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Biomedical subjects

L P Guo

Publications and source records attributed to L P Guo.

12 recordsLinked to original sources
PubMed2006

Magnetocrystalline anisotropy in permalloy revisited.

Permalloy with a body-centered-cubic structure has been grown on GaAs(001) by molecular beam epitaxy. Its magnetism, Curie temperature, and magnetic anisotropy are determined experimentally and compared to those of conventional face-centered-cubic Permalloy. Unexpectedly the vanishing magnetic cubic anisotropy in Permalloy is found to be independent of its atomic structure but depends only upon the stoichiometry of Fe and Ni in the FexNi1-x alloy. This observation is further investigated and confirmed by first-principles electronic band calculations, which help to understand the long-standing issue of why Permalloy should be a soft magnet.

Journal Article↗
PubMed2001

Studies of the inheritance of seed qualities and the exploitation of F2 heterosis in low gossypol strains in upland cotton.

Twenty cross combinations were made with 4 recessive glandless lines (gl2gl2 gl3gl3) used as females and 5 dominant glandless lines (Gl2eGl2e Gl3Gl3) used as male parents to estimate the genetic variance components of kernel oil and protein content of seeds, oil and protein index, and kernel index using a genetic model for parents, F2 and F3. The results showed that all the analyzed traits were mainly controlled by additive effects. Oil content was controlled mainly by maternal additive effect, and other traits by direct additive effect. The average heterosis of F2 over mid-parent based on population mean was -1.99% to 1.11% for all these traits. It suggests that little inbreeding depression exists for F2 and F3 seeds. There were 75% and 60% of the F2 and the F3 combinations in which open-pollinated seeds contained gossypol levels lower than 0.4 gkg-1. This result indicated that it is possible to screen and select high yielding F2 hybrids with a gossypol content lower than the regulated criterion and without lowering seed quality.

Genotype↗
PubMed2001

Effect of long-term fertilization on soil nitrate distribution.

A thirteen years long-term field fertilizer experiment was conducted to monitor the effect of different fertilization on soil nitrate distribution. The results showed: (1) Applying relative excessive N fertilizer could result large quantities of NO3- residue and NO3- movement downward in soil profiles; amending phosphate fertilizer or organic manure with nitrogen fertilizer together could significantly improve the status of NO3- leaching downward due to the balanced uptake of nutrients by crops. (2) Appropriate amounts of nitrogen fertilizer which was equal or smaller than the optimal fertilization rate could not result in more NO3- leaching in Northern China. (3) Precipitation influenced the amounts and depth of soil NO3- leaching: NO3- could move to 80 cm depth or below at autumn or at the next spring when rainfall was higher during the rainy season through July to September in North China.

Agriculture↗
PubMed2001

[A preliminary study on relationship between Atractylodes lancea and A. chinensis as analyzed by RAPD].

OBJECTIVE: To study the relationship between A. lancea and A. chinensis by RAPD analysis. METHOD: Using 10 random primers, RAPD of seven Atractylodes samples was performed. The result was analyzed by RAPDistance Package Version 1.04. RESULT: A total of 60 polymerphic loci were amplified. It appears that the Atractylodes samples tend to cluster in relation to their habitats, and A. lancea has close phylogenetic relationship with A. japonica. CONCLUSION: A certain correlation among the chemical composition, genetic diversity and geographic distribution has been revealed. It is reasonable to separate A. lancea from A. chinensis according to their habitats.

Atractylodes↗
PubMed1999

[p53 gene expression of human hepatoma cell lines and their sensitivities to parvovirus H-1].

DNA structure and expression of p53 gene in human hepatoma cell lines SMMC-7721, YY-8103 and a spontaneously transformed liver cell line L-02 were analysed using the following method: analysis of allelic losses on chromosome 17p, PCR/SSCP, Northern blot and immunoprecipitation. There was no point mutation found in the exons 4-9 of the p53 gene, and a low level of expression of p53 gene was detected in the three cell lines. These observations were in agreement to the reported results of the relevant experiment using the human hepatoma cell line QGY-7703. Sensitivities of these cell lines and other eight human hepatoma cell lines (QGY-7703, PLC/PRF/5, Tong/HCC, Huh-7, FOCUS, Hep3B, SK-Hep-1, HepG2) with known p53 backgrounds to parvovirus H-1 was assayed using MTT method. Abnormality in the structure and/or function was observed in all of the cell lines examined except HepG2. The cell line HepG2 with normal structure and function of the p53 gene was found to be the least sensitive to H-1 in comparison to all the cell lines which have defeated structure and/or function of the p53 gene. The present study serves as a preliminary evidence that enhancement of the sensitivity of human hepatoma cell lines to H-1 is correlated to the abnormality of the structure and/or function of the p53 gene.

