Biomedical subjects

F Yuan

Publications and source records attributed to F Yuan.

At least 37 records · Page 2Linked to original sources

PubMed2000

Preferential incorporation of G opposite template T by the low-fidelity human DNA polymerase iota.

DNA polymerase activity is essential for replication, recombination, repair, and mutagenesis. All DNA polymerases studied so far from any biological source synthesize DNA by the Watson-Crick base-pairing rule, incorporating A, G, C, and T opposite the templates T, C, G, and A, respectively. Non-Watson-Crick base pairs would lead to mutations. In this report, we describe the ninth human DNA polymerase, Pol(iota), encoded by the RAD30B gene. We show that human Pol(iota) violates the Watson-Crick base-pairing rule opposite template T. During base selection, human Pol(iota) preferred T-G base pairing, leading to G incorporation opposite template T. The resulting T-G base pair was less efficiently extended by human Pol(iota) compared to the Watson-Crick base pairs. Consequently, DNA synthesis frequently aborted opposite template T, a property we designated the T stop. This T stop restricted human Pol(iota) to a very short stretch of DNA synthesis. Furthermore, kinetic analyses show that human Pol(iota) copies template C with extraordinarily low fidelity, misincorporating T, A, and C with unprecedented frequencies of 1/9, 1/10, and 1/11, respectively. Human Pol(iota) incorporated one nucleotide opposite a template abasic site more efficiently than opposite a template T, suggesting a role for human Pol(iota) in DNA lesion bypass. The unique features of preferential G incorporation opposite template T and T stop suggest that DNA Pol(iota) may additionally play a specialized function in human biology.

Base Pairing↗

PubMed2000

Interstitial hydraulic conductivity in a fibrosarcoma.

Convective transport of therapeutic agents in solid tumors can be improved through intratumoral infusion. To optimize the convection, we investigated the dependence of the hydraulic conductivity on tissue deformation induced by interstitial fluid pressure gradient during the infusion. Two experimental systems were used in the investigation: 1) one-dimensional perfusion through tumor slices and 2) intratumoral infusion using a needle. With these systems, we found that the apparent hydraulic conductivity (K(app)) could be altered by several orders of magnitude in fibrosarcomas through changes in perfusion conditions. When the perfusion pressure was less than a threshold level, fluid flow in tissues could not be detected. When the perfusion pressure was increased above the threshold level, K(app) depended on perfusion system and pressure. The maximum variation in K(app) in fibrosarcomas reached 80,260-fold in our experiments. The large variation in K(app) could be explained by perfusion pressure-induced tissue deformation. These experimental data suggest that the hydraulic conductivity is very sensitive to tissue deformation and imply that it is possible to improve intratumoral infusion of therapeutic agents through optimization of infusion conditions.

Animals↗

PubMed2000

Development of cytotoxic cerebral edema in rats following intracaudatum injection of tACPD, an agonist of metabotropic glutamate receptors.

OBJECTIVE: To explore the involvement of metabotropic glutamate receptors (mGluRs) in the formation of cerebral edema. METHODS: Male Wistar rats weighing from 250 g to 300 g were used. Trans-1-aminocyclopentane-1, 3-diacarboxylic acid (tACPD), an agonist of mGluRs, was microinjected into the right caudatum. Brain water content was determined by a wet weight/dry weight technique and Na+, K+ and Ca2+ contents were measured by inductive Couple Plasma-9000 at 6 h, 24 h and 48 h post-injection. Extravasation of Evan's blue (EB) into the brain was determined as an indicator of disturbance in the blood-brain barrier (BBB) and endothelial cells. Histologic studies were performed under a Leitz microscope and a Philips EM208s electron microscope. RESULTS: Dose-dependent and time-related increase of brain water was induced after tACPD (10, 50, 500 and 1000 nmol) injection. A significant increase in Na+ and K+ content but not in Ca2+ content was observed. EB extravasation showed no blue stain, indicating no increase in BBB permeability induced by tACPD-injection. Electron microscope study confirmed this finding and revealed remarkable swelling of astrocytes especially endfoot processes of astrocytes around capillaries at 6 h after tACPD-injection. In addition, all changes mentioned above occurred in both caudatum. CONCLUSION: These results indicate that activation of mGluRs by tACPD injected into the caudatum induced cytotoxic brain edema and interfered with astrocyte K+ buffering. This may provide new clues for therapeutic intervention.

Animals↗

PubMed2000

[A report on investigation and clinical application of corneal storage media].

