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Biomedical subjects

D J Baylink

Publications and source records attributed to D J Baylink.

At least 91 records · Page 5Linked to original sources
PubMed1998

Alkaline phosphatase levels and osteoprogenitor cell numbers suggest bone formation may contribute to peak bone density differences between two inbred strains of mice.

Previous studies have shown that C3H/HeJ (C3H) mice have higher peak bone density than C57BL/6J (B6) mice, at least in part because of differences in rates of bone resorption. The current studies were intended to examine the alternative, additional hypothesis that the greater bone density in C3H mice might also be a consequence of increased bone formation. To that end, we measured two presumptive, indirect indices of bone formation and osteoblast number in these inbred strains of mice: alkaline phosphatase (ALP) activity in serum, bones, and bone cells; and the number of ALP-positive colony-forming units (CFU) in bone marrow stromal cell cultures. We found that C3H mice had higher serum levels of ALP activity than B6 mice at 6 (118 vs. 100 U/L, p < 0.03) and 32 weeks of age (22.2 vs. 17.2 U/L, p < 0.001). Tibiae from C3H mice also contained higher levels of ALP activity than tibiae from B6 mice at 6 (417 vs. 254 mU/mg protein, p < 0.02) and 14 weeks of age (132 vs. 79 mU/mg protein, p < 0.001), as did monolayer cultures of bone-derived cells from explants of 7.5-week-old C3H calvariae and femora (8.2 times more, p < 0.02, and 4.6 times more, p < 0.001, respectively). Monolayer cell cultures prepared by collagenase digestion of calvariae from newborn and 6-week-old mice also showed similar strain-dependent differences in ALP-specific activity (p < 0.001 for each). Our studies also showed more ALP-positive CFU in bone marrow stromal cell cultures from 8-week-old C3H mice, compared with B6 mice (72.3 vs. 26.1 ALP-positive CFU/culture dish, p < 0.001). A similar result was seen for ALP-positive CFU production at 6 and 14 weeks of age, and the difference was greatest for the CFU that contained the greatest numbers of ALP-positive cells. Because skeletal ALP activity is a product of osteoblasts and has been shown to correlate with rates of bone formation, and because the number of ALP-positive CFU is believed to reflect the number of osteoprogenitor cells, the current data are consistent with the general hypothesis that bone formation may be greater in C3H than B6 mice because of a difference in osteoblast number. Our data further suggest that peak bone density may be greater in C3H mice than B6 mice due to a combination of decreased bone resorption and increased bone formation.

Alkaline Phosphatase↗
PubMed1998

Effects of calcium depletion and repletion on serum insulin-like growth factor I and binding protein levels in weanling rats.

Previous studies in a weanling rat model indicated that dietary calcium depletion not only stimulated osteoclastic resorption but also inhibited bone formation. The present study sought to test whether the depletion-associated inhibition of bone formation is related to a reduction in serum insulin-like growth factor-I (IGF-I) and/or an increase in its binding proteins (IGFBPs). Twenty male weanling rats were divided into two weight-matched groups. The study group was subjected to a semisynthetic diet deficient in calcium (0.02% calcium) for 28 days, while the control group was pair-weighed on the same diet but containing 0.62% calcium. After the depletion phase, all rats were fed the same calcium-containing diet for an additional 14 days. Serum samples were obtained from each animal on a weekly basis and assayed for IGF-I and IGFBPs. During depletion, there was no statistically significant difference in serum IGF-I level between the study group and the control group. In contrast, the study group showed a statistically significant increase in several serum IGFBPs with apparent molecular size of 30-38 kD (IGFBP-3), 26-28 kD (IGFBP-1, -2, -5, and/or -6), and 24-25 kD (IGFBP-4), respectively, compared to the control group. There was no difference in nutritional intakes between the two groups of rats during depletion. During repletion, there was also no significant difference in serum IGF-I level between the control and study group. However, during the first 7 days of repletion, serum IGFBP-3 and the 26-28 kD IGFBP of the study group was significantly less than those of the control group, which then returned to the control level after 2 weeks of repletion. In summary: (1) calcium depletion in weanling rats increased several serum IGFBPs without an effect on IGF-I; and (2) calcium repletion induced an acute reduction in serum IGFBP-3. In conclusion, these findings represent the first evidence that the depletion-related inhibition of bone formation in the rat may be associated with an increase in several serum IGFBPs, which may act to inhibit the osteogenic actions of IGFs.

