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Biomedical subjects

J Luo

Publications and source records attributed to J Luo.

At least 361 records · Page 20Linked to original sources
PubMed1993

[Stress analysis with a laser microscope analyzer for acrylic base resin]

Acrylic resin are applied widely as a denture resin,its residual stress is closely related with aging and mechanical properties of denture resin.The authors tested the stress level of the base resin with a laser microscope stress analyzer in the study.The results indicated that there was not statistical differences between two curing methods is in water bath or under pressure.The residual stress in base resin can be concentrated at the area near to clasp wire which was embedded in base resin for reinforcing strength of denture base.The vibration caused by grind with stone wheel or impact in disc lasting with a hammer may increase the stress level in base.The authors pointed out some methods for reducing residual stress resin.

Journal Article↗
PubMed1993

Single cell clone from culture cells of Panax ginseng.

The plating efficiency of a single cell clone from culture cells of Panax ginseng can be influenced by the nutritional compositions of plating medium. In order to promote the growth of single cells, it was essential to establish an appropriate ratio between 2,4-D concentration and KT concentration in the MS medium. The best combination of these two hormones was 1.5 mg/l and 0.5 mg/l, respectively. Considering the formation of cell clones, the suitable NH2NO4 concentration and CaCl2.2H2O concentration should be 400 mg/l and 750 mg/l, respectively. The plating efficiency can also be effectively increased when the plating medium was suitably supplemented with succinic acid, arginine, vitamins, etc. In optimization of the nutritional compositions of the medium, the plating efficiency was increased 2.34 times against the control. The cells suspended for 12 days were most favorable for the formation of cell clones. Different plating efficiency was obtained with different cell plating density. There was a low plating efficiency when the cell plating density was lower than 4 x 10(3) cells/ml.

Amino Acids↗
PubMed1992

Characterization and epitope mapping of monoclonal antibodies directed against the beta' subunit of the Escherichia coli RNA polymerase.

Monoclonal antibodies (mAbs) raised against the beta' subunit of the Escherichia coli RNA polymerase were used to probe the structure and function of this subunit. Of the five anti-beta' monoclonal antibodies studied, only mAb 311G2 is a strong inhibitor of RNA polymerase activity. This antibody binds to an epitope which is exposed in both the assembled holoenzyme and isolated beta' subunit. In contrast, the null antibodies bind to the free beta' subunit but very weakly to native RNA polymerase. It would appear that the beta' domain in which their epitopes reside is either conformationally altered or blocked due to interaction with other subunits in native RNA polymerase. In order to locate the positions of the epitopes for these five monoclonal antibodies, a series of overlapping deletion mutants have been constructed by partial restriction and religation of the beta' gene present in pT7 beta' (Zalenskaya, K., Lee, J., Gujuluva, C. N., Shin, Y. K., Slutsky, M., nd Goldfarb, A. (1990) Gene 89, 7-12). The presence of the epitopes for each of the anti-beta' monoclonal antibodies was assessed by Western blotting. The results indicate that the epitopes for mAb 340F11, mAb 370F3, mAb 371D6, and mAb 372B2 are located between amino acids 817-876. This region may be important in enzyme assembly or subunit-subunit interaction. The epitope for the inhibitory antibody, mAb 311G2, is located between amino acids 1047-1093. This region may be involved in the catalytic function of RNA polymerase.

Antibodies, Monoclonal↗
PubMed1992

Laser photolysis of cytosine, cytidine and dCMP in aqueous solution.

Laser photolysis of cytosine and cytosine derivatives (cytidine and 2'-deoxycytidine-5'-monophosphate) using acetone as a sensitizer have been carried out in aqueous solution using a KrF laser. The absorption spectra of triplet states of cytosine and cytosine derivatives have been observed for the first time. From detailed kinetic analyses, the reaction mechanisms including triplet-triplet excitation transfer, and intramolecular excitation transfer within the exciplex arising from the interaction of triplet acetone with cytosine and cytosine derivatives, have been suggested. Accordingly, a series of kinetic parameters have also been obtained.

