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Biomedical subjects

L Cai

Publications and source records attributed to L Cai.

At least 19 recordsLinked to original sources
PubMed2003

Superinfection of Laodelphax striatellus with Wolbachia from Drosophila simulans.

Wolbachia are maternally inherited, intracellular alpha-proteobacteria that infect a wide range of arthropods. They manipulate the reproduction of hosts to facilitate their spread into host populations, through ways such as cytoplasmic incompatibility (CI), parthenogenesis, feminization and male killing. The influence of Wolbachia infection on host populations has attracted considerable interest in their possible role in speciation and as a potential agent of biological control. In this study, we used both microinjection and nested PCR to show that the Wolbachia naturally infecting Drosophila simulans can be transferred into a naturally Wolbachia-infected strain of the small brown planthopper Laodelphax striatellus, with up to 30% superinfection frequency in the F(12) generation. The superinfected males of L. striatellus showed unidirectional CI when mated with the original single-infected females, while superinfected females of L. striatellus were compatible with superinfected or single-infected males. These results are, to our knowledge, the first to establish a superinfected horizontal transfer route for Wolbachia between phylogenetically distant insects. The segregation of Wolbachia from superinfected L. striatellus was observed during the spreading process, which suggests that Wolbachia could adapt to a phylogenetically distant host with increased infection frequency in the new host population; however, it would take a long time to establish a high-frequency superinfection line. This study implies a novel way to generate insect lines capable of driving desired genes into Wolbachia-infected populations to start population replacement.

Animals↗
PubMed2002

Two-dimensional percolation and cluster structure of the random packing of binary disks.

In this paper we study the short-range correlated percolation and the cluster structure of two-dimensional (2D) random packing of binary disks with size ratio lambda in the range of 1-5. A Monte Carlo simulation model is used to generate the configuration of random packing first. Then a from-neighbor-to-neighbor propagation method is used to identify the number and sizes of the clusters. Results show that for lambda=1 the percolation threshold p(c) lies between the square and triangular site percolation thresholds. As lambda increases the percolation threshold p(c) (the area fraction of small disks) decreases. To characterize the cluster structure at the percolation threshold, we scale the cluster size s(c) with the cluster radius R as s(c) proportional, variant R(D). The fractal dimension D obtained lies between 1.86 and 1.88 and is independent of the size ratio lambda. This value is in good agreement with the 2D theoretical fractal dimension which is equal to 91/48.

Journal Article↗
PubMed2002

A slow release formulation of insulin as a treatment for osteoarthritis.

OBJECTIVE: To examine the potential of insulin, in a sustained delivery system, as a treatment for arthritis. DESIGN: The effect of insulin on matrix synthesis, matrix breakdown, and nitric oxide production in primary cartilage explants was examined. The activity of insulin on diseased cartilage from Dunkin Hartley guinea pigs, diabetic mice, and osteoarthritic patients was measured. The specificity of insulin stimulation was compared to that of IGF-I using osteoblasts and fibroblasts. Finally, the stability of insulin in a biologically relevant system was tested, and a slow-release formulation of insulin was developed and characterized. RESULTS: In articular cartilage explants, insulin stimulated proteoglycan (PG) synthesis, inhibited PG release and nitric oxide production, and overcame the detrimental effects of interleukin 1 (IL-1). The mechanism whereby insulin decreased matrix breakdown was through inhibition of aggrecanase activity. Insulin was active on cartilage at concentrations at which insulin does not cross-react with insulin-like growth factor I (IGF-I) receptors nor stimulate proliferation of other cells types. The response of cartilage to insulin did not diminish with age or disease. Insulin stimulated matrix synthesis in osteoarthritic cartilage and local treatment with insulin overcame endogenous suppression of matrix synthesis in diabetic cartilage. Poly-lactic-coglycolic acid (PLGA) was found to be an effective carrier for delivery of insulin, and PLGA-Insulin was active on articular cartilage in vitro and in vivo. CONCLUSIONS: As the incidence of arthritis increases with the aging population, an effective therapy to induce repair of cartilage is needed. Based on its biological activities, insulin appears to be an attractive protein therapeutic candidate. Maximum insulin effectiveness may require a sustained delivery system.

Aged↗
PubMed2001

An isothermal titration calorimetric method to determine the kinetic parameters of enzyme catalytic reaction by employing the product inhibition as probe.

