Two biochemical indices of mouse bone formation are increased, in vivo, in response to calcitonin

In a series of four studies, adult female Swiss-Webster mice were used to measure the effects of salmon calcitonin on two biochemical indices of local and systematic bone formation: (1) skeletal alkaline phosphatase activity--in serum and in extracts of calvaria and tibiae, and (2) calvarial collagenase-digestible protein synthesis--measured, acutely, in vitro. Subcutaneous calcitonin doses ranged from 50 to 400 mU/mouse/day (0.95-18.1 U/kg/day), and treatment schedules were continuous (daily) for 2-14 days, acute, or intermittent (2 days/week for 6 weeks). The effects of calcitonin on these bone formation indices (skeletal alkaline phosphatase and collagenase-digestible protein synthesis) were biphasic with respect to dose and treatment time, being increased in response to short-term, low-dose treatment, but not long-term, continuous treatment. The effects of long-term intermittent calcitonin treatment were dose-dependent increases in skeletal alkaline phosphatase in calvaria and serum (r = 0.948, P less than 0.02, and r = 0.960, P less than 0.01, respectively).

Surface properties of intraocular lens materials and their influence on in vitro cell adhesion

An in vitro model to assess lens epithelial cell adhesion to a variety of intraocular lens materials was developed. Rabbit anterior lens capsules were isolated and cultured in serum-containing medium. Test surfaces included poly(methyl methacrylate), two new silicones (SLM-1/UV, SLM-2/UV), two hydrogels (HEMA, Lidofilcon A), and polytetrafluoroethylene (PTFE). Following the application and culturing of cells on the test surfaces, adherent cells were removed by trypsinization and counted at eight and 24 hours. The material surfaces were characterized by electron spectroscopy for chemical analysis and scanning electron microscopy. The captive bubble technique was also used to assess interfacial free energy. More cells adhered to PMMA than to the other materials tested (P less than .01). The two silicones, HEMA, and PTFE did not differ significantly from each other; Lidofilcon A had the lowest cell adhesion of all materials tested. Cell adhesion results were related to the interfacial free energy of each material. Materials of low (less than 5 ergs/cm2) or high (greater than 40 ergs/cm2) interfacial free energies had lower cell adhesion than materials of intermediate free energies (5 to 40 ergs/cm2) which exhibited the highest cell adhesion.

Skeletal alkaline phosphatase specific activity is an index of the osteoblastic phenotype in subpopulations of the human osteosarcoma cell line SaOS-2

During continuous culture with serial passage, the human osteosarcoma cell line SaOS-2 showed a time-dependent decrease in skeletal alkaline phosphatase (ALP) activity. Because this was indicative of heterogeneity, subpopulations of SaOS-2 cells were isolated from replicate low-density cultures. The subpopulations were less heterogeneous and more stable (with respect to ALP) than the parent population. ALP specific activity in the subpopulations ranged from 0.05 to 2.3 U/mg protein, and cytochemical analyses indicated multiple steady-state levels of ALP activity per cell. The amount of ALP activity in SaOS-2 subpopulations was proportional to collagen production ([3H]proline incorporation into collagenase-digestible protein; r = .84, P less than .005), and to parathyroid hormone (PTH)-linked synthesis of cyclic adenosine monophosphate (cAMP) (r = .88, P less than .01). From these data, we inferred that ALP activity in SaOS-2 cells can provide a useful index of the osteoblastic phenotype, and that ALP activity, collagen production, and PTH-linked adenylate cyclase were coordinately regulated in these osteoblast-like osteosarcoma cells (ie, selection of subpopulations for ALP activity coselected for collagen synthesis and PTH-linked synthesis of cAMP). Further comparative studies showed that micromolar fluoride concentrations stimulated cell proliferation ([3H]thymidine incorporation into DNA) in low-ALP SaOS-2 subpopulations, but not in high-ALP cells (P less than .001), and that this differential sensitivity to fluoride was associated with an inverse correlation between fluoride-sensitive acid phosphatase and ALP activities (r = -.91, P less than .001).

