SciCombinator

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Concept: Platelet

188

Discovering the unintended ‘off-targets’ that predict adverse drug reactions is daunting by empirical methods alone. Drugs can act on several protein targets, some of which can be unrelated by conventional molecular metrics, and hundreds of proteins have been implicated in side effects. Here we use a computational strategy to predict the activity of 656 marketed drugs on 73 unintended ‘side-effect’ targets. Approximately half of the predictions were confirmed, either from proprietary databases unknown to the method or by new experimental assays. Affinities for these new off-targets ranged from 1 nM to 30 μM. To explore relevance, we developed an association metric to prioritize those new off-targets that explained side effects better than any known target of a given drug, creating a drug-target-adverse drug reaction network. Among these new associations was the prediction that the abdominal pain side effect of the synthetic oestrogen chlorotrianisene was mediated through its newly discovered inhibition of the enzyme cyclooxygenase-1. The clinical relevance of this inhibition was borne out in whole human blood platelet aggregation assays. This approach may have wide application to de-risking toxicological liabilities in drug discovery.

Concepts: Scientific method, Pharmacology, Blood, Chemotherapy, Platelet, Aspirin, Adverse drug reaction, Iatrogenesis

175

Type 2 diabetes is known to cause endothelial activation resulting in the secretion of von Willebrand factor (VWF). We have shown that levels of VWF in a glycoprotein Ib-binding conformation are increased in specific clinical settings. The aim of the current study is to investigate whether active VWF levels increase during aging and the development of diabetes within the population of patients suffering from type 2 diabetes. Patients and controls were divided into two groups based on age: older and younger than 60 years of age. VWF antigen, VWF propeptide, VWF activation factor and total active VWF were measured. Patients older than 60 years of age had increased levels of total active VWF, VWF activation factor and VWF propeptide compared to younger patients and controls. All measured VWF parameters were associated with age in diabetic patients. Total active VWF and VWF propeptide correlated with the period of being diagnosed with diabetes. Regression analyses showed that especially the VWF activation factor was strongly associated with diabetes in patients older than 60 years of age. In conclusion, we found that the conformation of VWF could be involved in the disease process of diabetes and that the VWF in a glycoprotein Ib-binding conformation could play a role as risk marker during the development of diabetes in combination with an increase in age. Our study shows that the active quality of VWF was more important than the quantity.

Concepts: Insulin, Diabetes mellitus type 2, Diabetes mellitus, Platelet, Von Willebrand factor, Von Willebrand disease, Heyde's syndrome, Weibel-Palade body

171

Silver nanoparticles supported on nanoscale silicate platelets (AgNP/NSP) possess interesting properties, including a large surface area and high biocide effectiveness. The nanohybrid of AgNP/NSP at a weight ratio 7/93 contains 5-nm Ag particles supported on the surface of platelets with dimensions of approximately 80×80×1 nm(3). The nanohybrid expresses a trend of lower cytotoxicity at the concentration of 8.75 ppm Ag and low genotoxicity. Compared with conventional silver ions and the organically dispersed AgNPs, the nanohybrid promotes wound healing. We investigated overall wound healing by using acute burn and excision wound healing models. Tests on both infected wound models of mice were compared among the AgNP/NSP, polymer-dispersed AgNPs, the commercially available Aquacel, and silver sulfadiazine. The AgNP/NSP nanohybrid was superior for wound appearance, but had similar wound healing rates, vascular endothelial growth factor (VEGF)-A levels and transforming growth factor (TGF)-β1 expressions to Aquacel and silver sulfadiazine.

Concepts: Wound healing, Angiogenesis, Coagulation, Platelet, Nanotechnology, Silver, Surface area

171

MicroRNAs (miRNAs) are small, non-coding RNAs that regulate various biological processes, primarily through interaction with messenger RNAs. The levels of specific, circulating miRNAs in blood have been shown to associate with various pathological conditions including cancers. These miRNAs have great potential as biomarkers for various pathophysiological conditions. In this study we focused on different sample types' effects on the spectrum of circulating miRNA in blood. Using serum and corresponding plasma samples from the same individuals, we observed higher miRNA concentrations in serum samples compared to the corresponding plasma samples. The difference between serum and plasma miRNA concentration showed some associations with miRNA from platelets, which may indicate that the coagulation process may affect the spectrum of extracellular miRNA in blood. Several miRNAs also showed platform dependent variations in measurements. Our results suggest that there are a number of factors that might affect the measurement of circulating miRNA concentration. Caution must be taken when comparing miRNA data generated from different sample types or measurement platforms.

