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Klotho plays an important role in the pathogenesis of cardiovascular disease in chronic kidney disease (CKD). Klotho is highly expressed in the kidney and parathyroid glands, but its presence in the vasculature is debated. Renal Klotho is decreased in CKD, but the effect of uremia on Klotho in other tissues is not defined. The effect of vitamin D receptor activator therapy in CKD on the expression of Klotho in various tissues is also in debate. In uremic rats (surgical 5/6th nephrectomy model), we compared 3 months of treatment with and without paricalcitol on Klotho immunostaining in the kidney, parathyroid glands, and aorta. With uremia, Klotho was unchanged in the parathyroid, significantly decreased in the kidney (66%) and the intimal-medial area of the aorta (69%), and significantly increased in the adventitial area of the aorta (67%) compared with controls. Paricalcitol prevented the decrease of Klotho in the kidney, increased expression in the parathyroid (31%), had no effect in the aortic media, but blunted the increase of Klotho in the aortic adventitia. We propose that fibroblasts are responsible for the expression of Klotho in the adventitia. In hyperplastic human parathyroid tissue from uremic patients, Klotho was higher in oxyphil compared with chief cells. Thus, under our conditions of moderate CKD and mild-to-moderate hyperphosphatemia in rats, the differential expression of Klotho and its regulation by paricalcitol in uremia is tissue-dependent.

p21 WAF1 and transforming growth factor-α mediate dietary phosphate regulation of parathyroid cell growth. Background The parathyroid (PT) hyperplasia induced by renal failure can be further enhanced by high dietary phosphate (P) or completely abolished by P restriction. To identify potential mechanisms mediating these opposing effects of dietary P on PT growth, this study first focused on p21 WAF1 (p21) because high P reduces while low P enhances serum 1,25-dihydroxyvitamin D, whose potent antiproliferative properties result from the induction of p21. In addition to reducing p21, high P-induced PT growth could result from increased PT expression of the growth promoter transforming growth factor-α (TGF-α), known to be elevated in hyperplastic and adenomatous human PT glands. Methods The time course for dietary P regulation of PT expression of TGF-α and p21 was assessed for seven days after 5/6 nephrectomy in rats and correlated with the degree of PT hyperplasia and secondary hyperparathyroidism. Results In P-restricted 5/6 nephrectomized rats, PT-p21 mRNA and protein increased by day 2, independent of changes in serum 1,25-dihydroxyvitamin D, and remained higher than in the high P counterparts for up to seven days. The PT hyperplasia of the high P group could not be attributed to a reduction of PT-p21 expression from normal control values. Instead, PT–TGF-α protein was higher in uremic rats compared with normal controls and increased further with high dietary P intake. PT levels of proliferating cell nuclear antigen (PCNA), an index of cell mitoses, correlated inversely with p21 and directly with TGF-α. Consistent with these findings, PT gland size and serum PT hormone levels, similar in both dietary groups at day 2, were higher in the high P group by day 5. Induction of p21 by low P and of TGF-α by high P was specific for the PT glands. Dietary P had no effect either on intestinal growth or p21 or TGF-α protein content. Conclusions These findings suggest that low P induction of p21 could prevent PT hyperplasia in early uremia, whereas high P enhancement of TGF-α may function as an autocrine signal to stimulate growth further.

