Biomedical subjects

H S Cheung

Publications and source records attributed to H S Cheung.

At least 73 records · Page 4Linked to original sources

PubMed1990

Stimulation of pyrophosphate production in articular cartilage by a platelet-derived factor is independent of mitogenesis.

The disordered production of extracellular inorganic pyrophosphate (PPi) by cartilage contributes to calcium pyrophosphate dihydrate crystal formation and associated diseases. We have previously shown that a factor(s) derived from human platelets markedly stimulates the accumulation of PPi in the media of porcine articular cartilage in organ culture. This is the first known physiologic modifier of PPi production by cartilage. We report herein that platelet derived growth factor (PDGF) is not the platelet factor responsible for PPi stimulation and that the active factor is not mitogenic for chondrocytes. PDGF added to the media of articular cartilage explants in the presence of 0.5% (platelet-poor) plasma (PPP) produces 3.92 +/- 1.6 mumol/L PPi compared with 2.85 +/- 0.7 mumol/L PPi in cartilage exposed to PPP alone. The platelet extract (PE) and PDGF are mitogenic for adult articular chondrocytes in high-density monolayer cultures. Anti-PDGF antibodies block the mitogenic effects of PDGF and PE. The uptake of thymidine labeled with tritium is 157% of control in cells exposed to PE, PPP, and polyclonal goat immunoglobulin G (IgG); 114% of control in cells exposed to PE, PPP, and anti-PDGF antibody; 148% of control in cells treated with PDGF, PPP, and goat IgG; and 98% of control in cells treated with PDGF, PPP, and anti-PDGF antibody. However, anti-PDGF antibody has no effect on PPi accumulation. PPi levels are 17.22 +/- 1.6 mumol/L in media from cartilage treated with PPP, goat IgG, and PE and 17.62 +/- 2.2 mumol/L in cartilage exposed to PE, PPP, and anti-PDGF antibody. We have further characterized the platelet factor responsible for the stimulation of PPi by cartilage. It is not mitogenic for chondrocytes, and it is not PDGF.

Animals↗

PubMed1990

Simultaneous occurrence of calcium pyrophosphate dihydrate and basic calcium phosphate (hydroxyapatite) crystals in a knee.

An 82-year-old man developed periarticular roentgenographic calcifications of the knee joint. Fragments of meniscus and peritendinous tissue were collected during total knee arthroplasty. Crystals were released from tissues by collagenase digestion. Calcium pyrophosphate dihydrate crystals were identified in the meniscus, and basic calcium phosphate crystals were identified in the peritendinous tissue. Methods of crystal identification included compensated polarized light microscopy, scanning electron microscopy with X-ray energy dispersive analysis, and X-ray diffraction.

Aged↗

PubMed1989

Molecular mechanism of basic calcium phosphate crystal-induced mitogenesis. Role of protein kinase C.

Synovial tissue hyperplasia in basic calcium phosphate deposition disease has been suggested to develop through the stimulation of cell growth by basic calcium phosphate (BCP) crystals deposited in joints. These crystals have been used in vitro to stimulate DNA synthesis in quiescent fibroblasts to experimentally study this proliferative disease. The stimulation of DNA synthesis, in density-arrested Balb/c 3T3 cells, by BCP crystals was inhibited after down-regulating protein kinase C activity with 12-O-tetradecanoyl-phorbol 13-acetate (TPA). No effect on platelet-derived growth factor (PDGF)-stimulated DNA synthesis was observed under the same conditions. The expression of c-myc and c-fos increased in response to BCP stimulation in a manner similar to the increase produced by stimulation with PDGF. The BCP stimulation of c-fos and c-myc messages was inhibited 60 and 90%, respectively, in TPA-pretreated, protein kinase C-down-regulated cells. The induction of these transcripts by PDGF was unaffected in cells pretreated with TPA. TPA was unable to stimulate c-fos and c-myc expression or DNA synthesis following protein kinase C down-regulation. Both PDGF and TPA stimulated phosphorylation of an 80-kDa protein, whereas BCP crystals had no effect on phosphorylation of this protein. The exposure of density-arrested Balb/c 3T3 cells to BCP crystals had no effect on high affinity epidermal growth factor receptor binding under conditions in which PDGF and TPA reduced epidermal growth factor binding. The data suggest that PDGF can act to stimulate c-fos and c-myc expression as well as DNA synthesis through a protein kinase C-independent pathway, whereas BCP crystals require at least endogenous levels of protein kinase C to stimulate these events.

