Thermolysin treatment: a new method for dermo-epidermal separation

Delivery of small hydrophilic molecules across the stratum corneum: Identification of model systems and parameters to study topical delivery of free amino acids

Free amino acids (FAAs) constitute the largest component (∼40 %) of the so-called natural moisturizing factors of the skin. Their level declines in dry skin conditions and one strategy to overcome this problem may involve the topical delivery of FAAs through appropriate strategy. The objective of the present study was therefore to identify alternative skin models and study the corneocyte-water partition coefficients (KCOR/W) and permeation coefficient (KP) of 18 FAAs. The KCOR/W was studied using standard protocols and the permeation studies were conducted using Franz diffusion cell. The results indicate that the FAAs have high partitioning behavior to the corneocytes. The KCOR/W values of the human COR and that of pig ear skin were better correlated with each other than that of keratin isolated from chicken feathers. The presence of lipid in the stratum corneum (SC), initial concentration of the FAAs, and permeation enhancers affect the KCOR/W. The FAAs have low permeation into the SC which suggests the need for permeation enhancers in designing dosage form containing these compounds. Even though the investigated mathematical models show good prediction of the Kp values, better prediction could be obtained by considering factors such as the possible entrapment of the FAAs by the CORs.

Comparison of Two Human Skin Cell Isolation Protocols and Their Influence on Keratinocyte and Fibroblast Culture

For the development of advanced therapies, the use of primary cells instead of cell lines is preferred. The manufacture of human tissue-engineered skin substitutes requires efficient isolation and culture protocols allowing a massive expansion of the cells in culture from an initial specimen of a minimal size. This study compared two skin cell isolation protocols, routinely applied in two clinical laboratories. Epithelial (keratinocytes) and dermal (fibroblasts) cells were isolated and cultured from three human skin biopsies (N = 3). The two-step digestion protocol (LOEX-Protocol) firstly used thermolysin to enzymatically disrupt the dermal-epidermal junction while, for the one-step digestion protocol (UPCIT-Protocol), mechanical detachment with scissors was applied. Then, the epidermal and dermal layers were digested, respectively, to achieve cell isolation. The cell size, viability, yield and growth were analyzed over five passages (P). The colony-forming efficiency (CFE) and Keratin 19 (K19) expression of epithelial cells were also assessed after P0 and P1. Regarding the dermal cells, no significant differences were observed in the tested parameters of isolation and culture. However, for the epithelial cells, viability was higher (93% vs. 85%) and the number of cells extracted per cm2 of skin was 3.4 times higher using the LOEX-Protocol compared to the UPCIT-Protocol. No significant difference was observed for any parameter once the keratinocytes were cultured from P1 to P4. The CFE and K19 expression decreased from P0 to P1 in both protocols, probably due to the culture process. This study shows that both protocols enable the efficient isolation of skin dermal and epithelial cells and subsequent culture to produce grafts destined for the treatment of patients.

Engineering diabetic human skin equivalent for in vitro and in vivo applications

The prevalence of diabetes is increasing worldwide. Diabetes contributes to 70% of all non-traumatic lower-limb amputations, which are directly caused by diabetic foot ulcers (DFU) that are difficult to heal. Non-healing diabetic ulcers represent one of modern society’s most difficult medical challenges. One of the promising initiatives to treat DFU is the grafting of autologous skin or stimulating the skin cells at the edge of the wound to proliferate and close the wound. The present study was to engineer a diabetic human skin equivalent (DHSE) that contains fibroblasts and keratinocytes extracted from the skin collected from diabetic patients. The DHSE was used to investigate whether exposure to low-intensity electrical stimulation (ES) could promote diabetic cell activity. The ES was generated by a direct current (DC) electric field of 20 or 40 mV/mm. We demonstrated that the fibroblasts and keratinocytes could be extracted from older diabetics, cultured, and used to engineer DHSE. Interestingly, the exposure of DHSE to ES led to a structural improvement through tissue stratification, increased Ki-67 expression, and the deposition of basement membrane proteins (laminin and type IV collagen). The DHSE exposed to ES showed a high level of keratin 5 and 14 expressions in the basal and supra-basal layers. The keratinocyte proliferation was supported by an increased secretion of the keratinocyte growth factor (FGF-7). Exposure to ES decreased the activity of metalloproteinases (MMP) 2 and 9. In conclusion, we extracted keratinocytes and fibroblasts from the skin of diabetic-old donors. These cells were used to engineer skin equivalents and demonstrate that ES can promote diabetic wound healing. This DHSE can be a promising tool for various in vitro studies to understand the wound healing mechanisms under chronic inflammatory conditions such as diabetes. The DHSE could also be used as an autologous substrate to cover the DFU permanently.

Regulatory T cells promote innate inflammation after skin barrier breach via TGF-β activation

Regulatory T cells (T_regs) use multiple mechanisms to attenuate inflammation and prevent autoimmunity. T_regs residing in peripheral (i.e., nonlymphoid) tissues have specialized functions; specifically, skin T_regs promote wound healing, suppress dermal fibrosis, facilitate epidermal regeneration, and augment hair follicle cycling. Here, we demonstrated that skin T_regs were transcriptionally attuned to interact with their tissue environment through increased expression of integrin and TGF-β pathway genes that influence epithelial cell biology. We identified a molecular pathway where skin T_regs license keratinocytes to promote innate inflammation after skin barrier breach. Using a single-cell discovery approach, we identified preferential expression of the integrin αvβ8 on skin T_regs Upon skin injury, T_regs used this integrin to activate latent TGF-β, which acted directly on epithelial cells to promote CXCL5 production and neutrophil recruitment. Induction of this circuit delayed epidermal regeneration but provided protection from Staphylococcus aureus infection across a compromised barrier. Thus, αvβ8-expressing T_regs in the skin, somewhat paradoxical to their canonical immunosuppressive functions, facilitated inflammation acutely after loss of barrier integrity to promote host defense against infection.

