Search PubMed⌕ Search

Biomedical subjects

J Fan

Publications and source records attributed to J Fan.

At least 325 records · Page 18Linked to original sources
PubMed1992

Membrane transport of folate compounds.

All eukaryotic cells and some prokaryotes that are unable to synthesize folic acid utilize membrane-associated transport systems for acquisition of the pre-formed vitamin or its coenzyme forms from external sources. These transport systems, in addition to providing folates essential for cell replication, are also important because of their role in the internalization of antifolates such as Methotrexate (MTX) that are used extensively in cancer chemotherapy. Information about the components and mechanism of folate transport systems has been derived, in large part, from studies with Lactobacillus casei and L1210 mouse leukemia cells, which serve as convenient models for prokaryotes and eukaryotes, respectively. L. casei contain a single folate transport system whose Kt value (i.e., concentration for half-maximum rate of uptake) for the preferred substrate folate is in the nanomolar range. The hydrophobic membrane-associated folate transport protein (18 kDa) has been purified to homogeneity and characterized. Expression of this transporter is repressed in cells grown on high concentrations (microM) of folate. L1210 cells contain two separate transport systems for folate compounds: (1) the low affinity system (Kt values for the preferred substrates 5-methyl- and 5-formyltetrahydrofolate and MTX in the microM range); and (2) the high affinity system (Kt for folate in the nM range). Fluorescein and biotin derivatives of MTX and folate, after conversion to N-hydroxysuccinimide esters, can be attached covalently to the transporters. These probes have been used for visualizing the transporters by fluorescence and electron microscopy and for their purification to homogeneity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Miniature urea sensor based on H(+)-ion sensitive field effect transistor and its application in clinical analysis.

An urea-ENFET (Enzyme field effect transistor) probe was made by covering one of the grids of the dual ISFET (Ion sensitive field effect transistor) with a membrane of cross-linked bovine serum albumin (BSA)-urease and the other with cross-linked BSA, and the response characteristics of the probe was then tested through differential measurements. In different concentrations of phosphate buffer, the sensor responded to various concentrations of urea solution within 10-60s. From the calibration curve plotted on logarithmic scales a linear concentration range of 1.0-8.0 mg/dl was acquired, and the correlation coefficient and response sensitivity were 0.997 and 50mV/dec. (mg/dl), respectively. However, in dilute urea solution, the sensor responded linearly to the contents of urea over the range of concentration of 0.1-1.0 mg/dl with a correlation coefficient of 0.998 and a response sensitivity of 12-15mV/mg/dl. The standard deviation and the variation coefficient for 20 performances responding to 100mg/dl urea in 0.01M pH7.0 phosphate buffer were found to be 1.39mV and 1.44%, respectively. The urea-ENFET was used for the determination of BUN (Blood urea nitrogen) and the BUN values were compared with those determined by enzymatic method, the repression equation and correlation coefficient for 50 assays were y = -0.1272 + 0.9695x and r = 0.9912, respectively. When the urea-ENFET was used for determining urea either in buffer solution or in serum for 250 runs over a period of 1.5 months (the enzyme FET was stored at 4 degrees C between measurements during this period), the observed decrease of response sensitivity was only about 10%.(ABSTRACT TRUNCATED AT 250 WORDS)

Biosensing Techniques↗
PubMed1992

Induction of fatty streak-like lesions in vitro using a culture model system simulating arterial intima.

In this study a two-compartment culture model of arterial intima was used for the in vitro induction of fatty streaklike lesions. The apparatus consisted of upper and lower compartments separated by a human amnion membrane stretched between them. Human umbilical vein endothelial cells (HUVECs) were cultured to confluence on the stromal surface of the amnion membrane. Maximal migration of blood mononuclear cells (MCs) through the HUVEC monolayer in response to a f-Met-Leu-Phe gradient was observed at 10(-8) mol/l; the migration was 3.29 times greater than that observed under the condition of random migration (control). In the study of MC transformation into lipid-laden cells in the amnion membrane (foam cell formation in 'arterial intima'), 10(6) MCs were incubated, in the presence of freshly prepared low-density lipoprotein (LDL; 100 microgram/ml). The lipid loading of MCs was time dependent. After 12 hours' incubation, 39% of the MCs that migrated into the amnion membrane contained a small number of lipid droplets, whereas the remaining 61% showed no lipid droplets. Only 1.7% of the cells contained a high number of lipid droplets in the cytoplasm and took on the appearance of foam cells. With time, the number of lipid-laden cells and the amounts of intracytoplasmic lipid droplets gradually increased. At 72 hours after incubation, 65.4% of the MCs were loaded with lipid droplets, and 20.9% of them, an eightfold increase over 12 hours of incubation, showed a foamy cell appearance. Because MCs consist of 70% monocytes and 30% lymphocytes, about 93% of the monocytes were filled with lipid after a 72-hour incubation. Ultrastructural examination showed that lipid-laden cells took on macrophage characteristics, such as wide and heterogeneous cytoplasm, indented nuclei, and abundant lysosomes. A minority of the MCs in the amnion were considered lymphocytes; they had scanty cytoplasm, round nuclei with abundant heterochromatin, no lysosomes, and no lipid vacuoles. In conclusion, the formation of an in vitro fatty streaklike lesion is demonstrated, and this is reminiscent of in vivo human atherogenesis.

