furocoumarin

Furocoumarins are a family of photoactive natural products that consist of a furan ring fused to a coumarin skeleton. They are typically classified into two structural groups: linear (psoralen-type) and angular (angelicin-type). These compounds absorb ultraviolet A (UVA) light and can form covalent bonds with DNA and other cellular components, a property that contributes to both their phototoxic effects and their therapeutic use in dermatology.

Natural occurrence and sources: Furocoumarins occur in a variety of plants, including citrus fruits (notably bergamottin and bergapten), celery, parsnips, parsley, and many members of the Apiaceae family. They are often concentrated in peels, seeds, or essential oils and can be present in grapefruit juice.

Mechanism and medical use: When exposed to UVA light, furocoumarins are activated and can form covalent adducts with thymine bases in DNA. After a second UVA exposure, this can lead to cross-linking and cytotoxic effects. This photochemical activity is exploited in PUVA therapy (psoralen plus UVA) for treating conditions such as psoriasis, vitiligo, and certain cutaneous lymphomas. In addition to therapeutic uses, furocoumarins can cause phytophotodermatitis—skin irritation and blistering following contact with plant material and sun exposure.

Safety and interactions: Exposure to furocoumarin-containing materials followed by sunlight can provoke phototoxic skin reactions. Additionally, furocoumarins in grapefruit and related citrus products can inhibit intestinal CYP3A4 enzymes, producing clinically relevant drug interactions. Proper handling and awareness are advised when working with plants rich in these compounds.