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Biomedical subjects

M Wang

Publications and source records attributed to M Wang.

At least 919 records · Page 51Linked to original sources
PubMed1992

Posttreatment exposure to camptothecin enhances the lethal effects of x-rays on radioresistant human malignant melanoma cells.

Little is known about the molecular mechanisms responsible for the survival recovery process(es) (known as potentially lethal damage repair), which occurs in mammalian cells following ionizing radiation. Previously, we presented data indicating a role for the DNA unwinding enzyme, topoisomerase I, in DNA repair. We now demonstrate that camptothecin, a specific inhibitor of topoisomerase I, causes dramatic radiosensitization of an extremely resistant human melanoma (U1-Mel) cell line. Camptothecin radiosensitized U1-Mel cells when it was administered either during or immediately following x-irradiation. U1-Mel cells were optimally radiosensitized with 4 microM camptothecin for a period of 4-6 hrs after x-irradiation. Enhanced cell killing by camptothecin was proportional to the initial extent of damage created by x-irradiation; the higher the dose of ionizing radiation, the greater the radiosensitization. The apparent synergy observed with camptothecin and x-rays was irreversible; camptothecin-treated U1-Mel cells were not able to carry out PLDR in a 48 hr period after the drug was removed. We hypothesize that the administration of camptothecin causes lesion modification through a topoisomerase I-mediated mechanism. These data support a role for topoisomerase I in DNA repair and indicate that camptothecin, or more effective derivatives, may have clinical use.

Camptothecin↗
PubMed1992

cAMP-induced desensitization of surface cAMP receptors in Dictyostelium: different second messengers mediate receptor phosphorylation, loss of ligand binding, degradation of receptor, and reduction of receptor mRNA levels.

Surface cAMP receptors on Dictyostelium cells are linked to several second messenger systems and mediate multiple physiological responses, including chemotaxis and differentiation. Activation of the receptor also triggers events which desensitize signal transduction. These events include the following: 1) loss of ligand binding without loss of receptor protein; 2) phosphorylation of the receptor protein, which may lead to impaired signal transduction; 3) redistribution and degradation of the receptor protein; and 4) decrease of cyclic AMP (cAMP) receptor mRNA levels. These mechanisms of desensitization were investigated with the use of mutant synag7, with no activation of adenylyl cyclase; fgdC, with no activation of phospholipase C; and fgdA, with defects in both pathways. cAMP-induced receptor phosphorylation and loss of ligand binding activity was normal in all mutants. In contrast, cAMP-induced degradation of the receptor was absent in all mutants. The cAMP-induced decrease of cAMP-receptor mRNA levels was normal in mutant synag7, but absent in mutant fgdC. Finally, the cAMP analogue (Rp)-cAMPS induced loss of ligand binding without inducing second messenger responses or phosphorylation, redistribution, and degradation of the receptor. We conclude that 1) loss of ligand binding can occur in the absence of receptor phosphorylation; 2) loss of ligand binding and receptor phosphorylation do not require the activation of second messenger systems; 3) cAMP-induced degradation of the receptor may require the phosphorylation of the receptor as well as the activation of at least the synag7 and fgdC gene products; and 4) cAMP-induced decrease of receptor mRNA levels requires the activation of the fgdC gene product and not the synag7 gene product. These results imply that desensitization is composed of multiple components that are regulated by different but partly overlapping sensory transduction pathways.

Animals↗
PubMed1992

Formation of 7-(4-oxobutyl)guanine in hepatic DNA of rats treated with N-nitrosopyrrolidine.

