Lens cultures,
calpains, and a
potential cure for
cataracts

Dr. Julie Sanderson

Senior Lecturer

University of East Anglia

A window on the world, our eyes are perhaps our most important sensory organs, and it’s for this reason that the loss of vision – and at the extreme end of the spectrum, blindness – is the chief fear of many.

One of the most globally prominent eye conditions is cataract, an ailment that causes a clouding of the eye’s lens, thereby causing a degradation of vision. Human lenses are particularly intricate. Day in, day out, this part of the eye needs to be able to continually relax and contract, in order to focus the light entering through the pupil onto the retina, which is located on the rear interior of the eye. Working with the cornea, the lens refracts light through microscopic, near-transparent cells known as lens fibres that contain a stunningly-arranged, crystalline structure of proteins. In cataract, cell and protein architecture is lost and, with it, the transparency of the lens.

The World Health Organisation (WHO) estimates that, worldwide, some 20 million individuals have been made blind due to cataracts in one or both eyes, and hundreds of millions more people are likely living with a cataract that causes a lesser degree of vision loss. This visual impairment has social, cultural and developmental effects the world over.

Globe turning into an eye

Justifiably, the WHO is working to reduce this number, set to rise in the coming decades as the global population ages – cataracts being more prevalent in the elderly. For instance, over half of those aged over 65 have a cataract development. Unfortunately though, treatments are currently restricted to invasive procedures – surgically removing the cataract lens from each eye and replacing each with an artificial replacement – that are usually offered after a loss of vision has occurred.

Thankfully, recent discoveries into the condition could mean that cataracts are treated much less intrusively, and before vision has not been significantly degraded. Dr Julie Sanderson, senior lecturer at the University of East Anglia’s (UEA’s) School of Pharmacy, is at the forefront of this research. Through building on a laudable body of research developed over the past few decades, she may soon be able to present the world with a definitive answer to the problem of cataracts.

Culturing a Lens

From the outset, Dr Sanderson’s work focused on the human lens. In 1989, in her PhD she noted that as we age, the concentrations of free sodium and calcium ions inside the cells that make up our lenses increase.

 

Electrical potential of the charges inside and outside of the cell membrane Electrical potential of the charges inside and outside of the cell membrane Electrical potential of the charges inside and outside of the cell membrane

This was seen to occur because of a number of reasons. As the lens cells aged, the membrane potential – the difference between the electrical potential of the charges inside and outside of the cell membrane – and the resistance of the membrane, meaning its ability to stop ions moving across it, both decreased. These changes allowed calcium to enter the cells. This element is essential to cell function, but if concentrations are too high it causes damage to the cell.

The findings were important, but the academic’s follow-up research resulted in a far wider-ranging discovery.

In 2000, in order to be able to conduct further research into the effects of raised calcium on lens cells, Dr Sanderson and her colleagues wanted to develop techniques to be able to study the human lens for extended periods of time.

In order to understand why the lens loses transparency in human cataracts, we needed to be able to simulate this process in the lab

Lens culture system

Dr Sanderson created a lens culture system that mimicked the nurturing environment of the eye, so that the cells of the lenses wouldn’t begin to degrade, become cloudy, and thus be inadequate for experimentation.

 

Lens culture system

Using donor eyes obtained from the East Anglian Eye Bank, the corneas were removed to be used as transplants. The lens was carefully dissected from the eye and kept in Eagle’s minimum essential medium – a manmade cell culture liquid that was made to mimic the composition of the medium that normally surrounds mammalian cells.

As a result of her work, the lenses stayed ‘alive’. By doing so, the team became the first in the world to maintain human lenses in a culture for an extended period of time, creating an experimental model within which lenses could be examined, and ocular drugs could be tested.

Cataract’s Cause

Animation of calcium entering the lens

As in many scientific experiments, this single study yielded more than one important discovery. While Dr Sanderson and her colleagues had discovered a means to keep lenses in-vitro, their research found something else: the lenses were being clouded when calcium increased, and moreover, this opacity was being caused by the degradation of proteins within the lens cells.

The results were intriguing, and implicated the involvement of calpain, a protease – enzymes that break down amino acid chains (proteins) – found in most mammals. Calpains exist in the cells of the eye, yet only begin to break down proteins when they are activated by calcium.

As Dr Sanderson had discovered in 1989, the breaking down of cell membranes in the eye – as people aged, for instance – allowed more calcium inside them.

After they’re activated, the calpains begin to break down the intricate crystalline protein structures in the lens. Slowly but surely, the structures break down and begin to scatter, not refract, the light entering through the pupil, and vision loss begins to occur.

The need to stop the activation of calpain was obviously very important, but given that cell membranes can’t currently be repaired, a different solution was needed.

At this point, Dr Sanderson’s involvement was reduced, but other researchers across the world picked up on the findings.

