Methemoglobinemia and eccentrocytosis in equine erythrocyte flavin adenine dinucleotide deficiency.

This research article reports on the symptoms and biochemical causes of a Spanish mustang mare’s persisting blood issues, which were eventually attributed to a cellular deficiency in flavin adenine dinucleotide (FAD), a molecule used in crucial cellular processes.

Biochemical Findings

• The report investigates the biochemical findings in a Spanish mustang mare suffering from persistent methemoglobinemia, eccentrocytosis and pyknocytosis – all conditions resulting from abnormal blood cells.
• The cause for these conditions was not found to be mediated by any external oxidant substances, meaning the triggers were internal, derived from the horse’s body itself.

Analyzing the Conditions

• Methemoglobinemia is characterized by an elevated level of methemoglobin, a type of hemoglobin molecule incapable of carrying oxygen. This was attributed to a deficiency in cytochrome-b5 reductase (Cb5R) activity, a biochemical process that protects red blood cells from damage.
• Eccentrocytosis and pyknocytosis refer to irregularities in the shape and formation of red blood cells. These particular conditions were attributed to a remarkable deficiency in activity of reduced nicotinamide adenine dinucleotide phosphate-dependent glutathione reductase (GR), an important antioxidant enzyme.
• The result of the deficient GR activity was a decreased concentration of glutathione, an antioxidant that prevents damage to cellular components caused by free radicals and reactive oxygen species, within the erythrocytes or red blood cells.

Key Finding: FAD Deficiency

• A significant discovery of the research was that upon adding flavin adenine dinucleotide (FAD) to the GR enzyme assay, the GR activity level increased to near normal values.
• This indicated a deficiency of FAD in the horse’s erythrocytes. Both enzymes identified as deficient in the horse’s blood cells, GR and Cb5R, use FAD as a cofactor, which suggests that the blood issues were resulting from an FAD deficiency.
• A unique aspect of the findings is that the FAD deficiency was traced back to a defect in erythrocyte riboflavin metabolism, a condition not previously documented in animals.