Relationship Between Disease Activity and Serum Levels of Vitamin D Metabolites and Parathyroid Hormone in Ankylosing Spondylitis

Vertebral fractures due to osteoporosis are a common but frequently unrecognized complication of ankylosing spondylitis (AS) and various factors may contribute to the development of osteoporosis in AS. It is known that inflammatory activity in rheumatic disease (i.e., proinflammatory cytokines) itself plays a possible role in the pathophysiology of bone loss. 1,25-Dihydroxyvitamin D₃ (1,25(OH)₂D₃) seems to be another possible candidate for mediatory function in regulating both the inflammatory process and bone turnover. The aim of this study was to evaluate the relation between disease activity, bone turnover and calciotropic hormones. In 70 patients with established AS and an age- and sex-matched control group, the relation between disease activity (erythrocyte sedimentation rate, C-reactive protein, Bath Ankylosing Spondylitis Disease Activity Index), and serum levels of vitamin D metabolites, parathyroid hormone (PTH), bone alkaline phosphatase (bAP) and urinary pyridinium crosslinks were determined. Serum levels of 1,25(OH)₂D₃ (p<0.01) and PTH (p<0.01) were negatively correlated with disease activity, the excretion of urinary pyridinium crosslinks showed a positive correlation with disease activity (p<0.01), and 1,25(OH)₂D₃ and PTH were positively correlated with bAP (p<0.01). These results indicate that high disease activity in AS is associated with an alteration in vitamin D metabolism and increased bone resorption. Furthermore, the decreased levels of 1,25(OH)₂D₃ may contribute to a negative calcium balance and inhibition of bone formation. Our results suggest further research is necessary to determine whether low levels of 1,25(OH)₂D₃ as an endogenous immune modulator suppressing activated T cells and cell proliferation may accelerate the inflammation process in AS. Received: 29 January 2001 / Accepted: 3 August 2001     

Effects of Postmenopausal Hormone Replacement Therapy With and Without Vitamin D3 on Circulating Levels of 25-Hydroxyvitamin D and 1,25-Dihydroxyvitamin D

The effects of postmenopausal hormone replacement therapy (HRT) and vitamin D₃ on vitamin D metabolites (25OHD and 1,25(OH)₂D) were studied in a population-based prospective 1-year study. The serum concentrations of intact parathyroid hormone (PTH), calcium, and phosphate were also studied. A total of 72 women were randomized into four treatment groups: HRT group (sequential combination of 2 mg estradiol valerate and 1 mg cyproterone acetate), Vit D₃ group (vitamin D₃ 300 IU/day + calcium lactate 500 mg/day), HRT + Vit D₃ group (both above) and placebo group (calcium lactate 500 mg/day). Serum samples were taken in March–April, when vitamin D formation from sunlight in Finland is minimal after the dark winter. Serum concentrations of 25OHD increased in the Vit D₃ group (33.5%, P < 0.001) and in the HRT + Vit D₃ group (38.2%, P < 0.001) but had not changed significantly in the HRT and placebo groups at the 1-year follow-up examination. Serum concentrations of calcitriol (1,25(OH)₂D) increased, however, only in the HRT group (23.7%, P < 0.05), and remained unchanged in other groups. Serum concentrations of PTH decreased by 23.2% (P < 0.05) in the placebo group, but did not change significantly in the other three groups. The concentrations of serum calcium increased in the nonhormone groups (P < 0.001), whereas serum phosphate concentrations decreased in the hormone groups (P < 0.05 and 0.001). Our results confirm the positive effect of 1 year of HRT on serum calcitriol. Vitamin D₃ supplementation increased 25OHD concentrations, but did not affect calcitriol concentrations even though the initial levels were low. Interestingly, the combination of HRT and vitamin D₃ did not increase serum calcitriol concentrations as much as HRT alone. Received: 14 June 1996 / Accepted: 17 June 1997     

Increased Serum 1,25-Dihydroxyvitamin D after Growth Hormone Administration is not Parathyroid Hormone-Mediated

