Ultrasound-assisted gatifloxacin delivery in mouse cornea, in vivo

A systematic review of ultrasound-mediated drug delivery to the eye and critical insights to facilitate a timely path to the clinic

Ultrasound has long been identified as a promising, non-invasive modality for improving ocular drug delivery across a range of indications. Yet, with 20 years of learnings behind us, clinical translation remains limited. To help address this, and in accordance with PRISMA guidelines, the various mechanisms of ultrasound-mediated ocular drug delivery have been appraised, ranging from first principles to emergent applications spanning both ex vivo and in vivo models. The heterogeneity of study methods precluded meta-analysis, however an extensive characterisation of the included studies allowed for semi-quantitative and qualitative assessments. Methods: In this review, we reflected on study quality of reporting, and risk of bias (RoB) using the latest Animal Research: Reporting of In Vivo Experiments (ARRIVE 2.0) guidelines, alongside the Systematic Review Centre for Laboratory animal Experimentation (SYRCLE) RoB tools. Literature studies from 2002 to 2022 were initially characterised according to methods of ultrasound application, ultrasound parameters applied, animal models employed, as well as safety and efficacy assessments. This exercise contributed to developing a comprehensive understanding of the current state of play within ultrasound-mediated ocular drug delivery. The results were then synthesised and processed into a guide to aid future study design, with the goal of improving the reliability of data, and to support efficient and timely translation to the clinic. Results: Key attributes identified as hindering translation included: poor reporting quality and high RoB, skewed use of animals unrepresentative of the human eye, and the over reliance of reductionist safety assessments. Ex vivo modelling studies were often unable to have comprehensive safety assessments performed on them, which are imperative to determining treatment safety, and represent a pre-requisite for clinical translation. Conclusion: With the use of our synthesised guide, and a thorough understanding of the underlying physicochemical interactions between ultrasound and ocular biology provided herein, this review offers a firm foundation on which future studies should ideally be built, such that ultrasound-mediated ocular drug delivery can be translated from concept to the coalface where it can provide immense clinical benefit.

Therapy for contact lens-related ulcers

PURPOSE OF REVIEW

The current review covers the current literature and practice patterns of antimicrobial therapy for contact lens-related microbial keratitis (CLMK). Although the majority of corneal ulcers are bacterial, fungus and acanthamoeba are substantial contributors in CLMK and are harder to treat due to the lack of commercially available topical medications and low efficacy of available topical therapy.

RECENT FINDINGS

Topical antimicrobials remain the mainstay of therapy for corneal ulcers. Fluoroquinolones may be used as monotherapy for small, peripheral bacterial ulcers. Antibiotic resistance is a persistent problem. Fungal ulcers are less responsive to topical medications and adjunct oral or intrastromal antifungal medications may be helpful. Acanthamoeba keratitis continues to remain a therapeutic challenge but newer antifungal and antiparasitic agents may be helpful adjuncts. Other novel and innovative therapies are being studied currently and show promise.

SUMMARY

Contact lens-associated microbial keratitis is a significant health issue that can cause vision loss. Treatment remains a challenge but many promising diagnostics and procedures are in the pipeline and offer hope.

Ultrasound-Enhanced Transcorneal Drug Delivery for Treatment of Fungal Keratitis

PURPOSE

Transcorneal drug delivery is hindered by ocular physical and biochemical properties, such as tear production, the epithelial layer of the cornea, and blinking. The aim of this study was to determine whether ultrasound can be applied to increase the transcorneal drug delivery of natamycin used in the treatment of fungal keratitis without dangerously overheating the surrounding ocular tissues.

METHODS

To verify the safety of various sets of ultrasound parameters, modeling studies were conducted using OnScale, an ultrasonic wave modeling software. Ultrasound parameters determined optimal for ocular tissue safety were used in a laboratory setting in a jacketed Franz diffusion cell setup. Histological images of the cross-section of the corneas used in experiments were examined for cell damage under a microscope.

RESULTS

Increases in transcorneal drug delivery were seen in every treatment parameter combination when compared with the sham treatment. The highest increase was 4.0 times for 5 minutes of pulsed ultrasound at a 25% duty cycle and a frequency of 400 kHz and an intensity of 0.5 W/cm 2 with statistical significance ( P < 0.001). Histological analysis revealed structural damage only in the corneal epithelium, with most damage being at the epithelial surface.

CONCLUSIONS

This study suggests that ultrasound is a safe, effective, and minimally invasive treatment method for enhancing the transcorneal drug delivery of natamycin. Further research is needed into the long-term effects of ultrasound parameters used in this study on human ocular tissues.

