Opioids and skin homeostasis, regeneration and ageing – What's the evidence?

Enkephalins and Pain Modulation: Mechanisms of Action and Therapeutic Perspectives

Enkephalins, a subclass of endogenous opioid peptides, play a pivotal role in pain modulation. Enkephalins primarily exert their effects through opioid receptors located widely throughout both the central and peripheral nervous systems. This review will explore the mechanisms by which enkephalins produce analgesia, emotional regulation, neuroprotection, and other physiological effects. Furthermore, this review will analyze the involvement of enkephalins in the modulation of different pathologies characterized by severe pain. Understanding the complex role of enkephalins in pain processing provides valuable insight into potential therapeutic strategies for managing pain disorders.

Delta opioid receptor expression correlates to skin ageing and melanin expression in Asian women

While the evidence for the implication of opioid receptors (OPr) in ageing is growing, there is, to our knowledge, no study focusing directly on changes in vivo cutaneous OPr expression with increasing age. We thus investigated OPr expression in 30 healthy female Asian volunteers in Southern China whose ages range from the early 20s to the early 60s. Excisional biopsies were taken from the sun-exposed extensor area of the lower arm and the photo-protected area of the upper inner arm. The thickness of the epidermal layers, melanin content, as well as expression of mu-opioid receptors (MOPr) and delta-opioid receptors (DOPr) were compared between different age ranges and photo-exposure status. Significant increased epidermal hypertrophy on the extensor surface was observed. There was significant reduction of DOPr in the epidermis with increasing age, independent of photo-ageing. The increase of melanin was significantly correlated with epidermal DOPr expression, not with MOPr expression. DOPr expression could thus serve as a marker for real biological ageing unaffected by chronic photo-exposure. Additionally, DOPr expression was inversely correlated with the deposition of melanin. Based on these results, we hypothesise that regulation of DOPr expression could be used to improve aged skin, including hyperpigmentation.

Cutaneous-immuno-neuro-endocrine (CINE) system: A complex enterprise transforming skin into a super organ

Skin is now emerging as a complex realm of three chief systems viz. immune system, nervous system, and endocrine system. The cells involved in their intricate crosstalk, namely native skin cells, intra-cutaneous immune cells and cutaneous sensory neurons have diverse origin and distinct functions. However, recent studies have explored their role beyond their pre-defined functional boundaries, such that the cells shun their traditional functions and adopt unconventional roles. For example, the native skin cells, apart from providing for basic structural framework of skin, also perform special immune functions and participate in extensive neuro-endocrine circuitry, which were traditionally designated as functions of cutaneous resident immune cells and sensory neurons respectively. At the cellular level, this unique collaboration is brought out by special molecules called neuromediators including neurotransmitters, neuropeptides, neurotrophins, neurohormones and cytokines/chemokines. While this intricate crosstalk is essential for maintaining cutaneous homeostasis, its disruption is seen in various cutaneous diseases. Recent study models have led to a paradigm shift in our understanding of pathophysiology of many such disorders. In this review, we have described in detail the interaction of immune cells with neurons and native skin cells, role of neuromediators, the endocrine aspect in skin and current understanding of cutaneous neuro-immuno-endocrine loop in one of the commonest skin diseases, psoriasis. An accurate knowledge of this unique crosstalk can prove crucial in understanding the pathophysiology of different skin diseases and allow for generation of targeted therapeutic modalities.

Hemorphin-Based Analgesia: A Mechanism of Cupping Technique?

Background and Objective

Cupping is a time-honoured traditional healing modality for pain management and remains favoured by professionals and lay people across several cultures today. However, the analgesic mechanism of cupping is still poorly understood. In addition, clinical guidelines for standardized applications of cupping are currently lacking. The awareness of cupping marks has provoked curiosity about the connection between skin color changes and their benefit for local pain relief. Computer simulation is a promising approach for numerical modeling the cupping-evoked erythrocyte emigration. Quantitative proteomic profiling of cupping-induced blister fluid exhibited a significant decrease in the abundance of haemoglobin β subunit. This finding provides a critical clue to paint a novel picture of the mechanism behind cupping. The hemorphins are a set of non-classical opioid peptides derived from the proteolysis of haemoglobin β subunit. In the present study, a probable mechanism of hemorphin-based cupping analgesia is proposed. The hemorphin could also act as a potential biomarker for objective and timely quantitative clinical assessment of cupping in the management of pain conditions. A seminal theory may open a new avenue for future translational research on promoting the efficacy and safety of cupping analgesia.

