Alpha-melanocyte-stimulating hormone counteracts the suppressive effect of UVB on Nrf2 and Nrf-dependent gene expression in human skin

Anthropogenic electromagnetic radiation alters the transcription levels of the genes encoding the SIFamide and myoinhibitory peptide and their receptors in Ixodes ricinus synganglion

The research of the influences of man-made electromagnetic fields on tick physiology has been very sparse and long neglected since the pioneer studies published in 1996 and 2000. Once multiple behavioral tests confirmed an attraction and possible perception of electromagnetic fields in ticks, a new interest in this topic erupted in recent years. In this study, qRT-PCR is utilized to determine the changes in the mRNA transcript levels of neuropeptides SIFamide and myoinhibitory peptide (mip and sifa) and their representative receptors (mip-r1 and sifa-r1) in the synganglia of the tick Ixodes ricinus irradiated by 900 MHz radiofrequency electromagnetic field. It was determined that 40 V/m intensity has a significant suppressory effect on the transcript levels of all genes after at least 60 minutes of constant exposure in both sexes. Commonly occurring intensity of radiation in urban areas (2 V/m) produced an elevation in mRNA levels after various timespans in every gene. A significant decrease of transcript abundances was detected in females after one hour of exposure to 2 V/m. Results of this study widen the knowledge of EMF-induced alterations in the neurophysiology of I. ricinus, the most commonly distributed hard tick in Europe.

Neuropeptide alpha-Melanocyte stimulating hormone preserves corneal endothelial morphology in a murine model of Fuchs dystrophy

Fuchs endothelial corneal dystrophy is a heterogenous disease with multifactorial etiology, and genetic, epigenetic, and exogenous factors contributing to its pathogenesis. DNA damage plays a significant role, with ultraviolet-A (UV-A) emerging as a key contributing factor. We investigate the potential application of neuropeptide α-melanocyte stimulating hormone (α-MSH) in mitigating oxidative stress induced endothelial damage. First, we examined the effects of α-MSH on a cultured human corneal endothelial cell line (HCEnC-21T) exposed to hydrogen peroxide (H2O2) induced oxidative DNA damage. We performed immunofluorescence and flow cytometry to assess DNA damage and cell death in the cultured cells. Additionally, we used an established mouse model that utilizes ultraviolet light to induce corneal endothelial cell damage resulting in decreased CEnC number, increased cell size variability, and decreased percentage of hexagonal cells. This endothelial decompensation leads to an increase in corneal thickness. Following UV-A exposure, the mice were systemically treated with α-MSH, either immediately after exposure (early treatment) or beginning two weeks post-exposure (delayed treatment). To evaluate treatment efficacy, we analyzed CEnC density and morphology using in vivo confocal microscopy, and central corneal thickness using anterior segment optical coherence tomography. Our findings demonstrated that α-MSH treatment effectively protects HCEnC-21T from free-radical induced oxidative DNA damage and subsequent cell death. In vivo, α-MSH treatment, mitigated the loss of CEnC density, deterioration of cell morphology and suppression of the resultant corneal swelling. These results underline the potential application of α-MSH as a therapeutic agent for mitigating corneal endothelial damage.

Journey through the spectacular landscape of melanocortin 1 receptor

The physiological role of α-melanocyte stimulating hormone in regulating integumental pigmentation of many vertebrate species has been recognized since the 1960's. However, its physiological significance for human pigmentation remained enigmatic until the 1990's. α-Melanocyte stimulating hormone and related melanocortins are synthesized locally in the skin, primarily by keratinocytes, in addition to the pituitary gland, and therefore act as paracrine factors for melanocytes. Human melanocytes express the melanocortin 1 receptor, which recognizes α-melanocyte stimulating hormone and the related adrenocorticotropic hormone as agonists. This review summarizes the current knowledge of the pleotropic effects of the activated melanocortin 1 receptor that maintain human melanocyte homeostasis by regulating melanogenesis and the response to environmental stressors, mainly solar radiation. Certain allelic variants of the melanocortin 1 receptor gene are associated with specific pigmentary phenotypes in various human populations. Variants associated with red hair phenotype compromise the function of the encoded receptor. Activation of the human melanocortin 1 receptor regulates eumelanin synthesis and enhances DNA damage response of melanocytes to solar radiation and oxidative stressors. We describe how synthetic selective melanocortin 1 receptor agonists can be efficacious as sunless tanning agents, for treatment of vitiligo and photosensitivity disorders, and for prevention of skin cancer, including melanoma.

E-Stilbenes: General Chemical and Biological Aspects, Potential Pharmacological Activity Based on the Nrf2 Pathway

Stilbenes are phytoalexins, and their biosynthesis can occur through a natural route (shikimate precursor) or an alternative route (in microorganism cultures). The latter is a metabolic engineering strategy to enhance production due to stilbenes recognized pharmacological and medicinal potential. It is believed that in the human body, these potential activities can be modulated by the regulation of the nuclear factor erythroid derived 2 (Nrf2), which increases the expression of antioxidant enzymes. Given this, our review aims to critically analyze evidence regarding E-stilbenes in human metabolism and the Nrf2 activation pathway, with an emphasis on inflammatory and oxidative stress aspects related to the pathophysiology of chronic and metabolic diseases. In this comprehensive literature review, it can be observed that despite the broad number of stilbenes, those most frequently explored in clinical trials and preclinical studies (in vitro and in vivo) were resveratrol, piceatannol, pterostilbene, polydatin, stilbestrol, and pinosylvin. In some cases, depending on the dose/concentration and chemical nature of the stilbene, it was possible to identify activation of the Nrf2 pathway. Furthermore, the use of some experimental models presented a challenge in comparing results. In view of the above, it can be suggested that E-stilbenes have a relationship with the Nrf2 pathway, whether directly or indirectly, through different biological pathways, and in different diseases or conditions that are mainly related to inflammation and oxidative stress.

Melanocortin 1 Receptor (MC1R): Pharmacological and Therapeutic Aspects

Melanocortins play crucial roles in regulating the stress response, inflammation, and skin pigmentation. In this review, we focus on the melanocortin 1 receptor (MC1R), a G protein-coupled receptor primarily known for regulating skin pigmentation and exhibiting anti-inflammatory effects. First, we provide an overview of the structure, signaling pathways, and related diseases of MC1R. Next, we discuss the potential therapeutic use of synthetic peptides and small molecule modulators of MC1R, highlighting the development of various drugs that enhance stability through amino acid sequence modifications and small molecule drugs to overcome limitations associated with peptide characteristics. Notably, MC1R-targeted drugs have applications beyond skin pigmentation-related diseases, which predominantly affect MC1R in melanocytes. These drugs can also be useful in treating inflammatory diseases with MC1R expression present in various cells. Our review underscores the potential of MC1R-targeted drugs to treat a wide range of diseases and encourages further research in this area.

The CNC-family transcription factor Nrf3 coordinates the melanogenesis cascade through macropinocytosis and autophagy regulation

Melanin is a pigment produced from the amino acid L-tyrosine in melanosomes. The CNC-family transcription factor Nrf3 is expressed in the basal layer of the epidermis, where melanocytes reside, but its melanogenic function is unclear. Here, we show that Nrf3 regulates macropinocytosis and autophagy to coordinate melanogenesis cascade. In response to an exogenous inducer of melanin production, forskolin, Nrf3 upregulates the core melanogenic gene circuit, which includes Mitf, Tyr, Tyrp1, Pmel, and Oca2. Furthermore, Nrf3 induces the gene expression of Cln3, an autophagosome-related factor, for melanin precursor uptake by macropinocytosis. Ulk2 and Gabarapl2 are also identified as Nrf3-target autophagosome-related genes for melanosome formation. In parallel, Nrf3 prompts autolysosomal melanosome degradation for melanocyte survival. An endogenous melanogenic inducer αMSH also activates Nrf3-mediated melanin production, whereas it is suppressed by an HIV-1 protease inhibitor, nelfinavir. These findings indicate the significant role of Nrf3 in the melanogenesis and the anti-melanogenic potential of nelfinavir.