Animals↗
PubMed1998

Effects of short-term calcium depletion and repletion on biochemical markers of bone turnover in young adult women.

The skeletal responses to calcium depletion and repletion in rodents have been well characterized, but those in humans are poorly understood. The present study sought to evaluate the effects of short term dietary calcium depletion and repletion on biochemical markers of bone turnover in 15 young Caucasian women (age, 21-30 yr). The study contained 3 phases: 1) 5 days of a regular diet containing more than 800 mg/day calcium to establish baseline values (baseline phase), 2) 22 days of a restricted diet containing less than 300 mg/day calcium (depletion phase), and 3) 7 days of a normal diet containing more than 800 mg/day calcium (repletion phase). Serum and urine samples were obtained from each subject during the baseline phase; on the first, second, and last days of the depletion phase; and on the third and last days of the repletion phase. Serum levels of calcium, PTH, 1,25-dihydroxyvitamin D3, osteocalcin, and C-terminal type I procollagen peptide (PICP) and urinary levels of calcium and deoxypyridinoline were determined. Serum and urinary calcium levels were significantly reduced, and serum PTH and 1,25-dihydroxyvitamin D3 levels were markedly increased during depletion. These changes were completely reversed after 1 week of repletion. Depletion also rapidly and significantly increased the urinary deoxypyridinoline level, indicating increased bone resorption. The increase also returned rapidly to baseline upon repletion. Calcium depletion had contrasting effects on bone formation markers; whereas depletion significantly reduced the serum PICP level, it significantly increased serum osteocalcin level. Past histomorphometric studies in rodents indicated that the number of mature but inactive osteoblasts was increased during depletion despite an inhibition of bone formation. Thus, it is speculated that although the reduction in serum PICP reflected the depletion-associated inhibition of bone formation, the increase in serum osteocalcin could represent this depletion-related increase in osteoblast number. During repletion, serum osteocalcin remained elevated above baseline. PICP recovered from its depressed level and increased above baseline, a finding consistent with past histomorphometric findings of increased bone formation during repletion. In summary, this study confirms that 1) a short calcium depletion period produces calcium stress in young women, which leads to rapid stimulation of bone resorption and inhibition of bone formation; and 2) a subsequent calcium repletion period could lead to a compensatory increase in bone formation. In conclusion, the skeletal responses to calcium depletion/ repletion in young women may be similar to those in rodents.

Adult↗
PubMed1998

Molecular mechanism of action of fluoride on bone cells.

Fluoride is an effective anabolic agent to increase spinal bone density by increasing bone formation, and at therapeutically relevant (i.e., micromolar) concentrations, it stimulates bone cell proliferation and activities in vitro and in vivo. However, the fluoride therapy of osteoporosis has been controversial, in large part because of a lack of consistent antifracture efficacy. However, information regarding the molecular mechanism of action of fluoride may improve its optimum and correct usage and may disclose potential targets for the development of new second generation drugs that might have a better efficacy and safety profile. Accordingly, this review will address the molecular mechanisms of the osteogenic action of fluoride. In this regard, we and other workers have proposed two competing models, both of which involve the mitogen activated protein kinase (MAPK) mitogenic signal transduction pathway. Our model involves a fluoride inhibition of a unique fluoride-sensitive phosphotyrosine phosphatase (PTP) in osteoblasts, which results in a sustained increase in the tyrosine phosphorylation level of the key signaling proteins of the MAPK mitogenic transduction pathway, leading to the potentiation of the bone cell proliferation initiated by growth factors. The competing model proposes that fluoride acts in coordination with aluminum to form fluoroaluminate, which activates a pertussis toxin-sensitive Gi/o protein on bone cell membrane, leading to an activation of cellular protein tyrosine kinases (PTKs), which in turn leads to increases in the tyrosine phosphorylation of signaling proteins of the MAPK mitogenic signal transduction pathway, ultimately leading to a stimulation of cell proliferation. A benefit of our model, but not the other model, is that it accounts for all the unique properties of the osteogenic action of fluoride. These include the low effective fluoride dose, the skeletal tissue specificity, the requirement of PTK-activating growth factors, the sensitivity to changes in medium phosphate concentration, the preference for undifferentiated osteoblasts, and the involvement of the MAPK. Unlike fluoride, the mitogenic action of fluoroaluminate is not specific for skeletal cells. Moreover, the mitogenic action of fluoroaluminate shows several important, different characteristics than that of fluoride. Thus, it is likely that our model of a fluoride-sensitive PTP represents the actual molecular mechanism of the osteogenic action of fluoride.

