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Biomedical subjects

L Liu

Publications and source records attributed to L Liu.

At least 955 records · Page 53Linked to original sources
PubMed1996

[Correction of the secondary deformity of reduction mammaplasty--the inframammary fold advancement].

The high position of the nipple-areola is one of the complications of reduction mammaplasty. The technique of lower thoracic advancement flap reestablishes a new inframammary fold. The edge of the advanced inferior flap is sutured to the chest wall and the rib cage. The advantages of the technique is that the scar is hidden in the depth of the inframammary fold and is usually fairly in-conspicuous. The technique gives an increasingly natural looking of the breast. The operation is appealingly easy and safe. Figures illustrate the effectiveness of this technique.

Adult↗
PubMed1996

Quantitative immunohistochemical estimates of O6-alkylguanine-DNA alkyltransferase expression in normal and malignant human colon.

A major mechanism of resistance to nitrosoureas is O6-alkylguanine-DNA-alkyltransferase. The alkyltransferase biochemical assay measures mean tissue activity but requires availability of fresh tissue and cannot assess tumor heterogeneity, an important component of tumor resistance to alkylating agents. We assessed the levels of alkyltransferase in human colon carcinoma and normal colon by biochemical assay, Western blot, conventional immunohistochemistry, and quantitative immunohistochemistry (using 5H7 and mT3.1 monoclonal IgGs) to correlate whole tissue levels with cell-specific expression. Alkyltransferase activity was 18.0 +/- 4.6 fmol/microgram DNA in normal colon and 15.0 +/- 6.5 fmol/microgram DNA in tumors. By Western blot estimates, alkyltransferase in normal colon was 14.8 +/- 4.2 fmol/microgram DNA and in tumors was 16.2 +/- 7.8 fmol/microgram DNA. Alkyltransferase estimates by biochemical and Western blots were correlated strongly (P < 0.0001). Conventional immunohistochemistry demonstrated that alkyltransferase was predominantly nuclear and in normal colon was concentrated in glandular epithelial mucosal cells close to the lumen, whereas in tumors, expression was heterogenous but localized to malignant epithelial cells. Two parameters of quantitative immunohistochemistry, integrated gray and mean gray, were correlated strongly with each other (P < 0.002) and with biochemical and Western blot estimates (P = 0.004-0.04). Thus, quantitative immunohistochemical estimates of alkyltransferase in fixed tissues are a reasonable alternative to biochemical analysis and have an added advantage of identifying heterogeneity of alkyltransferase expression in tumors.

Adult↗
PubMed1996

Vulnerability of multidrug-resistant tumor cells to the aromatic fatty acids phenylacetate and phenylbutyrate.

Cytotoxic chemotherapies often give rise to multidrug resistance, which remains a major problem in cancer management. In pursuit of alternative treatments for chemoresistant tumor cells, we tested the response of multidrug-resistant (MDR) tumor cell lines to the aromatic fatty acids phenylacetate (PA) and phenylbutyrate (PB), two differentiation inducers currently in clinical trials. Both compounds induced cytostasis and maturation of multidrug-resistant breast, ovarian, and colon carcinoma cells with no significant effect on cell viability. In contrast to their poor response to doxorubicin, the MDR cells were generally more sensitive to growth arrest by PA and PB than their parental counterparts. The aromatic fatty acids, like the differentiation-inducing aliphatic fatty acid butyrate, up-regulated mdr-1 gene expression. However, while butyrate increased multidrug resistance, PA and PB potentiated the cytotoxic activity of doxorubicin against MDR cells. The latter was associated with time-dependent declines in glutathione levels and in the activity of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, and glutathione S-transferase, the antioxidant enzymes implicated in cell resistance to free radical-based therapies. Taken together, our in vitro data indicate that PA and PB, differentiation inducers of the aromatic fatty acid class, may provide an alternative approach to the treatment of MDR tumors.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Carmustine and streptozocin in refractory melanoma: an attempt at modulation of O-alkylguanine-DNA-alkyltransferase.

