De la reconstruction a l’augmentation du corps humain en medecine restaurative et en cybernetique

Aux confluences historiques et conceptuelles de la modernité, de la technologie, et de l’« humain », les textes de notre corpus négocient et interrogent de façon critique les possibilités matérielles et symboliques de la prothèse, ses aspects phénoménologiques et spéculatifs : du côté subjectiviste et conceptualiste avec une philosophie de la conscience, avec Merleau-Ponty ; et de l’autre avec les épistémologues du corps et historiens de la connaissance Canguilhem et Foucault. Le trope prometteur de la prothèse impacte sur les formations discursives et non-discursives concernant la reconstruction des corps, là où la technologie devient le corrélat de l’identité. La technologie s’humanise au contact de l’homme, et, en révélant une hybridité supérieure, elle phagocyte l’humain du même coup. Ce travail de sociologie des sciences (Latour, 1989), ou encore d’anthropologie des sciences (Hakken, 2001) ou d’anthropologie bioculturelle (Andrieu, 1993; Andrieu, 2006; Andrieu, 2007a) se propose en tant qu’exemple de la contribution potentielle que l’anthropologie biologique et culturelle peut rendre à la médecine reconstructrice et que la médecine reconstructrice peut rendre à la plastique de l’homme ; l’anthropologie biologique nous concerne dans la transformation biologique du corps humain, par l’outil de la technologie, tant dans son histoire de la reconstruction mécanique et plastique, que dans son projet d’augmentation bionique. Nous établirons une continuité archéologique, d’une terminologie foucaldienne, entre les deux pratiques. Nous questionnons les postulats au sujet des relations nature/culture, biologie/contexte social, et nous présentons une approche définitionnelle de la technologie, pierre angulaire de notre travail théorique. Le trope de la technologie, en tant qu’outil adaptatif de la culture au service de la nature, opère un glissement sémantique en se plaçant au service d’une biologie à améliorer. Une des clés de notre recherche sur l’augmentation des fonctions et de l’esthétique du corps humain réside dans la redéfinition même de ces relations ; et dans l’impact de l’interpénétration entre réalité et imaginaire dans la construction de l’objet scientifique, dans la transformation du corps humain. Afin de cerner les enjeux du discours au sujet de l’« autoévolution » des corps, les théories évolutionnistes sont abordées, bien que ne représentant pas notre spécialité. Dans le cadre de l’autoévolution, et de l’augmentation bionique de l’homme, la somation culturelle du corps s’exerce par l’usage des biotechnologies, en rupture épistémologique de la pensée darwinienne, bien que l’acte d’hybridation évolutionnaire soit toujours inscrit dans un dessein de maximisation bionique/génétique du corps humain. Nous explorons les courants de la pensée cybernétique dans leurs actions de transformation biologique du corps humain, de la performativité des mutilations. Ainsi technologie et techniques apparaissent-elles indissociables de la science, et de son constructionnisme social.

Markers of systemic inflammation in diagnostics and in prediction of outcome of community-acquired infection

Sepsis is associated with a systemic inflammatory response. It is characterised by an early proinflammatory response and followed by a state of immunosuppression. In order to improve the outcome of patients with infection and sepsis, novel therapies that influence the systemic inflammatory response are being developed and utilised. Thus, an accurate and early diagnosis of infection and evaluation of immune state are crucial. In this thesis, various markers of systemic inflammation were studied with respect to enhancing the diagnostics of infection and of predicting outcome in patients with suspected community-acquired infection. A total of 1092 acutely ill patients admitted to a university hospital medical emergency department were evaluated, and 531 patients with a suspicion of community-acquired infection were included for the analysis. Markers of systemic inflammation were determined from a blood sample obtained simultaneously with a blood culture sample on admission to hospital. Levels of phagocyte CD11b/CD18 and CD14 expression were measured by whole blood flow cytometry. Concentrations of soluble CD14, interleukin (IL)-8, and soluble IL-2 receptor α (sIL-2Rα) were determined by ELISA, those of sIL-2R, IL-6, and IL-8 by a chemiluminescent immunoassay, that of procalcitonin by immunoluminometric assay, and that of C-reactive protein by immunoturbidimetric assay. Clinical data were collected retrospectively from the medical records. No marker of systemic inflammation, neither CRP, PCT, IL-6, IL-8, nor sIL-2R predicted bacteraemia better than did the clinical signs of infection, i.e., the presence of infectious focus or fever or both. IL-6 and PCT had the highest positive likelihood ratios to identify patients with hidden community-acquired infection. However, the use of a single marker failed to detect all patients with infection. A combination of markers including a fast-responding reactant (CD11b expression), a later-peaking reactant (CRP), and a reactant originating from inflamed tissues (IL-8) detected all patients with infection. The majority of patients (86.5%) with possible but not verified infection showed levels exceeding at least one cut-off limit of combination, supporting the view that infection was the cause of their acute illness. The 28-day mortality of patients with community-acquired infection was low (3.4%). On admission to hospital, the low expression of cell-associated lipopolysaccharide receptor CD14 (mCD14) was predictive for 28-day mortality. In the patients with severe forms of community-acquired infection, namely pneumonia and sepsis, high levels of soluble CD14 alone did not predict mortality, but a high sCD14 level measured simultaneously with a low mCD14 raised the possibility of poor prognosis. In conclusion, to further enhance the diagnostics of hidden community-acquired infection, a combination of inflammatory markers is useful; 28-day mortality is associated with low levels of mCD14 expression at an early phase of the disease.

