About Wild RosellaHere is some of the material I studied: 1. Courtesy Plants for a Future (http://www.pfaf.org) Roselle is an aromatic, astringent, cooling herb that is much used in the Tropics. It is said to have diuretic effects, to help lower fevers and is antiscorbutic[74, 238]. The leaves are antiscorbutic, emollient, diuretic, refrigerant, and sedative[269]. The leaves are very mucilaginous and are used as an emollient and as a soothing cough remedy. They are used externally as a poultice on abscesses[269]. The fruits are antiscorbutic[269]. The flowers contain gossypetin, anthocyanin, and the glycoside hibiscin[269].
These may have diuretic and choleretic effects, decreasing the viscosity of the blood, reducing blood pressure and stimulating intestinal peristalsis[269]. The leaves and flowers are used internally as a tonic tea for digestive and kidney functions[74, 238]. Experimentally, an infusion decreases the viscosity of the blood, reduces blood pressure and stimulates intestinal peristalsis[240]. The ripe calyces are diuretic and antiscorbutic[269]. The succulent calyx, boiled in water, is used as a drink in the treatment of bilious attacks[269]. The seeds are diuretic, laxative and tonic[269]. They are used in the treatment of debility[269]. The bitter root is aperitif and tonic[269]. The plant is also reported to be antiseptic, aphrodisiac, astringent, cholagogue, demulcent, digestive, purgative and resolvent[269].
It is used as a folk remedy in the treatment of abscesses, bilious conditions, cancer, cough, debility, dyspepsia, dysuria, fever, hangover, heart ailments, hypertension, neurosis, scurvy, and strangury[269].
One report says that the plant has been shown to be of value in the treatment of arteriosclerosis and as an intestinal antiseptic, though it does not say which part of the plant is used[269]. Simulated ingestion of the plant extract decreased the rate of absorption of alcohol, lessening the intensity of alcohol effects in chickens[269].
References are published below: 2. Information Courtesy of Renaissance Herbs USA.
Traditional Uses
The bracts and the thick, fleshy, red calyces (enveloping sepals) that form
the flower are commonly referred to simply as “roselle flower” and are
usually dried before use. As early as the 1930s, an infusion of the calyces
was noted as a traditional African treatment for the relief of cough and
bronchitis (Hutchinson and Dalziel, 1937), as well as hypertension (Morton,
1974; Sharaf, 1962); a use that may be even older in Iran (Haji Faraji and
Haji Tarkhani, 1999). In Thailand, the calyces of “krachiap” are used in the
treatment of high cholesterol levels, urinary bladder stones, kidney stones,
and as an expectorant (Farnsworth and Bunyaprephatsara, 1992). In Europe,
the calyces have been used in herbal medicine for treating high blood
pressure, heart diseases, nerve diseases, calcified arteries (El-Saadany et al.,
1991), arthritis (Stirn, 1978), arteriosclerosis (Perry and Metzger, 1980),
circulatory disorders, poor appetite, colds, catarrhs of the stomach and upper
respiratory tract, for dissolving phlegm, and as a diuretic and mild laxative.
Activity Studies
Cardioprotective and Related Effects
Antihypertensive Activity
Spontaneously hypertensive (SH) Wistar-Kyoto rats administered a water
extract of the calyces at an oral dosage (by gavage) of 1000 mg/kg/day for
up to 60 days showed significant decreases in diastolic and systolic blood
pressure (BP), body weight, urine output, and serum creatinine levels,
whereas serum uric acid levels were significantly increased. In
normotensive rats, the same dosage was found to significantly reduce
systolic and diastolic BP and water intake and to significantly increase
serum uric acid levels. Although serum levels of albumin, protein and
glucose were slightly raised, the changes were not significant.
The decrease in serum creatinine levels in both SH and normotensive rats
suggests that roselle improved kidney function; however, the increase in
serum uric acid suggests that prolonged use at such a high dosage could
result in urate kidney stone formation (see Safety) (Onyenekwe et al., 1999),
contrary to the use of roselle in folk medicine against kidney stones
(Farnsworth and Bunyaprephatsara, 1992).
An infusion of the dried and ground “petals” of roselle prepared in water at
100ºC was administered at a daily dosage of 250 mg/kg in the drinking
water of male Sprague-Dawley rats in a model of hypertension (renovascular
hypertension from renal artery clamping). After 2 weeks of treatment with
roselle, BP began to show a significant decrease and after 6 weeks diastolic
and systolic BP showed no significant difference compared to the control.
In addition, roselle significantly attenuated cardiac hypertrophy in the
hypertensive rats. Whereas the heart weight in the roselle-treated rats was
not significantly different from the normotensive control, it was significantly
less compared to the untreated renal-hypertensive group. Roselle had no
significant effect on the urine flow rate, kidney weight, body weight, and
hematocrit compared to the untreated hypertensive group, and plasma
electrolytes and serum creatinine showed no significant differences
compared to the normotensive control group. Plasma levels of potassium in
the roselle group showed a tendency to be higher (5.2 mmol/L), but were not
significantly different compared to the hypertensive (4.7 mmol/L) or
normotensive controls (4.4 mmol/L) (Odigie et al., 2003).
Antihypertensive activity has been demonstrated in a number animal studies
using various extract preparations of the calyces; however, the routes of
administration used, whether intravenous (Adegunloye et al., 1996; Ali et
al., 1991) or intraperitoneal (Jonadet et al., 1990; Sharaf, 1962), are not
applicable to human oral use and what mechanisms were proposed as the
basis of the activity from such studies must therefore be viewed as
circumspect. A study using isolated rat aortic rings from normotensive rats
found evidence to suggest that the relaxation of vascular smooth muscle
contractile activity from a water extract roselle “petals” to which they were
exposed is the result of both endothelium-dependent and –independent
mechanisms (Obeifuna et al., 1994). A similar, more recent study using a
methanolic extract of the calyces in isolated aortic rings of male
spontaneously hypertensive rats also found a vasodilator effect involving
endothelium-dependent and –independent pathways with the endotheliumdependent
vasodilator effect the result of “activation of endothelium-derived
nitric oxide/cGMP-relaxant pathway”, and that of the endotheliumindependent
effect possibly due to “inhibition of calcium (Ca+2) influx (Ajay
et al., 2006).
