Collagen IV, a promising serum biomarker for evaluating the prognosis of revascularization in a 2-kidney, 1-clip hypertensive rat model

OBJECTIVES The goal of this study was to investigate the expression of serum collagen IV and its value for evaluating the prognosis of revascularization in a 2-kidney, 1-clip hypertensive rat model. METHODS A total of 40 Sprague-Dawley rats were randomly and evenly divided into a control group and 3-, 10- and 20-day (D) groups (namely, the ischaemic time for 3, 10 and 20 days, respectively). The systolic blood pressure and laboratory values such as serum creatinine and collagen IV levels were measured before and after clipping the renal artery. Histological Masson staining and immunohistochemical staining of collagen IV were conducted in a kidney specimen from each group to assess the severity of renal fibrosis and the level of collagen IV expression. RESULTS After clipping, systolic blood pressure in the 3D, 10D and 20D groups increased significantly from 108 ± 8 to 126 ± 7 and from 153 ± 8 to 157 ± 6 mmHg, respectively (10D vs 20D group, P = 0.224; between other groups, P < 0.001). The expression of serum creatinine in the 3D, 10D and 20D groups increased significantly from 35.39 ± 5.64 to 57.53 ± 7.05, 101.86 ± 8.94 and 119.76 ± 9.37 mmol/l, respectively (between each group: P < 0.001). Serum collagen IV levels in the 10D and 20D groups increased significantly from 38.5 ± 10.4 to 60.8 ± 15.0 and 87.3 ± 11.5 ng/ml, respectively (control vs 3D group, P = 0.718; between other groups, P < 0.001). The Masson staining indicated that sclerotic changes in the glomeruli of the 10D and 20D groups significantly increased from 2.20 ± 1.03 to 15.20 ± 5.03 and 28.20 ± 7.07%, respectively (control vs 3D group, P = 0.175; between other groups, P < 0.001). The grade of tubulointerstitial damage in the 3D, 10D and 20D groups increased significantly from 0.30 ± 0.48 to 1.90 ± 0.74, 1.80 ± 0.79 and 3.20 ± 0.79, respectively (3D vs 10D group, P = 0.755; between other groups, P < 0.001). The semi-quantification from immunohistochemical staining indicated that the percentage of collagen IV positive areas in the 3D, 10D and 20D groups increased significantly from 3.50 ± 1.58 to 8.60 ± 2.11, 16.60 ± 8.55 and 23.10 ± 6.15, respectively (control vs 3D group, P = 0.043; 3D vs 10D group, P = 0.002; 10D vs 20D group, P = 0.011; between other groups, P < 0.001). The area under the curve of the receiver operating characteristic curve was 0.783 (P = 0.008; 95% confidence interval 0.634–0.932). There were positive associations of serum collagen IV levels with systolic blood pressure, serum creatinine and collagen IV quantification in kidney with correlation coefficients of 0.665, 0.775 and 0.628, respectively (P < 0.001). CONCLUSIONS As the clear ischaemia time–response relationship identified in our study indicates, the increase in serum collagen IV levels may be a satisfactory biomarker to indicate a poor prognosis of renal artery revascularization in a 2-kidney, 1-clip hypertensive rat model. However, it is perhaps not a good early biomarker for the early detection of renovascular hypertension.