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Introduction
The essential oil of East Indian sandalwood (Santalum album,
Santalaceae) has a long history of use in oriental medicine. The
interest in the usage of sandalwood oil and one of its main com-
pounds,
a
-santalol, as therapeutic substances has grown consid-
erably. The oil has been associated with chemopreventive activ-
ity since it has been found to enhance the activity of glutathione
S-transferase (GST) and to increase the level of acid-soluble sulf-
hydryl groups (SH) in mice [1]. Antiviral activity of sandalwood
oil has been demonstrated by Benencia et al. [2]. Okugawa et al.
[3] described the effects of
a
- and
b
-santalol on the central ner-
vous system. Their results showed that both fragrances could be
considered as neuroleptics with some resemblance to the phar-
macological activity of chlorpromazine. In recent years, the use
of fragrances for clinical purposes has been propagated [4]. A
study conducted at the Royal Sussex County Hospital [5] showed
that foot massage with the essential oil of lavender lowered
blood pressure as well as heart and respiratory rates of the pa-
tients in an intensive care unit. In a similar investigation at the
Middlesex Hospital in London [6] intensive care patients were
given foot massage using the essential oil of Citrus aurantium
(Neroli oil). The results suggested that massage with essential
oils positively affects the psychological state of the patients. To-
pical application of essential oils in a carrier lotion has been re-
ported by Macdonald [7]. This study demonstrated the enhance-
ment of conventional methods of arthritic pain relief by the
usage of essential oils. Although massage of essential oils is
used growingly for the improvement of the quality of life as
well as for the relief of various symptoms in patients, scientific
evaluations of the effects of transdermal administration of fra-
grances in healthy volunteers are rather scarce. Up to now, no ex-
periments about the effects of sandalwood oil and one of its main
components,
a
-santalol, on human physiological parameters and
Evaluation of the Effects of East Indian Sandalwood
Oil and
aa
-Santalol on Humans after Transdermal
Absorption
T. Hongratanaworakit
1
E. Heuberger
2
G. Buchbauer
2
Affiliation
1
Department of Pharmaceutical Chemistry, Faculty of Pharmaceutical Sciences, Srinakharinwirot University,
Nakorn-nayok, Thailand
2
Department of Pharmaceutical Chemistry, Center of Pharmacy, University of Vienna, Vienna, Austria
Correspondence
Dr. Tapanee Hongratanaworakit ´ Department of Pharmaceutical Chemistry ´
Faculty of Pharmaceutical Sciences ´ Srinakharinwirot University ´ Nakorn-nayok 26120 ´ Thailand ´
Fax: +66-37-395096 ´ E-mail: tapanee@swu.ac.th
Received June 12, 2003 ´ Accepted August 2, 2003
Bibliography
Planta Med 2004; 70: 3±7 ´ Georg Thieme Verlag Stuttgart ´ New York ´ ISSN 0032-0943 ´
DOI 10.1055/s-2004-815446
Abstract
The aim of the study was to investigate the effects of East Indian
sandalwood oil (Santalum album, Santalaceae) and
a
-santalol on
physiological parameters as well as on mental and emotional
conditions in healthy human subjects after transdermal absorp-
tion. In order to exclude any olfactory stimulation, the inhalation
of the fragrances was prevented by breathing masks. Eight phys-
iological parameters, i. e., blood oxygen saturation, blood pres-
sure, breathing rate, eye-blink rate, pulse rate, skin conductance,
skin temperature, and surface electromyogram were recorded.
Subjective mental and emotional condition was assessed by
means of rating scales. While
a
-santalol caused significant phys-
iological changes which are interpreted in terms of a relaxing/se-
dative effect, sandalwood oil provoked physiological deactiva-
tion but behavioral activation. These findings are likely to repre-
sent an uncoupling of physiological and behavioral arousal pro-
cesses by sandalwood oil.
Key words
Autonomic nervous system ´ human ´ sandalwood ´
a
-santalol ´
subjective evaluation ´ transdermal administration
Original Paper
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on behavioral measures after percutaneous administration have
been carried out. Therefore, the main objective of the present
study was to investigate the effects of these fragrance com-
pounds on parameters of the autonomic nervous system as well
as on mental and emotional conditions in healthy human sub-
jects following transdermal absorption.
