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Biomedical subjects

G G Chen

Publications and source records attributed to G G Chen.

At least 19 recordsLinked to original sources
PubMed2005

Shear force induced monodisperse droplet formation in a microfluidic device by controlling wetting properties.

Perpendicular flow is used to induce oil droplet breakup by using a capillary as water phase flow channel. It is a new route to produce monodisperse emulsions. The wetting properties of the fluids on the walls are exceedingly important parameters. Depending on the oil and water flow rates, different spatial distributions of the two phases as laminar, plugs, cobbles and drops, are obtained. The effects of two-phase flow rates on plugs and drop size are studied, and the different droplet formation mechanisms of plug flow and drop flow are discussed. Two quantitative equations utilized to predict the droplet size are developed.

Emulsions↗
PubMed2005

Cell death induced by ent-11alpha-hydroxy-15-oxo-kaur-16-en-19-oic-acid in anaplastic thyroid carcinoma cells is via a mitochondrial-mediated pathway.

The chemical compound ent-11alpha-hydroxy-15-oxo-kaur-16-en-19-oic-acid (5F), isolated from the Chinese herbal medicine plant Pteris semipinnata L, has been known to exert antitumor activity. However, the molecular mechanism of the action is not understood. In this study we demonstrated that apoptotic cell death induced by 5F in FRO cells was concentration- and time-dependent. The rapid increase in intracellular reactive oxygen species (ROS) levels was involved in the mechanism of cell death. c-Jun N-terminal kinase (JNK) activation and G2 block were related to cell death induced by 5F. Extracellular signal-related kinase (ERK) and p38 were also activated, but as survival signals in response to 5F treatment to counteract the induction of cell death. In the process of the induction of apoptotic cell death, Bax translocated into mitochondria, a reduction in Delta psi(m) was observed and a release of cytochrome c and apoptosis inducing factor (AIF) from mitochondria into the cytosol occurred, indicating that cell death induced by 5F was through a mitochondrial-mediated pathway.

Apoptosis Inducing Factor↗
PubMed2005

Differential role of hydrogen peroxide and staurosporine in induction of cell death in glioblastoma cells lacking DNA-dependent protein kinase.

Various DNA double-strand break repair mechanisms, in which DNA-dependent protein kinase (DNA-PK) has a major role, are involved both in the development and treatment of glioblastoma. The aim of the present study was to investigate how glioblastoma cells responded to hydrogen peroxide and staurosporine (STS) and how such a response is related to DNA-PK. Two human glioblastoma cell lines, M059J cells that lack DNA-PK activity, and M059K cells that express a normal level of DNA-PK, were exposed to hydrogen peroxide or STS. The response of the cells to hydrogen peroxide or STS was recorded by measuring cell death, which was detected by three different methods-MTT, annexin-V and propidium iodide staining, and JC-1 mitochondrial probe. The result showed that both hydrogen peroxide and STS were able to induce cell death of the glioblastoma cells and that the former was mainly associated with necrosis and the latter with apoptosis. Glioblastoma cells lacking DNA-PK were less sensitive to STS treatment than those containing DNA-PK. However, DNA-PK had no significant influence on hydrogen peroxide treatment. We further found that catalase, an antioxidant enzyme, could prevent cell death induced by hydrogen peroxide but not by STS, suggesting that the pathways leading to cell death by hydrogen peroxide and STS are different. We conclude that hydrogen peroxide and STS have differential effects on cell death of glioblastoma cells lacking DNA-dependent protein kinase. Such differential roles in the induction of glioblastoma cell death can be of significant value in selecting and/or optimizing the treatment for this malignant brain tumor.

Apoptosis↗
PubMed2005

Identification of hepatitis B virus X gene mutation in Hong Kong patients with hepatocellular carcinoma.

