Skin regeneration in deep second-degree scald injuries either by infusion pumping or topical application of recombinant human erythropoietin gel.

Large doses of recombinant growth factors formulated in solution form directly injected into the body is usual clinical practice in treating second-degree scald injuries, with promising results, but this approach creates side effects; furthermore, it may not allow appropriate levels of the factor to be sensed by the target injured tissue/organ in the specific time frame, owing to complications arising from regeneration. In this research, two delivery methods (infusion pumping and local topical application) were applied to deliver recombinant human erythropoietin (rHuEPO) for skin regeneration. First, rHuEPO was given in deep second-degree scald injury sites in mice by infusion pump. Vascularization was remarkably higher in the rHuEPO pumping group than in controls. Second, local topical application of rHuEPO gel was given in deep second-degree scald injury sites in rats. Histological analysis showed that epithelialization rate was significantly higher in the rHuEPO gel-treated group than in controls. Immunohistochemical studies showed that the rHuEPO gel-treated group showed remarkably higher expression of skin regeneration makers than the control group. An accurate method for visualization and quantification of blood vessel networks in target areas has still not been developed up to this point, because of technical difficulties in detecting such thin blood vessels. A method which utilizes a series of steps to enhance the image, removes noise from image background, and tracks the vessels edges for vessel segmentation and quantification has been used in this study. Using image analysis methods, we were able to detect the microvascular networks of newly formed blood vessels (less than 500 µm thickness), which participate in the healing process, providing not only nutrition and oxygen to grow tissues but also necessary growth factors to grow tissue cells for complete skin regeneration. The rHuEPO-treated group showed higher expression of stem cell markers (CD 31, CD 90, CD 71, and nestin), which actively contribute to in-wound-healing processes for new hair follicle generation as well as skin regeneration. Collectively, both rHuEPO group pumping into the systemic circulation system, and injection into the local injury area, prompted mice and rats to form new blood vessel networks in scald injury sites, which significantly participate in the scald healing process. These results may lead to the development of novel treatments for scald wounds.

The use of human sweat gland-derived stem cells for enhancing vascularization during dermal regeneration.

Vascularization is a key process in tissue engineering and regeneration and represents one of the most important issues in the field of regenerative medicine. Thus, several strategies to improve vascularization are currently under clinical evaluation. In this study, stem cells derived from human sweat glands were isolated, characterized, seeded in collagen scaffolds, and engrafted in a mouse full skin defect model for dermal regeneration. Results showed that these cells exhibit high proliferation rates and express stem cell and differentiation markers. Moreover, cells responded to angiogenic environments by increasing their migration (P<0.001) and proliferation (P<0.05) capacity and forming capillary-like structures. After seeding in the scaffolds, cells distributed homogeneously, interacting directly with the scaffold, and released bioactive molecules involved in angiogenesis, immune response, and tissue remodeling. In vivo, scaffolds containing cells were used to induce dermal regeneration. Here we have found that the presence of the cells significantly improved vascularization (P<0.001). As autologous sweat gland-derived stem cells are easy to obtain, exhibit a good proliferation capacity, and improve vascularization during dermal regeneration, we suggest that the combined use of sweat gland-derived stem cells and scaffolds for dermal regeneration might improve dermal regeneration in future clinical settings.

Skin regeneration with conical and hair follicle structure of deep second-degree scalding injuries via combined expression of the EPO receptor and beta common receptor by local subcutaneous injection of nanosized rhEPO.

