II. Report from the 9th World Congress for Microcirculation
Content Overview and Comments
Prof Michel René Boisseau – Department of Pharmacology – University of Bordeaux 2
This high-level scientific meeting, chaired by Prof Eric Vicaut, included 164 oral presentations, 277 posters, and 1360 authors. Emphasis was laid on the considerable progress made in the technologies used: capillaroscopy performed not only on the fingernail bed, the forearm, in animal mesentery models, and hamster cheek pouch, but also in vivo in the pia mater, or in organs. Furthermore, data collected by capillaroscopy or Doppler laser are now digital and are used in mathematical and physical models. Many animal models allow an in situ approach and, in particular, a genetic approach by a chromosome-mediated or gene transfer method. In addition, the use of animals with a single deficiency (knockout animal) enables a molecular approach to pathways of activation of cell function. The spectacular progress achieved in understanding microcirculatory processes is linked to their now recognized role in major organic dysfunction. In light of the large number of communications, the present review only reports results that the author considers novel and important.
New aspects in the physiology of the microcirculation
Adhesion and migration of blood cells in the microcirculation
Leukocyte adhesion takes place mainly in post-capillary venules under conditions of low shear rate flow (300 sec-1). Under such conditions, the platelets do not adhere (their adhesion requires higher shear stress conditions). Aggregation of red blood cells promotes the formation of a cell-free layer where leukocytes roll and adhere and from which platelets are rejected. Conversely, when there are fewer and more rigid red blood cells, platelet adhesion is promoted (G Nash, Birmingham).
Glucose-based polymers form bridges between the endothelium and leukocytes are organized into microvilli 16 μm in length, tethers forming a net whose mesh retains white blood cells. It should be noted that such microvilli have been described previously by morphologists. On the molecular level, the primary role in formation of these microvilli is attributed to the chemokine CXCL5, ITAM immunoreceptor tyrosine-based activation motif and tyrosine kinase SK. As soon as leukocyte adhesion is triggered, other chemokines are activated, oxygenated molecules are produced and endothelial permeability occurs (K Ley, La Jolla). Many other pathways contribute to such adhesion, in particular in diseased areas such as the area surrounding plaque and in ischemia-reperfusion. Thus, uPA increases adhesion while PAI decreases it (it is abolished in the PAI-/- mouse) (C Reichel Munich). The newly described function of strengthening is related to the protein kinase theta (A Bertram, Hanover).
Microvessel permeability, role of the glycocalyx
The glycocalyx, the superficial layer of endothelial cells, decreases leukocyte migration: syndecam -/- mice, thus deprived of a heparan sulfate in the glycocalyx, have higher migration (O Kehoe, Oswestry). Generally, the glycocalyx has to undergo shedding for migration to occur. This is due to activation of MMPs (matrix metalloproteinases) (H Lipowski, Penn State). In fact, the glycocalyx has many functions including a role in permeability: made thin by hyaluronidase, its permeability increases (L Gao, Penn State); conversely, citrulline injected into an animal model thickens it (K Wijnands, Maastricht).
From a structural standpoint, permeability is related to junctional proteins: thus PAF increases it by s-nitrosylation of these proteins (F Sanchez, Valdivia), for example, connexin-43 associated with NOS (A Straub, Charlottesville). During apoptosis (BAK-related) permeability increases as the result of cleavage of endothelial β-catenin. In the cochlea, occludin can be hyper-phosphorylated by an Na+K+ ATPase leading to rupture of the labyrinth barrier (X Shi, Portland). On the molecular level and among pathways, the key regulators are forms of VEGF (vascular endothelial growth factor) which insert into signaling complexes. Thus, a signalplex consists of activation of the VEGF-R2 receptor, calcium channels, γ phospholipase, and then downstream activation of eNOS, rho-rac and lastly of junctional proteins such as cadherin bound to actin in the cytoskeleton. This entire structure becomes spatially organized (D O Bates, Bristol). Furthermore, caveolae, in some places, play a part in permeability: this is the case in the fenestrated endothelium of the liver which depends on a balance between the constructive component caveolin and deconstructive aquaporin; the latter is implicated in portal hypertension (M Oda, Tokyo).
