Enhancement of corneal permeation of riboflavin-5'-phosphate through vitamin E TPGS: a promising approach in corneal trans-epithelial cross linking treatment

Repurposing FDA-approved drugs as NLRP3 inhibitors against inflammatory diseases: machine learning and molecular simulation approaches

Activation of NLRP3 (NOD-like receptor family, pyrin domain-containing protein 3) has been associated with multiple chronic pathologies, including diabetes, atherosclerosis, and rheumatoid arthritis. Moreover, histone deacetylases (HDACs), specifically HDAC6 is required for the NLRP3 inflammasome to assemble and activate. Thus, NLRP3 serves as an attractive target for the development of novel therapeutic approaches. Several companies are now attempting to develop specific modulators of the NLRP3 inflammasome, but only a handful of small molecules of NLRP3 inflammasome inhibitors, such as MCC950 and Tranilast, are currently available for clinical use. However, their use is limited due to severe side effects and short half-lives. Thus, the repurposing of FDA-approved drugs with NLRP3 inhibitory activity is needed. The present study was aimed at repurposing preexisting drugs that might act as safe and effective NLRP3 inhibitors. A library of 2,697 FDA-approved drugs was screened for binding with NLRP3 (PDB: 7ALV) using Glide (Schrödinger). The top seven FDA-approved drugs with potential binding affinities were selected based on docking scores and subjected to ADMET profiling using pkCSM and SwissADME. The binding of the ADMET-favorable FDA-approved drugs to NLRP3 was validated using MMGBSA (Prime) and Molecular Dynamics (Desmond) in the Schrödinger suite. ADMET profiling revealed that of the seven best docking drugs, empagliflozin and citicoline had good drug-likeness properties. Moreover, MMGBSA analysis and molecular dynamics demonstrated that empagliflozin and citicoline exhibited stable ligand-NLRP3 interactions in the presence of solvents. This study sheds light on the ability of various FDA-approved drugs to act as NLRP3 inhibitors.

Epi-off riboflavin with vitamin E TPGS (Ribocross®) cross-linking: one-year outcome

PURPOSE

To assess the short and mid-term outcomes of epithelium-off (epi-off) corneal collagen cross-linking using Riboflavin with Vitamin E TPGS (Epi-off Ribocross® CXL) for progressive keratoconus (KC).

DESIGN

Retrospective, single-center non-comparative interventional study.

METHODS

Patients with progressive keratoconus who underwent CXL using (Epi-off Ribocross® CXL) from May 2021 to May 2022 who completed at least 12 months of follow-up in Humanitas Clinical and Research Center, Rozzano, Milan, Italy. Corrected distance visual acuity with spectable (CDVA), tomographic parameters (Belin ABCD) and topographic parameters were evaluated at baseline and at last follow up.

RESULTS

Twenty eyes of twenty patients fulfilled inclusion criteria. CDVA remained stable at last follow up (0.88 ± 0.19 from 0.83 ± 0.21, p = 0.45) with a significant reduction in cylinder (1.97 ± 1.69 from 2.78 ± 2.19, p = 0.03). Kmax significantly improved from 53.18D ± 6.32 to 50.96 ± 5.3D (p = 0.005). At the last follow up, no case of progression was noted.

CONCLUSIONS

Epi-off Ribocross® CXL proved to be a safe treatment for progressive KC, with a stabilization of all cases at the one year follow up. Further studies are needed to confirm long-term stability.

A sterilizable platform based on crosslinked xanthan gum for controlled-release of polymeric micelles: Ocular application for the delivery of neuroprotective compounds to the posterior eye segment

TPGS (D-α-tocopheryl polyethylene glycol 1000 succinate) polymeric micelles show interesting properties for ocular administration thanks to their solubilization capability, nanometric size and tissue penetration ability. However, micelles formulations are generally characterized by low viscosity, poor adhesion and very short retention time at the administration site. Therefore, the idea behind this work is the preparation and characterization of a crosslinked film based on xanthan gum that contains TPGS micelles and is capable of controlling their release. The system was loaded with melatonin and cyclosporin A, neuroprotective compounds to be delivered to the posterior eye segment. Citric acid and heating at different times and temperatures were exploited as crosslinking approach, giving the possibility to tune swelling, micelles release and drug release. The biocompatibility of the platform was confirmed by HET-CAM assay. Ex vivo studies on isolated porcine ocular tissues, conducted using Franz cells and two-photon microscopy, demonstrated the potential of the xanthan gum-based platform and enlightened micelles penetration mechanism. Finally, the sterilization step was approached, and a process to simultaneously crosslink and sterilize the platform was developed.

Cyclosporine A micellar nasal spray characterization and antiviral action against SARS-CoV-2

The upper airways represent the point of entrance from where Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection spreads to the lungs. In the present work, α-tocopheryl-polyethylene-glycol succinate (TPGS) micelles loaded with cyclosporine A (CSA) were developed for nasal administration to prevent or treat the viral infection in the very first phases. The behavior of the micelles in presence of simulated nasal mucus was investigated in terms of stability and mucopenetration rate, evidencing long-term stability and fast diffusion across the glycoproteins matrix. Moreover, the spray characteristics of the micellar formulation and deposition profile in a silicon nasal model were studied using three nasal spray devices. Results allowed to identify the nasal spray pump (BiVax, Aptar) able to provide the wider and uniform deposition of the nasal cavity. The cyclosporine A micelles antiviral activity against SARS-CoV-2 was tested on the Omicron BA.1 variant using Vero E6 cells with protocols simulating treatment before, during and after the infection of the upper airways. Complete viral inactivation was observed for the cyclosporine-loaded micelles while a very low activity was evidenced for the non-formulated drug, suggesting a synergistic activity of the drug and the formulation. In conclusion, this work showed that the developed cyclosporine A-loaded micellar formulations have the potential to be clinically effective against a wide spectrum of coronavirus variants.

A review of the epithelial and stromal effects of corneal collagen crosslinking

Induced corneal collagen crosslinking and mechanical stiffening via ultraviolet-A photoactivation of riboflavin (UVA CXL) is now a common treatment for corneal ectasia and Keratoconus. Some effects of the procedure such as induced mechanical stiffening, corneal flattening, and cellular toxicity are well-known, but others remain more controversial. Authors report a variety of contradictory effects, and provide evidence based on individual results and observations. A full understanding of the effects of and mechanisms behind this procedure are essential to predicting its outcome. A growing interest in modifications to the standard UVA CXL protocol, such as transepithelial or accelerated UVA CXL, makes analyzing the literature as a whole more urgent. This review presents an analysis of both the agreed-upon and contradictory results reported and the various methods used to obtain them.

Recent advances in medicinal compounds related to corneal crosslinking

Corneal crosslinking (CXL) is the recognized technique to strengthen corneal collagen fibers through photodynamic reaction, aiming to halt progressive and irregular changes in corneal shape. CXL has greatly changed the treatment for keratoconus (KCN) since it was introduced in the late 1990's. Numerous improvements of CXL have been made during its developing course of more than 20 years. CXL involves quite a lot of materials, including crosslinking agents, enhancers, and supplements. A general summary of existing common crosslinking agents, enhancers, and supplements helps give a more comprehensive picture of CXL. Either innovative use of existing materials or research and development of new materials will further improve the safety, effectiveness, stability, and general applicability of CXL, and finally benefit the patients.

Comparison of topographic outcomes between HPMC based and vitamin E TPGS based riboflavin solutions after corneal cross-linking

PURPOSE

To compare the visual and topographic results between patients who underwent epithelium-off cross-linking using riboflavin solutions compounds hydroxypropyl methylcellulose (HPMC) 1.1% and D-alpha-tocopheryl polyethylene-glycol 1000 succinate (VE-TPGS).

