Acute patho-toxicological indicators of methaemoglobinemia

Seabra PS, Fonseca ADN, de Azevedo Sousa KM, de Oliveira SBB, Carneiro ADS, Coleman MD, Monteiro MC. Alpha-Lipoic Acid and Its Enantiomers Prevent Methemoglobin Formation and DNA Damage Induced by Dapsone Hydroxylamine: Molecular Mechanism and Antioxidant Action

Dapsone (DDS) therapy can frequently lead to hematological side effects, such as methemoglobinemia and DNA damage. In this study, we aim to evaluate the protective effect of racemic alpha lipoic acid (ALA) and its enantiomers on methemoglobin induction. The pre- and post-treatment of erythrocytes with ALA, ALA isomers, or MB (methylene blue), and treatment with DDS-NOH (apsone hydroxylamine) was performed to assess the protective and inhibiting effect on methemoglobin (MetHb) formation. Methemoglobin percentage and DNA damage caused by dapsone and its metabolites were also determined by the comet assay. We also evaluated oxidative parameters such as SOD, GSH, TEAC (Trolox equivalent antioxidant capacity) and MDA (malondialdehyde). In pretreatment, ALA showed the best protector effect in 2.5 µg/mL of DDS-NOH. ALA (1000 µM) was able to inhibit the induced MetHb formation even at the highest concentrations of DDS-NOH. All ALA tested concentrations (100 and 1000 µM) were able to inhibit ROS and CAT activity, and induced increases in GSH production. ALA also showed an effect on DNA damage induced by DDS-NOH (2.5 µg/mL). Both isomers were able to inhibit MetHb formation and the S-ALA was able to elevate GSH levels by stimulating the production of this antioxidant. In post-treatment with the R-ALA, this enantiomer inhibited MetHb formation and increased GSH levels. The pretreatment with R-ALA or S-ALA prevented the increase in SOD and decrease in TEAC, while R-ALA decreased the levels of MDA; and this pretreatment with R-ALA or S-ALA showed the effect of ALA enantiomers on DNA damage. These data show that ALA can be used in future therapies in patients who use dapsone chronically, including leprosy patients.

Fatal methemoglobinemia complicating alkaptonuria (ochronosis): a rare presentation

A 61-year-old female died in hospital with multiple organ failure 4 weeks following presentation with acute kidney injury, hemolytic anemia and methemoglobinemia. At autopsy, brown to black discoloration of cartilages was observed. Histology revealed brown pigmentation of the hyaline cartilage, with focal full-thickness erosion of the articular hyaline cartilage, characteristic of alkaptonuria (ochronosis). Although alkaptonuria is rarely fatal, this case illustrates a rare acute fatal complication. Accumulation of circulating homgentisic acid secondary to acute derangement of renal function is believed to have overwhelmed the endogenous antioxidant processes, resulting in hemolysis and methemoglobinemia, which were refractory to treatment. Small numbers of cases have previously been reported in the literature in patients known to suffer with the disease, all of which were preceded by acute kidney injury. Whilst the clinical diagnosis of alkaptonuria may be challenging, the autopsy findings of this rare condition are striking and this case illustrates the utility of the autopsy, albeit retrospectively, in arriving at a diagnosis. To our knowledge this is the first reported case where previously undiagnosed alkaptonuria has presented with methemoglobinemia.