1,25-Dihydroxyvitamin measurement

Reduction in the serum 1,25-dihydroxyvitamin D concentration has been reported as an indicator of increased lead absorption or lead levels in the blood (Rosen et al. 1980). Lead inhibits the formation of this active metabolite of vitamin D, which occurs in bone mineral metabolism (EPA 1986a Landrigan 1989). Children with PbB concentrations of 12-120 pg/dL lead showed decreased serum 1,25-dihydroxyvitamin D concentrations comparable to those found in patients with hypoparathyroidism, uremia, and metabolic bone disease (Mahaffey et al. 1982 Rosen et al. 1980). This biomarker is clearly not specific for lead exposure and several diseases can influence this measurement. 

Children with elevated PbB (12-120 pg/dL) were found to have significantly lower serum concentrations of the vitamin D metabolite 1,25-dihydroxy vitamin D compared with age-matched controls (p<0.001), and showed a negative correlation of serum 1,25-dihydroxyvitamin D with lead over the range of blood lead levels measured (Mahaffey et al. 1982 Rosen et al. 1980). 

In a further study, serum concentrations of 25-hydroxyvitamin D, 24,25-dihydroxyvitamin D and la,25-dihydroxyvitamin D were measured in 10 Cd-exposed subjects and 5 non-exposed subjects [100]. The Cd-exposed subjects were divided into two groups according to serum la,25-dihydroxyvitamin D levels. No significant differences for 25-hydroxyvitamin D were found between the Cd-exposed group with low or normal serum la,25-dihydroxyvitamin D and the... 

Measurement of BAP may be misleading in patients with fiver disease, severe osteomalacia, or increased concentrations of 1,25(0H)2D. bap maybe misleading in liver disease because of the cross-reactivity of current methods with fiver ALP. In severe osteomalacia, BAP maybe markedly increased without an increase in bone mineralization because of a mineralizing defect. Because 1,25-dihydroxyvitamin D regulates the synthesis of BAP and osteocalcin, both of these markers may be misleading in patients treated with calcitriol and in patients with abnormal concentrations of this hormone. 

Because type 1 collagen is also the major matrix of several other tissues, collagen propeptides are not as sensitive or specific for bone formation as osteocalcin or BAP. Measurement of procoUagen peptides may be helpful for assessing bone formation in patients treated with 1,25-dihydroxyvitamin D or in patients with abnormal concentrations of this hormone when osteocalcin and BAP may be misleading. 

Bilde DD, Suteri PK, Ryzen E, Haddad JG. Serum protein binding of 1,25-dihydroxyvitamin D A reevaluation by direct measurement of free metabolite levels. I Clin Endocrinol Metab 1985 61 969-75. 

OLT, with roughly 20% of patients experiencing a fracture within 1 year of transplant. Poor diets, lack of physical activity, reduced serum 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D, and abnormal parathyroid hormone concentrations are all thought to contribute pretransplant. Post-OLT corticosteroid therapy will also negatively impact bone metabolism, but may not be the sole reason for continued bone loss post-OLT. Mean bone mineral density (BMD) has taken a mean of 85 months to return to pre-OLT levels. Single-dose bisphosphonate infusion did not alter bone formation or resorption in the early (30 days) post-OLT period. " It is likely that lowering steroid doses, BMD screening, preventive measures, and calciiun and vitamin D supplementation will be the mainstay treatment options for this problem. ... 

The combination of low concentrations of lycopene together with 1,25-dihydroxyvitamin D3 exhibited a synergistic effect on inhibiting the proliferation of promyelocytic leukemia cells and on their differentiation. Further, an additive effect on cell-cycle progression was reported, whereby these authors concluded with a recommendation for the inclnsion of this carotenoid in the diet as a cancer-preventive measure. ... 

Analytical and clinical validation of an RIA for the measurement of 1,25-dihydroxyvitamin D was performed by Clive and co-workers. Vitamin D is a critical regulator of calcium and phosphorus homeostasis. This assay was specific for both 1,25-dihydroxyvitamin D2 and D3. The data collected during this study demonstrated that the RIA validated was a robust, accurate, and precise tool for the assessment of vitamin D. 

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