The Effect of Modifying Dietary Calcium Intake Pattern on the Circadian Rhythm of Bone Resorption

In order to assess day-to-day variations of the circadian rhythm of biochemical bone resorption markers, urinary morning (6–8 a.m.) and evening (7–10 p.m.) samples from 35 individuals were monitored during 3 subsequent days. The bone-specific deoxypyridinoline (DPD) crosslinks of type I collagen followed a circadian rhythm in all individuals. In contrast, no such pattern was observed in the urinary hydroxyproline/creatinine and calcium/creatinine measurements. The DPD crosslink measurements showed a much larger difference between the morning and evening samples collected within 1 day compared with the variation between the samples collected in the morning or evening on subsequent days, indicating the importance of adequate timing of urine sampling for clinical trials aiming to monitor effects on bone resorption. The analysis of DPD crosslinks was then used to evaluate the effects of different patterns of dietary calcium intake on the circadian rhythm of bone resorption in osteoporotic patients. No significant effect on the circadian rhythm of the DPD crosslinks was found after concentrating the normal daily calcium intake to the evening (6–10 p.m.) during 8 days (n = 7). Ingestion of a dietary calcium supplement (600 mg) at 10 p.m. during 8 days (n = 7) resulted in an increased urinary calcium excretion in the morning, and a flattening of the circadian peak and nadir concentrations of urinary DPD/creatinine. The absolute levels of DPD/creatinine in the morning and evening urine samples, respectively, were not significantly altered compared with the control day. We conclude that dietary calcium supplementation in the evening only marginally affects the circadian rhythm of urinary DPD crosslinks in established osteoporosis patients. Received: 23 December 1996 / Accepted: 1 November 1998     

Chronic acid ingestion promotes renal stone formation in rats treated with vitamin D3

OBJECTIVE: Although hypercalciuria, a well-established adverse effect of vitamin D3, can be a risk factor of renal stone formation, the risk of nephrolithiasis has not been well defined. The consumption of a diet high in acid precursors is often cited as a risk factor for the development of calcium-based kidney stones. In the present study, we investigated the effect of chronic acid ingestion on kidney stone formation in rats treated with calcitriol (1-25[OH]2 D3). METHODS: Control rats (C-C), calcitriol-treated rats (C-V; three treatments of 0.5 microg of calcitriol per week) and acid-ingested (water containing 0.21 mol/L NH4Cl), calcitriol-treated (three treatments of 0.5 microg of calcitriol per week) rats (A-V) were fed in metabolic cages. After 1 month, urine, blood, kidney and bone samples were analyzed. RESULTS: The A-V rats exhibited elevated serum calcium concentrations, urinary calcium and phosphate excretion, urinary type I collagen cross-linked N-peptide (NTx)/creatinine values, mRNA expression of osteopontin in the kidney, and renal calcium contents as well as decreased bone mineral densities, compared with the C-C and C-V rats. Urinary citrate excretion was lower and NaDC-1 mRNA expression in the kidney was higher in the A-V rats than in the C-C and C-V rats. Calcium phosphate kidney stones were found in the A-V rats. CONCLUSIONS: The ingestion of NH4Cl, an acid precursor, promotes calcium phosphate kidney stone formation in calcitriol-treated rats. The chronic intake of a diet rich in acid precursors may be a risk factor for the development of kidney stones in subjects who are being treated with calcitriol.     

A new biochemical marker of bone resorption for follow-up on treatment with nasal salmon calcitonin

