Showing papers in "Microcirculation in 2011"

Multifractal and lacunarity analysis of microvascular morphology and remodeling.

Abstract: Objective Classical measures of vessel morphology, including diameter and density, are employed to study microvasculature in endothelial membrane labeled mice. These measurements prove sufficient for some studies; however, they are less well suited for quantifying changes in microcirculatory networks lacking hierarchical structure. We demonstrate that automated multifractal analysis and lacunarity may be used with classical methods to quantify microvascular morphology. Methods Using multifractal analysis and lacunarity, we present an automated extraction tool with a processing pipeline to characterize 2D representations of 3D microvasculature. We apply our analysis on four tissues and the hyaloid vasculature during remodeling. Results We found that the vessel networks analyzed have multifractal geometries and that kidney microvasculature has the largest fractal dimension and the lowest lacunarity compared to microvasculature networks in the cortex, skin, and thigh muscle. Also, we found that, during hyaloid remodeling, there were differences in multifractal spectra reflecting the functional transition from a space filling vasculature which nurtures the lens to a less dense vasculature as it regresses, permitting unobstructed vision. Conclusion Multifractal analysis and lacunarity are valuable additions to classical measures of vascular morphology and will have utility in future studies of normal, developing, and pathological tissues.

Critical role for oxidative stress, platelets, and coagulation in capillary blood flow impairment in sepsis.

Abstract: Sepsis is a complex multifaceted response to a local infectious insult. One important facet is the circulatory system dysfunction, which includes capillary bed plugging. This review addresses the mechanisms of capillary plugging and highlights our recent discoveries on the roles of NO, ROS, and activated coagulation in platelet adhesion and blood flow stoppage in septic mouse capillaries. We show that sepsis increases platelet adhesion, fibrin deposition and flow stoppage in capillaries, and that NADPH oxidase-derived ROS, rather than NO, play a detrimental role in this adhesion/stoppage. P-selectin and activated coagulation are required for adhesion/stoppage. Further, platelet adhesion in capillaries (i) strongly predicts capillary flow stoppage, and (ii) may explain why severe sepsis is associated with a drop in platelet count in systemic blood. Significantly, we also show that a single bolus of the antioxidant ascorbate (injected intravenously at clinically relevant dose of 10 mg/kg) inhibits adhesion/stoppage. Our data suggest that eNOS-derived NO at the platelet-endothelial interface is anti-adhesive and required for the inhibitory effect of ascorbate. Because of the critical role of ROS in capillary plugging, ascorbate bolus administration may be beneficial to septic patients whose survival depends on restoring microvascular perfusion.

Placental vascular dysfunction in diabetic pregnancies: intimations of fetal cardiovascular disease?

Abstract: In the human placenta, the angioarchitecture of fetal vessels lying in maternal blood is useful for nutrient uptake, but it makes the synthesis, maturation and functioning of placental vessels vulnerable to any alterations in the fetal and maternal environment. This review discusses how the maternal diabetic milieu, and the resultant fetal hyperglycemia and hyperinsulinemia, may act together to produce an altered placental vascular phenotype, which includes increased angiogenesis, altered junctional maturity, increased vascular endothelial-like growth factor (VEGF), altered VEGF and insulin receptor profiles, and upregulation of genes involved in signal transduction, transcription and mitosis in placental endothelial cells. The placental vascular dysfunction does extend to other fetal vascular beds including endothelial cells from umbilical vessels, where there are reports of elevated basal iNOS activity and altered sensitivity to insulin. There is emerging evidence of epigenetic modulation of fetal endothelial genes in diabetes and long-term vascular consequences of this. Thus, placental vascular dysfunction in diabetes may be contributing to and describing disturbances in the fetal vasculature, which may produce an overt pathological response in later life if challenged with additional cardiovascular stresses.

Importance of anti-angiogenic factors in the regulation of skeletal muscle angiogenesis.

Abstract: The microcirculation is essential for delivery of oxygen and nutrients to maintain skeletal muscle health and function. The network of microvessels surrounding skeletal myocytes has a remarkable plasticity that ensures a good match between muscle perfusion capacities and myofiber metabolic needs. Depending on physiologic conditions, this vascular plasticity can either involve growth (e.g., exercise-induced angiogenesis) or regression (e.g., physical deconditioning) of capillaries. This angio-adaptative response is thought to be controlled by a balance between pro- and anti-angiogenic factors and their receptors. While changes in the expression or activity for pro-angiogenic factors have been well studied in response to acute and chronic exercise during the past two decades, little attention thus far has been devoted to endogenous negative regulators that are also likely to be important in regulating capillary growth/regression. Indeed, the importance and contribution of anti-angiogenic factors in controlling skeletal muscle angiogenesis remains poorly understood. Here, we highlight the emerging research related to skeletal muscle expression of several negative angiogenic factors and discuss their potential importance in controlling skeletal muscle angio-adaptation, particularly in physiologic response to physical activity.

