Platelet aggregates detected using quantitative phase imaging associate with COVID-19 severity.

BACKGROUND: The clinical spectrum of acute SARS-CoV-2 infection ranges from an asymptomatic to life-threatening disease. Considering the broad spectrum of severity, reliable biomarkers are required for early risk stratification and prediction of clinical outcomes. Despite numerous efforts, no COVID-19-specific biomarker has been established to guide further diagnostic or even therapeutic approaches, most likely due to insufficient validation, methodical complexity, or economic factors. COVID-19-associated coagulopathy is a hallmark of the disease and is mainly attributed to dysregulated immunothrombosis. This process describes an intricate interplay of platelets, innate immune cells, the coagulation cascade, and the vascular endothelium leading to both micro- and macrothrombotic complications. In this context, increased levels of immunothrombotic components, including platelet and platelet-leukocyte aggregates, have been described and linked to COVID-19 severity. METHODS: Here, we describe a label-free quantitative phase imaging approach, allowing the identification of cell-aggregates and their components at single-cell resolution within 30 min, which prospectively qualifies the method as point-of-care (POC) testing. RESULTS: We find a significant association between the severity of COVID-19 and the amount of platelet and platelet-leukocyte aggregates. Additionally, we observe a linkage between severity, aggregate composition, and size distribution of platelets in aggregates. CONCLUSIONS: This study presents a POC-compatible method for rapid quantitative analysis of blood cell aggregates in patients with COVID-19.

The human body produces a series of immune responses when it gets infected with SARS-CoV-2, the virus that causes COVID-19. One of these responses involves platelets, the blood clotting factor sticking to immune cells to form cell aggregates in the bloodstream. We aimed to understand the significance of these cell aggregates in COVID-19 disease progression. A quantitative imaging approach was used to investigate the number and components of these cell aggregates in SARS-CoV-2 infected patient blood. We observed blood from severe COVID-19 patients was associated with higher numbers and specific composition of cell aggregates. Our method can potentially support the risk stratification of severe patients to prevent complications in COVID-19 and other medical disorders, where immune cells are shown to aggregate.

Spotlight on Nerves: Portable Multispectral Optoacoustic Imaging of Peripheral Nerve Vascularization and Morphology.

Various morphological and functional parameters of peripheral nerves and their vascular supply are indicative of pathological changes due to injury or disease. Based on recent improvements in optoacoustic image quality, the ability of multispectral optoacoustic tomography, to investigate the vascular environment and morphology of peripheral nerves is explored in vivo in a pilot study on healthy volunteers in tandem with ultrasound imaging (OPUS). The unique ability of optoacoustic imaging to visualize the vasa nervorum by observing intraneural vessels in healthy nerves is showcased in vivo for the first time. In addition, it is demonstrated that the label-free spectral optoacoustic contrast of the perfused connective tissue of peripheral nerves can be linked to the endogenous contrast of hemoglobin and collagen. Metrics are introduced to analyze the composition of tissue based on its optoacoustic contrast and show that the high-resolution spectral contrast reveals specific differences between nervous tissue and reference tissue in the nerve's surrounding. How this showcased extraction of peripheral nerve characteristics using multispectral optoacoustic and ultrasound imaging could offer new insights into the pathophysiology of nerve damage and neuropathies, for example, in the context of diabetes is discussed.

Tranexamic acid impairs hippocampal synaptic transmission mediated by gamma aminobutyric acid receptor type A.

High-dose application of tranexamic acid (TXA), a widely used antifibrinolytic drug, can cause seizures in patients undergoing surgery. Mechanistically, seizures are considered to arise from an imbalance between inhibitory and excitatory synaptic transmission, whose main transmitters are gamma-aminobutyric acid (GABA) and glutamate. In the present study, we investigated the effects of TXA on neuronal excitability and synaptic transmission in the hippocampus, a structure that plays a pivotal role in human epilepsy. In acute slices of the murine hippocampus, fast depolarization-mediated imaging signals (FDSs) and postsynaptic currents (PSCs) were recorded using voltage-sensitive dye imaging and whole-cell patch clamp technique, respectively. FDSs and PSCs were evoked upon stimulation of the dentate gyrus and Schaffer collateral/associational commissural pathway, respectively. GABAA, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and N-methyl-d-aspartate (NMDA) receptor-mediated postsynaptic currents were isolated pharmacologically. Application of TXA enhanced FDS propagation in the hippocampus. Neither the resting membrane potential of the investigated neurones nor synaptic transmission mediated by AMPA or NMDA receptors was changed by the application of 1mM TXA. In contrast, TXA dose-dependently reduced GABAA receptor-mediated synaptic transmission. TXA induced the inhibition of GABAA receptor-mediated synaptic transmission in the hippocampus with a potency similar to that of its antagonistic properties against GABAA receptors in the basolateral amygdala (Kratzer et al., 2014). Since impairment of GABAergic transmission is a major cause of epileptic seizures, the observed effect might contribute to the proconvulsive properties of TXA.

Tranexamic acid impairs γ-aminobutyric acid receptor type A-mediated synaptic transmission in the murine amygdala: a potential mechanism for drug-induced seizures?

BACKGROUND: Tranexamic acid (TXA) is commonly used to reduce blood loss in cardiac surgery and in trauma patients. High-dose application of TXA is associated with an increased risk of postoperative seizures. The neuronal mechanisms underlying this proconvulsant action of TXA are not fully understood. In this study, the authors investigated the effects of TXA on neuronal excitability and synaptic transmission in the basolateral amygdala. METHODS: Patch clamp recordings and voltage-sensitive dye imaging were performed in acute murine brain slices. Currents through N-methyl-D-aspartate, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, and γ-aminobutyric acid receptor type A (GABAA) receptors were recorded. GABAA receptor-mediated currents were evoked upon electrical stimulation or upon photolysis of caged GABA. TXA was applied at different concentrations. RESULTS: Voltage-sensitive dye imaging demonstrates that TXA (1 mM) reversibly enhances propagation of neuronal excitation (mean ± SEM, 129 ± 6% of control; n = 5). TXA at concentrations of 0.1, 0.3, 1, 5, or 10 mM led to a dose-dependent reduction of GABAA receptor-mediated currents in patch clamp recordings. There was no difference in the half-maximal inhibitory concentration for electrically (0.76 mM) and photolytically (0.84 mM) evoked currents (n = 5 to 9 for each concentration), and TXA did not affect the paired-pulse ratio of GABAA receptor-mediated currents. TXA did not impact glutamatergic synaptic transmission. CONCLUSIONS: This study clearly demonstrates that TXA enhances neuronal excitation by antagonizing inhibitory GABAergic neurotransmission. The results provide evidence that this effect is mediated via postsynaptic mechanisms. Because GABAA receptor antagonists are known to promote epileptiform activity, this effect might explain the proconvulsant action of TXA.