Biomedical subjects

M Kong

Publications and source records attributed to M Kong.

At least 19 recordsLinked to original sources

PubMed2006

Spectrum of classical two-dimensional Coulomb clusters.

The frequency spectrum of a system of classical charged particles interacting through a Coulomb repulsive potential and which are confined in a two-dimensional parabolic trap is studied. It is shown that, apart from the well-known center-of-mass and breathing modes, which are independent of the number of particles in the cluster, there are more "universal" modes whose frequencies depend only slightly on the number of particles. To understand these modes the spectrum of excitations as a function of the number of particles is compared with the spectrum obtained in the hydrodynamic approach. The modes are classified according to their averaged vorticity and it is shown that these "universal" modes have the smallest vorticity and follow the hydrodynamic behavior.

Journal Article↗

PubMed2003

Assessment of recombinant factor VIIa as an antidote for bleeding induced in the rabbit by low molecular weight heparin.

While protamine sulfate reverses the anticoagulant effect of standard heparin, there currently is no effective antidote for low molecular weight heparin (LMWH)-induced bleeding. Recently, recombinant activated factor VII (rFVIIa) was approved by the FDA for use in hemophilia patients with factor (F)VIII or FIX inhibitors. However, this new pro-hemostatic agent has potential utility in other clinical scenarios. In this study, we utilized a well-characterized rabbit ear puncture model to test the efficacy of rFVIIa to reverse LMWH-induced prolonged bleeding. Animals were first treated with bolus intravenous LMWH (1800 anti-FXa U kg(-1)) which increased the primary bleeding time approximately fourfold and raised the plasma anti-FXa activity immediately and continuously throughout the 90-min experiment. In a randomized and blinded fashion, animals then received either rFVIIa (400 microg kg(-1)) or placebo by bolus intravenous injection, following which the ear puncture bleeding times were measured, along with blood levels of heparin (anti-FXa activity) and FVII. FVII activity increased 5.3-fold over baseline in treated animals, decreasing by only 24% over the full observation period. The rFVIIa-treated animals showed a slight decrease in bleeding time immediately after injection, but there was no statistically significant difference in bleeding after rFVIIa or placebo administration. In this study using a rabbit ear bleeding model, rFVIIa was not an effective antidote to LMWH-induced bleeding. However, the bolus injection of LMWH produced a very high blood anti-FXa level, which may have precluded rFVIIa effectiveness.

Animals↗

PubMed2003

Safety of plasmin in the setting of concomitant aspirin and heparin administration in an animal model of bleeding.

Plasmin is a direct thrombolytic which has been shown to have a strikingly favorable benefit to risk profile in comparison with plasminogen activators, notably tissue plasminogen activator (t-PA). As heparin is known to increase the risk of hemorrhage when co-administered with a plasminogen activator, we asked whether adjunct antithrombotic agents such as aspirin and heparin would affect the safety of plasmin. Three groups of rabbits were administered plasmin at a dose (4 mg kg-1) designed to induce significant decreases in antiplasmin, fibrinogen and factor (F)VIII, to about 25, 40 and 40%, respectively, of baseline values, but not cause prolongation of the ear puncture bleeding time. In a blinded and randomized trial, the results show that an intravenous aspirin bolus plus heparin administered as a bolus followed by a maintenance continuous infusion did not significantly prolong the bleeding time during plasmin infusion. These data indicate that in the rabbit, concomitant use of aspirin plus heparin does not affect the safety of a therapeutic dose of plasmin.

Animals↗

PubMed2002

Sperm binding to the human zona pellucida and calcium influx in response to GnRH and progesterone.