Activity-guided isolation of the active components of roselle is lacking;
however, among the various constituents of the calyces (Du and Francis,
1973), the anthocyanin delphinidin has shown potent endotheliumdependent
vasorelaxation, relaxing vessels of isolated thoracic aorta of male
Wistar rats precontracted with norepinephrine by 80.27% (Andriambeloson
et al., 1998). In bovine aortic endothelial cells, delphinidin caused cytosolic
free calcium to increase by increasing entry of calcium and releasing it from
intracellular stores (Martin et al., 2002). In human endothelial cells
(umbilical vein), delphinidin exhibited a concentration-dependent inhibition
of endothelial proliferation and cell migration of basal cells and in those
induced to proliferate by vascular endothelial growth factor (VEGF).
Delphinidin also inhibited neovascularization in developing chicken embryo.
The effective in concentration (10 mg/mL) in all three tests was calculated to
be achievable in vivo from consuming 6 glasses of red wine. Together,
these results suggest that delphinidin functions as an angiogenesis inhibitor
and may therefore be a value in the treatment of diseases in which new
capillary growth is a pathological characteristic (Favot et al., 2003), such as
atherosclerosis, ischemic heart disease, cancer (Verheul and Pinedo, 2003),
diabetic retinopathy, and age-related macular degeneration (Eichler et al.,
2006).
Cholesterol-lowering Activity
A number of animal studies have shown that roselle significantly reduces
serum cholesterol levels (Carvajal-Zarrabal et al., 2005; Chen et al., 2003;
El-Saadany et al., 1991; Hirunpanich et al., 2006). A water extract of roselle
containing 5% anthocyanins was administered to male Sprague-Dawley rats
fed a high-fructose diet and a another group fed a high-cholesterol diet (lard
oil and cholesterol) for 12 weeks. Added to the diets at concentrations of 10
and 20 g/kg feed, the extract significantly suppressed the fructose-induced
increase in serum triglyceride levels. The higher concentration significantly
lowered LDLc levels and both the low and high concentration of the extract
significantly decreased the ratio of LDL-c/HDL-c (by 27.6% and 48.3%,
respectively). In the rats fed a high-cholesterol diet, both the lower and
higher concentration of extract in the feed significantly decreased the total
cholesterol level, LDL-c, and the ratio of LDL-c/HDL-c; the latter by 52.5%
and 63.6%, respectively. With the exception of LDL-c, in each
measurement the effect was of greater significance from the higher dose
(Chen et al., 2004).
In a model of hypercholesterolemia in male albino rats induced by adding a
mixture of cholic acid and cholesterol to their feed for 12 weeks, the
addition of whole, dried, dark red calyces (Egyptian “brown” variety) to the
diet in place of starch in the feed for a subsequent 9 weeks (5% and 10% of
feed) resulted in significant decreases in total lipids, triglycerides, and
cholesterol, despite continued feeding of the high cholesterol diet. Although
the decreases were somewhat greater in the 10% feed group, the changes
were not of greater statistical significance. Therefore, only figures from the
5% group are provided here. Compared to the high-cholesterol group
without roselle, the 5% feed significantly decreased total serum lipids
(49.6%) and cholesterol (55.2%) and triglyceride levels of the blood (60%).
Significant decreases in total lipids, cholesterol, and triglycerides were also
found in the liver (34%, 55.5%, 40%, respectively) whereas only cholesterol
and triglyceride levels significantly decreased in the heart (27.8% and 27%,
respectively), kidneys (43.2% and 20.5%, respectively), and spleen
(93.44%% and 16%, respectively) (El-Saadany et al., 1991).
Serum levels of hepatic enzymes increased by the high-cholesterol diet were
significantly decreased by roselle in the case of GPT after 6 weeks (12.5%)
but not after 9 weeks, and GOT (28.8%) and alkaline and acid phosphatase
were significantly decreased after 9 weeks (58.2% and 9.33%, respectively).
The values of each were nearly restored to normal. Serum levels of uric acid
and creatinine were reduced in the groups fed roselle, possibly due to
improved renal function; however, the decreases were not statistically
significant. Serum levels of globulin and protein were significantly
increased by the high-cholesterol diet. Whereas roselle significantly
decreased the globulin level (31.7%), only the higher dosage significantly
lowered the serum protein level (23.7%). Serum free amino acid levels were
also significantly decreased in the roselle group (25.9%), yet in the
hypercholesterolemic rats not fed roselle the levels were increased relative to
the normal control (8.4%). The authors commented that it seems
hypercholesterolemic rats have difficulty assimilating amino acids in the
diet. Roselle feed also produced a moderate yet significant increase in
phospholipid levels, as found in the serum (44.5%), heart (20.7%), kidneys
(7.8%), and liver (34.6%), but not in the brain or spleen; the increases likely
representative of corrections in lipid metabolism (El-Saadany et al., 1991).
Male Sprague-Dawley rats were fed a high-cholesterol diet for 1 week
before being divided into groups with or without feed containing an ethanol
extract of the air-dried calyces (Sudan variety) at 5, 10, and 15 g/100 g of the
diet (in place of corn starch) for 4 weeks (ad libitum). A control group was
fed only the high-cholesterol diet and the results in the various groups were
compared. After 4 weeks, significant decreases were evident in levels of
serum LDL-c (40%, 42%, and 44%, respectively), triaglycerols (36%, 51%,
and 48%, respectively), and total lipids (35%, 16%, and 12%, respectively)
in the roselle groups compared to the cholesterol-fed control group, whereas
the total cholesterol level was only significantly reduced in the lowest
dosage group (43%). Although no significant changes were found in HDL-c
or phospholipid levels, the former increased 7% and the latter decreased
23% in the lowest roselle dosage group (Carvajal-Zarrabal et al., 2005).
