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N Loveridge

Publications and source records attributed to N Loveridge.

At least 55 records · Page 3Linked to original sources
PubMed1995

Dextran sulfate promotes the rapid aggregation of porcine bone-marrow stromal cells.

Despite the fact that cells of the mammalian stromal compartment of bone marrow have been shown to contain multipotential stem cells when studied in diffusion chambers it is notable that the same range of possible phenotypes (e.g., chondrocytic) has not been induced in freshly isolated marrow stromal cells in vitro. To investigate the possible role of glycoconjugates on phenotype expression, the effects of chondroitin sulfate, dermatan sulfate, dextran 500, and dextran sulfate on the cell morphology and differentiation of confluent porcine bone-marrow stromal-cell monolayers were studied. Of these glycosaminoglycan molecules only dextran sulfate induced confluent porcine bone-marrow stromal-cell monolayers to retract into tight, circular cell aggregates. Retraction began within 6 h, was complete after 3-5 days, and was dose dependent. Subsequent removal of dextran sulfate from the culture medium resulted in a return to a monolayer culture. Aggregated cells were essentially nonmitotic but dye exclusion indicated high cell viability. Dexamethasone, ascorbate, and beta-glycerophosphate produced no morphological change within 6 days when administered alone, but increased proliferation and aggregation in dextran sulfate-treated cultures. Immunocytochemistry of monolayer cultures revealed positive staining for type I but not type II collagen and addition of dexamethasone, ascorbate, and beta-glycerophosphate increased type I collagen deposition. In contrast, the centers of dextran sulfate-induced aggregates were positive for type II collagen, whereas type I collagen was only present at the periphery of the aggregates. Further addition of dexamethasone, ascorbate, and beta-glycerophosphate had little effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Changes in bone mass and metabolism after surgery for primary hyperparathyroidism.

BACKGROUND AND OBJECTIVE: Bone mass is often reduced in patients with primary hyperparathyroidism (pHPT) and is usually partially reversible after parathyroidectomy. However, site specific and overall skeletal benefits of surgery in mild asymptomatic pHPT remain uncertain. DESIGN: Cross-sectional and longitudinal studies. PATIENTS: Fourteen patients (12 women and 2 men) with pHPT. MEASUREMENTS: Baseline bone mass was assessed at the lumbar spine, left hip and whole body using dual-energy X-ray absorptiometry, and at the left os calcis using broad-band ultrasound attenuation. Changes in bone mass, serum intact PTH and osteocalcin, and urinary pyridinium cross-link excretion were recorded in 10 patients followed for 6 months after surgery. RESULTS: (1) Cross-sectional study: Baseline measurements at the lumbar spine and hip were inversely related to both the serum PTH concentration and the weight of the parathyroid gland removed at surgery. (2) Longitudinal study: Six months after adenectomy, bone mass had increased significantly at the femoral neck, greater trochanter, whole body and os calcis, but not at the lumbar spine or Ward's area. Serum PTH, osteocalcin and pyridinium cross-link excretion all fell significantly after surgery. The percentage increment in whole body bone mineral content at 6 months was proportional to the baseline PTH. CONCLUSION: In primary hyperparathyroidism, preoperative reductions and post-operative gains in bone mass are proportional to the initial serum PTH concentration. Mild primary hyperparathyroidism probably does not cause appreciable bone loss at clinically relevant fracture sites such as the spine and hip, and in such cases the overall skeletal benefits of surgery are likely to be negligible.

Aged↗
PubMed1995

Growth hormone and longitudinal bone growth in vivo: short-term effect of a growth hormone antiserum.

