Skin and Gut Microbiome in Hidradenitis Suppurativa: A Systematic Review

The gut-skin axis: a bi-directional, microbiota-driven relationship with therapeutic potential

This review explores the emerging term "gut-skin axis" (GSA), describing the bidirectional signaling that occurs between the skin and the gastrointestinal tract under both homeostatic and disease conditions. Central to GSA communication are the gut and skin microbiota, the microbial communities that colonize these barrier surfaces. By influencing diverse host pathways, including innate immune, vitamin D receptor, and Aryl hydrocarbon receptor signaling, a balanced microbiota contributes to both tissue homeostasis and host defense. In contrast, microbiota imbalance, or dysbiosis at one site, can lead to local barrier dysfunction, resulting in the activation of signaling pathways that can disrupt tissue homeostasis at the other site, potentially leading to inflammatory skin conditions such as atopic dermatitis and psoriasis, or gut diseases like Inflammatory Bowel Disease. To date, most research on the GSA has examined the impact of the gut microbiota and diet on skin health, but recent studies show that exposing the skin to ultraviolet B-light can beneficially modulate both the gut microbiome and intestinal health. Thus, despite the traditional focus of clinicians and researchers on these organ systems as distinct, the GSA offers new opportunities to better understand the pathogenesis of cutaneous and gastrointestinal diseases and promote health at both sites.

Spanish Hidradenitis Suppurativa Registry (REHS) of the Spanish Academy of Dermatology and Venereology: description and data from its first year of operation

INTRODUCTION

Hidradenitis suppurativa (HS) is a skin disease that significantly impacts patients' quality of life. There are still uncertainties surrounding its epidemiology, natural history, and the safety and effectiveness of existing treatments. The Spanish Academy of Dermatology and Venereology has promoted the creation of a Spanish Registry of patients with HS (REHS). The aim of this article is to present the REHS and provide the initial results obtained.

METHODS

The REHS is a prospective, multicenter, observational study that collects the clinical and epidemiological characteristics of patients with HS, as well as the safety and effectiveness of the medical and surgical treatments received.

RESULTS

Between June 2023 and June 2024, 359 patients were recruited from 23 Spanish centers. The average age of the patients is 37 years, and 53% of them are women. Over 70% of the patients are smokers or former smokers. One third have a family history of HS. The most frequent sites of disease onset are the axillae and groin. Median baseline IHS4 at recruitment was 4 (p25-p75=1-9), HiSQOL was 20 (p25-p75=8-36), and BMI was 27.3 (p25-p75=24-33.2). At least 82% of patients have received antibiotic therapy for their disease, and almost 20% a biologic drug.

CONCLUSIONS

We present data from the first patients enrolled in the REHS, which will allow for the generation of evidence on the natural course of the disease, as well as the effectiveness and safety of treatments in HS.

Skin microbiome and dermatologic disorders

Human skin acts as a physical barrier to prevent the entry of pathogenic microbes while simultaneously providing a home for commensal bacteria and fungi. Microbiome sequencing studies have demonstrated the unappreciated diversity and selectivity of these microbes. Functional studies have demonstrated the impact of specific strains to tune the immune system, sculpt the microbial community, provide colonization resistance, and promote epidermal barrier integrity. Recent studies have integrated the microbiome, immunity, and tissue integrity to understand their interplay in common disorders such as atopic dermatitis. In this Review, we explore microbiome shifts associated with cutaneous disorders with an eye toward how the microbiome can be mined to identify new therapeutic opportunities.

Hidradenitis suppurativa pathogenesis: Extrinsic factors

While genetic predisposition and immune dysregulation are recognized as key contributors to the development of hidradenitis suppurativa, accumulating research points to the influence of extrinsic factors in the pathogenesis of this condition. This review explores the roles of mechanical stress, altered skin and gut microbiome, tobacco smoking, diet, and paradoxical drug reactions as drivers of hidradenitis suppurativa onset and progression. A holistic management approach addressing these factors may be encouraged to improve disease outcomes. Further research is needed to fully determine the causal role of these extrinsic factors and their impact on treatment strategies.

