Effect of Ultraviolet Light Irradiation Combined with Riboflavin on Different Bacterial Pathogens from Ocular Surface Infection

Biomaterial composed of chitosan, riboflavin, and hydroxyapatite for bone tissue regeneration

Biomaterial engineering approaches involve using a combination of miscellaneous bioactive molecules which may promote cell proliferation and, thus, form a scaffold with the environment that favors the regeneration process. Chitosan, a naturally occurring biodegradable polymer, possess some essential features, i.e., biodegradability, biocompatibility, and in the solid phase good porosity, which may contribute to promote cell adhesion. Moreover, doping of the materials with other biocompounds will create a unique and multifunctional scaffold that will be useful in regenerative medicine. This study is focused on the manufacturing and characterization of composite materials based on chitosan, hydroxyapatite, and riboflavin. The resulting films were fabricated by the casting/solvent evaporation method. Morphological and spectroscopy analyses of the films revealed a porous structure and an interconnection between chitosan and apatite. The composite material showed an inhibitory effect on Staphylococcus aureus and exhibited higher antioxidant activity compared to pure chitosan. In vitro studies on riboflavin showed increased cell proliferation and migration of fibroblasts and osteosarcoma cells, thus demonstrating their potential for bone tissue engineering applications.

How Modifications of Corneal Cross-Linking Protocols Influence Corneal Resistance to Enzymatic Digestion and Treatment Depth

Purpose

The purpose of this study was to determine the effects of the Photoactivated Chromophore for Keratitis Corneal Cross-Linking (PACK-CXL) protocol modifications on corneal resistance to enzymatic digestion and treatment depth.

Methods

Eight hundred one ex vivo porcine eyes were randomly divided into groups of 12 to 86 corneas, treated with various epi-off PACK-CXL modifications, including acceleration (30 > 2 minutes, 5.4 J/cm2), increased fluence (5.4 > 32.4 J/cm2), deuterium oxide (D2O) supplementation, different carrier types (dextran versus hydroxypropyl methylcellulose [HPMC]), increased riboflavin concentration (0.1 > 0.4%), and riboflavin replenishment during irradiation (yes/no). Control group eyes did not receive PACK-CXL. A pepsin digestion assay was used to determine corneal resistance to enzymatic digestion. A phalloidin fluorescent imaging assay was used to determine the PACK-CXL treatment effect depth. Differences between groups were evaluated using a linear model and a derivative method, respectively.

Results

PACK-CXL significantly increased corneal resistance to enzymatic digestion compared to no treatment (P < 0.03). When compared to a 10 minute, 5.4 J/cm2 PACK-CXL protocol, fluences of 16.2 J/cm2 and higher increased corneal resistance to enzymatic digestion by 1.5- to 2-fold (P < 0.001). Other protocol modifications did not significantly change corneal resistance. A 16.2 J/cm2 fluence also increased collagen compaction in the anterior stroma, whereas omitting riboflavin replenishment during irradiation increased PACK-CXL treatment depth.

Conclusions

Increasing fluence will likely optimize PACK-CXL treatment effectiveness. Treatment acceleration reduces treatment duration without compromising effectiveness.

Translational Relevance

The generated data help to optimize clinical PACK-CXL settings and direct future research efforts.

Infectious keratitis after corneal crosslinking: systematic review

Corneal crosslinking is a U.S. Food and Drug Administration--approved therapy to stiffen the cornea and prevent progression of corneal ectasia in patients with keratoconus. The standard procedure involves removal of the corneal epithelium (epithelial-off) prior to treatment. Variations to the standard procedure include accelerated crosslinking and transepithelial procedures. This study reviewed what is known regarding the risk for infection after epithelial-off crosslinking, the spectrum of pathogens, and clinical outcomes. 26 publications were identified. All eyes were fit with a bandage contact lens postoperatively. Available data indicate that the overall frequency of infectious keratitis after epithelium-off crosslinking is low. Bacterial infections are the most common, with a mean time of presentation of 4.8 days postoperatively. The use of steroids and bandage contact lenses in the immediate postoperative period and/or a history of atopic or herpetic disease were associated with infection. These patients require intense postoperative care with prophylactic antiviral therapy when appropriate.

In Vitro Effect of Toluidine Blue Antimicrobial Photodynamic Chemotherapy on Staphylococcus epidermidis and Staphylococcus aureus Isolated from Ocular Surface Infection

Purpose

We evaluate the antimicrobial effect of toluidine blue O (TBO)-mediated photodynamic antimicrobial chemotherapy (PACT) on Staphylococcus epidermidis and Staphylococcus aureus isolated from ocular surface infection.

Methods

We selected 24 strains of bacteria for this study. The antimicrobial effect of different TBO concentrations, light irradiation, and duration were evaluated. After determining the optimal PACT parameters, four experimental groups were included: Group 1, TBO alone (T+L−); Group 2, light-emitting diode (LED) irradiation alone (T−L+); Group 3, TBO–LED irradiation combination (T+L+); and Group 4, no treatment group (T−L−). The antibacterial effect of PACT was evaluated with the colony survival fraction (SF) methods.

Results

The antibacterial effect of PACT on S. epidermidis and S. aureus was dose-dependent to light irradiation and TBO concentration. The optimal PACT parameters were a TBO concentration of 60 μM, light irradiation of 5.27 mW/cm²_, and an irradiation duration of 30 minutes. In group 1, 60 μM TBO without irradiation did not show any antibacterial effect on S. epidermidis (1.48E7 ± 1.5E6 colony-forming units [CFU]/mL) or S. aureus (1.45E7 ± 9E5 CFU/mL). In group 2, irradiation alone with 5.27 mW/cm² did not modify bacterial growth (S. epidermidis, 1.49E7 ± 1.43E6; S. aureus, 1.5E7 ± 1.2E6). In group 3, after treatment, bacteria density dropped to 4000 ± 1000 and 3E5 ± 1E5 CFU/mL in S. epidermidis and S. aureus groups, respectively (P < 0.001, P = 0.030). In group 4, there was uniform bacterial growth (S. epidermidis, 1.51E7 ± 1.5E6; S. aureus, 1.48E7 ± 1.5E6) before and after treatment.

Conclusions

TBO-mediated PACT had an antibacterial efficacy in vitro on S. epidermidis and S. aureus isolated from ocular surface infection.

Translational Relevance

As TBO-mediated PACT has a strong antibacterial effect to S. epidermidis and S. aureus in vitro, this approach may assist in the treatment of ocular surface infectious diseases.