Biomedical subjects

C C Chang

Publications and source records attributed to C C Chang.

At least 415 records · Page 23Linked to original sources

PubMed1991

Characterization and immunological comparison of isoenzymes of phospholipases A2 from snake venoms of different genera and families.

Phospholipases A2 (PLA2) were isolated and purified from the Taiwan cobra (Naja naja atra) and several snake species of the same or different genera by semipreparative cation-exchange and reversed-phase HPLC. They were shown to possess different enzymatic activity toward the synthetic substrate L-alpha-lecithin by the fatty-acid titration method. The immunological cross-reactivity of these structurally similar isotoxins was investigated using immunodiffusion, precipitin reaction and enzyme-linked immunosorbent assay (ELISA). PLA2 from the venoms of the same species such as the Taiwan cobra (Naja naja atra) and the Indian cobra (Naja naja naja) showed a high degree of antigenic resemblance whereas no immunoreactivity was observed among those PLA2 from different genera. Quantitative immunoreactivity assays by ELISA revealed the partial cross-reactivity between the antibody against PLA2 of Taiwan cobra and those isoenzymes from snakes of remotely-related species. The immunological relatedness between PLA2 of the representative snake species of different genera and families is shown to be correlated with the extent of sequence homology among these enzymes.

Amino Acid Sequence↗

PubMed1991

Chemosensitivity testing of an ovarian cancer cell line: comparison of MTT assay and [3H]-thymidine incorporation.

Chemosensitivity test has its role in cancer therapy. Using an accurate, efficient, and simple way to choose the proper chemosensitive drugs in our clinical study will help advance our work. The MTT assay is a rapid, precise, and new method to perform drug sensitivity assay. We used an ovarian cancer cell line (OC-3L-VGH) to compare the accuracy of the MTT and the [3H]-TdR incorporation assay in measuring chemosensitivity of 7 anticancer drugs. Good correlation was observed between the MTT and the [3H]-TdR assay for drug sensitivity testing (r = 0.893, P less than 0.001). Based on this study we found it may be preferable to use the MTT assay for chemosensitivity screening.

Drug Screening Assays, Antitumor↗

PubMed1991

Enhanced expression of heat shock protein and mRNA synthesis by type I interferon in human HL-60 leukemic cells.

The effects of IFN and mild hyperthermia on the responses of human promyelocytic HL-60 cells were investigated. Cells subjected to an elevated culture temperature (39.5 degrees-40.5 degrees C instead of 37 degrees C, herein referred to as heat-treated cells) showed an increase in heat shock proteins (HSPs) and corresponding mRNA synthesis, which were additionally potentiated by the presence of IFN. With cells cultured at 37 degrees C, IFN had no effect on HSP expression. The observed inhibition (40-70%) of RNA polymerase II-directed RNA synthesis (based on alpha-amanitin sensitivity) in isolated nuclei of heat-treated cells was also significantly reversed by the simultaneous addition of IFN. These data suggest that the IFN-amplified HSP gene expression may be involved in preventing irreversible damage or in fine tuning the recovery of mammalian cells from heat stress.

Cell Nucleus↗

PubMed1991

Hyperpolarization of denervated skeletal muscle by lemakalim and its antagonism by glybenclamide and tolbutamide.

