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Biomedical subjects

N Liu

Publications and source records attributed to N Liu.

At least 91 records · Page 5Linked to original sources
PubMed2000

Regional distribution of protein kinases in normal and odor-deprived mouse olfactory bulbs.

Unilateral naris closure produced dramatic down-regulation of tyrosine hydroxylase (TH) gene expression in periglomerular dopaminergic neurons in the olfactory bulb. To explore molecular mechanisms of TH gene regulation, the present study investigated the regional distribution of protein kinase A (PKAalpha), protein kinase C (PKCalpha), and CaM kinases II (CaMKIIalpha, beta) and IV (CaMKIV) in the normal olfactory bulb and in response to odor deprivation. Strong PKAalpha immunostaining was found in the glomerular, granule cell, external plexiform and olfactory nerve layers. PKCalpha staining was strong in granule cell and external plexiform layers but weak in the glomerular layer. Whereas CaMKIV was primarily found in granule cells, CaMKII was present in the glomerular, external plexiform, mitral cell and granule cell layers. No change in immunoreactivities of these kinases occurred in the olfactory bulb ipsilateral to naris closure. The expression of PKAalpha, PKCalpha and CaMKII, but not CaMKIV, in periglomerular cells suggests that these three kinases may play a role in TH gene regulation in the olfactory bulb. The lack of change in kinase protein levels after naris closure also suggests that any involvement of these kinases in TH gene expression in the olfactory bulb must be through altered kinase activity and not protein levels.

Animals↗
PubMed2000

Effects of pore mutations and permeant ion concentration on the spontaneous gating activity of OmpC porin.

Porins are trimers of beta-barrels that form channels for ions and other hydrophilic solutes in the outer membrane of Gram-negative bacteria. The X-ray structures of OmpF and PhoE show that each monomeric pore is constricted by an extracellular loop that folds into the channel vestibule, a motif that is highly conserved among bacterial porins. Electrostatic calculations have suggested that the distribution of ionizable groups at the constriction zone (or eyelet) may establish an intrinsic transverse electrostatic field across the pore, that is perpendicular to the pore axis. In order to study the role that electrostatic interactions between pore residues may have in porin function, we used spontaneous mutants and engineered site-directed mutants that have an altered charge distribution at the eyelet and compared their electrophysiological behavior with that of wild-type OmpC. We found that some mutations lead to changes in the spontaneous gating activity of OmpC porin channels. Changes in the concentration of permeant ions also altered this activity. These results suggest that the ionic interactions that exist between charged residues at the constriction zone of porin may play a role in the transitions between the channel's closed and open states.

Amino Acid Motifs↗
PubMed2000

A SXRF method for determining the relative concentration of trace elements in plasma protein affected by cisplatin.

This article presents an analytical method for the determination of the relative concentrations of trace elements in plasma protein by gel chromatography combined with SXRF (synchrotron radiation X-ray fluorescence). The fraction of plasma protein of male Kunming mice (body weight 24.2 +/- 0.3 g), treated with a cisplatin i.p. injection at a dose of 10 mg/kg, was obtained by the separation of a Sephadex G-50 column (buffered with ammonium acetate, pH 5.7). The SXRF experiments were performed at the Beijing Electron Positron Collider synchrotron radiation facility. The elements (Pt, S, Ca, Fe, Ni, Cu, Zn, Se, Br, and Sr) in the fraction of the plasma proteins (>22 kDa) were assayed using highly sensitive SXRF. The relative concentrations of elements were calculated by a normalization of Compton scattering intensity around 22 keV, after the normalization for the collection time of the X-ray spectrum and the counting of the ion chamber, and subtracting the contribution of the polycarbonate film for the supporting sample. The determination could prove that the element Pt in plasma was bound with macromolecular protein. Cu and S were present in the fraction of the protein in mice treated with cisplatin increase, and their ratios of treated/control were 1.66 +/- 0.06 and 1.78 +/- 0.33, respectively; Zn decreased to a ratio of 0.78 +/- 0.09. Our results are in agreement with others that cisplatin exposure leads to a marked loss of kidney copper and a moderate rise in kidney zinc. However, this article primarily describes one of the analytical methods used; it does not emphasize the results of the effect of cisplatin on trace elements in plasma protein.

