Intermittent versus continuous administration of 1,25-dihydroxyvitamin D3 in experimental renal hyperparathyroidism

Intraperitoneal Pulse Calcitriol in the Treatment of Secondary Hyperparathyroidism in Patients on Continuous Ambulatory Peritoneal Dialysis

Objective

To determine whether it is practicable to use intraperitoneal calcitriol to treat continuous ambulatory peritoneal dialysis (CAPD) patients with secondary hyperparathyroidism and whether this form of therapy is effective and safe.

Design

A prospective, nonrandomized study.

Setting

Division of Nephrology, Tertiary Hospital.

Method

Eight patients from our CAPD population were recruited (5 F,3 M), aged 24 to 63 years (mean 38.9 ± 7.6 yr). They had been on CAPD for 8 to 84 months (mean 47.6 ± 24.6 months). All the patients had bone biopsy -proven secondary hyperparathyroidism with 2 patients showing mixed lesions. The CAPD system was changed to the twinbag system (Ultrabag, Baxter Healthcare, McGaw Park, IL, U.S.A.) in all 8 patients, who were taught to inject the calcitriol directly through the short transfer set and the Tenckhoff catheter into the peritoneal cavity, twice per week before bedtime. Calcium carbonate or calcium acetate was used as the main phosphate binder. Intact parathyroid hormone level (iPTH), serum ionized calcium (iCa), serum phosphate, and serum total alkaline phosphatase (alk. phos.) levels were measured at baseline and then every 4 weeks. The mean duration of follow-up was 10.5 months ± 1.9 months.

Results

There was a significant drop of iPTH level from the pretreatment level of 100.6 ± 35.8 pmoll L to a level of 63.8 ± 48.7 pmoll L at 24 weeks (p = 0.036). The lowest level of iPTH attained was 43.4 ± 27.0 pmol/L at 48 weeks. Serum total alk. phos. also dropped from 232.4 ± 83.3 lUlL pretreatment to 147.9 ± 52.0 lUlL at 24 weeks (p = 0.017). The decrease in alk. phos. level paralleled the decrease in iPTH level. The mean serum iCa level did not show any significant rise throughout the study period. The maximum dose of calcitriol used was 6.6 ± 1.5 μg/week and the average dose of calcitriol was 5.4 ± 1.2 μg/week. One patient did not respond satisfactorily and she subsequently had a parathyroidectomy. Two episodes of peritonitis occurred during the study period, giving a peritonitis rate of one episode per 42 patient-months. There was no significant change in the urea clearance tests or the peritoneal equilibration tests before and after the study.

Conclusion

Intraperitoneal calcitriol is practicable, effective, and safe in the treatment of secondary hyperparathyroidism in CAPD patients.

Adynamic bone disease: from bone to vessels in chronic kidney disease

Adynamic bone disease (ABD) is a well-recognized clinical entity in the complex chronic kidney disease (CKD)-mineral and bone disorder. Although the combination of low intact parathyroid hormone (PTH) and low bone alkaline phosphatase levels may be suggestive of ABD, the gold standard for precise diagnosis is histomorphometric analysis of tetracycline double-labeled bone biopsies. ABD essentially is characterized by low bone turnover, low bone volume, normal mineralization, and markedly decreased cellularity with minimal or no fibrosis. ABD is increasing in prevalence relative to other forms of renal osteodystrophy, and is becoming the most frequent type of bone lesion in some series. ABD develops in situations with reduced osteoanabolic stimulation caused by oversuppression of PTH, multifactorial skeletal resistance to PTH actions in uremia, and/or dysregulation of Wnt signaling. All may contribute not only to bone disease but also to the early vascular calcification processes observed in CKD. Various risk factors have been linked to ABD, including calcium loading, ageing, diabetes, hypogonadism, parathyroidectomy, peritoneal dialysis, and antiresorptive therapies, among others. The relationship between low PTH level, ABD, increased risk fracture, and vascular calcifications may at least partially explain the association of ABD with increased mortality rates. To achieve optimal bone and cardiovascular health, attention should be focused not only on classic control of secondary hyperparathyroidism but also on prevention of ABD, especially in the steadily growing proportions of diabetic, white, and elderly patients. Overcoming the insufficient osteoanabolic stimulation in ABD is the ultimate treatment goal.

Calcitriol, calcidiol, parathyroid hormone, and fibroblast growth factor-23 interactions in chronic kidney disease

Objective

To review the inter-relationships between calcium, phosphorus, parathyroid hormone (PTH), parent and activated vitamin D metabolites (vitamin D, 25(OH)-vitamin D, 1,25(OH)₂-vitamin D, 24,25(OH)₂-vitamin D), and fibroblast growth factor-23 (FGF-23) during chronic kidney disease (CKD) in dogs and cats.

Data Sources

Human and veterinary literature.

Human Data Synthesis

Beneficial effects of calcitriol treatment during CKD have traditionally been attributed to regulation of PTH but new perspectives emphasize direct renoprotective actions independent of PTH and calcium. It is now apparent that calcitriol exerts an important effect on renal tubular reclamation of filtered 25(OH)-vitamin D, which may be important in maintaining adequate circulating 25(OH)-vitamin D. This in turn may be vital for important pleiotropic actions in peripheral tissues through autocrine/paracrine mechanisms that impact the health of those local tissues.

Veterinary Data Synthesis

Limited information is available reporting the benefit of calcitriol treatment in dogs and cats with CKD.

Conclusions

A survival benefit has been shown for dogs with CKD treated with calcitriol compared to placebo. The concentrations of circulating 25(OH)-vitamin D have recently been shown to be low in people and dogs with CKD and are related to survival in people with CKD. Combination therapy for people with CKD using both parental and activated vitamin D compounds is common in human nephrology and there is a developing emphasis using combination treatment with activated vitamin D and renin-angiotensin-aldosterone-system (RAAS) inhibitors.