Progressive accumulation of lanthanum in the liver of normal and uremic rats.BackgroundThe loss of renal function in chronic kidney disease (CKD) patients leads to a variety of metabolic disturbances that promote the development of secondary hyperparathyroidism (SH) and bone disease. One of these alterations, hyperphosphatemia, is a persistent problem in patients with CKD and is an important factor in the development and severity of SH as well as coronary artery and cardiac valve calcification. To help control serum phosphorus (P), phosphate binders are used to minimize intestinal absorption of P in these patients. Since the use of aluminum- and calcium-based phosphate binders can result in severe side effects, other phosphate binders have been proposed. One of these is lanthanum (La) carbonate.MethodsSince there is some controversy as to the degree La is absorbed by the intestine, whether it is deposited in tissues, and what effect its prolonged use would have in patients with chronic renal failure, we studied normal and uremic rats fed a control diet or a diet with La carbonate (1.5% elemental La) for 45, 90, or 110 days.ResultsAs expected, plasma creatinine increased after the induction of uremia and continued to increase with time. At 45 and 90 days, dietary La produced a reduction in plasma P in normal rats (N + La) [45 days: 3.15 ± 0.35 vs. normal control (NC) 4.41 ± 0.15 mg/dL, P < 0.01; 90 days: 3.20 ± 0.30 vs. 4.09 ± 0.15 mg/dL, P < 0.05], but not at 110 days. Plasma P was initially lower (45 days) in both groups of La-treated rats (U + La: 3.47 ± 0.28 vs. UC: 4.91 ± 0.27 mg/dL, P < 0.01), but was not at 90 and 110 days. Whole blood La content was not increased in rats fed the La diet and is, therefore, not a good indicator of the La content of tissue. La was increased in kidney, femur, and especially liver in normal and uremic rats fed the La diet. Uremia markedly enhanced tissue accumulation of La (liver, 110 days: N + La: 849 ± 152 vs. U + La: 2676 ± 479 ng/g wet wt, P < 0.01), which increased in a time-dependent manner. The increase in La in the liver of normal rats was 44-fold compared to control and 98-fold in the liver of uremic rats compared to uremic control.ConclusionLa accumulates in tissues, most strikingly in the liver, and renal failure accelerates the accumulation. While this was a relatively short-term study, La accumulation increased in a time-dependent manner. The effect of long-term La treatment on patients with chronic renal insufficiency needs to be evaluated.

Vascular calcification is associated with cardiovascular disease, the most common cause of death in chronic kidney disease (CKD). Patients with CKD are treated with vitamin D receptor activators (VDRAs); therefore, we determined if this treatment affects vascular calcification. Uremic rats were given vehicle, calcitriol, paricalcitol, or doxercalciferol three times a week for 1 month. Calcitriol significantly increased the serum calcium-phosphate product and aortic calcium content. Paricalcitol had no effect but the same dose of doxercalciferol significantly increased the calcium-phosphate product and the aortic calcium content, the latter being confirmed by von Kossa staining. To see if the increased aortic calcium was due to an increased serum calcium-phosphate product or to a differential effect of the two VDRAs, we lowered the dose of doxercalciferol and increased the dose of paricalcitol. A lower doxercalciferol did not increase the calcium-phosphate product but increased the aortic calcium content. A higher dose of paricalcitol still had no effect. Doxercalciferol treatment increased the mRNA and protein expression of the bone-related markers Runx2 and osteocalcin in the aorta, whereas paricalcitol did not. Hence, different VDRAs have different effects on vascular calcification in uremic rats. The effects are independent of the serum calcium-phosphate product suggesting independent mechanisms.

Effect of biological activity of PTH on its peripheral metabolism in the rat. Previous studies from our laboratory have characterized the peripheral metabolism of parathyroid hormone (PTH) in the dog using radioimmunoassay techniques following injection or infusion of biologically active, bovine PTH preparations. Other investigators have used biologically–inactive labelled PTH and interpreted their results as representative of the normal physiological processes. Since oxidized inactive PTH does not bind to PTH receptors and since we have found substantial differences between the tissue uptake of active and inactive PTH preparations, it is possible that results obtained with inactive PTH preparations may not totally represent the normal metabolism of PTH. Therefore, we performed studies in rats to compare the disappearance of immunoreactive PTH (i-PTH) from plasma following injection of active or inactive syn b-PTH 1–34. The maneuvers of bilateral ureteral ligation and bilateral nephrectomy were utilized to characterize the sites of tissue uptake of i-PTH. The results obtained indicate that inactive syn b-PTH 1–34 has a significantly slower disappearance from plasma than biologically active syn b-PTH 1–34. Reduction of glomerular filtration by acute bilateral ureteral ligation decreased the disappearance of oxidized PTH more than active PTH. Thus, the results indicate a major dependence on glomerular filtration for the removal of inactive syn b-PTH 1–34. The demonstration that the peripheral metabolism of active and inactive syn b-PTH 1–34 is not identical suggests that studies of the metabolism of inactive PTH preparations do not accurately reflect that of biologically active PTH.