Cytidine↗
PubMed1992

NMR study of self-paired parallel duplex of d(AAAAACCCCC) in solution.

The oligonucleotide d(A5C5) in solution forms a parallel self-duplex at neutral and low pH values. H2O NMR spectra at pH 5.1 indicate the presence of five imino resonances at lower temperatures; and the structure is stable up to 60 degrees C. These signals can arise only from the hemiprotonated C+.C pairs [Westhof, E. and Sundaralingham, M. (1980) Biochemistry 77, 1852-1856; Westhof, E. and Sundaralingham, M. (1980) J. Mol. Biol. 142, 331-361] and constitute the first direct observation of C+.C hemiprotonated pairs in solution. The cross peaks from H1's and more than five distinct AH8's in 500 MHz 1H 2D-NOESY spectra indicate that there are two conformationally different and energetically similar A-tracts. There is good qualitative agreement between NOESY data and two theoretically derived structures in which A-tracts are reverse Watson-Crick and reverse Hoogsteen base-paired, respectively.

Base Composition↗
PubMed1992

A predicted three-dimensional structure for the carcinoembryonic antigen (CEA).

A three-dimensional model for the carcinoembryonic antigen (CEA) has been constructed by knowledge-based computer modelling. Each of the seven extracellular domains of CEA are expected to have immunoglobulin folds. The N-terminal domain of CEA was modelled using the first domain of the recently solved NMR structure of rat CD2, as well as the first domain of the X-ray crystal structure of human CD4 and an immunoglobulin variable domain REI as templates. The remaining domains were modelled from the first and second domains of CD4 and REI. Link conformations between the domains were taken from the elbow region of antibodies. A possible packing model between each of the seven domains is proposed. Each residue of the model is labelled as to its suitability for site-directed mutagenesis.

Amino Acid Sequence↗
PubMed1992

Comparative effects of 6 week fructose, dextrose and starch feeding on fat-cell lipolysis in normal rats: effects of isoproterenol, theophylline and insulin.

The precise effects of fructose feeding on adipose tissue is not clearly known. Consequently, we studied the effects of fructose feeding on stimulated and inhibited in vitro lipolysis. Twenty seven male Sprague Dawley rats, 5 weeks of age, were fed for 6 weeks on one of three diets containing 57% CHO as fructose (F), dextrose (D) or starch (S). At week 6 the epididymal fat pad weights showed no difference between groups. Stimulation of lipolysis by isoproterenol or theophylline showed: decreased sensitivity of adipocytes to isoproterenol, but not to theophylline, in F (p less than 0.05); the maximal responses were decreased, but NS, after stimulation by either isoproterenol or theophylline. The maximal antilipolytic responses to insulin were increased in F (27%) and D (29%) when compared to S (16%), (p less than 0.05). Only, in F there was an increase (NS) in ED50 (0.63 +/- 0.23 ng/ml) compared to D (0.45 +/- 0.18) and S (0.29 +/- 0.18), indicating decreased sensitivity. Nonfasting plasma insulin and triglycerides were increased at the 6th week in F (p less than 0.01), without any change in plasma glucose levels. However, there was no difference in 12 h fasting plasma glucose, insulin or triglycerides. In conclusion, a 6 week 57% fructose containing diet in normal rats led to: 1) decreased lipid mobilization in the epididymal adipose tissue; and 2) increased nonfasting plasma insulin and triglycerides. Thus fructose, under these experimental conditions, seems to have adverse metabolic effects in normal rats.

Adipose Tissue↗
PubMed1992

Effects of partial hepatectomy on hepatic insulinlike growth factor binding protein-1 expression.