NRF2 in dermo-cosmetic: From scientific knowledge to skin care products

The skin is the organ that is most susceptible to the impact of the exposome. Located at the interface with the external environment, it protects internal organs through the barrier function of the epidermis. It must adapt to the consequences of the harmful effects of solar radiation, the various chemical constituents of atmospheric pollution, and wounds associated with mechanical damage: oxidation, cytotoxicity, inflammation, and so forth. In this biological context, a capacity to adapt to the various stresses caused by the exposome is essential; otherwise, more or less serious conditions may develop accelerated aging, pigmentation disorders, atopy, psoriasis, and skin cancers. Nrf2-controlled pathways play a key role at this level. Nrf2 is a transcription factor that controls genes involved in oxidative stress protection and detoxification of chemicals. Its involvement in UV protection, reduction of inflammation in processes associated with healing, epidermal differentiation for barrier function, and hair regrowth, has been demonstrated. The modulation of Nrf2 in the skin may therefore constitute a skin protection or care strategy for certain dermatological stresses and disorders initiated or aggravated by the exposome. Nrf2 inducers can act through different modes of action. Keap1-dependent mechanisms include modification of the cysteine residues of Keap1 by (pro)electrophiles or prooxidants, and disruption of the Keap1-Nrf2 complex. Indirect mechanisms are suggested for numerous phytochemicals, acting on upstream pathways, or via hormesis. While developing novel and safe Nrf2 modulators for skin care may be challenging, new avenues can arise from natural compounds-based molecular modeling and emerging concepts such as epigenetic regulation.

NRF2 in the Epidermal Pigmentary System

Melanogenesis is a major part of the environmental responses and tissue development of the integumentary system. The balance between reduction and oxidation (redox) governs pigmentary responses, for which coordination among epidermal resident cells is indispensable. Here, we review the current understanding of melanocyte biology with a particular focus on the "master regulator" of oxidative stress responses (i.e., the Kelch-like erythroid cell-derived protein with cap'n'collar homology-associated protein 1-nuclear factor erythroid-2-related factor 2 system) and the autoimmune pigment disorder vitiligo. Our investigation revealed that the former is essential in pigmentogenesis, whereas the latter results from unbalanced redox homeostasis and/or defective intercellular communication in the interfollicular epidermis (IFE). Finally, we propose a model in which keratinocytes provide a "niche" for differentiated melanocytes and may "imprint" IFE pigmentation.

Cytoglobin inhibits non-thermal plasma-induced apoptosis in melanoma cells through regulation of the NRF2-mediated antioxidant response

Melanoma arises from pigment-producing cells called melanocytes located in the basal layers of the epidermis of the skin. Cytoglobin (CYGB) is a ubiquitously expressed hexacoordinated globin that is highly enriched in melanocytes and frequently downregulated during melanomagenesis. Previously, we showed that non-thermal plasma (NTP)-produced reactive oxygen and nitrogen species (RONS) lead to the formation of an intramolecular disulfide bridge that would allow CYGB to function as a redox-sensitive protein. Here, we investigate the cytotoxic effect of indirect NTP treatment in two melanoma cell lines with divergent endogenous CYGB expression levels, and we explore the role of CYGB in determining treatment outcome. Our findings are consistent with previous studies supporting that NTP cytotoxicity is mediated through the production of RONS and leads to apoptotic cell death in melanoma cells. Furthermore, we show that NTP-treated solutions elicit an antioxidant response through the activation of nuclear factor erythroid 2-related factor 2 (NRF2). The knockdown and overexpression of CYGB respectively sensitizes and protects melanoma cells from RONS-induced apoptotic cell death. The presence of CYGB enhances heme-oxygenase 1 (HO-1) and NRF2 protein expression levels, whereas the absence impairs their expression. Moreover, analysis of the CYGB-dependent transcriptome demonstrates the tumor suppressor long non-coding RNA maternally expressed 3 (MEG3) as a hitherto undescribed link between CYGB and NRF2. Thus, the presence of CYGB, at least in melanoma cells, seems to play a central role in determining the therapeutic outcome of RONS-inducing anticancer therapies, like NTP-treated solutions, possessing both tumor-suppressive and oncogenic features. Hence, CYGB expression could be of interest either as a biomarker or as a candidate for future targeted therapies in melanoma.

Investigation of Morinda citrifolia Activities through Pinoresinol and α-EG Related Gene Expression

α-EG is a unique substance that was first found in the leaves and fruits of Morinda citrifolia (Mc) growing in Thailand using GC-MS at 52.33% and 54.12%. It was then concentrated and its abundance quantified, along with that of pinoresinol, via GC, compared to the standards in leaves, ufp, rfp, rawfs, and seeds. α-EG and pinoresinol, which have collagen stimulating, skin whitening, and an inhibitory effect on wrinkle formation, were found in different concentrations and amounts. Three different concentrations of the five Mc part extracts were tested on NHDF for gene expression related to the aforementioned activities, COL1A1, COL1A2, and COL3A1, FGF1 and FGF7 by qRT-PCR. The results showed various expression levels, both stimulatory and inhibitory, with different concentrations of plant parts and genes. Similar results were revealed when the experiments were performed with Morus alba (Ma), which was found to contain 20.48 g protein p/100 g leaves at concentrations of 3.11 mg/mL. The studied Mc parts seem to have advantages based on the stated objectives, gene type and level of activity of each plant part. Rawfs and leaves supplemented with Ma samples were selected for toxicity tests with PBMCs. The lack of both cell and DNA toxicity from the rawfs indicated that they can be used safely.

NRF3 Decreases during Melanoma Carcinogenesis and Is an Independent Prognostic Marker in Melanoma

The prognostic significance of the major redox regulator, nuclear factor erythroid-2-related factor 2 (NRF2), is recognized in many cancers, but the role of NRF3 is not studied. Analysis from the Gene Expression Omnibus datasets showed that NRF3 mRNA levels increased from benign to dysplastic naevi (p = 0.04). We characterized the immunohistochemical expression of NRF3 in 81 naevi, 67 primary skin melanomas, and 51 lymph node metastases. The immunohistochemical expression of cytoplasmic NRF3 decreased from benign to dysplastic naevi (p < 0.001) and further to primary melanomas (p < 0.001). High cytoplasmic NRF3 protein expression in pigment cells of the primary melanomas associated with worse melanoma-specific survival in multivariate analysis, specifically in the subgroup of patients with the lymph node metastases at the time of diagnosis (hazard ratio 3.179; 95% confidence interval 1.065-9.493; p = 0.038). Intriguingly, we did not observe associations between NRF3 and the traditional prognostic factors such as Breslow thickness, ulceration, or stage. Together, this data represents the primary description about the role of NRF3 in pigment tumours that is worthy of further explorations.

Shedding a New Light on Skin Aging, Iron- and Redox-Homeostasis and Emerging Natural Antioxidants

Reactive oxygen species (ROS) are necessary for normal cell signaling and the antimicrobial defense of the skin. However excess production of ROS can disrupt the cellular redox balance and overwhelm the cellular antioxidant (AO) capacity, leading to oxidative stress. In the skin, oxidative stress plays a key role in driving both extrinsic and intrinsic aging. Sunlight exposure has also been a major contributor to extrinsic photoaging of the skin as its oxidising components disrupt both redox- and iron-homeostasis, promoting oxidative damage to skin cells and tissue constituents. Upon oxidative insults, the interplay between excess accumulation of ROS and redox-active labile iron (LI) and its detrimental consequences to the skin are often overlooked. In this review we have revisited the oxidative mechanisms underlying skin damage and aging by focussing on the concerted action of ROS and redox-active LI in the initiation and progression of intrinsic and extrinsic skin aging processes. Based on these, we propose to redefine the selection criteria for skin antiaging and photoprotective ingredients to include natural antioxidants (AOs) exhibiting robust redox-balancing and/or iron-chelating properties. This would promote the concept of natural-based or bio-inspired bifunctional anti-aging and photoprotective ingredients for skincare and sunscreen formulations with both AO and iron-chelating properties.

