Abstract
A single herb can contain multiple constituents with diverse bioactivities. We found that the extract of Citrus unshiu peel (CUP), induced abnormal vasoconstriction responses on the freshly isolated rat aortic rings in vitro. CUP stimulated the vasoconstriction alone, and it suppressed the phenylephrine-stimulated vasoconstriction. We studied the reasons behind this abnormal vasoconstriction pattern. Major constituents of CUP were determined and evaluated for their vaso-activities. Notably, synephrine, a contractile agonist, and nobiletin, newly identified to have anti-contractile activity co-existed in CUP. Synephrine and nobiletin competitively blocked or activated the same contractile targets resulting in contradicting and abnormal vasoconstriction responses. Accordingly, the vasoconstriction pattern varies significantly depending on the relative contents of synephrine and nobiletin in CUP. Interestingly, this response pattern could be observed with another plant extract, Acorus gramineus Sol. Collectively, we demonstrated that active ingredients with contradicting bioactivities could co-exist in a single plant extract, interact and produce abnormal response patterns in bioassay, which would give an important insight into the interpretation of unusual activity patterns induced by plant extracts.
Highlights
Plants have many beneficial effects on human health as well as providing food or fiber [1]
To clarify the reason behind this, we identified the flavonoid constituents of Citrus unshiu peel (CUP) through high-performance liquid chromatography (HPLC) analysis and examined their activities, and contributions on the effects of CUP on vasoconstriction, in order to provide important insights to understand the bioactivities of plant extracts
Inhibition (%), which is calculated based on the effect size of PE-induced contraction, suggested that the anti-contractile effect of CUP was substantial, but when the contraction prompted during pre-incubation of CUP (Figure 1C), was excluded, the inhibitory effect was estimated to be negligible, resulting in a false positive
Summary
Plants have many beneficial effects on human health as well as providing food or fiber [1]. In bioassays for plant extracts, abnormal response patterns or inconsistency in potency or efficacy of activity are often observed [8]. This phenomenon is quite common, but in most cases, the reasons remain unknown, since there are multiple bioactive constituents even in a single plant extract, and many more interactions between them occur, that are difficult to elucidate. To clarify the reason behind this, we identified the flavonoid constituents of CUP through high-performance liquid chromatography (HPLC) analysis and examined their activities, and contributions on the effects of CUP on vasoconstriction, in order to provide important insights to understand the bioactivities of plant extracts
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