Global Transcriptomic Profiling of Innate and Adaptive Immunity During Aspergillus flavus Endophthalmitis in a Murine Model

Purpose

Fungal endophthalmitis is characterized by chronic inflammation leading to the partial or complete vision loss. Herein, we analyzed the transcriptomic landscape of Aspergillus flavus (A. flavus) endophthalmitis in C57BL/6 mice to understand the host-pathogen interactions.

Methods

Endophthalmitis was induced by intravitreal injection of A. flavus spores in C57BL/6 mice and monitored for disease progression up to 72 hours. The enucleated eyeballs were subjected to histopathological analysis and mRNA sequencing using the Illumina Nextseq 2000. Pathway enrichment analysis was performed to further annotate the functions of differentially expressed genes (DEGs) and validation of cytokines was performed in vitreous of patients with fungal endophthalmitis using multiplex ELISA.

Results

Transcriptomic landscape of A. flavus endophthalmitis revealed upregulated T-cell receptor signaling, PI3K-AKT, MAPK, NF-κB, JAK-STAT, and NOD like receptor signaling pathways. We observed significant increase in the T-cells during infection especially at 72 hours infection along with elevated expression levels of IL-6, IL-10, IL-12, IL-18, IL-19, IL-23, CCR3, and CCR7. Furthermore, host-immune response associated genes, such as T-cell interacting activating receptor, TNF receptor-associated factor 1, TLR1, TLR9, and bradykinin receptor beta 1, were enriched. Histopathological assessment validated the significant increase in inflammatory cells, especially T-cells at 72 hours post-infection along with increased disruption in the retinal architecture. Additionally, IL-6, IL-8, IL-17, TNF-α, and IL-1β were also significantly elevated, whereas IL-10 was downregulated in vitreous of patients with Aspergillus endophthalmitis.

Conclusions

Regulating T-cell influx could be a potential strategy to modulate the excessive inflammation in the retina and potentially aid in better vision recovery in fungal endophthalmitis.

A Novel and Low-cost Approach for Intravitreal Injection in an Experimental Model of Endophthalmitis

Purpose

Animal models are necessary in understanding the pathogenesis of endophthalmitis and are also necessary to assist the development of new therapeutics for this sight-threatening ocular inflammation. Hamilton syringes are usually preferred to inject pathogens when performing experiments on test subjects, however, this method has technical and financial disadvantages. In this study, we report the findings and assess the related benefits of applying a novel low-cost intravitreal injection technique to initiate endophthalmitis in a mouse model while using the Eppendorf tip and a 26G needle.

Methods

The 18-hr culture of clinical isolates of bacteria (Staphylococcus aureus and Pseudomonas aeruginosa) and fungus (Aspergillus flavus and Candida albicans) were resuspended to a final concentration of 10,000 colony forming units (CFU)/1 µL which were separately injected intravitreally into C57BL/6 mice (6-8 weeks) using a 0.1-2.5µL pipette attached to the modified Eppendorf tip with a 26G needle. The contralateral eye served as vehicle/uninjected control. Disease progression was determined by assessing the corneal haze, opacity, bacterial burden, and retinal histology of the eyes used in the model. Following euthanization, bacteria-infected mice were enucleated after 24 hr of the initial injection, and fungus-infected mice after 72 hr.

Results

Of the 50 mice injected, the modified technique was successful in 48 mice. Two mice were excluded due to cataract formed by accidental injury to the lens. The experimental endophthalmitis mice model successfully mimicked the natural clinical course. Clinical assessment and histopathology confirmed the influx of inflammatory cells into the posterior segment of the eye along with dissolution of retinal architecture.

Conclusion

Our novel method of injection using a modified Eppendorf tip and 26G needle yielded a cost-effective mouse model of clinical endophthalmitis, resulting in reproducible infection for understanding various aspects of its pathobiology.

