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Biomedical subjects

L Xiao

Publications and source records attributed to L Xiao.

At least 145 records · Page 8Linked to original sources
PubMed1997

Synthesis of Uniform Ferric Oxide Particles from Deionized Colloids

A modified method was employed to prepare monodispersed colloidal particles of ferric (hydrous) oxide. The method contains three steps: (i) preparation of uniform nuclei of ferric hydrous oxide via a so-called instantaneous nucleation method; (ii) purification of the nuclei suspension via dialysis; (iii) aging of the purified nuclei suspension in a reflux reactor at certain pH. Cubic and pseudocubic alpha-Fe2O3 monodisperse particles which are much smaller than the cubic alpha-Fe2O3 particles obtained from the same reactant through a usual method were produced by aging needle like nuclei at a lower pH. A close-packed three-dimensional QDs (quantum dots) superlattice structure 40 nm in edge length with cubic geometry was formed by self-aggregation between spherical amorphous ferric hydrous oxide nuclei 3-5 nm in diameter. The growth processes of the two kind particles were also illustrated. This study showed an approach to prepare smaller particles from aqueous metal salt solutions in relatively higher concentration, and ordered QDs superlattice structure by controlled self-aggregation of QDs in hydrosol.

Journal Article↗
PubMed1997

Hormonal activation of the striatum and the nucleus accumbens modulates paced mating behavior in the female rat.

Sexual behavior in the female rat has both sensorimotor and motivational components, which can be distinguished when the female rat is able to pace the rate of copulation. The experiments reported were conducted to determine whether estrogen application to the striatum and/or nucleus accumbens affects pacing behavior. In order to induce sexual receptivity, ovariectomized rats received sequential bilateral implants of 17beta-estradiol followed by progesterone into the ventromedial nucleus of the hypothalamus. Then, bilateral implants of 17beta-estradiol or cholesterol were administered into either the dorsolateral striatum or the nucleus accumbens. Pacing behavior was tested 4 hr later. It was found that intrastriatal application of estradiol significantly facilitated the percent exits exhibited after copulatory contact, whereas application of estradiol in the nucleus accumbens affected the return latency. To determine whether estrogen in the striatum or nucleus accumbens normally plays a role in pacing behavior, intrastriatal or intra-accumbens implants containing the steroidal antiestrogen ICI 182,780 or vehicle were given to ovariectomized female rats treated systemically with estrogen and progesterone. The antiestrogen treatment decreased the percent exits when delivered to the striatum and affected return latency when delivered to the nucleus accumbens. The results indicate that estrogen acts directly in the striatum and in the nucleus accumbens to differentially modulate specific components of pacing behavior.

Animals↗
PubMed1997

Induction of protective antibodies in Saimiri monkeys by immunization with a multiple antigen construct (MAC) containing the Plasmodium vivax circumsporozoite protein repeat region and a universal T helper epitope of tetanus toxin.

Previous attempts in inducing protective immunity against Plasmodium vivax in human volunteers and nonhuman primates with recombinant circumsporozoite (CS) proteins have been unsuccessful, largely due to the failure of generating antibodies against the protective B epitope AGDR in the CS protein repeat region. We report here an immunization study in Saimiri monkeys with a multiple antigen construct (MAC) containing the P. vivax CS protein repeat region and a T helper epitope of tetanus toxin formulated in different adjuvants. Monkeys immunized three times with MAC in copolymer P1005, copolymer P1005 plus RaLPS, or MF-75 had titers of antibodies against CS repeat, sporozoites and the protective B epitope AGDR significantly higher than those immunized with MAC in alum or PBS (P < 0.05). Antibody levels in animals that received P1005 were maintained at high level for 7 months after the last immunization. Upon challenge with 10000 sporozoites 2 weeks after the last immunization, 75% (three of four) of monkeys from the alum group, 50% (three of six) of monkeys from the P1005 plus RaLPS group, 40% (two of five) of monkeys from the P1005 group, 33% (two of six) of monkeys from the MF-75 group, and 17% (one of six) of monkeys from the MAC alone group were fully protected. When immunized animals were challenged again with 30000 sporozoites 22 weeks after the last immunization. 40% (two of five) monkeys from the P1005 group were fully protected. The remaining (three) in this group developed low parasitemia (< 2000 parasites mm-3 of blood) after significantly longer prepatent period (P < 0.05). In addition, 17% (one of six) of monkeys each from the P1005 plus RaLPS and MF-75 groups were also fully protected. Protected animals had higher levels of prechallenge anti-AGDR antibody titers than unprotected (1933 vs 281 for the first challenge, P > 0.05; 21527 vs 196 for the rechallenge, P < 0.05). Anti-AGDR antibody titers were positively correlated with the prepatent period of infected animals (r = 0.42 for the first challenge, P > 0.05; r = 0.60 for the rechallenge, P < 0.05) and negatively correlated with the peak parasitemia (r = -0.39 for the first challenge, P < 0.05; r = 0.50 for the rechallenge, P < 0.05). The results suggested that when combined with the use of potent adjuvants and T helper epitopes, MAC subunit vaccines may potentially offer protection against malaria infection.