Innervated skeletal muscles are endowed with K+ channels activatable by K+ channel openers. It is of interest to know whether the denervation-induced depolarization is due to a deficiency of such a K+ channel. In denervated mouse diaphragm, lemakalim, a K+ channel opener, effectively hyperpolarizes membrane and reduces membrane resistance, spontaneous activity as well as twitch force reversibly. Reductions of transmembrane K+ gradient diminish the lemakalim-induced hyperpolarization. In voltage-clamped fiber, lemakalim induces a long-lasting outward current. A current clamp experiment suggests a reversal potential of around -90 mV. On innervated diaphragm, lemakalim hyperpolarizes membrane and increases conductance if the muscle is predepolarized by anodal current. Lemakalim, however, is much less effective in overcoming the depolarization caused by crotamine, which activates Na+ channel. The effects of lemakalim are not attenuated by blockades of membrane Na+, Ca++ and Cl- permeabilities. Glybenclamide and tolbutamide, blockers of ATP-regulated K+ channel, antagonize the effects of lemakalim at low concentrations and produce slight membrane hyperpolarizations in denervated muscle, but marked membrane depolarizations in innervated muscle at higher concentrations. Cs+ depolarizes both innervated and denervated diaphragms and reduces the hyperpolarizing effect of lemakalim. The results suggest that lemakalim hyperpolarizes denervated muscle via glybenclamide sensitive K+ channels. It is inferred that a reduction of membrane K+ conductance rather than an increase of Na+ or Ca++ conductance contributes to the denervation-induced depolarization.

Animals↗

PubMed1990

Nicotinic actions of oxotremorine on murine skeletal muscle. Evidence against muscarinic modulation of acetylcholine release.

The effects of oxotremorine, arecoline and muscarine on neuromuscular transmission of mouse or rat phrenic nerve-diaphragm were investigated. For some studies of endplate potentials (e.p.p.s) the preparation was immobilized by cutting muscle fibers. Oxotremorine (0.3-10 microM) depolarized endplate membranes, reduced miniature e.p.p. amplitudes but increased frequency, induced spontaneous neural discharges and muscle fasciculations, and produced contracture of denervated mouse diaphragm. In mouse and young rat preparations pretreated with Mn2+, Co2+, Ni2+, Cd2+ or low Ca2+ Tyrode to depress evoked acetylcholine release, oxotremorine 0.3-1 microM increased indirect twitches as well as amplitudes and quantal contents of e.p.p.s. These increases were not observed when the synaptic transmission was not depressed, nor in adult rat preparations. The augmentation by oxotremorine of evoked acetylcholine release persisted in preparations pretreated with neostigmine (1 microM) and tetrodotoxin (20 nM), which inhibited acetylcholinesterase and oxotremorine-induced spontaneous neural discharges. These effects of oxotremorine were mimicked by arecoline but not by muscarine and were antagonized by tubocurarine (0.3 microM) but not by atropine (0.1-10 microM). Atropine alone did not affect indirect twitches, synaptic transmission, tetanic responses evoked by direct stimulation of diaphragms, nor the durations of muscle action potential. The direct twitch responses were only slightly increased by oxotremorine at 2-3 microM. Oxotremorine at high concentrations (greater than 2 microM), depressed indirect twitches and e.p.p. amplitude, and accelerated the run-down of trains of e.p.p.s. The IC50 on indirect twitches was reduced by pretreatment with diltiazem or proadifen, which are known to promote receptor desensitization.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1990

The role of an invariant tryptophan residue in alpha-bungarotoxin and cobrotoxin. Investigation of active derivatives with the invariant tryptophan replaced by kynurenine.

Ozone oxidation converted the single, invariant, tryptophan residue to N2-formylkynurenine in alpha-bungarotoxin and cobrotoxin. Upon this modification, the lethal toxicity was significantly reduced in cobrotoxin but mostly retained in alpha-bungarotoxin. Each neurotoxin containing kynurenine instead of tryptophan retained the same antigenicity as the native toxin. Fluorescence and CD spectroscopy revealed that, although the environment and state of the kynurenine residue were similar, [Kyn29]cobrotoxin was much more sensitive to pH change than alpha-[Kyn28]bungarotoxin. In terms of lethal toxicity and conformational stability, the invariant tryptophan residue appears to play a more important role in cobrotoxin, imparting a higher lethal toxicity than that in alpha-bungarotoxin, which has a disulfide bond at Cys29-Cys33.

Animals↗

PubMed1990

Infection of rat liver epithelial cells with v-Ha-ras: correlation between oncogene expression, gap junctional communication, and tumorigenicity.