To assess the effects of growth hormone (GH) on serum 1,25-dihydroxyvitamin D [1,25(OH)₂D], we performed the following prospective crossover study in six healthy, young, adult, white men. During each of two admissions for 2? days to a general clinical research center, subjects were placed on a daily dietary calcium intake of 400 mg. Serum calcium, phosphorus, 1,25(OH)₂D, immunoreactive intact parathyroid hormone (PTH), insulin-like growth factor I (IGF-I), IGF binding protein 3 (IGFBP3), tubular reabsorption of phosphate (TRP), and maximum tubular reabsorption of phosphate (TMP/GFR) were measured. Recombinant human GH (rhGH, Humatrope) (25 μg/kg/day subcutaneously for 1 week) was administered prior to and during one of the admissions. Results are expressed as mean ± SEM. Whereas serum 1,25(OH)₂D (58.9 ± 7.7 versus 51.6 ± 7.4 pg/ml, P < 0.01), serum phosphorus (4.5 ± 0.1 versus 3.7 ± 0.1 mg/dl, P < 0.01), TRP (92.0 ± 0.5 versus 87.8 ± 0.7 mg/dl, P < 0.005), TMP/GFR (4.6 ± 0.1 versus 3.5 ± 0.2, P < 0.005), and urinary calcium (602 ± 49 versus 346 ± 25 mg/day, P < 0.001) increased significantly, serum PTH decreased significantly (19.9 ± 1.9 versus 26.8 ± 4.0 pg/ml, P < 0.05) and serum calcium did not change when subjects received rhGH. These findings indicate that in humans, GH affects serum 1,25(OH)₂D independently of circulating PTH and that this effect is mediated by IGF-I. We propose, therefore, that one potential mechanism by which GH stimulates increases in bone mass is via modest increases in serum 1,25(OH)₂D. Received: 2 May 1996 / Accepted: 18 October 1996     

Prednisolone Induces an Increase in Serum Calcium Concentration: Possible Involvement of the Kidney, the Bone, and the Intestine

To evaluate the early effect of glucocorticoids on calcium metabolism, 15 subjects aged 22–58 years (5 males, 10 females) with chronic glomerulonephritis were orally treated with 40 mg daily of prednisolone. Five of these subjects were diagnosed with nephrotic syndrome and none had a serum creatinine concentration of more than 1.4 mg/dl. Serum specimens and 24-hour urine specimens were obtained just before and 24 hours after a single oral dose of prednisolone. Serum calcium, ionized calcium, phosphate, intact parathyroid hormone (PTH), intact osteocalcin and 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), and urinary excretion of calcium, phosphate, and deoxypyridinoline were measured. Both serum calcium and ionized calcium concentrations were significantly increased from 4.39 ± 0.10 to 4.47 ± 0.09 mEq/liter (P= 0.037) and from 2.48 ± 0.04 to 2.55 ± 0.04 mEq/liter (P= 0.002), respectively, 24 hours following a single oral dose of prednisolone. Serum intact PTH concentration slightly decreased, but the difference was not significant by statistical analysis. Serum intact osteocalcin concentration was markedly suppressed. In contrast, no significant changes were observed in urinary excretion of deoxypyridinoline. Serum 1,25(OH)₂D₃ concentration measured in five patients was significantly increased. No significant changes in urinary excretion of calcium was observed in the face of these findings. It thus follows that a single oral dose of prednisolone administration increases serum calcium and ionized calcium concentrations, possibly mediated by suppressed bone formation, increased intestinal absorption of calcium, and impaired urinary excretion of calcium. Received: 19 February 1998 / Accepted: 12 March 1999     

Circulating β2 Microglobulin in Relation to Bone Metabolism: Implications for Bone Loss with Aging

The aim of this cross-sectional study was to evaluate the relationships between circulating β₂ microglobulin (β₂ m) and bone mineral density (BMD), parameters of bone remodeling, vitamin D metabolites, parathyroid hormone (PTH), estradiol levels, and age in a group of 165 clinically healthy or osteoporotic, but otherwise normal untreated women. In this group of women, systemic β₂ m correlated with BMD (g/cm²) levels for total hip and Ward's triangle (r =−0.298, P < 0.0001; and r =−0.299, P < 0.0001, respectively), but only at the borderline level with BMD at the spine (r =−0.145, P= 0.0604). Serum β₂ microglobulin markedly correlated with age (r = 0.512, P= 0.0001). β₂ m levels correlated with indices of bone remodeling, as well as with serum creatinine and estradiol levels. However, after stratification of all analyses by age, body mass index, and serum 25OHD₃, 1,25(OH)₂D₃, PTH, or estradiol levels (using standard multiple regression and stepwise forward regression models), only 25OHD₃ was found to be an independent predictor of BMD at the hip, including Ward's triangle, as estradiol of BMD at the spine. On the other hand, β₂ m was not associated with BMD at any of the measured regions. Also, no association was found between serum PTH and BMD values. Therefore, systemic β₂ m seems to be an indicator of bone remodeling in the course of natural skeletal aging rather than a variable independently predicting bone loss. Received: 21 July 1998 / Accepted: 10 June 1999     

Vitamin D Therapy of Osteoporosis: Plain Vitamin D Therapy Versus Active Vitamin D Analog (D-Hormone) Therapy

