Metalloproteinase activity in growth plate chondrocyte cultures is regulated by 1,25-(OH)(2)D(3) and 24,25-(OH)(2)D(3) and mediated through protein kinase C.

During endochondral development, growth plate chondrocytes must remodel their matrix in a number of ways as they differentiate and mature. In previous studies, we have shown that matrix metalloproteinases (MMPs) extracted from matrix vesicles can extensively degrade aggrecan and that this is modulated by vitamin D metabolites in a manner involving protein kinase C (PKC). Matrix vesicles represent only a small component of the extracellular matrix, however, and it is unknown if the total metalloproteinase complement, including the MMPs and aggrecanases in the culture, is also regulated in a similar way. This study tested the hypothesis that vitamin D metabolites regulate the level of metalloproteinase activity in growth plate chondrocytes via a PKC-dependent mechanism and play a role in partitioning this proteinase activity between the media and cell layer (cells+matrix) in these cultures. To do this, resting zone cells (RC) were treated with 10(-9)-10(-7) M 24R,25-(OH)(2)D(3), while growth zone cells (GC) were treated with 10(-10)-10(-8) M 1alpha,25-(OH)(2)D(3). Cultures of both cell types were also treated with the PKC inhibitor chelerythrine in the presence and absence of vitamin D metabolites. At harvest, the media were either left untreated or treated to destroy metalloproteinase inhibitors, while enzyme activity in the cell layers was extracted with buffered guanidine and then treated like the media to destroy metalloproteinase inhibitors. Neutral metalloproteinase (aggrecan-degrading activity) activity was assayed on aggrecan-containing polyacrylamide gel beads and collagenase activity was measured on telopeptide-free type I collagen. Neutral metalloproteinase activity was found primarily in the cell layer of both cell types; however, activity was greater in extracts of GC cell layers. No collagenase activity could be detected in RC extracts until the metalloproteinase inhibitors were destroyed. In contrast, extracts of GC cell layers contained measurable activity without removing the inhibitors, and destroying the inhibitors resulted in a greater than two-fold increase in activity. No collagenase activity was found in the media of either cell type. 24,25-(OH)(2)D(3) caused a dose-dependent increase in neutral metalloproteinase activity in extracts of RC cells, but had no effect on collagenase activity. In contrast, 1,25-(OH)(2)D(3) caused a dose-dependent decrease in collagenase activity in extracts of GC cells, but had no effect on neutral metalloproteinase activity. In both cases, the effect of the vitamin D metabolite was mediated through the activation of PKC. These results support the hypothesis that metalloproteinases are involved in regulating the bulk turnover of collagen and aggrecan in growth plate chondrocytes and that the amount of metalloproteinase activity found is a function of the cell maturation state. Furthermore, 83-93% of neutral metalloproteinase activity and 100% of collagenase activity is localized to the cell layer. Moreover, the regulation of metalloproteinase activity by 1,25-(OH)(2)D(3) and 24,25-(OH)(2)D(3) involves a PKC-dependent pathway that is controlled by the target cell-specific vitamin D metabolite.     

Role of protein kinase C in 1,25(OH)(2)-vitamin D(3) modulation of intracellular calcium during development of skeletal muscle cells in culture