Design of a Controlled-Release Delivery Composite of Antibacterial Agent Gatifloxacin by Spherical Silica Nanocarrier

In this study, a spherical silica nanoparticle was explored as a gatifloxacin carrier synthesized by the chemical precipitation method. It was found that there was no new chemical bond formation during the loading process between gatifloxacin and silica, which implies that the binding was driven by physical interaction. In addition, the drug loading and encapsulation efficiency could be improved by appropriately increasing nano-silica content in the loading process. Meanwhile, the release rate of gatifloxacin after loading nano-silica was also improved, suggesting the successful design of a controlled-release delivery composite. The silica nanocarrier could significantly improve the antibacterial performance of Escherichia coli by 2.1 times, which was higher than the pure gatifloxacin. The 24 h bacteriostatic rate was higher than that of a simple mixture of silica nanoparticles and gatifloxacin. Strong reactive oxygen species (ROS) in GAT-SiO₂ NPs suggests that ROS might be associated with bactericidal activity. The synergy between the physicochemical effect and ROS production of this material is proposed as the mechanism of its antibacterial activity, which can also be confirmed by the cell membrane damage observed under electron microscopy and DNA damage experiments. Collectively, our finding indicates that nano-silica microspheres could serve as a promising carrier for the sustained release of gatifloxacin, thereby providing a new carrier design scheme for the improvement of the antibacterial effect.

Feasibility of Therapeutic Ultrasound Application in Topical Scleral Delivery of Avastin

Purpose

Macromolecules have been shown to be effective in vision-saving treatments for various ocular diseases, such as age-related macular degeneration and diabetic retinopathy. The current delivery of macromolecules requires frequent intraocular injections and carries a risk of serious adverse effects.

Methods

We tested the application of therapeutic ultrasound as a minimally invasive approach for the delivery of Avastin into the diseased regions of the eye. Avastin (bevacizumab) is an anti-vascular endothelial growth factor (VEGF) antibody with a molecular weight of 149 kDa. We tested the effectiveness and safety of Avastin delivery through rabbit sclera in vitro using a standard diffusion cell model. Ultrasound at frequencies of 400 kHz or 3 MHz with an intensity of 1 W/cm2 was applied for the first 5 minutes of 1-hour drug exposure. Sham treatments mimicked the ultrasound treatments, but ultrasound was not turned on. Absorbance measurements of the receiver compartment solution were performed at 280 nm using a spectrophotometer.

Results

Absorbance measurements indicated no statistical difference between the sham (n = 13) and 400 kHz ultrasound group (n = 15) in the delivery of Avastin through the sclera. However, the absorbance values were statistically different (P < 0.01) between the 3 MHz ultrasound group (0.004, n = 8) and the matched sham group (0.002, n = 7). There was 2.3 times increase in drug delivery in the 3 MHz ultrasound when compared to the corresponding sham group. Histological studies indicated no significant damage in the ultrasound-treated sclera due to ultrasound application.

Conclusions

Our preliminary results provided support that therapeutic ultrasound may be effective in the delivery of Avastin through the sclera.

Translational Relevance

Our study offers clinical potential for a minimally invasive retinopathy treatment.

Antibiofilm Efficacy of Luteolin Against Single and Dual Species of Candida albicans and Enterococcus faecalis

Candida albicans and Enterococcus faecalis biofilm-associated infections have been a huge challenge to the medical community. However, the efficacy of natural products against mixed biofilms of C. albicans and E. faecalis still remains largely unexploited. The aim of this study was to evaluate the efficacy of luteolin against planktonic cell growth, adhesion, and biofilm formation of C. albicans and E. faecalis in single and mixed cultures in vitro. The results showed that the minimum inhibitory concentrations of luteolin against planktonic cells of C. albicans, E. faecalis, and mixed cultures were 32 and 64 μg ml^–1, respectively. The results displayed that a remarkable variation in biofilm biomass, viability, structure, and composition of single and dual-species biofilms formed by mono- and dual-species biofilms of C. albicans and E. faecalis in the presence of luteolin was confirmed by mainly crystal violet staining assay (CVSA), optical microscope, field emission scanning electron microscope (FESEM), and confocal laser scanning microscope (CLSM). The tolerance of luteolin-treated single- and dual-species biofilms to antibiotics was found to obviously decrease, and the loss of biofilm matrix components (mainly polysaccharides and proteins) was revealed by CLSM. Moreover, luteolin was effective at inactivating biofilm cells, as well as destructing preformed biofilm structures by single and dual species by CVSA, FESEM, and CLSM. Collectively, these data indicate the potential of luteolin as a promising antibiofilm agent for the therapeutic management of biofilm-related infections induced by single and dual species of C. albicans and E. faecalis.

Equivalent effect of extracellular proteins and polysaccharides on biofilm formation by clinical isolates of Staphylococcus lugdunensis

Biofilm formation by Staphylococcus lugdunensis involves formation of an extracellular matrix; however, the identity of the constituents responsible for the structure of biofilms fabricated by different clinical strains is largely unclear. Here, biofilms produced by 24 clinical isolates of S. lugdunensis were characterized. The optimal medium for S. lugdunensis was selected, and the biofilm-forming capacity was assessed. Extracelullar polymeric substances (EPS) contributing to biofilm robustness were determined by evaluating the susceptibility of biofilms to EPS-degrading agents using field emission scanning electron microscopy and confocal laser scanning microscopy. Biofilm formation by the clinical isolates of S. lugdunensis was augmented by glucose supplementation. Further, extracellular DNA (eDNA), proteins, and polysaccharides were present in the 24 clinical isolates. Proteins and polysaccharides were the most common components within the S. lugdunensis biofilms, whereas the eDNA content was marginal in biofilm formation. Therefore, proteins and polysaccharides within biofilms may be used as the primary targets for developing eradication strategies to prevent S. lugdunensis biofilm formation.

