Keratinocyte-derived chemotactic cytokines: expressional modulation by nitric oxide in vitro and during cutaneous wound repair in vivo

Nitric oxide-based treatments improve wound healing associated with diabetes mellitus

Non-healing wounds are long-term complications of diabetes mellitus (DM) that increase mortality risk and amputation-related disability and decrease the quality of life. Nitric oxide (NO·)-based treatments (i.e., use of both systemic and topical NO· donors, NO· precursors, and NO· inducers) have received more attention as complementary approaches in treatments of DM wounds. Here, we aimed to highlight the potential benefits of NO·-based treatments on DM wounds through a literature review of experimental and clinical evidence. Various topical NO·-based treatments have been used. In rodents, topical NO·-based therapy facilitates wound healing, manifested as an increased healing rate and a decreased half-closure time. The wound healing effect of NO·-based treatments is attributed to increasing local blood flow, angiogenesis induction, collagen synthesis and deposition, re-epithelization, anti-inflammatory and anti-oxidative properties, and potent broad-spectrum antibacterial effects. The existing literature lacks human clinical evidence on the safety and efficacy of NO·-based treatments for DM wounds. Translating experimental favors of NO·-based treatments of DM wounds into human clinical practice needs conducting clinical trials with well-predefined effect sizes, i.e., wound reduction area, rate of wound healing, and hospital length of stay.

The Central Roles of Keratinocytes in Coordinating Skin Immunity

The function of keratinocytes (KCs) to form a barrier and produce cytokines is well-known, but recent progress has revealed many different roles for KCs in regulation of skin immunity. In this review, we provide an update on the current understanding of how KCs communicate with microbes, immunocytes, neurons, and other cells to form an effective immune barrier. We catalog the large list of genes and metabolites of KCs that participate in host defense and discuss the mechanisms of immune crosstalk, addressing how KCs simultaneously form a physical barrier, communicate with fibroblasts, and control immune signals. Overall, the signals sent and received by KCs are an exciting group of therapeutic targets to explore in the treatment of dermatologic disorders.

Liquid plasma promotes angiogenesis through upregulation of endothelial nitric oxide synthase-induced extracellular matrix metabolism: potential applications of liquid plasma for vascular injuries

BACKGROUND

Applications of nonthermal plasma have expanded beyond the biomedical field to include antibacterial, anti-inflammatory, wound healing, and tissue regeneration. Plasma enhances epithelial cell repair; however, the potential damage to deep tissues and vascular structures remains under investigation.

RESULT

This study assessed whether liquid plasma (LP) increased nitric oxide (NO) production in human umbilical vein endothelial cells by modulating endothelial NO synthase (eNOS) phosphorylation and potential signaling pathways. First, we developed a liquid plasma product and confirmed the angiogenic effect of LP using the Matrigel plug assay. We found that the NO content increased in plasma-treated water. NO in plasma-treated water promoted cell migration and angiogenesis in scratch and tube formation assays via vascular endothelial growth factor mRNA expression. In addition to endothelial cell proliferation and migration, LP influenced extracellular matrix metabolism and matrix metalloproteinase activity. These effects were abolished by treatment with NG-L-monomethyl arginine, a specific inhibitor of NO synthase. Furthermore, we investigated the signaling pathways mediating the phosphorylation and activation of eNOS in LP-treated cells and the role of LKB1-adenosine monophosphate-activated protein kinase in signaling. Downregulation of adenosine monophosphate-activated protein kinase by siRNA partially inhibited LP-induced eNOS phosphorylation, angiogenesis, and migration.

CONCLUSION

The present study suggests that LP treatment may be a novel strategy for promoting angiogenesis in vascular damage. Video Abstract.

Reprograming the immune niche for skin tissue regeneration - From cellular mechanisms to biomaterials applications

Despite the rapid development of therapeutic approaches for skin repair, chronic wounds such as diabetic foot ulcers remain an unaddressed problem that affects millions of people worldwide. Increasing evidence has revealed the crucial and diverse roles of the immune cells in the development and repair of the skin tissue, prompting new research to focus on further understanding and modulating the local immune niche for comprehensive, 'perfect' regeneration. In this review, we first introduce how different immunocytes and certain stromal cells involved in innate and adaptive immunity coordinate to maintain the immune niche and tissue homeostasis, with emphasis on their specific roles in normal and pathological wound healing. We then discuss novel engineering approaches - particularly biomaterials systems and cellular therapies - to target different players of the immune niche, with three major aims to i) overcome 'under-healing', ii) avoid 'over-healing', and iii) promote functional restoration, including appendage development. Finally, we highlight how these strategies strive to manage chronic wounds and achieve full structural and functional skin recovery by creating desirable 'soil' through modulating the immune microenvironment.

Hyperglycemia acts in synergy with hypoxia to maintain the pro-inflammatory phenotype of macrophages

Diabetic foot ulcers (DFUs) are characterized by a chronic inflammation state which prevents cutaneous wound healing, and DFUs eventually lead to infection and leg amputation. Macrophages located in DFUs are locked in an pro-inflammatory phenotype. In this study, the effect of hyperglycemia and hypoxia on the macrophage phenotype was analyzed. For this purpose, a microarray was performed to study the gene expression profile of macrophages cultivated in a high glucose concentration. Hyperglycemia upregulated the expression of pro-inflammatory cytokines such as TNF-α, IL-1, IL-6, chemokines and downregulated the expression of two receptors involved in phagocytosis (CD 36 and Class B scavenger type I receptors). In addition, eleven anti-apoptotic factors were upregulated whereas three pro-apoptotic genes were downregulated. Subsequently, the contribution of hypoxia and hyperglycemia to chronic inflammation and their potential synergistic effect was evaluated on activated THP-1 derived macrophages. A long term post activation effect (17 hours) was only observed on the upregulation of pro-inflammatory cytokines when hypoxia was combined with a high glucose concentration. In contrast, hyperglycemia and hypoxia did not have any effect on wound healing molecules such as TGF-β1. Taken together, the results show that hyperglycemia acts in synergy with hypoxia to maintain a chronic inflammation state in macrophages.

