Organic compound found in trees could prevent contact-lens eye infections

Cleaning your contact lenses is a tiresome process that has to be carried out carefully to avoid corneal infections caused by Pseudomonas aeruginosa bacteria that can result in serious complications of microbial keratitis. 

First, wash your hands with soap and dry them. Fill your clean contact lens case with fresh disinfecting solution. Rub the first contact lens with the disinfecting solution, and then rinse it with more solution. Place the contact lens into the storage case and close its chamber. Finally, repeat with the remaining lens. Although the process is tedious, the millions of people who don’t want to wear eyeglasses put up with it. 

Increasing numbers of contact-lens wearers 

In recent decades, there has been a global increase in the number of individuals wearing contact lenses. While generally well-tolerated, wearers may experience a range of complications, including corneal ulcers and keratitis. Studies in the past have found that existing disinfecting solutions are not effective for preventing biofilm – clusters of bacteria that attach to the surface of lenses. They can also cause harmful side effects. Now, a naturally-occurring material found in the bark of some trees has been discovered to be an effective disinfectant for the lenses.

Hydroquinine, an organic compound found in bark, is known to have several clinically important germs including Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae. Hydroquinine is already known to be an effective agent against malaria in humans, and it is also being used in the Netherlands to treat nocturnal muscle cramps. Until now, there has been little investigation into its drug-resistant properties.

The team behind the discovery – from the University of Portsmouth in England and Naresuan and Pibulsongkram Rajabhat universities in Thailand – has now explored the potential use of multipurpose formulas containing hydroquinine as a disinfectant for contact lenses.

They examined the antibacterial, anti-adhesion, and anti-biofilm properties of hydroquinine-formulated multi-purpose solutions (MPSs), and then compared it to two commercial MPSs; Opti-free Replenish and Q-eye. The natural compound killed 99.9 percent of bacteria at the time of disinfection. 

The paper, published in the journal Antibiotics under the title “Hydroquinine Enhances the Efficacy of Contact Lens Solutions for Inhibiting Pseudomonas aeruginosa Adhesion and Biofilm Formation,” says these findings could help in the development of novel disinfectants aimed at combating the P. aeruginosa bacteria. 

A shift away from chemical disinfecting solutions

Dr. Robert Baldock from the University of Portsmouth’s School of Pharmacy and Biomedical Sciences, said: “Commercially available disinfecting solutions comprised of several chemicals can sometimes cause reactions with painful side effects. We hoped to show that new agents made from natural products could be an excellent option to limit or reduce the risk of contact lens contamination. It’s exciting to see how this research has progressed; from discovery to exploring potential applications.”

Millions of corneal infections are reported every year that – in extreme cases – can result in permanent eye damage and vision loss. The risk of microbial keratitis doubles when someone wears contact lenses overnight or longer than the recommended daily amount. 

Corneal blindness resulting from microbial keratitis is emerging as a prominent cause of visual disability, according to the World Health Organization (WHO), which has also classified multidrug-resistant P. aeruginosa as one of the most concerning pathogens.

Drug-resistant bacteria occur in more than 2.8 million infections and are responsible for 35,000 deaths per year in the world. Antimicrobial resistance happens when germs change over time and no longer respond to medicines, making it difficult to treat infections. Amoxicillin and Trimethoprim are commonly prescribed antibiotics to which certain strains of P. aeruginosa have become resistant.  

Hopes for future use

Lead author, Sattaporn Weawsiangsang from the Faculty of Allied Health Sciences at Naresuan University, is a visiting researcher at the university in the UK. “Our initial findings suggest that soaking contact lenses in a multi-purpose solution containing hydroquinine is possibly helpful to prevent contamination and infection. However, further investigation is needed to determine whether hydroquinine itself also has adverse reactions or toxicity,” she said. 

“We are continuing to test the compound on a number of cells, and so far, the results are really promising. This potential development could contribute to the creation of new disinfectants from natural products, effectively combating P. aeruginosa. Hydroquinine is already known to be an effective agent against malaria in humans, and it is also being used in the Netherlands to treat nocturnal muscle cramps. Until now, there has been little investigation into its drug-resistant properties,” she concluded.