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B Y Li

Publications and source records attributed to B Y Li.

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

Effects of 5-HT released from platelets on thrombin-induced aggregation and ATP release in rabbit platelets in vitro.

AIM: To study the effects of arachidonic acid (AA)-induced endogenous serotonin (5-HT) release on platelet aggregation and ATP release by thrombin (Thr). METHODS: Platelet aggregation and release reaction were quantified by light transmission in platelet-rich-plasma (PRP) and the amount of ATP in medium. The effects of endogenous 5-HT were evaluated by the filtration of content in cuvette A (content A) containing endogenous 5-HT into cuvette B in which Thr-induced aggregation was observed in the absence/presence of ¿(+/-)-5 (Z)-7-[3-endophenylsulfonylamino [2.2.1] bicyclohept-2-exo-yl]heptanoic acid, sodium salt¿ (S-145) or/and methysergide (Met). RESULTS: (1) AA 100 and 200 mumol.L-1 induced aggregation and ATP release in cuvette A. When the aggregation reached a peak, the content A directly caused platelet aggregation in cuvette B, and it was inhibited by S-145 100 nmol.L-1, Met 30 mumol.L-1, and inhibited more potently by S-145 + Met. (2) In the presence of S-145 100 nmol.L-1 in cuvette B, aggregations by Thr 0.1 and 0.3 IU.L-1 were enhanced (P < 0.01) by the filtrate, while Thr 0.5 IU.L-1-caused ATP release was suppressed (P < 0.01) without the effect on aggregation. Preincubation with S-145 and Met, the effects of the filtrate on aggregation and ATP release were abolished. (3) By prolongation of the time intervals between filtration and addition of Thr, the aggregation was enhanced and ATP release was reduced. CONCLUSION: Endogenous 5-HT was released from activated platelet and plays, in turn, a role in the regulation of platelet aggregation by the superimposition of cytosolic-free calcium ([Ca2+]i) and the feedback loop to regulate release reaction and calcium.

Adenosine Triphosphate↗
PubMed1997

Effects of naltrexone and histamine antagonists on the antinociceptive activity of the cimetidine analog SKF92374 in rats.

A recent study showed that SKF92374, a structural analog of the histamine H2 receptor antagonist cimetidine, induces antinociception after intraventricular (i.v.t.) administration in the rat. SKF92374 lacked significant activity on H1 or H2 receptors, but had weak activity on H3 receptors. To test the hypothesis that SKF92374-induced antinociception is mediated by an action on H3 receptors, the effects of the H3 agonist R-alpha-methylhistamine (RAMH) and the H3 antagonist thioperamide (both by i.v.t. administration) were investigated on SKF92374 antinociception. SKF92374-induced antinociception was slightly enhanced by thioperamide (30 microg), but unaffected by a range of doses of RAMH (up to 2 microg). Furthermore, SKF92374-induced antinociception was not reduced by large doses of systemically-administered antagonists of H1 (pyrilamine), H2 (zolantidine), H3 (GT-2016), or opioid (naltrexone) receptors. These findings show that the novel compound SKF92374 induces antinociception by a non-opioid mechanism that does not utilize brain H1, H2 or H3 receptors.

Analgesics, Non-Narcotic↗
PubMed1997

Novel qualitative structure-activity relationships for the antinociceptive actions of H2 antagonists, H3 antagonists and derivatives.

Recent studies have shown that cimetidine, burimamide and improgan (also known as SKF92374, a cimetidine congener lacking H2 antagonist activity) induce antinociception after intracerebroventricular administration in rodents. Because these substances closely resemble the structure of histamine (a known mediator of some endogenous analgesic responses), yet no role for known histamine receptors has been found in the analgesic actions of these agents, the structure-activity relationships for the antinociceptive effects of 21 compounds chemically related to H2 and H3 antagonists were investigated in this study. Antinociceptive activity was assessed on the hot-plate and tail-flick tests after intracerebroventricular administration in rats. Eleven compounds induced time-dependent (10-min peak) and dose-dependent antinociceptive activity with no observable behavioral impairment. ED50 values, estimated by nonlinear regression, were highly correlated across nociceptive assays (r2 = 0.98, n = 11). Antinociceptive potencies varied more than 6-fold (80-464 nmol), but were not correlated with activity on H1, H2 or H3 receptors. Although highly potent H3 antagonists such as thioperamide lacked antinociceptive activity, homologs of burimamide and thioperamide containing N-aromatic substituents retained H3 antagonist activity and also showed potent, effective analgesia. A literature review of the pharmacology of these agents did not find a basis for their antinociceptive effects. Taken with previous findings, the present results suggest: 1) these compounds act on the brain to activate powerful analgesic responses that are independent of known histamine receptors, 2) the structure-activity profile of these agents is novel and 3) brain-penetrating derivatives of these compounds could be clinically useful analgesics.

