Vascular Transport Research Articles

Physiological and Proteomic Investigations to Study the Response of Tomato Graft Unions under Temperature Stress.

BackgroundGrafting is an established practice for asexual propagation in horticultural and agricultural crops. The study on graft unions has become of interest for horticulturists using proteomic and genomic techniques to observe transfer of genetic material and signal transduction pathways from root to shoot and shoot to root. Another reason to study the graft unions was potentially to observe resistance against abiotic stresses. Using physiological and proteomic analyses, we investigated graft unions (rootstock and scions) of tomato genotypes exposed to standard-normal (23/23 and 25/18°C day/night) and high-low temperatures (30/15°C day/night).ResultsGraft unions had varied responses to the diverse temperatures. High-low temperature, but not standard-normal temperature, induced the production of reactive oxygen species (ROS) in the form of H2O2 and O2-1 in rootstock and scions. However, the expression of many cell protection molecules was also induced, including antioxidant enzymes and their immunoblots, which also show an increase in their activities such as superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX). The graft interfaces thus actively defend against stress by modifying their physiological and proteomic responses to establish a new cellular homeostasis. As a result, many proteins for cellular defense were regulated in graft unions under diverse temperature, in addition to the regulation of photosynthetic proteins, ion binding/transport proteins, and protein synthesis. Moreover, biomass, hardness, and vascular transport activity were evaluated to investigate the basic connectivity between rootstock and scions.ConclusionsOur study provides physiological evidence of the grafted plants’ response to diverse temperature. Most notably, our study provides novel insight into the mechanisms used to adapt the diverse temperature in graft unions (rootstock/scion).

Histoenzymological Characteristics of Smooth Muscle Cells in Myocardial Vessels: A Comparative Study under Conditions of Increased Left or Right Ventricular Afterload.

Histoenzymological methods were used to study metabolism of smooth muscle cells of intramural myocardial arteries during experimental aortic or pulmonary artery stenosis. Aortic stenosis was accompanied by changes in smooth muscles of the left ventricle manifested by deceleration of tricarboxylic acid cycle, inhibition of oxidation of free fatty acids and their metabolites, flux redistribution in the glycolytic cascade, and inhibition of shuttle systems and biosynthetic processes. Similar metabolic alterations were observed in vessels of the ventricular septum, but they were not revealed in vessels of the right ventricle (except glycolysis stimulation). Under conditions of pulmonary artery stenosis, histoenzymological alterations in vascular smooth muscle of both ventricles and ventricular septum were similar, which attested to acceleration of tricarboxylic acid cycle, stimulation of oxidation of the free fatty acids with their metabolites, acceleration of glycolysis, and activation of the shuttle systems and biosynthetic processes. Comparative analysis of histoenzymological alterations revealed substantial differences in the character of metabolic changes under conditions of increased left and right ventricular afterload, which can be caused by peculiarities in myocardial blood flow, severity of circulatory disorders, severity of hypoxia, and intensity of processes maintaining ionic homeostasis in vascular smooth muscles and transport across the histohematic barriers. The data attest to important metabolic role of glycolysis in vascular smooth muscles of the myocardium, especially under conditions of enhanced afterload of the right ventricle.

Nitrogen recycling from the xylem in rice leaves: dependence upon metabolism and associated changes in xylem hydraulics.