Aging‐Associated Alterations in Contractility of Rat Mesenteric Lymphatic Vessels

Abstract: Objective: To evaluate the age-related changes in pumping of mesenteric lymphatic vessels in 9- and 24-month-old male Fisher344 rats. Methods: Lymphatic diameters, contraction amplitude, contraction frequency, and fractional pump flow were determined in isolated MLV before and after L-NAME application. Results: The data demonstrate a severe weakening of the lymphatic pump in aged MLV including diminished lymphatic contraction amplitude, contraction frequency, and as a result, lymphatic pump activity. The data also suggest that the imposed flow gradient-generated shear-dependent relaxation does not exist in aged rat MLV, and the sensitivity of both adult and aged MLV to such shear cannot be eliminated by nitric oxide (NO) synthases blockade. Conclusions: These data provide new evidence of lymphatic regional heterogeneity for both adult and aged MLV. In MLV, a constant interplay between the tonic and phasic components of the myogenic response and the shear-dependent release of NO predominantly determine the level of contractile activity; the existence of another shear-dependent, but NO-independent regulatory mechanism is probably present. Aging remarkably weakens MLV contractility, which would predispose this lymphatic network to lower total lymph flow in resting conditions and limit the ability to respond to an edemagenic challenge in the elderly.

Intrauterine growth restriction and developmental programming of the metabolic syndrome: a critical appraisal.

Abstract: According to the "small baby syndrome hypothesis," low birthweight and intrauterine growth restriction (IUGR) occurring in westernized countries mainly through altered placental flow, have been linked to increased metabolic syndrome risk in later life. Independency and causal mechanisms of this phenomenological association are a matter of controversy. By means of epidemiological as well as experimental methods, using meta-analyses and different rodent models of pre- and/or neonatal malnutrition and altered placental flow (uterine artery ligation; Lig), we systematically addressed the phenomenon. Our data and systematic literature analysis revealed that neither epidemiological nor experimental evidence seems to exist linking prenatal underfeeding, low birthweight, IUGR, or decreased placental flow in rats (Lig-model) as independent risk factors to increased metabolic syndrome risk in later life. Rather, pre- and/or neonatal overfeeding, elevated birthweight, rapid neonatal weight gain, and especially increased adiposity during critical periods of perinatal life may increase long-term risks. Perinatally acquired microstructural and epigenomic alterations in regulatory systems of metabolism and body weight seem to be critical, leading to a cardiometabolic risk disposition throughout life. While experimental data in Lig-offspring seem to be considerably biased, prenatal stress and postnatal overfeeding/rapid neonatal weight gain might be causally linked to a long-term deleterious outcome in growth restricted newborns. From a clinical point of view, prevention of causes of IUGR, as well as avoidance of perinatal overnourishment, might be prophylactic approaches to avoid perinatal programming of cardiometabolic risks.

MEK5 is activated by shear stress, activates ERK5 and induces KLF4 to modulate TNF responses in human dermal microvascular endothelial cells.

Abstract: Objective Endothelial cells (ECs) lining arteries respond to laminar shear stress (LSS) by suppressing pro-inflammatory changes, in part through the activation of MEK5, ERK5 and induction of KLF4. We examined if this anti-inflammatory pathway operates in human ECs lining microvessels, the principal site of inflammatory responses.

Dynamics of angiogenesis during wound healing: A coupled in vivo and in silico study

Abstract: Objective: The most critical determinant of restoration of tissue structure during wound healing is the re-establishment of a functional vasculature, which largely occurs via angiogenesis, specifically endothelial sprouting from the pre-existing vasculature. Materials and Methods: We used confocal microscopy to capture sequential images of perfused vascular segments within the injured panniculus carnosus muscle in the mouse dorsal skinfold window chamber to quantify a range of microcirculatory parameters during the first nine days of healing. This data was used to inform a mathematical model of sequential growth of the vascular plexus. The modeling framework mirrored the experimental circular wound domain and incorporated capillary sprouting and endothelial cell (EC) sensing of vascular endothelial growth factor gradients. Results: Wound areas, vessel densities and vessel junction densities obtained from the corresponding virtual wound were in excellent agreement both temporally and spatially with data measured during the in vivo healing process. Moreover, by perturbing the proliferative ability of ECs in the mathematical model, this leads to a severe reduction in vascular growth and poor healing. Quantitative measures from this second set of simulations were found to correlate extremely well with experimental data obtained from animals treated with an agent that targets endothelial proliferation (TNP-470). Conclusion: Our direct combination and comparison of in vivo longitudinal analysis (over time in the same animal) and mathematical modeling employed in this study establishes a useful new paradigm. The virtual wound created in this study can be used to investigate a wide range of experimental hypotheses associated with wound healing, including disorders characterized by aberrant angiogenesis (e.g., diabetic models) and the effects of vascular enhancing⁄disrupting agents or therapeutic interventions such as hyperbaric oxygen.

17β-estradiol and progesterone independently augment cutaneous thermal hyperemia but not reactive hyperemia.

Abstract: Please cite this paper as: Brunt, Miner, Meendering, Kaplan, and Minson (2011) 17β-Estradiol and Progesterone Independently Augment Cutaneous Thermal Hyperemia But Not Reactive Hyperemia Microcirculation 18(5), 347–355 Abstract Objective: We examined the impact of estradiol and progesterone on skin LH and RH in 25 healthy women Methods: Subjects were studied three times over 10–12 days Endogenous sex hormones were suppressed with a GnRHa Subjects were studied on day 4 of suppression (study day 1), three to four days later following treatment with either 17β-estradiol or progesterone (study day 2), and another three to four days later, following treatment with both estradiol and progesterone (study day 3) Subjects underwent identical LH and RH protocols on all study days LH is characterized by an initial peak in blood flow, followed by a prolonged plateau A brief nadir is seen between the phases Results: Blood flow values are expressed as percent maximum CVC Estradiol alone increased initial peak CVC from 71 ± 2% to 79 ± 2% (p = 0001) Progesterone alone increased initial peak CVC from 72 ± 2% to 78 ± 2% (p = 0046) Neither estradiol nor progesterone increased plateau CVC No significant changes were seen between study days 2 and 3 for either group No differences were observed in RH Conclusions: Both estradiol and progesterone increased initial peak CVC during LH, without altering plateau CVC There was no additive effect of estradiol and progesterone