Analgesics, Non-Narcotic↗
PubMed1996

The immunophilin FKBP12 functions as a common inhibitor of the TGF beta family type I receptors.

The immunophilin FKBP12 is an evolutionarily conserved abundant protein; however, its physiological roles remain poorly defined. Here we report that FKBP12 is a common cytoplasmic interactor of TGF beta family type I receptors. FKBP12 binds to ligand-free TGF beta type I receptor, from which it is released upon a ligand-induced, type II receptor mediated phosphorylation of the type I receptor. Blocking FKBP12/type I receptor interaction with FK506 nonfunctional derivatives enhances the ligand activity, indicating that FKBP12 binding is inhibitory to the signaling pathways of the TGF beta family ligands. Overexpression of a myristylated FKBP12 in Mv1Lu cell specifically inhibits two separate pathways activated by TGF beta, and two point mutations on FKBP12 (G89P, I90K) abolish the inhibitory activity of FKBP12, suggesting that FKBP12 may dock a cytoplasmic protein to the type I receptors to inhibit TGF beta family mediated signaling.

Activin Receptors, Type I↗
PubMed1996

The p21(RAS) farnesyltransferase alpha subunit in TGF-beta and activin signaling.

The alpha subunit of p21(RAS) farnesyltransferase (FNTA), which is also shared by geranylgeranyltransferase, was isolated as a specific cytoplasmic interactor of the transforming growth factor-beta (TGF-beta) and activin type I receptors with the use of the yeast two-hybrid system. FNTA interacts specifically with ligand-free TGF-beta type l receptor but is phosphorylated and released upon ligand binding. Furthermore, the release is dependent on the kinase activity of the TGF-beta type II receptor. Thus, the growth inhibitory and differentiative pathways activated by TGF-beta and activin involve novel mechanisms of serine-threonine receptor phosphorylation-dependent release of cytoplasmic interactors and regulation of the activation of small G proteins, such as p21(RAS).

Activin Receptors↗
PubMed1996

Characterization of the antinociceptive properties of cimetidine and a structural analog.

The antinociceptive and pharmacological properties of the H2 receptor antagonist cimetidine and a novel cimetidine analog, SKF92374, were characterized. On both the hot-plate and tail-flick nociceptive tests, cimetidine and SKF92374 induced complete, dose-related analgesic responses when injected into the lateral ventricle of rats. SKF92374 showed strong similarities to cimetidine in analgesic efficacy, slope of dose-response curves and chemical structure, suggesting that these compounds share a common analgesic mechanism. In contrast, histamine induced submaximal antinociceptive effects, and the H3 antagonist thioperamide, a known HA-releasing drug, had little or no analgesic effects. Compared with cimetidine, SKF92374 showed very weak activity (400-fold lower affinity) on H2 receptors in vitro (isolated guinea pig atrium) and in vivo (rat gastric secretion). In addition, SKF92374 (100 microM) had neither agonist nor antagonist action on guinea pig ileum H1 receptors. SKF92374 was also a weak competitive antagonist of N alpha-methylhistamine-induced inhibition of electrically induced contractions of the guinea pig ileum (Kd = 5.2 microM), an H3 receptor-mediated response. Autoradiographic binding assays in guinea pig brain confirmed a weak antagonism of H3 receptors by SKF92374. The compound (up to 10 microM) also had no effect on unpurified rat brain histamine N-methyltransferase activity. These results support the hypothesis that cimetidine induces analgesia by a novel brain mechanism unrelated to H1, H2 or H3 receptors.

Analgesics, Non-Narcotic↗
PubMed1996

Test of homogeneity.

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Analysis of Variance↗
PubMed1996

[Advance of gene therapy for neurological diseases by direct in vivo gene transfer].

Gene therapy for neurological diseases is a rapidly expanding field in neurosciences. It has been demonstrated that some viral vectors from HSV-1 (herpes simplex virus type 1), Ad (adenovirus) and AAV (adeno-associated virus) can transfer foreign genes into nondividing cell types (including neurons). In addition, physical/chemical methods are also used in direct in vivo gene transfer. The direct gene transfer techniques will open a new way to study neurophysiology, neuropathology and therapy for neurological diseases at molecular level. They will hopefully lead to surprising progress in gene therapy for neurological diseases.

Adenoviruses, Human↗
PubMed1996

Heterogeneity of human platelet density subpopulations in aggregation, secretion of ATP, and cytosolic-free calcium concentration.

