Primary hyperparathyroidism and osteoporosis in 2004

In patients with primary hyperparathyroidism, a definite diagnosis is the first step in the management strategy and relies on appropriately selected and carefully interpreted laboratory tests. Parathyroid hormone assays are being increasingly performed as part of the routine evaluation of osteoporosis. In this setting, laboratory tests are often consistent with primary hyperparathyroidism but should be interpreted with caution. Bone mineral density measurements are useful for assessing the impact of primary hyperparathyroidism. The recommended bone mineral density cutoffs for selecting patients requiring parathyroidectomy were lowered in 2003, and the number of surgically treated patients has increased as a result. Parathyroidectomy remains the treatment of choice given the low mortality associated with this procedure and the absence of pharmacological alternatives suitable for long-term use.

Skeletal abnormalities in Pth-null mice are influenced by dietary calcium

We have examined the role of PTH in the postnatal state in a mouse model of PTH deficiency generated by targeting the Pth gene in embryonic stem cells. Mice homozygous for the ablated allele, when maintained on a normal calcium intake, developed hypocalcemia, hyperphosphatemia, and low circulating 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] levels consistent with primary hypoparathyroidism. Bone turnover was reduced, leading to increased trabecular and cortical bone volume in PTH-deficient mice. When mutant mice were placed on a low-calcium diet, renal 25-hydroxyvitamin D 1 alpha-hydroxylase expression increased despite the absence of PTH, leading to a rise in circulating 1,25(OH)(2)D(3) levels, marked osteoclastogenesis, and profound bone resorption. These studies demonstrate the dependence of the skeletal phenotype in animals with genetically depleted PTH on the external environment as well as on internal hormonal and ionic circulatory factors. They also show that, although PTH action is the first defense against hypocalcemia, 1,25(OH)(2)D(3) can be mobilized, even in the absence of PTH, to guard against extreme calcium deficiency.

Phase I trial of 1alpha-hydroxyvitamin d(2) in patients with hormone refractory prostate cancer

This Phase I study of 1alpha-hydroxyvitamin D(2), an p.o. administered vitamin D analogue, in patients with advanced hormone-refractory prostate cancer was designed to assess the toxicity, pharmacokinetic and biological markers of drug activity, and lastly tumor response data to recommend a dose for Phase II studies. 1alpha-Hydroxyvitamin D(2) was administered daily at doses ranging from 5 to 15 microg/day. Patients were monitored for toxicity and tumor response, and blood and urine samples were collected for pharmacokinetics (1alpha,25-dihydroxyvitamin D(2) levels) and other parameters of biological activity (bone markers, parathyroid hormone, urine calcium, and serum phosphorus levels). Twenty-five patients were enrolled. Main toxicities were hypercalcemia with associated renal insufficiency. No other significant toxicity was seen. Pharmacokinetics showed an increase in the active metabolite 1alpha,25-dihydroxyvitamin D(2) that reached a plateau by week 4 despite continuous drug dosing. Elevation in daily urinary calcium excretion and serum phosphorus levels was seen, whereas a decrease in serum parathyroid hormone was evident. Two patients showed evidence of a partial response, whereas 5 others achieved disease stabilization for > or =6 months. 1alpha-Hydroxyvitamin D(2) was well tolerated with main toxicities being hypercalcemia and renal insufficiency. All of the toxicity was reversible with drug discontinuation. Evidence for drug activity was seen in surrogate markers, and pharmacokinetic analysis showed substantial increases in vitamin D metabolite levels among the various cohorts. Whereas the defined maximum tolerated dose was not reached, the recommended Phase II dose was 12.5 microg/day given continuously.

Toxicity and dose-response studies of 1alpha-hydroxyvitamin D2 in a retinoblastoma xenograft model

BACKGROUND

Although calcitriol (1,25-dihydroxycholecalciferol) and vitamin D(2) inhibit retinoblastoma growth in the athymic (nude) mouse xenograft (Y-79 cell line) model of retinoblastoma, they can cause severe toxicity.

OBJECTIVE

To examine the toxicity of and dose-dependent response for the inhibition of tumor growth for 1alpha-hydroxyvitamin D(2) (1alpha-OH-D(2)), an analogue with reduced systemic toxicity, in the athymic Y-79 mouse model.

METHODS

Mice were randomized into treatment and control groups for 5-week toxicity and dose-response studies. Treatment was via oral gavage 5 times per week. Dose-response studies measured tumor inhibition and drug serum levels. Tumor size and body weight were measured weekly together with various criteria for toxicity. Animals were euthanized at the end of the treatment period. Tumors and kidneys were harvested, and serum was analyzed for calcium and drug levels.