OBJECTIVE: To develop intermediate term storage media suitable for Chinese eye banks. METHODS: Corneal buttons of rabbits were stored in DX solution freshly prepared. After storage for several days, the survival rate of the corneal endothelial cells was examined, enzymohistochemical staining and ultrastructural examinations were carried out for the buttons. Thirty-seven human corneas stored in DX solution for 3 - 11 days were used for corneal transplantation, clinically. RESULTS: There was no significant difference between rabbit corneal buttons stored in DX sol. and in Optisol in any indices studied. 37 grafts were all transparent in 1 week after transplantation, and the mean endothelial cell density was (2,204.56 +/- 689.56) cells/mm(2). CONCLUSION: As a safe and efficient intermediate term (about 1 week) storage medium, DX sol. is appropriate for Chinese eye banks.

Adrenal Cortex Hormones↗

PubMed2000

[Experimental study on herpes simplex virus-1 functional gene latency in cornea].

OBJECTIVE: To investigate the possible existence of herpes simplex virus-1 (HSV-1) functional gene latency in cornea. METHODS: A herpes simplex keratitis (HSK) model was established in New Zealand White (NZW) rabbit corneas, latently infected corneas were transplanted to one eye of each naive NZW rabbit. One week after the operation, the corneal buttons were removed and divided into three portions. One portion was processed for HSV-1 antigen detection, another was for HVS-1 latency associated transcript (LAT), thymidine kinase (TK) and DNA polymerase gene detections by polymerase chain reaction (PCR), and the last portion after tissue culture for 3 weeks, it was co-cultured with rabbit kidney cells (RK) for one week, then the expression of HSV-1 antigen in the RK cells and this portion of corneal button was detected. RESULT: In the 15 corneal samples negative for HSV-1 antigen, LAT gene was detected in 8 samples, TK gene in 10 and DNA polymerase gene in 6 samples. HSV-1 antigen was detected in 3 samples of RK cells and 6 cultured corneal samples. CONCLUSION: HSV-1 functional genes are retained in latently infected cornea.

Animals↗

PubMed1999

The human REV1 gene codes for a DNA template-dependent dCMP transferase.

DNA is frequently damaged by various physical and chemical agents. DNA damage can lead to mutations during replication. In the yeast Saccharomyces cerevisiae, the damage-induced mutagenesis pathway requires the Rev1 protein. We have isolated a human cDNA homologous to the yeast REV1 gene. The human REV1 cDNA consists of 4255 bp and codes for a protein of 1251 amino acid residues with a calculated molecular weight of 138 248 Da. The human REV1 gene is localized between 2q11.1 and 2q11.2. We show that the human REV1 protein is a dCMP transferase that specifically inserts a dCMP residue opposite a DNA template G. In addition, the human REV1 transferase is able to efficiently and specifically insert a dCMP opposite a DNA template apurinic/apyrimidinic (AP) site or a uracil residue. These results suggest that the REV1 transferase may play a critical role during mutagenic translesion DNA synthesis bypassing a template AP site in human cells. Consistent with its role as a fundamental mutagenic protein, the REV1 gene is ubiquitously expressed in various human tissues.

Amino Acid Sequence↗

PubMed1999

Augmentation of transvascular transport of macromolecules and nanoparticles in tumors using vascular endothelial growth factor.

The goal of this investigation was to measure changes in vascular permeability, pore cutoff size, and number of transvascular transport pathways as a function of time and in response to vascular endothelial growth factor (VEGF), placenta growth factor (PIGF-1 and PIGF-2), or basic fibroblast growth factor (bFGF). Two human and two murine tumors were implanted in the dorsal skin chamber or cranial window. Vascular permeability to BSA (approximately 7 nm in diameter) and extravasation of polyethylene glycol-stabilized long-circulating liposomes (100-400 nm) and latex microspheres (approximately 800 nm) were determined by intravital microscopy. Vascular permeability was found to be temporally heterogeneous. VEGF superfusion (100 ng/ml) significantly increased vascular permeability to albumin in normal s.c. vessels, whereas a 30-fold higher dose of VEGF (3000 ng/ml) was required to increase permeability in pial vessels, suggesting that different tissues exhibit different dose thresholds for VEGF activity. Furthermore, VEGF superfusion (1000 ng/ml) increased vascular permeability to albumin in a hypopermeable human glioma xenograft in cranial window, whereas VEGF superfusion (10-1000 ng/ml) failed to increase permeability in a variety of hyperpermeable tumors grown in dorsal skin chamber. Interestingly, low-dose VEGF treatment (10 ng/ml) doubled the maximum pore size (from 400 to 800 nm) and significantly increased the frequency of large (400 nm) pores in human colon carcinoma xenografts. PIGF-1, PIGF-2, or bFGF did not show any significant effect on permeability or pore size in tumors. These findings suggest that exogenous VEGF may be useful for augmenting the transvascular delivery of larger antineoplastic agents such as gene targeting vectors and encapsulated drug carriers (typical range, 100-300 nm) into tumors.

