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Biomedical subjects

B Liu

Publications and source records attributed to B Liu.

At least 487 records · Page 27Linked to original sources
PubMed1996

Generation of primary tumor-specific CTL in vitro to immunogenic and poorly immunogenic mouse tumors.

This study investigated the generation of primary tumor-specific CTL activity in vitro to several mouse tumors. We report that the development of optimal primary tumor-specific CTL to the P815 mastocytoma, the EL4 thymoma, and the Lewis lung carcinoma is dependent on tumor Ags, on enhancement of T cell costimulation by B7.1, and on exogenous T helper activity in the form of IL-2 and IL-4. A relatively low concentration of IL-2 and IL-4 was required to limit the induction of lymphokine-activated killer cells. In the case of P815, the CTL were directed toward molecularly defined tumor rejection Ags. These primary cultures yielded long term T cell lines that were heterogeneous in fine tumor Ag specificity and in cytokine production.

Animals↗
PubMed1996

Effects of hydrogen/deuterium exchange on photosynthetic water cleavage in PS II core complexes from spinach.

H/D isotope exchange effects on P680+. reduction by Yz and electron abstraction from the water oxidizing complex (WOC) in redox state S3 by YZOX were analyzed in PS II core complexes from spinach by measurements of laser flash induced absorption changes at 820 nm and 355 nm. The results obtained reveal: (1) the rate of Yz oxidation by P680+. is almost independent of the substitution of exchangeable protons by deuterons; and (2) the reaction between YZOX and the WOC in S3 exhibits a kinetic H/D isotope exchange effect of similar magnitude as that recently observed in PS II membrane fragments [Renger, G., Bittner, T. and Messinger, J. (1994) Biochem. Soc. Trans. 22, 318-322]. Based on these results it is inferred that photosynthetic dioxygen formation comprises the cleavage of at least one hydrogen bond.

Deuterium↗
PubMed1996

PLD activation in Chinese hamster ovary (CHO) cells transfected with PGF2 alpha receptor cDNA.

Pertussis toxin-insensitive GTP-binding protein was observed to be involved in prostaglandin F2 alpha (PGF2 alpha)-induced phosphoinositide metabolism in Chinese hamster ovary (CHO) cells transfected with PGF2 alpha receptor cDNA (CHO-PGF2 alpha R cells) (Ito, S. et al. Biochem. Biophys. Res. Commun. 200: 756,1994). In the present study, we investigated PGF2 alpha-induced PLD activation in CHO-PGF2 alpha R cells. PLD activation was examined by measuring the production of [3H]phosphatidylbutanol ([3H]PBut), a specific product of the PLD-catalyzed transphosphatidylation reaction. PGF2 alpha-induced [3H]PBut formation was concentration-dependent with the maximal level obtained at 1 microM PGF2 alpha. The maximal [3H]PBut formation was observed at 2 min after addition of PGF2 alpha. Depletion of extracellular Ca2+ with EGTA suppressed PGF2 alpha-induced PLD activation by 50%. PKC inhibitors Ro31-8425 and calphostin C inhibited PGF2 alpha-induced [3H]PBut formation by 50%. PTK inhibitors genistein and herbimycin A failed to inhibit PGF2 alpha-induced PLD activation. A combination of maximal effective concentrations of PGF2 alpha (1 microM) and PMA (100 nM) enhanced PLD activation in an additive manner. Pretreatment of the cells with PMA for 2 h down-regulated PKC alpha and decreased PGF2 alpha-induced PLD activation. These results suggest that PLD activation by PGF2 alpha is mediated by both PKC-dependent and -independent pathways and that PKC alpha is involved in the former pathway.

Animals↗
PubMed1996

Analysis of mismatch repair genes in hereditary non-polyposis colorectal cancer patients.

Hereditary non-polyposis colorectal cancer (HNPCC) is an autosomal dominant disorder characterized by the early onset of colorectal cancer and linked to germline defects in at least four mismatch repair genes. Although much has been learned about the molecular pathogenesis of this disease, questions related to effective presymptomatic diagnosis are largely unanswered because of its genetic complexity. In this study, we evaluated tumors from 74 HNPCC kindreds for genomic instability characteristic of a mismatch repair deficiency and found such instability in 92% of the kindreds. The entire coding regions of the five known human mismatch repair genes were evaluated in 48 kindreds with instability, and mutations were identified in 70%. This study demonstrates that a combination of techniques can be used to genetically diagnose tumor susceptibility in the majority of HNPCC kindreds and lays the foundation for genetic testing of this relatively common disease.