In a double-blind, placebo-controlled, randomized group comparison, new and specific biochemical markers for bone resorption as follow-up parameters on the therapeutic response to nasal salmon calcitonin (sCT) were evaluated. Evaluation took place at an outpatient clinic where osteoporosis was being researched. The subjects included 208 women aged 68–72 treated for 2 years with either 50 IU, 100 IU, or 200 IU of nasal sCT or placebo; all groups received a daily calcium supplementation of 500 mg. Only 164 women fulfilled the study as valid completers. Markers were applied to frozen urine samples of a previously published intervention study of a new fasting urinary (fU) biochemical marker for bone resorption (CrossLaps^TM, ELISA) and the urinary excretion of cross-links (pyridinoline and deoxypyridinoline) was measured, all corrected for creatinine. Bone mineral density of the lumbar spine and rates of vertebral and peripheral fractures were measured after 2 years of treatment. The creatinine corrected urinary pyridinoline, deoxypyridinoline, and CrossLaps showed maximum decreases of 10–43% (95% confidence interval-29.5% to 9.6% and -75.1% to 9.3%;P < 0.01-0.001) after 6–9 months, after which the response leveled off. A significant difference among the four treatment groups was seen in fU CrossLaps(P < 0.01). The changes in spinal bone mass were significantly related to the decreases in fU CrossLaps: women with the highest response in spinal bone mass had decreases in fU CrossLaps of 44% (-83.5% to 7.4%) and women without response of 5% (-57.6% to 99.9%)P 0.001). In women who fractured during the 2-year period, fU CrossLaps remained unchanged, whereas decreases of 30% (-75.1% to 44.7%) were seen in women who did not fracture(P = 0.002). The results suggest that biochemical markers can be used to determine the optimum treatment regimen of nasal sCT. The response of the new marker, fU CrossLaps, significantly reflects the responses in bone mass of the spine and fracture rates.     

Effect of high protein diet on stone-forming propensity and bone loss in rats

BACKGROUND: High protein diets are believed to cause kidney stone formation and bone loss, but the mechanisms mediating these changes are unknown. The purpose of this study was to create an animal model of animal protein excess and to evaluate the response of kidney and bone to the dietary protein load. METHODS: Rats (12 per group) were pair-fed with a high (48%) and low (12%) casein diets that were otherwise identical in their content of sodium, potassium, calcium, phosphorus, and magnesium. RESULTS: Compared with the low casein group, the high casein group delivered a substantial acid load during 59 days of study, since it significantly decreased urinary pH, and increased urinary ammonium, titratable acidity, and net acid excretion. Animals on high casein diet also had higher urinary volumes. On the high casein diet, urinary calcium excretion was significantly higher and urinary citrate excretion and concentration was significantly lower. On the high casein diet, urinary saturation of calcium phosphate was higher. Serum calcitriol concentration did not significantly differ between the two groups. Histomorphometric analysis of femur procured after 59 days on the diet showed marked increase in bone resorption in the high casein group. Hypocitraturia was associated with increased activity of sodium-citrate cotransporter in renal cortical brush-border membranes (BBM) in the high casein group. CONCLUSION: Both the kidney and bone contribute to the pathogenesis of hypercalciuria during high casein diet in rats. Hypocitraturia is probably renal in origin. This rat model will be useful in elucidating the mechanisms by which high protein intake increases the risk of nephrolithiasis and bone loss in human beings.     

Biochemical effects of a single oral dose of calcium on bone metabolism in elderly Chinese women

Summary The biochemical effects of a single oral dose of 10 mmol of calcium on certain blood and urine variables were studied in 20 elderly postmenopausal subjects (mean age 72.3±6.2 years) with a very low dietary calcium intake (mean 7.2±3 mmol/day). Twelve hours after calcium administration, the plasma total calcium, phosphate and bicarbonate, and the urinary calcium/creatinine ratio rose, while the plasma parathyroid hormone and chloride, and urinary hydroxyproline/creatinine and phosphate/creatinine ratios fell. These results show that a single oral dose of calcium suppresses bone resorption in elderly women with low dietary calcium intake, and that long-term supplementation may be important in the prevention of osteoporosisrelated fractures.     

Phosphate, the renal tubule, and the musculoskeletal system

A component of ATP, phosphate is at the hub of the energy-related mechanisms operative in muscle cells. Together with calcium, phosphate is involved in bone tissue mineralization: thus, a chronic alteration in the metabolism of phosphate can induce bone and joint disorders. Diagnosis of chronic hypophosphatemia. Serum phosphate, calcium, and creatinine should be assayed simultaneously. Serum calcium is increased in hypophosphatemia caused by hyperparathyroidism and decreased in osteomalacia. Urinary phosphate excretion should be measured in patients with a normal serum calcium level and a serum phosphate level lower than 0.80 mmol/L. A decrease in urinary phosphate excretion to less than 10 mmol/24 h strongly suggests a gastrointestinal disorder, such as malabsorption, antacid use, or chronic alcohol abuse. In patients with a urinary phosphate excretion greater than 20 mmol/24 h, the maximal rate of tubular reabsorption of phosphate (TmPO4) and the ratio of TmPO4 over glomerular filtration rate (GFR) should be determined to look for phosphate diabetes. Manifestations and causes of phosphate diabetes in adults. Moderately severe phosphate diabetes in adults manifests as chronic fatigue, depression, spinal pain, and polyarthralgia, with osteoporosis ascribable to increased bone resorption. Although many cases are idiopathic, investigations should be done to look for X-linked vitamin D-resistant rickets missed during childhood, a mesenchymatous tumor, or Fanconi's syndrome with renal wasting of phosphate, glucose, and amino acids. Management of phosphate diabetes. Phosphate supplementation and, in patients with normal urinary calcium excretion, calcitriol produce some improvement in the symptoms and increase the bone mineral density. Whether dipyramidole is clinically effective remains unclear.     