Conclusion

The local analgesic effect of cupping is probable in the context of haemoglobin degradation that bestows the appearance of hemorphins along with engaging opioid receptor signalling. Exploring the potential novel mechanism of cupping analgesia facilitates seeking non-pharmacologic pain interventions.

Secretome of human umbilical cord mesenchymal stem cell maintains skin homeostasis by regulating multiple skin physiological function

Skin is the largest organ in the body and the first defense to resist various diseases and external stimuli that easily cause infection and inflammation. Aseptic inflammation, barrier damage, and foreign aid pressure induce the destruction and damage to the skin microenvironment. Subsequently, it destroys the skin's physiological function, leading to the maintenance and circulation of steady-state imbalance and aggravating the process of skin disorders. Our study evaluated the therapeutic potential of the secretome of human umbilical cord mesenchymal stem cells (UC-CM) for dermatological diseases in adult human skin cells, ex vivo skin tissue, and a 3D skin model. Our data suggested several advantages of UC-CM due to (1) their low cytotoxicity and sensitization properties; (2) their anti-inflammatory capacity for treating inflammatory chronic cutaneous diseases; (3) their enhanced capacity of the skin barrier for treating abnormal barrier metabolism; and (4) their positive impact on restoring skin homeostasis due to effective regulation ability of skin physiological function including cell apoptosis, detoxification, and anti-aging. We thus envisage that the possibility of harnessing the therapeutic potential of UC-CM might benefit patients suffering from inflammatory skin disorders such as atopic dermatitis, acne, and psoriasis.

Neuroendocrine signaling in the skin with a special focus on the epidermal neuropeptides

The skin, which is comprised of the epidermis, dermis, and subcutaneous tissue, is the largest organ in the human body and it plays a crucial role in the regulation of the body's homeostasis. These functions are regulated by local neuroendocrine and immune systems with a plethora of signaling molecules produced by resident and immune cells. In addition, neurotransmitters, endocrine factors, neuropeptides, and cytokines released from nerve endings play a central role in the skin's responses to stress. These molecules act on the corresponding receptors in an intra-, juxta-, para-, or autocrine fashion. The epidermis as the outer most component of skin forms a barrier directly protecting against environmental stressors. This protection is assured by an intrinsic keratinocyte differentiation program, pigmentary system, and local nervous, immune, endocrine, and microbiome elements. These constituents communicate cross-functionally among themselves and with corresponding systems in the dermis and hypodermis to secure the basic epidermal functions to maintain local (skin) and global (systemic) homeostasis. The neurohormonal mediators and cytokines used in these communications regulate physiological skin functions separately or in concert. Disturbances in the functions in these systems lead to cutaneous pathology that includes inflammatory (i.e., psoriasis, allergic, or atopic dermatitis, etc.) and keratinocytic hyperproliferative disorders (i.e., seborrheic and solar keratoses), dysfunction of adnexal structure (i.e., hair follicles, eccrine, and sebaceous glands), hypersensitivity reactions, pigmentary disorders (vitiligo, melasma, and hypo- or hyperpigmentary responses), premature aging, and malignancies (melanoma and nonmelanoma skin cancers). These cellular, molecular, and neural components preserve skin integrity and protect against skin pathologies and can act as "messengers of the skin" to the central organs, all to preserve organismal survival.