Systemic Inflammation in Preterm Infants

Even though mortality among preterm infants has decreased, their risk for chronic complications such as bronchopulmonary dysplasia (BPD) and neurological disability remains significant. One common risk factor for these is exposure to inflammation. The fetus may be exposed prenatally during maternal chorioamnionitis. Pre-eclampsia is also associated with low-grade maternal inflammation. Postnatally, local and systemic inflammation is present during respiratory distress syndrome (RDS). Furthermore, septic infections in the preterm infant are an important source of inflammatory stimuli and can lead to death in only a few hours. The diagnosis of septic infection is difficult, since reliable diagnostic markers are unavailable. This thesis evaluates peri- and postnatal systemic inflammation in preterm infants in septic infections, in RDS treated with mechanical ventilation and surfactant treatment, and in preterm infants prenatally exposed to chorioamnionitis and pre-eclampsia. Surface expressions of the activation markers CD11b, CD54, and CD62L, determined by flow cytometry on circulating phagocytes and T lymphocytes, serve as indicators of systemic inflammation. The main findings: I) In preterm infants with developing late-onset sepsis and fulminant necrotizing enterocolitis, a significant increase in CD11b expression on circulating phagocytes is already present on the day of onset of clinical symptoms. II) In preterm infants with RDS, circulating phagocytes become activated within hours after start of mechanical ventilation. In preterm infants treated for RDS with nasal continuous positive airway pressure, no such activation occurs. III) In preterm infants, RDS is associated during the first days of life with fewer circulating helper and cytotoxic T lymphocytes, of which the greater proportions are activated. Even greater proportions of circulating T cells are activated in infants subsequently developing BPD. IV) In preterm infants born after maternal pre-eclampsia, RDS-associated phagocyte CD11b up-regulation is greater than in preterm infants not exposed to pre-eclampsia during the first week of life. These findings suggest that I) an increase in CD11b expression on circulating phagocytes can identify preterm infants with late-onset sepsis as early as at sampling for blood culture and may thus aid in the diagnosis. II) In preterm infants with RDS, initiation of mechanical ventilation, but not the use of nasal continuous positive airway pressure, promotes a systemic inflammatory reaction; exogenous surfactant does not seem to promote inflammation. III) In addition to activation of circulating cells of the innate immunity in preterm infants with RDS, the circulating cells of the adaptive immunity are activated. The activation of adaptive immunity may link acute inflammation and development of chronic inflammation-associated problems such as BPD. IV) Maternal pre-eclampsia may prime neonatal immunity to react more strongly to postnatal stimuli. In conclusion, the preterm infant is exposed to numerous potentially injurious events such as intrauterine inflammation, respiratory distress syndrome (RDS), and systemic infections, all evoking systemic inflammation. Due to ongoing development of the lung and the brain, this may, in addition to acute injury, lead to aberrant lung and brain development and to clinical syndromes of BPD and neurologic sequelae.

