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Biomedical subjects

I R Dickson

Publications and source records attributed to I R Dickson.

At least 19 recordsLinked to original sources
PubMed1990

Changes with age in the urinary excretion of lysyl- and hydroxylysylpyridinoline, two new markers of bone collagen turnover.

Two intermolecular cross-linking amino acids, hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP), are promising markers in urine of collagen resorption because their levels in urine should reflect only collagen resorption and, unlike hydroxyproline, should not be influenced by degradation of either newly synthesized collagen molecules or noncollagenous proteins. Changes with age in the urinary excretion of HP and LP were studied in 24 h collections of urine from a group of 22 male and 27 female healthy subjects aged from 2 to 70 years. The pyridinolines were quantitated, utilizing their natural fluorescence, after resolution by reversed-phase HPLC. Levels of both pyridinolines were higher in children than in adults, but in adults no evidence of age or sex variations were observed except in the 20-30 year age group. Mean values of HP/Cr and LP/Cr in 37 adults (21-70 years) were 27.2 +/- 1.9 and 8.8 +/- 0.8 mumols/mol, respectively; in the 12 children (2-15 years) the mean values were 14.4 and 12.4 times higher than the respective adult values. Making certain assumptions, the mean amount of bone resorbed in normal adults was tentatively estimated at 1.9 g per 24 h. The finding that differences between children and adults in these relatively specific markers were greater than with hydroxyproline suggests that hydroxyproline values may considerably underestimate the actual amount of bone turnover occurring in growing children or overestimate the adult turnover rate.

Adult↗
PubMed1989

Vitamin A and bone formation. Different responses to retinol and retinoic acid of chick bone cells in organ culture.

The response of bone cells in organ culture to retinol and retinoic acid was studied. Both stimulated incorporation of [3H]thymidine into DNA by 16-day embryonic chick calvaria, but the time-course of the responses differed; the peak responses to retinol and retinoic acid occurred at about 18 h and 48 h, respectively. Although retinol inhibited chick bone collagen synthesis retinoic acid had no effect, but it did stimulate non-collagenous protein synthesis, whereas the effect on the latter of retinol was, if anything, inhibitory. When present with retinol, retinoic acid was able to attenuate the inhibitory effect of the former on chick bone collagen synthesis, but preincubation with retinoic acid had no such effect. In neonatal murine calvarial cultures, retinoic acid inhibited collagen synthesis selectively in the same manner as did retinol. The ability of chick osteoblasts to respond differently to retinol and retinoic acid suggests that both forms of the vitamin may have a role in bone formation and that their intracellular models of action may differ although the attenuation response indicates there may be some interaction between the two.

Animals↗
PubMed1989

Regulation of new osteoclast formation by a bone cell-derived macromolecular factor.

Medium conditioned by incubation with embryonic chick calvarial bones, which contain osteoblasts but not osteoclasts, stimulated new osteoclast formation in foetal long bone cultures and in adult bone marrow cultures formation of tartrate-resistant acid phosphatase (TRAP) positive cells was greatly stimulated. We have termed the factor responsible for this activity osteoclast growth/inducing factor (OGF). OGF was soluble, heat-stable and of size greater than 10kda. OGF activity was present also in mouse bone conditioned medium and in extracts of demineralized cortical diaphyseal bone of five-week-old chickens. OGF appeared to differ from the osteoblast-derived bone-resorbing factors previously observed as well as from macrophage colony stimulating factor (CSF-1). It is therefore probable that different locally secreted factors independently regulate the formation of osteoclasts and their activity.

Animals↗
PubMed1989

The carbonate environment in bone mineral: a resolution-enhanced Fourier Transform Infrared Spectroscopy Study.

