Tur-Fu Huang

Disintegrins: a family of integrin inhibitory proteins from viper venoms.

Abstract Disintegrins represent a new class of low molecular weight, RGD-containing, cysteine-rich peptides isolated from the venom of various snakes. They interact with the β 1 and β 3 families of integrins and their potency is at least 500–2000 times higher than short RGDX peptides. Analysis of the amino acid sequences of 14 different disintegrins suggests that the RGD sequence, in the spatial configuration determined by the appropriate pairing of the cysteine residues, functions as a cell recognition site. However, certain nonconserved amino acids appear to modify the activity of disintegrins, their specificity for various receptors, and their ability to compete specifically with various ligands.

TWO ANTIPLATELET AGENTS FROM MAGNOLIA OFFICINALIS

Magnolol and honokiol are two position isomers isolated from the bark of Magnolia officinalis. Both inhibited the aggregation and ATP release of rabbit platelet-rich plasma induced by collagen and arachidonic acid without affecting that induced by ADP, PAF or thrombin. Aggregation of washed platelets was more markedly inhibited than that of platelet-rich plasma, while the aggregation of whole blood was least affected by both inhibitors. Thromboxane B2 formation caused by collagen, arachidonic acid or thrombin was in each case inhibited by magnolol and honokiol. The rise of intracellular calcium caused by arachidonic acid or collagen was also suppressed by both agents. Collagen-induced intracellular calcium increase in the presence of indomethacin was suppressed by magnolol. It is concluded that the antiplatelet effect of magnolol and honokiol is due to an inhibitory effect on thromboxane formation and also an inhibition of intracellular calcium mobilization.

Characterization of snake venom components acting on blood coagulation and platelet function

Snake venoms can affect blood coagulation and platelet function in various ways. The physicochemical properties and the mechanisms of actions of the snake venom components affecting blood coagulation and platelet function are discussed.

Ultrasound stimulates cyclooxygenase-2 expression and increases bone formation through integrin, focal adhesion kinase, phosphatidylinositol 3-kinase, and Akt pathway in osteoblasts.

It has been shown that ultrasound (US) stimulation accelerates fracture healing in animal models and in clinical studies. Here we found that US stimulation transiently increased the surface expression of α2, α5, β1, and β3 integrins in cultured osteoblasts, as shown by flow cytometric analysis and immunofluorescence staining. US stimulation increased prostaglandin E2 formation and the protein and mRNA levels of cyclooxygenase-2 (COX-2). At the mechanistic level, anti-integrin α5β1 and αvβ3 antibodies or rhodostomin, a snake venom disintegrin, attenuated the US-induced COX-2 expression. Phosphatidylinositol 3-kinase (PI3K) inhibitors 2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride (LY294002) and wortmannin also inhibited the potentiating action of US. US stimulation increased the phosphorylation of focal adhesion kinase (FAK), extracellular signal-regulated kinases (ERK), p85 subunit of PI3K, and serine 473 of Akt. COX-2 promoter activity was enhanced by US stimulation in cells transfected with pCOX2-Luc. Cotransfection with dominant-negative mutant of FAK(Y397F), p85(Δp85), Akt(K179A), or ERK2(K52R) inhibited the potentiating action of US on COX-2 promoter activity. Expression of mineralized nodule was lower in dominant-negative mutants of FAK, p85, and Akt-transfected clones than in vector-transfected control cells. Taken together, our results provide evidence that US stimulation increases COX-2 expression and promotes bone formation in osteoblasts via the integrin/FAK/PI3K/Akt and ERK signaling pathway.

EDRF-release and Ca+(+)-channel blockade by magnolol, an antiplatelet agent isolated from Chinese herb Magnolia officinalis, in rat thoracic aorta.

