Biomedical subjects

L Li

Publications and source records attributed to L Li.

At least 289 records · Page 16Linked to original sources

PubMed2001

Effects of rigid and soft contact lens daily wear on corneal epithelium, tear lactate dehydrogenase, and bacterial binding to exfoliated epithelial cells.

OBJECTIVE: To determine the effects of lens type and oxygen transmissibility on human corneal epithelium during daily lens wear (DW). DESIGN: Prospective, randomized, double-masked, single-center, parallel treatment groups clinical trial. PARTICIPANTS: Two hundred forty-six patients fitted with: (1) high oxygen-transmissible soft lenses (n = 36), (2) hyper oxygen-transmissible soft lenses (n = 135), and (3) hyper oxygen-transmissible rigid gas-permeable (RGP) lenses (n = 75). INTERVENTION: Irrigation chamber to collect exfoliated epithelial surface cells, confocal microscopy, and tear collection at baseline, 2 weeks, and 4 weeks of DW. MAIN OUTCOME MEASURES: (1) Pseudomonas aeruginosa (PA) binding to exfoliated corneal epithelial surface cells, (2) central epithelial thickness, (3) superficial epithelial cell area, (4) epithelial surface cell exfoliation, and (5) tear lactate dehydrogenase (LDH). RESULTS: Four weeks of DW with the high oxygen-transmissible soft lens significantly increased PA binding from baseline 6.55 +/- 3.01 to 8.75 +/- 3.05 bacteria per epithelial cell (P < 0.01). By contrast, hyper oxygen-transmissible soft lens wear increased binding significantly less (6.13 +/- 2.45 to 7.62 +/- 3.06; P < 0.01), whereas hyper oxygen-transmissible RGP lens wear demonstrated no significant changes (5.91 +/- 2.40 to 6.13 +/- 2.17; P = 0.533). No significant change in central epithelial thickness was found after 4 weeks of DW in either soft lens; however, the epithelial thickness decreased by 9.8% (P < 0.001) with RGP lens wear. Epithelial cell surface area increased 3.3% and 4.1% with the high and hyper oxygen-transmissible soft lenses, respectively, and 10.5% with the hyper oxygen-transmissible RGP lens (P < 0.001). Epithelial desquamation significantly decreased in all groups (P < 0.001). Tear LDH levels increased for all test lenses (P < 0.001). CONCLUSIONS: Increased PA binding induced by wear of a conventional soft lens material is significantly greater than that induced by the new hyper oxygen-transmissible soft silicone hydrogel lens during DW. However, both soft materials showed significant increases in PA binding as compared with baseline controls. By contrast, hyper oxygen-transmissible RGP lens DW did not increase PA binding significantly. Taken together, these findings suggest for the first time both an oxygen effect as well as a difference between soft and rigid lens types on PA binding in DW.

Adult↗

PubMed2001

Molecular cloning and expression analysis of feline melanoma antigen (MAGE) obtained from a lymphoma cell line.

Melanoma antigens (MAGE) are regarded as inducing tumor-specific immune response and thought to be potential therapeutical agents for cancer immunotherapy. We hereby report the cloning of feline MAGE cDNA obtained from a lymphoma cell line derived from cat malignant lymphoma, and its expression pattern in tumor and normal tissues. The cDNA encoding the MAGE is 1668 base pairs (bp) in length, and contains an open reading frame (ORF) of 936 bp encoding a protein of 311 amino acids. The predicted amino acid sequence has 29-46% of homology with other MAGE proteins from human and mouse. mRNA transcripts for the feline MAGE were detected in certain tumors, but not in adult cat normal tissues except in testis, by reverse transcription polymerase chain reaction (RT-PCR) analysis. This indicates that the expression pattern of feline MAGE mRNA is similar to those of other MAGE family genes in tumors and normal tissues.

Amino Acid Sequence↗

PubMed2001

Transglutaminase in Plasmodium parasites: activity and putative role in oocysts and blood stages.

