No difference in intestinal strontium absorption after an oral or an intravenous 1,25(OH)2D3 bolus in normal subjects. For the European Study Group on Vitamin D in children with renal failure

Noteworthy idiosyncrasies of 1α,25-dihydroxyvitamin D3 kinetics for extrapolation from mouse to man: Commentary

Calcitriol or 1,25-dihydroxyvitamin D₃ [1,25(OH)₂ D₃ ] is the active ligand of the vitamin D receptor (VDR) that plays a vital role in health and disease. Vitamin D is converted to the relatively inactive metabolite, 25-hydroxyvitamin D₃ [25(OH)D₃ ], by CYP27A1 and CYP2R1 in the liver, then to 1,25(OH)₂ D₃ by a specific, mitochondrial enzyme, CYP27B1 (1α-hydroxylase) that is present primarily in the kidney. The degradation of both metabolites is mostly carried out by the more ubiquitous mitochondrial enzyme, CYP24A1. Despite the fact that calcitriol inhibits its formation and degradation, allometric scaling revealed strong interspecies correlation of the net calcitriol clearance (CL estimated from dose/AUC_∞ ), production rate (PR), and basal, plasma calcitriol concentration with body weight (BW). PBPK-PD (physiologically based pharmacokinetic-pharmacodynamic) modeling confirmed the dynamic interactions between calcitriol and Cyp27b1/Cyp24a1 on the decrease in the PR and increase in CL in mice. Close scrutiny of the literature revealed that basal levels of calcitriol had not been taken into consideration for estimating the correct AUC_∞ and CL after exogenous calcitriol dosing in both animals and humans, leading to an overestimation of AUC_∞ and underestimation of the plasma CL. In humans, CL was decreased in chronic kidney disease but increased in cancer. Collectively, careful pharmacokinetic data analysis and improved definition are achieved with PBPK-PD modeling, which embellishes the complexity of dose, enzyme regulation, and disease conditions. Allometric scaling and PBPK-PD modeling were applied successfully to extend the PBPK model to predict calcitriol kinetics in cancer patients.

Physicochemical properties of dietary phytochemicals can predict their passive absorption in the human small intestine

A diet high in phytochemical-rich plant foods is associated with reducing the risk of chronic diseases such as cardiovascular and neurodegenerative diseases, obesity, diabetes and cancer. Oxidative stress and inflammation (OSI) is the common component underlying these chronic diseases. Whilst the positive health effects of phytochemicals and their metabolites have been demonstrated to regulate OSI, the timing and absorption for best effect is not well understood. We developed a model to predict the time to achieve maximal plasma concentration (Tmax) of phytochemicals in fruits and vegetables. We used a training dataset containing 67 dietary phytochemicals from 31 clinical studies to develop the model and validated the model using three independent datasets comprising a total of 108 dietary phytochemicals and 98 pharmaceutical compounds. The developed model based on dietary intake forms and the physicochemical properties lipophilicity and molecular mass accurately predicts Tmax of dietary phytochemicals and pharmaceutical compounds over a broad range of chemical classes. This is the first direct model to predict Tmax of dietary phytochemicals in the human body. The model informs the clinical dosing frequency for optimising uptake and sustained presence of dietary phytochemicals in circulation, to maximise their bio-efficacy for positively affect human health and managing OSI in chronic diseases.

Nasal Levels of Antimicrobial Peptides in Allergic Asthma Patients and Healthy Controls: Differences and Effect of a Short 1,25(OH)2 Vitamin D3 Treatment

Background

Allergy is often accompanied by infections and lower levels of antimicrobial peptides (AMPs). Vitamin D has been shown to increase expression of selected AMPs. In this study we investigated whether antimicrobial peptide levels in nasal secretions of allergic asthma patients are lower than in healthy controls, and whether administration of the active form of vitamin D (1,25(OH)₂D3) affects these antimicrobial peptide levels.

Methods

The levels of antimicrobial peptides in nasal secretions were compared between 19 allergic asthma patients and 23 healthy controls. The effect of seven days daily oral treatment with 2 μg 1,25(OH)₂D3 on antimicrobial peptides in nasal secretions was assessed in a placebo-controlled cross-over clinical study.

Results

Levels of neutrophil α-defensins (human neutrophil peptides 1–3; HNP1-3) and lipocalin 2 (LCN2; also known as NGAL) were significantly lower in asthmatics, but no differences in LL-37 and SLPI were detected. Treatment with a short-term 1,25(OH)₂D3 caused a small increase in HNP1-3, but not when the asthma and control groups were analyzed separately. LL-37, LCN2 and SLPI did not change after treatment with 1,25(OH)₂D3.

Conclusion

Levels of the antimicrobial peptides HNP1-3 and LCN2 are lower in nasal secretions in asthmatics and are not substantially affected by a short-term treatment with active vitamin D.

Strontium oral load test in children with idiopathic hypercalciuria

Increased intestinal calcium absorption may play an important role in the pathogenesis of idiopathic hypercalciuria in children. Calcium absorption was assessed by an oral strontium load test in 22 prepubertal children (13 male) with idiopathic hypercalciuria, urinary calcium excretion 6.48 +/- 0.60 mg/kg per day (range 4.12-13.40 mg/kg per day), and ten healthy, young, normocalciuric controls (six male). After administration of 2.65 mg/kg of strontium chloride (SrCl(2)), the serum concentrations of strontium at 30 min, 60 min, 120 min, 240 min, and the fraction of the absorbed dose (FAD%) at 30 min, 60 min and 240 min, were similar in both groups. FAD% at 120 min was lower (P < 0.05) in hypercalciuric children than in controls (11.84 +/- 0.96% vs 15.87 +/- 1.77%). Values of the area under the curve were not different between both groups. In children with idiopathic hypercalciuria, serum basal intact parathyroid hormone (PTH) (r = -0.59, P = 0.004) and the 1,25-dihydroxyvitamin D/PTH ratio (r = 0.65; P = 0.001) were correlated with the serum concentration of strontium at 60 min. The study reported here provides, for the first time, the results of a strontium oral load test in children with idiopathic hypercalciuria. With this method no major alterations of intestinal calcium absorption were found in this disorder.

