Biomedical subjects

Y Liu

Publications and source records attributed to Y Liu.

At least 919 records · Page 51Linked to original sources

PubMed2000

Age-related decline in Ras/ERK mitogen-activated protein kinase cascade is linked to a reduced association between Shc and EGF receptor.

Numerous studies have demonstrated that the proliferative capacity of cells declines with age. Using rat primary hepatocytes as a model system, we recently demonstrated that this age-related decline in the proliferative response to mitogenic stimulation is associated with decreased activities of both extracellular signal-regulated kinase (ERK) and p70 S6 kinase (p70(S6k)). To unravel the molecular basis for age-related defects in the ERK pathway, we have now characterized the upstream signaling events that occur after epidermal growth factor (EGF) stimulation in young and aged hepatocytes. As previously noted for ERK, the activities of both MEK (the kinase immediately upstream of ERK) and Ras following EGF stimulation were significantly lower in aged hepatocytes. An examination of the EGF receptor (EGFR) revealed a similar amount of EGFR in the two age groups. Likewise, EGFR and Shc, an adaptor protein that plays a crucial role in linking EGFR to Ras activation, underwent tyrosine phosphorylation to a similar degree in both young and aged hepatocytes. However, in aged cells Shc was unable to form stable complexes with EGFR after EGF stimulation. Our results suggest that a decrease in the association between Shc and EGFR in aged cells underlies the age-related declines in the ERK signaling cascade and in proliferative capacity.

Adaptor Proteins, Signal Transducing↗

PubMed2000

The Chinese experience of hospital price regulation.

This paper analyzes the distortion effects of the hospital pricing policies in China. To help maintain equitable access to hospital services, the Chinese government regulates prices of hospital services, and provides subsidies to public hospitals. Comparing the regulated fees of selected hospital services with their average unit costs indicates that the average cost-recovery rate of the fees is only 50%. The fees for 90% of the services are less than their average unit costs, while the fees for the high-tech services exceed their costs. Moreover, the State Price Commission allowed a drug profit margin of 15-20% over the wholesale price. The distorted fee schedule affects the behaviour of hospitals. Empirical evidence revealed problems of violation of price regulations (charging a fee exceeding the regulated fee), over-provision of profitable high-tech services and over-prescription of drugs. The Chinese experience shows that low regulated fees cannot reduce the economic burden on patients, and that distorted medical fees can result in distorted service provision and low efficiency of medical resources. Strategies to correct for the price distortions are discussed.

China↗

PubMed2000

Metallothionein-null mice are more sensitive than wild-type mice to liver injury induced by repeated exposure to cadmium.

Liver is a major target organ of cadmium (Cd) toxicity following acute and chronic exposure. Metallothionein (MT), a low-molecular-weight, cysteine-rich, metal-binding protein has been shown to play an important role in protection against acute Cd-induced liver injury. This study investigates the role of MT in liver injury induced by repeated exposure to Cd. Wild-type and MT-I/II knockout (MT I/II-null) mice were injected sc with a wide range of CdCl(2) doses, 6 times/week, for up to 10 weeks, and their hepatic Cd content, hepatic MT concentration, and liver injury were examined. Repeated administration of CdCl(2) produced acute and nonspecific chronic inflammation in the parenchyma and portal tracts and around central veins. Higher doses produced granulomatous inflammation and proliferating nodules in liver parenchyma. Apoptosis and mitosis occurred concomitantly in liver following repeated Cd exposure, whereas necrosis was mild. As a result, significant elevation of serum enzyme levels was not observed. In wild-type mice, hepatic Cd concentration increased in a dose- and time-dependent manner, reaching 400 microgram/g liver, along with 150-fold increases in hepatic MT concentrations, the latter reaching 1200 microgram/g liver. In contrast, in MT I/II-null mice, hepatic Cd concentrations were about 10 microgram/g liver. Despite the lower accumulation of Cd in livers of MT I/II-null mice, the maximum tolerated dose of Cd was one-eighth lower than that for wild-type mice at 10 weeks, and liver injury was more pronounced in the MT I/II-null mice, as evidenced by increases in liver/body weight ratios and histopathological analyses. In conclusion, these data indicate that (1) nonspecific chronic inflammation, granulomatous inflammation, apoptosis, liver cell regeneration, and presumably, preneoplastic proliferating nodules are major features of liver injury induced by repeated Cd exposure, and (2) intracellular MT is an important protein protecting against this Cd-induced liver injury.

