Kumaran Kolandaivelu

Stent Thrombogenicity Early in High-Risk Interventional Settings Is Driven by Stent Design and Deployment and Protected by Polymer-Drug Coatings

Background— Stent thrombosis is a lethal complication of endovascular intervention. Concern has been raised about the inherent risk associated with specific stent designs and drug-eluting coatings, yet clinical and animal support is equivocal. Methods and Results— We examined whether drug-eluting coatings are inherently thrombogenic and if the response to these materials was determined to a greater degree by stent design and deployment with custom-built stents. Drug/polymer coatings uniformly reduce rather than increase thrombogenicity relative to matched bare metal counterparts (0.65-fold; P=0.011). Thick-strutted (162 &mgr;m) stents were 1.5-fold more thrombogenic than otherwise identical thin-strutted (81 &mgr;m) devices in ex vivo flow loops (P<0.001), commensurate with 1.6-fold greater thrombus coverage 3 days after implantation in porcine coronary arteries (P=0.004). When bare metal stents were deployed in malapposed or overlapping configurations, thrombogenicity increased compared with apposed, length-matched controls (1.58-fold, P=0.001; and 2.32-fold, P<0.001). The thrombogenicity of polymer-coated stents with thin struts was lowest in all configurations and remained insensitive to incomplete deployment. Computational modeling–based predictions of stent-induced flow derangements correlated with spatial distribution of formed clots. Conclusions— Contrary to popular perception, drug/polymer coatings do not inherently increase acute stent clotting; they reduce thrombosis. However, strut dimensions and positioning relative to the vessel wall are critical factors in modulating stent thrombogenicity. Optimal stent geometries and surfaces, as demonstrated with thin stent struts, help reduce the potential for thrombosis despite complex stent configurations and variability in deployment.

Non-adherence to cardiovascular medications

Despite evidence-based interventions, coronary heart disease (CHD) remains a leading cause of global mortality. As therapies advance, patient non-adherence to established treatments is well recognized. Non-adherence is a powerful confounder of evidence-based practice and can affect daily patient management, resulting in inappropriate therapeutic escalation with greater costs and potential for harm. Moreover, it increases risk for adverse cardiac events, including mortality. Yet, non-adherence is complex, remains difficult to define, and provider ability to identify its presence accurately remains limited. Improved screening tools are needed to detect at-risk patients, enabling appropriate targeting of interventions. Given the rapidly expanding global population with CHD and emerging clinical and cost-benefits of adherence, addressing non-adherence to prescribed therapies is a top priority.

Uremic Serum and Solutes Increase Post–Vascular Interventional Thrombotic Risk Through Altered Stability of Smooth Muscle Cell Tissue Factor

Background— Stent thrombosis (ST), a postinterventional complication with a mortality rate of 50%, has an incidence that rises precipitously in patients at risk. Chronic renal failure and end-stage renal disease have emerged as particularly strong ST risk factors, yet the mechanism remains elusive. Tissue factor (TF) is a crucial mediator of injury-related thrombosis and has been implicated for ST. We posit that uremia modulates TF in the local vessel wall to induce postinterventional thrombosis in patients with end-stage renal disease. Methods and Results— As a model of the de-endothelialized, postinterventional state, we exposed primary human vascular smooth muscle cells (vSMCs) pretreated with uremic serum (obtained from ESRD patients on hemodialysis) to coronary-like blood flow. vSMC TF expression, activity, stability, and posttranslational modification were examined after vSMCs were treated with uremic serum or solutes. We found significantly greater clot formation after uremic serum exposure, which was substantially reduced with the prior treatment with anti-TF neutralizing antibody. Uremic sera induced 2- to 3-fold higher TF expression and activity in vSMCs independent of diabetes mellitus. Relevant concentrations of isolated uremic solutes such as indole-3-acetic acid (3.5 &mgr;g/mL), indoxyl sulfate (25 &mgr;g/mL), and uric acid (80 &mgr;g/mL) recapitulated these effects in cell culture and the flow loop model. We show further that TF undergoes ubiquitination at baseline and that uremic serum, indole-3-acetic acid, and indoxyl sulfate significantly prolong TF half-life by inhibiting its ubiquitination. Conclusions— The uremic milieu is profoundly thrombogenic and upregulates vSMC TF levels by increasing TF stability and decreasing its ubiquitination. Together, these data demonstrate for the first time that the posttranslational regulation of TF in uremia may have a causative role in the increased ST risk observed in uremic patients. These data suggest that interventions that reduce vSMC TF may help to prevent ST and that uremic solutes should be considered as novel risk factors for ST in patients with chronic renal failure.

