The main function of the cardiovascular system is to deliver a sufficient quantity of oxygenated blood to the tissues, cells, and organs of the body in order to provide the cells with essential nutrients for metabolism and for the removal of waste products. All cells require and utilize oxygen. Oxygen is transported to various cells and tissues via red blood cells flowing through the microcirculation of an organism. Measurement of oxygen transport in the microcirculation has shown that about ten times more oxygen appears to leave the blood of arterioles than can be accounted for by diffusion. One possibility to explain the high oxygen loss is an increased release of oxygen due to exposure of blood to light. In the present in vitro study the release of oxygen from red blood cells was measured during exposure of the sample to light by monitoring the change in PO2 of the suspension during light exposure. A PO2 electrode was calibrated using PBS solution and utilized to monitor the change in current in the present study. Red blood cell suspensions were made using blood withdrawn from male Sprague-Dawley rats. The red blood cell suspension was placed in a closed sample chamber and exposed to light for 5 minutes. A method to correct for the drift of the PO2 electrode and temperature change during the experiment was implemented. The calculated change in PO2 of the RBC suspension due to light exposure was small. The change of PO2 in the sample chamber during light exposure was an average of 1.60 ± 0.9 mmHg (SEM). The contribution of photo-dissociation of oxygen from oxygenated hemoglobin molecules to the observed oxygen loss per RBC can account for only about 0.01% of the observed in vivo results. Therefore, light-associated oxygen release is negligible. These findings disprove the hypothesis of the present study, in which light exposure does not have a significant effect on oxygen release and thus rules out this possible explanation for the discrepancy between experiment and theory.

<p>One of today’s most widely spread health problems is urinary incontinence, affecting 60-80% of the US population from age 15 and up. Treatment based on the possibility to implant a scaffold seeded with the patients’ own urine-derived stem cells, hUSC, to regenerate the damaged muscle tissue, would prove effective. A main challenge in regenerating new tissue from cell-seeded scaffolds is the limited cell survival due to insufficient oxygen diffusion to the center of the scaffold. Ways of enhancing cell survival, and thereby, proliferation and differentiation, is by hypoxic preconditioning of the cells or implantation in an oxygen-release material. Hypoxic preconditioning has shown to enhance proliferation as well as the expression of vascular endothelial growth factor, VEGF, in for example human bone marrow derived stem cells, hBMSC. VEGF is involved in the establishment of vasculature structures and an upregulation of its expression may therefore help promote quicker angeogenisis, increasing the oxygen supply and the cell survival. Oxygen-release materials have shown to enhance cell survival and growth both <em>in vitro</em> and <em>in vivo</em>.<em></em></p><p>This study aims to investigate the effect of hypoxia on hUSC, during 9 days of hypoxic culturing (2.0% ± 0.1% O₂) with and without oxygen-release material (PLGA 75:25 with 5 w% CPO) <em>in vitro</em>. hBMSC, and human smooth muscle cells, hSMC, have been used as control groups. Cell proliferation, morphology, differentiation, production of VEGF, and expression of hypoxia inducible factor HIF-1α have been studied.</p><p>According to the results, combining hypoxic preconditioning of hUSC with implantation in oxygen-release material could be an effective way to regenerate muscular tissue. Hypoxic preconditioning enhanced cell proliferation, production of VEGF, and HIF-1α expression. The increase of VEGF and HIF-1α would promote vascularization when implanted. The oxygen-release material showed possible promotion of cell differentiation, which would augment the hUSCs’ myogenic differentiation, while supplying oxygen until the tissue’s vascular structure has been established.</p>

One of today’s most widely spread health problems is urinary incontinence, affecting 60-80% of the US population from age 15 and up. Treatment based on the possibility to implant a scaffold seeded with the patients’ own urine-derived stem cells, hUSC, to regenerate the damaged muscle tissue, would prove effective. A main challenge in regenerating new tissue from cell-seeded scaffolds is the limited cell survival due to insufficient oxygen diffusion to the center of the scaffold. Ways of enhancing cell survival, and thereby, proliferation and differentiation, is by hypoxic preconditioning of the cells or implantation in an oxygen-release material. Hypoxic preconditioning has shown to enhance proliferation as well as the expression of vascular endothelial growth factor, VEGF, in for example human bone marrow derived stem cells, hBMSC. VEGF is involved in the establishment of vasculature structures and an upregulation of its expression may therefore help promote quicker angeogenisis, increasing the oxygen supply and the cell survival. Oxygen-release materials have shown to enhance cell survival and growth both in vitro and in vivo. This study aims to investigate the effect of hypoxia on hUSC, during 9 days of hypoxic culturing (2.0% ± 0.1% O2) with and without oxygen-release material (PLGA 75:25 with 5 w% CPO) in vitro. hBMSC, and human smooth muscle cells, hSMC, have been used as control groups. Cell proliferation, morphology, differentiation, production of VEGF, and expression of hypoxia inducible factor HIF-1α have been studied. According to the results, combining hypoxic preconditioning of hUSC with implantation in oxygen-release material could be an effective way to regenerate muscular tissue. Hypoxic preconditioning enhanced cell proliferation, production of VEGF, and HIF-1α expression. The increase of VEGF and HIF-1α would promote vascularization when implanted. The oxygen-release material showed possible promotion of cell differentiation, which would augment the hUSCs’ myogenic differentiation, while supplying oxygen until the tissue’s vascular structure has been established.

