Expression of human beta-defensins HBD-1, HBD-2, and HBD-3 in cultured keratinocytes and skin substitutes

Polymeric biomaterials for wound healing

Skin indicates a person's state of health and is so important that it influences a person's emotional and psychological behavior. In this context, the effective treatment of wounds is a major concern, since several conventional wound healing materials have not been able to provide adequate healing, often leading to scar formation. Hence, the development of innovative biomaterials for wound healing is essential. Natural and synthetic polymers are used extensively for wound dressings and scaffold production. Both natural and synthetic polymers have beneficial properties and limitations, so they are often used in combination to overcome overcome their individual limitations. The use of different polymers in the production of biomaterials has proven to be a promising alternative for the treatment of wounds, as their capacity to accelerate the healing process has been demonstrated in many studies. Thus, this work focuses on describing several currently commercially available solutions used for the management of skin wounds, such as polymeric biomaterials for skin substitutes. New directions, strategies, and innovative technologies for the design of polymeric biomaterials are also addressed, providing solutions for deep burns, personalized care and faster healing.

Antimicrobial Peptides: Challenging Journey to the Pharmaceutical, Biomedical, and Cosmeceutical Use

Antimicrobial peptides (AMPs), or host defence peptides, are short proteins in various life forms. Here we discuss AMPs, which may become a promising substitute or adjuvant in pharmaceutical, biomedical, and cosmeceutical uses. Their pharmacological potential has been investigated intensively, especially as antibacterial and antifungal drugs and as promising antiviral and anticancer agents. AMPs exhibit many properties, and some of these have attracted the attention of the cosmetic industry. AMPs are being developed as novel antibiotics to combat multidrug-resistant pathogens and as potential treatments for various diseases, including cancer, inflammatory disorders, and viral infections. In biomedicine, AMPs are being developed as wound-healing agents because they promote cell growth and tissue repair. The immunomodulatory effects of AMPs could be helpful in the treatment of autoimmune diseases. In the cosmeceutical industry, AMPs are being investigated as potential ingredients in skincare products due to their antioxidant properties (anti-ageing effects) and antibacterial activity, which allows the killing of bacteria that contribute to acne and other skin conditions. The promising benefits of AMPs make them a thrilling area of research, and studies are underway to overcome obstacles and fully harness their therapeutic potential. This review presents the structure, mechanisms of action, possible applications, production methods, and market for AMPs.

Innate immunity and microbial dysbiosis in hidradenitis suppurativa – vicious cycle of chronic inflammation

Hidradenitis Suppurativa (HS) is a chronic multifactorial inflammatory skin disease with incompletely understood mechanisms of disease pathology. HS is characterized by aberrant activation of the innate immune system, resulting in activation of pathways that aim to protect against pathogenic microorganisms, and also contribute to failure to resolve inflammation. Imbalance in innate immunity is evident in deregulation of host antimicrobial peptides (AMPs) and the complement system associated with the microbiome dysbiosis. The pathology is further complicated by ability of pathogens associated with HS to overcome host immune response. Potential roles of major AMPs, cathelicidin, defensins, dermcidin, S100 proteins, RNAse 7 and complement proteins are discussed. Dysregulated expression pattern of innate immunity components in conjunction with bacterial component of the disease warrants consideration of novel treatment approaches targeting both host immunity and pathogenic microbiome in HS.

Therapeutic strategies for skin regeneration based on biomedical substitutes

Regenerative medicine and tissue engineering (TE) have experienced significant advances in the development of in vitro engineered skin substitutes, either for replacement of lost tissue in skin injuries or for the generation of in vitro human skin models to research. However, currently available skin substitutes present different limitations such as expensive costs, abnormal skin microstructure and engraftment failure. Given these limitations, new technologies, based on advanced therapies and regenerative medicine, have been applied to develop skin substitutes with several pharmaceutical applications that include injectable cell suspensions, cell-spray devices, sheets or 3Dscaffolds for skin tissue regeneration and others. Clinical practice for skin injuries has evolved to incorporate these innovative applications to facilitate wound healing, improve the barrier function of the skin, prevent infections, manage pain and even to ameliorate long-term aesthetic results. In this article, we review current commercially available skin substitutes for clinical use, as well as the latest advances in biomedical and pharmaceutical applications used to design advanced therapies and medical products for wound healing and skin regeneration. We highlight the current progress in clinical trials for wound healing as well as the new technologies that are being developed and hold the potential to generate skin substitutes such as 3D bioprinting-based strategies.

