Of laboratory mice and men
ANIMAL TESTING IS, understandably, a very sensitive issue. No sane person would want to hurt an animal unnecessarily. However, when a list is made (see below) of just some of the breakthroughs that have been achieved thanks to the use of animals in laboratories, an inconvenient truth emerges.
“The use of rodents is essential to the work done at the Alimentary Pharmabiotic Centre [APC] and to neuro scientific research generally,” says Prof John F Cryan, professor and chairman of the Department of Anatomy at the APC.
“Like humans, rodents have an intact nervous system and to be able to study the nervous system and GI [gastrointestinal] system effectively, we need to work on a system similar to our own.”
Over the years, many animals have been employed in scientific research – dogs, cats, chickens, guinea pigs, rats and so on. But mice have become the most widely used for a number of reasons. “They’re mammals, they’re easy to breed and to house, they’re light in weight and many of their systems are very similar to that of humans,” says Cryan.
“Most recently mice have been central to the huge success story in terms of modern molecular medicine and genetic modification,” he adds. “Through gene therapy, we are able to test any genetic hypothesis. If we find a specific gene causing a medical issue, we can simply knock out that gene and see how the system works for us without it.”
Genetic modification of mice was first used in the early 1990s, and the mouse genome was fully sequenced in 2002. Since then their contribution to finding treatments for all manner of genetic disorders – from muscular dystrophy to cystic fibrosis and Alzheimer’s disease – has been immeasurable. “We can humanise mice and put whatever genes in we want to mimic their involvement in a variety of disorders,” says Cryan.
Of course the mice used in Irish research are not collected from city streets or churches. They are bred in what are known as specific pathogen facilities. One such facility is located in Trinity College Dublin. “The mice are kept in very controlled, non-infected, sterile conditions,” explains Prof Pete Humphries of the Trinity College Institute of Neuroscience.
“Researchers using the facility have to shower every time they enter or leave. The facility is aired through a series of filters to make sure it is particle-free and completely sterile and there is a plant room on the roof which pumps pressurised air in. The whole thing was very carefully designed.”
Most of the mice in the facility are born, raised and die there. The sterile environment, says Humphries, not only allows for more concise testing, it also ensures the animals are kept in a very healthy, comfortable condition.
This, however, is rejected by the Irish Animal Rights Action Network. “Due to the lack of legal protection and transparency, mice and rats are often treated very poorly with few consequences,” they say. “They routinely die due to overcrowding in cages, starvation, dehydration, or use in unapproved experiments.”
However, according to the chairman of the Dublin City University ethics committee, Dr Donal Ó Mathúna, the regulation on animal testing couldn’t be any more stringent. “Animal research is more highly regulated, with more consistent guidelines and requirements, than even human research,” he says.
“Certainly one of the underlying aspects of the regulation would have to do with the degree of suffering and potential pain involved in a research area. Animals like rodents are clear-cut and the potential for pain is there. But it doesn’t just involve pain. Social dimensions and stress factors are also taken into account in the regulation.”
“There’s a very strict licensing system where every experiment is documented and ethically approved,” says one Irish neuroscientist who did not wish to be named.
“Everything is detailed and most people who sit on animal ethics boards are nonscientists. All research proposals using animals will be asked if there is pain involved, and if so if it is necessary and justified. It must not be painful, so many tests would be done under anaesthetic.”
Two bodies oversee all the regulation for this area in Ireland: the Food and Drug Administration and the European Medicines Agency. “Regulatory bodies who approve of all research with mice have required mandated approaches,” says Humphries.
“If we go to them with a potential new treatment for any condition, they’ll say, ‘Show us that it works’. We simply have to validate that it works through animal testing. If we can’t show the process works in a model system we won’t get approval. Nobody wants to work on animals, but we actually have no choice to make important breakthroughs.”
One such breakthrough was in an area of expertise for Humphries: eye disease. “Some of the conditions we look at include two debilitating eye conditions known as retinitis pigmentosa [RP] and Leber’s congenital amaurosis,” he says. “Both are genetic conditions and without researchers being able to make mouse models of each [the Trinity group reported a mouse with a so-called knockout of the rhodopsin gene as far back as 1997, mutations or changes within this gene causing a prevalent form of RP] it would be difficult to conceive of the treatments now being developed ever being successful.”
Translational research, from animal to human, doesn’t come without risks. In 1999, 18-year-old Jesse Gelsinger died from a reaction to a gene therapy treatment at the University of Pennsylvania’s Institute of Human Gene Therapy. “He was given a gene therapy for a liver condition known as OTC deficiency,” says Humphries. “However, he developed a severe reaction to the therapy that had been tested on mice first and he died.”
There have been other human tragedies where translational gene therapy research has gone wrong. But the contribution made by rodents in modern science can be seen from basic scientific education all the way up to the top echelons of advanced research.
“I use rats to teach first-year dissections in basic anatomy,” explains UL zoologist John Breen.
“You can’t understand by simply learning from diagrams. Plastic models don’t work either. Until learners see it for themselves they won’t make the connection between the diagrams and real life. If a small number of my students become surgeons, then it has been worthwhile.”
The pitter-patter of giant feats
Mice, rats and other rodents deserve a Nobel Prize for medicine given the number of crucial treatments they helped to discover.
The significance of Alexander Flemings discovery of penicillin in 1928 was not properly recognised until 1940 when more rigorous testing of the antibiotic was done on mice.
Scientists at Oxford University infected eight mice with a deadly dose of streptococci bacteria. An hour later, four of them received a penicillin injection. They survived, while the other four died.
As we now know, this discovery revolutionised the ability to treat all kinds of bacterial infections and led to the saving of millions of lives, both human and animal.
The big killer of humans and farm animals of the early 20th century, tuberculosis (TB), was also overcome through animal testing. In 1943, two soil microbiologists from Rutgers University in New Jersey injected a soil bacteria byproduct found in a sick chicken, known as streptomycin, into guinea pigs infected with TB. It cured the guinea pigs without harming them and led to the same antibiotics being used to treat humans.
Breast cancer is now the second most survivable female cancer. With a 77 per cent five-year survival rate, certain types of the condition can now be treated thanks to studies on rats that began in the 1950s.
This early research showed that hormone changes could induce breast tumours in rats, work which resulted in the development of tamoxifen. The drug blocks the growth of hormone-dependent breast cancers. Following its introduction in the 1990s in the UK, it was shown that tamoxifen led to a 30 per cent reduction in death rates.
More recently, advances have been made in a number of brain degenerative diseases. “Research into Alzheimers, Huntington’s, Parkinson’s, and some motor neuron diseases have all come on significantly thanks to gradual research therapies working with rodents,” says Prof Pete Humphries of Trinity College Dublin. “Armed with this research, we are then in a position to gradually move into human therapy.”
Rodents have also been crucial in other recent areas of research. “Mice are very important in terms of developing models suitable for central nervous system disorders,” says Prof John F Cryan of the UCC Alimentary Pharmabiotic Centre. “In addition, they are playing an increasingly important role in psychiatry.”