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L’objectif général de ce travail était d’évaluer l’effet du diabète de Type 1 et de l’hyperglycémie chronique (reflétée par un niveau élevé d’HbA1c), chez des patients indemnes de complications micro et macrovasculaires, sur la disponibilité en oxygène (O2) au niveau musculaire et cortical et ses répercussions sur l’aptitude physique aérobie. Dans un premier temps, nous nous sommes attardés à étudier l’effet du diabète et des niveaux élevés d’HbA1c sur les différentes étapes de la cascade d’oxygène (à savoir la diffusion alvéolo-capillaire, le transport artériel et la libération de l’O2 au niveau musculaire) ainsi que sur l’oxygénation musculaire estimée par la Spectroscopie dans le proche Infra-Rouge (NIRS) durant un exercice incrémental et voir les répercussions possibles sur la consommation maximale d’oxygène (&#12310;V &#775;O&#12311;_2max). Nous avons montré que les patients DT1 présentent une capacité de diffusion alvéolo-capillaire ainsi qu’une capacité de transport artériel d’O2 comparable aux sujets sains. En revanche, les patients ayant un niveau élevé d’HbA1c présentent une altération de &#12310;V &#775;O&#12311;_2max ainsi qu’une réduction du volume sanguin musculaire (reflétée par une baisse de l’hémoglobine totale) et une nette baisse de la déoxyhémoglobine (HHb) au niveau du muscle actif aux intensités proches de l’exercice maximal. Ce dernier résultat pourrait s’expliquer par l’affinité plus importante de HbA1c pour l’O2 et/ou une altération de la redistribution de débit sanguin entre les vaisseaux nutritifs et non nutritifs. L’altération du volume sanguin au niveau musculaire chez les patients présentant un mauvais contrôle glycémique peut prévenir les cliniciens du dysfonctionnement de la microcirculation survenant avant même qu’une microangiopathie se manifeste à l’état clinique (Étude 1). Dans un second temps, nous nous sommes intéressés à la fonction cérébrale. Notre objectif étant d’évaluer l’hémodynamique cérébrale durant un exercice incrémental maximal. Nous avons trouvé une altération de l’hémodynamique cérébrale (baisse de l’hémoglobine totale) aux intensités proches de l’exercice maximal chez les patients DT1 qui présentent un mauvais contrôle glycémique (Étude 2). Ces deux travaux nous montrent bien que les sujets diabétiques de type 1 indemnes des complications micro et/ou marcovasculaires présentent une faible aptitude physique aérobie qui peut s’expliquer à la fois par une altération de l’oxygénation musculaire et cérébrale. Ces études mettent également en évidence l’intérêt d’associer la NIRS avec un exercice maximal. Ce dernier place les tissus en situation de besoin maximal en O2 ce qui permet de mettre en exergue des altérations fonctionnelles de la microcirculation avant même l’apparition de complications microvasculaires détectables par les tests cliniques habituels. / This study sought to investigate whether type 1 diabetes and high levels of glycated hemoglobin (HbA1c) influence oxygen supply including alveolar capillary diffusion, oxygen delivery and release, to active muscle and prefrontal cortex during maximal exercise. We first studied the effect of high level of HbA1c on oxyhemoglobin dissociation at the active muscle measured by Near Infra-Red Spectroscopy (NIRS) during maximal exercise. We found that alveolar capillary diffusion and arterial oxygen content was comparable between patients with type 1 diabetes and healthy subjects. However, patients with inadequate glycemic control but without any clinically detectable vascular complications displayed an impaired aerobic capacity as well as a reduction in blood volume and a dramatic impairment in deoxyhemoglobin (HHb) increase in active skeletal muscle during intense exercise. The latter supports the hypotheses of an increase in O2 affinity induced by hemoglobin glycation and/or of a disturbed balance between nutritive and nonnutritive muscle blood flow. Furthermore, reduced exercise muscle blood volume in poorly controlled patients may warn clinicians of microvascular dysfunction occurring even before overt microangiopathy (Study 1). Secondly, we aimed at investigating prefrontal cortex hemodynamic during an incremental maximal exercise in patients with uncomplicated type 1 diabetes, taking into account chronic glycemic control. We observed that levels and changes in regional cerebral blood volume – as reflected by change in total hemoglobin – were lower at high intensities of exercise in patients with inadequate glycemic control (Study 2).In summary, the physiological stimulus of maximal exercise coupled with NIRS measurement highlighted subclinical disorders of both cerebral hemodynamic and muscle oxygenation in poorly-controlled patients with type 1 diabetes albeit free from any clinical microangiopathy.