Mechanisms of Action of Luteolin Against Single- and Dual-Species of Escherichia coli and Enterobacter cloacae and Its Antibiofilm Activities

Escherichia coli and Enterobacter cloacae are major foodborne pathogens and can form challenging single/mixed biofilms. A recent study demonstrated that luteolin (LUT) exhibits antibacterial activities against some pathogens; however, the mechanisms underlying the effects of LUT on planktonic and biofilm bacteria have never been fully elucidated. This study aimed to determine the antibacterial activity and its mechanism of action against E. coli and E. cloacae. Here, the antimicrobial mode of LUT was explored by evaluating alterations in both cell membrane integrity and cell morphology, and the antibiofilm activity of LUT was investigated using quantitative and qualitative assays. The results showed that minimal inhibitory concentration and minimum bactericidal concentration values of LUT against E. coli were 64 and 128 μg/mL and 128 and 256 μg/mL for E. cloacae mono- and dual-species, respectively. LUT impaired cell membrane integrity, as demonstrated by the remarkable increase in the number of membrane-damaged cells and definite variations in cell morphology. Moreover, LUT presented robust inhibitory effects on biofilm formation and the capacity to kill mono- and dual-species biofilm cells. Overall, these data show the potential benefit of using a natural antimicrobial and/or preservative in the food industry, LUT, to control mono- and mixed-species or biofilm-associated infections.

Efficacy of Chelerythrine Against Mono- and Dual-Species Biofilms of Candida albicans and Staphylococcus aureus and Its Properties of Inducing Hypha-to-Yeast Transition of C. albicans

Candida albicans and Staphylococcus aureus specifically often resulted in biofilm-associated diseases, ranging from superficial mucosal to life-threatening systemic infections. Recent studies reported that chelerythrine displayed antimicrobial activities against a few microorganisms, but its effects on mono- and dual-species biofilms of C. albicans and S. aureus have never been reported. The purpose of this study was to evaluate the efficacy of chelerythrine against mono- and dual-species biofilms, and explore its effect on the hyphal growth and the hypha-to-yeast transition of C. albicans. The results showed that minimum inhibitory concentrations (MICs) and minimum biofilm inhibitory concentration (MBIC_90S) of chelerythrine against planktonic cells of mono-species were 4 and 2 μg/mL, while the MIC and MBIC₉₀ were 6 and 3 μg/mL for dual-species. Meanwhile, the decrease in three matrix component levels and tolerance to antibiotics of biofilms formed by mono- and dual-species exposed to chelerythrine were confirmed by a confocal laser scanning microscope, in conjugation with five fluorescent dyes and a gatifloxacin diffusion assay. Moreover, C. albicans and S. aureus mono-species showed a 96.4, and 92.3% reduction, respectively, in 24-h preformed biofilm biomass in the presence of 128 µg/mL of chelerythrine. Similarly, preformed (24 h) dual-species biofilm biomass also displayed a significant reduction (90.7%) when treated with 192 μg/mL chelerythrine. Chelerythrine inhibited hyphae formation of C. albicans at 4 μg/mL, and C. albicans in hypha-form can be converted into yeast-form at 8 μg/mL of chelerythrine. Therefore, chelerythrine shows promise as a potential antimicrobial and antibiofilm agent for clinical effective treatments of mono- and mixed-species and/or biofilm-associated infections.

Sanguinarine Inhibits Mono- and Dual-Species Biofilm Formation by Candida albicans and Staphylococcus aureus and Induces Mature Hypha Transition of C. albicans

Previous studies have reported that sanguinarine possesses inhibitory activities against several microorganisms, but its effects on mono- and dual-species biofilms of C. albicans and S. aureus have not been fully elucidated. In this study, we aimed to evaluate the efficacy of sanguinarine for mono- and dual-species biofilms and explore its ability to induce the hypha-to-yeast transition of C. albicans. The results showed that the minimum inhibitory concentration (MIC) and minimum biofilm inhibitory concentration (MBIC90) of sanguinarine against C. albicans and S. aureus mono-species biofilms was 4, and 2 μg/mL, respectively, while the MIC and MBIC90 of sanguinarine against dual-species biofilms was 8, and 4 μg/mL, respectively. The decrease in the levels of matrix component and tolerance to antibiotics of sanguinarine-treated mono- and dual-species biofilms was revealed by confocal laser scanning microscopy combined with fluorescent dyes, and the gatifloxacin diffusion assay, respectively. Meanwhile, sanguinarine at 128 and 256 μg/mL could efficiently eradicate the preformed 24-h biofilms by mono- and dual-species, respectively. Moreover, sanguinarine at 8 μg/mL could result in the transition of C. albicans from the mature hypha form to the unicellular yeast form. Hence, this study provides useful information for the development of new agents to combat mono- and dual-species biofilm-associated infections, caused by C. albicans and S. aureus.