Normal intestinal calcium (Ca) absorption is an essential feature of bone homeostasis. As with many other organ systems, intestinal Ca absorption declines with aging, and this is one pathological factor that has been identified as a cause of senile osteoporosis in the elderly. This abnormality leads to secondary hyperparathyroidism, which is characterized by high serum parathyroid hormone (PTH) and an increase in bone resorption. Secondary hyperparathyroidism due to poor intestinal Ca absorption has been implicated not only in senile osteoporosis but also in age-related bone loss. Accordingly, in population-based studies, there is a gradual increase in serum PTH from about 20 years of age onward, which constitutes a maximum increase at 80 years of age of 50% of the basal value seen at 30 years of age. The cause of the increase in PTH is thought to be partly due to impaired intestinal Ca absorption that is associated with aging, a cause that is not entirely clear but at least in some instances is related to some form of vitamin D deficiency. There are three types of vitamin D deficiency: (1) primary vitamin D deficiency, which is due to a deficiency of vitamin D, the parent compound; (2) a deficiency of 1,25(OH)₂D₃ resulting from decreased renal production of 1,25(OH)₂D₃; and (3) resistance to 1,25(OH)₂D₃ action owing to decreased responsiveness to 1,25(OH)₂D₃ of target tissues. The cause for the resistance to 1,25(OH)₂D₃ could be related to the finding that the vitamin D receptor level in the intestine tends to decrease with age. All three types of deficiencies can occur with aging, and each has been implicated as a potential cause of intestinal Ca malabsorption, secondary hyperparathyroidism, and senile osteoporosis. There are two forms of vitamin D replacement therapies: plain vitamin D therapy and active vitamin D analog (or D-hormone) therapy. Primary vitamin D deficiency can be corrected by vitamin supplements of 1000 U a day of plain vitamin D whereas 1,25(OH)₂D₃ deficiency/resistance requires active vitamin D analog therapy [1,25(OH)₂D₃ or 1α(OH)D₃] to correct the high serum PTH and the Ca malabsorption. In addition, in the elderly, there are patients with decreased intestinal Ca absorption but with apparently normal vitamin D metabolism. Although the cause of poor intestinal Ca absorption in these patients is unclear, these patients, as well as all other patients with secondary hyperparathyroidism (not due to decreased renal function), show a decrease in serum PTH and an increase in Ca absorption in response to therapy with 1,25(OH)₂D₃ or 1α(OH)D₃. In short, it is clear that some form of vitamin D therapy, either plain vitamin D or 1,25(OH)₂D₃ or 1α(OH)D₃, can be used to correct all types of age-dependent impairments in intestinal Ca absorption and secondary hyperparathyroidism during aging. However, from a clinical standpoint, it is important to recognize the type of vitamin D deficiency in patients with senile osteoporosis so that primary vitamin D deficiency can be appropriately treated with plain vitamin D therapy, whereas 1,25(OH)₂D₃ deficiency/resistance will be properly treated with 1,25(OH)₂D₃ or 1α(OH)D₃ therapy. With respect to postmenopausal osteoporosis, there is strong evidence that active vitamin D analogs (but not plain vitamin D) may have bone-sparing actions. However, these effects appear to be results of their pharmacologic actions on bone formation and resorption rather than through replenishing a deficiency.     

Factors Associated with Cortical and Trabecular Bone Loss as Quantified by Peripheral Computed Tomography (pQCT) at the Ultradistal Radius in Aging Women

Peripheral quantitative computed tomography (pQCT) allows the separate determination of cortical and trabecular bone mineral density in the peripheral skeleton. This cross-sectional study was designed to examine the effects of healthy aging on pQCT measurements at the ultradistal radius. In a well-defined sample of 129 community-based women, aged 70–87 years, the differences in cortical and trabecular density over the age range were equivalent to losses of −0.41% and −0.65% per year, respectively. To investigate the mechanism of this age-related decline, we assessed relationships between both parameters and height, weight, body mass index, dietary calcium intake, grip strength, and serum concentrations of insulin-like growth factor-I (IGF-I), calcidiol (25(OH)D₃), calcitriol (1,25(OH)₂D₃), parathyroid hormone (PTH), and sex hormone binding globulin (SHBG). Multiple regression was used to adjust for potential confounders. Age was not significant after controlling for other covariables. Body mass index, grip strength, serum IGF-I, 25(OH)D₃, and PTH (1–84) were found to be independent predictors of total bone density. Including (total or free) 1,25(OH)₂D₃ did not improve the model precision. These findings provide evidence that, among other factors, the activity of the growth hormone-IGF-I-axis is of importance for skeletal integrity. Grip strength, serum IGF-I, and PTH (1–84) were discovered to be significantly related to cortical but not to trabecular density, suggesting that different mechanisms may be involved in compact and cancellous bone loss. Received: 2 May 1996 / Accepted: 18 June 1996     

1α-Hydroxyvitamin D2 Partially Dissociates Between Preservation of Cancellous Bone Mass and Effects on Calcium Homeostasis in Ovariectomized Rats

