Biomedical subjects

Shizu Suzuki

Publications and source records attributed to Shizu Suzuki.

3 recordsLinked to original sources

PubMed2003

Aromatase in bone: roles of Vitamin D3 and androgens.

We have mainly focused on the regulatory mechanism of cytochrome P450 aromatize in bone cells. Our previous study demonstrated a strong positive correlation of serum dehydroepiandrosterone sulfate (DHEA-S) and estrone (E1) with BMD in postmenopausal women but no correlation between serum estradiol (E2) and BMD in the same group. In addition, administration of DHEA to ovariectomized rat significantly increased BMD. These in vivo findings strongly suggested that circulating adrenal androgen may be converted to estrogen in osteoblast and may contribute to BMD maintenance. Actually, in cultured human osteoblast cells, DHEA was found to convert to androstenedione by 3beta-hydroxysteroid dehydrogenase (3beta-HSD) activity and then androstenedione to estrone through the apparent aromatase activity. The aromatase activity in cultured human osteoblast cells was significantly increased by dexamethasone (DEX). Interestingly, DEX and 1alpha,25-dihydroxyvitamin D3 (VD3) synergistically enhanced aromatase activity as well as P450arom mRNA expression. A little stronger induction of aromatase activity by DEX and VD3 was observed in cultured human fibroblasts. The increase of the aromatase activity by DEX and VD3 was accompanied with the increase of luciferase activity of fibroblast cells transfected with Exon 1b-promoter-luciferase construct, but not of osteoblasts transfected with the same construct, suggesting a different regulatory mechanism of aromatase by DEX and 1alpha,25-dihydroxyvitamin D3 (VD3) between these two cells despite the same promotor usage. In human bone cells, intracrine mechanism through aromatase activity, together with a positive regulation of aromatase activity by glucocorticoid and VD3, may contribute to the local production of estrogens, thus leading to protective effect against osteoporosis especially after menopause. The effect of sex steroids (estrogen versus testosterone) in bone remodeling was also briefly reviewed based on several recent findings in this field.

Androgens↗

PubMed2003

[DHEA and bone metabolism].

A strong positive correlation of serum dehydroepiandrosterone sulfate (DHEA-S) and estrone (E1) with bone mineral density (BMD) in postmenopausal women but no correlation between serum estradiol (E2) and BMD in the same group suggest that circulating adrenal androgen may be converted to estrogen in peripheral tissues including osteoblast and may contribute to BMD maintenance. Actually, in cultured human osteoblast cells, DHEA can be converted to androstenedione and then androstenedione to estrone through the apparent aromatase activity. In human bone cells, intracrine mechanism through aromatase activity may contribute to the local production of estrogens, thus leading to protective effect against osteoporosis especially after menopause.

English Abstract↗

PubMed2002

Dehydroepiandrosterone (DHEA) as a possible source for estrogen formation in bone cells: correlation between bone mineral density and serum DHEA-sulfate concentration in postmenopausal women, and the presence of aromatase to be enhanced by 1,25-dihydroxyvitamin D3 in human osteoblasts.

A significant positive correlation between bone mineral density (BMD) and serum dehydroepiandrosterone sulfate (DHEA-S) was found in 120 postmenopausal women (51-99 years old) but no correlation was seen between BMD and serum estradiol. In subset analysis, strong positive correlation of serum DHEA-S and estrone with BMD was observed in postmenopausal women aged less than 69 years old. To study a possible role of DHEA-S in preventing osteoporosis, we characterized aromatase activity converting androgens to estrogens in human osteoblasts, because postmenopausal women maintain considerable levels of adrenal androgens. Glucocorticoids at 10(-9) to 10(-7) M induced transiently the expression of and the enzymatic activity of aromatase cytochrome P450 (P450AROM) in primary cultured osteoblasts. 1,25-Dihydroxyvitamin D3 (1,25-(OH)(2)D(3)) alone did not induce the aromatase activity, but enhanced and maintained the glucocorticoid-induced P450AROM gene expression. Analysis of the activity of P450AROM gene 1b (I.4) promoter, which is used dominantly in human osteoblasts, indicated that the region from -888 bp to -500 bp, which does not contain a typical vitamin D responsive element, is responsible for the enhancing effect of 1,25-(OH)(2)D(3). These results may suggest that adrenal androgen, DHEA, is converted to estrone in osteoblast by P450AROM, which is positively regulated by glucocorticoid and 1,25-(OH)(2)D(3), and is important in maintaining BMD in the sixth to the seventh decade, after menopause.

24,25-Dihydroxyvitamin D 3↗