共查询到20条相似文献,搜索用时 0 毫秒
1.
Effect of various oxygen free radical generating systems and an oxidant H2O2 on brain endoplasmic reticulum (ER) membrane fluidity was examined using fluorescent membrane probe 1,6-diphenyl-1,3,5-hexatriene, DPH. The relative potency of free radical generating systems to decrease membrane fluidity increased in this order: FeCl3-EDTA, FeSO4-EDTA, FeSO4-EDTA/hydrogen peroxide. Potency to decrease membrane fluidity correlated well with these systems' potencies to induce lipid peroxidation, as detected by conjugated diene formation. Treatment of ER membranes with H2O2 had no effect on fluidity or conjugated diene formation. Using the two most potent free radical generating systems, FeSO4-EDTA and FeSO4-EDTA/hydrogen peroxide, a protective effect of the novel antihypoxic and antiarrhytmic drug stobadine was tested. Stobadine and two well-known antioxidants, -tocopherol acetate and butylated hydroxytoluene, demonstrated the ability to prevent free radical induced alterations in ER membrane fluidity. These results provide new evidence of stobadine's protective effect on membranes attacked by oxygen free radicals. 相似文献
2.
Błasiak J Arabski M Pertyński T Małecka-Panas E Woźniak K Drzewoski J 《Cell biology and toxicology》2002,18(4):279-288
Nickel is a toxic and carcinogenic environmental and occupational pollutant and quercetin is a dietary flavonoid that is reported
to modulate effects of many mutagens and carcinogens. We investigated the ability of nickel chloride to induce DNA damage
in human colonic mucosa cells in the presence of quercetin, using the alkaline comet assay. Nickel chloride (5–250 μmol/L)
evoked dose-dependent DNA damage and quercetin at 50 μmol/L decreased the extent of this damage. The cells exposed to nickel
chloride progressively removed their DNA damage and the presence of 50 μmol/L quercetin in the repair-incubation medium did
not affect the repair kinetics. Cells exposed to nickel and treated with endonuclease III, an enzyme recognizing oxidized
bases, displayed a greater extent of DNA damage than those not treated with the enzyme. Quercetin did not exert a significant
effect on the production of oxidized bases by nickel. Pretreatment of the cells with a nitrone spin trap, N-tert-butyl-α-phenylnitrone, decreased the extent of DNA damage evoked by nickel. Quercetin caused a further decrease in the extent
of the damage in the presence of the trap. The results obtained suggest that reactive oxygen species, including free radicals,
might be involved in the formation of DNA lesions induced by nickel chloride in colonic mucosa cells and that quercetin may
exert protective effects in these cells.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Elsa C. Chan Hitesh M. Peshavariya Guei-Sheung Liu Fan Jiang Shiang-Yong Lim Gregory J. Dusting 《Biochemical and biophysical research communications》2013,430(3):918-925
The synthesis of extracellular matrix including collagen during wound healing responses involves signaling via reactive oxygen species (ROS). We hypothesized that NADPH oxidase isoform Nox4 facilitates the stimulatory effects of the profibrotic cytokine transforming growth factor (TGF) β1 on collagen production in vitro and in vivo. TGFβ1 stimulated collagen synthesis and hydrogen peroxide generation in mouse cardiac fibroblasts, and both responses were attenuated by a scavenger of superoxide and hydrogen peroxide (EUK-134). Furthermore, by expressing a dominant negative form of Nox4 (Adv-Nox4ΔNADPH) in fibroblasts, TGFβ1-induced hydrogen peroxide production and collagen production were abrogated, suggesting that Nox4-dependent ROS are important for TGFβ1 signaling in collagen production. This was confirmed by the inhibitory effect of an adenovirus carrying siRNA targeting Nox4 (Adv-Nox4i) on TGFβ1-induced collagen synthesis and expression of activated myofibroblasts marker smooth muscle alpha actin. Finally we used a mouse model of subcutaneous sponge implant to examine the role of Nox4 in the local stimulatory effects of TGFβ1 on collagen accumulation in vivo. TGFβ1-induced collagen accumulation was significantly reduced when the sponges were instilled with Adv-Nox4ΔNADPH. In conclusion, Nox4 acts as an intermediary in the signaling of TGFβ1 to facilitate collagen synthesis. 相似文献
4.