An isothermal titration calorimetric (ITC) method was developed to measure the kinetic parameters of ribonuclease A catalytic hydrolysis of cytidine 2',3'-cyclic monophosphate. Employing the inhibition of product as a probe, the K(m), K(i), k(c), and DeltaH(m) can be determined by two simple calorimetric measurements. First, the substrate was titrated into the cell containing high concentration of enzyme. The molar reaction heat was calculated from the titration peak area divided by substrate moles per titration, and the initial catalytic reaction rate in the presence of various concentrations of product can be calculated from the peak height and the molar reaction heat. From Michaelis-Menten function in the presence of inhibitors, the relationship between K(m) and K(i) can be obtained. Then, the dissociation constant, which is equal to K(i), was measured by a regular ITC experiment. Thus, K(m) and k(c) can be calculated. The method developed here can be applied in other enzyme catalytic systems with inhibitive products.

Binding Sites↗
PubMed2001

Pathways by which interleukin 17 induces articular cartilage breakdown in vitro and in vivo.

Overexpression of interleukin (IL-)17 has recently been shown to be associated with a number of pathological conditions. Because IL-17 is found at high levels in the synovial fluid surrounding cartilage in patients with inflammatory arthritis, the present study determined the direct effect of IL-17 on articular cartilage. As shown herein, IL-17 was a direct and potent inducer of matrix breakdown and an inhibitor of matrix synthesis in articular cartilage explants. These effects were mediated in part by leukemia inhibitory factor (LIF), but did not depend on interleukin-1 activity. The mechanism whereby IL-17 induced matrix breakdown in cartilage tissue appeared to be due to stimulation of activity of aggrecanase(s), not matrix metalloproteinase(s). However, IL-17 upregulated expression of matrix metalloproteinase(s) in chondrocytes cultured in monolayer. In vivo, IL-17 induced a phenotype similar to inflammatory arthritis when injected into the intra-articular space of mouse knee joints. Furthermore, a related protein, IL-17E, was found to have catabolic activity on human articular cartilage. This study characterizes the mechanism whereby IL-17 acts directly on cartilage matrix turnover. Such findings have important implications for the treatment of degenerative joint diseases such as arthritis.

Animals↗
PubMed2001

IL-17s adopt a cystine knot fold: structure and activity of a novel cytokine, IL-17F, and implications for receptor binding.

The proinflammatory cytokine interleukin 17 (IL-17) is the founding member of a family of secreted proteins that elicit potent cellular responses. We report a novel human IL-17 homolog, IL-17F, and show that it is expressed by activated T cells, can stimulate production of other cytokines such as IL-6, IL-8 and granulocyte colony-stimulating factor, and can regulate cartilage matrix turnover. Unexpectedly, the crystal structure of IL-17F reveals that IL-17 family members adopt a monomer fold typical of cystine knot growth factors, despite lacking the disulfide responsible for defining the canonical "knot" structure. IL-17F dimerizes in a parallel manner like neurotrophins, and features an unusually large cavity on its surface. Remarkably, this cavity is located in precisely the same position where nerve growth factor binds its high affinity receptor, TrkA, suggesting further parallels between IL-17s and neurotrophins with respect to receptor recognition.

Amino Acid Sequence↗
PubMed2001

Synthesis and in vitro antitumor activity of oligonucleotide-tethered and related platinum complexes.

Three classes of hydroxy-tethered platinum(II) complexes have been synthesized from K(2)PtCl(4) and appropriate amino alcohols. A sequence of selective oxidation and hydrolysis has been developed to prepare hydroxy-tethered platinum(IV) complexes. A novel procedure for the synthesis of amminetrichloroplatinate(II) anion has been generated and used to synthesize a number of monohydroxy-tethered nonchelating platinum complexes. These tethered platinum complexes, including hydroxy-tethered, phosphoramidite-tethered, and monodeoxyribonucleotide-tethered platinum(II) and -(IV) complexes, have been examined in vitro for antitumor activity in both leukemia and ovarian cancer cell lines. Activity of some of these complexes was similar to cis-platin, and most of them showed much better potency than carboplatin. We observed an interesting structure-activity correlation for platinum(II) complexes for both PA-1 and SK-OV-3 ovarian cancer cell lines. However, platinum(IV) complexes showed much more diversified response among cancer cell lines studied. We observed enhanced selectivity among different cancer cell lines for some agents. The most promising is the monodeoxyribonucleotide-tethered platinum(IV) complex, which is the first analogue of the conjugates between a platinum fragment and monodeoxyribonucleotides, showing antitumor activity and selectivity among the cell lines. Finally, the p53 status of the cells appears to contribute to the effectiveness of these agents in that cells harboring wild-type p53 appear to be more sensitive to these agents.

