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Biomedical subjects

K Liu

Publications and source records attributed to K Liu.

At least 109 records · Page 6Linked to original sources
PubMed2000

Soluble polycyclic aromatic hydrocarbons in raw coals.

Polycyclic aromatic hydrocarbons (PAHs) are considered to be a group of compounds that pose potential health hazards since some PAHs are known carcinogens. During coal utilization processes, such as coal combustion and pyrolysis, PAHs released may be divided into two categories according to their formation pathways. One category is derived from complex chemical reactions and the other is from free PAHs transferred from the original coals. PAHs released from complex chemical reactions during combustion and pyrolysis have received considerable attention in recent years. However, free PAHs contained in raw coals have not been seriously considered as a source of these materials to be released during the utilization of coal. The goal of this study was to observe the relation between the content of PAHs in different coals and the elemental composition of the coals. In this study, eight bituminous coals with dry, ash-free carbon values varying from 65% to 90% were selected. Each coal was extracted with dichloromethane in a Soxhlet extractor for 6 h. The extracts were quantitatively analyzed with a gas chromatograph/mass spectrometer (GC-MS). More than 20 kinds of PAHs were identified. The total amount of PAHs determined varied from 1.2 to 28.3 mg/kg from the various coal types. The maximum total PAHs extracted was reached when the carbon content exceeded 84% by weight.

Anthracenes↗
PubMed2000

Ca(2+)-evoked serotonin secretion by parafollicular cells: roles in signal transduction of phosphatidylinositol 3'-kinase, and the gamma and zeta isoforms of protein kinase C.

Parafollicular (PF) cells secrete 5-HT in response to stimulation of a G-protein-coupled Ca(2+) receptor (CaR) by increased extracellular Ca(2+) (upward arrow[Ca(2+)](e)). We tested the hypothesis that protein kinase C (PKC) participates in stimulus-secretion coupling. Immunoblots from membrane and cytosolic fractions of isolated PF cells revealed conventional (alpha, betaI, and gamma), novel (delta and epsilon), and atypical (iota/lambda and zeta) PKCs. Only PKCgamma was found to have been translocated to the membrane fraction when secretion of 5-HT was evoked by upward arrow[Ca(2+)](e) or phorbol esters. Although phorbol downregulation caused PKCgamma to disappear, secretion was only partially inhibited. A similar reduction of upward arrow[Ca(2+)](e)-evoked secretion was produced by inhibitors of conventional and/or novel PKCs (Gö 6976, calphostin C, and pseudoA), and these compounds did not inhibit secretion at all when applied to phorbol-downregulated cells. In contrast, the phorbol downregulation-resistant component of secretion was abolished by pseudoZ, which inhibits the atypical PKCzeta. Stimulation of PF cells with upward arrow[Ca(2+)](e) increased the activity of immunoprecipitated PKCzeta (but not PKCiota/lambda), and the activity of this PKCzeta was inhibited by pseudoZ. PF cells were found to express regulatory (p85) and catalytic (p110alpha and p110beta) subunits of phosphatidylinositol 3'-kinase (PI3'-kinase). upward arrow[Ca(2+)](e) increased the activity of immunoprecipitated PI3'-kinase; moreover, PI3'-kinase inhibitors (wortmannin and LY294002) antagonized secretion. We suggest that PKC isoforms mediate secretion of 5-HT by PF cells in response to stimulation of the CaR. PKC involvement can be accounted for by PKCgamma and an isoform sensitive to inhibition by pseudoZ, probably PKCzeta, which is activated via PI3'-kinase.

Androstadienes↗
PubMed2000

Asymmetry in elementary events of magnetization reversal in a ferromagnetic/antiferromagnetic bilayer.

Real-time magneto-optical indicator film images reveal distinct asymmetry in the motion of a single domain wall in a wedged-NiFe/uniform-FeMn bilayer due to the nucleation and behavior of an exchange spring in the antiferromagnetic layer. Magnetization reversal from the ground state begins at the thick end of the wedge where the exchange anisotropy field (HE) is minimal and the magnetostatic field (HMS) is maximal, whereas reversal into the ground state begins from the thin end where HE is maximal and HMS is minimal.

Journal Article↗
PubMed2000

Human three-dimensional fibroblast cultures express angiogenic activity.

