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Biomedical subjects

M C Stewart

Publications and source records attributed to M C Stewart.

At least 19 recordsLinked to original sources
PubMed2006

ADAMTS5-mediated aggrecanolysis in murine epiphyseal chondrocyte cultures.

OBJECTIVE: Aggrecan degradation by aggrecanases [a disintegrin and metalloproteinase with thrombospondin-like motifs (ADAMTS) 1, 4, 5, 8, 9, 15] is considered to initiate much of the cartilage pathology seen in human arthritis, however, the proteinase responsible and its mode of control is unclear. The present work was done to examine mechanisms of aggrecanase control in a novel murine epiphyseal cell system and to determine whether ADAMTS5 alone is responsible for aggrecanolysis by these cells. METHODS: Epiphyseal cells from 4-day-old mice (wild type, TS-5 (-/-), CD44(-/-), syndecan-1(-/-), membrane type-4 matrix metalloproteinase [MT4MMP(-/-)]) were maintained in non-adherent aggregate cultures and aggrecanolysis studied by biochemical and histochemical methods. Confocal immunolocalization analyses were done with specific probes for ADAMTS5, hyaluronan (HA) and aggrecanase-generated fragments of aggrecan. RESULTS: Aggrecanolysis by these cells was specifically aggrecanase-mediated and it occurred spontaneously without the need for addition of catabolic stimulators. Chondrocytes from ADAMTS5-null mice were aggrecanase-inactive whereas all other mutant cells behaved as wild type in this regard suggesting that ADAMTS5 activity is not controlled by CD44, syndecan-1 or MT4MMP in this system. Immunohistochemical analysis supported the central role for ADAMTS5 in the degradative pathway and indicated that aggrecanolysis occurs primarily in the HA-poor pericellular region in these cultures. CONCLUSION: These findings are consistent with published in vivo studies showing that single-gene ADAMTS5 ablation confers significant protection on cartilage in murine arthritis. We propose that this culture system and the analytical approaches described provide a valuable framework to further delineate the expression, activity and control of ADAMTS-mediated aggrecanolysis in human arthritis.

ADAM Proteins↗
PubMed2005

Wetting and drying at a curved substrate: long-ranged forces.

We examine the interfacial properties of a hard spherical cavity, radius R , immersed in a solvent in which the fluid-fluid interaction potential contains both a hard-sphere repulsive part and an attractive - r(-6) component. Near to liquid-gas coexistence where the chemical potential deviation deltamu identical withmu- mu(co) (T) --> 0(+) complete wetting by the gas (drying) occurs and a coarse-grained effective Hamiltonian approach shows that the wall/liquid surface tension has a term in R(-2/3) , i.e., a leading-order power-law nonanalyticity in the curvature ( R-1 ) in the large cavity limit. For states sufficiently well removed from coexistence the surface tension can be expanded in integer powers of the curvature R-1 , provided R> R(c) with the length scale given by R(c) =2 gamma(gl) (infinity) / (Deltarhodeltamu) , where gamma(gl) (infinity) is the planar liquid/gas surface tension and Deltarho is the difference between the coexisting densities. However, even in these circumstances there are additional R-2 ln R contributions to the surface tension arising from the dispersion forces. An exact statistical mechanical sum rule is used to relate the density of the fluid at the point of contact with the cavity, rho ( R+ ,mu) , to the pressure of the reservoir and the surface tension. This predicts that rho ( R+ ,mu) acquires a term in R(-5/3) in the regime R< R(c) . Numerical results obtained by applying classical density functional theory to this model confirm all the predictions from the coarse-grained approach for both the surface tension and the contact density. We argue that our results for leading-order nonanalytic contributions are exact, i.e., they should remain valid in the presence of interface fluctuations, and we discuss briefly the repercussions for solvation phenomena and for other wetting situations.

Journal Article↗
PubMed2001

Rapid repair of titanium particle-induced osteolysis is dramatically reduced in aged mice.

Aseptic loosening is the most common cause of orthopaedic implant failure. This process is thought to be due to osteolysis induced by implant-derived wear particles. Teitelbaum and colleagues have recently developed a promising murine calvarial model of wear particle-induced osteolysis. However, prior to this study, this model had only been assessed qualitatively. We now report a reproducible, quantitative version of the calvarial model of wear particle-induced osteolysis, in which the extent of osteolysis (and repair) of entire parietal bones is assessed by histomorphometry of contact microradiographs. Using this model, we found that the osteolytic response is transient and rapidly repaired in one month old mice. The extent of osteolysis peaks 7 days after particle implantation and returns to baseline levels by 13 days. A similar amount of osteolysis and even more extensive repair is observed when particles are implanted repeatedly. In contrast, aged mice develop progressive osteolysis with no detectable repair. As a result, 26 month old mice have approximately 17-fold more osteolysis than one month old mice 21 days after particle implantation. Skeletally mature, adult mice (4-16 months old) show an intermediate pattern of response. Osteolysis in these mice peaks at 7 days after particle implantation but it is repaired more slowly than in the one month old mice. Taken together, these results underscore the role of an imbalance between bone resorption and bone formation in the development of aseptic loosening and suggest that agents that stimulate bone formation maybe useful in prevention or treatment of aseptic loosening.