A randomised trial of lung sealant versus medical therapy for advanced emphysema

Uncontrolled pilot studies demonstrated promising results of endoscopic lung volume reduction using emphysematous lung sealant (ELS) in patients with advanced, upper lobe predominant emphysema. We aimed to evaluate the safety and efficacy of ELS in a randomised controlled setting. Patients were randomised to ELS plus medical treatment or medical treatment alone. Despite early termination for business reasons and inability to assess the primary 12-month end-point, 95 out of 300 patients were successfully randomised, providing sufficient data for 3- and 6-month analysis. 57 patients (34 treatment and 23 control) had efficacy results at 3u2005months; 34 (21 treatment and 13 control) at 6u2005months. In the treatment group, 3-month lung function, dyspnoea, and quality of life improved significantly from baseline when compared to control. Improvements persisted at 6u2005months with >50% of treated patients experiencing clinically important improvements, including some whose lung function improved by >100%. 44% of treated patients experienced adverse events requiring hospitalisation (2.5-fold more than control, p=0.01), with two deaths in the treated cohort. Treatment responders tended to be those experiencing respiratory adverse events. Despite early termination, results show that minimally invasive ELS may be efficacious, yet significant risks (probably inflammatory) limit its current utility. Emphysematous lung sealant therapy is highly efficacious in some patients, but benefits bring significant risks http://ow.ly/JJ2vg

The Aryl Hydrocarbon Receptor is a Critical Regulator of Tissue Factor Stability and an Antithrombotic Target in Uremia

Patients with CKD suffer high rates of thrombosis, particularly after endovascular interventions, yet few options are available to improve management and reduce thrombotic risk. We recently demonstrated that indoxyl sulfate (IS) is a potent CKD-specific prothrombotic metabolite that induces tissue factor (TF) in vascular smooth muscle cells (vSMCs), although the precise mechanism and treatment implications remain unclear. Because IS is an agonist of the aryl hydrocarbon receptor (AHR), we first examined the relationship between IS levels and AHR-inducing activity in sera of patients with ESRD. IS levels correlated significantly with both vSMC AHR activity and TF activity. Mechanistically, we demonstrated that IS activates the AHR pathway in primary human aortic vSMCs, and further, that AHR interacts directly with and stabilizes functional TF. Antagonists directly targeting AHR enhanced TF ubiquitination and degradation and suppressed thrombosis in a postinterventional model of CKD and endovascular injury. Furthermore, AHR antagonists inhibited TF in a manner dependent on circulating IS levels. In conclusion, we demonstrated that IS regulates TF stability through AHR signaling and uncovered AHR as an antithrombotic target and AHR antagonists as a novel class of antithrombotics. Together, IS and AHR have potential as uremia-specific biomarkers and targets that may be leveraged as a promising theranostic platform to better manage the elevated thrombosis rates in patients with CKD.

Overcoming 'resistance' to antiplatelet therapy: targeting the issue of nonadherence

A wide range of interindividual variability in the measured and clinical effects of antiplatelet drugs exists. As patients with less platelet inhibition consistently have increased rates of adverse cardiovascular outcomes, a great deal of effort is being focused on understanding and treating this apparent resistance. Pharmacogenomic and pharmacodynamic methods to better delineate responders from nonresponders are being developed, and innovative strategies and novel, potent drugs capable of overcoming nonresponsiveness are in active clinical trials. Less attention has been paid to the confounding role that patient nonadherence has on individual response to antiplatelet therapy, but accruing evidence indicates that nonadherence has a dominant impact in real-world, outpatient settings, as compared with true, biochemical antiplatelet nonresponsiveness. Understanding the mechanisms of nonadherence and rigorously testing methods to overcome it are urgently needed to avoid the potential harm in delivering increasingly intense and expensive therapies to those who may not need it, while at the same time offering a way to improve overall health-care efficiency.

