Corneal critical barrier against the penetration of dexamethasone and lomefloxacin hydrochloride: evaluation by the activation energy for drug partition and diffusion in cornea

A Physiology-Based Mathematical Model to Understand Drug Delivery from Contact Lenses to the Back of the Eye

OBJECTIVE

Therapeutic contact lenses, able to store drug and deliver it to the eye surface in a sustained fashion, gained interest as an effective and patient-friendly alternative to eye drops. Recent animal studies also demonstrated the presence of therapeutic drug levels in the back of the eye after wearing drug-loaded contact lenses, thus opening the possibility of treating the posterior segment without need of invasive intraocular injections. The drug pathways from contact lenses to the back of the eye require further investigation.

METHODS

A mechanistic mathematical model was developed to evaluate the drug concentration over time in the tears, sclera and choroid, retina, aqueous humor and vitreous humor after the application of a therapeutic contact lens. The main drug transport mechanisms of the eye and the barrier properties of the different tissues were included in the model. Validation was performed by comparison with experimental data in literature.

RESULTS

The model predictions of drug concentration over time reflected the experimental data both in the anterior and posterior segment of the eye. The model can differentiate between contributions to transport from different pathways.

CONCLUSIONS

The model constitutes a first step towards the possibility of predicting the ocular drug distribution and the treatment efficacy in the early stage of contact lens development, and it may help reduce both the need for in vivo tests (with ethical and economic advantages) and the gap between the lens design and clinical application. It also allows for an improved understanding of drug transport in the eye.

Preclinical characterization of water-free cyclosporine eye drops - factors impacting ocular penetration ex vivo and in vivo

Although the efficacy of Cyclosporine A (CsA) in the management of ocular inflammation is well-demonstrated, ocular delivery remains challenging due to its hydrophobic nature. The semifluorinated alkane, perfluorobutylpentane (F4H5) has previously been suggested as an efficient vehicle for preparation of CsA eyedrops. Here we evaluated the influence of drop volume and the formulation aid, ethanol (EtOH), on ocular penetration of CsA and compared it to that of the commercial eyedrop, Ikervis, ex vivo and in vivo. Moreover, conjunctival and corneal tolerability after EtOH addition were evaluated ex vivo. The F4H5/EtOH vehicle was well tolerated and resulted in better corneal CsA penetration (AUC_{(0 - 4h)}: 63,008 ± 3,946 ng.h.g^-1) than Ikervis (AUC_{(0 - 4h)}: 10,328 ± 1,462 ng.h.g^-1) or F4H5 alone (AUC_{(0 - 4h)}: 50,734 ± 3,472 ng.h.g^-1) ex vivo. Interestingly, in vivo the CsA concentration in cornea, conjunctiva and lacrimal glands observed after administration of the F4H5 formulation (AUC_{(0.133-24 h)}: 7,741 ± 1,334 ng.h.g^-1, 1,313 ± 291 ng.h.g^-1, 48.2 ± 26.3 ng.h.g^-1) and F4H5/EtOH both at a reduced dose of 11 µl (AUC_{(0.133-24 h)}: 9,552 ± 1,738 ng.h.g^-1, 1,679 ± 285 ng.h.g^-1, 50.3 ± 21.1 ng.h.g^-1) was similar or even greater than what was observed on administration of 50 µl Ikervis (AUC_{(0.133-24 h)}: 9,943 ± 1,413 ng.h.g^-1, 2,069 ± 263 ng.h.g^-1, 30.6 ± 18.4 ng.h.g^-1). Thus, F4H5-based eyedrops were shown to deliver CsA more efficiently to anterior ocular tissues at a reduced dose in comparison to Ikervis, reducing dose wastage and minimizing any potential systemic side effects.

Asymmetry in Drug Permeability through the Cornea

The permeability through the cornea determines the ability of a drug or any topically applied compound to cross the tissue and reach the intraocular area. Most of the permeability values found in the literature are obtained considering topical drug formulations, and therefore, refer to the drug permeability inward the eye. However, due to the asymmetry of the corneal tissue, outward drug permeability constitutes a more meaningful parameter when dealing with intraocular drug-delivery systems (i.e., drug-loaded intraocular lenses, intraocular implants or injections). Herein, the permeability coefficients of two commonly administered anti-inflammatory drugs (i.e., bromfenac sodium and dexamethasone sodium) were determined ex vivo using Franz diffusion cells and porcine corneas in both inward and outward configurations. A significantly higher drug accumulation in the cornea was detected in the outward direction, which is consistent with the different characteristics of the corneal layers. Coherently, a higher permeability coefficient was obtained for bromfenac sodium in the outward direction, but no differences were detected for dexamethasone sodium in the two directions. Drug accumulation in the cornea can prolong the therapeutic effect of intraocular drug-release systems.