Emerging roles of keratinocytes in nociceptive transduction and regulation

Keratinocytes are the predominant block-building cells in the epidermis. Emerging evidence has elucidated the roles of keratinocytes in a wide range of pathophysiological processes including cutaneous nociception, pruritus, and inflammation. Intraepidermal free nerve endings are entirely enwrapped within the gutters of keratinocyte cytoplasm and form en passant synaptic-like contacts with keratinocytes. Keratinocytes can detect thermal, mechanical, and chemical stimuli through transient receptor potential ion channels and other sensory receptors. The activated keratinocytes elicit calcium influx and release ATP, which binds to P2 receptors on free nerve endings and excites sensory neurons. This process is modulated by the endogenous opioid system and endothelin. Keratinocytes also express neurotransmitter receptors of adrenaline, acetylcholine, glutamate, and γ-aminobutyric acid, which are involved in regulating the activation and migration, of keratinocytes. Furthermore, keratinocytes serve as both sources and targets of neurotrophic factors, pro-inflammatory cytokines, and neuropeptides. The autocrine and/or paracrine mechanisms of these mediators create a bidirectional feedback loop that amplifies neuroinflammation and contributes to peripheral sensitization.

Accelerated wound healing and its promoting effects of topical codeine on the healing of full-thickness cutaneous wound, evidences for modulating cytokines involved in pain, inflammation and collagen biosynthesis

INTRODUCTION

The inflammation and pain occur in all the wounds. Opioids drugs decrease pain and may act as an anti-inflammation. The current study was conducted to investigate the efficiency of the topical uses of Codeine on full-thickness excision wound models by focusing on relationship between pain mediators, inflammation and wound healing rate.

METHODS

Following the induction of anesthesia, a skin wound with a size of 7-mm punch was induced on the dorsal surfaces of each mouse. The mice were divided into five categories: groups I-III were daily administered 2.5%, 5%, and 10% Codeine gel; those in group IV were administered phenytoin cream, and group V (controls) received base ointment. To assess the effects of Codeine gel on the wound healing process, the wound area, histological parameters, and the relative protein expression of CXCR1, CXCR2, IL-6, IL-6R, PDGF, PDGFR, and COL1A along with the plasma concentrations of IL-1β, IL-10, and TNF-α were investigated on days 3, 7, and 14.

RESULTS

On days 7 and 14, the wound area was significantly lower in the treated mice compared to the controls (P < 0.05). Angiogenesis, collagen deposition, and epithelium thickness were significantly higher in the treatment groups compared to the control group (P < 0.05). The relative protein expressions of CXCR1, CXCR2, IL-6, and IL-6R and the plasma concentrations of IL-1β and TNF-α were significantly lower in the treated groups. Meanwhile, the relative protein expressions of PDGF, PDGFR, and COL1A and the plasma concentration of IL-10 were significantly higher in the treated mice (P < 0.05).

CONCLUSION

Administration of Codeine gel accelerated wound healing through decreasing the pain mediators, inflammation and promoting proliferative phase.

Opioidergic Signaling-A Neglected, Yet Potentially Important Player in Atopic Dermatitis

Atopic dermatitis (AD) is one of the most common skin diseases, the prevalence of which is especially high among children. Although our understanding about its pathogenesis has substantially grown in recent years, and hence, several novel therapeutic targets have been successfully exploited in the management of the disease, we still lack curative treatments for it. Thus, there is an unmet societal demand to identify further details of its pathogenesis to thereby pave the way for novel therapeutic approaches with favorable side effect profiles. It is commonly accepted that dysfunction of the complex cutaneous barrier plays a central role in the development of AD; therefore, the signaling pathways involved in the regulation of this quite complex process are likely to be involved in the pathogenesis of the disease and can provide novel, promising, yet unexplored therapeutic targets. Thus, in the current review, we aim to summarize the available potentially AD-relevant data regarding one such signaling pathway, namely cutaneous opioidergic signaling.