Vitamin D metabolites can prevent estrogen depletion-induced bone loss in ovariectomized (OVX) rats. Our aim was to compare the bone-protective effects of 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), 1α,25-dihydroxyvitamin D₂ (1,25(OH)₂D₂), 1α-hydroxyvitamin D₃ (1α(OH)D₃), and 1α-hydroxyvitamin D₂ (1α(OH)D₂) in OVX rats. 1α(OH)D₃ and 1α(OH)D₂ are thought to be activated in the liver to form 1,25(OH)₂D₃ and 1,25(OH)₂D₂, respectively. Forty-four 12-week-old female Fischer-344 rats were either OVX or sham-operated (SHAM). Groups of OVX rats (n = 7 each) received vehicle alone, 1,25(OH)₂D₃, 1,25(OH)₂D₂, 1α(OH)D₃, or 1α(OH)D₂, starting 2 weeks after surgery. All vitamin D metabolites were administered orally at a dose of 15 ng/day/rat. Urine and blood samples were collected 6, 9, 12, and 16 weeks after surgery. Serum samples were analyzed for total calcium and phosphate. Calcium, phosphate, creatinine, and free collagen cross-links (ELISA) were determined in urine. After tetracycline double labeling, the rats were sacrificed 16 weeks postsurgery, and the proximal tibiae and the first lumbar vertebrae were processed undecalcified for static and dynamic bone histomorphometry. 1,25(OH)₂D₃ and, to a slightly lesser extent, 1,25(OH)₂D₂ elevated vertebral cancellous bone mass in OVX rats to a level beyond that observed in SHAM animals, and both compounds increased serum calcium and urinary calcium excretion to similar extents. 1α(OH)D₃ and 1α(OH)D₂ resulted in a 64% and 84%, respectively, inhibition of ovariectomy-induced vertebral cancellous bone loss. In the proximal tibial metaphysis, all vitamin D metabolites tested could only partially prevent post-OVX trabecular bone loss, with a tendency for 1α(OH)D₃ to be the least active compound. The effects of 1α(OH)D₃ and 1α(OH)D₂ on calcium homeostasis differed markedly, however. The mean increase in urinary calcium excretion over the whole experiment was fivefold for 1α(OH)D₃, whereas the corresponding increase for 1α(OH)D₂ was only twofold. We conclude that, compared with 1α(OH)D₃, 1α(OH)D₂ combined at least equal or higher bone-protective activity in OVX rats with distinctly less pronounced effects on calcium homeostasis. This effect was not due to a differential action of the corresponding main activation products, 1,25(OH)₂D₃ and 1,25(OH)₂D₂. Received: 2 May 1996 / Accepted: 18 October 1996     

Increased Serum Levels of N-Telopeptides (NTx) of Bone Collagen in Postmenopausal Nigerian Women

Serum levels of cross-linked N-telopeptides (NTx) of bone collagen, alkaline phosphatase (ALP), and intact parathyroid hormone (PTH) were determined in 64 premenopausal (PRM) and 86 postmenopausal (PSM) women living in northern Nigeria. Serum NTx values were correlated with ALP activity (r = 0.31–0.58, P < 0.01) and PTH (0.32–0.35, P < 0.01)) in all of the subjects studied, and were also related to age (−0.47, P < 0.001) and body mass index (−0.45, P < 0.001) in PRM women. Menopause had the effect of increasing the circulating concentrations of NTx and ALP activity by 15% (P= 0.001) and 11% (P= 0.02), respectively; however, serum levels of PTH were not different between these two groups of women. Compared with Caucasian counterparts matched for age and body mass index, PSM Nigerian women had significantly increased circulating concentrations of NTx (21.7 versus 16.2 nmol BCE/liter, P= 0.01) and demonstrated a trend towards higher ALP activities and PTH levels. These results indicate that (1) discrete reference intervals should be defined for biochemical markers of bone metabolism in African populations, (2) Nigerian women have relatively higher rates of bone turnover, and (3) further investigation of the implications of increased serum NTx should be undertaken using physical methods such as dual X-ray absorptiometry (DXA) and bone ultrasound attenuation. Received: 16 September 1998 / Accepted: 10 January 1999     

Age-Related Decline of Bone Mass and Intestinal Calcium Absorption in Normal Males