Concepts: Gene, Blood, RNA, MicroRNA, Coagulation, Messenger RNA, Platelet, Antagomir

170

Adenosine diphosphate (ADP) is a critical regulator of platelet activation, mediating its actions through two G protein-coupled receptors, the P2Y(1) and P2Y(12) purinoceptors. Recently, we demonstrated that P2Y(1) and P2Y(12) purinoceptor activities are rapidly and reversibly modulated in human platelets, revealing that the underlying mechanism requires receptor internalization and subsequent trafficking as an essential part of this process. In this study we investigated the role of the small GTP-binding protein ADP ribosylation factor 6 (ARF6) in the internalization and function of P2Y(1) and P2Y(12) purinoceptors in human platelets. ARF6 has been implicated in the internalization of a number of GPCRs, although its precise molecular mechanism in this process remains unclear. In this study we show that activation of either P2Y(1) or P2Y(12) purinoceptors can stimulate ARF6 activity. Further blockade of ARF6 function either in cell lines or human platelets blocks P2Y purinoceptor internalization. This blockade of receptor internalization attenuates receptor resensitization. Furthermore, we demonstrate that Nm23-H1, a nucleoside diphosphate (NDP) kinase regulated by ARF6 which facilitates dynamin-dependent fission of coated vesicles during endocytosis, is also required for P2Y purinoceptor internalization. These data describe a novel function of ARF6 in the internalization of P2Y purinoceptors and demonstrate the integral importance of this small GTPase upon platelet ADP receptor function.

Concepts: Signal transduction, Adenosine triphosphate, Cell biology, Platelet, G protein-coupled receptor, Metabotropic glutamate receptor, Adenosine diphosphate, ADP ribosylation factor

169

The underlying cause of thrombosis in a large protein C (PC) deficient Vermont kindred appears to be multicausal and not explained by PC deficiency alone. We evaluated the contribution of coagulation factors to thrombin generation in this population utilizing a mathematical model that incorporates a mechanistic description of the PC pathway. Thrombin generation profiles for each individual were generated with and without the contribution of the PC pathway. Parameters that describe thrombin generation: maximum level (MaxL) and rate (MaxR), their respective times (TMaxL, TMaxR), area under the curve (AUC) and clotting time (CT) were examined in individuals ± PC mutation, ± prothrombin G20210A polymorphism and ± thrombosis history (DVT or PE). This family (n = 364) is shifted towards greater thrombin generation relative to the mean physiologic control. When this family was analyzed with the PC pathway, our results showed that: carriers of the PC mutation (n = 81) had higher MaxL and MaxR and greater AUC (all p<0.001) than non-carriers (n = 283); and individuals with a DVT and/or PE history (n = 13) had higher MaxL (p = 0.005) and greater AUC (p<0.001) than individuals without a thrombosis history (n = 351). These differences were further stratified by gender, with women in all categories generating more thrombin than males. These results show that all individuals within this family with or without PC deficiency have an increased baseline procoagulant potential reflective of increased thrombin generation. In addition, variations within the plasma composition of each individual can further segregate out increased procoagulant phenotypes, with gender-associated plasma compositional differences playing a large role.

Concepts: Blood, Coagulation, Platelet, Warfarin, Protein C, Factor V, Thrombin, Thrombophilia

168

Complex formation between coagulation factor VIII (FVIII) and von Willebrand factor (VWF) is of critical importance to protect FVIII from rapid in vivo clearance and degradation. We have now employed a chemical footprinting approach to identify regions on VWF involved in FVIII binding. To this end, lysine amino acid residues of VWF were chemically modified in the presence of FVIII or activated FVIII(a), which does not bind VWF. Nano-LC-mass spectrometry analysis showed that the lysine residues of almost all identified VWF peptides were not differentially modified upon incubation of VWF with FVIII or FVIIIa. However, Lys773 of peptide Ser766-Leu774 was protected from chemical modification in the presence of FVIII. In addition, peptide Ser764-Arg782, which comprises the first 18 amino acid residues of mature VWF, showed a differential modification of both Lys773 and the alpha amino group of Ser764. To verify the role of Lys773 and the N-terminal Ser764 for FVIII binding, we employed VWF variants in which either Lys773 or Ser764 was replaced by an alanine. Surface plasmon resonance analysis and competition studies revealed that VWF-K773A exhibits reduced binding to FVIII and FVIII light chain, which harbors the VWF binding site. In contrast, VWF-S764A revealed more effective binding to FVIII and FVIII light chain as compared to WT-VWF. The results of our study show that the N-terminus of VWF is critical for the interaction with FVIII, and that the residues Ser764 and Lys773 have an opposite role in the binding mechanism.

Concepts: Protein, Amino acid, Platelet, Von Willebrand factor, Von Willebrand disease, Factor VIII, Surface plasmon resonance, Lysine

168

Background. The treatment of choice in steroid-resistant immune thrombocytopenia is still controversial, due to the recent advent of new drugs (anti-CD20 antibodies and thrombopoietin mimetics) which have encouraged a generalized tendency to delay splenectomy. Consequently, the importance to define the efficacy and safety of splenectomy in the long-term is substantial. Patients and Methods. We retrospectively analyzed the data of 233 patients affected by immune thrombocytopenia, who underwent splenectomy between 1959 and 2001, in 6 European hematological Institutions and have now a minimum follow-up of 10 years from surgery. Results. Of the 233 patients, 180 (77%) achieved a complete response and 26 (11%) a response. Sixty-eight out of 206 (33%) responsive patients relapsed, mostly (75%) within 4 years from first response. In 92 patients (39.5%), further treatment was required after splenectomy, which was effective in 76 cases (83%). In 138 patients (59%) response was maintained, free of any treatment, at last contact. No significant association between baseline characteristics and likelihood of stable response was found. Overall, 73 (31%) and 58 (25%) patients experienced at least one infectious or hemorrhagic complication, which were fatal in 2 and 3 patients, respectively. A stable response to splenectomy was associated with a lower rate of infections (p=0.004) and hemorrhages (p<0.0001). Thrombosis developed in 18 patients (8%), fatal in 4. Conclusions. Splenectomy achieved a long-term stable responses in around 60% of cases. Complications mainly affected non-responding patients and were fatal in a minority of the cases.