Calcitonin has direct effects on 3[H]-thymidine incorporation and alkaline phosphatase activity in human osteoblast-line cells

Calcitonin had direct and dose-dependent actions on human osteoblast-line cells (in serum-free monolayer culture) to increase cell proliferation and alkaline phosphatase activity/mg cell protein. Salmon calcitonin increased (human osteosarcoma) SaOS-2 cell proliferation, as evidenced by dose-dependent increases in 3[H]-thymidine incorporation into DNA (e.g., 153% of control after 20 h exposure at 0.1 nM, P less than 0.01), and MTT (thyzolyl blue) reduction/deposition (e.g., 161% of control after 72 h exposure at 0.03 nM). Continuous exposure was not required to elicit these proliferative responses. These effects were not unique to salmon calcitonin or to SaOS-2 cells. Similar effects were seen with human calcitonin (but not heat-inactivated human calcitonin) and with (human osteosarcoma) TE-85 cells and human osteoblast-line cells prepared from femoral heads. In addition to effects on cell proliferation, calcitonin also increased alkaline phosphatase-specific activity in SaOS-2 cells (e.g., 180% of control after 72 h of exposure to 0.1 nM salmon calcitonin, P less than .005).

Calcitonin (but not calcitonin gene-related peptide) increases mouse bone cell proliferation in a dose-dependent manner, and increases mouse bone formation, alone and in combination with fluoride

Previous in vitro studies have shown that salmon calcitonin had direct effects to increase parameters associated with embryonic chicken bone formation and to increase mouse and chicken osteoblast-line cell proliferation. The current studies demonstrate increased cell proliferation (i.e., [3H]-thymidine incorporation into DNA and tetrazolium salt reduction/deposition) in the osteoblastic murine cell line MC-3T3-E1 in response to salmon calcitonin (P less than 0.005) and to human calcitonin (P less than 0.005), but not to human calcitonin gene-related peptide. The current studies also show that salmon calcitonin increased several indices of murine bone formation. We found that 72 hours of exposure to salmon calcitonin [at 5 mU/ml-about 0.37 nM; mU/ml = milliunits of calcitonin activity/ml incubation medium (at 4,000 U/mg protein)] increased net 45Ca deposition (121% of control, P less than 0.05), net [3H]-proline incorporation 149% of control, P less than 0.001), and alkaline phosphatase activity (146% of control, P less than 0.01), in neonatal mouse half-calvaria. The calcitonin-dependent increase in alkaline phosphatase activity was not affected by co-incubation with 1 nM parathyroid hormone. Co-incubation with fluoride (which also increased net [3H]-proline incorporation and alkaline phosphatase activity in neonatal mouse half-calvaria, P less than 0.05, for each) enhanced the osteogenic response to low-dose calcitonin, (i.e., co-incubation with fluoride shifted the biphasic calcitonin dose-response curve to a range of lower calcitonin concentrations). The calcitonin-fluoride combinations had proportional effects on net [3H]-proline incorporation and alkaline phosphatase in the treated mouse calvaria (r = 0.78, P less than 0.005).

Alkaline phosphatase activity from human osteosarcoma cell line SaOS-2: an isoenzyme standard for quantifying skeletal alkaline phosphatase activity in serum

