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Biomedical subjects

B Li

Publications and source records attributed to B Li.

At least 397 records · Page 22Linked to original sources
PubMed1998

In vivo expression of transforming growth factor-beta1 in humans: stimulation by cyclosporine.

BACKGROUND: Transforming growth factor-beta1 (TGF-beta1) is an immunoregulatory and fibrogenic cytokine. In an earlier in vitro study, we demonstrated that cyclosporine (CsA) increases TGF-beta1 transcription rate in human T lymphocytes. Herein, we explored whether CsA augments the in vivo expression of TGF-beta1 in humans. METHODS: The inherent difficulty in studying the in vivo effect of CsA in humans was circumvented by investigating stable end-stage renal disease patients who were preconditioned with CsA before their living donor renal transplantation. Sera and peripheral blood mononuclear cells were obtained from CsA-preconditioned patients and quantified for TGF-beta1 expression at the mRNA (by competitive polymerase chain reaction) and protein (sandwich enzyme-linked immunosorbent assay) levels. RESULTS: Our studies demonstrated a significant increase in TGF-beta1 expression after CsA therapy. The stimulatory effect was unique to TGF-beta1, and CsA did not increase interleukin (IL)-10, IL-6, IL-2, or tumor necrosis factor-alpha expression. CONCLUSIONS: Our first-time demonstration of a TGF-beta1-selective in vivo stimulatory effect of CsA in humans: (1) advances a TGF-beta1-centered hypothesis for the beneficial (immunosuppression) and detrimental (fibrosis, hypertension) effects of CsA use, and (2) broadens the mechanism of immunosuppressive action of CsA to include heightened expression of an endogenous immunosuppressive cytokine.

Cyclosporine↗
PubMed1998

Molecular characterization of type E Clostridium botulinum and comparison to other types of Clostridium botulinum.

Determination of nucleotide sequence upstream to the neurotoxin binding protein (NBP) gene of type E Clostridium botulinum has revealed an open reading frame whose stop codon is only 18 bp apart from the start codon of the NBP gene. Amino acid sequence derived from the corresponding nucleotide sequence suggested the existence of the open reading frame as a 47.8 kDa protein (P-48). Protein data bank search revealed that the 47.8 kDa protein has 80% sequence identity to P-47 of type F C. botulinum. The gene organization of type E. Clostridium botulinum was predicted and compared to other types of C. botulinum. In type E C. botulinum, genes for the P-48, the neurotoxin binding protein and the neurotoxin form an operon which was similar to that of type F C. botulinum. However, type E C. botulinum has a P-18 gene instead of P-21 gene observed in type F C. botulinum, both located upstream to their respective P-48/P-47 gene.

Amino Acid Sequence↗
PubMed1998

Genetic interaction between YPT6 and YPT1 in Saccharomyces cerevisiae.

Ypt6p, the yeast homologue of human RAB6, is required for protein trafficking at elevated temperatures. Biochemical data provide evidence that Ypt6p plays a role in an early step(s) of the secretory pathway: from ER to Golgi, or from cis to medial Golgi, or both. Here we show that overexpression of YPT1 suppresses the growth and secretion defects of a ypt6 temperature-sensitive (ts) strain. SLY1-20, encoding a dominant mutant allele that suppresses the lethal effect of YPT1, also suppresses the growth defect of a ypt6 ts strain. Conversely, SSD1, isolated as a suppressor of ypt6 ts, can suppress the growth defect of a ypt1 ts allele. These data suggest that Ypt6p has some redundant function with Ypt1p. However, overexpression of Ypt6p is toxic to a ypt1 ts strain, although it does not affect the growth of wild-type cells, suggesting that Ypt6p may sequester proteins shared with Ypt1p. This genetic evidence confirms the conclusion that Ypt6p is involved in an early step of the secretory pathway.

Biological Transport↗
PubMed1998

Intracellular calcium, DNase activity and myocyte apoptosis in aging Fischer 344 rats.

