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

The use of isotretinoin for acne - an update on optimal dosing, surveillance, and adverse effects

INTRODUCTION

Acne is a chronic, inflammatory, and immune mediated disease of pilosebaceous unit, highly prevalent in adolescents. It involves face, trunk, and back; may leave scars and affect quality of life. Early, effective, and safe treatment is the key for disease resolution. Oral isotretinoin is the unique treatment for cure or prolonged remission for moderate and severe acne, preventing psychosocial impact and scars. It inhibits sebaceous glands activity and has anti-inflammatory and immunoregulatory properties.

AREAS COVERED

We performed a comprehensive literature search on PubMed database, up to March 2020, regarding oral isotretinoin for acne treatment. We synthetized data about acne pathogenesis and mechanism of action, efficacy, and safety of isotretinoin.

EXPERT OPINION

This drug is effective, despite common, controllable, and reversible mucocutaneous side effects. Serious adverse events are rare and represent individual reactions. Teratogenicity is the most severe, requiring rigorous control. We believe that no other therapeutic option, even topicals combined to oral antibiotics accomplish same results. Recurrence after treatments other than isotretinoin is the rule, prolonging risk of scars, compromising skin appearance, and causing emotional distress in teenagers. If there is no absolute contraindication, isotretinoin should be the first line treatment for moderate to severe inflammatory acne.

Recent advances in understanding and managing acne

Multidisciplinary investigations into the pathogenesis of acne have significantly progressed over the past three years. Studies of the etiology of acne from the perspectives, for example, of sebaceous gland biology, sebum, genetics, keratinization, differentiation, hair cycles, immunology, bacteriology, and wound healing have elucidated its pathogenesis. This has led to the development of new therapies and paved the way for advanced studies that will enable the further evolution of acne treatment.

Inhibitory effect of the antimicrobial peptide BLP-7 against Propionibacterium acnes and its anti-inflammatory effect on acne vulgaris

Propionibacterium acnes (P. acnes) is a Gram-positive commensal bacterium, which is involved in the pathogenesis and inflammation of acne vulgaris. An antimicrobial peptide named bombinin-like peptide 7 (BLP-7), which was determined from Bombina orientalis, has been shown to possess certain antibacterial activity. This study was carried out with synthesized BLP-7 on the basis of the antimicrobial and anti-inflammatory activities against P. acnes in vitro and in vivo. The minimal inhibitory concentration (MIC) of BLP-7 against P. acnes is 5 μM. And BLP-7 exhibits strong resistance to heat, pH and salt concentration, but no significant cytotoxicity to normal human epidermal keratinocytes (NHEKs). Using the co-culture of P. acnes and NHEKs, this study demonstrated that BLP-7 significantly reduced the production of interleukin (IL)-8 and granulocyte-macrophage colony stimulating factor (GM-CSF), as well as the expression of these two pro-inflammatory cytokines at the transcriptional level. In a separate study, using the rat ear edema model, BLP-7 significantly suppressed P. acnes-induced skin inflammation, reducing the ear thickness by 54.21% of the negative control group. These results suggest that due to its anti-P. acnes and anti-inflammatory activities, BLP-7 could be used as a potential anti-acne agent.

Skin microbiota: Friend or foe in pediatric skin health and skin disease

The human integument and gastrointestinal tract host unique microbial ecosystems. Within the last decade, research has focused on understanding the contributions of the microbiota to human health and disease. The majority of skin microbiome studies involve adults. This review focuses on key studies conducted within the pediatric population and provides a framework for future skin microbiome work in this ever-expanding field. This article begins by exploring the skin microbiome at birth and reviews the impact of delivery mode on infant skin colonization. How skin microbial colonization evolves from infancy to adulthood and normal development impacts the abundance of skin commensals such as Streptococcus, Staphylococcus, and Cutibacterium is also highlighted. Finally, several skin microbiome research studies in common pediatric skin conditions are reviewed, including body odor, atopic dermatitis (AD), and acne. The bacteria involved in metabolizing sweat, the impact on body odor, and how this process evolves from childhood to adulthood is outlined. In AD, different bacteria genera that predominate in children and adults and the impact of current AD therapies on skin microbiota are explored. Finally, in acne, the understanding of how Cutibacterium acnes contributes to acne pathogenesis and how acne therapies impact the skin microbial communities is reviewed.

