CME Slides Forum - D. Fliser

A joint Congress by ERA-EDTA and ISN

ADMA, BLOOD PRESSURE AND RENAL FUNCTION: FROM SALTSENSITIVITY TO HEART FAILURE

Danilo Fliser, Homburg/Saar, Germany

Chair: Vladimir Teplan, Prague, Czech Republic

Christopher Wilcox, Washington, USA

fliser

Prof D. Fliser
Renal and Hypertensive Disease
University Medical Centre
Homburg/Saar, Germany

So Dear Chairmen, dear colleagues, Ladies and Gentlemen. It does not happen often that I’m quite comfortable with my allocated 15 minutes because when I reviewed all the data from the literature on ADMA, blood pressure and renal function from salt sensitivity to heart failure I had to realise there are not so many data.

So fortunately, from our own group we have done some studies, particularly on dose aspects of renal function and salt sensitivity in humans and this is one study done by Doctor Kielstein from a time when I was in Hannover. What we did was we took ADMA and infused it in a pharmacological study in healthy volunteers and we measured renal function invasively using the inulin and pH clearance and you see here the data on GFR measured by inulin clearance and the effective renal plasma flow measured by pH clearance and filtration fraction renovascular resistance. What we could show clearly is that ADMA is a biologically active NO inhibitor, at least in the renal circulation and here you see the infusion period of AMDA, which is here and exactly with starting the infusion the effective renal plasma flow significantly dropped. We repeated this experiment also with L-NAME and all of you who are familiar with L-NAME know that L-NAME must be converted in the liver to be biologically active. Therefore, this slight how do you say time lap in the action of L-NAME on effective renal plasma flow but in principal we have shown that ADMA and L-NAME which are usually used in such experiments are equally potent in depressing renal blood flow and increasing renovascular resistance. However, we used in these experiments doses which gave pathophysiological levels but they increased also blood pressure. It was not a big increase. There are studies using animals in the literature which show that if you infuse ADMA, you have large increases in blood pressure, we couldn’t repeat that. We had relatively minor increases in blood pressure with this major depression of renal function in the range of about 4-5 mmHg of mean arterial blood pressure.

Then we thought, well we will take ADMA and infuse it again into healthy male volunteers in a dose which dose not change blood pressure and again, we could not show this time not at the kidney but you see here that the second most important organ in the body, the brain, we could clearly show that there is a decrease of blood flow before and then after ADMA and red very easily to remember is blood flow and you see here by inspection it decreases.

What we showed in this study is also, with doses which do not modulate blood pressure there is a decrease of arterial viability or increase of stiffness already shown by Doctor Zoccali. There is an increase in stiffness already with these suppressor doses.

Therefore, we used then ADMA in another experiment where we used, as you can see, suppressor doses, no change of mean arterial blood pressure, pre- and post-infusion. However, we still have quite a large change in effective renal plasma flow. I have to remind you this is only 60 mm/min but you lose with ageing, every decade this amount of effective renal plasma flow. So with a suppressor dose of ADMA we induced an age alteration in renal blood flow which can be compared with 10 years of ageing in a normal human.

What we observed is that this effect was longstanding. This is after ADMA infusion and you see almost 2 hours after ADMA infusion an in parallel there was a decrease in urinary sodium excretion and quite an increase in sodium reabsorption showing that ADMA and I mustn’t show you all the data previously obtained with L-NAME infusion, works like an NO inhibitor or an eNOS inhibitor, like L-NAME in humans, it decreases renal perfusion, it increases reabsorption of sodium.

Well these are acute experiments. How is it in the long-term? Unfortunately, we don’t have long-term human experiments but very recently, half a year ago 2008, there was a study published by the Swedish Group in non-experimental designs, CKD design in hydronephrotic animals. This was partial unilateral uretal obstruction or bilateral uretal obstruction.

What the colleagues observed was an increase of ADMA levels in these animals. This is nothing new, we have seen it previously. If you are a CKD patient, you lose GFR and in parallel ADMA levels increase in blood.

What they also observed is there is a tremendous decrease of eNOS function in the medulla of these animals. It depends even if you have a unilateral or bilateral obstruction and in parallel with this decrease and this is a very hard picture to explain, I will try, there is a resetting of the tubulo-glomerular feedback which is important for sodium reabsorption in these animals. What happens in hydronephrotic animals is that this feedback is or the baseline is, you see it here, is set at the lower levels to lower stop-flow pressure levels.

What does this mean? This means that the perfusion of the kidney where sodium is reabsorbed is going down. So the kidney shuts down. You see if you add L-arginine and we had this discussion on L-arginine, then you can restore this stop-flow pressure and restore the tubulo-glomerular feedback. In parallel with these changes of tubulo-glomerular feedback there is a clear increase of salt sensitivity of the blood pressure of these animals. You see here very nice examples of the renal function curve. The renal function curve is the relationship between mean arterial blood pressure and sodium intake or excretion in this picture an. It is usually very steep you know this is from the physiology, you have a tremendous change in sodium intake but only a minor change in blood pressure. This is how renal function is normal or how kidney function to control volume, to control renal sodium reabsorption or to control blood pressure.

This is totally different in this study with the CKD animal model and there is a tremendous increase of blood pressure with minor changes in sodium intake. Well, these are indirect data but they show in the long-term, you see it here, over 30 days that there is clear increased sodium reabsorption and increased blood pressure with this sodium reabsorption in these animals. This can be directly inhibited or reversed by addition of L-arginine, an indirect proof that ADMA may be important for

inhibition of sodium excretion and increases the salt sensitivity of blood pressure in these animals. Well, what about human data? I will come to this human data showing only one additional experiment in mice. These are mice which have additional enzymes or DDH activity. We will hear after that what DDH is, I thought it would have been explained in the first talk. This is the enzyme which is responsible for the degradation of ADMA, about 80% of all ADMA in the body is degraded but is enzyme. These animals have additional activity of DDH and you see they have lower ADMA levels, they have more nitric oxide production and they have significantly lower blood pressure.

