Plants are incredibly clever organisms in having evolved over millions of years and survived predatory pressures, severe climatic events and ecological stressors, largely through their ability to produce and utilise chemicals. These compounds, known as phytochemicals or secondary metabolites, are the essence of phytopharmacology, the medicinal actions of plants.

We as humans are fortunate in being able to also benefit from this foresight by plants, as many of these secondary metabolites help to protect against and treat disease and ill health in humans, as well as slow down our aging processes.

Many drugs or single chemical entities with pharmacological activities have been developed from plants, and we know that individual phytochemicals such as morphine, atropine and digoxin are very potent medicines.  Also how these and most if not all other ‘active’ phytochemicals initiate their actions through modulating receptors and numerous physiological processes throughout our bodies.

However, for the majority of plants used medicinally, there exists little scientific knowledge about their phytochemistry, and what so-called ‘active constituents’, contribute to their therapeutic properties. There are exceptions to this, particularly those plants which have achieved high levels of usage or attracted significant research interest. For some of these, we now have an understanding from traditional knowledge as well as science, that most and probably all phytomedicines contain more than one or even numerous active constituents present. Also that within each individual plant some form of natural synergy between phytochemicals takes place in relation to bioactivity, pharmacokinetic and/or safety profiles.

Purification of many plant constituents often leads to a reduced intestinal absorption after oral administration. The presence of co-existing constituents including primary (carbohydrates, lipids, amino acids etc) and other secondary metabolites can often promote gastrointestinal absorption of pharmacologically active constituents by improving solubility, modulating the gut microbiome, increasing enterocyte membrane permeability, inhibiting liver metabolism, or promoting the formation of active metabolites⁽¹⁾.  

Drug discovery and bioprospecting is often about trying to separate a plant’s phytochemistry in to pieces, in an attempt to unmask a single ‘active constituent’, and subsequently purify and synthesise it or a chemically related potent derivative. In fact the published and undoubtedly much unpublished research field is littered with instances in which despite scientists doing their utmost to split medicinal plant extracts into different fractions, and from there work hard to further narrow down and finally identify the ‘active constituent’, it remains as elusive as the Holy Grail.

A recent study into the cytotoxicity and antimicrobial activities of Echinacea purpurea for example, which attempted to identify key active compounds, found the highest antimicrobial activity was shown by dichloromethane, ethyl acetate, and acetone extracts of the herb, whereas dichloromethane and n-hexane extracts showed the highest cytotoxic activity⁽²⁾. These extracts were therefore fractionated, and the obtained fractions also assessed for potency as cytotoxics. However, and to the perplexity of the researchers, when the cytotoxicity and bioactivity of these purified fractions was compared to those of the original ‘crude’ extracts, the original extracts were still superior, and showed greater bioactivity. This indicated the existence of a possible synergistic effect of different compounds in the whole extracts⁽²⁾.

Such findings are in fact commonplace in phytomedicine research. Of note is that despite what surely must have been billions of dollars of expenditure by pharmaceutical company researchers to date into identifying the active antidepressant constituent within the highly acclaimed plant St Johns Wort (Hypericum perforatum), it has yet to be revealed. 

Standardised extracts:

There are therefore many potential pitfalls with placing too much emphasis on individual phytochemicals when appraising the therapeutic properties of plant medicines, and the boundary between what is a natural or ‘whole extract’ rather than single chemical entity-based medicine, is often a shifting one. Risks include the usually unknown efficacy consequences of not having other types of secondary metabolites or facilitatory ‘team players’ present as occurs in nature, possible safety concerns, and erring excessively down a slippery slope towards the product becoming more like a drug rather than a herbal medicine.  As with other forms of medicine, there are also instances where commercial interests or poor science has highlighed specific phytochemicals as being essential for good clinical outcomes, with little evidence provided.

Despite these cautionary comments, it is often the relative richness or content of particular phytochemicals in a batch of herbal medicine, that largely determines whether the treatment is effective or not, and it can therefore be an important indicator of quality.