Amino Acid Sequence↗
PubMed1997

Adrenomedullin is a potent stimulator of osteoblastic activity in vitro and in vivo.

Adrenomedullin is a 52-amino acid vasodilator peptide produced in many tissues, including bone. It has 20% sequence identity with amylin, a regulator of osteoblast growth, and circulates in picomolar concentrations. The present study assesses whether adrenomedullin also acts on osteoblasts. At concentrations of 10(-12) M and greater, adrenomedullin produced a dose-dependent increase in cell number and [3H]thymidine incorporation in cultures of fetal rat osteoblasts. This effect was also seen with adrenomedullin-(15-52), -(22-52), and -(27-52), but adrenomedullin-(40-52) was inactive. These effects were lost in the presence of amylin blockers, suggesting they were mediated by the amylin receptor. Adrenomedullin also increased [3H]thymidine incorporation into cultured neonatal mouse calvaria but, unlike amylin, did not reduce bone resorption in this model. Adrenomedullin stimulated phenylalanine incorporation into both isolated osteoblasts and calvaria. When injected daily for 5 days over the calvariae of adult mice, it increased indexes of bone formation two- to threefold (P < 0.0001) and increased mineralized bone area by 14% (P = 0.004). It is concluded that adrenomedullin regulates osteoblast function and that it increases bone mass in vivo. The potential of this family of peptides in the therapy of osteoporosis should be further evaluated.

Adrenomedullin↗
PubMed1997

[Photographic diagnosis for common intraorbital tumors].

OBJECTIVE: To compare and analyze the modern photographic methods used for localization and analysis of the nature of intraorbital tumors. METHODS: B-scan, CT scan and magnetic resonance imaging (MRI) were used to examine six types of common intraorbital tumor (20 cases for each type). RESULTS: Each method can locate and show the nature of the lesions, and B-scan has a better value to display internal structure and dynamics of orbital lesions. CT can discover the lesions and exactly show their locations, while MRI is more valuable to display the optic nerve tumor and the extension of intraorbital tumor to extraorbital regions. CONCLUSIONS: All the above methods can locate and show the nature of intraorbital tumors, and each has its own special defects and advantages which can be complementary to one another.

Dermoid Cyst↗
PubMed1997

[Detection of bacterial DNA from cholesterol gallstones by NP-PCR and its clinical significance].

To search for bacterial DNA sequences in cholesterol gallstones with negative bacterial culture. We used nested primers polymerase chain reaction (NP-PCR) technique to amplify bacterial gene fragments were amplified in vitro from DNA extracted from cholesterol gallstones. Comparative 16S ribosomal RNA sequence analysis was used for elucidation of bacterial identification. The gallbladder gallstones of 30 patients were analyzed. Bacterial DNA was found in the stones of 26 patients. There was no difference either in cholesterol and water content or in harboring bacterial DNA of gallstones. E. coli-related DNA fragments were found in the stones of 8 patients (26.67%). Propionibacteria type DNA was found in the stones of 7 patients (23.33%). Stones of 2 patients (6.67%) harbored bacterial gene fragments with similarity of Streptococcus pyogenes. A more heterogeneous sequence collection was found in 7 patients (23.33%) and could be assigned to the multiple bacterial infections. Another stones of 2 patients (6.67%) had bacterial DNA with lower molecularweight which might be related to some unidentified bacteria. The results suggested that most cholesterol gallstones harbor bacterial DNA. It is important to determine whether these microorganisms are innocent bystanders or active participants in cholesterol gallstone formation.

