Oxidative Stress-Induced HMGB1 Release from Melanocytes: A Paracrine Mechanism Underlying the Cutaneous Inflammation in Vitiligo

TRPM2-dependent autophagy inhibition exacerbates oxidative stress-induced CXCL16 secretion by keratinocytes in vitiligo

Vitiligo is a depigmented skin disease due to the destruction of melanocytes. Under oxidative stress, keratinocyte-derived chemokine C-X-C motif ligand 16 (CXCL16) plays a critical role in recruiting CD8+ T cells, which kill melanocytes. Autophagy serves as a protective cell survival mechanism and impairment of autophagy has been linked to increased secretion of the proinflammatory cytokines. However, the role of autophagy in the secretion of CXCL16 under oxidative stress has not been investigated. Herein, we initially found that autophagy was suppressed in both keratinocytes of vitiligo lesions and keratinocytes exposed to oxidative stress in vitro. Autophagy inhibition also promoted CXCL16 secretion. Furthermore, upregulated transient receptor potential cation channel subfamily M member 2 (TRPM2) functioned as an upstream oxidative stress sensor to inhibit autophagy. Moreover, TRPM2-mediated Ca2+ influx activated calpain to shear autophagy related 5 (Atg5) and Atg12-Atg5 conjugate formation was blocked to inhibit autophagy under oxidative stress. More importantly, Atg5 downregulation enhanced the binding of interferon regulatory factor 3 (IRF3) to the CXCL16 promoter region by activating Tank-binding kinase 1 (TBK1), thus promoting CXCL16 secretion. These findings suggested that TRPM2-restrained autophagy promotes CXCL16 secretion via the Atg5-TBK1-IRF3 signaling pathway under oxidative stress. Inhibition of TRPM2 may serve as a potential target for the treatment of vitiligo. © 2024 The Pathological Society of Great Britain and Ireland.

The effects of advanced glycation end-products on skin and potential anti-glycation strategies

The advanced glycation end-products (AGEs) are produced through non-enzymatic glycation between reducing sugars and free amino groups, such as proteins, lipids or nucleic acids. AGEs can enter the body through daily dietary intake and can also be generated internally via normal metabolism and external stimuli. AGEs bind to cell surface receptors for AGEs, triggering oxidative stress and inflammation responses that lead to skin ageing and various diseases. Evidence shows that AGEs contribute to skin dysfunction and ageing. This review introduces the basic information, the sources, the metabolism and absorption of AGEs. We also summarise the detrimental mechanisms of AGEs to skin ageing and other chronic diseases. For the potential strategies for counteracting AGEs to skin and other organs, we summarised the pathways that could be utilised to resist glycation. Chemical and natural-derived anti-glycation approaches are overviewed. This work offers an understanding of AGEs to skin ageing and other chronic diseases and may provide perspectives for the development of anti-glycation strategies.

JAK inhibitors for the treatment of vitiligo

Vitiligo is an autoimmune disease involving melanocyte-targeting T cells initiated by environmental and genetic factors. Steroids and tacrolimus have been used as topical treatments. Recently, novel topical agents targeting Janus kinase (JAK), a family of tyrosine kinases that regulates cytokine signaling, have emerged. Ruxolitinib is the first approved in vitiligo therapy. Furthermore, ritlecitinib is currently under clinical trials for oral treatment of active vitiligo. In this review, we discuss the possibility of topical JAK inhibitors as promising options for the treatment of vitiligo with regard to their mechanism of action, efficacy and safety.

ISG15-USP18 Dysregulation by Oxidative Stress Promotes IFN-γ Secretion from CD8+ T Cells in Vitiligo

Excessive oxidative stress is thought to play pathologic roles in cellular senescence and autoimmune disorders by inducing inflammation and breaking down immune tolerance. In this study, we sought to identify the factors linking oxidative stress to autoimmunity and cellular senescence in vitiligo, where elevated oxidative stress plays an important role. RNA sequencing analysis of hydrogen peroxide-treated melanocytes revealed upregulation of ISG15. The upregulation of ISG15 was observed in vitiligo skin tissues as well as in the blood of patients with vitiligo, whereas USP18 downregulation was observed in vitiligo melanocytes and vitiligo skin tissues. Oxidative stress induced hypermethylation of the USP18 promoter region in keratinocytes and melanocytes, and USP18 promoter hypermethylation was also confirmed in vitiligo skin tissues. Our results indicate that USP18 promoter hypermethylation caused by oxidative stress increases ISG15 expression in keratinocytes and melanocytes along with senescence changes, leading CD8+ T cells to produce IFN-γ, the main pathogenic cytokine in vitiligo. Therefore, the ISG15-USP18 network may be important in oxidative stress-induced autoimmunity and cellular senescence in vitiligo pathogenesis.

The Role of Regulatory Cell Death in Vitiligo

Vitiligo is one of the common chronic autoimmune skin diseases in clinic, which is characterized by localized or generalized depigmentation and seriously affects the physical and mental health of patients. At present, the pathogenesis of vitiligo is not clear; mainly, heredity, autoimmunity, oxidative stress, melanocyte (MC) self-destruction, and the destruction, death, or dysfunction of MCs caused by various reasons are always the core of vitiligo. Regulatory cell death (RCD) is an active and orderly death mode of cells regulated by genes, which widely exists in various life activities, plays a pivotal role in maintaining the homeostasis of the organism, and is closely related to the occurrence and development of many diseases. With the deepening of the research and understanding of RCD, people gradually found that there are many different forms of RCD in the lesions and perilesional skin of vitiligo patients, such as apoptosis, autophagy, pyroptosis, ferroptosis, and so on. Different cell death modes have different mechanisms in vitiligo, and different RCDs can interact and regulate each other. In this article, the mechanism related to RCD in the pathogenesis of vitiligo is reviewed, which provides new ideas for exploring the pathogenesis and targeted treatment of vitiligo.

HMGB1 in the interplay between autophagy and apoptosis in cancer

Lysosome-mediated autophagy and caspase-dependent apoptosis are dynamic processes that maintain cellular homeostasis, ensuring cell health and functionality. The intricate interplay and reciprocal regulation between autophagy and apoptosis are implicated in various human diseases, including cancer. High-mobility group box 1 (HMGB1), a nonhistone chromosomal protein, plays a pivotal role in coordinating autophagy and apoptosis levels during tumor initiation, progression, and therapy. The regulation of autophagy machinery and the apoptosis pathway by HMGB1 is influenced by various factors, including the protein's subcellular localization, oxidative state, and interactions with binding partners. In this narrative review, we provide a comprehensive overview of the structure and function of HMGB1, with a specific focus on the interplay between autophagic degradation and apoptotic death in tumorigenesis and cancer therapy. Gaining a comprehensive understanding of the significance of HMGB1 as a biomarker and its potential as a therapeutic target in tumor diseases is crucial for advancing our knowledge of cell survival and cell death.

CXCL16 exacerbates Pseudomonas aeruginosa keratitis by promoting neutrophil activation

Pseudomonas aeruginosa (PA) keratitis is a major cause of blindness characterized by corneal inflammation. In a murine model of PA keratitis, we assessed the detrimental effects of CXC chemokine ligand 16 (CXCL16). Quantitative PCR (qPCR), western blotting (WB) and immunofluorescence were used to measure the expression and localization of CXCL16 and its receptor, CXC chemokine receptor 6 (CXCR6). Clinical scores, plate counting, and hematoxylin-eosin staining were used to assess infection severity and its exacerbation by CXCL16. Immunofluorescence, myeloperoxidase assays, and flow cytometry were used to detect neutrophil activity and colocalization with CXCR6. WB and immunofluorescence were used to measure levels of reactive oxygen species (ROS) and matrix metalloproteinases (MMPs). These methods also were used to measure the activation of downstream NF-κB signaling and its positive feedback on CXCL16 expression. ELISA, flow cytometry, and qPCR were used to measure the expression of CXCL2 and T helper 17 (Th17) cell-related genes. CXCL16 and CXCR6 expression was increased in infected corneas. Topical application of CXCL16 exacerbated keratitis by increasing corneal bacterial load and promoting neutrophil infiltration, whereas neutralizing antibody against CXCL16 had the opposite effect. CXCL16 also increased ROS and MMP levels. This neutrophil activation may be caused by its positive feedback with the NF-κB pathway and the upregulation of CXCL2 and Th17 cell related-genes. These data suggest that CXCL16 is an attractive therapeutic target for PA keratitis.

