Aggregation of platelets by muscle actin. A multivalent interaction model of platelet aggregation by ADP

β-Actin: An Emerging Biomarker in Ischemic Stroke

At present, the diagnosis of ischemic stroke mainly depends on neuroimaging technology, but it still has many limitations. Therefore, it is very important to find new biomarkers of ischemic stroke. Recently, β-actin has attracted extensive attention as a biomarker of a variety of cancers. Although several recent studies have been investigating its role in ischemic stroke and other cerebrovascular diseases, the understanding of this emerging biomarker in neurology is still limited. We examined human and preclinical studies to gain a comprehensive understanding of the literature on the subject. Most relevant literatures focus on preclinical research, and pay more attention to the role of β-actin in the process of cerebral ischemia, but some recent literatures reported that in human studies, serum β-actin increased significantly in the early stage of acute cerebral ischemia. This review will investigate the basic biology of β-actin, pay attention to the potential role of serum β-actin as an early diagnostic blood biomarker of ischemic stroke, and explore its potential mechanism in ischemic stroke and new strategies for stroke treatment in the future.

Plasma proteomic profile associated with platelet dysfunction after trauma

BACKGROUND

Coagulopathic bleeding is a major cause of mortality after trauma, and platelet dysfunction contributes to this problem. The causes of platelet dysfunction are relatively unknown, but a great deal can be learned from the plasma environment about the possible pathways involved.

OBJECTIVE

Describe the changes in plasma proteomic profile associated with platelet dysfunction after trauma.

METHODS

Citrated blood was collected from severely injured trauma patients at the time of their arrival to the Emergency Department. Samples were collected from 110 patients, and a subset of twenty-four patients was identified by a preserved (n = 12) or severely impaired (n = 12) platelet aggregation response to five different agonists. Untargeted proteomics was performed by nanoflow liquid chromatography tandem mass spectrometry. Protein abundance levels for each patient were normalized to total protein concentration to control for hemodilution by crystalloid fluid infusion prior to blood draw.

RESULTS

Patients with platelet dysfunction were more severely injured but otherwise demographically similar to those with retained platelet function. Of 232 proteins detected, twelve were significantly different between groups. These proteins fall into several broad categories related to platelet function, including microvascular obstruction with platelet activation, immune activation, and protease activation.

CONCLUSIONS

This observational study provides a description of the change in proteomic profile associated with platelet dysfunction after trauma and identifies twelve proteins with the most profound changes. The pathways involving these proteins are salient targets for immediate investigation to better understand platelet dysfunction after trauma and identify targets for intervention.

Plasma Gelsolin: Indicator of Inflammation and Its Potential as a Diagnostic Tool and Therapeutic Target

Gelsolin, an actin-depolymerizing protein expressed both in extracellular fluids and in the cytoplasm of a majority of human cells, has been recently implicated in a variety of both physiological and pathological processes. Its extracellular isoform, called plasma gelsolin (pGSN), is present in blood, cerebrospinal fluid, milk, urine, and other extracellular fluids. This isoform has been recognized as a potential biomarker of inflammatory-associated medical conditions, allowing for the prediction of illness severity, recovery, efficacy of treatment, and clinical outcome. A compelling number of animal studies also demonstrate a broad spectrum of beneficial effects mediated by gelsolin, suggesting therapeutic utility for extracellular recombinant gelsolin. In the review, we summarize the current data related to the potential of pGSN as an inflammatory predictor and therapeutic target, discuss gelsolin-mediated mechanisms of action, and highlight recent progress in the clinical use of pGSN.

Thymosin beta 4 regulation of actin in sepsis

INTRODUCTION

Sepsis is the dysregulated host response to an infection resulting in life-threatening organ damage. Thymosin Beta 4 is an actin binding protein that inhibits the polymerization of G-actin into F-actin and improves mortality when administered intravenously to septic rats. Thymosin Beta 4 decreases inflammatory mediators, lowers reactive oxygen species, up-regulates anti-oxidative enzymes, anti-inflammatory genes, and anti-apoptotic enzymes making it an interesting protein to study in sepsis.

AREAS COVERED

The authors summarize the current knowledge of actin and Thymosin Beta 4 as it relates to sepsis via a comprehensive literature search.

EXPERT OPINION

Sepsis results in measurable levels of F-actin in the circulation as well as a decreased concentration of Thymosin Beta 4. It is speculated that F-actinemia contributes to microcirculatory perturbations present in patients with sepsis by disturbing laminar flow. Given that Thymosin Beta 4 inhibits the polymerization of F-actin, it is possible that Thymosin Beta 4 decreases mortality in sepsis via the regulation of actin as well as its other anti-inflammatory properties and should be further pursued as a clinical trial in humans with sepsis.

