The Haptoglobin 2-2 Phenotype Affects Serum Markers of Iron Status in Healthy Males

Abstract

Human iron status is influenced by environmental and genetic factors. We hypothesized that the genetic polymorphism of haptoglobin (Hp), a hemoglobin-binding plasma protein, could affect iron status. Reference values of serum iron status markers were compared according to Hp phenotypes (Hp 1-1, Hp 2-1, Hp 2-2; determined by starch gel electrophoresis) in 717 healthy adults. Iron storage was investigated in peripheral blood monocyte-macrophages by measuring cytosolic L- and H-ferritins and by in vitro uptake of radiolabeled ((125)I) hemoglobin-haptoglobin complexes. In males but not in females, the Hp 2-2 phenotype was associated with higher serum iron (P <0.05), transferrin saturation (P <0.05), and ferritin (P <0.01) concentrations than Hp 1-1 and 2-1, whereas soluble transferrin receptor concentrations were lower (P <0.05). Moreover, serum ferritin correlated with monocyte L-ferritin content (r = 0.699), which was also highest in the male Hp 2-2 subgroup (P <0.01). In vitro, monocyte-macrophages took up a small fraction of (125)I-labeled hemoglobin complexed to Hp 2-2 but not to Hp 1-1 or 2-1. The Hp 2-2 phenotype affects serum iron status markers in healthy males and is associated with higher L-ferritin concentrations in monocyte-macrophages because of a yet undescribed iron delocalization pathway, selectively occurring in Hp 2-2 subjects.