Measurements of amino acids in the guttation fluid and in the xylem exudates of cut leaves from intact plants provide evidence of the remarkable efficiency with which these nitrogenous compounds are reabsorbed from the xylem sap. This could be achieved by mechanisms involving intercellular transport and/or metabolism. Developmental changes in transcripts and protein showed that transcripts for phosphoenolpyruvate carboxykinase (PEPCK) increased from the base to the leaf tip, and were markedly increased by supplying asparagine. Supplying amino acids also increased the amounts of protein of PEPCK and, to a lesser extent, of pyruvate, Pi dikinase. PEPCK is present in the hydathodes, stomata and vascular parenchyma of rice leaves. Evidence for the role of PEPCK was obtained by using 3-mercaptopicolinic acid (MPA), a specific inhibitor of PEPCK, and by using an activation-tagged rice line that had an increase in PEPCK activity, to show that activation of PEPCK resulted in a decrease in N in the guttation fluid and that treatment by MPA resulted in an increase in amino acids in the guttation fluid and xylem sap towards the leaf tip. Furthermore, increasing PEPCK activity decreased the amount of guttation fluid, whereas decreasing PEPCK activity increased the amount of xylem sap or guttation fluid towards the leaf tip. The findings suggest the following hypotheses: (i) both metabolism and transport are involved in xylem recycling and (ii) excess N is the signal involved in modulating xylem hydraulics, perhaps via nutrient regulation of water-transporting aquaporins. Water relations and vascular metabolism and transport are thus intimately linked.

Cellular and molecular mechanistic insight into the DNA-damaging potential of few-layer graphene in human primary endothelial cells

Despite graphene being proposed for a multitude of biomedical applications, there is a dearth in the fundamental cellular and molecular level understanding of how few-layer graphene (FLG) interacts with human primary cells. Herein, using human primary umbilical vein endothelial cells as model of vascular transport, we investigated the basic mechanism underlying the biological behavior of graphene. Mechanistic toxicity studies using a battery of cell based assays revealed an organized oxidative stress paradigm involving cytosolic reactive oxygen stress, mitochondrial superoxide generation, lipid peroxidation, glutathione oxidation, mitochondrial membrane depolarization, enhanced calcium efflux, all leading to cell death by apoptosis/necrosis. We further investigated the effect of graphene interactions using cDNA microarray analysis and identified potential adverse effects by down regulating key genes involved in DNA damage response and repair mechanisms. Single cell gel electrophoresis assay/Comet assay confirmed the DNA damaging potential of graphene towards human primary cells.

A branched-chain amino acid metabolite drives vascular fatty acid transport and causes insulin resistance.

Epidemiological and experimental data implicate branched chain amino acids (BCAAs) in the development of insulin resistance, but the mechanisms underlying this link remain unclear.1–3 Insulin resistance in skeletal muscle stems from excess accumulation of lipid species4, a process that requires blood-borne lipids to first traverse the blood vessel wall. Little is known, however, of how this trans-endothelial transport occurs or is regulated. Here, we leverage PGC-1α, a transcriptional coactivator that regulates broad programs of FA consumption, to identify 3-hydroxy-isobutyrate (3-HIB), a catabolic intermediate of the BCAA valine, as a novel paracrine regulator of trans-endothelial fatty acids (FA) transport. 3-HIB is secreted from muscle cells, activates endothelial FA transport, stimulates muscle FA uptake in vivo, and promotes muscle lipid accumulation and insulin resistance in animals. Conversely, inhibiting the synthesis of 3-HIB in muscle cells blocks the promotion of endothelial FA uptake. 3-HIB levels are elevated in muscle from db/db mice and from subjects with diabetes. These data thus unveil a novel mechanism that regulates trans-endothelial flux of FAs, revealing 3-HIB as a new bioactive signaling metabolite that links the regulation of FA flux to BCAA catabolism and provides a mechanistic explanation for how increased BCAA catabolic flux can cause diabetes.

Engineering nanoparticles to overcome barriers to immunotherapy.