Dermal-Epidermal Separation by Enzyme

The skin contains three primary layers: epidermis, dermis, and hypodermis. Separation of epidermal components from dermis (dermal-epidermal separation) is an important basic investigation technique for pharmacology, toxicology, and biology. There are different systems of epidermal separation, including typical methods of chemical, enzyme, heat, etc. Each approach has advantages versus disadvantages, and thus the appropriate method should be chosen for a given research question. Here we described the method of enzyme separation.

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.

The impact of high-dose acetylcholine on bovine corneal epithelium

PURPOSE

Ion channels are formed when acetylcholine (ACh) combines with specific receptors on the postsynaptic membrane. We are testing whether this occurs in vitro in corneal epithelial cells when exposed to ACh, using intracellular ascorbic acid (AA) as a tracer.

METHODS

The corneal epithelium was separated from Bowman's membrane as an intact sheet with thermolysin (TL). These cells were incubated in a medium containing phospholine iodide (Phi) to block acetylcholinesterase (AChE) activity, and then, five different groups of specimens were examined: the basic level of ACh and AA in the cells was tested in groups I and II, respectively. In groups III-V, the culture medium was supplemented with AA, ACh and ACh+AA, respectively, and following 2 hr of incubation the cells were tested for AA. AA was determined by high-performance liquid chromatography (HPLC) with UV detection, and ACh by LC-MS/MS.

RESULTS

The ACh concentration in the corneal epithelial cells was 23.7 ng/mg wet weight. AA values were as follows: preexposure 0.17 mg/g. After exposure to AA, ACh and ACh+AA, the values were 0.30, 0.12 and 0.21 mg/g, respectively. The AA concentration mechanism of the corneal epithelium was intact despite exposure to Phi and ACh.

CONCLUSION

The main observation is that the AA content of the corneal epithelium drops in response to ACh exposure. Various explanations are discussed, in particular the possibility that ACh exposure may cause cell membrane leakage through pores (nicotinic receptors). This would be similar to the moderate membrane leakage (depolarization) in neural synapses in response to ACh release. Interesting in vivo consequences may occur when considering that AChE is extremely UV sensitive, as this substance could be a target at which actinic radiation may influence the ACh-AChE complex in this epithelium.

Comparison of the enzymatic and explant methods for the culture of keratinocytes isolated from human foreskin

Currently, culture and growth keratinocytes are important stages in achieving a reliable and reproducible skin tissue. In the present study, two different methods, enzymatic and explant methods, for keratinocytes isolation from human foreskin were compared. Foreskins were cut into 2-3 mm pieces and placed in trypsin at 4°C overnight for separation of the epidermis from the dermis. Subsequently, these samples were divided into two groups: i) Keratinocytes separated from the epidermis by trypsin and ii) by the explant method. These keratinocytes were divided into two groups: i) With no feeder layer and ii) onto a type I collagen scaffold. The cells were evaluated using immunocytochemistry and 4',6-diamidine-2'-phenylindole dihydrochloride (DAPI) staining. In the enzymatic treatment, after 7-10 days no attached cells were found in the cell culture dishes. In the explant method, keratinocytes were separated after ~24 h, attached rapidly and formed big colonies into a collagen scaffold. In the absence of a feeder layer, small colonies were developed with rapid loss of proliferation within 2-3 days. Keratinocytes showed positive immunoreactivity for the pan-cytokeratin marker and keratinocytes' nuclei were clearly observed. This method could be applied and developed as a component of skin substitutes to treat burns and wounds and also in laboratory testing.

Evaluation of embryonic age and the effects of different proteases on the isolation and primary culture of chicken intestinal epithelial cells in vitro

The present study evaluates the effects of embryonic age and proteolytic enzymes on the isolation and primary culture of chicken enterocyte and to establish an effective technique for chicken intestinal epithelial cell (IEC) cultivation. Fourteen-day-old, 16-day-old and 18-day-old embryos (average weight: 52.23 ± 0.76 g, 50.86 ± 0.99 g, 48.98 ± 1.03 g) were the source for preparation of enterocyte culture, and trypsin-ethylene diamine tetraacetic acid, collagenase, thermolysin and combination of collagenase and thermolysin were used for digestion medium. Optimal culture protocols were determined by qualitative assays of proliferation. Cells isolated by using 14-day-old embryo and collagenase obtain the best attachment and growth in culture, and the production of continuously growing IEC cultures. Thus, we conclude that the use of collagenase as a dissociating enzyme and 14-day-old embryo as a source can be advantageously applied to the isolation of chicken IEC and this method may be useful for various applications and basic studies of the intestinal tract concerning such objects as physiology, immunology and toxicology.

