Anti-oxidant effects of the extracts from the leaves of Chromolaena odorata on human dermal fibroblasts and epidermal keratinocytes against hydrogen peroxide and hypoxanthine-xanthine oxidase induced damage

In cutaneous tissue repair, oxidants and antioxidants play very important roles. In local acute and chronic wounds, oxidants are known to have the ability to cause as cell damage and may function as inhibitory factors to wound healing. The administration of anti-oxidants or free radical scavengers is reportedly helpful, notably in order to limit the delayed sequelae of thermal trauma and to enhance the healing process. Extracts from the leaves of Chromolaena odorata have been shown to be beneficial for treatment of wounds. Studies in vitro of these extracts demonstrated enhanced proliferation of fibroblasts, endothelial cells and keratinocytes, stimulation of keratinocyte migration in an in vitro wound assay, up-regulation of production by keratinocytes of extracellular matrix proteins and basement membrane components, and inhibition of collagen lattice contraction by fibroblasts. In this study, the anti-oxidant effects of both total ethanol and polyphenolic extracts from the plant leaves on hydrogen peroxide and hypoxanthine-xanthine oxidase induced damage to human fibroblasts and keratinocytes were investigated. Cell viability was monitored by a colorimetric assay. The results showed that for fibroblasts, toxicity of hydrogen peroxide or hypoxanthine xanthine oxidase on cells was dose-dependent. Total ethanol extract (TEE) at 400 and 800 microg/ml showed maximum and consistent protective cellular effect on oxidant toxicity at low or high doses of oxidants. The 50 microg/ml concentration of TEE also had significant and slightly protective effects on fibroblasts against hydrogen peroxide and hypoxanthine-xanthine oxidase induced damage, respectively. For keratinocytes, a dose-dependent relationship of oxidant toxicity was only seen with hydrogen peroxide but the protective action of the extract correlated with oxidant dosage. TEE at 400 and 800 microg/ml showed dose-dependent effects with both low and high concentration of oxidants. TEE at 50 microg/ml had no effect on keratinocytes. Pre-treatment with the extracts did not show a protective effect on cells. Polyphenolic extract exhibited a slight anti-oxidant effect. Protection of cells against destruction by inflammatory mediators may be one of the ways in which the extracts from the plant, C. odorata, contribute to wound healing.     

Celosia argentea Linn. leaf extract improves wound healing in a rat burn wound model

Celosia argentea (CA) is used in traditional medicine for sores, ulcers, and skin eruptions. The present study was aimed at investigating the healing efficacy of CA extract in an ointment formulated (10 % w/w) as an alcohol extract of CA using a rat burn wound model. Wound closure occurred earlier in the treated rats (15 days vs. 30 in the untreated group; p < 0.05). Granulation tissue collected on every fifth day of healing showed an increase in collagen and hexosamine content at a faster rate in the treated wounds. This correlated with the accelerated wound closure observed in the treated groups. To probe the cellular basis of this effect, we investigated the effect of this extract on two major cellular responses; cell proliferation and cell motility, in two key cell lineages, fibroblasts and keratinocytes. CA was not toxic at concentrations of < 3 microg/ml in fibroblasts and < 30 microg/ml in keratinocytes. The alcohol extract promoted cell motility and proliferation of primary dermal fibroblasts at 0.1-1.0 microg/ml but did not alter these responses in primary keratinocytes. In an initial examination of molecular mechanisms, we found that the CA extract did not alter fibroblast and keratinocyte responses to the wound repair-associated epidermal growth factor receptor ligands. In short, we demonstrate a salutary action of the CA extract on wound healing, and suggest that this may be due to mitogenic and motogenic promotion of dermal fibroblasts.     

The potential of a niacinamide dominated cosmeceutical formulation on fibroblast activity and wound healing in vitro

Knowledge on the intrinsic mechanisms involved in wound healing provides opportunity for various therapeutic strategies. The manipulation of dermal fibroblast proliferation and differentiation might prove to beneficially augment wound healing. This study evaluated the combined effects of niacinamide, l ‐carnosine, hesperidin and Biofactor HSP® on fibroblast activity. The effects on fibroblast collagen production, cellular proliferation, migration and terminal differentiation were assessed. In addition, the authors determined the effects on in vitro wound healing. The optimal concentrations of actives were determined in vitro. Testing parameters included microscopic morphological cell analysis, cell viability and proliferation determination, calorimetric collagen detection and in vitro wound healing dynamics. Results show that 0·31 mg/ml niacinamide, 0·10 mg/ml l ‐carnosine, 0·05 mg/ml hesperidin and 5·18 µg/ml Biofactor HSP® proved optimal in vitro. The results show that fibroblast collagen synthesis was increased alongside with cellular migration and proliferation.     

