Modified-release oral calcifediol corrects vitamin d insufficiency with minimal cyp24a1 upregulation

SBMB 4321 No. of Pages 7 Contents lists available at Journal of Steroid Biochemistry & Molecular Biology Modified-release oral calcifediol corrects vitamin D insufficiency with minimal CYP24A1 upregulation Martin Petkovich , Joel Melnick Jay White Samir Tabash , Stephen Strugnell Charles W. Bishop a Cancer Research Institute, 355 Botterell Hall, Queen's University, Kingston, ON K7L 3N6, Canada b OPKO Health, Renal Division, Markham, ON L3R 6H3, Canada c OPKO Health, Renal Division, Miami, FL 33137, USA Vitamin D insufficiency is prevalent in chronic kidney disease (CKD) and associated with secondary Received 29 August 2014 hyperparathyroidism (SHPT) and increased risk of bone and vascular disease. Unfortunately, supplemen- Received in revised form 19 November 2014 tation of stage 3 or 4 CKD patients with currently recommended vitamin D does not reliably Accepted 21 November 2014 restore serum total 25-hydroxyvitamin D to adequacy (30 ng/mL) or effectively control SHPT. Preclinical Available online xxx and clinical studies were conducted to evaluate whether the effectiveness of vitamin D repletion depends, at least in part, on the rate of repletion. A modified-release (MR) oral formulation of calcifediol (25-hydroxyvitamin D was developed which raised serum 25-hydroxyvitamin D calcitriol levels gradually. Single doses of either bolus intravenous (IV) or oral MR calcifediol were administered to vitamin D Chronic kidney disease Vitamin D insufficiency deficient rats. Bolus IV calcifediol produced rapid increases in serum 25-hydroxyvitamin D FGF23, along with significant induction of CYP24A1 in both kidney and parathyroid gland. In contrast, oral MR calcifediol produced gradual increases in serum 25-hydroxyvitamin D calcitriol and achieved similar hormonal exposure, yet neither CYP24A1 nor FGF23 were induced. A 10-fold greater exposure to bolus IV than oral MR calcifediol was required to similarly lower intact parathyroid hormone (iPTH). Single doses of oral MR (450 or 900 mg) or bolus IV (450 mg) calcifediol were administered to patients with stage 3 or 4 CKD, SHPT and vitamin D insufficiency. Changes in serum 25-hydroxyvitamin D calcitriol and in plasma iPTH were determined at multiple time-points over the following 42 days. IV calcifediol produced abrupt and pronounced increases in serum 25-hydroxyvitamin D calcitriol, but little change in plasma iPTH. As in animals, these surges triggered increased vitamin D catabolism, as evidenced by elevated production of 24,25-dihydroxyvitamin D In contrast, MR calcifediol raised serum 25-hydroxyvitamin D and calcitriol gradually, and meaningfully lowered plasma iPTH levels. Taken together, these studies indicate that rapid increases in 25-hydroxyvitamin D CYP24A1 and FGF23 induction, limiting effective exposure to calcitriol and iPTH reduction in SHPT. They also support further investigation of gradual vitamin D repletion for improved clinical effectiveness.
This article is part of a Special Issue entitled "17th Vitamin D Workshop".
ã 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license supplementation is the standard of care for correcting vitamin D insufficiency in CKD , while vitamin D hormones (calcitriol and Vitamin D insufficiency is associated with chronic kidney other synthetic hormones) are used to control SHPT Both of disease (CKD) and gives rise to secondary hyperparathyroidism these therapeutic approaches have significant limitations.
(SHPT) which can lead to loss of bone density and elevated rates of "vitamin D") are absorbed fracture in renal patients . Vitamin D therapies are therefore less readily than more polar vitamin D compounds , and the widely used in the management of chronic kidney disease (CKD).
degree of absorption can vary considerably between patients Once absorbed, vitamin D must undergo two sequential hydrox- (ergocalciferol) ylations to be active: first at carbon 25 by CYP2R1 or CYP27A1 to form 25-hydroxyvitamin D, and then at carbon 1 by CYP27B1 to form 1,25-dihydroxyvitamin D . Hepatic 25-hydroxylation varies * Corresponding author. Tel.: +1 613 533 6791; fax: +1 613 533 6830.