AIM: To investigate thrombin (500 U.L-1)-, ADP (0.1-30 mumol.L-1)-, and 5-hydroxytryptamine (5-HT, 3 mumol.L-1)-induced aggregation, secretion of ATP and cytosolic-free calcium mobilization in density subpopulations of human washed platelets. METHODS: Using Percoll discontinuous gradient. RESULTS: The human platelets were separated into high density (HD), intermediate density (ID), and low density (LD) subpopulations, and their sizes were diminished with decreasing density (r = 0.978, P < 0.01). The magnitude of aggregations by thrombin, ADP, and 5-HT was more significant in HD platelets than that in LD platelets (P < 0.01). The amount of secretion of ATP induced by thrombin and ADP in HD platelets was also much higher than that in LD platelets (P < 0.01), except for 5-HT which did not cause the ensuring release reaction in any subpopulation of human platelets. Thrombin (1500 U.L-1)-, ADP (mumol.L-1)-, and 5-HT (3 mumol.L-1)-induced cytosolic-free calcium mobilization was evaluated as well. Results showed that the resting level of cytosolic-free calcium concentration ([Ca2+]i) was the same in all subpopulations, about 80-90 nmol.L-1. However, the level of [Ca2+]i mobilization was entirely different, heightened with increasing density. CONCLUSION: The function of HD platelets was much stronger and more active than that of LD platelets in human.

Adenosine Triphosphate↗
PubMed1996

Inhibitory effects of ONO-3708 and S-145 on shape change and aggregation of rabbit platelets induced by STA2.

AIM: To study the mode of inhibition of ONO-3708 and S-145, 2 antagonists of thromboxane A2 (TXA2) receptors, against the rabbit platelet shape change and aggregation induced by stable analogue of TXA2 (STA2). METHODS: The platelet shape change and aggregation were quantified by the light transmission through platelet-rich plasma (PRP) and the intracellular calcium concentration ([Ca2+]i) was measured by fluorescence and imaging. RESULTS: (1) In PRP, STA2 (3 mumol.L-1)-induced aggregation was inhibited by egtazic acid 3 mmol.L-1, ONO-3708 300 mumol.L-1, and S-145 1 mumol.L-1 (P < 0.01), but not by indometacin (Ind) 3 mumol.L-1. The shape change induced by STA2 was inhibited only by S-145 in a concentration-dependent manner. S-145 1 and 3 mumol.L-1 were required to inhibit the shape change and aggregation. (2) The inhibitory effect of S-145, but not ONO-3708, was increased along with the prolongation of preincubation. (3) ONO-3708 lost the inhibitory effect on STA2-induced aggregation after washing, while the inhibitory effect of S-145 was enhanced by prolongation of preincubation and remained after washing. (4) STA2 3 mumol.L-1-induced [Ca2+]i mobilization was unaffected by Ind, partially reduced by ONO-3708 and egtazic acid 3 mmol.L-1 (P < 0.01), but completely inhibited by S-145 (P < 0.01). CONCLUSION: S-145 and ONO-3708 were bound to a different site of the TXA2 receptor.

Animals↗
PubMed1995

Genetic construction of a phosphorylation site in ricin A chain: specific radiolabeling of recombinant proteins for localization and degradation studies.

Ricin A chain was modified by the addition of the heptapeptide LRRASLG (Kemptide) and a histidine tag for bacterial expression. The mutagenized toxin was purified by nickel column and could be phosphorylated in vitro by protein kinase A as demonstrated by labeling with [gamma-32P] ATP. Kemptide-A chain could be labeled even after reassociation with ricin B chain or disulfide linkage to antibody to form an immunotoxin. The 32P label in all cases was associated only with the A chain; ricin B chain and antibody were not kinase substrates alone or after conjugation. Kemptide-immunotoxin was tested in cytotoxicity assays and used to monitor internalization of the toxin moiety after [32P] phosphorylation.

Amino Acid Sequence↗
PubMed1995

Effects of MK-447 on thrombin-induced aggregation, secretion of ATP, and [Ca2+]i mobilization in rabbit platelets.

AIM: To study the effects of MK-447 on aggregation release reaction and intracellular calcium mobilization by thrombin. METHODS: Aggregation and release reaction were assessed by light transmission and ATP content in rabbit citrate platelet-rich plasma (PRP), and cytosolic-free calcium was measured by fluorescence and imaging. RESULTS: MK-447 (2-aminomethyl-4-t-butyl-6-iodophenol hydrochloride) induced a decrease in light transmission (DLT), so called platelet shape change, without detectable aggregation and secretion of ATP, and increased intracellular calcium concentration ([Ca2+]i) slightly in washed single platelet loaded with Fura 2, the peak value being about 160 nmol.L-1. These effects were not inhibited by egtazic acid 3 mmol.L-1 or indometacin 3 mumol.L-1. The pretreatment of PRP with MK-447 700 mumol.L-1 reduced the DLT by thrombin, potentiated and enhanced thrombin-induced aggregation and secretion of ATP in a concentration-dependent manner. Thrombin-induced [Ca2+]i mobilization (peak value: 369 +/- 45 nmol.L-1) was further enhanced by the administration of MK-447 at 2 min before the addition of thrombin, and the peak value reached 623 +/- 121 nmol.L-1 (P < 0.01). CONCLUSION: MK-447-induced platelet shape change was involved in intracellular calcium release in this preparation. MK-447 enhanced thrombin-induced aggregation and release reaction and these effects of MK-447 on aggregation and release reaction by thrombin might result from the synergistic effect of intracellular calcium mobilization.