Conductance
Propagation of the wave of depolarization along the endothelium of microvessels governs vasomotricity, two related factors. Propagation depends on junctional proteins: thus connexin 40 -/- mice respond less, comparatively, to electrical stimulation (C Sorensen, Copenhagen). The role of EDHF (endothelium-derived hyperpolarizing factor) is emphasized, associated with opening of calcium and potassium channels, but regulated by the TRP (transient receptor channel), which is over-activated in TRP -/- mice (H Schmidt, Lübeck).
The link between vasomotricity and conductance occurs by release of NO, but many other pathways exist. Thus hypoxia has a vasodilator effect via the potassium channels and hyperoxia has a vasoconstrictor role by production of HETE (hydroxyeicosatetraenoic acid) (A Ngo, Copenhagen). Electrical stimulation can lead to the production of PGI2 according to the pathway: COX-1, PGI-2 synthase, IP-receptor with a relaxant function (S Gohin, Lyon). Lastly, organ specificity exists. Thus, for pulmonary microvessels, vasomotricity related to entry of Ca2+ via the vanilloid channels is stopped by inhibition of MLCK (myosin light chain kinase) described in this congress as a new system of protection (J Parker, Mobile).
Hemorheology and the microcirculation
Contrary to firmly entrenched older concepts, moderate hyperviscosity, as observed in vascular disorders, is far from being injurious because red blood cells provide NO via a non-enzymatic mechanism, with eNOS being activated by shear stress (O Baskurt, Istanbul). Therefore, a higher quantity of red blood cells in the microcirculation makes more NO available, but this in a pulsatile vascular system constantly subjected to endothelial mediators (S Forconi, Siena). In rats, a 10% increase in the hematocrit lowers blood pressure, an event related to NO. NO acts in contact with the endothelium in the cell-free layer made thinner by high shear stress, which in turn allows hemoglobin to destroy it (Intaglietta concept) (M Intaglietta, La Jolla).
Vasomotion, a periodic rhythm independent of the capillaries, measurable by the Doppler laser method, has a function in the delivery of O2 to tissues, because low oxygen saturation enhances it (C Thorn, Exeter).
Aggregation of red blood cells (RBCs) is related to fibrinogen with a specific relation to phosphorylation of band 3. Fibrinogen decreases efflux of NO from RBCs by promoting nitrite derivative species, nitrates and s-nitroso-glutathione derivatives (C Saldanha, Lisbon).
In malaria (P. falciparum), proteins of the parasite are exported to the surface of RBCs, ie, kinases called FIKKs, and make the RBCs adhere to the endothelium, an essential pathological event (LM Kats, Melbourne).
Microvessel angiogenesis
Researchers consider that the Zebra fish is an ideal model to observe the formation of blood vessels, along with transgenic cell lines.
Hemostatic factors have a pro-angiogenic action: activated protein C stimulates the Ang/tyrosine-kinase-R2 receptor (N Minhas, Sydney). TXA2-R -/- mice have defective angiogenesis in a paw ischemia protocol; this is related to a defect in platelet and P-selectin activation resulting in a defect in recruiting the hemangiocytes CXCR4+VEGF1+ from the bone marrow (H Amano, Kanagawa). Lastly, thrombin participates in activation of PAR-4 (G protein-coupled activated receptor) responsible for sprouting of endothelial cells (E Garonna, London).
Adhesion proteins play a part in angiogenesis: the transmembrane part of ICAM (ICAM-1 tail) produces superoxide generation (ROS pathway), the basis of the process of angiogenesis (C Pattillo, Shreveport).
Hypoxia produces an angiogenic reaction in fibroblasts that express HIF (
During angiogenesis, new blood vessels organize spatially. Thus a fragment of rat arteriole placed in a collagen gel and re-implanted spatially reconstitutes a vascular tree with venules and capillaries (depending on plasticity) (S Nunes, Louisville). Using vital microscopy, it is observed that the implanted blood vessels connect by surrounding the host cells (depending on wrapping and tapping) (L Munn, Boston). An important finding is the need in all these processes for the provision of bone marrow stem cells activating the homing receptors. Lastly, many pathways regulate neoangiogenesis: thus, physical exercise is angiogenic, but muscles produce vasohibin-1 (VASH-1) which in turn inhibits the process. VASH-1 is increased in muscle in diabetic rats, thus contributing to capillary regression in diabetes (M Kishlyansky, Montreal).