METHODS

In this study, 37 eyes treated with HPMC and 29 eyes treated with VE-TPGS were evaluated retrospectively. Spherical equivalent (SE), refractive cylinder, corrected distance visual acuity tests (CDVA), corneal topography indices (flat and steep meridians' keratometry (K1 and K2)), maximum keratometry (K max), central, thinnest, and apical corneal thicknesses, the front and back keratoconus vertex index (KVf, KVb), and the surface asymmetry index of the front and back surface (SIf, SIb), and endothelial cell density were compared at baseline and postoperative follow-up visits (1, 3, 6, and 12months).

RESULTS

At the end of the 12th-month, K1, K2, and Kmax were decreased in both groups. In comparison to baseline, there was a decline in the HPMC group in the 3rd- month Kmax change, an increase was observed in the VE-TPGS group. In the 12th-month KVb change, an increase was observed in the HPMC group compared to the baseline, while a decrease was observed in the VE-TPGS group. The other parameters did not show a statistically significant difference between the groups (p > 0.05).

CONCLUSION

At the end of 12 months, both riboflavins were effective in stopping the progression of keratoconus and were safe for endothelium. Although both riboflavins provide a decrease in keratometry values, it can be said that VE-TPGS is superior to HPMC in correcting the ectasia on the posterior corneal surface.

Safety and Efficacy of Corneal Cross-Linking in Patients Affected by Keratoconus: Long-Term Results

The present study evaluated the effectiveness and safety of corneal collagen cross-linking (CXL). A total of 886 eyes with progressive keratoconus were enrolled in a retrospective cohort study in a tertiary care university hospital. CXL was performed using a standard epithelium-off Dresden protocol. Visual outcomes, maximum keratometry (Kmax), demarcation line measurements, and complications were recorded. Visual outcomes and keratometric data were analyzed in a subgroup comprising 610 eyes. Uncorrected distance visual acuity (UDVA) improved from 0.49 ± 0.38 LogMAR to 0.47 ± 0.39 LogMAR (p = 0.03, n = 610) three years after the procedure, while corrected distance visual acuity (CDVA) improved from 0.15 ± 0.14 LogMAR to 0.14 ± 0.15 LogMAR (p = 0.007, n = 610). A significant reduction of Kmax from 56.28 ± 6.10 to 54.98 ± 6.19 (p < 0.001, n = 610) was observed three years after CXL. In five eyes (0.82%, 5/610) keratoconus progression continued after CXL. Three eyes were retreated successfully with documented refractive and topographic stability after five years. In the 35 eyes that completed 10 years of follow-up, mean visual acuity and topographic parameters remained stable. In conclusion, CXL is a safe and effective treatment for avoiding keratoconus progression. Long-term data are encouraging, supporting a high safety profile for this procedure.

Predicting corneal cross-linking treatment efficacy with real-time assessment of corneal riboflavin concentration

PURPOSE

To assess predictability of tissue biomechanical stiffening induced by UV-A light-mediated real-time assessment of riboflavin concentration during corneal crosslinking (CXL) of human donor tissues.

SETTING

Studio Italiano di Oftalmologia, Rome, Italy.

DESIGN

Laboratory study.

METHODS

20 sclerocorneal tissues were randomly stratified to undergo CXL with either the epithelium intact (n = 12) or removed (n = 8). Samples underwent corneal soaking with 0.22% riboflavin formulation (RitSight) with dosing time of t = 10 minutes and t = 20 minutes in epithelium-off and epithelium-on protocols, respectively. All tissues underwent 9-minute UV-A irradiance at 10 mW/cm 2 using theranostic device (C4V CHROMO4VIS). The device used controlled UV-A light irradiation to induce both imaging and treatment of the cornea, providing a real-time measure of corneal riboflavin concentration and treatment efficacy (ie, theranostic score) during surgery. Tissue biomechanics were assessed with an air-puff device (Corvis), which was performed before and after treatment. A 3-element viscoelastic model was developed to fit the corneal deformation response to air-puff excitation and to calculate the mean corneal stiffness parameter (k c ).

RESULTS

Significant corneal tissue stiffening ( P < .05) was induced by the theranostic UV-A device in either CXL treatment protocol. Significant correlation was found between the theranostic score and the increase in k c ( R = 0.75; P = .003). The score showed high accuracy (94%) and precision (94%) to predict correctly samples that had improved tissue biomechanical strengthening.

CONCLUSIONS

Real-time assessment of corneal riboflavin concentration provided a predictive and precise approach for significant improvement of tissue strength on individual corneas, regardless of CXL treatment protocol.

Short-Term Effect of Conventional Versus Accelerated Corneal Cross-Linking Protocol on Corneal Geography and Stability

Purpose: To determine the 6-month effect of conventional (CXL30) and accelerated cross-linking with a UVA intensity of 9 mW/cm² (CXL10) on corneal stability and to investigate whether there was a difference in ABCD grading system parameters regarding the two different procedures. Methods: Twenty-eight eyes of 28 patients with a documented keratoconus (KN) progression were included. Patients were selected to undergo either epi off CXL30 or CXL10. At the baseline and the follow-up visits after one (V1), three (V2), and six months (V3), the patients underwent complete ophthalmic examination and corneal tomography. Results: In the CXL30 group, all the parameters from the ABCD grading system significantly changed from baseline to V3; parameter A decreased (p = 0.048), B and C increased (p = 0.010, p < 0.001), and D decreased (p < 0.001). In the CXL10 group, there were no changes in parameters A (p = 0.247) and B (p = 0.933), though parameter C increased (p = 0.001) and D decreased (p < 0.001). After an initial decline after one month, visual acuity (VA) recovered on V2 and V3 (p < 0.001), and median maximal keratometry (Kmax) decreased in both groups (p = 0.001, p = 0.035). In the CXL30 group, there were significant changes in other parameters; average pachymetric progression index (p < 0.001), Ambrósio relational thickness maximum (ARTmax) (p = 0.008), front and back mean keratometry (p < 0.001), pachymetry apex (PA) (p < 0.001), and front elevation (p = 0.042). However, in the CXL10 group, there were significant changes only in ARTmax (p = 0.019) and PA (p < 0.001). Conclusion: Both epi-off CXL protocols showed similar short-term efficacy in improving VA and Kmax, halting the progression of KN, and both similarly changed tomographic parameters. However, the conventional protocol modified the cornea more significantly.

Efficacy and Safety of Standard Corneal Cross-Linking Procedures Performed With Short Versus Standard Riboflavin Induction: A Save Sight Keratoconus Registry Study

PURPOSE

The objective of this study was to compare the effectiveness and safety of short versus standard riboflavin induction times in cross-linking (CXL) for keratoconus.

METHODS

A retrospective comparative study was conducted with data from the Save Sight Keratoconus Registry. Inclusion criteria were epithelium-off technique, standard UVA CXL protocol (3 mW/cm 2 for 30 minutes), riboflavin induction for 15 minutes (short) or 30 minutes (standard), and 1 year of follow-up data after CXL. Outcome measures included changes in best-corrected visual acuity (BCVA), keratometry in the steepest meridian (K2), maximum keratometry (Kmax), thinnest pachymetry (TCT), and adverse events. Analysis was conducted using mixed-effects regression models adjusted for age, sex, visual acuity, keratometry, pachymetry, practice, and eye laterality.