The control of longitudinal growth is poorly understood but GH is considered to be one of the major hormones regulating postnatal growth. However, there is dispute as to whether it has a direct or indirect action. To study the role of GH we used a polyclonal antiserum to rat GH and investigated changes in cell proliferation and enzyme activities associated with bone formation and resorption during longitudinal growth. IGF-I levels were measured by two independent RIAs, DNA synthesis by bromodeoxyuridine incorporation followed by immunocytochemistry and enzyme activities were quantified in situ by microdensitometry. After 1 day the percentage of chondrocytes undergoing DNA synthesis within the proliferative zone was reduced but no other parameters were affected. By day 4 the labelling index was the same as in pair-fed animals but the number of chondrocytes synthesising DNA was reduced as was the total width of the growth plate and that of the proliferative zone. Alkaline phosphatase (associated with mineralisation) was unchanged but glucose 6-phosphate dehydrogenase activity (associated with cell proliferation) was decreased. Osteoclastic tartrate-resistant acid phosphatase activity (associated with bone resorption) was also significantly reduced. Similar changes were apparent after 10 days. At no time was the circulating level of IGF-I decreased. These data suggest that, during longitudinal growth, GH affects the number of proliferating chondrocytes but not the percentage of cells undergoing DNA synthesis, indicating that its primary role may be on the commitment of prechondrocytes to a proliferative state. Furthermore, while GH does not seem to have any effect on skeletal mineralisation it may stimulate osteoclastic resorption of the primary spongiosa.

Acid Phosphatase↗
PubMed1994

Alterations in glycosaminoglycan concentration and sulfation during chondrocyte maturation.

We have used antibodies to chondroitin 4- and 6-sulfate and keratan sulfate along with Alcian blue staining of sulfated proteoglycans to investigate changes in content and sulfation within the avian growth plate. In normal chicks, chondroitin 4- and 6-sulfate content were similar in the proliferating and transitional zones but in the hypertrophic zone, chondroitin 4- and 6-sulfate were slightly lower (13% and 18%, respectively) and keratan sulfate was markedly lower (58%). Compared with the proliferative zone, Alcian blue staining of sulfated glycosaminoglycans was markedly lower in both the transitional (46%) and hypertrophic (22%) zones. In tibial dyschondroplasia, where chondrocyte maturation is arrested at the transitional zone, there was no difference in the chondroitin 4- and 6-sulfate or keratan sulfate staining between the proliferative and transitional zones, which were similar to normal birds. With Alcian blue staining there was no difference in the intensity of the staining within the proliferating zone compared with normal birds but staining in the transitional chondrocytes was markedly higher (39%). These results suggest that in the early steps of chondrocyte maturation there may be a decrease in the degree of glycosaminoglycan sulfation without any alteration in glycosaminoglycan concentration, and that further maturation may be accompanied by a change in the nature of the proteoglycans which may also affect the level of sulfation.

Alcian Blue↗
PubMed1994

Bone mineral density and metabolism in premenopausal women taking L-thyroxine replacement therapy.

BACKGROUND AND OBJECTIVE: Excess endogenous thyroxine causes bone loss, but the effects of exogenous thyroxine are disputed. We report on bone mass and metabolism in women taking L-thyroxine therapy. DESIGN: Cross-sectional and longitudinal studies. PATIENTS: Cross-sectional study: 40 healthy premenopausal women with autoimmune thyroiditis taking either physiological (serum TSH usually normal, 0.35-3.3 mU/l) or suppressive (serum TSH usually < 0.35 mU/l) doses of L-thyroxine; patients were also compared with previously acquired age and weight matched premenopausal volunteers with no history of thyroid dysfunction. Longitudinal study: 28 patients were followed-up > or = 1 year later. MEASUREMENTS: In all subjects bone mineral density (BMD) was measured at the anteroposterior lumbar spine and left hip (femoral neck, greater trochanter and Ward's area) using dual-energy X-ray absorptiometry, and physical activity assessed using the Framingham physical activity index. Serum osteocalcin (OC), PTH and vitamin D, and urinary pyridinoline and deoxypyridinoline excretion were measured in patients. RESULTS: Cross-sectional study: The patient groups were well matched for disease duration and physical activity although the suppressed group were slightly younger (mean 38.1 (SD 7.5) vs 43.3 (3.9) years, P < 0.05). BMD, serum OC, PTH and vitamin D, and urinary cross-link excretion did not differ significantly between the two groups. Multivariate analysis of the whole group suggested that BMD at the femoral neck and greater trochanter was related positively to weight and physical activity and negatively to thyroxine dose (microgram/kg/day) and patient age. At the lumbar spine BMD was reduced non-specifically in the presence of thyroid disease and treatment, but this effect appeared to decline with increasing duration of therapy. A similar analysis of the patient group suggested that urinary cross-link excretion correlated positively with thyroxine dose, and negatively with duration of treatment. Longitudinal study: Annualized changes in BMD were inversely related to thyroxine dose (microgram/kg/day) at all sites but achieved statistical significance only at the femoral neck and Ward's area. CONCLUSION: We did not find any effect of persistent historical TSH suppression on current bone mass, and this might relate to the relative insensitivity of older TSH assays. However, the cross-sectional and longitudinal data suggest that high daily doses of thyroxine in relation to patient body weight might adversely affect bone mass, particularly at the hip. These findings support the contention that excess exogenous thyroxine might predominantly deplete skeletal sites, such as the femoral neck, rich in cortical bone.

