Cytokines in single layer amnion allografts compared to multilayer amnion/chorion allografts for wound healing.

Human amniotic membrane allografts have proven effective at improving healing of cutaneous wounds. The mechanism of action for these therapeutic effects is poorly understood but is thought to involve the resident growth factors present in near term amniotic tissue. To determine the relative cytokine contribution of the amnion and chorion in amniotic allografts, the content of 18 cytokines involved in wound healing were measured in samples of PURION® Processed dehydrated amnion, chorion, and amnion/chorion membrane (dHACM) grafts by multiplex enzyme-linked immunosorbent assay array. Both amnion and chorion contained similar amounts of each factor when normalized per dry weight; however, when calculated per surface area of tissue applied to a wound, amnion contained on average only 25% as much of each factor as the chorion. Therefore, an allograft containing both amnion and chorion would contain four to five times more cytokine than a single layer amnion allograft alone. Both single layer amnion and multilayer allografts containing amnion and chorion are currently marketed for wound repair. To examine the role of tissue processing technique in cytokine retention, cytokine contents in representative dehydrated single layer wound care products were measured. The results demonstrated that cytokine content varied significantly among the allografts tested, and that PURION® Processed single layer amnion grafts contained more cytokines than other single layer products. These results suggest that PURION® Processed dHACM contains substantially more cytokines than single layer amnion products, and therefore dHACM may be more effective at delivering growth factors to a healing wound than amnion alone.

Angiogenic properties of dehydrated human amnion/chorion allografts: therapeutic potential for soft tissue repair and regeneration.

BACKGROUND: Chronic wounds are associated with a number of deficiencies in critical wound healing processes, including growth factor signaling and neovascularization. Human-derived placental tissues are rich in regenerative cytokines and have been shown in randomized clinical trials to be effective for healing chronic wounds. In this study, PURION® Processed (MiMedx Group, Marietta, GA) dehydrated human amnion/chorion membrane tissue allografts (dHACM, EpiFix®, MiMedx) were evaluated for properties to support wound angiogenesis. METHODS: Angiogenic growth factors were identified in dHACM tissues using enzyme-linked immunosorbent assays (ELISAs), and the effects of dHACM extract on human microvascular endothelial cell (HMVEC) proliferation and production of angiogenic growth factors was determined in vitro. Chemotactic migration of human umbilical vein endothelial cells (HUVECs) toward pieces of dHACM tissue was determined using a standard in vitro transwell assay. Neovascularization of dHACM in vivo was determined utilizing a murine subcutaneous implant model. RESULTS: Quantifiable levels of the angiogenic cytokines angiogenin, angiopoietin-2 (ANG-2), epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), heparin binding epidermal growth factor (HB-EGF), hepatocyte growth factor (HGF), platelet derived growth factor BB (PDGF-BB), placental growth factor (PlGF), and vascular endothelial growth factor (VEGF) were measured in dHACM. Soluble cues promoted HMVEC proliferation in vitro and increased endogenous production of over 30 angiogenic factors by HMVECs, including granulocyte macrophage colony-stimulating factor (GM-CSF), angiogenin, transforming growth factor ß3 (TGF-ß3), and HB-EGF. 6.0 mm disks of dHACM tissue were also found to recruit migration of HUVECs in vitro. Moreover, subcutaneous dHACM implants displayed a steady increase in microvessels over a period of 4 weeks, indicative of a dynamic intra-implant neovascular process. CONCLUSIONS: TAKEN TOGETHER, THESE RESULTS DEMONSTRATE THAT DHACM GRAFTS: 1) contain angiogenic growth factors retaining biological activity; 2) promote amplification of angiogenic cues by inducing endothelial cell proliferation and migration and by upregulating production of endogenous angiogenic growth factors by endothelial cells; and 3) support the formation of blood vessels in vivo. dHACM grafts are a promising wound care therapy with the potential to promote revascularization and tissue healing within poorly vascularized, non-healing wounds.

Properties of dehydrated human amnion/chorion composite grafts: Implications for wound repair and soft tissue regeneration.

PURION(®) processed dehydrated human amnion/chorion membrane (dHACM; MiMedx Group, Marietta, GA) tissue products were analyzed for the effectiveness of the PURION(®) process in retaining the native composition of the amniotic membrane and preserving bioactivity in the resulting products. dHACM was analyzed for extracellular matrix (ECM) composition through histological staining and for growth factor content via multiplex ELISA arrays. Bioactivity was assessed by evaluating endogenous growth factor production by human dermal fibroblasts in response to dHACM and for thermal stability by mechanical tests and in vitro cell proliferation assays. Histology of dHACM demonstrated preservation of the native amnion and chorion layers with intact, nonviable cells, collagen, proteoglycan, and elastic fibers distributed in the individual layers. An array of 36 cytokines known to regulate processes involved in inflammation and wound healing were identified in dHACM. When treated with dHACM extracts, bioactivity was demonstrated through an upregulation of basic fibroblast growth factor, granulocyte colony-stimulating factor, and placental growth factor biosynthesis, three growth factors involved in wound healing, by dermal fibroblasts in vitro. After conditioning at temperatures ranging from -78.7 to +73.5°C, dHACM retained its tensile strength and ability to promote proliferation of dermal fibroblasts in vitro. Elution experiments demonstrated a soluble fraction of growth factors that eluted from the tissue and another fraction sequestered within the matrix. The PURION(®) process retains the native composition of ECM and signaling molecules and preserves bioactivity. The array of cytokines preserved in dHACM are in part responsible for its therapeutic efficacy in treating chronic wounds by orchestrating a "symphony of signals" to promote healing.

Biological properties of dehydrated human amnion/chorion composite graft: implications for chronic wound healing.

Human amnion/chorion tissue derived from the placenta is rich in cytokines and growth factors known to promote wound healing; however, preservation of the biological activities of therapeutic allografts during processing remains a challenge. In this study, PURION® (MiMedx, Marietta, GA) processed dehydrated human amnion/chorion tissue allografts (dHACM, EpiFix®, MiMedx) were evaluated for the presence of growth factors, interleukins (ILs) and tissue inhibitors of metalloproteinases (TIMPs). Enzyme-linked immunosorbent assays (ELISA) were performed on samples of dHACM and showed quantifiable levels of the following growth factors: platelet-derived growth factor-AA (PDGF-AA), PDGF-BB, transforming growth factor α (TGFα), TGFß1, basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), placental growth factor (PLGF) and granulocyte colony-stimulating factor (GCSF). The ELISA assays also confirmed the presence of IL-4, 6, 8 and 10, and TIMP 1, 2 and 4. Moreover, the relative elution of growth factors into saline from the allograft ranged from 4% to 62%, indicating that there are bound and unbound fractions of these compounds within the allograft. dHACM retained biological activities that cause human dermal fibroblast proliferation and migration of human mesenchymal stem cells (MSCs) in vitro. An in vivo mouse model showed that dHACM when tested in a skin flap model caused mesenchymal progenitor cell recruitment to the site of implantation. The results from both the in vitro and in vivo experiments clearly established that dHACM contains one or more soluble factors capable of stimulating MSC migration and recruitment. In summary, PURION® processed dHACM retains its biological activities related to wound healing, including the potential to positively affect four distinct and pivotal physiological processes intimately involved in wound healing: cell proliferation, inflammation, metalloproteinase activity and recruitment of progenitor cells. This suggests a paracrine mechanism of action for dHACM when used for wound healing applications.