Co-delivery of G-CSF and EPO released from fibrin gel for therapeutic neovascularization in rat hindlimb ischemia model

Astragaloside IV improves angiogenesis under hypoxic conditions by enhancing hypoxia‑inducible factor‑1α SUMOylation

Improving angiogenic capacity under hypoxic conditions is essential for improving the survival of skin grafts, as they often lack the necessary blood supply. The stable expression levels of hypoxia‑inducible factor‑1α (HIF‑1α) in the nucleus directly affect the downstream vascular endothelial growth factor (VEGF) signaling pathway and regulate angiogenesis in a hypoxic environment. Astragaloside IV (AS‑IV), an active component isolated from Astragalus membranaceus, has multiple biological effects including antioxidant and anti‑diabetic effects, and the ability to provide protection from cardiovascular damage. However, the mechanisms underlying these effects have not previously been elucidated. The present study investigated whether AS‑IV promotes angiogenesis via affecting the balance between ubiquitination and small ubiquitin‑related modifier (SUMO) modification of HIF‑1α. The results demonstrated that persistent hypoxia induces changes in expression levels of HIF‑1α protein and significantly increases the proportion of dysplastic blood vessels. Further western blotting experiments showed that rapid attenuation and delayed compensation of SUMO1 activity is one of the reasons for the initial increase then decrease in HIF‑1α levels. SUMO1 overexpression stabilized the presence of HIF‑1α in the nucleus and decreased the extent of abnormal blood vessel morphology observed following hypoxia. AS‑IV induces vascular endothelial cells to continuously produce SUMO1, stabilizes the HIF‑1α/VEGF pathway and improves angiogenesis in hypoxic conditions. In summary, the present study confirmed that AS‑IV stimulates vascular endothelial cells to continuously resupply SUMO1, stabilizes the presence of HIF‑1α protein and improves angiogenesis in adverse hypoxic conditions, which may improve the success rate of flap graft surgery following trauma or burn.

COPD is deleterious for pericytes: implications during training-induced angiogenesis in skeletal muscle

Improvements in skeletal muscle endurance and oxygen uptake are blunted in patients with chronic obstructive pulmonary disease (COPD), possibly because of a limitation in the muscle capillary oxygen supply. Pericytes are critical for capillary blood flow adaptation during angiogenesis but may be impaired by COPD systemic effects, which are mediated by circulating factors. This study compared the pericyte coverage of muscle capillaries in response to 10 wk of exercise training in patients with COPD and sedentary healthy subjects (SHS). Fourteen patients with COPD were compared with seven matched SHS. SHS trained at moderate intensity corresponding to an individualized moderate-intensity patient with COPD trained at the same relative (%V̇o₂: COPD-RI) or absolute (mL·min^-1·kg^-1: COPD-AI) intensity as SHS. Capillary-to-fiber ratio (C/F) and NG2⁺ pericyte coverage were assessed from vastus lateralis muscle biopsies, before and after 5 and 10 wk of training. We also tested in vitro the effect of COPD and SHS serum on pericyte morphology and mesenchymal stem cell (MSC) differentiation into pericytes. SHS showed greater improvement in aerobic capacity (V̇o_2VT) than both patients with COPD-RI and patients with COPD-AI (Group × Time: P = 0.004). Despite a preserved increase in the C/F ratio, NG2⁺ pericyte coverage did not increase in patients with COPD in response to training, contrary to SHS (Group × Time: P = 0.011). Conversely to SHS serum, COPD serum altered pericyte morphology (P < 0.001) and drastically reduced MSC differentiation into pericytes (P < 0.001). Both functional capacities and pericyte coverage responses to exercise training are blunted in patients with COPD. We also provide direct evidence of the deleterious effect of COPD circulating factors on pericyte morphology and differentiation.NEW & NOTEWORTHY This work confirms the previously reported impairment in the functional response to exercise training of patients with COPD compared with SHS. Moreover, it shows for the first time that pericyte coverage of the skeletal capillaries is drastically reduced in patients with COPD compared with SHS during training-induced angiogenesis. Finally, it provides experimental evidence that circulating factors are involved in the impaired pericyte coverage of patients with COPD.

