Download Verbascum thapsus Recent Advances in Research REVIEW ARTICLE

PHYTOTHERAPY RESEARCH
Phytother. Res. 19, 733–739 (2005)
Published online in Wiley InterScience
(www.interscience.wiley.com).
DOI:
10.1002/ptr.1653
COMMON
MULLEIN (VERBASCUM
THAPSUS
L.)
733
REVIEW ARTICLE
Common Mullein (Verbascum thapsus L.):
Recent Advances in Research
Arzu Ucar Turker and Ekrem Gurel*
Abant Izzet Baysal University, Faculty of Science and Arts, Department of Biology, 14280 Bolu, Turkey
Common mullein (Verbascum thapsus L.) is a medicinal plant readily found in roadsides, meadows and
pasture lands and has been used to treat pulmonary problems, inflammatory diseases, asthma, spasmodic
coughs, diarrhoea and migraine headaches. Although it has been used medicinally since ancient times, the
popularity of common mullein has been increasing commercially for the past few years. Today, the dried
leaves and flowers, swallow capsules, alcohol extracts and the flower oil of this plant can easily be found in
health stores in the United States. The use of common mullein extracts in folk medicine begun recently to be
supported by an increasing number of research studies. This paper thoroughly reviewes all the scientific
research related to Verbascum thapsus L. including plant tissue cultures and the biological properties of this
plant. Copyright © 2005 John Wiley & Sons, Ltd.
Keywords: Verbascum thapsus L.; mullein; medicinal herb; Scrophulariaceae.
INTRODUCTION
BOTANY
The Scrophulariaceae family is an important family
of plants comprising over 200 genera and about 2500
species. They occur mostly in temperate and subtropical regions, and many of them produce flowers of great
beauty in either a garden setting or as roadside ‘weeds’.
The family includes Mimulus, Penstemon, Digitalis,
Veronica and Verbascum (Grieve, 1981). A number of
the Scrophulariaceae are, or have been, valued for their
curative properties and are widely employed both in
domestic and regular medicine. At least 250 species
of Verbascum are known. Of the species formerly used
in medicine, the most important is Verbascum thapsus
L. Common names include mullein, common mullein,
great mullein, wooly mullein, candlewick plant, velvet
plant, blanket leaf, white mans footsteps, Aaron’s
rod, Jacob’s staff, hedge taper, high taper, old man’s
flannel, lady’s foxglove and sı˝ır kuyru˝u (in Turkish)
(Strange, 1977).
The generic name of this plant, Verbascum, is
believed to be a corruption of barbascum, from the
Latin barba, meaning a beard, referring to the shaggy
appearance of the genus, while thapsus, its specific
name, may refer to the Greek island of that name,
where the species originally thrived. The word ‘mullein’
comes from the Middle English moleyne and the Old
French moleine, and originally from the Latin mollis,
meaning ‘soft’ and referring to the leaves (Strange,
1977).
Verbascum thapsus L. is a biennial, or rarely an annual
plant, with a deep tap root. In its first year, it produces
a low vegetative rosette up to 60 cm in diameter, which
overwinters and is followed in the succeeding growing
season by a stout flowering stem 0.3–2.0 m tall (Gross
and Werner, 1978). The basal leaves are oblong-obovate
to obovate-lanceolate and 10–40 cm long including the
petiole.
Cauline leaves are elliptic-lanceolate, decurrent,
gradually reduced up the stem and densely woolly with
branched hairs (Millspaugh, 1974). The leaf system is
so arranged that the smaller leaves above drop the rain
onto the larger ones below, which direct the water to
the roots. This is a necessary arrangement since mullein
grows mostly on dry soils. The stellately branched hairs,
which cover the leaves so thickly, act as a protective
coat, thus reducing moisture loss, and also providing a
defence. They prevent attack by creeping insects and
set up an intense irritation in the mucus membrane of
any grazing animals that may attempt to browse upon
them. The hairs are not confined to the leaves alone,
but are also on every part of the stem, on the calyces
and on the outside of the corollas, so that the whole
plant appears whitish or grey (Gross and Werner, 1978;
Whitson, 1991). According to Muzik (1970) these epidermal hairs hold away the droplets from the leaf surface so that they can protect the leaves from an aqueous
solution of 2,4-D. The homely but valuable ‘mullein
tea’, a remedy of the greatest antiquity for coughs and
colds, must always be strained through fine muslin to
remove any hairs that may be floating in the hot water,
which was poured over the flowers or leaves. They can
cause intolerable itching in the mouth (Grieve, 1981).