Ischemia-reperfusion injury in human liver transplantation : Mechanisms and effects on graft function

Liver transplantation is an established therapy for both acute and chronic liver failure. Despite excellent long-term outcome, graft dysfunction remains a problem affecting up to 15-30% of the recipients. The etiology of dysfunction is multifactorial, with ischemia-reperfusion injury regarded as one of the most important contributors. This thesis focuses on the inflammatory response during graft procurement and reperfusion in liver transplantation in adults. Activation of protein C was examined as a potential endogenous anti-inflammatory mechanism. The effects of inflammatory responses on graft function and outcome were investigated. Seventy adult patients undergoing liver transplantation in Helsinki University Central Hospital, and 50 multiorgan donors, were studied. Blood samples from the portal and the hepatic veins were drawn before graft procurement and at several time points during graft reperfusion to assess changes within the liver. Liver biopsies were taken before graft preservation and after reperfusion. Neutrophil and monocyte CD11b and L-selectin expression were analysed by flow cytometry. Plasma TNF-α, IL-6, IL-8, sICAM-1, and HMGB1 were determined by ELISA and Western-blotting. HMGB1 immunohistochemistry was performed on liver tissue specimens. Plasma protein C and activated protein C were determined by an enzyme-capture assay. Hepatic IL-8 release during graft procurement was associated with subsequent graft dysfunction, biliary in particular, in the recipient. Biliary marker levels increased only 5 7 days after transplantation. Thus, donor inflammatory response appears to influence recipient liver function with relatively long-lasting effects. Hepatic phagocyte activation and sequestration, with concomitant HMGB1 release, occurred during reperfusion. Neither phagocyte activation nor plasma cytokines correlated with postoperative graft function. Thus, activation of the inflammatory responses within the liver during reperfusion may be of minor clinical significance. However, HMGB1 was released from hepatocytes and were also correlated with postoperative transaminase levels. Accordingly, HMGB1 appears to be a marker of hepatocellular injury.

Hypoxia-Mediated Impairment of the Mitochondrial Respiratory Chain Inhibits the Bactericidal Activity of Macrophages

In infected tissues oxygen tensions are low. As innate immune cells have to operate under these conditions, we analyzed the ability of macrophages (M phi) to kill Escherichia coli or Staphylococcus aureus in a hypoxic microenvironment. Oxygen restriction did not promote intracellular bacterial growth but did impair the bactericidal activity of the host cells against both pathogens. This correlated with a decreased production of reactive oxygen intermediates (ROI) and reactive nitrogen intermediates. Experiments with phagocyte NADPH oxidase (PHOX) and inducible NO synthase (NOS2) double-deficient M phi revealed that in E. coli- or S. aureus-infected cells the reduced antibacterial activity during hypoxia was either entirely or partially independent of the diminished PHOX and NOS2 activity. Hypoxia impaired the mitochondrial activity of infected M phi. Inhibition of the mitochondrial respiratory chain activity during normoxia (using rotenone or antimycin A) completely or partially mimicked the defective antibacterial activity observed in hypoxic E. coli-or S. aureus-infected wild-type M phi, respectively. Accordingly, inhibition of the respiratory chain of S. aureus-infected, normoxic PHOX-/- NOS2(-/-) M phi further raised the bacterial burden of the cells, which reached the level measured in hypoxic PHOX-/- NOS2(-/-) M phi cultures. Our data demonstrate that the reduced killing of S. aureus or E. coli during hypoxia is not simply due to a lack of PHOX and NOS2 activity but partially or completely results from an impaired mitochondrial antibacterial effector function. Since pharmacological inhibition of the respiratory chain raised the generation of ROI but nevertheless phenocopied the effect of hypoxia, ROI can be excluded as the mechanism underlying the antimicrobial activity of mitochondria.

Adenylate Cyclase Toxin Promotes Internalisation of Integrins and Raft Components and Decreases Macrophage Adhesion Capacity

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Quantification of the effects of antibodies on the extra- and intracellular dynamics of Salmonella enterica.