Advances in immunotherapy have led to the development of a variety of promising therapeutics, including small molecules, proteins and peptides, monoclonal antibodies, and cellular therapies. Despite this wealth of new therapeutics, the efficacy of immunotherapy has been limited by challenges in targeted delivery and controlled release, that is, spatial and temporal control on delivery. Particulate carriers, especially nanoparticles have been widely studied in drug delivery and vaccine research and are being increasingly investigated as vehicles to deliver immunotherapies. Nanoparticle‐mediated drug delivery could provide several benefits, including control of biodistribution and transport kinetics, the potential for site‐specific targeting, immunogenicity, tracking capability using medical imaging, and multitherapeutic loading. There are also a unique set of challenges, which include nonspecific uptake by phagocytic cells, off‐target biodistribution, permeation through tissue (transport limitation), nonspecific immune‐activation, and poor control over intracellular localization. This review highlights the importance of understanding the relationship between a nanoparticle's size, shape, charge, ligand density and elasticity to its vascular transport, biodistribution, cellular internalization, and immunogenicity. For the design of an effective immunotherapy, we highlight the importance of selecting a nanoparticle's physical characteristics (e.g., size, shape, elasticity) and its surface functionalization (e.g., chemical or polymer modifications, targeting or tissue‐penetrating peptides) with consideration of its reactivity to the targeted microenvironment (e.g., targeted cell types, use of stimuli‐sensitive biomaterials, immunogenicity). Applications of this rational nanoparticle design process in vaccine development and cancer immunotherapy are discussed.

Complexity of vitamin E metabolism.

Bioavailability of vitamin E is influenced by several factors, most are highlighted in this review. While gender, age and genetic constitution influence vitamin E bioavailability but cannot be modified, life-style and intake of vitamin E can be. Numerous factors must be taken into account however, i.e., when vitamin E is orally administrated, the food matrix may contain competing nutrients. The complex metabolic processes comprise intestinal absorption, vascular transport, hepatic sorting by intracellular binding proteins, such as the significant α-tocopherol-transfer protein, and hepatic metabolism. The coordinated changes involved in the hepatic metabolism of vitamin E provide an effective physiological pathway to protect tissues against the excessive accumulation of, in particular, non-α-tocopherol forms. Metabolism of vitamin E begins with one cycle of CYP4F2/CYP3A4-dependent ω-hydroxylation followed by five cycles of subsequent β-oxidation, and forms the water-soluble end-product carboxyethylhydroxychroman. All known hepatic metabolites can be conjugated and are excreted, depending on the length of their side-chain, either via urine or feces. The physiological handling of vitamin E underlies kinetics which vary between the different vitamin E forms. Here, saturation of the side-chain and also substitution of the chromanol ring system are important. Most of the metabolic reactions and processes that are involved with vitamin E are also shared by other fat soluble vitamins. Influencing interactions with other nutrients such as vitamin K or pharmaceuticals are also covered by this review. All these processes modulate the formation of vitamin E metabolites and their concentrations in tissues and body fluids. Differences in metabolism might be responsible for the discrepancies that have been observed in studies performed in vivo and in vitro using vitamin E as a supplement or nutrient. To evaluate individual vitamin E status, the analytical procedures used for detecting and quantifying vitamin E and its metabolites are crucial. The latest methods in analytics are presented.

Spatio‐temporal Scaling of Vegetation Growth and Soil Formation from Percolation Theory

Core Ideas Solute or nutrient transport limits soil formation and vegetation growth Limitations on solute transport can only be understood within non‐Gaussian theories Three scaling relationships have a common origin in space and time Nutrient transport constraints limit vascular plant growth Solute transport constraints limit soil development Critical path analysis (CPA) is suited to calculating the hydraulic conductivity, K, of heterogeneous porous media by quantifying the paths of least resistance. Whenever CPA can be used to calculate K, advective transport scaling relationships from percolation theory should describe solute transport. Two solute transport relationships were applied to predict soil development and edaphic constraints on natural vegetation growth. These results used known exponents from percolation theory and known subsurface flow velocities. The typical flow velocity itself constrains the optimal growth rates of cultivars. The percolation scaling relationship constraining vegetation growth was shown to be in accord with data across time scales from hours to 100,000 yr, including more than a dozen studies (and two models) of tree growth. The scaling function for soil development explains time scales for the formation of soils from years to hundreds of millions of years. Data on soil development came from 23 different studies. The key unification is the common origin of the time and space coordinates for all three relationships in the transport time through a single pore of roughly micrometer size at a typical subsurface pore‐scale flow velocity. The distinction in evolving time scales is primarily a result of the hierarchical nature of vascular plant root systems, which speed up nutrient access relative to physical transport rates in the soil. The results help explain reductions in forest productivity with age, diminishing soil production with time, and the temporal distinction between chemical and biological processes in soils and their relevance to the global C cycle.

