Rapid simulation of glycoprotein structures by grafting and steric exclusion of glycan conformer libraries

Most membrane proteins are modified by covalent addition of complex sugars through N- and O-glycosylation. Unlike proteins, glycans do not typically adopt specific secondary structures and remain very mobile, shielding potentially large fractions of protein surface. High glycan conformational freedom hinders complete structural elucidation of glycoproteins. Computer simulations may be used to model glycosylated proteins but require hundreds of thousands of computing hours on supercomputers, thus limiting routine use. Here, we describe GlycoSHIELD, a reductionist method that can be implemented on personal computers to graft realistic ensembles of glycan conformers onto static protein structures in minutes. Using molecular dynamics simulation, small-angle X-ray scattering, cryoelectron microscopy, and mass spectrometry, we show that this open-access toolkit provides enhanced models of glycoprotein structures. Focusing on N-cadherin, human coronavirus spike proteins, and gamma-aminobutyric acid receptors, we show that GlycoSHIELD can shed light on the impact of glycans on the conformation and activity of complex glycoproteins.

Structure, dynamics, and stability of the smallest and most complex 71 protein knot

Proteins can spontaneously tie a variety of intricate topological knots through twisting and threading of the polypeptide chains. Recently developed artificial intelligence algorithms have predicted several new classes of topological knotted proteins, but the predictions remain to be authenticated experimentally. Here, we showed by X-ray crystallography and solution-state NMR spectroscopy that Q9PR55, an 89-residue protein from Ureaplasma urealyticum, possesses a novel 71 knotted topology that is accurately predicted by AlphaFold 2, except for the flexible N terminus. Q9PR55 is monomeric in solution, making it the smallest and most complex knotted protein known to date. In addition to its exceptional chemical stability against urea-induced unfolding, Q9PR55 is remarkably robust to resist the mechanical unfolding-coupled proteolysis by a bacterial proteasome, ClpXP. Our results suggest that the mechanical resistance against pulling-induced unfolding is determined by the complexity of the knotted topology rather than the size of the molecule.

Development of AAV-delivered broadly neutralizing anti-human ACE2 antibodies against SARS-CoV-2 variants

The ongoing evolution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), resulting in the emergence of new variants that are resistant to existing vaccines and therapeutic antibodies, has raised the need for novel strategies to combat the persistent global COVID-19 epidemic. In this study, a monoclonal anti-human angiotensin-converting enzyme 2 (hACE2) antibody, ch2H2, was isolated and humanized to block the viral receptor-binding domain (RBD) binding to hACE2, the major entry receptor of SARS-CoV-2. This antibody targets the RBD-binding site on the N terminus of hACE2 and has a high binding affinity to outcompete the RBD. In vitro, ch2H2 antibody showed potent inhibitory activity against multiple SARS-CoV-2 variants, including the most antigenically drifted and immune-evading variant Omicron. In vivo, adeno-associated virus (AAV)-mediated delivery enabled a sustained expression of monoclonal antibody (mAb) ch2H2, generating a high concentration of antibodies in mice. A single administration of AAV-delivered mAb ch2H2 significantly reduced viral RNA load and infectious virions and mitigated pulmonary pathological changes in mice challenged with SARS-CoV-2 Omicron BA.5 subvariant. Collectively, the results suggest that AAV-delivered hACE2-blocking antibody provides a promising approach for developing broad-spectrum antivirals against SARS-CoV-2 and potentially other hACE2-dependent pathogens that may emerge in the future.

Structural basis of an epitope tagging system derived from Haloarcula marismortui bacteriorhodopsin I D94N and its monoclonal antibody GD-26

Specific antibody interactions with short peptides have made epitope tagging systems a vital tool employed in virtually all fields of biological research. Here, we present a novel epitope tagging system comprised of a monoclonal antibody named GD‐26, which recognises the TD peptide (GTGATPADD) derived from Haloarcula marismortui bacteriorhodopsin I (HmBRI) D94N mutant. The crystal structure of the antigen‐binding fragment (Fab) of GD‐26 complexed with the TD peptide was determined to a resolution of 1.45 Å. The TD peptide was found to adopt a 3₁₀ helix conformation within the binding cleft, providing a characteristic peptide structure for recognition by GD‐26 Fab. Based on the structure information, polar and nonpolar forces collectively contribute to the strong binding. Attempts to engineer the TD peptide show that the proline residue is crucial for the formation of the 3₁₀ helix in order to fit into the binding cleft. Isothermal calorimetry (ITC) reported a dissociation constant K_D of 12 ± 2.8 nm, indicating a strong interaction between the TD peptide and GD‐26 Fab. High specificity of GD‐26 IgG to the TD peptide was demonstrated by western blotting, ELISA and immunofluorescence as only TD‐tagged proteins were detected, suggesting the effectiveness of the GD‐26/TD peptide tagging system. In addition to already‐existing epitope tags such as the FLAG tag and the ALFA tag adopting either extended or α‐helix conformations, the unique 3₁₀ helix conformation of the TD peptide together with the corresponding monoclonal antibody GD‐26 offers a novel tagging option for research.

Effects of Zentangle art workplace health promotion activities on rural healthcare workers

OBJECTIVES

Workplace health promotion activities have a positive effect on emotions. Zentangle art relaxes the body and mind through the process of concentrating while painting, achieving a healing effect. This study aimed to promote the physical and mental health of rural healthcare workers through Zentangle art-based intervention.

STUDY DESIGN

This was a quasi-experimental pilot study.

METHODS

A Zentangle art workshop was held from November 2019 to July 2020. A total of 40 healthcare workers were recruited. The participants were asked to provide baseline data, and the Brief Symptom Rating Scale (BSRS-5), work stress management effectiveness self-rating scale, General Self-Efficacy Scale (GSES), and Workplace Spirituality Scale (WSS) were administered before and after the workshop. SPSS 22.0 statistical package software was used to conduct the data analysis.

RESULTS

The median age (interquartile range [IQR]) was 32.00 years (23.00-41.75 years). The Wilcoxon signed-rank test revealed that the median (IQR) BSRS-5 postintervention score was 4.0 (1.25-5.0), which was lower than the preintervention score (P = 0.004). The postintervention score for the work stress management effectiveness self-rating scale was 36.5 (31.0-40.0), which was also lower than the preintervention score (P = 0.009). A higher score for the GSES or WSS indicated improvements in stress management and self-efficacy. The GSES postintervention score 25.00 (21.0-30.75) was significantly higher than the preintervention score (P = 0.010), and the WSS postintervention score 104.0 (88.0-111.75) was significantly higher than the preintervention score (P = 0.005).

