Proliferation Of Osteoblast-like Cells Research Articles

Proliferation, differentiation, and protein synthesis of human osteoblast-like cells (MG63) cultured on previously used titanium surfaces.

This study compared osteoblasts proliferation, differentiation, and protein synthesis on new and used titanium (Ti) disks to test the hypothesis that cleaning and resterilization of previously used Ti disks does not alter cell response to a particular surface. Ti disks of varying roughness were prepared by one of five different treatment regimens. Standard tissue culture plastic was used as a control. Human osteoblast-like cells (MG63) were cultured on the Ti disks and cell proliferation, cell differentiation, RNA synthesis and matrix production (collagen and noncollagen protein; proteoglycans) measured. After their first use, the disks were cleaned, resterilized by autoclaving, and MG63 cells cultured on them as before. At confluence, the same parameters were measured and cell behavior on new and used disks compared. When confluent cultures of cells on plastic were compared to those cultured on new Ti surfaces, cell number was reduced on the roughest surfaces and equivalent to plastic on the other surfaces. Cell number was further reduced when disks with the roughest surfaces were re-used; no differences in cell number could be discerned after cleaning and resterilization. Cell proliferation was inversely related to surface roughness and was less than seen on tissue culture plastic. Re-use of the Ti disks resulted in no change in cell proliferation rate. Alkaline phosphatase specific activity in isolated cells was lowest on the rougher surfaces; no differences between new and used disks were observed. Similarly, enzyme activity in the cell layer was decreased in cultures grown on rougher surfaces, with no effect of prior disk use being noted. RNA synthesis was decreased with respect to plastic in cultures on smoother surfaces and increased on rougher surfaces; prior disk use did not alter RNA synthesis. Collagen production by the cells was decreased on smoother surfaces, but was comparable to tissue culture plastic when grown on rougher surfaces. Non-collagen protein production was unaffected by culture surface and whether or not the disk had been previously used. Proteoglycan synthesis by cells was decreased on all surfaces studied and comparable on both new and used disks. The results of this study indicate that Ti implant surfaces are unaffected by cleaning and resterilization, although rougher surfaces may require more extensive cleaning than smoother ones. This suggests the possibility that implants, in the same patient, could be safely reused. In vivo studies in animals, however, need to be performed before clinical application can be considered.

Nitric oxide and bone.

Nitric oxide (NO), a mediator of cardiovascular homeostasis, neurotransmission, and immune function, has recently been found to have important effects in bone. Both constitutive and inducible forms of NO synthase are expressed by bone-derived cells, and cytokines such as interleukin-1 (IL-1), tumor necrosis factor (TNF), and interferon gamma (IFN-gamma), are potent stimulators of NO production. When combined with other cytokines, IFN-gamma markedly induces NO production, which suppresses osteoclast formation and activity of mature osteoclasts. This "superinduction" of NO is largely responsible for the selective inhibitory effect of IFN-gamma on cytokine-induced bone resorption. High concentrations of NO are also inhibitory for cells of the osteoblast lineage, and NO production appears to be partly responsible for the inhibitory effects of cytokines on osteoblast proliferation. At lower concentrations, however, NO has different effects. Moderate induction of NO potentiates bone resorption, and the constitutive production of NO at low concentrations promotes the proliferation of osteoblast-like cells and modulates osteoblast function. NO therefore appears to be an important regulatory molecule in bone with effects on cells of the osteoblast and osteoclast lineage and represents one of the molecules produced by osteoblasts which directly regulate osteoclastic activity. Stimulation of NO production in bone by proinflammatory cytokines raises the possibility that NO may be involved as a mediator of bone disease in conditions associated with cytokine activation, such as rheumatoid arthritis, tumor associated osteolysis, and postmenopausal osteoporosis.

