UVA irradiation of riboflavin generates oxygen-dependent hydroxyl radicals

Inactivation of Salmonella and avian pathogens on hatchery eggs using gas phase hydroxyl-radical process vs formaldehyde fumigation: Efficacy, hatching performance and grow-out of Chickens

Hatcheries have been identified as a significant source of Salmonella within poultry production. Consequently, there is a need for effective egg disinfection methods that can reduce the pathogen burden while preserving the egg integrity and embryo. The metrics for a successful egg disinfection method are typically a reduction in Total Aerobic Count (TAC) while retaining hatching rates. In this study, a gas phase hydroxyl-radical process was validated and verified as a hatchery egg disinfection method. The process is based on applying a hydrogen peroxide mist in combination with ozone gas and UV-C to generate antimicrobial hydroxyl radicals. The treatment (2 % hydrogen peroxide, 20 ppm ozone and 19 mJ/cm2 UV-C; designated as HR) for inactivating Salmonella (serotypes Enteritidis and Typhimurium) inoculated onto eggs could eliminate the pathogen (>5 log CFU/egg reduction) but left residual TAC (1.53 log CFU/egg reduction). Surface sterilization was achieved by a pre-treatment of eggs with the photo-catalyst riboflavin (13.75 mM) followed by 3 % hydrogen peroxide delivered at 70 °C prior to the hydroxyl-radical treatment (3 % hydrogen peroxide, 20 ppm ozone and 114 mJ/cm2 designated HRS). The surface sterilization of eggs coincided with the removal of the cuticle layer with the HRS treatment but not HR. The cuticle layer was also compromised by formaldehyde treatment. When the different treatments were applied to fertile hatchery eggs (n=50 eggs per treatment group), there was no significant difference in hatchery rate (64-74 %), with hatch to fertility being higher for disinfected eggs (89-97 %) compared to the non-treated control (80 %). The seven-day mortality (0 - 2 birds) and feed conversion ratio (1.59 - 1.75 kg/kg feed) did not significantly differ between the treated vs controls. The HR treatment could eliminate Enterococcus faecium, Escherichia coli (>5 log CFU/egg reduction) although HRS was required to inactivate Pseudomonas aeruginosa (>5 log CFU/egg reduction) and reduce Aspergillus niger spores (3.08±2.25 log CFU reduction). The study has provided treatment options for hatchery egg disinfection and alternative to formaldehyde treatment.

Corneal cross-linking

First introduced over 20 years ago as a treatment for progressive keratoconus, the original "Dresden" corneal cross-linking (CXL) protocol involved riboflavin saturation of the stroma, followed by 30 min of 3 mW/cm2-intensity ultraviolet-A (UV-A) irradiation. This procedure generates reactive oxygen species (ROS) that cross-link stromal molecules, thereby stiffening the cornea and counteracting the ectasia-induced weakening. Due to their large size, riboflavin molecules cannot readily pass through the corneal epithelial cell tight junctions; thus, epithelial debridement was performed. Moreover, the Dresden protocol necessitates a minimal corneal thickness of 400 μm to protect the endothelium from UV-induced damage. While the Dresden protocol is highly effective at enhancing corneal biomechanical strength, there was a strong desire for CXL procedures that would deliver Dresden-like strengthening in a shorter time, in corneas thinner than 400 μm, and without requiring epithelial debridement. This review explores the advancements and scientific discoveries that have enabled such improvements. Accelerated CXL protocols, utilizing our increased knowledge about the role of oxygen and photochemical reactions in the cornea have shortened and simplified the procedure duration while maintaining efficacy and safety, improving clinical workflow and patient compliance. CXL is not confined to improving biomechanics in corneal ectasia, but rather represents a technique that modulates corneal physiology and biochemistry on multiple levels. Accordingly, CXL indications have expanded to include treating other corneal ectasias, corneal neovascularization, corneal sterile melting, inflammatory dry eye and importantly, infectious keratitis in a procedure termed photoactivated chromophore for keratitis-CXL (PACK-CXL). In PACK-CXL, ROS have a direct pathogen-killing effect, and cross-linking enhances the cornea's resistance to pathogen-produced protease digestion through steric hindrance. The distinct requirements of PACK-CXL compared to ectasia treatment have led to the development of different CXL protocols, including higher UV fluences and other chromophore/light combinations, specifically rose bengal and green light. Additionally, combining CXL with vision-enhancing procedures like individualized wavefront- or topographically-guided excimer ablation can regularize a biomechanically stable cornea, improve visual acuity, and potentially eliminate the need for corneal transplantation, leading to long-term improvements in quality of life.

