Combined analysis of single-cell sequencing and bulk transcriptome sequencing reveals new mechanisms for non-healing diabetic foot ulcers

Diabetic foot ulcers (DFUs) pose a significant challenge in diabetes care. Yet, a comprehensive understanding of the underlying biological disparities between healing and non-healing DFUs remains elusive. We conducted bioinformatics analysis of publicly available transcriptome sequencing data in an attempt to elucidate these differences. Our analysis encompassed differential analysis to unveil shifts in cell composition and gene expression profiles between non-healing and healing DFUs. Cell communication alterations were explored employing the Cellchat R package. Pseudotime analysis and cytoTRACE allowed us to dissect the heterogeneity within fibroblast subpopulations. Our findings unveiled disruptions in various cell types, localized low-grade inflammation, compromised systemic antigen processing and presentation, and extensive extracellular matrix signaling disarray in non-healing DFU patients. Some of these anomalies partially reverted in healing DFUs, particularly within the abnormal ECM-receptor signaling pathway. Furthermore, we distinguished distinct fibroblast subpopulations in non-healing and healing DFUs, each with unique biological functions. Healing-associated fibroblasts exhibited heightened extracellular matrix (ECM) remodeling and a robust wound healing response, while non-healing-associated fibroblasts showed signs of cellular senescence and complement activation, among other characteristics. This analysis offers profound insights into the wound healing microenvironment, identifies pivotal cell types for DFU healing promotion, and reveals potential therapeutic targets for DFU management.

Arsenic Impairs Wound Healing Processes in Dermal Fibroblasts and Mice

Inorganic arsenic (NaAsO2) is a naturally occurring metalloid found in water resources globally and in the United States at concentrations exceeding the U.S. Environmental Protection Agency Maximum Contamination Level of 10 ppb. While exposure to arsenic has been linked to cancer, cardiovascular disease, and skin lesions, the impact of arsenic exposure on wound healing is not fully understood. Cultured dermal fibroblasts exposed to NaAsO2 displayed reduced migration (scratch closure), proliferation, and viability with a lowest observable effect level (LOEL) of 10 µM NaAsO2 following 24 h exposure. An enrichment of Matrix Metalloproteinase 1 (MMP1) transcripts was observed at a LOEL of 1 µM NaAsO2 and 24 h exposure. In vivo, C57BL/6 mice were exposed to 10 µM NaAsO2 in their drinking water for eight weeks, then subjected to two full thickness dorsal wounds. Wounds were evaluated for closure after 6 days. Female mice displayed a significant reduction in wound closure and higher erythema levels, while males showed no effects. Gene expression analysis from skin excised from the wound site revealed significant enrichment in Arsenic 3-Methyltransferase (As3mt) and Estrogen Receptor 2 (Esr2) mRNA in the skin of female mice. These results indicate that arsenic at environmentally relevant concentrations may negatively impact wound healing processes in a sex-specific manner.

Clinical value of combined serum MMP-2, MMP-9 and TIMP-1 for the prognosis of perianal fistula patients who received minimally invasive surgery

OBJECTIVE

This study aimed to investigate the clinical value of combined serum matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) for the prognosis of perianal fistula patients.

METHODS

Patients diagnosed and treated for perianal fistula by minimally invasive surgery (MIS) were enrolled. The concentrations of serum MMP-2, MMP-9 and TIMP-1 were measured at 24 h after surgery. Different levels of wound secretion, growth of granulation tissue and wound pain were used as criteria to evaluate surgical incision healing. The receiver operating characteristic curve was used to analyze the predicted assessment value.

RESULTS

The concentrations of serum MMP-2 and MMP-9 were significantly higher, while the concentrations of serum TIMP-1 at 24 h after surgery were significantly lower in the poor healing group than in the good healing group. It was further found that high levels of serum MMP-2 and MMP-9 were risk factors for poor healing, while high concentrations of serum TIMP-1 at 24 h after surgery were protective factors for poor healing.

CONCLUSION

High concentrations of serum MMP-2 and MMP-9 and low concentrations of serum TIMP at 24 h after surgery are risk factors for poor healing in perianal fistula patients who receive MIS, and the combined test has a higher predictive value.

Hyperbaric Oxygen Therapy Reduces Oxidative Stress and Inflammation, and Increases Growth Factors Favouring the Healing Process of Diabetic Wounds

Hyperbaric oxygen therapy (HBOT) is the clinical application of oxygen at pressures higher than atmospheric pressure. HBOT has been effectively used to manage diverse clinical pathologies, such as non-healing diabetic ulcers. The aim of the present study was to analyse the effects of HBOT on the plasma oxidative and inflammation biomarkers and growth factors in patients with chronic diabetic wounds. The participants received 20 HBOT sessions (five sessions/week), and blood samples were obtained at sessions 1, 5 and 20, before and 2 h after the HBOT. An additional (control) blood sample was collected 28 days after wound recovery. No significant differences were evident in haematological parameters, whereas the biochemical parameters progressively decreased, which was significant for creatine phosphokinase (CPK) and aspartate aminotransferase (AST). The pro-inflammatory mediators, tumour necrosis factor alpha (TNF-α) and interleukin 1β (IL-1β), progressively decreased throughout the treatments. Biomarkers of oxidative stress--plasma protein levels of catalase, extracellular superoxide dismutase, myeloperoxidase, xanthine oxidase, malondialdehyde (MDA) levels and protein carbonyls--were reduced in accordance with wound healing. Plasma levels of growth factors--platelet-derived growth factor (PDFG), transforming growth factor β (TGF-β) and hypoxia-inducible factor 1-alpha (HIF-1α)-- were increased as a consequence of HBOT and reduced 28 days after complete wound healing, whereas matrix metallopeptidase 9 (MMP9) progressively decreased with the HBOT. In conclusion, HBOT reduced oxidative and pro-inflammatory mediators, and may participate in activating healing, angiogenesis and vascular tone regulation by increasing the release of growth factors.

