Current status of the use of 1,25(OH)2D3 in the management of renal osteodystrophy

Association of cumulatively low or high serum calcium levels with mortality in long-term hemodialysis patients

BACKGROUND

The outcome-predictability of baseline and instantaneously changing serum calcium in hemodialysis patients has been examined. We investigated the mortality-predictability of time-averaged calcium values to reflect the 'cumulative' effect of calcium burden over time.

METHODS

We employed a Cox model using up-to-5-year (7/2001-6/2006) time-averaged values to examine the mortality-predictability of cumulative serum calcium levels in 107,200 hemodialysis patients prior to the use of calcimimetics, but during the time where other calcium-lowering interventions, including lower dialysate calcium, were employed.

RESULTS

Both low (<9.0 mg/dl) and high (>10.0 mg/dl) calcium levels were associated with increased mortality (reference: 9.0 to <9.5 mg/dl). Whereas mortality of hypercalcemia was consistent, hypocalcemia mortality was most prominent with higher serum phosphorus (>3.5 mg/dl) and PTH levels (>150 pg/ml). Higher paricalcitol doses shifted the calcium range associated with the greatest survival to the right, i.e. from 9.0 to <9.5 to 9.5 to <10.0 mg/dl. African-Americans exhibited the highest death hazard ratio of hypocalcemia <8.5 mg/dl, being 1.35 (95% CI: 1.22-1.49). Both a rise and drop in serum calcium over 6 months were associated with increased mortality compared to the stable group.

CONCLUSIONS

Whereas in hemodialysis patients cumulatively high or low calcium levels are associated with higher death risk, subtle but meaningful interactions with phosphorus, PTH, paricalcitol dose and race exist.

Pharmacological and clinical properties of calcimimetics: calcium receptor activators that afford an innovative approach to controlling hyperparathyroidism

Circulating levels of calcium ion (Ca2+) are maintained within a narrow physiological range mainly by the action of parathyroid hormone (PTH) secreted from parathyroid gland (PTG) cells. PTG cells can sense small fluctuations in plasma Ca2+ levels by virtue of a cell surface Ca2+ receptor (CaR) that belongs to the superfamily of G protein-coupled receptors (GPCR). Compounds that activate the CaR and inhibit PTH secretion are termed 'calcimimetics' because they mimic or potentiate the effects of extracellular Ca2+ on PTG cell function. Preclinical studies with NPS R-568, a first generation calcimimetic compound that acts as a positive allosteric modulator of the CaR, have demonstrated that oral administration decreases serum levels of PTH and calcium, with a leftward shift in the set-point for calcium-regulated PTH secretion in normal rats. NPS R-568 also suppresses the elevation of serum PTH levels and PTG hyperplasia and can improve bone mineral density (BMD) and strength in rats with chronic renal insufficiency (CRI). Clinical trials with cinacalcet hydrochloride (cinacalcet), a compound with an improved metabolic profile, have shown that long-term treatment continues to suppress the elevation of serum levels of calcium and PTH in patients with primary hyperparathyroidism (1HPT). Furthermore, clinical trials in patients with uncontrolled secondary hyperparathyroidism (2HPT) have demonstrated that cinacalcet not only lowers serum PTH levels, but also the serum phosphorus and calcium x phosphorus product; these are a hallmark of an increased risk of cardiovascular disease and mortality in dialysis patients with end-stage renal disease. Indeed, cinacalcet has already been approved for marketing in several countries. Calcimimetic compounds like cinacalcet have great potential as an innovative medical approach to manage 1HPT and 2HPT.