Exaggerated Neutrophil-Mediated Reperfusion Injury after Ischemic Stroke in a Rodent Model of Type 2 Diabetes

Abstract: Please cite this paper as: Ritter, Davidson, Henry, Davis-Gorman, Morrison, Frye, Cohen, Chandler, McDonagh and Funk (2011). Exaggerated Neutrophil-Mediated Reperfusion Injury after Ischemic Stroke in a Rodent Model of Type 2 Diabetes. Microcirculation 18(7), 552–561. Abstract Objective: We tested the hypothesis that both chronic and acute inflammatory processes contribute to worse reperfusion injury and stroke outcome in an experimental model of T2DM. Materials and Methods: Twelve- to thirteen-week-old male Zucker Diabetic Fatty (ZDF) rats vs. Zucker Lean Controls (ZLC) rats were tested at baseline and after middle cerebral artery occlusion (ischemia) and reperfusion (I–R). Neutrophil adhesion to the cerebral microcirculation, neutrophil expression of CD11b, infarction size, edema, neurologic function, sICAM, and cerebral expression of neutrophil–endothelial inflammatory genes were measured. Results: At baseline, CD11b and sICAM were significantly increased in ZDF vs. ZLC animals (p < 0.05). After I–R, significantly more neutrophil adhesion and cell aggregates were observed in ZDF vs. ZLC (p < 0.05); infarction size, edema, and neurologic function were significantly worse in ZDF vs. ZLC (p < 0.05). CD11b and sICAM-1 remained significantly increased in ZDFs (p < 0.05), and cerebral expression of IL-1β, GRO/KC, E-selectin, and sICAM were significantly induced in ZDF, but not ZLC groups (p < 0.05) after 2.5 hours of reperfusion. Conclusion: Both sides of the neutrophil–endothelial interface appear to be primed prior to I–R, and remain significantly more activated during I–R in an experimental model of T2DM. Consequently, reperfusion injury appears to play a significant role in poor stroke outcome in T2DM.

Oxidized low-density lipoprotein inhibits nitric oxide-mediated coronary arteriolar dilation by up-regulating endothelial arginase I.

Abstract: Oxidized low-density lipoprotein (OxLDL) causes impairment of endothelium-dependent, nitric oxide (NO)-mediated vasodilation involving l-arginine deficiency. However, the underlying mechanism remains elusive. Since arginase and endothelial NO synthase (eNOS) share the substrate l-arginine, we hypothesized that OxLDL may reduce l-arginine availability to eNOS for NO production, and thus vasodilation, by up-regulating arginase. To test this hypothesis, porcine subepicardial arterioles (70-130 μm) were isolated for vasomotor study and for immunohistochemical detection of arginase and eNOS expressions. The coronary arterioles dilated dose-dependently to the endothelium-dependent NO-mediated vasodilator serotonin. This vasodilation was inhibited in the same manner by NOS inhibitor N(G)-nitro-l-arginine methyl ester and by lumenal OxLDL (0.5 mg protein/mL). The inhibitory effect of OxLDL was reversed after treating the vessels with either l-arginine (3 mM) or arginase inhibitor difluoromethylornithine (DFMO; 0.4 mM). Consistent with vasomotor alterations, OxLDL inhibited serotonin-induced NO release from coronary arterioles and this inhibition was reversed by DFMO. Vascular arginase activity was significantly elevated by OxLDL. Immunohistochemical analysis indicated that OxLDL increased arginase I expression in the vascular wall without altering eNOS expression. Taken together, these results suggest that OxLDL up-regulates arginase I, which contributes to endothelial dysfunction by reducing l-arginine availability to eNOS for NO production and thus vasodilation.

Beta-adrenergic stimulation contributes to maintenance of endothelial barrier functions under baseline conditions.

Abstract: Please cite this paper as: Spindler and Waschke (2011). Beta-Adrenergic Stimulation Contributes to Maintenance of Endothelial Barrier Functions under Baseline Conditions. Microcirculation18(2), 118–127. Abstract Objectives: cAMP signaling within the endothelium is known to reduce paracellular permeability and to protect against loss of barrier functions under various pathological conditions. Because activation of β-adrenergic receptors elevates cellular cAMP, we tested whether β-adrenergic receptor signaling contributes to the maintenance of baseline endothelial barrier properties. Methods: We compared hydraulic conductivity of rat postcapillary venules in vivo with resistance measurements and with reorganization of endothelial adherens junctions in cultured microvascular endothelial cells downstream of β-adrenergic receptor-mediated changes of cAMP levels. Results: Inhibition of β-adrenergic receptors by propranolol increased hydraulic conductivity, reduced both cAMP levels and TER of microvascular endothelial cell monolayers and induced fragmentation of VE-cadherin staining. In contrast, activation by epinephrine both increased cAMP levels and TER and resulted in linearized VE-cadherin distribution, however this was not sufficient to block barrier-destabilization by propranolol. Similarly, PDE inhibition did not prevent propranolol-induced TER reduction and VE-cadherin reorganization whereas increased cAMP formation by AC activation enhanced endothelial barrier functions under baseline conditions and under conditions of propranolol treatment. Conclusions: Our results indicate that generation of cAMP mediated by activation of β-adrenergic receptor signaling contributes to the maintenance of endothelial barrier properties under baseline conditions.

