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Seasonal Variation of Phenolic Constituents and Medicinal Activities of Northern Labrador Tea, Rhododendron tomentosum ssp subarcticum, an Inuit and Cree First Nations Traditional Medicine

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Northern Labrador tea, Rhododendron tomentosum ssp. subarcticum, is one of the most commonly used medicinal plants by Inuit and other First Nations peoples of Canada. The phenolic profile and seasonal variation of this commonly used medicinal plant remains largely unknown. To assess optimal harvesting time, R. tomentosum was collected in accordance with traditional knowledge practices bimonthly throughout the snow-free summer in Iqaluit, Nunavut. The antioxidant potency was measured in a DPPH radical scavenging assay, and the anti-inflammatory activity was determined with a TNF-α production assay. The seasonal variation of phenolic content was assessed with HPLC-DAD for fifteen of the most abundant phenolic compounds; (+)-catechin, chlorogenic acid, PARA-coumaric acid, quercetin 3-O-galactoside (hyperoside), quercetin 3-O-glucoside (isoquercitrin), quercetin 3-O-rhamnoside (quercitrin), quercetin pentoside, myricetin, quercetin, 3 procyanidins, and 3 caffeic acid derivatives. The most abundant constituent was (+)-catechin, which made up 19 % of the total weight of characterized phenolics. There was significant seasonal variation in the quantity of all fifteen constituents assessed, whereas there was no seasonal variation of their total sum. The antioxidant activity was positively correlated with phenolic content and negatively correlated with daylight hours. The anti-inflammatory activity was negatively correlated with caffeic acid derivative 1 and daylight hours. Together these results demonstrate that the timing of harvest of R. tomentosum impacts the plant's phenolic content and its antioxidant and anti-inflammatory activities.
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Planta Medica
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Introduction
!
The use of traditional medicinal plants is widely
practiced in North American First Nations popula-
tions, with approximately 2500 plants identified
[1]. The pairing of traditional approaches with
modern medicine to treat illnesses in Aboriginal
populations often results in better compliance
than using conventional medicine alone [2]. Ill-
ness treatment with botanicals represents a new
challenge for care providers as the medicinal
plants often lack characterization, information,
or clinical support. This report focuses on the
phytochemical characterization and seasonal
quantification of a plant commonly used as a tra-
ditional medicine by multiple First Nations popu-
lations including the Canadian Inuit.
Rhododendron tomentosum (Stokes) Harmaja ssp.
subarcticum (Harmaja) G. Wallace, of the Erica-
ceae family, is a woody evergreen shrub com-
monly called northern Labrador tea. R. tomen-
tosum is endemic to the circumpolar subarctic
with a short snow-free growing season and long
daylight exposures. It is amongst the most com-
monly used medicinal plants in multiple Cana-
dian First Nations populations for the treatment
of type 2 diabetes [3, 4], respiratory illnesses [5],
infection [6], and other uses (l
"Table 1). There is
a strong consensus amongst populations for se-
lected usage of R. tomentosum for stomach ache,
cold symptoms, and toothache (l
"Table 1). Labra-
dor tea, Rhododendron groenlandicum, (Oeder)
Kron & Judd has overlapping habitat in sub-boreal
climates with northern Labrador tea and is often
used interchangeably with an occasional prefer-
ence for using the smaller northern Labrador tea
for children. These species differ phytochemically,
at least in their volatile oil contents, with
Abstract
!
Northern Labrador tea, Rhododendron tomento-
sum ssp. subarcticum, is one of the most com-
monly used medicinal plants by Inuit and other
First Nations peoples of Canada. The phenolic pro-
file and seasonal variation of this commonly used
medicinal plant remains largely unknown. To as-
sess optimal harvesting time, R. tomentosum was
collected in accordance with traditional knowl-
edge practices bimonthly throughout the snow-
free summer in Iqaluit, Nunavut. The antioxidant
potency was measured in a DPPH radical scaveng-
ing assay, and the anti-inflammatory activity was
determined with a TNF-αproduction assay. The
seasonal variation of phenolic content was as-
sessed with HPLCDAD for fifteen of the most
abundant phenolic compounds; (+)-catechin,
chlorogenic acid, para-coumaric acid, quercetin
3-O-galactoside (hyperoside), quercetin 3-O-glu-
coside (isoquercitrin), quercetin 3-O-rhamnoside
(quercitrin), quercetin pentoside, myricetin, quer-
cetin, 3 procyanidins, and 3 caffeic acid deriva-
tives. The most abundant constituent was (+)-cat-
echin, which made up 19 % of the total weight of
characterized phenolics. There was significant
seasonal variation in the quantity of all fifteen
constituents assessed, whereas there was no sea-
sonal variation of their total sum. The antioxidant
activity was positively correlated with phenolic
content and negatively correlated with daylight
hours. The anti-inflammatory activity was nega-
tively correlated with caffeic acid derivative 1
and daylight hours. Together these results dem-
onstrate that the timing of harvest of R. tomento-
sum impacts the plantʼs phenolic content and its
antioxidant and anti-inflammatory activities.
Supporting information available online at
http://www.thieme-connect.de/ejournals/toc/
plantamedica
Seasonal Variation of Phenolic Constituents
and Medicinal Activities of Northern Labrador Tea,
Rhododendron tomentosum ssp. subarcticum,
an Inuit and Cree First Nations Traditional Medicine
Authors Paleah Black1, Ammar Saleem 1, Andrew Dunford2, José Guerrero-Analco1, Brendan Walshe-Roussel1, Pierre Haddad 3,
Alain Cuerrier4, John T. Arnason 1
Affiliations 1Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
2Nunavut Research Institute, Iqaluit, Nunavut, Canada
3Department of Pharmacology, University of Montreal, Montreal, Quebec, Canada
4Plant Biology Research Institute, University of Montreal, Montreal, Quebec, Canada
Key words
l
"Rhododendron tomentosum
ssp. subarcticum
l
"Ericaceae
l
"northern Labrador tea
l
"seasonal variation
l
"phenolic compounds
l
"antiinflammatory
l
"Inuit
received Nov. 14, 2010
revised March 9, 2011
accepted March 12, 2011
Bibliography
DOI http://dx.doi.org/
10.1055/s-0030-1270968
Published online April 6, 2011
Planta Med © Georg Thieme
Verlag KG Stuttgart · New York ·
ISSN 00320943
Correspondence
John T. Arnason
Centre for Research
in Biotechnology
and Biopharmaceuticals
Department of Biology,
University of Ottawa
30 Marie Curie
Ottawa, ON, K1N 6N5
Canada
Phone: + 1 61 35 62 52 62
Fax: + 1 61 35 62 54 86
John.Arnason@uottawa.ca
Black P et al. Seasonal Variation of Planta Med
Original Papers
This is a copy of the authorʼs personal reprint
This is a copy of the authorʼs personal reprint
b
R. groenlandicum having more germacrone and R. tomentosum,
more ledol [7]. Populations today still use these plants as a topical
treatment for toothaches or wounds, and as a tea for general con-
sumption. R. tomentosum has demonstrated a variety of medici-
nal properties for the treatment of type 2 diabetes, including glu-
cose and insulin regulation, and oxidative stress protection [3, 4,
8]. In addition, R. tomentosum showed moderate inhibitory prop-
erties on drug-metabolizing isoforms of cytochrome P450s [9].