Mechanisms for the reduction of 24,25-dihydroxyvitamin D3 levels and bone mass in 24-hydroxylase transgenic rats

24-Hydroxylase (CYP24) is an enzyme distributed in the target tissues of 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3]. Two functions for this enzyme have been reported: One is production of 24,25-dihydroxyvitamin D3 [24,25(OH)2D3] and the other is inactivation of 1alpha,25(OH)2D3. To elucidate other physiologic roles of CYP24 in vivo, we previously generated rats that constitutively express the CYP24 gene. These transgenic (Tg) rats developed unexpected phenotypes, such as low plasma levels of 24,25(OH)2D3, lipidemia, and albuminuria. In this study, we elucidated the mechanisms for inducing low plasma 24,25(OH)2D3 levels and bone loss. Tg rats excreted massive amounts of vitamin D binding protein (DBP), which coincided with the loss of albumin. In Tg rats, the renal expression pattern of megalin, which serves as an endocytotic receptor responsible for the reuptake of urinary proteins such as DBP and albumin, was identical to that of the wild-type rats. Excreted albumin appeared to compete for the binding and reabsorption of the DBP-25-hydroxyvitamin D3 [25(OH)D3] complex with megalin, resulting in a loss of 25(OH)D3 into the urine and subsequent reduction of plasma 24,25(OH)2D3. In this prominent rat model of nephritis, supplementation of 25(OH)D3 was effective in preventing bone loss in an early stage of renal insufficiency.

22-oxacalcitriol suppresses secondary hyperparathyroidism without inducing low bone turnover in dogs with renal failure

BACKGROUND

Calcitriol therapy suppresses serum levels of parathyroid hormone (PTH) in patients with renal failure but has several drawbacks, including hypercalcemia and/or marked suppression of bone turnover, which may lead to adynamic bone disease. A new vitamin D analogue, 22-oxacalcitriol (OCT), has been shown to have promising characteristics. This study was undertaken to determine the effects of OCT on serum PTH levels and bone turnover in states of normal or impaired renal function.

METHODS

Sixty dogs were either nephrectomized (Nx, N = 38) or sham-operated (Sham, N = 22). The animals received supplemental phosphate to enhance PTH secretion. Fourteen weeks after the start of phosphate supplementation, half of the Nx and Sham dogs received doses of OCT (three times per week); the other half were given vehicle for 60 weeks. Thereafter, the treatment modalities for a subset of animals were crossed over for an additional eight months. Biochemical and hormonal indices of calcium and bone metabolism were measured throughout the study, and bone biopsies were done at baseline, 60 weeks after OCT or vehicle treatment, and at the end of the crossover period.

RESULTS

In Nx dogs, OCT significantly decreased serum PTH levels soon after the induction of renal insufficiency. In long-standing secondary hyperparathyroidism, OCT (0.03 microg/kg) stabilized serum PTH levels during the first months. Serum PTH levels rose thereafter, but the rise was less pronounced compared with baseline than the rise seen in Nx control. These effects were accompanied by episodes of hypercalcemia and hyperphosphatemia. In animals with normal renal function, OCT induced a transient decrease in serum PTH levels at a dose of 0.1 microg/kg, which was not sustained with lowering of the doses. In Nx dogs, OCT reversed abnormal bone formation, such as woven osteoid and fibrosis, but did not significantly alter the level of bone turnover. In addition, OCT improved mineralization lag time, (that is, the rate at which osteoid mineralizes) in both Nx and Sham dogs.

CONCLUSIONS

These results indicate that even though OCT does not completely prevent the occurrence of hypercalcemia in experimental dogs with renal insufficiency, it may be of use in the management of secondary hyperparathyroidism because it does not induce low bone turnover and, therefore, does not increase the risk of adynamic bone disease.

NPS R-568 halts or reverses osteitis fibrosa in uremic rats

Osteitis fibrosa is a common bone injury associated with secondary hyperparathyroidism (2(o)HPT). NPS R-568 is a phenylalkylamine derivative that acts as an agonist at the cell-surface Ca2+ receptor ("calcimimetic") and inhibits parathyroid hormone (PTH) secretion. In the present study, we tested whether NPS R-568 could ameliorate osteitis fibrosa in partially nephrectomized (Nx) rats with 2(o)HPT. Six months after surgery, Nx rats had developed mild but progressive 2(o)HPT and osteitis fibrosa. Two groups of Nx rats received NPS R-568 (3 and 30 mg/kg body wt x day) by daily gavage for 30 days, which led to a dose-related decrease in serum PTH levels and to a marked reduction in peritrabecular fibrosis (0.96 +/- 0.49% to < 0.1%). Furthermore, 2(o)HPT was associated with decreases in volumetric cortical bone mineral density (vCtBMD) and in cortical bone stiffness at the femoral midshaft. NPS R-568 significantly restored the deficits in vCtBMD and stiffness. These results indicate that NPS R-568 has beneficial effects on bones with osteitis fibrosa by normalizing serum PTH levels.