Carcinoma, Hepatocellular↗
PubMed1994

Use of an autonomous parvovirus vector for selective transfer of a foreign gene into transformed human cells of different tissue origins and its expression therein.

In this work, we report the transduction of a chloramphenicol acetyltransferase (CAT) reporter gene into a variety of normal and transformed human cells of various tissue origins. The vector used was MVM/P38cat, a recombinant of the prototype strain of the autonomous parvovirus minute virus of mice (MVMp). The CAT gene was inserted into the capsid-encoding region of the infectious molecular clone of MVMp genome, under the control of the MVM P38 promoter. When used to transfect permissive cells, the MVM/P38cat DNA was efficiently replicated and expressed the foreign CAT gene at high levels. By cotransfecting with a helper plasmid expressing the capsid proteins, it was possible to produce mixed virus stocks containing MVM/P38cat infectious particles and variable amounts of recombinant MVM. MVM/P38cat viral particles were successfully used to transfer the CAT gene and to express it in a variety of human cells. Both viral DNA replication and P38-driven CAT expression were achieved in fibroblasts, epithelial cells, T lymphocytes, and macrophages in a transformation-dependent way, but with an efficiency depending on the cell type. In transformed B lymphocytes, however, the vector was not replicated, nor did it express the CAT gene.

Animals↗
PubMed1991

Relevance of N-nitrosamines to oesophageal cancer in China.

Oesophageal cancer occurs at a very high frequency in certain areas of China, especially in Linxian county, Henan province. Previous studies suggested that N-nitroso compounds play a causative role. In order to study further the exposure of Linxian inhabitants, the intake of N-nitrosamines in the diet was determined. The total daily intake of volatile nitrosamines and of N-nitroso-N-methylbenzylamine (NMBzA) was higher in Linxian than in two other counties. NMBzA can induce cancer in animal and human oesophageal epithelium. Human fetal oesophageal epithelia were cultured with NMBzA for 4 h, and eight monkeys were treated with NMBzA. High-molecular-weight DNA extracted from explants and from the oesophageal epithelia of monkeys induced malignant transformation of NIH 3T3 cells. Alu and monkey-specific repeat sequences were present in transformed cells, and H-ras was found in the transforming DNA. Human fetal oesophageal epithelium cultured with NMBzA was transplanted into the mesentery of BALB/c nude mice. Tumours were found after eight months; and the Alu sequence was present in DNA extracted from tumours induced by NMBzA, showing that the tumours were of human origin. The results provide direct evidence that NMBzA is carcinogenic in human oesophageal epithelium and that N-nitrosamines are one of the causative factors of oesophageal cancer in Linxian county.

Animals↗
PubMed1988

Positive selection of human cells lacking several transformation parameters from an SV40-transformed culture by means of parvovirus H-1.

The simian virus 40 (SV40)-transformed, newborn human kidney cell line NB-F was found to be heterogeneous with respect to its sensitivity to parvovirus H-1. The majority of the cells sustain a productive H-1 infection which eventually causes their lysis. Yet, a small fraction of the cells appears to be much less susceptible to H-1. Such a resistance to H-1 infection is a stable, transmissible property of this subpopulation of cells which was denoted NB-FR. The heterogeneity of NB-F cells is also apparent from the distribution of their karyotypes, which is bimodal and peaks at 114 and 46 chromosomes/cell. In contrast, the great majority of NB-FR cells contain 41-50 chromosomes. H-1-resistant and -sensitive cells appear to be related in several respects: they both contain morphologically human chromosomes as well as multiple SV40 DNA inserts, and could not be distinguished by isoenzyme typing. It was investigated whether the degree of sensitivity to H-1 infection correlated with other phenotypic properties of the human cell derivatives. NB-F cultures exhibit a series of transformation parameters, such as SV40 T-antigen expression, poor contact inhibition, clonogenicity in semi-solid medium and high lectin agglutinability, which are all much reduced or even undetectable in NB-FR cells. These observations suggest that cell susceptibility to H-1 segregates with marker(s) of in vitro malignant transformation. Moreover, the data indicate that parvoviruses can be used to preferentially remove transformants from a mixed culture of normal and transformed cells.

