N,N9-Diacetyl-L-cystine—the Disulfide Dimer of N-acetylcysteine—Is a Potent Modulator of Contact Sensitivity/ Delayed Type Hypersensitivity Reactions in Rodents

Oral N-acetyl-L-cysteine (NAC) is used clinically for treatment of chronic obstructive pulmonary disease. NAC is easily oxidized to its disulfide. We show here that N,N9-diacetyl-L-cystine (DiNAC) is a potent modulator of contact sensitivity (CS)/delayed type hypersensitivity (DTH) reactions in rodents. Oral treatment of BALB/c mice with 0.003 to 30 mmol/kg DiNAC leads to enhancement of a CS reaction to oxazolone; DiNAC is 100 to 1000 times more potent than NAC in this respect, indicating that it does not act as a prodrug of NAC. Structure-activity studies suggest that a stereochemically-defined disulfide element is needed for activity. The DiNAC-induced enhancement of the CS reaction is counteracted by simultaneous NAC-treatment; in contrast, the CS reaction is even more enhanced in animals treated with DiNAC together with the glutathione-depleting agent buthionine sulfoximine. These data suggest that DiNAC acts via redox processes. Immunohistochemically, ear specimens from oxazolone-sensitized and -challenged BALB/c mice treated with DiNAC display increased numbers of CD8 cells. DiNAC treatment augments the CS reaction also when fluorescein isothiocyanate is used as a sensitizer in BALB/c mice; this is a purported TH2 type of response. However, when dinitrofluorobenzene is used as a sensitizer, inducing a purported TH1 type of response, DiNAC treatment reduces the reaction. Treatment with DiNAC also reduces a DTH footpadswelling reaction to methylated BSA. Collectively, these data indicate that DiNAC in vivo acts as a potent and effective immunomodulator that can either enhance or reduce the CS or DTH response depending on the experimental conditions. Oral N-acetyl-L-cysteine (NAC) has been used clinically as a remedy for chronic obstructive pulmonary disease for decades, and it is generally believed that its beneficial effect is due to a mucolytic activity. However, it has not been possible to demonstrate presence of the drug in epithelial lining fluid after oral administration (Cotgreave et al., 1987); this is not fully compatible with its proposed in vivo mucolytic activity. Moreover, NAC is reported to primarily reduce exacerbation rates in the disease (Boman et al., 1983). Considering this, it is possible that NAC acts in chronic obstructive pulmonary disease patients, at least in part, by enhancing their host