Aging↗
PubMed2000

Expression of cyclin-dependent kinase inhibitors in epiphyseal chondrocytes induced to terminally differentiate with thyroid hormone.

A growing body of evidence suggests that systemic hormones and peptide growth factors may exert their effects on cell growth and differentiation in part through regulation of the cell division cycle. We hypothesized that thyroid hormone regulates terminal differentiation of growth plate chondrocytes in part through controlling cell cycle progression at the G1/S restriction point. Our results support this hypothesis by demonstrating that treatment of epiphyseal chondrocytes with thyroid hormone under chemically defined conditions results in the arrest of DNA synthesis and the onset of terminal differentiation, indicating that thyroid hormone is one factor capable of regulating the transition between cell growth and differentiation in these cells. This terminal differentiation process is associated with induction of the cyclin/cyclin-dependent kinase inhibitors p21(cip-1 waf-1) and p27kip1, suggesting that thyroid hormone may regulate terminal differentiation in part by arresting cell cycle progression through induction of cyclin-dependent kinase inhibitors.

Animals↗
PubMed2000

Phenotypic stability of articular chondrocytes in vitro: the effects of culture models, bone morphogenetic protein 2, and serum supplementation.

Numerous in vitro culture models have been developed for the investigation of chondrocyte and cartilage biology. In this study, we investigated the stability of the chondrocytic phenotype in monolayer, aggregate, pellet, and explant culture models and assessed the effects of recombinant human bone morphogenetic protein 2 (rhBMP-2) and serum supplementation on the phenotype in each model. Phenotypic effects were assessed by analyses of procollagen type II, aggrecan, (V + C)- fibronectin, and procollagen type I messenger RNA expression. In monolayer cultures, we noted a characteristic loss of procollagen type II and induction of procollagen type I expression. The aggregate and pellet culture models supported matrix protein gene expression profiles more reflective of in vivo levels. In explant cultures, expression of matrix protein genes was consistently depressed. Treatment with rhBMP-2 significantly increased the expression of procollagen type II and aggrecan in monolayer cultures; however, other models showed comparatively little response. Similarly, serum supplementation significantly down-regulated procollagen type II and aggrecan expression in monolayer cultures but had less effect on gene expression in the other models. Serum supplementation increased procollagen type I expression in monolayer and aggregate cultures. These results suggest that the influence of exogenous BMP-2 and serum on expression of chondrocyte-specific matrix protein genes is influenced by aspects of substrate attachments, cellular morphology, and/or cytoskeletal organization. Finally, the analyses of fibronectin expression suggest that V and C region alternative splicing in chondrocytes is linked to the establishment of a three-dimensional multicellular complex.

Aggrecans↗
PubMed1999

Investigation of seroprevalence of respiratory virus infections in an infant population with a multiantigen fluorescence immunoassay using heel-prick blood samples collected on filter paper.

Respiratory viruses are an extremely common cause of childhood morbidity. However, the current seroprevalence of viruses in infant populations is difficult to establish because invasive venipuncture may be technically and ethically unacceptable. This prospective study aimed to establish the seroprevalence of respiratory viruses in an infant population by use of a novel multiantigen fluorescence immunoassay against common respiratory viruses, using heel-prick blood samples collected on filter paper. Mothers and babies were recruited in the immediate peripartum period in the Royal Maternity Hospital, Belfast. Cord blood samples at birth and heel-prick filter paper blood samples at 7 mo were collected for measurement of virus-specific IgG to respiratory syncytial virus, influenza A virus, adenovirus, and parainfluenza virus type 1, type 2, and type 3 by indirect immunofluorescence using a multiviral assay developed for this purpose. Of 386 mothers approached, 325 (84%) permitted follow-up at 7 mo, and of these, 256 (79%) agreed to the heel prick. From 234 paired samples, 125 infections were documented. Adenovirus infections were commonest, 53 (22.6%), followed by respiratory syncytial virus, 32 (13.7%); influenza A virus, 22 (9.4%); parainfluenza virus type 3, 14 (6%); parainfluenza virus type 1, 2 (0.85%); and parainfluenza virus type 2, 2 (0.85%). These results demonstrate the seroprevalence of a range of respiratory viruses in an infant population, using a novel multiviral immunoassay. The filter paper collection of blood samples and multiantigen assay format has implications for easy, widespread viral serodiagnosis in both seroepidemiology studies and in the diagnosis of pediatric viral illnesses. Filter paper permits recovery of respiratory virus-specific IgG and can be used as a simple and acceptable epidemiologic and diagnostic tool.

Antigens, Viral↗
PubMed1999

Drawing up clinical guidelines.

This report describes the processes involved in compiling a set of guidelines, locally developed by informal consensus, for the management of common paediatric medical problems in a teaching hospital.

Decision Making↗
PubMed1998

Facial measurements for frame design.