BACKGROUND: Chronic infection by hepatitis B virus (HBV) is the leading cause of hepatocellular carcinoma (HCC) in man. The viral transactivator HBV X (HBx) gene plays a critical role in the molecular pathogenesis of HBV-related HCC. OBJECTIVES: The aim of this study was to investigate whether there were particular HBx mutations associated with the Chinese Hong Kong patients with HCC. STUDY DESIGN: We have examined HBx in 113 tumor tissue samples from patients with HCC and 48 serum samples from the same group. In addition, we also examined the expression of HBx protein and the index of apoptotic cell death in tumor tissues of HCC. The entire coding region of HBx gene from the sample was sequenced and aligned with the published HBx gene sequence. RESULTS AND CONCLUSIONS: We have identified total 54 different types of mutations in HBx gene. HBx mutations occurred in a very high percentage of samples tested. Mutation of HBx was found in 95.2% and 95.3% of the tumor tissue and serum samples, respectively. Most of samples contained more than one type of the mutation. Relative risk analysis indicated that the mutations in 12 sites of tissue HBx and nine sites of serum HBx were highly associated with HCC, suggesting a potential role of these mutants in carcinogenesis. An insert mutation at position 204: Insert 204AGGCCC, was always found to co-exist with point mutations at 260 (G-->A) and 264 (G/C/T-->A). Furthermore, this particular pattern of HBx mutation was most frequently detected. Immunochemical staining of HBx protein revealed that the nuclear localization of HBx protein in hepatocytes of tumor tissues was highly associated with this particular pattern of HBx mutation. In conclusion, HBx mutation occurs frequently in HCC samples tested and a sample usually has multiple types of mutations. A special pattern of insert at 204 and point mutations at 260 and 264 was identified, and it appears to be associated with the nuclear localization of HBx protein. The development of multiple types of mutations in a given sample may contribute to the process of multiple steps in hepatocarcinogenesis.

Base Sequence↗
PubMed2005

Blocking BRE expression in Leydig cells inhibits steroidogenesis by down-regulating 3beta-hydroxysteroid dehydrogenase.

Conversion of cholesterol to biologically active steroids is a multi-step enzymatic process. Along with some important enzymes, like cholesterol side-chain cleavage enzyme (P450scc) and 3beta-hydroxysteroid dehydrogenase/isomerase (3beta-HSD), several proteins play key role in steroidogenesis. The role of steroidogenic acute regulatory (StAR) protein is well established. A novel protein, BRE, found mainly in brain, adrenals and gonads, was highly expressed in hyperplastic rat adrenals with impaired steroidogenesis, suggesting its regulation by pituitary hormones. To further elucidate its role in steroidogenic tissues, mouse Leydig tumor cells (mLTC-1) were transfected with BRE antisense probes. Morphologically the BRE antisense cells exhibited large cytoplasmic lipid droplets and failed to shrink in response to human chorionic gonadotropin. Although cAMP production, along with StAR and P450scc mRNA expression, was unaffected in BRE antisense clones, progesterone and testosterone yields were significantly decreased, while pregnenolone was increased in response to human chorionic gonadotropin stimulation or in the presence of 22(R)OH-cholesterol. Furthermore, whereas exogenous progesterone was readily converted to testosterone, pregnenolone was not, suggesting impairment of pregnenolone-to-progesterone conversion, a step metabolized by 3beta-HSD. That steroidogenesis was compromised at the 3beta-HSD step was further confirmed by the reduced expression of 3beta-HSD type I (3ss-HSDI) mRNA in BRE antisense cells compared with controls. Our results suggest that BRE influences steroidogenesis through its effects on 3beta-HSD action, probably affecting its transcription.

3-Hydroxysteroid Dehydrogenases↗
PubMed2004

Resistance to apoptosis of HPV 16-infected laryngeal cancer cells is associated with decreased Bak and increased Bcl-2 expression.