Earlier we described a kinetic assay for quantifying skeletal alkaline phosphatase (ALP) isoenzyme activity in serum. The precision of the assay depends on including ALP standards for the skeletal, hepatic, intestinal, and placental isoenzymes. We wondered whether human osteosarcoma cells could provide an efficient alternative to human bone or Pagetic serum as a source of the skeletal ALP standard. ALP activities prepared from five human osteosarcoma cell lines were compared with a bone-derived ALP standard with respect to heat stability and sensitivity to chemical effectors. Two of the cell lines (SaOS-2 and TE-85) contained ALP activities that resembled the bone-derived standard. We selected SaOS-2 cells for additional evaluation (as a potential source of isoenzyme standard), because they contained 40-50 times more ALP activity than did the TE-85 cells. To include the SaOS-2 cell-derived ALP activity in the quantitative isoenzyme assay, we diluted the enzyme in a solution containing heat-inactivated (i.e., ALP-negative) human serum. Surprisingly, this dilution caused a 60-125% increase in maximum enzyme activity. In the quantitative assay of ALP isoenzyme in serum, the SaOS-2 derived ALP was indistinguishable from the serum skeletal ALP standard, with respect to the above criteria and assay variations. Evidently ALP from SaOS-2 cells is suited as a standard for measuring skeletal ALP activity in this assay.

Alkaline phosphatase activity from human osteosarcoma cell line SaOS-2: an isoenzyme standard for quantifying skeletal alkaline phosphatase activity in serum

Earlier we described a kinetic assay for quantifying skeletal alkaline phosphatase (ALP) isoenzyme activity in serum. The precision of the assay depends on including ALP standards for the skeletal, hepatic, intestinal, and placental isoenzymes. We wondered whether human osteosarcoma cells could provide an efficient alternative to human bone or Pagetic serum as a source of the skeletal ALP standard. ALP activities prepared from five human osteosarcoma cell lines were compared with a bone-derived ALP standard with respect to heat stability and sensitivity to chemical effectors. Two of the cell lines (SaOS-2 and TE-85) contained ALP activities that resembled the bone-derived standard. We selected SaOS-2 cells for additional evaluation (as a potential source of isoenzyme standard), because they contained 40-50 times more ALP activity than did the TE-85 cells. To include the SaOS-2 cell-derived ALP activity in the quantitative isoenzyme assay, we diluted the enzyme in a solution containing heat-inactivated (i.e., ALP-negative) human serum. Surprisingly, this dilution caused a 60-125% increase in maximum enzyme activity. In the quantitative assay of ALP isoenzyme in serum, the SaOS-2 derived ALP was indistinguishable from the serum skeletal ALP standard, with respect to the above criteria and assay variations. Evidently ALP from SaOS-2 cells is suited as a standard for measuring skeletal ALP activity in this assay.

The anti-bone-resorptive agent calcitonin also acts in vitro to directly increase bone formation and bone cell proliferation

The studies summarized in this report were intended to determine whether salmon calcitonin had direct effects on bone formation indices in vitro. The results of these investigations demonstrate acute effects of calcitonin on skeletal tissues derived from embryonic chickens to increase calvarial cell proliferation ([3H]thymidine incorporation into DNA) and bone matrix synthesis ([3H]proline incorporation into collagen, as [3H]hydroxyproline) in intact calvaria and tibiae. The effects of calcitonin on [3H]thymidine incorporation were significant at 1 mU/ml (0.08 nM; P less than 0.05), additive with respect to the action(s) of F (calcitonin increased the maximum effect of F, and F increased the effect of low dose calcitonin; P less than 0.01 for each), associated with an increase in total cell protein (r = 0.82; P less than 0.02), and inversely dependent on osteoblastic differentiation (r = -0.96; P less than 0.005). The effects of calcitonin to increase bone matrix synthesis ([3H]hydroxyproline incorporation, 139% and 155% of untreated control values for tibiae and calvaria, respectively; P less than 0.005 for each) were maximal at approximately 5 mU/ml (0.4 nM) and associated with a proportional increase in alkaline phosphatase activity in the bones (r = 0.71; P less than 0.05 for tibiae). These effects of calcitonin were not dependent on continuous exposure. [3H]Thymidine incorporation was increased in calvarial cells 16 h after a 4-h limited (inductive) exposure to calcitonin (at 3 mU/ml; P less than 0.01). [3H]Proline incorporation in embryonic chicken calvaria was also increased during 3 days of limited exposure (i.e. 4 h/day) to 10 mU/ml calcitonin (P less than 0.02). The proliferative action(s) of calcitonin was not unique to chicken osteoblastline cells. Salmon calcitonin also increased [3H]thymidine incorporation in the transformed murine calvarial cell lines MMB and MC-3T3-E1 and in primary cultures of cells prepared from newborn mouse calvaria (P less than 0.05 for each). Furthermore, these effects were observed at calcitonin doses (3-30 mU/ml) that also decreased murine bone resorption (i.e. 45Ca release from prelabeled neonatal mouse calvaria; P less than 0.01).

