Propionibacterium acnesactivates caspase-1 in human neutrophils

Cutibacterium acnes and its complex host interaction in prosthetic joint infection: Current insights and future directions

Cutibacterium acnes is a commensal Gram-positive anaerobic bacterium that can also act as an opportunistic pathogen in various diseases, particularly in prosthetic joint infections (PJI). Throughout this review, we delve into the current understanding of the intricate interactions between C. acnes and host cells and discuss bacterial persistence in the host. C. acnes colonization and subsequent PJI set-up represent complex processes involving bacterial adhesion, immune recognition, and host response mechanisms. We highlight existing knowledge and gaps in specific host-pathogen interactions and stress the importance of acquiring additional information to develop targeted strategies for preventing and treating C. acnes-related PIJ.

Photodynamic Effects of Topical Photosensitizer, Photodithazine Using Micro-LED for Acne Bacteria Induced Inflammation

BACKGROUND

Photodynamic therapy (PDT) using topical photosensitizers has been widely used worldwide as a therapeutic modality for acne. However, there are no published reports on photodithazine PDT for acne treatment.

OBJECTIVE

We investigated the effectiveness of PDT with photodithazine and micro-LED treatment for acne bacteria-induced inflammation.

METHODS

We established an acne bacteria-induced inflammation model by injecting of Cutibacterium acnes into the backs of HR-1 mice. The mouse models were divided into seven groups for control and comparison. Topical photosensitizer (photodithazine) was administered to the mice, and then their acne lesions were exposed to a micro-light-emitting diode (micro-LED) source. The effectiveness of the treatment on acne lesions was evaluated through clinical findings and measurements of acne inflammation biomarkers using semi-quantitative reverse transcription polymerase chain reaction, and Western blot. Additionally, hematoxylin and eosin staining and immunohistochemical staining were employed to evaluate the changes in inflammatory cells and biomarkers in skin tissues.

RESULTS

Compared with the control groups treated with either LED or photosensitizer alone, the acne lesions were significantly reduced in severity and number after PDT. The mRNA and protein levels of biomarkers (interleukin [IL]-1α, IL-1β, tumor necrosis factor-α, Toll-like receptor 2, matrix metalloproteinase-2, and IL-8) exhibited variable decreases in the PDT group relative to the others. Moreover, there was a decline in inflammatory cells and biomarkers in skin specimens after PDT.

CONCLUSION

This in vivo study demonstrated that PDT using photodithazine and micro-LED technology is effective against inflammation induced by acne bacteria.

Autocrine IL-8 Contributes to Propionibacterium Acnes-induced Proliferation and Differentiation of HaCaT Cells via AKT/FOXO1/ Autophagy

OBJECTIVE

Proprionibacterium acnes (P. acnes)-induced inflammatory responses, proliferation and differentiation of keratinocytes contribute to the progression of acne vulgaris (AV). P. acnes was found to enhance the production of interleukin-8 (IL-8) by keratinocytes. This study aimed to investigate the role of IL-8 in P. acnes-induced proliferation and differentiation of keratinocytes and the underlying mechanism.

METHODS

The P. acnes-stimulated HaCaT cell (a human keratinocyte cell line) model was established. Western blotting and immunofluorescence were performed to detect the expression of the IL-8 receptors C-X-C motif chemokine receptor 1 (CXCR1) and C-X-C motif chemokine receptor 2 (CXCR2) on HaCaT cells. Cell counting kit-8 (CCK-8) assay, 5-ethynyl-20-deoxyuridine (EdU) assay and Western blotting were performed to examine the effects of IL-8/CXCR2 axis on the proliferation and differentiation of HaCaT cells treated with P. acnes, the IL-8 neutralizing antibody, the CXCR2 antagonist (SB225002), or the CXCR1/CXCR2 antagonist (G31P). Western blotting, nuclear and cytoplasmic separation, CCK-8 assay, and EdU assay were employed to determine the downstream pathway of CXCR2 after P. acnes-stimulated HaCaT cells were treated with the CXCR2 antagonist, the protein kinase B (AKT) antagonist (AZD5363), or the constitutively active forkhead box O1 (FOXO1) mutant. Finally, autophagy markers were measured in HaCaT cells following the transfection of the FOXO1 mutant or treatment with the autophagy inhibitor 3-methyladenine (3-MA).

RESULTS

The expression levels of CXCR1 and CXCR2 were significantly increased on the membrane of HaCaT cells following P. acnes stimulation. The IL-8/CXCR2 axis predominantly promoted the proliferation and differentiation of P. acnes-induced HaCaT cells by activating AKT/FOXO1/autophagy signaling. In brief, IL-8 bound to its receptor CXCR2 on the membrane of keratinocytes to activate the AKT/FOXO1 axis. Subsequently, phosphorylated FOXO1 facilitated autophagy to promote the proliferation and differentiation of P. acnes-induced keratinocytes.

CONCLUSION

This study demonstrated the novel autocrine effect of IL-8 on the proliferation and differentiation of P. acnes-induced keratinocytes, suggesting a potential therapeutic target for AV.

