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N L'Heureux

Publications and source records attributed to N L'Heureux.

9 recordsLinked to original sources
PubMed2001

A human tissue-engineered vascular media: a new model for pharmacological studies of contractile responses.

Our method for producing tissue-engineered blood vessels based exclusively on the use of human cells, i.e., without artificial scaffolding, has previously been described (1). In this report, a tissue-engineered vascular media (TEVM) was specifically produced for pharmacological studies from cultured human vascular smooth muscle cells (VSMC). The VSMC displayed a differentiated phenotype as demonstrated by the re-expression of VSMC-specific markers and actual tissue contraction in response to physiological stimuli. Because of their physiological shape and mechanical strength, rings of human TEVM could be mounted on force transducers in organ baths to perform standard pharmacological experiments. Concentration-response curves to vasoconstrictor agonists (histamine, bradykinin, ATP, and UTP) were established, with or without selective antagonists, allowing pharmacological characterization of receptors (H1, B2, and P2Y1, and pyrimidinoceptors). Sustained agonist-induced contractions were associated with transient increases in cytosolic Ca2+ concentration, suggesting sensitization of the contractile machinery to Ca2+. ATP caused both Ca2+ entry and Ca2+ release from a ryanodine- and caffeine-sensitive store. Increased cyclic AMP or cyclic GMP levels caused relaxation. This human TEVM displays many of functional characters of the normal vessel from which the cells were originally isolated, including contractile/relaxation responses, cyclic nucleotide sensitivity, and Ca2+ handling mechanisms comparable to those of the normal vessel from which the cells were originally isolated. These results demonstrate the potential of this human model as a versatile new tool for pharmacological research.

Adenosine Triphosphate↗
PubMed2000

Fluid shear stress increases membrane fluidity in endothelial cells: a study with DCVJ fluorescence.

Fluid shear stress (FSS) has been shown to be an ubiquitous stimulator of mammalian cell metabolism. Although many of the intracellular signal transduction pathways have been characterized, the primary mechanoreceptor for FSS remains unknown. One hypothesis is that the cytoplasmic membrane acts as the receptor for FSS, leading to increased membrane fluidity, which in turn leads to the activation of heterotrimetric G proteins (13). 9-(Dicyanovinyl)-julolidine (DCVJ) is a fluorescent probe that integrates into the cell membrane and changes its quantum yield with the viscosity of the environment. In a parallel-plate flow chamber, confluent layers of DCVJ-labeled human endothelial cells were exposed to different levels of FSS. With increased FSS, a reduced fluorescence intensity was observed, indicating an increase of membrane fluidity. Step changes of FSS caused an approximately linear drop of fluorescence within 5 s, showing fast and almost full recovery after shear cessation. A linear dose-response relationship between shear stress and membrane fluidity changes was observed. The average fluidity increase over the entire cell monolayer was 22% at 26 dyn/cm(2). This study provides evidence for a link between FSS and membrane fluidity, and suggests that the membrane is an important flow mechanosensor of the cell.

Cell Membrane↗
PubMed1999

Characterization of a new tissue-engineered human skin equivalent with hair.

We designed a new tissue-engineered skin equivalent in which complete pilosebaceous units were integrated. This model was produced exclusively from human fibroblasts and keratinocytes and did not contain any synthetic material. Fibroblasts were cultured for 35 d with ascorbic acid and formed a thick fibrous sheet in the culture dish. The dermal equivalent was composed of stacked fibroblast sheets and exhibited some ultrastructural organization found in normal connective tissues. Keratinocytes seeded on this tissue formed a stratified and cornified epidermis and expressed typical markers of differentiation (keratin 10, filaggrin, and transglutaminase). After 4 wk of culture, a continuous and ultrastructurally organized basement membrane was observed and associated with the expression of laminin and collagen IV and VII. Complete pilosebaceous units were obtained by thermolysin digestion and inserted in this skin equivalent in order to assess the role of the transfollicular route in percutaneous absorption. The presence of hair follicles abolished the lag-time observed during hydrocortisone diffusion and increased significantly its rate of penetration in comparison to the control (skin equivalent with sham hair insertion). Therefore, this new hairy human skin equivalent model allowed an experimental design in which the only variable was the presence of pilosebaceous units and provided new data confirming the importance of hair follicles in percutaneous absorption.

Adult↗
PubMed1998

A completely biological tissue-engineered human blood vessel.

Mechanically challenged tissue-engineered organs, such as blood vessels, traditionally relied on synthetic or modified biological materials for structural support. In this report, we present a novel approach to tissue-engineered blood vessel (TEBV) production that is based exclusively on the use of cultured human cells, i.e., without any synthetic or exogenous biomaterials. Human vascular smooth muscle cells (SMC) cultured with ascorbic acid produced a cohesive cellular sheet. This sheet was placed around a tubular support to produce the media of the vessel. A similar sheet of human fibroblasts was wrapped around the media to provide the adventitia. After maturation, the tubular support was removed and endothelial cells were seeded in the lumen. This TEBV featured a well-defined, three-layered organization and numerous extracellular matrix proteins, including elastin. In this environment, SMC reexpressed desmin, a differentiation marker known to be lost under standard culture conditions. The endothelium expressed von Willebrand factor, incorporated acetylated LDL, produced PGI2, and strongly inhibited platelet adhesion in vitro. The complete vessel had a burst strength over 2000 mmHg. This is the first completely biological TEBV to display a burst strength comparable to that of human vessels. Short-term grafting experiment in a canine model demonstrated good handling and suturability characteristics. Taken together, these results suggest that this novel technique can produce completely biological vessels fulfilling the fundamental requirements for grafting: high burst strength, positive surgical handling, and a functional endothelium.

