Vitamin D metabolism and bone histomorphometry in a patient with antacid-induced osteomalacia

A patient with hypophosphatemic osteomalacia secondary to ingestion of large amounts of phosphate-binding antacids is presented. Vitamin D metabolites were measured during the course of his illness and recovery and demonstrated an initially elevated concentration of 1,25-dihydroxyvitamin D, an undetectable level of 24,25-dihydroxyvitamin D, and a normal level of 25-hydroxyvitamin D. These metabolites returned to normal levels when the hypophosphatemia was corrected. Bone histomorphometry showed osteomalacia with increased resorption. The possible role of altered vitamin D metabolism in the pathogenesis of this disorder is discussed.

Production of C-24- and C-23-oxidized metabolites of 1,25-dihydroxycholecalciferol by cultured kidney cells (LLC PK1) and their presence in kidney in vivo

1,25-Dihydroxy[3H]cholecalciferol was converted into several more-polar metabolites by a cultured pig kidney cell line (LLC PK1). The production of metabolites was stimulated by pretreating the cells with unlabelled 1,25-dihydroxycholecalciferol. A similar profile of metabolites was observed on high-pressure-liquid-chromatographic analysis of an extract from the kidneys of rats dosed intravenously with 1,25-dihydroxy[3H]cholecalciferol. Among the metabolites detected were 1,24,25-trihydroxycholecalciferol, 1,25-dihydroxy-24-oxocholecalciferol, 1,23,25-trihydroxy-24-oxocholecalciferol and 1,25-dihydroxycholecalciferol-26,23-lactone. The results are in accord with data reported for intestinal 1,25-dihydroxycholecalciferol metabolism [Napoli, Pramanik, Royal, Reinhardt & Horst (1983) J. Biol. Chem. 258, 9100-9107]. These data indicate that C-23- and C-24-oxidation of 1,25-dihydroxycholecalciferol are phenomena common to calciferol target tissues, and that regulation of 1,25-dihydroxycholecalciferol homoeostasis is dependent on the rate of its metabolism in addition to the rate of its synthesis.

Extrarenal metabolism of 25-hydroxycholecalciferol in the rat: regulation by 1,25-dihydroxycholecalciferol

To determine the role of the kidney in regulation of 25-hydroxycholecalciferol (25OHD3, metabolism, the effects of 1,25-dihydroxycholecalciferol [1,25(OH)2D3] on 3H-25OHD3 were compared in intact and nephrectomized vitamin D-deficient rats. Sixteen hours after the intravenous administration of 3H-25OHD3, extracts of serum and pooled small intestinal mucosa were fractionated by Sephadex LH-20 column chromatography followed by high performance liquid chromatography. In intact rats, 1,25(OH)2D3 (50 ng/day i.p. for 7 days) increased mean serum 3H-24,25-dihydroxycholecalciferol [3H-24,25(OH)2D3] from 2 +/- 2-210 +/- 80 fmol/ml (mean +/- 1 SD), increased mean serum 3H-25,26-dihydroxycholecalciferol [3H-25,26(OH)2D3] from 2 +/- 2-12 +/- 6 fmol/ml and lowered mean serum 3H-1,25(OH)2D3 from 210 +/- 40-4 +/- 4 fmol/ml. Similarly, in nephrectomized animals, 1,25(OH)2D3 increased mean serum 3H-24,25-(OH)2D3 from 6 +/- 11-115 +/- 30 fmol/ml and increased mean serum 3H-25,26(OH)2D3 from 3 +/- 3-26 +/- 10 fmol/ml. Nephrectomy increased serum 3H-25(OH)D3 in untreated (from 1450 +/- 225-2675 +/- 225 fmol/ml serum) and 1,25(OH)2D3 treated rats (from 1600 +/- 175-3075 +/- 100 fmol/ml). 3H-1,25(OH)2D3 averaged 74 +/- 16% of total radioactivity in intestinal mucosa of untreated intact rats and was not detected in either the serum or intestinal mucosa of nephrectomized animals. The results suggest that in intact animals, extrarenal synthesis can account for substantial 24,25(OH)2D3 production and for most 25,26(OH)2D3 production.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation, identification, and metabolism of (23S,25R)-25-hydroxyvitamin D3 26,23-lactol. A biosynthetic precursor of (23S,25R)-25-hydroxyvitamin D3 26,23-lactone