The environment of carbonate ions in bones of different species (rat, rabbit, chicken, cow, human) was investigated by Fourier Transform Infrared Spectroscopy (FTIR) associated with a self-deconvolution technique. The carbonate bands in the v2 CO3(2-) domain show three components which were identified by using synthetic standards and different properties of the apatitic structure (ionic affinity for crystallographic locations, ionic exchange). The major component at 871 cm-1 is due to carbonate ions located in PO4(3-) sites (type B carbonate). A band at 878 cm-1 was exclusively assigned to carbonate ions substituting for OH-ions in the apatitic structure (type A carbonate). A band at 866 cm-1 not previously observed was shown to correspond to a labile carbonate environment. The intensity ratio of type A to type B carbonate appears remarkably constant in all bone samples. The 866 cm-1 carbonate band varies in its relative intensity in different species.

Animals↗
PubMed1989

Comparative studies of type X collagen expression in normal and rachitic chicken epiphyseal cartilage.

The levels of type X collagen in mineralizing normal chicken epiphyses and nonmineralizing rachitic chicken tibial epiphyses were measured and compared. Qualitative immunoperoxidase studies with anti-chick type X collagen monoclonal antibodies on sections from normal and rachitic cartilage demonstrated that the type X collagen levels in rachitic growth plates are reduced. Northern hybridization of mRNA and biosynthetic studies have confirmed that type X collagen synthesis in rickets is also decreased. In hypocalcemic rickets, the level of type X collagen mRNA is reduced by 80% whereas the level of type X collagen mRNA is only reduced by 50% in normocalcemic rickets. These observations provide additional evidence that type X collagen is involved in the process of cartilage mineralization and also suggest that the partial recovery of type X collagen synthesis in normocalcemic rickets may be related to the elevated plasma concentration of calcium. Calcium concentration may therefore play an important role in the control of type X collagen synthesis.

Animals↗
PubMed1988

Collagen cross-linking in human bone and articular cartilage. Age-related changes in the content of mature hydroxypyridinium residues.

The concentration in collagen of hydroxypyridinium cross-linking amino acids was measured in samples of bone and cartilage from human subjects aged from 1 month to 80 years. Cortical and cancellous bone samples were dissected and analysed separately. In both bone and cartilage, the content of this mature form of cross-link reached a maximum by 10-15 years of age (the amount in cartilage being 5-10 times that in bone), then stayed essentially in the same range throughout adult life. In bone the ratio of the two chemical variants of the mature cross-link, hydroxylysylpyridinoline to lysylpyridinoline, was constant throughout adult life at 3.5:1, whereas in cartilage it was always greater than 10:1. The ratio of hydroxypyridinium cross-links to borohydride-reducible keto-amine cross-links also changed with age. The reducible cross-links in bone collagen decreased steeply in content between birth and 25 years, but persisted in significant amounts throughout adult life. Reducible cross-links had virtually disappeared from cartilage by 10-15 years of age, being replaced by hydroxypyridinium residues, their maturation products. Cancellous and cortical bone collagens showed similar trends with age in their content of mature cross-links, though for each subject the concentration in cancellous bone was always lower than in cortical bone, presumably reflecting the higher turnover rate and hence the more immature state of cancellous bone.

Adolescent↗
PubMed1988

Influence of vitamin D status on the content of complexed acidic phospholipids in chick diaphyseal bone.

Calcium acidic phospholipid phosphate complexes cause hydroxyapatite formation in vitro and in vivo. Previous studies have shown that the amount of these complexed acidic phospholipids is altered in the bones of animals depleted of vitamin D and phosphate. To help differentiate the effects of vitamin D from those due to altered mineral metabolism, the amount of complexed acidic phospholipids present in diaphyseal bone was determined in five groups of chicks varying in calcium, phosphate and vitamin D status. Highest levels of complexed acidic phospholipids were found in chicks receiving vitamin D and having normal serum levels of Ca and P. Lowest levels were found in vitamin D-deficient chicks; levels were not altered in vitamin D-deficient chicks when their serum Ca was normalized. Intermediate levels were found in vitamin D-treated chicks fed a low Ca diet. Levels of the complexed acidic phospholipids were low in bones of hypophosphatemic, vitamin D-treated chicks but, when related to total lipid phosphorus content, values were similar to those of hypocalcemic chicks. These data suggest that while disturbances in calcium and phosphate metabolism which are present in rickets influence the bone content of these complexed acidic phospholipids, vitamin D may also play a direct role in their formation. Further, the ability of vitamin D to increase bone complexed acidic phospholipid content does not seem to be related to its hypercalcemic effect.

