Biomedical subjects

H Li

Publications and source records attributed to H Li.

At least 253 records · Page 14Linked to original sources

PubMed2001

African origin of modern humans in East Asia: a tale of 12,000 Y chromosomes.

To test the hypotheses of modern human origin in East Asia, we sampled 12,127 male individuals from 163 populations and typed for three Y chromosome biallelic markers (YAP, M89, and M130). All the individuals carried a mutation at one of the three sites. These three mutations (YAP+, M89T, and M130T) coalesce to another mutation (M168T), which originated in Africa about 35,000 to 89,000 years ago. Therefore, the data do not support even a minimal in situ hominid contribution in the origin of anatomically modern humans in East Asia.

Africa↗

PubMed2001

Crystallographic studies on endothelial nitric oxide synthase complexed with nitric oxide and mechanism-based inhibitors.

The crystal structure of the endothelial nitric oxide synthase (NOS) heme domain complexed with NO reveals close hydrogen bonding interactions between NO and the terminal guanidino nitrogen of the substrate, L-arginine. Dioxygen is expected to bind in a similar mode which will facilitate proton abstraction from L-Arg to dioxygen, a required step for O-O bond cleavage. Structures of mechanism-based NOS inhibitors, N(5)-(1-iminoethyl)-L-ornithine and N-(3-(aminomethyl)benzyl)acetamidine, provide clues on how this class of compounds operate as suicide substrate inhibitors leading to heme oxidation.

Amidines↗

PubMed2001

Matrix metalloproteinase inhibition attenuates left ventricular remodeling and dysfunction in a rat model of progressive heart failure.

BACKGROUND: Matrix metalloproteinase (MMP) activation contributes to tissue remodeling in several disease states, and increased MMP activity has been observed in left ventricular (LV) failure. The present study tested the hypothesis that MMP inhibition would influence LV remodeling and function in developing LV failure. METHODS AND RESULTS: LV size and function were measured in 5 groups of rats: (1) obese male spontaneously hypertensive heart failure rats (SHHF) at 9 months (n=10), (2) SHHF at 13 months (n=12), (3) SHHF rats treated with an MMP inhibitor during months 9 to 13 (PD166793 5 mg. kg(-1). d(-1) PO; n=14), (4) normotensive Wistar-Furth rats (WF) at 9 months (n=12), and (5) WF at 13 months (n=12). Plasma concentrations of the MMP inhibitor (116+/-11 micromol/L) reduced in vitro LV myocardial MMP-2 activity by approximately 100%. LV function and geometry were similar in WF rats at 9 and 13 months. LV peak +dP/dt was unchanged at 9 months in SHHF but by 13 months was reduced in the SHHF group compared with WF (3578+/-477 versus 5983+/-109 mm Hg/s, P</=0.05). LV volume measured at an equivalent ex vivo pressure (10 mm Hg) was increased in SHHF at 9 months compared with WF (443+/-12 versus 563+/-33 mL, P</=0.05) and increased further by 13 months (899+/-64 mL, P</=0.05). LV myocardial MMP-2 activity was increased by approximately 2-fold in SHHF at 9 and 13 months. With MMP inhibition, LV peak +dP/dt was similar to WF values and LV volume was reduced compared with untreated SHHF values (678+/-28 mL, P</=0.05). CONCLUSIONS: MMP activity contributes to LV dilation and progression to LV dysfunction in a rodent HF model, and direct MMP inhibition can attenuate this process.

Animals↗

PubMed2001

Morphological features and electrophysiological properties of serotonergic and non-serotonergic projection neurons in the dorsal raphe nucleus. An intracellular recording and labeling study in rat brain slices.

