Biomedical subjects

H S Cheung

Publications and source records attributed to H S Cheung.

At least 37 records · Page 2Linked to original sources

PubMed1999

Transduction mechanisms of porcine chondrocyte inorganic pyrophosphate elaboration.

OBJECTIVE: To investigate cellular signaling mechanisms that influence chondrocyte production of inorganic pyrophosphate (PPi), which promotes calcium pyrophosphate dihydrate (CPPD) crystal deposition. METHODS: Articular chondrocyte and cartilage cultures were stimulated with protein kinase C (PKC) activator and adenyl cyclase activator. Generation of extracellular PPi was measured. RESULTS: Adenyl cyclase activation resulted in diminished pyrophosphate generation. PKC activation stimulated pyrophosphate elaboration. CONCLUSION: Two signaling pathways, cAMP and PKC, modulate generation of extracellular pyrophosphate by cartilage and chondrocytes. They are novel targets for potentially diminishing extracellular pyrophosphate elaboration that leads to CPPD crystal deposition.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1999

Cellular responses to whitlockite.

Whitlockite crystals have been observed in both degenerating and normal articular cartilages. To determine their potential for inducing cartilage degeneration, we studied their ability to induce mitogenesis and synthesis and secretion of metalloproteases in vitro. Whitlockite crystals were found to stimulate cell proliferation and to stimulate synthesis and secretion of stromelysin and collagenase. However, they were less stimulatory than crystals that contained calcium (Ca) and phosphate without magnesium substitution for Ca. Whitlockite crystals elicit biologic cellular responses that suggest potential pathogenicity in arthritis, but are less potent than Ca phosphate crystals without magnesium.

Calcium Phosphates↗

PubMed1999

The role of crystals in articular tissue degeneration.

The deposition of calcium-containing crystals in articular tissues is probably an underrecognized event. Clinical observations indicate that exaggerated and uniquely distributed cartilage degeneration is associated with these deposits. Perhaps the most compelling argument favoring a role for crystals in causing osteoarthritis stems from their in vitro effects on articular tissues. In this short review, we will discuss the fact that crystals can cause the degeneration of articular tissues in 2 separate pathways. In the "Direct" pathway, crystals directly induce fibroblast-like synoviocytes to proliferate and produce metalloproteinases and prostaglandins. The other "Paracrine pathway" involves the interaction between crystals and macrophages/monocytes, which leads to synthesis and release of cytokines that can reinforce the action of crystals on synoviocytes and induce chondrocytes to secrete enzymes, eventually causing the degeneration of articular tissues.

Animals↗

PubMed1999

The role of crystals in osteoarthritis.

The deposition of calcium-containing crystals in articular tissues is probably an under-recognized event. Clinical observations indicate that an exaggerated and uniquely distributed cartilage degeneration is associated with these deposits. Measurements of putative markers of cartilage breakdown suggest that the presence of these crystals magnifies the degenerative process. In vitro studies indicate two potential mechanisms by which crystals cause degeneration. These involve the stimulation of mitogenesis in synovial fibroblasts and the secretion of proteases by cells that phagocytose these crystals. Approaches that might ameliorate the degenerative process may ensue from new information about how crystals form and how they exert their biologic effects.

Animals↗

PubMed1999

Phosphocitrate blocks nitric oxide-induced calcification of cartilage and chondrocyte-derived apoptotic bodies.

OBJECTIVE: To examine whether phosphocitrate (PC) will block nitric oxide-induced calcification of cartilage or chondrocyte-derived apoptotic bodies. DESIGN: Articular cartilage vesicles (ACV) or apoptotic bodies (AB) were isolated from untreated or 1mM sodium nitroprusside (SNP) treated porcine cartilage slices. Mineralization of ACV, AB, control untreated and SNP-treated cartilage were done in the presence or absence of PC (1mM)+/-ATP (1mM). RESULTS: PC [1mM] blocked both the ATP-dependent and -independent mineralization in ACV and AB, untreated and SNP treated cartilage. Moreover, PC had no effect on NTPPPH activity in either ACV or AB fraction in the presence or absence of ATP suggesting that PC did not block the mineralization through the inhibition of NTPPPH activity. CONCLUSIONS: PC inhibits nitric oxide-induced calcification of cartilage and cartilage-derived apoptotic bodies.

Animals↗

PubMed1998

Molecular mechanism of basic calcium phosphate crystal-induced activation of human fibroblasts. Role of nuclear factor kappab, activator protein 1, and protein kinase c.

