NANO-CARRIERS FOR GLAUCOMA

 

The conjunctiva forms an important obstacle that does not allow drugs between 20 and 40 kDa to pass through it. The permeability of the sclera is under debate. However, studies have shown that it is not strictly a barrier, because molecules with a molar mass up to 150 kDa are able to penetrate it. An important pharmacological requirement for topical medications for glaucoma is to overcome these anatomical obstacles.

Various periocular, extraocular and intraocular nano/micro-drug delivery systems (DDSs) have been engineered. A number of them have been found to be safe and efficacious as anti-glaucoma hypotensive agents. These DDSs include topical formulations, ocular inserts, drug-eluting contact lenses, ocular ring inserts, intracameral, intravitreal, subconjunctival and suprachoroidal injectable formulation/implants.

According to the size, drug carriers can be classified as implants (>1 mm), microparticles (MPs, particles with a size ranging from 1 to 1000 µm) and nanoparticles (NPs, particles with a size less than 1000 nm). Currently, NPs remain the most intensively used form due to their small size, easily modified surface, ability to adsorb, attach and encapsulate various substances, and favorable biocompatibility.

Nanocarriers can be prepared in a variety of forms, such as polymeric nanomicelles (self-assembled suspension of amphiphilic block copolymers with hydrophobic cores and hydrophilic shells) and nanoemulsions (a mixture of two immiscible liquids with surfactants).

The incorporation of drugs into nanocarriers may surpass the limitations of current treatment regimens by enhancing drug penetration, achieving targeted delivery, prolonging contact of drugs with ocular tissues, and sustaining in vivo release.

Unlike other agents, nanocarriers are equally effective in delivering lipophilic drugs, proteins, and even genes, which are difficult with conventional solvents. Nanocarriers are also able to protect the integrity of drug cargo before reaching the target sites. This property is particularly intriguing when transporting molecules such as neurotrophin and antibodies because these proteins easily degrade in vivo.

Based on their physical structures, drug carriers can be divided into reservoir-type and matrix-type drug delivery systems. In reservoir-type carriers, drug agents are trapped in an inner core, surrounded by a polymer wall that controls the rate of drug release. In matrix-type carriers, the agents are buried within and uniformly distributed throughout the polymer matrix.

In order to improve biocompatibility or optimize the drug release patterns different forms of materials or additives are often incorporated into one hybrid system.