Antibodies are known to be essential in controlling Salmonella infection, but their exact role remains elusive. We recently developed an in vitro model to investigate the relative efficiency of four different human immunoglobulin G (IgG) subclasses in modulating the interaction of the bacteria with human phagocytes. Our results indicated that different IgG subclasses affect the efficacy of Salmonella uptake by human phagocytes. In this study, we aim to quantify the effects of IgG on intracellular dynamics of infection by combining distributions of bacterial numbers per phagocyte observed by fluorescence microscopy with a mathematical model that simulates the in vitro dynamics. We then use maximum likelihood to estimate the model parameters and compare them across IgG subclasses. The analysis reveals heterogeneity in the division rates of the bacteria, strongly suggesting that a subpopulation of intracellular Salmonella, while visible under the microscope, is not dividing. Clear differences in the observed distributions among the four IgG subclasses are best explained by variations in phagocytosis and intracellular dynamics. We propose and compare potential factors affecting the replication and death of bacteria within phagocytes, and we discuss these results in the light of recent findings on dormancy of Salmonella.

The first non-mammalian CXCR3 in a teleost fish: Gene and expression in blood cells and central nervous system in the grass carp (Ctenopharyngodon idella)

A novel fish chemokine receptor gene, chemokine (C-X-C motif) receptor 3 (CXCR3)-like was isolated from the grass carp Ctenopharyngodon idella , with its full-length genomic sequence. The cDNA of grass carp CXCR3-like (gcCXCR3-like) consists of 1261 bp with a 49bp 5'-UTR and a 189 bp 3'-UTR. An open reading frame of 1023 bp encodes a 341-amino acid peptide, with seven transmembrane helices. The deduced amino acid sequence showed the same sequence identities (37.8%) with its counterparts in goat and human. The gcCXCR3-like gene consists of two exons, with one intervening intron, spaced over approximately 2 kb of genomic sequence. Phylogenetic analyses clearly demonstrated that the gcCXCR3-like resembles the CXCR3s of other vertebrates. Real-time PCR analysis showed that gcCXCR3-like was expressed in all tested organs except heart and the expression level of gcCXCR3-like was highest in brain. Flow cytometric analyses showed the positive rate of labelled leukocytes from the healthy grass carp was 17.3%, and the labelled leukocytes were divided into three types by cell sorting. Immunohistochemical localization revealed that gcCXCR3-like expressed in whole brain regions including cerebel, diencephalon, medulla oblongata, optic lobe, and rhinencephalon, and that the labelled leukocytes are actually populations of monocyte and/or phagocyte, lymphocyte and the granulocyte. It is considered that fish CXCR expression and their function may need to be investigated in both nervous and immune systems. (c) 2006 Elsevier Ltd. All rights reserved.

Influence of several non-nutrient additives on nonspecific immunity and growth of juvenile turbot, Scophthalmus maximus L.

The effects of three non-nutrient additives on nonspecific immunity and growth of juvenile turbot (Scophthalmus maximus L.) were studied in this feeding experiment. The five treatments are basal diet alone, basal diets containing three different additives [0.4 g kg(-1) of xylo-oligosaccharides (XOS), 1.3 g kg (-1) of yeast cell wall and 0.8 g kg (-1) of bile acids] individually or in combination. Two hundred and twenty-five turbots (average initial weight 151.3 +/- 11.3 g) were randomly allotted in five treatments with three replicates within each treatment in a 72-day period. Comparing with basal diet group, activities of C3, C4, phagocyte, lysozyme, specific growth rate and feed conversion rate in yeast cell wall, XOS and the combined groups was enhanced significantly (P < 0.05); however, these parameters in bile acid groups were increased slightly (P > 0.05) except for phagocyte (P < 0.05); superoxide dismutase activity in additive groups was not significantly increased (P > 0.05) except for the combined group (P < 0.05). In conclusion, supplementation of yeast cell wall and XOS enhanced the nonspecific immunity of juvenile turbot. Synergistic or additive effect of the three additives was not observed.

Burkholderia cenocepacia disrupts host cell actin cytoskeleton by inactivating Rac and Cdc42

Burkholderia cenocepacia, a member of the Burkholderia cepacia complex, is an opportunistic pathogen that causes devastating infections in patients with cystic fibrosis. The ability of B. cenocepacia to survive within host cells could contribute significantly to its virulence in immunocompromised patients. In this study, we explored the mechanisms that enable B. cenocepacia to survive inside macrophages. We found that B. cenocepacia disrupts the actin cytoskeleton of infected macrophages, drastically altering their morphology. Submembranous actin undergoes depolymerization, leading to cell retraction. The bacteria perturb actin architecture by inactivating Rho family GTPases, particularly Rac1 and Cdc42. GTPase inactivation follows internalization of viable B. cenocepacia and compromises phagocyte function: macropinocytosis and phagocytosis are markedly inhibited, likely impairing the microbicidal and antigen-presenting capability of infected macrophages. The type VI secretion system is essential for the bacteria to elicit these changes. This is the first report demonstrating inactivation of Rho family GTPases by a member of the B. cepacia complex.

