Title : Upcycled and sustainable cosmetics for atopic dermatitis
Abstract:
Atopic Dermatitis (AD) is a chronic, relapsing inflammatory skin disease characterized by pruritus, xerosis, and impaired skin barrier function, frequently associated with microbial dysbiosis. In AD, Staphylococcus aureus (SA) predominates and forms biofilms that exacerbate inflammation, while Staphylococcus epidermidis (SE), typically protective, may display altered behavior. Restoring microbial balance represents a promising therapeutic strategy. Humulus lupulus (hops), a byproduct of the brewing industry, is rich in bioactive compounds such as humulone, lupulone, and xanthohumol, with reported anti-inflammatory and antimicrobial properties. This study aimed to evaluate the safety and efficacy of an upcycled hop extract derived from brewing waste for potential application in AD.
The extract was obtained from beer production trubs via solid–liquid extraction using 96% ethanol and chemically characterized by HPLC. After solvent evaporation, the extract was dissolved in dimethyl sulfoxide (Extract A), propylene glycol (Extract B), and propylene glycol plus glycerin (Extract C). Microbiological quality was assessed according to the European Pharmacopoeia (Eur. Ph. 2.6.12). Safety was evaluated through cytotoxicity assays (MTT) in human keratinocytes (HaCaT) and murine macrophages (RAW 264.7) following 24 h exposure. Antioxidant capacity was determined using the DPPH radical scavenging assay. Antimicrobial activity against SA (ATCC 6538) and SE (ATCC 12228) was evaluated by determining minimum inhibitory concentration (MIC) and minimum lethal concentration (MLC) using broth microdilution, while biofilm inhibition was assessed via crystal violet staining. Statistical analysis was performed using one-way ANOVA with Dunnett’s multiple comparisons test.
HPLC analysis revealed humulone, lupulone, and xanthohumol as the major constituents of the hop extract. All formulations met microbiological quality requirements. The MIC for both SA and SE was 0.129% (w/v). The MLC was 0.515% (w/v) for SA and 1.030% (w/v) for SE, indicating a bacteriostatic effect for SE, and a bactericidal effect for SA. The extract significantly inhibited SA biofilm formation at MIC concentration, whereas SE required a five-fold higher concentration, suggesting selective antibiofilm activity (p < 0.05). Regarding safety, Extract A exhibited higher cytotoxicity, being biocompatible only at 0.03% (v/v), while Extract B showed improved cell viability, remaining compatible up to 2% (v/v) in HaCaT cells and 0.13% (v/v) in RAW 264.7 cells, and Extract C compatible up to 2% (v/v) in HaCaT cells and 0.50% (v/v) in RAW 264.7 cells. All extracts demonstrated low antioxidant activity (AAI < 0.04).
Overall, these results highlight the potential of upcycled hop extracts, particularly propylene glycol-based formulations, as safe and selective agents for modulating skin microbiota and improving skin health in Atopic Dermatitis. Ongoing studies are exploring their wound-healing and anti-inflammatory potential to further support their cosmetic and therapeutic application.
