Disorders of platelet function

The SARS-CoV-2/Receptor Axis in Heart and Blood Vessels: A Crisp Update on COVID-19 Disease with Cardiovascular Complications

The SARS-CoV-2 virus causing COVID-19 disease has emerged expeditiously in the world and has been declared pandemic since March 2020, by World Health Organization (WHO). The destructive effects of SARS-CoV-2 infection are increased among the patients with pre-existing chronic conditions and, in particular, this review focuses on patients with underlying cardiovascular complications. The expression pattern and potential functions of SARS-CoV-2 binding receptors and the attributes of SARS-CoV-2 virus tropism in a physio-pathological state of heart and blood vessel are precisely described. Of note, the atheroprotective role of ACE2 receptors is reviewed. A detailed description of the possible detrimental role of SARS-CoV-2 infection in terms of vascular leakage, including endothelial glycocalyx dysfunction and bradykinin 1 receptor stimulation is concisely stated. Furthermore, the potential molecular mechanisms underlying SARS-CoV-2 induced clot formation in association with host defense components, including activation of FXIIa, complements and platelets, endothelial dysfunction, immune cell responses with cytokine-mediated action are well elaborated. Moreover, a brief clinical update on patient with COVID-19 disease with underlying cardiovascular complications and those who had new onset of cardiovascular complications post-COVID-19 disease was also discussed. Taken together, this review provides an overview of the mechanistic aspects of SARS-CoV-2 induced devastating effects, in vital organs such as the heart and vessels.

Perioperative blood transfusion and blood conservation in cardiac surgery: the Society of Thoracic Surgeons and The Society of Cardiovascular Anesthesiologists clinical practice guideline

BACKGROUND

A minority of patients having cardiac procedures (15% to 20%) consume more than 80% of the blood products transfused at operation. Blood must be viewed as a scarce resource that carries risks and benefits. A careful review of available evidence can provide guidelines to allocate this valuable resource and improve patient outcomes.

METHODS

We reviewed all available published evidence related to blood conservation during cardiac operations, including randomized controlled trials, published observational information, and case reports. Conventional methods identified the level of evidence available for each of the blood conservation interventions. After considering the level of evidence, recommendations were made regarding each intervention using the American Heart Association/American College of Cardiology classification scheme.

RESULTS

Review of published reports identified a high-risk profile associated with increased postoperative blood transfusion. Six variables stand out as important indicators of risk: (1) advanced age, (2) low preoperative red blood cell volume (preoperative anemia or small body size), (3) preoperative antiplatelet or antithrombotic drugs, (4) reoperative or complex procedures, (5) emergency operations, and (6) noncardiac patient comorbidities. Careful review revealed preoperative and perioperative interventions that are likely to reduce bleeding and postoperative blood transfusion. Preoperative interventions that are likely to reduce blood transfusion include identification of high-risk patients who should receive all available preoperative and perioperative blood conservation interventions and limitation of antithrombotic drugs. Perioperative blood conservation interventions include use of antifibrinolytic drugs, selective use of off-pump coronary artery bypass graft surgery, routine use of a cell-saving device, and implementation of appropriate transfusion indications. An important intervention is application of a multimodality blood conservation program that is institution based, accepted by all health care providers, and that involves well thought out transfusion algorithms to guide transfusion decisions.

CONCLUSIONS

Based on available evidence, institution-specific protocols should screen for high-risk patients, as blood conservation interventions are likely to be most productive for this high-risk subset. Available evidence-based blood conservation techniques include (1) drugs that increase preoperative blood volume (eg, erythropoietin) or decrease postoperative bleeding (eg, antifibrinolytics), (2) devices that conserve blood (eg, intraoperative blood salvage and blood sparing interventions), (3) interventions that protect the patient's own blood from the stress of operation (eg, autologous predonation and normovolemic hemodilution), (4) consensus, institution-specific blood transfusion algorithms supplemented with point-of-care testing, and most importantly, (5) a multimodality approach to blood conservation combining all of the above.

Thrombin‐activated platelets induce proliferation of human skin fibroblasts by stimulating autocrine production of insulin‐like growth factor‐1

Platelet components have found successful clinical utilization to initiate or to accelerate tissue-repair mechanisms. However, the molecular pathways by which platelet factors contribute to tissue regeneration have not been fully elucidated. We have studied the effect of thrombin-activated platelets (TAPs) on cell growth in vivo and in cultured cell systems. Application of TAPs to ulcerative skin lesions of diabetic patients induced local activation of ERK1/2 and Akt/PKB. Moreover, when applied to cultured human skin fibroblasts, TAPs promoted cell growth and DNA synthesis and activated platelet-derived growth factor (PDGF) and insulin-like growth factor (IGF)-1 receptor tyrosine kinases. PDGF was released by TAPs and rapidly achieved a plateau. At variance, the release of IGF-1 was mainly provided by the TAPs-stimulated fibroblasts and progressively increased up to 48 h. The PDGF-R blocker Ag1296 reduced the activation of Akt/PKB and, at a lesser extent, of ERK1/2. Conversely, inhibition of IGF-1 signaling by Ag1024 and expression of a dominant-negative IGF-1R mutant selectively reduced the stimulation of ERK1/2 by TAPs and fibroblast-released factors, with minor changes of Akt/PKB activity. Thus, platelet factors promote fibroblast growth by acutely activating Akt/PKB and ERK1/2. Sustained activation of ERK1/2, however, requires autocrine production of IGF-1 by TAPs-stimulated fibroblasts.