Development and prevention of morphologic and ultrastructural changes in uremia-induced hyperplastic parathyroid gland

The detailed ultrastructural changes of uremia-induced hyperplastic parathyroid gland and the effects of current medical treatments for secondary hyperparathyroidism were investigated. Marked enlargement of parathyroid cell with accumulation of mitochondria and lipids and a significant increase in the thickness of the pericapillary area with increased fibrosis and appearance of fibroblast like cells were noted in the hyperplastic gland caused by uremia and phosphate retention. These ultrastructural changes and biochemical findings indicating hyperparathyroidism were significantly suppressed by all of the treatment using phosphate restriction, calcitriol, and cinacalcet. The characteristic ultrastructural changes, including the morphologic evidence of nodule formation, were indicated.

Intravenous calcitriol therapy in an early stage prevents parathyroid gland growth

BACKGROUND

Both the phenotypic alterations of parathyroid (PT) cells, e.g. down-regulation of the calcium-sensing receptor, and the increase of the PT cell number in nodular hyperplasia are the main causes of refractory secondary hyperparathyroidism. It is of great importance to prevent PT growth in an early stage.

METHODS

To examine a more effective method of calcitriol therapy for the prevention of PT hyperplasia, we randomized haemodialysis patients with mild hyperparathyroidism to receive either daily orally administered calcitriol (n = 33) or intravenous calcitriol (n = 27) over a 12-month study period. Calcitriol was modulated so as to keep the serum intact PTH level between 100 and 150 pg/ml.

RESULTS

Both groups showed similar reductions of the serum PTH level and similar increases in serum calcium. In both groups, there were no significant changes in the serum phosphate level. Long-term daily oral calcitriol therapy failed to prevent the increase of both maximum PT volume and total volume, as assessed by ultrasonography; however, intravenous calcitriol therapy successfully suppressed this progression. In the daily, oral group, both the bone-specific alkaline phosphatase (BAP) and the N-telopeptide cross-linked of type I collagen (NTX) significantly decreased, which was probably due to the PTH suppression. However, these bone metabolism markers remained stable in the intravenous group. The total dosage of calcitriol during the study was comparable in both groups.

CONCLUSIONS

These data indicate that intravenous calcitriol therapy in an early stage of secondary hyperparathyroidism is necessary to prevent PT growth and to keep a good condition of bone metabolism.

A comparison of dosing regimens of paricalcitol capsule for the treatment of secondary hyperparathyroidism in CKD stages 3 and 4

BACKGROUND

Intermittent dosing of calcitriol for secondary hyperparathyroidism (SHPT) has been associated with greater parathyroid hormone (PTH) reduction with fewer calcemic and phosphatemic effects than daily (QD) dosing.

METHODS

Secondary analyses of three randomized, double-blind, placebo-controlled multicenter studies in stage 3 and 4 chronic kidney disease (CKD) patients with SHPT were performed to compare three times per week (TIW) with QD dosing of paricalcitol. The pharmacokinetics of TIW and QD dosing of paricalcitol capsules were assessed in a separate group of healthy subjects.

RESULTS

Pharmacokinetics revealed similar steady state paricalcitol exposure between dosing regimens. In CKD patients, baseline data were similar between the TIW studies (n = 72, paricalcitol; n = 73, placebo) and QD studies (n = 35, paricalcitol; n = 40, placebo). Both dosing regimens resulted in similar efficacy (91%) for the primary end point of two consecutive > or = 30% decreases in intact PTH from baseline, but the QD regimen resulted in a greater percent reduction in intact PTH from baseline. The chances for developing increased serum calcium and phosphorus levels or Ca x P product were similar between paricalcitol and placebo groups for both treatment regimens. Furthermore, no difference in the risk for these elevations was detected between the TIW and QD regimens.

CONCLUSIONS

QD dosing of paricalcitol capsules is as efficacious as TIW dosing in achieving the primary end point (2 consecutive > or = 30% reductions in PTH) in stage 3 and 4 CKD patients with SHPT. Moreover, the QD regimen had no significant effect on hypercalcemia, hyperphosphatemia or Ca x P product as compared with placebo or intermittent dosing.

Parathyroid growth and regression in experimental uremia

Early 1,25-dihydroxyvitamin D(3) (VD(3)) therapy during the course of renal failure prevents the downregulation of VD(3) receptor (VDR), calcium-sensing receptor (CaSR) or p21, and the parathyroid (PT) growth. We hypothesized that VD(3) could restore the decreased expressions of VDR and CaSR, and cause regression in enlarged PT glands. 5/6 nephrectomized rats fed high-phosphorus diet were killed at 1, 3, 5, or 7 days and at 2, 3, 4, 8, or 12 weeks. VD(3)-treated rats were given VD(3) intraperitoneally for 1, 2, 3, or 4 weeks, starting 8 weeks after 5/6 nephrectomy. PT glands were weighed and subjected to immunohistochemical analyses for VDR, CaSR, p21, Ki67, and Tdt-mediated dUTP nick end-labeling (TUNEL) assay. The area per cell was measured as the parameter of cell size. The expression of VDR and p21 began to decrease at day 1, and Ki67 increased at day 3, but decreased thereafter. There was a significant increase in PT gland weight to week 12 with the increase of cell size. VD(3) treatment significantly increased both VDR and CaSR expressions 2 weeks after the start of injection, and reduced the PT gland weight at week 3 with significant increase of TUNEL-positive cells and decrease of cell size. Our results suggest that PT growth in uremic rats involves both PT cell proliferation and hypertrophy, in association with the reduction of VDR, CaSR, and p21 expressions. In addition, VD(3) treatment could reverse PT hyperplasia and hypertrophy via restoration of these proteins.