Although about 25% of all hip fractures occur in men, little is known about the pattern of their age-related bone loss and its main determinants. The aim of this cross-sectional study was to evaluate the age-related changes of intestinal calcium absorption, bone mass, and bone turnover in normal men. In 70 normal males (age 17–91 years), we measured spinal and forearm bone density (FBD) (by DXA), fractional intestinal calcium absorption (by oral test), serum immunoreactive parathyroid hormone (PTH), dietary calcium intake (diet records), biochemical markers of bone turnover (serum alkaline phosphatase (ALP), osteocalcin, urine calcium, creatinine, and hydroxyproline), and 1,25(OH)₂D₃ serum levels. Vertebral bone density (VBD) showed a modest decline before age 50 and a greater decline after age 50, whereas FBD presented a significant decrease with advancing age starting at age 40, suggesting a predominant age-related cortical bone loss. Intestinal calcium absorption (⁴⁷CaFA) and serum 1,25(OH)₂D₃ also presented an age-related decline similar to FBD. Simple correlation analysis revealed that age was significantly related to ⁴⁷CaFA (r = 0.60), calcium intake (r = 0.32), VBD and FBD (r = 0.79 and 0.63, respectively), serum 1,25(OH)₂D₃ (r = 0.69), and serum iPTH (r = 0.72). No significant correlation was found between age and biochemical markers of bone remodeling. Partial correlation and stepwise variable selection analyses, using ⁴⁷CaFA and bone mass as dependent variables, showed that in normal males, serum 1,25(OH)₂D₃ and dietary calcium intake were the main contributors (64%) to ⁴⁷CaFA variability, whereas only age accounted for 63% of VBD and age and dietary calcium accounted for 45% of FBD variability. These results indicate that bone loss in men accelerates after age 50 years and that among other factors, intestinal calcium malabsorption and 1,25(OH)₂D₃ serum levels play a role. Received: 19 November 1996 / Accepted: 26 January 1998     

Enhanced suppression of 1,25(OH)2D3 and intact parathyroid hormone in Graves' disease as compared to toxic nodular goiter

Summary 1,25(OH)₂D₃, 25OHD₃, and intact parathyroid hormone, as well as various parameters of calcium-phosphorus metabolism were measured in 38 patients with Graves' disease (GD) and in 24 patients with toxic nodular goiter (TNG). Plasma 1,25(OH)₂D₃ levels were lower in GD patients (82 ±29 pmol/liter) than in those with TNG (155±32 pmol/liter) (P<0.0005). The mean value of 1,25(OH)₂D₃ in 45 controls was intermediate between the two groups of patients (140±41) and the difference was statistically significant. GD patients before and after treatment had higher alkaline phosphatase (P<0.05), lower intact parathyroid hormone (PTH) (P<0.05), and lower 1,25(OH)₂D₃ levels (P<0.0005 in the hyperthyroid andP<0.01 in the euthyroid state) than TNG patients. We conclude that increased skeletal calcium resorption is due to elevated levels of T₃ causing suppression of 1,25(OH)₂D₃ production and of PTH levels in both groups of patients albeit of different degrees. Furthermore, we postulate that the profound suppression of 1,25(OH)₂D₃ in GD is secondary to an immune-mediated phenomenon.     

Regulation of calcium absorption by 1,25,dihydroxy-vitamin D—Studies of the effects of a bisphosphonate treatment

Summary In 10 patients with Paget's disease of bone and 2 patients with osteoporosis, we studied the effects of hypocalcemia and hypophosphatemia induced by disodium-(3-amino-1-hydroxypropylidene)-1,-bisphosphonate (APD) treatment on the serum concentration of PTH and 1,25-dihydroxyvitamin D [1,25(OH)₂D₃] and on calcium absorption and balance. The fall in serum calcium and phosphate was associated with a rise in the serum concentration of PTH and 1,25(OH)₂D₃, coupled with increases in net calcium absorption and calcium balance. The concentration of 1,25(OH)₂D₃ was significantly related (P<0.001) to the serum calcium (r=0.66), the serum phosphate (r=0.78), and the serum PTH (r=0.71), confirming the interrelated control of these parameters on 1,25(OH)₂D₃ production. Moreover, the rise in 1,25(OH)₂D₃ caused an appropriate rise in calcium absorption (r=0.74) and calcium balance (r=0.86), showing that this vitamin D metabolite contributes as a hormone to calcium homeostasis.     

The Effect of Intermittent Slow-Release Sodium Fluoride and Continuous Calcium Citrate Therapy on Calcitropic Hormones, Biochemical Markers of Bone Metabolism, and Blood Chemistry in Postmenopausal Osteoporosis