Animals↗

PubMed2000

Metallothionein-I/II null mice are more sensitive than wild-type mice to the hepatotoxic and nephrotoxic effects of chronic oral or injected inorganic arsenicals.

Metallothionein (MT) is a low-molecular-weight, sulfhydryl-rich, metal-binding protein that can protect against the toxicity of cadmium, mercury, and copper. However, the role of MT in arsenic (As)-induced toxicity is less certain. To better define the ability of MT to modify As toxicity, MT-I/II knockout (MT-null) mice and the corresponding wild-type mice (WT) were exposed to arsenite [As(III)] or arsenate [As(V)] either through the drinking water for 48 weeks, or through repeated sc injections (5 days/week) for 15 weeks. Chronic As exposure increased tissue MT concentrations (2-5-fold) in the WT but not in MT-null mice. Arsenic by both routes produced damage to the liver (fatty infiltration, inflammation, and focal necrosis) and kidney (tubular cell vacuolization, inflammatory cell infiltration, and interstitial fibrosis) in both MT-null and WT mice. However, in MT-null mice, the pathological lesions were more frequent and severe when compared to WT mice. This was confirmed biochemically, in that, at the higher oral doses of As, blood urea nitrogen (BUN) levels were increased more in MT-null mice (60%) than in WT mice (30%). Chronic As exposures produced 2-10 fold elevation of serum interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha levels, with greater increases seen by repeated injections than by oral exposure, and again, MT-null mice had higher serum cytokines than WT mice after As exposure. Repeated As injections also decreased hepatic glutathione (GSH) by 35%, but GSH-peroxidase and GSH-reductase were minimally affected. MT-null mice were more sensitive than WT mice to the effect of GSH depletion by As(V). Hepatic caspase-3 activity was increased (2-3-fold) in both WT and MT-null mice, indicative of apoptotic cell death. In summary, chronic inorganic As exposure produced injuries to multiple organs, and MT-null mice are generally more susceptible than WT mice to As-induced toxicity regardless of route of exposure, suggesting that MT could be a cellular factor in protecting against chronic As toxicity.

Administration, Oral↗

PubMed2000

Metallothionein-null mice are more susceptible than wild-type mice to chronic CdCl(2)-induced bone injury.

Cadmium (Cd) is an environmental pollutant and is toxic to a number of organs. Chronic exposure to Cd causes loss of bone mass and increased incidence of bone fractures, as seen in Itai-itai patients and laboratory animals. Metallothionein (MT), a low-molecular weight, cysteine-rich, metal-binding protein, has been shown to play an important role in the detoxication of Cd. Thus, this study was designed to test the hypothesis that MT protects against Cd-induced bone injury. Wild-type and MT-I/II knockout (MT-null) mice were given repeated sc injections of CdCl(2) over a wide range of doses for 10 weeks, and Cd-induced bone injury was examined. Cd produced dose- and time-dependent increases in bone Cd content. However, the concentration of Cd in bone was much lower than that found in the liver and kidney (11 vs 400 and 120 microg/g, respectively) of the same mice. There was no difference in bone Cd content between wild-type and MT-null mice. Repeated Cd injections produced a dose-dependent loss of bone mass (up to 25%), as shown by analysis of the femur, tibia, and lumbar vertebrae. The loss of bone mass was more marked in MT-null mice than in wild-type mice, as shown by dry bone weight, defatted bone weight, bone ash weight, and total calcium content. X-ray photography showed decreasing bone density along the entire bone length with increasing dose and time of Cd exposure. The decrease in bone density was more marked in MT-null mice than in wild-type mice at the same dose and time points. Histopathology showed dilatation of haversian canals with increased osteoid seams, rounded osteocytes with expanded pericellular space, and expansion of hyperplastic bone marrow into metaphyseal cortical bone. Again, these lesions were more marked in MT-null mice. In conclusion, this study demonstrates that deficiency in MT renders animals more susceptible to Cd-induced bone mass loss and bone injury, and thus indicates that MT plays a protective role in Cd-induced toxicity in bone, as it does in other tissues.