These results support the pharmacological activity of R. tomen-
tosum, with the suggestion that further in vivo and in vitro inves-
tigations be undertaken [3]. Although other Rhododendron spe-
cies have been phytochemically characterized [10, 11], the com-
position of R. tomentosum remains largely unknown.
Multiple epidemiological and clinical studies have confirmed
that antioxidant intake is associated with decreased prevalence
of cancer, improved memory function, increased physical endur-
ance capacity and cardioprotection, as well as being beneficial for
the treatment of type 2 diabetes [1215]. The antioxidant or phe-
nolic content of plants is known to vary throughout the annual
seasons due to genetic determinants and response to environ-
mental conditions, such as herbivory, UV exposure, day length,
temperature, and nutr ients [16, 17]. These seasonal trends may
be particularly dramatic in high latitude arctic environments
with a short summer season and long daylight hours [18]. Sea-
sonal variation has been well characterized in plants of commer-
cial importance. For example, higher levels of metabolites have
been reported in the summer months of greenhouse-grown
cherry tomatoes [16] and Australian-grown tea [19], which were
generally attributed to elevated UV levels and/or duration of sun-
light exposure. The phytochemical composition and anti-glyca-
tion principles of the medicinal plant, Vaccinium angustifolium
Ait., of the Ericaceae family, were also noted to vary according to
season [20]. When characterizing medicinal plants, it is impor-
tant to account for the seasonal variations of the quality of the
product to determine the optimal harvest time. The objectives
of this study were to quantify the most abundant phenolic com-
pounds, and antioxidant and anti-inflammatory activities in
R. tomentosum leaf extract throughout the growing season. It
was predicted that the peak phenolic content would correspond
to the longest daylight days of the season, which would in turn
correspond to the peak antioxidant and anti-inflammatory
activity.
Materials and Methods
!
Plant material and extraction
Rhododendron tomentosum ssp. subarcticum was collected bi-
monthly and in triplicate throughout the snow-free season from
May to September 2006 near Iqaluit, Nunavut, Canada (N 63°
45.3, W 68° 30.6). Collections were made according to tradition-
al methods described by the Inuit [5]; however, for convenience,
we used ethanol extractions instead of infusions. The f irst 10 cm
of the plant branch was removed and allowed to air dry in dark-
ness for 24 hours. Dried plant material was ground with a Wiley
Mill (A. H. Thomas Co.) to a pore size of 2 mm and extracted t wice
in 80% ethanol (10 mL/g) for 24 hours. The solvent was evapo-
rated; the homogenized extract was freeze-dried and stored in
amber vials at 20 °C (3 biological replicates, 8 collections, 24
samples). Voucher specimens were deposited and taxonomically
verified by Alain Cuerrier at the Marie-Victorin Herbarium of the
Plant Biology Research Institute, University of Montreal (IQAL04-
1A & B). Observations of the plantʼs phenological stage were pho-
tographed and recorded at the time of collection. Information on
daily meteorological conditions [21] and daylight hours [22]
Table 1 Uses of Rhododendron tomentosum ssp. subarcticum by Inuit and Cree nations.
First Nations Names Uses References
Inuit (Hudson Strait) Mamaittuqutik Tea; cold and flu symptoms; shallow breathing; toothache;
stomach ache; fuel
Cuerrier & Elders of Kangirsujuaq
(2005)
Inuit (Ungava Bay) Mamaittuqutik Tea; fuel; cold; cough; tuberculosis; tonic; shallow breathing Cuerrier & Elders of Kangirsua-
lujjuaq (2005)
Inuit (Hudson Bay) Tirluapik, tirlualuk,
mamaittuqutik,
mamaittuqutirlaq,
tirluk
Tea; toothache; stomach ache; emetic; cold; throat ache; aches
and pains; snow blindness
Cuerrier et al. (2006)
Inuit (Nunavut) Qisiqtuut;
Qijuktaaqpait
Fuel; sore throat and cough; tobacco; canker sores (in the mouth);
headache; eye problems; dry skin
Wilson (1978); Black et al. (2008);
Mallory & Aiken (2004); Ootoova
et al. (2001)
Inuit (Greenland) Kajaussat Tea Le Mouël (1969)
Iñupiat Tilaaqiuq Tea Jones (1983)
Inuit (Alaska; St.Lawrence;
Western Canada); Haida;
Nuxalk; Comox;
Ayuq (Yupik)
Ayʼut
Tea (with medicinal value); stomach ache; tuberculosis Oswalt (1957); Young & Hall
(1969); Anderson (1939); Ager &
Ager (1980); Griffin (2001)
Inuit (Naspakiak) Aiʼyut To purify rooms and get rid of ghosts; branches are lit and then
discarded
Oswalt (1957); Lantis (1959)
Gwichʼin La dee musket lidii
masgit
Tea; colds and hangovers; overall energy; nasal congestion Holloway & Alexander (1990);
Andre & Fehr (2001)
Cree (James Bay) Wiisichipikw-h
Uschiischipakw
Wounds and skin sores; mouth sores; headaches; stomach ache;
coughs; sore throat; cold; tonic; aches and pains; flu; diarrhea
Marshall (2006)
Marshall et al. (1989)
Cree (Hudson Bay) Headache; thirst; blurred vision; appetite; diarrhea; abscesses and
boils; toothache; back and kidney pain; rheumatism and arthritis;
infections; inflammation; heart and chest pain; fainting and weak-
ness; sore or swollen limbs; foot sores and numbness
Cuerrier et al. (in prep.)
Black P et al. Seasonal Variation ofPlanta Med
Original Papers
This is a copy of the authorʼs personal reprint
This is a copy of the authorʼs personal reprint
b
were obtained and reported as a two week average prior to the
date of plant collection (l
"Table 2).
Chemicals and standards
(+)-Catechin, chlorogenic acid, para-coumaric acid, myricetin,
quercetin, quercetin 3-O-galactoside, quercetin 3-O-glucoside,
quercetin 3-O-rhamnoside, procyanidin B1, procyanidin B2, pro-
cyanidin B3, resveratrol, and taxifolin (95% purity) were pur-
chased from Chromadex, Inc. HPLC grade water, acetonitrile, and
formic acid (99% purity) were purchased from Sigma-Aldrich.
