐regulation of glycolysis, as well as hypoxia; hence the energy gap, glucose‐metabolite accumulation, hyaluronic acid production and continuous cell division for survival.     

Pentafraction reduces the lung lymph response after endotoxin administration in the ovine model.

For the past half-century, several high molecular weight compounds have been used for volume expansion during cardiopulmonary resuscitation. However, the effectiveness and side effects of these different expanders are varied. We have compared plasma, pentastarch, and a new product, pentafraction, for effective plasma volume expansion before and after tissue injury with endotoxin administration. In each group, eight range ewes instrumented with a Swan-Ganz, arterial, and venous catheters, and lung and flank lymphatic cannulas were compared. Each group received 15 ml/kg of either 6% pentafraction, 6% pentastarch, or plasma followed two hours later by 1.5 micrograms/kg/0.5 hr E. Coli endotoxin over 30 min. Data were collected for an additional 24 hr after endotoxin administration. Our results indicated a plasma volume expansion in all three groups. However, the prior administration of pentafraction significantly attenuated the increase in the lung lymph flow and early evaluation of systemic vascular resistance noted with endotoxin in comparison to the other two groups.     

CNS myelin induces regulatory functions of DC-SIGN–expressing,antigen-presenting cells via cognate interaction with MOG

Myelin oligodendrocyte glycoprotein (MOG), a constituent of central nervous system myelin, is an important autoantigen in the neuroinflammatory disease multiple sclerosis (MS). However, its function remains unknown. Here, we show that, in healthy human myelin, MOG is decorated with fucosylated N-glycans that support recognition by the C-type lectin receptor (CLR) DC-specific intercellular adhesion molecule-3–grabbing nonintegrin (DC-SIGN) on microglia and DCs. The interaction of MOG with DC-SIGN in the context of simultaneous TLR4 activation resulted in enhanced IL-10 secretion and decreased T cell proliferation in a DC-SIGN-, glycosylation-, and Raf1-dependent manner. Exposure of oligodendrocytes to proinflammatory factors resulted in the down-regulation of fucosyltransferase expression, reflected by altered glycosylation at the MS lesion site. Indeed, removal of fucose on myelin reduced DC-SIGN–dependent homeostatic control, and resulted in inflammasome activation, increased T cell proliferation, and differentiation toward a Th₁₇-prone phenotype. These data demonstrate a new role for myelin glycosylation in the control of immune homeostasis in the healthy human brain through the MOG–DC-SIGN homeostatic regulatory axis, which is comprised by inflammatory insults that affect glycosylation. This phenomenon should be considered as a basis to restore immune tolerance in MS.Professional APCs are equipped with receptors that recognize, capture, and internalize antigens to facilitate their processing and presentation to T cells. Among APCs, DCs are unique in their capacity to stimulate naive T cells; however, their function is not restricted to the initiation of strong immune responses against pathogens, but also to regulate T cell homeostasis and prevent autoimmunity. Indeed, DCs efficiently support the in vitro generation and expansion of iT reg cells, regulate T reg cell homeostasis in vivo (Fehérvári and Sakaguchi, 2004; Cong et al., 2005), and even induce T cell anergy (Hawiger et al., 2001). Targeting of antigen to resting DCs via DEC-205 resulted in an unsustained expansion of antigen-specific CD4⁺ T cells that did not differentiate into effector cells (Hawiger et al., 2001). Similar functional unresponsiveness was observed in naive antigen-specific CD8⁺ T cells when splenic lymphoid DCs were exposed to dying cells loaded with cognate antigen (Liu et al., 2002). Unfortunately, reports on DC-lacking mice are controversial (Birnberg et al., 2008; Ohnmacht et al., 2009) and the precise role of DCs in the maintenance of peripheral tolerance in humans remains to be determined.C-type lectin receptors (CLRs), such as DEC-205 and DC-specific intercellular adhesion molecule-3–grabbing nonintegrin (DC-SIGN), have been proposed to play an important role in homeostatic control. DC-SIGN is a type II transmembrane receptor equipped with a Ca²⁺-dependent mannose-binding carbohydrate recognition domain with specificity for antigens decorated with high-mannose or Lewis-type structures (Appelmelk et al., 2003). Signaling crosstalk with TLRs has been demonstrated for DC-SIGN and some other CLRs on DCs (Geijtenbeek and Gringhuis, 2009). Although eight mouse genetic homologues are known (Park et al., 2001; Powlesland et al., 2006), none has the same glycan specificity, expression profile, or signaling properties as human DC-SIGN (García-Vallejo and van Kooyk, 2013). Hence, knowledge on the physiological functions of DC-SIGN is based on human in vitro data. Contrary to other antigen-uptake receptors, pathogen recognition by DC-SIGN often results in immune escape (van Kooyk and Geijtenbeek, 2003; Rappocciolo et al., 2008; Wang et al., 2008) and the carbohydrate ligands of DC-SIGN are also found on host glycoproteins, suggesting that DC-SIGN participates in the control of immune homeostasis (García-Vallejo and van Kooyk, 2009). Interaction of DC-SIGN with its ligands on immune cells mediates adhesion and favors communication during (cognate) interactions. DC-SIGN ligands on nonimmunological tissues, such as the tumor-associated epithelial proteins CEA and CEACAM1 (van Gisbergen et al., 2005) can enhance the cytokine response of DCs to the TLR4 ligand LPS in a similar way, as previously reported for the M. tuberculosis DC-SIGN ligand ManLAM, by synergistically increasing the LPS-mediated secretion of IL-10 (Geijtenbeek et al., 2003). Additionally, supernatants from CEA and CEACAM1-producing cell lines inhibited DC maturation and attenuated Th₁ skewing (Nonaka et al., 2008). Apparently, both tumor and pathogens have ways to escape immune activation by targeting a receptor that is able to transform proinflammatory into tolerogenic signals. DC-SIGN has therefore been proposed to be a homeostatic receptor that can be subverted by pathogens and tumors through changes in their glycan phenotype. However, DC-SIGN has not yet been found to recognize any autoantigen, or to support any role in the maintenance of peripheral tolerance in humans.The central nervous system (CNS) has evolved as an immune-privileged site to protect its vital functions from detrimental insults, by immune-mediated inflammation. Microglia are CNS-based APCs that continuously evaluate local changes in the CNS to activate the immune system during injury (Olson and Miller, 2004) or to maintain homeostasis in the steady state (Lambert et al., 2008). Accumulating evidence suggests that glycosylation plays a role in the control of peripheral tolerance to brain autoantigens. Induction of experimental autoimmune encephalomyelitis, the animal model of MS, is much more efficient when recombinant unglycosylated myelin oligodendrocyte glycoprotein (MOG) is used, in contrast to native MOG (Smith et al., 2005). Also, alterations in glycosyltransferases (Husain et al., 2008; Brynedal et al., 2010) or glycan-binding proteins (Hoppenbrouwers et al., 2009) have been linked to a higher incidence of MS. Yet, the molecular mechanisms behind this association remain unclear.Here, we show for the first time that a major autoantigen in MS, MOG, is recognized by DC-SIGN on APCs within the human brain, including microglia. The interaction results in the transmission of a tolerogenic signal characterized by increased IL-10 secretion and decreased T cell proliferation. Conversely, myelin particles lacking DC-SIGN ligands induce immunogenic signals characterized by inflammasome activation and enhanced T cell proliferation. Our results help to explain how an immunosuppressive milieu in the healthy human CNS is maintained through the glycosylation status of MOG/myelin that engages DC-SIGN, keeping local APCs in an immature nonpathogenic state.     

Emotion Differentiation and Emotion Regulation in High and Low Socially Anxious Individuals: An Experience-Sampling Study

The present study explored when and how emotional difficulties and poor quality of life arise in the everyday lives of socially anxious individuals. 264 freshmen-year college students completed an online survey for 11 consecutive days. Comparing individuals high (HSA) and low in social anxiety, results revealed that irrespective of daily positive emotion differentiation ability, HSAs engaged daily emotion suppression strategies, pointing to inflexible emotion regulation. Furthermore, HSAs with poor daily negative emotion differentiation used the least daily cognitive reappraisal. Finally, both expressive suppression and cognitive reappraisal showed group-specific effects on daily positive affect. Daily expressive suppression was more strongly associated with diminished daily positive affect in HSAs, and HSAs benefited less in terms of daily positive affect from daily use of cognitive reappraisal. Based on these findings, emotion differentiation ability and emotion regulation appear relevant clinical targets for individuals with social anxiety disorder.     

Ultra-protective tidal volume: how low should we go?