The activity of the enzyme O6-alkylguanine-DNA-alkytransferase (AGAT) protects cells from the cytotoxic effects of alkylating agents. This Phase II trial was designed to assess the efficacy of a strategy designed to modulate the resistance to carmustine (BCNU) mediated by AGAT using streptozocin (STZ) in patients with advanced refractory melanoma. Seventeen patients who had failed prior chemotherapy were treated with STZ at 500 mg/m2 daily for 4 days with BCNU at 150 mg/m2 on day 3. Peripheral blood lymphocytes for assay of AGAT activity levels were collected prior to therapy and following the third dose of STZ. There were two partial responses in the 15 patients evaluable for response (13%). Most patients received only a single cycle of therapy due to rapidly progressive disease. Two patients developed fatal pulmonary toxicity, and one developed myelodysplasia. Other toxicities included transient rises in liver function tests. AGAT levels decreased by a mean of 53% in 9 patients but actually increased over baseline in 3 patients while on therapy. Based on these data, BCNU and STZ are not an effective combination for the therapy of advanced refractory melanoma, and pulmonary toxicity due to this combination appears to be increased compared with BCNU alone. STZ is not an effective modulator of AGAT activity when given on this schedule. New strategies designed to deplete AGAT activity using O6-benzylguanine or temozolomide should be explored with careful attention to the possibility that this approach may potentiate both the toxicity and efficacy of BCNU.

Adult↗
PubMed1995

Colocalization of NADPH-diaphorase and dopamine beta-hydroxylase in the neuronal somata of the rat kidney.

Neuronal somata in the rat kidney are very often part of ganglionated plexus and contain nitric oxide synthase (NOS). Examining serial 100 microns slices of whole kidneys, we identified three subpopulations of neuronal somata by: (a) staining for NADPH-diaphorase (NADPH-d) histochemistry followed by the demonstration of dopamine beta-hydroxylase (DBH) by immunoperoxidase, and (b) staining for DBH by immunofluorescence followed by the demonstration of NADPH-d histochemical activity. The largest subpopulation of neuronal somata displayed both DBH immunoreactivity and NADPH-d histochemical activity. The second largest group of somata showed NADPH-d activity only. A small group of neuronal somata showed only DBH immunoreactivity. The presence of catecholaminergic characteristics in NOS-containing neuronal somata is unusual and raises the question as to their origin. Their heterogeneity suggests different functions for the different subpopulations.

Adrenergic Fibers↗
PubMed1995

Effect of ageing on human plasma glutathione concentrations as determined by high-performance liquid chromatography with fluorimetric detection.

A convenient method for the determination of reduced glutathione (GSH) and oxidized glutathione (GSSG) in human plasma by high-performance liquid chromatography with fluorescence detection is reported. This assay involves direct addition of human plasma to methanolic monobromobimane, for simultaneous protein precipitation and thiol derivatization. The assay was validated by addition of authentic GSH and GSSG to plasma samples. Plasma glutathione levels in Chinese male and female volunteers were found to decrease with increasing age (age groups 20-30, 30-40, 40-50, 50-60, and > 60; mean +/- S.E.M. 0.95 +/- 0.03, 0.77 +/- 0.02, 0.67 +/- 0.03, 0.51 +/- 0.02, 0.48 +/- 0.02 microM for male volunteers and 1.11 +/- 0.06, 0.76 +/- 0.03, 0.61 +/- 0.03, 0.53 +/- 0.04 and 0.43 +/- 0.04 microM for female volunteers). GSSG levels, in both males and females, did not show a correlation with age. There were no significant differences in GSH or GSSG levels among male and female volunteers of the same age group. These results suggest that elderly persons might be more susceptible to oxidative injury due to decreased plasma glutathione levels.

Adult↗
PubMed1995

Lung annexin II promotes fusion of isolated lamellar bodies with liposomes.

