Side Of Leaflets Research Articles

Impact of Variation in Commissural Angle between Fused Leaflets in the Functionally Bicuspid Aortic Valve on Hemodynamics and Tissue Biomechanics.

In subjects with functionally bicuspid aortic valves (BAVs) with fusion between the coronary leaflets, there is a natural variation of the commissural angle. What is not fully understood is how this variation influences the hemodynamics and tissue biomechanics. These variables may influence valvar durability and function, both in the native valve and following repair, and influence ongoing aortic dilation. A 3D aortic valvar model was reconstructed from a patient with a normal trileaflet aortic valve using cardiac magnetic resonance (CMR) imaging. Fluid-structure interaction (FSI) simulations were used to compare the effects of the varying commissural angles between the non-coronary with its adjacent coronary leaflet. The results showed that the BAV with very asymmetric commissures (120∘ degree commissural angle) reduces the aortic opening area during peak systole and with a jet that impacts on the right posterior wall proximally of the ascending aorta, giving rise to elevated wall shear stress. This manifests in a shear layer with a retrograde flow and strong swirling towards the fused leaflet side. In contrast, a more symmetrical commissural angle (180∘ degree commissural angle) reduces the jet impact on the posterior wall and leads to a linear decrease in stress and strain levels in the non-fused non-coronary leaflet. These findings highlight the importance of considering the commissural angle in the progression of aortic valvar stenosis, the regional distribution of stresses and strain levels experienced by the leaflets which may predispose to valvar deterioration, and progression in thoracic aortic dilation in patients with functionally bicuspid aortic valves. Understanding the hemodynamics and biomechanics of the functionally bicuspid aortic valve and its variation in structure may provide insight into predicting the risk of aortic valve dysfunction and thoracic aortic dilation, which could inform clinical decision making and potentially lead to improved aortic valvar surgical outcomes.

Membrane stiffness and myelin basic protein binding strength as molecular origin of multiple sclerosis

Myelin basic protein (MBP) and its interaction with lipids of the myelin sheath plays an important part in the pathology of multiple sclerosis (MS). Previous studies observed that changes in the myelin lipid composition lead to instabilities and enhanced local curvature of MBP-lipid multilayer structures. We investigated the molecular origin of the instability and found that the diseased lipid membrane has a 25% lower bending rigidity, thus destabilizing smooth >1,µm curvature radius structures such as in giant unilamellar vesicles. MBP-mediated assembling of lipid bilayers proceeds in two steps, with a slow second step occurring over many days where native lipid membranes assemble into well-defined multilayer structures, whereas diseased lipid membranes form folded assemblies with high local curvature. For both native and diseased lipid mixtures we find that MBP forms dense liquid phases on top of the lipid membranes mediating attractive membrane interactions. Furthermore, we observe MBP to insert into its bilayer leaflet side in case of the diseased lipid mixture, whereas there is no insertion for the native mixture. Insertion increases the local membrane curvature, and could be caused by a decrease of the sphingomyelin content of the diseased lipid mixture. These findings can help to open a pathway to remyelination strategies.

Side-dependent effect in the response of valve endothelial cells to bidirectional shear stress

Endothelial cells covering the aortic and ventricular sides of the aortic valve leaflets are exposed to different stresses, in particular wall shear stress (WSS). Biomechanical stimuli actively regulate valve tissue structure and induce remodeling events leading to valve dysfunction. Endothelial to mesenchymal transformation (EndMT), for example, has been associated with aortic valve disease. The biomechanical response of cells at different sides of the leaflets has not been clearly characterized. To analyze the mechanical response of valve endothelial cells (VECs) we developed a unique fluid activation device that applies physiologically relevant pulsatile WSS. We characterized the morphology and function of adult porcine aortic VECs derived from the opposite sides of aortic valve leaflets following exposure to different pulsatile WSS. We found that elongation and orientation of cells in response to pulsatile WSS depends on their side of origin. Quantification of gene expression confirms phenotypic differences between aortic and ventricular VECs. Aortic VECs exposed to pulsatile WSS similar to that in vivo at the tip of aortic side of the valve leaflet upregulated pro-EndMT (ACTA2, Snail, TGFβ1) and inflammation (ICAM-1, VCAM-1) genes, whereas expression of endothelial markers like PECAM-1 was decreased. Conversely, ventricular-VECs showed strong increase of PECAM-1 expression and no activation of pro-EndMT marker. Finally, we found that stress-induced genes are upregulated in both cell types, at higher levels in ventricular compared to aortic VECs. Application of physiological shear stress levels using a fluid activation device therefore reveals functional differences in VECs derived from opposite sides of the aortic valve leaflets.