Animals↗
PubMed1998

Serum levels of insulin-like growth factor binding proteins (IGFBP)-4 and -5 correlate with bone mineral density in growth hormone (GH)-deficient adults and increase with GH replacement therapy.

Adults with growth hormone deficiency (GHD) exhibit low bone mineral density (BMD) which improves by growth hormone (GH) replacement therapy. The insulin-like growth factor (IGF) system has an established role in mediating the effects of GH on bone and IGF binding proteins (IGFBP)-4 and IGFBP-5 have been shown to modulate the effects of IGFs in bone. Therefore, we studied serum levels of IGFBP-4 and IGFBP-5 and their relationship to serum levels of bone biochemical markers and BMD in adults with GH deficiency (GHD) before and during GH therapy. Serum levels of IGFBP-5 and IGFBP-4 were measured on samples from 20 patients (11 males) 22-57 years of age. All had IGF-I serum values below -2 standard deviation score. The first 6 months were placebo controlled and all received 3 years of active treatment with the mean dose 0.23 +/- 0.01 IU/kg/week divided into daily subcutaneous injections. Serum IGFBP-5 levels in GHD adults were low at baseline and positively related to total body, femoral neck, trochanter, and Ward's triangle BMD (r = 0.471, 0.549, 0.462, and 0.470, respectively, p < 0.05). The mean serum IGFBP-5 level increased by about 2-fold within 3 months after the initiation of GH therapy and was correlated with serum IGF-I (r = 0.719, 0.801, and 0.722 before and after 18 and 36 months, respectively,p < 0.001). A positive correlation between serum IGFBP-5 levels and lumbar spine BMD was found during GH treatment but not before. The percentage increase of serum IGFBP-5 after GH therapy showed a positive correlation with the percentage increase of total alkaline phosphate activity (r = 0.347 p < 0.05). In contrast to IGFBP-5, serum IGFBP-4 levels were positively related to body mass index (r = 0.607, p < 0.01). Baseline serum IGFBP-4 levels also correlated with total body, femoral neck, trochanter, and Ward's triangle BMD (r = 0.502, 0.590, 0.612, and 0.471, respectively,p < 0.05). The mean serum IGFBP-4 level was increased by 25% within 3 months after initiation of GH therapy and did not correlate with serum IGF-I levels. Although the above findings are consistent with the idea that GH-induced changes in serum IGFBP-5 and IGFBP-4 levels may in part mediate the anabolic effects of GH on bone tissue in adults with GHD, further studies are needed to establish the cause and effect relationship.

Adult↗
PubMed1998

Comparison of rates of change in bone density as measured by dual-energy X-ray absorptiometry and quantitative computed tomography in osteoporotic females treated with fluoride.