Acute Effects in Healthy Women of Oral Calcium on the Calcium-Parathyroid Axis and Bone Resorption as Assessed by Serum b-CrossLaps

The purpose of this investigation was to test the hypothesis that the decrease in bone resorption after the calcium (Ca) load can be assessed by serum type 1 collagen cross-linked C-telopeptide (Elecsys beta-CrossLaps, Roche) (S-CTX). Six young healthy women (23-27 years of age) and six healthy late postmenopausal women (63-69 years of age) with normal bone mineral density (BMD) received, after overnight fasting, 1 g of elemental Ca (in the form of calcium carbonate) dissolved in 250 ml of water or only plain water (fasting period). In addition, the late postmenopausal women were tested with an additional dose of 0.2 g of elemental Ca in 250 ml of water. Serum ionized Ca (S-iCa), S-CTX, plasma immunoreactive intact parathormone (P-PTH) were measured before and during the 5 hours after the oral intake of Ca. Urine was collected at regular intervals, and urinary Ca and creatinine were analyzed. In both the young and late postmenopausal subjects, the load with Ca resulted in a significant increase in S-iCa and urine Ca/creatinine ratio as well and a significant decrease of P-PTH and S-CTX compared with the fasting period. The comparison of the effects of 1 g Ca load between young and late postmenopausal women did not show any statistical significance in any measured parameters. In the late postmenopausal women, a significantly greater increase in S-iCa concentrations and a significantly greater decrease in P-PTH after 1 g were observed compared with those after a 0.2 g dose of Ca. During the first 3 hours, the load of both 1 g and 0.2 g of Ca induced a similar decrease in S-CTX. After 5 hours, however, S-CTX were significantly more suppressed after a 1 g dose than after a 0.2 g dose of Ca. In conclusion, a single oral morning dose of 1 g Ca suppresses bone resorption, as assessed by S-CTX, to a similar degree in both young and late postmenopausal women with normal Ca absorption. In healthy late postmenopausal women the load of 0.2 g of Ca carbonate significantly suppresses bone resorption.     

Calcium bioavailability from heated oyster shell-seaweed calcium (active absorbable algae calcium) as assessed by urinary calcium excretion

The bioavailability of heated oyster shell-seaweed calcium (active absorbable algae calcium, AAA Ca) was compared to that of calcium carbonate by measuring increases of urinary calcium excretion after oral load. Eight normal male volunteers ingested 1000 mg calcium in the form of either calcium carbonate (CaCO₃) or AAA Ca in a crossover design with a 1-week interval between the two tests. The urinary calcium/creatinine (Ca/Cr) ratio was measured from 4h before to 6h after the administration at 2-h intervals. Urinary calcium excretion 4–6 h after oral ingestion of AAA Ca was 249 ± 119% (SD) of the baseline level, which was significantly higher than that after calcium carbonate, 170 ± 103% (SD) (P = 0.039). Paired comparison of the increment of urinary Ca/Cr over the pretest level was also significantly greater 4–6h after the ingestion of AAA Ca (0.21 ± 0.14) than that after calcium carbonate (0.132 ± 0.158) (P = 0.025). AAA Ca is thus suggested to be more biologically available than calcium carbonate in human subjects.     

