Traditional Uses of Medicinal Plants from the Canadian Boreal Forest for the Management of Chronic Pain Syndromes
Article first published online: 16 MAR 2015
DOI: 10.1111/papr.12284
© 2015 World Institute of Pain
Issue
Pain Practice
- chronic pain;
- medicinal plants;
- aboriginal people;
- antinociceptive
Abstract
Objective
Chronic
pain is more prevalent in indigenous populations who often prefer
traditional remedies over allopathic drugs. Our objective was to
investigate the traditional uses of medicinal plants from the Canadian
boreal forest for the management of chronic pain syndromes.
Methods
We
reviewed the most extensive database on medicinal plants used by
aboriginal people of the Canadian boreal forest to investigate the
plants used in the management of 3 of the most common chronic pain
syndromes: arthritis/rheumatism; back pain; and headache/migraine. We
also reviewed the pharmacology and phytochemistry literature to
investigate concordance with indigenous knowledge.
Results
A
total of 114 medicinal plant species were reported, of which 27 (23.5%)
were used to treat more than 1 chronic pain syndrome. Pharmacological
or phytochemical evidence to explain plant function as chronic pain
remedy was available in the literature for only 38 species (33%), with
several species reported to have anti-inflammatory and analgesic
properties effective in treating chronic pain syndromes.
Conclusions
Our
study showed the potential of boreal plants as alternative and
complementary medicines for the treatment of chronic pain syndromes that
could be enhanced by further research on efficacy and safety issues.
Introduction
Chronic
pain can be defined as pain without apparent biological value that has
persisted beyond the normal tissue healing time, which is assumed to be
3 months.[1] Globally, chronic pain has become a major health problem,[2] affecting between 10% and 55.2% of the adult population.[3]
Chronic pain has considerable impact on quality of life as it can
notably alter productivity, social relationships, and the ability to
maintain an independent lifestyle.[4] Important socioeconomic costs result from the physical, psychological, and social impacts of chronic pain.[5-8]
Chronic
noncancer pain syndromes include conditions such as back pain, neck
pain, arthritis, osteoarthritis, migraines, headache, fibromyalgia,
irritable bowel syndrome, neuralgia, and chronic posttraumatic or
postoperative pain.[1] While pain affects all populations, it is not distributed equally across the globe.[2]
Cross-national research on prevalence of chronic pain found slightly
higher rates in developing countries (41%) than developed countries
(37%).[9] There is also evidence that chronic pain is more prevalent in indigenous populations.[10, 11]
This is particularly the case in Canada, where several studies have
reported chronic pain to affect a higher proportion of Aboriginal people
than non-Aboriginal people.[12-17]
Chronic pain management is often suboptimal and remains a challenge.[2, 18-20]
According to the National Aboriginal Health Organization, “relying
solely on bio-medical concepts of disease and of health […] is not
necessarily an effective system […] in Aboriginal populations.”[21] The healing properties of various plants are well-recognized by indigenous peoples around the world.[22-25] Traditional uses of medicinal plants for pain management have a long history and increasingly attract physicians’ attention.[26] Traditional health practices are highly prevalent in North American aboriginal populations.[27-30]
Hence, the potential of alternative and complementary medicine for
chronic pain treatment should be given more attention by researchers.
Numerous medicinal plants are used by Aboriginal people in Canada,[31] some of which specifically for chronic pain. Increasing pressure for better integration of traditional and western medicines[32, 33]
warrants systematic documentation of the therapeutic potential of
medicinal plants. Medicinal plants are a direct source of chemicals for
about 25% of currently used crude drugs, with another 25% as synthetic
drugs derived from chemically altered natural products.[34, 35]
We
reviewed the traditional uses of medicinal plants by the Aboriginal
people of the Canadian boreal forest for the management of chronic pain
syndromes. We also reviewed the pharmacology and phytochemistry
literature to investigate concordance with indigenous knowledge.
