Milk thistle extracts could enhance the UV-protection efficiency and stability of mineral filters in sunscreen formulations

Abstract

This paper was aimed to determine the total silymarin content, total antioxidant capacity, free radical scavenging activity of methanolic extracts obtained by ultrasonic assisted extraction of defatted milk thistle fruits, as well as to evaluate the sunscreen activity of the cream formulation containing milk thistle extract (MTE) using in vitro SPF method. Antibacterial and antibiofilm effect of extract was also evaluated. Moreover, the probable mode of action for the antioxidant activity of the extract detected via the in vitro assay was explored through molecular docking and molecular dynamics (MD) simulation. The total amount of silymarin in MTE was determined spectrophotometrically as silibinin equivalent. While the total antioxidant capacity of MTE and cream containing MTE was determined by the copper ions (Cu2+) reducing antioxidant capacity (CUPRAC) method, the radical scavenging capacity was determined by the 1,1-diphenyl-2-picryl-hydrazil (DPPH) method. Total tocopherol content was determined spectrophotometrically. In the present study, the amount of silymarin in the MTE was determined as 330.19 ± 1.95 mg silibinin equivalent/g-extract. The CUPRAC and DPPH values of MTE were calculated to be 2.49 ± 0.03, 0.675 ± 0.0006 mmol TE/g-extract, respectively, while the CUPRAC and DPPH values of the cream containing MTE were 0.327 ± 0.003, 0.156 ± 0.0006 mmol TE/g-cream, respectively. The total tocopherol content of the oils of milk thistle fruits was found to be 383.43 mg/kg oil. According to microbial tests results the MIC values of S. aureus and E. coli was detected 0.15625 and 0.3125, respectively. And inhibition rate of extract on biofilm formation on P. aeruginosa PAO1 was found 33 % rate. The molecular docking study demonstrated that the major constituent, silibinin, had a high potential of binding to the human peroxiredoxin 5. On the other hand, the MD simulation of the enzyme-silibinin complex revealed that the compound could be unstable in the binding region of the enzyme. The addition of MTE, which has antioxidant properties, to creams improved its effectiveness on sun protection and contributed to obtaining high SPF values. At the end of day 28 under accelerated test conditions, the combination of ZnO and MTE exhibited greater ability for sun protection compared to the cream containing ZnO as a sun filter agent. Additionally, milk thistle extracts is an ideal filter agent as an ingredient in sunscreens.