RESULTS

Doses of 0.1 to 1.2 microg/d were selected on the basis of toxicity studies for the dose-response trial. Tumor weight and volume in the 0.2-microg and 0.3-microg doses were significantly lower than in controls. Mortality rates and kidney calcification in mice treated with doses of 0.1 to 0.3 microg were lower than those observed in studies of calcitriol and vitamin D(2).

CONCLUSION

A vitamin D analogue, 1alpha-OH-D(2), inhibits tumor growth in this xenograft model of retinoblastoma with less toxicity than calcitriol and vitamin D(2).

Transforming growth factor-beta administration modifies cyclosporine A-induced bone loss

Cyclosporine A (CsA), a potent immunosuppressant used in transplantation, induces increased formation with excess resorption in the rat with resultant osteopenia. These findings are confirmed in the human model. Transforming growth factor-beta (TGF-beta) is reported to be involved in the coupling of bone formation with resorption and in vivo and in vitro stimulates osteoblasts, and in vitro inhibits osteoclasts. CsA stimulates secretion of TGF-beta1 in humans, which, while improving immunosuppression, may also contribute to renal toxicity. This study was performed determine whether exogenously administered TGF-beta would modify the bone effects of CsA. Male Sprague-Dawley rats, 6 months of age, were randomized to receive: TGF-beta and CsA vehicle (group A); TGF-beta 5 microg/kg three times per week and CsA vehicle (group B); TGF-beta vehicle and CsA 10 mg/kg (group C); or TGF-beta 5 microg/kg three times per week and CsA 10 mg/kg (group D). These were compared with control over 28 days. CsA, but not TGF-beta, increased serum 1,25(OH)(2)D levels throughout the study. CsA increased osteocalcin (BGP), but TGF-beta negated this effect. Histomorphometry confirmed the known effects of CsA, whereas TGF-beta alone had no effect. However, in combination, TGF-beta blocked CsA's effect and increased osteoblast recruitment and activity, as reflected by increased percent mineralizing surface, percent osteoid perimeter, bone formation rate (bone volume referent), and activation frequency. Thus, it appears as if TGF-beta administration may have potential in modulating the deleterious bone effects of CsA.

Diminished and erratic absorption of ergocalciferol in adult cystic fibrosis patients

BACKGROUND

Osteoporosis diminishes the quality of life in adults with cystic fibrosis (CF). Vitamin D deficiency resulting from malabsorption may be a factor in the etiology of low bone mineral density (BMD) in patients with CF.

OBJECTIVE

Absorption of oral ergocalciferol (vitamin D2) and the consequent response of 25-hydroxyvitamin D in 10 adults with CF and exocrine pancreatic insufficiency was compared with that of 10 healthy control subjects.

DESIGN

In this pharmacokinetic study, CF patients and control subjects were pair-matched on age, sex, and race. Each subject consumed 2500 microg oral vitamin D2 with a meal. The CF group also took pancreatic enzymes that provided > or = 80000 U lipase. Blood samples were obtained at baseline and at 5, 10, 24, 30, and 36 h after vitamin D2 consumption to measure serum vitamin D2 and 25-hydroxyvitamin D concentrations.

RESULTS

Vitamin D2 concentrations in all subjects were near zero at baseline. CF patients absorbed less than one-half the amount of oral vitamin D2 that was absorbed by control subjects (P < 0.001). Absorption by the CF patients varied greatly; 2 patients absorbed virtually no vitamin D2. The rise in 25-hydroxyvitamin D in response to vitamin D2 absorption was significantly lower over time in the CF group than in the control group (P = 0.0012).

CONCLUSIONS

Vitamin D2 absorption was significantly lower in CF patients than in control subjects. These results may help explain the etiology of vitamin D deficiency in CF patients, which may contribute to their low BMD.

Comparison of commercially available (125)I-based RIA methods for the determination of circulating 25-hydroxyvitamin D

BACKGROUND

Measurement of circulating 25-hydroxyvitamin D [25(OH)D] is important in the management of metabolic bone disease. The aim of this study was to compare two widely used methods for the quantification of circulating 25(OH)D with attention to their abilities to measure 25-hydroxylated ergocalciferol (vitamin D(2)) [25(OH)D(2)] and cholecalciferol (vitamin D(3)) [25(OH)D(3)].