Human neonatal fibroblasts were cultured on a lactate-glycollate copolymer scaffold for 12-16 days to form a three-dimensional dermal equivalent tissue. The cellular content of vascular endothelial growth factor (VEGF) mRNA in these three-dimensional cultures was 22-fold greater than that observed in the same fibroblasts grown as monolayers. No induction was shown by hepatocyte growth factor (HGF) or angiopoietin 1 indicating that the effect was specific to VEGF. The predominant VEGF splice variant, detected by RT-PCR corresponded to the 121 amino acid form, with less of the 165 amino acid form. The cell-associated forms (189 and 206 amino acids) comprised less than 1% of the total VEGF mRNA. VEGF and HGF proteins, determined by ELISA, were secreted in physiologically significant amounts, 0.5-4 ng per 24 h/10(6) cells. Conditioned medium from the three-dimensional cultures stimulated proliferation of endothelial cells in a dose-dependent manner and induced cellular expression of integrin alpha(v)beta(3). Conditioned medium from the same dermal fibroblasts cultured in monolayer showed little angiogenic activity in any of these assays. Using the chorioallantoic membrane (CAM) angiogenesis assay, the cultures stimulated blood vessel production 2.8-fold over scaffold alone. VEGF-neutralizing antibody reduced the vessel development in the CAM to the level in the scaffold control. Anti-HGF antibody had no significant effect. In conclusion, three-dimensional cultures of dermal equivalent tissue express angiogenic activity to a greater extent than monolayer cultures, some of which can be assigned to VEGF.

Allantois↗
PubMed2000

Fine-needle aspiration diagnosis of psammomatous melanotic schwannoma.

A 51-yr-old male presented with an 8-mo history of lower back pain. Computerized axial tomography (CT) and magnetic resonance imaging (MRI) studies showed a 3.5 X 3.0 cm sacral mass within the spinal canal in the region of the left S2 nerve root. A fine-needle aspirate biopsy (FNAB) was performed under CT guidance. The cytologic findings included a spindle-cell population with a fibrillary background arranged in a vaguely streaming pattern, wavy nuclei with mild atypia, wispy cytoplasm, rare intranuclear inclusions, and dilated vascular spaces. Some cells contained a nonrefractile granular brown pigment consistent with melanin. Also identified were calcified concentric laminations typical of psammoma bodies. Immunohistochemically, the neoplastic cells were strongly immunoreactive for S-100 protein and HMB-45. A diagnosis of psammomatous melanotic schwannoma was rendered. No stigmata of Carney's complex were identified on physical examination. The patient has declined the recommendation of surgical excision of the mass. We herein describe a case unequivocally diagnosed as psammomatous melanotic schwannoma by FNAB.

Antigens, Neoplasm↗
PubMed2000

Dynamic in vivo oxymetry using overhauser enhanced MR imaging.

A noninvasive method for in vivo measurement of the oxygen concentration has been developed. By introducing a novel contrast medium (CM) based on a single electron substance, it is possible to enhance the proton signal through the Overhauser effect. A low-field magnetic resonance scanner is used to image the proton nuclei of the object. The electron spin transition of the CM is saturated using rf irradiation. As a consequence, the nuclear polarization becomes enhanced through dipole-dipole interaction. The signal enhancement is a function of rf power and of the EPR line width of the substance, which is influenced by the oxygen concentration. The maximum in vivo enhancement has been measured to 60. Image data, generated with different scanning parameters, is used in a postprocessing method to generate images showing pO(2) and the contrast medium concentration, respectively. The mathematical foundation of the postprocessing algorithm is outlined. The results from phantom experiments and animal experiments, in which the oxygen content of the inspired gas was varied, are presented. The potential for human imaging is discussed. J. Magn. Reson. Imaging 2000;12:929-938.

Algorithms↗
PubMed2000

Reduced slab boundary artifact in multi-slab 3D fast spin-echo imaging.

The three-dimensional multi-slab fast spin-echo (3DFSE) sequence is a time-efficient technique for volume scanning which provides images with a good signal-to-noise ratio, adjustable contrast weighting, and high spatial resolution. Unfortunately, it suffers from slice-to-slice amplitude variation associated with imperfect slab definition. This slab boundary artifact becomes especially apparent when multiplanner reformatting is used to create alternate anatomical views. The shifted interleaved multi-volume acquisition (SIMVA) described here suppresses slab boundary artifact in image space. It displaces each slab (RF excitation) position incrementally along the slice (z) axis, in coordination with the primary phase encode step, so that the slab boundary artifact is converted into a correctable amplitude modulation in the primary phase encode direction (k(Y)-axis). After the Fourier transform in primary phase encoding, the slab boundary artifact is mapped into a different and less severe artifact on a different spatial axis. Preliminary measurements show that SIMVA reduces the slab boundary artifact by an order of magnitude in multiplanar reformatted views. Magn Reson Med 44:269-276, 2000.