A detailed examination of calcitropic hormones and biochemical markers of bone turnover, serum chemistry, and blood hematology was performed in 75 postmenopausal women allocated to two groups: placebo plus calcium citrate (400 mg Ca B.I.D.) (n = 36) or intermittent slow-release sodium fluoride (SRNaF, 25 mg B.I.D.) plus calcium citrate (n = 39). After 2 years of therapy, a significant reduction in serum immunoreactive parathyroid hormone (PTH) was seen for both groups (43 ± 18 SD–30 ± 11 ng/liter, in placebo and 46 ± 24–36 ± 10, in SRNaF P < 0.0001 for both groups). Serum 1,25(OH)₂D significantly fell in placebo-treated patients (91 ± 31–75 ± 34 pmol/liter, P= 0.001) but did not change for SRNaF-treated patients. This difference in response between placebo and SRNaF-treated groups was significant, P= 0.005. Urinary hydroxyproline significantly declined during treatment in both groups (130 ± 61–76 ± 38 μmol/day, for placebo and 138 ± 84–84 ± 38 for SRNaF, P= 0.001). Similar decreases in urinary N-telopeptide of type I collagen were also observed for both groups (305 ± 192–252 ± 197 nmoles BCE/day for placebo and 356 ± 230–220 ± 197, P= 0.0001 for SRNaF). Serum carboxyterminal propeptide of type I collagen (PICP) declined significantly in both the placebo and SRNaF groups (118 ± 38–101 ± 36 μg/liter, and 116 ± 47–105 ± 39, P= 0.0027). Serum osteocalcin did not change significantly for either group, but bone-specific alkaline phosphatase (BS-ALPase), another marker of bone formation, demonstrated a significant fall in the placebo group at 2 years of therapy (16.2 ± 6.7 U/liter–12.1 ± 3.5, P= 0.009) and a small increase in the SRNaF-treated patients (13.0 ± 4.1–15.0 ± 4.5). The observed difference in response of BS-ALPase between the placebo and treated groups was significant (P= 0.007). There were no significant changes within or between treatment groups for blood hematology or serum chemistries. Mean values for all parameters remained within established normal ranges. These findings suggest that administration of calcium citrate inhibited PTH secretion and thereby reduced bone resorption in both groups, indicated by a decline in serum PTH, urinary hydroxyproline, and N-telopeptide. A low turnover state of bone may have been produced in the placebo group taking calcium citrate alone, since serum PICP, BS-ALPase, and 1,25(OH)₂D also decreased. The addition of SRNaF prevented serum 1,25(OH)₂D from falling by an unknown mechanism. However, its anabolic action on the skeleton was best reflected by changes in BS-ALPase. Moreover, SRNaF appeared to exert no deleterious effects on blood chemistries or hematology during 2 years of administration. Received: 28 January 1996 / Accepted: 25 April 1997     

Bone Metabolism During Exercise and Recovery: The Influence of Plasma Volume and Physical Fitness

Understanding the reaction of bone to physical exercise is important for the development of strategies to increase and maintain bone mass. In this study the aim was to investigate the relationship among exercise intensity, physical capacity, and the biochemical responses, estimated by measuring biochemical markers of bone metabolism in serum. As a complement to the circulating concentrations we also accounted for the plasma volume shifts during and after exercise. The study included 10 men and 10 women, mean age 29 years, with a wide range of physical capacity, who performed a standardized running exercise test on a motor-driven treadmill with loads corresponding to 47 and 76% of VO₂ max (maximal oxygen uptake) followed by a maximal effort until exhaustion. Total work time was about 35 minutes. Venous blood samples were drawn at rest, after each load, and after 30 minutes and 24 hours of recovery. The reductions in plasma volume during exercise were 4.3% (P < 0.05) and 15.1% (P < 0.001) whereas after 24 hours in recovery there was an expansion of 7.5% (P < 0.001). There were marked, intensity-related, increases of PICP and tALP concentrations (P < 0.001) during exercise. Since these were of the order of plasma volume reduction they did not correspond to a change in the calculated circulating amount (content). However, as the concentrations returned to basal during recovery, the total circulating amounts were increased at this point (P < 0.05). Osteocalcin was also increased during recovery (P < 0.01), although concentrations were unchanged during the entire study. The amount (P < 0.001) and concentration (P < 0.05) of ICTP were also increased during follow-up. Serum PTH concentrations rose (P < 0.05) in proportion to the intensity of exercise and remained elevated during recovery. The subjects' VO₂ max demonstrated positive relationships to the biochemical responses to exercise in bone and BMD of the legs, and a negative relationship to basal PTH levels. Bone turnover and PTH secretion was stimulated by exercise, and low basal levels of PTH and high BMD were induced by a high level of physical fitness. These observations correlate well with the favorable effects of exercise and training on bone mass. Received: 5 November 1996 / Accepted: 23 April 1997     

Fluoride Treatment Increased Serum IGF-1, Bone Turnover,and Bone Mass,but Not Bone Strength,in Rabbits

