Ex vivo Model of Human Skin (hOSEC) as Alternative to Animal use for Cosmetic Tests

Treatment of aged wound healing models with FGF2 and ABT-737 reduces the senescent cell population and increases wound closure rate

Delayed tissue repair in the aged presents a major socio-economic and clinical problem. Age-associated delay in wound healing can be attributed to multiple factors, including an increased presence of senescent cells persisting in the wound. Although the transient presence of senescent cells is physiologic during the resolution phase of normal healing, increased senescent cell accumulation with age can negatively impact tissue repair. The objective of the study was to test interventional strategies that could mitigate the negative effect of senescent cell accumulation and possibly improve the age-associated delay in wound healing. We utilised a 3D in vitro senescent fibroblast populated collagen matrix (FPCM) to study cellular events associated with senescence and delayed healing. Senescent fibroblasts showed an increase in anti-apoptotic B-cell lymphoma 2 (BCL-2) family proteins. We hypothesized that reducing the senescent cell population and promoting non-senescent cell functionality would mitigate the negative effect of senescence and improve healing kinetics. BCL-2 inhibition and mitogen stimulation (FGF2) improved healing in the in vitro senescent models. These results were confirmed with an ex vivo human skin biopsy model. These data suggested that modulation of the senescent cell population with soluble factors improved the healing outcome in our in vitro and ex vivo healing models.

An improved human skin explant culture method for testing and assessing personal care products

BACKGROUND

Cultured human skin models have been widely used in the evaluation of dermato-cosmetic products as alternatives to animal testing and expensive clinical testing. The most common in vitro skin culture approach is to maintain skin biopsies in an airlifted condition at the interface of the supporting culture medium and the air phase. This type of ex vivo skin explant culture is not, however, adequate for the testing of cleansing products, such as shampoos and body washes. One major deficiency is that cleansing products would not remain confined on top of the epidermis and have a high chance of running off toward the dermal side, thus compromising the experimental procedure and data interpretation.

MATERIALS AND METHODS

Here, we describe an improved ex vivo method for culturing full-thickness human skin for the effective testing and evaluation of skin care products by topical application.

RESULTS

This newly developed ex vivo human skin culture method has the ability to maintain healthy skin tissues for up to 14 days in culture. Importantly, the model provides a quick and safe way to evaluate skin care products at different time points after single or repetitive topical applications using a combined regimen of leave-on and wash-off. We found that the results obtained using the new skin culture method are reproducible and consistent with the data collected from clinical testing.

CONCLUSION

Our new ex vivo skin explant method offers a highly efficient and cost-effective system for the evaluation and testing of a variety of personal care products and new formulations.

First ex vivo cultivation of human Demodex mites and evaluation of different drugs on mite proliferation

BACKGROUND

Demodex spp. mites are the most complex resident of the human skin microbiome. Although they are considered commensals, they can be pathophysiologically relevant in inflammatory skin diseases like rosacea. Until now, there is no culture system available for these mites except for using live vertebrate hosts.

OBJECTIVES

Our aim was to establish an ex vivo culture of human Demodex mites and to characterize the sebogenesis-dependent mite density.

METHODS

Demodex mites were cultivated in pilosebaceous units of human skin explants, called human organotypic skin explant culture (hOSEC). Furthermore, different sebogenesis-modifying additives were evaluated. Mites and mite survival were evaluated using light and fluorescence microscopy.

RESULTS

After 90 days of incubation, living Demodex mites - including eggs, larvae and nymphs - were detected in the dissected skin samples. Incubation for 30 days with anabolic steroids (testosterone and trenbolone) as well as retinol and retinoic acid (isotretinoin) yielded a reduced mite density.

CONCLUSIONS

With this technique, mites can be cultivated ex vivo for the first time, thereby establishing new ways to investigate Demodex spp. The sebostatic effect of isotretinoin might explain the mechanism of action in the off-label treatment of rosacea. We anticipate our findings to be the basis of an accelerated research on our most complex commensal, its life, biology and physiology.