BACKGROUND: Acceleration of skin regeneration is still an unsolved problem in the clinical treatment of patients suffering from deep burns and scalds. Although erythropoietin (EPO) has a protective role in a wide range of organs and cells during ischemia and after trauma, it has been recently discovered that EPO is not tissue-protective in the common ß subunit receptor (ßCR) knockout mouse. The protective capacity of EPO in tissue is mediated via a heteroreceptor complex comprising both the erythropoietin receptor (EPOR) and ßCR. However, proof of coexpression of these heterogenic receptors in regenerating skin after burns is still lacking. METHODS: To understand the role of nanosized recombinant human erythropoietin (rhEPO) in wound healing, we investigated the effects of subcutaneous injections of EPO on skin regeneration after deep second-degree scalding injuries. Our aim was to determine if joint expression of EPOR and ßCR is a prerequisite for the tissue-protective effect of rhEPO. The efficiency in wound regeneration in a skin scalding injury mouse model was examined. A deep second-degree dermal scald injury was produced on the backs of 20 female Balb/c mice which were subsequently randomized to four experimental groups, two of which received daily subcutaneous injections of rhEPO. At days 7 and 14, the mice were sacrificed and the effects of rhEPO were analyzed with respect to grade of re-epithelialization (wound closure) and stage of epidermal maturation. This was investigated using different histological parameters of epithelial covering, such as depth of the epidermal layer, epidermal stratification, and presence of conical and hair follicle structures. RESULTS: Expression of EPOR, ßCR, and growth hormone receptor at the mRNA and protein levels was demonstrated with reverse transcriptase polymerase chain reaction and Western blot analysis. After rhEPO treatment, the rate of re-epithelialization of the scalding injury was increased and the time to final wound closure was reduced. In addition, the quality of regenerated skin was improved. In this investigation, for the first time, we demonstrated coexpression of EPOR and ßCR at the RNA and protein levels in vivo using a deep second-degree scalding injury mouse model. These results highlight the potential role of rhEPO in the improved treatment of burns patients, which might be crucial for the development of innovative new therapy regimes. CONCLUSION: Local injection of nanosized rhEPO directly to the injury site rather than systemic administration for deep second-degree scalding injuries achieved complete skin regeneration with conical and hair follicle structure via combined expression of EPOR and ßCR.

The role of single cell derived vascular resident endothelial progenitor cells in the enhancement of vascularization in scaffold-based skin regeneration.

Increasing evidence suggests that vascular resident endothelial progenitor cells (VR-EPCs) are present in several organs, playing an important role in postnatal neovascularization. Here, we isolated and characterized VR-EPCs from cardiac tissue in vitro, evaluating their regenerative potential in vivo. VR-EPCs showed to be highly clonogenic and expressed several stem and differentiation markers. Under endothelial differentiation conditions, cells form capillary-like structures, in contrast to osteogenic or adipogenic differentiation conditions where no functional changes were observed. After seeding in scaffolds, cells were distributed homogeneously and directly attached to the scaffold. Then, cell seeded scaffolds were used to induce dermal regeneration in a nude mice full skin defect model. The presence of VR-EPCs enhanced dermal vascularization. Histological assays showed increased vessel number (p < 0.05) and cellularization (p < 0.05) in VR-EPCs group. In order to explore possible mechanisms of vascular regeneration, in vitro experiments were performed. Results showed that pro-angiogenic environments increased the migration capacity (p < 0.001) and ability to form capillary-like structures (p < 0.05) of VR-EPC. In addition, VR-EPCs secreted several pro-angiogenic molecules including VEGF and PDGF. These results indicate that a highly clonogenic population of VR-EPCs might be established in vitro, representing a new source for therapeutic vascularization in tissue engineering and regeneration.

Bioactivation of dermal scaffolds with a non-viral copolymer-protected gene vector.

The use of scaffolds in skin tissue engineering is accompanied with low regeneration rates and high risk of infection. In this study, we activated an FDA-approved collagen scaffold for dermal regeneration by incorporation of copolymer-protected gene vectors (COPROGs) to induce a temporary release of VEGF. In vitro results show that the presence of COPROGs did not affect the distribution, attachment, proliferation and viability of cells in the scaffold. A transient release of VEGF was observed for up to 3 weeks. Moreover a high amount of VEGF was also found in the cells and associated with the scaffold. In a full skin defect model in nude mice, VEGF levels were significantly increased compared to controls in VEGF gene activated scaffolds 14 d after implantation, but not in skin from the wound edge. Results showed an increased amount of non-adherent cells, especially erythrocytes, and von Willebrandt factor (vWF) and a yellow red appearance of gene activated scaffolds in relation to controls. This suggests the presence of leaky vessels. In this work we show that the bioactivation of collagen scaffolds with COPROGs presents a new technology that allows a local release of therapeutic proteins thus enhancing the regenerative potential in vivo.