METHODS

We used two commercially available, Food and Drug Administration-approved, radioiodine ((125)I)-based RIA kits for the detection of 25(OH)D (DiaSorin, Stillwater, MN and IDS Ltd, Tyne and Wear, United Kingdom). These methods were tested for general assay performance, including antibody specificity. Results were compared with those of an HPLC-based direct ultraviolet detection method.

RESULTS

Within- and between-run CVs were </=10%. Both methods quantitatively recovered 25(OH)D(3) added to serum, but only the DiaSorin kit quantitatively recovered 25(OH)D(2). The primary antibody in the IDS kit had unequal reactivities with pure 25(OH)D(2) and 25(OH)D(3), whereas the DiaSorin primary antibody reacted with them equally. In 50 patient samples assayed by HPLC, the IDS method, but not the DiaSorin method, underestimated total circulating 25(OH)D when significant circulating 25(OH)D(2) was present in patient samples.

CONCLUSIONS

Some immunoassays may underestimate total 25(OH)D when 25(OH)D(2) constitutes an appreciable part of the total.

Decreased bioavailability of vitamin D in obesity

BACKGROUND

Obesity is associated with vitamin D insufficiency and secondary hyperparathyroidism.

OBJECTIVE

This study assessed whether obesity alters the cutaneous production of vitamin D(3) (cholecalciferol) or the intestinal absorption of vitamin D(2) (ergocalciferol).

DESIGN

Healthy, white, obese [body mass index (BMI; in kg/m(2)) > or = 30] and matched lean control subjects (BMI </= 25) received either whole-body ultraviolet radiation or a pharmacologic dose of vitamin D(2) orally.

RESULTS

Obese subjects had significantly lower basal 25-hydroxyvitamin D concentrations and higher parathyroid hormone concentrations than did age-matched control subjects. Evaluation of blood vitamin D(3) concentrations 24 h after whole-body irradiation showed that the incremental increase in vitamin D(3) was 57% lower in obese than in nonobese subjects. The content of the vitamin D(3) precursor 7-dehydrocholesterol in the skin of obese and nonobese subjects did not differ significantly between groups nor did its conversion to previtamin D(3) after irradiation in vitro. The obese and nonobese subjects received an oral dose of 50000 IU (1.25 mg) vitamin D(2). BMI was inversely correlated with serum vitamin D(3) concentrations after irradiation (r = -0.55, P: = 0.003) and with peak serum vitamin D(2) concentrations after vitamin D(2) intake (r = -0.56, P: = 0.007).

CONCLUSIONS

Obesity-associated vitamin D insufficiency is likely due to the decreased bioavailability of vitamin D(3) from cutaneous and dietary sources because of its deposition in body fat compartments.

Rickets caused by excessive renal phosphate loss and apparent abnormal vitamin D metabolism in a cat

Rickets was diagnosed in a 1-year-old cat with a history of weakness, osteopenia, and recurrent fractures. Processes causing rickets include vitamin D deficiency caused by inadequate, nutrition, lack of exposure to sunlight, defective metabolism of parent vitamin D to active metabolites, inherited vitamin D receptor defects, hypoparathyroidism, chronic renal failure, renal loss of phosphate, or malabsorptive states resulting from gastrointestinal or hepatic diseases. On the basis of analysis of serum 25-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D2 and D3 concentrations, serum biochemical analysis, and urinary fractional clearance of electrolytes, the causes of rickets in our cat, were most compatible with a combination of excessive loss of phosphorus via the kidneys and deficient or abnormal hepatic 25-hydroxylation of vitamin D. Calcifediol treatment and twice daily administration of phosphate salts resulted in clinical improvement and increases in mineralization of the skeleton, as evidenced on radiographic evaluation.

Isolation and identification of 4,25-dihydroxyvitamin D2: a novel A-ring hydroxylated metabolite of vitamin D2

Vitamin D2 is less toxic in rats when compared to vitamin D3. Our laboratory has been involved in research projects which were directed towards identifying the possible mechanisms responsible for the toxicity differences between vitamins D2 and D3 in rats. The present research project was designed to isolate and identify new metabolites of vitamin D2 from serum of rats which were fed toxic doses of vitamin D2. Hypervitaminosis D2 was induced in 30 rats by feeding each rat with 1000 nmol of vitamin D2/day x 14 days. The rats were sacrificed on the 15th day and obtained 180 ml of serum. The lipid extract of the serum was directly analyzed by a straight phase HPLC system. The various vitamin D2 metabolites were monitored by their ultraviolet (UV) absorbance at 254 nm. One of the UV absorbing peaks did not comigrate with any of the known vitamin D2 metabolites. This unknown metabolite peak was further purified by HPLC and was then subjected to UV absorption spectrophotometry and mass spectrometry. The structure assignment of the new metabolite was established to be 4,25-dihydroxyvitamin D2 [4,25(OH)2D2] by the techniques of UV absorption spectrophotometry and mass spectrometry and by the new metabolite's susceptibility to sodium metaperiodate oxidation. At present the biological activity of this unique 'A-ring' hydroxylated vitamin D2 metabolite is not known. As this new metabolite is isolated from the serum of rats intoxicated with vitamin D2, we speculate that 4,25(OH)2D2 may be playing an important role in the deactivation of vitamin D2.