Transcatheter Aortic Valve Implantation Represents an Anti-Inflammatory Therapy Via Reduction of Shear Stress-Induced, Piezo-1-Mediated Monocyte Activation.

Aortic valve stenosis is an increasingly prevalent degenerative and inflammatory disease. Transcatheter aortic valve implantation (TAVI) has revolutionized its treatment, thereby avoiding its life-threatening/disabling consequences. Whether aortic valve stenosis is accelerated by inflammation and whether it is itself a cause of inflammation are unclear. We hypothesized that the large shear forces exerted on circulating cells, particularly on the largest circulating cells, monocytes, while passing through stenotic aortic valves result in proinflammatory effects that are resolved with TAVI. TAVI provides a unique opportunity to compare the activation status of monocytes under high shear stress (before TAVI) and under low shear stress (after TAVI). The activation status of monocytes was determined with a single-chain antibody, MAN-1, which is specific for the activated β2-integrin Mac-1. Monocyte function was further characterized by the adhesion of myocytes to stimulated endothelial cells, phagocytic activity, uptake of oxidized low-density lipoprotein, and cytokine expression. In addition, we designed a microfluidic system to recapitulate the shear rate conditions before and after TAVI. We used this tool in combination with functional assays, Ca2+ imaging, siRNA gene silencing, and pharmacological agonists and antagonists to identify the key mechanoreceptor mediating the shear stress sensitivity of monocytes. Last, we stained for monocytes in explanted stenotic aortic human valves. The resolution of high shear stress through TAVI reduces Mac-1 activation, cellular adhesion, phagocytosis, oxidized low-density lipoprotein uptake, and expression of inflammatory markers in monocytes and plasma. Using microfluidics and pharmacological and genetic studies, we could recapitulate high shear stress effects on isolated human monocytes under highly controlled conditions, showing that shear stress-dependent calcium influx and monocyte adhesion are mediated by the mechanosensitive ion channel Piezo-1. We also demonstrate that the expression of this receptor is shear stress dependent and downregulated in patients receiving TAVI. Last, we show monocyte accumulation at the aortic side of leaflets of explanted aortic valves. We demonstrate that high shear stress, as present in patients with aortic valve stenosis, activates multiple monocyte functions, and we identify Piezo-1 as the mainly responsible mechanoreceptor, representing a potentially druggable target. We demonstrate an anti-inflammatory effect and therefore a novel therapeutic benefit of TAVI.

Oviposition by the vagrant eriophyoid mite Aculops allotrichus on leaves of black locust tree, Robinia pseudoacacia

Leaf-dwelling mites often prefer to feed on young leaves and also are more likely to inhabit the abaxial leaf side. The aim of our study was to examine whether leaf age may affect production and distribution of eggs on black locust leaves by females of Aculops allotrichus. The eriophyoids were tested for 2.5 days on ‘trimmed’ compound leaves (with only two opposite leaflets left), which were maintained in vials filled with water. For the experiments we used leaves of three categories: (1) the ‘youngest’, in which both halves of the adaxial side of leaflets still adhered to each other (and usually remained folded for the next few hours), (2) ‘young’ with already unfolded leaflets, and (3) ‘mature’ with fully expanded leaflets. The tested females laid significantly more eggs on developing leaves than on ‘mature’ ones, although they deposited the highest number of eggs on the ‘young’ leaves. The distribution of eggs on adaxial or abaxial leaf sides also depended on leaf age. On the ‘youngest’ leaves, eriophyoids placed similar numbers of eggs on both sides of a blade. However, the older the leaf, the more willingly females deposited eggs on the abaxial side. Our biochemical and morphometrical analyses of black locust leaves indicated significant changes in the contents of nutrients and phenols within leaf tissue, and in the density of trichomes and thickness of the outer epidermal cell walls, correlated with leaf age. Their possible effects on the production and distribution of eggs on leaves by A. allotrichus are discussed.