Reduced stem growth, but no reserve depletion or hydraulic impairment in beech suffering from long-term decline

Under non-extreme drought conditions, reduced stem growth is not associated with reserve or hydraulic impairment in beech suffering from long-term decline. Global change is expected to increase the frequency and the intensity of drought events in temperate ecosystems. In some regions, this might be associated with an increase in tree decline. Of the ecophysiological mechanisms that have been proposed to explain tree decline, an impairment of the vascular transport system and/or carbon function are two of the most discussed. In a context of long-term decline caused by droughts, we investigated the functional differences between the carbon, nitrogen, and hydraulic functions of healthy and declining mature beech (Fagus sylvatica L.) trees. The study was carried out over two consecutive years with contrasting water availabilities. The radial growth of declining trees was clearly less than that of healthy trees, due to a lower growth rate, associated during the wet year with a shorter growth period. Leaf functional characteristics and hydraulic parameters (native embolism and cavitation vulnerability curves) were similar in healthy and declining trees. However, at the end of a growing season characterized by a dry spring, carbon reserves concentrations in young branches of declining trees were lower than those in healthy trees, though they recovered during the following non-constraining growing season. Our results did not indicate carbon starvation, nitrogen deficiency, or hydraulic failure. However, there seems to be some compensation mechanism related to reserve dynamics in the remaining living tissue of the declining trees. This study shows that the climate conditions of successive years are probably crucial for these functional adjustments to be operational.

50. Ex vivo lung perfusion. Initial steps toward organ repair

Policy changes in conjunction with protocolized donor management have doubled the number of organ donors over the last 20 years in the United States. Nevertheless, the percentage of lungs transplanted from donors of at least one other organ has only marginally increased, 16% in 1995 vs. 23% in 2013. The institution of the lung allocation score in 2005, increased the number of patients transplanted and reduced the waiting list mortality, 373 in 2005 vs. 173 in 2013. However, the number of patients removed from the waiting list because they are too sick to be transplanted tripled during the same time period, 61 in 2005 vs. 181 in 2013. There remains a pressing need to increase the number of suitable lungs for transplantation. The use of ex vivo lung perfusion (EVLP) holds the potential to increase the number of transplantable organs. Currently pig and human lungs can be perfused up to 12 h with minimal edema formation, opening the door for pre-transplant lung reconditioning. As we look to increase perfusion times, or bank lungs, modifications in the perfusion/ventilation strategy, metabolic support, and toxin removal from the circuit may become necessary. Nevertheless, 12 h may give us enough time to repair most organs. Current available therapies could be rapidly translated to lung repair before transplantation. Fluid clearance can be stimulated in ex vivo perfused human lungs by intratracheal instillation of terbutaline. Vascular permeability and epithelial fluid transport can be restored with allogeneic mesenchymal stem cells (MSC). Other MSC properties, such as the antibacterial secretion of indoleamine 2,3-dioxygenase, LL-37 peptide, the inmunomodulatory effects of IL-10 and IL-4 secretion, the inhibition of INF- γ and TNF- α , and the positive effects described on ischemia-reperfusion injury in the liver and kidney could translate cell administration during ex vivo perfusion in a therapy tailored to modulate a wide range of conditions affecting lung quality. Gene therapy has also been proposed as an option to recondition donor lungs ex vivo. Human lungs that received IL-10 transfection exhibited improved functional quality, increased oxygenation, decreased vascular resistance, improved cell–cell interaction, and presented a positive shift from a pro-inflammatory to an anti-inflammatory cytokine release environment. Finally, the idea of growing immunotolerated lungs “on demand” was recently proposed. Cadaveric rat lungs that were de-cellularized, re-cellularized, and transplanted demonstrated good function up to 7 days. These are only a few of the potential therapies under study for ex vivo use. As new areas of investigation arise, EVLP is expected to prove a reproducible, and physiologically sound platform for their evaluation.