In vitro studies on the antioxidant and growth stimulatory activities of a polyphenolic extract from Cudrania cochinchinensis used in the treatment of wounds in Vietnam

The leaves of Cudrania cochinchinensis, a Vietnamese folk remedy, have been suggested as a beneficial agent for wound healing. Animal studies and clinical observations in Vietnam have shown positive wound healing activity. We studied the effects of a polyphenolic extract from the plant on the proliferation of cells in culture and their response to oxidative damage by hydrogen peroxide. Fibroblasts were incubated with different concentrations of the extract in 0.4% fetal calf serum, and proliferation was monitored by a colorimetric assay. Cell damage was induced by exposure to hydrogen peroxide 7 x 10(-5) mol/L for 3 hours. The same colorimetric assay was used to assess cell damage and the protective effect of the extract against oxidative damage. The extract at low concentrations (0.1 to 5 microg/ml) had a stimulatory effect on fibroblast growth. The effect was significant by 7 days after the addition of the extract and was strongest at a concentration of 1 microg/ml of extract (p< or = 0.01). The extract at concentrations of 5 or 50 microg/ml protected fibroblasts and endothelial cells against hydrogen peroxide-induced damage. Pretreatment with the extract or exposure to extract simultaneously with hydrogen peroxide gave only partial protection against oxidative damage, whereas a combination of the two treatments gave complete protection (p< or = 0.005). Stimulation of fibroblast proliferation and protection of cells against destruction by inflammatory mediators may be ways in which the polyphenolic substances from the plant, Cudrania cochinchinensis, contribute to wound healing.     

Bioactive interleukin-8 is expressed in wounds and enhances wound healing

BACKGROUND: Wound healing is a sequential biological process that involves the integration of chemotaxis of neutrophils, mitosis and migration of keratinocytes, and remodeling of the scar, all of which are regulated by specific soluble mediators. To modulate wound healing specific mediators have to be identified and functionally characterized. Therefore we addressed this study on the polymorphonuclear leukocyte (PMN) attractant interleukin-8 (IL-8) and its function in epidermal wound healing. MATERIALS AND METHODS: Peptide purification, bioassays for PMN chemotaxis, and sequential IL-8 measurements were performed on human wound fluid from burn blisters and skin graft donor sites. Histology for IL-8 immunoreactivity was included. In vitro human keratinocytes were assayed for proliferation, migration, and integrin expression after IL-8 treatment. Wounding experiments with topical IL-8 were performed in a chimeric mouse model. RESULTS: IL-8 was found to be the major bioactive chemoattractant for PMNs in human blister and skin graft donor site wound fluids (mean levels ranging from 173 ng/ml Postoperative Day (POD) 1 to 2130 ng/ml (POD 5)). Released intracellular epidermal IL-8 immunoreactivity at the wound edge was considered as an immediate source of IL-8 while NH(2)-terminal analysis revealed the 77-amino-acid residue form as a second source of IL-8 possibly PMN derived. In vitro experiments on the effect of recombinant human (rh) IL-8 on keratinocyte proliferation revealed a rise in cell number (4.8-fold, ED(50) = 0.6 ng/ml), which was accompanied by an increase in cells in S phase and overexpression of the integrin subunit alpha6. In vivo topically applied IL-8 (1 microg/ml) on human skin grafts in a chimeric mouse model enhanced reepithelialization in IL-8 treated animals over controls due to elevated numbers of mitotic keratinocytes. Wound contraction was significantly diminished by topical IL-8. CONCLUSIONS: These results indicate the sequential function of endogenous IL-8 in all phases of human wound healing. Topical IL-8 may be useful in impaired wound healing.     