The role of annexin II in the secretion of lung surfactant was investigated using isolated lamellar bodies and/or liposomes as the model system for aggregation and fusion. We first compared membrane aggregation mediated by two forms of annexin II, annexin II monomer (Anx IIm) and annexin II tetramer (Anx IIt). Anx IIt required 20-fold less Ca2+ to mediate phosphatidylserine (PS) liposome aggregation compared to Anx IIm. Aggregation of lamellar bodies mediated by Anx IIt was 4-fold greater than that by Anx IIm at 1 mM Ca2+. These results suggest that Anx IIt may be the more active form in vivo. Fusion of lamellar bodies with PS liposomes was promoted by Anx IIt in a dose-dependent manner, with maximal fusion occurring at 10-15 micrograms/ml of Anx IIt. Fusion was dependent on Ca2+ and the phospholipid composition of liposomes. While the fusion of lamellar bodies with PS liposomes required 100 microM Ca2+, the fusion with PS/phosphatidylethanolamine (PE) (1:3) liposomes required only 10 microM Ca2+. Anx IIt-mediated lamellar body-liposome fusion was enhanced by arachidonic acid, a lung surfactant secretagogue and inhibited by 4.4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), an inhibitor of lung surfactant secretion. The data suggest that Anx IIt may play a role in the fusion of lamellar bodies with plasma membranes during lung surfactant secretion.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1995

Lowered brain glutathione by diethylmaleate decreased the glutamate release induced by cerebral ischemia in anesthetized rats.

The effect of lowered brain glutathione content on the glutamate release following cerebral ischemia was investigated. Diethylmaleate (4 mmol/kg, i.p.), a commonly used chemical reagent for tissue glutathione depletion, significantly reduced the ischemia-induced glutamate release. The release of another excitatory amino acid aspartate was not affected by the diethylmaleate administration. These results suggested that part of the elevated glutamate content induced by ischemia might result from the cellular GSH.

Anesthetics↗
PubMed1995

Cloning a cDNA from human NK/T cells which codes for a protein with high proline content.

A cDNA clone, B4-2, was isolated from a natural killer (NK) minus T cell subtractive library. The B4-2 clone coded for an mRNA of 2061 bp in length. It encodes a deduced 327 aa protein with a calculated molecular mass of 35.2 kDa. Searching of B4-2 DNA and protein sequences against various databases revealed no high homology to other sequences. However, B4-2 has an unusually high proline content (13%), contains a putative nuclear targeting sequence, and has several SPXX motifs which are frequently found in gene regulatory proteins. One of the stretches of prolines in B4-2 closely resembles the ligand for proteins with SH3 domains. Northern hybridization data showed that B4-2 is not a lymphoid specific gene and is expressed in a hepatoma cell line and also weakly transcribed or absent in a variety of other cells. A polyclonal antiserum raised against recombinant B4-2 recognizes a 32-34 kDa protein in lymphocytes.

Amino Acid Sequence↗
PubMed1995

Plasma and cerebrospinal fluid pharmacokinetics of O6-benzylguanine and time course of peripheral blood mononuclear cell O6-methylguanine-DNA methyltransferase inhibition in the nonhuman primate.

O6-Benzylguanine (O6BG) enhances the cytotoxicity of the nitrosoureas by irreversibly binding and inhibiting the DNA repair enzyme O6-methyl-guanine-DNA methyltransferase (MGMT). The plasma and cerebrospinal fluid (CSF) pharmacokinetics of O6BG and its active metabolite, O6-benzyl-8-oxoguanine, were studied in a nonhuman primate model after 200 mg/m2 had been injected i.v. The parent drug and the metabolite were measured with a reverse-phase HPLC assay. A pharmacokinetic model incorporating separate compartments for O6BG and the O6-benzyl-8-oxoguanine metabolite, first-order conversion of O6BG to the metabolite, and additional first-order elimination rate constants for each compound, was simultaneously fitted to the parent drug and metabolite plasma concentration time data. Elimination of O6BG from plasma was rapid; it had a half-life of 1.6 h and a clearance of 68 ml/min/m2. On the basis of the pharmacokinetic model, essentially all of the O6BG was converted to O6-benzyl-8-oxoguanine. The plasma pharmacokinetic profile of the metabolite differed considerably from that the parent drug. The half-life (14 h) was 10-fold longer and the area under the curve (2420 microM/h) was 11-fold higher than that of O6BG (212 microM/h). The clearance rate of O6-benzyl-8-oxoguanine was 6.4 ml/min/m2. The CSF:plasma ratio was 4.3% for O6BG and 36% for O6-benzyl-8-oxoguanine, and the metabolite area under the curve was 90-fold higher than that of O6BG in CSF. The excellent CSF penetration of the active metabolite provides a rationale for the use of O6BG as a chemosensitizing agent for brain tumors. We also studied the duration of MGMT inhibition in peripheral blood mononuclear cells. By 2 h after a 200 mg/m2 dose of O6BG, > 98% of MGMT activity was suppressed, and > 95% suppression of enzyme activity persisted at 18 and 48 h after the dose. By 2 weeks after the treatment, MGMT levels had returned to baseline. Persistent high concentrations of the active metabolite appear to provide a pharmacological explanation for the prolonged suppression of MGMT activity.

