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Biomedical subjects

H Chai

Publications and source records attributed to H Chai.

At least 37 records · Page 2Linked to original sources
PubMed1995

[The effects of 2-chloro-4-bromo-alpha-methylcinnamic acid on the neuromuscular transmission of toad].

The effects of 2-chloro-4-bromo-alpha-methylcinnamic acid sodium (SC1001 Na) on neuromuscular transmission were tested by means of intracellular recordings in isolated sciatic nerve-sartorius preparations of toad. The results were: (1) at a concentration of 0.1mmol/L, SC1001 Na had no effect on end-plate potential (EPP); at a concentration of 1 mmol/L, SC1001 Na reduced the amplitude of the EPP significantly, and the paired-pulse facilitation was also decreased; at a concentration of 10mmol/L, SC1001 Na blocked the EPP completely; (2) the 0.1 mmol/L and 1mmol/L groups of drug had no effect on the resting potential of the toad muscle fibers; the resting potential was reduced significantly by SC1001Na at the concentration of 10mmol/L, the action of 10mmol/L drug was irreversible. These results suggest that SC1001 Na may block the neuromuscular transmission of toad, and the blocking effect might be mainly due to a presynaptic mechanism.

Animals↗
PubMed1995

[A potentially new sodium channel blocker: 2-chloro-4-bromo-alpha-methylcinnamic acid].

The effects of 2-Chloro-4-Bromo-alpha-Methylcinnamic acid sodium (SC1001 Na) and some channel antagonists on the action potential (AP) and the resting potential (RP) were tested intracellularly in the sartorius muscle of the toad (Bufo bufo gargarizans). TEA (10mmol/L) and MnCl2 (10 mmol/L) had no effect on the amplitude of the AP, otherwise, TTX (1 mumol/L) blocked the AP completely. SC1001 Na at the concentration of 2mmol/L largely decreased the amplitude of the AP and expanded the duration of the AP (measured at 1/2 peak amplitude), but it had no effect on the RP. The effects of ms group of drug were reversible. Under the pretreatment of the muscle preparation with TEA (10 mmol/L), SC1001 Na still increased the duration of the AP while decreased its amplitude. At the concentration of 10mmol/L, SC1001 Na completely blocked AP and depolarized the RP significantly. These effects were not reversible. As the structure of SC1001 Na is different from that of heterocycloguanidine Na channel blocker, such as TTX, or that of local anesthetics, we infer that SC1001 Na may be a new sodium channel blocker.

Action Potentials↗
PubMed1994

Cytotoxic diterpenoids from Isodon megathyrsus.

A new diterpenoid, megathyrin A, together with three known compounds, rabdocoetsins B, C, and D, were isolated from the leaves of Isodon megathyrsus, and their structures and nmr spectral data were assigned by a combination of one- and two-dimensional nmr techniques. These compounds displayed significant cytotoxic activity.

Antimalarials↗
PubMed1994

Thalifaberidine, a cytotoxic aporphine-benzylisoquinoline alkaloid from Thalictrum faberi.

From Thalictrum faberi, thalifaberidine [1], a new aporphine-benzylisoquinoline alkaloid, together with four known alkaloids, thalifaramine [2], thalifaricine [3], thalifarazine [4], and thalifaronine [5], were isolated. Thalifaberidine [1] was identified as 6',8-desmethylthalifaberine, and its 1H- and 13C-nmr data were completely assigned through the use of one- and two-dimensional nmr techniques. Thalifaberidine [1], thalifaberine [6], and thalifasine [7] showed cytotoxic activity against several human cancer cell lines, as well as antimalarial activity.

Alkaloids↗
PubMed1994

[Study on red blood cell immune adherence function in coriaria lactone-induced epileptic seizure rats].

The immune adherence function of red blood cells in 17 rats was studied. It was found that the rosette rate of red blood cell C3b receptor (RBC-C3bRR) was 7.45 +/- 1.36% in the epilepsy group (8 rats), and 10.84 +/- 1.77% in the control group (9 rats); and that the rosette rate of red blood cell immune complex (RBC-ICR) was 7.42 +/- 2.62% in the epilepsy, and 10.80 +/- 1.72% in the control. As compared with the control group, the rosette rate of red blood cell C3b receptor was remarkably decreased in the epilepsy group (P < 0.05). There was no significant difference between the two groups in RBC-ICR. The results from this study demonstrated that the CL-induced seizures might result in decrease in red blood cell immune adherence function of the epilepsy rats.