Myocyte apoptosis increases with age in Fischer 344 rats, but the multiple molecular events implicated in this phenomenon remain to be identified. Several defects involving Ca2+ homeostasis, pH, and the expression of p53 and genes of the Bcl-2 protein family may contribute to the activation of myocyte death. Therefore, changes in intracellular pH, cytosolic Ca2+, DNase I and DNase II were measured in myocytes isolated by enzymatic digestion from rats of different ages. Moreover, the expression of p53, Bcl-2 and Bax in these cells was determined. Measurements of intracellular pH by BCECF fluorescence at 3, 12 and 24 months showed that this parameter did not change with age: 3 months, 7.20+/-0.05; 12 months, 7.21+/-0.07; 24 months, 7.18+/-0.09. In contrast, diastolic Ca2+ determined by the Fura 2-AM method increased progressively from 99.8+/-1.9 nm at 3 months to 136.3+/-9.6 nm at 24 months (P<0.001). Concurrently, DNase I activity evaluated by plasmid digestion assay in myocytes increased 3.2-fold from 3 to 24 months (P<0.02). Conversely, pH-dependent-DNase II remained essentially constant with age. Western blotting performed on ventricular myocytes did not detect significant changes in p53, Bax and Bcl-2 proteins with age. Similarly, immunocytochemically, the fraction of myocytes labeled by p53, Bax and Bcl-2 did not change from 3 to 24 months. In conclusion, myocyte aging is characterized by an increase in diastolic calcium which may activate DNase I triggering apoptosis, independently from the expression of p53, Bax and Bcl-2 in the cells.

Aging↗
PubMed1998

Pressure-volume relationships in sheep mesenteric lymphatic vessels in situ: response to hypovolemia.

We applied the principles of cardiac mechanics to study the contraction cycles of postnodal sheep mesenteric lymphatic vessels in an in situ preparation. A segment of intestinal lymphatic was isolated from lymph input and provided with Krebs solution from a reservoir. Pressure-volume relationships were assessed under various transmural pressure conditions using videomicroscopic techniques to measure diameter changes and a miniature catheter pressure transducer to monitor intralymphangion pressure. The contraction cycles were quite variable but, on average, exhibited three phases of systole and three phases of diastole with periods of isovolumetric contraction and relaxation. Elevations of transmural pressure up to 4 cm H2O resulted in significant increases in stroke volume, ejection fraction, pulse pressure, and output/minute but not contraction frequency. Regression analysis of the end systolic (ESPVR) and end diastolic pressure-volume relations (EDPVR) revealed a linear ESPVR (r2 = 0.83 +/- 0.03) and exponential EDPVR (r2 = 0.83 +/- 0.02), a result that is similar to that observed in cardiac contraction cycles. Following a 25% whole blood volume bleed (a stimulus known to enhance lymphatic pumping), significant increases in stroke volume, ejection fraction, and output/minute were observed up to transmural pressures of 4 cm H2O. While an index used to assess cardiac contractility (end systolic elastance-Ees) was not observed to change after the bleed, a shift to the left of the end-systolic pressure-volume relations compared with the sham-bled group (significant shift of regression lines for ESPVR) suggested that hemorrhage exerted a positive inotropic effect on mesenteric lymphatics.

Animals↗
PubMed1998

Purification and physical characterization of cloned human cAMP phosphodiesterases PDE-4D and -4C.

Individual isozymes of family four cyclic-nucleotide phosphodiesterases (PDE-4s) were characterized and compared in order to advance our understanding of how PDE-4s regulate cAMP levels in cells. Full-length and shorter clones containing various functional domains were constructed and overexpressed using a recombinant baculovirus-infected Sf9 insect cell system. One form each of PDE-4C and 4D was purified 125- and 534-fold, respectively, using anion-exchange and affi-gel blue chromatography. The purified material was unaltered in size on SDS-polyacrylamide gels during purification and nearly homogeneous (> 95%) as estimated by both staining and immunoblotting. Approximately 1 mg of PDE-4D (74.7 kDa) and 3.7 mg of PDE-4C (61.4 kDa) could be isolated from a 6-L culture of cells. The physical characteristics of Stokes' radius and sedimentation coefficient for PDE-4 enzymes cloned from each of the four isogenes were determined using size-exclusion chromatography and sedimentation in glycerol gradients. Calculations indicate that both long and short forms can form dimers, although evidence for monomers and higher-order subunit association was seen. Furthermore, the results clearly show that all long and short forms of PDE-4 are highly asymmetric molecules. This work has shown that large amounts of PDE-4 proteins can be purified and characterized physically and enzymatically to yield information that will enable a greater understanding of how PDE-4 enzymes function in cells.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1998

A possible basic cortical microcircuit called "cascaded inhibition." Results from cortical network models and recording experiments from striate simple cells.

