Phenotype and Antimicrobial Activity of Th17 Cells Induced by Propionibacterium acnes Strains Associated with Healthy and Acne Skin

Immune Activation and Glycolytic Responses to Cutibacterium acnes Cell Wall Polysaccharides

Carbohydrates are key components of many microbial cell walls and play a versatile role in immune recognition. In this study, we analyzed the carbohydrate cell wall composition of Cutibacterium acnes strains associated with healthy skin (denoted as CH) and acne-prone skin (denoted as CA) to understand their influence on host immune responses in acne. We identified glucose, mannose, and galactose as the primary monosaccharides, with minor amounts of fucose, N-acetylgalactosamine, and N-acetylglucosamine. Linkage analysis revealed structural variations between CH and CA strains: CH strains showed a balanced and diverse polysaccharide structure, whereas CA strains displayed a more rigid structure with 1→4 and branched 1→6 linkages, potentially contributing to inflammatory properties. Immunostimulatory assays revealed that C acnes carbohydrates induced IL-6 and IL-17 but not IL-1β, highlighting the role of carbohydrate structures in influencing cytokine responses. Treatment with sodium meta-periodate impaired this immunostimulatory activity, indicating that carbohydrate integrity is crucial for immune activation. In addition, analysis of single-cell RNA-sequencing data from acne lesions revealed elevated glycolytic activity in acne lesions in comparison with that in nonlesional skin, suggesting a Warburg-like effect that promotes inflammation. Our findings highlight the role of C acnes polysaccharides in immune modulation and inflammation, suggesting their potential as therapeutic targets for acne treatment.

Multi-target mechanisms and potential applications of quercetin in the treatment of acne vulgaris

Acne vulgaris, a prevalent inflammatory dermatosis, afflicts approximately 90% of adolescents globally. Despite the efficacy of conventional therapies, including antibiotics and retinoids, their use is frequently limited by adverse effects and the emergence of drug resistance. Quercetin, a naturally occurring flavonoid, has garnered significant attention owing to its diverse biological activities, encompassing anti-inflammatory, antioxidant, antimicrobial, and immunomodulatory properties. This review comprehensively explores the multi-target mechanisms of quercetin in the treatment of acne, focusing on its ability to modulate inflammatory cytokine production, oxidative stress pathways, sebaceous gland activity, and microbial populations. Additionally, quercetin promotes skin barrier repair and reduces post-inflammatory hyperpigmentation and scarring through its antioxidant and anti-fibrotic effects. Despite promising in vitro and preclinical findings, challenges such as quercetin's low bioavailability and lack of robust clinical evidence necessitate further research. Advanced delivery systems, including nanoparticles and combination therapies, may optimize its therapeutic potential. This review provides insights into the molecular mechanisms and clinical applications of quercetin, highlighting its potential as a safe and effective alternative for acne management.

Acne and the cutaneous microbiome: A systematic review of mechanisms and implications for treatments

BACKGROUND

Acne vulgaris is a pervasive skin disease characterized by inflammation of sebaceous units surrounding hair follicles. It results from the complex interplay between skin physiology and the intricate cutaneous microbiome. Current acne treatments, while effective, have major limitations, prompting a shift towards microbiome-based therapeutic approaches.

OBJECTIVES

This study aims to determine the relationship between acne and the cutaneous microbiome, assess the effects of current treatments on the cutaneous microbiome, and explore the implications for developing new therapies.

METHODS

A systematic review was performed using PubMed and SCOPUS databases within the last 10 years. Methodological quality was assessed independently by two authors. The search retrieved 1830 records, of which 26 articles met the inclusion criteria. Meta-analysis of alpha diversity change was assessed using fixed and randomized effect models per therapeutic group.

RESULTS

Eight studies pertain to the role of the cutaneous microbiome in acne, identifying C. acnes, S. aureus and S. epidermidis as key contributors through overproliferation, commensalism, or dysbiosis. Eleven studies discuss current acne treatments, including doxycycline (1), topical benzoyl peroxide (BPO) (4), isotretinoin (2), sulfacetamide-sulfur (SSA) (2) and aminolevulinic acid-photodynamic therapy (ALA-PDT) (2), identified as modulating the cutaneous microbiome as a mechanism of efficacy in acne treatment. Seven studies discuss new treatments with topical probiotics, plant derivatives, and protein derivatives, which contribute to acne clearance via modulation of dysbiosis, inflammatory markers and diversity indexes. A meta-analysis of the effects of existing therapeutics on the cutaneous microbiome identified benzoyl peroxide as the only treatment to facilitate significant change in diversity.

CONCLUSIONS

Despite the heterogeneity of study types and microbiome classifications limiting the analysis, this review underscores the complexity of microbial involvement in acne pathogenesis. It delineates the effects of acne therapeutics on microbial diversity, abundance, and composition, emphasizing the necessity for personalized approaches in acne management based on microbiome modulation.

Progress on Multiomics Research on Acne Vulgaris: A Literature Review

Acne vulgaris, a prevalent chronic inflammatory disease of the pilosebaceous unit, continues to present with a complex pathogenesis that is not fully understood. The advent of high-throughput sequencing technologies has revolutionized biomedical research, enabling the comprehensive use of multiomics analyses to study diseases with intricate mechanisms, such as acne. This review summarizes the progress in genomics, epigenomics, transcriptomics, proteomics, and metabolomics research on acne. By providing a comprehensive overview, we aim to enhance our understanding of acne pathogenesis and identify potential therapeutic targets that could inspire the prevention and treatment of acne.

Amplicon-based analysis reveals link between adolescent acne and altered facial skin microbiome induced by negative emotional states

Introduction

The skin microbiome is integral to maintaining skin homeostasis and is involved in the pathogenesis of acne. Emerging evidence supporting the 'brain-skin axis' suggests that psychological stress may exacerbate acne. Both negative emotional states and acne are highly prevalent among adolescents. Although research has begun to explore this relationship, the role of the skin microbiome in adolescents experiencing emotional disturbances and acne remains poorly understood.

Methods

166 adolescents aged 15-18 were divided into four distinct groups based on their emotional health and acne severity: no acne or negative emotions (NC), acne without negative emotions (NS), negative emotions without acne (YC), and acne with negative emotions (YS). Skin samples were collected from each participant's forehead and analyzed using high-throughput sequencing techniques, followed by comprehensive bioinformatics analyses to evaluate the microbial composition and diversity across the different groups.

Results

Adolescents with both acne and negative emotions exhibited significantly higher acne severity (IGA 2.675 ± 0.090) compared to the group with acne but without negative emotions (IGA 1.952 ± 0.136). Distinct microbial community patterns emerged among the groups, with acne-affected individuals displaying increased α-diversity. Additionally, negative emotions were associated with heightened β-diversity differences between acne-affected individuals. The predominant bacterial phyla identified were Firmicutes, Bacteroidetes, Proteobacteria, and Fusobacteria, with Acinetobacter being more abundant, and Roseomonas and Cutibacterium being less prevalent in adolescents experiencing negative emotions.

Conclusion

This study revealed that the bacterial biomarkers of the disease change when acne is accompanied by negative emotions. Cutibacterium, Acinetobacter, and Roseomonas may be key contributors to acne exacerbation. These findings underscore the importance of considering both emotional and microbiological factors in the management of adolescent acne, particularly within the context of the brain-skin connection.

Analysis of global trends and hotspots of skin microbiome in acne: a bibliometric perspective

BACKGROUND

Acne is a chronic inflammatory condition affecting the hair follicles and sebaceous glands. Recent research has revealed significant advances in the study of the acne skin microbiome. Systematic analysis of research trends and hotspots in the acne skin microbiome is lacking. This study utilized bibliometric methods to conduct in-depth research on the recognition structure of the acne skin microbiome, identifying hot trends and emerging topics.

METHODS

We performed a topic search to retrieve articles about skin microbiome in acne from the Web of Science Core Collection. Bibliometric research was conducted using CiteSpace, VOSviewer, and R language.

RESULTS

This study analyzed 757 articles from 1362 institutions in 68 countries, the United States leading the research efforts. Notably, Brigitte Dréno from the University of Nantes emerged as the most prolific author in this field, with 19 papers and 334 co-citations. The research output on the skin microbiome of acne continues to increase, with Experimental Dermatology being the journal with the highest number of published articles. The primary focus is investigating the skin microbiome's mechanisms in acne development and exploring treatment strategies. These findings have important implications for developing microbiome-targeted therapies, which could provide new, personalized treatment options for patients with acne. Emerging research hotspots include skincare, gut microbiome, and treatment.

CONCLUSION

The study's findings indicate a thriving research interest in the skin microbiome and its relationship to acne, focusing on acne treatment through the regulation of the skin microbiome balance. Currently, the development of skincare products targeting the regulation of the skin microbiome represents a research hotspot, reflecting the transition from basic scientific research to clinical practice.

