Highly integrated workflows for exploring cardiovascular conditions: Exemplars of precision medicine in Alzheimer's disease and aortic dissection.

For precision medicine to be implemented through the lens of in silico technology, it is imperative that biophysical research workflows offer insight into treatments that are specific to a particular illness and to a particular subject. The boundaries of precision medicine can be extended using multiscale, biophysics-centred workflows that consider the fundamental underpinnings of the constituents of cells and tissues and their dynamic environments. Utilising numerical techniques that can capture the broad spectrum of biological flows within complex, deformable and permeable organs and tissues is of paramount importance when considering the core prerequisites of any state-of-the-art precision medicine pipeline. In this work, a succinct breakdown of two precision medicine pipelines developed within two Virtual Physiological Human (VPH) projects are given. The first workflow is targeted on the trajectory of Alzheimer's Disease, and caters for novel hypothesis testing through a multicompartmental poroelastic model which is integrated with a high throughput imaging workflow and subject-specific blood flow variability model. The second workflow gives rise to the patient specific exploration of Aortic Dissections via a multi-scale and compliant model, harnessing imaging, computational fluid-dynamics (CFD) and dynamic boundary conditions. Results relating to the first workflow include some core outputs of the multiporoelastic modelling framework, and the representation of peri-arterial swelling and peri-venous drainage solution fields. The latter solution fields were statistically analysed for a cohort of thirty-five subjects (stratified with respect to disease status, gender and activity level). The second workflow allowed for a better understanding of complex aortic dissection cases utilising both a rigid-wall model informed by minimal and clinically common datasets as well as a moving-wall model informed by rich datasets.

Diagnosis of Aortic Graft Infection: A Case Definition by the Management of Aortic Graft Infection Collaboration (MAGIC).

OBJECTIVE/BACKGROUND: The management of aortic graft infection (AGI) is highly complex and in the absence of a universally accepted case definition and evidence-based guidelines, clinical approaches and outcomes vary widely. The objective was to define precise criteria for diagnosing AGI. METHODS: A process of expert review and consensus, involving formal collaboration between vascular surgeons, infection specialists, and radiologists from several English National Health Service hospital Trusts with large vascular services (Management of Aortic Graft Infection Collaboration [MAGIC]), produced the definition. RESULTS: Diagnostic criteria from three categories were classified as major or minor. It is proposed that AGI should be suspected if a single major criterion or two or more minor criteria from different categories are present. AGI is diagnosed if there is one major plus any criterion (major or minor) from another category. (i) Clinical/surgical major criteria comprise intraoperative identification of pus around a graft and situations where direct communication between the prosthesis and a nonsterile site exists, including fistulae, exposed grafts in open wounds, and deployment of an endovascular stent-graft into an infected field (e.g., mycotic aneurysm); minor criteria are localized AGI features or fever ≥38°C, where AGI is the most likely cause. (ii) Radiological major criteria comprise increasing perigraft gas volume on serial computed tomography (CT) imaging or perigraft gas or fluid (≥7 weeks and ≥3 months, respectively) postimplantation; minor criteria include other CT features or evidence from alternative imaging techniques. (iii) Laboratory major criteria comprise isolation of microorganisms from percutaneous aspirates of perigraft fluid, explanted grafts, and other intraoperative specimens; minor criteria are positive blood cultures or elevated inflammatory indices with no alternative source. CONCLUSION: This AGI definition potentially offers a practical and consistent diagnostic standard, essential for comparing clinical management strategies, trial design, and developing evidence-based guidelines. It requires validation that is planned in a multicenter, clinical service database supported by the Vascular Society of Great Britain & Ireland.

Peripheral arterial disease: a literature review.

