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Background There are increasing interests in natural compounds for cancer chemoprevention. Blocking agents represent an important class of chemopreventive compounds. They prevent carcinogens from undergoing metabolic activation and thereby suppressing their interaction with cellular macromolecular targets. Methods The effect of phenolic compounds isolated from Barleria cristata var. alba as chemopreventive agent was evaluated. The ethyl acetate fraction of B. cristata was subjected to different chromatographic techniques for isolation of its major phenolic compounds. The isolated compounds were evaluated for their potential to induce the cancer chemopreventive enzyme marker NAD(P)H quinonereductase 1 (NQO1) in murine Hepa-1c1c7 cell model. Results The ethyl acetate fraction of B. cristata var. alba yielded five known compounds identified as verbascoside (1), isoverbascoside (2), dimethoxyverbascoside (3), p-hydroxy benzoic acid (4), and apigenin-7-O-glucoside (5). Among the tested compounds, isoverbascoside (2) was shown to potently induce the activity of the enzyme in a dose –dependent manner. As a functional assay for detoxification, compound 2 was the strongest to protect Hepa-1c1c7 against the toxicity of menadione, a quinone substrate for NQO1. Conclusion This effect seemed to be attributed to the compound’s potential to induce both the catalytic activity and protein expression of NQO1 as revealed by enzyme assay and Western blotting, respectively. Electronic supplementary material The online version of this article (10.1186/s12906-018-2214-9) contains supplementary material, which is available to authorized users.

Background Egyptians recognized the healing power of herbs and used them in their medicinal formulations. Nowadays, “Attarin” drug shops and the public use mainly the Unani medicinal system for treatment of their health problems including improvement of memory and old age related diseases. Numerous medicinal plants have been described in old literature of Arabic traditional medicine for treatment of Alzheimer’s disease (AD) (or to strengthen memory). Methods In this study, some of these plants were evaluated against three different preliminary bioassays related to AD to explore the possible way of their bio-interaction. Twenty three selected plants were extracted with methanol and screened in vitro against acetylcholinesterase (AChE) and cycloxygenase-1 (COX-1) enzymes. In addition, anti-oxidant activity using DPPH was determined. Results Of the tested plant extracts; Adhatoda vasica and Peganum harmala showed inhibitory effect on AChE at IC50 294 μg/ml and 68 μg/ml respectively. Moreover, A. vasica interacted reversibly with the enzyme while P. harmala showed irreversible inhibition. Ferula assafoetida (IC50 3.2 μg/ml), Syzygium aromaticum (34.9 μg/ml) and Zingiber officinalis (33.6 μg/ml) showed activity against COX-1 enzyme. Potent radical scavenging activity was demonstrated by three plant extracts Terminalia chebula (EC50 2.2 μg/ml), T. arjuna (3.1 μg/ml) and Emblica officinalis (6.3 μg/ml). Conclusion Interestingly, differential results have been obtained which indicate the variability of the mode of actions for the selected plants. Additionally, the reversible interaction of A. vasica against AChE and the potent activity of F. assafoetida against COX-1 make them effective, new and promising agents for treatment of AD in the future, either as total extracts or their single bioactive constituents.