We conducted a retrospective comparison of the rates of change in vertebral bone density measured by two densitometric techniques: dual-energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT) in osteoporotic women treated with fluoride. To compare both densitometric methods, lumbar vertebral bone density was determined before and during fluoride therapy in 104 osteoporotic women. All patients signed an informed consent under a protocol approved by our University Institutional Review Board. All subjects had at least three serial measurements using both densitometric techniques over the studied time period. Linear regression was used to calculate rate of change values for each patient. In agreement with previous published reports, lumbar density increased linearly over time both with DXA and QCT. Rates of change determined by DXA and QCT were significantly correlated (r = 0.88, p < 0.0001) and this relationship was independent of the magnitude of the increase in density. Either densitometric technique may be used to evaluate the axial skeletal response to fluoride therapy.

Journal Article↗
PubMed1997

Structural and functional analysis of the 5'-flanking region of the human insulin-like growth factor binding protein (IGFBP)-4 gene.

More than 3 kb of the human (h)IGFBP-4 gene 5'-flanking region was sequenced and assessed for promoter activity. The hIGFBP-4 promoter resides within a CpG island and demonstrates strong basal activity in human osteoblast-like osteosarcoma and COS-7 monkey kidney cells. Transient transfection of cells with hIGFBP-4 promoter-linked deletion constructs demonstrated that multiple cooperating cis-acting elements within 836 bp of the 5'-flanking region contributed to overall promoter strength.

Animals↗
PubMed1997

Effects of inhibitors of signal transduction pathways on transforming growth factor beta1 and osteogenic protein-1-induced insulinlike growth factor binding protein-3 expression in human bone cells.

Signal transduction initiated by TGFbeta1 and OP-1 was studied in MG63 human osteosarcoma cells and in normal human bone cells (HBCs) in the presence of inhibitors of signal transduction events, using insulinlike growth factor binding protein-3 (IGFBP-3) production as an end point. Treatment of serum-free MG63 cells and normal HBCs with TGFbeta1 increased IGFBP-3 protein level several fold in the conditioned medium. This effect of TGFbeta1 was mediated by increased de novo synthesis because mRNA level increased to the same extent as protein level and TGFbeta1 treatment had very little effect on IGFBP-3 protease activity. The stimulatory effect of TGFbeta1 on IGFBP-3 production was inhibited in a dose-dependent manner by pretreatment with staurosporine, a protein kinase C inhibitor, or with vanadate, a phosphotyrosyl protein phosphatase inhibitor in both MG63 cells and normal HBCs. In addition, pretreatment with okadoic acid, an inhibitor of serine/threonine protein phosphatase, counteracted TGFbeta1 induction of IGFBP-3 production. Interestingly, pretreatment of MG63 cells or HBCs with staurosporine, vanadate, or okadoic acid augmented OP-1 stimulation of IGFBP3 production. Staurosporine- or vanadate-induced changes in IGFBP-3 protein levels in the presence of TGFbeta1 and OP-1 were associated with corresponding changes in IGFBP-3 mRNA levels in MG63 cells. These findings are consistent with the hypothesis that TGFbeta1 and OP-1 increase IGFBP-3 expression via distinct intracellular signal transduction pathways.

Bone Morphogenetic Protein 7↗
PubMed1997

Serum fluoride and serum osteocalcin levels in response to a novel sustained-release monofluorophosphate preparation: comparison with plain monofluorophosphate.