DPPH free radical scavenging assay
The free radical scavenging activity of each plant extract was
measured with a 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay ac-
cording to the method described previously [23] and modified
for use with a plate reader. Serial dilutions were prepared in
MeOH from a 2 mg/mL stock solution of each plant extract and
ascorbic acid. In a 96-well plate, 198µL of 100 uM DPPH solution
was added to 33 µL of extract in triplicate and allowed to stand
for 10 minutes at room temperature. The absorbance was read
with a Beckman®DU320 spectrophotometer at 517 nm. An in-
hibitory concentration at 50 % (IC50) was calculated for each ex-
tract from the linear portion of the dose-response curve of ascor-
bic acid and reported as the triplicate average. For graphical pur-
poses, the antioxidant activity was presented as 1/(IC50).
TNF-αanti-inflammatory assay
The anti-inflammatory activity of the plant extract was assessed
with a tumor necrosis factor-α(TNF-α) assay, where TNF-αpro-
duction was measured in a human acute monocytic leukemia cell
line (THP-1) following lipopolysaccharide (LPS) stimulation. THP-
1 cells (ATCC) were cultured in RPMI 1640 media (ATCC) supple-
mented with 1 % 0.05 mM beta-mercaptoethanol, 1 % penstrep
(Invitrogen), and 10% fetal bovine serum (Invitrogen), in a 37°C
humidified environment with 5 % CO2. Cells were transferred
(3 × 104cells/well) to a 96-well plate, followed by the addition of
the plant extract dissolved in 80% EtOH for a final volume of
300 µL/well and a f inal EtOH concentration of 0.5 %. Plant extracts
were assayed at 100 µg/mL. Parthenolide (Sigma-Aldrich), a well-
known anti-inflammatory sesquiterpene lactone found in fever-
few (Tanacetum parthenium), was used as a positive control at
10 µg/mL, and 0.5% EtOH was used as a vehicle control [24]. All
extracts and controls were assayed in triplicate. Following the ad-
dition of extracts and controls, cells were incubated for 2 hours,
stimulated with 1 µg/mL LPS purif ied from Escherichia coli (Sig-
ma-Aldrich) and allowed to incubate for 20 hours. An unstimu-
lated control containing 0.5% EtOH but no LPS was also assayed.
After incubation, cells were centrifuged at 2000 rpm for 10 min-
utes at room temperature. Cell culture supernatants were sepa-
rated and stored at 80 °C. DuoSet®ELISA development kits
(R & D Systems) were used to assess TNF-αproduction according
to the manufacturerʼs protocol. Raw TNF-αvalues (pg/mL) were
transformed into percent TNF-αresponse relative to the LPS-
stimulated EtOH vehicle control (set as 100% TNF-αproduction).
For graphical purposes, the anti-inflammatory activity was pre-
sented as 1/(percent TNF-αresponse relative to the vehicle con-
trol).
High-pressure liquid chromatography
HPLCDAD analysis was adapted from a previously described
method by Saleem et al. [25]. Analyses were carried out on an
Agilent 1100 series HPLCDAD-APCI/MSD system (Agilent Tech-
nologies, Inc.). The system consisted of an online degasser, a qua-
ternary pump (maximum pressure limit 400 bars), an auto sam-
pler with a 100 µL built-in injection loop, a column thermostat
compartment, a diode array detector with a f low cell (6 mm path
length, maximum pressure 400 bar). The mobile phase consisted
of water + 0.1 % formic acid (solvent A) and acetonitrile (solvent
B). A linear gradient of 1055 % B was applied in 25 min at a flow
rate of 1.5 mL/min. The separations were performed on a Luna 3u
C18(2) 100 A column (100 mm × 2.0 mm) connected with a secur-
ity guard (Phenomenex, Inc.). The column was washed for 5 min
with 100 % B in isocratic conditions and equilibrated for 5 min. All
extracts were dissolved at 40 mg/mL in 100 % methanol and one
µL was injected in triplicate. The elutions of target compounds
were monitored at DAD wavelengths of 250 nm and 325 nm. The
column oven temperature was maintained at 55 °C. Calibration
curves were constructed using Chemstation B.03.02 based on
the area under the peaks by injecting authentic standards serially
diluted within the concentration range that brackets the ex-
pected concentration in the plant extracts. The compounds with
tentative identification were quantified based on calibration
curves of chemically similar authentic compounds. Compounds
were identified based on comparison to retention times and UV
spectra of pure standards relative to a programmed library of
known UV spectra and further confirmed with mass spectrome-
try fragmentation patterns according to previously described
methods [25]. Co-chromatography was performed to monitor ex-
tracts using authentic standards (+)-catechin, chlorogenic acid,
para-coumaric acid, myricetin, quercetin, quercetin 3-O-galacto-
side, quercetin 3-O-glucoside, and quercetin 3-O-rhamnoside.
Statistical analysis
Seasonal variation of phytochemical quantities, antioxidant
DPPH activity, and anti-inflammatory TNF-αresponse were as-
sessed for normality and distribution and evaluated with one-
way analysis of variance (ANOVA) followed by the Tukey post
hoc test when appropriate. Wh en required, data was log10 trans-
formed. Total constituents were calculated as the sum of the
quantities of the fifteen characterized constituents. Two-tailed
Pearson correlations were used to detect associations between
seasonal data and medicinal properties. All analyses were per-
Table 2 Environmental conditionsa, percent yieldb, and phenological stage of
R. tomentosum seasonal collections.
Date Mean
Temperature
(low-high) (°C)
Precipi-
tation
(mm)
Day-
light
(h)
Percent
yield
(w/dw)
Phenological
stage
June 13 3.2 (0.26.1) 1.3 20.3 21.3 ± 2.3 Leaf buds
June 27 4.7 (1.87.6) 2.0 20.7 24.0 ± 1.7 Leaf growth
July 13 10.3 (5.615.0) 0.8 20.1 23.5± 2.0 Flowering
July 26 9.3 (5.213.3) 0.8 19.0 23.0± 0.6 Seed pod
development
August
9
7.2 (4.210.2) 0.3 17.6 23.7± 1.8 Seed pod
maturation
August
23
9.0 (5.012.9) 0.7 16.1 22.7± 2.0 Leaf growth
Sept 8 6.7 (3.310.2) 1.5 14.4 25.0 ± 2.5 Leaf grow th
Sept 30 3.0 (0.95.1) 1.2 12.1 25.3 ± 2.9 Leaf death;
red color
aMean temperature, precipitation, and daylight hours are presented as the 14-day
average preceding the 2006 collection date. bExtract percent yield was calculated as
[extract weight/dr y plant material weight (g/g)] × 100
Black P et al. Seasonal Variation of Planta Med
Original Papers
This is a copy of the authorʼs personal reprint
This is a copy of the authorʼs personal reprint
b
formed with SPSS 15.0 (SPSS, Inc.). Differences were considered
statistically significant when p < 0.05.
Supporting information
Chemical structures of the f ifteen phenolic constituents analyzed
in R. tomentosum leaf extract and HPLC chromatogram of
R. tomentosum leaf extract are available as Supporting Informa-
tion.
Results and Discussion
!
