Glycated hemoglobin is not an accurate indicator of glycemia in rainbow trout

Glycation occurs when glucose reacts non-enzymatically with proteins. This reaction depends upon time, ambient glucose concentration, and the molecular conformation of reactive amino acids. Little is known about protein glycation in fishes and the main objective of this study was to measure glycated hemoglobin (GHb) in rainbow trout, a glucose-intolerant species, under normoglycemic and hyperglycemic conditions. We also identified GHb isoforms in vivo and analyzed the structural environment surrounding potential glycation sites. Despite similar glycemia to healthy humans, GHb was an order of magnitude lower in rainbow trout (0.6%) compared with humans (6%) and was not affected by long-term hyperglycemia. Species differences in GHb appear to be related to differences in erythrocyte glucose, and differential expression and glycation of hemoglobin (Hb) isoforms may explain intraspecific differences in rainbow trout GHb. Computer analysis of glucose isomers (ringed-open and α- and β-pyranoses) interacting with the β-chain of rainbow trout HbI and HbIV, and human HbA did not reveal structural or energetic constraints for glucose binding (the initial step of glycation) for rainbow trout Hbs. Overall, there are significant differences between Hb glycation in humans and rainbow trout, and GHb does not appear to be an accurate indicator of glycemia over time in rainbow trout.