Synthesis, characterization, and anti-inflammatory potential of serotonin- and dopamine-conjugates of urolithin A

Advancements in understanding xenobiotic interactions with gut microbiota highlight bacteria-derived metabolites as a promising source of novel bioactive compounds. Urolithin A (UA), a postbiotic metabolite derived from ellagitannins, has been recognized for its anti-inflammatory properties. To enhance the bioactivity of UA, its derivatives (UADs) conjugated with dopamine (DopUA) or serotonin (SerUA) were synthesized, characterized and subjected to various in vitro bioassays

A synthesis strategy for UADs was developed and optimized. The identity and purity of the compounds were confirmed through HPLC-DAD-MS/MS and NMR analyses. The anti-inflammatory potential of UADs was evaluated in immortalized bone marrow-derived macrophages (iBMDMs) using qPCR to measure inflammatory markers expression, as well as FACS analysis and Griess assay to determine impact on cytokine secretion and nitrite production, respectively. Moreover, reporter cell lines were utilized to investigate the modulation of NF-κB and Nrf2 signaling pathways. Additionally, experiments using Caenorhabditis elegans Parkinson’s disease model aimed to provide first insight into UADs toxicity in vivo and impact on α-synuclein aggregation.

In vitro experiments demonstrated that at non-cytotoxic concentrations, DopUA showed the most potent reduction in nitrite production and secretion of key pro-inflammatory cytokines in comparison with parent compounds and SerUA. DopUA also modestly inhibited NF-κB activation in reporter cells. Neither of the compounds activated Nrf2 signaling in a respective reporter gene assay. In C. elegans, UADs neither impacted survival adversely nor influenced α-synuclein accumulation.

These findings indicate that neurotransmitter conjugation enhances UA's immunomodulatory effects. The study promotes the idea of utilizing UA as promising scaffold for the development of therapeutics targeting pro-inflammatory pathways.