Daily or intermittent calcitriol administration during growth hormone therapy in rats with renal failure and advanced secondary hyperparathyroidism

Growth hormone (GH) improves growth in children with chronic renal failure. The response to GH may be affected by the degree of secondary hyperparathyroidism and concurrent treatment with vitamin D. Forty-six rats underwent 5/6 nephrectomy (Nx) and were given a high-phosphorus diet (Nx-Phos) to induce advanced secondary hyperparathyroidism and divided into the following groups: (1) Nx-Phos (n = 10) received saline, (2) GH at 10 IU/kg per d (Nx-Phos+GH; n = 9), (3) GH and daily calcitriol (D) at 50 ng/kg per d (Nx-Phos+GH+daily D; n = 8), (4) GH and intermittent D (three times weekly) at 350 ng/kg per wk (Nx-Phos+GH+int D; n = 9), and (5) intact-control (n = 10). Serum parathyroid hormone (PTH) levels were elevated in Nx-Phos, but IGF-I levels did not change with growth hormone. Body length, tibial length, and growth plate width did not increase with either GH or calcitriol. Proliferating cell nuclear antigen staining, PTH/PTHrP receptor, bone morphogenetic protein-7, and fibroblast growth factor receptor-3 expression increased with GH alone or with intermittent calcitriol but were slightly diminished during daily calcitriol administration. GH enhanced IGF-I, IGF binding receptor-3, and GH receptor but declined with daily and intermittent calcitriol. Overall, there was no improvement in body length, tibial length, and growth plate width at the end of GH therapy, but selected markers of chondrocyte proliferation and chondrocyte differentiation increased, although these changes were attenuated by calcitriol. The combination of GH and calcitriol that is frequently used in children with renal failure and secondary hyperparathyroidism require further studies to evaluate the optimal dose and frequency of administration to increase linear growth and prevent bone disease.

Biochemical and Cellular Effects of Direct Maxacalcitol Injection into Parathyroid Gland in Uremic Rats

The most important etiological factors of resistance to medical treatments for secondary hyperparathyroidism are the decreased contents of the vitamin D receptor (VDR) and Ca-sensing receptor (CaSR) in parathyroid cells and a severely swollen parathyroid gland (PTG) as a result of hyperplasia. The effects of direct maxacalcitol (OCT) injection into PTG in terms of these factors were investigated in this study. The PTG of Sprague-Dawley rats that were 5/6 nephrectomized and fed a high-phosphate diet were treated by a direct injection of OCT (DI-OCT) or vehicle (DI-vehicle). The changes in serum intact parathyroid hormone (PTH), Ca(2+), and phosphorus levels, in VDR and CaSR expression levels in parathyroid cells, and in Ca(2+)-PTH curves were examined. Apoptosis was analyzed by the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling method and DNA electrophoresis for PTG. DI-OCT markedly decreased serum intact PTH level, and a significant difference in this level between DI-OCT and DI-vehicle was observed. However, serum Ca(2+) and phosphorus levels did not changed markedly in both groups. The upregulations of both VDR and CaSR, the clear shift to the left downward in the Ca(2+)-PTH curve, and the induction of apoptosis after DI-OCT were observed. These findings were not observed in the DI-vehicle-treated rats. Moreover, these effects of DI-OCT were confirmed by the DI-OCT into one PTG and DI-vehicle alone into another PTG in the same rat. DI-OCT may introduce simultaneous VDR and CaSR upregulations and the regression of hyperplastic PTG, and these effects may provide a strategy for strongly suppressing PTH levels in very severe secondary hyperparathyroidism.

Avoidance of direct injury to the peripheral nerve with maxacalcitol (22oxa-1,25(OH)2D3) in rats

BACKGROUND

Secondary hyperparathyroidism is one of the most common complications in patients with long-term end-stage renal disease. A recent report has stated that high doses of vitamin D derivatives injected directly into the parathyroid glands can reduce serum parathyroid hormone levels and suppress further enlargement of the parathyroid glands without side-effects. Maxacalcitol (22oxa-1,25(OH)(2)D(3); OCT) is a new vitamin D derivative that can be administered intravenously, and is available in Japan. Direct injection of OCT into enlarged parathyroid glands is a promising new treatment for moderate renal hyperparathyroidism. It is considered to be safe for surrounding tissues, such as peripheral nerves, but the actual effects of OCT on nerves have not yet been documented.

METHODS

We measured nerve conduction velocity (NCV) in 24 rat femoral nerves soaked in saline, ethanol, or OCT at various concentrations. Nerves from each group (saline, ethanol, OCT groups) were also examined by microscopy.

RESULTS

The mean NCV of rat femoral nerves was 33.67 +/- 1.39 m/s in the saline group. In the OCT group, the velocities were not changed at any of the concentrations tested, and there were no significant differences in NCVs between the saline and OCT groups. In the 50% ethanol group, the velocity decreased significantly to 8.98 +/- 4.78 m/s (P < 0.01). A histological study demonstrated the nerves soaked in OCT at 10 microg/mL to essentially be intact, while those soaked in anhydrous ethanol were damaged.

CONCLUSIONS

This study demonstrated that OCT administration does not affect peripheral NCV, indicating that OCT could possibly be used for the treatment of moderate renal hyperparathyroidism safely without nerve damage.

MEPE has the properties of an osteoblastic phosphatonin and minhibin

Matrix extracellular phosphoglycoprotein (MEPE) is expressed exclusively in osteoblasts, osteocytes and odontoblasts with markedly elevated expression found in X-linked hypophosphatemic rickets (Hyp) osteoblasts and in oncogenic hypophosphatemic osteomalacia (OHO) tumors. Because these syndromes are associated with abnormalities in mineralization and renal phosphate excretion, we examined the effects of insect-expressed full-length human-MEPE (Hu-MEPE) on serum and urinary phosphate in vivo, (33)PO(4) uptake in renal proximal tubule cultures and mineralization of osteoblast cultures. Dose-dependent hypophosphatemia and hyperphosphaturia occurred in mice following intraperitoneal (IP) administration of Hu-MEPE (up to 400 microg kg(-1) 31 h(-1)), similar to mice given the phosphaturic hormone PTH (80 microg kg(-1) 31 h(-1)). Also the fractional excretion of phosphate (FEP) was stimulated by MEPE [65.0% (P < 0.001)] and PTH groups [53.3% (P < 0.001)] relative to the vehicle group [28.7% (SEM 3.97)]. In addition, Hu-MEPE significantly inhibited (33)PO(4) uptake in primary human proximal tubule renal cells (RPTEC) and a human renal cell line (Hu-CL8) in vitro (V(max) 53.4% inhibition; K(m) 27.4 ng/ml, and V(max) 9.1% inhibition; K(m) 23.8 ng/ml, respectively). Moreover, Hu-MEPE dose dependently (50-800 ng/ml) inhibited BMP2-mediated mineralization of a murine osteoblast cell line (2T3) in vitro. Inhibition of mineralization was localized to a small (2 kDa) cathepsin B released carboxy-terminal MEPE peptide (protease-resistant) containing the acidic serine-aspartate-rich motif (ASARM peptide). We conclude that MEPE promotes renal phosphate excretion and modulates mineralization.

