Expression of tissue-type and urokinase-type plasminogen activator activities in chronic venous leg ulcers

Protease activity as a prognostic factor for wound healing in venous leg ulcers

BACKGROUND

Venous leg ulcers (VLUs) are a common type of complex wound that have a negative impact on people's lives and incur high costs for health services and society. It has been suggested that prolonged high levels of protease activity in the later stages of the healing of chronic wounds may be associated with delayed healing. Protease modulating treatments have been developed which seek to modulate protease activity and thereby promote healing in chronic wounds.

OBJECTIVES

To determine whether protease activity is an independent prognostic factor for the healing of venous leg ulcers.

SEARCH METHODS

In February 2018, we searched the following databases: Cochrane Central Register of Controlled Trials (CENTRAL), Ovid MEDLINE, Ovid Embase and CINAHL.

SELECTION CRITERIA

We included prospective and retrospective longitudinal studies with any follow-up period that recruited people with VLUs and investigated whether protease activity in wound fluid was associated with future healing of VLUs. We included randomised controlled trials (RCTs) analysed as cohort studies, provided interventions were taken into account in the analysis, and case-control studies if there were no available cohort studies. We also included prediction model studies provided they reported separately associations of individual prognostic factors (protease activity) with healing. Studies of any type of protease or combination of proteases were eligible, including proteases from bacteria, and the prognostic factor could be examined as a continuous or categorical variable; any cut-off point was permitted. The primary outcomes were time to healing (survival analysis) and the proportion of people with ulcers completely healed; the secondary outcome was change in ulcer size/rate of wound closure. We extracted unadjusted (simple) and adjusted (multivariable) associations between the prognostic factor and healing.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies for inclusion at each stage, and undertook data extraction, assessment of risk of bias and GRADE assessment. We collected association statistics where available. No study reported adjusted analyses: instead we collected unadjusted results or calculated association measures from raw data. We calculated risk ratios when both outcome and prognostic factor were dichotomous variables. When the prognostic factor was reported as continuous data and healing outcomes were dichotomous, we either performed regression analysis or analysed the impact of healing on protease levels, analysing as the standardised mean difference. When both prognostic factor and outcome were continuous data, we reported correlation coefficients or calculated them from individual participant data.We displayed all results on forest plots to give an overall visual representation. We planned to conduct meta-analyses where this was appropriate, otherwise we summarised narratively.

MAIN RESULTS

We included 19 studies comprising 21 cohorts involving 646 participants. Only 11 studies (13 cohorts, 522 participants) had data available for analysis. Of these, five were prospective cohort studies, four were RCTs and two had a type of case-control design. Follow-up time ranged from four to 36 weeks. Studies covered 10 different matrix metalloproteases (MMPs) and two serine proteases (human neutrophil elastase and urokinase-type plasminogen activators). Two studies recorded complete healing as an outcome; other studies recorded partial healing measures. There was clinical and methodological heterogeneity across studies; for example, in the definition of healing, the type of protease and its measurement, the distribution of active and bound protease species, the types of treatment and the reporting of results. Therefore, meta-analysis was not performed. No study had conducted multivariable analyses and all included evidence was of very low certainty because of the lack of adjustment for confounders, the high risk of bias for all studies except one, imprecision around the measures of association and inconsistency in the direction of association. Collectively the research indicated complete uncertainty as to the association between protease activity and VLU healing.

AUTHORS' CONCLUSIONS

This review identified very low validity evidence regarding any association between protease activity and VLU healing and there is complete uncertainty regarding the relationship. The review offers information for both future research and systematic review methodology.

Cigarette smoke condensate stimulates urokinase production through the generation of reactive oxygen species and activation of the mitogen activated protein kinase pathways in human gingival fibroblasts

BACKGROUND AND OBJECTIVE

Tobacco smoking is a significant risk factor for periodontal disease. It has been suggested that smoking may alter connective tissue remodeling in the periodontium. In the present study, we investigated whether cigarette smoke condensate modulates the production of the serine protease urokinase in human gingival fibroblasts.

MATERIAL AND METHODS

Primary cultures of human gingival fibroblasts were stimulated with cigarette smoke condensate. Urokinase production was evaluated through casein zymography and western blotting. Plasmin activation was assessed by means of a radial diffusion assay. The roles of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and reactive oxygen species in cigarette smoke condensate-stimulated urokinase production were studied using distinct selective inhibitors (SP600125, PD98059, N-acetyl cysteine). Reactive oxygen species production was determined using a fluorometric assay. Activation of ERK and JNK pathways were evaluated using western blots.

