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The relative abundance of DBP in serum permits the use of simple immunochemical techniques for measurements. Radioimmunoassay, rocket immune electrophoresis, single radial immunodiffusion, turbidimetry, nephelometry, and ELISA have been used [2]. Normal DBP levels can vary according to the used biochemical methodology but usually range from 200 to 600 mg/L in healthy subjects [21, 22]. There is no season-, weight-, or age-related variance of DBP levels [12, 23] but a circadian rhythm of DBP serum concentrations has been observed, with lower levels in the morning, followed by a rapid increase until reaching a plateau during the day [18]. The correction of vitamin D deficiency by supplementation does not change DBP levels [24]. The serum concentrations are lower in men than women, possibly due to the estrogen effect on its synthesis [23–25]. Furthermore, a hormonal contraceptive is associated with 13–25% higher concentrations of DBP, but, apparently, there are no differences in free hormone levels [26].

Decreased DBP levels are found in advanced liver disease (decreased production) [27], nephrotic syndrome, and diabetes mellitus with nephropathy (probably due to urinary loss). DBP is filtered through the glomerulus and in normal conditions, is reabsorbed by megalin-mediated endocytosis and catabolized by proximal tubule epithelial cells, reducing the urinary excretion to trace amounts. Acute tubular necrosis and glomerulonephropathies can disturb this process and DBP can be found in urine, as an early biomarker for kidney injury [28]. Lower levels of DBP were also found in inflammatory states, like acute injury or sepsis [29]. Compared to controls, individuals with musculoskeletal inflammatory disorders also showed lower levels of DBP, measured by two-dimensional gel electrophoresis. The reasons for the connection between inflammatory states and decreased DBP levels are still unknown, but it may be speculated that DBP, as a precursor for MAF, could be consumed by the increased formation of MAF and ensuing activation of macrophages and neutrophils at inflammation sites [30].