Symphytum officinale otherwise
known as comfrey, knitbone, boneset,
or blackwort, is a member of the Borage family (Boraginaceae). It is a large rooted perennial with large, rough, broadly
oval leaves
and puple-blue or pink bell-like flowers in furled clusters (Foster
& Duke,
2000). Comfrey is native to
Europe and western Asia and has been introduced and is now naturalized
in the
eastern U.S. and Canada. It can usually be found growing along stream
banks and
in moist meadows (Foster & Johnson, 2008). While it prefers damp
soils, it
can be grown in good garden soil (Foster & Johnson, 2008).
Comfrey
has
been used since at least 400 B.C. Both Greek and Roman
cultures utilized the plant in several different remedies. The Greek
physician
Dioscorides recommended comfrey for healing wounds and mending broken
bones.
Both civilizations made poultices from the leaves and roots to treat
external
wounds, while making comfrey tea for stomach ailments, internal
bleeding,
diarrhea, and other maladies. The plant was also used in the Middle
Ages as a
poultice and tea. During that time, the poultice was applied to
fractures,
bruises, and wounds while the tea was drunk to remedy internal injuries
(Foster
& Johnson, 2008). Comfrey remained a popular herbal remedy for
those
disorders as well as other various ailments including diarrhea,
dysentery,
bronchitis, tuberculosis, ulcers, and hemorrhoids for centuries (Foster
&
Johnson, 2008). Comfrey was also developed into ointments for
application to
bruises, sprains, strains, torn ligaments, burns, arthritis, and almost
any
kind of inflamed swelling. However, research began to surface in the
1970s and
1980s showing that all parts of the plant, and especially the roots,
contain
toxic pyrrolizidine (Foster & Duke, 2000). These findings have
prompted
countries such as the US, the United Kingdom, Australia, Canada, and
Germany to
ban all ingestible comfrey products. Since 2001, only preparations
designed for
topical use and some skin conditions have been approved for sale in the
U.S.
(Foster & Duke, 2000).
The
roots of comfrey contain many chemicals including allantoin,
mucopolysaccharides, flavones, steroidal saponins, pyrrolizidine
alkaloids, and
phenolic acids (mainly rosmarinic acid) (Roman, et. al 2008). Three of
the
primary chemicals, allantoin, pyrrolizidine alkaloids, and rosmarinic
acid,
have therapeutic characteristics. Allantoin
can
cause
cells to multiply, enhancing regeneration of damaged tissues.
Rosmarinic acid is known as an anti-inflammatory. Pyrrolizidine
alkaloids help
stop bleeding, but have been shown to damage the liver and cause tumors
in
laboratory animals (Foster & Johnson, 2008). These alkaloids occur
in a
number of different families in areas all over the world. Their
function is
unknown, but their bitter taste most likely plays a role in deterring
predators
(McLean, 1970).
Research
performed
by Spin-Neto, et. al. (2008) involved implanting
titanium rods in the tibiae of mature rats, and the subsequent
monitoring of
bone growth around them. Upon internal homeopathic treatment of S. officinale preparations, bone
formation was enhanced significantly, especially during the early
stages of
osseointegration. This suggests that comfrey has tissue mending
potential.
Comfrey
has
also been shown to promote wound healing and relieve
inflammation. Barna, et al (2007) found that a topically applied
preparation of
10% comfrey extract produced a faster initial reduction of wound sizes
in
patients after two to three days of application. Significant
anti-inflammatory
activity has also been demonstrated in
vivo (Bradley, 1992).
Comfrey’s
relationship
with
cancer is the subject of much debate. Gomes, et. al (2010) gave 10% comfrey ethanolic extract orally to rats that had induced cancer by the resistant
hepatocyte model (RHM).
Upon
macroscopic/microscopic
quantitative analysis, the authors found
reductions in
the number of pre-neoplastic macroscopic lesions, proliferating cell
nuclear
antigen positive cells, and acidophilic pre-neoplastic nodules, as well
as a
reduction in the percentage of cells in mitosis. Furthermore, the
percentage of
cells presenting megalocytosis and vacuolar degeneration was increased.
