Biomedical subjects

K W Ng

Publications and source records attributed to K W Ng.

At least 37 records · Page 2Linked to original sources

PubMed1998

Expression of rat homeobox gene, rHOX, in developing and adult tissues in mice and regulation of its mRNA expression in osteoblasts by bone morphogenetic protein 2 and parathyroid hormone-related protein.

The rat homeobox gene, rHox, was cloned from a rat osteosarcoma cDNA library. Southwestern and gel mobility shift analyses showed that rHox binds to the promoter regions of collagen (alpha1)I and osteocalcin genes while transient transfection with rHox resulted in repression of their respective promoter activities. In situ hybridization studies showed that rHox mRNA was widely expressed in osteoblasts, chondrocytes, skeletal muscle, skin epidermis, and bronchial and intestinal epithelial cells, as well as cardiac muscle in embryonic and newborn mice. However in 3-month-old mice, rHox mRNA expression was restricted to osteoblasts, megakaryocytes, and myocardium. Bone morphogenetic protein 2, a growth factor that commits mesenchymal progenitor cells to differentiate into osteoblasts, down-regulated rHox mRNA expression by 40-50% in UMR 201, a rat preosteoblast cell line, in a time- and dose-dependent manner. In contrast, PTH-related protein (PTHrP), recently shown to be a negative regulator of chondrocyte differentiation, significantly enhanced rHox mRNA expression in UMR 106-06 osteoblastic cells by 3-fold at 24 h while at the same time down-regulating expression of pro-alpha1(I) collagen mRNA by 60%. Expression of rHox mRNA in calvarial osteoblasts derived from PTHrP -/- mice was approximately 15% of that observed in similar cells obtained from normal mice. In conclusion, current evidence suggests that rHox acts as a negative regulator of osteoblast differentiation. Furthermore, down-regulation of rHox mRNA by bone morphogenetic protein 2 and its up-regulation by PTHrP support a role of the homeodomain protein, rHox, in osteoblast differentiation.

Animals↗

PubMed1998

Percutaneous intramedullary Kirschner wiring for displaced diaphyseal forearm fractures in children.

Displaced fractures of the forearm in children are often treated conservatively, but there is a relatively high incidence of redisplacement, malunion and consequent limitation of function. We have performed percutaneous Kirschner (K) wire fixation in 72 such children under the age of 14 years, of which 57 were reviewed for our study. Both the radius and ulna were fractured in 45 (79%), the radius only in eight and the ulna only in four. The mean initial angulation was 19 degrees in the lateral plane and 9 degrees in the anteroposterior plane for the radius and 15 degrees and 9 degrees, respectively, for the ulna. In 42 patients (74%) we performed closed reduction. In the remaining 15 (26%) closed reduction failed and an open reduction, through a minimal approach, was required before K wiring. At a mean follow-up of 20 months all patients had good functional results with an excellent range of movement. Only five had angulation of from 10 degrees to 15 degrees and none had nonunion, premature epiphyseal closure or deep infection. Percutaneous intramedullary K wiring for forearm diaphyseal fracture is a convenient, effective and safe operation, with minimal complications.

Adolescent↗

PubMed1997

The binding of a Fos/Jun heterodimer can completely disrupt the structure of a nucleosome.

An important first step in the chromatin remodelling process is the initial binding of a transcriptional activator to a nucleosomal template. We have investigated the ability of Fos/Jun (a transcriptional activator involved in the signal transduction pathway) to interact with its cognate binding site located in the promoter region of the mouse fos-related antigen-2 (fra-2) promoter, when this site was reconstituted into a nucleosome. Two different nucleosome assembly systems were employed to assemble principally non-acetylated or acetylated nucleosomes. The ability of Fos/Jun to interact with an acetylated or an unacetylated nucleosome differed markedly. Fos/Jun bound to an unacetylated nucleosome with only a 4- to 5-fold reduction in DNA binding affinity compared with naked DNA. Strikingly, the binding of Fos/Jun to a single high-affinity site incorporated into an acetylated nucleosome resulted in the complete disruption of nucleosomal structure without histone displacement. Moreover, this disruption was sufficient to facilitate the subsequent binding of a second transcription factor.

Acetylation↗

PubMed1997

Bone biology.

