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Biomedical subjects

C H Yang

Publications and source records attributed to C H Yang.

At least 199 records · Page 11Linked to original sources
PubMed1994

Mutational effects of space flight on Zea mays seeds.

The growth and development of more than 500 Zea mays seeds flown on LDEF were studied. Somatic mutations, including white-yellow stripes on leaves, dwarfing, change of leaf sheath color or seedling color were observed in plants developed from these seeds. When the frequency of white-yellow formation was used as the endpoint and compared with data from ground based studies, the dose to which maize seeds might be exposed during the flight was estimated to be equivalent to 635 cGy of gamma rays. Seeds from one particular holder gave a high mutation frequency and a wide mutation spectrum. White-yellow stripes on leaves were also found in some of the inbred progenies from plants displayed somatic mutation. Electron microscopy studies showed that the damage of chloroplast development in the white-yellow stripe on leaves was similar between seeds flown on LDEF and that irradiated by accelerated heavy ions on ground.

Chloroplasts↗
PubMed1994

Development of human epithelial cell systems for radiation risk assessment.

The most important health effect of space radiation for astronauts is cancer induction. For radiation risk assessment, an understanding of carcinogenic effect of heavy ions in human cells is most essential. In our laboratory, we have successfully developed a human mammary epithelial cell system for studying the neoplastic transformation in vitro. Growth variants were obtained from heavy ion irradiated immortal mammary cell line. These cloned growth variants can grow in regular tissue culture media and maintain anchorage dependent growth and density inhibition property. Upon further irradiation with high-LET radiation, transformed foci were found. Experimental results from these studies suggest that multiexposure of radiation is required to induce neoplastic transformation of human epithelial cells. This multihits requirement may be due to high genomic stability of human cells. These growth variants can be useful model systems for space flight experiments to determine the carcinogenic effect of space radiation in human epithelial cells.

Argon↗
PubMed1994

Heavy-ion induced genetic changes and evolution processes.

On Moon and Mars, there will be more galactic cosmic rays and higher radiation doses than on earth. Our experimental studies showed that heavy ion radiation can effectively cause mutation and chromosome aberrations and that high-LET heavy-ion induced mutants can be irreversible. Chromosome translocations and deletions are common in cells irradiated by heavy particles, and ionizing radiations are effective in causing hyperploidy. The importance of the genetic changes in the evolution of life is an interesting question. Through evolution, there is an increase of DNA content in cells from lower forms of life to higher organisms. The DNA content, however, reached a plateau in vertebrates. By increasing DNA content, there can be an increase of information in the cell. For a given DNA content, the quality of information can be changed by rearranging the DNA. Because radiation can cause hyperploidy, an increase of DNA content in cells, and can induce DNA rearrangement, it is likely that the evolution of life on Mars will be effected by its radiation environment. A simple analysis shows that the radiation level on Mars may cause a mutation frequency comparable to that of the spontaneous mutation rate on Earth. To the extent that mutation plays a role in adaptation, radiation alone on Mars may thus provide sufficient mutation for the evolution of life.

Animals↗
PubMed1994

Ethnic variation in the CYP2E1 gene: polymorphism analysis of 695 African-Americans, European-Americans and Taiwanese.

Human cytochrome P4502E1 (CYP2E1) is inducible by ethanol and is involved in metabolism of many known carcinogens including N-nitrosodimethylamine, butadiene, benzene, and carbon tetrachloride. A 50-fold variability in CYP2E1 enzyme activity in humans has been observed but it is unknown whether the basis for this variation is genetic or environmental. Recently, two restriction fragment length polymorphisms (RFLPs) within the CYP2E1 gene have been suggested as genetic markers of risk for cancer. The first was a Rsa I polymorphism in the 5' regulatory region that appeared to alter transcriptional activation of the gene and the second was a Dra I polymorphism located approximately 7000 bp downstream in an intron. Rare alleles at each of these loci have been associated with a reduced risk for lung cancer in Japanese and Swedish populations. We have used a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method to determine the genotype frequency for each of these CYP2E1 RFLPs in 695 individuals of Taiwanese, African-American or European-American background. Genotype and allele frequencies for Taiwanese were significantly different from those of African-Americans and European-Americans at either Rsa I or Dra I sites (p < 0.0001). Allele frequencies for African-Americans and European-Americans were significantly different at the Rsa I site (p = 0.03). The rare alleles (c2 and C) occurred at frequencies of 0.28 and 0.24 in Taiwanese, 0.01 and 0.08 in African-Americans, and 0.04 and 0.11 in European-Americans. In addition, we describe three haplotypes common to all three population samples and a fourth haplotype that was only detected in the Taiwanese population sample. This fourth haplotype may have been caused by a recombination event between these markers.(ABSTRACT TRUNCATED AT 250 WORDS)