The morphology and electrophysiological properties of serotonergic and non-serotonergic projection neurons in the dorsal raphe nucleus (DRN) of the rat were examined in frontal brain slices. Biocytin was injected intracellularly into the intracellularly recorded neurons. Then the morphology of the recorded neurons was observed after histochemical visualization of biocytin. The recorded neurons extending their main axons outside the DRN were considered as projection neurons. Subsequently, serotonergic nature of the neurons was examined by serotonin (5-HT) immunohistochemistry. The general form of the dendritic trees is radiant and poorly branching in both 5-HT- and non-5-HT neurons. However, the dendrites of the 5-HT neurons were spiny, whereas those of the non-5-HT neurons were aspiny. The main axons of both 5-HT- and non-5-HT neurons were observed to send richly branching axon collaterals to the DRN, ventrolateral part of the periaqueductal gray and the midbrain tegmentum. In response to weak, long depolarizing current pulses, the 5-HT neurons displayed a slow and regular firing activity. The non-5-HT neurons fired at higher frequencies even when stronger current was injected. Some other differences in electrophysiological properties were also observed between the 5-HT-immunoreactive spiny projection neurons and the 5-HT-immunonegative aspiny projection neurons.

Action Potentials↗

PubMed2001

Implications for isoform-selective inhibitor design derived from the binding mode of bulky isothioureas to the heme domain of endothelial nitric-oxide synthase.

Nitric oxide produced by nitric-oxide synthase (NOS) is not only involved in a wide range of physiological functions but also in a variety of pathological conditions. Isoform-selective NOS inhibitors are highly desirable to regulate the NO production of one isoform beneficial to normal physiological functions from the uncontrolled NO production of another isoform that accompanies certain pathological states. Crystal structures of the heme domain of the three NOS isoforms have revealed a very high degree of similarity in the immediate vicinity of the heme active site illustrating the challenge of isoform-selective inhibitor design. Isothioureas are potent NOS inhibitors, and the structures of the endothelial NOS heme domain complexed with isothioureas bearing small S-alkyl substituents have been determined (Li, H., Raman, C.S., Martásek, P., Král, V., Masters, B.S.S., and Poulos, T.L. (2000) J. Inorg. Biochem. 81, 133--139). In the present communication, the binding mode of larger bisisothioureas complexed to the endothelial NOS heme domain has been determined. These structures afford a structural rationale for the known inhibitory activities. In addition, these structures provide clues on how to exploit the longer inhibitor substituents that extend out of the active site pocket for isoform-selective inhibitor design.

Animals↗

PubMed2001

Imaging of small-scale features on 433 Eros from NEAR: evidence for a complex regolith.

On 25 October 2000, the Near Earth Asteroid Rendevous (NEAR)-Shoemaker spacecraft executed a low-altitude flyover of asteroid 433 Eros, making it possible to image the surface at a resolution of about 1 meter per pixel. The images reveal an evolved surface distinguished by an abundance of ejecta blocks, a dearth of small craters, and smooth material infilling some topographic lows. The subdued appearance of craters of different diameters and the variety of blocks and different degrees of their burial suggest that ejecta from several impact events blanketed the region imaged at closest approach and led to the building up of a substantial and complex regolith consisting of fine materials and abundant meter-sized blocks.

Journal Article↗

PubMed2001

Levels of ovine herpesvirus 2 DNA in nasal secretions and blood of sheep: implications for transmission.

A recently developed competitive PCR for ovine herpesvirus 2 (OvHV-2) was used to examine the levels of viral DNA in nasal secretions and peripheral blood leukocytes (PBL) of lambs and adult sheep. Viral DNA first appeared in the PBL of most lambs after about 3 months of age and the levels remained relatively constant thereafter. In most of the lambs (83%, n=12), viral DNA was undetectable by PCR in nasal secretions prior to 5 months of age. A dramatic rise of OvHV-2 DNA levels in the nasal secretions occurred starting at 5-6 months of age, which peaked at approximately 7 months. The highest level recorded in lamb nasal secretions was 7.5x10(8)copies/2microg DNA which were 75,000-100,000-fold higher than the levels in PBL of the same lambs. In adult sheep (n=10), the viral DNA levels in both PBL and nasal secretions were relatively stable over the 13-month period of the study, which included a lambing season. The data strongly suggest that neonatal lambs are not an important source for the transmission of OvHV-2 to clinically susceptible species, and that the nasal cavity is an important portal for shedding of infectious OvHV-2 in sheep. Furthermore, this study failed to identify a seasonal pattern in levels of viral DNA in nasal secretions or PBL of adult sheep that would provide a basis for the traditionally held belief that clinical cases of malignant catarrhal fever are significantly associated with lambing ewes.