This
indicates a reduction of cell proliferation, suggesting possible
anti-cancer
potential for S. officinale. Another
study by Roman, et al (2008) determined that total plant extracts
exhibit
cytostatic and mitoinhibitory properties of significant amplitude on
HeLa
neoplasic cells. The study attributes this inhibitory effect to
phenolic acids,
known to have anti-cancer and anti-oxidant properties, found in comfrey
root
extracts. In contrast, Stickel and Seitz (2000) found that
endogenous
pyrrolizidine
alkaloids caused a
substantial health hazard from hepatic
toxicity in humans and carcinogenic potential in rodents. Those
findings were supported by Mei, et al (2005), who
found comfrey exhibited mutagenic properties in rat liver that were
attributed to
pyrrolizidine alkaloids. In addition, comfrey
extracts were implicated as causing the destruction of small hepatic
veins, known as veno-occlusive disease,
leading to cirrhosis and liver failure (Stickel & Seitz, 2000).
The
pyrrolizidine alkaloids (PA’s) found in comfrey are one of the
leading plant toxins for animals and humans. The
Symphytum
species produce a variety of PA’s, including echimidine, intermedine,
lasiocarpine, lycopsamine, myoscorpine, symlandine, symphytine, and
symviridine
(Mei, et. al 2010). Herbal remedies containing these
alkaloids are reported to cause both mutations and cancer. Upon
ingestion, the
pyrrolizidine alkaloids are metabolized into highly reactive
electrophiles in
the liver, which react with cellular macromolecules forming adducts.
The
persistent nature of PA’s in animal tissue, along with modified DNA
adducts
which result, imply carcinogenic potential (Lewis, 2003). Mei, et. al
(2010) suggests
that the active metabolites interact with DNA in liver endothelial
cells and
hepatocytes, ultimately leading to damaged DNA (adducts), mutation
induction,
and carcinogenesis.
From Dioscorides’ De Materia Medica of ancient times to the naturopathic practices of today, S. officinale holds some therapeutic value, especially in preventing cancer cell proliferation, healing wounds, and reducing inflammation. However, the presence of pyrrolizidine alkaloids has brought many serious concerns to light, most importantly, their potential as a hepatotoxin, mutagen, and possible carcinogen. As a result, the use of comfrey products have either been banned or restricted to topical use in many areas of the world. Even though comfrey has harmful effects, proper knowledge and appropriate government regulation of this plant are essential for its continued medicinal use.
Barna, M., A. Kucera, M. Hladicova, & M. Kucera. 2007. Wound healing effects of a Symphytum herb extract cream (Symphytum X Uplandicum NYMAN: ): Results of a randomized, controlled double-blind study. Wien Med Wochenschr 157.21 (2007): 569-74.
Bradley, P.R. 1992. British Herbal Compendium. Vol. 1
Foster, S. & J. A. Duke. 2000. A Field Guide to Medicinal Plants and Herbs of Eastern and Central North America. Boston: Houghton Mifflin.
Foster, S. & R. L. Johnson. 2008. Desk Reference to Nature's Medicine. Washington, D.C.: National Geographic.
Gomes, M.F., Massoco C. de Oliveira, J.G. Xavier, & L.V. Bonamin. 2010. Comfrey (Symphytum officinale. l.) and experimental hepatic carcinogenesis: A short-term carcinogenesis model study. Evidence Based Complementary and Alternative Medicine. 7: 197-202.
Lewis, W.H. & M. Elvin-Lewis. 2003. Medical Botany. 2nd ed. Hoboken, NJ: John Wiley and Sons.
McLean, E.K. 1970. The toxic actions of pyrrolizidine (Senecio) alkaloids. Pharmacological Reviews 22: 429-483.
Mei, N., L. Guo, P.P. Fu, J.C. Fuscoe, & Y. Luan. 2010. Metabolism, genotoxicity, and carcinogenicity of comfrey. Journal of Toxicology and Environmental Health. 13: 509-26.
Mei, N., L. Guo, P.P. Fu, R.H. Heflich, & T. Chen. 2005. Mutagenicity of comfrey (Symphytum officinale) in rat liver. British Journal of Cancer. 92(5):873-5.
Roman, G.P., E. Neagu, V. Moroeanu, & G.L. Radu. 2008. Concentration of Symphytum officinale extracts with cytostatic activity by tangential flow ultrafiltration. Roumanian Biotechnological Letters 13: 4008-13.
Spin-Neto, R., M.M. Belluci, C.E. Sakakura, G. Scaf, M.T. Pepato, & E. Marcantonio. 2010. Homeopathic Symphytum officinale increases removal torque and radiographic bone density around titanium implants in rats. Homeopathy. 99: 249-54.
Stickel, F., & H.K. Seitz. 2000. The efficacy and safety of comfrey. Public Health Nutrition 3: 501-508.
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