23S,25R,26-Trihydroxyvitamin D3 and (23S,25R)-25-hydroxyvitamin D3 26,23-lactol were chemically synthesized, and the metabolism of the two compounds to (23S,25R)-25-hydroxyvitamin D3 26,23-lactone in chick kidney homogenates was studied. 23S,25R,26-trihydroxyvitamin D3 was efficiently metabolized to the lactone in kidney homogenates from vitamin D-supplemented chicks, but not from vitamin D-deficient chicks. In contrast, the (23S,25R)-25-hydroxyvitamin D3 26,23-lactol was converted to the lactone in kidney homogenates regardless of the vitamin D status of the animals used. A new metabolite was isolated in pure form from the incubation mixture of 23S,25R,26-trihydroxyvitamin D3 with kidney homogenates prepared from vitamin D-supplemented chicks. The metabolite was identified as (23S,25R)-25-hydroxyvitamin D3 26,23-lactol by its ultraviolet and mass spectra and by derivatization. The structure was confirmed by direct comparison with an authentic sample on high pressure liquid chromatography. The evidence suggests that the stereochemistries of the isolated lactol at the 23- and 25-positions are S and R, respectively.

Stereo-retained and stereo-selective lactonization of four diastereoisomers of 23,25,26-trihydroxyvitamin D3 in homogenates of kidney from vitamin D-supplemented chicks

To elucidate the biosynthesis of 25-hydroxyvitamin D3-26,23-lactone, various vitamin D3 derivatives were incubated individually with kidney homogenates prepared from vitamin D3-supplemented chicks, a preparation known to produce the 25-hydroxyvitamin D3-26,23-lactone from 25-hydroxyvitamin D3. The 25-hydroxyvitamin D3-26, 23-lactone produced in vitro was then separated, purified, identified, and quantitated by consecutive analysis by high-pressure liquid chromatography. The naturally occurring 23(S), 25(R)-25-hydroxyvitamin D3-26,23-lactone was produced from 23(S),25-dihydroxyvitamin D3, 25(R),26-dihydroxyvitamin D3, and 23(S),25(R),26-trihydroxyvitamin D3. 23(S),25 (S)-25-Hydroxyvitamin D3-26,23-lactone was synthesized from 25(S),26-dihydroxyvitamin D3 and 23(S),25(S),26-trihydroxyvitamin D3. The relative amounts of 25-hydroxyvitamin D3-26,23-lactones generated from the following vitamin D3 derivatives used as substrate (23(S),25(S),26-trihydroxyvitamin D3; 23(R),25(R),26-trihydroxyvitamin D3; 23(S),25(R),26-trihydroxyvitamin D3; 23(R),25(S),26-trihydroxyvitamin D3; 23(S), 25-dihydroxyvitamin D3; 23(R),25-dihydroxyvitamin D3; 25(S),26-dihydroxyvitamin D3; and 25(R),26-dihydroxyvitamin D3) are, respectively, 15:1.7:24:3.3:2.5:0:1:1.7. These results indicate that when the lactonization at C-23 and C-26 positions of various vitamin D3 derivatives occurred the stereochemical configuration at their C-23 and/or C-25 positions was not changed and the difference of the stereochemical configurations determined the rate of lactonization.

Opposing effects of cyclic adenosine-3',5'-monophosphate and cyclic guanosine-3',5'-monophosphate on the metabolism of 24-hydroxyvitamin D3 in isolated chick renal tubules