Bone is a metabolically active and highly organized tissue consisting of a mineral phase of hydroxyapatite and amorphous calcium phosphate crystals deposited in an organic matrix. Bone has two main functions. It forms a rigid skeleton and has a central role in calcium and phosphate homeostasis. Bone modelling is the process associated with growth and re-shaping of bones in childhood and adolescence. This is distinguished from bone remodelling, which describes the lifelong process whereby skeletal tissue is continually being resorbed and replaced in order to maintain skeletal integrity, shape and mass. Bone remodelling is controlled by systemic hormones and cytokines and is an integral part of the calcium homeostatic system. The maintenance of a normal, healthy skeletal mass depends on interactions between osteoblasts, osteoclasts and constituents of the bone matrix to keep the process of bone resorption and formation in balance. The factors, local and systemic, which regulate these processes are discussed.

Animals↗

PubMed1997

Temporal expression of PTHrP during endochondral bone formation in mouse and intramembranous bone formation in an in vivo rabbit model.

Expression of parathyroid hormone-related protein (PTHrP) messenger RNA (mRNA) and protein was investigated throughout the developmental progression of endochondral bone formation in mouse and intramembranous bone formation in an in vivo model in rabbit, using in situ hybridization and immunohistochemistry. Endochondral bone formation was investigated in a developing embryo, newborn, and adult mouse. In fetal long bones through to newborn (day 7), PTHrP mRNA and protein were consistently expressed in chondrocytes within the proliferative, transitional, and hypertrophic zones. In addition, high levels of PTHrP were also detected in osteoblasts on the surface of trabecular bone surfaces. Similarly, at the adult stage (week 7), PTHrP mRNA and protein were consistently expressed in chondrocytes at epiphyseal ends of the subarticular cartilage, within cortical periosteum, as well as in osteoblasts located at the metaphyseal trabecular bone surfaces. Using an in vivo intramembranous bone formation model in rabbits, expression of PTHrP mRNA and protein was demonstrated in preosteoblasts prior to trabecular bone formation (1-week bone harvest). As bone formed (2-, 3-, and 4-week bone tissue harvests), PTHrP mRNA and protein were highly expressed in actively synthesizing osteoblasts and in those osteocytes embedded within the superficial layers of the bone matrix. Lining osteoblasts and osteocytes buried deeply in the bone matrix displayed weak or no signal for PTHrP. The pattern of spatial and temporal expression of PTHrP demonstrated in cartilage cells and osteoblasts in the two systems suggests an important role of PTHrP in both endochondral and intramembranous bone formation.

Animals↗

PubMed1997

Differential inhibitory effects of melatonin analogs and three naphthalenic ligands on 2-[125I]iodomelatonin binding to chicken tissues.

We have compared the 50% inhibition values of 2-[125I]iodomelatonin ([125I]Mel) competition curves by melatonin and 3 naphthalenic ligands, N-[2-(7-methoxy-1-naphthyl) ethyl] cyclobutane carboxamide (S20642), N-propyl N-[2-(7-methoxy-1-naphtyl) ethyl] urea (S20753), and N-[2-(7-methoxy-1-naphthyl) ethyl] crotonamide (S20750), using membrane preparations of four tissues (lung, spleen, brain, and kidney) of the chicken simultaneously. In retired breeders, we have demonstrated that the affinities of S20642 were similar in the lung and spleen. However they were 2-fold lower in the brain and 80-fold lower in the kidney. Similar differential binding affinities to the melatonin receptors were observed in the four tissues of young male chicks. This suggests that age and sex have little influence on the differential inhibitory properties of melatonin and S20642 in the tissues studied. The addition of guanosine 5'-O-thiotriphosphate (GTPgammaS), which encouraged the uncoupling of melatonin receptor to the G protein complex, lowered the binding affinity of melatonin and S20642 in the tissues studied but their differential affinities in the four tissues were however maintained. The affinities of 5-methoxy-N-cyclopropanoyltryptamine (CPMT) in the kidney were also 5-10-fold lower than those in the lung, spleen, and brain of young male chicks. The distinctive differential affinities of melatonin, S20642, and CPMT for [125I]Mel binding sites in the chicken lung, spleen, brain, and kidney indicated that the binding sites in these tissues are heterogeneous. Our study implicated that the naphthalenic ligand S20642 may be a useful melatonin analog to distinguish melatonin receptor subtypes in tissues and a possible drug candidate worthwhile for further investigations.