Animals↗

PubMed2000

Metallothionein-I/II null mice are sensitive to chronic oral cadmium-induced nephrotoxicity.

Chronic exposure to cadmium (Cd) via food and drinking water is a major human health concern. We have previously shown that metallothionein (MT), a metal-binding protein, plays an important role in protecting against Cd toxicity produced by repeated sc injections. However, it is unclear whether MT protects against Cd-induced nephrotoxicity following chronic oral exposure, a route with obvious human relevance. To clarify this issue, MT-I/II knockout (MT-null) and background-matched wild-type (WT) mice were allowed free access to drinking water containing CdCl(2) (30, 100, and 300 ppm Cd), or feed containing CdCl(2) (100 ppm Cd) for 6 months, and the resultant nephrotoxicity was examined. Chronic oral Cd exposure produced a dose-dependent accumulation of Cd in liver and kidney of WT mice, reaching levels up to 50 microg Cd/g tissue. Immunohistological localization of renal MT indicated that chronic oral Cd exposure in WT mice greatly increased MT in the proximal tubules and the medulla, with cellular localization in both the cytoplasm and nuclei. As expected, no MT was detected in kidneys of MT-null mice. After 6 months of Cd exposure, tissue Cd concentrations in MT-null mice were only about one-fifth of that in WT mice. Even though the renal Cd concentrations were much lower in the MT-null mice, they were more sensitive than WT mice to Cd-induced renal injury, as evidenced by more severe nephropathic lesions, increased urinary excretion of gamma-glutamyl-transferase and glucose, and elevated blood urea nitrogen. Six months of Cd exposure to MT-null animals resulted in greater increases in renal caspase-3 activity, an indicator of apoptosis, than to WT mice. In conclusion, this study demonstrates that lack of MT renders MT-null mice vulnerable to Cd-induced nephrotoxicity after chronic oral exposure, the primary route of human Cd exposure.

Animals↗

PubMed2000

Molecular cloning and characterization of a tobacco MAP kinase kinase that interacts with SIPK.

A tobacco MAP kinase termed SIPK (Salicylic acid-Induced Protein Kinase) is activated in response to a variety of stress signals, including pathogen attack and wounding (S. Zhang and D.F. Klessig, Proc. Natl. Acad. Sci. USA 95:7225-7230, 1998; S. Zhang and D.F. Klessig, Proc. Natl. Acad. Sci. USA 95:7433-7438, 1998). Using the yeast two-hybrid system, we have identified a gene encoding a protein that interacts with SIPK but not the wounding induced protein kinase (WIPK), which is another tobacco MAP kinase. Sequence analysis indicated that this SIPK-interacting protein is a member of the MAP kinase kinase family; thus, it was named SIPK kinase (SIPKK). Co-immunoprecipitation experiments demonstrated that SIPKK and SIPK interact in vitro. Consistent with its putative function as a kinase, SIPKK phosphorylated myelin basic protein in vitro. Interestingly, SIPKK was induced at the mRNA level after Tobacco mosaic virus (TMV) infection or wounding, albeit with kinetics that are too slow to account for the activation of SIPK following these stimuli.

Amino Acid Sequence↗

PubMed2000

Gene therapy for spine fusion.

Spine fusion is a commonly performed yet often unsuccessful surgical procedure. As many as 40% of patients undergoing spine fusion may have a nonunion or failure to form a continuous bone bridge. This clinical challenge has focused much of the attention of osteoinductive bone growth factors toward spine applications. Clinical pilot and pivotal trials will show the feasibility of recombinant and purified bone growth factors to promote spine fusion in humans. Despite this, strategies of gene therapy for spine fusion and other bone healing applications are being pursued. This article reviews the state of the art of local gene therapy and highlights specific issues that must be addressed when pursuing a gene therapy program. Perhaps the most critical step in gene therapy for bone formation is choosing an appropriate osteoinductive gene. Such choices may be limited by differences in efficacy of the chosen gene and availability because of proprietary constraints. The choice of delivery vector is crucial and depends on the potency of the gene and the specific application intended. Establishing the effective dose, transduction time, and gene transfer method are important decisions. The choice of carrier material to form the scaffold for the new bone formation is paramount to successful bone formation. Finally, a strategy for in vitro and in vivo testing must be developed to maximize the chances of success in human trials.