Asian People↗
PubMed1994

Mutations Affecting Hyphal Colonization and Pyoverdine Production in Pseudomonads Antagonistic toward Phytophthora parasitica.

In previous studies, Pseudomonas putida 06909 and Pseudomonas fluorescens 09906 suppressed populations of Phytophthora parasitica in the citrus rhizosphere, suggesting that these bacteria may be useful in biological control of citrus root rot. In this study we investigated the mechanisms of antagonism between the bacteria and the fungus. Both bacteria colonized Phytophthora hyphae and inhibited the fungus on agar media. A hyphal column assay was developed to measure the colonization of bacteria on fungal hyphae and to enrich for colonization-deficient mutants. In this way we identified Tn5 mutants of each pseudomonad that were not able to colonize the hyphae and inhibit fungal growth in vitro. Colonization-deficient mutants were nonmotile and lacked flagella. Survival of nonmotile mutants in a citrus soil was similar to survival of a random Tn5 mutant over a 52-day period. Additional screening of random Tn5 mutants of both pseudomonads for loss of fungal inhibition in vitro yielded two distinct types of mutants. Mutants of the first type were deficient in production of pyoverdines and in inhibition of the fungus in vitro, although they still colonized fungal hyphae. Mutants of the second type lacked flagella and were not able to colonize the hyphae or inhibit fungal growth. No role was found for antibiotic production by the two bacteria in the inhibition of the fungus. Our results suggest that both hyphal colonization and pyoverdine production are important in the inhibition of Phytophthora parasitica by P. fluorescens and P. putida in vitro.

Journal Article↗
PubMed1994

Concomitant chemoradiotherapy for advanced epidermoid carcinoma of the uterine cervix: a preliminary report.

BACKGROUND: Because the prognosis of advanced carcinoma of the uterine cervix is poor, and has improved very little in the last 20 years, a prospective study was initiated to evaluate the feasibility, response and toxicities of concomitant chemoradiotherapy for such cervical cancer. METHODS: From May 1992 to December 1992, 22 patients entered the study, 21 of them completed the entire treatment. Their ages ranged from 47 to 72 years, median 57. There were 16 FIGO stage IIIB, and 5 stage IIB. Radiotherapy was administered using 1.8 Gy/day, five days a week, to the whole pelvis (50.4 Gy/28 fractions) with or without parametrial boost according to the tumor response. Intracavitary brachytherapy 5 Gy x five to six times was given after one or two weeks of rest. Chemotherapy consisted of etoposide 100 mg/m2 day 1 + cisplatin 50 mg/m2 day 1 + bleomycin 25 mg/m2/day day 2-3, repeated every two weeks during external irradiation. RESULTS: All 21 eligible patients achieved complete response, sustaining during a median follow-up time of 12 months. All the initially elevated tumor markers (SCC, CEA, CA-125) returned to normal range after treatment. The toxicity was well tolerated. CONCLUSIONS: Concomitant chemoradiotherapy for advanced cervical carcinoma is both feasible and effective, with acceptable toxicities. Long-term follow-up is mandatory, and a randomized trial to confirm the superiority of this protocol will be started soon.

Adult↗
PubMed1994

Enterococcal bacteremia in a medical center.

