Search

Long-term therapy with certain drugs, especially cytochrome P450 (P450; CYP)-inducing agents, confers an increased risk of osteomalacia that is attributed to vitamin D deficiency. Human CYP24A1, CYP3A4, and CYP27B1 catalyze the inactivation and activation of vitamin D and have been implicated in the adverse drug response. In this study, the inducibility of these enzymes and monohydroxylation of 25-hydroxyvitamin D3 (25OHD3) were evaluated after exposure to P450-inducing drugs. With human hepatocytes, treatment with phenobarbital, hyperforin, carbamazepine, and rifampin significantly increased the levels of CYP3A4, but not CYP24A1 or CYP27B1 mRNA. In addition, rifampin pretreatment resulted in an 8-fold increase in formation of the major metabolite of 25OHD3, 4β,25(OH)2D3. This inductive effect was blocked by the addition of 6',7'-dihydroxybergamottin, a selective CYP3A4 inhibitor. With human renal proximal tubular HK-2 cells, treatment with the same inducers did not alter CYP3A4, CYP24A1, or CYP27B1 expression. 24R,25(OH)2 D3 was the predominant monohydroxy metabolite produced from 25OHD3, but its formation was unaffected by the inducers. With healthy volunteers, the mean plasma concentration of 4β,25(OH)2D3 was increased 60% (p < 0.01) after short-term rifampin administration. This was accompanied by a statistically significant reduction in plasma 1α,25(OH)2D3 (-10%; p = 0.03), and a nonsignificant change in 24R,25(OH)2D3 (-8%; p = 0.09) levels. Further analysis revealed a negative correlation between the increase in 4β,25(OH)2D3 and decrease in 1α,25(OH)2D3 levels. Examination of the plasma monohydroxy metabolite/25OHD3 ratios indicated selective induction of the CYP3A4-dependent 4β-hydroxylation pathway of 25OHD3 elimination. These results suggest that induction of hepatic CYP3A4 may be important in the etiology of drug-induced osteomalacia., (Copyright © 2013 American Society for Bone and Mineral Research.)

Prolonged therapy with phenobarbital may cause vitamin D deficiency or osteomalacia. In the current study, we propose a novel mechanism for drug-induced osteomalacia involving impaired bioactivation of vitamin D(3) due to decreased 25-hydroxylation of vitamin D(3) in liver. The present data, using the pig as model, demonstrate direct effects by phenobarbital on the expression of CYP27A1 and CYP2D25, two important 25-hydroxylases. Treatment by phenobarbital markedly reduced the rate of 25-hydroxylation by primary hepatocytes and suppressed the cellular CYP27A1 mRNA levels. The rate of 25-hydroxylation by two different purified 25-hydroxylases, microsomal CYP2D25, and mitochondrial CYP27A1, respectively, was dose-dependently inhibited by phenobarbital. Reporter assay experiments in liver-derived HepG2 cells revealed a marked PXR-mediated transcriptional downregulation of the CYP2D25 promoter. In addition, the data indicate that phenobarbital might affect the mRNA stability of CYP2D25. Taken together, the data suggest that vitamin D(3) 25-hydroxylation may be suppressed by phenobarbital. A downregulation of 25-hydroxylation by phenobarbital may explain, at least in part, the increased risk of osteomalacia, bone loss, and fractures in long-term phenobarbital therapy.