In a previous study we found that sustained-release monofluorophosphate (MFP-SR), a novel, sustained-release MFP preparation, acutely maintained the basal therapeutic serum fluoride levels without causing the high serum peak levels associated with plain MFP administration. The objective of the present study was to determine (a) whether chronic MFP-SR administration would provide therapeutic serum fluoride levels, and (b) whether treatment with this new preparation would result in an increase in bone formation similar to that achieved with plain MFP. Bone formation was assessed by serum osteocalcin (OC) determination. We studied 17 postmenopausal women older than 60 years and suffering from primary osteoporosis. All had received a minimum of 6 months of continuous treatment with plain MFP at a dose of 152 mg/day (76 mg b.i.d.). Upon entering the study, the subjects were randomized, in a double-masked protocol, to receive either MFP-SR (76 mg b.i.d.) (n = 9) or placebo (n = 8) for 2 months, after which all subjects returned to the original plain MFP regimen. Serum fluoride and serum OC levels were determined monthly for 3 months. At the beginning of the study serum fluoride levels were in the accepted therapeutic range (5-10 microM) in all patients. Serum fluoride levels were maintained in the patients switched to MFP-SR. In contrast, serum fluoride levels decreased significantly (p < 0.005) in the placebo-treated control subjects and returned to therapeutic levels upon switching back to plain MFP. Similarly, serum OC levels remained elevated in the subjects switched to MFP-SR but dropped significantly (p < 0.001) in the placebo-treated group. Our results demonstrate that chronic MFP-SR administration, at a dose of 152 mg/day, results in maintenance of therapeutic serum fluoride levels and in stimulation of bone formation. Because we have previously reported that high, supratherapeutic post-absorptive serum fluoride levels are avoided by MFP-SR administration, this novel preparation may prevent side effects associated with plain MFP by reducing the amount of fluoride deposited in bone.

Aged↗
PubMed1997

Serum insulin-like growth factor binding protein (IGFBP)-4 and IGFBP-5 levels in aging and age-associated diseases.

Because impaired bone formation is a major contributor to the pathogenesis of senile (type II) osteoporosis, and because insulin-like growth factors (IGFs) have been shown to be important stimulators of bone formation in vitro and in vivo, studies have been focused towards clarifying the role of IGF system in the age-related impairment in bone formation. To evaluate if changes in circulating and bone cell production of IGF binding protein (IGFBP)-4 and IGFBP-5 could contribute to age-related impairment in bone formation, the authors measured serum and skeletal levels of IGFBP-5, and serum levels of IGFBP-4 during aging. Circulating levels of IGFBP-4 increased with age, whereas that of IGFBP-5 declined with age. Serum IGFBP-4 and IGFBP-5 levels showed significant positive correlations with serum levels of parathyroid hormone (PTH) and IGFs, respectively. In addition, skeletal content of IGFBP-5 declined with age. The age-related changes in IGFBP-4 and IGFBP-5 production could contribute, in part, to the decrease in osteoblast cell proliferation and deficiency in bone formation.

Adult↗
PubMed1997

Osteogenic protein-1 stimulates mRNA levels of BMP-6 and decreases mRNA levels of BMP-2 and -4 in human osteosarcoma cells.

Bone morphogenetic proteins (BMPs) are novel growth and differentiation factors that act on mesenchymal stem cells to initiate new bone formation in vivo and promote the growth and differentiation of cells in the osteoblastic lineage. In the present study, we examined the effects of recombinant human osteogenic protein-1 (also known as BMP-7) on the expression of related members of the BMP family using SaOS-2 and U2-OS, two human osteosarcoma cell strains. Evaluation of BMP-2, -4, and -6 mRNA expression indicates that OP-1 stimulated the mRNA levels of BMP-6 in both SaOS-2 cells (threefold) and U2-OS cells (fivefold) after 24 hours of treatment, while decreasing the mRNA levels of BMP-4 in SaOS-2 cells (80%) and BMP-2 and BMP-4 in U2-OS cells by 50% and 72%, respectively. BMP-2 mRNA expression, as examined by Northern blot analysis, was below detectable limits in SaOS-2 cultures. These results demonstrate that OP-1 modulates the mRNA expression of related members of the BMP family, suggesting a possible mode of action of OP-1 on the growth and differentiation of cells in the osteoblastic lineage in vitro.

Blotting, Northern↗
PubMed1997

Circulating and skeletal insulin-like growth factor-I (IGF-I) concentrations in two inbred strains of mice with different bone mineral densities.

