Measurement and interpretation of the plasma concentration of vitamin d and its metabolites.

摘要

Recent research has shown the importance of vitamin D status in the body. Vitamin D deficiency has been associated with fractures, poor physical function, and cardiovascular disease. The main marker of vitamin D status is 25-hydroxyvitamin D, a metabolite measured in serum. There are problems with this measurement because once in circulation nearly 99% of 25-hydroxyvitamin D is bound to plasma proteins, altering the biological activity. Some populations have more or less plasma proteins depending on factors such as age, and disease state. The main objective of this research is to develop the first validated equations for normalizing the concentration of 25-hydroxy vitamin D. The central hypothesis is that the concentration of 25OHD can be normalized based on the plasma binding capacity of each individual. The normalized concentration is the concentration that would produce a similar pharmacodynamic effect in an individual with normal plasma protein binding. The objective of this research was completed by accomplishing three main aims; creation of a new method to measure vitamin D3 and 25-hydroxyvitamin D3 using polydimethylsiloxane thin films, researching scientific literature for the binding constants of 25OHD3 to albumin and to DBP, and applying the normalizing equation to blood samples from healthy and dialysis volunteers, and data from published papers. Results to determine parameters to prepare samples for HPLC quantification was 25oC for 70 minutes and reconstitute with 75% acetonitrile:25% water for 45 minutes. The polydimethylsiloxane films were able to extract vitamin D compounds from various media, the vitamin D3 showed a plateau around 50 minutes. Correlations between normalized 25-hydroxyvitamin D and calcium showed the greatest improvement for healthy volunteers. Using data from published papers, the normalized concentration resulted in a reversed correlation than what the original authors reported. Polydimethylsiloxane is a new extraction phase for vitamin D, offering reproducibility, durability, and applicability for a wide range of samples. The normalizing equation and the correlations that were created allows for more precise exploration in vitamin D status. The normalized concentration will allow for personalized treatment plans based on patients' individual plasma protein amount resulting in decreased toxicity and better health outcomes.