Bioassay of 1,25-dihydroxyvitamin D in human plasma purified by partition, alkaline extraction, and high-pressure chromatography

Re-evaluating the role of vitamin D in the periodontium

The importance of vitamin D in maintaining skeletal health via the regulation of calcium has long been recognized as a critical function of this secosteroid. An abundance of literature shows an association between oral bone mineral density and some measure of systemic osteoporosis and suggests that osteoporosis/low bone mass may be a risk factor for periodontal disease. Recently, nonskeletal functions of vitamin D have gained notoriety for several reasons. Many cells that are not associated with calcium homeostasis have been demonstrated to possess membrane receptors for vitamin D. These include activated T and B lymphocytes, and skin, placenta, pancreas, prostate and colon cancer cells. In addition, vitamin D "insufficiency" is a worldwide epidemic and epidemiologic evidence has linked this condition to multiple chronic health problems, including cardiovascular and autoimmune diseases, hypertension and a variety of cancers. Interestingly, there is mounting evidence connecting diminished serum levels of vitamin D with increased gingival inflammation and supporting the concept of "continual vitamin D sufficiency" in maintaining periodontal health. The ability of vitamin D to regulate both the innate and the adaptive components of the host response may play an important role in this process. This review will examine the skeletal and nonskeletal functions of vitamin D, and explore its potential role in protecting the periodontium as well as in regulating periodontal wound healing.

How vitamin D works on bone

Vitamin D is important for the normal development and maintenance of bone. The elucidation of the vitamin D activation pathway and the cloning of the vitamin D receptor have advanced our understanding of the actions of vitamin D on bone. The preponderance of evidence indicates that 1,25(OH)₂D₃ enhances bone mineralization through its effects to promote calcium and phosphate absorption. Although 1,25(OH)₂D₃ stimulates bone resorption in vitro, treatment in vivo can prevent bone loss and fracture through several potential mechanisms. The development of vitamin D analogues has provided new therapeutic options for increasing bone mineral density and reducing fractures.

Alendronate/interleukin-1beta cotreatment increases interleukin-6 in bone and UMR-106 cells: dose dependence and relationship to the antiresorptive effect of alendronate

Aminobisphosphonates inhibit bone resorption but have been shown to elicit acute-phase-like elevations in interleukin-6 (IL-6) in bone in vitro. The current studies were carried out to determine the relationship between the antiresorptive effects of the aminobisphosphonate alendronate and its effects on IL-6. Resorption was elicited in cultured 19-day fetal rat limb bones by 72 h treatment with interleukin-1beta (IL-1beta). Bone mass was quantitated at the end of the culture period to assess resorption. IL-6 was determined by bioassay (7TD1 cell proliferation). IL-1beta (18 and 180 pM) stimulated bone resorption and increased IL-6. Alendronate (70 microM) inhibited the IL-1beta-stimulated resorption. Alendronate alone did not affect IL-6 production by the bones. The IL-6 production from bones stimulated with 18 pM IL-1beta was not significantly affected by alendronate, but the IL-6 production from bones stimulated with 180 pM IL-1beta plus alendronate (21 and 70 microM) was higher than with IL-1beta alone. Indomethacin (1 mM) inhibited the IL-6 increase elicited by 180 pM IL-1beta and the enhanced IL-6 production elicited by cotreatment with IL-1beta and alendronate. Since bone cultures contain multiple cell types, further experiments were carried out to determine whether alendronate could increase IL-1beta-stimulated IL-6 production in an osteoblast cell line, UMR-106. Alendronate alone did not affect IL-6 in UMR-106 cells. Alendronate (70 microM) in combination with IL-1beta (180, 1.8, or 8 nM), or 7 microM alendronate, in combination with 8 nM IL-1beta, significantly increased IL-6 in 48 h cell cultures. The results from the bone organ cultures show that alendronate can enhance IL-6 production elicited by higher concentrations of the cytokine IL-1beta in bone, but that this effect on IL-6 does not prevent the inhibitory actions of alendronate on bone resorption. The results with the UMR106 cells indicate that one cellular site at which this enhancement of IL-6 production can occur is the osteoblast.