Impact of dietary soy isoflavones in pregnancy on fetal programming of endothelial function in offspring.

Abstract: Epidemiological evidence suggests that soy-based diets containing phytoestrogens (isoflavones) afford protection against cardiovascular diseases (CVDs); however, supplementation trials have largely reported only marginal health benefits The molecular mechanisms by which the isoflavones genistein, daidzein, and equol afford protection against oxidative stress remain to be investigated in large scale clinical trials Isoflavones are transferred across the placenta in both rodents and humans, yet there is limited information on their actions in pregnancy and the developmental origins of disease Our studies established that feeding a soy isoflavone-rich diet during pregnancy, weaning, and postweaning affords cardiovascular protection in aged male rats Notably, rats exposed to a soy isoflavone-deficient diet throughout pregnancy and adult life exhibited increased oxidative stress, diminished antioxidant enzyme and eNOS levels, endothelial dysfunction, and elevated blood pressure in vivo The beneficial effects of refeeding isoflavones to isoflavone-deficient rats include an increased production of nitric oxide and EDHF, an upregulation of antioxidant defense enzymes and lowering of blood pressure in vivo This review focuses on the role that isoflavones in the fetal circulation may play during fetal development in affording protection against CVD in the offspring via their ability to activate eNOS, EDHF, and redox-sensitive gene expression

Hemodynamic Systems Analysis of Capillary Network Remodeling During the Progression of Type 2 Diabetes

Abstract: Please cite this paper as: Benedict, Coffin, Barrett and Skalak (2011). Hemodynamic Systems Analysis of Capillary Network Remodeling During the Progression of Type 2 Diabetes. Microcirculation18(1), 63–73. Abstract Objective: Early alterations in the skeletal muscle microvasculature may contribute to the onset and progression of type 2 diabetes (DM2) by limiting insulin and glucose availability to skeletal muscle. Microvascular alterations reported with DM2 are numerous and include impaired endothelium-mediated vasodilation, increased arteriole wall stiffness, and decreased capillary density. Most previous analyses of skeletal muscle microvascular architecture have been limited to skeletal muscle cross sections and thus have not presented an integrated, quantitative analysis of the relative significance of observed alterations to elevated microvascular network resistance and decreased blood flow. In this work, we tested the hypothesis that the onset of diabetes would influence microvascular architecture in a manner that would significantly increase capillary network resistance and reduce blood flow. Methods and Results: In whole-mount spinotrapezius muscle capillary networks from Zucker diabetic fatty (ZDF) rats before and after the onset of DM2, we found a significant 37% decrease in microvascular branching and a 19% decrease in microvessel length density associated with the onset of the disease. This was previously indiscernible in skeletal muscle cross-section data. Hemodynamic computational analysis revealed that the changes in DM2 capillary network connectivity result in a significant 44% decrease in computed capillary network flow compared to controls. A hemodynamic sensitivity analysis showed that DM2 networks were predicted to be less robust in their ability to maintain perfused network surface area in the event of upstream terminal arteriole constriction. Conclusions: This study illustrates that capillary network connectivity is altered by DM2 and this negatively impacts microvascular hemodynamics. This work can serve as a basis for a more quantitative approach to evaluating DM2 microvascular networks and their potential use as an early diagnostic aid and/or method for identifying therapeutic targets.

CCR7 mediates directed growth of melanomas towards lymphatics.

Abstract: Objective To determine whether chemotactic-metastasis, the preferential growth of melanomas towards areas of high lymphatic density, is CCL21/CCR7 dependent in vivo. Lymphatic endothelial cells (LECs) produce the chemokine CCL21. Metastatic melanoma cells express CCR7, its receptor, and exhibit chemotactic-metastasis, whereby metastatic cells recognise and grow towards areas of higher lymphatic density.

Substance P activates both contractile and inflammatory pathways in lymphatics through the neurokinin receptors NK1R and NK3R.

Abstract: Please cite this paper as: Chakraborty, Nepiyushchikh, Davis, Zawieja and Muthuchamy (2011). Substance P Activates Both Contractile and Inflammatory Pathways in Lymphatics Through the Neurokinin Receptors NK1R and NK3R. Microcirculation18(1), 24–35. Abstract Objective: The aim of this study was to elucidate the molecular signaling mechanisms by which substance P (SP) modulates lymphatic muscle contraction and to determine whether SP stimulates both contractile as well as inflammatory pathways in the lymphatics. Methods: A rat mesenteric lymphatic muscle cell culture model (RMLMCs) and known specific pharmacological inhibitors were utilized to delineate SP-mediated signaling pathways in lymphatics. Results: We detected expression of neurokinin receptor 1 (NK1R) and neurokinin receptor 3 (NK3R) in RMLMCs. SP stimulation increased phosphorylation of myosin light chain 20 (MLC20) as well as p38 mitogen associated protein kinase (p38-MAPK) and extracellular signal regulated kinase (ERK1/2) indicating activation of both a contractile and a pro-inflammatory MAPK pathway. Pharmacological inhibition of both NK1R and NK3R significantly affected the downstream SP signaling. We further examined whether there was any crosstalk between the two pathways upon SP stimulation. Inhibition of ERK1/2 decreased levels of p-MLC20 after SP activation, in a PKC dependent manner, indicating a potential crosstalk between these two pathways. Conclusions: These data provide the first evidence that SP-mediated crosstalk between pro-inflammatory and contractile signaling mechanisms exists in the lymphatic system and may be an important bridge between lymphatic function modulation and inflammation.

