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Conference paperSarvananthan S, Punjabi PP, Lewis F, et al., 2017,
The distribution and characteristics of endogenous cardiac stem cells in the atria and ventricle of the adult human heart, American College of Cardiology, Publisher: OXFORD UNIV PRESS, Pages: 535-535, ISSN: 0195-668X
Journal articlePirola S, Cheng Z, Jarral OA, et al., 2017,
On the choice of outlet boundary conditions for patient-specific analysis of aortic flow using computational fluid dynamics, Journal of Biomechanics, Vol: 60, Pages: 15-21, ISSN: 1873-2380
Boundary conditions (BCs) are an essential part in computational fluid dynamics (CFD) simulations of blood flow in large arteries. Although several studies have investigated the influence of BCs on predicted flow patterns and hemodynamic wall parameters in various arterial models, there is a lack of comprehensive assessment of outlet BCs for patient-specific analysis of aortic flow. In this study, five different sets of outlet BCs were tested and compared using a subject-specific model of a normal aorta. Phase-contrast magnetic resonance imaging (PC-MRI) was performed on the same subject and velocity profiles extracted from the in vivo measurements were used as the inlet boundary condition. Computational results obtained with different outlet BCs were assessed in terms of their agreement with the PC-MRI velocity data and key hemodynamic parameters, such as pressure and flow waveforms and wall shear stress related indices. Our results showed that the best overall performance was achieved by using a well-tuned three-element Windkessel model at all model outlets, which not only gave a good agreement with in vivo flow data, but also produced physiological pressure waveforms and values. On the other hand, opening outlet BCs with zero pressure at multiple outlets failed to reproduce any physiologically relevant flow and pressure features.
Journal articleSmyth E, Solomon A, Birrell MA, et al., 2017,
Influence of inflammation and nitric oxide upon platelet aggregation following deposition of diesel exhaust particles in the airways., British Journal of Pharmacology, Vol: 174, Pages: 2130-2139, ISSN: 0007-1188
Background and Purpose: Exposure to nanoparticulate pollution has been implicated in platelet-driven thrombotic events such as myocardial infarction. Inflammation and impairment of NO bioavailability have been proposed as potential causative mechanisms. It is unclear, however, whether airways exposure to combustion-derived nanoparticles such as diesel exhaust particles (DEP) or carbon black (CB) can augment platelet aggregation in vivo and the underlying mechanisms remain undefined. We aimed to investigate the effects of acute lung exposure to DEP and CB on platelet activation and the associated role of inflammation and endothelial-derived NO.Experimental Approach: DEP and CB were intratracheally instilled into wild-type (WT) and eNOS−/− mice and platelet aggregation was assessed in vivo using an established model of radio-labelled platelet thromboembolism. The underlying mechanisms were investigated by measuring inflammatory markers, NO metabolites and light transmission aggregometry.Key Results: Platelet aggregation in vivo was significantly enhanced in WT and eNOS−/− mice following acute airways exposure to DEP but not CB. CB exposure, but not DEP, was associated with significant increases in pulmonary neutrophils and IL-6 levels in the bronchoalveolar lavage fluid and plasma of WT mice. Neither DEP nor CB affected plasma nitrate/nitrite concentration and DEP-induced human platelet aggregation was inhibited by an NO donor.Conclusions and Implications: Pulmonary exposure to DEP and subsequent platelet activation may contribute to the reports of increased cardiovascular risk, associated with exposure to airborne pollution, independent of its effects on inflammation or NO bioavailability.
Journal articleKhan E, Ambrose N, Ahnstrom J, et al., 2016,
A low balance between microparticles expressing tissue factor pathway inhibitor and tissue factor is associated with thrombosis in Behçet’s Syndrome, Clinical and Experimental Rheumatology, Vol: 6, ISSN: 1593-098X
Thrombosis is common in Behçet’s Syndrome (BS), and there is a need for better biomarkers for risk assessment. As microparticles expressing Tissue Factor (TF) can contribute to thrombosis in preclinical models, we investigated whether plasma microparticles expressing Tissue Factor (TF) are increased in BS. We compared blood plasma from 72 healthy controls with that from 88 BS patients (21 with a history of thrombosis (Th+) and 67 without (Th−). Using flow cytometry, we found that the total plasma MP numbers were increased in BS compared to HC, as were MPs expressing TF and Tissue Factor Pathway Inhibitor (TFPI) (all p < 0.0001). Amongst BS patients, the Th+ group had increased total and TF positive MP numbers (both p ≤ 0.0002) compared to the Th- group, but had a lower proportion of TFPI positive MPs (p < 0.05). Consequently, the ratio of TFPI positive to TF positive MP counts (TFPI/TF) was significantly lower in Th+ versus Th− BS patients (p = 0.0002), and no patient with a TFPI/TF MP ratio >0.7 had a history of clinical thrombosis. We conclude that TF-expressing MP are increased in BS and that an imbalance between microparticulate TF and TFPI may predispose to thrombosis.