Animals↗

PubMed2001

Characterization of the magnitude and kinetics of xanthine oxidase-catalyzed nitrite reduction. Evaluation of its role in nitric oxide generation in anoxic tissues.

Xanthine oxidase (XO)-catalyzed nitrite reduction with nitric oxide (NO) production has been reported to occur under anaerobic conditions, but questions remain regarding the magnitude, kinetics, and biological importance of this process. To characterize this mechanism and its quantitative importance in biological systems, electron paramagnetic resonance spectroscopy, chemiluminescence NO analyzer, and NO electrode studies were performed. The XO reducing substrates xanthine, NADH, and 2,3-dihydroxybenz-aldehyde triggered nitrite reduction to NO, and the molybdenum-binding XO inhibitor oxypurinol inhibited this NO formation, indicating that nitrite reduction occurs at the molybdenum site. However, at higher xanthine concentrations, partial inhibition was seen, suggesting the formation of a substrate-bound reduced enzyme complex with xanthine blocking the molybdenum site. Studies of the pH dependence of NO formation indicated that XO-mediated nitrite reduction occurred via an acid-catalyzed mechanism. Nitrite and reducing substrate concentrations were important regulators of XO-catalyzed NO generation. The substrate dependence of anaerobic XO-catalyzed nitrite reduction followed Michaelis-Menten kinetics, enabling prediction of the magnitude of NO formation and delineation of the quantitative importance of this process in biological systems. It was determined that under conditions occurring during no-flow ischemia, myocardial XO and nitrite levels are sufficient to generate NO levels comparable to those produced from nitric oxide synthase. Thus, XO-catalyzed nitrite reduction can be an important source of NO generation under ischemic conditions.

Catalysis↗

PubMed2001

Down-regulation of vascular endothelial growth factor by tissue inhibitor of metalloproteinase-2: effect on in vivo mammary tumor growth and angiogenesis.

The tissue inhibitor of metalloproteinases-2 (TIMP-2) has at least two independent functions, i.e., regulation of matrix metalloproteinases and growth promoting activity. We investigated the effects of TIMP-2 overexpression, induced by retroviral mediated gene transfer, on the in vivo development of mammary tumors in syngeneic mice inoculated with EF43.fgf-4 cells. The EF43.fgf-4 cells established by stably infecting the normal mouse mammary EF43 cells with a retroviral expression vector for the fgf-4 oncogene, are highly tumorigenic and overproduce vascular endothelial growth factor (VEGF). Despite a promotion of the in vitro growth rate of EF43.fgf-4 cells overexpressing timp-2, the in vivo tumor growth was delayed. At day 17 post-cell injection, the volume of tumor derived from TIMP-2-overexpressing cells was reduced by 80% as compared with that obtained with control cells. Overexpression of TIMP-2 was associated with a down-regulation of VEGF expression in vitro and in vivo, a reduction of vessel size, density, and blood supply in the induced tumors. In addition, TIMP-2 completely inhibited the angiogenic activity of EF43.fgf-4 cell-conditioned medium in vitro using a rat aortic ring model. Our findings suggest that overexpression of TIMP-2 delays growth and angiogenesis of mammary carcinoma in vivo and that down-regulation of VEGF expression may play an important role in this TIMP-2-mediated antitumoral and antiangiogenic effects. Finally the in vivo delivery of TIMP-2, as assessed by i.v. injection of recombinant adenoviruses vectors, significantly reduced the growth of the EF43.fgf-4-induced tumors. This effect of TIMP-2 was shown to be equally comparable with that of angiostatin, a known potent inhibitor of angiogenesis.

Adenoviridae↗

PubMed2001

SMRTE inhibits MEF2C transcriptional activation by targeting HDAC4 and 5 to nuclear domains.

