Blood Pressure Regulation - Role of Potassium

Project titel: Oral potassium supplementation in healthy men - interactions with the renin-angiotensin-aldosterone system and the sympathetic nervous system Protocol number: KARAASS-1 EudraCT number: 2013-004460-66

Objective

The objective of the study is to investigate how an oral potassium supplementation, administrated in form of the drug Kaleorid® regulates the human blood pressure. More specific the objective is to test how an oral potassium supplementation interacts with:

• The renin-angiotensin-aldosterone system and
• The sympathetic nervous system

To do this we plan to conduct a randomized clinical placebo-controlled double-blinded crossover trial to test how the drug Kaleorid® affects components in the renin-angiotensin-aldosterone system and the sympathetic nervous system compared with placebo in healthy men.

Background The global burden of hypertension is huge. The estimated number of adults with hypertension in the year 2000 was 972 million and this number is expected to increase by about 60% to a total number of 1.56 billion in 2025 worldwide (1). In Denmark, the estimated prevalence of hypertension among the adult population lies between 26% and 40% (2). Hypertension is thus a wide spread disease and it is further known, that hypertension is one of the most important modifiable risk factors for cardiovascular, cerebrovascular and renal disease (3;4). In this study we investigate the role of potassium in the regulation of the human blood pressure.

It is accepted knowledge, that a potassium rich diet lowers blood pressure as demonstrated in the well constructed DASH (Dietary Approaches to Stop Hypertension) study (5). In addition to a high potassium level the DASH diet also contained high levels of magnesium, calcium and low-fat dairy products and a low level of saturated fat, so whether the blood pressure lowering effect of the DASH diet was merely a result of the high potassium level or a result of the combined diet is difficult to tell. Nonetheless a meta-analysis demonstrated a significant systolic and diastolic blood pressure lowering effect of administration of an high-dose oral potassium supplementation compared to placebo or administration of an low-dose oral potassium supplementation (6). The risk of stroke, the main adverse outcome of long time hypertension, has also been demonstrated to be reduced with a high dietary potassium intake (7). And one study demonstrated that, the need for antihypertensive medication in hypertensive subjects can be reduced after an increase in the dietary potassium intake from natural foods (8). A high dietary potassium intake thus seems beneficial.

Furthermore potassium depletion seems to have the opposite effect of potassium supplementation. Both in normotensive men and in patients with essential hypertension the blood pressure increased during potassium depletion (9;10).

Taken together, there is reliable evidence for an inverse correlation between potassium intake and the level of blood pressure. Nevertheless the mechanism behind this apparent inverse correlation is still a conundrum. Different hypothesis has been developed, mostly on the basis of animal studies. In the rat kidney, potassium depletion is expected to elicit retention of sodium and thereby hypertension. At the level of the arterial wall potassium depletion is expected to lower the intracellular potassium level in smooth muscle cells, which would lead to a depolarization of the membrane and thereby elicit contraction, increased peripheral vascular resistance and hypertension. On the other hand a high potassium diet is expected to elicit an endothelium-dependent vasodilatation. Another postulated mechanism is that high potassium levels in the cerebrospinal fluid would decrease the sympathetic outflow from the brain and thereby blood pressure. The mentioned theories (11) are mainly based on animal studies.

It is known that a high potassium intake in humans results in an increased aldosterone level in the blood (12). The increased aldosterone level secures the body against hyperkalemia during potassium loading. In theory this rise in aldosterone should also elicit an inappropriate sodium and volume retention and thereby hypertension. But it does not. The blood pressure remains unchanged (12) or decreases after a rise in potassium intake.

So the question is - Why does the potassium stimulated aldosterone secretion not result in hypertension?

In the laboratory of Molecular Biology at the Department of Nephrology P, Rigshospitalet, we have found some interesting results regarding potassium and aldosterone. Working with an in vitro model of aldosterone secretion in the form of the human adrenocortical cell line H295R, which has been proven to be a model for studying the function of the human adrenal cortex (13;14), we found interactions between extracellular potassium and components of the renin-angiotensin-aldosterone system (RAAS). The H295R cell line is a model of the human adrenocortical zona glomerulosa cells, which normally are the site of synthesis and secretion of aldosterone in the human body. Aldosterone secretion from these cells is mainly stimulated by angiotensin II (Ang II), as part of the activation of the RAAS, and by extracellular potassium in situations with rising levels of extracellular potassium. These two secretagogues are traditionally being look upon as independent. But our studies showed interactions between the two systems. It was found that stimulation of the H295R cells with high levels of extracellular potassium decreased the amount of Ang II type 1 receptors in the membrane of the cells, measured as a fall in the specific binding of radioactive labelled Ang II to the cells (15). This reduction in specific binding of radioactive labelled Ang II, was followed by a potassium induced reduction in the expression of the Ang II type 1 receptor gene (AGTR1) (15). This means that the Ang II sensitivity of human aldosterone producing cells is reduced by high levels of extracellular potassium in vitro and the hypothesis is that high levels of extracellular potassium thus modulate the renin-angiotensin-aldosterone system.

