Impact of Acacia bark extract tablets on the skin of healthy humans: a randomized, double-blind, placebo-controlled study

ABSTRACT

This study investigated the effects of proanthocyanidins derived from Acacia (Acacia mearnsii) bark extract in healthy Japanese adult subjects experiencing uncomfortable skin symptoms. All subjects were randomly allocated into two groups (n = 33 each) using a computerized random-number generator. The subjects received either Acacia bark extract tablets or placebo for 8 weeks. Evaluations included water content in the stratum corneum, transepidermal water loss (TEWL), Skindex-16, dermatology life quality index (DLQI), visual analog scale for desire to scratch, and blood tests. At 4 weeks, the symptom/feeling score of DLQI, subjective symptoms related to uncomfortable skin, and the desire to scratch were significantly reduced in the intervention group than in the placebo group. At 8 weeks, the intervention group exhibited significantly lower TEWL on facial skin than that in the placebo group. In conclusion, the intake of Acacia bark extract tablets reduced TEWL and improved dry and uncomfortable skin.

Graphical Abstract

Proanthocyanidins-derived from Acacia bark reduced TEWL and alleviated the symptoms of uncomfortable, dry skin (in Japanese: “muzumuzu” feeling) in healthy Japanese adult subjects.

KEYWORDS:

• Acacia bark extract
• proanthocyanidins derived from Acacia bark
• uncomfortable skin
• transepidermal water loss
• desire to scratch

The presence and progression of dry skin reduces protection against external pathogens, stimuli, endotoxins, and allergens [1–3]. As dry skin worsens, redness, itching, and edema of the skin surface can occur, leading to elevated levels of immunoglobulin E (IgE) in the blood [2,3]. Reportedly, itching caused by external agents leads to secretions of histamine, acetylcholine, and/or proteinases, even in healthy individuals [4]. Apart from external stimuli, the causes of dry skin include artificial sources. For example, use of domestic air conditioners lead to a dry environment, which affects the skin, mucosa of the eyes and nose, and potentially causes respiratory distress [5]. Moreover, evidence has demonstrated that itching is exacerbated by stress and scratching behavior [6], which may interfere with an individual’s sleep, work, or home routine and consequently reduce quality of life (QOL). It has been demonstrated that a decrease in QOL caused by chronic itching is equivalent to that caused by chronic pain [7]. Therefore, therapeutic solutions are required to relieve skin discomfort.

Polyphenols present in food, such as catechins, have been shown to effectively improve skin conditions [8–10]. These polyphenols inhibit allergic reactions, such as the secretion of histamine [11,12] and expression of high–affinity IgE receptor [13], thereby improving skin conditions. In addition to their anti-inflammatory properties, polyphenols reduce skin damage from ultraviolet irradiation through their antioxidant activity [14,15].

This study focused on the effectiveness of Acacia (Acacia mearnsii) bark extract, which contains an abundance of proanthocyanidins (a type of polyphenols), in the prevention of inflammation and allergic reactions.

The extract used in this study was obtained through hot water extraction from the bark of the Acacia tree. It comprises a mixture of monomer, dimer, trimer, and polymer compounds with structures based on flavan-3-ol, such as gallocatechin and robinetinidol [16,17]. Approximately 80% of these compounds are polyphenols [18,19]. A previous study demonstrated that Acacia bark extract possesses more powerful antioxidant properties than both vitamin C and catechin [20]. In addition, intake of Acacia bark extract prevents a decrease in ceramide levels, which are important for maintaining moisture in the skin. In mice with atopic dermatitis, Acacia bark extract suppressed the mRNA expression of ceramidase, a ceramide-degrading enzyme [21]. Thus, polyphenols in Acacia bark extract may prevent the desire to scratch, which is associated with atopic dermatitis, by preventing the development of dry skin. Although the ingestion of Acacia bark extract has been associated with a relief from the desire to scratch, previous studies have not provided sufficient evidence regarding the effectiveness of Acacia bark extract on humans with healthy skin. Therefore, the present study investigated the effect of proanthocyanidins derived from Acacia bark extract on the reduction of dryness in healthy Japanese adult subjects who were experiencing uncomfortable skin symptoms (e.g. a desire to scratch, which was not caused by an allergic reaction).

Methods

Study design

This was a randomized, double-blind, placebo-controlled, parallel-group study. The investigation was conducted at the Hiroo Dermatology Clinic & Mentors Inc. (Tokyo, Japan). The study protocol was approved by the ethical committee of the Takara Clinic, Medical Corporation Seishinkai (Tokyo, Japan), on July 10 2017 (approval number: 1707–1706-MZ01-03-TC). It was conducted in accordance with the principles of the Declaration of Helsinki (2013), the ethical guidelines for medical and health research involving human subjects in Japan, and broader medical ethics. Subjects were recruited from July 12 to September 9 2017, and the study was conducted from October 2 to December 16 2017. The protocol has been registered at the University Hospital Medical Information Network Clinical Trials Registry (UMIN000028199). The trial data were reported according to the CONSORT 2010 statement.

