Detection of apoptotic cells and expression of Ki-67 antigen, Bcl-2, p53 oncoproteins in human parathyroid adenoma

Gene expression profiles in parathyroid adenoma and normal parathyroid tissue

A parathyroid adenoma comprises 80-85% as a cause of primary hyperparathyroidism. The clonal origin of most parathyroid adenomas suggests a defect at the level of the gene controlling growth of the parathyroid cell or the expression of parathyroid hormone (PTH). Two genes, MEN1 and CCND1, a tumor suppressor and a proto-oncogene respectively, have been solidly established as primary tumorigenic drivers in parathyroid adenomas. As well, germline and somatic mutation of other genes involved in cell cycle regulation or PTH regulation have been discovered in parathyroid adenomas. Moreover, comparative genomic studies between parathyroid adenomas and normal parathyroid tissues have suggested more complex genetic landscape. Microarray analysis have revealed differential expression profiles of genes involved in cell cycle regulation, growth factors, apoptotic pathway, or PTH synthesis or regulation pathway such as CASR, GCM2 and KL (Klotho). Furthermore, recent next-generation sequencing analysis reconfirmed previous finding or revealed novel finding, suggesting signal peptidase complex subunit (SPCS2), ribosomal proteins (RPL23, RPL26, RPN1, RPS25), the endoplasmic reticulum membrane (SEC11C, SEC11A, SEC61G), Klotho, cyclin D1, β-catenin, VDR, CaSR and GCM2 may be important factors contributing to the parathyroid adenoma.

Interrelated role of Klotho and calcium-sensing receptor in parathyroid hormone synthesis and parathyroid hyperplasia

The pathogenesis of parathyroid gland hyperplasia is poorly understood, and a better understanding is essential if there is to be improvement over the current strategies for prevention and treatment of secondary hyperparathyroidism. Here we investigate the specific role of Klotho expressed in the parathyroid glands (PTGs) in mediating parathyroid hormone (PTH) and serum calcium homeostasis, as well as the potential interaction between calcium-sensing receptor (CaSR) and Klotho. We generated mouse strains with PTG-specific deletion of Klotho and CaSR and dual deletion of both genes. We show that ablating CaSR in the PTGs increases PTH synthesis, that Klotho has a pivotal role in suppressing PTH in the absence of CaSR, and that CaSR together with Klotho regulates PTH biosynthesis and PTG growth. We utilized the tdTomato gene in our mice to visualize and collect PTGs to reveal an inhibitory function of Klotho on PTG cell proliferation. Chronic hypocalcemia and ex vivo PTG culture demonstrated an independent role for Klotho in mediating PTH secretion. Moreover, we identify an interaction between PTG-expressed CaSR and Klotho. These findings reveal essential and interrelated functions for CaSR and Klotho during parathyroid hyperplasia.

Apoptosis in Primary Hyperparathyroidism

Primary hyperparathyroidism (PHPT) is defined by inappropriate elevation of parathormone, caused by parathyroid hyperplasia, also known as multi-gland disease (MGD), parathyroid adenoma (PA), or parathyroid carcinoma (PC). Although several studies have already been conducted, there is a lack of a definite diagnostic marker, which could unambiguously distinguish MGD from PA or PC. The accurate and prompt diagnosis has the key meaning for effective treatment and follow-up. This review paper presents the role of apoptosis in PHPT. The comparison of the expression of Fas, TRAIL, BCL-2 family members, p53 in MGD, PA, and PC, among others, was described. The expression of described factors varies among proliferative lesions of parathyroid gland; therefore, these could serve as additional markers to assist in the diagnosis.

Expression of TRAIL and Fas in Primary Hyperparathyroidism

AIM

Differentiating between parathyroid lesions is still difficult and ambiguous. In cases of primary hyperparathyroidism, appropriate and prompt diagnosis is of great importance for effective treatment and follow-up. A great amount of mechanisms contribute to the pathogenesis of primary hyperparathyroidism, such as disturbance in balance between pro- and anti-apoptotic factors. Therefore, we examined whether immunohistochemical expression of apoptotic factors, TNF-related apoptosis-inducing ligand (TRAIL) and Fas, could have clinical utility as a marker of proliferative lesions of parathyroid gland.