Proteomic landscape of extracellular vesicles in human retinal cells infected with Staphylococcus aureus and Pseudomonas aeruginosa: Role in endophthalmitis

Extracellular Vesicles (EVs) have evolved as a promising entity for developing diagnostic and therapeutic biomarkers. We profiled global EV proteome of EVs from Human retinal cells (ARPE-19) infected with S. aureus and P. aeruginosa. EVs were isolated by ultracentrifugation and subjected to LC-MS/MS for proteome analysis. In S. aureus infection, sequest identified 864 proteins, of which 81 were differentially expressed in comparison to control. Similarly, in P. aeruginosa infection, of 516 proteins identified, 86 were differentially expressed. Additionally, 38 proteins were exclusive to infected sets. KEGG and Gene Ontology revealed crucial dysregulated pathways involving proteins such as complement cascades, annexins and calpain-2, all playing major role in the pathogenesis of the disease. This study provides insight into the global EV proteome of S. aureus and P. aeruginosa endophthalmitis with their functional correlation and distinctive pattern of expression. Calpain-2 and C8a are attractive biomarkers for bacterial endophthalmitis.

Proteome profiling of Extracellular Vesicles in Pseudomonas aeruginosa endophthalmitis: Prognostic and therapeutic significance in a mouse model

Endophthalmitis is a sight-threatening infection and a serious consequence of complications during intraocular surgery or penetrating injury of which Pseudomonas aeruginosa is an important etiology. Extracellular vesicles (EVs) have evolved as a promising entity for developing diagnostic and therapeutic biomarkers due to their involvement in intracellular communication and pathogenesis of diseases. We aimed to characterise the protein cargo of extracellular vesicles, isolated from a murine (C57BL/6) model of P. aeruginosa endophthalmitis by LC-MS/MS at 24 h post infection (p.i). EVs were extracted by ultracentrifugation, characterized by Dynamic Light Scattering (DLS) and western blotting with tetraspannin markers, CD9 and CD81 and quantified by the ExoCet quantification kit. Multiplex ELISA was performed to estimate the levels of TNF-α, IL-6, IFN-γ and IL-1β. Proteomic analysis identified 2010 proteins (FDR ≤0.01) in EVs from infected mice eyes, of which 137 were differentially expressed (P-value ≤ 0.05). A total of 101 proteins were upregulated and 36 were downregulated. Additionally, 43 proteins were exclusive to infection set. KEGG and Gene Ontology revealed, Focal adhesion, Phagosome pathway, Complement cascade and IL-17 signalling pathway are crucial upregulated pathways involving proteins such as Tenascin, caveolin 1, caveolin 2, glutamine synthetase, microtubule-associated protein, C1, C8 and IL-17. Tenascin and caveolins are known to suppress anti-inflammatory cytokines further exacerbating the disease. The result of this study provides insight into the global extracellular vesicle proteome of P. aeruginosa endophthalmitis with their functional correlation and distinctive pattern of expression and tenascin, caveolin 1 and caveolin 2 are attractive biomarkers for P. aeruginosa endophthalmitis.

Retrobulbar Hyaluronidase Injection: Does It Reach the Eye?

PURPOSE

To determine if retrobulbar injection of hyaluronidase reaches the vitreous cavity, and to determine its concentration in the vitreous.

METHODS

Prospective case-control study. Patients undergoing evisceration with implant for noninfective blind eyes were enrolled in the study. Before the evisceration, a retrobulbar injection of 3,000 IU of hyaluronidase (2 ml) was injected. Time from injection to in vivo sampling of posterior vitreous was noted. Vitreous samples from controls were obtained from patients undergoing vitrectomy for retinal detachment or diabetic retinopathy. Concentration of hyaluronidase was assessed in all 30 samples. An ELISA-based microtiter-technique was used to evaluate the activity of hyaluronidase by an avidin-peroxidase-based procedure using an ELISA reader. Incubations were carried out at room temperature and at 37°C. All the samples were analyzed in duplicates, and the mean of each sample was plotted on a scatter plot.

RESULTS

Total of 30 vitreous samples were analyzed, of which 15 were controls and 15 were test samples. Of the 15 test samples, injection-to-sampling time was 0 to 20 minutes in 4 samples, 20 to 40 minutes in 6 samples, and 40 to 60 minutes in 5 samples. The highest concentration of hyaluronidase detected in control and test samples were 2.9 and 3.0 µg/ml, and the lowest concentration was 1.7 and 1.5 µg/ml (SD 0.3), respectively. There was no significant difference between control and test groups.