Negative interaction between twospotted spider mites and aphids mediated by feeding damage and honeydew

Among the herbivorous arthropods that feed on strawberry, the most important are the two-spotted spider mite (TSSM), Tetranychus urticae Koch, and several species of aphids. Mites and aphids belong to different guilds that coexist in the field and feed on the undersides of strawberry leaflets. However, the occurrence of large numbers of individuals of both species on the same leaflet is rarely recorded. We hypothesize that negative interactions between TSSM and aphids explain the intraplant distribution of these herbivores. We first examined the spatial coincidence of both herbivores in the field. Under experimental conditions, we then analyzed: (i) the rate of increase of TSSM and the aphid Chaetosiphon fragaefolii (Cockerell), growing individually and together; (ii) the effect of honeydew on TSSM preference; and (iii) the effect of previous strawberry leaflet damage by TSSM on C. fragaefolii preference. The proportion of TSSM that coincided with at least one aphid decreased as the percentage of leaflets with TSSM increased. The spatial coincidence index between aphids and TSSM increased together with the percentage of TSSM-infested leaflets. TSSM showed both a lower rate of increase when they shared the same leaflet with C. fragaefolii and lower fecundity on strawberry discs with honeydew. The rate of increase of C. fragaefolii did not change on co-occupied leaves, but the aphid species moved to the other side of leaflets shared with TSSM. Negative interactions resulting in a tendency for species to avoid each other, such as demonstrated herein, can affect distribution and performance of herbivorous arthropods.

Distribuição espacial de Calacarus Heveae feres na cultura da seringueira em Marinópolis - São Paulo

O objetivo deste trabalho foi estudar a distribuição espacial de Calacarus heveae Feres (Acari: Eriophyidae) na cultura da seringueira, tendo como base um monitoramento realizado com lupa de bolso. A área experimental, localizada em Marinópolis, São Paulo, com 1.000 plantas do clone RRIM 600, foi dividida em 100 parcelas de 10 plantas cada uma. Foram realizadas 16 coletas no período de dezembro de 2007 a junho de 2008. Nas coletas foram amostradas duas plantas por parcela, retirando-se de cada uma extremidade de ramo com 30 cm de comprimento. No laboratório, os ácaros foram avaliados com o uso de lupa de bolso de 20X de aumento, em seis folíolos por parcela, sendo três de cada ramo. A contagem dos ácaros foi realizada em duas áreas de 1 cm² na página superior dos folíolos, uma de cada lado da nervura principal. Os índices de dispersão estudados foram: razão variância/média (I), índice de Morisita (Id), coeficiente de Green (Cx) e expoente k da distribuição binomial negativa. C. heveae apresenta distribuição agregada em área de cultivo de seringueira. A distribuição espacial do ácaro ajusta-se ao modelo de distribuição binomial negativa.

In Vitro Characterization of Bicuspid Aortic Valve Hemodynamics Using Particle Image Velocimetry

The congenital bicuspid aortic valve (BAV) is associated with increased leaflet calcification, ascending aortic dilatation, aortic stenosis (AS) and regurgitation (AR). Although underlying genetic factors have been primarily implicated for these complications, the altered mechanical environment of BAVs could potentially accelerate these pathologies. The objective of the current study is to characterize BAV hemodynamics in an in vitro system. Two BAV models of varying stenosis and jet eccentricity and a trileaflet AV (TAV) were constructed from excised porcine AVs. Particle Image Velocimetry (PIV) experiments were conducted at physiological flow and pressure conditions to characterize fluid velocity fields in the aorta and sinus regions, and ensemble averaged Reynolds shear stress and 2D turbulent kinetic energy were calculated for all models. The dynamics of the BAV and TAV models matched the characteristics of these valves which are observed clinically. The eccentric and stenotic BAV showed the strongest systolic jet (V = 4.2 m/s), which impinged on the aortic wall on the non-fused leaflet side, causing a strong vortex in the non-fused leaflet sinus. The magnitudes of TKE and Reynolds stresses in both BAV models were almost twice as large as comparable values for TAV, and these maximum values were primarily concentrated around the central jet through the valve orifice. The in vitro model described here enables detailed characterization of BAV flow characteristics, which is currently challenging in clinical practice. This model can prove to be useful in studying the effects of altered BAV geometry on fluid dynamics in the valve and ascending aorta. These altered flows can be potentially linked to increased calcific responses from the valve endothelium in stenotic and eccentric BAVs, independent of concomitant genetic factors.

