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Thrombosis and bleeding are devastating adverse events in patients supported with blood-contacting medical devices (BCMDs). In this study, we delineated that high non-physiological shear stress (NPSS) caused platelet dysfunction that may contribute to both thrombosis and bleeding. Human blood was subjected to NPSS with short exposure time. Levels of platelet surface GPIbα and GPVI receptors as well as activation level of GPIIb/IIIa in NPSS-sheared blood were examined with flow cytometry. Adhesion of sheared platelets on fibrinogen, von Willibrand factor (VWF), and collagen was quantified with fluorescent microscopy. Ristocetin- and collagen-induced platelet aggregation was characterized by aggregometry. NPSS activated platelets in a shear and exposure time-dependent manner. The number of activated platelets increased with increasing levels of NPSS and exposure time, which corresponded well with increased adhesion of sheared platelets on fibrinogen. Concurrently, NPSS caused shedding of GPIbα and GPVI in a manner dependent on shear and exposure time. The loss of intact GPIbα and GPVI increased with increasing levels of NPSS and exposure time. The number of platelets adhered on VWF and collagen decreased with increasing levels of NPSS and exposure time, respectively. The decrease in the number of platelets adhered on VWF and collagen corresponded well with the loss in GPIbα and GPVI on platelet surface. Both ristocetin- and collagen-induced platelet aggregation in sheared blood decreased with increasing levels of NPSS and exposure time. The study clearly demonstrated that high NPSS causes simultaneous platelet activation and receptor shedding, resulting in a paradoxical effect on platelet function via two distinct mechanisms. The results from the study suggested that the NPSS could induce the concurrent propensity for both thrombosis and bleeding in patients. [ABSTRACT FROM AUTHOR]

Blood can become hypercoagulable by shear-induced platelet activation and generation of microparticles. It has been reported that nonphysiological shear stress (NPSS) could induce shedding of platelet receptor glycoprotein (GP) Iba, which may result in an opposite effect to hemostasis. The aim of this study was to investigate the influence of the NPSS on platelets and von Willebrand factor (vWF). Human blood was exposed to two levels of NPSS (25 Pa, 125 Pa) with an exposure time of 0.5 s, generated by using a novel blood-shearing device. Platelet activation (P-selectin expression, GPIIb/IIIa activation and generation of microparticles) and shedding of three platelet receptors (GPIbα, GPVI, GPIIb/IIIa) in sheared blood were quantified using flow cytometry. Aggregation capacity of sheared blood induced by ristocetin and collagen was evaluated using an aggregometer. Shear-induced vWF damage was characterized with Western blotting. Consistent with the published data, the NPSS caused significantly more platelets to become activated with increasing NPSS level. Meanwhile, the NPSS induced the shedding of platelet receptors. The loss of the platelet receptors increased with increasing NPSS level. The aggregation capacity of sheared blood induced by ristocetin and collagen decreased. There was a loss of high molecular weight multimers (HMWMs) of vWF in sheared blood. These results suggest that the NPSS induced a paradoxical effect. More activated platelets increase the risk of thrombosis, while the reduction in platelet receptors and the loss of HMWM-vWF increased the propensity of bleeding. The finding might provide a new perspective to understand thrombosis and acquired bleeding disorder in patients supported with blood contacting medical devices. [ABSTRACT FROM AUTHOR]

Non-surgical bleeding (NSB) is the most common clinical complication among heart failure (HF) patients supported by continuous-flow left ventricular assist devices (CF-LVADs). Understanding the role of platelet functionality contributing to NSB after CF-LVAD implantation is crucial for prevention and management of this adverse event. The aim of this study was to examine the role of intraplatelet reactive oxygen species (ROS) and platelet damage on the incidence of bleeding events after CF-LVAD implantation in HF patients. We recruited 25 HF patients implanted with CF-LVADs and 11 healthy volunteers as the control. Intraplatelet ROS generation, platelet mitochondrial damage and platelet apoptosis were quantified by flow cytometry. Among 25 patients, 8 patients developed non-surgical bleeding within one month after CF-LVAD implantation. Intraplatelet ROS, depolarized and apoptotic platelet were found to be pre-existing conditions in all baseline samples of the 25 HF patients when compared to the healthy volunteers. There was no significant difference in the levels of ROS between the non-bleeder and the bleeder groups prior to CF-LVAD implantation, although we noticed 2-fold and 1.5-fold rise in depolarized and apoptotic platelets, respectively, in the bleeder group compared to those in the non-bleeder group. Post implant levels of intraplatelet ROS, depolarized and apoptotic platelets increased and remained elevated in the bleeder group, whereas periodic decreases were noticed in the non-bleeder group, suggesting the potential role of platelet damage on bleeding incidence. ROS generation after CF-LVAD implantation positively associated with platelet apoptosis (ρ = 0.4263,p = 0.0023) and depolarized platelets (ρ = 0.4774,p = 0.0002), especially the latter. In conclusion, elevated intraplatelet ROS and platelet damage may be linked to the NSB among HF patients supported by CF-LVAD. These results provide mechanistic insights into the bleeding complication in patients with CF-LVAD support. [ABSTRACT FROM PUBLISHER]