Measurement of vascular water transport in human subjects using time‐resolved pulsed arterial spin labelling

Most approaches to arterial spin labelling (ASL) data analysis aim to provide a quantitative measure of the cerebral blood flow (CBF). This study, however, focuses on the measurement of the transfer time of blood water through the capillaries to the parenchyma (referred to as the capillary transfer time, CTT) as an alternative parameter to characterise the haemodynamics of the system. The method employed is based on a non-compartmental model, and no measurements need to be added to a common time-resolved ASL experiment. Brownian motion of labelled spins in a potential was described by a one-dimensional general Langevin equation as the starting point, and as a Fokker-Planck differential equation for the averaged distribution of labelled spins at the end point, which takes into account the effects of flow and dispersion of labelled water by the pseudorandom nature of the microvasculature and the transcapillary permeability. Multi-inversion time (multi-TI) ASL data were acquired in 14 healthy subjects on two occasions in a test-retest design, using a pulsed ASL sequence and three-dimensional gradient and spin echo (3D-GRASE) readout. Based on an error analysis to predict the size of a region of interest (ROI) required to obtain reasonably precise parameter estimates, data were analysed in two relatively large ROIs, i.e. the occipital lobe (OC) and the insular cortex (IC). The average values of CTT in OC were 260 ± 60 ms in the first experiment and 270 ± 60 ms in the second experiment. The corresponding IC values were 460 ± 130 ms and 420 ± 139 ms, respectively. Information related to the water transfer time may be important for diagnostics and follow-up of cerebral conditions or diseases characterised by a disrupted blood-brain barrier or disturbed capillary blood flow.

Resting myocardial blood flow quantification using contrast-enhanced magnetic resonance imaging in the presence of stenosis: A computational fluid dynamics study.

The extent to which atherosclerotic plaques affect contrast agent (CA) transport in the coronary arteries and, hence, quantification of myocardial blood flow (MBF) using magnetic resonance imaging (MRI) is unclear. The purpose of this work was to evaluate the influence of plaque induced stenosis both on CA transport and on the accuracy of MBF quantification. Computational fluid dynamics simulations in a high-detailed realistic vascular model were employed to investigate CA bolus transport in the coronary arteries. The impact of atherosclerosis was analyzed by inserting various medium- to high-grade stenoses in the vascular model. The influence of stenosis morphology was examined by varying the stenosis shapes but keeping the area reduction constant. Errors due to CA bolus transport were analyzed using the tracer-kinetic model MMID4. Dispersion of the CA bolus was found in all models and for all outlets, but with a varying magnitude. The impact of stenosis was complex: while high-grade stenoses amplified dispersion, mild stenoses reduced the effect. Morphology was found to have a marked influence on dispersion for a small number of outlets in the post-stenotic region. Despite this marked influence on the concentration-time curves, MBF errors were less affected by stenosis. In total, MBF was underestimated by -7.9% to -44.9%. The presented results reveal that local hemodynamics in the coronary vasculature appears to have a direct impact on CA bolus dispersion. Inclusion of atherosclerotic plaques resulted in a complex alteration of this effect, with both degree of area reduction and stenosis morphology affecting the amount of dispersion. This strong influence of vascular transport effects impairs the accuracy of MRI-based MBF quantification techniques and, potentially, other bolus-based perfusion measurement techniques like computed tomography perfusion imaging.

Easy Come, Easy Go: Capillary Forces Enable Rapid Refilling of Embolized Primary Xylem Vessels.

