The ancient Greek philosopher and physician Hippocrates, who is considered the father of modern medicine, once said “Let food be thy medicine and medicine be thy food”.
I wouldn’t be surprised if he also had garlic in mind. In celebration of World Food Day (16 October), I would like to take a closer look at this plant that is not only used in many of our favourite dishes, but could also be an ally in the fight against cancer.
Originating from Central Asia, garlic has been used in food preparation and as a medicine for approximately 4 000 years. No wonder it is said to be the elixir of life.
Among garlic’s health claims are that it lowers blood pressure and fights infections and parasites. It is also said to ward off vampires, to boost the immune system by providing strength and stamina, and to protect against illness.
The Codex Ebers, an Egyptian medical papyrus dating back to about 1550 BC, gives more than 800 therapeutic formulae, of which 22 mention garlic as an effective remedy for a variety of ailments including heart problems, headache, bites, worms and tumours.
Indeed, preserved garlic was found both in the archaeological site of Knossos in Crete, built in 1800-1400 BC; and in the tomb of King Tutankhamen dating back to 1500 BC.
During the time of the bubonic plague in Europe, doctors would wear a bird-like mask containing herbs and crushed garlic to purify and sterilise the air to protect against the Black Death.
Indeed, Louis Pasteur, in 1858, recognised garlic as a natural antibiotic, and it was used during both world wars when drugs were scarce, earning the name “Russian penicillin”.
Garlic is also a well-known stimulant. Egyptian labourers who built the pyramids ate it to increase strength, while Olympic contestants in Ancient Greece used it to enhance performance.
Roman soldiers and sailors even consumed it for endurance and stamina. Indeed, a number of yoga and Ayurveda practices today discourage garlic intake for its stimulatory properties, which may be partly due to its ability to strengthen the immune system.
Strong odour and sharp taste
Chemists have long been attracted to substances with strong odours, sharp tastes and marked physiological effects. Investigations over the last century have shown that the odorous substances in garlic belong to an interesting group of small sulphur-rich compounds.
The plant produces these compounds to protect itself against invasive threats. Being damaging to the plant itself, they are only produced when the clove is damaged (i.e. chopping or crushing), a mechanical mechanism that brings together the cysteine sulfoxide alliin and its enzyme allinase.
Together a reaction ensues to produce the strongly pungent and biologically active compound called allicin which has a strong antimicrobial activity (gargle with fresh garlic if you have a sore throat).
If allicin is heated (as in the cooking of food), two molecules can come together to combine into a number of secondary sulphur-rich compounds that include ajoene (ajo is Spanish for garlic) and diallyl trisulfide (DATS).
The transformation of allicin to ajoene and DATS can happen very slowly at room temperature or in the fridge, but happens quickly when allicin is heated.
Many medicinal compounds that plants produce as chemical defence against physiological threats, often offer protection against cancer.
It has long been known that populations who consume large quantities of garlic are at lower risk of developing certain cancers, particularly those of the gastro-intestinal tract. This could be because of garlic’s immune-strengthening properties, but may also be due to the ability of the compounds to target and harm cancer cells.
We have been studying the anti-cancer activity of ajoene and DATS for a number of years and found that the polysulfane functional group in the backbone of these molecules, is the chemical warhead responsible for both its chemistry and bioactivity.
We recently found that ajoene has many protein targets in breast cancer cells (approximately 650) which may partly explain why it is claimed to have so many health benefits. Indeed one of these proteins called Cox2 is also the protein that aspirin targets to stop the inflammatory response.
What’s interesting, is that ajoene binds to Cox2 and inhibits its activity, making it a natural non-steroidal anti-inflammatory drug. Overall, we found that ajoene was targeting proteins that were involved in metabolism, cellular processes and genetic information processing, all essential to the biology of cancer cells. What makes ajoene kill cancer cells, but avoid the healthy cells?
It may be that cancer cells, with their increased metabolic demand for protein synthesis, may be more susceptible to this small molecule than their healthy counterparts.
It is estimated that 60-80% of cancers are preventable as they are caused mainly by external factors. As we celebrate World Food Day, let’s remind ourselves that nature has provided us with a number of tools and resources that can help protect us against these cancers, with garlic being one of them.
*Dr Catherine H Kaschula is a senior lecturer in the Department of Chemistry and Polymer Science at Stellenbosch University.
