Visfatin Is Regulated by Rosiglitazone in Type 2 Diabetes Mellitus and Influenced by NFκB and JNK in Human Abdominal Subcutaneous Adipocytes

Abstract

Visfatin has been proposed as an insulin-mimicking adipocytokine, predominantly secreted from adipose tissue and correlated with obesity. However, recent studies suggest visfatin may act as a proinflammatory cytokine. Our studies sought to determine the significance of this adipocytokine and its potential role in the pathogenesis of T2DM. Firstly, we examined the effects of diabetic status on circulating visfatin levels, and several other adipocytokines, demonstrating that diabetic status increased visfatin*, TNF-α*** and IL-6*** compared with non-diabetic subjects (*p<0.05, **p<0.01, ***p<0.001, respectively). We then assessed the effects of an insulin sensitizer, rosiglitazone (RSG), in treatment naïve T2DM subjects, on circulating visfatin levels. Our findings showed that visfatin was reduced post-RSG treatment [vs. pre-treatment (*p<0.05)] accompanied by a reduction in HOMA-IR**, thus implicating a role for insulin in visfatin regulation. Further studies addressed the intracellular mechanisms by which visfatin may be regulated, and may exert pro-inflammatory effects, in human abdominal subcutaneous (Abd Sc) adipocytes. Following insulin (Ins) and RSG treatment, our in vitro findings highlighted that insulin (100 nM), alone, upregulated visfatin protein expression whereas, in combination with RSG (10 nM), it reduced visfatin*, IKKβ** and p-JNK1/2*. Furthermore, inhibition of JNK protein exacted a significant reduction in visfatin expression (**p<0.01), whilst NF-κB blockade increased visfatin (*p<0.05), thus identifying JNK as the more influential factor in visfatin regulation. Additional in vitro analysis on adipokines regulating visfatin showed that only Abd Sc adipocytes treated with recombinant human (rh)IL-6 increased visfatin protein (*p<0.05), whilst rh visfatin treatment, itself, had no influence on TNF-α, IL-6 or resistin secretion from Sc adipocytes. These data highlight visfatin's regulation by insulin and RSG, potentially acting through NF-κB and JNK mechanisms, with only rh IL-6 modestly affecting visfatin regulation. Taken together, these findings suggest that visfatin may represent a pro-inflammatory cytokine that is influenced by insulin/insulin sensitivity via the NF-κB and JNK pathways.

Stężenie wisfatyny u osób z otyłością w zależności od obecności świeżo wykrytych zaburzeń gospodarki węglowodanowej

“…Obesityassociated changes in circulating adipocytokines may contribute to both B-cell destruction and increased insulin resistance [12,13]. Visfatin, an adipocytokine with insulin-mimetic activity [1] and proinflammatory actions [8], is considered as a potential factor that may contribute to the development of diabetes in obese individuals.…”

“…Recent studies suggest that visfatin may also act as a proinflammatory cytokine and in this way may indirectly participate in the development of insulin resistance and type 2 diabetes [8].…”

Ubiquitin ligase Cbl-b and obesity-induced insulin resistance [Review]

“…The pro-inflammatory cytokines secreted by adipose tissue directly interfere with insulin signaling in insulin-sensitive organs, such as liver and skeletal muscle, while pro-inflammatory cytokines cause insulin resistance through activation of nuclear factor κB (NF-κB) and Jun N-terminal kinase (JNK) in these organs. Recently, the activation of the NF-κB and JNK pathways was reported in the adipose tissue of obese rodents and humans [7][8][9].…”

Low­‑quality manufactured immunoenzymatic assay kits as a source of confusion in science

“…3 The study by Körn-er et al 2 went unnoticed by Phoenix Pharmaceuticals and numerous investigators who still use their EIA. 4,5 We decided to inform scientists about the questionable quality of some EIA kits to increase their awareness about the issue. The choice they make is important and the quality of kits is crucial to obtain reliable results from research.…”