Identification of new drug targets in Mycobacterium avium and Mycobacterium tuberculosis

In this study, novel graphene oxide/chitosan nanocomposite coatings with long term drug-eluting potential are presented. The coatings are fabricated by the facile and reproducible electrophoretic deposition technique. Analysis of the prepared films shows that the graphene oxide nanosheets are exfoliated in the chitosan matrix. Fourier-transform infrared spectrometry reveals polymer attachment to the carboxylic bonds of graphene oxide, providing a strong interaction and exfoliation of the nanolayers. In vitro viability assay by human osteosarcoma cells (MG-63) demonstrates that the nanocomposite films are highly biocompatible up to 30 wt% graphene oxide, but at higher concentrations a slight cytotoxicity is noticed. Alkaline phosphates enzyme assay also reveals that the presence of graphene oxide nanosheets moderately hampers osteogenesis of the cultured cells. It is shown that vancomycin-loaded nanocomposite coatings gradually release the drug macromolecules for relatively long period of time (up to 4 weeks). The electrodeposited films also exhibit a high bactericidal potential against Gram-positive Staphylococcus aureus. Effects of graphene oxide nanosheets on the physicochemical, biological, antimicrobial and drug-eluting properties of electrodeposited chitosan films are presented and discussed. It is shown that the GO/CS films support the initial attachment, proliferation and growth of osteoblast-like cells.

Nonsteroidal progesterone receptor ligands. 2. High-affinity ligands with selectivity for bone cell progesterone receptors.

A novel series of nonsteroidal heterocycles was discovered which display cell-type selective, high-affinity (nanomolar) binding to the progesterone receptors from TE85 osteosarcoma cells but > 1 microM binding affinity to the progesterone receptors from T47D and ZR75 human breast carcinoma cells. Structure-activity relationships were developed for a set of these compounds, and a representative analog 1-(3,4-dichlorobenzoyl)-3-phenyl-1,4,5,6-tetrahydropyridazine++ + (1i, RWJ 25333) was chosen for further evaluation. RWJ 25333 stimulated the in vitro proliferation of human osteoblast-like cells but not human breast cells.

Effects of methotrexate on human osteoblasts in vitro: Modulation by 1,25-dihydroxyvitamin D3

This study was designed to investigate whether methotrexate (MTX), used in the treatment of rheumatoid arthritis (RA), affects proliferation and differentiation of human osteoblasts in culture. The effects of MTX were assessed by analyzing markers of proliferation and differentiation of human trabecular bone-derived osteoblast-like cells cultured in the presence or absence of 1,25-dihydroxyvitamin D3 (1,25[OH]2D3). Treatment of the osteoblastic cells with MTX resulted in a strong dose-dependent inhibition of cell proliferation with half maximal response at a dose of 30 nM. MTX did not interfere with cellular alkaline phosphatase (AP) activity, the number of cells expressing cytochemical AP, or basal osteocalcin production. Addition of 1,25(OH)2D3 to the cultures caused an enhanced AP expression and osteocalcin production coinciding with a decreased osteoblast proliferation. Coincubation of 1,25(OH)2D3 with MTX in doses > or = 100 nM further inhibited osteoblast growth and induced a significant stimulation of AP expression and activity, and production of osteocalcin above the values reached in the 1,25(OH)2D3 cultures. In conclusion, MTX proved to be a potent inhibitor of osteoblast proliferation but did not affect basal osteoblastic phenotypic expression. In the presence of the osteoblast differentiation-promoter, 1,25(OH)2D3, MTX further inhibited cell growth which was associated with enhanced AP activity and osteocalcin production. Thus, MTX may have profound effects on bone metabolism and remodeling by interfering with bone cell turnover.

Effects of growth hormone on phosphocalcium homeostasis and bone metabolism.

In this review the effects of growth hormone (GH) on phosphocalcium homeostasis and bone metabolism are reported. Some in vitro effects of GH on chondrocytes and osteoblasts are discussed too. The main GH effects on phosphocalcium homeostasis are the permissive action on renal 1 alpha-hydroxylase activity by the hypophosphatemic stimulus and the antiphosphaturic effect by the stimulation of the maximum rate of renal tubular reabsorption of phosphate. On bone, GH is able to stimulate bone turnover and to increase bone mass. In addition, GH stimulates type I and type III collagen metabolism. In vitro, GH increases the proliferation of chondrocytes from the human growing cartilage together with the levels of interleukin-6 in the supernatant. The hormone increases also the proliferation of the human osteosarcoma-derived osteoblast-like cells and augments the osteocalcin levels in the supernatant. Thus, GH markedly influences phosphocalcium homeostasis and bone metabolism in childhood and adolescence. In addition, it is possible that GH continues to play a role in bone physiology during adulthood when final height is reached.