Crosslinking with UV-A and riboflavin in progressive keratoconus: From laboratory to clinical practice - Developments over 25 years

Changes in the biomechanical and biochemical properties of the human cornea play an important role in the pathogenesis of ectatic diseases. A number of conditions in primarily acquired (keratoconus or pellucid marginal degeneration) or secondarily induced (iatrogenic keratectasia after refractive laser surgeries) ectatic disorders lead to decreased biomechanical stability. Corneal collagen cross-linking (CXL) represents a technique to slow or even halt the progression of ectatic pathologies. In this procedure, riboflavin is applied in combination with ultraviolet A radiation. This interaction induces the production of reactive oxygen species, which leads to the formation of additional covalent bonds between collagen molecules and subsequent biomechanical corneal strengthening. This procedure is so far the only method that partially interferes etiopathogenetically in the treatment of ectatic diseases that slows or stops the process of corneal destabilization, otherwise leading to the need for corneal transplantation. Besides, CXL process increases markedly resistance of collagenous matrix against digesting enzymes supporting its use in the treatment of corneal ulcers. Since the discovery of this therapeutic procedure and the first laboratory experiments, which confirmed the validity of this method, and the first clinical studies that proved the effectiveness and safety of the technique, it has been spread and adopted worldwide, even with further modifications. Making use of the Bunsen-Roscoe photochemical law it was possible to shorten the duration of this procedure in accelerated CXL and thus improve the clinical workflow and patient compliance while maintaining the efficacy and safety of the procedure. The indication spectrum of CXL can be further expanded by combining it with other vision-enhancing procedures such as individualized topographically-guided excimer ablation. Complementing both techniques will allow a patient with a biomechanically stable cornea to regularize it and improve visual acuity without the need for tissue transplantation, leading to a long-term improvement in quality of life.

Real-time monitoring of riboflavin concentration using different clinically available ophthalmic formulations for epi-off and epi-on corneal cross-linking

PURPOSE

To assess the feasibility of theranostics to determine the riboflavin concentration in the cornea using clinically available ophthalmic formulations during epithelium-off (epi-off) and transepithelial (epi-on) corneal cross-linking procedures.

METHODS

Thirty-two eye bank human donor corneas were equally randomized in eight groups; groups 1 to 3 and groups 4 to 8 underwent epi-off and epi-on delivery of riboflavin respectively. Riboflavin ophthalmic solutions were applied onto the cornea according to the manufacturers' instructions. The amount of riboflavin into the cornea was estimated, at preset time intervals during imbibition time, using theranostic UV-A device (C4V CHROMO4VIS, Regensight srl, Italy) and expressed as riboflavin score (d.u.). Measurements of corneal riboflavin concentration (expressed as µg/cm3) were also performed by spectroscopy absorbance technique (AvaLight-DH-S-BAL, Avantes) for external validation of theranostic measurements.

RESULTS

At the end of imbibition time in epi-off delivery protocols, the average riboflavin score ranged from 0.77 ± 0.38 (the average corneal riboflavin concentration was 213 ± 190 µg/cm3) to 1.79 ± 0.07 (554 ± 103 µg/cm3). In epi-on delivery protocols, the average riboflavin score ranged from 0.17 ± 0.01 to 0.67 ± 0.19 (corneal riboflavin concentration ranged from 6 ± 5 µg/cm3 to 122 ± 39 µg/cm3) at the end of imbibition time. A statistically significant linear correlation (P ≤ 0.05) was found between the theranostic and spectrophotometry measurements in all groups.

CONCLUSIONS

Real-time theranostic imaging provided an accurate strategy for assessing permeation of riboflavin into the human cornea during the imbibition phase of corneal cross-linking, regardless of delivery protocol. A large variability in corneal riboflavin concentration exists between clinically available ophthalmic formulations both in epi-off and epi-on delivery protocols.

