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Biomedical subjects

N Li

Publications and source records attributed to N Li.

At least 235 records · Page 13Linked to original sources
PubMed1999

Effects of crocin analogs on ocular blood flow and retinal function.

Ischemic retinopathy and age-related macular degeneration are the leading ocular diseases that cause blindness. The etiology of these diseases is due in part to the reduction of blood flow in the retina and/or choroid. Crocin analogs isolated from Crocus sativus L. were found to significantly increase the blood flow in the retina and choroid and to facilitate retinal function recovery. Increased blood flow due to vasodilation presumably improves oxygenation and nutrient supply of retinal structures. These results indicated that crocin analogs could be used to treat ischemic retinopathy and/or age-related macular degeneration. It was noted that disaccharide analogs of crocin, such as crocin-1 and crocin-2, were less potent than monosaccharide analogs of crocin, such as crocin-3 and crocin-4, constituting an interesting structure-activity relationship.

Animals↗
PubMed1999

Improvement of ocular blood flow and retinal functions with puerarin analogs.

Ischemic retinopathy and, particularly, age-related macular degeneration (AMD) are difficult eye diseases to treat. Since the etiology of these diseases is inadequate blood circulation in the retina and choroid, drugs which can improve blood circulation to these tissues should be beneficial to these diseases. Since fovea is avascular, AMD is closely related to choroidal vascular abnormalities, and drugs which show strong effects to increase choroidal blood flow would be particularly useful. Puerarin and all its derivatives, except ET (puerarin disubstituted with -CH2CH2OH), showed marked increase of choroidal blood flow at various time periods. Even ET showed a tendency to increase choroidal blood flow, though it was not statistically significant. As for b wave recovery, all puerarin analogs showed strong recovery of retinal function after ischemic insult for 30 min. These results indicate that puerarin analogs could be used for the treatment of ischemic retinopathy, and AMD in particular.

Animals↗
PubMed1999

Genetically determined aberrant down-regulation of FcgammaRIIB1 in germinal center B cells associated with hyper-IgG and IgG autoantibodies in murine systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is a multigenic disease associated with IgG hypergammaglobulinemia, IgG anti-nuclear antibodies and immune complex (IC)-type glomerulonephritis. In both human and murine SLE, one susceptibility allele has been mapped to the interval linked to the IgG Fc receptor II (FcgammaRII) gene on chromosome 1. In spontaneous SLE models of NZB and (NZB x NZW) F(1) mice, expression of FcgammaRIIB1, which acts as a negative regulator for B cells, was abnormally down-regulated in follicular germinal center B cells from aged mice, compared to findings in non-SLE NZW, while levels in non-germinal center B cells were practically identical. Such strain differences were also evident in young mice upon in vivo stimulation with foreign antigens. In the FcgammaRIIB promoter region, the NZB allele has two deletion sites, including transcription factor-binding sites. Analyses using (NZB x NZW) F(1) x NZW backcross mice showed that this NZB allele was significantly linked to hyper-IgG, irrespective of the MHC haplotype, while high levels of IgG antibodies specific for DNA were regulated by a combinatorial effect of the F(1)-unique MHC haplotype and the NZB FcgammaRIIB allele. Therefore, the FcgammaRIIB promoter polymorphism may possibly predispose to SLE through germinal center B cells abnormally down-regulating FcgammaRIIB1 expression upon autoantigen stimulations and thus escaping negative signals for IgG production.

Age Factors↗
PubMed1999

Cellular import of cobalamin (Vitamin B-12).

Recent studies have isolated and characterized human gastric intrinsic factor (IF) and transcobalamin II (TC II) genes, whose products mediate the import of cobalamin (Cbl; Vitamin B-12) across cellular plasma membranes. Analyses of cDNA and genomic clones of IF and TC II have provided some important insights into their sites of expression, structure and function. IF and TC II genes contain the same number, size and position of exons, and four of their eight intron-exon boundaries are identical. In addition, they share high homology in certain regions that are localized to different exons, indicating that IF and TC II may have evolved from a common ancestral gene. Both IF and TC II mediate transmembrane transport of Cbl via their respective receptors that function as oligomers in the plasma membrane. IF-mediated import of Cbl is limited to the apical membranes of epithelial cells; it occurs via a multipurpose receptor recently termed "cubilin," and the imported Cbl is usually exported out of these cells bound to endogenous TC II. On the other hand, TC II-mediated Cbl import occurs in all cells, including epithelial cells via a specific receptor, and the Cbl imported is usually retained, converted to its coenzyme forms, methyl-Cbl and 5'-deoxyadenosyl-Cbl, and utilized.