Amnion↗
PubMed1992

Endothelin. Immunohistologic localization in aorta and biosynthesis by cultured human aortic endothelial cells.

BACKGROUND: Endothelin-1 (ET-1) has been shown to exist in many organs and to have various biologic functions including vasoconstriction. However, an exact location of ET gene expression of the tissues is not fully investigated. Human aortic tissue was examined to elucidate the exact location of ET gene expression. EXPERIMENTAL DESIGN: Human aortas were obtained at autopsy and fixed in either conventional 10% formalin or 3% paraformaldehyde. The aortic thin sections were subjected to examinations of an immunohistochemistry and in situ hybridization of ET-1. Human aortic endothelial cells were cultured by a previously reported method. ET-1 released in the supernatant from the cultured endothelial cells was radioimmunoassayed. RESULTS: Immunohistologic study of ET-1 revealed a linear staining of the endothelial monolayer and diffuse staining in the intimal and medial smooth muscle cells on human aorta except for fetal aorta. In situ hybridization signals were intense in the endothelial cells from the elderly as well as younger subjects as examined with 35S-labeled anti-sense probe RNA. Fetal aortic endothelial cells revealed the least signals that meant developing but still immature gene translation. Smooth muscle cells showed positive but weak in situ hybridization signals. Control immunohistologic and hybridization studies were negative. ET-1 biosynthesis by cultured human aortic endothelial cells was invariably low in the subjects under the age of 50, ranging from 0.23 to 0.40 pmol/1 x 10(5) cells for 3 days. On the other hand, endothelial cells from the elderly subjects generally synthesized a greater amount of endothelin in vitro. CONCLUSIONS: These findings indicate that ET-1 is most highly expressed in endothelial cells, although not as highly but certainly, expressed in intimal and medial smooth muscle cells. This fact gives a new insight into the biophysiologic and pathologic roles of ET. In addition, these methods are applicable to investigate the gene expression of ET-1 in all organs and tissues.

Adolescent↗
PubMed1992

[Effect of depletion of glucocorticoid receptor in the production of multiple organ failure during endotoxemia].

Endotoxin (20 mg/kg B.W.) was injected intravenously to control (n = 12) and glucocorticoid receptor (GR) depletion rat model (n = 13, in which more than 80 percent of GR were blocked with a potent GR antagonist RU486). Four hours after injection of endotoxin, the changes in serum acid phosphatase (ACP) activity, phospholipase A2 (PLA2) activity and lipid peroxide (LPO) level were determined. The results showed that all of the indices were increased in the control rats after endotoxin injection (ACP 17.6 +/- 1.9 U/dL, PLA2 325.6 +/- 99.1 U, and LPO 6.0 +/- 0.4 nmol MDA.ml-1), but they were increased to even higher levels in the rats injected with both RU486 and endotoxin (ACP 30.1 +/- 7.6 U/dL, PLA2 633.7 +/- 70.6 U, and LPO 8.2 +/- 1.1 nmol MDP.ml-1). Furthermore, after presented multiple organ damage pathologically. These results suggested that the glucocorticoid insufficiency caused by the decrease of GR after severe trauma or shock may exacerbate the damage of endotoxin to the organs, so much so that glucocorticoid insufficiency might result in multiple organ failure. This article also discussed problem of glucocorticoid treatment.

Acid Phosphatase↗
PubMed1991

A population-based case-control study of endometrial cancer in Shanghai, China.