Approaches to Modulate the Chronic Wound Environment Using Localized Nucleic Acid Delivery

Significance: Nonhealing wounds have been the subject of decades of basic and clinical research. Despite new knowledge about the biology of impaired wound healing, little progress has been made in treating chronic wounds, leaving patients with few therapeutic options. Diabetic ulcers are a particularly common form of nonhealing wound. Recent Advances: Recently, investigation of therapeutic nucleic acids (TNAs), including plasmid DNA, small interfering RNA, microRNA mimics, anti-microRNA oligonucleotides, messenger RNA, and antisense oligonucleotides, has created a new treatment strategy for chronic wounds. TNAs can modulate the wound toward a prohealing environment by targeting gene pathways associated with inflammation, proteases, cell motility, angiogenesis, epithelialization, and oxidative stress. A variety of delivery systems have been investigated for TNAs, including dendrimers, lipid nanoparticles (NPs), polymeric micelles, polyplexes, metal NPs, and hydrogels. This review summarizes recent developments in TNA delivery for therapeutic targets associated with chronic wounds, with an emphasis on diabetic ulcers. Critical Issues: Translational potential of TNAs remains a key challenge; we highlight some drug delivery approaches for TNAs that may hold promise. We also describe current commercial efforts to locally deliver nucleic acids to modulate the wound environment. Future Directions: Localized nucleic acid delivery holds promise for the treatment of nonhealing chronic wounds. Future efforts to improve targeting of these nucleic acid therapies in the wound with both spatial and temporal control through drug delivery systems will be crucial to successful clinical translation.

Metalloproteinases and Wound Healing

Significance: Matrix metalloproteinases (MMPs) are present in both acute and chronic wounds. They play a pivotal role, with their inhibitors, in regulating extracellular matrix degradation and deposition that is essential for wound reepithelialization. The excess protease activity can lead to a chronic nonhealing wound. The timed expression and activation of MMPs in response to wounding are vital for successful wound healing. MMPs are grouped into eight families and display extensive homology within these families. This homology leads in part to the initial failure of MMP inhibitors in clinical trials and the development of alternative methods for modulating the MMP activity. MMP-knockout mouse models display altered wound healing responses, but these are often subtle phenotypic changes indicating the overlapping MMP substrate specificity and inter-MMP compensation. Recent Advances: Recent research has identified several new MMP modulators, including photodynamic therapy, protease-absorbing dressing, microRNA regulation, signaling molecules, and peptides. Critical Issues: Wound healing requires the controlled activity of MMPs at all stages of the wound healing process. The loss of MMP regulation is a characteristic of chronic wounds and contributes to the failure to heal. Future Directions: Further research into how MMPs are regulated should allow the development of novel treatments for wound healing.

Loss of keratinocyte focal adhesion kinase stimulates dermal proteolysis through upregulation of MMP9 in wound healing

OBJECTIVE

To investigate how epithelial mechanotransduction pathways impact wound repair.

BACKGROUND

Mechanical forces are increasingly recognized to influence tissue repair, but their role in chronic wound pathophysiology remains unknown. Studies have shown that chronic wounds exhibit high levels of matrix metalloproteinase 9 (MMP9), a key proteolytic enzyme that regulates wound remodeling. We hypothesized that epithelial mechanosensory pathways regulated by keratinocyte-specific focal adhesion kinase (FAK) control dermal remodeling via MMP9.

METHODS

A standard wound model was applied to keratinocyte-specific FAK knockout (KO) and control mice. Rates of wound healing were measured and tissue was obtained for histologic and molecular analyses. Transcriptional and immunoblot assays were used to assess the activation of FAK, intracellular kinases, and MMP9 in vitro. A cell suspension model was designed to validate the importance of FAK mechanosensing, p38, and MMP9 secretion in human cells. Biomechanical testing was utilized to evaluate matrix tensile properties in FAK KO and control wounds.

RESULTS

Wound healing in FAK KO mice was significantly delayed compared with controls (closure at 15 days compared with 20 days, P = 0.0003). FAK KO wounds demonstrated decreased dermal thickness and collagen density. FAK KO keratinocytes exhibited overactive p38 and MMP9 signaling in vitro, findings recapitulated in human keratinocytes via the deactivation of FAK in the cell suspension model. Functionally, FAK KO wounds were significantly weaker and more brittle than control wounds, results consistent with the histologic and molecular analyses.

CONCLUSIONS

Keratinocyte FAK is highly responsive to mechanical cues and may play a critical role in matrix remodeling via regulation of p38 and MMP9. These findings suggest that aberrant epithelial mechanosensory pathways may contribute to pathologic dermal proteolysis and wound chronicity.

The effect of prostaglandin analogs and prostamide on central corneal thickness

OBJECTIVE

The aim of this study was to verify the influence of prostaglandin analogs and prostamide on central corneal thickness (CCT).

METHODS

A prospective analysis was done of CCT in glautomatous patients submitted to monotherapy with prostaglandin analogs (latanoprost 0.005% or travoprost 0.004%) or prostamide (bimatoprost 0.03%) during an 8-week period. A control group of patients without any ocular medication was also evaluated. CCT measurements were performed with a commercially available ultrasound pachymeter. A total of 73 patients were included in this study. Mean age was 68.5 +/- 9.2 (range, 48-85) years old.

RESULTS

A statistically significant reduction in CCT was observed in all groups, except the control group (n = 21): Bimatoprost 0.03% group (n = 21): 544.41 +/- 35.4 vs. 540.35 +/- 35.9 microm (P = 0.039); travoprost 0.004% group (n = 17): 538.47 +/- 32.0 vs. 532.25 +/- 30.4 microm (P = 0.009); latanoprost 0.005% group (n = 14): 548.57 +/- 32.4 vs. 543.88 +/- 35.6 microm (P = 0.036).

CONCLUSION

Topical therapy with prostaglandin analogs and bimatoprost is associated with CCT reduction over a period of at least 8 weeks.

Increased matrix metalloproteinase-9 predicts poor wound healing in diabetic foot ulcers

OBJECTIVE

We studied the relationships of diabetic ulcer wound fluid matrix metalloproteinases (MMPs), tissue inhibitors of metalloproteinases (TIMPs), and transforming growth factor-beta1 (TGF-beta1) with wound healing rate.