In this study the effect of the sequential exposure of spermatozoa to progesterone and gonadotrophin-releasing hormone (GnRH) upon zona binding and the intracellular free Ca2+ concentration was evaluated. Sperm aliquots were treated as follows: (a) 0.7 micro mol l(-1) progesterone or 0.1% DMSO (progesterone solvent) followed by 50 nmol l(-1) of GnRH; (b) 50 nmol l(-1) of GnRH or distilled water (GnRH solvent) followed by 0.7 micro mol l(-1) of progesterone. Additional aliquots were incubated with DMSO or distilled water (controls) and with 0.7 micro mol l(-1) of progesterone or 50 nmol l(-1) of GnRH. All treatments were for 5 min. Motile spermatozoa were incubated in modified Tyrode's medium, at 37 degrees C, 5% CO2, 10 x 10(6) spermatozoa ml(-1), for 4.5 h. Intracellular Ca2+ concentration and sperm-zona binding was evaluated using fura 2 and the hemizona assay, respectively. GnRH and progesterone increased sperm-zona binding and the Ca2+ concentration. Regarding zona binding, the effect of GnRH was significantly greater when the spermatozoa had been previously treated with progesterone (progesterone-->GnRH=185 +/- 116 zona-bound spermatozoa versus DMSO-->GnRH=99 +/- 15, P < 0.001). On the other hand, previous treatment with GnRH did not modify their subsequent response to progesterone (GnRH-->progesterone= 114 +/- 19 zona-bound spermatozoa versus distilled water-->progesterone=108 +/- 22, NS). The results regarding intracellular Ca2+ showed a similar pattern. These findings suggest a priming effect of progesterone upon a GnRH-induced increase in sperm-zona binding and intracellular Ca2+.

Calcium↗

PubMed2001

Patched1 interacts with cyclin B1 to regulate cell cycle progression.

The initiation of mitosis requires the activation of M-phase promoting factor (MPF). MPF activation and its subcellular localization are dependent on the phosphorylation state of its components, cdc2 and cyclin B1. In a two-hybrid screen using a bait protein to mimic phosphorylated cyclin B1, we identified a novel interaction between cyclin B1 and patched1 (ptc1), a tumor suppressor associated with basal cell carcinoma (BCC). Ptc1 interacted specifically with constitutively phosphorylated cyclin B1 derivatives and was able to alter their normal subcellular localization. Furthermore, addition of the ptc1 ligand, sonic hedgehog (shh), disrupts this interaction and allows cyclin B1 to localize to the nucleus. Expression of ptc1 in 293T cells was inhibitory to cell proliferation; this inhibition could be relieved by coexpression of a cyclin B1 derivative that constitutively localizes to the nucleus and that could not interact with ptc1 due to phosphorylation-site mutations to ALA: In addition, we demonstrate that endogenous ptc1 and endogenous cyclin B1 interact in vivo. The findings reported here demonstrate that ptc1 participates in determining the subcellular localization of cyclin B1 and suggest a link between the tumor suppressor activity of ptc1 and the regulation of cell division. Thus, we propose that ptc1 participates in a G(2)/M checkpoint by regulating the localization of MPF.

Animals↗

PubMed2001

Cyclooxygenase-two (COX-2) modulates proliferation in aggressive fibromatosis (desmoid tumor).

Aggressive fibromatosis is a locally invasive soft tissue lesion. Seventy-five per cent of cases harbor a somatic mutation in either the APC or beta-catenin genes, resulting in beta-catenin protein stabilization. Cyclooxygenase-2 (COX-2) is an enzyme involved in prostaglandin synthesis that modulates the formation of colonic neoplasia, especially in cases due to mutations resulting in beta-catenin stabilization. Human aggressive fibromatoses and lesions from the Apc+/Apc1638N mouse (a murine model for Apc-driven fibromatosis) demonstrated elevated COX-2 levels. COX-2 blockade either by the selective agent DFU or by non-selective COX blocking agents results in reduced proliferation in human tumor cell cultures. Breeding mice with Cox-2-/- mice resulted in no difference in number of aggressive fibromatoses formed, but in a smaller tumor size, while there was a decrease in number of GI lesions by 50%. Mice fed various COX blocking agents also showed a decline in tumor size. COX-2 expression was regulated by tcf-dependent transcription in this lesion. COX-2 partially regulates proliferation due to beta-catenin stabilization in aggressive fibromatosis. Although COX blockade alone does not cause tumor regression, this data suggests that it may have a role as an adjuvant therapy to slow tumor growth in this lesion.