1.25(OH)2 cholecalciferol pulse therapy and the effects of different dialysis membranes on serum PTH levels of haemodialysis patients

Either oral, intravenous or subcutaneous 1.25(OH)2 cholecalciferol is used in the therapy of hyperparathyroidism, which is a serious complication in patients on haemodialysis. We studied a total of 30 patients (10 women and 20 men) and divided them into two groups depending on the different types of dialysis membranes used. In the polysulfone group, mean age was 43.7 +/- 0.97 years and the average dialysis period lasted 29.9 +/- 1.23 months. For the 15 cases in which we used cuprophane membrane the mean age was 40.2 +/- 1.31 years and the average dialysis period lasted 16.2 +/- 0.86 months. The calcium level of the dialysate in both groups was 1.5 mmol/l. According to the study protocol, the determined oral calcitriol dose was 0.07 mg/kg and it was administered intermittently. After one month on high dose calcitriol therapy, treatment was continued with a maintenance dose of 0.03 mg/kg for a further six months. As a phosphate binding agent, daily 3 g calcium carbonate was administered. Before starting this treatment protocol, patients went on a 1 mg/day calcitriol therapy, although the mean PTH level was 424.63 pg/ml and the mean serum alkaline phosphatase level was 290.2 U/l. During the pretreatment period, levels of PTH, alkaline phosphatase, ionized calcium, and total calcium remained significantly within normal limits as a result of the new therapy protocol applied. PTH and phosphorus clearance rates were compared in the patient groups in which different dialysis membranes had been used. PTH and phosphorus clearances were 15.2 +/- 3 ml/min and 239.1 +/- 19.2 ml/min, respectively, in the polysulfone membrane group, and 1.1 +/- 0.3 ml/min and 112.8 +/- 9.88 ml/min, respectively, in the cuprophane membrane group (p < 0.05).

Benefits of calcitriol therapy and serum phosphorus control in dogs and cats with chronic renal failure. Both are essential to prevent of suppress toxic hyperparathyroidism

Daily oral calcitriol at low doses is safe and effective in the control of renal secondary hyperparathyroidism in dogs and cats. Low doses of calcitriol are most effective when started early in uremia before the advanced stages of renal secondary hyperparathyroidism. At early stages calcitriol both diminishes PTH synthesis in the parathyroid cells present and prevents the hyperplasia that, if unchecked, results in the most extensive an difficult-to-control hyperparathyroidism. The salutary effects on the dog's or cat's sense of well being, appetite, activity, strength, and lifespan as reported by the veterinarians of our survey are attributed primarily to keeping PTH levels below a toxic threshold. Additionally, some of the benefits achieved by calcitriol are likely a direct consequence of calcitriol interacting with the vitamin D receptor in a wide variety of tissues throughout the body. Phosphorus restriction through a combination of diet and intestinal phosphate binders is important to allow calcitriol therapy to successfully lower PTH levels, but it likely has no direct effects that are independent of interactions involving calcitriol. Phosphorus restriction is also important to minimize chances for adverse tissue mineralization. Calcitriol therapy can be considered for treatment of chronic renal failure after serum phosphorus has been decreased to less than 6.0 mg/dL in patients in whom it was initially elevated. Calcitriol supplementation to dogs and cats with chronic renal failure makes good endocrinologic sense. Calcitriol deficits cause increased PTH and, as these two hormones are designed to maintain calcium and phosphorus homeostasis, the PTH increase is initially adaptive. One of the important effects of PTH is to stimulate additional calcitriol formation as a powerful means to raise blood calcium through increased calcium absorption from the diet. With too great an increase in PTH, however, its effects become harmful to many tissues due to the widespread distribution of the PTH receptor in many cell types that are likely normally responsive only to the paracrine PTH-related peptide that shares the PTH receptor. Exogenous supplemental calcitriol administration allows concentrations of calcitriol in the bloodstream to remain normal without the toxic consequences of excessive PTH secretion that would otherwise be provoked. Studies involving young dogs with subtotal nephrectomy may not parallel those on older dogs and cats with spontaneous chronic renal failure. In particular, higher doses are needed to effect PTH change in these young dogs than we have found necessary for older dogs and cats. Because survey participants agreed most strongly with the idea that their calcitriol-treated dogs and cats were living longer than comparably uremic animals they had treated previously, further studies to evaluate the ability of calcitriol to retard the progression of renal lesions and loss of excretory renal function seem warranted. Additional studies to document the beneficial effects of calcitriol on the many organs adversely affected by excess PTH during uremia are also needed because findings thoroughly documented and proven in humans and rats may not always extrapolate to dogs and cats.