Increase of cystathionine-γ-lyase (CSE) during late wound repair: Hydrogen sulfide triggers cytokeratin 10 expression in keratinocytes

The gaseous mediators nitric oxide (NO), carbon monoxide (CO) and lately also hydrogen sulfide (H₂S) have been described to contribute to the interplay of protein type- and lipid mediators in the regulation of wound healing. In particular, the recently reported role of H₂S in skin repair remains largely unresolved. Therefore we assessed the expressional kinetics of potential H₂S-producing enzymes during undisturbed skin repair: the cystathionine-γ-lyase (CSE), the cystathionine-β-synthase (CBS) and the 3-mercaptopyruvate sulfurtransferase (MPST). All three enzymes were not transcriptionally induced upon wounding and remained silent through the acute inflammatory and proliferative phase of skin repair. By contrast, CSE expression started to increase significantly at the later stages of healing, when cellular proliferation ceases within the granulation tissue and neoepidermis. The importance of H₂S production in late healing phases was supported by a strong induction of otherwise not-induced CBS to complement the loss of CSE function in CSE-deficient mice. Immunohistochemistry revealed hair follicle keratinocytes and basal keratinocytes of the neo-epidermis covering the wound area as sources of CSE expression. Subsequent in vitro studies implicated a role of CSE-derived H₂S for keratinocyte differentiation: the H₂S-donor GYY4137 markedly increased the Ca²⁺-triggered expression of the early keratinocyte differentiation markers cytokeratin 10 (CK10) and involucrin (IVN) in cultured human keratinocytes. Here, GYY4137-derived H₂S strongly enhanced CK10 expression by increasing the binding of RNA polymerase II to the CK10 promoter.

Comprehensive Transcriptional Profiling of the Gastrointestinal Tract of Ruminants from Birth to Adulthood Reveals Strong Developmental Stage Specific Gene Expression

One of the most significant physiological challenges to neonatal and juvenile ruminants is the development and establishment of the rumen. Using a subset of RNA-Seq data from our high-resolution atlas of gene expression in sheep (Ovis aries) we have provided the first comprehensive characterization of transcription of the entire gastrointestinal (GI) tract during the transition from pre-ruminant to ruminant. The dataset comprises 164 tissue samples from sheep at four different time points (birth, one week, 8 weeks and adult). Using network cluster analysis we illustrate how the complexity of the GI tract is reflected in tissue- and developmental stage-specific differences in gene expression. The most significant transcriptional differences between neonatal and adult sheep were observed in the rumen complex. Comparative analysis of gene expression in three GI tract tissues from age-matched sheep and goats revealed species-specific differences in genes involved in immunity and metabolism. This study improves our understanding of the transcriptomic mechanisms involved in the transition from pre-ruminant to ruminant by identifying key genes involved in immunity, microbe recognition and metabolism. The results form a basis for future studies linking gene expression with microbial colonization of the developing GI tract and provide a foundation to improve ruminant efficiency and productivity through identifying potential targets for novel therapeutics and gene editing.

A heterogeneous Ly-6B2+ leukocyte population consists of yet undescribed iNOS-expressing cell types in murine skin wounds

The gaseous mediator nitric oxide (NO) is a central regulatory molecule during the inflammatory phase of cutaneous tissue repair. The inducible NO-synthase (iNOS) represents the main isoform of the three NO producing enzymes at the wound site. In particular, keratinocytes and macrophages are described as main sources of iNOS-derived NO in skin wounds. Here we provide experimental evidence that Ly-6B2⁺ leukocytes are an additional cellular source of iNOS-derived NO in wounds. As wound iNOS protein expression temporally coincides with both macrophage and neutrophil infiltration, we used immunohistochemistry (IHC) and fluorescence-activated cell sorting (FACS) to address iNOS expression in both macrophages and neutrophil subsets. IHC analyses excluded F4/80⁺ macrophages as iNOS producers, but indicated Ly-6G/C (Gr-1)⁺ neutrophils to express iNOS in wound granulation tissue. A subsequent FACS-based analysis from cellular wound tissue preparations revealed an iNOS-expressing fraction of Ly-6B2-determined leukocytes that consisted of Ly-6G⁺ and Ly-6G^- cells, meaning that mainly mature neutrophils (Ly-6B2⁺/Ly-6G⁺) as well as inflammatory monocytes (Ly-6B2⁺/Ly-6G^-) are dominant iNOS-expressing cell types in the developing granulation tissue of acute wounds.

Influence of diabetes on the foreign body response to nitric oxide-releasing implants

The foreign body response (FBR) to nitric oxide (NO)-releasing subcutaneous implants was compared between healthy and streptozotocin-induced diabetic swine by evaluating inflammation, collagen capsule formation, and angiogenesis. Steel wire substrates were first modified with polyurethane membranes capable of diverse NO-release kinetics (NO fluxes and release durations of 0.8-630.0 pmol cm^-2 s^-1 and 2-13 d, respectively). The NO-releasing materials were implanted in the subcutis for 3, 10, or 25 d for histological and immunohistochemical evaluation of the FBR. A delayed, more severe inflammatory response to control (i.e., non-NO-releasing) implants was observed in diabetic pigs relative to healthy swine. Regardless of the animal disease state, each NO-releasing implant tested elicited reduced inflammation compared to controls at both 3 and 10 d. However, only the NO-release materials capable of releasing low NO fluxes (0.8-3.3 pmol cm^-2 s^-1) for 7-13 d durations mitigated the inflammatory response at 25 d. Using immunohistochemical staining for the endothelial cell surface marker CD-31, we also observed poor blood vessel development at non-NO-releasing implants in diabetic swine. Relative to controls, NO-releasing implants with the longest NO-release duration (13 d) increased blood vessel densities by 47.1 and 70.4% in the healthy and diabetic pigs, respectively. In the healthy model, tissues surrounding the long NO-release materials contained sparse amounts of collagen, whereas implants with shorter NO-release durations (2, 3, and 7 d) were characterized with a dense collagen encapsulation layer, similar to controls. Collagen deposition in diabetic swine was inhibited, and unaffected by NO. These results emphasize several key differences in the FBR in the setting of acute onset diabetes. The observation that NO release counteracts the more severe FBR in diabetic swine while simultaneously promoting tissue integration may help guide the design of medical implants (e.g., glucose sensors) with improved performance for diabetes management.