RESULTS

In gingival fibroblasts, cigarette smoke condensate potently stimulated urokinase production and plasmin activation. Cigarette smoke condensate-stimulated urokinase production was dependent on the activity of ERK/JNK pathways and was inhibited by the reactive oxygen species scavenger, N-acetyl cysteine. Cigarette smoke condensate strongly stimulated ERK and JNK phosphorylation and the generation of reactive oxygen species.

CONCLUSION

Cigarette smoke condensate stimulates urokinase production and plasmin activation in gingival fibroblasts. Moreover, cigarette smoke condensate-stimulated urokinase production depends on both the activation of ERK/JNK pathways and on the generation of intracellular reactive oxygen species. These results show that cigarette smoke may alter connective tissue remodeling by inducing production of the urokinase-type plasminogen activator through specific signaling pathways.

Recent insights into the causes of chronic leg ulceration in venous diseases and implications on other types of chronic wounds

Venous ulceration represents the most prevalent form of difficult-to-heal wounds and these problematic wounds require a significant amount of healthcare resources for their treatment. In order to develop effective treatment regimens a clearer understanding of the underlying pathological processes that lead to skin breakdown is required. However, to date, most of these studies have tended to focus on describing the pathology of already-established ulcers. By bringing together relevant aspects of diverse disciplines such as inflammation, cardiovascular, and connective tissue biology, we aim to provide an insight into how circulatory abnormalities that are caused by the underlying disease etiology can induce local tissue inflammation resulting in tissue breakdown. Initially this results in internal tissue damage but if the underlying disease is not treated, the internal tissue damage can worsen and lead to open ulceration. This article discusses the cause-and-effect relationships between chronic venous insufficiency and venous ulceration, focusing particularly on the biological processes that lead from the underlying disease condition to overt ulceration. Available evidence also suggests that formation of pressure, diabetic foot and arterial ulcers, and ulcers as results of blood disorders, is also likely to share some of the same biological processes as venous ulcers.

The overlapping of local iron overload and HFE mutation in venous leg ulcer pathogenesis

Chronic venous stasis determines red blood cell extravasation and either dermal hemosiderin deposits or iron-laden phagocytes. Several authors have suspected that iron could play a role in the pathogenesis of venous leg ulcers. They hypothesized that local iron overload could generate free radicals or activate a proteolytic hyperactivity on the part of metalloproteinases (MMPs) or else down-regulate tissue inhibitors of MMPs. However, they were unable to explain why iron deposits, visible in the legs of patients with chronic venous disease (CVD), cause lesions in only some individuals, whereas in others they do not. We hypothesized that such individual differences could be genetically determined and investigated the role of the C282Y and H63D mutations of the HFE gene. C282Y mutation significantly increases the risk of ulcer in primary CVD more than six times (OR = 6.69; 1.45-30.8; p = 0.01). Patients carrying the H63D variant have an earlier age of ulcer onset, by almost 10 years (p > 0.004). The increased risk of skin lesion and the early age of onset of the disease in HFE carriers confirm in a clinical setting that intracellular iron deposits of mutated macrophages have less stability than those of the wild type. We hypothesize that the physiologic iron protective mechanisms are affected by the HFE mutations and should be investigated in all diseases characterized by the combination of iron overload and inflammation.

Fibrin-induced skin fibrosis in mice deficient in tissue plasminogen activator

The deposition of fibrin is an integral part of the tissue repair process, but its persistence is also associated with a number of fibrotic conditions. This study addressed the hypothesis that reduced fibrinolysis and fibrin persistence are associated with an enhanced accumulation of collagen and the development of skin fibrosis. Decreased fibrinolysis was confirmed in fibrin gel cultures that contained human dermal fibroblasts plus the specific plasmin inhibitor alpha(2)-antiplasmin or dermal fibroblasts isolated from plasminogen activator (PA)-deficient mice. Collagen accumulation was significantly increased in the presence of inhibitor and in tPA-deficient, but not uPA-deficient, fibroblasts compared with controls. These findings were also confirmed using a skin fibrosis model in which multiple injections of fibrin were given subcutaneously to PA-deficient mice. Injection sites from tPA-deficient mice displayed significantly increased collagen levels compared with uPA-deficient mice and wild-type controls. Up-regulation of fibroblast procollagen gene expression and reduced activation of pro-MMP-1 appeared to mediate the increase in collagen by human dermal fibroblasts in the presence of alpha2-antiplasmin. These findings suggest that persistent fibrin is associated with enhanced collagen accumulation that may result in the development of fibrotic skin disorders in which reduced fibrinolysis is a feature.