Surface Characterization of Titanium Plates with Different Surface Treatments and Cellular Proliferation and Expression of Osteoblast-like Cells in vitro on their Surfaces

Surface Characterization of Titanium Plates with Different Surface Treatments and Cellular Proliferation and Expression of Osteoblast-like Cells in vitro on their Surfaces

Direct effect of calcium channel antagonists on osteoclast function: alterations in bone resorption and intracellular calcium concentrations.

Osteoclasts attach to mineralized surfaces and resorb bone matrix, releasing calcium into the area surrounding the osteoclast. The production of high levels of extracellular calcium increases intracellular calcium concentrations ([Ca2+]i), and bone resorption is decreased. To study this mechanism, the dihydropyridine-sensitive L-type calcium channel antagonists PN 200-110, (-)202-791, and nifedipine were studied for their effects on bone resorption using the disaggregated osteoclast pit assay. Changes in [Ca2+]i after treatment with these compounds were determined with the fluoroprobe fura2. In osteoclast-enriched cultures, significant decreases in bone resorption were noted in the presence of PN 200-110 and (-)202-791. The decrease in bone resorption correlated with an increase in [Ca2+]i. To determine whether the effects of these compounds on osteoclasts were mediated via osteoblasts, proliferation and differentiation of rat osteoblast-like cells (ROS 17/2.8) were examined after the addition of these agents. There were no changes in osteoblast proliferation or differentiation, as determined by [3H]thymidine incorporation and specific activity of alkaline phosphatase, after treatment with these compounds at concentrations that inhibited bone resorption in the disaggregated pit assay. This lack of effect of calcium channel antagonists on osteoblast growth and differentiation at concentrations used to inhibit osteoclast function suggests that the effects of PN 200-110 and (-)202-791 on the osteoclast are not mediated via the osteoblast. In addition, conditioned medium recovered from ROS 17/2.8 cultures treated with PN 200-110 or (-)202-791 had no effect on pit formation compared to the conditioned medium from cell-free cultures. This lack of effect of calcium channel conditioned medium on bone resorption provides additional evidence that PN 200-110 and (-)202-791 are decreasing bone resorption directly by altering osteoclast function, not through osteoblast-osteoclast interactions. The addition of (-)202-791 or PN 200-110 to osteoclasts resulted in a dose-dependent rise in [Ca2+]i. These data suggest that calcium channel antagonists may bind to the calcium channel of the osteoclast and lock it in an open state, leading to increased [Ca2+]i and decreased bone resorption.

Stimulation of interleukin-4 of cell proliferation and mRNA expression of alkaline phosphatase and collagen type I in human osteoblast-like cells of trabecular bone

Interleukin-4 (IL-4) potently inhibits bone resorption by preventing the differentiation of osteoclast precursors to osteoclasts. To elucidate the role of IL-4 in bone formation, we studied the effects of human IL-4 on human osteoblast-like cells obtained from trabecular bone, which showed increased osteocalcin production in response to l,25-(OH) 2D 3 in more than 10 passages. IL-4 stimulated the proliferation of osteoblast-like cells in a concentration-dependent manner, showing the minimal and maximal stimulatory effects at 10 pg/ml and 100–1000 pg/ml, respectively. IL-4 also stimulated the expression of alkaline phosphatase mRNA (1.7-fold) and the enzyme activity to the same extent at 10–100 pg/ml. Furthermore, IL-4 stimulated collagen type I mRNA expression in human osteoblast-like cells. The cytokine did not affect osteocalcin production in a short culture period (3 days). These in vitro findings suggest that IL-4, a bone-resorption-inhibitory cytokine produced by activated T cells in bone marrow, may exert an anabolic effect on osteoblast-like cells in trabecular bone through a paracrine mechanism.

Fluoride increases net 45Ca uptake by SaOS-2 cells: The effect is phosphate dependent.