MATERIALS AND METHODS

Parathyroid specimens of 58 consecutive patients who had undertaken surgery due to primary hyperparathyroidism were incubated with purified mouse monoclonal antihuman antibodies: anti-TRAIL and anti-Fas. Staining was considered positive when at least 5% of the cells showed immunoreactivity.

RESULTS

The percentage of cells which were positively stained for TRAIL in parathyroid hyperplasia was 9.65%, in parathyroid adenoma 8.31%, and in normal controls 2.24%. Immunoreactivity for TRAIL was detected in 91.89% of parathyroid hyperplasias, 85.71% of parathyroid adenomas, and none in healthy glands. The percentage of cells with a positive reaction to Fas in parathyroid hyperplasia was 8.92%, in parathyroid adenoma 8.09%, and in normal tissue 1.9%. The expression of Fas was found in 94.59% of parathyroid hyperplasias, 90.48% of parathyroid adenomas, and none in healthy glands.

CONCLUSIONS

In our study, hyperplasias demonstrated the highest expression of TRAIL and Fas, whereas in adenomas it was increased compared to normal tissue, but lower than in hyperplasias. These factors could be an additive tool in the differential diagnosis of parathyroid lesions.

Histology and immunohistochemistry of the parathyroid glands in renal secondary hyperparathyroidism refractory to vitamin D or cinacalcet therapy

BACKGROUND

Cinacalcet is a new effective treatment of secondary hyperparathyroidism (SHPT) in hemodialysis patients (HP), but the alterations of parathyroid gland (PTG) hyperplasia determined by cinacalcet and vitamin D have not been extensively investigated in humans.

METHODS

We performed histological analyses of 94 PTGs removed from 25 HP who underwent parathyroidectomy (PTx) because of SHPT refractory to therapy with vitamin D alone (group A=13 HP and 46 PTGs) or associated with cinacalcet (group B=12 HP and 48 PTGs). The number, weight, the macroscopic cystic/hemorrhagic changes, and type of hyperplasia of PTG (nodular=NH, diffuse=DH) were assessed. In randomly selected HP of group A (4 HP and 14 PTGs) and group B (4 HP and 15 PTGs), the labeling index of cells positive to Ki-67 and TUNEL and the semiquantitative score of immunohistochemistry staining of vitamin D receptor, calcium-sensing receptor, and vascular endothelial growth factor-α (VEGF-α) were measured in the entire PTGs and in the areas with DH or NH.

RESULTS

The number and weight of single and total PTG of each HP were similar in the two groups as well as the number of PTG with macroscopic cystic/hemorrhagic areas. TUNEL, Ki-67, and VEGF-α scores were higher in NH than in DH areas.

CONCLUSION

This observational study of a highly selected population of HP, submitted to PTx because SHPT refractory to therapy, shows that the macroscopic, microscopic, and immunochemistry characteristics of PTG in HP who received or did not receive cinacalcet before PTx did not differ significantly.

Parathyroid pathology: hyperparathyroidism and parathyroid tumors

CONTEXT

Primary hyperparathyroidism is the most common cause of hypercalcemia in the outpatient setting. Parathyroid adenomas are common, unlike other parathyroid tumors. This review presents a brief summary of current updates in parathyroid pathology.

OBJECTIVE

To review parathyroid development and discuss issues in hyperparathyroidism and diagnosis of parathyroid lesions, including the application of immunohistochemistry and molecular biology.

DATA SOURCES

Current texts, PubMed (National Library of Medicine) articles, and Memorial Sloan-Kettering Cancer Center archives.

