Treatment of renal osteodystrophy in children with 1αOHD3 and 24, 25(OH)2D3

Three pediatric patients with renal osteodystrophy were treated with 1αOHD₃ and 24, 25(OH)₂D₃. While serum calcium level significantly decreased, no significant effects were found on serum phosphorus, alkaline phosphatase, parathyroid hormone and urinary excretion of calcium. These results suggest that 24, 25(OH)₂D₃ may play some roles in bone and mineral metabolism.     

Does 24R,25(OH)2-vitamin D3 prevent postmenopausal bone loss?

Summary The effect of oral 24R,25(OH)₂-vitamin D₃ as a prophylactic for postmenopausal bone loss was examined. Fifty-eight healthy, early postmeno-pausal women entered a double blind therapeutic trial for 2 years. After an initial examination the women were randomized to treatment with 10 μg 24R,25(OH)₂D₃ daily or placebo. Participants were thereafter examined every 3 months (nine examinations in all). In both groups the forearm bone mineral (measured by single photon absorptiometry), the lumbar spine mineral, and the total body mineral (measured by dual photon absorptiometry) fell significantly and the same magnitude. Further-more, serum calcium, serum alkaline phosphatase concentration, and fasting urinary hydroxyproline were unchanged, as were the 24-hour urinary calcium excretion and the intestinal radiocalcium absorption. Our findings demonstrate that 24R,25(OH)₂D₃ treatment has no prophylactic effect on postmenopausal bone loss and does not alter calcium metabolic variables.     

24,25-(OH)2D3 Regulation of Matrix Vesicle Protein Kinase C Occurs Both During Biosynthesis and in the Extracellular Matrix

Plasma membranes and matrix vesicles isolated from rat costochondral resting zone chondrocyte cultures contain predominantly protein kinase C alpha (PKCα) and PKCζ, respectively, and the level of PKC specific activity in these membrane fractions is regulated by 24,25-(OH)₂D₃ [14]. In the present study, we examined whether the effect of 24,25-(OH)₂D₃ on membrane PKC is via genomic mechanisms during biogenesis and through a nongenomic mechanism after the matrix vesicles are resident in the matrix. There was a dose-dependent decrease in matrix vesicle PKC specific activity and a significant increase in plasma membrane enzyme activity in cultures treated for 90 minutes with 10⁻⁹–10⁻⁷ M 24,25-(OH)₂D₃. However, at 12 hours, matrix vesicle PKC was stimulated, but no effect was seen in the plasma membranes, suggesting that the effect seen at 90 minutes was due to a direct action of the hormone on PKC activity in the membrane, and that the effect seen at 12 hours was due to new matrix vesicle production with altered PKC content. Neither actinomycin D nor cycloheximide inhibited matrix vesicle PKC at 30, 60, or 90 minutes, but by 12 hours, these inhibitors blocked the effect of the hormone. 24,25-(OH)₂D₃-dependent plasma membrane PKC was sensitive to both actinomycin D and cycloheximide at early time points, but by 12 hours, no effect of the inhibitors was seen. Monensin did not alter basal plasma membrane PKC activity or the 24,25-(OH)₂D₃-dependent increase, suggesting that this increase was due to translocation of cytosolic PKC rather than new membrane synthesis. Monensin did not affect matrix vesicle PKC at early time points, but it decreased 24,25-(OH)₂D₃-dependent enzyme activity at later times, indicating that new matrix vesicle production was blocked. At least part of the effect of 24,25-(OH)₂D₃ on PKC involved phospholipase A₂ (PA₂). Quinacrine (a PA₂ inhibitor) alone had no effect on matrix vesicle PKC, but in cultures treated for 12 hours with quinacrine and 24,25-(OH)₂D₃, a synergistic increase in matrix vesicle PKC was observed. Quinacrine caused a time-dependent decrease in matrix vesicle PKC and a dose- and time-dependent increase in plasma membrane PKC when incubated directly with the membranes, supporting the hypothesis that PA₂ plays a role in the nongenomic regulation of PKC by 24,25-(OH)₂D₃. Experiments using anti-isoform specific antibodies showed that 24,25-(OH)₂D₃ modulated the distribution of PKCα, β, and ζ between the plasma membrane and matrix vesicle compartments via translocation and new PKC synthesis. Thus, the data support the hypothesis that 24,25-(OH)₂D₃ regulates matrix vesicles through two pathways: a genomic one at the stage of biosynthesis and packaging, and a second nongenomic mechanism acting directly upon matrix vesicles in the matrix. These data also indicate that matrix vesicle regulation consists of complex events with several different points of regulation. Received: 11 October 1996 / Accepted: 25 April 1997     