Food intake was significantly reduced only in the highest roselle dosage
group (15.8%). In the middle and highest dosage groups, significant
decreases were found in fecal dry weight per day (34.8% and 40.5%,
respectively), food efficiency (59% and 84%, respectively), and body weight
gain (59% and 87%, respectively). However, in the lowest dosage group the
only significant change among the same parameters was a 12% increase in
the fecal dry weight per day (Carvajal-Zarrabal et al., 2005). A previous
animal study of roselle also failed to show any inhibition of weight gain
from comparatively lower dosages (0.5% and 1% of the diet) (Chen et al.,
2003).
As to what might be responsible for the changes in body weight gain,
Carvajal-Zarrabal et al. (2005) hypothesized that the effect might be the
result of a decrease in food intake or a suppressive effect of the extract on
feeding, but only in the highest dosage group. As for the lower gain in body
weight in either of the higher dosage groups, one possibility raised by the
authors is the inhibition of a-amylase activity and the breakdown of
polysaccharides, thereby reducing carbohydrate absorption (Carvajal-
Zarrabal et al., 2005). A 50% aqueous methanol extract of the dried flowers
(obtained in Thailand) inhibited in vitro porcine pancreatic a-amylase
activity by 100%. Through isolation of the active principles, a-amylase
inhibition was shown from a major constituent of the extract known as
hibiscus acid, a lactone form of (+)-allo-hydroxycitric acid, otherwise
named (2S,3R)-HCA or (+)-HCA (Hansawasdi et al., 2000). In a human cell
(Caco-2) model system, hibiscus acid inhibited the breakdown of starch
which is made up of polysaccharides (Hansawasdi et al., 2001).
Further to the possible cause of the significant inhibition of weight gain by
roselle in rats fed a high-cholesterol diet, Carvajal-Zarrabal et al. (2005) also
hypothesized a synergy of effects resulting from the non-metabolized
polysaccharides and potential relaxant effects of roselle on smooth muscle
(Carvajal-Zarrabal et al., 2005); the latter demonstrated to be a dosedependent
effect of a methanol extract of roselle on rat ileal strip and from
intraperitoneal administration in rats which reduced intestinal transit and
potentiated the cathartic effect of castor oil (Salah et al., 2002). However, a
freeze-dried water decoction of the calyx at an oral dose of 400 and 800
mg/kg only produced mild cathartic activity and significant peristaltic
activity was absent (Haruna, 1997).
In attempting to offer an explanation for the significant decrease in
triaglycerols which was seen in the lowest to highest dosage groups at 36%,
51%, and 48%, respectively, Carvajal-Zarrabal et al. (2005) hypothesized
that hibiscus acid or “(+)-HCA” undergoes racemization by enzymes in the
intestinal flora to generate (-)-HCA. As the authors point out, (-)-HCA has
previously shown a hypotriglyceridemic effect in rats (Sullivan et al., 1972,
1973). However, because in this regard the effect of roselle was not dosedependent,
the middle dosage showing greater activity than the highest
dosage, the authors advised that their racemization hypothesis requires
further study (Carvajal-Zarrabal et al., 2005).
A further hypothetical explanation for the decrease in triaglycerol levels
could be based in part on the ability of roselle to inhibit and delay in vitro
adipocyte differentiation and subsequently their ability to accumulate
triglyceride. Preadipocyte cells undergo differentiation to become fat cells
with the ability to accumulate triglyceride and form fat droplets. Cultured
preadipocytes (3T3-L1 cells) treated with an adipogenic hormone mixture
(isobutylmethylxanthine, insulin, and dexamethasone) were transformed into
adipocytes in 6-8 days. With the addition of a freeze-dried water extract of
roselle (100 mg/mL) at the start of treatment with the hormone mixture and
at intervals of 48 h, cytoplasmic fat accumulation was significantly
inhibited, with accumulation of triglycerides only 27.6% the amount in
control cells. Tests showed that the effect was not the result of cytotoxic or
antiproliferative activity which were absent with high concentrations of
roselle (> 0.5 mg/mL) (Kim et al., 2003).
Further evidence of the inhibitory activity of roselle was demonstrated in
preadipocytes that had already differentiated for 4 days and were further
induced to differentiate by treatment with insulin. In these cells, roselle
inhibited intracellular accumulation of triglyceride by 50% relative to the
control. Subsequently, researchers sought to determine the activity of
roselle on the two major adipogenic transcription factors, PPARg and
C/EBPa In preadipocytes treated with insulin, roselle (100 mg/mL) reduced
the expression of PPARg and the effect was determined to be specific.
Roselle also suppressed the expression of C/EBPa , an effect that persisted
for 8 days. The effect on C/EBPa expression was measured in strict
accordance with the first appearance of cytoplasmic fat. The authors note
that this transcriptional factor appears to underlie the entire process of
adipocyte differentiation, a conclusion further supported by the effect of
roselle, for by inhibiting its expression terminal adipocyte differentiation
was inhibited (Kim et al., 2003).
Antiatherosclerotic Activity
Evidence of antiatherosclerotic activity of roselle is found in both in vitro
and in vivo studies. In vitro inhibition of hydrogen peroxide-induced lipid
peroxidation was demonstrated in erythrocytes incubated with a methanol
extract of the air-dried calyx. The extract significantly and dosedependently
(0.2-0.8 mg/mL) inhibited malondialdehyde (MDA) formation
(Suboh et al., 2004). Oxidatively modified low density lipoprotein (oxLDL)
is a major factor in atherosclerosis and stimulates its development. Potent in
vitro inhibition of copper sulfoxide-induced oxidation of rat LDL was shown
from an aqueous extract of the dried calyces and the effect was dosedependent
(0.1-0.5 mg/mL). At a concentration of 0.1 mg/mL, the
formation of thiobarbituric acid reactive substances (TBARs) was inhibited
by about 32% and by 60% from 0.25 mg/mL. Complete inhibition of
TBARs formation was found from a concentration of 5 mg/mL (Hirunpanich
et al., 2005).
