Biological Functions

• Provides an important component of most proteins, but called "non-essential" in adults because the body can make it from methionine.
• Precursor in the formation of glutathione. But "at low levels of intake, cysteine is preferentially incorporated into protein rather than GSH." (Quoted from Sulfur in Human Nutrition and Applications in Medicine, [PDF] by Stephen Parcell, ND. Published by Thorne Research. Parcell cites as his source for this: Grimble RF, Grimble GK. Immunonutrition: role of sulfur amino acids, related amino acids, and polyamines. Nutrition 1998;14:605-610.)
• Important self-generating water phase antioxidant on its own
• Essential cofactor for antioxidant enzymes
  • P450 Phase II enzymes require it to convert fat-soluble toxins into water-soluble GSH conjugates, in order to excrete them.
• Immune system
  • ensures adequate glutathione production for optimal T-cell proliferation
  • boosts the ability of T-cells to divide
  • improves T-cells' ability to attack foreign bodies
• Builds alpha-keratin, the chief protein constituent of fingernails, toe-nails, skin and hair
• Detoxifies acetaldehyde (in cigarette smoke and smog, also produced by the yeast Candida albicans and from the body's metabolism of alcohol
• "Excitatory, neurotransmitter properties, acting centrally and peripherally at NMDA (N-methyl-D-aspartate) type glutamate receptors (Parsons et al., 1997, cited in Langford, 6/05).

Requirements

• Sulfur
• L-histidine — cysteine dioxygenase (CDO), the primary regulating enzyme of cysteine, is composed of iron and L-histidine.
• Vitamin B6

Applications

• Heavy metal detoxification
  • direct involvement
  • protects cellular glutathione levels
• Prevention of liver cell death from acetaminophen poisoning

Testing: short of redoing the whole GS Liver Detox procedure, they can also just test the plasma cysteine and sulfate (without challenge).

An additive in pharmaceuticals: Langford (6/05) notes that "cysteine is commonly incorporated into pharmacological preparations as a stabilizer for peptides such as secretin."

Supplementing

L-Cysteine itself: there are a lot of Cysteine supplements. My nutritionist offered me Recancostat, which contains

• GSH (reduced Glutathione; they make a big deal about how easily Glutathione oxidizes, resulting in the form GSSH)
• Anthocyans (phenols! — I decided not to use it )
• L-Cysteine

Other substances which easily convert to L-Cysteine

• Cystine: a cysteine=cysteine dipeptide GSH precursor. The oxidized form of Cysteine. "Cystine enters the blood and the cells readily to yield two cysteine molecules that are used to create glutathione. In addition there is no toxicity and the glutathione levels do not fluctuate as much with this method." (From the Immunocal page, see below.) Available in undenatured (unbroken, uncooked) whey isolate products:
  • Immunocal —
  • ImmuneProRx —
• NAC (N-acetyl Cysteine)
• L-Methionine — Can be converted to Cysteine; this requires Folate, B-6 and B-12. (This is why if you take SAMe you should also take supplemental B vitamins.)

Contraindications:

• Diabetes: "People who have diabetes should be cautious about taking supplemental L-cysteine because it is capable of inactivating insulin." (InternalHealth.com) (This inactivation can even be used to abort attacks of hypoglycemia, see "Preventing Hypoglycemia, an abstract from Anti-Aging News, January 1982 Vo.2, No. 1 pg 6-7, on the Vitamin B1 -- Thiamine page on the site of Vibrant Life Vitamins.)
• Cystinuria: "Persons with cystinuria, a rare genetic condition that leads to the formation of cystine kidney stones, should not take L-cysteine.(InternalHealth.com)
• Genova Labs says “Most people with deficient sulfate and xenobiotic loads will benefit from cysteine and glutathione supplementation. Individuals with elevated plasma cysteine/sulfate ratios, however, may worsen with cysteine supplementation....”
  
  • Genova will test serum L-cysteine alone; you don't have to get the whole Detox Profile
• In addition to increasing or improving the function of CDO, is there any other way to bring down elevated cysteine?
• Too much cysteine
  • Due either to impaired sulfoxidation or faulty sulfation. [need a better description of how sulfation converts cysteine "on"]
  • Due to too much Vitamin B6
  • May result in Cysteine's damaging free radicals
  • May cause nerve damage if the inflammatory cytokine tumor necrosis factor (TNF) is also present
  • can inhibit its precursor methionine's other functions through feedback inhibition

Reducing elevated cysteine:

• Increasing or improving the function of CDO
• any other way?

My experience:

• I have too much cysteine in my blood, and too high a ratio of it in proportion to sulfate. See...
  • The report of my Great Smokies Liver Detox Profile
  • The Defect(s) in my Sulfur Metabolism.
• I need to avoid getting more cysteine into my blood.
• Also I intend to keep track of my plasma cysteine level; if I can get it lower somehow, I'd like to supplement again with Glutathione and Vitamin B12.
• However, many other tissues (besides my blood) show symptoms of cysteine deficiency. Plus I'm losing too much weight, though I eat as much as I can and try everything I can think of to help digest.
  
  Argh. I don't know enough about how cysteine works: how it gives me a liver attack, is high in my blood, and still not getting to where it's needed. I would like to talk to anyone else grappling with this. Please join the conversation at Yahoo!Sulfur Stories, or

For more information

• InternalHealth.com
• my pages
  • Glutatione Metabolism
  • Sulfur Metabolism
  • Glutathione conjugation in liver Phase II detox.
  • Acetaminophen Poisoning
  • SAMe
  • Homocysteine
  • Cumulative Trauma Disorder