Unfortunately, there are no data linking this significantly lower blood pressure to renal sodium reabsorption in these animals and I have to say these experiments have to be done in the future. Well, the situation in humans, we have almost no data.

We have already seen this slide presented by Doctor Zoccali and these are maybe 2 or 3 studies in essential hypertensives where indeed some kind of vascular function was related to ADMA levels but we do not have data of how it is in hypertensives or what I will show later on in patients with heart insufficiency, sodium reabsorption and blood pressure increase and ADMA. So I can only speculate that for example, kidney diseases and of course, hypertension lead through ADMA to renal sodium retention and add to hypertension in these conditions eventually to heart failure.

How about heart failure? So the first study showing that there is a connection between ours and one of the first studies was an experimental heart failure study where the colleagues have shown that in experimental heart failure here in rabbits there is an increase, you see here a dramatic increase in ADMA levels. They made additional experiments with an endothelin inhibitors and they could reverse part of this increase arguing that endothelin could be responsible for the increase of ADMA levels in these animals.

In another study done previously they could link ADMA levels in the experimental heart failure to GFR, to the renal function in these animals but these are the only data we really have from experimental studies.

Here already human data again obtained by Doctor Kielstein and I and we could show that in humans with heart failure, NIH class I or II there is a tremendous increase, you see it here in the smaller part of the figure, of the picture, there is a tremendous increase in ADMA levels and these increased ADMA levels significantly correlate with effective renal plasma flow in heart failure patients, an indirect evidence that ADMA may be also here important for changes in renal perfusion. That’s all on renal perfusion and renal sodium reabsorption in heart failure.

What we have shown is that if you infuse ADMA to healthy volunteers, you can depress cardiac output acutely.

You can increase systemic vascular resistance acutely and therefore, we also have done studies in experimental animals infusing ADMA with mini-pumps for 28 days. The data have not yet been published and what we saw was not only an increase in ADMA blood levels,

this is very difficult to measure but we also saw that ADMA significantly reduces in the long-term cardiac function, here cardiac output by increasing left ventricular and diastolic pressure.

So also after 28 days, which is quite a long period in mice you have a significant depression of cardiac function by infusion of ADMA.

Well what about again, human data? As the previous speaker pointed out, human data are important and actually doctor Zoccali by himself has shown that in CKD stage 5 patients that there is a significant correlation,

These data have been nicely reproduced in non-CKD patients recently last year in the European Heart Journal paper, in patients with heart failure where the investigators showed that ADMA levels are also related to cardiac function.

What they also showed and there is another paper on this topic published and only two of them they showed that these ADMA levels in heart failure patients, non-CKD patients are predictive for outcome in this patient population. I have to leave you here with this scarce data which could be important or which might draw a link between kidney disease, hypertension and heart failure, ADMA and renal dysfunction with renal reabsorption leading to hypertension and organ failure.

Chairman: Thank you very much for very comprehensive data and for keeping the time. The lecture is of course, open for discussion. Yes please.

Question: Thank you. My first question was what were the plasma concentrations of AMDA that you achieved in your infusion studies in humans? And how does that relate to physiological levels? The second question is in your heart failure data I think I noticed that SDMA was similarly associated with ADMA and I wondered if you could just comment on that association.

Dr. Fliser: Two short comments. First of all in our experiments with the infusion we made of course a titration experiment and what I showed you here are data with plasma levels which are approximately equal to those seen in CKD patients. So they are in principal pathophysiologically relevant, I do say in principal because we know that eNOS inhibition is intracellular and what we measure outside of the cell, although this plasma concentration of ADMA might be of relevance, might be of relevance very carefully stated to what happens intracellularly. Second question you’re correct and we know and this was not part of the topic. SDMA is probably not biologically active but it is a perfect marker of renal function and we have done together with Doctor Kielstein a recent NDT paper where we showed that SDMA perfectly correlates with GFR. So it might be that it’s only a marker for renal dysfunction in these heart failure patients.

Prof. Zoccali: Just a short comment about the relationship between ADMA and ventricular function and the left ventricular mass. It’s important that you specify, like you did, the population where you tested the relationship because if you test the relationship in the general population, you find no association. The only element of the cardiac geometry that is related with ADMA is the left atrium suggesting that ADMA may induce -- in ventricular relaxation.

Dr. Fliser: So ADMA is a little bit unusual I think you may agree in that it doesn’t raise blood pressure doses which severely reduce renal blood flow. I know that might be related to preferential effects on the pulmonary circulation and pulmonary hypertension limiting cardiac output. Do you think that is part of the answer?

Question: It could be. I can just speculate on that but we were really very, very struck by our results because we knew the results from Doctor Valence in his seminal paper in Lancet in 1992 where he infused ADMA in animals and they had quite large increases in blood pressure and we had tremendous problems with our ethical committee to get these studies through because the Gnudi publication said well you cannot give an NO inhibitor where there is an increase in blood pressure of 80 mmHg and so on. After we started and I have to say the first healthy volunteer who was infused with ADMA was Doctor Kielstein by himself. He had an increase in blood pressure but this was because he was very nervous and not because he received ADMA and then we realised it doesn’t really increase so much blood pressure.