Cystine/Cysteine
Cystine is classified as a nonessential amino acid. It is a sulfur-containing amino acid that is also required to make glutathione – a natural antioxidant that fights free-radical damage, and is therefore useful to those suffering from cancer and hardening of the arteries. Cystine also works closely with glutathione to remove toxins from the liver. Cystine is generally regarded as the more stable form of cysteine, another sulfur-containing amino acid (each molecule of cystine is made from two molecules cysteine) – although both amino acids can be converted to the other as needed. Cystine cannot be used by the body without adequate amounts of vitamin B6, vitamin B12 and folic acid. Although the body produces its own cystine, good sources are eggs, meat, dairy products and whole grains. Typical supplemental dosage of L-cysteine is 500 milligrams to 1.5 grams daily. (For more detailed information, please visit ISM’s searchable database: Nutraceutical Search.)
GENERAL CANCER
· The regulation of the plasma cystine level is disturbed in conditions with progressive skeletal muscle catabolism including cancer, HIV infection, and old age. These conditions show also a low plasma glutamine:cystine ratio indicative of an impaired hepatic cystine catabolism.
o FASEB J. 1997 Jan; 11(1): 84-92.
We now show that glutamate release from glioma cells is an obligatory by-product of cellular cystine uptake via system Xc, an electroneutral cystine– glutamate exchanger. Cystine is an essential precursor for the biosynthesis of glutathione, a major redox regulatory molecule that protects cells from endogenously produced reactive oxygen species (ROS). Inhibition of system Xc causes a rapid depletion of glutathione……. These data suggest that inhibition of cystine uptake into glioma cells through the pharmacological inhibition of system Xc may be a viable therapeutic strategy.
o Chung, WJ et al (2005).Inhibition of Cystine Uptake Disrupts the Growth of Primary Brain Tumors. J Neurosci, 25(31), 7101-10.