Validation of an in vivo wound healing model for the quantification of pharmacological effects on epidermal regeneration

Gene Expression Linked to Reepithelialization of Human Skin Wounds

Our understanding of the regulatory processes of reepithelialization during wound healing is incomplete. In an attempt to map the genes involved in epidermal regeneration and differentiation, we measured gene expression in formalin-fixed, paraffin-embedded standardized epidermal wounds induced by the suction-blister technique with associated nonwounded skin using NanoString technology. The transcripts of 139 selected genes involved in clotting, immune response to tissue injury, signaling pathways, cell adhesion and proliferation, extracellular matrix remodeling, zinc transport and keratinocyte differentiation were evaluated. We identified 22 upregulated differentially expressed genes (DEGs) in descending order of fold change (MMP1, MMP3, IL6, CXCL8, SERPINE1, IL1B, PTGS2, HBEGF, CXCL5, CXCL2, TIMP1, CYR61, CXCL1, MMP12, MMP9, HGF, CTGF, ITGB3, MT2A, FGF7, COL4A1 and PLAUR). The expression of the most upregulated gene, MMP1, correlated strongly with MMP3 followed by IL6 and IL1B. rhIL-1β, but not rhIL-6, exposure of cultured normal human epidermal keratinocytes and normal human dermal fibroblasts increased both MMP1 mRNA and MMP-1 protein levels, as well as TIMP1 mRNA levels. The increased TIMP1 in wounds was validated by immunohistochemistry. The six downregulated DEGs (COL7A1, MMP28, SLC39A2, FLG1, KRT10 and FLG2) were associated with epidermal maturation. KLK8 showed the strongest correlation with MKI67 mRNA levels and is a potential biomarker for keratinocyte proliferation. The observed gene expression changes correlate well with the current knowledge of physiological reepithelialization. Thus, the gene expression panel described in this paper could be used in patients with impaired healing to identify possible therapeutic targets.

The effect of a basic skin care product on the structural strength of the dermo-epidermal junction: An exploratory, randomised, controlled split-body trial

Skin ageing is associated with various structural alterations including a decreased strength of the dermo‐epidermal adhesion increasing the risk for shear type injuries (skin tears). Topical applications of basic skin care products seem to reduce skin tear incidence. The suction blister method leads to the artificial and controlled separation of dermis and epidermis. Therefore, time to blister formation may be used as outcome measuring the strength of dermo‐epidermal adhesion. We conducted an exploratory, randomised, controlled trial with a split‐body design on forearms in healthy female subjects (n = 12; mean age 70.3 [SD 2.1] years). Forearms assigned to the intervention were treated twice daily with petrolatum for 8 weeks. Suction blisters were induced on forearms after 4 and 8 weeks and time to blister formation was measured. Stratum corneum and epidermal hydration were measured and epidermal thickness was assessed via optical coherence tomography. Time to blistering was longer and stratum corneum as well as epidermal hydration was consistently higher in intervention skin areas. We conclude that topical application of basic skin care products may improve mechanical adhesion of the dermo‐epidermal junction and that the parameter “time to blistering” is a suitable outcome to measure dermo‐epidermal adhesion strength in clinical research.

Dermal-epidermal separation methods: research implications

Dermal-epidermal separation is an important basic investigation technique for pharmacology, toxicology and biology. To choose the optimal method for a given research need, we reviewed studies on epidermal separation. PubMed, Embase, and Web of Science were utilized. Different separation systems have been compared, including chemical, enzyme, heat and mechanical separation; each has advantages and disadvantages. Heat is simple but causes thermal damage. Chemical reagents are effective but disturb cellular electrolyte equilibrium. Enzymes provide complete separation, but destroy important components. Mechanical division does not alter physical and/or chemical integrity, but necessitates a relatively large sample and may cause cross-contamination of layers. Thus, the appropriate method should be chosen for a given research question, and no single method appears superior for all purposes.

