Increased Circulating CXCL10 in Non-Segmental Vitiligo Concomitant with Autoimmune Thyroid Disease and Alopecia Areata

Biomarkers in alopecia Areata: A systematic review and meta-analysis

BACKGROUND

Alopecia areata (AA) is an autoimmune non-scarring alopecia that affects the scalp or any hair-bearing areas in the body. The pathophysiology of AA is complex, but Th1, Th2, and Th17 cytokines dysregulation, as well as chemokines, immunoglobulins and other biomarkers have been shown to play a role in the pathogenesis of the disease.

OBJECTIVE

To conduct a systematic review and Meta-analysis to identify biomarkers that reflect AA activity and severity that could be used to better assess disease activity and response in both trials and clinical practice.

METHODS

A literature search was conducted using the PUBMED, EMBASE and the Cumulative Index to Nursing and Allied Health Literature (CINAHL) from inception to December 2021. Articles reporting on associations between AA and serum clinical biomarkers (cytokines, chemokines, antibodies, immunoglobulins, and others) were included. Serum biomarkers were identified in patients with AA and were correlated with disease severity and patient characteristics (ex. age, sex, comorbidities). The quality of the studies was assessed using the National Heart, Lung, and Blood Institute's Quality Assessment Tool for Case-Control Studies. Meta-analysis pooling of the standardized mean differences (SMD) by the method of Cohen using the common-effect inverse-variance model was performed. For the Meta-analysis, data was pulled for all the markers with a minimum of 4 studies with means and standard deviations. Analysis of data reported as Median with range or inter-quartile range (IQR) revealed that the data was too skewed to recommend calculation and use of mean with standard deviation (SD). If the data were not skewed, mean and SD were calculated.

RESULTS

One thousand seven hundred fourteen studies were screened, with 91 included, reporting on a total of 52 biomarkers. Meta-analyses revealed pooled SMD that were significant for interleukin 6 (IL6), C-reactive protein (CRP) and vitamin D.

CONCLUSIONS

Serum IL6 and CRP levels are significantly increased in patients with AA compared to healthy age and sex matched controls. Conversely, serum vitamn D levels are significantly decreased in patients with AA compared to healthy age and sex matched controls. This data has the potenail to influence the clinical guidelines for the diagnostic workup of AA to include testing the serum levels of CRP and vitamin D.

A meta-analysis of chemokines in vitiligo: Recruiting immune cells towards melanocytes

Chemokine research offers insightful information on the pathogenesis of cutaneous immune disorders, such as vitiligo. Compared to cytokines, the higher detectable levels of chemokines display promising potential as future disease biomarkers. Nonetheless, some published study results are contradictory, which can be attributed to patient characteristics and methodological differences. In this study, a meta-analysis was performed to compare chemokine expression in blood and skin samples from vitiligo patients versus healthy controls. Furthermore, the relationship between chemokine expression and disease activity was evaluated. Chemokine levels were investigated in 15 articles in the circulation and in 9 articles in vitiligo skin. Overall, some clear trends were observed. CXCR3 signaling by CXCL10 and CXCL9 has been confirmed by several reports, although CXCL10 showed more robust findings in blood samples. In this meta-analysis, CCL5, CXCL8, CXCL12, and CXCL16 levels were also significantly elevated. This indicates a complex immune pathway activation in vitiligo that overall supports a Th1-dominant response. Chemokines linked to the Th2 and Th17 pathways were less prevalent. Despite these findings, study protocols that examine a broader range of chemokines are encouraged, because current research is mostly focused on a small number of chemokines that were differentially expressed in previous studies.

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.

The Role of Oxidative Stress in the Pathogenesis of Vitiligo: A Culprit for Melanocyte Death

Vitiligo is a common chronic acquired pigmentation disorder characterized by loss of pigmentation. Among various hypotheses proposed for the pathogenesis of vitiligo, oxidative stress-induced immune response that ultimately leads to melanocyte death remains most widely accepted. Oxidative stress which causes elevated levels of reactive oxygen species (ROS) can lead to dysfunction of molecules and organelles, triggering further immune response, and ultimately melanocyte death. In recent years, a variety of cell death modes have been studied, including apoptosis, autophagy and autophagic cell death, ferroptosis, and other novel modes of death, which will be discussed in this review in detail. Oxidative stress is also strongly linked to these modes of death. Under oxidative stress, ROS could induce autophagy by activating the Nrf2 antioxidant pathway of melanocytes. However, persistent stimulation of ROS might eventually lead to excessive activation of Nrf2 antioxidant pathway, which in turn will inactivate autophagy. Moreover, ferroptosis may be triggered by oxidative-related transcriptional production, including ARE, the positive feedback loop related to p62, and the reduced activity and expression of GPX4. Therefore, it is reasonable to infer that these modes of death are involved in the oxidative stress response, and that oxidative stress also acts as an initiator for various modes of death through some complex mechanisms. In this study, we aim to summarize the role of oxidative stress in vitiligo and discuss the corresponding mechanisms of interaction between various modes of cell death and oxidative stress. These findings may provide new ideas for exploring the pathogenesis and potential therapeutic targets of vitiligo.