Synovial fluid basic calcium phosphate (BCP) crystals are markers of severe joint degeneration in osteoarthritis. BCP crystals cause mitogenesis of articular cells and stimulate matrix metalloprotease production, thus promoting degradation of articular tissues. Previous work suggested that BCP crystal-induced cell activation required intracellular crystal dissolution, induction of proto-oncogene expression, and activation of signal transduction pathways involving protein kinase C and mitogen-activated protein kinases. Here we further elucidate the mechanisms of BCP crystal-induced cell activation as BCP crystals activate transcription factors nuclear factor kappaB and activator protein 1 in human fibroblasts. We confirm the role of protein kinase C in BCP crystal-induced mitogenesis in human fibroblasts. In contrast, we demonstrate that BCP crystals do not activate signal transduction pathways involving protein tyrosine kinases or phosphatidylinositol 3-kinase. These data further define the mechanism of cell activation by BCP crystals and confirm its selectivity, an observation that may have therapeutic implications.

3T3 Cells↗

PubMed1998

Basic calcium phosphate crystal-induced collagenase production: role of intracellular crystal dissolution.

OBJECTIVE: To investigate the potential therapeutic effects of inhibiting intracellular dissolution of basic calcium phosphate (BCP) crystals in tissue culture by raising lysosomal pH using bafilomycin A1, a specific vacuolar pump inhibitor. DESIGN: 45Ca-labeled crystals were used to demonstrate intracellular crystal dissolution in human foreskin fibroblasts (HF). Mitogenesis was evaluated using [3H]thymidine incorporation assays and cell counts. Northern blot and Western blot were used to study collagenase [matrix metalloproteinase-1 (MMP1)] mRNA accumulation and protein secretion, respectively. RESULTS: Bafilomycin A1 inhibited intracellular dissolution of BCP crystals and caused a concentration-dependent inhibition of BCP crystal-induced mitogenesis. Doses of bafilomycin A1 which inhibited intracellular crystal dissolution and mitogenesis had no effect on BCP crystal-induced MMP1 mRNA accumulation or protein secretion. CONCLUSION: Raising lysosomal pH to inhibit intracellular BCP crystal dissolution attenuates the proliferative response to BCP crystals in HF but does not prevent metalloprotease synthesis and secretion. The therapeutic potential of lysosomotropic agents for preventing joint destruction in BCP crystal deposition disease is limited.

Anti-Bacterial Agents↗

PubMed1998

Intracellular calcium responses to basic calcium phosphate crystals in fibroblasts.

OBJECTIVE: To examine the intracellular calcium response to basic calcium phosphate (BCP) crystals in fibroblasts. DESIGN: In this study, intracellular calcium [Ca2+]i levels in fibroblasts were determined using the photoactive dye, fura-2. Interruption of these responses was accomplished by either removal of Ca2+ from the extracellular medium or addition of ammonium chloride that inhibits intracellular dissolution of BCP crystals by alkalinizing phagolysosomes. The effects of such interruptions on BCP induction expression of proto-oncogenes were demonstrated by the Northern blot analysis. RESULTS: Addition of media containing BCP crystals yielded an immediate 10-fold rise of [Ca2+]i over the baseline level in human fibroblasts. This peak was derived mostly from extracellular calcium and was not seen when BCP crystals in calcium-free media were added to fibroblasts. The [Ca2+]i concentration returned to the baseline level within 8 min. A second rise of [Ca2+]i started at 60 min and continued to increase up to at least 3 h. This peak was derived from intracellular dissolution of phagocytosed crystals and almost completely inhibited by 10 mM ammonium chloride. CONCLUSION: The initial transient [Ca2+]i increase probably serves as a second messenger leading to activation of early cellular responses such as c-fos expression which is important in BCP crystal-induced mitogenesis. The second, slower and more sustained rise of [Ca2+]i probably initiates other cellular processes needed for fibroblast mitogenesis.

Blotting, Northern↗

PubMed1997

Phosphocitrate inhibits a basic calcium phosphate and calcium pyrophosphate dihydrate crystal-induced mitogen-activated protein kinase cascade signal transduction pathway.

