A Novel Mechanism of Action for Salidroside to Alleviate Diabetic Albuminuria: Effects on Albumin Transcytosis across Glomerular Endothelial Cells

Salidroside (SAL) is a phenylethanoid glycoside isolated from the medicinal plant Rhodiola rosea. Rhodiola rosea has been reported to have beneficial effects on diabetic nephropathy (DN) and high glucose (HG) induced mesangial cell proliferation. Given the importance of caveolin-1 (Cav-1) in transcytosis of albumin across endothelial barrier, the present study was designed to elucidate whether SAL could inhibit Cav-1 phosphorylation and reduce the albumin transcytosis across glomerular endothelial cells (GECs) to alleviate diabetic albuminuria, as well as to explore its upstream signaling pathway. To assess the therapeutic potential of SAL and the mechanisms involved in DN albuminuria, we orally administered SAL to db/db mice, and the effect of SAL on the albuminuria was measured. The albumin transcytosis across GECs was explored in a newly established in-vitro cellular model. The ratio of albumin/creatinine was significantly reduced upon SAL treatment in db/db mice. SAL decreased the albumin transcytosis across GECs in both normoglycemic and hyperglycemic conditions. SAL reversed the HG-induced downregulation of AMP-activated protein kinase (AMPK) and upregulation of Src kinase, as well as blocked the upregulation Cav-1 phosphorylation. Meanwhile, SAL decreased the mitochondrial superoxide anion production and moderately depolarized mitochondrial membrane potential. We conclude that SAL exerts its proteinuria alleviating effects by downregulation of Cav-1 phosphorylation and inhibition of albumin transcytosis across GECs. These studies provide the first vidence for the interference with albumin transcytosis across GECs as a novel approach to the treatment of diabetic albuminuria.