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J Denton

Publications and source records attributed to J Denton.

At least 19 recordsLinked to original sources
PubMed2006

Morphological and glycosylation changes associated with the endometrium and ectopic lesions in a baboon model of endometriosis.

BACKGROUND: Endometriosis is one of the most common causes of infertility and pelvic pain. A baboon model has recently been developed whereby the intrapelvic injection of menstrual endometrium results in the induction of endometriotic lesions. We have used this model to investigate changes in ultrastructure and glycosylation of endometria from normal and diseased baboons. METHODS: Endometriosis was induced in eight female baboons; endometrial tissue and endometriotic lesions were removed on days 9-11 post ovulation between 3 and 16 months of disease and compared with endometrium from 17 control animals, using electron microscopy and lectin histochemistry. RESULTS: Ultrastructurally, diseased endometrial glands showed abnormalities in secretory vacuoles and an intracellular accumulation of glycogen; in later stages of the disease, glands resembled those of the late secretory phase endometrium. The abnormalities were mirrored by changes in glycan expression. In early disease, there was an increased binding of lectin from Dolichos biflorus agglutinin (DBA) to fucosylated N-acetylglucosamine residues, whereas in later stages, this binding generally decreased in association with the appearance of a late secretory phenotype. CONCLUSIONS: Endometriosis is accompanied by progressive changes in the gland architecture and biochemistry resulting in dyssynchrony within the window of uterine receptivity, which may result in the reduced fertility associated with this disease.

Animals↗
PubMed2005

Diabetes in rat pregnancy alters renal calcium and magnesium reabsorption and bone formation in adult offspring.

AIMS/HYPOTHESIS: We tested the hypothesis that diabetes in pregnancy can result in the in-utero reprogramming of renal calcium and magnesium handling and of bone formation in the offspring, which persists into adulthood. METHODS: Male offspring of streptozotocin-treated diabetic rats (OD rats) and of control non-diabetic animals (OC rats) were investigated as neonates and at 8, 12 and 16 weeks of age. RESULTS: Compared with OC rats, urinary calcium and magnesium output was significantly reduced in OD rats at every age studied; Na+ and K+ outputs were unaffected. The renal expression of proteins involved in the tubular reabsorption of calcium (calcium ATPase, calbindin-D28k and epithelial calcium channel) was increased in OD animals compared with that in OC animals. Additionally, we observed that adult OD rats had lower trabecular and higher cortical femoral bone volumes, explained by deposition of bone on the endosteal surface. CONCLUSIONS/INTERPRETATION: These data show that diabetes in pregnancy has profound effects on male offspring in terms of renal tubular calcium and magnesium reabsorption and the normal pattern of bone formation. These effects persist into adulthood. Such long-lasting effects of diabetes on kidney and the skeleton were not suspected and could have important implications for the health of children born to diabetic women.

Aging↗
PubMed2005

Skeletal bone morphology is resistant to the high amplitude seasonal leptin cycle in the Siberian hamster.

Recent studies have suggested that the adipocyte-derived hormone, leptin, plays a role in the regulation of metabolism. Here, we tested this hypothesis in the seasonally breeding Siberian hamster, as this species exhibits profound seasonal changes in adiposity and circulating leptin concentrations driven by the annual photoperiodic cycle. Male hamsters were kept in either long (LD) or short (SD) photoperiods. Following exposure to short photoperiods for 8 weeks animals exhibited a significant weight-loss and a 16-fold reduction of serum leptin concentrations. At Week 9, animals in both photoperiods were infused with leptin or PBS via osmotic mini-pump for 14 days. Chronic leptin infusion mimicked LD-like concentrations in SD-housed animals and caused a further decline in body weight and adipose tissue. In LD-housed animals, leptin infusion resulted in a significant elevation of serum concentrations above natural LD-like levels, but had no discernable effect on body weight or overall adiposity. Both bending and compression characteristics and histomorphometric measurements of trabecular bone mass were unaltered by leptin treatment or photoperiod. Our data therefore show that despite a high natural amplitude cycle of leptin, this hormone has no apparent role in the regulation of bone metabolism, and therefore do not support recent propositions that this hormone is an important component in the metabolism of bone tissue.

Animals↗
PubMed2005

The effects of lanthanum carbonate and calcium carbonate on bone abnormalities in patients with end-stage renal disease.