Calcium deposition diseases caused by calcium pyrophosphate dihydrate (CPPD) and basic calcium phosphate (BCP) crystals are a significant source of morbidity in the elderly. We have shown previously that both types of crystals can induce mitogenesis, as well as metalloproteinase synthesis and secretion by fibroblasts and chondrocytes. These responses may promote degradation of articular tissues. We have also shown previously that both CPPD and BCP crystals activate expression of the c-fos and c-jun proto-oncogenes. Phosphocitrate (PC) can specifically block mitogenesis and proto-oncogene expression induced by either BCP or CPPD crystals in 3T3 cells and human fibroblasts, suggesting that PC may be an effective therapy for calcium deposition diseases. To understand how PC inhibits BCP and CPPD-mediated cellular effects, we have investigated the mechanism by which BCP and CPPD transduce signals to the nucleus. Here we demonstrate that BCP and CPPD crystals activate a protein kinase signal transduction pathway involving p42 and p44 mitogen-activated protein (MAP) kinases (ERK 2 and ERK 1). BCP and CPPD also cause phosphorylation of a nuclear transcription factor, cyclic AMP response element-binding protein (CREB), on serine 133, a residue essential for CREB's ability to transactivate. Treatment of cells with PC at concentrations of 10(-3) to 10(-5) M blocked both the activation of p42/p44 MAP kinases, and CREB serine 133 phosphorylation, in a dose-dependent fashion. At 10(-3) M, a PC analogue, n-sulfo-2-aminotricarballylate and citrate also modulate this signal transduction pathway. Inhibition by PC is specific for BCP- and CPPD-mediated signaling, since all three compounds had no effect on serum-induced p42/P44 or interleukin-1beta induced p38 MAP kinase activities. Treatment of cells with an inhibitor of MEK1, an upstream activator of MAPKs, significantly inhibited crystal-induced cell proliferation, suggesting that the MAPK pathway is a significant mediator of crystal-induced signals.

Calcium Phosphates↗

PubMed1997

Dual metalloprotease inhibitors: mercaptoacetyl-based fused heterocyclic dipeptide mimetics as inhibitors of angiotensin-converting enzyme and neutral endopeptidase.

A series of 7,6- and 7,5-fused bicyclic thiazepinones and oxazepinones were generated and incorporated as conformationally restricted dipeptide surrogates in mercaptoacyl dipeptides. These compounds are potent inhibitors of angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP) both in vitro and in vivo. Compound 1a, a 7,6-fused bicyclic thiazepinone, demonstrated excellent blood pressure lowering in a variety of animal models characterized by various levels of plasma renin activity and significantly potentiated urinary sodium, ANP, and cGMP excretion in a cynomolgus monkey assay. On the basis of its potency and duration of action, compound 1a (BMS-186716) was advanced into clinical development for the treatment of hypertension and congestive heart failure.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1997

Calcium phosphate particle induction of metalloproteinase and mitogenesis: effect of particle sizes.

Calcium pyrophosphate dihydrate (CPPD) and basic calcium phosphate (BCP) crystals [hydroxyapatite (HA), octacalcium phosphate, tricalcium phosphate] are common in osteoarthritis knee effusions, and are often associated with low-grade synovial proliferation and inflammation. Calcium-containing crystals including HA, are known to have a number of biologic effects on culture cells such induction of mitogenesis, stimulation of Prostaglandin E2 (PGE2) production via the phospholipase A2/cyclo-oxygenase pathway, activation of phospholipase C and inositol phospholipid hydrolysis, induction of metalloproteinase synthesis and induction of proto-oncogenes (c-fos and c-myc). While endocytosis of HA particles is prerequisite of the mitogenic effect of calcium-containing crystals in fibroblasts, it is not known whether endocytosis is required for crystal-induced metalloproteinase synthesis. In the present series of experiments, we examine the effect of three different sizes (106, 46, and 17 microns mean diameters) well-characterized spherical HA particles on the induction of mitogenesis and metalloproteinase synthesis on human fibroblasts. We showed that endocytosis is required for HA particles to induce synthesis of metalloproteinases.

Biocompatible Materials↗

PubMed1996

Inhibition of calcium pyrophosphate dihydrate crystal formation in articular cartilage vesicles and cartilage by phosphocitrate.

Articular cartilage vesicles (ACV), isolated by differential centrifugation of adult hyaline articular cartilage collagenase digests, mineralized in the presence of calcium and ATP. Mineral analysis by microscopy, chemical analysis, energy-dispersive analysis, and infrared spectroscopy revealed crystals resembling calcium pyrophosphate dihydrate (CPPD). Adult articular cartilage also underwent ATP-dependent mineralization, supporting the contention that vesicles in situ fostered adult articular cartilage mineralization. Phosphocitrate (PC) is a recognized in vitro inhibitor of hydroxyapatite and calcium oxalate monohydrate crystal formation, but it is not known whether PC can similarly restrict CPPD crystal development. In the present study we examine the effect of PC, citrate, and n-sulfo-2-amino-tricarballylate (SAT, a PC analogue) on the ATP-induced CPPD crystal formation in both ACV and articular cartilage models. Only PC (10-1000 microM) blocked both the ATP-dependent and -independent mineralization in ACV in a dose-dependent fashion. At 1 mM, SAT and citrate blocked the ATP-independent mineralization. Similarly, only PC blocked both the ATP- and non-ATP-dependent mineralization in native articular cartilage slices. PC, SAT, and citrate had no effect on ACV nucleoside triphosphate pyrophosphohydrolase activity, suggesting that none of these agents blocked mineralization through the inhibition of nucleoside triphosphate pyrophosphohydrolase activity, which generates inorganic pyrophosphate from ATP.