Pro-Inflammatory Chemokines and Cytokines Dominate the Blister Fluid Molecular Signature in Patients with Epidermolysis Bullosa and Affect Leukocyte and Stem Cell Migration

Hereditary epidermolysis bullosa (EB) is associated with skin blistering and the development of chronic nonhealing wounds. Although clinical studies have shown that cell-based therapies improve wound healing, the recruitment of therapeutic cells to blistering skin and to more advanced skin lesions remains a challenge. Here, we analyzed cytokines and chemokines in blister fluids of patients affected by dystrophic, junctional, and simplex EB. Our analysis revealed high levels of CXCR1, CXCR2, CCR2, and CCR4 ligands, particularly dominant in dystrophic and junctional EB. In vitro migration assays demonstrated the preferential recruitment of CCR4⁺ lymphocytes and CXCR1⁺, CXCR2⁺, and CCR2⁺ myeloid cells toward EB-derived blister fluids. Immunophenotyping of skin-infiltrating leukocytes confirmed substantial infiltration of EB-affected skin with resting (CD45RA⁺) and activated (CD45RO⁺) T cells and CXCR2⁺ CD11b⁺ cells, many of which were identified as CD16b⁺ neutrophils. Our studies also showed that abundance of CXCR2 ligand in blister fluids also creates a favorable milieu for the recruitment of the CXCR2⁺ stem cells, as validated by in vitro and in-matrix migration assays. Collectively, this study identified several chemotactic pathways that control the recruitment of leukocytes to the EB-associated skin lesions. These chemotactic axes could be explored for the refinement of the cutaneous homing of the therapeutic stem cells.

Deletion of the Chemokine Binding Protein Gene from the Parapoxvirus Orf Virus Reduces Virulence and Pathogenesis in Sheep

Orf virus (ORFV) is the type species of the Parapoxvirus genus of the family Poxviridae and infects sheep and goats, often around the mouth, resulting in acute pustular skin lesions. ORFV encodes several secreted immunomodulators including a broad-spectrum chemokine binding protein (CBP). Chemokines are a large family of secreted chemotactic proteins that activate and regulate inflammation induced leukocyte recruitment to sites of infection. In this study we investigated the role of CBP in vivo in the context of ORFV infection of sheep. The CBP gene was deleted from ORFV strain NZ7 and infections of sheep used to investigate the effect of CBP on pathogenesis. Animals were either infected with the wild type (wt) virus, CBP-knockout virus or revertant strains. Sheep were infected by scarification on the wool-less area of the hind legs at various doses of virus. The deletion of the CBP gene severely attenuated the virus, as only few papules formed when animals were infected with the CBP-knock-out virus at the highest dose (10⁷ p.f.u). In contrast, large pustular lesions formed on almost all animals infected with the wt and revertant strains at 10⁷ p.f.u. The lesions for the CBP-knock-out virus resolved approximately 5–6 days p.i, at a dose of 10⁷ pfu whereas in animals infected with the wt and revertants at this dose, lesions began to resolve at approximately 10 days p.i. Few pustules developed at the lowest dose of 10³ p.f.u. for all viruses. Immunohistochemistry of biopsy skin-tissue from pustules showed that the CBP-knockout virus replicated in all animals at the highest dose and was localized to the skin epithelium while haematoxylin and eosin staining showed histological features of the CBP-knockout virus typical of the parent virus with acanthosis, elongated rete ridges and orthokeratotic hyperkeratosis. MHC-II immunohistochemistry analysis for monocytes and dendritic cells showed greater staining within the papillary dermis of the CBP-knock-out virus compared with the revertant viruses, however this was not the case with the wt where staining was similar. Our results show that the CBP gene encodes a secreted immunodulator that has a critical role in virulence and pathogenesis.

Molecular genetic analysis of orf virus: a poxvirus that has adapted to skin

Orf virus is the type species of the Parapoxvirus genus of the family Poxviridae. It induces acute pustular skin lesions in sheep and goats and is transmissible to humans. The genome is G+C rich, 138 kbp and encodes 132 genes. It shares many essential genes with vaccinia virus that are required for survival but encodes a number of unique factors that allow it to replicate in the highly specific immune environment of skin. Phylogenetic analysis suggests that both viral interleukin-10 and vascular endothelial growth factor genes have been "captured" from their host during the evolution of the parapoxviruses. Genes such as a chemokine binding protein and a protein that binds granulocyte-macrophage colony-stimulating factor and interleukin-2 appear to have evolved from a common poxvirus ancestral gene while three parapoxvirus nuclear factor (NF)-κB signalling pathway inhibitors have no homology to other known NF-κB inhibitors. A homologue of an anaphase-promoting complex subunit that is believed to manipulate the cell cycle and enhance viral DNA synthesis appears to be a specific adaptation for viral-replication in keratinocytes. The review focuses on the unique genes of orf virus, discusses their evolutionary origins and their role in allowing viral-replication in the skin epidermis.

Hyperbaric oxygen, vasculogenic stem cells, and wound healing

SIGNIFICANCE

Oxidative stress is recognized as playing a role in stem cell mobilization from peripheral sites and also cell function.

RECENT ADVANCES

This review focuses on the impact of hyperoxia on vasculogenic stem cells and elements of wound healing.

CRITICAL ISSUES

Components of the wound-healing process in which oxidative stress has a positive impact on the various cells involved in wound healing are highlighted. A slightly different view of wound-healing physiology is adopted by departing from the often used notion of sequential stages: hemostatic, inflammatory, proliferative, and remodeling and instead organizes the cascade of wound healing as overlapping events or waves pertaining to reactive oxygen species, lactate, and nitric oxide. This was done because hyperoxia has effects of a number of cell signaling events that converge to influence cell recruitment/chemotaxis and gene regulation/protein synthesis responses which mediate wound healing.