Artifacts↗
PubMed2000

Clinical and biochemical characteristics of growth hormone-secreting pituitary tumors.

To investigate the difference of biochemical characteristics on gsp-positive and gsp-negative growth hormone (GH)-secreting pituitary tumors, 18 GH-secreting pituitary tumors were examined for their clinical characteristics and gsp oncogenes. All patients received the pituitary function combinative stimulating test. It was found that there were no difference in the sex, age, tumor size, course of disease and plasma basal GH levels with gsp-positive and gsp-negative patients. The plasma levels of PRL were increased in most patients (11/18), and the plasma levels of TSH in gsp-positive patients were higher than those in gsp-negative patients (P < 0.05). There was no significant difference in the responses to pituitary combinative stimulating test in gsp-positive and gsp-negative patients. It was concluded that there was little difference in the clinical biochemical characteristics of gsp-positive with gsp-negative GH-secreting pituitary tumors.

Adult↗
PubMed2000

The regulatory effects of protein kinase C on the proliferation of cultured human low-passage meningioma cells.

The potential role of the protein kinase C (PKC)-mediated signal transduction pathways in growth regulation was evaluated and the effects and the possible mechanism of PKC inhibitor on low-passage human meningioma cells in vitro investigated. Freshly resected meningiomas obtained from the operation were placed into cell cultures. Cells from early-passage were used for the following experiments. The numbers of the cultured meningioma cells were counted to evaluate the effect of the PKC inhibitor staurosporine on proliferation of meningioma cells. The basal phosphatidylinositol (PI) turnover rate and the inhibitory rate of starosporine on the proliferation of the meningioma cells were detected. It was found that the proliferation of the low-passage human meningioma cells was inhibited by staurosporine in a dose-dependent manner. The inhibitory rate of staurosporine was positively correlated with the basal PI turnover rate (r = 0.58, P < 0.01). It was suggested that PKC-mediated signal pathway is involved in the proliferation of the low-passage human meningioma cells. The procedure that PKC regulated the proliferation of human meningioma cells is a complex procedure. It is necessary to make more research in order to explore a non-operation therapy or an adjuvant therapy.

Cell Division↗
PubMed2000

Interaction of the novel GH secretagogue hexarelin with GHRH in regulating the secretion of GH by cultured human pituitary somatotrophinomas in vitro.

The effects of the novel GH-releasing hexapeptide, Hexarelin, on the secretion of GH in cultured human pituitary somatotrophinomas was further investigated. Hexarelin (20 nmol/L) strongly stimulated GH secretion, which could be reduced by phloretin, but not by RP-cAMPS, an inhibitor of protein kinase A (PKA). (Ac-Tyr1,D-Arg2)-GRF(1-29)-NH2 failed to block the effects of Hexarelin but completely abolished the stimulation of GH secretion exerted by GHRH. When added alone to somatotrophinoma cell cultures, Hexarelin had no effect on cAMP levels, but it potentiated the stimulatory effects of GHRH. These results demonstrated that Hexarelin could directly stimulate GH secretion by human pituitary somatotrophs PKC-dependently, which might be contributed to the activation of the PI transduction system. In addition, Hexarelin could interact with GHRH on the adenylyl cyclase system.

Adenoma↗
PubMed2000

The role of protein kinase C and its effect on GHRH in the regulation of hormone secretion by somatotrophinomas.

Phorbol ester-induced release of growth hormone (GH) and prolactin (PRL) from human somatotrophic tumors was examined in vitro. 12-O-tetradecanoyl-phorbol-13-acetate (TPA) strongly stimulated GH and PRL secretion and showed an additive effect on GH secretion if used in combination with GH releasing hormone (GHRH). In contrast, staurosporine exerted a variable inhibitory effect on GH release. There was no correlation between such effects and gsp mutations. The findings suggested that TPA doesn't act directly through cAMP signal transduction system.