Interleukin-1 family cytokines at the crossroads of microbiome regulation in barrier health and disease

Recent advances in understanding how the microbiome can influence both the physiology and the pathogenesis of disease in humans have highlighted the importance of gaining a deeper insight into the complexities of the host-microbial dialogue. In tandem with this progress, has been a greater understanding of the biological pathways which regulate both homeostasis and inflammation at barrier tissue sites, such as the skin and the gut. In this regard, the Interleukin-1 family of cytokines, which can be segregated into IL-1, IL-18 and IL-36 subfamilies, have emerged as important custodians of barrier health and immunity. With established roles as orchestrators of various inflammatory diseases in both the skin and intestine, it is now becoming clear that IL-1 family cytokine activity is not only directly influenced by external microbes, but can also play important roles in shaping the composition of the microbiome at barrier sites. This review explores the current knowledge surrounding the evidence that places these cytokines as key mediators at the interface between the microbiome and human health and disease at the skin and intestinal barrier tissues.

Relationship between pyroptosis-mediated inflammation and the pathogenesis of prostate disease

The largest solid organ of the male genitalia, the prostate gland, is comprised of a variety of cells such as prostate epithelial cells, smooth muscle cells, fibroblasts, and endothelial cells. Prostate diseases, especially prostate cancer and prostatitis, are often accompanied by acute/chronic inflammatory responses or even cell death. Pyroptosis, a cell death distinct from necrosis and apoptosis, which mediate inflammation may be closely associated with the development of prostate disease. Pyroptosis is characterized by inflammasome activation via pattern recognition receptors (PRR) upon recognition of external stimuli, which is manifested downstream by translocation of gasdermin (GSDM) protein to the membrane to form pores and release of inflammatory factors interleukin (IL)-1β and IL-18, a process that is Caspase-dependent. Over the past number of years, many studies have investigated the role of inflammation in prostate disease and have suggested that pyroptosis may be an important driver. Understanding the precise mechanism is of major consequence for the development of targeted therapeutic strategies. This review summarizes the molecular mechanisms, regulation, and cellular effects of pyroptosis briefly and then discuss the current pyroptosis studies in prostate disease research and the inspiration for us.

Adipose-derived stem cells attenuate acne-related inflammation via suppression of NLRP3 inflammasome

BACKGROUND

Acne is a chronic facial disease caused by Propionibacterium acnes, which proliferates within sebum-blocked skin follicles and increases inflammatory cytokine production. Several therapeutic drugs and products have been proposed to treat acne, yet no single treatment that ensures long-term treatment efficacy for all patients is available. Here, we explored the use of facial autologous fat transplant of adipose-derived stem cells (ADSCs) to dramatically reduce acne lesions.

METHODS

THP-1 cells were treated with active P. acnes for 24 h at different multiplicities of infection, and alterations in inflammatory factors were detected. To study the effect of THP-1 on inflammasome-related proteins, we first co-cultured ADSCs with THP-1 cells treated with P. acnes and evaluated the levels of these proteins in the supernatant. Further, an acne mouse model injected with ADSCs was used to assess inflammatory changes.

RESULTS

Propionibacterium acnes-mediated stimulation of THP-1 cells had a direct correlation with the expression of active caspase-1 and interleukin (IL)-1β in an infection-dependent manner. ADSCs significantly reduced the production of IL-1β induced by P. acnes stimulation through the reactive oxygen species (ROS)/Nod-like receptor family pyrin domain-containing 3 (NLRP3)/caspase-1 pathway. The results showed that ADSCs inhibit the skin inflammation induced by P. acnes by blocking the NLRP3 inflammasome via reducing the secretion of IL-1β in vivo.

CONCLUSIONS

Our findings suggest that ADSCs can alter IL-1β secretion by restricting the production of mitochondria ROS, thereby inhibiting the NLRP3/caspase-1 pathway in P. acnes-induced inflammatory responses. This study indicates that anti-acne therapy can potentially be developed by targeting the NLRP3 inflammasome.

The Activity of Gold Nanoparticles Synthesized Using Helichrysum odoratissimum Against Cutibacterium acnes Biofilms

The human skin is home to millions of bacteria, fungi, and viruses which form part of a unique microbiome. Commensal microbes, including Cutibacterium acnes can occasionally become opportunistic resulting in the onset of dermatological diseases such as acne. Acne is defined as a chronic inflammatory disorder based on its ability to persist for long periods throughout an individual’s life. The synthesis of gold nanoparticles (AuNPs) was performed using the bottom-up approach by reduction of a gold salt (HAuCl₄.3H₂O) by the methanol extract (HO-MeOH) and aqueous decoction prepared from the dried aerial parts of Helichrysum odoratissimum (HO-Powder). The HO-MeOH and HO-Powder AuNPs were prepared as unstabilised (−GA) or stabilized (+GA) by the omission or addition of Gum Arabic (GA) as the capping agent. The characterization of the AuNPs was performed using Transmission Electron Microscopy (TEM), dynamic light scattering (DLS), Ultraviolet-Visual spectroscopy (UV-Vis), Thermogravimetric Analysis (TGA), X-Ray Diffraction (XRD) and Zeta-potential. The MBIC₅₀ values for HO-MeOH − GA and HO-MeOH + GA were 1.79 ± 0.78% v/v and 0.22 ± 0.16% v/v, respectively. The HO-Powder AuNPs showed potent inhibition of C. acnes cell adhesion to the 96-well plates. The HO-MeOH − GA and HO-Powder + GA exhibited IC₅₀ of 22.01 ± 6.13% v/v and 11.78 ± 1.78% v/v, respectively. The activity of the AuNPs validated the anti-adhesion activity of the methanol extract in the crude form. The study emphasizes the selectivity of H. odoratissimum AuNPs for the prevention of C. acnes cell adhesion and not antimicrobial activity, which may prevent the emergence of resistant strains of C. acnes through reduced bactericidal or bacteriostatic activity, while targeting mechanisms of pathogenesis.