Melanocortin 1 receptor activation protects against alpha-synuclein pathologies in models of Parkinson's disease

Background

Epidemiological studies suggest a link between the melanoma-related pigmentation gene melanocortin 1 receptor (MC1R) and risk of Parkinson’s disease (PD). We previously showed that MC1R signaling can facilitate nigrostriatal dopaminergic neuron survival. The present study investigates the neuroprotective potential of MC1R against neurotoxicity induced by alpha-synuclein (αSyn), a key player in PD genetics and pathogenesis.

Methods

Nigral dopaminergic neuron toxicity induced by local overexpression of aSyn was assessed in mice that have an inactivating mutation of MC1R, overexpress its wild-type transgene, or were treated with MC1R agonists. The role of nuclear factor erythroid 2-related factor 2 (Nrf2) in MC1R-mediated protection against αSyn was characterized in vitro. Furthermore, MC1R expression was determined in human postmortem midbrain from patients with PD and unaffected subjects.

Results

Targeted expression of αSyn in the nigrostriatal pathway induced exacerbated synuclein pathologies in MC1R mutant mice, which were accompanied by neuroinflammation and altered Nrf2 responses, and reversed by the human MC1R transgene. Two MC1R agonists were neuroprotective against αSyn-induced dopaminergic neurotoxicity. In vitro experiments showed that Nrf2 was a necessary mediator of MC1R effects. Lastly, MC1R was present in dopaminergic neurons in the human substantia nigra and appeared to be reduced at the tissue level in PD patients.

Conclusion

Our study supports an interaction between MC1R and αSyn that can be mediated by neuronal MC1R possibly through Nrf2. It provides evidence for MC1R as a therapeutic target and a rationale for development of MC1R-activating strategies for PD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13024-022-00520-4.

A Mixture of Topical Forms of Polydeoxyribonucleotide, Vitamin C, and Niacinamide Attenuated Skin Pigmentation and Increased Skin Elasticity by Modulating Nuclear Factor Erythroid 2-like 2

It is well-known that increased oxidative stress caused by ultraviolet B (UV-B) radiation induces melanogenesis and activates metalloproteinases (MMPs), which degrade collagen and elastin fibers, leading to decreased skin elasticity. Various antioxidant agents, such as vitamin C and niacinamide, have been evaluated for use as treatments for photoaging or skin pigmentation. In this study, we evaluated the ability of a topical liquid formula of polydeoxyribonucleotide (PDRN), vitamin C, and niacinamide (PVN) delivered via a microneedling therapy system (MTS) to attenuate photoaging and pigmentation by increasing nuclear factor erythroid 2-like 2 (NRF2)/heme oxygenase-1 (HO-1) and decreasing MMP expression in a UV-B-radiated animal model. The effects of the PVN were compared with those of individual PDRN and hydroquinone (HQ) compounds. The expression of NRF2/HO-1 significantly increased in response to HQ, PDRN, and PVN in UV-B-radiated animal skin. The activity of nicotinamide adenine dinucleotide phosphate hydrogen oxidase decreased in response to HQ, PDRN, and PVN, and the superoxide dismutase activity increased. The expression of tumor protein p53 and microphthalmia-associated transcription factor and tyrosinase activity decreased in response to HQ, PDRN, and PVN, and this decrease was accompanied by decreased melanin content in the skin. The expression of nuclear factor kappa-light-chain enhancer of activated B cells and MMP2/3/9 decreased in response to HQ, PDRN, and PVN in UV-B-radiated skin. However, the expression of collagen type I α1 chain and the amount of collagen fibers that were evaluated by Masson's trichrome staining increased in response to HQ, PDRN, and PVN. The contents of elastin fibers, fibrillin 1/2 and fibulin 5 increased in response to HQ, PDRN, and PVN. In conclusion, PVN delivered via MTS led to decreased melanogenesis and destruction of collagen and elastin fibers by MMPs, and, thus, PVN decreased skin pigmentation and increased skin elasticity.

The Neuropeptide Alpha-Melanocyte-Stimulating Hormone Is Critical for Corneal Endothelial Cell Protection and Graft Survival after Transplantation

Corneal transplantation is the most common form of tissue transplantation. The success of corneal transplantation mainly relies on the integrity of corneal endothelial cells (CEnCs), which maintain tissue transparency by pumping out excess water from the cornea. After transplantation, the rate of CEnC loss far exceeds that seen with normal aging, which can threaten sight. The underlying mechanisms are poorly understood. Alpha-melanocyte-stimulating hormone (α-MSH) is a neuropeptide that is constitutively found in the aqueous humor with both cytoprotective and immunomodulatory effects. The curent study found high expression of melanocortin 1 receptor (MC1R), the receptor for α-MSH, on CEnCs. The effect of α-MSH/MC1R signaling on endothelial function and allograft survival in vitro and in vivo was investigated using MC1R signaling-deficient mice (Mc1re/e mice with a nonfunctional MC1R). Herein, the results indicate that in addition to its well-known immunomodulatory effect, α-MSH has cytoprotective effects on CEnCs after corneal transplantation, and the loss of MC1R signaling significantly decreases long-term graft survival in vivo. In conclusion, α-MSH/MC1R signaling is critical for CEnC function and graft survival after corneal transplantation.

Implications of Oxidative Stress in the Pathogenesis and Treatment of Hyperpigmentation Disorders

Oxidative stress represents an imbalance between the generation of reactive oxygen and nitrogen species and the ability of antioxidant systems to decompose those products. Oxidative stress is implicated in the pathogenesis of hyperpigmentation, hypopigmentation, melanoma, and other skin diseases. Regulatory networks involving oxidative stress and related pathways are widely represented in hypopigmentation diseases, particularly vitiligo. However, there is no complete review into the role of oxidative stress in the pathogenesis of hyperpigmentation disorders, especially regarding associations involving oxidative stress and cellular signaling pathways. Here, we review oxidative and antioxidant systems, oxidative stress-induced signal transduction mechanisms, and effects of antioxidant drugs used in preclinical and clinical settings in hyperpigmentation disorders.

Biomimetic Melanosomes Promote Orientation-Selective Delivery and Melanocyte Pigmentation in the H2O2-Induced Vitiligo Mouse Model

Extremely limited drug retention and depigmentation represent the greatest barriers against vitiligo treatment advancement. Here, inspired by biological melanosomes, the primary melanin transporter, we developed biomimetic melanosomes to combat reactive oxygen species (ROS)-mediated melanocyte damage and depigmentation. Briefly, methylprednisolone (MPS) and melanin-mimicking polydopamine (PDA) were encapsulated inside lysine-proline-valine (KPV)-modified deformable liposomes (KPV-Lipos). Owing to their phospholipid bilayer flexibility and the specific affinity for melanocortin 1 receptor (MC1R), KPV-Lipos exhibited 1.43-fold greater skin deposition than traditional liposomes. The binding of KPV and its receptor also contributed to activating the cAMP-tyrosinase (TYR) signaling pathway, improving the endogenous melanin content. In addition, PDA mimicked melanosomes as it effectively increased the exogenous melanin content and scavenged ROS. Meanwhile, MPS inhibited inflammatory cytokine secretion, limiting the depigmented area. Ultimately, the biomimetic melanosomes affected the skin color of mice with H₂O₂-induced vitiligo. These melanosomes show potential as a universal platform for the self-supply of melanin by self-driven melanin synthesis with exogenous supplementation. Furthermore, this study offers ideas for the production of artificial packed melanosome substitutes for melanocyte-related diseases.

Elevated expression of NFE2L3 promotes the development of gastric cancer through epithelial-mesenchymal transformation

Gastric cancer (GC) is a malignant tumor with high mortality, but research on its molecular mechanisms remain limited. This study is the first to explore the biological role of nuclear factor NFE2L3 (nuclear factor, erythroid 2 like 3) in GC. We used Western blot and RT–qPCR to detect gene expression at the protein or mRNA level. Short hairpin RNA (shRNA) transfection was used to inhibit NFE2L3 expression. CCK-8 and colony formation assays were used to detect cell proliferation. Cell migration, invasion, cell cycle and apoptosis were detected by Transwell assays and flow cytometry. The results showed that NFE2L3 was highly expressed in gastric cancer tissues and promoted gastric cancer cell proliferation and metastasis. Inhibiting NFE2L3 expression blocks the cell cycle and increases the proportion of apoptotic cells, whereas NFE2L3 expression promotes the epithelial-mesenchymal transformation (EMT) process. In summary, NFE2L3 is highly expressed in gastric cancer and promotes gastric cancer cell proliferation and metastasis and the EMT process.