Transglutaminase was identified in malaria parasites by immunofluorescence microscopy using alpha-transglutaminase antiserum. Functional enzyme was demonstrated in vivo and in vitro using labeled polyamines that become incorporated into protein substrates through TGase activity. In Plasmodium falciparum intraerythrocytic parasites, transglutaminase activity was stage-dependent: it was weak in ring-forms but much stronger in trophozoites and schizonts. High levels of activity were detected in P. gallinaceum zygotes and ookinetes and in capsules of oocysts developing on mosquito midguts. Unlike most known transglutaminases, the enzymatic activity in Plasmodium was Ca(2+)-independent. Furthermore, levels of activity were similar at 37 and 26 degrees C. Parasite transglutaminase may be responsible for the modification of erythrocytic cytoskeleton in infected cells and it may facilitate the construction of oocyst capsules by cross-linking mosquito-derived basement membrane components with Plasmodium-derived proteins.

Aedes↗

PubMed2001

Nucleotide sequence and deduced amino acid sequence of the medium RNA segment of Oropouche, a Simbu serogroup virus: comparison with the middle RNA of Bunyamwera and California serogroup viruses.

The Bunyavirus genus of the family Bunyaviridae contains 18 serogroups. To date nucleotide sequence data has been obtained for three serogroups, Bunyamwera, California and Simbu, based on analysis of the small (S) RNA segment. In comparison, there is only nucleotide sequence data for the large and medium (M) RNA segments for members of the Bunyamwera and California serogroups. In this paper we report the nucleotide sequence of the M RNA of Oropouche (ORO) virus, a member of the Simbu serogroup. The M RNA was 4396 nucleotides in length with G1, G2 and NSm proteins similar in size to those reported for members of the Bunyamwera and California serogroups. However, there was limited nucleotide (50-52%) and amino acid (30-32%) homology between ORO virus M RNA and those of published members of the other two serogroups. The Bunyamwera and California serogroups are more closely related to each other than the Simbu serogroup virus Oropouche. These data were consistent with that previously reported for the S RNA (Saeed et al., 2000. J. Gen. Virol. 81, 743-748). It has been noted previously that three of four potential N-linked glycosylation sites of the Bunayamwera and California serogroups are conserved in G1 and G2 proteins. In contrast, ORO virus was found to have only three potential N-linked glycosylation sites of which only one, in G1, was conserved with members of the other two serogroups. Comparison of M RNA sequences of different strains of ORO virus revealed genetic variation consistent with that reported previously for the S RNA.

Amino Acid Sequence↗

PubMed2001

Jatobal virus is a reassortant containing the small RNA of Oropouche virus.

Jatobal (JAT) virus was isolated in 1985 from a carnivore (Nasua nasua) in Tucuruí, Pará state, Brazil and was classified as a distinct member of the Simbu serogroup of the Bunyavirus genus, family Bunyaviridae on the basis of neutralization tests. On the basis of nucleotide sequencing, we have found that the small (S) RNA of JAT virus is very similar (>95% identity) to that of Oropouche (ORO) virus, in particular, the Peruvian genotype of ORO virus. In comparison, limited nucleotide sequencing of the G2 protein gene, encoded by the middle (M) RNA, of JAT and ORO viruses, revealed relatively little identity (<66%) between these two viruses. Neutralization tests confirmed the lack of cross-reactivity between the viruses. These results suggest that JAT virus is a reassortant containing the S RNA of ORO virus. JAT virus was attenuated in hamsters compared to ORO virus suggesting that the S RNA of ORO virus is not directly involved in hamster virulence.

Amino Acid Sequence↗

PubMed2001

Biodegradation during contaminant transport in porous media: 3. Apparent condition-dependency of growth-related coefficients.