Animals↗
PubMed1997

From newborn to adult: phenotypic and functional properties of skin equivalent and human skin as a function of donor age.

The skin's most important function is to act as a barrier against fluid loss, microorganism infections, and percutaneous absorption. To fulfill this role, keratinocytes proliferate and differentiate to produce a protective layer: the stratum corneum. Because stem cells are responsible for the production of differentiated progeny and stem cells (K19-expressing cells) are less abundant in skin from older donors, the purpose of this study was to establish whether histological and functional properties of differentiating skin is influenced by donor age. The in vitro model developed for the evaluation of skin properties (Michel et al., 1995) was used to produce skin equivalents from newborn, child, and adult keratinocytes. Throughout maturation, skin equivalents were compared with corresponding skin biopsies for keratin, filaggrin, and transglutaminase expression. Percutaneous absorptions of hydrocortisone also were measured and correlated with lipid content. After 1 wk of immersed culture, the epidermal layer of newborn skin equivalents was thicker than child and adult epidermis. As expected, a greater proportion of cutaneous stem cells was present in newborn compared with children and adult skin equivalents. No age-related difference was observed for differentiation markers. When skin equivalents were cultured at the air-liquid interface, cell differentiation and stratum corneum formation were induced, and the age-related variation in the thickness of the epidermal layer disappeared. Percutaneous absorption through these matured skin equivalents did not vary with age. Their lipid density and profile were similar. Accordingly, skin biopsies exhibited comparable percutaneous absorption profiles independently of donor age. In conclusion, although newborn skin equivalents, or skin biopsies, contained more stem cells than child and adult counterparts, no age-related histological difference was observed in the differentiated tissues. Moreover, the functional barrier property of skins and matured skin equivalents did not vary with age. Therefore, both newborn and adult keratinocytes produce useful in vitro models to study epidermal differentiation processes involved in both normal and pathological states.

Absorption↗
PubMed1996

Effects of visible signs of contagious ecthyma on mass and survival of bighorn lambs.

External signs of contagious ecthyma became common in a population of Rocky Mountain bighorn sheep (Ovis canadensis) in Alberta, Canada, after it attained high density. Between 1990 and 1993, we studied effects of this disease on mass gain and survival of lambs. Prevalence and severity were independent of lamb sex. Lambs with large sores and scabs gained less mass than other lambs and were lighter the following spring as yearlings. There was no significant effect of the disease upon lamb survival, and contagious ecthyma did not appear to play a primary role on the dynamics of the study population.

Analysis of Variance↗
PubMed1993

In vitro construction of a human blood vessel from cultured vascular cells: a morphologic study.

PURPOSE: The purpose of this study was to create a tubular vascular model exclusively made of human cells and collagen. METHODS: The blood vessel equivalent was constructed with the three following human cell types: vascular smooth muscle cells, endothelial cells, and fibroblasts. A tissuelike structure was obtained from the contraction of a tubular collagen gel (human origin) by vascular smooth muscle cells, which created a media-like structure. An adventitia-like tissue was added around the media-like structure by embedding fibroblasts into a collagen gel. An endothelium was established within the tubular structure after intraluminal cell seeding. RESULTS: Cell orientation and gel contraction were followed up over time. Vascular smooth muscle cells developed a complex tridimensional network and were oriented in a circular fashion around the tube's axis. In contrast, fibroblasts were randomly oriented. A viable, homogeneous, and well-characterized endothelium was observed. These endothelial cells showed a slightly elongated structure and were oriented parallel to this vascular equivalent axis. CONCLUSION: An in vitro tridimensional vascular model that exhibits some phenotypic characteristics of in vivo vascular cells could be useful in the study of events that lead to atherosclerotic plaque formations.

Cells, Cultured↗
PubMed1984

Cytoplasmic retinoic acid-binding protein in retinoic acid-resistant human breast cancer sublines.

Two sublines resistant to the growth-inhibitory effects of retinoic acid (RA) have been isolated from the parental Hs578T wild-type (W.T.) human breast cancer cell line. These sublines (Hs578T-R-1 and Hs578T-R-2) have been growing normally in 10 microM RA during more than 18 months, and their RA-resistant phenotype has remained stable after the removal of RA. The resistance is specific for RA, since their growth is still inhibited by retinol. The intracellular incorporation of [3H]RA is not deficient in the RA-resistant sublines. Cytoplasmic RA-binding protein (cRABP) is present in Hs578T-R-1 and in Hs578T-R-2 and is not different in terms of maximum binding capacity or binding affinity from cRABP in Hs578T (W.T.). These results indicate that RA resistance in these sublines is not secondary to a defect of RA uptake or of binding of RA to cRABP; the resistance may result from a defect distal to binding to cRABP, or alternatively, cRABP may not mediate this effect of RA.

Binding, Competitive↗