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Biomedical subjects

P Feng

Publications and source records attributed to P Feng.

At least 109 records · Page 6Linked to original sources
PubMed1994

Rapid detection of food-borne pathogenic bacteria.

Recent advancements in biotechnology are rapidly altering the diagnostic procedures used in microbiologic analysis of foods. Biochemical identification tests have been miniaturized and automated, making them faster and more economical. Pathogenic bacteria that were previously isolated and identified after labor- and time-intensive enrichment and plating procedures can now be detected by measuring specific physicochemical changes resulting from their growth or metabolic activity. Nucleic acid and antibody-based assays are now used to rapidly and reliably detect pathogenic bacteria in foods. Nevertheless, foods offer unique challenges to the application of these techniques because of their complexity and variety, their interference with the rapid detection methods, and the need to detect pathogenic bacteria when they are present in foods at very low levels. Methods to sequester target pathogenic bacteria from interfering food components and to concentrate them in small volumes are needed to enable the efficient application of rapid detection and identification methods.

Bacteria↗
PubMed1994

[Radioligand binding assay of PHSA receptor on hepatocytes].

The radioligand binding assay of PHSA receptor on hepatocytes of 7 adults is reported. The presence of PHSA receptor was demonstrated in all the 7 adults, though the individual difference of the Kds and binding capacities among them was distinct with a higher standard derivation. The mean values of the Kds and binding capacities were as follows: Kd1 = 9.6769 +/- 5.2767fm-2, C1 = 86.1468 +/- 46.4129fm/micrograms; Kd2 = 103.1810 +/- 56.4770fm-2, C2 = 261.5302 +/- 175.9094fm/micrograms. The Scatchard plot was a curve which indicated the PHSA receptor on the hepatocyte was composed of two binding sites of different affinities and capacities. The possible mechanism and significance of PHSA receptor in the hepatotrophism are also discussed.

Adult↗
PubMed1993

Identification of a novel serum and growth factor-inducible gene in vascular smooth muscle cells.

We have used subtraction cloning to isolate a cDNA (PS4) that identified a serum-inducible mRNA of 1.9 kilobases in rabbit vascular smooth muscle cells. DNA sequence analysis revealed one major open reading frame encoding a 9,442 M(r) protein. Comparison of the DNA as well as the putative protein sequence with various data bases revealed no homology with other sequences. In vitro translation of synthesized PS4 mRNA generated a major polypeptide of 12 kDa. Serum stimulation of quiescent smooth muscle cells in culture induced a rapid increase in the level of PS4 mRNA. Expression of this message was detected by 1 h, peaked at approximately 4 h, and became undetectable by 12 h. The induction of PS4 by serum was completely blocked by cycloheximide, indicating its expression required prior protein synthesis. Epidermal growth factor, acidic fibroblast growth factor, and transforming growth factor-beta 1 also induced a strong increase in PS4 expression. By contrast, platelet-derived growth factor-BB was only able to mildly stimulate the level of PS4 mRNA and insulin-like growth factor-I was unable to enhance PS4 expression. There was a high level of PS4 mRNA in rabbit fetal muscle, esophagus, kidney, and lung, a low level in fetal aorta and heart, and an undetectable level in fetal liver, brain, as well as, in the placenta. The expression of PS4 in the corresponding adult tissues was low or undetectable. Our analysis indicate that PS4 expression is developmentally regulated and tightly controlled by growth factors, suggesting this novel gene has a role in cell growth and differentiation.

Amino Acid Sequence↗
PubMed1993

Identification of Escherichia coli serotype O157:H7 by DNA probe specific for an allele of uid A gene.

Isolates of Escherichia coli serotype O157:H7 were identified by an oligonucleotide probe, PF-27, containing a unique base substitution in the allele of the uid A gene. Colony hybridization analysis of 239 bacteria, including E. coli, Shiga-like toxin-producing serogroups of pathogenic E. coli and other enteric isolates showed that the probe reacted only with isolates of serotype O157:H7. Results of genetic analyses suggest that the base substitution in the allele does not contribute to the absence of uid A gene expression in O157:H7.

Alleles↗
PubMed1993

Identification, localization and developmental studies of rat prepro thyrotropin-releasing hormone mRNA in the testis.