Methodology
We identified traditional uses of medicinal plants for the treatment of chronic pain syndromes by reviewing the database of Medicinal plants used by Aboriginal people of the Canadian boreal forest (hereafter called the “mackiki database” after the Algonquin word for medicine; http://mackiki.uqat.ca). The mackiki database is an electronic searchable version of the list of medicinal plants first published in Uprety et al.[31]
and stemming from a review of 49 publications issued between 1881 and
2010 in scientific journals, books, theses, and reports. It is currently
the most comprehensive database on medicinal plants used by indigenous
people of the Canadian boreal forest. Many of the plants listed, or some
of their close relatives, are also found elsewhere in the boreal biome
(e.g, U.S.A., Fennoscandinavia, Russia). The boreal forest is the most
extensive forest biome in the world, encompassing about one-third of the
Earth's forest cover.[36]
The
546 species of the mackiki database were reviewed for reported use in
the management of: (1) arthritis and rheumatism (described as aching
bones/joints,
aching/affected/arthritic/inflamed/painful/stiff/sore/rheumatic joints,
arthritic pain, arthritis, joint/knee/rheumatic pain, numb
articulations, problems in joints, rheumatic complaints, or rheumatism);
(2) back pain (described as back/lumbar pain, backache, back paralysis,
pain in the back/lumbar region, sciatica, sore/sprained back); and (3)
headache/migraine (described as migraine, headache, head pain, sore
head). These 3 syndromes were selected as they are among the most common
chronic pain conditions reported in Canada.[17, 37, 38]
Symptoms of body pain, muscular pain, or sprains without specification
of body part were excluded. The classification of medicinal plants used
for the management of the 3 selected pain syndromes was achieved by 2
independent reviewers with expertise in the field of chronic pain, who
reached a consensus.
A list of medicinal
plants was prepared, providing Latin, English, and French names, mode(s)
of use, and reference(s) for each species. The taxonomic precision of
plant names reported in this paper depends on that from the original
sources. However, we verified currently accepted names and distribution
status (native vs. introduced) of each species in online nomenclature
sources (http://www.theplantlist.org, http://www.tropicos.org, http://plants.usda.gov, http://www.eFloras.org, and http://data.canadensys.net/vascan/search/).
Electronic
databases (ISI Web of Science, MEDLINE, Science Direct, Scopus, and
Google Scholar) were searched for each medicinal plant species to find
if phytochemical or pharmacological studies identified active principles
potentially responsible for the reported medicinal properties. Specific
search terms such as “pain”, “rheumatism”, “arthritis”, “joint pain”,
“back pain”, “backache”, “migraine”, “headache”, “chemical”,
“antinociceptive”, “analgesic”, “anti-inflammatory”, and “antioxidant”
were used along with species names.
Principal
component analysis (PCA) was used to determine if pain disorders
(dependent variable) were treated with particular combinations of plant
life forms, plant parts, or preparation modes (independent variables).[39]
Results
Taxonomic Diversity and Growth Habit
A
total of 114 species belonging to 45 taxonomic families were reported
to treat 1 or more of the 3 studied chronic pain syndromes (Table S1).
About twice as many plant species were used to treat
arthritis/rheumatism (59 species) and headache/migraine (63 species),
compared to back pain (26 species) (Table 1).
Most of the reported medicinal plant species were Angiosperms (92
species). Gymnosperms ranked second (15 species), followed by Fungi (4
species) and Pteridophytes (3 species). Well-represented families were
Asteraceae (14), followed by Ericaceae (8), Pinaceae (8), Rosaceae (7),
Cupressaceae (6), and Ranunculaceae (5). The highest prevailing life
form was herbs, followed by trees and shrubs, and, to a much lesser
extent, climbers and fungi (Figure 1). Nine species were introduced to the Aboriginal pain pharmacopoeia (marked with asterisks in Table S1).
