The Durk Pearson & Sandy Shaw®
Life Extension NewsTM
Volume 5 No.
5 • October 2002
Why We Take Cysteine Rather Than N-Acetylcysteine
N-Acetylcysteine is a xenobiotic (not normally found in the
body), although it is an acetylated form of the natural amino acid cysteine. It
can be sold as a dietary supplement even though it is a xenobiotic, because it
was being sold as a dietary supplement before passage of the Dietary Supplement
Health and Education Act, thereby "grandfathering" it. N-Acetylcysteine is
an FDA-approved prescription drug used in the treatment of Tylenol®
(acetaminophen) overdose (liver toxicity). N-Acetylcysteine treatment for this
purpose lasts up to about 3 days. The treatment works by increasing liver
Cysteine acts as the limiting natural precursor to
glutathione and increases its levels. (Methionine can also act as a precursor to
glutathione, but homocysteine is a byproduct of this pathway.) It is easier to
get permission to use N-acetylcysteine in human and even animal studies because
of its FDA-approved status. Moreover, there is a belief that cysteine is more
toxic than N-acetylcysteine because the latter is more water-soluble, and
cysteine can be oxidized to cystine. However, taking at least twice as much
vitamin C as cysteine prevents oxidation of cysteine to cystine (which can cause
cystine stones in the kidneys and urinary bladder).
The acetyl group in N-acetylcysteine is labile, that is, it
can acetylate many things indiscriminately. Aspirin, acetylsalicylic acid, also
contains an acetyl group, but its acetylation is more specific. Aspirin
acetylates a specific amino acid site in the enzyme that synthesizes thromboxane,
thus acting as an anticlotting agent. Since N-acetylcysteine has been tested for
and approved for a very short-term use, we do not feel that we know enough about
it to consider taking it on a long-term, everyday basis.
N-Acetylcysteine can inhibit blood clotting by increasing
prothrombin time. Hence, in combination with other anticlotting agents, such as
low-dose aspirin, ginkgo, or fish oils, blood-clotting time could be excessively
extended. Your doctor can easily check your prothrombin time, or it can be
inexpensively and safely tested at a walk-in clinical laboratory testing firm.
- Pol and Lebray. N-Acetylcysteine for paracetamol
poisoning: effect on prothrombin. Lancet 360:1115 (2002).