Clinical Significance and Microbiological Characteristics of Staphylococcus lugdunensis in Cutaneous Infections

Background/Objectives:Staphylococcus lugdunensis is a coagulase-negative staphylococcus (CoNS) commonly found on human skin. Unlike other CoNS, S. lugdunensis has a notable potential to cause severe infections comparable to Staphylococcus aureus. This study aimed to characterize the clinical and microbiological profile of patients with S. lugdunensis skin infections at a single center. Methods: We conducted a retrospective analysis of patient records from the Dermatology Department of the University Hospital of Heraklion, Greece, covering the period from January 2014 to January 2024. Patients' clinical presentations, demographics, infection sites, comorbidities, prior infections, antimicrobial treatments, and therapeutic responses were examined. Specimens were collected, transported, and processed according to standardized microbiological protocols. Bacterial identification and antibiotic susceptibility testing were performed using the Vitek 2 automated system and MALDI-TOF MS, with results interpreted according to Clinical and Laboratory Standards Institute (CLSI) criteria. Results: A total of 123 skin specimens positive for S. lugdunensis were analyzed. The cohort comprised 62 males (50.4%) and 61 females (49.6%), with a mean age of 40.24 ± 20.14 years. Most specimens were collected from pus (84%), primarily from below the waist (66.7%). Hidradenitis suppurativa (26%) was the most common condition associated with S. lugdunensis, followed by folliculitis, abscesses, ulcers, cellulitis, and acne. Co-infections with other bacteria were noted in 49.6% of cases, and 25.2% of infections were nosocomially acquired. The majority of patients (65%) received systemic antibiotics, predominantly amoxicillin/clavulanic acid, cefuroxime axetil, and doxycycline, with a cure rate of 100%. All isolates were susceptible to several antibiotics, though resistance to penicillin (28.5%) and clindamycin (36%) was observed. Conclusions:S. lugdunensis is a significant pathogen in skin infections, capable of causing severe disease. The high cure rate demonstrates the effectiveness of appropriate antibiotic therapy. Continued monitoring and antimicrobial stewardship are essential to manage resistance and ensure effective treatment.

Insights into Gut Microbiome Composition in Hidradenitis Suppurativa: A Comprehensive Examination of Dietary Habits and Environmental Influences

This study explores the relationship between dietary habits, environmental influences, and gut microbiome composition in individuals with hidradenitis suppurativa (HS), a chronic inflammatory skin condition. A cohort of 80 participants, equally divided into HS patients and healthy controls, was assessed through comprehensive questionnaires capturing demographics, dietary habits, and other health-related information. Fecal samples were collected and analyzed using next-generation sequencing to examine microbiome composition. Despite previous studies suggesting gut dysbiosis in HS, this research found no significant differences in alpha-diversity and Shannon diversity index between the groups. However, significant disparities in dietary habits were observed, with HS patients showing higher sugar and milk consumption. The study also identified a significant correlation between coffee consumption and the presence of certain bacterial genera. While the study did not reveal major differences in microbiome diversity, the findings on dietary habits and specific microbiome components suggest potential targets for therapeutic intervention. These results underscore the importance of further research into the gut-skin axis and its role in HS, aiming to enhance management strategies through dietary modifications and lifestyle interventions.

Microbiome Modulation in Acne Patients and Clinical Correlations

BACKGROUND

The imbalance of skin microbiota in acne can induce changes leading to induction or to aggravation of chronic inflammatory lesions; complex mechanisms are involved. Cutibacterium acnes (C. acnes) ribotypes RT4 and RT5 express more biofilm and are associated with inflammatory acne lesions. C. acnes RT6 is a non-acne ribotype, beneficial for the skin.

OBJECTIVES

In an open clinical trial, acne adults were included and assessed clinically at baseline and at month 2 using the Investigator Global Assessment of Acne (IGA) score. A topical emulsion was applied twice daily for 2 months (M2) in each included patient. In the same series of acne patients, skin swab samples were collected from acne patients at baseline and M2 from lesional and non-lesional skin; skin swabs were collected for the metagenomic long-read analysis of microbiota.