Inspired by our results in the laboratory, the objective of this present study is to verify the existence of such inhibitory interactions between high potassium levels and RAAS in vivo. The overall purpose is to clarify the role of potassium in the regulation of human blood pressure.

Hypotheses In this trial 4 weeks treatment with the drug Kaleorid®, 750mg, 3 tablets 3 times daily, equivalent to 90 mmol potassium daily, is tested against 4 weeks treatment with placebo, 3 tablets 3 times daily in a crossover design. In the end of each treatment period tests are done to investigate components in the renin-angiotensin-aldosterone system and the sympathetic nervous system.

Primary hypothesis and primary endpoint:

The primary hypothesis is that treatment with Kaleorid® will reduce the Ang II sensitivity of the human adrenal cortex and thereby reduce the Ang II stimulated aldosterone secretion. This hypothesis will be tested with an intravenous Ang II infusion and measurement of the following aldosterone response in blood samples. The test will be done twice in each study participant, after treatment with Kaleorid® and after treatment with placebo.

Primary endpoint: Ang II stimulated S-aldosterone

Secondary hypothesis:

The secondary hypothesis is that treatment with Kaleorid® will also reduce the Ang II sensitivity of the smooth muscle cells in the human vascular resistance vessels through a down regulation of the Ang II receptors in the membrane of the smooth muscle cells. This would elicit vasodilatation and a fall in blood pressure To test this we will measure the blood pressure and evaluate vascular tonus before, during and after the above mentioned intravenous Ang II infusion. Blood pressure before, during and after the intravenous Ang II infusion will be measured with Finger Plethysmography and conventional brachial blood pressure measurement. Vascular tonus before, during and after the intravenous Ang II infusion will be evaluated with the use of Impedance Cardiography, Finger Plethysmography and Doppler Ultrasound measurements of blood flow. Impedance Cardiography and Finger Plethysmography will be used to estimate total peripheral resistance (TPR). Doppler Ultrasound will be used to measure blood flow and calculate resistance index (RI) in the renal artery, celiac artery and superior mesenteric artery.

Finally we will take a fat biopsy from the gluteal region of the study participants after each treatment period. In these biopsies we expect to find vascular resistance vessels, which we will investigate for receptorfunction and receptorexpression. Different receptors will be investigated, among them the Ang II type 1 receptor.

Tertiary hypothesis:

The tertiary hypothesis is that treatment with Kaleorid® will interact with activity in the sympathetic nervous system.

To test this potential interaction we plan to measure P-epinephrine and P-norepinephrine in blood and measure the content of epinephrine and norepinephrine in a urine sample at the end of each treatment period. We further plan to measure P-epinephrine and P-norepinephrine in blood before, during and after the above mentioned intravenous Ang II infusion.

Methods

Design:

This is a randomized clinical placebo-controlled double-blinded crossover trial designed to test how the drug Kaleorid® affects components in the renin-angiotensin-aldosterone system and the sympathetic nervous system compared with placebo in healthy men.

After inclusion and baseline screening a group of healthy men with a normal office blood pressure will be randomized to either 4 weeks treatment with the drug Kaleorid®, 750mg, 3 tablets 3 times daily or to 4 weeks treatment with placebo tablets, 3 tablets 3 times daily.

On day 26 in the first treatment period the study participants meet at the hospital and receive the equipment to measure a 24-hours ambulatory blood pressure and collect a 48-hours urine sample. On the same day a blood sample, an electrocardiogram (ECG) and a fat biopsy from the gluteal region will be done.