BACKGROUND: The enterococci have become important nosocomial pathogens. They can cause multiple site infections and enterococcal bacteremia becomes more frequently associated with a high mortality rate. Previous studies of enterococcal bacteremia showed a variety of results. To establish the significance and importance of enterococci as nosocomial pathogens in this hospital, to characterize their clinical pictures and to search for the risk factors for mortality, this retrospective study was performed. METHODS: There were 208 cases of enterococcal bacteremia which occurred from 1988 to 1992. Twenty-seven cases had no medical charts, dismissing possibility of evaluation. Finally, 181 cases of enterococcal bacteremia were analysed. RESULTS: One hundred and eighteen episodes were nosocomial infections. Polymicrobial bacteremia occurred in 68.5% of the patients and the most common co-isolate was Pseudomonas aeruginosa. Those patients (78.5%) with underlying diseases and malignancies were the most common underlying problems. The portal of entry could be found in 69.6 percent of patients, with the gastrointestinal tract the most common sources. Antimicrobial susceptibility testing showed high gentamicin resistance rate (89.5%), and ampicillin still had about 80 percent sensitivity rate. The group who received specific antibiotic therapy for enterococcus showed lower mortality (36.4% versus 47.6%). Only one case had infective endocarditis. Forty-nine patients suffered from septic shock, the cause of 30 deaths. Totally 75 patients died during hospitalization. Besides sepsis, another major cause of death was their underlying diseases itself. CONCLUSIONS: Enterococci have no doubt become important nosocomial pathogens and enterococcal bacteremia were associated with high mortality, especially in elderly patients with underlying diseases such as malignancy or diabetes. When clinically dealing with sepsis from the gastrointestinal or biliary tract, especially when previous cephalosporins therapy showed no response, the possibility of enterococcal bacteremia should always be considered.

Adolescent↗
PubMed1994

Severe isolated acute hepatic graft-versus-host disease with vanishing bile duct syndrome.

A 28-year-old man with chronic myelogenous leukaemia in blastic transformation underwent allogeneic bone marrow transplantation from his HLA-identical brother. Severe, progressive cholestatic jaundice developed from day 25 and did not respond to repeated therapy with high-dose methylprednisolone. In addition to marked cholestasis, both liver biopsy (day 69) and autopsy (day 134) findings revealed total disappearance of interlobular bile ducts in all of the portal areas, although extrahepatic manifestations of GVHD were minimal. Isolated acute vanishing bile duct syndrome can occur as the most severe form of acute hepatic GVHD.

Acute Disease↗
PubMed1994

Neurological complications of varicella: a report of two cases.

Varicella (chickenpox) is the primary infection of Varicella-Zoster virus, characterized by generalized vesicular eruption, fever and mild constitutional symptoms. Chiefly infecting children of 1 to 14 years of age, the disease has been almost neglected because of its inevitable and benign outcome. Adults are rarely infected with an incidence of less than 20%. These two cases are presented of normal adults with marked neurological complications 10 and 14 days, respectively, following typical skin eruption of varicella. The first case developed transverse myelitis and the second, an encephalomyelitis. Neurological complications are very rare post-varicella infection. Although prognosis is good and complete recovery is the rule, still some morbidity with neurological sequelae and mortality have been reported. The present cases had extensive neurological deficit, despite aggressive treatment, making a high index of suspicion for differential diagnosis in patients who present with encephalitis. Especially following the typical exanthema of varicella, this possibility is emphasized and the literature is reviewed.

Adult↗
PubMed1993

Power spectral analysis of the electroencephalographic and hemodynamic correlates of propofol anesthesia in the rat: intravenous infusion.

Based on the tail-flick response to noxious thermal stimuli, we determined in the present study that effective antinociception could be achieved in adult male Sprague-Dawley rats 15 min after intravenous infusion of propofol at 60 mg/kg/h. Simultaneous power spectral analysis of the electroencephalographic (EEG) and systemic arterial pressure signals further revealed a concomitant depression of the activity of all EEG frequency bands (delta, theta, alpha, beta), alongside hypotension, negative inotropic and chronotropic actions, and attenuated baroreceptor reflex and vasomotor activity. These effects were congruent with a plasma concentration of propofol in the arterial blood of 1.70 +/- 0.13 micrograms/ml, as determined by high-performance liquid chromatography.