Membranal Expression of Calreticulin Induced by Unfolded Protein Response in Melanocytes: A Mechanism Underlying Oxidative Stress-Induced Autoimmunity in Vitiligo

Calreticulin (CRT), a damage-associated molecular pattern molecule, is reported to translocate from the endoplasmic reticulum to the membrane in melanocytes under oxidative stress. To investigate the potential role of CRT in the pathogenesis of vitiligo, we analyzed the correlation between CRT and ROS in serum and lesions of vitiligo, detected CRT and protein kinase RNA-like endoplasmic reticulum kinase (PERK) expression in vitiligo lesions, and studied the production of CRT and mediators of unfolded protein response (UPR) pathway and then tested the chemotactic migration of CD8+ T cells or CD11c+ CD86+ cells. Initially, we verified the overexpression of CRT in perilesional epidermis that was positively correlated with the disease severity of vitiligo. Furthermore, the PERK branch of UPR was confirmed to be responsible for the overexpression and membranal translocation of CRT in melanocytes under oxidative stress. We also found that oxidative stress-induced membranal translocation of CRT promoted the activation and migration of CD8+ T cells in vitiligo. In addition, dendritic cells from patients with vitiligo were also prone to maturation with the coincubation of melanocytes harboring membranal CRT. CRT could be induced on the membrane of melanocytes through UPR and might play a role in oxidative stress-triggered CD8+ T-cell response in vitiligo.

A case of vitiligo after COVID-19 vaccination: a possible role of thymic dysfunction

During the coronavirus disease 2019 (COVID-19) pandemic, vaccines help control the spread of infection. To date, 47 vaccines have been approved, with another 227 candidates in various stages of development. In the short period of time since the beginning of their use, evidence has begun to emerge of complications following vaccination in the form of the development or exacerbation of a number of pathological conditions (Block et al., 2022; Haseeb et al., 2022). For example, a population-based study in France identified 1612 cases of myocarditis and 1613 cases of pericarditis requiring hospital treatment within five months of vaccination (le Vu et al., 2022).

Exploring the mechanism of Liuwei Dihuang formula for promoting melanin synthesis in juvenile zebrafish based on network pharmacology and molecular docking

Background

Vitiligo stands as a challenging skin disorder with limited treatment options available. LiuWei DiHuang formula (LDF), a renowned Traditional Chinese medicine, has exhibited promising results in treating vitiligo over an extended period. However, the precise underlying mechanism of its action remains elusive.

Methods

Employing a comprehensive network pharmacology approach, this study identified active compounds and their corresponding targets within LDF, while also pinpointing vitiligo-associated targets sourced from the TCMSP database, OMIM, DisGenNET, and Genecards. A network was established to illustrate the connections between active compounds and targets, alongside a protein-protein interaction network. Further analyses, encompassing Gene Ontology (GO) function and KEGG pathway enrichment, were conducted using the DAVID platform. Molecular docking simulations were performed utilizing AutoDockTools and AutoDockVina software. To validate the outcomes of the systematic pharmacological investigation, experiments were conducted using juvenile zebrafish.

Results

The collective effort of the network pharmacology approach yielded a compilation of 41 compounds and 192 targets. Molecular docking simulations notably revealed the lowest binding energies for CAT-quercetin and CAT-Kaempferol interactions. The utilization of juvenile zebrafish experiments highlighted a significant increase in melanocyte count following methoxsalen and LDF treatment. Notably, LDF prominently augmented the expression levels of proteins related to melanogenesis. Additionally, LDF showcased the capacity to enhance CAT and SOD levels while concurrently reducing ROS and MDA activity. In contrast to the model group, substantial increases in protein and mRNA levels of Nrf2 and HO-1 were observed in response to LDF treatment (P < 0.05).

Conclusion

Through a meticulous network pharmacology approach, this study successfully predicted active components and potential targets associated with LDF's application in vitiligo treatment. The therapeutic effectiveness of LDF against vitiligo is postulated to stem from its regulation of oxidative stress factors and the Nrf2/HO-1 pathway.

Neutrophil extracellular traps enhance S. aureus skin colonization by oxidative stress induction and downregulation of epidermal barrier genes

Staphylococcus aureus is the most common cause of bacterial skin infections in humans, including patients with atopic dermatitis (AD). Polymorphonuclear neutrophils (PMNs) are the first cells to infiltrate an infection site, where they usually provide an effective first line of defense, including neutrophil extracellular trap (NET) formation. Here, we show that infiltrating PMNs in inflamed human and mouse skin enhance S. aureus skin colonization and persistence. Mechanistically, we demonstrate that a crosstalk between keratinocytes and PMNs results in enhanced NET formation upon S. aureus infection, which in turn induces oxidative stress and expression of danger-associated molecular patterns such as high-mobility-group-protein B1 (HMGB1) in keratinocytes. In turn, HMGB1 enhances S. aureus skin colonization and persistence by promoting skin barrier dysfunctions by the downregulation of epidermal barrier genes. Using patient material, we show that patients with AD exhibit enhanced presence of PMNs, NETs, and HMGB1 in the skin, demonstrating the clinical relevance of our finding.

Oxidative stress and ROS-mediated cellular events in RSV infection: potential protective roles of antioxidants

Respiratory syncytial virus (RSV), a member of the Pneumoviridae family, can cause severe acute lower respiratory tract infection in infants, young children, immunocompromised individuals and elderly people. RSV is associated with an augmented innate immune response, enhanced secretion of inflammatory cytokines, and necrosis of infected cells. Oxidative stress, which is mainly characterized as an imbalance in the production of reactive oxygen species (ROS) and antioxidant responses, interacts with all the pathophysiologic processes above and is receiving increasing attention in RSV infection. A gradual accumulation of evidence indicates that ROS overproduction plays an important role in the pathogenesis of severe RSV infection and serves as a major factor in pulmonary inflammation and tissue damage. Thus, antioxidants seem to be an effective treatment for severe RSV infection. This article mainly reviews the information on oxidative stress and ROS-mediated cellular events during RSV infection for the first time.

Metagenomic sequencing reveals altered gut microbial compositions and gene functions in patients with non-segmental vitiligo

BACKGROUND

Vitiligo has been correlated with an abnormal gut microbiota. We aimed to systematically identify characteristics of the gut microbial compositions, genetic functions, and potential metabolic features in patients with non-segmental vitiligo.

METHODS

Twenty-five patients with non-segmental vitiligo and 25 matched healthy controls (HCs) were enrolled. Metagenomic sequencing and bioinformatic analysis were performed to determine the gut microbiota profiles. Differences in gut microbiota diversity and composition between patients with vitiligo and HCs were analyzed. Gene functions and gut metabolic modules were predicted with the Kyoto Encyclopedia of Gene and Genomes (KEGG) and MetaCyc databases.

RESULTS

Compared with HCs, alpha diversity of intestinal microbiome in vitiligo patients was significantly reduced. At the species level, the relative abundance of Staphylococcus thermophiles was decreased, and that of Bacteroides fragilis was increased in patients with vitiligo compared with those of the HCs. Linear discriminant analysis (LDA) effect size (LEfSe) analysis revealed representative microbial markers of Lachnospiraceae_bacterium_BX3, Massilioclostridium_coli, TM7_phylum_sp_oral_taxon_348 and Bacteroides_fragilis for patients with vitiligo. KEGG gene function analysis showed that the NOD-like receptor signaling pathway was significantly enriched in patients with vitiligo. Gut metabolic modules (GMMs) analysis showed that cysteine degradation was significantly down-regulated, and galactose degradation was up-regulated in patients with vitiligo. A panel of 28 microbial features was constructed to distinguish patients with vitiligo from HCs.

