Markers of skin elasticity and their use

Abstract

To provide a novel method of evaluating skin elasticity using an indicator that enables objective and accurate assessment of elasticity and the degree of aging of skin.SOLUTION: The present invention relates to a method of assessing elasticity and the degree of aging of skin using lactic acid content in the stratum corneum of the skin as an indicator. Based on the lactic acid content of the skin stratum corneum obtained by the method of the present invention, cosmetics and topical agents customized to a subject for improvement and prevention of skin aging can be provided and skin care methods and the like customized to the subject can be proposed.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for evaluating skin elasticity by measuring the content of lactic acid in skin keratin.

Background Art

[0002] Skin is constantly exposed to various physical and chemical stresses such as ultraviolet rays, dryness, cold, heat, drugs, etc. As a result, the function of the skin deteriorates, and various skin aging phenomena become apparent. One of the skin aging phenomena is a decrease in elasticity. The elasticity of the skin is the force that tries to push back against external physical pressure and return to its original state, and it is one of the important functions for maintaining the constancy of the skin. The elasticity of the skin decreases due to internal factors such as age, external physical and chemical stimuli, and hormonal balance, and there are individual differences depending on the degree of external and internal factors.

[0003] Devices for measuring skin elasticity have been developed by regarding the skin as an elastic body. One of the typical measuring devices is the CUTOMETER (trade name) (manufactured by Courage&Khazaka). This device draws the skin surface into the probe opening in a negative pressure state, measures the skin length drawn into the opening with a prism, then releases the suction, and similarly measures the displacement length (return) when the suction is released, and determines the elasticity using this measurement result as a parameter (Non-Patent Document 1). Using the elasticity measured by this device as an index, the evaluation of skin aging degree and the evaluation of the effects of cosmetics have been widely popularized in the cosmetics industry and the beauty-related medical field.

[0004] Non-Patent Document 2 describes that the effect of yogurt using lactic acid bacteria on skin elasticity was evaluated using a cutometer. Thus, skin elasticity is recognized as an important parameter for evaluating the health state of the skin.

[0005] Furthermore, methods for measuring skin elasticity using chemical analytical techniques have also been proposed. Patent Document 1 describes a method for evaluating the viscoelasticity of skin from the expression level of Neutrophil gelatinase-associated lipocalin (NGAL) in human stratum corneum.

[0006] Lactic acid, as used in this invention, is one of the products of glycolysis, a pathway responsible for energy production in living organisms. During strenuous exercise, sugar is broken down in muscle cells as an energy source, and lactic acid accumulates via pyruvate. In the skin, it is secreted into the stratum corneum as a metabolite through metabolism, and is also contained in sweat. Methods have been devised to monitor the amount of lactic acid in bodily fluids such as sweat for the management of cancer and diabetes (Patent Document 2). However, it is not known that the amount of lactic acid in the stratum corneum of the skin is an effective indicator of skin elasticity. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 5866053 [Patent Document 2] Special Publication No. 2014-528086 [Non-patent literature]

[0008] [Non-Patent Document 1] Miyaji, Yoshiki et al., Aesthetic Dermatology, pp. 173-174 (2009) [Non-Patent Document 2] Yoshihisa Izawa et al., Journal of Intestinal Microbiota, 22, pp. 1-5 (2008) [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention aims to provide a new index that enables the prediction and evaluation of skin elasticity and the degree of aging. [Means for solving the problem]

[0010] The inventors of this invention conducted intensive research to solve the above problems and found that the lactic acid content in the stratum corneum of the skin correlates with skin elasticity and age, and that by using the lactic acid content in the stratum corneum as an indicator based on this correlation, the degree of skin elasticity and aging can be objectively and accurately evaluated, thus completing the present invention.

[0011] In other words, the present invention is as follows: (1) A method for evaluating skin elasticity, characterized by measuring the lactic acid content of the stratum corneum of the skin. (2) A method for evaluating skin elasticity, comprising a collection step of collecting keratin from the skin of a subject, a measurement step of measuring the lactic acid content of the keratin collected in the collection step, and a step of determining skin elasticity from the lactic acid content measured in the measurement step. (3) The evaluation method described in (2), wherein the process of collecting keratinized skin cells is performed by the tape stripping method. (4) A method for evaluating the degree of skin aging, characterized by measuring the lactic acid content of the stratum corneum of the skin. [Effects of the Invention]

