Wild parsnip (Pastinaca sativa)-induced photosensitization

Authors: Stegelmeier, Bryan; Colegate, Steven; Knoppel, Edward; ROOD, K - Utah State University; COLLETT, M - Massey University

Submitted to: Toxicon
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/3/2019
Publication Date: 6/4/2019
Citation: Stegelmeier, B.L., Colegate, S.M., Knoppel, E.L., Rood, K.A., Collett, M.G. 2019. Wild parsnip (Pastinaca sativa)-induced photosensitization. Toxicon. 167:60-66. https://doi.org/10.1016/j.toxicon.2019.06.007.
DOI: https://doi.org/10.1016/j.toxicon.2019.06.007

Interpretive Summary: Wild parsnip is a common weed that displaces nutritious forages and has been associated severe sensitivity to the sun in vestock and humans. Some wild parsnip related sores include blisters and vesicles similar to allergic plant-induced dermatitis. The objectives of this work are to develop a model of wild parsnip induced photosensitivity, chemically characterize potential wild parsnip photosensitizing toxins, and compare wild parsnip induced dermatitis with other topical and systemic photosensitizing agents. The wild parsnip from this poisoning incident contained four toxic furanocoumarins- xanthotoxin, bergapten, isopimpinellin, and imperatorin. Goats fed wild parsnip were largely unaffected except one doe that developed minimal dermatitis near the vulva. None of the plant toxins were detected in the blood of parsnip fed goats and a xanthotoxin treated goats had detectable serum xanthotoxin for less than 5 minutes after intravenous injection. Cutaneous application of plant extracts produced radiation-induced dermatitis similar to the controls, xanthotoxin and hypericin. These findings suggest that wild parsnip is a potent inducer of contact photosensitization with no evidence of allergic dermatitis. Its rapid metabolism and clearance especially in ruminants suggests it is less likely to cause systemic photosensitization.

Technical Abstract: Wild parsnip (Pastinaca sativa) has been associated with livestock and human photosensitization. An investigation of a natural occurrence of photosensitization of grazing horses identified wild parsnip as a possible cause. HPLC-MS and MS/MS analysis of this plant identified five furanocoumarins i.e., xanthotoxin, bergapten, isopimpinellin, imperatorin and a putative methoxyimperatorin. Goats fed this wild parsnip were largely unaffected. Xanthotoxin was not detected in the serum of parsnip-fed goats or in the serum of goats dosed orally or intravenous with purified xanthotoxin. Cutaneous application produced severe photodermatitis in goats and a horse consistent with topical exposure as the likely route to produce wild parsnip-induced photosensitivity. Wild parsnip-induced superficial necrotizing dermatitis was consistent with photodermatitis with no evidence of other allergic or inflammatory components.