Vitamin Deficiency, CD40L and VEGF in a Young Population with Sickle Cell Disease

Vitamin D deficiency is known to be common in patients with sickle cell disease (SCD). Vitamin D is important in multiple aspects of health, including the cardiovascular, immune and skeletal systems and its effects are mediated through the vitamin D receptor. The systems affected by vitamin D are also perturbed by SCD. Vitamin D deficiency is common in SCD, but its contribution to disease manifestations is being investigated. Vitamin D modulates the immune response and may have an effect on the levels of increased inflammation seen in individuals with SCD. In children and young adults with SCD at UNC Hospitals, we sought to determine the prevalence of vitamin D deficiency and its association with inflammatory markers and the influence of VDR haplotype. We report here on vitamin D status and several markers of inflammation.

We recruited pediatric and young adult SCD patients in their steady state attending routine periodic evaluations at the Pediatric and Adult Sickle Cell Clinics at the University of North Carolina Hospitals between February and June 2012. After consent, patients had their blood collected for inflammatory markers, 25-OH vitamin D and DNA. Patients with active pain crisis or recent illness were excluded. A chart review was done for the last 5 years to obtain SCD genotype, baseline white blood cell count, hemoglobin, platelets, calcium, phosphate and alkaline phosphatase. We measured inflammatory markers IL2, IL6, CD40L, TNFa, plasma VEGF and CD40L levels using ELISA (R&D Systems). At present only the VEGF and CD40L levels, along with baseline clinical laboratory data are available with the other inflammatory marker data expected shortly. Spearman's regression was used to examine potential correlations between continuous variables. A p value of < 0.05 was considered significant. P-values are considered nominal and are uncorrected for multiple analyses.

Vitamin D levels were measured in 78 patients, ages ranging from 2 to 26 years, with 55% males. The SCD genotypes were SS and Sb°Thal at 80%, SC and Sb⁺Thal at 20%. Thirty percent of patients were on hydroxyurea and ten percent of patients were on chronic exchange transfusions.

Severe vitamin D deficiency (<10 ng/mL) was present in 18%, mild to moderate deficiency (10–24 ng/mL) in 54% and only 28% were sufficient (>25 ng/mL). VEGF mean was 110.1 pg/mL (SD 125.8). CD40L mean was 642.2 pg/mL (SD 378.2). For the group as a whole, there were no correlations between the inflammatory markers and 25-OH vitamin D levels. However, when the group who was vitamin D deficient (< 25 ng/mL) was examined (n=39), vitamin D levels were inversely correlated with platelet count (rho= −0.3596, p =0.0246). Platelet count was positively correlated with CD40L level (rho= 0.3176, p= 0.0488). VEGF and CD40L levels were positively correlated (rho= 0.4520, p= 0.0039). Vitamin D levels are negatively correlated with age (rho= −0.3794, p = 0.0172). Restricting the analyses by age and gender did not change the results, nor did removing the individuals on hydroxyurea or chronic transfusions.

As has been noted previously, vitamin D deficiency is very common in people with sickle cell disease, including this young population, with mean age of 14 years. Inflammation is common as well, as reflected by the markedly elevated CD40L levels as well as the high-normal distribution of white cell count and platelet count. VEGF levels in adults with SCD appear to be elevated although are quite variable; VEGF appears to be a marker of inflammation in this disease. Little is known about VEGF levels in children with SCD. No associations between vitamin D levels and CD40L or VEGF levels were seen, however an inverse correlation between vitamin D level and platelet count was found. As platelets are a marker of inflammation, this suggests that further investigation of the relationship between vitamin D deficiency and inflammation could be fruitful. We anticipate having data concerning vitamin D and IL2, IL6 and TNFa in this group in the near future, as well as the ability to stratify the individuals by VDR haplotype.

Redding-Lallinger:Eli Lilly and Company: Research Funding.