Altered skin microbiome, inflammation, and JAK/STAT signaling in Southeast Asian ichthyosis patients.

BACKGROUND: Congenital ichthyosis (CI) is a collective group of rare hereditary skin disorders. Patients present with epidermal scaling, fissuring, chronic inflammation, and increased susceptibility to infections. Recently, there is increased interest in the skin microbiome; therefore, we hypothesized that CI patients likely exhibit an abnormal profile of epidermal microbes because of their various underlying skin barrier defects. Among recruited individuals of Southeast Asian ethnicity, we performed skin meta-genomics (i.e., whole-exome sequencing to capture the entire multi-kingdom profile, including fungi, protists, archaea, bacteria, and viruses), comparing 36 CI patients (representing seven subtypes) with that of 15 CI age-and gender-matched controls who had no family history of CI. RESULTS: This case-control study revealed 20 novel and 31 recurrent pathogenic variants. Microbiome meta-analysis showed distinct microbial populations, decreases in commensal microbiota, and higher colonization by pathogenic species associated with CI; these were correlated with increased production of inflammatory cytokines and Th17- and JAK/STAT-signaling pathways in peripheral blood mononuclear cells. In the wounds of CI patients, we identified specific changes in microbiota and alterations in inflammatory pathways, which are likely responsible for impaired wound healing. CONCLUSIONS: Together, this research enhances our understanding of the microbiological, immunological, and molecular properties of CI and should provide critical information for improving therapeutic management of CI patients.

Sarecycline inhibits protein translation in Cutibacterium acnes 70S ribosome using a two-site mechanism.

Acne vulgaris is a chronic disfiguring skin disease affecting ∼1 billion people worldwide, often having persistent negative effects on physical and mental health. The Gram-positive anaerobe, Cutibacterium acnes is implicated in acne pathogenesis and is, therefore, a main target for antibiotic-based acne therapy. We determined a 2.8-Šresolution structure of the 70S ribosome of Cutibacterium acnes by cryogenic electron microscopy and discovered that sarecycline, a narrow-spectrum antibiotic against Cutibacterium acnes, may inhibit two active sites of this bacterium's ribosome in contrast to the one site detected previously on the model ribosome of Thermus thermophilus. Apart from the canonical binding site at the mRNA decoding center, the second binding site for sarecycline exists at the nascent peptide exit tunnel, reminiscent of the macrolides class of antibiotics. The structure also revealed Cutibacterium acnes-specific features of the ribosomal RNA and proteins. Unlike the ribosome of the Gram-negative bacterium Escherichia coli, Cutibacterium acnes ribosome has two additional proteins, bS22 and bL37, which are also present in the ribosomes of Mycobacterium smegmatis and Mycobacterium tuberculosis. We show that bS22 and bL37 have antimicrobial properties and may be involved in maintaining the healthy homeostasis of the human skin microbiome.

Alterations in the Skin Microbiome in Dermatologic Diseases and with External Exposures: CME Part 2.

In Part I of our CME we reviewed the skin microbiome in healthy individuals. Part II reviews the evolving understanding of alterations in the skin microbiome in specific human diseases. We also discuss how the skin microbiome can change with environmental exposures and medications such as antibiotics as well as ongoing research on microbiome-based interventions.

The Human Skin Microbiome in Health: CME Part 1.

Human skin is home to a myriad of microorganisms, including bacteria, viruses, fungi, and mites, many of which are considered commensal microbes that aid in maintaining the overall homeostasis or steady-state condition of the skin and contribute to skin health. Our understanding of the complexities of the skin's interaction with its microorganisms is evolving. This knowledge is based primarily on in vitro and animal studies, and more work is needed to understand how this knowledge relates to humans. Here, we introduce the concept of the skin microbiome and discuss skin microbial ecology, some intrinsic factors with potential influence on the human skin microbiome, and possible microbiome-host interactions. The second article of this two-part CME series describes how microbiome alterations may be associated with skin disease, how medications can affect the microbiome, and what microbiome-based therapies are under investigation.

Rapid Remission of Plaque Psoriasis With Bimekizumab Treatment.