Animals↗
PubMed2000

Insecticide resistance and cross-resistance in the house fly (Diptera: Muscidae).

A house fly strain, ALHF, was collected from a poultry farm in Alabama after a control failure with permethrin, and further selected in the laboratory with permethrin for five generations. The level of resistance to permethrin in ALHF was increased rapidly from an initial 260-fold to 1,800-fold after selection. Incomplete suppression of permethrin resistance by piperonyl butoxide (PBO) and S,S,S,-tributylphosphorotrithioate (DEF) reveals that P450 monooxygenase- and hydrolase-mediated detoxication, and one or more additional mechanisms are involved in resistance to permethrin. The ALHF strain showed a great ability to develop resistance or cross-resistance to different insecticides within and outside the pyrethroid group including some relatively new insecticides. Resistance to beta-cypermethrin, cypermethrin, deltamethrin, and propoxur (2,400-4,200-, 10,000-, and > 290-fold, respectively, compared with a susceptible strain, aabys) in ALHF house flies was partially or mostly suppressed by PBO and DEF, indicating that P450 monooxygenases and hydrolases are involved in resistance to these insecticides. Partial reduction in resistance with PBO and DEF implies that multiresistance mechanisms are responsible for resistance. Fifteen- and more than fourfold resistance and cross-resistance to chlorpyrifos and imidacloprid, respectively, were not effected by PBO or DEF, indicating that P450 monooxygenases and hydrolases are not involved in resistance to these two insecticides. Forty-nine-fold cross-resistance to fipronil was mostly suppressed by PBO and DEF, revealing that monooxygenases are a major mechanism of cross-resistance to fipronil. Multiresistance mechanisms in the ALHF house fly strain, however, do not confer cross-resistance to spinosad, a novel insecticide derived from the bacterium Saccharopolyspora spinosa. Thus, we propose that spinosad be used as a potential insecticide against house fly pests, especially resistant flies.

Animals↗
PubMed2000

All-trans retinoic acid modulates fas expression and enhances chemosensitivity of human medulloblastoma cells.

Retinoic acid (RA) can promote human medulloblastoma cells Med-3 toward differentiation but is not sufficient to induce cell death, suggesting its limited effect on medulloblastomas. On the other hand, the differentiated tumour cells have been supposed to be more sensitive to chemotherapeutic drugs. To elucidate this possibility for medulloblastoma cells, 10 microM/l RA, 1.0 microg/ml cisplatin (CP) and their half-dosage combinations were utilized in this study to treat Med-3 cells and their influences in cell proliferation, morphology and death patterns were evaluated. In parallel, the expressions of Fas and its ligand (FasL) were analyzed by immunocytochemical staining and Western blot hybridization. Anti-Fas antibody was used to incubate the Med-3 cells pretreated by 10 microM/l RA or 1.0 microg/ml CP. It was revealed that RA and CP could inhibit cell growth but rarely induce apoptosis. Combination of half doses each of RA and CP effectively caused most of tumour cells to die of apoptosis within 6 days. FasL molecules in 29 kDa and 37 kDa were detected in Med-3 cells with and without the treatments. The Fas molecule around 30 kDa and located in the cytoplasm was found in the normally cultured cells and the cells treated by CP. An additional 45 kDa Fas band with the appearance of its cell surface labeling was detected in the cells treated by 10 microM/l RA and by 5 microM/l RA + 0.5 microg/ml CP. The anti-Fas antibody could efficiently induce apoptosis only in the cell populations pretreated by RA. Our data thus suggest that RA can enhance the chemosensitivity of human medulloblastoma Med-3 cells presumably via modulating the Fas expression pattern. The RA/CP combined regimen would be a potential therapeutic approach for medulloblastomas.

Antineoplastic Agents↗
PubMed2000

Frequent expression of soluble Fas and Fas ligand in Chinese stomach cancer and its preneoplastic lesions.