CONCLUSIONS

The study provides evidence that painting therapy can effectively relieve stress, reduce workplace stress and frustration, enhance self-efficacy, and increase commitment to work among healthcare workers, thus improving their physical, mental, and spiritual well-being. Zentangle art provides employees with multiple channels for expressing their emotions and can improve the physical and mental health of healthcare workers in the workplace. It is beneficial and cost-effective and can serve as a benchmark for peer learning.

Active Transport of Membrane Components by Self-Organization of the Min Proteins

Heterogeneous distribution of components in the biological membrane is critical in the process of cell polarization. However, little is known about the mechanisms that can generate and maintain the heterogeneous distribution of the membrane components. Here, we report that the propagating wave patterns of the bacterial Min proteins can impose steric pressure on the membrane, resulting in transport and directional accumulation of the component in the membrane. Therefore, the membrane component waves represent transport of the component in the membrane that is caused by the steric pressure gradient induced by the differential levels of binding and dissociation of the Min proteins in the propagating waves on the membrane surface. The diffusivity, majorly influenced by the membrane anchor of the component, and the repulsed ability, majorly influenced by the steric property of the membrane component, determine the differential spatial distribution of the membrane component. Thus, transportation of the membrane component by the Min proteins follows a simple physical principle, which resembles a linear peristaltic pumping process, to selectively segregate and maintain heterogeneous distribution of materials in the membrane. VIDEO ABSTRACT.

Structural and Functional Studies of a Newly Grouped Haloquadratum walsbyi Bacteriorhodopsin Reveal the Acid-resistant Light-driven Proton Pumping Activity

Retinal bound light-driven proton pumps are widespread in eukaryotic and prokaryotic organisms. Among these pumps, bacteriorhodopsin (BR) proteins cooperate with ATP synthase to convert captured solar energy into a biologically consumable form, ATP. In an acidic environment or when pumped-out protons accumulate in the extracellular region, the maximum absorbance of BR proteins shifts markedly to the longer wavelengths. These conditions affect the light-driven proton pumping functional exertion as well. In this study, wild-type crystal structure of a BR with optical stability under wide pH range from a square halophilic archaeon, Haloquadratum walsbyi (HwBR), was solved in two crystal forms. One crystal form, refined to 1.85 Å resolution, contains a trimer in the asymmetric unit, whereas another contains an antiparallel dimer was refined at 2.58 Å. HwBR could not be classified into any existing subgroup of archaeal BR proteins based on the protein sequence phylogenetic tree, and it showed unique absorption spectral stability when exposed to low pH values. All structures showed a unique hydrogen-bonding network between Arg⁸² and Thr²⁰¹, linking the BC and FG loops to shield the retinal-binding pocket in the interior from the extracellular environment. This result was supported by R82E mutation that attenuated the optical stability. The negatively charged cytoplasmic side and the Arg⁸²–Thr²⁰¹ hydrogen bond may play an important role in the proton translocation trend in HwBR under acidic conditions. Our findings have unveiled a strategy adopted by BR proteins to solidify their defenses against unfavorable environments and maintain their optical properties associated with proton pumping.

Proposed carrier lipid-binding site of undecaprenyl pyrophosphate phosphatase from Escherichia coli

Undecaprenyl pyrophosphate phosphatase (UppP), an integral membrane protein, catalyzes the dephosphorylation of undecaprenyl pyrophosphate to undecaprenyl phosphate, which is an essential carrier lipid in the bacterial cell wall synthesis. Sequence alignment reveals two consensus regions, containing glutamate-rich (E/Q)XXXE plus PGXSRSXXT motifs and a histidine residue, specific to the bacterial UppP enzymes. The predicted topological model suggests that both of these regions are localized near the aqueous interface of UppP and face the periplasm, implicating that its enzymatic function is on the outer side of the plasma membrane. The mutagenesis analysis demonstrates that most of the mutations (E17A/E21A, H30A, S173A, R174A, and T178A) within the consensus regions are completely inactive, indicating that the catalytic site of UppP is constituted by these two regions. Enzymatic analysis also shows an absolute requirement of magnesium or calcium ions in enzyme activity. The three-dimensional structural model and molecular dynamics simulation studies have shown a plausible structure of the catalytic site of UppP and thus provides insights into the molecular basis of the enzyme-substrate interaction in membrane bilayers.

Using Haloarcula marismortui bacteriorhodopsin as a fusion tag for enhancing and visible expression of integral membrane proteins in Escherichia coli

Membrane proteins are key targets for pharmacological intervention because of their vital functions. Structural and functional studies of membrane proteins have been severely hampered because of the difficulties in producing sufficient quantities of properly folded and biologically active proteins. Here we generate a high-level expression system of integral membrane proteins in Escherichia coli by using a mutated bacteriorhodopsin (BR) from Haloarcula marismortui (HmBRI/D94N) as a fusion partner. A purification strategy was designed by incorporating a His-tag on the target membrane protein for affinity purification and an appropriate protease cleavage site to generate the final products. The fusion system can be used to detect the intended target membrane proteins during overexpression and purification either with the naked eye or by directly monitoring their characteristic optical absorption. In this study, we applied this approach to produce two functional integral membrane proteins, undecaprenyl pyrophosphate phosphatase and carnitine/butyrobetaine antiporter with significant yield enhancement. This technology could facilitate the development of a high-throughput strategy to screen for conditions that improve the yield of correctly folded target membrane proteins. Other robust BRs can also be incorporated in this system.

Studying submicrosecond protein folding kinetics using a photolabile caging strategy and time-resolved photoacoustic calorimetry

Kinetic measurement of protein folding is limited by the method used to trigger folding. Traditional methods, such as stopped flow, have a long mixing dead time and cannot be used to monitor fast folding processes. Here, we report a compound, 4-(bromomethyl)-6,7-dimethoxycoumarin, that can be used as a "photolabile cage" to study the early stages of protein folding. The folding process of a protein, RD1, including kinetics, enthalpy, and volume change, was studied by the combined use of a phototriggered caging strategy and time-resolved photoacoustic calorimetry. The cage caused unfolding of the photolabile protein, and then a pulse UV laser (∼10(-9) s) was used to break the cage, leaving the protein free to refold and allowing the resolving of two folding events on a nanosecond time scale. This strategy is especially good for monitoring fast folding proteins that cannot be studied by traditional methods.

Structural basis of inhibition specificities of 3C and 3C-like proteases by zinc-coordinating and peptidomimetic compounds

Human coxsackievirus (CV) belongs to the picornavirus family, which consists of over 200 medically relevant viruses. In picornavirus, a chymotrypsin-like protease (3C(pro)) is required for viral replication by processing the polyproteins, and thus it is regarded as an antiviral drug target. A 3C-like protease (3CL(pro)) also exists in human coronaviruses (CoV) such as 229E and the one causing severe acute respiratory syndrome (SARS). To combat SARS, we previously had developed peptidomimetic and zinc-coordinating inhibitors of 3CL(pro). As shown in the present study, some of these compounds were also found to be active against 3C(pro) of CV strain B3 (CVB3). Several crystal structures of 3C(pro) from CVB3 and 3CL(pro) from CoV-229E and SARS-CoV in complex with the inhibitors were solved. The zinc-coordinating inhibitor is tetrahedrally coordinated to the His(40)-Cys(147) catalytic dyad of CVB3 3C(pro). The presence of specific binding pockets for the residues of peptidomimetic inhibitors explains the binding specificity. Our results provide a structural basis for inhibitor optimization and development of potential drugs for antiviral therapies.

