In previous posts, I discussed the unique strategies the cabbage butterfly larvae use to detoxify glucosinolates in their cabbage family host plants. What happens when humans consume cabbage? The cyanide generating isothiocyanates that are released when eating cabbage are detoxified by the glutathione-S-transferase (GST) pathways. In this detoxification, the toxic isothiocyanates react with glutathione instead of reacting to release cyanide. The glutathione conjugate is further processed to a mercaptan that is rapidly eliminated in the urine.
The GST reaction depletes the amount of glutathione in the cells and triggers an increase in both glutathione and many detoxification enzymes. Humans can eat cabbage because its toxins are quickly eliminated from the body. Cabbage is beneficial because it increases the ability to detoxify and eliminate other dietary and environmental toxins.
Insects not adapted to feeding on plants containing glucosinolates, use the same GST detoxification pathways that humans and other animals use. Insects such as armyworms can tolerate low levels of glucosinolates. However, at higher concentrations, the GST system is overwhelmed and the glutathione depleted*. After the depletion, the remaining glucosinolates will produce cyanide that will injure or kill the insect.
*Verena Jeschke, Jonathan Gershenzon, Daniel Giddings Vassão. A mode of action of glucosinolate-derived isothiocyanates: Detoxification depletes glutathione and cysteine levels with ramifications on protein metabolism in Spodoptera littoralis Insect Biochemistry and Molecular Biology. 71: 37-48.