Animals↗

PubMed2001

Plasmin induces local thrombolysis without causing hemorrhage: a comparison with tissue plasminogen activator in the rabbit.

The direct fibrinolytic enzyme, plasmin, was compared with tissue plasminogen activator (TPA) in rabbit models of local thrombolysis and fibrinolytic hemorrhage. Plasmin was produced by solid-phase urokinase activation of plasminogen and purified on benzamidine Sepharose. Applied as an intra-arterial infusion into the thrombosed abdominal aorta under conditions of unimpeded blood flow, plasmin (4 mg/kg) and TPA (2 mg/kg) achieved equivalent clot dissolution and flow restoration. Using the model of restricted blood flow into the thrombosed aorta, which limits local plasminogen supply, plasmin was superior to TPA in clot lysis and vascular reperfusion. Using similar dosages of plasmin (2 or 4 mg/kg) and TPA (1 or 2 mg/kg) in the earpuncture rebleed model. TPA induced rebleeding in a dose-dependent manner from prior puncture sites in 9 of 10 animals, while none of the 10 animals exposed to plasmin rebled from these sites. These results suggest that plasmin is an effective, unique thrombolytic agent, distinguished from the plasminogen activators in current usage by its striking safety profile.

Animals↗

PubMed2000

Epidermal growth factor-induced phosphatidylinositol 3-kinase activation and DNA synthesis. Identification of Grb2-associated binder 2 as the major mediator in rat hepatocytes.

In previous work we showed that the phosphatidylinositol 3-kinase (PI3-kinase), not the mitogen-activated protein kinase, pathway is necessary and sufficient to account for insulin- and epidermal growth factor (EGF)-induced DNA synthesis in rat hepatocytes. Here, using a dominant-negative p85, we confirmed the key role of EGF-induced PI3-kinase activation and sought to identify the mechanism by which this is effected. Our results show that EGF activates PI3-kinase with a time course similar to that of the association of p85 with three principal phosphotyrosine proteins (i. e. PY180, PY105, and PY52). We demonstrated that each formed a distinct p85-associated complex. PY180 and PY52 each constituted about 10% of EGF-activated PI3-kinase, whereas PY105 was responsible for 80%. PY105 associated with Grb2 and SHP-2, and although it behaved like Gab1, none of the latter was detected in rat liver. We therefore cloned a cDNA from rat liver, which was found to be 95% homologous to the mouse Grb2-associated binder 2 (Gab2) cDNA sequence. Using a specific Gab2 antibody, we demonstrated its expression in and association with p85, SHP-2, and Grb2 upon EGF treatment of rat hepatocytes. Gab2 accounted for most if not all of the PY105 species, since immunoprecipitation of Gab2 with specific antibodies demonstrated parallel immunodepletion of Gab2 and PY105 from the residual supernatants. We also found that the PI3-kinase activity associated with Gab2 was totally abolished by dominant negative p85. Thus, Gab2 appears to be the principal EGF-induced PY protein recruiting and activating PI3-kinase and mitogenesis.

Adaptor Proteins, Signal Transducing↗

PubMed2000

Cyclin F regulates the nuclear localization of cyclin B1 through a cyclin-cyclin interaction.

The key regulator of G(2)-M transition of the cell cycle is M-phase promoting factor (MPF), a complex composed of cdc2 and a B-type cyclin. Cyclin B1 nuclear localization involves phosphorylation within a region called the cytoplasmic retention signal, which also contains a nuclear export signal. The mechanism of MPF nuclear localization remains unclear since it contains no functional nuclear localization signal (NLS). We exploited the yeast two-hybrid screen to find protein(s) potentially mediating localization of cyclin B1 and identified a novel interaction between cyclin B1 and cyclin F. We found that cdc2, cyclin B1 and cyclin F form a complex that exhibits histone H1 kinase activity. Cyclin B1 and cyclin F also colocalize through immunofluorescence studies. Additionally, deletion analysis revealed that each putative NLS of cyclin F is functional. Taken together, the data suggest that the NLS regions of cyclin F regulate cyclin B1 localization to the nucleus. The interaction between cyclin B1 and cyclin F represents the first example of direct cyclin-cyclin binding, and elucidates a novel mechanism that regulates MPF localization and function.

