Long-term therapeutic effect of vitamin D analog doxercalciferol on diabetic nephropathy: strong synergism with AT₁ receptor antagonist

Abstract

The intrarenal renin-angiotensin system (RAS) plays a key role in the development of diabetic nephropathy. Recently, we showed that combination therapy with an AT 1 receptor blocker (ARB) and an activated vitamin D analog produced excellent synergistic effects against diabetic nephropathy, as a result of blockade of the ARB-induced compensatory renin increase. Given the diversity of vitamin D analogs, here we used a pro-drug vitamin D analog, doxercalciferol (1␣-hydroxyvitamin D 2), to further test the efficacy of the combination strategy in long-term treatment. Streptozotocin-induced diabetic DBA/2J mice were treated with vehicle, losartan, doxercalciferol (0.4 and 0.6 g/kg), or losartan and doxercalciferol combinations for 20 wk. Vehicle-treated diabetic mice developed progressive albuminuria and glomerulosclerosis. Losartan alone moderately ameliorated kidney injury, with renin being drastically upregulated. A similar therapeutic effect was seen with doxercalciferol alone, which markedly suppressed renin and angiotensinogen expression. The losartan and doxercalciferol combination most effectively prevented albuminuria, restored glomerular filtration barrier structure, and dramatically reduced glomerulosclerosis in a dose-dependent manner. These effects were accompanied by blockade of intrarenal renin upregulation and ANG II accumulation. These data demonstrate an excellent therapeutic potential for doxercalciferol in diabetic renal disease and confirm the concept that blockade of the compensatory renin increase enhances the efficacy of RAS inhibition and produces synergistic therapeutic effects in combination therapy.renin-angiotensin system; compensatory renin increase; albuminuria; glomerulosclerosis DIABETIC NEPHROPATHY (DN) is the most common renal complication of diabetes mellitus and a leading cause of end-stage renal disease, accounting for 44% of new cases in 2005 (9). It is well established that the renin-angiotensin system (RAS) is a major mediator of progressive renal injury. Since renal interstitial angiotensin (ANG) II levels are much higher than in the plasma (28), the local RAS in the kidney is believed to play the major damaging role in diabetic nephropathy. Kidney cells, including mesangial cells and podocytes, are able to synthesize all components of the RAS, including renin, the (pro)renin receptor, angiotensinogen (AGT), and ANG II receptors independently of the systemic RAS, making the kidney capable of maintaining a high level of local ANG II. Intrarenal renin and AGT levels are induced in diabetic animals (4, 48). In vitro studies showed that when exposed to high glucose levels, mesangial cells and podocytes increase renin and ANG II production (13,38,42). Intrarenal ANG II promotes the progression of renal injury via multiple pathways that increase glomerular permeability, induce oxidative stress, and promote the synthesis of profibrotic and proinflammatory factors and extracellular matrix (8,15). The consequence of the progression of diabetic renal injury is the development of protein...

Vitamin D Receptor Signaling in Podocytes Protects against Diabetic Nephropathy

“…The purified 4.1 kb PmeI DNA construct ( Figure 1A) was microinjected into fertilized embryos isolated from pregnant female DBA/2J mice, a genetic background known to be susceptible to diabetic renal injury. 14,16,22 PCR-based genotyping identified 3 positive pups of 62 born from the microinjection, and cross of these founder lines with DBA/2J mice resulted in germline transmission in lines 5 and 12. This study focused on line 5.…”

“…13 We reported that vitamin D analog therapy reduced albuminuria and prevented podocyte loss in experimental models of type 1 and type 2 diabetes. [14][15][16] We also showed that podocytes express the vitamin D receptor (VDR) that is highly inducible by 1,25(OH) 2 D 3 , 17 1,25(OH) 2 D 3 transcriptionally stimulated the expression of nephrin, a key slit diaphragm protein synthesized by podocytes, 18 and deletion of VDR in mice led to early onset and robust albuminuria in diabetic state. 19 Together these data suggest that podocytes may be a key antiproteinuric target of vitamin D 20 ; however, no study has directly addressed the renoprotective role of podocyte VDR signaling.…”

Diabetic Nephropathy from RAAS to Autophagy: The Era for New Players

“…Experimental studies have shown that VDR knockout mice have higher expression of renin, angiotensin, and angiotensin receptors under diabetic conditions and may develop severe renal injury resulting in early onset albuminuria, glomerulosclerosis, and interstitial fibrosis mainly due to local RAAS activation. Vitamin D exerts anti-inflammatory effects by modulating antigen-presenting cells' function, reducing expression of cytokine interleukin-12 (IL-12), and repressing transcription of genes encoding interleukin 2 (IL2) and interferon gamma [42][43][44].…”

Involvement of the Skeletal Renin-Angiotensin System in Age-Related Osteoporosis of Ageing Mice

“…Studies have shown that the increased activity of RAS in local tissue leads to the pathological process of target organs, like fibrosis, 3) oxidative stress 4) and inflammation. 5) Recent studies have shown that such components of RAS as renin, ACE, and Ang II receptors are expressed in the skeleton. 6) Functional studies have revealed that Ang II could stimulate the differentiation and activity of osteoclasts in vivo 7) and in vitro, 8) and that the activation of RAS induced high-turnover osteoporosis with accelerated bone resorption.…”