Animals↗
PubMed1999

The multiple roles of conserved arginine 286 of 1-aminocyclopropane-1-carboxylate synthase. Coenzyme binding, substrate binding, and beyond.

A pyridoxal 5'-phosphate (PLP)-dependent enzyme, 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (S-adenosyl-L-Met methylthioadenosine-lyase, EC 4.4.1.14), catalyzes the conversion of S-adenosyl-L-methionine (AdoMet) to ACC. A tomato ACC synthase isozyme (LE-ACS2) with a deletion of 46 amino acids at the C terminus was chosen as the control enzyme for the study of the function of R286 in ACC synthase. R286 of the tomato ACC synthase was mutated to a leucine via site-directed mutagenesis. The ACC synthase mutant R286L was purified using a simplified two-step purification protocol. Circular dichroism (CD) analysis indicated that the overall three-dimensional structure of the mutant was indistinguishable from that of the control enzyme. Fluorescence spectroscopy revealed that the binding affinity of R286L ACC synthase for its cofactor PLP was reduced 20- to 25-fold compared with control. Kinetic analysis of R286L showed that this mutant ACC synthase had a significantly reduced turnover number (k(cat)) of 8.2 x 10(-3) s(-1) and an increased K(m) of 730 microM for AdoMet, leading to an 8,000-fold decrease in overall catalytic efficiency compared with the control enzyme. Thus, R286 of tomato ACC synthase is involved in binding both PLP and AdoMet.

Amino Acid Sequence↗
PubMed1999

Determination of a protein structure by iodination: the structure of iodinated acetylxylan esterase.

Enzymatic and non-enzymatic iodination of the amino acid tyrosine is a well known phenomenon. The iodination technique has been widely used for labeling proteins. Using high-resolution X-ray crystallographic techniques, the chemical and three-dimensional structures of iodotyrosines formed by non-enzymatic incorporation of I atoms into tyrosine residues of a crystalline protein are described. Acetylxylan esterase (AXE II; 207 amino-acid residues) from Penicillium purpurogenum has substrate specificities towards acetate esters of D-xylopyranose residues in xylan and belongs to a new class of alpha/beta hydrolases. The crystals of the enzyme are highly ordered, tightly packed and diffract to better than sub-angström resolution at 85 K. The iodination technique has been utilized to prepare an isomorphous derivative of the AXE II crystal. The structure of the enzyme determined at 1.10 A resolution exclusively by normal and anomalous scattering from I atoms, along with the structure of the iodinated complex at 1.80 A resolution, demonstrate the formation of covalent bonds between I atoms and C atoms at ortho positions to the hydroxyl groups of two tyrosyl moieties, yielding iodotyrosines.

Acetylesterase↗
PubMed1999

Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR/DGGE)-based detection of clonal T-cell receptor gamma gene rearrangements in paraffin-embedded cutaneous biopsies in cutaneous T-cell lymphoproliferative diseases.

Polymerase chain reaction (PCR)-based amplification of T-cell receptor (TCR)-gamma genes is a novel technique that can detect a clone of T cells comprising less than 1% of the total T cells in a lymphoid infiltrate. Besides greater sensitivity than Southern blotting, this technique can be performed with smaller quantities of lower molecular weight genomic DNA as template. We retrospectively analyzed 12 paraffin-embedded biopsies of cutaneous T-cell lymphoma (CTCL), 1 case suspicious for CTCL, 1 case of granulomatous slack skin, and 8 cases of inflammatory skin diseases to determine if PCR-denaturing gradient gel electrophoresis (PCR-DGGE) analysis can detect TCR-gamma gene rearrangements on paraffin-embedded specimens. We were able to amplify Vgamma1-8 TCR sequences in each case and detected a dominant clone in 9 of 12 cases of CTCL and in granulomatous slack skin. We analyzed Vgamma9 sequences in 9 cases of CTCL and detected a dominant clone in 4 cases. This study demonstrates that PCR-DGGE can easily be applied retrospectively to cutaneous biopsies of lymphoproliferative diseases when fresh tissue is not available.

