Comparison of methylene blue, riboflavin, and N-acetylcysteine for the reduction of nitric oxide-induced methemoglobinemia

Objective: To investigate the treatment of nitric oxide (NO)induced methemo globinemia by methylene blue (MB), riboflavin, and N-acetylcysteine (NAC) i n vitro. Design: Prospective, controlled in vitro study. Setting: Research laboratory in a university hospital. Participants: Five healthy volunteers. Interventions: Generation of 16% to 18% of methemoglobin in red blood cells by NO and subsequent addition of MB, riboflavin, or NBC, Simultaneous NO ( 32 ppm) and MB or riboflavin exposure of red blood cells. Induction of 14% to 18% of methemoglobin in red blood cells by NO, subsequent addition of MB or riboflavin, and further incubation with NO (80 ppm). Measurements and Main Results:After discontinuation of NO, mean half-life f or methemoglobin was significantly reduced by MB from 356 mins (controls) t o 5 mins (10 mu M) in a dose-dependent manner (p <,001), NAG did not alter the half-life for methemoglobin, and a reduction from 356 to 168 mins was s een for 120 mu M riboflavin (p <.001), Methemoglobin formation after 3 hrs of NO exposure was 4.3% +/- 0.7% in controls and 0.3% +/- 0.1% with 10 mu M MB (p <.001); 1 mu M MB attenuated methemoglobin formation to 1.9% +/- 0.1 0/0 (p <.01). With riboflavin (120 mu M), methemoglobin was 2.2% +/- 0.5% v s. 3.2% +/- 0.6% in controls (p <.001), in the presence of high methemoglob in concentrations, further methemoglobin formation was inhibited by 1 and 1 0 mu M MB (p <.001) and attenuated by 0.1 mu M MB (p <.001) but not by ribo flavin. Conclusions: In vitro, NO-induced methemoglobin formation is significantly decreased by medium (1 mu M) and high (10 mu M) concentrations of MB and pa rtially by high riboflavin concentrations (120 mu M), NAC and low concentra tions of riboflavin do not alter methemoglobin formation.