Harvesting the potential of the human umbilical cord: isolation and characterisation of four cell types for tissue engineering applications

The human umbilical cord (UC) has attracted interest as a source of cells for many research applications. UC solid tissues contain four cell types: epithelial, stromal, smooth muscle and endothelial cells. We have developed a unique protocol for the sequential extraction of all four cell types from a single UC, allowing tissue reconstruction using multiple cell types from the same source. By combining perfusion, immersion and explant techniques, all four cell types have been successfully expanded in monolayer cultures. We have also characterised epithelial and Wharton's jelly cells (WJC) by immunolabelling of specific proteins. Epithelial cell yields averaged at 2.3 × 10(5) cells per centimetre UC, and the cells expressed an unusual combination of keratins typical of simple, mucous and stratified epithelia. Stromal cells in the Wharton's jelly expressed desmin, α-smooth muscle actin, elastin, keratins (K12, K16, K18 and K19), vimentin and collagens. Expression patterns in cultured cells resembled those found in situ except for basement membrane components and type III collagen. These stromal cells featured a sustained proliferation rate up to passage 12 after thawing. The mesenchymal stem cell (MSC) character of the WJC was confirmed by their expression of typical MSC surface markers and by adipogenic and osteogenic differentiation assays. To emphasise and demonstrate their potential for regenerative medicine, UC cell types were successfully used to produce human tissue-engineered constructs. Both bilayered stromal/epithelial and vascular substitutes were produced, establishing the versatility and importance of these cells for research and therapeutic applications.

Collagen XII and XIV, new partners of cartilage oligomeric matrix protein in the skin extracellular matrix suprastructure

The tensile and scaffolding properties of skin rely on the complex extracellular matrix (ECM) that surrounds cells, vasculature, nerves, and adnexus structures and supports the epidermis. In the skin, collagen I fibrils are the major structural component of the dermal ECM, decorated by proteoglycans and by fibril-associated collagens with interrupted triple helices such as collagens XII and XIV. Here we show that the cartilage oligomeric matrix protein (COMP), an abundant component of cartilage ECM, is expressed in healthy human skin. COMP expression is detected in the dermal compartment of skin and in cultured fibroblasts, whereas epidermis and HaCaT cells are negative. In addition to binding collagen I, COMP binds to collagens XII and XIV via their C-terminal collagenous domains. All three proteins codistribute in a characteristic narrow zone in the superficial papillary dermis of healthy human skin. Ultrastructural analysis by immunogold labeling confirmed colocalization and further revealed the presence of COMP along with collagens XII and XIV in anchoring plaques. On the basis of these observations, we postulate that COMP functions as an adapter protein in human skin, similar to its function in cartilage ECM, by organizing collagen I fibrils into a suprastructure, mainly in the vicinity of anchoring plaques that stabilize the cohesion between the upper dermis and the basement membrane zone.

Influence of human adipose-derived stromal cells on Wnt signaling in organotypic skin culture

BACKGROUND

Human adipose-derived stromal cells (hASCs) produce various cytokines. Also, there is a growing opinion that a large proportion of the useful effects of cell therapy may be attributable to the secretion of cytokines. Several reports suggested beneficial effects of hASCs on skin. These include antioxidant activity, accelerated wound healing, whitening effects, and antiaging. We investigated the effect of hASCs on skin Wnt signaling, which is associated with skin regeneration and differentiation.

METHODS

Pieces of human skin were cocultured with hASCs, and 2 chambered transwell culture plates were used to prevent direct contact between hASCs and skin. In the control group, pieces of skin were cultured without hASCs. Wnt1, Axin2, TCF1, LEF1, and DKK1 mRNA expressions were quantitatively assessed using real-time polymerase chain reaction. The expression levels of β-catenin were compared using Western blot and immunohistochemical analyses.

RESULTS

The Wnt1 and LEF1 mRNA expression of cultured skin was positively influenced by the presence of hASCs in culture medium (P<0.05). The total β-catenin protein level in hASC-cocultured skin was higher than that of the control group. Immunohistochemical staining showed that the β-catenin-stained area of dermis was larger in the hASC-cocultured group than in the control group, and most of the positively stained cells in the dermis were fibroblasts.

CONCLUSIONS

The results of the current study showed that hASCs promoted canonical Wnt signaling in organotypic skin culture through paracrine effects, and the increased Wnt signaling was mainly due to dermal fibroblasts.

Epidermal growth factor variations in amniotic membrane used for ex vivo tissue constructs

INTRODUCTION

The amniotic membrane (AM) is used for engineering ex vivo tissue constructs used in ocular surface reconstruction. Epidermal growth factor (EGF) content of the AM is believed to play a key role in supporting corneal epithelial cell expansion on AM. This study investigated EGF content in AM in relation to intra- and inter-donor variations and the effect of processing and preservation (handling).

METHODS

Fifteen human AM, both fresh and handled, were analyzed for EGF gene and protein expression by real-time polymerase chain reaction and ELISA, respectively.

RESULTS

EGF gene expression was predominantly seen in the AM epithelium (p<0.01). Similarly, EGF protein too was predominantly seen in the epithelial layer (p<0.01) for fresh and handled samples. EGF protein content varied between membranes (inter-donor) and at different sites within the same membrane (intra-donor). The highest EGF protein concentration was noted in the AM apical and mid-region epithelium. Significant EGF protein loss (p<0.01) was observed after handling.

CONCLUSION

There is a considerable variation in EGF content between and within donors. This is further affected by handling of the AM. Such variations could affect the clinical efficacy of tissue constructs. Current use of AM for ex vivo expansion of epithelial cells is not standardized and remains an area of concern.

