Background/Aims: To investigate the effects of peritubular capillary (PTC) loss and hypoxia on the progression of tubulointerstitial fibrosis in a rat model of aristolochic acid nephropathy (AAN). Methods: Female Wistar rats received Caulis aristolochiae manshuriensis (CAM) decoction by gavage for 8 weeks, and were sacrificed at 8, 12 and 16 weeks, respectively, after administration. Blood urea nitrogen (BUN), serum creatinine (Scr) and urinary protein were monitored prior to sacrifice. PTC loss and tubulointerstitial hypoxia were assessed by CD34 immunostaining and hypoxia-inducible factor-α subunit 1 (HIF-1α) expression, respectively. Myofibroblasts were assessed by α-smooth muscle actin (α-SMA) expression. The expression of angiogenic factor was assessed by vascular endothelial growth factor (VEGF). Results: AAN rats differed from controls by increased BUN, Scr and 24-hour urinary protein excretion rates. There was a progressive loss of PTCs in the AAN model, which was associated with the decreased expression of VEGF. A significant increase in nuclear localization of HIF-1α was seen 16 weeks after treatment with CAM decoction in the context of severe tubulointerstitial damage. Multifocal tubulointerstitial fibrosis was seen in AAN rats at weeks 12 and 16, predominantly in the area of the outer stripe and outer medulla. No significant pathologic changes were found in control rats. Conclusion: Following the reduction of PTCs density and up-regulation of HIF-1α, the tubulointerstitial fibrosis area increased. Ischemia and hypoxia are the important causes of severe tubulointerstitial fibrosis in AAN rats.

Keywords:
Peritubular capillary loss, Aristolochic acid nephropathy, Tubulointerstitial fibrosis
1.
Cosyns JP: Aristolochic acid and ‘Chinese herbs nephropathy’: a review of the evidence to date. Drug Saf 2003;26:33–48.
2.
Wojcikowski K, Johnson DW, Gobe G: Medicinal herbal extracts – renal friend or foe? 1. The toxicities of medicinal herbs. Nephrology (Carlton) 2004;9:313–318.
3.
Kang DH, Joly AH, Oh SW, et al: Impaired angiogenesis in the remnant kidney model. I. Potential role of vascular endothelial growth factor and thrombospondin-1. J Am Soc Nephrol 2001;12:1434–1447.
4.
Kim YG, Suga SI, Kang DH, et al: Vascular endothelial growth factor accelerates renal recovery in experimental thrombotic microangiopathy. Kidney Int 2000;58:2390–2399.
5.
Zoja C, Morigi M, Figliuzzi M, et al: Proximal tubular cell synthesis and secretion of endothelin-1 on challenge with albumin and other proteins. Am J Kidney Dis 1995;26:934–941.
6.
Bohle A, Mackensen-Haen S, Wehrmann M: Significance of postglomerular capillaries in the pathogenesis of chronic renal failure. Kidney Blood Press Res 1996;19:191–195.
7.
Ohashi R, Kitamura H, Yamanaka N: Peritubular capillary injury during the progression of experimental glomerulonephritis in rats. J Am Soc Nephrol 2000;11:47–56.
8.
Thomas SE, Anderson S, Gordon KL, et al: Tubulointerstitial disease in aging: evidence for underlying peritubular capillary damage, a potential role for renal ischemia. J Am Soc Nephrol 1998;9:231–242.
9.
Fine LG, Orphanides C, Norman JT: Progressive renal disease: the chronic hypoxia hypothesis. Kidney Int Suppl 1998;65:S74–S78.
10.
Norman JT, Clark IM, Garcia PL: Hypoxia promotes fibrogenesis in human renal fibroblasts. Kidney Int 2000;58:2351–2366.
11.
Jiang BH, Semenza GL, Bauer C, et al: Hypoxia-inducible factor 1 levels vary exponentially over a physiologically relevant range of O2 tension. Am J Physiol 1996;271:C1172–C1180.
12.
Zagzag D, Zhong H, Scalzitti JM, et al: Expression of hypoxia-inducible factor 1alpha in brain tumors: association with angiogenesis, invasion, and progression. Cancer 2000;88:2606–2618.
