Aminoethyl-isothiourea inhibits leukocyte production of reactive oxygen species and proinflammatory cytokines induced by streptococcal cell wall coiviponents in hunian whole blood

The incidence of severe invasive disease caused by serogroup A streptococci (GAS) is increasing, and to elucidate the role of streptococcal cell wall components in the inflammatory response, human whole blood was stimulated w ith lipoteichoic acid (LTA, 0.005-50 mug/mL) and peptidoglycan (10 and 100 mug/ml) from Streptococcus pyogenes. Both stimulants increased dose depende ntly the leukocyte release of cytokines many thousand fold: tumor necrosis factor alpha (0 to 158,000 +/- 4,900 pg/mL), interleukin (IL)-1 beta (85 +/ - 56 to 31,000 +/- 4,600 pg/mL), IL-6 (30 +/- 11 to 34,800 +/- 15,000 pg/mL ), and IL-8 (300 +/- 150 to 29,000 +/- 14,000 pg/mL). Intracellular leukocy te levels of reactive oxygen species (ROS) as measured by flow cytometry in creased 15-20 fold, from 25 to 400-500 mean fluorescence intensity. Aminoet hylisothiourea (AE-ITU), a relatively selective inhibitor of the inducible nitric oxide synthase (iNOS) and a ROS scavenger, reduced the cytokine prod uction by 70-100%, and intracellular leukocyte ROS levels by 50-70% (all P < 0.05). The non-selective NOS inhibitor N-nitro-L-arginine methyl ester (L -NAME) did not affect intracellular ROS levels, but it caused a moderate se lective inhibition of IL-8 production. Leukocyte NO production (measured up to 36 h) was not enhanced by LTA, peptidoglycan, inactivated streptococci, or cytokine combinations. The mechanisms for the anti-inflammatory effects of AE-ITU may be through a reduction of intracellular ROS levels, or throu gh a direct effect on signal transduction, whereas NO modulation is an unli kely mechanism.