In vitro evidence that local and systemic skeletal effectors can regulate 3[H]-thymidine incorporation in chick calvarial cell cultures and modulate the stimulatory actions(s) of embryonic chick bone extract

These investigations were intended to determine whether local and systemic skeletal effectors--3'5'-cyclic adenosine monophosphate (cAMP), prostaglandin E2 (PGE2), parathyroid hormone (PTH), 1,25-dihydroxyvitamin D (1,25(OH)2D), calcitonin, and NaF--could regulate 3[H]-thymidine incorporation (i.e., into DNA) in serum-free, monolayer cultures of embryonic chick calvarial cells, and/or modulate the activity of embryonic chick bone extracts to increase 3[H]-thymidine incorporation. In the absence of added bone extract, we found that calcitonin (0.1 U/ml), NaF (100 microM) and low-dose PTH (0.1 nM) stimulated 3[H]-thymidine incorporation, P less than .05 for each; isobutylmethylxanthine (IBMX--1 mM), 1,25OHD (10 nM), and high-dose PTH (10 nM) decreased 3[H]-thymidine incorporation; and PGE2 (1 microM) had no effect. The stimulatory actions of calcitonin, fluoride, and low-dose PTH were inductive, and the inhibitory actions of IBMX and 1,25(OH)2D were acute. PTH had complex time-dependent actions on 3[H]-thymidine incorporation, being inhibitory after 4-8 hours of exposure and stimulatory after 20-24 hours (P less than .001 for each). The effects of calcitonin, fluoride, and low-dose PTH to increase 3[H]-thymidine incorporation were greater in calvarial cell cultures enriched for undifferentiated osteoprogenitor cells than in cultures enriched for differentiated osteoblastlike cells. PTH inhibited 3[H]-thymidine incorporation in the latter (i.e., osteoblastlike) cultures (P less than .005). The inhibitory actions of IBMX and 1,25(OH)2D were independent of cell differentiation. Additional studies further revealed that these local and systemic skeletal effectors could also modulate the activity of embryonic chick bone extracts to increase 3[H]-thymidine incorporation in calvarial cell cultures. We found that calcitonin, fluoride, and low-dose PTH enhanced the effect of the extracts to increase 3[H]-thymidine incorporation (P less than .001 for each). These activations were noncompetitive, indicating (1) mechanistic differences between the stimulatory actions of the effectors and the chick bone extract (i.e., different rate-limiting steps for the effects of each on 3[H]-thymidine incorporation); and (2) that neither calcitonin, fluoride, nor 0.1 nM PTH altered the apparent affinity of the cells for stimulatory activity(s) in the extract. High-dose PTH was a noncompetitive inhibitor with respect to bone extract activity, indicating that the effect of 10 nM PTH to decrease 3[H]-thymidine incorporation was mechanistically distinct from the effect of the bone extract to increase 3[H]-thymidine incorporation.(ABSTRACT TRUNCATED AT 400 WORDS)

Time-dependent changes in bone, placental, intestinal, and hepatic alkaline phosphatase activities in serum during human pregnancy

