Vitamin D-Binding Protein Levels Linked to Psoriatic Arthritis

In biologic-naïve patients with psoriatic arthritis, vitamin D-binding protein (DPB) might be a new inflammatory biomarker, according to a small study published in the International Journal of Molecular Science.1The study also found that the total prohormone 25-hydroxyvitamin D [25(OH)D] level correlated well with free 25(OH)D levels in serum and was a reliable measure for vitamin D status, but free or total 25(OH)D serum levels were not associated with psoriasis disease severity.

“There are unmet needs regarding diagnostic biomarkers for early detection of psoriatic arthritis,” wrote Maria Siekkeri Vandikas, consultant dermato-venereologist at Gothenburg University in Stockholm, Sweden, and colleagues. “The present study confirmed that in patients with psoriasis, DBP levels were higher in those with self-reported arthropathy compared to those without, as shown before.”

DBP has a possible role in the pathogenesis or susceptibility of different autoimmune and inflammatory diseases. High levels of DBP have been reported in patients with psoriasis and may negatively affect free 25(OH)D concentrations. Since only the free fraction of a steroid hormone can exert biological action, according to the free hormone hypothesis, free 25(OH)D level may be a better biomarker of vitamin D status than total 25(OH)D level.

In this retrospective cross-sectional study, the researchers aimed to identify the strongest determinants for DBP levels. They also tested the free hormone hypothesis for vitamin D in psoriasis and looked at correlations between free 25(OH)D levels in serum and psoriasis disease severity compared with total 25(OH)D levels.

The study included 40 biologic-naive patients (25 men, 15 women; mean age 47 years; mean disease duration 24 years) with mild to severe plaque psoriasis. Patients were followed up at an outpatient clinic in Sweden, between 2013 and 2017. Psoriasis disease severity was assessed using high sensitivity C-reactive protein (CRP), Psoriasis Area Severity Index (PASI) and visual analogue scale (VAS).

Results showed that DBP levels were higher in patients with self-reported arthropathy than those without. This finding could not be explained by body mass index, age or other known confounding factors for high DBP levels, including female sex, diabetes, smoking, thyroid disease, or use of hormonal contraception or aspirin. Contrary to other studies, DBP levels were not associated with high sensitivity CRP levels, which the authors suggested may be explained by the small study sample. DBP levels were not associated with PASI and VAS either.

Total and free 25(OH)D levels correlated well and were inversely correlated to intact parathyroid hormone. However, only total 25(OH)D correlated to serum calcium levels. No correlations were found between free and/or total 25(OH)D serum levels and high sensitivity CRP, PASI and VAS.

The authors cited several study limitations, including the small sample size, the lack of healthy controls and that no clinical data were collected for specifying the self-reported arthropathy. “The free hormone hypothesis needs to be tested in larger populations of patients with psoriasis and a variety of comorbidities as well as ongoing treatment,” investigators concluded.

Reference:

Vandikas MS, Landin-Wilhelmsen K, Gillstedt M, Osmancevic A. Vitamin D-Binding Protein and the Free Hormone Hypothesis for Vitamin D in Bio-Naïve Patients with Psoriasis. International Journal of Molecular Sciences. 2022; 23(3):1302. https://doi.org/10.3390/ijms23031302