RESEARCH DESIGN AND METHODS

The ulcers were cleansed to remove exudates, and wound fluids were collected for analysis of MMP-2 and -9, TIMP-1, and TGF-beta1.

RESULTS

At presentation, MMP-9 and the MMP-9-to-TIMP-1 ratio correlated inversely with the wound healing rate at 28 days (P < 0.001). MMP-9 and the MMP-9-to-TIMP-1 ratio were lower in the 23 patients who achieved complete healing at 12 weeks versus the 39 who did not. The pro-MMP-9 concentration was predictive of healing within 12 weeks. Addition of cutoffs for TIMP-1 (>480 pg/ml) and TGF-beta (>115 pg/ml) further improved its predictive power (area under the curve 0.94).

CONCLUSIONS

These findings suggest that a milieu with high MMP-9 may be indicative of inflammation and poor wound healing. Measurements of MMP-9, TIMP-1, and TGF-beta in wound fluid may help to identify ulcers at risk of poor healing.

Fibronectin fragmentation is a feature of periodontal disease sites and diabetic foot and leg wounds and modifies cell behavior

BACKGROUND

Fibronectin (FN) undergoes fragmentation in periodontal disease sites and in poorly healing diabetic wounds. The biologic effects of FN fragments on wound healing remain unresolved. This study characterized the pattern of FN fragmentation and its effects on cellular behavior compared to intact FN.

METHODS

Polyclonal antibodies were raised against FN and three defined recombinant segments of FN and used to analyze gingival crevicular fluid from periodontal disease sites in systemically healthy subjects and in subjects with diabetes, as well as chronic leg and foot wound exudates from subjects with diabetes. Subsequently, the behavior of human gingival fibroblasts (hGFs) and HT1080 reference cells were analyzed by measuring cell attachment, migration, and chemotaxis in the presence of intact FN or recombinant FN fragments.

RESULTS

FN fragmentation was evident in fluids from periodontal disease sites and diabetic leg and foot wounds. However, no fragmentation pattern distinguished systemically healthy subjects from subjects with diabetes. hGFs and HT1080 cells required significantly higher concentrations of FN fragments to achieve attachment comparable to intact FN. Cells cultured on FN fragments also were morphologically different from cells cultured on full-length FN. Migration was reduced for hGFs cultured on FN fragments relative to full-length FN. In contrast, FN fragments increased HT1080 fibrosarcoma cell migration over intact FN.

CONCLUSIONS

FN fragmentation is a prominent feature of periodontal and chronic leg and foot wounds in diabetes. Furthermore, cell culture assays confirmed the hypothesis that exposure to defined FN fragments significantly alters cell behavior.

Matrix metalloproteinases and diabetic foot ulcers: the ratio of MMP-1 to TIMP-1 is a predictor of wound healing

AIMS

Matrix metalloproteinases (MMPs) play a major role in wound healing: they can degrade all components of the extracellular matrix. In diabetic foot ulcers there is an excess of MMPs and a decrease of the tissue inhibitors of MMPs (TIMPs). This imbalance is probably one cause of impaired healing. However, little is known about changes in MMPs during wound healing.

METHODS

Sixteen patients with neuropathic diabetic foot ulcers participated. Wound fluid was collected regularly during the 12-week follow-up period, for measurement of MMP-1, MMP-2, MMP-8, MMP-9 and TIMP-1. Results were analysed by the degree of wound healing: good healers (defined by a reduction of at least 82% in initial wound surface at 4 weeks) and poor healers (reduction of less than 82% in wound surface at 4 weeks).

RESULTS

In good healers, levels of MMP-8 and -9 secreted by inflammatory cells decreased earlier. The initial levels of MMP-1 were similar in good and poor healers (P = 0.1) but rose significantly at week 2 in good healers (P = 0.039). There was a significant correlation between a high ratio of MMP-1/TIMP-1 and good healing (r = 0.65, P = 0.008). Receiver Operator Curve (ROC) analysis showed that an MMP-1/TIMP-1 ratio of 0.39 best predicted wound healing (sensitivity = 71%, specificity = 87.5%).

CONCLUSIONS

A high level of MMP-1 seems essential to wound healing, while an excess of MMP-8 and -9 is deleterious, and could be a target for new topical treatments. The MMP-1/TIMP-1 ratio is a predictor of wound healing in diabetic foot ulcers.

Expression of MMP-9, MMP-10 and TNF-alpha and lack of epithelial MMP-1 and MMP-26 characterize pyoderma gangrenosum

BACKGROUND

Pyoderma gangrenosum (PG) is a non-infectious, autoimmune, chronic ulcer of the skin, often co-existing with inflammatory bowel disease (IBD). Matrix metalloproteinases (MMPs) have been implicated as mediators of tissue destruction in chronic cutaneous and intestinal wounds.

METHODS

Twenty-four skin biopsies with clinically and histologically confirmed PG and acute wounds were immunostained for MMP-1, -7, -8, -9, -10 and -26; tissue inhibitors of matrix metalloproteinase (TIMP)-1 and -3 and tumor necrosis factor-alpha (TNF-alpha).

RESULTS

MMP-1 was generally expressed by keratinocytes distal from the wound edge, whereas MMP-10 was detected abundantly in the epithelium. MMP-26 was positive in 42% at the migratory front. Abundant stromal expression was evident for MMP-1, -9 and -10, TIMP-1 and -3 and TNF-alpha. In acute wounds, stromal MMP-1, -9 and -10 and TNF-alpha were sparse.

CONCLUSIONS

Unlike in normally healing cutaneous wounds, MMP-1 and -26 were detected bordering the wound in only a minority of PGs and their lack may thus retard epithelial repair. Particularly, MMP-9 and -10 and TNF-alpha would be suitable therapeutic targets as they may contribute to the degradation of provisional matrices needed for migration in healing wounds. The presence of MMP-1, -9, -10 and -26 in both PG and IBD ulcers may suggest a similar pathogenesis for cutaneous and mucosal inflammation.

Matrix metalloproteinases as mediators of tissue injury in different forms of cutaneous lupus erythematosus

BACKGROUND

Matrix metalloproteinases (MMPs) contribute to tissue destruction, regeneration, inflammation and apoptosis and several of them are upregulated by ultraviolet (UV) radiation in skin. Although some MMPs associate with organ manifestations of systemic lupus erythematosus (SLE), their role in cutaneous lupus erythematosus (LE) is elusive.