Efficacy of a Postbiotic Formulation Combined With Microneedling for Mild-to-Moderate Acne: A Self-Control Study

BACKGROUND

Acne vulgaris significantly affects young individuals globally, with its onset associated with an increased prevalence of C acnes, a naturally occurring skin bacterium. In light of the rising concerns regarding antibiotic resistance and the potential for adverse effects, pharmacological interventions may not consistently represent the most suitable option. Nonpharmacological approaches, such as microneedling, offer promising alternative treatment modalities. Furthermore, the integration of postbiotics in skincare formulations for acne management has gained traction recently. Nonetheless, there remains a lack of sufficient evidence to establish the efficacy and safety of postbiotics when combined with microneedling.

OBJECTIVE

To assess the clinical effectiveness of a postbiotic formulation combined with microneedling in mild-to-moderate facial acne vulgaris.

METHODS

Twenty Chinese patients were enrolled, all received one treatment and were monitored 4 weeks posttreatment. The evaluation assessed symptom improvement, treatment safety, and patient satisfaction.

RESULTS

The global acne grading system (GAGS) score decreased more than half based on the baseline. Clinical photographs following treatment revealed improved the skin lesions and brightened skin tone. Statistics from VISIA showed excellent improvement in speckle, pore, red region, and porphyrin. No significant adverse reactions have been reported during the treatment period. Additionally, more than 85% were very satisfied or satisfied with the outcome.

CONCLUSION

Our results showed that the postbiotic formulation combined with microneedling may benefit the restoration of the skin barrier and the equilibrium of skin microbiota. This approach may help mitigate inflammation and address skin lesions, presenting a promising therapeutic avenue for the prevention and management of acne vulgaris.

Insights into early acne pathogenesis: Exploring intercellular dynamics and key dysregulated genes

The comprehensive changes and shared dysregulated signaling pathways in early stage acne remains largely unexplored. In our recently published paper entitled "Analysis of Intracellular Communication Reveals Consistent Gene Changes Associated with Early-Stage Acne Skin," we utilized single-cell RNA sequencing and spatial transcriptomics datasets from acne patients to analyze cell communication. We identified dysregulated genes linked to inflammatory responses and hyperkeratinization. This commentary discusses potential new markers across major skin cell types, including endothelial cells, fibroblasts, lymphocytes, myeloid cells, keratinocytes, and smooth muscle cells. Additionally, we discuss key dysregulated genes in acne lesions, focusing on the intricate interplay between inflammation and hyperkeratinization. Based on our findings, we explore potential FDA-approved treatments targeting two key pathways involved in acne pathogenesis. These insights provide new therapeutic targets for acne treatment.

Topical, light-based, and complementary interventions for acne: an overview of systematic reviews

BACKGROUND

Acne is a chronic inflammatory and immune-mediated disease of the pilosebaceous unit (the skin structure consisting of a hair follicle and its associated sebaceous gland). It is characterised by non-inflammatory lesions (open and closed comedones) and inflammatory lesions (papules, pustules, nodules, and cysts). Lesions may be present on the face, thorax, and back, with variable severity. Acne exhibits a global distribution and has a growing prevalence. Acne vulgaris is the most common form. Acne gives rise to complications such as scars and can seriously affect people's mental health, especially those with severe acne. Acne has a huge impact on the quality of life and self-esteem of those affected.

OBJECTIVES

To synthesise the existing evidence on the efficacy and safety of non-systemic pharmacological interventions and non-pharmacological interventions (physical therapy and complementary therapies) in the treatment of acne vulgaris and related skin complications.

METHODS

We searched the Cochrane Database of Systematic Reviews, Epistemonikos, MEDLINE, and Embase to 2 December 2021, and checked the reference lists of included reviews. At least two authors were responsible for screening, data extraction, and critical appraisal. We excluded reviews with high risk of bias as assessed with the ROBIS tool. We evaluated the overall certainty of the evidence according to GRADE (as carried out by the authors of the included reviews or ourselves). We provide comprehensive evidence from the review data, including summary of findings tables, summary of results tables, and evidence maps.

MAIN RESULTS

We retrieved and assessed a total of 733 records; however, only six reviews (five Cochrane reviews and one non-Cochrane review) with low risk of bias met the overview inclusion criteria. The six reviews involved 40,910 people with acne from 275 trials and 1316 people with acne scars from 37 trials. The age of the participants ranged from 10 to 59 years, with an average age range from 18 to 30 years. Four reviews included original trials involving only female participants and three reviews included original trials with only male participants. Main results for clinically important comparisons: Benzoyl peroxide versus placebo or no treatment: In two trials involving 1012 participants over 12 weeks, benzoyl peroxide may reduce the total (mean difference (MD) -16.14, 95% confidence interval (CI) -26.51 to -5.78), inflammatory (MD -6.12, 95% CI -11.02 to -1.22), and non-inflammatory lesion counts (MD -9.69, 95% CI -15.08 to -4.29) when compared to placebo (long-term treatment), but the evidence is very uncertain (very low-certainty evidence). Two trials including 1073 participants (time point: 10 and 12 weeks) suggested benzoyl peroxide may have little to no effect in improving participants' global self-assessment compared to placebo (long-term treatment), but the evidence is very uncertain (risk ratio (RR) 1.44, 95% CI 0.94 to 2.22; very low-certainty evidence). Very low-certainty evidence suggested that benzoyl peroxide may improve investigators' global assessment (RR 1.77, 95% CI 1.37 to 2.28; 6 trials, 4110 participants, long-term treatment (12 weeks)) compared to placebo. Thirteen trials including 4287 participants over 10 to 12 weeks suggested benzoyl peroxide may increase the risk of a less serious adverse event compared to placebo (long-term treatment), but the evidence is very uncertain (RR 1.46, 95% CI 1.01 to 2.11; very low-certainty evidence). Benzoyl peroxide versus topical retinoids: Benzoyl peroxide may increase the percentage change in total lesion count compared to adapalene (long-term treatment), but the evidence is very uncertain (MD 10.8, 95% CI 3.38 to 18.22; 1 trial, 205 participants, 12 weeks; very low-certainty evidence). When compared to adapalene, benzoyl peroxide may have little to no effect on the following outcomes (long-term treatment): percentage change in inflammatory lesion counts (MD -7.7, 95% CI -16.46 to 1.06; 1 trial, 142 participants, 11 weeks; very low-certainty evidence), percentage change in non-inflammatory lesion counts (MD -3.9, 95% CI -13.31 to 5.51; 1 trial, 142 participants, 11 weeks; very low-certainty evidence), participant's global self-assessment (RR 0.96, 95% CI 0.86 to 1.06; 4 trials, 1123 participants, 11 to 12 weeks; low-certainty evidence), investigators' global assessment (RR 1.16, 95% CI 0.98 to 1.37; 3 trials, 1965 participants, 12 weeks; low-certainty evidence), and incidence of a less serious adverse event (RR 0.77, 95% CI 0.48 to 1.25, 1573 participants, 5 trials, 11 to 12 weeks; very low-certainty evidence). Benzoyl peroxide versus topical antibiotics: When compared to clindamycin, benzoyl peroxide may have little to no effect on the following outcomes (long-term treatment): total lesion counts (MD -3.50, 95% CI -7.54 to 0.54; 1 trial, 641 participants, 12 weeks; very low-certainty evidence), inflammatory lesion counts (MD -1.20, 95% CI -2.99 to 0.59; 1 trial, 641 participants, 12 weeks; very low-certainty evidence), non-inflammatory lesion counts (MD -2.4, 95% CI -5.3 to 0.5; 1 trial, 641 participants, 12 weeks; very low-certainty evidence), participant's global self-assessment (RR 0.95, 95% CI 0.68 to 1.34; 1 trial, 240 participants, 10 weeks; low-certainty evidence), investigator's global assessment (RR 1.10, 95% CI 0.83 to 1.45; 2 trials, 2277 participants, 12 weeks; very low-certainty evidence), and incidence of a less serious adverse event (RR 1.27, 95% CI 0.98 to 1.64; 5 trials, 2842 participants, 10 to 12 weeks; low-certainty evidence). For these clinically important comparisons, no review collected data for the following outcomes: frequency of participants experiencing at least one serious adverse event or quality of life. No review collected data for the following comparisons: topical antibiotics versus placebo or no treatment, topical retinoids versus placebo or no treatment, or topical retinoids versus topical antibiotics.

AUTHORS' CONCLUSIONS

This overview summarises the evidence for topical therapy, phototherapy, and complementary therapy for acne and acne scars. We found no high-certainty evidence for the effects of any therapy included. Randomised controlled trials and systematic reviews related to acne and acne scars had limitations (low methodological quality). We could not summarise the evidence for topical retinoids and topical antibiotics due to insufficient high-quality systematic reviews. Future research should consider pooled analysis of data on new emerging drugs for acne treatment (e.g. clascoterone) and focus more on acne complications.