The biodegradation of organic contaminants in the subsurface has become a major focus of attention, in part, due to the tremendous interest in applying in situ biodegradation and natural attenuation approaches for site remediation. The biodegradation and transport of contaminants is influenced by a combination of microbial and physicochemical properties and processes. The purpose of this paper is to investigate the impact of hydrodynamic residence time, substrate concentration, and growth-related factors on the simulation of contaminant biodegradation and transport, with a specific focus on potentially condition-dependent growth coefficients. Two sets of data from miscible-displacement experiments, performed with different residence times and initial solute concentrations, were simulated using a transport model that includes biodegradation described by the Monod nonlinear equations and which incorporates microbial growth and oxygen limitation. Two variations of the model were used, one wherein metabolic lag and cell transport are explicitly accounted for, and one wherein they are not. The magnitude of the maximum specific growth rates obtained from calibration of the column-experiment results using the simpler model exhibits dependency on pore-water velocity and initial substrate concentration (C0) for most cases. Specifically, the magnitude of micron generally increases with increasing pore-water velocity for a specific C0, and increases with decreasing C0 for a specific pore-water velocity. Conversely, use of the model wherein observed lag and cell elution are explicitly accounted for produces growth coefficients that are similar, both to each other and to the batch-measured value. These results illustrate the potential condition-dependency of calibrated coefficients obtained from the use of models that do not account explicitly for all pertinent processes influencing transport of reactive solutes.

Biodegradation, Environmental↗

PubMed2001

Cloning, expression and processing of the CP2 neuropeptide precursor of Aplysia.

The cDNA sequence encoding the CP2 neuropeptide precursor is identified and encodes a single copy of the neuropeptide that is flanked by appropriate processing sites. The distribution of the CP2 precursor mRNA is described and matches the CP2-like immunoreactivity described previously. Single cell RT-PCR independently confirms the presence of CP2 precursor mRNA in selected neurons. MALDI-TOF MS is used to identify additional peptides derived from the CP2 precursor in neuronal somata and nerves, suggesting that the CP2 precursor may give rise to additional bioactive neuropeptides.

Amino Acid Sequence↗

PubMed2001

Contributions of the vestibular nucleus and vestibulospinal tract to the startle reflex.

The startle reflex is elicited by strong and sudden acoustic, vestibular or trigeminal stimuli. The caudal pontine reticular nucleus, which mediates acoustic startle via the reticulospinal tract, receives further anatomical connections from vestibular and trigeminal nuclei, and can be activated by vestibular and tactile stimuli, suggesting that this pontine reticular structure could mediate vestibular and trigeminal startle. The vestibular nucleus, however, also projects to the spinal cord directly via the vestibulospinal tracts, and therefore may mediate vestibular startle via additional faster routes without a synaptic relay in the hindbrain. In the present study, the timing properties of the vestibular efferent pathways mediating startle-like responses were examined in rats using electrical stimulation techniques. Transient single- or twin-pulse electrical stimulation of the vestibular nucleus evoked bilateral, startle-like responses with short refractory periods. In chloral hydrate-anesthetized rats, hindlimb electromyogram latencies recorded from the anterior biceps femoris muscle were shorter than those for stimulation of the trigeminal nucleus, and similar to those for stimulation of the caudal pontine reticular nucleus or ventromedial medulla. In awake rats, combining vestibular nucleus stimulation with either acoustic stimulation or trigeminal nucleus stimulation enhanced the whole-body startle-like responses and led to strong cross-modal summation without collision effects. In both chloral hydrate-anesthetized and awake rats, combining vestibular nucleus stimulation with ventromedial medulla stimulation produced a symmetrical collision effect, i.e. a loss of summation at the same positive and negative stimulus intervals, indicating a continuous connection between the vestibular nucleus and ventromedial medulla in mediating vestibular startle. By contrast, combining trigeminal nucleus stimulation with ventromedial medulla stimulation resulted in an asymmetric collision effect when the trigeminal nucleus stimulation preceded ventromedial medulla stimulation by 0.5 ms, suggesting that a monosynaptic connection between the trigeminal nucleus and ventromedial medulla mediates trigeminal startle. We propose that the vestibulospinal tracts participate strongly in mediating startle produced by activation of the vestibular nucleus. The convergence of the vestibulospinal tracts with the reticulospinal tract within the spinal cord therefore provides the neural basis of cross-modal summation of startling stimuli.

Acoustic Stimulation↗

PubMed2001

Extent of initial corneal injury as a basis for alternative eye irritation tests.