Association among plasma 1,25(OH)2D,ratio of 1,25(OH)2D to 25(OH)D,and prostate cancer aggressiveness

Background

African-American (AA) men tend to present with more aggressive prostate cancer (Gleason score >7) than European-American (EA) men. Vitamin D and its metabolites are implicated in prostate cancer biology with vitamin D deficiency, indicated by its metabolite levels in serum or plasma, usually observed in AA men.

Objective

To determine if 1, 25-dihydroxy vitamin D3 [1,25(OH)₂D] plasma levels in AA and EA prostate cancer patients alter the risk of having aggressive prostate cancer.

Design

Research subjects from the North Carolina-Louisiana Prostate Cancer Project (AA n = 435 and EA n = 532) were included. Plasma metabolites 1,25(OH)₂D and 25-hydroxyvitamin D3 [25(OH)D] were measured using liquid chromatography with tandem mass spectrophotometry. Research subjects were classified into low (Gleason sum < 7, stage T1-T2, and Prostate-specific antigen (PSA) < 9 ng/mL) or high (Gleason sum > 8 or Gleason sum = 7 with 4 + 3, or PSA > 20 ng/mL, or Gleason sum = 7 and stage T3-T4) aggressive disease.

Results

Research subjects in the second and third tertiles of plasma levels of 1, 25(OH)₂D had lower odds of high aggressive prostate cancer (AA [OR_T2vsT1: 0.66, 95%CI: 0.39-1.12; OR_T3vsT1: 0.83, 95%CI: 0.49-1.41] and EA [OR_T2vsT1: 0.68, 95%CI: 0.41-1.11; OR_T3vsT1: 0.67, 95%CI: 0.40-1.11]) compared with the first tertile, though confidence intervals included the null. Greater 1,25(OH)₂D/25(OH)D molar ratios were associated with lower odds of high aggressive prostate cancer more evidently in AA (OR_Q4vsQ1: 0.45, CI: 0.24-0.82) than in EA (OR_Q4vsQ1: 0.64, CI: 0.35-1.17) research subjects.

Conclusions

The 1,25(OH)₂D/25(OH)D molar ratio was associated with decreased risk of high aggressive prostate cancer in AA men, and possibly in EA men. Further studies analyzing vitamin D polymorphisms, vitamin D binding protein levels, and prostatic levels of these metabolites may be useful. These studies may provide a better understanding of the vitamin D pathway and its biological role underlying health disparities in prostate cancer.

     

Demonstration that the vitamin D metabolite 1,25(OH)2-vitamin D3 and not 24R,25(OH)2-vitamin D3 is essential for normal insulin secretion in the perfused rat pancreas

It has previously been shown that vitamin D deficiency impairs arginine-induced insulin secretion from the isolated, perfused rat pancreas (Science 1980; 209:823-25). Since vitamin D is known to be metabolized to 1,25-dihydroxyvitamin D3 (1,25[OH]2D3) and 24R,25-dihydroxyvitamin D3 (24,25[OH]2D3), it is essential to clarify which vitamin D metabolite has the important role of enhancing insulin secretion. In this report, a comparison is made of the relative efficacy of 3-wk repletion with vitamin D3 (980 pmol/day), 1,25(OH)2D3 (39 pmol/day or 195 pmol/day), and 24,25(OH)2D3 (650 pmol/day) on arginine-induced insulin secretion from the isolated, perfused rat pancreas; in this experiment, the daily caloric intake of the animals receiving vitamin D or its metabolites was controlled by pair feeding to the caloric intake of the vitamin D-deficient rats. 1,25(OH)2D3 repletion was found to completely restore insulin secretion to the levels seen in vitamin D3-replete, pair-fed controls in both the first and second phases, while 24R,25(OH)2D3 only partially improved insulin secretion, and then only in the first phase. Changes of both serum calcium levels and dietary caloric intake after vitamin D metabolite administration are concluded to play a lesser role on the enhancement of insulin secretion, since, in a separate experiment, vitamin D-deficient rats with normal serum calcium levels did not show recovery of insulin secretion equivalent to the vitamin D-replete animals under conditions of dietary pair feeding. These results suggest that 1,25(OH)2D3 but not 24,25(OH)2D3 plays an essential role in the normal insulin secretion irrespective of the dietary caloric intake and prevailing serum calcium levels.     