CONCLUSIONS

Primary hyperparathyroidism is most commonly seen with sporadic adenomas, followed by hyperplasia, multiple adenomas, and carcinoma. Autosomal dominant familial hyperparathyroidism syndromes should be considered in the evaluation of patients with parathyroid lesions, particularly in association with parathyroid carcinoma. While the incidence of parathyroid carcinoma is quite low, it is seen with a greater frequency in those patients with hyperparathyroidism-jaw tumor syndrome. Inactivation of the tumor suppressor gene HRPT2 can be identified in a large number of parathyroid carcinomas. Hence, germline HRPT2 gene mutations may reflect unrecognized syndromic patients.

Selected markers of proliferation and apoptosis in the parathyroid lesions: a spatial visualization and quantification

The aim of the paper was to apply a method for quantitative assessment of proliferation and apoptosis markers, based on their 3D visualization, in cases of parathyroid adenoma and hyperplasia. Material was obtained from 49 patients (32 females and 17 males) with primary hyperparahyroidism. Quantitative immunohistochemistry studies of Ki-67, proliferating cell nuclear antigen (PCNA) and bcl-2 were performed on digital microscopy images with the use of 3D visualization. The use of spatial visualization method allowed us to perform objective quantitative assessment of the studied immunohistochemical markers. The average cell nuclear fraction of Ki67+ was 1.8% in hyperplasia and 1.9% in adenoma cases while 3.5% in the controls. The highest expression of PCNA was found in parathyroid hyperplasia (22.9%) and significantly decreased in adenoma (12.5%) and in the control group (16.8%). The lower expression of bcl-2 in hyperplasia cases (mean area fraction of 0.172 per 1 mum(2), in contrast to 0.643 in adenomas and 0.648 in control) suggested that principal cells can be ready for apoptosis and may confirm the important role of bcl-2 protein in etiopathogenesis of hyperplasia of the parathyroid gland while PCNA might be a useful marker for differentiating adenoma from early hyperplasia in primary hyperparahyroidism cases.

Expression of p53, Ki-67 and Bcl-2 in parathyroid adenoma and residual normal tissue

The aim of this study was to investigate the expression of Ki-67, bcl-2 and p53 in parathyroid adenomas and their residual rim of normal parathyroid tissue. Specimens from 26 parathyroid adenomas were studied by immunohistochemical analysis for Ki-67, bcl-2 and p53 expression. Positive findings were noted for p53 in 4 (15%) adenomas and none of the residual rims of normal parathyroid tissue (p = 0.055); for Ki-67 in 15 (56%) adenomas and none of the residual rims of normal parathyroid tissue (p = 0.00002); and for bcl-2 in 19 (73%) adenomas and 8 (31%) residual rims of normal parathyroid tissue (p < 0.01). The high rate of Ki-67 expression may indicate susceptibility of parathyroid adenomas to clonal proliferation. The weak immunoreactive expression of p53, combined with a relatively strong expression of bcl-2, may contribute to the characteristic slow progression of these tumors.

Lymphomatoid papulosis associated with parathyroid nodular hyperplasia: report of a case

The association of cutaneous lymphoproliferative diseases and primary hyperparathyroidism (PHP) is infrequent, with only three cases reported to date. We present a patient with lymphomatoid papulosis (LyP) who developed hypercalcaemia secondary to parathyroid nodular hyperplasia. A review of the literature has revealed no similar cases; we therefore believe this to be the first description of the association between LyP and PHP.

Parathyroid neoplasms: clinical, histopathological, and tissue microarray-based molecular analysis

