Secondary Plant Products Causing Photosensitization in Grazing Herbivores: Their Structure, Activity and Regulation

Abstract

Photosensitivity in animals is defined as a severe dermatitis that results from a heightened reactivity of skin cells and associated dermal tissues upon their exposure to sunlight, following ingestion or contact with UV reactive secondary plant products. Photosensitivity occurs in animal cells as a reaction that is mediated by a light absorbing molecule, specifically in this case a plant-produced metabolite that is heterocyclic or polyphenolic. In sensitive animals, this reaction is most severe in non-pigmented skin which has the least protection from UV or visible light exposure. Photosensitization in a biological system such as the epidermis is an oxidative or other chemical change in a molecule in response to light-induced excitation of endogenous or exogenously-delivered molecules within the tissue. Photo-oxidation can also occur in the plant itself, resulting in the generation of reactive oxygen species, free radical damage and eventual DNA degradation. Similar cellular changes occur in affected herbivores and are associated with an accumulation of photodynamic molecules in the affected dermal tissues or circulatory system of the herbivore. Recent advances in our ability to identify and detect secondary products at trace levels in the plant and surrounding environment, or in organisms that ingest plants, have provided additional evidence for the role of secondary metabolites in photosensitization of grazing herbivores. This review outlines the role of unique secondary products produced by higher plants in the animal photosensitization process, describes their chemistry and localization in the plant as well as impacts of the environment upon their production, discusses their direct and indirect effects on associated animal systems and presents several examples of well-characterized plant photosensitization in animal systems.

Clinical and histopathological study of the phototoxic dermatitis in Zebu calves in grazing of Brachiaria decumbens

“…La presencia de sustancias fotodinámicas reactivas a la luz, producidas por las plantas superiores puede dar lugar a daños considerables en los tejidos sensibles, causando irritación, abrasión e infección secundaria de la piel (12). La DFS ocurre cuando sustancias hepatotóxicas, ya sea factores químicos (fenotiazinas, tetraciclinas o sulfonamidas), o factores biológicos (plantas tóxicas o agentes infecciosos como el hongo Phytomices chartarum) lesionan el hígado de forma suficiente para impedir a excreción de fitoporfirinas fotoactivas (13).…”

“…The presence of photodynamic substances produced by higher plants that are reactive to light can lead to significant damage to sensitive tissues and can cause irritation, abrasion and secondary skin infections (12). DFS occurs when hepatotoxic substances, whether chemical factors (phenothiazine, tetracycline or sulfonamide) or biological factors (toxic plants or infectious agents like the fungus Phytomices chartarum) cause sufficient damage the liver to prevent excretion of photoactive phytoporphyrins (13).…”

“…Phylloerythrin occurs as a normal byproduct of rumen function, when large amounts of chlorophyll are decomposed by bacteria in the gastrointestinal tract and are absorbed through the rumen into the bloodstream where sanguíneo donde se elimina vía hepática por el mecanismo de conjugación y excreción en la bilis (12). De tal manera que al no ser eliminada por el hígado lesionado, las concentraciones de filoeritrina aumentan en la circulación sistémica y posteriormente se acumulan en la piel y siendo este un agente fotodinámico absorbe ciertas longitudes de onda de luz ultravioleta (UV), tornándose activa y transmitiendo esta energía extra hacia las células circunyacentes; resultando en lesión celular (14).…”

“…Aunque el modo de acción de filoeritrina como agente fotodinámico es desconocido, los estudios han demostrado que se une al aparato de Golgi y a las mitocondrias; indicando que estos orgánulos pueden ser el blanco principal de este compuesto fototótoxico (12).…”

Plants that cause photosensitivity in ruminants in Brazil

“…Few plant compounds that cause primary photosensitivity have been clearly identified, due to the complex nature of this syndrome and the difficulty of confirming the specific mechanism of action of the compounds and their bioactive metabolites in animal tissues (QUINN et al, 2014). The use of gas chromatography and liquid chromatography coupled with mass spectrometry has improved the possibilities of identifying bioactive photosensitizing compounds in plants as well as in serum, urine, and the skin of animals (WESTON; MATHESIUS, 2013).…”