Stromal cell-derived factor-1/CXC chemokine receptor 4 axis in injury repair and renal transplantation

Stem cell therapy has shown promise in treating a variety of pathologies, such as myocardial infarction, ischaemic stroke and organ transplantation. The stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor-4 (CXCR4) axis plays a key role in stem cell mobilization. This review describes the important role of SDF-1 in tissue injury and how it works in tissue revascularization and regeneration via CXCR4. Furthermore, factors influencing the SDF-1/CXCR4 axis and its clinical potential in ischaemia reperfusion injury, such as renal transplantation, are discussed. Exploring signalling pathways of the SDF-1/CXCR4 axis will contribute to the development of stem cell therapy so that more clinical problems can be solved. Controlling directional homing of stem cells through the SDF-1/CXCR4 axis is key to improving the efficacy of stem cell therapy for tissue injury. CXCR4 antagonists may also be effective in increasing circulating levels of adult stem cells, thereby exerting beneficial effects on damaged or inflamed tissues in diseases that are currently not treated by standard approaches.

Reloadable multidrug capturing delivery system for targeted ischemic disease treatment

Human clinical trials of protein therapy for ischemic diseases have shown disappointing outcomes so far, mainly because of the poor circulatory half-life of growth factors in circulation and their low uptake and retention by the targeted injury site. The attachment of polyethylene glycol (PEG) extends the circulatory half-lives of protein drugs but reduces their extravasation and retention at the target site. To address this issue, we have developed a drug capture system using a mixture of hyaluronic acid (HA) hydrogel and anti-PEG immunoglobulin M antibodies, which, when injected at a target body site, can capture and retain a variety of systemically injected PEGylated therapeutics at that site. Furthermore, repeated systemic injections permit "reloading" of the capture depot, allowing the use of complex multistage therapies. This study demonstrates this capture system in both murine and porcine models of critical limb ischemia. The results show that the reloadable HA/anti-PEG system has the potential to be clinically applied to patients with ischemic diseases, who require sequential administration of protein drugs for optimal outcomes.

Dual Delivery of EPO and BMP2 from a Novel Modular Poly-ɛ-Caprolactone Construct to Increase the Bone Formation in Prefabricated Bone Flaps

Poly-ɛ-caprolactone (PCL) is a biocompatible polymer that has mechanical properties suitable for bone tissue engineering; however, it must be integrated with biologics to stimulate bone formation. Bone morphogenetic protein-2 (BMP2) delivered from PCL produces bone when implanted subcutaneously, and erythropoietin (EPO) works synergistically with BMP2. In this study, EPO and BMP2 are adsorbed separately on two 3D-printed PCL scaffold modules that are assembled for codelivery on a single scaffold structure. This assembled modular PCL scaffold with dual BMP2 and EPO delivery was shown to increase bone growth in an ectopic location when compared with BMP2 delivery along a replicate scaffold structure. EPO (200 IU/mL) and BMP2 (65 μg/mL) were adsorbed onto the outer and inner portions of a modular scaffold, respectively. Protein binding and release studies were first quantified. Subsequently, EPO+BMP2 and BMP2 scaffolds were implanted subcutaneously in mice for 4 and 8 weeks, and the regenerated bone was analyzed with microcomputed tomography and histology; 8.6±1.4 μg BMP2 (22%) and 140±29 IU EPO (69.8%) bound to the scaffold and <1% BMP2 and 83% EPO was released in 7 days. Increased endothelial cell proliferation on EPO-adsorbed PCL discs indicated protein bioactivity. At 4 and 8 weeks, dual BMP2 and EPO delivery regenerated more bone (5.1±1.1 and 5.5±1.6 mm(3)) than BMP2 alone (3.8±1.1 and 4.3±1.7 mm(3)). BMP2 and EPO scaffolds had more ingrowth (1.4%±0.6%) in the outer module when compared with BMP2 (0.8%±0.3%) at 4 weeks. Dual delivery produced more dense cellular marrow, while BMP2 had more fatty marrow. Dual EPO and BMP2 delivery is a potential method to regenerate bone faster for prefabricated flaps.