Lrig1 expression defines a distinct multipotent stem cell population in mammalian epidermis

Lrig1 is a marker of human interfollicular epidermal stem cells and helps maintain stem cell quiescence. We show that, in mouse epidermis, Lrig1 defines the hair follicle junctional zone adjacent to the sebaceous glands and infundibulum. Lrig1 is a Myc target gene; loss of Lrig1 increases the proliferative capacity of stem cells in culture and results in epidermal hyperproliferation in vivo. Lrig1-expressing cells can give rise to all of the adult epidermal lineages in skin reconstitution assays. However, during homeostasis and on retinoic acid stimulation, they are bipotent, contributing to the sebaceous gland and interfollicular epidermis. beta-catenin activation increases the size of the junctional zone compartment, and loss of Lrig1 causes a selective increase in beta-catenin-induced ectopic hair follicle formation in the interfollicular epidermis. Our results suggest that Lrig1-positive cells constitute a previously unidentified reservoir of adult mouse interfollicular epidermal stem cells.

Thermolysin in human cultured keratinocyte isolation

BACKGROUND: When treating extensively burned patients using cultured epidermal sheets, the main problem is the time required for its production. Conventional keratinocyte isolation is usually done using Trypsin. We used a modification of the conventional isolation method in order to improve this process and increase the number of colonies from the isolated epidermal cell population. PURPOSE: To compare the action of trypsin and thermolysin in the keratinocyte isolation using newborn foreskin. METHODS: This method used thermolysin as it selectively digests the dermo-epidermal junction. After dermis separation, the epidermis was digested by trypsin in order to obtain a cell suspension. RESULTS: Compared to the conventional procedure, these experiments demonstrated that in the thermolysin group, the epidermis was easily detached from the dermis, there was no fibroblast contamination and there were a larger number of keratinocyte colonies which had a significant statistical difference. CONCLUSION: The number of colonies in the thermolysin group was significantly greater than in the trypsin group.

Effect of extracts from the Chinese and European mole cricket on wound epithelialization and neovascularization: in vivo studies in the hairless mouse ear wound model

Until the end of World War II, oily extracts from the European mole cricket, Gryllotalpa gryllotalpa Linné, were used for treating nonhealing wounds and burns. In traditional Chinese medicine, extracts from the Chinese mole cricket, Gryllotalpa africana Beauvois, have been used to treat boils, abscesses, and ulcers successfully for over two centuries and are still being used today. The aim of this study was twofold: first, to measure the effect mole cricket extracts have on wound epithelialization and neovascularization, and second, to identify the active compounds in the Chinese and German mole cricket extracts. For the first aim, the hairless mouse ear wound model was used. The findings showed that wounds treated with the mole cricket extracts epithelialized significantly faster than control wounds 12.7+/-0.9 and 13.2+/-1.4 days vs. 16.3+/-2.2 days (mean+/-SD, p<0.05), respectively. While the rate of wound neovascularization was significantly increased in the first 3 days postwounding from that point on, the rate in treated wounds was the same as in controls. To identify the active compounds in the mole cricket extracts, the extracts were fractionated and tested in a foreskin basal keratinocyte cell culture assay. In this assay, the migration of keratinocytes is similar to skin cell migration or reepithelialization in a healing wound. Using this method, we found the active compound in the mole cricket extracts to be linoleic acid methyl ester. All other fatty acid structures that were isolated were found to be inactive.

Application of physical force is essential to enrich for epidermal stem cells in primary human keratinocyte isolation

We present an improved method to isolate epidermal cells and to enrich stem cell populations. The new method utilizes magnetic stirring during digestion of skin with trypsin-EDTA (magnetic stirring method). The magnetic stirring method significantly improves both cell yield and colony-forming efficiency (CFE) relative to conventional epidermal cell isolation methods, such as those involving trypsin-EDTA only, thermolysin, or dispase. The cell yield and the total number of colony-forming cells per square centimeter of adult foreskin were 7,064,000 +/- 95,000 cells and 96,030 +/- 31,990 cells by the magnetic stirring method, 1,128,000 +/- 111,000 cells and 10,192 +/- 2941 cells by trypsin-EDTA only, 3,279,000 +/- 842,000 cells and 5851 +/- 2989 cells by thermolysin, and 1,443,000 +/- 507,000 cells and 8843 +/- 3388 cells by dispase, respectively. The CFE was 1.15 +/- 0.32% by magnetic stirring, 0.95 +/- 0.35% by trypsin-EDTA only, 0.28 +/- 0.12% by thermolysin, and 0.83 +/- 0.30% by dispase. The levels of surface beta(1)-integrin expression skewed to the right with the magnetic stirring method, implying increased proportion of beta(1)-integrin-bright cells (putative stem cells). Isolated keratinocytes developed fully differentiated epidermis when they were grafted onto nude mice. In conclusion, cell isolation by the magnetic stirring method is advantageous over conventional epidermal cell isolation methods, by which full range of basal epidermal cells including stem cells, transiently amplifying cells, and differentiating cells can be isolated and allow shorter expansion time for maximal coverage of wound sites after biopsies are taken from patients.

