Biomedical subjects

L Liu

Publications and source records attributed to L Liu.

At least 361 records · Page 20Linked to original sources

PubMed2000

Metabolism of dauricine and identification of its main metabolites.

To study the metabolism of dauricine in vivo and in vitro and identify the structure of its main metabolites, urine of rats after drug administration as the samples of dauricine metabolism in vivo was studied. Rat liver S9 fraction was prepared and the oxygenation metabolism system reconstituted to perform phase I reaction of dauricine in vitro. TLC, HPLC-DAD and MS were used to analyze and identify dauricine and its main phase I metabolites in the samples. The results showed that besides the untransformed dauricine, in the urine samples there was little product of X' which had the same features of TLC, HPLC-DAD and MS as those of N-desmethyl dauricine (N-ddau). Part of dauricine could be transformed to a main metabolite X after incubating with S9 fraction in appropriate conditions. The molecular ion peak of X was m/z 611. The full scan MS2 spectrum of m/z 611 peak from S9 sample were m/z 580, m/z 566, m/z 552, m/z 206, which were same as those of N-ddau. Liver is the major organ for dauricine metabolism and part of dauricine is biotransformed by liver. The major metabolite is considered to be N-ddau.

Alkaloids↗

PubMed2000

Detection and its implication of heat stress protein 27 and P21 in nasopharyngeal carcinoma.

To study the expression of heat stress protein 27 (HSP27) and P21 in nasopharyngeal carcinoma (NPC) tissue, and to evaluate the significance of both HSP27 and P21 in the pathogenesis, development and prognosis of NPC. Indirect immunofluorescence method combined with SABC was applied. Our results showed that (1) the positive rates of HSP27 and P21 expressed in NPC tissue in 36 cases were 88.9% and 94.4%; (2) while in 10 hyperplastic nasopharyngitis tissues, the positive rate of HSP27 and P21 were both 5; (3) all the 5 normal tissues were negatively stained. It is obvious that a co-expressing tendency of HSP27 and P21 could be identified, and it was associated with the degree of malignancy and the clinical stage of NPC. It is concluded that the positive expression of HSP27 and P21 may have clinical significance in the evaluation of the occurring, development and prognosis of NPC, and in NPC treatment.

Adult↗

PubMed2000

Therapeutic effects of undercorrection by LASIK following RK and PRK for correction of high myopia.

In order to investigate the therapeutic effects of undercorrection following radial keratotomy (RK) and photorefractive keratectomy (PRK) for correction of high myopia by excimer laser in situ keratomileusis (LASIK), LASIK was performed on 32 eyes of 16 patients undergoing RK 2 years ago and 38 eyes of 20 patients undergoing PRK 1 year ago. The postoperative uncorrected visual was better than or equal to the preoperative spectacle corrected visual acuity in 49 of 70 eyes (70.00%) and achieved the best status of refraction in 64 of 70 (91.43%). The best postoperatively corrected visual in all operated eyes were equal to their preoperative ones respectively or just lost 1 line. No severe complication occurred during and after operation. It was suggested that LASIK was a better method for treatment of undercorrection following RK and PRK.

Adolescent↗

PubMed2000

Glial cell proliferation in the spinal cord after dorsal rhizotomy or sciatic nerve transection in the adult rat.