The pulmonary microcirculation
The study of microvessels in the lung is an example of a particular aspect in that specific events can be identified in it. Thus, TXA2 contracts arterioles but not venules in the lung (K E Watson, Madison). Cells in lung capillaries can be identified by the fact that they bind a lectin from Griffonia simplicifolia. This can be seen even though they have an actin-strengthened border (actin cortical rim) associated with RhoA (protein GTPase regulating the cytoskeleton) (T Stevens, Alabama). Subjected to high tension by strong ventilation in mice, this rim is protected and strengthened by PGI2 (iloprost). This disappears in siRNA-based Rap1 knockdown mice. Another particular aspect: in pulmonary hypoxia, the red blood cells produce H2O2 via a pathway involving cdb3 (protein cytoplasmic domain of band 3) (A Huertas, New York).
The lymphatic microvessels
The propagation of lymphatic fluid is related to a constriction-dilatation rhythmic cycle and to lymphatic pumping reacting to stretch of the lymphatic wall and to changes in transmural pressure. Regarding this cycle, which is similar to that of a pacemaker, lymphatic muscle cells (LMCs) react to the release of Ca2+ by the IP3 receptor, and then to temporary opening of the Ca2+ Cl- channels and lastly to depolarization associated with the Ca2+ L channels. Lymphatic pumping seems not to follow this series (M Imtiaz, Calgary). It is inhibited by VIP (vasoactive intestinal peptide), a neuro-immunomodulator produced by peptidergic nerves and the inflammatory cells. Its sites of action include the VPAC2 receptor (demonstrated by use of an antagonist), protein kinase A, and the ATP-sensitive K channels, but there is no interference with the metabolites of NO and COX (P Von der Weid, Calgary). A study with cannulation of lymphatics in the diaphragm in rats, on the surface of the pleura, demonstrated the existence of two types of channels, those on the surface, compliant, and others located deeper associated with pressure and stretching of cardiac and diaphragmatic movements (D Negrini, Milan). There are two types of muscle cells in the lymphatics (guinea pig mesentery): circular and elongated (fewer in number). The study of their functioning and the resulting mathematical model make it possible to understand that longitudinal cells synchronize movements in the channel by modulating the movement of Ca2+ (M Imtiaz, Calgary). Contractility of the thoracic duct is related to shear stress and is dependent on NO. A study of a segment of the rat thoracic duct made it possible to understand that the response to shear stress of eNOS is due to a Ca-independent pathway and that contractility, responding to flow, is controlled by the cGMP/PKG regulatory pathway (protein kinase controlled by cGMP involved in relaxation of LMCs) (O Gasheva, Temple).
Rats with metabolic syndrome have smaller diameter mesenteric lymphatics, with an accelerated cycle but decreased amplitude and an exaggerated response to substance P (M Muthuchamy, College Station). In old rats, the lymphatics have a reduced flow rate, related to the reduction of LMCs (A A Gashev, Temple). In mice with apolipoprotein E deficiency (apoE -/-), hypercholesterolemia is associated with a deficiency of lymphatic transport and of dendritic cells. Wider lymphatics are observed and there is a decrease in LMCs.
Microcirculatory damage in clinical practice
Metabolic syndrome, obesity and diabetes
Anatomical and in particular functional alterations of the microcirculation in subjects with metabolic syndrome, obesity and arterial hypertension are far from being an epiphenomenon. They are related to the pathogenesis of disorders even before they are clinically manifest and then when they worsen. Animal cell lines (obese Zucker rats) reproduce this same process. If we analyze cutaneous blood flow using a Doppler laser technique with a sophisticated low frequency method (wavelet transform), the former are decreased in their endothelial components. In an obese subject, peripheral vascular resistance is inversely correlated with the vasodilator effect of insulin and not with reactivity to acetylcholine (J Hornstra, Amsterdam).