Magnolol is an antiplatelet agent isolated from Chinese herb Magnolia officinalis. It inhibited norepinephrine (NE, 3 microM)-induced phasic and tonic contractions in rat thoracic aorta. At the plateau of the NE-induced tonic contraction, addition of magnolol caused two phases (fast and slow) of relaxation. These two relaxations were concentration-dependent (10-100 micrograms/ml), and were not inhibited by indomethacin (20 microM). The fast relaxation was completely antagonized by hemoglobin (10 microM) and methylene blue (50 microM), and disappeared in de-endothelialized aorta while the slow relaxation was not affected by the above treatments. Magnolol also inhibited high potassium (60 mM)-induced, calcium-dependent (0.03 to 3 mM) contraction of rat aorta in a concentration-dependent manner. 45Ca(+)+ influx induced by high potassium or NE was markedly inhibited by magnolol. Cyclic GMP, but not PGI2, was increased by magnolol in intact, but not in de-endothelialized aorta. It is concluded that magnolol relaxed vascular smooth muscle by releasing endothelium-derived relaxing factor (EDRF) and by inhibiting calcium influx through voltage-gated calcium channels.

What have snakes taught us about integrins

Abstract. Snake venoms contain unique components that affect cell-matrix interactions. Disintegrins represent a class of low molecular weight, Arg-Gly-Asp (RGD)-containing, cysteine-rich peptides purified from the venom of various snakes among the Viperidae and Crotalidae. They bind with various degrees of specificity to integrins αIIb  β3 , α5  β1 and αV  β3 expressed on cells. Snake venom metalloproteases (high molecular mass haemorrhagins) also contain disintegrin-like domains, in addition to zinc-chelating sequences. Membrane-anchored ADAMs (A Disintegrin And Metalloprotease domain), multidomain molecules consisting of metalloprotease, disintegrin-like, cysteine-rich, and epidermal growth factor domains, a transmembrane domain and a cytoplasmic tail, are a new family of proteins. In the light of the large number and wide distribution of ADAMs, they may participate in cell-cell fusion events, including sperm-egg binding and fusion, myoblast fusion and other cell-cell and cell-matrix interactions. The structure-function relationship of these molecules is discussed.

Antiplatelet actions of panaxynol and ginsenosides isolated from ginseng

The antiplatelet effect of panaxynol isolated from the diethyl ether layer was compared with those of ginsenosides from the butanol layer of Panax ginseng. Panaxynol (0.1 mg/ml) inhibited markedly the aggregation of washed platelets induced by collagen, arachidonic acid, ADP, ionophore A23187, PAF and thrombin while ginsenosides had no significant effect on the aggregation but ginsenoside Ro (1 mg/ml) inhibited the ATP release of platelets. Less inhibitory effect of panaxynol was observed in the aggregation of platelet-rich plasma. Thromboxane B2 formation of platelets was inhibited by panaxynol but not by ginsenosides. The antiplatelet effect of panaxynol was dependent on the incubation time and the aggregability of platelets inhibited by panaxynol could not easily be recovered after washing the platelets. In human platelet-rich plasma, panaxynol prevented secondary aggregation and completely blocked ATP release from platelets induced by epinephrine and ADP. Both panaxynol and ginsenoside Rg2 inhibited the rise of intracellular calcium caused by collagen. It is concluded that panaxynol is the most potent antiplatelet agent in ginseng and its mechanism of action is chiefly due to the inhibition of thromboxane formation.

Lycopene inhibits TNF-α-induced endothelial ICAM-1 expression and monocyte-endothelial adhesion