RESULTS

Two hundred eighty eyes (237 patients; mean, 27.3 ± 10.5 years old; 30% female) were included. The riboflavin induction time was short in 102 eyes (82 patients) and standard in 178 eyes (155 patients). The baseline characteristics (sex, mean age, BCVA, keratometry, and pachymetry [TCT]) were similar between the groups. At the 1-year follow-up visit, no statistically significant differences were observed in flattening in K2 and improvement in BCVA. Greater Kmax flattening [-1.5 diopters (D) vs. -0.5D, P = 0.031] and a greater proportion of >2% increase in TCT (23.5 vs. 11.3, P = 0.034) and haze (29 vs. 15, P = 0.005) were observed with short riboflavin induction.

CONCLUSIONS

Short and standard riboflavin induction times achieved similar degrees of flattening in K2 and improvement in vision. Greater improvements in Kmax and TCT were seen with short riboflavin times; however, this group had higher rates of haze.

An Alternative Device for the Topical Treatment of Oral Cancer: Development and Ex-Vivo Evaluation of Imiquimod-Loaded Polysaccharides Formulations

The topical use of imiquimod (IMQ), a non-specific immune response modifier, showed to be a promising therapeutic option for the early-stage treatment of some type of oral cancer, even when performed with a formulation (Aldara®) developed and approved for skin application. The aim of this work was the development of buccal formulations for the topical administration of IMQ with improved mucosal retention and reduced trans-mucosal permeation when compared to the reference formulation. Three different hydrogels based on carboxymethyl chitosan (CMChit), sodium alginate (A), and xanthan gum (X) in different combinations were prepared, and the loading of imiquimod was successfully performed by using a micellar formulation based on d-α-tocopheril polyethylene glycol 100 succinate (TPGS). Except for CMChit formulation, in all the other cases, the performance in vitro on the mucosa resulted comparable to the commercial formulation, despite the drug loading being 50-fold lower. Converting the gels in films did not modify the IMQ accumulated with respect to the correspondent gel formulation but produced as a positive effect a significant reduction in the amount permeated. Compared to the commercial formulation, this reduction was significant (p < 0.01) in the case of X film, resulting in an improvement of the retained/permeated ratio from 1 to 5.44. Mucoadhesion evaluation showed similar behavior when comparing the developed gels and the commercial formulation, and an excellent bioadhesion was observed for the films.

Cyclosporine-loaded micelles for ocular delivery: Investigating the penetration mechanisms

Cyclosporine is an immunomodulatory drug commonly used for the treatment of mild-to-severe dry eye syndrome as well as intermediate and posterior segment diseases as uveitis. The ocular administration is however hampered by its relatively high molecular weight and poor permeability across biological barriers. The aim of this work was to identify a micellar formulation with the ability to solubilize a considerable amount of cyclosporine and promote its transport across ocular barriers. Non-ionic amphiphilic polymers used for micelles preparation were tocopherol polyethylene glycol 1000 succinate (TPGS) and Solutol® HS15. Furthermore, the addition of alpha-linolenic acid was assessed. A second aim was to evaluate micelles fate in the ocular tissues (cornea and sclera) to shed light on penetration mechanisms. This was possible by extracting and quantifying both drug and polymer in the tissues, by studying TPGS hydrolysis in a bio-relevant environment and by following micelles penetration with two-photon microscopy. Furthermore, TPGS role as permeation enhancer on the cornea, with possible irreversible modifications of tissue permeability, was analyzed. Results showed that TPGS micelles (approx. 13 nm in size), loaded with 5 mg/ml of cyclosporine, promoted drug retention in both the cornea and the sclera. Data demonstrated that micelles behavior strictly depends on the tissue: micelles disruption occurs in contact with the cornea, while intact micelles diffuse in the interfibrillar pores of the sclera and form a reservoir that can sustain over time drug delivery to the deeper tissues. Finally, cornea quickly restore the barrier properties after TPGS removal from the tissue, demonstrating its potential good tolerability for ocular application.

Synthesis and Incorporation of Quaternary Ammonium Silane Antimicrobial into Self-Crosslinked Type I Collagen Scaffold: A Hybrid Formulation for 3D Printing

Novel 3D-biomaterial scaffold is constructed having a combination of a new quaternary ammonium silane (k21) antimicrobial impregnated in 3D collagen printed scaffolds cross linked with Riboflavin in presence of d-alpha-tocopheryl poly(ethyleneglycol)-1000-succinate. Groups of "0.1% and 0.2% k21", and "0.1% and 0.2% Chlorhexidine (CHX)" are prepared. k21/CHX with neutralized collagen is printed with BioX. Riboflavin is photo-activated and examined using epifluorescence for Aggregatibacter actinomycetemcomitans (7-days). Collagen is examined using TEM and measured for porosity, and shape-fitting. Raman and tandem mass/solid-state are performed with molecular-docking and circular-dichroism. X-ray diffractions, rheological tests, contact angle, and ninhydrin assay are conducted. k21 samples demonstrated collagen aggregates while 0.1% CHX and 0.2% CHX showed irregularities. Porosity of control and "0.1% and 0.2% k21" scaffolds show no differences. Low contact angle, improved elastic-modulus, rigidity, and smaller strain in k21 groups are seen. Bacteria are reduced and strong organic intensities are seen in k21 scaffolds. Simulation shows hydrophobicity/electrostatic interaction. Crosslinking is observed in 0.2% CHX/79% and 0.2% k21/80%. Circular dichroism for k21 are suggestive of triple helix. XRD patterns appear at d = 5.97, 3.03, 2.78, 2.1, and 2.90 A°. 3D-printing of collagen impregnated with quaternary ammonium silane produces a promising scaffold with antimicrobial potency and structural stability.

Topo-Pachimetric Accelerated Epi-On Cross-Linking Compared to the Dresden Protocol Using Riboflavin with Vitamin E TPGS: Results of a 2-Year Randomized Study

In the present study (clinical trial registration number: NCT05019768), we compared the clinical outcome of corneal cross-linking with either the standard Dresden (sCXL) or the accelerated custom-fast (aCFXL) ultraviolet A irradiation protocol using riboflavin–D-α-tocopheryl poly(ethylene glycol)-1000 succinate for progressive keratoconus. Fifty-four eyes of forty-one patients were randomized to either of the two CXL protocols and checked before treatment and at the 2-year follow-up. The sCXL group was subjected to CXL with 30 min of pre-soaking and 3 mW/cm² UVA irradiation for 30 min. The aCFXL group was subjected to CXL with 10 min of pre-soaking and UVA irradiation of 1.8 ± 0.9 mW/cm² for 10 min ± 1.5 min. In both groups, a solution of riboflavin–vitamin E TPGS was used. Uncorrected distance visual acuity, corrected distance visual acuity, pachymetry, Scheimpflug tomography, and corneal hysteresis were performed at baseline and after 24 months. Both groups showed a statistically significant improvement in corrected distance visual acuity, and keratometric and corneal hysteresis compared to baseline conditions; no statistically significant differences in outcomes between the two groups were observed. Improvement in refractive, topographic, and biomechanical parameters were observed after sCXL and aCFXL, making the riboflavin–VE-TPGS solution an effective option as a permeation enhancer in CXL procedures. Deeper stromal penetration of riboflavin could be complemented by photo-protection against UVA and free radicals formed during photoinduced processes.

The Effect of Sodium Iodide on Stromal Loading, Distribution and Degradation of Riboflavin in a Rabbit Model of Transepithelial Corneal Crosslinking

Purpose

To evaluate effects of sodium iodide (NaI) on riboflavin concentration in corneal stroma before and during ultraviolet A (UVA) light exposure using a novel transepithelial corneal collagen crosslinking (CXL) procedure (EpiSmart CXL system, CXL Ophthalmics, Encinitas CA).