Adolescent↗
PubMed1999

Identification of mycobacterial DNA in cutaneous lesions of sarcoidosis.

Sarcoidosis is a multisystemic granulomatous disease of uncertain etiology. Recently, mycobacterial DNA especially Mycobacterium tuberculosis and Mycobacterium avium complex were detected in lung tissue and bronchial lavage fluid from patients with sarcoidosis by polymerase chain reaction (PCR) assays in 30% to 50% cases. Moreover, cell wall-defective form (CWDF) acid-fast bacteria have been isolated from skin lesions of patients with sarcoidosis which were later confirmed as M. avium complex by PCR assays. CWDF acid-fast bacteria were also found to grow from the blood of 95% patients with active sarcoidosis demonstrating a mycobacterial origin similar to M. tuberculosis. In view of these reports, we investigated 20 cases of cutaneous sarcoidosis using PCR/restriction enzyme pattern analysis (PCR/REPA) to detect mycobacterial DNA from paraffin-embedded skin biopsy samples. The method involves restriction enzyme analysis of nested PCR products obtained with primers encoding for the 65-KDa protein common to all mycobacteria. Using three restriction enzymes, the mycobacterial DNA from PCR product was differentiated to the species level. All the 20 cases had clinical and histologic evidence of sarcoidosis. Special stains for fungi (PAS) and mycobacteria (Fite) were negative and no foreign body was identified on polaroscopic examination in any of the cases. The cell lysates of M. tuberculosis, Mycobacterium bovis, Mycobacterium avium-intracellulare, Mycobacterium kansasii and Mycobacterium marinum from Centers for Disease Control (CDC) were used as standard control for PCR/REPA. Eight cases of foreign body granuloma, seven normal skin samples from the margin of surgical excisions and 5 cases of dermatitis were used as negative controls, and 4 cases of cutaneous tuberculosis were used as positive controls. Mycobacterial DNA was detected by PCR in 16 of the 20 cases of sarcoidosis. PCR/REPA subtyped 8 of these to M. tuberculosis complex (2 cases), M. avium-intracellulare (4 cases), M. kansasii (2 cases) while the other 8 cases were non-tuberculous mycobacteria. All four cases of cutaneous tuberculosis were positive by PCR and had a typical M. tuberculosis PCR/REPA pattern. Mycobacterial DNA was not detected in any of the negative controls. Our results demonstrated that mycobacterial DNA is present in 80% of cutaneous lesions of sarcoidosis and these mycobacteria may play a role in the pathogenesis of sarcoidosis.

Adult↗
PubMed1999

Tea preparations protect against DMBA-induced oral carcinogenesis in hamsters.

The preventive effects of green tea, tea pigments, and mixed tea (a composite of whole water extract of green tea, tea polyphenols, and tea pigments) on 7,12-dimethyl-benz[a]anthracene (DMBA)-induced oral carcinogenesis in golden Syrian hamsters were studied. The right buccal pouches of animals were topically treated with 0.5% DMBA three times per week for 15 weeks. Animals were killed separately after 6, 10, and 15 weeks of DMBA treatment. Oral tumors were counted and measured, and mean tumor burden was calculated. The incidence of preneoplastic lesions and micronucleated cells, the number and volume of silver-stained nucleolar organizer regions (AgNOR), the labeling index of proliferating cell nuclear antigen, and the level of epidermal growth factor receptor expression were studied. The results showed that oral administration of 1.5% green tea, 0.1% tea pigments, and 0.5% mixed tea as the sole source of drinking water for two weeks before initiation of the DMBA treatment and until the end of the experiment significantly reduced the mean tumor burden and the incidence of dysplasia and oral carcinoma (p < 0.01). The frequency of micronucleated cells, the number of AgNOR, the total volume of AgNORs, the labeling index of proliferating cell nuclear antigen, and the level of epidermal growth factor receptor expression in the oral mucosal cells were also significantly reduced (p < 0.01). These results clearly indicated that tea preparations could effectively inhibit DMBA-induced oral carcinogenesis in hamsters. Protection from DNA damage and suppression of cell proliferation could be important mechanisms of the anticarcinogenic effects of the tea preparations.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1999

Effect of dental material HEMA monomer on human dental pulp cells.

