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Biomedical subjects

X D Li

Publications and source records attributed to X D Li.

At least 55 records · Page 3Linked to original sources
PubMed1999

[Establishment of an apoptosis model of vascular smooth muscle cells induced by ultraviolet-C radiation in vitro].

After a 10-min exposure to 254 nm UV-C radiation, aortic SMCs of rat were found to undergo apoptosis, characterized by cell shrinkage, condensation of cytoplasm, membrane blebbing, appearance of apoptotic body and DNA ladder in the agarose gel. Therefore, UV-C radiation can be used to generate a useful model for the investigation of the molecular regulatory mechanisms underlying SMCs apoptosis.

Animals↗
PubMed1998

Effects of mutations in the gamma-phosphate binding site of myosin on its motor function.

The role of the highly conserved residues in the gamma-phosphate binding site of myosin upon myosin motor function was studied. Each of five residues (Ser181, Lys185, Asn235, Ser236, and Arg238) in smooth muscle myosin was mutated. K185Q has neither a steady state ATPase nor an initial Pi burst. Although ATP and actin bind to K185Q, it is not dissociated from actin by ATP. These results indicate that the hydrolysis of bound ATP by K185Q is inhibited. S236T has nearly normal basal Mg2+-ATPase activity, initial Pi burst, ATP-induced enhancement of intrinsic tryptophan fluorescence, and ATP-induced dissociation from actin. However, the actin activation of the Mg2+-ATPase activity and actin translocation of S236T were blocked. In contrast S236A has nearly normal enzymatic properties and actin-translocating activity. These results indicate that 1) the hydroxyl group of Ser236 is not critical as an intermediary of proton transfer during the ATP hydrolysis step, and 2) the bulk of the extra methyl group of the threonine residue in S236T blocks the acceleration of product release from the active site by actin. Arg238, which interacts with Glu459 at the Switch II region, was mutated to Lys and Ile, respectively. R238K has essentially normal enzymatic activity and motility. In contrast, R238I does not hydrolyze ATP or support motility, although it still binds ATP. These results indicate that the charge interaction between Glu459 and Arg238 is critical for ATP hydrolysis by myosin. Other mutants, S181A, S181T, and N235I, showed nearly normal enzymatic and motile activity.

Actins↗
PubMed1998

Deletion analysis of protein kinase Calpha reveals a novel regulatory segment.

Using a combined pharmacological and genetic approach, we have identified aa 260-280 in the C2 region as a critical factor in the catalytic function of protein kinase Calpha (PKCalpha). Progressive truncations from the N-terminus as well as selected internal deletion mutants were expressed in Saccharomyces cerevisiae and tested for altered sensitivity to dequalinium, a PKC inhibitor whose target site was previously mapped to the catalytic domain. PKC mutants representing truncations of up to 158 amino acid residues (aa) from the N-terminus (ND84 and ND158) displayed 60-63% inhibition of kinase activity by 50 microM dequalinium, somewhat more sensitive than the wild-type PKCalpha enzyme (45% inhibition). Mutant ND262, lacking N-terminal aa 1-262, was inhibited by almost 72% with 50 microM dequalinium, but mutant ND278, which lacked an additional 16 aa, was inhibited by only 9% of total activity. This result suggests that a C-terminal segment of the C2 region (aa 263-278) influences inhibition by dequalinium at low micromolar concentrations. An internal deletion mutant (D260-280) which retains the entire primary structure of PKCalpha except for aa 260-280, was similarly inhibited by only 4% with 50 microM dequalinium. In the absence of dequalinium and despite the presence of a nearly complete regulatory domain, this mutant exhibited constitutive activity (both in vitro and in a phenotypic assay with S. cerevisiae) that could not be further stimulated even by the potent activator TPA. Taken together, our findings suggest that, in the native structure of PKCalpha, the segment described by aa 260-280 regulates PKCalpha activity and influences the sensitivity of PKCalpha to dequalinium.

Animals↗
PubMed1998

Regional imager for low-resolution functional imaging of the brain with diffusing near-infrared light.