Animals↗

PubMed1999

Available volume fraction of macromolecules in the extravascular space of a fibrosarcoma: implications for drug delivery.

Steric exclusion of molecules in the extravascular space of tissues can be quantified by the available volume fraction (K(AV)). Despite its clinical importance, however, there is a paucity of data in the literature regarding the available volume fraction of macromolecules in the extravascular space of tumor tissues. In this study, we quantified K(AV) of inulin, BSA, and dextran molecules of Mr 10,000-2,000,000 in polymer gels and fibrosarcoma tissues. The measurement involved: (a) sectioning of gels or tumor tissues into thin slices (approximately 600 microm) using a Vibratome, (b) ex vivo incubation of the slices in solutions containing fluorescently labeled tracers, and (c) quantification of the equilibrium tracer concentrations in both slices and solutions. We found that K(AV) in gels decreased monotonically when the Mr of dextran was increased from Mr 10,000 to 2,000,000. However, K(AV) in tumor tissues was insensitive to the molecular weight of dextran in the range between Mr 10,000 and 40,000. There was a sharp decrease in K(AV) from 0.28 +/- 0.14 to 0.10 +/- 0.06 when the molecular weight was increased from Mr 40,000 to 70,000. In addition to the molecular weight dependence, K(AV) was heterogeneous in tumors, with intertumoral difference being greater than intratumoral variation. The interstitial fluid space, which was quantified by K(AV) of inulin, was 50% of the total tissue volume. These data indicate that the fraction of the extravascular volume in tumors that is accessible to large therapeutic agents is heterogeneous and depends on the size of agents.

Animals↗

PubMed1999

BRCA1 inhibition of estrogen receptor signaling in transfected cells.

Mutations of the breast cancer susceptibility gene BRCA1 confer increased risk for breast, ovarian, and prostatic cancers, but it is not clear why the mutations are associated with these particular tumor types. In transient transfection assays, BRCA1 was found to inhibit signaling by the ligand-activated estrogen receptor (ER-alpha) through the estrogen-responsive enhancer element and to block the transcriptional activation function AF-2 of ER-alpha. These results raise the possibility that wild-type BRCA1 suppresses estrogen-dependent transcriptional pathways related to mammary epithelial cell proliferation and that loss of this ability contributes to tumorigenesis.

BRCA1 Protein↗

PubMed1999

[Content of metals in different diameter airborne particles and effect on micronuclei formation in human lymphocytes].

Using a five stage sampling scheme, airborne particles were collected in a residential area of Taiyuan city. The contents of four metals, including Ni, Pb, Cd and Cr in different diameter airborne particles were determined by atomic absorption spectrophotometry. The mutagenicity of the extracts of airborne particles was investigated by means of Cytokinesis-blocking(CB) method. The results showed that the pollution of airborne particles in the residential area was very serious. The smaller the airborne particles are the more it contains metal elements. The metal content of the particles less than 1.1 microns is the highest among different diameter airborne particles. The extracts of airborne particles induced a significant increase in micronuclei formation to a certain degree, especially the particles less than 1.1 microns increased in micronuclei formation. It is suggested that the extracts of different diameter particles are with strong mutagenicity.

Air Pollutants↗

PubMed1999

Characteristics of I(K) and its response to quinidine in experimental healed myocardial infarction.

INTRODUCTION: Mechanisms and drug treatment of serious ventricular arrhythmias in patients with healed myocardial infarction (HMI) are incompletely understood, in part because the electrophysiology and pharmacology of myocytes from noninfarcted regions of HMI hearts are not well characterized. METHODS AND RESULTS: We studied the delayed rectifier potassium current (I(K)) and quinidine responsiveness of single left ventricular subendocardial myocytes isolated from the region remote to the border zone of healed infarct myocardium (4 to 6 mm from scar edge) in cat hearts 2 months after coronary artery occlusion. Subendocardial cells isolated from corresponding regions of normal cat hearts provided controls. I(K) activation and tail currents were recorded using whole cell, voltage clamp techniques. Membrane capacitance of cells remote to HMI (187 +/- 7 pF) was significantly greater than normal (155 +/- 6 pF; P < 0.001). Action potential durations (APDs) recorded from myocytes in remote regions were prolonged (APD90 = 247 +/- 10 msec) compared to normal (214 +/- 11 msec; P < 0.05). Quinidine (1 microM) significantly prolonged APD90 in normal cells but not in remote cells. Density of I(K) (tail current) was significantly decreased in remote cells (3.1 +/- 0.3 pA/pF) compared to normal (3.9 +/- 0.3 pA/pF; P < 0.05), and voltage-dependent activation of I(K) was shifted in the positive direction. Quinidine had significantly less incremental blocking effect on I(K) already blunted by regional hypertrophy compared to its effect on normal cells in remote cells. IC50 shifted to 0.95 microM in remote cells compared with 0.50 microM in normal cells. CONCLUSION: Cells in noninfarct region remote from the scar are hypertrophied and display altered electrophysiology. Their reduced I(K) responsiveness to quinidine may explain, in part, failure of quinidine to prolong APD in such cells. Moreover, dispersion of repolarization may be decreased by the effect of quinidine on normal cells.