Åke Sjöholm 《Bioscience reports》1996,16(5):415-423
The insulin-producing pancreatic islet -cell, characterized by low proliferative potential, is normally not responsive to the polypeptide epidermal growth factor (EGF) or its homolog transforming growth factor (TGF-). Since EGF receptors in other tissues can be up-regulated by other growth factors and by cytokines, we have in this paper investigated whether such a -cell responsiveness to TGF-, or EGF, can be conferred by co-culture with interferon (IFN-), tumor necrosis factor (TNF-) or transforming growth factor (TGF-) in various combinations. To this end, fetal rat pancreatic islets enriched in -cells were isolated and cultured for 3 days with or without 200 pM or 20 nM TGF-. It was found that neither of these TGF- concentrations affected -cell mitogenesis, insulin content or insulin secretion. However, IFN- (1000 U/ml) evoked a modest stimulation of -cell replication, while suppressing insulin secretion and leaving the islet insulin content unaltered. TNF- (1000 U/ml), on the other hand, affected none of these parameters either alone or in any combination with TGF- or IFN-. However, when TNF- or IFN-, either alone or in combination, were combined with the cytokine interleukin-1, this resulted in islet disintegration, whereas the latter cytokine alone did not exert any gross necrotic changes evident by light microscopy. TGF- (500 pM) stimulated insulin secretion but did not influence islet insulin content or -cell mitogenesis either alone or in combination with TGF- (200 pM or 20 nM). In no instance could any mitogenic or secretory response to low or high concentrations of TGF- be conferred by IFN-, TNF- or TGF- whether used alone or in combinations. Hence, responsiveness to TGF- or EGF in the -cell obviously cannot be achieved by any of these peptides.Abbreviations EGF
epidermal growth factor
- IFN-
interferon
- TGF-
transforming growth factor
- TGF-
transforming growth factor
- TNF-
tumor necrosis factor 相似文献
5.
Zhi-Chun Ding Qi Zheng Bin Cai Wen-Hao Yu Xin-Chen Teng Yang Wang Guo-Ming Zhou Hou-Ming Wu Hong-Zhe Sun Ming-Jie Zhang Zhong-Xian Huang 《Journal of biological inorganic chemistry》2007,12(8):1173-1179
Human metallothionein-3 (hMT3), also named human neuronal growth inhibitory factor (hGIF), is attractive due to its distinct
neuronal growth inhibitory activity, which is not shown by other human MT isoforms. It has been reported that the neuronal
growth inhibitory activity arises from the N-terminal β-domain rather than its C-terminal α-domain. However, previous bioassay
results have shown that the single β-domain is less effective at inhibiting the neuron growth than that in intact hMT3 on
a molar basis, which suggests that the α-domain is indispensable to the neuronal growth inhibitory activity of hMT3. In order
to confirm this assumption, we constructed two domain-hybrid mutants, the β(MT3)–β(MT3) mutant and the β(MT3)–α(MT1) mutant,
and investigated their structural and metal binding properties by UV-vis spectroscopy, CD spectroscopy, pH titration, DTNB
reaction, EDTA reaction, etc. The results showed that stability of the Cd3S9 cluster of the β(MT3)–β(MT3) mutant decreased significantly while the Cd3S9 cluster of the β(MT3)–α(MT1) mutant had a similar stability and solvent accessibility to that of hMT3. Interestingly, the
bioassay results showed that the neuronal growth inhibitory activity of the β(MT3)–β(MT3) mutant decreased significantly,
while the β(MT3)–α(MT1) mutant showed similar inhibitory activity to hMT3. Based on these results, we conclude that the α-domain
is indispensable and plays an important role in modulating the stability of the metal cluster in the β-domain by domain–domain
interactions, thus influencing the bioactivity of hMT3.
Z.-C. Ding and Q. Zheng contributed equally to this work. 相似文献
6.