Animals↗
PubMed1993

1H- and 13C-nmr assignments of phyllanthin and hypophyllanthin: lignans that enhance cytotoxic responses with cultured multidrug-resistant cells.

Complete 1H-nmr data and unambiguous assignments of the 13C-nmr spectra of phyllanthin [1] and hypophyllanthin [2] were obtained through extensive nmr studies, including homonuclear COSY, homonuclear decoupling, APT, HETCOR, nOe difference, selective INEPT, and COLOC experiments. The absolute configuration of hypophyllanthin [2] was determined by cd. Neither of these lignans demonstrated significant cytotoxic activity when evaluated with a battery of cultured mammalian cells, but both were found to enhance the cytotoxic response mediated by vinblastine with multidrug-resistant KB cells. In addition, 1 was found to displace the binding of vinblastine with membrane vesicles derived from this cell line, suggesting an interaction with the P-glycoprotein.

Animals↗
PubMed1993

Bisamides from Aglaia species: structure analysis and potential to reverse drug resistance with cultured cells.

The structure of pyramidatine [1], a new bisamide alkaloid from leaves of Aglaia pyramidata, was determined through extensive nmr studies, including homonuclear COSY, NOESY, APT, HETCOR, and selective INEPT techniques. Revision of the 13C-nmr assignment of piriferine [2], an alkaloid previously isolated from A. pirifera, was achieved by examination of several 2D nmr spectra (homonuclear COSY, NOESY, and HETCOR) and confirmed by selective INEPT nmr experiments. Evaluation of the cytotoxic potential of the two alkaloids, along with two other bisamides from Aglaia odorata, odorine [3] and 5'-epi-odorine [4], was carried out in eleven human cancer cell lines. None of these bisamides showed significant cytotoxicity. Nevertheless, piriferine [2], odorine [3], and 5'-epi-odorine [4] were found to inhibit the growth of the vinblastine-resistant KB cells by enhancing the anticancer activity of vinblastine.

Alkaloids↗
PubMed1993

Structure and stereochemistry of pectinolides A-C, novel antimicrobial and cytotoxic 5,6-dihydro-alpha-pyrones from Hyptis pectinata.

By bioactivity-directed fractionation, three new antimicrobial and cytotoxic 5,6-dihydro-alpha-pyrones, pectinolides A-C, have been isolated from Hyptis pectinata (Lamiaceae). The absolute stereochemistry of pectinolide A [1] was established as 6S-[(3S-acetyloxy)-1Z-heptenyl]-5S-(acetyloxy)-5 ,6-dihydro-2H-pyran-2-one, on the basis of spectral, chiroptical, and chemical evidence. The structures of pectinolides B [2] and C [3] were determined as the monodeacetylated forms of 1 by comparison of their spectral data and chemical correlation with the prototype compound. Staphylococcus aureus and Bacillus subtilis were sensitive to pectinolide A [1] in the concentration range of 6.25-12.5 micrograms/ml. Compounds 1-3 exhibited significant cytotoxic activity (ED50 < 4 micrograms/ml) against a variety of tumor cell lines.

Animals↗
PubMed1993

Cytotoxic and antimalarial alkaloids from the bulbs of Crinum amabile.

From the bulbs of Crinum amabile (Amaryllidaceae), a new alkaloid (-)-amabiline [1], together with the known alkaloids (-)-lycorine [2], (-)-buphanisine [3], (-)-augustine [4], and (+)-crinamine [5], were isolated. The structural characterization of 1 and the revised 1H- and 13C-nmr assignments of 2 are discussed. Alkaloids 2, 4, and 5 were found to be the principal cytotoxic and antimalarial constituents.

Alkaloids↗
PubMed1993

Cytotoxic and antimalarial alkaloids from the tubers of Stephania pierrei.