The conversion of 25-hydroxyvitamin D3 (25 OH D3) to 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3), 24,25-dihydroxyvitamin D3 (24,25-(OH)2D3) and 1,24,25-trihydroxyvitamin D3 (1.24,25-(OH)3D3) was studied in renal tubules prepared from chicks raised on a vitamin D deficient diet with or without vitamin D supplementation. As described previously, in tubules from vitamin D deficient chicks, cyclic AMP caused an increase in the net accumulation of 1,25-(OH)2D3, the major metabolite formed under these circumstances. This stimulation was shown to be due to an increased maximum velocity of the hydroxylation reaction. There was also a significant inhibition of the net accumulation of 24,25-(OH)2D3. Cyclic GMP caused a significant inhibition of 1,25-(OH)2D3 formation and stimulation of the net accumulation of 24,25-(OH)2D3. In chicks supplemented with high doses of vitamin D, 24,25-(OH)2D3 was the major metabolite of 25 OH D3 detected and 1-hydroxylase activity was negligible. Under these circumstances, neither cyclic AMP nor cyclic GMP affected net accumulation of 24,25(OH)2D3. This suggested that the apparent effect of the nucleotides on formation of 24,25-(OH)2D3 may have been due to further metabolism of 24,25-(OH)2D3 when 1-hydroxylase activity was high. It is concluded that cyclic AMp and cyclic GMP have reciprocal effects on renal 25 OH D3-1-hydroxylase activity, and both should be considered potential intracellular regulators of 25 OH D3 metabolism.

Biological activity assessment of the vitamin D metabolites 1,25-dihydroxy-24-oxo-vitamin D3 and 1,23,25-trihydroxy-24-oxo-vitamin D3

Two new metabolites of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], namely 1,25(OH)2-24-oxo-vitamin D3 and 1,23,25(OH)3-24-oxo-vitamin D3, have been prepared in vitro using chick intestinal mucosal homogenates. To investigate the binding of 1,25(OH)2-[23-3H]-24-oxo-D3 and 1,23,25(OH)3-[23-3H]-24-oxo-D3 to the chick intestinal receptor we have isolated both metabolites in radioactive form using an incubation system containing 1,25(OH)2-[23,24-3H))-D3 with a specific radioactivity of 5.6 Ci/mmol. Both metabolites were highly purified by using Sephadex LH-20 chromatography followed by high-pressure liquid chromatography (HPLC). Sucrose density gradient sedimentation analysis showed specific binding of both tritium-labeled metabolites to the chick intestinal cytosol receptor. Experiments were carried out to determine the relative effectiveness of binding to the chick intestinal mucosa receptor for 1,25(OH)2D3. The results are expressed as relative competitive index (RCI), where the RCI is defined as 100 for 1,25(OH)2D3. Whereas the RCI obtained for 1,25(OH)2-24-oxo-D3 was 98 +/- 2 (SE), the RCI for 1,23,25(OH)3-24-oxo-D3 was only 28 +/- 6 (SE). Also, the biological activity of both new metabolites was assessed in vivo in the chick. In our assay for intestinal calcium absorption, 1,25(OH)2-24-oxo-D3 was active at a dose level of 1.63 and 4.88 nmol/bird (at 14 h), whereas 1,23,25(OH)3-24-oxo-D3 showed only weak biological activity in this system. In our assay for bone calcium mobilization, administration of both new metabolites showed modest activity at the 4.88-nmol dose level, which was reduced at the 1.63-nmol dose level. The results indicate that biological activity declines as 1,25(OH)2D3 is metabolized to 1,24R,25(OH)3D3, 1,25(OH)2-24-oxo-D3, and then 1,23,25(OH)3-24-oxo-D3.

Nutrient and mineral retention and vitamin D absorption in low-birth-weight infants: effect of medium-chain triglycerides

A randomized prospective study of the effect of medium-chain triglycerides (MCT) upon the absorption and retention of major minerals and nutrients, as well as upon 25-hydroxy vitamin D levels, was performed in low-birth-weight infants. Ten infants received a high-calcium and vitamin D-containing formula, which contained 50% of its fat as MCT, while ten other infants received a similar formula in which all the fat was in long-chain triglycerides. There was a five-day delay in reaching full oral feeding volumes, and therefore there was a delay in the onset of the balance study in the MCT group, primarily due to gastrointestinal symptoms. There was a significant improvement in the percent of fat absorption (P less than .05) with MCT, but no difference in the percent of absorption or retention of calcium, phosphorus, sodium, or nitrogen. 25-Hydroxy vitamin D levels decreased in both groups after full oral feeding volumes had been established, but all values were within normal ranges. At the high intake levels of calcium and vitamin D given to the infants, MCT did not increase major mineral or nutrient absorption.