The ESR signal of NO bound to hemoglobin was detected during the ischemia-reperfusion of myocardium with low temperature ESR technique, and the synergic effects of NO and oxygen free radicals in the injury of the process were studied with this technique. Oxygen free radicals and NO bound to β-subunit of hemoglobin (β-NO complex) could be detected simultaneously in the ischemia-reperfused myocardium. Those signals could not be detected from the normal myocardium even in the presence of L-arginme. However, those signals could be detected and were dose-dependent with L-arginine in the ischemia-reperfused myocardiums and the signal could be suppressed with the inhibitor of NO synthetase, NG-nitro-L-arginine methylester (NAME). Measurement of the activities of lactate dehydrogenase (LDH) and creatine kinase (CK) in the coronary artery effluent of ischemia-reperfused heart showed that L-arginine at lower concentration (<1 mmol/L) could protect the heart from the ischemia-reperfusion injury but at higher con 相似文献
7.
Rates of oxidation of α-tocopherol by the hydroxyl- and superoxide free radicals were measured. The radicals were produced in known yields by radiolysis of aqueous solutions with gamma rays. Two main systems were used to dissolve the tocopherol; micelles, made up from charged and uncharged amphiphiles, and membranes made from dimyristyl phosphatidylcholine which could be charged by addition of stearyl amine or dicetyl phosphate. The HO. radicals were efficient oxidants of α-tocopherol in all systems, with up to 83% of radicals generated in micelle and 32% in membrane suspensions initiating the oxidation. The HO radical was an even more effective oxidant, but when most of it was in the O form at neutral or alkaline pH, the oxidation rates became low. Tocopherol held in positively charged micelles or membranes was oxidized at a higher rate by the O than in uncharged or negative particles. Possible biological significance of these results is discussed. 相似文献
8.
Effects of ornithine on neutrophil (PMN) free amino acid and α-keto acid profiles and immune functions in vitro 总被引:2,自引:0,他引:2
Mühling J Fuchs M Campos M Gonter J Sablotzki A Engel J Welters ID Wolff M Matejec R Dehne MG Menges T Krüll M Hempelmann G 《Amino acids》2004,27(3-4):313-319
Summary. The objective of this study was to determine the effects of ornithine on polymorphonuclear leucocyte (PMN) free amino- and -keto acid profiles, superoxide anion (O2–) generation, hydrogen peroxide (H2O2) formation and released myeloperoxidase acitivity (MPO). Exogenous ornithine significantly increased PMN asparagine, glutamine, asparatate, glutamate, arginine, citrulline, alanine, -ketoglutarate and pyruvate as intracellular ornithine increased. Concerning PMN immune function markers ornithine increased H2O2-generation and MPO acitivity while O2–-formation was decreased. We believe therefore that ornithine is important for affecting PMN susceptible free amino- and -keto acid pool although the mechanisms are not yet clear. This may be one of the determinants in PMN nutrition considerably influencing and modulating PMN host defense capability. 相似文献
9.
To improve photodynamic activity of the parent hypocrellin B (HB), a tetra-brominated HB derivative (compound 1) was synthesized in high yield. Compared with HB, compound 1 has enhanced red absorption and high molar extinction coefficients. The photodynamic action of compound 1, especially the generation mechanism and efficiencies of active species (Sen·-, O·-2 and 1O2) were studied using electron paramagnetic resonance (EPR) and spectrophotometric methods. In the deoxygenated DMSO solution of compound 1, the semiquinone anion radical of compound 1 is photogenerated via the self-electron transfer between the excited and ground state species. The presence of electron donor significantly promotes the reduction of compound 1. When oxygen is present, superoxide anion radical (O·-2) is formed via the electron transfer from Sens·- to the ground state molecular oxygen. The efficiencies of Sens·- and O·-2 generation by compound 1 are about three and two times as much as that of HB, respectively. Singlet oxygen (1O2) can be produced via the energy transfer from triplet compound 1 to ground state oxygen molecules. The quantum yield of singlet oxygen (1O2) is 0.54 in CHCl3 similar to that of HB. Furthermore, it was found that the accumulation of Sens·- would replace that of O·-2 or 1O2 with the depletion of oxygen in the sealed system. 相似文献
10.
《Comparative biochemistry and physiology. A, Comparative physiology》1991,98(2):473-476
- 1.1. The effect of TGF-β and bFGF on lipoprotein lipase activity in chicken adipocyte precursors was investigated.
- 2.2. Lipoprotein lipase activity was reduced by up to 80% by incubation with TGF-β whereas bFGF had no effect.