Effect of hemodialysis on the pharmacokinetics of 19-nor-1alpha,25-dihydroxyvitamin D2

The vitamin D2 analogue 19-nor-1alpha,25-dihydroxyvitamin D2 (paricalcitol) has been tested for the treatment of secondary hyperparathyroidism in patients with end-stage renal disease. Clinical studies have shown that paricalcitol reduces serum parathyroid hormone (PTH) levels with minimal potential to cause hypercalcemia, a common side effect of vitamin D3 therapy. Paricalcitol is typically administered intravenously after hemodialysis (HD). Because the administration of paricalcitol before or during dialysis would be desirable, the effect of HD on paricalcitol pharmacokinetics was investigated. Six patients requiring HD received a single dose of paricalcitol, 0.08 microg/kg, intravenously approximately 2 hours before HD, and blood samples were collected by venipuncture immediately before and 15 minutes after HD. Also, pairs of pre- and postdialyzer blood samples were collected approximately 1 and 2 hours after the start of HD. Plasma concentrations of paricalcitol in the samples were determined by a specific high-performance liquid chromatography (HPLC)/radioreceptor assay (RRA) with a lower limit of quantification of 40 pg/mL. Compared with previous pharmacokinetic studies in HD patients, plasma concentrations (100 to 250 pg/mL) during the 4-hour period were consistent with predicted values for this dose, and there was no apparent increase in paricalcitol clearance during HD. Pre- and postdialyzer plasma concentrations of paricalcitol were compared statistically using a paired t-test. Postdialyzer concentrations tended to be slightly higher than those predialyzer, but the differences were not statistically significant (P = 0.11). Thus, HD essentially had no effect on plasma concentrations of paricalcitol, suggesting that paricalcitol can be administered at any time during dialysis.

Unique 24-hydroxylated metabolites represent a significant pathway of metabolism of vitamin D2 in humans: 24-hydroxyvitamin D2 and 1,24-dihydroxyvitamin D2 detectable in human serum

We have produced evidence for a new metabolic pathway for vitamin D2 in humans involving the production of 24-hydroxyvitamin D2 (24OHD2) and 1,24-dihydroxyvitamin D2 [1,24-(OH)2D2]. These metabolites were produced after either a single large dose (10(6) IU) of vitamin D2 or repeated daily doses between 10(3) and 5 x 10(4) IU. We developed assay systems for the metabolites in human serum and showed that in some chronically treated patients, the concentration of 1,24-(OH)2D2 equalled that of 1,25-(OH)2D2 at about 100 pmol/L. The metabolites were identified by high performance liquid chromatography with diode array spectrophotometry for 24OHD2 and by high resolution gas chromatography-mass spectrometry for 1,24-(OH)2D2. We show that 1,24-(OH)2D2 synthesis can be stimulated by PTH, indicating a renal origin for this metabolite and postulate that it is formed from 24OHD2, which may be synthesized in liver. We conclude from this study that vitamin D2 gives rise to two biologically active products, 1,24-(OH)2D2 and 1,25-(OH)2D2, and that 1,24-(OH)2D2 could be an attractive naturally occurring analog of 1,25-(OH)2D3 for clinical use.

Saccharated ferric oxide (SFO)-induced osteomalacia: in vitro inhibition by SFO of bone formation and 1,25-dihydroxy-vitamin D production in renal tubules