Porphyrins produced by acneic Cutibacterium acnes strains activate the inflammasome by inducing K+ leakage

Some Cutibacterium acnes subgroups dominate on healthy skin, whereas others are frequently acne associated. Here we provide mechanistic insights into this difference, using an anaerobic keratinocyte-sebocyte-C. acnes co-culture model. An acneic C. acnes strain as well as its porphyrins activates NRLP3 inflammasome assembly, whereas this was not observed with a non-acneic strain. Low levels of intracellular K⁺ in keratinocytes stimulated with extracted porphyrins or infected with the acneic strain were observed, identifying porphyrin-induced K⁺ leakage as trigger for inflammasome activation. Using a panel of C. acnes strains, we found that porphyrin production and IL-1β release are correlated and are higher in acneic strains. This demonstrates that the latter produce more porphyrins, which interact with the keratinocyte cell membrane, leading to K⁺ leakage, NLRP3 inflammasome activation, and IL-1β release and provides an explanation for the observation that some C. acnes strains are associated with healthy skin, whereas others dominate in acneic skin.

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We developed an anaerobic keratinocyte-sebocyte-C. acnes co-culture model

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Acneic C. acnes strains and their porphyrins activate NRLP3 inflammasome assembly

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Activation of the NRLP3 inflammasome is not observed in non-acneic strains

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Porphyrins from acneic C. acnes activate the inflammasome by inducing K⁺ leakage

Suppressive Effect of Two Cucurbitane-Type Triterpenoids from Momordica charantia on Cutibacterium acnes-Induced Inflammatory Responses in Human THP-1 Monocytic Cell and Mouse Models

Cutibacterium acnes (formerly Propionibacterium acnes) is one of the major bacterial species responsible for acne vulgaris. Numerous bioactive compounds from Momordica charantia Linn. var. abbreviata Ser. have been isolated and examined for many years. In this study, we evaluated the suppressive effect of two cucurbitane-type triterpenoids, 5β,19-epoxycucurbita-6,23-dien-3β,19,25-triol (Kuguacin R; KR) and 3β,7β,25-trihydroxycucurbita-5,23-dien-19-al (TCD) on live C. acnes-stimulated in vitro and in vivo inflammatory responses. Using human THP-1 monocytes, KR or TCD suppressed C. acnes-induced production of interleukin (IL)-1β, IL-6 and IL-8 at least above 56% or 45%, as well as gene expression of these three pro-inflammatory cytokines. However, a significantly strong inhibitory effect on production and expression of tumor necrosis factor (TNF)-α was not observed. Both cucurbitanes inhibited C. acnes-induced activation of the myeloid differentiation primary response 88 (MyD88) (up to 62%) and mitogen-activated protein kinases (MAPK) (at least 36%). Furthermore, TCD suppressed the expression of pro-caspase-1 and cleaved caspase-1 (p10). In a separate study, KR or TCD decreased C. acnes-stimulated mouse ear edema by ear thickness (20% or 14%), and reduced IL-1β-expressing leukocytes and neutrophils in mouse ears. We demonstrated that KR and TCD are potential anti-inflammatory agents for modulating C. acnes-induced inflammation in vitro and in vivo.

Cutibacterium acnes is an intracellular and intra-articular commensal of the human shoulder joint

BACKGROUND

Cutibacterium acnes (C acnes) is a mysterious member of the shoulder microbiome and is associated with chronic postoperative complications and low-grade infections. Nevertheless, it is unclear whether it represents a contaminant or whether it accounts for true infections. Because it can persist intracellularly in macrophages at several body sites, it might in fact be an intra-articular commensal of the shoulder joint.

METHODS

In 23 consecutive, otherwise healthy patients (17 male, 6 female; 58 years) who had no previous injections, multiple specimens were taken from the intra-articular tissue during first-time arthroscopic and open shoulder surgery. The samples were investigated by cultivation, genetic phylotyping, and immunohistochemistry using C acnes-specific antibodies and confocal laser scanning microscopy.