Applying tidal volumes of less than 6 mL/kg might improve lung protection in patients with acute respiratory distress syndrome. In a recent article, Retamal and colleagues showed that such a reduction is feasible with conventional mechanical ventilation and leads to less tidal recruitment and overdistension without causing carbon dioxide retention or auto-positive end-expiratory pressure. However, whether the compensatory increase in the respiratory rate blunts the lung protection remains unestablished.Further reducing tidal volumes beyond the standard 6 mL/kg is an appealing goal in patients with acute respiratory distress syndrome (ARDS) [1]. Such reduction could decrease the tidal stretch imposed on the lung, potentially attenuating further the ventilator-induced lung injury [2]. In fact, tidal volumes of less than 6.5 mL/kg and as low as 4 mL/kg were recently associated with increased survival in patients with ARDS [3]. One of the main obstacles to such a strategy is the potential for carbon dioxide (CO₂) retention and severe acidosis. To avoid this, specialized techniques, such as high-frequency oscillatory ventilation and extracorporeal CO₂ removal, have been previously tested with mixed results [4-6].In the previous issue of Critical Care, Retamal and colleagues proposed that lower tidal volumes could be used with conventional positive-pressure ventilation without leading to CO₂ retention [1]. A reduction in tidal volume from 6 to 4 mL/kg was feasible with a decrease in the instrumental dead space and an increase in the respiratory rate. In patients with ARDS, the dead space is a marker of disease severity [7]. Consequently, very low tidal volumes can be difficult to use in practice, especially in very sick patients, because the necessary increase in respiratory rate might cause significant auto-positive end-expiratory pressure (auto-PEEP). Luckily, patients with severe ARDS also tend to have low lung compliance [8], making their lungs inflate and deflate fast. Therefore, this restrictive ventilatory pattern allows the safe use of high respiratory rates without leading to significant auto-PEEP.Retamal and colleagues [1] should be congratulated for their careful design of the ventilator protocol in the 4 mL/kg phase, which allowed an effective CO₂ elimination. The bottom line is that if one decides to use very low tidal volumes with high respiratory rates, attention to the details is invaluable. First, the removal of any dispensable dead space, including substituting an external heated humidifier by the heat-moisture exchanger, is imperative. Second, the use of volume-controlled ventilation helps to keep short inspiratory times. Peak airway pressures may increase, but the preserved expiratory time guarantees low auto-PEEP and, consequently, low plateau pressures. For safety, plateau pressures and auto-PEEP should be measured periodically. Third, in selected cases with high recruitability, the alveolar dead space can be minimized through recruitment maneuvers and higher PEEP values. Finally, the use of a short end-inspiratory pause is encouraged to improve the CO₂ elimination [9]. These measures will improve the safety and optimize the CO₂ elimination of a strategy with very low tidal volumes, even with higher-than-normal respiratory rates.However, even successfully avoiding CO₂ retention, this strategy has yet to be proven effective in terms of further lung protection. We believe that two aspects should be taken into consideration. The first is whether the strategy attenuated the mechanisms of lung injury. The authors performed computed tomography scans in all patients at tidal volumes of both 4 and 6 mL/kg and showed that the amount of cyclic recruitment-derecruitment and hyperinflation decreased after reducing the tidal volume. Although the absolute reduction was small (less than 1% of the lung weight), this finding is suggestive of decreased injury per breath. The second aspect is that an increased respiratory rate can be injurious per se [10]. It would be important to know whether the compensatory increase of the respiratory rate blunted the protective effect per breath of the tidal volume reduction.This tradeoff was emphasized recently in a model of the energy delivered by the ventilator as a surrogate for the potential lung damage [11]. Decreases in tidal volume require disproportionate increases in respiratory rate to maintain alveolar ventilation, and so more energy can be delivered to the lungs even at reduced stress and strain per breath. Though purely theoretical, this hypothesis helps reconcile our expectation of a further protective effect of very low tidal volumes with the recent findings of harmful or null effect of oscillatory high-frequency ventilation [5,6]. In these trials, it is possible that the reduction in lung injury per breath was offset by the very high respiratory rates applied.Finally, Retamal and colleagues [1] followed their patients for 5 to 30 minutes only. Since lower tidal volumes tend to promote atelectasis, especially under insufficient PEEP [12], a longer observation time perhaps would have shown an increase in atelectasis and driving pressures, opposing the benefits initially achieved.In conclusion, we are convinced that a strategy with very low tidal volumes (4 mL/kg) is feasible with conventional positive-pressure ventilation. This strategy could be used in patients with high plateau pressures or high driving pressures with standard 6 mL/kg tidal volumes, but we need more data in terms of lung protection before we can recommend this strategy to every patient with ARDS.