E-mail address: (M. Petkovich).
widely in efficiency and, together with variable absorption, 0960-0760/ ã 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/).
Please cite this article in press as: M. Petkovich, et al., Modified-release oral calcifediol corrects vitamin D insufficiency with minimal CYP24A1 upregulation, J. Steroid Biochem. Mol. Biol. (2014),

SBMB 4321 No. of Pages 7 M. Petkovich et al. / Journal of Steroid Biochemistry & Molecular Biology xxx (2014) xxx–xxx complicates the determination of optimal dose Significant vitamin D deficient diet for 8 weeks after which detectable serum percentages of CKD patients receiving vitamin D supplements do not 25-hydroxyvitamin D was negligible. Two groups of twenty-five attain targeted levels of serum 25-hydroxyvitamin D .
rats were administered a single 0.4 mL IV injection of either Recommended repletion comprises intermittent high dose calcifediol (4.5 mg) or vehicle (30:50:20, v/v/v propylene glycol: regimens which may trigger accelerated vitamin D catabolism . A saline:ethanol). Two additional groups of 25 rats were adminis- comprehensive review of the topic concluded that vitamin D tered by gavage hard shell gelatin capsules containing an MR supplementation is generally ineffective in clinical management of formulation of calcifediol (4.5 mg) or the MR calcifediol formula- CKD patients .
tion alone (comprising a wax matrix). The MR formulation Vitamin D hormones induce the desired clinical responses in progressively released calcifediol over a 12-hour period during target tissues, such as increased intestinal calcium uptake and in vitro dissolution testing. Serum or plasma were collected post- suppression of iPTH production, by directly activating the vitamin dose at 0, 0.08, 0.25, 0.5, 1, 2, 4, 8, 12 and 24 h.
D receptor . Production of 1,25-dihydroxyvitamin D by renal CYP27B1 is controlled by feedback inhibition, thereby protecting 2.1.2. Plasma iPTH tissues from overexposure. However, vitamin D hormone therapy Determined with the rat iPTH ELISA kit (Immutopics, San is not subject to feedback regulation and can readily cause Clemente, CA, USA).
oversuppression of iPTH, hypercalcemia and hyperphosphatemia, leading to adynamic bone disease and vascular calcification .
2.1.3. Serum FGF23 Hormones also accelerate vitamin D catabolism and raise target Measured using an FGF23 ELISA kit (Kainos Laboratories, Tokyo, tissue resistance by inducing CYP24A1 which can mitigate the desired therapeutic responses and exacerbate vitamin D insuffi- 2.1.4. CYP24A1, CYP27B1 and PTH mRNA The limitations of current vitamin D supplementation and Kidney and parathyroid gland tissue samples were excised and hormone replacement therapies have led us to re-examine frozen in RNAlater1 and were processed using an automated hard calcifediol (25-hydroxyvitamin D as a potentially effective tissue homogenizer. RNA was isolated using TRIzol1 Reagent intervention for restoring adequate serum levels of 25-hydrox- (Invitrogen). The ThermoScriptTM RT-PCR System kit (Invitrogen) yvitamin D and safely controlling SHPT. Calcifediol is more readily was used to create cDNA from 10 mg of RNA. The TaqMan1 probes absorbed than vitamin D and requires only 1-hydroxylation specific for rat Cyp24A1 (Cat. # Rn01423141_g1), Cyp27B1 for activation, which remains under physiological feedback regulation. We investigated whether gradual delivery of calcife- (Rn99999916_s1) were designed and manufactured by Applied diol, using a modified-release (MR) formulation for oral adminis- Biosystems Inc., (Foster City, CA). Quantitative real-time PCR was performed using an ABI Prism 7000 sequence detection system improving its effectiveness. The nonclinical and clinical studies (Applied Biosystems) using Taqman Universal PCR Master Mix (ABI described herein compared MR and bolus intravenous (IV) #4304437). The relative expression value was calculated by the calcifediol with regard to effects on serum levels of vitamin D using GAPDH as endogenous control. Data metabolites, plasma iPTH, serum FGF23, and tissue expression of were normalized such that the level of expression in control rats the catabolic enzyme CYP24A1.
was equal to 1.0.
