Antioxidant Status of Red Blood Cells Is a Modifying Factor of Clinical Manifestation of Unstable Hemoglobin Variant Hana [α2β2 63 (E7) His-Asn)].
Authors: Solna Renata , Dolezel Petr , Mlejnek Petr , Divoky Vladimir 
Published: October 2019

Hemoglobin Hana [α2β2 63 (E7) His-Asn)] was described in a Moravian family from the Czech Republic as an unstable hemoglobin variant with mild Heinz body hemolytic anemia, elevated levels of methemoglobin (12–13%), and variable reticulocytosis (1.8–11%) in the proband and her sister.1 Surprisingly, their mother is asymptomatic, although she expresses the same aberrant variant of the β-globin gene. We did not detect any differences in the globin gene expression (based on wild-type and mutant globin mRNA from reticulocytes and βA and βHana chains measured by HPLC).1 Iron metabolism indices were within normal range in all family members. G6PD status in both parents was normal. To test whether the erythrocyte antioxidant capacity affects severity of this unstable hemoglobinopathy, key antioxidant parameters, including content of reduced (GSH) and oxidized glutathione (GSSG), activity of superoxide dismutase (SOD), catalase (CAT), and NADH-methemoglobin reductase (MetHb RED) were examined. Our results revealed that erythrocytes of both children exhibited lower GSH content, the ratio of GSSG/GSH was increased 6 to 7 times, and their catalase activity was decreased to 71–77% of the average control activity (Table 1). The increased ratio of GSSG/GSH could be related to the accumulation of peroxides in erythrocytes of the children and reflects lower ability of the enzyme antioxidant system to eliminate free oxygen radicals. In contrast, erythrocytes of their mother exhibited normal values of all these measured parameters except the activity of SOD, which was increased by 32% above normal level (Table 1). Activities of some antioxidant enzymes are altered in cigarette smokers2 and the mother is a heavy smoker (with elevated CO-Hb to 5.5%). We hypothesize she might benefit from higher SOD activity caused by activation of “oxidative stress genes” and that could, in turn, enhance the ability of her erythrocytes to deal with superoxide and hydrogen peroxide accumulation which results in more efficient prevention of hemoglobin oxidation. In the children, the decrease in hydrogen peroxide catabolizing capacity due to lower erythrocyte catalase activity strongly associates with a more severe clinical manifestation of this unstable hemoglobinopathy. Our findings suggest that alterations (either inherent or caused by extrinsic factors) in the levels of red blood cell antioxidant defense enzymes represent modifying factors affecting the clinical manifestation of Heinz body hemolytic anemia associated with an unstable hemoglobin variant.

Table 1: Levels of erythrocyte antioxidant systems in the family members Unaffected Mother Daughter 1 with HA Daughter 2 with HA Normal controls (n = 10) Range a - spectrophotometry, b - HPLC-MS GSHa(μmol/g Hb) 3.7 2.9 2.7 3.9±0.6 3.3–4.5 GSSG/GSHb 0.35 1.9 1.5 0.27±0.2 0.12–0.42 MetHb RED (U/g Hb) 15 15 14 16±2.8 13–19 SOD (U/g Hb) 2707 2325 1933 2052±311 1741–2363 CAT (U/g Hb) 282 227 245 320±57 263–377