INTRODUCTION: Peripheral arterial disease (PAD) is a common vascular condition that affects both quality of life and life expectancy with an increased risk of cardiovascular events. SOURCES OF DATA: A literature search was carried out of Pub-Med, MEDLINE, the Cochrane Library and Google Scholar from the establishment of these databases up to February 2012. The search was performed by using the keywords 'peripheral arterial disease' and one of the following words: 'management', 'investigations', 'risk factors', 'epidemiology', 'revascularization', 'cryoplasty', 'atherectomy' and 'gene therapy'. Studies were limited to those published in English language. AREAS OF AGREEMENT: Aggressive risk factors modification is needed to reduce cardiovascular-related mortality in PAD patients. AREAS OF CONTROVERSY: Choice of endovascular or surgical intervention remains controversial in an ever-evolving field. GROWING POINTS: There is a rapid expansion of endovascular technologies aiming to improve the effectiveness of this modality. AREAS TIMELY FOR DEVELOPING RESEARCH: The advances in the fields of gene therapy and therapeutic angiogenesis mean these are potential future treatments. Tissue engineering is a developing area and aims to produce grafts with similar patency and infection profiles to those of autologous material. Further elucidation of the pathophysiology of atherosclerosis is required to provide new targets for pharmacotherapy.

Gene therapy in the treatment of peripheral arterial disease.

BACKGROUND: Peripheral arterial disease remains a significant global health burden despite revolutionary improvements in endovascular techniques over the past decade. The durability of intervention for critical limb ischaemia is poor, and the condition is associated with high morbidity and mortality rates. To address this deficiency, alternative therapeutic options are being explored. Advances in the fields of gene therapy and therapeutic angiogenesis have led to these being advocated as potential future treatments. METHODS: Relevant medical literature from PubMed, Embase, the Cochrane Library and Google Scholar from the inception of these databases to June 2011 was reviewed. RESULTS: Encouraging outcomes in preclinical trials using a variety of proangiogenic growth factors have led to numerous efficacy and safety studies. However, no clinical study has shown significant benefit for gene therapy over placebo. CONCLUSION: Identifying the optimal site for gene delivery, choice of vector and duration of treatment is needed if gene therapy is to become a credible therapeutic option for peripheral arterial disease.

Assessment of the antimicrobial activity of acellular vascular grafts.

Several studies have reported biological vascular grafts to be more resistant to microbial infection than synthetic counterparts in vivo. Indeed, small intestinal submucosa (SIS) materials have previously been reported to be antimicrobial. The aim of this study was to assess the antimicrobial activity and the ability to resist biofilm formation of a novel acellular vascular graft and compare it to commercially available alternatives using a range of organisms: MRSA, MSSA, Staphylococcus epidermidis, Enterococcus faecalis, Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa and Candida albicans. This was achieved using a modified disk diffusion assay and extraction of the materials into solution followed by minimum inhibitory concentration assays. To assess resistance to biofilm formation a novel biofilm assay was developed which compared the total colony forming units (CFU) recovered from each material and identification of the percentage of CFU which were loosely attached, residing within the biofilm or attached to the biomaterial. The results indicated a lack of antimicrobial activity for all materials tested, including SIS. The biological materials were more resistant to the formation of a biofilm compared to Dacron.

Comparative stability of sodium tetradecyl sulphate (STD) and polidocanol foam: impact on vein damage in an in-vitro model.

OBJECTIVES: To compare the half-life of STD and polidocanol air-based foams and the damage they inflict upon human great saphenous vein in an in-vitro model. METHODS: The time for the volume of 3% STD and polidocanol foams to reduce by 10% (T(90)) and 50% (T(50)) was recorded in an incubator at 37 °C. Segments of proximal GSV harvested during varicose vein surgery were filled with foam for 5 or 15 min. Histological analysis determined percentage endothelial cell loss and depth of media injury. RESULTS: Median (±IQR) T(90) and T(50) for polidocanol were 123.3 s (111.7-165.6) and 266.3 s (245.6-383.1) versus 102.03 s (91.1-112) and 213.13 s (201-231.6) for STD (T(90)p = 0.008, T(50)p = 0.004). Median endothelial loss with polidocanol was; 63.5% (62.2-82.8) and 85.9% (83.8-92.5) versus 86.3% (84.8-93.7) and 97.64% (97.3-97.8) for STD after 5 and 15 min (p = 0.076 and p = 0.009). The median depth and % media thickness injured were 0 µm (0-0 µm) and 0% for both assessments with polidocanol versus 37.4 µm (35.3-45.8 and 43.4 µm (42.1-46.7) and 3.5% (3.1-3.6) and 5.3% (3.7-6.0) after 5 and 15 min for STD (p < 0.01 for all comparisons). CONCLUSION: Although polidocanol foam shows greater stability than STD foam perhaps remaining in the vein for longer, endothelial cell loss and damage to the media were significantly greater with STD.

