At the Cambridge Medicine Masterclass earlier this month, I listened to a lecture led by Sonja Dunbar, and was truly intrigued. If I’m honest, it was the lecture I thought I would be least interested in, as I expected it to focus on herbal remedies and the likes, yet it was much more medicine focused.
66% of all drugs have their origins in nature, and infant 80% of people in underdeveloped countries rely on traditional remedies from plants. Thus, their used simply cannot be ignored. Yet, what was a really interesting proposition was why are so many compounds in plants beneficial to humans? It is absurd to think that plants exist for our benefit, there are abundant defences to stop us using them. Spikes, thorns, bristles and chemical poisons all with the intention of helping the plant live longer, and protect the plants form those who are likely to eat it. A key example of this is the classic stinging nettle. These contain histamine, responsible for the itching felt after a sting and acetylcholine, a neurotransmitter. These are contained in a trichome, a specialised ‘hair’ in plants which is very similar to a hollow needle. Alongside this, stinging nettles contain Leukotriene, which promotes information and causes blood plasma to leak out of the membrane and lysosomes to swell, and serotonin. All of these chemicals are pumped in you your body when you are stung by a nettle.
This leads us to the scarcity-accessibility hypothesis, where a plant in an environment where it is more likely to be eaten, for example when other plants are scarce is likely to have the most defences. Examples of such plants are Holly and cacti, both of which have visible mechanical defences – holly with its spiked leaves, and cacti with their needle-
An interesting example of a plant which attempts to deter you form eating it, is the chilli. Chill is detected by TRPVI, the same receptor as vanilla, and vanillin and capsaicin are in fact structurally very similar. However, vanillin cannot get through the cell membrane, yet capsaicin can, and therefore binds to the receptor and tigers the brain into thinking you’ve eaten something hot. For most humans, this would not be a pleasurable experience and would put you off eating a chilli again. However, it gets better. Chilli’s receive no benefit from being eaten by mammals, as we grind and crunch seeds up due to our molars. Their seeds are therefore broken apart and cannot germinate to produce more plants. Although, birds eat chilli’s and don’t seem to find them hot. Why? Because birds don’t crush or grind the seeds, simply pass them through their digestive system and disperse them. They can travel great distances in a short space of time meaning that very little competition between the plants remains, and so birds do not find chilli’s hot, as the plant benefits from being consumed.
So, what are some examples of plants used in medicine? Foxgloves, contain digitoxin which helps to controlyour heart rate. It is a cardiac glycoside which interferes with sodium-potassium pumps, calcium ions and polarisation. In a high dose, it causes irregular heart rates, yet in a low does, it is very useful. Thus, from digitoxin digoxin has been developed, with less side affects and thus less associated dangers than the ‘pure’ substance, but with a very similar chemical structure.
Similarly, Aloe Vera contains 98.5% water, mannose-6-phosphate sugars and a collagen triple helix. It can be used in the treatment of thermal and radiation burns. It has been known to reduce swelling, stimulate faster tissue synthesis and help keep the wound clean and hydrated due to the high water content. Thus, it is used in many suncreams, after suns and in a gel to help prevent wounds from infection.
The lecture also spoke about the 2015 Nobel Prize in physiology or medicine. In 2013 there were 198 million cases of malaria, and is a disease which can easily escape detection due to the life cycle of the parasite. Theparasite enters liver cells where it can replicate for 2 weeks without detection. Eventually, the liver cells rupture and release the parasite, which consequently goes on to infect red blood cells. Here, the parasite escapes detection by wrapping itself in the cell membranes of cells from the organism – which will not be recognised as something harmful by the immune system. Cinchona is an example of an early malaria remedy, which was so heavily sought after the plant nearly went extinct. Artemisinin also treats the fever of malaria, and with cold extraction, reduces 100% of the parasite load in monkeys and mice – incredible. Consequently, the death toll form malaria in the past 15 years has declined by 50%, and it is great to see the Nobel Prize being awarded for a medicine being developed for disease in underdeveloped/developing countries. This is because it takes around 12 years and £1.2 billion to take a drug to market, not something which is affordable to such counties, but malaria is a disease which takes millions of lives, and so any advancements could save countless lives.
What I learnt from this lecture is that biodiversity mattersin the hunt for new drugs. There are still plants we don’t know exist, and plants we do know exist but don’t yet recognise their uses. In destroying the biodiversity of our world, for example by deforestation, we could potentially be destroying cures for diseases. The ecology of the world we life in is important to allow us to survive, and while plants don’t exist for out benefit, they are incredibly useful.
(Source: Sonja Dunbar, Nature’s Medicine Cabinet Lecture, Cambridge University)