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Keywords:

  • clinical assessment;
  • pigmentation;
  • skin colour;
  • skin whitening;
  • α-bisabolol

Synopsis

  1. Top of page
  2. SynopsisRésumé
  3. Introduction
  4. Materials and methods
  5. Results and discussion
  6. Acknowledgement
  7. References

Although skin pigmentation, which results from the production and distribution of melanin in the epidermis, is the major physiological defence against solar irradiation, hyperpigmentation is a common and distressing problem caused by various inflammatory skin disorders, such as eczema, allergic contact dermatitis and irritant contact dermatitis. We evaluated the effects of a preparation containing α-bisabolol on pigmented skin of a group of subjects. The effectiveness of the active compound, α-bisabolol, in a base-cream preparation for the treatment of pigmented skin was tested on 28 female subjects as follows: the cream was applied once a day to the back for 8 weeks. These same women also applied a vehicle control cream to the pigmented skin. The results were evaluated by clinical and biophysical test methods. After 8 weeks of treatment of the α-bisabolol-containing cream, there was significant lightening effect in the pigmented skin for the majority of the subjects who tested the cream.

Résumé

Effet blanchissant de l’α-bisabolol chez les femmes asiatiques

Bien que la pigmentation de la peau, qui résulte de la production et de la distribution de mélanine dans l’épiderme, soit la défense physiologique majeure contre l’irradiation solaire, l’hyperpigmentation est un problème commun et pénible causé par diverses affections cutanées inflammatoires, comme l’eczéma, la dermatite allergique de contact et la dermatite d’irritation de contact. Nous avons évalué les effets d’une préparation contenant de l’α-bisabolol sur la peau pigmentée d’un groupe de sujets. L’efficacité du composé actif α-bisabolol, dans une crème de base pour le traitement de peau pigmentée a étéévalué sur 28 sujets féminins comme suit : la crème a été appliquée une fois par jour sur le dos pendant 8 semaines. Ces mêmes femmes ont aussi appliqué une crème véhicule de contrôle sur la peau pigmentée. Les résultats ont étéévalués par des méthodes cliniques et biophysiques. Après 8 semaines de traitement par la crème contenant de l’α-bisabolol, il y avait un effet éclaircissant significatif de la peau pigmentée pour la majorité des sujets.


Introduction

  1. Top of page
  2. SynopsisRésumé
  3. Introduction
  4. Materials and methods
  5. Results and discussion
  6. Acknowledgement
  7. References

Skin pigmentation, which results from the production and distribution of melanin in the epidermis, is the major physiological defence against solar irradiation. In mammals, melanin synthesis is stimulated by a large number of effectors, including 1-oleyl-2-acetyl-glycerol [1], ultraviolet-B radiation [2], cAMP-elevating agents (forskolin, IBMX, α-MSH, glycyrrhizin) [3–6] and placental total lipid fraction [7].

Hyperpigmentation is a common and distressing problem caused by various inflammatory skin disorders, such as eczema, allergic contact dermatitis and irritant contact dermatitis [8, 9]. Epidermal and dermal hyperpigmentation may depend on either increased numbers of melanocytes or melanogenic enzyme activities [10]. Abnormal release of α-MSH, as well as ultraviolet light, chronic inflammation, and rubbing of the skin, are triggering factors for these disorders [11, 12]. As a result of the prevalent localization in skin, acquired hyperpigmentation has psychosocial and cosmetic relevance, and many efforts have focused on screening for depigmenting agents. Until now, several compounds have been identified as depigmenting agents. Among these are arbutin, hydroquinone and kojic acid [13].

α-Bisabolol [1-methyl-4(1,5-dimethyl-1-hydroxhex-4(5)-enyl)-cyclohexen-1] is a monocyclic sesquiterpene alcohol (Fig 1) and known to possess anti-inflammatory, analgesic, antibiotic and gastric-protective properties [14–17]. Moreover, we recently found that α-bisabolol inhibits α-MSH-induced melanogenesis by suppressing CREB phosphorylation, which is induced by protein kinase A (PKA), and also that α-bisabolol may be an effective inhibitor of hyperpigmentation [18].

image

Figure 1.  Structure of α-bisabolol [1-methyl-4(1,5-dimethyl-1-hydroxhex-4(5)-enyl)-cyclohexen-1].