2. Materials, methods and results 2.1.5. Vitamin D metabolites Serum samples were spiked with [26,27-2H 2.1. Non-clinical studies serve as internal standards and extracted using Accubond II ODS-C mg, 1 mL SPE cartridges (Agilent Technologies, Palo Alto, CA). The collected fractions were Adult male Sprague Dawley rats (6–8 weeks of age) from Hilltop dried under nitrogen, and residues were reconstituted in 50 mL of Lab Animals Inc., (Scottdale, PA, USA) were maintained on a (80/20; v/v) and analyzed using LC–MS/MS Fig. 1. Effect of bolus IV or oral MR calcifediol administration on serum calcifediol and calcitriol levels in rats. Male rats were maintained on a vitamin D deficient diet for 8 weeks and then divided into 4 treatment groups. Each group received a single 4.5 mg dose of bolus IV calcifediol (solid circles) or oral MR calcifediol (solid squares) or the corresponding vehicles (open circles and squares). Serum levels of calcifediol (A) and calcitriol (B) were measured at the indicated time points post-dose. Error bars indicate standard deviation (SD). Asterisks denotes significant differences between IV and MR treatment groups (P < 0.05).
Please cite this article in press as: M. Petkovich, et al., Modified-release oral calcifediol corrects vitamin D insufficiency with minimal CYP24A1 upregulation, J. Steroid Biochem. Mol. Biol. (2014),

SBMB 4321 No. of Pages 7 M. Petkovich et al. / Journal of Steroid Biochemistry & Molecular Biology xxx (2014) xxx–xxx Fig. 2. Effect of bolus IV or oral MR calcifediol administration on mediators of vitamin D metabolism in rats. Expression of kidney CYP24A1 transcripts (A), serum intact FGF23 (B), kidney CYP27b1 transcripts (C) and parathyroid gland CYP24A1 transcripts (D) were measured in vitamin D deficient rats sacrificed at the indicated time points following treatment with a single 4.5 mg dose of bolus IV calcifediol (solid circles) or oral MR calcifediol (solid squares) or the corresponding IV or MR vehicles (open circles and squares).
Asterisks denote significant differences between IV and MR treatment groups (P < 0.05).
(Waters Alliance HPLC-Waters Quattro Ultima Mass Spectrometer, post-dose. Kidney CYP27B1 mRNA transcript levels were rapidly Milford, MA).
and completely suppressed with IV calcifediol treatment by 8 h and remained suppressed at 24 h (C). In contrast, neither MR 2.1.6. Statistical analysis calcifediol nor vehicle treatment caused significant changes in ANOVA (one- or two-way) and Bonferroni Multiple Comparison serum FGF23 or CYP27B1 expression.
post-test were used to determine statistical significance set at A rapid and prominent surge in CYP24A1 expression was p < 0.05.
observed in parathyroid gland tissue obtained from animals treated with bolus IV calcifediol which peaked at 4 h post-dose 2.2. Results from non-clinical studies A single bolus IV dose of calcifediol (4.5 mg) increased serum calcifediol levels to approximately 320 ng/mL within 5 min A). Thereafter, calcifediol levels dropped to 110 ng/mL by 30 min and to 96 ng/mL by 24 h. A single oral dose of MR calcifediol (4.5 mg) produced a detectable rise in serum calcifediol at 3 h post- dose, which peaked 2 h later at 16 ng/mL and dropped to 10 ng/mL by 24 h. No changes in serum calcifediol were noted in animals treated with vehicles.