OBJECTIVES

Our aim was to evaluate the expression of MMPs in SLE, subacute cutaneous LE (SCLE) and discoid LE (DLE) skin lesions and their relation to apoptosis and epidermal changes.

METHODS

Lesional skin biopsies from 20 patients with SLE, 20 with DLE and 17 with SCLE, and from UVA/UVB-photoprovoked skin of healthy volunteers were immunostained using antibodies to multiple MMPs and tissue inhibitors of metalloproteinases (TIMPs). The TUNEL (terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labelling) method was used for detection of apoptosis.

RESULTS

MMP-3, -10, -19 and -26 were abundantly expressed by keratinocytes in SLE, DLE and SCLE skin samples. MMP-7 was detected in keratinocytes in regions of oedema and vacuolization especially in SLE and SCLE, while MMP-14 was only occasionally observed in keratinocytes. Photoprovocation did not induce MMP-10 or -26 expression in skin of healthy volunteers. Epithelial TIMP-1 expression was low while occasional positive fibroblasts were seen in the dermis. TIMP-3 was abundantly expressed in the epidermis, endothelial cells and macrophages.

CONCLUSIONS

Different subtypes of cutaneous LE are fairly similar in their MMP expression profile. MMP-3 and -10 mediate both epidermal changes and dermal tissue remodelling but are not present in lymphocytes. Low expression of TIMP-1 suggests that lupus skin is characterized by proteolytic events, and targeted action using selective MMP inhibitors may reduce lupus-induced damage in inflamed tissues.

Collagenase-2 (MMP-8) and matrilysin-2 (MMP-26) expression in human wounds of different etiologies

Wound healing involves highly controlled events including reepithelialization, neoangiogenesis, and reformation of the stromal compartment. Matrix metalloproteinases (MMPs) are a family of neutral zinc-dependent endopeptidases known to be essential for the wound-healing process. MMP-8 (collagenase-2) is a neutrophil-derived highly effective type I collagenase, recently indicated to be important for acute wound healing. MMP-26 is a more recent and less well-studied member of the MMP family. Our aim was to study the expression of MMP-8 and MMP-26 in human cutaneous wound repair and chronic wounds using histological methods and cell culture. MMP-8 expression was associated with epithelial cells, neutrophils, and other inflammatory cells in chronic human wounds. MMP-26 was prominently expressed in the extracellular compartment of most chronic wounds in close vicinity to the basement membrane area. MMP-26 was also expressed in acute day 1 wounds with declining expression thereafter. In vitro wound experiments showed that both MMP-8 and MMP-26 were expressed by migrating human mucosal keratinocytes. Inhibiting MMP-26 resulted in aberrant keratinocyte migration and proliferation. We conclude that MMP-8 and MMP-26 are differentially expressed in acute and chronic wounds.

Venous leg ulcers - the search for a prognostic indicator

Disordered cell function within chronic wounds generates many parameters that can be measured to differentiate between healing and non healing status. Theoretically, these may form the basis of a wound assessment system to define disease severity and response to treatment. In a review of tissue, wound exudate and microbiology studies of venous leg ulcers, we identify many such parameters that are associated with healing status. These include cytokines, proteases and their inhibitors, senescence markers, oxidative stress markers and microbiological status defined by culture. Some of these, such as protease level in wound exudate, have been proposed as prognostic indicators of healing status and many more could be considered potential markers to incorporate into a wound assessment system. However, no published data are available that validate known wound components to accurately reflect wound progression on a single patient basis. Rather than further characterisation of the expression of known wound biomarkers, the development of an accurate and objective test for prediction of chronic wound outcome requires identification of an appropriate combination of novel molecules that vary coordinately with healing status.

Cyclic mechanical strain-induced proliferation and migration of human airway smooth muscle cells: role of EMMPRIN and MMPs

Airway smooth muscle (ASM) proliferation and migration are major components of airway remodeling in asthma. Asthmatic airways are exposed to mechanical strain, which contributes to their remodeling. Matrix metalloproteinase (MMP) plays an important role in remodeling. In the present study, we examined if the mechanical strain of human ASM (HASM) cells contributes to their proliferation and migration and the role of MMPs in this process. HASM were exposed to mechanical strain using the FlexCell system. HASM cell proliferation, migration and MMP release, activation, and expression were assessed. Our results show that cyclic strain increased the proliferation and migration of HASM; cyclic strain increased release and activation of MMP-1, -2, and -3 and membrane type 1-MMP; MMP release was preceded by an increase in extracellular MMP inducer; Prinomastat [a MMP inhibitor (MMPI)] significantly decreased cyclic strain-induced proliferation and migration of HASM; and the strain-induced increase in the release of MMPs was accompanied by an increase in tenascin-C release. In conclusion, cyclic mechanical strain plays an important role in HASM cell proliferation and migration. This increase in proliferation and migration is through an increase in MMP release and activation. Pharmacological MMPIs should be considered in the pursuit of therapeutic options for airway remodeling in asthma.

Human Skin and Gingival Keratinocytes Show Differential Regulation of Matrix Metalloproteinases When Combined With Fibroblasts in 3-Dimensional Cultures

BACKGROUND

Matrix metalloproteinases (MMP) and their inhibitors are expressed in tissues during interactions between keratinocytes and fibroblasts. Maintaining the balance between MMPs and their inhibitors is critical; failure to do so can lead to severe tissue damage or complete destruction, as seen in periodontal disease. Previously we showed that 3-dimensional (3-D) cultures of homotypically-combined skin and gingival cells mimicked the tissues in protein and lipid production, but heterotypic cultures did not.

METHODS

We examined the production and activation of MMPs in these homotypic and heterotypic combinations of skin and gingival keratinocytes and fibroblasts during the critical time that they reformed the tissues. Primary fibroblasts and keratinocytes were isolated from normal human gingiva and skin and grown in 3-D cultures for up to 42 days. MMP-1, MMP-2, and MMP-9 in the media and inhibition of MMPs from these cultures were analyzed.