A prospective, double-blind study of growth failure in children with chronic renal insufficiency and the effectiveness of treatment with calcitriol versus dihydrotachysterol. The Growth Failure in Children with Renal Diseases Investigators

Because controlled trials in adults have shown accelerated deterioration of renal function in a small number of patients receiving calcitriol for renal osteodystrophy, we initiated a prospective, randomized, double-blind study of the use of calcitriol versus dihydrotachysterol in children with chronic renal insufficiency. We studied children aged 1 1/2 through 10 years, with a calculated glomerular filtration rate between 20 and 75 ml/min per 1.73 m2, and with elevated serum parathyroid hormone concentrations. Ninety-four patients completed a mean of 8.0 months of control observations and were randomly assigned to a treatment period; 82 completed the treatment period of at least 6 months while receiving a calcitriol dosage (mean +/- SD) of 17.1 +/- 5.9 ng/kg per day or a dihydrotachysterol dosage of 13.8 +/- 3.3 micrograms/kg per day. With treatment the height z scores for both calcitriol- and dihydrotachysterol-treated groups showed no differences between the two groups. In relation to cumulative dose, there was a significant decrease in glomerular filtration rate for both calcitriol and dihydrotachysterol; for calcitriol the rate of decline was significantly steeper (p = 0.0026). The treatment groups did not differ significantly with respect to the incidence of hypercalcemia (serum calcium concentration > 2.7 mmol/L (> 11 mg/dl)). We conclude that careful follow-up of renal function is mandatory during the use of either calcitriol or dihydrotachysterol because both agents were associated with significant declines in renal function. There was no significant difference between calcitriol and dihydrotachysterol in promoting linear growth or causing hypercalcemia in children with chronic renal insufficiency. Dihydrotachysterol, the less costly agent, can be used with equal efficacy.

Recent advances in pediatric metabolic bone disease: the consequences of altered phosphate homeostasis in renal insufficiency and hypophosphatemic vitamin D-resistant rickets

Over the past decade our understanding of the pathogenesis of altered mineral homeostasis in chronic renal failure (CRF) and X-linked hypophosphatemic vitamin D-resistant rickets (XLH) has increased, and has provided a rational approach for the use of the 1 alpha-hydroxylated analogues of vitamin D in their therapy. Recent evidence suggests that intracellular phosphate (Pi) retention in CRF plays a major role in decreasing serum 1,25-dihydroxyvitamin D (1,25(OH)2D) levels, which are responsible for the progressive rise in serum parathyroid hormone (PTH) concentrations through the direct action of 1,25(OH)2D on the parathyroid gland. 1,25(OH)2D levels affect the number of intracellular 1,25(OH)2D receptors, preproPTH mRNA levels and the set point for calcium suppression of PTH release. Further in experimental CRF, the maintenance of normal 1,25(OH)2D levels prevents parathyroid gland hyperplasia. These studies indicate that depressed renal 1 alpha-hydroxylase activity due to Pi retention is a major factor in directly increasing PTH secretion, which in turn contributes significantly to the severity of renal osteodystrophy. Thus the aim of therapy in early CRF should be to maintain normal levels of 1,25(OH)2D which can be achieved by either dietary Pi restriction and oral Pi binders or by administering small doses of 1 alpha-hydroxylated metabolites. The long term consequences of these two different therapeutic regimens still need to be assessed. In XLH, evidence is rapidly accumulating that alterations in 1 alpha-hydroxylase activity secondary to impaired Pi handling by the proximal renal tubule, results in decreased serum 1,25(OH)2D levels, which might be responsible for a number of the associated abnormalities documented in both treated and untreated XLH patients. These abnormalities include decreased calcium and Pi absorption by the intestine and low normal serum calcium values. In vitamin D- and Pi-treated patients 1,25(OH)2D levels are further depressed, with a resultant increase in PTH values, and the development of tertiary hyperparathyroidism in a small number of patients. The use of 1 alpha-hydroxylated analogues rather than vitamin D together with Pi supplements decreases the severity of hyperparathyroidism, improves Pi absorption from the intestine and markedly ameliorates the degree of osteomalacia. Whether long-term therapy with these analogues will prevent the development of tertiary hyperparathyroidism in patients with XLH is unclear.

