The first three studies in this thesis address the mechanism for the aberrant fall in serum 1,25-dihydroxyvitamin D$ sb3$ (1,25-(OH)$ sb2$D$ sb3 rbrack$ and increase in renal 1,25-(OH)$ sb2$D$ sb3$-24-hydroxylase(24-hydroxylase) activity in X-linked hypophosphatemic mice (Hyp). The 24-hydroxylase is the first enzyme in the C-24 oxidation pathway that degrades the vitamin D hormone to its final inactivation product, calcitroic acid. We demonstrated that: (i) the aberrant increase in 24-hydroxylase activity in Pi-deprived Hyp mice is specific to the kidney and is the result of an increase in enzyme Vmax, immunoreactive protein and mRNA abundance; (ii) the increase in 24-hydroxylase mRNA in both Pi-deprived Hyp mice and 1,25-(0H)$ sb2$D$ sb3$-treated normal littermates can be ascribed to an increase in the transcriptional activity of the 24-hydroxylase gene; (iii) 24-hydroxylase transcripts in normal mice, Pi-deprived Hyp and normal mice and 1,25-(OH)$ sb2$D$ sb3$-treated normal mice are localized to the proximal tubule by in situ hybridization; and (iv) recombinant human growth hormone administration normalizes the aberrant increase in 24-hydroxylase but that this response is not sufficient to correct serum 1,25-(OH)$ sb2$D$ sb3$ levels in Pi-deprived Hyp mice. / The fourth study addresses the mechanism whereby EB 1089, an analogue of 1,25-(OH)$ sb2$D$ sb3,$ is less calcemic than the vitamin D hormone, while being more potent in its antiproliferative action. We demonstrate that: (i) EB 1089 has a 50-fold lower affinity than 1,25-(OH)$ sb2$D$ sb3$ for the vitamin D catabolic enzyme, 24-hydroxylase; and (ii) EB 1089 and 1,25-(OH)$ sb2$D$ sb3$ exhibit tissue-specific differences in vitamin D receptor-mediated responses in vivo that may be ascribed, at least in part, to differences in binding affinities for the vitamin D receptor.

Proefschrift--Utrecht. / Title also in English. Summary in English. Vita. Includes bibliographical references.

Proefschrift--Utrecht. / Title also in English. Summary in English. Vita. Includes bibliographical references.

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Background: Recent research is revealing the high rate of false-positive screening results for IEMs in the NICU population. No study published to date has specifically studied the possible relationship between nutrition and newborn screening in this population. Objective: It is suspected that NICU infants who receive PN are more likely to have abnormal newborn screening results than infants who receive EN. An understanding of the role of nutrition will assist in developing protocols for screening in the NICU and decrease false-positives. Design: Infants admitted to the NICU between January 1-June 30, 2009 were included in this retrospective chart review study (n=339). The type of nutrition and timing of its initiation was recorded and compared to newborn screening results to identify correlations with false-positives. Statistical analysis included means, percentages, Fisher's exact test, Chi-square test, and the Cochran-Mantel-Haenszel test. Results: Nutrition type was significantly associated with newborn screening (p<0.001); those who received parenteral nutrition were more likely to have a false-positive. For infants who also received PN, EN of breast milk exclusively increased risk of an abnormal screen more than formula exclusively or breast milk plus formula. The timing of parenteral nutrition had no effect on screening. Premature infants who received PN exclusively had a higher percentage of false-positives than those who received EN Conclusions: Although the hypothesis could not be statistically supported, PN appears to contribute to false-positive newborn screens. More research is needed to ascertain the role of EN and GA in newborn screening and to develop standardized protocols. / Master of Science

Addendum inserted at back Includes bibliographical references (leaves 266-287). 1. Introduction -- 2. Materials and general methods -- 3. Characterisation and partial purification of the lysosomal sulphate transporter -- 4. Identification of proteins involved in lysosomal sulphate transport -- 5. The relationship between a sulphate anion transporter family and the lysosomal sulphate transporter -- 6. Investigation of sulphate transport in human skin fibroblasts -- 7. Concluding remarks