Biological evaluation of extracts prepared from the tubers of Stephania pierrei revealed cytotoxic and antimalarial activity. During the course of separation, two new aporphine alkaloids, (-)-asimilobine-2-O-beta-D-glucoside [2] and (-)-nordicentrine [8], in addition to twenty-one known isoquinoline alkaloids, were isolated. Each isolate was assessed for cytotoxic and antimalarial activities. It was found that the cytotoxicity of S. pierrei was mainly due to the presence of the aporphine alkaloids containing the 1,2-methylenedioxy group 3-10, whereas the antimalarial activity was attributed to the nonquaternary aporphine alkaloids 1, 3-10 and the tetrahydroprotoberberines possessing a phenolic functionality, 13-15, 18. None of the isolates showed a degree of selectivity comparable to that of antimalarial drugs such as chloroquine, quinine, mefloquine, and artemisinin. Comparison of the alkaloid content of S. pierrei and Stephania erecta strongly suggested separate identities for the two plants.

Animals↗
PubMed1993

Cytotoxic constituents from Hyptis verticillata.

A new cytotoxic (P-388 ED50 4 microgm/ml) arylnaphthalene lignan has been isolated from the Mexican medicinal plant Hyptis verticillata (Lamiaceae) and characterized as 5-methoxydehydropodophyllotoxin [1]. Eight additional lignans were also obtained by bioactivity-directed fractionation using the brine shrimp lethality test. Of these, the dehydro-beta-peltatin methyl ether 2 (P-388 ED50 1.8 microgm/ml) is reported for the first time as a natural product isolate. The other bioactive compounds were identified as dehydropodophyllotoxin [3], deoxydehydropodophyllotoxin [4]. (--)-yatein [5], 4'-demethyldeoxypodophyllotixin [6], isodeoxypodophyllotoxin [7], deoxypicropodophyllin [8], and beta-apopicropodophyllin [9]. Each of these compounds was evaluated against a panel of cell lines comprising a number of human cancer cell types [breast, colon, fibrosarcoma, lung, prostate, KB, and KB-VI (a multi-drug resistant cell line derived from KB)] and murine lymphocytic leukemia (P-388). Lignans 1-4 showed marginal cytotoxic activity against the human cell lines tested. In contrast, compounds 5-9 demonstrated a general nonspecific activity comparable to that of podophyllotoxin [12] (ED50 < 10-2 microgm/ml). In addition, the antimitotic potential of these compounds was determined in the astrocytoma (ASK) assay. Finally, the plant was also shown to contain the flavonoid sideritoflavone (KB ED50 1.6 microgm/ml) and the known pentacyclic triterpenoids ursolic, maslinic, 2 alpha-hydroxyursolic and oleanolic acids.

Animals↗
PubMed1993

[Effect of SC1001-sodium on ADA activity of the thymus, spleen and brain in repeated seizure rats].

Twenty nine adult SD rats in the experiment were randomly separated into two groups. Nineteen rats of them were intramuscularly injected (i.m.) with Coriaria lactone (CL, 2.5 mg/kg for female rat; 30 mg/kg for male rat) two days a time, continued 28 times, to induce repeated seizures, as the experimental group. The control group (n = 10) was injected with normal saline (N.S.) in the same volume as that of CL. The rats of experimental group were subdivided into a treatment group (n = 9) with SC1001Na (200 mg/kg) and a placebo group (n = 10) receiving N.S. in the same volume as that of SC1001 Na. All rats of repeated seizure were administered once every day for a week. The results indicated that SC1001Na (200 mg/kg) could inhibit in some degree the growth of immune organs (spleen and thymus) and significantly decrease the ADA activity of thymus, cerebrum and cerebellum, suggesting that the antiepileptic mechanism of SC1001Na is probably related with the decreased activity of ADA and the increased adenosine level in brain.

Adenosine Deaminase↗
PubMed1993

Glycosylation and high-level secretion of human tumour necrosis factor-beta in recombinant baculovirus-infected insect cells.