We have reported previously the formation of two structurally distinct exocyclic guanine adducts (adducts 1 and 6) in liver DNA of F344 rats treated with N-nitrosopyrrolidine (NPYR). In this study, we detected and characterized a previously unidentified guanine adduct in liver DNA of NPYR-treated rats. The structure of this adduct was established as 7-(4-oxobutyl)guanine (adduct 2) by comparison with the synthetic standard and confirmed by NaBH4 reduction to 7-(4-hydroxybutyl)guanine. The level of adduct 2 in liver DNA of F344 rats treated with 450 mg/kg of NPYR by i.p. administration was 643 +/- 9 mumol/mol guanine, approximately one-third of the level of adduct 1. This study is the first to demonstrate the in vivo formation of a formylalkyl-substituted guanine adduct by a nitrosamine.

Animals↗
PubMed1992

Isoproterenol increases defibrillation energy requirements in dogs.

The effect of intravenous isoproterenol on the energy requirements for successful defibrillation (DF) was examined in anesthetized dogs following cholinergic blockade with atropine (n = 5) and following treatment with d- and d,l-sotalol (n = 16). Defibrillation shocks were administered through left and right ventricular epicardial patch electrodes and the energy requirements for DF were studied using two different methods. Multiple shocks of varying energies were delivered and the energies required for 50% success (E50) and 80% success (E80) in DF were estimated using logistic regression. Atropine (0.04 mg/kg) increased E50 by 32 +/- 30% (p = 0.046) and E80 by 39 +/- 38% (p = ns). Subsequent administration of isoproterenol (10 micrograms/ml), increasing the heart rate by 52 +/- 35% (p = 0.025), resulted in a further 108 +/- 21% (p = 0.015) and 88 +/- 55% (p = 0.02) rise in E50 and E80 values, respectively. In a second set of experiments, d- (n = 9) and d,l-sotalol (n = 7) (4 mg/kg bolus followed by 0.025 mg/kg/min maintenance infusion) were administered and baseline curves relating delivered energy to % success in DF were calculated. Isoproterenol (10 +/- 4 micrograms/min) was given to increase the heart rate by 54 +/- 32% (p less than 0.025), and resulted in decreases in % success at each of two energy levels, falling in the midrange of the dose-response curve. Following d,l-sotalol, % successful shocks fell from 60 +/- 15 to 42 +/- 28% (p less than 0.05); following d-sotalol, the % success fell from 66 +/- 13 to 38 +/- 36% (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Cytosolic alkalinization mediated by abscisic Acid is necessary, but not sufficient, for abscisic Acid-induced gene expression in barley aleurone protoplasts.

We investigated whether intracellular pH (pH(i)) is a causal mediator in abscisic acid (ABA)-induced gene expression. We measured the change in pH(i) by a "null-point" method during stimulation of barley (Hordeum vulgare cv Himalaya) aleurone protoplasts with ABA and found that ABA induces an increase in pH(i) from 7.11 to 7.30 within 45 min after stimulation. This increase is inhibited by plasma membrane H(+)-ATPase inhibitors, which induce a decrease in pH(i), both in the presence and absence of ABA. This ABA-induced pH(i) increase precedes the expression of RAB-16 mRNA, as measured by northern analysis. ABA-induced pH(i) changes can be bypassed or clamped by addition of either the weak acids 5,5-dimethyl-2,4-oxazolidinedione and propionic acid, which decrease the pH(i), or the weak bases methylamine and ammonia, which increase the pH(i). Artificial pH(i) increases or decreases induced by weak bases or weak acids, respectively, do not induce RAB-16 mRNA expression. Clamping of the pH(i) at a high value with methylamine or ammonia treatment affected the ABA-induced increase of RAB-16 mRNA only slightly. However, inhibition of the ABA-induced pH(i) increase with weak acid or proton pump inhibitor treatments strongly inhibited the ABA-induced RAB-16 mRNA expression. We conclude that, although the ABA-induced the pH(i) increase is correlated with and even precedes the induction of RAB-16 mRNA expression and is an essential component of the transduction pathway leading from the hormone to gene expression, it is not sufficient to cause such expression.

Journal Article↗
PubMed1992

Dormancy of the barley grain is correlated with gibberellic Acid responsiveness of the isolated aleurone layer.

