IN VITRO REDUCTION IN VISCOSITY OF HUMAN TRACHEOBRONCHIAL SECRETIONS BY ACETYLCYSTEINE

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Abstract
N-acetyl-L-cysteine (Mucomyst) markedly reduced in vitro the viscosity of human sputum and tracheobronchial secretions. The mucolytic activity of N-acetyl-L-cysteine was considerably greater than that of various inorganic salts; and, in contrast to that of salts, the activity of N-acetyl-L-cysteine was pH and concentration dependent. N-acetyl-L-cySteine, or its parent compound, L-cysteine, reduced the viscosity of secretions from persons with all types of pulmonary diseases, including one specimen from a case of non-purulent emphysema which was resistant to deoxyrlbonuclease. Ribo-nuclease was tested with 2 specimens, one from a patient with nonpuru-lent emphysema and 1 from a patient with chronic suppurative bronchitis, and was not active with either. Sputum specimens and tracheobronchial secretions, either nonhomogenlzed or homogenized with water or saline, increased in viscosity within an hour after exposure to air at 37[degree]C or at room temperature; however, the viscosities of specimens treated with N-acetyl-L-cysteine in vitro were markedly reduced and showed no indication of reversal during a similar period. Chemical analysis of human pulmonary secretions indicated mat the values obtained were consistent with those reported in the literature. Of particular interest was the finding that sputum on a dry weight basis contained approximately 140 mg of protein and 68 [mu]mols of disulfide sulfur /g, which provides a basis for the hypothesis that the mucolytic activity of N-acetyl-L-cysteine involves a sulfhydryl-disulfide interchange reaction.