RESULTS

In 10 patients (43.5%), cultures were C acnes-positive. Phylotype IA1 dominated the subcutaneous samples (71%), whereas type II dominated the deep tissue samples (57%). Sixteen of 23 patients (69.6%) were C acnes-positive by immunohistochemistry; in total, 25 of 40 samples were positive (62.5%). Overall, 56.3% of glenohumeral immunohistochemical samples, 62.5% of subacromial samples, and 75% of acromioclavicular (AC) joint samples were positive. In 62.5% of the tested patients, C acnes was detected immunohistochemically to reside intracellularly within stromal cells and macrophages.

DISCUSSION

These data indicate that C acnes is a commensal of the human shoulder joint, where it persists within macrophages and stromal cells. Compared with culture-based methods, immunohistochemical staining can increase C acnes detection. Phylotype II seems to be most prevalent in the deep shoulder tissue. The high detection rate of C acnes in osteoarthritic AC joints might link its intra-articular presence to the initiation of osteoarthritis.

In Vitro and In Vivo Screening of Wild Bitter Melon Leaf for Anti-Inflammatory Activity against Cutibacterium acnes

Cutibacterium acnes (formerly Propionibacterium acnes) is a key pathogen involved in the development and progression of acne inflammation. The numerous bioactive properties of wild bitter melon (WBM) leaf extract and their medicinal applications have been recognized for many years. In this study, we examined the suppressive effect of a methanolic extract (ME) of WBM leaf and fractionated components thereof on live C. acnes-induced in vitro and in vivo inflammation. Following methanol extraction of WBM leaves, we confirmed anti-inflammatory properties of ME in C. acnes-treated human THP-1 monocyte and mouse ear edema models. Using a bioassay-monitored isolation approach and a combination of liquid–liquid extraction and column chromatography, the ME was then separated into n-hexane, ethyl acetate, n-butanol and water-soluble fractions. The hexane fraction exerted the most potent anti-inflammatory effect, suppressing C. acnes-induced interleukin-8 (IL-8) production by 36%. The ethanol-soluble fraction (ESF), which was separated from the n-hexane fraction, significantly inhibited C. acnes-induced activation of mitogen-activated protein kinase (MAPK)-mediated cellular IL-8 production. Similarly, the ESF protected against C. acnes-stimulated mouse ear swelling, as measured by ear thickness (20%) and biopsy weight (23%). Twenty-four compounds in the ESF were identified using gas chromatograph–mass spectrum (GC/MS) analysis. Using co-cultures of C. acnes and THP-1 cells, β-ionone, a compound of the ESF, reduced the production of IL-1β and IL-8 up to 40% and 18%, respectively. β-ionone also reduced epidermal microabscess, neutrophilic infiltration and IL-1β expression in mouse ear. We also found evidence of the presence of anti-inflammatory substances in an unfractionated phenolic extract of WBM leaf, and demonstrated that the ESF is a potential anti-inflammatory agent for modulating in vitro and in vivo C. acnes-induced inflammatory responses.

Caspase-1 inflammasome activity in patients with Staphylococcus aureus bacteremia

The inflammasome is a multiprotein complex that mediates caspase‐1 activation with subsequent maturation of the proinflammatory cytokines IL‐1β and IL‐18. The NLRP3 inflammasome is known to be activated by Staphylococcus aureus, one of the leading causes of bacteremia worldwide. Inflammasome activation and regulation in response to bacterial infection have been found to be of importance for a balanced host immune response. However, inflammasome signaling in vivo in humans initiated by S. aureus is currently sparsely studied. This study therefore aimed to investigate NLRP3 inflammasome activity in 20 patients with S. aureus bacteremia (SAB), by repeated measurement during the first week of bacteremia, compared with controls. Caspase‐1 activity was measured in monocytes and neutrophils by flow cytometry detecting FLICA (fluorescent‐labeled inhibitor of caspase‐1), while IL‐1β and IL‐18 was measured by Luminex and ELISA, respectively. As a measure of inflammasome priming, messenger RNA (mRNA) expression of NLRP3, CASP1 (procaspase‐1), and IL1B (pro‐IL‐1β) was analyzed by quantitative PCR. We found induced caspase‐1 activity in innate immune cells with subsequent release of IL‐18 in patients during the acute phase of bacteremia, indicating activation of the inflammasome. There was substantial interindividual variation in caspase‐1 activity between patients with SAB. We also found an altered inflammasome priming with low mRNA levels of NLRP3 accompanied by elevated mRNA levels of IL1B. This increased knowledge of the individual host immune response in SAB could provide support in the effort to optimize management and treatment of each individual patient.

Neisseria meningitidis-Induced Caspase-1 Activation in Human Innate Immune Cells Is LOS-Dependent

