Dimethyl fumarate ameliorates fungal keratitis by limiting fungal growth and inhibiting pyroptosis

The therapeutic effect and mechanism of carnosic acid in Aspergillus fumigatus keratitis

Fungal keratitis is a vision-threatening corneal infectious disease. However, clinically therapeutic medicines cannot attain ideal efficacy due to limited control of fungal virulence and excessive inflammatory response. Carnosic acid (CA) is a phenolic diterpene, which has been reported to have multiple abilities including antibacterial, anti-inflammatory and antioxidant. The therapeutic efficacy and potential mechanism of CA in fungal keratitis remain unknown. This study aimed to confirm the therapeutic role and potential mechanism of CA in Aspergillus fumigatus (A. fumigatus)-caused keratitis. In this study, we demonstrated that CA markedly suppressed the growth of A. fumigatus hyphae, the generation of biofilms and the integrity of the hyphal membrane. A. fumigatus-related genes (RodA, RodB, FKs, Rho1, CshA-C and Cyp51A-B) levels were suppressed under CA treatment. CA at 5 μg/mL and 10 μg/mL obviously promoted cell proliferation. In A. fumigatus-infected mice cornea, CA relieved the severity of corneal impairment, inhibited neutrophil recruitment and fungal load. Compared with inactivated hyphae, CA down-regulated the mRNA and protein levels of inflammatory cytokines, Dectin-1, NLRP3, cleaved caspase-1, IL-18 and IL-1β. Moreover, Curdlan (a specific agonist of Dectin-1) stimulation could promote the expression of NLRP3, cleaved caspase-1, IL-18 and IL-1β, which could be down-regulated by CA treatment. In conclusion, CA displays antifungal function on A. fumigatus. CA ameliorates the prognosis of keratomycosis by suppressing inflammatory cytokines production, which is regulated by Dectin-1 and pyroptosis.

Piperine inhibits fungal growth and protects against pyroptosis in Aspergillus fumigatus keratitis by regulating the mTOR/HIF-1α pathway

PURPOSE

To confirm the antifungal ability of piperine (PIP) and to assess its therapeutic potential in the treatment of Aspergillus fumigatus (A. fumigatus) keratitis.

METHODS

The toxicity of PIP was measured to determine the optimal therapeutic concentration both in human corneal epithelial cells (HCECs), RAW264.7 cells and mice fungal keratitis models. The antifungal efficacy of PIP was confirmed through the minimum inhibitory concentration (MIC) test, biofilm formation inhibition test, Calcofluor white and PI staining, and anti-adhesion of A. fumigatus conidia test. Hematoxylin-eosin (HE) staining, corneal fungal load assay, RT-qPCR, western blot, and Elisa were used to assess the therapeutic effect and anti-inflammatory ability of PIP in fungal keratitis. The significance of the mTOR/HIF-1α signal pathway after PIP treatment of A. fumigatus keratitis was evaluated.

RESULTS

PIP had no obvious toxicity to HCECs, RAW 264.7 cells, or mouse cornea at the concentration of 30 µg/mL. PIP effectively inhibited A. fumigatus from growing and showed synergistic effects when combined with NATA. PIP not only reduced fungal load and the aggregation of inflammatory cells, but also dramatically reduced the expression levels of NLRP3, caspase-1, cleaved caspase-1, GSDMD, GSDMD-N, IL-18, and IL-1β, which were linked to pyroptosis. Additionally, PIP decreased mTOR phosphorylation and HIF-1α expression. The pretreatment with mTOR agonists reversed the inhibition of NLRP3, caspase-1, cleaved caspase-1, GSDMD, GSDMD-N, IL-18, and IL-1β protein levels caused by PIP.

CONCLUSION

PIP exhibited antifungal and anti-inflammatory properties, and alleviated pyroptosis in A. fumigatus keratitis via inhibiting the mTOR/HIF-1α signaling pathway.

Hydroxytyrosol downregulates inflammatory responses via Nrf2/HO-1 axis during fungal keratitis and exerts antifungal effects

PURPOSE

This study aims to explore the protective effect and underlying mechanism of hydroxytyrosol (HT) in fungal keratitis.