Anthropometric data for the purpose of spectacle frame design are scarce in the literature. Definitions of facial features to be measured with existing systems of facial measurement are often not specific enough for frame design and manufacturing. Currently, for individual frame design, experienced personnel collect data with facial rules or instruments. A new measuring system is proposed, making use of a template in the form of a spectacle frame. Upon fitting the template onto a subject, most of the measuring references can be defined. Such a system can be administered by lesser-trained personnel and can be used for researches covering a larger population.

Anthropometry↗
PubMed1998

Ophthalmic anthropometry for Hong Kong Chinese adults.

A database of ophthalmic anthropometry is established which is useful for the design of spectacles for southeast Asian people. Statistical analysis reveals significant variations in the facial dimensions between male and female subjects. Results of the study are given separately for each sex and for the combined population. Hong Kong Chinese are found to have larger frontal angles, bigger angles of splay, and a less prominent bridge in the nose. Spectacle frames should be designed according to the targeted gender population, and to accommodate the characteristics of Asian faces.

Adolescent↗
PubMed1997

Expression of p21CIP1/WAF1 in chondrocytes.

During endochondral ossification, proliferative activity of chondrocytes is arrested and the cells undergo terminal hypertrophic differentiation. We examined the expression of the cyclin-dependent kinase inhibitor, p21(CIP1/WAF1) in permanent cartilage (xyphoid and articular cartilage) and in cartilage undergoing endochondral ossification (growth plate, epiphyseal ossification centers, and costochondral junctions) to determine if p21 is up-regulated in chondrocytes during hypertrophic differentiation. Northern blot analyses demonstrated expression of p21 in chondrocytes undergoing endochondral ossification and from sites of permanent cartilage. Quantitative analyses of Northern data showed an association between expression of the hypertrophic-specific marker, collagen type X, and the level of 21 expression. In situ hybridization of rodent femoropatellar joints and costochondral junctions localized p21 mRNA to chondrocytes within both the proliferative and hypertrophic zones of the growth plates, in chondrocytes involved in formation of the epiphyseal ossification centers, and in articular chondrocytes. Immunohistochemical analyses of p21 expression in the same tissues demonstrated comparatively higher levels of p21 protein in postmitotic chondrocytes. These data suggest that p21 is active in cell cycle regulation in chondrocytes, and that increased p21 expression is associated with hypertrophic differentiation.

Animals↗
PubMed1995

Acute febrile diarrhoea in horses: 86 cases (1986-1991).

Eighty-six horses presented for examination at the Rural Veterinary Centre between January 1986 to December 1991 with acute diarrhoea. The average age of affected horses was 3.2 +/- 0.2 years (mean +/- SE), with 69% three years or younger. Sixty-one horses were male (36 stallions, 25 geldings) and 83 horses were Thoroughbreds (47) or Standardbreds (36). Sixty-six horses were undergoing routine training at the time of onset of diarrhoea. Eight horses were afflicted with a non-specific illness within one to five days before the onset of diarrhoea, whereas eight horses developed diarrhoea during or within 48 h of discontinuation of antimicrobial therapy. Three horses developed the diarrhoea within 24 h of road transportation. Clinically, the disorder was characterised by a fever, sudden onset of profuse diarrhoea, clinical evidence of dehydration (estimated to be 5 to 12% of body weight at the time of admission) and shock. Degenerative leucopaenia, hyponatraemia, hypochloraemia, hyperkalaemia, hyperglycaemia and azotaemia were characteristic laboratory findings. Laminitis was a sequel in about 30% of cases. The cause of diarrhoea remained undetermined in most cases. Salmonellas were isolated from faecal or tissue samples in only two cases. Similarly, there was no evidence of seroconversion to Erhlichia risticii in 17 cases. Sixty-two of the horses survived the acute phase of the disease in response to supportive care. In horses that did not survive, necropsies were performed and revealed sanguineous or turbid peritoneal fluid. The colonic and caecal walls were oedematous and thickened with serosal congestion and discolouration of these organs evident grossly.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1992

A study of reference lines for mandibular plane angles.

Four mandibular plane angles, MP-sella nasion, MP-Frankfort horizontal, MP-articulare nasion, and MP-gnathion occiput, were compared. Highly significant correlations were found among all four. The relation of an extension of the mandibular plane to the posterior inferior outline of the cranium was found to provide a valid indication of mandibular plane angle. Articulare nasion was found to be the reference line most likely to provide a true indication of the mandibular inclination rather than a reflection of a variation in the reference line itself.

Cephalometry↗
PubMed1992

Changing trends in approach to wheezy children by family doctors.

The prevalence of asthma in children appears to have increased dramatically over the past 20 years. There is evidence that some of this increase is due to earlier recognition and relabeling of symptoms such as wheeze. In this study we set out to see if increased awareness of the presentation of asthma in young children has led to earlier diagnosis by family doctors and a decrease in the number of courses of antibiotics given before the introduction of bronchodilators. The family doctor records of 769 children aged 0-5 years were examined retrospectively by an independent paediatrician. One third had at least one documented episode of wheeze and the prevalence of asthma was 10.5%. The mean age of diagnosis was 2.59 years although the mean age at which bronchodilators were introduced was 2.22 years. 22 children, who were never recorded as being asthmatic, were nevertheless appropriately treated with bronchodilators.

Age Factors↗