In severe obesity, subcutaneous adipose tissue cell-derived cytokines are early markers of impaired glucose tolerance and are modulated by quercetin

Background: Excessive adiposity provides an inflammatory environment. However, in people with severe obesity, how systemic and local adipose tissue (AT)-derived cytokines contribute to worsening glucose tolerance is not clear.

Methods: Ninty-two severely obese (SO) individuals undergoing bariatric surgery were enrolled and subjected to detailed clinical phenotyping. Following an oral glucose tolerance test, participants were included in three groups, based on the presence of normal glucose tolerance (NGT), impaired glucose tolerance (IGT), or type 2 diabetes (T2D). Serum and subcutaneous AT (SAT) biopsies were obtained and mesenchymal stem cells (MSCs) were isolated, characterized, and differentiated in adipocytes in vitro. TNFA and PPARG mRNA levels were determined by qRT-PCR. Circulating, adipocyte- and MSC-released cytokines, chemokines, and growth factors were assessed by multiplex ELISA.

Results: Serum levels of IL-9, IL-13, and MIP-1β were increased in SO individuals with T2D, as compared with those with either IGT or NGT. At variance, SAT samples obtained from SO individuals with IGT displayed levels of TNFA which were threefold higher compared to those with NGT, but not different from those with T2D. Elevated levels of TNFα were also found in differentiated adipocytes, isolated from the SAT specimens of individuals with IGT and T2D, compared to those with NGT. Consistent with the pro-inflammatory milieu, IL-1β and IP-10 secretion was significantly higher in adipocytes from individuals with IGT and T2D. Moreover, increased levels of TNFα, both mRNA and secreted protein were detected in MSCs obtained from IGT and T2D, compared to NGT SO individuals. Exposure of T2D and IGT-derived MSCs to the anti-inflammatory flavonoid quercetin reduced TNFα levels and was paralleled by a significant decrease of the secretion of inflammatory cytokines.

Conclusion: In severe obesity, enhanced SAT-derived inflammatory phenotype is an early step in the progression toward T2D and maybe, at least in part, attenuated by quercetin.