Journal articleLightman S, Taylor SRJ, Bunce C, et al., 2015,
Pegylated interferon-alpha-2b reduces corticosteroid requirement in patients with Behcet's disease with upregulation of circulating regulatory T cells and reduction of Th17, Annals of the Rheumatic Diseases, Vol: 74, Pages: 1138-1144, ISSN: 0003-4967
Objective To determine whether the addition of 26 weeks of subcutaneous peginterferon-α-2b could reduce the requirement for systemic corticosteroids and conventional immunosuppressive medication in patients with Behçet's disease (BD).Methods We conducted a multicentre randomised trial in patients with BD requiring systemic therapy. Patients were randomised to 26 weeks of peginterferon-α-2b in addition to their standard care or to standard care only and followed 6-monthly for 3 years with BD activity scores and quality of life questionnaires. Patients at one centre had blood taken to measure regulatory T cells (Tregs) and Th17 cells.Results 72 patients were included. At months 10–12, while among the entire patient population there was no difference in the corticosteroid dose or immunosuppression use between the treatment groups (adjusted OR 1.04, 95% CI 0.34 to 3.19), post hoc analysis revealed that in patients who were on corticosteroids at baseline the corticosteroid requirement was significantly lower in the peginterferon-α-2b (6.5 (5–15) mg/day) compared with the non-interferon group (10 (8.25–16.5) mg/day, p=0.039). Furthermore, there was a trend towards an improved quality of life that became significant by 36 months (p=0.008). This was associated with a significant rise in Tregs and a decrease in Th17 cells which was still present at 1 year and 6 months after the interferon was stopped. The safety profile was similar with adverse events in 10% in both groups.Conclusions The addition of peginterferon-α-2b to the drug regime of BD patients did not significantly reduce their corticosteroid dose required at 1 year. However, in those on corticosteroids at baseline post hoc analysis demonstrated that the addition of peginterferon-α-2b did result in a significant reduction in corticosteroid dose with a significantly improved quality of life and trend to reduce other required immunosuppressive agents. This effect
Journal articleAmbrose N, Khan E, Ravindran R, et al., 2015,
The exaggerated inflammatory response in behçet's syndrome: Identification of dysfunctional post-transcriptional regulation of the IFN?/CXCL10 (IP-10) pathway, Clinical and Experimental Immunology, Vol: 181, Pages: 427-433, ISSN: 1365-2249
The mechanisms underlying the exaggerated inflammatory response in Behçet's syndrome (BS) remain poorly understood. We investigated the response of CD14+ blood monocytes to interferon (IFN)-γ, focusing on the chemokine CXCL10. Chemokine synthesis and release were analysed at a protein and mRNA level following stimulation with IFN-γ. Findings in BS patients were compared with 25 healthy controls (HC), 15 rheumatoid arthritis (RA) and 15 systemic lupus erythematosus (SLE) disease control patients. BS monocytes produced significantly more CXCL10 protein than HC monocytes from 2 h following IFN-γ stimulation, despite equivalent quantities of mRNA, suggesting more efficient translation. This was significantly more pronounced in BS with high disease activity and in those with ocular and neurological clinical manifestations. The imbalance between CXCL10 protein and mRNA expression was not observed in either RA or SLE patients, and was not seen with other chemokines studied (CXCL9, CXCL11 and CCL2). Furthermore, BS monocytes treated with an alternative stimulant (LPS) did not show abnormal tumour necrosis factor (TNF)-α release. Sucrose density gradients to segregate monocyte CXCL10 mRNA into free RNA or polysome-associated RNA showed equal proportions in BS and HC samples, suggesting that the difference between BS and HC may be due to reduced negative control of CXCL10 translation in BS at a post-initiation level. We conclude that BS monocytes have dysfunctional post-transcriptional regulation of CXCL10 mRNA, resulting in over-expression of CXCL10 protein upon IFN-γ stimulation. As CXCL10 is a chemokine that recruits mononuclear cells, this abnormality may contribute to the exaggerated inflammatory responses that characterizes BS.
