Abstract
This review summarizes recent knowledge about the use of the amino acid l-Cysteine (l-Cys) through diet, nutritional supplements or drugs with the aim to improve human health or treat certain diseases. Three databases (PubMed, Scopus, and Web of Science) and different keywords have been used to create a database of documents published between 1950 and 2017 in scientific journals in English or Spanish. A total of 60,885 primary publications were ultimately selected to compile accurate information about the use of l-Cys in medicine and nutritional therapies and to identify the reported benefits of l-Cys on human health. The number of publications about the use of l-Cys for these purposes has increased significantly during the last two decades. This increase seems to be closely related to the rise of nutraceutical industries and personalized medicine. The main evidence reporting benefits of l-Cys usage is summarized. However, the lack of accurate information and studies based on clinical trials hampers consensus among authors. Thus, the debate about the role and effectiveness of supplements/drugs containing l-Cys is still open.
Highlights
L -cysteine ( L -Cys) is a non-essential amino acid and is one of the building blocks required for the synthesis of proteins
Cys is synthesized from methionine thanks to two chemical reactions [3]
The analysis considers the use/administration of L-Cys as part of the formulations of drugs, information available in scientific databases to identify the effects of the usage of L-Cys in human nutraceuticals, or through food supplementation
Summary
L -cysteine ( L -Cys) is a non-essential amino acid and is one of the building blocks required for the synthesis of proteins. It contains sulfur in the form of a thiol group (-SH) at the end of its side chain [1] (Figure 1). The -SH group is responsible for the high reactive capacity of the amino acid, and is responsible for many of its biological functions in human beings. L-Cys is the amino acid establishing disulfide bridges, a type of covalent bond that plays a fundamental role in the folding and stabilization of the tertiary structure of the proteins, thereby supporting their biological activities [2,3]. The presence of conserved Cys in protein motifs found in all organisms could indicate that this feature was harnessed in early evolution to support enzyme catalysis, transcriptional regulation, protein folding, and 3-dimensional structure [4,5].
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