Based on studies that have characterized the extent of injury occurring with irritants of differing type and severity, we have proposed that extent of initial injury is the principal mechanism underlying ocular irritation. We report here our efforts to apply this hypothesis, as a mechanistic basis, to the development of an alternative eye irritation assay using an ex vivo rabbit corneal model. Rabbit eyes were obtained immediately after sacrifice or from an abattoir and 8.5-mm diameter corneal buttons were removed and cultured overnight at an air-liquid interface under serum-free conditions. Buttons were exposed to materials of differing type (surfactant, acid, base, alcohol and aldehyde) and irritancy (slight to severe) that had been previously characterized microscopically in the rabbit low-volume eye test. Exposure was accomplished by applying 1.5 microl of an irritant to a sterile, 3 mm diameter, filter paper disk and then placing the disk on the center of the corneal button for 10 s. After removal of the disk, buttons were washed and cultured for 3, 24 or 48 h. Buttons were then evaluated for extent of injury using a Live/Dead staining kit and fluorescent microscopy to measure cell size of live surface epithelial cells, area of epithelial denudation and depth of stromal injury. Ex vivo exposure to slight irritants generally reduced surface epithelial cell size (i.e. erosion) while exposure to mild irritants produced epithelial denudation with variable injury to the corneal stroma. Severe irritants generally produced extensive epithelial denudation and damaged the corneal stroma and endothelium. Overall, ex vivo extent of injury significantly correlated with in vivo extent of injury as measured in previous animal tests (r=0.81, P<0.001). These findings indicate that extent of corneal injury, as shown to be associated with ocular irritation occurring in vivo, can be applied to the development of a mechanistically-based alternative eye irritation model. We believe that this approach may ultimately lead to an alternative assay to replace the use of animals in ocular irritation testing.

Acetic Acid↗

PubMed2001

Leigh syndrome in an infant resulting from mitochondrial DNA depletion.

Leigh syndrome is an encephalomyelopathy that results from a heterogeneous group of mitochondrial disorders characterized by symmetric brainstem spongioform lesions. An infant born with hypotonia and lactic acidosis was found to have symmetric brainstem lesions on T(2)-weighted magnetic resonance imaging consistent with Leigh syndrome. Muscle biopsy failed to reveal ragged-red fibers or cells devoid of cytochrome C oxidase or succinate dehyrogenase. Southern blot analysis of mitochondrial DNA isolated from the patient's quadriceps muscle indicated severe mitochondrial DNA depletion, which was suggested as the cause for the Leigh syndrome seen in this patient. Consideration of mitochondrial DNA depletion as an etiology when evaluating the patient with Leigh syndrome is encouraged.

Biopsy↗

PubMed2001

Patterning of muscle acetylcholine receptor gene expression in the absence of motor innervation.

The patterning of skeletal muscle is thought to depend upon signals provided by motor neurons. We show that AChR gene expression and AChR clusters are concentrated in the central region of embryonic skeletal muscle in the absence of innervation. Neurally derived Agrin is dispensable for this early phase of AChR expression, but MuSK, a receptor tyrosine kinase activated by Agrin, is required to establish this AChR prepattern. The zone of AChR expression in muscle lacking motor axons is wider than normal, indicating that neural signals refine this muscle-autonomous prepattern. Neuronal Neuregulin-1, however, is not involved in this refinement process, nor indeed in synapse-specific AChR gene expression. Our results demonstrate that AChR expression is patterned in the absence of innervation, raising the possibility that similarly prepatterned muscle-derived cues restrict axon growth and initiate synapse formation.

Agrin↗

PubMed2001

Hemogen is a novel nuclear factor specifically expressed in mouse hematopoietic development and its human homologue EDAG maps to chromosome 9q22, a region containing breakpoints of hematological neoplasms.

We cloned a novel murine gene, designated Hemogen (hemopoietic gene), which was sequentially expressed in active hematopoietic sites and downregulated in the process of blood cell differentiation. Hemogen transcripts were specifically detected in blood islands, primitive blood cells and fetal liver during embryogenesis, and then remained in bone marrow and spleen in adult mice. Immunostaining demonstrated that Hemogen was a nuclear protein. We also identified a human homologue of Hemogen, named EDAG, which was mapped to chromosome 9q22, a leukemia breakpoint. Like Hemogen, EDAG exhibited specific expression in hematopoietic tissues and cells. Taken together, these data are consistent with Hemogen and EDAG playing an important role in hematopoietic development and neoplasms.