Chronic homocysteine exposure upregulates endothelial adhesion molecules and mediates leukocyte: endothelial cell interactions under flow conditions.

AIMS: Homocysteine upregulates expression of adhesion molecules on endothelial cells which recruits leukocytes and initiates atherosclerosis. Endothelial cells in hyperhomocysteinemic patients are continuously exposed to high levels of homocysteine. This study exposed adult endothelial cells and endothelial cells from immune naïve foetal tissue to homocysteine chronically and studied effects on cellular adhesion molecule expression under static and flow conditions. METHODS: Human umbilical vein endothelial cells (HUVEC) and human saphenous vein endothelial cells (HSVEC) were cultured in medium containing 1 mM dl-homocysteine or l-cysteine for 5-9 days. Proliferation was assessed. Cells were subjected to flowing neutrophils and numbers of tethered, rolled fixed and transmigrated neutrophils on endothelial cells were counted and compared to controls. Immunofluorescence staining with antibodies against Intercellular adhesion molecule-1 (ICAM-1), E-selectin and P-selectin were used to quantify expression. RESULTS: Chronic treatment with 1 mM homocysteine inhibited proliferation of HUVEC and HSVEC. Homocysteine treated cells showed significantly increased expression of ICAM-1, E-selectin and to a lesser extent P-selectin. In both cell types, homocysteine significantly increased interactions between neutrophils and endothelial cells under flow conditions (p < 0.05) while cysteine had no effect. CONCLUSION: Endothelial cells from adult and immune naïve foetal tissue showed similar responses to chronic treatment with homocysteine.

The impact of different concentrations of sodium tetradecyl sulphate and initial balloon denudation on endothelial cell loss and tunica media injury in a model of foam sclerotherapy.

INTRODUCTION: Recanalisation rates (20-32%) 1-3 years after truncal vein foam sclerotherapy (FS) suggest thrombotic occlusion rather than irreversible vein wall injury. This study examines the injury inflicted by sodium tetradecyl sulphate (STD) foam before and after balloon endothelial denudation (BD). METHODS: In 20 patients undergoing great saphenous vein (GSV) stripping 1.5 cm proximal GSV were harvested (controls). The next 1.5 cm were harvested after in situ BD (n = 10) or no denudation (n = 10). These test segments were filled with 1% or 3% STD foam (5 min), flushed and fixed in formalin. Percentage endothelial cell loss (ECL) and tunica media injury were determined (H&E staining) and collagen structure assessed (transmission electron microscopy, TEM). RESULTS: Controls showed no injury. 1% and 3% STD foam caused 86.3% and 92.2% ECL (p < 0.001 versus controls; 1% versus 3%, p = 0.55). Endothelial cells persisted in all sections. BD increased ECL (1%: 96.9%, 3%: 98.1%, p = 0.01) Tunica media injury (smooth muscle vacuolation) was minimal (8.9% (1% STD) and 12% (3% STD) of its depth) and not enhanced by BD (1%: 8.7%, p = 0.93; 3%: 11.3%; p = 0.86). No collagen disruption occurred (TEM). CONCLUSIONS: Balloon denudation increased ECL but did not facilitate tunica media injury. Equivalent injury was inflicted by 1% and 3% STD.

Postconditioning: current controversies and clinical implications.