Concepts: Immune system, Antibody, Blood, Retrospective, Platelet, Leukemia, Bleeding, Idiopathic thrombocytopenic purpura

167

BACKGROUND: Brazilin, isolated from the heartwood of Caesalpinia sappan L., has been shown to possess multiple pharmacological properties. METHODS: In this study, platelet aggregation, flow cytometry, immunoblotting analysis, and electron spin resonance (ESR) spectrometry were used to investigate the effects of brazilin on platelet activation ex vivo. Moreover, fluorescein sodium-induced platelet thrombi of mesenteric microvessels was also used in in vivo study. RESULTS: We demonstrated that relatively low concentrations of brazilin (1 to 10 muM) potentiated platelet aggregation induced by collagen (0.1 mug/ml) in washed human platelets. Higher concentrations of brazilin (20 to 50 muM) directly triggered platelet aggregation. Brazilin-mediated platelet aggregation was slightly inhibited by ATP (an antagonist of ADP). It was not inhibited by yohimbine (an antagonist of epinephrine), by SCH79797 (an antagonist of thrombin protease-activated receptor [PAR] 1), or by tcY-NH2 (an antagonist of PAR 4). Brazilin did not significantly affect FITC-triflavin binding to the integrin alphaIIbbeta3 in platelet suspensions. Pretreatment of the platelets with caffeic acid phenethyl ester (an antagonist of collagen receptors) or JAQ1 and Sam.Q4 monoclonal antibodies raised against collagen receptor glycoprotein VI and integrin alpha2beta1, respectively, abolished platelet aggregation stimulated by collagen or brazilin. The immunoblotting analysis showed that brazilin stimulated the phosphorylation of phospholipase C (PLC)gamma2 and Lyn, which were significantly attenuated in the presence of JAQ1 and Sam.Q4. In addition, brazilin did not significantly trigger hydroxyl radical formation in ESR analysis. An in vivo mouse study showed that brazilin treatment (2 and 4 mg/kg) significantly shortened the occlusion time for platelet plug formation in mesenteric venules. CONCLUSION: To the best of our knowledge, this study provides the first evidence that brazilin acts a novel collagen receptor agonist. Brazilin is a plant-based natural product, may offer therapeutic potential as intended anti-thrombotic agents for targeting of collagen receptors or to be used a useful tool for the study of detailed mechanisms in collagen receptors-mediated platelet activation.

Concepts: Signal transduction, Cell biology, In vivo, Platelet, Receptor antagonist, Serotonin, Inverse agonist, GPVI

167

In this work we investigated the formation, reactivity and anti-platelet activity of various mixed disulfide conjugates of clopidogrel. Our results showed that the production of the active metabolite (AM) from 2-oxoclopidogrel by human liver microsomes (HLMs) is greatly affected by the thiol reductants used. Among the ten thiol compounds tested, glutathione (GSH) is most efficient in producing the AM at a rate of 167 pmoles AM/min/mg HLM. Interestingly, no AM but only the mixed disulfide conjugates were formed in the presence of 6-chloropyridazine-3-thiol (CPT), 2,5-dimethylfuran-3-thiol (DFT), and 3-nitropyridine-2-thiol (NPT). The MS and MS2 spectra of the conjugates of these thiol compounds confirmed the presence of a mixed disulfide bond linkage between the AM and the thiol reductants. Kinetic studies revealed that the mixed disulfide conjugates were capable of exchanging thiols with GSH to release the AM with second order rate constants ranging from 1.2 to 28 M(-1)s(-1). The mixed disulfide conjugates of CPT and NPT showed potent inhibition of platelet aggregation after pre-treatment with 1 mM GSH, confirming that the AM is responsible for the anti-platelet activity of clopidogrel. Collectively, our results provide strong support for a P450-mediated bioactivation mechanism involving the initial formation of a glutathionyl conjugate followed by thiol-disulfide exchange with another GSH molecule to release the AM. Furthermore, the stable mixed disulfide conjugates identified in this study provide a platform to quantitatively generate the therapeutic AM without the need for P450-mediated bioactivation. This property can be further explored in order to overcome the inter-individual variability in clopidogrel therapy.

Concepts: Platelet, Disulfide bond, Glutathione, Sulfur, Cysteine, Thiol, Dithiothreitol, Thiol-disulfide exchange