A 60-year-old man with portal hypertensive gastropathy due to type C liver cirrhosis developed severe bone pains, marked hypophosphatemia with inappropriately increased urinary excretion of phosphate (%TRP; 9.6%), and hyperalkaline phosphatasia, after intravenous administration of saccharated ferric oxide (SFO) at a dose of 80-240 mg/week over a period of more than 5 years. The total iron infused was estimated to be more than 25 g. On a diagnosis of SFO-induced osteomalacia, the infusion of iron was immediately discontinued, and phosphate and vitamin D2 (1000 IU/day) were administered. Serum levels of 25-OHD2 increased after 1 week, whereas levels of 1,25-(OH)2D2 did not increase until 3 months later, accompanied by improvement of renal tubular reabsorption of phosphate and gradual improvement of the bone pains. The patient has been doing well for the last 2 years, with normal serum levels of phosphate, calcium, and alkaline phosphatase, without any supplementation of phosphate, vitamin D, or iron-containing agents. In primary culture of neonatal mouse renal tubules, in which 1,25-(OH)2D3 was produced from 25-OHD3 in response to PTH, SFO significantly inhibited PTH-induced production of 1,25-(OH)2D3 at 30 mumol/L, which is attainable in the urine of patients receiving a therapeutic intravenous dose of SFO. Furthermore, SFO decreased the calcium content and inhibited 45Ca incorporation in cultured fetal mouse parietal bones at 3 mumol/L. Such SFO concentration may be transiently observed in the plasma of patients receiving excessive intravenous doses of SFO for a prolonged period. These in vitro findings together with the clinical observations suggest that SFO, after filtration through the glomerulus and reabsorption in the proximal renal tubules, impaired proximal renal tubular function, such as tubular reabsorption of phosphate and 1 alpha-hydroxylase activity, leading to hypophosphatemic osteomalacia. Furthermore, it is highly likely that SFO in the peripheral blood, when transferrin is saturated with iron, may impair bone formation and aggravate osteomalacia. Although SFO-induced osteomalacia is reversible simply by discontinuation of the agent, excessive and prolonged administration of SFO should be avoided.

Simplified method for the determination of 25-hydroxy and 1alpha,25-dihydroxy metabolites of vitamins D2 and D3 in human plasma. Application to nutritional studies

A simplified method for the determination of 25-hydroxy and 1alpha,25-dihydroxy metabolites of vitamins D2 and D3 in human plasma was developed. Plasma samples were deproteinizated and applied to a Bond Elut C18OH cartridge to separate 25-hydroxyvitamin D (25-OH-D) and 1alpha,25-dihydroxyvitamin D [1,25(OH)2D] fractions. The 25-OH-D fraction was purified by a Bond Elut C18 cartridge and 25-OH-D2 and 25-OH-D3 were assayed by HPLC using a Zorbax SIL column. The 1,25(OH)2D fraction obtained above was subsequently applied to HPLC using a Zorbax SIL column to separate 1,25(OH)2D2 and 1,25(OH)2D3 fractions which were determined by a radioreceptor assay (RRA) using calf thymus receptor. The method was applied to nutritional studies.

Inappropriate phosphate excretion in idiopathic hypercalciuria: the key to a common cause and future treatment?

AIMS

To present experimental evidence in support of a proposed common cause for absorptive hypercalciuria, renal hypercalciuria, renal phosphate leak and enhancement of 1,25-(OH)2-vitamin D concentrations in patients presenting with renal stone disease; and to suggest further investigation with a view to new management.

METHODS

An oral calcium loading test was administered to 15 patients with renal stones and 10 normal controls in the fasting state: urine and blood were collected hourly. After the second urine sample, 400 mg calcium dissolved in water was administered orally. Serum calcium, albumin, parathyroid hormone (PTH), and phosphate were measured together with urine calcium clearance and urinary phosphate from which the TmPO4/glomerular filtration rate (GFR) ratio was calculated. Serum 1,25-(OH)2-vitamin D was measured in the first serum sample. In addition, 24 hour urine calcium results were collected retrospectively from the patients' case notes over the previous 18 months.

RESULTS

In the basal state, renal stone patients had an overall greater phosphaturia (lower TmPO4/GFR: median 1.72 compared with 2.10 in controls) and increased calcium clearance. Serum corrected calcium and PTH concentrations did not differ between the groups. After calcium loading, serum calcium and urine calcium clearance rose in both groups, with patients with renal stones experiencing a greater percentage fall in phosphaturia. In both groups TmPO4/GFR fell (greater phosphaturia) with increased serum corrected calcium, with the patients showing notably greater phosphaturia for any given calcium concentration. Patients also had notably greater phosphaturia compared with the serum calcium concentration for any given PTH value. Serum 1,25-(OH)2-vitamin D was higher in patients than controls and for any 1,25-(OH)2-vitamin D concentration phosphaturia measured against serum calcium was greater in patients than controls. 1,25-(OH)2-vitamin D did not correlate with phosphaturia relative to serum calcium concentrations within the patient and control groups.

