1,25(OH)2D3 and calcipotriol (MC903) have similar effects on the induction of osteoclast-like cell formation in human bone marrow cultures

Reduced osteoclastogenesis and RANKL expression in marrow from women taking alendronate

Alendronate (AL) is commonly used for the prevention and treatment of osteoporotic fractures. Little is known about the effects of AL administration on osteoclast differentiation from human marrow progenitor cells. We used marrow discarded during orthopedic surgery to test the hypothesis that cultures of bone marrow-derived stem cells (BMCs) from subjects receiving AL (+AL) may differ from control subjects with respect to in vitro osteoclast differentiation and regulatory factors. The number of osteoclasts generated in BMC cultures from control subjects was 4.7-fold greater than that from +AL subjects (P = 0.015). RANKL expression in +AL BMCs was 57% of that in controls (P = 0.001), and OPG expression in +AL BMCs was greater than in controls (153%, P = 0.01). The mean RANKL/OPG ratio in BMCs was 0.65 ± 0.35 for +AL specimens and 1.28 ± 0.53 for controls (P = 0.031). In addition, we assessed the direct effect of AL on expression of RANKL and OPG in marrow stromal cells isolated from nine control women. Treatment with AL downregulated RANKL expression and upregulated OPG expression, with an average 50% decrease in RANKL/OPG ratio at 10(-7) M (P = 0.004). These results show that osteoclast differentiation is dysregulated in marrow isolated from +AL subjects. Furthermore, AL may inhibit human osteoclastogenesis by affecting the key regulatory genes in marrow cells.

Differentiation of heterogeneous phenotypes in human osteoblast cultures in response to 1,25-dihydroxyvitamin D3

1,25(OH)2D3 (1,25-dihydroxyvitamin D3) inhibits the cell proliferation of human osteoblast-like cell cultures, but stimulates the synthesis of two of the phenotypic markers of the osteoblast, alkaline phosphatase and osteocalcin. It is not known whether all cells which synthesize alkaline phosphatase also synthesize osteocalcin in response to 1,25(OH)2D3. In this study we addressed this question by examining the response of human osteoblast-like cell cultures to 1,25(OH)2D3, using concurrent histochemical and immunochemical staining for alkaline phosphatase and osteocalcin, respectively. The cells were grown in the presence or absence of 1,25(OH)2D3 (10(-9) M) for 48 h. Co-localisation of osteocalcin and alkaline phosphatase in osteoblast-like cell cultures showed that not all cells which synthesize osteocalcin (about 9%) in response to 1,25(OH)2D3 synthesize alkaline phosphatase (about 24%) and vice versa. There was also a proportion of osteoblast-like cells which produce both osteocalcin and alkaline phosphatase simultaneously (about 12%). These findings suggest that during differentiation of bone-derived cells in cultures, in response to 1,25(OH)2D3, heterogeneous phenotypes with respect to expression of alkaline phosphatase and osteocalcin appear.

Phorbol ester-like action of staurosporine on the cAMP response to prostaglandin E2 in two macrophage-like cell lines at distinct differentiation stages

The purpose of this study is to investigate the involvement of protein kinase C (PKC) in prostaglandin E2 (PGE2)-stimulated cAMP production of two macrophage-like cell lines (G3 and XC). XC cells are thought to be placed at a more differentiated stage than G3 cells [Orikasa et al. (1991) Cell Immunol. 132, 350-365]. In RPMI 1640 containing 10% (v/v) heat-inactivated foetal calf serum (FCS), in which the cAMP response of both cells to PGE2 increased with duration of culture, XC cells showed greater response than G3 cells at 2 days of culture. In alpha-minimum essential medium (alpha-MEM) containing 20% (v/v) heat-inactivated horse serum (HS), the cAMP response of both cells was apparently greater than that in RPMI 1640 containing 10% (v/v) FCS. These cells increased cAMP production also in response to PGE1 and PGF2 alpha, and the order of potency in increase was PGE1 > PGE2 >> PGF2 alpha. Interestingly, a short-term (20 min) treatment with phorbol 12-myristate 13-acetate (PMA), a direct activator of PKC or staurosporine, a relatively specific inhibitor of PKC, augmented the PGE2-stimulated cAMP production in these cells cultured in alpha-MEM containing 20% (v/v) HS. However, a long-term (24 h) treatment with these compounds did not alter the cAMP response. In G3 cells, PMA appeared more potent than staurosporine in terms of augmentation, whereas in XC cells, the former appeared less potent than the latter.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of synthetic vitamin D analogues on breast cancer cell proliferation in vivo and in vitro