Subjects

In this study, the inclusion criterion was healthy Japanese adult subjects experiencing desire to scratch, uncomfortable skin, and dry skin (in Japanese: “muzumuzu” feeling) on the face and hands. The exclusion criteria were as follows: (a) any medical history of a malignant tumor, heart failure, or myocardial infarction; (b) undergoing treatment for any of the following chronic diseases: arrhythmia, liver failure, kidney failure, cerebrovascular disease, rheumatism, diabetes mellitus, hyperlipidemia, hypertension, or any other chronic diseases; (c) daily intake of “Food for Specified Health Uses” and/or “Foods with Function Claims”; (d) diagnosis of restless legs syndrome; (e) diagnosis of atopic dermatitis; (f) daily use of skin care products with the exception of a cream/essence, skin pack, skin lotion, milky lotion, sunscreen, and all-in-one products; (g) regular skin care treatments (massages) or use of beauty devices (facial equipment); (h) severe sunburn within one month prior to signing the study’s informed consent form, or plans to expose the skin to sun during the intervention period; (i) regular use of medications, including herbal medicines and/or supplements; (j) allergy to medications and/or products associated with the study substances, or having allergic skin; (k) pregnancy, lactation, or expected/planned pregnancy during the study period; (l) participation in another clinical study within the last 3 months prior to signing the study’s informed consent form; and (m) anyone judged as ineligible to participate in this study by the principal physician.

All subjects were enrolled through the website https://www.go106.jp/ operated by ORTHOMEDICO Inc. (Tokyo, Japan). The study protocol was comprehensively explained to all subjects. Written informed consent was obtained from all subjects prior to their participation in the study at ORTHOMEDICO Inc. office. No subject was part of the sponsors or funding companies.

Determination of sample size

Evidence regarding the effect of the intake of tablets containing Acacia bark extract on the water content of the stratum corneum water in humans is currently limited. Thus, the difference between the intervention and placebo group was hypothetically large in this study. According to a study conducted by Cohen [22], the effect-size (d) was 0.80, α was set to 0.05 and β to 0.20. Consequently, the calculated sample size per group was determined to be 33 subjects (factoring in a dropout rate over the study period). Therefore, it was estimated that a total of 66 subjects would be required for this randomized, double-blind, placebo-controlled, parallel-group study.

Enrollment, randomization, and blinding

Sixty-six healthy subjects experiencing uncomfortable skin and dry skin symptoms (in Japanese: “muzumuzu” feeling) were enrolled in this study. The principal physician declared the subjects as eligible to participate. Among subjects with thymus and activation-regulated chemokine (TARC) levels <450 pg/mL and non-specific IgE levels <170 IU/mL in prior to baseline intake, those with relatively high levels of transepidermal water loss (TEWL) were selected. An allocation controller not directly involved in this study, randomly assigned subjects to either the intervention group (n = 33) or placebo group (n = 33) using a computerized random-number generator. The allocation was based on the mean value and standard deviation of TEWL, gender, and age. Furthermore, none of the persons related to this study (i.e. subjects, physicians, or assessor of outcomes) were aware of the group assignments or were involved in the allocation. The allocation controller stored the allocation data (assignment sheet) in a safety cabinet until key-opening day.

Intervention

The test tablets were obtained from mimozax Co., Ltd. (Hiroshima, Japan), and the Acacia bark extract present in the test tablet was prepared as follows: Acacia bark was chopped and extracted using boiling water, and the extract was dried using a spray dryer. The extract is rich in proanthocyanidins, which are known as wattle tannins [23]. The Folin-Ciocalteu method was used to determine the total proanthocyanidins content of the tablet [24]. In addition, the tablet was analyzed using high-performance liquid chromatography, and robinetinidol-(4α,8)-catechin concentration was analyzed according to a previously described qualitative analysis method [24]. All subjects were administered Acacia bark extract tablets or placebo (six tablets per day) to be taken with water in the morning or after breakfast for a period of 8 weeks. The test tablets contained 180 mg (catechin-equivalent) or 245 mg (A. mearnsii proanthocyanidin-equivalent) of proanthocyanidins derived from Acacia bark as functional substance per day. The placebo tablets did not contain proanthocyanidins derived from Acacia bark but were indistinguishable in appearance.

Examination items

The schedule of this study is shown in Table 1. Examinations were conducted at baseline and 4 and 8 weeks after initiating the intervention. Subjects were requested to avoid alcohol consumption and excessive exercise for 24 h prior to the examination. Furthermore, subjects were requested not to consume any food or drinks (including test food), except water, for 6 h prior to the examination.

Table 1. The schedule of enrollment, intervention, and assessments in this study.

				Post-allocation
TIME POINT	Enrollment	Baseline	Allocation	Initiation of intake	4 weeks after intake	8 weeks after intake
ENROLLMENT:
Eligibility screen	×
Informed consent	×
Allocation			×
INTERVENTIONS:
Intervention group
Placebo group
ASSESSMENTS:
Objective evaluations on the skin items		×			×	×
Skindex-16		×			×	×
DLQI		×			×	×
Desire to scratch and blood test		×			×	×
Physical examination		×			×	×
Urinalysis		×			×	×
Hematological and blood biochemical tests		×			×	×
Daily record
Medical questionnaire		×			×	×

DLQI, Dermatology Life Quality Index

Primary outcome: objective evaluations of skin items

Objective evaluation of skin was performed through assessment of the water content in the stratum corneum (arbitrary unit; a.u.) and TEWL (g/h/m²) on the cheek (the intersection of the vertical line from the outer canthus of the right eye and the horizontal line in the middle of the nose) and back of the hand (between the thumb and index finger). The measurement was performed in triplicate at each examination and the mean was calculated. Subjects were requested to wash their face and hands and remain in a room at a temperature of 23 ± 5ºC with a humidity of 50 ± 15% for at least 10 minutes prior to the evaluation. Following at least 10 minutes of acclimation, the water content in the stratum corneum and TEWL were evaluated using the Corneometer® CM825 (Courage +Khazaka Electronic GmbH, Cologne, Germany) and Tewameter® TM300 (Courage +Khazaka Electronic GmbH, Cologne, Germany), respectively.