Introduction The structural integrity of platelet receptors is essential for platelets to function normally in hemostasis and thrombosis in response to physiological and pathological stimuli. The aim of this study was to examine the shedding of two key platelet receptors, glycoprotein (GP) Iba and GPVI, after exposed to the non-physiological high shear stress environment which commonly exists in blood contacting medical devices and stenotic blood vessels. Materials and Methods In this in vitro experiment, we exposed healthy donor blood in our specially designed blood shearing device to three high shear stress levels (150, 225, 300 Pa) in combination with two short exposure time conditions (0.05 and 0.5 sec.). The expression and shedding of platelet GPIba and GPVI receptors in the sheared blood samples were characterized using flow cytometry. The ability of platelet aggregation induced by ristocetin and collagen related to GPIba and GPVI in the sheared blood samples, respectively, was evaluated by aggregometry. Results and Conclusions Compared to the normal blood, the surface expression of platelet GPIba and GPVI in the sheared blood significantly decreased with increasing shear stress and exposure time. Moreover, the platelet aggregation induced by ristocetin and collagen reduced remarkably in a similar fashion. In summary non-physiological high shear stresses with short exposure time can induce shedding of platelet GPIba and GPVI receptors, which may lead platelet dysfunction and influence the coagulation system. This study may provide a mechanistic insight into the platelet dysfunction and associated bleeding complication in patients supported by certain blood contacting medical devices. Highlights • High shear stress with short exposure time induces platelet receptors shedding. Non-physiological high shear stress induces reduction of platelet aggregation. • High shear stress in VADs is related with bleeding complication in patients. [ABSTRACT FROM AUTHOR]

Stroke continues to be a major adverse event in advanced congestive heart failure (CHF) patients after continuous-flow left ventricular assist device (CF-LVAD) implantation. Abnormalities in mitochondrial oxidative phosphorylation (OxPhos) have been critically implicated in the pathogenesis of neurodegenerative diseases and cerebral ischemia. We hypothesize that prior stroke may be associated with systemic mitochondrial OxPhos abnormalities, and impaired more in post-CF-LVAD patients with risk of developing new stroke. We studied 50 CF-LVAD patients (25 with prior stroke, 25 without); OxPhos complex proteins (complex I [C.I]-complex V [C.V]) were measured in blood leukocytes. Both at baseline (pre-CF-LVAD) and postoperatively (post-CF-LVAD), the prior-stroke group had significantly lower C.I, complex II (C.II), complex IV (C.IV), and C.V proteins when compared to the no-prior-stroke group. Oxidative phosphorylation proteins were significantly decreased in prior-stroke group at post-CF-LVAD compared to pre-CF-LVAD. Machine learning Least Absolute Shrinkage and Selection Operator (LASSO) and Random Forest modeling identified six prognostic factors that predicted postoperative stroke with an area under the receiver operating characteristic (ROC) curve (AUC) of 0.93. Oxidative phosphorylation protein reduction appeared to be associated with the new stroke after implantation. Our study found for the first time the existence of mitochondrial dysfunction at the peripheral level in CHF patients with prior ischemic stroke even before CF-LVAD implantation. The changes in OxPhos protein expression could serve as biomarkers in predicting new post-CF-LVAD strokes., Competing Interests: Disclosure: The authors have no conflicts of interest to report., (Copyright © ASAIO 2024.)

This study investigated cardiac stress and mitochondrial oxidative phosphorylation (OxPhos) in human donation after circulatory death (DCD) hearts regarding warm ischemic time (WIT) and subsequent cold storage and compared them with that of human brain death donor (DBD) hearts. A total of 24 human hearts were procured for the research study-6 in the DBD group and 18 in the DCD group. DCD group was divided into three groups ( n = 6) based on different WITs (20, 40, and 60 min). All hearts received del Nido cardioplegia before being placed in normal saline cold storage for 6 h. Left ventricular biopsies were performed at hours 0 , 2 , 4 , and 6 . Cardiac stress [nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits: 47-kDa protein of phagocyte oxidase (p47 phox ), 91-kDa glycoprotein of phagocyte oxidase (gp91 phox )] and mitochondrial oxidative phosphorylation [OxPhos, complex I (NADH dehydrogenase) subunit of ETC (CI)-complex V (ATP synthase) subunit of ETC (CV)] proteins were measured in cardiac tissue and mitochondria respectively. Modulation of cardiac stress and mitochondrial dysfunction were observed in both DCD and DBD hearts. However, DCD hearts suffered more cardiac stress (overexpressed NADPH oxidase subunits) and diminished mitochondrial OxPhos than DBD hearts. The severity of cardiac stress and impaired oxidative phosphorylation in DCD hearts correlated with the longer WIT and subsequent cold storage time. More drastic changes were evident in DCD hearts with a WIT of 60 min or more. Activation of NADPH oxidase via overproduction of p47 phox and gp91 phox proteins in cardiac tissue may be responsible for cardiac stress leading to diminished mitochondrial oxidative phosphorylation. These protein changes can be used as biomarkers for myocardium damage and might help assess DCD and DBD heart transplant suitability. NEW & NOTEWORTHY First human DCD heart research studied cardiac stress and mitochondrial dysfunction concerning WIT and the efficacy of del Nido cardioplegia as an organ procurement solution and subsequent cold storage. Mild to moderate cardiac stress and mitochondrial dysfunction were noticed in DCD hearts with WIT 20 and 40 min and cold storage for 4 and 2 h, respectively. These changes can serve as biomarkers, allowing interventions to preserve mitochondria and extend WIT in DCD hearts.