The inflorescence is a spike-like raceme 20–50 cm
long and approximately 3 cm in diameter. It is usually
very dense; rare axillary racemes may arise from the
* Correspondence to: Dr E. Gurel, Abant Izzet Baysal University, Faculty
of Science and Arts, Department of Biology, 14280 Bolu, Turkey.
E-mail: [email protected]
734
A. U. TURKER AND E. GUREL
upper leaves. The sessile flowers are usually one per
axil with pedicels less than 2 mm and slightly irregular
with rotate corollas (Millspaugh, 1974). Individual
flowers of mullein are ephemeral, opening before dawn
and closing before mid-afternoon of the same day. They
are protogynous, the style maturing first and then bending downward once the anthers appear. The flowers
are also autogamous, self-pollination occurring at the
end of the day if cross-pollination has not occurred.
The style returns to its original position and the corolla
closes, pushing the still receptive stigma against the
anthers. The calyx consists of five lanceolate or ovate
sepals, 7–9 mm long with caudate tips. The corolla
is 20–25 mm broad consisting of five yellow (rarely
white) petals. Stamens are irregular and attached
to the corolla, three upper filaments are shorter and
densely white-villous, the lower two are longer and
glabrous. Anthers are larger and coloured. The ovary
is superior and two-celled. The fruit is an ovoid, stellatepubescent, capsule 3–6 mm long, longer than the calyx
and splits into two valves at maturity. There are numerous brown seeds, 0.5–1.0 mm long which are six-sided
and have angular lateral surfaces with rows of pits
(Abrams, 1951; Davis, 1965–1985; Munz and Keck, 1973;
Gross and Werner, 1978; Radford et al., 1968). Chromosome counts from plants collected in Ottawa and
British Colombia gave 2n = 36 (Packer, 1964; Mulligan,
1961). Other counts from European material have given
2n = 34 and 2n = 36 (Darlington and Wylie, 1955; Love
and Love, 1961) and n = 9, 11, 17 (Love and Love, 1961).
DISTRIBUTION
V. thapsus L. is native to Europe and Asia. It was probably introduced into North America several times as a
medicinal herb. It was introduced in the mid-1700s to
Virginia as a piscicide (fish poison) and spread rapidly
(Semenza et al., 1978). In Turkey, common mullein is
distributed in Black Sea region (Kastamonu, Ordu,
Trabzon, Rize, Çoruh) and commonly found in riversides, forests, Corylus and Quercus scrub and volcanic
tuff (Davis, 1965–1985). V. thapsus L. grows wild
on stony ground in wasteland, woodland clearings
and roadsides. It does well in shallow, well-drained,
nitrogen-rich soils (Semenza et al., 1978). It occurs in
areas where the mean annual precipitation is 50–150 cm
and the growing season is at least 140 days (Gross and
Werner, 1978).
MEDICINAL OR HISTORICAL USES
Historically, mullein has been used as a remedy for the
respiratory tract, particularly in cases of irritating coughs
with bronchial congestion (Hoffman, 1988). Mullein
leaves and flowers have expectorant and demulcent
properties which are used by herbalists to treat respiratory problems such as bronchitis, dry coughs, whooping
cough, tuberculosis, asthma and hoarseness (Grieve,
1981; Mabey, 1988; Berk, 1996). The flowers are mildly
diuretic and have a soothing and antiinflammatory
effect on the urinary tract (Mabey, 1988). The leaves
are also diuretic, helping to reduce inflammation of the
urinary system and to counter the irritating effect of
acid urine (Ambasta, 1986; Tyler, 1993; 1994). Some
herbal texts extend the therapeutic use to pneumonia
and asthma (Grieve, 1981).
The leaves, roots and the flowers are also anodyne,
antiseptic, antispasmodic, astringent, emollient, nervine,
vulnerary, analgesic, antihistaminic, anticancer, antioxidant, antiviral, bacteristat, cardiodepressant, oestrogenic, fungicide, hypnotic and sedative (Lucas, 1969;
Harris, 1972; Null and Null, 1972; Grieve, 1981).
The demulcent and emollient properties come from
the polysaccharide mucilage and gums that soothe the
irritated tissue. The expectorant property is the result
of saponins that stimulate fluid production. The antiinflammatory property is due to iridoid glycosides and
flavonoids that decrease inflammation (Grieve, 1981).