Meningococcal disease such as sepsis and meningitidis is hallmarked by an excessive inflammatory response. The causative agent, Neisseria meningitidis, expresses the endotoxin lipooligosaccharide (LOS) that is responsible for activation of immune cells and the release of proinflammatory cytokines. One of the most potent proinflammatory cytokines, interleukin-1β (IL-1β), is activated following caspase-1 activity in the intracellular multiprotein complex called inflammasome. Inflammasomes are activated by a number of microbial factors as well as danger molecules by a two-step mechanism-priming and licensing of inflammasome activation-but there are no data available regarding a role for inflammasome activation in meningococcal disease. The aim of this study was to investigate if N. meningitidis activates the inflammasome and, if so, the role of bacterial LOS in this activation. Cells were subjected to N. meningitidis, both wild-type (FAM20) and its LOS-deficient mutant (lpxA), and priming as well as licensing of inflammasome activation was investigated. The wild-type LOS-expressing parental FAM20 serogroup C N. meningitidis (FAM20) strain significantly enhanced the caspase-1 activity in human neutrophils and monocytes, whereas lpxA was unable to induce caspase-1 activity as well as to induce IL-1β release. While the lpxA mutant induced a priming response, measured as increased expression of NLRP3 and IL1B, the LOS-expressing FAM20 further increased this priming. We conclude that although non-LOS components of N. meningitidis contribute to the priming of the inflammasome activity, LOS per se is to be considered as the central component of N. meningitidis virulence, responsible for both priming and licensing of inflammasome activation.

The role of Cutibacterium acnes in auto-inflammatory bone disorders

Chronic nonbacterial osteomyelitis (CNO) and SAPHO (synovitis, acne, pustulosis, hyperostosis and osteitis) syndrome are auto-inflammatory disorders manifesting as chronic inflammation of bones and joints, which in SAPHO is often accompanying by skin changes. The aetiology of these diseases is unknown, but includes genetic, infectious and immunological components. It has been proposed that Cutibacterium (formerly Propionibacterium) acnes plays a role in the pathogenesis. In this review, we summarise reported cases of CNO or SAPHO syndrome in which C. acnes has been isolated from bones. To identify cases, a search was done in May 2018 using the MEDLINE Ovid interface (1946 to present). We found 14 publications reporting 98 patients with auto-inflammatory bone disorders, of whom 48 (49%) had positive bone biopsies for C. acnes. This bacterium was more frequently isolated from open biopsies than percutaneous ones (43/69 (62%) vs 1/7 (14%); p = 0.04) and biopsies were more frequently positive in patients who presented with simultaneous skin manifestations (19/36 (53%) vs 4/12 (33%); p = 0.03).Conclusion: In patients with CNO or SAPHO, C. acnes can be isolated from open biopsies suggesting that in these patients, C. acnes might be a pathogen rather than a contaminant. The fact that biopsies are more frequently positive in patients who present with simultaneous skin manifestations suggests that these individuals might have a genetic predisposition for impaired clearance of C. acnes. What is known • Chronic nonbacterial osteomyelitis (CNO) and SAPHO (synovitis, acne, pustulosis, hyperostosis and osteitis) syndrome are auto-inflammatory disorders manifesting as inflammation of bones. Both diseases are an important differential diagnosis in children who present with symptoms of (multifocal) osteomyelitis. • The pathogenesis of CNO and SAPHO is multifactorial emcompassing genetic, infectious and immunological components, including interleukin (IL)-1 dysregulation. There is a controversy as to whether Cutibacterium (formerly Propionibacterium) acnes plays a role in the aetiology of CNO and SAPHO. It has been postulated that the presence of C. acnes might trigger auto-inflammatory chronic inflammation in genetically predisposed individuals. What is new • In patients with CNO or SAPHO, C. acnes can be isolated more frequently from open biopsies, than from percutaneous ones, suggesting that C. acnes might be a pathogen rather than a contaminant. • Biopsies are more frequently positive in patients who present with simultaneous skin manifestations suggesting that these individuals might have a genetic predisposition for impaired clearance of C. acnes. Impaired C. acnes clearance likely leads to increased IL-1 beta (β) production by skin cells, bone cells and phagocytes, which is one of the main cytokines underlying chronic inflammatory bone disorders.

The influence of prostatic Cutibacterium acnes infection on serum levels of IL6 and CXCL8 in prostate cancer patients

Background

Chronic prostatic inflammation, caused by Cutibacterium acnes (C. acnes), has been proposed to influence the risk of prostate cancer development. In vitro studies have demonstrated the capacity of C. acnes to induce secretion of Interleukin 6 (IL6) and C-X-C motif chemokine ligand 8 (CXCL8) by prostate epithelial cells. Both these inflammatory mediators have been implicated in prostate cancer pathophysiology. In this cohort study, we aimed to investigate the influence of prostatic C. acnes on serum levels of IL6 and CXCL8.

Methods

We recruited 99 prostate cancer patients who underwent radical prostatectomy at Örebro University Hospital. The cultivation of pre-operatively obtained prostate biopsies identified C. acnes in 60 of the 99 patients. Levels of IL6 and CXCL8 in pre-operative serum samples were analyzed using ELISA, and concentrations were compared between prostate cancer patients with and without prostatic C. acnes infection using standard statistical methods.

Results

No statistical differences were observed in serum levels of IL6 and CXCL8 between subjects with and without prostatic C. acnes infection.

Conclusions

Our results indicate that prostatic C. acnes infection may give rise to low-grade inflammation with little effect on systemic levels of IL6 and CXCL8.