Bolus IV calcifediol produced a rapid increase in serum calcitriol from baseline (which was below the limit of quantitation) to 1.1 ng/ mL by 4 h (B). Serum calcitriol returned toward baseline by 24 h. MR calcifediol produced detectable increases in calcitriol (>0.1 ng/mL) as early as 1 h post-dose and levels rose gradually to 0.6 ng/mL by 24 h. No significant changes in serum calcium or phosphorus were observed for either treatment group over the 24-hour post-dose period (data not shown).
Pharmacodynamic changes associated with the observed increases in serum calcifediol and calcitriol are shown in A Fig. 3. Effect of bolus IV or oral MR calcifediol administration on plasma iPTH levels CYP24A1 expression in the kidney which reached a 40-fold in rats. Plasma iPTH levels were determined in vitamin D deficient rats treated with increase by 4–8 h post-dose. In contrast, MR calcifediol produced bolus IV calcifediol (solid circles), MR capsules (solid squares) or the corresponding detectable increases in kidney CYP24A1 expression after 4 h which MR vehicle capsules (open squares). Baseline iPTH level corresponds to mean iPTH peaked at only 6-fold above baseline by 12 h. No changes in levels obtained in vehicle control animals over the course of the treatment period.
CYP24A1 expression were observed in vehicle-treated animals.
Data for the IV vehicle were equivalent to the MR vehicle and were omitted for improved clarity. Both IV and MR iPTH treatment groups were significantly different Serum FGF23 levels increased significantly only in animals from their correspnding vehicle controls at all time points post-treatment as receiving bolus IV calcifediol (B) and remained higher 24 h denoted by asterisks (P < 0.05).
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SBMB 4321 No. of Pages 7 M. Petkovich et al. / Journal of Steroid Biochemistry & Molecular Biology xxx (2014) xxx–xxx Fig. 4. Effect of bolus IV or oral MR calcifediol administration on serum levels of calcifediol and 1,25-dihydroxyvitamin D in patients. Patients with stage 3 or 4 CKD, SHPT and vitamin D insufficiency were treated with a single bolus IV injection of 448 mg calcifediol (solid circles) or single doses of oral MR calcifediol (450 mg–solid triangles; 900 mg– solid squares). Serum samples obtained at the indicated time points were analyzed for (A) calcifediol (25(OH)D and (B) 1,25-dihydroxyvitamin D. Data are corrected for baseline values. Asterisk denotes significant differences at all time points post-treatment between IV and MR treatment groups (P < 0.05).
at a level 13-fold higher than baseline D). In contrast, MR capsules progressively released calcifediol over a 12-hour parathyroid gland CYP24A1 expression rose more gradually in period (data not shown). For IV dosing, 0.56 mL (448 mg) of animals treated with MR calcifediol, peaking at 12 h post-dose at a level 5-fold higher than baseline. Plasma iPTH was equally (30:50:20, v/v/v), was injected within 1 min into a peripheral suppressed in both treatment groups at 24 h post-dose ).
vein. The strengths of the dosing formulations were verified prior to and after administration.
2.3. Clinical studies 2.3.3. Sample analysis Blood samples were collected at 18, 12 and 6 h pre-dose to Twenty-nine (29) subjects with stage 3 or 4 CKD, SHPT and establish baseline values. For the oral dose groups, post-dose blood vitamin D insufficiency (defined as serum total 25-hydroxyvitamin D samples were collected at 2, 4, 6, 8, 10, 12, 16, 20, 24, 30, 36, and below 30 ng/mL) were randomized to one of three treatment groups.
