Glucose metabolism and hemoglobin reactivity in human red blood cells exposed to the tryptophan metabolites 3-hydroxyanthranilate, quinolinate and picolinate.

ABSTRACT

Glucose metabolism and hemoglobin reactivity in intact human erythrocytes were assessed in the presence of the tryptophan metabolites, 3-hydroxyanthranilate (3-HAT), quinolinate and picolinate. Of these compounds, only 3-HAT altered red cell oxidative status by inducing, in a dose-dependent manner, formation of methemoglobin and non-functional oxidation products of hemoglobin, and by increasing both net glycolytic flux and flux through the hexose monophosphate shunt. 3-HAT also decreased the normal lactate to pyruvate production ratio with pyruvate accumulating at the expense of lactate. These findings are consistent with the auto-oxidative reactivity of quinolinate, picolinate, and 3-HAT in that only 3-HAT undergoes base-catalyzed auto-oxidation (Dykens et al., Biochem Pharmacol 36 211-217, 1987). Lactate and pyruvate added to the medium in physiologic concentrations uncoupled oxidative glycolysis from reductive glycolysis, resulting in accumulation of pyruvate in the presence of 3-HAT with little increase in total glycolytic flux. Superoxide dismutase (SOD), which accelerates 3-HAT auto-oxidation in vitro (Dykens et al., Biochem Pharmacol 36 211-217, 1987), exacerbated HAT-mediated oxidative insult by increasing methemoglobin formation, hexose monophosphate shunt flux, and pyruvate accumulation. Persistence of 3-HAT-induced red cell metabolic responses and oxidative damage in the presence of SOD, DETAPAC (diethylenetriaminepentaacetic acid) and formate suggests that an organic-based radical, perhaps the anthranilyl radical produced during 3-HAT auto-oxidation, is the proximate agent exerting oxidative stress. Slow rates of auto-oxidation indicate that 3-HAT may be useful as a probe of antioxidant mechanisms in normal and diseased red blood cells.