The stereochemical configuration of the natural 23,25,26-trihydroxyvitamin D3

Four possible diastereoisomers of 23,25,26-trihydroxyvitamin D3 were synthesized and compared with the natural metabolite. The 4 synthetic diastereoisomers could be separated into 4 peaks by high-performance liquid chromatography. The natural 23,25,26-trihydroxyvitamin D3 comigrated with 23(S),25(R),26-trihydroxyvitamin D3. This result unequivocally demonstrates that the stereochemistry of the natural 23,25,26-trihydroxyvitamin D3 has the 23(S) and 25(R) configuration.

The effects of calciferol and its metabolites on patients with chronic renal failure. II. Calcitriol, 1 alpha-hydroxyvitamin D3, and 24,25-dihydroxyvitamin D3

The available data with regard to the use of calcitriol, 1 alpha-hydroxyvitamin D3 (1 alpha-OH D3), and 24,25-dihydroxyvitamin D3 (24,25-[OH]2D3) in the management of chronic renal insufficiency are reviewed. Patients with mild to moderate osteitis fibrosa experience substantial improvement with either calcitriol or 1 alpha-OH D3 therapy. However, few patients experience a reversal to normal in histologic characteristics of bone. The conditions of patients with osteomalacia do not respond to either calcitriol or 1 alpha-OH D3 therapy. The bone lesion appearing in these patients is most likely a toxic effect of aluminum. The prognosis is usually poor, but the conditions of some patients may respond to administration of 24,25-(OH)2D3 together with calcitriol. Preliminary data suggest that use of chelating agents may be beneficial. In this group of patients, 24,25-(OH)2D3 administration together with calcitriol may be beneficial.

Effect of aluminum on normal and uremic rats: tissue distribution, vitamin D metabolites, and quantitative bone histology

The effects of intraperitoneal aluminum chloride (1.5 mg aluminum/kg/day for 9 weeks) were studied in normal and uremic rats. Parameters measured included tissue aluminum, serum vitamin D metabolites, and quantitative bone histology. Aluminum administration increased tissue concentrations of this metal in uremic and nonuremic animals. Bone aluminum concentrations were higher in uremic rats (121 +/- 27 mg/kg compared to 47 +/- 4), whereas liver values were higher in the nonuremic group (175 +/- 47 mg/kg compared to 100 +/- 36). Serum concentrations of 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D were reduced in uremia, but aluminum was without apparent effect on any vitamin D metabolite. Aluminum, in the doses administered, caused no skeletal changes in nonuremic animals. Some uremic, non-aluminum-treated rats developed osteomalacia and marrow fibrosis. However, osteomalacia was more severe and the osteoclast count was higher in the uremic, aluminum-treated rats. In this group of animals the mineral apposition rate was reduced at the metaphyseal endosteum but increased at the periosteum, indicating different control mechanisms at the two sites.

Do tissues other than the kidney produce 1,25-dihydroxyvitamin D3 in vivo? A reexamination

Recent experiments have shown that 1,25-dihydroxyvitamin D3-like material is produced in cultured nonrenal cells and may be present in the sera of anephric patients. We reexamined the question of whether 1,25-dihydroxyvitamin D3 can be synthesized extrarenally in the rat in vivo. To intact, sham-operated, ureter-ligated, or acutely nephrectomized vitamin D-deficient rats raised on a diet normal in calcium and phosphorus, we gave a physiologic dose of high-specific-activity 25-hydroxy-[3H]vitamin D3 (3.6-3.8 microCi; approximately equal to 25 pmol per rat). Twenty-four hours later we examined their tissues and plasma for the presence of radiolabeled 1,25-dihydroxyvitamin D3. Large amounts of radioactivity that behaved chromatographically as identical with authentic 1,25-dihydroxyvitamin D3 were present in the plasma, bone, and intestine of the intact, sham-operated, or ureter-ligated rats. However, no radioactivity eluting in a manner similar to 1,25-dihydroxyvitamin D3 was found in plasma, bone, or intestine of acutely nephrectomized rats. We conclude that, in the acutely nephrectomized living rat, 1,25-dihydroxyvitamin D3 is not present in plasma, bone, or intestine in quantities detectable by the sensitive techniques we have used. No conversion of 25-hydroxyvitamin D3 to 1,25-dihydroxyvitamin D3 was observed during a 24-hr period after nephrectomy of vitamin D-deprived rats. This fact casts doubt upon the significance of the in vitro production of 1,25-dihydroxyvitamin D3 by nonrenal cells as an in vivo phenomenon.