Secondary outcomes

Secondary outcomes included gloss (arbitrary unit; a.u.) and viscoelasticity (arbitrary unit; a.u.) on the cheek and back of the hand. Gloss and viscoelasticity of the skin were evaluated using a Skin-Glossymeter GL200 (Courage +Khazaka Electronic GmbH, Cologne, Germany) and Cutometer® dual MPA580 (Courage +Khazaka Electronic GmbH, Cologne, Germany), respectively.

The skin conditions 1 week prior to the examination were assessed using the Japanese version of Skindex-16 [25,26] and Dermatology Life Quality Index (DLQI) [27,28]. In addition, subjective symptoms of the desire to scratch were evaluated using the visual analog scale (VAS), in which a 100-mm horizontal line was printed. The left end (0 mm) was defined as the best condition (no desire to scratch), whereas the right end (100 mm) was defined as the worst condition (very frequent desire to scratch). The subjects were requested to draw a vertical line across the horizontal line at the point that most accurately described their desire to scratch.

Furthermore, the levels of TARC and IgE in the blood – biomarkers of atopic dermatitis and allergic reactions – were determined. This measurement was performed by LSI Medience Corporation (Tokyo, Japan).

Safety evaluation

The physical examination conducted included height, weight, body mass index, body fat percentage, systolic and diastolic blood pressures, and pulse rate. Height was measured once at baseline to calculate the body mass index. Urine samples were collected to evaluate levels of protein, glucose, urobilinogen, bilirubin, ketone bodies, pH, and occult blood. These measurements were performed by LSI Medience Corporation. Hematological testing was conducted to assess the following: leukocyte count, erythrocyte count, hemoglobin, hematocrit value, platelet count, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, and differentiation of white blood cells (percentage of neutrophils, lymphocytes, monocytes, eosinophils, and basophils). Furthermore, biochemical testing evaluated the following: AST, ALT, γ-GT, ALP, LD, LAP, total bilirubin, direct bilirubin, indirect bilirubin, cholinesterase, ZTT, total protein, urea nitrogen, creatinine, uric acid, calcium, serum amylase, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglycerides, glycoalbumin, serum iron, sodium, potassium, chloride, inorganic phosphorus, glucose, and hemoglobin A1c. Hematological and biochemical testing was perfomed by LSI Medience Corporation. Subjects were requested to complete a medical questionnaire to determine their health status at each assessment point. Additionally, subjects reported medication dosage and any changes in their physical condition on a daily basis.

Statistical analysis

All statistical analyses were two-sided without adjustment for multiple comparisons, and the significance level was set at 1% and 5%. Data analysis was performed using the SPSS Version 23.0 (IBM Japan, Ltd., Tokyo, Japan) and Microsoft Excel 2013 (Microsoft Japan Co., Ltd., Tokyo, Japan) software. Moreover, subjects with an ingestion rate <90% and/or those who violated the compliance of the study were excluded from the analysis.

Demographic data of the subjects included gender, age, and physical characteristics. The data at baseline and degree of change were analyzed using Student’s t-test, and the data after intake was analyzed using analysis of covariance (ANCOVA). ANCOVA was applied for comparisons between groups, using the baseline values as covariates. Furthermore, urinalysis data was analyzed using the chi-square test at baseline and at 4 and 8 weeks after intake.

Results

Subjects

All subjects in this study had an ingestion rate ≥90%. However, six subjects total were excluded from the analysis; one and five subjects were excluded for missing data and violation of the compliance rules, respectively (Figure 1). Therefore, this analysis was performed on the per-protocol dataset. The demographic characteristics of the subjects did not differ significantly between groups (Table 2).

Table 2. Subject background information.

Item	Intervention group (n = 30)	Placebo group (n = 30)	P value
Gender (Male/Female)	7/23	8/22	1.000
Age (years)	44.3 ± 9.8	44.8 ± 9.1	0.817
Body height (cm)	162.6 ± 7.5	160.9 ± 7.7	0.386
Body weight (kg)	55.5 ± 12.4	55.3 ± 10.6	0.960
Body mass index (kg/m^2)	20.8 ± 3.2	21.2 ± 2.8	0.568
Body fat percentage (%)	23.4 ± 5.5	24.4 ± 6.3	0.506
Systolic blood pressure (mmHg)	118.0 ± 14.6	120.5 ± 18.2	0.559
Diastolic blood pressure (mmHg)	74.3 ± 11.5	76.6 ± 13.0	0.474
Pulse rate (bpm)	71.1 ± 11.7	75.9 ± 11.5	0.116

The data are presented as the mean ± standard deviation

Figure 1. The flowchart of participants in this study.

Objective evaluations of skin items

At baseline, there were no significant differences observed between the intervention and placebo groups. After 8 weeks of intake, the intervention group showed a significant reduction from 16.7 ± 4.9 to 19.4 ± 6.2 g/h/m² in TEWL [the variation between baseline and 8 weeks of intake (Δ8 weeks); 2.7 ± 4.0 g/h/m²] compared with that reported in the placebo group (from 15.8 ± 4.6 to 21.3 ± 7.7 g/h/m²) (Δ8 weeks; 5.5 ± 5.7 g/h/m²; 8 weeks of intake, P = 0.029; Δ8 weeks, P = 0.030; Figure 2(b), Figure 3). For other assessments in the objective evaluation of skin items, there were no significant differences between groups throughout the intervention period (Figure 2(a), Figure 2(c–h)).

Figure 2. Objective evaluations on the skin items in the intervention (closed diamond, n = 30) and placebo (open circle, n = 30) groups at each assessment point. (a) moisture on the facial skin surface, (b) transepidermal water loss on the face, (c) facial gloss, (d) facial skin viscoelasticity, (e) moisture on the hand skin surface, (f) transepidermal water loss on the hand, (g) skin gloss on the hand, and (h) skin viscoelasticity on the hand. Bars display the standard error of the mean.