FUTURE DIRECTIONS

Our alternative perspective of the stages of wound healing eases recognition of the multiple sites where oxidative stress has an impact on wound healing. This aids the focus on mechanistic events and the interplay among various cell types and biochemical processes. It also highlights the areas where additional research is needed.

Chemokines and Their Receptors Are Key Players in the Orchestra That Regulates Wound Healing

SIGNIFICANCE

Normal wound healing progresses through a series of overlapping phases, all of which are coordinated and regulated by a variety of molecules, including chemokines. Because these regulatory molecules play roles during the various stages of healing, alterations in their presence or function can lead to dysregulation of the wound-healing process, potentially leading to the development of chronic, nonhealing wounds.

RECENT ADVANCES

A discovery that chemokines participate in a variety of disease conditions has propelled the study of these proteins to a level that potentially could lead to new avenues to treat disease. Their small size, exposed termini, and the fact that their only modifications are two disulfide bonds make them excellent targets for manipulation. In addition, because they bind to G-protein-coupled receptors (GPCRs), they are highly amenable to pharmacological modulation.

CRITICAL ISSUES

Chemokines are multifunctional, and in many situations, their functions are highly dependent on the microenvironment. Moreover, each specific chemokine can bind to several GPCRs to stimulate the function, and both can function as monomers, homodimers, heterodimers, and even oligomers. Activation of one receptor by any single chemokine can lead to desensitization of other chemokine receptors, or even other GPCRs in the same cell, with implications for how these proteins or their receptors could be used to manipulate function.

FUTURE DIRECTIONS

Investment in better understanding of the functions of chemokines and their receptors in a local context can reveal new ways for therapeutic intervention. Understanding how different chemokines can activate the same receptor and vice versa could identify new possibilities for drug development based on their heterotypic interactions.

Impaired wound repair in adult endoglin heterozygous mice associated with lower NO bioavailability

Endoglin (Eng) is a transmembrane glycoprotein that is mainly expressed in endothelial cells, but it is also present in the epidermis and skin appendages. To address the role of Eng in cutaneous wound healing, we compared the kinetics of reepithelialization in Eng heterozygous null (Eng(+/-)) mice and their normal littermates (Eng(+/+)) following skin wounds. The wound area was significantly larger in Eng(+/-) than in Eng(+/+) mice from 2 to 8 days after injury; overall wound closure was delayed by 1 to 2 days. In Eng(+/-) mice, keratinocytes at the wound edges exhibited impaired proliferation but were more migratory, as shown by their elongated morphology and increased keratin 17 expression. Inhibition of nitric oxide (NO) synthesis delayed healing in Eng(+/+) but not in Eng(+/-) mice. Administration of the NO donor LA-803 accelerated wound closure in Eng(+/-) mice, with no effect on normal littermates. The acute stimulation with 12-O-tetradecanoylphorbol-13-acetate (TPA) enhanced Eng expression in mouse epidermal keratinocytes in vivo and in vitro associated with hyperproliferation. Similarly, the skin of Eng(+/-) mice failed to mount a hyperplastic response to acute stimulation with TPA. These results demonstrate an important involvement of Eng in wound healing that is associated with NO bioavailability.

Anti-oxidant, anti-inflammatory and immunomodulating properties of an enzymatic protein hydrolysate from yellow field pea seeds

PURPOSE

Enzymatic protein hydrolysates of yellow pea seed have been shown to possess high anti-oxidant and anti-bacterial activities. The aim of this work was to confirm the anti-oxidant, anti-inflammatory and immunomodulating activities of an enzymatic protein hydrolysate of yellow field pea seeds.

METHODS

The anti-oxidant and anti-inflammatory properties of peptides from yellow field pea proteins (Pisum sativum L.) were investigated in LPS/IFN-γ-activated RAW 264.7 NO⁻ macrophages. The immunomodulating potential of pea protein hydrolysate (PPH) was then studied in a murine model.

RESULTS

Pea protein hydrolysate, after a 12 h pre-treatment, showed significant inhibition of NO production by activated macrophages up to 20%. Moreover, PPH significantly inhibited their secretion of pro-inflammatory cytokines, TNF-α- and IL-6, up to 35 and 80%, respectively. Oral administration of PPH in mice enhanced the phagocytic activity of their peritoneal macrophages and stimulated the gut mucosa immune response. The number of IgA+ cells was elevated in the small intestine lamina propria, accompanied by an increase in the number of IL-4+, IL-10+ and IFN-γ+ cells. This was correlated to up-regulation of IL-6 secretion by small intestine epithelial cells (IEC), probably responsible for B-cell terminal differentiation to IgA-secreting cells. Moreover, PPH might have increased IL-6 production in IECs via the stimulation of toll-like receptors (TLRs) family, especially TLR2 and TLR4 since either anti-TLR2 or anti-TLR4 was able to completely abolish PPH-induced IL-6 secretion.

CONCLUSIONS

Enzymatic protein degradation confers anti-oxidant, anti-inflammatory and immunomodulating potentials to pea proteins, and the resulted peptides could be used as an alternative therapy for the prevention of inflammatory-related diseases.

Effects of Antioxidant and Nitric Oxide on Chemokine Production in TNF-α-stimulated Human Dermal Microvascular Endothelial Cells