| Pain categories | Plants |
|---|---|
Arthritis/rheumatism
59
| Abies balsamea, Achillea millefolium, Acorus americanus, Acorus calamus, Alnus viridis ssp. crispa, Anemone canadensis, Arctium minus, Arctostaphylos alpina, Artemisia frigida, Brassica sp., Carya cordiformis, Carya laciniosa, Carya ovata, Castilleja coccinea, Caulophyllum thalictroides, Chamerion angustifolium ssp. angustifolium, Cicuta douglasii, Cirsium arvense, Comptonia peregrina, Cornus canadensis, Eupatorium perfoliatum, Fomes fomentarius, Gaultheria procumbens, Heracleum maximum, Inonotus obliquus, Juniperus virginiana, Kalmia angustifolia, Larix laricina, Lycopodium obscurum, Medicago sativa, Mentha arvensis, Monarda fistulosa, Morella pensylvanica, Nuphar lutea, Ostrya virginiana, Phryma leptostachya, Phytolacca americana var. americana, Picea glauca, Plantago major, Platanthera dilatata var. leucostachys, Populus tremuloides, Prunus pensylvanica, Pulsatilla patens ssp. multifida, Pyrola grandiflora, Rhododendron groenlandicum, Rhus typhina, Rumex aquaticus, Rumex orbiculatus, Rumex salicifolius var. mexicanus, Salix sp., Sanicula odorata, Shepherdia canadensis, Sorbus americana, Taxus canadensis, Thuja occidentalis, Trillium grandiflorum, Tsuga canadensis, Vaccinium myrtilloides, Vitis vulpina |
Back pain
26
| Abies balsamea, Abies lasiocarpa, Achillea millefolium, Acorus calamus, Arctostaphylos uva-ursi, Artemisia norvegica ssp. saxatilis, Betula papyrifera, Chamaecyparis thyoides, Chimaphila umbellata, Cirsium sp., Crataegus sp., Hydrophyllum virginianum, Juniperus communis, Juniperus horizontalis, Kalmia angustifolia, Maianthemum racemosum ssp. racemosum, Matteuccia struthiopteris, Nuphar lutea, Picea glauca, Picea mariana, Pinus strobus, Rhododendron groenlandicum, Ribes glandulosum, Rubus occidentalis, Salix sp., Sorbus decora |
Headache/migraine
63
| Achillea millefolium, Achillea millefolium ssp. lanulosa var. lanulosa, Acorus americanus, Acorus calamus, Amelanchier alnifolia, Anemone multifida, Anemone sp., Apocynum androsaemifolium, Aralia racemosa, Arctium minus, Arctostaphylos uva-ursi, Artemisia frigida, Castilleja miniata, Chamaecyparis thyoides, Chamaedaphne calyculata, Comptonia peregrina, Cornus sericea, Cynoglossum virginianum var. boreale, Erigeron strigosus, Eurybia macrophylla, Fomes pinicola, Gaultheria procumbens, Helenium autumnale, Heracleum maximum, Hymenoxys richardsonii, Ilex mucronata, Impatiens capensis, Inula helenium, Juniperus virginiana, Kalmia angustifolia, Lappula squarrosa, Larix laricina, Maianthemum canadense, Maianthemum racemosum ssp. racemosum, Mentha aquatica, Monarda fistulosa, Nuphar lutea, Pedicularis lanata, Picea glauca, Picea mariana, Pinus resinosa, Pinus strobus, Polygonatum biflorum var. commutatum, Pteris aquiline, Pulsatilla patens ssp. multifida, Ranunculus acris, Rhododendron groenlandicum, Rhododendron tomentosum, Salix lucida, Salix sp., Sarracenia purpurea, Sium suave, Sorbus americana, Sorbus scopulina, Symphyotrichum puniceum, Symplocarpus foetidus, Taxus canadensis, Thuja occidentalis, Thuja plicata, Trametes suaveolens, Vaccinium myrtilloides, Valeriana dioica var. sylvatica, Viburnum lantanoides |
Figure 1. Frequency of medicinal plant species in different growth habits.
Parts Used and Remedy Formulation
Almost all plant parts were used to prepare different remedies (Figure 2).
Apart from whole plants, the most frequently used plant parts were
underground parts and leaves/needles. A total of 164 herbal formulations
were reported (Figures 2 and 3).
Although the mode of remedy formulation was not always specified, a
pattern emerged from the available information, with ingested or inhaled
preparations more frequent than applied ones (Figure 3).
Figure 2. Number of remedies prepared using different plant parts.
Figure 3. Type and number of remedy formulations.
