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Biomedical subjects

P L Yu

Publications and source records attributed to P L Yu.

At least 19 recordsLinked to original sources
PubMed1997

Regression estimator in ranked set sampling.

Ranked set sampling (RSS) utilizes inexpensive auxiliary information about the ranking of the units in a sample to provide a more precise estimator of the population mean of the variable of interest Y, which is either difficult or expensive to measure. However, the ranking may not be perfect in most situations. In this paper, we assume that the ranking is done on the basis of a concomitant variable X. Regression-type RSS estimators of the population mean of Y will be proposed by utilizing this concomitant variable X in both the ranking process of the units and the estimation process when the population mean of X is known. When X has unknown mean, double sampling will be used to obtain an estimate for the population mean of X. It is found that when X and Y jointly follow a bivariate normal distribution, our proposed RSS regression estimator is more efficient than RSS and simple random sampling (SRS) naive estimators unless the correlation between X and Y is low (/rho/ < 0.4). Moreover, it is always superior to the regression estimator under SRS for all rho. When normality does not hold, this approach could still perform reasonably well as long as the shape of the distribution of the concomitant variable X is only slightly departed from symmetry. For heavily skewed distributions, a remedial measure will be suggested. An example of estimating the mean plutonium concentration in surface soil on the Nevada Test Site, Nevada, U.S.A., will be considered.

Biometry↗
PubMed1997

[Multifactor analysis on proliferative retinopathy in elderly patients with type II diabetes].

UNLABELLED: To evaluate the importance of different risk factors and their mutual interactions in the occurrence of proliferative diabetic retinopathy (PDR) in the elderly patients with type II diabetes, an investigation was carried out on the relationship between PDR and various risk factors in 98 elderly cases of type II diabetes by way of stepwise regression analysis method. Results showed: (1) the average course of PDR was longer than that of diabetic patients without diabetic retinopathy (P < 0.01). Patients with PDR had higher values of BUN (P < 0.01), Cr(P < 0.05), GHbA1c(P < 0.01) and TC(P < 0.01) than those without retinopathy. Patients with PDR had higher coincidences of hypertension, coronary artery disease, proteinuria and urine microalbumin than those without retionpathy (P < 0.01) respectively, (2) multifactor analysis showed that BUN was one of the most important variables positively correlated with PDR, second to it in orders were the course of diabetes militus, GHbA1c, hypertention, proteinuria and urine microalbumin and TC. CONCLUSION: To prevent the occurrence and progress of PDR in the elderly patients with type II diabetes, it is important not only to control blood sugar, but to control blood pressure and relieve renal damage.

Aged↗
PubMed1996

Functional expression of the dihydrofolate reductase domain of Leishmania major dihydrofolate reductase-thymidylate synthase bifunctional protein.

The dihydrofolate reductase (DHFR) domain of the bifunctional dihydrofolate reductase-thymidylate synthase from Leishmania major has been subcloned and expressed as a soluble protein in Escherichia coli strain PA414 harboring plasmid pLMDHFR. Homogeneous L. major DHFR was obtained by chromatography on methotrexate-Sepharose followed by DE52. The purified enzyme migrated as a single 25-kDa protein on SDS-PAGE. The native molecular weight was determined to be 26 kDa, indicating that the isolated domain is a monomer. N-terminal sequence analysis revealed that serine, the second amino acid in the coding sequence, was the N-terminal amino acid of the protein. The enzyme showed a pH optimum similar to that of the bifunctional protein. For purified DHFR, the Km values were <1.0 microM for H2folate and <1.0 microM for NADPH. The kcat of the most active DHFR preparation was 5 s-1. The Km and kcat values were similar to those of the bifunctional enzyme.

Amino Acid Sequence↗
PubMed1996

Effect of nimodipine on infectious brain edema in rabbits.