A highly sensitive method for large-scale measurements of 1,25-dihydroxyvitamin D

A quantitative method for measuring 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) was developed utilizing a luciferase reporter gene under the control of the highly inducible 25-hydroxyvitamin D3 24-hydroxylase promoter in a stably transfected cell line. Transient transfections with constructs containing the 24-hydroxylase gene promoter 5' to a luciferase reporter were first performed in cell lines with high levels of vitamin D receptor, i.e., the rat osteosarcoma (ROS 17/2.8) and human breast cancer (T-47D) cell lines. ROS 17/2.8 cells, stably transfected with the plasmid, gave a 60-fold stimulation with 10(-10) M 1,25-(OH)2D3. A standard curve was constructed showing a large range of response to 1,25-(OH)2D3 (1 pg to 1 ng). The assay was adapted to microtiter plates, which permits a large number of samples to be assayed simultaneously. Other metabolites of vitamin D and analogs such as 25-hydroxyvitamin D3, 24,25-dihydroxyvitamin D3, and 1 alpha-hydroxyvitamin D3 have negligible effects on the detection of 1,25-(OH)2D3, thus eliminating the need for purification of sample. The sensitivity of the method permitted the use of 100 microliters of serum with excellent results. Comparison of this method with a commercially available assay demonstrates that it gives higher sensitivity, simpler manipulations, and comparable results.

Parathyroid hormone-induced resorption in fetal rat limb bones is associated with production of the metalloproteinases collagenase and gelatinase B

The role of matrix metalloproteinases in parathyroid hormone (PTH)-induced bone resorption was assayed using a fetal rat limb bone culture system. Cotreatment of bones with PTH and recombinant inhibitor of metalloproteinases, TIMP-1, in vitro, inhibited the PTH-stimulated 45Ca release from the limb bones without affecting beta-glucuronidase release. TIMP-1 was fully effective when added during only the final 24 h of a 72 h culture with PTH but was ineffective when added for only the first 24 h of the 72 h culture. In contrast, calcitonin (CT) was effective when added for either the first 24 or the final 24 h of the culture. Using in situ hybridization, the mRNA for collagenase was detected in mononuclear cells of cultured bone. Treatment of the bones with PTH resulted in an increase in the number of cells producing collagenase mRNA, some of which had osteoclastic morphology, PTH also caused a dramatic induction of the mRNA for the 92-kD gelatinase B metalloproteinase in both mononuclear and osteoclastic cells. There was no detectable mRNA for the metalloproteinases stromelysin-1, stromelysin-2, or matrilysin in PTH-treated or control cultures. These results suggest that PTH-induced bone resorption is mediated, at least in part, by the induction of collagenase and gelatinase B mRNA in bone cells.

Triiodothyronine potentiates the stimulatory effects of interleukin-1 beta on bone resorption and medium interleukin-6 content in fetal rat limb bone cultures

It has been demonstrated that thyroid hormones stimulate osteoclasts indirectly and that this effect is mediated by products of other cell types present in bone. To determine if interleukin-6 (IL-6) could be a mediator of thyroid hormone action, we investigated the effect of 3,5,3'-triiodothyronine (T3) on bone resorption (45Ca release) and on the IL-6 concentration in medium from cultured 19-day-old fetal rat limb bones. T3 alone increased 45Ca release significantly only at a fairly high concentration (10(-6)M) under the conditions used. T3 alone, over a 10(-11)-10(-6) M concentration range, failed to elicit a detectable effect on the medium IL-6 content. However, T3 potentiated the stimulatory effect of interleukin-1 beta (IL-1 beta) on IL-6 production in a dose-dependent manner. T3, 10(-8) M, also significantly increased IL-1 beta-stimulated calcium release. Inhibition of IL-1 beta with 1 muM interleukin-1 receptor antagonist (IL-1ra) abrogated the potentiating effects of T3 on IL-1 beta-stimulated IL-6 production and blocked the combined effect of T3 and IL-1 beta on 45Ca release. One micromolar indomethacin significantly, but not completely, inhibited the effect of IL-1 beta, as well as the combined effect of IL-1 beta and T3 on resorption and IL-6 production, indicating the involvement of prostaglandins in these actions. Consistent with this, 1 microM prostaglandin E1 (PGE1) significantly increased both the IL-6 production and the calcium release. By potentiating the effect of IL-1 beta, T3 increased bone resorption at much lower concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Gas chromatographic-mass fragmentographic determination of serum 1 alpha,25 dihydroxyvitamin D3