Advantages of adjusting the initial dose of intravenous calcitriol according to PTH levels

BACKGROUND

To assess the usefulness of starting calcitriol therapy with a dose proportional to the degree of hyperparathyroidism, 141 patients from 28 centers were treated with intravenous calcitriol for 6 months. The aim was to achieve a final PTH between 125 and 250 pg/mL. Patients with serum PTH>250 pg/mL were included in the study and divided into 4 groups according to baseline PTH levels.

METHODS

The study was completed by 100 patients, a third of which were treated strictly according to the protocol, labeled "compliants"; thus, calcitriol was started according to baseline PTH levels. Two thirds of patients, labeled "noncompliants," showed one or more violation in the dosage regimen.

RESULTS

After 2 months of treatment with calcitriol, 59% of the "compliants" and 35% of the "noncompliants" decreased their PTH levels>40% (P = 0.022), 70%, and 49%, respectively after 3 months of treatment. After 3 months of treatment, 67% of the "compliants" reached the target (PTH 125 to 250 pg/mL) in contrast with 23% of the "noncompliants" (P < 0.001). The number of hypercalcemic and hyperphosphatemic episodes was significantly lower in the "compliants" group (P < 0.006).

CONCLUSION

These results demonstrate several advantages when calcitriol therapy is started with a dose proportional to the severity of hyperparathyroidism.

Use of vitamin D analogs in chronic renal failure

Renal osteodystrophy is the term used to describe the spectrum of bone diseases associated with chronic renal failure. Deficiency of 1,25-dihydroxycholecalciferol (calcitriol) plays a major role in the development of renal osteodystrophy, in particular the evolution of secondary hyperparathyroidism. In recent decades, our understanding of the complex interactions between calcium, phosphorus, vitamin D, and parathyroid hormone (PTH) has increased, resulting in a rational approach to therapy in which vitamin D analogs have become an essential component. The initial vitamin D analogs that have been in widespread clinical use include calcitriol (1,25-[OH](2)D(3)) and alfacalcidol (1alpha-[OH]D(3)). These agents have been extensively studied to optimize their effects on secondary hyperparathyroidism. The occurrence of significant hypercalcemia and hyperphosphatemia limiting their use has led to the development of alternative vitamin D analogs that effectively reduce PTH secretion without causing these complications. Recently, 3 such analogs, 22-oxa-1,25-(OH)(2)D(3) (OCT), 1alpha-(OH)D(2) (doxercalciferol), and 19-nor-1,25-(OH)(2)D(2) (paricalcitol), have been released for clinical use. Only paricalcitol has been studied in comparative human clinical trials with calcitriol in dialysis patients. Preliminary findings suggest a clinical advantage over calcitriol, however, analysis of the larger comparative studies are forthcoming.

Is there an optimal parathyroid hormone level in end-stage renal failure: the lower the better?

Skeletal resistance to parathyroid hormone is well defined in patients with chronic renal failure. In recent years, with the increased frequency of development of adynamic bone disease, it has been recognized that secondary hyperparathyroidism must exist as a 'trade off' mechanism to maintain skeletal bone remodeling in this patient population. An optimal level of intact parathyroid hormone to maintain the normal skeletal bone turnover is believed to be between 2.0 and 2.5 times the upper limit of normal parathyroid hormone. It has very recently been argued that the optimal parathyroid hormone level for maintenance of skeletal bone remodeling may be insufficient to prevent the extraskeletal complications of coronary artery calcifications, calcific valvular heart disease, and cardiac death. To provide optimal health care for these patients several new treatments have been developed, including use of new vitamin D analogs, calcimimetic agents, and noncalcium-based phosphorus binders. It is anticipated that with lower suppression of parathyroid hormone by these vitamin D analogs, intermittent suppression of parathyroid hormone with calcimimetic agents, and the use of noncalcium phosphorus binders (Renageltrade) by regulating serum calcium, the resultant phosphorus concentrations will provide an optimal parathyroid hormone activity to maintain skeletal bone remodeling, while preventing extraskeletal complications.

Management of disturbed calcium metabolism in uraemic patients: 1. Use of vitamin D metabolites

Chronic renal failure is characterized by diminished synthesis of, and resistance to, the active vitamin D metabolite 1,25-dihydroxy-vitamin D3 (1,25(OH)2D3, calcitriol). Calcitriol results from the biotransformation of the precursor 25-hydroxy-vitamin D3 (25(OH)D3) to 1,25(OH)2D3. 25(OH)D3 is synthesized in the liver, and 1alpha-hydroxylase, the rate-limiting enzyme for its biotransformation into the most active metabolite, 1,25(OH)2D3, is located in the kidney. The regulation of 1alpha-hydroxylase in renal failure is not well known. Recent work indicates that, in contrast to previous opinion, 1alpha-hydroxylase is predominantly expressed not in the proximal tubule but in the distal tubule [1]. In vivo, the main stimulatory signal is presumably parathyroid hormone (PTH) and the main inhibitory signal hyperphosphataemia. Both signals are altered in renal failure. There is also evidence that the renal 1alpha-hydroxylase becomes substrate-dependent in patients with renal failure. This means that a higher concentration of the precursor 25(OH)2D3 will result in a higher rate of transformation into the active metabolite 1,25(OH)2D3 in renal patients. Calcitriol is not exclusively synthesized in the kidney, but may also be synthesized in extra-renal tissues, e.g. activated monocytes/macrophages [2], particularly in granuloma [3] as shown by anephric uraemic patients who develop hypercalcaemia and elevated calcitriol concentrations when sarcoidosis [4] or tuberculosis [5] supervenes. On the other hand, calcitriol is less effective in uraemia. This may be to some extent due to diminished expression of vitamin D receptors [6], particularly in parathyroid glands when they undergo nodular transformation [7], but there may also be resistance to calcitriol at the post-receptor level [8]. In a series of elegant experiments [9,10], calcitriol resistance has been related to disturbed genomic effects of active vitamin D because the interaction of the vitamin D receptor ligand complex with vitamin D-responsive elements (VDREs) upstream of vitamin D-regulated genes was disturbed by the action of low molecular weight substances in uraemia, which have not been completely characterized. The role of genetically determined polymorphisms of the vitamin D receptor in the genesis of disturbed calcium metabolism of renal failure is currently unclear.

