Search PubMed⌕ Search

Biomedical subjects

L Huang

Publications and source records attributed to L Huang.

At least 451 records · Page 25Linked to original sources
PubMed1996

Enhanced insulin action due to targeted GLUT4 overexpression exclusively in muscle.

Dysregulation of GLUT4, the insulin-responsive glucose transporter, is associated with insulin resistance in skeletal muscle. Although skeletal muscle is the major target of insulin action, muscle GLUT4 has not been linked causally to whole-body insulin sensitivity and regulation of glucose homeostasis. To address this, we generated a line of transgenic mice that overexpresses GLUT4 in skeletal muscle. We demonstrate that restricted overexpression of GLUT4 in fast-twitch skeletal muscles of myosin light chain (MLC)-GLUT4 transgenic mice induces a 2.5-fold increase in insulin-stimulated 2-deoxyglucose uptake in transgene-overexpressing cells. Consequently, glycogen content is increased in the fast-twitch skeletal muscles under insulin action (5.75 +/- 1.02 vs. 3.24 +/- 0.26 mg/g). This indicates that insulin-stimulated glucose transport is partly rate-limiting for glycogen synthesis. At the whole-body level, insulin-stimulated glucose turnover is increased 2.5-fold in unconscious MLC-GLUT4 mice. Plasma glucose and insulin levels in MLC-GLUT4 mice are altered as a result of increased insulin action. In 2- to 3-month-old MLC-GLUT4 mice, fasting insulin levels are decreased (0.43 +/- 0.05 vs. 0.74 +/- 0.10 microgram/l), whereas normal fasting glycemia is maintained. Conversely, 7- to 9-month-old MLC-GLUT4 mice exhibit decreased fasting glycemia (5.75 +/- 0.73 vs. 8.11 +/- 0.57 mmol/l) with normal insulin levels. Fasting plasma lactate levels are elevated in both age groups (50-100%). Additionally lipid metabolism is affected by skeletal muscle GLUT4 overexpression. This is indicated by changes in plasma free fatty acid and beta-hydroxybutyrate levels. These studies underscore the importance of GLUT4 in the regulation of glucose homeostasis and its interaction with lipid metabolism.

Animals↗
PubMed1996

Antagonism of lactic acid bacteria towards Staphylococcus aureus and Escherichia coli on agar plates and in milk.

The antagonistic effect of lactic acid bacteria (LAB, including Lactobacillus acidophilus, L. bulgaricus, L. casei and Streptococcus thermophilus) on Staphylococcus aureus and Escherichia coli was evaluated on MRS agar with the deferred and cross-streaking techniques, and in milk with the plate counting method. All LAB were repressive to S aureus and E coli on the agar medium. However, their suppressive activity was significantly reduced when the agar medium was buffered to pH 7.2. In normal milk, L acidophilus strains A and B, S thermophilus and its combinations with L acidophilus A and L bulgaricus 6032 were inhibitory to S aureus, while in mastitic milk, only S thermophilus and its combinations showed inhibition. L acidophilus A and L bulgaricus 34104 were repressive to E coli growth in normal milk. S thermophilus and its combinations were inhibitory to E coli in both the normal and mastitic milk samples. These results indicate that the antagonistic activity of LAB on pathogenic bacteria varied with the type of media in which the tests were done, and that testing of in vitro antagonism in milk would be more informative than that in artificial media for in vivo tests concerning the possible roles of competitive microbiological ecology in mastitis control.

Agar↗
PubMed1996

Design, synthesis, cytotoxic properties and preliminary DNA sequencing evaluation of CPI--N-methylpyrrole hybrids. Enhancing effect of a trans double bond linker and role of the terminal amide functionality on cytotoxic potency.

In an approach to the design and exploration of the properties of cyclopropylindole (CPI)-lexitropsin conjugates as potential anticancer agents. CPI--N-methylpyrroles of two separate classes have been synthesized and characterized. These comprise structures (i) in which the N-methylpyrrole moiety bears amide groups of different sizes and (ii) in which both flexible and rigid linkers are introduced between the CPI and N-methylpyrrole units. The extent and the relative rates of DNA cleavage following alkylation and thermal treatment by these CPI conjugates were determined by an agarose gel mobility shift assay. The DNA sequence preferences of the seven new agents were also determined in a preliminary study by high-resolution polyacrylamide gel electrophoresis and contrasted with that of CC-1065. The CPI--N-methylpyrrole agents avoid the major alkylation sites of CC-1065, but all alkylate the minor CC-1065 site of 5'AATA and exhibit a consensus sequence of 5'-N.A/T.A/T.A. The cytotoxicities of these compounds were determined against KB human tumor cells in vitro. Compound 6, bearing a 4-butyramide group in the N-methylpyrrole, is 100 times more potent that 7 which lacks an amide group, while 10 which bears a rigid trans double bond linker is 1000 times more potent than its flexible ethyl-linked counterpart.