Structural basis of mercury- and zinc-conjugated complexes as SARS-CoV 3C-like protease inhibitors

Five active metal-conjugated inhibitors (PMA, TDT, EPDTC, JMF1586 and JMF1600) bound with the 3C-like protease of severe acute respiratory syndrome (SARS)-associated coronavirus were analyzed crystallographically. The complex structures reveal two major inhibition modes: Hg(2+)-PMA is coordinated to C(44), M(49) and Y(54) with a square planar geometry at the S3 pocket, whereas each Zn(2+) of the four zinc-inhibitors is tetrahedrally coordinated to the H(41)-C(145) catalytic dyad. For anti-SARS drug design, this Zn(2+)-centered coordination pattern would serve as a starting platform for inhibitor optimization.

Synthesis, crystal structure, structure-activity relationships, and antiviral activity of a potent SARS coronavirus 3CL protease inhibitor

A potent SARS coronavirus (CoV) 3CL protease inhibitor (TG-0205221, Ki = 53 nM) has been developed. TG-0205221 showed remarkable activity against SARS CoV and human coronavirus (HCoV) 229E replications by reducing the viral titer by 4.7 log (at 5 microM) for SARS CoV and 5.2 log (at 1.25 microM) for HCoV 229E. The crystal structure of TG-0205221 (resolution = 1.93 A) has revealed a unique binding mode comprising a covalent bond, hydrogen bonds, and numerous hydrophobic interactions. Structural comparisons between TG-0205221 and a natural peptide substrate were also discussed. This information may be applied toward the design of other 3CL protease inhibitors.

Mechanism of the maturation process of SARS-CoV 3CL protease

Severe acute respiratory syndrome (SARS) is an emerging infectious disease caused by a novel human coronavirus. Viral maturation requires a main protease (3CL(pro)) to cleave the virus-encoded polyproteins. We report here that the 3CL(pro) containing additional N- and/or C-terminal segments of the polyprotein sequences undergoes autoprocessing and yields the mature protease in vitro. The dimeric three-dimensional structure of the C145A mutant protease shows that the active site of one protomer binds with the C-terminal six amino acids of the protomer from another asymmetric unit, mimicking the product-bound form and suggesting a possible mechanism for maturation. The P1 pocket of the active site binds the Gln side chain specifically, and the P2 and P4 sites are clustered together to accommodate large hydrophobic side chains. The tagged C145A mutant protein served as a substrate for the wild-type protease, and the N terminus was first digested (55-fold faster) at the Gln(-1)-Ser1 site followed by the C-terminal cleavage at the Gln306-Gly307 site. Analytical ultracentrifuge of the quaternary structures of the tagged and mature proteases reveals the remarkably tighter dimer formation for the mature enzyme (K(d) = 0.35 nm) than for the mutant (C145A) containing 10 extra N-terminal (K(d) = 17.2 nM) or C-terminal amino acids (K(d) = 5.6 nM). The data indicate that immature 3CL(pro) can form dimer enabling it to undergo autoprocessing to yield the mature enzyme, which further serves as a seed for facilitated maturation. Taken together, this study provides insights into the maturation process of the SARS 3CL(pro) from the polyprotein and design of new structure-based inhibitors.

Charge stabilization in nonpolar solvents

While the important role of electrostatic interactions in aqueous colloidal suspensions is widely known and reasonably well-understood, their relevance to nonpolar suspensions remains mysterious. We measure the interaction potentials of colloidal particles in a nonpolar solvent with reverse micelles. We find surprisingly strong electrostatic interactions characterized by surface potentials, |ezeta|, from 2.0 to 4.4 k(B)T and screening lengths, kappa(-1), from 0.2 to 1.4 microm. Interactions depend on the concentration of reverse micelles and the degree of confinement. Furthermore, when the particles are weakly confined, the values of |ezeta| and kappa extracted from interaction measurements are consistent with bulk measurements of conductivity and electrophoretic mobility. A simple thermodynamic model, relating the structure of the micelles to the equilibrium ionic strength, is in good agreement with both conductivity and interaction measurements. Since dissociated ions are solubilized by reverse micelles, the entropic incentive to charge a particle surface is qualitatively changed from aqueous systems, and surface entropy plays an important role.

Grain boundary scars and spherical crystallography

We describe experimental investigations of the structure of two-dimensional spherical crystals. The crystals, formed by beads self-assembled on water droplets in oil, serve as model systems for exploring very general theories about the minimum-energy configurations of particles with arbitrary repulsive interactions on curved surfaces. Above a critical system size we find that crystals develop distinctive high-angle grain boundaries, or scars, not found in planar crystals. The number of excess defects in a scar is shown to grow linearly with the dimensionless system size. The observed slope is expected to be universal, independent of the microscopic potential.

Electric-field-induced capillary attraction between like-charged particles at liquid interfaces

Nanometre- and micrometre-sized charged particles at aqueous interfaces are typically stabilized by a repulsive Coulomb interaction. If one of the phases forming the interface is a nonpolar substance (such as air or oil) that cannot sustain a charge, the particles will exhibit long-ranged dipolar repulsion; if the interface area is confined, mutual repulsion between the particles can induce ordering and even crystallization. However, particle ordering has also been observed in the absence of area confinement, suggesting that like-charged particles at interfaces can also experience attractive interactions. Interface deformations are known to cause capillary forces that attract neighbouring particles to each other, but a satisfying explanation for the origin of such distortions remains outstanding. Here we present quantitative measurements of attractive interactions between colloidal particles at an oil-water interface and show that the attraction can be explained by capillary forces that arise from a distortion of the interface shape that is due to electrostatic stresses caused by the particles' dipolar field. This explanation, which is consistent with all reports on interfacial particle ordering so far, also suggests that the attractive interactions might be controllable: by tuning the polarity of one of the interfacial fluids, it should be possible to adjust the electrostatic stresses of the system and hence the interparticle attractions.