Effect of ultraviolet radiation on the Nrf2 signaling pathway in skin cells

PURPOSE

Excessive exposure of skin to solar radiation is associated with greatly increased production of reactive oxygen and nitrogen species (ROS, RNS) resulting in oxidative stress (OS), inflammation, immunosuppression, the production of matrix metalloproteinase, DNA damage and mutations. These events lead to increased incidence of various skin disorders including photoaing and both non-melanoma and melanoma skin cancers. The ultraviolet (UV) part of sunlight, in particular, is responsible for structural and cellular changes across the different layers of the skin. Among other effects, UV photons stimulate oxidative damage to biomolecules via the generation of unstable and highly reactive compounds. In response to oxidative damage, cytoprotective pathways are triggered. One of these is the pathway driven by the nuclear factor erythroid-2 related factor 2 (Nrf2). This transcription factor translocates to the nucleus and drives the expression of numerous genes, among them various detoxifying and antioxidant enzymes. Several studies concerning the effects of UV radiation on Nrf2 activation have been published, but different UV wavelengths, skin cells or tissues and incubation periods were used in the experiments that complicate the evaluation of UV radiation effects.

CONCLUSIONS

This review summarizes the effects of UVB (280-315 nm) and UVA (315-400 nm) radiation on the Nrf2 signaling pathway in dermal fibroblasts and epidermal keratinocytes and melanocytes. The effects of natural compounds (pure compounds or mixtures) on Nrf2 activation and level as well as on Nrf2-driven genes in UV irradiated human skin fibroblasts, keratinocytes and melanocytes are briefly mentioned as well.HighlightsUVB radiation is a rather poor activator of the Nrf2-driven pathway in fibroblastsUVA radiation stimulates Nrf2 activation in dermal fibroblastsEffects of UVA on the Nrf2 pathway in keratinocytes and melanocytes remain unclearLong-term Nrf2 activation in keratinocytes disturbs their normal differentiationPharmacological activation of Nrf2 in the skin needs to be performed carefully.

Anti-Inflammatory and Pro-Differentiating Properties of the Aryl Hydrocarbon Receptor Ligands NPD-0614-13 and NPD-0614-24: Potential Therapeutic Benefits in Psoriasis

The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor expressed in all skin cell types, plays a key role in physiological and pathological processes. Several studies have shown that this receptor is involved in the prevention of inflammatory skin diseases, e.g., psoriasis, atopic dermatitis, representing a potential therapeutic target. We tested the safety profile and the biological activity of NPD-0614-13 and NPD-0614-24, two new synthetic AhR ligands structurally related to the natural agonist FICZ, known to be effective in psoriasis. NPD-0614-13 and NPD-0614-24 did not alter per se the physiological functions of the different skin cell populations involved in the pathogenesis of inflammatory skin diseases. In human primary keratinocytes stimulated with tumor necrosis factor-α or lipopolysaccharide the compounds were able to counteract the altered proliferation and to dampen inflammatory signaling by reducing the activation of p38MAPK, c-Jun, NF-kBp65, and the release of cytokines. Furthermore, the molecules were tested for their beneficial effects in human epidermal and full-thickness reconstituted skin models of psoriasis. NPD-0614-13 and NPD-0614-24 recovered the psoriasis skin phenotype exerting pro-differentiating activity and reducing the expression of pro-inflammatory cytokines and antimicrobial peptides. These data provide a rationale for considering NPD-0614-13 and NPD-0614-24 in the management of psoriasis.

Participation of keratinocyte- and fibroblast-derived factors in melanocyte homeostasis, the response to UV, and pigmentary disorders

Human epidermal melanocytes play a central role in sensing the environment and protecting the skin from the drastic effects of solar ultraviolet radiation and other environmental toxins or inflammatory agents. Melanocytes survive in the epidermis for decades, which subjects them to chronic environmental insults. Melanocytes have a poor self-renewal capacity; therefore, it is critical to ensure their survival with genomic stability. The function and survival of melanocytes is regulated by an elaborate network of paracrine factors synthesized mainly by epidermal keratinocytes and dermal fibroblasts. A symbiotic relationship exists between epidermal melanocytes and keratinocytes on the one hand, and between melanocytes and dermal fibroblasts on the other hand. Melanocytes protect epidermal keratinocytes and dermal fibroblasts from the damaging effects of solar radiation, and the latter cells synthesize biochemical mediators that maintain the homeostasis, and regulate the stress response of melanocytes. Disruption of the paracrine network results in pigmentary disorders, due to abnormal regulation of melanin synthesis, and compromise of melanocyte survival or genomic stability. This review provides an update of the current knowledge of keratinocyte- and fibroblast-derived paracrine factors and their contribution to melanocyte physiology, and how their abnormal production is involved in the pathogenesis of common pigmentary disorders.

UVB protective effects of Sargassum horneri through the regulation of Nrf2 mediated antioxidant mechanism

The present study aimed to evaluate the protective effect of a methanol extract of Sargassum horneri (SHM), which contains 6-hydroxy-4,4,7a-trimethyl-5,6,7,7a-tetrahydrobenzofuran-2(4H)-one (HTT) and apo-9'-fucoxanthinone, against ultraviolet B (UVB)-induced cellular damage in human keratinocytes and its underlying mechanism. SHM significantly improved cell viability of UVB-exposed human keratinocytes by reducing the generation of intracellular reactive oxygen species (ROS). Moreover, SHM inhibited UVB exposure-induced apoptosis by reducing the formation of apoptotic bodies and the populations of the sub-G1 hypodiploid cells and the early apoptotic cells by modulating the expression of the anti- and pro-apoptotic molecules, Bcl-2 and Bax, respectively. Furthermore, SHM inhibited NF-κB p65 activation by inducing the activation of Nrf2/HO-1 signaling. The cytoprotective and antiapoptotic activities of SHM are abolished by the inhibition of HO-1 signaling. In further study, SHM restored the skin dryness and skin barrier disruption in UVB-exposed human keratinocytes. Based to these results, our study suggests that SHM protects the cells against UVB-induced cellular damages through the Nrf2/HO-1/NF-κB p65 signaling pathway and may be potentially useful for the prevention of UVB-induced skin damage.

The α-melanocyte-stimulating hormone/melanocortin-1 receptor interaction: A driver of pleiotropic effects beyond pigmentation

Melanocortin-1 Receptor (MC1R), when stimulated by alpha-melanocyte-stimulating hormone (α-MSH), is a driver of eumelanogenesis. Brown/black eumelanin is an effective filter against ultraviolet radiation (UVR) and is a scavenger of free radicals. Several polymorphic variants of MC1R are frequent in red-head people. These polymorphisms reduce the ability of MC1R to promote eumelanogenesis after its activation and spontaneous pheomelanogenesis take place. Since pheomelanin can act as an endogenous photosensitizer, people carrying MC1R polymorphisms are more susceptible to skin cancer. Here, we summarize current knowledge on the biology of MC1R beyond its ability to drive eumelanogenesis. We analyze its capacity to cope with oxidative insult and consequent DNA damage. We describe its ability to transduce through different pathways. We start from the canonical pathway, the cAMP/protein kinase A (PKA) pathway mainly involved in promoting eumelanogenesis, and protection from oxidative damage, and we then move on to describe more recent knowledge concerning ERK pathways, phosphoinositide 3-kinase (PI3K) pathway/AKT, and α-MSH/Peroxisome proliferators activated receptor-γ (PPAR-γ) connection. We describe MC1R polymorphic variants associated with melanoma risk which represent an open window of clinical relevance.