Methods

Riboflavin solutions with NaI (Ribostat, CXL Ophthalmics, Encinitas CA) and without NaI were used for CXL in rabbits using EpiSmart. A pilot study determined sufficient riboflavin loading time. Four rabbits were dosed and monitored. Riboflavin fluorescence intensity was assessed from masked slit-lamp photos. A 12 min loading time was selected. Sixteen additional rabbits received the two formulae in contralateral eyes for CXL. Riboflavin uptake was assessed at 0, 10, 15, 20, 25, and 30 min of UVA exposure using a scale for riboflavin fluorescence previously validated against stromal concentration. Post sacrifice, corneal stromal samples were analyzed for concentrations of riboflavin and riboflavin 5ʹ-phosphate.

Results

Eyes dosed with NaI riboflavin had higher riboflavin grades compared to eyes dosed with the NaI-free riboflavin formulation immediately after riboflavin loading and persisting throughout UVA exposure, with significantly higher (P < 0.01 to < 0.05) riboflavin grades from 15 through 25 min of UVA exposure. Riboflavin grades decreased more slowly in eyes dosed with NaI riboflavin through 25 minutes of UVA exposure. Minor conjunctival irritation was noted with or without NaI.

Conclusion

The addition of NaI to riboflavin solution is associated with increased riboflavin concentration in corneal stroma throughout a clinically relevant time course of UVA exposure. This effect may be a combination of enhanced epithelial penetration and reduced riboflavin photodegradation and should enhance intrastromal crosslinking.

Enhancement in corneal permeability of riboflavin using cyclodextrin derivates complexes as a previous step to transepithelial cross-linking

Corneal cross-linking has been described as an effective treatment to slow the progression of keratoconus. The standard protocol entails corneal epithelial removal to allow the diffusion of riboflavin into the stroma. Although, de-epithelization can generate risks or complications that transepithelial cross-linking tries to solve or avoid. Different formulations were developed after verifying that hydroxypropyl-β-cyclodextrin (HPβCD) and sulfobuthylether-β-cyclodextrin (SBEβCD) in a 20% concentration, increased the solubility of practically insoluble in water drugs such as riboflavin from 0.12 mg/mL to 0.35 mg/mL and 0.29 mg/mL respectively. These values were higher when chitosan and arginine were added to the formulation, showing solubility of 0.78 mg/mL when HPβCD concentration was not modified. Ex vivo corneal permeability was measured after having kept in contact bovine corneas with intact epithelium for 5 h with the 0.1 mg/mL riboflavin solution, the formulations developed and a reproduced nanoemulsion from another work. Riboflavin's permeability was increased when cyclodextrins, chitosan, and arginine were part of the formulations, compared to the control drug solution. The best permeability coefficient was reached when riboflavin was combined with 40% (w/v) HPβCD, 0.5% (w/w) arginine, and 0.5% (w/w) chitosan. After having carried out toxicity studies as bovine corneal opacity and permeability (BCOP) and Heńs Egg Test - Chorioallantoic Membrane Test (HET-CAM) it was verified that both, the active ingredients and the excipients of the different formulations were not harmful without generating irritation, loss of transparency or corneal permeability alterations. The results show the great potential of the ocular developed solution for their use in transepithelial cross-linking for keratoconus treatment.

Compaction of very thin corneas from ultraviolet A riboflavin-vitamin E transepithelial cross-linking

The purpose of the study was to determine the decrease in pachymetry of very thin corneas with advanced keratoconus due to corneal compaction from the ultraviolet-A (UV-A) irradiation phase of transepithelial (epi-on) cross-linking. Twenty removed corneal buttons were obtained from patients who underwent penetrating keratoplasty for advanced keratoconus. Removed corneal buttons selected from among the post-surgical specimens for this study had intact epithelium, no scarring or surgical cautery, endothelial cell density >2500 cells/mm², and average pachymetry over the measured points of below 400 μm. Corneas were mounted in a Franz chamber. Each epithelial surface was soaked in isotonic riboflavin and D-alpha-tocopheryl polyethylene glycol 1000 succinate (Ribocross® IROMED Group, Italy) for 15 min. Pachymetry was measured at three points over both the shielded and unshielded corneal halves for each corneal button. Surfaces were then washed in saline to remove the Ribocross®. Shields from UV-A irradiation over half of each cornea were then fixed to stand 5 mm above the test corneas. UV-A irradiation using the custom fast cross-linking (CF-CXL) protocol was then performed for the typical 10 ± 1.5 min, for a total energy of 1.08 ± 0.6 J/cm² after which pachymetry was re-measured. The average percent change in pachymetry was -0.43% ± 0.38% (maximum -1.06%) in the shielded half. Pachymetry change was -6.2% ± 2.2% (maximum 12%) in the cross-linked halves. In conclusion, we estimate that the change in corneal thickness from corneal compaction due to the cross-linking reaction itself was -5.8% ± 2.2%. Scanning electron microscopy of cross-linked corneal segments showed stromal fiber contraction.

Corneal Cross-Linking for Keratoconus: Current Knowledge and Practice and Future Trends

Corneal collagen cross-linking (CXL) with riboflavin is an accepted universal standard of care for our keratoconus patients with progressive disease. It has been a game changer in how we manage keratoconus. Early diagnosis and treatment is essential in paediatric patients as younger patients progress more rapidly and have poorer transplant outcomes. There is an ongoing debate around standard, accelerated, and transepithelial protocols of CXL, the role of CXL, and the combination of laser refractive surgery. Future developments will improve CXL safety and efficacy and the scope of utilization, but we must be careful not to leap too far ahead with clinical applications before publication of basic science research and good clinical results with standardized protocols.

Effectiveness and Safety of Topical Chlorhexidine and Vitamin E TPGS in the Treatment of Acanthamoeba Keratitis: A Survey on 29 Cases

This study aimed to test the effectiveness of a solution of chlorhexidine (CHX) and D-α-tocopheryl polyethylene glycol succinate (Vitamin E TPGS or TPGS) in the treatment of Acanthamoeba keratitis (AK) via a prospective, interventional case series study. Twenty-nine consecutive patients with AK were enrolled. At baseline, best-corrected visual acuity (BCVA), slit lamp examination, confocal microscopy, and polymerase chain reaction (PCR) were performed. Topical therapy with CHX 0.02% and VE-TPGS 0.2% was administered hourly/24 h for the first day, hourly in the daytime for the next three days, and finally, every two hours in the daytime up to one month. BCVA and ocular inflammation were recorded after two weeks, four weeks, and three months from baseline. Mean logMAR BCVA significantly improved at two weeks (0.78) compared to baseline (1.76), remaining stable over time (0.80 at four weeks, 0.77 at three months). Ocular inflammation improved in 14 eyes at 2 weeks, with further slow improvements in all cases. At three months, no patient had signs of corneal inflammation. The presence of corneal scars was first recorded at the two-week follow-up, with an enlargement at the four-week follow-up. At the three-month follow-up, 19 eyes still showed corneal opacities. In conclusion, the tested solution was shown to be effective for the treatment of AK. Furthermore, it might represent a good first-line treatment.

