Kazutoshi Mizunashi

Effect of omeprazole, an inhibitor of H+, K+-ATPase, on bone resorption in humans

SummaryOmeprazole is an inhibitor of gastric H+, K+-ATPase. Although the major proton transport of osteoclast is mediated by a vacuolar-type H+-ATPase which is different from the gastric H+, K+-ATPase,in vitro studies have demonstrated that omeprazole inhibits bone resorption. In this study, the effect of omeprazole on bone resorption was evaluated in patients who had a history of gastric ulcer and were treated with maintenance doses of H2 blocker without any gastric complaints at the study time. H2 blocker administration was changed to omeprazole treatment in the study group and to no treatment in the control group. Urinary excretion of hydroxyproline and calcium decreased after omeprazole treatment in the study group. Serum intact PTH, alkaline phosphatase, osteocalcin, and tartrate-resistant acid phosphatase (TRAP) increased in this group. In the control group, there were not any changes in these parameters. The discrepancy between serum TRAP and urinary excretion of hydroxyproline and calcium in the study group was thought to be due to the suppression of bone resorption by omeprazole, which probably interfered the acidification at resorption lacunae and resulted in the inactivation of TRAP and other lysosomal enzymes. The results of our study suggest the possibility that the specific inhibitors of the osteoclastic proton pump (such as bafilomycins) will more effectively suppress bone resorption and be useful for the treatment of metabolic bone diseases with increased bone resorption.

Relationship between Ca-dependent change of serum PTH and extracellular Ca2+-sensing receptor expression in parathyroid adenoma.

Abnormal PTH secretion and cell growth in hyperparathyroid tissues are accompanied with reduced expression of Ca2+-sensing receptor (CaR) which plays a key role in Ca-regulated PTH release. In this study, we examined the receptor expression in parathyroid adenomas using specific anti-CaR antibody and investigated relationship between CaR expression in adenomatous tissues and parameters of Ca-dependent change of serum PTH. The results show a considerable variation in the number of CaR positive cells among the adenomatous tissues. Expression of the receptor protein was not related to set-point error but was more reduced in the patients with more elevated minimum or baseline levels of serum PTH. CaR expression was severely reduced in the patients with highly elevated maximum serum PTH, while the receptor expression was also decreased in some patients with normal maximum serum PTH. Baseline level / maximum level ratio of serum PTH was increased in these patients. In conclusion, reduced CaR expression is related to abnormality in three parameters of PTH secretion (minimum serum PTH, maximum serum PTH, and baseline level / maximum level ratio of serum PTH) and may contribute to hypersecretion from parathyroid adenomas.

Heterogeneity of pseudohypoparathyroidism type I from the aspect of urinary excretion of calcium and serum levels of parathyroid hormone

SummaryUrinary excretion of calcium (Ca) was measured in 9 patients with pseudohypoparathyroidism (PHP) type I—3 with Albrights hereditary osteodystrophy (AHO): AHO(+) and 6 without AHO: AHO(−)—and in 13 with idiopathic hypoparathyroidism (IHP), treated with active vitamin D3 (1,25(OH)2D3 or 1αOHD3) to maintain serum Ca levels at 8.4–9.5 mg/dl. Fasting urinary excretion of Ca in PHP was significantly lower than that in IHP. Moreover, fasting urinary excretion of Ca in PHP AHO(+) was lower than that in PHP AHO(−). This difference was also seen in the urine after oral loading of Ca. Urinary excretion, of sodium (Na) was not different between PHP AHP(+) and PHP AHO(−). Serum levels of immunoreactive PTH in PHP AHO(+) were higher than those in PHP AHO(−). The difference in urinary excretion of Ca between PHP AHO(+) and PHP AHO(−) may come from the difference in the circulating levels of PTH.

Long-term observations of vertebral fractures in spinal osteoporotics

SummaryThe changes in the number and distributions of vertebral fractures were studied from the long-term observations (average 7 years) of 21 spinal osteoporotic patients. Distribution of wedge fractures was biphasic with peak frequencies at the midthoracic and thoracolumbar spine. Biconcave fractures occurred predominantly in the lumbar spine. These patterns of distribution did not change during the period of observation. The rate of biconcave fracture increased, the rate of wedge fracture decreased, and that of collapse remained the constant in follow-up. The changes in the number of fractures were divided into three types; increasing, plateau, and unchanged type. With the advance of osteoporosis, the increasing type was considered to change into the plateau type, which is probably the terminal stage of spinal osteoporosis. The unchanged type, in contrast, was distinct from the other two types because of increased spinal bone mineral density and decreased urinary calcium, which suggests that spinal osteoporosis is heterogeneous with regard to calcium metabolism.