Blistering time as a parameter for the strength of dermoepidermal adhesion: a systematic review and meta-analysis

Skin ageing is associated with a flattening of the dermoepidermal junction and a less effective anchoring system, predisposing to bulla formation, trauma and shear-type injuries. An artificial and controlled technique for standardized dermoepidermal separation is the suction blister method, whereby the strength of dermoepidermal adhesion is characterized by blistering time. To identify and quantify influencing factors on blistering time in healthy humans. A search in the Medline and Embase databases (1946 to June 2014) and in reference lists was conducted. In total, results of 146 suction blister experiments in 3418 individuals reported in 59 publications were analysed. The median blister diameter was 6 mm (IQR 5-6) and the median suction pressure was -210 mmHg (IQR -200 to -300), resulting in a median blistering time of 75 min (IQR 48-120). In the multivariate model, skin temperature and age were the strongest predictors for suction blistering time (P < 0·001, R(2) adjusted  = 0·707). This strong association between temperature and suction blistering indicates that the dermoepidermal junction loses its strength with increasing skin temperature. This finding supports the practice of skin and tissue cooling to prevent injuries. The increased vulnerability of the skin seems to exist irrespectively of applied mechanical loads. We conclude that blistering time is an important and clinically relevant (outcome) parameter measuring the structural and mechanical integrity of deeper cutaneous layers.

Alternatives for animal wound model systems

In this chapter a review of animal model systems already being utilized to study normal and pathologic wound healing is provided. We also go into details on alternatives for animal wound model systems. The case is made for limitations in the various approaches. We also discuss the benefits/limitations of in vitro/ex vivo systems bringing everything up to date with our current work on developing a cell-based reporter system for diabetic wound healing.

A minimally invasive human in vivo cutaneous wound model for the evaluation of innate skin reactivity and healing status

Individual variability in skin reactivity and healing capacity after trauma are important clinical issues. The aims were to develop an in vivo, human wound model based on a standardised minimal skin injury and to demonstrate therapeutic effect of simple wound therapies in terms of morphological wound outcome with changes in skin blood perfusion as a quantified indicator of wound healing. In a series of experiments, wounds were induced on the normal forearm skin of volunteers using a blood collection lancet. This was well tolerated. Wounds were assessed by naked eye examination or laser Doppler perfusion imaging (LDPI) at baseline and at up to 6 further time points up to 96 h in control wounds and wounds treated by commonly used occlusive dressing options. Assessment by clinical observation with 10x magnification showed over 96 h a progression of erythema, surface crust, a new keratinisation layer and finally healed areas. LDPI quantifying wound erythema showed a peak at 24 h and near normal levels at 96 h. Inter-individual variability was evident but intra-individual variability was much less pronounced. Wounds treated with occlusion showed a statistically significant more rapid return to baseline blood perfusion as measured by LDPI compared to controls supported by favourable healing parameters in the clinical assessment. The paper exemplifies use of non-invasive, bioengineering technique for quantification of individual innate variability in skin reactivity, wound healing capacity and therapeutic effect in a well-tolerated in vivo, human, minimal skin trauma model.

Effects of a topically applied wound ointment on epidermal wound healing studied by in vivo fluorescence laser scanning microscopy analysis

Epidermal wound healing is a complex and dynamic regenerative process necessary to reestablish skin integrity. Fluorescence confocal laser scanning microscopy (FLSM) is a noninvasive imaging technique that has previously been used for evaluation of inflammatory and neoplastic skin disorders in vivo and at high resolution. We employed FLSM to investigate the evolution of epidermal wound healing noninvasively over time and in vivo. Two suction blisters were induced on the volar forearms of the study participants, followed by removal of the epidermis. To study the impact of wound ointment on the process of reepithelization, test sites were divided into two groups, of which one test site was left untreated as a negative control. FLSM was used for serial/consecutive evaluations up to 8 days. FLSM was able to visualize the development of thin keratinocyte layers developing near the wound edge and around hair follicles until the entire epidermis has been reestablished. Wounds treated with the wound ointment were found to heal significantly faster than untreated wounds. This technique allows monitoring of the kinetics of wound healing noninvasively and over time, while offering new insights into the potential effects of topically applied drugs on the process of tissue repair.

Epidermal wound healing in severe sepsis and septic shock in humans

Introduction

The effect of sepsis on epidermal wound healing has not been previously studied. It was hypothesised that epidermal wound healing is disturbed in severe sepsis.