Nonlinear optical crosslinking (NLO CXL) for correcting refractive errors

Ultraviolet A (UVA) light-based photoactivation of riboflavin (Rf) to induce corneal crosslinking (CXL) and mechanical stiffening is now a well-known treatment for corneal ectasia and Keratoconus that is being used in a topographically guided photorefractive intrastromal CXL (PiXL) procedure to treat low degrees of refractive errors. Alternative approaches for non-invasive treatment of refractive errors have also been proposed that use femtosecond lasers (FS) that provide much faster, more precise, and safer results than UVA CXL. One such treatment, nonlinear optical crosslinking (NLO CXL), has been able to replicate the effects of UVA CXL, while producing a smaller area of cellular damage and requiring a shorter procedure time. Unlike UVA CXL, the treatment volume of NLO CXL only occurs within the focal volume of the laser, which can be placed at any depth and scanned into any pattern for true topographically guided refractive correction. This review presents our experience with using FS lasers to photoactivate Rf and perform highly controlled corneal CXL that leads to mechanical stiffening and changes in corneal shape.

A Novel Vitamin E TPGS-Based Formulation Enhances Chlorhexidine Bioavailability in Corneal Layers

Keratitis is a severe condition characterized by inflammation of the cornea following a local trauma. The most common ocular disease is the bacterial one, which requires an antibiotic treatment. The major limitation of this therapy is the resistance of the antibiotic. For this reason, alternative procedures have been developed and consist of antimicrobial molecules. One of the most used is the chlorhexidine gluconate, which has shown activity versus Gram-positive and Gram-negative bacteria and fungi. In addition to its efficiency, chlorhexidine shows low toxicity levels for mammalian cells and is a low-cost molecule. Despite its multiple benefits, chlorhexidine, if used at concentrations higher than 0.02% (w/w), can cause local eye irritation. Additionally, its poor penetrability through the cornea makes necessary frequent instillation of eye drops for a prolonged time. Due to these limitations, alternative drug delivery strategies are required. Here, we report a novel formulation based on the combination of d-alpha-tocopherol polyethylene glycol 1000 succinate with chlorhexidine, which results in higher accumulation of the drug in human corneas measured by liquid chromatography and strong antimicrobial activity. Moreover, this formulation does not cause any toxic effect on human cells and is well tolerated by rabbit eyes. Therefore this novel formulation represents a good candidate for the treatment of keratitis that overcomes the risk of antibiotic resistance.

Enhanced Transepithelial Riboflavin Delivery Using Femtosecond Laser-Machined Epithelial Microchannels

Purpose

This study describes a femtosecond laser (FS) approach to machine corneal epithelial microchannels for enhancing riboflavin (Rf) penetration into the cornea prior to corneal crosslinking (CXL).

Methods

Using a 1030-nm FS laser with 5- to 10-µJ pulse energy, the corneal epithelium of slaughterhouse rabbit eyes was machined to create 2-µm-diameter by 25-µm-long microchannels at a density of 100 or 400 channels/mm². Rf penetration through the microchannels was then determined by applying 1% Rf in phosphate-buffered saline for 30 minutes followed by removal of the cornea and extraction from the central stromal button. Stromal Rf concentrations were then compared to those obtained using standard epithelial debridement or 0.01% benzalkonium chloride (BAK) to disrupt the epithelial barrier.

Results

Microchannels formed using a 5-µJ/pulse at a density of 400 channels/mm² achieved a stromal Rf concentration that was 50% of that achieved by removal of the corneal epithelium and imbibing with 1% Rf. Stromal Rf levels were also equal to that of debrided corneas soaked with 0.5% Rf, threefold higher than those soaked with 0.1% Rf, and twofold higher than corneas soaked in BAK without epithelial debridement. Organ culture of treated corneas showed a normal corneal epithelium following FS machining while BAK-treated corneas showed extensive epithelial and stromal damage at 24 hours posttreatment.

Conclusions

FS corneal epithelial machining can be used to enhance penetration of Rf into the stroma for corneal CXL.

Translational Relevance

The creation of epithelial microchannels allows for stromal Rf concentrations high enough to perform true transepithelial crosslinking.

Effects of an antioxidant protective topical formulation on retinal tissue of UV-exposed rabbits

PURPOSE

The aim of this study has been to evaluate the protective effect of a topical antioxidant formulation containing riboflavin, d-α-tocopheryl polyethylene glycol (TPGS vitamin E), proline, glycine, lysine, and leucine against UV-B-induced damage in in vivo rabbit retina.

METHODS

Twenty male albino rabbits were used. Animals were divided into four groups of five animals each. Control group did not receive any UV irradiation. The first group (IG) was irradiated with a UV-A lamp for 30 min; the second (IG30) and the third (IG60) groups received UV irradiation for 30 and 60 min, respectively, and were topically treated with 1 drop (approximately 50 µl) of the antioxidant formulation, every 15 min, starting 1 h before irradiation, until the end of the UC exposure.

RESULTS

The retina of IG group showed extensive destruction of the retinal pigment epithelium (RPE) and of the cones and rods layer. The retina of G30 group showed a lesser destruction of both RPE and cones and rods layer. In the G60 group, retina showed an irregular thickening of the RPE, with massive edema of the inner and outer layer immediately adjacent together with a significant reduction of the photoreceptor number.

CONCLUSION

Our results demonstrate that a topical application of eye drops containing riboflavin, d-α-tocopheryl polyethylene glycol (TPGS vitamin E), proline, glycine, lysine, and leucine counteracts UV retinal injury in exposed retina rabbits.

Reaction-diffusion model as framework for understanding the role of riboflavin in “eye defence” formulations

Analysis of UV-visible spectra, performed on commercial riboflavin-based eye drops, showed that absorbance is a saturating function of vitamin concentration. This implies a threshold concentration, C_t, such that for riboflavin concentration > C_t the absorbance remains constant and the effectiveness of the eye drops is independent of the dose used. These experimental results were combined with a diffusion–reaction model to elucidate the mechanism of action within the cornea. The model predicts that the eye drops have a low effectiveness on UVB and UVC, while they have a good performance for UVA. Indeed, at the center of the cornea the transmittance is significantly reduced and after 1 h it is reduced by about 70% compared to a cornea devoid of eye drops.

Analysis of UV-visible spectra, performed on commercial riboflavin-based eye drops, showed that absorbance is a saturating function of vitamin concentration.

Novel riboflavin/VE-TPGS modified universal dentine adhesive with superior dentine bond strength and self-crosslinking potential

OBJECTIVE

To modify a universal dentine adhesive with different concentrations of riboflavin and D-Alpha 1000 Succinate polyethylene (VE-TPGS) as a chemical enhancer and to assess the micro-tensile bond strength (24h/12 months), determine resin penetration, measurement of intermolecular interactions and cytotoxicity.

MATERIALS AND METHODS

An experimental adhesive system based on bis-GMA, HEMA and hydrophobic monomer was doped with RF0.125 (RF - Riboflavin) or RF/VE-TPGS (_0.25/0.50) and submitted to μTBS evaluation. Resin dentine slabs were prepared and examined using SEM and TEM. Adhesion force was analysed on ends of AFM cantilevers deflection. Quenched peptide assays were performed using fluorescence scanner and wavelengths set to 320nm and 405nm. Cytotoxicity was assessed using human peripheral blood mononuclear cell line. Molecular docking studies were carried out using Schrödinger small-molecule drug discovery suite 2018-2. Data from viable cell results was analyzed using one-way ANOVA. Bond strength values were analysed by two-way ANOVA. Nonparametric results were analyzed using a Kruskal-Wallis test at a 0.05 significance level.

