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A joint Congress by ERA-EDTA and ISN |
ADMA, ENDOTHELIAL DYSFUNCTION AND THE RISK OF CARDIOVASCULAR AND RENAL DISEASES |
Carmine Zoccali, Reggio Calabria, Italy |
Chair:
Duk-Hee Kang, Seoul, Korea |
Detlef Schöndorff, New York, USA
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Prof
C. Zoccali |
Slide 1
Dear Chairs, dear colleagues.
Slide 2
Endothelial dysfunction is a sort of mantra of modern medicine. It is at the basis of atherosclerosis but it is supposed that it also engenders other diseases like diabetes.
Slide 3
To introduce the theme I will start with a basic reaction of the endothelial cell. The reaction whereby L-arginine is transformed into nitric oxide. Being a fundamental reaction for life this is highly modulated. In fact if you infuse acetylcholine, acetylcholine stimulates the enzyme and more nitric oxide is produced. Vice versa, we have also endogenous inhibitors of the system and one of these is asymmetric dimethyl arginine. As you can see, this aminoacid is identical to L-arginine but it has just two added methyls. These two added methyls block the enzyme in that they compete with L-arginine and in doing so they reduce the synthesis of nitric oxide. You can remove the inhibition by ADMA by giving great amounts of L-arginine. This is a competitor, the competitor that blocks the enzyme is removed and nitric oxide synthesis is restored.
Slide 4
Reactive oxygen species are important at endothelial level. This is so because the enzyme, nitric oxide synthase is a geneous enzyme. When you have huge amounts of reactive oxygen species, the enzyme stops producing nitric oxide and catalyses the production of superoxide and hydrogen peroxide. You can remove the effect of reactive oxygen species by giving huge amounts; I underline huge amounts of anti-oxidants like vitamin E.
Slide 5
What about the relationship between reactive oxygen species and ADMA? There is indeed a relationship because reactive oxygen species block the enzymes that degrade ADMA, DDAH and there are in vitro data showing that there is a feedback into this reaction because ADMA can also increase the production of reactive oxygen species.
Slide 6
Now, let me translate these very simple concepts into clinical physiology. We can infuse many of the substances that I mentioned into the forearm, to measure the changes in forearm blood flow to estimate endothelial function. For example, we may estimate the potential for endothelium to induce vasodilatation by stimulating nitric oxide by acetylcholine, as I said at the start. We can also estimate the involvement of endogenous inhibitors by co-infusing acetylcholine and L-arginine. Finally, we can also estimate the involvement of oxidative stress by co-infusing acetylcholine and vitamin C.
Slide 7
In this graph the acetylcholine infusion rate is plotted against the forearm blood flow change expressed in proportional terms. As you can see in normal subjects there is a nice dose-response relationship and at the top dose of acetylcholine the forearm blood flow is 6 times higher than at baseline. If you co-inject L-arginine, the response moves upwards and this upward movement gives you an idea of the role of endogenous inhibitors.
In essential hypertensives the response is subnormal, clearly subnormal and this has been confirmed in several laboratories worldwide.
Now what is the role of reactive oxygen species in this low response in essential hypertensives? If we inject vitamin C, we observe that the response normalises. There is a nice paper by Taddei published more than 10 years ago in Circulation nicely showing this response.
Slide 8
What about ADMA in essential hypertensives? ADMA in essential hypertensives is almost 40% higher than in normal subjects. As you can see ADMA both in normal subjects and in essential hypertensive is in the so-called normal range of these aminoacids less than 1 µmol/L.
Let’s plot now the effect of L-arginine in the response in this particular group of essential of hypertensives. As in the previous study by Taddei you see in baseline conditions the response in essential hypertensives is subnormal but if we co-infuse acetylcholine and L-arginine, the response normalises.
Now, this reminds me the effect of vitamin C. Let me hypothesise that the response to acetylcholine is in part influenced by ADMA and also by reactive oxygen species suggesting that the two compounds are in the same causal pathway.
Slide 9
In this respect we have very fresh data published early this year by Professor Wilcox’s group. Professor Wilcox’s group found that ADMA peroxidation products are nicely associated with each other and more importantly that both ADMA and lipid peroxidation products are inversely associated with acetylcholine inducing vasorelaxation in the microvessel isolated in humans.
Slide 10
Now what about the relationship in patients with CKD? This is a paper by a group of investigators in Ankara leaded by Mahmut Yilmaz and Mahmut Yilmaz found that there is a nice relationship between flow-mediated vasodilatation and oxidised LDL. The higher oxidised LDL, that is the higher oxidative stress the lower the flow-mediated vasodilatation.
In this paper there was a parallel relationship between ADMA and the GFR, an inverse one. The lower the GFR, the higher ADMA. So it comes as no surprise that ADMA in CKD was also associated with flow-mediated vasodilatation.