OBJECTIVES: Postconditioning of ischaemic tissue, via mechanical or pharmacological manipulation, offers an exciting avenue towards amelioration of ischaemia-reperfusion injury. Born from the concept of ischaemic preconditioning, postconditioning is advantageous in that prior knowledge of the ischaemic insult is not required, and thus clinical translation may be further reaching. This review explores the current evidence and controversies in both animal and human studies and multiple organ systems. METHODS: A Medline search was conducted to identify English-language articles with 'postconditioning' as a keyword. Two independent researchers scrutinised the literature search for potentially relevant articles. Reference lists from selected articles were manually searched for further relevant articles. RESULTS AND CONCLUSIONS: Postconditioning has been shown to be successful in reducing ischaemia-reperfusion injury in both animal models and clinical trials. Human studies are presently limited to cardiac studies, but there is scope for research into other organ systems with potential beneficial effects, particularly within the field of vascular surgery where ischaemia-reperfusion occurs by nature of both - the disease and the intervention.

Endothelial progenitor cells as a therapeutic option in peripheral arterial disease.

BACKGROUND: Endothelial progenitor cells (EPC) are a subpopulation of bone-marrow mononuclear cells that are capable of generating new blood vessels in areas of ischaemia or infarction. This review examines the regenerative potential of EPC to ameliorate peripheral ischaemia. METHODS: An online search was done using OVID Medline Search, PubMed, and Cochrane Review Database, for all reviews and original articles in English concerning progenitor or bone-marrow mononuclear cells. RESULTS AND CONCLUSION: There are many controversies in EPC research, especially in the areas of identification, characterization, and therapeutic use. Both animal and human studies have shown benefits from using EPC to combat peripheral arterial and cerebrovascular disease. To bring EPC into wider clinical use, larger controlled clinical trials and better methods of augmenting EPC function and lifespan are required. Until then EPC should be used under robust trial conditions with ethical approval.

Academia and MMC: uncomfortable bed-fellows?

In the changing times of Modernising Medical Careers (MMC), the role of research in training remains unclear. Here we discuss the merits of research in surgical training, new avenues for academia during MMC and the obstacles that trainees may face.

The surgical application of point-of-care haemostasis and platelet function testing.

BACKGROUND: Disordered coagulation complicates many diseases and their treatments, often predisposing to haemorrhage. Conversely, patients with cardiovascular disease who demonstrate antiplatelet resistance may be at increased thromboembolic risk. Prompt identification of these patients facilitates optimization of haemostatic dysfunction. Point-of-care (POC) tests are performed 'near patient' to provide a rapid assessment of haemostasis and platelet function. METHODS: This article reviews situations in which POC tests may guide surgical practice. Their limitations and potential developments are discussed. The paper is based on a Medline and PubMed search for English language articles on POC haemostasis and platelet function testing in surgical practice. RESULTS: POC tests identifying perioperative bleeding tendency are already widely used in cardiovascular and hepatic surgery. They are associated with reduced blood loss and transfusion requirements. POC tests to identify thrombotic predisposition are able to determine antiplatelet resistance, predicting thromboembolic risk. So far, however, these tests remain research tools. CONCLUSION: POC haemostasis testing is a growing field in surgical practice. Such testing can be correlated with improved clinical outcome.

Role of ischaemic preconditioning in liver regeneration following major liver resection and transplantation.

Liver ischaemic preconditioning (IPC) is known to protect the liver from the detrimental effects of ischaemic-reperfusion injury (IRI), which contributes significantly to the morbidity and mortality following major liver surgery. Recent studies have focused on the role of IPC in liver regeneration, the precise mechanism of which are not completely understood. This review discusses the current understanding of the mechanism of liver regeneration and the role of IPC in this setting. Relevant articles were reviewed from the published literature using the Medline database. The search was performed using the keywords "liver", "ischaemic reperfusion", "ischaemic preconditioning", "regeneration", "hepatectomy" and "transplantation". The underlying mechanism of liver regeneration is a complex process involving the interaction of cytokines, growth factors and the metabolic demand of the liver. IPC, through various mediators, promotes liver regeneration by up-regulating growth-promoting factors and suppresses growth-inhibiting factors as well as damaging stresses. The increased understanding of the cellular mechanisms involved in IPC will enable the development of alternative treatment modalities aimed at promoting liver regeneration following major liver resection and transplantation.