Acne: Transient Arrest in the Homeostatic Host-Microbiota Dialog?

We propose that acne vulgaris represents a naturally developing, transient inflammatory interaction of adolescent facial skin with its new microbial/chemical milieu (Cutibacterium acnes, sebum), replacing a state of previous childhood skin homeostasis. This concept might explain why acne is characterized by strong regional and age specificity, prevalent occurrence, and resolution.

Potential Role of the Microbiome in Acne: A Comprehensive Review

Acne is a highly prevalent inflammatory skin condition involving sebaceous sties. Although it clearly develops from an interplay of multiple factors, the exact cause of acne remains elusive. It is increasingly believed that the interaction between skin microbes and host immunity plays an important role in this disease, with perturbed microbial composition and activity found in acne patients. Cutibacterium acnes (C. acnes; formerly called Propionibacterium acnes) is commonly found in sebum-rich areas and its over-proliferation has long been thought to contribute to the disease. However, information provided by advanced metagenomic sequencing has indicated that the cutaneous microbiota in acne patients and acne-free individuals differ at the virulent-specific lineage level. Acne also has close connections with the gastrointestinal tract, and many argue that the gut microbiota could be involved in the pathogenic process of acne. The emotions of stress (e.g., depression and anxiety), for instance, have been hypothesized to aggravate acne by altering the gut microbiota and increasing intestinal permeability, potentially contributing to skin inflammation. Over the years, an expanding body of research has highlighted the presence of a gut–brain–skin axis that connects gut microbes, oral probiotics, and diet, currently an area of intense scrutiny, to acne severity. This review concentrates on the skin and gut microbes in acne, the role that the gut–brain–skin axis plays in the immunobiology of acne, and newly emerging microbiome-based therapies that can be applied to treat acne.

Acne, the Skin Microbiome, and Antibiotic Treatment

Acne vulgaris is a chronic skin disorder involving hair follicles and sebaceous glands. Multiple factors contribute to the disease, including skin microbes. The skin microbiome in the follicle is composed of a diverse group of microorganisms. Among them, Propionibacterium acnes and Malassezia spp. have been linked to acne development through their influence on sebum secretion, comedone formation, and inflammatory response. Antibiotics targeting P. acnes have been the mainstay in acne treatment for the past four decades. Among them, macrolides, clindamycin, and tetracyclines are the most widely prescribed. As antibiotic resistance becomes an increasing concern in clinical practice, understanding the skin microbiome associated with acne and the effects of antibiotic use on the skin commensals is highly relevant and critical to clinicians. In this review, we summarize recent studies of the composition and dynamics of the skin microbiome in acne and the effects of antibiotic treatment on skin microbes.

Propionibacterium acnes and Acne Vulgaris: New Insights from the Integration of Population Genetic, Multi-Omic, Biochemical and Host-Microbe Studies

The anaerobic bacterium Propionibacterium acnes is believed to play an important role in the pathophysiology of the common skin disease acne vulgaris. Over the last 10 years our understanding of the taxonomic and intraspecies diversity of this bacterium has increased tremendously, and with it the realisation that particular strains are associated with skin health while others appear related to disease. This extensive review will cover our current knowledge regarding the association of P. acnes phylogroups, clonal complexes and sequence types with acne vulgaris based on multilocus sequence typing of isolates, and direct ribotyping of the P. acnes strain population in skin microbiome samples based on 16S rDNA metagenomic data. We will also consider how multi-omic and biochemical studies have facilitated our understanding of P. acnes pathogenicity and interactions with the host, thus providing insights into why certain lineages appear to have a heightened capacity to contribute to acne vulgaris development, while others are positively associated with skin health. We conclude with a discussion of new therapeutic strategies that are currently under investigation for acne vulgaris, including vaccination, and consider the potential of these treatments to also perturb beneficial lineages of P. acnes on the skin.