A patient with classic clinical and biochemical features of tumor-induced osteomalacia (hypophosphatemia, phosphaturia, and undetectable serum concentrations of 1,25-dihydroxyvitamin D [1,25(OH)2D]) was studied before and after resection of a benign extraskeletal chondroma from the plantar surface of the foot. Presurgical laboratory evaluation was notable for normal serum concentrations of calcium, intact parathyroid hormone (PTH), parathyroid hormone-related protein (PTHrP), and osteocalcin, increased serum alkaline phosphate activity, and frankly elevated urinary cyclic adenosine monophosphate (cAMP) and pyridinium cross-link excretion. Quantitative histomorphometry showed severe osteomalacia and deep erosions of the cancellous surface by active osteoclasts. After resection, serum 1,25(OH)2D normalized within 24 h, while renal tubular phosphorus reabsorption and serum phosphorus did not normalized until days 2 and 3, respectively; serum Ca declined slightly, and serum intact PTH, osteocalcin, and urinary pyridinium cross-link excretion increased dramatically. Urinary cAMP excretion declined immediately after resection and then began to increase concomitant with the increase in serum intact PTH. A second bone biopsy taken 3 months after resection demonstrated complete resolution of the osteomalacia, increased mineral apposition rate (1.09 mu/day), resorption surface (9.2%), mineralizing surface (71%), and bone formation rate (0.83 mm3/mm2/day), and marked decrease in cancellous bone volume (13.1%) and trabecular connectivity compared with first biopsy. Tumor extracts did not affect phosphate transport in renal epithelial cell lines or 1 alpha-hydroxylase activity in a myelomonocytic cell line. The patient's course suggests that the normal 1,25(OH)2D and phosphorus metabolism is due to a tumor product that may be acting via stimulation of adenylate activity. Increased bone resorption prior to surgical resection suggests that the tumor may also produce an osteoclast activator. The rise in resorption surface and pyridinium cross-link excretion, increase in serum osteocalcin and bone mineralization, normalization of osteoid width, and fall in cancellous bone volume after resection are consistent with healing of osteomalacia by rapid remodeling.

The study was carried out to evaluate the clinical validity and usefulness of serum tartrate-resistant acid phosphatase (TRAP) activity determined using an improved spectrophotometric assay. Enzyme activity was measured in 84 normal subjects and in 109 patients with common metabolic bone diseases. Mean values of serum TRAP activity in male subjects (n = 19; 10.4 +/- 2.15 U l-1) were not significantly different from those found in female subjects (n = 65; 10.8 +/- 1.8 U l-1). In the latter group mean values were significantly raised in post-menopausal subjects (10.5 +/- 2.0 U l-1; p less than 0.01) compared with mean values in pre-menopausal women (8.45 +/- 1.8 U l-1). We found a significant inverse correlation between serum TRAP activity values and bone mineral density (BMD) measured both at an ultradistal radial point (n = 33, r = -0.506; p less than 0.01), and at the lumbar spine (n = 57, r = -0.261; p less than 0.05). Mean serum TRAP activity values in patients with metabolic bone diseases were: primary hyperparathyroidism, n = 30: 14.2 +/- 4.89 U l-1, p less than 0.001 vs normal subjects; chronic maintenance haemodialysis, n = 19: 17.4 +/- 6.7, p less than 0.001; metastatic cancer, n = 13: 21.2 +/- 6.3, p less than 0.001; post-surgical hypoparathyroidism, n = 10: 9.9 +/- 1.8, NS; involutional osteoporosis, n = 20: 12.5 +/- 2.3 p less than 0.001; Paget's disease, n = 10: 16.8 +/- 3.5, p less than 0.001; osteomalacia, n = 7: 19.5 +/- 3.31, p less than 0.001.(ABSTRACT TRUNCATED AT 250 WORDS)

In an attempt to detect biochemical evidence of metabolic bone disease in the aged, we measured plasma parathyroid hormone (PTH) concentrations, in addition to plasma calcium, phosphorus, alkaline phosphatase and creatinine levels, in elderly White, Black and Indian women. All three ethnic groups demonstrated raised mean PTH concentrations. The Black patients, however, showed the greatest mean PTH elevation and the lowest plasma calcium level. Increased PTH secretion in elderly females may reflect either an age-related decline in renal function or subclinical osteomalacia. Elderly Black women seem particularly susceptible to the latter disorder, probably because of dietary and environmental factors.