Animals↗
PubMed2001

Roles of vitamin C in radiation-induced DNA damage in presence and absence of copper.

Exposure to either ionizing radiation or certain transition metals results in generation of reactive oxygen species that induce DNA damage, mutation, and cancer. Vitamin C (a reactive oxygen scavenger) is considered to be a dietary radioprotective agent. However, it has been reported to be genotoxic in the presence of certain transition metals, including copper. In order to explore the capacity of vitamin C to protect DNA from radiation-induced damage, and the influence of the presence of copper on this protection, we investigated vitamin C-mediated protection against radiation-induced damage to calf thymus DNA in vitro in the presence or absence of copper(II). Vitamin C (0.08-8.00 mM, pH 7.0) significantly reduced DNA damage induced by gamma-irradiation (30-150 Gy) by 30-50%, similar to the protective effect of glutathione. However, vitamin C plus copper (50 microM) significantly enhanced gamma-radiation-induced DNA damage. Low levels of added copper (5 microM), or chelation of copper with 1-N-benzyltriethylenetetraine tetrahydrochloride (BzTrien) and bathocuprinedisulfonic acid (BCSA), abolished the enhanced damage without diminishing the protective effect of vitamin C. These results indicate that vitamin C can act as: (1) an antioxidant to protect DNA damage from ionizing radiation; and (2) a reducing agent in the presence of copper to induce DNA damage. These effects are important in assessing the role of vitamin C, in the presence of mineral supplements or radioprotective therapeutic agents, particularly in patients with abnormally high tissue copper levels.

Animals↗
PubMed2001

The effects of lead on transient outward currents of acutely dissociated rat dorsal root ganglia.

The effects of Pb2+ on transient outward currents (TOCs) were investigated on rat dorsal root ganglia (DRG) neurons at postnatal days of 15 approximately 21, using the conventional whole-cell patch-clamp technique. In media-sized (35 approximately 40 microm) neurons and in the presence of 50 mM TEA, TOCs that preliminarly included an A-current (IA) and a D-current (ID), were clearly present and dominant. Application of Pb2+ lengthened the initial delay of TOCs and increased the onset-peak time in a concentration-dependent manner. The amplitudes of initial outward current peak were reduced with increasing Pb2+ concentrations. The inhibitory effects of Pb2+ on TOCs were reversible with 80 approximately 90% of current reversed in 2 approximately 10 min at 1 approximately 400 microM Pb2+. For the normalized activation curves fitted by a single Boltzmann equation under each condition, there was a shift to more depolarized voltages with increasing concentrations of Pb2+. The V1/2 and the slope factor (k) increased from 12.76+/-1.49 mV and 15.31+/-1.66 mV (n=10) under control condition to 39.91+/-5.44 mV (n=10, P<0.01) and 21.39+/-3.13 mV (n=10, P<0.05) at 400 microM Pb2+, respectively, indicating that Pb2+ decreased the activation of TOCs. For the normalized steady-state inactivation curves, the V1/2 and the k increased from -92.31+/-2.72 and 8.59+/-1.36 mV (n=10) to -55.65+/-3.67 (n=10, P<0.01) and 23.02+/-2.98 mV (n=10, P<0.01) at 400 microM Pb2+, respectively. The curves were shifted to more depolarized voltages by Pb2+, indicating that channels were less likely to be inactivated at higher concentrations of Pb2+ at any given potential. The fast (tf) and slow (ts) decay time-constants were both significantly increased by increasing concentrations of Pb2+ (n=10, P<0.05), indicating that Pb2+ increased the decay time-course of TOCs. These effects were concentration-dependent and partly reversible following washing. Ca2+ modulated the TOCs gating and might share same binding site with Pb2+, for which Ca2+ had very low affinity. In summary, the results demonstrated that Pb2+ was a dose- and voltage-dependent, and reversible blocker of TOCs in rat DRG neurons. After Pb2+ application, normal sensory physiology of DRG neurons was affected, and these neurons might display aberrant firing properties that resulted in abnormal sensations. This variation caused by Pb2+ could underlie the toxical modulation of sensory input to the central nervous system.