Human papillomavirus type 16 (HPV 16) plays an etiological role in human laryngeal carcinoma. Apoptosis is closely associated with various biological processes including oncogenesis. This study investigated how HPV 16 oncoproteins E6 and E7 affect apoptosis in human laryngeal cancer cells. We established two human laryngeal cancer cell lines that expressed HPV 16 E6 and E7, respectively. Using these two cell lines, we found that both E6 and E7 exhibited an inhibitive effect on apoptosis induced by tumor necrosis factor alpha and cycloheximide. In both transfected cell lines, the expression of pro-apoptotic Bak was reduced and that of anti-apoptotic Bcl-2 was over-expressed. However, the expression of caspase-3 and caspase-8 was not significantly different between the E6- and E7-transfected cells and the control cells without HPV 16. p53 Protein was not detected in either the transfected or the non-transfected cells. Our study indicates that: (1) HPV 16 E6 and E7 oncoproteins are capable of inhibiting apoptosis in laryngeal squamous carcinoma cells; (2) the mechanism modulated by E6 and E7 involves the over-expression of Bcl-2 and the down-regulation of Bak; (3) the anti-apoptotic pathway is not related to the level of p53, caspase-3, or caspase-8. These results suggest that the dysregulation of apoptotic molecules Bak and Bcl-2 by HPV 16 E6 and E7 plays a role in the prolongation of cell survival, which may subsequently contribute to the development of human laryngeal cancer.

Animals↗
PubMed2004

Inhibitory effects of budesonide, desloratadine and dexamethasone on cytokine release from human mast cell line (HMC-1).

OBJECTIVE: To determine the inhibitory potency of budesonide on interleukin (IL)-4, 6 and 8, GM-CSF and TNF-alpha release from the human mast cell line (HMC-1) in comparison with the systemic glucocorticosteroid, dexamethasone, and H(1) antagonist, desloratadine. METHODS: HMC-1 was stimulated with 25 ng/ml phorbol 12- myristate 13-acetate (PMA) and 2.5 x 10(-7) M ionomycin (A23187) for 6, 12 and 24 h in both the presence and absence of 10(-6)-10(-10) M concentrations of the test drugs. Culture supernatants were collected and assayed by ELISAs. RESULTS: HMC-1 produced substantial amounts of GM-CSF and IL-8 and smaller amounts of TNF-alpha, IL-4 and IL-6 after being stimulated with PMA together with A23187. Budesonide and dexamethasone had potent inhibitory effects and desloratadine had modest inhibitory effects on the release of these cytokines. Budesonide was more potent than dexamethasone at most concentrations and time points. IL-4 was the cytokine which was most susceptible to inhibition by the three tested drugs. The inhibitory effects, in some cases, were time- and concentration-dependent. CONCLUSION: Budesonide had a potent inhibitory effect on cytokine release from HMC-1. Its potency was greater than that of both dexamethasone and desloratadine.

Budesonide↗
PubMed2004

Over-expression of Bcl-2 against Pteris semipinnata L-induced apoptosis of human colon cancer cells via a NF-kappa B-related pathway.

Ent-11 alpha-hydroxy-15-oxo-kaur-16-en-19-oic-acid (5F), an antitumor component, is a chemical compound isolated from Pteris semipinnata L (PsL), a Chinese traditional herb. We examined whether 5F could affect apoptosis in human colon cancer HT-29 cells, and test whether and how the over-expression of Bcl-2 and Bcl-xL could offset the effect of 5F on cell growth. The result demonstrated that 5F significantly induced apoptosis of HT-29, as shown by MTT assay and DNA fragmentation measurement. Treatment of HT-29 with 5F increased both p38 and iNOS levels, suggesting these two molecules may contribute to the apoptotic effect of 5F. Over-expression of Bcl-2 or Bcl-xL attenuated the increase of p38 and iNOS induced by 5F. The cells with Bcl-2 or Bcl-xL over-expression showed an elevation of nuclear factor kappa B (NF-kappa B) activity, accompanying a significant reduction of 5F-induced apoptosis. Furthermore, inhibition of NF-kappa B by I k B alpha SR, which is a powerful inhibitor of NF-kappa B, restored the ability of 5F to induce apoptosis in the cells transfected with Bcl-2. These data strongly indicated that the apoptotic effect of 5F on HT-29 was closely associated with the activity of NF-kappa B, which was up-regulated by Bcl-2 and Bcl-xL. In conclusion, 5F induced apoptosis in HT-29 cells and this apoptotic effect was associated with the high level of p38 and iNOS expression. The apoptotic effect of 5F could be significantly offset by over-expression of either Bcl-2 or Bcl-xL. Bcl-2, and to the less extent, Bcl-xL, were able to increase the activity of NF-kappa B, which was a known anti-apoptotic molecule in human colon cancer cells.

