Serum concentrations of vitamin D-binding protein (Group-specific component) in cystic fibrosis

Abstract

Vitamin D-binding protein (DBP) concentrations were determined in the sera of 90 cystic fibrosis homozygotes, 57 obligate heterozygotes, and 46 normal controls. Very significantly lower mean concentrations were found in the sera of CF homozygotes compared with both heterozygotes and controls (P less than 0.01, Wilcoxon Rank Sums Test). Subdivision of the samples by Gc phenotype showed that this relationship held true both in the Gc1 and Gc2-1 phenotypes. The small sample size of the Gc2 genotype makes the significance levels of limited usefulness, but the pattern of variation of DBP levels among CF homozygotes, heterozygotes, and controls was consistent with that observed for the Gc1 and Gc2-1 classes. Haptoglobin levels showed high coefficients of variation when compared among CF homozygotes, obligate heterozygotes, and controls, presumably because of nonspecific elevation in the acute-phase response. Alpha 2-macroglobulin levels were, if anything, slightly elevated in CF homozygotes compared with controls, while albumin levels showed no significant mean differences between these groups. Since the DBP concentration does not vary with age nor with levels of vitamin D and its metabolites, we interpret our results to mean that DBP levels are specifically decreased in cystic fibrosis, perhaps as the result of impaired glycosylation of the protein.

Vitamin D bioavailability in cystic fibrosis: a cause for concern?

“…Dietary manipulation (high‐fat or carbohydrate diet) in order to obtain various proportions of vitamin D 3 carrier proteins did not alter hepatic extraction of vitamin D 3 57 . These findings are important in light of the diminished circulating levels of some lipoproteins and DBP reported in cystic fibrosis patients 50,51,58 …”

“…Because of their lipophilicity, circulating vitamin D molecules are bound to Gc‐globulin, to DBP, and, to a lesser extent, to albumin. A low concentration of DBP was described in cystic fibrosis patients, possibly as the result of impaired glycosylation of the protein 50,51 . This raises the question of whether decreased levels of DBP may affect the dispersal and availability of vitamin D metabolites to their target cells and tissues in cystic fibrosis patients.…”

Vitamin D Deficiency in Cystic Fibrosis

“…Decreased storage of both produced and consumed vitamin D may also be due to decreased levels of vitamin D binding protein (DBP) in CF patients, a phenomenon known to exist for 3 decades [26]. DBP shuttles vitamin D from the intestine to fat beds.…”

Vitamin D Deficiency Is Associated with Pulmonary Exacerbations in Children with Cystic Fibrosis

“…The cause of vitamin D deficiency in CF is multifactorial, including pancreatic insufficiency, reduced sunlight exposure, poor body fat stores, and decreased vitamin D-binding protein (14,15). Increased risk of vitamin D deficiency may be intrinsic to the CF transmembrane conductance regulator mutation, as those with CF given high doses of ergocalciferol with pancreatic enzymes have less absorption and impaired conversion to 25-OHD than control subjects (16).…”