The purpose of this study was the cytotoxicity assay of dental material HEMA monomer to human dental pulp cell by MTT method and application of the flow cytometry to analyze effect of dental material on the cell cycle progression. The result of MTT method showed the inhibition of cell growth and 50% inhibitory concentration (IC50) of HEMA monomer in human dental pulp cell was 815.19 micrograms/ml. The result of the flow cytometry showed that there was a perturbation on human dental pulp cell cycle progression at the phases of Sand G2M with a dose-dependent manner. Biomaterials including dental materials should be safety to human bodies. Presently, many methods for testing the cytotoxicity of biomaterials were suggested. [1-2] MTT method is one of the cytotoxicity assay. It was provided by Monsmnn. [3] MTT is a kind of tetrazolium salt [3-(4,5-dimethylthiazol-2yi)-2,5-diphenyl tetrazolium bromide]. MTT method is the rapid, precision and quantitative colorimetric assay for cytotoxicity. It can be used to measure the proliferation, cytotoxicity or activation of living cells and is capable of handling large number of samples. Many investigators have used this advanced method.[4] Flow cytometry (FCM) analyzes the quantity of DNA bonded with dyes in each cell. It can provided the information of the cell cycle progression in detail. Currently, flow cytometry has been widely and successfully used in various fields of basic science research and clinical medicine. This FCM technology also can be used to study the cytotoxicity of dental materials and evaluate the biocompatibility of dental materials.[5-6] The contents of the study were (1) cytotoxicity assay on dental material HEMA monomer in human dental pulp cells by MTT method. (2) application flow cytometry to analyze the effect of dental material HEMA monomer on the cell cycle progression of the human dental pulp cells.

Cell Cycle↗
PubMed1999

[Reduction of forehead integrated EMG and integrated alpha wave through mechanical chair vibration using progressive relaxation by Mitani method].

An experiment was conducted to investigate the effects of respondent revised progressive relaxation by Mitani Method (new PR) on left frontal (Fpl) electromyogram (EMG) and electroencephalogram (EEG) alpha waves. 20 subjects, 10 males, 10 females, mean age = 29, SD = 10.05, were divided into the experimental group and the control group. The experimental group received the respondent new PR. Intermittent two minutes vibrations and five minutes rests, namely DV 15-9-4.5. V vibration were given at shoulder and leg. The Fpl integrated EMG, integrated alpha wave and time of alpha wave appearance were measured by Mitani System. Results showed that only the experimental group showed significant integrated EMG reduction at Fpl. Alpha waves tended to appear more frequently. Integrated alpha wave, however, decreased significantly. Combined mean of integrated EMG and integrated alpha wave also decreased significantly. These results suggest the quick reduction of energy expenditure or entering into a deep relaxation of neuro-muscle circuit by the mechanical respondent New PR. As for operant New PR, experiment including such EEG data is not yet performed.

Adult↗
PubMed1999

Activation of haemostasis by exercise, mental stress and adrenaline: effects on platelet sensitivity to thrombin and thrombin generation.