Base Sequence↗
PubMed1996

Estrogen alters MPTP-induced neurotoxicity in female mice: effects on striatal dopamine concentrations and release.

The effects of estrogen on MPTP-induced neurotoxicity of the nigrostriatal dopaminergic system were examined in C57Bl and CD-1 mice. Ovariectomized mice with and without estrogen were treated with MPTP or its vehicle. The effects of these treatments on striatal dopamine concentrations and L-DOPA-stimulated dopamine and L-3,4-dihydroxyphenylacetic acid (DOPAC) release in vitro were determined. Dopamine concentrations of C57Bl mice receiving estrogen before MPTP were significantly greater than those of non-estrogen-treated MPTP mice as well as estrogen-treated mice receiving the MPTP vehicle. Dopamine concentrations of the CD-1 mice did not differ with these treatments. L-DOPA-evoked dopamine release values of estrogen-treated C57Bl mice were significantly increased compared with non-estrogen-treated mice. No such differences were observed in the MPTP-treated C57Bl mice. DOPAC release rates were similar to that of dopamine in these C57Bl mice. In the CD-1 mice estrogen also produced a significant increase in L-DOPA-evoked dopamine release; however, this response was unaltered by MPTP treatment. A significant increase in L-DOPA-evoked DOPAC output was obtained only for estrogen-treated CD-1 mice. Both strains show very similar responses to the estrogen treatment, but differential responses of dopamine release to L-DOPA between the C57Bl and CD-1 mice were obtained with regard to the interactive effects of estrogen and MPTP. Our results suggest that in addition to its role as modulator, estrogen may also function as a neuroprotectant against MPTP neurotoxicity of the nigrostriatal dopaminergic system in the C57Bl mouse.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1996

Calcium signals and protein tyrosine kinases are required for the induction of c-jun in Jurkat cells stimulated by the T cell-receptor complex and oxidative signals.

The regulation of c-jun plays an important role in T cell activation, proliferation, and expression of interleukin-2. In the present study, we determined whether Ca2+ signals and the activity of protein tyrosine kinases (PTKs) were required for the induction of c-jun in Jurkat cells stimulated with cross-linked anti-T cell receptor/CD3 antibodies or exposed to oxidative stress in the form of micromolar concentrations of H2O2. Jurkat cells exhibited rapid elevations in intracellular calcium [Ca2+]i levels in response to H2O2 and cross-linked anti-CD3 antibodies that mainly reflected the influx of extracellular Ca2+. The Ca2+ flux in response to oxidative signals was distinguished by an exquisite sensitivity to inhibition with Ni2+, suggesting the involvement of cation channels. PTK activity was needed for [Ca2+]i elevations in response to both oxidative and anti-CD3 signals, although H2O2 induction of [Ca2+]i increases was more resistant to inhibition by genistein than anti-CD3 [Ca2+]i responses. Both oxidative signals and anti-CD3 stimulation induced increased levels of c-jun and c-fos mRNA. The increased expression of c-jun with H2O2 was preceded by [Ca2+]i increases and accompanied by activation of c-Jun aminoterminal kinases (JNKs), as well as increased AP-1 binding activity. Induction of c-jun with oxidative signals and anti-CD3 was also shown to be crucially dependent on [Ca2+]i elevations because the chelation of [Ca2+]i with BAPTA resulted in a dose-dependent inhibition of c-jun expression. Furthermore, inhibition studies demonstrated that the optimal induction of c-jun mRNA in response to oxidative signals required PTK as well as protein kinase C (PKC). Thus, these findings suggest that both [Ca2+]i signals and the activity of PTKs are essential for the optimal expression of c-jun in response to TCR/CD3 signals and changes in redox potentials.

Antibody Formation↗
PubMed1996

Studies on the mechanisms of stress wave propagation in the chest subjected to impact and lung injuries.