MATERIALS AND METHODS

Acne patients with a gravity score IGA of >1<3 were included in this pilot study. An emulsion of O/W formulated with vegetal extract of Umbelliferae associated with a polysaccharide at 1% was applied twice daily for 2 months. At baseline and M2 clinical assessments were made; skin swab samples were also taken for microbiota analysis from lesional and non-lesional skin in each included patient. Extractions of genomic DNA (gDNA) from swab samples from baseline and from M2 were made, followed by full-length (V1-V9) amplification of the 16S rDNA and sequencing of amplicon libraries for strain-level bacterial community profiling.

RESULTS

In a series of 32 adult acne patients, the mean initial IGA scale was 3.1; at M2 the IGA scale was 1.5 (p < 0.001). The mean decrease in acne lesions was by 63%. Microbiome metagenomic long-read analysis in these series was mainly dominated by C. acnes followed by Staphylococcus epidermidis (S. epidermidis). The density of C. acnes ribotypes RT6 (non-acne strain) was increased at M2 compared to baseline and the density of ribotypes C. acnes RT1 to RT5 was decreased at M2, compared to baseline (p < 0.0001). S. epidermidis ribotypes (1 to 36) were non significantly increased at M2, compared to baseline (p < 0.1).

CONCLUSIONS

In a series of 32 acne patients that applied an emulsion based on vegetal extract of Umbelliferae and a polysaccharide at 1% twice daily, a significant clinical improvement in IGA scale for acne lesions was seen at M2, compared to baseline (p < 0.0001). The clinical improvement was correlated with an improvement in skin microbiome at M2 compared to baseline, indicated by the increase in the relative abundance of non-acne strain of C. acnes ribotype 6 and of the decrease in the relative abundance of acne strains ribotypes C. acnes RT1 to RT5.

Very low-calorie ketogenic diet (VLCKD): a therapeutic nutritional tool for acne?

BACKGROUND

Acne, a chronic inflammatory disease impacting the pilosebaceous unit, is influenced significantly by inflammation and oxidative stress, and is commonly associated with obesity. Similarly, obesity is also associated with increased inflammation and oxidation. The role of diet in acne remains inconclusive, but the very low-calorie ketogenic diet (VLCKD), known for weight loss and generating anti-inflammatory ketone bodies, presents promising potential. Despite this, the effects of VLCKD on acne remain underexplored. This study aimed to investigate the efficacy of a 45-day active phase of VLCKD in reducing the clinical severity of acne in young women with treatment-naïve moderate acne and grade I obesity.

METHODS

Thirty-one women with treatment-naïve moderate acne, grade I obesity (BMI 30.03-34.65 kg/m2), aged 18-30 years, meeting inclusion/exclusion criteria, and consenting to adhere to VLCKD were recruited. Baseline and post-intervention assessments included anthropometric measurements, body composition, phase angle (PhA), trimethylamine N-oxide (TMAO) levels, and reactive oxygen metabolite derivatives (dROMs) as markers of inflammation, dysbiosis, and oxidative stress, respectively. A comprehensive dermatological examination, incorporating the Global Acne Grading System (GAGS) and the Dermatology Life Quality Index (DLQI), was conducted for all women.

RESULTS

VLCKD resulted in general improvements in anthropometric and body composition parameters. Significantly, there were significant reductions in both the GAGS score (Δ%: - 31.46 ± 9.53, p < 0.001) and the DLQI score (Δ%: - 45.44 ± 24.02, p < 0.001) after the intervention. These improvements coincided with significant decreases in TMAO (p < 0.001) and dROMs (p < 0.001) levels and a significant increase in PhA (Δ%: + 8.60 ± 7.40, p < 0.001). Changes in the GAGS score positively correlated with changes in dROMs (p < 0.001) and negatively with PhA (p < 0.001) even after adjusting for Δ% FM. Changes in the DLQI score positively correlated with changes in dROMs (p < 0.001) and negatively with PhA (p < 0.001) even after adjustment for Δ% FM.