Animals↗
PubMed1986

A comparison of proteoglycan from chick cartilage of different types and a study of the effect of vitamin D on proteoglycan structure.

Normal chick growth cartilage contains mainly large proteoglycans that interact well with hyaluronic acid. In contrast normal articular and sternal cartilages contain mainly smaller molecules that interact poorly with hyaluronic acid. Similar smaller proteoglycans are present in all the cartilages in the rachitic state. The smaller proteoglycans all appear to be synthesized as such, and not to arise from degradation of larger molecules unless such degradation occurs extremely rapidly after synthesis. Supplementation of the vitamin D-deplete animals with calcium resulted in the production of large proteoglycans by the growth cartilage, but did not affect the size of the proteoglycan produced by the articular or sternal cartilages. It would appear that in these chicks the chondrocytes of the growth cartilage may be unique in their ability to produce large aggregating proteoglycans, and in their response to plasma calcium levels.

Animals↗
PubMed1985

The effects of parathyroid hormone on osteoblast-like cells from embryonic chick calvaria.

A bone cell fraction was isolated from 16 day old embryonic chick calvaria using a sequential enzymatic digestion procedure. The fraction contained cells, of an osteoblast-like character, which responded to parathyroid hormone (PTH) and prostaglandin E2, but not to calcitonin, in terms of increased production of cyclic AMP. Primary cultures of cells maintained their responsiveness to PTH for at least 2 weeks after reaching confluence. Production of alkaline phosphatase by the bone cells was inhibited when 1,25(OH)2 vitamin D3 was added to cultures at concentrations of 10(-8)M or greater. When cells were cultured in the presence of PTH a biphasic effect was observed; alkaline phosphatase levels were stimulated at low concentrations of this hormone but were decreased at higher concentrations. The latter finding appears consistent with observations that PTH can in vivo exert either anabolic or catabolic effects on bone, depending upon the circulating level of hormone present.

Alkaline Phosphatase↗
PubMed1985

The influence of vitamin D metabolites on collagen synthesis by chick cartilage in organ culture.

When growth cartilage from rachitic chicks was cultured in the presence of the calcium-regulating hormone 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3), collagen resorption was increased and collagen synthesis decreased compared to control cultures containing no hormone. The minimum concentration of the hormone that caused a statistically significant inhibition of collagen synthesis was 10(-8) mol/l. Collagen synthesis by growth cartilage from normal chicks was also reduced by 1,25-(OH)2D3, showing that it was not an abnormal response of vitamin D-depleted tissue. 25-Hydroxyvitamin D3 and 24,25-dihydroxyvitamin D3 also inhibited collagen synthesis by cultures of growth cartilage but only at higher metabolite concentrations. 1,25-Dihydroxyvitamin D3 (10(-7) mol/l) did not significantly inhibit collagen synthesis by cultures of articular fibrocartilage and of sternal cartilage, tissues that do not calcify physiologically. The minimum concentration of 1,25-(OH)2D3 (10(-9) mol/l) necessary to cause decreased collagen synthesis by embryonic chick calvaria was lower than the value obtained with growth cartilage; this suggests that bone cells may be more sensitive to the hormone in this respect than are growth cartilage chondrocytes. These findings provide evidence of a direct role of 1,25-(OH)2D3 in the control of endochondral bone formation which is consistent with its primary role in the maintenance of plasma calcium homeostasis.

Animals↗
PubMed1985

Changes with age in the non-collagenous proteins of human bone.