Stress-induced activation of haemostasis may be involved in the triggering of acute coronary syndromes. We compared the effects of mental stress, dynamic exercise and adrenaline infusion on platelet sensitivity to thrombin using flow-cytometric analysis of platelet fibrinogen binding in whole blood, and platelet aggregability using filtragometry ex vivo, in healthy volunteers. Furthermore, we assessed thrombin generation [prothrombin fragment 1+2 (F1+2) and thrombin-antithrombin complexes in plasma] and thrombin activity (fibrinopeptide A in plasma). Exercise (bicycle ergometry) enhanced thrombin-induced platelet fibrinogen binding (P<0.05) and platelet aggregability (P<0.01), and elevated F1+2, thrombin-antithrombin complexes and fibrinopeptide A (P<0.05 for all three). Adrenaline infusion enhanced thrombin-induced platelet fibrinogen binding and platelet aggregability (P<0.05), and elevated thrombin-antithrombin complexes (P<0.05), whereas F1+2 and fibrinopeptide A levels were not significantly affected. Mental stress increased platelet sensitivity to high concentrations of thrombin only, and produced small increases in levels of thrombin-antithrombin complexes. Time control experiments showed no important changes with repeated measurements during rest. Platelet responses to exercise and adrenaline were reversible, with recovery 60 min later. Thus, heavy exercise and high levels of adrenaline reversibly increased platelet aggregability and platelet sensitivity to thrombin, and enhanced thrombin formation; the effects were most pronounced during exercise. Mental stress only weakly affected these parameters.

Adult↗
PubMed1999

Is NF-kappaB the sensor of oxidative stress?

NF-kappaB is a dimeric transcription factor that is involved in the regulation of a large number of genes that control various aspects of the immune and inflammatory response. It is activated by a variety of stimuli ranging from cytokines, to various forms of radiation, to oxidative stress (such as exposure to H2O2). Recent studies have advanced our understanding of the signal transduction pathway leading to NF-kappaB activation by cytokines and will provide insights for the mechanism by which NF-kappaB is regulated by oxidative stress. An important question that is yet to be answered is whether reactive oxygen species play a physiological role in NF-kappaB activation.

Biosensing Techniques↗
PubMed1999

Neither endogenous nor inhaled nitric oxide influences the function of circulating platelets in healthy volunteers.

Experimental models have indicated prothrombotic effects of inhibition of nitric oxide (NO) production, and anti-thrombotic effects of inhaled NO, but the influence of NO on platelet function in vivo in humans is not well established. We therefore investigated the effects of systemic inhibition of NO synthesis by N(G)-monomethyl-L-arginine (L-NMMA) and of NO inhalation on platelet function in vivo. On two occasions, L-NMMA (13.5 mg/kg) or saline infusion was administered to 14 healthy volunteers in a double-blind cross-over study. After a 30 min infusion of L-NMMA or placebo, NO inhalation (30 p.p.m) was added during the remaining 30 min of infusion, on both occasions. Measurements included filtragometry ex vivo (reflecting platelet aggregability), flow-cytometric evaluation of platelets in whole blood (fibrinogen binding and P-selectin expression), plasma beta-thromboglobulin (reflecting platelet secretion), cGMP in platelets and plasma, thrombin generation markers (thrombin fragment 1+2 and thrombin-antithrombin complexes) in plasma, and bleeding time. L-NMMA increased blood pressure and decreased heart rate. NO inhalation did not influence blood pressure or heart rate, but caused a 3-fold elevation in plasma cGMP levels (P<0.001). Neither L-NMMA nor NO influenced filtragometry readings or flow-cytometric determinations of platelet fibrinogen binding and P-selectin expression. Furthermore, plasma beta-thromboglobulin, platelet cGMP and thrombin generation markers were not influenced by either treatment. Bleeding time was not influenced by L-NMMA compared with placebo, but was increased by approximately 25% during NO inhalation (P<0.01), whether NO synthesis had been inhibited or not. The prolongation of bleeding time by inhaled NO was not accompanied by any effect on the platelet variables assessed. The present results indicate that circulating platelets are not influenced by endogenous or inhaled NO, presumably due to the rapid inactivation of NO in the blood. This does not exclude possible effects of endothelial NO in the interface between the blood and the vessel wall.

Adult↗
PubMed1999

Effect of tetrandrine on morphine dependence in isolated guinea pig ileum.