Calcipotriol (MC903) is a novel vitamin D analogue which effects cellular differentiation and proliferation in vitro and has reduced effects on calcium metabolism in vivo. In the present study its in vitro activity was evaluated using the MCF-7 breast cancer cell line, and its effects on calcium metabolism and mammary tumour growth were measured in vivo in adult female rats. Calcipotriol was compared to the natural metabolite of vitamin D3, 1 alpha,25-dihydroxycholecalciferol [1,25(OH)2D3] and its synthetic analogue 1 alpha hydroxycholecalciferol [1 alpha(OH)D3]. Both calcipotriol and 1,25(OH)2D3 produced significant inhibition of MCF-7 cell proliferation at a concentration of 5 x 10(-11) M. Intraperitoneal administration of calcipotriol to normal female rats showed that the analogue was 100-200 times less active than 1,25(OH)2D3 in raising serum calcium concentration and urinary calcium excretion. Anti-tumour activity of the vitamin D analogues was investigated in vivo using the nitrosomethylurea-induced rat mammary tumor model. Rats, maintained on a low calcium diet, were treated with 1 alpha(OH)D3 (0.25 and 1.25 micrograms/kg). Both doses produced a response rate of 25% but hypercalcaemia developed. Treatment with calcipotriol (50 micrograms/kg) of rats maintained on a normal laboratory diet caused inhibition of tumour progression (response rate 17%) without the development of severe hypercalcaemia. This study supports the concept that vitamin D derivatives may inhibit breast cancer cell proliferation in vivo.

Vitamin D analogues and psoriasis

Topical vitamin D analogues offer a new, effective, more convenient and generally well-tolerated option for the treatment of psoriasis. Only psoriasis vulgaris has been intensively studied, but other forms of the disease may also respond. Both calcitriol and calcipotriol have been shown to be effective in numerous clinical trials, and the latter has compared well with betamethasone valerate and short-contact dithranol in controlled studies. Their mechanism of action is not yet fully understood and may prove complex. The most important effect may be a direct regulation of keratinocyte proliferation and differentiation. However, these compounds also have potent immunological properties, and may act by inhibition of cytokine production by keratinocytes or lymphocytes. Topical application of vitamin D analogues appears generally to be remarkably safe, but hypercalcaemia and hypercalciuria may develop if large quantities are used.

Actions of calcipotriol (MC 903), a novel vitamin D3 analog, on human bone-derived cells: comparison with 1,25-dihydroxyvitamin D3

The actions of a novel vitamin D3 analog calcipotriol (MC 903), on human bone-derived cells were compared to those of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. Both calcipotriol and 1,25-(OH)2D3 inhibited the proliferation of human osteoblast-like cells in a dose-dependent manner (10(-10)-10(-6) M), an effect observed at different cell densities. Lower concentrations of either agent exerted no marked effect on the growth of the cells compared to untreated cultures. Calcipotriol and 1,25-(OH)2D3 were equipotent in stimulating the activity of alkaline phosphatase and the synthesis of osteocalcin in human osteoblast-like cells. The stimulation of alkaline phosphatase activity and osteocalcin synthesis by both compounds was evident by 24 h and was increased progressively up to 96 h in a dose-dependent manner over the concentration range of 10(-10)-10(-6) M. The increment in both proteins was dependent on cell density and was attenuated at higher cell densities. In contrast to these actions, neither calcipotriol nor 1,25-(OH)2D3 (10(-14)-10(-6) M) affected the synthesis of prostaglandin E2. These studies indicate that calcipotriol and 1,25-(OH)2D3 exhibit a similar spectrum of activity on human osteoblast-like cells in vitro.

MC903, an analogue of 1,25-dihydroxyvitamin D3, increases the synthesis of nerve growth factor

The effect of MC903, an analogue of 1,25-dihydroxyvitamin D3, on the expression of the nerve growth factor (NGF) gene has been studied in L cells. MC903 induces an increase in both NGF mRNA and protein with a time course similar to that obtained with 1,25-dihydroxyvitamin D3. This finding points to the potential importance of 1,25-dihydroxyvitamin D3 derivatives in the treatment of NGF-sensitive disorders.

1,25(OH)2D3 induces differentiation of osteoclast-like cells from human bone marrow cultures

Multinucleated cells were generated from human bone marrow cultured in the presence of 10(-6)M 1,25(OH)2D3 and 10(-6)M all-trans-retinoic acid for 3-4 weeks. These multinucleated cells have the phenotypic and functional characteristics of osteoclasts as judged by (a) immunostaining with osteoclast specific monoclonal antibodies 13C2 and 23C6 (b) expression of tartrate resistant acid phosphatase, an enzyme marker of osteoclast differentiation; and (c) the ability to resorb bone in vitro. The multinucleated cells appeared to form by fusion of large mononuclear cells. The monoclonal antibodies 13C2 and 23C6 stained 60-90% of the multinucleated cells, and 40-60% of the large mononuclear cells. Tartrate resistant acid phosphatase activity was expressed by 80-95% of the multinucleated cells and 60-80% of the large mononuclear cells. Scanning electron microscopy of bone wafers co-incubated with the multinucleated cells, for 7 days, revealed resorption pits. These findings suggest that in the presence of 1,25(OH)2D3 the marrow cells differentiated into multinucleated and large mononucleated cells in which a proportion of them expressed osteoclast phenotype and resorbed bone.