Sensory restoration of the skin graft on a free muscle flap: experimental rabbit study.

Transplantation of a muscle flap with free skin graft for wound coverage is a common procedure in reconstructive microsurgery. However, the grafted skin has little or no sensation. Restoration of the sensibility of the grafted skin on the transferred muscle is critically important, especially in palmar hand, plantar foot, heel, and oral cavity reconstruction. The purpose of this study was to investigate the possibility of sensory restoration of the grafted skin on a trimmed muscle surface that has been sensory neurotized after sensory nerve-to-motor nerve transfer, using the rabbit gracilis muscle as an animal model. The ipsilateral saphenous nerve (sensory) was transferred to the motor nerve of the gracilis muscle for sensory neurotization. A 4 x 4-cm2 area of skin island over the midportion of the gracilis muscle was harvested as a full-thickness skin graft. The upper half of the gracilis muscle was then excised, becoming a rough surface. The harvested skin was reapplied on the trimmed rough surface of the muscle. After 6 months, retrograde and antegrade horseradish peroxidase labeling studies were performed through skin and muscle injection. The group with a free skin graft was compared with the group with an intact surface of the gracilis muscle. This study clearly shows that sensory nerves can regenerate and penetrate into the trimmed muscle surface and grow into the overlying grafted skin. However, if the muscle surface is intact as with the compared group, sensory reinnervation of the grafted skin is not possible.     

Reconstruction of composite through-and-through mandibular defects with a double-skin paddle fibular osteocutaneous flap

Microsurgical reconstruction of composite through-and-through defects of the oral cavity involving mucosa, bone, and external skin has often required two free flaps or double-skin paddle scapular or radial forearm flaps for successful functional and aesthetic outcomes. A safe, reliable technique using a double-skin paddle fibular osteocutaneous flap to restore the intraoral lining, mandibular bone, and external skin is described. A large elliptical or rectangular skin paddle is designed 90 degrees to the longitudinal axis of the fibula, over the junction of the middle and distal thirds of the lower leg, based only on the posterolateral septocutaneous perforators. This skin flap can be draped anteriorly and posteriorly over the fibular bone to reconstruct both the intraoral defect and the external skin defect. The area between the two skin islands of the intraoral flap and the external flap is deepithelialized and left as a dermal bridge between the two skin islands, as opposed to the creation of two separate vertical skin paddles, each based on a septocutaneous perforator. The transverse dimension of the flap can be as great as 14 cm, extending to within 1 to 2 cm of the tibial crest anteriorly and as far as the midline posteriorly, and with a length of up to 26 cm, this flap should be more than sufficient for reconstruction of most through-and-through defects. This technique has allowed the successful reconstruction of large composite defects, with missing intraoral lining, mandibular bone, and external skin, for 16 patients, with 100 percent survival of both skin islands in all cases and without the development of any orocutaneous fistulae.     

The composition and characteristics of skin and muscle collagens from a freshwater catfish grown in biologically treated tannery effuent water

The skin of catfish Gariepinus spp. reared in tannery effuent water (ETP) had an increased collagen content, decreased acid solubility and high carbohydrate association as compared with skin of normal fish. The skin collagen in either fish was composed of three distinct α chains with mobilities different from that of vertebrate type I α chains and two of these three chains were invariably present in the muscle collagen. The amino acid composition of ETP fish skin and muscle collagens were similar but were characterized by higher degrees of proline and lysine hydroxylation, indicating higher stability. Both the skin and muscle collagens had significantly high denaturation temperatures. Electron microscopy of in vitro reconstituted fibrils of skin and muscle collagens of ETP fish displayed defined periodicities of around 64 nm. This demonstrates that the polymorphism in skin collagen chains is not confined to marine fish. There was a close similarity in the composition of skin and muscle collagens and the ETP environment influences the solubility and stability of the skin collagen. It is hypothesized that the third chain may play a role in the anchorage of skin to muscle, as such chain composition is now evident in fish such as hake, cod and catfish where the musculature is strongly attached to the skin.     

