Cysteine

Cysteine is an amino acid found in many proteins. Its derivative, N-acetyl-L-cysteine (NAC), is commonly found in food and is synthesized by the body. NAC is also available as a supplement. It performs a few important functions, including breaking down mucus; producing glutathione, an important antioxidant; and protecting the body from acetaminophen toxicity.

Uses

NAC offers a variety of potential therapeutic uses, particularly in the prevention and/or treatment of the following conditions.

• Respiratory diseases. NAC may reduce the lung injury that occurs in adult respiratory distress syndrome (ARDS). NAC may also improve some of the symptoms associated with chronic bronchitis.
• Cardiovascular disease. NAC, in combination with nitroglycerin (a drug that dilates blood vessels), has been shown to significantly reduce the incidence of acute heart attacks in patients with angina pectoris (pain in the center of the chest induced by exercise). NAC has also been shown to reduce damage caused by heart attack and to cause an increase in HDL-cholesterol ("good cholesterol") levels.
• Acetaminophen poisoning. NAC is commonly used in the treatment of acetaminophen overdoses, reducing kidney damage if given within eight hours.
• Corneal damage in the eye. Animal studies indicate that NAC may help reduce damage to corneal cells, such as cataracts, that is related to smoking.

• NAC may also have a therapeutic benefit for people who are HIV-positive and for those with Sjogren's syndrome, which involves dryness of the eyes.

Dietary Sources

The primary dietary sources of NAC include the following.

• wheat germ
• granola
• oat flakes
• ricotta
• cottage cheese
• yogurt
• pork, sausage meat
• chicken, turkey, duck
• luncheon meat

Other Forms

NAC is available as a supplement in several forms. These include the following.

• NAC aerosol spray (prescription)
• NAC liquid solution (prescription)
• L-Cysteine powder
• Cysteine/NAC tables or capsules

How to Take It

Recommended doses of NAC vary depending on the health condition being treated. The following list provides guidelines for the most common uses.

• Bronchial disease: 200 mg two times per day
• HDL cholesterol: 1,200 to 3,600 mg per day
• Acetaminophen poisoning (treatment delivered in-hospital): The typical oral dosage of NAC is 140 mg/kg body weight, followed four hours later by 70 mg/kg every four hours for an additional 17 doses. Oral treatment must be started within eight hours of an acetaminophen overdose. Oral NAC is typically administered for 72 hours; intravenous NAC for 20 to 52 hours.
• Antioxidant protection/general health: 500 mg per day to start. Individuals may increase the dose to 3 to 4 g per day as tolerated.

Precautions

NAC and cysteine have several potential side effects. Taking high doses (over 7 g) of cysteine may be harmful and should be avoided. Oral NAC may cause nausea, vomiting, and diarrhea. Intravenously administered NAC to treat acetaminophen poisoning may cause a variety of potentially severe reactions. Intravenous NAC combined with nitroglycerin may cause hypotension (low blood pressure).

In addition, individuals with cystinuria (a urinary condition) should avoid, or limit, their intake of cysteine supplements. Toxic forms of cysteine that should not be used are D-cysteine, D-cystine, and 5-methyl cysteine.

Possible Interactions

Using this supplement after taking nitroglycerin, a medication commonly used for the treatment of angina and chest pain, may increase the chances of experiencing a headache (one of the potential side effects associated with nitroglycerin).

Supporting Research

Borowitz JD, et al. Combined use of nitroglycerin and N-acetylcysteine in the management of unstable angina pectoris. Circulation. Apr 1988; 77(4): 787-794.

Braverman ER, Pfeiffer CC. The Healing Nutrients Within: Facts, Findings and New Research on Amino Acids. New Canaan: Keats Publishing, Inc.; 1987: 87-119.

Budavari S, O'Neil MJ, Heckelman PE, Kinneary JF, eds. The Merck Index. 12^th ed. Whitehouse Station: Merck & Co., Inc.; 1996.

Carter EA. Enhanced acetaminophen toxicity associated with prior alcohol consumption in mice; prevention by N-acetylcysteine. Alcohol. Jan-Feb 1987; 4(1): 69-71.

Christman BW, Bernard GR. Antilipid mediator and antioxidant therapy in adult respiratory distress syndrome. New Horiz. Nov 1993; 1(4): 623-630.

Davreux CJ, et al. N-acetylcysteine attenuates acute lung injury in the rat. Shock. Dec 1997; 8(6): 432-438.

Flanagan RJ, et al. Use of N-acetycysteine in clinical toxicology. Am J Med. Sep 30 1991; 91(3C): 131S-139S.

Franceschini G, et al. Dose-related increase in HDL-cholesterol levels after N-acetylcysteine in man. Pharmacol Res. Oct-Nov 1993; 28(3): 213-218.

Hultberg B, et al. Plasma homocysteine and thiol compound fractions after oral administration of N-acetylcysteine. Scand J Clin Lab Invest. Oct 1994; 54(6): 417-422.

Iversen HK. N-acetylcysteine enhances nitroglycerin-induced headache and cranial artery response. Clin Pharmacol Ther. 1992;52:125-133.

Jackson IM, et al. Efficacy and tolerability of oral acetylcysteine (Fabrol) in chronic bronchitis: a double-blind placebo controlled study. J Int Med Res. 1984; 12(3): 198-206.

Marchetti G, et al. Use of N-acetylcysteine in the management of coronary artery diseases. Cardiologia. Jul 1999; 44(7): 633-637.

Murray MT, Pizzorno J. Encyclopedia of Natural Medicine 2^nd ed. Rocklin: Prima Publishing; 1998: 455-458, 558-563, 818-825.

Orten JM, Neuhaus OW. Human Biochemistry. 10^th ed. St. Louis: The C.V Mosby Company; 1982: 721-723.

Pelle E, et al. Protection against cigarette smoke-induced damage to intact transformed rabbit corneal cells by N-acetyl-L-cysteine. Cell Biol Toxicol. Aug 1998; 14(4): 253-259.

Perry HE, Shannon MW. Efficacy of oral versus intravenous N-acetylcysteine in acetaminophen ovedose:results of an open-label, clinical trial. J Pediatr. Jan 1998;132(1): 149-152.

Roederer M, et al. N-acetylcysteine: a new approach to anti-HIV therapy. AIDS Res Hum Retroviruses. Feb 1992; 8(2): 209-217.

Ruiz FJ, et al. N-acetyl-L-cysteine potentiates depressor response to captopril and enalaprilat in SHRs. Am J Physiol. Sep 1994; 267 (3 Pt 2): R767-772.

Smilkstein MJ, et al. Efficacy of oral N-acetylcysteine in the treatment of acetaminophen overdose. Analysis of the national multicenter study (1976 to 1985). N Engl J Med. Dec 15 1988; 319(24): 1557-1562.

Stavem K. Anaphylactic reaction to N-acetylcysteine after poisoning with paracetamol. Tidsskr Nor Laegeforen. May 30 1997; 117(14): 2038-2039.

Walters MT, et al.. A double-blind, cross-over, study of oral N-acetylcysteine in Sjogren's syndrome. Scand J Rheumatol Suppl. 1986; 61: 253-258.

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