p21 WAF1 and TGF-α mediate parathyroid growth arrest by vitamin D and high calcium. Background High dietary phosphorus (P) worsens uremia-induced parathyroid (PT) hyperplasia through increases in the growth promoter transforming growth factor-alpha (TGF-α). In contrast, P restriction prevents PT hyperplasia by inducing the cell cycle inhibitor p21. Since 1,25(OH) 2 D 3 -antiproliferative action in various cell types involve increases in p21, we studied whether induction of p21 by 1,25(OH) 2 D 3 or the vitamin D analog, 19-Nor-1,25(OH) 2 D 2 , could counteract the PT hyperplasia induced by high dietary P in early uremia. Methods Normal (N) and uremic (U; 5/6 nephrectomized) female Sprague-Dawley rats were fed high P (HP), low P (LP) or high Ca (HCa) diets and administered intraperitoneally (IP) either vehicle or vitamin D metabolites for seven days, as follows: N-HP; U-HP + vehicle; U-HP + 1,25(OH) 2 D 3 (4 ng/day); U-HP + 19-Nor-1,25(OH) 2 D 2 (30 ng/day); U-LP; U-HCa. Serum PTH and PT gland weight assessed secondary hyperparathyroidism. Immunohistochemical quantitation of two markers of mitotic activity, Ki67 and PCNA measured PT hyperplasia. Immunohistochemical expression of PT p21 and TGF-α addressed potential mechanisms regulating PT cell growth. Results 1,25(OH) 2 D 3 and 19-Nor-1,25(OH) 2 D 2 were effective in suppressing both PTH secretion and PT hyperplasia induced by uremia and high dietary P independent of increases in ionized Ca. Both vitamin D compounds enhanced PT p21 expression and prevented high P-induced increases in PT TGF-α content. Induction of PT p21 and reduction of TGF-α content also occurred when uremia-induced PT hyperplasia was suppressed by high dietary Ca. Conclusions In early uremia, vitamin D suppression of high P-induced PT hyperplasia and high dietary Ca arrest of PT growth involve induction of PT p21 and prevention of increases in TGF-α.

A novel mechanism for skeletal resistance in uremia.BackgroundIn treating secondary hyperparathyroidism, the target level of serum intact parathyroid hormone (I-PTH) should be three to five times normal to prevent adynamic bone disease. In circulation, there is a non-(1-84) PTH-truncated fragment, likely 7-84, which, in addition to PTH 1-84, is measured by most I-PTH immunoradiometric (IRMA) assays, giving erroneously high I-PTH values. We have developed a new IRMA assay in which the labeled antibody recognizes only the first six amino acids of the PTH molecule. Thus, this new IRMA assay (Whole PTH) measures only the biologically active 1-84 PTH molecule.MethodsUsing this new IRMA assay (Whole PTH) and the Nichols “intact” PTH assay, we compared the ability of each assay to recognize human PTH (hPTH) 1-84 and hPTH 7-84 and examined the percentage of non-1-84 PTH in circulation and in parathyroid glands. Possible antagonistic effects of the 7-84 PTH fragment on the biological activity of 1-84 PTH in rats were also tested.ResultsIn 28 uremic patients, PTH values measured with the Nichols assay, representing a combined measurement of both hPTH 1-84 and hPTH 7-84, were 34% higher than with the Whole assay (hPTH 1-84 only); the median PTH was 523 versus 318 pg/mL (P < 0.001). Similar results were found in 14 renal transplant patients. In osteoblast-like cells, ROS 17.2, 1-84 PTH (10-8 mol/L) increased cAMP from 18.1 ± 1.25 to 738 ± 4.13 mmol/well. Conversely, the same concentration of 7-84 PTH had no effect. In parathyroidectomized rats fed a calcium-deficient diet, 7-84 PTH was not only biologically inactive, but had antagonistic effects on 1-84 PTH in bone. Plasma calcium was increased (0.65 mg/dL) two hours after 1-84 PTH treatment, while 7-84 PTH had no effect. When 1-84 PTH and 7-84 PTH were given simultaneously in a 1:1 molar ratio, the calcemic response to 1-84 PTH was decreased by 94%. In normal rats, the administration of 1-84 PTH increased renal fractional excretion of phosphate (11.9 to 27.7%, P < 0.001). However, when 1-84 PTH and 7-84 PTH were given simultaneously, the 7-84 PTH decreased the phosphaturic response by 50.2% (P < 0.005). Finally, in surgically excised parathyroid glands from six uremic patients, we found that 44.1% of the total intracellular PTH was the non-PTH (1-84), most likely PTH 7-84.ConclusionIn patients with chronic renal failure, the presence of high circulating levels of non–1-84 PTH fragments (most likely 7-84 PTH) detected by the “intact” assay and the antagonistic effects of 7-84 PTH on the biological activity of 1-84 PTH explain the need of higher levels of “intact” PTH to prevent adynamic bone disease.