We hypothesized that fluoride partly acts by changing the levels of circulating calcium-regulating hormones and skeletal growth factors. The effects of oral fluoride on 24 female, Dutch-Belted, young adult rabbits were studied. The rabbits were divided into two study groups, one control and the other receiving about 16 mg fluoride/rabbit/day in their drinking water. After 6 months of fluoride dosing, all rabbits were euthanized and bone and blood samples were taken for analyses. Fluoride treatment increased serum and bone fluoride levels by over an order of magnitude (P < 0.001), but did not affect body weight or the following serum biochemical variables: urea, creatinine, phosphorus, total protein, albumin, bilirubin, SGOT, or total alkaline phosphatase. No skeletal fluorosis or osteomalacia was observed histologically, nor did fluoride affect serum PTH or Vitamin D metabolites (P > 0.4). BAP was increased 37% (P < 0.05) by fluoride; serum TRAP was increased 42% (P < 0.05); serum IGF-1 was increased 40% (P < 0.05). Fluoride increased the vertebral BV/TV by 35% (P < 0.05) and tibial ash weight by 10% (P < 0.05). However, the increases in bone mass and bone formation were not reflected in improved bone strength. Fluoride decreased bone strength by about 19% in the L5 vertebra (P < 0.01) and 25% in the femoral neck (P < 0.05). X-ray diffraction showed altered mineral crystal thickness in fluoride-treated bones (P < 0.001), and there was a negative association between crystal width and fracture stress of the femur (P < 0.02). In conclusion, fluoride's effects on bone mass and bone turnover were not mediated by PTH. IGF-1 was increased by fluoride and was associated with increased bone turnover, but was not correlated with bone formation markers. High-dose fluoride treatment did not improve, but decreased, bone strength in rabbits, even in the absence of impaired mineralization. Received: 5 November 1996 / Accepted: 3 January 1997     

Ascorbate Increases the 1,25 Dihydroxyvitamin D3-Induced Monocytic Differentiation of HL-60 Cells

1,25 Dihydroxyvitamin D₃ (calcitriol) induces differentiation of HL-60 leukemia cells. We studied the in vitro effect of a physiological concentration of ascorbate as potentiator of 1,25 dihydroxyvitamin D₃ [(OH)₂D₃] activity by determining different markers of differentiation: nitroblue tetrazolium reduction, nonspecific esterase activity, and the expression of CD11b and CD14 surface antigens. Nitroblue tetrazolium reduction and nonspecific esterase activity increased up to 50% in the presence of both 1,25 (OH)₂D₃ plus 0.2 mM ascorbate (ASC), compared with (OH)₂D₃ as a unique agent. ASC also increased the expression of specific surface antigens (CD11b and CD14) during differentiation induced by 1,25 (OH)₂D₃, the effect being more pronounced after 48 hours of treatment with 10⁻⁸ M 1,25 (OH)₂D₃. Furthermore, 1,25 (OH)₂D₃ alone increased intracellular cAMP level during differentiation, and the addition of ASC increased its concentration from 60 to 100% above the level reached with 1,25 (OH)₂D₃ as unique agent. ASC did not enhance the antiproliferative effect of calcitriol, suggesting that it only affects the ability of 1,25 (OH)₂D₃ to promote differentiation of HL-60 cells. Received: 9 June 1995 / Accepted: 19 February 1996     

Influence of PTH and 1,25(OH)2D on calcium homeostasis and bone mineral content after gastric surgery

Summary In 57 patients surgically treated for ulcer, we found low 25OHD concentrations, elevated 1,25(OH)₂D concentrations, (P<0.001), a normal iPTH level, and a not significantly reduced bone mineral content (BMC) measured by single photon absorptiometry. The 25OHD concentrations were highest in patients regularly taking tablets containing vitamin D (P<0.05), whereas the 1,25 (OH)₂D concentrations and the BMC values were not affected by vitamin D intake. The most severe calcium metabolic disturbances were seen in 15 Billroth I resected patients whose BMC was 89.4±12.4% of normal. Although the dietary intake of calcium and vitamin D complied with the Scandinavian recommendations and calcium absorption was in the lower part of the normal range, the general state of nutrition appears to influence the bone mass of such patients. In the patients as a group, the 1,25(OH)₂D concentrations were significantly related to BMC (r=0.42,P<0.001) and biochemical signs of bone resorption (r=0.68,P<0.001) and formation (r=0.42,P<0.001) Conversely, no relationship could be detected between serum iPTH and bone mass or bone turnover. We suggest that the high 1,25(OH)₂D concentrations found after gastric resections express a compensatory process leading to an increase in calcium absorption, and that the initial event in this sequence is a trend toward low serum calcium levels. With increased demands on this regulation or lack of precursor for 1,25(OH)₂D synthesis, bone mass declines through the action of 1,25(OH)₂D and/or PTH.     