Materials and Methods
Subjects and fragrance compounds
Thirty-six healthy volunteers aged between 19 and 32 years
(mean age 23.18 2.64 years) took part in the experiments. Sub-
jects were tested in individual sessions and randomly assigned to
either the control group or one of two experimental groups, i. e., a
sandalwood oil group and an
a
-santalol group. Each group con-
sisted of 12 subjects. They were fully briefed, gave written in-
formed consent to all aspects of the study (Viennese ethic com-
mission's permissions No. 324/96, 419/98) and were free to with-
draw at any time. East Indian sandalwood oil (commercially
available from Dragoco GmbH, Holzminden, Germany, product
No. 16 598) and the main component
a
-santalol were used as fra-
grances in this study. East Indian sandalwood oil was identified
by Dr. Leo Jirovetz, Department of Pharmaceutical Chemistry,
University of Vienna. The most prominent constituents are san-
talols (90%). A voucher specimen (No. 4/942130) is deposited in
the refrigerator (4 8C) at room number 2E464 of that department.
a
-Santalol was separated from a mixture of
a
- and
b
-santalols
(Sigma-Aldrich Chemie GmbH, D-89 555 Steinheim, Germany,
CAS 11031-45-1) via argentation column chromatography [8].
Complete identification of each obtained santalol was accom-
plished by
1
H- and
13
C-NMR-spectroscopy and GC-MS, and com-
parison of these data with those in the literature [3].
Fragrance administration
In the experimental groups, 20 % (w/w) solutions of either san-
dalwood oil or
a
-santalol in peanut oil were used. One mL of
this solution was applied to the skin of the lower abdomen of
each subject. In the control group, 1 mL of the placebo substance,
i. e., pure peanut oil, was used. In all groups subjects were sup-
plied with pure air by breathing masks in order to prevent any
olfactory stimulation.
Experimental design
The experimental design is shown in Fig.1. One session consisted
of two trials of 20 minutes each. At the beginning as well as at the
end of each trial, subjective mental and emotional condition was
assessed by visual analogue scales (VAS). Physiological para-
meters were recorded continuously during each trial. In the first
trial, which served as a control for influences of the experimental
set-up, the placebo substance was administered to all subjects.
In the second trial the placebo was again administered to the
control group, whereas in the experimental groups the appropri-
ate fragrance was administered.
Acquisition of physiological parameters
Blood oxygen saturation (BOS), breathing rate (BR), eye-blink
rate (EBR), pulse rate (PR), skin conductance (SC), skin tempera-
ture (ST), and surface electromyogram (EMG) were recorded si-
multaneously and in real time on the non-dominant side of the
body. All parameters were measured using MP100WSW hard-
ware (Biopac Systems, Inc., Santa Barbara, California, USA) in-
cluding sensors and Ag/AgCl surface electrodes and Acqknowledge
software (V3.2.6, 1992±1997, Biopac Systems, Inc., Santa Bar-
bara, California, USA). Systolic blood pressure (SBP) and diastolic
blood pressure (DBP) were measured in the dominant arm by
sphygmomanometry using an automated system (Hartmann Digi-
tal HG160, Paul Hartmann AG, D-89522 Heidenheim). Details of
the recording system and procedure have been described else-
where [17].
Visual analogue scales (VAS)
VAS were used to assess subjective mental and emotional condi-
tions. They consisted of 100 mm lines for six items: relaxation,
vigor, calmness, attentiveness, mood and alertness. Each subject
was asked to mark his or her feeling for each item between the
two possible extremes.
Procedure
All experiments were conducted in a bright and quiet room. Am-
bient temperature was 21± 24 8C. Upon arrival, the volunteers
were interviewed about their personal data, i. e.; name, age, sex,
weight and height. In addition, they were asked about the rating
of mental and emotional condition. After completion of the inter-
view and rating scales, SBP and DBP were measured. Subse-
quently, subjects were informed about the proceedings. The
electrodes and sensors were attached to the suitable positions.