The role of v-Ha-ras oncogene in tumorigenesis in an in vitro/in vivo model system was studied by investigating the expression of the Ha-ras gene, gap junctional intercellular communication, and tumorigenicity as endpoints. Infection of a Fischer 344 rat liver epithelial cell line (WB 344) with a retrovirus containing the v-Ha-ras oncogene resulted in altered cell morphology and decreased contact sensitivity. Gap junctional intercellular communication in v-Ha-ras infected WB cells (WBHa-ras), assessed by fluorescence redistribution after photobleaching (FRAP), microinjection/dye transfer, and scrape-loading/dye transfer techniques, was markedly decreased compared with the level in control WB cells. Injection of 10(7) WBHa-ras cells into the portal vein of male F344 rats caused multiple focal hepatic lesions within 1 and 2 wk, merging to large invading tumors after 3 and 4 wk. Examination of the methylation pattern of the Ha-ras gene in WBHa-ras and control WB cells showed that the infected Ha-ras gene was relatively hypomethylated in comparison to the normal cellular Ha-ras gene, indicating a greater potential for expression. There was an increased level of Ha-ras mRNA in hepatomas as compared with both adjacent nontumor liver tissue and liver tissue obtained from normal animals. Three cell lines derived from three different primary hepatic tumors induced by an injection of WBHa-ras cells in a F344 rat displayed similar growth characteristics, levels of gap junctional communication, and methylation patterns as the original WBHa-ras cells. The results of these studies have established a strong positive correlation between expression of the Ha-ras oncogene, reduced gap junctional intercellular communication, decreased contact sensitivity, and tumorigenicity of the v-Ha-ras-infected rat liver epithelial cells.

Animals↗

PubMed1990

Effect of recombinant human lipocortin I on brain oedema in a rat glioma model.

Glucocorticoids have been extensively used to treat brain oedema, but little is known on the mechanisms of steroids in the prevention and resolution of tumour-induced brain oedema. Recently, the mechanism of steroid action is thought to involve synthesis of proteins with antiphospholipase activity called lipocortins. In a previous study, we have demonstrated the efficacy of dexamethasone (DEX) in resolving peritumoural oedema in a rat glioma model. Using the same model, we studied the effect of recombinant human lipocortin I on the resolution of peritumoural oedema. Intracerebral tumours were produced in 6-week-old Wistar rats by implantation of rat glioma C6 cells. In comparison with sham-operated controls, the tumour-implanted animals showed significant increase in the cortical water content, which was reduced by DEX administration to the level in the sham-operated controls. The water content within the tumour was also significantly decreased by DEX treatment. On the other hand, there was no difference in water content between lipocortin-treated and non-treated animals. These findings suggest that tumour-induced brain oedema can be reduced by DEX treatment but not by lipocortin. In conclusion, it is doubtful whether glucocorticoids exert their action in resolving brain oedema by inducing PLA2 inhibitory proteins named lipocortins.

Animals↗

PubMed1990

Thymidylate synthetase gene as a quantitative mutation marker in Chinese hamster cells.

A quantitative mutation marker for cultured mammalian cells is presented which uses a selective medium containing folinic acid, aminopterin and thymidine (the 'FAT' medium) to select for mutants deficient in thymidylate synthetase (TS) activity. Optimization of FAT medium was carried out using Chinese hamster V79 cell lines having 3 levels of TS activity. By manipulating the concentration of folinic acid in FAT medium, TS-deficient mutants can be readily selected. TS mutation is inducible in a dose-dependent manner by either ethyl methanesulfonate or ultraviolet light irradiation. Expression time for TS mutation was also determined using two concentrations of ethyl methanesulfonate and found to be very short, being 1 or 2 days. This newly characterized TS mutation marker should be useful in the study of both spontaneous and induced mutagenesis.

Animals↗

PubMed1990

The modulation of gap junctional communication by gossypol in various mammalian cell lines in vitro.