Pruritus: A Sensory Symptom Generated in Cutaneous Immuno-Neuronal Crosstalk

Pruritus or itch generated in the skin is one of the most widespread symptoms associated with various dermatological and systemic (immunological) conditions. Although many details about the molecular mechanisms of the development of both acute and chronic itch were uncovered in the last 2 decades, our understanding is still incomplete and the clinical management of pruritic conditions is one of the biggest challenges in daily dermatological practice. Recent research revealed molecular interactions between pruriceptive sensory neurons and surrounding cutaneous cell types including keratinocytes, as well as resident and transient cells of innate and adaptive immunity. Especially in inflammatory conditions, these cutaneous cells can produce various mediators, which can contribute to the excitation of pruriceptive sensory fibers resulting in itch sensation. There also exists significant communication in the opposite direction: sensory neurons can release mediators that maintain an inflamed, pruritic tissue-environment. In this review, we summarize the current knowledge about the sensory transduction of pruritus detailing the local intercellular interactions that generate itch. We especially emphasize the role of various pruritic mediators in the bidirectional crosstalk between cutaneous non-neuronal cells and sensory fibers. We also list various dermatoses and immunological conditions associated with itch, and discuss the potential immune-neuronal interactions promoting the development of pruritus in the particular diseases. These data may unveil putative new targets for antipruritic pharmacological interventions.

The Expression Pattern of Genes Related to Melanogenesis and Endogenous Opioids in Psoriasis

The melanocortin system is a major regulator of stress responses in the skin and is responsible for the induction of melanin synthesis through activation of melanogenesis enzymes. The expression of both melanocortin system genes and melanogenesis enzyme genes is altered in psoriasis, and the focus here was on twelve genes related to the signal transduction between them. Additionally, five endogenous opioid system genes that are involved in cutaneous inflammation were examined. Quantitative real-time-PCR was utilized to measure mRNA expression in punch biopsies from lesional and non-lesional skin of psoriasis patients and from the skin of healthy control subjects. Most of the genes related to melanogenesis were down-regulated in patients (CREB1, MITF, LEF1, USF1, MAPK14, ICAM1, PIK3CB, RPS6KB1, KIT, and ATRN). Conversely, an up-regulation occurred in the case of opioids (PENK, PDYN, and PNOC). The suppression of genes related to melanogenesis is in agreement with the reported reduction in pigmentation signaling in psoriatic skin and potentially results from the pro-inflammatory environment. The increase in endogenous opioids can be associated with their involvement in inflammatory dysregulation in psoriasis.

Neurocosmetics in Skincare—The Fascinating World of Skin–Brain Connection: A Review to Explore Ingredients, Commercial Products for Skin Aging, and Cosmetic Regulation

The “modern” cosmetology industry is focusing on research devoted to discovering novel neurocosmetic functional ingredients that could improve the interactions between the skin and the nervous system. Many cosmetic companies have started to formulate neurocosmetic products that exhibit their activity on the cutaneous nervous system by affecting the skin’s neuromediators through different mechanisms of action. This review aims to clarify the definition of neurocosmetics, and to describe the features of some functional ingredients and products available on the market, with a look at the regulatory aspect. The attention is devoted to neurocosmetic ingredients for combating skin stress, explaining the stress pathways, which are also correlated with skin aging. “Neuro-relaxing” anti-aging ingredients derived from plant extracts and neurocosmetic strategies to combat inflammatory responses related to skin stress are presented. Afterwards, the molecular basis of sensitive skin and the suitable neurocosmetic ingredients to improve this problem are discussed. With the aim of presenting the major application of Botox-like ingredients as the first neurocosmetics on the market, skin aging is also introduced, and its theory is presented. To confirm the efficacy of the cosmetic products on the market, the concept of cosmetic claims is discussed.

Hair Growth Promotion by δ-Opioid Receptor Activation

Literature has revealed that the delta opioid receptor (DOR) exhibited diverse pharmacological effects on neuron and skin. In the present study, we have investigated whether the activation of DOR has hair-growth promotion effects. Compared with other opioid receptor, DOR was highly expressed in epidermal component of hair follicle in human and rodents. The expression of DOR was high in the anagen phase, but it was low in the catagen and telogen phases during mouse hair cycle. Topical application of UFP-512, a specific DOR agonist, significantly accelerated the induction of the anagen in C₃H mice. Topical application of UFP-512 also increased the hair length in hair organ cultures and promoted the proliferation and the migration of outer root sheath (ORS) cells. Similarly, pharmacological inhibition of DOR by naltrindole significantly inhibited the anagen transition process and decreased hair length in hair organ cultures. Thus, we further examined whether Wnt/β-catenin pathway was related to the effects of DOR on hair growth. We found that Wnt/β-catenin pathway was activated by UFP-512 and siRNA for β-catenin attenuated the UFP-512 induced proliferation and migration of ORS cells. Collectively, result established that DOR was involved in hair cycle regulation, and that DOR agonists such as UFP-512 should be developed for novel hair-loss treatment.