Effect of Atropa belladonna L. on skin wound healing: Biomechanical and histological study in rats and in vitro study in keratinocytes, 3T3 fibroblasts, and human umbilical vein endothelial cells

The effect of Atropa belladonna L. (AB) aqueous extract on skin wound healing was studied in male Sprague–Dawley rats subjected to two parallel full-thickness skin incisions on the back. Specimens for histological evaluation were collected on days 2 and 5 whereas for biomechanical testing, they were collected on day 5. In the in vitro study, a different concentration of AB extract was used to test the differentiation of keratinocytes using a panel of selected antibodies, proliferation, and cell survival of 3T3 fibroblasts and human umbilical vein endothelial cells using the MTT-assay. Results of the in vivo experiments showed in AB-treated wounds a shortened process of inflammation and accelerated collagen formation, as well as significantly increased wound stiffness as compared with control tissues. The in vitro examination showed that control keratinocytes were cytokeratin 19 free, while samples exposed to the highest AB extract concentration expressed CK19. Moreover, all concentrations were stimulatory to human umbilical vein endothelial cell proliferation. In addition, only the AB extract at the lowest tested concentration increased fibroblast growth, but higher concentrations decreased cell survival. In conclusion, our results indicate that the AB water extract positively affects early phases of skin wound healing in rats. However, the in vitro results on the inverse relation between the concentration of the AB extract and its effects on cell proliferation may be important for future research.     

The effects of caffeine on wound healing

The purine alkaloid caffeine is a major component of many beverages such as coffee and tea. Caffeine and its metabolites theobromine and xanthine have been shown to have antioxidant properties. Caffeine can also act as adenosine‐receptor antagonist. Although it has been shown that adenosine and antioxidants promote wound healing, the effect of caffeine on wound healing is currently unknown. To investigate the effects of caffeine on processes involved in epithelialisation, we used primary human keratinocytes, HaCaT cell line and ex vivo model of human skin. First, we tested the effects of caffeine on cell proliferation, differentiation, adhesion and migration, processes essential for normal wound epithelialisation and closure. We used 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl tetrazolium bromide (MTT) proliferation assay to test the effects of seven different caffeine doses ranging from 0·1 to 5 mM. We found that caffeine restricted cell proliferation of keratinocytes in a dose‐dependent manner. Furthermore, scratch wound assays performed on keratinocyte monolayers indicated dose‐dependent delays in cell migration. Interestingly, adhesion and differentiation remained unaffected in monolayer cultures treated with various doses of caffeine. Using a human ex vivo wound healing model, we tested topical application of caffeine and found that it impedes epithelialisation, confirming in vitro data. We conclude that caffeine, which is known to have antioxidant properties, impedes keratinocyte proliferation and migration, suggesting that it may have an inhibitory effect on wound healing and epithelialisation. Therefore, our findings are more in support of a role for caffeine as adenosine‐receptor antagonist that would negate the effect of adenosine in promoting wound healing.     

地白忍煎剂对人角朊细胞增殖及抗氧化损伤的作用

目的　观察地白忍煎剂对人角朊细胞增殖和抗氧化损伤的生物学效应。　方法　体外培养人角朊细胞,分别加入不同浓度的地白忍煎剂,设不同培养时相点计数细胞增殖率并绘制细胞生长曲线,比较细胞增殖速度的变化;在培养液中加入次黄嘌呤-黄嘌呤氧化酶、过氧化氢,模拟超氧阴离子（O     

Cell surface engineering using glycosylphosphatidylinositol anchored tissue inhibitor of matrix metalloproteinase‐1 stimulates cutaneous wound healing

The balance between matrix metalloproteinases and their endogenous tissue inhibitors (TIMPs) is an important component in effective wound healing. The biologic action of these proteins is linked in part to the stoichiometry of TIMP/matrix metalloproteinases/surface protein interactions. We recently described the effect of a glycosylphosphatidylinositol (GPI) anchored version of TIMP‐1 on dermal fibroblast biology. Here, cell proliferation assays, in vitro wound healing, electrical wound, and impedance measurements were used to characterize effects of TIMP‐1‐GPI treatment on primary human epidermal keratinocytes. TIMP‐1‐GPI stimulated keratinocyte proliferation, as well as mobilization and migration. In parallel, it suppressed the migration and matrix secretion of dermal myofibroblasts, and reduced their secretion of active TGF‐β1. Topical application of TIMP‐1‐GPI in an in vivo excisional wound model increased the rate of wound healing. The agent positively influenced different aspects of wound healing depending on the cell type studied. TIMP‐1‐GPI counters potential negative effects of overactive myofibroblasts and enhances the mobilization and proliferation of keratinocytes essential for effective wound healing. The application of TIMP‐1‐GPI represents a novel and practical clinical solution for facilitating healing of difficult wounds.     