Chemokines have been implicated convincingly in the driving of leukocyte emigration in different inflammatory reactions. Multiple signaling mechanisms are reported to be involved in intracellular activation of chemokine expression in vascular endothelial cells by various stimuli. Nevertheless, redox-regulated mechanisms of chemokine expression in human dermal microvascular endothelial cells (HDMEC) remain unclear. This study examined the effects of pyrrolidine dithiocarbamate (PDTC, 0.1 mM) and spermine NONOate (Sper-NO, 1 mM) on the secretion and gene expression of chemokines, interleukin (IL)-8, monocyte chemotactic protein (MCP)-1, regulated upon activation normal T cell expressed and secreted (RANTES), and eotaxin. This study also addresses PDTC and Sper-NO effects on activation of nuclear factor kappa B (NF-kappaB) induced by TNF-alpha (10 ng/ml). Treatment with TNF-alpha for 8 h significantly increased secretion of IL-8, MCP-1, and RANTES, but not of eotaxin, in cultured HDMEC. Up-regulation of these chemokines was suppressed significantly by pretreatment with PDTC or Sper-NO for 1 h, but not by 1 mM 8-bromo-cyclic GMP. The mRNA accumulation of IL-8, MCP-1, RANTES, and eotaxin, and activation of NF-kappaB were induced by TNF-alpha for 2 h; all were suppressed significantly by the above two pretreatments. These findings indicate that both secretion and mRNA accumulation of IL-8, MCP-1, and RANTES in HDMEC induced by TNF-alpha are inhibited significantly by pretreatment with PDTC or Sper-NO, possibly via blocking redox-regulated NF-kappaB activation. These results suggest that restoration of the redox balance using antioxidant agents or nitric oxide pathway modulators may offer new opportunities for therapeutic interventions in inflammatory skin diseases.

Orf virus-encoded chemokine-binding protein is a potent inhibitor of inflammatory monocyte recruitment in a mouse skin model

The parapoxvirus orf virus causes pustular dermatitis in sheep and is transmissible to humans. The virus encodes a secreted chemokine-binding protein (CBP). We examined the ability of this protein to inhibit migration of murine monocytes in response to CC inflammatory chemokines, using chemotaxis assays, and its effects on monocyte recruitment into the skin, using a mouse model in which inflammation was induced with bacterial lipopolysaccharide. CBP was shown to bind murine chemokines CCL2, CCL3 and CCL5 with high affinity by surface plasmon resonance and it completely inhibited chemokine-induced migration of monocytes at a CBP:chemokine molar ratio of 4:1. In the mouse, low levels of CBP potently inhibited the recruitment of Gr-1+/CD11b+ monocytes to the site of inflammation in the skin but had little effect on neutrophil recruitment, suggesting that this factor plays a role in disrupting chemokine-induced recruitment of specific immune cell types to infection sites.

Redox signals in wound healing

Physical trauma represents one of the most primitive challenges that threatened survival. Healing a problem wound requires a multi-faceted comprehensive approach. First and foremost, the wound environment will have to be made receptive to therapies. Second, the appropriate therapeutic regimen needs to be identified and provided while managing systemic limitations that could secondarily limit the healing response. Unfortunately, most current solutions seem to aim at designing therapeutic regimen with little or no consideration of the specific details of the wound environment and systemic limitations. One factor that is centrally important in making the wound environment receptive is correction of wound hypoxia. Recent work have identified that oxygen is not only required to disinfect wounds and fuel healing but that oxygen-dependent redox-sensitive signaling processes represent an integral component of the healing cascade. Over a decade ago, it was proposed that in biological systems oxidants are not necessarily always the triggers for oxidative damage and that oxidants such as H2O2 could actually serve as signaling messengers and drive several aspects of cellular signaling. Today, that concept is much more developed and mature. Evidence supporting the role of oxidants such as H2O2 as signaling messenger is compelling. A complete understanding of the continuum between the classical and emergent roles of oxygen requires a thorough consideration of current concepts in redox biology. The objective of this review is to describe our current understanding of how redox-sensitive processes may drive dermal tissue repair.

Skin wound healing in the SKH-1 female mouse following inducible nitric oxide synthase inhibition

BACKGROUND

The inducible isoform of the nitric oxide (NO) synthase (NOS) enzyme (iNOS) is upregulated by inflammatory mediators and/or other pathological stresses, generating high, sustained levels of NO. Cumulative data suggest a role for NO in the regulation of skin wound healing, although it is not clear to what extent NO generated by iNOS, and possibly endothelial NOS (eNOS), contribute to that healing process. Because of the current lack of understanding regarding the contribution of iNOS in wound healing, as well as the lack of wound healing data available for SC-842, an iNOS inhibitor, this in vivo study was conducted to investigate the possible role of SC-842 in interfering with wound healing.

OBJECTIVES

This study evaluated whether inhibition of iNOS affects incisional skin wound healing.

METHODS

Using a cutaneous full-thickness, sutured, incisional wound model in hairless SKH-1 mice, the role of iNOS in the wound healing process was evaluated by comparing in vivo effects of the iNOS inhibitor, SC-842, at various doses that result in selective inhibition of iNOS as well as nonselective NOS inhibition (as evidenced by elevated blood pressure resulting in inhibition of eNOS and/or neuronal NOS). Dexamethasone was used as a positive control.

RESULTS

There were no differences in wound healing at day 28 postwounding, as evaluated by tensile strength and histology, between SC-842- and vehicle-treated animals. A decrease in tensile strength was noted at day 14 postwounding in wounds from the mid- and high-dose-treated animals as compared with vehicle-treated animals, but this difference was slight and was not associated with histological differences from vehicle-treated controls.

CONCLUSIONS

These data indicate that iNOS inhibition does not adversely affect the healing of incisional wounds in SKH-1 mice as assessed over 28 days by wound tensile strength and histology.

Cytokine and chemokine release upon prolonged mechanical loading of the epidermis

At this moment, pressure ulcer risk assessment is dominated by subjective measures and does not predict pressure ulcer development satisfactorily. Objective measures are, therefore, needed for an early detection of these ulcers. The current in vitro study evaluates cytokines and chemokines [interleukin 1alpha (IL-1alpha), interleukin 1 receptor antagonist (IL-1RA), tumor necrosis factor alpha (TNF-alpha) and interleukin 8 (CXCL8/IL-8)] as early markers for mechanically-induced epidermal damage. Various degrees of epidermal damage were induced by subjecting commercially available epidermal equivalents (EpiDerm) to increasing pressures (0, 50, 75, 100, 150, and 200 mmHg) for 24 h, using a loading device. At the end of the loading experiment, tissue damage was assessed by histological examination and by evaluation of the cell membrane integrity. Cytokines and chemokines were determined in the culture supernatant. Sustained epidermal loading resulted in an increased release of IL-1alpha, IL-1RA, TNF-alpha and CXCL8/IL-8. This was first observed at 75 mmHg, when the tissue was only slightly damaged. Swollen cells, vacuoles, necrosis and affected cell membranes were observed at pressures higher than 75 mmHg. Furthermore, at 150 and 200 mmHg, the cells in the lower part of the epidermis were severely compressed. In conclusion, IL-1alpha, IL-1RA, TNF-alpha and CXCL8/IL-8 are released in vitro as a result of sustained mechanical loading of the epidermis. The first increase in cytokines and chemokines was observed when the epidermal tissue was only slightly damaged. Therefore, these cytokines and chemokines are potential markers for the objective, early detection of mechanically-induced skin damage, such as pressure ulcers.