We studied 45 patients with typical and 8 with atypical parathyroid adenomas as well as 20 with parathyroid carcinomas. Clinical, pathological, and molecular analyses were conducted on all adenomas. Clinical data were analyzed for 20, histopathologic slides for 16, and tissue specimens for 8 patients with carcinoma. Molecular expression profiles were investigated by immunohistochemistry (IHC) for Ki-67, p53, mdm2, p21, Bcl-2, cyclin D1, and p27 on paraffin-embedded tissues arrayed on tissue microarrays. Trabecular growth and vascular, capsular, and soft-tissue invasion were characteristic of parathyroid carcinomas but not of typical adenomas. No adenomas recurred. Seventy-four percent of carcinomas recurred, most in the neck. Seventy-nine percent of patients with such illness died of disease after an indolent, multiply recurrent course responsive to repeated resections; the 5-year survival rate was 50%. High Ki-67 proliferative index was seen in 2% of adenomas and 25% of carcinomas, whereas p27 expression was present in 80% of adenomas and 18% of carcinomas. The molecular phenotype, p27(+)Bcl-2(+)Ki-67(-)mdm2(+), was observed in 76%, 29%, and 0% of typical and atypical adenomas and carcinomas, respectively. The complexity of molecular phenotypes increased with tumor aggressiveness. Parathyroid carcinoma is an aggressive disease with a propensity for multiple recurrences. It is characterized by capsular, vascular, and soft-tissue invasion. Recurrence portends poor outcome. Molecular markers, Ki-67 and p27, may distinguish parathyroid carcinoma from adenoma. The molecular phenotype, p27(+)Bcl-2(+)Ki-67(-)mdm2(+), appears to be unique to nonmalignant parathyroid tumors, and multimarker phenotypes are more complex in carcinomas.

Mechanisms of secondary hyperparathyroidism

Small decreases in serum Ca(2+) and more prolonged increases in serum phosphate (P(i)) stimulate the parathyroid (PT) to secrete parathyroid hormone (PTH), and 1,25(OH)(2)D(3) decreases PTH synthesis and secretion. A prolonged decrease in serum Ca(2+) and 1,25(OH)(2)D(3), or increase in serum P(i), such as in patients with chronic renal failure, leads to the appropriate secondary increase in serum PTH. This secondary hyperparathyroidism involves increases in PTH gene expression, synthesis, and secretion, and if chronic, to proliferation of the PT cells. Low serum Ca(2+) leads to an increase in PTH secretion, PTH mRNA stability, and PT cell proliferation. P(i) also regulates the PT in a similar manner. The effect of Ca(2+) on the PT is mediated by a membrane Ca(2+) receptor. 1,25(OH)(2)D(3) decreases PTH gene transcription. Ca(2+) and P(i) regulate the PTH gene posttranscriptionally by regulating the binding of PT cytosolic proteins, trans factors, to a defined cis sequence in the PTH mRNA 3'-untranslated region, thereby determining the stability of the transcript. PT trans factors and cis elements have been defined.

Pathogenesis of parathyroid dysfunction in end-stage renal disease

The parathyroid functions to maintain normal calcium and phosphate homeostasis and is central to normal bone physiology. In end-stage renal disease (ESRD), there is a failure of these normal homeostatic mechanisms with the frequent development of secondary hyperparathyroidism, which contributes to the pathogenesis of renal bone disease. The phosphate retention of ESRD, together with the reduced serum calcium and 1,25-dihydroxycholecalciferol vitamin D(3) (1,25[OH](2)D(3)) concentrations are the known factors that determine the progression to secondary hyperparathyroidism. 1,25(OH)(2)D(3) markedly decreases parathyroid hormone (PTH) gene transcription, whereas the effects of calcium and phosphate are on PTH mRNA stability, PTH secretion, and parathyroid cell proliferation. The mechanisms of these effects are discussed in this review.

Hyperplasia of the parathyroid gland without secondary hyperparathyroidism

BACKGROUND

Low dietary phosphorus (P) prevents parathyroid gland (PTG) hyperplasia and the development of secondary hyperparathyroidism (SH) in uremic rats. The present study explores the effects of P restriction on parathyroid hormone (PTH) synthesis and secretion and PT cell growth in rats with established SH and PTG hyperplasia.

METHODS

Normal and 5/6 nephrectomized rats were fed a high P (0.8%) diet. After two weeks, the normal rats and half of the uremic rats were sacrificed (U-HP) while the remaining uremic rats were switched to a low P (0.2%) diet (U-HP-LP).

