Arrest of hyperparathyroid bone disease with dihydrotachysterol in patients undergoing chronic hemodialysis

Bone and mineral metabolism in childhood end-stage renal disease

Renal osteodystrophy represents a spectrum from high to low turn-over lesions of bone, and the specific pattern may change during the evolution of chronic renal failure and as a consequence of specific therapeutic interventions. Although secondary hyperparathyroidism remains the predominant histologic lesion in patients undergoing maintenance dialysis, recent evidence indicates higher frequency of adynamic lesion not associated with aluminum intoxication. The different factors involved in the development of each of the histologic subtypes have been described together with the clinical manifestations of renal bone disease in childhood. Avoidance of aluminum-containing medications and the intermittent administration of calcitriol are effective approaches for the management of the renal bone diseases. The long-term consequences of the adynamic lesion remain to be determined.

Renal osteodystrophy

Over the past decade important advances in our understanding of the pathophysiology and treatment of renal osteodystrophy have been made. In particular, the role of calcitriol deficiency in the genesis of hyperparathyroidism in early renal failure is now better understood. So too are the effects of aluminium on bone, and whereas the more florid aluminium related disease is now unusual the more subtle effects of aluminium are now being appreciated. There is still a major problem in the long-term treatment of hyperparathyroid bone disease. The reasons why parathyroid gland proliferation continues to occur on dialysis therapy require a better understanding of cellular events regulating hormone production and parathyroid cell replication. The case for early intervention with vitamin D is now strong but whether such an approach materially influences the long-term outcome is not yet established. Changes in the approach to treatment and in the modalities used for renal replacement therapy will continue to modify the nature of the bone disease.

Total parathyroidectomy and autogenous parathyroid graft placement for treatment of hyperparathyroidism due to chronic renal failure

We treated 33 patients with chronic renal insufficiency and severe hyperparathyroidism with total parathyroidectomy and placement of an autogenous parathyroid graft in the forearm musculature. Postoperative biochemical data, symptomatic data, or both were available in 28 of the patients, of whom all but 1 showed evidence of improvement. Immunoreactive parathyroid hormone studies were made from 9 to 52 months postoperatively in 22 patients. Background immunoreactive parathyroid hormone levels markedly decreased after surgery and were in the optimum range in 18 patients. In the other four patients, immunoreactive parathyroid hormone levels remained above the optimum range, but in only one of the four did symptoms and biochemical parameters fail to improve. Gradients for immunoreactive parathyroid hormone across the forearm musculature were demonstrable in 18 of 22 patients, which proved the secretory function of the graft. One patient required resection of a portion of the grafted tissue on two occasions because of recurrent hypercalcemia. The technique of total parathyroidectomy and autogenous parathyroid grafting seems to be a valid alternative to subtotal parathyroidectomy for the treatment of uremic secondary hyperparathyroidism.

Pharmacology and therapeutic use of vitamin D and its analogues

The term vitamin D is generally used to describe a number of chemically related compounds with common antirachitic properties, but which have differences in the rapidity of their action, the way they are produced in the body, and the conditions under which their results are optimal. Ergocalciferol, cholecalciferol, 25-hydroxycholecalciferol (calcifediol), dihydrotachysterol, 1 alpha-hydroxycholecalciferol (alfacalcidol), and 1,25-dihydroxycholecalciferol (calcitriol) are currently the most commonly used vitamin D metabolites. In man, cholecalciferol produced on the skin and the fraction obtained from the diet in the gastrointestinal tract are converted in the liver to 25-hydroxycholecalciferol and then in the kidney to 1,25-dihydroxycholecalciferol. The demonstration of these metabolic pathways has helped to elucidate the aetiology of such conditions a hepatobiliary osteodystrophy, drug-induced anticonvulsant osteomalacia, the hypocalcaemia of hypoparathyroidism and above all azotaemic osteodystrophy. In the therapy of azotaemic osteodystrophy, the period of 'vitamin D resistance' when large doses of vitamin D2 and D3 had to be used is now over, and these patients can be efficiently and successfully treated with almost physiological doses of 1 alpha-hydroxycholecalciferol and 1,25-dihydroxycholecalciferol. Attention to diet, calcium supplements and oral phosphate binders are also important. During repetitive haemodialysis, the above principles still hold true, but in some of these patients an osteomalacic syndrome resistant to 1,25-dihydroxycholecalciferol has been recognised. These patients readily become hypercalcaemic when given 1,25-dihydroxycholecalciferol and their fractures and osteomalacia do not improve. Aluminium intoxication, possibly related to the use of impure dialysis fluid, is currently thought to be the most likely explanation of this dialysis osteomalacic syndrome.