Adenosine Triphosphate↗

PubMed1996

Specific inhibition of basic calcium phosphate and calcium pyrophosphate crystal-induction of metalloproteinase synthesis by phosphocitrate.

Calcium pyrophosphate dihydrate (CPPD) and basic calcium phosphate (BCP) crystal deposition diseases are a group of heterogeneous arthritides which are a significant source of morbidity in the elderly. Both crystals induced mitogenesis and metalloproteinase (MP) synthesis and secretion by fibroblasts and chondrocytes which may promote degradation of intra-articular tissue. We have previously shown that phosphocitrate (PC), an inhibitor of hydroxyapatite crystallization, specifically blocks BCP crystal-induced mitogenesis in 3T3 cells. This led us to examine the effect of PC on BCP and CPPD crystal induction of MP synthesis in human fibroblasts. PC (10(-3) to 10(-4) M) specifically inhibited the crystal-induced collagenase and stromelysin mRNA accumulation while having no effect on epidermal growth factor-induced or basal levels of mRNA for both enzymes. Western blots (collagenase) of conditioned media confirmed that PC blocked crystal-induced proteinase secretion as well. Moreover, PC (10(-3) M) also blocked the crystal induction of c-fos and c-jun. Since FOS and JUN proteins form a transacting activator (AP-1) for expression of collagenase and stromelysin genes, PC may block the synthesis of both enzymes by inhibiting the transcription of c-fos and c-jun.

1-Methyl-3-isobutylxanthine↗

PubMed1996

The paranasal sinuses before and after radiotherapy for nasopharyngeal carcinoma: a computed tomographic study.

A study comparing the pre- and post-radiotherapy computed tomographic scans of patients treated for nasopharyngeal carcinoma revealed that the incidence of major mucosal abnormality was significantly increased and approximately doubled after radiotherapy. The most significant factor predicting major mucosal abnormality after radiotherapy was the presence of tumour in the sinus before treatment. In the maxillary sinus there was significant association of major mucosal abnormality before and after radiotherapy although this was not so for the other sinuses. The mucosal changes observed were evident as early as six months after radiotherapy.

Adult↗

PubMed1996

Abnormalities of the paranasal sinuses in patients with nasopharyngeal carcinoma: a computed tomographic study.

A retrospective study of computed tomography scans of the paranasal sinuses of 131 control subjects in Hong Kong revealed minor mucosal abnormalities in more than half of the ethmoid sinuses. Major abnormalities were present in seven per cent of maxillary, five per cent of anterior ethmoid and four per cent of posterior ethmoid sinus. In 85 patients with nasopharyngeal carcinoma the prevalence of minor mucosal abnormalities in the sinuses was similar to that of the control group but major mucosal abnormalities were significantly more common in the anterior and posterior ethmoids at 15 per cent and 21 per cent of the respective sinuses (p < 0.001).

Adult↗

PubMed1996

Choledocholithiasis: comparison of MR cholangiography and endoscopic retrograde cholangiography.

PURPOSE: To prospectively compare magnetic resonance (MR) cholangiography with endoscopic retrograde cholangiography (ERC) in the diagnosis of choledocholithiasis. MATERIALS AND METHODS: Forty-seven patients with suspected choledocholithiasis underwent non-breath-hold, heavily T2-weighted, respiratory-triggered turbo spin-echo MR cholangiography. They then underwent ERC within 5 hours. The results of the two procedures were compared in 45 patients. RESULTS: The absence of ductal dilatation was shown in 16 patients at MR cholangiography and at ERC. MR cholangiography showed common duct dilatation in 28 of the 29 patients with dilatation shown at ERC. MR cholangiography helped correctly identify 18 of the 19 patients with choledocholithiasis and 22 of the 26 patients without choledocholithiasis. Sensitivity with MR cholangiography was 95%, specificity was 85%, positive predictive value was 82%, and negative predictive value was 96%. Two of the false-positive findings were due to pneumobilia. CONCLUSION: Non-breath-hold MR cholangiography is as accurate for the evaluation of choledocholithiasis as ERC.