A water extract of the sun-dried calyx (5 mg) showed significant in vitro
inhibition of linoleic acid peroxidation. At 12.5 days the activity was
stronger than that of 200 ppm of either BHA or DL-a-tocopherol. In the
same assay, the total phenolic fraction of the extract (14.4 mg/g of calyx)
inhibited linoleic acid peroxidation by 93%. In a liposome model system
using egg lecithin, the extract (1 mg) inhibited peroxidation by 62.8%, as
evident in the significant reduction of MDA formation (Duh and Yen, 1997).
Using the total anthocyanin fraction of the dried calyces (standardized to
cyanidin and delphinidin), in vitro concentrations of 0.5-1.5 mg/mL
significantly inhibited TBARs formation in human LDL (obtained from
healthy volunteers) oxidized by copper sulfoxide. In the same model,
concentrations of 1-2 mg/mL significantly inhibited oxidation as measured
by electrophoretic mobility; however, lower concentrations were ineffective.
When antioxidative activity of the anthocyanin fraction was measured
according to fragmentation of apoprotein B (apoB, the main protein in
LDL), 0.25, 0.5, and 1 mg/mL inhibited fragmentation by 45%, 49%, and
71%, respectively (Chang et al., 2006).
oxLDL contributes to apoptosis of cells in atherosclerotic lesions and to
plaque rupture. Since macrophages are one of the populations effected by
oxLDL, the total anthocyanins were tested for the ability to reduce
cytotoxicity of oxLDL and, thereby, premature death (apoptosis) of
macrophages caused by oxLDL. Compared to untreated macrophages
(RAW 264.7 cells) exposed to oxLDL, cell viability was significantly
increased by the anthocyanins (0.01-0.5 mg/mL), suggesting a potential
preventive activity against atherosclerosis (Chang et al., 2006).
The antiatherosclerotic activity of roselle was examined in New Zealand
white male rabbits fed a high-cholesterol diet for 10 weeks, with and without
a freeze-dried water extract of roselle. Dosages were based on what would
be pharmacologically suitable for humans (0.5% and 1% of the diet). The
extract was found to contain 2.5% anthocyanins, 1.43% flavonoids, and
1.7% polyphenolic acids. A decrease in atherosclerosis was observed in the
roselle groups as evidenced by the following: a decrease in the quantity of
foam cells in atherosclerotic lesions of the thoracic aorta; fewer numbers of
oxidized LDL-positive macrophage-derived foam cells in lesions of the
aortic arch; the absence of mild calcification of the media of arteries; and a
decrease in atherosclerotic lesions on the inner surface of the thoracic aorta
of approximately 20% to 25% (Chen et al., 2003).
From the 1% dosage, roselle extract inhibited plasma LDL-c by 55% and
total cholesterol by 28%. Because either dosage reduced LDL-c levels to a
similar degree, the lower dosage may have produced the maximal effect.
The LDL-c/HDL-c ratio significantly decreased in the 0.5% roselle group,
but not in the 1% group. At 1% of the diet, roselle reduced plasma
triglyceride levels by 53% and almost restored them to normal. The
decrease in triglyceride levels from the lower dosage was not significantly
different compared to the 1% dosage and all together the decreases ranged
from 46% to 59%. The authors concluded that overall, the
antiatherosclerotic activity of the roselle extract in rabbits was comparable to
that of the cholesterol-lowering drug probucol. Body weight and daily food
intake in any of the groups showed no significant differences and serum
HDL-c levels showed no change (Chen et al., 2003).
The potential antiatherosclerotic activity of a water extract of the dried
calyces obtained in Thailand was examined in hypercholesterolemic male
Sprague-Dawley rats continuously administered cholesterol. The extract
was administered at daily intragastric dosages of 250, 500 and 1,000 mg/kg
for 6 weeks. In preliminary tests, a higher dosage of the roselle extract
(2,000 mg/kg i.g.) was no more hypolipidemic than 1,000 mg/kg. Because
the higher dosage produced weight loss and diarrhea, the lower dosage was
chosen as the maximum effective dose. None of the dosages had any effect
of HDL-c levels and only the highest dosage significantly lowered the
atherogenic index. The lowest dosage failed to lower total cholesterol, LDLc,
or triglyceride levels; however, the higher dosages lowered total
cholesterol levels by 22% and 26%, respectively, LDL-c by 22% and 32%,
respectively, and triglyceride levels by 33% and 28%, respectively. The
decreases in lipid parameters from either dosage were statistically of equal
significance (Hirunpanich et al., 2006).
TBARs formation in LDL obtained from the hypercholesterolemic rats was
significantly inhibited by each of the dosages of roselle, thereby
demonstrating in vivo antioxidant activity. The results were equally
significant regardless of the dosage and equal in significance to the results
obtained from atorvastatin (10 mg/kg i.g.), a potent hypolipidemic drug with
a known ability to inhibit the oxidation of LDL and to inhibit HMG-CoA
reductase. TBARs formation was lowered by atorvastatin by about 35% and
by the respective dosages of roselle by 45% (250 mg), 23% (500 mg/kg),
and 25% (1,000 mg/kg). However, ex vivo copper-induced oxidation of
LDL and conjugated diene formation were only slightly inhibited by the
extract following any of the dosages (Hirunpanich et al., 2006).