Licochalcone A attenuates acne symptoms mediated by suppression of NLRP3 inflammasome

Activation of the NACHT, LRR and PYD domains-containing protein 3 (NLRP3) inflammasome by Propionibacterium acnes (P. acnes) is critical for inducing inflammation and aggravating the development of acne lesions. We searched for available small-molecule inhibitors of the NLRP3 inflammasome that could be topically administered for the treatment of acne. We found that licochalcone A, a chalconoid isolated from the root of Glycyrrhiza inflate, was an effective inhibitor for P. acnes-induced NLRP3 inflammasome activation. Licochalcone A blocked P. acnes-induced production of caspase-1(p10) and IL-1β in primary mouse macrophages and human SZ95 sebocytes, indicating the suppression of NLRP3 inflammasome. Licochalcone A suppressed P. acnes-induced ASC speck formation and mitochondrial reactive oxygen species. Topical application of licochalcone A to mouse ear skin attenuated P. acnes-induced skin inflammation as shown by histological assessment, ear thickness measurement, and inflammatory gene expression. Licochalcone A reduced caspase-1 activity and IL-1β production in mouse ear injected with P. acnes. This study demonstrated that licochalcone A is effective in the control of P. acnes-induced skin inflammation as an efficient inhibitor for NLRP3 inflammasome. Our study provides a new paradigm for the development of anti-acne therapy via targeting NLRP3 inflammasome.

Cytosolic Recognition of Microbes and Pathogens: Inflammasomes in Action

Infection is a dynamic biological process underpinned by a complex interplay between the pathogen and the host. Microbes from all domains of life, including bacteria, viruses, fungi, and protozoan parasites, have the capacity to cause infection. Infection is sensed by the host, which often leads to activation of the inflammasome, a cytosolic macromolecular signaling platform that mediates the release of the proinflammatory cytokines interleukin-1β (IL-1β) and IL-18 and cleavage of the pore-forming protein gasdermin D, leading to pyroptosis. Host-mediated sensing of the infection occurs when pathogens inject or carry pathogen-associated molecular patterns (PAMPs) into the cytoplasm or induce damage that causes cytosolic liberation of danger-associated molecular patterns (DAMPs) in the host cell. Recognition of PAMPs and DAMPs by inflammasome sensors, including NLRP1, NLRP3, NLRC4, NAIP, AIM2, and Pyrin, initiates a cascade of events that culminate in inflammation and cell death. However, pathogens can deploy virulence factors capable of minimizing or evading host detection. This review presents a comprehensive overview of the mechanisms of microbe-induced activation of the inflammasome and the functional consequences of inflammasome activation in infectious diseases. We also explore the microbial strategies used in the evasion of inflammasome sensing at the host-microbe interaction interface.

Staphylococcus epidermidis from prosthetic joint infections induces lower IL-1β release from human neutrophils than isolates from normal flora

The aim of this study was to test the hypothesis that Staphylococcus epidermidis isolated from prosthetic joint infections (PJIs) differs from S. epidermidis isolated from normal flora in terms of its capacity to induce activation of caspase-1 and release of IL-1β in human neutrophils. The amount of active caspase-1 was determined over 6 h by detecting Ac-YVAD-AMC fluorescence in human neutrophils incubated with S. epidermidis isolates from PJIs (ST2) or normal flora. The amount of IL-1β was detected by ELISA in neutrophil supernatants after 6 h of incubation. Mean IL-1β release was lower after incubation with S. epidermidis from PJIs compared to isolates from normal flora, but no statistically significant difference was found in active caspase-1. Substantial inter-individual differences in both active caspase-1 and IL-1β were noted. These results suggest that evasion of innate immune response, measured as reduced capacity to induce release of IL-1β from human neutrophils, might be involved in the predominance of ST2 in S. epidermidis PJIs, but that other microbe-related factors are probably also important.

Lower activation of caspase-1 by Staphylococcus epidermidis isolated from prosthetic joint infections compared to commensals

Nosocomial sequence types of Staphylococcus epidermidis dominate in prosthetic joint infections. We examined caspase-1 activation in human neutrophils after incubation with Staphylococcus epidermidis isolated from prosthetic joint infections and normal skin flora. Active caspase-1 was lower after incubation with isolates from prosthetic joint infections than after incubation with commensal isolates. Both host and isolate dependent differences in active caspase-1 were noted. Our results indicate that there might be a host-dependent incapacity to elicit a strong caspase-1 response towards certain strains of S. epidermidis. Further experiments with a larger number of individuals are warranted.

Cutibacterium (formerly Propionibacterium) acnes infections associated with implantable devices

INTRODUCTION

Cutibacterium acnes (C. acnes), a Gram-positive biofilm-forming rod implicated in acne vulgaris, is increasingly recognized for its role in implant-associated infections. The diagnosis of C. acnes implant-associated infections remains challenging. The optimal treatment is a combination of both surgical intervention and antibiotic therapy. Areas covered: In this review, we discuss the different types of implant-associated infections caused by C. acnes. We also highlight the clinical manifestations pertaining to the various sites of infection, and identify several risk factors previously reported in the literature. We then cover the diagnostic laboratory markers, such as IL-6 and AD-1, optimizing C. acnes recovery in culture, and the specific molecular techniques. Finally, we examine the various effective antibiotic regimens and identify some preventive methods against C. acnes infections. Expert commentary: Biomarkers such as IL-6 and AD-1 should be further investigated for the diagnosis of C. acnes implant-associated infections. The use of 16S rRNA gene sequencing and other molecular techniques should be further explored in this setting. Longer incubation periods should be requested whenever C. acnes infection is suspected. If the clinical suspicion is high, sonication of the excised implant should be encouraged. Research should focus on developing effective anti-biofilm agents. Finally, preventive methods such as hair removal prior to surgery should be further explored.