Action Potentials↗
PubMed2001

Timing of metamorphosis and the onset of the negative feedback loop between the thyroid gland and the pituitary is controlled by type II iodothyronine deiodinase in Xenopus laevis.

Two important features of amphibian metamorphosis are the sequential response of tissues to different concentrations of thyroid hormone (TH) and the development of the negative feedback loop between the pituitary and the thyroid gland that regulates TH synthesis by the thyroid gland. At the climax of metamorphosis in Xenopus laevis (when the TH level is highest), the ratio of the circulating precursor thyroxine (T4) to the active form 3,5,3'-triiodothyronine (T3) in the blood is many times higher than it is in tissues. This difference is because of the conversion of T4 to T3 in target cells of the tadpole catalyzed by the enzyme type II iodothyronine deiodinase (D2) and the local effect (cell autonomy) of this activity. Limb buds and tails express D2 early and late in metamorphosis, respectively, correlating with the time that these organs undergo TH-induced change. T(3) is required to complete metamorphosis because the peak concentration of T4 that is reached at metamorphic climax cannot induce the final morphological changes. At the climax of metamorphosis, D2 expression is activated specifically in the anterior pituitary cells that express the genes for thyroid-stimulating hormone but not in the cells that express proopiomelanocortin. Physiological concentrations of T3 but not T4 can suppress thyrotropin subunit beta gene expression. The timing and the remarkable specificity of D2 expression in the thyrotrophs of the anterior pituitary coupled with the requirement for locally synthesized T3 strongly support a role for D2 in the onset of the negative feedback loop at the climax of metamorphosis.

Animals↗
PubMed2001

Topological testing of the mechanism of homology search promoted by RecA protein.

To initiate homologous recombination, sequence similarity between two DNA molecules must be searched for and homology recognized. How the search for and recognition of homology occurs remains unproven. We have examined the influences of DNA topology and the polarity of RecA-single-stranded (ss)DNA filaments on the formation of synaptic complexes promoted by RecA. Using two complementary methods and various ssDNA and duplex DNA molecules as substrates, we demonstrate that topological constraints on a small circular RecA-ssDNA filament prevent it from interwinding with its duplex DNA target at the homologous region. We were unable to detect homologous pairing between a circular RecA-ssDNA filament and its relaxed or supercoiled circular duplex DNA targets. However, the formation of synaptic complexes between an invading linear RecA-ssDNA filament and covalently closed circular duplex DNAs is promoted by supercoiling of the duplex DNA. The results imply that a triplex structure formed by non-Watson-Crick hydrogen bonding is unlikely to be an intermediate in homology searching promoted by RecA. Rather, a model in which RecA-mediated homology searching requires unwinding of the duplex DNA coupled with local strand exchange is the likely mechanism. Furthermore, we show that polarity of the invading RecA-ssDNA does not affect its ability to pair and interwind with its circular target duplex DNA.

DNA↗
PubMed2001

Apolipoprotein A-II modulates the binding and selective lipid uptake of reconstituted high density lipoprotein by scavenger receptor BI.