Animals↗

PubMed2000

Cerebral hemodynamics in human acute ischemic stroke: a study with diffusion- and perfusion-weighted magnetic resonance imaging and SPECT.

Nineteen patients with acute ischemic stroke (<24 hours) underwent diffusion-weighted and perfusion-weighted (PWI) magnetic resonance imaging at the acute stage and 1 week later. Eleven patients also underwent technetium-99m ethyl cysteinate dimer single-photon emission computed tomography (SPECT) at the acute stage. Relative (ischemic vs. contralateral control) cerebral blood flow (relCBF), relative cerebral blood volume, and relative mean transit time were measured in the ischemic core, in the area of infarct growth, and in the eventually viable ischemic tissue on PWI maps. The relCBF was also measured from SPECT. There was a curvilinear relationship between the relCBF measured from PWI and SPECT (r = 0.854; P < 0.001). The tissue proceeding to infarction during the follow-up had significantly lower initial CBF and cerebral blood volume values on PWI maps (P < 0.001) than the eventually viable ischemic tissue had. The best value for discriminating the area of infarct growth from the eventually viable ischemic tissue was 48% for PWI relCBF and 87% for PWI relative cerebral blood volume. Combined diffusion and perfusion-weighted imaging enables one to detect hemodynamically different subregions inside the initial perfusion abnormality. Tissue survival may be different in these subregions and may be predicted.

Acute Disease↗

PubMed2000

Inhibition of adenosine uptake and augmentation of ischemia-induced increase of interstitial adenosine by cilostazol, an agent to treat intermittent claudication.

Cilostazol (Pletal), a quinolinone derivative with a cyclic nucleotide phosphodiesterase type 3 (PDE3) inhibitory activity, was recently approved by the Food and Drug Administration for treatment of symptoms of intermittent claudication (IC). However, the underlying mechanisms of action are not entirely clear. In this study, we showed that cilostazol inhibited adenosine uptake into cardiac ventricular myocytes, coronary artery smooth muscle, and endothelial cells with a median effective concentration (EC50) approximately 10 microM. In vivo, cilostazol increased cardiac interstitial adenosine levels after a 2-min ischemia in rabbit hearts (329 +/- 92% increase vs. 102 +/- 29% ischemia alone). The combination of cilostazol and 2-min ischemia reduced infarction from subsequent 30-min regional ischemia and 3 h of reperfusion (infarct size was 18 +/- 4% vs. 53 +/- 3% in the hearts with 2-min ischemia alone or 48 +/- 2% in the hearts treated with cilostazol alone). In contrast, milrinone had no effect on either adenosine uptake or interstitial adenosine levels. These data show that cilostazol, unlike milrinone, inhibits adenosine uptake, and thus potentiates adenosine accumulation from a 2-min ischemia. Future studies are needed to investigate the role of adenosine in the treatment of IC by cilostazol.

Adenosine↗

PubMed2000

Color Doppler flow imaging of the facial artery and vein.

The purpose of this study was to provide some guidelines with respect to the location of the facial vessels, display the potential inverted blood flow of the facial artery, and reemphasize the value of color Doppler ultrasound studies in flap planning. An anatomic study of the facial artery and vein was done using color Doppler ultrasonography in 12 adults. The artery and the vein were located together at the lower border of the mandible. Around the oral commissure and under the nasal ala, they were located apart from each other with variable distances. This divergence of the facial vein from the artery is important information in the planning of axial pattern flaps. Furthermore, the reverse flow was observed in 12 patients after the blood flow of the facial artery was stopped by applying pressure manually at the lower border of the mandible. Observation of the reversed flow confirms the possibility of safe elevation of a retrograde flow-arterialized flap based on the distal portion of the facial artery.

Adolescent↗

PubMed2000

Clarification of the ripple phase of lecithin bilayers using fully hydrated, aligned samples.