Factor XIII expression within aortic valves and its plasma activity in patients with aortic stenosis: association with severity of disease

Aortic valve stenosis (AS) shares several similarities with atherosclerosis. Factor XIII (FXIII) has been detected within atherosclerotic plaques and may contribute to the development of atherosclerosis via multiple mechanisms. In the current study, we sought to investigate FXIII expression within human stenotic aortic valves and its association with severity of the disease. We prospectively enrolled 91 consecutive patients with AS scheduled for isolated valve replacement. Valvular FXIII subunit A (FXIII-A), fibrin and macrophages expression was evaluated by immunostaining. FXIII-A subunit transcripts and FXIII-A Val34Leu polymorphism was determined by real-time PCR. Plasma FXIII (pFXIII) activity was measured. We demonstrated that the valvular FXIII-A was predominantly expressed on the aortic side of leaflets, colocalized with alternatively activated macrophages (AAM). Areas stained for FXIII-A showed positive correlations with valvular fibrin presence, degree of calcification, pFXIII activity and the severity of AS, reflected by mean and maximum transvalvular gradients (all, p<0.001). The FXIII-A mRNA in the stenotic leaflets was significantly elevated compared to control leaflets. Interestingly, pFXIII activity was also positively correlated with mean (p<0.001) and maximum (p=0.001) transvalvular gradient. The FXIII-A Val34Leu polymorphism did not affect FXIII-A and fibrin expression in AS valves. In conclusion, the study is the first to show abundant expression of FXIII-A at the mRNA and protein levels within human stenotic aortic valves, which is associated with the severity of AS. Our findings might suggest that FXIII in the stenotic valves is presented in AAM and may be involved in the AS progression.

Open balloon aortic valvuloplasty in aortic stenosis: Implications for transcatheter aortic valve implantations

Balloon aortic valvuloplasty (BAV) plays a crucial role in transcatheter aortic valve implantation (TAVI). However, data on morphology during BAV are lacking. During surgical aortic valve replacement, open BAV was performed as a non-therapeutic in-vivo model prior to aortic valve excision. Twenty-six patients with severe aortic stenosis were included in the study after ethics committee approval. A valvuloplasty balloon was advanced from the open aorta, across the stenotic aortic valve and was rapidly inflated and deflated. All patients except for one had tricuspid aortic valves with severe visible calcification on the aortic side of leaflets. All valves were successfully dilated. Only in the presence of severe central calcific noduli, fractures occurred in the middle portion of the leaflets in three and in the commissural part in four patients. No embolization of valvular debris occurred, however, ten coronary leaflets partially reached coronary orifices, resulting in three near-obstructions. The present study visualized for the first time the behaviour of bulky leaflet calcifications during valvuloplasty. Fractures in the middle portion of the free edge may occur whenever a huge calcification completely affects the whole leaflet area. No signs of embolization were observed, possibly explaining low stroke rates during TAVI procedures.

First Report of Soybean Rust Caused by Phakopsora pachyrhizi on Kudzu (Pueraria montana var. lobata) in Illinois.

Soybean rust, caused by Phakopsora pachyrhizi Syd., first was observed in the continental United States during 2004 on soybean (Glycine max (L.) Merr.) in Louisiana (4), and on kudzu (Pueraria montana (Lour.) Merr. var. lobata (Willd.) Maesen & Almeida) in Florida (2). Kudzu is a leguminous weed that is prevalent in the southern United States with its range extending northward into other states including Illinois. In October 2009, a kudzu patch located in Pulaski County in southern Illinois was investigated for the presence of soybean rust. Twenty-five leaflets were collected, and the abaxial sides of leaflets were evaluated visually for the presence of uredinia with a dissecting microscope. Uredinia and urediniospores were found on two leaflets. When viewed with a compound microscope, urediniospores were hyaline, echinulate, and measured 20 × 25 μm. On the basis of uredinia and urediniospores, the disease tentatively was identified as soybean rust caused by P. pachyrhizi. To confirm the identification, one leaflet with pustules was assayed with a Soybean Rust QuickStix Diagnostic Kit (Envirologix, Portland, ME). For the other leaflet, the area of the pustule was excised (approximately 28 mm2) and an area of the leaflet at the margin on the opposite half of the leaflet with no visible pustule (approximately 54 mm2) was excised. DNA was extracted from the excised areas of the leaflet for confirmation by quantitative PCR (Q-PCR) using primers and probe specific to P. pachyrhizi and P. meibomiae (Arthur) Arthur (1). Both the QuickStix Diagnostic Kit and the Q-PCR confirmed the diagnosis as soybean rust caused by P. pachyrhizi. Q-PCR also suggested the presence of a nonsporulating latent rust infection on the same kudzu leaflet at the margin on the opposite side of the midrib. Soybean rust first was confirmed on soybean in Illinois in 2006 (3), but to our knowledge, this is the first observation of the disease on kudzu in the state. This report confirms that at least some kudzu plants in Illinois are susceptible to soybean rust and that latent kudzu infection may exist without outward signs of the fungus. Currently, this is the most northern observation of soybean rust on kudzu in North America. It is unknown what role, if any, Illinois kudzu will play in the epidemiology of soybean rust in the state. Since kudzu tops die after the first frost, there is no expectation of P. pachyrhizi to overwinter in Illinois on kudzu as it does in some states adjacent to the Gulf of Mexico.

