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Biomedical subjects

A Tsai

Publications and source records attributed to A Tsai.

At least 37 records · Page 2Linked to original sources
PubMed1998

Induction of a TH1 type cellular immune response to the human immunodeficiency type 1 virus by in vivo DNA inoculation.

DNA inoculation is capable of producing antigens intracellularly for ultimate presentation to the cellular and humoral components of the immune system and has potential for vaccine strategies against a number of infectious pathogens including HIV-1. It is well documented that the antigenic diversity of HIV-1 and its high level of nucleotide mutations during reverse transcription can lead to escape from immune surveillance. However, data suggest that a CD8-mediated cytotoxic T lymphocyte response may be less susceptible to escape mutants. We have shown previously that in vivo inoculation of rodents and non-human primates with plasmid expression vectors encoding HIV-1 gene products leads to production of HIV-1 antigens and results in the production of both cellular and humoral immune responses. In addition we have also demonstrated previously that these responses lead to protection in several in vivo models. We further demonstrate here that the cellular response induced is a type TH1 response and specific lysis of HIV-infected targets is CD8-mediated.

AIDS Vaccines↗
PubMed1997

Clinical predictors of oxidized low-density lipoprotein in patients with coronary artery disease.

Oxidized low-density lipoprotein (LDL) may play a key role in the initiation and progression of atherosclerosis. Risk factors for elevated levels of oxidized LDL are not well established and may be important in identifying individuals who may benefit from antioxidant supplementation or interventions to reduce oxidant stress. The purpose of this study was to determine if clinical parameters predict levels of oxidized LDL. We evaluated the relation between clinical parameters and oxidized LDL in 45 nonsmoking, nondiabetic patients (39 men and 6 women) with coronary artery disease. Oxidized LDL was assessed by measurement of conjugated dienes, lipid peroxides, and thiobarbituric reactive substances (TBARS) at 0 hours to evaluate baseline oxidant stress and postincubation with an oxidizing agent to assess the capacity of LDL for peroxidation. Results were lipid standardized and were not materially altered by multivariate adjustment. Significant predictors of increased oxidized LDL included female sex, family history of premature cardiovascular disease, increased percent body fat, increased body mass index, increased heart rate at rest, history of smoking, exercise <4 times per week, and no regular wine consumption. These data suggest that clinical parameters correlate with levels of oxidized LDL and may be useful in identifying patients at risk for increased oxidant stress.

Adult↗
PubMed1997

A comparison of volume conductor effects on body surface Laplacian and potential ECGS: a model study.

The objective of this investigation is to study, using a computer model, the torso volume conductor effects on body surface potential electrograms and body surface Laplacian electrograms. A spherical volume conductor model was used to approximate the torso and the heart. Myocardial electrical events were approximated by two distributed dipole-layers representing activation wavefronts propagating from the endocardium to the epicardium. The present computer simulation results indicate that the body surface Laplacian maps provide enhanced performance over the body surface potential maps in resolving the configurations of two activation wavefronts over the anterior wall of the heart.

Body Surface Potential Mapping↗
PubMed1997

Antioxidant nutrient supplementation reduces the susceptibility of low density lipoprotein to oxidation in patients with coronary artery disease.