We have developed a near-infrared spectroscopy system for low-resolution regional imaging of the brain. Our regional imager employs two intensity-modulated (frequency-domain) diode lasers operating at 779 and 834 nm, respectively, in order to produce macroscopic waves of diffusing photons. The interaction of these diffusive waves with tissue depends on laser modulation frequency, laser wavelength and the optical properties of the sample tissue volume. The lasers can be modulated over a range of frequencies from 50 to 400 MHz. Light is coupled to and from the head using a pad that has 12 source and 4 detector positions within an area of approximately 40 cm2. The pad can be moved to different positions on the head. Measurements from different source-detector combinations enable reconstruction of low-resolution images of the tissue volume beneath the pad. For example, we have made two-dimensional back-projection images of model systems in order to demonstrate the capabilities of the regional imager. We also present preliminary results from initial clinical studies at the Children's Hospital of Philadelphia.

Brain↗
PubMed1997

Potential roles of osteopontin and alphaVbeta3 integrin in the development of coronary artery restenosis after angioplasty.

Angioplasty procedures are increasingly used to reestablish blood flow in blocked atherosclerotic coronary arteries. A serious complication of these procedures is reocclusion (restenosis), which occurs in 30-50% of patients. Migration of coronary artery smooth muscle cells (CASMCs) to the site of injury caused by angioplasty and subsequent proliferation are suggested mechanisms of reocclusion. Using both cultured human CASMCs and coronary atherectomy tissues, we studied the roles of osteopontin (OPN) and one of its receptors, alphavbeta3 integrin, in the pathogenesis of coronary restenosis. We also measured the plasma levels of OPN before and after angioplasty and determined the effect of exogenous OPN on CASMC migration, extracellular matrix invasion, and proliferation. We found that cultured CASMCs during log phase of growth and smooth muscle cell layer of the coronary atherosclerotic tissues of patients express both OPN mRNA and protein at a significantly elevated level compared with controls. Interestingly, whereas the baseline plasma OPN levels in control samples were virtually undetectable, those in patient plasma were remarkably high. We also found that interaction of OPN with alphavbeta3 integrin, expressed on CASMCs, causes migration, extracellular matrix invasion, and proliferation. These effects were abolished when OPN or alphavbeta3 integrin gene expression in CASMCs was inhibited by specific antisense S-oligonucleotide treatment or OPN-alphavbeta3 interaction was blocked by treatment of CASMCs with antibodies against OPN or alphavbeta3 integrin. Our results demonstrate that OPN and alphavbeta3 integrin play critical roles in regulating cellular functions deemed essential for restenosis. In addition, these results raise the possibility that transient inhibition of OPN gene expression or blocking of OPN-alphavbeta3 interaction may provide a therapeutic approach to preventing restenosis.

Adolescent↗
PubMed1997

Large-scale preparation of two new ribosome-inactivating proteins--cinnamomin and camphorin from the seeds of Cinnamomum camphora.

An improved method for large-scale preparation of cinnamomin and camphorin from the seeds of Cinnamomum camphora has been developed. Cinnamomin is a type II ribosome-inactivating protein (RIP), while camphorin is a type I RIP. Cinnamomin was purified by a single step of acid-treated Sepharose 4B affinity chromatography instead of gel filtration. Camphorin was purified by anion-exchange chromatography and gel filtration successively from the eluant not retained by the affinity column. Using this improved method, 620 mg of cinnamomin and 14.2 mg of camphorin were obtained from 500 g of wet seed, while only 10.6 mg of cinnamomin and 4.7 mg of camphorin were obtained by the previous method. Cinnamomin and camphorin purified by this method were homogeneous in SDS-denatured polyacrylamide gel electrophoresis. These two RIPs are multifunctional proteins. The assay of the enzymatic activities of cinnamomin and camphorin showed that both of them exhibit RNA N-glycosidase and supercoil-dependent endonuclease activities, while camphorin also exhibits superoxide dismutase activity.

Algal Proteins↗
PubMed1996

Gradual shutdown of virus production resulting in latency is the norm during the chronic phase of human immunodeficiency virus replication and differential rates and mechanisms of shutdown are determined by viral sequences.