IL-17 in skin infections and homeostasis

Interleukin (IL) 17 is a proinflammatory cytokine belonging to a structurally related group of cytokines known as the IL-17 family. It has been profoundly studied for its contribution to the pathology of autoimmune diseases. However, it also plays an important role in homeostasis and the defense against extracellular bacteria and fungi. IL-17 is important for epithelial barriers, including the skin, where some of its cellular targets reside. Most of the research work on IL-17 has focused on its effects in the skin within the context of autoimmune diseases or sterile inflammation, despite also having impact on other skin conditions. In recent years, studies on the role of IL-17 in the defense against skin pathogens and in the maintenance of skin homeostasis mediated by the microbiota have grown in importance. Here we review and discuss the cumulative evidence regarding the main contribution of IL-17 in the maintenance of skin integrity as well as its protective or pathogenic effects during some skin infections.

Potential functionality of Cutibacterium acnes extracellular vesicles in atopic dermatitis and acne vulgaris: A comparative proteomic analysis

BACKGROUND

Cutibacterium acnes is a commensal bacterium residing in healthy skin and plays a critical role in maintaining skin homeostasis. C. acnes has been considered closely related to acne vulgaris, while recent studies suggest that C. acnes and its metabolites may have a protective role in atopic dermatitis (AD) by modulating the immune system and maintaining skin homeostasis. Extracellular vesicles (EVs) are small membranous vesicles secreted by bacteria that participate in bacteria-host interactions.

METHODS

This study first compared C. acnes EVs from AD lesions (AD-EVs), acne lesions (Acne-EVs), and healthy skin (NC-EVs), using Label-free quantitative LC-MS/MS and validated differently expressed proteins by parallel reaction monitoring (PRM). Then Normal Human Epidermal Keratinocytes (NHEK) and human primary keratinocytes (KC) were treated with C. acnes EVs isolated from different groups, and the expressions of inflammatory factors were measured by quantitative real-time PCR and Western blotting.

RESULTS

Compared with the acne group, the AD group showed greater downregulation of proteins related to energy metabolism and carbon source utilization pathway. Differences in protein profile in AD and acne lesion-separated C. acnes EVs correspond to the abnormal sebum secretion pattern in both diseases. C. acnes EVs from different groups affected different expressions of Th1 and Th2 inflammatory factors and epidermal barrier markers in NHEK and KC, indicating different immunomodulatory potentials.

CONCLUSIONS

This study observed distinct proteomic differences between AD-EVs and Acne-EVs, and provided insights into the functional differences of C. acnes EVs in AD and acne.

Analysis of intracellular communication reveals consistent gene changes associated with early-stage acne skin

A comprehensive understanding of the intricate cellular and molecular changes governing the complex interactions between cells within acne lesions is currently lacking. Herein, we analyzed early papules from six subjects with active acne vulgaris, utilizing single-cell and high-resolution spatial RNA sequencing. We observed significant changes in signaling pathways across seven different cell types when comparing lesional skin samples (LSS) to healthy skin samples (HSS). Using CellChat, we constructed an atlas of signaling pathways for the HSS, identifying key signal distributions and cell-specific genes within individual clusters. Further, our comparative analysis revealed changes in 49 signaling pathways across all cell clusters in the LSS- 4 exhibited decreased activity, whereas 45 were upregulated, suggesting that acne significantly alters cellular dynamics. We identified ten molecules, including GRN, IL-13RA1 and SDC1 that were consistently altered in all donors. Subsequently, we focused on the function of GRN and IL-13RA1 in TREM2 macrophages and keratinocytes as these cells participate in inflammation and hyperkeratinization in the early stages of acne development. We evaluated their function in TREM2 macrophages and the HaCaT cell line. We found that GRN increased the expression of proinflammatory cytokines and chemokines, including IL-18, CCL5, and CXCL2 in TREM2 macrophages. Additionally, the activation of IL-13RA1 by IL-13 in HaCaT cells promoted the dysregulation of genes associated with hyperkeratinization, including KRT17, KRT16, and FLG. These findings suggest that modulating the GRN-SORT1 and IL-13-IL-13RA1 signaling pathways could be a promising approach for developing new acne treatments.

Innate lymphoid cell-based immunomodulatory hydrogel microspheres containing Cutibacterium acnes extracellular vesicles for the treatment of psoriasis

Psoriasis is a chronic skin inflammation influenced by dysregulated skin microbiota, with the role of microbiota in psoriasis gaining increasing prominence. Bacterial extracellular vesicles (bEVs) serve as crucial regulators in the interaction between hosts and microbiota. However, the mechanism underlying the therapeutic potential of bEVs from commensal bacteria in psoriasis remains unclear. Here, we investigated the therapeutic role of Cutibacterium acnes (C. acnes)-derived extracellular vesicles (CA-EVs) in psoriasis treatment. To prolong the active duration of CA-EVs, we encapsulated them in gelatin methacrylate (GelMA) to fabricate hydrogel microspheres (CA-EVs@GHM) with sustained release properties. As GelMA degraded, CA-EVs were gradually released, maintaining a high concentration in mouse skin even 96 h post-treatment. In human keratinocyte cells (HaCaT), CA-EVs@GHM enhanced resistance to Staphylococcus aureus (S. aureus), promoted proliferation and migration of HaCaT cells exposed to S. aureus, and significantly reduced the expression of inflammatory genes such as interleukin (IL)-6 and C-X-C motif chemokine ligand 8 (CXCL8). In vivo, CA-EVs@GHM, more potent than CA-EVs alone, markedly attenuated proinflammatory gene expression, including tumor necrosis factor (TNF), Il6, Il17a, Il22 and Il23a in imiquimod (IMQ)-induced psoriasis-like mice, and restored skin barrier function. 16S rRNA sequencing revealed that CA-EVs@GHM might provide therapeutic effects against psoriasis by restoring microbiota diversity on the back skin of mice, reducing Staphylococcus colonization, and augmenting lipid metabolism. Furthermore, flow cytometry analysis showed that CA-EVs@GHM prevented the conversion of type 2 innate lymphoid cells (ILC2) to type 3 innate lymphoid cells (ILC3) in psoriasis-like mouse skin, reducing the pathogenic ILC3 population and suppressing the secretion of IL-17 and IL-22. In summary, our findings demonstrate that the long-term sustained release of CA-EVs alleviated psoriasis symptoms by controlling the transformation of innate lymphoid cells (ILCs) subgroups and restoring skin microbiota homeostasis, thus offering a promising therapy for psoriasis treatment. STATEMENT OF SIGNIFICANCE: Cutibacterium acnes, which is reduced in psoriasis skin, has been reported to promote skin homeostasis by regulating immune balance. Compared to live bacteria, bacterial extracellular vesicles (bEVs) are less prone to toxicity and safety concerns. bEVs play a pivotal role in maintaining bacterial homeostasis and modulating the immune system. However,bEVs without sustained release materials are unable to function continuously in chronic diseases. Therefore, we utilized hydrogel microspheres to encapsulate Cutibacterium acnes (C. acnes)-derived extracellular vesicles (CA-EVs), enabling long term sustained release. Our findings indicate that, CA-EVs loaded gelatin methacrylate hydrogel microspheres (CA-EVs@GHM) showed superior therapeutic effects in treating psoriasis compared to CA-EVs. CA-EVs@GHM exhibited a more significant regulation of pathological type 3 innate lymphoid cells (ILC3) and skin microbiota, providing a promising approach for microbiota-derived extracellular vesicle therapy in the treatment of skin inflammation.

Multi-omics signatures reveal genomic and functional heterogeneity of Cutibacterium acnes in normal and diseased skin

Cutibacterium acnes is the most abundant bacterium of the human skin microbiome since adolescence, participating in both skin homeostasis and diseases. Here, we demonstrate individual and niche heterogeneity of C. acnes from 1,234 isolate genomes. Skin disease (atopic dermatitis and acne) and body site shape genomic differences of C. acnes, stemming from horizontal gene transfer and selection pressure. C. acnes harbors characteristic metabolic functions, fewer antibiotic resistance genes and virulence factors, and a more stable genome compared with Staphylococcus epidermidis. Integrated genome, transcriptome, and metabolome analysis at the strain level unveils the functional characteristics of C. acnes. Consistent with the transcriptome signature, C. acnes in a sebum-rich environment induces toxic and pro-inflammatory effects on keratinocytes. L-carnosine, an anti-oxidative stress metabolite, is up-regulated in the C. acnes metabolome from atopic dermatitis and attenuates skin inflammation. Collectively, our study reveals the joint impact of genes and the microenvironment on C. acnes function.

