Predictors of vitamin D status in subjects that consume a vitamin D supplement.

BACKGROUND/OBJECTIVE: Although dietary supplement use has increased significantly among the general population, the interplay between vitamin D supplementation and other factors that influence vitamin D status remains unclear. The objective of this study was to identify predictor variables of vitamin D status in free-living subjects to determine the extent to which vitamin D supplements and other factors influence vitamin D status. SUBJECTS/METHODS: This was a retrospective, cross-sectional study involving 743 volunteers. Serum 25-hydroxy-vitamin D (25(OH)D) level and the variables diet, supplement usage, latitude of residence, ethnicity, age and body mass index (BMI) were used to predict vitamin D status in a summer and winter cohort. RESULTS: Supplemental vitamin D3 consumption was the most significant positive predictor, whereas BMI was the most significant negative predictor, of vitamin D status in each cohort. Other positive predictors were fortified beverage and dairy consumption in the summer and winter cohort, respectively. Negative predictors were: African American, Asian and Hispanic race in the summer; latitude of residence >36°N, Asian and Hispanic ethnicity in the winter. Mean(± s.d.) 25(OH)D levels were 101.1 (± 42.1) and 92.6 (± 39.0) nmol/l in summer and winter, respectively. Comparing non-supplement vs supplement users, approximately 38 vs 2.5% in the winter and 18 vs 1.4% in the summer had vitamin D levels <50 nmol/l. CONCLUSIONS: Vitamin D supplementation was the most significant positive predictor of vitamin D status. Collectively, these data point to the practicality of utilizing vitamin D supplements to reduce hypovitaminosis D in adults throughout the United States.

Development of an in vivo preclinical screen model to estimate absorption and bioavailability of xenobiotics.

The purpose of this study was to develop an in vivo screening method for rapid preclinical characterization of absorption and bioavailability of large numbers of compounds. This effort involved several steps. First, a pharmacokinetic characterization of a reference compound was conducted in the monkey. These data were used to verify theoretical calculations of a maximal portal dose-normalized area under the concentration-time curve. Next, a monkey screen was implemented using mixtures of up to five compounds each (i.e., cassettes) to estimate the bioavailability of approximately 200 compounds. Cassettes were administered as a single intraduodenal dose to a single monkey followed by simultaneous portal and systemic blood sampling. Definitive studies were then conducted to determine absolute bioavailability of 14 of these compounds. The studies with the reference compound demonstrated that the theoretical methodology based on a single intraduodenal dose with portal and systemic sampling provided consistent estimates of bioavailability. In the screen studies, approximately 75% of the test compounds were excluded from further evaluation due to poor absorption. Of the 14 compounds selected for follow-up evaluation from both well and poorly absorbed compounds, the absolute bioavailability of 10 of them were correctly classified from the screening data. The remaining 4 compounds were false positives, which showed low bioavailability; no false negatives were encountered. This approach allows for a rapid and reliable screen to evaluate absorption and bioavailability using a single dose in a preclinical model.

Selective elevation of glutathione levels in target tissues with L-2-oxothiazolidine-4-carboxylate (OTC) protects against hyperoxia-induced lung damage in protein-energy malnourished rats: implications for a new treatment strategy.

It has become recognized that enhancing the antioxidant defense system during the early phase of rehabilitation is important to the survival of wasting protein-energy malnourished (PEM) patients. In this study, we compared the efficacy of dietary protein replenishment and supplementation with L-2-oxothiazolidine-4-carboxylate (OTC, 3.5 mg/d), a cysteine precursor, to protect against hyperoxia-induced lung damage in PEM rats. The PEM rats were produced by feeding weanling rats a protein-deficient diet (0.5% protein) for 14 d. PEM rats were then divided in three dietary treatment groups, 0.5% protein (-Pr), 0.5% protein plus the OTC supplement (+OTC), or 15% protein (+Pr) during 4 d of either hyperoxia (85% O2) or air exposure. Increased lung-to-body weight ratios, indicative of oxidative tissue damage, were observed following exposure to hyperoxia in -Pr and +Pr rats, but not in +OTC rats, even though the OTC supplement and the 15% protein diet contained a comparable amount of cysteine. Tissue reduced glutathione (GSH) status, GSH-dependent enzyme activity and antioxidant defense enzyme activities were monitored in the lung, liver and blood during 4 d of hyperoxia exposure. OTC supplementation enhanced GSH levels significantly in the lung of PEM rats, whereas protein repletion significantly elevated blood GSH concentrations. The protective effect of OTC was not a function of changes in activity of GSH-dependent enzymes or oxygen defense enzymes in the lung. These results indicate that a short-term strategy that selectively elevates GSH levels in the lung is more effective than protein repletion in protecting against hyperoxia-induced oxidative lung damage in PEM rats.

Peptide aldehyde inhibitors of cathepsin K inhibit bone resorption both in vitro and in vivo.

We have shown previously that cathepsin K, a recently identified member of the papain superfamily of cysteine proteases, is expressed selectively in osteoclasts and is the predominant cysteine protease in these cells. Based upon its abundant cell type-selective expression, potent endoprotease activity at low pH and cellular localization at the bone interface, cathepsin K has been proposed to play a specialized role in osteoclast-mediated bone resorption. In this study, we evaluated a series of peptide aldehydes and demonstrated that they are potent cathepsin K inhibitors. These compounds inhibited osteoclast-mediated bone resorption in fetal rat long bone (FRLB) organ cultures in vitro in a concentration-dependent manner. Selected compounds were also shown to inhibit bone resorption in a human osteoclast-mediated assay in vitro. Chz-Leu-Leu-Leu-H (in vitro enzyme inhibition Ki,app = 1.4 nM) inhibited parathyroid hormone (PTH)-stimulated resorption in the FRLB assay with an IC-50 of 20 nM and inhibited resorption by isolated human osteoclasts cultured on bovine cortical bone slices with an IC-50 of 100 nM. In the adjuvant-arthritic (AA) rat model, in situ hybridization studies demonstrated high levels of cathepsin K expression in osteoclasts at sites of extensive bone loss in the distal tibia. Cbz-Leu-Leu-Leu-H (30 mg/kg, intraperitoneally) significantly reduced this bone loss, as well as the associated hind paw edema. In the thyroparathyriodectomized rat model, Cbz-Leu-Leu-Leu-H inhibited the increase in blood ionized calcium induced by a 6 h infusion of PTH. These data indicate that inhibitors of cathepsin K are effective at reducing osteoclast-mediated bone resorption and may have therapeutic potential in diseases of excessive bone resorption such as rheumatoid arthritis or osteoporosis.