CONCLUSION

Retrobulbar injection did not result in higher concentration of hyaluronidase in the posterior vitreous compared with controls when measured up to 60 minutes following injection.

Clinical Utility of COVID-19 Real Time-Polymerase Chain Reaction Testing of Ocular Tissues of Non-COVID-19 Cornea Donors Deemed Suitable for Corneal Retrieval and Transplantation

PURPOSE

The purpose of this study was to evaluate the prevalence of SARS-CoV-2 in human postmortem ocular tissues of asymptomatic donors and its implications on our eye banking protocols.

METHODS

The expression of SARS-CoV-2 RNA was assessed by reverse transcription-polymerase chain reaction in corneal rims and conjunctival tissues from 100 donors who were found suitable for transplantation as per the donor screening guidelines of the Global Alliance of Eye Bank Associations. The donor's clinical history and cause of death were assessed for secondary analysis.

RESULTS

Of 200 ocular tissues (100 corneal and 100 conjunctival) from the same 1 eye of 100 surgical-intended donors, between September 2020 and April 2021, the overall positivity rate for SARS-CoV-2 was ∼1% (2/200). Both the ocular samples that tested positive were conjunctival biopsies (2/100, 2%), whereas corneal samples were negative (0/100, 0%) in both donors. The causes of donor death were trauma in 51 donors, suicide in 33, cardiac arrest in 7, electric shock in 5, metabolic cause in 2, malignancy in 1, and snake bite in 1. None of the donors had a medical history suggestive of COVID infection or possible contact. None of the recipients from the donors were reported to have any systemic adverse event after keratoplasty until the follow-up of 6 weeks.

CONCLUSIONS

The overall prevalence of SARS-CoV-2 was 1% (2% for conjunctival and 0% for corneal samples, P value = 0.5) in the donors who were found suitable for cornea recovery and transplantation. The findings of exceptionally low positive rates in our samples validate the criticality of history-based donor screening and do not support the necessity of postmortem PCR testing as a criterion for procurement and subsequent use for corneal transplantation.

Multidrug-Resistant Pseudomonas aeruginosa Triggers Differential Inflammatory Response in Patients With Endophthalmitis

Purpose

Infections with multidrug-resistant Pseudomonas aeruginosa (MDR-PA) lead to poor clinical outcomes in endophthalmitis patients, and its interactions with the host immune system remain largely unknown. The current study aimed to determine the association of MDR-PA infection with the cytokine expression profile in patients with endophthalmitis.

Methods

Vitreous of 12 patients with culture-proven MDR-PA along with 12 samples from antibiotic-susceptible P. aeruginosa (S-PA) and 20 non-infectious controls were included in the study. Expression patterns of IL-6, IL-10, IL-1α, IL-1β, IFN-γ, TNF-α, IL-8, and GM-CSF in the vitreous were analyzed by multiplex immunoassay and correlated with the clinical severity. We also assessed the phosphorylation level of different immune pathway molecules.

Results

In the MDR-PA group, significantly (P < 0.05) increased expression of IL-6, IL-8, IL-10, IL-1β, and TNF-α was observed in comparison with the S-PA group. The increased inflammatory mediators in MDR-PA correlated with the disease severity. Additionally, the increased expression of inflammatory mediators was positively correlated to the activation levels of Akt, STAT3, JNK, p70 S6 kinase, and NF-кB (P < 0.05) in the MDR-PA group.

Conclusions

The current study shows the differential host immune response and phosphorylation levels of signaling molecules in MDR-PA endophthalmitis, thereby linking antibiotic resistance with distinct immune regulation.

Translational Relevance

This study provides evidence for the use of inflammatory mediator levels of IL-6, IL-8, IL-10, IL-1β, and TNF-α as potential diagnostic biomarkers of MDR endophthalmitis warranting prompt administration of immune modulators to avoid irreversible damage to the retina and vision loss.