Calcium citrate markedly enhances aluminum absorption from aluminum hydroxide

The effect of calcium citrate on intestinal aluminum absorption, assessed by the increment in urinary aluminum excretion, was evaluated in eight normal men. Baseline urinary aluminum excretion was determined for 2 days; thereafter, subjects ingested aluminum hydroxide for 3 days. In a cross-over study, subjects were given either calcium citrate, 950 mg four times a day, or placebo during the 3 days of aluminum hydroxide ingestion (2.4 g/d). Plasma aluminum levels were measured on the second control day and the third day of aluminum hydroxide ingestion. Baseline urinary aluminum excretion was 0.02 +/- 0.004 (6.5 +/- 1.1 micrograms/g creatinine) and 0.03 +/- 0.005 mumol/mmol creatinine (7.4 +/- 1.3 micrograms/g creatinine). These values increased during aluminum hydroxide therapy, but values were much greater when calcium citrate was ingested with aluminum hydroxide. On 3 consecutive days, urinary aluminum excretion levels were 11.1 +/- 3.23, 8.8 +/- 2.9, and 5.3 +/- 0.7 times greater during the administration of calcium citrate with aluminum hydroxide than with aluminum hydroxide alone. Plasma aluminum levels did not differ in the two treatment groups. Thus, calcium citrate markedly enhances the absorption of aluminum from aluminum hydroxide and the two must not be prescribed together in patients with renal failure.     

Urinary calcium excretion at extremes of sodium intake in normal man

To elucidate the relationship between the renal regulation of sodium and calcium excretion at extremes of sodium intake, we studied 6 normal men ingesting a fixed, 400 mg/day calcium intake and four levels of sodium intake from 10 to 1,500 mEq/day. Serum ionized calcium was not influenced by sodium intake. Blood pressure and cardiac index increased modestly. Urinary calcium excretion increased to 262 +/- 53 mg/day (mean +/- SE). Plasma norepinephrine concentration, serum PTH levels, hematocrit, total serum protein concentrations and CO2 content decreased with increasing sodium intake. Urinary cAMP increased as sodium intake was raised from 10 to 300 mEq/day, but subsequently decreased to basal values. Urinary calcium and sodium excretion were related (p less than 0.001) in a nonlinear fashion as were the fractional excretions of these cations (p less than 0.001). The filtered calcium load and the fractional calcium excretion were directly and linearly related (p less than 0.001). We conclude that the effect of sodium intake on urinary calcium excretion principally reflects changes in the filtered calcium load rather than changes in renal sodium handling. Calcium homeostasis at extremes of sodium intake does not appear to be critically dependent upon PTH-mediated mechanisms. The data suggest that the proximal tubule has a remarkable capacity to dissociate calcium resorption from that of sodium.     

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     

Renal handling of calcium in the early newborn period

Urinary calcium excretion was studied in two matched groups of 28 clinically-well preterm and fullterm infants between 24 and 48 hours of life. In the developmental period from 28 to 40 weeks gestation, urinary calcium excretion was positively correlated to the gestational age (r = 0.583, P less than 0.01), serum calcium levels (r = 0.512, P less than 0.01), the rate of glomerular filtration (r = 0.715, P less than 0.001), and urinary cyclic AMP excretion (r = 0.717, P less than 0.001). Urinary calcium excretion was independent of sodium and calcium intake, and urinary sodium and phosphate excretion. The mean fractional total calcium excretion and fractional ionized calcium excretion in babies less than or equal to 32 weeks was less than 1.0%, compared to greater than 2.5% for sodium. Serum calcium levels were positively correlated with gestational age (r = 0.803, P less than 0.001), and serum phosphate levels (r = 0.85, P less than 0.001). Whole blood ionized calcium levels were positively correlated to gestational age (r = 0.625, P less than 0.001), and serum total calcium levels (r = 0.440, P less than 0.05). The newborn kidney in babies less than or equal to 32 weeks gestation, did not have impaired conservation of calcium as for sodium; and neither sodium nor calcium intake appeared to affect urinary calcium excretion in the well newborn infant. Probably neither excess excretion of calcium nor serum phosphate levels contribute to early neonatal hypocalcemia.     

Hypercalcemia during the osteogenic phase after rat marrow ablation coincides with increased bone resorption assessed by the NTx marker