Action Potentials↗

PubMed1999

Altered growth and viral gene expression in human papillomavirus type 16-containing cancer cell lines treated with progesterone.

This study explores interactions between high-risk human papillomavirus type 16 (HPV-16) and the female sex hormone progesterone in the growth of tumor cells and viral oncogene expression. For both the cervical cancer cell line CaSki containing integrated HPV-16 DNA and the laryngeal carcinoma cell line HEp-2 transfected with HPV-16 DNA, prolonged progesterone treatment enhances their colony formation efficiency both on plastic surface and in soft agar. In contrast, progesterone has no effect on the HPV-negative cervical cancer cell line C-33A or the untransfected HEp-2 parental cells. Progesterone increases HPV-16 E6/E7 oncogene transcription in both HPV-16-containing cell lines. A detectable increase requires at least 3 days of treatment, and this delayed response may be due, at least in part, to increased stability of viral transcripts as determined by actinomycin D treatment. The progesterone antagonist RU 486 and nuclease-resistant oligomers containing HPV-16 progesterone response element are able to abrogate the enhancement by progesterone on cell growth and E6/E7 gene transcription. Taken together, these results support the notion that progesterone can be a cofactor in HPV-related malignancies.

Carcinoma, Squamous Cell↗

PubMed1999

[Expression of transforming growth factor alpha and its relationship with HBV infection in hepatocellular carcinomas].

OBJECTIVE: To assess the expression of TGF alpha in hepatocellular carcinoma and its relationship with HBV infection. METHODS: Using in situ hybridization and streptavidin-peroxidase immunohistochemistry to detect TGF alpha mRNA, TGF alpha protein and HBV DNA in 53 cases of HCC and 14 cases of controls. RESULTS: Positive rates of TGF alpha mRNA and TGF alpha protein in carcinoma tissue were 30.2% and 73.6% respectively, which were higher than in normal controls (P < 0.05). The expression of TGF alpha mRNA and TGF alpha protein was increased significantly in dysplastic liver cells (DLC) locating aside from the tumor tissue in comparing with those of non-dysplastic liver cells (NDLC) (P < 0.05). Positive rates of HBV DNA in carcinoma tissue and paratumorous liver tissue were 56.6% and 60.4% respectively, which were higher than in the normal controls (P < 0.001). Positive rate of HBV DNA in the nuclei of tumor tissues, tissue of the dysplastic areas and non-dysplastic areas was lowering down successively (P < 0.05). There was a significant relationship between expression of TGF alpha mRNA and TGF alpha protein in the carcinoma tissues and HBV DNA in the tumorous and its surrounding tissues respectively. CONCLUSIONS: Expression of TGF alpha in carcinoma tissues was closely associated with the existence of HBV DNA and TGF alpha may participate in the early stage of liver carcinogenesis. The increased expression of HBV DNA in nuclei may serve as an important morphology marker in distinguishing carcinoma from DLC and NDLC.

Carcinoma, Hepatocellular↗

PubMed1998

Endothelial cell death, angiogenesis, and microvascular function after castration in an androgen-dependent tumor: role of vascular endothelial growth factor.

The sequence of events that leads to tumor vessel regression and the functional characteristics of these vessels during hormone-ablation therapy are not known. This is because of the lack of an appropriate animal model and monitoring technology. By using in vivo microscopy and in situ molecular analysis of the androgen-dependent Shionogi carcinoma grown in severe combined immunodeficient mice, we show that castration of these mice leads to tumor regression and a concomitant decrease in vascular endothelial growth factor (VEGF) expression. Androgen withdrawal is known to induce apoptosis in Shionogi tumor cells. Surprisingly, tumor endothelial cells begin to undergo apoptosis before neoplastic cells, and rarefaction of tumor vessels precedes the decrease in tumor size. The regressing vessels begin to exhibit normal phenotype, i.e., lower diameter, tortuosity, vascular permeability, and leukocyte adhesion. Two weeks after castration, a second wave of angiogenesis and tumor growth begins with a concomitant increase in VEGF expression. Because human tumors often relapse following hormone-ablation therapy, our data suggest that these patients may benefit from combined anti-VEGF therapy.

