Commentary: Matrix metalloproteinase-13 unlucky for the forming thrombus

Matrix metalloproteinases (MMPs) are calcium‐dependent zinc‐containing endoproteases involved in extracellular matrix and non‐matrix protein degradation.1 In the latest issue of Research and Practice in Thrombosis and Haemostasis, Howes and colleagues2 investigated the role of MMP‐13 in platelet aggregation and thrombus formation and identified that MMP‐13 could engage important platelet receptors and influence platelet function in vitro. MMP‐13 is of great cardiovascular interest as expression of this metalloproteinase is significantly upregulated in a host of atherothrombotic and inflammatory conditions.

Platelet activation in trauma and other inflammatory conditions

Platelets play critical roles in thrombosis, inflammation, and wound healing, which are essential in response to trauma. These processes are primarily driven through the immunoreceptor tyrosine-based activation motif (ITAM)-containing receptors, glycoprotein VI (GPVI) and C-type lectin-like receptor 2 (CLEC-2). This study aimed to investigate; (i) the effects of Alarmins released following trauma on platelet reactivity and the mechanisms involved; (ii) establish whether soluble GPVI (sGPVI), a platelet activation marker is elevated in trauma and other inflammatory conditions; (iii) determine whether the CLEC-2 ligand, podoplanin, is elevated in inflammatory conditions and (iv) establishing the role of GPVI and platelets in cutaneous wound healing. The nuclear-related Alarmin, histones, induced robust platelet activation both in vitro and in vivo. Histone-induced platelet activation was mediated through GPVI in vitro However, this pathway was found not to underlie histone-induced lowering of platelet count in vivo and is most likely to result from mediators released following vascular damage. GPVI shedding was shown to be induced following activation by thrombin, through a pathway dependent on fibrin generation. sGPVI was found to be a marker for platelet activation during a variety of inflammatory disorders, notably in association with sepsis. Furthermore, GPVI shedding reflects platelet activation by collagen and potentially thrombin-induced fibrin generation

Novel therapeutics and emerging technology in haemostasis and thrombosis: highlights from the British society for haemostasis and thrombosis annual meeting

The 2023 annual meeting of the British Society for Haemostasis and Thrombosis (BSHT) was held in Birmingham, United Kingdom. The theme of this year's meeting was novel therapeutics and emerging technology. Here, the exciting research presented at the meeting is discussed

Trivalent nanobody-based ligands mediate powerful activation of GPVI, CLEC-2 and PEAR1 in human platelets whereas FcγRIIA requires a tetravalent ligand

Background: Clustering of the glycoprotein receptors GPVI, CLEC-2, FcγRIIA and PEAR1 leads to powerful activation of platelets through phosphorylation of tyrosine in their cytosolic tails and initiation of downstream signalling cascades. GPVI, CLEC-2 and FcγRIIA signal through YxxL motifs that activate Syk. PEAR1 signals through a YxxM motif that activates phosphoinositide 3-kinase (PI3K). Current ligands for these receptors have an undefined valency and show significant batch variation and, for some, uncertain specificity. Objectives: We have raised nanobodies against each of these receptors and multimerised them to identify the minimum number of epitopes to achieve robust activation of human platelets. Methods: Divalent and trivalent nanobodies were generated using a flexible glycine-serine linker. Tetravalent nanobodies utilise a mouse Fc domain (IgG2a, which does not bind to FcγRIIA) to dimerise the divalent nanobody. Ligand affinity measurements were determined by surface plasmon resonance. Platelet aggregation, ATP secretion and protein phosphorylation were analysed using standardised methods. Results: Multimerisation of the nanobodies led to a stepwise increase in affinity with divalent and higher-order nanobody oligomers having sub-nanomolar affinity. The trivalent nanobodies to GPVI, CLEC-2 and PEAR1 stimulated powerful and robust platelet aggregation, secretion and protein phosphorylation at low nanomolar concentrations. A tetravalent nanobody was required to activate FcγRIIA with the concentration-response relationship showing a greater variability and reduced sensitivity compared to the other nanobody-based ligands, despite a sub-nanomolar binding affinity. Conclusions: The multivalent nanobodies represent a series of standardised, potent agonists for platelet glycoprotein receptors. They have applications as research tools and in clinical assays

The Value of Success: Acquiring Gains, Avoiding Losses, and Simply Being Successful