Marrow ablation is a model of bone turnover in which the excavated tibial intramedullary cavity is rapidly and reproducibly filled by osteoblasts with new woven bone (days 6-8), which is then rapidly resorbed by osteoclasts (days 10-15). We showed previously (Magnuson et al., 1997) that marrow ablation induces a dramatic hypercalcemia and hypercalciuria in rats that unexpectedly peaked at the time of maximal osteogenesis and continued throughout the subsequent resorption phase. Based upon the amount of calcium mobilized and a peak of urinary hydroxyproline, we suggested that the hypercalcemia and hypercalciuria were due to increased systemic osteoclastic bone resorption induced by marrow ablation. We now apply a new enzyme-linked immunosorbent assay for rodent alpha(2)(I) N-telopeptide (NTx), a marker of bone resorption, to the marrow ablation model to demonstrate that excretion of NTx parallels that of calcium release in the operated control group. Specifically, maximal NTx/creatinine excretion coincides with the onset of hypercalcemia on days 7-8. A peak of NTx was also observed in methylprednisolone- and deflazacort-treated ablated animals. Analyses for urinary free deoxypyridinoline crosslink failed to detect a significant ablation-induced change in excretion. Interleukin 6 activity was increased in all operated control and glucocorticoid-treated groups after marrow ablation, whereas serum parathyroid hormone remained at presurgical levels in operated controls throughout the 15-day study period. The NTx results confirm that bilateral tibial marrow ablation induces a burst of extratibial bone resorption and hypercalcemia 7-8 days later. We have estimated that the osteogenic phase of the ablation model deposits 40 mg of calcium as hydroxyapatite crystals within the intramedullary cavity on days 6-8; this represents 33%-50% of the total blood calcium content of a young rat. We hypothesize that the size and rapidity of this demand for ionized calcium is met through an extratibial bone resorption pathway of osteoclast formation and activation that anticipates and fulfills this need, and that is initiated at the time of marrow ablation.     

Biochemical Variables in Pre- and Postmenopausal Women: Reconciling the Calcium and Estrogen Hypotheses

There is controversy as to whether the rise in urinary calcium at the menopause is the cause or the result of the rise in bone resorption at that time. In an attempt to resolve this issue, we have compared the relevant biochemical variables in 102 premenopausal volunteers (mean age 37 years; range 21–52) and 86 apparently normal postmenopausal women (mean age 55 years; range 40–60). We measured the fasting serum calcium, creatinine, proteins, electrolytes and intact parathyroid hormone (PTH), and the urinary calcium and creatinine both after an overnight fast and in a 24-h collection. We calculated serum calcium fractions, creatinine clearance and the notional tubular maximum reabsorptive capacity for calcium. Creatinine excretion and clearance were lower in the post- than in the premenopausal women after correction for surface area and age. Total serum calcium was higher in the post- than in the premenopausal women but this was accounted for by the higher ligand concentrations in the former. Fasting and 24-h urinary calcium were also higher in the post- than in the premenopausal women due in part to the former’s higher filtered load of calcium (due to their higher serum complexed calcium) but mainly to their reduced tubular reabsorption of calcium despite their slightly raised serum PTH. Our analysis resolves the rise in urinary calcium at the menopause into its two components: increased filtered load and reduced tubular reabsorption. The changes in these two variables, neither of which can be attributed to increased bone resorption, produce an increase in calcium requirement that is sufficient to account for postmenopausal bone loss. However, the translation of this menopausal increase in calcium requirement into an increase in bone resorption at near-normal serum PTH levels requires some menopause-dependent change in the responsiveness of the bone to calcium demand. We suggest that this change may occur at the level of the osteoclasts and that estrogen may modify the calcium feedback setpoint in these cells in a manner analogous to calcitonin. This model resolves the apparent conflict between the estrogen and calcium hypotheses and explains the synergism between these two treatment modalities. Received: 8 June 1998 / Accepted: 5 September 1998     

Phosphore,tubule rénal et appareil ostéoarticulaire

A component of ATP, phosphate is at the hub of the energy-related mechanisms operative in muscle cells. Together with calcium, phosphate is involved in bone tissue mineralization: thus, a chronic alteration in the metabolism of phosphate can induce bone and joint disorders. Diagnosis of chronic hypophosphatemia. Serum phosphate, calcium, and creatinine should be assayed simultaneously. Serum calcium is increased in hypophosphatemia caused by hyperparathyroidism and decreased in osteomalacia. Urinary phosphate excretion should be measured in patients with a normal serum calcium level and a serum phosphate level lower than 0.80 mmol/L. A decrease in urinary phosphate excretion to less than 10 mmol/24 hours strongly suggests a gastrointestinal disorder, such as malabsorption, antacid use, or chronic alcohol abuse. In patients with a urinary phosphate excretion greater than 20 mmol/24h, the maximal rate of tubular reabsorption of phosphate (TmPO₄) and the ratio of TmPO₄ over glomerular filtration rate (GFR) should be determined to look for phosphate diabetes. Manifestations and causes of phosphate diabetes in adults. Moderately severe phosphate diabetes in adults manifests as chronic fatigue, depression, spinal pain, and polyarthralgia, with osteoporosis ascribable to increased bone resorption. Although many cases are idiopathic, investigations should be done to look for X-linked vitamin D-resistant rickets missed during childhood, a mesenchymatous tumor, or Fanconi syndrome with renal wasting of phosphate, glucose, and amino acids. Management of phosphate diabetes. Phosphate supplementation and, in patients with normal urinary calcium excretion, calcitriol produce some improvement in the symptoms and increase the bone mineral density. Whether dipyramidole is clinically effective remains unclear.     