Bimekizumab is a novel humanized bispecific monoclonal immunoglobulin G1 (IgG1) antibody that dually inhibits both IL-17A and IL-17F. Investigation of the pivotal role of IL-17A, and more recently, IL-17F, in the pathogenesis of psoriasis has underscored the utility of biologics targeting these cytokines in the treatment of the disease. Treatments include the anti-IL-17 biologics specifically targeted against IL-17A (secukinumab and ixekizumab) or its receptor (brodalumab). Recent clinical trials proved the efficacy and safety of bimekizumab in the treatment of moderate-to-severe plaque psoriasis and even showed it to be superior to other psoriasis biologic treatments in regards to efficacy and rapidity of response. These are important factors to consider when discussing treatment options with patients as psoriasis patients commonly desire fast-acting results. In this case, we describe clearance of moderate-to-severe plaque psoriasis within 72 hours of treatment with bimekizumab, one of the fastest reported clearance times in the medical literature. J Drugs Dermatol. 2024;23(8):694-696. doi:10.36849/JDD.8381.

Topical Clindamycin in the Management of Acne Vulgaris: Current Perspectives and Recent Therapeutic Advances.

Clindamycin is a lincosamide-derivate antibiotic that has been widely used both systemically and topically for approximately 5 decades. The antimicrobial profile of clindamycin primarily covers several gram-positive bacteria and anaerobic bacteria, with multiple clinical applications supported in the literature and with widespread real-world use. Topical clindamycin has been used primarily for the treatment of acne vulgaris, with both monotherapy and combination therapy formulations available commercially. This article reviews the use of clindamycin as a topical agent with emphasis on therapy for acne vulgaris, and addresses modes of action, reported anti-inflammatory properties that may relate to therapeutic outcomes, recommendations to avoid the emergence of antibiotic-resistant bacteria, tolerability and safety considerations, and published data from clinical studies completed over a span of several years. A discussion of a newly FDA-approved triple-combination formulation is also included.  J Drugs Dermatol. 2024;23(6):438-445.     doi:10.36849/JDD.8318.

Human keratin 1/10-1B tetramer structures reveal a knob-pocket mechanism in intermediate filament assembly.

To characterize keratin intermediate filament assembly mechanisms at atomic resolution, we determined the crystal structure of wild-type human keratin-1/keratin-10 helix 1B heterotetramer at 3.0 Å resolution. It revealed biochemical determinants for the A11 mode of axial alignment in keratin filaments. Four regions on a hydrophobic face of the K1/K10-1B heterodimer dictated tetramer assembly: the N-terminal hydrophobic pocket (defined by L227K1, Y230K1, F231K1, and F234K1), the K10 hydrophobic stripe, K1 interaction residues, and the C-terminal anchoring knob (formed by F314K1 and L318K1). Mutation of both knob residues to alanine disrupted keratin 1B tetramer and full-length filament assembly. Individual knob residue mutant F314AK1, but not L318AK1, abolished 1B tetramer formation. The K1-1B knob/pocket mechanism is conserved across keratins and many non-keratin intermediate filaments. To demonstrate how pathogenic mutations cause skin disease by altering filament assembly, we additionally determined the 2.39 Å structure of K1/10-1B containing a S233LK1 mutation linked to epidermolytic palmoplantar keratoderma. Light scattering and circular dichroism measurements demonstrated enhanced aggregation of K1S233L/K10-1B in solution without affecting secondary structure. The K1S233L/K10-1B octamer structure revealed S233LK1 causes aberrant hydrophobic interactions between 1B tetramers.

Update of the keratin gene family: evolution, tissue-specific expression patterns, and relevance to clinical disorders.

Intermediate filament (IntFil) genes arose during early metazoan evolution, to provide mechanical support for plasma membranes contacting/interacting with other cells and the extracellular matrix. Keratin genes comprise the largest subset of IntFil genes. Whereas the first keratin gene appeared in sponge, and three genes in arthropods, more rapid increases in keratin genes occurred in lungfish and amphibian genomes, concomitant with land animal-sea animal divergence (~ 440 to 410 million years ago). Human, mouse and zebrafish genomes contain 18, 17 and 24 non-keratin IntFil genes, respectively. Human has 27 of 28 type I "acidic" keratin genes clustered at chromosome (Chr) 17q21.2, and all 26 type II "basic" keratin genes clustered at Chr 12q13.13. Mouse has 27 of 28 type I keratin genes clustered on Chr 11, and all 26 type II clustered on Chr 15. Zebrafish has 18 type I keratin genes scattered on five chromosomes, and 3 type II keratin genes on two chromosomes. Types I and II keratin clusters-reflecting evolutionary blooms of keratin genes along one chromosomal segment-are found in all land animal genomes examined, but not fishes; such rapid gene expansions likely reflect sudden requirements for many novel paralogous proteins having divergent functions to enhance species survival following sea-to-land transition. Using data from the Genotype-Tissue Expression (GTEx) project, tissue-specific keratin expression throughout the human body was reconstructed. Clustering of gene expression patterns revealed similarities in tissue-specific expression patterns for previously described "keratin pairs" (i.e., KRT1/KRT10, KRT8/KRT18, KRT5/KRT14, KRT6/KRT16 and KRT6/KRT17 proteins). The ClinVar database currently lists 26 human disease-causing variants within the various domains of keratin proteins.