RESULTS

These experiments determined that skin fibroblasts grown with skin or gingival keratinocytes secrete increased amounts of MMP-1 compared to gingival fibroblasts; that the interaction of keratinocytes with fibroblasts decreases the amount of MMP-2 produced by the fibroblasts in 3-D cultures; that skin keratinocytes, but not gingival keratinocytes, interact with fibroblasts to upregulate expression of the active form of MMP-9; and that medium conditioned by gingival 3-D cultures does not contain an inhibitor of MMP-9.

CONCLUSION

Varying the type of fibroblast beneath the keratinocytes allowed us to determine that skin and gingival keratinocytes differentially regulate the production and activation of MMP-9, but not MMP-2, a finding that could influence the success of tissue grafting after periodontal surgery.

LETTER TO THE EDITOR: The Other Side: Failure in Fair and Balanced Reporting

Matrix metalloproteinases (MMPs) and their tissue inhibitors play important roles in the wound-healing process. An imbalance in the expression of these molecules is thought to contribute to the failure of chronic ulcers to heal. We investigated whether a mitogenic bovine whey extract enriched with growth factors modulated the expression and activity of MMP-2 and -9, and the tissue inhibitor of MMP-2 (TIMP-2) in chronic leg ulcers. Wound fluids and biopsies were collected from chronic leg ulcer patients whose ulcers were treated topically for 4 weeks with placebo or mitogenic bovine whey extract at concentrations of 2.5, 10, and 20 mg/mL. The levels of MMP-2 and -9 in wound fluid samples was assessed by gelatin zymography and showed a decrease in active MMP-2 in the 2.5 and 10.0 mg/mL mitogenic bovine whey extract-treated ulcers compared with placebo (p<0.05). Immunohistochemical analysis of ulcer biopsies for MMP-2, -9, and TIMP-2 expression showed a reduction in the number of MMP-2-positive dermal fibroblasts in the mitogenic bovine whey extract-treated ulcers compared with pretreatment biopsies (p<0.05) that persisted over the course of the study. In contrast, a transient increase in the number of MMP-9- and TIMP-2-positive cells was observed in mitogenic bovine whey extract treated ulcer biopsies compared with pretreatment levels (p<0.05). These results show that topical application of mitogenic bovine whey extract was able to modulate the expression of MMP-2, -9, and TIMP-2 in chronic leg ulcers and that its constituent growth factors may have the potential to redress the proteolytic imbalance observed in nonhealing chronic ulcers.

Epithelial tissue-type plasminogen activator expression, unlike that of urokinase, its receptor, and plasminogen activator inhibitor-1, is increased in chronic venous ulcers

BACKGROUND

The plasminogen activation system represents a potent mechanism of extracellular proteolysis and is an essential component of normal wound healing. It has also been implicated in the pathogenesis of chronic, nonhealing ulcers. Traditionally, urokinase-type plasminogen activator (uPA) has been associated with pericellular proteolytic activity involved in tissue remodelling processes, and tissue-type plasminogen activator (tPA) mainly with intravascular fibrinolysis.

OBJECTIVES

The present study was conducted to characterize the spatial distribution of the various plasminogen activation system components in chronic ulcers and acute, well-granulating wounds.

METHODS

The expression of uPA, tPA, urokinase receptor (uPAR), plasminogen activator inhibitor-1 (PAI-1), and vitronectin was investigated by immunohistochemical staining, in addition to uPA, tPA and PAI-1 expression by in-situ hybridization, in samples from eight chronic venous ulcers, five decubitus ulcers, five well-granulating acute wounds and five normal skin samples.

RESULTS

In chronic venous leg ulcers tPA mRNA was detected in basal and suprabasal keratinocytes at the leading wound edge, while in well-granulating wounds and in decubitus ulcers tPA mRNA was expressed only in a few keratinocytes. However, tPA was widely expressed in fibroblast- and macrophage-like cells in the stroma of well-granulating wounds, while less tPA was detected in the granulation tissue of chronic ulcers. tPA mRNA and protein were localized in the superficial granular layers in normal skin. Although no qualitative differences in expression of uPA, PAI-1 or uPAR in the wound edge keratinocytes in chronic ulcers vs. normally granulating wounds were found, their expressions were more pronounced in the granulation tissue of well-granulating wounds.

CONCLUSIONS

These results suggest that in poorly healing venous leg ulcers, the pattern of tPA expression is altered in keratinocytes at the leading edge of the wound, and the patterns of tPA, uPA and PAI-1 expression are altered in the granulation tissue.

Survival of Apligraf in acute human wounds

Apligraf consists of bovine collagen dermis seeded with allogeneic male fibroblasts and keratinocytes. It is been shown to promote healing, but the length of persistence and pathological features have not been characterized previously in acute wounds. Forty-eight deep dermal wounds were created and Apligraf, a split-skin graft (SSG), or a dressing was applied. Biopsies of wounds were taken for immunohistochemical analysis and polymerase chain reaction was performed to detect the Y chromosome from Apligraf cells in 14 female wounds. Male allogeneic DNA was detected in wounds for the first 4 weeks. All subsequent time points were negative apart from one biopsy at 6 weeks. The wounds took 4-9 weeks to heal, with the Apligraf exhibiting no features of engraftment. This was in contrast to the rapid healing seen in the SSG control group. Histology revealed a more intense cellular infiltrate, but less vascularization below Apligraf compared with controls. Evidence of an epidermal-mesenchymal interaction was observed. This is the first article to elucidate the survival of Apligraf allogeneic cells in acute wounds in immunocompetent human subjects for up to 6 weeks and demonstrates that in the management of acute surgical wounds, Apligraf has a role only as a temporary biological dressing.