Streptolysin O enhances keratinocyte migration and proliferation and promotes skin organ culture wound healing in vitro

ML-05, a modified form of the hemolytic and cytotoxic bacterial toxin, streptolysin O, is currently being investigated as a treatment for collagen-related disorders such as scleroderma and fibrosis. Furthermore, ML-05 may be effective in promoting wound healing and alleviating the formation of hypertrophic scars and keloids. To investigate the effects of ML-05 on wound-healing processes, in vitro wound-healing scratch assays (using human primary epidermal keratinocytes and dermal fibroblasts) and a human skin organ culture wound model were utilized. ML-05 markedly enhanced keratinocyte migration and proliferation in wound scratch assays. ML-05 did not affect either proliferation or migration of dermal fibroblasts, indicating that ML-05's effects on cell migration/proliferation may be keratinocyte-specific. ML-05 was tested in a dose-dependent manner in a skin organ culture wound model using two different application methods: Through the culture media (dermal exposure) or direct topical treatment of the wound surface. ML-05 was found to accelerate wound healing as measured by reepithelialization, particularly after topical application. Therefore, ML-05 may have potential as a wound-healing agent that promotes reepithelialization through stimulation of keratinocyte migration and proliferation.     

bFGF对体外关节软骨细胞创伤愈合与增殖的影响

目的：探讨碱性成纤维细胞生长因子（ｂａｓｉｃ ｆｉｂｒｏｂｌａｓｔ ｇｒｏｗｔｈ ｆａｃｔｏｒ,ｂＦＧＦ）对关节软骨细胞创伤愈合与增殖行为的影响。方法;采用体外创伤愈合模型及ＭＴＴ比色方法,对软骨细胞创伤愈合与增殖行为进行分析。结果：ｂＦＧＦ浓度为５ｎｇ／ｍｌ时,即可显著促进软骨细胞创伤愈合,浓度为５０ｎｇ／ｍｌ时,其促进作用达到最大值。     

Green light emitting diodes accelerate wound healing: Characterization of the effect and its molecular basis in vitro and in vivo

Because light‐emitting diodes (LEDs) are low‐coherent, quasimonochromatic, and nonthermal, they are an alternative for low level laser therapy, and have photobiostimulative effects on tissue repair. However, the molecular mechanism(s) are unclear, and potential effects of blue and/or green LEDs on wound healing are still unknown. Here, we investigated the effects of red (638 nm), blue (456 nm), and green (518 nm) LEDs on wound healing. In an in vivo study, wound sizes in the skin of ob/ob mice were significantly decreased on day 7 following exposure to green LEDs, and complete reepithelialization was accelerated by red and green LEDs compared with the control mice. To better understand the molecular mechanism(s) involved, we investigated the effects of LEDs on human fibroblasts in vitro by measuring mRNA and protein levels of cytokines secreted by fibroblasts during the process of wound healing and on the migration of HaCat keratinocytes. The results suggest that some cytokines are significantly increased by exposure to LEDs, especially leptin, IL‐8, and VEGF, but only by green LEDs. The migration of HaCat keratinocytes was significantly promoted by red or green LEDs. In conclusion, we demonstrate that green LEDs promote wound healing by inducing migratory and proliferative mediators, which suggests that not only red LEDs but also green LEDs can be a new powerful therapeutic strategy for wound healing.     

In vitro toxicity of photodynamic antimicrobial chemotherapy on human keratinocytes proliferation

This in vitro experimental study has been designed to assess the effects of photodynamic antimicrobial chemotherapy (PACT) on human keratinocytes proliferation. Human keratinocytes (HaCaT) monolayers (～0.5 cm²) have been irradiated with 635 nm red laser light with a fluence of 82.5 or 112.5 J/cm² in the absence or presence of toluidine (TB). Cell proliferation, monolayer area coverage, cytokeratin 5 (K5) and filaggrin (Fil) expression, and metalloproteinase (MMP)-2 and MMP-9 activity were measured after 72 h from laser irradiation. HaCaT proliferation was reduced by TB staining. Cell exposure to both low- and high-fluence laser irradiation in both presence and absence of TB staining reduced their proliferation and monolayer area extension. Moreover both laser treatments were able to reduce K5 and Fil expression and MMP-9 production in keratinocytes not treated with TB. These data indicate that PACT could exert toxic effects on normal proliferating keratinocytes present around parodontal pockets. The observed reduced cell proliferation along with a reduced production of enzymes involved in wound healing could alter the clinical outcome of the patients treated with PACT.     