The robust behavior, the degree of response linearity, and the aspect of contrast gain control in visual cortical simple cells are (amongst others) the result of the interplay between excitatory and inhibitory afferent and intracortical connections. The goal of this study was to suggest a simple intracortical connection pattern, which could also play a role in other cortical substructures, in order to generically obtain these desired effects within large physiological parameter ranges. To this end we explored the degree of linearity of spatial summation in visual simple cells experimentally and in different models based on half-wave rectifying cells ("push-pull models"). Visual cortical push-pull connection schemes originated from antagonistic motor-control models. Thus, this model class is widely applicable but normally requires a rather specific design. On the other hand we showed that a more generic version of a push-pull model, the so-called cascaded inhibitory intracortical connection scheme, which we implemented in a biologically realistic simulation, naturally explains much of the experimental data. We investigated the influence of the afferent and intracortical connection structure on the measured linearity of spatial summation in simple cells. The analysis made use of the relative modulation measure, which is easy to apply but is limited to moving sinusoidal grating stimuli. We introduced two basic push-pull models, where the order of threshold nonlinearity and linear summation is reversed. Very little difference is observed with the relative modulation measure for these models. Alterative models, like half-wave squaring models, were also briefly discussed. Of all model parameters, the ratio of excitation to inhibition in the simple cell exerts the most crucial influence on the relative modulation. Linearity deteriorates as soon as excitatory and inhibitory inputs are imbalanced and the relative modulation drops. This prediction was tested experimentally by extracellular recordings from cat area 17 simple cells and we found that about 62% showed a significant deviation from linear behavior. The problem that individual basic push-pull models are hard to distinguish experimentally led us to suggest a different solution. In order to generically account for the observed behavior (e.g., imbalance of excitation versus inhibition), we suggested a rather generic version of a push-pull model where it no longer mattered about (the hard-to-distinguish) fine differences in connectivity. Thus, we introduced a new class of biophysically realistic models ("cascaded inhibition"). This model class requires very little connection specificity and is therefore highly robust against parameter variations. Up to 25 cells are connected to each target cell. Thereby a highly interconnected network is generated, which also leads to disinhibition at some parts of an individual receptive field. We showed that the performance of these models simulates the degree of linearity and its variability in recal simple cells with comparatively high accuracy. This behavior can be explained by the self-regulating properties of a cascaded inhibitory connection scheme by which the balance between excitation and inhibition at a given cell is improved by the joint network effects. The virtues and the generic design of this connection pattern, therefore, allow to speculate that it is used also in other parts of the cortex.

Animals↗
PubMed1998

Reciprocal expression of bcl-2 and p53 oncoproteins in urothelial dysplasia and carcinoma of the urinary bladder.

In order to investigate if and when the bcl-2 oncoprotein is activated in bladder tumorigenesis and its relationship with p53 overexpression and patient survival, we studied bcl-2 and p53 expression immunohistochemically in matched normal urothelium, dysplasia and cancer specimens selected by step-sectioning from 54 radically resected bladders for non-metastatic transitional cell carcinoma (TCC). In normal urothelium and mild dysplasia, bcl-2 was restricted to the basal cell compartment, while in moderate and severe dysplasia its expression was detectable also in the upper regions. Excess bcl-2 immunoreactivity was found in 27 (50%) of carcinomas, and a larger proportion of high-grade TCCs showed bcl-2 expression compared with that of low-grade TCCs (P < 0.05). Overexpression of p53 protein showed a increasing trend toward the progression of bladder tumorigenesis (P < 0.01) and a significant reciprocal correlation was found between bcl-2 and p53 expression in either various dysplasias (P < 0.01) or carcinoma (P < 0.05). With the evolution from mild dysplasia to carcinoma in individual cases, loss of bcl-2 expression was more frequently observed in superficial (P < 0.02) or low-grade carcinoma (P < 0.05) than in muscle-invasive or high-grade carcinoma. Furthermore, patients with negative immunostaining for both bcl-2 and p53 in cancer lesions had a significantly more favorable prognosis compared with those with positive immunostaining for the oncoproteins (P < 0.05), although bcl-2 by itself did not predict patient survival. We suggest that aberrant activated bcl-2, which is seen earlier than p53, appears to facilitate bladder tumorigenesis and to enhance tumor aggression in some extent.

