Análise da expressão de genes responsivos à hipóxia em pacientes com anemia falciforme: influência do tratamento com hidroxiuréia

Abstract

Hypoxia and hemoglobin S (HbSS) polymerization are the two cardinal triggers responsible for both erythrocyte sickling as well as of all clinical events in sickle cell anemia (SCA), a disease with many pathophysiological and molecular aspects that remain unclear. Despite being a permanent feature of SCA, there is still no consensus on the definition or management of hypoxia in sickle cell patients, and studies on its role in the pathogenic mechanisms of the disease, or on how it influences the clinical complications or hydroxyurea (HU) treatment, gold standard in the treatment of SCA, are lacking. Therefore, this study aimed to investigate the expression of hypoxia response genes in SCA and to analyze the dose-response to HU of angiogenesis, DNA damage and repairs, and clinicallaboratorial markers. The study population comprised 97 patients of both sexes, of ages ranging from 18 to 68 years, stratified into two groups: SS group (no HU, n=29) and SSHU group (treated with HU, n=68). The SSHU group was further stratified into subgroups according to the daily dose of the drug that patients already used: SSHU-0.5g (n=13); SSHU-1g (n=40) and SSHU-≥1.5g (n=15). A control group included 73 healthy individuals who were voluntary blood donors. The mRNA expression of the HIF-1α, VEGF, ATM, and ATR genes was measured by qPCR and associated with clinical and laboratory characteristics of the patients as well as with the daily dose of the drug. The main results included overexpression of all hypoxia-responsive genes tested here (p<0.01) in patients compared to healthy individuals, and a significant association between the concentration of Hb F and the genes under study. The ATM and ATR genes were associated with heart disease events (ATM, p<0.01; ATR, p=0.048) and with leg ulcers (ATM, p=0.048), and a significant association was identified between the variable number of episodes of pain and both VEGF and ATM expression. Individuals treated with HU showed reduction in HIF-1α, VEGF, ATM, and ATR expression compared to those untreated. Gene expression in the patients revealed a doseeffect relationship: individuals in the SSHU-0.5g group showed higher HIF-1α and VEGF expression than SSHU-1g and SSHU-≥1.5g individuals. SSHU-1g patients showed significant reduction in ATM gene expression compared to SSHU-0.5g patients and of ATR gene expression compared to both SSHU-0.5g and SSHU-≥1.5g individuals. The results of the present study show that hypoxic stress and its interference in gene expression may be involved in both the severity and treatment of the SCA. The results also suggest that the HIF-1α, VEGF, ATM and ATR genes act through mechanisms together, in view of the correlations obtained, and that HU has a notable and important dose-effect relationship with the aforementioned genes. So far, this is the first study that investigates the relationship of genes concerning the mechanisms of hypoxia, angiogenesis and DNA damage and repair, as well as their influence on the clinical characteristics of sickle cell patients and their correlation with treatment.