An investigation of the influence of reactive oxygen species produced from riboflavin-5'-phosphate by blue or violet light on the inhibition of WiDr colon cancer cells

Riboflavin-5'-phosphate (FMN), an innocuous product of riboflavin (RF) phosphorylation, is vital for humans. FMN is sensitive to light illumination, as indicated by reactive oxygen species (ROS) formation. This investigation was undertaken to evaluate the influence of blue light illumination (BLI) and violet light illumination (VLI) upon FMN to develop a method to inhibit WiDr colon cancer cells by FMN photolysis. When FMN is subjected to BLI and VLI, it inhibits WiDr colon cancer cells by generating superoxide radical anions (O2•-). The respective reduction rates are 42.6 and 81.9 % in WiDr colon cancer cells for FMN treated with BLI and VLI at 20 W/m2 for 0.5 h. FMN treated with VLI inhibits WiDr colon cancer cells more effectively than BLI. Propidium iodide (PI) is a fluorescent dye that is used to detect abnormal DNA due to cell death by apoptosis or necrosis. The PI-positive count for nuclei increased significantly for the WiDr colon cancer cells that were treated with FMN under VLI at 20 W/m2 for 0.5 h. FMN photolysis achieved using VLI allows efficient photodynamic therapy (PDT) by triggering the cytotoxicity of FMN on WiDr colon cancer cells.

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.

Riboflavin-Promoted In Situ Photoactivation of Dihydroalkaloid Prodrugs for Cancer Therapy

Cancer therapies usually suffer from poor targeting ability and serious side effects. Photoactivatable cancer therapy has the significant advantage of a high spatiotemporal resolution, but most photoactivatable prodrugs require decoration with stoichiometric photocleavable groups, which are only responsive to ultraviolet irradiation and suffer from low reaction efficiency. To tackle these challenges, we herein propose a photoactivation strategy with biogenic riboflavin as the photosensitizer to promote the in situ transformation of noncytotoxic dihydroalkaloid prodrugs dihydrochelerythrine (DHCHE), dihydrosanguinarine (DHSAN), and dihydronitidine (DHNIT) into anticancer alkaloid drugs chelerythrine (CHE), sanguinarine (SAN), and nitidine (NIT), respectively, which can efficiently kill cancer cells and inhibit in vivo tumor growth. Meanwhile, the photoactivatable transformation can be in situ monitored by green-to-red fluorescence conversion, which will contribute to easy controlling of the therapeutic dose. The proposed photoactivatable transformation mechanism was also explored by density functional theory (DFT) calculations. We believe this riboflavin-promoted and imaging-guided photoactivation strategy is promising for precise cancer therapy.

Theranostic-guided corneal cross-linking: Preclinical evidence on a new treatment paradigm for keratoconus

Theranostics is an emerging therapeutic paradigm of personalized medicine; the term refers to the simultaneous integration of therapy and diagnostics. In this work, theranostic-guided corneal cross-linking was performed on 10 human sclero-corneal tissues. The samples were soaked with 0.22% riboflavin formulation and underwent 9 minutes UV-A irradiance at 10 mW/cm² using theranostic device, which provided both a measure of corneal riboflavin concentration and a theranostic score estimating treatment efficacy in real time. A three-element viscoelastic model was developed to fit the deformation response of the cornea to air-puff excitation of dynamic tonometry and to calculate the mean corneal stiffness parameter before and after treatment. Significant correlation was found between the theranostic score and the increase in mean corneal stiffness (R = 0.80; P < .001). Accuracy and precision of the theranostic score in predicting the induced corneal tissue stiffening were both 90%. The riboflavin concentration prior to starting the UV-A photo-therapy phase was the most important variable to allow corneal cross-linking to be effective. Theranostic UV-A light mediated imaging and therapy enables the operator to adopt a precise approach for achieving highly predictable biomechanical strengthening on individual corneas.

Corneal cross-linking in patients with keratoconus: up to 13 years of follow-up

INTRODUCTION

To evaluate long-term safety and efficacy of corneal collagen cross-linking (CXL) in patients with keratoconus up to 13 years.

MATERIALS AND METHODS

In this mono-centre exploratory study, we included all consecutive patients who underwent CXL in our cornea centre from 01/01/2007 to 12/30/2011 and met the inclusion criteria. CXL was performed in all patients according to the Dresden protocol. Evaluation included best-corrected visual acuity (BCVA), topographic keratometry by Scheimpflug corneal tomography and endothelial cell count (ECC). Follow-up measurements were taken up to 13 years after treatment were compared with baseline values.