Comparative effects of schisandrin A, B, and C on Propionibacterium acnes-induced, NLRP3 inflammasome activation-mediated IL-1β secretion and pyroptosis

Propionibacterium acnes, a common pathogen associated with acne, is also responsible for various surgical infections. Schisandrin A, schisandrin B and schisandrin C, the representative lignans of Schisandra chinensis (Turcz.) Baill. extract, inhibit P. acnes-induced inflammation. However, their effects on P. acnes-induced IL-1β secretion and pyroptosis mediated by NLRP3 inflammasome activation remain unknown. In this study, we compared the effects of schisandrin A, B, and C (Sch A, B, and C) on IL-1β secretion and pyroptosis in P. acnes-infected THP-1 cells. As NLRP3 plays important roles in P. acnes-mediated inflammation and pyroptosis, we also investigated the effects of Schs on P. acnes-induced NLRP3 inflammasome activation by measuring the levels of NLRP3, active caspase-1, and mature IL-1β, and activity of caspase-1. Our results showed that Sch A, B, and C suppressed P. acnes-induced pyroptosis. Further, the three lignans significantly suppressed NLRP3 inflammasome activation, with the following potency: Sch C > Sch B > Sch A. Three lignans also inhibited the production of mitochondrial ROS and ATP release. Additionally, Sch B and C almost completely prevented the efflux of K^+., whereas Sch A had a relatively weak effect. Collectively, our novel findings showed that Sch A, B, and C effectively suppressed IL-1β secretion and pyroptosis by inhibiting NLRP3 inflammasome activation in P. acnes-infected THP-1 cells. Thus, Schs may be promising agents for the treatment of P. acnes-related infections.

What's new in the physiopathology of acne?

There are four central factors that contribute to acne physiopathology: the inflammatory response, colonization with Propionibacterium acnes, increased sebum production and hypercornification of the pilosebaceous duct. In addition, research in the areas of diet and nutrition, genetics and oxidative stress is also yielding some interesting insights into the development of acne. In this paper we review some of the most recent research and novel concepts revealed in this work, which has been published by researchers from diverse academic disciplines including dermatology, immunology, microbiology and endocrinology. We discuss the implications of their findings (particularly in terms of opportunities to develop new therapies), highlight interrelationships between these novel factors that could contribute to the pathology of acne, and indicate where gaps in our understanding still exist.

Modulation of Th1/Th2 immune responses by killed Propionibacterium acnes and its soluble polysaccharide fraction in a type I hypersensitivity murine model: induction of different activation status of antigen-presenting cells

Propionibacterium acnes (P. acnes) is a gram-positive anaerobic bacillus present in normal human skin microbiota, which exerts important immunomodulatory effects, when used as heat- or phenol-killed suspensions. We previously demonstrated that heat-killed P. acnes or its soluble polysaccharide (PS), extracted from the bacterium cell wall, suppressed or potentiated the Th2 response to ovalbumin (OVA) in an immediate hypersensitivity model, depending on the treatment protocol. Herein, we investigated the mechanisms responsible for these effects, using the same model and focusing on the activation status of antigen-presenting cells (APCs). We verified that higher numbers of APCs expressing costimulatory molecules and higher expression levels of these molecules are probably related to potentiation of the Th2 response to OVA induced by P. acnes or PS, while higher expression of toll-like receptors (TLRs) seems to be related to Th2 suppression. In vitro cytokines production in cocultures of dendritic cells and T lymphocytes indicated that P. acnes and PS seem to perform their effects by acting directly on APCs. Our data suggest that P. acnes and PS directly act on APCs, modulating the expression of costimulatory molecules and TLRs, and these differently activated APCs drive distinct T helper patterns to OVA in our model.

Proteome analysis of human sebaceous follicle infundibula extracted from healthy and acne-affected skin

Acne vulgaris is a very common disease of the pilosebaceous unit of the human skin. The pathological processes of acne are not fully understood. To gain further insight sebaceous follicular casts were extracted from 18 healthy and 20 acne-affected individuals by cyanoacrylate-gel biopsies and further processed for mass spectrometry analysis, aiming at a proteomic analysis of the sebaceous follicular casts. Human as well as bacterial proteins were identified. Human proteins enriched in acne and normal samples were detected, respectively. Normal follicular casts are enriched in proteins such as prohibitins and peroxiredoxins which are involved in the protection from various stresses, including reactive oxygen species. By contrast, follicular casts extracted from acne-affected skin contained proteins involved in inflammation, wound healing and tissue remodeling. Among the most distinguishing proteins were myeloperoxidase, lactotransferrin, neutrophil elastase inhibitor and surprisingly, vimentin. The most significant biological process among all acne-enriched proteins was ‘response to a bacterium’. Identified bacterial proteins were exclusively from Propionibacterium acnes. The most abundant P. acnes proteins were surface-exposed dermatan sulphate adhesins, CAMP factors, and a so far uncharacterized lipase in follicular casts extracted from normal as well as acne-affected skin. This is a first proteomic study that identified human proteins together with proteins of the skin microbiota in sebaceous follicular casts.