48 h, and at 4, 7, 14, 21, 28, and 42 days. For the IV group, post-dose samples were collected at 5, 10, 15, and 30 min, at 1, 2, 4, 6, 8, 12, 24, and 48 h, and at 4, 7, 14, 21, 28, and 42 days. Blood samples were Subjects were orally administered a single oral dose of MR shipped to Spectra Clinical Research (Rockleigh, New Jersey) for all calcifediol (either 450 mg or 900 mg) or a single bolus IV injection analyses except determinations of serum calcifediol and 24,25- of calcifediol (448 mg). For the oral doses, 5 or 10 capsules (90 mg dihydroxyvitamin D for which samples were forwarded to each) were administered after an overnight fast with water inVentiv (Québec, QC, Canada) for analysis by a high performance (maximum 12 ounces) within 15 m. The MR capsules used in these liquid chromatographic method with tandem mass spectrometry clinical studies were similar to those used in the non-clinical detection (HPLC–MS/MS). Spectra determined the level of studies, also comprising a wax matrix to effect the more gradual 1,25-dihydroxyvitamin D in serum using an Immunodiagnostic release of calcifediol. In vitro dissolution testing showed that the Systems Ltd. (IDS) Enzyme Immuno Assay (EIA) kit.
Please cite this article in press as: M. Petkovich, et al., Modified-release oral calcifediol corrects vitamin D insufficiency with minimal CYP24A1 upregulation, J. Steroid Biochem. Mol. Biol. (2014),

SBMB 4321 No. of Pages 7 M. Petkovich et al. / Journal of Steroid Biochemistry & Molecular Biology xxx (2014) xxx–xxx Fig. 5. Effect of bolus IV or oral MR calcifediol administration on plasma iPTH levels in patients. Patients with stage 3 or 4CKD, SHPT and vitamin D insufficiency were treated with a single bolus IV injection of 448 mg calcifediol (solid circles) or single doses of oral MR calcifediol (450 mg–solid triangles; 900 mg–solid squares). Plasma samples obtained at the indicated time points were analyzed for iPTH. Data are corrected for baseline values. Plasma iPTH was not determined at 96-hours post-dose. Asterisk denotes significant difference between IV and MR treatment groups at 72 h. (P < 0.05).
2.3.4. Statistical analysis 6.9 and 14.2 ng/mL for the oral MR groups. Exposure was Differences between treatment groups were analyzed by a approximately dose-proportional with the oral MR 450 mg and one- or two-sided t-test, as appropriate, with statistical signifi- 900 mg doses.
cance set at p < 0.05.
2.4.2. Serum 1,25-dihydroxyvitamin D 2.4. Results of clinical studies Mean baseline concentrations of serum 1,25-dihydroxyvitamin D were 19.3, 21.2 and 26.5 pg/mL for the IV (448 mg) and MR 2.4.1. Serum calcifediol (450 mg and 900 mg) treatment groups, respectively. Mean The effects of single bolus IV versus oral MR administration of baseline-adjusted concentrations over the 96-hour post-dose calcifediol on baseline-adjusted serum calcifediol levels are period are shown for the three treatment groups in B.
shown in A for 0–96 h. Mean baseline concentrations were Following bolus IV calcifediol, mean concentration of serum 23.7 ng/mL for the 448-mg IV group and 18.3 and 18.7 ng/mL for 1,25-dihydroxyvitamin D rapidly increased by up to 13 pg/mL at the MR 450 mg and 900 mg groups, respectively. Peak mean 6 h post-dose. In contrast, mean concentrations in the oral MR calcifediol concentrations were observed at 0.5 h after bolus IV groups gradually increased and peaked at approximately 3 and dosing versus 13.1 and 13.6 h post-dose for oral MR dosing at 7 pg/mL over baseline, respectively, by 48 h post-dose. The mean 450 mg and 900 mg, respectively. Exposure to calcifediol, based on AUC was 7449 and 2530 pg.h/mL for the IV (448 mg) and MR observed area-under-the-curve (AUC) and maximum concentra- (900 mg) treatment groups, respectively, and these values did was far higher after IV than MR administration: mean not differ significantly. AUC in the 450 mg MR group was baseline corrected C 110.3 ng/mL for the IV group and Fig. 6. Effect of bolus IV or oral MR calcifediol administration on plasma 24,25-dihydroxyvitamin D levels in patients. Patients with stage 3 or 4 CKD, SHPT and vitamin D insufficiency were treated with a single bolus IV injection of 448 mg calcifediol (solid circles) or single doses of oral MR calcifediol (450 mg–solid triangles; 900 mg–solid squares). Plasma samples obtained at the indicated time points were analyzed for 24,25-dihydroxyvitamin D Data are expressed as percent of baseline values.