CONCLUSIONS

The gut microbial profiles and genetic functions of patients with vitiligo were distinct from those of the HCs. The identified gut microbial markers may potentially be used for earlier diagnosis and treatment targets.

Circulatory levels of alarmins in patients with non-segmental vitiligo: Potential biomarkers for disease diagnosis and activity/severity assessment

Background

Non-segmental vitiligo (NSV) is an autoimmune skin disorder that is difficult to determine disease activity/severity and thus to treat. Alarmins have emerged as promising biomarkers in various diseases, so further confirmation of their potential roles in NSV would be of considerable value. With the present work, we aimed to determine the serum levels of alarmins in patients with NSV, correlate these alarmins with disease activity and severity, and analyze the predictive value of the combination of these markers.

Methods

104 NSV patients and 56 healthy controls were enrolled at the Xijing Hospital of Fourth Military Medical University between September 1, 2018, and June 30, 2019. The serum levels of alarmins (including IL-33, IL-1α, S100A9, S100A12, S100B, and HMGB1) were measured with enzyme-linked immunosorbent assays. The predictive performance of these biomarkers was evaluated with the area under the receiver operating characteristic curve (AUC), sensitivity, specificity, and other representative statistics.

Results

A total of 104 patients with NSV (mean [SD] age, 34.2 [13.0] years; 62 [59.6%] male) and 56 healthy controls (mean [SD] age, 34.8 [13.5] years; 34 [60.7%] male) were enrolled. For vitiligo diagnosis, S100B had the highest sensitivity (92.31%), whereas HMGB1 had the highest specificity (85.71%); the combination of IL-1α, S100B, S100A9, and HMGB1 increased the AUC value to 0.925, with a sensitivity of 87.50% and a specificity of 85.71%. Multivariate logistic regression analysis showed S100B (OR, 1.019; 95% CI, 1.002-1.038; P =0.03), S100A9 (OR, 1.002; 95% CI, 1.001-1.003; P<0.001), and HMGB1 (OR, 1.915; 95% CI, 1.186-3.091; P =0.008) were significantly associated with vitiligo activity. S100A9 had the highest accuracy in discriminating patients at the active stage from the stable stage, with an AUC value of 0.827. The combination of these alarmins had an AUC value of 0.860 to assess disease activity, with a sensitivity of 90.00% and a specificity of 72.97%. Furthermore, S100B (r=0.61, P <0.001), S100A9 (r=0.33, P <0.001), and HMGB1 (r = 0.51, P <0.001) levels were positively correlated with the affected body surface area (BSA) in NSV patients.

Conclusions

Serum S100B, S100A9, and HMGB1 might be biomarkers for diagnosing and assessing the activity/severity of NSV, either used alone or in combination.

Damage-associated molecular patterns in vitiligo: igniter fuse from oxidative stress to melanocyte loss

OBJECTIVES

The pathogenesis of vitiligo remains unclear. In this review, we comprehensively describe the role of damage associated molecular patterns (DAMPs) during vitiligo pathogenesis.

METHODS

Published papers on vitiligo, oxidative stress and DAMPs were collected and reviewed via database searching on PubMed, MEDLINE and Embase, etc.

RESULTS

Oxidative stress may be an important inducer of vitiligo. At high oxidative stress levels, damage-associated molecular patterns (DAMPs) are released from keratinocytes or melanocytes in the skin and induce downstream immune responses during vitiligo. Treatment regimens targeting DAMPs can effectively improve disease severity.

DISCUSSION

DAMPs play key roles in initiating host defenses against danger signals, deteriorating the condition of vitiligo. DAMP levels in serum and skin may be used as biomarkers to indicate vitiligo activity and prognosis. Targeted therapies, incorporating HMGB1, Hsp70, and IL-15 could significantly improve disease etiology. Thus, novel strategies could be identified for vitiligo treatment by targeting DAMPs.

GATA3 ameliorates melanocyte injuries in vitiligo through SIRT3‐mediated HMGB1 deacetylation

Vitiligo is a skin depigmentation disorder. GATA3 expression is downregulated in vitiligo patients, and its role and regulatory mechanism in vitiligo are unclear. GATA3 and HMGB1 levels were detected by qRT-PCR in peripheral blood cells of vitiligo patients and healthy controls, as well as H₂ O₂ -treated PIG1 cells. Their expression correlation was assessed by Pearson analysis. qRT-PCR, MTT assay, Ki67 immunostaining, flow cytometry, ELISA and Western blot were applied to determine GATA3 expression, cell survival, cell proliferation, cell apoptosis, melanin contents, and melanin-related protein expressions. The cellular distributions of HMGB1 and its deacetylation levels were detected by Western blot. The binding of GATA3 to SIRT3 promoter and effects on SIRT3 expression and HMGB1 deacetylation was determined by dual-luciferase assay, ChIP assay, and Western blot. GATA3 was decreased, and HMGB1 was increased in vitiligo. Pearson correlation assay showed that they were negatively correlated. H₂ O₂ significantly inhibited cell survival, proliferation, melanin secretion, and melanin-related protein expressions but remarkably increased cell apoptosis. GATA3 overexpression could distinctly reverse the effects of H₂ O₂ through decreasing HMGB1 expression and retained HMGB1 in nuclear due to the decreased HMGB1 acetylation. GATA3 bound to the SIRT3 and subsequently decreased H₂ O₂ -induced HMGB1 acetylation. Overexpressing HMGB1 or knockdown of SIRT3 could reverse the effects of GATA3 overexpression. GATA3 inhibited H₂ O₂ -induced injury in PIG1 cells and enhanced melanin secretion by SIRT3-regulated HMGB1 deacetylation, which might provide new evidence to treat vitiligo.

Identification of CKS2 and RRM2 as potential markers of vitiligo using bioinformatics analysis

Previous studies have attempted to elucidate the molecular mechanism of vitiligo; however, its pathogenesis remains unclear. This study aimed to explore biomarkers related to vitiligo through bioinformatic analysis. The microarray datasets GSE53146 and GSE65127 were downloaded from the Gene Expression Omnibus database. Firstly, differentially expressed genes (DEGs) in GSE53146 were screened, and then an enrichment analysis was performed. Secondly, the protein-protein interaction (PPI) network of DEGs was constructed using the STRING database, and the key genes were screened using the MCODE plugin in Cytoscape and verified using GSE65127. Finally, quantiseq was used to evaluate immune cell infiltration in vitiligo, then to observe the correlation between biomarkers and immune cells. In total, 544 DEGs were identified, including 342 upregulated and 202 downregulated genes. Gene Ontology (GO) enrichment showed that DEGs were related to inflammatory and immune responses, and Kyoto Encyclopedia of Genes and Genomes enrichment showed that DEGs were involved in many autoimmune diseases. In the PPI network, 7 key genes, CENPN, CKS2, PLK4, RRM2, TPX2, CCNA2, and CDC45 were identified by MCODE cluster and verified using the GSE65127 dataset. With an area under the curve (AUC) > 0.8 as the standard, 2 genes were screened, namely CKS2 and RRM2. Further immune infiltration analysis showed that M2 macrophages were involved in the pathogenesis of vitiligo, whereas CKS2 and RRM2 were both related to M2 macrophages. This study shows that CKS2 and RRM2 have potential as biomarkers of vitiligo and provides a theoretical basis for a better understanding of the pathogenesis of vitiligo.

Unraveling the relation between vitiligo, Interleukin 17, and serum amyloid A

BACKGROUND

There is debate concerning the precise etiopathogenesis of vitiligo. According to certain theories, a series of inflammatory responses that mediate the loss of melanocytes are caused by both cellular and humoral immune responses. It has also been demonstrated that Interleukin 17 (IL-17) promotes melanocyte death and inhibits melanogenesis through different mechanisms. Serum Amyloid A (SAA) levels are over-expressed in autoimmune diseases. Th17 cytokines are regulated by serum amyloid A proteins.

