L-arginine Treatment in Mild Hypertension

Scientific background

Essential Hypertension is characterized by endothelial dysfunction with impaired vasorelaxation.

Reduced nitric oxide bioavailability, which is considered a hallmark of endothelial dysfunction, plays an important role in mediating blood pressure elevation. Accumulating evidence demonstrates a critical role of nitric oxide in blood pressure regulation. Released from the endothelial cells, nitric oxide increases 30,50-cyclic-guanosine monophosphate (cGMP) production and subsequent cGMP-dependent protein kinase (PKG) activation in the underneath vascular smooth muscle cells (VSMCs), resulting in vasodilatation. The investigators and others have shown that inhibition of NO synthesis increase blood pressure in normal pregnant rats and different animal models. In vivo studies confirmed an essential role of nitric oxide in vasorelaxation of large human arteries. Impairment in nitric oxide-mediated vasodilatation in brachial, coronary, and renal arteries has been demonstrated in patients with essential hypertension.

Several mechanisms have been found responsible for nitric oxide deficiency in hypertension. One of them is deficit of the NO substrate, L-arginine. L-arginine transport is impaired in hypertensive and normotensive patients with a genetic background of essential hypertension, and the offspring of essential hypertensive patients are characterized by a reduced response to acetylcholine linked to a defect in the nitric oxide pathway. These data represent the link between L-arginine and the onset of essential hypertension. The Km of endothelial nitric oxide synthase for L-arginine is about 3mmol/l, but the concentration of plasma L-arginine rarely falls below 60mmol/l in pathological conditions. An elevation in asymmetric dimethylarginine (ADMA, an endogenous NO competitive inhibitor) levels may explain this 'L-arginine paradox'. The administration of excess exogenous L-arginine displaces the competitive inhibitor, improves intracellular transport of this amino acid, and restores NO production to physiological levels. In fact L-arginine supplementation improved endothelial dysfunction in hypertension.

Administration of L arginine in humans have not shown uniform blood pressure responses. A meta-analysis published in 2011 was able to find only 11 articles dealing with l-arginine administration and blood pressure. The population studies were heterogeneous. Compared with placebo, oral L-arginine intervention was associated with an average net change ranging from -23.0 to 2.8 mm Hg for SBP and from -11.0 to 1.0 mm Hg for diastolic BP. Most trials showed an intervention-related trend toward BP reductions, but only a few reached statistical significance.

Endothelial dysfunction leads to an increase in arterial stiffness, a known marker that increases cardiovascular morbidity and mortality. Arterial stiffness can be measured by non invasive methodology, e.g.; measuring carotid-femoral pulse wave velocity, augmentation index, aortic pulse pressure and aortic systolic blood pressure.

Whether administration of l-arginine improved arterial stiffness in patients with mild hypertension it is not known.

Arginoline is a dietary supplement that contains L-arginine at a concentration of 5 g/L. It is possible to dilute with water or take chilled. It is produced by Pharmayeda, an Israeli industry.

Clinical observational studies [personal communication] have shown that at a dose of 60 ml\day [10 gr of l-arginine] flow mediated vasodilation improves, suggesting an increase in nitric oxide function.

Methods

Office Blood Pressure (OBP) measurement:

OBP will be measured with a Suntech 247 digital automated device. BP will be determined 3 times at one min. interval each. The mean of the second and third measurements will be noted as the OBP of the visit.

ABPM:

24 hours ABPM will be performed with an Oscar 2 ABPM device of SunTech Medical. The Oscar 2 ABPM device is clinically validated to all 3 internationally recognized protocols (British Heart Society, American Society of Hypertension and the Association for the Advancement of Medical Instrumentation).

Blood pressure is measured in a 20 min. interval at day time and a 30 min. interval at night time. The patients are requested to fill a diary with their activities during the ABPM study, including their subjective evaluation of the sleeping quality.

Measurement of arterial stiffness:

The SphygmoCor X-CEL System (AtCor Medical, Sydney, Australia) will be used.

The system derives (non invasively) the ascending aortic pressure waveform from the brachial waveform using a validated generalised transfer function.

The SphygmoCor X-CEL system measures the carotid-femoral pulse wave velocity (PWV), the speed of the arterial pressure waveform as it travels through the descending aorta to the femoral artery, which is detected from simultaneously measured carotid and femoral arterial pulses.

Design

The study is a matched double blind study with an experimental group and a placebo group. As the number of the groups is small (20 in each group) the patients will be matched according to age, sex and BMI during the recruitment phase, in order to get to comparable groups. The principal investigator is responsible of the matching.

The experimental group will receive arginoline 30 ml twice a day and the placebo group will receive placebo at the same schedule

Visits:

Week -2:

Sign of informed consent

Office BP. Physical examination. BMI.

Blood exams: Hemoglobin (g%), urea (mg%), creatinine (mg%), Natrium (mEq/l), Potassium (mEq/l), alanine transaminase (ALT),Aspartate aminotransferase (AST), gamma-glutamyl transpeptidase (GGT), glucose, cholesterol and triglycerides. and lipid profile.

Urine analysis: microalbuminuria (morning spot)

All patients will receive a booklet with detailed information about healthy life style recommendation to lower blood pressure.

Hypertensive patients on monotherapy will stop treatment.

Week 0

ABPM

Measurement of Central aortic blood pressure and arterial stiffness

Blind group allocation (experimental or placebo group).

Week 2

Office BP measurement.

Week 4

Office BP measurement

Week 6

Office BP measurement

Week 8: ABPM, office BP,

Repeat blood and urine exams as detailed at week -2.

Measurement of Central aortic blood pressure and Arterial stiffness

Statistical evaluation

Will be done using the IBM SPSS statistical software. Pi<0.05 is considered significative