23-Keto-25-hydroxyvitamin D3: a vitamin D3 metabolite with high affinity for the 1,25-dihydroxyvitamin D specific cytosol receptor

A new metabolite of 23,25-dihydroxyvitamin D3 has been generated with kidney homogenates prepared from vitamin D treated chicks. The metabolite was purified with three high-performance liquid chromatographic steps and was identified as 23-keto-25-hydroxyvitamin D3 by ultraviolet absorption spectroscopy, mass spectrometry, and chemical reactivity. The R stereoisomer of 23,25-dihydroxyvitamin D3 was 10-fold more effective as an in vitro precursor to 23-keto-25-hydroxyvitamin D3 than was the naturally occurring S stereoisomer. Approximately 500 ng of 23-keto-25-hydroxyvitamin D3 was necessary to produce the same degree of intestinal-calcium transport as 25 ng of vitamin D3--a difference of about 20-fold. 23-Keto-25-hydroxyvitamin D3 was not active at stimulating bone calcium resorption at the doses and times tested. This new vitamin D3 metabolite, however, had greater affinity than 25-hydroxyvitamin D3 to both the rat plasma vitamin D binding protein and the 1,25-dihydroxyvitamin D specific cytosol receptor. Heretofore, only 1 alpha-hydroxylated metabolites of 25-hydroxyvitamin D3 or analogues possessing a pseudo 1 alpha-hydroxy group were known to bind to the 1,25-dihydroxyvitamin D receptor with higher affinity than 25-hydroxyvitamin D3. Ketone formation at the 23 position, therefore, is the first side-chain modification of 25-hydroxyvitamin D3 that results in enhanced binding to the 1,25-dihydroxyvitamin D receptor binding protein.

1 alpha,25-Dihydroxyvitamin D3 and 1 alpha-hydroxyvitamin D3 prolong survival time of mice inoculated with myeloid leukemia cells

Syngeneic SL mice inoculated with murine myeloid leukemia cells (M1) all died of leukemia within 30 days. Treatment three times a week with 12.5-50 pmol per mouse of either 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3], the active form of vitamin D3, or its synthetic analog, 1 alpha-hydroxyvitamin D3 [1 alpha(OH)D3], considerably prolonged the survival time of mice inoculated with M1 cells. 1 alpha(OH)D3 was more effective than 1 alpha,25(OH)2D3 in increasing the survival time of the mice. 1 alpha(OH)D3 also increased the survival time of nude mice inoculated with M1 cells. The 1 alpha(OH)[3H]D3 administered intraperitoneally to tumor-bearing mice was converted very rapidly to 1 alpha,25(OH)2-[3H]D3. The chronic administration of 25 pmol of 1 alpha(OH)D3 to tumor-bearing mice for 30 days caused no appreciable hypercalcemia. These results indicate clearly that 1 alpha,25(OH)2D3 is effective not only in inducing differentiation of M1 cells in vitro, as previously reported [Abe, E., Miyaura, C., Sakagami, H., Takeda, M., Konno, K., Yamazaki, T., Yoshiki, S. & Suda, T. (1981) Proc. Natl. Acad. Sci. USA 78, 4990-4994], but also in prolonging the survival time of mice inoculated with M1 cells.

Maternal-infant vitamin D relationships during breast-feeding

To evaluate the effect of maternal dietary vitamin D intake on infant vitamin D status in a country with a temperate climate, but where the commercial milk supply is not vitamin D fortified, this randomized, double-blind study was conducted on term mother-infant pairs during the winter months. Well-nourished, white nursing mothers were given a placebo, 500 IU vitamin D/day or 1,000 IU vitamin D/day; their infants were not given supplemental vitamin D. After six weeks, mothers receiving supplemental vitamin D had higher levels of 25-hydroxyvitamin D than had mothers receiving placebo. A direct relationship was observed between maternal and infant levels of 25-hydroxyvitamin D at six weeks, implying that maternal vitamin D intake directly affects the vitamin D concentration in breast milk. A control group of infants who had received 400 IU vitamin D/day had even higher concentrations of 25-hydroxyvitamin D, suggesting that infant supplementation with vitamin D is more efficacious than maternal supplementation. Despite the favorable climate in South Africa, during winter breast-fed infants have low serum vitamin D values if maternal dietary vitamin D intake is low.

