Asymmetric dimethylarginine accumulates in the kidney during ischemia/reperfusion injury.

Ischemia/reperfusion injury is the leading cause of acute tubular necrosis. Nitric oxide has a protective role against ischemia/reperfusion injury; however, the role of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, in ischemia/reperfusion injury remains unclear. ADMA is produced by protein arginine methyltransferase (PRMT) and is mainly degraded by dimethylarginine dimethylaminohydrolase (DDAH). Here we examined the kinetics of ADMA and PRMT and DDAH expression in the kidneys of ischemia/reperfusion-injured mice. After the injury, DDAH-1 levels were decreased and renal and plasma ADMA values were increased in association with renal dysfunction. Renal ADMA was correlated with 8-hydroxy-2'-deoxyguanosine, a marker of oxidative stress. An antioxidant, N-acetylcysteine, or a proteasomal inhibitor, MG-132, restored these alterations. Infusion of subpressor dose of ADMA exacerbated renal dysfunction, capillary loss, and tubular necrosis in the kidneys of ischemia/reperfusion-injured wild mice, while damage was attenuated in DDAH transgenic mice. Thus, ischemia/reperfusion injury-induced oxidative stress may reduce DDAH expression and cause ADMA accumulation, which may contribute to capillary loss and tubular necrosis in the kidney.

Proteinuria elevates asymmetric dimethylarginine levels via protein arginine methyltransferase-1 overexpression in a rat model of nephrotic syndrome.

AIMS: Proteinuria is an independent risk factor for cardiovascular disease (CVD) in patients with chronic kidney disease (CKD). Asymmetric dimethylarginine (ADMA) is a mediator of endothelial dysfunction and is associated with proteinuria in CKD patients. Thus, ADMA can partially account for the increased risk of CVD in CKD patients presenting proteinuria. However, a causal relationship between proteinuria and ADMA remains to be demonstrated. MAIN METHODS: We first investigated whether and how proteinuria might increase ADMA levels in adriamycin (ADR)-treated rats. Next, we examined the effects of human serum albumin (HSA) on ADMA production by human renal proximal tubular epithelial cells (RPTECs) cultured in vitro. KEY FINDINGS: Proteinuria was associated with ADMA levels in ADR treated rats. Although ADR treatment did not affect the expression levels of the dimethylarginine dimethylaminohydrolase (DDAH)-1 or -2 enzymes that degrade ADMA, it significantly increased the expression levels of protein arginine methyltransferase-1 (PRMT-1) that facilitates the production of ADMA. HSA increased the generation of reactive oxygen species in RPTECs, which was blocked by the anti-oxidant N-acetylcysteine (NAC) or an inhibitor of NADPH oxidase. Furthermore, HSA increased ADMA generation by RPTECs in a dose- and time-dependent manner and induced gene expression of PRMT-1 but not DDAHs, which were also suppressed by NAC. SIGNIFICANCE: Our data suggest that proteinuria might enhance ADMA generation in tubular cells, at least in part via the overexpression of PRMT-1 triggered by oxidative stress. Our findings thereby propose a mechanistic link between proteinuria and ADMA levels in CKD patients.

Interstitial Foxp3-positive T cells may predict renal survival in patients with myeroperoxidase anti-neutrophil cytoplasmic antibody-associated glomerulonephritis.

1. Regulatory T cells (T(reg)) and cytotoxic T cells (CTL) are involved in various immune diseases. However, the prognostic impact of T(reg) and CTL in patients with myeroperoxidase anti-neutrophil cytoplasmic antibody-associated glomerulonephritis (MPO-ANCA-GN) is not well known. Therefore, in the present study, we examined the relationship between expression of forkhead box P3 (Foxp3) and T cell intracytoplasmic antigen (TIA)-1, T(reg) and CTL markers and renal survival in patients with MPO-ANCA-GN. 2. Forty patients with MPO-ANCA-GN and 10 patients with minimal change nephrotic syndrome (MCNS) underwent physical examination, determination of blood chemistry and renal biopsy. Immunohistochemical staining for Foxp3 and TIA-1 was performed on paraffin-embedded renal sections. 3. Although almost all patients received standard immunosuppressive treatment for 6 months, seven MPO-ANCA-GN patients needed maintenance haemodialysis (HD), whereas 33 patients did not (non-HD). Both Foxp3- and TIA-1-positive cells were detected in the interstitium and glomeruli of MPO-ANCA-GN patients, whereas they were rarely detected in patients with MCNS. The total crescent rate was significantly higher in the HD group than in the non-HD group (35.9 +/- 3.5 vs 65.8 +/- 7.4, respectively). In the interstitium, the age-adjusted Foxp3/TIA-1 ratio was significantly higher in the non-HD group than in the HD group (0.016 +/- 0.016 vs 0.004 +/- 0.008, respectively; P < 0.05). The Foxp3/TIA-1 ratio, but not the Foxp3/CD3 ratio, remained significantly higher in the non-HD group than in the HD group even after adjustment for crescent rate. Age- and total crescent rate-adjusted renal survival rates were higher in patients with a Foxp3/TIA-1 ratio > or = 0.06 than in patients with a Foxp3/TIA-1 ratio < 0.06 (P = 0.02). 4. The results of the present study suggest that T(reg) could play a protective role against MPO-ANCA-GN and that a decreased Foxp3/TIA-1 ratio in interstitial areas may predict future renal failure in patients with MPO-ANCA-GN.