Evaluation of His6-Metal Assemblies as a Drug Delivery Vehicle in the Treatment of Anterior Segment Disease Using a Corneal Inflammation Model

Keratitis is a common ophthalmological disease and also a common cause of blindness (second only to cataracts). This disease is routinely treated by topical administration of dexamethasone sodium phosphate (Dexp). However, due to the presence of anatomical and physiological barriers, frequent administration is needed, often resulting in poor patient compliance and diverse side effects. In this work, Dexp was in situ encapsulated into a His₆-metal assembly (HmA) to generate Dexp@HmA, which was utilized in the ocular delivery of Dexp. The physicochemical properties of HmA and Dexp@HmA particles were characterized in detail using various techniques such as dynamic light scattering (DLS), scanning electron microscopy (SEM), and UV-vis spectroscopy. Compared to commercial Eudragi and reported PLGA nanoparticles, HmA showed higher encapsulation efficiency (EE%) and higher loading capacity (LC wt %) of Dexp. Dexp@HmA displayed pH-dependent release; after 33 days at pH 5.8, 6.5, and 7.2, 100%, 65%, and 42% of Dexp, respectively, had been released. In addition, HmA and Dexp@HmA showed low cytotoxicity to macrophages and to all common ocular cell types tested. The effect of Dexp@HmA on corneal inflammation was evaluated using in vitro and in vivo models. Our results demonstrate that Dexp@HmA is much superior to free Dexp in both in vitro and in vivo models. These positive results suggest that HmA may represent a promising candidate nanocarrier for the treatment of various diseases of the anterior segment of the eye.

In Silico Ocular Pharmacokinetic Modeling: Delivery of Topical FK962 to Retina

PURPOSES

To establish the in silico ocular pharmacokinetic modeling for eye drops, and to simulate the dose regimen for FK962 in human choroid/retinal diseases.

METHODS

Pharmacokinetics for FK962 in vivo was performed by a single instillation of drops containing 0.1% ¹⁴C-FK962 in rabbit eyes. Permeation of FK962 across the cornea, sclera, and choroid/retina was measured in vitro. Neurite elongation by FK962 was measured in cultured rat retinal ganglion cells. Parameters from the experimental data were used in an improved in silico model of ocular pharmacokinetics of FK962 in man.

RESULTS

The mean concentration of FK962 in ocular tissues predicted by in silico modeling was consistent with in vivo results, validating the in silico model. FK962 rapidly penetrated into the anterior and posterior segments of the eye and then diffused into the vitreous body. The in silico pharmacokinetic modeling also predicted that a dose regimen of 0.0054% FK962 twice per day would produce biologically effective concentrations of FK962 in the choroid/retina, where FK962 facilitates rat neurite elongation.

CONCLUSIONS

Our in silico model for ocular pharmacokinetics is useful (1) for predicting drug concentrations in specific ocular tissues after topical instillation, and (2) for suggesting the optimal dose regimens for eye drops. The pharmacodynamics for FK962 produced by this model may be useful for clinical trials against retinal neuropathy.

Prevalence of ocular hypertension and glaucoma in patients with chronic ocular graft-versus-host disease

PURPOSE

To evaluate the prevalence of ocular hypertension (OHT) and glaucoma in patients with chronic ocular graft-versus-host disease (GVHD).

METHODS

We performed a retrospective chart review of 218 patients diagnosed with chronic ocular GVHD. Ocular hypertension was defined as intraocular pressure (IOP) ≥ 24 mmHg in either eye without any glaucomatous optic disc changes. Glaucoma suspect was defined as optic disc changes with a cup-to-disc ratio ≥ 0.7 in either eye or asymmetry of ≥ 0.3 between the two eyes. Glaucoma was defined by glaucomatous optic disc changes plus glaucomatous visual field defects in two consecutive reliable visual field tests. The number of cases of ocular hypertension, glaucoma, and glaucoma suspects was evaluated.