Most CD4+ lymphocytes in lymph nodes of both asymptomatic HIV-1-infected individuals and AIDS patients are nonproductively or latently infected. It is not clear how these cells come about because infection of resting lymphocytes results in abortive infection and infection of activated lymphocytes results in productive infection. The frequency and mechanisms underlying nonproductive or latent HIV infections of normal CD4+ lymphocytes largely remain unexplored, and because HIV latency has principally been studied in latently infected cell clones of established cell lines, it is not even clear how often this type of infection occurs in cell lines. We demonstrate herein that chronic HIV replication in populations of normal phytohemagglutinin-stimulated peripheral blood CD4(+)-enriched lymphocytes, as well as an established T-cell line (CEM), gradually shuts down in the vast majority of cells. The nonproducing cells in these cultures still harbored HIV provirus, and HIV could be reactivated in CEM cells by treatment with phorbol ester, showing that this was latent infection. Thus, HIV's life cycle should probably be considered as consisting of two phases an acute exponential rise in production of virus progeny which levels at some peak, followed by a gradual decline of progeny production during the chronic phase leading to viral latency. Temporal analyses of the steady-state levels of viral mRNAs in populations of chronically infected CEM cells as virus production declined revealed the two mechanisms of HIV latency which have previously been described in the OM-10.1 and U1 or ACH-2 latently infected cell clones (i.e., apparent overall shutdown of HIV transcription and "blocked early-stage latency" involving enhanced splicing of viral pre-mRNAs) However, which mechanism was employed, as well as the rate of shutdown, depended on the virus strain.

CD4-Positive T-Lymphocytes↗
PubMed1996

Purification of a new ribosome-inactivating protein from the seeds of Cinnamomum porrectum and characterization of the RNA N-glycosidase activity of the toxic protein.

Porrectin, a new type II ribosome-inactivating protein (RIP), was purified from the seeds of the camphor tree (Cinnamomum porrectum) by affinity chromatography on acid-treated Sepharose 4B. Porrectin is a glycoprotein (M(r)64,500, sugar content 2.5%) consisting of an A-chain (M(r)30,500) and a B-chain (M(r)33,500) linked by the disulfide bond. The terminal sugar of glycan in porrectin B-chain is determined to be mannose. By non-denaturing polyacrylamide gel electrophoresis, porrectin displayed three isoforms that have different pl values with the same molecular weight. Porrectin is a potent inhibitor of eukaryotic protein synthesis in the rabbit reticulocyte lysate system. The molecular mechanism of action of porrectin on rat liver ribosomes is demonstrated to be specific for RNA N-glycosidase. The cleavage site is the adenosine at position 4324 (rat liver 28S rRNA) embedded in the highly conserved ricin/alpha-sarcin ('R/S') domain.

Algal Proteins↗
PubMed1995

Intrinsic factors of apatite influencing its amorphization during plasma-spray coating.

Hydroxyapatite coatings were prepared from differently treated starting powders to investigate the intrinsic factors of apatite influencing its amorphization during plasma-spray coating. The joint analyses of X-ray diffraction and infrared spectra show that the vacancies located on missing hydroxyl sites retard the amorphous/crystalline conversion and enforce retention of the amorphous component; the absorbed water molecules that pre-exist in the starting powder can be incorporated into the vacancies in the hydroxyapatite lattice during plasma-spray coating and compensate for the missing hydroxyls so as to promote the transformation of amorphous into crystalline apatite in the coating process. The more vacancies there are in the apatite structure due to missing hydroxyl sites, the more amorphous the component in the resultant coatings. Moreover, the amorphous phase formed in this way is stable in room conditions.

Biodegradation, Environmental↗
PubMed1992

Aplysia californica contains a novel 12-lipoxygenase which generates biologically active products from arachidonic acid.