RESULTS

High dietary P induced a significant increase in serum P, PTH, and PTG weight, but not ionized calcium compared to normal animals fed the same diet (N-HP). P restriction returned serum P and PTH to normal levels by one week. In contrast, PTG size did not regress and glands remained enlarged for up to eight weeks with no evidence of apoptosis. Ribonuclease protection assay and metabolic labeling studies demonstrated similar PTH/actin mRNA ratios and 35S-labeled PTH among the three groups. Intracellular intact PTH was higher in U-HP and U-HP-LP rats compared to N-HP animals with no differences between the two uremic groups. PTG-PTH content correlated only with PTG weight, and serum PTH only with serum P. The PTG secretory response to calcium remained intact.

CONCLUSIONS

In established chief-cell hyperplasia, P restriction restores normal serum PTH levels without affecting PTG hyperplasia, PTH synthesis, PTG cytosolic PTH or the PTH secretory response to calcium, suggesting an impaired exocytosis of PTH.

Failure of high doses of calcitriol and hypercalcaemia to induce apoptosis in hyperplastic parathyroid glands of azotaemic rats

BACKGROUND

Whether calcitriol administration, which is used to treat secondary hyperparathyroidism in dialysis patients, induces regression of parathyroid-gland hyperplasia remains a subject of interest and debate. If regression of the parathyroid gland were to occur, the presumed mechanism would be apoptosis. However, information on whether high doses of calcitriol can induce apoptosis of parathyroid cells in hyperplastic parathyroid glands is lacking. Consequently, high doses of calcitriol were given to azotaemic rats and the parathyroid glands were evaluated for apoptosis.

METHODS

Rats were either sham-operated (two groups) or underwent a two-stage 5/6 nephrectomy (three groups). For the first 4 weeks, all rats were given a high (1.2%) phosphorus (P) diet to stimulate parathyroid gland growth and then were changed to a normal (0.6%) P diet for 2 weeks. At week 7, three of the five groups were given high doses of calcitriol (500 pmol/100 g body weight) intraperitoneally every 24 h during 72 h before sacrifice. The five groups during week 7 were: (i) normal renal function (NRF)+0.6% P diet; (ii) NRF+0.6% P+calcitriol; (iii) renal failure (RF)+0.6% P; (iv) RF+1.2% P+calcitriol; and (v) RF+0.6% P+calcitriol. Parathyroid glands were removed at sacrifice and the TUNEL stain was performed to detect apoptosis.

RESULTS

At sacrifice, the respective serum calcium values in calcitriol-treated groups (groups 2, 4, and 5) were 15.52+/-0.26, 13.41+/-0.39 and 15.12+/-0.32 mg/dl. In group 3, PTH was 178+/-42 pg/ml, but in calcitriol-treated groups, PTH values were suppressed, 8+/-1 (group 2), 12+/-2 (group 4), and 7+/-1 pg/ml (group 5). Despite, the severe hypercalcaemia and marked PTH suppression in calcitriol-treated groups, the percentage of apoptotic cells in the parathyroid glands was very low (range 0.08+/-0.04 to 0.25+/-0.20%) and not different among the five groups.

CONCLUSIONS

We found no evidence in hyperplastic parathyroid glands that apoptosis could be induced in azotaemic rats by the combination of high doses of calcitriol and severe hypercalcaemia despite the marked reduction in PTH levels that was observed.