The relationship between barley grain dormancy and gibberellic acid (GA(3)) responsiveness of aleurone layers has been investigated. Barley (Hordeum distichum L. cvs Triumph and Kristina) grains were matured under defined conditions in a phytotron. Grains of Triumph plants grown under long-day/warm conditions had lower dormancy levels than grains of plants grown under short-day/cool conditions. Aleurone layers isolated from grains of long-day Triumph plants secreted more alpha-amylase and had a higher responsiveness to GA(3) as measured by alpha-amylase secretion. Storage of the grains increased both the percentage of germination and the responsiveness of the aleurone to GA(3). Use of different sterilization methods to break dormancy confirmed the correlation between germination percentage and aleurone layer GA(3) responsiveness. The response of embryoless Triumph grains to GA(3) was lower than that of the isolated aleurone layers, suggesting a role of the starchy endosperm in regulating the GA(3) response of the aleurone layer. Grains of the cultivar Kristina harvested from short day- and long day-grown plants lacked dormancy, and their isolated aleurone layers had a similar responsiveness to GA(3) as measured by alpha-amylase secretion. The data indicate that the physiological state of the aleurone layers contributes to the percentage germination of the grains.

Journal Article↗
PubMed1992

Expression, self-assembly, and antigenicity of the Norwalk virus capsid protein.

Norwalk virus capsid protein was produced by expression of the second and third open reading frames of the Norwalk virus genome, using a cell-free translation system and baculovirus recombinants. Analysis of the expressed products showed that the second open reading frame encodes a protein with an apparent molecular weight of 58,000 (58K protein) and that this protein self-assembles to form empty viruslike particles similar to native capsids in size and appearance. The antigenicity of these particles was demonstrated by immunoprecipitation and enzyme-linked immunosorbent assays of paired serum samples from volunteers who developed illness following Norwalk virus challenge. These particles also induced high levels of Norwalk virus-specific serum antibody in laboratory animals following parenteral inoculation. A minor 34K protein was also found in infected insect cells. Amino acid sequence analysis of the N terminus of the 34K protein indicated that the 34K protein was a cleavage product of the 58K protein. The availability of large amounts of recombinant Norwalk virus particles will allow the development of rapid, sensitive, and reliable tests for the diagnosis of Norwalk virus infection as well as the implementation of structural studies.

Antibody Formation↗
PubMed1992

Determination of whether tomato spotted wilt virus replicates in Toxorhynchites amboinensis mosquitoes and the relatedness of this virus to phleboviruses (family Bunyaviridae).

Tomato spotted wilt virus (TSWV) has been reported to be morphologically, molecularly and structurally similar to viruses in the family Bunyaviridae. By various types of enzyme-linked immunosorbent assays (ELISA) and Western blot hybridizations, we tested TSWV with antibodies to 12 viruses in the Phlebovirus genus of this family. Serological relatedness was not found between TSWV and phleboviruses. However, one preparation of antibody to Arumowot virus reacted with a 53-kD protein from healthy plant extracts. Six-day-old adult Toxorhynchites amboinensis mosquitoes were inoculated with purified TSWV. Infectious virus was not detected in any of the injected insects during the 5-week test period. However, TSWV antigens were detected in these mosquitoes by ELISA at the original injected level for at least a week after injection. TSWV antigen concentration began to decrease thereafter, but remained at detectable levels for as long as 5 weeks after injection. However, there was no evidence that TSWV replicated in mosquitoes.

Animals↗
PubMed1992

Rabbit trachealis tension responses to receptor-mediated agonists are diminished by elastase.