Animals↗

PubMed2000

Gonadotropin-releasing hormone-stimulated sperm binding to the human zona is mediated by a calcium influx.

The mechanism by which GnRH increases sperm-zona pellucida binding in humans was investigated in this study. We tested whether GnRH increases sperm-zona binding in Ca(2+)-free medium and in the presence of Ca(2+) channel antagonists. We also examined the GnRH effect on the intracellular free Ca(2+) concentration ([Ca(2+)](i)). Sperm treatment with GnRH increased sperm-zona binding 300% but only when Ca(2+) was present in the medium. In Ca(2+)-free medium or in the presence of 400 nM nifedipine, 80 microM diltiazem, or 50 microM verapamil, GnRH did not influence sperm-zona binding. GnRH increased the [Ca(2+)](i) in the sperm in a dose-dependent manner. The maximum effect was reached with 75 nM GnRH. The GnRH-induced increase in [Ca(2+)](i) was fast and transient, from a basal [Ca(2+)](i) of 413 +/- 22 nM to a peak value of 797 +/- 24 nM. The GnRH-induced increase in [Ca(2+)](i) was entirely due to a Ca(2+) influx from the extracellular medium because the increase in [Ca(2+)](i) was blocked by the Ca(2+) chelator EGTA and by the Ca(2+) channel antagonists nifedipine and diltiazem. These antagonists, however, were not able to inhibit the progesterone-activated Ca(2+) influx. On the contrary, T-type calcium channel antagonists pimozide and mibefradil did not affect GnRH-activated Ca(2+) influx but inhibited the progesterone-activated Ca(2+) influx. Finally, the GnRH-induced Ca(2+) influx was blocked by two specific GnRH antagonists, Ac-D-Nal(1)-Cl-D-Phe(2)-3-Pyr-D-Ala(3)-Arg(5)-D-Glu(AA)(6)-GnRH and Ac-(3,4)-dehydro-Pro(1),-p-fluoro-D-Phe(2), D-Trp(3,6)-GnRH. These results suggest that GnRH increases sperm-zona binding via an elevation of [Ca(2+)](i) through T-type, voltage-operated calcium channels.

Calcium↗

PubMed2000

Effects of intraduodenal glucose and fructose on antropyloric motility and appetite in healthy humans.

Oral fructose empties from the stomach more rapidly and may suppress food intake more than oral glucose. The purpose of the study was to evaluate the effects of intraduodenal infusions of fructose and glucose on antropyloric motility and appetite. Ten healthy volunteers were given intraduodenal infusions of 25% fructose, 25% glucose, or 0.9% saline (2 ml/min for 90 min). Antropyloric pressures, blood glucose, and plasma insulin, gastric inhibitory peptide (GIP), and glucagon-like peptide-1 (GLP-1) were measured concurrently; a buffet meal was offered at the end of the infusion. Intraduodenal fructose and glucose suppressed antral waves (P < 0. 0005 for both), stimulated isolated pyloric pressure waves (P < 0.05 for both), and increased basal pyloric pressure (P = 0.10 and P < 0. 05, respectively) compared with saline, without any significant difference between them. Intraduodenal glucose increased blood glucose (P < 0.0005), as well as plasma insulin (P < 0.0005) and GIP (P < 0.005) more than intraduodenal fructose, whereas there was no difference in the GLP-1 response. Intraduodenal fructose suppressed food intake compared with saline (P < 0.05) and glucose (P = 0.07). We conclude that, when infused intraduodenally at 2 kcal/min for 90 min 1) fructose and glucose have comparable effects on antropyloric pressures, 2) fructose tends to suppress food intake more than glucose, despite similar GLP-1 and less GIP release, and 3) GIP, rather than GLP-1, probably accounts for the greater insulin response to glucose than fructose.