Osteomalacic myopathies are rare. They can prevail, however, and occur before bone abnormalities. The diagnosis must rest on clinical observation since the histopathologic images are not specific. On the other hand the demonstration of muscular weakness is very frequent during osteomalacia. In fact two types of manifestations correspond to the same anatomopathologic lesions. These are myopathic changes observed also during light microscopy, histoenzymologic and ultrastructural examination in the 10 patients examined. On the basis of these morphologic changes, muscular involvement can be considered to be part of the osteomalacia syndrome. The contribution of various factors including secondary hyperparathyroidism, vitamin D metabolism disorders, and phosphorus depletion is discussed. It is probable that many of them act together, causing reversible changes in muscular fibers. The intimate mechanisms of these changes are unknown.

Anticonvulsant drug-induced disorders in mineral and bone metabolism are discussed. 'Anticonvulsant osteomalacia' includes hypocalcaemia, elevated serum alkaline phosphatase, decreased serum 25-hydroxycholecalciferol (25 OHD3), radiological and histological signs of osteomalacia and a lower bone mineral content (BMC) than normal. The pathophysiological mechanism behind anticonvulsant osteomalacia is thought be an induction of the microsomal enzyme system in the liver, leading to a disturbance in the metabolism of vitamin D and a resulting vitamin D deficiency. It has been shown that treatment with vitamin D2 increase BMC whereas serum calcium was unchanged. Treatment with vitamin D3 or 25 OHD3 increases serum calcium whereas BMC was unchanged. These findings suggest that vitamin D2 and D3 are metabolized differently in anticonvulsant treated patients. With the present knowledge, preventive treatment of this relative mild pathological condition is not generally indicated.

Of 837 epileptics over 16 years of age treated with mono- or combined hydantoin therapy 20.3% showed radiographic signs of anticonvulsant osteomalacia. With the exception of the patients with severe disturbances of the skeletal system no positive correlation was found with duration of therapy. The percentage of moderate bone changes was the highest in the patients treated for 1 to 2 years; the percentage of severe bone changes in the group treated over 10 years. The rate of osteomalacia correlated with the total dose of hydantoin, phenobarbital, or primidone; the correlation with the dose per year was even more evident. The risk of osteomalacia rose distinctly with doses over 3000 equivalent units/year. The patients with combined hydantoin-barbiturate treatment showed a higher risk than those treated with phenytoin alone. The rate of osteomalacia was the highest in the patients aged under 20 years and over 50 years. Males showed a relatively higher rate of osteomalacia than females, they were treated however with a higher dose per year. The chemical parameters blood alkaline phosphatase and 25-hydroxycholecalciferol corresponded to the radiographic signs, whereas calcium and anorganic phosphate showed no correlation. Early routine radiologic and chemical control especially of the epileptic patients with high risk of osteomalacia should be routinely performed in future.

The value of the estimation of liver and bone isoenzyme of alkaline phosphatase in a series of 500 admissions to a geriatric unit is described. A raised total alkaline phosphatase was found in 40 patients and this was due to raised levels of the bone isoenzyme in about two-thirds of these. Its value in diagnosis of treatable bone disease is emphasized.

Radio-isotope bone scanning was used to detect osteomalacia in 17 elderly subjects who had equivocal biochemical evidence of this condition. The scan was positive in 10 of the 17 subjects. Bone biopsy confirmed osteomalacia in all 10, but also identified a further two cases. Isotope bone scanning is a practical and relatively non-invasive method of detecting osteomalacia in elderly subjects.

Based on our experience on more than one hundred cases, bone remodelling in rickets and osteomalacia was investigated. Histomorphometry using tetracycline labelling on nineteen ribs and fibula biopsy specimen revealed a marked increase in number of osteon with osteoid seam, a slight decrease in number of resorption cavity, and extremely depressed tetracycline uptake, of 9.7% on average. The attempt to measure bone formation rate by double tetracycline labelling has failed. Analysing the dynamic behaviour of serum alkaline phosphatase, the hypothesis that the serum alkaline phosphatase was regulated by the three factors, activity of osteoblast, number of osteoblast and elution coefficient from the cell, was presented. Both accretion rate and urinary hydroxyproline excretion showed variable values, from low to high. Although bone remodelling in rickets and osteomalacia was always low at the cellular level, it could be low, normal or high at tissue or organ levels.