Insulinlike growth factor binding proteins modulate the action of the insulinlike growth factors in various bioassays and may regulate the bioavailability of the insulinlike growth factors in vivo. Because the insulinlike growth factors may influence hepatic regeneration, we have examined the effect of partial hepatectomy on serum insulinlike growth factor binding proteins and on the abundance of insulinlike growth factor binding protein-1 messenger RNA in the liver. All rats were fasted before and after partial hepatectomy or sham operation to avoid the confounding effects of difference in food intake. Using a conventional protocol, 70% of the liver was removed, and groups of four or five rats were killed at different intervals after partial hepatectomy. Sham-operated rats served as controls. Pooled sera from each group of rats were analyzed by ligand blotting with 125I-insulinlike growth factor-I. Liver RNA from individual rats was analyzed by slot-blot and Northern-blot hybridization. A small decrease in the 39- to 42-kD insulinlike growth factor binding protein was apparent in sera from both the sham-operated and partial hepatectomized rats. In contrast, a dramatic increase (fivefold) in the 29-kD serum insulinlike growth factor binding protein (insulinlike growth factor binding protein-1) was apparent only in the partial hepatectomized rats. Hepatic insulinlike growth factor binding protein-1 messenger RNA abundance was significantly increased (1.99 +/- 0.18-fold; p less than 0.05) at 1 hr, reached a peak of 2.32 +/- 0.22-fold (p less than 0.01) at 3 hr after partial hepatectomy and returned to basal levels over the subsequent 6 to 12 hr.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Tetraplex formation of d(GGGGGTTTTT): 1H NMR study in solution.

The oligonucleotide d(G5T5) can in principle form a fully matched duplex with G.T pairing and/or a tetraplex. Non-denaturing gel electrophoresis, circular dichroism and NMR experiments show that the tetraplex is exclusively formed by this oligomer in solution. In the presence of its complementary strand d(A5C5) at low temperature, d(G5T5) forms the tetraplex over the normally expected Watson-Crick duplex. However, when d(G5T5) and d(A5C5) are mixed together in equimolar amounts and heated for several minutes at 85 degrees C, and then allowed to cool, the product was essentially the Watson-Crick duplex. The lack of resolution in the 500 MHz 1H NMR spectra and the presence of extensive spin diffusion do not allow us to derive a quantitative structure for the tetraplex from the NMR data. However, we find good qualitative agreement between the NOESY and MINSY data and a theoretically derived stereochemically sound structure in which the G's and T's are part of a parallel tetraplex.

Base Sequence↗
PubMed1992

Neither dietary fructose, dextrose nor starch modifies in vitro glycerol release by adipocytes from streptozotocin-diabetic rats.

Because we found previously that fructose feeding could alter lipolytic responses to isoproterenol and insulin in normal rats, we studied the effects of the same diet in neonatal, streptozotocin-diabetic rats. Twenty-seven 5-wk-old diabetic Sprague-Dawley rats were fed a diet containing 57% carbohydrate as either fructose, dextrose or starch for 6 wk. At the end of the nutritional period, plasma glucose and insulin concentrations in fed rats were similar in the three diabetic groups. Plasma triacylglycerol concentrations were higher in the fructose-fed group than in the other two groups (P < 0.05). Neither the maximal adipocyte lipolytic response (fructose = 1147 +/- 165%, starch = 1823 +/- 329% and dextrose = 1287 +/- 239% of basal values) nor the sensitivity to isoproterenol (ED50) was changed by the dietary carbohydrate exchange. The maximal antilipolytic action of insulin (starch = 68 +/- 10%, dextrose = 41 +/- 13%, fructose = 95 +/- 29% of stimulated lipolysis values) was comparable in the three diet groups. Thus, 6 wk of fructose feeding in diabetic rats increased plasma triacylglycerol concentrations, but had no detectable effect on plasma glucose or insulin concentrations, isoproterenol-induced lipolysis or the antilipolytic action of insulin.

Adipose Tissue↗
PubMed1992

Mortality among dust-exposed Chinese mine and pottery workers.