Aged↗
PubMed1998

The effect of acetazolamide on passive and active transport of fluorescein across the blood-retina barrier in retinitis pigmentosa complicated by macular oedema.

BACKGROUND: The carbonic anhydrase inhibitor acetazolamide (AZM) reduces macular oedema in some patients with retinitis pigmentosa. To better understand the oedema-reducing effect of AZM, the effect of AZM on passive permeability and active transport of fluorescein across the blood-retina barrier was studied in patients with retinitis pigmentosa and varying degrees of macular oedema. METHOD: The selection of patients was based on an introductory examination including vitreous fluorometry for qualitative assessment of the vitreous. Macular oedema was graded by fluorescein angiographic leakage. The effect of AZM on the transport properties of the blood-retina barrier was determined by differential spectrofluorometry, in a randomised, double-masked, cross-over study, comprising 2 weeks' treatment with AZM (500 mg/day) and 2 weeks' treatment with placebo. The penetration ratio, defined as the ratio between vitreous concentration 3 mm in front of the retina and the plasma integral, was determined for fluorescein and its metabolite fluorescein glucuronide at 30-60 min and at 120 min after fluorescein injection. Passive permeability and unidirectional permeability in the direction vitreous to blood, due to outward active transport of fluorescein, were determined in those cases where the curves for vitreous concentration of fluorescein could be fitted to a mathematical model. Visual acuity was tested by use of ETDRS standard logarithmic charts. RESULTS: Twenty-two patients volunteered to participate in the study. Signs of significant vitreous detachment/liquefaction caused the exclusion of ten patients after the introductory examination. Nine patients with approximately intact vitreous and varying degrees of oedema completed the cross-over study. AZM treatment was related to a decrease in the penetration ratio of 21% for fluorescein (P=0.01) and of 22% for fluorescein glucuronide (P=0.004). Passive permeability and unidirectional permeability were determined in seven patients. AZM caused a decrease of 27% in the passive permeability of fluorescein (from 1.1 x 10(1) nm/s, P=0.031), and a 95% increase in unidirectional permeability of fluorescein (from 1.2 x 10(2) nm/s, P=0.047). AZM led to a reduction in the grade of macular oedema as determined by fluorescein angiography in three out of seven patients. Only small improvements (< or =5 letters) in visual acuity were noted. CONCLUSION: The present study indicates that the oedema-reducing effect of AZM is due to decreased leakage and stimulated active transport across the blood-retina barrier.

Acetazolamide↗
PubMed1998

Cytokine gene activity in AML cells in vivo in patients.

The proliferation of acute myelogenous leukemia cells is dependent upon cytokine stimulation. Additionally, there is a body of literature which reports that leukemia cells produce GMCSF, IL6, and other cytokines. The study reported here, using an rt-multiplex polymerase method, determined the presence or absence of transcripts in freshly obtained AML cells for the following cytokine or cytokine-related genes: IL 1beta, IL1ra, TNF alpha, GMCSF, IL6, flt 3, and hSCF. This demonstrated that leukemia cell populations usually contain transcripts for IL1beta, TNF alpha, flt 3 and flt 3 ligand in vivo and that transcripts for the other cytokines only appear after the leukemia cells are processed in vitro. The presence of TNF alpha transcripts appears to be associated with resistance to remission induction therapy. Furthermore, the transcript profile of the leukemia cells can change during remission induction therapy. The data also demonstrate the assessment of cytokine production by leukemia cells after in vitro manipulation should not be extrapolated to the in vivo situation.

Adult↗
PubMed1998

Adjuvant action of Chenopodium quinoa saponins on the induction of antibody responses to intragastric and intranasal administered antigens in mice.