We extracted 1 alpha,25-dihydroxyvitamin D3[1 alpha,25(OH)2D3] from 10 mL serum using Sep-Pak C18 and Sep-Pak Silica mini-columns and normal-phase high performance liquid chromatography (HPLC) separation for analysis by gas chromatography-mass fragmentography (GC-MS). A GC-MS method was optimised using manual tuning for ion mass calibration and selective ion monitoring (SIM) for quantitation. Serum 1 alpha,25(OH)2D3 was identified by superimposition of the m/z 452 and 501 ion peaks and by overlapping the m/z 452 ion peak with that of its authentic standard. It was quantitated from the relative peak areas of its m/z 452 ion and the m/z 363 ion of vitamin D2, the internal standard. Twenty picograms of 1 alpha,25(OH)2D3 gave a peak with a signal-to-noise ratio of 26:1. Between-batch coefficient of variation (CV) for 1 alpha,25(OH)2D3 standard was < 13%. However, serum analysis was less precise, within-batch CV being 20%. The analytical recovery was about 70% and detection limit 0.5 pg/mL. When compared with a commercial radioreceptor assay we still found our method to be sensitive, specific, and adequate for confirmative and semiquantitative analysis of serum 1 alpha,25(OH)2D3.

Thyroid hormones increase insulin-like growth factor I content in the medium of rat bone tissue

The mechanism of action of thyroid hormones on bone is still not clear. At low concentrations, they stimulate bone formation; at high concentrations, they elicit bone resorption in vitro and in vivo. In the present study we investigated the effect of T3 and T4 as well as their active and inactive analogs (TRIAC, SKF L-94901, rT3, and DIT) on the IGF-I and TNF-alpha content in the medium of UMR-106 rat osteoblastic cells and fetal rat limb bones. In the dose-response studies, a biphasic increase in medium IGF-I was observed in both cells and limb bones, with peak stimulatory concentrations of 10(-8) M for T3 and 10(-7) M for T4 in both systems. At higher concentrations, at which thyroid hormones elicit bone resorption, the stimulatory effect diminished and finally was no longer detectable. The active analogs TRIAC and SKF L-94901 also enhanced IGF-I release in UMR-106 cells. The inactive compounds rT3 and DIT failed to increase IGF-I in these cultures. The protein content of the cell culture wells exposed to high concentrations of thyroid hormones was similar to those containing low concentrations, indicating that the decrease in IGF-I content at high doses was not due to toxic effects. This was also confirmed by trypan blue exclusion. Time course studies with UMR-106 cells revealed a significant increase in medium IGF-I after 2 days of incubation. No significant further increase was observed after this up to 5 days of culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Interactions of tumor necrosis factor with local and systemic factors in fetal rat limb bones

In many tissues the actions of tumor necrosis factor-alpha (TNF) are indirectly mediated through the production of autacoids or other cytokines. To determine the role that these factors might have in the action of TNF on bone resorption, we examined the effects of several selective inhibitors on TNF-stimulated resorption. The cyclooxygenase inhibitor indomethacin did not prevent TNF-stimulated resorption in fetal rat limb bones. Stimulation of resorption by TNF was also unaffected by the platelet activating factor antagonist WEB 2086. A 17.5 kD interleukin receptor antagonist protein, at concentrations that completely blocked the bone-resorbing actions of maximally effective concentrations of interleukin (IL)-1 beta, failed to affect the stimulatory actions of TNF. TNF-stimulated resorption was inhibited by both interferon-gamma and dexamethasone. Dexamethasone inhibited TNF-stimulated resorption more effectively than it inhibited parathyroid hormone (PTH)-stimulated resorption. When bones were treated simultaneously with low concentrations of TNF and PTH, potentiation of the bone-resorbing effects was elicited. These results suggest that TNF stimulates resorption through a pathway different from that by which PTH produces its effects. Transforming growth factor-beta (TGF-beta) enhanced responses to TNF; TGF-beta failed to inhibit the effects of TNF, even in long-term culture or when bones were pretreated with TGF-beta. Synergistic interactions between TNF and several other bone-resorbing factors have now been demonstrated. In contrast to the actions of TNF on certain other functions, the bone-resorbing effects of TNF, as determined in the fetal rat limb bone system, do not seem to be mediated by PAF, IL-1, or prostaglandins.