Proliferation of glial cells is one of the hallmarks of CNS responses to neural injury. These responses are likely to play important roles in neuronal survival and functional recovery after central or peripheral injury. The boundary between the peripheral nervous system (PNS) and CNS in the dorsal roots, the dorsal root transitional zone (DRTZ), marks a distinct barrier for growth by injured dorsal root axons. Regeneration occurs successfully in the PNS environment, but ceases at the PNS-CNS junction. In order to understand the role of different glial cells in this process, we analysed the proliferation pattern of glial cells in central (CNS) and peripheral (PNS) parts of the dorsal root and the segmental white and grey spinal cord matter after dorsal rhizotomy or sciatic nerve transection in adult rats 1-7 days after injury. Monoclonal antibody MIB-5 or antibodies to bromodeoxyuridine were used to identify proliferating cells. Polyclonal antibodies to laminin were used to distinguish the PNS and CNS compartments of the dorsal root. Dorsal root lesion induced glial cell proliferation in the CNS as well as PNS beginning at 1 day, with peaks from 2 to 4 days postoperatively. After sciatic nerve injury, cell proliferation occurred only in the CNS, was minimal at 1 day, and peaked from 2 to 4 days postoperatively. Double immunostaining with specific glial cell markers showed that after dorsal root transection 60% of the proliferating cells throughout the postoperative period examined were microglia, 30% astrocytes and 10% unidentified in the CNS, while in the PNS 40% were Schwann cells, 40% macrophages and 20% unidentified. After sciatic nerve injury virtually all proliferating cells were microglia. These findings indicate that non-neuronal cells in the CNS and PNS are extremely sensitive to the initial changes which occur in the degenerating dorsal root axons, and that extensive axonal degeneration is a prerequisite for astroglial and Schwann cell, but not microglial cell, proliferation.

Age Factors↗

PubMed2000

Horizontal transfer of archaeal genes into the deinococcaceae: detection by molecular and computer-based approaches.

Members of the Deinococcaceae (e.g., Thermus, Meiothermus, Deinococcus) contain A/V-ATPases typically found in Archaea or Eukaryotes which were probably acquired by horizontal gene transfer. Two methods were used to quantify the extent to which archaeal or eukaryotic genes have been acquired by this lineage. Screening of a Meiothermus ruber library with probes made against Thermoplasma acidophilum DNA yielded a number of clones which hybridized more strongly than background. One of these contained the prolyl tRNA synthetase (RS) gene. Phylogenetic analysis shows the M. ruber and D. radiodurans prolyl RS to be more closely related to archaeal and eukaryal forms of this gene than to the typical bacterial type. Using a bioinformatics approach, putative open reading frames (ORFs) from the prerelease version of the D. radiodurans genome were screened for genes more closely related to archaeal or eukaryotic genes. Putative ORFs were searched against representative genomes from each of the three domains using automated BLAST. ORFs showing the highest matches against archaeal and eukaryotic genes were collected and ranked. Among the top-ranked hits were the A/V-ATPase catalytic and noncatalytic subunits and the prolyl RS genes. Using phylogenetic methods, ORFs were analyzed and trees assessed for evidence of horizontal gene transfer. Of the 45 genes examined, 20 showed topologies in which D. radiodurans homologues clearly group with eukaryotic or archaeal homologues, and 17 additional trees were found to show probable evidence of horizontal gene transfer. Compared to the total number of ORFs in the genome, those that can be identified as having been acquired from Archaea or Eukaryotes are relatively few (approximately 1%), suggesting that interdomain transfer is rare.

Archaea↗

PubMed2000

Characterization of MLH1 and MSH2 DNA mismatch repair proteins in cell lines of the NCI anticancer drug screen.

PURPOSE AND METHODS: The lack of a functional DNA mismatch repair (MMR) pathway has been recognized as a common characteristic of several different types of human cancers due to mutation affecting one of the MMR genes or due to promoter methylation gene silencing. These MMR-deficient cancers are frequently resistant to alkylating agent chemotherapy such as DNA-methylating or platinum-containing compounds. To correlate drug resistance with MMR status in a large panel of human tumor cell lines, we evaluated by Western blot the cellular levels of the two MMR proteins most commonly mutated in human cancers, MLH1 and MSH2, in the NCI human tumor cell line panel. This panel consists of 60 cell lines distributed among nine different neoplastic diseases. RESULTS: We found that in most of these cell lines both MLH1 and MSH2 were expressed, although at variable levels. Five cell lines (leukemia CCRF-CEM, colon HCT 116 and KM12 and ovarian cancers SK-OV-3 and IGROV-1) showed complete deficiency in MLH1 protein. MSH2 protein was detected in all 57 cell lines studied. Absence of MLH1 protein was always linked to resistance to the methylating chemotherapeutic agent temozolomide. This resistance was independent of cellular levels of O6-alkylguanine DNA alkyltransferase. Based on data available for review in the NCI COMPARE database, cellular levels of MLH1 and MSH2 did not correlate significantly with sensitivity to any standard anticancer drug or with any characterized molecular target already tested against the same panel of cell lines. CONCLUSION: Based on evaluation of 60 tumor cell lines in the NCI anticancer drug screen, MLH1 deficiency was more common than MSH2 deficiency and was always associated with a high degree of temozolomide resistance. These data will enable correlations with other drug sensitivities and molecular targets in the COMPARE database to evaluate linked processes in tumor drug resistance.