Previous in vitro studies have shown that the effect of fluoride to increase avian osteoblast-like cell proliferation was dependent on the phosphate concentration. In vitro studies have further revealed that fluoride could also have direct effects on osteoblast-like cells to increase phosphate uptake and transiently increase cytosolic calcium. The current studies were intended to determine whether fluoride could increase net 45Ca uptake by human osteosarcoma (SaOS-2) cells and, if so, whether those effects would also be phosphate dependent. The results of these studies indicate that fluoride increased net 45Ca uptake by SaOS-2 cells, with biphasic dose and time dependencies. After 30 minutes of exposure, net 45Ca uptake was increased to a greater extent by 50 microM fluoride (217 +/- 16% of control, P < 0.001) than by 200 microM fluoride; and the stimulatory effect of 100 microM fluoride on net 45Ca uptake was greater after 20 minutes (187 +/- 22% of control, P < 0.001) than after 60 minutes (122 +/- 7% of control, P < 0.05). These effects of fluoride to increase net 45Ca uptake were dependent on the phosphate concentration in the medium. Fluoride had no effect on net 45Ca uptake in medium containing 0.4 mM phosphate, but increased net 45Ca uptake in medium containing 1.2 or 2.0 mM phosphate (P < 0.005). As the phosphate concentration was increased, the biphasic fluoride dose-response curve was shifted to a lower range of fluoride concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Mitogenic responsiveness of human bone cells in vitro to hormones and growth factors decreases with age.

Bone loss with aging may at least in part be due to inadequate bone formation. In this study, we examined whether the proliferation of osteoblast-like cells in vitro in response to local and systemic factors might be attenuated with age. A total of 36 cultures of osteoblast-like cells were obtained from outgrowths of human trabecular bone. Parathyroid hormone, growth hormone, calcitonin, transforming growth factor beta, insulin-like growth factor I, and platelet-derived growth factor BB dose dependently increased DNA synthesis in all cultures. Increases in DNA synthesis with each of these factors were significantly negatively correlated with donor age in cultures obtained from the iliac crest bone of 50- to 70-year-old women. Cells from 61- to 70-year-old donors required approximately 10-fold higher concentrations of growth factors and hormones to yield comparable increases in DNA synthesis than cells from 51- to 60-year-old donors. A significant negative correlation between age and mitogenic responsiveness to platelet-derived growth factor and growth hormone, but not toward the other factors, was also observed in cultures from the femoral head trabecular bone of 60- to 90-year-old women. Our findings suggest that bone loss with aging may be partially due to a decreased capacity of osteoblasts to proliferate in response to systemic or locally released osteotropic factors.

Growth hormone stimulates proliferation and differentiation of normal human osteoblast-like cells in vitro.

In this study we investigated the direct, short-term effects of human growth hormone (hGH) on the biology of normal adult human osteoblast-like (hOB) cells cultured from trabecular bone explants. In Subconfluent cultures, hGH stimulated hOB proliferation in a dose-dependent fashion (P < 0.001, n = 15) with half-maximal effects at a concentration of 10 ng/ml. These mitogenic effects were detectable within 24 hours as shown by bromodeoxyuridine labeling. In confluent cultures containing mainly quiescent cells, hGH increased levels of alkaline phosphatase (P < 0.05, n = 10) and to a lesser degree levels of procollagen type I carboxyterminal propeptide (PICP) (P = 0.07, n = 9). Effects on osteocalcin (bone GLa protein, BGP) levels were highly variable among different cell strains and only 7 of 10 cell strains showed a stimulatory response (P = 0.16). We also studied the effects of hGH on osteoblastic production of insulin-like growth factor I (IGF-I) and IGF-II as well as the production of GH-dependent, insulin-like growth factor binding protein 3 (IGFBP-3). Under basal conditions, human osteoblasts produced IGF-II and IGFBP-3 in the conditioned medium. When stimulated with hGH, minor insignificant increase in both IGF-II and IGFBP-3 (125% and 126% of control, respectively) were detectable. No IGF-I was detectable in the conditioned medium under basal conditions or after stimulation with hGH. In conclusion, the results obtained in this study suggest that GH exerts direct anabolic effects on human osteoblasts.

Osteoblast-like cell (MC3T3-E1) proliferation on bioerodible polymers: an approach towards the development of a bone-bioerodible polymer composite material

An osteogenic cell line (MC3T3-E1) was used to study the potential of bioerodible polymers and ceramics to support osteoblast growth for a proposed bone-polymer composite for skeletal tissue repair. MC3T3-E1 cells were seeded on to 50:50 poly(lactide-co-glycolide), hydroxyapatite, 50:50 hydroxyapatite/poly(lactide-co-glycolide), and the poly(anhydride), poly(bis(p-carboxyphenoxy) propane surfaces. Cell attachment and growth on these surfaces was found to be highest on poly(lactide-co-glycolide), the least on hydroxyapatite and hydroxyapatite/ poly(lactide-co-glycolide) combinations gave intermediate values. The order of adhesion and growth of MC3T3-E1 cells on the polymer and ceramic systems was poly(lactide-co-glycolide) is greater than hydroxyapatite/poly(lactide-co-glycolide) which is greater than hydroxyapatite. Negligible growth was found on poly(bis( p-carboxyphenoxy) propane. High alkaline phosphatase activity for the cells grown on poly(lactide-co-glycolide) and hydroxyapatite/poly(lactide-co-glycolide) confirmed retention of the osteoblast phenotype. This in vitro evaluation suggests that poly(lactide-co-glycolide) and hydroxyapatite/poly(lactide-co-glycolide) combinations may be candidate biomaterials for the construction of a cell-polymer matrix for skeletal tissue regeneration.