Adult↗
PubMed1997

[Change of serum lipid, apolipoprotein during cholesterol gallstone formation in rabbit model].

In order to study the formation of cholesterol gallstone through rabbit model which was induced by high cholesterol diet (HCD), we investigated the rabbits' serum lipoprotein cholesterols and apolipoprotein (apo) at 1 week (1w), 2 weeks (2w), 3 weeks (3w) and 4 weeks (4w) in comparison with those of a control group respectively. The results were as follows: (1) of 10 rabbits subjected to experiment, 4, 6, and 7 rabbits were found to have induced-cholesterol gallstones in the 2w, 3w and 4w groups respectively. (2) The serum concentrations of total cholesterol (TC), triglyceride (TG), phospholipid (PL), low density lipoprotein cholesterol (LDL-C) and very low density lipoprotein chloesterol (VLDL) increased significantly (1w, 2w, 3w and 4w groups vs control group, P < 0.05), especially in the 3w and 4w groups; the surum concentrations of high density lipoprotein cholesterol and its subfractions (HDL-C, HDL2-C, HDL3-C) decreased slightly (vs control group, P > 0.05). (3) The serum contents of apoB100, apoC II and apoC III increased significantly (vs control group, P < 0.05), especially in the 3w and 4w groups; the serum apoA I reduced gradually in 1w, 2w and 3w groups, and decreased greatly in 4w group (vs control group, P < 0.05). The results demonstrated that owing to the intake of high cholestrol diet with the passage of time, the increased concentrations of serum VLDL-C, apoB, apoC II and apoC III possibly caused an enhanced secretion of biliary cholesterol into bile; that the decreased serum apoA I level might reduce the secretion of anti-nucleating factor into bile. All of these factors and changes may play important roles during the formation of cholesterol gallstones.

Animals↗
PubMed1996

Formation of hydroxyeicosatetraenoic acids from hemozoin-catalyzed oxidation of arachidonic acid.

Hemozoin, a heme byproduct of hemoglobin digestion by malaria parasites, is released into the blood stream of the host upon lysing of infected erythrocytes. Since heme-compounds are potent catalysts of lipid peroxidation, we evaluated the catalytic ability of Plasmodium falciparum-derived hemozoin to oxidize arachidonic acid to hydroxyeicosatetraenoic acids (HETEs). Hemozoin, beta-hematin, and hematin all catalyzed the formation of 15-, 12- and 5-HETE as major products. Although there were no significant differences in total amounts of HETEs generated by hemozoin relative to hematin or beta-hematin, there were significant differences in the proportions of certain isomers. 15-HETE was the predominant isomer generated by hemozoin catalysis while 5-HETE was the major product formed by hematin catalysis. Since HETEs are important vasoactive mediators, the non-enzymatic oxidation of arachidonic acid by hemozoin catalysis may contribute to some of the pathophysiology associated with severe and cerebral malaria.

Animals↗
PubMed1996

Quantitation of RT-PCR amplified cytokine mRNA by aequorin-based bioluminescence immunoassay.

We described here a bioluminescence-based immunoassay for the quantitation of RT-PCR amplified cytokine mRNA. This technique uses a standard RT-PCR procedure, with the following modifications. The forward primer in the PCR reaction is labeled with a 5' biotin molecule. Following PCR, a digoxigenin-conjugated oligonucleotide probe is hybridized to the target biotin-labeled DNA template. The hybridized duplex is captured onto a streptavidin-coated microtiter plate. The bound product is quantitated by adding digoxigenin-specific antibodies conjugated with the photoprotein aequorin. The amount of specific DNA captured onto the plate is quantitated by triggering the bioluminescence reaction through the addition of calcium ions. This technique detected as low as 40 amol of amplified cytokine products, or 500 copies of templates when 27 PCR cycles were used. The high sensitivity of this technique enables the quantitation of target DNA during the exponential phase of the PCR reaction. The aequorin-bioluminescence assay is an alterative non-radioactive method for the quantitation of PCR products.