Inhibitory Effects of 1,25(OH)2D3 on Membrane-Associated and Cytosolic Casein Kinase Activity in MC3T3-E1 Osteoblast-like Cells

The secretion of phosphorylated matrix proteins is high in osteoblasts. Phosphorylation of these proteins may be catalyzed by casein kinases (CK), and CK may play an important role in the site of bone mineralization. In this study, we examined the effects of 1,25(OH)₂D₃ on CK activities in MC3T3-E1 osteoblast-like cells. Different concentrations (ranging from 10⁻⁷ to 10⁻¹¹M) of 1,25(OH)₂D₃ were included in a culture medium. After incubation for various lengths of time, MC3T3-E1 cells were homogenized and segregated into cytosolic (c) and microsomal (m) fractions. To measure CK activity, each fraction was used as an enzyme source to phosphorylate casein. MC3T3-E1 cells showed the highest cCK activity after incubation for 21 days, and showed the highest mCK activity after incubation for 14 days. 1,25(OH)₂D₃ inhibited mCK activity at the early stage of culture, but inhibited cCK activity at the late stage of culture. In contrast, 1,25(OH)₂D₃ had a slight stimulatory effect on CK activity in the culture medium of MC3T3-E1 cells. Our data suggest that cCK and mCK may play different roles in the function of osteoblasts, and 1,25(OH)₂D₃ regulates intracellular and extracellular casein kinase activities related to the function of osteoblasts. Received: 26 June 1997 / Accepted: 23 March 1998     

Increase of bone volume in vitamin D-repleted rats by massive administration of 24R,25(OH)2D3

Summary A large dose of 24R,25(OH)₂D₃ was administered to the vitamin D-repleted rat to examine its effect on the bone. Male Wistar rats were fed a diet containing 0, 0.025, 1.25, 4.0, and 12.5 ppm 24R,25(OH)₂D₃ for 2 years starting at age 6 weeks. The estimated amounts of daily intake of 24R,25(OH)₂D₃ were 0, 93, 4640, 14680, and 49580 ng/100 g body weight, respectively. No notable difference was found in either the weight or the death rate of the animal. The long-term administration of massive doses of 24R,25(OH)₂D₃ did not lead to hypercalcemia nor did it affect the blood phosphorus, alkaline-phosphatase, or creatinine levels. Radiographs revealed a striking increase in the bone density on the bones from the animals treated with 1.25 ppm or more 24R,25(OH)₂D₃. Direct single photon absorptiometry revealed a dose-dependent increase in total bone minerals of both the femur and coccyx. Histological examination revealed a marked increase in the cortical thickness of the femur as well as in the cancellous bone volume of the coccyx. Polarizing microscopy demonstrated the lamellar structure of the bone, and undecalcified sections confirmed the increase of mineralized bone. Ash weight, calcium, phosphorus, and magnesium contents on the tibia and fibula also indicated the ascending dose-dependent increase up to 150% of the control. The parameters of bone size were not altered in any group. These results clearly suggest that 24R,25(OH)₂D₃ given in massive doses has the pharmacological action of increasing bone volume in the rat without causing remarkable hypercalcemia.     