SH-29 and SK-119 Attenuates Air-Pollution Induced Damage by Activating Nrf2 in HaCaT Cells

Air pollution has been repeatedly linked to numerous health-related disorders, including skin sensitization, oxidative imbalance, premature extrinsic aging, skin inflammation, and increased cancer prevalence. Nrf2 is a key player in the endogenous protective mechanism of the skin. We hypothesized that pharmacological activation of Nrf2 might reduce the deleterious action of diesel particulate matter (DPM), evaluated in HaCaT cells. SK-119, a recently synthesized pharmacological agent as well as 2,2′-((1E,1′E)-(1,4-phenylenebis(azaneylylidene))bis(methaneylylidene))bis(benzene-1,3,5-triol) (SH-29) were first evaluated in silico, suggesting a potent Nrf2 activation capacity that was validated in vitro. In addition, both compounds were able to attenuate key pathways underlying DPM damage, including cytosolic and mitochondrial reactive oxygen species (ROS) generation, tested by DC-FDA and MitoSOX fluorescent dye, respectively. This effect was independent of the low direct scavenging ability of the compounds. In addition, both SK-119 and SH-29 were able to reduce DPM-induced IL-8 hypersecretion in pharmacologically relevant concentrations. Lastly, the safety of both compounds was evaluated and demonstrated in the ex vivo human skin organ culture model. Collectively, these results suggest that Nrf2 activation by SK-119 and SH-29 can revert the deleterious action of air pollution.

Strategies to apply 3Rs in preclinical testing

Animal experimentation has been fundamental in biological and biomedical research. To guarantee the maximum quality, efficacy and/or safety of products intended for the use in humans in vivo testing is necessary; however, for over 60 years, alternative methods have been developed in response to the necessity to reduce the number of animals used in experimentation, to guarantee their welfare; resorting to animal models only when strictly necessary. The three Rs (Replacement, Reduction, and Refinement), seek to ensure the rational and respectful use of laboratory animals and maintain an adequate projection in terms of bioethical considerations. This article describes different approaches to apply 3Rs in preclinical experimentation for either research or regulatory purposes.

Ex vivo model of human skin (hOSEC) for assessing the dermatokinetics of the anti-melanoma drug Dacarbazine

Alternative models to replace animals in experimental studies remain a challenge in testing the effectiveness of dermatologic and cosmetic drugs. We proposed a model of human organotypic skin explant culture (hOSEC) to assess the profile of cutaneous drug skin distribution, adopting dacarbazine as a model, and respective new methodologies for dermatokinetic analysis. The viability tests were evaluated in primary keratinocytes and fibroblasts, and skin by MTT and TTC assays, respectively. Then, dacarbazine was applied to the culture medium, and the hOSEC method was applied to verify the dynamics of skin distribution of dacarbazine and determine its dermatokinetic profile. The results of cell and tissue viability showed that both were considered viable. The dermatokinetic results indicated that dacarbazine can be absorbed through the skin, reaching a concentration of 36.36 µg/mL (18,18%) of the initial dose (200 µg/mL) after 12 h in culture. Histological data showed that the skin maintained its structure throughout the tested time that the hOSEC method was applied. No apoptotic cells were observed in the epidermal and dermal layers. No visible changes in the dermo-epidermal junction and no inflammatory processes with the recruitment of defense cells were observed. Hence, these findings suggest that the hOSEC concept as an alternative ex vivo model for assessing the dynamics of skin distribution of drugs, such as dacarbazine, and determining their respective dermatokinetic profiles.