AIMS

To measure serum levels of IL-17 and SAA in vitiligo patients aiming to explain their possible role in disease pathogenesis and the other aim is to correlate their levels with disease activity and severity.

METHODS

This study included 60 vitiligo patients and 40 healthy age and sex controls. Enzyme-linked immunosorbent assay was used to measure serum levels of SAA and IL-17.

RESULTS

This study revealed significant increase in levels of serum IL-17 and SAA in patients than controls (p < 0.05). Both markers showed significant positive correlations with VASI score and duration of vitiligo; only IL-17 showed statistically significant positive correlation with VIDA scores. Patients with vitiligo showed a statistically significant positive connection between serum IL-17 levels and SAA (γ = 0.992, p-value <0.05).

CONCLUSION

Increased serum level of IL-17 and SAA in vitiligo patients together with their positive relation to vitiligo severity and the duration of the disease show that these two markers play a key role in the vitiligo development.

Role of HMGB1 in Vitiligo: Current Perceptions and Future Perspectives

Vitiligo is a chronic depigmenting disorder of the skin and mucosa caused by the destruction of epidermal melanocytes. Although the exact mechanism has not been elucidated, studies have shown that oxidative stress plays an important role in the pathogenesis of vitiligo. High mobility group box protein B1 (HMGB1) is a major nonhistone protein and an extracellular proinflammatory or chemotactic molecule that is actively secreted or passively released by necrotic cells. Recent data showed that HMGB1 is overexpressed in both blood and lesional specimens from vitiligo patients. Moreover, oxidative stress triggers the release of HMGB1 from keratinocytes and melanocytes, indicating that HMGB1 may participate in the pathological process of vitiligo. Overall, this review mainly focuses on the role of HMGB1 in the potential mechanisms underlying vitiligo depigmentation under oxidative stress. In this review, we hope to provide new insights into vitiligo pathogenesis and treatment strategies.

Alarmins in autoimmune diseases

Alarmins are endogenous, constitutively expressed, chemotacting and immune activating proteins or peptides released because of non-programmed cell death (i.e. infections, trauma, etc). They are considered endogenous damage-associated molecular patterns (DAMPs), able to induce a sterile inflammation. In the last years, several studies highlighted a possible role of different alarmins in the pathogenesis of various autoimmune and immune-mediated diseases. We reviewed the relevant literature about this topic, for about 160 articles. Particularly, we focused on systemic autoimmune diseases (systemic lupus erythematosus, rheumatoid arthritis, idiopathic inflammatory myopathies, ANCA-associated vasculitides, Behçet's disease) and cutaneous organ-specific autoimmune diseases (vitiligo, psoriasis, alopecia, pemphigo). Finally, we discussed about future perspectives and potential therapeutic implications of alarmins in autoimmune diseases. In fact, identification of receptors and downstream signal transducers of alarmins may lead to the identification of antagonistic inhibitors and agonists, with the capacity to modulate alarmins-related pathways and potential therapeutic applicability.

Current Concepts of Vitiligo Immunopathogenesis

Vitiligo is an acquired immune-mediated disorder of pigmentation clinically characterized by well-defined depigmented or chalk-white macules and patches on the skin. The prevalence of vitiligo varies by geographical area, affecting 0.5% to 2% of the population. The disease imposes a significant psychological burden due to its major impact on patients’ social and emotional aspects of life. Given its autoimmune background, vitiligo is frequently associated with other autoimmune diseases or immune-mediated diseases. Vitiligo is a multifaceted disorder that involves both genetic predisposition and environmental triggers. In recent years, major predisposing genetic loci for the development of vitiligo have been discovered. The current findings emphasize the critical role of immune cells and their mediators in the immunopathogenesis of vitiligo. Oxidative-stress-mediated activation of innate immunity cells such as dendritic cells, natural killer, and ILC-1 cells is thought to be a key event in the early onset of vitiligo. Innate immunity cells serve as a bridge to adaptive immunity cells including T helper 1 cells, cytotoxic T cells and resident memory T cells. IFN-γ is the primary cytokine mediator that activates the JAK/STAT pathway, causing keratinocytes to produce the key chemokines CXCL9 and CXCL10. Complex interactions between immune and non-immune cells finally result in apoptosis of melanocytes. This paper summarizes current knowledge on the etiological and genetic factors that contribute to vitiligo, with a focus on immunopathogenesis and the key cellular and cytokine players in the disease’s inflammatory pathways.

The delicate relation between melanocytes and skin immunity: A game of hide and seek

Melanocytes exhibit a complex and intriguing relationship with the skin immune response, leading to several clinical conditions. In some disorders, inappropriate melanocyte destruction (e.g., vitiligo, halo naevi) is problematic, while in others, immune tolerance should be broken (melanoma). Important parts of the dysregulated pathways have been unraveled in pigment disorders, ranging from upregulated interferon (IFN)-γ signaling to memory T cells, regulatory T cells, and immune checkpoints. Although a network of many factors is involved, targeting key players such as IFN-γ or checkpoint inhibitors (e.g., programmed death-ligand 1 (PD-L1)] can shift the balance and lead to impressive outcomes. In this review, we focus on the immunological mechanisms of the most common inflammatory disorders where the interaction of the immune system with melanocytes plays a crucial role. This can provide new insights into the current state of melanocyte research.

Multimodal analyses of vitiligo skin identifies tissue characteristics of stable disease

Vitiligo is an autoimmune skin disease characterized by the destruction of melanocytes by autoreactive CD8⁺ T cells. Melanocyte destruction in active vitiligo is mediated by CD8⁺ T cells, but the persistence of white patches in stable disease is poorly understood. The interaction between immune cells, melanocytes, and keratinocytes in situ in human skin has been difficult to study due to the lack of proper tools. We combine noninvasive multiphoton microscopy (MPM) imaging and single-cell RNA-Seq (scRNA-Seq) to identify subpopulations of keratinocytes in stable vitiligo patients. We show that, compared with nonlesional skin, some keratinocyte subpopulations are enriched in lesional vitiligo skin and shift their energy utilization toward oxidative phosphorylation. Systematic investigation of cell-to-cell communication networks show that this small population of keratinocyte secrete CXCL9 and CXCL10 to potentially drive vitiligo persistence. Pseudotemporal dynamics analyses predict an alternative differentiation trajectory that generates this new population of keratinocytes in vitiligo skin. Further MPM imaging of patients undergoing punch grafting treatment showed that keratinocytes favoring oxidative phosphorylation persist in nonresponders but normalize in responders. In summary, we couple advanced imaging with transcriptomics and bioinformatics to discover cell-to-cell communication networks and keratinocyte cell states that can perpetuate inflammation and prevent repigmentation.

Thiol-Disulfide Homeostasis in Skin Diseases

Oxidative stress represents the imbalance between oxidants and antioxidants and has been associated with a wide range of diseases. Thiols are the most important compounds in antioxidant defense. There is an equilibrium between thiols and their oxidized forms, disulfides, known as dynamic thiol-disulfide homeostasis (TDH). In 2014, Erel and Neselioglu developed a novel automated assay to measure thiol and disulfide levels. Subsequently, many researchers have used this simple, inexpensive and fast method for evaluating TDH in various disorders. We have reviewed the literature on the role of TDH in skin diseases. We identified 26 studies that evaluated TDH in inflammatory diseases (psoriasis, seborrheic dermatitis, atopic dermatitis, vitiligo, acne vulgaris and rosacea), allergic diseases (acute and chronic urticaria) and infectious diseases (warts, pityriasis rosea and tinea versicolor). The results are heterogeneous, but in most cases indicate changes in TDH that shifted toward disulfides or toward thiols, depending on the extent of oxidative damage.