Second messengers in thrombin-stimulated bone resorption

Characterized human thrombins and two commercial bovine thrombin preparations were examined for their effects on bone resorption and on the cyclic AMP and phosphoinositide second messenger systems in bone. Human alpha- and gamma-thrombins, as well as both bovine thrombin preparations, stimulated bone resorption in vitro, whereas catalytically inactivated human diisopropylfluorophosphate (DIP)-alpha-thrombin did not significantly stimulate resorption. Human alpha-thrombin and a commercial bovine thrombin preparation increased cyclic AMP production in fetal rat limb bones, but another bovine commercial thrombin preparation and gamma-thrombin did not. Except for DIP-alpha-thrombin, all thrombins increased production of inositol phosphates in fetal rat limb bones at concentrations that stimulated resorption. In time course studies, bovine thrombin increased label in inositol trisphosphate at 30 s, with decreasing effects at later times. Inositol monophosphate increased progressively over 30 min. Our results are consistent with thrombin-stimulated bone resorption being mediated at least partially through the inositol phosphate pathway.

24- and 26-homo-1,25-dihydroxyvitamin D3 analogs: potencies on in vitro bone resorption differ from those reported for cell differentiation

It has been proposed that the stimulatory effects of 1,25-dihydroxyvitamin D on bone resorption may be mediated through actions on differentiation of marrow cells into monocytic osteoclast precursors. In human promyelocytic leukemia cells (HL-60), 24- and 26-homo-1,25-dihydroxyvitamin D3 and their delta 22 analogs and 24,24-dihomo-1,25-dihydroxyvitamin D3 are 10-fold more potent than 1,25-dihydroxyvitamin D3, and delta 22-24,24,24-trihomo-1,25-dihydroxyvitamin D3 is equipotent with 1,25-dihydroxyvitamin D3 in inducing differentiation into the monocytic phenotype. The effect of these 1,25-dihydroxyvitamin D3 analogous on resorption of fetal rat limb bones in vitro was determined in the present study. 1,25-Dihydroxyvitamin D3 was equipotent with 24-homo-1,25-dihydroxyvitamin D3, delta 22-24-homo-1,25-dihydroxyvitamin D3, 26-homo-1,25-dihydroxyvitamin D3, and delta 22-26-homo-1,25-dihydroxyvitamin D3 for in vitro bone resorption, whereas 24,24-dihomo-1,25-dihydroxyvitamin D3 and delta 22-24,24,24-trihomo-1,25-dihydroxyvitamin D3 were inactive. The failure of these analogs to show a higher bone-resorbing activity than 1,25-dihydroxyvitamin D3 were inactive. The failure of these analogs to show a higher bone-resorbing activity than 1,25-dihydroxyvitamin D3 provides evidence to suggest that the mechanism of 1,25-dihydroxyvitamin D3-induced bone resorption may not involve stimulation of monocytic cell differentiation.