The impact of skin colour on human photobiological responses

Terrestrial solar ultraviolet radiation (UVR) exerts both beneficial and adverse effects on human skin. Epidemiological studies show a lower incidence of skin cancer in people with pigmented skins compared to fair skins. This is attributed to photoprotection by epidermal melanin, as is the poorer vitamin D status of those with darker skins. We summarize a wide range of photobiological responses across different skin colours including DNA damage and immunosuppression. Some studies show the generally modest photoprotective properties of melanin, but others show little or no effect. DNA photodamage initiates non‐melanoma skin cancer and is reduced by a factor of about 3 in pigmented skin compared with white skin. This suggests that if such a modest reduction in DNA damage can result in the significantly lower skin cancer incidence in black skin, the use of sunscreen protection might be extremely beneficial for susceptible population. Many contradictory results may be explained by protocol differences, including differences in UVR spectra and exposure protocols. We recommend that skin type comparisons be done with solar‐simulated radiation and standard erythema doses or physical doses (J/m²) rather than those based solely on clinical endpoints such as minimal erythema dose (MED).     

Metabolism of Skin-Absorbed Resveratrol into Its Glucuronized Form in Mouse Skin

Resveratrol (RESV) is a plant polyphenol, which is thought to have beneficial metabolic effects in laboratory animals as well as in humans. Following oral administration, RESV is immediately catabolized, resulting in low bioavailability. This study compared RESV metabolites and their tissue distribution after oral uptake and skin absorption. Metabolomic analysis of various mouse tissues revealed that RESV can be absorbed and metabolized through skin. We detected sulfated and glucuronidated RESV metabolites, as well as dihydroresveratrol. These metabolites are thought to have lower pharmacological activity than RESV. Similar quantities of most RESV metabolites were observed 4 h after oral or skin administration, except that glucuronidated RESV metabolites were more abundant in skin after topical RESV application than after oral administration. This result is consistent with our finding of glucuronidated RESV metabolites in cultured skin cells. RESV applied to mouse ears significantly suppressed inflammation in the TPA inflammation model. The skin absorption route could be a complementary, potent way to achieve therapeutic effects with RESV.     

Identification and origin of oestradiol-binding protein in immature rat skin. Demonstration of oestrophilic alpha-foetoprotein synthesis and secretion by developing rat skin explants in culture.

Oestrophilic alpha-foetoprotein (alpha FP) is found in high concentrations in developing rat skin cytosol. Elevated levels of alpha FP observed in foetal-rat skin decreased during development, and the protein became undetectable after 3 weeks of postnatal life. The developmental profile of alpha FP in skin is different from that in foetal blood. alpha FP in skin arises as a result of its synthesis in situ in the epidermal cells. Synthesis of alpha FP in skin is demonstrated by linear incorporation of [14C]leucine into immunoprecipitable, intracellular alpha FP by skin explants during 6 h in culture. Secretion is demonstrated by incorporation into alpha FP in culture medium. The rate of alpha FP synthesis in skin also declined with age and its synthesis is completely switched off 2 weeks after birth. The skin alpha FP level during development is regulated by controlling the rate of its synthesis in skin. alpha FP synthesized and secreted by skin is immunologically, electrophoretically and, with respect to molecular weight and oestradiol-binding properties, similar to that found in foetal serum. alpha FP was also identified as the major oestradiol-binding protein present in newborn-rat skin or secreted by newborn-rat skin explants in culture.     

Physical characterization of the stratum corneum of an in vitro psoriatic skin model by ATR-FTIR and Raman spectroscopies

The stratum corneum is an important permeability barrier for the skin. The disorganization of the skin protective barrier characterizes some skin diseases such as psoriasis. Indeed, psoriatic skin is known to be more permeable than normal human skin. An in vitro human skin substitute may be obtained by the auto-assembly method. This method was adapted to produce psoriatic substitutes. FTIR spectroscopy is a well-established method to evaluate the order of hydrocarbon chains in terms of population of trans and gauche conformers. Using ATR-FTIR, we have compared the physicochemical properties of the stratum corneum in skin models derived from uninvolved and involved psoriatic cells with those derived from normal cells. Our results suggest that the stratum corneum of involved psoriatic skin substitutes is less organized than that of normal skin substitutes. Also, it seems that the properties of uninvolved psoriatic skin may vary with seriousness of the disease. The development of a new psoriatic skin model would be helpful in the design of new treatments and to increase the understanding of the mechanisms of this pathology.     

