By Daniel Otunge
I have always wondered why some alcohol blind, maim and even kill people who consume them. In Kenya, consumption of what is popularly referred to as ‘illicit brews’ has made many men and women blind and sent many to their makers earlier than expected.
Similarly, methanol-induced deaths occurred in Laos recently. This prompted the UK Science Media Center to ask experts to explain why.
According to Prof Alastair Hay, Professor (Emeritus) of Environmental Toxicology, University of Leeds, the risk from methanol is twofold. Methanol breaks down in the body to formaldehyde and then formic acid.
Prof Hay explains that formic acid upsets the acid /base balance in blood; the primary consequence initially affects someone’s breathing. However, it also affects many other organs, including the kidneys. Disturbing acid/base balance and disrupted breathing eventually affect the heart and cause it to stop functioning.
He explains that formaldehyde attacks nerves, particularly the optic nerve, and blindness is a potential risk. “Depending on the severity of poisoning, treatment may require dialysis to remove methanol from the blood while at the same time keeping someone mildly drunk by administering ethanol.
Prof Hay adds that ethanol alone may suffice if the poisoning is not too severe, and only blood tests will determine this. “The principle behind administering ethanol is simple: it delays methanol metabolism. The same liver enzyme, alcohol dehydrogenase, breaks down both alcohols. However, the enzyme prefers ethanol.
So, ethanol acts as a competitive inhibitor, preventing methanol breakdown but markedly slowing it down. It allows the body to vent methanol from the lungs, some through the kidneys, and a little through sweat.
The environmental toxicologist concludes that avoiding forming toxic levels of formaldehyde is critical.
Similarly, Prof Oliver Jones, Professor of Chemistry at RMIT University, explained that methanol toxicity is caused by how the body processes (metabolizes) it. “Methanol itself is a type of alcohol, similar in structure to the ethanol in alcoholic drinks but far more toxic. Methanol’s chemical formula is CH3OH, while ethanol is C2H5OH.
He said that methanol is first acted on in the body by an enzyme called alcohol dehydrogenase, which converts it into a compound called formaldehyde (CH2O).
According to the chemistry professor, formaldehyde is then transformed by an enzyme called formaldehyde dehydrogenase to become formic acid (HCO2H), a formate ion (HCO2-) in the blood.
“The build-up of formic acid /formate in the blood causes the toxicity. Formic acid blocks the action of another enzyme called cytochrome oxidase. This enzyme is critical to how the body uses oxygen to generate energy. If it stops working, cells cannot take up or use oxygen from the blood even when oxygen levels are normal. Lack of oxygen causes problems in various organs as the cells die. The build-up of formic acid in the blood also causes metabolic acidosis, a severe imbalance of electrolytes.”
Prof Jones explained that symptoms of methanol poisoning include vomiting, seizures, and dizziness. The optic nerve seems to be particularly vulnerable to methanol toxicity, so there is the potential for temporary or permanent blindness and even death.
“While thankfully rare, methanol poisoning is severe, and treatment should be given at a hospital.
He explained that methanol poisoning is treated by stopping the alcohol dehydrogenase enzyme from creating toxic by-products. This can be accomplished by using a drug to inhibit the enzyme directly or by giving the patient ethanol to keep the alcohol dehydrogenase enzyme busy processing it to process the methanol into dangerous byproducts.
He noted that dialysis of the blood to remove methanol and toxic breakdown products can also be an option.