A human neutralizing antibody specific to Ang-2 inhibits ocular angiogenesis.

Abstract: Please cite this paper as: Rennel, Regula, Harper, Thomas, Klein and Bates (2011). A Human Neutralizing Antibody Specific to Ang-2 Inhibits Ocular Angiogenesis. Microcirculation 18(7), 598–607. Abstract Objective: Angiogenesis, a critical contributor to ocular as well as neoplastic diseases, is stimulated by endothelial production of angiopoietin-2 (Ang2). Our objective was to determine the requirement of ocular angiogenesis for Ang2 in animal models of disease. Methods: We developed and compared the effect of a novel human Ang2 antibody with a pan-angiopoietin strategy on angiogenesis in ocular angiogenesis in animal models of oxygen-induced retinopathy, and laser photocoagulation and confirmed its efficacy in xenografted human colorectal tumors. Results: Human anti-Ang2 and anti-angiopoietin1(Ang1)/Ang2 antibodies blocked colorectal carcinoma growth in immuno-compromised mice (p < 0.001, n = 6). Injection of 1 μg of Ang2 or Ang2/Ang1 antibody-inhibited angiogenesis in models of retinal (p < 0.001, n = 6), and choroidal neovascularization (p < 0.001, n = 11–13 per group) to levels similar to that with anti-VEGF antibodies. There was no difference between Ang2 specific and Ang1/Ang2 bi-specific antibodies. In vitro, Ang2 antibodies showed no cytotoxicity and did not inhibit endothelial cell migration or proliferation. Conclusion: Thus, human Ang2 antibodies are potentially therapeutic agents for ocular neovascularization in models of retinal and choroidal neovascularization, in the absence of VEGF inhibition.

Bifurcations: focal points of particle adhesion in microvascular networks.

Abstract: Please cite this paper as: Prabhakarpandian, Wang, Rea-Ramsey, Sundaram, Kiani, and Pant (2011). Bifurcations: Focal Points of Particle Adhesion in Microvascular Networks. Microcirculation. 18(5), 380–389. Abstract Objective: Particle adhesion in vivo is dependent on the microcirculation environment, which features unique anatomical (bifurcations, tortuosity, cross-sectional changes) and physiological (complex hemodynamics) characteristics. The mechanisms behind these complex phenomena are not well understood. In this study, we used a recently developed in vitro model of microvascular networks, called SMN, for characterizing particle adhesion patterns in the microcirculation. Methods: SMNs were fabricated using soft-lithography processes followed by particle adhesion studies using avidin and biotin-conjugated microspheres. Particle adhesion patterns were subsequently analyzed using CFD-based modeling. Results: Experimental and modeling studies highlighted the complex and heterogeneous fluid flow patterns encountered by particles in microvascular networks resulting in significantly higher propensity of adhesion (>1.5×) near bifurcations compared with the branches of the microvascular networks. Conclusion: Bifurcations are the focal points of particle adhesion in microvascular networks. Changing flow patterns and morphology near bifurcations are the primary factors controlling the preferential adhesion of functionalized particles in microvascular networks. SMNs provide an in vitro framework for understanding particle adhesion.

Effect of suspending viscosity on red blood cell dynamics and blood flows in microvessels.

Abstract: Please cite this paper as: Zhang (2011). Effect of Suspending Viscosity on Red Blood Cell Dynamics and Blood Flows in Microvessels. Microcirculation 18(7), 562–573. Abstract To obtain a better understanding of the beneficial effect of high plasma viscosity observed in hemodilution and resuscitation experiments, we conducted a computational study to investigate the suspending viscosity effect on red blood cell (RBC) dynamics and blood flow behaviors in microvessels. For single RBCs in simple shear or channel flows, RBCs appear more flexible as indicated by the tank-treading motion in shear flows and the strong transverse migration in channel flows. For the multiple RBC flows in straight channels, our results indicate no significant change with the suspending viscosity in stable flow structure and hemorheologic behaviors, under both constant flow and forcing conditions. However, due to the increase in apparent cell deformability in a more viscous medium, the cell-free layer (CFL) can be established in a shorter distance along the channel. Considering the multilevel bifurcated structure of the microvascular network, this change in CFL development distance may affect the phase skimming and RBC separation processes at the downstream bifurcation, and therefore the microcirculation performance in the tissue. This may suggest a possible mechanism for the high functional capillary density associated with a high suspending viscosity observed in experiments.

Glycine and taurine equally prevent fatty livers from Kupffer cell-dependent injury: an in vivo microscopy study.

