Bioassay Screening and Mechanism Study of Herbal Medicines

1.2.2 Bioassay Screening and Mechanism Study of Herbal Medicines

Scientists have spent over a hundred years trying to screen new drug candidates from herbal medicines. Recently, due to the rapid growth of products of herbal medicine or alternative medicine all over the world, their efficacy and safety have become more and more important. More attention has been drawn to the preventative and therapeutic mechanism study of herbal medicines. For both reasons, bioassay study on herbs is indispensible. Thanks to the advancement of biological technologies, more and more bioassays are available for mechanism study. The mechanism of many effective herbal medicines has been elucidated, such as the well-known ginkgo, Echinacea, red clover, black cohosh, ginseng, and many Chinese and other traditional herbs. Bioassays in vitro are usually followed by in vivo animal tests to further confirm the functional mechanism and understand the absorption, metabolism, and toxicity in living bodies.

Bioassay is commonly performed using enzymes, receptors, genes, cells, and sometimes tissues. In comparison to screening for new drug candidates of single compounds, screening herbal extracts or fractions is relatively difficult due to the solubility or complex composition in herbal samples. Compounds in an extract might interfere with each other, or more specifically, the activity of one compound might be masked by another in the mixture due to the adverse effect or toxicity of the latter. So, the bioassay result of an herbal extract should be carefully evaluated, particularly when a high-throughput method is applied, not only due to the mentioned interference, but also because of the dramatically varied concentrations of bioactive components in different samples prepared under the same conditions.

Mechanism study for herbal medicine does not necessarily use high-technology equipment. The most important thing is to select the right targets. Different enzymes, receptors, or genes should be tested for mechanism of an herbal extract. Assays at different levels should be applied to ensure the positive or negative research results. Evaluation of estrogenic activity of red clover and black cohosh extracts using different bioassays can be used as an example.2

In many cases, the corresponding bioactive components for the functional mechanism of herbal medicines are common or universally distributed compounds. Such results may disappoint researchers looking for new drug development, but they are very helpful to scientists who are dedicated to explaining the functions of herbs or willing to understand more about physiological functions of these common com- pounds in the human body. Examples include linolic acid, a cyclooxygenase (COX) inhibitor in Angelica pubescens3 and an estrogenic agonist in Vitex agnus-castus L. (chaste berry),4 and Nω-methylserotonin, a serotonin agonist in black cohosh.5

Soure: Traditional Herbal Medicine Research Methods, Edited by Willow J.H. Liu Copyright © 2011 John Wiley & Sons, Inc.

REFERENCES

2. Liu, J.H., et al. (2001) Evaluation of estrogenic activities of plant extracts on the potential treatment of menopausal symptoms. Journal of Agricultural and Food Chemistry 49(5):2472–2479.

3.  Liu, J.H., et al. (1998) Inhibitory effect of Angelica pubescens f. biserrata on 5-lipooxygenase and cyclooxygenase. Planta Medica 64(6):525–529.

4.  Liu, J.H., et al. (2004) Isolation of linoleic acid as an estrogenic compound from the fruits of Vitex agnus-castus L. (chaste berry). Phytochemistry 11(1):18–23.

5. Powell, S.L., et al. (2008) In vitro serotonergic activity of black cohosh and identification of Nω- methylserotonin as a potential active constituent. Journal of Agricultural and Food Chemistry 56(24):11718–11726.