Reduced vascular responsiveness to adiponectin in hyperlipidemic rats--mechanisms and significance

Deficiency of adiponectin (APN), an adipocyte-derived vascular protective molecule, contributes to diabetic vascular injury. The current study determined whether obesity/hyperlipidemia may alter the vascular response to APN, and investigated the involved mechanisms and pathologic significance. Adult male Sprague-Dawley rats were fed a regular or high-fat diet (HF) for 4-16 weeks. Circulating APN levels, aortic pAMPK/AMPK, peNOS/eNOS, and APN receptor expression levels were determined. Compared to time-matched animals fed control diet, plasma APN levels in HF-diet animals were significantly increased at 8 weeks, and rapidly declined thereafter. Despite unchanged or elevated circulating APN levels, phosphorylated AMPK and eNOS in vascular tissue were significantly reduced at all observed time points. Recombinant full-length APN (rAPN)-induced AMPK/eNOS phosphorylation and vasodilatation were significantly reduced in 16-week obese/hyperlipidemic aortic segments. Vascular APN receptor 1 (AdipoR1) and receptor 2 (AdipoR2) expression were significantly reduced 16 weeks after HF-diet. Pre-incubation of rAPN with obese/hyperlipidemic plasma, but not with normal plasma, significantly reduced its AMPK and eNOS activation effect, and blunted its protective effect against TNFalpha-induced HUVEC apoptosis. This study demonstrated for the first time that obesity/hyperlipidemia reduces vascular responsiveness to APN. Modification/inactivation of APN by unidentified factors present in obese/hyperlipidemic plasma, decreased vascular AdipoR1/R2 expression, and reduced circulating APN levels contribute to reduced vascular responsiveness to APN at different stages of the obese condition. Reduced APN bioactivity allows unmitigated TNFalpha pro-apoptotic and pro-inflammatory actions, contributing to vascular injury in obesity/hyperlipidemia.