METHODS

Mouse models with Aspergillus fumigatus (A. fumigatus) keratitis, human corneal epithelial cells (HCECs) and RAW 264.7 cells were used in this study. Methods employed included MIC assay, biofilm formation test, hyphal immunofluorescence staining and adhesion test to assess the antifungal activity of HT. The severity of keratitis was evaluated using slit-lamp examination and HE staining. Draize eye test was used to measure corneal tolerance to HT. Corneal macrophages were detected by immunofluorescence staining. Reactive oxygen species (ROS) production in cytoplasm was quantified using DCFH-DA. Mitochondrial membrane potential was detected by JC-1. RT-PCR, ELISA and western blot were used to measure the expression of cytokines, as well as Nrf2 and HO-1 levels.

RESULTS

HT inhibited A. fumigatus growth, biofilm formation and conidial adhesion, and downregulated the expression of genes related to cell-wall assembly and morphogenesis. In fungal keratitis mouse models, HT significantly alleviated corneal inflammation, decreased the expression of cytokines and the accumulation of macrophages. In vitro, HT attenuated A. fumigatus-induced cytokine overexpression in HCECs or RAW 264.7 cells, and this effect was counteracted by an Nrf2 inhibitor. In RAW 264.7 cells stimulated with A. fumigatus, HT downregulated M1 markers expression, upregulated M2 markers expression, reduced ROS production, and restored mitochondrial membrane potential. Notably, these effects of HT were negated by pretreatment with an Nrf2 inhibitor.

CONCLUSIONS

This study underscores HT's efficacy against A. fumigatus growth and corneal invasion, its ability to mitigate fungi-induced inflammation, and its capacity to eliminate ROS via activation of the Nrf2/HO-1 signaling pathway. These findings suggest that HT holds therapeutic promise for fungal keratitis.

Autoimmune responses to myelin-associated proteins as diagnostic and prognostic biomarkers of relapsing-remitting multiple sclerosis: Associations with human herpesvirus-6 and Epstein-Barr virus reactivation

BACKGROUND

The pathogenesis of relapsing-remitting multiple sclerosis (RRMS) is linked to autoimmune attacks against myelin proteins, and reactivation of Epstein-Barr virus (EBV) and human herpesvirus 6 (HHV-6). However, the connection between viral reactivation and autoimmune biomarkers has remained unclear.

OBJECTIVES

To investigate immunoglobulin (Ig)G/IgA/IgM responses targeting myelin-related proteins in association with EBV and HHV-6 replication markers in RRMS.

METHODS

We recruited 55 patients with RRMS and 63 healthy controls and assessed IgG/IgA/IgM responses against seven myelin-related components, as well as EBV nuclear antigen 1 (EBNA-1) and deoxyuridine-triphosphate nucleotidohydrolase (dUTPases). Disability was evaluated using the Expanded Disability Status Scale (EDSS) and disease progression using the Multiple Sclerosis Severity Score (MSSS).

RESULTS

IgG/IgA/IgM levels targeting seven myelin-related proteins were significantly higher in RRMS than in controls. IgG against myelin basic protein (MBP) (IgG-MBP), IgM-myelin-associated glycoprotein (IgM-MAG)-37-60, IgA-MBP, and IgA-myelin-oligodendrocyte-glycoprotein (IgA-MOG-31-55) distinguished RRMS from controls with a predictive accuracy of 96.6 % (sensitivity = 95.7 %, specificity = 95.2 %) and an area under the ROC curve of 0.991. A large part of the variance in the EDSS (around 75 %) and MSSS score (62.8 %) was explained by IgG-MBP, IgM-MBP, IgA-MOG-31-55, and IgM-MAG. Part of the variance (47.4 %) in the IgG/IgA/IgM responses to myelin-related proteins was explained by immune responses to EBNA and dUTPases of EBV and HHV-6.

CONCLUSIONS

Autoimmune reactivities targeting myelin-related proteins are valuable biomarkers of RRMS and the severity and progression of RRMS. Reactivation of EBV and HHV-6 may trigger or maintain these autoimmune responses thereby impacting disease progression.