The environmental conditions of R. tomentosum growing at the
collection site in Iqaluit, Nunavut, are characterized by long day-
light hours and a short snow-free growing season (l
"Table 2).
R. tomentosum unfolds leaf buds in June, soon after the snow cov-
er melts, and average minimum temperatures are above freezing.
The longest day of the year, June 21, had 20.83 hours of sunlight
(sunrise to sunset), and 3.17 hours of twilight. Flowers are pro-
duced in July, the warmest month with an average high temper-
ature of 15 °C and a low of 5.2°C. At the end of September, daily
temperature lows can be below freezing once again, and the
leaves of R. tomentosum turn red. Plants thriving in arctic tundra
have particular genetic, physiological, and phytochemical adap-
tations for growth in this climate [26,27].
Fifteen phytochemicals were identified and quantified in
R. tomentosum leaf extract throughout their growing season
(Fig. 1S, Supporting Information). HPLCDAD with a detection at
325 nm was used to quantif y chlorogenic acid, para-coumaric ac-
id, myricetin, quercetin, quercetin 3-O-galactoside, quercetin 3-
O-glucoside, quercetin pentoside, quercetin 3-O-rhamnoside,
and three caffeic acid derivatives, and HPLCDAD with a detec-
tion at 280 nm was used to quantify (+)-catechin and three pro-
cyanidins (Fig. 2S, Supporting Information).
Of the fifteen constituents quantified, (+)-catechin, quercetin
pentoside, and quercetin 3-O-galactoside were the most abun-
dant (l
"Fig. 1), in agreement with previous findings for
R. tomentosum [25]. Firstly, (+)-catechin had a seasonal average
of 6.75 mg/gDW (milligrams of extrac t per gram of plant dry
weight) and range of 3.2110.2 mg/gDW. Quercetin pentoside
had a seasonal average of 4.79 mg/gDW and range of 3.44
5.83 mg/gDW. Quercetin 3-O-galactoside had a seasonal average
of 4.58 mg/gDW and range of 3.515.96 mg/gDW. The quantities
of all three of these compounds were at maxima in September
when the leaves of R. tomentosum turn red.
Similarly, procyanidin B3 and procyanidin B2, the fourth and fifth
most abundant compounds, displayed seasonal maxima in Sep-
tember (l
"Fig. 2). The seasonal average quantities of procyanidin
B2 and procyanidin B3 were 2.93 mg/gDW and 3.91 mg/gDW, re-
spectively. Procyanidin B1 was one of the least abundant com-
pounds with a seasonal average quantity of 0.99 mg/gDW and a
maximal quantity in June (l
"Fig. 2).
In contrast, the quantities of the three caffeic acid derivatives did
not follow this seasonal trend with maxima occurring in Septem-
ber (l
"Fig. 3). Interestingly, it appears that caffeic acid derivative
1 and caffeic acid derivative 2 follow an opposite mirror image
seasonal trend with their respective seasonal minima and maxi-
ma occurring in August. Caffeic acid derivative 1, the seventh
most abundant compound, had a seasonal average quantity of
2.01 mg/gDW, with seasonal maxima of 2.66 mg/gDW occurring
in June. Caffeic acid derivative 2, the sixth most abundant com-
pound, had a seasonal average of 2.62 mg/gDW, with seasonal
maxima of 3.68 mg/gDW occurring in July. Caffeic acid derivative
3, one of the least abundant compounds, had a seasonal average
quantity of 0.58 mg/gDW, with seasonal maxima of 1.07 mg/
gDW occurring in August.
Myricetin, quercetin, quercetin 3-O-glucoside, and quercetin 3-
O-rhamnoside had relatively low seasonal average concentrations
(l
"Fig. 4). Quercetin 3-O-rhamnoside showeda 500 % spike in con-
centration in mid-July, which corresponded to R. tomentosum
flowering. Quercetin and quercetin 3-O-glucoside both had sea-
sonal minima at the end of August and maxima in September.
Chlorogenic acid and para-coumaric acid had relatively low sea-
sonal average concentrations and displayed similar seasonal
trends with a maximal concentration at the end of June (l
"Fig. 5).
The sum of the fifteen phenolic compounds did not significantly
vary throughout the season; however, there was a clear growth
dilution trend (l
"Fig. 6). At the beginning of the summer growing
season in June, there was a seasonal minimum concentration of
total compounds, 28.8 mg/gDW. Two weeks later this concentra-
tion rose to 38.6 mg/gDW, which corresponded to the timing of
Fig. 1 Seasonal variation of the mean quantities ± SEM of the three most
abundant compounds in R. tomentosum leaf extract; A(+)-catechin,
Bquercetin pentoside, and Cquercetin 3-O-galactoside. Different letters
indicate significant collection date differences at p 0.05.
Black P et al. Seasonal Variation ofPlanta Med
Original Papers
This is a copy of the authorʼs personal reprint
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b
R. tomentosum metabolic activation and leaf bud development
(l
"Table 2). The total concentration then fell throughout July as
the leaves grew and flowers were produced resulting in a dilution
of phenolics and allocation of resources to reproductive organs.
After the plant flowered, the phenolic content consistently in-
creased again until it reached its seasonal maxima in September,
at 40.0 mg/gDW, which corresponded to the cessation of growth
and leaves turning red. Late August or early September is tradi-
tionally known to be the optimal time for harvest of this medici-
nal plant by the Inuit [28].
As expected, the DPPH antioxidant activity of R. tomentosum dis-
played a similar seasonal trend as the total sum of compounds,
whereas there was no such relationship with the TNF-αanti-in-
flammatory activity (l
"Fig. 7). There was a significant correlation
between antioxidant activity DPPH IC50 and the total sum of con-
stituents (r = 0.77; p = 0.02), a trend that has been well estab-
lished [29, 30]. There was no correlation between anti-inflamma-
tory activity and total sum of constituents. The average DPPH
antioxidant activity was 103.4 µg/mL with seasonal minima,
113.9 µg/mL, occurring in July when the plant was growing and
producing flowers, and a seasonal maxima, 89.6 µg/mL, in Sep-
tember when the leaves were turning red. The positive control,
L-ascorbic acid, had an IC50 of 46.6 µg/mL, resulting in an average
R. tomentosum extract percentage of positive control of 45%. The
positive control ratio (ascorbic acid logIC50/plant extract logIC50)
of our extract was 0.83. The antioxidant activity found in the
R. tomentosum leaf extract was generally in agreement with pre-
viously reported values [3, 4] despite varying sampling locations,
seasonal collection dates, and testing procedures.
The average TNF-αanti-inflammatory activity was 64.3 % of ve-
hicle control, with the minima occurring in July (98.0 %) and max-
ima in August (41.1%), after which time the activity proceeded to
decrease throughout September when the leaves of R. tomento-
sum are turning red. The TNF-αanti-inf lammatory activity for
the positive control, parthenolide, was 3.2% of vehicle control.