*: P < 0.05 vs. the Placebo group; †: Effect-size and 95% confidence interval

Figure 3. Variation in transepidermal water loss on the face in the intervention (black bar, n = 30) and placebo (white bar, n = 30) groups at 8 weeks after intake. Bars display the standard error of the mean.

*: P < 0.05 vs. the Placebo group; †: Effect-size and 95% confidence interval

Skindex-16 score

There were no significant differences observed between the intervention and placebo groups at 4 and 8 weeks after intake (Figure 4).

Figure 4. Scores of skindex-16 in the intervention (closed diamond, n = 30) and placebo (open circle, n = 30) groups at each assessment point. (a) symptom domain scores, (b) emotion domain scores, and (c) functioning domain scores. Bars display the standard error of the mean.

DLQI

At baseline, there were no significant differences observed between the intervention and placebo groups. Moreover, at 4 weeks after intake, the intervention group showed significantly reduced subjective symptoms according to the symptom/feeling score (from 1.10 ± 0.80 to 0.33 ± 0.61 points) compared with the placebo group (from 1.07 ± 1.08 to 0.73 ± 0.83 points; P = 0.019, Figure 5(a-1)). Furthermore, the intervention group showed significantly reduced subjective symptoms based on the symptom/feeling score in response to the question: “Over the last week, how itchy, sore, painful, or stinging has your skin been?” (from 0.77 ± 0.50 to 0.20 ± 0.41 points) compared with the placebo group (from 0.60 ± 0.67 to 0.57 ± 0.63 points; P = 0.002, Figure 5(a-2)). At 4 weeks after intake, the intervention group presented a significantly higher treatment subscale score of the DLQI (from 0.23 ± 0.43 to 0.13 ± 0.35 points) than that of the placebo group (from 0.23 ± 0.50 to 0.00 ± 0.00 points; P = 0.038; Figure 5(f)). There were no significant differences for other assessments in the DLQI between groups throughout the intervention period (Figure 5(b), Figure 5(c–e), Figure 5(g))

Figure 5. Scores of DLQI in the intervention (closed diamond, n = 30) and placebo (open circle, n = 30) groups at each assessment point. (a-1) symptom/feeling, (a-2) question 1 “Over the last week, how itchy, sore, painful or stinging has your skin been?” (the subscale scores of symptom/feeling), (b) daily activities, (c) leisure, (d) work/school, (e) personal relationships, (f) treatment, and (g) total score. Bars display the standard error of the mean.

*: P < 0.05, **: P < 0.01 vs. the Placebo group; †: Effect-size and 95% confidence interval. DLQI, Dermatology Life Quality Index

Desire to scratch and blood tests

At 4 weeks after intake, the intervention group exhibited significantly reduced subjective symptoms with regard to the desire to scratch (from 29.5 ± 23.7 to 17.1 ± 20.2 mm) compared with those reported in the placebo group (from 31.8 ± 26.2 to 27.7 ± 22.8 mm; P < 0.050, Figure 6). No significant differences were observed between the intervention and placebo groups at baseline and at 8 weeks after intake. Furthermore, the levels of TARC and IgE remained within the normal range (TARC: <450 pg/mL; IgE level: ≤170 IU/mL, data not shown) and did not change significantly between the groups.

Figure 6. VAS results of desire to scratch in the intervention (closed diamond, n = 30) and placebo (open circle, n = 30) groups at each assessment point. Bars display the standard error of the mean.

*: P < 0.05 vs. the Placebo group; †: Effect-size and 95% confidence interval. VAS, Visual Analogue Scale

Safety evaluation

Safety evaluation demonstrated no significant differences in physical examination and urinalysis. Although the intervention group (89.1 ± 33.8 μg/dL) showed a significantly lower serum iron level at 8 weeks than that in the placebo group (109.5 ± 44.7 μg/dL, P = 0.009), it was within the reference range (Tables 3–5).

Table 3. The results of the safety evaluation (physical examination).

Item	Group	Baseline	4 weeks after intake	8 weeks after intake
Height (cm)	Intervention group (n = 30)	162.6 ± 7.5	－	－
	Placebo group (n = 30)	160.9 ± 7.7
Body weight (kg)	Intervention group (n = 30)	55.5 ± 12.4	55.9 ± 12.8	55.9 ± 12.7
	Placebo group (n = 30)	55.3 ± 10.6	55.6 ± 10.6	55.5 ± 10.7
BMI (kg/m^2)	Intervention group (n = 30)	20.8 ± 3.2	21.0 ± 3.4	21.0 ± 3.3
	Placebo group (n = 30)	21.2 ± 2.8	21.3 ± 2.7	21.3 ± 2.8
Body fat percentage (%)	Intervention group (n = 30)	23.4 ± 5.5	24.0 ± 6.1	24.3 ± 6.1
	Placebo group (n = 30)	24.4 ± 6.3	24.9 ± 6.1	24.9 ± 6.6
Systolic blood pressure (mmHg)	Intervention group (n = 30)	118.0 ± 14.6	114.7 ± 14.3	115.2 ± 14.3
	Placebo group (n = 30)	120.5 ± 18.2	114.9 ± 15.3	116.4 ± 11.9
Diastolic blood pressure (mmHg)	Intervention group (n = 30)	74.3 ± 11.5	73.6 ± 12.0	73.4 ± 11.9
	Placebo group (n = 30)	76.6 ± 13.0	75.3 ± 10.9	74.6 ± 9.5
Pulse rate (bpm)	Intervention group (n = 30)	71.1 ± 11.7	72.9 ± 13.1	73.5 ± 10.7
	Placebo group (n = 30)	75.9 ± 11.5	75.1 ± 10.9	73.9 ± 10.3

The data are presented as the mean ±standard deviation

BMI, body mass index

Table 4. The results of the safety evaluation (urinalysis).