MC1R: Front and Center in the Bright Side of Dark Eumelanin and DNA Repair

Melanin, the pigment produced by specialized cells, melanocytes, is responsible for skin and hair color. Skin pigmentation is an important protective mechanism against the DNA damaging and mutagenic effects of solar ultraviolet radiation (UV). It is acknowledged that exposure to UV is the main etiological environmental factor for all forms of skin cancer, including melanoma. DNA repair capacity is another major factor that determines the risk for skin cancer. Human melanocytes synthesize eumelanin, the dark brown form of melanin, as well as pheomelanin, which is reddish-yellow in color. The relative rates of eumelanin and pheomelanin synthesis by melanocytes determine skin color and the sensitivity of skin to the drastic effects of solar UV. Understanding the complex regulation of melanocyte function and how it responds to solar UV has a huge impact on developing novel photoprotective strategies to prevent skin cancer, particularly melanoma, the most fatal form, which originates from melanocytes. This review provides an overview of the known differences in the photoprotective effects of eumelanin versus pheomelanin, how these two forms of melanin are regulated genetically and biochemically, and their impact on the DNA damaging effects of UV exposure. Additionally, this review briefly discusses the role of paracrine factors, focusing on α-melanocortin (α-melanocyte stimulating hormone; α-MSH), in regulating melanogenesis and the response of melanocytes to UV, and describes a chemoprevention strategy based on targeting the melanocortin 1 receptor (MC1R) by analogs of its physiological agonist α-MSH.

Breaking the frontiers of cosmetology with antimicrobial peptides

Antimicrobial peptides (AMPs) are mostly endogenous, cationic, amphipathic polypeptides, produced by many natural sources. Recently, many biological functions beyond antimicrobial activity have been attributed to AMPs, and some of these have attracted the attention of the cosmetics industry. AMPs have revealed antioxidant, self-renewal and pro-collagen effects, which are desirable in anti-aging cosmetics. Additionally, AMPs may also be customized to act on specific cellular targets. Here, we review the recent literature that highlights the many possibilities presented by AMPs, focusing on the relevance and impact that this potentially novel class of active cosmetic ingredients might have in the near future, creating new market outlooks for the cosmetic industry with these molecules as a viable alternative to conventional cosmetics.

Cell therapy for severe burn wound healing

Cell therapy has emerged as an important component of life-saving procedures in treating burns. Over past decades, advances in stem cells and regenerative medicine have offered exciting opportunities of developing cell-based alternatives and demonstrated the potential and feasibility of various stem cells for burn wound healing. However, there are still scientific and technical issues that should be resolved to facilitate the full potential of the cellular devices. More evidence from large, randomly controlled trials is also needed to understand the clinical impact of cell therapy in burns. This article aims to provide an up-to-date review of the research development and clinical applications of cell therapies in burn wound healing and skin regeneration.

Burn Wound Healing and Tissue Engineering

In 2016 the American Burn Association held a State of the Science conference to help identify burn research priorities for the next decade. The current paper summarizes the work of the sub-committee on Burn Wound Healing and Tissue Engineering. We first present the priorities in wound healing research over the next 10 years. We then summarize the current state of the science related to burn wound healing and tissue engineering including determination of burn depth, limiting burn injury progression, eschar removal, management of microbial contamination and wound infection, measuring wound closure, accelerating wound healing and durable wound closure, and skin substitutes and tissue engineering. Finally, a summary of the round table discussion is presented.