No difference in intestinal strontium absorption after oral or IV calcitriol in children with secondary hyperparathyroidism. The European Study Group on Vitamin D in Children with Renal Failure

BACKGROUND

Oral and intravenous calcitriol bolus therapy are both recommended for the treatment of secondary hyperparathyroidism, but it has been claimed that the latter is less likely to induce absorptive hypercalcemia. The present study was undertaken to verify whether intravenous calcitriol actually stimulates intestinal calcium absorption less than oral calcitriol and whether it is superior in suppressing parathyroid hormone (PTH) secretion.

METHODS

Twenty children (16 males, age range of 5.1 to 16.9 years, mean creatinine clearance 21.9 +/- 11.5 mL/min/1.73 m2, range of 7.4 to 52.7) with chronic renal failure (CRF) and secondary hyperparathyroidism [median intact PTH (iPTH), 327 pg/mL; range 143 to 1323] received two single calcitriol boli (1.5 mg/m2 body surface area) orally and intravenously using a randomized crossover design. iPTH and 1,25(OH)2D3 levels were measured over 72 hours, and intestinal calcium absorption was measured 24 hours after the calcitriol bolus using stable strontium (Sr) as a surrogate marker. Baseline control values for Sr absorption were obtained in a separate group of children with CRF of similar severity.

RESULTS

The peak serum level of 1,25(OH)2D3 and area under the curve baseline to 72 hours (AUC0-72h) were significantly higher after intravenous (IV) calcitriol (AUC0-72h oral, 1399 +/- 979 pg/mL. hour vs. IV 2793 +/- 1102 pg/mL. hour, P < 0.01), but the mean intestinal Sr absorption was not different [SrAUC0-240min during the 4 hours after Sr administration 2867 +/- 1101 FAD% (fraction of the absorbed dose) vs. 3117 +/- 1581 FAD% with oral and IV calcitriol, respectively]. The calcitriol-stimulated Sr absorption was more then 30% higher compared with control values (2165 +/- 176 FAD%). A significant decrease in plasma iPTH was noted 12 hours after the administration of the calcitriol bolus, which was maintained for up to 72 hours without any differences regarding the two routes of administration.

CONCLUSIONS

These results demonstrate that under acute conditions, intravenous and oral calcitriol boli equally stimulate calcium absorption and had a similar efficacy in suppressing PTH secretion.

Current medical management of secondary hyperparathyroidism

The treatment of secondary hyperparathyroidism (HPT) in patients with chronic renal disease has improved markedly in recent years. The skeletal pain, disabling fractures, tendon ruptures, and myriad other symptoms associated with HPT can now be avoided, and the quality of life of patients with end-stage renal disease is improved. Control of hyperphosphatemia, maintenance of normocalcemia, and appropriate dosing of vitamin D analogues can prevent HPT in many cases. Palatable, nutritious diets should be followed; serum calcium, phosphorus, alkaline phosphatase, and parathyroid hormone should be monitored; and treatment regimens should be adjusted accordingly. If prevention fails, and even if severe HPT develops, many of these patients can still be controlled medically with correction of hyperphosphatemia and high doses of intravenous calcitriol. In our experience, only a few patients require surgical parathyroidectomy (usually noncompliant patients or patients whose HPT has been poorly managed from early uremia). The essence to medical management is to correct the two most important pathogenetic factors of HPT, hyperphosphatemia, and calcitriol deficiency. We present the current approach to the management of HPT, with highlights of recent advances.

Comparison of treatments for mild secondary hyperparathyroidism in hemodialysis patients. Durham Renal Osteodystrophy Study Group

Comparison of treatments for mild secondary hyperparathyroidism in hemodialysis patients.

BACKGROUND

In the management of patients with mild secondary hyperparathyroidism, it is not known whether calcium supplementation alone is sufficient to correct abnormalities in bone and mineral metabolism or if calcitriol is needed in either physiologic oral or intravenous pharmacologic doses.

METHODS

This was a 40-week prospective nonmasked trial of 52 patients [parathyroid hormone (PTH) 150 to 600 pg/mL] who were randomized to receive escalating doses of either calcium carbonate (CaCO3) alone (calcium group, N = 11), daily oral calcitriol (oral group, N = 20), or intermittent intravenous calcitriol (IV group, N = 21). The groups were compared with regard to changes in serum intact PTH, serum bone-specific alkaline phosphatase (BAP), incidence of hypercalcemia (>10.5 mg/dL), and hyperphosphatemia (>6.5 mg/dL).