The effects of gossypol were examined in several cell lines including hamster V79 lung fibroblasts, WB-344 rat liver oval cells, human osteosarcoma cells and LC540 rat Leydig cells. Gossypol had little cytotoxic effects in these cell lines except at high concentrations. Plasma membrane integrity was maintained in LC540 except at high concentrations of gossypol. Gossypol did not increase mutational frequency as examined by the hypoxanthine guanine phosphoribosyl transferase and Na+,K(+)-ATPase loci in V79 cells. Gossypol inhibited gap junctional intercellular communication in some but not all of the cell lines. This selectivity might be the basis for the sensitivity of certain tissues or organs to gossypol. For example, the Leydig cell, which is the component of a target organ system for toxicity, was sensitive to gossypol. Modulation of gap junctional functions might play a significant role in both pharmacological and toxicological effects of gossypol.

Animals↗

PubMed1990

Organic calcium channel antagonists provoke acetylcholine receptor autodesensitization on train stimulation of motor nerve.

The effects of nicardipine and other organic Ca2(+)-channel antagonists on the responses induced by indirect train stimulation (3 s, 50-100 Hz) were studied in mouse phrenic nerve diaphragm preparations. Nicardipine at 1-10 microM, which alone did not affect single or tetanic contractions or the amplitude of evoked endplate potentials and spontaneous miniature endplate potentials, caused tetanic contraction to fade completely in the presence of 0.3 microM neostigmine or 50 microM diisopropylfluorophosphate. In combination with these anticholinesterases, nicardipine caused a severe run-down and shortening of endplate potentials in 1-2 s. This effect on endplate potentials was dependent on stimulus frequency and on extracellular Ca2+. The effect was accelerated by intracellular injection of Ca2+, but retarded by injection of EGTA. The amplitudes of miniature endplate potentials and the evoked endplate depolarization were also depressed during repetitive stimulation. On termination of repetitive stimulation, all postsynaptic responses, including evoked endplate potentials, miniature endplate potentials and single twitches, recovered to pre-train level in 3-10 s. These results suggest that the postsynaptic nicotinic receptors had lost the functional activity during repetitive stimulation. The time-courses of the aforementioned changes initiated by repetitive stimulation were similar to the fast phase of desensitization induced by acetylcholine. The irreversible action of alpha-bungarotoxin on acetylcholine receptor was attenuated in the presence of nicardipine and neostigmine if repetitive stimulation was applied. The same effects were observed with other organic Ca2(+)-channel antagonists (diltiazem, verapamil and nifedipine) as well as agonist (methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyr idine- 5-carboxylate, BAY K8644), but not with Mn2+, theophylline or caffeine. It is inferred that organic Ca2(+)-channel antagonists interact directly with acetylcholine receptor ion channel, enhance its autodesensitization liability and thus cause extinction of endplate potentials on repetitive stimulation.

Animals↗

PubMed1990

In situ (6-4)photoproduct determination by laser cytometry and autoradiography.

The UV-induced (6-4)photoproducts and their repair in individual human cells were quantitatively determined by argon-laser imaging microspectrofluorometry or autoradiography with a well-characterized monoclonal antibody against (6-4)photoproducts. (6-4)Photoproduct induction curves were linear as a function of UV dose, using both methods. The formation of (6-4)photoproducts was detected in the cells irradiated with as low as 10 and 25 J/m2 of UV by autoradiography and laser cytometry, respectively. Normal cells repaired more than 80% of the initial damage within 4 h post irradiation. In contrast, almost no repair was observed in xeroderma pigmentosum cells (complementation group A) within 8 h.

Antibodies, Monoclonal↗

PubMed1990

Increased flap survival after sensory denervation with capsaicin accompanied by delay.

