Anti-Inflammatory Markers Are Associated with Glomerular Filtration Rate In Adults with Sickle Cell Disease.

Abstract 1652

Sickle cell disease (SCD) is characterized by increased systemic inflammation. Further, in a significant number of adult SCD patients, renal dysfunction and failure occur and are risk factors for early mortality. While some evidence supports a relationship between inflammation and renal dysfunction in the general population, this association has not yet been established in SCD. Recently, inflammatory biomarkers including TNFα (tumor necrosis factor alpha), C reactive protein (CRP), interleukin 6 (IL-6), and CD40 ligand (CD40L) were shown to be associated with chronic kidney disease (CKD) in a cohort of offspring of European descent participating in the Framingham study. Inflammatory markers were increased and glomerular filtration rates (GFR) were decreased in those with CKD compared to individuals with normal kidney function (Upadhyay, et al. 2010). Increased CRP has also been associated with CKD in African Americans participating in the Jackson Heart study (Fox, et al. 2010). Our goal was to determine if single nucleotide polymorphisms (SNPs) in inflammatory genes are associated with GFR in our population of SCD patients. To test this, we analyzed 55 haplotype tagging SNPs within 14 pro- and anti-inflammatory genes in 675 DNA samples from SCD patients ascertained from Duke University, University of North Carolina-Chapel Hill, and Emory University. SNP genotyping was performed using Taqman genotyping assays from Applied Biosystems. Genetic associations with GFR were examined using allele tests and multiple regression analysis (SAS version 9.1.3, Cary, NC). After controlling for age, gender, and use of hydroxyurea, SNPs in IL-1RN (rs452204), IL-10 (rs3024498), IL-12B (rs2195940), and IL-13 (rs1295687 and rs2069744) were significantly associated with GFR, with nominal p values ranging from 0.048 to 0.01. The two IL-13 SNPs were not found to be in linkage disequilibrium (LD) with each other (r²=0.017). After correcting for multiple testing, the SNPs in IL-10, IL-12B, and IL-13 (rs1295687 only) remained significant, with p values of 0.0134, 0.0084 and 0.0123, respectively. We then used regression analyses to test for pairwise interactions among all five of the SNPs, including each as a main effect in our analyses. Significant interactions were observed between rs1295687 in IL-13 and SNPs in IL-1RN (p=0.0174), IL-10 (p=0.0014), and rs2069744, also in IL-13 (p=0.0054). However, there was no significant interaction between IL-12B and any other SNP. The functional significance of these SNPs is presently unknown. All of the markers are located in introns except for the IL-10 marker, which is located in the 3’ untranslated region of the gene. Our findings in SCD support previous data from the general population showing associations among inflammatory markers, GFR and renal dysfunction. Interestingly, the SNPs which displayed significant interactions in the prediction of GFR are all located in anti-inflammatory genes (IL-13, IL-1RN and IL-10). In one previous study, macrophages that were stimulated with IL-4 and IL-13 ex vivo to produce IL-10, instead of TNFα and interferon gamma (IFNγ), protected against in vivo renal injury when infused into severe combined immunodeficiency (SCID) mice with doxorubicin-induced nephropathy (Wang, et al. 2007). The role of genetic factors that correlate with changes in GFR in adults with SCD requires replication in additional patient cohorts. Most importantly, our findings suggest that further investigation into the role of pro-inflammatory and anti-inflammatory pathways in the deterioration of kidney function in SCD is warranted.