Quantitative variations of the isoforms in haptoglobin 1-2 and 2-2 individual phenotypes

Haptoglobin is a hemoglobin-binding protein presenting in humans three distinct phenotypes (Hpt 1-1, Hpt 1-2, or Hpt 2-2). The Hpt 1-2 and Hpt 2-2 phenotypes are in turn represented by populations of isoforms. The relative amounts of the major isoforms of Hpt 1-2 and Hpt 2-2 were found to differ not only in different individuals, but also in the same individual before and after a physical effort. Exercise-dependent changes in the plasma concentrations of ascorbate, urate, α-tocopherol, retinol, and glutathione were also observed, but correlations between such changes and those of the amount for any isoform were not found. Samples of Hpt 1-2 or Hpt 2-2 were challenged with oxidants (H2O2 with ferrous ions, spermine–NO, KO2, and 3-morpholinosydnonimine), but the isoform levels were not altered. Hpt 2-2 isoforms were present in Hpt 1-2, as minor species. Furthermore, different isoforms exhibited different hemoglobin binding abilities. Thus, these parameters should also be taken into consideration in studies correlating Hpt phenotypes prevalence with pathologies or functional differences.