Aging↗

PubMed1997

Gastric adenocarcinoma with microangiopathic hemolytic anemia and disseminated intravascular coagulation: a case report.

The case reported was a 54-year-old woman with adenocarcinoma of the stomach who developed microangiopathic hemolytic anemia (MHA) and disseminated intravascular coagulation (DIC). Clinical and laboratory data pertaining to this patient are presented. The patient died of multiple organ failure on the 12th hospital day. Since 1962, a total of 96 cases of MHA occurring in patients with malignancy have been reported. About half of them occurred in patients with gastric carcinoma. The possible pathogenesis of MHA and disseminated intravascular coagulation in patients with gastric adenocarcinoma is discussed.

Adenocarcinoma, Mucinous↗

PubMed1996

The role of gp130-mediated signals in osteoclast development: regulation of interleukin 11 production by osteoblasts and distribution of its receptor in bone marrow cultures.

Interleukin (IL)-11 is a multifunctional cytokine whose role in osteoclast development has not been fully elucidated. We examined IL-11 production by primary osteoblasts and the effects of rat monoclonal anti-mouse glycoprotein 130 (gp130) antibody on osteoclast formation, using a coculture of mouse osteoblasts and bone marrow cells. IL-1, TNF alpha, PGE2, parathyroid hormone (PTH) and 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25(OH)2D3) similarly induced production of IL-11 by osteoblasts, but IL-6, IL-4, and TGF beta did not. Primary osteoblasts constitutively expressed mRNAs for both IL-11 receptor (IL-11R alpha) and gp130. Osteotropic factors did not modulate IL-11R alpha mRNA at 24 h, but steady-state gp130 mRNA expression in osteoblasts was upregulated by 1 alpha,25(OH)2D3, PTH, or IL-1. In cocultures, the formation of multinucleated osteoclast-like cells (OCLs) in response to IL-11, or IL-6 together with its soluble IL-6 receptor was dose-dependently inhibited by rat monoclonal anti-mouse gp130 antibody. Furthermore, adding anti-gp130 antibody abolished OCL formation induced by IL-1, and partially inhibited OCL formation induced by PGE2, PTH, or 1 alpha,25(OH)2D3. During osteoclast formation in marrow cultures, a sequential relationship existed between the expression of calcitonin receptor mRNA and IL-11R alpha mRNA. Osteoblasts as well as OCLs expressed transcripts for IL-11R alpha, as indicated by RT-PCR analysis and in situ hybridization. These results suggest a central role of gp130-coupled cytokines, especially IL-11, in osteoclast development. Since osteoblasts and mature osteoclasts expressed IL-11R alpha mRNA, both bone-forming and bone-resorbing cells are potential targets of IL-11.

Animals↗

PubMed1996

Insulin receptor expression in bone.

Insulin is known to be an important osteotropic hormone. To date, no study has specifically addressed the possibility that insulin receptor expression may be regulated by differentiation in bone. We report a heterogeneous distribution of insulin receptor (IR) within neonatal rat calvaria using a specific monoclonal antibody to the beta-subunit of the rat insulin receptor (CT-1). Specific binding of CT-1 to mature osteoblasts was demonstrated, with little binding over periosteal tissues or osteocytes. Using enzymatically derived subpopulations of calvarial cells, we showed a correlation between alkaline phosphatase activity and insulin-stimulated 2-deoxyglucose (2-DOG) uptake and increased 125I-insulin binding. Since primary calvarial cultures contain many cell types, we compared 125I-insulin binding, insulin-stimulated 2-DOG uptake, and Northern blot analysis of IR mRNA in the clonal preosteoblast-like cell line UMR 201-10B and the mature osteoblast cell line UMR 106-01. It is shown that UMR 106-01 cells possess higher levels of IR mRNA, insulin binding, and insulin-stimulated glucose uptake, and that insulin up-regulated expression of mRNA of the glucose transporter GLUT1 by 3-fold. In contrast, insulin binding was negligible in UMR 201-10B cells, which expressed much lower levels of IR mRNA. UMR 201-10B cells did not possess an insulin-sensitive glucose uptake system, although they express GLUT1 mRNA. These data are consistent with the hypothesis that, as in muscle and fat, insulin receptor expression correlates with the stage of osteoblast differentiation in vivo and in vitro.