Echinacea

Traditional use of both Echinacea purpurea and Echinacea angustifolia is based upon the root, yet when products based upon these north American native plants (and in particular E. purpurea) began to be commercialized, the principle plant part utilized by some companies, became the whole plant or flowering aerial parts.

Alkylamides (alkamides) on the other hand, are now regarded as the major bioavailable and active components in oral forms of Echinacea(^3,4,5), and highest levels of these are found in the traditionally used root, and not the cheaper flowering tops^(6,7,8). Alkylamide-enriched extracts also show the strongest anti-inflammatory activity^(9,10) and have the ability to both dampen down an over-activated immune system in certain situations, as well as enhance its infection prophylactic ability, in others ^{(11, 12)}.

For many years and still today with some companies, measurements of ‘total phenolics’ in echinacea have been used as an apparent indicator of quality, and by implication therefore, of the immunomodulatory and anti-inflammatory actions for which Echinacea is best known. Given that the assay for total phenolics incorporates a wide range of phytochemicals with a simple or polyphenolic structure, including flavonoids, tannins, cichoric and caftaric acid, and that many of these exhibit poor oral bioavailability and have not been strongly associated with Echinacea’s principle actions, this analytical method appears to have little relevance to the relative quality or potency, of most Echinacea extracts.

The immunomodulatory and anti-inflammatory effects of alkylamides, have been shown to be dose-related in many studies. This fact, combined with traditional use involving doses of up to 30 grams of root in some cases, reinforces the importance of taking adequate amounts of these key tongue-tingling compounds and thus using products that have a guaranteed alkylamide content, wherever possible.

Echinacea extracts have also been shown to modulate endogenous cannabinoid receptors, and alkylamides have again been strongly associated with these effects^(13-14). As with research into the anti-inflammatory properties of Echinacea, recent studies support potential applications for peripheral inflammatory pain such as arthritis and burns, again reflecting the traditional uses of these plants by indigenous north Americans. Other investigations have found Echinacea purpurea root extracts to improve insulin resistance, enhance glucose uptake in adipocytes and activate peroxisome proliferator-activated receptor γ, with alkylamides being contributory^{(15, 16)}.

The complex interactions of bacteria and fungi (endophytes) living symbiotically with Echinacea in its natural state, and their possible modulation of the gut microbiome, is another new area of investigation^{(17, 18)}.

Receptor binding studies involving both crude plant extracts and phytochemically-rich fractions or individual phytochemicals, will continue to reveal more about mechanism(s) of action of our medicinal plants in the future, as well as inform us about ‘new’ (but often simply forgotten), potential applications in clinical practice.