Amino Acid Sequence↗

PubMed2001

Application of an integrated matrix-assisted laser desorption/ionization time-of-flight, electrospray ionization mass spectrometry and tandem mass spectrometry approach to characterizing complex polyol mixtures.

Polyols are being used in a wide range of industrial applications including surfactants and precursors for grafted polymers. The characterization of polyols is of significance in correlating compositions and structures with their properties. We illustrate two real world examples where traditional analytical methods including GPC and NMR failed to reveal compositional differences, but the combination of matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF), electrospray ionization mass spectrometry (ESI MS), and MS/MS can produce compositional information required for problem solving. The first example involves failure analysis of four ethylene oxide and propylene oxide (EO/PO) copolymer products. The results from the mass spectrometry analysis unequivocally demonstrate that one of the samples has a small variation in copolymer composition, leading to its abnormal activity. The second example is in the area of deformulation of complex polyol mixtures. Two samples displaying similar properties and activities were found to be two different polyol blends. One of the samples is a more cost-effective product. These examples demonstrate that MALDI, ESI MS, and MS/MS should be seriously considered as an integrated component of an overall polyol characterization program in product failure analysis and deformulation.

Journal Article↗

PubMed2001

Reactions of atomic transition-metal ions with long-chain alkanes.

Understanding metal ion interactions with long-chain alkanes not only is of fundamental importance in the areas of organometallic chemistry, surface chemistry, and catalysis, but also has significant implication in mass spectrometry method development for the analysis of polyethylene. Polyethylene represents one of the most challenging classes of polymers to be analyzed by mass spectrometry. In this work, reactions of several transition-metal ions including Cr+, Mn+, Fe+, Co+, Ni+, Cu+, and Ag+ with long-chain alkanes, C28H58 and C36H74, are reported. A metal powder and the nonvolatile alkane are co-deposited onto a sample target of a laser desorption/ionization (LDI) time-of-flight mass spectrometer. The metal ions generated by LDI react with the vaporized alkane during desorption. It is found that all these metal ions can form adduct ions with the long-chain alkanes. Fe+, Co+, and Ni+ produce in-source fragment ions resulting from dehydrogenation and dealkylation of the adduct ions. The post-source decay (PSD) spectra of the metal-alkane adduct ions are recorded. It is shown that PSD of Ag+ alkane adduct ions produces bare metal ions only, suggesting weak binding between this metal ion and alkane. The PSD spectra of the Fe+, Co+, and Ni+ alkane adduct ions display extensive fragmentation. Fragment ions are also observed in the PSD spectra of Cr+, Mn+, and Cu+ alkane adduct ions. The high reactivity of Fe+, Co+, and Ni+ is consistent with that observed in small alkane systems. The unusually high reactivity of Cr+, Mn+, and Cu+ is rationalized by a reaction scheme where a long-chain alkane first forms a complex with a metal ion via ion/induced dipole interactions. If sufficient internal energy is gained during the complex formation, metal ions can be inserted into C-H and C-C bonds of the alkane, followed by fragmentation. The thermal energy of the neutral alkane is believed to be the main source of the internal energy acquired in the complex. Finally, the implication of this work on mass spectrometry method development for polyethylene analysis is discussed.

Journal Article↗

PubMed2001

Lithium and transition metal ions enable low energy collision-induced dissociation of polyglycols in electrospray ionization mass spectrometry.

Electrospray ionization tandem mass spectrometry has the potential to be widely used as a tool for polymer structural characterization. However, the backbones or molecular chains of many industrial polymers including functional polyglycols are often difficult to dissociate in tandem mass spectrometers using low energy collision-induced dissociation (CID). We present a method that uses Li+ and transition metal ions such as Ag+ as the cationization reagents for electrospray ionization in an ion trap mass spectrometer. It is shown that lithium and transition metal polyglycol adduct ions can be readily fragmented with low energy CID. Comparative results from different cationization reagents in their abilities of producing both MS spectra and CID spectra are shown. This method opens the possibility of using conventional and readily available low energy CID tandem MS to study polyglycol structures.