		Baseline		4 weeks after intake		8 weeks after intake
Item	Group	Within the normal range	Outside the normal range	Within the normal range	Outside the normal range	Within the normal range	Outside the normal range
Protein	Intervention group (n = 30)	26	4	23	7	26	4
	Placebo group (n = 30)	26	4	25	5	25	5
Glucose	Intervention group (n = 30)	30	0	30	0	30	0
	Placebo group (n = 30)	30	0	29	1	30	0
Urobilinogen	Intervention group (n = 30)	30	0	30	0	30	0
	Placebo group (n = 30)	28	2	30	0	29	1
Bilirubin	Intervention group (n = 30)	30	0	30	0	30	0
	Placebo group (n = 30)	30	0	30	0	30	0
pH	Intervention group (n = 30)	27	3	28	2	29	1
	Placebo group (n = 30)	28	2	29	1	29	1
Occult blood	Intervention group (n = 30)	25	5	22	8	20	10
	Placebo group (n = 30)	25	5	23	7	24	6
Ketone bodies	Intervention group (n = 30)	30	0	30	0	30	0
	Placebo group (n = 30)	29	1	28	2	30	0

The data are presented as the number of participants

Table 5. The results of the safety evaluation (blood tests).

Item	Reference value	Group	Baseline	4 weeks after intake	8 weeks after intake
Leukocyte count (/μL)	3300–9000	Intervention group (n = 30)	5536.7 ± 1435.4	5506.7 ± 1284.4	5263.3 ± 1205.0
		Placebo group (n = 30)	5813.3 ± 1439.8	5500.0 ± 1232.9	5503.3 ± 1377.3
Erythrocyte count (×10^4/μL)	M: 430–570	Intervention group (n = 30)	450.1 ± 44.1	453.8 ± 50.3	453.4 ± 46.8
	F: 380–500	Placebo group (n = 30)	447.8 ± 47.6	450.1 ± 53.7	452.5 ± 54.6
Hemoglobin (g/dL)	M: 13.5–17.5	Intervention group (n = 30)	13.5 ± 1.4	13.6 ± 1.6	13.5 ± 1.6
	F: 11.5–15.0	Placebo group (n = 30)	13.4 ± 1.5	13.4 ± 1.4	13.5 ± 1.4
Hematocrit value (%)	M: 39.7–52.4	Intervention group (n = 30)	42.1 ± 3.9	42.8 ± 4.2	42.7 ± 4.2
	F: 34.8–45.0	Placebo group (n = 30)	41.7 ± 3.7	42.4 ± 3.9	42.6 ± 3.7
Platelet count (×10^4/μL)	14.0–34.0	Intervention group (n = 30)	26.9 ± 4.5	29.0 ± 5.4	28.8 ± 5.6
		Placebo group (n = 30)	27.5 ± 4.9	28.8 ± 6.0	28.6 ± 6.0
Mean corpuscular volume (fL)	85–102	Intervention group (n = 30)	93.8 ± 4.8	94.4 ± 4.8	94.4 ± 4.9
		Placebo group (n = 30)	93.5 ± 7.7	94.9 ± 7.8	94.8 ± 7.6
Mean corpuscular hemoglobin (pg)	28.0–34.0	Intervention group (n = 30)	30.0 ± 1.7	30.0 ± 1.6	29.9 ± 1.9
		Placebo group (n = 30)	30.0 ± 3.1	30.0 ± 2.9	30.0 ± 2.9
Mean corpuscular hemoglobin concentration (%)	30.2–35.1	Intervention group (n = 30)	32.0 ± 1.1	31.7 ± 1.1	31.6 ± 1.2
		Placebo group (n = 30)	32.0 ± 1.3	31.6 ± 1.1	31.7 ± 1.2
Percentage of neutrophils (%)	40.0–75.0	Intervention group (n = 30)	57.6 ± 9.0	59.1 ± 7.4	59.2 ± 7.4
		Placebo group (n = 30)	60.2 ± 9.2	58.9 ± 9.1	59.0 ± 10.0
Percentage of lymphocytes (%)	18.0–49.0	Intervention group (n = 30)	34.8 ± 8.4	32.9 ± 6.2	32.9 ± 7.0
		Placebo group (n = 30)	32.3 ± 9.0	32.6 ± 9.0	32.7 ± 9.9
Percentage of monocytes (%)	2.0–10.0	Intervention group (n = 30)	4.7 ± 1.1	4.8 ± 1.2	4.8 ± 1.1
		Placebo group (n = 30)	4.9 ± 1.2	5.2 ± 1.5	5.2 ± 1.4
Percentage of eosinophils (%)	0.0–8.0	Intervention group (n = 30)	2.1 ± 1.2	2.4 ± 2.0	2.2 ± 1.5
		Placebo group (n = 30)	1.9 ± 1.0	2.7 ± 2.2	2.4 ± 1.7
Percentage of basophils (%)	0.0–2.0	Intervention group (n = 30)	0.77 ± 0.40	0.80 ± 0.44	0.88 ± 0.54
		Placebo group (n = 30)	0.68 ± 0.39	0.68 ± 0.42	0.65 ± 0.39
AST (U/L)	10–40	Intervention group (n = 30)	19.8 ± 5.5	20.6 ± 6.3	20.7 ± 6.4
		Placebo group (n = 30)	21.1 ± 15.0	20.3 ± 9.8	20.7 ± 8.9
ALT (U/L)	5–45	Intervention group (n = 30)	16.1 ± 8.7	17.2 ± 9.9	18.0 ± 12.4
		Placebo group (n = 30)	15.5 ± 9.4	15.9 ± 7.2	15.0 ± 6.8
γ-GT (U/L)	M: ≤80	Intervention group (n = 30)	18.8 ± 9.2	20.4 ± 9.5	19.5 ± 9.3
	F: ≤30	Placebo group (n = 30)	23.3 ± 22.0	23.9 ± 23.1	22.4 ± 19.7
ALP (U/L)	100–325	Intervention group (n = 30)	179.2 ± 45.5	186.1 ± 49.8	180.2 ± 44.9
		Placebo group (n = 30)	165.8 ± 35.3	176.3 ± 43.5	172.3 ± 43.9
LD (U/L)	120–240	Intervention group (n = 30)	181.5 ± 23.7	182.3 ± 26.9	183.2 ± 22.8
