Prof. Isabelle Six INSERM Unit 1088 Jules Verne University of Picardie Amiens, France. Slide 1. Slide 2

Transcription

1 Effects of phosphate on vascular function New insights Isabelle Six, Amiens, France Chairs: Griet Glorieux, Ghent, Belgium Alberto Ortiz, Madrid, Spain Prof. Isabelle Six INSERM Unit 1088 Jules Verne University of Picardie Amiens, France Slide 1 Slide 2

2 As you know, high serum phosphorous levels increase risk of death due to cardiovascular disease both in patients with CKD and in people with normal kidney function. Phosphorous concentration in the upper range of normal: greater carotid intima-media thickness, overt atherosclerosis, increased risk of cardiovascular disease and induced endothelial dysfunction. Slide 3 CKD is associated with increased cardiovascular mortality, arterial calcifications, hyperphosphatemia and endothelial dysfunction. Slide 4

3 Several studies have shown Slide 5 that vascular calcification is one of the possible mechanisms linking high phosphate levels to adverse cardiovascular outcomes in patients with chronic renal failure. It has been demonstrated that controlling serum phosphorous slows the progression of vascular calcifications and may have a beneficial impact on the survival of haemodialysis patients. Slide 6

4 The aims of the present study were to investigate the role of phosphate in vascular dysfunction in both CKD and intact renal function and investigate the therapeutic potential of a phosphate binder, Sevelamer to prevent these disturbances. Slide 7 First of all, we tested effects of in vitro exposure to high phosphate concentration. The direct effects on vascular reactivity were analysed by stimulating the cells with increasing concentrations of phosphate and measuring changes in the isometric force. The effects of phosphate on ROS production and Erk activation were analysed using HUVEC, a human vascular smooth muscle cells culture. To study long-term effects of high phosphate concentration autocrines were placed in culture with phosphate for 8 days. Slide 8

5 We investigated the effects of a high phosphate diet on aortic reactivity in non-ckd and CKD mice Slide 9 and compared them with the effects in mice fed a normal diet. The standard diet contained 0.65% of phosphate. We opted for a double amount of phosphate in the diet, 1.3% and an intermediate level 1%.

6 Slide 10 In the second part, we investigated the effects of Sevelamer treatment first of all in vitro. Aortic rings were placed in culture with phosphate for 5 days with addition or not of Sevelamer the last 6 days of culture. Slide 11

7 Sevelamer effects were initiated in vivo in CKD mice. Sevelamer or placebo was administrated as a 3% mix with animal --. Sevelamer treatment was started 2 weeks after CKD induction and continued for 8 weeks. Slide 12 For results the addition of phosphate induced a concentration-dependent vascular constriction, which however was significantly less intensive in 18 weeks from CKD mice than from non-ckd mice. Moreover, the contractions of 18 weeks from non-ckd mice were abolished by --- scavenger of --. Slide 13

8 In models phosphate at concentrations of 2 and 3 mmol increased ROS production only in smooth muscle cells culture. Moreover, phosphate induced a concentration-dependent Erk activation in smooth muscle cells culture. Slide 14 We investigated the effect of a high phosphate diet on aortic reactivity in non-ckd and CKD mice. The high phosphate diet increased constriction in response to Phenylephrine. Slide 15 CKD had no effect on vascular constriction capacity. Slide 16

9 However, CKD-induced endothelial dysfunction as demonstrated by an impairment in relaxation in response to acetylcholine. Similarly, a high phosphate diet induced endothelin dysfunction and dysfunction was not further aggravated by CKD. Slide 17 dysfunction was not further aggravated by CKD. Slide 18

10 In the same model endothelial cells were examined by immunostaining. Slide 19

11 This figure clearly shows that a very high phosphate diet induced endothelial cell loss. Slide 20 In CKD animals, a cell effect was observed with the 1% phosphate diet. Slide 21

12 In the non-ckd 1% phosphate diet group there was no focal detachment or denudation of endothelial cells. However, there were subendothelial vacuoles possibly indicative of imminent endothelial detachment. Slide 22 We examined adhesion molecule expression and we demonstrated that CKD induced an increase in the expression of adhesion molecules VCAM-1 and ICAM-1. In the same manner, a high phosphate diet was associated with an increase in VCAM-1 and ICAM-1 expression. Slide 23

13 In the second part, the therapeutical effect of Sevelamer was investigated. Exposure of aortic rings to 3 mmol of phosphate for 8 days resulted in lower relaxation. Slide 24 This decrease was entirely abolished in the presence of Sevelamer. Slide 25

