Effect of tyramine, a dietary amine, on glycerol and lactate release by isolated adipocytes from old rats

Amine degradation by adipocyte amine oxidases leads to the production of metabolites that interact with lipid and glucose metabolisms and their hormonal regulations. To further investigate these interactions, we determined the effect of a dietary amine, tyramine (TYR), on glycerol and lactate releases , respectively taken as indices of lipolytic and glycolytic activities of isolated adipocytes. Old male Wistar rats were used to prepare adipocytes by collagenase dissociation of retroperitoneal fat pads. The two tested doses of tyramine (10 µM and 1 mM) had no effect on basal glycerol release. On the other hand, TYR, at the highest dose tested (1 mM), weakly but significantly increased basal lactate release, which was elevated in adipocytes from old rats. Norepinephrine (NE), highly stimulated adipocyte lipolysis with a submaximal effect at 1 µM which was slightly but significantly inhibited by TYR 1 mM. Insulin 1 nM (INS) also poorly inhibited the NE-stimulated lipolysis in adipocytes isolated from old rats. TYR was able to potentiate the poor antilipolytic efficiency of INS. Under similar conditions, a high dose of NE greatly reduced lactate production and TYR (1 mM) reversed this inhibition of lactate release. INS was also able to totally reverse the inhibitory effect of NE on lactate release, but there was no potentiation between insulin and tyramine effects. It can be concluded that high doses of TYR interact with norepinephrine and insulin, at least on the control of glycerol and lactate release, by counteracting catecholamine effects and by mimicking insulin actions.La degradación de aminas por las amino-oxidasas del tejido adiposo produce metabolitos capaces de influir sobre los metabolismos lipídico y glucídico y su regulación hormonal. Para investigar acerca de estos efectos, se ha estudiado el efecto de la tiramina (TIR), una amina presente en la dieta, sobre la producción de glicerol y de lactato, como índice respectivo de la lipolisis y de la glicolisis. A partir de tejidos adiposo perirrenal de viejos machos de rata Wistar se aislaron adipocitos tras digestión con colagenasa. Se estudió in vitro el efecto de la tiramina a dos concentraciones, 10 µM y 1 mM sobre la liberación de glicerol y de lactato. Ninguna de ellas modificó la liberación basal de glicerol, pero la mayor estimuló la liberación basal de lactato,, ya bastante elevada. La norepinefrina (NE) estimuló fuertemente la lipolisis con un efecto submáximo a 1 µM, que fué inhibido parcial pero significativamente por TIR 1 mM. La producción basal de lactato se redujo por dosis elevadas de NE y esta inhibición se anuló por adición TIR 1 mM. Ademas, la tiramina fue capaz de reforzar la débil acción antilipolítica de la insulina en los adipocitos estimulados por norepinefrina de ratas viejas. Por otra parte, la insulina anuló el efecto inhibidor de la NE sobre la producción basal de lactato sin que se observara potenciación por la presencia de TIR. Estos resultados parecen indicar que la tiramina, a dosis elevadas, puede reemplazar parcialmente el efecto de la insulina e influir sobre el control de la liberación de glicerol y de lactato por la norepinefrina

Amine oxidase substrates for impaired glucose tolerance correction

Amine oxidases are widely distributed from microorganisms to vertebrates and produce hydrogen peroxide plus aldehyde when catabolizing endogenous or xenobiotic amines. Novel roles have been attributed to several members of the amine oxidase families, which cannot be more considered as simple amine scavengers. Semicarbazide-sensitive amine oxidase (SSAO) is abundantly expressed in mammalian endothelial, smooth muscle, and fat cells, and plays a role in lymphocyte adhesion to vascular wall, arterial fiber elastic maturation, and glucose transport, respectively. This latter role is detailed and the perspectives opened by the insulin-like actions of amine oxidase substrates are discussed in the present review. Independent studies have demonstrated that SSAO substrates and monoamine oxidase substrates mimic diverse insulin effects in adipocytes: glucose transport activation, lipogenesis stimulation and lipolysis inhibition. These substrates also stimulate in vitro adipogenesis. Acute in vivo administration of amine oxidase substrates improves glucose tolerance in rats, mice and rabbits, while chronic treatments with benzylamine plus vanadate exert an antihyperglycaemic effect in diabetic rats. Dietary supplementations with methylamine, benzylamine or tyramine have been evidenced to influence metabolic control in rodents by increasing glucose tolerance or decreasing lipid mobilisation, without noticeable changes in the plasma markers of lipid peroxidation or protein glycation, despite adverse effects on vasculature. Thus, the ingested amines are not totally degraded at the intestinal barreer and can act on adipose and vascular tissues. In regard with this influence on metabolic control, more attention must be paid to the composition or supplementation in amines in foods and nutraceutics