In vitro protective effects of an anthocyanin extract against palmitic acid-induced inflammation and insulin resistance in 3T3-L1 murine adipocytes

The metabolic syndrome is characterized by various risk factors as hyperglycemia, dyslipidemia, obesity and hypertension. Excessive storage of fatty acid and dysfunction of adipose tissue in obese subjects produce an inflammatory state which is the main cause of development of obesity-correlated pathologies (Guilherme et al., 2008; Hotamisligil, 2006).Pro inflammatory adipokines and free fatty acid (FFA) activate kinases triggering inflammatory pathway and insulin-resistance. Anthocyanins, a subclass belonging to the flavonoid family widely present in diet, have been shown to have several healthy effects. Indeed, it has been reported that dietary intake of anthocyanins produces anti-inflammatory effects and improve insulin-resistance (Jennings et al., 2014). However, the molecular mechanisms involved in their effects are not fully known. The present study was designed to investigate the in vitro protective effect of an anthocyanin-rich extract from bilberries and black currants on inflammation and insulin-resistance induced by high concentrations of palmitic acid (PA), the main circulating fatty acid, in murine adipocytes. Fully differentiated 3T3-L1 adipocytes were pretreated with anthocyanins (ACN) extract for 24 h before they were exposed to PA 1mM for 24 h. For investigation of insulin signaling pathway, cells were also stimulated with insulin (100nM) for 15 minutes. After, NF-kB proinflammatory pathway and PI3K/Akt insulin signaling were evaluated. NF-kB is the most important transcriptional factor that plays a pitoval role in the inflammatory processes and the kinase IKK is its main activator. Thus, toevaluate the effects of ACN extract on adipocytes inflammation NF-kB pathway was studied. Results demonstrated that ACN extract was able to inhibit, in a dose-dependent way, PA-induced nuclear translocation of NF-kB, as observed by reduced nuclear proteinof p65 (NF-kB) and IKK phosphorylation. Moreover, ACN pretreatment prevented PA-induced IL-6 gene expression. In order to examine the effect of ACN extract on insulin resistance, PI3K, pAkt and GLUT-1 protein levels were evaluated. Exposure of adipocytes to PA decreases PI3K and pAkt levels and transmembrane translocation of GLUT-1carrier so demonstrating a reduced insulin-sensitivity. Conversely, the pretreatment with ACN extract improved insulin sensitivity, increasing all these markers, in PA exposed adipocytes. These dataclarify the mechanisms that underline the protective effect of anthocyanins, suggesting that the assumption of this ACN extract could reduce the development of inflammation and insulin resistance induced by PA on adipose tissue. Bibliographic References • Guilherme A, Virbasius JV, Puri V, et al. (2008) Adipocyte dysfunctions linking obesity to insulin resistance and type 2 diabetes. Nat Rev Mol Cell Biol 9, 367–377. • Hotamisligil GS (2006) Inflammation and metabolic disorders. Nature 444, 860–867. • Jennings A, Welch AA, Spector T, et al. (2014) Intakes of anthocyanins and flavones are associated with biomarkers of insulin resistance and inflammation in women. J Nutr 144, 202–208.