Activated protein C reduces tissue hypoxia, inflammation, and apoptosis in traumatized skeletal muscle during endotoxemia

Comparative label-free mass spectrometric analysis of temporal changes in the skeletal muscle proteome after impact trauma in rats

Proteomics offers the opportunity to identify and quantify many proteins and to explore how they correlate and interact with each other in biological networks. This study aimed to characterize changes in the muscle proteome during the destruction, repair, and early-remodeling phases after impact trauma in male Wistar rats. Muscle tissue was collected from uninjured control rats and rats that were euthanized between 6 h and 14 days after impact injury. Muscle tissue was analyzed using unbiased, data-independent acquisition LC-MS/MS. We identified 770 reviewed proteins in the muscle tissue, 296 of which were differentially abundant between the control and injury groups (P ≤ 0.05). Around 50 proteins showed large differences (≥10-fold) or a distinct pattern of abundance after injury. These included proteins that have not been identified previously in injured muscle, such as ferritin light chain 1, fibrinogen γ-chain, fibrinogen β-chain, osteolectin, murinoglobulin-1, T-kininogen 2, calcium-regulated heat-stable protein 1, macrophage-capping protein, retinoid-inducible serine carboxypeptidase, ADP-ribosylation factor 4, Thy-1 membrane glycoprotein, and ADP-ribosylation factor-like protein 1. Some proteins increased between 6 h and 14 days, whereas other proteins increased in a more delayed pattern at 7 days after injury. Bioinformatic analysis revealed that various biological processes, including regulation of blood coagulation, fibrinolysis, regulation of wound healing, tissue regeneration, acute inflammatory response, and negative regulation of the immune effector process, were enriched in injured muscle tissue. This study advances the understanding of early muscle healing after muscle injury and lays a foundation for future mechanistic studies on interventions to treat muscle injury.

Thrombomodulin, Plasminogen Activator Inhibitor-1 and Protein C Levels, and Organ Dysfunction in Sepsis

Since endothelial function is closely related to organ dysfunction in sepsis and the relationship among endothelial injury, organ dysfunction, and other biomarkers remains unclear, we aimed to evaluate the correlation among endothelial injury, organ dysfunction, and several biomarkers in patients with sepsis.

Design

This was a retrospective observational study.

Setting

The study was conducted in a university hospital with 14 mixed ICU beds.

Patients

ICU patients with sepsis from June 2011 to December 2017 were enrolled in this study.

Interventions

Endothelial biomarkers (soluble thrombomodulin, plasminogen activator inhibitor-1, and protein C) and markers of inflammation and coagulation were evaluated during the ICU stay. Sequential Organ Failure Assessment scores were assessed for 7 days after ICU admission to determine organ dysfunction. Variables were compared among five stratified groups according to the Sequential Organ Failure Assessment score (0-2, 3-5, 6-8, 9-12, and 13-24). Regression analysis and 95% CIs were used to evaluate trends in biomarkers.

Measurements and Main Results

The patients were divided into five stratified groups (Sequential Organ Failure Assessment 0-2, n = 159 [20.5%]; Sequential Organ Failure Assessment 3-5, n = 296 [38.2%]; Sequential Organ Failure Assessment 6-8, n = 182 [23.5%]; Sequential Organ Failure Assessment 9-12, n = 75 [9.7%]; Sequential Organ Failure Assessment 13-24, n = 31 [4.0%]). Protein C activity was significantly correlated with the severity of organ dysfunction. It was lower on day 1, increased upon successful treatment, and was significantly higher in groups with lower Sequential Organ Failure Assessment scores.

Conclusions

Trends and activity of protein C were superior in predicting organ dysfunction compared with other endothelial biomarkers. Monitoring the level of protein C activity is an ideal tool to monitor organ dysfunctions in patients with sepsis.

Physiological cerebrovascular remodeling in response to chronic mild hypoxia: A role for activated protein C

Activated protein C (APC) is a serine protease that promotes favorable changes in vascular barrier integrity and post-ischemic angiogenic remodeling in animal models of ischemic stroke, and its efficacy is currently being investigated in clinical ischemic stroke trials. Interestingly, application of sub-clinical chronic mild hypoxia (CMH) (8% O2) also promotes angiogenic remodeling and increased tight junction protein expression, suggestive of enhanced blood-brain barrier (BBB) integrity, though the role of APC in mediating the influence of CMH has not been investigated. To examine this potential link, we studied CMH-induced cerebrovascular remodeling after treating mice with two different reagents: (i) a function-blocking antibody that neutralizes APC activity, and (ii) exogenous recombinant murine APC. While CMH promoted endothelial proliferation, increased vascular density, and upregulated the angiogenic endothelial integrins α5β1 and αvβ3, these events were almost completely abolished by functional blockade of APC. Consistent with these findings, addition of exogenous recombinant APC enhanced CMH-induced endothelial proliferation, expansion of total vascular area and further enhanced the CMH-induced right-shift in vessel size distribution. Taken together, our findings support a key role for APC in mediating physiological remodeling of cerebral blood vessels in response to CMH.

