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Chronic-progressive glomerular disease represents one of the most common causes of endstage renal failure worldwide. The disease course is generally characterized by a progressive loss of renal function up to terminal organ failure and often of nephrotic proteinuria. In affected kidneys, histology is characterised typically by fibrosis, inflammation and proliferation. This study was designed to explore the preventive potential of selective AT2-receptor stimulation by Compound 21 on the progressive loss of function in the animal model of the anti-thy1-induced, chronic-progressive glomerulosclerosis of the rat. Furthermore it was analyzed, whether benefical actions of AT2-receptor stimulation is associated with the antifibrotic, anti-inflammatory and antiproliferative effects, all of which are under controversial discussion. The animal model of the anti-thy1-induced, chronic-progressive glomerulosclerosis is based on male Wistar-rats, which undergo uninephrectomy and subsequent intravenous injection of mAb 1-22-3 antibody. This antibody is specifically directed against thy1-like epitopes of mesangial cells and leads to a complement-dependent cell lysis. In the course of the disease, this initial iatrogenic insult develops into an autoprogressive process of renal damage that ends in terminal uremia. This animal model is independent from extrarenal injurious stimuli and so it is especially suitable for investigations of chronic–progressive kidney diseases, which course is primarily controlled by intrarenal processes.
Thirty male Wistar-rats were arranged in three experimental groups: con = normal control animals (n=6); cGS = animals with uninephrectomy and injection of mAb 1-22-3 antibody, but without Compound 21 treatment (n=12); cGS+C21 = animals with uninephrectomy, antibody injection and Compound 21 treatment (n=12). Twenty weeks after the induction of the cGS, blood, urine and the remaining kidney were collected from the rats in order to measure representative parameters of renal function, fibrosis, inflammation and proliferation. The representative parameters of renal function were proteinuria, systolic blood pressure, plasma concentration of urea and creatinine and glomerular filtration rate. Furthermore, analysis involved histological matrix score, deposition of collagen I, renal infiltration by macrophages and lymphocytes and number of proliferative and apoptotic renal cells. In addition to these parameters, renal expression of TGF-ß1, fibronectin, col I and α-SMA were measured on level of mRNA and proteins. Expression of PAI-1, TIMP-1, MCP-1, IL6, TNF-α and the AT2-receptor was determined at the level of mRNA-expression. In summary, the results of this investigation show that treatment with Compound 21 as a selective agonist of the AT2-receptor leads to an effective slow down of progression in rats with cGS. Thereby, protective actions of Compound 21 involved antifibrotic, antiinflammatory and antiproliferative effects. In particular, treatment of cGS with Compound 21 led to a significant decrease of fibrotic parameters. At histological level: glomerular (-27% (p < 0.01)), tubulointerstitial (-61% (p < 0.001)) matrix score; glomerular (-39% (p < 0.005)), tubulointerstitial (-40% (p < 0.005)) col I deposition. At the level of mRNA-expression: TGF-ß1 -39%, fibronectin -42% (p < 0.005), col I -37% (p < 0.005), PAI-1 -49% (p < 0.01) and TIMP-1 -58%. And at the level of protein-expression: TGF-ß1 -77%, fibronectin -21% and col I -36%. Selective stimulation of the AT2-receptor led to a decreases of the inflammatory arameters at the different investigation levels, too: histology: glomerular (-55% (p < 0.05)), tubulointerstitial (-77% (p < 0.001)) number of CD3-positive cells and glomerular (-58% (p < 0.01)), tubulointerstitial (-50% (p < 0.01)) number of ED1-positive cells; mRNA-Expression: IL6 -48% (p < 0.05), TNF-α -35% (p < 0.05) and MCP-1 -59% (p < 0.05). Furthermore the proliferative and apoptotic activity of renal cells was significantly reduced by Compound 21 treatment at the different levels: histology: glomerular (-61% (p < 0.01)), tubulointerstitial (-69% (p < 0i001) number of PCNA- positive cells and glomerular (-55% (p < 0.01)), tubulointerstitial (-39% (p < 0.05)) number of TUNEL-positive cells. mRNA-expression: α-SMA -45% (p < 0.05). Protein-expression: α-SMA -30%. Via these pathways, AT2-receptor stimulation led to a substantial decrease of diseases progression and accordingly the animals showed improved renal function: plasma concentration of creatinine -39% (p < 0.05) and urea -34% and glomerular filtration rate -42% (p < 0.05). Systolic blood pressure was decreased by -8% (p <0.05) and proteinuria by -21%, respectively.
The results of this work provide an important contribution in the understanding in the progression of glomerular renal disease in veterinary medicine. Furthermore, they establish AT2 receptor stimulation as novel and effective treatment opportunity.
These findings suggest that that AT2-receptor stimulation may be beneficial in human chronic-progressive glomerular disease as well. In future investigations the combination of Compound 21 with the established agents and therapy concepts of the chronic-progressive kidney diseases should be examined in order to optimize those and potentially even to develop new ones.