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Based on in vitro studies, it has been postulated that α-bisabolol could be used topically to prevent and correct hyperpigmentation. Taking these effects of α-bisabolol into account, we experimentally evaluated impact of α-bisabolol on the hyperpigmented skin.

Materials and methods

  1. Top of page
  2. SynopsisRésumé
  3. Introduction
  4. Materials and methods
  5. Results and discussion
  6. Acknowledgement
  7. References

A double-blind, vehicle-controlled, randomized trial was performed to evaluate the clinical effects of the use of cream containing 0.5%α-bisabolol on pigmented skin over a 2-month period. This study was conducted in agreement with the ‘Declaration of Helsinki’ and approved by the Ethics Committee of the IEC Korea Skin Research Center in Suwon, Korea.

Human subjects

Twenty-eight healthy Korean female subjects, aged 32–52 years (mean ± SD = 39.5 ± 5.3 years) were chosen for this study and gave signed, informed consent. The detailed skin types of the 28 women were: dry type (12, 43%) and normal type (16, 57%). In addition, skin phototypes of subjects are III or IV. These phototypes are classified by the Fitzpatrick’ skin phototype. Subjects with a known allergy to any ingredients in the cream or those who had used topical applications of any cream on the back during the preceding month were not included. No topical application of any other product onto the back was permitted. The other exclusion criteria were: acute or chronic illness likely to necessitate a treatment with corticoids; and disorders resulting from excessive consumption of alcohol or toxic substances.

Preparation of cream containing 0.5%α-bisabolol

α-Bisabolol (98%) was purchased from Sigma Chemical Co. (St Louis, MO, U.S.A.).

Oil-in-water cream with or without 0.5%α-bisabolol was prepared. The cream contained several principal ingredients including glycerin, methylparahydroxybenzoate, phenoxyethanol, xanthan gum, squalane, polysorbate 80 and beeswax. Cream with or without α-bisabolol (0.5%) was applied to the tested region (the back).

UV B and A-induced pigmentation and treatment of tested cream

The first day of the study, a solar exposure (UV B & A) with a solar simulator (ORIEL® Instruments, Stratford, CT, U.S.A.) was performed on the back of each subject with a geometric progression of 20%, to determine 16–24 h later the minimal erythema dose (M.E.D.-first reaction of redness). Each subject was then subjected to an UV B & A pigmentation on two previously delimited areas on back of about 2.25 cm2 (1.5 cm × 1.5 cm), with the same solar simulator, at an intensity corresponding to 2 M.E.D. previously determined. Second and third additional UV B & A exposures of 0.5–3.0 M.E.D. (depending on each subject’s reaction) are then performed on each area, after a 2- or 3-day interval. Finally, we obtained a pigmentation equivalent to a decrease of L* value of about 3–4 units. The last exposure was performed about 7 days before the start of repeated applications of the test cream. All subjects applied once a day for 8 weeks as much as amounts of cream containing 0.5%α-bisabolol or of the equivalent control cream containing vehicle which is necessary for the tested region (the back) (1.5 cm × 1.5 cm = 2.25 cm2).

General conditions during measurement

To minimize variability in skin measurements caused by exogenous factors that might affect the subjects’ general skin condition and lead to avoidable bias, the measurements took place in a humidity- and temperature-controlled room; the temperature of this room was 22 ± 2°C and the ambient humidity was 45 ± 5%. Subjects’ skin was given 30 min to adjust to the room conditions before measurements.

Assessment of skin colour

The spectrophotometer CM2600d (Minolta, Osaka, Japan) was used to measure skin colour. The L, a and b values were recorded. However, the L value was used as an indication of skin darkness. The unit was calibrated each use against colour standards to ensure reproducibility between each evaluation data. At least five readings were taken on each site on the back and averaged.

Clinical assessment of skin colour

Before treatment and 4, and 8 weeks after treatment, the investigator clinically evaluated the skin colour of the skin based on 10 points scale at each time points.

Safety evaluation

The safety of the sample was assessed by clinical examination by a dermatologist at 4 and 8 weeks. This assessment took into consideration the elements reported by subjects (subjective and objective signs), as well as those noted by the dermatologist (clinical signs). The frequency, duration and intensity of the signs and a possible relationship with the tested products were investigated. The subjective and objective signs were defined as:

Subjective signs: itching, stinging, burning, stiffening, tightening, etc.

