Commentary: Effects of Equisetum arvense Ointment on Dermal Wound Healing in Rats

Dr. Cockbill is the Section Editor for the Veterinary Wounds section   This original research was designed to evaluate the effect of two different concentrations of Equisetum arvense L. (horsetail) on the rate of dermal wound healing of scarified wounds on the backs of 56 albino Wistar rats. Equisetum derives from the Latin roots equus (“horse”) and seta (“bristle”). Horsetail has been described as a topical aid to wound healing in many historical phytotherapeutical books,¹ but these uses have largely been based on anecdote and clinical tradition rather than scientific evidence.   It is known that ashes from horsetail stems were utilised to treat burns long before Westerners settled in America; the natives also used horsetail as a poultice to treat open wounds. The Roman physician, Galen, claimed that horsetail healed severed tendons and ligaments and helped stop nosebleeds. Over the centuries, the herb has gained a significant reputation as an aid to wound healing.¹   Horsetails have an unusual chemistry compared to most other plants.² They are rich in silica and it is these silicates and silicic acid that promote the migration of leucocytes and neutrophils to the wound to cleanse it thereby initiating the inflammatory phase of the healing process. Silicic acid and silicates from the herb provide nearly 2%–3% elemental silicon. As these silicon-containing compounds are readily absorbed, they may be used to facilitate calcium absorption.   Equisetum arvense L. has also been shown to contain 15 bioflavonoids, as well as minerals such as manganese, potassium, and calcium and several alkaloids, including nicotine. Bioflavonoids are known to increase vitamin C absorption. The antioxidant and free radical scavenging properties of vitamin C help with calcium absorption, collagen formation, and increased wound healing rates. Therefore, the horsetail plant may have been used for its effects on bone growth and collagen formation, as well as repairing damaged connective tissue, thereby improving its strength and elasticity.³ Horsetail is also astringent and makes an excellent clotting agent, staunching wounds, stopping nosebleeds, and reducing the coughing up of blood.³   The aforementioned study affirms that there are many active components of horsetail that would influence the healing rates of the experimental wounds created. The authors mention the authentication of the plant material, but the leaves were later described as being “powdered” before use with no mention of their eventual particle size and uniformity. The experimental method used to ensure even distribution of the leaf particles within the ointment base mixture should have been described and some assessment of the possible solubility and consequent distribution of the actives from the powdered leaves within this excipient should have been undertaken. Obviously, concentration of the actives, not just the percentages of leaf powder, applied will play a significant role in the healing of the wounds. However, the active components of the leaves were not extracted or analysed so there is no indication of which, and in what concentrations and/or combinations, were the major contributors to the increased wound healing rates observed.   It would have been interesting to know the reasoning behind selection of the 1:1 mixture of Vaseline™ and lanolin used as the base for the ointment formulation. Vaseline Petroleum Jelly is a proprietary preparation comprised of mineral oils, paraffin, and microcrystalline waxes, and its application to a wound creates a moist wound-healing environment at the surface of the skin by sealing the wound from the external environment. This effect will also affect wound-healing rates.   Lanolin is a yellow, waxy substance secreted by the sebaceous glands of animals, such as sheep and goats. Most lanolin used by humans comes from domestic sheep and is known to have the potential to produce an allergic skin reaction among a small percentage of people applying formulations that contain it to conditions such as eczema, so it cannot be considered totally inert. Both of these ointments are soft and easily applied and therefore the reasoning behind their selection and mixing proportions should have been expressed.   This research and the primitive experiments described therein serve to corroborate, in some measure, the anecdotal evidence derived over the centuries of the contribution made by the application of horsetail to the increased healing rate of wounds. It is critical to understand that significant conclusions cannot be drawn solely from this work regarding the herb’s mode of action. However, the work does provide useful, groundbreaking information but this should only be regarded as a baseline from which more sophisticated, scientific evaluations might be developed.

References

1. Wichtl M, ed. Herbal Drugs and Phytopharmaceuticals. 3rd English ed. Stuttgart, Germany: MedPharm Scientific Publishers; 2004;195–199. 2. Bown D. Royal Horticultural Society Encyclopedia of Herbs and Their Uses. London: Dorling Kindersley Publishers; 1995. 3. Chevallier A. Encyclopedia of Medicinal Plants. New York, NY: DK Publishing; 1996:96.
Address correspondence to: Dr. Sarah Cockbill Welsh School of Pharmacy Cardiff University, Redwood Building King Edward VII Avenue Cardiff, CF10 3XF United Kingdom Phone: 44 029 2087 6241 E-mail: cockbill@cardiff.ac.uk