Advances in Skin Regeneration Using Tissue Engineering

Tissue engineered skin substitutes for wound healing have evolved tremendously over the last couple of years. New advances have been made toward developing skin substitutes made up of artificial and natural materials. Engineered skin substitutes are developed from acellular materials or can be synthesized from autologous, allograft, xenogenic, or synthetic sources. Each of these engineered skin substitutes has their advantages and disadvantages. However, to this date, a complete functional skin substitute is not available, and research is continuing to develop a competent full thickness skin substitute product that can vascularize rapidly. There is also a need to redesign the currently available substitutes to make them user friendly, commercially affordable, and viable with longer shelf life. The present review focuses on providing an overview of advances in the field of tissue engineered skin substitute development, the availability of various types, and their application.

Melanocortins and the melanocortin 1 receptor, moving translationally towards melanoma prevention

Beginning in the last decade of the twentieth century, the fields of pigment cell research and melanoma have witnessed major breakthroughs in the understanding of the role of melanocortins in human pigmentation and the DNA damage response of human melanocytes to solar ultraviolet radiation (UV). This began with the cloning of the melanocortin 1 receptor (MC1R) gene from human melanocytes and the demonstration that the encoded receptor is functional. Subsequently, population studies found that the MC1R gene is highly polymorphic, and that some of its variants are associated with red hair phenotype, fair skin and poor tanning ability. Using human melanocytes cultured from donors with different MC1R genotypes revealed that the alleles associated with red hair color encode for a non-functional receptor. Epidemiological studies linked the MC1R red hair color variants to increased melanoma risk. Investigating the impact of different MC1R variants on the response of human melanocytes to UV led to the important discovery that the MC1R signaling activates antioxidant, DNA repair and survival pathways, in addition to stimulation of eumelanin synthesis. These effects of MC1R were absent in melanocytes expressing 2 MC1R red hair color variants that result in loss of function of the receptor. The importance of the MC1R in reducing UV-induced genotoxicity in melanocytes led us to design small peptide analogs of the physiological MC1R agonist α-melanocortin (α-melanocyte stimulating hormone; α-MSH) for the goal of utilizing them for melanoma chemoprevention.

Nonviral human beta defensin-3 expression in a bioengineered human skin tissue: a therapeutic alternative for infected wounds

The innate immune system differentially regulates the expression of host defense peptides to combat infection during wound healing. We enhanced the expression of a host defense peptide, human beta defensin-3 (hBD-3), in keratinocytes to generate a three-dimensional biologic dressing to improve healing of infected wounds. The NIKS human keratinocyte cell line was stably transfected ex vivo with a construct containing an epidermis-specific promoter driving hBD-3 (NIKS(hBD) (-3) ) using nonviral methods. Levels of hBD-3 mRNA and protein in three-dimensional skin tissue produced from NIKS(hBD) (-3) were determined using quantitative polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. Tissue architecture was characterized by hematoxylin and eosin staining and by indirect immunofluorescence using proliferation and keratinocyte differentiation markers. Antimicrobial activity was assessed using an in vitro bacterial growth assay and in vivo using a murine burn infection model. Three-dimensional full thickness skin tissues containing epidermal NIKS(hBD) (-3) or control NIKS possessed histologic features of interfollicular epidermis and exhibited normal tissue growth and differentiation. NIKS(hBD) (-3) tissue contained approximately fivefold more hBD-3 protein than tissue containing unmodified control NIKS. In vitro studies showed that NIKS(hBD) (-3) tissue produced a significant reduction in the growth of Staphylococcus aureus multiple peptide resistance factor (mprF) compared with control tissue. In an in vivo infected murine burn model, NIKS(hBD) (-3) tissue resulted in a 90% reduction in bacterial growth. These results demonstrate that sustained delivery of hBD-3 by a bioengineered skin tissue results in a therapeutically relevant reduction in growth of a S. aureus strain in an animal model of infected third-degree burn wounds.

Understanding the roles of gingival beta-defensins

Gingival epithelium produces β-defensins, small cationic peptides, as part of its contribution to the innate host defense against the bacterial challenge that is constantly present in the oral cavity. Besides their functions in healthy gingival tissues, β-defensins are involved in the initiation and progression, as well as restriction of periodontal tissue destruction, by acting as antimicrobial, chemotactic, and anti-inflammatory agents. In this article, we review the common knowledge about β-defensins, coming from in vivo and in vitro monolayer studies, and present new aspects, based on the experience on three-dimensional organotypic culture models, to the important role of gingival β-defensins in homeostasis of the periodontium.

