Mechanisms of increased mitochondria-dependent necrosis in Wiskott-Aldrich syndrome platelets.

Wiskott-Aldrich syndrome (WAS) is associated with thrombocytopenia of unclear origin. We investigated real-time cytosolic calcium dynamics, mitochondrial membrane potential and phoszphatidylserine (PS) exposure in single fibrinogen-bound platelets using confocal microscopy. The WAS platelets had higher resting calcium levels, more frequent spikes, and their mitochondria more frequently lost membrane potential followed by PS exposure (in 22.9% of platelets vs 3.9% in controls; P<0.001) after the collapse of the last mitochondria. This phenomenon was inhibited by the mitochondrial permeability transition pore inhibitor cyclosporine A, as well by xestospongin C and lack of extracellular calcium. Thapsigargin by itself caused accelerated cell death in the WAS platelets. The number of mitochondria was predictive of PS exposure: 33% of platelets from WAS patients with fewer than five mitochondria exposed PS, while only 12% did among those that had five or more mitochondria. Interestingly, healthy donor platelets with fewer mitochondria also more readily became procoagulant upon PAR1/PAR4 stimulation. Collapse of single mitochondria led to greater cytosolic calcium increase in WAS platelets if they had one to three mitochondria compared with platelets containing higher numbers. A computer systems biology model of platelet calcium homeostasis showed that smaller platelets with fewer mitochondria could have impaired calcium homeostasis because of higher surface-to-volume ratio and greater metabolic load, respectively. There was a correlation (C=0.81, P<0.02) between the mean platelet size and platelet count in the WAS patients. We conclude that WAS platelets readily expose PS via a mitochondria-dependent necrotic mechanism caused by their smaller size, which could contribute to the development of thrombocytopenia.

Unique Combination of Diamond-Blackfan Anemia and Lynch Syndrome in Adult Female: A Case Report.

We present an extremely rare clinical case of a 38-year-old Russian patient with multiple malignant neoplasms of the uterus and colon caused by genetically confirmed two hereditary diseases: Diamond-Blackfan anemia and Lynch syndrome. Molecular genetic research carried out by various methods (NGS, Sanger sequencing, aCGH, and MLPA) revealed a pathogenic nonsense variant in the MSH6 gene: NM_000179.2: c.742C>T, p.(Arg248Ter), as well as a new deletion of the chromosome 15's locus with the capture of 82,662,932-84,816,747 bp interval, including the complete sequence of the RPS17 gene. The lack of expediency of studying microsatellite instability in endometrial tumors using standard mononucleotide markers NR21, NR24, NR27, BAT25, BAT26 was demonstrated. The estimated prevalence of patients with combination of Diamond-Blackfan anemia and Lynch syndrome in the world is one per 480 million people.

Platelet function and bleeding at different phases of childhood immune thrombocytopenia.

Immune thrombocytopenia (ITP) is believed to be associated with platelet function defects. However, their mechanisms are poorly understood, in particular with regard to differences between ITP phases, patient age, and therapy. We investigated platelet function and bleeding in children with either persistent or chronic ITP, with or without romiplostim therapy. The study included 151 children with ITP, of whom 56 had disease duration less than 12 months (grouped together as acute/persistent) and 95 were chronic. Samples of 57 healthy children were used as controls, while 5 patients with leukemia, 5 with aplastic anemia, 4 with MYH9-associated thrombocytopenia, and 7 with Wiskott-Aldrich syndrome were used as non-ITP thrombocytopenia controls. Whole blood flow cytometry revealed that platelets in both acute/persistent and chronic ITP were increased in size compared with healthy donors. They were also pre-activated as assessed by PAC1, CD62p, cytosolic calcium, and procoagulant platelet levels. This pattern was not observed in other childhood thrombocytopenias. Pre-activation by CD62p was higher in the bleeding group in the chronic ITP cohort only. Romiplostim treatment decreased size and pre-activation of the patient platelets, but not calcium. Our data suggest that increased size, pre-activation, and cytosolic calcium are common for all ITP platelets, but their association with bleeding could depend on the disease phase.

Platelet function and bleeding in chronic lymphocytic leukemia and mantle cell lymphoma patients on ibrutinib.

BACKGROUND: Therapy with irreversible Bruton's tyrosine kinase inhibitor ibrutinib in chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL) is associated with bleeding. OBJECTIVES: To propose the predictive markers of such bleeding, as well as mechanisms responsible for decreased bleeding at later therapy stages. PATIENTS/METHODS: We investigate platelet functional activity in 50 CLL and 16 MCL patients on ibrutinib using flow cytometry and light transmission aggregometry. RESULTS: Prior to treatment, both patient groups had decreased platelet counts; impaired aggregation with adenosine diphosphate (ADP); and decreased binding of CD62P, PAC1, and annexin V upon stimulation. Bleeding in patients treated with ibrutinib was observed in 28 (56%) CLL patients, who had decreased aggregation with ADP and platelet count before therapy. Their platelet count on therapy did not change, platelet aggregation with ADP steadily improved, and aggregation with collagen first decreased and then increased in anticorrellation with bleeding. Bleeding in MCL was observed in 10 (62%) patients, who had decreased dense granule release before therapy. ADP and ristocetin induced platelet aggregation in ibrutinib-treated MCL patients increased on therapy, while collagen-induced aggregation evolved similarly to CLL patients. CONCLUSIONS: Our results suggest that ibrutinib-dependent bleeding in CLL patients involves three mechanisms: decreased platelet count (the most important discriminator between bleeding and non-bleeding patients), impaired platelet response to ADP caused by CLL, and inhibition by ibrutinib. Initially, ibrutinib shifts the balance to bleeding, but then it is restored because of the improved response to ADP.

Bleeding tendency and platelet function during treatment with romiplostim in children with severe immune thrombocytopenic purpura.

It has been suggested that platelet function in chronic immune thrombocytopenic purpura (ITP) may be abnormal. Thrombopoietin mimetics used for treatment can affect it, but the data remain limited. We investigated platelet function of 20 children diagnosed with severe ITP (aged 1-16 years, 12 females and eight males). Platelet functional activity in whole blood was characterized by flow cytometry before and after stimulation with SFLLRN plus collagen-related peptide. Levels of CD42b, PAC1, and CD62P, but not CD61 or annexin V, were significantly increased (P < 0.05) in resting platelets of patients before treatment compared with healthy donors. On average, PAC1 and CD62P in patients after activation were also significantly elevated, although some patients failed to activate integrins. Romiplostim (1-15 µg/kg/week s.c.) was prescribed to seven patients, with clinical improvement in six. Interestingly, one patient had clinical improvement without platelet count increase. Eltrombopag (25-75 mg/day p.o.) was given to four patients, with positive response in one. Others switched to romiplostim, with one stable positive response, one unstable positive response, and one non-responding. Platelet quality improved with romiplostim treatment, and their parameters approached the normal values. Our results suggest that platelets in children with severe ITP are pre-activated and abnormal, but improve with treatment.