Thyrotropin-releasing hormone (TRH) plays the central regulatory role in the hypothalamic-pituitary-thyroid axis, but is also present in many extra-hypothalamic loci. The adult rat testis has been identified previously as a source of hypothalamic neuropeptides including TRH. To investigate whether the TRH gene is transcribed in testis, the identification and localization of prepro(pp) TRH mRNA and TRH were studied. Northern blot analyses of ppTRH mRNA in the adult rat testis showed a 2.0 kb band, hybridized with a ppTRH cRNA probe. This band was 0.4 kb greater than the 1.6 kb hypothalamic band. The concentration of ppTRH mRNA in the adult testis was approximately 13% of that found in the hypothalamus. Developmental studies of testicular ppTRH mRNA revealed that no ppTRH mRNA could be detected at the earliest stage (day 8). However, hybridization signals were detected on day 20 and increased progressively on days 35, 45 and 70 by 5.8, 6.4, and 9.8-fold, respectively. In addition, ppTRH mRNA was determined in Leydig cells by Northern analyses of elutriated testicular cell fractions. TRH was also measured in the rat testes at different developmental stages by RIA. TRH concentrations paralleled ppTRH mRNA during development. TRH was localized to Leydig cells by immunohistochemistry. These results indicate that ppTRH mRNA and TRH are present in the rat testis, especially in the Leydig cells. The changes of ppTRH gene expression and the concentration of TRH in the rat testis are developmentally dependent. TRH may function as a new paracrine or autocrine regulator of testicular function.

Animals↗
PubMed1993

A truncated isoform of the thyrotropin-releasing hormone receptor is expressed in the rat central nervous system as well as in the pituitary gland.

Using the reverse transcription-polymerase chain reaction (RT-PCR), a cDNA encoding the entire rat thyrotropin-releasing hormone receptor (TRH-R) was isolated from normal rat pituitary gland mRNA. In addition, a novel truncated isoform of TRH-R which lacks 52 base pairs (bp) in the carboxyl (C-) terminal tail was isolated. This truncation, probably generated by alternate splicing, causes a frame-shift and results in a truncated TRH-R 25 amino acids shorter and with a different C-terminal amino acid sequence than the longer type receptor. This truncated TRH-R mRNA, along with the longer receptor form, was found to be expressed throughout the rat pituitary gland and brain.

Amino Acid Sequence↗
PubMed1993

Identification of thyrotropin-releasing hormone receptor messenger RNA in the rat central nervous system and eye.

TRH exerts a wide variety of neuropharmacological actions by interacting with specific receptors in the central nervous system (CNS). Specific binding sites for TRH have been identified also in the mammalian retina. However, whether TRH receptors (TRH-R) in the brain and retina are identical in structure with those in the anterior pituitary gland is presently unknown. In this study, TRH-R gene expression was examined by Northern blot analysis in the CNS and eye using a cloned rat pituitary TRH-R cDNA. Northern analysis demonstrated a specific hybridization band of approximately 3.8 kb in hypothalamus, cerebrum, cerebellum, brain stem, spinal cord, and eye, indistinguishable from that characterized in pituitary gland. These data strongly support the hypothesis that a TRH receptor similar or identical to that cloned from the pituitary occurs in the retina and throughout the CNS.

Animals↗
PubMed1993

N-acetylation phenotype and genotype and risk of bladder cancer in benzidine-exposed workers.

Several studies in subjects occupationally exposed to arylamine carcinogens have shown increased risks for bladder cancer associated with the slow acetylator phenotype. To follow up these reports, a case-control study of N-acetylation and bladder cancer risk was carried out among subjects occupationally exposed to benzidine, in benzidine dye production and use facilities in China. Thirty-eight bladder cancer cases and 43 controls from these factories were included for study of acetylation phenotype, by dapsone administration, and for polymorphisms in the NAT2 gene, by a polymerase chain reaction (PCR)-based test. In contrast to previous studies, no increase in bladder cancer risk was found for the slow N-acetylation phenotype (OR = 0.3; 95% CI = 0.1-1.3) or for slow N-acetylation-associated double mutations in NAT2 (OR = 0.5; 95% CI = 0.1-1.8). Examination of specific mutations and adjustment for age, weight, city and tobacco use did not alter the results. When examined by level of benzidine exposure in the cases, the bladder cancer risks associated with low (OR = 0.3, 95% CI = 0.0-2.2), medium (OR = 0.7, 95% CI = 0.1-4.5) and high (OR = 0.6, 95% CI = 0.1-3.5) exposure showed no interaction between genotype and benzidine exposure, within the range of exposures experienced by subjects in this study. This study, which is the first to incorporate phenotypic and genotypic analyses, provides evidence that the NAT2-related slow N-acetylation polymorphism is not associated with an increased risk of bladder cancer in workers exposed to benzidine, and may have a protective effect.