Microcirculation and Venous Ulcers: A Review

Recent histological and immunocytochemical analyses of venous leg ulcers suggest that lesions observed in the different stages of chronic venous insufficiency (CVI) may be related to an inflammatory process. This inflammatory process leads to fibrosclerotic remodeling of the skin and then to ulceration. The vascular network of the most superficial layers of the skin appears to be the target of the inflammatory reaction. Hemodynamic forces such as venous hypertension, circulatory stasis, and modified conditions of shear stress appear to play an important role in an inflammatory reaction accompanied by leukocyte activation which clinically leads to CVI: venous dermatitis and venous ulceration. The leukocyte activation is accompanied by the expression of integrins and by synthesis and release of many inflammatory molecules, including proteolytic enzymes, leukotrienes, prostaglandin, bradykinin, free oxygen radicals, cytokines, and possibly other classes of inflammatory mediators. The inflammatory reaction perpetuates itself, leading to liposclerotic skin and subcutaneous tissue remodeling. In light of the mechanisms of venous ulcer formation cited above, therapy in the future might be directed against leukocyte activation in order to diminish the magnitude of the inflammatory response. With this in mind, the attention of many investigators has been drawn to two different drugs with an anti-inflammatory effect: pentoxifylline and flavonoids.

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.

IL-8-stimulated expression of urokinase-type plasminogen activator in human skin and human epidermal cells

Extracellular matrix (ECM) remodeling is essential for normal development and tissue repair. Although many roles for extracellular proteinases in the breakdown of ECM have been established, the regulations of these proteinases in human tissue are not fully understood. Inflammatory cytokines have been implicated in the regulation of several matrix metalloproteinases. To determine whether these mediators have a similar effect on fibrinolysis and the remodeling of the fibrin provisional matrix, we examined the role of cytokines on the regulation of urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA) in human skin. In this report, we show that interleukin-8 (IL-8), but not other cytokines tested, is a potent inducer of the 38-kDa uPA in organ-cultured human skin. In addition, the uPA inhibitor, PAI-1, was not affected by IL-8. When primary epidermal human keratinocytes were treated with IL-8, 55-kDa pro-uPA was significantly induced in the conditioned medium. The mRNA expression of uPA in the keratinocytes was found to be constitutively elevated and was not affected by IL-8. To support such a notion, activation of the 5'-flanking promoter of the human uPA gene was measured using the CAT reporter assay. Consistent with the results of mRNA measurement, the promoter is constitutively active in keratinocytes and is not affected by IL-8. In contrast, the promoter construct is neither active in the dermal fibroblasts nor stimulated by the cytokine. This differential transactivation of uPA gene in these cells indicates that keratinocyte-specific factors may govern the basal expression of the gene. These results indicate a complex regulation of uPA expression in epidermal cells.

Leg Ulcers: Biochemical Factors

Objective:

To review the biochemical mechanisms underlying the development of skin changes leading to ulceration in patients with chronic venous disease.

Methods:

Searches of Medline and Embase medical literature databases were undertaken. Cochrane Reviews were studied for relevant articles. Hand-searching of non-indexed journals was undertaken.

Synthesis:

Increased leucocyte activation has been shown in patients with venous disease as well as increased expression of soluble endothelial adhesion molecules. Histological studies of the skin in patients with chronic venous disease show a pervascular infiltration of the capillaries of the papillary plexus (the most superficial part of the dermis) with monocytes, macrophages and connective tissue proteins including fibrin. Fibrosis of the skin and subcutaneous tissues may be initiated by increased gene expression and production of transforming growth factor-beta1. Vascular endothelial growth factor may be involved in the capillary proliferation that has been reported in the skin by a number of authors. Increased expression of several tissue metalloproteinases (MMPs) has been reported both in lipsclerotic skin and peri-ulcer skin. The tissue inhibitors of metalloproteinases (TIMPs) are also increased and the net result is unclear. Treatment of venous disease using micronised purified flavonoid fraction moderates some of the inflammatory markers, including leucocyte ligand expression and endothelial adhesion molecule shedding. These compounds have also been shown to reduce leucocyte-endothelial adhesion in animal models of ischaemia-reperfusion injury.

Conclusions:

Many inflammatory processes have now been shown to be involved in the development of the skin changes in patients with chronic venous disease. However, the precise sequence of events which leads to leg ulceration is still unclear. Pharmacological treatments aimed at moderating some of these inflammatory processes are now under investigation as potential ways of treating patients with the more advanced stages of venous disease.