Avaliação farmacogenética de resposta ao uso da hidroxiureia em pacientes com doença falciforme atendidos no Hemocentro Regional de Governador Valadares

Abstract

Sickle cell disease (SCD) is a serious global public health problem, with great impact on the morbidity and mortality of the affected population. To date, hydroxyurea (HU) is considered the most successful pharmacological therapy for SCD since it promotes a reduction in the number and severity of sickle cell events, improves hematological parameters, reduces the number of hospitalizations and increases the expectation and quality of life of the patients. Although the benefits of the treatment with HU are evident, there is a large inter-individual variability of pharmacological response and genetic factors seem to be partially associated with this variation. Thus, the aim of the present study is to investigate whether single nucleotide polymorphisms (SNPs) in four candidates genes related to the pharmacokinetics and pharmacodynamics of HU affect the hematological response to such a drug. For this, 185 patients were evaluated with SCD, treated with HU (93) or untreated (92). The mean hemoglobin (Hb), hematocrit (Hct), reticulocytes (Rct) and global leukometry (LG) levels were measured at five different times over 18 months, while fetal hemoglobin (HbF) levels were analyzed before and after pharmacological treatment. Patients were grouped as "responders" to HU if HbF levels were higher than 20%, while those patients with levels below this value were considered "non-responders". Genomic DNA was extracted from the whole blood and samples were then genotyped by real-time PCR (qPCR) for the polymorphisms G>T (rs1799983) and T>C (rs2070744) on the eNOS gene, C>T (rs17599586) of ARG1 gene, A>C (rs766432) and G>A (rs4671393) of the gene BCL11A and G>A (rs9960464) of the UTA gene. The analysis of the association between the categorical variables was done by chi-square test or Fisher's exact test. For continuous variables with normal distribution, analyses were performed using ANOVA followed by the unpaired t-test and the variables that did not follow normal distribution were analyzed by the Wilcoxon, Kruskal-Wallis tests followed by Mann-Whitney. The multivariate and logistic regression analyses were performed through the stepwise method by software R. The population studied presented a mean age of 15.8 ± 11.3 years and was made up of 54% of male volunteers. The genotypic and allelic frequencies for the six SNPs studied were in Hardy-Weinberg equilibrium and were similar to those found in other populations. Patients with the GT genotype for rs1799983 polymorphism of the eNOS gene showed higher Hb values when compared to patients homozygous for the G allele (r=0,364; p=0,033). In addition, the frequency of AC and CC genotypes in the BCL11A gene (A>C polymorphism rs766432) was higher among the responders when compared to the non-responders group (p=0,03). In addition, patients with the GA genotype for the UTA gene polymorphism also responded better to HU therapy when compared to those with the GG genotype (p=0,005). No other significant influences were found in the other polymorphisms evaluated after logistic regression analysis. In conclusion, this work is a pioneer in evaluating the influence of polymorphisms in eNOS, ARG1, BCL11A and UTA genes in the response to HU in patients with sickle cell disease in Minas Gerais. The findings suggest that patients with the GT genotype for rs1799983 of the eNOS gene showed higher Hb values when compared to GG genotype. The A> C polymorphisms (rs766432) in the BCL11A (p=0,001) and G> A gene (rs9960464) of the UTA gene (p=0,005) appear to affect the hematological response to HU, and patients who have at least one copy of less frequent allele may present higher chance of respond to pharmacological treatment.