High density lipoprotein (HDL) represents a mixture of particles containing either apoA-I and apoA-II (LpA-I/A-II) or apoA-I without apoA-II (LpA-I). Differences in the function and metabolism of LpA-I and LpA-I/A-II have been reported, and studies in transgenic mice have suggested that apoA-II is pro-atherogenic in contrast to anti-atherogenic apoA-I. The molecular basis for these observations is unclear. The scavenger receptor BI (SR-BI) is an HDL receptor that plays a key role in HDL metabolism. In this study we investigated the abilities of apoA-I and apoA-II to mediate SR-BI-specific binding and selective uptake of cholesterol ester using reconstituted HDLs (rHDLs) that were homogeneous in size and apolipoprotein content. Particles were labeled in the protein (with (125)I) and in the lipid (with [(3)H]cholesterol ether) components and SR-BI-specific events were analyzed in SR-BI-transfected Chinese hamster ovary cells. At 1 microg/ml apolipoprotein, SR-BI-mediated cell association of palmitoyloleoylphosphatidylcholine-containing AI-rHDL was significantly greater (3-fold) than that of AI/AII-rHDL, with a lower K(d) and a higher B(max) for AI-rHDL as compared with AI/AII-rHDL. Unexpectedly, selective cholesterol ester uptake from AI/AII-rHDL was not compromised compared with AI-rHDL, despite decreased binding. The efficiency of selective cholesterol ester uptake in terms of SR-BI-associated rHDL was 4-5-fold greater for AI/AII-rHDL than AI-rHDL. These results are consistent with a two-step mechanism in which SR-BI binds ligand and then mediates selective cholesterol ester uptake with an efficiency dependent on the composition of the ligand. ApoA-II decreases binding but increases selective uptake. These findings show that apoA-II can exert a significant influence on selective cholesterol ester uptake by SR-BI and may consequently influence the metabolism and function of HDL, as well as the pathway of reverse cholesterol transport.

Animals↗
PubMed2001

Time-dependent alignment and orientation of molecules in combined electrostatic and pulsed nonresonant laser fields.

We examine the time evolution of states created by the nonadiabatic interaction of a polar molecule with combined electrostatic and pulsed nonresonant laser fields and show that the orientation due to the electrostatic field alone can be greatly enhanced by restricting the angular amplitude of the molecule by the pulsed laser field. An analytic model indicates that in the short-pulse limit the interaction is governed by an impulsive transfer of action from the radiative field to the molecule.

Journal Article↗
PubMed2001

The external granule layer of the developing chick cerebellum generates granule cells and cells of the isthmus and rostral hindbrain.

The external granule layer (EGL) on the dorsal surface of the developing cerebellum consists of neural progenitors originating from the rostral rhombic lip (RRL). The RRL and the EGL were thought to give rise exclusively to the granule neurons of the cerebellum (Alder et al., 1996). To study the fate of individual RRL cells, we used a retroviral library to mark clones in the chick embryo at Hamberger-Hamilton stages 10-12. RRL clones comprised the EGL and cerebellar granule cells, as expected. Surprisingly, however, as many as 50% of the RRL clones also contained cells ventral to the cerebellum proper. Ventral derivatives were found in clones with a medial origin, as well as in those with a lateral origin along the RRL. Some of the ventral progeny appeared to be in the process of migration, whereas others appeared to be differentiating neurons in the isthmus and the rostral hindbrain region, including the locus coeruleus (LC) and pontine reticular formation. Furthermore, the Phox2a marker of LC precursors was detected in the EGL within the anterior aspect of the cerebellum. A stream of cells originating in the EGL and expressing Phox2a was observed to terminate ventrally in the LC. These data demonstrate that single RRL progenitor cells are not restricted to producing only cerebellar granule cells; they produce both cerebellar granule cells and ventral derivatives, some of which become hindbrain neurons. They also suggest that some progeny of the EGL escape the cerebellum via the anterior aspect of the cerebellar peduncles, to contribute to the generation of ventral structures such as the LC.

Alkaline Phosphatase↗
PubMed2001

A novel Q378X mutation exists in the transmembrane transporter protein ABCC6 and its pseudogene: implications for mutation analysis in pseudoxanthoma elasticum.

Pseudoxanthoma elasticum (PXE) is an inherited disorder of the elastic tissue with characteristic progressive calcification of elastic fibers in skin, eye, and the cardiovascular system. Recently mutations in the ABCC6 gene, encoding a transmembrane transporter protein, were identified as cause of the disease. Surprisingly, sequence and RFLP analysis for exon 9 with primers corresponding to flanking intronic sequence in diseased and haplotype negative members from all of our families and in a control population revealed either a homozygous or heterozygous state for the Q378X (1132C-->T) nonsense mutation in all individuals. With the publication of the genomic structure of the PXE locus we had identified the starting point of a large genomic segmental duplication within the locus in the cytogenetic interval defined by the Cy19 and Cy185 somatic cell hybrid breakpoints on chromosome 16p13.1. By means of somatic cell hybrid mapping we located this starting point telomeric to exon 10 of ABCC6. The duplication, however, does not include exon 10, but exons 1-9. These findings suggest that one or several copies of an ABCC6 pseudogene (psiABCC6) lie within this large segmental duplication. At least one copy contains exons 1-9 and maps to the chromosomal interval defined by the Cy163 and Cy11 breakpoints. Either this copy and/or an additional copy of psiABCC6 within Cy19-Cy183 carries the Q378X mutation that masks the correct identification of this nonsense mutation as being causative in pseudoxanthoma elasticum. Long-range PCR of exon 9 starting from sequence outside the genomic replication circumvents interference from the psiABCC6 DNA sequences and demonstrates that the Q378X mutation in the ABCC6 gene is associated with PXE in some families. These findings lead us to propose that gene conversion mechanisms from psiABCC6 to ABCC6 play a functional role in mutations causing PXE.