Adaptor Proteins, Signal Transducing↗

PubMed2000

Capsaicin, acid and heat-evoked currents in rat trigeminal ganglion neurons: relationship to functional VR1 receptors.

Activation of primary trigeminal (TG) neurons by protons, capsaicin, or heat can evoke a variety of sensations, including tingling, stinging, warmth, and burning. Capsaicin and acid are trigeminal stimulants that are important in gustatory physiology. These stimuli can activate H(+)-gated ion channels and heterologously expressed VR1 receptors (vanilloid receptor 1). We have obtained evidence by using electrophysiological and pharmacological measurements on TG neurons that these three stimuli can activate many receptors, and we have determined the extent they behave similarly to VR1 receptors and H(+)-gated channels from the DEGenerin/ENaC superfamily. Whole-cell recordings from rat TG neurons revealed that protons evoked transient (Tp), sustained (Sp), and biphasic (TSp) currents. Tp currents had reversal potentials (Vr) of 24-45 mV, a pH(0.5) range from 5.5 to 6.5, and were inhibited by amiloride, suggesting the presence of functional H(+)-gated channels. Sp currents were inhibited by the VR1 antagonist capsazepine, had Vr's approximately 0 mV, and had pH(0.5) = 6.4. Capsaicin also activated transient (Tc), sustained (Sc), and biphasic (TSc) currents. At pH 5.9, the sensitivity of the Sc currents increased by about a factor of 10, which may partially account for the synergistic responses of acid in foods containing capsaicin. Heating TG neurons evoked a thermally active, capsazepine-inhibitable current with threshold temperature of 43 degrees C and Vr = 5 mV that is also present in neurons activated by and protons (Sp) and capsaicin (Sc). These data suggest that TG neurons have functional receptors that behave similarly to VR1. Activation of such receptors should result in a burning sensation, whereas activation of the transient and biphasic currents should result in other taste descriptors.

Acids↗

PubMed2000

Apparent string shortening concomitant with letter crowding.

In our previous studies of the crowding effect, we have observed that human observers tend to underestimate the length of a letter string (the number of letters in the string) when the letters are close to visual acuity, and the interletter spacings are small. In this study, we asked our observers to identify letters in randomly presented four-letter and five-letter strings. We found that, when a priori knowledge of the lengths of letter strings was not available, the probability of underestimating string length increased with decreasing interletter spacing. The causes of underestimation errors appeared to be the omission of an interior letter and the merging of two neighboring letters. Since our experiments were conducted in the foveal region, neither spatial uncertainty nor split attention can explain the underestimation errors. The effect of the point spread function of the eye on closely packed letter strings is discussed.

Adult↗

PubMed2000

Rescue of infectious classical swine fever and foot-and-mouth disease virus by RNA transfection and virus detection by RT-PCR after extended storage of samples in Trizol.