As to what constituents might be responsible for the hypolipidemic activity
of the extract, the authors speculated that the high content of pectin in the
calyces is likely involved, along with mucilage polysaccharides
(Hirunpanich et al., 2006). However, studies supporting their hypothesis are
lacking. For example, although hypocholesterolemic effects of pectin in
humans have been observed from an average dose of 4.7 g/day (Brown et
al., 1999), the highest amount of crude pectin in the calyces is reported to be
2% to 4%, whether in Thai, Senegalese, Indian, Middle American, or
Egyptian strains of the plant (El Afry et al., 1980). No studies were found
on the potential hypocholesterolemic activity of the polysaccharides of
roselle. Antioxidant Activity
An ethanol extract of the dried flowers of roselle from Nigeria was further
extracted to obtain a chloroform-soluble fraction (HSCF) and an ethyl
acetate-soluble fraction (HSEA). In vitro scavenging of hydroxyl radical,
hydrogen peroxide, and superoxide anion radical production was found with
greater potency from HSEA (IC50 = 90, 91, and 98 mg/mL, respectively)
compared to HSCF (IC50 = 100, 110, and 130 mg/mL, respectively). By
comparison, the potency of vitamin E was considerably less (IC50 = 520,
245, and 375 mg/mL, respectively), as was quercetin (IC50 = 250, 345, and
480 mg/mL, respectively). When compared for total antioxidant activity in a
peroxidase system for equivalent activity to that of vitamin C, HSEA was
significantly more potent than HSCF (value = 8.6 vs. 4.6, respectively) and
held a significantly greater content of total phenolics (201.4 vs. 98.5 mg/g,
respectively) (Farombi and Fakoya, 2005).
Using the dried calyces obtained from Egypt, a decoction and a series of
cold infusions (2 g dried petals in 100 mL water) were tested for antioxidant
activity using Briggs-Rauscher oscillating reaction, a method developed for
wine. The reaction generates hydroperoxyl radicals in a medium to simulate
pro-oxidant conditions. According to the Briggs-Rauscher Antioxidant
Index (BRAI), overall antioxidant potential was less than that of red wine
and greatest from the 3-minute (100ºC) decoction measured at 37ºC (BRAI
= 665) and the 30- and 180-minute cold infusions measured at 37ºC (BRAI
= 571 and 522, respectively). Longer extraction times failed to produce
increased activity. A 30-minute cold infusion with the addition of 12% v/v
ethanol to simulate wine showed no greater activity than the 180-minute
cold infusion; however, 3 days later it was the only preparation without signs
of decay. Since the quantity of gallic acid equivalents corresponded to the
degree of BRAI, it is reasonable to suppose that that polyphenol content
corresponded to the antioxidants activity. In terms of acidity, the extraction
methods showed no significant differences, likely because the acids are more
readily extractable in water. For example, the 30-minute cold infusion and
the decoction showed comparable pH and total acidity values (Prenesti et al.,
2007).
A water extract of the sun-dried calyces exhibited dose-dependent
scavenging of the DPPH radical (1,1-diphenyl-2-picrylhydrazyl) with
concentrations of 5, 15, and 25 mg/mL inhibiting radical formation by
49.9%, 771.%, and 88.6%, respectively (Duh and Yen, 1997). From an
ethanol extract of the dried flowers obtained in an herbal pharmacy in
Taiwan, an ethyl-acetate-soluble fraction showed greater scavenging of the
DPPH radical (EC50 = 0.017 mg/mL) than either a chloroform-soluble
fraction or an insoluble ethyl acetate fraction. However, in the xanthine
oxidase (XO) assay in which XO “catalyses the oxidation of hypoxanthine to
xanthine and of xanthine to uric acid”, the chloroform-soluble fraction was
the most potent inhibitor of XO activity (EC50 = 0.742 mg/mL) (Tseng et al.,
1997).
The total anthocyanin fraction of the dried calyces (standardized to cyanidin
and delphinidin) dose-dependently scavenged the DPPH radical by greater
than 50% at concentrations of 0.05 mg/mL and more. Specifically, 0.05,
0.075, 0.10, 0.50, and 1 mg/mL scavenged the radical by 62.4%, 83.1%,
95.4%, >100%, and >100%, respectively (Chang et al., 2006). However,
others reported that the total anthocyanins of the dried flowers at a
concentration of 0.20 mg/mL quenched the DPPH radical by about 50%
(Wang et al., 2000).
The petals of a cultivar of roselle (F141) grown in Taiwan were dried (50ºC
for 36 hours) before preparing a hot water extract made by boiling them in
water for 3 minutes (1 g/100 mL). The antioxidant activity of the extract in
the ferric reducing ability of plasma (FRAP) assay was shown to correlate
with the results obtained in the ORAC (oxygen radical absorbance capacity)
assay and total antioxidant status (TAS) method. The results clearly suggest
that either of these methods would accurately measure the antioxidant
activity of roselle. Preliminary tests showed that extracts of the petals
prepared at 3-5 minutes of boiling held the maximum antioxidant activity.
Using the FRAP assay, the antioxidant activity of the extract was compared
to those of coffee and tea also prepared by boiling in water for 3 minutes (1
g/300 mL). Samples of green and black teas, bottled orange juice, and red
and white wines obtained from commerce were used for further
comparisons. Red wine showed a value of about 20 which was by far the
greatest of all the substances tested. Among the teas, green tea held the
greatest antioxidant activity with a value of about 8, which was comparable
to that of rose wine and orange juice. The value of the roselle extract was
about 16%-25% that of green tea or about 1.28-2 (Tsai et al., 2002).
When the anthocyanin content of the roselle extract correlated with
antioxidant capacity in the FRAP assay, efforts were made to fractionate the
extract to characterize the component anthocyanins responsible. Delphinidin
3-sambubioside was responsible for the red pigmentation of the extract and
constituted 85% of the anthocyanins while cyanidin 3-sambubioside
(provisionally identified) appeared to account for the pink pigmentation.
Respectively, they accounted for 48% and 3% of the antioxidant activity
obtained in the FRAP assay, while the remaining 24% of activity was
attributed to brown pigments composed of phenolics. Total phenolic
compounds in the extract (23 mg/g dry weight) was similar in quantity to
that of currents, strawberries, and other fruits. Stored at 20ºC for 15 weeks,
the petals still held 90% of their original phenolic compounds. Dried at
75ºC and stored for 15 weeks at 40ºC, only 15% of the phenolics were lost;
however, the percentage of anthocyanins fell from about 80% to 50% while
the content of other phenolics increased. This result was consistent with the
known ability of some anthocyanins to undergo transformation during
storage and appear in the form of polymerized phenolics. The authors
concluded that roselle petals represent “a good source of antioxidants” and
that although relatively stable during storage, the antioxidant activity “will
ultimately depend on the bioavailability of the anthocyanins” (Tsai et al.,
2002) (see Pharmacokinetics). Antimutagenic Activity
In a study on the potential antigenotoxic activity of roselle, a chloroformsoluble
fraction (HSCF) and an ethyl acetate-soluble fraction (HSEA) of an
ethanol extract of the dried flowers was administered to rats (100 or 250
mg/kg p.o. by gavage) for 6 days while another group received vitamin C
(200 mg/kg p.o. by gavage). The extract fractions significantly inhibited the
formation of micronucleated polychromatic erythrocytes induced by sodium
arsenite (2.5 mg/kg p.o. by gavage) and even after 24 hours, the rate of
inhibition from the extracts (60% and 70%, respectively) was greater than
that of vitamin C (50%) (Farombi and Fakoya, 2005).
