eG Coated Stents Exhibit Enhanced Endothelial Wound Healing Characteristics

Purpose Despite their widespread use, a significant fraction of coronary stents suffer from in-stent restenosis and stent thrombosis. Stent deployment induces extensive injury to the vascular endothelium. Rapid endothelial wound closure is essential for the success of a stenting procedure. A recent study has demonstrated that the BuMA Supreme® sirolimus-eluting stent exhibits particularly attractive strut coverage characteristics. A unique feature of this stent is the presence of a thin brush layer of poly-butyl methacrylate (PBMA), covalently bonded to the stent’s cobalt-chromium frame via electro-grafting (eG™). The present study aimed to determine whether the PBMA coating has an effect on endothelial cell wound healing and stent strut coverage. Methods We used an in vitro coronary artery model whose wall consisted of an annular collagen hydrogel and whose luminal surface was lined with a monolayer of endothelial cells. Mechanical wounding of the endothelial lining was preformed prior to deployment of a bare cobalt-chromium stent either with or without the PBMA layer. The migration of fluorescently labeled endothelial cells was monitored automatically over a period of 48 h to determine endothelial wound healing rates. Results Quantitative assessment of endothelial wound healing rates within the simulated arterial model is achievable using automated image analysis. Wound healing is significantly faster (44% faster at 48 h) for stents with the PBMA eG Coating™ compared to bare metal stents. Conclusion The PBMA eG Coating™ has the effect of promoting endothelial wound healing. Future studies will focus on elucidating the mechanistic basis of this observation.

Frequency and magnitude of intermittent hypoxia modulate endothelial wound healing in a cell culture model of sleep apnea

Intermittent hypoxia (IH) has been implicated in the cardiovascular consequences of obstructive sleep apnea (OSA). However, the lack of suitable experimental systems has precluded assessment as to whether IH is detrimental, protective, or both for the endothelium. The aim of the work was to determine the effects of frequency and amplitude of IH oxygenation swings on aortic endothelial wound healing. Monolayers of human primary endothelial cells were wounded and subjected to constant oxygenation (1%, 4%, 13%, or 20% O2) or IH at different frequencies (0.6, 6, or 60 cycles/h) and magnitude ranges (13–4% O2 or 20–1% O2), using a novel well-controlled system, with wound healing being measured after 24 h. Cell monolayer repair was similar at 20% O2 and 13% O2, but was considerably increased (approximately twofold) in constant hypoxia at 4% O2. The magnitude and frequency of IH considerably modulated wound healing. Cycles ranging 13–4% O2 at the lowest frequency (0.6 cycles/h) accelerated endothelial wound healing by 102%. However, for IH exposures consisting of 20% to 1% O2 oscillations, wound closure was reduced compared with oscillation in the 13–4% range (by 74% and 44% at 6 cycles/h and 0.6 cycles/h, respectively). High-frequency IH patterns simulating severe OSA (60 cycles/h) did not significantly modify endothelial wound closure, regardless of the oxygenation cycle amplitude. In conclusion, the frequency and magnitude of hypoxia cycling in IH markedly alter wound healing responses and emerge as key factors determining how cells will respond in OSA. NEW & NOTEWORTHY Intermittent hypoxia (IH) induces cardiovascular consequences in obstructive sleep apnea (OSA) patients. However, the vast array of frequencies and severities of IH previously employed in OSA-related experimental studies has led to controversial results on the effects of IH. By employing an optimized IH experimental system here, we provide evidence that the frequency and magnitude of IH markedly alter human aortic endothelial wound healing, emerging as key factors determining how cells respond in OSA.

Abstract 468: Smooth Muscle Cells Accelerate Endothelial Regeneration Through a Protein Kinase C-delta-Dependent Secretion of CXCR2 Ligands

Background: Efficient regeneration of denuded endothelial cells (ECs) is an important process that counteracts the pro-stenotic activities. Unfortunately, this natural healing process is frequently compromised by disease conditions such as diabetes. Protein kinase C-delta (PKCδ) plays a complex role in the arterial injury response by regulating apoptosis of vascular smooth muscle cells (SMCs) as well as production of chemokines capable of attracting resident and circulating cells. In this study, we explored whether SMCs participate in endothelial repair through a PKCδ-dependent paracrine mechanism. Methods and Results: Following balloon injury to the rat carotid, SMC-specific gene transfer of Prkcd accelerated reendothelialization compared to the empty vector, reflected by a larger area excluded from Evans blue measured 14 days post injury (59.60±5.01% vs 25.38±7.52%). In contrast, SMC-specific knockdown of endogenous Prkcd delayed reendothelialization compared to the non-targeting shRNA control (41.31±6.54% vs 70.31±5.97%). In vitro , media conditioned by AdPKCδ-infected SMCs increased endothelial wound healing without affecting their proliferation and viability. In addition, SMCs in a PKCδ-dependent fashion attracted circulating angiogenic cells (CACs), a cell population that promotes neovascularization via production of angiogenic factors. A PCR-based array analysis identified Cxcl1 and Cxcl7 among others as PKCδ-mediated chemokines produced by SMCs. Blocking CXCL7 or CXCR2 significantly inhibited endothelial wound healing and CAC migration in response to AdPKCδ-infected SMC conditioned media. In vivo , PKCδ overexpression in SMCs following balloon injury increased CXCL7 production and stimulated CACs recruitment to injured arteries. Furthermore, insertion of a Cxcl7 cDNA in the lentiviral vector that carries a Prkcd shRNA overcame the negative effects of Prkcd knockdown on reendothelialization. Conclusions: Regeneration of denuded endothelium involves multiple cell types from the vascular wall as well as circulation. SMCs stimulate reendothelialization in a PKCδ-dependent paracrine mechanism, likely through CXCL7-mediated recruitment of ECs from uninjured endothelium and CACs from circulation.