Evolution of shear stress, protein expression, and vessel area in an animal model of arterial dilatation in hemodialysis grafts

Abstract

Purpose: To evaluate the wall shear stress, protein expression of matrix metalloproteinase (MMP)-2 and MMP-9 and tissue inhibitor of matrix metalloproteinase (TIMP)-1 and TIMP-2, and vessel area over time in a porcine model for polytetrafluoroethylene (PTFE) hemodialysis grafts.

Materials and methods: In 21 pigs, subtotal renal infarction was created, and 28 days later, a PTFE graft was placed to connect the carotid artery to the ipsilateral jugular vein. Phase-contrast magnetic resonance imaging was used to measure blood flow and vessel area at 1, 3, 7, and 14 days after graft placement. Wall shear stress was estimated from the law of Poiseuille. Animals were killed at day 3 (n = 7), day 7 (n = 7), and day 14 (n = 7) and expression of MMP-2, MMP-9, TIMP-1, and TIMP-2 were determined at the grafted and control arteries.

Results: The mean wall shear stress of the grafted artery was higher than in the control artery at all time points (P < .05). It peaked by day 3 and decreased by days 7-14 as the vessel area nearly doubled. By days 7-14, there was a significant increase in active MMP-2 followed by a significant increase in pro-MMP-9 and active MMP-9 by day 14 (P < .05, grafted artery vs control). TIMP-1 expression peaked by day 7 and then decreased, whereas TIMP-2 expression was decreased at days 7-14.

Conclusions: The wall shear stress of the grafted artery peaks by day 3, with increased MMP-2 activity by days 7-14, followed by increase pro-MMP-9 and active MMP-9 by day 14. In addition, the vessel area nearly doubled.

Fig. 1

Upper panel is magnetic resonance imaging with phase contrast magnetic resonance angiography (MRI with PC MRA) performed at day 14. Left lower panel is the phase contrast MRA showing the direction of the blood vessels in opposite direction as depicted by black in the grafted artery and white in the control artery. Right lower panel is the magnitude of the blood flow in the same vessels.

Fig. 1

Upper panel is magnetic resonance imaging with phase contrast magnetic resonance angiography (MRI with PC MRA) performed at day 14. Left lower panel is the phase contrast MRA showing the direction of the blood vessels in opposite direction as depicted by black in the grafted artery and white in the control artery. Right lower panel is the magnitude of the blood flow in the same vessels.

Fig. 2

MRI measurements of the artery-to-graft anastomosis at day 1, day 3, day 7, and day 14. The wall shear stress calculated from the MRI data. At all time points, the mean wall shear stress of the grafted artery was significantly higher (P<0.05) than the control artery. By day 3, the wall shear stress is significantly higher than days 7 and 14 (P<0.05). The mean wall shear stress of the control artery was 1.2 ± 0.4 N/m². Data are mean ± SD.

Fig. 3

Upper graph representing the appropriate protein band of pro MMP-2 by zymography. GA is the grafted artery and CA is the control artery. Lower graph is semiquantitative analysis performed at day 3, 7, and 14. The normalized density of pro MMP-2 at the grafted artery was significantly higher than the control artery by day 14. (*) is a significantly higher value (P<0.05). Data are mean ± SD.

Fig. 4

Upper graph representing the appropriate protein band of MMP-9 by zymography. GA is the grafted artery and CA is the control artery. Lower graph is semiquantitative analysis performed at day 3, 7, and 14. The normalized density of MMP-9 at the grafted artery was significantly higher than the control artery by day 14. (*) is a significantly higher value (P<0.05). Data are mean ± SD.

Fig. 5

Upper graph representing the appropriate protein band of MMP-9 by zymography. GA is the grafted artery and CA is the control artery. Lower graph is semiquantitative analysis performed at day 3, 7, and 14. The normalized density of MMP-9 at the grafted artery was significantly higher than the control artery by day 14. (*) is a significantly higher value (P<0.05). Data are mean ± SD.

Fig. 6

Upper graph representing the appropriate protein band of TIMP-1 by Western blot. GA is the grafted artery and CA is the control artery. Graph representing appropriate band for IgG from Western blot for protein loading. Lower graph is semiquantitative analysis performed at day 3, 7, and 14. The normalized density of TIMP-1 at the grafted artery was significantly higher than the control artery by day 7. (*) is a significantly higher value (P<0.05). Data are mean ± SD.

Fig. 7

Upper graph representing the appropriate protein band of TIMP-2 by Western blot. GA is the grafted artery and CA is the control artery. Graph representing appropriate band for IgG from Western blot for protein loading. Lower graph is semiquantitative analysis performed at day 3, 7, and 14. The normalized density of TIMP-2 was significantly lower (*) at days 7–14 when compared to control artery. (*) is a significantly lower value (P<0.05). Data are mean ± SD.