[0012] According to the method of the present invention, a new marker that correlates with skin elasticity and the degree of aging is used as an indicator, allowing for objective and accurate evaluation of skin elasticity and the degree of aging. Since the method of the present invention uses stratum corneum collected from subjects as a sample, it is rapid, simple, and burdenless to the subjects. Dedicated measuring devices such as a cutometer are unnecessary, simplifying skin elasticity measurement. Furthermore, the stratum corneum can be easily collected by tape stripping and transported by simple means such as mail, enabling the measurement of skin elasticity from a large number of subjects in one location. Additionally, the lactic acid content of the stratum corneum can be used as a new indicator of aging. [Brief explanation of the drawing]

[0013] [Figure 1] This chart shows the measurement of skin deformation obtained when operating the Cute Meter. [Figure 2] It is a diagram showing a correlation analysis between the lactic acid content in skin keratin and the skin elasticity parameter (Ur / Uf). [Figure 3] It is a diagram showing a correlation analysis between the lactic acid content in skin keratin and the age of the subjects. [Figure 4] It is a diagram showing a partial correlation analysis between the lactic acid content in skin keratin and skin elasticity when the influence of age is removed.

Mode for Carrying Out the Invention

[0014] The present invention is a method for evaluating skin elasticity, characterized by measuring the lactic acid content in skin keratin. The lactic acid in the present invention is represented by CH3CH(OH)COOH. It has optical isomers, including D-form, L-form, and DL (racemic) form, and any of them may be used, preferably the L-form. Also, salts such as Na, K, and Ca may be targeted.

[0015] The skin keratin in the present invention refers to the cells constituting the stratum corneum, which is the outermost layer of the skin. It is also called the stratum corneum or keratinocytes. Since keratin is usually naturally peeled off as dirt and dandruff along with metabolism, it can be obtained from the skin surface. Preferably, it is obtained by peeling with an adhesive tape (tape strip), scraping the skin surface with a razor, paper, or the like, and more preferably by tape strip. The sampling location can be anywhere on the skin to be analyzed, but in order to remove the influence of external agents such as cosmetics, sweat, and sebum, it is preferable to wash with soap, facial cleanser, etc. and wipe with alcohol, etc. before sampling the keratin.

[0016] The method for measuring the lactic acid of the present invention is not particularly limited as long as it is a detectable method, but it is possible to quantify using liquid chromatography (HPLC), gas chromatography (GC), or the like. Also, detection kits using colorimetry or fluorescence utilizing enzyme reactions are commercially available and can be used. Since the lactic acid content in the measured keratin varies depending on the amount of the sampled keratin, it is preferable to correct it with the amount of keratin, such as the total protein amount of keratin, the number of keratin, the stained area, etc.

[0017] The elasticity of the skin in the present invention refers to the force that tries to return when a physical pressure is applied from the outside of the skin, and is also called the firmness, elasticity, resilience, etc. of the skin. The measurement of skin elasticity by the cutometer of the prior art is performed as follows. Standardly, suction is performed for 5 seconds at a suction pressure of 300 mb with a suction diameter of 6 mm, and then the displacement of the deformed skin when it is released is analyzed. As a measurement parameter of skin elasticity that can be obtained by a cutometer, the return elastic ratio (Ur / Uf) obtained by analyzing the displacement of the skin deformed at a certain suction pressure and time as described above is mainly used for evaluation. A typical chart of the measurement of the skin displacement amount over time by a cutometer is shown in FIG. 1. In FIG. 1, Uf: the elongation of the skin during suction (corresponding to Uf1 in FIG. 1), Ur: the immediate contraction (corresponding to Ur1 in FIG. 1). The parameter used as an index of skin elasticity is the immediate (instantaneous) contraction rate with respect to the elongated length of the skin during suction = the elastic modulus during contraction (Ur / Uf). The elasticity of the skin is the closer to 1, the more elastic it is, and human skin is around 0.2 to 0.5.

[0018] The method for evaluating skin elasticity in the present invention is to evaluate the degree of skin elasticity of a subject from whom the cutin has been collected based on the finding that the content of lactic acid in the skin cutin increases as the decrease in elasticity progresses. In the evaluation, the skin cutin to be used for the evaluation is prepared, the content of lactic acid in the cutin is measured, and the elasticity is evaluated based on the content. The content of lactic acid in the skin cutin is calculated as an absolute value or a relative value (such as a ratio or difference from a comparison target or a reference content). The "evaluation" referred to here does not include a diagnosis by a doctor, and even when a doctor's diagnosis intervenes for a specific disease caused by aging, it means assisting the diagnosis, and specifically, it means obtaining data for diagnosis.