Novel anti-bacterial activities of β-defensin 1 in human platelets: suppression of pathogen growth and signaling of neutrophil extracellular trap formation

Human β-defensins (hBD) are antimicrobial peptides that curb microbial activity. Although hBD's are primarily expressed by epithelial cells, we show that human platelets express hBD-1 that has both predicted and novel antibacterial activities. We observed that activated platelets surround Staphylococcus aureus (S. aureus), forcing the pathogens into clusters that have a reduced growth rate compared to S. aureus alone. Given the microbicidal activity of β-defensins, we determined whether hBD family members were present in platelets and found mRNA and protein for hBD-1. We also established that hBD-1 protein resided in extragranular cytoplasmic compartments of platelets. Consistent with this localization pattern, agonists that elicit granular secretion by platelets did not readily induce hBD-1 release. Nevertheless, platelets released hBD-1 when they were stimulated by α-toxin, a S. aureus product that permeabilizes target cells. Platelet-derived hBD-1 significantly impaired the growth of clinical strains of S. aureus. hBD-1 also induced robust neutrophil extracellular trap (NET) formation by target polymorphonuclear leukocytes (PMNs), which is a novel antimicrobial function of β-defensins that was not previously identified. Taken together, these data demonstrate that hBD-1 is a previously-unrecognized component of platelets that displays classic antimicrobial activity and, in addition, signals PMNs to extrude DNA lattices that capture and kill bacteria.

Platelets are small cells in the bloodstream whose primary function is to stop bleeding. In addition to their clotting functions, we show that human platelets stall bacterial growth. This inhibitory property of platelets is due to β-defensin 1, a small antimicrobial protein that kills bacteria. β-defensin 1 also induces white blood cells to discharge spider-like webs that trap and kill bacteria. Together, these findings indicate that human platelets use β-defensin 1 to fight off bacterial infection.

Active wound coverings: bioengineered skin and dermal substitutes

Extensive skin loss and chronic wounds present a significant challenge to the clinician. With increased understanding of wound healing, cell biology, and cell culture techniques, various synthetic dressings and bioengineered skin substitutes have been developed. These materials can protect the wound, increase healing, provide overall wound coverage, and improve patient care. The ideal skin substitute may soon become a reality.

Introduction of human β-defensin-3 into cultured human keratinocytes and fibroblasts by infection of a recombinant adenovirus vector

Cultured epidermal autografts and cultured skin substitute are vulnerable to infection. Human beta defensin (HBD)-3 is an antimicrobial peptide that exhibits a wide-spectrum antimicrobial activity against gram-positive/negative bacteria and fungi. This study determined whether normal human keratinocytes (NHKs) and human dermal fibroblasts (HDFs) transfected with the HBD-3 gene secrete HBD-3 peptide with an antimicrobial activity. An adenovirus vector with an HBD-3 cDNA inserted downstream of the CMV promoter (ADhBD3) was created. The HBD-3 gene was introduced into NHKs and HDFs via ADhBD3 infection. HBD-3 gene expression in each type of transfected cells was evaluated by RT-PCR. The presence of HBD-3 peptide in the culture supernatants of each type of transfected cells was evaluated by Western blotting. The antimicrobial activities of the culture supernatants of each type of transfected cells against several bacterial strains were also measured. Both NHKs and HDFs infected with ADhBD3 expressed the HBD-3 gene and secreted HBD-3 peptide into culture supernatants. These supernatants exhibited a strong bacteriocidal activity against a Staphylococcus aureus reference strain and methicillin-resistant S. aureus (MRSA). NHKs and HDFs transfected with the HBD-3 gene secrete HBD-3 peptide with an antimicrobial activity against S. aureus and MRSA.