Alkylating Agents↗
PubMed1996

The role of transforming growth factor alpha in rat craniofacial development and chondrogenesis.

To explore the possible role of transforming growth factor alpha (TGF-alpha) in craniofacial development, its expression in the craniofacial region of rat embryos from embryonic day (d) 9 to d 20 was examined by in situ hybridisation and immunostaining. The TGF-alpha transcripts were first detected in the neural fold of embryonic d 9 and 10 embryos. In the craniofacial region, the TGF-alpha transcripts were not detected until embryonic d 16 in mesenchyme surrounding the olfactory bulb, within the olfactory bulb, the nasal capsule, vomeronasal organ, and vibrissal follicle. In addition, TGF-alpha message was detected in mesenchyme in the vicinity of Meckel's cartilage, and in the dental epithelium and lamina. This expression pattern of TGF-alpha transcripts persisted until embryonic d 17 but disappeared by d 18. The presence of TGF-alpha protein largely coincided with TGF-alpha message although, unlike the message, it persisted throughout later embryogenesis in the craniofacial region. The possible function of TGF-alpha in chondrogenesis was explored by employing the micromass culture technique. Cartilage nodule formation in mesenchymal cells cultured from rat mandibles in the presence of TGF-alpha was significantly inhibited. This inhibitory effect of TGF-alpha on chondrogenesis was reversed by addition of antibody against the EGF receptor, which crossreacts with the TGF-alpha receptor. The inhibitory effect of TGF-alpha on chondrogenesis in vitro was further confirmed by micromass culture using mesenchymal cells from rat embryonic limb bud. Taken together, these results demonstrate the involvement of TGF-alpha in chondrogenesis during embryonic development, possibly by way of a specific inhibition of cartilage formation from mesenchymal precursor cells.

Animals↗
PubMed1996

Direct gene transfer to mouse melanoma by intratumor injection of free DNA.

Long-term expression of a reporter gene has previously been reported in skeletal and cardiac muscles after direct injection of naked plasmid DNA. In this study, we have shown that the direct injection of free plasmid DNA into mouse melanoma BL6 solid tumor can also result in a high level of transfection. THe average amount of chloramphenicol acetyltransferase (CAT) expressed by injecting 30 micrograms plasmid DNA containing a CAT gene into a single BL6 tumor was 1.9 +/- 1.0 ng, which is comparable to that reported in the skeletal muscle. Cationic liposomes, Lipofectamine and DC-chol/DOPE, inhibited gene expression in a dose-dependent manner. Transgene expression by free DNA persisted for at least 10 days. The size of tumor did not seem to affect the gene expression, but proper choice of a diluent solution for DNA was an important factor. Genes driven by the CMV promoter were expressed much more efficiently than genes driven by the SV40 or T7 promoter. Optimal dosage of injected DNA was from 30 to 70 micrograms per tumor. Other mouse melanomas, human melanomas and cervical carcinomas are also able to express directly injected plasmid DNA, but the transfection efficiency is lower than the BL6 tumor. Direct injection of free plasmid DNA is a simple and effective approach and might be a potential method for cancer gene therapy.

Animals↗
PubMed1996

Factors influencing the drug sensitization of human tumor cells for in situ lipofection.

The cisplatin induced enhancement of in situ lipofection was optimized by considering the factors that can increase the degree of sensitization. Two other anticancer drugs, mechlorethamine (nitrogen mustard) and taxol, enhanced CAT gene expression but the degree of sensitization was not as great as cisplatin. Besides human 2008 ovarian cancer cells we also found that human lung (A549) and head and neck cancer cells (SCC 25) were transiently sensitized by cisplatin. The transfectability of the two commercially available cationic liposomes, Lipofectin and LipofectAmine, was either weak or not consistent among tumors tested. In vivo transfection efficiency of 2008 cells was the highest at 1 microgram DNA per nmol or microgram liposome with all three cationic liposomes. In vitro transfection efficiency of 2008 cells at 1:1 (microgram of DNA:nmole of DC-chol/DOPE liposome) increased in a dose-dependent manner while at 1:10, an optimal ratio for in vitro lipofection, rapidly decreased with an increase in dose. This result indicated that there was a correlation between in vivo and in vitro lipofection at 1:1 ratio for delivering liposomal DNA. Most of the DNA injected into the tumor was concentrated in the tumor and in the skin above the tumor whether cisplatin was preinjected or liposomes were used as carriers.