The effect of capsaicin, combined with delayed surgical procedures, was studied in adult rats. After denervation of the experimental subjects' cutaneous nerves with capsaicin, the time required for the flaps to become completely necrotic was prolonged; when accompanied by delayed flap raising for a period of up to eight weeks, the flap survival rate was increased. Although there were no significant differences in flap survival between the control and the capsaicin animals undergoing flap raising with no delay, increased vascularity and flap survival were confirmed in capsaicin animals in whom procedures had been delayed. Maximum flap survival was found in capsaicin animals undergoing a six-week delay in the procedures. These results suggest that sensory nerves play an important role in flap survival, perhaps in the areas of flap vascular supply and tension control of the A-V shunt in the microcirculation of a flap.

Animals↗

PubMed1990

Facilitation by 3,4-diaminopyridine of regenerative acetylcholine release from mouse motor nerve.

1. Effects of 3,4-diaminopyridine (DAP) on endplate potentials (e.p.ps) were studied in mouse phrenic nerve-hemidiaphragms. 2. In cut muscle preparations, low concentrations of DAP (2-20 microns) increased the amplitude of e.p.ps and shifted the curve relating Ca2+ concentration to e.p.p. amplitude leftward. 3. High concentration of DAP (40-4000 microns) prolonged the duration of e.p.ps dose-dependently up to one hundred fold (ca. 200 ms), yielding, in addition to the normal phasic e.p.p., a prolonged plateau depolarization component which was often preceded by an upstroke depolarization. During the plateau depolarization, nerve stimulations did not evoke any e.p.p. 4. The plateau component of prolonged e.p.ps was suppressed by tubocurarine, verapamil, nifedipine, Mn2+ and Cd2+ (but not by atropine) at low concentrations that had negligible effect on the amplitude of miniature e.p.ps or the phasic component of e.p.ps. Abolition of the plateau component by these agents restored the capability of the nerve terminal to evoke e.p.ps on nerve stimulation. 5. Low concentrations of neostigmine (0.01-0.02 microns) markedly lengthened DAP-prolonged e.p.ps. However, the regenerative endplate depolarization evoked in the presence of high concentrations of neostigmine (0.3-0.5 microns) was not prolonged by DAP. 6. Tetraethylammonium (1 mM) did not provoke prolonged e.p.ps but acted cooperatively with DAP to prolong the duration of plateau depolarization. At a high concentration (3 mM), tetraethylammonium depressed the amplitude of miniature e.p.ps and abolished DAP-prolonged e.p.ps. 7. In uncut muscle preparations, DAP apparently did not modify the time course and amplitude of miniature e.p.ps. Upon direct stimulation by current injection at endplate, DAP increased the muscle action potentials by only about 30%, but induced no prolonged depolarization. 8. These results suggest that the prolonged e.p.ps induced in the presence of DAP are due to a regenerative release of acetylcholine from motor nerve and the induction probably involves a presynaptic Ca2+ channel different from that for normal e.p.ps. It may be inferred that the regenerative acetylcholine release is recruited by Ca2 + channels modulated by nicotinic receptors and K+ channels.

4-Aminopyridine↗

PubMed1990

Chemical, oncogene and growth factor inhibition gap junctional intercellular communication: an integrative hypothesis of carcinogenesis.

Most, if not all, cancer cells have some dysfunction in gap-junction-mediated intercellular communication, either because of defects in cell adhesion or inability to have functional gap junctional communication. In addition, most, if not all, tumor-promoting chemicals and conditions down-regulate gap junction function, while some antitumor-promoting chemicals can up-regulate gap junctional communication. Several oncogenes are associated with down-regulation of gap junction function and several hormone and growth regulators, known to be tumor promoters, are also able to down-regulate gap junction function. On the other hand, some tumor suppressor genes have been linked to the up-regulation of gap junctions. Based on these observations, it is hypothesized that, if a progenitor cell is unable to perform gap junctional intercellular communication, normal growth control and cell differentiation would not be possible, thereby favoring the development of malignant neoplasia.

Animals↗

PubMed1990

Mechanisms of the synergistic interactions between organic calcium channel antagonists and various neuromuscular blocking agents.

