Scientists at the Hyderabad-based CSIR-Centre for Cellular and Molecular Biology (CSIR-CCMB) have developed a novel drug-delivery system for treating fungal keratitis.
Keratitis is the inflammation of the eye, which starts with redness and itching and might eventually lead to blindness. Keratitis is caused by both bacteria and fungi. Fungi attach themselves to the cornea and release enzymes that break down the corneal proteins for their nutritional requirements. In the process, the cornea also gets inflamed. Corneal damage causes wound and scar formation leading to severe visual impairment. It is estimated that about 30% cases of keratitis in India lead to blindness. In the developed countries, keratitis arises due to increased use of contact lenses.
Treating keratitis infection is currently a challenge as it is difficult to maintain therapeutic dose at the corneal surface for long periods as blinking and tear formation washes off the drug. To address this challenge, a two-member team led by Dr. Ch. Mohan Rao of CCMB has developed protein-based nanoparticles that encapsulate the drug. Certain antibodies attached to the outer surface of the nanoparticles help in anchoring the nanoparticles to the corneal surface.
The infected cornea expresses a set of receptors (TLR4) that get expressed when infection sets in. The team has used antibodies to these receptors to anchor the nanoparticles to the cornea. “If the infection is severe, more receptors are expressed on the cornea and more nanoparticles get bound to the receptors. Since they are bound, the residence time in the eye is long; neither blinking nor tear formation washes off the nanoparticles,” says Dr. Rao who is the corresponding author of the paper.
Interestingly, the enzymes secreted by fungi breakdown the gelatine protein of nanoparticles that encapsulates the drug, thus releasing the drug. Like in the case of the receptors, more enzymes are secreted when infection is severe leading to more drug being released from the nanoparticles. “So drug release depends on the concentration of the enzymes in the microenvironment and hence the severity of the infection,” Dr. Rao says.
“The gelatine protein acts as an alternative nutrient for the fungi. The fungi also degrade the gelatine-based nanoparticle to derive nutrients thus minimising the damage to the corneal tissue. In the process, it releases the drug. In a sense, the fungi are committing suicide by consuming the gelatine protein,” says Saad M. Ahsan from CCMB and the first author of the paper.
The trials carried out on rats were encouraging on all counts. Both, the infection and inflammation were addressed to significantly improve the treatment outcome.
As the residence time of the nanoparticle containing the drug is longer in the eye, the frequency of drug administration gets reduced significantly. “In animal trials we found that application of the drug once every 12 hours was sufficient to completely clear the infection in seven-eight days,” Dr. Rao says. The results were published in the journal Nanoscale.
Since the use of antibodies on the surface of the nanoparticle will make the drug expensive, the researchers are working on designing a short peptide that can be used in place of the antibodies. They are planning to carry out one more animal trial on monkeys or rabbits before starting trials on humans. “We plan to start trials on larger animals in two-three months,” Dr. Rao says.
Dr. Rao says that the technology that they developed is like platform technology and can be adopted to treat other eye disease as well.