Phase IIb randomized CONTROL study demonstrates a novel topical isotretinoin formulation, TMB-001, is safe and effective in participants with either recessive X-linked or autosomal recessive lamellar congenital ichthyosis.

BACKGROUND: In two severe congenital ichthyosis subtypes, autosomal recessive lamellar ichthyosis (ARCI-LI) and X-linked recessive ichthyosis (XLRI), cutaneous manifestations include widespread scaling. Approved topical treatment options are limited to emollients and keratolytics. AIM: This analysis from the randomized phase IIb CONTROL study assessed whether the efficacy and safety of TMB-001, a novel topical isotretinoin ointment formulation, differed between ARCI-LI and XLRI subtypes. METHODS: Participants ≥ 9 years with genetically confirmed XLRI or ARCI-LI and ≥ 2 (of 4) Visual Index for Ichthyosis Severity (VIIS) assessment areas with ≥ 3 scaling score were randomized 1 : 1 : 1 to TMB-001 0.05%/TMB-001 0.1%/vehicle, twice daily for 12 weeks. The proportion of participants with ≥ 50% reduction vs. baseline in VIIS scaling (VIIS 50; primary endpoint) and ≥ 2-grade reduction in Investigator's Global Assessment (IGA)-scaling score vs. baseline (key secondary endpoint) were evaluated. Adverse events (AEs) were monitored. RESULTS: Among enrolled participants (TMB-001 0.05%, n = 11; 0.1%, n = 10; and vehicle, n = 12), 52% had ARCI-LI and 48% XLRI subtypes. Mean age was 33.6 and 35.4 years for participants with ARCI-LI and XLRI, respectively. Overall, 33%, 50% and 17% of participants with ARCI-LI and 100%, 33% and 75% of participants with XLRI achieved VIIS 50 in the TMB-001 0.05%, TMB-001 0.1% and vehicle groups, respectively (nominal P = 0.24 for 0.05% vs. vehicle, intent-to-treat population). Improvement of ≥ 2-grade IGA score was observed in 33%, 50% and 0% of participants with ARCI-LI and 83%, 33% and 25% of participants with XLRI in the TMB-001 0.05%, TMB-001 0.1% and vehicle groups, respectively (nominal P = 0.03 for 0.05% vs. vehicle, intention-to-treat population). Most AEs were application-site reactions. CONCLUSION: Regardless of congenital ichthyosis subtype, TMB-001 demonstrated greater proportions of participants achieving VIIS 50 and ≥ 2-grade IGA improvement vs. vehicle.

Characteristics and outcomes for participants with congenital ichthyosis who responded to treatment with the topical isotretinoin formulation TMB-001: results from the Phase IIb CONTROL study.

BACKGROUND: Emollients and keratolytics are frequently used to manage symptoms of congenital ichthyosis (CI). Systemic retinoid treatment is complicated by teratogenicity and dose-limiting adverse effects. OBJECTIVES: This analysis from the randomized Phase IIb CONTROL study investigated the characteristics of participants who responded to treatment with TMB-001, a novel topical isotretinoin ointment formulation. METHODS: Participants ≥ 9 years of age with genetically confirmed CI and ≥ 2 (out of 4) Visual Index for Ichthyosis Severity (VIIS) assessment areas with ≥ 3 scaling score were randomized 1 : 1 : 1 to TMB-001 0.05%, TMB-001 0.1% or vehicle, twice daily for 12 weeks. Efficacy endpoints included the proportion of participants with ≥ 50% reduction in VIIS-scaling (VIIS-50) compared with baseline and ≥ 2-grade reduction in Investigator's Global Assessment (IGA)-scaling score compared with baseline. Changes in body surface area (BSA) involvement, Dermatology Life Quality Index (DLQI) scores and Itch-Numeric Rating Scale (I-NRS) scores were assessed. RESULTS: Among the 33 participants (11 randomized to TMB-001 0.05%, 10 to TMB-001 0.1% and 12 to vehicle), median age was 29 years (range 9-80), and most were male (64%) and White (79%). Baseline demographics were generally similar among participants who did or did not achieve TMB-001 treatment success. Participants who had lower mean BSA involvement and higher DLQI and I-NRS scores at baseline were more likely to achieve VIIS-50. Similarly, higher baseline DLQI and I-NRS scores were associated with IGA response; BSA involvement was similar for IGA responders vs. nonresponders. CONCLUSIONS: Higher DLQI and I-NRS scores at baseline were associated with participants achieving treatment success by VIIS-50 and IGA response. Lower BSA involvement was associated with VIIS-50 success.