Alkaline Phosphatase↗

PubMed1996

Lack of effect of bilateral removal of accessory sex glands on sexual behaviour in the male golden hamster (Mesocricetus auratus).

In the golden hamster removal of the male accessory sex glands (ASG) may impair fertility because of heavy embryonic wastage. As in the rat, induction of pregnancy and parturition in this species depends on adequate vaginocervical stimulation exerted by the stud at the time of mating. It is possible that embryos fail to develop because of adverse effects on copulatory behaviour consequent upon the absence of accessory sex glands and their associated neural input. The aim of the present study was to test this hypothesis. The results showed that intromission latency, ejaculation latency, intromission frequency, interval of ejaculatory series, postejaculatory pause, ejaculatory frequency and duration of ejaculation were not affected by bilateral section of ampullary glands, coagulating glands, dorsolateral prostate, seminal vesicles, ventral prostate or all of the ASG. It was also concluded that none of the ASG function in the elicitation of sexual behaviour in this species.

Animals↗

PubMed1996

Characterization of sounds emanating from the human temporomandibular joints.

Sounds from the temporomandibular joint were recorded on audiotape from 238 individuals by placing microphones in both ears. The recordings were later digitized at a sample rate of 1.7 kHz with 10-bit resolution and stored on computer disk. At least two open-close cycles were assessed from each individual; 2707 different individual sounds were analysed in the time and frequency domains. The sounds were classified as: (a) single, short duration (clicks), (b) multiple, short-duration (creaks) and (c) long duration (crepitus). The sounds were further subclassified into either high or low amplitude by (i) the attack, which produced hard and soft categories and (ii) comparing the amplitude between sides-bilateral sounds were those with amplitudes differing by < 40 mV; the rest were unilateral. To establish the robustness of the classification 42 acoustic events were selected to be classified visually by three observers on two separate occasions. Intraobserver agreement was 82% (kappa = 0.75) while interobserver agreement was 60% (kappa = 0.71). Statistically significant differences were noted between all classifications of sound. These were most marked in the time domain. A simple, automated classification scheme was devised that was capable of categorizing the sounds with 82% agreement (kappa = 0.71) compared to a human observer.

Adolescent↗

PubMed1996

Dexamethasone modulates insulin receptor expression and subcellular distribution of the glucose transporter GLUT 1 in UMR 106-01, a clonal osteogenic sarcoma cell line.

Corticosteroids have profound effects on bone metabolism, though the underlying mechanisms remain unclear. They are also known to alter glucose metabolism, in part by induction of insulin resistance. To determine whether corticosteroids impair glucose metabolism in bone cells, we have examined the actions of dexamethasone (DEX) on glucose transport and insulin receptor expression using osteoblast-like UMR 106-01 cells. DEX was shown to inhibit basal 2-deoxyglucose uptake by up to 30% in a time- and dose-dependent manner. It inhibited insulin-stimulated glucose transport by 13%. By Northern and Western blot analysis, DEX was shown to stimulate insulin receptor mRNA and protein by up to 5.6-fold, but it had no effect on expression of the glucose transporter GLUT 1 mRNA or protein under basal conditions. However, DEX augmented insulin-stimulated GLUT 1 mRNA and protein levels. By Scatchard analysis of labelled insulin binding, DEX increased insulin receptor number per cell by 54%. Subcellular fractionation and Western blot analysis demonstrated that DEX caused a redistribution of immunoreactive GLUT 1 from plasma membrane to intracellular microsomes, resulting in a 21% decrease in GLUT 1 at the plasma membrane. These data suggest that (i) DEX impairs basal glucose transport by post-translational mechanisms in UMR 106-01 cells, (ii) DEX increases insulin receptor mRNA, protein and insulin binding and (iii) the inhibition of glucose transport by DEX dominates its effects on the insulin receptor. It is possible that DEX inhibition of glucose transport in osteoblasts may contribute to steroid-induced osteoporosis.

Animals↗

PubMed1995

Tumor necrosis factor alpha facilitates nuclear actions of retinoic acid to regulate expression of the alkaline phosphatase gene in preosteoblasts.