Animals↗

PubMed1989

Augmentation of inorganic pyrophosphate elaboration in cartilage by serum factors.

The disordered production of inorganic pyrophosphate (PPi) by articular cartilage is thought to have an important role in the pathogenesis of calcium pyrophosphate dihydrate deposition disease and perhaps osteoarthritis. We have previously shown that fetal calf serum added to the culture media of porcine articular cartilage explants increases the elaboration of PPi into the ambient media. We have examined this PPi stimulatory activity by studying the effects of adult human serum (HS), serum derived from adult human plasma (HP), and an acid-alcohol extract of human platelets (PE) on PPi production in cartilage organ culture. Ten percent HS produces a 1.4-fold increase in PPi production after 48 h of culture, while cartilage incubated in media containing 10% HP produces no more PPi than that incubated in media alone. PE stimulates a mean 2-fold increase in PPi production at 48 h in the presence of low concentrations of HP, and has no effect alone. It does not appear to up-regulate the activity of the ectoenzyme nucleoside triphosphate pyrophosphohydrolase (NTPPPH), nor does it promote the release of enzyme substrate into the extracellular space. Cartilage exposed to 0.5% HP and PE has 1.51 +/- 0.36 units of NTPPPH activity whereas cartilage exposed to 0.5% HP alone has 1.52 +/- 0.41 units of enzyme activity. PE does not increase the release of [14C]adenine-labeled compounds into the media. Approximately 13% of soluble 14C counts was found in the media of chondrocytes treated with PE while 18% of counts was released in the presence of HP alone. We have demonstrated a factor or factors present in FCS, HS, and an acid-ethanol extract of human platelets which represent(s) the first known physiologic modulators of PPi production in articular cartilage and may increase PPi production without affecting NTPPPH activity.

Adenine↗

PubMed1989

Induction of expression of c-fos and c-myc protooncogenes by basic calcium phosphate crystal: effect of beta-interferon.

Basic calcium phosphate (BCP) crystals control the traverse of cells from the G0-G1 to S-phase of the cell cycle and initiate proliferation by rendering fibroblasts competent to respond to insulin-like growth factors in plasma. The present study examines whether BCP crystals induce transcription of the protooncogenes c-fos and c-myc and the effect of beta-interferon (IFN-beta) on protooncogene transcription as well as BCP crystal-induced DNA synthesis. Stimulation of density-arrested BALB/c-3T3 cells with either BCP crystal or platelet-derived growth factor (PDGF) results in maximal accumulation of c-fos mRNA at 30 min after stimulation. Induction of c-myc transcription by BCP crystal or PDGF occurs within 1 h and is maximal at around 3 h after stimulation. Simultaneous addition of IFN-beta with either BCP crystals or PDGF had little effect on c-fos induction but delayed both c-myc message accumulation and entry into S phase. The delay in c-myc message induction after IFN-beta treatment cannot account for the observed delay in the onset of DNA synthesis, since IFN-beta can be added at up to 6 h after stimulation with either PDGF or BCP crystals, and a similar delay in the onset of DNA synthesis is still observed.

Calcium Phosphates↗

PubMed1989

Differential deoxyadenosine toxicity to immature rabbit cartilage in vitro. A model for the chondro-osseous dysplasia of adenosine deaminase deficiency.

Deoxyadenosine metabolism was investigated in rabbit growth plate and articular cartilage to elucidate the biochemical basis for the chondro-osseous dysplasia observed in adenosine deaminase (ADA) deficiency. Models of ADA deficiency, the combination of deoxy-adenosine and either of 2 ADA inhibitors, were selectively toxic to immature cartilage, supporting the hypothesis that the chondro-osseous dysplasia of ADA deficiency is the consequence of the enzyme deficiency. Depletion of ATP may play a role in the altered chondrocyte viability and function observed in this model.

Adenosine Deaminase↗

PubMed1989

Growth of osteoblasts on porous calcium phosphate ceramic: an in vitro model for biocompatibility study.