Acetylation↗
PubMed1993

Correlation between N-acetyltransferase activity and NAT2 genotype in Chinese males.

Eighty-four healthy Chinese male control subjects derived from an occupation-based case-control study of bladder cancer were evaluated for hepatic N-acetyltransferase activity by dapsone and for NAT2 genotype using allele-specific amplification of peripheral leukocyte DNA by the polymerase chain reaction. Fifty-nine percent of the overall variation in acetylation activity was explained by genotype (p < 0.0001). The remaining variation in acetylation was not associated with dapsone N-hydroxylation activity, age, current smoking status, or weight in the study population, or within any genotype subgroup. Although acetylation activity in the homozygous mutant group did not overlap with the other genotype categories, there was moderate overlap in acetylation between the heterozygous mutant and wildtype groups, and substantial variation in acetylation within them. Considering all subjects with the identical NAT2 genotype as phenotypically similar and all subjects with differing NAT2 genotypes as phenotypically distinct may result in misclassification of metabolic risk factors in epidemiological investigations. As such, it would seem prudent, where possible, to collect both acetylation phenotype and NAT2 genotype data, since the advantages and limitations of these two sources of information complement, and serve to assess the accuracy of each other.

Aged↗
PubMed1993

Transcriptional regulation of the rat tissue type plasminogen activator gene: localization of DNA elements and nuclear factors mediating constitutive and cyclic AMP-induced expression.

We have characterized tissue type plasminogen activator (tPA) promoter elements and nuclear factors required for follicle-stimulating hormone (FSH)-induced transcription of the rat tPA gene in granulosa cells and constitutive expression of the gene in the rat neuroblastoma cell line B103. Run-on transcription analysis of isolated nuclei revealed that B103 cells transcribe the tPA gene at a high and constitutive level, while FSH was found to induce tPA gene transcription in a rapid and transient manner in granulosa cells. The maximal FSH-induced transcription rate was obtained after 20 min and was similar in the absence or presence of the protein synthesis inhibitor cycloheximide. However, in the presence of cycloheximide, tPA transcription was not turned off but continued at a high rate for several hours. This phenomenon may at least partly explain the earlier finding that tPA mRNA is superinduced by FSH in the presence of cycloheximide. DNase I footprinting analysis of the first 621 bp of the tPA promoter revealed a total of six regions that interact with nuclear factors from B103 and granulosa cells. Deletion of the promoter region from positions -269 to -621, a region that includes the two most-upstream footprints, had no effect on constitutive or FSH-induced transcription in transient expression experiments. Nuclear extracts from both granulosa cells and B103 cells showed strong binding to a consensus cyclic AMP-responsive element (CRE) at positions -178 to -185 and a neighboring binding site for nuclear factor 1 (NF1) at positions -145 to -158. The factors binding to these two regions were identified as members of the CRE-binding protein and NF1 families of transcription factors, respectively. Footprints were also obtained over two GC boxes at positions -64 to -71 and -41 to -49. These footprints were more pronounced with nuclear extracts from B103 cells than with extracts from untreated or FSH-treated granulosa cells, but gel shift assays indicate that similar amounts of two distinct factors bind to the two GC boxes in both cell types. Transfection experiments using promoter constructs with inactivated promoter elements indicate that both the CRE and NF1 sites contribute to the FSH responsiveness of the rat tPA gene in granulosa cells, while only the NF1 site is important for constitutive expression in B103 cells. The two GC boxes were found to be necessary both for constitutive expression in B103 cells and for FSH-induced expression in granulosa cells, and inactivation of both GC boxes essentially eliminated the tPA promoter activity in both cell types.

Animals↗
PubMed1993

Interactions of fiber and nonstructural carbohydrates on lactation and ruminal function.