Asterisks denote significant differences between IV and MR treatment groups (P < 0.05).
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SBMB 4321 No. of Pages 7 M. Petkovich et al. / Journal of Steroid Biochemistry & Molecular Biology xxx (2014) xxx–xxx 2.4.3. Plasma iPTH suppressed. The faster calcifediol is supplied, the more calcitriol is Baseline levels of plasma iPTH were 184 pg/mL for the IV group, produced initially. The abrupt increase in serum calcifediol after and 168 and 238 pg/mL, respectively, for the MR 450 and 900 mg bolus IV dosing produced a corresponding surge in serum calcitriol, groups. Mean percent changes in iPTH from baseline were minimal which in turn triggered upregulation of CYP24A1 in both kidney over the post-dose period for the bolus IV and lower oral MR dose and parathyroid gland. Increased expression of CYP24A1 appears groups. However, mean percent reduction in plasma iPTH was to have attenuated the further rise of serum calcitriol (serum significant and sustained for the higher oral MR dose, reaching not measured) and, after approximately 20% between 24 and 72 h post-dose (No suppression of renal CYP27B1, drove serum calcitriol in the rats significant increases in serum calcium were observed in any back to baseline levels at 24 h post-dose. In contrast, MR dosing treatment group during the post-dose period (data not shown).
gradually increased both serum calcifediol and calcitriol, yielding calcitriol exposures that were greater in the rats and nearly 2.4.4. Serum 24,25-dihydroxyvitamin D equivalent in patients.
Baseline levels of 24,25-dihydroxyvitamin D In rats, the strong upregulation of CYP24A1 by bolus IV for the IV group, and 0.86 and 0.87 ng/mL, respectively, for the MR dosing appeared to have been triggered both by the rapid 450 and 900 mg groups. Mean values fluctuated around baseline increase in calcitriol levels and the significant elevation of for the MR 450 mg group and increased approximately 0.2 ng/mL FGF23 expression. These same factors may have also caused the for the MR 900 mg group. Mean values increased more dramati- almost complete and sustained suppression of renal CYP27B1.
cally over the course of the study for the IV group and reached Although, at the end of the treatment period, serum calcitriol levels approximately 1.0 ng/mL over baseline by two weeks post- returned to baseline levels, FGF23 remained elevated. We do dose, remaining at this level to the end of the study ).
not presently know the mechanism sustaining FGF23 levels; CYP27B1 expression and maintain CYP24A1 elevation. This FGF23 "memory" effect would be expected to have an impact Numerous non-clinical and clinical studies have investigated on the efficacy of subsequent dosing, further supporting gradual the therapeutic potential of vitamin D supplementation to control repletion over bolus treatments.
SHPT and manage metabolic bone disease in CKD patients .
Previous studies have demonstrated that increased expression Although there is general consensus that vitamin D repletion has of CYP24A1 in kidney and extra-renal target tissues is an important role in treating these patients, the body of published differentially regulated following increased calcitriol production literature shows that supplementation with cholecalciferol or . This differential regulation may depend on whether ergocalciferol is generally unreliable in correcting vitamin D the target tissue in question can respond to FGF23 and insufficiency and ineffective in controlling SHPT .
whether FGF23 levels have been increased by vitamin D Further, there is no consistent view regarding how vitamin D supplements should best be administered. Published studies have The observed PTH lowering in rats was equivalent at 24 h used daily doses of from 700 to 4000 IU/day, weekly doses of post-dose after both IV and MR dosing. However, we postulate that 5000 to 50,000 IU, and monthly doses of 50,000 to 300,000 IU.