The breathing mask was attached to the subject's face to cover
nose and mouth. Following THAT, subjects applied 1 ml of the
placebo substance to the skin of their lower abdomen by them-
selves for approximately 2 ± 3 minutes. The area was then cov-
ered with plastic film. Then, the recording of physiological
parameters was started. After completion of the first trial the rat-
ing scales were presented. SBP and DBP were measured at the
end of the first trial. This procedure was repeated in the second
trial.
Data reduction
The physiological recordings of each subject were computed trial
by trial using AcqKnowledge
software. For each subject and
Fig. 1 Experimental design.
Hongratanaworakit T et al. Evaluation of the ¼ Planta Med 2004; 70: 3 ± 7
Original Paper
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every parameter the mean value in the second trial was subtracted
from the mean value in the first trial to give the individual inter-
trial difference score. Additionally, for each subject difference
scores between blood pressure measurements 2 and 4 were cal-
culated. For subjective ratings, on each scale the distance of the
mark from the left-hand side was measured in mm. Individual
difference scores between ratings 2 and rating 4 were calculated
for each item.
Statistical analysis
Systat 9.0 (SPSS Inc., 1999) was used for data analysis. Mann-
Whitney U test and Kruskal-Wallis one-way analysis of variances
were used in this study. The effects of fragrances on physiological
parameters and ratings of mental and emotional condition were
determined by comparing the difference scores between the
control group and the experimental groups. Furthermore, the
difference scores of the sandalwood oil group were compared to
those of the
a
-santalol group in order to detect differences in the
effectiveness of the fragrances.
Correlational analyses were performed by means of Bravais-
Pearson correlation and Spearman rank-order correlation. To
evaluate correlations among physiological parameters the Bra-
vais-Pearson correlation was carried out. Spearman rank-order
correlation coefficient was used to analyze the relation between
subjective ratings and physiological parameters.
Results
Physiological parameters
Mean and SEM of physiological parameters of the control group
and the experimental groups are presented in Table 1. Mean dif-
ference scores of PR of the control group and the experimental
groups are shown in Fig. 2. Comparison of the difference scores
revealed a significantly larger decrease of PR in the
a
-santalol
group than in the control group (P = 0.050). Mean difference
scores of EBR of the control group and the experimental groups
are shown in Fig. 3. The difference scores of the sandalwood oil
group and the
a
-santalol group were in significant contrast to
that of the control group (control versus sandalwood oil:
P = 0.025; control versus
a
-santalol: P = 0.033). Mean differ-
ence scores of SBP between measurement 2 and 4 for the control
group and the experimental groups are shown in Fig. 4. The dif-
ference scores of the sandalwood oil group and the
a
-santalol
group were in marginal contrast to that of the control group
(control versus sandalwood: P = 0.073; control versus
a
-santa-
lol: P = 0.093). No significant effects of the sandalwood oil or
a
-santalol on BR, on SCL, on ST, on EMG, DBP, and on BOS were
found (p > 0.1 for all, data not shown).
Mental and emotional conditions
Mean difference scores of attentiveness between rating 2 and
rating 4 for the control group and the experimental groups are
shown in Fig. 5. Comparison of these difference scores (control
versus sandalwood oil) revealed a trend towards an increase of
subjective attentiveness in the sandalwood oil group (P =0.088).
No significant effects of sandalwood oil or
a
-santalol on subjective
Fig. 2 Mean difference scores and SEM of pulse rate for the control
group, the sandalwood oil group, and the
a
-santalol group. Asterisks
(**) on the top of the error bars indicate significant differences (P
£
0.050) between the experimental groups and the control group.
Fig. 3 Mean difference scores and SEM of eye-blink rate for the con-
trol group, the sandalwood oil group, and the
a
-santalol group. Aster-
isks (**) on the top of the error bars indicate significant differences (P
£
0.050) between the experimental groups and the control group.