Age-related changes in non-receptor dependent generation of reactive oxygen species from phagocytes of healthy adults

Several authors have shown that neutrophil generation of reactive oxygen species (ROS) declines with advancing age. Similar changes have also been suggested in monocytes. In both cases alterations in second messenger activity have been implicated as the most likely explanation for these observations. The aim of this study was to investigate the effect of age on phagocyte ROS generation, stimulated by the direct activation of protein kinase C (PKC). Venous blood was drawn from normal healthy subjects, cells were separated on a double density gradient into mononuclear and polymorphonuclear (pmn) cells. Phorbol myristate acetate (PMA) was employed as a cell stimulus. Superoxide generation was measured by cytochrome c reduction and myeloperoxidase (MPO) products by measurement of peak luminol chemiluminescence (CL). Fifty-eight subjects, 25 males and 33 females, were studied, median age 49 years (range 26-88 years). Polymorphonuclear cell superoxide generation was significantly higher in males and there was a trend towards higher pmn MPO product generation in males. Using Spearman's ranked correlation coefficient, monocyte superoxide generation was negatively correlated with age (r = -0.473, P <0.001). No changes in the generation of MPO products was found. There were also trends towards a negative correlation of pmn cytochrome c reduction and peak luminol CL with age in males but not females. Since PMA directly activates protein kinase C, reduced monocyte superoxide generation with increasing age appears to be related to alterations in the ROS generating system downstream of the cell receptor. Impaired monocyte superoxide generation may have implications for non-specific defence against certain infections and early tumour growth in the elderly. Factors underlying these changes in monocyte function therefore require further study.

How hydrogen peroxide and CXCL8 modulate neutrophil recruitment "in vivo"

Tese de doutoramento, Ciências Biomédicas (Biologia Celular e Molecular), Universidade de Lisboa, Faculdade de Medicina, 2014

Host factors and genetic susceptibility to infections due to intracellular bacteria and fastidious organisms.

While genetic polymorphisms play a paramount role in tuberculosis (TB), less is known about their contribution to the severity of diseases caused by other intracellular bacteria and fastidious microorganisms. We searched electronic databases for observational studies reporting on host factors and genetic predisposition to infections caused by intracellular fastidious bacteria published up to 30 May 2014. The contribution of genetic polymorphisms was documented for TB. This includes genetic defects in the mononuclear phagocyte/T helper cell type 1 (Th1) pathway contributing to disseminated TB disease in children and genome-wide linkage analysis (GWAS) in reactivated pulmonary TB in adults. Similarly, experimental studies supported the role of host genetic factors in the clinical presentation of illnesses resulting from other fastidious intracellular bacteria. These include IL-6 -174G/C or low mannose-binding (MBL) polymorphisms, which are incriminated in chronic pulmonary conditions triggered by C. pneumoniae, type 2-like cytokine secretion polymorphisms, which are correlated with various clinical patterns of M. pneumoniae infections, and genetic variation in the NOD2 gene, which is an indicator of tubal pathology resulting from Chamydia trachomatis infections. Monocyte/macrophage migration and T lymphocyte recruitment defects are corroborated to ineffective granuloma formation observed among patients with chronic Q fever. Similar genetic polymorphisms have also been suggested for infections caused by T. whipplei although not confirmed yet. In conclusion, this review supports the paramount role of genetic factors in clinical presentations and severity of infections caused by intracellular fastidious bacteria. Genetic predisposition should be further explored through such as exome sequencing.