AIM: To evaluate the effects of tetrandrine (Tet) and nimodipine (Nim) on the morphine (Mor) withdrawal response in the isolated guinea pig ileum. METHODS: The withdrawal contracture was elicited by addition of naloxone (Nal) (1 mumol.L-1) to the isolated naive ileum incubated with Mor (3 mumol.L-1) at 37.5 degrees C for 4 h or to the ileum obtained from Mor-dependent guinea pig. RESULTS: When Nim (0.01, 0.05, and 0.1 mumol.L-1) or Tet (1, 10, and 50 mumol.L-1) was added 1 min before Nal in the naive ilea bathed in Krebs solution containing Mor, or when the ilea from Mor-dependent guinea pigs were incubated with Nim (0.01, 0.05, and 0.1 mumol.L-1) or Tet (1, 10, and 50 mumol.L-1) for 15 min, or when Nim (5 and 10 mg.kg-1, i.p.) or Tet (15 and 30 mg.kg-1, i.p.) was administered in vivo to Mor-dependent guinea pigs, the Nal-precipitated withdrawal contracture was significantly decreased in a dose-dependent manner. CONCLUSION: Tet and Nim, Ca2+ channel blockers, could inhibit the Nal-precipitated Mor withdrawal response in the isolated guinea pig ileum.

Alkaloids↗
PubMed1999

[Intragraft mRNA expression in small intestinal allograft rejection].

OBJECTIVE: To investigate the changes of intragraft mRNA expression of IL-2, IFN-gamma, perforin, granzyme B during small intestinal allograft rejection in rats. METHODS: Heterotopic small intestinal transplantation was performed with inbred rat F344/N(RT1(1)) and inbred rat Wistar/A (RT1-Ak, RT1-Ed). All recipients were divided into four groups; group I, Wistar; group II, Wistar-->Wistar; group III, F344-->Wistar; and group IV, F344-->Wistar + cyclosporine A(6 mg/kg.d-1). The grafts were harvested on POD 3, 5 and 7, All graft samples were examined histologically. The intragraft mRNA expression of IL-2, IFN-gamma, perforin and granzyme B was determined. RESULTS: 1. The histological examination showed that mild acute rejection occurred on POD 3 in group III, moderate acute rejection on POD 5, severe acute rejection on POD 7, while none of group II had histologic evidence of acute rejection. The histologic evidence of group IV indicated that cyclosporine A could effectively controll acute allograft rejection. 2. The gene expression was almost negative in group I. Only on POD 5 was the IL-2 mRNA expression of group III significantly higher than that of group II (P < 0.05). The IFN-gamma mRNA expression of group III was significantly higher than that of group II and group IV (P < 0.01) on POD 3, 5 and 7. The level of perforin and granzyme B mRNA expression was significant higher in group III than in the other two control groups only on POD 5 and POD 7. CONCLUSIONS: IL-2, IFN-gamma, perforin and granzyme B play important roles in small intestinal allograft rejection. Detection of these molecules gene expression with RT-PCR, especially the gene expression of IFN-gamma, perforin and granzyme can become an early, specific, sensitive and clinically valuable diagnostic tool for small intestinal allograft rejection. Furthermore, anti-rejection therapy or induction of immune tolerance could be achieved by breaking down these molecules gene transcription.

Animals↗
PubMed1999

[Effect of Astragalus Angelica Mixture on lipoprotein lipase and lecithin cholesterol acyltransferase of nephrotic rats].

OBJECTIVE: To investigate the mechanism of Astragalus Angelica Mixture (AAM) effect of regulating lipid metabolism disturbance in nephrotic rats. METHODS: To examine the effects of AAM on serum albumin, lipid levels, and activities of lipoprotein lipase (LPL) and lecithin-cholesterol acyltransferase (LCAT), which are key enzymes for catabolism of lipid, in immune-induced nephrotic hyperlipidemia rats and exogenous hyperlipidemia rats. RESULTS: Serum albumin was reduced, lipid increased significantly, LPL activity decreased significantly and the LCAT activity was relatively insufficient in nephrotic rats. Activities of LPL and LCAT increased significantly in AAM treated nephrotic rats. There were no change of activities of LPL and LCAT in exogenous hyperlipidemia rats and AAM showed no effect on the activities of these two enzymes. CONCLUSION: The effect of AAM in regulating lipid metabolism might be due to enhancing the clearance of triglyceride and cholesterol-rich lipoprotein by improving the activities of LPL and LCAT.

Animals↗