Usnic acid, uncoupling

Limited studies have documented phytotoxic effects of usnic acid including inhibition of transpiration and oxygen evolving processes in maize and sunflower seedlings.23 Studies of mouse mitochondria have suggested that (+)-usnic acid uncouples oxidative phosphorylation at levels of 1 pM.1 However, a definitive explanation of the phytotoxicity of usnic acid had, to our knowledge, never been reported. Thus, we have attempted to determine the phytotoxic mode of action for (-)-usnic acid.33... 

Dibenzofurans (Phe furan Phe) include various fungal infection-induced plant antifungal compounds (phytoalexins) such as the Rosaceae-derived cotonefuran (from Cotoneaster lactea) and a-pyrofurans (from Pyrus communis). Usnic acid from lichens (notably Usnea species) is anti-mycobacterial, anti-mitotic, an uncoupler and a potent inhibitor of plant protoporphyrinogen synthetase and 4-hydroxphenylpyruvate dioxygenase. 

Usnic acid Usnea articulata (lichen) Uncoupler (< 1)... 

In mouse primary hepatocytes, treatment with 5 fiM usnic acid for 16 hours resulted in 98% cell death that appeared to be associated with cell necrosis rather than apoptosis. Results indicated that usnic acid was associated with inhibition and uncoupling of the electron transport chain in mitochondria. Usnic acid triggered oxidative stress by increasing free radical generation, and the oxidative stress appears to be critical in usnic acid-induced hepa-totoxicity (Han et al. 2004). 

---