GTP-Binding Protein alpha Subunits, Gs↗
PubMed2000

Isolation and analysis of a new developmentally regulated gene from amastigotes of Leishmania mexicana mexicana.

Leishmania differentiates from the promastigote to the amastigote stage during its digenetic life cycle. Characterization of the developmentally regulated genes during that process would help to elucidate the mechanisms of gene regulation. In this study, specific fragments of mRNAs from the amastigote stage of L. mexicana mexicana were discriminated from those of the promastigote and metacyclic stages by differential display. This technique combined with spliced-leader polymerase chain reaction allowed isolation of the complete gene VG7A5. The sequence of this gene did not align with any published L. mexicana sequence. More than one copy of this gene was identified in the genome by Southern-blot analysis and was transcribed exclusively in the amastigote stage. At 20 bp upstream from the splice AG site it has a trans-splicing polypyrimidine tract. The gene encodes the subcellular localization motifs 5'-GGACT and AAGCT-3' in the 3' untranslated region of the mRNA. The open reading frame of the gene VG7A5 predicts a polypeptide of 587 amino acid residues that has a KGRR amidation motif near its carboxyl terminus, suggesting that in the mammalian host this protein may be involved in the process of acute inflammation.

5' Untranslated Regions↗
PubMed2000

Mechanisms for genetically predetermined differential quantitative expression of HLA-A and -B antigens.

Previous studies showed that different HLA-A and -B antigens are differentially expressed in cells. Their relative quantities are genetically predetermined and inherited according to Mendelian laws. To investigate mechanisms responsible for this differential expression, a correlation study between the relative quantities of different HLA-A and -B proteins and their mRNA levels in eight different HLA-phenotyped lymphoblastoid cell lines (LCLs) were performed. The results show proportional correlation in all the studied cell lines except those that are positive for HLA-A24. Study of the turnover of HLA antigens reveals that different HLA-A and -B antigens are proportionally degraded. Measurement of the relative quantities of HLA-A and -B mRNAs in six LCLs before and after treatment with 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB), an inhibitor of RNA polymerase II, demonstrates that HLA-A and -B mRNAs are proportionally degraded except slight differences in two LCLs. Measurement of the relative quantities of different HLA-A and -B pre-mRNAs in nuclei shows that they are not proportional to the relative quantities of their respective mature mRNAs in cytoplasm in four of six LCLs. These results indicate that combinations of different regulatory steps which include gene transcription, pre-mRNA splicing and mRNA degradation are involved in the genetically predetermined quantitative differential expression of HLA-A and -B antigens. Transcription of HLA genes and splicing of HLA pre-mRNAs appear to be the dominant regulatory steps.

Cell Line, Transformed↗
PubMed2000

Seven-year tracking of dietary factors in young adults: the CARDIA study.

OBJECTIVES: This report determines the extent to which young adults in the highest and lowest intake quintiles of 13 nutrients remain in the same or adjacent quintiles (i.e., "tracked") relative to each other, over 7 years. METHODS: Data from baseline and year 7 of the CARDIA study were divided into race/gender-specific quintiles for each nutrient and cross-tabulated. RESULTS: For most nutrients, over 60% of those in the lowest absolute intake quintile at year 0 remained in the lowest or second-lowest quintile at year 7. A similar pattern was seen with highest absolute intake quintiles at years 0 and 7. Tracking was attenuated when nutrient density, rather than absolute intake, was examined. CONCLUSIONS: Ingrained dietary habits may cause high- or low-intake groups to retain relative ranking, even in the face of secular, age-, or lifestyle-related trends in dietary intake.

Adult↗
PubMed2000

Efficacy of intrathecal neostigmine for the relief of postinguinal hemiorrhaphy pain.