		Placebo group (n = 30)	185.5 ± 24.6	182.9 ± 25.2	188.3 ± 26.0
LAP (U/L)	M: 45–81F: 37–61	Intervention group (n = 30)	49.4 ± 6.5	49.5 ± 6.9	48.2 ± 6.2
		Placebo group (n = 30)	49.7 ± 8.5	48.7 ± 8.2	48.0 ± 7.3
Total bilirubin (mg/dL)	0.2–1.2	Intervention group (n = 30)	0.92 ± 0.38	0.82 ± 0.32	0.84 ± 0.37
		Placebo group (n = 30)	0.76 ± 0.21	0.77 ± 0.21	0.79 ± 0.27
Direct bilirubin (mg/dL)	0.0–0.2	Intervention group (n = 30)	0.09 ± 0.04	0.07 ± 0.05	0.08 ± 0.05
		Placebo group (n = 30)	0.09 ± 0.03	0.08 ± 0.04	0.09 ± 0.05
Indirect bilirubin (mg/dL)	0.2–1.0	Intervention group (n = 30)	0.83 ± 0.35*	0.75 ± 0.28	0.76±0.35
		Placebo group (n = 30)	0.67 ± 0.21	0.69 ± 0.19	0.71 ± 0.23
Cholinesterase (U/L)	M: 234–493	Intervention group (n = 30)	316.0 ± 74.7	326.5 ± 77.8	322.3 ± 72.5
	F: 200–452	Placebo group (n = 30)	296.9 ± 52.9	305.1 ± 64.8	308.3 ± 64.9
ZTT (U)	2.0–12.0	Intervention group (n = 30)	6.5 ± 3.2	6.1 ± 2.9	6.0 ± 2.9
		Placebo group (n = 30)	7.8 ± 2.9	7.3 ± 2.7	7.2 ± 2.8
Total protein (g/dL)	6.7–8.3	Intervention group (n = 30)	7.3 ± 0.4*	7.2 ± 0.3	7.2 ± 0.4
		Placebo group (n = 30)	7.5 ± 0.4	7.4 ± 0.4	7.4 ± 0.4
Urea nitrogen (mg/dL)	8.0–20.0	Intervention group (n = 30)	12.6 ± 2.9	12.9 ± 3.2	13.2 ± 2.7
		Placebo group (n = 30)	12.8 ± 4.1	12.3 ± 2.7	12.5 ± 3.3
Creatinine (mg/dL)	M: 0.61–1.04	Intervention group (n = 30)	0.70 ± 0.12	0.67 ± 0.14	0.66 ± 0.13
	F: 0.47–0.79	Placebo group (n = 30)	0.73 ± 0.14	0.69 ± 0.14	0.69 ± 0.13
Uric acid (mg/dL)	M: 3.8–7.0	Intervention group (n = 30)	4.6 ± 1.2	4.5 ± 1.2	4.5 ± 1.3
	F: 2.5–7.0	Placebo group (n = 30)	4.7 ± 1.4	4.5 ± 1.3	4.4 ± 1.3
Sodium (mEq/L)	137–147	Intervention group (n = 30)	140.57 ± 1.83	140.90 ± 1.67	141.33 ± 1.99
		Placebo group (n = 30)	140.50 ± 1.55	140.80 ± 1.94	141.03 ± 1.43
Potassium (mEq/L)	3.5–5.0	Intervention group (n = 30)	4.2 ± 0.4	4.1 ± 0.3	4.0 ± 0.4
		Placebo group (n = 30)	4.3 ± 0.4	4.1 ± 0.4	4.1 ± 0.4
Chloride (mEq/L)	98–108	Intervention group (n = 30)	101.5 ± 2.4	101.5 ± 2.6	102.0 ± 2.4
		Placebo group (n = 30)	101.0 ± 2.2	101.2 ± 1.9	101.8 ± 1.9
Calcium (mg/dL)	8.4–10.4	Intervention group (n = 30)	9.4 ± 0.3	9.3 ± 0.3	9.3 ± 0.4
		Placebo group (n = 30)	9.4 ± 0.5	9.3 ± 0.4	9.4 ± 0.4
Inorganic phosphorus (mg/dL)	2.5–4.5	Intervention group (n = 30)	3.39 ± 0.41	3.54 ± 0.47	3.55 ± 0.40
		Placebo group (n = 30)	3.41 ± 0.47	3.54 ± 0.49	3.51 ± 0.54
Serum iron (μg/dL)	M: 50–200	Intervention group (n = 30)	107.0 ± 37.0	95.8 ± 39.1	89.1 ± 33.8**
	F: 40–180	Placebo group (n = 30)	97.6 ± 38.2	95.7 ± 32.9	109.5 ± 44.7
Serum amylase (U/L)	40–122	Intervention group (n = 30)	83.0 ± 27.7	88.2 ± 36.3	89.6 ± 39.5
		Placebo group (n = 30)	81.7 ± 37.2	78.9 ± 30.7	81.0 ± 28.2
Total cholesterol (mg/dL)	120–219	Intervention group (n = 30)	207.9 ± 36.5	209.7 ± 43.2	205.4 ± 42.7
		Placebo group (n = 30)	207.9 ± 41.9	211.9 ± 39.2	211.4 ± 31.0
HDL cholesterol (mg/dL)	M: 40–85	Intervention group (n = 30)	73.9 ± 21.0	75.1 ± 22.5	75.8 ± 24.4
	F: 40–95	Placebo group (n = 30)	68.9 ± 18.0	71.7 ± 19.7	72.6 ± 21.3
LDL cholesterol (mg/dL)	65–139	Intervention group (n = 30)	116.2 ± 29.1	119.7 ± 30.1	114.3 ± 31.5
		Placebo group (n = 30)	116.4 ± 35.4	122.0 ± 31.6	119.9 ± 25.6
Triglyceride (mg/dL)	30–149	Intervention group (n = 30)	81.0 ± 51.9	78.2 ± 52.2	80.4 ± 52.2
		Placebo group (n = 30)	113.9 ± 113.5	92.2 ± 58.2	93.6 ± 57.0
Glucose (mg/dL)	70–109	Intervention group (n = 30)	81.7 ± 13.7	81.1 ± 6.4	80.8 ± 6.8
		Placebo group (n = 30)	82.7 ± 8.4	82.3 ± 10.8	81.6 ± 8.2
Hemoglobin A1c (%)	4.6–6.2	Intervention group (n = 30)	5.23 ± 0.22	5.27 ± 0.21	5.24 ± 0.18
		Placebo group (n = 30)	5.21 ± 0.33	5.28 ± 0.34	5.28 ± 0.32
Glycoalbumin (%)	12.3–16.5	Intervention group (n = 30)	14.39 ± 1.04	14.24 ± 1.05	14.24 ± 1.05
		Placebo group (n = 30)	14.16 ± 1.11	14.00 ± 1.12	13.97 ± 1.12