RESULTS

PTH levels decreased in all groups (P < 0.01, paired t-test). In the calcium group, PTH (mean +/- SEM) decreased from 325 +/- 46.2 to 160 +/- 44.5 pg/mL. In the oral group, it decreased from 265 +/- 26.4 to 125 +/- 23.7 pg/mL, and in the IV group, it decreased from 240 +/- 27.7 to 65 +/- 10.0 pg/mL. Upon analysis of covariance, controlling for the initial PTH level, we found no differences in the PTH response between the groups (P > 0.10). In contrast, the BAP concentration increased from 20.7 +/- 7.6 to 27.5 +/- 7.0 microg/L in the calcium group (P = 0.17), decreased from 20. 6 +/- 3.9 to 17.8 +/- 4.5 microg/L in the oral group (P = 0.26), and from 19.1 +/- 2.6 to 10.6 +/- 1.1 microg/L in the IV group (P = 0. 007). Serum calcium increased significantly in all groups from 8.4 +/- 0.25 to 9.0 +/- 0.28, 8.5 +/- 0.16 to 9.2 +/- 0.27, and 8.7 +/- 0.16 to 9.4 +/- 0.18 mg/dL in the calcium, oral, and IV groups, respectively (P = NS difference between groups). Serum phosphorus was significantly lower in the calcium group throughout the study (P = 0.02). Hypercalcemic episodes were 2.0 +/- 0.8, 3.0 +/- 0.6, and 3. 4 +/- 0.6 per patient-year (P > 0.10), and hyperphosphatemic episodes were 0.9 +/- 0.56, 4.2 +/- 0.79 and 4.9 +/- 0.84 in the calcium, oral, and IV groups, respectively (P < 0.01).

CONCLUSION

In mild secondary hyperparathyroidism, all three strategies are effective. High-dose CaCO3 alone may be sufficient to control PTH with a favorable side-effect profile, but calcitriol appears to have additional suppressive effects on bone that are greater following the intravenous route of administration and may increase the risk of adynamic bone disease.

Cell biology of parathyroid hyperplasia in uremia

Marked parathyroid hyperplasia of heterogeneous degrees is often seen in chronic dialysis patients with severe secondary hyperparathyroidism. In uremia, parathyroid cell proliferation is initially stimulated by decreased concentration of calcium ions and calcitriol and also by direct effect of phosphate accumulation, leading to diffuse hyperplasia of the parathyroid. Then, small nodules caused by monoclonal cell proliferation form within diffuse hyperplasia, which progress to form nodular hyperplasia. Cells in nodular hyperplasia have a lower density of calcitriol receptor and calcium-sensing receptor than diffuse hyperplasia and are thus more resistant to medical therapy, including calcitriol pulse therapy. One of these nodules may grow more vigorously than the others and may finally occupy a large part of the enlarged gland. Genetic mutations and rearrangements of these cells in nodular hyperplasia remain to be fully elucidated in the near future to establish an effective method for the prevention of parathyroid hyperplasia in uremia.

Strontium causes osteomalacia in chronic renal failure rats

BACKGROUND

We recently reported an association between increased bone strontium (Sr) levels and osteomalacia in dialysis patients.

METHODS

To delineate whether or not Sr acts as a causal factor in the development of osteomalacia, we devised the following study: four groups of chronic renal failure (CRF) rats were given Sr, aluminum (Al), both of these compounds or none of the elements (controls).

RESULTS

Administration of Sr and/or A1 resulted in increased bone levels of the respective elements. Histological examination revealed impairment of mineralization in the Sr group and to a lesser extent in the Al group as compared to the control group. There was also a significant increase in osteoid area in the Sr group, but not in the Al group. No differences in bone surface or erodic perimeter were noted between the various study groups. Histochemically, Sr could be localized in calcified bone, mainly in new bone close to the osteoid/calcification front, a critical site of bone mineralization. Histochemical findings were confirmed by electron probe X-ray microanalysis.

CONCLUSIONS

These findings indicate that Sr accumulation in chronic renal failure rats resulted in the development of osteomalacic lesions, in contrast to the Al group where adynamic bone disease was induced in the present set-up. Further studies are required to define the mechanism by which way Sr causes osteomalacia in chronic renal failure rats.

Effect of 1,25 (OH)2 vitamin D3 on glomerulosclerosis in subtotally nephrectomized rats

In the past, there has been considerable concern that treatment with active vitamin D might accelerate progression independent of hypercalcemia and hypercalcuria. Nevertheless, 1,25(OH)2D3 has known antiproliferative properties and has also been shown to inhibit renal growth. Since glomerular growth is a permissive factor for the development of glomerulosclerosis, we reasoned that 1,25(OH)2D3 might even attenuate progression. To test this working hypothesis we performed two experiments of 8 and 16 weeks duration, respectively, to compare subtotally nephrectomized (SNX) rats treated with ethanol and SNX treated with 1,25(OH)2D3. Control animals were sham operated and pair-fed with SNX animals. 1,25(OH)2D3 (3 ng/100 g body wt/day) was administered by osmotic minipump. 1,25(OH)2D3 had no significant effect on systolic blood pressure and only a transient effect on weight gain. SNX reduced the number of glomeruli (left kidney) from an average of 3.3 x 10(4) to 1.2 x 10(4) per kidney. Mean glomerular volume was 3.87 +/- 0.71 x 10(6) microns 3 in sham operated animals and significantly (P < 0.05) higher (10.1 +/- 1.75 x 10(6) microns 3) in untreated animals 16 weeks after SNX. Glomerular volume was significantly (P < 0.05) less in 1,25(OH)2D3 treated SNX [10.1 +/- 1.75 in ethanol vs. 7.04 +/- 1.78 in 1,25(OH)2D3 treated SNX]. In parallel, there was significantly (P < 0.01) less glomerulosclerosis [glomerulosclerosis index 1.16 +/- 0.14 in the ethanol treated SNX vs. 0.80 +/- 0.16 in SNX treated with 1,25(OH)2D3] in the eight week experiment. Albuminuria was significantly (P < 0.01) lower in 1,25(OH)2D3 treated than in ethanol treated SNX (mean 0.785 mg/24 hr, range 0.43 to 1.80, vs. 3.75 mg/24 hr, 1.29 to 14.2). The morphological data were directionally analogous in a second 16 week experiment. Only slight changes of the vascular sclerosis index and tubulointerstitial index were seen in SNX and were not affected by 1,25(OH)2D3 further. To prove that the effect of 1,25(OH)2D3 was independent of PTH, parathyreoidectomized SNX rats without or with 1,25(OH)2D3 treatment were examined seven days post-SNX. PCNA staining showed suppression of cell proliferation. Furthermore, in situ hybridization for transforming growth factor-B (TGF-beta) showed less vascular and tubular expression in 1,25(OH)2D3 treated rats. We conclude that 1,25(OH)2D3 has antiproliferative actions during the compensatory growth of nephrons in response to subtotal nephrectomy. These effects are independent of PTH. The data document that 1,25(OH)2D3 reduces renal cell proliferation and glomerular growth as well as glomerulosclerosis and albuminuria as indicators of progressive glomerular damage.