Comparisons of PCBs dechlorination occurrences in various contaminated sediments

A comparison was made of reductive dechlorination occurrences of polychlorinated biphenyls (PCBs) by microorganisms collected from contaminated sediments including Er-Jen River (Tainan, Taiwan), Hudson River (Ft. Edward, NY), Silver Lake (Pittsfield, MA) and Puget Sound (Washington State). Comparisons was made in terms of chromatographic data (referring to the biological activity, including microbial availability) and thermodynamic data (demonstrating the selectivity of anaerobic microorganisms in the dechlorination of chlorinated compounds). Chromatographic data was established in terms of difference in relative retention time (delta ln RRT) and thermodynamic data was estimated as heat of reaction (delta H(r)0). Both were calculated and correlated to occurrences of dechlorination reactions. Observed dechlorination reactions for individually introducing PCB congener had delta ln RRT levels measured as >0.47 (Er-Jen River), >0.29 (Hudson River), >0.36 (Silver Lake) and >0.45 (Puget Sound, for Aroclor 1254 dechlorination). Critical of delta H(r)0 and delta ln RRT values showed that Hudson River and Silver Lake microorganisms were capable of dechlorinating PCBs through reactions with larger H(r)0 value (lower levels of released energy) and smaller delta ln RRT value compared with those found in Er-Jen River and Puget Sound sediments. Differences in the critical delta ln RRT values of these sediments may be due to differences in their levels of PCB contamination.

Inhibition by magnolol of formylmethionyl-leucyl-phenyl alanine-induced respiratory burst in rat neutrophils

The influence of the plant product magnolol on neutrophil superoxide anion (O2-*) generation has been investigated in the rat. Intraperitoneal injection of magnolol (30mg kg(-1)) significantly inhibited the formylmethionyl-leucyl-phenylalanine (fMLP)-induced respiratory burst in rat whole blood ex-vivo. Magnolol also inhibited the 02-* generation with an IC50 (concentration resulting in 50% inhibition) of 15.4+/-1.6 microM and O2 consumption in rat neutrophils in-vitro. Magnolol weakly inhibited the O2-* generation in the xanthine-xanthine oxidase system, decreased cellular cyclic AMP level and had no effect on cyclic GMP levels. It weakly inhibited neutrophil cytosolic protein kinase C activity but did not alter porcine heart protein kinase A activity. Magnolol attenuated fMLP-induced protein tyrosine phosphorylation with an IC50 of 24.0+/-1.9 microM and the phosphorylation of mitogen-activated protein kinase p42/44 with an IC50 of 28.5+/-4.5 microM. However, magnolol alone activated neutrophil phospholipase D activity as determined by the formation of phosphatidic acid and phosphatidyl-ethanol in the presence of ethanol. In the presence of NADPH, the arachidonate-activated NADPH oxidase activity in a cell-free system was weakly suppressed by magnolol. These results suggest that the inhibition of respiratory burst in fMLP-activated neutrophils by magnolol is probably attributable mainly to the attenuation of protein tyrosine phosphorylation and p42/44 mitogen-activated protein kinase activation, and partly to the suppression of protein kinase C and NADPH oxidase activities.

Possible involvement of protein kinase c inhibition in the reduction of phorbol ester-induced neutrophil aggregation by magnolol in the rat

The influence of the plant product magnolol on neutrophil aggregation has been investigated in the rat. Magnolol inhibited phorbol 12-myristate 13-acetate (PMA)-activated rat neutrophil aggregation in a concentration-dependent manner with an IC50 (concentration resulting in 50% inhibition) of 24.2 +/- 1.7 microM. Magnolol suppressed the enzyme activity of neutrophil cytosolic and rat brain protein kinase C (PKC) over the same range of concentrations at which it inhibited the aggregation. Magnolol did not affect PMA-induced cytosolic PKC-alpha and -delta membrane translocation or trypsin-treated rat-brain PKC activity, but attenuated [3H]phorbol 12,13-dibutyrate binding to neutrophil cytosolic PKC. These results suggest that the inhibition of PMA-induced rat neutrophil aggregation by magnolol is probably attributable, at least in part, to the direct suppression of PKC activity through blockade of the regulatory region of PKC.

Blockade of protein kinase C is involved in the inhibition by cycloheterophyllin of neutrophil superoxide anion generation

Cycloheterophyllin, a prenylflavone, inhibited the superoxide anion (O2-) generation from formylmethionyl-leucyl-phenylalanine (fMLP)- and phorbol 12-myristate 13-acetate (PMA)-stimulated rat neutrophils in a concentration-dependent manner with IC50 values of 47.0 +/- 5.0 and 1.7 +/- 0.4 microM, respectively. Cycloheterophyllin had no effect on O2- generation in xanthine-xanthine oxidase system and during dihydroxyfumaric acid (DHF) autoxidation. Cycloheterophyllin exerted a concentration-dependent inhibition of neutrophil cytosolic protein kinase C (PKC) and rat brain PKC, but had no effect on porcine heart protein kinase A (PKA). Unlike staurosporine, cycloheterophyllin did not affect the trypsin-treated rat brain PKC. [3H]Phorbol 12,13-dibutyrate ([3H]PDB) binding to neutrophil cytosolic PKC was significantly suppressed by cycloheterophyllin. However, cycloheterophyllin had negligible effect on the PMA-induced membrane translocation of PKC-beta and PKC-delta in neutrophils. Moreover, the fMLP-induced [Ca2+]i elevation and inositol trisphosphate (IP3) formation of neutrophils were not affected by cycloheterophyllin at concentrations which significantly suppressed the O2- generation. In cell-free system, addition of arachidonate (AA) into the mixture of cytosol and membrane fractions of the resting neutrophils to make NADPH oxidase assembly and activation. Cycloheterophyllin had no effect on O2- generation in AA-activated cell-free system. These results suggest that the suppression of PKC activity through the interaction with the regulatory region of PKC is involved in the inhibition by cycloheterophyllin of the O2- generation in rat neutrophils.

Investigation of the inhibition by acetylshikonin of the respiratory burst in rat neutrophils