BACKGROUND: Renal osteodystrophy is a common complication of end-stage renal disease (ESRD) and is a major cause of morbidity in patients with ESRD. High serum levels of phosphorus, calcium and parathyroid hormone are associated with the development of this disease. The effects on bone of treatment with lanthanum carbonate, a new phosphate binder, and calcium carbonate were assessed in patients with ESRD. METHODS: This was an open-label, multicenter, parallel-group study. Patients were recruited within 12 weeks of commencing dialysis. Following screening, phosphate binder administration was stopped, tetracycline labeling administered and a transiliac bone biopsy taken. After randomization to lanthanum carbonate or calcium carbonate, patients were titrated to an optimum dose for 8 weeks and maintained at this dose for 44 weeks. The bone was then labeled and a second biopsy taken. Biopsy samples were analyzed histomorphometrically. RESULTS: Paired bone biopsies from 33 lanthanum carbonate- and 30 calcium carbonate-treated patients were suitable for analysis. None of the patients on either treatment developed osteomalacia. Assessment of activation frequency changes showed that 41% of biopsies from lanthanum carbonate-treated patients moved towards normal (observed values at the follow-up biopsy were closer to expected values than were the baseline values, so patients were considered to be improved) compared with 23% of calcium carbonate-treated patients (p = 0.15). CONCLUSIONS: This study indicates that there was no evidence of aluminum-like toxicity with lanthanum carbonate after 1 year of treatment in ESRD patients commencing dialysis, and there appeared to be a beneficial effect on bone-cell function and activity compared with calcium carbonate.

Adult↗
PubMed2002

Adipocytic proportion of bone marrow is inversely related to bone formation in osteoporosis.

AIMS: Preliminary studies have suggested that there is an increase in adipocytic tissue in osteoporotic (OP) bone, supporting in vitro evidence for a switch in differentiation of stromal cells from the osteoblastic to the adipocytic lineage. To investigate this the variation of the ratio of adipose tissue to haemopoietic/stromal tissue in OP bone was measured. METHODS: The ratio of adipocytic to haemopoietic/stromal tissue (A/H) was measured by semi-automated image analysis in iliac crest biopsies from 127 patients with osteoporosis (84 female patients, 48 male patients; mean age, 55 years; range, 5-80). Fourteen patients with normal histomorphometric data (nine women; five men; mean age, 48 years; range 21-70) acted as controls. RESULTS: The ratio of A/H was higher in OP bone than in the normal controls (OP mean 43.06% v normal mean 22.4%; p < 0.001). Multiple regression analysis showed that 98.5% of the variability in the A/H ratio was the result of age and several measures of bone formation, including cancellous wall thickness, osteoid volume, cancellous thickness, cortical wall thickness, cancellous apposition rate, and bone formation rate, together with cancellous separation (each significant at p < 0.001). Those with the greatest effect on the A/H ratio (in decreasing order) were cancellous apposition rate, osteoid volume, and age. CONCLUSIONS: Cancellous apposition rate, osteoid volume, and age were associated with the increase in the proportion of adipose tissue present in OP bone. Of these, cancellous apposition rate reflects osteoblast activity, indicating that the increase in the volume of adipose tissue in osteoporosis is associated with reduced bone formation, supporting the postulated switch in differentiation of stromal cells from the osteoblastic to the adipocytic pathway in osteoporosis.

Adipocytes↗
PubMed2001

A novel cell culture model of chondrocyte differentiation during mammalian endochondral ossification.

Endochondral ossification (EO) occurs in the growth plate where chondrocytes pass through discrete stages of proliferation, maturation, hypertrophy, and calcification. We have developed and characterized a novel bovine cell culture model of EO that mirrors these events and will facilitate in vitro studies on factors controlling chondrocyte differentiation. Chondrocytes derived from the epiphyses of long bones of fetal calves were treated with 5-azacytidine (aza-C) for 48 h. Cultures were maintained subsequently without aza-C and harvested at selected time points for analyses of growth and differentiation status. A chondrocytic phenotype associated with an extensive extracellular matrix rich in proteoglycans and collagen types II and VI was observed in aza-C-treated and -untreated cultures. aza-C-treated cultures were characterized by studying the expression of several markers of chondrocyte differentiation. Parathyroid hormone-related protein (PTHrP) and its receptor, both markers of maturation, were expressed at days 5-9. Type X collagen, which is restricted to the stage of hypertrophy, was expressed from day 11 onward. Hypertrophy was confirmed by a 14-fold increase in cell size by day 15 and an increased synthesis of alkaline phosphatase during the hypertrophic period (days 14-28). The addition of PTHrP to aza-C-treated cultures at day 14 led to the down-regulation of type X collagen by 6-fold, showing type X collagen expression is under the control of PTHrP as in vivo. These findings show that aza-C can induce fetal bovine epiphyseal chondrocytes to differentiate in culture in a manner consistent with that which occurs during the EO process in vivo.