Effects of Buprenorphine, Chlorhexidine, and Low-level Laser Therapy on Wound Healing in Mice

Systemic buprenorphine and topical antiseptics such as chlorhexidine are frequently used in research animals to aid in pain control and to reduce infection, respectively. These therapeutics are controversial, especially when used in wound healing studies, due to conflicting data suggesting that they delay wound healing. Low-level laser therapy (LLLT) has been used to aid in wound healing without exerting the systemic effects of therapies such as buprenorphine. We conducted 2 studies to investigate the effects of these common treatment modalities on the rate of wound healing in mice. The first study used models of punch biopsy and dermal abrasion to assess whether buprenorphine HCl or 0.12% chlorhexidine delayed wound healing. The second study investigated the effects of sustained-released buprenorphine, 0.05% chlorhexidine, and LLLT on excisional wound healing. The rate of wound healing was assessed by obtaining photographs on days 0, 2, 4, 7, and 9 for the punch biopsy model in study 1, days 0, 1, 2, 4, 6, 8, 11, and 13 for the dermal abrasion model in study 1, and days 0, 3, 6, and 10 for the mice in study 2. Image J software was used to analyze the photographed wounds to determine the wound area. When comparing the wound area on the above days to the original wound area, no significant differences in healing were observed for any of the treatment groups at any time period for either study. Given the results of these studies, we believe that systemic buprenorphine, topical chlorhexidine, and LLLT can be used without impairing or delaying wound healing in mice.

Translational Neuroendocrinology of Human Skin: Concepts and Perspectives

Human skin responds to numerous neurohormones, neuropeptides, and neurotransmitters that reach it via the vasculature or skin nerves, and/or are generated intracutaneously, thus acting in a para- and autocrine manner. This review focuses on how neurohormones impact on human skin physiology and pathology. We highlight basic concepts, major open questions, and translational research perspectives in cutaneous neuroendocrinology and argue that greater emphasis on neuroendocrine human skin research will foster the development of novel dermatological therapies. Furthermore, human skin and its appendages can be used as highly accessible and clinically relevant model systems for probing nonclassical, ancestral neurohormone functions. This calls for close interdisciplinary collaboration between dermatologists, skin biologists, neuroendocrinologists, and neuropharmacologists.

FBNTI, a DOR-Selective Antagonist That Allosterically Activates MOR within a MOR-DOR Heteromer

This report describes the unique pharmacological profile of FBNTI, a potent DOR antagonist that acts as a MOR agonist via an allosteric mechanism. Binding of FBNTI to opioid receptors expressed in HEK 293 cells revealed a 190-fold greater affinity for DOR (K_i = 0.84 nM) over MOR (K_i = 160 nM). In mice, intrathecal FBNTI produced potent antinociception (ED₅₀ = 46.9 pmol/mouse), which was antagonized by selective MOR antagonists (CTOP, β-FNA). Autoantagonism of the MOR agonism by FBNTI was observed above the ED₇₅ dose, suggesting antagonism of activated MOR. That FBNTI is devoid of agonism in DOR knockout mice is consistent with allosteric activation of the MOR protomer via FBNTI bound to within a MOR-DOR heteromer. This proposed mechanism is supported by calcium mobilization assays, which indicate that FBNTI selectively activates the MOR-DOR heteromer and functionally antagonizes the MOR protomer at >ED₇₅. The unprecedented mode of MOR activation by FBNTI may be responsible for the lack of tolerance after intrathecal (i.t.) administration. FBNTI was highly effective upon topical administration to the ipsolateral hind paw in the Hargreaves assay (EC₅₀ = 0.17 ± 0.08 μM) and without significant contralateral activity, suggesting a lack of systemic exposure.