Presence of 25-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3 24-hydroxylase in vitamin D target cells of rat yolk sac

In the pregnant rat, the yolk sac, which possesses true placental functions, is a vitamin D target organ. We tested its ability to hydroxylate 25-hydroxy- and 1,25-dihydroxyvitamin D3 (25-OHD3 and 1,25-(OH)2D3). 24,25-Dihydroxy- and 1,24,25-trihydroxyvitamin D3 were produced by rat yolk sac homogenates incubated with tritiated 25-OHD3 and 1,25-(OH)2D3. Rat yolk sac homogenates also formed small amounts of 25,26-dihydroxyvitamin D3. These newly synthesized metabolites were isolated and identified by Sephadex LH-20 chromatography, high performance liquid chromatography, and periodate cleavage. Yolk sac 25-OHD3- and 1,25-(OH)2D3-24-hydroxylases were present in mitochondria and were of a mixed function oxidase nature. They were detected in the yolk sac as early as day 12 in the embryonic period and until the end of gestation. No hydroxylation occurred in maternal liver, amnion, fetal brain, or skin homogenates. Both 24-hydroxylases were detected in pure isolated rat yolk sac endodermal cells. This may be of physiological importance, since they are the 1,25-(OH)2D3 target cells in the yolk sac. Injection of 1,25-(OH)2[3H]D3 into rat yolk sac vitelline veins strongly suggested that the yolk sac vitelline veins strongly suggested that the yolk sac produced 1,24,25-(OH)3D3 in vivo. We conclude that the yolk sac and more precisely its endodermal cells may help to control vitamin D metabolism within the fetoplacental unit.

Vitamin D deficiency in rats with normal serum calcium concentrations

Rats were raised after weaning on a vitamin D-deficient diet which used whole wheat and casein as the major protein source. For at least the first year of life, plasma calcium concentrations of these rats were the same as those of vitamin D-replete rats, and the rate of growth was normal for at least 6 months. The following evidence establishes the vitamin D deficiency of the rats (both male and female) on this diet: (i) plasma levels of 1,25-dihydroxycholecalciferol (1,25-dihydroxyvitamin D3) became undetectable after 6 weeks on the diet; (ii) by 4 months of age, the epiphyseal growth plates of the tibia were significantly enlarged and disorganized; (iii) when subjected to fracture in a dynamic torsion machine, the femur showed marked weakening as indicated by stress analysis; (iv) isolated kidney cells from the deficient rats showed a 3-fold increase in 25-hydroxyvitamin D 1-hydroxylase activity. When mother rats were placed on the vitamin D-deficient diet during lactation, plasma calcium values in the pups decreased and remained low throughout life and there was a stunted body growth pattern. It is concluded that hypocalcemia is not a necessary manifestation of vitamin D deficiency, that the onset of vitamin D deficiency during neonatal life influences the calcium homeostatic system, and that the normocalcemic, vitamin D-deficient animal provides an experimental model in which the effects of vitamin D deficiency can be studied independently of hypocalcemia.

24-hydroxylation of 25-hydroxyvitamin D3: is it required for embryonic development in chicks?

As shown previously, laying hens given 1,25-dihydroxyvitamin D3 as their sole source of vitamin D produce fertile eggs having normal shells, but only 35 to 55 percent of the embryos are normal. Giving these hens additional 25-hydroxyvitamin D3, 24,25-dihydroxyvitamin D3, or 24,24-difluoro-25-hydroxyvitamin D3 at 1.25 nanomoles per day resulted in 90 to 100 percent normal embryos, and hence, hatchability. Since 24,24-difluoro-25-hydroxyvitamin D3 cannot be 24-hydroxylated, 24-hydroxylation is not required for this function of 25-hydroxyvitamin D3.