OBJECTIVE: This study sought to determine the effect of antioxidant supplementation on the susceptibility of low density lipoprotein (LDL) to oxidation in patients with established cardiovascular disease (CVD). BACKGROUND: Data are inconsistent regarding the role of antioxidant nutrients in the prevention of CVD. METHODS: The study design was a 12-week, double-blind, placebo-controlled clinical trial. Patients with CVD (n = 45) were randomized to 1) placebo control; 2) 400 IU of vitamin E, 500 mg of vitamin C, 12 mg of beta-carotene (mid-dose); or 3) 800 IU of vitamin E, 1,000 mg of vitamin C, 24 mg of beta-carotene (high dose) daily. Reduced susceptibility of LDL to oxidation was estimated by an increase in lag phase (minutes). Baseline and 6- and 12-week measurements of lipoproteins and lag phase were obtained. Plasma levels of antioxidants were measured at baseline and 12 weeks. RESULTS: Concentrations of alpha-tocopherol, vitamin C and beta-carotene significantly increased in the mid- and high dose groups during the trial. Lag phase significantly increased from baseline (190.1 +/- 63.8 min [mean +/- SD]) to 12 weeks (391.1 +/- 153.0 min) in the high dose group (p < 0.01). A nonsignificant increase in lag phase in the mid-dose group was observed during the same time interval. A dose response was found for mean percent change from baseline to 12 weeks for lag phase for the placebo, mid- and high dose groups (p = 0.004 for trend). CONCLUSIONS: A high dose combination of antioxidant nutrients reduces the susceptibility of LDL to oxidation in patients with CVD and may be useful in secondary prevention.

Adult↗
PubMed1995

Spectroscopic evidence for reaction of prostaglandin H synthase-1 tyrosyl radical with arachidonic acid.

The coupling between the peroxidase and cyclooxygenase activities of prostaglandin H synthase (PGHS) has been proposed to be mediated by a critical tyrosyl radical through a branched chain mechanism (Dietz, R., Nastainczyk, W., and Ruf, H. H. (1988) Eur. J. Biochem. 171, 321-328). In this study, we have examined the ability of PGHS isoform-1 (PGHS-1) tyrosyl radicals to react with arachidonate. Anaerobic addition of arachidonate following formation of the peroxide-induced wide doublet or wide singlet tyrosyl radical led to disappearance of the tyrosyl radicals and emergence of a new EPR signal, which is distinct from known PGHS-1 tyrosyl radicals. The new radical was clearly derived from arachidonate because its EPR line shape changed when 5,6,8,9,11,12,14,15-octadeuterated arachidonate was used. Subsequent addition of oxygen to samples containing the fatty acyl radical resulted in regeneration of tyrosyl radical EPR. In contrast, the peroxide-generated tyrosyl radical in indomethacin-treated PGHS-1 (a narrow singlet) failed to react with arachidonate, consistent with the cyclooxygenase inhibition by indomethacin. These results indicate that the peroxide-generated wide doublet and wide singlet tyrosyl radicals serve as immediate oxidants of arachidonate bound at the cyclooxygenase active site to form a carbon-centered fatty acyl radical, which reacts with oxygen to form a hydroperoxide. These observations represent the first direct evidence of chemical coupling between the peroxidase reaction and arachidonate oxygenation in PGHS-1 and support the proposed role for a tyrosyl radical in cyclooxygenase catalysis.

Animals↗
PubMed1994

How does NO activate hemeproteins?

NO was reported to activate guanylate cyclase and, recently, prostaglandin H synthase. NO interaction with the heme component in different hemeproteins is determined by ligand property, electronic configuration of the heme iron and the specific effects contributed by the protein structure. It is found that although NO interaction with the free heme provides some common rules of interaction, the consequences of NO binding to different hemeproteins should be dealt with individually.

Hemeproteins↗
PubMed1994

Characterization of the tyrosyl radicals in ovine prostaglandin H synthase-1 by isotope replacement and site-directed mutagenesis.