A microRNA focus on acne

Acne (syn. acne vulgaris) is a common inflammatory skin disorder associated with puberty and adolescence. The disease is characterized by comedoneous lesions, papules, pustules, and nodules that are mostly found on the face. These lesions are caused by intricate interactions between the pilosebaceous unit and the Cutibacterium acnes (C. acnes) bacteria. Unhealthy acne and its aftereffects, like pigment changes and scarring, have a detrimental impact on one's quality of life. Recent years have seen a sharp increase in the approval of nucleic acid therapies (NATs), such as antisense oligonucleotides and short-interfering RNA medications, for rare diseases for which there are few or no effective treatments. These developments suggest that NATs may be useful in acne treatment plans down the road, as do clinical trials for microRNA (miRNA) modulation in skin contexts. We highlight promising miRNA targets for anti-acne therapy in this review. We outline the pathophysiology of acne in brief and emphasize the functions of C. acnes. Next, we concentrate on the distinct impacts of biofilm and planktonic C. acnes on a Toll-like receptor 2 axis that spans miR-146a-5p, which was recently discovered. Before discussing the potential contributions of miR-21-5p, miR-233-3p, and miR-150-5p to inflammatory axes in acne, we evaluate miR-146a-5p in sebocytes. Finally, we address patient involvement in miRNA-related acne research and translational perspectives.

Alterations in epidermal stem cells within the pilosebaceous unit in atrophic acne scars

BACKGROUND

Atrophic acne scarring is a common sequela of inflammatory acne, causing significant problems for affected patients. Although prolonged inflammation and subsequent aberrant tissue regeneration are considered the underlying pathogenesis, the role of epidermal stem cells, which are crucial to the regeneration of pilosebaceous units, remains unknown.

OBJECTIVES

To examine the changes occurring in epidermal stem cells in atrophic acne scars.

METHODS

Changes in collagen, elastic fibre and human leukocyte antigen (HLA)-DR expression were analysed in normal skin and inflammatory acne lesions at days 1, 3 and 7 after development. The expression of epidermal stem cell markers and proliferation markers was compared between normal skin and mature atrophic acne scar tissue.

RESULTS

In acne lesions, inflammation had invaded into pilosebaceous units over time. Their normal structure had been destructed and replaced with a reduced amount of collagen and elastic fibre. Expression of stem cell markers including CD34, p63, leucine-rich repeat-containing G protein-coupled receptor (LGR)6 and LGR5, which are expressed in the interfollicular epidermis, isthmus and bulge of hair follicles, significantly decreased in atrophic acne scar tissue compared to normal skin. Epidermal proliferation was significantly reduced in scar tissue.

CONCLUSIONS

These findings suggest that as inflammatory acne lesions progress, inflammation gradually infiltrates the pilosebaceous unit and affects the resident stem cells. This disruption impedes the normal regeneration of the interfollicular epidermis and adnexal structures, resulting in atrophic acne scars.

Immunobiology of IL-26

T helper 17 (Th17) cells produce a set of cytokines that include IL-17 family members, IL-21, IL-22, and IL-26. These cytokines all contribute to the classic function of Th17 cells in combatting extracellular infection and promoting inflammation in autoimmune diseases. However, of the Th17 cytokines, only IL-26 has direct antimicrobial activity against microbes and can activate a broad range of immune cells through its ability to bind DNA and trigger pattern recognition receptors. It is noteworthy that IL-26 is produced by mammalian cells, including human Th17 cells, but is absent in rodents. As such, IL-26 is a potential therapeutic target to augment host immune responses against microbial pathogens but also to prevent inflammation and tissue damage in a variety of autoimmune diseases.

Analysis of Intracellular Communication Reveals Consistent Gene Changes Associated with Early-Stage Acne Skin

A comprehensive understanding of the intricate cellular and molecular changes governing the complex interactions between cells within acne lesions is currently lacking. Herein, we analyzed early papules from six subjects with active acne vulgaris, utilizing single-cell and high-resolution spatial RNA sequencing. We observed significant changes in signaling pathways across seven different cell types when comparing lesional skin samples (LSS) to healthy skin samples (HSS). Using CellChat, we constructed an atlas of signaling pathways for the HSS, identifying key signal distributions and cell-specific genes within individual clusters. Further, our comparative analysis revealed changes in 49 signaling pathways across all cell clusters in the LSS- 4 exhibited decreased activity, whereas 45 were upregulated, suggesting that acne significantly alters cellular dynamics. We identified ten molecules, including GRN, IL-13RA1 and SDC1 that were consistently altered in all donors. Subsequently, we focused on the function of GRN and IL-13RA1 in TREM2 macrophages and keratinocytes as these cells participate in inflammation and hyperkeratinization in the early stages of acne development. We evaluated their function in TREM2 macrophages and the HaCaT cell line. We found that GRN increased the expression of proinflammatory cytokines and chemokines, including IL-18, CCL5, and CXCL2 in TREM2 macrophages. Additionally, the activation of IL-13RA1 by IL-13 in HaCaT cells promoted the dysregulation of genes associated with hyperkeratinization, including KRT17, KRT16, and FLG. These findings suggest that modulating the GRN-SORT1 and IL-13-IL-13RA1 signaling pathways could be a promising approach for developing new acne treatments.

Microbiome: Role in Inflammatory Skin Diseases

As the body's largest organ, the skin harbors a highly diverse microbiota, playing a crucial role in resisting foreign pathogens, nurturing the immune system, and metabolizing natural products. The dysregulation of human skin microbiota is implicated in immune dysregulation and inflammatory responses. This review delineates the microbial alterations and immune dysregulation features in common Inflammatory Skin Diseases (ISDs) such as psoriasis, rosacea, atopic dermatitis(AD), seborrheic dermatitis(SD), diaper dermatitis(DD), and Malassezia folliculitis(MF).The skin microbiota, a complex and evolving community, undergoes changes in composition and function that can compromise the skin microbial barrier. These alterations induce water loss and abnormal lipid metabolism, contributing to the onset of ISDs. Additionally, microorganisms release toxins, like Staphylococcus aureus secreted α toxins and proteases, which may dissolve the stratum corneum, impairing skin barrier function and allowing entry into the bloodstream. Microbes entering the bloodstream activate molecular signals, leading to immune disorders and subsequent skin inflammatory responses. For instance, Malassezia stimulates dendritic cells(DCs) to release IL-12 and IL-23, differentiating into a Th17 cell population and producing proinflammatory mediators such as IL-17, IL-22, TNF-α, and IFN-α.This review offers new insights into the role of the human skin microbiota in ISDs, paving the way for future skin microbiome-specific targeted therapies.

Understanding Type 3 Innate Lymphoid Cells and Crosstalk with the Microbiota: A Skin Connection

Innate lymphoid cells (ILCs) are a diverse population of lymphocytes classified into natural killer (NK) cells, ILC1s, ILC2s, ILC3s, and ILCregs, broadly following the cytokine secretion and transcription factor profiles of classical T cell subsets. Nonetheless, the ILC lineage does not have rearranged antigen-specific receptors and possesses distinct characteristics. ILCs are found in barrier tissues such as the skin, lungs, and intestines, where they play a role between acquired immune cells and myeloid cells. Within the skin, ILCs are activated by the microbiota and, in turn, may influence the microbiome composition and modulate immune function through cytokine secretion or direct cellular interactions. In particular, ILC3s provide epithelial protection against extracellular bacteria. However, the mechanism by which these cells modulate skin health and homeostasis in response to microbiome changes is unclear. To better understand how ILC3s function against microbiota perturbations in the skin, we propose a role for these cells in response to Cutibacterium acnes, a predominant commensal bacterium linked to the inflammatory skin condition, acne vulgaris. In this article, we review current evidence describing the role of ILC3s in the skin and suggest functional roles by drawing parallels with ILC3s from other organs. We emphasize the limited understanding and knowledge gaps of ILC3s in the skin and discuss the potential impact of ILC3-microbiota crosstalk in select skin diseases. Exploring the dialogue between the microbiota and ILC3s may lead to novel strategies to ameliorate skin immunity.

Exploring the association between rosacea and acne by integrated bioinformatics analysis

Clinically, rosacea occurs frequently in acne patients, which hints the existence of shared signals. However, the connection between the pathophysiology of rosacea and acne are not yet fully understood. This study aims to unveil molecular mechanism in the pathogenesis of rosacea and acne. We identified differentially expressed genes (DEGs) by limma and weighted gene co-expression network analysis and screened hub genes by constructing a protein-protein interaction network. The hub genes were verified in different datasets. Then, we performed a correlation analysis between the hub genes and the pathways. Finally, we predicted and verified transcription factors of hub genes, performed the immune cell infiltration analysis using CIBERSORT, and calculated the correlation between hub genes and immune cells. A total of 169 common DEGs were identified, which were mainly enriched in immune-related pathways. Finally, hub genes were identified as IL1B, PTPRC, CXCL8, MMP9, CCL4, CXCL10, CD163, CCR5, CXCR4, and TLR8. 9 transcription factors that regulated the expression of hub genes were identified. The infiltration of γδT cells was significantly increased in rosacea and acne lesions and positively linked with almost all hub genes. These identified hub genes and immune cells may play a crucial role in the development of rosacea and acne.