Animals↗
PubMed2000

The PDZ-interacting domain of cystic fibrosis transmembrane conductance regulator is required for functional expression in the apical plasma membrane.

Polarization of cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP-activated chloride channel to the apical plasma membrane in epithelial cells is critical for vectorial chloride transport. Previously, we reported that the C terminus of CFTR constitutes a PDZ-interacting domain that is required for CFTR polarization to the apical plasma membrane and interaction with the PDZ domain-containing protein EBP50 (NHERF). PDZ-interacting domains are typically composed of the C-terminal three to five amino acids, which in CFTR are QDTRL. Our goal was to identify the key amino acid(s) in the PDZ-interacting domain of CFTR with regard to its apical polarization, interaction with EBP50, and ability to mediate transepithelial chloride secretion. Point substitution of the C-terminal leucine (Leu at position 0) with alanine abrogated apical polarization of CFTR, interaction between CFTR and EBP50, efficient expression of CFTR in the apical membrane, and chloride secretion. Point substitution of the threonine (Thr at position -2) with alanine or valine had no effect on the apical polarization of CFTR, but reduced interaction between CFTR and EBP50, efficient expression of CFTR in the apical membrane as well as chloride secretion. By contrast, individual point substitution of the other C-terminal amino acids (Gln at position -4, Asp at position -3 and Arg at position -1) with alanine had no effect on measured parameters. We conclude that the PDZ-interacting domain, in particular the leucine (position 0) and threonine (position -2) residues, are required for the efficient, polarized expression of CFTR in the apical plasma membrane, interaction of CFTR with EBP50, and for the ability of CFTR to mediate chloride secretion. Mutations that delete the C terminus of CFTR may cause cystic fibrosis because CFTR is not polarized, complexed with EBP50, or efficiently expressed in the apical membrane of epithelial cells.

Animals↗
PubMed2000

Placenta growth factor (PlGF) induces vascular endothelial growth factor (VEGF) secretion from mononuclear cells and is co-expressed with VEGF in synovial fluid.

The aims of this study were (i) to determine whether PlGF, VEGF and PlGF/VEGF heterodimers are detected in synovial fluid (SF) and plasma samples from patients with a range of arthropathies; (ii) to describe whether any correlation exists between SF PlGF, VEGF and PlGF/VEGF heterodimer levels and the total and differential SF leucocyte counts; and (iii) to investigate the regulation of peripheral blood mononuclear cell (PBMC) VEGF secretion by stimuli relevant to inflammatory joints. PlGF, VEGF and PlGF/VEGF heterodimer levels were measured in the SF and plasma of patients with a range of arthropathies and normal controls by ELISA. Western blotting for PlGF was performed on SF from three patients with rheumatoid arthritis (RA) and primary inflammatory arthropathies. VEGF was quantified in cell culture supernatants after stimulation with lipopolysaccharide (LPS), PlGF or cobalt ions of PBMC isolated from RA patients and controls. PlGF and VEGF were detected in all SF samples. PlGF/VEGF heterodimers were detected in 10.2% of SF samples, most frequently in RA samples. Western blotting confirmed the presence of PlGF in RA SF. PlGF was detected in 52% of RA and 31% of control plasma samples, and VEGF was detected in 38% of RA and 38% of control plasma samples. PlGF/VEGF heterodimers were detected in 21% of RA samples and none of the control samples. In primary inflammatory arthropathy patients, SF PlGF and VEGF levels correlated significantly with the SF total leucocyte count and the neutrophil count. PlGF was the most potent inducer of PBMC VEGF production in both RA and control subjects. This is the first report of the detection of PlGF and PlGF/VEGF heterodimers in the SF of patients with inflammatory arthropathies, and we have shown for the first time that PlGF up-regulates PBMC VEGF production. PlGF may therefore play a key role in the production of VEGF in the inflammatory joint.