Dimethyl fumarate alleviates Staphylococcus pseudintermedius-induced cell damage by inhibiting pyroptosis and bacterial virulence

The resistance of pathogenic bacteria to various clinical antibiotics is the major problem in treating bacterial keratitis. Dimethyl fumarate (DMF) has good anti-fungal and anti-inflammatory effects in fungal keratitis, but its effect on bacterial keratitis is unclear. This study aims to investigate DMF's anti-inflammatory and antibacterial effects. The pyroptosis model was constructed by intracellular infection of canine corneal epithelial cells (CCECs) with Staphylococcus pseudintermedius (S. pseudintermedius), and 200 μM DMF was added to explore its function. Western blot, ELISA, immunostaining, flow cytometry, qRT-PCR, and bacterial counts were used to examine the expression of the NLRP3-GSDMD signaling pathway, virulence genes, and oxidant mediators. 111 clinical keratitis isolates or S. pseudintermedius were treated with different concentrations of DMF to detect bacterial growth and biofilm formation. Adding DMF resulted in the inhibition of the NLRP3-GSDMD pathway while activating the NRF2 pathway. This led to a decrease in pyroptosis rate, intracellular bacteria count, and ROS content. Additionally, DMF blocked the mRNA expression of virulence genes ebpS, hlgB, siet, lukS-I, PVL, icaA, icaD, spsD, and spsL associated with S. pseudintermedius infection. Furthermore, DMF demonstrated concentration-dependent inhibition of the growth of clinical isolates and the formation of S. pseudintermedius biofilm. In conclusion, our results indicate that DMF can inhibit pyroptosis and the growth of various clinical isolates, making it a novel ophthalmic drug with anti-inflammatory and antibacterial properties.

Oriented cellulose hydrogel: Directed tissue regeneration for reducing corneal leukoplakia and managing fungal corneal ulcers

Fungal corneal ulcer is one of the leading causes of corneal blindness in developing countries. Corneal scars such as leukoplakia are formed due to inflammation, oxidative stress and non-directed repair, which seriously affect the patients' subsequent visual and life quality. In this study, drawing inspiration from the oriented structure of collagen fibers within the corneal stroma, we first proposed the directional arrangement of CuTA-CMHT hydrogel system at micro and macro scales based on the 3D printing extrusion method combined with secondary patterning. It played an antifungal role and induced oriented repair in therapy of fungal corneal ulcer. The results showed that it effectively inhibited Candida albicans, Aspergillus Niger, Fusarium sapropelum, which mainly affects TNF, NF-kappa B, and HIF-1 signaling pathways, achieving effective antifungal functions. More importantly, the fibroblasts interacted with extracellular matrix (ECM) of corneal stroma through formation of focal adhesions, promoted the proliferation and directional migration of cells in vitro, induced the directional alignment of collagen fibers and corneal stromal orthogonally oriented repair in vivo. This process is mainly associated with MYLK, MYL9, and ITGA3 molecules. Furthermore, the downregulation the growth factors TGF-β and PDGF-β inhibits myofibroblast development and reduces scar-type ECM production, thereby reducing corneal leukoplakia. It also activates the PI3K-AKT signaling pathway, promoting corneal healing. In conclusion, the oriented CuTA-CMHT hydrogel system mimics the orthogonal arrangement of collagen fibers, inhibits inflammation, eliminates reactive oxygen species, and reduces corneal leukoplakia, which is of great significance in the treatment of fungal corneal ulcer and is expected to write a new chapter in corneal tissue engineering.

Chelerythrine ameliorates Aspergillus fumigatus keratitis through suppressing the LOX-1/p38 MAPK signaling pathway

PURPOSE

Aspergillus fumigatus (A. fumigatus) keratitis is a type of infectious corneal disease that significantly impairs vision. The objective of this study is to evaluate the therapeutic potential of chelerythrine (CHE) on A. fumigatus keratitis.