The present study examined the effects of elastase, in concentrations present in respiratory secretions, on airway smooth muscle contractile responses in vitro and the magnitude of the airway epithelial inhibition of smooth muscle tension. Experiments were performed on 126 full-thickness tracheal strips from 25 rabbits. Isometric tension responses to acetylcholine (10(-8) to 10(-4) M) and potassium chloride (10 to 110 mM) were examined before and after a 5-min exposure to either porcine pancreatic elastase (PPE) or human neutrophil elastase (HNE). PPE (5 to 40 micrograms/100 microliters) reduced the tension response to acetylcholine but had no effect on the tension response to potassium chloride. PPE and HNE (20 micrograms/100 microliters) produced similar effects. Mechanical removal of the epithelium per se significantly (P less than 0.005) decreased the ED50 response to acetylcholine but did not affect maximal tension. However, the airway epithelial inhibitory effect on the acetylcholine tension response was similar in the presence and absence of PPE (20 micrograms/100 microliters). These data suggest that the diminution of tracheal smooth muscle tension responses to receptor-mediated agonists induced by elastase is a direct effect on the muscle and is not mediated by an effect of elastase on the respiratory epithelium.

Acetylcholine↗
PubMed1992

Inherited congenital adrenal hyperplasia in the rabbit: absent cholesterol side-chain cleavage cytochrome P450 gene expression.

We investigated adrenal steroidogenic enzymes, their activity and mRNA expression, and in vitro biosynthesis of an enzyme in rabbits with congenital adrenal hyperplasia (CAH; weight: CAH, 19 +/- 5 mg/adrenal; normal, 2.7 +/- 1.0 mg/adrenal). Serum pregnenolone (delta 5-P) levels in CAH newborn rabbits (12-36 h) were normal (mean/range, 438/51-2191 ng/dl), but corticosterone levels were low [0.05 +/- 0.05 microgram/dl; P less than 0.001 vs. normal (0.66 +/- 0.57)]. Serum Na+ levels in CAH newborn rabbits were in the normal range (143 +/- 30 meq/liter), but K+ levels were elevated [7 +/- 1.1 meq/liter; P less than 0.05 vs. normal (5.9 +/- 0.6 meq/liter)]. Minced normal adrenal tissue incubated with [3H] cholesterol (30-100 pmol/flask) and ACTH (100 mU/flask) produced [3H]delta 5-P (newborn, 21 and 45 fmol/100 mg; adult, 3 and 5 fmol/100 mg) and [3H]corticosterone (newborn, 23 fmol/100 mg; adult, 11.3 fmol/100 mg), but CAH adrenals produced no product (less than 1.3 fmol/100 mg). Adrenal mitochondria from normal newborn rabbits produced delta 5-P (4.4-7 nmol/mg protein), but CAH adrenals did not, while CAH adrenal mitochondria demonstrated over 4 times greater 11 beta-hydroxylase activity. A Western blot of adrenal homogenate from normal newborn rabbits revealed a cholesterol side-chain cleavage cytochrome P450 (P450scc)-immunoreactive species (mol wt, 53 x 10(3), but this species was absent in CAH adrenals; CAH adrenals had a normal adrenodoxin and intensified 17 alpha-hydroxylase cytochrome P450 (P450(17)alpha) band compared to normal adrenals. In vitro translation of RNA in a cell-free rabbit reticulocyte lysate system containing [35S] methionine yielded a precursor P450scc protein (mol wt, 58.5 x 10(3)) with normal adrenal RNA, but not with CAH adrenal RNA. P450scc mRNA was detected in all normal adrenals, but was not detected in all CAH adrenals. 21-Hydroxylase cytochrome P450 mRNA expression was detected at a similar level in both normal and CAH adrenals. We conclude that CAH in the rabbit is caused by inherited absent P450scc gene expression. The clinical, pathological, and biochemical manifestations of P450scc deficiency in the rabbit are nearly identical to the human disorder. Increased 11 beta-hydroxylase activity and increased P450(17)alpha on Western blot of CAH adrenals indicate altered gene expression of other steroidogenic enzymes due to CAH. Further molecular analysis of the P450scc gene in this animal CAH model will facilitate understanding of P450scc deficiency CAH.