Effect of 1 alpha, 25(OH)2D3 on experimental rat nephrotoxic serum nephritis

We studied immunoregulatory effects of 1 alpha, 25(OH)2D3 in vivo using experimental rat nephrotoxic serum nephritis (NTSN). Experimental rats were divided into 3 groups according to the doses of 1 alpha (OH)D3, i.e. the control group (untreated group), the D30.02 group (0.02 microgram/Kg/day), and D30.5 group (0.5 microgram/Kg/day). The present study demonstrated that rats with NTSN receiving 0.5 microgram/Kg/day of 1 alpha (OH)D3 showed much lower urinary protein excretion as well as lesser histopathological changes in both heterologous and autologous phase as compared with rats without such treatments. On the other hand, the results in the D30.02 group varied. And also, the following were demonstrated in the D30.5 group as compared with the control group: 1) CH50 levels were maintained almost normally, 2) the staining of rat C3 was clearly lesser, 3) the number of intraglomerular OX41 and W3/13 labelled cells was significantly lower, 4) the response of cultured spleen lymphocytes stimulated with ConA and LPS was clearly inhibited, 5) the helper T cell/suppressor T cell ratio was lower, and 6) the staining of rat IgG was lesser. Therefore, it was speculated that the inhibitory effects of 1 alpha, 25(OH)2D3 on complement activation might play important roles. And also, we postulated that the following mechanisms were involved: 1) the inhibition of antibody generation due to the blocking of T lymphocyte proliferation and functions and; 2) the inhibition of intraglomerular macrophage infiltration caused by blocking of T lymphocyte functions. In conclusion, our study indicated that 1 alpha, 25(OH)2D3 had a new facet of immunoregulatory function in experimental rat NTSN.     

Maleic acid-induced impaired conversion of 25(OH)D3 to 1,25(OH)2D3: implications for Fanconi's syndrome

Conversion of 25-hydroxyvitamin D3 [25(OH)D3] to 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] occurs exclusively in the renal cortex. To determine whether a disorder of the renal cortical tubule capable of causing Fanconi's syndrome can also impair the synthesis of 1,25(OH)2D3, we investigated whether conversion of 25(OH)D3 to 1,25(OH)2D3 was reduced by maleic acid. In vitamin D-deficient rats, maleic acid was administered i.v. over two hours. Thirty minutes after its initiation, when the complex renal tubule dysfunction had occurred, 3H-25(OH)D3 was administered i.v. as a bolus. Five hours afterwards, the amount of 3H-1,25(OH)2D3 recovered in the kidney, small intestine mucosa, and blood was one-third to one-half that in tissues of control rats that received acetazolamide or only saline or were subjected only to the surgical procedure. The glomerular filtration rate, as measured by inulin clearance, did not decrease significantly with maleic acid. In intact vitamin D-deficient chicks, 24 and 22 hr after i.p. administration of maleic acid and 14C-vitamin D3, respectively, the amount of 14C-1,25(OH)2D3 recovered in small intestine mucosa was reduced by one-half when compared to saline-treated controls. In kidney homogenates and isolated renal tubules of vitamin D-deficient chicks, activity of 25-hydroxyvitamin D3-1-hydroxylase was diminished immediately after maleic acid was administered in vivo or added in vitro to the incubation medium, respectively. These data provide the first demonstration that the renal capacity to convert 25(OH)D3 to 1,25(OH)2D3 can be substantially impaired in vivo by a renal disorder in which the glomerular filtration rate is not reduced.     

1Alpha,25-dihydroxyvitamin D(3) - not just a calciotropic hormone

1Alpha,25-dihydroxyvitamin D(3), the hormonal form of vitamin D(3), is widely appreciated to play a central role in calcium and phosphorous homeostasis. It is becoming increasingly clear, however, that the sterol also plays an important role in the regulation of cellular growth, central nervous system function, and immune responsiveness. In this review, I will highlight some of the mechanisms by which 1alpha,25-dihydroxyvitamin D(3) regulates cellular growth, alters central nervous system function, and immune function.     

Osteonal remodeling and mechanical properties of the femoral cortex in rabbits treated with 24R,25(OH)2D3