- 3.3. Contrary to that found with the 3T3-L1 preadipocyte cell line it was not necessary for TGF-β to be present prior to the start of differentiation in order to be effective.
- 4.4. Incubation of adipocyte precursors with actinomycin D abolished the effect of TGF-β suggesting that synthesis of a protein effector is required.
- 5.5. These results indicate differences in responsiveness to TGF-β and bFGF between primary chicken adipocyte precursors and some preadipocyte cell lines.
11.
《The International journal of biochemistry》1994,26(7):891-897
- 1.1. α-Difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase significantly abolished stimulation of protein synthesis evoked by EGF, TGF-α or -β 1 in L6 and fetal bovine myoblasts.
- 2.2. The participation of polyamines in early events evoked by growth factors was shown by a significant stimulation of ornithine decarboxylase and Sdenosylmethionine decarboxylase activity as well as increased concentration of spermidine and spermine in L6 cells exposed to TGF-α and EGF.
- 3.3. TGF-β 1 at a high concentration (1 ng/ml) increased protein synthesis in L6 myoblasts but inhibited it in fetal bovine myoblasts. Metabolic effects of TGF-β 1 in L6 cells was associated with an enhancement of decarboxylase activities, however there were no significant changes in cellular polyamine concentrations. Presented data suggest that polyamines are involved in the signal transduction pathway of EGF, TGF-α, and -β 1 in L6 and fetal bovine myoblasts.
12.
H. A. Schmid F. Schäfer H. Sann E. Simon 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1995,176(2):149-158
The responsiveness of spontaneously active neurons in the subfornical organ (SFO) of adult ducks to angiotensin II (ANGII), norepinephrine (NE), isoproterenol (Iso, -agonist), phenylephrine (Phe,
1-agonist) and clonidine (Clo,
2-agonist) was investigated in brain slices with extracellular recording technique. 64% (n=90) of the neurons increased their activity after superfusion with ANGII, the rest were unresponsive. Application of NE activated 10 and inhibited 8 neurons (n=22); the excitation being correlated with an excitatory ANGII responsiveness of the same neurons and the inhibition with the absence of an ANGII responsiveness. Iso activated 74% (n=58) and Clo inhibited 88% (n=16) of the investigated neurons. Phe did not have an effect on the majority (60%) of the neurons and produced both excitatory and inhibitory actions on the remaining cells. These results offer a plausible explanation for the dose dependent dipsogenic effect of Iso and the failure of NE to elicit dose dependent drinking, which can be explained by its dual, excitatory and inhibitory effect on SFO neurons. It is further concluded, that peripherally applied Iso exerts its dipsogenic action in high concentration by a direct excitatory effect on SFO neurons via the open blood brain barrier. Under physiological conditions, afferent neuronal input of still unknown origin might specifically modulate the activity of SFO neurons, because plasma concentrations of NE are probably not high enough to activate SFO neurons from the blood side of the blood brain barrier.Abbreviations
ACSF
artificial cerebrospinal fluid
-
ANGII
angiotensin II
-
Clo
clonidine
-
Iso
isoproterenol
-
NE
norepinephrine
-
NTS
nucleus of the solitary tract
-
Phe
phenylephrine
-
SFO
subfornical organ 相似文献
13.
Núria Romero Mercè Capdevila Pilar González-Duarte Baldomero Oliva 《Journal of molecular modeling》1996,2(11):417-426
Several mutant forms of rat liver Cd5,Zn2-metallothionein 2 (Cd5,Zn2-MT 2) [1] have been computationally modelled and analysed. All terminal cysteines (5, 13, 19, 21, 26, 29, 33, 36, 41, 48, 57 and 59, Figure 1) have been independently substituted by three other co-ordinating amino-acids (aspartate, glutamate and histidine), and the side-chains of the mutated residues have been modelled to co-ordinate the seven metal ions while minimizing the conformational variations with respect to the wild type protein. We have compared the ability of the putative mutant forms to maintain the MT binding properties. Substitution by aspartate residue best preserves the 3D MT structure. In addition, the mutations C5H plus C21H/E/D show neighbouring impairments that prevent their simultaneous substitution. Although replacement of cysteine by aspartate is feasible in all cases, to our knowledge there is no example of aspartate and cysteine residues co-ordinating to the same zinc atom. Accordingly, the use of histidine or glutamate instead of aspartate cannot be ruled out. The mutant forms in the -domain of Cd5,Zn2-MT 2 have yielded more neighbouring contacts than those in the -domain, which is corroborated by the accessible surface areas [2] of the sulfur atoms [3] in the native form.Abbreviations MT
metallothionein
- CD5,Zn2-MT
Cadmium, Zinc-metallothionein
- RMSD
Root Mean Square Deviation
- PDB
Protein Data Bank
- FEP
Free Energy Perturbation
- CnX
mutant form of cysteine n (n = residue number) substituted by X (X = H, E or D, with H = histidine, E = glutamate, D = aspartate)
- CnX/Y
mutant forms CnX and CnY 相似文献
14.