Antioxidant activity was not correlated to anti-inf lammatory ac-
tivity despite the well characterized use of phenolics as anti-in-
flammatory agents. Inf lammatory signaling cascades include free
Fig. 2 Seasonal variation of the quantities ± SEM of the three procyanidin
compounds assessed in R. tomentosum leaf extract; Aprocyanidin B1,
Bprocyanidin B2, and Cprocyanidin B3. Different letters indicate signifi-
cant collection date differences at p 0.05.
Fig. 3 Seasonal variation of the quantities ± SEM of the three caffeic acid
derivatives assessed in R. tomentosum leaf extract; Acaffeic acid derivative
1, Bcaffeic acid derivative 2 and, Ccaffeic acid derivative 3. Different let-
ters indicate significant collection date differences at p 0.05.
Black P et al. Seasonal Variation of Planta Med
Original Papers
This is a copy of the authorʼs personal reprint
This is a copy of the authorʼs personal reprint
b
radicals, which lead to the activation of nuclear factor κBandthe
transcription of TNF-αinflammatory cytokine [31]. Many tradi-
tionally used medicinal plants and phytochemical compounds,
such as parthenolide, are known to target these pathways as
anti-inflammatory therapies [32]. The peak anti-inflammatory
activity was observed at the end of August, which corresponded
to the traditional collection timing of R. tomentosum [28]. Meth-
anol extracts of Labrador tea (Ledum groenlandicum, a taxonom-
ical synonym of Rhododendron groenlandicum) have also been
previously reported to possess anti-inflammatory activity in a
rat paw edema model [33].
By conducting partial correlations of each phenolic constituent
and the DPPH antioxidant or TNF-αanti-inflammatory activities
of R. tomentosum leaves, we were able to identify the most active
compounds associated with each medicinal property. Anti-
oxidant and anti-inflammatory activities were also assessed for
their relationship to the environmental conditions, including
precipitation, temperatures, and photoperiod sunlight hours. A
correlation between anti-inflammatory activity and phenolic
content has been previously suggested [14]; however, this was
not the case in our study. Anti-inflammatory activity (1/[% TNF-
αresponse relative to the vehicle control]) was also negatively
correlated to total daylight hours (l
"Fig. 8 B). Furthermore, there
was a negative correlation between anti-inflammatory activity
Fig. 5 Seasonal variation of the quantities ± SEM of compounds in
R. tomentosum leaf extract; Achlorogenic acid and Bpara-coumaric acid.
Different letters indicate significant collection date dif ferences at p 0.05.
Fig. 6 Seasonal variation of the total quantity ± SEM of the fifteen com-
pounds assessed in R. tomentosum leaf extract. Different letters indicate
significant collection date differences at p 0.05.
Fig. 4 Seasonal variation of the quantities ± SEM
of compounds in R. tomentosum leaf extract; A)
myricetin, B) quercetin 3-O-rhamnoside, C) querce-
tin, and D) quercetin 3-O-glucoside. Different let-
ters indicate significant collection date differences
at p 0.05.
Black P et al. Seasonal Variation ofPlanta Med
Original Papers
This is a copy of the authorʼs personal reprint
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b
and caffeic acid derivative 1, the 7th most abundant character-
ized phytochemical. Caffeic acid phenethyl ester has demonstrat-
ed anti-inflammatory activity in vivo [37], although each caffeic
acid derivative may have varying activities. In fact, many of the
compounds quantified in this study have been shown to possess
in vitro and in vivo anti-inflammatory activity, including cate-
chin, chlorogenic acid, and quercetin [38]. As none of these com-
pounds were significantly correlated to the anti-inflammatory
activity, it is hypothesized that they were not present in large
enough amounts to individually influence the anti-inflammatory
activity of R. tomentosum, and the phytochemical constituents re-
sponsible for this activity remain obscure. On the other hand,
anti-inflammatory activity (1/[% TNF-αresponse relative to the
vehicle control]) had a significant negative correlation with caf-
feic acid derivative 1 (r = 0.72; p = 0.04), the seventh most abun-
dant compound. Antioxidant activity (1/DPPH IC50)hadasignifi-
cant positive correlation with (+)-catechin (r = 0.80; p = 0.02) and
procyanidin B2 (r = 0.83; p = 0.01), the first and fifth most abun-
dant compounds identified, respectively.
Previous studies have highlighted the importance of photopro-
tection particularly in environments with low temperatures and
a long photoperiod [18,34]. However, concentrations of (+)-cate-
chin (r = 0.73; p = 0.04) and procyanidin B2 (r = 0.71; p = 0.05),
and antioxidant activity (1/DPPH IC50) (r = 0.72; p = 0.05) were
negatively correlated to total daylight hours (l
"Fig. 8 A). In tem-
perate climates and greenhouse conditions, it is well established
that plants increase their phenolic content in response to ele-
vated solar radiation exposure [17,35,36]. In our study, the pro-
nounced growth dilution trend may have hidden any such corre-
lation since the timing of the highest sun exposure (June) also
corresponded to rapid leave growth of R. tomentosum.
Considering the widespread use of R. tomentosum as a medicinal
plant to First Nations and Inuit peoples of Canada, it is important
to characterize its phenolic constituents and medicinal activities,
as well as to determine how these properties vary throughout the
collection season. The seasonal variation of phenolic constituents
and medicinal properties has implications for optimal harvest
time and consistency of product. Our results show a significant
seasonal variation of phenolic constituents and medicinal prop-
erties of R. tomentosum, with an optimal harvest time at the end
of August to September for our study location, which corrobo-
rated traditional knowledge.
Acknowledgements
!
The authors wish to express their gratitude to the traditional
healers of Nunavut and Cree territories, the Nunavut Research In-
stitute for project collaboration, and to the reviewers for their
critical reading of this manuscript. This study was partly funded
by the CIHR Team in Aboriginal Antidiabetic Medicines.
Fig. 8 Correlation between daily sunlight hours and Ainverse antioxidant
DPPH IC50 activity and Binverse anti-inflammatory TNF-αactivity com-
pared to the negative control.
Fig. 7 Seasonal variation ± SEM of R. tomentosum leaf extract for; Aanti-
oxidant DPPH activity [1/(IC50 µg/mL)] and Banti-inflammatory TNF-α
activity [1/(% TNF-αrelative to vehicle control)]. Different letters indicate
significant collection date differences at p 0.05.