A method for storing samples containing classical swine fever virus (CSFV) or foot-and-mouth disease virus (FMDV), respectively, was developed, which abolishes the infectivity of both plus strand RNA viruses, and allows storage of samples above 0 degrees C for an extended time, yet preserves the viral RNA in a state which allows its detection by reverse transcription-polymerase chain reaction (RT-PCR), and even rescue of infectious virus after transfection of the extracted RNA into susceptible cells. Supernatants from infected cell cultures as well as organs from diseased animals were stored in Trizol(R) for 1-4 weeks at -20 degrees C, 4 degrees C, room temperature, or 37 degrees C. RNA was then extracted and used subsequently for RT-PCR, as well as transfection into susceptible cells to initiate the replication of progeny virus. Formaldehyde-fixed samples were also included in this study. Storage up to 4 weeks at 37 degrees C in Trizol(R) still yielded positive RT-PCR results and rescue of infectious virus upon RNA transfection. In contrast, formaldehyde fixation reduced drastically the detectability of viral RNA. This method represents a safe and inexpensive alternative to -70 degrees C (dry ice) storage or transport of samples, and abolishes the biosafety risks involved in shipping deep-frozen infectious materials.

Animals↗

PubMed2000

Bufokinin: immunoreactivity, receptor localization and actions in toad intestine and mesenteric circulation.

In this study, we have mapped the immunoreactivity and the binding sites for bufokinin, a tachykinin peptide from the toad intestine. Dense bufokinin-immunoreactive fibers were present at the myenteric plexus, but no cell bodies were stained, suggesting an extrinsic origin. Bufokinin nerve fibers were also associated with submucosal blood vessels and mesenteric arteries. Autoradiographic binding sites for [(125)I]Bolton-Hunter-bufokinin were densely localized over the intestinal circular and longitudinal muscle, submucosal blood vessels and the endothelium of mesenteric arteries. Mesenteric veins had minimal immunoreactivity and binding sites. In the anesthetized toad, topical application of bufokinin onto the mesentery caused a 2.7-fold increase in arterial blood flow, observed using intravital microscopy. This study supports a role for bufokinin as an endogenous spasmogen and hemodynamic regulator in the toad intestine.

Animals↗

PubMed2000

The determination of oxalic acid, oxamic acid, and oxamide in a drug substance by ion-exclusion chromatography.

Oxalic acid, oxamic acid and oxamide are potential impurities in some active pharmaceutical ingredients (API). The retention and separation of oxalic and oxamic acids are particularly challenging using conventional reversed-phase HPLC due to their high polarity. An ion-exclusion chromatography (IEC) method has been shown to provide good separation and sensitivity for the three oxalate-related impurities in a hydrophobic API matrix. The method uses a Dionex IonPac ICE-ASI column with 95/5 (v/v) 0.1% sulfuric acid/acetonitrile as the mobile phase and UV detection at 205 nm. Development and validation of this method are described.

Chromatography, Gel↗

PubMed2000

Regulation of AMPA receptor-mediated synaptic transmission by clathrin-dependent receptor internalization.

Redistribution of postsynaptic AMPA- (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid-) subtype glutamate receptors may regulate synaptic strength at glutamatergic synapses, but the mediation of the redistribution is poorly understood. We show that AMPA receptors underwent clathrin-dependent endocytosis, which was accelerated by insulin in a GluR2 subunit-dependent manner. Insulin-stimulated endocytosis rapidly decreased AMPA receptor numbers in the plasma membrane, resulting in long-term depression (LTD) of AMPA receptor-mediated synaptic transmission in hippocampal CA1 neurons. Moreover, insulin-induced LTD and low-frequency stimulation-(LFS-) induced homosynaptic CA1 LTD were found to be mutually occlusive and were both blocked by inhibiting postsynaptic clathrin-mediated endocytosis. Thus, controlling postsynaptic receptor numbers through endocytosis may be an important mechanism underlying synaptic plasticity in the mammalian CNS.

Adaptor Protein Complex alpha Subunits↗

PubMed2000

Transplant vasculopathy: viral anti-inflammatory serpin regulation of atherogenesis.

