Article

Human plasma transport of vitamin D after its endogenous synthesis.

Department of Medicine, University of Pennsylvania, Philadelphia 19104.
Journal of Clinical Investigation (Impact Factor: 13.77). 06/1993; 91(6):2552-5.
Source: PubMed

ABSTRACT Transport of vitamin D3 from its sites of cutaneous synthesis into the circulation has been assumed to be via the plasma vitamin D binding protein (DBP). We studied vitamin D transport from the skin in seven healthy volunteers who received whole body irradiation with 27 mJ/cm2 dosage of ultraviolet B light (290-320 nm). Samples of venous blood were collected serially in EDTA and immediately chilled. In KBr, plasma samples were ultracentrifuged to provide a rapid separation of proteins of density < and > 1.3 g/ml. Upper and lower phases and serial fractions were analyzed for vitamin D3 (extraction, HPLC), cholesterol (enzyme assay), and human DBP (hDBP) (radial immunodiffusion). Total plasma vitamin D (basal level < 1 ng/ml) increased by 10 h and peaked at 24 h (9 +/- 1 ng/ml). 98% of the D3 remained at the density > 1.3 layers for up to 7 d, whereas cholesterol (> 85%) was detected at density < 1.3 and all of the hDBP was at density > 1.3. In three volunteers who each ingested 1.25 mg of vitamin D2, the total plasma D2 increased to 90 +/- 32 ng/ml by 4 h, and the D2 was evenly distributed between the upper and lower layers at 4, 8, and 24 h after the dose, indicating a continuing association of the vitamin with chylomicrons and lipoproteins, as well as with hDBP. Actin affinity chromatography removed D3 from plasma of irradiated subjects, indicating the association of the D3 with DBP. These findings indicate that endogenously synthesized vitamin D3 travels in plasma almost exclusively on DBP, providing for a slower hepatic delivery of the vitamin D and the more sustained increase in plasma 25-hydroxycholecalciferol observed after depot, parenteral administration of vitamin D. In contrast, the association of orally administered vitamin D with chylomicrons and lipoproteins allows for receptor-mediated, rapid hepatic delivery of vitamin D, and the reported rapid but less-sustained increases in plasma 25-hydroxycholecalciferol.

2 Bookmarks
 · 
104 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The constantly increasing requests for the measurement of serum 25-hydroxyvitamin D over the last years has led reagent manufacturers to market different automated and semi-automated methods, that being unfortunately not fully harmonized, yield different results. Liquid chromatography coupled to tandem mass spectrometry has more recently been introduced. This approach allows the distinction between the two forms of 25-hydroxyvitamin D and to measure other metabolites. This approach also requires harmonization to curtail the differences between the different analytical methods. To meet this requirement, the American national institutes of health (NIH), the CDC (Center for disease control and prevention) in Atlanta, the NIST (National institute of standards and technology) and the vitamin D Reference laboratory of Ghent University have pooled their expertise to develop a standardization program. This article reviews the main elements and the difficulties of the automated and semi-automated methods for 25-hydroxyvitamin D, from sample preparation to the analytical phase, as well as those related to mass spectrometry. It also addresses the issues related to the clinical decision thresholds and the possibility of measurements in different biological liquids.
    Annales de biologie clinique 02/2015; 73(1):79-92. · 0.42 Impact Factor
  • Source
    Research and Science Today. 07/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: To ascertain the protective role of calcitriol in the development of diabetic nephropathy and unravel the mechanism of the protective effects. In this prospective study, 69 patients were screened for type 1 diabetes, and 31 patients with type 1 diabetes were enrolled. Among these 31 patients, 24 patients had insufficient or deficient levels of serum vitamin D and 21 patients complied with calcitriol and were followed up. At baseline, these 21 patients who suffered from vitamin D deficiency or insufficiency displayed elevated inflammation markers and urinary albumin excretion in contrast with patients with sufficient vitamin D. Simultaneously, serum 25(OH)D3 level was negatively associated with serum and urinary inflammation markers, such as TNF-α, IL-6, and ICAM-1. Six months later, even though glycol-metabolism was not alleviated, all the serum and urinary inflammation markers decreased significantly. Meanwhile, proteinuria declined with inflammation markers. Calcitriol supplementation alleviated inflammation and proteinuria in patients with type 1 diabetes. Calcitriol might delay the development of diabetic nephropathy through suppressing inflammation.
    International Journal of Clinical and Experimental Medicine 01/2014; 7(12):5437-44. · 1.42 Impact Factor

Full-text (2 Sources)

Download
21 Downloads
Available from
May 28, 2014