The mullein combines the expectorant action of its
saponins with the soothing effect of its mucilage, making this a most useful herb for the treatment of hoarseness, tight coughs, bronchitis, asthma and whooping
cough (Mabey, 1988). The dried leaves are sometimes
smoked in an ordinary tobacco pipe to relieve the irritation of the respiratory mucus membrane, and will
completely control the hacking cough of consumption.
The leaves are employed with equal benefit when made
into cigarettes, for asthma and spasmodic coughs. The
flowers placed in a bottle and set in the sunshine are
said to yield a fatty matter valuable as a cure for haemorrhoids. Fomentations and poultices of the leaves have
been found serviceable in haemorrhoidal complaints.
Mullein is said to be of much value in diarrhoea, from
its combination of demulcent with astringent properties,
this combination strengthening the bowels at the same
time (Grieve, 1981; Mabey, 1988). In Europe, a sweetened infusion of the flowers strained in order to separate the rough hairs is used as a domestic remedy for
mild catarrhs and colic. A conserve of the flowers has
also been employed against ringworm, and a distilled
water of the flowers was long reputed to be a cure for
burns and erysipelas (Millspaugh, 1974; Grieve, 1981).
A decoction of leaves was used as a hearth stimulant.
A decoction of roots febrifuge is used to alleviate toothache and also to relieve cramps, convulsions and
migraines. The juice of the plant and powder made
from the dried roots is said to quickly remove rough
warts when rubbed on them (Tyler, 1993; 1994). An oil
produced by macerating mullein flowers in olive oil,
stored in a corked bottle during prolonged exposure
to the sun, or by keeping it near the fire for several
days, is used as a local application in country districts
in Germany for piles and other mucus membrane
inflammations, and also for frost bite and bruises.
Mullein oil is recommended for earache and discharge
from the ear, and for any eczema of the external ear
and its canal (Mabey, 1988; Yarnell, 1997). Mullein oil
is a valuable destroyer of disease germs (Chopra et al.,
1956; Milspaugh, 1974). The fresh flowers, steeped for
21 days in olive oil, are said to make an admirable
bactericide. An alcohol tincture is prepared by homoeopathic chemists, from the fresh herb with spirits of wine,
which has proved beneficial for migraines or sick headaches of long standing, with oppression of the ear
(Bianchini and Corbetta, 1977; Lewis and Elvin-Lewis,
1977). The seeds of mullein are said to be toxic and
should not be used in any of these preparations (Berk,
1996). The seeds when thrown into the water are said
COMMON MULLEIN (VERBASCUM THAPSUS L.)
to intoxicate fish, and are used by poachers for that
purpose, being slightly narcotic. Major toxic elements
affecting the circulatory, respiratory and central nervous
systems of the fish include saponin, rotenone and glycoside. The common mullein causes fish to have difficulty
in breathing (Wilhelm, 1974).
Swedish settlers called it wild tobacco and tied
the leaves around their feet and arms when they
had the ague. Some prepared a tea from the leaves
for dysentery. A decoction of the roots was injected
into the wounds of cattle when afflicted with worms,
which caused them to die and fall out. Also some
American Indian tribes (Mohegans, Penobscots,
Catawbas, Chochtaws, Creeks, Forest Potawatomis and
Menominees) used common mullein as a medicinal
herb (Moerman, 1986). The Mohegans smoked them
to relieve asthma and sore throat, and the Penobscots
smoked the dried and powdered leaves for asthma. The
Catawbas boiled the root and sweetened it to make
syrup for croup in children. The leaves were mashed
and applied as a poultice for pain and swelling, sprains,
bruises and wounds. The Chochtaws put the leaves on
the head as a headache poultice. The Creeks boiled the
roots with those of Button Willow for a drink used for
coughs. The leaves were also boiled and the patient
bathed in the infusion while it was hot. The Forest
Potawatomis smoked the dried leaves for asthma, but
it is not certain whether they learned the practice from
the whites or vice versa. A smoke smudge was made of
the leaves and the fumes inhaled for catarrh and to
revive an unconscious patient. The Menominees smoked
the root for pulmonary diseases. Whites smoked the
leaves for asthma and bronchitis and that the flowers
were believed to be diuretic and had been used for
tuberculosis (Moerman, 1986; Vogel, 1990).
