from the Journal of Advanced Research
l-Arginine is one of the most metabolically versatile amino acids. In addition to its role in the synthesis of nitric oxide, l-arginine serves as a precursor for the synthesis of polyamines, proline, glutamate, creatine, agmatine and urea. Several human and experimental animal studies have indicated that exogenous l-arginine intake has multiple beneficial pharmacological effects when taken in doses larger than normal dietary consumption. Such effects include reduction in the risk of vascular and heart diseases, reduction in erectile dysfunction, improvement in immune response and inhibition of gastric hyperacidity. This review summarises several positive studies and personal experiences of l-arginine. The demonstrated anti-aging benefits of l-arginine show greater potential than any pharmaceutical or nutraceutical agent ever previously discovered.
Current interest in l-arginine is focused mainly on its close relationship with the important signal molecule nitric oxide (NO). l-Arginine is the only substrate in the biosynthesis of NO, which plays critical roles in diverse physiological processes in the human body including neurotransmission, vasorelaxation, cytotoxicity and immunity.
from NIH PubChem
is an essential amino acid in juvenile humans, Arginine
is a complex amino acid, often found at active site in proteins and enzymes due to its amine-containing side chain. Arginine
may prevent or treat heart and circulatory diseases, combat fatigue, and stimulate the immune system. It also boosts production of nitric oxide
, relaxing blood vessels, and treating angina and other cardiovascular problems. Arginine
is also an important intermediate in the urea
cycle and in detoxification of nitrogenous wastes. (NCI04)
Studies have shown that is has improved immune responses to bacteria, viruses and tumor cells; promotes wound healing and regeneration of the liver; causes the release of growth hormones; considered crucial for optimal muscle growth and tissue repair.
Mechanism of Action
Many of supplemental L-arginine's activities, including its possible anti-atherogenic actions, may be accounted for by its role as the precursor to nitric oxide
or NO. NO is produced by all tissues of the body and plays very important roles in the cardiovascular system, immune system and nervous system. NO is formed from L-arginine via the enzyme nitric oxide
synthase or synthetase (NOS), and the effects of NO are mainly mediated by 3,'5' -cyclic guanylate
or cyclic GMP
. NO activates the enzyme guanylate
cyclase, which catalyzes the synthesis of cyclic GMP
from guanosine triphosphate
or GTP. Cyclic GMP
is converted toguanylic acid
via the enzyme cyclic GMP
phosphodiesterase. NOS is a heme-containing enzyme with some sequences similar to cytochrome P-450 reductase. Several isoforms of NOS exist, two of which are constitutive and one of which is inducible by immunological stimuli. The constitutive NOS found in the vascular endothelium is designated eNOS and that present in the brain, spinal cord and peripheral nervous system is designated nNOS. The form of NOS induced by immunological or inflammatory stimuli is known as iNOS.
iNOS may be expressed constitutively in select tissues such as lung epithelium. All the nitric oxide
synthases use NADPH
(reduced nicotinamide adenine
) and oxygen
(O2) as cosubstrates, as well as the cofactors FAD (flavin adenine dinucleotide), FMN (flavin mononucleotide), tetrahydrobiopterin
and heme. Interestingly, ascorbic acid
appears to enhance NOS activity by increasing intracellular tetrahydrobiopterin
. eNOS and nNOS synthesize NO in response to an increased concentration of calcium
ions or in some cases in response tocalcium
-independent stimuli, such as shear stress. In vitro studies of NOS indicate that the Km of the enzyme for L-arginine is in the micromolar range. The concentration of L-arginine in endothelial cells, as well as in other cells, and in plasma is in the millimolar range. What this means is that, under physiological conditions, NOS is saturated with its L-arginine substrate. In other words, L-arginine would not be expected to be rate-limiting for the enzyme, and it would not appear that supraphysiological levels of L-arginine which could occur with oral supplementation of the amino acid^would make any difference with regard to NO production. The reaction would appear to have reached its maximum level. However, in vivo studies have demonstrated that, under certain conditions, e.g. hypercholesterolemia, supplemental L-arginine could enhance endothelial-dependent vasodilation and NO production.