The effects of Mn2+, neomycin and four organic Ca2(+)-channel antagonists (OCA): nicardipine, nifedipine, diltiazem and verapamil on the neuromuscular blocking activities of tubocurarine, succinylcholine (SCh), decamethonium and neomycin were studied in isolated mouse phrenic nerve-diaphragm preparations. The effective concentration of SCh for 50% inhibition (IC50) of single indirect twitch responses were reduced markedly by more than 3-fold when the preparations were pretreated with OCA at 10 microM; the latter alone did not appreciably affect the indirect twitch response or the amplitude of miniature endplate potentials. The neuromuscular blocking effect of decamethonium was also enhanced synergistically by OCA to a similar extent. On the other hand, under the comparable condition. the combined uses of OCA plus tubocurarine or neomycin, neomycin plus tubocurarine or SCh, and Mn2+ plus tubocurarine, SCh or neomycin all resulted in insignificant potentiation. These results suggest that OCA have a specific effect to enhance the agonist effect of depolarizing agents on nicotinic acetylcholine receptors. Nicardipine at 2 microM non-competitively inhibited depolarizations of endplates elicited by SCh and decamethonium and abolished them completely at 10 microM nicardipine. The IC50's in inhibiting endplate potentials and miniature endplate potentials by SCh and decamethonium were also reduced 2 to 3.5-fold by nicardipine. It is inferred that OCA are endowed with a unique capability to allosterically affect the postsynaptic nicotinic acetylcholine receptor, promoting its desensitization liability, hence synergistic interaction with depolarizing agents. Presynaptic effects of OCA are probably not involved.

Animals↗

PubMed1990

Idiopathic hypothalamic hypogonadism with polyostotic fibrous dysplasia: report of a case.

A 48-year-old man with Albright's syndrome and hypogonadism is presented. Eunuchoid status, hypogenitalia and hypogonadotropinemia were associated with pathological fracture and deformity of bones. GnRH test revealed minimal LH response and delayed FSH peak. After pulsatile GnRH priming, the LH response to GnRH increased. Results of other provocative hypothalamic-pituitary tests were consistent with hypothalamic lesions. To the best of our knowledge, this is the first report of a male patient with Albright's syndrome and idiopathic hypothalamic hypogonadism. The hypothesis of endocrinopathy and its relation to other components of this syndrome were reviewed.

Fibrous Dysplasia, Polyostotic↗

PubMed1990

Albright's syndrome with acromegaly and Hashimoto's thyroiditis: report of a case.

The case of a 35-year-old woman with Albright's syndrome, acromegaly and Hashimoto's thyroiditis is presented. She had noted deformity of the left mandible and chest from childhood. She developed persistent galactorrhea and amenorrhea after the delivery of her second child. X ray of the skull, and a head CT, revealed a pituitary tumor and fibrous dysplasia of the left mandible, sphenoid, zygomatic bone and pteryoid plate. Serum GH and PRL levels were markedly elevated. She received recontouring surgery of the left mandible, and a pathological examination confirmed the diagnosis of fibrous dysplasia. Chest X ray also showed fibrous dysplastic change of the left 4th, 5th, 6th and 7th ribs and left clavicle. Because of poor response to bromocriptine, she received a craniotomy to remove the pituitary macroadenoma. Pathological examination of the tumor revealed an acidophilic tumor. Postoperative radiotherapy was given for residual active tumor. She developed adrenal crisis two months after radiotherapy when she discontinued replacement therapy. The diagnosis of Hashimoto's thyroiditis was arrived at by palpation of the goiter, elevated thyroid antibodies, ultrasound pictures of the thyroid, fine needle aspiration cytology and hypothyroidism. To our knowledge, this is the first report of Albright's syndrome with Hashimoto's thyroiditis. The hypothesis of autoimmune disease is proposed to explain the hypofunction of the endocrine glands associated with Albright's syndrome.

Acromegaly↗