Regulation of muscle cell Ca(2+) metabolism by 1, 25-dihydroxy-vitamin D(3) [1,25(OH)(2)D(3)] is mediated by the classic nuclear mechanism and a fast, nongenomic mode of action that activates signal transduction pathways. The role of individual protein kinase C (PKC) isoforms in the regulation of intracellular Ca(2+) levels ([Ca(2+)](i)) by the hormone was investigated in cultured proliferating (myoblasts) and differentiated (myotubes) chick skeletal muscle cells. 1,25(OH)(2)D(3) (10(-9) M) induced a rapid (30- to 60-s) and sustained (>5-min) increase in [Ca(2+)](i) which was markedly higher in myotubes than in myoblasts. The effect was suppressed by the PKC inhibitor calphostin C. In differentiated cells, PKC activity increased in the particulate fraction and decreased in cytosol to a greater extent than in proliferating cells after 5-min treatment with 1,25(OH)(2)D(3). By Western blot analysis, these changes were correlated to translocation of the PKC alpha isoform from cytosol to the particulate fraction, which was more pronounced in myotubes than in myoblasts. Specific inhibition of PKC alpha activity using antibodies against this isoform decreased the 1, 25(OH)(2)D(3)-induced [Ca(2+)](i) sustained response associated with Ca(2+) influx through voltage-dependent calcium channels. Neomycin, a phospholipase C (PLC) inhibitor, blocked its effects on [Ca(2+)](i), PKC activity, and translocation of PKC alpha. Exposure of myotubes to 1,2-dioleyl-rac-glycerol (1,2-diolein), also increased [Ca(2+)](i), PKC activity, and the amount of PKC alpha associated with the particulate fraction. Changes in [Ca(2+)](i) induced by diolein were inhibited by calphostin C and nifedipine. The results indicate that PKC alpha activation via PLC-catalyzed phosphoinositide hydrolysis is part of the mechanism by which 1, 25(OH)(2)D(3) regulates muscle intracellular Ca(2+) through modulation of the Ca(2+) influx pathway of the Ca(2+) response to the sterol.     

Phosphate uptake in chick kidney cells: effects of 1,25(OH)2D3 and 24,25(OH)2D3

Phosphate homeostasis is controlled in part by absorption from the intestine, and reabsorption in the kidney. While the effect of Vitamin D metabolites on enterocytes is well documented, in the current study we assess selected responses in primary cultures of kidney cells. Time course studies revealed a rapid stimulation of phosphate uptake in cells treated with 1,25(OH)(2)D(3), relative to controls. Dose-response studies indicated a biphasic curve with optimal stimulation at 300 pM 1,25(OH)(2)D(3) and inhibition at 600 pM seco-steroid. Antibody 099--against the 1,25D(3)-MARRS receptor - abolished stimulation by the steroid hormone. Moreover, phosphate uptake was mediated by the protein kinase C pathway. The metabolite 24,25(OH)(2)D(3), which was found to inhibit the rapid stimulation of phosphate uptake in intestinal cells, had a parallel effect in cultured kidney cells. Finally, the 24,25(OH)(2)D(3) binding protein, catalase, was assessed for longer term down regulation. In both intestinal epithelial cells and kidney cells incubated with 24,25(OH)(2)D(3) for 5-24h, both the specific activity of the enzyme and protein levels were decreased relative to controls, while 1,25(OH)(2)D(3) increased both parameters over the same time periods. We conclude that the Vitamin D metabolites have similar effects in both kidney and intestine, and that 24,25(OH)(2)D(3) may have effects at the level of gene expression.     