Association of different cell types and inflammation in early acne vulgaris

Acne vulgaris, one of the most common skin diseases, is a chronic cutaneous inflammation of the upper pilosebaceous unit (PSU) with complex pathogenesis. Inflammation plays a central role in the pathogenesis of acne vulgaris. During the inflammatory process, the innate and adaptive immune systems are coordinately activated to induce immune responses. Understanding the infiltration and cytokine secretion of differential cells in acne lesions, especially in the early stages of inflammation, will provide an insight into the pathogenesis of acne. The purpose of this review is to synthesize the association of different cell types with inflammation in early acne vulgaris and provide a comprehensive understanding of skin inflammation and immune responses.

Microbe Interactions within the Skin Microbiome

The skin is the largest human organ and is responsible for many important functions, such as temperature regulation, water transport, and protection from external insults. It is colonized by several microorganisms that interact with each other and with the host, shaping the microbial structure and community dynamics. Through these interactions, the skin microbiota can inhibit pathogens through several mechanisms such as the production of bacteriocins, proteases, phenol soluble modulins (PSMs), and fermentation. Furthermore, these commensals can produce molecules with antivirulence activity, reducing the potential of these pathogens to adhere to and invade human tissues. Microorganisms of the skin microbiota are also able to sense molecules from the environment and shape their behavior in response to these signals through the modulation of gene expression. Additionally, microbiota-derived compounds can affect pathogen gene expression, including the expression of virulence determinants. Although most studies related to microbial interactions in the skin have been directed towards elucidating competition mechanisms, microorganisms can also use the products of other species to their benefit. In this review, we will discuss several mechanisms through which microorganisms interact in the skin and the biotechnological applications of products originating from the skin microbiota that have already been reported in the literature.

Functional divergence of a bacterial enzyme promotes healthy or acneic skin

Acne is a dermatologic disease with a strong pathologic association with human commensal Cutibacterium acnes. Conspicuously, certain C. acnes phylotypes are associated with acne, whereas others are associated with healthy skin. Here we investigate if the evolution of a C. acnes enzyme contributes to health or acne. Two hyaluronidase variants exclusively expressed by C. acnes strains, HylA and HylB, demonstrate remarkable clinical correlation with acne or health. We show that HylA is strongly pro-inflammatory, and HylB is modestly anti-inflammatory in a murine (female) acne model. Structural and phylogenic studies suggest that the enzymes evolved from a common hyaluronidase that acquired distinct enzymatic activity. Health-associated HylB degrades hyaluronic acid (HA) exclusively to HA disaccharides leading to reduced inflammation, whereas HylA generates large-sized HA fragments that drive robust TLR2-dependent pathology. Replacing an amino acid, Serine to Glycine near the HylA catalytic site enhances the enzymatic activity of HylA and produces an HA degradation pattern intermediate to HylA and HylB. Selective targeting of HylA using peptide vaccine or inhibitors alleviates acne pathology. We suggest that the functional divergence of HylA and HylB is a major driving force behind C. acnes health- and acne- phenotype and propose targeting of HylA as an approach for acne therapy.

T cell and bacterial microbiota interaction at intestinal and skin epithelial interfaces

Graphical Abstract.

New insights into the role of Cutibacterium acnes-derived extracellular vesicles in inflammatory skin disorders

Cutibacterium acnes (C. acnes) is one of the most prevalent bacteria that forms the human skin microbiota. Specific phylotypes of C. acnes have been associated with the development of acne vulgaris, while other phylotypes have been linked to healthy skin. In this scenario, bacterial extracellular vesicles (EVs) play a role in the interkingdom communication role with the human host. The purpose of this study was to examine the impact of EVs generated by various phylotypes of C. acnes on inflammation and sebum production using different in vitro skin cell types. The main findings of this study reveal that the proteomic profile of the cargo embodied in the EVs reflects distinct characteristics of the different C. acnes phylotypes in terms of life cycle, survival, and virulence. The in vitro skin cell types showed an extended pro-inflammatory modulation of SLST A1 EVs consistently triggering the activation of the inflammation-related factors IL-8, IL-6, TNFα and GM-CSF, in comparison to SLST H1 and SLST H2. Additionally, an acne-prone skin model utilizing PCi-SEB and arachidonic acid as a sebum inducer, was employed to investigate the impact of C. acnes EVs on sebum regulation. Our findings indicated that all three types of EVs significantly inhibited sebum production after a 24-h treatment period, with SLST H1 EVs exhibiting the most pronounced inhibitory effect when compared to the positive control. The results of this study highlight the protective nature of C. acnes SLST H1 EVs and their potential use as a natural treatment option for alleviating symptoms associated with inflammation and oily skin.

Treatment response to isotretinoin correlates with specific shifts in Cutibacterium acnes strain composition within the follicular microbiome

There are no drugs as effective as isotretinoin for acne. Deciphering the changes in the microbiome induced by isotretinoin in the pilosebaceous follicle of successfully treated patients can pave the way to identify novel therapeutic alternatives. We determined how the follicular microbiome changes with isotretinoin and identified which alterations correlate with a successful treatment response. Whole genome sequencing was done on casts from facial follicles of acne patients sampled before, during and after isotretinoin treatment. Alterations in the microbiome were assessed and correlated with treatment response at 20 weeks as defined as a 2-grade improvement in global assessment score. We investigated the α-diversity, β-diversity, relative abundance of individual taxa, Cutibacterium acnes strain composition and bacterial metabolic profiles with a computational approach. We found that increased β-diversity of the microbiome coincides with a successful treatment response to isotretinoin at 20 weeks. Isotretinoin selectively altered C. acnes strain diversity in SLST A and D clusters, with increased diversity in D1 strains correlating with a successful clinical response. Isotretinoin significantly decreased the prevalence of KEGG Ontology (KO) terms associated with four distinct metabolic pathways inferring that follicular microbes may have limited capacity for growth or survival following treatment. Importantly, these alterations in microbial composition or metabolic profiles were not observed in patients that failed to achieve a successful response at 20 weeks. Alternative approaches to recapitulate this shift in the balance of C. acnes strains and microbiome metabolic function within the follicle may be beneficial in the future treatment of acne.

The updates and implications of cutaneous microbiota in acne

Acne is a chronic inflammatory skin disorder that profoundly impacts the quality of life of patients worldwide. While it is predominantly observed in adolescents, it can affect individuals across all age groups. Acne pathogenesis is believed to be a result of various endogenous and exogenous factors, but the precise mechanisms remain elusive. Recent studies suggest that dysbiosis of the skin microbiota significantly contributes to acne development. Specifically, Cutibacterium acnes, the dominant resident bacterial species implicated in acne, plays a critical role in disease progression. Various treatments, including topical benzoyl peroxide, systemic antibiotics, and photodynamic therapy, have demonstrated beneficial effects on the skin microbiota composition in acne patients. Of particular interest is the therapeutic potential of probiotics in acne, given its direct influence on the skin microbiota. This review summarizes the alterations in skin microbiota associated with acne, provides insight into its pathogenic role in acne, and emphasizes the potential of therapeutic interventions aimed at restoring microbial homeostasis for acne management.

Role of Tumor Necrosis Factor-α Inhibitors in the Treatment and Occurrence of Acne: A Systematic Review

Importance

Tumor necrosis factor-α inhibitors (TNFis) approved to treat several inflammatory diseases are sometimes used off label to treat severe forms of acne that are refractory to conventional therapies. However, use of TNFis can also be followed by acne occurrence, suggesting an association between TNFis and acne. Most of the literature on the topic comprises case reports and series that have not been reviewed in a systematic manner.

Objective

To characterize the demographic characteristics, clinical presentations, treatments, and outcomes of patients receiving TNFis to treat acne and patients who develop acne following treatment of other conditions with TNFis.

Evidence Review

A systematic literature review was performed and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses reporting guidelines. PubMed and Web of Science were searched from inception through October 17, 2022. Included studies reported on patients of any sex or age who received TNFis whose treatment was followed by resolution or occurrence of acne. Two independent reviewers screened studies based on predefined criteria and extracted data from each study, which were quantitatively combined.

