To date, correlation of various structures to specific pharmacological activity is somewhat limited. The structural heterogeneity of ginsenosides, their multiple mechanisms of action, and the diverse experimental methods used to evaluate their activities pose challenges in assembling a collective hierarchy of SAR. In this article we summarized some views regarding sugar moieties with antioxidant activity, sugar molecules with cancer chemoprevention, and stereoselectivity. SAR comparisons of homologs that differ in a single structural attribute are still needed to generate consistent lines of evidence to support the role of specific structural components as requisites in ginsenosides for their activities. A better understanding of the structure-activity relationships is required for helpful modifications to produce novel agents in medical oncology.
A total of 98 ginsenosides have been identified from American ginseng, including naturally occurring compounds and those resulting from steaming or biotransformation. With the development of chemical and analytical techniques and the characterization of novel compounds, the diversity of ginseng saponins is constantly revealed. The ginsenoside family can also be expanded through the characterization of novel compounds from a closely related genus like Oplopanax
(Huang et al., 2010
; Li et al., 2010c
). Chemical modification further produces a series of novel compounds and expands the targets for the pharmacological activities of ginsenosides. Although many ginsenosides have been characterized from American ginseng, their potential effects have not been quantitatively compared under standard conditions.
Multiple pharmacological actions of American ginseng have been observed on the central nervous, cardiovascular, endocrine, and immune systems. Their neuroprotective, cardioprotective, antidiabetic, antioxidant and anticancer properties have been reviewed above. Reports of the effectiveness of ginseng are sometimes contradictory, perhaps because the chemical content of ginseng root or root extract differs, depending on the method of extraction, subsequent handling, or even the season of its collection. The high variability in ginsenoside composition of ginseng among different species and batches may contribute to equally high variability in efficacy (Vuksan and Sievenpiper, 2005
). For example, five batches representative of Ontario-grown American ginseng root produced comparable reductions of postprandial glycemia in healthy individuals; yet 40% of batches may not exert antihyperglycemic activity (Dascalu et al., 2007
; Sievenpiper et al., 2004a
). American ginseng with a similar profile could have similar efficacy. Unmeasured components such as different peptidoglycans (quinquefolans for American ginseng), various ginsenans, peptides, polysaccharides, fatty acids, and other organic compounds may be active.
Obviously, we must know more to answer the questions about the observed effects of ginseng in complementary and alternative medicine. In the future, widespread interest in American ginseng seems certain to ensure continued research with this herb. With the trend of interdisciplinary research and the development of modern combinatorial techniques, the possibility of gaining novel agents from ginseng seems promising.