AIM: To study the effect of nimodipine (Nim) on infectious brain edema (BE). METHODS: An infectious BE model was induced by injection of Bordetella pertussis suspension (BPS) into right internal carotid artery in rabbits. Eighteen rabbits were randomly divided into 3 groups (n = 6). Group BE: BPS (0.6 mL.kg-1) was given; group NS: normal saline was given as control; group Nim: 10 min after injection of BPS, Nim, 10 micrograms.kg-1, was injected i.v. as a bolus followed by continuous infusion of 0.75 microgram.kg-1.min-1. All the rabbits were kept under observation for 4 h. Evans blue staining was assessed; water, calcium, calmodulin (Cal), and sodium contents were determined in the right brain. RESULTS: Nim vs BE: water 82.2 +/- 1.0% vs 84.4 +/- 1.2 (P < 0.01); calcium 10.5 +/- 1.3 mmol.kg-1 dry tissue vs 17.5 +/- 1.4 (P < 0.01); Cal 15.9 +/- 1.8 mumol.kg-1 wet tissue vs 24.0 +/- 3.0 (P < 0.01); sodium 173 +/- 7 mmol.kg-1 dry tissue vs 275 +/- 38 (P < 0.05). No significant difference for Evans blue staining between the two groups. CONCLUSION: Nim had beneficial effect on the infectious BE.

Animals↗
PubMed1995

Trypanosoma brucei dihydrofolate reductase-thymidylate synthase: gene isolation and expression and characterization of the enzyme.

The gene encoding the bifunctional dihydrofolate reductase (DHFR) and thymidylate synthase (TS) of Trypanosoma brucei brucei has been isolated and expressed in Escherichia coli, and the enzyme has been purified and characterized. The coding sequence of the DHFR-TS is 1581 nt, encoding a 527-amino-acid protein of 58,505 Da. The gene was expressed under control of the trc promoter in pKK233-2. The resulting expression plasmid conferred trimethoprim resistance to E. coli DH5 alpha and complemented the TS deficiency in chi 2913recA cells indicating the presence of active DHFR and TS. DHFR-TS was purified by methotrexate-Sepharose chromatography. In addition to the full-length enzyme, the purified enzyme contained 31 and 31.5-kDa forms of the enzyme that cross-reacted with anti-L. major DHFR-TS antibodies; one was truncated at the N- and C termini, and the other at only the C terminus. Despite the presence of sufficient TS for complementation, TS activity was not detectable in the crude extract or in the final purified enzyme preparation. Although the majority of the enzyme appears to be full length, it is possible that the TS domain has been degraded by one of more residues, which would inactivate the ability to synthesize thymidylate. Kinetic analysis of DHFR yielded kcat and Km values similar to those of related enzymes. The T. brucei DHFR has Ki values for antimicrobial antifolates pyrimethamine and trimethoprim which are significantly lower than the closely related T. cruzi or L. major DHFRs or than human DHFR.

Amino Acid Sequence↗
PubMed1995

[Effect of tetramethylhyrazine on proliferation of human fetal mesangial cells].

Tetramethylhyrazine (TMP) 0.6 and 1.2 mmol were added to human fetal mesangial cell (MC) cultures for 6 days, and the amounts of MC (cells/ml) were 37580 +/- 3475 and 27350 +/- 3418 respectively, significantly lower than that 71850 +/- 5108 in control (P < 0.05). The 3H-TdR incorporation by the MC with corresponding TMP were 1017 +/- 201 and 583 +/- 271, also significantly lower, than that 3575 +/- 306 in control (P < 0.01). After adding the TMP (1 mmol) to the cultures, the IL-6 bioactivity were 2118 +/- 215 that were markedly lower than those in controls (4128 +/- 351, P < 0.01). It revealed that the TMP inhibited the growth of MC and the mechanism of its inhibition might be due to that TMP could reduce the IL-6.

Cell Division↗
PubMed1994

Expression, purification, and characterization of thymidylate synthase from Lactococcus lactis.

The thymidylate synthase (TS) gene from Lactococcus lactis has been highly expressed in Escherichia coli. The TS protein was purified by sequential chromatography on Q-Sepharose and phenyl-Sepharose. Six grams of cell pellet yielded 140 mg of homogeneous TS. TS is a highly conserved enzyme, and several of the conserved amino acid residues that have been implicated in catalytic function are altered in L. lactis TS. By use of a 3-dimensional homology model, we have predicted covariant changes that might compensate for these differences. With the large amounts of L. lactis TS now available, studies can be pursued to understand the structure-function relationships of this enzyme compared to other TSs and to confirm the presumed roles of the compensatory changes predicted in the homology model.