This study examines the molecular mechanisms of interaction between tumor necrosis factor alpha (TNF alpha) and retinoic acid on the expression of the alkaline phosphatase gene by rat clonal preosteoblastic cells. In this cell line, alkaline phosphatase mRNA was not constitutively expressed but was progressively induced by treatment with 1 microM retinoic acid, detectable by 6 h. Combining retinoic acid with 0.6 nM TNF alpha resulted in alkaline phosphatase mRNA appearing by 2 h, as well as enhanced expression above that observed with retinoic acid alone at 6, 12, and 24 h. Nuclear run-on analysis showed constitutive transcription of the alkaline phosphatase gene in control and TNF alpha-treated cells. At 4 h, retinoic acid, alone or combined with TNF alpha, increased alkaline phosphatase gene transcriptional rate by 2-fold. However, at 24 h, while no retinoic acid effect was retained, retinoic acid plus TNF alpha resulted in a 5-fold increase in alkaline phosphatase transcriptional rate. Examination of the distribution of nuclear alkaline phosphatase mRNA demonstrated that pre-spliced precursor mRNA was localized to the nuclear matrix in control and all treatment groups. Retinoic acid caused a time-dependent accumulation of mature, spliced alkaline phosphatase mRNA located in the non-matrix and cytoplasmic fractions, implying a post-transcriptional action of retinoic acid in nuclear processing and nucleocytoplasmic transport. Adding TNF alpha with retinoic acid greatly enhanced this effect, which was observed after 4 h, prior to any detectable interaction between TNF alpha and retinoic acid on gene transcription. In sharp contrast, only a negligible amount of nuclear processing occurred in control and TNF alpha-treated cells. This study reveals distinct interactions between TNF alpha and retinoic acid at post-transcriptional as well as transcriptional levels to regulate expression of the alkaline phosphatase gene in preosteoblasts.

Alkaline Phosphatase↗

PubMed1995

Retinoic acid stimulates glucose transporter expression in L6 muscle cells.

Factors that regulate the tissue specific and developmental expression of the GLUT4 gene, whose transcribed protein is primarily responsible for mediating insulin stimulated glucose transport, are poorly defined. In this study we examined the effects of retinoic acid, a circulating factor that can promote cellular differentiation, on glucose uptake and glucose transporter expression in cultured L6 muscle cells. At the myoblast stage, treatment with 1 microM retinoic acid for 24 h increased both 1 h and 8 h insulin stimulated uptake of 2-deoxyglucose by more than twofold. A dose and time dependent effect of retinoic acid on 8 h insulin stimulated 2-deoxyglucose uptake was observed at both the myoblast and myocyte stage. Comparatively little effect from retinoic acid treatment was found on basal uptake at either stage. In myoblast cells, retinoic acid increased the content of GLUT4 mRNA in a dose and time dependent manner, an effect that was partially attenuated by insulin. In myocytes retinoic acid increased GLUT4 mRNA levels to 2.3 times basal. Nuclear run-on studies indicate that the increased GLUT4 mRNA represents enhanced transcriptional activity. The results suggest a role for retinoic acid in regulation of expression of the GLUT 4 gene in muscle cells.

Analysis of Variance↗

PubMed1995

rHox: a homeobox gene expressed in osteoblastic cells.

Homeodomain proteins are characterized by a conserved domain with a helix-turn-helix motif. These proteins act as regulatory factors in tissue differentiation and proliferation. However, their role in the regulation of osteoblast differentiation is unknown. In this study we have identified and characterized a homeobox gene in osteoblast-like cells. This gene, termed rHox, was isolated from a cDNA library derived from rat osteoblast-like cells. The nucleotide sequence of the 1,375 base pair (bp) cDNA contains a noncoding leader sequence of 329 bp, a 735 bp open reading frame, and 312 bp of 3' noncoding sequence. Sequence comparison demonstrates that rHox is identical to the mouse Pmx gene (also called MHox) at the amino acid level and 90% homologous at the nucleotide level. Both Southwestern blotting and gel shift analyses indicate that rHox has potential to bind both the collagen I alpha 1 and the osteocalcin promoters. Transfection experiments using an rHox expression vector showed a strong repression of target promoter activity, regardless of whether the target promoters contained homeodomain binding response elements. These data suggest that rHox is a potent negative regulator of gene expression, although the specific role of rHox in bone gene regulation remains to be determined.