Protoxylem plays an important role in the hydraulic function of vascular systems of both herbaceous and woody plants, but relatively little is known about the processes underlying the maintenance of protoxylem function in long-lived tissues. In this study, embolism repair was investigated in relation to xylem structure in two cushion plant species, Azorella macquariensis and Colobanthus muscoides, in which vascular water transport depends on protoxylem. Their protoxylem vessels consisted of a primary wall with helical thickenings that effectively formed a pit channel, with the primary wall being the pit channel membrane. Stem protoxylem was organized such that the pit channel membranes connected vessels with paratracheal parenchyma or other protoxylem vessels and were not exposed directly to air spaces. Embolism was experimentally induced in excised vascular tissue and detached shoots by exposing them briefly to air. When water was resupplied, embolized vessels refilled within tens of seconds (excised tissue) to a few minutes (detached shoots) with water sourced from either adjacent parenchyma or water-filled vessels. Refilling occurred in two phases: (1) water refilled xylem pit channels, simplifying bubble shape to a rod with two menisci; and (2) the bubble contracted as the resorption front advanced, dissolving air along the way. Physical properties of the protoxylem vessels (namely pit channel membrane porosity, hydrophilic walls, vessel dimensions, and helical thickenings) promoted rapid refilling of embolized conduits independent of root pressure. These results have implications for the maintenance of vascular function in both herbaceous and woody species, because protoxylem plays a major role in the hydraulic systems of leaves, elongating stems, and roots.

Radiosynthesis of 6'-Deoxy-6'[18F]Fluorosucrose via Automated Synthesis and Its Utility to Study In Vivo Sucrose Transport in Maize (Zea mays) Leaves.

Sugars produced from photosynthesis in leaves are transported through the phloem tissues within veins and delivered to non-photosynthetic organs, such as roots, stems, flowers, and seeds, to support their growth and/or storage of carbohydrates. However, because the phloem is located internally within the veins, it is difficult to access and to study the dynamics of sugar transport. Radioactive tracers have been extensively used to study vascular transport in plants and have provided great insights into transport dynamics. To better study sucrose partitioning in vivo, a novel radioactive analog of sucrose was synthesized through a completely chemical synthesis route by substituting fluorine-18 (half-life 110 min) at the 6’ position to generate 6’-deoxy-6’[18F]fluorosucrose (18FS). This radiotracer was then used to compare sucrose transport between wild-type maize plants and mutant plants lacking the Sucrose transporter1 (Sut1) gene, which has been shown to function in sucrose phloem loading. Our results demonstrate that 18FS is transported in vivo, with the wild-type plants showing a greater rate of transport down the leaf blade than the sut1 mutant plants. A similar transport pattern was also observed for universally labeled [U-14C]sucrose ([U-14C]suc). Our findings support the proposed sucrose phloem loading function of the Sut1 gene in maize, and additionally demonstrate that the 18FS analog is a valuable, new tool that offers imaging advantages over [U-14C]suc for studying phloem transport in plants.

METHANE FLUX FROM A SUBTROPICAL RESERVOIR LOCATED IN THE FLOODPLAINS OF RIVER YAMUNA, INDIA

Tropical and subtropical reservoirs are considered to be a strong anthropogenic source of methane (CH4) emissions worldwide due to high temperature, augmented carbon and nutrient loadings. Thus, CH4 emission estimation from tropical/subtropical reservoirs is critical for preparation of green house gas emission budgets. The Present study estimates CH4 flux from a subtropical freshwater manmade Okhla reservoir located on the river Yamuna, National Capital Region, India. Results showed that Okhla reservoir transformed into a potential CH4 emission source after flooding as the CH4 flux increased by 3.81 orders of magnitude with a net contribution of 171.96 mgm(-2)d(-1). Enhanced CH4 flux is primarily attributed to elevated organic and nutrient loadings to reservoir via river's inflow water, high percentage of shallow areas and presence of dense aquatic vegetation mainly Eichhornia crassipes and Typha angustifolia. These aquatic weeds not only facilitate vascular CH4 transport but also provide substantial amounts of biomass for methanogens to generate CH4. Results also revealed that the summer season exhibited significantly higher CH4 flux (Kruskal-Wallis H-Test; p < 0.05) as compared to monsoon and winter seasons due to prevalence of more favorable water and soil conditions for CH4 emissions including temperature, redox potential, water depth, dissolved oxygen, biological oxygen demand and plant biomass.