The Current Status of Antioxidants in the Treatment of Vitiligo in China

Little is known about the use of antioxidants in the clinical treatment of vitiligo. To investigate the specific use of antioxidants in the treatment of vitiligo and the possible reasons behind its use in China, we conducted a prospective questionnaire-based study using an online questionnaire comprising 26 questions in 5 areas. A total of 323 clinical frontline dermatologists participated in this study. Differences among groups were compared using Pearson’s chi-square test. Ordinal logistic regression was used to develop knowledge–use multiple regression models. Among the 323 dermatologists, 293 (90.7%) approved the oxidative stress theory of vitiligo, and 182 (56.3%) encouraged the use of antioxidants for treating vitiligo; nonetheless, only 11.8% frequently treated vitiligo with antioxidants. Insufficient knowledge of antioxidants was a significant predictor of lower frequency of antioxidant usage (adjusted odds ratio, 0.401 [95% confidence interval, 0.256-0.629]; $P<.001$ ). The predictors associated with higher antioxidant efficacy included advanced or rapid progression, moderate or moderate-to-severe vitiligo, age of 0–2 years or 13–18 years, segmental vitiligo, oral and topical combination therapy, and course duration of <1 month. The use of antioxidants for treating vitiligo is highly encouraged; however, the rates of their clinical use are considerably low. Insufficient knowledge of antioxidants is associated with a lower frequency of antioxidant usage. The synergistic curative efficacy of antioxidants could be affected by the stage, type, severity, age of patients with vitiligo, and method of using antioxidants.

MicroRNA-637 Relieves Oxidative Damage in Human Melanocytes Through Down-Regulating Transient Receptor Potential Melastatin 2 Expression

Background: Vitiligo, a chronic, autoimmune destruction of melanocytes, caused by the disappearance of epidermal melanocytes, but the mechanism is not fully understood. Although emerging evidence demonstrated that abnormal regulation of microRNAs (miRNAs) were associated with the pathogenesis of diseases, the functions of miR-637 in vitiligo remain unclear. Objective: This research was designed to explore the potential roles of miR-637 in hydrogen peroxide (H2O2)-induced human primary melanocytes in vitiligo. Methods: Human primary melanocytes were induced by 250 μmol/L H2O2 for 4 h to establish oxidative injury of melanocytes model. Cell viability and apoptosis analyzed by MTT and flow cytometry assay, respectively. The relevance between miR-637 and transient receptor potential melastatin 2 (TRPM2) was checked using TargetScan and dual luciferase reporter gene assay. The expression of miR-637 and TRPM2 was evaluated using qRT-PCR and/or Western blot analysis. Reactive oxygen species (ROS) accumulation, superoxide dismutase (SOD) and catalase (CAT) activities were measured using specific assay kits. In addition, the expression of Bcl-2 and Bax were evaluated using Western blot assay. Results: TRPM2 was up-regulated, while miR-637 was down-regulated in H2O2-stimulated human primary melanocytes. TRPM2 directly interacted with miR-637. Up-regulation of miR-637 memorably increased miR-637 level and inhibited TRPM2 expression. Furthermore, miR-637 mimic fortified cell viability, reduced apoptotic cells, enhanced Bcl-2 expression, reduced Bax level, as well as inhibited the ratio of Bax/Bcl-2 in H2O2-induced melanocytes. Meanwhile, miR-637 mimic obviously suppressed the accumulation of ROS and increased SOD and CAT activity. Nevertheless, all these findings were inverted by TRPM2-plasmid. Likewise, TRPM2-siRNA led to increased cell viability, reduced apoptotic cells, enhanced Bcl-2 expression, reduced Bax level, inhibited Bax/Bcl-2 ratio, inhibited ROS production, but increased SOD and CAT activity in H2O2-induced melanocytes. Conclusion: Our findings suggested that TRPM2 was up-regulated, while miR-637 was down-regulated in injurious melanocytes of vitiligo. Up-regulation of miR-637 relieved oxidative stress-stimulated melanocyte injury via down-regulating TRPM2 expression. Our results provide new insights into the functions of miR-637 in the development of vitiligo, indicating that miR-637 may be a latent target for vitiligo therapy.

The mechanism of HMGB1 secretion and release

High mobility group box 1 (HMGB1) is a nonhistone nuclear protein that has multiple functions according to its subcellular location. In the nucleus, HMGB1 is a DNA chaperone that maintains the structure and function of chromosomes. In the cytoplasm, HMGB1 can promote autophagy by binding to BECN1 protein. After its active secretion or passive release, extracellular HMGB1 usually acts as a damage-associated molecular pattern (DAMP) molecule, regulating inflammation and immune responses through different receptors or direct uptake. The secretion and release of HMGB1 is fine-tuned by a variety of factors, including its posttranslational modification (e.g., acetylation, ADP-ribosylation, phosphorylation, and methylation) and the molecular machinery of cell death (e.g., apoptosis, pyroptosis, necroptosis, alkaliptosis, and ferroptosis). In this minireview, we introduce the basic structure and function of HMGB1 and focus on the regulatory mechanism of HMGB1 secretion and release. Understanding these topics may help us develop new HMGB1-targeted drugs for various conditions, especially inflammatory diseases and tissue damage.

A nuclear protein that gets released after cell death or is actively secreted by immune cells offers a promising therapeutic target for treating diseases linked to excessive inflammation. Daolin Tang from the University of Texas Southwestern Medical Center in Dallas, USA, and colleagues review how cellular stresses can trigger the accumulation of HMGB1, a type of alarm signal protein that promotes the recruitment and activation of inflammation-promoting immune cells. The researchers discuss various mechanisms that drive both passive and active release of HMGB1 into the space around cells. These processes, which include enzymatic modifications of the HMGB1 protein, cell–cell interactions and molecular pathways of cell death, could be targeted by drugs to lessen tissue damage and inflammatory disease caused by HMGB1-induced immune responses

Patho-immunological mechanisms of vitiligo: the role of the innate and adaptive immunities and environmental stress factors

Epidermal melanocyte loss in vitiligo, triggered by stresses ranging from trauma to emotional stress, chemical exposure or metabolite imbalance, to the unknown, can stimulate oxidative stress in pigment cells, which secrete damage-associated molecular patterns that then initiate innate immune responses. Antigen presentation to melanocytes leads to stimulation of autoreactive T-cell responses, with further targeting of pigment cells. Studies show a pathogenic basis for cellular stress, innate immune responses and adaptive immunity in vitiligo. Improved understanding of the aetiological mechanisms in vitiligo has already resulted in successful use of the Jak inhibitors in vitiligo. In this review, we outline the current understanding of the pathological mechanisms in vitiligo and locate loci to which therapeutic attack might be directed.

The Promising Role of Chemokines in Vitiligo: From Oxidative Stress to the Autoimmune Response

Vitiligo is a common chronic autoimmune skin disorder featured with depigmented patches and underlying destruction of melanocytes in the lesional skin. Multiple factors and mechanisms have been proposed for the etiopathogenesis of vitiligo, among which oxidative stress has been widely accepted as a key factor in initiating melanocyte loss. The altered redox status caused by oxidative stress, including the overproduction of reactive oxygen species (ROS) and the decreased activity of the antioxidant system in the skin, surrenders the resistance of melanocytes to exogenous or endogenous stimuli and eventually impairs the normal defense mechanism, leading to the absence of melanocytes. Considering the important role of innate and adaptive immunity in vitiligo, there is mounting evidence revealing an association between oxidative stress and autoimmunity. Since the significant changes of chemokines have been documented in vitiligo in many recent studies, it has been suggested that ROS-mediated chemotactic signals are not only the biomarkers of disease progression and prognosis but also are involved in the pathogenesis of vitiligo by facilitating the innate and adaptive immune cells, especially melanocyte-specific T cells, trafficking to the lesional areas of vitiligo. In this review, we discuss the interaction between oxidative stress and autoimmune response orchestrated by chemokines, including CXCL16-CXCR6 axis, CXCL9/CXCL10-CXCR3 axis, and other altered chemokines in vitiligo, and we also try to provide insight into potential therapeutic options through targeting these pathways.

