Tyramine is found in foodstuffs, the richest being
cheeses, sausages, and
wines.
Tyramine has been recognized to release
catecholamines from
nerve endings and to trigger hypertensive reaction. Thereby,
tyramine-free
diet is recommended for depressed
patients treated with irreversible inhibitors of monoamine
oxidases (
MAO) to limit the
risk of
hypertension.
Tyramine is a substrate of
amine oxidases and also an agonist at
trace amine-associated receptors. Our aim was to characterize the
dose-dependent effects of
tyramine on
human adipocyte metabolic functions. Lipolytic activity was determined in
adipocytes from
human subcutaneous
abdominal adipose tissue.
Glycerol release was increased by a fourfold factor with classical lipolytic agents (1 μM
isoprenaline, 1 mM isobutylmethylxanthine) while the
amine was ineffective from 0.01 to 100 μM and hardly stimulatory at 1 mM.
Tyramine exhibited a partial antilipolytic effect at 100 μM and 1 mM, which was
similar to that of
insulin but weaker than that obtained with
agonists at purinergic A1 receptors, α2-
adrenoceptors, or
nicotinic acid receptors. Gi-
protein blockade by
Pertussis toxin abolished all these antilipolytic responses save that of
tyramine. Indeed,
tyramine antilipolytic effect was impaired by
MAO-A inhibition.
Tyramine inhibited
protein tyrosine phosphatase activities in a manner sensitive to
ascorbic acid and
amine oxidase inhibitors. Thus, millimolar
tyramine restrained
lipolysis via the
hydrogen peroxide it generates when oxidized by
MAO. Since
tyramine plasma levels have been reported to reach 0.2 μM after
ingestion of 200 mg
tyramine in healthy individuals, the direct effects we observed
in vitro on
adipocytes could be nutritionally relevant only when the
MAO-dependent hepato-intestinal detoxifying system is overpassed