Combined culture and metagenomic analyses reveal significant shifts in the composition of the cutaneous microbiome in psoriasis

BACKGROUND

The treatment of psoriasis has been revolutionized by the development of biologic therapies. However, the pathogenesis of psoriasis, in particular the role of the cutaneous microbiome, remains incompletely understood. Moreover, skin microbiome studies have relied heavily on 16S rRNA sequencing data in the absence of bacterial culture.

OBJECTIVES

To characterize and compare the cutaneous microbiome in 20 healthy controls and 23 patients with psoriasis using metagenomic analyses and to determine changes in the microbiome during treatment.

METHODS

Swabs from lesional and nonlesional skin from patients with psoriasis, and from controls matched for site and skin microenvironment, were analysed using both 16S rRNA sequencing and traditional culture combined with mass spectrometry (MALDI-TOF) in a prospective study.

RESULTS

Psoriasis was associated with an increased abundance of Firmicutes and a corresponding reduction in Actinobacteria, most marked in lesional skin, and at least partially reversed during systemic treatment. Shifts in bacterial community composition in lesional sites were reflected in similar changes in culturable bacteria, although changes in the microbiota over repeated swabbing were detectable only with sequencing. The composition of the microbial communities varied by skin site and microenvironment. Prevotella and Staphylococcus were significantly associated with lesional skin, and Anaerococcus and Propionibacterium with nonlesional skin. There were no significant differences in the amount of bacteria cultured from the skin of healthy controls and patients with psoriasis.

CONCLUSIONS

Shifts in the cutaneous microbiome in psoriasis, particularly during treatment, may shed new light on the pathogenesis of the disease and may be clinically exploited to predict treatment response. What's already known about this topic? Alterations in the composition of the cutaneous microbiome have been described in psoriasis, although methodological differences in study design prevent direct comparison of results. To date, most cutaneous microbiome studies have focused on 16S rRNA sequencing data, including both living and dead bacteria. What does this study add? This prospective observational study confirms that changes in the composition of the cutaneous microbiome, detected by 16S rRNA sequencing, are consistent with those identified by bacterial culture and mass spectrometry. The changes in the microbiome during antipsoriasis therapy should be further investigated to determine whether these represent potential novel biomarkers of treatment response. What is the translational message? Characterization of cutaneous microbiota may ultimately move into the clinic to help facilitate treatment selection, not only by optimizing currently available treatments, but also by identifying new therapeutic targets.

Propionibacterium acnes-induced immunopathology correlates with health and disease association

Genomic studies revealed the existence of health- and acne-associated P. acnes strains and suggested novel approaches for broadening understanding of acne vulgaris. However, clinical association of P. acnes with disease or health has yet to be corroborated experimentally. Current animal models of acne do not closely mimic human disease and have unclear translational value. We have developed a murine model of acne by combining P. acnes inoculation with topical application of a synthetic human sebum. We showed that human sebum promoted persistence of intradermally injected P. acnes with little loss of viability after 1 week and permitted use of more physiologic inoculums. Application of acne-associated P. acnes RT4/5 strains led to development of moderate to severe skin pathology compared with application of health-associated type II P. acnes strains (RT2/6). RT4/5 P. acnes strains uniformly induced higher levels of KC (IL-8), IL-1α, IL-1β, and IL-6 in vitro and in vivo compared with type II P. acnes strains. Overall, our data provide immunopathologic corroboration of health and disease association of clinical P. acnes strains and inform on a platform to query putative virulence factors uncovered by genomic studies.

IL-26, a Cytokine With Roles in Extracellular DNA-Induced Inflammation and Microbial Defense

Interleukin 26 (IL-26) is the most recently identified member of the IL-20 cytokine subfamily, and is a novel mediator of inflammation overexpressed in activated or transformed T cells. Novel properties have recently been assigned to IL-26, owing to its non-conventional cationic, and amphipathic features. IL-26 binds to DNA released from damaged cells and, as a carrier molecule for extracellular DNA, links DNA to inflammation. This observation suggests that IL-26 may act both as a driver and an effector of inflammation, leading to the establishment of a deleterious amplification loop and, ultimately, sustained inflammation. Thus, IL-26 emerges as an important mediator in local immunity/inflammation. The dysregulated expression and extracellular DNA carrier capacity of IL-26 may have profound consequences for the chronicity of inflammation. IL-26 also exhibits direct antimicrobial properties. This review summarizes recent advances on the biology of IL-26 and discusses its roles as a novel kinocidin.

