From Plant to Patient: Thapsigargin, a Tool for Understanding …
63
not touch it, imported cattle would feed on it and perish of diarrhea [8, 9]. The
resin was prepared by extracting the roots with ethanol followed by concentration of
the solution. The bark was removed from roots collected from December to March
and used in traditional medicine for the treatment of leanness, chronic diseases of
the lungs, and sterility. By carefully avoiding contact with the other parts of the
roots than the bark the Arabs were able to avoid skin eruptions whereas the Kabyles
were covered in suppurating sores [10, 11]. The resin was used extensively as a
counterirritant [10, 12] and was described in several pharmacopoeias including the
French Pharmacopoeia from 1937. Examination of the descriptions of the effects
of plasters containing the resin, however, indicates that the plasters must have been
very unpleasant remedies [10, 12, 13]. The biological activities of botanicals from
T. garganica provoked scientific interest in phytochemicals from this species. Intensive research inspired by the late Professor Finn Sandberg (University of Uppsala,
Sweden), but initiated at the Royal Danish School of Pharmacy (Copenhagen) in
1973 revealed that the species was a source of unique compounds with outstanding
chemical and pharmacological properties.
The major active principle was isolated in 1978 [14], and elucidated structurally
as the hexaoxygenated guaianolide 1 [15–17], and named thapsigargin (Fig. 2). In
addition to 1, a number of other polyoxygenated guaianolides were isolated from
extracts of the roots. Since harvesting of the roots meant killing of the plant it was
preferred in our later studies, which involved extraction of gram amounts of 1, to
isolate these compound from the fruits of the plant (Fig. 1) [18]. Collection of the
fruits is a non-invasive procedure and much easier than collecting the roots.
Stress induced by damaging plants has also highlighted the apparent ecological
function of thapsigargin (1) and its derivatives. Thapsigargins are thought to be a
group of defense compounds against herbivory and are generally toxic to all animals
as they inhibit SERCA in both vertebrates and invertebrates [19]. This activity is
responsible for the potent toxicity of these plants. The biosynthesis and production
of 1 and related compounds is induced upon damaging the plant. Indeed, there is
a significant change in a plant’s chemical profile after plant damage, and models
suggest that thapsigargins represent both a constitutive and induced intraspecific
defense. Thapsigargins are clearly the dominant defense compounds in these plants,
and they seem to be produced through a common biosynthetic pathway with little
diversity [20, 21].
The potent skin irritation provoked by purified thapsigargin (1) led to investigations of its effects on isolated cells (Section 8.3). Thapsigargin (1) was found to induce
release of histamine from mast cells and mediators from other cells belonging to the
immune system if the cells were incubated in Ca
2+ -containing media. Persuasion of
Dr. Ole Thastrup to assay if these effects could be related to an influence of the Ca
2+
homeostasis led to the discovery that 1 inhibits SERCA pumps with a subnanomolar
affinity (Section 12.3). Today, thapsigargin (1) has become an important tool for
investigating Ca
2+ homeostasis, ER stress responses, and cell death.
63
not touch it, imported cattle would feed on it and perish of diarrhea [8, 9]. The
resin was prepared by extracting the roots with ethanol followed by concentration of
the solution. The bark was removed from roots collected from December to March
and used in traditional medicine for the treatment of leanness, chronic diseases of
the lungs, and sterility. By carefully avoiding contact with the other parts of the
roots than the bark the Arabs were able to avoid skin eruptions whereas the Kabyles
were covered in suppurating sores [10, 11]. The resin was used extensively as a
counterirritant [10, 12] and was described in several pharmacopoeias including the
French Pharmacopoeia from 1937. Examination of the descriptions of the effects
of plasters containing the resin, however, indicates that the plasters must have been
very unpleasant remedies [10, 12, 13]. The biological activities of botanicals from
T. garganica provoked scientific interest in phytochemicals from this species. Intensive research inspired by the late Professor Finn Sandberg (University of Uppsala,
Sweden), but initiated at the Royal Danish School of Pharmacy (Copenhagen) in
1973 revealed that the species was a source of unique compounds with outstanding
chemical and pharmacological properties.
The major active principle was isolated in 1978 [14], and elucidated structurally
as the hexaoxygenated guaianolide 1 [15–17], and named thapsigargin (Fig. 2). In
addition to 1, a number of other polyoxygenated guaianolides were isolated from
extracts of the roots. Since harvesting of the roots meant killing of the plant it was
preferred in our later studies, which involved extraction of gram amounts of 1, to
isolate these compound from the fruits of the plant (Fig. 1) [18]. Collection of the
fruits is a non-invasive procedure and much easier than collecting the roots.
Stress induced by damaging plants has also highlighted the apparent ecological
function of thapsigargin (1) and its derivatives. Thapsigargins are thought to be a
group of defense compounds against herbivory and are generally toxic to all animals
as they inhibit SERCA in both vertebrates and invertebrates [19]. This activity is
responsible for the potent toxicity of these plants. The biosynthesis and production
of 1 and related compounds is induced upon damaging the plant. Indeed, there is
a significant change in a plant’s chemical profile after plant damage, and models
suggest that thapsigargins represent both a constitutive and induced intraspecific
defense. Thapsigargins are clearly the dominant defense compounds in these plants,
and they seem to be produced through a common biosynthetic pathway with little
diversity [20, 21].
The potent skin irritation provoked by purified thapsigargin (1) led to investigations of its effects on isolated cells (Section 8.3). Thapsigargin (1) was found to induce
release of histamine from mast cells and mediators from other cells belonging to the
immune system if the cells were incubated in Ca
2+ -containing media. Persuasion of
Dr. Ole Thastrup to assay if these effects could be related to an influence of the Ca
2+
homeostasis led to the discovery that 1 inhibits SERCA pumps with a subnanomolar
affinity (Section 12.3). Today, thapsigargin (1) has become an important tool for
investigating Ca
2+ homeostasis, ER stress responses, and cell death.