Adolescent↗
PubMed1999

Differential patterns of altered bone formation in different bone compartments in established osteoporosis.

AIM: To investigate the level of bone formation in the different bone compartments in cases of established osteoporosis, as previous work has concentrated on trabecular bone alone. METHODS: Bone formation rates were measured histomorphometrically, in the periosteal (P), cortical (C), subcortical (SC), and trabecular (T) compartments in iliac crest biopsies from 159 patients with established osteoporosis. The values were standardised using age and sex matched control data and patterns of differential change determined by analysis of parametric status (increased, normal, reduced). RESULTS: Mean bone formation was reduced in all four compartments. This was more marked (4.4/4.1 standard deviations below the mean in C/T, v 2.3/0.9 in P/SC) and more frequent (reduced in 81.5%/78.3% in T/C, v 43.3%/44% in P/SC) in the trabecular and cortical compartments than in the periosteal or subcortical bone. Parametric status was equal in trabecular and cortical bone in 85.4% of cases, and in periosteal and subcortical bone in 65.7%, but in all four compartments in only 35.1%, indicating differential alteration of bone formation in the two sets of compartments (T/C v P/SC). CONCLUSIONS: Altered trabecular bone formation is important in osteoporosis, but there are differential patterns of alteration in the other three compartments, emphasising the presence of different microenvironments in bone; thus the effect on the cortical compartment was similar to that on the trabecular, while the subcortical and periosteal compartments also showed linkage. The linkage between the two pairs was divergent, indicating different control of bone formation, with resultant different patterns of perturbation in osteoporosis.

Adult↗
PubMed1999

A simple, inexpensive method for teaching how membrane potentials are generated.

We have developed a simple laboratory exercise that uses an inexpensive dialysis membrane (molecular weight cutoff = 100) to illustrate the generation of membrane potentials (Vm) across plasma membranes of animal cells. A piece of membrane approximately 2.0 cm2 is mounted in an Ussing-like chamber. One chamber half is designated cytosol and the other half external. Chamber sidedness helps students relate their findings to those of real cells. As in real cells, outward directed K+ concentration gradients [high cytosolic K+ concentration ([K+]c) and low extracellular K+ concentration] generate cytosol electrically negative Vm with a slope of approximately -45 mV/decade change in [K+]c. The polarity of Vm reflects the outward flow of potassium ions because flow of the larger counterion, H2PO4-, is restricted to the pores in the membrane. A slope less than Nernstian (<59 mV/decade) suggests that the membrane is slightly permeable to H2PO4-. Importantly, this facilitates teaching the use of the Nernst equation to quantify the relationship between ion concentration ratios across membranes and magnitude of Vm. For example, students use their data and calculate a permeability ratio PK/PH2PO4 that corresponds to a slope of approximately 24% less than Nernstian. This calculation shows that Nernstian slopes are achieved only when permeability to the counterion is zero. Finally, students use the concept of membrane capacitance to calculate the number of ions that cross the membrane. They learn where these ions are located and why the bulk solutions conform to the principle of electroneutrality.

Animals↗
PubMed1999

A PDZ-interacting domain in CFTR is an apical membrane polarization signal.

Polarization of the cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP-activated chloride channel, to the apical plasma membrane of epithelial cells is critical for vectorial transport of chloride in a variety of epithelia, including the airway, pancreas, intestine, and kidney. However, the motifs that localize CFTR to the apical membrane are unknown. We report that the last 3 amino acids in the COOH-terminus of CFTR (T-R-L) comprise a PDZ-interacting domain that is required for the polarization of CFTR to the apical plasma membrane in human airway and kidney epithelial cells. In addition, the CFTR mutant, S1455X, which lacks the 26 COOH-terminal amino acids, including the PDZ-interacting domain, is mispolarized to the lateral membrane. We also demonstrate that CFTR binds to ezrin-radixin-moesin-binding phosphoprotein 50 (EBP50), an apical membrane PDZ domain-containing protein. We propose that COOH-terminal deletions of CFTR, which represent about 10% of CFTR mutations, result in defective vectorial chloride transport, partly by altering the polarized distribution of CFTR in epithelial cells. Moreover, our data demonstrate that PDZ-interacting domains and PDZ domain-containing proteins play a key role in the apical polarization of ion channels in epithelial cells.

