Measurement of PTH Fragments for Assessment of Renal Bone Disease in Hemodialysis Patients

BACKGROUND

Renal bone pathology involves a spectrum from 'high-turnover' to 'low-turnover bone disease' (adynamic bone disease, classical osteomalacia). The diagnosis of the latter usually requires bone biopsy. Inhibitory parathyroid hormone (PTH) fragments may be useful for its noninvasive diagnosis.

METHODS

A cross-sectional study was performed in 54 patients on chronic hemodialysis which involved measurements of intact PTH (iPTH; Nichols assay), total PTH (tPTH; Scantibodies assay), and the cyclase-activating PTH fragment (CAP). The level of cyclase-inactive PTH fragment (CIP) was calculated. At the same time, serum calcium, phosphorus, and alkaline phosphatase levels as well as the current therapy for secondary hyperparathyroidism were recorded. In selected patients, bone radiographs were evaluated for osteitis fibrosa.

RESULTS

A high correlation (r = 0.94) was found between iPTH and tPTH, with the tPTH levels being lower by 30-40%. A similar association was also found for CAP (r = 0.988) and for CIP (r = 0.93). 3 out of the 54 patients had a CAP/CIP ratio of < or =1 which has been associated with adynamic bone disease. A higher CIP ratio was significantly associated with the use of aluminum-hydroxide- and calcium-containing phosphate binders.

CONCLUSIONS

iPTH and tPTH assays are highly correlated. In a general hemodialysis patient population, low-turnover bone disease appears to be rare, when the CAP/CIP ratio is used as a marker. A high CIP value was associated with therapy using aluminum hydroxide, a drug known to carry a risk of adynamic bone disease.

[Treatment of osteoporosis from the socioeconomic perspectives]

Health economic evaluation for osteoporosis suffers from methodological limitations. For example, osteoporosis results in various types of fractures each with different impact on patients. Another example is that some therapeutic drugs have extraskeletal benefits and adverse events. Osteoporosis and resultant fracture has profound effects on patients' life expectancy and quality of life, which, however, is not well understood. To promote the health economic evaluation for osteoporosis is our urgent research project in Japan.

Steroid and xenobiotic receptor and vitamin D receptor crosstalk mediates CYP24 expression and drug-induced osteomalacia

The balance between bioactivation and degradation of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] is critical for ensuring appropriate biological effects of vitamin D. Cytochrome P450, family 24-mediated (CYP24-mediated) 24-hydroxylation of 1,25(OH)2D3 is an important step in the catabolism of 1,25(OH)2D3. The enzyme is directly regulated by vitamin D receptor (VDR), and it is expressed mainly in the kidney, where VDR is also abundant. A recent report suggests that activation of steroid and xenobiotic receptor (SXR) also enhances the expression of CYP24, providing a new molecular mechanism of drug-induced osteomalacia. However, here we showed that activation of SXR did not induce CYP24 expression in vitro and in vivo, nor did it transactivate the CYP24 promoter. Instead, SXR inhibited VDR-mediated CYP24 promoter activity, and CYP24 expression was very low in tissues containing high levels of SXR, including the small intestine. Moreover, 1,25(OH)2D3-induced CYP24 expression was enhanced in mice lacking the SXR ortholog pregnane X receptor, and treatment of humans with the SXR agonist rifampicin had no effect on intestinal CYP24 expression, despite demonstration of marked CYP3A4 induction. Combined with our previous findings that CYP3A4, not CYP24, plays the dominant role in hydroxylation of 1,25(OH)2D3 in human liver and intestine, our results indicate that SXR has a dual role in mediating vitamin D catabolism and drug-induced osteomalacia.

