Lactobacillus plantarum ferment of forsythia suspensa mitigates UVB-induced photoaging in HaCaT keratinocytes by modulating the metabolite profile and enhancing anti-photoaging activities

The aqueous extract and Lactobacillus plantarum fermentation broth were prepared from forsythia as plant raw material, and the two extracts were investigated for the evaluation of cosmetic efficacy in antioxidant, anti-inflammatory repair, and safety after the establishment of the UVB damage HaCaT cell model. The results showed that the forsythia fermentation broth and the aqueous extract had good scavenging activities against DPPH radicals, hydroxyl radicals, ABTS radicals and reactive oxygen species, and the fermentation broth had significantly stronger antioxidant effects than the aqueous extract. At the level of protein expression and gene transcription, the forsythia fermentation broth reduced the content of inflammatory factors (TNF-α, IL-8, IL-6, IL-1β) and apoptotic factors (Caspase-3, Caspase-9, Bax, Bcl-2) in the cells and even tended to the normal level, and the effect was higher than that of aqueous solution as the blank control, which indicated that the forsythia fermentation broth had anti-inflammatory and restorative effects. Full metabolite profiling by chromatographic tandem mass spectrometry (HPLC-MS/MS) of the aqueous extract and forsythia fermentation broth revealed that the fermentation broth modulated the metabolite profile. This modulation was associated with significantly enhanced protective effects, as evidenced by boosted oxidative stress and anti-inflammatory responses at the cellular level against UVB-induced HaCaT cells. Using chicken embryo allantoic membrane eye irritation experiment and erythrocyte haemolysis experiment on the aqueous extract and forsythia fermentation broth for safety evaluation experiments, the irritation scores were 0.09, 0.08, respectively, and there was no haemolysis of blood vessels, which indicated that the aqueous extract of forsythia and the fermentation solution did not have eye irritation, and that the use of forsythia fermentation broth in a safe range had no detrimental effect on cell membranes and was not irritating.