Expression of stanniocalcin in zona glomerulosa and medulla of normal human adrenal glands, and some adrenal tumors and cell lines

Stanniocalcin (STC) is a calcium (Ca)‐regulating hormone that was originally discovered in the fish Stannius body, which is a unique endocrine organ. Hypercalcemia increases STC secretion, which inhibits Ca uptake by the gills and normalizes serum Ca level. In this study we investigated the STC expression in human normal and abnormal adrenal cells. Immunohistochemistry using monoclonal antibody against STC revealed specific staining in zona glomerulosa and medulla of normal human adrenal glands. STC was also detected in human adrenal tumors, such as pheochromocytoma, differentiated neuroblastoma, and aldosterone‐producing adenoma, and cultured adrenal tumor cells (rat pheochromocytoma PC‐12 cells and human neuroblastoma NB‐1 cells). However, undifferentiated human adrenal neuroblastoma was negative for STC staining. Reverse transcription polymerase chain reaction demonstrated STC mRNA expression in cultured PC‐12 cells and NB‐1 cells. Following several studies indicating that zona glomerulosa cells of adrenal glands express neuroendocrine properties, STC expression in normal and abnormal adrenal cells provides additional evidence to support the neuroendocrine differentiation of these cells. In conclusion, STC may be useful as a new cell marker of adrenal glands under physiological and pathological conditions.

Synaptotagmin I Expression in Mast Cells of Normal Human Tissues, Systemic Mast Cell Disease, and a Human Mast Cell Leukemia Cell Line

Synaptotagmin I (STG I) is a Ca2+ sensor and one of the synaptic vesicle proteins that mediate exocytosis. To determine the mechanism of release of large granules from mast cells, we studied by immunohistochemistry the presence of STG I in mast cells in normal human tissues simultaneously with the mast cell markers mast cell tryptase (tryptase) and c-kit. The tumor cells of systemic mast cell disease (SMCD) and a human mast cell leukemia cell line (HMC-1) were also examined. Human mast cells in normal tissues and the tumor cells of SMCD expressed STG I as well as mast cell tryptase (tryptase) and c-kit. STG I mRNA and its products in HMC-1 were examined by RT-PCR analysis and immunocytochemistry, respectively. STG I expression in HMC-1 cells was compared with that in cells stimulated and non-stimulated by phorbol 12-myristate 13-acetate and also with that in NB-1 and PC12 cells, known to express STG I. STG I mRNA was detected in both non-stimulated and stimulated HMC-1 cells and in NB-1 and PC12 cells. STG I immunoreactivity was weaker than NB-1 or PC12 immunoreactivity. However, it increased in the stimulated HMC-1 cells. Mast cells expressed STG I in various states. STG I may mediate exocytosis of large granules in mast cells.

Effects of parathyroid hormone on urinary excretion of N-acetyl-β-D-glucosaminidase in idiopathic hypoparathyroidism and pseudohypoparathyroidism

SummaryN-acetyl-β-D-glucosaminidase(NAG) is a lysosomal enzyme predominantly located in renal proximal tubules. In idiopathic hypoparathyroidism(IHP), 100 Units of human PTH(1–34) increased urinary excretion of NAG from 0.029±0.027 to 0.173±0.035 U/1GF (p<0.05) in two patients before treatment and from 0.025±0.004 to 0.189±0.092U/1GF (p<0.02) in four patients during treatment with active vitamin D3 (1,25(OH)2D3 or 1αOHD3). In pseudohypoparathyroidism(PHP), PTH did not significantly increase the urinary excretion of NAG in one patient with before treatment (0.048 to 0.025 U/1GF) and four patients during treatment with active vitamin D3 (0.018±0.008 to 0.036±0.015 U/1GF). Increase in urinary excretion of NAG after injection of PTH may be a new indicator of renal effect of PTH.