1. The ability of acetylshikonin to inhibit the respiratory burst in rat neutrophils was characterized and the underlying mechanism of action was also assessed in the present study. 2. Acetylshikonin caused an irreversible and a concentration-dependent inhibition of formylmethionylleucyl-phenylalanine (fMLP) plus dihydrocytochalasin B (CB)- and phorbol 12-myristate 13-acetate (PMA)-induced superoxide anion (O2.-) generation with IC50 values of 0.48 +/- 0.03 and 0.39 +/- 0.03 microM, respectively. Acetylshikonin also inhibited the O2 consumption in neutrophils in response to fMLP/CB as well as to PMA. 3. Acetylshikonin did not scavenge the generated O2.- in the xanthine-xanthine oxidase system or during dihydroxyfumaric acid (DHF) autoxidation but, on the contrary, acetylshikonin enhanced the O2.- generation in these cell-free oxygen radical generating systems. 4. Acetylshikonin inhibited the formation of inositol trisphosphate (IP3) (39.0 +/- 7.8% inhibition at 10 microM, P < 0.05) in neutrophils in response to fMLP. 5. Both the neutrophil cytosolic protein kinase C (PKC) activity and the PMA-induced PKC associated with the membrane were unaffected by acetylshikonin. 6. Acetylshikonin did not affect the porcine heart protein kinase A (PKA) activity. Upon exposure to acetylshikonin, the cellular cyclic AMP level was decreased in neutrophils in response to fMLP. 7. The cellular formation of phosphatidic acid (PA) and, in the presence of ethanol, phosphatidylethanol (PEt) induced by fMLP/CB were inhibited by acetylshikonin (60.1 +/- 7.3 and 63.2 +/- 10.5% inhibition, respectively, at 10 microM, both P < 0.05). Moreover, acetylshikonin attenuated the fMLP/CB-induced protein tyrosine phosphorylation (about 90% inhibition at 1 microM). 8. In PMA-activated neutrophil particulate NADPH oxidase preparations, acetylshikonin did not inhibit, but enhanced, the O2.- generation in the presence of NADPH. However, acetylshikonin decreased the membrane associated p47phox in PMA-activated neutrophils (about 60% inhibition at 1 microM). 9. Collectively, these results suggest that the attenuation of protein tyrosine phosphorylation and a failure in the assembly of a functional NADPH oxidase complex probably contribute predominantly to the inhibition of respiratory burst in neutrophils by acetylshikonin. In contrast, the blockade of phospholipase C (PLC) and phospholipase D (PLD) pathways play only a minor role in this respect.

2',5'-Dihydroxychalcone as a potent chemical mediator and cyclooxygenase inhibitor

Eleven chalcone derivatives have been tested for their inhibitory effects on platelet aggregation in rabbit platelet suspension and the activation of mast cells and neutrophils. Arachidonic acid-induced platelet aggregation was potently inhibited by almost all the compounds and some also had a potent inhibitory effect on collagen-induced platelet aggregation and cyclooxygenase. Some hydroxychalcone derivatives showed strong inhibitory effects on the release of beta-glucuronidase and lysozyme, and on superoxide formation by rat neutrophils stimulated with the peptide fMet-Leu-Phe (fMLP). We found that the anti-inflammatory effect of 2',5'-dihydroxychalcone was greater than that of trifluoperazine. 2'5'-Dihydroxy and 2',3,4,5'-tetrahydroxyl chalcones, even at low concentration (50 microM), tested in platelet-rich plasma from man almost completely inhibited secondary aggregation induced by adrenaline. These results suggest that the anti-platelet effects of the chalcones are mainly a result of inhibition of thromboxane formation.

Cellular localization of the inhibitory action of abruquinone A against respiratory burst in rat neutrophils

1. The possible mechanisms of action of the inhibitory effect of abruquinone A on the respiratory burst in rat neutrophils in vitro was investigated. 2. Abruquinone A caused an irreversible and a concentration-dependent inhibition of formylmethionylleucyl-phenylalanine (fMLP) plus dihydrocytochalasin B (CB)- and phorbol 12-myristate 13-acetate (PMA)-induced superoxide anion (O2.-) generation with IC50 values of 0.33 +/- 0.05 microgram ml-1 and 0.49 +/- 0.04 microgram ml-1, respectively. 3. Abruquinone A also inhibited O2 consumption in neutrophils in response to fMLP/CB and PMA. However, abruquinone A did not scavenge the generated O2.- in xanthine-xanthine oxidase system and during dihydroxyfumaric acid (DHF) autoxidation. 4. Abruquinone A inhibited both the transient elevation of [Ca2+]i in the absence of [Ca2+]o (IC50 7.8 +/- 0.2 micrograms ml-1) and the generation of inositol trisphosphate (IP3) (IC50 10.6 +/- 2.0 micrograms ml-1) in response to fMLP. 5. Abruquinone A did not affect the enzyme activaties of neutrophil cytosolic protein kinase C (PKC) and porcine heart protein kinase A (PKA). 6. Abruquinone A had no effect on intracellular guanosine 3':5'-cyclic monophosphate (cyclic GMP) levels but decreased the adenosine 3':5'-cyclic monophosphate (cyclic AMP) levels. 7. The cellular formation of phosphatidic acid (PA) and phosphatidylethanol (PEt) induced by fMLP/ CB was inhibited by abruquinone A with IC50 values of 2.2 +/- 0.6 micrograms ml-1 and 2.5 +/- 0.3 micrograms ml-1, respectively. Abruquinone A did not inhibit the fMLP/CB-induced protein tyrosine phosphorylation but induced additional phosphotyrosine accumulation on proteins of 73-78 kDa in activated neutrophils. 8. Abruquinone A inhibited both the O2.- generation in PMA-activated neutrophil particulate NADPH oxidase (IC50 0.6 +/- 0.1 microgram ml-1) and the iodonitrotetrazolium violet (INT) reduction in arachidonic acid (AA)-activated cell-free system (IC50 1.5 +/- 0.2 micrograms ml-1) 9. Collectively, these results indicate that the inhibition of respiratory burst in rat neutrophils by abruquinone A is mediated partly by the blockade of phospholipase C (PLC) and phospholipase D (PLD) pathways, and by suppressing the function of NADPH oxidase through the interruption of electron transport.

Inhibition by abruquinone A of phosphoinositide-specific phospholipase C activation in rat neutrophils

In rat neutrophils, formyl-Met-Leu-Phe (fMLP)-induced phosphate formation was inhibited by abruquinone A (IC50 value about 32.7 +/- 6.4 microM) as well as by a putative phospholipase C inhibitor, [6-[[17 beta-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole- 2,5-dione (U73122) (IC50 value about 11.3 +/- 1.2 microM). The reduction in inositol phosphate levels appeared to reflect inhibition of phospholipase C activity because the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) catalyzed by a soluble fraction from neutrophils was also inhibited by abruquinone A (IC50 value about 31.4 +/- 5.6 microM) over the same range of concentrations. Although abruquinone A alone induced Ca2+ and Mn2+ influx into neutrophils in Ca(2+)-containing medium, abruquinone A, like U73122, inhibited Ca2+ release (IC50 value about 23.5 +/- 0.5 microM) from internal stores in Ca(2+)-free medium. These results indicate that abruquinone A inhibits the activity of phosphoinositide-specific phospholipase C in neutrophils.