Findings

A total of 53 studies reporting on 64 patients who received TNFis for the treatment of acne (n = 47) or who experienced acne after treatment with TNFis for a different condition (n = 17) (mean age, 28.7 years; range, 12-64 years; 6 female individuals [8.8%]) were included. The TNFis used included adalimumab, infliximab, and etanercept. Among the 47 patients treated for acne with TNFis, most had previously received antibiotics (31 [66.0%]) or isotretinoin (32 [68.1%]). Most (44 [93.6%]) experienced partial improvement (25 [53.2%]) or clearance (19 [40.4%]) with very few adverse effects reported (3 [6.4%]). Acne manifested as part of an inflammatory syndrome for 30 patients (63.8%). Among the 17 patients treated TNFis for a different condition followed by the occurrence of acne, only 1 patient (5.9%) reported having a history of acne. Therapy with TNFis was either discontinued (8 [47.1%]) or altered (6 [35.3%]) in most patients due to acne occurrence, typically with improvement in symptoms.

Conclusions and Relevance

The results of this systematic review suggest that TNFis can be effective in treating refractory acne but can also be associated with the occurrence of acne in certain instances. Further studies elucidating the role that TNF plays in treating and inducing acne could yield insight into off-label TNFi use and acne pathogenesis, potentially guiding clinical care of patients with acne treated or induced by TNFis.

A propensity score matched cohort study identifying an association of acne, but not oral antibiotic or isotretinoin use, with risk of incident inflammatory bowel disease

BACKGROUND

Concerns remain regarding whether oral antibiotic or isotretinoin use for acne is associated with increased risk of inflammatory bowel disease (IBD); little is known about whether acne itself is associated with IBD.

OBJECTIVE

To determine whether isotretinoin exposure, oral tetracycline-class antibiotic exposure, and/or acne itself are associated with IBD.

METHODS

A propensity score matched cohort study was performed using TriNetX between 2001 and 2022 to compare the 1-year incidence of IBD between those without acne compared to those with acne managed without systemic medications, acne managed with oral tetracycline-class antibiotics, and acne managed with isotretinoin.

RESULTS

There was a statistically significant association between acne and risk of incident IBD (odds ratio: 1.42; 95% confidence interval: 1.23-1.65). There was no statistically significant association between oral tetracycline-class antibiotic or isotretinoin exposure and IBD.

LIMITATIONS

Use of electronic health data; potential for misclassification bias.

CONCLUSION

This matched cohort study identifies an association between acne and IBD. These data provide further reassurance regarding the use of isotretinoin in the treatment of acne.

A protocol to detect human CD4+ T cell extracellular traps using scanning electron microscopy

We present a protocol to detect extracellular traps (ETs) induced by Cutibacterium acnes in cultured TH17 clones. We first describe the isolation of C. acnes-specific TH17 clones by sterile cell sorting. We then detail the in vitro induction of ETs in TH17 clones stimulated by C. acnes and the imaging of released ETs using scanning electron microscopy. This protocol can be applied to the study of other ETs released by other T cell subsets. For complete details on the use and execution of this protocol, please refer to Agak et al. (2021).1.

Recent advances in understanding inflammatory acne: Deciphering the relationship between Cutibacterium acnes and Th17 inflammatory pathway

Acne vulgaris is a common chronic inflammatory skin disease of the pilosebaceous units. Four factors contribute to acne: hyperseborrhea and dysseborrhea, follicular hyperkeratinisation, skin microbiome dysbiosis and local immuno-inflammation. Recent key studies have highlighted a better understanding of the important role of Cutibacterium acnes (C. acnes) in the development of acne. Three major findings in the last decade include: (1) the ability of C. acnes to self-organize in a biofilm associated with a more virulent activity, (2) the loss of the C. acnes phylotype diversity and (3) the central role of the Th17 pathway in acne inflammation. Indeed, there is a close link between C. acnes and the activation of the Th17 immuno-inflammatory pathway at the initiation of acne development. These mechanisms are directly linked to the loss of C. acnes phylotype diversity during acne, with a predominance of the pro-pathogenic phylotype IA1. This specifically contributes to the induction of the Th17-mediated immuno-inflammatory response involving skin cells, such as keratinocytes, monocytes and sebocytes. These advancements have led to new insights into the underlying mechanisms which can be harnessed to develop novel treatments and diagnostic biomarkers. A major disadvantage of traditional treatment with topical antibiotics is that they induce cutaneous dysbiosis and antimicrobial resistance. Thus, future treatments would no longer aim to 'kill' C. acnes, but to maintain the skin microbiota balance allowing for tissue homeostasis, specifically, the restoration of C. acnes phylotype diversity. Here, we provide an overview of some of the key processes involved in the pathogenesis of acne, with a focus on the prominent role of C. acnes and the Th17-inflammatory pathways involved.

Evaluation of Serum Levels of Interleukins 6, 8, 17 and 22 in Acne Vulgaris: A Cross-Sectional Study

Background

Acne vulgaris (AV) is a chronic, multifactorial, inflammatory skin disease, and it is now becoming increasingly clear that the inflammatory pathway is involved at a very early in the pathogenesis of acne. The Th17 cells, the activators of this cell line and its downstream effector cytokines, are all likely to have a critical role in inducing and maintaining the disease.

Aim

To analyse the role of interleukins (ILs) 6, 8, 17 and 22 in the pathogenesis of acne.

Materials and Methods

Sixty patients of AV and thirty age- and sex-matched controls were included in our study. Serum levels of interleukins 6, 8, 17 and 22 were determined using an enzyme-linked immunosorbent assay (ELISA), and thereafter, levels were correlated with the severity of acne.

Result

Serum levels of IL-6, IL-8, IL-17 and IL-22 were 0.15 ± 0.0174 pg/ml, 0.38 ± 0.080 pg/ml, 0.19 ± 0.0075 pg/ml and 0.23 ± 0.0152 pg/ml in cases, respectively, and 0.13 ± 0.0095 pg/ml, 0.14 ± 0.034 pg/ml, 0.13 ± 0.0033 pg/ml and 0.21 ± 0.0099 pg/ml in controls, respectively. The difference in levels between cases and controls was significant for IL-8 and IL-17, while for IL-6 and IL-22 the difference was insignificant. There was a highly significant positive correlation between IL-8 and IL-17 levels. IL-6 and IL-8 showed a significant positive correlation with the severity of disease.

Conclusion

IL-8 and IL-17 play a critical effector role in the pathogenesis of AV. IL-6-stimulated Th17 cells are likely the major producers of IL-8 in acne lesions.

Myrtus communis and Celastrol enriched plant cell culture extracts control together the pivotal role of Cutibacterium acnes and inflammatory pathways in acne

INTRODUCTION

Acne is a multifactorial inflammatory disease of the pilosebaceous unit in which Cutibacterium acnes is one of the main triggers. A strong predominance of C. acnes phylotype IA1 is present in acne skin with higher biofilm organization and virulence, promoting local immuno-inflammation, especially the Th17 pathway.

OBJECTIVES

We evaluated the single and combined pharmacological properties of the plant extracts, Myrtus communis (Myrtacine®) and Celastrol enriched plant cell culture (CEE) extracts on the C. acnes/Th17 pathway.

METHODS

The effect of Myrtacine® on the virulence of C. acnes phylotype IA1 was quantified according to the expression of several related genes. The activity of Myrtacine® and CEE on the inflammatory cascade was assessed using monocytes-derived dendritic cells (Mo-DC) stimulated with membranes or biofilms of the C. acnes phylotype IA1. Finally, the effect of CEE on the Th17 pathway was studied using C. acnes stimulated sebocyte 2D cultures and 3D skin tissue models containing preactivated Th17 cells.

RESULTS

Myrtacine® had an anti-virulence effect, evident as a significant and strong inhibition of the expression of several virulence factor genes by 60%-95% compared to untreated controls. Myrtacine® and CEE significantly inhibited proinflammatory cytokine (IL-6, IL-8, IL-12p40 and TNF-α) production by Mo-DC in response to C. acnes phylotype IA1. Interestingly, these two ingredients resulted in synergistic inhibition of most cytokines when used in combination. Finally, we demonstrated an inhibitory effect of CEE, in solution or formulated at 0.3%, specifically on IL-17 release by Th17 lymphocytes in a C. acnes-stimulated sebocyte 2D cultures and by Th17-lymphocytes integrated in a 3D skin models.

CONCLUSIONS

2D and 3D models were developed to represent relevant and specific pathways involved in acne. Myrtacine® and CEE were shown to alter one or more of these pathways, indicating their potential beneficial effects on this disease.

The effect of the ketogenic diet on Acne: Could it be a therapeutic tool?