METHODS

The antifungal activity of CHE was assessed through various tests including the minimum inhibitory concentration test, scanning electron microscopy, transmission electron microscopy, propidium iodide uptake test and plate count. Neutrophil infiltration and activity were assessed using immunofluorescence staining and the myeloperoxidase test. RT-PCR, western blotting assay, and ELISA were performed to measure the expression levels of proinflammatory cytokines (IL-1β and IL-6), NF-E2-related factor (Nrf2), heme oxygenase-1 (HO-1), and lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), as well as to determine the ratio of phosphorylated-p38 (p-p38) mitogen-activated protein kinase (MAPK) to p38 MAPK.

RESULTS

In vitro, CHE inhibited the growth of A. fumigatus conidia, reduced fungal hyphae survival, and prevented fungal biofilm formation. In vivo, CHE reduced the severity of A. fumigatus keratitis and exhibited an excellent anti-inflammatory effect by blocking neutrophil infiltration. Furthermore, CHE decreased the expression levels of proinflammatory cytokines and LOX-1 at both mRNA and protein levels, while also decreasing the p-p38 MAPK/p38 MAPK ratio. Additionally, CHE increased the expression levels of Nrf2 and HO-1.

CONCLUSION

CHE provides protection against A. fumigatus keratitis through multiple mechanisms, including reducing fungal survival, inducing anti-inflammatory effects, enhancing Nrf2 and HO-1 expression, and suppressing the signaling pathway of LOX-1/p38 MAPK.

Recent advances in NLRP3 inflammasome in corneal diseases: Preclinical insights and therapeutic implications

NLRP3 inflammasome is a cytosolic multiprotein complex formed in response to exogenous environmental stress and cellular damage. The three major components of the NLRP3 inflammasome are the innate immunoreceptor protein NLRP3, the adapter protein apoptosis-associated speck-like protein containing a C-terminal caspase activation and recruitment domain, and the inflammatory protease enzyme caspase-1. The integrated NLRP3 inflammasome triggers the activation of caspase-1, leading to GSDMD-dependent pyroptosis and facilitating the maturation and release of inflammatory cytokines, namely interleukin (IL)-18 and IL-1β. However, the inflammatory responses mediated by the NLRP3 inflammasome exhibit dual functions in innate immune defense and cellular homeostasis. Aberrant activation of the NLRP3 inflammasome matters in the etiology and pathophysiology of various corneal diseases. Corneal alkali burn can induce pyroptosis, neutrophil infiltration, and corneal angiogenesis via the activation of NLRP3 inflammasome. When various pathogens invade the cornea, NLRP3 inflammasome recognizes pathogen-associated molecular patterns or damage-associated molecular patterns to engage in pro-inflammatory and anti-inflammatory mechanisms. Moreover, chronic inflammation and proinflammatory cascades mediated by the NLRP3 inflammasome contribute to the pathogenesis of diabetic keratopathy. Furthermore, overproduction of reactive oxygen species, mitochondrial dysfunction, and toll-like receptor-mediated activation of nuclear factor kappa B drive the stimulation of NLRP3 inflammasome and participate in the progression of dry eye disease. However, there still exist controversies regarding the regulatory pathways of the NLRP3 inflammasome. In this review, we provide a comprehensive overview of recent advancements in the function of NLRP3 inflammasome in corneal diseases and its regulatory pathways primarily through studies using animal models. Furthermore, we explore prospects for pharmacologically targeting pathways associated with NLRP3.

Metabolic regulation of the host-fungus interaction: from biological principles to therapeutic opportunities

Fungal infections present a significant global public health concern, impacting over 1 billion individuals worldwide and resulting in more than 3 million deaths annually. Despite considerable progress in recent years, the management of fungal infections remains challenging. The limited development of novel diagnostic and therapeutic approaches is largely attributed to our incomplete understanding of the pathogenetic mechanisms involved in these diseases. Recent research has highlighted the pivotal role of cellular metabolism in regulating the interaction between fungi and their hosts. In response to fungal infection, immune cells undergo complex metabolic adjustments to meet the energy demands necessary for an effective immune response. A comprehensive understanding of the metabolic circuits governing antifungal immunity, combined with the integration of individual host traits, holds the potential to inform novel medical interventions for fungal infections. This review explores recent insights into the immunometabolic regulation of host-fungal interactions and the infection outcome and discusses how the metabolic repurposing of immune cell function could be exploited in innovative and personalized therapeutic approaches.