13.
Zhu S, Liu J, Chen L, et al: Chemopreventive effect of five drugs on renal interstitial fibrosis induced by an aristolochic acid-containing Chinese herb in rats. Am J Nephrol 2005;25:23–29.
14.
Rodriguez-Pena A, Eleno N, Duwell A, et al: Endoglin upregulation during experimental renal interstitial fibrosis in mice. Hypertension 2002;40:713–720.
15.
Moriyama T, Kawada N, Ando A, et al: Up-regulation of HSP47 in the mouse kidneys with unilateral ureteral obstruction. Kidney Int 1998;54:110–119.
16.
Seron D, Alexopoulos E, Raftery MJ, et al: Number of interstitial capillary cross-sections assessed by monoclonal antibodies: relation to interstitial damage. Nephrol Dial Transplant 1990;5:889–893.
17.
Depierreux M, Van Damme B, Vanden Houte K, et al: Pathologic aspects of a newly described nephropathy related to the prolonged use of Chinese herbs. Am J Kidney Dis 1994;24:172–180.
18.
Yang Li Lx-m, Wang Su-xia, Wang Hai-yan: Peritubular capillary injury in Chinese herb guan-mu-tong-induced acute tubular necrosis. Chin J Intern Med 2005;44:525–529.
19.
Choi YJ, Chakraborty S, Nguyen V, et al: Peritubular capillary loss is associated with chronic tubulointerstitial injury in human kidney: altered expression of vascular endothelial growth factor. Hum Pathol 2000;31:1491–1497.
20.
Harris DC, Chan L, Schrier RW: Remnant kidney hypermetabolism and progression of chronic renal failure. Am J Physiol 1988;254:F267–F276.
21.
Safran M, Kaelin WG Jr: HIF hydroxylation and the mammalian oxygen-sensing pathway. J Clin Invest 2003;111:779–783.
22.
Kairaitis LK, Wang Y, Gassmann M, et al: HIF-1alpha expression follows microvascular loss in advanced murine adriamycin nephrosis. Am J Physiol 2005;288:F198–F206.
23.
Hopfl G, Ogunshola O, Gassmann M: HIFs and tumors–causes and consequences. Am J Physiol 2004;286:R608–R623.
24.
Gerber HP, McMurtrey A, Kowalski J, et al: Vascular endothelial growth factor regulates endothelial cell survival through the phosphatidylinositol 3′-kinase/Akt signal transduction pathway: requirement for Flk-1/KDR activation. J Biol Chem 1998;273:30336–30343.
25.
Ferrara N: Role of vascular endothelial growth factor in the regulation of angiogenesis. Kidney Int 1999;56:794–814.
26.
Moriyama T, Kawada N, Nagatoya K, et al: Fluvastatin suppresses oxidative stress and fibrosis in the interstitium of mouse kidneys with unilateral ureteral obstruction. Kidney Int 2001;59:2095–2103.
27.
Goumenos DS, Brown CB, Shortland J, et al: Myofibroblasts, predictors of progression of mesangial IgA nephropathy? Nephrol Dial Transplant 1994;9:1418–1425.
28.
Utsunomiya Y, Kawamura T, Abe A, et al: Significance of mesangial expression of alpha-smooth muscle actin in the progression of IgA nephropathy. Am J Kidney Dis 1999;34:902–910.
29.
Essawy M, Soylemezoglu O, Muchaneta-Kubara EC, et al: Myofibroblasts and the progression of diabetic nephropathy. Nephrol Dial Transplant 1997;12:43–50.
30.
Diamond JR, van Goor H, Ding G, et al: Myofibroblasts in experimental hydronephrosis. Am J Pathol 1995;146:121–129.
31.
Epstein FH, Agmon Y, Brezis M: Physiology of renal hypoxia. Ann NY Acad Sci 1994;718:72–81; discussion 81–72.
32.
Suga SI, Phillips MI, Ray PE, et al: Hypokalemia induces renal injury and alterations in vasoactive mediators that favor salt sensitivity. Am J Physiol 2001;281:F620–F629.
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2006
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