Absorptiometry, Photon↗
PubMed1994

The effect of high phosphorus intake on calcium and phosphorus retention and bone turnover in growing lambs.

Growing lambs were fed diets that just met their requirement for Ca but which supplied either 1 or 3 times their requirement for P and the effects on Ca and P retention and on bone turnover were monitored. Feeding the high P diet had no adverse effect on Ca and P absorption or retention or on bone formation rate. Bone resorption rate was a little higher in lambs fed the high P diet but there were no differences between treatments in plasma parathyroid hormone, 1,25-dihydroxyvitamin D3 or 25-hydroxyvitamin D3 levels or in bone mineral content. It would appear from these results that feeding diets that are rich in P is unlikely to have any adverse effect on skeletal mineralization in the lamb provided that their minimum requirement for Ca is met.

Acid-Base Equilibrium↗
PubMed1994

Effects of a polyclonal antiserum to rat growth hormone on circulating insulin-like growth factor (IGF)-I and IGF-binding protein concentrations and the growth of muscle and bone.

A polyclonal antiserum to rat GH (anti-rGH) injected into rats for 3 or 8 weeks markedly reduced the weight, total protein and RNA content of muscles of the hind limb. These effects were prevented when bovine GH (bGH) was administered simultaneously. In a second experiment, the effects of 8 weeks of treatment with anti-rGH on the growth of the whole body, muscle and bone were investigated. Body weights of rats were decreased by 58% by treatment with anti-rGH; muscle weights were reduced by slightly more than the decrease in body weight (by 64%, 65% and 61% respectively for plantaris, soleus and gastrocnemius). The weight of the tibia was decreased by 54%, its length was decreased by 23%, cortical width and overall width were reduced by 26% and 18% respectively, suggesting a possible role for GH in osteoclastic activity. Serum total insulin-like growth factor-I (IGF-I) concentrations were decreased by 80-90% in both experiments by anti-rGH; these changes were prevented in the first experiment by concurrent treatment with anti-rGH and bGH. The serum IGF-binding protein-3 (IGFBP-3) concentration was also decreased by anti-rGH in experiment 1 (by 86%); the response of the 28-32 kDa IGFBPs was smaller (-35%), and was restored to control values by simultaneous injection of bGH. Western immunoblotting using an antiserum to IGFBP-2 showed that there was a marked decrease from neonatal to adult stages which was independent of anti-rGH treatment. This clearly demonstrated a dissociation of the reciprocal relationship supposed to exist between IGFBPs-2 and -3. The 24 kDa IGFBP-4 was unaffected by anti-rGH but replacement therapy with bGH doubled its concentration. Although the effects on body and muscle weight were prevented when rats were given anti-rGH and bGH simultaneously, the possibility of mediation by other hormones cannot be precluded.

Animals↗
PubMed1993

In vivo effect of 1,25-dihydroxycholecalciferol on the proliferation and differentiation of avian chondrocytes.