CONCLUSIONS

It is proposed that patients with idiopathic hypercalciuria have an "inappropriately' high phosphate excretion for any given serum calcium concentration. Loss of phosphate may induce increased activation of 1,25-(OH)2-vitamin D. Some of the commonly described causes of stone formation may be manifestations of a single mechanism.

Effect of age on the intestinal absorption of vitamin D3-palmitate and nonesterified vitamin D2 in the term human infant

This study was undertaken to investigate the utility of vitamin D3-palmitate as a nutritional supplement and thus define the intestinal absorption profile of vitamin D2 and vitamin D3 liberated after its cleavage from vitamin D3-palmitate in the human infant at various postnatal ages. The subjects for study consisted of 48 normal infants that were simultaneously administered 0.07 and 0.08 micromol/kg BW vitamin D as vitamin D3-palmitate and nonesterified vitamin D2 respectively, by orogastric tube. Blood samples were obtained before and 6, 12, and 24 h postadministration and analyzed simultaneously for vitamins D2 and D3. For data analysis, the infants were divided into two groups based on postnatal age: group 1, 1 day of age; and group 2, more than 10 days of age. Data were analyzed using the integrated peak area under the absorption curve for each subject. All subjects demonstrated the ability to absorb vitamin D after oral administration, although postnatal age as well as vitamin form had a profound effect on the absorption of vitamin D2 and vitamin D3 liberated from vitamin D3-palmitate. Nonesterified vitamin D2 is well absorbed both in very young and older infants, although absorption efficiency increases with age, perhaps due to increased bile acid secretion. Liberation of vitamin D3 from vitamin D3-palmitate was shown to increase, perhaps due to gastrointestinal tract maturation, beyond 10 days of age, probably coinciding with the secretion of intestinal esterases. Our data indicate that both forms of the orally administered vitamin approach equivalency in their abilities to elevate circulating vitamin D levels in the human infant at a postnatal age of approximately 89 days. Thus, vitamin D3-palmitate would appear not to be dietarily equivalent to free vitamin D as a nutritional source of vitamin D in the human neonate.

Metabolism of 1 alpha-hydroxyvitamin D2 to activated dihydroxyvitamin D 2 metabolites decreases endogenous 1 alpha, 25-dihydroxyvitamin D 3 in rats and monkeys

The vitamin D analog 1 alpha-hydroxyvitamin D2 (1 alpha-OHD2) is under development for the treatment of secondary hyperparathyroidism and metabolic bone disease. This analog is metabolized in vivo to the natural active dihydroxylated metabolite of vitamin D2, 1 alpha,25-dihydroxyvitamin D2 [1 alpha,25-(OH)2D2]. To study the metabolism of this analog, an assay involving HPLC separation and purification of metabolites followed by RRA with the vitamin D receptor was developed to quantitate the active metabolites of the analog and the endogenous active metabolite of vitamin D3, 1 alpha,25-(OH)2D3, from the same blood sample. This assay was used to determine blood levels of active dihydroxylated vitamin D compounds in rats and monkeys treated with oral 1 alpha-OHD2. As the circulating 1 alpha,25-(OH)2D2 level increased dose dependently in these rats and monkeys, a concomitant decrease in the endogenous 1 alpha,25-(OH)2D3 was observed. In rats orally administered more than 2.5 micrograms 1 alpha-OHD2/kg.day, a second active metabolite of 1 alpha-OHD2, 1 alpha,24-(OH)2D2, was detected in concentrations similar to those of 1 alpha,25-(OH)2D2. These results indicate that the regulatory control of endogenous vitamin D metabolism as well as analog metabolism must be considered when assessing the therapeutic potential of a vitamin D analog.

Functional improvement with vitamin D replenishment in a cohort of frail, vitamin D-deficient older people

OBJECTIVE

To evaluate functional improvement in a population of frail, homebound older persons with low vitamin D status as vitamin D stores improve.

DESIGN

Randomized, controlled intervention study.

SETTING

Subjects' homes and a nursing facility in Baltimore, Maryland.

PARTICIPANTS

The first 32 subjects (community-dwelling, homebound older subjects from the Johns Hopkins Elder Housecall Program and nursing home residents from the Johns Hopkins Geriatrics Center) entered in a longitudinal study of vitamin D replacement.

MEASUREMENTS

Baseline 25-hydroxyvitamin D levels were measured and repeated at least 1 month after therapy with either placebo or vitamin D (ergocalciferol). Subjects were also administered the Frail Elderly Functional Assessment (FEFA) questionnaire, an instrument demonstrated to be reliable, valid, and sensitive to small increments of functional change in this population.