A case-control study of 268 patients with endometrial cancer and 268 population controls was conducted during 1988-1990 in Shanghai, China, to evaluate etiologic factors in a population whose risk had not been substantially altered by the use of exogenous estrogens. In spite of this, the major risk factors resembled those found in other studies. The risk of endometrial cancer was significantly elevated among nulligravidas (OR = 5.4, 95% CI = 2.0-14.6) and decreased with number of pregnancies (p less than 0.01). Late age at menopause was associated with increased risk, while early age at menarche was unrelated. Use of oral contraceptives for more than 2 years was associated with a reduction in endometrial cancer risk (OR = 0.4, 95% CI = 0.1-1.2), while short-term use of oral contraceptives and other methods of contraception were unrelated. Obesity was a strong predictor of risk, with women in the highest quartile of weight having 2.5 times the risk of those in the lowest quartile. In contrast to many other studies, cigarette smokers were at elevated risk (OR = 1.7, 95% CI = 0.9-3.0). Risk was also elevated among women reporting a history of gall-bladder disease, polycystic ovaries, menstrual symptoms, and non-estrogen hormone use.

Abortion, Induced↗
PubMed1991

Biotin derivatives of methotrexate and folate. Synthesis and utilization for affinity purification of two membrane-associated folate transporters from L1210 cells.

Biotin derivatives of methotrexate and folate (2-(biotinamido)ethyl-1,3'-dithiopropionyldiaminopentyl methotrexate and/or folate), in which carboxyl groups of the functional components are joined by a disulfide-containing spacer, have been synthesized, purified by DEAE-Trisacryl chromatography, and characterized by high pressure liquid chromatography and mass spectrometry. These bifunctional, dissociable probes were utilized for the single-step purification to homogeneity of two folate transport proteins (43 and 39 kDa) from L1210 cells. Treatment of the 39-kDa protein with peptide N-glycosidase F produced a smaller component (32 kDa); the 43-kDa protein, conversely, was unchanged by this procedure. When the 39-kDa transporter in intact cells was labeled with a fluorescein derivative of folate and then treated with phosphoinositol-specific phospholipase C, complete loss of fluorescence was observed. Alternatively, there was no change in fluorescence when the 43-kDa transporter was labeled with a fluorescein derivative of methotrexate and treated with the enzyme. These results indicate that the 43-kDa transporter is a nonglycosylated, integral membrane protein, whereas the 39-kDa counterpart is heavily glycosylated and anchored exofacially to the membrane by a glycosylphosphatidylinositol component.

Animals↗
PubMed1991

[A preliminary study on the cellular mechanism of hypotensive effect of high calcium diet in spontaneously hypertensive rats].

Significant reduction of both systolic blood pressure and body weight could be observed in SHRs after being fed with high calcium diet for about 7 weeks (P less than 0.01), with some changes of characteristics in ion transport in RBCs. The intracellular content of Na+, K+, the basic and calmodulin-stimulated activity of calcium-pump, and the calcium membrane binding ability on RBCs in SHR were determined. The intracellular content of K+ and the calmodulin-stimulated activity of calcium-pump in SHR fed with high calcium diet were significantly higher than those in SHR fed with normal calcium diet (P less than 0.01). The ratio of intracellular Na+ to K+ and the calcium membrane binding ability were found to be significantly reduced in SHR fed with high calcium diet (P less than 0.05). The systolic blood pressure in SHR fed with high calcium diet was found to be correlated inversely with the calmodulin-stimulated activity of calcium-pump and the intracellular K+ content (r = -0.720, r = -0.663 respectively, P less than 0.01). Thus, the hypotensive effect of chronic high calcium diet may be mediated through the changes in plasma ion transport, which most likely resulted from the changes in composition and structure of plasma membrane. The exact mechanism concerning the reduced calcium membrane binding ability in SHR fed with high calcium diet still remained unknown.

Animals↗
PubMed1990

Visualization of folate transport proteins by covalent labeling with fluorescein methotrexate.

Fluorescein-methotrexate (F-MTX) has been synthesized by an improved procedure and separated via chromatography on DEAE-Trisacryl into the alpha- and gamma-isomers. Purity of each isomer was verified by TLC, HPLC, and absorbance spectra. Identity of the alpha- and gamma-isomers was established by the following biological criteria: the gamma-isomer inhibited dihydrofolate reductase and was hydrolyzed by carboxypeptidase G2 (at the pteroate-glutamate linkage). The alpha-isomer, conversely, was unreactive in both systems, which is consistent with the specificity of these enzymes. Based upon these results, the gamma-isomer was selected for covalent labeling of proteins. Fluorescent bands were observed when the 22 kDa human dihydrofolate reductase and the 18 kDa folate transporter from Lactobacillus casei were treated with gamma-F-MTX (activated by N-hydroxysuccinimide) and subjected to SDS-PAGE. The probe was also useful for visualizing in situ the micromolar folate transport protein in L1210 cells.

