L-cysteine is a conditionally essential amino acid, one of only three sulfur-containing amino acids, the others being taurine (which can be produced from L-cysteine) and L-methionine (from which L-cysteine can be produced in the body by a multi-step process). Cysteine plays a role in the sulfation cycle, acting as a sulfur donor in phase II detoxification and as a methyl donor in the conversion of homocysteine to methionine.136-138 Cysteine also helps synthesize glutathione, the body’s most important intracellular antioxidant and a vital detoxifier.139-142
N-acetyl-L-cysteine (NAC) is the acetylated form of L-cysteine that has been used to break up pulmonary and bronchial mucous.143-146 It is very efficiently absorbed and has been shown to protect cells directly and support the immune system.146-155 NAC is an antioxidant and a free radical-scavenging agent that increases intracellular glutathione at the cellular level. NAC can act as a precursor for glutathione synthesis as well as a stimulator of the cytosolic enzymes involved in glutathione regeneration.146 NAC has been shown to protect against oxidative stress-induced neuronal death in cultured granule neurons.156
References available upon request.