Experience with 1,25-dihydroxycholecalciferol therapy in undergoing hemodialysis patients with progressive vitamin D2-treated osteodystrophy

Six long-term hemodialysis patients with progressive skeletal deterioration during long-term pharmacologic vitamin D2 therapy were treated for six to 12 months with oral 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) to determine its therapeutic effectiveness in vitamin D2-unresponsive osteodystrophy. On bone biopsy, three of the patients had severe osteomalacia and three showed predominant osteitis fibrosa. Previous therapies, including phosphate binders and dialysis schedules, were maintained. The three patients with osteomalacia and the two with osteitis fibrosa showed clinical deterioration. There was no significant change in serum calcium, phosphate, alkaline phosphatase, bone densitometry, immunoreactive parathyroid hormone levels or bone histology. Roentgenograms showed multiple new fractures of ribs and femoral necks in the patients with osteomalacia and increased bone resorption in two of three patients with osteitis fibrosa. 1,25-(OH)2D3 dosage had to be decreased in all patients because of hypercalcemia with a mean tolerated dose of 0.22 microgram/day. In these patients, 1,25-(OH)2D3 was not effective therapy for progressive osteodystrophy unresponsive to pharmacologic vitamin D2.

The management of renal osteodystrophy

Hyperparathyroidism is the main cause of renal bone disease. At the moment its progress can be retarded by controlling plasma calcium and phosphate. But the prevention and cure of hyperparathyroidism without surgery eludes us. There is a suggestion that the administration of some metabolite of Vitamin D may be more successful. Osteomalacia on the other hand does not appear to be an important problem and is easily prevented and cured.

Bone demineralization in renal failure: a longitudinal study of the distal femur using photon absorptiometry

The bone mineral content (BMC) of the lower end of the femur was measured by photon absorptiometry in 87 patients with chronic renal failure. The gamma-ray photon source was Am241. Serial measurements were obtained for up to two years. The mean BMC of the adult patients, comprising: 18 pre-dialysis (CRF), 41 chronic haemodialysis (CHD) and 19 renal transplant (RT) patients were all significantly lower than controls with the exception of the male CRF group. Two adults and one child on chronic haemodialysis showed a significant rate of bone loss (less than 2% per year). In one of these adults the addition of daily oral 1 alpha hydroxycholecalciferol was associated with no further reduction in BMC. Two children and one adult on chronic haemodialysis showed a significant rate of increase in BMC (less than 2% per year). This adult had had a tendency to loss of BMC on standard CHD treatment but after receiving parenteral 1,25 dihydroxycholecalciferol three times weekly showed a significant rate of loss of BMC on serial measurement. Two adults and one child with CRF had a significant rate of increase in BMC on standard treatment.

The use of high calcium dialysate in the treatment of renal osteomalacia

Four chronic haemodialysis patients suffering from osteomalacia were treated by increasing their dialysate calcium concentration from 1-40 to 2-15 mM/I. Bone biopsies were taken before and after 22 weeks of this treatment and a further biopsy was taken in one patient after 52 weeks. Symptomatic cure occurred in one patient with mild osteomalacia and some improvement osteomalacia and hyperparathyroidism. Bone biopsies showed slight improvement in the patient with mild osteomalacia after 22 weeks, and considerable improvement after 25 weeks. In the patient with mixed histology, the osteitis fibrosa subsided and the osteomalacia became a little worse after 22 weeks. There was no histologic improvement in the two patients with severe osteomalacia after 22 weeks. It is concluded that high calcium dialysis is not an effective treatment for renal osteomalacia.

Bone scan in chronic dialysis patients with evidence of secondary hyperparathyroidism and renal osteodystrophy

Bone scans in 13 of 14 patients on chronic dialysis were found to be abnormal. Symmetrical increased activity was noted in the calvarium, mandible, sternum, shoulders, vertebrae, and the distal aspects of the femur and tibia, as well as the patella. The scan abnormality is felt to be most likely the result of secondary hyperparathyroidism because of clinical and laboratory data, and, in four, confirmatory tissue diagnoses. The scan findings support the data of some earlier investigations on bone isotopic accretion in hyperparathyroidism. However, co-existing osteomalacia giving rise to abnormal activity in some of the patients cannot be excluded. Dihydrotachysterol may have minimized the extent of osteomalacia in these patients. Osteoporosis was probably present in some patients, but it appears differently on scan. Osteosclerosis was not detected on radiographic examination. Scan manifestations, especially mandibular activity, were pronounced and appeared earlier than the radiographic changes. The degree and extent of abnormal activity correlated with the length of dialysis and the level of alkaline phosphatase.