To gain some quantitative understanding of the nature and properties of stress wave propagation and the pathological characteristics of lung injuries, pressure values at eight sites in the lungs during an impact period were recorded. The lung injury severity scores in the corresponding regions were determined in 11 dogs, which were subjected to blunt, left lateral impact at a velocity of 16.33 m/sec with a 24.5% compressive response. The results showed that the pressure value at the contact point was the greatest and that pressure decreased significantly from left side to right side. However, at the left hilum a second pressure peak developed. The pressure value at the contact point was 0.68 and 0.50 times greater than those at left lung and left hilum, respectively. The speed at which the pressure at the contact point rose was much faster than the speed at other points. The lung injury scores at different sites corresponded well with the pressure values (p < 0.001). The data indicated that the reflection and refraction of the stress waves result in the accumulation of forces at some points, transferring more energy to the tissues at those points. Therefore, the severity of injury at these points in these tissues was more severe.

Animals↗
PubMed1996

Experimental studies on the hemodynamic changes after thoracic impact injury.

Hemodynamic changes were monitored in eight dogs subjected to blunt impact (velocity = 19m/s) in the cardiac region. There was a transitory cardiac arrest for 1 to 2 seconds in some animals after trauma. The heart rate decreased markedly at 30 minutes after trauma, and recovered at 4 hours. At 15 minutes after trauma, the cardiac index, stroke volume index, left ventricular stroke work index, and mean artery pressure were much lower than that before trauma (p < 0.05 or p < o.o1). However, the mean pulmonary artery pressure, pulmonary capillary wedge pressure, and central venous pressure at 30 minutes after trauma were higher than that before trauma (p < 0.05). The above changes recovered generally at 8 to 16 hours after trauma. The pathological results showed that superficial spotty or flat hemorrhages and ecchymoses were most common in the injured heart. Severe contusion on the anterior wall of the left or right ventricle was also seen.

Animals↗
PubMed1996

Relationship between the dynamic parameters and injury severity of chest subject to impact.

Seventeen dogs were subjected to blunt left lateral impact at velocities from 7.14 m/s to 19.05 m/s. The impacts to the thoracic wall were recorded by accelerometers fixed on the ribs at the impacted point and other areas. From this information the dynamic parameters (compression response, instantaneous deformation velocities, and viscous response) were calculated. The thoracic injury scores were recorded according to the Abbreviated Injury Scale (AIS-85). The results showed that the chest was a viscoelastic structure. The dynamic parameters of the chest wall were correlated with the physical parameters in exponential function or logarithmic function. There was a more significant relationship between viscous criterion and injury score among the various parameters. The relationship curve was sigmoid. The results indicated that the viscous response might be a valid parameter for indicating the severity of injury.

Animals↗
PubMed1996

Pathologic study of thoracic impact injury involving a movable impact pattern.

The left thoracic walls of 28 rabbits were subjected to lateral blunt impact in a movable impact pattern. The impact velocities ranged from 7.95 m/s to 16.13 m/s, and the compression response ranged from 15.69% to 46.14% of the thoracic width. The surviving animals were sacrificed at 6 hours after trauma and were autopsied. Injury scores were assigned according to the hemorrhage area and the injury type (e.g., rupture or rib fracture). When compared with the pathologic characteristics of the thoracic injury involving a relatively static impact pattern, the severity of thoracic injury involving a movable impact pattern was milder. Also there were more significant differences in the severity of injury to lungs and ribs on the left as compared with the right sides. The viscous criterion is still a good parameter reflecting the severity of injury to lungs and heart. The severity of rib injury was mainly related to compression response.

Animals↗
PubMed1996

Pathologic study of thoracic impact injury involving a relatively static impact pattern.

Fifty-five rabbits were subjected to left thoracic wall lateral blunt impact involving a relatively static impact pattern. The impact velocities ranged from 7.92 m/s to 16.33 m/s and the compression response ranged from 14.08% to 45.84% of the thoracic width. The surviving animals were sacrificed 6 hours after trauma and autopsies were performed. The lung was divided into bronchial and alveolar regions. Injury scores were assigned according to the hemorrhage area and the injury type (e.g., rupture or rib fracture). The results showed that the severity of bronchial injury was greater than alveolar injury when the impact velocity was low. However, alveolar injury was much more severe than bronchial injury at all levels of impact displacement when the impact velocity was high. The ratio of left/right lung injury decreased when the product of impact velocity and compression criterion increased. The latter was also well correlated with the severity of lung and heart injuries. In addition, the severity of rib injury was mainly related to compression response.