A novel human ex vivo skin model to study early local responses to burn injuries

Burn injuries initiate numerous processes such as heat shock response, inflammation and tissue regeneration. Reliable burn models are needed to elucidate the exact sequence of local events to be able to better predict when local inflammation triggers systemic inflammatory processes. In contrast to other ex vivo skin culture approaches, we used fresh abdominal skin explants to introduce contact burn injuries. Histological and ultrastructural analyses confirmed a partial-thickness burn pathology. Gene expression patterns and cytokine production profiles of key mediators of the local inflammation, heat shock response, and tissue regeneration were analyzed for 24 h after burn injury. We found significantly increased expression of factors involved in tissue regeneration and inflammation soon after burn injury. To investigate purely inflammation-mediated reactions we injected lipopolysaccharide into the dermis. In comparison to burn injury, lipopolysaccharide injection initiated an inflammatory response while expression patterns of heat shock and tissue regeneration genes were unaffected for the duration of the experiment. This novel ex vivo human skin model is suitable to study the local, early responses to skin injuries such as burns while maintaining an intact overall tissue structure and it gives valuable insights into local mechanisms at the very beginning of the wound healing process after burn injuries.

Fully Three-Dimensional Bioprinted Skin Equivalent Constructs with Validated Morphology and Barrier Function

Development of high-throughput, reproducible, three-dimensional (3D) bioprinted skin equivalents (BPSEs) that are morphologically and functionally comparable to native skin tissue is advancing research in skin diseases, and providing a physiologically relevant platform for the development of therapeutics, transplants for regenerative medicine, and testing of skin products like cosmetics. Current protocols for the production of engineered skin grafts are limited in their ability to control 3D geometry of the structure and contraction leading to variability of skin function between constructs. In this study, we describe a method for the biofabrication of skin equivalents (SEs) that are fully bioprinted using an open-market bioprinter, made with commercially available primary cells and natural hydrogels. The unique hydrogel formulation allows for the production of a human-like SE with minimal lateral tissue contraction in a multiwell plate format, thus making them suitable for high-throughput bioprinting in a single print with fast print and relatively short incubation times. The morphology and barrier function of the fully 3D BPSEs are validated by immunohistochemistry staining, optical coherence tomography, and permeation assays.

Kinetic Cytokine Secretion Profile of LPS-Induced Inflammation in the Human Skin Organ Culture

Several in vitro models that mimic different aspects of local skin inflammation exist. The use of ex vivo human skin organ culture (HSOC) has been reported previously. However, comprehensive evaluation of the cytokine secretory capacity of the system and its kinetics has not been performed. Objective: the aim of the current study was to investigate the levels and secretion pattern of key cytokine from human skin tissue upon lipopolysaccharide (LPS) stimulation. HSOC maintained in an air–liquid interface was used. Epidermal and tissue viability was monitored by MTT and Lactate Dehydrogenase (LDH) activity assay, respectively. Cytokine levels were examined by ELISA and multiplex array. HSOCs were treated without or with three different LPS subtypes and the impact on IL-6 and IL-8 secretion was evaluated. The compounds enhanced the secreted levels of both cytokines. However, differences were observed in their efficacy and potency. Next, a kinetic multiplex analysis was performed on LPS-stimulated explants taken from three different donors to evaluate the cytokine secretion pattern during 0–72 h post-induction. The results revealed that the pro-inflammatory cytokines IL-6, IL-8, TNFα and IL-1β were up-regulated by LPS stimuli. IL-10, an anti-inflammatory cytokine, was also induced by LPS, but exhibited a different secretion pattern, peak time and maximal stimulation values. IL-1α and IL-15 showed donor-specific changes. Lastly, dexamethasone attenuated cytokine secretion in five independent repetitions, supporting the ability of the system to be used for drug screening. The collective results demonstrate that several cytokines can be used as valid inflammatory markers, regardless of changes in the secretion levels due to donor’s specific alterations.

An Engineered Infected Epidermis Model for In Vitro Study of the Skin's Pro-Inflammatory Response