The silencing mediator for retinoic acid and thyroid hormone receptors (SMRT) mediates transcriptional repression by recruiting histone deacetylases (HDACs) to the DNA-bound nuclear receptor complex. The full-length SMRT (SMRTe) contains an N-terminal sequence that is highly conserved to the nuclear receptor corepressor N-CoR. To date, little is known about the activity and function of the full-length SMRTe protein, despite extensive studies on separated receptor interaction and transcriptional repression domains. Here we show that SMRTe inhibits MEF2C transcriptional activation by targeting selective HDACs to unique subnuclear domains. Indirect immunofluorescence studies with anti-SMRTe antibody reveal discrete cytoplasmic and nuclear speckles, which contain RARalpha in an RA-sensitive manner. Formation of the SMRTe nuclear speckles results in recruitment of several class I and class II HDACs to these subnuclear domains in a process depending on HDAC enzymatic activity. Intriguingly, although HDAC4 is located primarily in the cytoplasm, coexpression of SMRTe dramatically translocates HDAC4 from the cytoplasm into the nucleus, where HDAC4 prevents MEF2C from activating muscle differentiation. SMRTe also translocates HDAC5 from diffusive nucleoplasm into discrete nuclear domains. Accordingly, SMRTe synergizes with HDAC4 and 5 to inhibit MEF2C transactivation of target promoter, suggesting that nuclear domain targeting of HDAC4/5 may be important in preventing muscle cell differentiation. These results highlight an unexpected new function of the nuclear receptor corepressor SMRTe for its role in regulating cellular trafficking of nuclear receptor and selective HDACs that may play an important role in regulation of cell growth and differentiation.

Active Transport, Cell Nucleus↗

PubMed2001

Using selective withdrawal to coat microparticles.

We report a method that uses the process of selective withdrawal of one fluid through a second immiscible fluid to coat small particles with polymer films. Fluid is withdrawn through a tube with its orifice slightly above a water-oil interface. Upon increasing the flow rate, there is a transition from a state where only oil is withdrawn to a state where the water, containing the particles to be coated and appropriate prepolymer reagents, is entrained in a thin spout along with the oil. The entrained particles eventually cause the spout interface to break, producing a thin coat of controllable thickness around each particle, which can be subsequently polymerized using chemical reagents, light, or heat. This method allows flexibility in the chemical composition and thickness of the conformal coatings.

Benzoates↗

PubMed2001

Determination of formaldehyde in blood plasma by high-performance liquid chromatography with fluorescence detection.

An HPLC method was developed for the determination of formaldehyde in human blood plasma. The method was based on the determination of the fluorescent product of the chemical reaction between formaldehyde and ampicillin. A 0.2-ml aliquot of blood plasma was reacted directly with ampicillin under acidic and heating conditions. The reaction product was extracted from the matrix with diethyl ether and analyzed by reversed-phase HPLC with fluorescence detection. Recoveries of spiked formaldehyde at the low ppm (microg/ml) level were between 93% and 102% with relative standard deviations less than 8%. The limits of detection and quantitation of formaldehyde in blood plasma samples were 0.46 microg/ml and 0.87 microg/ml, respectively.

Calibration↗

PubMed2001

The manganese stabilizing protein (MSP) and the control of O2 evolution in the unicellular, diazotrophic cyanobacterium, Cyanothece sp. ATCC 51142.

The unicellular diazotrophic cyanobacterium, Cyanothece sp. ATCC 51142 temporally separates N2 fixation from photosynthesis. To better understand the processes by which photosynthesis is regulated, we have analyzed Photosystem (PS) II O2 evolution and the PSII lumenal proteins, especially the Mn stabilizing protein (MSP). We describe a procedure using glycine betaine to isolate photosynthetic membranes from Cyanothece sp. that have high rates of PSI and PSII activity. Analysis with these membranes demonstrated similar patterns of O2 evolution in vivo and in vitro, with a trough at the time of maximal N2 fixation and with a peak in the late light period. The pattern of PSI activity was also similar in vivo and in vitro. We cloned the genes for MSP (psbO) and the 12 kDa protein (psbU) and analyzed their transcriptional properties throughout the diurnal cycle. We suggest that the changes in PSII activity in Cyanothece sp. were due to conformational changes in a highly flexible MSP, a suggestion which can now be studied in a chimera. The Cyanothece sp. psbO gene has been transformed into Synechocystis sp. PCC 6803; MSP and O2 evolution in the resulting transformant had properties that were similar to those in Cyanothece sp., providing additional confirmation for the properties of Cyanothece sp. MSP.