Mor-Cohen R Rosenberg N Einav Y Zelzion E Landau M Mansour W Averbukh Y Seligsohn U 《The Journal of biological chemistry》2012,287(12):8879-8891
The β3 subunit of αIIbβ3 and αvβ3 integrins contains four epidermal growth factor (EGF)-like domains. Each domain harbors four disulfide bonds of which one is unique for integrins. We previously discerned a regulatory role of the EGF-4 Cys-560-Cys-583 unique bond for αIIbβ3 activation. In this study we further investigated the role of all four integrin unique bonds in both αIIbβ3 and αvβ3. We created β3 mutants harboring serine substitutions of each or both cysteines that disrupt the four unique bonds (Cys-437-Cys-457 in EGF-1, Cys-473-Cys-503 in EGF-2, Cys-523-Cys-544 in EGF-3, and Cys-560-Cys-583 in EGF-4) and transfected them into baby hamster kidney cells together with normal αv or αIIb. Flow cytometry was used to measure surface expression of αIIbβ3 and αvβ3 and their activity state by soluble fibrinogen binding. Most cysteine substitutions caused similarly reduced surface expression of both receptors. Disrupting all four unique disulfide bonds by single cysteine substitutions resulted in variable constitutive activation of αIIbβ3 and αvβ3. In contrast, whereas double C437S/C457S and C473S/C503S mutations yielded constitutively active αIIbβ3 and αvβ3, the C560S/C583S mutation did not, and the C523S/C544S mutation only yielded constitutively active αIIbβ3. Activation of C523S/C544S αvβ3 mutant by activating antibody and dithiothreitol was also impaired. Molecular dynamics of C523S/C544S β3 in αIIbβ3 but not in αvβ3 displayed an altered stable conformation. Our findings indicate that unique disulfide bonds in β3 differently affect the function of αIIbβ3 and αvβ3 and suggest a free sulfhydryl-dependent regulatory role for Cys-560-Cys-583 in both αIIbβ3 and αvβ3 and for Cys-523-Cys-544 only in αvβ3. 相似文献
15.
16.
Current research is based on the synthesis of novel (E)-4-aryl-2-(2-(pyren-1-ylmethylene)hydrazinyl)thiazole derivatives (3–15) by adopting two steps route. First step was the condensation between the pyrene-1-carbaldehyde (1) with the thiosemicarbazide to afford pyrene-1-thiosemicarbazone intermediate (2). While in second step, cyclization between the intermediate (2) and phenacyl bromide derivatives or 2-bromo ethyl acetate was carried out. Synthetic derivatives were structurally characterized by spectroscopic techniques such as EI-MS, 1H NMR and 13C NMR. Stereochemistry of the iminic double bond was confirmed by NOESY analysis. All pure compounds 2–15 were subjected for in vitro β-glucuronidase inhibitory activity. All molecules were exhibited excellent inhibition in the range of IC50 = 3.10 ± 0.10–40.10 ± 0.90 μM and found to be even more potent than the standard d-saccharic acid 1,4-lactone (IC50 = 48.38 ± 1.05 μM). Molecular docking studies were carried out to verify the structure-activity relationship. A good correlation was perceived between the docking study and biological evaluation of active compounds. 相似文献
17.
18.