The flowering stem was used dried by Greeks and
Romans as a taper dipped in tallow for light. Mullein
torches were said to repel witches. There is evidence
that at one time it was a ‘magical plant’ of the ancients.
Agrippa, a general and minister under Caesar Augustus,
claimed that the scent from the leaves had an overpowering effect on demons. Mullein was thought to be
an ingredient in brews and love potions, and mentioned
in incantations used by witches during the Middle Ages.
The women of Rome also infused the flowers and mixed
the resulting liquid with lye, using it as a wash to turn
their hair golden yellow (Strange, 1977).
BIOLOGICAL STUDIES
Williams and Kemp (1976) showed that seedlings of
V. thapsus L. collected from a range of cold to warm
temperature habitats (based on altitude and latitude)
exhibit similar rates of photosynthesis within a temperature range 20°–35 °C. Only at the highest temperature tested, 40 °C, the seedlings from the warmest
habitat (low altitude and latitude) exhibit higher photosynthetic rates than those from the coolest habitat.
They concluded that the ability of an individual plant
to photosynthesize over a broad range of temperature
has contributed to mullein’s success across a diversity
of habitats (Gross and Werner, 1978).
Williams et al. (1975) reported a CO2 compensation
point of 58 vpm CO2 for V. thapsus L. and on this basis
735
concluded that the species had a C3 photosynthetic
pathway. Wuenscher (1970) shaved the dense trichomes
of the leaves of V. thapsus L. and found that the
unshaved half of the leaf was consistently warmer than
the shaved half. The hairs must, then, affect the leaf
energy exchange, since two halves of the same leaf,
differing only in the presence of hairs, reached different equilibrium temperatures. Convection and the
latent heat loss are reduced by the hairs although
the hairs have little effect on radiation absorption. The
transpiration rate is reduced in hairy leaves. All of these
effects are explained by an increase in boundary layer
thickness caused by the hairs. The boundary layer forms
above the surface of the hair coating rather than directly over the leaf surface. This thickens the boundary
layer by the distance to which the hairs extend from
the leaf surface. Increased transpiration resistance has
obvious ecological significance for V. thapsus L., which
grows on dry, exposed sites. The dense hair coating
is an efficient water-conserving mechanism. Parkhurst
(1976), evaluating the work of Wuenscher (1970),
showed by calculation that the main effect of the
trichomes was to increase stomatal resistance with only
a slight increase in boundary layer resistance.
Lortie and Aarssen (1997) demonstrated that
clipping the shoot apex of V. thapsus L. resulted in
significantly more branches, and the branching intensity could not be increased by greater resource levels
in mullein when the apical meristem was intact. Branching was stimulated by the addition of nutrients only
when the shoot apex was damaged. These results indicated that nutritional status does not solely determine
the degree of branching expressed in mullein.
Glier and Caruso (1973) demonstrated that decreasing temperatures were observed to induce starch
degradation in the roots of mullein. Virtually no starch
remains in the roots when the acclimation period of
decreasing temperature was followed by an extended
period of exposure to 4 °C. The breakdown of starch
which was presumed to occur in late autumn under
field conditions may provide cryoprotective chemicals
for the over-wintering rosette. Such chemicals might
also serve as an energy source for the bolting process, which occurs during the following spring or early
summer. Later, they showed that the starch content in
roots of V. thapsus L. was reduced when rosettes were
exposed to low temperatures because of the increased
activities of the starch degradative enzymes (Glier and
Caruso, 1974). They also (Glier and Caruso, 1977b)
reported that two nonspecific enzymes, namely, acid
and alkaline phosphatase increased their activities in
Verbascum roots exposed to decreasing temperatures;
alkaline phosphatase was of more importance than acid
phosphatase in over-wintering rosettes. It was known
that mullein had a cold-requirement for bolting and
that applied gibberellin substituted for this requirement
(Caruso and Glier, 1970). Glier and Caruso (1977a)
also described the influence of gibberellin on the activities of starch degradative enzymes and phosphatase.
There was a sharp decrease in starch in the roots of
Verbascum as a result of treating rosettes with GA3
and all three starch degradative enzymes revealed
increases in their activities. Also, application of GA3
resulted in an increase in the activity of alkaline
phosphatase in roots and rosettes showed an early
response to applied gibberellin.