To investigate the frequency and pattern of Fas and FasL expression in the gastric mucosa at different stages of gastrocarcinogenesis, the combined examinations of pathology, immunocytochemistry and Western blot hybridisation were performed on the cancer specimens as well as their preneoplastic and non-cancerous counterparts. The frequencies of Fas and FasL expression were found to be 6.3% (1/16) and 62.5% (10/16) in non-cancerous mucosa, 60% (6/10) and 80% (8/10) in atrophic gastritis, 75% (9/12) and 83% (10/12) in intestinal metaplasia, 100% in both dysplasia Grades II (20/20) and Grade III (15/15) and 4 types of gastric carcinomas (74/74). Two forms of FasL protein in 37 kDa and 26 kDa were detected in all FasL+ cases. Soluble Fas (30 kDa) but not the membrane-type (43 kDa) is predominantly expressed in the Fas+ cases. Our data thus suggest a close correlation of soluble Fas with stomach tumour progression P<0.01. The sFas protein, together with the tumor-derived soluble and membrane FasL, may confer on the transforming and transformed gastric epithelial cells an immune advantage enabling escape from endogenous and exogenous suicide signal(s).

Fas Ligand Protein↗
PubMed2000

[Quick RNA extraction from specified morphological region in frozen sections and its RT-PCR application].

OBJECTIVE: To establish a method for quick RNA extraction from specified histological region in frozen sections so as to avoid cross RNA contamination among different types of cells/tissues and to achieve specific RT-PCR amplification. METHODS: Prepare serial frozen sections 5microm in thickness for histological and immunocytochemical examination. Based on the results, make one or two pieces of 20 microm section and select a specified region for quick RNA extraction and RT-PCR analysis. RESULTS: RNA extraction can be finished within an hour and the data of RT-PCR obtained within 6 hours. Besides the high performance, this method can efficiently exclude pseudo positive or pseudo negative results caused by inter-cellular RNA contamination. CONCLUSION: This method is an important complement to the current techniques for RNA extraction and RT-PCR.

Frozen Sections↗
PubMed2000

Human cytochrome P-450 3A4: in vitro drug-drug interaction patterns are substrate-dependent.

Testosterone, terfenadine, midazolam, and nifedipine, four commonly used substrates for human cytochrome P-450 3A4 (CYP3A4), were studied in pairs in human liver microsomes and in microsomes from cells containing recombinant human CYP3A4 and P-450 reductase, to investigate in vitro substrate-substrate interaction with CYP3A4. The interaction patterns between compounds with CYP3A4 were found to be substrate-dependent. Mutual inhibition, partial inhibition, and activation were observed in the testosterone-terfenadine, testosterone-midazolam, or terfenadine-midazolam interactions. However, the most unusual result was the interaction between testosterone and nifedipine. Although nifedipine inhibited testosterone 6beta-hydroxylation in a concentration-dependent manner, testosterone did not inhibit nifedipine oxidation. Furthermore, the effect of testosterone and 7,8-benzoflavone on midazolam 1'-hydroxylation and 4-hydroxylation demonstrated different regiospecificities. These results may be explained by a model in which multiple substrates or ligands can bind concurrently to the active site of a single CYP3A4 molecule. However, the contribution of separate allosteric sites and conformational heterogeneity to the atypical kinetics of CYP3A4 can not be ruled out in this model.

Cytochrome P-450 CYP3A↗
PubMed2000

Alternative splicing of RHAMM gene in chinese gastric cancers and its in vitro regulation.

OBJECTIVE: To identify the receptor of hyaluronic acid mediated motility (RHAMM), expression pattern(s) in the gastric mucosa with various lesions and to elucidate the effect of hyaluronic acid(HA) on in vitro RHAMM expression. METHODS: Immunocytochemical staining and Western blot hybridization were performed to check the expression patterns and locations of RHAMM molecules in the noncancerous, preneoplastic and malignant gastric specimens. RHAMM expression of the two stomach cancer cell lines cultured conventionally or under the conditions with gelatin or HA supplementation was evaluated as well. RESULTS: Mr 93000-95000 intracellular RHAMM, so-called IHABP, proteins were detected in 17% noncancerous mucosa. The multiple spectrums and increased frequencies of RHAMM expression could be observed in the majority of the cancer cases with both intracellular and cell surface labeling. HA but not gelatin could promote membrane type RHAMM (mRHAMM) expression of stomach cancer cells in a dose associated pattern. CONCLUSION: The expression of mRHAMM variants is closely associated with tumor progression, which may be promoted and modulated by HA.