A cohort study of approximately 68,000 persons employed during 1972 to 1974 at metal mines and pottery factories in south central China was conducted to evaluate mortality from cancer and other diseases among workers exposed to different levels of silica and other dusts. A follow-up of subjects through December 31, 1989 revealed 6,192 deaths, a number close to that expected based on Chinese national mortality rates. There was, however, a nearly 6-fold increase in deaths from pulmonary heart disease (standard mortality ratio, 581; 95% confidence interval 538 to 626), and a 48% excess of mortality from nonmalignant respiratory diseases (standard mortality ratio, 148; 95% confidence interval, 139 to 158), primarily because of a more than 30-fold excess of pneumoconiosis. Pulmonary heart disease and noncancerous respiratory disease rates rose in proportion to dust exposure. Cancer mortality overall was not increased among the miners or pottery workers. There was no increased risk of lung cancer, except among tin miners, and trends in risk of this cancer with increasing level of dust exposure were not significant. Risks of lung cancer were 22% higher among workers with than without silicosis. The findings indicate that respiratory disease continues to be an occupational hazard among Chinese miners and pottery workers, but that cancer risks are not as yet strongly associated with work in these dusty trades.

Air Pollutants, Occupational↗
PubMed1992

Quantitative computer analysis of the sounds of isolated motor unit action potentials.

To develop quantitative measures of motor unit action potential (MUAP) sounds, we correlated Fourier domain features of isolated, individual MUAPs with classic time domain measurements. There were moderate correlations between amplitude or duration measurements, and absolute low-frequency (39 to 234 Hz) energy and amplitude of the peak frequency, and high correlations between the composite time domain feature of amplitude x duration, and total energy, amplitude of the peak frequency, and absolute low-frequency energy. Polyphasic potentials have multiple peaks in the magnitude component of the Fourier transform. Phase information appears to convey the "crisp" sound of MUAPs close to the recording electrode. The clinical description of "large" or "small" MUAPs by sound is likely based on absolute low-frequency energy, and incorporates both amplitude and duration information. We conclude that features of isolated MUAPs may be analyzed in the Fourier domain, and that they correlate closely with traditionally used measures of known diagnostic significance. The sound of the EMG used by clinical electromyographers is amenable to quantitative analysis.

Action Potentials↗
PubMed1992

Differential expression of the insulin-like growth factor binding proteins in spontaneously diabetic rats.

Diabetes-induced growth retardation in the rodent is associated with both reduced circulating insulin-like growth factor-I (IGF-I) and enhanced levels of inhibitors of somatomedin activity. IGF-binding proteins (IGFBPs) are present in the circulation and tissue fluids and are believed to modulate the actions of IGF-I. Since elevated concentrations of the IGFBPs may contribute to the enhanced somatomedin-inhibitor activity observed in serum from diabetic animals, we have examined the amounts of hepatic IGFBP-1, -2, -3 and -4 mRNA in the spontaneously diabetic BioBreeding/Worcester rat. The study used two types of diabetic animal: mildly diabetic animals, which received suboptimal insulin treatment (0.5-1 U/day) and diabetic animals, which received intensive insulin treatment (3-6 U/day). A significant increase in the amount of IGFBP-1 and IGFBP-2 mRNA was seen 1 month and 3 months after the onset of diabetes. Intensive insulin treatment for 3 weeks normalized the amount of IGFBP-1 mRNA in diabetic rats and resulted in a decrease in IGFBP-2 mRNA. In contrast to the increase in IGFBP-1 and IGFBP-2 mRNA, a significant decrease in IGFBP-3 mRNA was seen in diabetic rats (54.6% of control, P less than 0.0005 and 64.6% of control, P less than 0.005 for 1 and 3 months respectively) and intensive insulin treatment for 3 weeks did not restore the IGFBP-3 mRNA level in diabetic rats. No significant difference in IGFBP-4 mRNA levels was seen in diabetic compared with non-diabetic rats. When serum was analysed by ligand blotting the major finding was a reduction in the 39-42 kDa binding protein. No increase in 29-30 kDa IGFBP in the serum was detected in the diabetic rats. From these studies we conclude that the major change in IGFBPs in mildly hyperglycaemic spontaneously diabetic rats is a decrease in IGFBP-3. The changes in hepatic IGFBP-1 and -2 mRNA do not appear to be of sufficient magnitude to result in an increase in serum concentrations of these binding proteins.

