Elevated serum heme oxygenase-1 in pediatric sickle cell disease: Insights from the SickleGenAfrica Network

Sickle cell disease (SCD) is characterized by chronic hemolysis, resulting in the release of extracellular heme, which contributes to oxidative stress and inflammation. Heme oxygenase-1 (HO-1), an inducible enzyme that degrades heme into cytoprotective by-products, plays a critical role in mitigating heme-induced toxicity. This study analyzed serum HO-1 levels in 2309 individuals with SCD (53% female; median age: 12 years) from the SickleGenAfrica cohort, comprising 57% hemoglobin SS disease (Hb SS), 30% hemoglobin SC disease (Hb SC), 3.1% Hb sickle beta plus thalassemia (Sβ+ thalassemia), and 9.9% Hb S-hereditary persistence of fetal hemoglobin (Hb S-HPFH). Median HO-1 levels were threefold higher in children under 16 years (69.8 ng/mL; interquartile range [IQR]: 29.8-137.6) compared to adults (23.1 ng/mL; IQR: 7.8-62.4; P < 0.001), with peak levels observed in the 6-10-year age group. Across all subgroups, including sex, genotype, and hydroxyurea use, children consistently exhibited higher HO-1 levels than adults, with Hb SS patients showing the highest levels. Haptoglobin and hemopexin, key scavengers of hemoglobin and heme, respectively, were depleted in all patients, particularly in children. Overall, HO-1 levels in SCD patients were markedly elevated compared to healthy populations. These findings highlight the pronounced elevation of HO-1 in pediatric SCD patients, suggesting its potential protective role against heme-induced toxicity, especially during childhood.