Interaction of IGF-I and 1 alpha, 25(OH)2D3 on receptor expression and growth stimulation in rat growth plate chondrocytes

Growth plate cartilage cell express receptors for, and are affected by both IGF-I and 1 alpha, 25(OH)2D3. The studies were undertaken to investigate interaction between these two hormone systems, that is, (i) to study effects of 1 alpha, 25(OH)2D3 on IGF-type 1 receptors (IGFIR), on IGF-I stimulated cell replication, colony formation, and on alkaline phosphatase activity (AP), and conversely, (ii) to study the effect of IGF-I on vitamin D receptor (VDR) expression on 1 alpha, 25(OH)2D3 stimulated growth parameters and on AP activity. Freshly isolated rat tibial chondrocytes were grown in monolayer cultures, (serum-free) or in agarose stabilized suspension cultures (0.1% FCS). Vitamin D receptor and IGFIR were visualized by immunostaining with the monoclonal antibody (mAb) 9A7 gamma and mAb alpha IR3, respectively, and quantitated by RT-PCR for mRNA and by Scatchard analysis using [3H]-1,25(OH)2D3 and [125I]-alpha IR3. Cell proliferation was measured by [3H]-thymidine incorporation, growth curves in monolayer cultures, and by colony formation in agarose-stabilized suspension cultures. IGF-I dose-dependently increased [3H]-thymidine incorporation. 1 alpha, 25(OH)2D3, but not 1 beta, 25(OH)2D3 was stimulatory at low ((10-12 M) and slightly inhibitory at high (10-8 M) concentrations. The effect of IGF-I was additive to that of 1 alpha, 25 (OH)2D3 [IGF-I 60 ng/ml, 181 +/- 12.7; 1 alpha, 25(OH)2D3 10(-12) M, 181 +/- 9.8%, IGF-I + 1 alpha, 25(OH)2D3, 247 +/- 16.7%, P < 0.05 by ANOVA] and specifically obliterated by polyclonal IGF-I antibody (AB-1). Interaction could also be confirmed in suspension cultures. IGFIR mRNA and [125I]-alphaIR3 binding was increased by low (10(-12) m) but not by high (10(-8) M) concentrations of 1 alpha, 25(OH)2D3. Homologous up-regulation by IGF-I (60 ng/ml) was specifically inhibited by AB-1 and markedly amplified by coincubation with 1 alpha, 25(OH)2D3 (10(-12)m). Immunostaining with alpha IR3 showed specific IGFIR expression in rat growth cartilage, but not liver tissue. Stimulation of chondrocytes with 1 alpha, 25(OH)2D3 or IGF-I suggested some increase of receptor expression in single cells, but the predominant effect was increased recruitment of receptor positive cells, Vitamin D receptor expression was markedly stimulated (fourfold) by IGF-I (60 ng/ml), but not IGF-II and inhibited by actinomycin D. This study shows that IGF-I and 1 alpha, 25(OH)2D3 mutually up-regulate their respective receptors in growth plate chondrocytes. In parallel, they have additive effects on cell proliferation and colony formation suggesting independent effector pathways.

Parathyroid hormone suppression by 22-oxacalcitriol in the severe parathyroid hyperplasia

The suppression of parathyroid hormone (PTH) secretion by the administration of 1,25-dihydroxyvitamin D [1,25(OH)2D3] and 22-oxacalcitriol (OCT) was evaluated in nude mice transplanted with human hyperplastic parathyroid tissue. The parathyroid tissue was obtained for transplantation from a patient with severe secondary hyperparathyroidism who had undergone a parathyroidectomy. Tissue specimens were transplanted into the gluteus muscle of female nude mice. Animals were divided into two groups; one group was fed a normal diet, and the other group was fed a low calcium diet during the administration of OCT and 1,25(OH)2D3. OCT and 1,25(OH)2D3 were intraperitoneally administered two times every week, for a total of eight times. Serum calcium and phosphate levels were significantly higher in the mouse administered 1,25(OH)2D3 than in the mouse administered OCT. Serum alkaline phosphatase activity was elevated similarly in the mouse administered either OCT or 1,25(OH)2D3. OCT strongly suppressed human PTH secretion from the graft in mice with normal serum calcium levels as did 1,25(OH)2D3. However, human PTH secretion from the graft was stimulated by the administration of a low-calcium diet, despite OCT and 1,25(OH)2D3 administration. In summary, OCT and 1,25(OH)2D3 suppress PTH secretion even from severe secondary hyperplastic parathyroid tissue only in mice with normal or high calcium serum levels.

Calcitriol administration in end-stage renal disease: intravenous or oral?

1,25-Dihydroxyvitamin D deficiency plays an important role in the pathogenesis of secondary hyperparathyroidism, and adequate replacement of this hormone is considered essential to normalize parathyroid gland function and restore bone homeostasis in patients with advanced renal failure. Although initial uncontrolled clinical trials suggested the superiority of intravenous calcitriol treatment, more recent controlled investigations show that different routes (oral versus intravenous), frequency (daily versus intermittent), and dosing (physiological versus pharmacological) of calcitriol administration are clinically equivalent. Overall, the response to calcitriol treatment depends more on the severity of secondary hyperparathyroidism and the presence of confounding variables, such as hyperphosphatemia and acquired abnormalities of parathyroid cell function, than the method of calcitriol administration.