Anesthesia↗
PubMed1993

Power spectral analysis of the electroencephalographic and hemodynamic correlates of propofol anesthesia in the rat: intravenous bolus administration.

Based on the tail-flick response to noxious thermal stimuli, we determined in the present study that the minimal effective antinociceptive dose of propofol in adult, male Sprague-Dawley rats, given in an intravenous bolus manner, was 10 mg/kg. Simultaneous power spectral analysis of the electroencephalographic (EEG) and systemic arterial pressure signals further revealed a concomitant transient suppression of the EEG activity, primarily in the theta and sigma bands, alongside minor hypotensive and negative inotropic and chronotropic actions, but with maintained vasomotor tone. These alterations followed a time course that paralleled the plasma concentration of propofol in the arterial blood, as detected by high-performance liquid chromatography.

Anesthesia, Intravenous↗
PubMed1993

Infrequent transposition of Ac in lettuce, Lactuca sativa.

The maize transposable element Activator (Ac) is being used to develop a transposon mutagenesis system in lettuce, Lactuca sativa. Two constructs containing the complete Ac from the waxy-m7 locus of maize were introduced into lettuce and monitored for activity using Southern analysis and PCR amplification of the excision site. No transposition of Ac was detected in over 32 transgenic R1 plants, although these constructs were known to provide frequent transposition in other species. Also, no transposition was observed in later generations. In subsequent experiments, transposition was detected in lettuce calli using constructs that allowed selection for excision events. In these constructs, the neomycin phosphotransferase II gene was interrupted by either Ac or Ds. Excision was detected as the ability of callus to grow on kanamycin. Synthesis of the transposase from the cDNA of Ac expressed from the T-DNA 2' promoter resulted in more frequent excision of Ds than was observed with the wild-type Ac. No excision was observed with Ds in the absence of the transposase. The excision events were confirmed by amplification of the excision site by PCR followed by DNA sequencing. Excision and reintegration were also confirmed by Southern analysis. Ac/Ds is therefore capable of transposition in at least calli of lettuce.

Base Sequence↗
PubMed1993

Transactivation of Ds elements in plants of lettuce (Lactuca sativa).

The maize transposable element, Activator (Ac), is being used to develop a transposon mutagenesis system in lettuce, Lactuca sativa. In this paper, we describe somatic and germinal transactivation of Ds by chimeric transposase genes in whole plants. Constructs containing either the Ds element or the Ac transposase open reading frame (ORF) were introduced into lettue. The Ds element was located between either the 35S or the Nos promoter and a chimeric spectinomycin resistance gene (which included a transit peptide), preventing expression of spectinomycin resistance. The genomic coding region of the Ac transposase was expressed from the 35S promoter. Crosses were made between 104 independent R1 plants containing Ds and three independent R1 plants expressing transposase. The excision of Ds in F1 progenies was monitored using a phenotypic assay on spectinomycin-containing medium. Green sectors in one-third of the F1 families indicated transactivation of Ds by the transposase at different developmental stages and at different frequencies in lettuce plants. Excision was confirmed using PCR and by Southern analysis. The lack of green sectors in the majority of F1 families suggest that the majority of T-DNA insertion sites are not conducive to excision. In subsequent experiments, the F1 plants containing both Ds and the transposase were grown to maturity and the F2 seeds screened on medium containing spectinomycin. Somatic excision was again observed in several F2 progeny; however, evidence for germinal excision was observed in only one F2 family.

Base Sequence↗
PubMed1993

Lymphoblast colony-culture assay in acute lymphoblastic leukemia: a quantitative approach.