Comparative review of the pharmacokinetics of vitamin D analogues

This article reviews the pharmacokinetic characteristics of calcitriol, paricalcitol, and doxercalciferol, and provides an overview of the metabolism of vitamin D. Calcitriol and paricalcitol have similar pharmacokinetic profiles, with terminal half-lives ranging from 5 to 10 hours in healthy subjects to 15-30 hours in patients undergoing dialysis. Both are active on intravenous administration and little of the active agent remains in the circulation after 24 hours, although they are normally given every 48-72 hours. Doxercalciferol is a prohormone, requiring hepatic metabolism to the active metabolite 1alpha,25-(OH)2D2. The half-life of 1alpha,25-(OH)2D2 is about 34 hours in healthy subjects and about 45 hours in dialysis patients, resembling physiologic blood concentrations of endogenous vitamin D. More studies are warranted to determine the disposition of the vitamin D analogues, especially in selected populations such as pediatric and geriatric dialysis patients.

No difference in intestinal strontium absorption after oral or IV calcitriol in children with secondary hyperparathyroidism. The European Study Group on Vitamin D in Children with Renal Failure

BACKGROUND

Oral and intravenous calcitriol bolus therapy are both recommended for the treatment of secondary hyperparathyroidism, but it has been claimed that the latter is less likely to induce absorptive hypercalcemia. The present study was undertaken to verify whether intravenous calcitriol actually stimulates intestinal calcium absorption less than oral calcitriol and whether it is superior in suppressing parathyroid hormone (PTH) secretion.

METHODS

Twenty children (16 males, age range of 5.1 to 16.9 years, mean creatinine clearance 21.9 +/- 11.5 mL/min/1.73 m2, range of 7.4 to 52.7) with chronic renal failure (CRF) and secondary hyperparathyroidism [median intact PTH (iPTH), 327 pg/mL; range 143 to 1323] received two single calcitriol boli (1.5 mg/m2 body surface area) orally and intravenously using a randomized crossover design. iPTH and 1,25(OH)2D3 levels were measured over 72 hours, and intestinal calcium absorption was measured 24 hours after the calcitriol bolus using stable strontium (Sr) as a surrogate marker. Baseline control values for Sr absorption were obtained in a separate group of children with CRF of similar severity.

RESULTS

The peak serum level of 1,25(OH)2D3 and area under the curve baseline to 72 hours (AUC0-72h) were significantly higher after intravenous (IV) calcitriol (AUC0-72h oral, 1399 +/- 979 pg/mL. hour vs. IV 2793 +/- 1102 pg/mL. hour, P < 0.01), but the mean intestinal Sr absorption was not different [SrAUC0-240min during the 4 hours after Sr administration 2867 +/- 1101 FAD% (fraction of the absorbed dose) vs. 3117 +/- 1581 FAD% with oral and IV calcitriol, respectively]. The calcitriol-stimulated Sr absorption was more then 30% higher compared with control values (2165 +/- 176 FAD%). A significant decrease in plasma iPTH was noted 12 hours after the administration of the calcitriol bolus, which was maintained for up to 72 hours without any differences regarding the two routes of administration.

CONCLUSIONS

These results demonstrate that under acute conditions, intravenous and oral calcitriol boli equally stimulate calcium absorption and had a similar efficacy in suppressing PTH secretion.

Immunochemical studies on the putative plasmalemmal receptor for 1, 25(OH)(2)D(3). I. Chick intestine

Antisera were raised against the NH(2)-terminus of the putative basal lateral membrane (BLM) receptor for 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3); BLM-VDR]. In Western analyses of BLM proteins, antibody (Ab) 099 was monospecific for a 64.5-kDa band. A protein of 64.5 kDa was also labeled by the affinity ligand [(14)C]1, 25(OH)(2)D(3)-bromoacetate; label was diminished in the presence of excess unlabeled secosteroid. The monoclonal antibody against the nuclear VDR (9A7) failed to detect an appropriate band in BLM fractions. Preincubation of isolated intestinal cells with Ab 099, but not 9A7, affected the following two 1,25(OH)(2)D(3)-mediated signal transduction events: augmented intracellular calcium and protein kinase C activity. Subcellular distribution of Ab 099 reactivity by Western analyses and fluorescence microscopy revealed the highest concentrations in BLM followed by the endoplasmic reticulum. Exposure of isolated intestinal cells to 1,25(OH)(2)D(3) for 10 s or vascular perfusion of duodena for 5 min resulted in a time-dependent increase in nuclear localization of the BLM-VDR antigen, as judged by electron microscopy, whereas 24, 25-dihydroxyvitamin D(3) failed to increase antigenic labeling in nuclei. Densitometric quantitation of Western blots of subcellular fractions prepared from isolated intestinal cells treated with vehicle or 1,25(OH)(2)D(3) confirmed a hormone-induced increase of putative BLM-VDR in the nucleus. It is concluded that a novel cell surface binding protein for 1,25(OH)(2)D(3) has been identified.