Linear growth and anthropometric and nutritional measurements in children with mild to moderate renal insufficiency: a report of the Growth Failure in Children with Renal Diseases Study

During the control period of the Growth Failure in Children With Renal Diseases Study, investigators at 23 centers were able to observe and characterize growth and to make anthropometric and nutritional measurements in 82 children with mild to moderate renal insufficiency. As a multicenter, controlled clinical trial designed to study the relative efficacy of 1,25-dihydroxyvitamin D3 and dihydrotachysterol in the treatment of renal osteodystrophy, no prior vitamin D exposure and a creatinine clearance of 25 to 75 ml/min/1.73 m2 were criteria for entrance into the clinical trial. Ages ranged from 18 months to 11 years (mean 5.6 +/- 3.1 years), and distribution by age category was as follows: 38%, 1 to 3 years; 28%, 4 to 6 years; and 34%, 7 to 10 years. There was a 3:1 male/female ratio; 72% of the patients had congenital disease by the International Classification of Diseases (ninth revision). Mean creatinine clearance was 49.5 +/- 20 ml/min/1.73 m2. The C-terminal parathyroid hormone values (1121 +/- 1562 pg/ml) were well above 2 SD of the mean of a normal growing population of similar age. Parathyroid hormone values correlated with degree of renal insufficiency (r = -0.57) and with height by bone age but not with chronologic height or growth velocity. The bone age/height age ratio, a predictor of growth potential in normal children, was low for the entire series of patients (0.88 +/- 0.35) but failed to correlate with growth velocity and was negatively correlated with rising parathyroid hormone levels. Average values for height, weight, triceps skin fold, mid-arm muscle circumference, and body mass index were within 2 SD of the mean of the normal population, although measurements for the 1- to 3-year age group were significantly less than those of the older patients. Total energy intake averaged less than 86% of the recommended dietary allowances; total protein intake was more than 161% of the allowance. Nitrogen balance in 23 patients was positive and correlated most significantly with increasing energy intake (r = 0.6). Growth velocity, calculated from the interval gain during the month control period, averaged +0.3 SD, with the highest growth velocity z scores recorded for those with acquired disease. A growth velocity index, expressed as the slope of the regression between change in height SD and growth velocity z score, was used to describe the growth accomplished in the control period by age category.(ABSTRACT TRUNCATED AT 400 WORDS)

Tissue calcium in uraemia

The content of calcium in the thoracic aorta, the heart and the kidney was determined in rats with moderate renal failure treated with 1.25-dihydroxycholecalciferol (1.25-DHCC) 100 ng/kg/day and Verapamil 20 mg/kg/day. In the aorta the content of calcium was significantly increased in uraemic rats and this increase was significantly augmented after administration of 1.25-DHCC. In the kidney no increase in calcium was seen in rats with uraemia, but treatment with 1.25-DHCC increased the calcium content significantly. This increase was not correlated to the serum calcium x phosphate product, which was almost normal. In the heart no changes in the content of calcium were observed. Verapamil did not influence the effect of 1.25-DHCC. It is concluded that administration of 1.25-DHCC per se may increase the content of calcium in the aorta and kidney in rats with moderate uraemia and possibly in this way sensitize the tissue to the development of tissue calcification.

