25-Hydroxyvitamin D requirement for maintaining skeletal health utilising a Sprague-Dawley rat model

To study the role of vitamin D to optimise bone architecture, we have developed an animal model to investigate the effects of frank vitamin D-deficiency as well as graded depletion of circulating 25-hydroxyvitamin D(3) (25D) levels on the skeleton. Rats fed on dietary vitamin D levels from 0 to 500 ng/day achieved diet-dependent circulating levels of 25D ranging from 11 to 115 nmol/L. Levels of serum 1,25-dihydroxyvitamin D(3) (1,25D) increased as dietary vitamin D increased between 0 and 200 ng/day at which point a maximum level was achieved and retained with higher vitamin D intakes. The renal levels of 25-hydroxyvitamin D-1alpha-hydroxylase (CYP27B1) mRNA were highest in animal groups fed on vitamin D between 0 and 300 ng/day. In contrast, renal 25-hydroxyvitamin D 24-hydroxylase (CYP24) mRNA levels increased as dietary vitamin D increased achieving maximum levels in animals receiving 500 ng vitamin D/day. This animal model of vitamin D depletion is suitable to provide invaluable information on the serum levels of 25D and dietary calcium intake necessary for optimal bone structure. Such information is essential for developing nutritional recommendations to reduce the incidence of osteoporotic hip fractures.

Quantification of mRNA for the vitamin D metabolizing enzymes CYP27B1 and CYP24 and vitamin D receptor in kidney using real-time reverse transcriptase- polymerase chain reaction

Critical to an understanding of the control of 1,25-dihydroxyvitamin D (1,25D) activity is a molecular appreciation of the regulation of three genes, 25-hydroxyvitamin D-1alpha-hydroxylase (CYP27B1), 25-hydroxyvitamin D-24-hydroxylase (CYP24) and vitamin D receptor (VDR). We now report the sensitivity, reproducibility and accuracy of a real-time reverse transcriptase-polymerase chain reaction protocol (Taqman) for the quantification of mRNA levels for these genes in total RNA extracted from kidney tIssue. The sensitivity of the protocol was at least 150 copies of mRNA per reaction. Reproducibility, expressed as the coefficient of variation, ranged between 14 and 30% at the level of approximately 10(4) copies of mRNA per reaction. Accuracy was estimated at greater than 95% for each of these mRNAs. This protocol allows for the comparison of absolute mRNA levels in extracted total RNA in kidneys from animals fed diets containing different levels of calcium, ranging from 0.05% to 1%. Serum 1,25D levels were decreased when the dietary calcium concentration was increased (P<0.05). The levels of CYP27B1 mRNA were highest in the animals fed the 0.05% calcium diet (P<0.01). Conversely, CYP24 and VDR mRNA levels were highest in the animals fed the 1% calcium diet (P<0.01). Both CYP27B1 and CYP24 mRNA levels were major determinants of serum 1,25D levels when dietary calcium intakes were varied in these adult animals (Multiple R(2)=0.70, P<0.01). No significant relationship was detected between kidney CYP27B1 and serum parathyroid hormone (PTH) suggesting that serum calcium may regulate CYP27B1 mRNA expression directly during normocalcaemia. Low levels of CYP24 mRNA were associated with high PTH levels. These findings suggest that kidney CYP24 activity, possibly regulated by factors such as PTH, acts in concert with kidney CYP27B1 to control serum 1,25D levels.