Acne is a chronic inflammatory disease of the pilosebaceous unit resulting from androgen-induced increased sebum production, altered keratinization, inflammation, and bacterial colonization of the hair follicles of the face, neck, chest and back by Propionibacterium acnes. Overall, inflammation and immune responses are strongly implicated in the pathogenesis of acne. Although early colonization with Propionibacterium acnes and family history may play an important role in the disease, it remains unclear exactly what triggers acne and how treatment affects disease progression. The influence of diet on acne disease is a growing research topic, yet few studies have examined the effects of diet on the development and clinical severity of acne disease, and the results have often been contradictory. Interestingly, very low-calorie ketogenic diet (VLCKD) has been associated with both significant reductions in body weight and inflammatory status through the production of ketone bodies and thus it has been expected to reduce the exacerbation of clinical manifestations or even block the trigger of acne disease. Given the paucity of studies regarding the implementation of VLCKD in the management of acne, this review aims to provide evidence from the available scientific literature to support the speculative use of VLCKD in the treatment of acne.

Photodynamic therapy treats acne by altering the composition of the skin microbiota

BACKGROUND

Acne is the eighth-most prevalent inflammatory skin disease with no optimal treatment. Photodynamic therapy (PDT) is an effective treatment for severe acne.

AIMS

The effect of PDT on the composition and diversity of skin microflora in severe acne patients was studied.

MATERIALS AND METHODS

A total of 18 patients with severe acne and 8 healthy individuals were selected for this study. Patients were treated with 5-aminolevulinic acid-mediated PDT once a week three times in total; the skin microbiome was measured by 16S ribosomal RNA gene sequencing before and after treatment (1 week after each PDT).

RESULTS

The microflora composition was different between healthy controls and patients, and between patients before and after treatment. Alpha diversity indices were lower in patients than those in control. There were 15 bacterial genera with high relative abundance that had noticeable changes during treatment. At the genus level,particularly Cutibacterium acnes (C. acnes formerly Propionibacterium acnes), there was no statistically significant difference among different group. The abundances of Staphylococcus epidermidis and Staphylococcus aureus were low.

DISCUSSION

The microbial composition is different between severe acne patients acne patients and healthy individuals. The therapeutic efficacy of severe acne treated with PDT is associated with the composition and diversity of skin microbiota.

CONCLUSION

The skin microbial composition changes after PDT treatment. PDT is an effective method for the treatment of severe acne.

Evolution of the facial skin microbiome during puberty in normal and acne skin

BACKGROUND

The composition of the skin microbiome varies from infancy to adulthood and becomes most stable in adulthood. Adult acne patients harbour an 'acne microbiome' dominated by specific strains of Cutibacterium acnes. However, the precise timing of skin microbiome evolution, the development of the acne microbiome, and the shift to virulent C. acnes strain composition during puberty is unknown.

OBJECTIVES

We performed a cross-sectional pilot study in a paediatric population to understand how and when the skin microbiome composition transitions during puberty and whether a distinct 'acne microbiome' emerges in paediatric subjects.

METHODS

Forty-eight volunteers including males and females, ages 7-17 years, with and without acne were enrolled and evaluated for pubertal development using the Tanner staging criteria. Sebum levels were measured, and skin microbiota were collected by sterile swab on the subject's forehead. DNA was sequenced by whole genome shotgun sequencing.

RESULTS

A significant shift in microbial diversity emerged between early (T1-T2) and late (T3-T5) stages of puberty, coinciding with increased sebum production on the face. The overall relative abundance of C. acnes in both normal and acne skin increased during puberty and individual C. acnes strains were uniquely affected by pubertal stage and the presence of acne. Further, an acne microbiome signature associated with unique C. acnes strain composition and metabolic activity emerges in late puberty in those with acne. This unique C. acnes strain composition is predicted to have increased porphyrin production, which may contribute to skin inflammation.

CONCLUSIONS

Our data suggest that the stage of pubertal development influences skin microbiome composition. As children mature, a distinct acne microbiome composition emerges in those with acne. Understanding how both puberty and acne influence the microbiome may support novel therapeutic strategies to combat acne in the paediatric population.

A pilot study on the efficacy of topical lotion containing anti-acne postbiotic in subjects with mild -to -moderate acne

Introduction

Acne can compromise facial esthetics and become a mental burden, especially when it occurs in puberty. Skincare cosmetics with anti-acne efficiency is more convenient than other treatment modalities, such as dietary supplements, in certain circumstances. The purpose of this study was to investigate the efficacy of an anti-acne lotion in alleviating acne.

Methods

In our study, an anti-acne lotion containing ferment lysate produced by Lactiplantibacillus plantarum VHProbi® E15 were applied to subjects with mild -to -moderate acne over 4 weeks. The efficacy was evaluated based on instrumental measurements using Visia®-CR and CK-MPA® system.

Results and discussion

The anti-acne lotion exhibited favorable safety, meeting the stringent criteria for the detection of microbes, heavy metals, toxicity, and irritation. After 2 weeks of treatment, a statistically significant improvement in acne lesions was observed compared to baseline (P < 0.01), and this continued to the end of the study. After 4 weeks of treatment, the transepidermal water loss (P < 0.05) and sebum production (P < 0.05) were significantly decreased in subjects compared to baseline. In addition, the pore/area of interest (AOI) and stratum corneum hydration displayed slightly positive changes throughout treatment. Thus, we conclude that applying topical anti-acne lotion may be safe and confer effective benefits in people with mild -to -moderate acne and represents a promising therapeutic option for acne.

Skin Barrier Function and the Microbiome

Human skin is the largest organ and serves as the first line of defense against environmental factors. The human microbiota is defined as the total microbial community that coexists in the human body, while the microbiome refers to the collective genome of these microorganisms. Skin microbes do not simply reside on the skin but interact with the skin in a variety of ways, significantly affecting the skin barrier function. Here, we discuss recent insights into the symbiotic relationships between the microbiome and the skin barrier in physical, chemical, and innate/adaptive immunological ways. We discuss the gut-skin axis that affects skin barrier function. Finally, we examine the effects of microbiome dysbiosis on skin barrier function and the role of these effects in inflammatory skin diseases, such as acne, atopic dermatitis, and psoriasis. Microbiome cosmetics can help restore skin barrier function and improve these diseases.

The Role of Cutibacterium acnes in Sarcoidosis: From Antigen to Treatable Trait?

Cutibacterium acnes (C. acnes, formerly Propionibacterium acnes) is considered to be a non-pathogenic resident of the human skin, as well as mucosal surfaces. However, it also has been demonstrated that C. acnes plays a pathogenic role in diseases such as acne vulgaris or implant infections after orthopedic surgery. Besides a role in infectious disease, this bacterium also seems to harbor immunomodulatory effects demonstrated by studies using C. acnes to enhance anti-tumor activity in various cancers or vaccination response. Sarcoidosis is a systemic inflammatory disorder of unknown causes. Cultures of C. acnes in biopsy samples of sarcoidosis patients, its presence in BAL fluid, tissue samples as well as antibodies against this bacterium found in serum of patients with sarcoidosis suggest an etiological role in this disease. In this review we address the antigenic as well as immunomodulatory potential of C. acnes with a focus on sarcoidosis. Furthermore, a potential role for antibiotic treatment in patients with sarcoidosis will be explored.

Prostate Infiltration by Treg and Th17 Cells as an Immune Response to Propionibacterium acnes Infection in the Course of Benign Prostatic Hyperplasia and Prostate Cancer

Benign prostatic hyperplasia (BPH) and prostate cancer (PCa) belong to the most frequent diseases in ageing men. It has been proposed that prostate chronic inflammation is a risk factor for the development of both BPH and PCa. However, potential stimuli that cause or maintain inflammation in the prostate gland are still poorly characterized. Bacterial infections seems to be one of the potential sources of prostatitis. Recent studies show that Propionibacterium acnes (P. acnes) is the most prevalent microorganism in the prostate gland and may be a predisposing factor for inflammation of prostatic tissue. It indicates that P. acnes may contribute to cancer development by enhancing proinflammatory responses, as well as by modifying the prostate extracellular environment. In this review, we discuss the potential role of P. acnes in the development of BPH and PCa and highlight the importance of regulatory T CD4(+)FoxP3(+) (Treg) and Th17 cells in response to P. acnes infection in the context of both prostate diseases.

The immunomodulatory potential of phage therapy to treat acne: a review on bacterial lysis and immunomodulation

Background

Characterized by an inflammatory pathogenesis, acne is the most common skin disorder worldwide. Altered sebum production, abnormal proliferation of keratinocytes, and microbiota dysbiosis represented by disbalance in Cutibacterium acnes population structure, have a synergic effect on inflammation of acne-compromised skin. Although the role of C. acnes as a single factor in acne development is still under debate, it is known that skin and skin-resident immune cells recognize this bacterium and produce inflammatory markers as a result. Control of the inflammatory response is frequently the target for acne treatment, using diverse chemical or physical agents including antibiotics. However, some of these treatments have side effects that compromise patient adherence and drug safety and in the case of antibiotics, it has been reported C. acnes resistance to these molecules. Phage therapy is an alternative to treat antibiotic-resistant bacterial strains and have been recently proposed as an immunomodulatory therapy. Here, we explore this perspective about phage therapy for acne, considering the potential immunomodulatory role of phages.