Bcl-2 and Bax expression in cartilage and bone cells after high-dose corticosterone treatment in rats

The expression of Bcl-2 and Bax has been evaluated by immunohistochemistry in normal rats, and in rats after treatment with high-dose corticosterone (CORT). Proliferative (PC) and maturative/hypertrophic (MaHC) chondrocytes of the growth plate have been examined, as well as osteoblasts (Obs), osteocytes (Ots) and osteoclasts (Ocs) of the metaphyseal secondary spongiosa. For each cell type, the Bcl-2 and Bax immunopositive cells were expressed as a percentage of the total number of cells. Bcl-2 and Bax expression was considered to be enhanced when the percentage of positive cells rose. Bcl-2 and Bax were expressed in all cell types, and two main kinds of labeling distribution, both suggestive of association with intracellular organelles, were observed in the cytoplasm: scarce and spotty labeling (type 1) or abundant, granular and diffuse labeling (type 2). In some cases, nuclear membranes could also be seen to be positive. Positive PCs and Obs generally showed a labeling of type 1, MaHCs and Ocs of type 2, while Ots varied with labeling of type 1 or type 2. CORT administration induced a fall in the percentage of Bcl-2 immunopositive cells, and a rise in that of Bax immunopositive cells, in PCs and Ots. The same trend was observed in MaHCs, although the Bcl-2 decrease was not significant. The percentage of Bcl-2 and Bax immunopositive Obs rose, and their labeling distribution shifted from type 1- to type 2-labeled cells. Ocs showed the highest immunopositivity for both Bcl-2 and Bax, which did not change after CORT administration. These data suggest that CORT treatment, by lowering Bcl-2, and raising Bax expression, may promote the apoptotic process in PCs, MaHCs and Ots. Obs, however, do not undergo the same variations. This finding, together with the results of a previous study showing that CORT administration raises the frequency of apoptotic Obs, does not support a direct relationship between apoptosis and Bax overexpression, at least in Obs. The CORT effect might be related to cell types and their state of differentiation, so that Bcl-2 and Bax might regulate not only the machinery of cell death, but also cell proliferation and differentiation.

Apoptosis in parathyroid hyperplasia of patients with primary or secondary uremic hyperparathyroidism

BACKGROUND

Chronic oversecretion of parathyroid hormone (PTH) is associated with parathyroid hyperplasia, reflecting a disturbed balance between cell proliferation and apoptosis. This study addressed the unsolved issue of apoptosis in hyperparathyroidism.

METHODS

Parathyroid glands from 19 patients with primary (1 degrees ) and 11 patients with secondary (2 degrees ) uremic hyperparathyroidism, as well as 13 normal parathyroid glands, were examined. Apoptosis was evaluated by terminal deoxynucleotidyl transferase (Tdt)-mediated dUTP nick end-labeling assay (TUNEL). Because the apoptotic process is regulated by several oncoproteins, the expression of Bcl-2 and Bax was analyzed by immunohistochemistry.

RESULTS

The numbers of apoptotic cells in 1 degrees parathyroid adenoma (0.99 +/- 0.03 per 1000 cells, mean +/- SE, P < 0.009) and 2 degrees parathyroid hyperplasia (1.20 +/- 0.54 per 1000 cells, P < 0.005) were significantly higher than in normal parathyroid tissue (0.13 +/- 0. 06 per 1000 cells). Light microscopy examination of hyperplastic parathyroid tissue from a uremic patient showed the presence of nuclei with dense chromatin characteristic of apoptosis. Bcl-2 staining was strong in normal tissues but weak or negative in several sections of 1 degrees and 2 degrees hyperparathyroid tissues, mostly in nodular areas. Bax staining was homogeneous in normal tissue but patchy in several hyperplastic tissues.

CONCLUSION

These results suggest that hyperparathyroidism is associated with a compensatory increase in apoptosis, possibly favored by a diminished Bcl-2/Bax ratio. This renders highly improbable the hypothesis that parathyroid hyperplasia is due to a decreased rate of apoptosis.

Bcl-2 Gene Family in Endocrine Pathology: A Review

BcI-2 is a member of a large multigene family, which includes genes that can inhibit or promote apoptosis. The regulation of apoptosis is achieved by homo- or heterodimerization of their proteins through four highly conserved domains. Bcl-2 protein is a strong cell death suppressor in a wide range of cell types and under a variety of stimuli. Bcl-2 and the other members of this family are differentially expressed in the endocrine glands and disregulation of their expression seems to contribute to the neoplastic transformation in these organs. The significance of bcl-2 and the related proteins for endocrine pathology at the experimental and clinical level is reviewed in this article.