So to summarise briefly, in patients with CKD endothelial function is associated with GFR, with oxidative stress and with ADMA.
Slide 11
Now these are functional data what about outcome data? As you know, outcome data are fundamental for clinicians. The relationship between endothelial function and oxidative stress is responsible for cardiovascular sequelae and this was shown 8 years ago in a much quoted paper by Heitzer.
Heitzer studied patients with proven coronary artery disease. He found that in this cohort of patients the response to acetylcholine had a wide range. As you can see here, the range here is wider than what I showed previously. Heitzer divided the population in two parts on the basis of the median value. Those with a response greater than median that is with normal, relatively well-preserved endothelial function and the other group below the median relatively compromised endothelial function.
Slide 12
When he looked at cardiovascular event free survival, there was a huge difference between patients with well-preserved endothelial function and those with compromised endothelial function. As you can see, the cardiovascular event rate in the two groups differed by as much as 50%.
Slide 13
So what about now the analysis in this same study of the relationship between oxidative stress and cardiovascular events? To make this analysis the population was divided into 2 groups; those without incident cardiovascular events on follow-up and those with incident cardiovascular events on follow-up. Let’s start form the first group, those without incident cardiovascular events. In this group as you can see, the response was relatively well-preserved. It was well-preserved in the upper part of the normal range but also non modifiable by vitamin C. This means that here the oxidative stress had very little role.
Slide 14
What about the group with incident cardiovascular events? Here the response was in the lower part of the normal range but increased remarkably after vitamin C administration implying that oxidative stress had a role in facilitating the higher rate of cardiovascular events in these patients. What about ADMA?
Slide 15
The link between ADMA and cardiovascular events and mortality was examined in a high risk cohort like in cohorts of patients with coronary heart disease documented by coronary angiography. In these cohorts, for example, about 2500 patients were included and the population was divided in 2 quartiles. As compared to the first quartile, the risk for all-cause death and cardiovascular death was by 80% higher in those with ADMA in the fourth quartile that is with high ADMA.
Slide 16
This paper went along with previous findings which were published early in this decade in patients with ESRD. Again, here patients were classified according to quartiles and as in the previous study, the higher the ADMA quartile, the higher the risk of all-cause death and cardiovascular death. As you know, confirming findings in a given cohort, in other cohorts is important for gauging the generalizability of the findings. More recently these data were confirmed in a cohort in Japan and in a second cohort by Doctor Aucella in Italy. The paper is impressed in Atherosclerosis.
Slide 17
Now what about CKD and events? If you divide the population with CKD according to median ADMA, you see that those with higher ADMA, 50% of patients with high ADMA, you see the risk of death is considerably higher and the risk of progression to ESRD goes in parallel with the risk of death.
Slide 18
Now, these findings again, go along with more recent findings that were published this year in Diabetics. In diabetics the appearance of, or the worsening of albuminuria is more marked in patients with high ADMA.
Slide 19
Now let me conclude. I’ve shown that oxidative stress and endothelial dysfunction are pervasive in cardiovascular and renal disease.
That perhaps these alterations are at the crossroads of the so-called ‘cardiorenal link’. Of course, these functional studies document that ADMA and oxidative stress are critical factors in endothelial dysfunction.
Finally, whether countering oxidative stress and ADMA by new treatments may have a beneficial effect on clinical outcomes remains to be tested and today I know you will hear fresh data from all the speakers in this area. Thank you.
Slide 20
Chairman: Thank you very much it was very attractive and the lecture is open for questions, remarks. You have several minutes, so please questions from the audience? If not, may I ask? No doubt that also age could play a role in the endothelial dysfunction. Are there some differences with respect to the age or gender, for instance, in the chronic renal failure patients?
Prof. Zoccali: You see in my particular cohort if you refer to ESRD, age was not a covariate of ADMA and there was no interaction between age and ADMA in determining the outcome. But in a huge population-based study Rainer Berger a person with whom I have a longstanding collaboration found ADMA to be related also with age which is not in patients with ESRD.
Chairman: Yes Professor Wilcox?
Question: So your data would predict I think that supplementation with arginine might improve endothelial function and since that’s a predictor of cardiovascular disease, renal disease progression would be beneficial. So have you got any insight to why those trials have not been very encouraging?
Prof. Zoccali: This is an important question. You see you should keep well separate the in vivo functional studies in the forearm from extrapolation on clinical outcomes. The hard reality is that there may even be the risk of increasing clinical events by giving L-arginine. Clinical trials with L-arginine in men have been truly disappointing and now I don’t recommend administering L-arginine as a therapeutic agent. Please remember that most products that are on the market about L-arginine are chloride salt and by administering chloride salt you acidify the patient. So be careful when using L-arginine.
Chairman: Last question from the audience? If not thank you once again.