The data are presented as the mean ± standard deviation.

aP < 0.05，

bP < 0.01 vs. the placebo group AST, aspartate aminotransferase; ALT, alanine aminotransferase; γ-GT, gamma-glutamyl transpeptidase; ALP, alkaline phosphatase; LD, lactate dehydrogenase; LAP, leucine aminopeptidase; ZTT, zinc sulfate turbidity test; HDL-Cholesterol, high-density lipoprotein cholesterol; LDL-cholesterol, low-density lipoproteincholesterol

Discussion

The present study showed that an eight-week intake of tablets containing proanthocyanidins derived from Acacia (A. mearnsii) bark extract (Acacia bark extract) significantly reduced TEWL on facial skin. Although there were no significant differences reported in the water content of the stratum corneum between the two groups, the mean score was increased in the intervention group during the study (data not shown). The reduction of TEWL is one of the most effective approaches in retaining the water content of the stratum corneum [29] and indicates the prevention of dry skin. Furthermore, strictinin, a type of tea polyphenol, inhibits the production of specific IgE [30]. The present study showed that the ingestion of the proanthocyanidins present in Acacia bark extract may lead to a decrease in the production of IgE. However, there were no significant changes observed in the production of non-specific IgE in healthy Japanese adult subjects in this study. Hence, the effect of Acacia bark extract on IgE may be minimal. Guo et al. [31] reported that in hairless mice, an increase in the levels of tumor necrosis factor (TNF)-α and inflammation induced by human sebum resulted in a significant increase in TEWL. However, levels of IgE in the serum remained the same. These results suggested that inflammation induced by the presence of excess sebum is more likely an irritant than an indicator for allergic contact dermatitis. Consequently, the intake of Acacia bark extract tablets significantly decreased TEWL in humans without atopic dermatitis through a mechanism independent of IgE.

According to a study conducted by Ikarashi et al. [32], the intake of Acacia bark extract suppressed the expression of TNF-α in white adipose tissue of obese diabetic KKAy mice. Furthermore, some food ingredients other than Acacia bark extract have been shown to suppress the expression of TNF-α, leading to the alleviation of inflammation and reduction of TEWL. Reportedly, the intake of Korean red ginseng (KRG) significantly interrupted any increase in TEWL and significantly suppressed the expression of TNF-α in NC/Nga mice treated with 2,4,6-trinitrochlorobenzene [33]. In addition, a study conducted by Lee and Cho [34] demonstrated that KRG possesses anti-inflammatory properties, which suppress the mRNA levels of TNF-α. Furthermore, the intake of KRG protected against the onset and progression of dry skin through TEWL reduction. In another study, the intake of nutmeg extract suppressed the expression of TNF-α mRNA and reduced TEWL in mice with atopic dermatitis-like skin lesions induced through American house dust mite extract [35]. Kim B and Kim HS [36] reported that a novel peptide B (peptide sequences; RRFSLLRY), a protease-activated receptor 2 antagonist, reduced the expression of inflammatory cytokines such as TNF-α and interleukin-6 and decreased TEWL in hairless mice. In a clinical study conducted by Zhao et al. [37], an ointment containing Portulaca oleracea extract combined with calcipotriol suppressed the expression of TNF-α and reduced TEWL in patients with psoriasis. The findings of these previous studies suggest that the mechanism for the reduction of TEWL and inflammation using proanthocyanidins derived from Acacia bark involves the suppression of TNF-α.