The occurrence of these dysfunctions can be followed in the rat receiving fructose supplementation (E Bouskela, Rio de Janeiro) and similarly in the hamster subjected to a high-fat diet where the occurrence of insulin resistance is also noted (R R S Costa, Rio de Janeiro); but these alterations are partially improved by aerobic exercise (B S C Boa, Rio de Janeiro). A study of the function of microvessels by fingernail bed capillaroscopy in obese young women without a patent metabolic disorder showed a functional and thus predictive alteration and higher adiponectin and leptin levels (LG Kremer & N R Villela, Rio de Janeiro).
Perivascular fat has a modulator effect on arterioles via the action of mediators in conjunction with NO-dependent and -independent vasomotor modulation of the endothelium. It appears that such fat, or its effects, are decreased in an obese subject (A S Greenstein, Manchester). This is to be compared with the decrease in adiponectin in the perivascular fat of db/db mice resulting in a loss of vasodilation related to insulin (R I Meijer, Amsterdam). In rats subjected to such diets, in vivo capillaroscopy reveals capillary rarefaction in striated muscle (M V Machado, Rio de Janeiro). The mother’s nutritional status during pregnancy has an influence on the outcome of obesity and arterial hypertension (L Poston, London). In eclampsia in diabetic women, pathways of defense are altered: anti-oxidant Nrf2/ARE and anti-hypertensive EPHX2 (G E Mann, London) (M P Koeners, Utrecht). In populations of male subjects, correspondence between a fatty diet and functional disorders was demonstrated with video-capillaroscopy (C Buss, Rio de Janeiro), in particular in the Amsterdam longitudinal study (N J Wijnstok, Amsterdam).
In diabetes, the accumulation of advanced glycation end (AGE) products acts on the microvessels: thus the arteries of rats subjected to AGE products lose their endothelium-dependent reactivity (M Azzawi, Manchester).
In monkeys subjected to experimental diabetes, vasomotion progressively decreases (X Tigno, Tempa).
Microvessels and arterial hypertension
In spontaneously hypertensive rats, insulin resistance is attributed to cleavage of the extracellular domain of the insulin receptor by proteases, above all MMPs, which also cleave the 2 adrenergic receptor, thus accounting for blood pressure elevation (F A Delano, La Jolla). In spontaneously hypertensive mice, injection of angiotensin II produces cerebral bleeding associated with oxidative stress and activation of MMPs. These two activities are related. In addition, superoxide dismutase diminishes the effects of Ang II (worsening in SOD -/- mice). This effect of Ang II, which involves remodeling, is more dangerous that that of norepinephrine (D D Heistad, Iowa City).
In humans, different types of microcirculatory disorders occur: decreased capillary density, tortuous blood vessels, sacculation, slow speed of red blood cells, and an increase in myogenic tone (Y Guo, Beijing). A decrease in endothelium-dependent vasodilatation is also observed (I Tikhomirova, Yaroslavl). The red blood cells acclimate to hypertension: their deformability increases depending on arterial stiffness, as measured in the carotid artery (M Fornal, Krakow). In a cohort of hypertensive men with hypercholesterolemia, the increase in blood flow associated with hyperemia (Doppler method) is inversely correlated with levels of von Willebrand factor (C Serban, Timisoara).
Microvessels and atherogenesis
During atherogenesis, recruitment of monocytes is essential, but neutrophils are associated with it. A study of aortic recruitment in mice with a chemoreceptor deficiency has made it possible to confirm that monocytes use CCR1 and CCR5 receptors; neutrophils use CCR2 and CXCR2 receptors (O Soehlein, Aachen). In addition, neutrophils recruit early, at the start of plaque formation with the chemoattractant CCL5 (M Dreschler, Aachen). The role of MIF, a ligand of CXCR, has been clarified: in association with the CD74 gene, it inhibit the migration of macrophages and thus growth of the plaque (N Tuchscheerer, Aachen). Development of the vasa vasorum is accompanied by development of the atherosclerotic plaque.
