Protective effects of Alfa-lipoic acid against palmitate-induced inflammation and insulin resistance in 3T3-L1 hypertrophic adipocytes

Obesity, one of the most prevailing health concerns worldwide, is a metabolic disorder of multifactorial origin correlated with elevated morbidity and mortality rates. It predisposes to the metabolic syndrome and is characterized by free fatty acids accumulation and alteration of circulating adipokine levels that promote a lipotoxicity state and cause oxidative stress, chronic inflammation, and insulin resistance in adipose tissue. Over the years, Alfa-lipoic acid (ALA), a sulfur-containing coenzyme required for the mitochondrial dehydrogenase reactions leading to ATP formation, has gained a considerable attention as pleiotropic compound with potential therapeutic use in many chronic diseases. In fact, even if ALA’s pharmacological effects are primarily related with its antioxidant activity, in recent years, epidemiological evidence have shown marked anti-obesity and insulin sensitizing effects. Therefore, we evaluated the in vitro potential beneficial effects of ALA in counteracting an inflammatory condition and an insulin resistance state in 3T3-L1 hypertrophic adipocytes exposed to high concentrations of palmitic acid (PA). Fully differentiated 3T3-L1 adipocytes were pretreated with different concentrations of ALA (1-25-100 μM) for 24 h and then, in order to induce cellular hypertrophy, exposed to PA (1 mM) for 24 h. To evaluate the insulin-resistance condition, cells were subsequently treated with insulin 100 nM. Western blotting analysis, Real‐time PCR and Oil Red O staining were applied for investigating the mechanism involved in adipocytes dysfunction. The results obtained show that ALA pretreatment, dose‐dependently reduces lipid accumulation and PPARγ protein levels induced by PA. In addition, PA was able to induce NF-κB proinflammatory pathway, resulting in IKK activation, p65/NF-κB nuclear accumulation increase and IL-6 mRNA up-regulation, which are considerably reduced by ALA pretreatment. Moreover, PA induced insulin-resistance with a significant inhibition of P3K/Akt signaling pathway, followed by a downstream reduction of the glucose transporter GLUT-1. ALA pretreatment reverted these effects and improved insulin signaling, resulting in an insulin-sensitizing effect. This study demonstrates a positive potential of ALA against obesity comorbidities, suggesting the protective activity of this compound in the prevention of pathological conditions linked to obesity.