Neuropeptides and neurohormones in immune, inflammatory and cellular responses to ultraviolet radiation

Humans are exposed to varying amounts of ultraviolet radiation (UVR) through sunlight. UVR penetrates into human skin leading to release of neuropeptides, neurotransmitters and neuroendocrine hormones. These messengers released from local sensory nerves, keratinocytes, Langerhans cells (LCs), mast cells, melanocytes and endothelial cells (ECs) modulate local and systemic immune responses, mediate inflammation and promote differing cell biologic effects. In this review, we will focus on both animal and human studies that elucidate the roles of calcitonin gene-related peptide (CGRP), substance P (SP), nerve growth factor (NGF), nitric oxide and proopiomelanocortin (POMC) derivatives in mediating immune and inflammatory effects of exposure to UVR as well as other cell biologic effects of UVR exposure.

Involvement of adenylate cyclase/cAMP/CREB and SOX9/MITF in melanogenesis to prevent vitiligo

Vitiligo is autoimmune, acquired, idiopathic, chronic, and progressive de/hypopigmentary cutaneous condition that targets the cell-producing pigment called melanin. It binds to a thread of great disappointment and emotional stress in societies. Combining multiple stress-related theories like toxic compound accumulation, autoimmunity, mutations, altered cellular environment, infection, impaired migration/proliferation, and immunological mismatch of anti-melanocyte and self-reactive T-cells that cause melanocytes damage is formulated resulting in vitiligo. Vitiligo has an orphan status for drug synthesis. Still, different therapies are available, with topical steroids and narrow-band ultraviolet-B monotherapy being the most common treatments, others including medical, physical, or surgical, but not effective. Each modality has its baggage of disadvantages and side effects. Stimulation of the transcriptional process for melanogenesis is mainly achieved by the cAMP-dependent activation of several melanogenic genes by MITF. In this review, we summarized that cAMP encourages the expression of the enzyme tyrosinase, TYRP1, TYRP2, and most other biological effects of cAMP are mediated through the cAMP-dependent PKA pathway resulting in CREB phosphorylation. It has been shown that TYRP1 and 2 do not have cAMP response elements (CREs) in promoting regions; the regulation of these genes by cAMP occurs through the direct participation of MITF during melanogenesis. The available medicines, therefore, only provide symptomatic relief, but do not stop the disease progression. In addition, the treatment process needs to be changed; existing approaches need to be overlooked for patients who are suffering and therefore analyze its efficacy and safety to achieve a favorable risk-benefit ratio.

Nuclear factor erythroid 2-related factor 2 (Nrf2) as a potential therapeutic target for vitiligo

Vitiligo is an autoimmune disease of the skin which causes loss of melanocytes from the epidermis. Recently, it is demonstrated that oxidative stress (OS) plays a significant role in the immuno-pathogenesis of vitiligo. A major mechanism in the cellular defense against OS is activation of the nuclear factor erythroid2-related factor (Nrf2)-Kelch-like ECH-associated protein 1(Keap1)-antioxidant responsive element (ARE) signaling pathway. Recently it has been shown that vitiligo melanocytes have impaired Nrf2-ARE signaling. A number of drugs including those known as Nrf2 activators and those known to possess effects to activate Nrf2, have been used in treating vitiligo with certain therapeutic effects. Also, studies have shown that a number of compounds can protect melanocytes against OS via activating Nrf2. These compounds may be considered as candidates for developing new drugs for vitiligo in the future. Nrf2 can be considered as a potential therapeutic target for vitiligo.

Extracellular fraction of adipose tissue as an innovative regenerative approach for vitiligo treatment

Vitiligo is a common, disfiguring autoimmune disease that negatively affects patients' self-esteem and quality of life. Current treatments are moderately effective in reversing disease and promoting melanocyte regeneration. Thus, therapeutic advanced strategies are emerging from regenerative medicine. It has recently emerged that adipose tissue secretome may be used as a cell-free therapy in skin regeneration since paracrine functions of adipose-derived stem cells alone are responsible for most of the therapeutic effect of stem cells in several animal disease models. In this study, we tested the effect of adipose tissue extracellular fraction (AT-Ex) isolated from lipoaspirates on dermal and epidermal vitiligo cells in vitro. Using this experimental model, we demonstrated that molecules secreted by adipose tissue ameliorate the capability to counteract oxidative stress by a physiological stimulation of intracellular antioxidant enzymes and positively impact on cell proliferation. Due to the presence of Wnt-secreted factors, AT-Ex treatment promotes glycogen synthase kinase 3β inactivation and consequently Wnt/β-catenin pathway activation. Collectively, our findings show that AT-Ex could be useful as a natural approach to improve treatment of vitiligo.

Phosphodiesterase Inhibitors for Alzheimer's Disease: A Systematic Review of Clinical Trials and Epidemiology with a Mechanistic Rationale

BACKGROUND

Preclinical studies, clinical trials, and reviews suggest increasing 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP) with phosphodiesterase inhibitors is disease-modifying in Alzheimer's disease (AD). cAMP/protein kinase A (PKA) and cGMP/protein kinase G (PKG) signaling are disrupted in AD. cAMP/PKA and cGMP/PKG activate cAMP response element binding protein (CREB). CREB binds mitochondrial and nuclear DNA, inducing synaptogenesis, memory, and neuronal survival gene (e.g., brain-derived neurotrophic factor) and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α). cAMP/PKA and cGMP/PKG activate Sirtuin-1, which activates PGC1α. PGC1α induces mitochondrial biogenesis and antioxidant genes (e.g.,Nrf2) and represses BACE1. cAMP and cGMP inhibit BACE1-inducing NFκB and tau-phosphorylating GSK3β.

OBJECTIVE AND METHODS

We review efficacy-testing clinical trials, epidemiology, and meta-analyses to critically investigate whether phosphodiesteraseinhibitors prevent or treat AD.

RESULTS

Caffeine and cilostazol may lower AD risk. Denbufylline and sildenafil clinical trials are promising but preliminary and inconclusive. PF-04447943 and BI 409,306 are ineffective. Vinpocetine, cilostazol, and nicergoline trials are mixed. Deprenyl/selegiline trials show only short-term benefits. Broad-spectrum phosphodiesterase inhibitor propentofylline has been shown in five phase III trials to improve cognition, dementia severity, activities of daily living, and global assessment in mild-to-moderate AD patients on multiple scales, including the ADAS-Cogand the CIBIC-Plus in an 18-month phase III clinical trial. However, two books claimed based on a MedScape article an 18-month phase III trial failed, so propentofylline was discontinued. Now, propentofylline is used to treat canine cognitive dysfunction, which, like AD, involves age-associated wild-type Aβ deposition.

CONCLUSION

Phosphodiesterase inhibitors may prevent and treat AD.

Copper/Zinc Superoxide Dismutase in Human Skin: Current Knowledge

Superoxide dismutase is widespread in the human body, including skin and its appendages. Here, we focus on human skin copper/zinc superoxide dismutase, the enzyme that protects skin and its appendages against reactive oxygen species. Human skin copper/zinc superoxide dismutase resides in the cytoplasm of keratinocytes, where up to 90% of cellular reactive oxygen species is produced. Factors other than cell type, such as gender, age and diseased state influence its location in skin tissues. We review current knowledge of skin copper/zinc superoxide dismutase including recent studies in an attempt to contribute to solving the question of its remaining unexplained functions. The research described here may be applicable to pathologies associated with oxidative stress. However, recent studies on copper/zinc superoxide dismutase in yeast reveal that its predominant function may be in signaling pathways rather than in scavenging superoxide ions. If confirmed in the skin, novel approaches might be developed to unravel the enzyme's remaining mysteries.

The enigma and challenges of vitiligo pathophysiology and treatment

Vitiligo is the most common acquired pigmentary disorder, which afflicts 0.5%-1% of the world population, and is characterized by depigmented skin patches resulting from melanocyte loss. Vitiligo has a complex etiology and varies in its manifestations, progression, and response to treatment. It presents as an autoimmune disease, evidenced by circulating melanocyte-specific antibodies, and association with other autoimmune diseases. However, autoimmunity may be secondary to the high oxidative stress in vitiligo skin and to intrinsic defects in melanocytes and their microenvironment, which contribute to aberrant stress response, neo-antigenicity, and susceptibility of melanocytes to immune attack and apoptosis. There is also a genetic predisposition to vitiligo, which sensitizes melanocytes to environmental agents, such as phenolic compounds. Currently, there are different treatment modalities for re-pigmenting vitiligo skin. However, when repigmentation is achieved, the major challenge is maintaining the pigmentation, which is lost in 40% of cases. In this review, we present an overview of the clinical aspects of vitiligo, its pathophysiology, the intrinsic defects in melanocytes and their microenvironment, and treatment strategies. Based on lessons from the biology of human melanocytes, we present our perspective of how repigmentation of vitiligo skin can be achieved and sustained.

