Ellagic acid effects in healthy mice and in the Experimental Autoimmune Encephalomyelitis model: from neurotransmission to neuroinflammation

Ellagic acid (EA) is a dietary polyphenol derived from ellagitannins, widely recognized for its neuroprotective properties. Growing evidence indicates that EA’s neurobiological actions may, at least in part, depend on the modulation of noradrenergic transmission. Previous work from our research group demonstrated, through in vitro and ex vivo approaches, that EA acts as a partial agonist at presynaptic α₂-adrenergic receptors, thereby enhancing noradrenaline (NA) release from central nerve terminals (i.e. synaptosomes). However, EA's limited solubility and bioavailability restrict its access to the central nervous system (CNS), redirecting scientific interest towards its gut-derived metabolites, the urolithins (UROs). In my thesis project, I first investigated the neuromodulatory mechanisms of the three main urolithins: Urolithin A (UroA), Urolithin B (UroB), and Urolithin C (UroC), with particular attention to their ability to influence noradrenergic transmission via presynaptic α₂-adrenergic autoreceptors and consequently to modulate NA release. Results from in vitro studies revealed that UroA, but not UroB or UroC, activates α₂-adrenergic receptor subtypes, exhibiting an agonist-like effect. Building upon these mechanistic insights, I evaluated the impact of a novel Ellagic acid microdispersion (EAm) formulation with enhanced solubility, following an oral chronic administration in healthy adult mice. EAm treatment induced α₂-adrenergic autoreceptor desensitization, increased cortical and hippocampal noradrenaline exocytosis, and elicited a mild yet consistent reduction in anxiety-like behaviours accompanied by increased exploratory activity. Additionally, EAm preserved intestinal barrier integrity and promoted a shift in gut microbiota composition toward beneficial taxa, suggesting a functional interplay between microbiota modulation and noradrenergic regulation. I next examined the effects of EAm on the Experimental Autoimmune Encephalomyelitis (EAE) mouse model, which closely mimics the key neuropathological and immunological features of multiple sclerosis (MS). Chronic administration of EAm significantly alleviated clinical disease severity, preserved myelin structure, and reduced both microglial and astrocytic activation. Moreover, EAm treatment restored noradrenergic signalling in the spinal cord and cortex of treated EAE mice, when compared to untreated EAE animals, in line with previous findings on EA’s immunomodulatory properties. Beyond these neurobiological effects, EAm improved several behavioural outcomes in EAE mice. Treated animals displayed enhanced motor coordination and showed reduced anxiety- and depression-like behaviours, together with greater exploratory drive. These effects were reflected in 10 increased locomotor and exploratory activity in the Open Field test, more head-dipping behaviour in the Hole Board Maze, and higher grooming frequency in the Splash test, consistent with both neuroprotective and antidepressant-like actions. Notably, this study highlights a novel dual mechanism of action for EAm: mitigating immune-mediated neuroinflammation while concurrently targeting the noradrenergic system, which is deeply involved in immune regulation and in the emotional and cognitive symptoms associated with MS. By integrating these two dimensions, the findings highlight the intricate connection between inflammation, neurotransmitter imbalance, and mood disturbances in demyelinating conditions, and point out the noradrenergic modulation as a valuable therapeutic target. Overall, these data demonstrate that EAm treatment exerts broad neuroimmune effects, restoring noradrenergic tone, reducing glial reactivity, improving synaptic efficiency, and normalizing behavioural and gut–brain interactions. Together, these outcomes support the potential of EAm as an effective complementary nutritional–therapeutic approach for managing neuroinflammatory and demyelinating disorders.