Saponins extracted from the seed of Chenopodium quinoa (quinoa) were studied for their ability to act as mucosal adjuvants upon their intragastric or intranasal administration together with model antigens in mice. Quinoa saponins, co-administered intragastrically or intranasally with cholera toxin or ovalbumin, potentiated specific IgG and IgA antibody responses to the antigens in serum, intestinal and lung secretions. The potentiating effect of the saponins appeared, to some extent, mediated by increased permeability of the mucosa, allowing increased uptake of the antigen. The intragastric administration of 99mTc-radio-labeled human serum albumin together with quinoa saponins revealed an increased presence of the radiolabeled protein in blood, liver, spleen and lungs of mice. This study indicates the potential of quinoa saponins as adjuvants for mucosally administered vaccines.

Adjuvants, Immunologic↗
PubMed1998

Comparison of recombinant human PDE4 isoforms: interaction with substrate and inhibitors.

Four cyclic-nucleotide phosphodiesterase (PDE) genes belonging to the PDE4 family (PDE4A, 4B, 4C and 4D) have been identified. All four isogenes, including several deletions and alterations of the amino, carboxyl and central catalytic domains, were expressed in insect cells. Lysates were characterised for enzyme activity by using the Km for substrate and the EC50 for activation by the cofactor Mg2+. The catalytic domain alone appears to be sufficient for the normal enzymatic function of PDE4 proteins. Substrate affinity varied by less than 2-fold between catalytic-domain forms of the PDE4A, 4B and 4D isogenes and the long forms (PDE4A5, PDE4B1 and PDE4D3). The affinity for Mg2+ varied by less than 4-fold between long and catalytic-domain forms of PDE4A and 4B. The catalytic-domain form of PDE4D, however, had a 12-fold lower affinity for Mg2+ that was restored by including a portion of the amino-terminal domain, upstream conserved region-2 (UCR2). This result suggests that the Mg2+-binding site of PDE4D involves the UCR2 region. Inhibition of the PDE4 proteins by synthetic compounds is apparently affected differently by the domains. For PDE4B, the catalytic domain is sufficient for interactions with the inhibitors studied: IBMX, trequinsin, rolipram, TVX 2706, RP 73401 and RS-25344. For PDE4D the catalytic-domain form is less sensitive than the long form to inhibition by RS-25344, rolipram and TVX 2706, by 1463-, 11-and 12-fold, respectively. Addition of UCR2 to the catalytic-domain form of PDE4D restored all the lost sensitivities. The catalytic-domain form of PDE4A showed a reduced inhibitor affinity with RS-25344 and TVX 2706 by 77- and 90-fold, respectively. Both catalytic-domain and long forms of PDE4 isogenes interacted with equal affinity with the non-specific inhibitors IBMX and trequinsin, as well as the very potent PDE4-specific inhibitor RP 73401. Other potent and specific PDE4 inhibitors, such as rolipram, RS-25344 or TVX 2706, appear to utilize non-catalytic domain interactions with PDE4D and 4A to supplement those within the catalytic domains. These observations suggest a different relation between amino and catalytic domains in PDE4D relative to PDE4B. We therefore propose a model to illustrate these isogene-specific PDE4 domain interactions with substrate, inhibitors and the co-factor Mg2+. The model for PDE4D is also discussed in relation to changes in the activation curve for Mg2+ and sensitivity to RS-25344 that accompany phosphorylation of the long form by protein kinase A.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1998

A comparison of the stiffness, density and composition of bone from the calcar femorale and the femoral cortex.

The stiffness, density and composition were compared in bone from the calcar femorale and cortical bone from the mid-shaft of the femur from an elderly group of clinically normal patients. Variation of properties through the thickness of the bone and the stiffness, measured using ultrasound, in directions parallel and perpendicular to the bone axis were also investigated. The calcar was less stiff (30.5 GPa) than the cortical bone (33.0 GPa) (P=0.04). It was also slightly less dense (2.01 compared with 2.05 g cm-3, P<0.001)and had a lower mineral content (56.7% of wet mass) than the femoral cortex (58.0%, P<0.05). At both sites the bone stiffness, density and mineral content decreased from the outer layer towards the inside. The stiffness was greatest in an axial direction and least in a radial direction with the tangential stiffness slightly greater than the radial, indicating an orthotropic symmetry. These results show that bone from the calcar has similar material properties to cortical bone, and provide a baseline for further studies investigating possible changes in the calcar in osteoporosis which may increase our understanding of the mechanisms underlying fractures of the neck of the femur.

Journal Article↗