A significant correlation between the activity of the bone isoenzyme or serum alkaline phosphatase and the urinary hydroxyproline excretion in osteomalacia, osteoporosis, primary hyperparathyroidism with osteodystrophy, Paget's disease, secondary bone tumours, and in a control group was found (P less than 0.001). This close correlation was not observed between these variables in patients with active acromegaly. Diagnosis determined from these indices of formation and turnover of bone matrix agreed with that established by histological and histochemical examination of bone, by X-ray investigation of the skeleton, and by the radionuclear 85Sr test. The relationship between the activity of bone isoenzyme and urinary hydroxyproline excretion differed in metabolic bone diseases with a high bone turnover, in patients with osteoporosis and in patients with early osteoclastic bone metastases.

Altogether 15 partially independent measurements of bone mass in 100 women with clinical and roentgenological signs of osteoporosis were correlated to the alkaline phosphatase activities of the same individuals. There was a slight but significant negative correlation indicating an increasing alkaline phosphatase activity with decreasing bone mass. This correlation was not caused by interaction of age. There was no correlation or morphological signs of osteomalacia. The changes could not be explained by fractures. It is suggested that a slight increase in the alkaline phosphatase activity in women with a more severe osteoporosis is related to bone resorption.

Osteomalacia in New Zealand and Australia has previously been thought rare. The medical records of 22 elderly inpatients diagnosed as having osteomalacia on biopsy criteria in Dunedin between January 1980 and December 1983 were reviewed. Risk factors, mode of presentation, month of presentation, biochemistry, bone biopsy, bright line counting and bone scans were assessed. Our findings, and a review of the diagnosis of osteomalacia in the elderly are discussed. We conclude that in the elderly, osteomalacia is not uncommon, and recommend increased attention to risk factors and biochemical screening.

To study post-gastrectomy metabolic bone disorders, we measured the radial bone mineral content (BMC), serum levels of calcium, inorganic phosphorus, alkaline phosphatase, and 25-hydroxyvitamin D(25-OH-D) in 59 patients with partial- and 39 patients with total gastrectomy. Total gastrectomy patients manifested a higher incidence of decreased BMC levels than did partial gastrectomy patients (56 per cent vs. 25 per cent). Patients subjected to the Billroth II procedure, especially females, manifested abnormally low BMC values. The decline in BMC was age-related; it was pronounced in females. At 10 years postoperatively, many of the partial gastrectomy patients manifested markedly low BMC levels; in totally gastrectomized patients this finding was made at less than 5 years postoperatively. Approximately 30 per cent of our patients showed abnormalities in serum minerals, alkaline phosphatase or 25-OH-D.

Hypocalcaemia and hypophosphataemia either on admission or before discharge from hospital are poor discriminators for the presence of subclinical osteomalacia in the elderly. Reliance has to be placed on the measurement of alkaline phosphatase even though false positive tests are common. Use of paired admission and predischarge data reduces the false positive rate by approximately 50% thereby reducing the requirement for histological confirmation of the diagnosis of osteomalacia. Since the prevalence of osteomalacia is low in this type of hospital population, any measure which reduces the requirement for bone biopsy is of considerable practical value.

Four patients had symptomless osteomalacia at the time of starting regular haemodialysis. After 21-40 months they became hypophosphataemic and developed disabling skeletal symptoms. In each case an exacerbation of histological osteomalacia was shown. Symptoms improved after measures designed to raise serum inorganic phosphate concentrations or vitamin D administration, or both. Patients undergoing maintenance haemodialysis should have their serum phosphate and alkaline phosphatase levels monitored every month. Predialysis phosphate levels below 1 mmol/1 (3 mg/100 ml) and rising serum alkaline phosphatase concentrations are danger signals. If the diagnosis is confirmed early aggressive treatment should be started.