MAIN RESULTS

All subjects started with 25-hydroxyvitamin D levels less than 15 ng/mL. Those subjects whose levels improved by at least 3 ng/mL (> assay coefficient of variation) also demonstrated improvement in FEFA score. Regression analysis between change in FEFA score compared with change in 25-hydroxyvitamin D was significant (r = .4; P = .02).

CONCLUSIONS

In this cohort of homebound older people, improvement in vitamin D status was associated with functional improvement as measured by the FEFA questionnaire.

Compensation for the interracial variance in the cutaneous synthesis of vitamin D

We investigated the homeostatic compensation for the lower cutaneous synthesis of vitamin D in heavily melanized persons. Vitamin D2 (50,000 IU) was administered in a single oral dose to 24 young adults, 12 blacks and 12 whites, matched for age, gender, and socioeconomic status. We also included a group of eight healthy elderly white adults as representatives of a population with a nonracial mechanism for decreased cutaneous vitamin D synthesis. Plasma determinants were performed under basal conditions and at 6, 10, and 24 hours after vitamin D intake. Basal 25-hydroxyvitamin D (25-OH-D) levels were significantly lower in blacks (12.5 +/- 2.2 ng/ml (mean +/- SEM)) and in elderly whites (19.2 +/- 1.9 ng/ml), compared with young whites (30.2 +/- 3.0 ng/ml (p < 0.0001)); levels of basal 1,25-dihydroxyvitamin D (1,25(OH)2 -D) did not differ between groups. The vitamin D blood curve was similar between groups after the oral vitamin D2 load. Increases in 25-OH-D were 91.7 +/- 15.9% in blacks, 18.8 +/- 5.2% in young whites, and 28.6 +/- 6.9 in elderly whites; 1,25(OH)2-D levels increased slightly and did not differ between groups, although in blacks the change over time was significant (p < 0.05). As a whole, the study populations exhibited a strong relation between basal and peak 25-OH-D (r = -0.80; p < 0.001). Levels of intact parathyroid hormone and serum calcium of blacks and young whites did not differ within or between groups throughout the test.(ABSTRACT TRUNCATED AT 250 WORDS)

Pseudo-vitamin D deficiency: absence of 25-hydroxyvitamin D 1 alpha-hydroxylase activity in human placenta decidual cells

Pseudo-Vitamin D Deficiency Rickets (PDDR), an heritable defect in renal 25-hydroxyvitamin D 1 alpha-hydroxylase activity, leads to insufficient synthesis of 1 alpha, 25-dihydroxyvitamin D (calcitriol) and the early onset of severe rickets which can only be offset by replacement therapy with calcitriol. The nature of the underlying mutation remains unknown. Hydroxylation of 25-hydroxyvitamin D in the 1 alpha-position is not restricted to the renal tubular cells. We have previously shown that human decidual cells do produce calcitriol and that the enzyme activity was regulated by feedback mechanisms. We now demonstrate that cells isolated from the decidua of PDDR patients lack that function making them likely targets for the mutation. This suggests that the decidual and renal enzymes (or a controller of their activity) are encoded by the same gene. Thus the PDDR placenta represents a source of mutant cells for further investigation of the PDDR molecular defect.

Skeletal response to recombinant human growth hormone (rhGH) in children treated with long-term corticosteroids

Corticosteroid therapy causes osteopenia and growth retardation in children; such changes are associated with diminished rates of bone formation and turnover. Since growth hormone activates bone remodeling, the biochemical and skeletal responses to rhGH were evaluated in four pediatric patients, aged 12.8 +/- 3 years, with long-term corticosteroid use (5 +/- 2 years). Recombinant human growth hormone (rhGH), 0.125 mg/kg, was given 3 times/week by subcutaneous injection for 12 months. Iliac crest bone biopsies were obtained after double tetracycline labeling before and at the end of rhGH therapy; serum levels of calcium, phosphorus, alkaline phosphatase, parathyroid hormone (intact), 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D3, osteocalcin (BGP), and insulin-like growth factor-1 (IGF-1) were measured every 3 months during the treatment period. The average dose of prednisone was 0.24 +/- 0.05 mg/kg/day initially, and this did not change during the study. Serum calcium, phosphorus, alkaline phosphatase, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D3, and BGP were unchanged during the rhGH therapy, but the serum IGF-1 level increased by 71%, p < 0.01. Eroded bone perimeter and cancellous bone area did not change significantly during rhGH therapy. Bone formation rates rose from 423 +/- 475 to 781 +/- 407 microns2/mm2/day, p < 0.05, and the length of double tetracycline-labeled bone perimeter increased by 85%, p < 0.05. The bone formation rate in the growth hormone group exceeded the values of an age-matched reference group (14.3 +/- 3 years), 780 +/- 407 microns2/mm2/day versus 411 +/- 479 microns2/mm2/day, p < 0.05.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium regulating hormones in healthy elderly men: relation to intestinal calcium absorption