Folic Acid Protects Melanocytes from Oxidative Stress via Activation of Nrf2 and Inhibition of HMGB1

Vitiligo is a cutaneous depigmentation disease due to loss of epidermal melanocytes. Accumulating evidence has indicated that oxidative stress plays a vital role in vitiligo via directly destructing melanocytes and triggering inflammatory response that ultimately undermines melanocytes. Folic acid (FA), an oxidized form of folate with high bioavailability, exhibits potent antioxidant properties and shows therapeutic potential in multiple oxidative stress-related diseases. However, whether FA safeguards melanocytes from oxidative damages remains unknown. In this study, we first found that FA relieved melanocytes from H₂O₂-induced abnormal growth and apoptosis. Furthermore, FA enhanced the activity of antioxidative enzymes and remarkably reduced intracellular ROS levels in melanocytes. Subsequently, FA effectively activated nuclear factor E2-related factor 2 (Nrf2) pathway, and Nrf2 knockdown blocked the protective effects of FA on H₂O₂-treated melanocytes. Additionally, FA inhibited the production of proinflammatory HMGB1 in melanocytes under oxidative stress. Taken together, our findings support the protective effects of FA on human melanocytes against oxidative injury via the activation of Nrf2 and the inhibition of HMGB1, thus indicating FA as a potential therapeutic agent for the treatment of vitiligo.

Clinical Significance of Serum Oxidative Stress Markers to Assess Disease Activity and Severity in Patients With Non-Segmental Vitiligo

Non-segmental vitiligo (NSV) is a chronic autoimmune disease characterized by progressive depigmentation of the skin. Oxidative stress (OS) has been proposed as one among the main principal causes in the development and establishment of a sustained autoimmune state in patients with NSV. However, the disease-associated OS biomarkers in clinical practice are not well studied. In this study, we found significantly reduced antioxidant enzymes [catalase (CAT) and superoxide dismutase (SOD)], total antioxidant capacity (TAC), and increased levels of lipid oxidation product malondialdehyde (MDA) and oxidative DNA damage byproduct [8-hydroxy-2-deoxyguanosine (8-OHdG)] in serum of NSV patients compared with healthy controls (HC). Serum TAC, MDA, and 8-OHdG levels were correlated with disease activity in all patients with NSV and much lower in patients receiving conventional treatment in the past 1 year compared to that without treatment. In addition, both serum MDA and 8-OHdG levels were significantly correlated with CXCL10 expression in patients with NSV. And the serum TAC, MDA, and 8-OHdG levels were also correlated with affected body surface area and Vitiligo Area Scoring Index score in patients with NSV. This study demonstrates dysregulated OS status in patients with NSV and provides the evidence that the serum TAC, MDA, and 8-OHdG have a capacity to indicate the activity and severity in patients with NSV.

HSF1-Dependent Autophagy Activation Contributes to the Survival of Melanocytes Under Oxidative Stress in Vitiligo

Autophagy plays a protective role in oxidative stress‒induced melanocyte death. Dysregulated autophagy increases the sensitivity of melanocytes in response to oxidative damage and promotes melanocyte degeneration in vitiligo. However, the molecular mechanism underlying this process is not fully understood. In this study, using RNA-sequencing technology, we compared the transcriptome change between normal and vitiligo melanocytes with or without treatment of oxidative stress. We found that ATG5 and ATG12, the critical components for autophagosome formation, were significantly reduced in vitiligo melanocytes under oxidative stress. Mechanistically, HSF1 is the prime transcription factor for both ATG5 and ATG12, accounting for the reduced level of ATG5 and ATG12 in vitiligo melanocytes. Deficiency of HSF1 led to accumulation of intracellular ROS, imbalance of mitochondrion membrane potential, and apoptosis in melanocytes exposure to oxidative stress. Furthermore, overexpression of HSF1 could ameliorate oxidative stress‒induced melanocytes death through the activation of autophagy by upregulating ATG5 and ATG12. These findings suggested that targeting HSF1-ATG5/12 axis could prevent oxidative stress‒induced melanocyte death and may be used as a therapeutic strategy for vitiligo treatment.

Development of a Multi-Target Strategy for the Treatment of Vitiligo via Machine Learning and Network Analysis Methods

Vitiligo is a complex disorder characterized by the loss of pigment in the skin. The current therapeutic strategies are limited. The identification of novel drug targets and candidates is highly challenging for vitiligo. Here we proposed a systematic framework to discover potential therapeutic targets, and further explore the underlying mechanism of kaempferide, one of major ingredients from Vernonia anthelmintica (L.) willd, for vitiligo. By collecting transcriptome and protein-protein interactome data, the combination of random forest (RF) and greedy articulation points removal (GAPR) methods was used to discover potential therapeutic targets for vitiligo. The results showed that the RF model performed well with AUC (area under the receiver operating characteristic curve) = 0.926, and led to prioritization of 722 important transcriptomic features. Then, network analysis revealed that 44 articulation proteins in vitiligo network were considered as potential therapeutic targets by the GAPR method. Finally, through integrating the above results and proteomic profiling of kaempferide, the multi-target strategy for vitiligo was dissected, including 1) the suppression of the p38 MAPK signaling pathway by inhibiting CDK1 and PBK, and 2) the modulation of cellular redox homeostasis, especially the TXN and GSH antioxidant systems, for the purpose of melanogenesis. Meanwhile, this strategy may offer a novel perspective to discover drug candidates for vitiligo. Thus, the framework would be a useful tool to discover potential therapeutic strategies and drug candidates for complex diseases.

Ginsenoside Rk1 protects human melanocytes from H2O2‑induced oxidative injury via regulation of the PI3K/AKT/Nrf2/HO‑1 pathway

Vitiligo is a cutaneous depigmentation disorder caused by melanocyte injury or aberrant functioning. Oxidative stress (OS) is considered to be a major cause of the onset and progression of vitiligo. Ginsenoside Rk1 (RK1), a major compound isolated from ginseng, has antioxidant activity. However, whether RK1 can protect melanocytes against oxidative injury remains unknown. The aim of the present study was to investigate the potential protective effect of RK1 against OS in the human PIG1 melanocyte cell line induced with hydrogen peroxide (H₂O₂), and to explore its underlying mechanism. PIG1 cells were pretreated with RK1 (0, 0.1, 0.2 and 0.4 mM) for 2 h followed by exposure to 1.0 mM H₂O₂ for 24 h. Cell viability and apoptosis were determined with Cell Counting Kit‑8 and flow cytometry assays, respectively. The activity levels of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH‑Px) were analyzed using ELISA kits. Protein expression levels, including Bax, caspase‑3, Bcl‑2, phosphorylated‑AKT, AKT, nuclear factor erythroid 2‑related factor 2 (Nrf2), heme oxygenase‑1 (HO‑1), cytosolic Nrf2 and nuclear Nrf2, were analyzed using western blot analysis. In addition, the expression and localization of Nrf2 were detected by immunofluorescence. RK1 treatment significantly improved cell viability, reduced the apoptotic rate and increased the activity levels of SOD, CAT and GSH‑Px in the PIG1 cell line exposed to H₂O₂. In addition, RK1 treatment notably induced Nrf2 nuclear translocation, increased the protein expression levels of Nrf2 and HO‑1, and the ratio of phosphorylated‑AKT to AKT in the PIG1 cells exposed to H₂O₂. Furthermore, LY294002 could reverse the protective effect of RK1 in melanocytes against oxidative injury. These data demonstrated that RK1 protected melanocytes from H₂O₂‑induced OS by regulating Nrf2/HO‑1 protein expression, which may provide evidence for the application of RK1 for the treatment of vitiligo.