Little is known about the function of the non-collagenous proteins in the organic matrix of bone. Information about these proteins was obtained from studies of human cortical bone. Analysis of fractions of bone differing in density showed that 96% of the alpha 2HS-glycoprotein and 58% of the albumin was associated with the mineralized phase. A study of age-related changes in the composition of bone showed that the amounts present of alpha 2HS-glycoprotein, albumin, sialoprotein, soluble collagen and of EDTA-soluble protein were all higher in bone from children than in adults. In subjects aged over 60 y the content in bone of albumin, sialoprotein and of total protein was similar to that of children. These differences could not be correlated with age-related changes in the calcium/hydroxyproline ratio nor with previous reports of alterations in the crystal structure and the physical properties of human cortical bone. This suggests that these proteins are unlikely to be involved in stabilization of the mineralized matrix or in influencing the physical properties of bone; their function appears more likely to be related to bone formation and turnover.

Adolescent↗
PubMed1984

The influence of dihydroxylated vitamin D metabolites on bone formation in the chick.

The ability of 1,25(OH)2D3 and of 24,25(OH)2D3 to prevent or to heal rickets in chicks was evaluated by studies of plasma biochemistry, growth plate histology, bone morphometry and microradiography, and bone mineralization. 1,25(OH)2D3 at a dose of 100 ng/day produced fewest abnormalities compared with vitamin D3-treated control chicks. Bone growth was slightly greater than vitamin D3-treated controls in chicks given a lower dose of this metabolite; the reverse was observed in chicks given a higher dose. 24,25(OH)2D3 was less effective than 1,25(OH)2D3 in preventing rickets even at doses as high as 400 ng/day. Treatment of rachitic chicks with doses of 24,25(OH)2D3 up to 300 ng/day produced no healing effect on the bone lesions, in marked contrast to the beneficial effects observed with 1,25(OH)2D3.

Animals↗
PubMed1982

Studies of the effects of cholecalciferol upon the metabolism of rachitic chick growth cartilage.

When a physiological dose of cholecalciferol was given to rachitic chicks, an early response was increased amino acid incorporation into growth cartilage protein, including collagen, but no evidence was found for induction of specific protein synthesis as in the intestine. Increased release into the medium of 45Ca and of hydroxyproline was observed when growth cartilage tissue was incubated in medium containing 1,25-dihydroxycholecalciferol. These studies suggest that the metabolism of cartilage tissue from the zones of proliferation and maturation was more affected than tissue from the zones of hypertrophy and calcification. Cholecalciferol metabolites may therefore have a direct effect upon chondrocytes as well as on bone cells during endochondral bone formation.

Animals↗
PubMed1979

Effect of vitamin D deficiency on bone formation in the chick.

1. The process of diaphyseal bone formation can be investigated by studying the rate of incorporation of radioactive precursors, administered in vivo into bone fractions of increasing density. 2. In the 4-week-old vitamin D-treated chick most of the osteoid becomes calcified within 12h and almost all within 2 days. The low-density calcified phase that is formed is converted into a higher density form and within 7 days the greater proportion of the calcified tissue is in the higher density form. 3. In the vitamin D-deficient chick of similar age the rate of calcification of osteoid is decreased, as is the rate of conversion into the higher density phase with the resultant accumulation of the lower density calcified form. 4. The higher density phase probably corresponds to hydroxyapatite and the lower density one to the ACP-pase described by Termine & Posner [(1967) Calcif. Tissue Res. 1, 8--23]. 5. The disorder in the process of calcification seems to be unrelated to the alteration in blood Ca2+ and phosphate concentrations, but related to the presence or absence of cholecalciferol.

Animals↗
PubMed1978

A comparative study of the proteoglycan of growth cartilage of normal and rachitic chicks.

1. Proteoglycan was isolated from growth cartilage of normal and rachitic chicks. 2. The proteoglycan from normal cartilage showed differences in chemical composition and physical properties from a comparable fraction isolated from bovine nasal cartilage. 3. The proteoglycan from rachitic-chick cartilage was of smaller size than tis normal counterpart, though of similar average chemical composition. 4. Differences between proteoglycan from normal and rachitic cartilages can be explained in terms of limited proteolytic cleavage.

Animals↗