脂多糖对皮肤成纤维细胞生物学特性的影响及与创面愈合的关系

目的探讨脂多糖（lipopolysaccharide，LPS）对皮肤成纤维细胞增殖和胶原合成的影响，以研究细菌内毒素与皮肤创面愈合的关系。方法取正常皮肤按黄勇等方法行成纤维细胞培养后，分为1个对照组及6个实验组。实验组分别与终浓度为0．005、0．010、0．050、0．100、0．500和1．000μg／ml大肠杆菌LPS（E．coli055：B5）培养，对照组为DMEM培养。分别通过MTT比色法及细胞计数法观察各组1～9d吸光度（A）值和细胞数量的变化；于LPS加入后7d细胞处于融合状态时，通过^3H-脯氨酸掺入、胃蛋白酶消化法检测细胞胶原合成量的变化，并绘制细胞生长曲线。结果与对照组比较，0．005～0．500μg／ml组A值增加，于5～9d差异有统计学意义（P〈0．05）；1．000μg／ml组A值降低，于3～9d差异有统计学意义（P〈0．05）。与对照组比较，0．005～0．500μg／ml组促进细胞胶原合成，且0．100μg／ml组作用达高峰（P〈0．05），1．000μg／ml LPS抑制细胞胶原合成，差异有统计学意义（P〈0．05）。与对照组比较，0．005～0．500μg／ml组细胞数量明显增加，分别于3～6d、1～6d、3～6d、2～6d及3～6d时比较，差异均有统计学意义（P〈0．05）；1．000μg／ml组细胞数量明显降低，于2～9d差异有统计学意义（P〈0．05）。结论在一定浓度范围内LPS促进成纤维细胞增殖和胶原蛋白合成，但过高浓度LPS则产生抑制效应。提示一定量的细菌内毒素可能有利于皮肤创面愈合，当内毒素过多时将对创面愈合产生负面作用。     

Trehalose promotes functional recovery of keratinocytes under oxidative stress and wound healing via ATG5/ATG7

Wounds are in a stressed state, which precludes healing. Trehalose is a stress metabolite that protects cells under stress. Here, we explored whether trehalose reduces stress-induced wound tissue damage. A stress model was prepared by exposing human keratinocytes to hydrogen peroxide (H₂O₂), followed by trehalose treatment. Trehalose effects on expression of the autophagy-related proteins ATG5 and ATG7 and cell proliferation and migration were evaluated. For in vivo verification, a wound model was established in Sprague–Dawley rats, to measure the effects of trehalose wound-healing rate and reactive oxygen species (ROS) content. Histological changes during wound healing and trehalose's effects on ATG5 and ATG7 expression, necrosis, and apoptosis were examined·H₂O₂ stress increased ATG5 and ATG7 expression in vitro, but this was insufficient to prevent stress-induced damage. Trehalose further increased ATG5/ATG7 levels, which restored proliferation and increased migration by depolymerizing the cytoskeleton. However, trehalose did not exert these effects after ATG5 and ATG7 knockout. In vivo, the ROS content was higher in the wound tissue than in normal skin. Trehalose increased ATG5/ATG7 expression in wound tissue keratinocytes, reduced necrosis, depolymerized the cytoskeleton, and promoted cell migration, thereby promoting wound healing.     

Low concentration amino-bisphosphonates stimulate human keratinocyte proliferation and in vitro wound healing

Amino-bisphosphonates (N-BPs) are widely used to treat a great variety of clinical conditions involving altered calcium metabolism, as well as to prevent bone metastases. The use of N-BPs, however, display well-known side effects, including cellular toxicity, mainly at soft tissue and mucosal level, that arise from N-BPs ability to induce cell apoptosis when administered at clinically relevant concentrations. The aim of this study was to evaluate, in an in vitro wound healing model, the effect of N-BPs low concentration (10 nM-10 μM) stimulation on keratinocyte cellular behaviour. Human keratinocytes were treated with neridronate and zoledronate, two N-BPs with different chemical structure and clinical potency, but sharing a common pharmacological target: farnesyl pyrophosphate (FPP) synthase. Surprisingly, at the tested concentrations, both drugs stimulated keratinocytes proliferation, upregulating cytokeratin 5 while downregulating filaggrin expression, and wound healing ability, without any significant effect on matrix metalloproteinase (MMP)-9 activity. The lack of N-BPs effect on MMP-9 activity indicates that wound closure, in our experimental model, is mainly due to an increase in cell proliferation rather than to an increase in cell migration. Therefore, it can be hypothesised that the observed wound healing results could be ascribed to an N-BPs mediated reduction of FPP endogenous levels, thus suggesting new possible clinical applications for these compounds.     

