Objective
At the end of this session attendees will know how herbs work pharmacologically as well as by action, providing a strong rationale for their use in veterinary practice where we do not have equivalent drugs.
Western Herbal Remedies - Modes of Action and Efficacy
Medicinal plants form the basis of healthcare for more than 80% of the world's current population, and their animals! For the rest of the planet, plants are critical to pharmaceutical research and drug development, with many plant constituents providing the basis of many of our conventional drugs. It's estimated that 25% of drugs contain plant-derived active ingredients and 50% if fungal products are included. An even larger percent are based on semi-synthetic or wholly synthetic ingredients originally isolated from plants.
Plant medicines are different from drugs, however. A single plant can contain thousands of different bioactive phyto-compounds. And when herbal medicines are combined into formulas, the final medicine can have even more. This complexity is one of the most challenging aspects of herbal medicine research today.
The use of medicinal herbs and bioactive phytochemicals and our scientific knowledge of them comprise the modern field of phytosciences. This relatively new science involves the fields of medicine, biochemistry, physiology, chemistry, toxicology, agriculture and other diverse areas. Much of the contemporary research in herbs is about trying to determine whether traditional herb uses are actually supported, and by what mechanism. While there is ample scientific evidence on many isolated phytochemicals (mainly animal studies) and their physiological effects, we still do not understand the complete activity of most herbs, nor their effects when in combination. There are also other components in medicinal herbs such as minerals, sugars, vitamins, amino acids, lipids and other pharmacologically "lesser important" constituents that can support health and healing.
An important resource is Dr. Duke's Phytochemical and Ethnobotanical Database www.ars-grin.gov/duke which can be accessed to find out what nutritional and other constituents occur within any given herb and which herbs contain a particular constituent.
Several of the most common constituent categories with research that supports their traditional and modern use include:
Flavonoids - found in many plants and in high levels in hawthorn, grapes, elderflower and bilberry. Flavonoids and proanthocyanidins (which are oligomers of flavonoids) are almost universally antioxidant, most are anti-inflammatory and anti-neoplastic, anti-allergic and they reduce capillary permeability and fragility.
Anthraquinones - are red or yellow pigments found in well-known laxative herbs including aloe vera, senna, yellow dock, turkey rhubarb and cascara. Their laxative effects have been supported by pharmacological research, and they also have anti-inflammatory action.
Coumarins - are found in many plants including lavender, horse chestnut, dandelion, solanaceous plants, poppies and sweet clover, Parsley and Angelica. Its fermentation product dicoumarol is a potent anti-clotting agent and forms the basis of warfarin. Coumarin actions include antibacterial, spasmolytic, vasodilative and anti-edema. As medical herbs, they have use as venous & lymphatic vessel tonics.
Alkaloids - are derived from amino acids and tend to be bitter tasting (thus acting on the digestive system). They are precipitated by tannins, so should not be mixed together (tannins can therefore be used to treat acute alkaloid toxicity). Pyrrolizidine alkaloids as a subgroup are important for their potential toxicity, for example in Comfrey. Another group, isoquinoline alkaloids, include berberine, hydrastine and sanguinarine found in herbs such as barberry, Oregon Grape root, goldenseal and bloodroot). These alkaloids have actions that include antimicrobial, antioxidant, antiinflammatory, ionotropic and antineoplastic.
Saponins - generally have a sweet taste and lather in water. They are found in herbs such as wild yam, Panax Ginseng, Astragalus, licorice and ivy. They tend to have steroidal molecules with the ability to modulate effects on steroidal receptors. They have demonstrated antiinflammatory and antiviral effects. They increase mucus production in the lungs and act as expectorants and reduce cholesterol. Saponin glycosides can cause hemolysis in large amounts, but when used normally are extremely safe.