Aligned samples of lipid bilayers have been fully hydrated from water vapor in a different type of x-ray chamber. Our use of aligned samples resolves issues concerning the ripple phase that were ambiguous from previous powder studies. In particular, our x-ray diffraction data conclusively demonstrate that, on cooling from the L alpha to the P beta' phase, both chiral and racemic samples of dipalmitoyl phosphatidylcholine (DPPC) exhibit phase coexistence of long and short ripples with a ripple wavelength ratio lambda L/lambda S approximately 1.8. Moreover, the long ripple always forms an orthorhombic unit cell (gamma L = 90 degrees), strongly supporting the possibility that these ripples are symmetric. In contrast, gamma S for short ripples was consistently different from 90 degrees, implying asymmetric ripples. We continue to find no evidence that chirality affects the structure of rippled bilayers. The relative thermodynamic stability of the two types of ripples was investigated and a qualitative free energy diagram is given in which the long ripple phase is metastable. Finally, we suggest a kinetic mechanism, involving loss of water, that promotes formation of the metastable long ripple phase for special thermal protocols.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2000

Purification, characterization, and molecular cloning of the gene of a seed-specific antimicrobial protein from pokeweed.

A small cysteine-rich protein with antimicrobial activity was isolated from pokeweed (Phytolacca americana) seeds and purified to homogeneity. The protein inhibits the growth of several filamentous fungi and gram-positive bacteria. The protein was highly basic, with a pI higher than 10. The entire amino acid sequence of the protein was determined to be homologous to antimicrobial protein (AMP) from Mirabilis jalapa. The cDNA encoding the P. americana AMP (Pa-AMP-1) and chromosomal DNA containing the gene were cloned and sequenced. The deduced amino acid sequence shows the presence of a signal peptide at the amino terminus, suggesting that the protein is synthesized as a preprotein and secreted outside the cells. The chromosomal gene shows the presence of an intron located within the region encoding the signal peptide. Southern hybridization showed that there was small gene family encoding Pa-AMP. Immunoblotting showed that Pa-AMP-1 was only present in seeds, and was absent in roots, leaves, and stems. The Pa-AMP-1 protein was secreted into the environment of the seeds during germination, and may create an inhibitory zone against soil-borne microorganisms. The disulfide bridges of Pa-AMP-1 were identified. The three-dimensional modeling of Pa-AMP-1 indicates that the protein has a small cystine-knot folding, a positive patch, and a hydrophobic patch.

Amino Acid Sequence↗

PubMed2000

A novel PtII-dibenzo-18-crown-6 (DB18C6) complex

The novel Pt(II)-dibenzo-18-crown-6 (DB18C6) title complex, &mgr;-[tetrakis(thiocyanato-S)platinum(II)]-N:N'-bis[2,5,8,15,18, 21-hexaoxatricyclo[20.4.0.1(9,14)]hexacosa-1(22),9(14),10,12,23, 25-hexaene-kappa(6)O]potassium(I), [K(C(20)H(24)O(6))](2)[Pt(SCN)(4)], has been isolated and characterized by X-ray diffraction analysis. The structure analysis shows that the complex displays a quasi-one-dimensional infinite chain of two [K(DB18C6)](+) complex cations and a [Pt(SCN)(4)](2-) anion, bridged by K(+).pi interactions between adjacent [K(DB18C6)](+) units.

Journal Article↗

PubMed2000

Tetrakis(diethylamino)phosphonium bromide hemihydrate.

The structure of the title compound, C(16)H(40)N(4)P(+).Br(-).0. 5H(2)O or [P¿N(C(2)H(5))(2)¿(4)]Br.0.5H(2)O, at 130 K has Z' = 4 and is ionic, with Br not bonded to P. The P atoms are tetrahedral, with P-N distances in the range 1.628 (2)-1.6400 (19) A. The N atoms are approximately planar. The water molecules form cyclic hydrogen-bonded [(H(2)O)(2)Br(2)](2-) units about inversion centers, with O.Br distances in the range 3.425 (2)-3.611 (3) A.

Journal Article↗

PubMed2000

The development and validation of an algorithm for real-time computerised fetal heart rate monitoring in labour.