Methods

Blister wounds were induced in 35 patients with severe sepsis and in 15 healthy controls. The healing of the wounds was followed up by measuring transepidermal water loss and blood flow in the wound, reflecting the restoration of the epidermal barrier function and inflammation, respectively. The first set of suction blisters (early wound) was made within 48 hours of the first sepsis-induced organ failure and the second set (late wound) four days after the first wound. In addition, measurements were made on the intact skin.

Results

The average age of the whole study population was 62 years (standard deviation [SD] 12). The mean Acute Physiology and Chronic Health Evaluation II (APACHE II) score on admission was 25 (SD 8). The two most common causes of infections were peritonitis and pneumonia. Sixty-six percent of the patients developed multiple organ failure. The decrease in water evaporation from the wound during the first four days was lower in septic patients than in the control subjects (56 g/m² per hour versus 124 g/m² per hour, P = 0.004). On the fourth day, septic patients had significantly higher blood flow in the wound compared with the control subjects (septic patients 110 units versus control subjects 47 units, P = 0.001). No difference in transepidermal water loss from the intact skin was found between septic patients and controls. Septic patients had higher blood flow in the intact skin on the fourth and on the eighth day of study compared with the controls.

Conclusions

The restoration of the epidermal barrier function is delayed and wound blood flow is increased in patients with severe sepsis.

Artificial Barrier Repair in Wounds by Semi-Occlusive Foils Reduced Wound Contraction and Enhanced Cell Migration and Reepithelization in Mouse Skin

The repair of the permeability barrier to prevent the entry of harmful substances into the body is a goal in wound healing. Semi-occlusive foils, which provide an artificial barrier, are commonly used for the treatment of wounds. We examined the effects of foils on wound contraction, cell migration, and reepithelization. Full-thickness skin wounds in mice were covered with occlusive latex foils or semi-occlusive water vapor-permeable hydrocolloid foils for either the entire, the first half, or the second half of the wound-healing period. We found that application of foils for the entire healing period initially reduced wound healing during the first week of treatment, whereas healing was enhanced during the second week. Foils were found to reduce wound contraction, but enhanced reepithelization during the second week of wound healing because of increased proliferation and migration of keratinocytes. These effects were also noted when the hydrocolloid foils were applied for the second part of the healing period, only. The fully occlusive latex foil led to irritation of the skin, whereas less irritation occurred under semi-occlusive conditions. In summary, we found that artificial barrier repair with semi-occlusive foils in wounds reduced wound contraction and enhanced cell migration and reepithelization without irritation.

Effect of jaundice and its resolution on wound re-epithelization, skin collagen synthesis, and serum collagen propeptide levels in patients with neoplastic pancreaticobiliary obstruction

BACKGROUND

Wound and anastomotic healing is considered to be delayed in patients with obstructive jaundice. The study was designed to find out whether the healing of experimental suction blister wounds, skin collagen synthesis, and serum procollagen levels are affected by obstructive jaundice, and if biliary drainage may cause any alterations in these processes.

PATIENTS AND METHODS

Suction blisters were induced on 24 patients with obstructive jaundice caused by neoplastic pancreaticobiliary obstruction and 17 control patients with the corresponding condition without jaundice, to compare healing parameters and collagen synthesis between the groups. A second set of suction blisters were induced on 13 formerly jaundiced patients after the resolution of jaundice and on 14 control patients, to find out whether drainage or time modifies healing or collagen synthesis. By using this model, it is possible to evaluate the re-epithelization and inflammation on wound healing and to assess the baseline skin collagen synthesis. The healing of suction blisters was followed up by measuring water evaporation and blood flow in the wound. Blister fluids and serum samples were collected to study collagen propeptides.

RESULTS

Healing of the blister wound was unaffected by obstructive jaundice. Drainage had no effect on healing. The baseline synthesis of type I and type III collagen in the skin was decreased in jaundiced patients. Biliary drainage improved the synthesis. Serum type III procollagen propeptide levels were elevated in jaundiced patients, but began to normalize after drainage.