Animals↗
PubMed1996

Cloning of the human erythropoietin exons and their expression in COS-7 cells.

Human erythropoietin exons (hEPO-E) were isolated from a Chinese fetal liver DNA library by using the PCR method with gene recombination. One nucleotide mutation was found in exon 3 leading to the Leu in position 62 being changed to Ser. The hEPO-E coding for the full-length mature protein was inserted into different clone sites of PSV-2-dhfr to create different transferring plasmids (pSV2-dhfr/F1, pSV2/F2, pSV2-dhfr/F3, pSV2-dhfr/F4, pSV2-dhfr/G1, and pSV2-dhfr/G3) which were transfected into COS-7 cells. Results obtained from the comparative experiments indicate that biological activity of hEPO was found in all culture supernatants and its expression level was higher than that of its genome.

Amino Acid Sequence↗
PubMed1996

[The turn-over flap of the frontalis muscle used for eye-socket depression with contraction of the conjunctival capsule].

We were used to repair the eye-socket depression and contraction after eyeball loss with fat, dermis or rib cartilage implantation. This "stuffing method" has some disadvantages, including absorption and exposure of the implant. In recent years the authors have used a turn-over flap of the frontalis muscle to treat eye-socket depression with contraction of the conjunctival capsule. Satisfactory results have been found at postoperative follow-up.

Adolescent↗
PubMed1996

[Three dimensional reconstruction of human endometrial spiral arteries preinsertion and postinsertion of IUD].

OBJECTIVE: To investigate the micro-three dimensional changes of endometrial spiral arteries after insertion of different intrauterine devices (IUD). METHODS: Nine endometrium specimens were obtained from fertile age women, 3 from preinsertion, 3 obtained 3 months after insertion of TCu220C IUD, and 3 specimens obtained 3 months after insertion of gamma Cu IUD (releasing indomethacin 20 micrograms/day). All samples were collected in late secretory phase and were sectioned serially. By a TV camera, the images of sections were sent from a light microscope to a computer and converted into digital data. The spiral arteries of endometrium were reconstructed and visualized on a workstation by means of the software package for the three dimensional reconstruction and visualization. The curvature and torsion of the spiral arteries were calculated. RESULTS: In preinsertion group, the spiral arteries curved regularly in three dimensions, and the average diameter was 22.69 microns, the average curvature was 0.96 and the average torsion was 1.27. The spiral arteries of gamma Cu IUD group had similar appearances as the preinsertion group. However, in TCu220C IUD group, the curves were irregular, and the average diameter was 17.99 microns, the average curvature was 1.48 and average torsion 1.86. CONCLUSION: The three dimensional reconstruction of human endometrial spiral arteries was done by means of computerassisted reconstruction technology for the first time. The endometrium spiral arteries changed in morphology after insertion of copper IUD, and indomethacin may have contrary effects on copper.

Adult↗
PubMed1996

[Primary epididymal tumors: report of 24 cases].

24 cases of primary epididymal tumors including 23 benign and 1 malignant tumors were treated. In these cases, 66.7% situated at epididymal tail, and 12.5% involved both tail and body. Smooth muscle tumor of one case was bilateral, and adenomatoid tumor of another one was multiple. The symptoms of primary epididymal tumors were mild even absent, so the tumor was easily confused with non-tumorous mass of epididymis. Benign epididymal tumor should be differentiated from tuberculosis, chronic inflammation or granuloma. Besides signs of malignant mass, malignant epididymal tumor usually showed thickened spermatic cord, especially enlarged ductus deferens. The removal of the tumor mass or whole epididymis of the same side could cure benign epididymal tumor without recurrence. Malignant epididymal tumor should be treated as malignancy of testis or spermatic cord, with adjuvant chemotherapy or radiotherapy as indicated by the pathological type.

Adenomatoid Tumor↗
PubMed1995

Endosomolytic activity of cationic liposomes enhances the delivery of human immunodeficiency virus-1 trans-activator protein (TAT) to mammalian cells.