Summary The increase of bone mass by therapeutics does not always mean the enhancement of bone quality. The purpose of this study is to clarify the changes of osteonal remodeling and the mechanical properties of femoral cortex in rabbits treated with 24 R, 25 (OH)₂D₃. Fifteen NZW rabbits (3 kg B.W.) were divided into three groups of 5 animals each. Groups 1, 2, and 3 were given vehicle, 10 g/kg, and 100 g/kg 24R,25(OH)₂D₃, respectively, daily for 8 weeks. At the end of the experiment, the left femur was removed and bone mineral content (BMC) was measured with single photon absorptiometry. Serum 24,25(OH)₂D concentrations reached levels of approximately 15 and 200 times that of the controls in groups 2 and 3, respectively. Neither 25(OH)D nor 1,25(OH)₂D level showed any significant change in either group. Group 3 showed significant increase in mineral content and density in the epimetaphyseal regions, but the increase at the diaphyseal region did not reach a statistically significant level. Mechanical test for torsion was conducted for mid-cortical regions. After the test, bone pieces were bonded together with adhesive to reconstruct the original form, and undecalcified cross-sectional sections were made at the diaphyses. Fluorescent microscopy disclosed a marked reduction of remodeling in secondary osteonal bone area. The numbers for double-labeled osteons for groups 1, 2, and 3 were 2.47±0.819, 1.14±1.02^* and 0.137±0.307^* N/mm², respectively, and the numbers for osteons with resorption lacunae were 1.37±0.721, 0.412±0.370^* and 0.268±0.339^** N/mm², respectively. However, neither structural stiffness nor strength correlated with the indices of osteonal remodeling; instead, they were significantly correlated with bone mineral contents. Normalized mechanical parameters for torsion were almost the same for all three groups. This study clearly demonstrated that reduced osteonal remodeling by 24R,25(OD)₂D₃ does not affect the mechanical properties of the cortex, and the increase in bone density by the agent is considered to be accompanied by an increase in its mechanical strength (^* P< 0.05, ^** P< 0.01).     

Oral supplementation with 25(OH)D3 versus vitamin D3: Effects on 25(OH)D levels,lower extremity function,blood pressure,and markers of innate immunity

To test the effect of 25(OH)D₃ (HyD) compared to vitamin D₃ on serum 25‐hydroxyvitamin D levels (25(OH)D), lower extremity function, blood pressure, and markers of innate immunity. Twenty healthy postmenopausal women with an average 25(OH)D level of 13.2 ± 3.9 ng/mL (mean ± SD) and a mean age of 61.5 ± 7.2 years were randomized to either 20 µg of HyD or 20 µg (800 IU) of vitamin D₃ per day in a double‐blind manner. We measured on 14 visits over 4 months, 25(OH)D serum levels, blood pressure, and seven markers of innate immunity (eotaxin, interleukin [IL]‐8, IL‐12, interferon gamma‐induced protein 10 kDa [IP‐10], monocyte chemotactic protein‐1 [MCP‐1], macrophage inflammatory protein beta [MIP‐1β], and “Regulated upon Activation, Normal T‐cell Expressed, and Secreted” [RANTES]). At baseline and at 4 months, a test battery for lower extremity function (knee extensor and flexor strength, timed up and go, repeated sit‐to‐stand) was assessed. All analyses were adjusted for baseline measurement, age, and body mass index. Mean 25(OH)D levels increased to 69.5 ng/mL in the HyD group. This rise was immediate and sustained. Mean 25(OH)D levels increased to 31.0 ng/mL with a slow increase in the vitamin D₃ group. Women on HyD compared with vitamin D₃ had a 2.8‐fold increased odds of maintained or improved lower extremity function (odds ratio [OR] = 2.79; 95% confidence interval [CI], 1.18–6.58), and a 5.7‐mmHg decrease in systolic blood pressure (p = 0.0002). Both types of vitamin D contributed to a decrease in five out of seven markers of innate immunity, significantly more pronounced with HyD for eotaxin, IL‐12, MCP‐1, and MIP‐1 β. There were no cases of hypercalcemia at any time point. Twenty micrograms (20 µg) of HyD per day resulted in a safe, immediate, and sustained increase in 25(OH)D serum levels in all participants, which may explain its significant benefit on lower extremity function, systolic blood pressure, and innate immune response compared with vitamin D₃. © 2012 American Society for Bone and Mineral Research     

Loss via peritoneal fluid as a factor for low 25(OH)D3 level in peritoneal dialysis patients

Background/aims  

In patients with end-stage renal disease (ESRD), the 25-hydroxyvitamin D3 (25(OH)D3) level is known to be lower compared to that of the normal population. In the present study, we evaluated the influences of dialysis methods on the serum 25(OH)D3 level in patients with ESRD who are treated with hemodialysis and peritoneal dialysis.