Serial cultivation of chicken keratinocytes, a composite cell type that accumulates lipids and synthesizes a novel β-keratin

The epidermis of birds differs from that of mammals by the presence of intracellular lipid droplets and the absence of sebaceous glands. We describe here the cultivation of chicken epidermal keratinocytes; these cells cannot be grown in medium supplemented with the usual fetal bovine serum even in the presence of supporting 3T3 cells, but they can grow from single cells in the presence of supporting 3T3 cells and 10% chicken serum. As revealed by their cell structure, their protein composition, and their gene expression, chicken keratinocytes possess the general properties of mammalian keratinocytes. They ultimately undergo in culture a process of terminal differentiation in which their nucleus is destroyed and a cornified envelope is formed. Chicken keratinocytes also show important properties that mammalian keratinocytes do not possess: they accumulate neutral lipids, usually in the form of a single perinuclear droplet; they accumulate carotenoids; they synthesize beta-keratins; and their multiplication requires a non-lipid factor, present in chicken serum but not in fetal calf serum. The lipid-synthesizing function of sebocytes in mammals is carried out by the keratinocytes themselves in birds. The availability of cultured chicken keratinocytes should allow studies that were hitherto impossible such as the tracing of the keratinocyte lineage during development of the chicken embryo and the investigation of the complete life cycle of viruses that require specific chicken keratinocyte products (such as Marek's disease virus).

Basonuclin 2: an extremely conserved homolog of the zinc finger protein basonuclin

Basonuclin is a zinc finger protein specific to basal keratinocytes and germ cells. In keratinocytes, basonuclin behaves as a stem cell marker and is thought to be a transcription factor that maintains proliferative capacity and prevents terminal differentiation. The human gene is located on chromosome 15. We have discovered in the chicken the existence of basonuclin 2, a basonuclin homolog. We also report the entire sequence of mouse and human basonuclin 2; the corresponding genes are located on mouse chromosome 4 and human chromosome 9. Although the amino acid sequence of basonuclin 2 differs extensively from that of basonuclin 1, the two proteins share essential features. Both contain three paired zinc fingers, a nuclear localization signal, and a serine stripe. The basonuclin 2 mRNA has a wider tissue distribution than the basonuclin 1 mRNA: it is particularly abundant in testis, kidney, uterus, and intestine. The extreme conservation of the basonuclin 2 amino acid sequence across vertebrates suggests that basonuclin 2 serves an important function, presumably as a regulatory protein of DNA transcription.

Time and Dose-related Ultraviolet B Damage in Viable Pig Skin Explants Held in a Newly Developed Organ Culture System¶

For facilitating photochemical and toxicological studies an ex vivo skin model was developed in our laboratory using skin from domestic pigs. The model comprised the use of a complete skin piece, including the dermis and stratum corneum, of bigger areas to make future topical applications easier. Fully differentiated skin explants (5 x 50 mm, thickness 5 mm) were irradiated with ultraviolet B (UVB; 1-10 kJ/m2; 6 W/m2). Directly thereafter they were brought in culture (Dulbeccos modified Eagles medium containing hydrocortisone; air/liquid interface) for a maximum of 144 h. In nonirradiated skin explants, signs of tissue degeneration were observed after 48 h in culture (hematoxylin and eosin, light microscope). However, keratinocytes, isolated enzymatically (thermolysin and trypsin) at different time intervals in culture from nonirradiated skin explants showed negligible loss in viability (trypan blue exclusion) and increased apoptosis (terminal deoxynucleotidyl transferase-mediated deoxy uridine triphosphatase nick end labeling assay) for up to 72 h. Explants irradiated with a single dose of UVB showed a clear and reproducible dose- and time-dependent tissue degeneration, loss in keratinocyte viability and increase in apoptosis compared with nonirradiated explants at the same time interval. In conclusion, the presently designed ex vivo pig skin model can be a useful and cheap tool for future investigations of short-term UV-induced effects in combination with phototoxic and photoprotective compounds.

Enzymatic dissociation of keratinocytes from human skin biopsies for in vitro cell propagation

Four techniques for dissociation of skin biopsies were compared to identify the method of choice for optimal expansion of isolated keratinocytes. Equivalent biopsies were obtained from 4 healthy human subjects and each divided into four parts. One part was minced and placed in a trypsinizing flask containing 0.05% trypsin and 0.01% ethylenediaminetetraacetic acid (EDTA). Released cells were harvested hourly. With the other parts, the epidermis was separated from the dermis after treatment with 0.5 mg/nml thermolysin, 2.5 mg/ml Dispase, or 0.17% trypsin and the epidermal portions were minced and incubated for 1 h in trypsin:EDTA. The cells were cocultivated with irradiated 3T3 fibroblasts to study the keratinocytes proliferative capacity. Freshly isolated cells were immunostained with anti-vimentin antibodies or grown in fibroblast-supportive conditions to detect the presence of human dermal fibroblasts. The mean number of cells dissociated per cm2 biopsy was higher after trypsin:EDTA digestion of a dermis-containing biopsy using a trypsinizing flask (4.0x 10(6) cells/cm2) compared to a biopsy where dermis-epidermis had been separated by thermolysin (2.8x 10(6) cells/cm2), Dispase (2.3x 10(6) cells/cm2) or trypsin (1.1 x 10(6) cells/cm2). Between 0.5% and 4% of the cells dissociated from a dermis-containing biopsy were human fibroblasts. This comprised more than twice the number of fibroblasts obtained by using epidermal/dermal split techniques. The proliferative capacity in primary and secondary culture was higher in cells isolated by trypsin:EDTA incubation in the trypsinizing flask or after epidermal-dermal separation using thermolysin, suggesting that Dispase or trypsin may have a more detrimental effect on the isolated keratinocytes. Our results show that dissociating the cells by trypsin:EDTA incubation in a trypsinizing flask or after epidermal-dermal separation using thermolysin, are preferable methods for isolating keratinocytes from human skin.