We have explored the use of cationic liposomes to deliver the human immunodeficiency virus-1 trans-activator protein tat using a reporter gene expression assay. The human epidermoid carcinoma cell A431 stably transfected with a reporter gene under the control of human immunodeficiency virus-1 promoter was used as a target cell. Phosphatidylcholine-containing cationic liposomes had no detectable tat delivery activity. In contrast, delivery of tat was enhanced by up to 150-fold using cationic liposomes enriched with dioleoyl phosphatidylethanolamine (DOPE), a lipid which readily transforms a bilayer into a nonbilayer structure. Enhanced delivery of tat by DOPE-containing liposomes was most likely the result of the endosomolytic activity of the liposome. This phospholipid-rich formulation showed no toxicity at concentrations sufficient for maximal delivery of tat. A variety of cationic liposome formulations which contain DOPE were tested successfully for tat delivery.

Cations↗
PubMed1995

GRB2 and SH-PTP2: potentially important endothelial signaling molecules downstream of the TEK/TIE2 receptor tyrosine kinase.

TEK is a newly cloned receptor tyrosine kinase that is expressed predominantly in the endothelium of actively growing blood vessels. Disruption of TEK function in transgenic mice results in a profound defect in vascular development leading to embryonic lethality. These studies show that TEK signaling is indispensable for the development of the embryonic vasculature and suggest that TEK signaling may also be required for the development of the tumor vasculature. Because the ligand for TEK has not been identified, it has been difficult to study signal transduction by this important endothelial receptor. To circumvent this problem, a soluble TEK kinase domain (GTEKH) was developed which could be easily purified, autophosphorylated, and radiolabeled. Using the autophosphorylated, radiolabeled GTEKH to probe a mouse embryo expression library only two candidate signaling molecules were isolated, SH-PTP2 and GRB2. Autophosphorylated GTEKH associated with GRB2 and SH-PTP2 from endothelial lysates and not with PI3 kinase or PLC gamma. The association of GRB2 and SH-PTP2 with TEK was highly dependent on specific tyrosine residues in the TEK c-tail. These studies identify GRB2 and SH-PTP2 as potentially important mediators of TEK signaling that may trigger crucial endothelial responses during embryonic vascular development and during pathologic vascular growth.

Adaptor Proteins, Signal Transducing↗
PubMed1995

The reaction of trimethylamine dehydrogenase with electron transferring flavoprotein.

The kinetics of electron transfer between trimethylamine dehydrogenase (TMADH) and its physiological acceptor, electron transferring flavoprotein (ETF), has been studied by static and stopped-flow absorbance measurements. The results demonstrate that reducing equivalents are transferred from TMADH to ETF solely through the 4Fe/4S center of the former. The intrinsic limiting rate constant (klim) and dissociation constant (Kd) for electron transfer from the reduced 4Fe/4S center of TMADH to ETF are about 172 s-1 and 10 microM, respectively. The reoxidation of fully reduced TMADH with an excess of ETF is markedly biphasic, indicating that partial oxidation of the iron-sulfur center in 1-electron reduced enzyme significantly reduces the rate of electron transfer out of the enzyme in these forms. The interaction of the two unpaired electron spins of flavin semiquinone and reduced 4Fe/4S center in 2-electron reduced TMADH, on the other hand, does not significantly slow down the electron transfer from the 4Fe/4S center to ETF. From a comparison of the limiting rate constants for the oxidative and reductive half-reactions, we conclude that electron transfer from TMADH to ETF is not rate-limiting during steady-state turnover. The overall kinetics of the oxidative half-reaction are not significantly affected by high salt concentrations, indicating that electrostatic forces are not involved in the formation and decay of reduced TMADH-oxidized ETF complex.

Electron Transport↗
PubMed1995

Detection of exocytosis at individual pancreatic beta cells by amperometry at a chemically modified microelectrode.

Amperometry at a carbon fiber microelectrode modified with a composite of ruthenium oxide and cyanoruthenate was used to monitor chemical secretions of single pancreatic beta cells from rats and humans. When the insulin secretagogues glucose, tolbutamide, and K+ were applied to the cell, a series of randomly occurring current spikes was observed. The current spikes were shown to be due to the detection of chemical substances secreted from the cell. Chromatography showed that the primary secreted substance detected by the electrode was insulin. The current spikes were strongly dependent on external Ca2+, had an average area that was independent of the stimulation method, and had an area distribution which corresponded to the distribution of vesicle sizes in beta cells. It was concluded that the spikes were due to the detection of concentration pulses of insulin secreted by exocytosis.

Animals↗