Interleukin-8 levels and activity in delayed-healing human thermal wounds

There are numerous causes for slow or delayed wound healing. Because slowly healing wounds are often inflamed, we quantitated the inflammatory chemokine, interleukin-8, produced by slowly healing human burn wounds and compared this to interleukin-8 from healed wounds and normal intact skin. Interleukin-8 levels were increased significantly in unhealed wounds (19.7 ng/ml) compared to healed wounds (7.7 ng/ml) or normal skin (5.7 ng/ml). Interleukin-8 in these ranges was added to adult human keratinocytes and fibroblasts. Interleukin-8 significantly decreased keratinocyte replication but had no effect on fibroblast replication. The rate or final degree of fibroblast populated collagen lattice contraction was inhibited at interleukin-8 concentrations between 10 and 30 ng/ml, but not altered at concentrations below 10 ng/ml and above 100 ng/ml. The concurrent application of indomethacin at 10 microg/ml reversed this interleukin-8 induced inhibition. Interleukin-8 inhibited myosin ATPase activity, apparently by reducing the phosphorylation of nonmuscle myosin light chain. We conclude that elevated levels of interleukin-8 may be found during delayed healing, and these elevated interleukin-8 levels may directly contribute to retarded wound closure.     

In vitro human cord blood platelet lysate characterisation with potential application in wound healing

Platelets contain abundant growth factors and cytokines that have a positive influence on the migration and proliferation of different cell types by modulating its physiopathological processes. As it is known that human umbilical cord blood platelet lysate (UCB‐PL) contains a supraphysiological concentration of growth factors, in the present study, we investigated its effectiveness in wound‐healing processes. Human UCB‐PL was obtained by the freeze/thaw of platelet concentrate (1.1 × 10⁹ platelets/L), and its effect was evaluated on human or mouse endothelial cells, monocytes, fibroblasts, and keratinocytes in different concentrations. Human UCB‐PL was observed to have high levels of pro‐angiogenic growth factor than peripheral blood platelet‐rich plasma. Among the cell lines, different concentrations of human UCB‐PL were necessary to influence their viability and proliferation. For L929 cells, 5% of total volume was necessary, while for human umbilical vein endothelial cell, it was 10%. Cell migration on monocytes was increased with respect to the positive control, and scratch closure on keratinocytes was increased with respect to serum‐free medium with only 10% of human UCB‐PL. We concluded that the human UCB‐PL may be useful to produce a large amount of standard platelet concentrates sufficient for several clinical‐scale expansions avoiding inter‐individual variability, which can also be used as a functional tool for clinical regenerative application for wound healing.     

Effect of hyperbaric oxygen on human skin cells in culture and in human dermal and skin equivalents

A critical stage of cutaneous wound healing is the development and maturation of the epidermis. In the aged, and in certain pathologies, this repair process is compromised due to a variety of deficiencies, one of which is tissue oxygenation. Several phases of wound healing are dependent on adequate tissue oxygen levels, and hyperbaric oxygenation has been shown to transiently elevate these levels. The use of human cell monolayers, dermal equivalents and human skin equivalents provide excellent opportunities for studying wound healing using in vivo relevant models. The goal of this study was to examine the effect of hyperbaric oxygen on cell proliferation, differentiation, and matrix biosynthesis in monolayer cultures and epidermopoiesis in the developing skin equivalent. Normal human dermal fibroblasts, keratinocytes and melanocytes, dermal equivalents and skin equivalents were exposed to hyperbaric oxygen at pressures up to three atmospheres, for up to 10 consecutive daily treatments lasting 90 minutes each. Increase in fibroblast proliferation (cf., 30% at 1 atmosphere after 10 days treatment), was observed without a significant effect on proliferation of normal human melanocytes and glycosaminoglycan synthesis. Stimulation of collagen synthesis after two days of treatment was only significant at 1 atmosphere (about 20% increase) but this differential was not observed after 5 days of treatment. Hyperbaric oxygenation above 2 atmospheres, inhibited proliferation of fibroblasts and keratinocytes in cell monolayer cultures (e.g., a 10 day treatment at 3 atmospheres appeared cytostatic to keratinocytes). In contrast, hyperbaric treatment up to 3 atmospheres dramatically enhanced keratinocyte differentiation, and epidermopoiesis in the complete human skin equivalent. These results support the importance of hyperbaric oxygen therapy in wound healing, and should provide an insight into oxygen utilization during repair of peripheral human tissue. The results also show the utility of the human skin equivalent as a model for evaluation of parameters involved in wound healing.