Use of tissue-engineered skin to study in vitro biofilm development

BACKGROUND

Biofilms are aggregations of microorganisms that have been identified as potential pathogens in the chronicity of nonhealing wounds. OBJECTIVE To develop an in vitro wound model to study biofilms using Graftskin, a tissue-engineered skin equivalent.

MATERIALS AND METHODS

Graftskin constructs were divided into sections, and wounds were created on each section. Bacterial suspensions with a concentration of 10(6) CFU/mL were prepared from cultures of pathogenic isolates of Pseudomonas aeruginosa and Staphylococcus aureus. A 25-microL aliquot of each suspension was deposited in the center of wounds created on the Graftskin. Sections were incubated at various time points, and a biopsy was then taken from the wounded and inoculated area. Sections were visualized with light (hematoxylin and eosin) and epifluorescent microscopy (calcofluor white and ethidium bromide). RESULTS Biofilm was observed on the wound model. Biofilm formation was dependent on time of Graftskin exposure to the bacteria. Biofilm was visualized in the S. aureus group at an earlier time point than in the P. aeruginosa group.

CONCLUSIONS

We demonstrated biofilm formation in vitro using a wound model. This model may provide a basis on which future studies may explore therapeutic modalities to prevent and eradicate pathogenic bacterial biofilm. The authors have indicated no significant interest with commercial supporters.

Phase I/II clinical evaluation of StrataGraft: a consistent, pathogen-free human skin substitute

BACKGROUND

Large wounds often require temporary allograft placement to optimize the wound bed and prevent infection until permanent closure is feasible. We developed and clinically tested a second-generation living human skin substitute (StrataGraft). StrataGraft provides both a dermis and a fully-stratified, biologically-functional epidermis generated from a pathogen-free, long-lived human keratinocyte progenitor cell line, Neonatal Immortalized KeratinocyteS (NIKS).

METHODS

Histology, electron microscopy, quantitative polymerase chain reaction, and bacterial growth in vitro were used to analyze human skin substitutes generated from primary human keratinocytes or NIKS cells. A phase I/II, National Institute of Health-funded, randomized, safety, and dose escalation trial was performed to assess autograft take in 15 patients 2 weeks after coverage with StrataGraft skin substitute or cryopreserved cadaver allograft.

RESULTS

StrataGraft skin substitute exhibited a fully stratified epidermis with multilamellar lipid sheets and barrier function as well as robust human beta defensin-3 mRNA levels. Analysis of the primary endpoint in the clinical study revealed no differences in autograft take between wound sites pretreated with StrataGraft skin substitute or cadaver allograft. No StrataGraft-related adverse events or serious adverse events were observed.

CONCLUSIONS

The major finding of this phase I/II clinical study is that performance of StrataGraft skin substitute was comparable to cadaver allograft for the temporary management of complex skin defects. StrataGraft skin substitute may also eliminate the risk for disease transmission associated with allograft tissue and offer additional protection to the wound bed through inherent antimicrobial properties. StrataGraft is a pathogen-free human skin substitute that is ideal for the management of severe skin wounds before autografting.

Host defense peptides in wound healing

Host defense peptides are effector molecules of the innate immune system. They show broad antimicrobial action against gram-positive and -negative bacteria, and they likely play a key role in activating and mediating the innate as well as adaptive immune response in infection and inflammation. These features make them of high interest for wound healing research. Non-healing and infected wounds are a major problem in patient care and health care spending. Increasing infection rates, growing bacterial resistance to common antibiotics, and the lack of effective therapeutic options for the treatment of problematic wounds emphasize the need for new approaches in therapy and pathophysiologic understanding. This review focuses on the current knowledge of host defense peptides affecting wound healing and infection. We discuss the current data and highlight the potential future developments in this field of research.

Expression of Human Beta Defensin 4 in Genetically Modified Keratinocytes Enhances Antimicrobial Activity

Defensins are cationic peptides of the innate host defense system with antimicrobial activity against many of the microorganisms commonly found in burn units. Beta defensins are variably expressed in the epithelia of skin and other organs. Human beta defensin 4 reportedly has antimicrobial activity against Pseudomonas aeruginosa and is not normally expressed in intact skin. Genetic modification was used to ectopically express human beta defensin 4 in cultured primary epidermal keratinocytes. Keratinocytes expressing human beta defensin 4 showed significantly elevated antimicrobial activity against clinically-isolated P. aeruginosa compared with controls. These results suggest that genetic modification of keratinocytes can increase their resistance to microbial contamination. Bioengineered skin replacements containing human beta defensin 4-modified keratinocytes may be useful for transplantation to contaminated burn wounds.