Effect of high-calcium diet on urinary oxalate excretion in urinary stone formers

The effect of mild high-calcium diet or regular-calcium diet on urinary calcium excretion, urinary oxalate excretion, urinary calcium/creatinine ratio, urinary oxalate/creatinine ratio, and the probability of being a stone former (PSF) were studied in 85 patients with idiopathic urolithiasis. Intake of high-calcium diet for 5-6 days reduced (p less than 0.01-p less than 0.001) urinary oxalate excretion, urinary oxalate/creatine ratio and PSF in patients with idiopathic hypercalciuria. Under the regular-calcium diet, administration of 60 mg/day of pyridoxal phosphate for 3 months lowered (p less than 0.05-p less than 0.01) urinary oxalate excretion, urinary oxalate/creatinine ratio and PSF in patients with idiopathic hypercalciuria alone. From these findings, intake of mild high-calcium diet appears to be beneficial to decrease the urinary oxalate excretion and PSF in patients with idiopathic hypercalciuria. Pyridoxal phosphate has all the features of suppressing such risk factors for stone formation in patients with idiopathic hypercalciuria.     

The effects of menopause and estrogen replacement therapy on the renal handling of calcium

Mineral metabolism was studied in 99 premenopausal and 80 postmenopausal women both before and after 9–14 months of treatment with 50 µg/day transdermal estradiol. In estrogen-repleted subjects (premenopausal women and postmenopausal women on estrogen replacement therapy) total serum calcium was significantly lower (0.065 mmol/l;p<0.001) than in those who were estrogen-depleted (untreated postmenopausal women). This difference was smaller but still significant for calculated ultrafiltrable calcium (UFCa: 0.02–0.03 mmol/l;p<0.001). However, ionized calcium (both calculated and measured) was not different in the two groups of women. This finding explains why estrogen repletion does not induce changes in the serum level of intact parathyroid hormone (PTH), despite lower total or ultrafiltrable serum calcium. In a parallel study we have shown that intravenous administration of aminobutane bisphosphonate, a powerful inhibitor of bone resorption, produces similar decreases in serum calcium which were associated with significant increases in intact PTH.Estrogen-depleted women had, on the one hand, significantly higher serum levels of bicarbonate, anion gap, complexed calcium, pH, phosphate and alkaline phosphatase, and higher rates of tubular reabsorption of phosphate and urinary excretion of calcium and hydroxyproline. On the other hand they had lower serum chloride levels and lower rates of tubular reabsorption of calcium.Altogether these findings might indicate that estrogen deficiency decreases renal sensitivity to PTH. This is responsible for the higher serum phosphate and bicarbonate levels, the resulting mild metabolic alkalosis leading to higher serum levels of complexed ultrafiltrable calcium and higher rates of urinary excretion of calcium, but unchanged serum levels of ionized calcium and PTH.     

Hypophosphatemic rickets with hypocalciuria following long-term treatment with aluminum-containing antacid

We present what we believe is the first case of rickets following prolonged treatment with aluminum containing antacids that bind phosphate, in an 18-year-old mentally retarded boy with cerebral palsy and spastic quadriplegia. As expected, serum calcitriol was increased and urinary phosphate excretion was very low. However, in contrast to all published cases of antacid induced hypophosphatemic osteomalacia in adults, despite a substantial increase in bone resorption reflected by urinary total hydroxyproline excretion, urinary calcium excretion was low rather than high, and significant hypocalcemia occurred after antacids were ceased and a phosphate salt administered. We suggest that the skeleton was so under-mineralized because of growth during prolonged phosphate deficiency, possibly augmented by anticonvulsant administration and immobilization, that increased bone resorption did not release enough calcium to cause hypercalciuria, or to prevent hypocalcemia during resumption of normal mineralization.     