Extracellular Actin in Health and Disease

This review considers the functions of extracellular actin - cell surface bound, associated with extracellular matrix, or freely circulating. The role of this protein in different pathological processes is analyzed: its toxic effects and involvement in autoimmune diseases as an autoantigen. The extracellular actin clearance system and its role in protection against the negative effects of actin are characterized. Levels of free-circulating actin, anti-actin immunoglobulins, and components of the actin clearance system as prognostic biomarkers for different diseases are reviewed. Experimental approaches to protection against excessive amounts of free-circulating F-actin are discussed.

Recombinant plasma gelsolin infusion attenuates burn-induced pulmonary microvascular dysfunction

Reduced plasma concentrations of the extracellular actin-binding proteins gelsolin and Gc-globulin correlate with pulmonary failure and death in humans after injury. The purpose of this study was to investigate the role of plasma gelsolin in the pathophysiology of inflammation-induced lung injury. We postulated that plasma gelsolin levels decrease at an early time point after burn injury and that the intravenous infusion of gelsolin prevents burn-induced pulmonary microvascular dysfunction. Adult Sprague-Dawley rats were randomized to undergo a 40% body surface area thermal injury (Burn) or manipulation without burn (Sham). Plasma gelsolin and Gc-globulin concentrations were determined at various times during the first 6 days of injury by Western blotting. Other animals were randomized to receive either recombinant human gelsolin (0.078, 0.78, or 7.8 mg) or albumin (7.8 mg) before and 8 h after Burn or Sham. Twenty-four hours later, pulmonary microvascular permeability was assessed by measuring the capillary filtration by use of an isolated, perfused lung model. We found that plasma gelsolin levels of burn-injured rats decreased to 10% of normal levels within 12 h and remained below normal levels for up to 6 days postinjury. Gc-globulin values also fall, but to a lesser extent and only transiently. Treatment of burned animals with intravenous infusions of recombinant human gelsolin prevented the increase in pulmonary microvascular permeability that accompanies this injury. Our findings are consistent with the hypothesis that plasma gelsolin depletion contributes to the pathophysiology of pulmonary microvascular dysfunction during inflammation.

Plasma concentration of Gc-globulin is associated with organ dysfunction and sepsis after injury

OBJECTIVE

Clinical and experimental studies suggest that the proteins of the extracellular actin scavenger system have a role in the pathophysiological processes taking place in critically ill and injured patients. Circulating levels of Gc-globulin and gelsolin are reduced shortly after severe trauma, and admission levels of Gc-globulin are associated with survival. Herein, we sought to measure the association between admission levels of Gc-globulin and postinjury organ dysfunction and infection. We also wanted to describe the serial changes in Gc-globulin in these severely injured patients.

DESIGN

Prospective cohort.

SETTING

Intensive care unit at a county hospital that serves as a level one trauma center.

PATIENTS

Ninety-eight consecutive trauma victims admitted to the intensive care unit for >24 hrs during a 4-month period.

MEASUREMENTS AND MAIN RESULTS

Circulating levels of Gc-globulin were measured by using immunonephelometry. All patients were evaluated daily to obtain the necessary data for assessment of organ dysfunction and sepsis. The median Gc-globulin concentration at admission was 127 mg/L in patients who developed severe multiple organ dysfunction compared with 184 mg/L in patients who did not (p =.001). The admission level of Gc-globulin was comparable to known risk factors such as age and injury severity score, regarding development of organ dysfunction. Plasma concentrations of Gc-globulin remained significantly lower in patients who developed respiratory failure and sepsis, compared with patients who did not develop these complications (p =.02 and p=.015, respectively).

CONCLUSIONS

Admission plasma concentration of Gc-globulin is lower in patients who develop organ dysfunction and sepsis after traumatic injury. These data, combined with the work of others, support the hypothesis that actin release and depletion of the extracellular actin scavenger system proteins are associated with, and may contribute in part to, the complications of sepsis and organ dysfunction, particularly respiratory failure and thrombocytopenia.