Risk factor awareness in patients with peripheral arterial disease.

AIM: This study was designed to determine how aware patients with peripheral arterial disease (PAD) were with regard to the risk factors (RF) associated with atherosclerosis. METHODS: Seventy patients (49 men; median age 72 years, range 42-89 years) with PAD admitted as inpatients to the department of vascular surgery over a three-month period were asked to complete a single-paged questionnaire. Data were also obtained from the hospital notes with regard to gender, age, actual RFs that each patient suffered from, admission route (elective or acute), drug history and diagnosis. RESULTS: Diabetes mellitus (DM): 16 patients (23%) had DM, 15 (94%) of whom were aware of their condition, but only 5 (31%) believed DM to be a vascular RF. Smoking: 53 patients (76%) were either current smokers or had recently stopped smoking, only 31 (58%) of which knew smoking to be a cardiovascular RF. Hypercholestero-laemia: 41patients (59%) had been diagnosed with hypercholesterolaemia, 29 (71%) of which actually knew their cholesterol level was elevated, but only 10 (25%) believed it to be a RF for vascular disease. Hypertension: 40 patients (57%) were known hypertensives, 75% of which knew that they had hypertension but only 10% knew that it was a RF for vascular disease. CONCLUSION: RF awareness amongst patients with PAD is suboptimal. Intensive efforts need to be undertaken to educate this patient cohort in order to improve consciousness for best medical therapy.

The role of endothelial cell reactive antibodies in peripheral vascular disease.

The mechanism by which a small but significant proportion of patients with peripheral vascular disease (PVD) rapidly progress to critical ischaemia is unclear. Both experimental and clinical data suggest a role for autoantibodies in the pathogenesis of atherosclerotic disease, particularly in the accelerated atherosclerosis seen in patients with systemic lupus erythematosus and the anti-phospholipid syndrome. This review examines the evidence for a role for endothelial cell reactive autoantibodies in PVD and the potential mechanisms by which these autoantibodies could contribute to the acceleration of atherosclerosis in a proportion of patients. The identification of such markers could lead to the identification of patients with PVD who are at risk of developing critical ischaemia and may warrant early and aggressive intervention.

Neutrophils and the endothelium in post-ischemic alterations in skeletal muscle blood flow.

Thromboxane A2, leukotriene B4, and NE are all released from ischemic muscle during reperfusion. Thromboxane A2 levels peaked at 10 min and this potent vasoconstrictor may be responsible for low reflow. Neutrophil elastase levels did not rise until 240 min of reperfusion, following that of leukotriene B4 at 120 min, indicating that neutrophil recruitment and activation is a relatively late event following revascularization. In conclusion, it would appear that endothelial factors have a significant role in the vasomotor changes that account for low reflow. Equally altered neutrophil function almost certainly contributes to the final development of reperfusion injury.

The role of cilostazol in the treatment of intermittent claudication.

This paper represents a review, by experts, of current opinion and information on intermittent claudication (IC) and the role that cilostazol plays in its treatment. IC is a common and debilitating condition that has a significant adverse impact on health-related quality of life (HR-QoL). It is currently under-recognised as a powerful marker of increased cardiovascular (CV) risk. The clinical priority is secondary prevention -- sometimes referred to as best medical therapy aimed at reducing CV risk. However, the priority for most patients (often overlooked by clinicians) is symptom relief: an increase in walking distance leading to an improvement in HR-QoL. The symptoms of IC may be improved by exercise, pharmacotherapy, and when these are unsuitable or unsuccessful, endovascular or surgical intervention. Cilostazol is indicated for the improvement of maximal and pain-free walking distance in patients with IC who do not have rest pain or tissue necrosis. In clinical trials, cilostazol improved symptoms both objectively and subjectively, and also improved HR-QoL. Cilostazol is usually well tolerated, with adverse events being generally mild to moderate in intensity, and transient or resolved after symptomatic treatment (e.g. non-prescription analgesics). Such events only infrequently require permanent drug withdrawal. There are no interactions with other drugs commonly prescribed in patients with IC, such as statins and anti-platelet agents. Cilostazol also has a range of potentially beneficial effects that may in the future be proven to decrease CV risk and modify the underlying process of atherosclerosis. Cilostazol represents the best evidence-based pharmacological therapy available for the symptoms of IC and should be the first-line treatment for symptom improvement in appropriate patients. Based on the available treatment strategies, the paper presents a suggested algorithm for the management of IC highlighting the role of cilostazol.