Apoptosis in neuroendocrine tumours

Acquired resistance to apoptosis in neuroendocrine tumours (NETs) may promote clonal expansion and enhance the likelihood that subsequent mutations lead to growth or persistence of the neoplastic clone. Recent studies have demonstrated that deregulation of programmed cell death may be a critical component in multistep tumourigenesis of NETs and that the frequent expression of the Bcl-2 oncoprotein in these tumours may contribute to their pathogenesis. The genetic complementation of simultaneously deregulated Bcl-2 and c-Myc may be implicated in the multistep tumourigenesis of human NETs. Furthermore, because the efficacy of cytotoxic chemotherapy relies on its ability to induce programmed cell death, resistance to apoptosis typically correlates with chemoresistance, a phenomenon that is typical in NETs. Consideration of how oncogenes affect rates of cell death, in addition to augmenting growth, has already provided valuable insights into the biology of cancer. Understanding the molecular and cellular features of this process may enable the development and application of more effective and potentially curative treatment strategies in which the induction of programmed cell death is an integral component.

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.

Prevention of renal osteodystrophy in peritoneal dialysis

BACKGROUND

Renal osteodystrophy (ROD) is still one of the major long-term complications in end-stage renal disease leading to considerable morbidity. Despite some progress in understanding the pathogenesis of secondary hyperparathyroidism (sHPT) during recent years, prevention and treatment of ROD is still suboptimal, requiring surgical parathyroidectomy in 6 to 10% of all patients on dialysis after 10 years. In addition, the spectrum of bone lesions has changed, with non-aluminum-related adynamic bone disease (ABD) found in up to 43% of peritoneal dialysis (PD) patients.

METHODS

Current recommendations concerning prevention of ROD in PD based on the literature and personal recent data were reviewed. The focus is on (i) the importance of early prophylactic intervention to prevent parathyroid gland hyperplasia, (ii) the pathogenesis of ABD, and (iii) the role of metabolic acidosis in ROD.

RESULTS

There is ample evidence that sHPT starts early during the course of renal failure and results from both hypersecretion of PTH by parathyroid cells and glandular hyperplasia. As shown by experimental and clinical studies, established parathyroid cell hyperplasia is hardly reversible by pharmacological means, and therefore prevention of parathyroid cell proliferation needs to start early. Recent data from randomized trials document the efficacy and safety of low dose active vitamin D (0.125 to 0.25 microgram/day) and/or an oral calcium substitute to prevent progression of sHPT in patients with mild to moderate renal failure. Since little is known about the pathogenesis, natural course and clinical impact of ABD in PD, specific therapeutic concepts have not yet been generated. Diabetes and advanced age are established risk factors, whereas the role of calcium and vitamin D overtreatment or the type of dialysis (PD vs. HD) are still controversial. Currently no evidence for different functional behavior of the parathyroids in ABD and sHPT has been found. The role of circulating or local factors such as cytokines, growth factors or the presence of advanced glycation end-product (AGE)-modified matrix proteins for the pathogenesis of either type of ROD deserves further investigation. Avoiding oversuppression of parathyroid gland and the use of low calcium dialysate may help prevent ABD. There is growing evidence that a correction of metabolic acidosis will influence ROD by both direct effects on the bone and on parathyroid cell function. New dialysate composition for CAPD with a high HCO3 concentration will allow normalization of acid-based metabolism in PD patients. Their effects on ROD under long term conditions remain to be determined.

CONCLUSION

Therapeutic efforts should aim to prevent the development of parathyroid gland hyperplasia and sHPT early during the course of renal failure, and should include the use of low dose vitamin D therapy and oral calcium substitution as well as correction of metabolic acidosis. Concerning ABD, more information is needed regarding the causes and consequences of this type of bone lesion to develop a more specific therapy.