Objective: Haptoglobin (Hp) is upregulated in both inflammation and obesity. The low chronic inflammatory state, caused by massive adipose tissue macrophage (ATM) infiltration found in obesity, and low adiponectin have been implicated in the development of insulin resistance and hepatosteatosis. The aim of this work was to investigate whether and how Hp interferes with the onset of obesity-associated complications.
Research design and methods: Hp-null (Hp(-/-)) and wild-type (WT) mice were metabolically profiled under chow-food diet (CFD) and high-fat diet (HFD) feeding by assessing physical parameters, glucose tolerance, insulin sensitivity, insulin response to glucose load, liver triglyceride content, plasma levels of leptin, insulin, glucose, and adiponectin. ATM content was evaluated by using immunohistochemistry (anti-F4/80 antibody). Adiponectin expression was measured in Hp-treated, cultured 3T3-L1 and human adipocytes.
Results: No genotype-related difference was found in CFD animals. HFD-Hp(-/-) mice revealed significantly higher glucose tolerance, insulin sensitivity, glucose-stimulated insulin secretion, and adiponectin expression and reduced hepatomegaly/steatosis compared with HFD-WT mice. White adipose tissue (WAT) of HFD-Hp(-/-) mice showed higher activation of insulin signaling cascade, lower ATM, and higher adiponectin expression. Hp was able to inhibit adiponectin expression in cultured adipocytes.
Conclusions: We demonstrated that in the absence of Hp, obesity-associated insulin resistance and hepatosteatosis are attenuated, which is associated with reduced ATM content, increased plasma adiponectin, and higher WAT insulin sensitivity.