Biological fate and clinical implications of arginine metabolism in tissue healing

Since its discovery in 1987, many biological roles (including wound healing) have been identified for nitric oxide (NO). The gas is produced by NO synthase using the dibasic amino acid L-arginine as a substrate. It has been established that a lack of dietary L-arginine delays experimental wound healing. Arginine can also be metabolized to urea and ornithine by arginase-1, a pathway that generates L-proline, a substrate for collagen synthesis, and polyamines, which stimulate cellular proliferation. Herein, we review subjects of interest in arginine metabolism, with emphasis on the biochemistry of wound NO production, relative NO synthase isoform activity in healing wounds, cellular contributions to NO production, and NO effects and mechanisms of action in wound healing.

The Basic Science of Wound Healing

Understanding wound healing today involves much more than simply stating that there are three phases: "inflammation, proliferation, and maturation." Wound healing is a complex series of reactions and interactions among cells and "mediators." Each year, new mediators are discovered and our understanding of inflammatory mediators and cellular interactions grows. This article will attempt to provide a concise report of the current literature on wound healing by first reviewing the phases of wound healing followed by "the players" of wound healing: inflammatory mediators (cytokines, growth factors, proteases, eicosanoids, kinins, and more), nitric oxide, and the cellular elements. The discussion will end with a pictorial essay summarizing the wound-healing process.

p68 DEAD Box RNA Helicase Expression in Keratinocytes

Nitric oxide (NO) represents a short lived mediator that pivotally drives keratinocyte movements during cutaneous wound healing. In this study, we have identified p68 DEAD box RNA helicase (p68) from an NO-induced differential keratinocyte cDNA library. Subsequently, we have analyzed regulation of p68 by wound-associated mediators in human and murine keratinocytes. NO, serum, growth factors, and pro-inflammatory cytokines were potent inducers of p68 expression in the cells. p68 was constitutively expressed in the epithelial compartment of murine skin. Upon injury, we found a transient down-regulation of overall p68 protein in wound tissue. However, p68 did not completely disappear during early wound repair, as we found an expression of p68 protein in isolated wound margin tissue 24 h after wounding. Moreover, immunohistochemistry and cell fractionation analysis revealed a restricted localization of p68 in keratinocyte nuclei of the developing epithelium. Accordingly, cultured keratinocytes also showed a nuclear localization of the helicase. Moreover, confocal microscopy revealed a strong localization of p68 protein within the nucleoli of the cells. Functional analyses demonstrated that p68 strongly participated in keratinocyte proliferation and gene expression. Keratinocytes that constitutively overexpressed p68 protein were characterized by a marked increase in serum-induced proliferation and vascular endothelial growth factor expression, whereas down-regulation of endogenous p68 using small interfering RNA markedly attenuated serum-induced proliferation and vascular endothelial growth factor expression. Altogether, our results suggest a tightly controlled expression and nucleolar localization of p68 in keratinocytes in vitro and during skin repair in vivo that functionally contributes to keratinocyte proliferation and gene expression.

Nitric oxide promotes mitogen-induced dna synthesis in human dermal fibroblasts through cGMP

1. Nitric oxide (NO) is a free radical with multiple functions in cellular pathophysiology. Nitric oxide has been proven to play an important role in wound healing; however, the mechanisms by which NO may promote wound healing are not clearly understood. We have investigated the effect of NO on growth factor-induced DNA synthesis in human dermal fibroblasts to suggest interactions between growth factors and NO as a possible mechanism for the role of NO in wound healing. 2. The NO donor sodium nitroprusside (SNP) significantly (P < 0.001) increased fetal bovine serum-induced thymidine incorporation into the DNA of human dermal fibroblasts. The maximal comitogenic concentration of SNP (100 micro mol/L) was also found to significantly (twofold; P < 0.01) enhance fibroblast growth factor- or platelet-derived growth factor-induced DNA synthesis. 3. Nitric oxide treatment significantly increased the production of cGMP. 8-Bromo-cGMP, a stable structural analogue of cGMP, was found to markedly potentiate (P < 0.001) the growth factor-induced DNA synthesis. 4. This study concludes that NO and cGMP promote growth factor-induced DNA synthesis in dermal fibroblasts, suggesting another possible mechanism by which NO may promote skin wound healing.

Inhibition of nuclear factor kappa B activation and inducible nitric oxide synthase transcription by prolonged exposure to high glucose in the human keratinocyte cell line HaCaT

BACKGROUND

In human skin, inducible nitric oxide synthase (iNOS) appears to be a key enzyme during wound healing and has roles in protection from infection. We speculated that diabetic skin complications such as delayed wound healing and skin infection were due to iNOS activity altered by high glucose in skin keratinocytes.

OBJECTIVES

The purpose of this study was to see how high levels of glucose affect iNOS activity in the human keratinocyte cell line (HaCaT).

METHODS

HaCaT cells were exposed to high glucose for 1 day or 10 days. We measured nitric oxide (NO) end product nitrite in the culture medium using the Griess reagent, and intracellular tetrahydrobiopterin (BH(4), a cofactor of NOS) content by using high-performance liquid chromatography, analysed the expression level of iNOS mRNA by the reverse transcriptase-polymerase chain reaction method and evaluated the DNA binding activity of nuclear factor kappa B (NF-kappaB) by enzyme-immunoassay.