Advances in generation of three-dimensional skin equivalents: pre-clinical studies to clinical therapies

The inability of two-dimensional cell culture systems to adequately map the structure and function of complex organs like skin necessitates the development of three-dimensional (3D) skin models. A diverse range of 3D skin equivalents have been developed over the last few decades for studying complex properties of skin as well as for drug discovery and clinical applications for skin regeneration in chronic wounds, such as diabetic foot ulcers, where the normal mechanism of wound healing is compromised. These 3D skin substitutes also serve as a suitable alternative to animal models in industrial applications and fundamental research. With the emergence of tissue engineering, new scaffolds and matrices have been integrated into 3D cell culture systems, along with gene therapy approaches, to increase the efficacy of transplanted cells in skin regeneration. This review summarizes recent approaches to the development of skin equivalents as well as different models for studying skin diseases and properties and current therapeutic applications of skin substitutes.     

New insights into the pathogenesis of vitiligo: imbalance of epidermal cytokines at sites of lesions

Vitiligo is a skin disease that is caused by selective destruction of melanocytes and is characterized by white spots. Melanocytes and keratinocytes seem to exhibit a functional close relationship, mediated at least in part by keratinocyte-derived cytokines, which seem important for survival and activity of melanocytic cells. We wanted to investigate the hypothesis that in vitiligo the expression of epidermal cytokines may be modified compared with normal skin. In 15 patients with active, non-segmental vitiligo, biopsies were obtained from lesional, perilesional and non-lesional skin; normal skin from five healthy donors was also tested. Tissue sections were tested using immunohistochemistry for the expression of keratinocyte-derived cytokines with stimulating activity, such as granulocyte-monocyte colony stimulating factor (GM-CSF), basic fibroblastic growth factor (bFGF), and stem cell factor (SCF) or with inhibiting activity, such as interleukin 6 (IL-6) and tumour necrosis factor alpha (TNF-alpha) on melanocytes. Cytokine receptors and specific melanocytic markers were also investigated. No melanocyte was identified in lesional skin by means of specific markers or c-kit receptor, whereas in perilesional, non-lesional and healthy skin, melanocytes were found in similar number. In vitiligo skin a significantly lower expression of GM-CSF, bFGF and SCF was found, and a significantly higher expression of IL-6 and TNF-alpha was detected, compared with perilesional, non-lesional and healthy skin. In conclusion, we provided evidence that a significant change of epidermal cytokines exists in vitiligo skin compared with perilesional, non-lesional and healthy skin, suggesting that the cytokine production of epidermal microenvironment may be involved in vitiligo.     

The structure and mechanical design of rhinoceros dermal armour.

The collagenous dermis of the white rhinoceros forms a thick, protective armour that is highly specialized in its structure and material properties compared with other mammalian skin. Rhinoceros skin is three times thicker than predicted allometrically, and it contains a dense and highly ordered three-dimensional array of relatively straight and highly crosslinked collagen fibres. The skin of the back and flanks exhibits a steep stress-strain curve with very little 'toe' region, a high elastic modulus (240 MPa), a high tensile strength (30 MPa), a low breaking strain (0.24) and high breaking energy (3 MJm-3) and work of fracture (78 kJm-2). By comparison, the belly skin is somewhat less stiff, weaker, and more extensible. In compression, rhinoceros skin withstands average stresses and strains of 170 MPa and 0.7, respectively, before yielding. As a biological material, rhinoceros dorsolateral skin has properties that are intermediate between those of 'normal' mammalian skin and tendons. This study shows that the dermal armour of the rhinoceros is very well adapted to resist blows from the horns of conspecifics, as might occur during aggressive behaviour, due to specialized material properties as well as its great thickness.     