On day 28 in the first treatment period the study participants meet at the hospital again. This day to be further tested with the intravenous Ang II infusion followed by continuous measurement of blood pressure and the aldosterone response (using blood samples). Before, during and after the intravenous Ang II infusion blood pressure will be measured with Finger Plethysmography and conventional brachial blood pressure measurement. Vascular tonus before, during and after the intravenous Ang II infusion will be evaluated with the use of Impedance Cardiography, Finger Plethysmography and Doppler Ultrasound measurements of blood flow.

After this first period of treatment and testing a washout period of two weeks is inserted. After two weeks washout, the study participants crossover and starts the treatment again (second treatment period). The former Kaleorid® treated individuals become placebo treated individuals, and the former placebo treated individuals become Kaleorid® treated individuals. After another 4 weeks of treatment, the same tests as done after the first period of treatment is repeated.

Investigational drugs, Randomization, Blinding and Statistics:

The drug Kaleorid® and the placebo tablets constitute the investigational drugs in this clinical trial on humans. The drug Kaleorid® is purchased and delivered by the regional pharmacy of the Capital Region of Denmark. The placebo tablets are manufactured and delivered by the regional pharmacy of the Capital Region of Denmark. The same pharmacy is responsible for the randomization of the treatment, packing of the investigational drugs and labelling of the investigational drugs. The delivered tablet containers are not labelled with content, so the treatment is planned blinded for both study participants and investigators - so intentional double-blinded.

Since the design of the study is a cross-over design, statistics for paired data is planned to be used for evaluation of the results. A power calculation on the primary endpoint has been done according to standard criteria and 25 study participants are sufficient.

Experimental procedures:

Day 7 On day 7 in both treatment periods the study participants has a blood sample done to measure potassium, sodium, creatinine and eGFR. This is merely a safety blood sample to test that the study participants can tolerate the investigational drugs and do not develop hyperkalemia.

Day 26 On day 26 in both treatment periods the study participants meet at the hospital and receive the equipment to measure a 24-hours ambulatory blood pressure and collect a 48-hours urine sample. On the same day a blood sample, an electrocardiogram (ECG) and a fat biopsy from the gluteal region will be done.

The fat biopsies will be performed by a surgical skilled physician. After removal the biopsies are immediately transferred to ice-cold physiological buffer and transported to the laboratory at Glostrup Research Institute. At the laboratory small arterioles in the biopsies are dissected free from fat and connective tissue using a microscope. The dissected arterioles are sectioned into 1-2 mm length cylindrical segments which are either immediately used for vasomotor response studies or stored at -80°C for molecular studies. For vasomotor response studies, the isolated arteriole segments are mounted in a Mulvany-Halpern wire-myograph, whereby it is possible to test the physiological response of the vessel after adding different hormones e.g. Ang II. The molecular studies consist of quantitative real-time PCR to quantify the mRNA expression of the relevant receptor genes, western blot to analyse receptor protein expression and immunohistochemistry to analyse receptor localization.

Day 28 On day 28 in both treatment periods the study participants meet at the hospital again. After handing back the equipment used for the 24-hours ambulatory blood pressure and the urine sample the study participants are being tested with the intravenous Ang II infusion. The Ang II infusion is done with the study participant in a supine position. The Ang II infusion is given intravenously at a dosage of 5 ng/kg/min for 30 min. The chosen dosage and length of duration is based on other studies and is safe (16-18). Before, during and after the Ang II infusion blood samples are taking from another intravenous access to analyse the blood for S-aldosterone, P-angiotensin II, Plasma renin activity, P-epinephrine, P-norepinephrine and N-PRO-ANP.

Before, during and after the infusion the study participants are monitored closely. Blood pressure is measured with conventional brachial blood pressure measurement but also with Finger Plethysmography, which gives a continuous blood pressure assessment. Continuous Impedance Cardiography gives a continuous assessment of cardiac output and together with the blood pressure we are able to estimate total peripheral resistance during the Ang II infusion. In addition blood flow in the central arteries of the abdomen, are measured using Doppler Ultrasound.

Practical Feasibility This is a clinical trial with medicinal products in humans. The trial is approved by the Danish Health and Medicines Authority and the trial is registered in the EudraCT database with the EudraCT number: 2013-004460-66.

Under existing legislation clinical trials with medicinal products in humans must follow the rules of GCP (Good Clinical Practice). In accordance with this, the trial is monitored by the GCP unit at Copenhagen University Hospital.

The trial is approved by The Committees on Health Research Ethics in the Capital Region of Denmark.

In conclusion all necessary authorities have approved the trial.

Funding This study is supported by The Danish Heart Foundation.