Serum homocysteine
Homocysteine increases the risk of vasospasm associated with atherosclerotic plaque. In mice heterozygous for serum homocysteine, a coronary artery is highly reactive to acetylcholine and has less NO due to a decrease in eNOS activity, which is corrected by folic acid (N Qipshidze, Louisville). Under the same conditions, excessive production of TXA2 derived from COX2, ROS and a PGI2 deficiency have been demonstrated, all of which indicate a major deficiency of vasomotor regulation in small arterioles (A Koller, New York & Pecs). Permeability of the pia mater, increased by perfusion of fibrinogen in normal mice, is enhanced in mice heterozygous for hyperhomocysteinemia (cystathionine β-synthase knockout -/+ mice) (D Lominadze, Louisville). Low vitamin B concentrations and elevated homocysteine levels are risk factors for Alzheimer’s disease. A correlation appears between P-tau protein in the CSF and plasma homocysteine and conversely for levels of folates. A diet resulting in elevated levels of homocysteine in rats is accompanied by an increase in P-tau protein in the CSF (W Herrmann, Hamburg). In the setting of the emAmsterdam Growth and Health Longitudinal Study, 259 subjects were examined by fingernail bed capillaroscopy: disorders, such as capillary rarefaction, were correlated with plasma homocysteine (J Hornstra, Amsterdam).
Shock, sepsis and acute inflammatory conditions
Sepsis
The authors do not hesitate to state that sepsis is a disorder of the microcirculation and this is true in all models and clinical cases. Capillary “stop flow” involves tissue anoxia, but also inflammatory disorders, disorders of hemostasis, endothelial functioning with oxidative stress and leukocyte activation (D De Backer, Brussels). In a mouse model of sepsis, the formation of microthrombi in microvessels was related to iNOS (abolished in iNOS -/- mice), and NADPH oxidase (abolished in gp91phox-/- mice). In a mouse model of pulmonary sepsis, ANP (atrial natriuretic peptide) protected the thin alveolar endothelial barrier against the accumulation of leukocytes and from enhanced permeability to Evans blue. In fact, this protection disappeared in the ANP -/- mouse (A Birukova, Chicago). Experimental endotoxinemia (LPS) in mice produces multiple organ dysfunction and sepsis. This condition is conserved by the immunomodulator DEHA associated with SOV (sodium orthovanadate) a phosphatase inhibitor (D Pavlovic, Greifswald).
Inflammation
In experimental colitis in mice, microvascular thromboses were related to IL6 (no effect in the IL6 -/- mouse). In the same model, thromboses associated with Ang II were related to lymphocyte activation. These experimental findings demonstrate the links between inflammation and thrombosis (K Tyml, London). In a mouse model of intestinal inflammation, activation of PARs (protease-activated receptors) produced the recruitment of leukocytes in a microvenule. Yet PARs are activated by many products, such as thrombin, trypsin, factors Xa and VIIa. In this model, the injection of protease inhibitors into the colon (elafin, secretory leukocyte response inhibitor) reduced leukocyte recruitment (M Majima, Sagamihara). Lipoxins and eicosanoids produced in the cell are anti-inflammatory. Thus LXA4 binds to the G-coupled receptor Fpr2/ALX of the macrophages, and then the complex is internalized (PKC-dependent) by inducing phagocytosis of neutrophils undergoing apoptosis. This function is absent in Fpr2 -/- mice. Synthetic compounds analogous to some lipoxins may be used in therapeutic practice (C Godson, Dublin). Endothelial protection is also dependent on Notch 4. Under the effect of TNF, it is under-regulated, while Notch2 is over-regulated. This imbalance produces apoptosis of endothelial cells by the effect of survivin. Notch 2 knockdown mice escape this effect and have high levels of survivin (B Charreau, Nantes). Cultures of human endothelial cells subjected to LPS in the presence of CORM-3, a compound that delivers CO, were protected by CO with respect to oxygenated species, while CO produced a decrease in the expression of metalloprotein SOD- 3 (membrane superoxide dismutase) (S Mizuguchi, London). In mice subjected to sepsis of the colon by dextran, the intestinal flora exacerbated the lesions, partly by high recruitment of leukocytes on the wall of intestinal microvessels, which does not occur in germ-free mice (J Alexander, Shreveport). The same authors observed in the same mouse model of colitis that inflammation worsened because of intense angiogenesis of microvessels, in particular related to high expression of VEGF-A. Introduction into the mouse of a VEGF-A inhibitor (adenovirus encoding rVEGF164b) significantly reduced this event.