Quality of Life, Anxiety, and Depression in Patients With Early-Stage Mycosis Fungoides and the Effect of Oral Psoralen Plus UV-A (PUVA) Photochemotherapy on it

Background: Little is known about psychological discomfort and quality of life (QoL) in early stage mycosis fungoides (MF) and the effect of psoralen plus UV-A (PUVA) on it.

Objective: To evaluate QoL, anxiety, and depression with validated instruments in early stage MF patients and whether PUVA treatment improves it.

Methods: Patients with stage IA to IIA MF were treated with PUVA twice weekly for 12–24 weeks, followed by maintenance treatment or not, in a prospective randomized clinical trial. Patients completed a questionnaire on DLQI as well as the Hospital Anxiety and Depression Scale (HADS) prior to therapy, after their last PUVA exposure, and after the PUVA maintenance or observance phase.

Results: For 24 patients with early stage MF, completed questionnaires were available and analyzed. Prior to treatment, 17% reported strong (DLQI > 10) and 29% moderate impairment (DLQI 6–10) in QoL; 33% of patients reported HADS scores indicating anxiety, and 21% reported scores indicating depression. PUVA significantly improved overall QoL by reducing mean DLQI scores by 58.6% (p = 0.003), HADS-A by 30% (p = 0.045), and HADS-D by 44% (p = 0.002). Improvements in QoL and psychological well-being seemed to be sustained, irrespective of maintenance treatment or not.

Limitations: Small sample size.

Conclusions: PUVA sustainably improves QoL and psychological well-being in patients with early stage MF.

Clinical trial registration:ClinicalTrials.gov identifier: NCT01686594.

Potential of Skin Microbiome, Pro- and/or Pre-Biotics to Affect Local Cutaneous Responses to UV Exposure

The human skin hosts innumerable microorganisms and maintains homeostasis with the local immune system despite the challenges offered by environmental factors such as ultraviolet radiation (UVR). UVR causes cutaneous alterations such as acute (i.e., sunburn) and chronic inflammation, tanning, photoaging, skin cancer, and immune modulation. Phototherapy on the other hand is widely used to treat inflammatory skin diseases such as psoriasis, atopic dermatitis, polymorphic light eruption and graft-versus-host disease (GvHD), as well as neoplastic skin diseases such as cutaneous T cell lymphoma, among others. Previous work has addressed the use of pro- and pre-biotics to protect against UVR through anti-oxidative, anti-inflammatory, anti-aging, anti-carcinogenic and/or pro-and contra-melanogenic properties. Herein, we discuss and share perspectives of the potential benefits of novel treatment strategies using microbes and pro- and pre-biotics as modulators of the skin response to UVR, and how they could act both for protection against UVR-induced skin damage and as enhancers of the UVR-driven therapeutic effects on the skin.

Non-neuronal kappa-opioid receptor activation enhances epidermal keratinocyte proliferation, and modulates mast cell functions in human skin ex vivo

Kappa-opioid receptor (KOR) activation reportedly elicits anti-inflammatory responses and can downregulate neuropeptide release from sensory nerve fibers. While this renders KOR agonists (KORAs) potentially interesting therapeutics in skin diseases associated with neurogenic inflammation, it remains poorly understood how KOR agonists impact on human skin and dermal mast cells (MCs) ex vivo, in the absence of functional innervation. The KORA 5a was administrated to the culture medium (200 nmol/L and 1 µmol/L) in human skin organ culture, thus mimicking a "systemic" mode of application. We show that KORA significantly increased epidermal thickness and upregulated the number and proliferation of epidermal keratinocytes. Unexpectedly, it also stimulated epidermal keratinocyte apoptosis in situ, compared with vehicle. Moreover, KORA significantly decreased the number of c-Kit-positive MCs, but did not significantly alter the number or degranulation of mature (tryptase- or toluidine blue-positive) MCs. These pilot observations render the tested KORA (5a) an interesting candidate for the management of inflammatory dermatoses in which MC-dependent neurogenic skin inflammation plays an important role (e.g. atopic dermatitis, psoriasis).