Aequorin↗
PubMed1996

Differential transcription of the human spermidine/spermine N1-acetyltransferase (SSAT) gene in human lung carcinoma cells.

The expression of spermidine/spermine N1-acetyltransferase (SSAT), the rate-limiting enzyme in the catabolism of polyamines, is highly regulated by a number of factors including the natural polyamines and their analogues. The phenotype-specific cytotoxicity that occurs in response to a class of polyamine analogues, the diethylpolyamines, is associated with a phenotype-specific superinduction of SSAT in human non-small-cell lung carcinomas, whereas in non-responding cell types, including the small-cell lung carcinomas, the superinduction of SSAT does not occur. In this study, we have investigated the molecular basis of this phenotype-specific SSAT induction in human lung carcinoma cells in response to N1,N12-diethylspermine (BESpm). To facilitate the study of transcriptional regulation, we have cloned and characterized 11 kb of the human SSAT locus, including 3500 bp of the 5' promoter region. Nuclear run-on transcription studies suggest that the initial induction of SSAT results from an increase in the rate of gene transcription. Results from Northern blot analysis and ribonuclease protection assays indicate a differential expression of SSAT mRNA between the analogue-responsive H157 and non-responsive H82 cells. There is no detectable SSAT mRNA in H82 cells, even after a 24-h analogue treatment, whereas SSAT mRNA in H157 cells was detectable by Northern blot analysis and increased more than 100-fold following drug exposure. Furthermore, nuclear run-on transcription assays do not detect any active transcription of SSAT gene in either treated or untreated H82 cells. These results indicate that at least one component of the phenotype-specific induction of SSAT appears to be due to differences in transcriptional regulation of the gene. In addition, mapping of DNase I-hypersensitive sites of the SSAT gene suggest that the cell type-specific promoter/enhancer utilization may control the expression of the SSAT gene in differentially sensitive cell types in vivo.

Acetyltransferases↗
PubMed1996

Isolation of a polyamine transport deficient cell line from the human non-small cell lung carcinoma line NCI H157.

In an effort to study the mechanism underlying the observed phenotype-specific response of human lung cancer cell lines to a polyamine analogue, N1,N12-bis(ethyl)spermine(BESpm), we have isolated a BESpm resistant cell line from the BESpm-sensitive large cell lung carcinoma line NCI H157. The mutant line exhibits identical growth rates in the presence or absence of the analogue. However, the overall growth of mutant cells reaches stationary phase earlier than that of the parental cells. In contrast to the parental cells, where a superinduction of spermidine/spermine N1-acetyltransferase (SSAT) is associated with BESpm toxicity, treatment of this resistant line with BESpm did not induce SSAT mRNA or enzyme activity. BESpm treatment was not effective in depleting the intracellular polyamine pools and very low intracellular BESpm levels were detected. This BESpm resistance is not mediated by multidrug resistance (MDR) protein, since these cells maintain their sensitivity to the antineoplastic agent adriamycin. Treatment of these cells with methylglyoxal bis(guanylhydrazone) (MGBG), an AdoMetDC inhibitor which enters cell using polyamine transport system, shows no inhibition of cell growth. Our data suggest that these mutant cells are deficient in polyamine transport. Consistent with this hypothesis, exogenous polyamines did not prevent difluoromethylornithine (DFMO) induced growth inhibition in the mutant cells.

Acetyltransferases↗
PubMed1996

Plasmodium falciparum: involvement of additional receptors in the cytoadherence of infected erythrocytes to microvascular endothelial cells.