The injection of LPS in mice produced leukocyte adhesion in glomeruli of the kidney, but also the release of angiopoietin II endothelial cell Weibel-Palade bodies, the basis of protection of renal function (absent in Ang II -/- mice) (N F Kurniati, Groningen).
Shock
In hemorrhagic shock, multiple organ failure occurs and is related to dissemination of pancreatic enzymes into the blood. These enzymes cleave the extracellular domain from the insulin receptor in the microvessels, thus creating insulinresistance and hyperglycemia. This auto-digestion can be moderated by administration of protease inhibitors (F Delano, La Jolla). The role of auto-digestion was also found in a rat model where permeability of the intestinal mucosa was increased: the dissemination of pancreatic enzymes produced shock (E Kistler, La Jolla). After occlusion of the rat splanchnic artery, shock developed related to dissemination of chymotrypsin, elastase and trypsin through the endothelium by digestion of mucin and the extracellular domain of E-cadherin within a few minutes. These processes can be reduced by anti-enzymes (M Chang, La Jolla).
Ischemia-reperfusion
In the mouse intestine ischemia-reperfusion (I/R) model, leukocyte adhesion to the endothelium is the primary event. Adhesion occurs solely in post-capillary venules, but is promoted by failure of NO upstream, ie, in the arterioles. Once they are in the interstitium, the leukocytes promote migration and then degranulation of mast cells, which are responsible for generation of Ang II, which itself promotes activity of NADPH oxidase, inactivating NO (and tests using ACh). Thus, I/R associates leukocyte migration and vasomotor dysfunction upstream (R J Korthuis, Columbia). In the mouse intestine I/R model, hematopoietic stem cells are recruited by microvessels of the mucosa under the influence of SDF-1 (A Yemm, Birmingham). The same process occurs in I/R n the mouse kidney: stem cells obey homing factors (including the hematopoietic markers CD18 and CD44) and accumulate in ischemic areas (R White, Birmingham).
In the mouse intestine I/R model, microthrombi form in villi, due to activated, adherent platelets (decrease in P-sel -/- mice). Platelet inhibition and administration of anti-P-selectin decrease leukocyte adhesion (I Holyer, Birmingham).
Therapeutic aspects were emphasized. I/R by occlusion of a coronary artery in the rat was moderated after administration of a Chinese traditional medicine preparation: the size of an infarction was decreased, and there was less action of MMPs and TGF and of CD68 macrophages (X Wei, Beijing). Other Chinese authors specify the use of a polyphenol, total salvianolic acid. In I/R of the rat mesenteric arteries, this product reduced the generation of oxygenated species and neutrophil activation (Y Liu, Beijing). The effects of I/R in the dog heart by ligation of the coronary artery were attenuated by the infusion of fructose-1-6 diphosphate, increasing the energy of glycolysis and decreasing free radical and cytokine production (A Markov, Jackson).
Neuronal lesions associated with I/R in the rat hippocampus were attenuated by a period of preconditioning, which acts by overregulation of UCP2 (uncoupling protein) a mitochondrial anti-oxidant or ghrelin, an activator of UCP2, which acts on eNOS (Y Liu, Beijjing). For the same anti-oxidative reasons, UCP2 reduces the accumulation of leukocytes in the microvenules of the rat cremaster muscle in I/R (A Bougle, Paris). The same authors showed that preconditioning prevents stress in the endoplasmic reticulum of myocardial cells in culture by inhibiting the CHOP pathway of apoptosis including the Bax/Bcl-2 ratio. Similarly, in I/R induced in the rat paw, preconditioning attenuated lesions and in particular apoptosis of muscle cells by expression of calreticulin, an endoplasmic reticulum protein that binds calcium.