Glutathione dynamics determine the therapeutic efficacy of mesenchymal stem cells for graft-versus-host disease via CREB1-NRF2 pathway

Glutathione (GSH), the most abundant nonprotein thiol functioning as an antioxidant, plays critical roles in maintaining the core functions of mesenchymal stem cells (MSCs), which are used as a cellular immunotherapy for graft-versus-host disease (GVHD). However, the role of GSH dynamics in MSCs remains elusive. Genome-wide gene expression profiling and high-throughput live-cell imaging assays revealed that CREB1 enforced the GSH-recovering capacity (GRC) of MSCs through NRF2 by directly up-regulating NRF2 target genes responsible for GSH synthesis and redox cycling. MSCs with enhanced GSH levels and GRC mediated by CREB1-NRF2 have improved self-renewal, migratory, anti-inflammatory, and T cell suppression capacities. Administration of MSCs overexpressing CREB1-NRF2 target genes alleviated GVHD in a humanized mouse model, resulting in improved survival, decreased weight loss, and reduced histopathologic damages in GVHD target organs. Collectively, these findings demonstrate the molecular and functional importance of the CREB1-NRF2 pathway in maintaining MSC GSH dynamics, determining therapeutic outcomes for GVHD treatment.

Transepidermal UV radiation of scalp skin ex vivo induces hair follicle damage that is alleviated by the topical treatment with caffeine

Objectives

Although the effect of ultraviolet radiation (UVR) on human skin has been extensively studied, very little is known on how UVR impacts on hair follicle (HF) homeostasis. Here, we investigated how solar spectrum UVR that hits the human skin surface impacts on HF biology, and whether any detrimental effects can be mitigated by a widely used cosmetic and nutraceutical ingredient, caffeine.

Methods

Human scalp skin with terminal HFs was irradiated transepidermally ex vivo using either 10 J/cm²UVA (340–440 nm) + 20 mJ/cm²UVB (290–320 nm) (low dose) or 50 J/cm²UVA + 50 mJ/cm²UVB (high dose) and organ‐cultured under serum‐free conditions for 1 or 3 days. 0.1% caffeine (5.15 mmol/L) was topically applied for 3 days prior to UV exposure with 40 J/cm²UVA + 40 mJ/cm²UVB and for 3 days after UVR. The effects on various toxicity and vitality read‐out parameters were measured in defined skin and HF compartments.

Results

Consistent with previous results, transepidermal UVR exerted skin cytotoxicity and epidermal damage. Treatment with high and/or low UVA+UVB doses also induced oxidative DNA damage and cytotoxicity in human HFs. In addition, it decreased proliferation and promoted apoptosis of HF outer root sheath (ORS) and hair matrix (HM) keratinocytes, stimulated catagen development, differentially regulated the expression of HF growth factors, and induced perifollicular mast cell degranulation. UVR‐mediated HF damage was more severe after irradiation with high UVR dose and reached also proximal HF compartments. The topical application of 0.1% caffeine did not induce skin or HF cytotoxicity and stimulated the expression of IGF‐1 in the proximal HF ORS. However, it promoted keratinocyte apoptosis in selected HF compartments. Moreover, caffeine provided protection towards UVR‐mediated HF cytotoxicity and dystrophy, keratinocyte apoptosis, and tendential up‐regulation of the catagen‐promoting growth factor.

Conclusion

Our study highlights the clinical relevance of our scalp UV irradiation ex vivo assay and provides the first evidence that transepidermal UV radiation negatively affects important human HF functions. This suggests that it is a sensible prophylactic strategy to integrate agents such as caffeine that can act as HF photoprotectants into sun‐protective cosmeceutical and nutraceutical formulations.

Discovery of a Highly Selective MC1R Agonists Pentapeptide to Be Used as a Skin Pigmentation Enhancer and with Potential Anti-Aging Properties

One of the first lines of cutaneous defense against photoaging is (a) the synthesis of melanin and (b) the initiation of an oxidative stress response to protect skin against the harmful effects of solar radiation. Safe and selective means to stimulate epidermal pigmentation associated with oxidative stress defense are; however, scarce. Activation of the melanocortin-1 receptor (MC1R) on epidermal melanocytes represents a key step in cutaneous pigmentation initiation and, additionally, it regulates cellular defense mechanisms like oxidative stress and DNA-repair. Thus, making the activation of MC1R an attractive strategy for modulating skin pigmentation and oxidative stress. In this context, we designed and synthesized pentapeptides that act as MC1R agonists. These peptides bound, with high potency, to MC1R and activated cAMP synthesis in CHO cells expressing human MC1R. Using one lead pentapeptide, we could show that this activation of MC1R was specific as testing the activation of other G-protein coupled receptors, including the MC-receptor family, was negative. In vitro efficacy on mouse melanoma cells showed similar potency as for the synthetic MC1R agonist alpha-melanocyte stimulating hormone (NDP-alpha-MSH). Moreover, we could reproduce this activity in human skin tissue culture. The lead pentapeptide was able to induce ex-vivo protein expression of key melanogenesis markers melanocyte inducing transcription factor (MITF), tyrosinase (TYR), and tyrosinase-related protein 1 (TYRP-1). Concerning oxidative stress response, we found that the pentapeptide enhanced the activation of Nrf2 after UVA-irradiation. Our results make this pentapeptide an ideal candidate as a skin pigmentation enhancer that mimics alpha-MSH and may also have anti-photoaging effects on the skin.

Signaling Pathways, Chemical and Biological Modulators of Nucleotide Excision Repair: The Faithful Shield against UV Genotoxicity

The continuous exposure of the human body's cells to radiation and genotoxic stresses leads to the accumulation of DNA lesions. Fortunately, our body has several effective repair mechanisms, among which is nucleotide excision repair (NER), to counteract these lesions. NER includes both global genome repair (GG-NER) and transcription-coupled repair (TC-NER). Deficiencies in the NER pathway underlie the development of several DNA repair diseases, such as xeroderma pigmentosum (XP), Cockayne syndrome (CS), and trichothiodystrophy (TTD). Deficiencies in GG-NER and TC-NER render individuals to become prone to cancer and neurological disorders, respectively. Therefore, NER regulation is of interest in fine-tuning these risks. Distinct signaling cascades including the NFE2L2 (NRF2), AHR, PI3K/AKT1, MAPK, and CSNK2A1 pathways can modulate NER function. In addition, several chemical and biological compounds have proven success in regulating NER's activity. These modulators, particularly the positive ones, could therefore provide potential treatments for genetic DNA repair-based diseases. Negative modulators, nonetheless, can help sensitize cells to killing by genotoxic chemicals. In this review, we will summarize and discuss the major upstream signaling pathways and molecules that could modulate the NER's activity.

The alpha-melanocyte-stimulating hormone acts as a local immune homeostasis factor in experimental allergic asthma

BACKGROUND

Originally, the neuropeptide α-melanocyte-stimulating hormone (α-MSH) has been described as a mediator of skin pigmentation. However, recent studies have shown that α-MSH is able to modulate inflammation in various tissues including the lung. So far, it is still not clear whether α-MSH also plays a role in allergic bronchial asthma.

OBJECTIVE

This study aimed at investigating the role and regulatory mechanisms of α-MSH in asthma pathogenesis.

METHODS

α-MSH levels were measured in bronchoalveolar lavage (BAL) fluid of asthmatic and non-asthmatic individuals as well as of healthy mice and mice with experimental asthma. Wild-type mice were sensitized to ovalbumin (OVA) and exposed to an OVA aerosol in order to induce experimental allergic asthma. α-MSH was administrated intratracheally, the α-MSH antibody intraperitoneally prior each OVA challenge. Airway inflammation, cytokine production, mucus production, airway hyperresponsiveness and receptor expression were assessed.