OBJECTIVE: To develop and validate a computerised algorithm for the interpretation of the characteristics of fetal heart rate monitoring in labour. DESIGN: Prospective observational study. SETTING: Labour ward in a tertiary hospital. SAMPLE: Intrapartum cardiotocograms from 24 pregnancies. METHODS: A computerised algorithm was developed to assess the fetal heart baseline rate, variability, the number of accelerations and the number of decelerations. Twenty five minute segments of cardiotocograms were interpreted by the algorithm and also by seven expert reviewers independently. The reviewers were unaware of the outcome of labour. The reliability of the characteristics of cardiotocography and the validity of the computerised algorithm were assessed using the intraclass correlation coefficient and weighted kappa statistic for continuous and ordinal variables respectively. RESULTS: The inter rater reliability of the baseline fetal heart rate and the number and type of decelerations was good (intraclass correlation coefficient 0.93, 0.93 and 0.79, respectively). The reliability of baseline variability (kappa = 0.27) and accelerations (intraclass correlation coefficient = 0.27) was poor. The computerised algorithm had good agreement with the reviewers for the baseline fetal heart rate (intraclass correlation coefficient 0.91 to 0.98) and the number of decelerations (intraclass correlation coefficient 0.82 to 0.91), but was less valid as regards the number of late decelerations (intraclass correlation coefficient 0.68 to 0.85) and the number of accelerations (intraclass correlation coefficient 0.06 to 0.80), and was invalid as regards baseline variability (kappa 0.00 to 0.34). CONCLUSIONS: The high level of validity of the computerised algorithm for the estimation of the baseline fetal heart rate and the number of decelerations justifies its further technical development.

Adolescent↗

PubMed2000

Endogenous hepatocyte growth factor ameliorates chronic renal injury by activating matrix degradation pathways.

BACKGROUND: Hepatocyte growth factor (HGF) has been shown to promote tubule repair and renal regeneration following acute injury; however, whether HGF also modulates the development and progression of chronic renal diseases that are characterized by progressive tissue fibrosis is uncertain. To examine this question, this study investigated the functional consequence of blocking endogenous HGF signaling in vivo in a model of chronic renal disease. The effects of HGF on the processes of matrix synthesis and degradation in cultured renal epithelial cells were also examined. METHODS: The level of activity of the HGF/c-met axis was examined in rats following 5/6 nephrectomy at multiple time points. To determine the effects of HGF in modulating chronic renal injury, HGF action was blocked in remnant kidney rats using an anti-HGF antibody. The effects of HGF on extracellular matrix (ECM) synthesis and degradation were examined in renal epithelial cells by (35)S-methionine labeling, Western blotting, and zymographic analysis. RESULTS: An increase in renal and systemic production of HGF coupled with an increase in renal c-met was observed in rats with remnant kidneys. When HGF action was blocked by the administration of an anti-HGF antibody, rats experienced a rapid decrease in glomerular filtration rate and increased renal fibrosis. Kidney sections from the antibody-treated rats displayed a marked increase in ECM accumulation and in alpha-smooth muscle actin-positive cells in both the interstitium and tubular epithelium. In vitro studies revealed that HGF reduced net ECM accumulation by human proximal tubule cells (HKC), and this effect was abolished by incubating cells with an anti-HGF antibody. HGF did not alter the ECM synthetic rate in HKC cells. Rather, it markedly increased collagenase such as matrix metalloproteinase-9 (MMP-9) protein expression, as evidenced by Western blotting and zymographic analysis. HGF also decreased the expression of tissue inhibitors of matrix metalloproteinase-1 (TIMP-1) and TIMP-2, the endogenous inhibitors of MMPs. CONCLUSION: These results suggest that HGF is a potent antifibrogenic factor both in vitro and in vivo. Endogenous activation of HGF tends to preserve kidney structure and function in rats with chronic renal disease by activating matrix degradation pathways.

Animals↗

PubMed2000

New developments in the biology of the glucagon-like peptides GLP-1 and GLP-2.

Glucagon-like peptides 1 and 2 (GLP-1 and GLP-2) are coencoded within a single mammalian proglucagon precursor, and are liberated in the intestine and brain. GLP-1 exerts well known actions on islet hormone secretion, gastric emptying, and food intake. Recent studies suggest GLP-1 plays a central role in the development and organization of islet cells. GLP-1 receptor signaling appears essential for beta cell signal transduction as exemplified by studies of GLP-1R-/- mice. GLP-2 promotes energy assimilation via trophic effects on the intestinal mucosa of the small and large bowel epithelium via a recently cloned GLP-2 receptor. The actions of GLP-2 are preserved in the setting of small and large bowel injury and inflammation. The biological actions of the glucagon-like peptides suggest they may have therapeutic efficacy in diabetes (GLP-1) or intestinal disorders (GLP-2).

Animals↗