Aged male subjects often have osteoporosis and it has been suggested that the cause is an age-related lack of vitamin D. We evaluated the calcium regulating endocrine mechanism in healthy aged males in order to verify this hypothesis. We studied serum levels of PTH and 1,25(OH)2D in relation to intestinal calcium absorption, radial bone mass density (BMD) and osteocalcin plasma levels in 30 healthy elderly men (61-88 yr.). 1,25(OH)2D levels and calcium absorption, assessed by oral strontium test, did not change with age with respect to a young control group. PTH was higher (p < 0.02) in the elderly than in the control group, and correlated positively with nephrogenous cAMP levels (p < 0.01; r = 0.65). Radial BMD (measured by single photon absorptiometry) was lower (p < 0.01) in elderly than in young subjects and negatively correlated with age (p < 0.01; r = -0.45). Osteocalcin levels, used as a mark of bone turnover, were unchanged. The data suggest that decreased 1,25(OH)2D levels are not a feature of normal male aging. Senile hyperparathyroidism could compensate for impairments in endogenous metabolism of vitamin D in elderly males and maintain calcium absorption at an efficient level, without increasing bone turnover.

Progressively increased serum 1,25-dihydroxyvitamin D2 concentration in a hypoparathyroid patient with protracted hypercalcemia due to vitamin D2 intoxication

A 76-year-old female patient who had been taking vitamin D2 100,000 U/day for more than 14 years due to hypoparathyroidism following total throidectomy was admitted because of protracted hypercalcemia. On admission, the levels of serum vitamin D2 (99.8 ng/ml) and 25-OHD2 (356 ng/ml) were very high, and 1,25-(OH)2D2 was low (4.0-18.7 pg/ml). Serum D3' 25-OHD3 and 1,25-(OH)2D3 were below the normal range. Despite intensive hydration with saline, intravenous hyperalimentation with phosphate- and calcium-free nutrients, and administration of glucocorticoid and calcitonin, the hypercalcemia persisted, accompanied by hypoproteinemia, edema, pleural effusion and congestive heart failure. The serum D2 and 25-OHD2 concentrations remained high and were accompanied by a gradual increase in 1,25-(OH)2D2 (121 pg/ml), which further increased after the administration of bisphosphonate (pamidronate) to 183 pg/ml. Seventeen months later, serum calcium and 1,25-(OH)2D2 were normalized but serum D2 and 25-OHD2 remained high. The serum 24,25-(OH)2D2/25-OHD2 ratio was relatively constant throughout her clinical course, whereas the low serum 1,25-(OH)2D2/25-OHD2 ratio at admission gradually increased during admission, suggesting that the increase in serum 1,25-(OH)2D2 is due to increased production rather than decreased degradation. The administration of pamidronate further increased serum 1,25-(OH)2D2. These features of the clinical course demonstrate that the 1,25-dihydroxyvitamin D concentration in hypercalcemic patients with protracted vitamin D intoxication may be decreased, normal or increased. Possible factors responsible for a protracted increase in serum 1,25-(OH)2D2 are body weight loss, hypoproteinemia, and phosphate depletion. In addition, some bisphosphonates would certainly promote PTH-independent production of 1,25-(OH)2D2.

Preliminary study of multiple increasing oral doses of dimethyl-APD on bone metabolism dynamics and safety profile

A random block study, with 50, 100, 200 and 400 mg of 3-dimethylamino-1-hydroxypropylidene-1, 1-bisphosphonate or dimethyl APD and 300, 600 and 900 mg of 3-amino-1-hydroxypropylidene-1, 1-bisphosphonate or pamidronate (APD), in daily oral doses, showed that all doses were active when assessed in patients with Paget's bone disease. Dimethyl APD administration was followed by an increase in 1.25 (HO)2D levels, an effect that must be confirmed. Neither severe side effects nor significant laboratory abnormalities were detected despite some decrease in white blood cell count seen with the higher dose of APD. Gastrointestinal tolerance of dimethyl APD was acceptable but further investigation is required.