The first 2 PCA axes, respectively, explained 66.74% and 33.26% of the variance in treated chronic pain syndromes (Figure 4).
The first axis separates back pain from headache/migraine, whereas the
second axis separates arthritis/rheumatism from the former 2 syndromes.
The PCA scatter plot showed different combinations of plant life forms,
parts used, and preparation methods used for each syndrome.
Arthritis/rheumatism was mostly treated with herbs and climbers, as
whole plants or aboveground parts. Plants were mostly applied (poultice,
oil), or ingested (juice, tea/infusion, chewed raw). Back pain was
mostly treated with trees (wood and underground parts) and shrubs
(fruits and leaves). Plants were applied or ingested (decoction).
Headache/migraine was mostly treated with shrubs (flowers, fruits,
leaves). Plants were applied or inhaled.
Figure 4. Principal
Component Analysis (PCA) showing different pain syndromes (circles),
plant parts (black), preparations (green), and life forms (blue).
Multiple-Use Species
Of
the 114 species, 27 (23.5%) were reported to treat more than 1 pain
syndrome. Seven species (6%) were reported to treat all 3 pain
syndromes: Achillea millefolium; Acorus calamus; Kalmia angustifolia; Nuphar lutea; Picea glauca; Rhododendron groenlandicum; and Salix
sp. All of these species showed evidence, either phytochemical or
pharmacological, of having pain relief properties (Table S1). Twenty
species (17.5%) were used to treat at least 2 pain syndromes, of which
14 were used to treat arthritis/rheumatism and headache/migraine (Acorus americanus, Arctium minus, Artemisia frigida, Comptonia peregrina, Gaultheria procumbens, Heracleum maximum, Juniperus virginiana, Larix laricina, Monarda fistulosa, Pulsatilla patens ssp. multifida, Sorbus americana, Taxus canadensis, Thuja occidentalis, and Vaccinium myrtilloides), 5 were used to treat back pain and heahache/migraine (Arctostaphylos uva-ursi, Chamaecyparis thyoides, Maianthemum racemosum ssp. racemosum, Picea mariana, and Pinus strobus), and only 1 species was used to treat arthritis/rheumatism and back pain (Abies balsamea).
Of the 14 species used to treat arthritis/rheumatism and
headache/migraine, 7 were reported to have pain relief properties. Of
the 5 species used to treat back pain and headache/migraine, 3 had pain
relief properties. The only species used to treat arthritis/rheumatism
and back pain also had pain relief properties (Table S1).
Pharmacological and Phytochemical Evidence
We
found either pharmacological or phytochemical evidence to explain plant
use in chronic pain treatment for 38 species (33%) (Table S1), with
several species reported to have antioxidant or anti-inflammatory
properties (30 and 12 species, respectively). Analgesic and
antinociceptive properties were also reported, but less frequently (9
species). Eight species had both phytochemical and pharmacological
evidence (Achillea millefolium, Amelanchier alnifolia, Caulophyllum thalictroides, Medicago sativa, Phytolacca americana var. americana, Plantago major, Rhododendron tomentosum, Salix
sp.), whereas 30 species had only pharmacological evidence. The
chemicals reported to be useful to treat chronic pain syndromes included
alkaloids, amino acids, anthocyanin, asparagin, bitters, caffeic acid,
coumarins, flavonoids, glycosides, isovaleric acid, lignanes, lipids,
phenolic acid, phytoestrogens, polyphenols, polysaccharides, salicylic
acid, saponins, steroids, sterols, tannins, terpenoids, and vitamins. Of
the 8 species for which pharmacological evidence was available, 2 were
used to treat all 3 chronic pain syndromes (Achillae millefolium and Salix sp.), 2 were used only for headache/migraine (Amelanchier alnifolia and Rhododendron tomentosum), and the remaining 4 were used only for arthritis/rheumatism (Caulophyllum thalictroides, Medicago sativa, Phytolacca americana var. americana, Plantago major).