Recent work has demonstrated differences in femoral bone mineral density between two common inbred strains of mice, C3H/HeJ (C3H) and C57BL/6J (B6), across a wide age range. To investigate one possible mechanism that could affect acquisition and maintenance of bone mass in mice, we studied circulatory and skeletal insulin-like growth factor-I (IGF-I) and femoral bone mineral density (F-BMD) by pQCT in C3H and B6 progenitor strains, as well as serum IGF-I obtained from matings between these two strains and mice bred from subsequent F1 intercrosses (F2). Serum IGF-I measured by radioimmunoassay was more than 35% higher in virgin progenitor C3H than virgin B6 at 1, 4, 8, and 10 months of age, and in 8-month-old C3H compared with B6 retired breeders (p < 0.001). In the progenitors, there was also a strong correlation between serum IGF-I and serum alkaline phosphatase (r = 0.51, p = 0.001). In the 4 month F1 females IGF-I levels and F-BMD were intermediate between C3H and B6 progenitors. In contrast, groups of F2 mice with the highest or lowest BMD also had the highest or lowest serum IGF-I (p = 0.0001). IGF-I accounted for > 35% of the variance in F-BMD among the F2 mice. Conditioned media from newborn C3H calvarial cultures had higher concentrations of IGF-I than media from B6 cultures, and cell layer extracts from C3H calvariae exhibited greater alkaline phosphatase activity than cultures from B6 calvarial cells (p < 0.0001). The skeletal content of IGF-I in C3H tibiae, femorae, and calvariae (6-14 weeks of age) was also significantly higher than IGF-I content in the same bones of the B6 mice (p < 0.05). These data suggest that a possible mechanism for the difference in acquisition and maintenance of bone mass between these two inbred strains is related to systemic and skeletal IGF-I synthesis.

Aging↗
PubMed1997

Osteogenic protein-1 stimulates production of insulin-like growth factor binding protein-3 nuclear transcripts in human osteosarcoma cells.

To begin delineating molecular mechanisms by which osteogenic protein-1 (OP-1) modulates its effect on the insulin-like growth factor (IGF) system in human skeletal cells, we evaluated time-course effects of OP-1 on the expression of IGFBP-3 messenger RNA (mRNA) in human SaOS-2 osteosarcoma cells and found that 100 ng/ml of OP-1 increased (maximum 10.7-fold at 24 h; P < 0.01) the level of IGFBP-3 mRNA in a time-dependent manner (from 3-36 h; treatment x time interaction, P < 0.001). The stimulatory effect of OP-1 on IGFBP-3 mRNA was not promoted by transcript stabilization; actually, OP-1 treatment selectively increased the decay of mRNA for IGFBP-3 (T1/2 = 5 h vs. 24 h for OP-1 and controls), but not for IGFBP-4 or beta-actin. Conversely, OP-1 acutely increased IGFBP-3 nuclear transcript abundance in total RNA samples ranging between 1-24 h of treatment. After 6 h of treatment, OP-1 produced an average 4-fold increase (P < 0.02; n = 4 experiments) in the level of IGFBP-3 nuclear transcripts vs. a 3-fold increase (P < 0.01; n = 2 experiments) in mRNA abundance. The OP-1 stimulated induction of IGFBP-3 nuclear transcript and mRNA expression was dependent on de novo protein synthesis. Transient transfection experiments were undertaken to isolate putative OP-1 stimulatory cis-elements within 1.8-kb of the IGFBP-3 5'-flanking region in SaOS-2 and TE-85 osteosarcoma cells. In these experiments, OP-1 did not stimulate IGFBP-3 proximal promoter activity in either cell line, thus suggesting that OP-1 reactive domains may be located either beyond the currently established 5'-flanking region, or within internal exon/intron regions of the IGFBP-3 gene. In conclusion, OP-1 treatment stimulates IGFBP-3 expression in human osteoblastic cells by a mechanism that largely promotes the production of IGFBP-3 nuclear transcripts, a process that requires de novo protein synthesis, and overrides an OP-1-induced targeted degradation of IGFBP-3 steady-state mRNA.

Actins↗
PubMed1997

Fluoride at mitogenic doses induces a sustained activation of p44mapk, but not p42mapk, in human TE85 osteosarcoma cells.