Alternative Splicing↗
PubMed2000

Expression of hyaluronan receptors CD44 and RHAMM in stomach cancers: relevance with tumor progression.

Interactions of hyaluronic acid (HA) with its binding proteins CD44 and RHAMM (receptor for HA-mediating motility) have been proposed to be important in promoting tumor progression and dissemination. However, a comparative study of their expression patterns in stomach cancer and its associated lesions is not yet available. To address this issue, the combined examinations of pathology, immunocytochemistry and Western blot hybridization were performed on advanced gastric cancer specimens as well as their preneoplastic and non-cancerous counterparts. Alternative CD44 expression was observed in the gastric mucosa with different lesions. CD44 proteins harboring variant exon 6 (CD44 v6) was detected only in cancer tissues with a total positive rate of 14% (10/74). Intracellular RHAMM molecules in Mr 93000 to 95000 were expressed in 3/31 non-cancerous mucosa. RHAMM detection rates increased along with tumor progression. Irrespective of the differences of gross and morphological pattern, majority (54/74) of cancer cases expressed multiple RHAMM isoforms in Mr 40000-45000, 64000, 70000-73000, 85000 and 93000-95000 with the appearance of cell surface immunocytochemical labeling. Among CD44 variant isoforms, v6 is more relevant with malignant transformation of gastric epithelium. Expression of RHAMM, especially the cell surface variants, is closely correlated with tumor progression (P<0.01). Expression of CD44 and RHAMM may benefit the invasion and metastasis of gastric cancer cells presumably in a reciprocal manner.

Blotting, Western↗
PubMed2000

Eosinophilic ulcer of the oral mucosa: a clinicopathological analysis.

OBJECTIVE: To explore the clinical characteristics, histologic features, method of treatment, and possible etiology of eosinophilic ulcer of the oral mucosa. METHOD: Eight cases of eosinophilic ulcer of the oral mucosa were analyzed. RESULTS: In all cases, the ulcer site was the tongue. Ulcers were unifocal, had a benign course, and three of patients had a history of EUOM recurrence. Pathological features showed an extensive inflammatory cell infiltration, with predominantly eosinophilic cells throughout the submucosa. All ulcers were treated with either conservative excision or incisional biopsy. CONCLUSIONS: Eosinophilic ulcer is a rare, self-limiting benign disease that often appears in older adults or children. Its etiology remains obscure and may be associated with traumatic factors. This study provides useful information on clinical and pathological features, diagnosis, treatment, and prognosis, as well as the possible etiology of this disease.

Adolescent↗
PubMed2000

Alternation of Na(+)-Ca2+ exchange in rat cardiac sarcolemmal membranes during different phases of sepsis.

OBJECTIVE: To study the alteration of Na(+)-Ca2+ exchange in rat cardiac sarcolemmal membrane during phases of septic shock. METHODS: Sepsis was induced by cecal ligation and puncture (CLP). Na(+)-Ca2+ exchange was assayed by radioactive analysis. RESULTS: Na(+)-dependent 45Ca2+ uptake was decreased by 62%-69% in late phase of sepsis, whereas it was not affected in early phase of sepsis. Na(+)-Ca2+ exchange stimulated by 5' guanylyl imidodiphosphate [Gpp (NH) p] was decreased by 65.7% in late phase of sepsis but unaltered in early phase of sepsis. Two agonists (angiotensin II and phenylephrine) coupled to Gq and a protein kinase C activator, phorbol 12-myristate 13-acetate (PMA) all inhibited Na(+)-Ca2+ exchange in late phase of sepsis. Na(+)-Ca2+ exchange activities induced by phosphorylation of Na(+)-Ca2+ exchange were decreased in late phase of sepsis, whereas inhibition of Na(+)-Ca2+ exchange by dephosphorylation was increased both in early and late phases of sepsis. CONCLUSION: The alteration of Na(+)-Ca2+ exchange during different phases of sepsis might be related to the activities of Gq, protein kinase C, and phosphorylation/dephosphorylation.

