Hop derived fraction rich in beta acids and prenylflavonoids regulates the inflammatory response in dendritic cells differently from quercetin: unveiling metabolic changes by mass spectrometry-based metabolomics

Dendritic cells (DCs) represent a heterogeneous family of immune cells that link innate and adaptive immunity, their activation is linked to metabolic changes that are essential to support their activity and function. Hence, targeting DCs metabolism represents an opportunity to modify the inflammatory and immune response. Among natural matrices, Humulus lupulus (Hop) compounds has recently shown immunomodulatory and anti-inflammatory activity. This study aims to evaluate the ability of specific Hop fractions to modulate DCs metabolism after stimulation with lipopolysaccharide (LPS) by an untargeted metabolomics approach and compare their effect with the flavonol quercetin. Following liquid chromatography-based fractionation, three fractions (A, B, C) were obtained and tested. Cytokines and gene expression were evaluated by ELISA and qPCR respectively, while untargeted metabolomics analysis was performed with a combined HILIC-HRMS and DI-FT-ICR approach. Fraction Hop C and quercetin were both able to reduce the production of several inflammatory cytokines such as IL-6, IL-1α, IL-1β and TNF, but, differently from quercetin, the Hop C mechanism is independent of extracellular iron-sequestration, and showed a significant upregulation of Nrf2/Nqo1 pathway and Ap-1 when compared to quercetin. Untargeted analysis revealed the modulation of several key pathways linked to pro-inflammatory and glycolytic phenotypes. In particular, Hop C treatment was able to modulate the oxidative and non-oxidative steps of pentose phosphate pathway (PPP), reduce the inflammatory mediator succinate, citrulline, as well as purine-pyrimidine metabolism, differently from quercetin. These results highlight the potential anti-inflammatory mechanism of specific Hop derived compounds, in restoring dysregulated metabolism in DCs, which could be used in preventive or adjuvant therapies to suppress undesired inflammatory response.