14 In this model Sevelamer was able to improve deleterious effects Slide 26 of high phosphate concentration. Slide 27

15 In the same model, endothelial immunostaining revealed a loss of endothelial integrity in aortic rings exposed to 3 mmol of phosphate for 8 days with only 70% of endothelial cells remaining present on the luminal surface. The adjunction of Sevelamer reduced the deleterious impact of phosphate on the endothelium with maintenance of integrity of 82%. Slide 28 In this protocol

16 Slide 29 Sevelamer effect was investigated in vivo in CKD mice. CKD under a normal phosphate diet had no effect on vasoconstriction but induced endothelial dysfunction as demonstrated by a weaker response to acetylcholine. Slide 30

17 Sevelamer treatment significantly improved the CKD-induced endothelial dysfunction. Slide 31 In the same model we analysed adhesion molecule expression and we demonstrated that CKD under Slide 32 a normal phosphate diet led to stronger stimulation of endothelial VCAM-1 and ICAM-1

18 expression. Slide 33 Treatment with Sevelamer attenuated the VCAM-1 and ICAM-1 upregulation in CKD mice. Slide 34 To summarise, we demonstrated in this study that increasing phosphate induced a contraction of aortic rings and a decrease in endothelium-dependent relaxation, an increase of ROS expression and Erk activation, a loss of endothelium integrity associated with an increase of adhesion molecule expression.

19 Slide 35 CKD by itself induced an impairment of endothelial-dependent relaxation and an increase of adhesion molecule expression. Sevelamer treatment can improve this phenomenon. Slide 36

20 Sevelamer treatment can improve this phenomenon. Slide 37 In conclusion, changes in extracellular phosphorous concentration may directly modulate vascular function and thereby modulate the vascular smooth muscle response to physiological or pathological stimuli in normal and CKD mice. Perspectives are to establish if serum phosphorous lowering and/or dietary phosphate restriction can improve arterial function in humans. Slide 38

21 To conclude definitively if you need more information about this study, you can check the paper published in Cardiovascular Research. Thank you for your attention. Slide 39 Chairman: Thank your Isabelle for this presentation. The paper is now open for discussion. Are there questions from the audience? Thank you. Question: Maybe it's a stupid question, I'm not an expert at all but if you add Sevelamer to the phosphate, there is eventually no free phosphate available,is this correct? Prof. Six: In which case I wonder whether you should not see no effect at all anymore, in other words it should look like the control without the phosphate on your slides and it doesn't. Can you enlighten me here? We have few protocols, in the first one we put phosphate, in the second one we put Sevelamer in the presence of CKD. If I understand your question, the question is to put Sevelamer and phosphate together? You still have an effect of the phosphate plus Sevelamer versus the control on your slides and I wouldn't expect to see any effects all the phosphate should be gone in the presence of Sevelamer but maybe I don't understand it right. In culture models we put phosphate in the first two days and after we put Sevelamer in the 6 lag days of culture. We have a control with phosphate alone and with Sevelamer alone during the 8 days of culture. Question: OK thanks. We have no effect of course of Sevelamer only in culture.

22 Chairman: Are there any more questions from the audience? Question: I wonder if Sevelamer captures other uremic toxins like when used in a CKD in vivo model? Other things form phosphate? Prof. Six: Yes in the study we targeted just phosphate with Sevelamer but probably we can imagine a pleiotropic effect of Sevelamer in other uremic toxins and it will be great to test the effect of other uremic toxins in this kind of model. Question: Ok thank you. Question: Isabelle in humans in the clinic Sevelamer hydrochloride is associated with acidosis. When you added Sevelamer hydrochloride to the cultures did the ph change? Prof. Six: Nothing, we checked all the parameters in the culture medium and we had no effect on ph and no effect on other parameters. In culture and in the model of vascular reactivity. Question: Another question, in the aortic rings in culture the endothelial cells were lost. Why were they lost? Were they dying? If they were dying what was the mode of cell death? Do you have an idea on that? Prof. Six: The growth of endothelial cells? The endothelial cells were lost in the aortic rings, I understood when you cultured the aortic rings. When you culture the aorta, you have the same effect on endothelial cells as when you pick up minutes before. You have no growth of endothelial ells, you have a perfect aorta when you put the aorta in a cultured --- and no growth of endothelial cells in this aorta in some conditions. Question: OK, maybe I didn't understand correctly but I understood that endothelial cells were lost from the rings, that was not the case ok. Thank you. Chairman: We have time for one more question. Question: But you said ---- to activate --- the question is of phosphate mediated by oxidative stress? In other words if you prevent oxidative stress in the presence of phosphate, would you blunt Erk 1, 2 phosphorylation? Prof. Six: No we didn't block Erk 1, 2 phosphorylation. We proved the effects of phosphate on ROS production. We proved the effect of ROS production on contraction effects but we didn't block Erk activation. We didn't. Question: Thank you. Chairman: Ok thank you.