Journal articleIqbal MB, Johns M, Cao J, et al., 2014,
PARP-14 combines with tristetraprolin in the selective posttranscriptional control of macrophage tissue factor expression, Blood, Vol: 124, Pages: 3646-3655, ISSN: 0006-4971
Tissue factor (TF) (CD142) is a 47 kDa transmembrane cell surface glycoprotein that triggers the extrinsic coagulation cascade and links thrombosis with inflammation. Although macrophage TF expression is known to be regulated at the RNA level, very little is known about the mechanisms involved. Poly(adenosine 5′-diphosphate [ADP]-ribose)-polymerase (PARP)-14 belongs to a family of intracellular proteins that generate ADP-ribose posttranslational adducts. Functional screening of PARP-14–deficient macrophages mice revealed that PARP-14 deficiency leads to increased TF expression and functional activity in macrophages after challenge with bacterial lipopolysaccharide. This was related to an increase in TF messenger RNA (mRNA) stability. Ribonucleoprotein complex immunoprecipitation and biotinylated RNA pull-down assays demonstrated that PARP-14 forms a complex with the mRNA-destabilizing protein tristetraprolin (TTP) and a conserved adenylate-uridylate-rich element in the TF mRNA 3′ untranslated region. TF mRNA regulation by PARP-14 was selective, as tumor necrosis factor (TNF)α mRNA, which is also regulated by TTP, was not altered in PARP-14 deficient macrophages. Consistent with the in vitro data, TF expression and TF activity, but not TNFα expression, were increased in Parp14−/− mice in vivo. Our study provides a novel mechanism for the posttranscriptional regulation of TF expression, indicating that this is selectively regulated by PARP-14.
Journal articleApostoli GL, Solomon A, Smallwood MJ, et al., 2014,
Role of inorganic nitrate and nitrite in driving nitric oxide-GMP-mediated inhibition of platelet aggregation in vitro and in vivo, Journal of Thrombosis and Haemostasis, Vol: 12, Pages: 1880-1889, ISSN: 1538-7933
BackgroundNitric oxide (NO) is a critical negative regulator of platelets that is implicated in the pathology of thrombotic diseases. Platelets generate NO, but the presence and functional significance of NO synthase (NOS) in platelets is unclear. Inorganic nitrate/nitrite is increasingly being recognized as a source of bioactive NO, although its role in modulating platelets during health and vascular dysfunction is incompletely understood.MethodsWe investigated the functional significance and upstream sources of NO–cGMP signaling events in platelets by using established methods for assessing in vitro and in vivo platelet aggregation, and assessed the bioconversion of inorganic nitrate to nitrite during deficiency of endothelial NOS (eNOS).ResultsThe phosphodiesterase 5 (PDE5) inhibitor sildenafil inhibited human platelet aggregation in vitro. This inhibitory effect was abolished by a guanylyl cyclase inhibitor and NO scavengers, but unaffected by NOS inhibition. Inorganic nitrite drove cGMP-mediated inhibition of human platelet aggregation in vitro and nitrate inhibited platelet function in eNOS−/− mice in vivo in a model of thromboembolic radiolabeled platelet aggregation associated with an enhanced plasma nitrite concentration as compared with wild-type mice.ConclusionsPlatelets generate transient, endogenous cGMP signals downstream of NO that are primarily independent of NOS and may be enhanced by inhibition of PDE5. Furthermore, nitrite can generate transient NO–cGMP signals in platelets. The absence of eNOS leads to enhanced plasma nitrite levels following nitrate administration in vivo, which negatively impacts on platelet function. Our data suggest that inorganic nitrate exerts an antiplatelet effect during eNOS deficiency, and, potentially, that dietary nitrate may reduce platelet hyperactivity during endothelial dysfunction.
Journal articleSmyth E, Solomon A, Vydyanath A, et al., 2014,
Induction and enhancement of platelet aggregation in vitro and in vivo by model polystyrene nanoparticles, Nanotoxicology, Vol: 9, Pages: 356-364, ISSN: 1743-5404
Abstract Nanoparticles (NPs) may come into contact with circulating blood elements including platelets following inhalation and translocation from the airways to the bloodstream or during proposed medical applications. Studies with model polystyrene latex nanoparticles (PLNPs) have shown that NPs are able to induce platelet aggregation in vitro suggesting a poorly defined potential mechanism of increased cardiovascular risk upon NP exposure. We aimed to provide insight into the mechanisms by which NPs may increase cardiovascular risk by determining the impact of a range of concentrations of PLNPs on platelet activation in vitro and in vivo and identifying the signaling events driving NP-induced aggregation. Model PLNPs of varying nano-size (50 and 100 nm) and surface chemistry [unmodified (uPLNP), amine-modified (aPLNP) and carboxyl-modified (cPLNP)] were therefore examined using in vitro platelet aggregometry and an established mouse model of platelet thromboembolism. Most PLNPs tested induced GPIIb/IIIa-mediated platelet aggregation with potencies that varied with both surface chemistry and nano-size. Aggregation was associated with signaling events, such as granule secretion and release of secondary agonists, indicative of conventional agonist-mediated aggregation. Platelet aggregation was associated with the physical interaction of PLNPs with the platelet membrane or internalization. 50 nm aPLNPs acted through a distinct mechanism involving the physical bridging of adjacent non-activated platelets leading to enhanced agonist-induced aggregation in vitro and in vivo. Our study suggests that should they translocate the pulmonary epithelium, or be introduced into the blood, NPs may increase the risk of platelet-driven events by inducing or enhancing platelet aggregation via mechanisms that are determined by their distinct combination of nano-size and surface chemistry.
Journal articleSolomon A, Smyth E, Mitha N, et al., 2013,
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