RESULTS

α-MSH levels in BAL of asthmatic individuals and mice were significantly higher compared to healthy controls. In a mouse model of experimental asthma, α-MSH neutralization increased airway inflammation and mucus production, whereas local administration of α-MSH significantly reduced inflammation of the airways. The beneficial effects were further associated with decreased levels of eosinophilic chemoattractant factors that are released by MC5R-positive T helper 2 and airway epithelial cells.

CONCLUSION AND CLINICAL RELEVANCE

α-MSH acts as a regulatory factor to maintain local immune homeostasis in allergic bronchial asthma.

Are melanocortin peptides future therapeutics for cutaneous wound healing?

Cutaneous wound healing is a complex process divided into different phases, that is an inflammatory, proliferative and remodelling phase. During these phases, a variety of resident skin cell types but also cells of the immune system orchestrate the healing process. In the last year, it has been shown that the majority of cutaneous cell types express the melanocortin 1 receptor (MC1R) that binds α-melanocyte-stimulating hormone (α-MSH) with high affinity and elicits pleiotropic biological effects, for example modulation of inflammation and immune responses, cytoprotection, antioxidative defense and collagen turnover. Truncated α-MSH peptides such as Lys-Pro-Val (KPV) as well as derivatives like Lys-d-Pro-Thr (KdPT), the latter containing the amino acid sequence 193-195 of interleukin-1β, have been found to possess anti-inflammatory effects but to lack the pigment-inducing activity of α-MSH. We propose here that such peptides are promising future candidates for the treatment of cutaneous wounds and skin ulcers. Experimental approaches in silico, in vitro, ex vivo and in animal models are outlined. This is followed by an unbiased discussion of the pro and contra arguments of such peptides as future candidates for the therapeutic management of cutaneous wounds and a review of the so-far available data on melanocortin peptides and derivatives in wound healing.

NDP-MSH reduces oxidative damage induced by palmitic acid in primary astrocytes

Recent findings relate obesity to inflammation in key hypothalamic areas for body weight control. Hypothalamic inflammation has also been related to oxidative stress. Palmitic acid (PA) is the most abundant free fatty acid found in food, and in vitro studies indicate that it triggers a pro-inflammatory response in the brain. Melanocortins are neuropeptides with proven anti-inflammatory and neuroprotective action mediated by melanocortin receptor 4 (MC4R), but little is known about the effect of melanocortins on oxidative stress. The aim of this study was to investigate whether melanocortins could alleviate oxidative stress induced by a high fat diet (HFD) model. We found that NDP-MSH treatment decreased PA-induced reactive oxygen species production in astrocytes, an effect blocked by the MC4R inhibitor JKC363. NDP-MSH abolished nuclear translocation of Nrf2 induced by PA and blocked the inhibitory effect of PA on superoxide dismutase (SOD) activity and glutathione levels while it also per se increased activity of SOD and γ-glutamate cysteine ligase (γ-GCL) antioxidant enzymes. However, HFD reduced hypothalamic MC4R and brain derived neurotrophic factor mRNA levels, thereby preventing the neuroprotective mechanism induced by melanocortins.

UVB-mediated down-regulation of proteasome in cultured human primary pterygium fibroblasts

Background

Pterygium is a condition characterized by epithelial overgrowth of the cornea, inflammatory cell infiltration and an abnormal extracellular matrix accumulation. Chronic UV exposure is considered as a pathogenic factor of this disease. Proteasome is an intracellular multi-subunit protease complex that degrades intracellular proteins. Among proteasome subunits the β5 (PSMB5), bearing chymotrypsin-like activity. It is considered as the main proteasome subunit and its expression is mediated by Nrf2-ARE pathway in many cell types. This study investigates the expression of PSMB5 in pterygium and the effect of UVB irradiation on its expression and activity in pterygium fibroblasts.

Methods

Normal conjunctival and pterygium specimens were obtained from the bulbar conjunctiva of patients undergoing cataract surgery and from patients with pterygium undergoing surgical removal of primary tissue, respectively. Fibroblasts were isolated upon treatment of specimens with clostridium collagenase. The expression of PSMB5 and Nrf2 in tissues and cells was ascertained by RT-PCR analysis and western blotting. Cell survival was measured by the MTT method and the proteasome chymotrypsin-like activity was determined by fluorometry.

Results

RT-PCR analysis showed that the expression of PSMB5 was significantly lower in pterygium than in normal conjunctiva. The expression of PSMB5 was mediated by the Nrf2/ARE pathway as indicated by using the Nrf2 activator Oltipraz. The expression of PSMB5 and Nrf2 by pterygium fibroblasts was suppressed in a dose dependent manner following UVB radiation of 0–50 mJ/cm² doses. The expression of PSMB5, but not of Nrf2, remained at almost the control levels, when UVB exposure was performed after pre-incubation of cells with the src kinases inhibitor PP2. UVB irradiation had very low deleterious effect on fibroblasts survival, while it did not affect the proteasome chymotrypsin-like activity.

Conclusion

In pterygium fibroblasts, UVB exposure leads to down-regulation of Nrf2/ARE-mediated PSMB5 gene expression, in which src kinases may be implicated. This effect may be partially responsible for the lower expression of PSMB5 detected in pterygium as compared to normal conjunctiva.

Melatonin and Its Metabolites Ameliorate UVR-Induced Mitochondrial Oxidative Stress in Human MNT-1 Melanoma Cells

Melatonin (Mel) is the major biologically active molecule secreted by the pineal gland. Mel and its metabolites, 6-hydroxymelatonin (6(OH)Mel) and 5-methoxytryptamine (5-MT), possess a variety of functions, including the scavenging of free radicals and the induction of protective or reparative mechanisms in the cell. Their amphiphilic character allows them to cross cellular membranes and reach subcellular organelles, including the mitochondria. Herein, the action of Mel, 6(OH)Mel, and 5-MT in human MNT-1 melanoma cells against ultraviolet B (UVB) radiation was investigated. The dose of 50 mJ/cm² caused a significant reduction of cell viability up to 48%, while investigated compounds counteracted this deleterious effect. UVB exposure increased catalase activity and led to a simultaneous Ca⁺⁺ influx (16%), while tested compounds prevented these disturbances. Additional analysis focused on mitochondrial respiration performed in isolated mitochondria from the liver of BALB/cJ mice where Mel, 6(OH)Mel, and 5-MT significantly enhanced the oxidative phosphorylation at the dose of 10⁻⁶ M with lower effects seen at 10⁻⁹ or 10⁻⁴ M. In conclusion, Mel, 6(OH)Mel and 5-MT protect MNT-1 cells, which express melatonin receptors (MT1 and MT2) against UVB-induced oxidative stress and mitochondrial dysfunction, including the uncoupling of oxidative phosphorylation.

The potential role of antioxidants in mitigating skin hyperpigmentation resulting from ultraviolet and visible light-induced oxidative stress

Oxidative stress is an integral element that influences a variety of biochemical reactions throughout the body and is known to play a notable role in melanogenesis. Exogenous triggers of oxidative stress, such as ultraviolet radiation (UVR) and visible light (VL), lead to pigment formation through somewhat different pathways, but both share a common endpoint-the potential to generate cosmetically undesirable hyperpigmentation. Though organic and inorganic sunscreens are available to protect against the UVR portion of the electromagnetic spectrum, coverage is lacking to protect against the VL spectrum. In this manuscript, we review the phases of tanning, pathways of melanogenesis triggered by UVR and VL, and the associated impact of oxidative stress. We also discuss the known intrinsic mechanisms and paracrine regulation of melanocytes that influence their response to UVR. Understanding these mechanisms and their role in UVR-induced hyperpigmentation should potentially lead to identification of useful targets that can be coupled with antioxidant therapy to alleviate this effect.