Animals↗
PubMed1990

Insulin-like growth factor-I enhances luteinizing hormone binding to rat ovarian theca-interstitial cells.

We tested the hypothesis that insulin-like growth factor-I (IGF-I) stimulates ovarian androgen production by increasing theca-interstitial cell luteinizing hormone (LH) binding affinity and/or binding capacity. We then investigated the role of transcriptional and translational events in mediating these actions of IGF-I. LH bound to saturable, high affinity binding sites on rat ovarian theca-interstitial cells. Preincubation with LH produced a decrease in LH binding capacity with no effect on LH binding affinity. Treatment with IGF-I, both in the absence and presence of LH, increased LH binding capacity 1.5- to 2-fold with no change in LH binding affinity. Androgen production was increased progressively by LH, suggesting that LH-stimulated steroidogenesis is not tightly coupled to LH receptor downregulation. IGF-I increased androgen synthesis in proportion to its upregulation of LH binding capacity. Transcriptional inhibition with dichlorobenzimidazole riboside inhibited the IGF-I-mediated increase in LH binding capacity but had no effect on androgen production. Translational inhibition with cycloheximide inhibited both the IGF-I-mediated increase in LH binding and stimulation of androgen synthesis. We conclude that IGF-I increases theca-interstitial cell LH binding capacity and reverses the LH-induced downregulation of LH binding sites. The enhancement of LH binding by IGF-I is compatible with transcriptional mediation whereas the effect of IGF-I on androgen synthesis appears to be mediated by a direct effect of the peptide on the translational process(es) involved in steroidogenesis.

Androsterone↗
PubMed1989

Visualization of membrane-associated folate transport proteins.

Transport of Methotrexate (MTX) into cells, via the "reduced folate" transport system, is a critical factor in the effectiveness of the drug in cancer chemotherapy, and defective transport is one of the principal types of resistance to MTX. Probes capable of detecting membrane-associated folate transport proteins (ftp's) in individual cells are potentially useful for identifying structural and functional domains and for investigating mechanisms of substrate translocation. Polyclonal antibody to highly purified ftp from Lactobacillus casei, in conjunction with a second, gold-labeled antibody, has been used to visualize, via electron microscopy, the protein in Triton-treated membrane fragments and in the membrane and cytoplasm of spheroplasts. To visualize ftp in L1210 cells, the substrate-binding site was first labeled covalently with activated fluorescein-Methotrexate, and the cells were then treated with anti-fluorescein antibody and the gold-labeled antibody.

Animals↗
PubMed1989

Hyperkinetic hemodynamic pattern in some borderline hypertension: differential responses to alpha and beta agonists.

Twenty eight male borderline hypertensive patients(BH), mean age of 19.72 +/- 2.80 years, were studied and matched with 28 normal controls (NC). Alpha-adrenergic responsiveness was estimated with DPD15 (the dosage of neosynephrine required for an increase of diastolic pressure of 15mmHg); beta-adrenergic responsiveness with CD25 (the dosage of isoproterenol required for an increase of heart rate of 25 beats/minute). Using CD25 of 1.0ug (mean of the NC), the BH could be subdivided into two specific types: 13 patients (46%) whose CD25 less than 1.0 ug, 0.50 +/- 0.24 (m +/- SD) had a hyperkinetic pattern; the remaining 15 patients (54%) whose CD25 greater than 1.0ug, 1.76 +/- 0.32 (m +/- SD), had a normokinetic one. Values of DPD15 of the two types were comparable. Cardiac index (CI, L/min/M2) and total peripheral resistance (TPR, dynes/sec/cm-5) of the two types manifested significant differences, both p less than 0.001. When plotting CI and TPR versus CD25, good correlations were obtained. In the BH group, the coefficient r was -0.73 between CI and CD25, + 0.70 between TPR and CD25; correlations were poor when plotting versus DPD15. Similar correlations also happened in the NC. The present study suggests that coexistence of two different hemodynamic patterns may be due to the imbalance resulted from the interaction between alpha-adrenergic responsiveness and beta-adrenergic responsiveness.

Adrenergic alpha-Agonists↗
PubMed1989

[Studies on saponins from the leaves of Panax japonicus var. bipinnatifidus(Seem.)Wu et Feng].