Animals↗
PubMed2000

Advanced glycosylation end products increase diacylglycerol levels in cultured human umbilical vein endothelial cells.

OBJECTIVE: To study whether the diacylglycerol (Dia) signaling pathway is stimulated by advanced glycosylation end products (AGEP) and to test the effect of vitamin E and aminoguanidine (AG) on the elevation of Dia induced by AGEP in cultured human umbilical vein endothelial cells (HUVECs). METHODS: The effects of AGEP on Dia levels in cultured HUVEC were studied with radio-enzymatic assay. Quantitative measurements of 32P phosphatidic acid were achieved by thin-layer chromatography and autoradiography. RESULTS: The Dia levels in HUVECs were increased by AGEP modified bovine serum albumin (AGEP-BSA) in a dose-dependent, biphasic manner. The early phase was rapid and transient, peaking at 15 s; the late phase reached the maximal level at 10 min and then decayed slowly. Dia levels in HUVEC exposed to different concentrations (50, 100 and 200 mg/L) of AGEP-BSA (341 +/- 14, 678 +/- 16, and 873 +/- 18 pmol/L, respectively vs control 225 +/- 10 pmol/L) and AGEP-BSA samples with various glycosylation times (4, 8 and 12 weeks) were significantly increased (270 +/- 12, 394 +/- 16, and 556 +/- 19 pmol/L) as compared with the controls. 50 and 100 mmol/L of vitamin E can reduce AGEP-BSA-induced Dia levels from 873 +/- 18 pmol/L to 764 +/- 29 and 441 +/- 21 pmol/L in HUVEC, respectively. In AG-treated (100 mmol/L) groups, the same concentration (100 and 200 mg/L) of AGEP-BSA-induced elevation of Dia was decreased to 312 +/- 8 and 351 +/- 13 pmol/L, respectively. Glycosylated low-density lipoprotein (LDL) did not affect Dia levels. CONCLUSION: AGEP causes a robust stimulation of the Dia/protein kinase C pathway in HUVEC. Vitamin E can attenuate the AGEP-BSA-induced elevation of Dia levels. AG can suppress the ability of AGEP-BSA to increase Dia levels in HUVEC.

Diglycerides↗
PubMed2000

Effect of advanced glycosylation end products on activity of protein kinase C in human peripheral blood mononuclear cells.

OBJECTIVES: To investigate the effect of advanced glycosylation end products (AGEs) on the activity of protein kinase C (PKC) in human peripheral blood mononuclear cells (PBMC) and to observe whether aminoguanidine (AG) can influence the effect of AGEs. METHODS: After PBMC were isolated from human peripheral blood and incubated with different concentrations of AGEs-BSA for various periods, total PKC activity in PBMC was determined by measuring the incorporation of 32P from [gamma-32 P] ATP into a special substrate using Promega PKC assay kit. RESULTS: AGEs-BSA increased the total PKC activity in PBMC from 83.43 +/- 6.57 pmol/min/mg protein to 116.8 +/- 13.82 pmol/min/mg protein with a peak at 15 min. AGEs-BSA also increased the total PKC activity in a concentration-dependent manner from 83.1 +/- 6.4 pmol/min/mg protein (control) to 119.1 +/- 13.3 pmol/min/mg protein (control vs AGEs-BSA 400 mg/L, P < 0.01). Furthermore, AGEs-BSA induced an elevation of PKC activity in a glycosylating time-related manner, from 80.9 +/- 8.2 (control) to 118.3 +/- 11.5 pmol/min/mg protein (glycosylation for 12 wk, P < 0.01). The total PKC activity stimulated by AGEs-BSA pretreated with AG (100, 200 mg/L) was markedly lower than that of AGEs-BSA group not pretreated with AG (P < 0.05, P < 0.01). CONCLUSIONS: AGEs-BSA increased the total PKC activity in PBMC in a concentration and incubation time dependent manner. The ability of AGEs-BSA to stimulate PKC activity was markedly decreased by pretreatment of AGEs-BSA with AG.

Cells, Cultured↗
PubMed2000

[Retinoic acid enhances chemosensitivity of medulloblastoma cells in vitro and its potential mechanism].