Osteomalacia may be a contributory factor in some patients in the development of fractures of the femoral neck and complicate the subsequent management. The level of serum alkaline phosphatase is often valuable in the diagnosis of metabolic bone disease but rises after any uncomplicated fracture, and since such a rise may limit the diagnostic usefulness of this measurement in detecting osteomalacia its extent was assessed in 106 patients. In the majority serum levels were normal on admission, rising after seven to nine days to reach a maximum within a month after fracture. Elevated levels on admission were found in patients with osteomalacia, liver damage or where there had been a delay of several weeks between injury and admission. In a small number of patients normal levels on admission subsequently reached very high values, usually in association with comminution or instability of the fracture. Elevated levels persisted for six to twelve weeks after fracture, the major influence upon the level at this time being the maximum value achieved rather than the presence of osteomalacia. If patients are to be screened for osteomalacia, the alkaline phosphatase must be measured within the first week after a fracture to avoid the distorting influences of the fracture itself.

Plasma calcium and phosphate concentrations and alkaline phosphatase activities were examined retrospectively in 50 patients with histologically proven osteomalacia and 50 age- and sex-matched control subjects with normal bone histology. An abnormal plasma alkaline phosphatase activity was more useful than an abnormal plasma calcium or phosphate concentration in distinguishing between normal and osteomalacic subjects, producing a false-negative rate of 14% and a false-positive rate of 8%. False-negative and false-positive rates of 10% and 8% respectively were obtained when the presence of an abnormality in any one of the three biochemical measurements was used as a predictor of histological osteomalacia. When discriminant analysis was applied to plasma calcium, phosphate and alkaline phosphatase together a false-negative rate of 12% and a false-positive rate of 0% was obtained.Sixty-two patients in whom a diagnosis of osteomalacia was suspected were investigated prospectively, using both single biochemical abnormalities and the classification functions derived from the discriminant analysis of all three biochemical measurements to predict the presence or absence of histological osteomalacia. Plasma alkaline phosphatase activity gave false-negative and false-positive rates of 10% and 32% respectively but was a more reliable predictor of abnormal bone histology than were plasma calcium or plasma phosphate concentrations or the presence of an abnormality in any one of the three measurements. Discriminant analysis using plasma calcium, phosphate and alkaline phosphatase together produced a false-negative rate of 16% and a false-positive rate of 10%. We conclude that plasma alkaline phosphatase activity is the best single routine biochemical screening test for osteomalacia, although a high false-positive rate may occur. Direct discriminant analysis of plasma calcium, phosphate and alkaline phosphatase together provides a more sensitive method of detecting histological osteomalacia which should be useful in determining the prevalence of osteomalacia within high-risk populations.

Polyacrylamide gel electrophoresis (PAGE) of alkaline phosphatase (AP) was performed in 116 patients with elevated AP and in 36 controls. Results were compared with clinical data and with the heat inactivation techniques for AP isoenzyme separation. This latter method is simple but approximate; it is without value in the case of coexistent bone and liver pathology. PAGE gave a clear separation of liver, bile, bone, and intestinal AP isoenzymes. Disagreement with clinical data was rare (6 out of 86) and occurred in cases of associated bone and liver pathology (with 1 exception only), where one of these two abnormalities was not detected. Heat inactivation is useful as a screening test. If the cause of the elevated AP remains unknown after a few simple examinations, PAGE should then be utilized. Although more time-consuming, it is certainly more effective in the separation of AP isoenzymes.

Vitamin D deficiency is a previously unreported complication of therapy with hypnotics, and we here report a case of osteomalacia associated with long-term glutethimide administration. There was evidence of pronounced hepatic enzyme induction, and the plasma half-time of (3)H vitamin D(3) was decreased by this drug. In addition, raised levels of serum gamma-glutamyl transpeptidase, 5-nucleotidase, and leucine aminopeptidase were observed and the patient excreted large amounts of xylulose. These changes were reversed by stopping the glutethimide.