Examination of the inhibitory effect of norathyriol in formylmethionyl-leucyl-phenylalanine-induced respiratory burst in rat neutrophils

Norathyriol, aglycone of a xanthone C-glycoside mangiferin isolated from Tripterospermum lanceolatum, concentration dependently inhibited the formylmethionyl-leucyl-phenylalanine (fMLP)-induced superoxide anion (O2.-) generation and O2 consumption in rat neutrophils. In cell-free oxygen radical generating system, norathyriol inhibited the O2.- generation during dihydroxyfumaric acid (DHF) autoxidation and in hypoxanthine-xanthine oxidase system. fMLP-induced transient elevation of [Ca2/]i and the formation of inositol trisphosphate (IP3) were significantly inhibited by norathyriol (30 microM) (about 30 and 46% inhibition, respectively). Norathyriol concentration dependently suppressed the neutrophil cytosolic phospholipase C (PLC). In contrast with the marked attenuation of fMLP-induced protein tyrosine phosphorylation (about 70% inhibition at 10 microM norathyriol), norathyriol only slightly modulated the phospholipase D (PLD) activity as determined by the formation of phosphatidic acid (PA) and, in the presence of ethanol, phosphatidylethanol (PEt). Norathyriol did not modulate the intracellular cyclic AMP level. In the presence of NADPH, the phorbol 12-myristate 13-acetate (PMA)-activated particulate NADPH oxidase activity was suppressed by norathyriol in a concentration-dependent manner and the inhibition was noncompetitive with respect to NADPH. Norathyriol inhibited the iodonitrotetrazolium violet (INT) reduction in arachidonic acid (AA)-activated cell-free NADPH oxidase system at the same concentration range as those used in the suppression of PMA-activated particulate NADPH oxidase activity. Taken together, these results suggest that the scavenging ability of norathyriol contributes to the reduction of generated O2.-, however, the inhibition of O2.- generation from neutrophils by norathyriol is attributed to the blockade of PLC pathway, the attenuation of protein tyrosine phosphorylation, and to the suppression of NADPH oxidase through the interruption of electrons transport.

Inhibition by HAJ11 of respiratory burst in neutrophils and the involvement of protein tyrosine phosphorylation and phospholipase D activation

1. The possible mechanisms of the inhibitory effect of ethyl 2-(3-hydroxyanilino)-4-oxo-4,5-dihydrofuran-3-carboxylate (HAJ11) on the respiratory burst of rat neutrophils in vitro was investigated. 2. HAJ11 caused a reversible and a concentration-dependent inhibition of formyl-Met-Leu-Phe (fMLP)-induced superoxide anion (O2.-) generation (IC50 4.9 +/- 0.7 microM) and O2 consumption (IC50 4.9 +/- 1.5 microM). Concanavalin A (Con A)- and NaF-induced O2.- generation were also suppressed by HAJ11. However, HAL11 was a weak inhibitor of the phorbol 12-myristate 13-acetate (PMA)-induced responses. 3. HAJ11 did not scavenge the /2.- generation in the xanthine-xanthine oxidase system and dihydroxyfumaric acid (DHF) autoxidation. 4. HAJ11 showed no activity on fMLP-induced inositol phosphates formation and [Ca2+]i elevation in intact neutrophils. In addition, HAJ11 had no effect on neutrophil cytosolic phospholipase C (PLC) activity. 5. HAJ11 reduced fMLP-induced phosphatidic acid (PA) (IC50 29.1 +/- 6.5 microM) and phosphatidylethanol (PE+) (IC50 22.6 +/- 1.9 microM) formation in a concentration-dependent manner. HAJ11 also reduced protein tyrosine phosphorylation in neutrophils stimulated by fMLP. 6. HAJ11 was a weak inhibitor of neutrophil cytosolic protein kinase C (PKC) activity, and had a negligible effect on brain PKC. Cellular cyclic nucleotides levels were not altered by HAJ11. In addition, HAJ11 did not affect protein kinase A (PKA) activity. 7. HAJ11 had not effect on the O2.- generation of PMA-activated and arachidonic acid (AA)-activated NADPH oxidase preparations. 8. Taken together these results indicate that the inhibition of respiratory burst by HAJ11 probably mainly occurs through inhibition of protein tyrosine phosphorylation and phospholipase D (PLD) activity.

Novel antiplatelet constituents from formosan moraceous plants

Sixteen constituents from Formosan Moraceous plants were tested for their antiplatelet activities in rabbit platelet suspension and human platelet-rich plasma. Cycloartocarpin A, cycloheterophyllin, broussochalcone A, kazinol A, broussoaurone A, and broussoflavonol F showed strong inhibition of arachidonic acid (AA)-induced platelet aggregation. Of the compounds tested, broussochalcone A exhibited the most potent inhibition of platelet aggregation induced by AA (IC50 = 6.8 microM). The antiplatelet effects of cycloheterophyllin, broussochalcone A, kazinol B, broussoaurone A, and broussoflavonol F are partially due to an inhibitory effect on cyclooxygenase.

Inhibition of plasma extravasation by abruquinone A, a natural isoflavanquinone isolated from Abrus precatorius

Polymyxin B-induced hind-paw edema was suppressed by abruquinone A, an isoflavanquinone isolated from Abrus precatorius, in normal as well in adrenalectomized mice. Unlike dexamethasone, abruquinone A did not increase the liver glycogen content in fasting adrenalectomized mice. The volume of exuded plasma was significantly reduced by abruquinone A in neurogenic inflammation, passive cutaneous anaphylactic reaction and compound 48/80-induced ear edema. Histamine-, serotonin-, bradykinin- and substance P-induced plasma extravasation in ear edema was also suppressed by abruquinone A. Abruquinone A, like isoproterenol, significantly reduced the bradykinin- and substance P-induced plasma extravasation in normal as well as in compound 48/80-pretreated mice. In addition, abruquinone A suppressed the bradykinin- and substance P-induced ear edema to a significantly greater extent than diphenhydramine/methysergide did. In the in vitro experiments, abruquinone A suppressed the compound 48/80-induced histamine and beta-glucuronidase released from isolated rat peritoneal mast cell preparations. These results suggest that the anti-inflammatory effect of abruquinone A is mediated partly via the suppression of the release of chemical mediators from mast cells and partly via the prevention of vascular permeability changes caused by mediators. The glucocorticoid activity and the release of glucocorticoid hormones from the adrenal gland are probably not involved.

