Bipolar Disorder in Youth is Associated with Increased Low Molecular Weight Fraction of Vitamin D Binding Protein
Authors: Petrov Brawnie , Aldoori Ayat , Algorta Guillermo Perez , Yang Kefeng , Yasmeen Rumana , Gracious Barbara , Fristad Mary , Ziouzenkova Ouliana 
Published: November 2023

In recent years, the United States adolescent population has seen an epidemic increase in major mood disorders (MMD), such as bipolar disorder (BP) and major depressive disorder (MDD). MMD continues to be one of the most under‐diagnosed mental health problems in adolescents. The dependence of MMD on genetic and dietary factors, as well as inflammation, impedes the identification of biomarkers for sensitive diagnostics and therapies.

Recent studies in MMD patients identified deregulated inflammation, mediated in concert by immunomodulatory vitamin D as well as cytokine monocyte chemotactic protein‐1 (MCP‐1) and interleukin‐6 (IL‐6) regulated by a transcriptional regulator nuclear factor‐kappa B (NF‐κB). The goal of our study was to test association of these previously reported factors with MMD in a mixed cohort of adolescent patients (age range 10–17, age mean 13.71 ±1.86) with different MMD (MDD: n=12, BP n=11) compared to healthy (n=13). We also assessed the overall level of inflammation in these subjects using cell based reporter assay for NFκB activation.

Initially, we found that levels of all measured factors were not different between healthy and MMD youth. We then considered that vitamin D function depends on its carrier, vitamin D binding protein (VDBP). VDBP also has inflammatory function and activates macrophages after enzymatic processing of the VDBP O‐linked carbohydrate. Taking into account different functions of low (VDBP‐L) and high molecular weight (VDBP‐H) fractions of VDBP, we investigated VDBP levels in patients’ plasma by three methods: western blot, mono‐and polyclonal enzyme‐linked immunosorbent assay (ELISA).

Western blot revealed heterogeneous VDBP‐L and VDBP‐H fractions. The VDBP measured by the mono‐ and polyclonal ELISA lacked the necessary specificity to recognize the differences between healthy, BP, and MDD patients. Polyclonal ELISA showed an inverse correlation with vitamin D concentrations in the blood in MDD patients (r= −0.71, P =0.013). There was significant positive correlation between VDBP‐H and VDBP measured by monoclonal ELISA in healthy patients (r= 0.64, P =0.018), but an inverse correlation in MMD patients (r= −0.44, P =0.035), suggesting that VDBP‐H has an altered structure and affinity to monoclonal anti‐VDBP antibody in MMD. In consonance, there was inverse correlation between the ratio of VDBP‐L to VDBP‐H and VDBP measured by monoclonal ELISA for both BP and MMD patients (r=0.79, P =0.002 and r=0.63, P =0.001, respectively). Moreover, the ratios of VDBP‐L:VDBP‐H correlate with NF‐κB activation in healthy patients (r=0.55, P =0.05), indicating an inflammatory contribution of VDBP‐L fraction. Inflammatory function of VDBP appears to overcome vitamin D transport function in MMD patients.

Differences in mono‐ and polyclonal ELISA measurements of VDBP also highlight their low accuracy in measurement of VDBP. Western blot method enables quantitative analyses of heterogeneous VDBP fractions. We found significantly increased levels (130.5%, P=0.02) of VDBP‐L in BP compared to healthy (100%) subjects. MDD patients showed a trend to increase in VDBP‐L (119%, P =0.08) compared to healthy. Our data suggests VDBP‐L as a candidate marker for BP and warranted its validation in the larger cohort of adolescent and adult MMD patients.

Support or Funding Information

This research was supported by the American Egg Board (20020728) and from Novo Nordisk Pharmaceuticals (10040042). The project was supported by NIH grants R21OD017244, by the National Center for Research Resources UL1RR025755 and NCI P30CA16058 (OSUCCC), and supported by the NIH Roadmap for Medical Research.