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Beware the bitter veg!
In 2018, JAMA Dermatology published two cases of hair loss, amongst other symptoms, of individuals who reported eating bitter Cucurbits – members of the Cucurbitaceae family: squash, courgettes, pumpkins, and melons. These were reported as cases of Toxic Squash Syndrome, a type of poisoning resulting from ingestion of a toxin named Cucurbitacin E. Here, I will explain what is known about this syndrome, as well as briefly discuss known therapeutic uses of cucurbitacins.
Remarkably little research into Toxic Squash Syndrome exists, perhaps because it is a rare occurrence. However, the disease can be truly severe. Symptoms ranging from nausea, diarrhoea, vomiting, hair loss, gastrointestinal bleeding and even one case of death have been reported, typically lasting up to a week. Often cases are known to result from the ingestion of inedible ornamental gourds and bitter squashes, but perhaps more interestingly are those cases from cross-pollination or self-seeding of home grown plants, as was reported in a 1984 study in the Journal of Food protection (see below).
The bitter taste of the offending vegetables, typically bred out by plant breeders, actually signifies a high density of the toxin Cucurbaticin E, a natural defence mechanism of the plants against predatory mammals and insects. In self-seeded or cross-pollinated plants, genetic recombination may lead to altered expression of the gene encoding one or more stages of the toxin’s synthesis pathway, thus leading to its overproduction. This phenomenon is not only known amongst home growers – it has also been reported in commercial seed or even shop-bought Cucurbits. A widescale recall of courgette seeds was reported by the BBC in 2020 for this exact reason. However, the latter cases are incredibly rare, and the main message is to always buy Cucurbit plants and seeds from a reputable source when growing at home.
More recently, study into Cucurbitacin E has focussed not the effects of its ingestion but rather its therapeutic and insecticidal properties. In much smaller doses, cucurbitacins are reported to have significant anti-metastatic, cytotoxic, and anti-inflammatory properties, thus making them a molecule of interest for possible treatment of a wide range of cancers (see review publication by Xiuping and colleagues below). Additionally, Cucurbitacin E has been shown to be an effective insecticide against aphids, suggesting possible commercial use in agriculture.
Finally, and somewhat unrelated, since the research on this subject was quite sparse, I thought it might be interesting to give an update on my polytunnel project. In the summer I hope to grow squashes, courgettes and melons, and now I know to be wary of a bitter taste. As of early March 2021, one large raised bed has been filled with a mix of ericaceous soil, grit, compost, and bark. This bed will contain the chilli, cardamom, and ginger plants, and has a second plastic cover for additional heat retention. Now, the remaining 4 beds, shown below, need to be filled with a mix of topsoil, grit, and compost, which have arrived in an assortment of bags. A number of plants and seeds have also been ordered to arrive over the coming months. Additionally, the peach and apricot trees have started to bud a little – my fruit crumble dream springs to life!
- Firstly, this short study from the Journal of Food Protection in 1984 details a basic breeding study used to confirm the bitterness and toxicity of Cucurbit plants. Fortunately quite a simple study, this was the only study I could find on the topic, but I think despite its age, the same truths hold.
- Next, these case studies describe the cases of individuals studying from Toxic Squash Syndrome in the journal JAMA Dermatology.
- Finally, this review by Xiuping and colleagues in the journal Anti-Cancer Drugs outlines key cucurbitacin studies of the last 50 years. This detailed review clearly outlines key opportunities for use of cucurbaticins for cancer therapy.
Written by Joshua Williams for the UCL Genetics Society:
3 responses to “Toxic Squash”
this was so interesting, and a bit scary!! However, the positive effects are incredible fascinating. Are there specific ways of knowing if you have toxic squash or is it all in the first bite?
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Thank you for your thoughtful question! As far as my reading has led me to believe, there are no current tests for this toxic trait in squash. Perhaps if the trait was mapped to a specific gene, then Southern blot analysis would allow identification of the condition in single plants or seeds. However, this is neither practical for the home grower due to the equipment involved, nor for the industrial grower, who would have to test far too many seeds or plants.
One interesting possibility that I can think of is some synthetic tool that might give a toxic plant a distinctive visible characteristic e.g. strange leaf colouring. This could involve genetic modification to add a gene whose product interacts only with Cucurbitacin E, thus allowing a spectrum of responses to different densities of the toxin in the growing plant.
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