Influence of dialysate calcium concentration and vitamin D on serum parathyroid hormone during repetitive dialysis

An acute rise or decrease in parathyroid hormone (PTH) secretion was found in 30 patients, dialyzed with, respectively, low (5 mg/100 ml) or high (7.5 mg/100 ml) calcium concentration. The percentage changes were, respectively, +35% and -47% when a N-terminal antiserum measuring predominantly the glandular PTH was used. Only relatively small changes, respectively, +3% and -17%, were found using a C-terminal antiserum which detects preferentially smaller PTH fragments. Predialysis serum PTH concentration increases significantly with increasing duration of repetitive hemodialysis treatment using an intermediate (6 and 6.4 mg/100 ml) concentration of calcium in the dialysate. No such increase could be found in two other groups of patients treated with high-calcium (7.5 mg/100 ml) dialysis. Moreover, a significant but temporary decrease in predialysis serum PTH concentration occurred two months after a rise in dialysate calcium concentration from 6 to 7.5 mg/100 ml. Treatment with pharmacologic doses of vitamin D3 in selected patients (renal osterdystrophy or children) always resulted in a definite suppression of serum PTH concentration during 14 treatment periods in ten patients. After cessation of vitamin D3 treatment, serum PTH concentration returned to high levels in four out of five patients. These data fail to confirm the long-term involution of secondary hyperparathyroidism using high-calcium dialysis. Vitamin D treatment, however, results in a much more pronounced decrease in serum PTH concentrations, but sustained therapy is necessary.

Vitamin D in solution: conformations of vitamin D3, 1alpha,25-dihydroxyvitamin D3, and dihydrotachysterol3

Solution conformations of the A and seco B rings of vitamin D(3), 1(alpha), 25-dihydroxyvitamin D(3), 1(alpha)-hydroxyvitamin D(3), and dihydrotachysterol(3) have been established by high resolution, 300-megahertz proton magnetic resonance spectroscopy. The A ring of these steroids is dynamically equilibrated between two chair conformers. For vitamin D(3), 1(alpha)-hydroxyvitamin D(3), and 1(alpha),25-dihydroxyvitamin D(3) the relative proportions of the two conformers are 1 : 1, whereas dihydrotachysterol3 exists principally as only one conformer. Thus, the substituent groups on the A ring may be either equatorially or axially oriented, and suggests a refinement of the existing topological model for vitamin D hormonal activity.

Vitamin D: concerning the relationship between molecular topology and biological function

Structure-function relationships for vitamin D, its metabolites, and analogs are discussed with particular emphasis on the A-ring conformation. It is emphasized that the A-ring of these seco-steroids consists of a pair of rapidly equilibrating chair conformers. As a consequence, different chair conformations produce different orientations of substituent groups in the A-ring. It is proposed that the 1alpha-hydroxyl of 1alpha,25-dihydroxyvitamin D(3) or its geometric equivalent in analogs must occupy the equatorial, as opposed to the axial, orientation for optimization of biological activity. This proposal is discussed in relation to existing published data on structure-function relationships and the steroid hormone model of action for the biologically active form of vitamin D. This three-dimensional topological model suggests the synthesis of other vitamin D analogs.

The effects in the rat of varying intakes of dietary calcium, phosphorus, and hydrogen ion on hyperparathyroidism due to chronic renal failure

Renal failure of 4 wk duration in rats led to parathyroid enlargement, increased bone resorption, and decreased tubular reabsorption of phosphate by the remnant kidney. The degree of hyperparathyroidism was influenced by each of the three dietary factors investigated. In the first study increasing calcium intake reduced the size of the parathyroids by increasing calcium and reducing phosphate absorption. In the second study phosphate intake was linearly related to parathyroid gland size in the uremic animals and associated with rising plasma phosphate levels. In the last study acidosis led directly to increased bone resorption but small parathyroid glands associated with elevated ionized calcium levels. Alkalosis lowered the serum ionized calcium and led to parathyroid enlargement and the expected associated findings. It was shown that parathyroid weight reflected both metabolic activity as judged by amino acid uptake, and the content of immunoassayable parathyroid hormone. In all studies gland weight was inversely related to serum ionized calcium.

Dihydrotachysterol: a calcium active steroid not dependent upon kidney metabolism

The activity of dihydrotachysterol and cholecalciferol was determined in nephrectomized or sham-operated vitamin D-depleted rats using in vitro transport of calcium and phosphate by everted intestinal preparations as the index of physiologic response. The activity of dihydrotachysterol was not reduced by absence of the kidneys whereas that of cholecalciferol was markedly inhibited so that at least a 10-fold greater dose of the latter was necessary to produce an equivalent effect in the nephrectomized rat as in the control. Dihydrotachysterol is therefore equipotent with cholecalciferol in the anephric rat although much less active in the intact animal.