Rosmarinic acid alleviates fungal keratitis caused by Aspergillus fumigatus by inducing macrophage autophagy

Fungal keratitis (FK) is an infectious keratopathy can cause serious damage to vision. Its severity is related to the virulence of fungus and response of inflammatory. Rosmarinic acid (RA) extracted from Rosmarinus officinalis exhibits antioxidant, anti-inflammatory and anti-viral properties. The aim of this study was to investigate the effect of RA on macrophage autophagy and its therapeutic effect on FK. In this study, we demonstrated that RA reduced expression of proinflammatory cytokine, lessened the recruitment of inflammatory cells in FK. The relative contents of autophagy markers, such as LC3 and Beclin-1, were significantly up-regulated in RAW 264.7 cells and FK. In addition, RA restored mitochondrial membrane potential (MMP) of macrophage to normal level. RA not only reduced the production of intracellular reactive oxygen species (ROS) but also mitochondria ROS (mtROS) in macrophage. At the same time, RA induced macrophage to M2 phenotype and down-regulated the mRNA expression of IL-6, IL-1β, TNF-α. All the above effects could be offset by the autophagy inhibitor 3-Methyladenine (3-MA). Besides, RA promote phagocytosis of RAW 264.7 cells and inhibits spore germination, biofilm formation and conidial adherence, suggesting a potential therapeutic role for RA in FK.

Targeting inflammasomes and pyroptosis in retinal diseases-molecular mechanisms and future perspectives

Retinal diseases encompass various conditions associated with sight-threatening immune responses and are leading causes of blindness worldwide. These diseases include age-related macular degeneration, diabetic retinopathy, glaucoma and uveitis. Emerging evidence underscores the vital role of the innate immune response in retinal diseases, beyond the previously emphasized T-cell-driven processes of the adaptive immune system. In particular, pyroptosis, a newly discovered programmed cell death process involving inflammasome formation, has been implicated in the loss of membrane integrity and the release of inflammatory cytokines. Several disease-relevant animal models have provided evidence that the formation of inflammasomes and the induction of pyroptosis in innate immune cells contribute to inflammation in various retinal diseases. In this review article, we summarize current knowledge about the innate immune system and pyroptosis in retinal diseases. We also provide insights into translational targeting approaches, including novel drugs countering pyroptosis, to improve the diagnosis and treatment of retinal diseases.

Involvement of cGAS/STING Signaling in the Pathogenesis of Candida albicans Keratitis: Insights From Genetic and Pharmacological Approaches

Purpose

Fungal keratitis (FK) is an invasive corneal infection associated with significant risk to vision. Although the cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING) signaling pathway has been recognized for its role in defending against viral infections, its involvement in FK still remains largely unclear. This study sought to elucidate the contribution of the cGAS/STING signaling pathway to the pathogenesis of FK.

Methods

The expression of cGAS/STING signaling components was assessed in a murine model of Candida albicans keratitis through RNA sequencing, western blot analysis, immunofluorescence staining, and real-time PCR. Both genetic (utilizing Sting1gt/gt mice) and pharmacological (using C176) interventions were employed to inhibit STING activity, allowing for the evaluation of resultant pathogenic alterations in FK using slit-lamp examination, clinical scoring, hematoxylin and eosin (H&E) staining, fungal culture, and RNA sequencing. Subconjunctival administration of the NOD-like receptor protein 3 (NLRP3) inflammasome inhibitor MCC950 was performed to evaluate FK manifestations following STING activity blockade. Furthermore, the impact of the STING agonist diABZI on FK progression was investigated.