Cytological and ultrastructural investigation on osteoblastic and preosteoclastic cells grown in vitro in the presence of ipriflavone: Preliminary results

The effects of ipriflavone on bone cells were studied in vitro on pre-osteoclastic (FLG 29.1) and osteoblast-like (Saos-2) cells grown for 48 h either separately or in co-cultures, with or without the addition of PTH. Histological, ultrastructural and histochemical (TRAP-activity demonstration) methods were used. The main results show that ipriflavone reduces replication of FLG 29.1 cells and inhibits TRAP production by these cells both in controls and in co-cultures treated with PTH. Moreover, it has a moderate stimulatory effect on proliferation of osteoblast-like cells and reduces the PTH-induced degenerative changes of Saos-2 cells. These results suggest that the inhibitory effect of ipriflavone on FLG 29.1 cells might be indirect and might be mediated by the osteoblast-like cells.

Human platelet factor 4 is a direct inhibitor of human osteoblast-like osteosarcoma cell growth

The effect of purified human platelet factor 4, a platelet alpha-granule protein, on the growth of the human osteoblastic osteosarcoma cell lines Saos-2 and G-292 was investigated. Platelet factor 4 (20 ng/ml to 2 micrograms/ml) caused a significant, dose-dependent inhibition of human osteoblast-like osteosarcoma cell proliferation. Platelet factor 4 exerted its inhibitory effect under all growth conditions tested: serum-free, serum-stimulated and thrombin-stimulated. The platelet factor 4-induced cell inhibition was not associated with a cytotoxic effect on the cells (assessed by lactate dehydrogenase release). The inhibitory effect of platelet factor 4 was not affected by the presence of indomethacin in the cultures, indicating that the effect was prostaglandin-independent. These results suggest that platelet factor 4 has direct antitumor effects and that it may be important in pathological and physiological processes of bone.

Stimulatory effects of estrogen and progesterone on proliferation and differentiation of normal human osteoblast-like cells in vitro

Here we report that osteoblast-like cells derived from female and male adult human trabecular bone are able to directly respond to 17 beta-estradiol (E2) and progesterone (P). In short-term (1 day) cultures using serum-free and phenol red-free medium, both steroid hormones were found to stimulate DNA synthesis and growth of the human osteoblast-like cells. P was more potent in stimulating osteoblast growth compared to E2. On the other hand, E2 showed a stronger differentiation-inducing effect as determined by analysis of the number of cells displaying cytochemical alkaline phosphatase (AP) activity, a marker for the mature osteoblast phenotype. Combination of E2 and P resulted in a further increase in DNA synthesis, but did not further affect the number of cells expressing AP activity. In conclusion, female sex steroids may be involved in regulating bone mass in human adults via a direct anabolic action on the bone forming cells.

Proliferative effect of PGD 2 on osteoblast-like cells; Independent activation of pertussis toxin-sensitive GTP-binding protein from PGE 2 or PGF 2α

PGD 2 stimulated DNA synthesis and decreased alkaline phosphatase activity dose-dependently between 10 nM and 10 μM in osteoblast-like MC3T3-E1 cells. PGD 2 had little effect on cAMP production, but caused very rapid enhancement of phosphoinositide (PI) hydrolysis dose-dependently between 10 nM and 10 μM. The formation of inositol trisphosphate (IP 3) induced by PGD 2 reached the peak within 1 min and decreased thereafter, which is more rapid than that induced by PGE 2 or PGF 2α and both PGE 2 and PGF 2α affected PGD 2-induced IP 3 formation additively. Pertussis toxin (PTX) inhibited both PGD 2-induced formation of inositol phosphates and DNA synthesis. The degree of these PTX (1 μg/ml)-induced inhibitions was similar. In addition, neomycin, a phospholipase C inhibitor, inhibited PGD 2-induced DNA synthesis as well as the formation of IP 3, and the patterns of both inhibitions were similar. In the cell membranes, PTX-catalyzed ADP-ribosylation of a 40-kDa protein was significantly attenuated by pretreatment of PGD 2. Time course of the attenuation of PTX-catalyzed ADP-ribosylation by PGD 2 was apparently different from that by PGE 2 or PGF 2α. These results indicate that PGD 2 activates PTX-sensitive GTP-binding protein independently from PGE 2 or PGF 2α and stimulates PI hydrolysis resulting in proliferation of osteoblast-like cells.