CONCLUSION

Healing of an experimental blister wound is not disturbed by obstructive jaundice. The decreased baseline skin collagen synthesis is partly restored by the resolution of jaundice. The results indicate that cell protein synthesis is disturbed earlier than cell dynamics in obstructive jaundice. The elevated serum PIIINP levels, which are most likely to be related to early fibrosis in liver, decreased after drainage.

Real-time monitoring of keratin 5 expression during burn re-epithelialization1

BACKGROUND

Keratin is a major protein produced during epithelialization following burn injury and is a useful marker for assessing wound healing. Transgenic mice expressing enhanced green fluorescent protein (EGFP) driven by the keratin 5 (K5) promoter (K5GFP mice) were used to monitor keratin expression, and thus, re-epithelialization of burn wounds.

MATERIALS AND METHODS

K5GFP transgenic mice were created using conventional techniques, with PCR and Southern blot confirmation of transgene incorporation, followed by selection of the line with the most intense and consistent basal epithelial EGFP expression. Epi-fluorescent microscopy of 24 K5GFP mouse flanks and 10 negative littermate controls was used to characterize EGFP intensity, before wounding and serially for 30 days after administration of a standardized burn wound and excision. Biopsy sections of K5GFP and negative control mice were stained with K5 antibody and imaged with confocal microscopy to characterize the distribution of EGFP and K5 at baseline and after injury and to examine the correlation between K5 expression and EGFP expression during healing.

RESULTS

Green fluorescence intensity increased at the advancing wound margin of burned K5GFP mice, reaching a maximum between days 12 and 15 post-burn and then decreasing as healing completed. K5 and EGFP expression increased in parallel in burned K5GFP mice as demonstrated by confocal microscopy.

CONCLUSION

EGFP expression correlated with K5 expression during wound healing and therefore serves as a good marker of re-epithelialization. This transgenic model allows noninvasive, real-time assessment of in vivo K5 expression and will be useful in the study of wound healing.

Immunohistological distribution of the tight junction components ZO-1 and occludin in regenerating human epidermis

BACKGROUND

Molecular characterization of tight junction proteins during the past few years has provided novel methods for studying these specialized junctions. Tight junctions have recently been characterized in the granular cell layer of human epidermis, and the role of these junctions in the epidermal barrier is now being re-evaluated.

OBJECTIVES

To investigate the expression of tight junction components during the re-epithelialization of suction blisters and the regeneration of the corneal layer after tape stripping.

METHODS

Suction blisters were induced in eight healthy volunteers, and skin biopsies were taken 4 or 6 days afterwards. The restoration of epidermal barrier function was evaluated by measuring water evaporation (WE) from the wound area. Tape stripping was performed on three volunteers to remove the corneal layer. The tissues were immunolabelled using indirect immunofluorescence or the avidin-biotin method.

RESULTS

Prior to the biopsies, WE from the blister wounds was markedly elevated in comparison with normal skin. In the epidermis surrounding the blister, occludin and ZO-1 were expressed in the granular cell layer only. In the hyperproliferative zone adjacent to the border of the blister, the expression of ZO-1 was redistributed into several spinous cell layers, while occludin expression was restricted to the upper epidermis. In the leading edge of migrating keratinocytes, both proteins were expressed exclusively in the most superficial layer of keratinocytes. Double labelling for ZO-1 and involucrin showed expression of both proteins in the same layers of hyperproliferative keratinocytes, while the expression patterns were clearly different in the migrating keratinocytes.

CONCLUSIONS

Tight junctions of regenerating epidermis may provide a functional barrier prior to regeneration of the corneal layer.