Black P et al. Seasonal Variation of Planta Med
Original Papers
This is a copy of the authorʼs personal reprint
This is a copy of the authorʼs personal reprint
b
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Black P et al. Seasonal Variation ofPlanta Med
Original Papers
This is a copy of the authorʼs personal reprint
This is a copy of the authorʼs personal reprint
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Rhododendron tomentosum (Ledum palustre) is an aromatic plant traditionally used for alleviating rheumatic complaints which makes it a potential candidate for a natural drug in rheumatoid arthritis (RA) treatment. However, the effects of plants' volatiles on apoptosis of synovial fibroblasts and infiltrating leucocytes of RA synovia, have not been reported. Volatile fraction of R. tomentosum is chemically variable and chemotypes of the plants need to be defined if the oil is to be used for therapeutic purposes. In the presented work, cluster analysis of literature data enabled to define 10 chemotypes of the plant. The volatile fractions of known composition were then tested for bioactivity using a RA-specific in vitro models. Essential oils of two wild types (γ-terpineol and palustrol/ledol type) and one in vitro chemotype (ledene oxide type) were obtained by hydrodistillation and their bioactivity was tested in two in vitro models: I - peripheral blood lymphocytes of healthy volunteers and II - synoviocytes and immune cells isolated from synovia of RA patients. The influence of oils on blood lymphocytes' proliferation and apoptosis rates of synovia-derived cells was determined by flow cytometry. Dose-dependent inhibitory effect of the serial dilutions of R. tomentosum oils on proliferation rates of blood lymphocytes was found. At 1:400 dilutions, all the tested oils increased the number of necrotic cells in synovial fibroblasts from RA synovia. Additionally, increased proportions of late apoptotic cells were observed in leucocyte populations subjected to oils at 1:400 dilution.
Thesis
Les Peuples autochtones à travers le monde sont disproportionnellement touchés par le diabète. Parmi ces peuples, les Cris d’Eeyou Istchee et les Pekuakamilnuatsh, au Québec (Canada), ainsi que les Parikwene, en Guyane française (France), recourent à leur médecine locale pour soigner cette maladie. En 173 entrevues semi-dirigées, 208 participants venant de ces communautés et/ou travaillant dans leurs services de santé ont décrit ces médecines. Une méthode de recherche mixte, combinant des analyses thématiques à des statistiques multivariées, est développée pour analyser ces descriptions.Ces analyses ont montré que les participants cris, ilnu et parikwene décrivent leurs médecines en lien avec le diabète tant par les différents éléments du monde naturel, que les pratiques et coutumes locales qui en découlent, que les concepts les liant au territoire. Les pharmacopées à base animales et végétales font parties des thèmes les plus discutés. Plus de 381 espèces (109 animaux, 267 plantes, cinq lichens et champignons) lient les systèmes médicinales et alimentaires ensemble via des notions associées au bien-être ou aux propriétés organoleptiques. Au Québec, là où la population autochtone est plus impliquée dans les services de santé, il existe un rapprochement de la description des médecines locales entre le secteur de la santé et ses usagers.De façon générale, la place de l’alimentation dans les médecines locales ne peut être négligée dans le contexte du diabète. De plus, ces médecines sont indissociables du territoire qui offre un espace de guérison, de subsistance, et de continuité culturelle. Cela renvoie, in fine, à des questions importantes sur la reconnaissance des droits autochtones et des droits fonciers.
Chapter
Rhododendron tomentosum (marsh tea, previously Ledum palustre), a fragrant shrub with characteristic evergreen leaves and white flowers, grows in Europe, Asia, and North America. It has been used for centuries in folk medicine to treat rheumatic diseases, lung problems, and infections as well as due to its repellent properties. In North America, the tonic beverage known as “Labrador tea”, derived from the indigenous tradition and made from R. tomentosum, R. groenlandicum and R. neoglandulosum leaves, is prepared until now. The modern biological research confirm anti-inflammatory, analgesic, antimicrobial and insecticidal effect of the discussed plant material, indicating an important role of the essential oil as an active ingredient. However, obtaining the volatile fraction from R. tomentosum ground material for pharmacological studies is difficult because marsh tea is the endangered species in some countries. Moreover, as many as ten chemotypes of R. tomentosum on the Eurasian continent have been distinguished, due to the chemical composition of the essential oil. Such heterogeneity of the plant material is problematic, assuming its use for medical purposes. Therefore, the shoot in vitro culture was initiated for the first time for receiving the R. tomentosum biomass, being the complex source of biologically active volatile compounds, regardless of environmental conditions. The microshoots were subsequently adapted for large laboratory scale cultivation in commercial and prototype bioreactors. The RITA® temporary immersion system, containing SH medium with 24.60 μM 2-isopentenyladenine and 592.02 μM adenine, provided the highest growth parameters of biomass (Gi = 280%) and the intensified biosynthesis of the essential oil (500 μl 100 g⁻¹ dry weight), surpassing the productivity of the aged shoots of the mother plant (300 μl 100 g⁻¹ dry weight). The main terpenes of the obtained volatile fraction were ledene oxide (II) (13%), shyobunone (8%), p-cymene (7%), and alloaromadendrene (6%). In order to increase the essential oil content in the R. tomentosum microshoots, elicitation strategy was applied, using methyl jasmonate and the selected abiotic and biotic elicitors. In response to stress caused by the aphid extract and Pectobacterium carotovorum lysate, the accumulation of the volatile fraction increased by 14%. In addition, the full protocol for micropropagation of marsh tea was developed, including initiation, multiplication, elongation, rooting, hardening, and adaptation of the seedlings to in vivo conditions, for ex situ protection of the discussed endangered species. This article reviews the importance of R. tomentosum from a medical point of view as well as the biotechnological approach obtaining an alternative source of this valuable biomass.
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Backgroud: Rhododendron przewalskii Maxim. is an evergreen shrub that is used as a traditional medicine in China. However, the modern pharmacology and the chemical components of this plant has not been studied. In this paper, we aimed to investigate the antifungal, anti-inflammatory and antioxidant activities and underlying mechanism of its aqueous and ethanol extracts, and analyze their chemical composition and active compounds of R. przewalskii . Methods: The antifungal activity was determined in vitro , and anti-inflammatory and antioxidant activities and underlying mechanism of its aqueous and ethanol extracts were evaluated in vitro and in RAW 264.7 cells. The chemical composition were analyzed using UPLC-ESI-Q-TOF/MS, and the contents of six compounds were determined via HPLC. Results: Both extracts of R. przewalskii showed promising anti-inflammatory activity in vitro ; decreased the production of four inflammatory cytokines, namely, nitric oxide, IL-1β, IL-6 and TNF- ɑ , in RAW 264.7 cells induced by lipopolysaccharide; and exhibited weak cytotoxicity. The extracts significantly scavenged DPPH radicals, superoxide radicals and hydroxyl radicals to exert antioxidant effects in vitro . The two extracts also exhibited cellular antioxidant activity by increasing superoxide dismutase and CAT activities and decreasing malondialdehyde content in RAW 264.7 cells induced by LPS. However, the antifungal activity of the two extracts was weak. Nine flavonoid s were identified by UPLC-ESI-Q-TOF/MS. Of these, six compounds were analyzed quantitatively, including avicularin, quercetin, azaleatin, astragalin and kaempferol, and five compounds (myricetin 3-O-galactoside, paeoniflorin, astragalin, azaleatin and kaempferol) were found in this species for the first time. These compounds demonstrated antioxidant activities that were similar to those of the R. przewalskii extracts and were thought to be the active compounds in the extracts . Conclusion: R. przewalskii extracts presented promising anti-inflammatory and antioxidant activities. The extracts contained amounts of valuable flavonoids (8.98 mg/g fresh material) that were likely the active compounds in the extract contributing to the potential antioxidant activity. These results highlight the potential of R. przewalskii as a source of natural antioxidant and anti-inflammatory agents for the pharmaceutical industry.