Ensuring Dermatologists Practice Enhanced Antibiotic Stewardship With Sarecycline Mnemonic.

It must be ensured that dermatologists practice enhanced antibiotic stewardship to combat antimicrobial resistance and negative consequences of microbiome dysbiosis. In order to help achieve this, we have developed a mnemonic ENLIGHTEN to help healthcare providers and patients understand sarecycline’s features.J Drugs Dermatol. 2023;22(10):1061 doi:10.36849/JDD.7437R1.

Sarecycline interferes with tRNA accommodation and tethers mRNA to the 70S ribosome.

Sarecycline is a new narrow-spectrum tetracycline-class antibiotic approved for the treatment of acne vulgaris. Tetracyclines share a common four-ring naphthacene core and inhibit protein synthesis by interacting with the 70S bacterial ribosome. Sarecycline is distinguished chemically from other tetracyclines because it has a 7-[[methoxy(methyl)amino]methyl] group attached at the C7 position of ring D. To investigate the functional role of this C7 moiety, we determined the X-ray crystal structure of sarecycline bound to the Thermus thermophilus 70S ribosome. Our 2.8-Å resolution structure revealed that sarecycline binds at the canonical tetracycline binding site located in the decoding center of the small ribosomal subunit. Importantly, unlike other tetracyclines, the unique C7 extension of sarecycline extends into the messenger RNA (mRNA) channel to form a direct interaction with the A-site codon to possibly interfere with mRNA movement through the channel and/or disrupt A-site codon-anticodon interaction. Based on our biochemical studies, sarecycline appears to be a more potent initiation inhibitor compared to other tetracyclines, possibly due to drug interactions with the mRNA, thereby blocking accommodation of the first aminoacyl transfer RNA (tRNA) into the A site. Overall, our structural and biochemical findings rationalize the role of the unique C7 moiety of sarecycline in antibiotic action.

Sarecycline treatment for acne vulgaris: Rationale for weight-based dosing and limited impact of food intake on clinical efficacy.

Tetracycline-class antibiotics are frequently prescribed by dermatologists, commonly for acne vulgaris. Gastrointestinal absorption of first and second-generation tetracycline-class antibiotics, including doxycycline and minocycline, may be reduced by co-administration with food, resulting in potentially lower clinical efficacy. Development of novel compounds and formulations that are not impacted by diet could improve compliance, absorption, and effectiveness among patients. The objective of this study is to investigate weight-based dosing protocols and the impact of food intake, including high-fat meals, on the absorption, and clinical efficacy of sarecycline, a novel oral narrow-spectrum third-generation tetracycline-class antibiotic approved by the Food and Drug Administration for acne vulgaris treatment. Data from 12 clinical studies were analyzed using population pharmacokinetic modeling, exposure-response modeling and pharmacodynamics to evaluate sarecycline dosing recommendations. The extent of exposure is estimated to decrease by 21.7% following co-administration of a sarecycline tablet with a high-fat meal. Based on the PopPK-PD model, this is equivalent to a decrease in efficacy of 0.9 inflammatory lesions, which is not clinically meaningful. Sarecycline can be administered using weight-based dosing with or without food. Co-administration with high-fat food has a limited impact on clinical efficacy. The pharmacokinetics of oral sarecycline may provide added convenience and support ease of use and improved compliance for acne vulgaris patients.

Molecular Modeling of Pathogenic Mutations in the Keratin 1B Domain.

Keratin intermediate filaments constitute the primary cytoskeletal component of epithelial cells. Numerous human disease phenotypes related to keratin mutation remain mechanistically elusive. Our recent crystal structures of the helix 1B heterotetramer from keratin 1/10 enabled further investigation of the effect of pathologic 1B domain mutations on keratin structure. We used our highest resolution keratin 1B structure as a template for homology-modeling the 1B heterotetramers of keratin 5/14 (associated with blistering skin disorders), keratin 8/18 (associated with liver disease), and keratin 74/28 (associated with hair disorder). Each structure was examined for the molecular alterations caused by incorporating pathogenic 1B keratin mutations. Structural modeling indicated keratin 1B mutations can harm the heterodimer interface (R265PK5, L311RK5, R211PK14, I150VK18), the tetramer interface (F231LK1, F274SK74), or higher-order interactions needed for mature filament formation (S233LK1, L311RK5, Q169EK8, H128LK18). The biochemical changes included altered hydrophobic and electrostatic interactions, and altered surface charge, hydrophobicity or contour. Together, these findings advance the genotype-structurotype-phenotype correlation for keratin-based human diseases.