Predicting response to endovascular therapies: Dissecting the roles of local lesion complexity, systemic comorbidity, and clinical uncertainty

Through decades of use and refinement, endovascular stents have become part and parcel of the management of obstructive atherosclerotic lesions. Upon stent placement, a variety of biophysical reactions ensue, governed not only by the mechanical and material properties of the device, but also the impact these properties have on the local vascular biology. Anatomic changes and vascular deformations give rise to solid mechanical and fluid forces that are the proximate, functional drivers of the induced reparative response. Powerful computational tools and advanced imaging techniques allow us to define these forces with high precision and increasingly, at a patient-specific level. We have also gained fundamental insights into how these forces influence subcellular and cellular processes, and, through application of a variety of model systems, how they subsequently drive an integrated tissue response. Clinical studies extend understanding to actual patients and pathophysiologic scenarios. These tools and insights take on added weight given the real risks that accompany the many substantial benefits of stenting. Complex lesions remain difficult to manage and continue to be associated with worse outcomes. While many patients respond well to treatment, others suffer treatment failures and recurrent events - sometimes catastrophic. Overcoming such variability requires that we move towards individualized treatment plans. Doing so necessitates that we develop not just a qualitative understanding of involved phenomena, but a quantitative ability to predict integrated outcomes. Given the multi-scale nature of the vascular response to stenting, it is critical that models, be they computational, bench-top, animal, or clinical, can be verified, validated, and made interrelated. This review provides an overview of the biophysics governing endovascular stenting, their integration in real-world endovascular settings, and how simulation and statistical approaches are helping to bridge the gap between qualitative model understanding and quantitative clinical prediction.

Extent of flow recirculation governs expression of atherosclerotic and thrombotic biomarkers in arterial bifurcations

AIMSnAtherogenesis, evolution of plaque, and outcomes following endovascular intervention depend heavily on the unique vascular architecture of each individual. Patient-specific, multiscale models able to correlate changes in microscopic cellular responses with relevant macroscopic flow, and structural conditions may help understand the progression of occlusive arterial disease, providing insights into how to mitigate adverse responses in specific settings and individuals.nnnMETHODS AND RESULTSnVascular architectures mimicking coronary and carotid bifurcations were derived from clinical imaging and used to generate conjoint computational meshes for in silico analysis and biocompatible scaffolds for in vitro models. In parallel with three-dimensional flow simulations, geometrically realistic scaffolds were seeded with human smooth muscle cells (SMC) or endothelial cells and exposed to relevant, physiological flows. In vitro surrogates of endothelial health, atherosclerotic progression, and thrombosis were locally quantified and correlated best with an quantified extent of flow recirculation occurring within the bifurcation models. Oxidized low-density lipoprotein uptake, monocyte adhesion, and tissue factor expression locally rose up to three-fold, and phosphorylated endothelial nitric oxide synthase and Krüppel-like factor 2 decreased up to two-fold in recirculation areas. Isolated testing in straight-tube idealized constructs subject to static, oscillatory, and pulsatile conditions, indicative of different recirculant conditions corroborated these flow-mediated dependencies.nnnCONCLUSIONSnFlow drives variations in vascular reactivity and vascular beds. Endothelial health was preserved by arterial flow but jeopardized in regions of flow recirculation in a quasi-linear manner. Similarly, SMC exposed to flow were more thrombogenic in large recirculating regions. Health, thrombosis, and atherosclerosis biomarkers correlate with the extent of recirculation in vascular cells lining certain vascular geometries.

Low background, pulsatile, in vitro flow circuit for modeling coronary implant thrombosis.

We have developed an in vitro method for creating pulsatile flows to mimic coronary type flow patterns on a beat-to-beat basis. The flow is created by accelerating fluid loops about an axis, inducing relative wall motion. Using this technique, a variety of oscillating flow patterns can be generated and modulated. Such flow generation offers the potential to monitor sensitive, flow-dependent, biological parameters like thrombosis while minimizing background disturbances from pump action and circuit effects. We examined this potential by measuring the loop occlusion time for loops stented with stainless steel 7-9 NIR stents and stentless control loops.

Microbial lysate upregulates host oxytocin

Neuropeptide hormone oxytocin has roles in social bonding, energy metabolism, and wound healing contributing to good physical, mental and social health. It was previously shown that feeding of a human commensal microbe Lactobacillus reuteri (L. reuteri) is sufficient to up-regulate endogenous oxytocin levels and improve wound healing capacity in mice. Here we show that oral L. reuteri-induced skin wound repair benefits extend to human subjects. Further, dietary supplementation with a sterile lysate of this microbe alone is sufficient to boost systemic oxytocin levels and improve wound repair capacity. Oxytocin-producing cells were found to be increased in the caudal paraventricular nucleus [PVN] of the hypothalamus after feeding of a sterile lysed preparation of L. reuteri, coincident with lowered blood levels of stress hormone corticosterone and more rapid epidermal closure, in mouse models. We conclude that microbe viability is not essential for regulating host oxytocin levels. The results suggest that a peptide or metabolite produced by bacteria may modulate host oxytocin secretion for potential public or personalized health goals.