Alleles↗
PubMed2001

Cold adaptive thermogenesis in small mammals from different geographical zones of China.

The mechanisms of thermogenesis and thermoregulation were studied in the tree shrew (Tupaia belangeri) and greater vole (Eothenomys miletus) of the subtropical region, and Brandt's vole (Microtus brandti), Mongolian gerbil (Meriones unguiculatus), Daurian ground squirrel (Spermophilus dauricus) and plateau pika (Ochotona curzoniae) of the northern temperate zone. Resting metabolic rate (RMR) and non-shivering thermogenesis (NST) increased significantly in T. belangeri, E. miletus, M. brandti and M. unguiculatus after cold acclimation (4 degrees C) for 4 weeks. In T. belangeri, the increase in RMR and thermogenesis at liver cellular level were responsible for enhancing the capacity of enduring cold stress, and homeothermia was simultaneously extended. Stable body temperature in M. brandti, E. miletus, M. unguiculatus and O. curzoniae was maintained mainly through increase in NST, brown adipose tissue (BAT) mass and its mitochondrial protein content, and the upregulation of uncoupling protein (UCP1) mRNA, as well as enhancement of the activity of cytochrome C oxidase, alpha-glycerophosphate oxidase and T(4) 5'-deiodinase in BAT mitochondria. The RMR in O. curzoniae and euthermic S. dauricus was not changed, while NST significantly increased during cold exposure; the former maintained their stable body temperature and mass, while body temperature in the latter declined by 4.8 degrees C. The serum T(3) concentration or ratio of T(3)/T(4) in all the species was enhanced after cold acclimation. Results indicated that: (1) the adaptive mechanisms of T. belangeri residing in the subtropical region to cold are primarily by increasing RMR and secondly by increasing NST, and the mechanisms of thermogenesis are similar to those in tropical mammals; (2) in small mammals residing in northern regions, the adaptation to cold is chiefly to increase NST; (3) the mechanism of cold-induced thermogenesis in E. miletus residing in subtropical and high mountain regions is similar to that in the north; (4) a low RMR in warm environments and peak RMR and NST in cold environments enabled M. unguiculatus to tolerate a semi-desert climate; (5) O. curzoniae has unusually high RMR and high NST, acting mainly via increasing NST to adapt to extreme cold of the Qinghai-Tibet Plateau; (6) the adaptation of euthermic S. dauricus to cold is due to an increase in NST and a relaxed homeothermia; and lastly (7) the thyroid hormone is involved in the regulation of cold adaptive thermogenesis in all the species studied.

Adaptation, Physiological↗
PubMed2001

Steroidal saponins from Tribulus terrestris.

Three new steroidal saponins were isolated from the fruits of Tribulus terrestris, and their structures were elucidated as (25R,S)-5 alpha-spirostane-12-one-3 beta-ol-3-O-beta-xylopyranosyl(1-->2)- [beta-xylopyranosyl(1-->3)]-beta-glucopyranosyl(1-->4)-[alpha-rhamno- pyranosyl(1-->2)]-beta-galactopyranoside; 26-O-beta-glucopyranosyl-(25S)-5 alpha-furostane-12-one-3 beta,22 alpha,26-triol-3-O-beta-glucopyranosyl(1-->2)-beta-galactopyranoside; 26-O-beta-glucopyranosyl-(25S)-5 alpha-furostane-12-one-3 beta,22 alpha,26-triol-3-O-beta-glucopyranosyl(1-->4)-[alpha- rhamnopyranosyl(1-->2)]-beta-galactopyranoside, respectively, by spectroscopic analysis and color reaction.

Carbohydrate Sequence↗