Rapid alignment of collagen fibers in the dermis of undermined and not undermined skin stretched with a skin-stretching device

A controlled, quantitative histochemical study was performed in five piglets to establish changes in undermined and not undermined stretched skin. The skin was stretched with a stretching device for 30 minutes to close a large skin defect. On each flank of the piglet, at a standard position, 9 x 9-cm wounds were created under general anesthesia. On one flank, the surrounding skin was undermined cranially and caudally over a 10-centimeter area. Sections of skin biopsies obtained during stretching were stained with picrosirius red and studied with routine light microscopy and polarized light microscopy in combination with image analysis. The length of collagen fibers was analyzed as a parameter of changes in the dermis resulting from skin stretching. This newly developed quantitative method appeared to be valid, specific, and reproducible, allowing for objective determination of changes in the length of the fibers in the plain of the sections. Changes in the orientation of collagen fibers in the dermis as a result of skin stretching were thereby determined. Epidermal thickness did not change significantly under the influence of stretching forces in both undermined and not undermined skin. However, the orientation of the collagen fibers changed significantly as a result of skin stretching. In undermined wounds, parallel alignment and elongation of the fibers in the plane of the sections was already observed after 15 minutes of stretching. The fibers became aligned in the direction of the stretching force, perpendicular to the wound margin. After 30 minutes of stretching, the mean major axes of the collagen fibers were longest in the plane of the sections (p < 0.001). This meant that elongation and parallel alignment of the collagen fibers had occurred. Stretching of not undermined skin for 15 minutes resulted in significantly stronger parallel alignment in the plane of the sections as compared with undermined skin. This was less well defined after 30 minutes of stretching in not undermined skin. It is concluded that skin stretching with a skin-stretching device for 30 minutes results in significant histomorphological changes of collagen fibers in the dermis of both undermined and not undermined skin. The fibers realign rapidly as a result of stretching forces and become aligned in the direction of the stretching force, perpendicular to the wound margin. These dynamic changes in collagen fibers explain the significantly decreased wound closing tension resulting from skin stretching and explain how skin stretches beyond its inherent extensibility.     

Metabolic changes in the skin of rats of various ages. Oxygen consumption and uptake of glucose

1. Parallel determinations of the oxygen consumption by skin slices with glucose or galactose as substrate and of the concentration of DNA of the skin of various ages of rats were carried out to study the metabolic changes of the skin with age. 2. Both the oxygen consumption and the DNA content of the skin decreased rapidly till the attainment of maturity; thereafter the rate of decrease in oxygen consumption was lower whereas the concentration of DNA was constant. The decrease in the oxygen consumption during the early developmental period is thus due to the loss of cells, but the decrease in the older rats may be due to a decline in the activity of the cells of the skin as a result of aging. 3. The uptake of glucose by the skin decreased with increasing age.     

Validity and reliability of Raman spectroscopy for carotenoid assessment in cattle skin

Carotenoids are powerful antioxidants capable of helping to protect the skin from the damaging effects of exposure to sun by reducing the free radicals in skin produced by exposure to ultraviolet radiation, and they may also have a physical protective effect in human skin. Since carotenoids are lipophilic molecules which can be ingested with the diet, they can accumulate in significant quantities in the skin. Several studies on humans have been conducted to evaluate the protective function of carotenoids against various diseases, but there is very limited published information available to understand the mechanism of carotenoid bioavailability in animals. The current study was conducted to investigate the skin carotenoid level (SCL) in two cattle skin sets – weaners with an unknown feeding regime and New Generation Beef (NGB) cattle with monitored feed at three different ages. Rapid analytical and sensitive Raman spectroscopy has been shown to be of interest as a powerful technique for the detection of carotenoids in cattle skin due to the strong resonance enhancement with 532 nm laser excitation. The spectral difference of both types of skin were measured and quantified using univariate and linear discriminant analysis. SCL was higher in NGB cattle than weaners and there is a perfect classification accuracy between weaners and NGB cattle skin using carotenoid markers as a basis. Further work carried out on carotenoid rich NGB cattle skin of 8, 12 and 24 months of age identified an increasing trend in SCL with age. The present work validated the ability of Raman spectroscopy to determine the skin carotenoid level in cattle by comparing it with established HPLC methods. There is an excellent correlation of R² = 0.96 between the two methods that could serve as a model for future application for larger population studies.     

