Tandem immunoaffinity chromatography for plasma 1 alpha,25-dihydroxyvitamin D3 utilizing two antibodies having different specificities: a novel and powerful pretreatment tool for 1 alpha,25-dihydroxyvitamin D3 radioreceptor assays

Advances and challenges in the measurement of 1,25-dihydroxyvitamin D: a comprehensive review

Vitamin D has received significant attention from clinical societies, researchers, and the general population in recent years. While 25-hydroxyvitamin D (25(OH)D) is the most commonly-used biomarker of vitamin D status, 1α,25-dihydroxyvitamin D (1,25(OH)2D), its bioactive form, plays a critical role in regulating calcium and phosphorus homeostasis and is also involved in the immune system and cellular differentiation. Consequently, accurate measurements of 1,25(OH)2D can aid in the differential diagnosis of calcium-related disorders such as hypocalcemia in vitamin D-dependent rickets and hypercalcemia due to inappropriate increase of serum 1,25(OH)2D in granulomatous diseases. However, due to its lipophilicity and very low circulating concentration, the measurement of 1,25(OH)2D is particularly challenging. Over the past several decades, numerous efforts have been made to develop sensitive, specific, and practical laboratory methods for measuring 1,25(OH)2D. Methods using radioreceptor assay, radioimmunoassay, enzyme immunoassay, enzyme-linked immunosorbent assay, automated chemiluminescent immunoassay, and liquid chromatography-tandem mass spectrometry have been described. Each of these methods has unique advantages and limitations, and some are no longer used. Despite the sophisticated methods in use today, substantial variations between methods still exist. A concerted effort toward standardization of 1,25(OH)2D measurement is needed to ensure accurate and reliable results across laboratories and methods.

Production and characterization of monoclonal antibodies against a novel 1alpha,25-dihydroxyvitamin D3-bovine serum albumin conjugate linked through the 11alpha-position

To obtain an antibody which is useful for developing a selective immunoaffinity chromatography (IAC) of 1alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3], which is an effective pretreatment tool for determining this metabolite in biological fluids, a variety of monoclonal antibodies have been produced against a novel haptenic derivative, 11alpha-hemiglutaryloxy-1alpha,25-dihydroxyvitamin D3, linked to bovine serum albumin. BALB/c, A/J and C57BL/6 mice, as well as Wistar and SD rats, were immunized with the hapten-carrier conjugate and the titer of the anti-1,25(OH)2D3 antibody in serum was examined. Spleen cells from A/J mice or SD rats, which showed a high titer, were fused with P3/NS1/1-Ag4-1 myeloma cells. After serial screening by enzyme-linked immunosorbent assay and radioimmunoassay, sixteen kinds of hybridoma clones secreting different anti-1,25(OH)2D3 antibodies were established. Scatchard analysis revealed that 12 antibodies out of 16 have enough affinity to 1,25(OH)2D3 (Ka>10(9) M[-1]). By a cross-reaction study using various related compounds, two antibodies, M114 and M129, both derived from A/J mice, were found to have suitable specificity. Although they showed relatively high cross-reactivities with the 1,25(OH)2D3 derivatives having 24-hydroxylated (both 20%) or lactonized (30%, 8.9%) side chain, all the tested 1alpha-deoxy-type metabolites, some of which interfere with the 1,25(OH)2D3 assays, were successfully discriminated [25(OH)D3: 0.67%, 0.40%; 24,25(OH)2D3: 0.27%, 0.24%; 25(OH)D3 3-sulfate: 0.11%, 0.14%]. These monoclonal antibodies will be applicable for developing not only IAC but also various immunoassay procedures.