Differential effects of 1,25-(OH)2D3 and 22-oxacalcitriol on phosphate and calcium metabolism. 1,25-dihydroxyvitamin D3 has been used with success in the treatment of secondary hyperparathyroidism associated with chronic renal failure. However, frequently 1,25-(OH)2D3 induces hypercalcemia, especially in those patients ingesting large doses of calcium carbonate, precluding the administration of therapeutic doses of 1,25-(OH)2D3. In addition, control of serum phosphorus is a persistent problem in patients maintained on chronic hemodialysis and 1,25-(OH)2D3 treatment can aggravate the hyperphosphatemia. Thus, ideally an analog of 1,25-(OH)2D3 that can suppress PTH with minor effects on calcium (Ca) and phosphate (PO4) metabolism would be an ideal tool to control secondary hyperparathyroidism. We have shown that 22-oxa-1,25-(OH)2D3 (OCT), an analog of 1,25-(OH)2D3 with little calcemie activity, can suppress PTH mRNA in normal rats and in cultured bovine parathyroid cells with equipotency to 1,25-(OH)2D3. To further characterize the differential effects of 1,25-(OH)2D3 and OCT on Ca and PO4 metabolism we performed several experiments in intact and parathyroidectomized (PTX) rats. In metabolic studies in four groups of normal rats 1,25-(OH)2D3 treatment (8 ng/day) significantly increased the intestinal Ca absorption from 15.2 ± 2.68% to 30.5 ± 2.85% (P < 0.01), while the same dose of OCT had no effect. A dose of 200 ng/day of OCT increased intestinal Ca absorption similarly to the 8 ng/day dose of 1,25-(OH)2D3, from 10.6 ± 2.49% to 24.8 ± 2.35% (P < 0.01). Results for intestinal PO4 absorption were similar to those for Ca. Eight ng/day of 1,25-(OH)2D3 increased intestinal PO4 absorption from 21.8 ± 1.94 to 32.6 ± 2.70% (P < 0.01), while the same dose of OCT had no effect. The 200 ng/day dose of OCT increased intestinal PO4 absorption in a manner comparable to the 8 ng/day dose of 1,25-(OH)2D3, from 20.3 ± 1.92 to 29.2 ± 1.74% (P < 0.01). Similar patterns were observed for urinary Ca and phosphorus excretion. To further characterize the bone-resorbing effects of 1,25-(OH)2D3 and OCT, studies were performed in three groups of PTX rats fed a PO4-deficient diet. 1,25-dihydroxy vitamin D3 (200 ng/day) increased plasma phosphorus to 6.09 ± 0.26 mg/dl as compared to 2.41 ± 0.33 mg/dl in vehicle-treated animals. On the other hand, plasma phosphorus increased to only 3.55 ± 0.23 mg/dl in OCT-treated animals. We conclude that in normal rats OCT is much less active than 1,25-(OH)2D3 in stimulating both intestinal absorption and urinary excretion of Ca and phosphorus. Also as shown in PTX rats fed a PO4-deficient diet, OCT is much less effective in raising plasma phosphorus most likely by bone resorption. Thus, OCT, an analog of 1,25-(OH)2D3, can suppress PTH without significant changes in plasma Ca and phosphorus making it an ideal drug for the treatment of secondary hyperparathyroidism.