Apoptosis↗
PubMed2001

Immunohistochemical analysis of pro-apoptotic Bid level in chronic hepatitis, hepatocellular carcinoma and liver metastases.

Bid, a member of the Bcl-2 family, mediates apoptosis by inducing the release of proapoptotic factors. The expression of Bid in liver diseases has not been investigated. This study evaluated Bid level in various liver diseases including hepatocellular carcinoma (HCC), liver metastases from colorectal cancer, chronic hepatitis and liver cirrhosis. The expression of Bid in tumorous tissues of HCC was lower than that in their corresponding non-tumorous tissues from the same patient. Heavy staining with Bid antibody was found in some localized tumorous liver tissues from patients with poorly differentiated tumors. In patients with chronic hepatitis and liver cirrhosis, there were gradient tumor-development centers, a gradient increase in reaction with Bid antibody from the middle of the center to its edge. The gradient tumor-development center was also found in non-tumorous tissues of HCC, suggesting that occurrence of this center in chronic hepatitis might be an early pathologic sign of HCC development. Bid was also expressed in the epithelial cells in tissues from liver metastases and their expression was often stronger than in the non-tumorous liver tissues. Heavy nuclear staining of Bid was not uncommon in these metastatic cells. The different patterns of staining between primary and secondary liver tumors may reflect a difference in tumor origin and in cell type. Nuclei of metastatic cells, though positive for Bid, still showed a considerable mitotic activity, indicating that they were in active proliferation rather than on a pathway deemed to be apoptotic. In conclusion, this study shows that the Bid level is decreased in HCC except in poorly differentiated HCC in which cells may undergo a process of apoptosis or necrosis. The existence of gradient tumor-development center in chronic hepatitis, liver cirrhosis and non-tumorous tissues from HCC may serve as a pathologic marker of a carcinogenic change of cell phenotypes.

BH3 Interacting Domain Death Agonist Protein↗
PubMed2001

Induction of Fas and Fas ligand expression on malignant glioma cells by Kupffer cells, a potential pathway of antiliver metastases.

Kupffer cells play an important role in controlling the growth and development of liver metastases. However, the pathway of Kupffer cells against tumor metastases is not clear. In the present study, we set up an experimental model to investigate the mechanisms on how Kupffer cells kill tumor cells which metastasize to the liver. Malignant glioma cells were cocultured with Kupffer cells or treated with culture medium collected from lipopolysaccharide (LPS)-activated Kupffer cells. The results showed that the interaction between Kupffer cells and malignant glioma cells significantly stimulated the generation of tumor necrosis factoralpha (TNFalpha). TNFalpha was mainly produced by Kupffer cells, as its level in culture medium obtained from LPS-treated Kupffer cells was not significantly different from that of malignant glioma cells treated with the same medium. Both Kupffer cells and LPS/Kupffer cell-conditioned supernatants induced expression of Fas and Fas ligand on malignant glioma cells. Subsequently a significant proportion of malignant glioma cells became apoptotic, as evidenced by positive staining of annexin V and propidium iodine and an increase in cellular DNA fragmentation. Therefore, this study supports a novel pathway of Kupffer cells against liver metastases, in which tumor cells were apoptotic via the Fas-Fas ligand system induced by TNFalpha released from Kupffer cells.