Fluence plays a critical role on the subsequent distribution of chemotherapy and tumor growth delay in murine mesothelioma xenografts pre-treated by photodynamic therapy.

The pre-conditioning of tumor vessels by low-dose photodynamic therapy (L-PDT) was shown to enhance the distribution of chemotherapy in different tumor types. However, how light dose affects drug distribution and tumor response is unknown. Here we determined the effect of L-PDT fluence on vascular transport in human mesothelioma xenografts. The best L-PDT conditions regarding drug transport were then combined with Lipoplatin(®) to determine tumor response. Nude mice bearing dorsal skinfold chambers were implanted with H-Meso1 cells. Tumors were treated by Visudyne(®) -mediated photodynamic therapy with 100 mW/cm(2) fluence rate and a variable fluence (5, 10, 30, and 50 J/cm(2) ). FITC-Dextran (FITC-D) distribution was assessed in real time in tumor and normal tissues. Tumor response was then determined with best L-PDT conditions combined to Lipoplatin(®) and compared to controls in luciferase expressing H-Meso1 tumors by size and whole body bioluminescence assessment (n = 7/group). Tumor uptake of FITC-D following L-PDT was significantly enhanced by 10-fold in the 10 J/cm(2) but not in the 5, 30, and 50 J/cm(2) groups compared to controls. Normal surrounding tissue uptake of FITC-D following L-PDT was significantly enhanced in the 30 J/cm(2) and 50 J/cm(2) groups compared to controls. Altogether, the FITC-D tumor to normal tissue ratio was significantly higher in the 10 J/cm(2) group compared others. Tumor growth was significantly delayed in animals treated by 10 J/cm2-L-PDT combined to Lipoplatin(®) compared to controls. Fluence of L-PDT is critical for the optimal distribution and effect of subsequently administered chemotherapy. These findings have an importance for the clinical translation of the vascular L-PDT concept in the clinics.

Three-dimensional human arterial wall models for in vitro permeability assessment of drug and nanocarriers

Monolayers of endothelial cells (1L-ECs) have been generally used as in vitro vascular wall models to study the vascular mechanisms and transport of substances. However, these two-dimensional (2D-) system cannot represent the properties of native vascular walls which have a 3D-structure and are composed of not only ECs, but also smooth muscle cells (SMCs) and other surrounding tissues. Here in, 5-layered (5L) 3D-arterial wall models (5L-AWMs) composed of EC monolayer and 4-layered SMCs were constructed by hierarchical cell manipulation. We applied the 5L-AWMs to evaluate their barrier function and permeability to nano-materials in order to analyze drug, or drug nanocarrier permeability to the blood vessel in vitro. Barrier property of the 3D-AWMs was confirmed by Zonula occludens (ZO-1) staining and their transendothelial electrical resistance (TEER), which was comparable to 1L-ECs, while the SMCs showed close to zero. The effect of substance size to permeability across the 5L-AWMs was clearly observed from dextrans with various molecular weights, which agreed well with the known phenomena of the in vivo blood vessels. Importantly, transport of nano-materials could be observed across the depth of 5L-AWMs, suggesting the advantage of 3D-AWMs over general 2D-systems. By using this system, we evaluate the transport of 35nm phenylalanine-modified poly(γ-Glutamic Acid) nanoparticles (γ-PGA-Phe NPs) as a candidate of biodegradable drug carrier. Interestingly, despite of having comparable size to dextran-2000k (28nm), the γ-PGA-Phe NPs distinctly showed approximately 20 times faster transport across the 5L-AWMs, suggesting the effect of intrinsic properties of the substance on the transport. This in vitro evaluation system using the 3D-AWMs is therefore useful for the design and development of nano-drug carriers for treatment of vascular diseases, such as atherosclerosis.

USNCTAM perspectives on mechanics in medicine.