Sterols and sterolins - are fats, also known as phytosterols present in all plants, fruits and vegetables and are chemically similar to cholesterol. Beta-sitosterol is the major phytosterol in higher plants and Beta sitosterolin is its glycoside. Animal studies have demonstrated that phytosterols have antiinflammatory and antipyretic, antineoplastic, glucose-lowering and immune-modulating activity.
Tannins - are generally astringent in nature due to their ability to bind protein and other molecules. They are found in many herbs including oak bark, black tea, blackberry, oak galls, black tea and witch-hazel. They are used as astringents for wounds, have styptic activity; antiinflammatory and anti-ulcer action in the gastrointestinal tract and are valuable in the treatment of diarrhea.
Volatile oils - are found in aromatic herbs and include the common kitchen herbs such as peppermint, lemon balm, fennel, rosemary, cardamom and cinnamon. They are variously used to stimulate digestion and reduce flatulence (carminatives) and have shown spasmolytic activity on tracheal and gastrointestinal smooth muscle; expectorant activity affecting mucociliary clearance, antiinflammatory activity and antiseptic activity.
Knowing something about the active constituents of herbs is important; however, herbalists think of plants as more than the sum of their constituents, and we avoid considering a researched "active constituent" as being the central reason for a plant's efficacy. There is much more to it! In fact, the art and science of herbal medicine involves a complex individualized therapeutic intervention where the actions of individual herbs are employed together in a formula to alter the underlying physiology of the patient. Herbs can be thought to work through their scientifically supported pharmacological actions, their traditional "actions", and in modern phytotherapy, a combination of these two understandings.
An example is devil's claw (Harpagophytum procumbens). This is a South African plant used traditionally for joint pain. It contains iridoid glycosides, mainly harpagoside, sugars, triterpenes, phytosterols, phenolic acids and glycosides and flavonoids. Devil's claw is now recognised in Western herbal medicine as an herbal treatment for arthritic and back pain.1 There are several clinical studies that support its use in osteoarthritis and lower back pain. Daily doses, standardized to 50 mg or 100 mg harpagoside, may be better than placebo for short-term improvements in pain and may reduce use of rescue medication (two trials, 315 participants, low-quality evidence). Another trial demonstrated relative equivalence to 12.5 mg per day of rofecoxib (Vioxx®) but was of very low quality (one trial, 88 participants, very low quality).2
Studies are still unclear as to which actives in devil's claw provide the benefit; however, several studies have demonstrated the efficacy of devil's claw in the relief of arthritic conditions.3 What has been established is that devil's claw Harpagophytum tuberous root contains harpagoside and β-sitosterol. It has antiinflammatory and analgesic properties, probably through suppression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase expression.4 In addition, devil's claw extracts have potential analgesic effects in the case of acute postoperative pain and chronic neuropathic pain.5
Other studies revealed that H. procumbens exhibits antioxidant, anti-diabetic, anti-epileptic, antimicrobial and antimalarial activities amongst others.6 If we were to reduce devil's claw to one main active, we might lose the synergistic benefits of the whole plant.
Interestingly, devil's claw has also been used for the treatment of proximal intertarsal, distal interdistal and tarso-metatarsal joints and of muscular disorders in race horses. Ten horses were treated with 0.5 mg/kg of a 3:1 extract of devil's claw and compared to ten horses treated with phenylbutazone over 60 days. Six horses receiving the devil's claw showed a marked improvement of symptoms, even compared with the control group. The dose used in the horses is considerably lower than the dose used to treat human patients by the way (typically 10 mg/kg); however, it might be that horses are more sensitive to devil's claw.7
On the other hand, knowing a constituent has a particular action can help guide us about the possible uses of an herbal medicine. An example of this is found in the medicinal herb barberry (Berberis aquifolium). The main "active" is an alkaloid berberine, which has documented anti-giardial, antiviral, antibacterial, antiinflammatory, cardiovascular and antifungal properties. There are other herbs containing berberine including goldenseal (Hydrastis canadensis) and Oregon Grape root. These herbs have a traditional use and phytotherapeutic use for treating gastrointestinal infections.