Animals↗
PubMed1995

Identification and characterization of an interleukin-3 receptor-associated 110-kDa serine/threonine kinase.

We recently reported that interleukin-3 (IL-3) stimulation of the murine IL-3-responsive cell line, B6SUtA1, results in the rapid phosphorylation of the beta subunit of the IL-3 receptor (IL-3R), not only on tyrosine residues but on serine/threonine (Ser/Thr) residues as well. Since this occurred even at 4 degrees C, it suggested that a Ser/Thr-specific kinase might be closely associated with the IL-3R. To test this possibility, IL-3R complexes were isolated with anti-IL-3R (alpha IL-3R) antibodies, and in vitro phosphorylation studies were undertaken. These revealed the presence of a 110-kDa protein that was heavily phosphorylated in vitro on serine and threonine residues and that bound selectively to gamma-ATP-Sepharose beads. Moreover, this protein, which was not the 110-kDa subunit of phosphatidylinositol 3-kinase, was tyrosine phosphorylated in response to IL-3 and was specifically labeled in vitro with azido-[32P]ATP. These data, together with in vitro kinase inhibitor studies, suggest that an as yet uncharacterized H7- and staurosporine-sensitive 110-kDa Ser/Thr kinase may be constitutively associated with the IL-3R and activated following IL-3 stimulation. A comparison of IL-3R and erythropoietin receptor complexes suggests that this 110-kDa protein may be preferentially associated with the IL-3R.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1995

Binding of prenylated and polybasic peptides to membranes: affinities and intervesicle exchange.

The small GTP-binding protein G25K and the protein K-Ras 4B contain prenyl groups (geranylgeranyl and farnesyl, respectively) that are thioether linked to a C-terminal cysteine which is methylated on its alpha-carboxyl group. These proteins, like many other prenyl proteins, also have a string of basic residues near their C-termini. A series of prenylated peptides based on the C-terminal sequences of human brain G25K and human K-Ras 4B were synthesized and analyzed for their membrane binding affinities. G25K peptides containing an N-terminal N-acetyltryptophan group were studied because their binding to membranes containing a trace of dansylated phospholipid could be detected by fluorescence resonance energy transfer. The G25K peptide lacking a prenyl group and a C-terminal methyl ester did not detectably bind to vesicles, and binding was enhanced by more than 500-fold if the peptide was geranylgeranylated. For the farnesylated peptide, methylation of the C-terminus increased membrane affinity by at least 60-fold if the vesicles contained phosphatidylserine and by 3-fold if they lacked this acidic lipid. The geranylgeranylated and methylated G25K peptide remains irreversibly attached to vesicles over several minutes only if the vesicles contain phosphatidylserine, whereas the corresponding nonmethylated or farnesylated and methylated peptides dissociate rapidly (less than a few seconds) from neutral or anionic vesicles. Farnesylation of the nonmethylated K-Ras 4B peptide enhances its affinity to vesicles containing acidic phospholipids (phosphatidylglycerol or phosphatidylserine) by 70-fold, and methylation leads to an additional dramatic (150-fold) increase in membrane affinity.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

Post-transcriptional mechanisms are responsible for the reduction in lipoprotein lipase activity in cardiomyocytes from diabetic rat hearts.