The Effect of Activated Protein C on Attenuation of Ischemia-Reperfusion Injury in a Rat Muscle Flap Model

Ischemia-reperfusion injury is often the final and irreversible factor causing flap failure in microsurgery. The salvage of a microsurgical flap with an ischemia-reperfusion injury contributes to the success of microsurgical flap transfers. Activated protein C (APC), a serine protease with anticoagulant and anti-inflammatory activities, has been shown to improve ischemic flap survival. To date, APC has yet to be applied to models of free flap with ischemia-reperfusion injury. In this study, we aimed to investigate the effect of APC on gracilis flap ischemia-reperfusion injury induced by gracilis vessels clamping and reopening. Sixty male Sprague-Dawley rats were randomly divided into 2 groups. After 4 hours of clamping for ischemia, flaps were reperfused and recombinant human APC (25 μg/kg) or saline was injected in the flaps through pedicles. At 0, 1, 4, 18, and 24 hours after injection (n = 6 for each time point), the tissue samples were harvested. The muscle viability at 24 hours in saline group was 54.8% (15.1%), whereas the APC-treated group was 90.0% (4.3%) (P < 0.05). The induced nitric oxide synthase (iNOS) mRNA expression increased with the time after reperfusion, which were 0.93 (0.25) to 2.09 (0.22) in saline group, and 0.197 (0.15) to 0.711 (0.15) in the APC-treated group. iNOS mRNA expression in the APC-treated group was significantly higher than the saline group at 1, 18, and 24 hours (P < 0.05). Numerous inflammatory cells were observed infiltrating and invading the muscle fibers in the saline group more than the APC-treated group. Increased number of polymorphonuclear cells was also noted in the saline group compared with the APC-treated group (P < 0.05). In conclusion, APC treatment can significantly attenuate ischemia-reperfusion injury and increase the survival of the free flap through down-regulating iNOS mRNA expression and reducing the inflammatory cells. Further research is still needed to be done on various mechanisms in which APC is protective to prevent tissue damage.

Endothelial barrier dysfunction in septic shock

The endothelium provides an essential and selective membrane barrier that regulates the movement of water, solutes, gases, macromolecules and the cellular elements of the blood from the tissue compartment in health and disease. Its structure and continuous function is essential for life for all vertebrate organisms. Recent evidence indicates that the endothelial surface does not have a passive role in systemic inflammatory states such as septic shock. In fact, endothelial cells are in dynamic equilibrium with a myriad of inflammatory mediators and elements of the innate immune and coagulation systems to orchestrate the host response in sepsis. The barrier function of the endothelial surface is almost uniformly impaired in septic shock, and it is likely that this contributes to adverse outcomes. In this review, we will highlight recent advances in the understanding of the signalling events that regulate endothelial function and molecular events that induce endothelial dysfunction in sepsis. Endothelial barrier repair strategies as a treatment for sepsis include modulation of C5a, high-mobility group box 1 and VEGF receptor 2; stimulation of angiopoietin-1, sphingosine 1 phosphate receptor 1 and Slit; and a number of other innovative approaches.

Pathophysiology of microcirculatory dysfunction and the pathogenesis of septic shock

Multiple experimental and human trials have shown that microcirculatory alterations are frequent in sepsis. In this review, we discuss the various mechanisms that are potentially involved in their development and the implications of these alterations. Endothelial dysfunction, impaired inter-cell communication, altered glycocalyx, adhesion and rolling of white blood cells and platelets, and altered red blood cell deformability are the main mechanisms involved in the development of these alterations. Microcirculatory alterations increase the diffusion distance for oxygen and, due to the heterogeneity of microcirculatory perfusion in sepsis, may promote development of areas of tissue hypoxia in close vicinity to well-oxygenated zones. The severity of microvascular alterations is associated with organ dysfunction and mortality. At this stage, therapies to specifically target the microcirculation are still being investigated.