Androgens↗

PubMed1998

Regulation of transport pathways in tumor vessels: role of tumor type and microenvironment.

Novel anti-neoplastic agents such as gene targeting vectors and encapsulated carriers are quite large (approximately 100-300 nm in diameter). An understanding of the functional size and physiological regulation of transvascular pathways is necessary to optimize delivery of these agents. Here we analyze the functional limits of transvascular transport and its modulation by the microenvironment. One human and five murine tumors including mammary and colorectal carcinomas, hepatoma, glioma, and sarcoma were implanted in the dorsal skin-fold chamber or cranial window, and the pore cutoff size, a functional measure of transvascular gap size, was determined. The microenvironment was modulated: (i) spatially, by growing tumors in subcutaneous or cranial locations and (ii) temporally, by inducing vascular regression in hormone-dependent tumors. Tumors grown subcutaneously exhibited a characteristic pore cutoff size ranging from 200 nm to 1.2 microm. This pore cutoff size was reduced in tumors grown in the cranium or in regressing tumors after hormone withdrawal. Vessels induced in basic fibroblast growth factor-containing gels had a pore cutoff size of 200 nm. Albumin permeability was independent of pore cutoff size. These results have three major implications for the delivery of therapeutic agents: (i) delivery may be less efficient in cranial tumors than in subcutaneous tumors, (ii) delivery may be reduced during tumor regression induced by hormonal ablation, and (iii) permeability to a molecule is independent of pore cutoff size as long as the diameter of the molecule is much less than the pore diameter.

Adenocarcinoma↗

PubMed1998

Transvascular drug delivery in solid tumors.

The microvessel wall is a barrier for the delivery of various therapeutic agents to tumor cells. Tumor microvessels are, in general, more permeable to macromolecules than normal vessels. The hyperpermeability is presumably due to the existence of large pore structures in the vessel wall, induced by various cytokines. The cutoff pore size is tumor dependent, as determined by transport studies of nanoparticles. The vascular permeability is heterogeneous in tumors and dependent on physicochemical properties of molecules as well as the ultrastructure of the vessel wall. The ultrastructure is dynamic and can be modulated by the tumor microenvironment. The microenvironment itself can be altered by the transvascular transport because the transport may facilitate angiogenesis, reduce blood flow, and induce interstitial hypertension in tumors. Future studies of transport need to address mechanisms of the barrier formation and emphasize development of novel strategies for circumventing or exploiting the vascular barrier.

Animals↗

PubMed1998

[The effects of transcutaneous electrical stimulation during sleep on obstructive sleep apnea].

OBJECTIVE: To study the effects of transcutaneous electrical stimulation during sleep on obstructive sleep apnea syndrom (OSAS). METHOD: Sixteen patients with OSAS were studied by polysomnography during all-night sleep with and without submental transcutaneous electrical stimulation (TES) of the genioglossus. RESULT: Fourteen of the 16 patients (87%) who accepted the TES were treated successfully (reduction of Al > 50%). The average apnea index showed a decrease of 29 events per hour when the TES were performed (P < 0.001). The average apnea time decreased from 22 to 7 sec (P < 0.001). The apnea time/TST decreased from 27% +/- 11% to 7% +/- 3%. The lowest SaO2 increased from 71% to 87% (P < 0.001). TES did not cause arousal. The sleep stages of SWS, and REM sleep effect (SE) increased significantly. CONCLUSION: TES is a conservative but effective treatment in patients with obstructive sleep apnea syndrome, although it failed to improve central sleep apnea.

Aged↗

PubMed1998

[A preliminary observation on nuclear changes of human corneal endothelial cells in different kinds of corneal diseases].

OBJECTIVE: To investigate the influence of different kinds of corneal diseases on corneal endothelial cells. METHODS: The endothelial cells of 91 corneal buttons obtained at the time of penetrating keratoplasty (PKP) were stained by 1% alizarin red and 0.25% trypan blue and observed under biomicroscope. RESULTS: Binuclear and polynuclear endothelial cells were found in every buttons. CONCLUSION: Under special conditions, the human corneal endothelial cells possibly have stronger ability of mitosis and compensation.

Adolescent↗