Methodology

Literature review was performed using four different databases (Europe PubMed Central-ePMC, Google Scholar, PubMed, and ScienceDirect). Articles were ordered and selected according to their year of publication, number of citations, and quartile of the publishing journal.

Results

The use of lytic bacteriophages to control bacterial infections has proven its promising results, and anti-inflammatory effects have been found for some bacteriophages and phage therapy. These effects can be related to bacterial elimination or direct interaction with immune cells that result in the regulation of pro-inflammatory cytokines. Studies on C. acnes bacteriophages have investigated their lytic activity, genomic structure, and stability on different matrices. However, studies exploring the potential of immunomodulation of these bacteriophages are still scarce.

Conclusions

C. acnes bacteriophages, as well as other phages, may have direct immunomodulatory effects that are yet to be fully elucidated. To our knowledge, to the date that this review was written, there are only two studies that investigate anti-inflammatory properties for C. acnes bacteriophages. In those studies, it has been evidenced reduction of pro-inflammatory response to C. acnes inoculation in mice after bacteriophage application. Nevertheless, these studies were conducted in mice, and the interaction with the immune response was not described. Phage therapy to treat acne can be a suitable therapeutic alternative to C. acnes control, which in turn can aid to restore the skin's balance of microbiota. By controlling C. acnes colonization, C. acnes bacteriophages can reduce inflammatory reactions triggered by this bacterium.

T Cell Extracellular Traps: Tipping the Balance Between Skin Health and Disease

The role of extracellular traps (ETs) in the innate immune response against pathogens is well established. ETs were first identified in neutrophils and have since been identified in several other immune cells. Although the mechanistic details are not yet fully understood, recent reports have described antigen-specific T cells producing T cell extracellular traps (TETs). Depending on their location within the cutaneous environment, TETs may be beneficial to the host by their ability to limit the spread of pathogens and provide protection against damage to body tissues, and promote early wound healing and degradation of inflammatory mediators, leading to the resolution of inflammatory responses within the skin. However, ETs have also been associated with worse disease outcomes. Here, we consider host-microbe ET interactions by highlighting how cutaneous T cell-derived ETs aid in orchestrating host immune responses against Cutibacterium acnes (C. acnes), a commensal skin bacterium that contributes to skin health, but is also associated with acne vulgaris and surgical infections following joint-replacement procedures. Insights on the role of the skin microbes in regulating T cell ET formation have broad implications not only in novel probiotic design for acne treatment, but also in the treatment for other chronic inflammatory skin disorders and autoimmune diseases.

Characterization of a Cutibacterium acnes Camp Factor 1-Related Peptide as a New TLR-2 Modulator in In Vitro and Ex Vivo Models of Inflammation

Cutibacterium acnes (C. acnes) has been implicated in inflammatory acne where highly mutated Christie-Atkins-Munch-Petersen factor (CAMP)1 displays strong toll like receptor (TLR)-2 binding activity. Using specific antibodies, we showed that CAMP1 production was independent of C. acnes phylotype and involved in the induction of inflammation. We confirmed that TLR-2 bound both mutated and non-mutated recombinant CAMP1, and peptide array analysis showed that seven peptides (A14, A15, B1, B2, B3, C1 and C3) were involved in TLR-2 binding, located on the same side of the three-dimensional structure of CAMP1. Both mutated and non-mutated recombinant CAMP1 proteins induced the production of C-X-C motif chemokine ligand interleukin (CXCL)8/(IL)-8 in vitro in keratinocytes and that of granulocyte macrophage-colony stimulating factor (GM-CSF), tumor necrosis factor (TNF)-α, IL-1β and IL-10 in ex vivo human skin explants. Only A14, B1 and B2 inhibited the production of CXCL8/IL-8 by keratinocytes and that of (GM-CSF), TNF-α, IL-1β and IL-10 in human skin explants stimulated with rCAMP1 and C. acnes. Following pretreatment with B2, RNA sequencing on skin explants identified the 10 genes displaying the strongest differential expression as IL6, TNF, CXCL1, CXCL2, CXCL3, CXCL8, IL-1β, chemokine ligand (CCL)2, CCL4 and colony stimulating factor (CSF)2. We, thus, identified a new CAMP1-derived peptide as a TLR-2 modulator likely to be a good candidate for clinical evaluation.

The Role of Skin Immune System in Acne

Acne vulgaris is a skin disease that often occurs in adolescence and in young adulthood. The main pathogenic factors are hyperkeratinization, obstruction of sebaceous glands, stimulation of sebaceous gland secretion by androgens, and bacterial colonization of sebaceous units by Cutibacterium acnes, which promotes inflammation. Little is known about the role of skin immune cells in the development of acne lesions. The aim of the study was to try to understand the role of skin immune cells in the course of acne. Recent studies have shown that there are at least four major pathways by which Cutibacterium acnes interacts with the innate immune system to induce inflammation: through TLRs, activating inflammasomes, inducing the production of matrix metalloproteinases (MMPs), and stimulating antimicrobial peptide (AMP) activity. Cells of adaptive immune response, mainly Th1 and Th17 lymphocytes, also play an important role in the pathogenesis of acne. It is worth emphasizing that understanding the role of the skin’s immune cells in the pathogenesis of acne may, in the future, contribute to the application of modern therapeutic strategies that would avoid addiction to antibiotics, which would alleviate the spectrum of resistance that is now evident and a current threat.

The Kinocidin Interleukin-26 Shows Immediate Antimicrobial Effects Even to Multi-resistant Isolates

The cationic proinflammatory cytokine Interleukin 26 (IL-26) shows antibacterial activity and inhibits the replication of cytomegalovirus and hepatitis C virus. This study evaluates the early microbicidal activities of IL-26 against major bacterial species including multi-resistant variants and Candida albicans. Recombinant IL-26 was bacterially expressed and studied for its microbicidal effects in culture. We show that IL-26 has strong 90% bactericidal activities against Enterococcus faecalis, Enterococcus faecium, Staphylococcus aureus, and Acinetobacter baumannii. Similarly, IL-26 sensitivity was also detectable in vancomycin-resistant Enterococcus species, methicillin-resistant S. aureus, and carbapenem-resistant A. baumannii clinical isolates. Additionally, a significant, albeit weak fungicidal effect against Candida albicans was observed. Activities against Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa were not detectable. The proinflammatory cytokine and kinocidin IL-26 shows strong bactericidal activities against A. baumannii and, almost selectively, against Gram-positive bacteria.

Interplay Between Skin Microbiota Dysbiosis and the Host Immune System in Psoriasis: Potential Pathogenesis

Psoriasis is a multifactorial immune-mediated disease. The highly effective and eligible treatment for psoriasis is limited, for its specific pathogenesis is incompletely elucidated. Skin microbiota is a research hotspot in the pathogenesis of immune-mediated inflammatory skin diseases nowadays, and it may have significant involvement in the provocation or exacerbation of psoriasis with broadly applicable prospects. It is postulated that skin microbiota alternation may interplay with innate immunity such as antimicrobial peptides and Toll-like receptors to stimulate T-cell populations, resulting in immune cascade responses and ultimately psoriasis. Achieving a thorough understanding of its underlying pathogenesis is crucial. Herein, we discuss the potential immunopathogenesis of psoriasis from the aspect of skin microbiota in an attempt to yield insights for novel therapeutic and preventive modalities for psoriasis.

Surfactin inhibits the growth of Propionibacterium acnes by destroying the cell wall and membrane

Propionibacterium acnes plays a major role in acne vulgaris. In the pre-experiment, the growth of P. acnes was inhibited effectively using surfactin; however, the antibacterial mechanism has not been described. Therefore, the aim of this study was to evaluate antibacterial activity and analyse the mechanism of surfactin against P. acnes. Minimum inhibitory concentration, time-killing kinetics and scanning electron microscopy were used to evaluate the activity of surfactin against P. acnes, which showed that 128 μg ml^-1 effectively inhibited growth. Cell wall permeability was evaluated by detecting the extracellular alkaline phosphatase activity, which increased to 1·83- and 2·32-fold after incubating with 128 and 256 μg ml^-1 of surfactin for 10 h, respectively. Propidium iodide fluorescence, leakage of nucleic acid, protein, K⁺ , and Ca²⁺ , membrane potential and the leakage of calcein from small unilamellar vesicles all increased after incubation with surfactin, indicating that its strong biological activities act mainly by altering membrane integrity. In a mouse model of acne, surfactin significantly reduced P. acnes-induced epidermal swelling and erythema. These results indicate that surfactin effectively inhibited the growth of P. acnes by destroying the cell wall and membrane, and is a potential candidate for acne treatment.