Arginine, in its L form, is an important semiessential proteinogenic amino acid. It is the sole supplier of the neurotransmitter nitric oxide. A deficiency of arginine promotes the development of arteriosclerosis and other so-called diseases of civilization.
What is arginine?
Arginine is the proteinogenic amino acid with the highest content of nitrogen in the molecule. It is an optically active molecule whose L-form is involved in protein building. In the following, when arginine is mentioned, only L-arginine is meant. It was first isolated as a silver salt. The name arginine comes from the Latin term for silver (argentum). Arginine is an alkaline amino acid. When dissolved in water, it always reacts alkaline. In the process, a hydrogen ion of the slightly dissociated water is bound by the guanidine nitrogen. In undissolved form, arginine represents an inner salt because the proton of the acid group migrates to the more basic guanidino residue. The guanidino group is always protonated in solution, regardless of whether it is in an acidic, neutral, or basic environment. This tendency to protonate confers hydrophilic properties to proteins containing strong arginine. As a result, these proteins can be better dissolved in water. In metabolism, arginine is synthesized as part of the urea cycle.
Function, effects, and roles
Arginine performs a variety of functions in the organism. First, it is a proteinogenic amino acid and a component of many proteins. Proteins containing arginine react alkaline and are hydrophilic. Furthermore, due to its nitrogen richness in the molecule, arginine is the sole source of the neurotransmitter nitric oxide. Nitric oxide (NO) is responsible for the dilation of blood vessels. Thus, it ensures the adequate supply of oxygen to the organs. The dilation of the blood vessels lowers blood pressure and the body becomes more efficient under greater stress. Due to its vasodilatory effect, arginine is widely used by strength athletes to enhance performance and build muscle. By the strengthening of the power also the fat dismantling is favored. The positive effects of arginine curb, among other things, cardiovascular diseases or diabetes mellitus. It also inhibits platelet aggregation through the formation of NO, so that the development of thrombosis is impeded. At the same time, the effect of NO also has a positive influence on erectile dysfunction. Arginine also plays a metabolic role in the conversion of ammonia to urea. When amino acids are broken down, the toxic ammonia is formed as a breakdown product. With the help of arginine, the body is detoxified by the conversion of ammonia into urea. In addition, arginine also has a positive effect on the immune system. Especially in cases of severe injuries, infections or after operations, additional supplementation with arginine improves the cellular immune response. Increased phagocytosis is observed, while at the same time preventing disturbances in vascular function.
Formation, occurrence, properties, and optimal levels
Arginine is synthesized in the organism and thus does not belong to the essential amino acids. It occurs in urea metabolism as a metabolite and is also produced from other amino acids as part of urea metabolism. However, there are situations in which there is an increased demand that cannot be met by higher production. This is especially the case in the growing organism and in stressful situations. Therefore, it represents an essential amino acid for children and adolescents. For adults it is semi-essential, because the consumption often exceeds the new production in the body. Therefore, attention should be paid to a diet rich in arginine. Arginine is particularly abundant in nuts, fish (tuna, shrimp) and meat (chicken and lamb). In case of high performance requirements, it can also be taken additionally as a supplement. In old age and diseases such as arteriosclerosis and cardiovascular diseases, the need for arginine increases again. The need is also dependent on environmental conditions, which are manifested in oxidative stress.
Diseases and disorders
Multiple studies support the health-promoting effects of arginine. Arginine deficiency leads to accelerated development of atherosclerosis, diabetes mellitus, impotence and many other health disorders. The immune system is also weakened.The most important factor for the positive effects of arginine is its ability to form nitric oxide (NO). The vasodilatory properties of NO particularly prevent the formation of atherosclerosis. This is due, on the one hand, to better blood circulation in the blood vessels and, on the other hand, to the inhibition of platelet aggregation. It has long been clear that significant improvements occur with additional administration of L-arginine in patients with arteriosclerosis in the early stages, vascular diseases, high blood pressure or erectile dysfunction. Until recently, however, the European Food Safety Authority (EFSA) doubted the benefit of additional supplementation of arginine in healthy individuals. According to recent findings, however, the health value of arginine has been confirmed even in healthy individuals, especially in the context of the highest performance requirements. Beside a healthy way of life the nutrition with arginine-rich food has a preventive effect against degenerative illnesses in the age. In later life, the concentration of asymmetric dimethylarginine (ADMA) increases 4-fold. ADMA is the antagonist of arginine and degrades nitric oxide. It is formed during the methylation of arginine and is also known as a mortality factor because it accelerates the formation of atherosclerosis and subsequent diseases. The exact mechanism of formation of ADMA is not yet known. To restore the ratio of arginine to ADMA to normal, the arginine concentration must increase 40-fold. Additional administration of arginine can prevent or at least delay the formation of atherosclerosis. Arginine is also used to treat hyperammonemia.