Water permeation barrier in isolated cutaneous newborn rat epidermis

Abnormal water barrier function occurs in irritated skin and certain cutaneous diseases. Methods have been compared for separating the epidermis (site of the barrier) from the whole skin without disturbing the barrier function. The epidermis was separated from newborn rat skin by (1) exposure to 10% trypsin at 4 degrees C for 16 h, (2) exposure to 0.2% dispase at 4 degrees C for 16 h, (3) heating for 50 s at 55 degrees C, (4) or heating for 40 s at 50 degrees C after the whole skin was kept in medium at the air-liquid interface for 1 day at 35 degrees C. Water permeation of the isolated epidermis was then measured immediately or after 3, 5, 8, and 10 days of maintenance at the air-liquid interface. The water permeation barrier constant (kp) was 1.9+/-0.9 cm/h in intact rat skin. At 0 day of maintenance, the kp of the epidermis was 2.1+/-0.9 after treatment with trypsin, 3.8+/-1.2 after dispase, and 4.3+/-1.4 after immediate heating, or 2.2+/-0.7 cm/h after culture and heating. The dispase and heating methods disrupted the barrier to a greater extent than did the trypsin and culture-heating methods. The latter two methods allowed the kp to be maintained at low levels for 8 days (kp for trypsin 2.8+/-0.9 and 2.5+/-0.8 for culture-heating). Epidermis isolated by the trypsin or culture-heating techniques and maintained at the air-liquid interface can be used to study the mechanism by which barrier function is disrupted by chemicals.

Bovine corneal stroma and epithelium reconstructed in vitro: characterisation and response to surfactants

In order to define safety profiles and proper handling procedures for new industrial products, it is essential to determine their potential for ocular irritation. The Draize test is normally employed but it involves using rabbits. There is today a great need for all researchers to limit the use of animals for laboratory experiments and to encourage the development and adoption of alternative in vitro methods to evaluate the potential toxicity of new products. This study proposes a three-dimensional model of bovine corneal stroma and epithelium that is not only easy to reproduce but may also be used in the toxicological field as an alternative to animal experimentation. The data presented here show that this model allows the growth of epithelium similar in features to in vivo epithelium. Basal cells are cube-shaped, whereas superficial areas are horizontally longer; desmosomes and 64 kDa keratin, as a marker for differentiation of corneal epithelial cells, are both expressed; the basal lamina is synthesised also. The 3-[4,5-dimethylthiazol-2-yl]2,5-diphenyltetrazolium bromide (MTT) assay was carried out on the model to evaluate the toxicity of some surfactants: benzalkonium chloride, Triton X-100, sodium dodecylsulphate and Tween 20. Since the in vitro data fit very well the results of the Draize test in vivo as reported in the literature, the three-dimensional culture may be used to predict the potential cytotoxicity of surfactants.

Permanent skin replacement using chimeric epithelial cultured sheets comprising xenogeneic and syngeneic keratinocytes

The present study was undertaken to evaluate the possibility of permanent skin replacement using chimeric xenogeneic-syngeneic graftable sheets previously obtained in vitro. Newborn (<3 days old) BALB/c and human keratinocytes were isolated and cocultured in different ratios as follows: 50% BALB/c to 50% human and 25% BALB/c to 75% human keratinocytes. Four to 5 days after culture and prior to their grafting, all chimeric sheets contained both cell types in ratios similar to those used to seed the initial chimeric cultures. Fourteen and 30 days after chimeric sheet grafting onto BALB/c mice dorsum, the newly generated cutaneous tissue showed a histologically well-organized epidermis presenting basal and suprabasal cell layers. Cutaneous cells in these structures secreted laminin and type IV collagen in blood vessels, and at ground level of the dermoepidermal junction there were signs of physiologically active skin. Cell phenotyping revealed the presence of only syngeneic keratinocytes, whereas xenogeneic cells were passively eliminated without a total rejection of the chimeric implant. This selective and passive elimination of xenogeneic keratinocytes went through cellular and humoral immunity activation. Data suggest that this chimeric culture method can be used for cutaneous therapies such as large congenital nevi, skin ulcers, and extensively burned skin. Indeed, for large third-degree wounded skin treatment, this culture method may shorten the time (4-5 weeks) needed for cell growth and graftable sheet production. Moreover, since the ultimate aim in allogeneic and xenogeneic transplantation is to achieve an immunological acceptance and tolerance to these foreign tissues, the chimeric culture approach may provide ways to lighten tolerance phenomena on cutaneous tissue.

Multiparameter flow cytometric characterization of epidermal cell suspensions prepared from normal and hyperproliferative human skin using an optimized thermolysin-trypsin protocol

Reliable flow cytometric analysis of normal and diseased skin requires pure epidermal single-cell suspensions. Several methods to separate the dermis from the epidermis are available. The proteolytic enzyme thermolysin separates the epidermis from the dermis at the lamina lucida and therefore permits reliable dermoepidermal separation. In the present study an optimized cell isolation procedure using thermolysin and trypsin is described, which is particularly suitable for punch biopsies. A 16-20-h (overnight) incubation of biopsies taken from normal and hyperproliferative skin with thermolysin (0.5 mg/ml) at 4 degrees C produced a selective separation of the dermis and epidermis. After a 30-min trypsin incubation (0.25 mg/ml) at 37 degrees C a cell suspension was produced which was characterized by minimal cell damage (cellular debris and clumps), a high recovery of basal cells and high quality DNA histograms. Furthermore, dermal contamination was very low. The thermolysin-trypsin separation methodology followed by triple-labelling flow cytometry provided a precise quantification of the percentage of keratin 10-positive cells, vimentin-positive cells and cells in S and G2M phases. Proliferative activity was selectively measured in the basal, the suprabasal and the non-keratinocyte compartment at various time intervals during epidermal regeneration after adhesive tape stripping. In contrast to the non-keratinocytes, the percentage of cells in S and G2M phases in the basal keratinocytes and in the suprabasal compartment increased 44-48 h after stripping. The increased proliferation following tape stripping was paralleled by an increased invasion of vimentin-positive cells into the epidermis and preceded by a decreased number of keratin 10-positive cells. Thermolysin-trypsin separation followed by three-colour flow cytometry permits a highly selective characterization of normal and hyperproliferative epidermis.