BACKGROUND: Surgical and ischemic injury to the artery wall initiates vascular wound-healing responses that stimulate atherosclerotic plaque growth. The plasminogen activators have cellular chemotactic, adhesion, and proteolytic activity. Serp-1 is a secreted myxoma virus glycoprotein serpin that binds and inhibits plasminogen activators. We have examined the effects of Serp-1 on plaque growth and inflammatory cell invasion in animal models after balloon injury and after aortic allograft transplant. METHODS: We used histologic analysis to assess 4 animal models of angioplasty-mediated injury and 2 models of aortic allograft transplant for intimal hyperplasia and cellular invasion. We assessed plasminogen activator (uPA and tPA) and inhibitor (PAI-1) expression in rat iliofemoral arteries after balloon injury using Western blot, enzyme activity, and quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). RESULTS: Plaque growth after balloon injury decreased after Serp-1 treatment in all balloon-injury models tested. Transplant vasculopathy also significantly decreased in 2 rat models of aortic allograft transplant. Infusion of a Serp-1 active site mutant, that lacked plasminogen activator inhibiting activity, did not inhibit plaque growth. Quantitative RT-PCR detected increased transcription of PAI-1 mRNA. Increased PAI-1 protein and enzyme-inhibitory activity was also detected in Serp-1-treated arteries by activity assay and Western blot. CONCLUSIONS: Thrombolytic serpins are central regulatory agents in vascular wound-healing responses. Investigation of the inhibitory mechanisms of viral serpins may provide new insights into atherogenesis.

Angioplasty, Balloon↗

PubMed2000

Neural network modeling for surgical decisions on traumatic brain injury patients.

Computerized medical decision support systems have been a major research topic in recent years. Intelligent computer programs were implemented to aid physicians and other medical professionals in making difficult medical decisions. This report compares three different mathematical models for building a traumatic brain injury (TBI) medical decision support system (MDSS). These models were developed based on a large TBI patient database. This MDSS accepts a set of patient data such as the types of skull fracture, Glasgow Coma Scale (GCS), episode of convulsion and return the chance that a neurosurgeon would recommend an open-skull surgery for this patient. The three mathematical models described in this report including a logistic regression model, a multi-layer perceptron (MLP) neural network and a radial-basis-function (RBF) neural network. From the 12,640 patients selected from the database. A randomly drawn 9480 cases were used as the training group to develop/train our models. The other 3160 cases were in the validation group which we used to evaluate the performance of these models. We used sensitivity, specificity, areas under receiver-operating characteristics (ROC) curve and calibration curves as the indicator of how accurate these models are in predicting a neurosurgeon's decision on open-skull surgery. The results showed that, assuming equal importance of sensitivity and specificity, the logistic regression model had a (sensitivity, specificity) of (73%, 68%), compared to (80%, 80%) from the RBF model and (88%, 80%) from the MLP model. The resultant areas under ROC curve for logistic regression, RBF and MLP neural networks are 0.761, 0.880 and 0.897, respectively (P < 0.05). Among these models, the logistic regression has noticeably poorer calibration. This study demonstrated the feasibility of applying neural networks as the mechanism for TBI decision support systems based on clinical databases. The results also suggest that neural networks may be a better solution for complex, non-linear medical decision support systems than conventional statistical techniques such as logistic regression.

Adolescent↗

PubMed2000

A non-invasive method for measuring preimplantation embryo physiology.

The physiology of the early embryo may be indicative of embryo vitality and therefore methods for non-invasively monitoring physiological parameters from embryos could improve preimplantation diagnoses. The self-referencing electrophysiological technique is capable of non-invasive measurement of the physiology of individual cells by monitoring the movement of ions and molecules between the cell and the surrounding media. Here we use this technique to monitor gradients of calcium, potassium, oxygen and hydrogen peroxide around individual mouse preimplantation embryos. The calcium-sensitive electrode in self-referencing mode identified a region of elevated calcium concentration (approximately 0.25 pmol) surrounding each embryo. The calcium gradient surrounding embryos was relatively steep, such that the region of elevated calcium extended into the medium only 4 microns from the embryo. By contrast, using an oxygen-sensitive electrode an extensive gradient of reduced dissolved oxygen concentration was measured surrounding the embryo and extended tens of micrometres into the medium. A gradient of neither potassium nor hydrogen peroxide was observed around unperturbed embryos. We also demonstrate that monitoring the physiology of embryos using the self-referencing technique does not compromise their subsequent development. Blastocyts studied with the self-referencing technique implanted and developed to term at the same frequency as did unexamined, control embryos. Therefore, the self-referencing electrode provides a valuable non-invasive technique for studying the physiology and pathophysiology of individual embryos without hindering their subsequent development.