24,25(OH)2D3 enhances the calcemic effect of 1,25(OH)2D3

The effect of 24,25(OH)2D3 on 1,25(OH)2D3-induced hypercalcemia was studied in normal rats. Serum (S) levels and urinary excretion of Ca2+ (UCaV) were measured in (a) control rats, (b) rats receiving a daily sc injection of 54 ng 1,25(OH)2D3, (c) rats receiving 24,25(OH)2D3 in the same dose and same manner, and (d) rats receiving 1,25(OH)2D3 + 24,25(OH)2D3. The animals were housed in metabolic cages and 24-hr urine specimens were collected. After 24 hr SCa2+ increased similarly with 1,25(OH)2D3 and with 1,25(OH)2D3 + 24,25(OH)2D3, while 24,25(OH)2D3 alone did not change SCa2+. UCaV after 24 hr increased significantly less (P less than 0.025) with 1,25(OH)2D3 + 24,25(OH)2D3 than with 1,25(OH)2D3 alone. After 5 days of 1,25(OH)2D3, SCa2+ rose from 5.1 +/- 0.15 to 6.29 +/- 0.08 whereas 1,25(OH)2D3 + 24,25(OH)2D3 effected a greater increase in SCa2+ up to 6.63 +/- 0.09 (P less than 0.01). 24,25(OH)2D3 alone did not change SCa2+. UCaV after 5 days of treatment rose similarly with 1,25(OH)2D3 and with 1,25(OH)2D3 + 24,25(OH)2D3. After 10 days of 1,25(OH)2D3 SCa2+ was 6.17 +/- 0.15 meq/liter while with the combination SCa2+ rose to 6.74 +/- 0.2 (P less than 0.025). 24,25(OH)2D3 alone did not change SCa2+. These results show that (a) 24,25(OH)2D3 alone does not alter SCa2+ in normal rats, (b) combined administration of 1,25(OH)2D3 + 24,25(OH)2D3 enhances the hypercalcemic response to 1,25(OH)2D3 without a parallel increase in UCaV, and (c) it is suggested that the effect of 24,25(OH)2D3 on serum Ca2+ level, at least partly, may result from its hypocalciuric effect.     

1,25-二羟维生素D3的生物学效应

1,25-二羟维生素D3是维生素D3的活性形式,其生物学效应是由基因组与非基因组两种机制介导的。维生素D3除了具有钙磷代谢调节作用外,还具有其他更为广泛的生物学效应。1,25-二羟维生素D3能够抑制多种类型细胞的增殖,诱导细胞的凋亡和分化,调节机体免疫系统功能,保护中枢神经系统,以及保护基因等。     

1,25(OH)2D3 increases calcium and phosphatidylinositol metabolism in differentiating cultured human keratinocytes

The effect of 1,25(OH)(2)D(3) on the intracellular calcium, (Ca(+2))i, in both cultured human keratinocytes and in cultured human dermal fibroblasts was investigated. When the intracellular calcium (Ca(+2))i in cultured human keratinocytes, grown in a serum-free medium containing 1.8 mM calcium, was measured by the fluorescent calcium-indicator, Furu-2, the (Ca(+2)i increased 154%, 202%, and 409% over the control value after incubation with 1,25(OH)(2)D(3) at 10(-10) m, 10(-8) m, and 10(-6) m, respectively. This response was immediate (15 seconds), specific (no effect with either 25(OH)D(3) at 10(-8) m or vitamin D(3) at 10(-8) m), and occurred with or without EGTA in the medium. In contrast, 1,25(OH)(2)D(3) did not increase the (Ca(2+))i in either cultured human keratinocytes that were grown in low calcium (0.05 mm), serum-free medium or in cultured human dermal fibroblasts that were grown in medium containing 0.05 mm calcium and 1% serum. The effect of 1,25(OH)(2)D(3) on the the turnover of phosphatidylinositol was investigated as a possible cause for the observed increase in (Ca(+2)i. Cultured human keratinocytes that were incubated with (3)H-inositol demonstrated a 50 % +/- 10% increase in the triphosphated, plasma membrane-bound metabolite of phosphatidylinositol, PIP(2), by 15 seconds, followed by a rapid decrease at 30 seconds, then a return toward basal levels by 1 minute. Lysophosphatidylinositol, which results from the sn-2 deacylation of phosphatidylinositol by phospholipase A(2), decreased 20% +/- 8% within 30 seconds, then increased to 200% +/- 10% of the control value by 5 minutes. The accumulation of IP(3) was increased 50% to 100% above the control value within 30 seconds and this increase was substained during the 5-minute incubation period. Stimulation of phosphatidylinositol turnover by 1,25(OH)(2)D(3) was not detected in either cultured human keratinocytes that were grown in serum-free, low calcium medium or in cultured human dermal fibroblasts that were grown in 1% serum.     