Amino Acid Sequence↗
PubMed1998

The bcl-2 knockout mouse exhibits marked changes in osteoblast phenotype and collagen deposition in bone as well as a mild growth plate phenotype.

Histological examination of long bones from 1-day-old bcl-2 knockout and age-matched control mice revealed no obvious differences in length of bone, growth plate architecture or stage of endochondral ossification. In 35-day-old bcl-2 knockout mice that are growth retarded or 'dwarfed'. the proliferative zone of the growth plate appeared slightly thinner and the secondary centres of ossification less well developed than their age-matched wild-type controls. The most marked histological effects of bcl-2 ablation were on osteoblasts and bone. 35-day-old knockout mouse bones exhibited far greater numbers of osteoblasts than controls and the osteoblasts had a cuboidal phenotype in comparison with the normal flattened cell appearance. In addition, the collagen deposited by the osteoblasts in the bcl-2 knockout mouse bone was disorganized in comparison with control tissue and had a pseudo-woven appearance. The results suggest an important role for Bcl-2 in controlling osteoblast phenotype and bone deposition in vivo.

Animals↗
PubMed1998

Luminal L-alanine stimulates exocytosis at the K+-conductive apical membrane of Aplysia enterocytes.

In Aplysia intestine, stimulation of Na+ absorption with luminal alanine increases apical membrane K+ conductance (GK,a), which presumably regulates enterocyte volume during stimulated Na+ absorption. However, the mechanism responsible for the sustained increase in plasma membrane K+ conductance is not known for any nutrient-absorbing epithelium. In the present study, we have begun to test the hypothesis that the alanine-induced increase in GK,a in Aplysia enterocytes results from exocytic insertion of K+ channels into the apical membrane. We used the fluid-phase marker horseradish peroxidase to assess the effect of alanine on apical membrane exocytosis and conventional microelectrode techniques to assess the effect of alanine on fractional capacitance of the apical membrane (fCa). Luminal alanine significantly increased apical membrane exocytosis from 1.04 +/- 0.30 to 1.39 +/- 0.38 ng. min-1. cm-2. To measure fCa, we modeled the Aplysia enterocyte as a double resistance-capacitance (RC) electric circuit arranged in series. Several criteria were tested to confirm application of the model to the enterocytes, and all satisfied the model. When added to the luminal surface, alanine significantly increased fCa from 0.27 +/- 0. 02 to 0.33 +/- 0.04 (n = 10) after 4 min. There are two possible explanations for our findings: 1) the increase in exocytosis, which adds membrane to the apical plasma membrane, prevents plasma membrane fracture, and 2) the increase in exocytosis delivers K+ channels to the apical membrane by exocytic insertion. After the alanine-induced depolarization of apical membrane potential (Va), there is a strong correlation (r = 0.96) between repolarization of Va, which reflects the increase in GK,a, and increase in fCa. This correlation supports the exocytic insertion hypothesis for activation of GK,a.

Alanine↗
PubMed1998

Isolated plantar fracture-dislocation of the middle cuneiform.

A previously unreported case of plantar dislocation of the medial cuneiform is described. The significance of this injury does not lie in its rarity, but in the amount of force required to cause such an injury. This large force may cause bony disruption, along with significant soft-tissue injury, and even compartment syndrome. Analysis of the preoperative evaluation, including the importance of a computed axial tomographicscan, operative intervention, and postoperative care are discussed.

Adult↗
PubMed1998

Blood vessel density in canine osteosarcoma.

Canine osteosarcoma is a prevalent bone neoplasm which has similarities to the human disease. We used a retrospective study to investigate the possibility that tumor vascularity may provide useful prognostic information, indicative of the role of this parameter in progression of this cancer. We quantified microvessel density in 52 histological specimens of primary tumor, immunostained for von Willebrand's Factor to identify vascular endothelium. For the 20 cases not euthanized at presentation or lost to follow-up, we found significantly higher tumor microvascular densities in animals presenting with detectable pulmonary metastases (5 of 20), and significantly lower densities in animals without metastatic disease at presentation, but later surviving to develop pulmonary metastases (7 of 20; P < 0.05). Animals with no evidence of pulmonary metastases at time of death (8 of 20) had intermediate vascular densities in their tumors. The results of this preliminary study suggest that vascularity of the primary tumor may be an indication of tumor progression. Future studies with a larger number of cases should establish whether vascular density can be a useful prognostic parameter for canine osteosarcoma.

Animals↗