A gas that kills can save lives too

Carbon monoxide, a gas devoid of taste, colour or odour, has a bad rap: It’s often deemed a killer, thanks to its lethal effects. Although most carbon monoxide is generated on Earth due to the partial burning of fossil fuels like coal, the gas is present in trace quantities in our atmosphere and beyond. It is the second-most common molecule with two atoms in the Universe, constituting about 10% of all carbon sources. Since the invention of fire, humans have known the noxious effects of carbon monoxide: the Greeks and Romans used it as a weapon to kill enemies and for executions and the Nazis used it in the ghastly gas chambers. Experts speculate that the gas may have played a role in the accidental deaths of Cleopatra and Princess Diana.

When inhaled in large quantities, carbon monoxide wreaks havoc in the blood. It displaces oxygen in the haemoglobin, the red-coloured, oxygen-carrying protein in the blood. The carbon monoxide-haemoglobin bond is about 200 times stronger than oxygen-haemoglobin. The body tissues are now deprived of oxygen, causing asphyxiation and death. Thus the bad press for the gas. However, in humans and other organisms, carbon monoxide plays a vital role as a gaseous neurotransmitter, rallying signals between nerve cells. It is produced in trace quantities each day when heme, an iron-containing molecule, is broken down by an enzyme called heme oxygenase. And, humans have known about the benefits of the gas, too.

For centuries, Indigenous people in North America have known the gas’s brain-alerting effect as they used it during fireside rituals, and as an anaesthetic to subdue bees with smoke to harvest honey. Although there has been documented evidence of anti-inflammatory, antimalarial and antibiotic effects of carbon monoxide since the 18th century, researchers in the last decade have taken a fresh look at the therapeutic effects of carbon monoxide to alleviate pain and treat conditions like sepsis, sickle cell disease, cancer, heart diseases and complications resulting from organ transplantation. However, one challenge remains: finding the safest method to deliver a known-toxic gas into our bodies without harm. Once that’s feasible, this dreaded gas could become a life-saver!