Cadmium accelerates bone loss in ovariectomized mice and fetal rat limb bones in culture

Loss of bone mineral after ovariectomy was studied in mice exposed to dietary cadmium at 0.25, 5, or 50 ppm. Results show that dietary cadmium at 50 ppm increased bone mineral loss to a significantly greater extent in ovariectomized mice than in sham-operated controls. These results were obtained from two studies, one in which skeletal calcium content was determined 6 months after ovariectomy and a second in which 45Ca release from 45Ca-prelabeled bones was measured immediately after the start of dietary cadmium exposure. Furthermore, experiments with 45Ca-prelabeled fetal rat limb bones in culture demonstrated that Cd at 10 nM in the medium, a concentration estimated to be in the plasma of mice exposed to 50 ppm dietary Cd, strikingly increased bone resorption, from 27 +/- 2% (mean +/- SEM) 45Ca release in cultures with no added cadmium to 68 +/- 6% release in cultures containing cadmium (n = 4). These in vitro results indicate that cadmium may enhance bone mineral loss by a direct action on bone. Results of the in vivo studies are consistent with a significant role of cadmium in the etiology of Itai-Itai disease among postmenopausal women in Japan and may in part explain the increased risk of postmenopausal osteoporosis among women who smoke.

Chromatography of fat-soluble vitamins in clinical chemistry

A review is presented of current gas and liquid chromatographic methods for the determination of the fat-soluble vitamins A, D, E and K and the provitamin A beta-carotene in biological samples of human origin. For each vitamin, the discussion successively focuses on procedures for sample preparation, gas and liquid chromatographic systems and principles of detection. The emphasis is on liquid chromatography, which is gradually becoming a standard technique in fat-soluble vitamin assays. New trends in the liquid chromatography of these compounds include the use of smaller particles and shorter columns, to improve speed, and the advance of electrochemical detection as an alternative to absorbance and fluorescence detection. Bonded phases, both normal and reversed phase, tend to be preferred over underivatized silica as column supports. Gas chromatography remains of particular value in combination with mass spectrometry, a technique which may form the basis of reference methods. In general, despite the availability of well established analytical methods for fat-soluble vitamins, the wealth of recent literature in this area indicates that there continues to be a need for new assays with enhanced speed, specificity and sensitivity.

Application of the rat thymus receptor in a specific, sensitive and simplified assay of 1,25-dihydroxyvitamin D in blood serum

A simple method has been employed to prepare crude nuclear extract from rat thymus, using hypertonic buffer after previous treatment with hypotonic buffer. The preparation is free from serum vitamin D-binding protein and contains a 3.7 S receptor molecule, which specifically binds 1,25-dihydroxyvitamin D-3 (1,25-(OH)2D3). The receptor is of high affinity (KD = 0.85 X 10(-11) M at O degrees C) and low capacity (260-460 fmol/g tissue). The Scatchard analysis of ligand binding results in a concave downward curve. The Hill analysis of the same data gives good linear fitting (r = +0.971) with the Hill coefficient nH = 1.63. These facts indicate positive cooperativity between two ligand binding sites of the rat thymus 1,25-(OH)2D3 receptor. The preparation was used in a competitive protein binding assay of 1,25-(OH)2D in serum extracts, purified on Sep-Pak C18 followed by silica Sep-Pak cartridges. The method was sensitive to 0.5 pg/tube (2.0 ng/l) when 1 ml of serum was extracted. Intra- and interassay coefficients of variation were 9% and 14%, respectively. The serum 1,25-(OH)2D concentration estimated in 33 children (mean age 6.5 +/- 3 years) was 46.6 +/- 18.4 ng/l (mean +/- S.D.).

Cyclosporine A inhibits calcemic hormone-induced bone resorption in vitro

We have investigated the in vitro effects of cyclosporine (CsA), a potent immunosuppressive agent, on bone resorption induced by calcemic hormones. CsA inhibited parathyroid hormone (PTH), prostaglandin E2, 1,25-dihydroxy vitamin D3 (1,25(OH)2D3), and osteoclast-activating factor induced resorption of fetal rat limb bones in a dose-dependent manner. Established ongoing resorptive activity in bone was also inhibited by CsA. The CsA inhibition of bone resorption could be partially surmounted by higher concentrations of PTH and 1,25(OH)2D3. The inhibitory effects of CsA on limb bone resorption were reversible. Neither protein nor DNA synthesis were inhibited by treatment of limb bones with CsA. Thus, the inhibitory effect of this agent on bone resorption is not a cytotoxic one. These data could suggest that the induction of bone resorption by the calcemic hormones involves an immune cell derived mediator such as a lymphokine.