Adenosine Triphosphate↗
PubMed1995

Relationship between platelet density and platelet aggregation, ATP release, and cytosolic-free calcium mobilization in rabbits.

AIM: To study the relationship of platelet density and platelet functions, including aggregation, ATP release, and intracellular calcium mobilization. METHODS: Platelet density was evaluated by discontinuous gradients of Percoll and cytosolic-free calcium concentration in single platelets was measured by fluorescence and imaging. RESULTS: Rabbit platelets were assorted into 3 subpopulations using discontinuous gradients of Percoll: high density (HD, > 1.062, 20%-30%), intermediate density (ID, around 1.057, 40%-50%) and, low density (LD, < 1.051, 10%-15%). The sizes of platelets in these subpopulations were widely different (HD: 725 +/- 76; ID: 443 +/- 47; and LD: 307 +/- 46) and well correlated with the density (r = 0.988, P < 0.01). Thrombin 0.5 U-induced aggregations in the 3 subpopulations were 78 +/- 8%, 69 +/- 4%, and 62 +/- 3%, respectively and a difference was found between HD and LD (P < 0.05). The amounts of ATP released during aggregation were 4.7 +/- 0.9, 3.4 +/- 1.0, and 2.6 +/- 0.6 mumol/4 x 10(5) platelets in HD, ID, and LD groups, respectively. Thrombin 150 U-induced [Ca2+]i mobilization in HD (990 +/- 130 nmol L-1) was different (P < 0.01) from those in ID (410 +/- 80 nmol L-1) and LD (400 +/- 40 nmol L-1). Serotonin (5-HT) 3 mumol L-1 also caused [Ca2+]i mobilization in single-washed platelet subpopulations and results were similar to those of thrombin although it did not induce any detectable aggregation or release reaction. CONCLUSION: Platelet functions and intracellular calcium concentraotion were increased with platelet density in rabbits.

Adenosine Triphosphate↗
PubMed1995

Calcium mobilization in density subpopulations of rabbit washed platelets.

To estimate the responsiveness of an individual platelet, rather than a group of platelets, we determined the intracellular calcium concentration ([Ca2+]i) of single platelets using digital imaging microscopy after density fractionation. The mean [Ca2+]i of non-fractionated resting single platelets was 74.0 +/- 4.2 nM (n = 71). Immediately after thrombin stimulation (100 mu/ml), [Ca2+]i increased markedly in the entire cytoplasm, reaching maximum levels of 400-1000 nM, and decreased slightly thereafter. These maximum levels varied markedly from cell to cell in non-fractionated platelets. Although there was no significant difference in the resting levels of [Ca2+]i of single platelets even after density fractionation, the peak [Ca2+]i levels after thrombin stimulation (10 and 100 mu/ml) in platelets with higher density ( > 1.062) were significantly higher than those in platelets with intermediate density (1.052-1.061) or lower density ( < 1.051). This higher responsiveness of higher-density platelets in calcium mobilization was accompanied by higher aggregability and higher reactivity in the release reaction. These results suggest that higher responsiveness in higher-density platelets may be explained by the higher reactivity in [Ca2+]i mobilization.

Animals↗
PubMed1994

Recombinant hybrid toxin with dual enzymatic activities. Potential use in preparing highly effective immunotoxins.

Bacterial toxins and ribosomal inhibitory proteins isolated from plants are used to prepare tumor-specific cytotoxic conjugates. The ability of these conjugates to kill tumor cells depends on binding, internalization, translocation to cytoplasm, and translation inhibition. Modulation of any one of these processes can improve cytotoxicity. Since bacterial and plant toxins act at a distinct step in translation, a combination of their activities could be more effective. Therefore, a chimeric protein was prepared by genetically fusing the coding region of the ricin A chain (RTA) and the fragment A of diphtheria toxin (DTA). The hybrid protein (RTA-DTA) expressed in bacteria retained the N-glycosidase activity of the RTA and ADP-ribosylation activity of the DTA. The hybrid toxin was more potent than the ricin A chain (11-fold) and the diphtheria toxin (50-fold) in inhibiting cell-free translation. Immunotoxin made with the hybrid toxin was about 100- and 1000-fold more effective than RTA or DTA conjugate, respectively, in inhibiting tumor cell growth in vitro. These results indicate that the hybrid toxin with dual activities could be useful in preparing potent immunotoxins with better anti-tumor cell activity.

Base Sequence↗