Inhibition by gomisin C (a lignan from Schizandra chinensis) of the respiratory burst of rat neutrophils

1. The possible mechanisms of action of the inhibitory effect of gomisin C on the respiratory burst of rat neutrophils in vitro was investigated. 2. The peptide formyl-Met-Leu-Phe (FMLP) induced superoxide anion (O2-) formation and O2 consumption, which was inhibited by gomisin C in a concentration-dependent manner (IC50 21.5 +/- 4.2 micrograms ml-1 for O2- formation). Gomisin C also suppressed O2- formation and consumption at low concentrations of phorbol myristate acetate (PMA) with an IC50 value of 26.9 +/- 2.1 micrograms ml-1 for O2- formation. However, gomisin C did not affect the responses induced by a high concentration of PMA. 3. Gomisin C had no effect on O2- generation and uric acid formation in the xanthine-xanthine oxidase system, and failed to alter O2- generation during dihydroxyfumaric acid (DHF) autoxidation, indicating that it does not scavenge superoxide. 4. Like trifluoperazine (TFP), gomisin C attenuated the activity of PMA-activated neutrophil particulate NADPH oxidase in a concentration-dependent manner. 5. Gomisin C reduced the elevations of cytosolic free Ca2+ in neutrophils stimulated by FMLP in the presence or absence of EDTA. Cyclopiazonic acid (CPA) induced the release of Ca2+ from intracellular stores and this was also reduced by gomisin C. However, the Ca2+ influx pathway activated by CPA was not affected by gomisin C. 6. The cellular cyclic AMP level was markedly increased by forskolin, but not by gomisin C. Moreover, the inositol phosphate levels in FMLP-activated neutrophils were not affected by gomisin C. 7. These results show that the inhibitory action of gomisin C on the respiratory burst is not mediated by changes in cellular cyclic AMP or in inositol phosphates, or by scavenging O2- released from neutrophils, but may be mediated partly by the suppression of NADPH oxidase and partly by the decrease of cytosolic Ca2+ released from an agonist-sensitive intracellular store.

Suppressive effect of 2-phenyl-4-quinolone (YT-1) on hind-paw edema and cutaneous vascular plasma extravasation in mice

Like indomethacin, BW755C, diphenhydramine and methysergide, 2-phenyl-4-quinolone (YT-1) suppressed the polymyxin B-induced hind-paw edema. This inhibitory effect of YT-1 was also demonstrated in adrenalectomized mice. YT-1 inhibited the antidromic stimulation of saphenous nerve-induced plasma leakage in dorsal paw skin and reduced the volume of plasma exudation in PCA reaction. Bradykinin-, substance P- and compound 48/80-induced mouse ear edema was suppressed by YT-1 in a dose-dependent manner. In isolated rat peritoneal mast cells, YT-1 produced a dose-dependent inhibition of bradykinin-, substance P- and compound 48/80-induced histamine and beta-glucuronidase release. YT-1 also reduced the TXB2 formation from PMN leukocytes with IC50 2.0 +/- 0.5 microM, however with little effect on LTB4 formation. Histamine- and serotonin-induced plasma exudation in ear edema were reduced by YT-1. Moreover, the maximal response of ileum contraction caused by histamine and serotonin were also suppressed by YT-1 in a dose-dependent manner. In compound 48/80-pretreatment mice, YT-1 failed to suppress the bradykinin- and substance P-induced ear edema to a significantly greater extent than diphenhydramine combined with methysergide did. These results indicate that the inhibitory effect of YT-1 on local edema formation is not through the release of steroid hormones from adrenal gland, and is probably by suppressing the release of chemical mediators from mast cells, inhibition of prostaglandins formation, and noncompetitive but selective protection of the vasculature against the histamine- and serotonin-induced plasma extravasation.

Anti-inflammatory and analgesic effects of magnolol

Magnolol, isolated from Magnolia officinalis, inhibited mouse hind-paw edema induced by carrageenan, compound 48/80, polymyxin B and reversed passive Arthus reaction. Acetic acid-induced writhing response was depressed by magnolol, indomethacin and ibuprofen. The lethality of endotoxin challenge was reduced by pretreatment with magnolol, indomethacin and BW755C, a dual cyclo-oxygenase/lipoxygenase inhibitor. The recovered myeloperoxidase activity in edematous paw was significantly decreased in mice pretreated with magnolol and BW755C. Suppression of edema was demonstrated not only in normal mice but also in adrenalectomized animals. Magnolol was less potent on reducing PGD2 formation in rat mast cell than that of indomethacin. Unlike dexamethasone, magnolol did not increase liver glycogen level. The results suggest that the anti-inflammatory effect of magnolol was neither mediated by glucocorticoid activity nor through releasing steroid hormones from adrenal gland. The action of magnolol is proposed to be dependent on reducing the level of eicosanoid mediators.

Comparison of kinin-forming and amidolytic activities of four trimucases, oedema-producing and kinin-releasing enzymes, from Trimeresurus mucrosquamatus venom

Four kinin-releasing enzymes, trimucase I, II, III and IV, isolated from Trimeresurus mucrosquamatus venom (TMV) caused rat hind-paw swelling. Trimucase I and III were less potent than trimucase II and IV in this effect. Pretreatment with diphenhydramine or methysergide significantly reduced trimucase-induced paw swelling, while aspirin had no effect. Cellulose sulphate pretreatment suppressed the oedematous responses elicited by trimucases. The residual response was further depressed by diphenhydramine and methysergide. Trimucases also caused kinin generation in-vitro from rat plasma. This kinin-forming activity was in the order of trimucase II greater than IV greater than or equal to III greater than I greater than TMV. All trimucases hydrolysed chromogenic peptides N-benzoyl-Pro-Phe-Arg p-nitroanilide, N-benzoyl-Phe-Val-Arg p-nitroanilide and DL-Val-Leu-Arg p-nitroanilide; the order of this amidolytic activity was trimucase I greater than II greater than III greater than or equal to IV. These data indicate that the effects of venom kinin-releasing enzymes on plasma kininogen are not parallel to their amidolytic effects.

Edematous response caused by [Thi5,8,D-Phe7]bradykinin, a B2 receptor antagonist, is due to mast cell degranulation

[Thi5,8,D-Phe7]bradykinin caused hind-paw edema and degranulation of isolated peritoneal mast cells in a dose-dependent manner. Pretreatment with diphenhydramine/methysergide or compound 48/80 completely suppressed the edematous response caused by [Thi5,8,D-Phe7]bradykinin, whereas bradykinin-induced hind-paw swelling was only partially inhibited by diphenhydramine and methysergide pretreatment; the residual response was significantly further depressed by [Thi5,8,D-Phe7]bradykinin. Neither the bradykinin- nor [Thi5,8,D-Phe7]bradykinin-induced edematous response was significantly affected by aspirin or BW755C. The mast cell degranulation caused by [Thi5,8,D-Phe7]bradykinin and bradykinin was inhibited by gangliosides but not by heparin. These results suggest that the edematous response elicited by [Thi5,8,D-Phe7]bradykinin was mainly due to the actions of mediators released by the degranulation of mast cells. Unlike bradykinin, [Thi5,8,D-Phe7]bradykinin was devoid of a direct exudation-promoting effect but exerted an antagonistic effect on the direct effect of kinin. If the influence of mast cells degranulation could be minimized, [Thi5,8,D-Phe7]bradykinin could be used as a tool to evaluate the role of kinin in the edematous response in inflammation.