Abstract: Background: IRI still is a major problem in liver surgery due to warm ischemia and organ manipulation. Steatosis is not only induced by diabetes, hyperalimentation, alcohol and toxins, but also chemotherapy given before resection. Since steatotic livers are prone to Kupffer cell-dependent IRI, protection of steatotic livers is of special interest. This study was designed to compare the effect of taurine and glycine on IRI in steatotic livers. Materials and Methods: Steatosis was induced with ethanol (7 g ⁄ kg b.w.; p.o.) in female SD rats. Ten minutes after inactivation of Kupffer cells with taurine or glycine (300 mM; i.v.), left liver lobes underwent 60 minutes of warm ischemia. Controls received the same volume of valine (300 mM; i.v.) or normal saline. After reperfusion, white blood cell-endothelial interactions and latex-bead phagocytosis by Kupffer cells were investigated. Liver enzymes were measured to estimate injury. For statistical analysis, ANOVA and Student’s t-test were used. Results: Glycine and taurine significantly decreased leukocyteand platelet-endothelium interactions and latex-bead phagocytosis (p < 0.05). Liver enzymes were significantly lower after glycine and taurine (p < 0.05). Conclusions: This study shows that preconditioning with taurine or glycine is equally effective in preventing injury to fatty livers most likely via Kupffer cell-dependent mechanisms.

Influence of Maternal Nutritional Status on Vascular Function in the Offspring

Abstract: Please cite this paper as: Poston (2011). Influence of Maternal Nutritional Status on Vascular Function in the Offspring. Microcirculation 18(4), 256–262. Abstract Suboptimal maternal nutritional status has been implicated in the development of cardiovascular risk in the child. Initially inferred from studies of low-birthweight children, investigations in cohorts of women subjected to famine provide direct evidence for an independent influence of the mother’s diet on the cardiovascular health of her child. Animal studies from rodents and sheep have shown associations between maternal undernutrition and raised blood pressure, as well as abnormalities in resistance artery function, particularly in endothelium-dependent responses. Early life exposure to the influences of maternal over nutritional states, e.g. obesity and excessive gestational weight gain, has also been associated with markers of cardiovascular risk in man, and animal models have shown raised blood pressure and endothelial dysfunction in offspring of diet-induced obese dams. Increased sympathetic tone is commonly associated with hypertension in animal models of both under nutritional and over nutritional states. This and several other similarities may indicate commonality of mechanism and could reflect supranormal nutritional status in postnatal life in both conditions.

The microcirculation: a target for developmental priming.

Abstract: There is increasing evidence that the early life environment, of which nutrition is a key component, acts through developmental adaptations to set the capacity of cardiovascular and metabolic pathways, and ultimately the limits to physiological challenges in later life. Sub-optimal maternal nutrition and fetal growth result in reduced microvascular perfusion and functional dilator capacity, which are strongly associated with later development of obesity, type 2 diabetes and hypertension. These conditions are also linked to microvascular rarefaction and remodeling that together limit capillary recruitment, reduce exchange capacity and increase diffusion distances of metabolic substrates, and increase local and overall peripheral resistance. Changes in small vessel structure and function may be seen very early, long before the onset of overt cardiovascular and metabolic disease, and may thus be a target for early therapeutic and life style intervention strategies. This article explores how a disadvantageous microvascular phenotype may result from perinatal priming and how developmental plasticity may become an important and additional risk determinant in susceptibility to cardio-metabolic disease in adult life.

Smooth muscle Ca(2+) -activated and voltage-gated K+ channels modulate conducted dilation in rat isolated small mesenteric arteries.

Abstract: Please cite this paper as: Beleznai, Yarova, Yuill and Dora (2011). Smooth Muscle Ca2+-Activated and Voltage-Gated K+ Channels Modulate Conducted Dilation in Rat Isolated Small Mesenteric Arteries. Microcirculation 18(6), 487–500. Abstract Objective: To assess the influence of blocking smooth muscle large conductance Ca2+-activated K+ channels and voltage-gated K+ channels on the conducted dilation to ACh and isoproterenol. Materials and Methods: Rat mesenteric arteries were isolated with a bifurcation, triple-cannulated, pressurized and imaged using confocal microscopy. Phenylephrine was added to the superfusate to generate tone, and agonists perfused into a sidebranch to evoke local dilation and subsequent conducted dilation into the feed artery. Results: Both ACh− and isoproterenol-stimulated local and conducted dilation with similar magnitudes of decay with distance along the feed artery (2000 μm: ∼15% maximum dilation). The gap junction uncoupler carbenoxolone prevented both conducted dilation and intercellular spread of dye through gap junctions. IbTx, TEA or 4-AP, blockers of large conductance Ca2+-activated K+ channels and voltage-gated K+ channels, did not affect conducted dilation to either agonist. A combination of either IbTx or TEA with 4-AP markedly improved the extent of conducted dilation to both agonists (2000 μm: >50% maximum dilation). The enhanced conducted dilation was reflected in the hyperpolarization to ACh (2000 μm: Control, 4 ± 1 mV, n = 3; TEA with 4-AP, 14 ± 3mV, n = 4), and was dependent on the endothelium. Conclusions: These data show that activated BKCa and KV-channels serve to reduce the effectiveness of conducted dilation.

Assessment of blood flow changes in human skin by microdialysis urea clearance.