Mise au point de nanoparticules polymères pour l'administration parentérale d'agents anticancéreux hydrophobes

Plusieurs agents anticancéreux très puissants sont caractérisés par une solubilité aqueuse limitée et une toxicité systémique importante. Cette dernière serait liée d’une part à la solubilisation des agents anticancéreux à l’aide de surfactifs de bas poids moléculaire, connus pour leur toxicité intrinsèque, et d’autre part, par le manque de spécificité tissulaire des anticancéreux. Les vecteurs colloïdaux à base de polymères permettraient de résoudre certains défis liés à la formulation d’agents anticancéreux hydrophobes. D’abord, les polymères peuvent être sélectionnés afin de répondre à des critères précis de compatibilité, de dégradation et d’affinité pour le médicament à formuler. Ensuite, le fait d’encapsuler l’agent anticancéreux dans un vecteur peut améliorer son efficacité thérapeutique en favorisant son accumulation au niveau du tissu cible, i.e. la tumeur, et ainsi limiter sa distribution au niveau des tissus sains. Des travaux antérieurs menés au sein de notre laboratoire ont mené à la mise au point de micelles à base de poly(N-vinyl-pyrrolidone)-bloc-poly(D,L-lactide) (PVP-b-PDLLA) capables de solubiliser des agents anticancéreux faiblement hydrosolubles dont le PTX. Ce dernier est commercialisé sous le nom de Taxol® et formulé à l’aide du Crémophor EL (CrEL), un surfactif de bas poids moléculaire pouvant provoquer, entre autres, des réactions d’hypersensibilité sévères. Bien que les micelles de PVP-b-PDLLA chargées de PTX aient démontré une meilleure tolérance comparée au Taxol®, leur potentiel de ciblage tumoral et leur efficacité thérapeutique étaient similaires à la forme commerciale à doses égales. Ceci était possiblement dû au fait que les micelles étaient rapidement déstabilisées et ne pouvaient retenir leur cargo suite à leur administration intraveineuse. Nous avons donc décidé de poursuivre les travaux avec un autre type de vecteur, soit des nanoparticules, qui possèdent une stabilité intrinsèque supérieure aux micelles. L’objectif principal de cette thèse de doctorat était donc de mettre au point des nanoparticules polymères pour l’administration parentérale d’agents anticancéreux faiblement solubles dans l’eau. Les nanoparticules devaient permettre d’encapsuler des agents anticancéreux hydrophobes et de les libérer de manière contrôlée sur plusieurs jours. De plus, elles devaient démontrer un temps de circulation plasmatique prolongée afin de favoriser l’accumulation passive du médicament encapsulé au niveau de la tumeur. La première partie du travail visait à employer pour la première fois le copolymère amphiphile PVP-b-PDLLA comme émulsifiant dans la préparation de nanoparticules polymères. Ainsi, une méthode de fabrication des nanoparticules par émulsion huile-dans-eau a été appliquée afin de produire des nanoparticules à base de PDLLA de taille inférieure à 250 nm. Grâce aux propriétés lyoprotectrices de la couronne de PVP présente à la surface des nanoparticules, celles-ci pouvaient retrouver leur distribution de taille initiale après lyophilisation et redispersion en milieu aqueux. Deux anticancéreux hydrophobes, soit le PTX et l’étoposide (ETO), ont été encapsulés dans les nanoparticules et libérés de ces dernières de façon contrôlée sur plusieurs jours in vitro. Une procédure de « salting-out » a été appliquée afin d’améliorer le taux d’incorporation de l’ETO initialement faible étant donnée sa solubilité aqueuse légèrement supérieure à celle du PTX. Le second volet des travaux visait à comparer le PVP comme polymère de surface des nanoparticules au PEG, le polymère le plus fréquemment employé à cette fin en vectorisation. Par le biais d’études d’adsorption de protéines, de capture par les macrophages et de biodistribution chez le rat, nous avons établi une corrélation in vitro/in vivo démontrant que le PVP n’était pas un agent de surface aussi efficace que le PEG. Ainsi, malgré la présence du PVP à la surface des nanoparticules de PDLLA, ces dernières étaient rapidement éliminées de la circulation sanguine suite à leur capture par le système des phagocytes mononucléés. Par conséquent, dans le troisième volet de cette thèse, le PEG a été retenu comme agent de surface, tandis que différents polymères biodégradables de la famille des polyesters, certains synthétiques (PDLLA et copolymères d’acide lactique/acide glycolique), d’autres de source naturelle (poly(hydroxyalkanoates)(PHAs)), ont été investiguées comme matériaux formant le cœur des nanoparticules. Il en est ressorti que les propriétés physicochimiques des polyesters avaient un impact majeur sur l’efficacité d’encapsulation du PTX et son profil de libération des nanoparticules in vitro. Contrairement aux PHAs, les polymères synthétiques ont démontré des taux d’incorporation élevés ainsi qu’une libération contrôlée de leur cargo. Des études de pharmacocinétique et de biodistribution ont démontré que les nanoparticules de PDLLA dotées d’une couronne de PEG conféraient un temps de circulation plasmatique prolongé au PTX et favorisaient son accumulation tumorale. Les nanoparticules polymères représentent donc une alternative intéressante au Taxol®.