Clinical Features, Immunopathogenesis, and Therapeutic Strategies in Vitiligo

Vitiligo is an autoimmune disease of the skin characterized by epidermal melanocyte loss resulting in white patches, with an approximate prevalence of 0.5-2% worldwide. Several precipitating factors by chemical exposure and skin injury present commonly in patients with vitiligo. Although the diagnosis appears to be straightforward for the distinct clinical phenotype and specific histological features, vitiligo provides many challenges including chronicity, treatment resistance, frequent relapse, associated profound psychosocial effect, and negative impact on quality of life. Multiple mechanisms are involved in melanocyte disappearance, including genetics, environmental factors, and immune-mediated inflammation. Compelling evidence supports the melanocyte intrinsic abnormalities with poor adaptation to stressors leading to instability and release of danger signals, which will activate dendritic cells, natural killer cells, and innate lymphoid cells to initiate innate immunity, ultimately resulting in T-cell mediated adaptive immune response and melanocyte destruction. Importantly, the cross- talk between keratinocytes, melanocytes, and immune cells, such as interferon (IFN)-γ signaling pathway, builds inflammatory loops that give rise to the disease deterioration. Improved understanding of the immune pathogenesis of vitiligo has led to the development of new therapeutic options including Janus kinase (JAK) inhibitors targeting IFN-γ signaling pathways, which can effectively reverse depigmentation. Furthermore, definition of treatment goals and integration of comorbid diseases into vitiligo management have revolutionized the way vitiligo is treated. In this review, we highlight recent developments in vitiligo clinical aspects and immune pathogenesis. Our key objective is to raise awareness of the complexity of this disease, the potential of prospective therapy strategies, and the need for early and comprehensive management.

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.

Rhododendrol-induced leukoderma update II: Pathophysiology, mechanisms, risk evaluation, and possible mechanism-based treatments in comparison with vitiligo

A small proportion of individuals utilizing cosmetics containing rhododendrol developed leukoderma with various pathological conditions, in some cases indistinguishable from vitiligo. In this review, we investigate and evaluate the major considerations for developing rhododendrol‐induced leukoderma based on data from original or review articles published in the literature to provide a wide range of information regarding the pathophysiology, mechanisms, risk evaluation, and possible mechanism‐based treatments. We compile and discuss the latest information, including data related to the cytotoxicity of rhododendrol, cytoprotective functions, and involvement of the immune system, and consider the possibility of novel treatments based on the differences between individual patients and on the mechanism underlying the onset of the condition. Understanding the pathophysiology of rhododendrol‐induced leukoderma helps not only elucidate the mechanisms of non‐segmental vitiligo onset and progression, but also suggests prevention and treatment.

Targeting Innate Immunity to Combat Cutaneous Stress: The Vitiligo Perspective

Multiple factors are involved in the process leading to melanocyte loss in vitiligo including environmental triggers, genetic polymorphisms, metabolic alterations, and autoimmunity. This review aims to highlight current knowledge on how danger signals released by stressed epidermal cells in a predisposed patient can trigger the innate immune system and initiate a cascade of events leading to an autoreactive immune response, ultimately contributing to melanocyte disappearance in vitiligo. We will explore the genetic data available, the specific role of damage-associated-molecular patterns, and pattern-recognition receptors, as well as the cellular players involved in the innate immune response. Finally, the relevance of therapeutic strategies targeting this pathway to improve this inflammatory and autoimmune condition is also discussed.

Inhibition of Cochlear HMGB1 Expression Attenuates Oxidative Stress and Inflammation in an Experimental Murine Model of Noise-Induced Hearing Loss

Noise-induced hearing loss (NIHL) is a common inner ear disease but has complex pathological mechanisms, one of which is increased oxidative stress in the cochlea. The high-mobility group box 1 (HMGB1) protein acts as an inflammatory mediator and shows different activities with redox modifications linked to the generation of reactive oxygen species (ROS). We aimed to investigate whether manipulation of cochlear HMGB1 during noise exposure could prevent noise-induced oxidative stress and hearing loss. Sixty CBA/CaJ mice were divided into two groups. An intraperitoneal injection of anti-HMGB1 antibodies was administered to the experimental group; the control group was injected with saline. Thirty minutes later, all mice were subjected to white noise exposure. Subsequent cochlear damage, including auditory threshold shifts, hair cell loss, expression of cochlear HMGB1, and free radical activity, was then evaluated. The levels of HMGB1 and 4-hydroxynonenal (4-HNE), as respective markers of reactive nitrogen species (RNS) and ROS formation, showed slight increases on post-exposure day 1 and achieved their highest levels on post-exposure day 4. After noise exposure, the antibody-treated mice showed markedly less ROS formation and lower expression of NADPH oxidase 4 (NOX4), nitrotyrosine, inducible nitric oxide synthase (iNOS), and intercellular adhesion molecule-1 (ICAM-1) than the saline-treated control mice. A significant amelioration was also observed in the threshold shifts of the auditory brainstem response and the loss of outer hair cells in the antibody-treated versus the saline-treated mice. Our results suggest that inhibition of HMGB1 by neutralization with anti-HMGB1 antibodies prior to noise exposure effectively attenuated oxidative stress and subsequent inflammation. This procedure could therefore have potential as a therapy for NIHL.

Mechanisms of melanocyte death in vitiligo

Vitiligo is an autoimmune depigment disease results from extensive melanocytes destruction. The destruction of melanocyte is thought to be of multifactorial causation. Genome-wide associated studies have identified single-nucleotide polymorphisms in a panel of susceptible loci as risk factors in melanocyte death. But vitiligo onset can't be solely attributed to a susceptive genetic background. Oxidative stress triggered by elevated levels of reactive oxygen species accounts for melanocytic molecular and organelle dysfunction, a minority of melanocyte demise, and melanocyte-specific antigens exposure. Of note, the self-responsive immune function directly contributes to the bulk of melanocyte deaths in vitiligo. The aberrantly heightened innate immunity, type-1-skewed T helper, and incompetent regulatory T cells tip the balance toward autoreaction and CD8+ cytotoxic T lymphocytes finally execute the killing of melanocytes, possibly alarmed by resident memory T cells. In addition to the well-established apoptosis and necrosis, we discuss several death modalities like oxeiptosis, ferroptosis, and necroptosis that are probably employed in melanocyte destruction. This review focuses on the various mechanisms of melanocytic death in vitiligo pathogenesis to demonstrate a panorama of that. We hope to provide new insights into vitiligo pathogenesis and treatment strategies by the review.

Panax ginseng-Derived Extracellular Vesicles Facilitate Anti-Senescence Effects in Human Skin Cells: An Eco-Friendly and Sustainable Way to Use Ginseng Substances

Ginseng is a traditional herbal medicine in eastern Asian countries. Most active constituents in ginseng are prepared via fermentation or organic acid pretreatment. Extracellular vesicles (EVs) are released by most organisms from prokaryotes to eukaryotes and play central roles in intra- and inter-species communications. Plants produce EVs upon exposure to microbes; however, their direct functions and utility for human health are barely known, except for being proposed as delivery vehicles. In this study, we isolated EVs from ginseng roots (GrEVs) or the culture supernatants of ginseng cells (GcEVs) derived from Panax ginseng C.A. Meyer and investigated their biological effects on human skin cells. GrEV or GcEV treatments improved the replicative senescent or senescence-associated pigmented phenotypes of human dermal fibroblasts or ultraviolet B radiation-treated human melanocytes, respectively, by downregulating senescence-associated molecules and/or melanogenesis-related proteins. Based on comprehensive lipidomic analysis using liquid chromatography mass spectrometry, the lipidomic profile of GrEVs differed from that of the parental root extracts, showing significant increases in 70 of 188 identified lipid species and prominent increases in diacylglycerols, some phospholipids (phosphatidylcholine, phosphatidylethanolamine, lysophosphatidylcholine), and sphingomyelin, revealing their unique vesicular properties. Therefore, our results imply that GEVs represent a novel type of bioactive and sustainable nanomaterials that can be applied to human tissues for improving tissue conditions and targeted delivery of active constituents.