Two new saponins, bipinnatifidusoside F1(XII) and F2(XIII), were isolated along with eleven known saponins from the dried leaves of Panax japonicus var.bipinnatifidus(Seem.)Wu et Feng collected in the Range of Qinling Mountains in China. By spectrometric analysis(FAB-MS,1H and 13CNMR,1H-1H COSY), their structures were elucidated as dammar-25(26)-ene-3 beta, 12 beta, 20(S),24 zeta-tetraol-(20-O-beta-D-glucopyranosyl)-3-O- beta-D-glucopyranosyl(1-2)-beta-D-glucopyranoside (bipinnatifidusodie F1) and dammar-22(23) ene-3 beta, 12 beta, 20(S),24 zeta-tetraol-(20-O-beta-D-glucopyranosyl)-3-O-beta- D-glucopyranosyl(1-2)-beta-D-glucopyranoside (bipinnatifidusoside F2), respectively. The known saponins were identified as ginsenoside F1,F2,F3,Rg2,Re,Rd,Rb1,Rb3, 24(S)-pseudoginsenoside F11, panasenoside and majoroside F1. Compared with bipinnatifidusoside F2, majoroside F3 was corrected as dammar-22(23)-ene-3 beta, 12 beta,20(S),24 zeta-tetraol-(20-O-beta-D- glucopyranosyl)-3-O-beta-D-glucopyranoside.

Chemical Phenomena↗
PubMed1987

DMSO potentiates aminonucleoside of puromycin nephrosis in rats.

Dimethyl sulphoxide (DMSO), 3 g/kg body weight, administered daily by the intraperitoneal route, potentiated the proteinuria and formation of tubular casts in aminonucleoside of puromycin (PA) induced nephrosis in Sprague-Dawley rats. The effect was evident at 4 as well as 8-9 days following PA administration. In the absence of PA, DMSO did not induce proteinuria or cast formation. The mechanism by which DMSO enhanced proteinuria and cast formation is not known.

Animals↗
PubMed1986

Analysis of surface deposits on intrauterine contraceptive devices.

Surface deposits on stainless steel contraceptive devices removed from the uterus after varying periods of insertion were examined and analyzed by means of scanning electron microscopy (SEM), X-ray energy dispersive analysis (XEDA), Augar electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and atomic absorption spectrophotometry for microquantitative analysis. The data obtained were compared with the data for copper-bearing IUDs (TCu200) obtained by the same method. The wire coils of stainless steel IUDs which had been in situ for 5 years showed no obvious changes, but copper wire coils showed varying degrees of erosion after the same period of time. Analysis clearly showed that the wire coils of both types of IUD were encrusted with deposits. Deposition began earlier on copper-bearing IUDs than on stainless steel IUDs (27 days and 3 months after insertion, respectively). This process began earlier than has previously been reported in the literature. The amount of deposit increased with duration of insertion, but there were large individual variations. The microanalysis showed that the principal component of the deposit on both types of IUD was calcium, which was present in the crystal form of calcium carbonate. The substances attaching to the crystals were similar to the nitrogenous organic compounds. We suggest that the mechanism regulating the deposited formation may be similar to that of calculus. The influence of these deposits on complications relating to IUD insertion, such as uterine bleeding and accidental pregnancy, is briefly discussed in this article. The subject should be studied in greater detail.

Calcium Carbonate↗
PubMed1986

Expression of the Epstein-Barr virus 138-kDa early protein in Escherichia coli for the use as antigen in diagnostic tests.

We have attempted to produce the 138-kDa early protein (ep 138) of Epstein-Barr virus (EBV) in Escherichia coli. This protein was found, by immunoprecipitation, to be a clinically relevant antigen, especially for the determination of the IgA-titer in patients with nasopharyngeal carcinoma (NPC). Since the expression of the entire ep 138 coding region was unsuccessful, we synthesized only the antigenic parts of this protein. Potential antigenic sites were predicted from the amino acid sequence by combining values for hydrophilicity with calculated estimates of the secondary structure. The two predicted fragments were found to be antigenic, but only one of them was stably expressed in E. coli as a non-fusion protein. This stable protein fragment was, in turn, able to stabilize the second antigenic fragment forming an autologous fusion protein, consisting exclusively of EBV-derived sequences. The resulting product reacts particularly well with IgA antibodies of NPC patients indicating its diagnostic value for NPC.

Antigens, Viral↗
PubMed1986

Detection of antibody to LAV/HTLV-III in sera from hemophiliacs in China.

Using ELISA, Western blots and immunofluorescence techniques, we identified seropositivity for lymphadenopathy-associated virus/human lymphotropic virus-III (LAV/HTLV-III) in 4 of 18 hemophiliacs and 1 AIDS patient. The four seropositive patients had received factor VIII prepared by Armour Company. The hemophiliacs are all asymptomatic. Given this documentation of introduction of LAV/HTLV-III into China, a national surveillance program is underway.

Acquired Immunodeficiency Syndrome↗