A combination of immunocytochemistry and in situ biochemistry has been used to determine the in vivo effects of 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] on the proliferation and differentiation of chondrocytes. Chicks were fed a diet supplemented with 1,25-(OH)2D3 (2.5, 5, or 10 micrograms/kg diet) for 3 weeks, and measurements were made in sections of growth plate of chondrocyte proliferation and rate of maturation through the growth plate [using bromodeoxyuridine (BrdUrd) labeling] and also chondrocyte differentiation [assessed by alkaline phosphatase (ALP) activity]. The labeling indices of the control and supplemented chicks were similar (23.1 +/- 1.3 versus 23.2 +/- 1.6%); however, within a 21 h period the BrdUrd-positive cells of the supplemented chicks had moved down the growth plate significantly farther than in the control chicks (71.0 +/- 2.8 versus 52.6 +/- 1.8%). Greater ALP (mean integrated absorbance) activity higher up the growth plate of the supplemented chicks indicated a more differentiated phenotype in cells closer to the epiphyseal junction. Within individual transitional chondrocytes ALP activity in the 10 micrograms/kg supplemented chicks was 26.6 +/- 0.85, which was significantly higher (p < 0.01) than that of the control chicks (19.2 +/- 0.9). These results suggest that 1,25-(OH)2D3 in vivo does not increase the rate of chondrocyte proliferation but accelerates the onset of maturation.

Alkaline Phosphatase↗
PubMed1993

Preliminary characterization of porcine bone marrow stromal cells: skeletogenic potential, colony-forming activity, and response to dexamethasone, transforming growth factor beta, and basic fibroblast growth factor.

Neonatal pig bone marrow stromal cells (PBMSC) were tested in vivo and in vitro to establish their use as a large-animal model for the study of skeletogenesis. When implanted in diffusion chambers in athymic mice for 6-8 weeks, both freshly isolated pig bone marrow and passage 2 PBMSC formed partially mineralized cartilage, bone-like material, and fibrous tissue. The cartilage showed metachromatic, perilacunar staining with toluidine blue and safronin O, alcian blue staining for chondroitin and keratan sulfate, and intense immunostaining for type II collagen. Osteocalcin was immunolocalized to the mineralized regions, consistent with the formation of bone. Alkaline phosphatase was primarily observed in cell layers at boundaries between tissue types. Unstimulated monolayer cultures of PBMSC produced type I but not type II collagen, responded to dexamethasone (10(-8) M) with a 1.7-fold increase in alkaline phosphatase activity, and were stimulated to divide by basic fibroblast growth factor (1.5-fold; EC50 1 ng/ml). Transforming growth factor beta (TGF-beta) blocked both dexamethasone-induced alkaline phosphatase expression (EC50, 1 ng/ml of TGF-beta) and the mitogenic effects of bFGF (EC50 0.06 ng/ml of TGF-beta). When incubated for 10-14 days in medium containing dexamethasone, beta-glycerophosphate and ascorbate PBMSC formed mineralized nodules. Calcification occurred in the middle of the aggregates and was associated with intensely alkaline phosphatase positive cells and a dense type I collagen-rich matrix. PBMSC also displayed colony-forming unit-fibroblastic activity, with approximately 1 in 80 of the plated cells formed colonies > 128 cells over 14-21 days. PBMSC therefore mimic the known activities of stromal cells from other species, including the human, suggesting that they are a valid model for skeletal research.

Alkaline Phosphatase↗
PubMed1993

Molybdenum-induced changes in the epiphyseal growth plate.

Molybdenum (Mo), at high concentrations, induces changes in the epiphyseal growth plate through its effects on copper (Cu) metabolism but it is unclear whether or not Mo can induce changes independent of its effects on copper status. To this end, the effect of Mo on longitudinal bone growth was examined in rats. Dietary Mo was given either as ammonium heptamolybdate or as ammonium tetrathiomolybdate, the latter producing a marked Cu deficiency. There was a significant reduction in longitudinal bone growth in both groups; however, growth plate width was increased only in the Cu-deficient animals due to an increase in the width of the zone of transitional/hypertrophic chondrocytes. Both glucose 6-phosphate dehydrogenase activity and cell proliferation (assessed by bromodeoxyuridine incorporation) were markedly decreased in the proliferating zone of the growth plate in both Mo-treated groups. These changes were not apparently related to changes in circulating vitamin D metabolites or insulin-like growth factor-1. The results indicate that excess Mo impairs cell proliferation within the growth plate, whereas the effects of copper deficiency are more related to chondrocyte differentiation. Thus, Mo can induce changes in longitudinal bone growth which are distinct from those resulting from Cu deficiency.