Article
Ethnopharmacological relevance Erica arborea known as Khlenj in Algeria is a small shrub belonging to Ericaceae family. E. arborea Aqueous extract (EAAE) is used in traditional medicine for anti-inflammatory, diuretic, antimicrobial, and antiulcer purposes. Aim of the study To our knowledge, no data reveal the combination between in-vivo anti-inflammatory and toxicological studies of EAAE. For this purpose, the aim of this study is to evaluate the biological activity cited above and asses its safety. Material and methods Anti-inflammatory activity was undergone using carrageenan-induced paw edema and croton oil-induced ear edema. The acute and sub-acute toxicity were conducted following the OECD guidelines 423 and 407 respectively. Phytochemical identification was carried out using HPLC-DAD-MS. Quantitative evaluation of polyphenols; flavonoids and antioxidant activity of EAAE were also determined. Results Oral administration of EAAE (250 and 500 mg/kg) significantly (p <0.05) reduced the edema induced by carrageenan. Administration of EAAE dosed at 250 and 500 mg/kg exhibited efficacy in reducing edema induced by croton oil. The acute administration of EAAE at doses of 2000 and 5000 mg/kg did not cause any mortality or adverse effects indicating that the LD50 is above 5000 mg/kg. The prolonged administration of EAAE (500 and 1000 mg/kg) showed a significant reduction in triglycerides levels in male and female rats whereas no significant changes in other biochemical and hematological parameters were observed. Histopathological damages were recorded in both liver and kidney animal’s tissues of both sexes treated with medium and maximum doses of EAAE. Phytochemical characterization of EAAE revealed a high amount of phenolic compounds, HPLC-DAD-MS analysis led to the identification of chlorogenic acid and five flavonol glycosides: myricetin pentoside, quercetin 3-O-glucoside, myricetin 3-O-rhamnoside, quercetin-3-O-pentoside, and quercetin-3-O-rhamnoside. Conclusion In the light of the results obtained in this study, EAAE corroborates the popular use to treat the anti-inflammatory impairments. EAAE can be considered as non-toxic in acute administration and exhibited a moderate toxicity in sub-acute administration. High phenolic content and in-vitro antioxidant activity observed indicate that EAAE may reduce oxidative stress markers in-vivo.
Article
Labrador Tea (Rhododendron groenlandicum) has been an important food and medicinal plant to First Nations communities in North America for millenia, but little is known of its geochemical properties. Using plants from 10 sites in 4 provinces, including pristine and industrial regions, and employing the metal-free, ultraclean SWAMP laboratory facilities and procedures, we provide an estimate of the natural abundance of trace elements in the leaves, and the extent of their release during hot water extraction. Elements decrease in abundance in the order Mn > Al > Fe > Zn > Cu > Ni > V > Pb > La > Mo > Y > La > Tl > Cd > Th > Ag. The greatest concentrations of conservative, lithophile elements such as Al, La, Th and Y, are found in samples collected on lands reclaimed from open pit bitumen mines in northern Alberta, reflecting elevated inputs of atmospheric dusts. In contrast, micronutrients such as Cu and Zn are remarkably uniform which suggests that these are supplied almost exclusively by plant uptake via roots. Deionized, reverse osmosis water is more effective in removing some elements (e.g. Al, La, Y, Fe, Zn, Cd) whereas others are more readily extracted using groundwater (e.g. Cu, Ni, Pb); V behaves independently of water composition. In both types of water, the elements most readily extracted are plant micronutrients (Mn, Ni, Cu, and Zn) whereas those supplied primarily by dust exhibit much lower yields; Al shows behaviour intermediate between these two extremes. While element concentrations in the infusions increase with increasing concentrations in the leaves, the abundance of potentially toxic chalcophile elements such as Cd, Pb, Sb and Tl in the infusions are extremely low (ng/l). Plants from British Columbia, Ontario and Quebec provide evidence of atmospheric Pb contamination, yielding greater ratios of Pb/La compared to the samples from Alberta where crustal values are found. Given that this plant is common and found across the northern half of the continent, it shows great promise as a tool for biomonitoring of air quality. For consumers, Labrador Tea may represent an important dietary source of Mn.
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At least 175 food plants and 52 beverage plants were gathered by Native Peoples in eastern Canada. Iroquoian agriculturalists of southern Ontario cultivated corn, beans, squash, tobacco, and sunflowers, and gathered the greatest variety of food plants. Southern and eastern Algonkian hunters and gatherers ate a wide variety of wild plant foods including fleshy fruits, nuts, greens, and underground parts. Little is known about the use of wild food plants by northern Cree and Naskapi.Nutritional data for gathered plants indicate that many of these species exceed conventional plant sources for vitamins and minerals. Vitamin A, vitamin C, calcium, iron, and fibre are particularly well represented in certain gathered plants. Some wild plant foods require special preparation or must be consumed in limited quantities because they contain toxic secondary metabolites.Over 400 plants are used in native medicine. Native medicine consists of rational and ritualistic components. Treatment of physical disorders, whose origin could be determined, was effective. At least 105 medicinal plants have a real effectiveness based on phytochemical constituents. Conifers were the most widely used group of plants in this category. Antibiotic monoterpenes, polyacetylenes and alkaloids, astringent tannins, and analgesic monoterpenes and salicylates are among the most rationally and widely used plant constituents.There is need for more research into nutritional constituents and pharmacological properties to assess the value and potential of plants used by Native People of eastern Canada.
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The traditional medicinal uses of plants by the Inuit of Nunavut, Canada were analysed using quantitative ethnobotanical methodology. Traditional knowledge was collected during interviews with volunteer Inuit informants and from historical interview transcripts. A total of 13 different species were mentioned, which included 1 moss, 1 algae, 1 fungus, and 10 vascular plant species. An informant consensus index value, Fic > 0.7, for many use categories revealed a high level of informant agreement, consistent with a well-preserved oral tradition and low flora biodiversity. The documentation of this information is a useful tool for the preservation of Inuit culture, as well as for the integration of Inuit traditional medicine with Western medical practices in Arctic communities (Inuit Qaujimajatuqangit, IQ).Dans cet article, les auteurs discutent de l'utilisation des plantes médicinales par les Inuits du Nunavut, Canada, en s'appuyant sur une méthode quantitative en ethnobotanique. Le savoir traditionnel a été obtenu lors d'interviews réalisées auprès d'informateurs inuits ainsi qu'à partir d'anciennes interviews retranscrites. Au total, 13 espèces différentes ont été mentionnées, dont 1 bryophyte, 1 algue, 1 mycète et 10 plantes vasculaires. Un index de consensus des informateurs (Fic) a été calculé permettant aux auteurs de montrer que la plupart des catégories d'utilisations possèdent de fortes valeurs de Fic > 0,7 qui indiquent que les informateurs se rejoignent sur l'utilisation de la médecine traditionnelle. Aussi, la tradition orale des Inuits a été bien sauvegardée. La faible diversité floristique contribue également aux valeurs obtenues. L'information recueillie dans cet article permet de documenter et de préserver un savoir traditionnel important pour les Inuits et pour l'intégration de leur médecine à même les cliniques de santé moderne des communautés arctiques, soit l'Inuit Qaujimajatuqangit (IQ).