Topical use of dexpanthenol in skin disorders

Pantothenic acid is essential to normal epithelial function. It is a component of coenzyme A, which serves as a cofactor for a variety of enzyme-catalyzed reactions that are important in the metabolism of carbohydrates, fatty acids, proteins, gluconeogenesis, sterols, steroid hormones, and porphyrins. The topical use of dexpanthenol, the stable alcoholic analog of pantothenic acid, is based on good skin penetration and high local concentrations of dexpanthenol when administered in an adequate vehicle, such as water-in-oil emulsions. Topical dexpanthenol acts like a moisturizer, improving stratum corneum hydration, reducing transepidermal water loss and maintaining skin softness and elasticity. Activation of fibroblast proliferation, which is of relevance in wound healing, has been observed both in vitro and in vivo with dexpanthenol. Accelerated re-epithelization in wound healing, monitored by means of the transepidermal water loss as an indicator of the intact epidermal barrier function, has also been seen. Dexpanthenol has been shown to have an anti-inflammatory effect on experimental ultraviolet-induced erythema. Beneficial effects of dexpanthenol have been observed in patients who have undergone skin transplantation or scar treatment, or therapy for burn injuries and different dermatoses. The stimulation of epithelization, granulation and mitigation of itching were the most prominent effects of formulations containing dexpanthenol. In double-blind placebo-controlled clinical trials, dexpanthenol was evaluated for its efficacy in improving wound healing. Epidermal wounds treated with dexpanthenol emulsion showed a reduction in erythema, and more elastic and solid tissue regeneration. Monitoring of transepidermal water loss showed a significant acceleration of epidermal regeneration as a result of dexpanthenol therapy, as compared with the vehicle. In an irritation model, pretreatment with dexpanthenol cream resulted in significantly less damage to the stratum corneum barrier, compared with no pretreatment. Adjuvant skin care with dexpanthenol considerably improved the symptoms of skin irritation, such as dryness of the skin, roughness, scaling, pruritus, erythema, erosion/fissures, over 3 to 4 weeks. Usually, the topical administration of dexpanthenol preparations is well tolerated, with minimal risk of skin irritancy or sensitization.

Topical synthetic inhibitor of matrix metalloproteinases delays epidermal regeneration of human wounds

Matrix metalloproteinases (MMPs) degrade extracellular proteins during epithelialization of wounds. To evaluate the biological significance of MMPs in epidermal healing, the synthetic broad-spectrum MMP inhibitor GM 6001 (also called Galardin and Ilomastat) was applied topically to standardized human wounds. GM 6001 (10 microg/microl) or vehicle alone was applied every second day onto 4 de-roofed 6 mm suction blister wounds on the volar forearm of healthy male volunteers for 12 days. GM 6001 delayed healing by 2-4 days as assessed macroscopically and microscopically. In situ hybridization or immunohistochemistry showed that MMP-1 (interstitial collagenase) was present in and MMP-2 (gelatinase A) close to laterally migrating keratinocytes whereas MMP-9 (gelatinase B) was seen during maturation of new epidermis. MMP-1 was undetectable in blister roofs (normal epidermis) and found in low levels in normal skin. Total MMP-1 activities increased about 100-fold in wounds, independent of treatment, compared to normal skin as analyzed by specific ELISA-based activity assay. By gelatin zymography, MMP-2, but not MMP-9, was detected in blister roofs and wound healing was associated with increased active MMP-2 and latent MMP-9 levels. GM 6001 prevented activation of MMP-2 and increased latent MMP-9 levels. GM 6001 delayed re-appearance of laminin-5, the synthesis of which correlated with epidermal regeneration. Restoration of stratum corneum, measured indirectly by transepidermal water loss, was also impaired (P<0.05) in the GM 6001 group. In conclusion, pharmacological MMP inhibition delayed epidermal regeneration in vivo, suggesting that MMPs are required to restore epidermis after epidermal ablation in humans.

Models for use in wound healing research: a survey focusing on in vitro and in vivo adult soft tissue

Many different factors must be considered before selecting a wound healing model to use for a specific study. A wide variety of models have been developed that examine different aspects of the repair response, both in vitro and in vivo. In this review article, we focus on those systems that are most widely used for studies on adult soft tissue healing. Advantages and disadvantages of each are discussed, along with relevant background information to help guide decision-making.

Delayed restoration of epidermal barrier function after suction blister injury in patients with diabetes mellitus

AIMS

Diabetes mellitus is a risk factor for compromised wound healing. The present study examines the restoration of the epidermal barrier function using the suction blister wound model.