The involvement of additional ligands in the cytoadhesion of PRBC to endothelial cells was studied by the use of human microvascular endothelial cells (HMEC-1), brain microvascular endothelial cells (HBEC-51), umbilical vein endothelial (HUVEC), and C32 melanoma cells as well as soluble CD36, ICAM-1, and thrombospondin in the adhesion assays. Immunostaining showed that ICAM-1 and thrombospondin were expressed by all cell lines, whereas CD36 and VCAM-1 were expressed constitutively only by C32 melanoma cells and HBEC-51, respectively; none of these cells had basal expression of E-selectin. Bindings of the parental HB3 parasite strain to HMEC-1 and HUVEC were higher than that to HBEC-51 and C32 melanoma cells. Selections by panning the parental HB3 through HMEC-1 (HB3EC-6 line) or C32 melanoma cells (HB3C32-6 to HMEC-1 was higher than that to C32 melanoma cells. Antibody or peptide blockade against CD36, ICAM-1, and thrombospondin or preincubation of target cells with TNF-alpha and IFN-gamma did not significantly alter the binding intensity of HB3EC-6 to HMEC-1 and HB3C32-6 to C32 melanoma cells. Preincubation of HMEC-1 with IL-4, however, reduced its binding with HB3EC-6. In vitro selection did not enhance the binding of PRBC to plate-bound CD36 or thrombospondin; binding to ICAM-1 was negligible. The binding of both selected lines was inhibited by dextran sulfate and sulfatides, but not by chondroitin sulfate A. These results suggested that in addition to CD36 and thrombospondin, sulfated glycoconjugates were probably concurrently utilized by these PRBC as receptors. Experiments with freshly isolated Kenyan parasites indicated that they also exhibited a similar mechanism of binding to endothelial cells.

Animals↗
PubMed1996

Tricyclic antidepressants inhibit human natural killer cells.

The commonly used antidepressants imipramine, amitriptyline, and nortriptyline were found to significantly inhibit human natural killer (NK) cell-mediated cytolysis in vitro and suppress the stimulation of NK cells by IFN-gamma. This is a previously unrecognized biologic property of these drugs with psychotropic activity. Tricyclic antidepressants did not decrease effector-target cell conjugation formation, nor did they induce target cell resistance to NK lysis, indicating that the drugs might interfere with the killing mechanism of the effector cells. Kinetic data reveal that the drug interference is related to an early postbinding event in the activation of NK cells. Results also showed that the inhibitory effect of tricyclic antidepressants on human NK cell activity occurred in parallel to an increase in intracellular cyclic GMP concentration. However, the attenuation in the cyclic GMP formation by methylene blue, a selective inhibitor of soluble guanylate cyclase, was not accompanied by a corresponding increase in NK cell cytolytic activity. It is suggested that the stimulation of cyclic GMP was not directly involved in the inhibitory effect of antidepressants on NK cells and perhaps was a secondary phenomenon. This immune cell modulatory property of tricyclic antidepressants seems to indirectly provide evidence for the concept that human brain neurons and NK cells might share regulatory system(s).

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1996

Efficacy of albendazole and fenbendazole against Giardia infection in cattle.

Efficacies of albendazole and fenbendazole in suppressing Giardia cyst output of infected calves were evaluated in two clinical trials. In the first trial, 18 naturally infected calves were allocated to an untreated control group (n = 9) and an albendazole-treated group (n = 9). Calves in the treated group were given 20 mg/kg-1 oral albendazole once daily for 3 days. Compared to controls, treated calves showed 98.5%, 97.6% and 90.8% reductions in cysts per gram of feces (cpg) 1, 2 and 6 weeks respectively after the start of treatment. In a second trial, 13 infected calves were allocated to an untreated control group (n = 6) and a fenbendazole-treated group (n = 7). Calves in the treated group were given 10 mg kg-1 fenbendazole orally twice daily for 3 days. Compared to the control group, treatments reduced cpg counts by 100%, 98.5% and 59.5% 1, 2, and 3 weeks respectively after the start of treatment. Both albendazole and fenbendazole appeared to be effective in suppressing cyst excretion by Giardia-infected calves.

Albendazole↗
PubMed1996

Influence of adjuvants on murine immune responses against the C-terminal 19 kDa fragment of Plasmodium vivax merozoite surface protein-1 (MSP-1).