Cancers, tumors and microvessels
Cell proliferation and apoptosis are major processes in oncology. Melatonin increases apoptosis of human umbilical cells in culture. It binds to MT1 and MT2 (melatonin G-coupled receptors) and to nuclear receptors producing activity of PKC-α, which in turn under-regulates the receptors (P Cui, Beijing).
Histology of hepatic metastases from colon cancer shows an increase in density of the microvessels, and therefore increased angiogenic activity. The localization of genes by qRT-PCR shows the presence in tissue adjacent to metastases of CD31 (PECAM) and HIF1 , which are members of the VEGF family (which have in common the HRE sequence (hypoxia-responsive element). Elevated levels of the RNA of Tie2 and a high Ang-2/Ang-1 ratio are noted. Therefore, the liver offers metastases a “permissive” angiogenic environment, thus promoting their development (G Van Der Wahl, Groningen).
Endocan (or ESM-1: endothelium-specific molecule) appears to be an important new marker in oncology. It is expressed in excess in glioblastoma, lung cancer, angiosarcoma and liposarcoma. It is related to VEGF activity and can be assayed in the plasma by ELISA (M Delehedde, Lille).
Remodeling
Remodeling includes all changes in the arterial wall leading to plaque formation and weakening. It is based on differentiation and migration of LMC. Epoxy eicosatetraeonic acids (ETAs) moderate this process but are converted into less protective products by SEH (soluble epoxide hydrolase), which can be inhibited pharmacologically (J D Imig, Milwaukee). Diabetic pregnant female rats present defective remodeling of uterine arteries. This is due to a signaling defect in EDHF, which is improved by activation of IKCa channels (N Gonika, Burlington). In obese diabetic rats, with high amounts of AGEs, an increase in blood flow produces hypertrophy of arterial wall resistance related to oxidative stress and COX2 activity (L Loufrani, Angers). In experimental colitis in mice, the processes of angiogenesis are the basis for remodeling of microvessels of the colon mucosa, resulting in serious symptoms. In fact, this is due in large part to VEGF-A. Mice treated with an adenovirus coding for VEGF164b, the isoform that inhibits VEGF-A, present very attenuated symptoms of colitis produced by trinitrobenzene (TNBS) (W Cromer, Shreveport).
Contrary to remodeling such as increased plaque size, remodeling of small arteries subjected to hypertension and/or reduction of blood flow consists of a reduction in their diameter. A mechanism of action is ROS-dependent activation of MMPs by the combined effect of norepinephrine and Ang II (L A Martinez-Lemuz, Columbia). This also depends on translocation in the membrane of LMCs of transglutaminase activity (J Van Den Akker, Amsterdam). Remodeling of uterine arteries can be triggered by intra-uterine stress: the injection of silicone (G Osol, Burlington). In the pulmonary circulation, the vasoactive peptide urotensin-II presides over remodeling through the F-box protein pathway: Fox 03 overregulating MMP2. This function disappears in the Fox03a -/- mouse (I Diebold, Munich).
Remodeling of microvessels involves several steps and, in particular, reconstitution of their muscle wall. This function is due to PDGF BB supplied by bone marrow cells and not by the local endothelium, as demonstrated in irradiated mice and PDGF -/- (L Glaw, Charlottesville).