Adult↗

PubMed2000

[Use of high-field nulear magnetic resonance spectroscopy for the analysis of stereoselective metabolites of ibuprofen (R)-enantiomer in rat urine].

AIM: To study the metabolic chiral inversion and chiral metabolites of R-(-)-ibuprofen. METHODS: Following administration of R-(-)-ibuprofen (250 mg.kg-1), analysis was performed on rat urine purified extracts obtained by solid phase extraction onto C-18 bonded silica gel, then the metabolites of ibuprofen were detected and identified by 1HNMR spectroscopy. RESULTS: Except for a little ibuprofen, there were 2'-hydroxy-ibuprofen and its glucuronide, 1'-carboxy-ibuprofen glucuronide and ibuprofen glucuronide in rat urine. 2'-hydroxy-ibuprofen is the main metabolite. 1'-carboxy-ibuprofen glucuronide and ibuprofen glucuronide were diastereoisomers. CONCLUSION: There was the phenomenon of metabolic chiral inversion, whereby the R-enantiomer is transformed in vivo to its active S-antipode via an unusual process.

Animals↗

PubMed1999

Regulation of glycogen synthase in rat hepatocytes. Evidence for multiple signaling pathways.

We examined the signaling pathways regulating glycogen synthase (GS) in primary cultures of rat hepatocytes. The activation of GS by insulin and glucose was completely reversed by the phosphatidylinositol 3-kinase inhibitor wortmannin. Wortmannin also inhibited insulin-induced phosphorylation and activation of protein kinase B/Akt (PKB/Akt) as well as insulin-induced inactivation of GS kinase-3 (GSK-3), consistent with a role for the phosphatidylinositol 3-kinase/PKB-Akt/GSK-3 axis in insulin-induced GS activation. Although wortmannin completely inhibited the significantly greater level of GS activation produced by the insulin-mimetic bisperoxovanadium 1,10-phenanthroline (bpV(phen)), there was only minimal accompanying inhibition of bpV(phen)-induced phosphorylation and activation of PKB/Akt, and inactivation of GSK-3. Thus, PKB/Akt activation and GSK-3 inactivation may be necessary but are not sufficient to induce GS activation in rat hepatocytes. Rapamycin partially inhibited the GS activation induced by bpV(phen) but not that effected by insulin. Both insulin- and bpV(phen)-induced activation of the atypical protein kinase C (zeta/lambda) (PKC (zeta/lambda)) was reversed by wortmannin. Inhibition of PKC (zeta/lambda) with a pseudosubstrate peptide had no effect on GS activation by insulin, but substantially reversed GS activation by bpV(phen). The combination of this inhibitor with rapamycin produced an additive inhibitory effect on bpV(phen)-mediated GS activation. Taken together, our results indicate that the signaling components mammalian target of rapamycin and PKC (zeta/lambda) as well as other yet to be defined effector(s) contribute to the modulation of GS in rat hepatocytes.

Animals↗

PubMed1999

Alkaloids from the roots of goniothalamus griffithii

Three new alkaloids-griffithazanone A (1), griffithdione (2), and griffithinam (3)-were isolated from the roots of Goniothalamus griffithii, along with six known compounds, 4-methyl-2,9, 10-(2H)-1-azaanthracenetrione (4), velutinam, aristololactam BI, aristololactam BII, aristololactam AII, and norcepharanone B. Their structures were elucidated on the basis of spectral and chemical methods. The absolute configuration of griffithazanone A (1) was determined by the preparation of Mosher's esters.

Journal Article↗

PubMed1999

Gonadotrophin-releasing hormone antagonists inhibit sperm binding to the human zona pellucida.