Relationship of admission plasma gelsolin levels to clinical outcomes in patients after major trauma

Actin-scavenging proteins, e.g., plasma gelsolin, counteract the pathophysiological consequences of actin leaked into the circulation from dying cells, but the capacity of this defense system can be overwhelmed by massive tissue injury. We examined the prognostic implications of plasma gelsolin levels obtained near the time of admission to our level I Trauma Unit on the subsequent clinical course in a group of patients with severe traumatic injuries. Blood samples were obtained from 13 patients shortly after major trauma and 11 healthy volunteers who served as the control group. Plasma gelsolin levels were assayed by quantitative Western blotting. Duration of mechanical ventilation, stay in the Trauma Intensive Care Unit, and development of acute respiratory distress syndrome (ARDS) were measured as clinical outcomes reflecting the complexity of the hospital course. Subsequently, we evaluated an additional 52 patients after major and minor trauma to extend our earlier observations. Plasma gelsolin concentrations were significantly lower in our 13 original patients compared with healthy controls. Levels below 250 mg/L (> 2 standard deviations below the mean of the control group) were associated with prolonged mechanical ventilation and a stay in the intensive care unit >/= 13 days. Both patients whose gelsolin level was < 100 mg/L in this first series developed ARDS. Including all 65 patients, 6 of the 10 patients who developed ARDS had admission gelsolin levels less than 250 mg/L, compared with only 7 of the 55 patients without ARDS (p = 0.0028). The mean gelsolin levels were 193 and 400 mg/L in patients with and without ARDS, respectively (p < 0.0001) and 398 mg/L in survivors versus 259 mg/L for patients who expired (p < 0.0001). Ten of the 13 patients (77%) with gelsolin levels at the time of admission more than 2 SD below the control mean had "bad outcomes," defined as mechanical ventilation for >/= 13 days in the Trauma Intensive Unit, ARDS, and/or death. Plasma gelsolin levels appear to be an early prognostic marker in patients experiencing major trauma. Whether circulating gelsolin serves a biologically vital function or is simply depleted after massive trauma cannot be determined from our study. The potential therapeutic benefits of infusions of recombinant human plasma gelsolin for patients in whom multiorgan dysfunction commonly follows a serious but self-limited insult have not yet been investigated.

Actin polymerization enhances Pasteurella haemolytica leukotoxicity

Pasteurella haemolytica leukotoxin is cytotoxic to bovine leukocytes, causing increased cell membrane permeability, osmotic swelling, release of cytosolic proteins and cell lysis. These studies were designed to test if leukotoxin causes release of the cytoskeletal protein, actin, from bovine leukemia cells and if purified actin-influenced bacterial growth or leukotoxin production. Culture supernatants caused a 7-fold decrease in viability of bovine leukemia cells and increased cell permeability that was accompanied by release of beta-actin into the cell culture supernatant. Exposing P. haemolytica to purified actin solutions induced the conversion of monomeric G-actin to polymerized F-actin. This conversion was partially inhibited by bovine P. haemolytica immune, but not pre-immune, serum. Loss of streptomycin resistance following treatment of the organism with acridine orange ablated the polymerizing activity. Incubation of P. haemolytica in the presence of purified F-actin did not affect growth but resulted in culture supernatant that had 3.0-3.9-fold greater leukotoxicity compared to medium alone or medium containing G-actin, heat-denatured actin or albumin. The effect of actin on leukotoxicity was concentration-dependent and directly associated with increases in secreted leukotoxin. The interaction between P. haemolytica and actin is potentially detrimental to the host by inducing polymerization of actin into insoluble filaments and by enhancing leukotoxicity.

Mechanism of action of the platelet aggregation inhibitor purified from Agkistrodon halys (mamushi) snake venom

The platelet aggregation inhibitor purified from Agkistrodon halys snake venom inhibited rabbit platelet aggregations induced by thrombin, sodium arachidonate, collagen or ionophore A-23187. The IC50 was about 11 micrograms/ml in platelet aggregation regardless of which aggregation inducer was used. beta-Mercaptoethanol abolished both the phospholipase A enzymatic and platelet aggregation inhibitory activities of this venom inhibitor. p-Bromophenacyl bromide-treated venom inhibitor lost almost completely its phosphilipase A enzymatic activity, but retained its platelet aggregation inhibitory effect. In the presence of EGTA, the venom inhibitor still showed the same inhibitory activity on thrombin-, sodium arachidonate-, collagen- or ionophore A23187-induced platelet aggregations triggered by successive addition of Ca2+. The activation of platelet phospholipase A and the serotonin release reaction triggered by Ca2+ influx were unaffected by this venom inhibitor. It also inhibited the clot retraction of platelet-rich plasma. It is concluded that the inhibitory effect of the venom inhibitor on platelet aggregation is independent of its phospholipase A enzymatic activity. Its mode of action is different from those of other known platelet inhibitory drugs. This venom inhibitor possibly acts on a common step subsequent to platelet shape change, leading to inhibition of platelet aggregation.