RESULTS

The study enrolled 168 eyes. The mean age of our patients was 26.3 years ± 7.8 years. A complete topographic dataset was available 1 year postoperatively for 142 eyes, 5 years postoperatively for 105 eyes, 10 years postoperatively for 61 eyes and 13 years postoperatively for 9 eyes. BCVA increased statistically significant after 1 year, 5 years and 10 years and non-significantly after 13 years. All keratometric parameters with exception of posterior astigmatism showed a statistically significant decrease after 1 year, 5 years and 10 years. After 13 years, the decrease was statistically significant only in Kmax, K2 and thinnest cornea. No significant changes in ECC were detected. Three eyes received Re-CXL, none of the eyes received penetrating keratoplasty and no infections occurred in this cohort.

CONCLUSIONS

CXL can slow down or even stop the progression of keratoconus in the majority of cases. The effect is long-lasting with excellent safety.

A novel low-cost indigenous goggle design for oxygen delivery in oxygen supplemented accelerated corneal collagen cross-linking

PURPOSE

Our study aims to describe a novel low-cost indigenous design of goggles for delivery of oxygen during oxygen supplemented accelerated corneal collagen cross-linking (CXL).

METHODS

The goggles were prepared by modifying the safety goggles available in personal protective equipment (PPE) kit. The goggle has two side openings covered with plugs. One plug was removed to insert a tubing for oxygen delivery at a rate of 5 litres/minute. A 20-gauge intravenous cannula was introduced from superior aspect of the goggle for measuring oxygen saturation in periocular environment.

RESULTS

The procedure could be successfully performed without any intraoperative difficulty with an oxygen concentration between 80-90% throughout procedure. The time to achieve maximum concentration after switching on oxygen supply was between 30-60 s. None of our patients complained of any discomfort due to goggles. There was no mechanical interference of the goggles with the UV delivery system and a focused UV light could be delivered. The opening in goggles allowed for uninterrupted alignment and centration of UV light at the corneal level. The effective cost of the goggles, canula and tubing amounted to 400INR (5.50USD). There was no distortion, kinking or slippage of the tubing allowing for uninterrupted oxygen flow. These goggles could be sterilized multiple times using plasma sterilization.

CONCLUSION

The current modified cost-effective goggle design could be an effective alternative to the currently available oxygen delivery goggles, especially in a low resource setting.

Photo-Oxidation of Therapeutic Protein Formulations: From Radical Formation to Analytical Techniques

UV and ambient light-induced modifications and related degradation of therapeutic proteins are observed during manufacturing and storage. Therefore, to ensure product quality, protein formulations need to be analyzed with respect to photo-degradation processes and eventually protected from light exposure. This task usually demands the application and combination of various analytical methods. This review addresses analytical aspects of investigating photo-oxidation products and related mediators such as reactive oxygen species generated via UV and ambient light with well-established and novel techniques.

[Principles of corneal cross-linking : Presentation based on the development of the various treatment protocols]

BACKGROUND

Corneal cross-linking (CXL) is used to treat corneal ectatic diseases. The aim is to improve the reduced consolidation of the cornea in order to halt further corneal protrusion and therefore subsequent deterioration of the optical imaging proportions.

MATERIAL AND METHODS

In this article the principles of corneal cross-linking based on riboflavin and UV light are presented including recent research results. Furthermore, the most important treatment protocols including standard CXL (S-CXL), accelerated CXL (A-CXL), transepithelial CXL (TE-CXL) and the approach of the CXL procedure for thin corneas are explained.

RESULTS

The CXL method depends on four major components, the riboflavin solution, oxygen, UV light and the availability of cross-linking sites on the collagen tissue. According to the present state of knowledge, the photochemical process of the CXL method induces covalent bonds between the fibrils and proteoglycans and thus stabilizes the collagen fibers, resulting in corneal consolidation. In addition to the S‑CXL, which has proven its effectiveness and safety in a large number of studies, there are other treatment protocols that have been developed based on the Bunsen-Roscoe law of reciprocity. The A‑CXL protocol has the advantage of having a shorter irradiation time but it seems to be less effective than the S‑CXL protocol concerning the increase in corneal stiffness. The use of TE-CXL has so far not yet gained acceptance in the clinical practice.

CONCLUSION

The CXL procedures primarily aim to stabilize the cornea. In the future, in addition to stabilization of the cornea, simultaneous improvement of visual acuity will be the main focus.