Short-Chain Fatty Acids from Cutibacterium acnes Activate Both a Canonical and Epigenetic Inflammatory Response in Human Sebocytes

The regulation of cutaneous inflammatory processes is essential for the human skin to maintain homeostasis in the presence of the dense communities of resident microbes that normally populate this organ. Forming the hair follicle-associated sebaceous gland, sebocytes are specialized lipid-producing cells that can release inflammatory mediators. Cytokine and chemokine expression by pilosebaceous epithelial cells (i.e., sebocytes and follicular keratinocytes) has been proposed to contribute to the common human skin disease acne vulgaris. The underlying mechanisms that drive inflammatory gene expression in acne-involved pilosebaceous epithelial cells are still unknown because almost all sebaceous follicles contain dense concentrations of bacteria yet only some show an inflammatory reaction. In this study, we hypothesized that metabolites from the abundant skin-resident microbe Propionibacterium acnes can influence cytokine expression from human sebocytes. We show that short-chain fatty acids produced by P. acnes under environmental conditions that favor fermentation will drive inflammatory gene expression from sebocytes. These molecules are shown to influence sebocyte behavior through two distinct mechanisms: the inhibition of histone deacetylase (HDAC) activity and the activation of fatty acid receptors. Depletion of HDAC8 and HDAC9 in human sebocytes resulted in an enhanced cytokine response to TLR-2 activation that resembled the transcriptional profile of an acne lesion. These data provide a new insight into the regulation of inflammatory gene expression in the skin, further characterize the contribution of sebocytes to epidermal immunity, and demonstrate how changes in the metabolic state of the skin microbiome can promote inflammatory acne.

Recent advances in understanding Propionibacterium acnes ( Cutibacterium acnes) in acne

The skin commensal Propionibacterium acnes, recently renamed Cutibacterium acnes, along with the other major pathophysiological factors of increased seborrhea, hyperkeratinization of the pilosebaceous unit, and inflammation, has long been implicated in the pathogenesis of acne. Recent advances have contributed to our understanding of the role of P. acnes in acne. Although there are no quantitative differences in P. acnes of the skin of patients with acne compared with controls, the P. acnes phylogenic groups display distinct genetic and phenotypic characteristics, P. acnes biofilms are more frequent in acne, and different phylotypes may induce distinct immune responses in acne. P. acnes plays a further important role in the homeostasis of the skin’s microbiome, interacting with other cutaneous commensal or pathogenic microorganisms such as Staphylococcus epidermidis, Streptococcus pyogenes, and Pseudomonas species. In the era of increasing antimicrobial resistance, the selection of acne treatment targeting P. acnes and the prevention of antibiotic resistance play a key role in improving outcomes in acne patients and public health.

Alteration of the cutaneous microbiome in psoriasis and potential role in Th17 polarization

BACKGROUND

Psoriasis impacts 1-3% of the world's population and is characterized by hyper-proliferation of keratinocytes and increased inflammation. At the molecular level, psoriasis is commonly driven by a Th17 response, which serves as a major therapeutic target. Microbiome perturbations have been associated with several immune-mediated diseases such as atopic dermatitis, asthma, and multiple sclerosis. Although a few studies have investigated the association between the skin microbiome and psoriasis, conflicting results have been reported plausibly due to the lack of standardized sampling and profiling protocols, or to inherent microbial variability across human subjects and underpowered studies. To better understand the link between the cutaneous microbiota and psoriasis, we conducted an analysis of skin bacterial communities of 28 psoriasis patients and 26 healthy subjects, sampled at six body sites using a standardized protocol and higher sequencing depth compared to previous studies. Mouse studies were employed to examine dermal microbial-immune interactions of bacterial species identified from our study.