RESULTS

Thirty-three patients (15 %) were diagnosed with OHT, eight patients (3.6 %) with suspicion of glaucoma, and one patient (0.4 %) with glaucoma. OHT occurred within 6 months of developing ocular GVHD in 60 % of the cases and within the first year in 76 %. High IOP normalized in 67 % of patients when the dosage of topical or systemic corticosteroids was lowered, and 27 % of patients required anti-glaucoma therapy.

CONCLUSIONS

Ocular hypertension is a common complication in patients with ocular GVHD, with a prevalence of 15 %. The rise in intraocular pressure is often transient and resolves with management of corticosteroids in most cases. However, clinicians should be aware that nearly one-third of the patients with OHT might require anti-glaucoma treatment. The prevalences of glaucoma and suspicion of glaucoma were not higher than in the general population.

Analysis of steady state and non-steady state corneal permeation of diclofenac

The present study was undertaken for characterization of the steady state and non steady state corneal permeation kinetics of diclofenac potassium (DCP) using statistical moment theory.

Ocular penetration and pharmacokinetics of topical clarithromycin eye drops to rabbits

PURPOSE

To evaluate the ocular pharmacokinetics of clarithromycin (CLA) eye drops topically applied to the corneas of rabbits.

METHODS

One 50-μL drop of CLA (0.25%) was administered to each New Zealand white rabbit in a single dose group, and one 50-μL drop of CLA was administered 6 times at 5-min intervals to each rabbit in a loading dose group. The effect of debridement on corneal penetration was also investigated in a de-epithelium group. The drug concentrations in the cornea and aqueous humor (AH) were assayed using high-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS) analysis.

RESULTS

Maximum CLA levels were achieved in the corneas and AH at 15 and 60 min, respectively, in the intact epithelium eyes in the single dose group (24.54±10.64 μg/g and 0.78±0.22 μg/mL, respectively, mean±the standard error of the mean, n=8). In the loading dose group, 30 min after the last application, the CLA level in the corneas reached 92.26±17.62 μg/g. In the loading dose group, the drug levels in the corneas and AH were significantly increased compared with the drug levels in the corneas with the intact epithelium and de-epithelium eyes in the single dose group at the corresponding time points (P<0.05). The estimated CLA half-lives in the corneas and AH for the intact eyes were 103.28 and 132.61 min, respectively.

CONCLUSION

Therapeutic CLA levels can be achieved in rabbit corneas after topically applying the drug with eye drops.

Moxifloxacin modifies corneal fibroblast-to-myofibroblast differentiation

BACKGROUND AND PURPOSE

Fibroblast-to-myofibroblast differentiation is associated with scarring, an important issue in corneal surgery. Moxifloxacin (MOX), commonly applied to prevent post-operative infection, would benefit more if it modifies fibroblast-to-myofibroblast differentiation other than antimicrobial activity. Our purpose was to explore whether MOX has anti-fibrotic effect in human corneal fibroblasts (HCFs).

EXPERIMENTAL APPROACH

HCFs were incubated in MOX-containing medium concurrently with TGF-β1 (co-treatment), before (pretreatment) or after (post-treatment) adding TGF-β1. HCF contractility was evaluated with a type I collagen gel contraction assay. Expression of α-smooth muscle actin (α-SMA), Smad2, phospho-Smad2-Ser467, Smad4 and Smad7 was determined by immunoblotting. Formation of α-SMA-positive filaments and distribution of active Smad2 were observed under confocal microscopy. Expression of TGF-β receptor types I (TGFBR1) and II (TGFBR2) was assessed with flow cytometry.

KEY RESULTS

MOX did not affect gel contractility or α-SMA filament formation in HCFs without TGF-β1 stimulation. MOX did, however, retard HCF-containing gel contractility and α-SMA filament formation following TGF-β1 stimulation in the pretreatment and co-treatment groups but not in the post-treatment group. MOX blocked the expression of Smad2, phospho-Smad2-Ser467 and TGFBR1 under TGF-β1 incubation. Additionally, MOX enhanced Smad7 expression in TGF-β1-incubated HCFs, but did not interfere with TGF-β-triggered Smad2 nuclear translocation or Smad4 expression.

CONCLUSIONS AND IMPLICATIONS

MOX inhibited TGF-β-induced fibroblast-to-myofibroblast differentiation via blocking TGFBR1 and enhancing Smad7 expression. MOX should be used before or during surgery to achieve these effects. These results suggest a de novo mechanism by which MOX participates in corneal wound healing.