Ferroin in dyes degradation by Fenton-like process: a chemical waste recycling perspective

Published literature describes the formation of the Fe (II)-phenanthroline complex (ferroin) as a stop way for Fenton processes, reducing radical yield. By contrast, this study presents evidence that ferroin can be activated by UVA in mildly acidic media in a photo-Fenton-like process. Because ferroin is the main waste from total iron determination in environmental samples, a recycling approach is suggested. Based on the best practices of waste management planning, an application of the proposed method for treating another chemical waste is presented. Titrimetric ammonia determination waste containing 2.67 mg L^-1 methyl red azo dye and 1.33 mg L^-1 methylene blue was degraded using the optimized experimental conditions: pH = 5.2-5.4; [H₂O₂] = 310 mg L^-1; [ferroin] = 1.4 mg L^-1; temperature = 36 ± 1 °C; reaction time = 165 min under UVA irradiation. Attenuation of most intense spectroscopic bands for the dyes achieved 94% (510 nm) and 96% (665 nm) reduction for methyl red and methylene blue, respectively, with degradation of ferroin itself. The present work brings empirical evidence that is possible to recycle ferroin as photo-Fenton-like process catalyst, as well as determine the best conditions for providing less acidic treated effluents with negligible suspended solid concentration, better than that obtained from classical photo-Fenton processes.

Three-year clinical observation of the outcomes of transepithelial and epithelial-off accelerated corneal collagen crosslinking treatment for different types of progressive keratoconus

In the present study, the clinical and long-term effects of accelerated transepithelial corneal collagen crosslinking (ATE-CXL) and accelerated epithelial-off corneal collagen crosslinking (A-CXL) for the treatment of different types of progressive keratoconus were compared. A total of 70 patients, including 96 eyes with advanced keratoconus, were enrolled in the study. ATE-CXL or A-CXL was performed on one or two eyes of each subject according to corneal thickness, keratoconus type and surgical approach. Patients were divided into the following four groups: Group A, ATE-CXL for central keratoconus; group B, A-CXL for central keratoconus; group C, ATE-CXL for peripheral keratoconus; and group D, A-CXL for peripheral keratoconus. Uncorrected distant visual acuity (UDVA), best-corrected distant (BD)VA and corneal astigmatism (CA) were evaluated in all patients by routine ophthalmology pre-operatively and 3 years post-operatively. Topographical features, including maximum corneal curvature (K_max), thinnest corneal thickness (TCT), anterior corneal elevation (ACE) and corneal endothelial cell density (ECD) were also compared across groups. The results suggested that pre- and post-operative UDVA, BDVA, K_max, CA and ACE values differed in all four groups (P<0.05), whereas no differences were observed between pre- and post-operative TCT and ECD (P>0.05). Concordant results were obtained between groups A and C and groups B and D. ATE-CXL achieved better control of central keratoconus UDVA, K_max and CA as compared with A-CXL. The difference between pre- and post-operative UDVA, K_max and CA as compared with A-CXL was highly correlated with the change in intraocular pressure and treatment effectiveness. There was a statistically significant improvement in BDVA with ATE-CXL for treatment of central keratoconus compared with that after A-CXL treatment (P=0.032). There were statistically significant improvements in BDVA (P=0.047), CA (P=0.045) and ACE (P=0.012) with A-CXL treatment of peripheral keratoconus when compared with ATE-CXL treatment. Central, and to a lesser extent, peripheral, keratoconus may be effectively controlled by either approach, with disease stabilization 3 years later. ATE-CXL is suggested to be the most suitable treatment for keratoconus of <400 µm with a corneal thickness of >400 µm; however, A-CXL yields superior long-term outcomes.

ROS-mediated lipid peroxidation as a result of Cu(ii) interaction with FomA protein fragments of F. nucleatum: relevance to colorectal carcinogenesis