The skin of fish as a transport epithelium: a review

The primary function of fish skin is to act as a barrier. It provides protection against physical damage and assists with the maintenance of homoeostasis by minimising exchange between the animal and the environment. However in some fish, the skin may play a more active physiological role. This is particularly true in species that inhabit specialised environmental niches (e.g. amphibious and air-breathing fish such as the lungfish), those with physiological characteristics that may subvert the need for the integument as a barrier (e.g. the osmoconforming hagfish), and/or fish with anatomical modifications of the epidermis (e.g. reduced epithelial thickness). Using examples from different fish groups (e.g. hagfishes, elasmobranchs and teleosts), the importance of fish skin as a transport epithelium for gases, ions, nitrogenous waste products, and nutrients was reviewed. The role of the skin in larval fish was also examined, with early life stages often utilising the skin as a surrogate gill, prior to the development of a functional branchial epithelium.     

Using Raman Spectroscopy in Studying the Effect of Propylene Glycol,Oleic Acid,and Their Combination on the Rat Skin

The permeability enhancement effect of oleic acid (OA) and propylene glycol (PG) as well as their (1:1 v/v) combined mixture was studied using rat skin. The percutaneous drug administration is a challenge and an opportunity for drug delivery. To date, there is limited research that illustrates the mechanism of penetration enhancers and their combinations on the skin. This project aims to explore the skin diffusion and penetration enhancement of PG, OA, and a combination of PG-OA (1:1 v/v) on rat skin and to identify the potential synergistic effect of the two enhancers utilizing Raman spectroscopy. Dissected dorsal skin was treated with either PG or OA or their combination for predetermined time intervals after which the Raman spectra of the treated skin were collected with the enhancer. A spectrum of the wiped and the washed skin were also collected. The skin integrity was tested before and after exposure to PG. The skin histology proved that the skin integrity has been maintained during experiments and the results indicated that OA disrupted rat skin lipid as evident by changes in the lipid peak. The results also showed that PG and OA improved the diffusion of each other and created faster, yet reversible changes of the skin peaks. In conclusion, Raman spectroscopy is a potential tool for ex vivo skin diffusion studies. We also concluded that PG and OA have potential synergistic reversible effect on the skin.     

Stressed out mitochondria: The role of mitochondria in ageing and cancer focussing on strategies and opportunities in human skin

Mitochondrial DNA damage has been used as a successful and unique biomarker of tissue stress. A valuable example of this is sun damage in human skin which leads to ageing and skin cancer. The skin is constantly exposed to the harmful effects of sunlight, such as ultraviolet radiation, which causes it to age with observable characteristic features as well as clinical precancerous lesions and skin cancer. Formation of free radicals by the sun's harmful rays which contribute to oxidative stress has been linked to the induction of deletions and mutations in the mitochondrial DNA. These markers of mitochondrial DNA damage have been proposed to contribute to the mechanisms of ageing in many tissues including skin and are associated with many diseases including cancer. In this article we highlight the role of this important organelle in ageing and cancer with particular emphasis on experimental strategies in the skin.     