24,25(OH)2D3 enhances the calcemic effect of 1,25(OH)2D3 in PTX rats

The effect of 24,25(OH)2D3 on 1,25(OH)2D3-induced hypercalcemia was studied in parathyroidectomized (PTX) rats for 10 days. Serum (S) and urinary Ca excretion (UCaV) were measured in (a) control rats, (b) rats receiving a daily sc injection of 54 ng 1,25(OH)2D3, (c) rats receiving 24,25(OH)2D3 in the same dose and same manner, and (d) rats receiving 1,25(OH)2D3 + 24,25(OH)2D3. Our results show that (i) 24,25(OH)2D3 alone does not increase SCa2+ in PTX rats, (ii) combined administration of 1,25(OH)2D3 + 24,25(OH)2D3 enhances the hypercalcemic response to 1,25(OH)2D3 without a parallel increase in UCaV, (iii) combined administration of 1,25(OH)2D3 + 24,25(OH)2D3 reduces the rise in urinary excretion of Ca2+ compared with that of rats receiving 1,25(OH)2D3 alone for 10 days, and (iv) these alterations are independent of parathyroid hormone.     

Effects of 1,25(OH)2D3 and 25(OH)D3 on C2C12 Myoblast Proliferation,Differentiation, and Myotube Hypertrophy

An adequate vitamin D status is essential to optimize muscle strength. However, whether vitamin D directly reduces muscle fiber atrophy or stimulates muscle fiber hypertrophy remains subject of debate. A mechanism that may affect the role of vitamin D in the regulation of muscle fiber size is the local conversion of 25(OH)D to 1,25(OH)₂D by 1α‐hydroxylase. Therefore, we investigated in a murine C2C12 myoblast culture whether both 1,25(OH)₂D₃ and 25(OH)D₃ affect myoblast proliferation, differentiation, and myotube size and whether these cells are able to metabolize 25(OH)D₃ and 1,25(OH)₂D₃. We show that myoblasts not only responded to 1,25(OH)₂D₃, but also to the precursor 25(OH)D₃ by increasing their VDR mRNA expression and reducing their proliferation. In differentiating myoblasts and myotubes 1,25(OH)₂D₃ as well as 25(OH)D₃ stimulated VDR mRNA expression and in myotubes 1,25(OH)₂D₃ also stimulated MHC mRNA expression. However, this occurred without notable effects on myotube size. Moreover, no effects on the Akt/mTOR signaling pathway as well as MyoD and myogenin mRNA levels were observed. Interestingly, both myoblasts and myotubes expressed CYP27B1 and CYP24 mRNA which are required for vitamin D₃ metabolism. Although 1α‐hydroxylase activity could not be shown in myotubes, after treatment with 1,25(OH)₂D₃ or 25(OH)D₃ myotubes showed strongly elevated CYP24 mRNA levels compared to untreated cells. Moreover, myotubes were able to convert 25(OH)D₃ to 24R,25(OH)₂D₃ which may play a role in myoblast proliferation and differentiation. These data suggest that skeletal muscle is not only a direct target for vitamin D₃ metabolites, but is also able to metabolize 25(OH)D₃ and 1,25(OH)₂D₃. J. Cell. Physiol. 231: 2517–2528, 2016. © 2016 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.     

1,25(OH)2D3 increases cytosolic Ca++ concentration of osteoblastic cells, clone MC3T3-E1

Effect of 1,25(OH)2D3 in vitro on cytosolic Ca++ concentration of osteoblastic cells (MC3T3-E1) was studied. Marked but transient increase of cytosolic Ca++ concentration of osteoblastic cells was observed following the addition of 10 pg/ml of 1,25(OH)2D3, but not with 10 pg/ml of 24,25(OH)2D3. The increase of cytosolic Ca++ concentration of osteoblastic cells by 1,25(OH)2D3 was not observed when the cells were incubated in Ca++ free medium. Therefore, it was concluded that 1,25(OH)2D3 increased cytosolic Ca++ concentration of osteoblastic cells through the increase of Ca++ influx into the cells.     