Lipoprotein lipase (LPL) activity is reduced in cardiomyocytes from rat hearts following the acute (4-5 day) induction of diabetes with 100 mg/kg streptozotocin. The molecular basis for this inhibitory effect of diabetes on LPL activity was investigated by measuring steady-state LPL mRNA content and the synthesis and turnover of LPL protein ([35S]methionine incorporation into immunoprecipitable LPL protein in pulse and pulse-chase experiments) in control and diabetic cardiomyocytes. LPL activity was reduced to approx. 50% of control in diabetic cardiomyocytes, but LPL mRNA levels and turnover (degradation) of newly synthesized LPL were unchanged. Synthesis of total protein and LPL were reduced to 72% and 71% of control respectively; therefore, relative rates of LPL synthesis were the same in control and diabetic cardiomyocytes. The diabetes-induced reduction in LPL synthesis was accompanied by a decrease in LPL mass to 78% of control, and a decrease in enzyme specific activity (0.48 to 0.33 m-unit/ng of LPL protein) since the decline in catalytic activity was greater than the decrease in LPL synthesis and mass. Thus, post-transcriptional mechanisms involving a reduction in LPL synthesis as part of a generalized decrease in total protein synthesis, together with a post-translational mechanism(s) that result in accumulation of inactive LPL protein, are responsible for the decreased LPL activity in cardiomyocytes from diabetic rat hearts.

Animals↗
PubMed1995

Cinnamic acid: a natural product with potential use in cancer intervention.

Cinnamic acid, a naturally occurring aromatic fatty acid of low toxicity, has a long history of human exposure. We now show that cinnamic acid induces cytostasis and a reversal of malignant properties of human tumor cells in vitro. The concentration causing a 50% reduction of cell proliferation (IC50) ranged from 1 to 4.5 mM in glioblastoma, melanoma, prostate and lung carcinoma cells. Using melanoma cells as a model, we found that cinnamic acid induces cell differentiation as evidenced by morphological changes and increased melanin production. Moreover, treated cells had reduced invasive capacity associated with modulation of expression of genes implicated in tumor metastasis (collagenase type IV, and tissue inhibitor metalloproteinase 2) and immunogenicity (HLA-A3, class-I major histocompatibility antigen). Further molecular analysis indicated that the anti-tumor activity of cinnamic acid may be due in part to the inhibition of protein isoprenylation known to block mitogenic signal transduction. The results presented here identify cinnamic acid as a new member of the aromatic fatty acid class of differentiation-inducers with potential use in cancer intervention.

Antineoplastic Agents↗
PubMed1995

Germline p16INK4A mutation and protein dysfunction in a family with inherited melanoma.

The gene encoding the cell cycle inhibitor p16INK4A (also known as p16, MTS1, CDKN2 and INK4) has been mapped to human chromosome band 9p21, a region that also contains a putative melanoma susceptibility gene. Although germline mutations in the coding region of the p16INK4A gene have been detected in some families with inherited melanoma, many other families show no evidence of such mutations and hence the role of p16INK4A in the development of this tumor is still unclear. In this report, we describe a family with inherited melanoma in which a novel mutation in exon 2 of the p16INK4A gene segregates with the disease. The mutant gene encodes a protein with an in-frame deletion of two amino acids (Asp96 and Leu97). We show that the mutant protein is functionally abnormal: it is unable to bind cdk4 in vitro and does not inhibit colony formation in tertiary passage rat embryo fibroblasts. Moreover, in a metastatic lesion from one patient the wild type p16INK4A allele was deleted and the mutant allele retained. We conclude that family members carrying this germline mutation in the p16INK4A gene are predisposed to melanoma. By extension, these findings implicate the p16INK4A gene in the development of some cases of familial melanoma.

Alleles↗
PubMed1995

Molecular genetic analysis of the duplication of human inducible nitric oxide synthase (NOS2) sequences.

In previous studies, we found multiple copies of inducible nitric oxide synthase gene (NOS2)-like sequences in the human genome and mapped them to the pericentric region of chromosome 17. Here, we describe the cloning and sequencing of exon22 regions from three of these NOS2-like sequences. We have also mapped another NOS2-like sequence to human chromosome 14. Since there are multiple NOS2-like sequences present in the human genome, we have also carried out Zoo Blot hybridisation analysis using a NOS2 cDNA probe. Our data suggest that duplication of NOS2-like sequences occurred very recently in primate evolution.

Amino Acid Oxidoreductases↗