The ability of the studied FomA protein fragments of Fusobacterium nucleatum (Fn) with copper(ii) ions (Cu(ii)-Ac-KGHGNGEEGTPTVHNE-NH2 (1Cu) and its cyclic analogue Cu(ii)-cyclo(KGHGNGEEGTPTVHNE) (2Cu)) to induce reactive oxygen species (ROS) generation, as a result of red-ox processes, was determined by UV-Vis, luminescence methods, spin trapping and cyclic voltamperometry. The contribution of 1O2 and ˙OH to DNA degradation was proved using gel electrophoresis. Furthermore, the pronounced generation of ROS by mouse colon carcinoma cells (CT26) stimulated by both copper(ii) complexes was confirmed. A fluorescence method allowed the total amounts of ROS generated inside the CT26 cells to be detected, while the spin trapping technique proved that free radicals mainly attached to the membrane surface. These last results are in agreement with the data obtained from the ICP-MS method, which demonstrates that 1Cu and 2Cu complexes are not efficiently accumulated inside the cell. Furthermore, the role of ROS in lipid peroxidation was established. The above-mentioned factors may clearly indicate the contribution of ROS generated by the studied copper(ii) complexes to colonic cell damage, which can lead to a carcinogenesis process. This study may be an important step to recognize and understand the mechanism of colon cancer initiation.

Corneal Cross-Linking: The Science Beyond the Myths and Misconceptions

PURPOSE

There has been a recent explosion in the variety of techniques used to accomplish corneal cross-linking (CXL) for the treatment of ectatic corneal diseases. To understand the success or failure of various techniques, we review the physicochemical basis of corneal CXL and re-evaluate the current principles and long-standing conventional wisdom in the light of recent, compelling, and sometimes contradictory research.

METHODS

Two clinicians and a medicinal chemist developed a list of current key topics, controversies, and questions in the field of corneal CXL based on information from current literature, medical conferences, and discussions with international practitioners of CXL.

RESULTS

Standard corneal CXL with removal of the corneal epithelium is a safe and efficacious procedure for the treatment of corneal ectasias. However, the necessity of epithelium removal is painful for patients, involves risk and requires significant recovery time. Attempts to move to transepithelial corneal CXL have been hindered by the lack of a coherent understanding of the physicochemistry of corneal CXL. Misconceptions about the applicability of the Bunsen-Roscoe law of reciprocity and the Lambert-Beer law in CXL hamper the ability to predict the effect of ultraviolet A energy during CXL. Improved understanding of CXL may also expand the treatment group for corneal ectasia to those with thinner corneas. Finally, it is essential to understand the role of oxygen in successful CXL.

CONCLUSIONS

Improved understanding of the complex interactions of riboflavin, ultraviolet A energy and oxygen in corneal CXL may provide a successful route to transepithelial corneal CXL.

Non-invasive optical method for real-time assessment of intracorneal riboflavin concentration and efficacy of corneal cross-linking

Keratoconus is the primary cause of corneal transplantation in young adults worldwide. Riboflavin/UV-A corneal cross-linking may effectively halt the progression of keratoconus if an adequate amount of riboflavin enriches the corneal stroma and is photo-oxidated by UV-A light for generating additional cross-linking bonds between stromal proteins and strengthening the biomechanics of the weakened cornea. Here we reported an UV-A theranostic prototype device for performing corneal cross-linking with the ability to assess corneal intrastromal concentration of riboflavin and to estimate treatment efficacy in real time. Seventeen human donor corneas were treated according to the conventional riboflavin/UV-A corneal cross-linking protocol. Ten of these tissues were probed with atomic force microscopy in order to correlate the intrastromal riboflavin concentration recorded during treatment with the increase in elastic modulus of the anterior corneal stroma. The intrastromal riboflavin concentration and its consumption during UV-A irradiation of the cornea were highly significantly correlated (R = 0.79; P = .03) with the treatment-induced stromal stiffening effect. The present study showed an ophthalmic device that provided an innovative, non-invasive, real-time monitoring solution for estimating corneal cross-linking treatment efficacy on a personalized basis.

The Effect of Ascorbic Acid (Vitamin C) on Transepithelial Corneal Cross-Linking in Rabbits

PURPOSE

To evaluate the effects of ascorbic acid (vitamin C), the main antioxidant agent in the cornea on transepithelial corneal cross-linking (CXL) where the main mechanism is oxidation.

METHODS

Twenty eyes of 20 rabbits were divided into 3 groups: Group 1 (7 eyes) had transepithelial corneal CXL after being fed with normal diet; Group 2 (7 eyes) had corneal CXL after once-daily subcutaneous injections of 200 mg of ascorbic acid in addition to normal diet; and the control group (6 eyes) was fed with normal diet but did not have corneal CXL performed. Ascorbic acid levels were measured in aqueous humor and plasma, and biomechanical measurements were applied to the cornea.