Relationship between serum 25-hydroxyvitamin D and bone resorption markers in vitamin D insufficiency

It is known that nursing-home patients with vitamin D insufficiency have elevated serum parathyroid hormone (PTH) as well as raised serum alkaline phosphatase (ALP). Although it is well known that vitamin D insufficiency and secondary hyperparathyroidism are common among the elderly in western countries, there is continuing controversy over the level of serum 25-hydroxyvitamin D [25(OH)D] necessary for bone health. We approached this issue by examining the relationships between serum 25(OH)D, ionized calcium, PTH, and ALP and the urinary bone resorption markers hydroxyproline, pyridinoline, and deoxypyridinoline, corrected for creatinine (OHPr/Cr, Pyd/Cr, and Dpd/Cr, respectively), in 486 postmenopausal women of mean age 63 (SD 9.5) years, who were referred to our osteoporosis and menopause clinics for investigation. When the patients were divided into two groups with 25(OH)D above and below 20 nmol/L, 30 nmol/L, 40 nmol/L, 50 nmol/L, 60 nmol/L, or 70 nmol/L, the most significant differences between the two groups thus derived was found at a serum 25(OH)D level of 60 nmol/L (P < 0.001 for all markers). The most significant difference between groups for serum PTH was found when the patients were divided at a serum 25(OH)D of 50 nmol/L. PTH, OHPr/Cr, Pyd/Cr, and ALP were inversely related to serum 25(OH)D. PTH was inversely related to serum ionized calcium. There was a trend for ionized calcium to be positively related to 25(OH)D, but this did not reach statistical significance. We conclude that rises in three bone resorption markers and ALP can be detected in postmenopausal women when the serum 25(OH)D level falls below 60 nmol/L. Levels above this may be required for optimal bone health.

Defining 'relative' androgen deficiency in aging men: how should testosterone be measured and what are the relationships between androgen levels and physical, sexual and emotional health?

In men, bioavailable and free testosterone levels decline by about 1.0 and 1.2% per year, respectively, after the age of 40. The definition of clinically relevant androgen deficiency in the aging male remains uncertain. Clinical features common to both aging and androgen deficiency include decreased muscle mass and strength, and increased fatigue, increased fat mass, loss of libido, erectile dysfunction, impaired cognitive function and depression. It is, however, difficult to separate the effect on plasma testosterone of concomitant disease, compared with the effects of a decrease in testosterone levels alone. Testosterone supplementation has been shown to be effective in improving many of the clinical features of androgen deficiency in the older male, and is safe, at least in the short term. The maximum benefit occurs in those men with the lowest testosterone levels.

An open, crossover trial of calcium-fortified milk in prevention of early postmenopausal bone loss

OBJECTIVE

To establish whether calcium-enriched milk reduces bone loss in women who are within five years of the menopause and have a basal calcium intake < or = 1,250 mg.

DESIGN

Two-year open, crossover study.

SETTING

A community-based study carried out in Adelaide, South Australia, between September 1997 and June 2000.

PARTICIPANTS

115 women recruited by newspaper advertisement, who were less than five years postmenopausal, were not taking hormone or other therapy that could affect bone and had a usual calcium intake < or = 1,250 mg daily.

INTERVENTION

Participants were randomly allocated to Group 1 (who received a supplement of 3 L of calcium-fortified milk weekly in the first year) or Group 2 (who followed their usual diets in the first year). In the second year, Group 1 reverted to their usual diets, and Group 2 received the milk supplement.

MAIN OUTCOME MEASURES

Difference in loss of bone mineral density (BMD) at the spine and forearm in the same individuals on and off the milk supplement; urinary excretion of bone resorption markers in a subset of 72 participants in the first year.

RESULTS

With each woman serving as her own control, the rate of bone loss from the spine was 1.76 percentage points less when the women were taking the milk supplement than when they were on their usual diet (95% CI, 0.54%-2.98%; P=0.006). However, there was no significant difference in bone loss in the forearm. Fasting urine levels of two markers of bone resorption (hydroxyproline and deoxypyridinoline) were significantly lower in 36 women in the milk group than in 36 women in the usual-diet group (P=0.03 for both markers).

CONCLUSION

Supplementing the diet with calcium-fortified milk early in the postmenopausal period delays bone loss at the spine but not at the forearm, and reduces the excretion of bone resorption markers.