Biomaterial implantation in animals is commonly used for biocompatibility studies as well as examination of long-term interaction between tissue and the test material. An in vitro cell culture model is proposed as an alternative which will save animal lives and reduce the pain and discomfort of animals used for such studies. In this study the biomaterial was matched to the cell types typical of the implant site of the particular material: porous calcium phosphate ceramic, used as dental and orthopaedic implants, with periosteal fibroblasts, osteoblasts and chondrocytes. All three cell types attached on to the ceramic and formed multicellular layers. Numbers of periosteal fibroblasts, osteoblasts and chondrocytes increased 29-, 23- and 17-fold, respectively, during the 10 wk period. Osteoblasts retained their phenotypic expression by producing only Type I collagen. Parathyroid hormone (PTH, 50 nM) suppressed the alkaline phosphatase activity of osteoblasts by over 50% and increased cAMP by more than 10-fold over control cultures.

Alkaline Phosphatase↗

PubMed1989

Solubilization of hydroxyapatite crystals by murine bone cells, macrophages and fibroblasts.

Calcium phosphate ceramic is widely used as implant material. It is made up of hydroxyapatite, beta-tricalcium phosphate or various combinations of both. In the present study, we use an in vitro model to examine the role of cell-mediated resorption of calcium phosphate ceramic implant material. We compare the abilities of two sequential enzymatic released populations of bone cells from murine calvaria (Population II and Population V), macrophages and dermal fibroblasts to solubilize 45Ca-labelled hydroxyapatite crystals. These crystals were incubated with each of the cell types for 24 h in the presence or absence of parathyroid hormone, prostaglandin E2, calcitonin, and 1,25-dihydroxyvitamin D3. The amount of cell-mediated hydroxyapatite solubilization was determined by measuring the radioactivity in an aliquot of the supernatant after centrifugation. Using dermal fibroblasts as a baseline, relative abilities of macrophages, Population II and Population V to degrade crystals were 10.5, 5 and 2 times that of fibroblasts. Crystal-cell contact was required. While none of the bone resorption agents tested had any effect on this process, crystal dissolution by bone cells was inhibited by two lysosomotropic agents, NH4Cl and chloroquine.

Ammonium Chloride↗

PubMed1988

Mechanisms of connective tissue damage by crystals containing calcium.

From available clinical, radiographic, and synovial fluid findings, coupled with in vivo radiolabelled crystal turnover data and in vitro experimental data, a hypothesis has been formulated relative to the pathogenesis of BCP crystal deposition diseases (Fig. 2). Synovial lining cells phagocytose BCP crystals and particulate collagens in the joint fluid. During and/or after internalization these cells are stimulated in a variety of ways: 1) protease synthesis and secretion is relentlessly stimulated, which may damage joint tissues producing clinically evident loss of collagenous tissues including cartilage, bone, and tendon, and which may release additional amounts of crystals and particulate collagens into the synovial fluid, completing a vicious cycle; 2) PGE2 production is greatly augmented; 3) DNA synthesis is stimulated as a result of increased inositol phospholipid turnover and intracellular crystal dissolution. The increased number of synovial cells also augments the total local generation of proteases and prostenoids. Mechanical factors such as trauma or joint overuse also contribute to the pathogenesis of joint destruction as discussed in the article on the clinical aspects of BCP crystal deposition.

Animals↗

PubMed1987

Endocytosis is required for the mitogenic effect of basic calcium phosphate crystals in fibroblasts.

Basic calcium phosphate (BCP) crystals stimulate mitosis of cultured fibroblasts and synoviocytes in vitro. Although intimate crystal-cell contact is required for mitogenesis, and lysosomotropic agents such as chloroquine and ammonium chloride block the mitogenic effect of crystals, the requirement of endocytosis has not been demonstrated. Synthetic BCP crystals, uniformly trace-labeled with 45Ca, were added to cultured, quiescent, confluent human foreskin fibroblasts in the presence or absence of ammonium chloride. After 4 or 24 hours, cultures were pulsed with 3H thymidine. The cells were then released with EDTA and trypsin, and fractionated on preformed Percoll density gradients. Fractions were analyzed for incorporation of 45Ca and [3H]thymidine and cell number. The cells containing 45Ca crystals also were heavily labeled with thymidine. Ammonium chloride decreased the amount of crystals endocytosed, and inhibited mitogenesis. These data suggest that mitogenesis induced by BCP crystals is preceded by endocytosis and dissolution in the acidic environment of phagolysosomes.

