Effects of cytokine gene polymorphisms on il-10, tnf-α levels and oxidative stress in sickle cell disease patients from Mulago hospital, Uganda

Abstract

Sickle cell disease is a major cause of death in children under 5 years in Africa. Chronic oxidative stress and the release of inflammatory cytokines contribute to sickle cell disease pathogenesis and thus complicate the clinical management of this haemoglobinopathy. Polymorphisms in cytokine genes potentially influence increased cytokine production, a key risk factor for severe disease in sickle cell disease patients. Therefore, the purpose of this study was to investigate the frequency of cytokine gene polymorphisms and their effect on plasma levels of IL-10, TNF-α/β and malondialdehyde in sickle cell disease patients. This was a case control study, involving 178 sickle cell disease patients against 189 healthy controls. The extent of oxidative stress was evaluated using malondialdehyde by spectrophotometry while IL-10 and TNF-α/β levels were measured using the Enzyme Linked Immuno-Sorbent Assay. The Amplification Refractory Mutation System-PCR was used to genotype IL-10 and TNF-α/β gene polymorphisms in the Ugandan population. Descriptive analysis showed significantly higher (p= 0.0063) median plasma levels of malondialdehyde in sickle cell disease patients (2.615µM) as compared to healthy controls (2.490µM). A similar trend was observed with median plasma levels of IL-10 in patients (20.37pg/ml) as compared to healthy controls (7.5pg/ml). The most frequent genotype for IL-10 (1082) gene polymorphism in the sampled Ugandan population was heterozygous GA. However, its homozygous GG (1082) (22.12pg/ml), the higher producer for IL-10 that was found to be significantly associated (p= 0.0234) with increased plasma levels of this cytokine in sickle cell disease patients as compared to other genotypes (GA+AA) (13.94pg/ml) with the mutant allele. Similarly, higher levels of malondialdehyde were found to be significantly (p<0.0001) associated with homozygous GG (1082) for IL-10. The most frequent and only reported genotype for TNF-α/β gene polymorphisms was heterozygous GA in both patients and controls, thus no association was made for the cytokines. Therefore, results from this study show that sickle cell disease is associated with increased levels of oxidative stress that predispose patients to severe forms of the disease. Also, a protective role has been suggested for IL-10 with increased plasma levels of this cytokine standing as a potential biomarker for reduced sickle cell disease severity. In this study, a significant influence of cytokine gene polymorphisms on plasma levels of cytokines and possibly malondialdehyde has been established but not its overall effect on the clinical outcome of sickle cell disease.