Several free radical species, attributed to tyrosyl radicals, have been previously observed by electron paramagnetic resonance (EPR) spectroscopy during reaction of pure ovine prostaglandin H synthase-1 (PGHS-1) with hydroperoxide or fatty acid substrates. The identity and location of amino acid residue(s) involved in formation of these radicals has been investigated using wild type and mutant PGHS-1 expressed in transfected COS-1 cells. Upon reaction with hydroperoxide, detergent extracts from microsomes of cells expressing wild type ovine PGHS-1 rapidly produced EPR signals made up of a broad component, resembling either the wide doublet or the wide singlet seen in reactions of the purified ovine enzyme, mixed with a variable proportion of a narrow component. Isotope replacement with perdeuterated tyrosine and phenylalanine in wild type PGHS-1 caused no change in enzymatic activity or capability to form a peroxide-induced radical, but the radical was an isotropic singlet without any wide features. This loss of splitting in the deuterated enzyme establishes that the wide radical signal in PGHS-1 is indeed a tyrosyl radical, validating the earlier assignment based on spectral similarities with a tyrosyl radical in ribonucleotide reductase. A Y385F mutation abolished cyclooxygenase but not peroxidase activity, and the peroxide-induced EPR was narrowed to a singlet essentially identical with that obtained with indomethacin-treated ovine enzyme. Isotopic replacement with perdeuterated tyrosine and phenylalanine in the Y385F mutant led to further narrowing of the peroxide-induced EPR to an isotropic singlet, establishing that this radical also involved a tyrosine residue. A Y355F mutant exhibited some decrease in cyclooxygenase activity, but the peroxidase activity and the peroxide-induced radical characteristics were not significantly different from those of the wild type enzyme, indicating that Tyr355 is not involved in tyrosyl radical formation in PGHS-1.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1994

Selective inhibition of neuronal protein synthesis by retrogradely transported ricin.

The ability of the lectin, ricinus communis agglutinin I (ricin120), to undergo retrograde axonal transport and cause degeneration of neuronal cell bodies has been frequently exploited to establish the origin of peripheral axons. Since this cytotoxic action of ricin results from its inactivation of ribosomes, the retrogradely transported lectin was employed in the present study to inhibit protein synthesis in dorsal root ganglion (DRG) neurons whose axons project into the lumbar nerve trunk of bullfrog tadpoles. The procedure was developed to examine, during tadpole metamorphosis, the ratio of fast-transported radiolabeled protein accumulating at the proximal side of a nerve trunk ligature to the total newly synthesized protein in the cell bodies of origin. The relatively small diameter and fragility of the developing lumbar nerve trunks necessitated introduction of ricin by bath application to the cut nerve end rather than by intraneural injection. Consistent uptake of ricin was achieved by pretreatment with the phospholipase A2 inhibitor, mepacrine, that blocks resealing of severed nerve fibers. Optimal time and dosage of ricin were established by determining the maximal achievable inhibition of [35S]methionine into DRG protein. In stage XVI tadpoles, maximal inhibition of approximately to 65% was observed after 16 h incubation in 2.5 mg/ml ricin. As evidence that neuronal protein synthesis was effectively suppressed, there was no detectable anterograde axonal transport of [35S]protein subsequent to ricin treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Regulation of pancreatic amylase and lipase gene expression by diet and insulin in diabetic rats.

Although insulin has been proposed to mediate the dietary regulation of pancreatic amylase, its interaction with diet in the regulation of amylase and lipase is not well understood and was examined in diabetic rats fed diets high in carbohydrate (HC), protein (HP), or fat (HF) and treated with insulin. Diabetes, independent of diet, decreased amylase content (97%; P < 0.0001) and mRNA (90%; P < 0.0001), but insulin only restored amylase content and mRNA to respective dietary control values. Diabetes, independent of diet, also increased lipase mRNA 1.6-fold (P < 0.004) but interacted (P < 0.0003) with diet on lipase content, resulting in opposite effects in HC- (increased 202%) and HF-diabetic rats (decreased 40%). Insulin partially restored lipase content and mRNA to respective dietary control values. Diet, independent of diabetes, regulated amylase content (P < 0.0001) and mRNA (P < 0.0003), which were three- to fourfold greater in HC- than in HF-fed rats, and lipase content (P < 0.001) and mRNA [rat pancreatic lipase 1 (rPL-1), P < 0.04; rPL-3, P < 0.0001], which were 1.8-fold greater in HF- than in HC- or HP-fed rats. Insulin failed to stimulate maximal amylase gene expression in HP- or HF-fed diabetic rats, suggesting that it is necessary, but not sufficient, for this dietary regulation. Differential regulation of lipase activity and mRNA by diet and insulin raises the possibility that lipase gene expression is regulated by a complex interaction of diet and insulin.