Abstract: The aim of this thesis was to develop and evaluate a new way of monitoring blood flow with microdialysis. A thin catheter consisting of a semipermeable membrane is implanted in the tissue being studied. The catheter is perfused by a solution that closely resembles interstitial fluid, and small water-soluble substances are allowed to diffuse passively through the pores of the membrane with the aim at reaching equilibrium with the surrounding tissue. The minimally invasive character of microdialysis, and its ability to sample from the organ being studied, make microdialysis attractive in most research settings as well as for clinical surveillance. It has, however, become increasingly evident that microdialysis under conditions of non-equilibrium - for example, fluctuating regional blood flow, will alter the results gained. We have therefore aimed to explore the possibilities of developing a new marker of blood flow that will yield information about changes in blood flow that occur in the area of the microdialysis catheter itself. We hypothesised that the changes in the diffusion of exogenous urea could be used as markers of changes in tissue blood flow. The theoretical basis for this approach is that the mass transfer of urea will increase across the dialysis membrane secondary to increased blood flow. As removal of urea from the vicinity of the dialysis membrane increases with increased blood flow, the concentration gradient of urea between the perfusate and tissue will also increase. This in turn will result in a greater loss of urea from the perfusate. The changes noted in retrieval of urea from dialysate by the system are therefore thought to be inversely related to changes in blood flow. We tested our hypothesis in two species of animal (rat and pig) and in man, and in three organ systems (muscle, liver, and skin), and present four papers that indicate that the urea clearance technique provides reliable and reproducible results. The technique was evaluated against conventional metabolic markers (lactate and glucose), the ethanol clearance technique (microdialysis), laser Doppler perfusion imaging (LDPI), and polarisation light spectroscopy (TiVi). We present evidence that the urea clearance technique can be used to assess blood flow in the organs studied reliably and reproducibly with microdialysis. The microdialysis technique is minimally invasive and safe for the recipient, and catheters can easily be implanted during operation to monitor organs at risk. Urea is easily analysed as a standard assay among other “basic” metabolic markers (in a standard microdialysis kit) and has favourable characteristics with a standardised measurement system that is routinely used for monitoring metabolites in the clinic. The technique is also effective when used at lower perfusate flow rates (<1 μl/minute), which is advantageous as the recovery of metabolic markers increases at low perfusate flow rates.

Connective Tissue Growth Factor (CTGF/CCN2) Mediates Angiogenic Effect of S1P in Human Dermal Microvascular Endothelial Cells

Abstract: Please cite this paper as: Markiewicz, Nakerakanti, Kapanadze, Ghatnekar and Trojanowska (2011). Connective Tissue Growth Factor (CTGF/CCN2) Mediates Angiogenic Effect of S1P in Human Dermal Microvascular Endothelial Cells. Microcirculation18(1), 1–11. Abstract Objective: The primary objective of this study was to examine the potential interaction between S1P, a pleiotropic lipid mediator, and CTGF/CCN2, a secreted multimodular protein, in the process of endothelial cell migration. The secondary objective was to determine whether C- and N-terminal domains of CTGF/CCN2 have a specific function in cell migration. Materials and Methods: Migration of HDMECs was examined in monolayer wound healing “scratch” assay, whereas capillary-like tube formation was examined in three-dimensional collagen co-culture assays. Results: We observed that S1P stimulates migration of HDMECs concomitant with upregulation of CTGF/CCN2 expression. Furthermore, the blockade of endogenous CTGF/CCN2 via siRNA abrogated S1P-induced HDMEC migration and capillary-like tube formation. Full-length CTGF induced cell migration and capillary-like tube formation with a potency similar to that of S1P, while C-terminal domain of CTGF was slightly less effective. However, N-terminal domain had only a residual activity in inducing capillary-like tube formation. Conclusions: This study revealed that CTGF/CCN2 is required for the S1P-induced endothelial cell migration, which suggests that CTGF/CCN2 may be an important mediator of S1P-induced physiological and pathological angiogenesis. Moreover, this study shows that the pro-migratory activity of CTGF/CCN2 is located in the C-terminal domain.

Cell-free layer formation in small arterioles at pathological levels of erythrocyte aggregation.

Abstract: Objective: To test our hypothesis that an elevation in the aggregation level of red blood cells found in human pathological conditions will significantly enhance cell-free layer formation in small arterioles. Methods: Visualization of arteriolar blood flow in rat cremaster muscle was carried out in both normal and reduced flow conditions before and after Dextran 500 infusion to simulate physiological and pathological levels of red blood cell aggregation in humans. Results: Both normalized mean ( p< 0.0001) and SD ( p< 0.002) of the layer width were significantly enhanced after hyperaggregation induction in reduced flow conditions (mean pseudoshear rate = 57.3 ± 7.2 ⁄sec). Normalized mean and SD of the layer width generally increased with decreasing vessel radius and this effect was most pronounced with hyper-aggregation in reduced flow conditions. The threshold pseudoshear rate at which the layer formation became more pronounced when compared with non-aggregating condition was higher with hyper-aggregation (217 ⁄sec) than normal-aggregation induction (139 ⁄sec). Conclusion: Our findings confirmed the formation of a prominent cell-free layer in the arterioles under higher shear conditions at pathological aggregation levels and this effect became more pronounced in smaller arterioles in normalizing the layer to the vessel radius.

Role of neuronal nitric oxide synthase in modulating microvascular and contractile function in rat skeletal muscle.