Table 1 Mean and SEM of physiological parameters of the control
group and the experimental groups
PR SBP EBR
C trial 1 Mean (SEM) 67.737
(2.801)
117.167
(2.330)
18.916
(2.897)
trial 2 Mean (SEM) 66.526
(2.529)
120.000
(2.610)
21.183
(3.322)
SAN trial 1 Mean (SEM) 66.686
(2.742)
119.333
(2.520)
19.350
(4.003)
trial 2 Mean (SEM) 64.369
(2.398)
117.667
(2.970)
18.713
(3.560)
a
-SAN trial 1 Mean (SEM) 72.381
(2.643)
128.750
(3.130)
13.203
(2.713)
trial 2 Mean (SEM) 69.278
(2.516)
128.000
(3.520)
11.572
(2.556)
C: control group, SAN: Sandalwood oil group,
a
-SAN:
a
-santalol group; PR: pulse rate, SBP:
systolic blood pressure, EBR: eye-blink rate.
Hongratanaworakit T et al. Evaluation of the ¼ Planta Med 2004; 70: 3± 7
Original Paper
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vigor, alertness, mood, relaxation, and calmness were found (p >
0.1 for all, data not shown).
Correlations
In the control group changes of subjective attentiveness were
correlated with changes of PR and SBP: the more attentive sub-
jects rated themselves, the more PR and SBP rose (
r
= ±0.734
and ±0.591, respectively). Also, a relation between changes of
DBP and SCL was revealed: the more DBP increased, the less
SCL rose (r = ±0.628, P = 0.029). Additionally, interactions be-
tween changes of subjective calmness, attentiveness, and re-
laxation were found: the more calm subjects felt, the more re-
laxed and the less attentive they judged themselves (
r
=
+ 0.733 and ±0.704, respectively). Moreover, changes of subjec-
tive alertness interacted with changes of subjective vigor: the
more alert subjects felt, the more vigorous they rated them-
selves (
r
= + 0.746).
In the sandalwood oil group changes of subjective attentive-
ness were correlated with changes of SBP: the more attentive
subjects rated themselves, the less SBP rose (
r
= + 0.536). Addi-
tionally, interactions between changes of subjective calmness
and relaxation were found: the more calm subjects felt, the
more relaxed they felt (
r
= + 0.755). Moreover, changes of sub-
jective alertness interacted with changes of subjective mood:
the more alert subjects felt, the more cheerful they rated them-
selves (
r
= + 0.663).
In the
a
-santalol group relations between changes of SBP, SCL
and PR were revealed: the less SBP increased, the less SCL rose
(r = + 0.806, P = 0.002); the less PR increased, the less SCL rose
(r = + 0.597, P = 0.041). Additionally, interactions between
changes of subjective vigor, attentiveness, and alertness were
found: the more vigorous subjects felt, the more alert and atten-
tive they judged themselves (
r
= + 0.620 and + 0.732, respective-
ly); the more alert subjects felt, the more attentive they rated
themselves (
r
= + 0.524).
Discussion
In the present investigation essential sandalwood oil and one of
its main components
a
-santalol were administered transdermal-
ly to healthy subjects. Inhalation of the fragrances was prevented
by breathing masks in order to eliminate effects of subjective
odor evaluation. Physiological parameters, i. e., blood oxygen sa-
turation, blood pressure, eye-blink rate, pulse rate, breathing
rate, skin conductance, skin temperature, and surface electro-
myogram, were recorded as indicators of the arousal level of the
autonomic nervous system. In addition, subjects had to rate their
mental and emotional condition in terms of relaxation, vigor,
calmness, attentiveness, mood, and alertness in order to assess
subjective behavioral arousal. Transdermal absorption of sandal-
wood oil led to a significant decrease of eye-blink rate and a
trend towards a larger decrease of systolic blood pressure. Gener-
ally, eye movement and blink rate are indicative of cognitive pro-
cessing and the level of arousal [9]. Therefore, the decrease of
blink rate may be interpreted as a decrease of arousal. Since
blood pressure is determined by the activity of the sympathetic
branch of the ANS a decrease of systolic blood pressure shows a
decrease of sympathetic tone, i. e., a decrease of physiological
arousal. At the behavioral level, subjects in the sandalwood oil
group rated themselves more attentive than subjects in the con-
trol group. This finding points towards an increase of arousal in
terms of self-evaluation. Correlational analyses showed that
changes of subjective attentiveness were correlated with chang-
es of systolic blood pressure in both groups. The more systolic
blood pressure decreased in subjects in the control group the
less attentive they rated themselves, i. e., in this group a decrease
of physiological arousal was correlated with a decrease in behav-
ioral activation. In contrast, the more systolic blood pressure de-
creased in subjects in the sandalwood oil group the more atten-
tive they judged themselves. Obviously, in the latter group a de-
crease of physiological activation was correlated with an
increase of arousal at the subjective level. This finding may indi-
cate that massage of essential sandalwood oil results in the un-
coupling of physiological and behavioral arousal processes [10].