Oestrogen deficiency impairs intestinal calcium absorption in the rat

1. The effects of ovariectomy on the relationships between calcium consumption and calcium balance and its components were assessed in adult (10-14 months) sham-operated and ovariectomized (Ovx) rats fed a semi-synthetic diet with the calcium content varying between 0.02 and 0.4%. 2. Adaptation to dietary calcium restriction was monitored for 47 days from commencement of a 0.02 % Ca diet. 3. Response to 1,25-dihydroxyvitamin D (20 ng kg-1 day-1) administration in sham and Ovx rats and oestradiol (E2) (20 microgram kg-1 day-1) replacement in Ovx rats was assessed in rats fed a 0.05% Ca diet. 4. Ovx rats had lower intercepts for the relationships between calcium consumption and both calcium balance (P < 0.005) and intestinal calcium absorption (P < 0.005) compared with sham rats, but 1,25-dihydroxyvitamin D was not reduced in Ovx rats. 5. The magnitude of adaptation to dietary calcium restriction was unaffected by ovariectomy. 6. Intestinal calcium absorption was stimulated by an equivalent amount in sham and Ovx rats following 1, 25-dihydroxyvitamin D administration, although this did not reach statistical significance for sham (sham, t = 1.91, n.s.; Ovx, t = 3. 18, P < 0.05). 7. Oestradiol replacement in Ovx rats induced a marked increase in intestinal calcium absorption (t = 8.25, P < 0. 005), without stimulating circulating 1,25-dihydroxyvitamin D levels and led to a marked increase in calcium balance (t = 6.89, P < 0. 005). 8. These data indicate that the impairment of intestinal calcium absorption following ovariectomy is not the result of reduced circulating 1,25-dihydroxyvitamin D or reduced intestinal responsiveness to 1,25-dihydroxyvitamin D. Moreover E2 stimulates intestinal calcium absorption probably by a direct effect on the intestine.

The effect of oophorectomy on calcium homeostasis

Postmenopausal bone loss is associated with a rise in the fasting urine calcium excretion which has been proposed to be a possible cause of increased bone resorption. The oophorectomized rat is widely used as a model of postmenopausal bone loss, but preliminary data suggest that urine calcium excretion is not increased following oophorectomy in this animal model. However the present detailed experimental protocol demonstrated that oophorectomy in adult rats increased the obligatory urine calcium excretion compared with ovary-intact rats (P < 0.001). Importantly urine hydroxyproline excretion was positively correlated with urine calcium only in the oophorectomized rats (P = 0.003). This urine calcium was positively correlated with urine phosphate excretion when dietary sodium was low (P < 0.001) and with urine sodium excretion when dietary sodium was elevated (P = 0.003). Calcium balance studies indicated a greater fall in calcium accretion in growing, oophorectomized rats (6 to 15 weeks of age) compared with ovary-intact animals and intestinal calcium secretion was the major component of the calcium balance to be affected. Losses of calcium in the urine were relatively minor in these growing rats.

Oophorectomy in young rats impairs calcium balance by increasing intestinal calcium secretion

Calcium balance and its major components (true calcium absorption, urinary calcium excretion and intestinal calcium secretion) were assessed by a 6-d balance technique in young (6-wk-old) rats fed a diet containing 7.2 g Ca/kg diet. Following either oophorectomy (oophx) or sham operation, the balance study was repeated at 9, 12 and 15 wk of age. Calcium balance decreased with age but remained positive in each group [mean (pooled SEM): sham, (6 wk) 0.86 to (15 wk) 0.27 (0.03) mmol/d (P < 0.0001); oophx, (6 wk) 0.91 to (15 wk) 0.22 (0.03) mmol/d (P < 0.0001)]. Analysis of variance of the change in calcium balance indicated that there was a significantly greater reduction in calcium balance in the oophx group compared with the sham-operated group. Intestinal calcium absorption decreased in each group with age [sham: (6 wk) 46.3% to (15 wk) 22.6% (1.5%) (P < 0.0001); oophx: (6 wk) 48.2% to (15 wk) 21.2% (1.5%) (P < 0.0001)]. There was a marked rise in intestinal calcium secretion in the oophx group compared with the sham-operated group at 6 wk post-operation (12 wk of age) [oophx: 0.33 (0.02) mmol/d; sham: 0.23 (0.02) mmol/d (P < 0.01)]. Urinary calcium excretion was not affected by either age or oophorectomy. We conclude that oophorectomy in young rats leads to a reduction in calcium accumulation, which is mainly the result of an increase in intestinal calcium secretion.