Antigens, Viral, Tumor↗
PubMed1988

Inhibitory effect of parvovirus H-1 on cultured human tumour cells or transformed cells.

The present study establishes the in vitro system for studying the oncosuppression activity of parvovirus and discovers that parvovirus H-1 can be grown cytolytically in various human cancer cell lines, which include 4 hepatoma cell lines (QGY-7703, SMMC-7721, Bel-7402, PLC/PRF/5), 3 gastric cancer cell lines (SGC-7901, MGC-80-3, MKN-28) and 1 naspharynx cancer cell line (CNE). The growth of two primary gastric cancer cell cultures from surgical cancer tissue were also inhibited by the infection of H-1. The sensitivity of cancer cells to H-1 may relate to their differentiation states. On the contrary, H-1 can neither be grown cytolytically in normal liver or stomach cells, nor inhibit their growth. Transformation of human skin fibroblasts with Simian Virus 40 activated their sensitivity to H-1. Our results thus indicate that the antineoplastic activity of H-1 in vivo involves at least its direct inhibiting or killing malignant cells.

Carcinoma, Hepatocellular↗
PubMed1988

Transformation of cultured human fetal gastric fibroblasts with physico-chemical agents.

Treatment of early passage human fetal gastric fibroblasts with ultraviolet (UV) light and the chemical carcinogen ethyl nitrosourea (ENU) in succession resulted in an immortally growing cell line, named GTS 8502. The cells of this line display typical transformation characteristics, such as irregularly shaped nuclei, heteroploidization of karyotype and frequent appearance of heteromorphic chromosomes, the enhanced volume ratio of nucleus to cytoplasm, multinucleoli, appearance of microvilli on the surface of the cells and agglutination reaction to lectin concanavalin A. The transformants have high growing and mitotic indices and the ability of focus-formation on monolayers and anchorage independent growth in soft agar medium. Moreover, these cells induced tumours in nude mice or in immunosuppressed new-born rats through heterotransplantation. The results of various methods including electromicroscopy and histochemical analyses indicate that GTS 8502 cells are of fibroblast origin. Our results thus indicate that synergism of two carcinogens may raise the transformation ratio of normal human cells, which is otherwise extremely low. The transformation of human cells may be utilized to detect environmental carcinogens.

Animals↗
PubMed1987

Determination of N-nitrosamines in gastric juice and urine and a comparison of endogenous formation of N-nitrosoproline and its inhibition in subjects from high- and low-risk areas for oesophageal cancer.

Samples of gastric juice were collected from a high-risk area for oesophageal cancer in China and analysed for N-nitroso compounds. N-Nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), N-nitrosomethylbenzylamine (NMBzA), N-nitrosopyrrolidine (NPYR) and N-nitrosopiperidine (NPIP) were identified in descending order of concentration. Several unknown compounds were also detected in the fasting gastric juice. A positive correlation was found between the amount of nitrosamines in gastric juice and the degree of severity of lesions of the oesophageal epithelium: the amounts of nitrosamines in gastric juice from subjects with a normal oesophageal epithelium were lower than those in subjects with marked dysplasia or carcinoma of the oesophagus. In addition, 1500 samples of 24-h urine were collected from various communes in six high-risk areas and two low-risk areas for this cancer in China and analysed for N-nitrosamino acids. Subjects in high-risk areas excreted higher levels than those in low-risk areas. Intake of L-proline resulted in marked increases in levels of urinary N-nitrosoproline (NPRO) in inhabitants from both high- and low-risk areas. Intake of moderate doses of vitamin C, alpha-tocopherol and zinc by high-risk subjects reduced the urinary levels of N-nitrosamino acids to those found in undosed subjects in low-risk areas, suggesting a rational basis for prevention in high-risk areas.

China↗