Various fractions of an ethanol extract of the dried flowers obtained from an
herbal pharmacy in Taiwan were shown to inhibit tert-butyl hydroperoxideinduced
unscheduled DNA synthesis in rat hepatocytes. While significant
inhibition of DNA damage was evident in most cases from 0.10 and 0.20
mg/mL of the extracts, greatest inhibition was found from a ethyl acetatesoluble
fraction (40% and 64%, respectively) and a chloroform-soluble
fraction (35% and 60%, respectively) (Tseng et al., 1997).
Hepatoprotective Activity
From an ethanol extract of the dried flowers obtained in an herbal pharmacy
in Taiwan, an ethyl-acetate-soluble and a chloroform-soluble fraction (0.10
and 0.20 mg/mL) significantly inhibited tert-butyl hydroperoxide-induced
leakage of lactate dehydrogenase (LDH) in cultured hepatocytes of rats. The
same fractions also significantly inhibited lipid peroxidation in the
hepatocyte cultures, as evident in the significant decreases of
malondialdehyde (MDA) formation. In each test, the higher concentration
showed greater statistical significance than the lower concentration (p < 0.01
vs. p < 0.05) (Tseng et al., 1997). Rat primary hepatocytes pretreated with
the total anthocyanins of the dried flowers (0.10 and 0.20 mg/mL) also
showed significant protection from the increases in MDA and LDH induced
by tert-butyl hydroperoxide (t-BHP) (Wang et al., 2000).
An ethanol extract of the dried flowers of roselle from Nigeria was further
extracted to obtain a chloroform-soluble fraction (HSCF) and an ethyl
acetate-soluble fraction (HSEA). In vitro lipid peroxidation of rat liver
microsomes (CCl4-NADPH-stimulated system) was shown from either
fraction at 25 mg/mL which inhibited peroxidation by 32% and 38%
respectively, and at 100 mg/mL, by 80% and 89%, respectively (Farombi
and Fakoya, 2005).
Inhibition of lipid peroxidation of the liver was demonstrated in male Wistar
rats orally administered 100 mg/kg/day and 250 mg/kg/day of HSCF and
HSEA. MDA production resulting from liver lipid peroxidation (induced by
FeCl2-ascorbic acid-ADP mixture, i.p.) was significantly inhibited by
simultaneous treatment of the rats with either dosage of either extract
fraction. Inhibition of MDA formation was comparable from HSEA (250
mg: 41.5% inhibition; 100 mg: 21.7% inhibition) and HSCF (250 mg: 39.1%
inhibition; 100 mg: 21.2% inhibition). Their activity was equally significant
and the higher dosages produced protective activity comparable to that of atocopherol
(100 mg/kg/day; 46.3% inhibition) (Farombi and Fakoya, 2005).
In a rat model of chronic fibrosis (carbon tetrachloride-induced), the
antifibrotic activity of a water extract of roselle containing 1.43%
flavonoids, 1.7% polyphenols, and 2.5% anthocyanins was compared to that
of silymarin. Along with twice-weekly treatment with CCl4, for 7 weeks,
male rats were administered roselle as part of their daily diet at
concentrations of 0%, 1%, 2%, and 5% or silymarin (200 mg/kg p.o. 4 times
per week). Immediately after the 7th week, CCl4 was withdrawn and roselle
and silymarin were continued for a further 2 weeks. The results at 9 weeks
showed that the extract produced a dose-dependent decrease in lipid
peroxidation as evidenced by the decrease in TBARs formation in the liver
which were nearly restored to normal levels in the group receiving the 5%
dose. The effect of the 2% dose was equally significant (p < 0.01) and the
decrease in TBARs from the 1% dose was equal in significance to that of
silymarin (p < 0.05). Both silymarin and the 2% and 5% doses of roselle
significantly ameliorated the decrease in glutathione (GSH) levels of the
liver. The increase in serum levels of aspartate aminotransferase (AST)
induced by CCl4 was dose-dependently decreased by the roselle extract.
While each dose was equal in significant to the decrease in rats administered
silymarin (each p < 0.01), the decreases produced by two highest doses of
roselle showed little difference compared to those from silymarin. The
CCl4–induced increase in serum alanine aminotransferase levels (ALT) was
also dose-dependently decreased by roselle. The decreases from the higher
doses were equally significant to those in the group administered silymarin
(p < 0.01). While still significant (p < 0.05), the decrease in ALT from
lower dosage of roselle was about half that of either silymarin or the highest
dose of the roselle extract. In the MTT assay, no cytotoxicity to hepatic
stellate cells was evident from concentrations of the roselle extract at 2
mg/mL or less. In isolated hepatocytes, treatment with the extract at 4
mg/mL had no effects. Finally, in the severity scores of histopathological
evidence of liver fibrosis in the rats treated with roselle or silymarin, the
incidence of fibrosis was significantly reduced in all the treatment groups
(each p < 0.01). The score in the group administered the lowest dosage of
roselle was about one quarter the score in the CCl4–treated control group and
the incidence of fibrosis in the other treatment groups was zero. Similarly,
the incidence of fatty metamorphosis in the lowest roselle dosage group was
about half that of CCl4–treated control group (p < 0.05) whereas the
incidence in the other groups was zero (each p < 0.01) (Liu et al., 2006).