PTH suppression would not have been sustained for much longer The impact of rate of administration on effectiveness of vitamin after IV dosing because CYP24A1 was increased in both kidney and D therapies has been poorly investigated. In this paper, we present parathyroid gland, serum FGF23 was elevated and CYP27B1 was results from parallel studies in which calcifediol was delivered suppressed. This is supported by the greater and more sustained either rapidly as an IV bolus, or gradually via an oral MR PTH suppression observed in CKD patients between 24 and 72 h formulation, to vitamin D deficient rats or patients with stage 3 after the 900 mg MR dose.
or 4 CKD, SHPT and vitamin D insufficiency. Our findings suggest Bolus IV administration of calcifediol induced a 40-fold surge in that rate of delivery is an important determinant of vitamin D kidney CYP24A1 expression by 4–8 h post-dose. This rapid hormone production, and therefore of therapeutic efficacy, and induction of CYP24A1 was similar to that observed previously in that gradual delivery allows more effective treatment of both rats (46-fold increase in kidney and 25-fold increase in intestine) vitamin D insufficiency and SHPT in CKD patients.
following 2.5 weeks of high-dose vitamin D (three treatments per In the presented studies, bolus IV calcifediol produced rapidly week of 25,000 IU each) This previous study demonstrated rising and higher drug exposures than oral MR calcifediol, due to a that consecutive rapid administrations of vitamin D progressively substantially faster calcifediol release rate and higher bioavailabil- raised CYP24A1 levels, attenuating the intended impact of ity. IV dosing also caused abrupt, large increases in serum treatment. Recent clinical studies have shown that treatment 1,25-dihydroxyvitamin D. In vitamin D deficient rats, IV dosing of CKD patients with bolus cholecalciferol results in a shift of triggered high expression of CYP24A1 and, subsequently, FGF23, vitamin D balance to net degradation with increased production of then near-complete suppression of CYP27B1 and significant iPTH 24,25-dihydroxyvitamin D reduced production of 1,25-dihydrox- lowering. MR calcifediol yielded equivalent iPTH suppression by yvitamin D and increased FGF23 expression . Consistent with gradually elevating drug exposure and had no dramatic impact on our findings, bolus cholecalciferol was not effective at suppressing serum 1,25-dihydroxyvitamin D, serum FGF23, CYP24A1 and iPTH. In our study, patients receiving bolus calcifediol exhibited CYP27B1. The gradual increase of CYP24A1 expression in the MR elevated and sustained production of 24,25-dihydroxyvitamin D treated animals is likely due to the gradual restoration of vitamin D This likely reflects elevated CYP24A1 expression both in the kidney status in these animals. In CKD patients, IV administration yielded as well as in other vitamin D target tissues, but the mechanism higher serum 24,25-dihydroxyvitamin D underlying continued production of 24,25-dihydroxyvitamin D greater CYP24A1 activity, but negligible PTH suppression. Con- over 42 days is unknown.
versely, MR administration gradually raised serum calcifediol and It is notable that both rat and patient responses to different 1,25-dihydroxyvitamin D without significantly elevating serum rates of calcifediol administration were similar. This supports the 24,25-dihydroxyvitamin D, and produced meaningful, sustained use of the model to further investigate mechanisms affecting the iPTH suppression.
efficacies of different vitamin D repletion regimens including Data from these studies indicate that renal production of comparisons between oral IR and MR formulations both in single- calcitriol is driven by the supply of calcifediol until CYP27B1 is dose and repeat dose studies.
Please cite this article in press as: M. Petkovich, et al., Modified-release oral calcifediol corrects vitamin D insufficiency with minimal CYP24A1 upregulation, J. Steroid Biochem. Mol. Biol. (2014), SBMB 4321 No. of Pages 7 M. Petkovich et al. / Journal of Steroid Biochemistry & Molecular Biology xxx (2014) xxx–xxx Taken together, the studies presented herein indicate that the rate at which vitamin D therapy is administered can have a significant impact on treatment outcomes. Further, they support continued investigation of MR calcifediol as a treatment of SHPT inpatients with CKD and vitamin D insufficiency.
Support for these studies was provided by OPKO Health, Renal Division. We thank Drs. Christian Helvig and Dominic Cuerrier for technical suggestions. M.P. is supported by funding from the Canadian Institutes of Health Research.
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