Breaking down the Barrier: Topical Liposomes as Nanocarriers for Drug Delivery into the Posterior Segment of the Eyeball

Abstract

Topical instillation is the most widely preferred noninvasive route of drug administration to treat diseases affecting the anterior segment of the eye. Nonetheless, the ocular bioavailability for deeper ocular tissues is very low. Different routes of administration, such as intravitreal injections, periocular injections, and systemic administration, have been used to deliver drugs into the posterior segment ocular tissues. However, the presence of blood-retinal barriers (BRBs) makes systemic administration an impractical approach, whereas the drug delivery with the periocular administration route is compromised by ocular static and dynamic barriers. On the other hand, intravitreal injection, the most common and widely recommended route for drug administration to treat posterior ocular diseases, is related to several side effects such as endophthalmitis, hemorrhage, retinal detachment, and poor patient tolerance. Diverse strategies to overcome ocular barriers have been explored for topical drop formulations in order to deliver drugs into the posterior segment ocular tissues. In this chapter, we will review the promising topical nanocarriers for drug delivery into the posterior segment of the eye, emphasizing the use of liposomes for topical ophthalmic formulations targeting the vitreous cavity and the retina.

Lipid-Based Nanocarriers as Topical Drug Delivery Systems for Intraocular Diseases

“…Each chamber is a fluid-filled cavity with aqueous humor produced by the ciliary processes of the ciliary body, which is in charge of nourishing the lens and keeping the intraocular pressure of this segment. Conversely, the posterior segment represents the resting two-thirds of the eye demarcated from the lens to the optic nerve, including specific structures such as the neural retina, retinal pigment epithelium, choroid, sclera and the vitreous humor, which provides nutrients to the lens and gives support to the retina [ 17 , 18 , 19 , 20 , 21 ]. Figure 1 and Figure 2 depict both regions along with the ocular barriers explained in the next section.…”

“…As mentioned before, the topical route represents the most manageable approach considering its major advantages, such as patient treatment adherence, easy, non-invasive administration, low cost, availability in the market [ 22 ] and the decreased incidence of complications [ 20 ]. Ointments, emulsions and suspensions comprise the different forms of conventional formulations used in the present day with delivery supremacy in terms of bioavailability, solubility and increased residence time in the precorneal area.…”

Suprachoroidal Delivery of Viral and Nonviral Gene Therapy for Retinal Diseases

“…35 Liposomes, vesicles formed by phospholipid bilayers, are biocompatible and can be tailored for various sizes, release rates, hydrophilicity, and lipophilicity. 36 Furthermore, the lipid bilayer of liposomes can integrate and pass through cell membranes without the need for electroporation. 37 While liposomes containing genetic material have been evaluated for posterior eye diseases when applied topically, intravitreally, or subretinally, 38 the application of liposomes delivered in the SCS is limited to a few preclinical applications.…”

Therapies Based on Nanoparticles for Eye Drug Delivery

“…The posterior segment represents the major ocular structure; it is composed of vitreous humor, sclera, macula, choroid, retina, and optic nerve ( Fig. 1) [12,13].…”

“…In the context of ophthalmology, NPs are of interest for their ability to increase the solubility of hydrophobic drugs, their capability to provide sustained drug release with reduced toxicity and improved efficacy, their ability to prolong drug retention time and enhancement of drug penetration through ocular barriers, and their proficiency to direct drugs to specific tissues and cells [19]. The different routes of ocular drug administration of NPs include topical, oral/systemic, subconjunctival, subtenon, retrobulbar, intracameral, and IVT [13].…”