[0019] In this invention, skin elasticity can be evaluated by comparing the lactic acid content in the stratum corneum with a predetermined standard content. As the standard content, for example, the lactic acid content can be determined by taking the average value for each group, such as high elasticity group, medium elasticity group, low elasticity group, or age group. Alternatively, a correlation diagram between the lactic acid content in the stratum corneum and skin elasticity or age may be created in advance, and the lactic acid content of the subject may be compared with that correlation diagram.

[0020] The present invention will now be described in more detail based on examples, but the present invention is not limited to these examples. [Examples]

[0021] Example 1: Relationship between lactic acid content in skin stratum corneum and skin elasticity This study involved 102 female subjects aged 36-55 years. After washing their faces, the subjects acclimatized in an air-conditioned room for 15 minutes, and then the elasticity of the cheek skin was measured using a cutometer (Courage & Khazaka). Subsequently, a 1 x 3 cm piece of cellophane tape was applied to the measured skin, and the stratum corneum was peeled off. The tape was cut into strips and immersed in a water / methanol mixture for 10 minutes to extract lactic acid. The lactic acid content in the extract was quantified by HPLC. After removing the tape, the proteins contained in the stratum corneum attached to the tape were measured using a BCA protein assay kit (ThermoFisher). The amount of lactic acid per unit amount of stratum corneum protein was calculated and declared as the amount of lactic acid contained in the stratum corneum.

[0022] These measurement results are shown in Figure 2. As a result, a significant negative correlation was observed between the subjects' skin elasticity and the amount of lactate in the stratum corneum (Pearson's product-moment correlation coefficient: -0.2457, p=0.0152). Therefore, it was shown that lower levels of lactate in the stratum corneum were associated with higher skin elasticity, and higher levels of lactate in the stratum corneum were associated with lower skin elasticity, indicating that the amount of lactate in the stratum corneum is an indicator of skin elasticity.

[0023] Example 2: Relationship between lactic acid content in skin stratum corneum and age The study involved 178 subjects (41 in their 20s, 55 in their 30s, 54 in their 40s, 21 in their 50s, and 7 in their 60s, all female). After washing their faces, the subjects were allowed to acclimate for 15 minutes in an air-conditioned room. Then, the elasticity of the cheek skin and the lactic acid content of the stratum corneum were measured using the same method as in Example 1.

[0024] Figure 3 shows the distribution of lactic acid levels in the stratum corneum and the age of the subjects. The results showed a significant positive correlation between the subjects' age and the amount of lactic acid in the stratum corneum (Pearson's product-moment correlation coefficient: 0.2741, p=0.0003). Therefore, it was shown that the amount of lactic acid in the stratum corneum was lower in younger individuals and higher in older individuals, suggesting that the amount of lactic acid in the stratum corneum can be an indicator of aging.

[0025] Figure 4 shows the distribution of residual differences in skin elasticity and residual differences in stratum corneum lactate content after removing the effects of age. The results showed a significant negative correlation between skin elasticity and residual differences in stratum corneum lactate content (partial correlation coefficient: -0.1535, p=0.0476). Therefore, even after removing the effects of age, lower stratum corneum lactate content was associated with higher skin elasticity, and higher stratum corneum lactate content was associated with lower skin elasticity, indicating that stratum corneum lactate content serves as an indicator of skin elasticity. [Industrial applicability]

[0026] According to the method of the present invention, the elasticity and degree of aging of the skin can be objectively and accurately evaluated. Based on the lactic acid content of the stratum corneum obtained by the method of the present invention, it is possible to provide subjects with customized cosmetics and topical agents for improving or preventing skin aging, as well as suggest skincare methods.

Claims

1. A method for evaluating skin elasticity, characterized by measuring the lactic acid content of keratinocytes in the skin.

2. A method for evaluating skin elasticity, comprising a collection step of collecting keratin from a subject's skin by tape stripping, a measurement step of measuring the lactic acid content of the keratin collected in the collection step, and a step of determining skin elasticity from the lactic acid content measured in the measurement step.

3. A method for evaluating the degree of skin aging, characterized by measuring the lactic acid content of keratinized skin cells.

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