Amino Acid Sequence↗
PubMed1994

Synthetic and oxidative studies on 8-(arylamino)-2'-deoxyguanosine and -guanosine derivatives.

Facile aerial oxidation is a general feature of guanine ribo- and 2'-deoxyribonucleosides that are substituted at the 8-position by an aminoaryl group. In previous work, it had been suggested that two of the major oxidation products are a pair of diastereomers having a spiro structure. These were presumed to be related by a chiral difference at the spiro carbon atom. The pattern of the oxidative process involves a contraction of the pyrimidine ring. It was thought to be analogous to that suggested by other investigators for the oxidation of uric acid, but for which no really definitive evidence had been presented. We have been able now to isolate in a crystalline state one of the diastereomers produced by the aerial oxidation of 8-phenylaminoguanosine under alkaline conditions. Analysis by X-ray diffraction has now confirmed the type of spiro structure promulgated previously. These findings also imply that spiro compounds are likely to be produced during the aerial oxidation of any 8-arylaminoguanine nucleoside or 2'-deoxynucleoside. In addition, this work adds considerable weight to the results of Poje and Sokolic-Maravic who proposed that a spiro intermediate is produced during the aerial oxidation of uric acid (12,13). However, they found this compound to be unstable to base, in contrast to the arylaminoguanine oxidation products. In the course of the above work we showed that the 8-arylamino derivatives of guanosine can be converted by the Barton deoxygenation method to the corresponding 2'-deoxyribonucleosides. This makes available a number of the latter compounds, which are not easily prepared by other methods.

DNA Adducts↗
PubMed1994

[Histological and immunohistochemical study and AgNOR analysis of smooth muscle tumors of the digestive tract].

Smooth muscle tumors of the esophagus (n = 29), stomach (n = 30), small intestine (n = 31) and large intestine (n = 12) were examined histologically and immunohistochemically for vimentin (Vim), desmin (Des), S100, fibronectin (FN) and cytokeratin (Cyt) and for nucleolar organizer regions (AgNOR). There were 49 cases of leiomyoma (LM), 51 cases of leiomyosarcoma (LS) and 2 cases of leiomyoblastoma(LB). Histologically, LS was characterized by cellular atypia, more cells in mitosis and invasion to adjacent normal tissue. No mitotic figure was observed in LM. AgNOR was more abundant in number in LS than LM (P < 0.001), but it had no direct relation to tumor size, number of cells in mitosis and patients' survival period. Immunohistochemical studies of Vim, Des, S100, FN and Cyt revealed that none of them was very helpful in the differential diagnosis of LM from LS.

Adolescent↗
PubMed1992

Effectiveness of enteric coated pancreatic enzymes given before meals in reducing steatorrhea in children with cystic fibrosis.

In vitro data indicate that length of enzyme incubation with food critically affects enzyme dissolution and presumably effectiveness. This study compared the effectiveness of enteric coated (EC) pancreatic enzymes given before meals with those given during meals (15 minutes after beginning of meal) in reducing steatorrhea in well-nourished children with cystic fibrosis. Eight children (6 years 11 months old to 14 years 7 months old) were studied in the General Clinical Research Center at Indiana University Hospital, Indianapolis. A crossover study design randomly assigned enzymes before or during meals during two consecutive 7-day treatment periods for each child. No difference in fat excretion was documented for the total group when the children who took enzymes before meals were compared with those who took enzymes during meals. However, a stepwise multiple regression analysis of the difference (before minus during) in fat excretion on sex, age, enzyme number, and treatment order documented a positive correlation of age with fat excretion (r = .83). Mean fat excretion in younger children (less than 10 years old) decreased significantly when enzymes were given before meals (7.14 +/- 1.95%) rather than during meals (9.92 +/- 1.61%) (P = .004). The difference in fat excretion (mean = 2.78 +/- 0.55%, range = 1.4% to 4%) translates into a half to one full year's growth potential. Younger children with cystic fibrosis may benefit clinically from taking EC enzymes before meals.