Discussion
We
showed the uses of medicinal plants from the Canadian boreal forest to
treat chronic pain syndromes as a source of alternative and
complementary medicine. Some of these plants are already at the basis of
commercialized drugs,[40] and others might help develop drugs with fewer side effects.[41]
Fewer species were reported to be used for back pain than for
arthritis/rheumatism or headache/migraine. As back pain is a growing
health problem,[42]
further ethnobotanical investigations could help identify more plant
species. Herbs are the primary source of medicinal plant species
traditionally used to treat chronic pain syndromes, followed by trees,
most likely because herbs are more diverse and abundant. Whole plants,
underground parts, and leaves/needles are the most frequently used plant
parts to prepare medicinal remedies for chronic pain management.
Underground parts are likely preferred to prepare traditional remedies
because they generally contain higher concentrations of bioactive
compounds.[43, 44]
Two-thirds
of the plants for which traditional uses were reported for chronic pain
syndromes have not yet been subjected to phytochemical or
pharmacological studies, and thus data are scant with regards to their
efficacy and safety. It was reported that many chemicals having
antioxidant, anti-inflammatory, and analgesic properties were produced
by the medicinal plants and used in chronic pain treatment. Flavonoids,
terpenoids, alkaloids, and phenols are particularly known for their
antinociceptive properties.[41, 45-47] It is worth noting that all reported chemicals possess anti-inflammatory properties.[48] For example, antioxidants are anti-inflammatory in nature.[49]
Many glycosides combined with vitamins, polyphenolic glycosides
(flavonoids), alkaloid glycosides, glycosides in the group of
antibiotics, glycopeptides, cardiac glycosides, steroids and terpenoid
glycosides, also possess anti-inflammatory properties.[50, 51] Coumarins also possess anti-inflammatory properties.[52] Plants containing polysaccharides are the most potent in curing inflammatory diseases.[48]
Plant extracts could provide a safe and effective therapeutic approach for the treatment of pain,[53, 54]
but safety has to be assessed in randomized controlled trials and
observational studies representative of different conditions such as
pregnancy, polymedication, or multiple comorbidities. While
ethnobotanical studies generally do not indicate if risks are associated
with traditional uses of medicinal plants for pain management, rigorous
and controlled studies are needed[55] as some side effects of traditional medicinal remedies have been reported.[56]
Therefore, 2 lines of research are necessary before integrating
traditional uses of medicinal plants to health care systems: (1) plants
need to be evaluated in terms of efficacy and (2) plants need to be
evaluated for their potential side effects and interactions (plant-plant
or plant-synthetic drugs) in case of polymedication. Studies are also
needed in pharmacognosy, ie, the standardization, authentication, and
study of natural drugs.
Principal
component analysis results indicated that different plant parts and
preparation modes are used to treat the 3 chronic pain syndromes. This
could help orient future bio-prospecting investigations. Bio-prospecting
activities should ensure safeguarding of local people's intellectual
property rights, equitable revenue sharing, and application of
sustainable harvesting guidelines including respect for the conservation
status of plant species.[57, 58] Unfortunately, these issues have not yet been properly addressed by relevant policy in Canada.[59]
The
limitations of our study are inherent to the limitations of the mackiki
database, which was derived from a limited number of studies published
over a long time period and covering a wide geographical area.
Nevertheless, the available phytochemical and pharmacological evidence
concords with indigenous knowledge. The database did not allow us to
easily distinguish between medicinal plants used for the treatment of
acute and chronic pain. However, this is not an issue for arthritis, as
it is a recognized chronic health problem.[60] About 20% of migraine and 5% of back pain patients develop chronic symptoms,[61, 62]
and we thus chose not to discard information on these pain syndromes.
Moreover, several drugs used to treat migraines or back pain are the
same, whether the condition is acute or chronic.[63, 64]
Globally, we provided insight on the potential of boreal plants as
alternative and complementary medicines for the treatment of chronic
pain syndromes that could be enhanced by further research on efficacy
and safety issues.
Acknowledgements
The
authors declare no conflicts of interest and no financial interests
related to this study. Funding was provided by the Aboriginal Peoples
Research and Knowledge Network (DIALOG). Nabiha Benyamina Douma, PhD
student in clinical sciences at Université du Quebec en
Abitibi-Témiscamingue, contributed to the classification of medicinal
plants.