RESULTS

RF/VE-TPGS_0.25 groups showed highest bond strength results after 24-h storage in artificial saliva (p<0.05). RF/VE-TPGS_0.50 groups showed increased bond strength after 12-months of ageing. RF/VE-TPGS modified adhesives showed appreciable presence of a hybrid layer. Packing fraction indicated solid angle profiles describing well sized density and topology relations for the RF/VE-TPGS adhesives, in particular with the RF/VE-TPGS_0.50 specimens. Qualitative analysis of the phenotype of macrophages was prominently CD163+ in the RF/VE-TPGS_0.50. Both the compounds showed favourable negative binding energies as expressed in terms of 'XP GScore'.

CONCLUSION

New formulations based on the incorporation of RF/VE-TPGS in universal adhesives may be of significant potential in facilitating penetration, distribution and uptake of riboflavin within the dentine surface.

Fluorophotometric Determination of Riboflavin Concentrations in a Human Artificial Anterior Chamber Model

PURPOSE

Corneal cross-linking (CXL) requires an adequate corneal riboflavin impregnation, which is clinically assessed by verification of a riboflavin "flare" in the anterior chamber. We set out to replace this subjective assessment with an objective measurement method and evaluated fluorophotometry as an apparatus-based technique for riboflavin detection in the anterior chamber.

METHODS

In an artificial anterior chamber model using human corneas and a modified Fluorotron fluorophotometer, we determined the detection limits of riboflavin concentrations across native corneas by comparison measurements of the same concentrations in glass cuvettes. Subsequently, standard CXL procedures with corneal application of riboflavin were simulated and the proportions of riboflavin entering the anterior chamber were measured fluorophotometrically.

RESULTS

The measurement results of the riboflavin dilution series in the artificial anterior chamber showed a very high concordance with the results obtained in a glass cuvette (Pitman test P = 0.329). In the CXL simulation, the mean riboflavin concentration measured in the anterior chamber increased within 15 minutes from 5 (±1) to 903 (±204) ng/mL and stood at 1089 (±56) ng/mL after 30 minutes.

CONCLUSIONS

Fluorophotometry is able to measure riboflavin in an artificial anterior chamber across human corneas over a wide range of concentrations and it reliably detects the increasing riboflavin signal in simulated CXL procedures.

TRANSLATIONAL RELEVANCE

The replacement of the subjective riboflavin detection by a technically straightforward, objective detection method might increase patient safety and treatment efficiency in CXL.

Ex Vivo Conjunctival Retention and Transconjunctival Transport of Poorly Soluble Drugs Using Polymeric Micelles

This paper addresses the problem of ocular delivery of lipophilic drugs. The aim of the paper is the evaluation of polymeric micelles, prepared using TPGS (d-α-Tocopheryl polyethylene glycol 1000 succinate), a water-soluble derivative of Vitamin E and/or poloxamer 407, as a vehicle for the ocular delivery of dexamethasone, cyclosporine, and econazole nitrate. The research steps were: (1) characterize polymeric micelles by dynamic light scattering (DLS) and X-ray scattering; (2) evaluate the solubility increase of the three drugs; (3) measure the in vitro transport and conjunctiva retention, in comparison to conventional vehicles; (4) investigate the mechanisms of enhancement, by studying drug release from the micelles and transconjunctival permeation of TPGS; and (5) study the effect of micelles application on the histology of conjunctiva. The data obtained demonstrate the application potential of polymeric micelles in ocular delivery, due to their ability to increase the solubility of lipophilic drugs and enhance transport in and across the conjunctival epithelium. The best-performing formulation was the one made of TPGS alone (micelles size ≈ 12 nm), probably because of the higher mobility of these micelles, an enhanced interaction with the conjunctival epithelium, and, possibly, the penetration of intact micelles.

Penetration Enhancers in Ocular Drug Delivery

There are more than 100 recognized disorders of the eye. This makes the development of advanced ocular formulations an important topic in pharmaceutical science. One of the ways to improve drug delivery to the eye is the use of penetration enhancers. These are defined as compounds capable of enhancing drug permeability across ocular membranes. This review paper provides an overview of anatomical and physiological features of the eye and discusses some common ophthalmological conditions and permeability of ocular membranes. The review also presents the analysis of literature on the use of penetration-enhancing compounds (cyclodextrins, chelating agents, crown ethers, bile acids and bile salts, cell-penetrating peptides, and other amphiphilic compounds) in ocular drug delivery, describing their properties and modes of action.

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.

Synergistic effects of VE-TPGS and riboflavin in crosslinking of dentine

OBJECTIVE

Effect of d-alpha-tocopheryl poly(ethyleneglycol)-1000-succinate (VE-TPGS) with riboflavin-5'-phosphate solution on crosslinking of dentine collagen was investigated to analyze collagen's structural integrity.

METHODS

VE-TPGS was added to RF-solution, at RF/VE-TPGS (w/w) ratios of 0.125/0.250 and 0.125/0.500. Demineralized dentine beams were used (10wt.% phosphoric acid), rinsed using deionized-water and analysed using ELISA (Human MMP2 ELISA; Human CTSK/Cathepsin-K for MMP2 and Cathepsin K analysis). AFM of dentine collagen-fibrils structure was done before and after dentine specimens' placement in mineralization solution and tested after 14days in artificial saliva/collagenase (AS/Co) solution. The specimens were tested after 24h in mineralization solution for surface/bulk elastic modulus. Nano-indentation was carried out for each specimen on intertubular-dentine with lateral spacing of 400nm. Reduced elastic-modulus and nano-hardness were calculated and collagen content was determined using hydroxyproline-assay. Micro-Raman were performed. TEM was carried out to study structural variations of dentine-collagen in artificial-saliva (collagenase). Data were presented as mean±standard deviation and analyzed by SPSS v.15, by analysis of variance.

RESULTS

Synergetic effect of VE-TPGS was observed with RF through higher structural integrity of dentine collagen-fibrils shown by TEM/AFM. Superior surface/bulk mechanical stability was shown by nano-indentation/mechanical testing. Improvement in collagenase degradation resistance for hydroxyproline release was observed and lower endogenous-protease release of MMP-2/Cathepsin-K. Raman-analysis analysed chemical interactions between RF and collagen confirming structural-integrity of collagen fibrils after crosslinking. After 24h mineralization, AFM showed mineral depositions in close association with dentine-collagen fibrils with RF/VE-TPGS formulations.

SIGNIFICANCE

Potential synergetic effect of RF/VE-TPGS was observed by reflection of higher structural integrity and conformational-stability of dentine-collagen fibrils.

Study of penetration mechanism of labrasol on rabbit cornea by Ussing chamber, RT-PCR assay, Western blot and immunohistochemistry

Labrasol, as a non-ionic surfactant, can enhance the permeation and absorption of drugs, and is extensively used in topical, transdermal, and oral pharmaceutical preparations as an emulsifier and absorption enhancer. Recent studies in our laboratory have indicated that labrasol has a strong absorption enhancing effect on different types of drugs in vitro and in vivo. This study was performed to further elucidate the action mechanism of labrasol on the corneal penetration. In this research, the fluorescein sodium, a marker of passive paracellular transport of tight junction, was selected as the model drug to assess the effect of labrasol on in vitro corneal permeability. To investigate the continuous and real-time influence of labrasol on the membrane permeability and integrity, the Ussing chamber system was applied to monitor the electrophysiological parameters. And, furthermore, we elucidated the effect of labrasol on excised cornea at the molecular level by application of RT-PCR, Western blot, and immunohistochemical staining. The results indicated that labrasol obviously enhance the transcorneal permeability of fluorescein sodium, and the enhancement was realized by interacting with and down-regulating the associated proteins, such as F-actin, claudin-1 and β-catenin, which were contributed to cell-cell connections, respectively.