A water extract of the dried flowers obtained from a herb store in Cairo,
Egypt was tested in a rat model of acute hepatotoxicity induced by
administration of the pro-oxidant immunosuppressant azothioprine (AZP).
Male Wistar rats were administered the extract of roselle (10 mL /kg p.o. by
gavage, equivalent to 540 mg/kg) daily for 5 weeks. One hour after the first
dose, they were treated with a single dose of AZP (50 mg/kg i.p.). Roselle
significantly ameliorated increases in serum AST and ALT activity (p <
0.05) induced by AZP, reducing the increase in AST by about 37% and the
increase in ALT by 100%. According to hepatic levels of MDA, liver lipid
peroxidation in the rats was completely inhibited by roselle. Levels of
endogenous antioxidants in the liver were significantly decreased by AZP.
However, hepatic glutathione (GSH), superoxide dismutase (SOD), and
catalase (CAT) activities in the group treated with roselle showed no
significant decrease. For example, CAT activity was 71% normal (vs.
34.21% in the AZP group) and the decrease in SOD was ameliorated by
about 63%. Upon histopathological examination, necrotic changes seen in
the AZP group were prevented in the group treated with roselle plus AZP.
With the exception of a few degenerated cells, the livers of the roselletreated
rats were normal (Amin and Hamza, 2005).
Male Sprague-Dawley rats were treated with the total anthocyanin fraction
of the dried flowers (50, 100, and 200 mg/kg p.o. by gavage) for 4
consecutive days before treatment with t-BHP (0.2 mmol/kg i.p.) on the 5th
day. The increase in hepatic MDA levels was significantly ameliorated by
each dosage of the anthocyanins. Although the t-BHP-induced decrease in
hepatic GSH was only significantly ameliorated in the highest anthocyanin
dosage group, the level of GSH was higher than that of the untreated control
group. The t-BHP-induced increase in serum levels of ALT was only
significantly decreased by the highest dosage of anthocyanins and of AST by
the two highest dosages (Wang et al., 2000)
The potential protective effects of roselle and the total anthocyanin fraction
against paracetamol (acetaminophen)-induced hepatotoxicity was examined
in male Wistar rats. An infusion was prepared of the dried calyces obtained
in Saudi Arabia by allowing 10 g to steep at room temperature for 24 hours
in distilled water (990 mL). Fresh infusions were prepared daily throughout
the study and administered to the rats in lieu of drinking water (10% w/v) for
up to 4 weeks before the administration of paracetamol in a single dose (700
mg/kg p.o.) (Ali et al., 2003). The total anthocyanins were extracted
according to previous published methods (Tseng et al., 1997) and dissolved
in distilled water for oral administration at dosages of 50-200 mg/kg for 5
consecutive days before administration of paracetamol on the 6th day.
Paracetamol significantly decreased hepatic GSH and significantly increased
the liver weight and serum ALT, AST, and sorbitol dehydrogenase (SD).
Pretreatment with the infusion of roselle for 2, 3 and 4 weeks significantly
inhibited the decrease in hepatic GSH and the increase in liver weight.
Serum ALT and AST were only significantly decreased in the group
pretreated with roselle for 4 weeks. Levels of SD were significantly
decreased only in the groups pretreated for 3 or 4 weeks. However, the
histology of the liver revealed no difference compared to rats administered
paracetamol and water. In the rats pretreated with the total anthocyanins of
roselle, hepatic GSH levels were significantly and dose-dependently
protected in all the dosage groups and in the highest dosage group the level
attained was 88% of the control group treated with water. Liver weight and
serum ALT, AST, and sorbitol were significantly decreased only in the
groups administered the total anthocyanins at 100 and 200 mg/kg. In the
highest dosage group, the indices of hepatotoxicity and the liver
histopathology were not significantly different from those of the control
group. The authors of the study concluded that although the
hepatoprotective constituents of roselle remain to be characterized, the
activity can be partially if not largely attributed to the anthocyanins (Ali et
al., 2003). Anti-inflammatory Activity
An infusion of roselle prepared by allowing the powdered calyces to steep
overnight in distilled water was tested for inhibition of carrageenan-induced
hind foot edema, yeast-induced pyrexia, and analgesia using the hot-plate
method. Rats of either sex were administered an acute dose of the infusion
(500 mg/kg p.o.) prior to each test. Roselle infusion failed to inhibit paw
edema and pyrexia, yet significantly prolonged the reaction time in the hot
plate method (p < 0.05) (Dafallah and Al-Mustafa, 1996).
Dermatological Activity
Roselle is reported to inhibit the in vitro growth of Staphylococcus epidermis
(minimum inhibitory concentration = 0.625 mg/mL; minimum bactericidal
concentration = 5 mg/mL), a microorganism involved in superficial
infections of the skin. Weaker activity was found against the growth of
Propionibacterium acnes (MIC = 2.5 mg/mL; MBC = 5 mg/mL), an
organism associated with the development of inflammatory acne
(Chomnawang et al., 2005).
The total crude polysaccharide fraction and 4 subfractions were isolated
from the flowers of roselle and tested for proliferative and other effects on
human keratinocytes (HaCaT cells). The crude polysaccharide fraction (0.1-
10 mg/mL) significantly increased the rate of proliferation by 10% to 20%.