Antimicrobial barrier of an in vitro oral epithelial model

OBJECTIVE

Oral epithelia function as a microbial barrier and are actively involved in recognizing and responding to bacteria. Our goal was to examine a tissue engineered model of buccal epithelium for its response to oral bacteria and proinflammatory cytokines and compare the tissue responses with those of a submerged monolayer cell culture.

DESIGN

The tissue model was characterized for keratin and beta-defensin expression. Altered expression of beta-defensins was evaluated by RT-PCR after exposure of the apical surface to oral bacteria and after exposure to TNF-alpha in the medium. These were compared to the response in traditional submerged oral epithelial cell culture.

RESULTS

The buccal model showed expression of differentiation specific keratin 13, hBD1 and hBD3 in the upper half of the tissue; hBD2 was not detected. hBD1 mRNA was constitutively expressed, while hBD2 mRNA increased 2-fold after exposure of the apical surface to three oral bacteria tested and hBD3 mRNA increased in response to the non-pathogenic bacteria tested. In contrast, hBD2 mRNA increased 3-600-fold in response to bacteria in submerged cell culture. HBD2 mRNA increased over 100-fold in response to TNF-alpha in the tissue model and 50-fold in submerged cell culture. Thus, the tissue model is capable of upregulating hBD2, however, the minimal response to bacteria suggests that the tissue has an effective antimicrobial barrier due to its morphology, differentiation, and defensin expression.

CONCLUSIONS

The oral mucosal model is differentiated, expresses hBD1 and hBD3, and has an intact surface with a functional antimicrobial barrier.

Microarray analysis of gene expression in cultured skin substitutes compared with native human skin

Cultured skin substitutes (CSS), prepared using keratinocytes, fibroblasts, and biopolymers, can facilitate closure of massive burn wounds by increasing the availability of autologous tissue for grafting. But because they contain only two cell types, skin substitutes cannot replace all of the functions of native human skin. To better understand the physiological and molecular differences between CSS and native skin, we undertook a comprehensive analysis of gene expression in native skin, cultured keratinocytes, cultured fibroblasts, and skin substitutes using Affymetrix gene chip microarrays. Hierarchical tree clustering identified six major clusters of coordinately regulated genes, using a list of 1030 genes that were the most differentially expressed between groups. These clusters correspond to biomarker pools representing expression signatures for native skin, fibroblasts, keratinocytes, and cultured skin. The expression analysis revealed that entire clusters of genes were either up- or downregulated upon combination of fibroblasts and keratinocytes in cultured skin grafts. Further, several categories of genes were overexpressed in CSS compared with native skin, including genes associated with hyperproliferative skin or activated keratinocytes. The observed pattern of expression indicates that CSS in vitro, which display a well-differentiated epidermal layer, exhibit a hyperproliferative phenotype similar to wounded native skin.

Antimicrobial peptides: effectors of innate immunity in the skin

The ability of the cutaneous barrier to help defend the body against pathogens relies on both acquired and innate immune responses. Recently, a large body of research has suggested that a critical component of the innate immune response in the skin is 3 antimicrobial peptides: the cathelicidins, defensins, and dermcidins. These 3 classes of peptides have been shown to act as antimicrobials by directly inhibiting pathogen growth as well as potentiating other branches of the innate, humoral, and cell-mediated immune system. Here, we review the antimicrobial peptides with an emphasis on their role in the cutaneous immune response. We present an overview of defensin, cathelicidin, and dermcidin physiology, elucidating their various functions. In addition, we delve into the role of these peptides in specific dermatologic conditions including wound healing, atopy, and microbial infection. Finally, we discuss the future of antimicrobial peptide research including therapeutic options.