Corneal Cross-Linking: Evaluating the Potential for a Lower Power, Shorter Duration Treatment

Purpose:

To determine the cross-linking effect of a riboflavin ultraviolet-A (UV-A) corneal cross-linking treatment that is both shorter and has lower energy than the Dresden protocol.

Methods:

In a first experiment, 12 human corneas were presoaked with riboflavin and then irradiated with UV-A at 3 mW/cm² after clearing the surface of riboflavin, with no added riboflavin during irradiation. Percent UV-A transmission through the corneas was measured at intervals up to 30 minutes. A second experiment involved 24 porcine corneas. Eight were de-epithelialized, presoaked in riboflavin for 30 minutes, and irradiated at 1.5 mW/cm² for 10 minutes. An additional 8 were riboflavin treated and similarly irradiated, but with epithelium intact and a final 8 corneas were not treated. Young modulus was measured in all 24 corneas at the end of the experiment.

Results:

The first experiment showed essentially complete riboflavin oxidation after only 10 minutes. Based on these results, a shortened UV-A exposure cross-linking experiment was designed using a reduced UV-A fluence of 1.5 mW/cm², an endothelial exposure within safety limits in humans. With this protocol Young modulus was the same in the irradiated porcine corneas but with epithelium intact as in the untreated corneas. In contrast, Young modulus increased by a factor of 1.99 in the UV-A cross-linked corneas at 1.5 mW/cm² for 10 minutes with the epithelium removed.

Conclusions:

A shorter, lower energy protocol than the Dresden protocol seems to provide a significant increase in Young modulus, similar to published results with higher energy, longer exposure protocols.

Corneal collagen crosslinking for corneal ectasias: a review

PURPOSE

To review the published literature on corneal collagen crosslinking (CXL).

METHODS

Importance has been placed on seminal publications, systemic reviews, meta-analyses, and randomized controlled clinical trials. Where such evidence was not available, cohort studies, case-controlled studies, and case series with follow-up greater than 12 months were examined.

RESULTS

Corneal collagen crosslinking with riboflavin and ultraviolet A (UVA) 370 nm radiation appears to be capable of arresting the progression of ectatic corneal disorders, with most studies reporting significant improvements in visual, keratometric, and topographic measurements. Its mode of action at the molecular level is undetermined. Follow-up is limited to 5-10 years but suggests sustained stability and enhancement in corneal shape with time. Nearly all published long-term data and comparative studies are with epithelium-off techniques. Epithelium-on investigations suggest some efficacy but less than with epithelium-off treatments and long-term data are unavailable. Accelerated techniques with higher UVA fluencies and shorter treatments times, delivering the same UVA energy dosage, are the subject of recent investigation, with some laboratory and clinical studies suggesting reduced efficacy compared to the standard 3 mW/cm2 for 30 minutes irradiation procedure. Combined methodologies of CXL with techniques such as photorefractive keratectomy and intrastromal rings show promise but long-term follow-up is indicated. Sight-threatening complications of CXL are rare.

CONCLUSIONS

Studies of epithelium-off CXL with irradiation at 3 mW/cm2 for 30 minutes support its efficacy. Refinement in techniques may allow for safer and more rapid procedures with less patient discomfort but require further investigation.

Transepithelial Corneal Cross-Linking With Vitamin E-Enhanced Riboflavin Solution and Abbreviated, Low-Dose UV-A: 24-Month Clinical Outcomes

Purpose:

To report the clinical outcomes with 24-month follow-up of transepithelial cross-linking using a combination of a d-alpha-tocopheryl polyethylene-glycol 1000 succinate (vitamin E-TPGS)-enhanced riboflavin solution and abbreviated low fluence UV-A treatment.

Methods:

In a nonrandomized clinical trial, 25 corneas of 19 patients with topographically proven, progressive, mild to moderate keratoconus over the previous 6 months were cross-linked, and all patients were examined at 1, 3, 6, 12, and 24 months. The treatments were performed using a patented solution of riboflavin and vitamin E-TPGS, topically applied for 15 minutes, followed by two 5-minute UV-A treatments with separate doses both at fluence below 3 mW/cm² that were based on preoperative central pachymetry.

Results:

During the 6-month pretreatment observation, the average Kmax increased by +1.99 ± 0.29 D (diopter). Postoperatively, the average Kmax decreased, changing by −0.55 ± 0.94 D, by −0.88 ± 1.02 D and by −1.01 ± 1.22 D at 6, 12, and 24 months. Postoperatively, Kmax decreased in 19, 20, and 20 of the 25 eyes at 6 months, 12 months, and 24 months, respectively. Refractive cylinder was decreased by 3 months postoperatively and afterward, changing by −1.35 ± 0.69 D at 24 months. Best spectacle-corrected visual acuity (BSCVA) improved at 6, 12, and 24 months, including an improvement of −0.19 ± 0.13 logarithm of the minimum angle of resolution units at 24 months. There was no reduction in endothelial cell count. No corneal abrasions occurred, and no bandage contact lenses or prescription analgesics were used during postoperative recovery.

Conclusions:

Transepithelial cross-linking using the riboflavin-vitamin E solution and brief, low-dose, pachymetry-dependent UV-A treatment safely stopped keratoconus progression.

Characterization of Heterogeneity and Spatial Distribution of Phases in Complex Solid Dispersions by Thermal Analysis by Structural Characterization and X-ray Micro Computed Tomography

PURPOSE

This study investigated the effect of drug-excipient miscibility on the heterogeneity and spatial distribution of phase separation in pharmaceutical solid dispersions at a micron-scale using two novel and complementary characterization techniques, thermal analysis by structural characterization (TASC) and X-ray micro-computed tomography (XμCT) in conjunction with conventional characterization methods.

METHOD

Complex dispersions containing felodipine, TPGS, PEG and PEO were prepared using hot melt extrusion-injection moulding. The phase separation behavior of the samples was characterized using TASC and XμCT in conjunction with conventional thermal, microscopic and spectroscopic techniques. The in vitro drug release study was performed to demonstrate the impact of phase separation on dissolution of the dispersions.

RESULTS

The conventional characterization results indicated the phase separating nature of the carrier materials in the patches and the presence of crystalline drug in the patches with the highest drug loading (30% w/w). TASC and XμCT where used to provide insight into the spatial configuration of the separate phases. TASC enabled assessment of the increased heterogeneity of the dispersions with increasing the drug loading. XμCT allowed the visualization of the accumulation of phase separated (crystalline) drug clusters at the interface of air pockets in the patches with highest drug loading which led to poor dissolution performance. Semi-quantitative assessment of the phase separated drug clusters in the patches were attempted using XμCT.

CONCLUSION

TASC and XμCT can provide unique information regarding the phase separation behavior of solid dispersions which can be closely associated with important product quality indicators such as heterogeneity and microstructure.