RESULTS

Short-term exposure (1 day) to a high level of glucose increased BH(4) and iNOS activity at the post-translational level. However, long-term exposure (10 days) to high glucose downregulates NF-kappaB binding activity and inhibits iNOS transcription and its activity.

CONCLUSIONS

Pretreatment with high glucose for 10 days down-regulated NF-kappaB activity and inhibited iNOS transcription and NO production, implying the involvement of a deficiency in NO synthesis in both skin infection and impaired wound healing in diabetic patients.

Nitric oxide and wound healing

Nitric oxide is a short-lived free radical that acts at the molecular, cellular, and physiologic level. Since its discovery almost 20 years ago it has proven itself as an important element in wound healing. This review highlights many of the important aspects of nitric oxide in wound healing, including a review of the basic biology of nitric oxide, its role as part of the cytokine cascade and as a promoter of angiogenesis, as well as its more recently elucidated role in apoptosis.

Nitric oxide and wound repair

NO produced by both iNOS and eNOS plays many important roles in wound healing, from the inflammatory phase through to scar remodeling. NO has cytostatic, chemotactic, and vasodilatory effects during early wound repair, regulates proliferation and differentiation of several cell types, modulates collagen deposition and angiogenesis, and affects wound contraction. The data accumulated thus far indicates that the timing, level, and site of NO production are highly coordinated in normal wound repair. Defining states resulting from either inadequate substrate or depressed enzyme expression appear to contribute to impaired wound repair; however, NO represents only one factor in the complex process of wound healing. Approaches to improve NO availability may be of therapeutic value.

Effects of high glucose on NO synthesis in human keratinocyte cell line (HaCaT)

BACKGROUND

There is a possibility that alteration of nitric oxide (NO) synthesis by high glucose leads to a variety of diabetic complications.

OBJECTIVE

In this study, we examined whether NO synthesis is altered by high glucose in spontaneously immortalized human keratinocyte cell line (HaCaT) that have three isoforms of NO synthases (NOS).

METHODS

We measured NO end product nitrite in the culture medium using the Griess reagent and analyzed mRNA expression of three isoforms of NOS in HaCaT cells by RT-PCR.

RESULTS

High glucose enhanced constitutively produced NO production in HaCaT cells, which persisted for 10 days and was attenuated by an inhibitor of protein kinase C (PKC), without altering eNOS/nNOS mRNA levels. Cytokine stimulation induced iNOS mRNA in HaCaT cells. Pretreatment with high glucose for 24 h enhanced cytokine-induced NO production in HaCaT cells. However, when these cells were exposed to high glucose for 10 days, cytokine treatment did not induce iNOS mRNA and nitrite production.

CONCLUSION

These diverse alterations in NO production by high glucose may be involved in impaired host-defense and wound healing in the skin of diabetic patients.

Nitric oxide donors suppress chemokine production by keratinocytes in vitro and in vivo

Nitric oxide (NO) is involved in the modulation of inflammatory responses. In psoriatic skin, NO is highly produced by epidermal keratinocytes in response to interferon-gamma and tumor necrosis factor-alpha. In this study, we investigated whether the NO donors, S-nitrosoglutathione (GS-NO) and NOR-1, could regulate chemokine production by human keratinocytes activated with interferon-gamma and tumor necrosis factor-alpha. In addition, we studied the effects of the topical application of a GS-NO ointment on chemokine expression in lesional psoriatic skin. NO donors diminished in a dose-dependent manner and at both mRNA and protein levels the IP-10, RANTES, and MCP-1 expression in keratinocytes cultured from healthy patients and psoriatic patients. In contrast, constitutive and induced interleukin-8 production was unchanged. GS-NO-treated psoriatic skin showed reduction of IP-10, RANTES, and MCP-1, but not interleukin-8 expression by keratinocytes. Moreover, the number of CD14(+) and CD3(+) cells infiltrating the epidermis and papillary dermis diminished significantly. NO donors also down-regulated ICAM-1 protein expression without affecting mRNA accumulation in vitro, and suppressed keratinocyte ICAM-1 in vivo. Finally, NO donors inhibited nuclear factor-kappa B and STAT-1, but not AP-1 activities in transiently transfected keratinocytes. These results define NO donors as negative regulators of chemokine production by keratinocytes.

Effects of nitric oxide releasing poly(vinyl alcohol) hydrogel dressings on dermal wound healing in diabetic mice

Healing of chronic wounds such as diabetic foot ulcers is a significant clinical problem. Methods of accelerating healing in these difficult lower extremity sites include use of growth factor-loaded gels, hyperbaric oxygen, grafts, and artificial skin replacements. Nitric oxide (NO) has been proposed as a possible active agent for enhancing wound healing. This study examines the in vitro and in vivo responses to a novel hydrogel that produces therapeutic levels of NO. A hydrogel wound dressing was fabricated using ultraviolet light-initiated polymerization from poly(vinyl alcohol) with a NO donor covalently coupled to the polymer backbone. NO release from the NO-modified hydrogel was shown to occur over a time period of up to 48 hours, and there was no associated decrease in fibroblast growth or viability in vitro associated with NO hydrogels. Fibroblasts in culture with NO hydrogels had an increased production of extracellular matrix compared with cells cultured without the NO hydrogels. Preliminary animal studies in a diabetic mouse, impaired wound healing model were conducted comparing low (0.5 mM) and high (5 mM) doses of NO. Time to complete closure was similar in control wounds and NO-treated wounds; however, at 8 days control wounds were significantly smaller than NO-treated wounds. By days 10 to 13 this delay was no longer apparent. Granulation tissue thickness within the wounds at days 8 and 15 and scar tissue thickness after wound closure were increased in animals exposed to higher dose NO hydrogels. The results of this study suggest that exogenous NO released from a hydrogel wound dressing has potential to modulate wound healing.

Nitric oxide and wound repair: role of cytokines?