Schiött A Johansson AC Widegren B Sjögren HO Lindvall M 《Cancer immunology, immunotherapy : CII》2000,48(10):579-587
The cytokine transforming growth factor β-1 (TGFβ1), was transfected into a TGFβ1-negative rat colon carcinoma. The growth
of isografts of TGFβ1-expressing tumors was compared to that of vector control transfectants. The TGFβ1 transfectant grew
significantly more slowly after intrahepatic isografting than did vector control and wild-type tumors. The TGFβ1-transfected
tumor tissue had significantly greater infiltration of both CD4+ and CD8+ T lymphocytes than did the vector control tumor. The tumor-infiltrating leukocytes (TIL) from TGFβ1-transfected tumor secreted
significantly more of the cytokines interleukin-10 (IL-10) and tumor necrosis factor α (TNFα) than did TIL from the vector
control tumor. The TGFβ1 transfectant also demonstrated a significantly slower outgrowth in immunodeficient SCID mice, supporting
a non-T-lymphocyte-dependent mechanism for the tumor retardation. In SCID mice, the TGFβ1-transfected tumor demonstrated significantly
greater infiltration of both granulocytes and macrophages than did the vector control transfectant. We also demonstrated a
direct inhibitory effect of rat TNFα on tumor proliferation in vitro. These results suggest that TGFβ1 induces a local secretion
of immunomodulating cytokines and that this may influence monocytes, lymphocytes and granulocytes to retard tumor outgrowth.
Received: 7 July 1999 / Accepted: 12 August 1999 相似文献
19.
Nor Faeizah Ibrahim Hamizah Shahirah Hamezah Daijiro Yanagisawa Mayumi Tsuji Yuji Kiuchi Kenjiro Ono Ikuo Tooyama 《Biochemistry and Biophysics Reports》2021
One of the neuropathological hallmarks of Alzheimer's disease (AD)—causing neurodegeneration and consequent memory deterioration, and eventually, cognitive decline—is amyloid-β (Aβ) aggregation forming amyloid plaques. Our previous study showed the potential of a tocotrienol-rich fraction—a mixture of naturally occurring of vitamin E analogs—to inhibit Aβ aggregation and restore cognitive function in an AD mouse model. The current study examined the effect of three vitamin E analogs—α-tocopherol (α-TOC), α-tocotrienol (α-T3), and γ-tocotrienol (γ-T3)—on Aβ aggregation, disaggregation, and oligomerization in vitro. Thioflavin T (ThT) assay showed α-T3 reduced Aβ aggregation at 10 μM concentration. Furthermore, both α-T3 and γ-T3 demonstrated Aβ disaggregation, as shown by the reduction of ThT fluorescence. However, α-TOC showed no significant effect. We confirmed the results for ThT assays with scanning electron microscopy imaging. Further investigation in photo-induced cross-linking of unmodified protein assay indicated a reduction in Aβ oligomerization by γ-T3. The present study thus revealed the individual effect of each tocotrienol analog in reducing Aβ aggregation and oligomerization as well as disaggregating preformed fibrils. 相似文献
20.
Ruijian Wang Xueying Yang Renjun Gao Ye Yang Xiaojuan Wang Shugui Cao 《Journal of Molecular Catalysis .B, Enzymatic》2009,56(2-3):131-135
Two secondary alcohol glucosides, cyclohexyl-α-d-glucoside and cyclohexyl-β-d-glucoside, were synthesized via the condensation reaction of cyclohexanol with d-glucose in a biphase system catalyzed by α-glucosidase and β-glucosidase, respectively. The effects of pH, water content, glucose concentration and metal ions on the yield of glucosides were studied. The optimum catalytic conditions established for α-glucosidase was 25% (v/v) water content, 2.5 mol/L glucose concentration and pH 2.0, and for β-glucosidase was 30% (v/v) water content, 2.0 mol/L glucose and pH 5.0. The maximum yield of glucoside was 13.3 mg/mL for cyclohexyl-α-d-glucoside and 8.9 mg/mL for cyclohexyl-β-d-glucoside. Synthesis progress was monitored by TLC and quantitatively analyzed by pre-derived capillary gas chromatography (GC). The retention time was 12.34 min for the α isomer and 12.96 min for the β isomer, respectively. With an anomeric purity of more than 99.5%, the two glucosides display excellent site-specific catalysis by α- and β-glucosidase. Herein, we present a general method to produce anomerically pure glucosides via a one-step bio-reaction in a biphase system. This method could potentially be applied in glucosylation of primary and secondary alcohols or other reactions requiring glucosylation. 相似文献