Animals↗
PubMed2001

Decreased expression of Bid in human hepatocellular carcinoma is related to hepatitis B virus X protein.

As a mitochondrial membrane death ligand, Bid oligomerises Bak to release cytochrome C and its deficiency renders hepatocytes resistant to apoptosis induced by Fas. The Bid level in hepatocellular carcinoma (HCC) is unknown. In this report, we examined the expression of Bid protein and mRNA in HCC cancerous tissues and their corresponding non-cancerous ones. The effect of the hepatitis B x protein (HBx) on the expression of Bid was also evaluated by transfecting hepatoma cells with the HBx gene. The results showed that the expression of Bid was significantly lower in cancerous tissues than that in their corresponding non-cancerous tissues. Immunohistochemical study revealed that Bid molecule was mainly localised in hepato-cytoplasm. Some nuclei were also positive for Bid antigen though to a lesser degree. In vitro experiments demonstrated that the expression of Bid in cells transfected with HBx was significantly lower than that in the cells without HBx transfection. This finding suggests that HBx may play a causative role in the reduction of Bid expression in HCC. This in vitro result is, to some degree, supported by clinical data that all the HCC examined are positive for hepatitis B virus (HBV). We conclude from this data that the expression of Bid in HCC is significantly decreased and the reduction of Bid may result from a mechanism associated with HBx, a major hepatocarcinogenic product from HBV. The imbalance of increased anti-apoptosis and decreased pro-apoptosis seen in HCC is a critical mechanism leading to the uncontrolled growth of tumour cells. Therefore, this study suggests that a deficiency in the expression of Bid may contribute to the development of such an imbalance in HCC.

BH3 Interacting Domain Death Agonist Protein↗
PubMed2000

Current and future treatments for cognitive deficits in dementia.

In this article, we primarily focus on the treatment approaches currently marketed and in advanced stages of development for Alzheimer's disease (AD). Amyloid plaques and neurofibrillary tangles remain the pathologic hallmarks of AD, and much progress has been made in unraveling the molecular biology of these changes. In addition, there is also intense research into inflammatory and oxidative mechanisms as well as vascular and neurochemical alterations in AD. Therapies targeted at these mechanisms are discussed.

Aged↗
PubMed1997

Effects of low-intensity AC and/or DC electromagnetic fields on cell attachment and induction of apoptosis.

Rat tendon fibroblast (RTF) and rat bone marrow (RBM) osteoprogenitor cells were cultured and exposed to AC and/or DC magnetic fields in a triaxial Helmholtz coil in an incubator for up to 13 days. The AC fields were at 60 and 1000 Hz and up to 0.25 mT peak to peak, and the DC fields were up to 0.25 mT. At various combinations of field strengths and frequencies, AC and/or DC fields resulted in extensive detachment of preattached cells and prevented the normal attachment of cells not previously attached to substrates. In addition, the fields resulted in altered cell morphologies. When RTF and RBM cells were removed from the fields after several days of exposure, they partially reattached and assumed more normal morphologies. An additional set of experiments described in the Appendix corroborates these findings and also shows that low-frequency EMF also initiates apoptosis, i.e., programmed cell death, at the onset of cell detachment. Taken together, these results suggest that the electromagnetic fields result in significant alterations in cell metabolism and cytoskeleton structure. Further work is required to determine the relative effect of the electric and magnetic fields on these phenomena. The research has implications for understanding the role of fields in affecting bone healing in fracture nonunions, in cell detachment in cancer metastasis, and in the effect of EMF on organisms generally.

Animals↗
PubMed1994

Chloroplast molecular chaperone-assisted refolding and reconstitution of an active multisubunit coupling factor CF1 core.