A novel bile salts-lipase polymeric film-infused minitablet system for enhanced oral delivery of cholecalciferol

Few researchers have investigated the use of multiple physiological enhancers combined with synthetic carriers to augment delivery of nutraceuticals. The current work describes the development of an oral delivery system termed a bioactive association platform (BAP) capable of delivering nutraceutical actives from a formulation framework specifically for enhancing the in vitro and in vivo performance of model vitamin, cholecalciferol (Vitamin D₃). Synthesis of a novel triple vitamin minitablet and an optimized bile salt/lipase alginate-glycerin film provided unique oral components for inclusion in a BAP capsule. Component validation and physicochemical characterizations included comparative ex vivo permeability, chemical structure mapping, thermodynamic analysis and magnetic resonance imaging. In vitro dissolution studies of the BAP produced an area under the dissolution curve (AUC) for cholecalciferol release that was 28% greater than a conventional comparator product. A total of 84.01% of cholecalciferol was released from the BAP within 3 h versus only 59% from a comparator. Ex vivo permeation studies revealed superior cholecalciferol membrane diffusion from the triple vitamin minitablet BAP component. In vivo performance showed a greater mean change from baseline cholecalciferol to peak plasma levels (C_max) from the BAP compared to the comparator (55.66 versus 46.05 ng/mL). Cholecalciferol bioavailability was improved in vivo with an AUC_0-inf from the BAP that was 3.2× greater than the conventional product. The BAP was also superior at improving and maintaining serum levels of the main metabolite, 25-hydroxyvitamin D₃, compared to the conventional system. In vitro and in vivo results thus confirmed improvements in cholecalciferol dissolution, membrane permeability and plasma drug levels. The study results position the BAP as an ideal oral vehicle for enhanced delivery of cholecalciferol.

α-Tocopherols modify the membrane dipole potential leading to modulation of ligand binding by P-glycoprotein

α-Tocopherol (vitamin E) has attracted considerable attention as a potential protective or palliative agent. In vitro, its free radical-scavenging antioxidant action has been widely demonstrated. In vivo, however, vitamin E treatment exhibits negligible benefits against oxidative stress. α-Tocopherol influences lipid ordering within biological membranes and its derivatives have been suggested to inhibit the multi-drug efflux pump, P-glycoprotein (P-gp). This study employs the fluorescent membrane probe, 1-(3-sulfonatopropyl)-4-[β[2-(di-n-octylamino)-6-naphthyl]vinyl] pyridinium betaine, to investigate whether these effects are connected via influences on the membrane dipole potential (MDP), an intrinsic property of biological membranes previously demonstrated to modulate P-gp activity. α-Tocopherol and its non-free radical-scavenging succinate analog induced similar decreases in the MDP of phosphatidylcholine vesicles. α-Tocopherol succinate also reduced the MDP of T-lymphocytes, subsequently decreasing the binding affinity of saquinavir for P-gp. Additionally, α-tocopherol succinate demonstrated a preference for cholesterol-treated (membrane microdomain enriched) cells over membrane cholesterol-depleted cells. Microdomain disruption via cholesterol depletion decreased saquinavir's affinity for P-gp, potentially implicating these structures in the influence of α-tocopherol succinate on P-gp. This study provides evidence of a microdomain dipole potential-dependent mechanism by which α-tocopherol analogs influence P-gp activity. These findings have implications for the use of α-tocopherol derivatives for drug delivery across biological barriers.

Novel in situ gel systems based on P123/TPGS mixed micelles and gellan gum for ophthalmic delivery of curcumin

Curcumin, a natural polyphenol compound, has been widely reported for diverse pharmacological effects and already been investigated for eye diseases. However, the water-insolubility of curcumin and the inherent penetration barriers in cornea make it difficult for curcumin to enter eye. This work aimed to develop ion-sensitive curcumin-loaded Pluronic P123 (P123)/D-a-tocopheryl polyethylene glycolsuccinate (TPGS) mixed micelle in situ gels (CUR-MM-ISGs) to prolong ocular retention time and improve cornea permeability. Central composite design-response surface methodology was applied for the optimization of curcumin-loaded P123/TPGS mixed micelles (CUR-MMs). Characterization tests showed that CUR-MMs were in spherical shape with small size and low critical micelle concentration. After dispersing the micelles in gellan gum solution (0.2%, w/w) at the ratio of 3:1 and 1:1 (v/v), respectively, CUR-MM-ISGs were formed and presented transparent appearance. Sustained release profile was obtained in vitro for both CUR-MM-ISGs (3:1 or 1:1, v/v). The irritation test proved that CUR-MM-ISGs as ophthalmic formulations were gentle and biocompatible towards ocular tissues. In addition, the ex vivo corneal penetration study indicated that the cumulative drug permeation amount of CUR-MM-ISGs (3:1, v/v) was respectively 1.16-fold and 1.32-fold higher than CUR-MM-ISGs (1:1, v/v) and curcumin solution. It can be concluded from these results that the developed ion-sensitive mixed micelle in situ gel system is a potential ophthalmic delivery carrier for curcumin as a poorly soluble drug.

Corneal collagen cross-linking: a review

The aim was to review the published literature on corneal collagen cross-linking. The emphasis was on the seminal publications, systemic reviews, meta-analyses and randomized controlled trials. Where such an evidence did not exist, selective large series cohort studies, case controlled studies and case series with follow-up preferably greater than 12 months were included. Riboflavin/Ultraviolet A (UVA) corneal collagen cross-linking appears to be the first treatment modality to halt the progression of keratoconus and other corneal ectatic disorders with improvement in visual, keratometric and topographic parameters documented by most investigators. Its precise mechanism of action at a molecular level is as yet not fully determined. Follow-up is limited to 4-6 years at present but suggests continued stability and improvement in corneal shape with time. Most published data are with epithelium-off techniques. Epithelium-on studies suggest some efficacy but less than with the epithelium-off procedures and long-term data are not currently available. The use of Riboflavin/UVA CXL for the management of infectious and non-infectious keratitis appears very promising. Its use in the management of bullous keratopathy is equivocal. Investigation of other methodologies for CXL are under investigation.

Fast-dissolving ocular films of riboflavin acetate conjugate for treatment of keratoconus in UVA-CXL procedure: ex vivo permeation, hemolytic toxicity and apoptosis detection

BACKGROUND

Attempts to facilitate corneal epithelial penetration of riboflavin (Rb) without de-epithelization, so far, include the use of penetration enhancers, to devitalize corneal epithelium in order to disturb tight epithelial interjunctional complexes and zonulae occludentes. Though such approaches result in sufficient epithelial permeability of Rb to guarantee efficacy of CXL procedure, they lack the evidences of safety. Prodrug with improved lipophilicity targeted toward esterases and amidases has proven to be an effective and promising approach to overcome lipophilic corneal epithelial barrier.

OBJECTIVES

Fast-dissolving ocular films of newly synthesized and characterized riboflavin lipid conjugate (RbLDC) were developed to overcome corneal epithelial barrier resistance for treatment of keratoconus. The safety concern of the film was assessed by in vitro hemolytic toxicity and in vitro apoptosis detection for its safe clinical use.

RESULTS

The optimized film was tough, flexible and dissolved rapidly within 36.86 s in simulated tear fluid, pH 7.4. FE-SEM/EDX showed smooth surfaces of films and evidenced the quantitative elemental similarity, indicating drug homogeneity. The permeation profile of F18 demonstrated 13.28-fold increased permeation of RbLDC relative to Rb solution across intact cornea. Safety was confirmed by 3.74% hemolysis and 10% apoptosis.

CONCLUSION

Safe and efficient RbLDC fast-dissolving ocular films capable of overcoming corneal epithelial barrier resistance to avoid surgical intervention of corneal epithelial debridement were developed.

Toward the practical implementation of eye-related bioavailability prediction models

The development and registration of reformulated ophthalmic products (OPs) requires eye-related bioavailability (BA) assessments. Common BA algorithms associated with other routes of application, such as the oral route, cannot be easily applied to eye-related BA testing. Here, we provide an analysis of the current literature and suggestions for further directions in the development of high-capacity, cost-effective, and highly predictive nonclinical models of eye-related drug BA. One, or a combination of these models, has the potential for routine use in research laboratories and/or the pharmaceutical industry to overcome various obstacles in reformulated OP development and registration.