Animals↗
PubMed1996

Half-dose aprotinin does not affect haemorheological properties in patients undergoing bypass surgery.

OBJECTIVE: To investigate haemorheological changes in patients undergoing coronary artery bypass grafting and to determine whether the protective effect on haemorheology of high-dose aprotinin also exists under a half-dose regimen. METHODS: Forty patients were studied in a double-blind, placebo-controlled study design. Patients in the aprotinin group received half of the standard high dose of aprotinin during surgery. Erythrocyte and white-cell clogging rates as well as whole blood and plasma viscosity were measured. Viscosity results were expressed as a ratio to the viscosity of saline. RESULTS: Erythrocyte and white-cell clogging rates were increased significantly, whereas whole blood and plasma viscosity were decreased significantly during cardiopulmonary bypass. The reduction in viscosity had a strong correlation to haemodilution. There was no significant difference in any of the measured variables between the aprotinin and the placebo groups. CONCLUSION: This study showed that blood cell damage occurred during cardiopulmonary bypass surgery, as measured by a raised clogging rate. This tendency was the same in both groups and therefore no increased potential for microthrombi could be attributed to aprotinin haemorheologically. However, half-dose aprotinin did not show any preserving effect in haemorheology when the blood-cell clogging rate and blood viscosity were studied.

Aged↗
PubMed1996

A kinesin-like protein, KatAp, in the cells of arabidopsis and other plants.

The kinesin-like proteins (KLPs) are a large family of plus- or minus-end-directed microtubule motors important in intracellular transport, mitosis, meiosis, and development. However, relatively little is known about plant KLPs. We prepared an antibody against two peptides in the microtubule binding domain of an Arabidopsis KLP (KatAp) encoded by the KatA gene, one of a family of genes encoding KLPs whose motor domain is located near the C terminus of the polypeptide. Such KLPs typically move materials toward the minus end of microtubules. An immunoreactive band (Mr of 140,000) corresponding to KatAp was demonstrated with this antibody on immunoblots of Arabidopsis seedling extracts. During immunofluorescence localizations, the antibody produced weak, variable staining in the cytoplasm and nucleus of interphase Arabidopsis suspension cells but much stronger staining of the mitotic apparatus during division. Staining was concentrated near the midzone during metaphase and was retained there during anaphase. The phragmoplast was also stained. Similar localization patterns were seen in tobacco BY-2 cells. The antibody produced a single band (Mr of 130,000) in murine brain fractions prepared according to procedures that enrich for KLPs (binding to microtubules in the presence of AMP-PNP but not ATP). A similar fraction from carrot suspension cells yielded a cross-reacting polypeptide of similar apparent molecular mass. When dividing BY-2 cells were lysed in the presence of taxol and ATP, antibody staining moved rapidly toward the poles, supporting the presence of a minus-end motor. Movement did not occur without ATP, with AMP-PNP, or with ATP plus antibody. Our results indicate that the protein encoded by KatA, KatAp, is expressed in Arabidopsis and is specifically localized to the midzone of the mitotic apparatus and phragmoplast. A similar protein is also present in other species.

Amino Acid Sequence↗
PubMed1996

Normal six-degree-of-freedom motions of knee joint during level walking.

The purpose of this study was to find an effective way for in vivo measurement of joint motion and give the normal knee motion according to this method. The joint model proposed by Grood and Suntay (1983) was chosen; the origin of the tibia was modified for the convenience of in vivo test. A computerized 6 degree-of-freedom electrogoniometer (EGM) was used in the measurement. Repeated tests on one subject were performed to establish the reliability of the method. Knee motions obtained from 42 males during level walking were expressed as flexion-extension, abduction-adduction, external-internal rotation, lateral-medial translation, anterior-posterior translation, and superior-inferior translation. The results showed that, with the proper choice of the origin of the tibia, the EGM could depend much less on external landmarks and be more effective for the joint measurement.