Amino Acid Sequence↗

PubMed2001

Selective detection of individual DNA molecules by capillary polymerase chain reaction.

On-line capillary polymerase chain reaction (PCR) coupled with laser-induced fluorescence detection was successfully demonstrated for individual DNA molecules. A single 30-microm-i.d. fused-silica capillary was used both as the reaction vessel and for isolating single molecules. SYBR green I dye was added into the reaction mixture for dynamic fluorescent labeling. Because of the small inside diameter of the capillary, PCR-amplified DNA fragments from single molecules were localized in the capillary, providing discrete product zones with concentrations at readily detectable levels. By counting the number of peaks in the capillary via electromigration past a detection window, the number of starting DNA molecules could be determined. With selective primer design, only the molecule of interest was detected. Amplification of the 110-bp fragment from an individual human beta-globin gene and the 142-bp fragment from an individual HIV-1 DNA was demonstrated. This opens the possibility of highly selective and sensitive disease diagnosis at a very early stage.

Benzothiazoles↗

PubMed2001

The human homologue of the yeast DNA repair and TFIIH regulator MMS19 is an AF-1-specific coactivator of estrogen receptor.

Steroid/nuclear hormone receptors are ligand-dependent transcriptional regulators that control gene expression in a wide array of biological processes. The transcriptional activity of the receptors is mediated by an N-terminal ligand-independent transcriptional activation function AF-1 and a C-terminal ligand-dependent transcriptional activation function AF-2. The nuclear receptor coactivator RAC3 (also known as AIB1/ACTR/pCIP/TRAM-1/SRC-3) is amplified in breast cancer cells, where it forms a complex with estrogen receptor (ER) and enhances AF-2 activity of the receptor. Here, we identify a putative human homologue of the yeast DNA repair and transcriptional regulator MMS19 as a RAC3-interacting protein. The human MMS19 interacts with the N-terminal PAS-A/B domain of RAC3 in vivo and in vitro through a conserved C-terminal domain. Interestingly, the human MMS19 also interacts with estrogen receptors in a ligand-independent manner but not with retinoic acid receptor or thyroid hormone receptor. Overexpression of the interacting domain of hMMS19 strongly inhibits ER-mediated transcriptional activation, indicating a dominant negative activity. In contrast, over expression of the full-length hMMS19 enhances ER-mediated transcriptional activation. We find that hMMS19 stimulates the AF-1 activity of ERalpha, but not the AF-2 activity, suggesting that hMMS19 may be an AF-1-specific transcriptional coactivator of estrogen receptor.

Amino Acid Sequence↗

PubMed2001

Role of retinoid receptor coactivator pockets in cofactor recruitment and transcriptional regulation.

The nuclear receptor for retinoic acid (RAR) forms a heterodimeric complex with the retinoid X receptor (RXR). This RXR/RAR heterodimer binds to the promoter of retinoic acid target genes and recruits coactivators and corepressors to regulate gene expression. Currently, the relative role of each receptor monomer in regulating coactivator and corepressor recruitment remains unclear. Here we show that the receptor-associated coactivator 3 (RAC3) uses two separate LXXLL motifs to bind RAR and RXR. The mutation of the coactivator-binding pockets of RAR and RXR abolishes RAC3 binding. Although the coactivator pocket of RXR is essential for the function of the RXR homodimer, it has a minor role for the recruitment of RAC3 and trans-activation by the RXR/RAR heterodimer. Consistently, deletion of the activation helix of RXR enhances binding of RAC3 to the heterodimer, and mutation of the coactivator pocket of RXR had little effect on RXR/RAR activity. In contrast, the coactivator pocket and the activation helix of RAR are absolutely required. We also show that different residues of the RAR coactivator pocket are used differently for interactions with the corepressor silencing mediator for retinoid and thyroid hormone receptor (SMRT) and coactivator. These results indicate a differential role for each retinoid receptor to the overall binding of cofactors and regulation of transcription by the retinoid receptor heterodimer.