The analgesic hybrid of dermorphin/substance P and analog of enkephalin improve wound healing in streptozotocin-induced diabetic rats

The purpose of this study was to investigate the effect of the peptide analgesic hybrid compounds: AWL3106 analog of dermorphin and substance P (7-11), and biphalin enkephalin analog on wound healing in streptozotocin-induced diabetic rats. The diabetes was induced in 6-7 week-old male Wistar rats by intraperitoneal injection of streptozotocin. After 70 days, the wounds were created on the back of the rats and then, once a day for 21 days, the dressing containing lanolin ointment, 10% of keratin scaffolds, and 1 mM of AWL3106 or biphalin was applied. The wounds histology were analyzed by hematoxylin and eosin staining. The orientation and organization of collagen was analyzed by Masson's trichome staining. The number of macrophages, blood vessels, and fibroblasts were visualized by CD68, CD34, and vimentin immunoreactivity, respectively. Our results demonstrated that the wound area of AWL3106- and biphalin-treated groups was greatly reduced (up to 47% on the 7 day) in comparison with untreated diabetic groups. The immunohistochemical staining of macrophages demonstrated that AWL3106 and biphalin accelerated inflammatory progression and subsequently decreased persistent inflammation. The histological analysis showed that the structure of tissue in the groups under the study was very similar to the one of wound tissue in N-DM group. The H&E and Masson's trichome staining demonstrated that the orientation and organization of collagen as well as the number and shape of blood vessels were better in 3106- and BIF-treated group than in DM group. In conclusion, the obtained data suggested that our hybrid peptides enhanced wound healing, particularly by accelerating the inflammatory phase and promoted the wound closure.

Influence of Pain and Analgesia on Orthopedic and Wound-healing Models in Rats and Mice

The surgical stress response and resulting physiologic changes can lead to postoperative complications and negatively impact animal welfare. Although appropriate pain management is crucial to reduce the pain and stress response to surgery, analgesic choice can significantly affect bone and wound healing. This review aims to summarize data from rat and mouse studies and to provide recommendations for integrating analgesia into orthopedic and wound healing models in these species. Data from other species, such as humans, rabbits and other rodents, is included, where available. From these data, we conclude that for orthopedic surgical models, opioids, local anesthetics and dissociative agents have minimal impact on fracture healing; cyclooxygenase 2 (COX2) selective nonsteroidal antiinflammatory drugs (NSAID) may be used in the shortterm; and steroids should be avoided. For wound healing models, short-term systemic or topical opioids have negligible impact on wound healing; NSAID or local anesthetics may be used short-term; and systemic steroids should be avoided. Alternative analgesics such as tramadol, gabapentin, ketamine, and acetaminophen warrant consideration and further evaluation for both orthopedic and wound healing models. In all cases, researchers and veterinarians should work together to determine the appropriate analgesic plan to minimize pain, as well as to minimize unwanted effects on the orthopedic and wound healing models themselves.

The Use of Naltrexone in Dermatology. Current Evidence and Future Directions

Naltrexone is a competitive opioid receptor antagonist approved as supportive treatment in alcohol dependence and opioid addiction. At a dose of 50-100 mg daily, naltrexone is used off-label in dermatology for the treatment of trichotillomania and different types of pruritus. At a dose as low as 1- 5 mg per day, naltrexone demonstrates immunomodulatory action i.e. modulates Toll-like receptors signaling, decreases release of proinflammatory cytokines (tumor necrosis factor, interleukin-6, interleukin- 12), inhibits T lymphocyte proliferation, down-regulates the expression of chemokine receptors and adhesion molecules. The efficacy of standard and low doses of naltrexone in a variety of dermatological disorders has been reported. These include diseases such as familial benign chronic pemphigus (Hailey-Hailey disease), dermatomyositis, systemic sclerosis, psoriasis and lichen planopilaris. Optimistic preliminary findings, low cost of therapy and good tolerance make naltrexone a promising alternative therapy or adjunct drug in dermatology.

