Screening plant extracts for inhibition of hair glycation

抄録

Objectives: It has been reported that hair glycated over time from the root to the tip exhibits changes in physical properties, such as a decrease in breaking strength. However, few studies have examined the inhibition of hair glycation. In this study, we examined the anti-glycation effect of plant extracts to identify materials that inhibit hair glycation. Methods: A total of 26 plant extracts were used as the cosmetic ingredients. A glycation solution was prepared with 0.1 mol/L phosphate buffer (PB; pH 7.4), 5.0 mol/L glucose, and 5.0 mg/mL keratin; the sample to be tested was then added to this solution. After thermal reaction, the levels of advanced glycation end products (AGEs) produced in the reaction solution were measured using the fluorescence method (excitation wavelength 370 nm / detection wavelength 440 nm), and the AGE production inhibitory rate was calculated. In the primary screening, each sample was adjusted to a final concentration of 0.1 mg/mL in the reaction solution with deionized water, and the AGE production inhibition rate was measured. In the secondary screening, half maximal inhibitory concentration (IC50) was calculated and evaluated for samples with an AGE production inhibition rate of 75% or more obtained in the primary screening. Next, we obtained hair samples from healthy women in their 30s who had no history of beauty treatment, and verified the anti-glycation effects of the plant extracts. To verify the anti-glycation effect, the hair sample was immersed in 0.1 mol/L phosphate buffer (pH 7.4) containing 1.2 mol/L of glucose and 0.1 mg/mL of each sample, and reacted at 50°C for 10 days. Hair protein was extracted, and the levels of fluorescent AGEs were measured. The physical properties of the hair were measured using a tensile tester at ambient temperature (25°C) and humidity (65% RH). Results: Following primary screening, 75% or more of the AGE production inhibitory effect was observed in 9 out of 26 samples. The secondary screening results showed that the IC50 of rooibos extract had a stronger anti-glycation effect than the IC50 of aminoguanidine. An in vitro hair test showed that rooibos extract inhibited the production of fluorescent AGEs (production inhibition rate 82.4%). In addition, the breaking strength of the glycated hair was reduced by 20.8% compared to that of the un-glycated hair; however, after treatment with the rooibos extract, the reduction in breaking strength due to glycation could be suppressed to 4.9%. Conclusion: Rooibos extract was found to have an inhibitory effect on the production of fluorescent AGEs in hair proteins. It also showed an inhibitory effect on the decrease in the breaking strength of the hair due to glycation. These results indicate that the addition of rooibos extract to hair cosmetics may help inhibit the changes in the physical properties of hair caused by glycation.