BACKGROUND: Intrathecal administration of various doses of neostigmine has been reported to produce analgesia without neurotoxicity in both animal and human studies. The present study was undertaken to evaluate the efficacy and safety of intrathecal neostigmine for the relief of pain for patients having undergone inguinal herniorrhaphy surgery. METHODS: Sixty men scheduled for elective inguinal herniorrhaphy with spinal anaesthesia were randomly allocated to three groups: group I (n=20) received intrathecal (IT) tetracaine 15 mg, group II (n=20) received IT tetracaine 15 mg+ neostigmine 50 microg, and group III (n=20) received IT tetracaine 15 mg+neostigmine 100 microg. The onset of anaesthesia, duration of analgesia, time to use of first rescue analgesics, the overall 24 h VAS pain scores and the incidence of adverse effects were recorded for 24 h postdrug administration. RESULTS: Onset of anaesthesia (time to T6 sensory block) was significantly faster for group II and III patients compared with group I patients. Motor block (time to lift leg) was greatly prolonged for group III patients, with an average of 6.4 h, compared with 4.1 h for group II patients. Group III patients also showed a later onset of postsurgical pain, lower overall 24-h VAS pain score and prolonged time to first rescue analgesics than did group II patients. There was a significantly greater incidence of adverse effects associated with IT neostigmine, especially nausea and vomiting. CONCLUSION: Our study showed that intrathecal neostigmine at 50 pg or 100 microg enhanced the onset of tetracaine anaesthesia and provided analgesia lasting for 6-9 h, although increased incidences of prolonged motor blockade and nausea or vomiting were noted.

Adult↗
PubMed2000

A glimpse of a possible amyloidogenic intermediate of transthyretin.

Studies have indicated that partially unfolded states occur under conditions that favor amyloid formation by transthyretin (TTR), as well as other amyloidogenic proteins. In this study, we used hydrogen exchange measurements to show that there is selective destabilization of one half of the beta-sandwich structure of TTR under such conditions. This provides more direct information about conformational fluctuations than previously available, and will facilitate design of future experiments to probe the intermediates critical to amyloid formation.

Amides↗
PubMed2000

Donor and recipient leukocytes in organ allografts of recipients with variable donor-specific tolerance: with particular reference to chronic rejection.

We have attributed organ engraftment to clonal exhaustion-deletion of host-versus-graft and graft-versus-host reactions that are reciprocally induced and governed by migratory donor and recipient leukocytes. The so-called donor passenger leukocytes that migrate from the allograft into the recipients have been thoroughly studied (chimerism), but not the donor leukocytes that remain in, or return to, the transplanted organ. Therefore, using flow cytometry we determined the percentage and lineages of donor leukocytes in cell suspensions prepared from Lewis (LEW) cardiac allografts to 100 days posttransplantation. The LEW hearts were transplanted to naïve untreated Brown Norway (BN) recipients (group 2), to naïve BN recipients treated with a 28-day or continuous course of tacrolimus (TAC) (groups 3 and 4), and to drug-free BN recipients pretolerized by earlier bone marrow cell (BMC) or orthotopic LEW liver transplantation (groups 5 and 6). The findings in the heart cell suspensions were correlated with the results from parallel histopathologic-immunocytochemical studies and other studies of the grafts and of host tissues. Although the LEW heart allografts were rejected in 9.6 days by the unmodified recipients of group 2, all beat for 100 days in the recipients of groups 3 through 6. Nevertheless, all of the long-surviving cardiac allografts (but not the isografts in group 1) were the targets of an immune reaction at 5 days, reflected by dramatic increases in the ratio of leukocytes to nonleukocyte nucleated cells from normal values of 1:5-1:6 to 1:1-5:1 and by manifold other evidence of a major inflammatory event. The acute changes returned to baseline by 100 days in the chronic rejection (CR) free hearts of groups 4 and 6, but not in the CR-afflicted hearts of short-course TAC group 3 or the less-severely damaged hearts of the BMC-prime group 5. The freedom from CR in groups 4 and 6 was associated with a large donor contribution to the intracardiac leukocyte population at 5 days (28.6% and 22% in the respective groups) and at 100 days (30.5% in group 4 and 8.4% in group 6) compared with 2% and 1.2% at 100 days in the CR-blighted allografts of the partially tolerant animals of groups 3 and 5. Whether large or small, the donor leukocyte fraction always included a subset of class II leukocytes that had histopathologic features of dendritic cells. These class II(+) cells were of mixed myeloid (CD11b/c(+)) and lymphoid lineages; their migration was markedly inhibited by TAC and accelerated by donor-specific priming and TAC discontinuance. Although a large donor leukocyte population and a normal leukocyte/nonleukocyte cell ratio were associated with freedom from CR, these findings and the lineage profile of the intracardiac leukocytes were not associated with tolerance in the animals of groups 3 and 4 under active TAC treatment. The findings in this study, singly and in their entirety, are compatible with our previously proposed leukocyte migration-localization paradigm of organ allograft acceptance and tolerance.

Animals↗