Oral calcitriol and calcium: efficient therapy for uremic hyperparathyroidism

Therapy with orally administered calcitriol often does not adequately control the biochemical manifestations of secondary hyperparathyroidism in uremic patients. This may be due to inadequate serum concentrations of 1.25(OH)2 vitamin D and/or to insufficient dietary calcium supplementation. In the present study, therefore, we examined the effect on parathyroid function of calcitriol and calcium carbonate, administered orally, in doses sufficient to normalize the serum 1.25(OH)2 vitamin D and calcium concentrations. After nine months of combined therapy, marked suppression of immunoreactive PTH occurred in the absence of hypercalcemia. Furthermore, prolonged therapy resulted in additional suppression of the PTH concentrations comparable in magnitude to that reported following intravenous calcitriol therapy and was associated with a mild degree of hypercalcemia similar to that which occurs with intravenous therapy. Euparathyroidism was achieved in 25% of the patients by 15 months of treatment. In conclusion, secondary hyperparathyroidism can be effectively controlled with combined oral therapy without significant hypercalcemia in selected patients with end-stage renal failure. This salutary effect may result from direct actions of 1.25(OH)2D on the parathyroid gland and/or gastrointestinal tract, or from an overall action of combined treatment to restore calcium homeostasis.

Reduced binding of [3H]1,25-dihydroxyvitamin D3 in the parathyroid glands of patients with renal failure

This study examined the hypothesis that altered binding of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) to parathyroid receptors might be involved in the pathogenesis of secondary hyperparathyroidism associated with chronic renal failure. The binding of [3H]1,25-(OH)2D3 to hyperplastic parathyroid glands obtained from seven patients with chronic renal failure was measured. These values were compared with those for binding to hyperplastic parathyroid tissue obtained from six patients who had received renal transplants and for binding to parathyroid adenomas removed from five patients who had primary hyperparathyroidism. We found that Nmax (an estimate of the concentration of 1,25-(OH)2D3 receptors) was reduced (42 +/- 15 fmol per milligram of protein) in patients with chronic renal failure as compared with patients with transplanted kidneys (78 +/- 24 fmol per milligram of protein) and patients with primary hyperparathyroidism (114 +/- 30). Nmax correlated inversely with the severity of renal dysfunction, the serum level of phosphorus, and the logarithm of the serum level of immunoreactive parathyroid hormone. These observations suggest that 1,25-(OH)2D3 binding by parathyroid tissue is reduced in chronic renal failure. This may contribute to the pathogenesis of secondary hyperparathyroidism by reducing the inhibition by 1,25-(OH)2D of parathyroid hormone secretion. The low serum levels of 1,25-(OH)2D in chronic renal failure may accentuate this effect.

Main endocrine modulators of vitamin D hydroxylases in human pathophysiology

Vitamin D is considered to be devoid of direct biological activity. It must be first hydroxylated in the liver by a 25-hydroxylase (25OHase), then in the kidney by a 1 alpha-hydroxylase (1 alpha OHase) which is responsible for the synthesis of the active metabolite, 1,25-dihydroxyvitamin D (1,25(OH)2D). The activity of 1 alpha OHase is known to be under the control of a series of endocrine modulators, particularly parathyroid hormone (PTH) and estrogens. We report here our studies in humans concerning the behaviour of vitamin D hydroxylases in some pathological conditions. In chronic liver disease no severe impairment of vitamin D-25-hydroxylation has been observed, except in the latest stages: this is probably due to the great functional reserve of the liver, so that normal levels of serum 25OHD can be maintained on condition that the vitamin D supply is adequate. 1 alpha OHase is impaired in chronic renal failure due to the decrease in the number of functioning nephrons. It has been demonstrated that kidney transplantation restores normal 1,25(OH)2D levels. A decrease in 1,25(OH)2D production due to reduced PTH stimulation has been observed in hypoparathyroidism: in these patients a subcutaneous substitution therapy with synthetic human parathyroid hormone resulted in restoration of normal 1,25(OH)2D levels. A reduced activity of 1 alpha OHase due to reduced estrogen stimulation plays a key role in postmenopausal osteoporosis. In these patients estrogens increase 1,25(OH)2D levels, as it has been demonstrated directly and indirectly. In the aforementioned pathological conditions an impairment of calcium absorption has been observed; it was directly related to the reduced production of 1,25(OH)2D. Treatment with 1,25(OH)2D3 was effective in restoring normal calcium absorption. In postmenopausal osteoporosis the reduced levels of 1,25(OH)2D were accompanied by serum levels of 25-hydroxyvitamin D (25OHD) higher than in age-matched control women. In these cases long-term treatment with physiological doses of 1,25(OH)2D3 resulted in a progressive decrease in 25OHD serum levels which approached to the normal range. These findings are likely to be related one to another: the low 1,25(OH)2D levels are responsible for reduced product-inhibition of 25OHase, so that the synthesis of 25OHD increases. A similar mechanism occurs in renal failure and in hypoparathyroidism.