The chloroplast coupling factor 1 (CF1) is composed of five kinds of subunits with a stoichiometry of alpha 3 beta 3 gamma delta epsilon. Reconstitution of a catalytically active alpha 3 beta 3 gamma core from urea-denatured subunits at a physiological pH is reported here. A restoration of approximately 90% of the CF1 ATPase activity has been observed. The reconstitution was achieved by using subunits overexpressed in Escherichia coli, purified, and combined in the presence of MgATP, K+, and a mixture of several chloroplast molecular chaperones at pH 7.5. The combination of chaperonin 60 and chaperonin 24 failed to reconstitute the active CF1 core, as did the GroEL/GroES pair (E. coli chaperonin 60/10 homologues). Characteristics of the reconstituted ATPase were very close to those of the native complex, including methanol-reversible inhibition by the purified epsilon subunit of CF1 and sensitivity to inhibition by azide and by tentoxin. In reconstitution with a mixture of tentoxin-resistant and -sensitive beta subunits, the extent of inhibition by tentoxin depended on the proportion of sensitive subunits in the reconstitution mixture. Finally, a model for the assembly of the CF1 core alpha 3 beta 3 gamma structure is proposed.

Chloroplasts↗
PubMed1993

Import and assembly of the beta-subunit of chloroplast coupling factor 1 (CF1) into isolated intact chloroplasts.

The transit peptide gene of the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase from Nicotiana plumbaginifolia was fused to the tentoxin-resistant beta-subunit gene of chloroplast coupling factor 1 (CF1) from Nicotiana tabacum via a linker sequence. The consequent fusion gene encodes the entire gene sequences of both the transit peptide and the beta-subunit of CF1 without a single change of amino acid residues. The fusion gene was in vitro expressed in a coupled transcription-translation system as a 62-kDa precursor and was imported into isolated intact chloroplasts of Nicotiana longiflora. The imported precursor was found to be processed to the expected mature beta-subunit size. Evidence is presented that radioactively labeled beta-subunit was incorporated into mature CF1 and not just nonspecifically associated with the thylakoid membranes. Since the fusion protein containing only the transit peptide sequence was imported and apparently correctly processed, it may not be necessary to include N-terminal amino acids of the mature small subunit for correct proteolytic cleavage in the chloroplast stroma.

Amino Acid Sequence↗
PubMed1988

Inhibitor of cyclic AMP-dependent protein kinase blocks opioid-induced prolongation of the action potential of mouse sensory ganglion neurons in dissociated cell cultures.

The duration of the calcium component of the action potential (APD) of dorsal root ganglion (DRG) neurons in mouse spinal cord-ganglion explants has been shown to be dually modulated via excitatory and inhibitory opioid receptors. In order to determine if opioid-induced APD prolongation is modulated by receptors that are positively coupled to the adenylate cyclase (AC)/cyclic AMP second messenger system, whole-cell recordings were made from mouse DRG neurons grown in dissociated cell cultures. Tests for opioid responsivity were carried out after intracellular dialysis of an inhibitor of cAMP-dependent protein kinase (PKI). In control recordings, both DADLE-induced APD prolongation as well as shortening were prevented by co-perfusion with the opioid antagonist, diprenorphine (10 nM). Intracellular dialysis of PKI in these neurons completely blocked opioid-induced APD prolongation but did not attenuate APD shortening generally elicited by higher opioid concentrations. Bath perfusion of 10 nM DADLE elicited APD prolongation in 59% of the DRG neurons (n = 34) tested with control solution in the recording pipette, whereas none showed APD prolongation when the pipette contained PKI (n = 18). In control tests with 1 microM DADLE, the APD was prolonged in 37% of the cells and shortened in 26% (n = 19); in contrast, a matched group of PKI-treated cells showed no APD prolongation, whereas 42% showed APD shortening (n = 26). The results support the hypothesis that opioid-induced APD prolongation in DRG neurons is mediated by opioid receptor subtypes that are positively coupled via Gs to AC/cAMP-dependent voltage-sensitive ionic conductances.

Action Potentials↗