Alkaline Phosphatase↗
PubMed1993

Mitogenic action of insulin-like growth factor-I on human osteosarcoma MG-63 cells and rat osteoblasts maintained in situ: the role of glucose-6-phosphate dehydrogenase.

The mechanisms involved in the mitogenic actions of insulin-like growth factor-I (IGF-I) on skeletal cells are at present unclear. We have investigated the role of glucose-6-phosphate dehydrogenase (G6PD) in this mechanism and provide strong evidence that stimulation of G6PD activity is required for the growth promoting activities of IGF-I. IGF-I (10 ng/ml) significantly elevated G6PD activity in MG-63 human osteosarcoma cells within 30 min which preceded the IGF-I induced DNA synthesis in these cells. Inhibition of G6PD activity by epiandrosterone decreased DNA synthesis in IGF-I stimulated MG-63 cells but this was partly overcome by the addition of a combination of the four deoxyribonucleosides. IGF-I did not cause a general increase in cell metabolism as succinate dehydrogenase and iso-citrate dehydrogenase activity were not altered. Although IGF-I caused a significant increase in lactate dehydrogenase activity this was not inhibited by epiandrosterone. The culture of metatarsals of 4-week-old rats with IGF-I (10 ng/ml) also stimulated G6PD activity in osteoblasts lining the metaphyseal trabeculae.

Androsterone↗
PubMed1993

Micronutrients and longitudinal growth.

The present review has concentrated on the control of longitudinal growth and the relative importance of certain micronutrients. By far the most significant of these is 1.25(OH)2D3 which is now being recognized, not only for its role in maintaining Ca homeostasis, but also its major role in chondrocyte differentiation within the growth plate.

Bone Development↗
PubMed1993

Studies on growth plate chondrocytes in situ: cell proliferation and differentiation.

In man, attaining full longitudinal growth and skeletal maturity may go towards preventing later problems, such as osteoporosis. In farmed species, it is becoming increasingly apparent that muscle growth or the calcium demands for reproduction have outstripped the ability of the skeleton to provide both support and sufficient calcium. Thus, understanding the mechanisms that control longitudinal growth is of vital importance. Methods for studying chondrocyte proliferation and differentiation increasingly rely on the use of isolated cells, but these do not reproduce in vivo conditions. It is therefore necessary to be able to assess chondrocyte function in situ in order to understand fully the actions of possible growth promoters and therapeutic agents. The control of chondrocyte proliferation seems to be heavily dependent on GH, which probably acts directly on the resting and proliferating chondrocytes (Fig. 3). In the former, it seems to regulate the commitment of prechondrocytes to the proliferative state, but the mechanisms whereby it achieves this are unclear. What is also unclear is the proportion of growth that is GH dependent and how much, if at all, the control of IGF-I production by nutritional and other factors contributes to longitudinal growth. The in situ biochemical approach has provided strong evidence that both TGF-beta and the c-myc proto-oncogene are involved in chondrocyte differentiation and may be early markers of this process (Fig. 3). Indirect evidence exists to support a role for c-myc expression in chondrocyte differentiation, as TGF-beta has been reported to have its mechanisms of action modulated by c-myc expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Effects of acute acid loading on parathyroid hormone secretion and on urinary calcium and cAMP excretion in the growing lamb.

Growing lambs fed a diet containing NaHCO3 were made acidotic by intravenously infusing HCl at the rate of 1 mmol/min over a 4 h period. Acid infusion led to a fall in blood and urine pH and a prompt increase in urinary Ca excretion. This in turn led to a fall in plasma Ca concentration and a rise in parathyroid hormone (PTH) levels. Urinary cAMP excretion was unaffected by acid infusion. In separate experiments lambs made acidotic by feeding a diet containing NH4Cl were given infusions of PTH at the rate of 1 microgram/h. Infusion of the hormone was accompanied by a rise in plasma Ca and an increase rather than a decrease in urinary Ca excretion and no change in urinary cAMP excretion. These results point to the kidney as the primary site of response to acid loading in the lamb, a failure to reabsorb Ca in these conditions necessitating the release of PTH and an increase in bone resorption in order to maintain normal plasma Ca levels.