Wound infection is a major clinical challenge that can significantly delay the healing process, can create pain, and requires prolonged hospital stays. Pre-clinical research to evaluate new drugs normally involves animals. However, ethical concerns, cost, and the challenges associated with interspecies variation remain major obstacles. Tissue engineering enables the development of in vitro human skin models for drug testing. However, existing engineered skin models are representative of healthy human skin and its normal functions. This paper presents a functional infected epidermis model that consists of a multilayer epidermis structure formed at an air-liquid interface on a hydrogel matrix and a three-dimensionally (3D) printed vascular-like network. The function of the engineered epidermis is evaluated by the expression of the terminal differentiation marker, filaggrin, and the barrier function of the epidermis model using the electrical resistance and permeability across the epidermal layer. The results showed that the multilayer structure enhances the electrical resistance by 40% and decreased the drug permeation by 16.9% in the epidermis model compared to the monolayer cell culture on gelatin. We infect the model with Escherichia coli to study the inflammatory response of keratinocytes by measuring the expression level of pro-inflammatory cytokines (interleukin 1 beta and tumor necrosis factor alpha). After 24 h of exposure to Escherichia coli, the level of IL-1β and TNF-α in control samples were 125 ± 78 and 920 ± 187 pg/mL respectively, while in infected samples, they were 1429 ± 101 and 2155.5 ± 279 pg/mL respectively. However, in ciprofloxacin-treated samples the levels of IL-1β and TNF-α without significant difference with respect to the control reached to 246 ± 87 and 1141.5 ± 97 pg/mL respectively. The robust fabrication procedure and functionality of this model suggest that the model has great potential for modeling wound infections and drug testing.

Experimental models and methods for cutaneous wound healing assessment

Wound healing studies are intricate, mainly because of the multifaceted nature of the wound environment and the complexity of the healing process, which integrates a variety of cells and repair phases, including inflammation, proliferation, reepithelialization and remodelling. There are a variety of possible preclinical models, such as in mice, rabbits and pigs, which can be used to mimic acute or impaired for example, diabetic and nutrition-related wounds. These can be induced by many different techniques, with excision or incision being the most common. After determining a suitable model for a study, investigators need to select appropriate and reproducible methods that will allow the monitoring of the wound progression over time. The assessment can be performed by non-invasive protocols such as wound tracing, photographic documentation (including image analysis), biophysical techniques and/or by invasive protocols that will require wound biopsies. In this article, we provide an overview of some of the most often needed and used: (a) preclinical/animal models including incisional, excisional, burn and impaired wounds; (b) methods to evaluate the healing progression such as wound healing rate, wound analysis by image, biophysical assessment, histopathological, immunological and biochemical assays. The aim is to help researchers during the design and execution of their wound healing studies.

Mimicking cigarette smoke exposure to assess cutaneous toxicity

Cigarette smoke stands among the most toxic environmental pollutants and is composed of thousands of chemicals including polycyclic aromatic hydrocarbons (PAHs). Despite restrict cigarette smoking ban in indoor or some outdoor locations, the risk of non-smokers to be exposed to environmental cigarette smoke is not yet eliminated. Beside the well-known effects of cigarette smoke to the respiratory and cardiovascular systems, a growing literature has shown during the last 3 decades its noxious effects also on cutaneous tissues. Being the largest organ as well as the interface between the outer environment and the body, human skin acts as a natural shield which is continuously exposed to harmful exogenous agents. Thus, a prolonged and/or repetitive exposure to significant levels of toxic smoke pollutants may have detrimental effects on the cutaneous tissue by disrupting the epidermal barrier function and by exacerbating inflammatory skin disorders (i.e. psoriasis, atopic dermatitis). With the development of very complex skin tissue models and sophisticated cigarette smoke exposure systems it has become important to better understand the toxicity pathways induced by smoke pollutants in more realistic laboratory conditions to find solutions for counteracting their effects. This review provides an update on the skin models currently available to study cigarette smoke exposure and the known pathways involved in cutaneous toxicity. In addition, the article will briefly cover the inflammatory skin pathologies potentially induced and/or exacerbated by cigarette smoke exposure.