Human transforming growth factor-alpha stimulates bone resorption in vitro

Tumor-derived transforming growth factors (TGF) have been proposed as possible mediators of hypercalcemia in malignancy. We have studied the action of recombinant human TGF-alpha in cultured bone cells and in bone explant cultures. In clonal UMR-106 rat osteosarcoma cells, TGF-alpha and epidermal growth factor (EGF) were equipotent in binding to the EGF receptor. TGF-alpha and EGF both stimulated resorption of neonatal mouse calvaria, and maximal responses were obtained with 10 ng/ml of TGF-alpha after 72 h in culture. The effects of both TGF-alpha and EGF in calvaria, but not those of parathyroid hormone, were inhibited by 5 X 10(-7) M indomethacin. Fetal rat limb bone cultures were less sensitive to TGF-alpha than neonatal mouse calvaria, with a concentration of 30 ng/ml being required to stimulate resorption in this system. The bone-resorbing activity of TGF-alpha in fetal rat bones was inhibited by 10 ng/ml calcitonin but not by 5 X 10(-7) M indomethacin. EGF at concentrations up to 300 ng/ml did not stimulate resorption of the limb bones at time periods up to 66 h. The results indicate that human TGF-alpha is a potent bone-resorbing agent, and support the concept that this growth factor exhibits some effects distinct from those of EGF. TGF-alpha could play an etiologic role in the hypercalcemia of malignancy.

10-Keto or 25-hydroxy substitution confer equivalent in vitro bone-resorbing activity to vitamin D3

The biological activities of 10-keto derivatives of vitamin D3 and 25-hydroxyvitamin D3 were determined in bone organ culture. Fetal rat limb bones prelabeled with 45Ca were incubated for 60 h with 10-keto-25-hydroxyvitamin D3, 10-keto-vitamin D3, 1,25-dihydroxyvitamin D3, 25-hydroxyvitamin D3, or vitamin D3. Resorption was quantified by release of 45Ca. Substitution of a keto group in the 10 position of the vitamin D3 molecule resulted in a compound equal in potency to 25-hydroxyvitamin D3. When a 10-keto group was substituted in the 25-hydroxy vitamin D3 molecule, the potency was increased 20- to 40-fold. In contrast, 1,25-dihydroxyvitamin D3 was 7500-fold more potent than 25-hydroxyvitamin D3. Since 10-keto-25-hydroxyvitamin D3 has a retention time close to that of 1,25-dihydroxyvitamin D3 on normal-phase HPLC eluted with isopropanol:hexane, it is a possible artifact in the assay of 1,25-dihydroxyvitamin D3. Based upon the observed relative activities of the two compounds, the concentration of 10-keto-25-hydroxyvitamin D3 would have to be greater than 0.8 ng/ml for it to interfere in the bioassay of 1,25-dihydroxyvitamin D3.

A sensitive and simplified radioimmunoassay for 1,25-dihydroxyvitamin D3

A sensitive radioimmunoassay system for 1 alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3] with an improved extraction procedure has been developed. Following one-step extraction and prepurification of 1,25(OH)2D3 by 'Extrelut-1' minicolumns final purification was achieved by high-performance liquid chromatography (HPLC) using a radial compression separation system equipped with a mu Porasil cartridge. The HPLC method applied allows the purification of 4 extracts/h. Recovery of 1,25(OH)2[3H]D3 after HPLC was 77 +/- 2.6% (mean +/- SD, n = 51). Since the recovery of 1,25(OH)2[3H]D3 was very reproducible, addition of labelled steroid to each single serum sample for monitoring recovery was omitted. The sensitivity of the assay was 0.8 pg/tube resulting in a detection limit of 3 ng/l, when 1 ml of serum was extracted. Intra-assay and inter-assay coefficients of variation were 12% and 16.8%, respectively. Serum 1,25(OH)2D3 concentration in 30 normal subjects (mean age: 25 yr) was 55 +/- 12 ng/l (mean +/- SD). In 55 elderly patients (mean age: 77 yr) the 1,25(OH)2D3 serum level was 32 +/- 12 ng/l (mean +/- SD) and in three patients with chronic renal failure on 1,25(OH)2D3 therapy 146 +/- 67 ng/l (mean +/- SD). Patients with chronic renal failure had reduced 1,25(OH)2D3 serum levels (mean 5.4 ng/l, range less than 3-11 ng/l, n = 10). In one patient with renal failure, following kidney transplantation the serum 1,25(OH)2D3 and creatinine levels were monitored from the 4th to the 12th post-surgical day: a highly significant negative correlation (r = 0.85) was found.