RESULTS

Skin microbiome profiling based on sequencing the 16S rRNA V1-V3 variable region revealed significant differences between the psoriasis-associated and healthy skin microbiota. Comparing the overall community structures, psoriasis-associated microbiota displayed higher diversity and more heterogeneity compared to healthy skin bacterial communities. Specific microbial signatures were associated with psoriatic lesional, psoriatic non-lesional, and healthy skin. Specifically, relative enrichment of Staphylococcus aureus was strongly associated with both lesional and non-lesional psoriatic skin. In contrast, Staphylococcus epidermidis and Propionibacterium acnes were underrepresented in psoriatic lesions compared to healthy skin, especially on the arm, gluteal fold, and trunk. Employing a mouse model to further study the impact of cutaneous Staphylcoccus species on the skin T cell differentiation, we found that newborn mice colonized with Staphylococcus aureus demonstrated strong Th17 polarization, whereas mice colonized with Staphylococcus epidermidis or un-colonized controls showed no such response.

CONCLUSION

Our results suggest that microbial communities on psoriatic skin is substantially different from those on healthy skin. The psoriatic skin microbiome has increased diversity and reduced stability compared to the healthy skin microbiome. The loss of community stability and decrease in immunoregulatory bacteria such as Staphylococcus epidermidis and Propionibacterium acnes may lead to higher colonization with pathogens such as Staphylococcus aureus, which could exacerbate cutaneous inflammation along the Th17 axis.

Vaccinating against Acne: Benefits and Potential Pitfalls

Acne vulgaris is treated with antibiotics and retinoids, but side effects are numerous. Novel safe and efficient therapies are still needed. Wang et al. demonstrate that the secreted virulence factor Christie-Atkins-Munch-Peterson factor 2 from Propionibacterium acnes, a bacterium involved in acne pathogenesis, promotes inflammatory responses. This proinflammatory property could be inhibited by antibodies to Christie-Atkins-Munch-Peterson factor 2, suggesting Christie-Atkins-Munch-Peterson factor 2 as a candidate target in acne vaccination. This work supports the concept of acne immunotherapy, but questions about selection of target antigens remain open.

Update in the management of acne in adolescence

PURPOSE OF REVIEW

This review will update the pediatric provider on recent data on the pathogenesis and treatment of acne in adolescent patients. A special focus was made to summarize recent guidelines and fill in several identified practice gaps.

RECENT FINDINGS

Our understanding of the pathogenesis of acne is greatly expanding and data is emerging to tie diet, particularly the role of IGF-1 with inflammation in acne. Additionally, stronger recommendations to limit antibiotic usage in acne are being made worldwide. Although retinoids are considered the base of most effective acne treatment strategies, data suggests that all providers need to emphasize their importance in maintenance of acne.

SUMMARY

An effective acne management strategy targets multiple pathogenic factors in acne, using a retinoid as the foundation. Systemic antibiotics for moderate-to-severe acne should be used for acute management, then discontinued at 3-4 months, while maintaining on topical treatments. If therapy is ineffective, alternate treatments, such as combined oral contraceptives in females or isotretinoin, should be promptly employed to prevent prolonged psychological impact and cutaneous scarring.

Isolation and Identification of the Follicular Microbiome: Implications for Acne Research

Our understanding of the microbiome and the role of Propionibacterium acnes in skin homeostasis and acne pathogenesis is evolving. Multiple methods for sampling and identifying the skin's microbiome exist, and understanding the differences between the abilities of various methods to characterize the microbial landscape is warranted. This study compared the microbial diversity of samples obtained from the cheeks of 20 volunteers, collected by surface swab, pore strips, and cyanoacrylate glue follicular biopsy, all sequenced with 16S rRNA sequencing (V1-V3) and whole-genome metagenomic sequencing. The sequencing method of choice influenced the detection of microbial profiles as whole-genome sequencing captured more species diversity, including viruses, compared with 16S sequencing. The relative abundance of bacterial or fungal species and overall diversity did not differ between sampling methods. However, the viral composition of the skin's surface is unique compared with the follicle, suggesting distinct viral niches within the skin. P. acnes bacteria, ribotypes, and bacteriophages were identified equally by all sampling methods indicating that the sampling method, whether for the skin's surface or follicle, does not impact P. acnes-related characterization and that all may be equally useful for acne-related research studies.