Adolescent↗
PubMed1991

Effectiveness and safety of small vs. large doses of enteric coated pancreatic enzymes in reducing steatorrhea in children with cystic fibrosis: a prospective randomized study.

Among cystic fibrosis (CF) centers, usual doses of enteric coated (EC) pancreatic enzymes vary from one to six capsules per meal based upon arbitrary criteria for stool and growth patterns. Large doses of non-EC enzymes are associated with increased serum urate (SU) and urinary uric acid (UUA) but data are unavailable for EC enzymes. This study compared the effectiveness and safety of a relatively large dose (patient's usual dose) versus a small dose (1/4 usual dose) of EC enzymes in nine nourished children with CF, regarding decreasing fecal fat and stool nitrogen losses and maintaining normal SU and UUA concentrations. A crossover study design randomly assigned large or small doses to two consecutive 7 day treatment periods within each child. Large doses of EC enzymes reduced steatorrhea and increased SU and UUA. SU was normal with both treatments and UUA was normal, i.e., 17 of 18 values were between the 10th and 95th percentiles for healthy children eating a normal diet. When fat excretion was greater than 10% with small doses of EC enzymes, large doses resulted in reduced fat excretion and normal UUA. These data suggest that large doses of EC enzymes reduce steatorrhea and are safe in patients who have malabsorbtion with small doses.

Celiac Disease↗
PubMed1991

Genetic analysis of a lactococcal plasmid replicon.

The sequence and genetic organization was determined of the 2508 bp lactococcal portion of pFX2, which was derived from a cryptic Lactococcus lactis subsp. lactis plasmid and used as the basis for construction of a series of lactococcal vectors. A lactococcal plasmid plus origin and two replication protein-coding regions (repA and repB) were located. RepA has a helix-turn-helix motif, a geometry typical of DNA-binding proteins. RepB shows a high degree of homology to the plasmid replication initiation proteins from other gram-positive bacteria and Mycoplasma. The transcribed inverted repeat sequence between repA and repB could form an attenuator to regulate pFX2 replication. Up-stream of the ori site, and in a region which was non-essential for replication, a 215 bp sequence identical to the staphylococcal plasmid pE194 and carrying the RSA site was identified. The genetic organization of this lactococcal plasmid replicon shares significant similarity with pE194 group plasmids.

Amino Acid Sequence↗
PubMed1991

A new model of global postischemic reperfusion in rabbit.

An ideal model of global ischemia in rabbits has not yet been developed. The present study describes a new model of global postischemic reperfusion (GPIR) in the rabbit, characterized by lack of systemic hypotension. The experimental procedure involves reversible occlusion of the bilateral internal carotid arteries (ICA) and bilateral external carotid arteries (ECA) for 60 min combined with permanent ligation of bilateral vertebral arteries (VA). This grouping is called 6-artery occlusion (6AO). Sixty minutes after the occlusion, bilateral ICA and bilateral ECA were released for 120 min at which time the experiment was terminated. The results revealed severely depressed EEG activity; Water content of brain tissue increased to 80.33 +/- 1.20% (control 78.28 +/- 0.59%, p less than 0.01); K, Mg, and Zn decreased (p less than 0.05 or p less than 0.01), and were negatively correlated with tissue water content. Na increased (p less than 0.05) and correlated with water content of brain. No significant changes were observed in lipid peroxide (LPO) levels, but the activity of superoxide dismutase (SOD) of brain tissue decreased (p less than 0.01), and was negatively correlated with water content (r = -0.5808, p less than 0.05). These results were compared with those obtained with the model of 4-artery (bilateral common carotid arteries (CCA) and VA) occlusion (4AO) and suggested that the brain damage be more severe with 6AO than with 4AO.

Animals↗
PubMed1991

Production of recombinant products in yeasts: a review.

This paper reviews the use of yeasts to produce heterologous proteins via the development of transformation systems. The ability to genetically engineer yeast cells has many advantages over prokaryotic systems. Yeasts are already well established in fermentation procedures, are able to secrete glycosylated and modified proteins to render the proteins biologically active, and yeasts do not secrete toxic chemicals. With the techniques available it is possible to explore yeasts as hosts for the expression and secretion of commercially-useful proteins.

Genetic Vectors↗