24,25-(OH)2D3 regulates protein kinase C through two distinct phospholipid-dependent mechanisms

We have previously shown that 24,25-(OH)₂D₃ plays a major role in resting zone (RC) chondrocyte differentiation and that this vitamin D metabolite regulates protein kinase C (PKC). The aim of the present study was to identify the signal transduction pathway used by 24,25-(OH)₂D₃ to stimulate PKC activation. Confluent, fourth passage RC cells from rat costochondral cartilage were used to evaluate the mechanism of PKC activation. Treatment of RC cultures with 24,25-(OH)₂D₃ for 90 min produced a dose-dependent increase in diacylglycerol (DAG). Addition of R59022, a diacylglycerol kinase inhibitor, significantly increased PKC activity in cultures treated with 24,25-(OH)₂D₃. Addition of dioctanoylglycerol (DOG) to plasma membranes isolated from RC increased PKC activity 447-fold. Addition of pertussis toxin or cholera toxin to control cultures elevated basal PKC activity. When added together with 10⁻⁹ M 24,25-(OH)₂D₃, there was an additive effect on PKC activity but in cultures treated with 10⁻⁸ M 24,25-(OH)₂D₃, only the hormone-dependent stimulation of PKC was observed. The phospholipase C inhibitor, U73-122, had no effect on PKC activity, indicating that the DAG produced in response to 24,25-(OH)₂D₃ is not derived from phosphatidylinositol. Addition of the tyrosine kinase inhibitor, genistein, also had no effect on 24,25-(OH)₂D₃-stimulated PKC, further supporting the hypothesis that phospholipase C is not involved in the mechanism and that phospholipase D is responsible for the increase in DAG production. Phospholipase A₂ inhibitors, quinacrine and AACOCF3, and the cyclooxygenase inhibitor indomethacin increased PKC activity in the RC cultures. Exogenous PGE₂, one of the downstream products of phospholipase A₂ action, inhibited PKC activity. These results suggest that 24,25-(OH)₂D₃ regulates PKC activity by two distinct phospholipid-dependent mechanisms: production of DAG via phospholipase D and inhibition of the production of PGE₂ via inhibition of phospholipase A₂ and cyclooxygenase. © 1996 Wiley-Liss, Inc.     

Effect of ageing on the expression of protein kinase C and its activation by 1,25(OH)2-vitamin D3 in rat skeletal muscle

To characterize age-induced effects on muscle protein kinase C (PKC) and its regulation by the steroid hormone 1,25(OH)2-vitamin D3 [1,25(OH)2D3], changes in PKC activity and the expression and translocation of the specific PKC conventional isoforms alpha and beta, novel isoforms delta, epsilon, and theta and atypical isoform zeta were studied in homogenates and subcellular fractions from skeletal muscle of young (3 months) and aged (24 months) rats treated in vitro with 1,25(OH)2D3. The hormone (10(-9) M) increased total and membrane PKC activity, within 1 min, and these effects were completely blunted in muscle from aged rats. The presence of PKC isoenzymes was shown by Western blot analysis with the use of specific antibodies. The expression of PKC alpha, beta and delta was greatly diminished in old rats, whereas age-related changes were less pronounced in the isoforms epsilon, theta and zeta. After a short exposure (1 min) of muscle to 1,25(OH)2D3, increased amounts of PKC alpha and beta in muscle membranes and reverse translocation (from membrane to cytosol) of PKC epsilon were observed only in young animals. The data indicate that, in rat muscle, ageing impairs calcium-dependent PKC (alpha and beta) and calcium-independent PKC (delta, epsilon, theta and zeta) signal transduction pathways under selective regulation by 1,25(OH)2D3.     