METHODS

The healing process was evaluated over time by measuring water evaporation (WE) and blood flow (BF) in the wound area. Seventeen Type 1 diabetic males and 11 non-diabetic control males were studied.

RESULTS

At the onset, the WE of diabetic patients was 116 +/- 11 g x m(-2) x h(-1) and that of controls 95 +/- 13 g x m(-2) x h(-1) (P < 0.001). On the second day, the WE of diabetic patients was 90 +/- 21 g x m(-2) x h(-1) and that of controls 60 +/- 24 g x m(-2) x h(-1) (P < 0.02). The most profound difference was encountered during the fourth day, when the WE of diabetic patients was 40 +/- 17 g x m(-2) x h(-1) and that of controls 14 +/- 8 g x m(-2) x h(-1) (P < 0.001). The value recorded on the fourth day was 37% of the onset value in diabetic patients and 16% in controls (P < 0.001). Eight days after wounding the values were close to that of normal skin in both diabetic and control subjects. At the onset, the BF was 93 +/- 20 (arbitrary units) in diabetic men and 112 +/- 18 in controls (P = 0.02). On the second, fourth and eighth day there was no significant differences.

CONCLUSIONS

The results suggest that restoration of the epidermal barrier function is delayed in the patients with diabetes. There were also a trend toward an initially weaker inflammatory response.

Increased prevalence of vitiligo, but no evidence of premature ageing, in the skin of patients with bp 3243 mutation in mitochondrial DNA in the mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes syndrome (MELAS)

The MELAS syndrome (mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes) belongs to the category of mitochondrial disorders. The most common molecular aetiology of the syndrome is a mutation at base pair (bp) 3243 in the mitochondrial genome (mtDNA). The phenotype is varied and, apart from central nervous system involvement, the patients with this mutation may present with neurosensory hearing loss, diabetes mellitus and cardiomyopathy. These phenotypes suggest that organs dependent on aerobic metabolism suffer most. We investigated the possible clinical and physiological manifestations of impaired energy metabolism in the skin of 28 patients with the bp 3243 mutation in mtDNA. Non-invasive sonography and laser Doppler flowmetry were used to measure skin thickness and the blood flow of the skin. Skin collagen synthesis was assayed from suction blister fluid. Evaporimetry was used to assess the re-epithelialization rate of suction blister wounds. Histochemistry and immunohistochemistry were used to evaluate the melanocytes and pigment in the skin. Vitiligo was found in three of the 28 patients (11%), which was markedly more than in the general population. Histological findings showed an absence of pigment, but an apparently normal distribution of melanocytes in the dermoepidermal junction. Seborrhoeic eczema and atopy were also somewhat more frequent. No features of premature ageing, such as a marked decrease in skin thickness, blood flow, collagen synthesis or re-epithelialization rate, were demonstrated.

Effects of PUVA and UVB treatments on restoration of epidermal barrier function and vascular response after suction blister injury in human skin in vivo

PUVA and UVB phototherapies are used in the treatment of psoriasis and other inflammatory skin diseases. Ultraviolet radiation causes inflammation and modulates cell kinetics in the skin. PUVA also has an inhibitory effect on skin DNA synthesis. In this study, the effects of PUVA and UVB treatments on epidermal would healing were examined using the suction blister wound model. The healing of the wound was studied indirectly by measuring water evaporation and blood flow in the wound area. On the fourth day, water evaporation was more abundant in PUVA-treated patients (42 +/- 5 g/m2h) than in UVB treated (36 +/- 4 g/m2h) or control patients (27 +/- 3 g/m2h) (analysis of variance, the least significant difference test at a level of 0.05). The P value for the difference of means between the PUVA and control groups was 0.014. Blood flow was also more abundant during the fourth (PUVA 162 +/- 11 arbitrary units, UVB 122 +/- 10, controls 115 +/- 15) and sixth (PUVA 108 +/- 18, UVB 73 +/- 17, controls 57 +/- 13) day in PUVA treated patients (analysis of variance, the least significant difference test at a level of 0.05). The results suggest that PUVA treatment decreases the restoration of the epidermal barrier function. The PUVA-treated patients also showed a more intense and prolonged vascular response that may be due to PUVA-related inflammation.