Evidence for abnormal regulation of circulating 1 alpha, 25-dihydroxyvitamin D in patients with pulmonary tuberculosis and normal calcium metabolism

Available evidence indicates that hypercalcemia in pulmonary tuberculosis results from increases in circulating 1 alpha, 25-dihydroxyvitamin D [1 alpha, 25(OH)2D]. To further characterize vitamin D metabolism in this disorder, the effects of vitamin D, 100,000 units a day for 4 days, were compared in 25 normal subjects and 11 patients with active pulmonary tuberculosis who were normocalcemic and had not had hypercalcemia. Serum calcium, phosphorus, 25-hydroxyvitamin D (25-OHD) and 1 alpha, 25(OH)2D were measured. Whereas vitamin D increased mean serum 25-OHD from 20 +/- 2 (+/- SE) to 40 +/- 5 ng/ml (P less than 0.001) and did not change mean serum 1 alpha, 25(OH)2D in the normals (33 +/- 2 vs. 31 +/- 2 pg/ml), it increased mean serum 25-OHD from 21 +/- 4 to 55 +/- 13 ng/ml (P less than 0.05) and mean serum 1 alpha, 25(OH)2D from 28 +/- 2 to 35 +/- 3 pg/ml (P less than 0.05) in the patients. Serum calcium was normal and remained within the normal range in all subjects and patients. The findings indicate that there is a modest but significant abnormality in the regulation of circulating 1 alpha, 25(OH)2D in normocalcemic patients with pulmonary tuberculosis. The results are similar to those previously reported by us in normocalcemic patients with sarcoidosis.

24-Oxo and 26,23-lactone metabolites of 1,25-dihydroxyvitamin D3 have direct bone-resorbing activity

The biological activities of several 24-oxo and 26,23-lactone metabolites of vitamin D were determined in bone organ cultures. The 24-oxo metabolites were significantly more potent bone-resorbing agents than the lactones. 1,25-(OH)2-24-oxo-D3 had 0.18 X the bone-resorbing activity of 1,25-(OH)2D3 in fetal rat limb bones and was equipotent with 1,25-(OH)2D3 in neonatal mouse calvaria. In the limb bone system, 1,23,25-(OH)3-24-oxo-D3 had 0.08 X the activity of 1,25-(OH)2D3. 1,25-(OH)2D3 and 1,25-(OH)2-24-oxo-D3 had a similar time course of bone-resorbing effects in both bone culture systems. The most potent of the lactones, 1,25S-(OH)2D3-26,23R-lactone, had approximately 0.009 X the activity of 1,25-(OH)2D3 and approximately 500 times the activity of the 25S-OH-D3-26,23R-lactone. The 25S and 1,25S lactones were more potent than the 25R and 1,25R isomers. In experiments designed to determine whether either 1,25-(OH)2-24-oxo-D3 or 25R-OH-D3-26,23S-lactone could prevent the bone-resorbing activity of 1,25-(OH)2D3, no inhibitory effects were observed. The results suggest that conversion to the lactones represents a substantial inactivation step, whereas conversion to 24-oxo-derivatives results in less reduction in biological activity.

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.

Metabolic and drug profiling

Over recent years, advances in analytical technology have greatly improved our ability to study the metabolism of compounds from either endogenous or erogenous sources. The application of gas-liquid chromatography, mass spectrometry, high-performance liquid chromatography and immunological approaches are discussed in relation to the analysis of steroids, bile acids, organic acids, prostaglandins, porphyrins and bile pigments, amino acids, proteins, nucleotides, catecholamines, vitamins and drugs.