While we understand that plants are very complex from a phytochemical perspective, a common question that comes up is "well there are so many chemicals in a plant, how do we know what's working and how do we know we aren't going to poison our patient?" Because we are used to dealing with veterinary drugs that have side effects and potential for toxicity, it can be a challenge to get our heads around the chemical complexity of herbs. The reality is we don't always know how a plant works, nor do we know for sure the complete phytochemical makeup of a plant. We also have to deal with a degree of variability that we don't see in conventional pharmaceuticals! This is why herbal medicine is largely dependent on tradition and on experience and empirical observation, even in contemporary veterinary herbal medicine.
Many other actions are completely understandable to us; there are antacid, anthelmintic, antiinflammatory and antimicrobial herbs, for example. Others, for example alteratives, anodynes, adaptogens, galactagogues are not. They were words in common use to the orthodox veterinary practitioner and becoming increasingly more common again in the contemporary veterinary herbal literature. One of the most common ways herbs were employed was by their action, and their effect on an organ, tissue or system. The aim of the alterative action, for example, is to achieve a profound effect on the whole metabolic process. The action of such alterative herbs has always been considered to consist of stimulating the eliminative processes in various organs, tissues and even cells. Alteratives are the least recognised and perhaps most useful remedies that we should (re)consider in modern veterinary practice.
Alteratives may work in the following ways:
1. Mobilising toxicity from tissues eventually to the bloodstream for removal by the organs of elimination. Increase the efficiency of removal of exogenous and endogenous toxins.
2. Assisting the function and structure of the organs of elimination in removing such toxins by, for example, improving blood flow.
3. They are by definition slow to work and inconspicuous in their action - at once the main advantage therapeutically and the reason why they are frequently misunderstood and found to be disappointing. They don't work overnight!
These alteratives might not get the scientific stamp of approval, but to reject them is to reject a major tool, unique to herbal medicine in the treatment of chronic inflammatory disease.
By knowing the actions, affinities of a plant for an organ, or tissue, and the particulars of the patient, an herb might be chosen for its breadth of action for a particular patient or as a single herb for a particularly strong action. In modern veterinary herbal practice, with an understanding of the actions of herbs, knowing the scientific basis for their efficacy (where it exists), as well as the pathophysiology of a particular condition, we can strategise the selection and use of particular herbs to treat our animal patients.
References
1. Chrubasik S, Conradt C, Roufogalis BD. Effectiveness of Harpagophytum extracts and clinical efficacy. Phytother Res. 2004;18(2):187–189.
2. Oltean H, Robbins C, van Tulder MW, et al. Herbal medicine for low-back pain. Cochrane Database Syst Rev. 2014;Dec 23:12.
3. Gagnier JJ, Chrubasik S, Manheimer E. Harpagophytum procumbens for osteoarthritis and low back pain: a systematic review. BMC Complement Altern Med. 2004;4(1):13.
4. Jang MH, Lim S, Han SM, et al. Harpagophytum procumbens suppresses lipopolysaccharide-stimulated expressions of cyclooxygenase-2 and inducible nitric oxide synthase in fibroblast cell line L929. J Pharmacol Sci. 2003;93:367–371.
5. Lim D, Kim J, Han D. Analgesic effect of Harpagophytum procumbens on postoperative and neuropathic pain in rats. Molecules. 2014;19(1):1060–1068.
6. Mncwangi N, Chen W, Vermaak I. Devil's claw - a review of the ethnobotany, phytochemistry and biological activity of Harpagophytum procumbens. J Ethnopharmacol. 2012;143(3):755–771.
7. Montavon S. Efficacy of a phytotherapeutic preparation based on Harpagophytum procumbens in case of bone spavin of adult horses [in French]. Prat Vet Equine. 1994;26(1):49–53.