L-Cysteine is a conditionally essential amino acid.1,2 It is produced from L-methionine through the transsulfuration pathway.1 L-Cysteine can also be derived from dietary sources and protein turnover. It is a precursor in the biosynthesis of the intracellular antioxidant glutathione . L-Cysteine supplementation increases GSH levels as well as decreases oxidative stress and pro-inflammatory cytokine levels in various rat and porcine disease models, including type 2 diabetes, aging, and inflammatory bowel disease (IBD). It is also an excitotoxin, inducing neuronal damage by overactivation of NMDA receptors.2
1.Yin, J., Ren, W., Yang, G., et al.L-Cysteine metabolism and its nutritional implicationsMol. Nutr. Food Res.60(1)134-146(2016) 2.Janáky, R., Varga, V., Hermann, A., et al.Mechanisms of L-cysteine neurotoxicityNeurochem. Res.25(9-10)1397-1405(2000)