Over decades, the theoretical and applied mechanics community has developed sophisticated approaches for analysing the behaviour of complex engineering systems. Most of these approaches have targeted systems in the transportation, materials, defence and energy industries. Applying and further developing engineering approaches for understanding, predicting and modulating the response of complicated biomedical processes not only holds great promise in meeting societal needs, but also poses serious challenges. This report, prepared for the US National Committee on Theoretical and Applied Mechanics, aims to identify the most pressing challenges in biological sciences and medicine that can be tackled within the broad field of mechanics. This echoes and complements a number of national and international initiatives aiming at fostering interdisciplinary biomedical research. This report also comments on cultural/educational challenges. Specifically, this report focuses on three major thrusts in which we believe mechanics has and will continue to have a substantial impact. (i) Rationally engineering injectable nano/microdevices for imaging and therapy of disease. Within this context, we discuss nanoparticle carrier design, vascular transport and adhesion, endocytosis and tumour growth in response to therapy, as well as uncertainty quantification techniques to better connect models and experiments. (ii) Design of biomedical devices, including point-of-care diagnostic systems, model organ and multi-organ microdevices, and pulsatile ventricular assistant devices. (iii) Mechanics of cellular processes, including mechanosensing and mechanotransduction, improved characterization of cellular constitutive behaviour, and microfluidic systems for single-cell studies.

Directed transport of bacteria-based drug delivery vehicles: bacterial chemotaxis dominates particle shape.

Several attenuated and non-pathogenic bacterial species have been demonstrated to actively target diseased sites and successfully deliver plasmid DNA, proteins and other therapeutic agents into mammalian cells. These disease-targeting bacteria can be employed for targeted delivery of therapeutic and imaging cargos in the form of a bio-hybrid system. The bio-hybrid drug delivery system constructed here is comprised of motile Escherichia coli MG1655 bacteria and elliptical disk-shaped polymeric microparticles. The transport direction for these vehicles can be controlled through biased random walk of the attached bacteria in presence of chemoattractant gradients in a process known as chemotaxis. In this work, we utilize a diffusion-based microfluidic platform to establish steady linear concentration gradients of a chemoattractant and investigate the roles of chemotaxis and geometry in transport of bio-hybrid drug delivery vehicles. Our experimental results demonstrate for the first time that bacterial chemotactic response dominates the effect of body shape in extravascular transport; thus, the non-spherical system could be more favorable for drug delivery applications owing to the known benefits of using non-spherical particles for vascular transport (e.g. relatively long circulation time).

A synthesis of methane emissions from 71 northern, temperate, and subtropical wetlands.

Wetlands are the largest natural source of atmospheric methane. Here, we assess controls on methane flux using a database of approximately 19 000 instantaneous measurements from 71 wetland sites located across subtropical, temperate, and northern high latitude regions. Our analyses confirm general controls on wetland methane emissions from soil temperature, water table, and vegetation, but also show that these relationships are modified depending on wetland type (bog, fen, or swamp), region (subarctic to temperate), and disturbance. Fen methane flux was more sensitive to vegetation and less sensitive to temperature than bog or swamp fluxes. The optimal water table for methane flux was consistently below the peat surface in bogs, close to the peat surface in poor fens, and above the peat surface in rich fens. However, the largest flux in bogs occurred when dry 30-day averaged antecedent conditions were followed by wet conditions, while in fens and swamps, the largest flux occurred when both 30-day averaged antecedent and current conditions were wet. Drained wetlands exhibited distinct characteristics, e.g. the absence of large flux following wet and warm conditions, suggesting that the same functional relationships between methane flux and environmental conditions cannot be used across pristine and disturbed wetlands. Together, our results suggest that water table and temperature are dominant controls on methane flux in pristine bogs and swamps, while other processes, such as vascular transport in pristine fens, have the potential to partially override the effect of these controls in other wetland types. Because wetland types vary in methane emissions and have distinct controls, these ecosystems need to be considered separately to yield reliable estimates of global wetland methane release.