Quality control of botanicals: Are we using marker compounds that actually matter?
How do we derive the quality of a botanical? Currently, it is standard practice to use “marker compounds” to evaluate the quality of botanicals. This marker compound, when high, should indicate a plant with good biological activity. For example the marker compound of eucalyptus is eucalyptol. Higher levels of eucalyptol should indicate a better quality extraction, lower levels a poor extraction.
Now what if I told you that this isn’t necessarily the case? What if we are basing the quality of a plant on a marker compound that is not related to the plant’s biological activity? A few weeks ago we published a paper about this very possibility.
We tested plants from three different sources for their levels of marker compounds and their levels of biological activity and then compared the results to see how well marker compound levels predicted biological activity. Here is what we found:
Very few plants had a correlation between marker compound and biological activity. The best of the plants we tested was eucalyptus and its marker compound eucalyptol. In this case, regardless of whether or not eucalyptol is the marker compound, eucalyptol levels were a good predictor of activity.
The majority of plants did not demonstrate any correlation between their marker compound and their biological activity. The most striking example was echinacea, which has three marker compounds. None of these correlated with the biological activity.
What are the implications of these findings?
Marker compounds aren’t necessarily a good method for standardizing botanicals. In the case that a marker compound correlates with activity, it can be useful. It is possible that as the marker compound increases in a plant, the active constituent also increases. However, if a marker compound doesn’t correlate with activity then other methods must be sought to determine the quality of the plant.
Biological assays should be considered as an alternative to marker compounds for the standardization of plants.
Just because a plant has low levels of a marker compound does not mean it has low activity. In fact, some of our samples with the lowest marker compound levels had the highest activity. We could be tossing aside or undervaluing plants just because they have low levels of marker compounds! What a tragic waste! In addition, a single plant may have multiple medicinal uses and we should consider whether a marker compound correlates with the specific activity we are looking for from a plant. For example, when considering Melissa officinalis are we basing our evaluation of quality on a marker corresponding with anxiolytic activity, antiviral activity or neither?
The way we have been evaluating our tinctures has misinformed our assessment of their quality. In the future we need to find more accurate marker compounds and/or rely more on biological assays to assess the biological activity of these plants. This will enable us to prepare more effective medicine and prevent us from wasting valuable plant material.
Read the published paper: http://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0159857