Objective signs: redness, oedema, scale, papule, etc.

Statistical analysis

All statistical analyses were performed by ANOVA with statview Statistical Package 5.0 (SAS Institute, Cary, NC, U.S.A.). A P-value of less than 0.05 was considered significant.

Results and discussion

  1. Top of page
  2. SynopsisRésumé
  3. Introduction
  4. Materials and methods
  5. Results and discussion
  6. Acknowledgement
  7. References

Table I summarizes the results of 2 months of once a day treatment with the active cream and control vehicle. Spectrophotometer CM2600d L values were used as an objective assessment of skin colour. Over the 2-month period, although the control vehicle showed a little change in skin colour (Table I and Fig. 2), there was no significance. In case of 0.5%α-bisabolol-containing cream, it showed stronger whitening effect than vehicle control. After 4 weeks of treatment, almost 105% decrease in skin colour was observed compared with vehicle control (P < 0.05). Namely, after 4 weeks, ΔL(T4w − T0w)s of 0.5%α-bisabolol cream and vehicle cream were 1.81 ± 1.3 and 0.88 ± 1.3, respectively. In addition, a further reduction down to 2.24 ± 1.2 (P < 0.05) was reached after 8 weeks of treatment with 0.5%α-bisabolol cream (Fig. 2). This value corresponded to a 24% improvement in skin colour compared with after 4 weeks of treatment with 0.5%α-bisabolol cream.

Table I.   Result of spectrophotometer measurement
ΔL*, Txw − T0wVehicleα-Bisabolol
  1. Δ, variation with regard to the initial value (after tanning).

  2. *P < 0.05 compared with vehicle control.

Δ(T4w − T0w)0.88 ± 1.31.81 ± 1.3*
Δ(T8w − T0w)1.29 ± 1.52.24 ± 1.2*
image

Figure 2.  Result of spectrophotometer measurement. A CM2600d spectrophotometer was used to measure the L, a and b values of the skin, with the L value being used as an indication of skin darkness. Each unit was calibrated against colour standards prior to each use to ensure reproducibility of the data and at least five readings from each site were collected and averaged. Data are expressed as the mean ± S.D. *P < 0.05 compared with vehicle control.

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With respect to clinical evaluations, no significant improvements were observed with the 0.5%α-bisabolol. After 1 month, a 6% decrease in the clinical assessment of skin colour was observed. However, this was not statistically significant compared with vehicle control (a 5.6% decrease). 0.5%α-bisabolol showed increasing effects on lightening skin colour over time. After 2 months, 0.5%α-bisabolol induced a 9% decrease in skin colour which is not significant compared with vehicle control (8.5% decrease).

In safety tests, there were no reactions in any subjects based on the 4- and 8-week readings. That is, we did not observe any adverse reactions, such as erythema, burning, and pruritus, related to the use of α-bisabolol in study subjects. α-bisabolol cream was considered safe for use in subjects.

It has been well known that cAMP signalling pathway plays a key role in the regulation of melanogenesis, augmenting the enzymatic activity of pre-existing tyrosinase and increasing the amount of tyrosinase mRNA [3–5]. Through activation of PKA and CREB transcription factors, cAMP promotes increased expression of microphthalmia-associated transcription factor (MITF) [19], a melanocyte-specific transcription factor crucial for melanocyte development and differentiation [20, 21]. As a result, MITF binds to and activates the tyrosinase promoter, which stimulates melanogenesis [22, 23]. Our previous study demonstrated that α-bisabolol inhibits melanogenesis, and the mechanisms underlying its action may be mediated by blocking CREB phosphorylation [18].

Taken together, the data gathered in these studies suggest that α-bisabolol has a lightening effect in in vivo skin and also that utilization of the depigmenting effect of α-bisabolol might be useful as an adjunctive therapy for treatment of hyperpigmentation-related disorders, as well as for whitening.

Acknowledgement

  1. Top of page
  2. SynopsisRésumé
  3. Introduction
  4. Materials and methods
  5. Results and discussion
  6. Acknowledgement
  7. References

This work was supported by a grant from the Korean Small and Medium Business Administration (S1033203).

References

  1. Top of page
  2. SynopsisRésumé
  3. Introduction
  4. Materials and methods
  5. Results and discussion
  6. Acknowledgement
  7. References
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