Creatine as biomarker

Abstract

Creatine (Cr) is a nitrogenous organic compound which plays a relevant function in the cellular energy metabolism supplying high-energy phosphate groups to the cell through the creatine kinase-phosphocreatine system. Over time, additional information about extra functions of Cr has been reported, such as its role as antioxidant, antiapoptotic, neuroprotective, or neurotransmitter. Half of the body requirements of Cr are supplied by diet, and the rest is synthesized endogenously by two enzymes, L-arginine:glycine amidinotransferase (AGAT) and S-adenosyl-L-methionine:N-guanidinoacetate methyltransferase (GAMT). Cr is internalized into the cells through a specific membrane Cr transporter. Three inherited metabolic disorders have been described, involving the biosynthetic pathway (GAMT and AGAT deficiencies) and the transporter of Cr (CRTR). These diseases are known as cerebral Cr deficiency syndromes. The measurement of Cr is used worldwide as the biomarker for the biochemical diagnosis of these diseases. Furthermore, numerous investigations have been carried out to analyze the relation between Cr and other metabolic pathways, such as the mitochondrial respiratory chain, the urea cycle, the methylation, or the transsulfuration pathways. In addition to the role of Cr as biomarker in the biosynthesis and transport of Cr disorders, this chapter is focused on the role of Cr as biomarker of different pathologies including mitochondrial diseases, congenital urea cycle defects, kidney and liver diseases, cancer processes, thyroid defects, and autism.