The Potential Therapeutic Role of the HMGB1-TLR Pathway in Epilepsy

Epilepsy is one of the most common serious neurological disorders, affecting over 70 million people worldwide. For the treatment of epilepsy, antiepileptic drugs (AEDs) and surgeries are widely used. However, drug resistance and adverse effects indicate the need to develop targeted AEDs based on further exploration of the epileptogenic mechanism. Currently, many efforts have been made to elucidate the neuroinflammation theory in epileptogenesis, which may show potential in the treatment of epilepsy. In this respect, an important target protein, high mobility group box 1 (HMGB1), has received increased attention and has been developed rapidly. HMGB1 is expressed in various eukaryotic cells and localized in the cell nucleus. When HMGB1 is released by injuries or diseases, it participates in inflammation. Recent studies suggest that HMGB1 via Toll-like receptor (TLR) pathways can trigger inflammatory responses and play an important role in epilepsy. In addition, studies of HMGB1 have shown its potential in the treatment of epilepsy. Herein, the authors analyzed the experimental and clinical evidence of the HMGB1-TLR pathway in epilepsy to summarize the theory of epileptogenesis and provide insights into antiepileptic therapy in this novel field.

Involvement of RAGE and Oxidative Stress in Inflammatory and Infectious Skin Diseases

The surface receptor for advanced glycosylation end-products (RAGE) and its soluble (sRAGE) and endogenous secretory (EN-RAGE) forms belong to the superfamily of toll-like receptors and play important roles in inflammation and autoimmunity, directly or through binding with advanced glycosylation end-products (AGE) and advanced oxidation protein products (AOPP). We reviewed the literature on the role of RAGE in skin diseases. Research in this field is still rather limited (28 articles) but suggests the involvement of RAGE and RAGE-related pathways in chronic inflammatory diseases (lupus, psoriasis, atopic dermatitis, and lichen planus), infectious diseases (leprosy, Staphylococcus aureus-induced skin lesions), alterations of the repairing processes in diabetic skin, systemic sclerosis, and ulcers. These data prompt further research in this field, which not only will be useful to better understand the pathogenetic mechanisms of diseases, but is also likely to have intriguing clinical implications. Indeed, when their role in the complex and multifactorial inflammatory balance will be adequately defined, RAGE and related molecules could be used as markers of disease severity and/or response to treatment. Moreover, future promising therapeutic perspectives could be topical administration of some of these molecules (e.g., sRAGE) to modulate local inflammatory response and/or the development of anti-RAGE antibodies for systemic treatment.

The fate of melanocyte: Mechanisms of cell death in vitiligo

Loss of melanocytes (MCs) is the most notable feature of vitiligo. Hence, it is critical to clarify the mechanisms of MC destruction in vitiligo. Apoptosis is most widely studied cell death pathways in vitiligo. In addition, the other two forms of cell death, conventional necrosis and autophagy seem to be involved in the death of vitiligo MCs under certain situations. Moreover, new types of regulated cell death including necroptosis, pyroptosis, and ferroptosis may also participate in the pathogenesis of vitiligo. Anoikis is likely to be connected with the death of detached MCs, which is provoked specifically by loss of anchorage. Primary phagocytosis, later called phagoptosis can execute death of viable cells, probably partly responsible for the loss of MCs in vitiligo. In this review, we aim to summarize the latest insights into various forms of MC death in vitiligo and discuss the corresponding mechanisms.

An update on Vitiligo pathogenesis

Vitiligo, the most common depigmenting disorder of the skin, is undergoing a period of intense advances in both disease understanding and therapeutic possibilities leading the way to the beginning of a new era for the disorder. Its pathophysiology has gathered the attention of researchers for years, and many advances have been made in the clarification of the interaction between different factors that result in depigmented macule formation. The complex interplay between non-immunological and immunological factors in vitiligo is key for the development of the disease, and the participation of cells other than melanocytes, such as keratinocytes, fibroblasts, natural killer cells, and innate lymphoid cells, has been shown. Recent advances have also brought to the understanding of the complex part played by a specific subtype of T cells: T-resident memory cells. This review analyzes some of the most recent insights in vitiligo pathogenesis underlining the interactions between different cell types, which are the basis for the therapeutic approaches under development.

Homocysteine induces melanocytes apoptosis via PERK-eIF2α-CHOP pathway in vitiligo

Vitiligo is a depigmentation disorder that develops as a result of the progressive disappearance of epidermal melanocytes. The elevated level of amino acid metabolite homocysteine (Hcy) has been identified as circulating marker of oxidative stress and known as a risk factor for vitiligo. However, the mechanism underlying Hcy-regulated melanocytic destruction is currently unknown. The present study aims to elucidate the effect of Hcy on melanocytic destruction and its involvement in the pathogenesis of vitiligo. Our results showed that Hcy level was significantly elevated in the serum of progressive vitiligo patients. Notably, Hcy induced cell apoptosis in melanocytes via activating reactive oxygen species (ROS) and endoplasmic reticulum (ER) stress protein kinase RNA-like ER kinase (PERK)-eukaryotic translation initiation factor 2α (eIF2α)-C/EBP homologous protein (CHOP) pathway. More importantly, folic acid, functioning in the transformation of Hcy, could lower the intracellular Hcy level and further reverse the apoptotic effect of Hcy on melanocytes. Additionally, Hcy disrupted melanogenesis whereas folic acid supplementation could reverse the melanogenesis defect induced by Hcy in melanocytes. Taken together, Hcy is highly increased in vitiligo patients at progressive stage, and our in vitro studies revealed that folic acid could protect melanocytes from Hcy-induced apoptosis and melanin synthesis inhibition, indicating folic acid as a potential benefit agent for patients with progressive vitiligo.

Vitiligo, From Physiopathology to Emerging Treatments: A Review

Vitiligo is a chronic inflammatory skin disease leading to the loss of epidermal melanocytes. To date, treatment options for vitiligo patients are limited, lack sustained efficacy, and are mainly based on off-label use of immunosuppressive agents, such as systemic or topical steroids or topical calcineurin inhibitors, in association with the use of ultraviolet light. However, recent insights into the understanding of the immune pathogenesis of the disease have led to the identification of several therapeutic targets and the development of targeted therapies that are now being tested in clinical trials. In this review, based on the physiopathology of the disease, we summarize emerging targets that could be developed for the treatment of vitiligo and discuss recent and ongoing developments of drugs for the management of the disease.

Tranilast Directly Targets NLRP3 to Protect Melanocytes From Keratinocyte-Derived IL-1β Under Oxidative Stress

The activation of NLRP3 inflammasome-IL-1β pathway in keratinocytes contributes to the melanocyte death via autoimmunity-dependent manner in vitiligo. As a safe small-compound drug employed frequently in clinic, tranilast (TR) is newly reported to block the activation of NLRP3 inflammasome in macrophage. Nevertheless, whether keratinocyte-derived IL-1β damages melanocytes in an autoimmunity-independent way and whether TR could ameliorate the melanocyte damage via inhibiting the NLRP3-IL-1β pathway in keratinocyte still are not clear. In the present study, we initially found that TR could impede the secretion of IL-1β from keratinocytes by interfering the NLRP3 oligomerization. More importantly, we illustrated that TR could decrease the melanocyte apoptosis, improve the melanogenesis, and have the capacity to optimize the melanosome translocation by abolishing the keratinocyte-derived IL-1β. Additionally, TR could mitigate the secretion of inflammatory cytokines such as IL-6, IL-8, TNF-α, and IL-18 in keratinocytes under oxidative stress. In short, our data indicate that IL-1β plays detrimental roles in the melanocyte survival, melanogenesis, melanosome translocation and the secretion of inflammatory cytokines, and TR could be a promising therapeutic strategy in vitiligo by attenuating the keratinocyte-derived IL-1β under oxidative stress.