Microparticles and microvessels
Vesicles
Microparticles are membrane vesicles which detach from groups of cells and are able to enter the microcirculation because they are small. Those most investigated are from platelets and have a prothrombotic action. They are not uniform or uniformly distributed. Thus, the microparticles CD42b+ with hematopoietic value are found in diabetes and CD62P and CD63+ in coronary artery disease (S Nomura, Osaka). In human cerebral malaria and in experimental malaria in mice, levels of microparticles are elevated and their number is correlated with severity. In sepsis, microparticles are formed from monocytes that are carriers of signals of inflammation and activate the kinases ERK 1 and 2 in situ (V Combes, Sydney). In cerebral malaria, not only do the microparticles adhere to and activate the endothelium of cerebral microvessels, they also adhere to red blood cells infected by the parasite and to which they provide the platelet antigen CD41 (GP Iib IIIa), with the resultant increased adhesion of red blood cells to blood vessels (G Grau, Camperdown). In arterial hypertension, and in coronary artery disease, the microparticles produce various effects: coagulating by their phosphatidyl-serine content, a pro-apoptotic effect, but they participate in vascular renovation, an ambivalent effect (C M Boulanger, Paris). This was demonstrated in athymic mice (athymic nude mice) undergoing arterial occlusion: endothelial regeneration after elimination of ischemia was related to provision of blood outgrowth endothelial cells but accelerated by the addition of platelet microparticles (S Mause, Aachen).
Particles
Microparticles also come from inhaled airborne pollutants. Rats subjected to particles from diesel fuel by tracheal intubation present not only with local but also systemic disorders that are detectable in isolated muscle: arteriolar vasodilation, an increase in shear stress, and vasoconstriction upstream (K Porter, Morgantown). Under the same conditions, the same authors demonstrated in the rat that inhalation of TIO2 nanoparticles, derived from titanium and used in industrial applications, reduced the bioavailability of NO in microvessels in an isolated muscle and an increase in sensitivity of α-adrenergic receptors (T Knuckles, Morgantown). Nanoparticles (200 nm) can also be beneficial: biodegradable, they are captured by endothelial cells in culture (diabetic rat) and increase cofactor BH4 of eNOS (C Meininger, Temple).
Lifestyle, exercise and training
Intense physical exercise is harmful insofar as, under the effect of oxidative shock, the recruitment of capillaries does not occur. Nevertheless, it involves preconditioning that is protective for subsequent exercise (T Gori, Siena). In obese rats, where capillary muscle recruitment is lacking, exercise is beneficial and diminishes the expression in skeletal muscle of anti-angiogenic factors such as thrombospondin TSP-1 and increases the expression of VEGF-A (P Forn, Toronto).
Rehabilitation in the elderly in a specialized institution involves rheological improvement. Measurements recorded with a LORCA viscosimeter show improvement in deformability of red blood cells and a decrease in their tendency to aggregate (K Filar-Mierzwa, Cracow). In elderly rats, the observation of blood vessels in the brain (by confocal microscopy combined with laser application) shows the rarefaction of capillaries. This anomaly is correlated with an insufficient antioxidant potential (increased MDA). Subject to a program of swimming, these animals improved (S Viboolvorakul, Bangkok). In coronary arteries of old rats, a decrease was observed in AMP protein kinase, resulting in a decrease in contractile activity. This anomaly markedly improved with exercise (J Muller-Delp, Gainesville). All these events are found in elderly subjects: rarefaction of capillaries, alteration of cutaneous blood flow, and a poor response to hyperemia (F G Lopez, Rio de Janeiro). In the elderly, a decrease in cutaneous blood flow is observed in response to hyperthermia, which is due, independently of other vasomotor factors, to a decrease in the number of C sensory fibers in the skin (effect utilized in topically applied anesthetic creams). This process is attenuated by physical training (J M Saxton, Sheffield). In the same type of concept, compression of the sciatic nerve in rats altered the vasodilator effect of pressure on the corresponding limb (laser Doppler method), which can be attributed to lesions of C fibers (J Pelletier, Lyon).
In trained cyclists, vasomotor reactivity is high, as measured with the laser Doppler method. Such reactivity is attributed to the intervention of NO and PGI2, but also to independent events that persist after neutralization of these products (H Lenasi, Ljubljana).
CONCLUSION
This congress presented an update on novel findings obtained in sophisticated scientific experiments and models. Many therapeutic targets were mentioned, but are not described in detail in this report. Let us mention the effects of antioxidants, some of which are obtained from Chinese plants, the effect of irbesartan, which inhibits angiotensin II, of DEHA, of synthetic prostacyclins, and of sildenafil, which acts by iontophoresis in Raynaud’s syndrome, and also acupuncture, which can act on eNOS associated with microvessels.