Human tumour necrosis factor-beta (TNF-beta) was produced in eukaryotic cells using the insect baculovirus cloning and expression system. A novel insect signal sequence, the honey-bee (Apis mellifera) prepromelittin secretory sequence, was used to aid in the post-translational modifications, glycosylation and secretion of recombinant human TNF-beta. Human TNF-beta cDNA was cloned using the insect baculovirus vector pAcC4s. Expression of the human TNF-beta was regulated by the insect Autographa californica nuclear-polyhedrosis-virus polyhedrin promoter. The 5' end of the TNF-beta cDNA was fused to the honey-bee prepromelittin signal sequence on the baculovirus vector. Insect [Spodoptera frugiperda (Sf9)] cells infected with the recombinant baculovirus secreted high levels of recombinant human TNF-beta into the culture medium. The amount of TNF-beta secreted by the Sf9 cells was estimated to be 28 micrograms of TNF-beta/ml of culture medium at 60-72 h post infection. The secreted human TNF-beta was a 22.5 kDa polypeptide which was glycosylated. Amino acid sequencing of the N-terminus of the recombinant human TNF-beta purified from the infected Sf9-cell culture confirmed that the secreted product was indeed human TNF-beta. This demonstrates that the honey-bee prepromelittin signal sequence was efficiently recognized and accurately cleaved in the Sf9 insect cells. The insect-derived TNF-beta exhibited a high cytotoxic activity similar to that of the native human TNF-beta when assessed by cytotoxic assays using murine L929 cells. Thus the insect baculovirus expression vector can be used for the production of abundant quantities of biologically active, glycosylated human TNF-beta protein.

Amino Acid Sequence↗
PubMed1992

Observations of synaptic efficacy and paired-pulse facilitation in area CA1 of hippocampal slices from coriaria lactone-kindled rats.

The changes of population spike(PS)/population excitatory postsynaptic potential (EPSP) slope relationship and paired-pulse facilitation (PPF) were primarily investigated with extracellular recording in stratum pyramidale to stimulation of Schaffer collaterals in CA1 region of hippocampal slices from coriaria lactone (CL)-kindled and control rats. The results were as follows: (1) neither spontaneous nor evoked epileptiform bursts were found in all hippocampal slices from CL-kindled and control rats; (2) the synaptic efficacy, expressed by the ratio of PS/EPSP slope, at low stimulation intensity ranging from 10-30% of its maximum was significantly increased on CL-kindled rats (P less than 0.05); and (3) although PPF was found in all slices, the PPF strength only at stimulation intensity of 10 and 20% of maximum was augmented remarkably in CL-kindled rats (P less than 0.002 and 0.024, respectively). According to the results from our previous work, we suggested that the increment of PS/EPSP slope ratio and PPF strength at low stimulation intensity may result from the potentiation of excitatory synaptic activity or/and the change of intrinsic excitability of pyramidal neurons.

Action Potentials↗
PubMed1992

Cytotoxic activity of cardenolides from Beaumontia brevituba stems.

Five known cardenolides, digitoxigenin (1), oleandrigenin (2), digitoxigenin alpha-L-cymaroside (3), digitoxigenin beta-gentiobiosyl-alpha-L-cymaroside (4), and delta 16-digitoxigenin beta-D-glucosyl-alpha-L-cymaroside (5), were isolated from the stems of Beaumontia brevituba Oliver by cytotoxicity-directed fractionation monitored by a cultured human lung cancer cell line. The cytotoxic activity of these compounds was evaluated with a panel of twelve human and murine cancer cell lines. The lignan glycoside, syringaresinol beta-D-glucoside, was obtained for the first time in the form of its levo-enantiomer.

Animals↗
PubMed1992

[Effects of adrenergic agonist on population spike in CA1 region of hippocampal slices from partial and full kindled rats].

Effects of adrenergic agonist on population spike (PS) amplitude were studied extracellularly at CA1 region of hippocampal slices from partial and full kindled rats with coriaria lactone (1-1.25 mg/kg, two days a time, i.m.) and compared with those from control rats. 5 mumol/L norepinephrine (NE) increased PS; 50 mumol/L NE decreased it slightly. 5 mumol/L isoproterenol (ISO) increased PS. 100 mumol/L phenylephrine (PE) decreased it. The effects of increasing and decreasing PS could be antagonised by beta and alpha adrenergic antagonists, respectively. The effects of NE and PE on PS amplitude showed no significant difference between the control and kindled rats. The effect of beta-adrenergic agonist ISO on PS amplitude in hippocampal slices from partial kindled rats was less than that of control (P < 0.01). The effect of ISO on PS of full kindled rats was partially recovered.

Animals↗