Acidosis↗
PubMed1993

The control of chondrocyte differentiation during endochondral bone growth in vivo: changes in TGF-beta and the proto-oncogene c-myc.

The expression of transforming growth factor-beta and the c-myc proto-oncogene was studied in situ in the chondrocytes of the tibial growth plate of normal chicks and those with avian tibial dyschondroplasia in which the chondrocytes are developmentally arrested in the transitional phase between proliferation and differentiation. This results in an accumulation of unmineralised and avascular cartilage. Dyschondroplastic chicks showed reduced c-myc expression in the transitional chondrocytes but unaltered levels in the proliferating chondrocytes. Transforming growth factor-beta expression was reduced in the transitional chondrocytes of dyschondroplastic chicks. In areas where the lesion was being repaired there was evidence of increased expression of both c-myc protein and transforming growth factor-beta. Addition of 1,25-dihydroxyvitamin D to the diet, which is known to reduce the incidence of dyschondroplasia, resulted in an increase in c-myc production. These results suggest that both transforming growth factor-beta and the proto-oncogene c-myc may be important elements of the cascade of events that lead to chondrocyte differentiation, hypertrophy and mineralisation.

Alkaline Phosphatase↗
PubMed1992

The proto-oncogene c-myc is involved in cell differentiation as well as cell proliferation: studies on growth plate chondrocytes in situ.

A combination of immunocytochemistry and microdensitometry has been used to localize and quantify the expression of the proto-oncogene c-myc within chondrocytes of the proximal growth plates of rat and chick long bones. Although the c-myc protein was localized in all chondrocytes of the growth plate of both species the most intense staining was restricted to the proliferating and differentiating chondrocytes. These were identified by their ability to synthesize DNA (bromodeoxyuridine positive) and the presence of alkaline phosphatase activity, respectively. Species differences did exist with the c-myc concentration of the chick proliferating and differentiating chondrocytes being higher (128% and 240%, respectively) than the respective chondrocytes of the rat. The higher c-myc concentration in the chick proliferating chondrocytes paralleled the differences in the bromodeoxyuridine labelling index between the two species. In the rat, the concentration of c-myc protein present in the differentiating chondrocytes was 74% higher than in the respective proliferating chondrocytes, while in the chick it was 146% higher. The data not only provides further evidence for a role of the c-myc protein in cell proliferation but also suggests involvement of this protein in chondrocyte differentiation and/or hypertrophy.

Alkaline Phosphatase↗
PubMed1992

Cell proliferation and enzyme activities associated with the development of avian tibial dyschondroplasia: an in situ biochemical study.

Avian tibial dyschondroplasia is a disorder of endochondral ossification which results in the accumulation of noncalcified, avascular cartilage. We have investigated the changes in cell proliferation and enzyme activities within specific cell types in the growth plate of chickens with differing severity of the disease using in situ biochemical techniques that allow the quantification of enzyme activity in unfixed undecalcified sections of tissue. Lactate dehydrogenase activity in the prehypertrophic zone and tartrate-resistant acid phosphatase activity in osteoclasts/chondroclasts were not affected by the severity of the disease. Glucose 6-phosphate dehydrogenase activity in both the proliferating and prehypertrophic zones of the growth plate was reduced in chicks with both moderate and severe lesions. Cell proliferation within the proliferating chondrocytes was slightly reduced in the severely affected birds. Alkaline phosphatase activity in the prehypertrophic chondrocytes was markedly elevated in chicks with moderate and severe lesions. These results rule out an increased rate of chondrocyte proliferation as a possible mechanism for the development of tibial dyschondroplasia. The aetiology of the disease therefore appears to be related to the control of chondrocyte differentiation, mineralization, and vascularization by local and/or systemic growth factors.

Acid Phosphatase↗