Inflammatory mediators such as TNF-alpha and interleukin (IL)-1beta, and IL-8, which can enhance binding of low-density lipoprotein (LDL) to endothelium and upregulate expression of leukocyte adhesion molecules on endothelium during atherogenesis. Lycopene, a natural carotenoid from tomato and other sources, has been shown to prevent cardiovascular diseases in epidemiological studies. However, its anti-inflammatory action mechanism remains unclear. In the present study, we studied the effect of lycopene on TNF-alpha-induced signaling in human umbilical endothelial cells (HUVECs). We found that TNF-alpha-induced intercellular adhesion molecule-1 (ICAM-1) expression in HUVECs was inhibited by lycopene, whereas cyclooxygenase-2 (COX-2) and platelet-endothelial cell adhesion molecule (PECAM-1) expression were not affected. A further analysis indicated that lycopene attenuated TNF-alpha-induced IkappaB phosphorylation, NF-kappaB expression, and NF-kappaB p65 translocation from cytosol to nucleus. In line with this, TNF-alpha-induced NF-kappaB-DNA but not AP1-DNA complexes formation was inhibited by lycopene, as determined by the electrophoretic mobility shift assay (EMSA). On the other hand, lycopene did not affect TNF-alpha-induced p38 and extracellular matrix-regulated kinase1/2 (ERK1/2) phosphorylation and interferon-gamma (IFN-gamma)-induced signaling, suggesting that lycopene primarily affects TNF-alpha-induced NF-kappaB signaling pathway. In a functional study, lycopene dose-dependently attenuated monocyte adhesion to endothelial monolayer but not that adhesion to extracellular matrix. Taken together, we provided here the first evidence showing that lycopene is able to inhibit TNF-alpha-induced NF-kappaB activation, ICAM-1 expression, and monocyte-endothelial interaction, suggesting an anti-inflammatory role of lycopene and possibly explaining in part why lycopene can prevent cardiovascular diseases.

Vasodilatory action mechanisms of apigenin isolated from Apium graveolens in rat thoracic aorta

The effect of apigenin, isolated from Apium graveolens, on the contraction of rat thoracic aorta was studied. Apigenin inhibited the contraction of aortic rings caused by cumulative concentrations of calcium (0.03-3 mM) in high potassium (60 mM) medium, with an IC50 of about 48 microM. After pretreatment it also inhibited norepinephrine (NE, 3 microM)-induced phasic and tonic contraction in a concentration (35-140 microM)-dependent manner with an IC50 of 63 microM. At the plateau of NE-induced tonic contraction, addition of apigenin caused relaxation. This relaxing effect of apigenin was not antagonized by indomethacin (20 microM) or methylene blue (50 microM), and still existed in endothelial denuded rat aorta or in the presence of nifedipine (2-100 microM). Neither cAMP nor cGMP levels were changed by apigenin. Both the formation of inositol monophosphate caused by NE and the phasic contraction induced by caffeine in the Ca(2+)-free solution were unaffected by apigenin. 45Ca2+ influx caused by either NE or K+ was inhibited by apigenin concentration-dependently. It is concluded that apigenin relaxes rat thoracic aorta mainly by suppressing the Ca2+ influx through both voltage- and receptor-operated calcium channels.

Potent platelet aggregation inhibitor from Trimeresurus gramineus snake venom.

Using DEAE-Sephadex A-50 column chromatography and gel filtration, a potent platelet aggregation inhibitor from Trimeresurus gramineus venom was purified. It was an acidic phospholipase A, rich in aspartic acid, glutamic acid and half-cystine, with an isoelectric point of 3.6. At a concentration of 10 micrograms/ml, the purified inhibitor showed a marked inhibitory effect on platelet aggregations induced by adenosine diphosphate, collagen, sodium arachidonate and ionophore A-23187 in rabbit platelet-rich plasma, washed platelet suspension, as well as in thrombin-degranulated platelet suspension. The ID50 of this venom inhibitor was about 2.5-5 micrograms/ml in platelet aggregations induced by all these aggregation inducers. The action of this inhibitor could be partially antagonized by phosphatidylethanolamine. High concentration of Ca2+ (5 mM) did not reverse the inhibitory action even in the presence of ionophore A-23187. The [14C]serotonin release induced by sodium arachidonate and thrombin was unaffected. Malonic dialdehyde formation induced by these aggregation inducers remained unchanged. Basal and prostaglandin E1-stimulated cAMP levels were not altered by this inhibitor. No lactate dehydrogenase was released even at a concentration of 62.5 micrograms/ml. Polylysine-induced platelet agglutination was not affected. beta-Mercaptoethanol inactivated both its phospholipase A enzymatic and platelet inhibitory activities, while p-bromophenacyl bromide only inactivated the former activity. The possibility of acting on a common final step of platelet aggregation, i.e. the intercellular adhesion between the activated platelets, was proposed.