Whereas a neutral subfraction showed no activity, 3 acidic subfractions were
significantly active, stimulating proliferation by up to 30%. Concentrationdependent
activity was absent, however; likely due to the activation of
membrane-associated receptors and the subsequent involvement of
transduction cascades. Further tests using natural human keratinocytes
found significant stimulation of differentiation from the crude
polysaccharide fraction (10 mg/mL). Tests using the MTT assay revealed
that the enhanced proliferation of HaCaT cells by the polysaccharides did
not involve increased energy metabolism and that they were devoid of
cyctotoxicity. The authors concluded that while extracts of roselle rich in
highly acidic polysaccharides have some rationale for use in cosmetic or
dermatological applications, bioavailability and relevant concentrations
remain to be determined (Brunold et al., 2004). Clinical Trials
The antihypertensive activity of roselle was examined in a randomized
controlled trial in 80 patients with moderate essential hypertension. The
number of antihypertensive medications taken prior to trial entry was limited
to no more than two and those with thyroid disease, diabetes, secondary
hypertension, or cardiovascular abnormalities were excluded. After
discontinuing their medications, patients of either sex (average age 52 years)
were randomized to receive 150 g of ordinary blended tea (control) or
blended roselle tea prepared by boiling 2 teaspoons of the tea in water for
20-30 minutes. Both the identities and effects of the teas were unknown to
the patients. The dosage was one glassful per day for 12 days and the
patient groups (31 in the roselle group and 23 in the control group) were
matched for sex, BMI, cigarette smoking, and family history of
hypertension. On day 12, a significant decrease in BP was evident in the
roselle group compared to the control group with systolic BP decreased 1.8-
fold and diastolic BP decreased 2.1-fold. Three days after stopping the teas,
systolic BP increased 8.7-fold and diastolic BP increased 11.9-fold
compared to the control group (Haji Faraji and Haji Tarkhani, 1999).
A randomized controlled trial of a standardized extract of the dried calyx
was conducted in patients of either sex (ages 30-80) diagnosed with mild to
moderate hypertension. The purpose of the trial was to compare the
tolerability and effectiveness of roselle extract to captopril, an angiotensinconverting
enzyme (ACE) inhibitor used in the management of hypertension
and congestive heart failure. The control group of 37 patients received
tablets of captopril (25 mg twice daily for 4 weeks) while the treatment
group of 53 subjects received 10 g of roselle extract powder (9.6 mg
anthocyanins per dose; determined by a colorimetric method) prepared as an
infusion drunk once daily before breakfast for the same period. None of the
patients had received antihypertensive treatments for one month or more
prior to the trial and subjects diagnosed with cardiopathy, secondary
hypertension, diabetes, cancer, pregnancy, hepatic disease, or nephropathy
were allowed entry. Seventy subjects completed the trial. There were 32
remaining in the captopril group after 4 were removed due to rising blood
pressure (BP) and one withdrew for nonmedical reasons. Thirty-eight
remained in the roselle group after 14 dropped out due to the bitter taste of
the extract and another was removed due to rising BP (Herrera-Arellano et
al., 2004).
After 4 weeks there were significant decreases in BP in both groups and
although the results were slightly superior in the captopril group, those in the
roselle group were not significantly different. Therapeutic effectiveness was
achieved in 78.95% of the roselle group and 84.38% of the captopril group.
Tolerability of the treatments was good in both groups and was not
significantly different. In addition, urinary secretion of sodium and the
density of the urine were significantly decreased in the roselle group
compared to baseline, but there no significant changes in potassium,
chlorine, or pH. At this, the authors of the study point out that aldosterone
antagonist- and spironolactone-type diuretics, both potassium-sparing
diuretics, produce similar effects and that therefore the “diuretic activity” of
roselle may be similar, although the hypothesis remains to be proved
(Herrera-Arellano et al., 2004). Pharmacokinetics
An open-label trial of an aqueous extract powder of the dried calyces was
conducted in 6 healthy volunteers in order to obtain information on the
pharmacokinetic parameters of its anthocyanin content. The volunteers, all
nonsmokers aged 24-28 years, were instructed to abstain from foods rich in
anthocyanins or polyphenols for a period of 24 hours prior to the treatment
which consisted of a single dose of 10 g of the extract powder diluted in
water taken after an 8-hour fast. Calculated according to cyanidin
equivalents, the content of total anthocyanin per dose was 147.4 mg. The
administered dose was mainly composed of delphinidin-3-sambubioside
(81.6 mg) and cyanidin-3-sambubioside (62.6 mg) and held minor amounts
of delphinidin-3-glucoside (3.0 mg) and cyanidin-3-glucoside (0.18 mg).
The amount of the two main anthocyanins and of the total anthocyanins
excreted in urine over 7 hours was very low and there was little variability
between the rates of the individual main anthocyanin components. Between
the subjects, however, the relative amounts of total anthocyanins excreted
varied by around 60%. The terminal half-life of delphinidin-3-sambubioside
was longest at 3.34 hours and that of the total anthocyanins (2.63 h) and
cyanidin-3-sambubioside (2.18 h) were about the same. Among the
subjects, half-life variability was lowest for total anthocyanins (1.7-3.95 h)
and highest for cyanidin-3-sambubioside (1.15-7.5 h). Peak concentrations
in plasma were close to the urinary excretion times and there was no lag
time in absorption of the anthocyanins following oral intake. The median
peak plasma times of the individual anthocyanins following intake was 1.5
hours and they showed no obvious differences. In the absence of finding
metabolites of the administered anthocyanins (methylated metablolites,
glucuronides, or sulphates), it was evident that the individual anthocyanins
from the roselle extract remained intact as glycosidic forms and that little of
the total anthocyanins (0.018%) was excreted in the urine. This result was in
keeping with the findings of others in studies of the 7-h urinary excretion of
total anthocyanins after dietary administration of red wine (0.18% over 7 h)
and red grape juice (0.23%) (Frank et al., 2005). Drug Interactions
The effect of a sugar-sweetened water extract of the dried calyces (30 g/L)
on the pharmacokinetics of acetaminophen (1,000 mg orally) was examined
in 6 healthy male volunteers aged 26-30 years. The results showed that
taken alone or together with drinking one liter of the water extract, there was
no significant difference in the absorption pharmacokinetics of
acetaminophen; however, the terminal elimination half-life of
acetaminophen was significantly shortened, indicating that roselle enhanced
elimination of the drug. Based on their results, the authors concluded that
roselle should be taken at least 3-4 h after acetaminophen (Kolawole and
Maduenyia, 2004). Safety
No evidence of toxicity has been found from normal human doses of roselle
(approximately 10.5-12.6 g/day) (Akindahunsi and Olaleye, 2003) and a
water extract of the dried calyces showed no mutagenicity in the Ames test
(Duh and Yen, 1997).
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