Red Blood Cell Deformability and Secondary Hyperparathyroidism in Uremic Patients on Maintenance Hemodialysis

The possible relationship between red blood cell (RBC) deformability and secondary hyperparathyroidism (HPT) in 23 patients on maintenance hemodialysis was examined. Secondary HPT was evaluated by means of serum biochemistry (parathyroid hormone, calcium, phosphorus, and alkaline phosphatase) and radiographic examinations. This study showed that RBC deformability is markedly reduced in hemodialyzed patients when compared with normal controls. No significant correlation between RBC deformability and the hematochemical changes associated with secondary HPT was found. No difference in RBC deformability was observed as far as the activity (alkaline phosphatase) and the severity (radiographic findings) of secondary HPT are concerned. Effective treatment of secondary HPT by either pharmacological means (1 alpha, 25-dihydroxycholecalciferol therapy) or surgical removal was not associated with consequent improvement in RBC deformability. It is concluded that secondary HPT is probably not a major factor influencing RBC deformability in uremic patients on maintenance hemodialysis.

Renal osteodystrophy in children treated with 1,25-dihydroxy-cholecalciferol [1,25-(OH)2D3]. Histologic bone studies

Eleven uremic children with osteodystrophy aged 3 to 17 years were studied during administration of 1,25-(OH)2D3 for periods up to 21 months. Nine children presented with pure hyperparathyroidism, one with osteomalacia and one with mixed bone disease. Bone biopsies were performed before initiation of therapy and after 6 to 21 months of treatment following double tetracycline labeling. Skeletal lesions were improved but not cured in 5 of 9 children with hyperparathyroidism. In three instances lesions remained unchanged and worsened in one. No significant change was observed in the child with osteomalacia. Moderate improvement was noted in the patient with mixed bone disease. The propensity to develop hypercalcemia was the major factor associated with treatment failure since it precluded administration of adequate amounts of medication. Therapy with 1,25-(OH)2D3 was associated with a spectacular improvement in growth velocity in two of six children under age twelve.

Bone disease in long-term hemodialysis patients with low dialysate aluminium

The dialysis unit in Sunderland uses softener water treatment with low Al concentration (dialysate mean Al 22 micrograms/L) but employs continuous oral Al (OH)3 to control serum phosphate. Thirty-one patients, 22 males and 9 females, with a mean age of 45 years, maintained on hemodialysis for a mean of 48 months were studied. Patients had higher Al concentrations than normal controls (p less than 0.001) and the postdialysis serum Al levels were also significantly higher than the predialysis levels. Twenty-four of 31 patients had evidence of hyperparathyroidism on radiology but only 4 of 31 had fractures. From a histopathological point of view, the patients were found to have no lesions (4 patients), osteitis fibrosa alone (17 patients), and osteitis fibrosa combined with osteomalacia (5 patients). The effect of 1-alpha(OH)D3 treatment was checked by repeated bone biopsies. One case of the last group showed no improvement of osteitis fibrosa, while osteomalacia progressed to severe. We conclude that both antacids and dialysate contribute to the serum and tissue Al accumulation in Sunderland Renal Unit, where over a period of ten years only one patient developed Al-related osteomalacia.