3T3 Cells↗

PubMed1995

Transforming growth factor beta 1 stimulates bone formation and resorption in an in-vivo model in rabbits.

The influence of TGF beta 1 on bone was studied in a titanium device implanted into the tibia of rabbits. TGF beta 1 was infused via an Alzet osmotic pump calibrated to deliver at a rated of 200ng daily for 2 weeks before replacement. A hollow channel is incorporated into the device into which tissue can grow, and the histological sequence of events was observed over 6 weeks. In control samples, the rod-shaped piece of tissue at 2W consisted of spindle-shaped cells in the center, flanked at both ends by islands of trabecular bone lined by cuboidal osteoblasts and osteoclasts. By 4W, ingrowth of bone reached the center if the specimen, by which time, the bone surfaces were apposed by a single layer of flattened osteoblasts. However, osteoclastic resorption continued unabated so that by 6W, only a thin layer of cortical bone remained, enclosing a marrow cavity with hemopoietic elements. Significant differences were observed in samples continuously infused with TGF beta 1. At 2W, trabecular bone had reached further towards the center of the specimen and the granulation tissue was made up of cells that were more plump and cuboidal compared to the spindle cells of control sample. At 3W, there was increased bone volume and osteoid seams were thicker, covering a greater extent of the trabeculae surfaces. At 4W, the bony trabeculae were up to 3 times thicker than control trabeculae. There was very active bone resorption with many multinucleate osteoclasts and multilayered aggregates of cuboidal osteoblasts lining bony surfaces. Yet at 6W, the morphological appearance was similar to control samples.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Marrow development and its relationship to bone formation in vivo: a histological study using an implantable titanium device in rabbits.

During embryogenesis, the creation of marrow sinusoids is intimately related to the coupled processes of osteogenesis and osteoclastic resorption. We set out to further define the relationship between bone formation and marrow development by implanting an intraosseous titanium device into the tibiae of rabbits which permits the examination of bone formation under standardized and reproducible conditions as well as allowing repeated sampling of new bone. A hollow channel is incorporated into the device into which tissue can grow. The device was left in place for 6 weeks to allow osseous integration to occur, after which the initial rod of new tissue growth was removed and subsequent histological and immunohistological sequence of events observed over the next 7 weeks. Interpretation of its morphological changes was further aided by concurrent histomorphometric studies. Because the channel was in direct continuity with the marrow cavity and isolated from the endosteum, immediate marrow regeneration was expected, following dissolution of the blood clot. Instead, our studies indicated that hemopoietic marrow cells, including the erythroid and myeloid series as well as megakaryocytes, did not appear until 3 weeks after implantation of the chamber when the newly formed bone had been remodeled to form an expanded marrow cavity. This intraosseous device is a useful in vivo model for studying the development of bone marrow hemopoietic and nonhemopoietic stromal cells and our results confirm the previous observation that influx of marrow cellular elements follow the formation of bone during endochondral as well as intramembranous ossification.

Animals↗

PubMed1995

Invasive Haemophilus influenzae type b infections in children hospitalized in Hong Kong, 1986-1990. Hong Kong Hib Study Group.

A 5-year territory-wide retrospective survey of invasive Haemophilus influenzae type b diseases was conducted in Hong Kong. Between 1986 and 1990, 57 cases (28 male) were recorded in children less than 12 years old (37 cases of meningitis, 9 of septicaemia and 11 of bacteraemic pneumonia). The annual incidence for children less than 5 years old was 2.7 per 10(5) (95% confidence interval (CI) 2.0-3.5). Of the 57 cases, 39 were Chinese and 18 non-Chinese (7 Vietnamese refugees, 6 Caucasians, 5 others). The annual incidence in Vietnamese refugees less than 5 years old was 42.7 per 10(5) (95% CI 17.2-87.9), giving a relative risk of 18.5 (95% CI 8.3-41.0). Chinese patients (68%) were under-represented as Chinese accounted for at least 94% of the population. Moreover, 14 of the 39 Chinese patients had pre-existing medical problems, compared with only 1 of the 18 non-Chinese patients patients had pre-existing medical problems, compared with only 1 of the 18 non-Chinese patients (p = 0.022).

Child↗