Adult↗

PubMed1995

Cardiovascular effects of the novel dual inhibitor of neutral endopeptidase and angiotensin-converting enzyme BMS-182657 in experimental hypertension and heart failure.

Combined neutral endopeptidase (NEP) and angiotensin-converting enzyme (ACE) inhibition produces greater acute hemodynamic effects than either treatment alone. We investigated whether BMS-182657 (BMS), which bears inhibitory activities against both NEP and ACE, elicited similar enhanced effects. BMS inhibited NEP and ACE, in vitro (IC50 = 6 and 12 nM, respectively) and the pressor response to Ang I in rats. In deoxycorticosterone acetate (DOCA)-salt hypertensive rats sensitive to NEP inhibition but not to ACE inhibition, BMS at 100 mumol/kg i.v. lowered mean arterial pressure (MAP) from 180 +/- 6 to 151 +/- 5 mm Hg. In sodium-depleted, spontaneously hypertensive rats (SHR) sensitive to ACE inhibition but not to NEP inhibition, BMS at 100 mumol/kg p.o. lowered MAP from 151 +/- 4 to 123 +/- 5 mm Hg. Cardiomyopathic hamsters with heart failure were administered vehicle or one of the following (30 mumol/kg i.v.): the ACE inhibitor enalaprilat; the NEP inhibitor SQ-28603; or BMS. Enalaprilat and SQ-28603 had minimal hemodynamic effects. BMS decreased left ventricular end-diastolic pressure by 12 +/- 2 and 10 +/- 1 mm Hg and left ventricular systolic pressure by 27 +/- 2 and 23 +/- 3 mm Hg at 30 and 60 min, respectively (P < .05 vs. each other group). These changes were associated with a 40% increase in cardiac output, a 47% decrease in peripheral vascular resistance and a lowering of MAP by 21 +/- 3 mm Hg at 60 min (P < .05 vs. each other group). There were no significant differences in the changes in heart rate or left ventricular stroke work index among the four groups. Hence, BMS-182657 is a dual inhibitor of NEP and ACE, is antihypertensive irrespective of the activity of the renin-angiotensin system and has acute hemodynamic effects in hamsters with heart failure greater than those produced by selective inhibition of NEP or ACE. The NEP and ACE inhibitory activities of BMS-182657 act synergistically and mimic the interaction resulting from combining selective inhibitors of these enzymes.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1994

The role of cyclic-3',5'-adenosine monophosphate in prostaglandin-mediated inhibition of basic calcium phosphate crystal-induced mitogenesis and collagenase induction in cultured human fibroblasts.

Synovial fluid basic calcium phosphate (BCP) crystals are associated with severe destructive arthropathies characterised by synovial proliferation and non-inflammatory degradation of intra-articular collagenous structures. BCP crystals stimulate fibroblast and chondrocyte mitogenesis, metalloprotease secretion and prostaglandin production. As a tissue protective effect of prostaglandins has been suggested, we recently studied the effect of PGE1 on BCP crystal-induced mitogenesis and collagenase mRNA accumulation in human fibroblasts (HF). We demonstrated a dose-dependent inhibition of BCP crystal-induced mitogenesis and collagenase mRNA accumulation. The mechanism of PGE1 inhibition of BCP crystal-induced mitogenesis and collagenase mRNA accumulation was therefore explored. PGE1 (100 ng/ml) increased HF intracellular cAMP 40-fold over control. BCP alone caused no such change but inhibited the PGE1-induced increase in intracellular cAMP by at least 60%. The PGE1-induced increase in intracellular cAMP was also blocked by the adenyl cyclase inhibitor, 2',5'-dideoxyadenosine (ddA) (10 microM) and ddA reversed the PGE1-mediated inhibition of BCP crystal-induced mitogenesis. Dibutyryl cAMP also inhibited BCP crystal-induced mitogenesis in a concentration-dependent manner. Agents which increase intracellular cAMP levels such as the adenyl cyclase activator forskolin and the phosphodiesterase, inhibitor 3-isobutyl-1-methylxanthine (IBMX) mimicked the effect of PGE1 on HF collagenase mRNA levels. PGE1 inhibits the biologic effects of BCP crystals through the cAMP signal transduction pathway and such inhibition may have significant therapeutic implications.

1-Methyl-3-isobutylxanthine↗