Calcium Phosphates↗

PubMed1987

Distribution of type I, II, III and V in the pepsin solubilized collagens in bovine menisci.

The inner one-third (IM) of both lateral and medial menisci resembles hyaline cartilage, both in gross appearance and histological examination, while the outer two-thirds (OM) is fibrocartilaginous in appearance. Collagen was extracted with pepsin, purified with anion and cation exchange column chromatographies and examined by differential salt precipitation, cyanogen bromide-peptide analysis and SDS gel electrophoresis. IM constitutes approximately 10% of the wet weight of whole meniscus, is made up of 70% collagen of which 34% is pepsin soluble. IM is composed of 60% type II and 40% type I collagen. OM is made up of 80% collagen of which 17% is pepsin soluble. The predominant collagen of OM is type I with a trace amount of types III and V (less than 1%).

Animals↗

PubMed1987

Suppression of active collagenase from calcified lapine synovium by Arteparon.

Collagenase has been implicated in the pathogenesis of several arthropathies. Arteparon [glycos-aminoglycan (GAG) polysulfate] is a proteinase inhibitor that is being investigated as a therapeutic agent in osteoarthritis. We found that cultures of calcified lapine synovium release collagenase, one tenth of which is already activated. Normal synovium produces no active collagenase. GAG polysulfate suppresses the amount of active collagenase by one half. GAG polysulfate may interfere with the activation process of collagenase.

Animals↗

PubMed1986

Mitogenic activity of hydroxyapatite: requirement for somatomedin C.

Synovial hyperplasia is a feature of the chronic synovitis associated with basic calcium phosphate crystals [hydroxyapatite (HA), octacalcium phosphate, tricalcium phosphate] and calcium pyrophosphate. Each of these crystals stimulated mitosis of cultured human skin fibroblasts or canine synovial fibroblasts in a concentration-dependent fashion. We examined the effect of pure somatomedin C (Sm-C) on HA crystal induced mitogenesis. Confluent cultures of human fibroblasts were rendered quiescent by incubation in the presence of 1% platelet-poor-Sm-C free plasma (PPSCFP) for 24 hours. HA crystals stimulated thymidine incorporation 2.3-fold over control value. Addition of Sm-C significantly augmented the effect of HA crystals (P less than 0.01). Nearly identical effects were observed in the presence of 100 micrograms/ml HA crystals or 15 ng/ml PDGF. Monoclonal antibodies against Sm-C had little effect on the basal 3H thymidine uptake by control cells incubated in 1% PPSCFP but blocked over 50% of the HA crystal or PDGF-induced 3H thymidine incorporation both in the presence or absence of Sm-C. The incomplete blocking suggested either the presence of other "progression" factors, such as insulin-like growth factor II in the conditioned media or the possibility that HA or PDGF in high enough dosage enabled cells to escape their dependence on Sm-C for DNA synthesis.

Cells, Cultured↗

PubMed1986

Adenosine deaminase deficiency and chondro-osseous dysplasia.

An in vitro model of ADA deficiency is selectively toxic to cartilage from immature rabbits with a greater effect on growth plate than articular cartilage. The selective toxicity observed appears to be the consequence of ATP depletion. These results support the hypothesis that the chondro-osseous dysplasia observed in patients with ADA deficiency is caused by the disordered metabolism that results from the enzyme deficiency.

Adenosine Deaminase↗

PubMed1986

Endocytosis precedes dissolution of basic calcium phosphate crystals by murine macrophages.

Murine peritoneal macrophages were incubated with 45Ca-labeled basic calcium phosphate (BCP) crystals in the presence or absence of cytochalasin B. Untreated macrophages solubilized 30-50% of 45Ca-BCP in 24 hours. Dissolution began within 3 hours and was linear thereafter. Twenty-three percent of BCP was cell-associated by 3 hours. Endocytosis of crystal occurred continuously throughout the incubation. Endocytosis of crystal did not affect the migration of macrophages through Percoll density gradients. Addition of cytochalasin B did not prevent cell-association of BCP, but inhibited solubilization in a dose-dependent manner. Virtually all cell-associated BCP was removed when cytochalasin B-treated cells were washed with EDTA, suggesting that the crystals were only bound to the surface. In contrast, cell-associated BCP in untreated cells was only partially removed by EDTA, suggesting that endocytosis of crystal had occurred. We conclude that cell association of BCP is not sufficient for its dissolution, and that endocytosis precedes solubilization of BCP crystals by macrophages.

