Hordenine does not directly activate triglyceride breakdown in adipocytes but is a MAO interacting agent

The consumption of dietary supplements advertised as slimming agents is increasing with the prevalence of obesity.However, several of these supplements are adulterated with pharmacologically active substances or with ingredients lacking any demonstration of their efficiency.Alongside the phytochemicals endowed with lipolytic properties such as caffeine or synephrine, the alkaloid hordenine, naturally present in germinated barley and in other plants, belongs to such ingredients added to dietary supplements advertised to improve lipid mobilization in consumers.Since the lipolytic properties of hordenine were not documented so far, we aimed to verify the in vitro rapid effects of hordenine on rodent adipocyte lipolytic and antilipolytic responses.It was found that different doses of hordenine do not activate or inhibit lipolysis in mouse fat cells, which were responsive to the stimulatory (isoprenaline, forskolin) or inhibitory (insulin) control of triglyceride breakdown.Moreover, in human adipose tissue, hordenine interacted with monoamine oxidase (MAO) and competed for the oxidation of radiolabeled tyramine while it was not a substrate, or an inhibitor of the semicarbazide-sensitive amine oxidase involved in the degradation of benzylamine.Our results indicated that hordenine does not reproduce the already documented antilipolytic effects of tyramine or the lipolytic action of synephrine, two of its closely related naturally occurring phenethylamines.