Fig. 15.9  CCI of MPSS on 17 patients with acute graft rejection. (a) Example of a patient with acute graft rejection before treatment and at day 10 after three CCI of MPSS. (b) Visual acuity of 17 patients with acute graft rejection before treatment

The mean best corrected visual acuity of all 17 patients during the last follow-up visit was 0.37 ± 0.2 compared to 0.06 ± 0.05 before initiation of the iontophoresis treatment. The mean follow-up time was 13.7 months with a range of 5–29 months for the 17 patients. No significant side effects associated with the iontophoresis treatment were observed.

In 2005, Horwath-Winter et al. treated 16 patients with iodide iontophoresis for the treatment of dry eye. The patients were treated for 10 days and compared with the patients receiving iodide application without current. Significant and increased duration of symptom improvement and conditions were observed in the group of patients treated with iontophoresis (Horwath-Winter et al. 2005).

Since then, several studies have been undertaken with the Eyegate transscleral iontophoresis system. Results should be published soon and possibly lead to FDA approval.

15.5  Applications of Iontophoresis to Ocular Gene Therapy

Iontophoresis has been mostly used to promote the ocular delivery and intracellular entry single strand oligonucleotides. Asahara et al. reported on the use of iontophoresis for promoting intraocular penetration of topically applied nucleic acid. After transcorneal iontophoresis, a topically applied 6-FAM labeled 23 base antisense ODN of human aldose reductase was detected in the aqueous humor, the vitreous

and retina after 5, 10 and 20 min, respectively. Optimal parameters in this study were 1.5 mA (gradually reached in 2 min) and 100 V of alternating current, applied for 5 min. No sign of ocular toxicity was reported. In this single report, transcorneal iontophoresis after delivery of a plasmid encoding GFP yielded green fluorescence in the rabbit cornea, anterior chamber angle and the ciliary subepithelial tissues (Asahara et al. 2001). In our hands, direct transcorneal and transscleral iontophoresis in rabbit and rat eyes did not enhance the transfection of reporter gene plasmids to corneal or intraocular tissues (unpublished data). However, iontophoresis of ODNs applied at a current of 500 mA (1 mA/cm2) enhanced their intraocular penetration. Significant intraocular concentration of ODNs within the iris/ciliary body complex was initially observed at 1 h, and a significant accumulation within the retina/choroid complex was observed at 6 h (Berdugo et al. 2003). In this study, we used a custommade polyethylene-coated transcorneoscleral eye probe with annular surface of 0.5 cm2 covering the cornea, the limbus and the scleral area adjacent to the limbus. A 27-gauge needle placed in the rat leg served as the anodal return electrode.

Furthermore, using antisense-NOSII ODN we successfully achieved significant down-regulation of NOSII expression in the iris/ciliary body tissues of rat eyes with endotoxin-induced uveitis (Voigt et al. 2002a–c).

After transcorneoscleral iontophoresis (1.5 mA/cm2 for 5 min) of fluorescent phosphorothioate anti-VEGF-R-2 ODN in rat eyes, we observed ODN in all corneal layers (with higher concentrations within Descemet membrane) and in the iris. When corneal neovessels were present, ODN was detected in vascular endothelial cells and in infiltrating leucocytes. ODN extracted from the tissues 90 min after iontophoresis were found intact.

Using a specifically designed transpalpebral iontophoresis device, we studied the internalization of ODN in the retinal layers of new born rd1/rd1 mice. In this mouse model, rapid retinal degeneration occurs as a result (in part) of a point mutation in the gene encoding the b-subunit of rod photoreceptor cGMP-phosphodiesterase (b- PDE). Transpalpebral cathodal saline iontophoresis was more efficient than anodal iontophoresis in enhancing the penetration of intravitreally injected ODN (encoding for the sense wild type b-PDE) in the nuclei of all retinal layers. Moreover, photoreceptor delivery of ODN was significantly higher when cathodal saline transpalpebral iontophoresis was applied prior to the ODN injection. This study thus illustrates that a tissue postiontophoretic penetration enhancement takes place (Andrieu-Soler et al. 2006, 2007).

15.6  Future Developments

Given the possibility of deliberate manipulation of the properties of the skin charge distribution by altering the formulation of the physicochemical properties of the permeant, or the formulation vehicle in which a permeant molecule is applied, clinical consideration must be given to how a drug and an iontophoretic controller device are coupled to the target tissue. For ophthalmic applications, the current drug solutions

prepared for iontophoretic treatment often employ formulations developed for other drug delivery modalities (e.g., drops). These solutions are not ideal as they have not been adapted to target ocular surfaces using an electrical field. For iontophoretic applications to the skin, more advanced semi-solid and gel formulations, often modified after those developed for passive transdermal drug delivery, are readily compatible with the skin surface. These formulation vehicles allow for manipulation of electrical conductivity, bioadhesion and viscoelastic properties to assure compatibility and stability over the desired application time. Moreover, deliberate formulations for ophthalmic drug interest are envisioned as a needed aspect of the development of ocular iontophoresis.

In the future, reverse iontophoresis may be used to dose intraocular biomarkers allowing for instant diagnostic. Delivery of the therapeutic compounds could then be modulated in response to this specific biodiagnostic.

The first step towards this future is to allow iontophoresis to enter clinical practice.

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