Animals↗
PubMed1991

Genomic sequences homologous to the protein kinase region of the bifunctional herpes simplex virus type 2 protein ICP10.

The large subunit of herpes simplex virus type 2 (HSV-2) ribonucleotide reductase (ICP10) consists of two functional domains. The amino (N)-terminal domain at residues 1-411 has serine/threonine-specific kinase activity (PK domain) and is encoded by a DNA fragment with transforming potential (15,17). The remaining region is required for ribonucleotide reductase activity (RR domain) (14, 15). Computer-assisted comparison of the ICP10 sequence to the EMBL database 21 has revealed sequences within the RR domain that are common to all RR1 proteins. Motifs homologous to the catalytic domains of all PKs were identified in the PK region (15). However, based on this database all other sequences were unique. Secondary structure analysis of the PK and RR junction region of ICP10 identified twist angle variations with helical periodicity characteristic of enhancer elements. Sequences homologous to a segment of the PK domain were amplified and cloned from human DNA using the polymerase chain reaction (PCR), suggesting that the PK domain may have originated from a cellular gene.

Amino Acid Sequence↗
PubMed1991

Physiologic and subjective effects of respirator mask type.

The effect of alternate airflow path designs on full-face mask air-purifying respirators was assessed in 14 healthy volunteers during submaximal exercise. Respirator designs included no respirator (N), full-face mask, dual-cartridge with no nasal deflector (FN), full-face mask respirator with nasal deflector (FD), and a powered air-purifying respirator (PA). Physiologic effects were measured by using respiratory inductive plethysmography and subjective responses by two visual analog scales. There were significant effects of airflow path design upon the physiologic parameters of ventilation, tidal volume, and mean flow rate. There were no significant physiologic or subjective differences between the full-face mask respirators with and without the nasal deflector in place. The PA had less physiologic impact than the nonpowered models but did not show significant subjective benefit. The study suggests that both subjective and objective physiologic responses must be utilized in assessing respirator design.

Adult↗
PubMed1991

Human T-cell leukemia virus type II Rex binding and activity require an intact splice donor site and a specific RNA secondary structure.

The human T-cell leukemia virus type II (HTLV-II) regulatory protein Rex augments cytoplasmic levels of unspliced gag-pol mRNA by acting through a Rex-responsive element (RxRE) in the long terminal repeat. Purified Rex protein binds to long terminal repeat mRNA. Here, using an immunobinding assay to measure the binding of Rex protein to mutated RxRE RNAs, we show that efficient Rex binding requires a stem-bulge-loop RNA secondary structure (nucleotides [nt] 465 to 500) and specific sequences both within the stem-bulge (nt 470 to 476) and within a conserved upstream splice donor site (nt 449 to 455). Rex function in a transient transfection expression system correlates with Rex protein-RxRE RNA binding. The ability of HTLV-II Rex to interact directly with the HTLV-II splice donor site suggests that HTLV-II Rex may increase expression of unspliced gag-pol mRNA, in part, by inhibiting splicing.

Base Sequence↗
PubMed1991

Artificial intelligence-assisted occupational lung disease diagnosis.

An artificial intelligence expert-based system for facilitating the clinical recognition of occupational and environmental factors in lung disease has been developed in a pilot fashion. It utilizes a knowledge representation scheme to capture relevant clinical knowledge into structures about specific objects (jobs, diseases, etc) and pairwise relations between objects. Quantifiers describe both the closeness of association and risk, as well as the degree of belief in the validity of a fact. An independent inference engine utilizes the knowledge, combining likelihoods and uncertainties to achieve estimates of likelihood factors for specific paths from work to illness. The system creates a series of "paths," linking work activities to disease outcomes. One path links a single period of work to a single possible disease outcome. In a preliminary trial, the number of "paths" from job to possible disease averaged 18 per subject in a general population and averaged 25 per subject in an asthmatic population. Artificial intelligence methods hold promise in the future to facilitate diagnosis in pulmonary and occupational medicine.

Artificial Intelligence↗