Efficacy of 19-Nor-1,25-(OH) 2 D 2 in the prevention and treatment of hyperparathyroid bone disease in experimental uremia. Background The control of parathyroid hyperplasia and high circulating parathyroid hormone (PTH) levels is crucial in preventing secondary hyperparathyroidism (SH) in renal failure. Parathyroid gland enlargement and elevated levels of PTH are major contributors to increase bone resorption, a feature of renal osteodystrophy. Methods These studies assessed the efficacy of the 1,25(OH) 2 D 3 analog, 19-Nor-1,25(OH) 2 D 2 (19-Nor), in the prevention (protocol I) and treatment (protocol II) of SH and renal osteodystrophy in uremic rats. In protocol I, normal and uremic rats were fed a high phosphorus diet for 2 months; uremic rats were administered intraperitoneal injections of either vehicle or 19-Nor (200ng three times a week). In protocol II, normal and uremic rats were fed a high phosphorus diet for 4 months; 2 months after the onset of uremia, rats were administered either intraperitoneal vehicle or 19-Nor (200ng three times a week). Serum PTH and bone histology were used to assess the degree of SH. Results 19-Nor was effective in preventing (protocol I) and suppressing (protocol II) the significant SH induced by uremia and further enhanced by a high phosphorus diet. In protocol I, bone histology in uremic controls showed a threefold increase in the cancellous bone mass compared to normal rats. This expansion in unmineralized bone was accompanied by 5-, 1.5-, and 7-fold increases in eroded surface, mineralization lag time (MLT), and bone formation rate (BFR/BS), respectively. Moreover, cortical bone porosity in untreated uremic rats increased 267-fold compared to normal animals. 19-Nor ameliorated these changes in cancellous and cortical bone. In protocol II, the reported indices worsened even further. In contrast, 2 months of 19-Nor treatment improved bone histology by reducing cortical bone porosity, woven bone formation, MLT, and BFR/BS. Conclusion In an experimental model of chronic renal failure (CRF), 19-Nor prevents SH and ameliorates the histomorphometric changes induced by uremia and high phosphorus diet. In addition, 19-Nor suppresses serum PTH and improves bone histology in uremic rats with established severe SH. Further studies in patients with CRF are necessary to define the clinical applicability of 19-Nor on bone histology in humans.

In his letter to the editor, De Broe et al.1 states that 'lanthanum appears to have an innocent localization, being confined to the hepatic endosomal/lysosomal compartment during passage through the liver into bile.' For the well-being of our patients, we certainly hope that this is correct. De Broe et al. also states that in a 78-week study, lanthanum accumulation in rats reaches a steady state. This study was carried out in normal rats, not uremic animals. Whereas we saw this trend in normal rats as well, in uremic rats, we saw progressive accumulation of lanthanum in the liver that did not reach a steady state over the course of our 110-day study. We are not concerned with what happens in normal rats as normal individuals will not be taking lanthanum carbonate. The greater accumulation of lanthanum in liver of uremic rats is likely owing to the increased gastrointestinal absorption of lanthanum seen in uremia which has been reported by several laboratories, including De Broe's group. More work needs to be carried out in order to understand the mechanism(s) behind this increased gastrointestinal absorption. In reference to the table included in De Broe's letter, we are glad to see that liver enzymes in patients taking lanthanum carbonate for up to 2 years seem unaffected. Although liver enzymes are good indicators of hepatic integrity, cases of cirrhosis have been seen in the presence of normal liver enzymes, and liver biopsy is the gold standard in assessing the integrity of hepatic tissue. At no point do we suggest that lanthanum carbonate produces liver toxicity, but we feel that the progressive accumulation of lanthanum seen in uremic rats dictates close monitoring of those patients taking lanthanum carbonate. Our concern is for our patients.