Microcirculatory alterations: potential mechanisms and implications for therapy

Multiple experimental and human trials have shown that microcirculatory alterations are frequent in sepsis. In this review, we discuss the characteristics of these alterations, the various mechanisms potentially involved, and the implications for therapy. Sepsis-induced microvascular alterations are characterized by a decrease in capillary density with an increased number of stopped-flow and intermittent-flow capillaries, in close vicinity to well-perfused capillaries. Accordingly, the surface available for exchange is decreased but also is highly heterogeneous. Multiple mechanisms may contribute to these alterations, including endothelial dysfunction, impaired inter-cell communication, altered glycocalyx, adhesion and rolling of white blood cells and platelets, and altered red blood cell deformability. Given the heterogeneous nature of these alterations and the mechanisms potentially involved, classical hemodynamic interventions, such as fluids, red blood cell transfusions, vasopressors, and inotropic agents, have only a limited impact, and the microcirculatory changes often persist after resuscitation. Nevertheless, fluids seem to improve the microcirculation in the early phase of sepsis and dobutamine also can improve the microcirculation, although the magnitude of this effect varies considerably among patients. Finally, maintaining a sufficient perfusion pressure seems to positively influence the microcirculation; however, which mean arterial pressure levels should be targeted remains controversial. Some trials using vasodilating agents, especially nitroglycerin, showed promising initial results but they were challenged in other trials, so it is difficult to recommend the use of these agents in current practice. Other agents can markedly improve the microcirculation, including activated protein C and antithrombin, vitamin C, or steroids. In conclusion, microcirculatory alterations may play an important role in the development of sepsis-related organ dysfunction. At this stage, therapies to target microcirculation specifically are still being investigated.

Recombinant activated protein C treatment improves tissue perfusion and oxygenation in septic patients measured by near-infrared spectroscopy

INTRODUCTION

The purpose was to test the hypothesis that muscle perfusion, oxygenation, and microvascular reactivity would improve in patients with severe sepsis or septic shock during treatment with recombinant activated protein C (rh-aPC) (n = 11) and to explore whether these parameters are related to macrohemodynamic indices, metabolic status or Sequential Organ Failure Assessment (SOFA) score. Patients with contraindications to rh-aPC were used as a control group (n = 5).

MATERIALS AND METHODS

Patients were sedated, intubated, mechanically ventilated, and hemodynamically monitored with the PiCCO system. Tissue oxygen saturation (StO2) was measured using near-infrared spectroscopy (NIRS) during the vascular occlusion test (VOT). Baseline StO2 (StO2 baseline), rate of decrease in StO2 during VOT (StO2 downslope), and rate of increase in StO2 during the reperfusion phase were (StO2 upslope) determined. Data were collected before (T0), during (24 hours (T1a), 48 hours (T1b), 72 hours (T1c) and 96 hours (T1d)) and 6 hours after stopping rh-aPC treatment (T2) and at the same times in the controls. At every assessment, hemodynamic and metabolic parameters were registered and the SOFA score calculated.

RESULTS

The mean +/- standard deviation Acute Physiology and Chronic Health Evaluation II score was 26.3 +/- 6.6 and 28.6 +/- 5.3 in rh-aPC and control groups, respectively. There were no significant differences in macrohemodynamic parameters between the groups at all the time points. In the rh-aPC group, base excess was corrected (P < 0.01) from T1a until T2, and blood lactate was significantly decreased at T1d and T2 (2.8 +/- 1.3 vs. 1.9 +/- 0.7 mmol/l; P < 0.05). In the control group, base excess was significantly corrected at T1a, T1b, T1c, and T2 (P < 0.05). The SOFA score was significantly lower in the rh-aPC group compared with the controls at T2 (7.9 +/- 2.2 vs. 12.2 +/- 3.2; P < 0.05). There were no differences between groups in StO2 baseline. StO2 downslope in the rh-aPC group decreased significantly at all the time points, and at T1b and T2 (-16.5 +/- 11.8 vs. -8.1 +/- 2.4%/minute) was significantly steeper than in the control group. StO2 upslope increased and was higher than in the control group at T1c, T1d and T2 (101.1 +/- 62.1 vs. 54.5 +/- 23.8%/minute) (P < 0.05).

CONCLUSIONS

Treatment with rh-aPC may improve muscle oxygenation (StO2 baseline) and reperfusion (StO2 upslope) and, furthermore, rh-aPC treatment may increase tissue metabolism (StO2 downslope). NIRS is a simple, real-time, non-invasive technique that could be used to monitor the effects of rh-aPC therapy at microcirculatory level in septic patients.