Regulation of Osteogenic Differentiation of Human Bone Marrow Stromal Cells: Interaction Between Transforming Growth Factor-β and 1,25(OH)2 Vitamin D3 In Vitro

Bone marrow stromal cells are believed to play a major role in bone formation as a major source of osteoprogenitor cells, however, very little is known about how the osteogenic differentiation of these cells is regulated by systemic hormones and local growth factors. We examined the effects of TGF-β and its interaction with 1,25(OH)₂ Vitamin D₃ [1,25(OH)₂D₃] on the differentiation and proliferation of human bone marrow stromal cells (hBMSC) in secondary cultures. Alkaline phosphatase (ALP) activity was inhibited by TGF-β (0.1–10 ng/ml) and increased by 1,25(OH)₂D₃ (50 nM), however, co-treatment of TGF-β and 1,25(OH)₂D₃ synergistically enhanced ALP activity with maximal stimulation occurring at about 8 days after treatment. This synergistic effect was independent of proliferation because, in contrast to TGF-β alone, combined treatment with TGF-β and 1,25(OH)₂D₃ had no effect on hBMSC proliferation. As no synergistic effect was seen with combinations of 1,25(OH)₂D₃ and other osteotrophic growth factors, including BMP-2, IGF-I, and basic fibroblast growth factor (bFGF), it would seem likely that the synergistic interaction is specific for TGF-β. The increased ALP activity was due to an enhancement of 1,25(OH)₂D₃-induced ALP activity by TGF-β, rather than vice versa. In contrast, TGF-β inhibited 1,25(OH)₂D₃-induced osteocalcin production. Taken together, these results indicate that TGF-β and 1,25(OH)₂D₃ act synergistically to stimulate the recruitment of BMSC to the osteoblast lineage. This interaction may play an important role in bone remodeling. Received: 24 March 1998 / Accepted: 1 February 1999     

Effects of moderate endurance exercise on calcium, parathyroid hormone, and markers of bone metabolism in young women

We investigated the short-term (1 hour–3 days) effects of a 45 minute run on calcium, parathyroid hormone, the carboxyterminal propeptide of type I procollagen (PICP), and the immunoactive carboxyterminal telopeptide of type I collagen in serum (ICTP) in young females. Fourteen healthy young women, aged 25.2 ± 0.6 years (mean ± SEM) with regular menstruations, participated. The test was outdoor jogging for 45 minutes at an intensity of 50% of VO_{2 max}. Blood samples were collected 15 minutes before the test and 1, 24, and 72 hours after the test. The measured values were adjusted for changes in plasma volume. A significant decrease of ionized calcium was observed at 1 hour (P < 0.001) and 72 hours (P < 0.05) and a significant increase of parathyroid hormone (PTH) was noted 24 (P < 0.01) and 72 hours (P < 0.05) after the test. A significant decrease of PICP at 1 hour (P < 0.05) was followed by an increase after 24 (P < 0.01) and 72 hours (P < 0.001) and a significant increase in ICTP was noted at 24 and 72 hours (P < 0.05). A strong positive correlation was found between serum levels of PICP and ICTP (r = 0.55–0.84; P < 0.05) throughout the experiment. In conclusion, young females showed biochemical signs of increased bone collagen turnover and altered homeostasis of calcium and PTH after a single bout of moderate endurance exercise. Received: 19 October 1995 / Accepted: 14 June 1996     

Elevated Collagen Turnover in Nigerian Children with Calcium-Deficiency Rickets

Calcium deficiency is a major etiological determinant of rickets in Nigerian children and is accompanied by undermineralization of the developing bone matrix which is composed largely of type I collagen. We have assessed types I and III collagen metabolism by measuring the circulating concentrations of the N- and C-terminal propeptides (intact PINP and PICP) and the C-terminal telopeptide (ICTP) of type I collagen, and the N-terminal propeptide (PIIINP) of type III collagen in 94 healthy Nigerian children and in 44 children aged 1–5 years with active calcium-deficiency rickets. In active rickets the mean levels of the four collagen metabolites were approximately twofold higher than in the healthy children, despite a wide variation of individual values. Mean intact PINP was 812 ± 279 versus 403 ± 189 μg/liter; PICP was 573 ± 265 versus 348 ± 229 μg/liter; PIIINP was 16.8 ± 8.6 versus 10.8 ± 3.6 μg/liter, and ICTP was 28.4 ± 17.2 versus 11.9 ± 4.1 μg/liter (all P < 0.001), in rachitic and healthy children, respectively. Healthy children younger than 3 years had higher levels of all the collagen metabolites than those between 3 and 5 years (all P < 0.05). Alkaline phosphatase was greater in rickets than in the healthy group (P < 0.001) whereas mean osteocalcin levels were slightly lower (P= 0.09). 1,25(OH)₂D correlated with all the collagen propeptides, but not with ICTP in the healthy children. No such correlations were found in rickets, where there was a poor inverse correlation between 1,25(OH)₂D and ICTP. These data suggest that collagen turnover is elevated in cases of calcium-deficiency rickets, where vitamin D status is adequate, possibly indicating increased turnover of undermineralized osteoid. Received: 15 October 1996 / Accepted: 5 March 1997