Wound healing involves platelets, inflammatory cells, fibroblasts, and epithelial cells. All of these cell types are capable of producing nitric oxide (NO), either constitutively or in response to inflammatory cytokines, through the activity of nitric oxide synthases (NOSs): eNOS (NOS3; endothelial NOS) and iNOS (NOS2; inducible NOS), respectively. Indeed, pharmacological inhibition or gene deletion of these enzymes impairs wound healing. The wound healing mechanisms that are triggered by NO appear to be diverse, involving inflammation, angiogenesis, and cell proliferation. All of these processes are controlled by defined cytokine cascades; in many cases, NO appears to modulate these cytokines. In this review, we summarize the history and present state of research on the role of NO in wound healing within the framework of modulation of cytokines.

Regulation of eNOS in normal and diabetes-impaired skin repair: implications for tissue regeneration

An important role of inducible nitric oxide (NO) synthase for epithelial action during skin repair has been well established. Although a delayed healing of skin wounds has been recently described for eNOS-deficient mice, a participation of endothelial-type NO synthase (eNOS) in skin repair largely remains unclear. In this study we determined the expression pattern of eNOS during wound healing in healthy and in diabetic mice. Remarkably, normal repair in healthy animals was characterized by a moderate induction of eNOS at the mRNA and protein level, whereas diabetes-impaired healing was associated with a clearly reduced eNOS protein expression. Immunohistochemistry revealed the endothelial lining of blood vessels within the granulation tissue, and also keratinocytes of the wound margins, the developing neo-epithelium, and the hair follicles to express eNOS protein. Keratinocyte-derived expression of eNOS could be confirmed at the mRNA level in vitro for human primary keratinocytes and the keratinocyte cell line HaCaT. Furthermore, eNOS enzymatic activity most likely contributes to epithelial regeneration, as eNOS-deficient (eNOS -/-) animals exhibited reduced wound margin epithelia associated with reduced keratinocyte proliferation.

Nitric oxide drives skin repair: novel functions of an established mediator

Wound healing of the skin represents a highly ordered process of important tissue movements that aims for a rapid closure of the wound site and a subsequent regeneration of the injured tissue. The factors ensuring the intercellular communication during repair are only known in part. However, although protein-type mediators are well-established players in this process, it has become evident that the diffusible, gaseous molecule nitric oxide (NO) participates in the orchestration of wound healing. The role of wound-derived NO that critically influences macrophage, fibroblast, and keratinocyte behaviour within the intercellular communication network during repair is subject of this review. Thus, cutaneous wound healing prototypically reflects processes that generally occur also in kidney injury and regeneration.

Cell-density-regulated chemotactic responsiveness of keratinocytes in vitro

Keratinocytes represent the main constituents of the epidermis and have been found to play a regulatory role in a variety of inflammatory skin diseases. The functional activity of keratinocytes is highly heterogeneous, and depends on the cell localization in the epidermal architecture, and the maturation or differentiation state of the cells. Spontaneously proliferating HaCaT cells, showing several similarities to basal epidermal keratinocytes, were found to respond to external chemoattractants, including the chemokines RANTES (regulated on activation normal T cell expressed and secreted) and interleukin-8 and the mu-opioid agonist DAMGO ([d-ala2, N-Me-Phe4, Gly-ol5]enkephalin) in migration assays. The chemotactic responsiveness was highly dependent on the cell density of the monolayer, with greatest chemotactic activity at the highest cell density. Whereas RANTES was found to be the most potent chemoattractant, constitutive RANTES production was also detected in the HaCaT cultures. We found an inverse correlation between constitutive RANTES production and chemotactic responsiveness toward external RANTES, suggesting a possible functional down-modulation of the RANTES receptors, CC chemokine receptor 1 and CC chemokine receptor 5, during culture. Results from confocal laser scanning microscopy showed reduced CC chemokine receptor 1, but not CC chemokine receptor 5, expression by HaCaT cells at low cell densities, which was abolished in the presence of neutralizing antibodies against RANTES. The total CC chemokine receptor 1 pool (surface and intracellular receptors), however, showed no significant change during in vitro culture. Chemotactic responsiveness toward RANTES was directly correlated with the level of CC chemokine receptor 1 surface expression. Taken together these results show that with keratinocyte proliferation and the progressive increase in cell density there are dramatic alterations in keratinocyte function.

Targeting tumor necrosis factor alpha. New drugs used to modulate inflammatory diseases

Since its discovery, the understanding of the roles for TNF-alpha in human biology and disease has grown. Receptors for TNF are found on virtually all cell types, and many physiologic processes seem to be altered by TNF-alpha. The understanding of how TNF-alpha is involved in the pathophysiology of diseases, such as inflammatory diseases, has allowed the development of new drugs that can interfere with excess TNF-alpha and thus has allowed novel therapies for rheumatoid arthritis and Crohn's disease. As the role of TNF-alpha in other diseases becomes better understood, such TNF-alpha-modulating drugs may find further applications. In the skin, TNF-alpha is prominent cytokine that seems to be important in allergic and irritant contact dermatitis and inflammatory skin conditions. Modulating TNF-alpha activity in the skin may provide therapeutic benefits for a variety of skin conditions (Table 4). Tumor necrosis factor-alpha levels are elevated in skin lesions of psoriasis. A few reports have already suggested that etanercept and infliximab may offer a therapeutic effect in patients with psoriasis. Clinical studies evaluating the true efficacy of these drugs in psoriasis are under way. Specifically, the authors and others are involved in a double-blind, placebo-controlled study to assess the efficacy of etanercept for psoriasis. Thalidomide has been used off-label with some success to treat a number of dermatologic diseases, including several inflammatory skin conditions. Etanercept and infliximab might perhaps prove efficacious for inflammatory skin conditions as well. Finally, it is possible that drugs targeting TNF-alpha may have yet-unrecognized serious side effects. Because TNF-alpha seems to be a central cytokine in UVR-induced apoptosis, the chronic use of TNF-alpha-altering drugs might increase the risk for skin cancers. Tumor necrosis factor-alpha also plays some role in cutaneous wound healing; the effect these drugs might have on this process is also unknown at this time. Certainly, much is already [table: see text] known about TNF-alpha and how it plays many central roles. This understanding has allowed the development of useful new drugs for intractable disease. As the understanding of TNF-alpha and other cytokine biology increases, so will the number of potential therapeutic agents.