Animals↗

PubMed2000

Selective enzymatic degradations of poly(L-lactide) and poly(epsilon-caprolactone) blend films.

Solution cast films were prepared from poly(L-lactide) (PLLA) and poly(epsilon-caprolactone) (PCL) as well as from three blends, namely B75, B50, and B25 with PLLA/PCL proportions of 75/25, 50/50, and 25/75, respectively. The enzymatic degradation of square samples (10 x 10 x 0.2 mm) cut from the films was investigated at 37 degrees C in a pH = 8.6 Tris buffer containing proteinase K or in a pH = 7.0 phosphate buffer containing Pseudomonas lipase. It was confirmed that proteinase K can degrade amorphous domains of PLLA, but cannot degrade crystalline PLLA or PCL. In contrast, Pseudomonas lipase can degrade both amorphous and crystalline PCL but cannot degrade PLLA. The two faces of solution cast films showed different morphologies due to the solvent evaporation process. The lower face appeared more crystalline than the upper face because of the plasticizing effect of solvent entrapped inside which allowed crystallization to proceed. Therefore, the lower face was more resistant to enzymatic attack by proteinase K in the cases of PLLA and the blends. The two polymers in the blends exhibited well separated crystalline domains. PCL seemed to constitute the continuous phase of the blends with formation of large size spherulites when the PCL content was over 50%. The selective degradation of PCL or PLLA components revealed the inner morphology of the blends where microspherelike or islandlike patterns were observed.

Calorimetry, Differential Scanning↗

PubMed2000

Cyclic core dendrimer as a new kind of vector for gene transfer into mammalian cells.

Cyclic core dendritic polymer is a new type of synthetic polymers. The ability of generation 4 of the dendrimer with a core of 1,4,7,10-tetraazacyclododecane to function as an effective gene delivery vector was investigated. Results from fluorescence in situ hybridization (FISH) show that the pCH 110 plasmid DNA was transferred into human small intestine cancer metastatic ascites (HICMA) cells induced by this kind of dendrimer as a vector. The transferred LacZ, GFP and luciferase genes were highly expressed in the transfected HICMA, COS-7 and 293 cells. These studies demonstrate that the dendrimer can transfect mammalian cells in vitro which offers an alternatively efficient method for mammalian gene transfer.

Animals↗

PubMed2000

Developmental regulation of the L-type calcium channel alpha1C subunit expression in heart.

We used Northern analyses, RNase protection assays and immunoblot analyses to examine the relationship among developmental age of the heart, abundance of mRNA and L-type calcium channel alpha1C subunit protein, and to establish the size of the native protein in heart. Northern analysis, RNase protection assays, and immunoblots were used to study RNA and protein from rat heart of various ages. In fetal and adult ventricles there was a predominant 8.3-kb transcript for the alpha1C subunit with no change in transcript size during development. RNase protection assays demonstrated a 2-fold increase in abundance of the DHP receptor message during postnatal development. Immunoblots identified a 240 kD protein, corresponding to the predicted molecular mass of the full length alpha1C subunit. No change in size of protein for the alpha1C subunit was observed at any developmental stage and there was no evidence for a truncated isoform. There was an approximate 2-fold increase in alpha1C subunit protein in ventricular homogenates during postnatal development. Thus, in the developing rat heart, alterations in calcium channel properties during development appear to result neither from alternative splicing that produces a smaller transcript for the alpha1C subunit nor from expression of a truncated protein, but at least in part from transcriptionally-regulated expression of the 240 kDa polypepde.

Age Factors↗