Metabolomics provides novel understanding of Melissa officinalis mechanism of action ensuring its calming effect on dogs.

BACKGROUND: Animal welfare encompasses both its physical and mental states. This latter could be altered by several psychological-related disorders including stress and anxiety. To address these issues, Melissa officinalis, a Lamiaceae plant, ensuring the anxiolytic-type effects, is widely used. In this study, the main aim was to explore the effect of a commercial hydro-alcoholic Melissa officinalis extract (MOE) and its major compound rosmarinic acid (RA) on dogs' behavior and metabolome. To do so, twenty healthy beagle dogs were randomly assigned to 4 dietary supplements (5 dogs/group): the first group received a placebo supplemented with maltodextrose (200 mg/kg), the second group was supplemented with MOE (200 mg/kg), the third group received RA at a dose of 10.6 mg/kg, and the fourth group was administered α-casozepine (AC) at a dose of 225 mg in capsule form. Dogs' behavior was monitored after 4 weeks of treatment using a standardized evaluation grid developed by Oniris. In addition, 4-hydroxybyturic acid (GHB) was quantified to study the effect of the supplementations on the metabolites of γ-aminobutyric acid (GABA) biosynthetic pathway. Moreover, the impact of all supplementations on dogs' metabolome was assessed using untargeted metabolomics at the end of the supplementation period. RESULTS: Results demonstrated significant differences between the mean behavioral score of placebo group (-3.4) compared to MOE (2.0), RA (1.4), and AC (0.8) groups. In addition, GHB measurement revealed a decrease in its quantity in all supplemented groups compared to the control. Moreover, untargeted metabolomics uncovered several metabolic pathways, that were impacted by MOE supplementation linked to lipids and bile acids metabolism. Furthermore, RA supplementation impacted fatty acids and lipids metabolism pathways while supplementation with AC affected pathways linked to lysine and sphingolipids metabolism. CONCLUSIONS: Our study demonstrated a calming effect of MOE on beagles and proposes a novel hypothesis that sheds new light on its potential mechanism of action. This study underlines metabolomics as an effective tool for gaining deep insights into the metabolic changes associated with supplementation.