Lymphoblast colony-culture of adult acute lymphoblastic leukemia (ALL) was studied to explore its clinical implication. Among 13 marrow cultures from ALL patients with full-blown disease, 11 developed leukemic colonies. A type of colony, very similar to a lymphoblastic colony and possibly T-cell in origin, could be found in four cultures of the six control marrows. To minimize the difficulty in differentiating a leukemic blast colony and a normal lymphocyte colony, based solely on morphology, a quantitative approach was used. Since both the mean of blast colony count and the mean of blast percentage of leukemic marrow were significantly higher than those of the control group, mean value plus two standard deviations of the control group were defined arbitrarily as upper normal limits. The defined normal range was then used to examine the relationship between results of the cultures and clinical outcome for the ALL patients. Early relapse or incomplete remission following chemotherapy could be predicted in four patients by these quantitative colony-culture assays 0.5-2 months before full-blown disease. The low colony count and low blast percentage in the colony-culture assay of the fifth patient is compatible with the clinical observation of continuous remission. One culture, growing clusters only, had an increased blast percentage; this correlated well with cytogenetic relapse two months later. In summary, the quantitative colony-culture assay could detect morphologically unidentifiable leukemic cells in ALL patients with early relapse or incomplete remission. This quantitative colony-culture system, though not ultrasensitive in the detection of minimal residual leukemic cells, was of potential value as a prognostic assay.

Adolescent↗
PubMed1993

Prolonged haloperidol and reduced haloperidol plasma concentrations after decanoate withdrawal.

Haloperidol and reduced haloperidol plasma concentrations were measured in twelve schizophrenic patients upon cessation of haloperidol decanoate (HLD) treatment. Each patient received HLD 100 mg every 4 weeks for five injections. After the fifth injection, HLD was discontinued. Haloperidol and reduced haloperidol plasma concentrations were obtained prior to cessation and at weeks 1, 3, 4, 5, 7, 9, 11, and 13 post-injection. Haloperidol and reduced haloperidol plasma concentrations were assayed by HPLC. Both haloperidol and reduced haloperidol plasma concentrations were detectable 13 weeks post HLD discontinuation. Maximal haloperidol plasma concentrations were observed at one week post cessation and gradually declined. The mean elimination half-life for haloperidol was 27.4 +/- 8.6 days (range 19.0-47.0 days). Reduced haloperidol plasma concentrations declined very slowly. Our results show that both haloperidol and reduced haloperidol plasma concentrations can remain for extended time periods after HLD is discontinued.

Adult↗
PubMed1993

Role of copper resistance in competitive survival of Pseudomonas fluorescens in soil.

A copper-resistant strain (09906) of Pseudomonas fluorescens that was isolated from a citrus grove soil is being investigated as a biological control agent for Phytophthora root rot. Since citrus grove soils in California are often contaminated with copper from many years of copper fungicide applications, the role of copper resistance in survival of strain 09906 was investigated. Three copper-sensitive Tn5 mutants were obtained with insertions in different chromosomal DNA regions. These insertions were not in the chromosomal region that hybridized with the copper resistance operon (cop) cloned from Pseudomonas syringae. A copper-sensitive mutant survived as well as the wild type in a sterile loamy sand without added copper, but with 10 and 15 micrograms of CuSO4 added per g of soil, populations of the copper-sensitive mutant were 27- and 562-fold lower, respectively, than that of the wild type after a 25-day period. In a sterilized citrus grove soil, populations of the copper-sensitive mutant and wild-type strain were similar, but in nonsterile citrus soil, populations of the copper-sensitive mutant were 112-fold lower than the wild type after 35 days. These data suggest that copper resistance genes can be important factors in persistence of P. fluorescens in soil contaminated with copper. In addition, these genes appear to play a role in competitive fitness, even in soils with a low copper content.

Agriculture↗
PubMed1993

Calcified brain metastasis.

Two patients with rare cases of calcified brain metastases are reported. The relatively benign clinical course and prolonged survival are stressed. The first patient had an adenocarcinoma of unknown origin with three calcified brain metastases. The patient underwent an incisional brain biopsy without radiotherapy and survived for 2 years and 9 months. The second patient had a squamous cell carcinoma of the lung with a large, solitary brain metastasis. The brain tumor was calcified and remained stable without progression for at least 4 months before surgical resection.

Adenocarcinoma↗