Amylases↗
PubMed1993

Purification and characterization of recombinant human thyrotropin (TSH) isoforms produced by Chinese hamster ovary cells: the role of sialylation and sulfation in TSH bioactivity.

The biological significance of glycosylation variants of pituitary glycoprotein hormones remains controversial because of the indirect methods usually employed to determine carbohydrate composition or structure as well as the use of unreliable biological/immunological ratio to determine bioactivity. We have previously characterized recombinant human TSH (rhTSH) secreted by Chinese hamster ovary cells attached to microcarrier beads in a large scale bioreactor after stable transfection of hCG alpha and hTSH beta minigenes. In the present study rhTSH has been used as a model to determine structure-function relationships of different isoforms of glycoprotein hormones. We have now produced greater than 200 mg rhTSH using a hollow fiber bioreactor. The highly purified rhTSH produced in the hollow fiber bioreactor (rhTSH-N) as well as rhTSH commercially produced in a large scale bioreactor (rhTSH-G) were quantitated by immunoassays, receptor binding assay, and amino acid analysis and further characterized by a variety of physico-biochemical methods, including chromatofocusing and carbohydrate analysis. rhTSH-G, rhTSH-N, as well as pituitary human TSH (phTSH) have been separated by chromatofocusing on a Mono P column into several isoforms with different pI values. Compositional analysis of the fractions showed higher sialic acid content in the more acidic rhTSH-G fractions. phTSH acidic isoforms showed higher total sulfate and sialic acid contents than the more basic fractions. The bioactivities of various TSH isoforms based on rigorous quantitation of mass by amino acid analysis determined in three different FRTL-5 cell bioassays showed that the more basic and less sialylated fractions of rhTSH-G were more active than the more acidic fractions. In contrast to the in vitro data, highly sialylated and acidic rhTSH-G isoforms showed longer plasma half-lives and higher in vivo bioactivity than the basic forms. These results indicate that secreted rhTSH, similar to intrapituitary phTSH, exists as a mixture of charge isoforms that are related at least in part to the degree of sialylation. The degree of sialylation, highly dependent on the bioreactor production conditions, appears to be the major factor affecting the charge heterogeneity, MCR, and bioactivity of rhTSH.

Amino Acids↗
PubMed1992

[Loss of catecholaminergic neuron in the hypothalamus of multiple system atrophy].

Autonomic failure is one of the primary clinical features of multiple system atrophy (MSA); while the hypothalamus is thought to be a higher center regulating the autonomic nervous system. In the hypothalamus, catecholamine depletion had been confirmed by neurochemical studies but no marked changes had yet been demonstrated by pathological studies. Using three MSA and three control cases, we evaluated the quantitative changes of catecholamine (CA)-containing neurons in the hypothalamus. As markers of CA neurons, neuromelanin (NM)- and tyrosin hydroxylase (TH)-containing neurons were stained by Fontana-Masson and the immunohistochemical technique alternatively. Serial coronal sections, 10 microns thick, were evaluated every tenth section for NM neurons, while two sections were evaluated for TH neurons. The distributions of NM and TH neurons were almost identical; most of them were clustered in the periventricular and arcuate nuclei. The mean numbers of NM and TH neurons per slice were significantly lower in MSAs than in the controls (T test, p less than 0.01); the former were 21.0, 31.6, and 13.7 in MSAs and 78.4, 54.1, and 84.3 in the controls, while the latter were 1.5, 15.5, and 20.5 in MSAs and 48.0, 62.0, and 50.5 in the controls. The clinico-pathological correlation was suggested by the significant differences in the number of TH neurons between two MSA cases: a case with severe orthostatic hypotension and a case with a milder one. The ratio of TH and NM neurons, as obtained from the adjusted sections, was constant in all MSA cases, and there was a positive statistical correlation, but it altered in each control case.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