Furthermore, a previous study demonstrated that the intake of proanthocyanidins derived from Acacia (A. mearnsii) bark increased the moisture content of the skin and decreased TEWL in mice with atopic dermatitis. The intake of proanthocyanidins derived from Acacia bark suppressed the mRNA expression of ceramidase (the enzyme which degrades ceramide), preventing a decrease in the levels of ceramide [21]. Ceramide is present in the stratum corneum and acts as a defense mechanism by retaining moisture between cells and preventing excess water permeation [38,39]. In this study, Acacia bark extract may suppress the expression of ceramidase even in skin without atopic dermatitis, resulting in decreased TEWL.

The intake of Acacia bark extract tablets improved QOL related to skin conditions, as assessed by the symptom/feeling score and question one of the DLQI: “over the last week, how itchy, sore, painful or stingy has your skin been?” Although the treatment score in the intervention group was higher than that recorded in the placebo group, this score was similar to that reported by healthy subjects in a previous study [27]; therefore, there was no clinical meaning. VAS assessment showed that Acacia bark extract tablets improved the desire to scratch at 4 weeks after intake. The desire to scratch is associated with the production of nitric oxide (NO) [40]. A previous study demonstrated that Acacia bark extract possesses a five- to seven-fold higher scavenging activity for superoxides than that possessed by vitamin C and catechins, indicating the powerful antioxidant properties of Acacia bark extract [20]. Another previous study demonstrated that green tea possesses free radical-scavenging activity based on the following chemical compounds: (−)-epigallocatechin 3-O-gallate, (−)-gallocatechin 3-O-gallate, (−)-epicatechin 3-O-gallate, (−)-epigallocatechin, (+)-gallocatechin, (−)-epicatechin, and (+)-catechin [41]. These compounds have demonstrated direct scavenging activity against NO and superoxide and have a similar structure to that of proanthocyanidins derived from A. mearnsii bark, which are known for their powerful antioxidant properties [20]. Andoh and Kuraishi [40] suggested that NO induces responses related to the desire to scratch and is a key antipruritic agent. Furthermore, polyphenols reduce skin damage from solar ultraviolet radiation through their antioxidant and anti-inflammatory activities [14,15]. These findings suggested that the intake of Acacia bark extract suppressed the desire to scratch by scavenging NO and alleviating skin damage caused by solar ultraviolet radiation, resulting in improved QOL related to skin conditions.

Based on the present results, the intake of proanthocyanidins derived from Acacia bark reduced TEWL significantly on the facial skin of healthy Japanese adult subjects experiencing uncomfortable skin symptoms through a mechanism independent of IgE. The following potential mechanism of TEWL regulation is proposed. Proanthocyanidins derived from Acacia bark may reduce TEWL and inflammation by suppressing TNF-α. Furthermore, proanthocyanidins derived from Acacia bark retain the levels of ceramide and possibly reduce TEWL on skin without atopic dermatitis by suppressing the expression of ceramidase. In addition, ingestion of proanthocyanidins derived from Acacia bark reduces skin damage caused by dry skin/desire to scratch and inflammation through the antioxidant and anti-inflammatory properties of polyphenols. Thus, the uncomfortable symptoms of dry skin were alleviated, resulting in improved QOL related to skin conditions.

Despite the significantly lower serum iron levels in the intervention group at 8 weeks, serum iron level was included as the reference value. A different study using the same tablet for 4 weeks but with a five-fold increase in dosage reported no effects in serum iron levels [42]. Therefore, the significant difference in serum iron level observed in this study has no clinical relevance.

Our study design has several limitations. First, the sample size should be increased to obtain accurate results. Second, the face and hands were exposed to external factors; therefore, it is also necessary to verify the effect of Acacia bark extract on these exposed skin parts. Finally, further studies concerning these versatile aspects should investigate the fundamental underlying mechanism involved in reducing uncomfortable skin symptoms using Acacia bark extract to better understand our study. However, this study demonstrated that Acacia bark extract tablets containing proanthocyanidins derived from A. mearnsii significantly reduced TEWL from the facial skin of healthy Japanese adult subjects experiencing uncomfortable skin symptoms.

Conclusions

The eight-week intake of tablets containing proanthocyanidins derived from Acacia bark reduced TEWL and alleviated the symptoms of uncomfortable, dry skin (in Japanese: “muzumuzu” feeling) in healthy Japanese adult subjects. Furthermore, the intake of Acacia bark extract tablets was found to be completely safe under the conditions of the study.

Author Contribution

T. H., S. Y., and N. S. designed the study. S. O. was involved the study conceptions and managing the research expenses. Furthermore, A. B. drafted the manuscript. T. I. (MD) was the principal investigator and managed the physical conditions of all subject at his clinic. All authors reviewed and approved the final manuscript.

Acknowledgments

The authors would like to thank all the subjects and staff who participated in this study. Special appreciation is extended to Kenichi Kakino of the Evaluation Center of Health And Nutrition Inc. for his contribution.

Disclosure statement

This sponsor of this study, mimozax Co., Ltd. entrusted ORTHOMEDICO Inc., with conducting the study. S. O belongs to mimozax Co., Ltd. and T. H., S. Y., N. S., and A. B. all belong to ORTHOMEDICO Inc. T. I. (MD), belongs to Hiroo Dermatology Clinic & Mentors Inc., and is the principal investigator.

Additional information

Funding

This study was supported by mimozax Co., Ltd.