Early basement membrane formation following the grafting of cultured epidermal sheets detached with thermolysin or Dispase

The basement membrane zone is important for graft adhesion and stability. The aim of the present study was to visualize the regeneration of the basement membrane and determine the sequential appearance of its constituents in the early postgrafting period of cultured human epidermal sheets. A keratinocyte single cell suspension, devoid of dermal fibroblast contamination, was obtained from human skin by a two-step tissue digestion method with thermolysin and trypsin. After culturing, epidermal sheets were generated, detached enzymatically by incubating with thermolysin (for 20-30 min) or Dispase (for 45-60 min), and deposited on a muscular graft bed of athymic mice. Immunohistochemistry and ultrastructural analyses were performed on biopsies harvested 2, 4 and 21 days postgrafting. Bullous pemphigoid antigens and laminin were detected at the dermo-epidermal junction, showing an almost continuous line 2 days postgrafting. Type IV collagen was generally absent at this time, but it was detected 4 days postgrafting. Type VII collagen was labelled as a discontinuous line of increasing intensity from 2 to 21 days postgrafting. Ultrastructural analysis revealed hemidesmosomes and a discontinuous lamina densa 2 days postgrafting, and a complete basement membrane with a continuous lamina densa, hemidesmosomes and anchoring fibrils 21 days postgrafting. The sequence of appearance of major basement membrane components was similar for cultured sheets detached with thermolysin or Dispase. However, it differed from that of other wound healing models. Results are discussed in terms of the variable keratinocyte migration requirement between various wound healing models.

Surface ultrastructure of human dermis and wounds

Scanning electron microscopic observations of the de-epidermalized surfaces of wounds and control skin reveal the architecture of dermal collagen. At wound edges there is a transition from the normal regular rete peg structure through erratically shaped finger-like projections with buds, to the relatively flat surface of granulation tissue. A corresponding change in the ultrastructure of dermal collagen is seen from normal areas where bundles of thick fibres are made up from finer fibrils, through a transitional zone where only fine fibrils are visible, to the granulation tissue where a disorganised amorphous structure is seen. It is suggested that the fibrous tissue surface at the edges of healing wounds is extensively remodelled after it is covered by epidermal cells.

Improvement of human keratinocyte isolation and culture using thermolysin

We propose a modification of the conventional keratinocyte isolation method which has shown a significant improvement in the purity, colony forming efficiency (c.f.e.) and growth capacity of the isolated epidermal cell population. This method utilized thermolysin since it selectively digests the dermo-epidermal junction. Following separation from the dermis, the epidermis was digested with trypsin to obtain a single cell suspension. Compared with the conventional procedure, this isolation method was shorter and resulted in (i) cells displaying a higher colony forming efficiency, (ii) cells reaching confluence 1-3 days earlier, (iii) cells not contaminated by fibroblasts, (iv) a cell population containing all the basal layer keratinocytes. These cells were suitable for the establishment of primary cultures and could be subcultured. Such cell populations should be advantageous in studies of epithelial-mesenchymal interactions in which keratinocyte populations, free of fibroblasts, are desirable. In the treatment of extensively burned patients using cultured epidermal sheets, the main problem remains the time required for their production. Thus, the absence of fibroblast overgrowth of the keratinocyte cultures and the significantly reduced time to obtain confluent cultures and epidermal sheets with our method have very important implications for the treatment of large burn wounds.

Isolation and maintenance of the human pilosebaceous duct: 13-cis retinoic acid acts directly on the duct in vitro

The human pilosebaceous duct was isolated and maintained for 7 days in defined medium, and defined medium supplemented with 1 microM 13-cis retinoic acid. Freshly isolated ducts retained their in vivo morphology, showing a stratified squamous keratinizing epithelium. On maintenance there was a loss of basic duct architecture, and a significant reduction in the rate of [methyl-3H] thymidine uptake. The addition of 1 microM 13-cis retinoic acid resulted in an improved duct architecture and caused a further significant reduction in the rate of [methyl-3H] thymidine uptake. [Methyl-3H] thymidine autoradiography showed that freshly isolated ducts maintained their in situ pattern of cell division. It was difficult to discern the region of cell division in ducts maintained for 7 days, but the degree of graining reflected the measured rates of [methyl-3H] thymidine uptake into PCA precipitable material. The pattern of keratin synthesis of the freshly isolated duct was similar to patterns previously described for the duct in situ. This study reports the successful isolation and maintenance of the human pilosebaceous duct, and demonstrates that 13-cis retinoic acid acts directly at the level of the duct.