736
A. U. TURKER AND E. GUREL
Gross (1981) showed that the rosette sizes of V.
thapsus L. gives a reliable estimate of an individual’s
fate the following year. A minimum size must be
reached before a plant is capable of flowering and the
probability of flowering increases steadily with rosette
size. For mullein, all rosettes with a diameter greater
than 41 cm flower the subsequent year and rosettes less
than 9 cm in diameter do not flower. Conversely, the
probability of death decreases with increasing rosette
size.
According to Reinartz (1980; 1984a), plant size has
a large impact on plant fitness; within V. thapsus
L. populations large plants develop faster, flower earlier and produce more seed. Compared with other
monocarpic species, V. thapsus L. has an extremely low
reproductive effort (11%–23% of biomass) and seed
output (4%–8%). The reproductive efforts and seed
output of other monocarpic species average 40%
and 25%, respectively (Reinartz, 1984b). Differences
between cohorts of mullein in plant size and the year
of flowering were primarily environmentally induced;
however, the variation between cohorts in a number of
other characters appeared to have a genetic basis
(Reinartz, 1984c).
The seeds of V. thapsus L. are contained in a capsule
with two cells. Salisbury (1942) reported that the mean
number of capsules per explant was 226 ± 42 (SD; n =
37), with an average of 596 ± 30 (SD; n = 16) seeds per
capsule. This gives an approximate average of 10 000–
180 000 seeds per individual plant, each seed averaging
0.067 mg (Gross, 1980; Gross and Werner, 1982). The
seeds possess no specialized morphological adaptations
for dispersal by wind or animals. The capsules split open
along the longitudinal axis when mature, and movement of the stalk by wind or a large animal is required
to release the seeds from the parent. Seeds are dispersed as far as 11 m, although 93% of them fall within
5 m and 75% of them fall within 1 m of the parent
plant. Darlington and Steinbauer (1961) recorded that
the seeds of mullein remain viable for up to 35 years
but Kivilaan and Bandurski (1981) noticed that seeds
may remain viable for over 100 years and in Denmark
viable seeds of V. thapsus were collected from soil
samples archaeologically dated from 1300 A.D.
(Ødum, 1965).
Mullein seeds may germinate under a wide variety
of environmental conditions. Germination is completely
inhibited below 10 °C and at constant temperatures
above 40 °C (Semenza et al., 1978). Chilling during
the winter lowers the temperature requirement for
germination; thus, seeds brought to the surface in the
autumn by soil disturbance are able to germinate early
the next spring (Baskin and Baskin, 1981). Semenza
et al. (1978) found that only 35% of seeds germinated
in the dark, compared with 93% germination in the
light. This light sensitivity varies seasonally, but on
the whole, only those seeds, which lie at, or near the
soil surface (0.5 cm or less) will be able to germinate. If
seed burial occurs due to subsequent disturbance or
heavy rains rapidly sifting the seeds below the soil
surface, germination may be reduced or prevented
through light deprivation (Gross, 1980).
There are some natural enemies (insects and pathogens) of common mullein such as the curculionid
weevil (Gymnaetron tetrum Fab.) which is specific to
V. thapsus L. and was introduced to North America
from Europe (Burcham, 1937). The larvae mature in
the capsules (Sleeper, 1954) and destroy up to 50% of
the seeds. Weevils were responsible for the predation
of 57% of mullein capsules (Pottmeyer, 1985). The other
insect, the mullein moth (Cucullia verbasci) feeds and
develops on mullein species. There are some pathogens which cause disease in common mullein such
as Erysiphe cichoracearum (powdery mildew) and
Phymatotrichum omnivorum (root rot) (Gross and
Werner, 1978).
Although extracts from mullein can inhibit the growth
of wheat seedlings, it is not a serious agricultural weed,
since it can be controlled by cultivation. In overgrazed
or poor pastures, the presence of common mullein represents a further degradation of the pasture because
grazing animals avoid eating mullein. This species is
not allelopathic, allergenic or poisonous to humans
(Gross and Werner, 1978).
Filippini et al. (1990) examined the commercial powdered samples of V. thapsus L. flowers and powdered
samples of V. thapsus L. cultivated in the Botanical
Garden of the University of Padua by using SEM.
Contamination of a commercial powdered sample of
V. thapsus L. flowers with plant material not belonging
to a Verbascum species was observed.