To measure changes in bone alkaline phosphatase (EC 3.1.3.1) activity in serum as a function of duration of pregnancy, we adapted our existing alkaline phosphatase (ALP) isoenzyme assay (which has been used to measure bone, hepatic, and intestinal ALP activities in serum, in the absence of placental ALP) to allow quantification of individual ALP isoenzyme activities in the presence of placental ALP. The resulting CV for repeat measurements of bone ALP activity in artificial isoenzyme mixtures ranged from 23% for samples in which the bone isoenzyme represented 7% of total ALP activity to 11% for samples in which bone ALP accounted for 48% of total ALP activity. Values for repeat determinations of bone ALP activity in human serum samples (i.e., including samples obtained from pregnant women and from nonpregnant controls) varied by an average of 18%. We find, in initial applications of this method, that (a) the amount of bone ALP activity in serum is increased during pregnancy (P less than .001), and remains increased at six weeks postpartum, in non-lactating women (P less than .001), and (b) bone ALP activity at term was not significantly different in pregnant women with pre-eclampsia, diabetes, premature rupture of membranes, or premature labor, compared with normal pregnancies at term. Our data support the hypothesis that maternal bone formation may be increased during pregnancy.

Time-dependent changes in bone, placental, intestinal, and hepatic alkaline phosphatase activities in serum during human pregnancy

To measure changes in bone alkaline phosphatase (EC 3.1.3.1) activity in serum as a function of duration of pregnancy, we adapted our existing alkaline phosphatase (ALP) isoenzyme assay (which has been used to measure bone, hepatic, and intestinal ALP activities in serum, in the absence of placental ALP) to allow quantification of individual ALP isoenzyme activities in the presence of placental ALP. The resulting CV for repeat measurements of bone ALP activity in artificial isoenzyme mixtures ranged from 23% for samples in which the bone isoenzyme represented 7% of total ALP activity to 11% for samples in which bone ALP accounted for 48% of total ALP activity. Values for repeat determinations of bone ALP activity in human serum samples (i.e., including samples obtained from pregnant women and from nonpregnant controls) varied by an average of 18%. We find, in initial applications of this method, that (a) the amount of bone ALP activity in serum is increased during pregnancy (P less than .001), and remains increased at six weeks postpartum, in non-lactating women (P less than .001), and (b) bone ALP activity at term was not significantly different in pregnant women with pre-eclampsia, diabetes, premature rupture of membranes, or premature labor, compared with normal pregnancies at term. Our data support the hypothesis that maternal bone formation may be increased during pregnancy.

Monofluorophosphate is hydrolyzed by alkaline phosphatase and mimics the actions of NaF on skeletal tissues, in vitro

These studies were intended to assess the osteogenic activity of monofluorophosphate (MFP) in vitro, and to identify the enzyme(s) responsible for MFP hydrolysis-alkaline phosphatase (ALP) and/or acid phosphatase (AcP). ALP and AcP activities were determined by hydrolysis of p-nitrophenylphosphate (PNPP) at pH greater than 8 and pH 5.5, respectively, and MFP hydrolysis was determined, between pH 5.5 and pH 9.0, from measurements of [fluoride ion], using an ion-specific electrode. We found (1) that MFP was an alternative substrate for purified ALP, but not for AcP; (2) that MFPase activity in the embryonic chick resembled ALP, but not AcP, with respect to pH-dependent hydrolysis, sensitivity to effectors (r = 0.98, P less than .001), and tissue distribution (r = 0.96, P less than .001); and (3) that intestinal MFPase activity in the embryonic chick co-purified with ALP activity (r = 0.93, P less than .01) and resembled ALP, but not AcP, in its distribution along the small intestine, being highest in the duodenum and lowest in the distal ileum (r = 0.96, P less than .001). We also found that in vitro exposure to MFP increased (1) the proliferation rate of embryonic chick calvarial cells in serum-free monolayer cultures (i.e., 3[H]-thymidine incorporation into DNA, P less than .001); (2) ALP activity in calvarial cells (P less than .005) and in intact calvaria (P less than .05); and (3) collagen production by intact calvaria (i.e., 3[H]-proline incorporation as 3[H]-hydroxyproline, P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)