Fig. 4 Mean difference scores and SEM of systolic blood pressure for
the control group, the sandalwood oil group, and the
a
-santalol group.
Asterisks (*) on the top of the bars indicate significant differences
(0.050
t
; P
£
0.100) between the experimental groups and the control
group.
Fig. 5 Mean difference scores and SEM of subjective attentiveness for
the control group, the sandalwood oil group, and the
a
-santalol group.
Asterisks (*) on the top of the bars indicate significant differences
(0.050
t
; P
£
0.100) between the experimental groups and the control
group.
Hongratanaworakit T et al. Evaluation of the ¼ Planta Med 2004; 70: 3 ± 7
Original Paper
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The observed effects of essential sandalwood oil are not precisely
characterized by concepts like relaxation or sedation, since deac-
tivation on both the physiological level and on the level of self-
evaluation is associated with these concepts. Massage of essen-
tial sandalwood oil, however, reduced the level of arousal of the
autonomic nervous system but did not lead to deactivation at the
behavioral level, i. e. after the administration of the oil subjects
did not feel more relaxed or drowsy, but in contrast reported to
feel more attentive than before the application of the oil. Thus,
the effects of essential sandalwood oil may be characterized by
the concept of ªharmonizationº rather than relaxation/sedation
which has also been described for the essential oil of lavender
[11], [12]. The decrease of eye-blink rate was not correlated with
changes in self-evaluation. This finding suggests the effective-
ness of pharmacological mechanisms, e. g., direct interactions
between fragrance molecules and receptor sites which are in-
volved in the regulation of ANS arousal. Due to their high lipophi-
licity fragrance molecules easily penetrate the blood-brain barri-
er [13], and animal experiments have shown that they interact
with various receptor types in the brain, e.g., GABA
A
[14], gluta-
mate [15], D
2
and 5-HT
2A
[16]. Therefore, it seems likely that es-
sential sandalwood oil exerts its effects by an interaction with
central (e. g., hypothalamic, limbic) structures which control the
level of physiological and/or behavioral arousal. Transdermal ad-
ministration of
a
-santalol, like essential sandalwood oil, pro-
voked a significant decrease of eye-blink rate which represents
a decrease of arousal. In addition,
a
-santalol caused a significant
decrease of pulse rate. Since pulse rate is mainly controlled by
the parasympathetic nervous system the decrease of pulse rate
after percutaneous absorption of
a
-santalol is likely to show an
increase in vagal tone, i. e., a decrease of ANS arousal. As in the
sandalwood oil group, a trend towards a larger decrease of systo-
lic blood pressure in subjects in the
a
-santalol group as compar-
ed with subjects in the control group was revealed which again
indicates a decrease of physiological arousal. Thus,
a
-santalol
may be characterized as physiologically relaxing. However, ad-
ministration of
a
-santalol had no effects on subjective mental
and emotional conditions. Moreover, changes of physiological
parameters were not correlated to changes of subjective mental
and emotional conditions. It may again be speculated that the
observed effects of
a
-santalol on the physiological parameters
occur via pharmacological mechanisms.
In conclusion, our investigation showed ªharmonizingº effects of
the essential oil of East Indian sandalwood and relaxing/sedative
effects of one of its main compounds,
a
-santalol. In addition, the
present study showed that transdermal administration offers the
opportunity to exclude psychological mechanisms that are active
when odorous substances are applied by means of inhalation
[17], [18] and to separately investigate effects of fragrances
mediated by pharmacological mechanisms.
Acknowledgements
The authors are grateful to Srinakharinwirot University, Thailand
(grant for T.H.) and to Dragoco, GmbH (now Symrise), Vienna, for
the interest in this study.
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