Functional Testing of a Skin Topical Formulation In Vivo: Objective and Quantitative Evaluation in Human Skin Scarring Using a Double-Blind Volunteer Study with Sequential Punch Biopsies

Objective: Many topicals claim an efficacious role in skin scar management with limited evidence. Our aim is to present a clear format for functional testing of a skin scarring ointment, using noninvasive and invasive measurements, categorizing findings under the physiological, structural, and mechanical parameters of a scar. Approach: A double-blinded, randomized volunteer research study of 45 subjects receiving an ointment composing of natural ingredients against a widely used antiscarring topical used as a positive control with temporal sequential punch biopsies (up to 16 weeks) was evaluated using noninvasive quantitative devices and validated by gene and protein studies. Results: Outcome measures included physiological, mechanical, and structural features of scars. Significant non-invasive findings included an increase in skin hydration (p < 0.05) at week (W) 4, 8, and 12, and elasticity (W16; p = 0.009). These findings were validated by immunohistochemistry (IHC) and quantitative real-time PCR (qRT-PCR). Hyaluronic acid IHC (W4 p = 0.014, W12 p = 0.034, and W16 p = 0.042), qRT-PCR (W16 p = 0.049); Collagen I (W16 p = 0.034, and 0.049) IHC and qRT-PCR, respectively. Collagen III qRT-PCR (W12 p = 0.035, and W16 p = 0.32); elastin IHC (W12 p = 0.044); and fibronectin IHC (W4 p = 0.009, W12 p = 0.038, and W16 p = 0.026). Innovation: Utilizing this model allows for quantitative, objective evaluation of any topical, where previously there has been a paucity of relevant methods to evaluate their effect. Conclusions: The positive effect of a topical formulation with an unknown mechanism of action on early cutaneous scar maturation over progressive sequential time points is now evidenced using noninvasive and invasive techniques with the findings categorized on the basis of scarring parameters.

Nanofibered Gelatin-Based Nonwoven Elasticity Promotes Epithelial Histogenesis

Regarding tissue regeneration, mechanics of biomaterials gains progressive importance. Therefore, this study reports on in situ crosslinked electrospun gelatin nonwoven mats (NWMs) whose distinct modulus of elasticity (ME) promotes epithelial tissue formation in a graded manner. NWMs, comprising fiber diameters in various distributions, yield an ME of about 2.1, 3.2, and 10.9 kPa. A two-step approach of preclinical in vitro validation identifies the elasticity of 3.2 kPa as superior to the other, regarding the histogenetic epithelial outcome. Hence, this 3.2 kPa candidate NWM is colonized with oral mucosal epithelial keratinocytes in the absence or presence of mesenchymal fibroblasts and/or endothelial cells. Evaluation of epithelial histogenesis at days 1 to 10 occurs by colorimetric and fluorescence-based immunohistochemistry (IHCH) of specific biomarkers. These include cytokeratins (CK) 14, CK1, and involucrin that indicate different stages of epithelial differentiation, as well as the basement membrane constituent collagen type IV and Ki-67 as a proliferation marker. Intriguingly, histogenesis and IHCH reveal the best resemblance of the native epithelium by the NWM alone, irrespective of other cell counterparts. These findings prove the gelatin NWM a convenient cell matrix, and evidence that NWM mechanics is important to promote epithelial histogenesis in view of prospective clinical applications.

Comparison of various methods to analyse toxic effects in human skin explants: Rediscovery of TTC assay

Skin explants are a suitable model which can replace dermatological experiments on animals or human volunteers. In this study, we searched for a fast, cheap and reproducible method for screening skin explant viability after treatment with UVA radiation or/and chemical agents. We compared frequently used methods: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), neutral red (NR) and lactate dehydrogenase (LDH) activity assay with a rarely used 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) assay for the evaluation of UVA radiation and/or chlorpromazine and 8-methoxypsoralen effect as model agents. Histological analysis of skin explants was also performed by a simple haematoxylin-eosin method. Only the TTC assay was able to show the toxicity of model agents in a dose- and concentration-dependent manner. LDH assay was partially able to demonstrate results comparable to the TTC method, however, the agents' effect was less pronounced. The MTT and NR assays completely failed in the evaluation. Haematoxylin-eosin staining showed discrete structural changes in samples treated with UVA alone and CPZ+UVA, but only after 48h. Therefore, the method is not useful for screening of toxic or phototoxic effects either. In conclusion, the TTC assay was the most suitable for the evaluation of toxicity or phototoxicity in ex vivo skin.