Caffeine decreases vitamin D receptor protein expression and 1,25(OH)2D3 stimulated alkaline phosphatase activity in human osteoblast cells

Of the various risk factors contributing to osteoporosis, dietary/lifestyle factors are important. In a clinical study we reported that women with caffeine intakes >300 mg/day had higher bone loss and women with vitamin D receptor (VDR) variant, tt were at a greater risk for this deleterious effect of caffeine. However, the mechanism of how caffeine effects bone metabolism is not clear. 1,25-Dihydroxy vitamin D₃ (1,25(OH)₂D₃) plays a critical role in regulating bone metabolism. The receptor for 1,25(OH)₂D₃, VDR has been demonstrated in osteoblast cells and it belongs to the superfamily of nuclear hormone receptors. To understand the molecular mechanism of the role of caffeine in relation to bone, we tested the effect of caffeine on VDR expression and 1,25(OH)₂D₃ mediated actions in bone. We therefore examined the effect of different doses of caffeine (0.2, 0.5, 1.0 and 10 mM) on 1,25(OH)₂D₃ induced VDR protein expression in human osteoblast cells. We also tested the effect of different doses of caffeine on 1,25(OH)₂D₃ induced alkaline phosphatase (ALP) activity, a widely used marker of osteoblastic activity. Caffeine dose dependently decreased the 1,25(OH)₂D₃ induced VDR expression and at concentrations of 1 and 10 mM, VDR expression was decreased by about 50–70%, respectively. In addition, the 1,25(OH)₂D₃ induced alkaline phosphatase activity was also reduced at similar doses thus affecting the osteoblastic function. The basal ALP activity was not affected with increasing doses of caffeine. Overall, our results suggest that caffeine affects 1,25(OH)₂D₃ stimulated VDR protein expression and 1,25(OH)₂D₃ mediated actions in human osteoblast cells.     

Rapid effects of 1,25(OH)2 vitamin D3 on signal transduction systems in colonic cells.

Previous work from our laboratory demonstrated that 1,25(OH)2D3 rapidly stimulated hydrolysis of membrane polyphosphoinositides (PI) in rat colonocytes and in Caco-2 cells, generating the second messengers DAG and IP3. [Ca2+]i subsequently increased due to IP3-mediated release of intracellular Ca2+ stores, and to Ca2+ influx through a receptor-mediated Ca channel. Studies examining purified antipodal plasma membranes and experiments using Caco-2 cell monolayers found that 1,25(OH)2D3 influenced PI turnover only in the basolateral (BLM) and not brush border (BBM) membranes. Vitamin D analogues with poor affinity for the vitamin D receptor were found to effectively stimulate PI turnover, suggesting the presence of a unique vitamin D receptor in the BLM. Studies from our laboratory have demonstrated saturable, reversible binding of 1,25(OH)2 D3 to colonocyte BLM. Recently, we found that 1,25(OH)2D3 activated the tyrosine kinase c-src in colonocyte BLM by a heterotrimeric guanine nucleotide binding protein (G-protein)-dependent mechanism, with subsequent phosphorylation, translocation to the BLM, and activation of PI-specific phospholipase C gamma. Due to the rise in [Ca2+]i and DAG, two isoforms of protein kinase C (PKCalpha and PKCbeta2), but not other isoforms were activated by 1,25(OH)2D3 in rat colonocytes. Recent studies demonstrated that the seco-steroid translocated the beta2 isoform to the BLM, but not the BBM. In contrast, the alpha isoform did not translocate to either antipodal plasma membrane, but modulated IP3-mediated Ca2+ release from the endoplasmic reticulum. Preliminary studies have shown that 1,25(OH)2D3 also activated phosphatidylcholine phospholipase D (PLD) in Caco-2 cells, generating phosphatidic acid and contributing to the sustained rise in DAG. PLD stimulation occurred by both PKC-dependent and -independent mechanisms. Inhibitors of G-proteins, c-src, and PKC blunted the seco-steroid-mediated activation of PLD. Cells stably transfected with sense PKCalpha showed increased 1,25(OH)2D3-stimulated PLD activation, whereas transfectants with antisense PKCalpha had an attenuated response. In addition, 1,25(OH)2D3 also regulated PLD by activating the monomeric G-protein rho A by a mechanism independent of the G-protein/ c-src/PKC pathway.     