Physiologic stimulation of identified neurons in ganglia of the marine mollusk, Aplysia californica, leads to the generation of arachidonic acid metabolites. Using various preparations of Aplysia nervous tissue, we have identified 12-lipoxygenase products including the inactive 12-hydroxyeicosatetraenoic acid (12-HETE) and the biologically active 12-ketoeicosatetraenoic acid (12-KETE) and 8-hydroxy-11(12)-epoxyeicosatrienoic acid (8-HEpETE). Each of these metabolites can be derived from the intermediate 12-hydroperoxyeicosatetraenoic acid (12-HPETE), which can itself activate several identified neurons in Aplysia. In spite of conflicting results in studies of mammalian brain 12-lipoxygenase, Aplysia nervous tissue clearly contains an enzymatic activity which generates stereochemically pure 12(S)-HETE. This activity is destroyed by boiling and is sensitive to nonspecific lipoxygenase inhibitors but not to agents specific for other lipoxygenases or the cyclooxygenase enzyme. The Aplysia 12-lipoxygenase is highly enriched in neural tissue and is almost completely absent in the neural sheath, which is composed primarily of connective tissue and muscle. Preliminary purification has shown that, in contrast to the previously characterized 12-lipoxygenases, the Aplysia enzyme is associated with membrane fractions and is not found in the cytosol. Further studies are in progress to determine the kinetic properties and to define the cellular and subcellular distribution of this novel lipoxygenase.

Animals↗
PubMed1992

Isolation of Getah virus from mosquitos collected on Hainan Island, China, and results of a serosurvey.

An isolate of Getah virus was obtained from Culex mosquitos collected in Mao'an Village, Baoting County, Hainan Province, China, in 1964. The virus (strain M-1) replicated in laboratory-bred Aedes aegypti and Cx. fatigans (= quinquefasciatus), and was transmitted by laboratory-bred Ae. albopictus to healthy newborn albino mice. Skeletal muscles of newborn albino mice experimentally infected with the virus showed degeneration, atrophy, necrosis, and inflammatory changes of muscle fibers. Antibody prevalence in humans and animals ranged from 10.3% by neutralization tests of samples from healthy people in 1979 to 26.4% by CF tests of samples from people with febrile illnesses in 1982. The high prevalence of antibody in pigs, horses, and goats (17.6% to 37.5%) indicated that infection with Getah or a closely related virus is relatively common in domestic animals.

Adolescent↗
PubMed1991

Radiation-protective and platelet aggregation inhibitory effects of five traditional Chinese drugs and acetylsalicylic acid following high-dose gamma-irradiation.

High doses of 60Co radiation (4.0-8.0 Gy) in mice, rats and rabbits caused increases in rate of platelet aggregation during the first 5 days after irradiation. The inhibitory effects of the extracts of five Chinese drug plants and acetylsalicylic acid on rate of platelet aggregation were observed in both in vitro and in vivo tests, averaging 23-53% in vitro and 46-69% in vivo. Antiradiation tests on mice vs. 7.5-8.0 Gy of gamma-radiation, using the plant extracts and acetylsalicylic acid as protective agents, increased survival rates by 8-50% for the plant extracts and 35% for acetylsalicylic acid.

Animals↗
PubMed1987

[Benign tumor and pseudotumor of the gallbladder--report of 40 patients].

Benign tumor and pseudotumor of the gallbladder are infrequently reported in our country. In this paper, 5 patients with benign tumor (3 tubular adenoma, 1 leiomyoma and 1 fibroma) and 35 pseudotumor (26 cholesterol polyps and 9 inflammatory polyps) of the gallbladder are presented. Most patients presented a typical clinical manifestation of chronic cholecystitis. Oral cholecystography gave a lower detection rate. B-ultrasonography was able to show the presence of neoplasm in the gallbladder (37/40). Correct diagnosis was established by operation and pathology. In this series, all patients were cured by cholecystectomy. The authors believe that, for the neoplasms detected by B-ultrasonography with definite clinical symptoms or with a diameter of more than 1.0 cm, cholecystectomy is indicated. For those older or weaker patients with milder symptoms or with neoplasms less than 1.0 cm in diameter, periodic B-ultrasonography follow-up is suggested.

Adenoma↗
PubMed1986

Purification of the thermostable direct hemolysin of Vibrio parahaemolyticus by immunoaffinity column chromatography.

A simple method involving immunoaffinity column chromatography to purify the thermostable direct hemolysin of Vibrio parahaemolyticus was developed. The thermostable direct hemolysin purified from the culture supernatant of a strain isolated from the first reported case of V. parahaemolyticus infection in China in 1985 was indistinguishable from the hemolysins purified from strains isolated in Japan.

Chromatography, Affinity↗