Lens Clouding
No lens clouding Lens clouding

Cataract Appearing Over Time

Drag the slider below to see the development of a cataract over time in a cultured lens

A CALPAIN
INHIBITOR

Picking up on the wide body of research including Dr Sanderson’s work, academics in New Zealand begin to search for a treatment. Joined by the UEA academic, James Morton and his team looked to one of the country’s most well-known inhabitants for answers.

The team had noted that a number of the country’s sheep were experiencing an inherited form of cataract that was causing them to go blind. Further investigation showed that, as in human cataracts, calcium was increased in the lens, and that this caused the activation of calpain. Knowing that combatting this could be key to stopping calpain activation in the human lens, the team began developing a drug that inhibited the activation of calpain in the eye, thereby stopping the protease’s destructive streak.

 

sheep

The drug worked, but the differences in the calpains that exist between sheep and humans meant that it couldn’t simply be applied to human lenses. The development of the drug needed investment, and given the predisposition of pharmaceutical companies to develop non-risky drugs, private investment was needed.

Across the Tasman Sea, Australian entrepreneur Tim Lovell took it on himself to spearhead the investigation. After winning both public and private funding to license the New Zealand team’s drug, he recruited Dr Sanderson and her colleague in the School of Biological Sciences at UEA, Dr Michael Wormstone, under a new company – Calpain Therapeutics – with an aim to see if it could be effective for human use.

The team are still at work, but the current results are promising. Using the lens culture research developed by Dr Sanderson in 2000, the team are looking into all avenues, and despite hurdles relating to the supply of donor lenses, the future is bright.

Sheep in a field

“I would hope it wouldn’t take much longer. We have done a few studies that indicate that it might be effective, but there is more to do.”

Julie Sanderson

Moreover, there’s potential for the drug to involve a delivery system as novel as the drug itself. Dr Sanderson’s concurrent research into glaucoma has initiated the development of a means of drug delivery that sidesteps the use of eye-drops entirely. Traditionally, eye drops result in close to 95% of the active ingredient being lost, with only the slim remainder moving into the eye and performing a therapeutic effect.

Instead, Dr Sanderson working with Dr Sheng Qi in the School of Pharmacy and Dr Matthew Alexander in the School of Mathematics at UEA and also Professor David Broadway, a glaucoma consultant at the Norfolk and Norwich University Hospital are in the process of developing a system that delivers the drug via a contact lens, allowing the drug to be administered – close to waste-free – to the eye throughout the day. While this system might not necessarily be used in the calpain inhibitor treatment, it demonstrates the fast pace of the research community.

But what about the potential for Calpain Therapeutics’ drug? If Dr Sanderson’s past research into the eyes of salmon is anything to go by, the effects could be game-changing.

Looking through a fisheye lens

In the early 2000s, Dr Sanderson was approached by Norwegian scientists in order to assist with an all-together different research effort.

From the late 1990s, the country’s many salmon farms (as well as those in Ireland and Scotland) had been afflicted by a particularly expensive problem. Countless salmon were developing cataracts, resulting in the salmons’ welfare being impacted, and the Norwegian fish farming industry losing some €27.9 million. Up to 80% of all salmon were affected, with many dying or becoming more susceptible to disease.

Norwegian researchers set about understanding why this was taking place. The team’s research – utilising Dr Sanderson’s expertise in culturing lenses – identified that the formation of cataracts was due to a deficiency in the amino acid histidine and its metabolite, N-acetyl histidine.

“Finding a reason why the histidine was important… physiology, pathophysiology, pharmacology. That’s my role – thinking about what is happening inside cells.”

This amino acid was shown to be crucial to the salmon’s sight. In nature, as the species makes the transition from fresh to saltwater, their lenses must respond to the changing osmolarity (the concentration of solutes) of the surrounding water. In essence, without histidine, the cells of the lens would dehydrate, causing cataracts to develop.

Why weren’t the salmon receiving histidine? The answer related to their diet. In the historical farming process, salmon would receive histidine by ingesting haemoglobin – a major constituent of the blood meal that farmed salmon had been traditionally fed.

After the BSE crisis that had occurred in Europe during the 1990s, blood meal had been removed from the salmon’s diet out of fear of contamination, and this had resulted in the formation of cataracts in the fish. The results were tested in the field, and the assumptions were found to be correct.

Immediately, the findings were applied across the European Union, and the resulting increase in histidine in the salmon’s diet meant that the formation of cataracts in the farmed species was practically eradicated in the EU. This was then adopted worldwide.

Dr Sanderson’s work into calpains continues, but hopes are high that Calpain Therapeutics’ new drug could reduce the impacts of cataracts the world over, much to the same effect as the revelations regarding histidine.

By eliminating the need to wait for cataracts to develop before treatment is administered, reducing patients’ recovery time, and improving the ease of access to care, the futures of millions across the world could be improved, bestowing the gift of sight to countless individuals, in a truly novel way.

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