The development and use of x-ray fluorescence (XRF) to monitor the in vivo release of proteins in hydrogel matrices, retention of immunological adjuvants, and transdermal absorption in drug delivery

The objectives of this study were to employ a non-invasive radio-chemical approach to the measurement of the release of protein from hydrogels following subcutaneous administration, monitor the release of antigen proteins in immunological adjuvants, and monitor the absorption of compounds through the skin for drug delivery. Bovine serum albumin (66 kDa) was iodinated and incorporated into varying concentrations of Carbopol-940 gel. These formulations were injected into rats and monitored by X-ray Fluorescence (XRF). After the subcutaneous administration to rats, an {dollar}sp{lcub}241{rcub}{dollar}Am source was used to induce the emission of iodine X-rays which were subsequently detected by a Si(Li) detector positioned over the site of administration. There was a threshold concentration for Carbopol-940 of approximately 10 mg/mL at pH 7.4 before an increase of protein retention times was seen. Thereafter, as the concentration increased, retention times increased. Proteins of varying molecular weights but similar pl (isoelectric point) were then iodinated and incorporated into 1.4% Carbopol-940 gels at a concentration of 50 mg/mL. The XRF measurements illustrated that the release of protein from Carbopol formulations was dependent on molecular weight, with 50% disappearance times ranging from 6.2 hours for insulin (5.7 kDa) to 13.3 hours for thyroglobulin (660 kDa). Some proteins followed one-component first-order absorption, while others exhibited two-component first-order absorption. Iodinated bovine serum albumin (I-BSA) was also incorporated into an alginate gel formed by the addition of BaBr{dollar}sb2{dollar}. After the administration of I-BSA in an alginate gel, the decrease in the signals for Ba and I (indicative of the presence of alginate and BSA, respectively), as well as the spectator ion Br were measured simultaneously.; The release of I-BSA in Freund's adjuvant, Alum at 50% and 25%, and Pluronic F-127 followed first order kinetics, and was released at a rate significantly slower than without the use of the adjuvant matrix. This would allow for an enhancement of antibody production toward the antigen I-BSA.; Various bromo- and iodo- labeled compounds in enhancers were applied to the dorsal region of the neck of female Sprague-Dawley rats and monitored in-vivo. The effect of enhancers, the treatment of the skin, the type of label, and the position of the label were all studied. The trend among the iodo and bromo substituted benzoic acids indicated that the ortho substituted benzoic acids absorbed to a greater extent than the meta substituted benzoic acids, which in turn absorbed to a greater extent than the para substituted benzoic acids. The removal of the stratum corneum through tape stripping, or other physical means, resulted in differences in the types of absorption between unaltered skin and damaged skin for some compounds, while, for others, no major differences were seen. An example of the differences seen from the condition of the skin was 5-lodosalicylic acid in DMSO. which exhibited Fickian diffusion in damaged skin, but two-component zero-order or two-component first-order kinetics in undamaged skin. The extent of absorption over a 24 hour period was statistically equivalent.; A secondary XRF human study was performed using a samarium foil as the source of the secondary X-rays. Lower X-rays yields from the model compound Vioform were offset by the significantly lower radiation dose the patient received resulting in a 2:1 increase of the signal to dose ratio. (Abstract shortened by UMI.)...