Novel pharmacological approaches for the treatment of acne vulgaris

INTRODUCTION

Acne vulgaris is the most common skin disease worldwide; yet, current treatment options, although effective, are associated with unwanted side effects, chronicity, relapses and recurrences. The adequate control of the four pathogenic mechanisms, involved in the appearance of acne lesions, is paramount to treatment success.

AREAS COVERED

The authors discuss and evaluate the pathogenic pathways related to the mechanisms of action of novel molecules, which are currently under investigation for the treatment of acne vulgaris. The manuscript is based on comprehensive searches made through PubMed, GoogleScholar and ClinicalTrial.gov, using different combination of key words, which include acne vulgaris, pathogenesis, treatment, sebogenesis and Propionibacterium acnes.

EXPERT OPINION

In the near future, more effective treatments with fewer side effects are expected. The use of topical antiandrogens, acetylcholine inhibitors and PPAR modulators seem to be promising options for controlling sebum production. Retinoic acid metabolism-blocking agents and IL-1α inhibitors have the potential to become legitimate alternative options to retinoid therapy in the management of infundibular dyskeratosis. Indeed, the authors believe that there will likely be a decline in the use of antibiotics for controlling P. acnes colonization and targeting the inflammation cascade.

Autoinflammatory bone disorders: update on immunologic abnormalities and clues about possible triggers

PURPOSE OF REVIEW

To provide an update on the genetics and immunologic basis of autoinflammatory bone disorders including chronic recurrent multifocal osteomyelitis including the monogenic forms of the disease.

RECENT FINDINGS

Ongoing research in murine, canine and human models of sterile bone inflammation has solidified the hypothesis that sterile bone inflammation can be genetically driven. Mutations in Pstpip2, LPIN2 and IL1RN have been identified in monogenic autoinflammatory bone disorders that have allowed more detailed dissection of the immunologic defects that can produce sterile osteomyelitis. Recent studies in murine chronic multifocal osteomyelitis, deficiency of the interleukin-1 receptor antagonist (DIRA), Majeed syndrome and SAPHO syndrome reveal abnormalities in innate immune system function. IL-1 pathway dysregulation is present in several of these disorders and blocking IL-1 therapeutically has resulted in control of disease in DIRA, Majeed syndrome and in some cases of SAPHO and CRMO. Basic research demonstrates the importance of the innate immune system in disease pathogenesis and offers clues about potential disease triggers.

SUMMARY

Research and clinical data produced over the last several years support the important role of innate immunity in sterile osteomyelitis. Based on what has been learned in the monogenic autoinflammatory bone disorders, IL-1 is emerging as an important pathway in the development of sterile bone inflammation.

Propionibacterium acnes: an update on its role in the pathogenesis of acne

In recent years, significant progress has been made in the understanding of the pathophysiological mechanisms of acne and the role of Propionibacterium acnes. With this review, the authors aim to provide an update on the current understanding of the role of P. acnes in the development of acne lesions and analysing the potential implications for future treatments. A total of 188 articles published between January 1980 and March 2013 were searched using key words such as acne, P. acnes, microbiology, Corynebacterium acnes, acne vulgaris, pathogenesis, antibiotic, vaccination and a combination of those key words. From those articles, 77 were analysed in depth. Recent data confirm that P. acnes has a strong proinflammatory activity and targets molecules involved in the innate cutaneous immunity, keratinocytes and sebaceous glands of the pilosebaceous follicle and leads to the development of comedones. Furthermore, the profile of its different strains may differ between healthy subjects and acne patients. The better understanding of the role of P. acnes may allow for new perspectives in the treatment of acne. Novel therapies should target molecules implicated in the activation of innate immunity, including toll-like receptors, protease-activated receptors and topical antimicrobial peptides; the latter may be an alternative to topical antibiotics and thus a solution for limiting bacterial resistance induced by topical macrolides. Vaccines may also be promising. However, the most appropriate candidate remains to be selected.

Role of inflammasomes and their regulators in prostate cancer initiation, progression and metastasis

Prostate cancer is one of the main cancers that affect men, especially older men. Though there has been considerable progress in understanding the progression of prostate cancer, the drivers of its development need to be studied more comprehensively. The emergence of resistant forms has also increased the clinical challenges involved in the treatment of prostate cancer. Recent evidence has suggested that inflammation might play an important role at various stages of cancer development. This review focuses on inflammasome research that is relevant to prostate cancer and indicates future avenues of study into its effective prevention and treatment through inflammasome regulation. With regard to prostate cancer, such research is still in its early stages. Further study is certainly necessary to gain a broader understanding of prostate cancer development and to create successful therapy solutions.