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To expand the armamentarium of treatment for chronic kidney disease (CKD), we explored the utility of boosting endogenously synthesized N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP), which is augmented by inhibition of the angiotensin converting enzyme. Male BALB/c mice underwent unilateral ureteral ligation (UUO) or sham operation and received exogenously administered Ac-SDKP delivered via a subcutaneous osmotic minipump or Captopril treatment by oral gavage. Seven days after UUO, there were significant reductions in the expression of both collagen 1 and collagen 3 in kidneys treated with Ac-SDKP or Captopril, and there was a trend towards reductions in collagen IV, α-SMA, and MCP-1 versus control. However, no significant attenuation of interstitial injury or macrophage infiltration was observed. These findings are in contrary to observations in other models and underscore the fact that a longer treatment time frame may be required to yield anti-inflammatory effects in BALB/c mice treated with Ac-SDKP compared to untreated mice. Finding an effective treatment regimen for CKD requires fine-tuning of pharmacologic protocols.

Bone marrow-derived mesenchymal stem cells (BM-MSCs) have recently shown promise as a therapeutic tool in various types of chronic kidney disease (CKD) models. However, the mechanism of action is incompletely understood. As renal prognosis in CKD is largely determined by the degree of renal tubular injury that correlates with residual proteinuria, we hypothesized that BM-MSCs may exert modulatory effects on renal tubular inflammation and epithelial-to-mesenchymal transition (EMT) under a protein-overloaded milieu. Using a co-culture model of human proximal tubular epithelial cells (PTECs) and BM-MSCs, we showed that concomitant stimulation of BM-MSCs by albumin excess was a prerequisite for them to attenuate albumin-induced IL-6, IL-8, TNF-α, CCL-2, CCL-5 overexpression in PTECs, which was partly mediated via deactivation of tubular NF-κB signaling. In addition, albumin induced tubular EMT, as shown by E-cadherin loss and α-SMA, FN and collagen IV overexpression, was also prevented by BM-MSC co-culture. Albumin-overloaded BM-MSCs per se retained their tri-lineage differentiation capacity and overexpressed hepatocyte growth factor (HGF) and TNFα-stimulating gene (TSG)-6 via P38 and NF-κB signaling. Albumin-induced tubular CCL-2, CCL-5 and TNF-α overexpression were suppressed by recombinant HGF treatment, while the upregulation of α-SMA, FN and collagen IV was attenuated by recombinant TSG-6. Neutralizing HGF and TSG-6 abolished the anti-inflammatory and anti-EMT effects of BM-MSC co-culture in albumin-induced PTECs, respectively. In vivo, albumin-overloaded mice treated with mouse BM-MSCs had markedly reduced BUN, tubular CCL-2 and CCL-5 expression, α-SMA and collagen IV accumulation independent of changes in proteinuria. These data suggest anti-inflammatory and anti-fibrotic roles of BM-MSCs on renal tubular cells under a protein overloaded condition, probably mediated via the paracrine action of HGF and TSG-6.

Angiotensin-converting enzyme inhibitors (ACEi) are widely employed to deter the progression of chronic kidney disease (CKD). Besides controlling hypertension and reduction of intra-glomerular pressure, ACEi appear to have anti-fibrotic effects in the renal cortex. N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP), an endogenous tetrapeptide that is degraded by ACE, has also been shown to ameliorate the pro-fibrotic phenotype displayed in CKD in our recent study. Whether the anti-fibrotic properties of ACEi are mediated by Ac- SDKP has not been fully investigated. To delineate the role of Ac-SDKP in ACE blockade, 12-week-old male BALB/c mice underwent sham operation or unilateral ureteric obstruction (UUO). UUO mice were subjected to: i) vehicle; ii) captopril or iii) captopril in conjunction with S17092, a prolyl oligopeptidase inhibitor. After 7 days, mice were sacrificed and kidneys harvested for analyses. After UUO, there were heightened expressions of collagen I, collagen III, fibronectin and a-SMA associated with significant levels of tubulointerstitial injury on histological examination. Furthermore, p44/42 Mitogen-Activated Protein Kinase (MAPK) and Transforming Growth Factor Beta 1(TGF-ß1) signaling were up-regulated. These were significantly ameliorated by captopril treatment alone but unaffected by co-administration of captopril with S17092. Captopril treatment had resulted in elevated urinary Ac-SDKP levels, an effect which was eliminated by the co-administration with S17092. This study allowed the investigation of the renoprotective property of ACEi in the absence of Ac-SDKP and proved conclusively that Ac-SDKP is the prime anti-fibrotic mediator of captopril, acting via p44/42 MAPK and TGF-ß1 signaling pathways. Future research to expand CKD armamentarium should explore the utility of augmenting Ac-SDKP levels. [ABSTRACT FROM AUTHOR]

Bone morphogenetic protein 7 (BMP7) has been reported to confer renoprotective effects in acute and chronic kidney disease models, but its potential role in Type 2 diabetic nephropathy remains unknown. In cultured human proximal tubular epithelial cells (PTECs), exposure to advanced glycation end-products (AGEs) induced overexpression of intercellular adhesion molecule 1 (ICAM1), monocyte chemoattractant protein 1 (MCP1), interleukin 8 (IL-8) and interleukin 6 (IL-6), involving activation of p44/42 and p38 mitogen-activated protein kinase (MAPK) signalling. BMP7 dose-dependently attenuated AGE-induced up-regulation of ICAM1, MCP1, IL-8 and IL-6 at both mRNA and protein levels. Moreover, BMP7 suppressed AGE-induced p38 and p44/42 MAPK phosphorylation and reactive oxygen species production in PTECs. Compared with vehicle control, uninephrectomized db/db mice treated with BMP7 for 8 weeks had significantly lower urinary albumin-to-creatinine ratio (3549 -- 816.2 μg/mg compared with 8 6 1 2 - 2037 μg/mg, P = 0.036), blood urea nitrogen (33.26- 1.09 mg/dl compared with 37.49 - 0.89 mg/dl, P = 0.006), and renal cortical expression of ICAM1 and MCP1 at both gene and protein levels. In addition, BMP7-treated animals had significantly less severe tubular damage, interstitial inflammatory cell infiltration, renal cortical p38 and p44/42 phosphorylation and lipid peroxidation. Our results demonstrate that BMP7 attenuates tubular pro-inflammatory responses in diabetic kidney disease by suppressing oxidative stress and multiple inflammatory signalling pathways including p38 and p44/42 MAPK. Its potential application as a therapeutic molecule in diabetic nephropathy warrants further investigation. [ABSTRACT FROM AUTHOR]