[Diagnosis of the deep partial-thickness burn wound of Skh-1 mouse with Optical Coherence Tomography].

OBJECTIVE: To evaluate the application value of Optical Coherence Tomography (OCT) in the diagnosis of the depth of burn wound. METHODS: Deep partial-thickness scald models of Skh-1 mice were reproduced using self-made steam scald appliance. The scald wounds were scanned with OCT 3 hours, or 3 and 8 days after injury respectively. Scanned wound tissue was harvested for histological examination right after each episode of OCT imaging. Normal skin of mice was scanned and examined with the above-mentioned methods at the same time. RESULTS: Compared with those of the normal skin, collagen in the dermis was denatured after steam scald, and it was imaged as vanishing or reduction in birefringence in OCT detection. The structure change intensity was related to the pathological process of the wounds and consistent with the corresponding histological results. CONCLUSIONS: OCT is a noninvasive technique. It can be used to diagnose the depth of burn wound in real time.

The use of glandular-derived stem cells to improve vascularization in scaffold-mediated dermal regeneration.

Clinical success in tissue regeneration requires improvements in vascularization capacity of scaffolds. Several efforts have been made in this field including cellular and acellular technologies. In this work we combined the use of stem cells derived from pancreas or submandibular glands expressing green fluorescent protein (GFP(+)) with a commercially available scaffold for dermal regeneration. Cells were isolated, characterized and seeded in a scaffold for dermal regeneration. Scaffolds containing cells were used to induce dermal regeneration in a full skin defect model. After 3 weeks of in vivo regeneration, tissues were harvested and vascularization was analyzed. Results showed that gland-derived stem cells displayed stem cell features and presented multipotential differentiation capacity because they were able to differentiate in cell types representing the 3 different germ layers. After seeding, cells were homogeneously distributed and formed focal adhesions with the scaffold. Metabolic assays showed that cells can be cultured for at least 3 weeks in the scaffold. In vivo, the presence of pancreatic or submandibular stem cells significantly enhanced the vascularization compared to empty scaffolds. Presence of gland-derived stem cells in the regenerating tissue was confirmed by the detection of GFP expression in the wound area. In order to explore the possible mechanisms behind the improvement in vascular regeneration, in vitro experiments were performed, showing that gland-derived stem cells could contribute by angiogenic and vasculogenic mechanisms to this process. Our results suggest that the combined use of stem cells derived from glands and scaffold for dermal regeneration could be a rational alternative to improve vascularization in scaffold-mediated dermal regeneration.

Ex vivo method to visualize and quantify vascular networks in native and tissue engineered skin.

BACKGROUND AND AIMS: Neovascularization plays a pivotal role in tissue engineering and tissue regeneration. However, reliable technologies to visualize and quantify blood vessel networks in target tissue areas are still pending. In this work, we introduce a new method which allows comparing vascularization levels in normal and tissue-engineered skin. MATERIALS AND METHODS: Normal skin was isolated, and vascular dermal regeneration was analyzed based on tissue transillumination and computerized digital segmentation. For tissue-engineered skin, a bilateral full skin defect was created in a nude mouse model and then covered with a commercially available scaffold for dermal regeneration. After 3 weeks, the whole skin (including scaffold for dermal regeneration) was harvested, and vascularization levels were analyzed. RESULTS: The blood vessel network in the skin was better visualized by transillumination than by radio-angiographic studies, the gold standard for angiographies. After visualization, the whole vascular network was digitally segmented showing an excellent overlapping with the original pictures. Quantification over the digitally segmented picture was performed, and an index of vascularization area (VAI) and length (VLI) of the vessel network was obtained in target tissues. VAI/VLI ratio was calculated to obtain the vessel size index. CONCLUSIONS: We present a new technique which has several advantages compared to others, as animals do not require intravascular perfusions, total areas of interest can be quantitatively analyzed at once, and the same target tissue can be processed for further experimental analysis.