Direct toxicity Many furanocoumarin compounds are toxic. The
phytochemicals enter the nucleus of
epithelial cells and form a bond (cross-linking) with the
DNA when exposed to UV, which causes cell death and causes
inflammation via activation of the
arachidonic acid cascade. The result is known as
phytophotodermatitis, a serious skin inflammation. Furanocoumarins produced by plants may serve as a
defense mechanism against predators such as
insects and
mammals. It is also likely that furanocoumarins are related to a plant's natural defense against
fungal attack. In particular, the linear furanocoumarins (
psoralen,
bergapten, and
methoxsalen), which occur naturally in
Apiaceae,
Rutaceae, and other plant families, are known to be toxic to fungi. Plants that cause phytophotodermatitis usually contain linear furanocoumarins. The
toxin can sometimes be found even in the most common foods, including
carrots,
parsley,
limes, and
lemons, as reported in the
New England Journal of Medicine in the case of a man who manually squeezed a dozen limes and then inadvertently exposed his hand directly to the sunlight without precaution, triggering a severe phytophotodermatitis for several months. The identified culprit was the prolonged exposure of both his hands to lime juice followed by that of sunlight UV. Furanocoumarins have various effects which can specifically
increase or
decrease (depending on the drug) the blood levels of many pharmaceuticals in ways that can be life-threatening, so
FDA-approved drugs include warnings for grapefruit. ==See also==