Sigmoidal Curve Shift in Idiopathic Hypoparathyroidism and Pseudohypoparathyroidism

Abstract. The sigmoidal curves plotting serum parathyroid hormone (PTH) against serum Ca in primary hyperparathyroidism and secondary hyperparathyroidism due to renal failure deviate to the right. We previously found the leftward curve shift in PTH-deficient hypoparathyroidism. In the present study, we investigated the curve shift in pseudohypoparathyroidism (PHP) with secondary hyperparathyroidism due to target organ resistance to PTH. In renal failure the sigmoidal curves move to the left after vitamin D3 treatment. We also examined the effect of vitamin D3 on the curve shift in pseudohypoparathyroidism (PHP) and idiopathic hypoparathyroidism (IHP). Before vitamin D3 treatment, the sigmoidal curve deviated to the left in both types of hypoparathyroidism. After vitamin D3 treatment it moved to the right. These results indicate that vitamin D3 and/or extracellular Ca modify the relationship between PTH and Ca dynamics even in hypoparathyroid disorders with decreased or increased maximum serum PTH. Following vitamin D3 treatment, the point plotting baseline serum PTH against baseline serum Ca moved to the right at first in accordance with the rightward shift of the sigmoidal curve and then the point moved downward in PHP or downward in IHP. These changes suggest that vitamin D3 resets PTH secretion at a higher extracellular Ca level at first and then suppresses it in a time-dependent manner. 1,25(OH)2D3 and/or extracellular Ca may be the determinant factors of the sigmoidal curve shift in hypoparathyroid disorders. Mechanisms other than the Ca sensing system error may contribute to the curve shift.

The effect of endogenous parathyroid hormone, exogenous calcitonin, and dibutyryl cyclic AMP on urinary excretion of N-acetyl-β-D-glucosaminidase

Urinary excretion of N-acetyl-β-D-glucosaminidase (NAG) transiently increases after PTH(1–34) infusion in idiopathic hypoparathyroidism (IHP) but this response is impaired in pseudohypoparathyroidism (PHP) type I. We investigated the effects of endogenous PTH, exogenous calcitonin (CT), and dibutyryl cAMP (DBcAMP) on urinary excretion of NAG. Urinary NAG excretion in 14 patients with primary hyperparathyroidism (1oHPT) was more than in normal subjects (P<0.001) and decreased after parathyroidectomy (P<0.01). Urinary NAG excretion increased after the infusion of 1.5 MRC/kg of eel CT in eight normal subjects (P<0.001), two patients with IHP, and a patient with PHP type Ib but not in a patient with PHP type Ia. The increases of urinary NAG excretion by CT and by PTH(1–34) were positively correlated with the increases of urinary cAMP excretion (r=0.752; P<0.001 and r=0.534; P<0.002, respectively). Urinary NAG excretion increased after DBcAMP infusion in five normal subjects (P<0.01), two patients with IHP, and two with PHP type I. The increase of urinary NAG by 6.0 mg/kg of DBcAMP was more than by 2.5 mg/kg of DBcAMP in normal subjects (P<0.01). The increase of urinary NAG by 2.5 mg/kg of DBcAMP in PHP type I was comparable with that by 6.0 mg/kg in normal subjects, suggesting a hyperresponsiveness to DBcAMP in PHP type I. Urinary excretion of NAG is a useful indicator of renal tubular responsiveness to PTH and CT. Cyclic AMP-dependent mechanism is probably involved in PTH and CT-induced increase in urinary excretion of NAG.

Ratio of Baseline Level/Maximum Level of Serum PTH in Pseudohypoparathyroidism and Primary Hyperparathyroidism

The ratio of baseline level/maximum level of serum parathyroid hormone (PTH) is high in PTH-deficient hypoparathyroidism and it decreases after vitamin D3 treatment. There is a reversed sigmoidal relationship between the ratio and baseline serum Ca level. In this study, we further investigated the value of this ratio as a parameter of Ca-dependent changes of serum PTH in hyperparathyroid subjects. As in PTH-deficient hypoparathyroidism, the ratio in pseudohypoparathyroidism was high before vitamin D3 treatment and it decreased after 1,25(OH)2D3 treatment. The increased ratio may reflect the stimulated baseline PTH secretion from parathyroid cells perceiving the decrease in baseline extracellular Ca level. The points plotting the ratio against baseline serum Ca level were on the regression curve deduced from the data in PTH-deficient hypoparathyroidism. This result indicates that the relationship between the ratio and the baseline extracellular Ca level is unrelated to the variation in maximum secretion. The sigmoidal changes of serum PTH in patients with parathyroid adenoma were classified as follows. The first was with the upward and rightward curve shift, the second was only with the rightward curve shift, and the third was with the rightward curve shift, the increased minimum serum PTH, and the increased baseline/maximum ratio of serum PTH. These findings suggest that the decreased suppressibility of PTH secretion and the stimulated baseline secretion may develop without the increase in maximum secretion in some cases with parathyroid adenoma. In conclusion, the ratio of baseline level/maximum level of serum PTH may unfold a new aspect of secretion abnormality of parathyroid glands in several forms of parathyroid disorders.