Results

Compared to uninfected corneas, those infected with C. albicans exhibited increased expression of cGAS/STING signaling components, as well as its elevated activity. Inhibiting cGAS/STING signaling exacerbated the advancement of FK, as evidenced by elevated clinical scores, augmented fungal load, and heightened inflammatory response, including NLRP3 inflammasome activation and pyroptosis. Pharmacological inhibition of the NLRP3 inflammasome effectively mitigated the exacerbated FK by suppressing STING activity. Conversely, pre-activation of STING exacerbated FK progression compared to the PBS control, characterized by increased fungal burden and reinforced inflammatory infiltration.

Conclusions

This study demonstrates the essential role of the cGAS/STING signaling pathway in FK pathogenesis and highlights the necessity of its proper activation for the host against FK.

Formononetin protects against Aspergillus fumigatus Keratitis: Targeting inflammation and fungal load

PURPOSE

To investigate the potential treatment of formononetin (FMN) on Aspergillus fumigatus (A. fumigatus) keratitis with anti-inflammatory and antifungal activity.

METHODS

The effects of FMN on mice with A. fumigatus keratitis were evaluated through keratitis clinical scores, hematoxylin-eosin (HE) staining, and plate counts. The expression of pro-inflammatory factors was measured using RT-PCR, ELISA, or Western blot. The distribution of macrophages and neutrophils was explored by immunofluorescence staining. The antifungal properties of FMN were assessed through minimum inhibitory concentration (MIC), propidium iodide (PI) staining, fungal spore adhesion, and biofilm formation assay.

RESULTS

In A. fumigatus keratitis mice, FMN decreased the keratitis clinical scores, macrophages and neutrophils migration, and the expression of TNF-α, IL-6, and IL-1β. In A. fumigatus-stimulated human corneal epithelial cells (HCECs), FMN reduced the expression of IL-6, TNF-α, IL-1β, and NLRP3. FMN also decreased the expression of thymic stromal lymphopoietin (TSLP) and thymic stromal lymphopoietin receptor (TSLPR). Moreover, FMN reduced the levels of reactive oxygen species (ROS) induced by A. fumigatus in HCECs. Furthermore, FMN inhibited A. fumigatus growth, prevented spore adhesion and disrupted fungal biofilm formation in vitro. In vivo, FMN treatment reduced the fungal load in mice cornea at 3 days post infection (p.i.).

CONCLUSION

FMN demonstrated anti-inflammatory and antifungal properties, and exhibited a protective effect on mouse A. fumigatus keratitis.

Mesoporous zinc oxide-based drug delivery system offers an antifungal and immunoregulatory strategy for treating keratitis

Fungal keratitis is a refractory eye disease that is prone to causing blindness. Fungal virulence and inflammatory responses are two major factors that accelerate the course of fungal keratitis. However, the current antifungal drugs used for treatment usually possess transient residence time on the ocular surface and low bioavailability deficiencies, which limit their therapeutic efficacy. In this work, natamycin (NATA)-loaded mesoporous zinc oxide (Meso-ZnO) was synthesized for treating Aspergillus fumigatus keratitis with excellent drug-loading and sustained drug release capacities. In addition to being a carrier for drug delivery, Meso-ZnO could restrict fungal growth in a concentration-dependent manner, and the transcriptome analysis of fungal hyphae indicated that it inhibited the mycotoxin biosynthesis, oxidoreductase activity and fungal cell wall formation. Meso-ZnO also promoted cell migration and exhibited anti-inflammatory role during fungal infection by promoting the activation of autophagy. In mouse models of fungal keratitis, Meso-ZnO/NATA greatly reduced corneal fungal survival, alleviated tissue inflammatory damage, and reduced neutrophils accumulation and cytokines expression. This study suggests that Meso-ZnO/NATA can be a novel and effective treatment strategy for fungal keratitis.

Pyroptosis in microbial infectious diseases

Pyroptosis is a gasdermins-mediated programmed cell death that plays an essential role in immune regulation, and its role in autoimmune disease and cancer has been studied extensively. Increasing evidence shows that various microbial infections can lead to pyroptosis, associated with the occurrence and development of microbial infectious diseases. This study reviews the recent advances in pyroptosis in microbial infection, including bacterial, viral, and fungal infections. We also explore potential therapeutic strategies for treating microbial infection-related diseases by targeting pyroptosis.