Matrix metalloproteinase activity and immunohistochemical profile of matrix metalloproteinase-2 and -9 and tissue inhibitor of metalloproteinase-1 during human dermal wound healing

Proteolytic activity is required for the turnover of the extracellular matrix during wound healing. Matrix metalloproteinases can collectively cleave all components of the extracellular matrix, with the endogenous tissue inhibitor of metalloproteinase-1 regulating their activity. Breast tissue taken at varying postoperative times (n= 92) or during surgery (controls, n= 17), was used to investigate the temporal and spatial activity of matrix metalloproteinase-2 and -9 and tissue inhibitor of metalloproteinase-1 during human wound healing. Matrix metalloproteinase activity, determined using a quenched fluorescence substrate assay, increased during early healing (3-8 weeks) compared to controls, and then decreased between 24 and 36 weeks after surgery (p < 0.05 until 24 weeks, Mann-Whitney U-test). Immunohistochemistry scores for matrix metalloproteinase-9 expression were significantly elevated compared to controls in scar endothelial cells and fibroblasts from 2 until 12 and 20 weeks, respectively. Matrix metalloproteinase-2 staining was observed exclusively in fibroblasts, reaching maximum levels 8-12 weeks after surgery, decreasing by 1.5 years but remaining significantly increased. Tissue inhibitor of metalloproteinase-1 staining was relatively sparse but was significantly increased until 8 weeks after surgery. These results show that matrix metalloproteinases are present at elevated levels during early wound healing, when angiogenesis occurs, and suggest that matrix metalloproteinase-9 may play a significant role. The later expression of matrix metalloproteinase-2 and -9 in fibroblasts suggests a role in extracellular matrix remodeling.

Molecular, histologic, and gross phenotype of skin wound healing in red Duroc pigs reveals an abnormal healing phenotype of hypercontracted, hyperpigmented scarring

This study examined dermal wound healing in juvenile red Duroc pigs and determined that these animals exhibit a unique healing phenotype at multiple levels. Gross and histologic analysis revealed that full-thickness and deep dermal (1.8 mm deep) wounds both heal via formation of hypercontracted, hyperpigmented scars. Molecular analysis using reverse-transcriptase polymerase chain reaction and porcine-specific primer sets revealed that types I and III collagen, heat shock protein 47, bone morphogenetic protein-1, several proteoglycans, and tissue inhibitor of metalloproteinases 1-3 all showed a unique biphasic pattern of mRNA expression compared to previous results with Yorkshire pigs. This pattern was characterized by an initial peak of expression early after wounding, followed by a return to near-normal levels by days 28-42, and then a second increase in mRNA levels at days 56-70. The second phase of increased gene expression correlated with an increased collagen deposition as observed by picrosirius red staining and polarizing light microscopy. Reverse-transcriptase polymerase chain reaction analysis also revealed a prolonged expression of matrix metalloproteinase-2 compared to previous findings in the Yorkshire strain. Further characterization of the genetics and molecular biology associated with the red Duroc phenotype may provide insight into aberrant human wound healing.

A potent, selective inhibitor of matrix metalloproteinase-3 for the topical treatment of chronic dermal ulcers

The pathology of chronic dermal ulcers is characterized by excessive proteolytic activity which degrades extracellular matrix (required for cell migration) and growth factors and their receptors. The overexpression of MMP-3 (stromelysin-1) and MMP-13 (collagenase-3) is associated with nonhealing wounds, whereas active MMPs-1, -2, -9, and -14 are required for normal wound healing to occur. We describe the synthesis and enzyme inhibition profile of (3R)-3-[([(1S)-2,2-dimethyl-1-(([(1S)-2-methoxy-1-phenylethyl]amino)carbonyl)propyl]amino)carbonyl]-6-(3-methyl-4-phenylphenyl)hexanoic acid (UK-370,106, 7), which is a potent inhibitor of MMP-3 (IC(50) = 23 nM) with >1200-fold weaker potency vs MMP-1, -2, -9, and -14. MMP-13, which may also contribute to the pathology of chronic wounds, was inhibited about 100-fold less potently by compound 7. Compound 7 potently inhibited cleavage of [(3)H]-fibronectin by MMP-3 (IC(50) = 320 nM) but not cleavage of [(3)H]-gelatin by either MMP-2 or -9 (up to 100 microM). Compound 7 had little effect, at MMP-3 selective concentrations, on keratinocyte migration over a collagen matrix in vitro, which is a model of the re-epithelialization process. Following iv (rat) or topical administration to dermal wounds (rabbit), compound 7 was cleared rapidly (t(1/2) = 23 min) from plasma, but slowly (t(1/2) approximately 3 days) from dermal tissue. In a model of chronic dermal ulcers, topical administration of compound 7 for 6 days substantially inhibited MMP-3 ex vivo. These data suggest compound 7 is sufficiently potent to inhibit MMP-3-mediated matrix degradation while leaving unaffected cellular migration mediated by MMPs 1, 2, and 9. These properties make compound 7 a suitable candidate for progression to clinical trials in human chronic dermal wounds, such as venous ulcers.

Profiles of matrix metalloproteinases and their tissue inhibitors in intraperitoneal drainage fluid: relationship to wound healing

Matrix degradation and remodeling occurs during wound healing, thereby aiding tissue repair, angiogenesis, and cell migration. It is dependent on the balance between proteinases and their inhibitors, namely the matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs). Acute wound fluid samples (n = 58 patients) were collected daily from the intraperitoneal drain placed after colorectal surgery from the first postoperative day until drain removal. Three laboratory techniques were performed: enzyme linked immunosorbent assays (MMP-1, MMP-3, TIMP-1, TIMP-2), gelatinase activity assays (MMP-2, MMP-9), and quenched fluorescent substrate hydrolysis (total MMP activity). Levels were correlated with each postoperative day, wound healing, and surgical outcome (p < 0.05, Spearman's correlation). Significant negative (MMP-9, MMP-3, MMP-8, TIMP-2, total MMP activity) and positive (MMP-2, TIMP-1) correlations were observed with the postoperative day, e.g., total MMP-9: day 1, median, 121 (range, 12-189) ng/ml; day 3, 46 (8-179); day 5, 31 (0-155), day 7, 20 (6-58). Differences were also observed with the type of operation, estimated blood loss, and length of operation and with postoperative complications. MMPs and TIMPs are involved in wound healing after elective colorectal cancer surgery and their levels in drain fluid may act as markers of wound healing and surgical outcome.

