Early predictive value of platelet function for clinical outcome in sepsis

OBJECTIVE

Sepsis is the leading course of morbidity and mortality in critically ill patients. This study aimed to evaluate the predictive value of the platelet aggregation for mortality in patients with sepsis. In addition, the relationship between impaired mitochondria and the platelet aggregation was explored.

METHOD

This was a prospective, observational cohort study. The platelet aggregation rate in response to adenosine diphosphate (ADP) was assessed. The primary outcome was 28-day mortality. Platelet mitochondrial parameters, including adenosine triphosphate(ATP), mitochondrial membrane potential (MMP) and mitochondrial permeability transition pore (mPTP) opening, were measured. Platelet mitochondrial ultrastructure was observed using transmission electron microscopy.

RESULTS

86 patients with 65 survivors and 21 non-survivors were enrolled. Platelets of non-survivors with sepsis were hyporesponsive to ADP, in terms of maximal aggregation rate (P < 0.001). Receiver operating characteristic curves analysis demonstrated that the AUC estimated 28-day mortality for platelet aggregation rate was 0.814. At the optimal cut-off value of 35.8% for platelet aggregation rate, the sensitivity was 86.2% and the specificity was 66.7%. Kaplan-Meier analysis showed that a platelet aggregation rate of less than 35.8% was associated closely with poor survival. After adjusting for lactate by Cox regression analysis, platelet aggregation rate was identified as an independent predictor for the probability of 28-day mortality. Compared with survivors, non-survivors showed a significant reduction in platelet ATP and MMP-index (both P < 0.001), and a remarkable increase in mPTP opening (P < 0.001). ATP and MMP-index were positively correlated with platelet aggregation rate (R square=0.75, R square=0.44, respectively).

CONCLUSION

Platelet aggregation rate could be an early predictive biomarker for mortality in sepsis. Impaired platelet mitochondrial activity affects platelet aggregation and correlates with the severity of sepsis.

Small procoagulant platelets in diabetes type 2

BACKGROUND

Strong agonist provocation in vitro creates small procoagulant platelets characterized by down-regulated fibrinogen receptors as judged from surface α_IIbβ₃ activation specific antibody (PAC-1). They further show increased surface Annexin V (binds to platelet membrane phosphatidylserine), lysosomal-associated membrane protein 1 (LAMP-1) (indicates lysosomal release) and exhibit disturbed mitochondria integrity as estimated from mitochondrial transmembrane potential changes. We postulated that some circulating platelets activate continuously thereby forming procoagulant populations in vivo. This study aimed to identify such platelets in diabetes type 2 a condition predisposing for thrombotic events.

METHODS

A linear Percoll™ gradient covering the density span 1.090 to 1.040 kg/L was used to separate whole blood platelets from type 2 diabetic subjects (n = 12) into 17 density subpopulations. The gradient contained theophylline, prostaglandin E₁ and EDTA to prevent platelet activation in vitro. A multi-colour flow cytometer was employed for analysing the characteristics mentioned above for all density separated small-sized platelet subfractions.

RESULTS AND CONCLUSION

Small platelets were enriched in medium-dense subfractions (nos. 10-13) (1.065-1.053 kg/L). Their PAC-1 activities were significant lower (p < 0.001) as compared to other small-sized subpopulations. They further exposed enhanced surface Annexin V and LAMP-1 together with lower mitochondrial transmembrane potentials. In diabetes type 2 such small circulating platelets showed procoagulant features.

Mitochondria and microbiota dysfunction in COVID-19 pathogenesis

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Mitochondria are the hub of cellular oxidative homeostasis.

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Mitochondria are the major source of reactive oxygen species (ROS).

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Extracellular mitochondria are found in blood, in circulating platelets and vesicles.

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COVID-19 pathogenesis is aggravated by the hyper- inflammatory state.

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Inflammation activates events leading to microbiota & mitochondrial oxidative damage.

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Mitochondrial damage contributes to coagulopathy, ferroptosis & microbial dysbiosis.

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Blood & platelet mitochondria dysfunction may accelerate systemic coagulopathy events.

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Targeting mitochondria dysfunction may provide useful therapeutic strategies against COVID-19 pathogenesis.

The COVID-19 pandemic caused by the coronavirus (SARS-CoV-2) has taken the world by surprise into a major crisis of overwhelming morbidity and mortality. This highly infectious disease is associated with respiratory failure unusual in other coronavirus infections. Mounting evidence link the accelerated progression of the disease in COVID-19 patients to the hyper-inflammatory state termed as the “cytokine storm” involving major systemic perturbations. These include iron dysregulation manifested as hyperferritinemia associated with disease severity. Iron dysregulation induces reactive oxygen species (ROS) production and promotes oxidative stress. The mitochondria are the hub of cellular oxidative homeostasis. In addition, the mitochondria may circulate “cell-free” in non-nucleated platelets, in extracellular vesicles and mitochondrial DNA is found in the extracellular space. The heightened inflammatory/oxidative state may lead to mitochondrial dysfunction leading to platelet damage and apoptosis. The interaction of dysfunctional platelets with coagulation cascades aggravates clotting events and thrombus formation. Furthermore, mitochondrial oxidative stress may contribute to microbiota dysbiosis, altering coagulation pathways and fueling the inflammatory/oxidative response leading to the vicious cycle of events.

Here, we discuss various cellular and systemic incidents caused by SARS-CoV-2 that may critically impact intra and extracellular mitochondrial function, and contribute to the progression and severity of the disease. It is crucial to understand how these key modulators impact COVID-19 pathogenesis in the quest to identify novel therapeutic targets that may reduce fatal outcomes of the disease.