CONCLUSION

Given the side effects of drugs used for acne, there is an increasing need for safe, tolerable, and low-cost treatments that can be used for acne disease. The 45-day active phase of VLCKD demonstrated notable improvements in acne severity, and these improvements seemed to be attributable to the known antioxidant and anti-inflammatory effects of VLCKD.

Very low-calorie ketogenic diet (VLCKD) in the management of hidradenitis suppurativa (Acne Inversa): an effective and safe tool for improvement of the clinical severity of disease. Results of a pilot study

BACKGROUND

Hidradenitis suppurativa (HS), an inflammatory-based dermatological condition often associated with obesity, poses significant challenges in management. The very low-calorie ketogenic diet (VLCKD) has shown efficacy in addressing obesity, related metabolic disorders, and reducing chronic inflammation. However, its effects on HS remain underexplored. In this prospective pilot study, we aimed to investigate the impact of a 28-day active phase of VLCKD on HS in a sample of treatment-naive women with HS and excess weight.

METHODS

Twelve women with HS and overweight or obesity (BMI 27.03 to 50.14 kg/m2), aged 21 to 54 years, meeting inclusion/exclusion criteria and agreeing to adhere to VLCKD, were included. Baseline lifestyle habits were assessed. The Sartorius score was used to evaluate the clinical severity of HS. Anthropometric parameters (waist circumference, weight, height, and body mass index), body composition via bioelectrical impedance analysis, levels of trimethylamine N-oxide (TMAO), oxidized low-density lipoprotein (oxLDL), and derivatives of reactive oxygen metabolites (dROMs) were assessed at baseline and after 28 days of the active phase of VLCKD.

RESULTS

VLCKD led to general improvements in anthropometric parameters and body composition. Notably, a significant reduction in the Sartorius score was observed after the intervention (Δ%: - 24.37 ± 16.64, p < 0.001). This reduction coincided with significant decreases in TMAO (p < 0.001), dROMs (p = 0.001), and oxLDL (p < 0.001) levels. Changes in the Sartorius score exhibited positive correlations with changes in TMAO (p < 0.001), dROMs (p < 0.001), and oxLDL (p = 0.002).

CONCLUSION

The 28-day active phase of VLCKD demonstrated notable improvements in HS severity and associated metabolic markers, highlighting the potential utility of VLCKD in managing HS and its association with metabolic derangements in women with overweight or obesity.

Pathological and Therapeutical Implications of Pyroptosis in Psoriasis and Hidradenitis Suppurativa: A Narrative Review

This manuscript explores the role of pyroptosis, an inflammatory programmed cell death, in the pathogenesis of two chronic dermatoses, psoriasis and hidradenitis suppurativa (HS). The diseases, though clinically diverse, share common pathogenetic pathways involving the unbalanced interaction between the adaptive and innate immune systems. This review focuses on the molecular changes in psoriatic and HS skin, emphasizing the activation of dendritic cells, secretion of interleukins (IL-17, IL-22, and TNF-α), and the involvement of inflammasomes, particularly NLRP3. This manuscript discusses the role of caspases, especially caspase-1, in driving pyroptosis and highlights the family of gasdermins (GSDMs) as key players in the formation of pores leading to cell rupture and the release of proinflammatory signals. This study delves into the potential therapeutic implications of targeting pyroptosis in psoriasis and HS, examining existing medications like biologics and Janus kinase inhibitors. It also reviews the current limitations and challenges in developing therapies that selectively target pyroptosis. Additionally, the manuscript explores the role of pyroptosis in various inflammatory disorders associated with psoriasis and HS, such as inflammatory bowel disease, diabetes mellitus, and cardiovascular disorders. The review concludes by emphasizing the need for further research to fully elucidate the pathomechanisms of these dermatoses and develop effective, targeted therapies.