Bipolar Disorder in Youth is Associated with Increased Low Molecular Weight Fraction of Vitamin D Binding Protein

Genetic, dietary and inflammatory factors contribute to the etiology of major mood disorders (MMD), thus impeding the identification of specific biomarkers to assist in diagnosis and treatment. We tested association of vitamin D and inflammatory markers in 36 adolescents with bipolar disorder (BD) and major depressive disorder (MDD) forms of MMD and without MMD (non‐mood control). We also assessed the overall level of inflammation using a cell‐based reporter assay for nuclear factor‐kappa B (NFkB) activation and measuring antibodies to oxidized LDL. We found that these factors were similar between non‐mood and MMD youth. To identify potential biomarkers, we developed a screening immunoprecipitation‐sequencing approach based on inflammatory brain glia maturation factor beta (GMFβ). We discovered that a homologue of GMFβ in human plasma is low molecular weight vitamin D binding protein (DBP‐L). DBP‐L was 8 times more abundant in plasma of BD compared to control participants. DBP‐L is a product of enzymatic cleavage, transforming DBP into a macrophage‐activating factor. DBP levels in participants' plasma were validated using western blot, whereas mono‐ and polyclonal ELISA did not recognize DBP‐L. We found significantly increased levels of total DBP and DBP‐L in BD compared to control participants. The DBP responds early to cellular damage by scavenging actin and activating inflammatory cells. Our data suggest DBP and DBP‐L as marker candidates of BD warranting their validation in a larger cohort of adolescent and adult MMD patients. Support or Funding Information The project was supported by NIH grants R01 MH073801 (M.F., L.E.A.), R21OD017244 (O.Z., B.P., X.L.), the National Center for Research Resources UL1RR025755, UL1TR001070, and NCI P30CA16058 (OSUCCC), and the NIH Roadmap for Medical Research. Dr. Gracious' time and costs of the blood draw, supplies, and vitamin D assays were funded by the NCH/OSU Dept. of Psychiatry and Behavioral Health Jeffrey Research Fellowship and The Research Institute at Nationwide Children's Hospital, respectively. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Center for Research Resources or the National Institutes of Health. 1 Serum 25‐hydroxyvitamin D levels are inversely correlated with BMI in combined groupsInverse linear correlation between vitamin D concentrations in plasma and BMI measured in combined groups of patients with and without MMD. Pearson correlation2 Different association between high molecular weight fraction of DBP measured by western and DBP measured by monoclonal ELISA in study groups with and without MMD(A) Representative example shows high and low molecular weight portions of DBP (DBP‐H and DBP‐L, respectively) in plasma from participants measured by western blot. (B–E) Linear correlation between DBP‐H measured by western blot BDP measured by ELISA in same patients from a control (B), MMD (C), MMD (D), and BD (E) groups.3 Different association between serum vitamin D levels and DBP measured by polyclonal ELISA in study groups with and without MMDVitamin D (25‐hydroxy vitamin D) levels were measured in serum by HPLC. DBP measured by polyclonal ELISA, (A, B) Linear correlation between vitamin D and DBP in participants without MMD (non‐mood controls) (A) and in those with MDD (B). Significance was examined using Pearson test, p >0.05 was not significant.4 Increased DBP‐L levels in participants with BD(A, B) DBP‐L (A) and total DBP(B) protein expression levels were quantified based on western blot analysis in serum obtained from participants in control, MMD, and BD groups. Lines represent the values obtained from individual patients. Red line shows the mean value in each group. Group comparison was measured using ANOVA one‐way analysis.