Vegetative reproduction does not occur in V. thapsus
L. (Gross and Werner, 1978; Gross, 1980).
Caruso (1971) showed that excised internodal segments of flowering specimens of V. thapsus L. with
vascular tissues grew and formed numerous buds on a
simple nutrient medium which lacked added growth
regulator. Pith explants without vascular tissues became
brown in a matter of 2 to 3 weeks with no visible sign
of growth. Endogenous growth regulators supplied by
vascular tissues were believed to be major factors in
bud formation in excised internodal segments of this
species.
An in vitro culture protocol for common mullein
was established by Turker et al. (2001). Explants (leaf
discs, petioles and roots) were cultured on Murashige
and Skoog minimal organics (MSMO) medium with
benzyladenine (BA) or kinetin (KIN). The best shoot
proliferation was obtained from leaf discs and petiole
explants with 3 mg/L BA. Leaf discs were cultured
on MSMO medium with 3 mg/L BA in combination with naphthalene acetic acid (NAA) or 2,4dichlorophenoxyacetic acid (2,4-D). More shoot
development was obtained with 3 mg/L BA and
1 mg/L NAA. Shoots were transferred to rooting
media containing different levels of NAA or 2,4-D. Most
shoots developed roots on medium with 1 mg/L NAA.
Plants were transferred to vermiculite and subsequently
to potting media and maintained in a greenhouse.
ACTIVE INGREDIENTS OF V. THAPSUS L.
The constituents of V. thapsus L. include polysaccharides; iridoid glycosides including harpagoside; harpagide and aucubin (especially in the leaf);
flavonoids, including 3 methylguercitin, hesperedin and
verbascoside; saponins and volatile oils (Pascual Teresa
et al., 1978a; 1978b; 1980; Hattori and Hatanaka, 1958;
Khuroo et al., 1988; Mehrotra et al., 1989; Warashina
et al., 1991; 1992).
COMMON MULLEIN (VERBASCUM THAPSUS L.)
Pascual Teresa et al. (1978a) isolated veratric acid
and a-spinasterol from the benzene extract of capsules
of V. thapsus L. From the hydrolysed ethanol extract,
the triterpene A, saikogenin A, benzyl alcohol and
methylfurfural were isolated. They also showed that
the seed oil from mullein (benzene extract) had the
following components: fatty acids: palmitic, steriac, oleic,
linoleic, linolenic, arachic and behenic. Unsaponifiable
matter: b -sitosterol and ergosta-7-en-3-b -ol (Pascual
Teresa et al., 1978b). Phenylethanoid and lignan
glycosides (Warashina et al., 1992), sterones, iridoid
glycosides and sesquiterpene acid (Khuroo et al., 1988;
Warashina et al., 1991) and verbacoside, a new luteolin
glycoside (Mehrotra et al., 1989) were obtained from
whole plants of V. thapsus L. Bourquelot and Bridel
(1910) discovered the verbascose, an oligosaccharide in
the root of the mullein. Hattori and Hatanaka (1958)
demonstrated the oligosaccharides in V. thapsus L. and
distribution of mono- and oligosacharides in various
organs of the plant in various stages was studied.
Pascual Teresa et al. (1980) isolated four saponins
from the capsules of V. thapsus L., thapsuine A,
thapsuine B, hydroxythapsuine A and hydroxythapsuine
B with a chromatographic separation on silica gel (TLC).
Crushed capsules (5 kg) were extracted with benzene
and ethanol and subjected to chromatography on silica
gel and sephadex. They obtained 300 mg thapsuine A
and 460 mg thapsuine B.
Bom et al. (1998) purified a-galactosidase from the
roots of V. thapsus L. using hybrid affinity chromatography with good recovery.
An extraction and analytical protocol for saponins
was established for Verbascum thapsus L. (Turker
et al., 2003). Four different kinds of plant sample were
analysed; (i) field-grown, (ii) in vitro cultured, (iii) commercially obtained leaves and (iv) field-grown capsules.
A cleanup procedure with octadecyl (C18) solid phase
extraction columns was used prior to HPLC (high pressure liquid chromatography) analysis. Ilwensisaponin
A was used as an external standard and digitoxin as an
internal standard. C18 reverse phase column and gradient elutions (acetonitrile with 0.1% orthophosphoric
acid and water with 0.1% orthophosphoric acid) were
used for HPLC analysis. Commercially obtained leaves
had a higher concentration of saponin (0.215 mg/g
tissue) than other leaves (0.081–0.198 mg/g tissue) or
the capsule samples (0.016 mg/g tissue).