Bone blood flow and in vitro proliferation of bone marrow and trabecular bone osteoblast-like cells in ovariectomized rats.

Ovariectomy in the rat induces a rapid osteopenia associated with an elevated bone turnover. One hundred and twenty-day-old rats were ovariectomized (OVX) or sham-operated (n = 6-8 per group and per time period studied). 45Ca accretion rate and bone blood flow (microspheres trapping technique) in the femurs were determined at 28, 42, 84, and 119 days after ovariectomy. Both parameters were markedly increased by 84 days and subsided thereafter. At the 42nd day, when bone turnover was maximal, bone marrow and trabecular bone cultures were obtained from sham-operated and ovariectomized animals (n = 10/group). Proliferation rate of bone marrow cells and trabecular osteoblast-like cells estimated by fibroblast colony-forming units (FCFU) efficiency and cell counting was markedly increased in primary and secondary cultures in ovariectomy. These data fitted well with the enhanced number of osteoblasts observed in situ in the long bone metaphyses of estrogen-depleted animals. As estrogens were shown in the literature to inhibit proliferation of the red cell line and of other hemopoietic lines, it is possible that estrogens, through a general mechanism, inhibit hemopoietic and stromal lines and also the proliferation of bone marrow-derived trabecular bone cells.

Myeloma affects both the growth and function of human osteoblast-like cells

Myeloma behaves differently to other osteolytic tumours which metastasize to bone, in that the latter usually provoke reactive bone formation in the host bone. A previous study showed that a myeloma cell line (GM1500) secreted an osteoblast-inhibiting factor(s). The present study was undertaken to determine whether other myeloma cells also secreted a factor(s) which inhibited both cell proliferation and DNA synthesis of osteoblast-like cells and whether the myeloma also affected the function of osteoblasts. The results showed that a second cell line (Karpas 707) as well as myeloma tissue taken from two patients had a similar effect. The myeloma cells did not affect total collagen or protein synthesis, and did not affect the overall degree of mineralization. A biphasic effect was seen on alkaline phosphatase activity. Thus, although the proliferation of the pre-osteoblast was affected, the synthetic functions of the osteoblasts were not.

Effect of ipriflavone and estrogen on the differentiation and proliferation of osteogenic cells.

The effect of ipriflavone (IP) on the proliferation and differentiation of rat osteoblast-like (ROB) cells and human periodontal ligament fibroblasts (HPLF) was studied in the presence and absence of estrogen. ROB cells were isolated from newborn rat calvaria by sequential collagenase digestion and HPLF from the outgrowth of human periodontal ligament in culture. The alkaline phosphatase (ALP) activity, employed as a marker of bone cell differentiation, was significantly enhanced by IP in both cell types; however, the concentration at which IP had a maximal effect was lower in ROB cells than in HPLF (10(-10) versus 10(-7) M, respectively). Cell proliferation judged by DNA content was either constant (ROB cells) or slightly increased (HPLF) by IP up to 10(-10) M, and decreased significantly above that concentration. In addition, the dose-dependent effect of estrogen on the growth and differentiation of each cell type in the presence and absence of IP was also tested. At the concentrations of IP which showed maximum effects in the induction of ALP, 10(-10) M for ROB cells and 10(-7) M for HPLF, IP inhibited DNA increase in an estrogen-independent manner. Estradiol (10(-11)-10(-9) M) itself increased the growth rate of both cell types significantly in a dose-dependent manner. Regardless of the concentrations of estradiol tested, ALP activities of both ROB cells and HPLF were elevated by the addition of IP. The ratio of ALP in the presence and absence of IP was similar over the range of estradiol concentrations tested.(ABSTRACT TRUNCATED AT 250 WORDS)