Matrix metalloproteinases and their tissue inhibitors in severely burned children

Severe burns cause not only skin injury but several marked systemic derangements. During wound healing, matrix metalloproteinases (MMPs) and the tissue inhibitors of metalloproteinases play an important role in tissue regeneration and remodeling processes. Therefore, in the present study, we determined the serum levels of MMPs and tissue inhibitor of metalloproteinase-1 in burn patients over time. Serum samples from 12 severely burned children (mean age 7.9 +/- 2.5 years) with >40% total body surface area burns were obtained within 0.5 hours, 3, 7, and 21 days after injury. Pro-MMP-1, MMP-3, MMP-9, and tissue inhibitor of metalloproteinase-1 serum levels were assayed by enzyme-linked immunoassay and compared to normal healthy volunteers. Two-way analysis of variance and Bonferroni's test were used for statistical analysis. Pro-MMP-1 levels in the serum were significantly elevated by the seventh day after burn. MMP-3 and MMP-9 levels showed significant increases by day 3 and 21 compared to normals, respectively. Tissue inhibitor of metalloproteinase-1 levels did not change with time after burn but were significantly higher by 3 days after burn compared to normal serum. In conclusion, changes in MMPs and tissue inhibitor of metalloproteinase-1 occur in burn patients and those changes may be a mechanism beneficial to wound healing.

Immunohistochemical studies on proteoglycan expression in normal skin and chronic ulcers

BACKGROUND

Proteoglycans (PGs) represent a large family of complex molecules. They are found either as integral membrane components or constituents of the extracellular matrix. Their protein backbones are linked to different glycosaminoglycans, such as dermatan-, chondroitin-, keratan- or heparan sulphate. The molecules have specific functions during developmental processes as well as in diseases, such as cancer and inflammation.

OBJECTIVES

The expression patterns of various cell-associated heparan and chondroitin/dermatan-sulphate PGs in human skin and chronic venous ulcers were investigated.

METHODS

Tissue sections from 11 patients with chronic venous ulcers were used in this study. Monoclonal antibodies were used for detection of the proteoglycans syndecan-1, -2 and -4, glypican, CD44 and perlecan.

RESULTS

The different PGs exhibited individual staining patterns. Syndecan-1 and -4 and glypican expression in chronic ulcers differed from the staining in normal skin. Whereas the expression of syndecan-4 and glypican in intact skin was mostly in the pericellular regions of keratinocytes, the epidermal cells from the wound edge contained mostly intracellular PGs. In the wound edge, syndecan-4 was predominantly expressed by epidermal basal layer cells. Syndecan-1 was less expressed at the epidermal wound margins. PGs bind growth factors, regulate proteolytic activity and act as matrix receptors.

CONCLUSIONS

The altered expression patterns of glypican and syndecan-1 and -4 in chronic ulcers reflect their possible roles during inflammation and cell proliferation. Hence, analysis of PG expression should be of interest in future studies on normal as well as defective wound healing.

Plasminogen activation in venous leg ulcers

BACKGROUND

Venous leg ulceration results from chronic venous insufficiency of the lower extremities. We recently showed that matrix metalloproteinase (MMP) -2 plays a major part in the pathogenesis of venous leg ulcers. In vitro activation of recombinant MMP-2 is controlled by the activity of the urokinase-type plasminogen activator (uPA), which acts as a fibrin-independent plasminogen activator. The activity of MMP-2 is potentiated by binding of uPA to the uPA receptor (uPAR).

OBJECTIVES

We aimed to clarify the role of plasminogen activation in venous leg ulcers.

METHODS

The expression of uPA, uPAR, the tissue-type plasminogen activator, and plasminogen activator inhibitor (PAI) -1 and PAI-2 was investigated using reverse transcription followed by polymerase chain reaction and Western blotting.

RESULTS

These provided direct evidence of elevated expression of uPA and uPAR at the mRNA and protein levels in venous leg ulcers, in comparison with healthy skin. By immunohistochemistry, elevated expression of uPA and uPAR was detected. Fibrin zymography showed significantly elevated endogenous uPA activity in venous leg ulcers in comparison with healthy controls.

CONCLUSIONS

Our findings indicate venous leg ulcers to be characterized by elevated plasminogen activation, suggesting that this enzyme cascade plays a crucial part in maintaining proteolytic activity in venous leg ulcers.

Proteinases, their inhibitors, and cytokine profiles in acute wound fluid

Wound healing is a complex process involving the interactions of many different cell types, matrix components and biological factors, including proteinases and cytokines. This study compared the levels of proteinases (matrix metalloproteinases and plasminogen activators), proteinase inhibitors (tissue inhibitors of metalloproteinases and plasminogen activator inhibitors), inflammatory cytokines and growth factors in acute wound fluid samples collected from the surgical drains of elective breast (n = 24) and colorectal (n = 26) patients on the first postoperative day. Gelatin zymography was used to determine matrix metalloproteinase-2 and -9 levels, quenched fluorescence substrate hydrolysis was applied for total MMP activity and enzyme-linked immunoassays were used to quantitate other factors. Colorectal wound fluid samples showed significantly (p < 0.05) greater levels of the matrix metalloproteinases (MMP-1, 2, 3, and 9), tissue inhibitor of metalloproteinases-1, urokinase plasminogen activator receptor and the inflammatory cytokines (interleukin-1beta, -6, and tumor necrosis factor-alpha); e.g., matrix metalloproteinase-3 colon; median 275 (range 11-2.530) ng/ml; breast; 530-400. However, tissue plasminogen activator and growth factor levels (epidermal growth factor, platelet-derived growth factor, basic fibroblast growth factor, transforming growth factor-beta1) were significantly greater in breast samples; e.g., epidermal growth factor breast 468 (103-1, 444) pg/ml; colon 57(1-573). There was no difference in the levels of urokinase type plasminogen activator, plasminogen activator inhibitor-1 and -2, tissue inhibitor of metalloproteinases -2 or vascular endothelial growth factor. Acute wound fluid from different surgical wounds showed different profiles of proteinases, proteinase inhibitors, and cytokines. This may lead to differences in the rate of tissue remodeling and therefore healing in these two wounds in vivo.