Previous work from our laboratory indicated that gonadotrophin-releasing hormone (GnRH) increases human sperm-zona pellucida binding. Here we present evidence that GnRH antagonists inhibit sperm-zona pellucida binding in humans. Motile spermatozoa (10(7) cells/ml) were incubated in modified Tyrode's medium at 37 degrees C, in 5% CO(2) in air. After 4.5 h, aliquots of spermatozoa were treated with saline (control) or with different concentrations of GnRH antagonists (test). Each sperm aliquot was then tested in the hemizona binding assay. In this assay, the control aliquot was incubated with half a human zona pellucida (hemizona) and the test aliquot was incubated with the matching half. After 20 min, the hemizonae were withdrawn and the number of zona-bound spermatozoa counted using phase-contrast microscopy. In addition, the effect of GnRH antagonists upon the pattern of sperm movement, frequency of sperm-zona pellucida collisions, and percentage of living and acrosome-reacted spermatozoa was determined. The results indicated that treatment with GnRH antagonists decreased the number of zona-bound spermatozoa and did not change the pattern of sperm movement, frequency of sperm-zona collisions, and percentage of acrosome-reacted spermatozoa. We suggest that this action of GnRH antagonists may be due to an effect on zona receptors on the sperm plasma membrane.

Female↗

PubMed1999

Metabolic and genetic determinants of HDL metabolism and hepatic lipase activity in normolipidemic females.

The metabolic and genetic determinants of HDL cholesterol (HDL-C) levels and HDL turnover were studied in 36 normolipidemic female subjects on a whole-food low-fat metabolic diet. Lipid, lipoprotein, and apolipoprotein levels, lipoprotein size, and apolipoprotein turnover parameters were determined, as were genetic variation at one site in the hepatic lipase promoter and six sites in the apolipoprotein AI/CIII/AIV gene cluster. Menopause had no significant effect on HDL-C or turnover. Stepwise multiple regression analysis revealed that HDL-C was most strongly correlated with HDL size, apolipoprotein A-II (apoA-II), and apolipoprotein A-I (apoA-I) levels, which together could account for 90% of the variation in HDL-C. HDL size was inversely correlated with triglycerides, body mass index, and hepatic lipase activity, which together accounted for 82% of the variation in HDL size. The hepatic lipase promoter genotype had a strong effect on hepatic lipase activity and could account for 38% of the variation in hepatic lipase activity. The apoA-I transport rate (AI-TR) was the major determinant of apoA-I levels, but AI-TR was not associated with six common genetic polymorphism in the apoAI/CIII/AIV gene cluster.A simplified model of HDL metabolism is proposed, in which A-I and apoA-II levels combined with triglycerides, and hepatic lipase activity could account for 80% of the variation in HDL-C.

Adult↗

PubMed1998

[A new method for study of the effect of drugs on cancer cells--31PNMR with perfused cell system].

31P NMR was performed for the studies on the metabolic changes of endogenous phosphorus-containing molecules in KB and HCT-8 cells exposed to taxol at a concentration of 10(-6) mol.L-1. Using the perfusion method, the cells can be detected for a longer time by NMR, so as to give continuous spectra of the two cell-lines during the perfusion with and without the drug. The spectra showed that the levels of ATP peaks for both cells enhanced during the perfusion with the drug, but the change of the level is more prominent in KB cells than in HCT-8 cells. This shows that KB cells are more sensitive to taxol than HCT-8 cells. This is in coincident with the result in the cytotoxicity studies. However, the experiment using vincristine at the same concentrations demonstrated that the level of the ATP peak was not changed significantly.

Adenosine Triphosphate↗

PubMed1998

[The structures elucidation of isodopharicin D and F].

Two new compounds were isolated from Isodon pharicus (Prain) Murata. Their structures were determined to be 3 alpha, 11 beta, 13 alpha-trihydroxy-entkaur-16-en-15-one (1), named isodopharicin D, and 11 beta, 13 alpha, 15 alpha-trihydroxy-entkaur-16-en-3 alpha-beta-D-glucoside (2), named isodopharicin F by chemical and spectral evidence.

Diterpenes↗