Identification of tissue factor in experimental aortic valve sclerosis

Aortic valve sclerosis (AVS) shares epidemiological and histological similarities with atherosclerosis. Tissue factor (TF), the main initiator of blood coagulation, is present in atherosclerotic plaques and contributes to their thrombogenicity. We aimed to analyze valvular TF expression in addition to other components of atherosclerosis in two models of AVS. Forty-five rabbits were randomly assigned to receive either normal chow (Ctrl, n=15), or 1% cholesterol-enriched chow alone (Hyperchol, n=15) or associated with vitamin D(2) (VitD, n=15), for 12 weeks. Aortic valve (AV) performance, leaflet structure, cellular and lipid infiltration, and TF expression were assessed using Doppler, histology, and immunohistochemistry, respectively, and TF activity was evaluated in AV leaflets. Hyperchol and VitD animals developed abnormal leaflet thickening, with a significant alteration of AV performance in VitD animals. Leaflet thickening was related to the development of fatty plaque neolesions on the aortic side of the leaflets, displaying extracellular matrix disorganization, lipid and cellular infiltration, and calcification in VitD animals. TF was found on the leaflet aortic side in Ctrl animals and was identified in AVS lesions in both Hyperchol and VitD animals. TF immunostaining area and valvular activity increased significantly across the three groups. Experimental AVS lesions that are present on the aortic side of leaflets display numerous characteristics of vascular atherosclerosis, including TF expression. Identification of TF associated with other components of the atherosclerotic process in AVS lesions strengthens the link between atherosclerosis and AVS.

Structure of the Multidrug Transporter EmrD from Escherichia coli

EmrD is a multidrug transporter from the Major Facilitator Superfamily that expels amphipathic compounds across the inner membrane of Escherichia coli. Here, we report the x-ray structure of EmrD determined to a resolution of 3.5 angstroms. The structure reveals an interior that is composed mostly of hydrophobic residues, which is consistent with its role transporting amphipathic molecules. Two long loops extend into the inner leaflet side of the cell membrane. This region can serve to recognize and bind substrate directly from the lipid bilayer. We propose that multisubstrate specificity, binding, and transport are facilitated by these loop regions and the internal cavity.

Differential accumulation of intimal monocyte-macrophages relative to lipoproteins and lipofuscin corresponds to hemodynamic forces on cardiac valves in mice.

We have studied the distribution of monocyte-macrophages, lipids, and lipoproteins in sections of aorta and aortic valves from mice fed an atherogenic diet. By immunocytochemical analysis with Mac-1 and F4/80 antibodies, apolipoprotein B antibody, and oil red O staining, three discrete regions were identified: 1) the aortic wall of the sinus of Valsalva, which contained deposits of lipid that colocalized with lipoproteins and monocyte-macrophages; 2) the sides of the aortic valve leaflets facing the ventricle, which did not contain lipids or lipoproteins but which were lined with macrophages that colocalized with lipofuscin; and 3) the sides of the leaflets facing the aorta, which did not contain lipids, lipoproteins, monocyte-macrophages, or lipofuscin deposits. This pattern of distribution resembles the expected distribution of mechanical forces, especially those of systolic blood flow, which in the three areas are predominantly 1) low-shear disturbed flow, 2) high-shear laminar flow, and 3) low-shear laminar flow, respectively. These findings suggest that lesions in the mouse closely resemble early atherosclerotic lesions in humans and other primates with respect to monocyte-macrophage and lipoprotein accumulation. The results also strikingly demonstrate that the accumulation of monocyte-macrophages and lipoproteins can occur independently, with spatial differences corresponding to the distribution of hemodynamic forces.

Discrimination between epicuticular and intracuticular wax in blackberry leaves: Ultrastructural and chemical evidence

Epicuticular wax on the adaxial leaflet side of blackberry ( Rubus fruticosus) occurred as wax knobs and irregular-shaped platelets. Removal of the epicuticular wax by a collodion film revealed the wax-free cuticle surface. This allowed the selective extraction of epicuticular wax from the film and subsequently of intracuticular wax from the cuticle. Epicuticular wax amounted to approx. 90% of total cuticular wax, only about 10% were present as intracuticular wax. The epicuticular wax contained mainly alcohol acetates, free alcohols and esters with lesser amounts of fatty acids and alkanes. Intracuticular wax was composed of free alcohols, alcohol acetates and fatty acids together with small proportions of triterpenoid acids, alkanes and esters.