Four Holstein cows averaging 147 DIM and fitted with ruminal and duodenal cannulas were used in a 4 x 4 Latin square trial to determine diet effects on DMI, milk production, and ruminal metabolism. Diets contained either rapidly or slowly degraded NDF, referred to as low fill and high fill, respectively, combined with two percentages of nonstructural carbohydrate. Treatments were 39% nonstructural carbohydrate (low or high fill) and 29% nonstructural carbohydrate (low or high fill). Intake of DM was not affected by either fill or nonstructural carbohydrate. Ruminal NDF digestibilities averaged 43.1 and 35.6% for the low fill and high fill diets, respectively. Ruminally digested nonstructural and total carbohydrate increased, but milk production decreased, as nonstructural carbohydrate increased from 29 to 39% in diets. Liquid and solid ruminal passage rates, as measured by Co-EDTA and Yb, respectively, were reduced by either 39% nonstructural carbohydrate or low fill diets. Lower microbial N flow to the duodenum and lower efficiency of microbial growth also were observed for diets with 39% nonstructural carbohydrate. The combination of 39% nonstructural carbohydrate and rapidly degraded fiber gave the highest DM and nonstructural carbohydrate digestion in the rumen but resulted in low microbial N synthesis per day and the least microbial N per kilogram of OM digested.

Animal Feed↗
PubMed1993

Effects of 4-[4''-(2'',2'',6'',6''-tetramethyl-1''-piperidinyloxy)amino]-4'-de methylepipodophyllotoxin on immune function in mice.

4-[4''-(2'',2'',6'',6''-Tetramethyl-1''-piperidinyloxy)amino]-4'- demethylepipodophyllotoxin (GP-7) 10-40 mg.kg-1 ip daily for 7 d reduced the specific antibody formation of splenocytes, serum agglutinin titer, and hemolysin HC50 in mice immunized with SRBC. GP-7 inhibited the footpad delayed hypersensitivity reaction and decreased the weights of spleen and thymus, but did not affect the phagocytic function of the peritoneal macrophages. In vitro the proliferation of mouse splenic lymphocytes activated by Con A was markedly inhibited by GP-7 in a concentration- dependent manner. At concentrations of 0.05-5 mg.L-1, the inhibition rates were 24-96%. These results suggested that GP-7 was an immunosuppressive agent.

Agglutinins↗
PubMed1992

IGFBP-3 gene expression and estrogen receptor status in human breast carcinoma.

Insulin-like growth factors (IGF) I and II are potent mitogens for breast carcinoma proliferation. IGF-mediated proliferative activity can be markedly enhanced by the presence of specific IGF-binding proteins (IGFBPs). IGFBP-3 has been shown to enhance IGF-mediated growth in a number of systems. Studies have demonstrated IGFBP-3 secretion only in estrogen receptor (ER)-negative breast carcinoma cell lines while IGFBP-3 could not be detected in media conditioned by ER-positive cell lines. We investigated whether a relationship exists between ER status and IGFBP-3 mRNA expression in human breast carcinoma biopsy specimens. We have detected IGFBP-3 mRNA in breast carcinoma tissue obtained from patients utilizing in situ hybridization. Quantitation of IGFBP-3 mRNA levels was performed utilizing image cytometry. There was a significantly higher expression of IGFBP-3 mRNA in ER-negative breast carcinoma specimens when compared to the ER-positive specimens. Whether this higher expression of IGFBP-3 mRNA and presumed secretion of IGFBP-3 by ER-negative tumors play a role in the rapid proliferation and poor prognosis of these tumors remains to be determined.

Breast Neoplasms↗
PubMed1992

Mortality and incidence of bladder cancer in benzidine-exposed workers in China.

We examined bladder cancer mortality and incidence to 1981 in 1,972 workers employed in benzidine-exposed jobs in Tianjin, Shanghai, and Jilin, China, between 1972 and 1977, and in 1,974 unexposed workers employed during the same time period. In comparison to general population rates, in the benzidine-exposed group the ratio of observed to expected deaths (SMR) was 17.5 (95% C.I.: 7.5-34.5) and the ratio of observed to expected incident cases (SIR) was 25.0 (95% C.I.: 16.9-35.7). No excess was noted in the unexposed group. The 25-fold increase in bladder cancer incidence in the exposed group was related to level of exposure, with the SIR rising from 4.8 for low exposure to 36.2 for medium exposure, and 158.4 for high exposure. Risks were elevated both for producers of benzidine (SIR = 45.7; 95% C.I.: 20.9-86.8) and for users (SIR = 20.9; 95% C.I.: 12.9-32.0) of benzidine dyes. Benzidine-exposed workers who smoked tobacco had a 31-fold risk (95% C.I.: 20.4-46.4), while non-smoking workers had an 11-fold risk (95% C.I.: 3.6-25.8), suggestive of a multiplicative relationship between these two carcinogens.

Air Pollutants, Occupational↗