Sulfur is an essential element for the entire biological kingdom because of its incorporation into amino acids, proteins and other biomolecules. Sulfur atoms are also important in the iron-containing flavoenzymes. Unlike humans, plants can use inorganic sulfur to synthesize sulfur-containing amino acids. Therefore, plants are an important source of sulfur for humans. Sulfur-containing compounds are found in all body cells and are indispensable for life. Some of sulfur-containing antioxidant compounds are, cysteine, methionine, taurine, glutathione, lipoic acid, mercaptopropionylglycine, N-acetylcysteine, and the three major organosulfur compounds of garlic oil, diallylsulfide, diallyldisulfide and diallyltrisulfide. In a comparison of the structure-function relationship among these sulfur-containing antioxidant compounds, dihydrolipoic acid (the reduced form of LA) is the most effective antioxidant. Dihydrolipoic acid contains two sulfhydryl groups and can undergo further oxidation reaction to form lipoic acid. The antioxidative activities of sulfur-containing compounds follow a general trend, the more highly reduced forms are stronger antioxidants and the number of sulfur atoms determine, at least in part, their modulatory activites on the glutathione related antioxidant enzymes. In this article, the antioxidant effects and the antioxidative activities, of sulfur-containing amino acids, are reviewed. In addition, the general antioxidant effects and the structure-function relationship of some sulfur-containing compounds are also reviewed.
Acetylcysteine/pharmacology ; Amino Acids, Sulfur/*pharmacology ; Antioxidants/*pharmacology ; Cysteine/pharmacology ; Glutathione/pharmacology ; Methionine/pharmacology ; Structure-Activity Relationship ; Taurine/pharmacology ; Thioctic Acid/pharmacology ; Thiopronine/pharmacology

BACKGROUND: The purpose of this study was to determine the adequate loading and maintenance doses of N-acetylcyseteine (NAC) for patients suffering from acute ROS-induced injury. METHODS: Concentrations of extra cellular NAC, cysteine (Cys), cystine (Cyst2), and methionine (Met) were measured in vitro, at which more than 50% of the intracellular ROS raised by paraquat were suppressed using Swiss 3T3 fibroblasts. An in vivo pharmacokinetic study followed on a healthy subject to determine the proper loading and maintenance doses of reduced NAC following intravenous administration of 25 mg/kg NAC. RESULTS: In vivo, NAC suppressed ROS in a dose dependant manner. 10 mM of NAC suppressed about 50% of ROS, and was comparable to 10 micro M of Cys and Met and 400 micro M of Cys2. In vitro, the elimination of half-life was achieved at 2.88+/-1.14 h for NAC and at 3.68+/-1.84 h for total NAC. The body clearances were 1.23+/-0.77 L h (-1) kg (-1) and 0.56+/-0.27 L h (-1) kg (-1) and the volumes of distribution were 3.07+/-0.10 L kg (-1) and 3.00+/-0.11 L kg (-1), respectively. The loading and maintenance NAC doses used to reach the target concentration of 10 mM, were 5010 mg. kg (-1) and 2250 mg min (-1) kg (-1), respectively. CONCLUSION: NAC provides an antioxidant effect on ROS produced by paraquat in vivo. However, in vitro, our results showed that the intravenous NAC dose could not be estimated from NAC plasma concentration or its metabolites.
Sulfur/*blood ; Reactive Oxygen Species ; Humans ; Glutathione/blood ; Amino Acids/*blood/chemistry ; Acetylcysteine/*administration & dosage/pharmacokinetics/pharmacology