Amino Acid Motifs↗

PubMed2001

AdTIMP-2 inhibits tumor growth, angiogenesis, and metastasis, and prolongs survival in mice.

TIMP-2 is a natural matrix metalloproteinase (MMP) inhibitor that prevents the degradation of extracellular matrix proteins. It abolishes the hydrolytic activity of all activated members of the metalloproteinase family and in particular that of MT1-MMP, MMP-2, and MMP-9, which are selective for type IV collagenolysis. Since MMPs have been implicated in both cancer progression and angiogenesis, we generated a recombinant adenovirus to deliver human TIMP-2 (AdTIMP-2) and evaluated its anticancer efficiency in three murine models. Our results demonstrated that overexpression in vitro of TIMP-2 inhibited the invasion of both tumor and endothelial cells without affecting cell proliferation. Its in vivo efficiency has been evaluated in murine lung cancer LLC, and colon cancer C51 in syngeneic mice as well as in human breast cancer MDA-MB231 in athymic mice. Preinfection of tumor cells by AdTIMP-2 resulted in an inhibition of tumor establishment in more than 50% of mice in LLC and C51 models and in 100% mice in the MDA-MB231 model. A single local injection of AdTIMP-2 into preestablished tumors of these three types significantly reduced tumor growth rates by 60--80% and tumor-associated angiogenesis index by 25--75%. Lung metastasis of LLC tumor was inhibited by >90%. In addition, AdTIMP-2-treated mice showed a significantly prolonged survival in all the cancer models tested. These data demonstrate the potential of adenovirus-mediated TIMP-2 therapy in cancer treatment.

Adenoviridae↗

PubMed2001

Acceleration of atherogenesis by COX-1-dependent prostanoid formation in low density lipoprotein receptor knockout mice.

The cyclooxygenase (COX) product, prostacyclin (PGI(2)), inhibits platelet activation and vascular smooth-muscle cell migration and proliferation. Biochemically selective inhibition of COX-2 reduces PGI(2) biosynthesis substantially in humans. Because deletion of the PGI(2) receptor accelerates atherogenesis in the fat-fed low density lipoprotein receptor knockout mouse, we wished to determine whether selective inhibition of COX-2 would accelerate atherogenesis in this model. To address this hypothesis, we used dosing with nimesulide, which inhibited COX-2 ex vivo, depressed urinary 2,3 dinor 6-keto PGF(1alpha) by approximately 60% but had no effect on thromboxane formation by platelets, which only express COX-1. By contrast, the isoform nonspecific inhibitor, indomethacin, suppressed platelet function and thromboxane formation ex vivo and in vivo, coincident with effects on PGI(2) biosynthesis indistinguishable from nimesulide. Indomethacin reduced the extent of atherosclerosis by 55 +/- 4%, whereas nimesulide failed to increase the rate of atherogenesis. Despite their divergent effects on atherogenesis, both drugs depressed two indices of systemic inflammation, soluble intracellular adhesion molecule-1, and monocyte chemoattractant protein-1 to a similar but incomplete degree. Neither drug altered serum lipids and the marked increase in vascular expression of COX-2 during atherogenesis. Accelerated progression of atherosclerosis is unlikely during chronic intake of specific COX-2 inhibitors. Furthermore, evidence that COX-1-derived prostanoids contribute to atherogenesis suggests that controlled evaluation of the effects of nonsteroidal anti-inflammatory drugs and/or aspirin on plaque progression in humans is timely.

6-Ketoprostaglandin F1 alpha↗