Osteoporosis and Klinefelter's syndrome

OBJECTIVE

We wanted to measure forearm mineral density and bone-related biochemical variables in patients with Klinefelter's syndrome.

DESIGN

Measurements made in patients with Klinefelter's syndrome were compared to those obtained in age-matched normal male volunteers.

PATIENTS

We studied 22 patients with Klinefelter's syndrome (12 of whom had received sex hormone therapy) and 22 control subjects.

MEASUREMENTS

We measured forearm mineral density, forearm fat content, fat-corrected forearm mineral density, plasma calcium and ionized calcium, serum osteocalcin, testosterone and dehydroepiandrosterone sulphate, and urinary hydroxyproline/creatinine ratio.

RESULTS

Forearm mineral density was lower in the Klinefelter's group than in the control subjects (P less than 0.05) and below the control range in 5 patients. The fat content of the forearm was greater in the Klinefelter's group (P less than 0.002). Serum osteocalcin and testosterone were lower, while ionized calcium and the urinary hydroxyproline/creatinine ratio were higher in the Klinefelter's group (P less than 0.002). Serum dehydroepiandrosterone sulphate and testosterone were significantly related in the Klinefelter's group (r = 0.64, P less than 0.001), but not in the controls (r = 0.22, NS). Forearm mineral density and fat-corrected forearm mineral density were significantly related to serum testosterone in the Klinefelter's group (r less than 0.63; P less than 0.01), but not in the control subjects (r less than 0.03, NS).

CONCLUSIONS

Decreased bone density occurs in about 25% of patients with Klinefelter's syndrome and probably reflects both decreased bone formation and increased bone resorption.

Calcium absorption in normal and osteoporotic postmenopausal women

Hourly fractional absorption of radiocalcium (alpha), serum calcitriol, and a number of other variables were measured in 152 normal and 148 osteoporotic postmenopausal women. Alpha, body weight, and serum albumin were all significantly lower in the osteoporotic than in the normal women, and plasma alkaline phosphatase, fasting urinary calcium, sodium, and hydroxyproline were all significantly higher in the osteoporotic than in the normal group. The most significant determinant of alpha in each group was the serum calcitriol concentration, but calcium absorption relative to serum calcitriol was significantly lower in the osteoporotic than in the normal women. The serum calcitriol level was slightly but not significantly lower in the osteoporotic than in the normal group and accounted for only 20% of the difference in alpha between them. The implied "resistance" to calcitriol in the osteoporotic group was significantly related to serum albumin and body weight but independent of age. Urinary hydroxyproline was an inverse function of alpha and a positive function of fasting urinary calcium in the osteoporotic group.

Malabsorption of calcium in corticosteroid-induced osteoporosis

We have examined the relation between radiocalcium absorption and serum 1,25-dihydroxyvitamin D [1,25(OH)2D3] levels in a set of 60 postmenopausal women on corticosteroid therapy (29 with and 31 without vertebral compression fractures) and compared these results with those from 31 normal postmenopausal women age-matched with the "normal" corticosteroid-treated women. Radiocalcium absorption was a function of serum 1,25(OH)2D3 in both corticosteroid-treated groups and in the set as a whole, but the impaired calcium absorption in the corticosteroid-treated patients with osteoporosis was not accounted for by their slightly reduced serum 1,25(OH)2D3 levels. This apparent resistance to the intestinal action of 1,25(OH)2D3 was quantified by a Z score which expresses, in standard deviation units, the difference between the measured calcium absorption and that predicted from the 1,25(OH)2D3 level. The Z score was significantly reduced in the osteoporotic group. Vertebral mineral density (VMD) was measured by quantitative computed tomography in 43 of the corticosteroid-treated cases and in all the normal postmenopausal women; analysis by VMD yielded similar conclusions.

