Histidine is the only amino acid, the essentiality of which is still debated. In the 40s of XX century, W.C. Rose discovered a paradoxical fact: histidine is essential for rats and other animals, but is non-essential for healthy adults. The essentiality of histidine in infants was soon established. Only this century Japanese biochemists discovered an enzyme that catalyzes the last reaction in the histidine biosynthesis. This enzyme is present in all studied animal species, but with different activity, which is the indicator by which one can judge the essentiality of histidine for a particular organism. At the same time, it has been clearly shown that in patients with uremia, histidine becomes an essential amino acid and its addition to the diet together with amino acids essential for a healthy person improves nitrogen balance. Since then, a number of studies have been conducted on this topic. It was noticed that, unlike other nonessential amino acids, patients with uremia are characterized by low intracellular and plasma histidine concentrations. Patients with uremia are unable to maintain nitrogen balance with a diet low in histidine. In addition, it was found that histidine is an effective "scavenger" for hydroxyl radicals and singlet oxygen and therefore is able to protect low density lipoproteins from oxidation. The anti-inflammatory effect of histidine is also noted in uremia. Although the reasons for low extracellular and intracellular histidine concentrations in uremia are not clear, its oral and intravenous administration has a beneficial effect on nitrogen metabolism. This article examines the non-essentiality of histidine in healthy adults and its essentiality in patients with uremia, as well as unique among amino acids the beneficial effect of histidine in uremia.

Keywords: histidine, amino acids, uremia