Effect of hsien-ho-t'sao (Agrimonia pilosa) on experimental thrombosis in mice

The water extract of Hsien-Ho-T'sao (HHT) prolonged the tail bleeding time in conscious mice. This antihemostatic effect was dose-dependent and exhibited a biphasic pattern; i.e. its activity declined at doses higher than 0.5 mg/kg. the prolonged bleeding time persisted for at least 12 hr and maximal effect was observed at 3 hr after the oral administration of HHT 500 mg/kg. HHT was effective in preventing ADP-induced acute pulmonary thromboembolic death in mice, while aspirin and indomethacin had no effect on this model. HHT, like aspirin and indomethacin, also reduced the mortality in collagen- and sodium arachidonate-induced thromboembolic death. All three drugs caused no significant protection in endotoxin shock. HHT was found to suppress platelet aggregation markedly, but little effect on blood coagulation. In conclusion, HHT was proved to be effective in the treatment of acute pulmonary thromboembolism, and this effect was mainly due to its antiplatelet action.

Antihemostatic and antithrombotic effects of XC386

XC386 prolonged the tail bleeding time in the conscious mice. This effect was dose-dependent and persisted for at least six hours after the oral administration. XC386 was effective in preventing ADP-induced acute pulmonary thromboembolic death in mice at dose of 100 mg/kg. Aspirin and indomethacin had no effect on this model. XC386 also reduced the mortality rate in collagen- induced thromboembolic death at the same dose as aspirin and indomethacin (200 mg/kg). All three drugs caused no significant protection in endotoxin shock. XC386 was found to suppress collagen-induced platelet aggregation, but did not affect blood coagulation. In conclusion, XC386 was proved to be as effective as aspirin and indomethacin in preventing the death of acute pulmonary thromboembolism.

Antihemostatic and antithrombotic effects of capsaicin in comparison with aspirin and indomethacin

Capsaicin prolonged the tail bleeding time in the conscious mice. This effect was dose-dependent and maximal effect was observed at 3 hr after the oral administration. Capsaicin was effective in preventing death caused by ADP-induced acute pulmonary thromboembolism in mice at dose of 25 mg/kg, while aspirin and indomethacin had no effect at 200 mg/kg. Capsaicin also reduced the mortality in collagen- and sodium arachidonate-induced thromboembolic death at dose of 25 and 50 mg/kg, respectively, and aspirin and indomethacin were also effective in these models but only when the dose was higher than 200 mg/kg. Capsaicin, aspirin or indomethacin could not protect mice from endotoxin shock. Capsaicin was found to suppress platelet aggregation markedly, but did not affect blood coagulation. In conclusion, capsaicin was proved to be more effective than aspirin and indomethacin in preventing the death of acute pulmonary thromboembolism, and this effect could be due to its inhibition on platelet aggregation.

Antiplatelet effect of hsien-ho-t'sao (Agrimonia pilosa)

The water extract of Hsien-Ho-T'sao (HHT) produced a dose-dependent inhibition on collagen-induced aggregation of platelet-rich plasma (PRP). The IC50 was about 3.5 mg/ml. In addition, HHT inhibited also the aggregation induced by ADP, A23187 or arachidonate in PRP. Greater inhibition was observed in the preparation of washed platelets. Increase of the calcium concentration in medium could not overcome the inhibitory effect of HHT. ATP release from platelets induced by collagen or A23187 was inhibited by HHT. In the presence of EDTA, ATP release caused by thrombin or A23187 was also inhibited by HHT. Malondialdehyde and thromboxane B2 formation was greatly inhibited by HHT in platelets challenged by collagen and thrombin. In arachidonate-stimulated platelets, thromboxane B2, but not malondialdehyde formation was inhibited. HHT showed more marked inhibition on aggregation in the presence of indomethacin, creatine phosphate/creatine phosphokinase or a combination of both. Hydrogen peroxide-induced hemolysis was marked reduced by HHT. It was concluded that HHT might have some membrane-active properties which interfered with the activation of phospholipase A2.

Antiplatelet effect of capsaicin

Capsaicin was found to be a potent inhibitor of platelet aggregation and release reaction. It inhibited the aggregation of rat platelet induced by collagen and thrombin, but only slightly reduced those of AA and A23187. The IC50 on collagen-induced platelet aggregation was about 85 micrograms/ml. Less inhibition was observed in the aggregation of platelet-rich plasma. Increase of the calcium concentration could not overcome the inhibitory effect. Washing of the capsaicin-pretreated platelets only partially reversed the inhibition. Capsaicin also inhibited ATP release induced by thrombin and A23187 in the presence of EDTA. MDA and TXB2 formation were markedly inhibited by capsaicin in platelets challenged by collagen, thrombin and A23187. In AA-stimulated platelets, MDA formation was slightly decreased and TXB2 formation was not affected. Capsaicin showed more marked inhibition in the presence of CP/CPK, indomethacin or a combination of both. Capsaicin reduced the hemolysis of RBCs induced by hydrogen peroxide or hypotonicity. It was concluded that capsaicin had some membrane stabilizing property and this might lead to the interference of the activation of phospholipase A2.

XC 386: a new antiplatelet agent

XC386 was a new antiplatelet compound, which inhibited the aggregation and release reaction of rat platelet-rich plasma induced by collagen. This inhibition was dose-dependent and the IC50 was calculated to be 1 mM on collagen-induced aggregation. In washed platelets, the aggregations induced by ADP and collagen were much more markedly inhibited by XC386 than those induced by thrombin, A23187 and arachidonate. High calcium (4 to 8 mM) could not antagonize the inhibition. XC386 did not alter the malondialdehyde (MDA) and thromboxane B2 (TXB2) levels of resting platelets. But MDA formation induced by collagen, thrombin and A23187, and TXB2 formation induced by collagen and thrombin were significantly inhibited, while both formations induced by arachidonate were not changed. Combination of indomethacin or CP/CPK and XC386 enhanced markedly the inhibitory effect of XC386 on collagen- or A23187-induced aggregation. It was concluded that XC386 might inhibit platelet aggregation before the step of arachidonic acid release by phospholipase A2.

Antihemostatic effect of Hsien-Ho-T'sao (Agrimonia pilosa)

Bleeding time in rats was markedly prolonged after the administration of the water extract of Hsien-Ho-T'sao. This antihemostatic effect was more marked in the group of i.p. injection of the drug than in the group of p.o. administration for 2 or 7 consecutive days. Blood coagulation studies showed that plasma prothrombin time, activated partial thromboplastin time and stypven time were prolonged, while thrombin time and fibrinogen level were not changed. The thromboelastographic recording showed that reaction time was prolonged and maximal elasticity of clot was decreased. In addition, ADP- and collagen- induced aggregations of platelet-rich plasma were suppressed. In conclusion, the prolongation of the bleeding time might be due to both anticoagulant and antiplatelet action of the drug.