Urinary oxalate determination by use of immobilized oxalate oxidase in a continuous-flow system

In this procedure, oxalate oxidase (EC 1.2.3.4) immobilized in a continuous-flow system is used to determine oxalate in urine. The hydrogen peroxide formed from oxalate is detected by use of a color reaction with peroxidase (EC 1.11.1.7), 3-methyl-2-benzothiazoline hydrazine, and N,N-dimethylalanine. However, urine contains an oxalate oxidase inhibitor, which cannot be removed by heating, ion-exchange resins, or cellulose columns. This makes it necessary to precipitate the oxalate before assay. The overall assay system is accurate (oxalate recovery, 95.9%), sensitive (less than or equal to 5 mumol/L), precise (within-batch CV less than 1.25%, between-batch CV less than 5%), and relatively rapid (60 samples per working day). The assay system has better accuracy than an established chemical method and a gas-chromatographic method, and is considerably less arduous than and correlates well (r = 0.94) with a modified chemical method. The reference interval for urinary oxalate excretion is 0.16-0.56 mmol per day (n = 97). Only nonphysiological concentrations of ascorbate interfere with the assay, by increasing the oxalate result in the overall assay, presumably by post-micturition formation of oxalate from ascorbate in the urine samples.

Urinary oxalate determination by use of immobilized oxalate oxidase in a continuous-flow system

In this procedure, oxalate oxidase (EC 1.2.3.4) immobilized in a continuous-flow system is used to determine oxalate in urine. The hydrogen peroxide formed from oxalate is detected by use of a color reaction with peroxidase (EC 1.11.1.7), 3-methyl-2-benzothiazoline hydrazine, and N,N-dimethylalanine. However, urine contains an oxalate oxidase inhibitor, which cannot be removed by heating, ion-exchange resins, or cellulose columns. This makes it necessary to precipitate the oxalate before assay. The overall assay system is accurate (oxalate recovery, 95.9%), sensitive (less than or equal to 5 mumol/L), precise (within-batch CV less than 1.25%, between-batch CV less than 5%), and relatively rapid (60 samples per working day). The assay system has better accuracy than an established chemical method and a gas-chromatographic method, and is considerably less arduous than and correlates well (r = 0.94) with a modified chemical method. The reference interval for urinary oxalate excretion is 0.16-0.56 mmol per day (n = 97). Only nonphysiological concentrations of ascorbate interfere with the assay, by increasing the oxalate result in the overall assay, presumably by post-micturition formation of oxalate from ascorbate in the urine samples.

Preparation and characterization of a human serum matrix suitable for quality control or reference materials

We describe the preparation of a human serum based matrix suitable for inclusion in long-term control materials. The procedure entails the removal of cells, fibrin and lipoproteins from blood to produce a clear, stable material which has been stored frozen at -70 degrees C for up to 14 mth without any apparent deterioration. When incorporated into a quality control material, storage at 4 degrees and -20 degrees C may cause a change in several unstable constituents, but the material remains optically clear. A noticeable reduction in lipoprotein as a result of the preparative procedure is probably responsible for the continued clarity of the matrix. The nature of the matrix has been examined by polyacrylamide gel electrophoresis and does not reveal any unusual protein bands, whereas commercially available materials when similarly examined often reveal protein bands not present in normal serum. The matrix has been used to prepare control material for the Chemical Pathology Quality Assurance Programme Group of the Royal College of Pathologists of Australasia/Australian Association of Clinical Biochemists.