RESULTS

There was a significant difference in ascorbic acid levels of plasma (P = 0.008) and aqueous humor (P = 0.006) between group 1 and 2. The Young's modulus values of group 1 and 2 were similar (P = 0.741) and were significantly higher than the control group (P = 0.02 and P = 0.01). The increase rate in Young's modulus values was 37.3% in group 1 and 43.9% in group 2 compared to control group. The ultimate strain values in group 1 and 2 were similar (P = 0.632) and were significantly higher than control group (P = 0.04, P = 0.03). The ultimate stress values in group 1 and 2 were similar (P = 0.836) and were significantly lower than control group (P = 0.001, P = 0.001).

CONCLUSIONS

Systemic vitamin C does not appear to decrease effectiveness of transepithelial corneal CXL. Therefore, there is no reason to stop or reduce vitamin C supplementation before corneal CXL therapy.

UVA-activated riboflavin improves the strength of human dentin

The aim of this study was to evaluate the effects of UVA-activated riboflavin (UVA-RF) on the mechanical properties of non-demineralized human dentin. Dentin specimens obtained from 20 teeth were randomly divided into the following four groups: group 1 (control): no treatment, group 2 (low UVA-RF): specimens were exposed to UVA-RF for 10 min, group 3 (medium UVA-RF): specimens were exposed to UVA-RF for 30 min, and group 4 (high UVA-RF): specimens were exposed to UVA-RF for 60 min. Three-point flexural test and Raman spectroscopic analyses were performed. The mean flexural strengths (MPa) were 129.96, 128.96, 144.21, and 147.54, and the mean elastic modulus (GPa) were 8.59, 8.38, 10.21, and 9.87 for groups 1 to 4, respectively. Raman spectra showed chemical modifications of dental collagen under medium and high UVA-RF treatment. We conclude that medium and high UVA-RF increases the strength of non-demineralized human dentin by collagen crosslinking.

Protein Oxidation Levels After Different Corneal Collagen Cross-Linking Methods

PURPOSE

To evaluate advanced oxidation protein products (AOPP) levels, superoxide dismutase (SOD) enzyme activity, and total sulfhydryl (TSH) levels in rabbit corneas after different corneal collagen cross-linking (CXL) methods.

METHODS

Eighteen eyes of 9 adult New Zealand rabbits were divided into 3 groups of 6 eyes. The standard CXL group was continuously exposed to UV-A at a power setting of 3 mW/cm for 30 minutes. The accelerated CXL (A-CXL) group was continuously exposed to UV-A at a power setting of 30 mW/cm for 3 minutes. The pulse light-accelerated CXL (PLA-CXL) group received UV-A at a power setting of 30 mW/cm for 6 minutes of pulsed exposure (1 second on, 1 second off). Corneas were obtained after 1 hour of UV-A exposure, and 360-degree keratotomy was performed. SOD enzyme activity, AOPP, and TSH levels were measured in the corneal tissues.

RESULTS

Compared with the standard CXL and A-CXL groups (133.2 ± 8.5 and 140.2 ± 6.2 μmol/mg, respectively), AOPP levels were found to be significantly increased in the PLA-CXL group (230.7 ± 30.2 μmol/mg) (P = 0.005 and 0.009, respectively). SOD enzyme activities and TSH levels did not differ between the groups (P = 0.167 and 0.187, respectively).

CONCLUSIONS

CXL creates covalent bonds between collagen fibers because of reactive oxygen species. This means that more oxygen concentration during the CXL method will produce more reactive oxygen species and, thereby, AOPP. This means that in which CXL method occurs in more oxygen concentration that will produce more reactive oxygen species and thereby AOPP. This study demonstrated that PLA-CXL results in more AOPP formation than did standard CXL and A-CXL.

Interaction of ultraviolet light with the cornea: clinical implications for corneal crosslinking

Understanding ultraviolet (UV) interaction with the human corneal tissue is of interest among corneal specialists given the widespread application of corneal crosslinking. This article reviews the current knowledge of light interaction with the cornea in the UV wavelength range. It also uses a novel experimental study to illustrate the role of 2 important corneal properties that have not yet been clarified: the epithelial contribution to overall UVA corneal absorbance and the regional anisotropy of UVA light transmittance. Finally, it presents the most recent insights into how different methods of UVA light irradiation and corneal soaking with riboflavin influence the outcome of corneal crosslinking.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.