Epidermal maturation arrest

BACKGROUND

Cutaneous wound repair involves a complex and temporal integration of cytokines, formed blood components, extracellular matrix, and parenchymal cells. The normal healing process can be impeded at any step along its path by a variety of factors.

OBJECTIVE

We present four cases of abnormal wound repair in patients whose defects were left to heal by second intention following Mohs micrographic surgery. In particular, these patients experienced an unusual delay in healing with an apparent arrest of epidermal maturation.

RESULTS

Each appeared to respond to a topical steroid and/or ibuprofen. The intent of this therapy was to inhibit products of the arachadonic acid cascade or other cytokines that may have been hindering normal epidermal differentiation.

CONCLUSION

We present four case reports, a brief review of epidermal reconstitution in wounds, and a possible explanation for why our therapy may have hastened wound repair in our patients.

The proteolytic environment of chronic wounds

A consistent feature of chronic leg and pressure ulcers is chronic inflammation associated with an elevated infiltration of neutrophils. Neutrophils and their proteases have been implicated in mediating the tissue damage associated with a variety of chronic inflammatory diseases. This review discusses our current understanding of the proteolytic enzymes found in chronic wounds and attempts to relate this information to the abundant presence of neutrophils. In addition, the implications that the proteolytic environment may have for current and future treatment strategies of chronic nonhealing wounds are discussed.

Role of matrix metalloproteinases and their inhibition in cutaneous wound healing and allergic contact hypersensitivity

Normal wounds can heal by secondary intention (epidermal migration to cover a denuded surface) or by approximation of the wound edges (e.g., suturing). In healing by secondary intention, epidermis-derived MMPs are important. Keratinocyte migration begins within 3-6 hr post injury, as basal cells detach from underlying basal lamina and encounter a dermal substratum rich in type I collagen. Cell contact with type I collagen in vitro stimulates collagenase-1 expression, which is mediated by the alpha 2 beta 1 integrin, the major keratinocyte collagen-binding receptor. Collagenase-1 activity alone is necessary and sufficient for keratinocyte migration over a collagen subsurface. Stromelysins-1 and -2 are also found in the epidermis of normal acute wounds. Stromelysin-2 co-localizes with collagenase-1 and may facilitate cell migration over non-collagenous matrices of the dermis. In contrast, stromelysin-1 is expressed by keratinocytes behind the migrating front and which remain on basal lamina, i.e., the proliferative cell population. Studies with stromelysin-1-deficient mice that suggest this MMP plays a role in keratinocyte detachment from underlying basement membrane to initiate cell migration. In chronic ulcers, MMP levels are markedly elevated, in contrast to their precise temporal and spatial expression in acute wounds. Both collagenase-1 and stromelysin-1 are found in fibroblasts underlying the nonhealing epithelium, and stromelysin-1 expression is especially prominent. Two key questions underlie the use of MMP inhibitors and wound healing: (1) will these agents impair normal reepithelialization in wounds that heal by secondary intention; and (2) can MMP inhibitors be effective therapy for chronic ulcers? The answer to neither is known. Batimastat and marimastat appear not to interfere with normal wound healing, but only in sutured surgical wounds, a situation in which MMP expression has practically no role. We also show the first example of an in vivo immune response, contact hypersensitivity, which is dependent upon MMP activity. Using gene-deficient mice, we demonstrate that stromylysin-1 (MMP-3) is required for sensitization, whereas gelatinase B (MMP-9) is required for timely resolution of the reaction to antigenic challenge.

Cell migration and MMP-9 secretion are increased by epidermal growth factor in HaCaT-ras transfected cells

Mutated RAS oncoproteins and epidermal growth factor (EGF) are thought to contribute to the proliferative, invasive and metastatic properties of transformed cells. In the present study, we investigated the role of EGF in two H-ras transfected clones and compared it to that in the parental cell line, HaCaT and primary cultured keratinocytes. Our findings show that the motility on type I collagen, measured by the migration index, was similar for both the HaCaT cell line and normal human keratinocytes, whereas it was higher for the HaCaT-ras clones. These results suggest an involvement of the ras oncogene in the stimulation of cell migration. EGF in cell pretreatment or during the migration assay also caused an increase in migration of all the cells, but preserved the difference between HaCaT and HaCaT-ras. However, no significant difference in EGF-R expression was detected between normal cultured keratinocytes, HaCaT and HaCaT-ras cell lines with or without EGF pretreatment. Moreover, when the cells were stimulated with EGF, the MMP-9 activity was greatly increased in a dose-dependent manner in all the cells, and EGF stimulation particularly highlights the increased amount of MMP-9 in HaCaT-ras cells compared to HaCaT cells. In conclusion, EGF is able to enhance motility and to up-regulate MMP-9 activity in all cells, but with a higher impact in HaCaT-ras cells without an overexpression of EGF-R. As EGF acts in synergy with the H-ras mutation, they could be implicated in the local invasion by the HaCaT-ras clones.

Matrix metalloproteinases in skin

Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases collectively capable of degrading essentially all extracellular matrix components. These enzymes can be produced by several different types of cells in skin such as fibroblasts, keratinocytes, macrophages, endothelial cells, mast cells, and eosinophils and their activity can be specifically inhibited by TIMPs (tissue inhibitors of metalloproteinases), which bind to active MMPs with 1:1 stoichiometry. In general, MMPs are not constitutively expressed in skin but are induced temporarily in response to exogenous signals such as various cytokines, growth factors, cell matrix interactions and altered cell-cell contacts. At present, more evidence is accumulating that MMPs play an important role in proteolytic remodeling of extracellular matrix in various physiologic situations, including developmental tissue morphogenesis, tissue repair, and angiogenesis. On the other hand, MMPs play an important pathogenetic role in excessive breakdown of connective tissue components, e.g. in rheumatoid arthritis, osteoarthritis, chronic ulcers, dermal photoageing, and periodontitis, as well as in tumor cell invasion and metastasis. In this review we discuss the role of MMPs and TIMPs in human skin based on new observations on the regulation of the expression of MMPs, on their substrate specificity, and MMP expression in physiologic and pathologic conditions of skin involving matrix remodeling. Furthermore, therapeutic modalities based on regulating MMP activity will be reviewed.