Effect of homocysteine on cytokine production by human endothelial cells and monocytes.

BACKGROUND: Hyperhomocysteinaemia is an independent risk factor in the development of cardiovascular disease. Although homocysteine has been shown to affect endothelial cell function, the mechanisms by which it induces disease states are still poorly understood. Here, we report the ability of homocysteine to influence inflammatory cytokine/chemokine production by human saphenous vein endothelial cells, peripheral blood monocytes and monocyte-derived macrophages. METHODS: Human saphenous vein endothelial cells, peripheral blood monocytes and monocyte-derived macrophages were treated with homocysteine (0.1-5 mmol/L) for 4 and/or 24h. Tumour necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-6 and IL-8 production was measured in the cell culture media using commercially available enzyme-linked immunosorbent assays. RESULTS: Interleukin-6 production by human saphenous vein endothelial cells was significantly stimulated following a 24-h treatment with homocysteine, whilst IL-8 concentrations were inhibited after both 4- and 24-h treatments. Homocysteine was also found to stimulate IL-1beta production by human peripheral blood monocytes and TNF-alpha production by monocyte-derived macrophages. CONCLUSIONS: Overall, results from this study suggest that homocysteine alters the profile of cytokine/chemokine production by endothelial cells and macrophages. This altered profile may be important in the inflammatory events that initiate or enhance the development of atherosclerotic lesions.

Cholesterol embolisation. A lethal complication of instrumentation of an aneurysmal aorta: a case report.

A case of cholesterol embolisation (CE) following instrumentation of an aneurysmal aorta is presented. The patient developed myalgias, livedo reticularis in the buttocks, suprapubic area and legs, that progressed to patchy gangrene and renal failure. Maximum conservative management including heparin, iloprost and haemodialysis was ineffective, in keeping with previous reports that there is no known therapy for CE. The aetiology, presentation, treatment and prognosis of this condition is discussed. With the ever increasing use of endovascular treatment of abdominal aortic aneurysms, this complication may be more frequently encountered.

The effects of margination and red cell augmented platelet diffusivity on platelet adhesion in complex flow.

The effects of platelet margination and enhanced platelet diffusivity, as induced by red blood cells, on the adhesion of platelets, were investigated for a range of haematocrits, under 2D axi-symmetric flow, simulating previous in vitro experiments [Microvasc. Res. 17 (1979), 238-262]. The effect of margination was incorporated via use of an elevated platelet inlet mass fraction, Phie, in a manner similar to that of Wootton [Ann. Biomed. Eng. 29 (2001), 321-329], and a shear and haematocrit dependent platelet diffusivity, according to the model presented by Zydney and Colton [Physico Chem. Hydrodyn. 10 (1988), 77-96] was used. A combination of the two models was required to simulate the deposition of platelets to a collagen coated surface, under the complex flow, which exhibited a recirculation zone and stagnation point. Results obtained showed qualitative agreement with in vitro results, for a range of haematocrits (11-50%), and also showed that the effects of margination were not linearly dependent on haematocrit. Agreement may be improved in future simulations by incorporating the effects of depleted cell concentrations in the vortex which have been observed previously [Phil. Trans. Roy. Soc. (Lond.) B279 (1977), 413-445]. It would also be advantageous to devise a full mathematical description for platelet margination effects as a function of shear rate and haematocrit and a description of the accompanying effect of apparent blood viscosity.