SCREENING STUDIES
McCutcheon et al. (1992) used the disc diffusion method
to show the antibiotic activity of common mullein leaves
and demonstrated that a methanol extract of leaves
had antibacterial activity against Escherichia coli
[inhibition zone (iz); 8.0–10.0 mm], Mycobacter phlei
(iz; 8.0–10.0 mm) and Staphylococcus aureus methicillinresistant (iz; 10.1–15.0 mm).
The methanol extract of common mullein leaves
was found to partially inhibit the cytopathic effects of
bovine herpesvirus type 1, two double-stranded DNA
viruses, which causes respiratory, genital, conjunctival
or encephalitic infections which become latent in the
trigeminal ganglion (McCutcheon et al., 1995). Moreover, this extract had antifungal activity against Micro-
737
sporum cookerii (iz; 8.0–10.0 mm) and M. gypseum (iz;
8.0–10.0 mm) (McCutcheon et al., 1994).
Pardo et al. (1998) isolated iridoid glycosides
lateroside 1, harpagoside 2, ajugol 3 and aucubin 4
from an ethanol extract of the roots of mullein that
exhibits antigermination activity on the seeds of barley
(Hordeum vulgare). Bioassays indicated that at 3 mm
concentration, compounds 1, 2 and 4 showed moderate
inhibition of seed germination. Aucubin 4 was the most
active against root elongation and ajugol 3 showed no
activity in the bioassays on barley seed germination
and growth.
Biological activities of common mullein extracts
and commercial mullein products were assessed using
selected bench-top bioassays (Turker and Camper,
2002). Bioassays included antibacterial, antitumour, and
two toxicity assays (i.e. brine shrimp and radish seed
bioassay). Extracts were prepared in water, ethanol and
methanol and their biological activities assessed. For
extractions, three different sources of leaves (fieldgrown, in vitro cultured and commercially obtained)
and capsules (from field-grown plants) were used.
Commercial products of common mullein (tea bags,
swallow capsules, an alcohol extract and flower oil) and
purified saponins were also assessed. The disc diffusion
assay (Kirby-Bauer method) and six different bacterial
strains (Escherichia coli, Pseudomonas aeruginosa
and Klebsiella pneumoniae which are gram-negative
bacteria, and Streptococcus pyogenes, Staphylococcus
aureus and Staphylococcus epidermidis which are grampositive bacteria) were used for antimicrobial activity
assessment. In general, aqueous extracts were the most
effective and showed antibacterial activity against K.
pneumoniae and S. aureus. Methanol extracts from leaf
materials showed little antibacterial activity only against
K. pneumoniae. Generally, commercial products and
purified saponins showed little or no antibacterial
activity against these bacteria (except for the flower oil
sample showing inhibition to K. pneumoniae, E. coli, P.
aeruginosa and S. aureus). Agrobacterium tumefaciensinduced tumours in potato tissue were inhibited by all
common mullein extracts, commercial products and
purified saponins. Methanol extracts of in vitro-grown
leaves and commercially obtained leaves inhibited
tumour formation better than the other methanol,
ethanol and water extracts. The results of brine shrimp
bioassay showed that extracts of mullein were toxic
at higher doses (around 1000 mg/L). Among aqueous
extractions, decoctions had more toxicity (LC50 <
1000 mg/L) than the infusion extracts. In a radish seed
bioassay, at high doses (10 000 mg/L), all extracts
affected the root length. However, at 1000 mg/L, the
extracts did not affect the root length as much. Seed
germination was also inhibited by mullein extracts at
7500 mg/L. Low doses (1000 mg/L) affected germination, but not as much as higher doses. Ethanol extracts
inhibited seed germination more than other types of
extracts.
CONCLUSION
Verbascum thapsus L. (common mullein) is a herb with
a long history of use in folk medicine. The commercial
popularity of this plant has been increasing for the past
738
A. U. TURKER AND E. GUREL
few years with the growing interest in herbs and preferring the ‘greener’ lifestyle. Today in health food
stores, one can easily find dried leaves and flowers,
swallow capsules, alcohol extracts and flower oil of
mullein in USA. The screening studies (bioassays
results) mentioned here confirm the popular utilization
of mullein extracts in folk medicine as a remedy for
respiratory disorders, tumour formation, urinary tract
infection and certain skin diseases. With these results,
V. thapsus L. has some scientific justification as a
medicinal herb. In the future more different bioassays
related to the biological activity of common mullein
can be performed and a more scientific rationale for
this plant may be obtained.
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