Le récepteur CD36 : implication dans le développement de l'athérosclérose et dans le recrutement des leucocytes aux sites inflammatoires

Le CD36 est un récepteur éboueur de classe B exprimé par plusieurs types cellulaires dont les macrophages et les cellules endothéliales de la microvasculature. Le CD36 présente une haute affinité de liaison pour les ligands lipidiques tels que les lipoprotéines oxydées de basse densité (LDLox). De part sa capacité à internaliser les LDLox au niveau des macrophages et de son implication dans la formation des cellules spumeuses, le CD36 joue un rôle critique dans le développement des lésions athérosclérotiques. Nous avons testé l'hypothèse selon laquelle le EP 80317, un ligand synthétique sélectif du CD36, exerce des effets anti-athérosclérotiques chez les souris déficientes en apolipoprotéine E. Un traitement prolongé (12 semaines) avec le EP 80317 réduit fortement (de 51%) la surface des lésions athérosclérotiques par comparaison aux souris témoins. L'effet anti-athérosclérotique est associé à une diminution des taux de cholestérol plasmatique, à une réduction de l’internalisation des LDLox au niveau des macrophages et à une augmentation de l’expression des protéines impliquées dans le transport inverse du cholestérol. De plus, un traitement par le EP 80317 est également associé une diminution de l’expression aortique et plasmatique de protéines pro-inflammatoires. Nos études ont aussi montré un rôle pour le CD36 dans le recrutement des phagocytes mononucléés au niveau des lésions athérosclérotiques, tel que démontré par une réduction de l’accumulation des phagocytes mononucléés radiomarqués CD36–/– par rapport aux cellules CD36+/+. À l’échelle moléculaire, nous avons montré que les phospholipides oxydés induisent la phosphorylation de la kinase Pyk2 des podosomes des monocytes/macrophages de manière dépendante de l’expression du CD36 et de Src. Cette phosphorylation est atténuée par un traitement par le EP80317. Nos résultats appuient le rôle important du CD36 dans l’athérosclérose et suggèrent que les ligands synthétiques qui modulent la fonction du CD36 représentent potentiellement une nouvelle classe d'agents anti-athérosclérotiques. Le CD36 exprimé par les cellules endothéliales de la microvasculature est un récepteur de l’hétérodimère protéique S100A8/A9. Ces protéines s’associent à l’acide arachidonique intracellulaire (AA) des neutrophiles polymorphonucléaires (PMN) et le complexe S100A8/A9/AA peut être sécrété par les PMN activés au contact de l’endothélium. Nous avons vérifié l’hypothèse selon laquelle le CD36 exprimé par la microvasculature est impliqué dans le métabolisme transcellulaire de l’AA par la liaison du complexe S100A8/A9/AA et la réponse inflammatoire. Chez deux modèles murins d'inflammation aiguë (ischémie/reperfusion des membres inférieurs et poche d’air dorsale), nous avons observé que la réponse inflammatoire, notamment l’accumulation des PMN au niveau des sites inflammatoires, est diminuée en moyenne de 63% chez les souris CD36-/-. De même, un traitement par le EP 80317 ou par les anticorps anti-S100A8/A9 diminue chacun de 60% en moyenne l’extravasation des PMN vers les tissus inflammatoires. L’administration simultanée des deux traitements n’a aucun effet supplémentaire, et ces traitements n’exercent aucun effet chez les souris CD36-/-. Nos résultats appuient le rôle du récepteur CD36 de la microvasculature dans la régulation de la réponse inflammatoire. L’utilisation des ligands synthétiques du CD36 pourrait représenter une nouvelle avenue thérapeutique dans le traitement des réponses inflammatoires aiguës.