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Nonenzymatic formation of advanced glycation end products (AGEs) is accelerated under hyperglycemic conditions characteristic of type 2 diabetes mellitus and contributes to the development of vascular complications. As such, inhibition of AGE formation represents a potential therapeutic target for the prevention and treatment of diabetic complications. In the present study, ethanolic extracts of 17 medicinal plants were assessed for inhibitory effects on in vitro AGE formation through fluorometric and immunochemical detection of fluorescent AGEs and N(ε)-(carboxymethyl)lysine adducts of albumin (CML-BSA), respectively. Most extracts inhibited fluorescent AGE formation with IC (50) values ranging from 0.4 to 38.6 µg/mL and all extracts reduced CML-BSA formation but to differing degrees. Results obtained through both methods were highly correlated. Antiglycation activities were positively correlated with total phenolic content, free radical scavenging activity and reduction in malonyldiadehyde levels following oxidation of low-density lipoprotein, but negatively correlated with lag time to formation of conjugated dienes. Together, these results provide evidence that antioxidant phenolic metabolites mediate the antiglycation activity of our medicinal plant collection, a relationship that likely extends to other medicinal and food plants.
Book
Reactive oxygen species (ROS) are produced during the interaction of metabolism with oxygen. As ROS have the potential to cause oxidative damage by reacting with biomolecules, research on ROS has concentrated on the oxidative damage that results from exposure to environmental stresses and on the role of ROS in defence against pathogens. However, more recently, it has become apparent that ROS also have important roles as signalling molecules. A complex network of enzymatic and small molecule antioxidants controls the concentration of ROS and repairs oxidative damage, and research is revealing the complex and subtle interplay between ROS and antioxidants in controlling plant growth, development and response to the environment. This book covers these new developments, generally focussing on molecular and biochemical details and providing a point of entry to the detailed literature. It is directed at researchers and professionals in plant molecular biology, biochemistry and cell biology, in both the academic and industrial sectors.
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The Arctic comprises c20% of North America. The varied physical environment is outlined, and comments are made on the significance of soils and permafrost. Brief notes are given on palaeobotany. The vegetation includes 1) tall shrub tundra (Salix, Alnus and Betula 2-5 m high) along stream banks, steep slopes and lake shores; 2) low shrub tundra (Salix and Betula 40-60 cm high) on slopes and uplands beyond the forest tundra; 3) dwarf shrub heath and tussock tundras on rolling terrain with soils of intermediate drainage; 4) graminoid-moss tundra on poorly-drained soils; and 5) cushion plant-herb-cryptogam polar sedidesert on wind-exposed sites. There are general reductions in plant cover and height, reductions in woody and vascular plant species, and increases in lichens and mosses from the Low to the High Arctic. Plant growth is restricted where soils become saturated in spring and bake hard later in summer. These soils lack N and have few "safe sites' for vascular plants to become established. Comments are made on succession and vegetation response to fire. Standing crop and plant production are described, and there is discussion on life history patterns and physiological adaptations, including reproduction and plant establishment, plant growth and phenology. -P.J.Jarvis
Article
A leaf survey of 206 Rhododendron species, subspecies and varieties showed that the genus possesses a relatively uniform flavonoid pattern. Three compounds which are generally rare in the angiosperms, gossypetin, azaleatin and caryatin, occur in 76, 34 and 10 per cent of the species respectively. Quercetin and leucoanthocyanidins are present in all taxa, while dihydroflavonols are present in 68 per cent, myricetin in 51 per cent and kaempferol in 23 per cent of the sample. Gossypetin is notably absent from the subgenus Pentanthera while caryatin characterises the single subgenus Hymenanthes. Of the three dihydroflavonols, dihydroquercetin and dihydromyricetin are reported in the genus for the first time, the former being isolated as the 3-arabinoside. The flavonols of Rhododendron leaf were found to be present as the 3-arabinosides, 3-rhamnosides, 3-galactosides and 3-glucosides. Simpler phenols were surveyed in leaves of 55 species with the following results: orcinol in 7 per cent, hydroquinone in 9 per cent, rhododendrol in 37 per cent, o-coumaric acid in 19 per cent, gentisic acid in 80 per cent and gallic acid in 84 per cent. Taxonomically, the results generally support the accepted sectional and subsectional classifications, although they suggest that on chemical grounds certain species might be misplaced. Phyletically, the data indicate that the genus still retains a wide range of primitive phenolic characters. Geographically, the separation of R. lochae, the only Australian species, from the rest of the genus in S.E. Asia is reflected in its chemistry.
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IntroductionBiosynthetic aspects of phenolic metabolismStress-induced phenylpropanoid metabolismAntioxidant properties of phenolic compoundsBiological targets of phenolic antioxidantsProoxidant properties of phenolic compoundsAntiherbivore properties of phenolicsConclusions
Article
Free radical scavenging activity of 21 tropical plant extracts was evaluated using 1,1-diphenyl-2-picrylhydrazyl assay (DPPH). Total phenolic compounds and flavonoids were determined using Folin–Ciocalteu and HPLC, respectively. Results of the study revealed that all the plants tested exhibited excellent antioxidant activity with IC50 in the range of 21.3 to 89.6 μg/mL. The most potent activity was demonstrated by Cosmos caudatus (21.3 μg/mL) and Piper betle (23.0 μg/mL) that are not significantly different than that of -tocopherol or BHA. L. inermis extract was found to consist of the highest concentration of phenolics, catechin, epicatechin, and naringenin. High content of quercetin, myricetin, and kaempferol were identified in Vitex negundo, Centella asiatica, and Sesbania grandiflora extracts, respectively. Luteolin and apigenin, on the other hand, were found in Premna cordifolia and Kaempferia galanga extracts. Strong correlation (R = 0.8613) between total phenolic compounds and total flavonoids (R = 0.8430) and that of antioxidant activity of the extracts were observed. The study revealed that phenolic, in particular flavonoids, may be the main contributors to the antioxidant activity exhibited by the plants. Practical Application: Potent antioxidant from natural sources is of great interest to replace the use of synthetic antioxidants. In addition, some of the plants have great potential to be used in the development of functional ingredients/foods that are currently in demand for the health benefits associated with their use.