Structural Basis for How Biologic Medicines Bind their Targets in Psoriasis Therapy.

As biologic therapies become first line treatments for many inflammatory disorders, it becomes increasingly important for the practicing physician to be familiar with how these drugs function at the molecular level. This information is useful in making therapeutic decisions and helping patients understand their treatment options. It is critical to patient safety and clinical response that the molecular differences between these drugs inform prescribing practices. To this end, we present and analyze the available structural biology information about the biologics used in the treatment of psoriasis including inhibitors of tumor necrosis factor alpha (TNFα), interleukin-17 (IL-17), and interleukin-23 (IL-23). We describe and analyze the molecular surface character of known binding epitopes for medications in these classes, showing that significant differences exist in epitope location, hydrophobicity, and charge. Some of these differences can be correlated with clinical data, but our analysis ultimately points to the need for more structural information to allow for a better understanding of the structure-function relationship of biologic therapies.

Crystal Structure of Keratin 1/10(C401A) 2B Heterodimer Demonstrates a Proclivity for the C-Terminus of Helix 2B to Form Higher Order Molecular Contacts.

We previously determined the crystal structure of the wild-type keratin 1/10 helix 2B heterodimer at 3.3 Å resolution. We proposed that the resolution of the diffraction data was limited due to the crystal packing effect from keratin 10 (K10) residue Cys401. Cys401K10 formed a disulfide-linkage with Cys401 from another K1/10 heterodimer, creating an "X-shaped" structure and a loose crystal packing arrangement. We hypothesized that mutation of Cys401K10 to alanine would eliminate the disulfide-linkage and improve crystal packing thereby increasing resolution of diffraction and enabling a more accurate side chain electron density map. Indeed, when a K10 Cys401Ala 2B mutant was paired with its native keratin 1 (K1) 2B heterodimer partner its x-ray crystal structure was determined at 2.07 Å resolution; the structure does not contain a disulfide linkage. Superposition of the K1/K10(Cys401Ala) 2B structure onto the wild-type K1/10 2B heterodimer structure had a root-mean-square-deviation of 1.88 Å; the variability in the atomic positions reflects the dynamic motion expected in this filamentous coiled-coil complex. The electrostatic, hydrophobic, and contour features of the molecular surface are similar to the lower resolution wild-type structure. We postulated that elimination of the disulfide linkage in the K1/K10(Cys401Ala) 2B structure could allow for the 2B heterodimers to bind/pack in the A22 tetramer configuration associated with mature keratin intermediate filament assembly. Analysis of the crystal packing revealed a half-staggered anti-parallel tetrameric complex of 2B heterodimers; however, their register is not consistent with models of the A22 mode of tetrameric alignment or prior biochemical cross-linking studies.

More than keratitis, ichthyosis, and deafness: Multisystem effects of lethal GJB2 mutations.

BACKGROUND: Infant death in keratitis-ichthyosis-deafness (KID) syndrome is recognized; its association with specific genotypes and pathophysiology is inadequately understood. OBJECTIVE: We sought to discover characteristics that account for poor outcomes in lethal KID syndrome. METHODS: We collected 4 new cases and 9 previously reported, genotyped cases of lethal KID syndrome. We performed new molecular modeling of the lethal mutants GJB2 p.A88V and GJB2 p.G45E. RESULTS: Infant death occurred in all patients with GJB2 p.G45E and p.A88V; it is unusual with other GJB2 mutations. Early death with those 2 "lethal" mutations is likely multifactorial: during life all had ≥1 serious infection; most had poor weight gain and severe respiratory difficulties; many had additional anatomic abnormalities. Structural modeling of GJB2 p.G45E identified no impact on the salt bridge previously predicted to account for abnormal central carbon dioxide sensing of GJB2 p.A88V. LIMITATIONS: This clinical review was retrospective. CONCLUSION: GJB2 p.G45E and p.A88V are the only KID syndrome mutations associated with uniform early lethality. Those electrophysiologically severe mutations in GJB2 reveal abnormalities in many organs in lethal KID syndrome. All patients with KID syndrome may have subtle abnormalities beyond the eyes, ears, and skin. Early genotyping of KID syndrome births will inform prognostic discussion.