BackgroundAutologous arteriovenous (AV) fistulas are the first choice for vascular access but have a high risk of non-maturation due to insufficient vessel adaptation, a process dependent on nitric oxide (NO)-signaling. Chronic kidney disease (CKD) is associated with oxidative stress that can disturb NO-signaling. Here, we evaluated the influence of CKD on AV fistula maturation and NO-signaling.MethodsCKD was established in rats by a 5/6th nephrectomy and after 6 weeks, an AV fistula was created between the carotid artery and jugular vein, which was followed up at 3 weeks with ultrasound and flow assessments. Vessel wall histology was assessed afterwards and vasoreactivity of carotid arteries was studied in a wire myograph. The soluble guanylate cyclase (sGC) activator BAY 60–2770 was administered daily to CKD animals for 3 weeks to enhance fistula maturation.ResultsCKD animals showed lower flow rates, smaller fistula diameters and increased oxidative stress levels in the vessel wall. Endothelium-dependent relaxation was comparable but vasorelaxation after sodium nitroprusside was diminished in CKD vessels, indicating NO resistance of the NO-receptor sGC. This was confirmed by stimulation with BAY 60–2770 resulting in increased vasorelaxation in CKD vessels. Oral administration of BAY 60–2770 to CKD animals induced larger fistula diameters, however; flow was not significantly different from vehicle-treated CKD animals.ConclusionsCKD induces oxidative stress resulting in NO resistance that can hamper AV fistula maturation. sGC activators like BAY 60–2770 could offer therapeutic potential to increase AV fistula maturation.

Short-term thrombotic occlusion and compliance mismatch hamper clinical use of synthetic small-diameter tissue engineered vascular grafts. It is felt that preconditioning of the graft with intimal (endothelial) and medial (vascular smooth muscle) cells contributes to patency of the graft. Autologous, non-vessel-derived cells are preferred because of systemic vascular pathology and immunologic concerns. We tested in a porcine model whether cultured bone marrow-derived mononuclear cells, also referred to as mesenchymal stem cells (MSC), are a potential source of intimal or medial cells in vascular tissue engineering. We show that MSC cultured in endothelial medium do not gain an endothelial phenotype or functional characteristics, even after enrichment for CD31, culturing under flow, treatment with additional growth factors (vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF)-2), or co-culture with microvascular endothelial cells (EC). On the other hand, we show that MSC cultured in MSC medium, but not in smooth muscle cell medium, show phenotypical and functional characteristics of vascular smooth muscle cells. We conclude that bone marrow-derived MSCs can be used as a bona fide source of medial, but not EC in small-diameter vascular tissue engineering.

The number of patients with renal failure is 240 million worldwide, with 20% being dependent on dialysis. Renal failure increases the risk to develop cardiovascular diseases and could be related to vessel wall dysfunction.Gaining a better understanding of arterial dysfunction under uremic conditions and especially its effect on NO‐soluble guanylate cyclase (sGC) mediated vasorelaxation.For uremic rats, 5/6 nephrectomy (n=21) was performed in Wistar rats. After six weeks, both carotid arteries were removed and analyzed in a wire‐myograph. Different compounds were used to investigate NO‐dependent and ‐independent vasomotor pathways.SNP and Deta NONOate showed significant differences in vasorelaxation between sham and 5/6 nephrectomy group with a 0.5 log IC50 difference in NO‐induced relaxation (P<0.0001). This difference was endothelial independent as acetylcholine induced effects were blocked with L‐NAME. Also NO independent, but sGC heam dependent and independent, (Bay 41‐2272 and Bay 60‐2770, respectively) vasorelaxation showed significant differences (p<0.01 and p<0.0001). When sGC was oxidized with ODQ, sham group was more potent in relaxation for both compounds as compared to uremic rats.Reduced vasorelaxation in uremic rats is related to NO‐resistance of smooth muscle cells. Our results point toward an oxidized state of sGC as the main cause of vasomotor dysfunction in uremic rats.

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Preconditioning of a synthetic graft with autologous cells is considered the best option to obtain functional vascular grafts. These cells are preferably isolated from an easy accessible patient‐autologous source, such as bone marrow or blood. We investigated if bone marrow‐derived mesenchymal stem cells (MSCs) can be isolated, cultured and instructed to gain a vascular smooth muscle cell (SMC) phenotype.MSCs were isolated from porcine bone marrow by gradient centrifugation and cultured in MSC or SMC‐defined culture media. Cells were analysed for SMC phenotype by determination of mRNA and protein expression of alpha‐SMA, calponin, desmin and collagen.Porcine MSCs can be reproducibly isolated and cultured. No eminent differences in growth dynamics (doubling time, morphology) were observed between animals. Cells grew in multiple layers and showed mesenchymal morphology with an elongated cell shape. Induction of expression of all SMC markers, both at mRNA and protein level, was observed and was highest in cells cultured in MSC‐defined medium.We conclude that porcine MSCs can be reproducibly isolated and differentiated into cells with SMC‐phenotype with sufficient efficacy. We show that the current protocol allows the MSCs to be readily used for application in small diameter vascular grafts.