How do medicines work?
Fighting Pathogens
A pathogen is a biological agent that causes disease or illness to its host. Examples of pathogens that infect humans are:
Bacteria
Bacteria are microscopic, single-celled organisms. They are prokaryotic. Some bacteria are helpful, and others cause disease.
Examples:
Yersinia pestis - causes Black Plague
Escherichia coli - diarrhoea
Mycobacterium tuberculosis - tuberculosis
viruses
Viruses are submicroscopic infectious agents that can only replicate if they are inside a host cell. They consist of genetic material wrapped in a protein capsule. Scientists debate about whether they are living or non-living organisms.
Examples:
SARS Coronavirus-2 - COVID-19
Human Immunodeficiency Virus - HIV/AIDS
Varicella Zoster Virus - Chickenpox & Shingles
parasites
Parasites are microscopic multi-cellular organisms. They can live inside or on the human body. The definition of a parasite is an organism that gets a benefit like food or shelter from its host, without contributing anything to the host.
Examples:
Plasmodium falciparum - Malaria
Toxoplasma gondii - toxoplasmosis
Sarcoptes scabiei - scabies
Enterobius vermicularis - pinworm
fungi
Fungi are eukaryotic multicellular organisms which include yeast, moulds and mushrooms.
Examples:
Tinea pedis - Athlete's foot
Candida auris - A new, multi-drug resistant fungus
prions
Prions are submicroscopic infectious agents made of proteins. They are non-living, and they are not organisms.
Prions are misfolded proteins which cause healthy proteins to also misfold when they get close.
Examples:
Bovine Spongiform Encephalitis - Mad Cow Disease
Transmissible Spongiform Encephalopathy - Kuru
So how do we treat these infections?
In order to treat infections from different types of pathogens, we need to understand how they work, and what their weak points are. There are many different ways to combat these diseases. For example, if we can design molecules that break down the cell walls of bacteria, those bacteria will die. But this mechanism won't work for bacteria that don't have cell walls. Conversely, many antiviral medications are aimed at preventing a virus from getting inside a human cell, rather than killing them (note: can something die if it was never alive?). Below we discuss a few examples of the many methods scientists have come up with to combat these diseases.
Some methods are more effective than others, but scientists also have to weigh up the side effects. Is the treatment good enough to justify negative side effects?
Unfortunately, just because a medicine once worked to combat a pathogen, doesn't mean it always will. You may have heard the term resistance in the news.
As pathogens are also living things, they can evolve to reduce their vulnerability to certain medicines. Scientists are concerned that many antibiotics will not be useful for much longer, which means that it is really important for us to keep developing new medicines. But who is going to fund this expensive research, particularly when we have a large range of antibiotics available right now?
The E$$ENTIAL MEDICINE$ project is hoping we might inspire you to become involved in solving this problem with us.
Antibiotics
Scientists have developed many different classes of antibiotics, which treat bacterial infections in different ways. Scroll down to see three examples.
Recall that bacteria are unicellular prokaryotic organisms.
Benzylpenicillin
Pencillins work by preventing the bacteria from synthesising a molecule called peptidoglycan. This molecule is a key building block in the cell wall of the bacteria, which provides the wall with the strength it needs to survive within the human body. Without a fully functioning cell wall, the bacteria cells die and the patient can recover.
doxycycline
Doxycycline is a tetracycline antibiotic which prevents bacterial growth by binding to the ribosome and preventing it from functioning. The ribosome is an important organelle for the bacteria, because it controls protein synthesis. Without protein synthesis, the bacterial cells cannot produce essential proteins or reproduce. It eventually dies, and the patient can recover.
Delafloxacin
Delafloxacin is a fourth generation fluoroquinolone which inhibits the activity of key proteins involved in bacterial cell replication. If bacterial cells cannot replicate, no new bacterial cells are made to replace those that die naturally. The bacterial infection of the patient subsides and the patient can recover.
Antivirals
Recall that viruses are simple entities made of genetic material inside a protein capsid. Sometimes, this is surrounded by a protective membrane. Anti-viral medications cannot 'kill' viruses, as they are not alive. Antiviral medications generally focus on interrupting the process of replicating genetic material.
Tenofovir
Tenofovir binds to a protein called reverse transcriptase and prevents it from working.
Reverse transcriptase is a protein which creates new DNA strands from RNA material. If the virus cannot create new DNA strands, it cannot replicate.
Remdesivir
The mechanism of action for remdesivir is currently unclear. Recently, scientists have been focussing on trying to understand this medicine as it may possibly help with the treatment of COVID-19.
Remdesivir possibly presents the synthesis of RNA material.
If a virus cannot create RNA material, it cannot replicate.
Antiparastics
The mechanism of action of many antiparasitic medications are unknown.
hydroxychloroquine
The mechanism of action of hydroxychloroquine against malaria parasites is not known.
Artemisinin
The mechanism of artemisinin was recently discovered by scientists that work in a field called chemical proteomics. Artemisinin binds to 124 proteins that the malaria parasite uses to grow and function, making them unable to work and killing the parasite.
Examples
Summary Questions
Why do you think that it is important that medicines which target pathogens attack specific pathogen cells or proteins?
If you were a scientist developing a medicine for a pathogenic disease, which disease would you work on and why?