Vaccination with irradiated cercariae of Schistosoma mansoni preferentially induced the accumulation of interferon-gamma producing T cells in the skin and skin draining lymph nodes of mice

Cytokine response to schistosomula of Schistosoma mansoni was evaluated in the skin of mice during the initial 72 h following infection. These studies showed a significant increase in the levels of IL-4 and IL-10 message in the skin in areas of cercarial penetration. The IL-4 message was detectable in the skin as early as 8 h after infection and the message for IL-10 appeared from 16 h after infection. However, mRNA for IFN-gamma was undetectable in the skin samples for up to 72 h after infection with normal cercariae. In sharp contrast, vaccination with irradiated cercariae induced IFN-gamma and IL-2 responses in the skin within 24 h. Analysis of the cytokine profile of cells isolated from the skin during these early time points showed that T cells are probably not a source of IL-4 or IL-10 in the skin of mice infected with normal cercariae. However, in vaccinated animals, the majority of the IFN-gamma is derived from skin-residing T cells. In vaccinated animals, responses in the skin were mirrored in the skin-draining lymph nodes as well. Analysis of the CD4/CD8 ratio showed a significant decrease in the skin following vaccination suggesting an increase in CD8+ cells. Interestingly however, when vaccinated animals were challenged with normal cercariae, there was a significant reduction in IFN-gamma response in the skin and its draining lymph nodes. These results show that vaccination with irradiated cercariae of S. mansoni, preferentially induce the accumulation of IFN-gamma producing T cells in the skin and skin-draining lymph nodes of mice.     

Corticotropin releasing hormone and its function in the skin.

The skin, as the largest organ of the body, is strategically located as a barrier between the external and internal environments, being permanently exposed to noxious stressors such as bursts of radiation (solar, thermal), mechanical energy, or chemical and biological insults. Because of its functional domains and structural diversity, the skin must have a constitutive mechanism for dealing with the stressors. Activities of the skin are mostly regulated by local cutaneous factors and stressed skin can generate signals to produce rapid (neural) or slow (humoral) responses to local or systemic levels. Thus, the skin neuroendocrine system is comprised of locally produced neuroendocrine mediators that interact with corresponding specific receptors through para- or autocrine mechanisms. Furthermore, it is known for several years that the corticotropin-releasing hormone (CRH)/ pro-opiomelanocorticotropin (POMC) skin system fulfils analogous functions to the hypothalamic-pituitary-adrenal (HPA) stress axis. Additionally, skin cells produce hormones, neurotansmitters and neuropeptides, having the corresponding receptors and the skin itself is able to fulfill a multidirectional communication between endocrine, immune and central nervous systems as well as other internal organs. In summary, the skin expresses an equivalent of the prominent hypothalamic-pituitary-adrenal stress axis that may act as a cutaneous defense system, operating as a coordinator and executor of local responses to stress, in addition to its normal function: the preservation of body homeostasis.     

Cryptic patterning of avian skin confers a developmental facility for loss of neck feathering

Vertebrate skin is characterized by its patterned array of appendages, whether feathers, hairs, or scales. In avian skin the distribution of feathers occurs on two distinct spatial levels. Grouping of feathers within discrete tracts, with bare skin lying between the tracts, is termed the macropattern, while the smaller scale periodic spacing between individual feathers is referred to as the micropattern. The degree of integration between the patterning mechanisms that operate on these two scales during development and the mechanisms underlying the remarkable evolvability of skin macropatterns are unknown. A striking example of macropattern variation is the convergent loss of neck feathering in multiple species, a trait associated with heat tolerance in both wild and domestic birds. In chicken, a mutation called Naked neck is characterized by a reduction of body feathering and completely bare neck. Here we perform genetic fine mapping of the causative region and identify a large insertion associated with the Naked neck trait. A strong candidate gene in the critical interval, BMP12/GDF7, displays markedly elevated expression in Naked neck embryonic skin due to a cis-regulatory effect of the causative mutation. BMP family members inhibit embryonic feather formation by acting in a reaction-diffusion mechanism, and we find that selective production of retinoic acid by neck skin potentiates BMP signaling, making neck skin more sensitive than body skin to suppression of feather development. This selective production of retinoic acid by neck skin constitutes a cryptic pattern as its effects on feathering are not revealed until gross BMP levels are altered. This developmental modularity of neck and body skin allows simple quantitative changes in BMP levels to produce a sparsely feathered or bare neck while maintaining robust feather patterning on the body.