Adrenal Glands↗
PubMed1992

Normal and elevated 3 alpha-androstanediol glucuronide concentrations in women with various causes of hirsutism and its correlation with degree of hirsutism and androgen levels.

We investigated peripheral androgen metabolic activity in 54 hirsute females (HF) by evaluating the serum 3 alpha-androstanediol glucuronide (3AG) concentration, hirsutism score (HS), and etiology of hirsutism. Based on basal and ACTH-stimulated steroid profiles (1 h post-Cortrosyn, 0.25 mg, i.v. bolus), the causes of hirsutism were determined to be increased adrenal androgen production (greater than 2 SD above normal mean), increased ovarian testosterone (T) production (greater than 2 SD above normal mean basal T of ovarian source only), or idiopathic cause (normal steroid profile). Serum 3AG levels in each group of HF were significantly higher (P less than 0.01-0.001) than those in normal females [normal: 2.9 +/- 0.94 nmol/L (n = 28); HF: increased adrenal androgen production of undefined cause, 7.7 +/- 7.5 nmol/L (n = 14); 21-hydroxylase deficiency, 7.6 +/- 7.4 nmol/L (n = 5); increased ovarian T production 5.5 +/- 3.5 nmol/L (n = 18); idiopathic cause, 5.8 +/- 4.8 nmol/L (n = 17)]. However, normal 3AG levels (less than 5.2 nmol/L) were present in 50-67% of HF in each group. Collectively, 3AG levels in HF correlated significantly (P less than 0.01) with dehydroepiandrosterone (DHEA; r = 0.41) and DHEA sulfate (DS; r = 0.44), while the correlation with androstenedione (r = 0.15) or T (r = 0.19) was not significant. Serum 3AG and adrenal androgen levels decreased in all subjects after dexamethasone treatment (0.5-1 mg at hour of sleep; 2 mg/day for 3-5 days). The correlation between 3AG and HS was significant (r = 0.6-0.74; P less than 0.01-0.001) only in HF with increased adrenal androgen secretion and idiopathic cause, and was not significant (r = 0.42) in HF with increased ovarian T secretion. There was no significant correlation between androgen levels and HS. We conclude that the serum 3AG level was not consistently elevated in HF and did not differ significantly between the various causes. Significant correlations between 3AG and DHEA/DS levels, and the simultaneous decrease in 3AG and adrenal androgens after dexamethasone administration in HF suggest that adrenal androgens contribute significantly to 3AG production. The significant correlation between 3AG and HS in HF with increased adrenal androgen secretion and idiopathic cause indirectly suggests an adrenal androgen contribution to both 3AG production and hirsutism in these HF. The insignificant correlation between 3AG and HS in HF with increased ovarian T secretion may result from a confounding effect of ovarian T on hirsutism.

Adolescent↗
PubMed1992

Variability in behavioral impairment involved in the rising and falling BAC curve.

The purpose of this pilot study was to measure variability in behavior impairment at specific levels of the rising and falling blood alcohol concentration (BAC) curve. Behavior impairment was measured for anticipation and reaction time in addition to a variety of visual skills. Also of interest was the variability in impairment involved at specific BAC levels under single-dose and double-dose conditions. The experimental design was a variation on a 2 x 2 factorial with repeated measures on the dose of alcohol. All subjects took part in two experimental sessions, single-dose and double-dose. Sixteen (8 male and 8 female) paid subjects ages 21-40 participated in the study. Testing procedures included repeated measures on reaction time, anticipation time, perceptual vision acuity and depth perception. Breath-alcohol measures were sampled continuously at 5-minute intervals and used to plot absorption time, peak BAC and elimination time. Results showed that the average peak BAC for the double-dose was significantly higher than that of the single-dose condition. However, there were no significant differences between the single-dose and double-dose condition in either absorption time or elimination time. The performance pattern for reaction time, anticipation time and depth perception showed more impairment in the rising BAC limb than in the falling BAC limb. It is noteworthy that specific individuals exhibited different levels of impairment at a given BAC level, depending on whether the session was single- or double-dose, suggesting that one's current BAC level is less a measure of impairment than is the total quantity of alcohol consumed. A follow-up procedure to examine practice effects was conducted on eight volunteer students. Identical testing procedures, using no alcohol, produced no significant practice effects after a 3-hour period.

