GLS and Hepatic fibrosis: Of note, glutamic acid is a non-essential amino acid, derived mainly via the catabolism of glutamine (glutaminolysis) in the liver.28 Interestingly, a recent study from Du and colleagues has demonstrated that the liver isoform of glutaminase may be upregulated by the hepatic stellate cells, as they require glutaminolysis to satisfy their energetic demand.29 Similarly, higher levels of lysine, an essential amino acid which is mainly catabolised in the liver, were specifically associated with liver fibrosis in this study.