Pullulan Based Bioconjugates for Ocular Dexamethasone Delivery

Abstract

Posterior segment eye diseases are mostly related to retinal pathologies that require pharmacological treatments by invasive intravitreal injections. Reduction of frequent intravitreal administrations may be accomplished with delivery systems that provide sustained drug release. Pullulan-dexamethasone conjugates were developed to achieve prolonged intravitreal drug release. Accordingly, dexamethasone was conjugated to ~67 kDa pullulan through hydrazone bond, which was previously found to be slowly cleavable in the vitreous. Dynamic light scattering and transmission electron microscopy showed that the pullulan-dexamethasone containing 1:20 drug/glucose unit molar ratio (10% w/w dexamethasone) self-assembled into nanoparticles of 461 ± 30 nm and 402 ± 66 nm, respectively. The particles were fairly stable over 6 weeks in physiological buffer at 4, 25 and 37 °C, while in homogenized vitreous at 37 °C, the colloidal assemblies underwent size increase over time. The drug was released slowly in the vitreous and rapidly at pH 5.0 mimicking lysosomal conditions: 50% of the drug was released in about 2 weeks in the vitreous, and in 2 days at pH 5.0. In vitro studies with retinal pigment epithelial cell line (ARPE-19) showed no toxicity of the conjugates in the cells. Flow cytometry and confocal microscopy showed cellular association of the nanoparticles and intracellular endosomal localization. Overall, pullulan conjugates showed interesting features that may enable their successful use in intravitreal drug delivery.

Pharmacokinetics of Pullulan–Dexamethasone Conjugates in Retinal Drug Delivery

“…Similar synthetic strategy was applied to prepare versions with green fluorescent label starting from pullulan-DEX, namely BDP-pullulan-DEX and BDP-pullulan (Supporting Information, SI-1). The chemical identity of the conjugates (Figure 1) was confirmed by the NMR spectroscopy (SI-1 and in Kicková et al [26]).…”

“…Cy3-pullulan-DEX and Cy3-pullulan have recently been prepared and characterized by Kicková et al [26]. Similar synthetic strategy was applied to prepare versions with green fluorescent label starting from pullulan-DEX, namely BDP-pullulan-DEX and BDP-pullulan (Supporting Information, SI-1).…”

“…In most studies, drugs have been physically encapsulated into the polysaccharide formulations, such as polymeric micelles or nanoparticles [13,[23][24][25], whereas chemical covalent conjugation technologies have not been applied for ocular in vivo drug delivery with polysaccharides. Recently, the chemical conjugation through hydrazone bond was used to generate peptide-dexamethasone and pullulan-dexamethasone conjugates that were investigated in vitro [10,26]. In contrast to the ocular field, polymeric drug conjugates have been widely investigated to provide site-specificity and extended drug release in some other medical indications [27][28][29][30][31][32].…”

“…In this study, we investigated dexamethasone conjugates of pullulan that were obtained with recently published synthetic procedures [26]. Dexamethasone was conjugated to pullulan through a hydrazone bond that is expected to control drug release under the acidic intracellular compartments (endosomes or lysosomes).…”

Advances in Ocular Drug Delivery Systems

“…Pullulan is an interesting platform to produce this kind of conjugate for drug delivery and it is a polysaccharide produced by Aureobasidium pullulans that possesses the main requisites for invasive administration: biodegradability, water solubility and biocompatibility. In this context, Kicková et al [ 6 ] developed a new pullulan-dexamethasone conjugate as a potential intravitreal drug delivery system. Dexamethasone was selected as a model drug since it is a hydrophobic corticosteroid used as an anti-inflammatory and immune suppressing drug in ophthalmology.…”