Adult↗
PubMed1996

Polyprotein processing in Southampton virus: identification of 3C-like protease cleavage sites by in vitro mutagenesis.

A genomic clone of the small, round-structured virus Southampton virus (SV) was constructed from a set of overlapping PCR amplicons. Sequence analysis confirmed the absence of mutations and accurate ligation of the PCR products. The SV cDNA was cloned into a vector for in vitro production of RNA and subsequent translation by rabbit reticulocyte lysate. Two polypeptides corresponding to the N-terminal and C-terminal regions of the viral polyprotein were expressed in Escherichia coli and used to produce murine antisera for detection of translation products. Three major translation products of 113, 48, and 41 kDa were identified in a coupled transcription-translation system. The large 113-kDa protein reacted with antisera raised against the C-terminal region of the polyprotein and represents a precursor of the viral RNA polymerase. The 48-kDa protein detected in vitro reacted specifically with antisera raised against the polyprotein N terminus, showing that translation was initiated in SV at the three tandem in-frame AUG codons at the 5' end of the genome. A series of nested 3' deletions of the large open reading frame encoding the viral polyprotein was used to define the translation initiation site and genomic location of the viral protease. The results are consistent with a model in which translation of the viral genome is initiated at one of the three in-frame AUG codons starting at nucleotide position 5 and in which active viral protease is produced following translation of a region located between NheI (nucleotide 3052) and SphI (nucleotide 4056), resulting in rapid cleavage of a large precursor protein. Abolition of the viral 3C-like protease activity by site-directed mutagenesis of the putative active-site cysteine (Cys-1238) resulted in production of a large protein of approximately 200 kDa which reacted with both N-terminal and C-terminal antisera. Two potential polyprotein cleavage sites containing the preferred picornaviral QG recognition site were identified on either side of the putative 2C-like helicase region of the polyprotein. Proteolysis at these positions would give rise to products with relative molecular masses identical to those of the products detected in the rabbit reticulocyte system. Site-directed mutagenesis was used to introduce a single base change which resulted in the substitution of glutamine residues with proline residues at amino acids 399 and 762. These mutations completely abolished cleavage of the polyprotein at these positions and gave rise to alternative products with molecular masses which matched the predicted sizes for a single cleavage at either Q-399 or Q-762. These data indicate that the small, round-structured virus Southampton virus produces a 3C-like protease which has two primary cleavage sites at positions 399 and 762. Proteolytic cleavage at these positions releases the putative viral 2C-like helicase.

Amino Acid Sequence↗
PubMed1996

Uncoupling of contractile function from mitochondrial TCA cycle activity and MVO2 during reperfusion of ischemic hearts.

In this study we determined whether contractile function becomes uncoupled during reperfusion of ischemic hearts from mitochondrial tricarboxylic acid (TCA) cycle activity or myocardial O2 consumption (MVO2). Isolated working rat hearts perfused with buffer containing 1.2 mM palmitate and 11 mM glucose were subjected to 30 min of global ischemia followed by 60 min of aerobic reperfusion. During reperfusion, cardiac work recovered to 26.5 +/- 5.4% (n = 29) of preischemic levels, even though TCA cycle activity, fatty acid beta-oxidation, glucose oxidation, glycolysis, and MVO2 rapidly recovered. As a result, the efficiency of coupling between cardiac work and TCA cycle activity and between cardiac work and mitochondrial respiration decreased during reperfusion. In contrast, coupling of TCA cycle activity to MVO2 during reperfusion recovered to preischemic values. Addition of 1 mM dichloroacetate at reperfusion resulted in a significant increase in both cardiac work and cardiac efficiency during reperfusion. This was associated with a significant decrease in H+ production due to an improved balance between glycolysis and glucose oxidation. These data demonstrate that mitochondrial function and overall myocardial ATP production quickly recover in rat hearts after a 30-min period of global ischemia. However, mitochondrial ATP production is not efficiently translated into mechanical work during reperfusion. This may be due to an imbalance between glycolysis and glucose oxidation, resulting in an increase in H+ production and a decrease in cardiac efficiency.

Adenosine Triphosphate↗