Comparison of fetal rat limb bones and neonatal mouse calvaria: effects of parathyroid hormone and 1,25-dihydroxyvitamin D3

The relative responses of fetal rat limb bones and neonatal mouse calvaria to parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) were examined in organ culture. Limb bones were cultured in dishes in BGJ + 1 mg/ml bovine serum albumin (bSA) or DMEM + 15% heat-inactivated horse serum (hS). Calvaria were either cultured in dishes with one of the above two media or in roller tubes in DMEM + hS. The order of sensitivity to PTH was: calvaria in roller tubes greater than limb bones in dishes in DMEM + hS greater than limb bones in dishes in BGJ + bSA greater than or equal to calvaria in dishes in DMEM + hS greater than calvaria in dishes in BGJ + bSA. The most sensitive system (i.e., calvaria in roller tubes) showed significant resorption in response to 10(-10)M PTH at 48 h. The least sensitive system did not respond to 3 X 10(-8)M PTH after the same length of time. The greater response in DMEM + hS compared with BGJ + bSA appeared to be due to the protein component of the medium. The order of sensitivity to 1,25(OH)2D3 was: calvaria in roller tubes = long bones in culture dishes in BGJ + bSA greater than long bones in culture dishes in DMEM + hS greater than calvaria in dishes in DMEM + hS greater than calvaria in dishes in BGJ + bSA. The most sensitive systems showed resorption in response to 10(-11)M 1,25(OH)2D3 by 72 h. The least sensitive system failed to respond to 10(-9)M 1,25(OH)2D3 after the same length of time. The nature of the protein constituent did not seem to influence the response of the limb bones to 1,25(OH)2D3. The results indicated that although the responses of the two bone systems to the calcemic hormones were qualitatively similar, media and culture conditions could markedly affect the sensitivity.

Evidence for extrarenal production of 1 alpha ,25-dihydroxyvitamin D in man

Recent studies provide evidence for extrarenal production of 1 alpha ,25-dihydroxyvitamin D [1 alpha ,25(OH)2D]. To investigate this possibility, serum vitamin D, 25-hydroxyvitamin D (25-OHD), 24,25-dihydroxyvitamin D [24,25(OH)2D], and 1 alpha ,25(OH)2D were measured in eight adult anephric subjects. All were undergoing hemodialysis and three of them were receiving vitamin D, 50,000 or 100,000 U/d. Serum vitamin D was elevated in two of the patients given vitamin D and was abnormally low in the others. Mean serum 25-OHD was increased in patients given vitamin D (94.0 +/- 7.6 ng/ml) and was normal in the others (16.4 +/- 0.9 ng/ml, P less than 0.001). Mean serum 24,25(OH)2D was normal in patients given vitamin D (1.38 +/- 0.27 ng/ml) and was low in the others (0.25 +/- 0.08 ng/ml, P less than 0.001). Serum 24,25(OH)2D correlated significantly with serum 25-OHD (r = 0.848, P less than 0.01). Mean serum 1 alpha ,25(OH)2D determined by receptor assay was 5.8 +/- 1.9 pg/ml in patients who were not given vitamin D and was 14.1 +/- 0.6 in those who were given vitamin D (P less than 0.001). Serum 1 alpha ,25(OH)2D correlated significantly with serum 25-OHD (r = 0.911, P less than 0.01). Mean serum 1 alpha ,25(OH)2D, measured by bioassay, was 8.3 +/- 1.9 pg/ml in patients who were given vitamin D and was 15.9 +/- 2.4 pg/ml in those who were given vitamin D (P less than 0.05). There was a significant correlation between the values for serum 1 alpha ,25(OH)2D obtained with the two methods (r = 0.728, P less than 0.01). The results (a) provide evidence in man for extrarenal production of both 24,25(OH)2D and, by two independent assays, of 1 alpha , 25(OH)2D, and (b) indicate that serum values of the two dihydroxy metabolites of vitamin D in anephric subjects vary with the serum concentration of the precursor 25-OHD.