The renal bone diseases in children treated with dialysis

Renal osteodystrophy represents a spectrum from high- to low-turnover bone lesions. The specific pattern, however, may change during selected therapeutic interventions. As in the past, osteitis fibrosa remains the most frequent histologic lesion in pediatric patients on dialysis, although recently the prevalence of low-turnover bone lesions without aluminum toxicity has been increasing in the pediatric population. This may be a consequence of aggressive calcitriol and calcium therapy. The different factors involved in the development of secondary hyperparathyroidism include hyperphosphatemia, hypocalcemia, altered vitamin D synthesis, impairments in parathyroid hormone (PTH) secretion and metabolism, and, recently, possible downregulation of renal PTH/PTH-rP messenger RNA receptor. New developments in molecular biology have demonstrated the relationship between vitamin D and PTH. The use of high-dose pulse intravenous, intraperitoneal, and oral calcitriol therapy has significantly decreased serum PTH levels and retarded the progression of osteitis fibrosa. These therapeutic interventions, however, may have led to the development of adynamic bone lesions. The impact of adynamic bone lesions in the young and growing skeleton remains to be determined.

Molecular basis for the management of secondary hyperparathyroidism in chronic renal failure

Recent clinical and experimental data suggest that the resistance of parathyroid cells to the physiological concentration of calcitriol plays an important role in the pathogenesis and the progression of secondary hyperparathyroidism in chronic renal failure. This resistance is due to the decreased density of the calcitriol receptor in parathyroid cells, which may result from impaired upregulation of calcitriol receptor. Since patients with larger parathyroid glands were more resistance to calcitriol pulse therapy than those with smaller glands and calcitriol receptor density inversely correlated with gland weight, the size of the parathyroid gland may serve as a marker for the degree of resistance to calcitriol. Furthermore, the possible role of phosphorus in the control of parathyroid function has been suggested recently. Thus, it is most important to prevent the progression of parathyroid hyperplasia in chronic renal failure by the early use of active vitamin D, calcitriol pulse therapy, and dietary phosphorus restriction.

The importance of dosing intravenous calcitriol in dialysis patients with severe hyperparathyroidism

The current study evaluates the use of intravenous (IV) calcitriol in 10 patients with severe hyperparathyroidism (HPTH). Patients with parathyroid hormone (PTH) > 1,200 pg/m and serum P < 6.5 mg/dL were studied. Ten patients with a mean PTH of 1,826 +/- 146 pg/mL were treated for a mean of 48 weeks with a dose of IV calcitriol commensurate to the level of PTH. The initial calcitriol dose had to be increased in seven patients. The mean maximum dose of calcitriol was 3.8 micrograms thrice weekly. There was a dramatic decrease in PTH levels, and by the end of the study it was 211 +/- 48 pg/mL. Alkaline phosphatase decreased from 582 +/- 3 to 120 +/- 12 IU/L. Serum Ca and P remained unchanged in most patients. There were three episodes of hyperphosphatemia in one patient, and another had a hypercalcemic episode. In conclusion, patients with severe HPTH respond very well to IV calcitriol, provided that dosing of calcitriol is commensurate to PTH levels, and hyperphosphatemia is kept under control.

Vitamin D therapy in patients receiving dialysis

Secondary hyperparathyroidism is found in a large proportion, but not all patients on dialysis. Calcitriol controls moderate hyperparathyroidism in most patients but only in a proportion of those with advanced hyperparathyroidism. Patients with nodular parathyroid hyperplasia respond less frequently, presumably because of monoclonal growth and diminished calcitriol-receptor expression by parathyroid cells. In patients with nodular parathyroid hyperplasia, parathyroidectomy is an important alternative to calcitriol treatment. A priori reasoning indicates that prophylactic administration of calcitriol (to prevent parathyroid hyperplasia) is a reasonable option, but currently no controlled evidence for long-term efficacy of this approach without side effects is available. Intermittent administration of calcitriol by intravenous or oral routes is effective and, at least in experimental studies, superior to continuous calcitriol. However, in clinical comparisons, no superiority of intravenous versus oral or daily versus intermittent calcitriol has been documented. Calcitriol treatment must be closely supervised to prevent hypercalcemia, hyperphosphatemia, and excessive suppression of parathyroid hormone. Because of an altered dose response relationship, parathyroid hormone levels should not be completely normalized so as to prevent low bone turnover (adynamic bone lesion).

Oral pulse therapy with vitamin D3 for control of secondary hyperparathyroidism

Twelve dialysis patients received oral pulse therapy with 1-alpha-hydroxyvitamin D3 in a dose of 0.1 microgram/kg body weight twice weekly and daily calcium carbonate (1.5-3.5 g) for a period of 8-12 months. This treatment was very effective in suppressing secondary hyperparathyroidism without causing hypercalcaemia and/or hyperphosphataemia.

Evidence of healing of secondary hyperparathyroidism in chronically hemodialyzed uremic patients treated with long-term intravenous calcitriol

The aim of this study was to assess the effect of a long-term course of high-dose i.v. pulses of calcitriol (CLT) on hyperparathyroid bone disease (HBD) and functional mass of parathyroid glands of chronically hemodialyzed uremic (CHU) patients. We prospectively studied nine CHU patients treated with CLT, 30 ng/kg/body wt, i.v., thrice weekly over a period of eight months. Plasma concentrations of intact parathyroid hormone (iPTH), bone GLA protein (bGLA) and bone isoenzyme of alkaline phosphatase (biALP) were sampled throughout. Transiliac bone biopsies were made before and after the start of CLT therapy. Double scanning scintigraphy of the neck with 201Tl-99Tc was made before, during and eight months after the start of the treatment. All patients but one, who later responded to higher than planned CLT doses, had significant decreases of plasma iPTH (F = 76; P < 0.0001; ANOVA). The mean pretreatment value of PTH was 966 +/- 160 (mean +/- SE) pg/ml and it had decreased significantly by the first week (T = 2.4, P < 0.04), and had fallen an average of 80% by the 35th week. Ionized plasma calcium concentration was 1.19 +/- .01 mmol/liter which rose significantly (F = 13.5; P < 0.0001) by the 14th week to maximal peak levels, averaging 1.34 +/- .02 mmol/liter. Changes in biALP were parallel to those of iPTH, while bGLA tended to increase immediately after the start of the therapy and to significantly decrease thereafter (T = 3.2; P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)