A large network of spatially contiguous, yet anatomically distinct regions in medial frontal cortex is involved in reward processing. Although it is clear these regions play a role in critical aspects of reward-related learning and decision-making, the individual contributions of each component remains unclear. We explored dissociations in reward processing throughout several key regions in the reward system and aimed to clarify the nature of previously observed outcome-related activity in a portion of anterior medial orbitofrontal cortex (mOFC). Specifically, we tested whether activity in anterior mOFC was related to processing successful actions, such that this region would respond similarly to rewards with and without tangible benefits, or whether this region instead encoded only quantifiable outcome values (e.g., money). Participants performed a task where they encountered monetary gains and losses (and non-gains and non-losses) during fMRI scanning. Critically, in addition to the outcomes with monetary consequences, the task included trials that provided outcomes without tangible benefits (participants were simply told that they were correct or incorrect). We found that anterior mOFC responded to all successful outcomes regardless of whether they carried tangible benefits (monetary gains and non-losses) or not (controls). These results support the hypothesis that anterior mOFC processes rewards in terms of a common currency and is capable of providing reward-based signals for everything we value, whether it be primary or secondary rewards or simply a successful experience without objectively quantifiable benefits

Effect of Hydrocortisone on Mortality and Organ Support in Patients With Severe COVID-19: The REMAP-CAP COVID-19 Corticosteroid Domain Randomized Clinical Trial.

Importance: Evidence regarding corticosteroid use for severe coronavirus disease 2019 (COVID-19) is limited. Objective: To determine whether hydrocortisone improves outcome for patients with severe COVID-19. Design, Setting, and Participants: An ongoing adaptive platform trial testing multiple interventions within multiple therapeutic domains, for example, antiviral agents, corticosteroids, or immunoglobulin. Between March 9 and June 17, 2020, 614 adult patients with suspected or confirmed COVID-19 were enrolled and randomized within at least 1 domain following admission to an intensive care unit (ICU) for respiratory or cardiovascular organ support at 121 sites in 8 countries. Of these, 403 were randomized to open-label interventions within the corticosteroid domain. The domain was halted after results from another trial were released. Follow-up ended August 12, 2020. Interventions: The corticosteroid domain randomized participants to a fixed 7-day course of intravenous hydrocortisone (50 mg or 100 mg every 6 hours) (n = 143), a shock-dependent course (50 mg every 6 hours when shock was clinically evident) (n = 152), or no hydrocortisone (n = 108). Main Outcomes and Measures: The primary end point was organ support-free days (days alive and free of ICU-based respiratory or cardiovascular support) within 21 days, where patients who died were assigned -1 day. The primary analysis was a bayesian cumulative logistic model that included all patients enrolled with severe COVID-19, adjusting for age, sex, site, region, time, assignment to interventions within other domains, and domain and intervention eligibility. Superiority was defined as the posterior probability of an odds ratio greater than 1 (threshold for trial conclusion of superiority >99%). Results: After excluding 19 participants who withdrew consent, there were 384 patients (mean age, 60 years; 29% female) randomized to the fixed-dose (n = 137), shock-dependent (n = 146), and no (n = 101) hydrocortisone groups; 379 (99%) completed the study and were included in the analysis. The mean age for the 3 groups ranged between 59.5 and 60.4 years; most patients were male (range, 70.6%-71.5%); mean body mass index ranged between 29.7 and 30.9; and patients receiving mechanical ventilation ranged between 50.0% and 63.5%. For the fixed-dose, shock-dependent, and no hydrocortisone groups, respectively, the median organ support-free days were 0 (IQR, -1 to 15), 0 (IQR, -1 to 13), and 0 (-1 to 11) days (composed of 30%, 26%, and 33% mortality rates and 11.5, 9.5, and 6 median organ support-free days among survivors). The median adjusted odds ratio and bayesian probability of superiority were 1.43 (95% credible interval, 0.91-2.27) and 93% for fixed-dose hydrocortisone, respectively, and were 1.22 (95% credible interval, 0.76-1.94) and 80% for shock-dependent hydrocortisone compared with no hydrocortisone. Serious adverse events were reported in 4 (3%), 5 (3%), and 1 (1%) patients in the fixed-dose, shock-dependent, and no hydrocortisone groups, respectively. Conclusions and Relevance: Among patients with severe COVID-19, treatment with a 7-day fixed-dose course of hydrocortisone or shock-dependent dosing of hydrocortisone, compared with no hydrocortisone, resulted in 93% and 80% probabilities of superiority with regard to the odds of improvement in organ support-free days within 21 days. However, the trial was stopped early and no treatment strategy met prespecified criteria for statistical superiority, precluding definitive conclusions. Trial Registration: ClinicalTrials.gov Identifier: NCT02735707