Human Hybrid Antimicrobial Peptides for Corneal Infection: From Molecular Dynamic Simulation to In Vivo Animal Studies

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Cornea - the transparent window located at the front part of the eye - serves as a critical structure to normal vision and ocular surface defence. Damage to the cornea can lead to permanent scarring with subsequent visual impairment or blindness. Corneal blindness represents the 5th leading cause of blindness globally, affecting approximately 2 million of the world population. Bacterial corneal infection is the most common culprit, with contact lens wear and trauma being the main risk factors. Affected patients are usually debilitated by pain and visual impairment and they often require long-term hospital admissions for intensive antibiotic treatment. However there has been a growing concern on the declining antibiotic efficacy due to emerging resistance of organisms to antibiotic (i.e. antimicrobial resistance) in infections affecting the eyes and other parts of the body. In addition studies have shown the formation of biofilm (a slimy collection of microorganisms that grow on the surface) during bacterial corneal infection, which enhances their virulence and resistance to antibiotic. These issues highlight the urgent need for alternative effective antimicrobial treatment, ideally with anti-biofilm efficacy.Antimicrobial peptides (AMPs) have recently shown promise as potential therapeutic agents due to their unique organisms-killing (i.e. antimicrobial) ability against a wide range of infective organisms such as bacteria, viruses, fungi and parasites. They are important components of the innate immune system that can be found in various parts of the human body, including the ocular surface. They are made up of amino acids (the basic structural units of protein) and are highly positive-charged. They exert their antimicrobial effect by disrupting the negatively charged membrane (outer surface coating) of the microorganisms, culminating in killing of these pathogens.Over the years, we have profiled a spectrum of AMPs from the ocular surface. Notably, some of these human AMPs, including human beta-defensin (HBD)-2, HBD-3 and LL-37 were shown to have higher activity during corneal infection, highlighting their crucial roles in ocular surface defence. The AMPs also exhibit anti-biofilm, anti-cancer, and wound healing properties. However, the potential clinical utility of AMPs is currently limited by several issues such as toxicity to human cells, instability in certain body environment and the susceptibility to breakdown by human / bacterial enzymes. These have led to the innovation of newer generation AMPs, which involves substituting the amino acids within the AMPs or combining two different types of AMPs (hybrid peptide), using human and non-human AMPs sequences. These newer generation AMPs have demonstrated enhanced antimicrobial effect, better stability and lower toxicity to human tissues. Our primary aim is to create and develop efficacious and safe human-derived hybrid AMPs for corneal infection. Recently we have developed several hybrid AMPs with potential efficacy against a variety of bacteria and we now aim to investigate and optimise the efficacy and safety of our hybrid AMPs using a series of experiments, including computer simulation, laboratory experiments with laboratory grown and donated corneal tissues, as well as using tear and blood samples from healthy volunteers. We will then validate the efficacy and safety of our designed AMPs using rationally and ethically designed animal studies, which is an essential step before we could test our AMPs in human clinical trials. These proposed experiments will be conducted collaboratively in UK and Singapore. Successful development of these AMPs could enable us to bridge the gap between fundamental laboratory research and clinical application of AMPs, ultimately benefitting patients with ocular and potentially non-ocular infections. This may also offer a potential solution to the antimicrobial resistance, which is currently emerging as a global health threat.