Aniline derivative-induced methemoglobin in rats.

Methemoglobinemia and hemolysis are the most prominent side-effects of exposure to a wide variety of arylamine drugs, including agricultural and industrial chemicals. Recent studies with aniline and dapsone have identified N-hydroxyl metabolites as the red blood cell (RBC) mediators. This study examines the time-course methemoglobinemic potential of several halogenated aniline phenylhydroxylamines. Symptoms of aniline poisoning include headache, fatigue, dizziness, respiratory and cardiac arrest, and possibly death. Initial studies indicated that the parent compounds are converted to their toxic metabolites (N-hydroxylamine), which enter the RBC and react with oxyhemoglobin. Consequent reduction of molecular oxygen to active oxygen species occurs, leading to RBC damage. Our laboratory is investigating the role of redox cycling and an alternative hypothesis--that a "hydroxylamine-centered" radical formed during arylhydroxylamine-oxyhemoglobin reaction results in RBC injury. The methemoglobinemic capacities of several structurally related N-hydroxy derivatives of aniline--phenylhydroxylamine (PHA), p-fluoro-, p-chloro-, p-bromo-, and p-iodo-PHA--were studied spectrophotometri-cally by treating washed rat RBC at concentrations ranging from 30 to 300 microM of the test compounds for up to 240 minutes. The results showed dose- and time-dependent changes in the induction of methemoglobin (MetHb) by aniline derivatives. The MetHb levels peaked to as high as 75% and remained elevated up to 240 minutes, depending on the electronegativity of halogenated phenylhydroxylamine aniline. This study supports the previous findings that there may be several aniline-derived metabolites other than PHA that are capable of inducing MetHb. The minimum dose required to induce this effect and duration of the MetHb may vary with the test agent.