References

1. Zhao, Q., Luan, X., Zheng, M., Tian, X. H., Zhao, J., Zhang, W. D., & Ma, B. L. Synergistic Mechanisms of Constituents in Herbal Extracts during Intestinal Absorption: Focus on Natural Occurring Nanoparticles. Pharmaceutics, 2020;12(2), 128.
2. Coelho, J., Barros, L., Dias, M. I., Finimundy, T. C., Amaral, J. S., Alves, M. J., Calhelha, R. C., Santos, P. F., & Ferreira, I. C. F. R. (2020). Echinacea purpurea (L.) Moench: Chemical Characterization and Bioactivity of Its Extracts and Fractions. Pharmaceuticals (Basel, Switzerland), 13(6), 125.
3. Dietz B, Heilmann J, Bauer R. Absorption of dodeca-2E,4E,8Z,10E/Z-tetraenoic acid isobutylamides after oral application of Echinacea purpurea tincture. Planta Med. 2001;67(9):863-864. 
4. Goel V, Chang C, Slama JV, et al. Alkylamides of Echinacea purpurea stimulate alveolar macrophage function in normal rats. Int Immunopharmacol. 2002;2(2-3):381-38.
5. Jager H, Meinel L, Dietz B, et al. Transport of alkamides from Echinacea species through Caco-2 monolayers. Planta Med. 2002;68(5):469-471.
6. Stevenson LM, Matthias A, Banbury L, et al. Modulation of macrophage immune responses by Echinacea. Molecules. 2005;10(10):1279-1285. 
7. Bauer R, Remiger P. TLC and HPLC Analysis of Alkamides in Echinacea Drugs1,2. Planta Med. 1989;55(4):367-371.Qu L, Chen Y, Wang X, Scalzo R, Davis JM. Patterns of Variation in Alkamides and Cichoric Acid in Roots and Aboveground Parts of Echinacea purpurea (L.) Moench. HortScience. 2005;40(5):1239-1242.
8. Woelkart K, Koidl C, Grisold A, et al. Bioavailability and pharmacokinetics of alkamides from the roots of Echinacea angustifolia in humans. J Clin Pharmacol. 2005;45(6):683-689.
9. Gulledge TV, Collette NM, Mackey E, et al. Mast cell degranulation and calcium influx are inhibited by an Echinacea purpurea extract and the alkylamide dodeca-2E,4E-dienoic acid isobutylamide. J Ethnopharmacol. 2018;212:166-174. 
10. LaLone CA, Rizshsky L, Hammer KD, et al. Endogenous levels of Echinacea alkylamides and ketones are important contributors to the inhibition of prostaglandin E2 and nitric oxide production in cultured macrophages. J Agric Food Chem. 2009;57(19):8820-8830.
11. Vieira SF, Gonçalves VMF, Llaguno CP, et al. On the Bioactivity of Echinacea purpurea Extracts to Modulate the Production of Inflammatory Mediators. Int J Mol Sci. 2022;23(21):13616.
12. Rasmussen PL, Effects of Echinacea on virus induced Cytokines. Phytonews 24, 2006,Feb. Published by Phytomed Medicinal Herbs Ltd, Auckland, New Zealand. ISSN 1175-0251.
13. Liu R, Caram-Salas NL, Li W, Wang L, Arnason JT, Harris CS. Interactions of Echinacea spp. Root Extracts and Alkylamides With the Endocannabinoid System and Peripheral Inflammatory Pain. Front Pharmacol. 2021;12:651292.
14. Gholami M, Amri J, Pazhoohan S, Sadegh M. Anticonvulsive and anti-epileptogenesis effects of Echinacea purpurea root extract, an involvement of CB2 receptor. J Complement Integr Med. 2021;19(4):879-886.
15. Kotowska, D., El-Houri, R. B., Borkowski, K., Petersen, R. K., Fretté, X. C., Wolber, G., Grevsen, K., Christensen, K. B., Christensen, L. P., & Kristiansen, K. (2014). Isomeric C12-alkamides from the roots of Echinacea purpurea improve basal and insulin-dependent glucose uptake in 3T3-L1 adipocytes. Planta medica, 80(18), 1712–1720.
16. Choi, K. M., Kim, W., Hong, J. T., & Yoo, H. S. (2017). Dodeca-2(E),4(E)-dienoic acid isobutylamide enhances glucose uptake in 3T3-L1 cells via activation of Akt signaling. Molecular and cellular biochemistry, 426(1-2), 9–15. 
17. Todd DA, Gulledge TV, Britton ER, et al. Ethanolic Echinacea purpurea Extracts Contain a Mixture of Cytokine-Suppressive and Cytokine-Inducing Compounds, Including Some That Originate from Endophytic Bacteria. PLoS One. 2015;10(5):e0124276. 
18. Maggini, V., Bettini, P. P., Fani, R., Firenzuoli, F., & Bogani, P. (2023). Echinacea purpurea microbiota: bacterial-fungal interactions and the interplay with host and non-host plant species in vitro dual culture. Plant biology (Stuttgart, Germany), 25(2), 246–256.Gerstmeier J, Seegers J, Witt F, et al. Ginkgolic Acid is a Multi-Target Inhibitor of Key Enzymes in Pro-Inflammatory Lipid Mediator Biosynthesis. Front Pharmacol. 2019;10:797.