Effects of catecholamines on blood pressure in the long bone marrow cavity in rats with bisphosphonate-induced osteopetrosis

Osteopetrosis is a congenital metabolic bone disease characterized by skeletal sclerosis resulting from defective osteoclast-mediated bone resorption. The disease may, inter alia, be caused by the administration of bisphosphonates (e.g. pamidronate) particularly in young humans. The issue of the effect of pamindronate-induced osteopetrosis on the function of blood circulation and autonomic nervous system remains open. In order to clarify this problem, the present study concentrated on the effect of catecholamines on blood pressure in the marrow cavity in rats with pamindronate-induced osteopetrosis. The experiments consisted in pamidronate administration to young male Wistar rats at doses of 3 mg/kg sc, for 3 or 6 weeks. Norepinephrine, epinephrine, isoprenaline as well as adrenoceptor antagonists (phentolamine and propranolol) were administered to the controls and the rats with pamindronate-induced osteopetrosis. The examinations demonstrated that rats with pamidronate-induced osteopetrosis displayed increased blood pressure in the marrow cavity. In addition, a disorder in the effect of catecholamines on blood pressure in the marrow cavity of osteopetrotic bone was observed.

Effect of D-003, a Mixture of Very High Molecular Weight Aliphatic Acids, on Prednisolone-Induced Osteoporosis in Sprague-Dawley Rats

BACKGROUND

Drugs inhibiting cholesterol biosynthesis may affect bone metabolism through inhibition of the mevalonate pathway resulting in the inhibition of protein prenylation required for osteoclast activity. D-003 is a mixture of high molecular weight aliphatic primary acids purified from sugar-cane (Saccharum officinarum) wax, with cholesterol-lowering effects demonstrated in experimental and clinical studies. D-003 inhibits cholesterol biosynthesis through indirect regulation of HMG-CoA reductase activity. A previous study demonstrated that D-003 prevented bone loss and bone resorption on ovariectomy-induced osteoporosis in rats. Corticosteroid-induced osteoporosis is the result of changes affecting calcium homeostasis, but the hallmark of corticosteroid-induced bone loss is the direct effects on bone cells, such as inhibition of osteoblastogenesis, promotion of apoptosis of osteoblasts and osteocytes, and decrease in bone formation.

OBJECTIVE

To determine whether D-003 could prevent the bone loss induced with prednisolone in Sprague-Dawley rats.

METHODS

Rats were randomly distributed in five groups (ten rats per group): a sham-operated control and four groups orally treated with prednisolone 6 mg/kg for 80 days; a positive control orally treated with vehicle; and three groups orally treated with D-003 at 5, 25 and 200 mg/kg, respectively. Rats were killed, bones removed and histological variables of bone resorption and formation studied for histomorphometry.

RESULTS

Compared with the sham group, prednisolone significantly (p < 0.01) reduced trabecular bone volume (TBV), while D-003 significantly (p < 0.001) and dose-dependently prevented the prednisolone-induced reduction of TBV. Treatment with prednisolone lowered (p < 0.001) trabecular thickness (TbTh) and number (TbN), while increasing (p < 0.001) the gap between trabeculae. D-003 (5, 25 and 200 mg/kg/day) significantly (p < 0.001) and dose-dependently prevented the reduction of TbTh and TbN and the increase of trabecular gap induced with prednisolone. Treatment with prednisolone increased both the surface and number of osteoclasts compared with sham (p < 0.001). D-003 (5-200 mg/day), however, prevented this effect (p < 0.001 for all comparisons). D-003 also prevented (p < 0.001) the reduction of osteoblast surface (ObS/BS) induced by prednisolone. Osteonecrotic areas were observed in all positive controls, but in none of the sham animals. Positive controls showed hypertrophy of bone marrow adipocytes and lipid-laden pluripotential stromal cells in bones. A significant and dose-dependent reduction of the frequency of animals showing prednisolone-induced osteo-necrosis was observed across the doses of D-003 (5, 25 and 200 mg/kg) investigated here.

CONCLUSIONS

D-003 (5, 25 and 200 mg/kg) prevented trabecular bone loss and femoral neck osteonecrosis induced with prednisolone in Sprague Dawley rats, also increasing osteoblast surface and reducing bone resorption parameters. These results suggest that D-003 could be useful for managing corticosteroid-induced osteoporosis.