Redox- and bio-activity of apocynin (acetovanillone) in tobacco, a plant phenolic that alleviates symptoms of autoimmune diseases in animals

Abstract

Apocynin (APO) was shown to be the major constituent of early herbal medicines used to reduce painful suffering from many ailments. Because of its proven utility in rat models, it is now an active candidate for treating humans for several major autoimmune diseases such as Alzheimer's, arthritis, and cardiovascular diseases. In plant research, APO is referred to as acetovanillone, a secondary metabolite that is induced in the leaf apoplast during bacterial invasion. Since its role in plants is unknown, we examined whether any of the attributes found in medical studies could found in plants. In medical studies, APO is considered to be an NADPH oxidase (NOX) inhibitor, however when tested in tobacco suspension cells, APO failed to inhibit NOX activity. In addition, when APO was used to pretreat plants against virulent or avirulent pathovars of Pseudomonas syringae, there was no reduction of symptoms. When pathovars were incubated with 100 μM APO for 90 min, there was only a slight decrease in the bacterial population, suggesting that it was not toxic. In animals, a key step for the inhibition of NOX by APO appears to be its oxidation by myeloperoxidase, yielding dimers and trimers. In vitro studies using pH 6, which is more comparable the plant environment, APO oxidation by horseradish peroxidase yielded similar products. We monitored the redox potential during some of these experiments, trying to begin looking at this parameter, which like pH, can have a more global effect on closed systems such as the apoplast. Phenolics such as APO that are induced upon bacterial ingress, seem likely to play a role in the plant bacterial interaction, but it will require additional and creative research to find and fully understand this role.