The immunogenicity of a yeast-expressed 19 kDa fragment of P vivax MSP-1 in the presence of different adjuvant formulations was evaluated. ICR mice were immunized with the 19 kDa antigen, using Freund's, alum, and block copolymer P1005 in water-in-oil (W/O) or oil-in-water (O/W) emulsions with or without detoxified lipopolysaccharide (RaLPS) as adjuvants. Five weeks following immunization with the antigen, mice were boosted with asexual blood-stage antigens. Three weeks after the last immunization with the 19 kDa antigen, mice from the Freund's group and most groups that received P1005 as adjuvant had higher total IgG titres than those that received alum as adjuvant or antigen alone. Antibody responses after the antigen immunization were predominantly of the IgG1 isotype, but mice in the Freund's and P1005 (W/O or O/W emulsion with or without RaLPS) groups also had high titres of IgG2a and IgG2b. Antibody titres against merozoites increased in all groups after the parasite antigen boost. IgG2a levels in the group that received antigen in P1005 plus RaLPS in the W/O emulsion were higher than those receiving Freund's, alum or the other copolymer adjuvants. The high IgG2a titres in this group were associated with reduced IL-10 production.

Adjuvants, Immunologic↗
PubMed1996

Immunosuppressive properties of plasma and lymphocytes from the human retroplacental blood.

The retroplacental compartment in which maternal blood is in direct and continuous contact with trophoblasts derived from the fetus seems to be the place where maternal and fetal cells regulate each others' activities. To assess the role of the retroplacental compartment in the immune regulation of pregnancy, 10 healthy pregnant women were selected for evaluation of the immune activity of their lymphocytes and plasma from the retroplacental blood. The results showed that the proliferation and cytotoxic capacity of these lymphocytes, but not of maternal peripheral lymphocytes, against fetal cells were significantly inhibited in undirect mixed lymphocyte culture and direct cell-mediated cytotoxic assay, respectively. The plasma from retroplacental blood showed significant immunosuppressive properties and depressed the proliferation of maternal peripheral lymphocytes stimulated by fetal HLA as well as the cytotoxic activity of these cells against the fetal lymphocytes. The present data suggest that the retroplacental compartment seems to be an immunosuppressive barrier, protecting the fetus from maternal rejection.

Cytotoxicity, Immunologic↗
PubMed1996

Sulfated polyanions inhibit invasion of erythrocytes by plasmodial merozoites and cytoadherence of endothelial cells to parasitized erythrocytes.

Sulfated proteoglycans have been shown to be involved in the binding of sporozoites of malaria parasites to hepatocytes. In this study, we have evaluated the effect of sulfated glycosaminoglycans on the invasion of erythrocytes by Plasmodium falciparum merozoites and cytoadherence of parasitized erythrocytes (PRBC) to endothelial cells. Invasion of erythrocytes by HB3EC-6 (an HB3 line selected for high binding to endothelial cells) was inhibited by dextran sulfate 500K, dextran sulfate 5K, sulfatides, fucoidan, and heparin but not by chondroitin sulfate A. With the exception of sulfatides, the invasion-inhibitory effect was not mediated by killing of parasites. Cytoadherence of HB3EC-6 to human microvascular endothelial cells (HMEC-1) and inhibited by these sulfated glycoconjugates. The highly sulfated dextran sulfate 500K had the highest inhibitory effect on both invasion and cytoadherence, whereas the positively charged protamine sulfate promoted cytoadherence. Because preincubation of PRBC with sulfated glycosaminoglycans and treatment of target cells with heparinase had no significant inhibition on cytoadherence, it is unlikely that sulfated glycoconjugates are used directly by endothelial cells as cytoadhesion receptors. In an vivo experiment, we found that the administration of dextran sulfate 500K to CBA/Ca mice infected with Plasmodium berghei ANKA reduced parasitemia and delayed the death associated with anemia. These observations suggest that sulfated polyanions inhibit the invasion of erythrocytes by merozoites and cytoadherence of PRBC to endothelial cells by increasing negative repulsive charge and sterically interfering with the ligand-receptor interaction after binding to target cells.

Animals↗