Animals↗

PubMed1986

The importance of renal net acid excretion as a determinant of fasting urinary calcium excretion.

To evaluate the effects of changing rates of fixed acid production on fasting urine Ca/creatinine, we studied five healthy men fed constant diets during control conditions (serum HCO3 27.3 +/- 2.6 SD mEq/liter and blood H+ 40.4 +/- 1.5 microEq/liter) and then during the administration of NH4Cl 3.0 mEq/kg/day (serum HCO3 22.5 +/- 4.9 mEq/liter; P less than 0.025, and H+ 46.8 +/- 2.3 mEq/liter; P less than 0.005). In addition to the expected increase in daily urinary Ca excretion from 5.2 +/- 2.0 to 12.5 +/- 3.0 mmole/day; P less than 0.001 as daily urinary net acid excretion was increased from 48 +/- 32 to 257 +/- 33 mEq/day; P less than 0.001 we observed that fasting urinary net acid/creatinine excretion also increased from 2.9 +/- 1.2 to 11.1 +/- 1.2 mEq/mmole creatinine; P less than 0.001 and fasting urine Ca/creatinine increased from 0.158 +/- 0.111 to 0.456 +/- 0.109 mmole/mmole creatinine; P less than 0.005. The additional Ca appearing in the urine during acidosis ultimately reflected augmented net bone resorption since daily urinary hydroxyproline excretion was increased from 0.232 +/- 0.062 to 0.377 +/- 0.108 mmole/day; P less than 0.01. Since variations in diet composition can cause fixed acid production and thus renal net acid excretion to vary from about zero to 200 mEq/day, such a range could cause fasting Ca/creatinine to vary from 0.09 to 0.37 mmole/mmole (0.03 to 0.13 mg/mg) and should be taken into account in the evaluation of fasting Ca/creatinine.

Acid-Base Equilibrium↗

PubMed1985

Crystal-induced endogenous pyrogen production. A further look at gouty inflammation.

We found previously that crystals of sodium urate and silicon dioxide (silica) can stimulate the production of endogenous pyrogen (EP), now called interleukin-1 (IL-1), the polypeptide mediator of fever and other aspects of inflammation. We have confirmed and extended the work with urate crystals and have examined 2 other crystals associated with joint problems, hydroxyapatite (HA) and calcium pyrophosphate dihydrate (CPPD). The crystals were added to suspensions of human blood leukocytes (2.5 X 10(6) monocytes/dose, with 10% fresh autologous plasma); after 18 hours of incubation, the EP content of the supernatants was assayed in the rabbit pyrogen test. HA and CPPD crystals neither induced EP production nor reduced the amount of staphylococci-induced EP. Presized (10 - 40 micron) urate crystals were pyrogenic, but less so than the unsized and aggregated urate crystals investigated previously and reexamined here. On ultrasonication, the aggregated urate crystals became first more pyrogenic and then less so as the crystals were dispersed and broken down. Ultrasound did not impart pyrogenicity to HA or CPPD crystals: their failure to stimulate EP/IL-1 production from leukocytes in vitro indicates a difference in their phlogistic properties, compared with crystals of urate or silica. The results with urate crystals have pathogenetic implications in a number of areas of gouty inflammation: initiation of the acute attack, other aspects of the acute-phase response, polyarticular involvement, and the inflammatory consequences of chronic stimulation by tophaceous material.

Calcium Pyrophosphate↗

PubMed1985

In vitro cartilage formation on porous hydroxyapatite ceramic granules.

Porous hydroxyapatite ceramic granules (diameter 0.5-1 mm) provide an excellent in vitro matrix for cell growth. Canine chondrocytes maintained their collagen (Type II) phenotype up to 11 mo when cultured on these granules. Chondrocytes proliferated throughout the 13 mo of culture. Cells divided and added on to form multilayers around each ceramic granule. By the end of 11 mo, some layers were thicker than the diameter of the granules. Cell number per culture dish increased 240-fold over the original number of cells seeded in 8 mo of culture. Morphologically, chondrocytes remained spherical and formed cohesive multilayers as early as 1 wk. Metachrometric extracellular matrix was evident by the first week and increased through the 13 mo period.

Animals↗