Fluoride, at micromolar concentrations, stimulates bone cell proliferation in vitro. In this study, we sought to test whether fluoride at mitogenic doses increases the tyrosyl phosphorylation level and specific activity of a mitogen-activated protein kinase (MAPK) in human TE85 osteosarcoma cells. Analysis by immunoprecipitation with antiphosphotyrosine antibody followed by Western analysis using an anti-pan extracellular signal-regulated kinase antibody revealed that fluoride at the optimal mitogenic dose (i.e. 100 mumol/L) induced a time-dependent increase in the steady state tyrosyl phosphorylation level of p44mapk, but not p42mapk, with the maximal increase (4- to 13-fold) after 1-3 h fluoride treatment. The effect was sustained in that a 9-fold increase was seen after 12 h of the fluoride treatment. The sustained nature of the effect is consistent with an inhibition of dephosphorylation rather than a direct stimulation of phosphorylation. The fluoride effect on the tyrosyl phosphorylation level of p44mapk was dose dependent, with the optimal dose being 100 mumol/L fluoride. The mitogenic dose of fluoride also increased the specific activity and the in-gel kinase activity of p44mapk, but not that of p42mapk, in a time-dependent manner similar to the effect on the p44mapk tyrosyl phosphorylation level. Fluoride at the same micromolar doses did not increase cell proliferation, tyrosyl phosphorylation, or specific activity of any MAPK in human skin foreskin fibroblasts, which are fluoride-nonresponsive cells. Consistent with the interpretation that the effect of fluoride on the steady state tyrosyl phosphorylation level of p44mapk is a consequence of an inhibition of a phosphotyrosyl phosphatase (PTP), mitogenic doses of orthovanadate, a bone cell mitogen and a PTP inhibitor, also increased the steady state tyrosyl phosphorylation level of p44mapk, but not p42mapk, in a time-dependent sustained manner similar to that observed with fluoride. Together, these findings support the concept that inhibition of a PTP activity in bone cells could lead to an activation of MAPK activity.

Bone and Bones↗
PubMed1997

Insulin-like growth factor (IGF)-I, -II, IGF binding proteins (IGFBP)-3, -4, and -5 levels in the conditioned media of normal human bone cells are skeletal site-dependent.

The skeleton in its function of affording strength and support to the body is subject to differential mechanical loading which has been implicated to mediate some of its effects on bone formation via the insulin-like growth factors (IGFs), which are important regulators of bone metabolism. We, therefore, sought to conduct the present study with the hypothesis that the skeletal site-dependent differences in mechanical loading and other variables including stage of osteoblast differentiation would be associated with site-specific differences in the production of the IGF system components. To test this hypothesis, conditioned media (CM) from normal human bone cells (control and IGF-II-treated 48-h cultures) from five different skeletal sites were obtained and assayed for IGF-I, IGF-II (following separation of IGF binding proteins [IGFBPs]), IGFBP-3, IGFBP-4, and IGFBP-5 protein levels employing specific radioimmunoassays for each protein. IGF-I levels were lower than any other IGF system component but were significantly different between the various sites tested. IGF-II levels were greatest in the CM from mandibular cells, followed by calvarial and rib cells, and least in the marrow stromal cells. IGFBP-3 levels were highest in the CM of vertebral cells and lowest in the CM of rib and mandibular cells. The relative abundance of IGFBP-4 in decreasing order was observed in mandibular, calvarial, vertebral, rib, and stromal cells' CM. IGFBP-5 was produced maximally by the calvarial cells, followed by the mandibular, vertebral, stromal, and rib cells. IGFBP-4 appeared to be the IGF system component most abundantly produced by all the cell types from the skeletal sites tested. On a molar basis, the IGFBPs in general were estimated to be produced at a higher magnitude than the IGFs. These findings indicate that there are skeletal site-dependent differences in the production of IGF system components and suggest that the regulation of bone metabolism may vary at the various skeletal sites.

Bone and Bones↗