-IBIS-1.7.0-
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amino acid
cysteine
Nutrition
definition
L-Cysteine
» overview:
Cysteine is a water soluble amino acid containing the sulfur containing thiol group. Thiol is in the common antibacterial agent, merthiolate.
Active in fatty acid synthase
Contributes to the structure of proteins as cystine
The Greeks used garlic and the element sulfur to treat a variety of ailments, such as psoriasis, rheumatoid arthritis and psychosis.
Constituent of glutathione
As glutathione, it is an antioxidant necessary for the protection of proteins. It is used by the liver to detoxify formaldehyde, acetaminophen, benzpyrene and many other compounds.
Selenium is required to keep glutathione in its reduced form so it acts as an antioxidant.
Several tests have been devised using 24 hour urine collection of D-glucaric acid and or mercapturic acid to evaluate toxicity in the body.
Can be converted to glucose, plays a part in carbohydrate energy metabolism
» metabolism:
Cysteine is one of the sulfur containing amino acids used for the synthesis of glutathione, which is very critical in detoxification. The thiol group is the active part of the molecule which serves as a reducing agent to prevent oxidation of tissues. Glutathione is synthesized from glutamate and glycine as well.
Glutathione acts as one of the major detoxifiers in the body, but it must be in the reduced form to work properly. Sometimes glutathione will be listed on the label of a product, however it will not be specifically listed as being reduced. The unreduced form is much cheaper and is not metabolically active. Riboflavin, niacinamide and glutathione reductase are all essential cofactors for generating reduced glutathione. Once the cysteine moieties become oxidized, they combine to form cystine. Cystine taken by itself is poorly absorbed. Forms include reduced glutathione, N-acetyl cysteine, and cysteine.
An inborn error in metabolism, cystinuria, occurs in 7 out of every 10,000 births. The excessive excretion of cystine results in low levels of cysteine in the brain and causes mental retardation. In addition, excessive accumulation of cystine in the kidneys can result in the formation of cystine crystals which can damage the kidneys. Low cystine levels have been found in allergy, asthma, depression, psychosis, rheumatoid arthritis and hypertension.
» function:
Transport across cell membranes: It is part of amino acid transport across cell membranes.
Cell membrane integrity, this includes RBCs and mucosal cells.
Cancer prevention
Synthesis of fatty acids
Taurine precursor and bile acid conjugator
» Chinese:
Nourishes the Xue (Blood); tonifies Yin; benefits the Skin; promotes the generation of new tissue; blackens the hair; cools the Xue (Blood); clears Heat; dissolves Toxins; treats Thirsting and Wasting Disease.
» requirements:
RDA: non essential
Average intake in the U.S.: 5-100 mg per day
» food sources:
Cysteine is very difficult to measure
Wheat germ, yogurt, duck
(USDA: Composition of Foods. USDA handbook #8 Washington DC, ARS, USDA, 1976-1986)
» deficiency:
A lack of cysteine results in a deficiency of glutathione which may result in mental retardation. A deficiency of glutathione results in diminished macrophage activity, increased fragility of RBCs, increased susceptibility to cancer and other toxins. A reduced level can be found in people who are protein deficient or who are fasting.
» therapeutics:
Detoxification and heavy metal toxicity: Cysteine has been shown to be effective against molybdenum and cobalt toxicity. It has been shown to protect against liver toxins. One study showed that the ability of the body to make cysteine from N-acetyl cysteine makes it critical in its effectiveness in preventing chemotherapy damage. See Glutathione in Materia Medica for list of Toxins Requiring Glutathione. (Check environmental toxicities via 24 hr urine collection of D-glucaric acid and or mercapturic acid). (Marz, p. 78, 1997.)
Bronchitis and/or asthma (COPD, cystic fibrosis, emphysema etc.): 1-3 g per day N-acetyl cysteine has been found to have mucolytic activity as well as immune enhancing properties. Chronic smokers may benefit from cysteine supplementation. It may be used in an aerosol form.
Immune enhancement: 1-3 g per day. This is especially effective against clostridium in the gastrointestinal tract. It helps prevent translocation.
Cancer (including radiation and chemotherapy): N-acetyl cysteine form 1-3 g per day, as an adjunct treatment for cancer and for people receiving chemotherapy treatments. NAC has been shown to mitigate the toxicity of acetaminophen, doxorubicin, cyclophophamide, ifosfamide, and radiation.
Psoriasis
Hair loss/alopecia: 1-5 g per day. The hair and fingernails are composed of keratin which is 12% cysteine. Certain types of baldness may respond to cysteine.
AIDS: In vitro studies have shown N-acetyl cysteine inhibits HIV.
Diabetes mellitus: Especially in ketosis as DM patients will generally excrete increased amounts of sulfur containing amino acids.
Liver disease including cirrhosis and fatty liver disease caused by alcohol: Studies show mild effects at large doses
» dosage:
0.5 - 1 g per day
Dosages should start low (500 mg) and can work up to 4-5 grams per day. Excess cysteine can cause an increase in cystine which can be nephrotoxic)
Works synergistically with vitamin C, vitamin E, vitamin B6, selenium, magnesium, zinc and vanadium.
» toxicity:
Cysteine has very little toxicity. No toxicity has been reported even at 10 g per day taken orally. Cystine, however, has been shown to have toxic effects as in Fanconis syndrome and cystinosis. Fanconis syndrome causes kidney damage resulting from the accumulation of cystine crystals. Cystinosis results in kidney damage as well. Both conditions may be treated with D-penicillamine 1.5-2.0 gms per day. D-penicillamine is dimethyl cysteine and seems to inhibit the cystine formation but does not effect cysteine. Large IV doses of cysteine have resulted in increased accumulation of cystine in the kidneys and resultant damage.
L-cystine, D-cysteine, D-cystine, and 5-methyl cysteine not recommended for use
N-acetyl cysteine (NAC) safe up to 10 gm per day even in pregnancy; it has a nauseating taste and smell and may cause vomiting. Side effects of large IV doses include: hyperactivity, loss of balance, convulsions
» contraindications:
L-cystine, D-cysteine, D-cystine, and 5-methyl cysteine not recommended for use
» interactions:
None known.
footnotes
Braverman and Pfeiffer, pp. 87-119
Marz, Russell. Medical Nutrition From Marz. Second Edition. Portland, OR. 1997
USDA: Composition of Foods. USDA Handbook #8 Washington DC, ARS, USDA, 1976-1986