Method for quantifying cutaneous pigmentation in animals and preliminary study in humans

Synopsis A preoccupation with aesthetics and a real desire for social development has brought about an increase in the demand for safe, effective depigmenting products among African and Asian populations. For many years now, we have used an experimental model which uses the black mouse CS BL/6/JICO. As a result of developing needs and the necessity to check the results obtained from animals on humans, we have had to change the methodology in order to take into account the specific characteristics of human skin. After a summary of the protocol used on the mouse, here you will find a description of the technical changes which had to be made in order to carry out the study on humans. The results of a comparative test between the two models are given. This was carried out with a cosmetic preparation containing 2% hydroquinone introduced via a vector that facilitates its absorption. The depigmentation observed in the animal model was not found significant in humans. Taking into consideration the large number of differences between individuals, and in order to demonstrate a significant result on humans, it would be necessary to use a larger experimental group, treated for a longer period than that normally used with animals.

The effect of the proteolytic enzyme savinase on human plantar skin in vitro

The effect of the proteolytic enzyme savinase on human plantar skin in vitro was examined by light and electron microscopy to elucidate the morphological involvement of activated savinase in human epidermis. Light microscopic examination of incubated skin fragments demonstrated that the histological changes produced by savinase in the epidermis, including the stratum corneum, depended upon pH value, enzyme concentration and incubation time. After incubation in 0.1% savinase in phosphate buffer, pH 8.0, for 2 h at 35 degrees C, the stratum corneum revealed a serrated appearance at the free edges, the viable cell layers showed acantholysis, particularly in the suprabasal area. Digestion of cytoplasmic components of horny cells was observed by electron microscopy, but both cell membranes and desmosomes remained intact. Detachment of basal and spinous cells was found in the viable epidermal cell layers. The main cytoplasmic changes consisted of the presence of numerous cytoplasmic processes and vesicular formations. The results of this study indicate that activated savinase digests the intercellular substance in the viable cell layers, but it does not digest horny cells without physical rupture of the cell membrane.

An ultrastructural comparison of dermo-epidermal separation techniques

Dermo-epidermal separation through the lamina lucida is an essential technique for immunoblotting studies and for the diagnostic immunofluorescence of autoimmune bullous diseases. The most widely used methods of producing skin separation in the laboratory are suction blister induction and incubation in 1 molar sodium chloride. More recently the use of a proteolytic enzyme, thermolysin, has been described for this purpose. We examined the electron microscopic appearance of five suction blisters, five skin specimens separated by 1 M NaCl, and five treated with thermolysin. Both suction blister formation and treatment with 1 M NaCl resulted in a clean separation through the lamina lucida in all specimens examined. However specimens treated with thermolysin developed intra-epidermal separation in four cases without any lamina lucida separation in three. Suction blister formation was associated with hemidesmosome disruption. Incubation in 1 M NaCl remains the most reproducible, convenient, and reliable method of producing dermo-epidermal separation in the laboratory.

Two groups of bullous pemphigoid antigens are identified by affinity-purified antibodies

The bullous pemphigoid antigen was originally described as a 240-kD protein extracted from human epidermis, but a subsequent report has described patients' sera which react with epidermal proteins of molecular masses 240, 200, 180, 97, and 77 kD. We have evaluated the heterogeneity of the pemphigoid antigens identified by the sera of 10 patients with clinically typical bullous pemphigoid. We used indirect immunofluorescence and Western immunoblots of epidermal extracts prepared from epidermis separated by either 1 M salt or 20 mM EDTA to characterize the reactivity of both crude sera and affinity-purified antibodies. Affinity purification of antibodies was performed with either normal human epidermis or protein bands blotted onto nitrocellulose as immunoabsorbents. The anti-basement membrane antibody titers determined by indirect immunofluorescence on the saline- and EDTA-separated epidermis were identical. Despite this, Western blots of extracts prepared from EDTA-separated epidermis demonstrated greater amounts of the 240-kD antigen than saline split skin. Multiple antigens were recognized in epidermal extracts on Western blots by most crude BP sera, including bands at 240, 200, 160, and 100 kD. Different sera reacted with these antigens with a markedly different intensity, falling into two major groups, those bearing antibodies to the 240-200-kD antigens and those with antibodies to the 160-100-kD components. When epidermis was used as a substrate for affinity purification of bullous pemphigoid antibodies, the eluted antibodies reacted with multiple bands on Western blots, demonstrating the reactivity of anti-basement membrane zone antibodies with multiple proteins. Antibodies eluted from several individual bands of immunoblots were found to react with the basement membrane on indirect immunofluorescence. When these nitrocellulose-purified antibodies were reapplied to Western blots, they cross-reacted within two groups, the 240-200 kD antigens and the 160-100 kD antigens. We conclude that pemphigoid antigens are best demonstrated when EDTA-split skin is used for extraction and that different pemphigoid sera may contain antibodies to two separate groups of basement membrane zone antigens.

The use of cultured epithelial and endothelial cells for drug transport and metabolism studies

In an effort to develop novel strategies for delivery of drug candidates arising from rational drug design and recombinant DNA technology, pharmaceutical scientists have begun to employ the techniques of cell culture to study drug transport and metabolism at specific biological barriers. This review describes some of the general factors that should be considered in developing a cell culture model for transport studies and metabolism studies. In addition, we review in detail the recent progress that has been made in establishing, validating, and using cell cultures of epithelial barriers (e.g., cells that constitute the intestinal, rectal, buccal, sublingual, nasal, and ophthalmic mucosa as well as the epidermis of the skin) and the endothelial barriers (e.g., brain microvessel endothelial cells).