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Pomegranate juice (PJ) is a beverage with potential beneficial effects due to its high content of polyphenols. The objective of this study is to explore at a molecular level the direct properties of PJ and its two main polyphenolic components, punicalagin and ellagic acid, on adipocyte functions. Increasing doses of PJ were tested using radiometric methods to determine amine oxidase activities in human adipose tissue preparations. The influences on lipogenic and lipolytic activity were also assessed by radiochemical and colorimetric assays. The results showed a dose-dependent capacity of PJ to inhibit the monoamine oxidase and the semicarbazide-sensitive amine oxidase activities present in human adipose tissue. PJ also inhibited lipogenesis and lipolysis in mouse and human adipose cells, while punicalagin and ellagic acid inhibited lipolysis rather than lipogenesis. However, the combination of punicalagin and ellagic acid resulted in a synergistic action in impairing MAO activity or basal glucose incorporation into lipids.

The juices of berries or red fruits are appreciated as a source of antioxidants with potential health effects. However, they are rich in carbohydrates, an aspect that could be considered negative in view of diabetes and obesity epidemics. Indeed, it is the high polyphenol content of these beverages that is beneficial. When drinking such natural beverages, the consumers have the feeling of following a diet rich in fruit, recognized to reduce the risk of oxidative stress, cardiovascular injury, cancer, and neurodegenerative disorders. In this chapter, the polyphenol content will be compared between cranberry (Vaccinium macrocarpon), blueberry (Vaccinium myrtillus), sour cherry (Punica granatum), and pomegranate (P. granatum) juices. These juices are not a source of resveratrol, the most known polyphenol found in red wines, but the phenolic compounds they contain (punicalagins, ellagic acid, phenolic acids, and kuromanin) are more than mere antioxidants. These polyphenols exhibit superoxide radical scavenging activity and bacteriostatic properties and are protective for their plant of origin. Once ingested, they interact with various enzymes in human tissues, and with intestinal microbiota. We will focus attention on the interplay between extracts of such juices and monoamine oxidase (MAO) activity. MAO is involved in the metabolism of brain neurotransmitters and is expressed in peripheral tissues such as adipose tissue and produces hydrogen peroxide when degrading dietary amines (e.g., tyramine). We report that lyophilisates of fruit juices and their polyphenols inhibit human MAO. In addition, the red fruit polyphenols inhibit alpha-glucosidase, a key enzyme of glucose metabolism. Thus, polyphenols of red fruits juices should have beneficial effects on consumers not only in terms of antioxidant potential, but also as a consequence of modulation of amine degradation and metabolism, potentially acting on the mood and adiposity of the consumers.

Publisher Summary The control of fat-cell function by the catecholamines involves at least five different adrenoceptor subtypes: three β-adrenoceptors (βARS) (for example, β1-, β2-, and β3-), one α2AAR and one α1BAR, the importance of which differs according to cell differentiation stage and animal species. Some essential features concerning fat-cell α2AR is considered here. In fat cells, α2ARs are coupled to adenylyl cyclase through Gi proteins (Gi1,Gi2, and Gi3 proteins have been identified in fat cells). An important short-term metabolic action of catecholamines in fat cells is related to the control of the changes in cyclic adenosine monophosphate (cAMP) levels promoted by βAR-mediated stimulation versus α2AR-mediated inhibition of adenylyl cyclase activity. Intracellular cAMP changes alone are sufficient to meet the requirements for stimulation of cAMP-dependent protein kinase and subsequent lipolysis activation by hormone-sensitive lipase. Selective α2AR stimulation promotes adenylyl cyclase inhibition, reduction of intracellular cAMP levels, and antilipolysis. When considering the role of α2-AR in mature adipocytes, there are minor species-specific variations in the pharmacology of fat-cell α2AR that appear to be species variants of the α2A subtype (encoded by the α2-C10 gene) existing in human fat cells. The importance of the fat-cell α2AR varies according to the species, the sex, the age, and the degree of obesity in humans and mammalian models. Striking differences exist in the distribution of fat cell α2AAR according to the anatomical location of the fat deposits. In most human fat cells, α2AAR numerically predominate over β1/β2AR. Preferential recruitment of the α2AR, at lower catecholamine concentrations than for the β1/β2AR, has been studied for epinephrine and norepinephrine. These studies suggest that catecholamines, via α2AR-dependent pathways, are able to regulate adhesion and actin cytoskeleton activity in white fat-cell precursors by interfering with the integrin-mediated pathway.