OBJECTIVE: To elucidate the chemosensitivity of retinoic acid (RA)-differentiated medulloblastoma Med-3 cells to conventional anti-cancer drug and to determine the potential genetic factor(s) mediating this sensitivity. METHODS: Ten mumol/L RA, 5 micrograms/ml cisplatin (DDP) and their combination with one half concentration of each were used respectively to treat human medulloblastoma cell line Med-3 in vitro. Cell proliferation, morphology and death pattern as well as Fas/FasL expressions were analyzed by multiple approaches. RESULTS: Both soluble and membrane FasL could be detected in the treated and untreated Med-3. Fas was positive in the cytoplasm of Med-3 cells and the cells could produce soluble Fas. DDP had no obvious effect on Fas expression. RA up-regulated Fas expression and translocalization from cytoplasm to cell membrane of the treated cells. Neither RA nor DDP could trigger apoptosis but in combination could effectively induce apoptosis. CONCLUSION: RA could enhance the apoptotic susceptibility of Med-3 cells to DDP presumably through modulating the Fas expression pattern. Combined RA/DDP regimen would have potential clinical value in the management of medulloblastomas.

Antineoplastic Agents↗
PubMed2000

[Breast cancer accompanied by Paget's disease: an anlysis of 34 cases].

OBJECTIVE: To better understand the clinical and pathological features, diagnosis, treatment and prognosis of Paget's disease accompanying breast cancer. METHODS: From 1958 to 1997, 34 such patients were operated and pathologically confirmed. RESULTS: Breast cancer combined with Pagat's disease accounted for 0.9% of the total number of breast cancer patients treated in the same period of time. The mean age of patients was 47.3 years, and the mean duration of symptoms was 23.9 months. The patients received combination treatment with surgery as the major treatment modality. Among patients with nipple change as the first symptom, 26.7% of them had positive axillary nodes. The rate of metastasis was 26.7% as confirmed by surgical pathology. The 5-, 10-, and 20-year survival rate was 93.1%, 78.1% and 67.0%, respectively. Among those with palpable mass as the first symptom, metastasis to the axillary lymph nodes occurred in 52.6% of the cases, and distant metastasis in 42.1% of the cases. The rate of 5-, 10- and 20-year survival rate was 60.5%, 53.8% and 53.8%, respectively. CONCLUSION: Paget's disease, as a special form of breast cancer, may accompany cancer inside of the breast. In patients whose disease is confined to the nipple, their prognosis is better than those accompanied by palpable mass in the breast.

Adult↗
PubMed2000

[The expression of interleukin-6 mRNA and autosecretion in human leukemic cells].

OBJECTIVE: To make a comprehensive and systematic study on the constructive expression of IL-6 mRNA and IL-6 autosecretion in human leukemic cells and discuss the effect of IL-6 autosecretion on the specific binding of IL-6-PE40 fusion protein to targeted leukemic cells. METHODS: Semi-quantitative RT-PCR, sequencing and ELISA were used to detect the constructive expression of IL-6 mRNA and autosecretion level of IL-6 protein in human leukemic cell lines, such as U937, HL60, KG1, TF1, K562, HuT28, CEM and Raji. RESULTS: The relative expression level of IL-6 mRNA in myelocytic, monocytic and erythrocytic leukemic cell lines including HL60, U937, KG1 and TF1 and lymphoblastic leukemic cell lines such as CEM, HuT28 and Raji is very weak, ranging from 0.03 to 0.07. However, K562, an chronic myelocytic leukemic cell line, had the highest level 1.25 among the 8 leukemic cell lines and the level was also higher than that of the positive control U266 multiple myeloma cell line. Based on ELISA assay of IL-6, there were remarkable differences between the 8 leukemic cell lines, their secretion of IL-6 could be divided into 3 levels, i.e. high, moderate and low secretion type. CONCLUSION: These observations imply that the intrinsic expression and secretion of IL-6 differ obviously among different leukemic cell lines. Autocrine IL-6 may prevent IL-6-PE40 fusion protein from specific binding to targeted leukemic cells and consequently affect its specific killing toxicity.

Cell Line, Tumor↗