Abstract: Please cite this paper as: Copp, Hirai, Ferguson, Musch and Poole (2011). Role of Neuronal Nitric Oxide Synthase in Modulating Microvascular and Contractile Function in Rat Skeletal Muscle. Microcirculation 18(6), 501–511. Abstract Objective: This investigation tested the hypothesis that selective nNOS inhibition would lower the dynamic microvascular O2 delivery/utilization () balance (which sets the Po2mv) in rat skeletal muscle at rest and during contractions. Methods: Anesthetized male Sprague–Dawley rats had their spinotrapezius muscles exposed for blood flow (radiolabeled microspheres), (direct Fick calculation), Po2mv (phosphorescence quenching), or exteriorized for force production measurement during electrically induced contractions (1 Hz, 6–8 V, 180 seconds) pre- and post-nNOS inhibition with 2.1 μmol/kg of the selective nNOS inhibitor SMTC. Results: At rest, spinotrapezius blood flow was not different whereas SMTC reduced (27%) resulting in an elevated precontracting baseline Po2mv (control: 31.2 ± 1.6, SMTC: 37.1 ± 2.0 mmHg, p 0.05) which occurred despite an elevated (∼8%) muscle force production. Conclusions: These data demonstrate important physiological roles for nNOS-derived NO during contractions in healthy rat skeletal muscle and implicate maladaptations in nNOS function in pathological conditions associated with reduced NO bioavailability.

Inhibition of VE-cadherin proteasomal degradation attenuates microvascular hyperpermeability.

Abstract: Please cite this paper as: Sawant, Tharakan, Adekanbi, Hunter, Smythe and Childs (2011). Inhibition of VE-Cadherin Proteasomal Degradation Attenuates Microvascular Hyperpermeability. Microcirculation18(1), 46–55. Abstract Objective: VE-cadherin, an integral component of the adherens junction complex, is processed through the endosome–lysosome pathway and proteasome system for degradation. Our objective was to determine if inhibition of this pathway would protect against microvascular hyperpermeability. Methods: To induce VE-cadherin degradation, we utilized a mutant VE-cadherin protein that lacks the extracellular domain (rVE-cad CPD). Intravital microscopy was employed to study the changes in microvascular permeability in rat mesenteric postcapillary venules. Rat lung microvascular endothelial cell (RLMEC) monolayers were utilized in parallel studies. The adherens junction integrity was determined using VE-cadherin and β-catenin immunofluorescence. TOPflash/FOPflash transfection and luciferase reporter assay were performed to study β-catenin-mediated transcriptional activation. Results: rVE-cad CPD (2.5 μg/mL of blood volume) increased hyperpermeability significantly (p < 0.05). The VE-cadherin siRNA as well as rVE-cad CPD induced significant increase in monolayer hyperpermeability (p < 0.05). Transfection of rVE-cad CPD disrupted adherens junctions evidenced by discontinuity in β-catenin and VE-cadherin immunofluorescence (p < 0.05). Proteasome inhibitor MG132 attenuated rVE-cad CPD induced monolayer hyperpermeability and adherens junction damage. Conclusions: VE-cadherin disruption in animals results in hyperpermeability. Parallel studies in RLMEC demonstrated similar results. In addition, inhibition of proteasomal degradation attenuated microvascular hyperpermeability. These findings have significance in understanding the role of VE-cadherin in regulating vascular hyperpermeability.

Lymphatics: at the interface of immunity, tolerance, and tumor metastasis.

Abstract: Please cite this paper as: Shields (2011). Lymphatics: At the Interface of Immunity, Tolerance, and Tumor Metastasis. Microcirculation 18(7), 517–531. Abstract The lymphatic system has long been accepted as a passive escape route for metastasizing tumor cells. The classic view that lymphatics solely regulate fluid balance, lipid metabolism, and immune cell trafficking to the LN is now being challenged. Research in the field is entering a new phase with increasing evidence suggesting that lymphatics play an active role modulating inflammation, autoimmune disease, and the anti-tumor immune response. Evidence exists to suggest that the lymphatics and chemokines guide LN bi-functionally, driving immunity vs. tolerance according to demand. At sites of chronic inflammation, autoimmunity, and tumors, however, the same chemokines and aberrant lymphangiogenesis foster disease progression. These caveats point to the existence of a complex, finely balanced relationship between lymphatics and the immune system in health and disease. This review discusses emerging concepts in the fields of immunology, tumor biology, and lymphatic physiology, identifying critical, overlapping functions of lymphatics, the LN and lymphoid factors in tipping the balance of immunity vs. tolerance in favor of a growing tumor.

Functional dilator capacity is independently associated with insulin sensitivity and age in central obesity and is not improved by high dose statin treatment.

Abstract: Objective:? to test the hypothesis that: (i) functional microvascular dilator capacity is independently associated with insulin sensitivity and age in individuals with central adiposity at risk of cardiovascular disease (CVD); and (ii) functional microvascular dilator capacity is improved by high dose statin treatment. Methods:? functional dilator capacity (measured as change in laser Doppler blood flux from baseline during post occlusive reactive hyperemia [peak flux%resting flux; PF%RF] and flowmotion (power spectral density [PSD] analysis)) were assessed in 40 people with central adiposity and one or more other CVD risk factors. Measurements were made at rest and during acute hyperinsulinaemia before and six months after high dose atorvastatin (40 mg daily) or placebo. Results:? insulin-induced change in PF%RF was independently associated with insulin sensitivity (M/I) (r = 0.46 p = 0.02) and age (r = ?0.46 p = 0.02), which together explained almost half of the variance in PF%RF (adjusted r2 = 0.37, p = 0.008). Whilst atorvastatin decreased LDL cholesterol by 51% (p Conclusions:? insulin sensitivity and age are independently associated with an insulin-induced change in functional microvascular dilator capacity in individuals with central adiposity at risk of CVD. Dilator capacity is not improved by six months high dose statin treatment