Meticillin-resistant Staphylococcus aureus infection in diabetic mice enhanced inflammation and coagulation

BALB/cA mice were used to study the interaction of diabetes and meticillin-resistant Staphylococcus aureus (MRSA) infection on pathogen distribution, cytokine profile and inflammatory and endothelial-injury markers, as well as coagulation and anticoagulation factors. Meticillin-susceptible S. aureus (MSSA) infection did not cause death within the experimental period. MRSA-infected nondiabetic and diabetic mice died on 19·1±1·4 and 10·6±0·7 days post-infection (p.i.), respectively. MRSA and MSSA infection in diabetic mice did not result in symptomatic bacteraemia; however, MRSA infection in diabetic mice significantly reduced glucose levels (P<0·05). Diabetic mice showed significantly higher levels of C-reactive protein, fibrinogen, fibronectin and von Willebrand factor than nondiabetic mice (P<0·05), and MRSA infection further elevated the plasma levels of these inflammatory and endothelial markers (P<0·05). Before infection, diabetic mice had significantly higher plasminogen activator inhibitor-1 (PAI-1) activity, lower antithrombin III (AT-III) and protein C activities (P<0·05), and MRSA infection significantly increased PAI-1 activity further and reduced the activity of AT-III and protein C (P<0·05). MRSA infection increased the production of three Th1 cytokines, interleukin 2 (IL-2), tumour necrosis factor alpha and gamma interferon, in diabetic mice (P<0·05); however, three Th2 cytokines, IL-4, IL-6, IL-10, were elevated at 2 and 4 days p.i., and then dropped gradually. MRSA infection in diabetic mice accelerated the inflammation process, endothelial injury and blood coagulation in diabetic mice. Therefore, the development of proper infection diagnosis and timely use of effective treatments for MRSA-infected diabetic individuals is important and necessary.

Impaired primary hemostasis with normal platelet function in Duchenne muscular dystrophy during highly-invasive spinal surgery

A defective, normal or enhanced hemostasis has been reported in Duchenne muscular dystrophy (DMD). A retrospective analysis of intra-and postoperative (up to 36 h) estimated blood losses was performed in 156 patients undergoing spinal surgery for: DMD (n = 31), idiopathic scoliosis (IS) (n = 70), poliomyelitis (n = 10), cerebral palsy (CP) (n = 28), spinal muscular atrophy (SMA) (n = 17). Platelet aggregation and bleeding times were also investigated in DMD patients. Immunohistochemistry for dystrophin was performed in platelets, megakaryocytes and blood vessels of normal tissues. DMD patients showed significantly higher intraoperative estimated blood losses (DMD: 3495+/-890 ml; IS: 2269+/-804 ml; poliomyelitis: 2582+/-1252 ml; CP: 2071+/-683 ml; SMA: 2464+/-806 ml; P < 0.05), while postoperative blood losses were similar among different groups. Higher estimated blood losses in DMD were independent of the duration of surgery, body weight, gender, age, vertebral levels or preoperative Cobb angle. DMD children had significantly prolonged bleeding times, but retained normal platelet function. From control samples dystrophin was expressed in vascular smooth muscle cells, but not in platelets. DMD appears to be characterized by immediate bleeding during highly-invasive surgery and increased bleeding time without platelet abnormalities. Considering dystrophin expression in normal vascular smooth muscle cells, these results altogether suggest a selective defect of primary hemostasis in DMD, likely to be due to impaired vessel reactivity.

Defective platelet aggregation in uremia is transiently worsened by hemodialysis

Bleeding is a prominent feature of uremia and remains a significant cause of morbidity in hemodialysis (HD)-dependent patients. To measure the impact of the HD procedure, we performed a prospective cross-over study in eight patients placed consecutively for 2-week periods each on low-flux biocompatible polymethylmethacrylate, low-flux complement-activating cuprophane, and high-flux biocompatible polysulfone membranes. The primary measure of platelet function studied was shear-induced platelet aggregation (SIPA), which has been shown to be a physiologically relevant marker of platelet function and involves the interaction of von Willebrand factor (vWf) with platelet membrane glycoproteins (GP) Ib and IIb-IIIa. Flow-cytometric analysis of the surface expression of platelet membrane GP Ib and GP IIb-IIIa was performed using fluorescein isothiocyanate (FITC)-conjugated monoclonal antibodies CD42b and CD41a, respectively. Multivariate analysis did not demonstrate a statistically significant effect of the type of dialysis membrane on platelet aggregation, calcium flux, or thromboxane B2 production. There was a marked decrease of SIPA in HD patients (pre-HD, mean +/- SEM, 19% +/- 3%) compared with normal controls (43% +/- 3%, P < 0.001), with a further decrease after the HD procedure (post-HD, 12% +/- 2%, P = 0.015 compared with pre-HD). This intradialytic decrease in SIPA correlated with a decrease in GP Ib (pre-HD, 385 +/- 21 mean fluorescence intensity [MFI]; post-HD, 285 +/- 21 MFI, P = 0.0001). GP IIb-IIIa was also significantly decreased post-HD (pre-HD, 1,022 +/- 70 MFI; post-HD, 881 +/- 64 MFI, P = 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Trilinolein inhibits epinephrine-induced human platelet aggregation

At concentrations ranging from 10(-9) to 10(-6) M, trilinolein inhibited epinephrine-induced platelet aggregation. This inhibition was accompanied by reduced ATP release and thromboxane B2 formation. However, concentration-response curves for the interaction between trilinolein and epinephrine showed that trilinolein was unlikely a competitive antagonist of epinephrine. Platelet aggregation induced by collagen, thrombin, ADP or arachidonic acid was not inhibited. This study supported the theory that this type of triglyceride may have therapeutic potential but the definite mechanism for its effect remains to be answered.