How UV Light Touches the Brain and Endocrine System Through Skin, and Why

The skin, a self-regulating protective barrier organ, is empowered with sensory and computing capabilities to counteract the environmental stressors to maintain and restore disrupted cutaneous homeostasis. These complex functions are coordinated by a cutaneous neuro-endocrine system that also communicates in a bidirectional fashion with the central nervous, endocrine, and immune systems, all acting in concert to control body homeostasis. Although UV energy has played an important role in the origin and evolution of life, UV absorption by the skin not only triggers mechanisms that defend skin integrity and regulate global homeostasis but also induces skin pathology (e.g., cancer, aging, autoimmune responses). These effects are secondary to the transduction of UV electromagnetic energy into chemical, hormonal, and neural signals, defined by the nature of the chromophores and tissue compartments receiving specific UV wavelength. UV radiation can upregulate local neuroendocrine axes, with UVB being markedly more efficient than UVA. The locally induced cytokines, corticotropin-releasing hormone, urocortins, proopiomelanocortin-peptides, enkephalins, or others can be released into circulation to exert systemic effects, including activation of the central hypothalamic-pituitary-adrenal axis, opioidogenic effects, and immunosuppression, independent of vitamin D synthesis. Similar effects are seen after exposure of the eyes and skin to UV, through which UVB activates hypothalamic paraventricular and arcuate nuclei and exerts very rapid stimulatory effects on the brain. Thus, UV touches the brain and central neuroendocrine system to reset body homeostasis. This invites multiple therapeutic applications of UV radiation, for example, in the management of autoimmune and mood disorders, addiction, and obesity.

Focusing on the Opioid System for Addiction Biomarker Discovery

Substance use disorders (SUD) and behavioral addictions are devastating conditions that impose a severe burden on all societies, and represent difficult challenges for clinicians. Therefore, biomarkers are urgently needed to help predict vulnerability, clinical course, and response to treatment. Here, we elaborate on the potential for addiction biomarker discovery of the opioid system, particularly within the emerging framework aiming to probe opioid function in peripheral tissues. Mu, delta, and kappa opioid receptors all critically regulate neurobiological and behavioral processes that define addiction, and are also targeted by major pharmacotherapies used in the management of patients with SUD. We propose that opioid biomarkers may have the potential to improve and guide diagnosis and therapeutic decisions in the addiction field.

Opioids and opioid receptors orchestrate wound repair

We have previously shown that topical opioids including morphine and its congeners promote healing of full thickness ischemic wounds in rats. We examined the contribution of mu opioid receptor (MOPr)-mediated healing of full thickness ischemic wounds using MOPr and delta or kappa opioid receptor knockout (KO) mice. Wound closure in the early (day 5) as well as later phases was delayed in topical morphine or PBS-treated MOPr-KO mice compared with reciprocal treatments of wounds in wild-type (WT) mice. MOPr expression was significantly upregulated at 30 min in the wound margins and colocalized with wound margins and vasculature in the epidermal and dermal layers of the skin. We next examined whether neuropeptide expression was involved in the mechanism of MOPr-mediated wound closure. Substance P (SP) and calcitonin gene-related peptide immunoreactivity (ir) was significantly increased in the skin of MOPr-KO mice as compared with WT mice. Neuropeptide-ir was increased significantly in PBS-treated wounds of MOPr and WT mice, but morphine treatment reduced neuropeptide immunoreactivity in both as compared with PBS. Wounding of keratinocytes led to the release of opioid peptide beta-endorphin (β-END) in conditioned medium, which stimulated the proliferation of endothelial cells. MOPr-selective (D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2, CTOP) and nonselective OPr antagonist naloxone-inhibited endothelial proliferation induced by wounded keratinocyte-conditioned medium. In addition, accelerated wound area closure in vitro by morphine was suppressed by methylnaltrexone, a nonselective OPr antagonist with high affinity for MOPr. Morphine and its congeners stimulated the proliferation of endothelial cells from WT mice but not those from MOPr-KO mice. Furthermore, morphine-induced mitogen-activated protein kinase/extracellular signal-regulated kinase phosphorylation in endothelial cells was significantly decreased in MOPr-KO mice as compared with WT mice. Collectively, these data suggest that MOPr plays a critical role in the proliferation phase with the formation of granulation tissue during wound healing.