N-acetylcysteine (NAC), an analogue and precursor of reduced glutathione, has been in clinical use for more than 30 yrs as a mucolytic drug. It has also been proposed for and/or used in the therapy and/or prevention of several respiratory diseases and of diseases involving an oxidative stress, in general. The objective of the present study was to evaluate the effect of long-term treatment with NAC on influenza and influenza-like episodes.A total of 262 subjects of both sexes (78% ≥65 yrs, and 62% suffering from nonrespiratory chronic degenerative diseases) were enrolled in a randomized, doubleblind trial involving 20 Italian Centres. They were randomized to receive either placebo or NAC tablets (600 mg) twice daily for 6 months. Patients suffering from chronic respiratory diseases were not eligible, to avoid possible confounding by an effect of NAC on respiratory symptoms.NAC treatment was well tolerated and resulted in a significant decrease in the frequency of influenza-like episodes, severity, and length of time confined to bed. Both local and systemic symptoms were sharply and significantly reduced in the NAC group. Frequency of seroconversion towards A/H 1 N 1 Singapore 6/86 influenza virus was similar in the two groups, but only 25% of virus-infected subjects under NAC treatment developed a symptomatic form, versus 79% in the placebo group. Evaluation of cell-mediated immunity showed a progressive, significant shift from anergy to normoergy following NAC treatment.Administration of N-acetylcysteine during the winter, thus, appears to provide a significant attenuation of influenza and influenza-like episodes, especially in elderly high-risk individuals. N-acetylcysteine did not prevent A/H 1 N 1 virus influenza infection but significantly reduced the incidence of clinically apparent disease. Eur Respir J 1997; 10: 1535-1541

One hundred and six compounds, subdivided into 12 chemical classes (5 polycyclic aromatic hydrocarbons, 7 epoxides and N-oxides, 5 nitro aromatics and heterocycles, 12 aromatic and heterocyclic amines, 2 azo compounds, 17 hydrazine derivatives, 16 miscellaneous aliphatics, 5 miscellaneous heterocycles, 11 miscellaneous organics, 11 hexavalent and 7 trivalent chromium compounds, 8 miscellaneous inorganics), were studied in the Salmonella/microsome test. Fifty-eight of them (54.7%) were found to be mutagenic and 4 additional compounds (3.8%) yielded a positive response following nitrosation in human gastric juice. The results are presented in a tabulated form, providing the following information for each test compound: (a) mutagenic response in 5 S. typhimurium his- strains (TA1535, TA1537, TA1538, TA98, TA100); (b) range of activity for positive compounds or maximum dose tested for negative compounds (in nmol/plate); (c) mutagenic potency (in revertants/nmol compound), varying over a 6.5 x 10(6)-fold range; (d) effect of S-9 mix containing rat (Aroclor)liver S-9 fractions on the mutagenic response (activation, increase, no change or decrease); (e) remarks concerning the influence of other metabolic systems (up to 10 different rat tissue S-9 fractions, mouse S-9 fractions, human S-9 fractions, cell preparations or biological fluids), the interaction between different compounds, the stability and the formation of mutagenic derivatives in human gastric juice and other experimental details. Overlapping of mutagenicity and carcinogenicity data was not evaluated, since the experimental protocol intentionally included a number of non-carcinogenic mutagens and of non-mutagenic carcinogens, with the aim of explaining in some cases the conflicting nature of in vivo and in vitro conclusions.

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N-acetylcysteine (NAC) is often administered to respiratory patients with histories of exposure to noxious agents (e.g. cigarette smoke and atmospheric pollutants), which are known to act as glutathione (GSH) depletors and as cancer initiators and/or promoters. Since NAC is a precursor of intracellular GSH, we investigated its effects on GSH metabolism and on the biotransformation of carcinogenic and/or mutagenic compounds. In vitro, NAC induced a significant increase in oxidized glutathione (GSSG) reductase activity in rat liver preparations and counteracted the mutagenicity of direct-acting compounds (such as epichlorohydrin, hydrogen peroxide, 4-nitroquinoline-N-oxide and dichromate), as a result of its reducing and scavenging properties. At high concentrations, the drug completely inhibited the mutagenicity of procarcinogens (cigarette smoke condensate, tryptophan pyrolysate, cyclophosphamide, 2-aminofluorene, benzo(a)pyrene and aflatoxin B1) by binding their electrophilic metabolites. In contrast, their metabolic activation was stimulated by decreasing NAC concentrations, especially when liver preparations from enzyme-induced rats were used. Lung and liver subcellular preparations of rats treated in vivo with NAC, in various combinations with enzyme inducers and/or GSH depletors, also affected the mutagenicity of a number of compounds. NAC generally increased intracellular GSH and restored its levels following depletion. It did not affect the levels nor the spectral properties of cytochromes P-450 in pulmonary and hepatic microsomes, whereas it stimulated, especially in Aroclor-pretreated animals, cytosolic enzyme activities involved in NADP or GSSG reduction (G6PD, 6PGD and GSSG reductase) and in the reductive detoxification of xenobiotics (DT diaphorase). When administered with the diet, at a nontoxic posology (120 mg/kg b.w.), NAC markedly inhibited the induction of lung tumors in mice by a potent carcinogen (urethane)