Mitochondrial alkaline phosphatase as an intracellular signal in the synthesis of 1,25(OH)2D3 and 24,25(OH)2D3 in LLC-PK1 cells

In previous works we have found a mitochondrial alkaline phosphatase (AP) activity in LLC-PK1. The aim of this work has been to study the possible involvement of mitochondrial AP activity in the synthesis of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) from the substrate 25(OH)D3. Renal phenotype LLC-PK1 cells were incubated with 25(OH)D3 as substrate and treated with or without 1,25(OH)2D3, forskolin, 12-myristate-13-acetate (PMA) and 1,25(OH)2D3 in conjunction with PMA. Incubation of LLC-PK1 cells with forskolin (adenylate cyclase activator) not only stimulated the 1-hydroxylase and inhibited the 24-hydroxylase activities but also increased the mitochondrial AP activity. The addition of 1,25(OH)2D3, the main activator of 24-hydroxylase, produced a decrease of mitochondrial AP activity, a decrease of 1,25(OH)2D3 synthesis and an increase of the 24,25(OH)2D3 synthesis. Incubation with PMA, a potent activator of protein kinase C, did not produce any changes in mitochondrial AP activity, but an inhibition of 1,25(OH)2D3 and an activation of 24,25(OH)2D3 synthesis were found. Moreover, incubation of LLC-PK1 cells with PMA in conjunction with 1,25(OH)2D3 produced an additive effect in the decrease of 1,25(OH)2D3 and an increase of 24,25(OH)2D3 synthesis remaining mitochondrial AP activity as cells treated only with 1,25(OH)2D3. Our results suggest that mitochondrial AP activity could be involved as an intracellular signal in the regulation of 25(OH)D3 metabolism to the synthesis of 1,25(OH)2D3 and 24,25(OH)2D3 in renal phenotype LLC-PK1 cells through cAMP protein kinase system.     

Biologic effect of 1,24(R)(OH)2D3 versus 1,25(OH)2D3 administration in chronic renal failure

1,24(R)(OH)2D3 is a synthetic analogue of 1,25(OH)2D3 which binds to the same receptors as the physiologic metabolite with a lower affinity. The aim of the present study was to compare the activity of 1,24(R)(OH)2D3 and 1,25(OH)2D3 on several target organs in patients with chronic renal failure. Treatment with 1,24(R)(OH)2D3 at doses of either 1 or 2 μg daily was carried out in two groups of 9 patients, with serum creatinine of 4.61 ± 1.59 and 4.66 ± 1.46 mg/dl, respectively. Doses of 1,25(OH)2D3 were 0.5 and 1 μg daily and were administered to 9 and 13 patients, serum creatinine of 4.52 ± 1.67 and 4.3 ± 1.16 mg/dl, respectively. Treatment periods were of 2 weeks. Administration of 1,25(OH)2D3, 1 μg, induced significant increments of intestinal calcium absorption (ICA), ionized calcium, osteocalcin, serum creatinine, urine Ca/GFR, and a decrease in iPTH. 1,25(OH)2D3, 0.5 μg, induced a significant increase in ICA and osteocalcin and a decrease in iPTH. Similarly 1,24(OH)2D3, 2 μg daily, significantly stimulated ICA and raised serum levels of osteocalcin and creatinine while lowering serum iPTH. In addition, 1,24(R)(OH)2D3 administration induced a significant fall of serum 1,25(OH)2D3. Following 1 μg, only osteocalcin increased. Therefore, the dose of 2 μg of 1,24(R)(OH)2D3 has biologic activity similar to 0.5 μg 1,25(OH)2D3 (4:1). However the activity ratio on osteocalcin production appears to be 2:1. In addition, 1,24(R)(OH)2D3 is able to inhibit renal tubular 1-hydroxylase. In conclusion 1,24(R)(OH)2D3 may prove to be useful in the treatment of metabolic bone disease.