Preliminary evidence of early bone resorption in a sheep model of acute burn injury: an observational study

Treatment with bisphosphonates within the first 10 days of severe burn injury completely prevents bone loss. We therefore postulated that bone resorption occurs early post burn and is the primary explanation for acute bone loss in these patients. Our objective was to assess bone for histological and biomechanical evidence of early resorption post burn. We designed a randomized controlled study utilizing a sheep model of burn injury. Three sheep received a 40 % total body surface area burn under isoflurane anesthesia, and three other sheep received cotton-smoke inhalation and served as control. Burned sheep were killed 5 days post procedure and controls were killed 2 days post procedure. Backscatter scanning electron microscopy was performed on iliac crests obtained immediately postmortem along with quantitative histomorphometry and compression testing to determine bone strength (Young’s modulus). Blood ionized Ca was also determined in the first 24 h post procedure as was urinary CTx. Three of three sheep killed at 5 days had evidence of scalloping of the bone surface, an effect of bone resorption, whereas none of the three sheep killed at 2 days post procedure had scalloping. One of the three burned sheep killed at 5 days showed quantitative doubling of the eroded surface and halving of the bone volume compared to sham controls. Mean values of Young’s modulus were approximately one third lower in the burned sheep killed at 5 days compared to controls, p = 0.08 by unpaired t test, suggesting weaker bone. These data suggest early post-burn bone resorption. Urine CTx normalized to creatinine did not differ between groups at 24 h post procedure because the large amounts of fluids received by the burned sheep may have diluted urine creatinine and CTx and because the urine volume produced by the burned sheep was threefold that of the controls. We calculated 24 h urinary CTx excretion, and with this calculation CTx excretion/24 h in the burned sheep was nearly twice that of the controls. Moreover, whole blood ionized Ca measured at 3- to 6-h intervals over the first 24 h in both burn and control sheep showed a 6 % reduction versus baseline in the burned sheep with <1 % reduction in the control animals. This sheep model was previously used to demonstrate upregulation of the parathyroid calcium-sensing receptor within the timeframe of the present study. Because both early bone resorption, supported by this study, and calcium-sensing receptor upregulation, consistent with the observed reduction in blood ionized Ca, are mediated by proinflammatory cytokines that are present as part of the post-burn systemic inflammatory response, we may postulate that post-burn upregulation of the parathyroid calcium-sensing receptor may be an adaptive response to clear the blood of excess calcium liberated by cytokine-mediated bone resorption.     

The Walker 256/B carcinosarcoma in thyroparathyroidectomized rats: A model to evaluate inhibitors of bone resorption

Summary The Walker 256/B mammary carcino-sarcoma implanted in male Fischer rats was used to evaluate bone resorption inhibitors. The model was improved by thyroparathyroidectomizing the animals to avoid counter-regulation by parathyroid hormone or calcitonin, by pair-feeding them, and by using 2 hour fasting calciuria as a resorption index to minimize the influence of differences in growth or in intestinal calcium absorption. Over a 10 day period, the control animals displayed a progressive increase of plasma calcium (Ca) and fasting urinary Ca excretion, a decrease of plasma phosphate, and an increase of urinary phosphate excretion. Osteocalcin did not change. The daily administration of dichloromethylene bisphosphonate (Cl₂MBP) totally prevented the increase of fasting urinary Ca excretion, whereas plasma Ca remained at a higher level than thyroparathyroidectomized (TPTX) control rats. Osteocalcin decreased. Two new aminobisphosphonates, 4-amino-1-hydroxybutylidene-1,1-bisphosphonate (AHBuBP), and 6-amino-1-hydroxyhexylidene-1,1-bisphosphonate (AHHexBP) had a similar effect. The order of potency shown by the three bisphosphonates was similar to that reported using the metaphyseal bone density evaluation method in growing rats: AHBuBP>AHHexBP>Cl₂MBP, the difference each time being one order of magnitude. The analysis of the relationship between urinary and plasma values in tumor-bearing animals suggested an increased renal tubular reabsorption of Ca and a decreased reabsorption of phosphate (P_i). Therefore, in this model of malignant osteolysis, urinary Ca excretion is the best marker for bone resorption.