Effects and Mechanism of Nicotinamide Against UVA- and/or UVB-mediated DNA Damages in Normal Melanocytes

Melanoma incidences are increasing rapidly, and ultraviolet (UV) radiation from the sun is believed to be its major contributing factor. UV exposure causes DNA damage in skin which may initiate cutaneous skin cancers including melanoma. Melanoma arises from melanocytes, the melanin-producing skin cells, following genetic dysregulations resulting into hyperproliferative phenotype and neoplastic transformation. Both UVA and UVB exposures to the skin are believed to trigger melanocytic hyperplasia and melanomagenesis. Melanocytes by themselves are deficient in repair of oxidative DNA damage and UV-induced photoproducts. Nicotinamide, an active form of vitamin B3 and a critical component of the human body's defense system has been shown to prevent certain cancers including nonmelanoma skin cancers. However, the mechanism of nicotinamide's protective effects is not well understood. Here, we investigated potential protective effects and mechanism of nicotinamide against UVA- and/or UVB- induced damage in normal human epidermal melanocytes. Our data demonstrated an appreciable protective effect of nicotinamide against UVA- and/or UVB- induced DNA damage in melanocytes by decreasing both cyclobutane pyrimidine dimers and 8-hydroxy-2'-deoxyguanosine levels. We found that the photoprotective response of nicotinamide was associated with the activation of nucleotide excision repair genes and NRF2 signaling. Further studies are needed to validate our findings in in vivo models.

MC1R: Front and Center in the Bright Side of Dark Eumelanin and DNA Repair

Melanin, the pigment produced by specialized cells, melanocytes, is responsible for skin and hair color. Skin pigmentation is an important protective mechanism against the DNA damaging and mutagenic effects of solar ultraviolet radiation (UV). It is acknowledged that exposure to UV is the main etiological environmental factor for all forms of skin cancer, including melanoma. DNA repair capacity is another major factor that determines the risk for skin cancer. Human melanocytes synthesize eumelanin, the dark brown form of melanin, as well as pheomelanin, which is reddish-yellow in color. The relative rates of eumelanin and pheomelanin synthesis by melanocytes determine skin color and the sensitivity of skin to the drastic effects of solar UV. Understanding the complex regulation of melanocyte function and how it responds to solar UV has a huge impact on developing novel photoprotective strategies to prevent skin cancer, particularly melanoma, the most fatal form, which originates from melanocytes. This review provides an overview of the known differences in the photoprotective effects of eumelanin versus pheomelanin, how these two forms of melanin are regulated genetically and biochemically, and their impact on the DNA damaging effects of UV exposure. Additionally, this review briefly discusses the role of paracrine factors, focusing on α-melanocortin (α-melanocyte stimulating hormone; α-MSH), in regulating melanogenesis and the response of melanocytes to UV, and describes a chemoprevention strategy based on targeting the melanocortin 1 receptor (MC1R) by analogs of its physiological agonist α-MSH.

Resveratrol: from diet to topical usage

The stilbene derivative resveratrol (3,5,4'-trihydroxy-stilbene; RESV) has become the subject of interest of many researchers and the pharmaceutical industries due to its well-acclaimed beneficial biological activities. Although earlier research tended to focus on the effects of RESV on cardiovascular disorders, many other studies have described the beneficial effects of RESV in the areas of cancer chemoprevention and inflammation and interest of researchers on this compound is still increasing. It is now well accepted that the effect of RESV is not just due to its so called "antioxidant" activity but mainly (if not only) because of the ability of this compound to trigger cell signaling pathways and gene expression involved in cellular defense systems. Many "in vitro" studies on RESV did not take into account that although its oral absorption is about 75% it undergoes rapid metabolism and the concentration in the blood stream is almost undetectable. For this reason interest in the topical usage of RESV by cosmeceutical skin care brands has exponentially increased in the last decade reporting in general very promising results on its beneficial effect in protecting the skin from outdoor insults, but there is still some controversy on its topical usage mainly surrounding the concentration used. Therefore, more basic research on the topical application of RESV should be performed to better understand the way it prevents cutaneous damage and whether it could be recommended as a preventive skin aging agent for all skin insults.

αMSH prevents ROS-induced apoptosis by inhibiting Foxo1/mTORC2 in mice adipose tissue

Alpha-melanocyte stimulating hormone (αMSH) is an important adenohypophysis polypeptide hormone that regulates body metabolic status. To date, it is well known that the disorder of hypothalamic αMSH secretion is related to many metabolic diseases, such as obesity and type II diabetes. However, the underlying mechanisms are poorly understood. In our study, we focused on the reactive oxygen species (ROS)-induced adipocyte apoptosis and tried to unveil the role of αMSH in this process and the signal pathway which αMSH acts through. Kunming white mice were used and induced to oxidative stress status by hydrogen peroxide (H2O2) injection and a significant reduction of αMSH were found in mice serum, while elevated ROS level and mRNA level of pro-apoptotic genes were observed in mice adipose tissue. What is more, when detect the function of αMSH in ROS-induced apoptosis, similar inhibitory trend was found with the oxidative stress inhibitor N-acetyl-L-cysteine (NAC) in ROS-induced adipocyte apoptosis and this trend is αMSH receptor melanocortin 5 receptor (MC5R) depended, while an opposite trend was found between αMSH and Foxo1, which is a known positive regulator of adipocyte apoptosis. Further, we found that the repress effect of αMSH in adipocytes apoptosis is acting through Foxo1/mTORC2 pathway. These findings indicate that, αMSH has a strong inhibitory effect on ROS-induced adipocyte apoptosis and underlying mechanism is interacting with key factors in mTOR signal pathway. Our study demonstrated a great role of αMSH in adipocyte apoptosis and brings a new therapeutic mean to the treatment of obesity and diabetes.

Ultraviolet Radiations: Skin Defense-Damage Mechanism

UV-radiations are the invisible part of light spectra having a wavelength between visible rays and X-rays. Based on wavelength, UV rays are subdivided into UV-A (320-400 nm), UV-B (280-320 nm) and UV-C (200-280 nm). Ultraviolet rays can have both harmful and beneficial effects. UV-C has the property of ionization thus acting as a strong mutagen, which can cause immune-mediated disease and cancer in adverse cases. Numbers of genetic factors have been identified in human involved in inducing skin cancer from UV-radiations. Certain heredity diseases have been found susceptible to UV-induced skin cancer. UV radiations activate the cutaneous immune system, which led to an inflammatory response by different mechanisms. The first line of defense mechanism against UV radiation is melanin (an epidermal pigment), and UV absorbing pigment of skin, which dissipate UV radiation as heat. Cell surface death receptor (e.g. Fas) of keratinocytes responds to UV-induced injury and elicits apoptosis to avoid malignant transformation. In addition to the formation of photo-dimers in the genome, UV also can induce mutation by generating ROS and nucleotides are highly susceptible to these free radical injuries. Melanocortin 1 receptor (MC1R) has been known to be implicated in different UV-induced damages such as pigmentation, adaptive tanning, and skin cancer. UV-B induces the formation of pre-vitamin D3 in the epidermal layer of skin. UV-induced tans act as a photoprotection by providing a sun protection factor (SPF) of 3-4 and epidermal hyperplasia. There is a need to prevent the harmful effects and harness the useful effects of UV radiations.

The activation of PPARγ by 2,4,6-Octatrienoic acid protects human keratinocytes from UVR-induced damages

Increasing attention is addressed to identify products able to enhance skin photoprotection and to prevent skin carcinogenesis. Several studies have demonstrated that the α-melanocyte stimulating hormone (αMSH), acting on a functional MC1R, provides a photoprotective effect by inducing pigmentation, antioxidants and DNA repair. We discovered a link between αMSH and the nuclear receptor Peroxisome Proliferator-Activated Receptor-γ (PPARγ), suggesting that some of the αMSH protective effects may be dependent on PPARγ transcriptional activity. Moreover, we demonstrated that the activation of PPARγ by the parrodiene 2,4,6-octatrienoic acid (Octa) induces melanogenesis and antioxidant defence in human melanocytes and counteracts senescence-like phenotype in human fibroblasts. In this study, we demonstrate that the activation of PPARγ by Octa exerts a protective effect against UVA- and UVB-induced damage on normal human keratinocytes (NHKs), the major target cells of UV radiation. Octa promotes the antioxidant defence, augments DNA repair and reduces the induction of proteins involved in UV-induced DNA damage response. Our results contribute to deepen the analysis of the αMSH/PPARγ connection and suggest perspectives for the development of new molecules and formulations able to prevent cutaneous UV damage by acting on the different skin cell populations through PPARγ activation.