Microcirculation and mitochondria in sepsis: getting out of breath

PURPOSE OF REVIEW

To present the recent findings obtained in clinical and experimental studies examining microcirculatory alterations in sepsis, their link to mitochondrial dysfunction, and current knowledge regarding the impact of these alterations on the outcome of septic patients.

RECENT FINDINGS

Interlinked by a mutual cascade effect and driven by the host-pathogen interaction, microcirculatory and mitochondrial functions are impaired during sepsis. Mitochondrial respiration seems to evolve during the course of sepsis, demonstrating a change from reversible to irreversible inhibition. The spatiotemporal heterogeneity of microcirculatory and mitochondrial dysfunction suggests that these processes may be compartmentalized. Although a causal relationship between mitochondrial and microcirculatory dysfunction and organ failure in sepsis is supported by an increasing number of studies, adaptive processes have also emerged as part of microcirculatory and mitochondrial alterations. Treatments for improving or preserving microcirculatory, mitochondrial function, or both seem to yield a better outcome in patients.

SUMMARY

Even though there is evidence that microcirculatory and mitochondrial dysfunction plays a role in the development of sepsis-induced organ failure, their interaction and respective contribution to the disease remains poorly understood. Future research is necessary to better define such relationships in order to identify therapeutic targets and refine treatment strategies.

[Microcirculation of intensive care patients. From the physiology to the bedside]

The microcirculation is unique in its anatomy and physiology and is a self-contained organ system within the human body. It is the site where gas exchange and nutrient supply takes place, but it is also the site which experiences pathological alterations during various shock states and therefore compromises the oxygen supply to tissues and organs. Systemic inflammation for example leads amongst others to increased heterogeneous blood flow, formation of interstitial edema, altered viscosity, leukocyte activation, disturbances in the coagulation system, and to a breakdown of the endothelial barrier function. These alterations inevitably lead to limitations of the oxygen supply to tissues. Without interruption of these pathomechanisms, the dysfunction of the microcirculation will consequently result in organ dysfunction. In this review article a short description of the microcirculatory physiology, the interaction between the macrocirculation and the microcirculation, as well as microcirculatory alterations generated by a systemic inflammatory response will be given. Finally, various therapy options will be described, which, experimentally, can lead to an improvement in microcirculatory dysfunction.

Protein C: a potential biomarker in severe sepsis and a possible tool for monitoring treatment with drotrecogin alfa (activated)

Introduction

Drotrecogin alfa (activated; DrotAA) treatment, a 96-hour infusion, reduces 28-day mortality in severe sepsis to approximately 25%. The question remains whether a longer infusion or higher dose could increase rate of survival. The goal of this study was to identify a dependable, sensitive measure with which to monitor disease progression and response in patients during DrotAA treatment.

Methods

Data on severe sepsis patients included in PROWESS (placebo-controlled, double-blind, randomized study of 850 DrotAA and 840 placebo individuals) and ENHANCE (single-arm, open-label study of 2,375 DrotAA patients) studies were analyzed. In these studies, DrotAA (24 μg/kg per hour) or placebo was infused for 96 hours and patients were followed for 28 days. Data on six laboratory measures and five organ dysfunctions were systematically analyzed to identify a potential surrogate end-point for monitoring DrotAA therapy and predicting 28-day mortality at the end of therapy. To allow comparison across variables, sensitivity and specificity analyses identified cut-off values for preferred outcome, and relative risks for being above or below cut-offs were calculated, as was the 'proportion of treatment effect explained' (PTEE) to identify biomarkers that contribute to benefit from DrotAA.

Results

Protein C was the only variable that correlated with outcome across all analyses. Using placebo data, a baseline protein C under 40% was established as a useful predictor of outcome (odds ratio 2.12). Similar odds ratios were associated with cut-off values of other biomarkers, but the treatment benefit associated with DrotAA was significantly greater below the cut-off than above the cut-off only for protein C (relative risk for 28-day mortality 0.66 versus 0.88; P = 0.04). Protein C was the only end-of-infusion biomarker that potentially explained at least 50% of the benefit from DrotAA (PTEE 57.2%). The PTEE was 41% for cardiovascular Sequential Organ Failure Assessment score and for d-dimer. At the end of infusion (day 4), protein C categories (≤40%, 41% to 80%, and > 80%) remained significantly related to mortality, regardless of treatment assignment.

Conclusion

Based on systematic analyses of 11 variables measured in severe sepsis clinical trials, protein C was the only variable consistently correlated with both DrotAA treatment effect and survival. Further study is needed to determine whether longer infusions or higher doses of DrotAA would achieve the goal of normalizing protein C in more patients with severe sepsis.