Just before stepping through the mirror in Lewis Carroll’s novel Through the Looking Glass, Alice stops to ponder if ‘looking-glass milk’ will be good for the cat.
Mirror image forms are as serious a business for today’s medicine researchers as it was for Alice. The University of Malta, in conjunction with colleagues at Mater Dei Hospital and across Europe, is investigating the characteristics of chiral drugs that are used in the treatment of epilepsy.
A molecule that is chiral is physically not symmetric; it thus has a ‘mirror image’ form that looks different in the way that a right hand looks different from a left hand. Often only one of these two chiral forms has the desired drug properties – the other one may even cause unwanted side effects.
Most modern drugs therefore contain just one chiral form of the drug molecule. Achieving this isn’t always easy, though; there are relatively few useful reactions that yield single chiral forms rather than a roughly equal mix of both.
These mirror images, scientifically known as enantiomers, may have distinct characteristics.
In nature, one enantiomer of biological molecules such as L-amino acids or D-glucose (simple sugar) (the building blocks of proteins and carbohydrates respectively), are preferentially produced.
Enantiomers may have distinct properties. For example, the smell and taste of an orange and a lemon, which depends on whether the molecule limonene is right- or left-handed; just as right or left carvone gives different tastes to caraway seeds or spearmint oil.
During the past decades, there has been a major stimulus in understanding the role of chiral discrimination in the action of medicines.
Putting it very simply, just as a left hand does not fit properly into a right-handed glove, one enantiomer of a specific medicine may not fit properly into the correct receptor in the body resulting in different pharmacological actions. Perhaps the most dramatic case was the thalidomide tragedy, marketed during the 1960s as a sedative for pregnant women, many of whom later gave birth to deformed children.
The research team at the University of Malta is looking at active epilepsy, which is one of the most serious neurological conditions with considerable socio-economic implications. The heterogeneity of epilepsy and large inter-patient response to drugs means that achieving seizure-free therapy without any side effects still has a long way to go.
Knowledge of the efficacy of chirality may help in the understanding of the unexpected toxicity and efficacy of these medications resulting in their more rational use. In turn, understanding the chiral nature of the site of action of these antiepileptic drugs and the molecular structure of drug receptors can lead to new strategies for drug design.
Trivia and facts
• One of the first drugs to come into common usage, Aspirin is still one of the most researched drugs in the world, with an estimated 700 to 1,000 clinical trials conducted each year.
• $3 billion worth of cancer drugs is thrown away every year, unused.
• According to the World Health Organisation, as of 2011, there were 12,420 different types of diseases and related health problems.
• Bayer, the pharmaceutical giant responsible for Aspirin, once marketed heroin as a non-addictive morphine substitute and cough suppressant.
For more trivia see www.um.edu.mt/think
Sound bites
• The GRAPES-3 muon telescope recorded a burst of galactic cosmic rays of about 20 GeV, on June 22, 2015, lasting for two hours. The burst occurred when a giant cloud of plasma ejected from the solar corona, and moving with a speed of about 2.5 million kilometres per hour struck our planet, causing a severe compression of Earth’s magnetosphere from 11 to four times the radius of Earth. It triggered a severe geomagnetic storm that generated aurora borealis, and radio signal blackouts in many high-latitude countries.
https://www.sciencedaily.com/releases/2016/11/161103125930.htm
• Measurements reveal the relationship between individual CO2 emissions and the Arctic’s shrinking summer sea ice. For each ton of carbon dioxide that any person on our planet emits, three square metres of Arctic summer sea ice disappear. These figures enable us for the first time to grasp the individual contribution to global climate change. The study from the Max Planck Institute concludes that the two degrees Celsius global warming target agreed on in the most recent UN Climate Conference will not allow Arctic summer sea ice to survive.
https://www.sciencedaily.com/releases/2016/11/161104145708.htm
For more soundbites, listen to Radio Mocha on Radju Malta 2 every Monday and Friday at 1pm www.facebook.com/RadioMochaMalta/