Carbohydrate Sequence↗

PubMed2001

Laser desorption ionization and MALDI time-of-flight mass spectrometry for low molecular mass polyethylene analysis.

Polyethylene's inert nature and difficulty to dissolve in conventional solvents at room temperature present special problems for sample preparation and ionization in mass spectrometric analysis. We present a study of ionization behavior of several polyethylene samples with molecular masses up to 4000 Da in laser desorption ionization (LDI) time-of-flight mass spectrometers equipped with a 337 nm laser beam. We demonstrate unequivocally that silver or copper ion attachment to saturated polyethylene can occur in the gas phase during the UV LDI process. In LDI spectra of polyethylene with molecular masses above approximately 1000 Da, low mass ions corresponding to metal-alkene structures are observed in addition to the principal distribution. By interrogating a well-characterized polyethylene sample and a long chain alkane, C94H190, these low mass ions are determined to be the fragmentation products of the intact metal-polyethylene adduct ions. It is further illustrated that fragmentation can be reduced by adding matrix molecules to the sample preparation.

Indicators and Reagents↗

PubMed2001

The tethered agonist approach to mapping ion channel proteins--toward a structural model for the agonist binding site of the nicotinic acetylcholine receptor.

BACKGROUND: The integral membrane proteins of neurons and other excitable cells are generally resistant to high resolution structural tools. Structure-function studies, especially those enhanced by the nonsense suppression methodology for unnatural amino acid incorporation, constitute one of the most powerful probes of ion channels and related structures. The nonsense suppression methodology can also be used to incorporate functional side chains designed to deliver novel structural probes to membrane proteins. In this vein, we sought to generalize a potentially powerful tool - the tethered agonist approach - for mapping the agonist binding site of ligand-gated ion channels. RESULTS: Using the in vivo nonsense suppression method for unnatural amino acid incorporation, a series of tethered quaternary ammonium derivatives of tyrosine have been incorporated into the nicotinic acetylcholine receptor. At three sites a constitutively active receptor results, but the pattern of activation as a function of chain length is different. At position alpha149, there is a clear preference for a three-carbon tether, while at position alpha93 tethers of 2-5 carbons are comparably effective. At position gamma55/delta57 all tethers except the shortest one can activate the receptor. Based on these and other data, a model for the receptor binding site can be developed by analogy to the acetylcholine esterase crystal structure. CONCLUSION: Through the use of nonsense suppression techniques, the tethered agonist approach has been made into a general tool for probing receptor structures. When applied to the nicotinic receptor, the method places new restrictions on developing models for the agonist binding site.

Animals↗

PubMed2001

Improved method for automatic identification of lung regions on chest radiographs.

RATIONALE AND OBJECTIVES: The authors performed this study to evaluate an algorithm developed to help identify lungs on chest radiographs. MATERIALS AND METHODS: Forty clinical posteroanterior chest radiographs obtained in adult patients were digitized to 12-bit gray-scale resolution. In the proposed algorithm, the authors simplified the current approach of edge detection with derivatives by using only the first derivative of the horizontal and/or vertical image profiles. In addition to the derivative method, pattern classification and image feature analysis were used to determine the region of interest and lung boundaries. Instead of using the traditional curve-fitting method to delineate the lung, the authors applied an iterative contour-smoothing algorithm to each of the four detected boundary segments (costal, mediastinal, lung apex, and hemidiaphragm edges) to form a smooth lung boundary. RESULTS: The algorithm had an average accuracy of 96.0% for the right lung and 95.2% for the left lung and was especially useful in the delineation of hemidiaphragm edges. In addition, it took about 0.775 second per image to identify the lung boundaries, which is much faster than that of other algorithms noted in the literature. CONCLUSION: The computer-generated segmentation results can be used directly in the detection and compensation of rib structures and in lung nodule detection.

Algorithms↗