Singapore Drugs Database

Indication

Used for nutritional supplementation, also for treating dietary shortage or imbalance.

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 to guanylic 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 dinucleotide phosphate) 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 to calcium-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.

Pharmacokinetics

Absorption

Absorbed from the lumen of the small intestine into the enterocytes. Absorption is efficient and occurs by an active transport mechanism.

Distribution

Metabolism

Some metabolism of L-arginine takes place in the enterocytes. L-arginine not metabolized in the enterocytes enters the portal circulation from whence it is transported to the liver, where again some portion of the amino acid is metabolized.

Elimination

Toxicity

Oral supplementation with L-arginine at doses up to 15 grams daily are generally well tolerated. The most common adverse reactions of higher doses from 15 to 30 grams daily are nausea, abdominal cramps and diarrhea. Some may experience these symptoms at lower doses.

Active Ingredient/Synonyms

(2S)-2-amino-5-(carbamimidamido)pentanoic acid | (2S)-2-amino-5-guanidinopentanoic acid | (S)-2-amino-5-guanidinopentanoic acid | (S)-2-Amino-5-guanidinovaleric acid | Arg | Arginine | L-(+)-Arginine | L-Arg | L-Arginin | R | L-Arginine |

Indication

Supplemental L-lysine has putative anti-herpes simplex virus activity. There is preliminary research suggesting that it may have some anti-osteoporotic activity.

Mechanism of Action

Proteins of the herpes simplex virus are rich in L-arginine, and tissue culture studies indicate an enhancing effect on viral replication when the amino acid ratio of L-arginine to L-lysine is high in the tissue culture media. When the ratio of L-lysine to L-arginine is high, viral replication and the cytopathogenicity of herpes simplex virus have been found to be inhibited. L-lysine may facilitate the absorption of calcium from the small intestine.

Pharmacokinetics

Absorption

Absorbed from the lumen of the small intestine into the enterocytes by an active transport process

Distribution

Metabolism

Hepatic

Elimination

Active Ingredient/Synonyms

(S)-2,6-diaminohexanoic acid | (S)-lysine | (S)-α,ε-diaminocaproic acid | 6-ammonio-L-norleucine | L-2,6-Diaminocaproic acid | L-lys | L-Lysin | LYS | Lysina | Lysine | Lysine acid | Lysinum | L-Lysine |