Adult↗
PubMed1992

Differential binding of (+) and (-) gossypol to plasma protein and their entry into rat testis.

Concentrations of (+) and (-) gossypol were measured by high performance liquid chromatography after they were incubated with plasma proteins in vitro. The concentration of (-) gossypol decreased more than the concentration of (+) gossypol. A similar decrease in free gossypol concentrations in the blood plasma of rats was observed after intravenous infusion of gossypol enantiomers. The concentration of (-) gossypol was also found to be lower than the concentration of (+) gossypol at the blood-testis barrier. The biological effect of (-) gossypol probably results from its stereospecific binding to extra- and intracellular proteins in vivo and inhibition of the biological activity of some proteins.

Animals↗
PubMed1992

Development of collagen fibers and vasculature of the fetal TMJ.

Using 12 human fetuses, histological development and changes in connective fiber structure and fine vascular patterns have been investigated in various fetal gestational stages by light and scanning electron microscopy. The main arterial supply of the articular disc was from the bilaminar region and pterygoideus lateralis muscle. The vascular network on the disc surface was related with fluid secretion. When the bilaminar region was compressed, it caused ischemia and fibrosis as the main pathological changes in TMJ derangement. A decrease in fluid from blood vessels might occur in TMJ degeneration. Collagen fibers in the disc passed mainly anteroposteriorly. In the anterior and posterior bands, muscular tendon fibers came from the pterygoideus lateralis muscle and superior stratum of the bilaminar region. In the posterior band three-dimensional structures of collagen fibers suitable for load bearing were observed. The compass network and process on the disc showed the normal structure that is formed gradually and has functions including dispersion, pressure bearing, friction-proofing and storage of the synovial fluid. Attachments of the disc were suitable for disc function. Large elastic fibers in the posterolateral part of the superior stratum of the bilaminar region may be antagonistic to the upper head of the pterygoideus lateralis muscle fibers passing medioanteriorly, indicating that this antagonism is available for disc function.

Collagen↗
PubMed1992

How the degenerate signal is recognized and delivered in the course of protein translocation across biological membranes.

Protein translocation across a membrane is generally directed by a degenerate signal peptide encoded in the nascent polypeptide chains. Effective signal recognition and the subsequent traversal of the polypeptide chain through the membrane are ensured by the mechanism of cotranslational translocation and/or by chaperone molecules which universally bind to nascent polypeptides and keep them under-structured and translocation-competent. In order to decipher the degenerate signal with a high degree of fidelity, the cells seem to have evolved a multistep signal recognition and relay mechanism, by which a weak, less-specific interaction between individual signal peptides and a defined signal recognition factor can take place, while the highly specific signal delivery can be achieved by only allowing the correct, effective signals to pass through all check-points along the relay cascade. In addition, a "double recognition" and energy-dependent "proof-reading" mechanism may be involved in single steps of such weak-bond interactions.

Biological Transport, Active↗
PubMed1992

[Determination of oleanolic acid in Achyranthes bidentata BLume and its preparations by supercritical fluid chromatography].

Capillary SFC was used for the determination of oleanolic acid in Achyranthes bidentata BLume and its preparations Tianmawan, Jinguishenqiwan and Hechedazaowan. The amount of oleanolic acid in the root of Achyranthes bidentata BLume was 1.75-2.19% (mean +/- SD = 1.94 +/- 0.17%). The limit of detection was 9.605 x 10(-11) g. The method is highly sensitive, accurate, reproducible, simple, rapid and specific, so, it can be extensively used for the determination of other preparations and crude herbs.

Chromatography↗