Trichosanthin induced calcium-dependent generation of reactive oxygen species in human choriocarcinoma cells

Clinical Use of Toxic Proteins and Peptides from Tian Hua Fen and Scorpion Venom

Traditional Chinese Medicine (TCM) has been practiced in China for thousands of years. As a complementary and alternative treatment, herbal medicines that are frequently used in the TCM are the most accepted in the Western world. However, animal materials, which are equally important in the TCM practice, are not well-known in other countries. On the other hand, the Chinese doctors had documented the toxic profiles of hundreds of animals and plants thousand years ago. Furthermore, they saw the potential benefits of these materials and used their toxic properties to treat a wide variety of diseases, such as heavy pain and cancer. Since the 50s of the last century, efforts of the Chinese government and societies to modernize TCM have achieved tremendous scientific results in both laboratory and clinic. A number of toxic proteins have been isolated and their functions identified. Although most of the literature was written in Chinese, this review provide a summary, in English, regarding our knowledge of the clinical use of the toxic proteins isolated from a plant, Tian Hua Fen, and an animal, scorpion, both of which are famous toxic prescriptions in TCM.

Structural and Functional Investigation and Pharmacological Mechanism of Trichosanthin, a Type 1 Ribosome-Inactivating Protein

Trichosanthin (TCS) is an RNA N-glycosidase that depurinates adenine-4324 in the conserved α-sarcin/ricin loop (α-SRL) of rat 28 S ribosomal RNA (rRNA). TCS has only one chain, and is classified as type 1 ribosome-inactivating protein (RIP). Our structural studies revealed that TCS consists of two domains, with five conserved catalytic residues Tyr70, Tyr111, Glu160, Arg163 and Phe192 at the active cleft formed between them. We also found that the structural requirements of TCS to interact with the ribosomal stalk protein P2 C-terminal tail. The structural analyses suggest TCS attacks ribosomes by first binding to the C-terminal domain of ribosomal P protein. TCS exhibits a broad spectrum of biological and pharmacological activities including anti-tumor, anti-virus, and immune regulatory activities. This review summarizes an updated knowledge in the structural and functional studies and the mechanism of its multiple pharmacological effects.

Dual-emissive fluorescence measurements of hydroxyl radicals using a coumarin-activated silica nanohybrid probe

This work reports a novel dual-emissive fluorescent probe based on dye hybrid silica nanoparticles for ratiometric measurement of the hydroxyl radical (˙OH). In the probe sensing system, the blue emission of coumarin dye (coumarin-3-carboxylic acid, CCA) immobilized on the nanoparticle surface is selectively enhanced by ˙OH due to the formation of a coumarin hydroxylation product with strong fluorescence, whereas the emission of red fluorescent dye encapsulated in the silica nanoparticle is insensitive to ˙OH as a self-referencing signal, and so the probe provides a good quantitative analysis based on ratiometric fluorescence measurement with a detection limit of 1.65 μM. Moreover, the probe also shows high selectivity for ˙OH determination against metal ions, other reactive oxygen species and biological species. More importantly, it exhibits low cytotoxicity and high biocompatibility in living cells, and has been successfully used for cellular imaging of ˙OH, showing its promising application for monitoring of intracellular ˙OH signaling events.

Trichosanthin suppresses the proliferation of glioma cells by inhibiting LGR5 expression and the Wnt/β-catenin signaling pathway

Studies have indicated that trichosanthin (TCS), a bioactive protein extracted and purified from the tuberous root of Trichosanthes kirilowii (a well-known traditional Chinese medicinal plant), produces antitumor effects on various types of cancer cells. However, the effects of TCS on glioma cells are poorly understood. The objective of this study was to investigate the antitumor effects of TCS on the U87 and U251 cell lines. The in vitro effects of TCS on these two cell lines were determined using a Cell Counting Kit-8 (CCK-8) assay, Annexin V-FITC staining, DAPI staining, Transwell assays, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assays, 5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethyl-imidacar-bocyanine iodide (JC-1) staining and western blotting, which was utilized to assess the expression of leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5) and key proteins in the Wnt/β-catenin signaling pathway. Our data indicated that TCS inhibited the proliferation of glioma cells in a dose- and time-dependent manner and played a role in inhibiting glioma cell invasion and migration. Additional investigation revealed that the expression levels of LGR5 and of key proteins in the Wnt/β-catenin signaling pathway were markedly decreased after TCS treatment. The results suggest that TCS may induce apoptosis in glioma cells by targeting LGR5 and repressing the Wnt/β-catenin signaling pathway. In the future, in vivo experiments should be conducted to examine the potential use of this compound as a novel therapeutic agent for gliomas.

Anti-tumor action of trichosanthin, a type 1 ribosome-inactivating protein, employed in traditional Chinese medicine: a mini review

Trichosanthin (TCS) as a midterm abortifacient medicine has been used clinically in traditional Chinese medicine for centuries. Additionally, TCS manifests a host of pharmacological properties, for instance, anti-HIV and anti-tumor activities. TCS has been reported to inhibit cell growth of a diversity of cancers, including cervical cancer, choriocarcinoma, and leukemia/lymphoma, etc. This article purported to review the various anti-tumor activities of TCS and the mechanism of apoptosis it induced in these tumor cells. These research progresses provide an insight into cancer research and treatment as well as disclose new pharmacological properties of the ancient but popular Chinese medicine.

The anti-herpetic activity of trichosanthin via the nuclear factor-κB and p53 pathways

AIMS

Trichosanthin (TCS) is a type I ribosome-inactivating protein. We have previously shown that TCS induces a more potent apoptosis in infected cells over uninfected cells, but the mechanism underlying it is unclear. In this study, we explored the anti-HSV-1 mechanism of TCS through the nuclear factor-κB (NF-κB) and p53 pathways in human epithelial carcinoma (HEp-2) cells with wild type p53.

MAIN METHODS

The western blot, electrophoretic mobility shift assay, chromatin immunoprecipitation assay, enzyme-linked immunosorbent assay and cytokinesis-block micronucleus were applied in this study.

KEY FINDINGS

It was shown that TCS inhibited the HSV-1-induced NF-κB activation. Meanwhile, in HSV-1 infected cells, TCS treatment activated significantly more p53 and BAX, with no DNA damage and less S phase arrest compared with uninfected cells. The activation of BAX in infected cells correlated with the cell death signaling of p53.

SIGNIFICANCE

Taken together, these results suggest that the anti-HSV-1 effect of TCS is related to its suppression of NF-κB activation and regulation of p53-dependent cell death in infected cells.

Trichosanthin enhances anti-tumor immune response in a murine Lewis lung cancer model by boosting the interaction between TSLC1 and CRTAM

Trichosanthin (TCS), extracted from the Chinese medicinal herb Trichosanthes kirilowi, has shown promise for the inhibition of tumor growth. However, its immunomodulatory effect on tumor-host interaction remains unknown. In this study, we focused on the effect of TCS on murine anti-tumor immune response in the 3LL Lewis lung carcinoma tumor model and explored the possible molecular pathways involved. In addition to inhibiting cell proliferation and inducing apoptosis in the 3LL tumor, TCS retarded tumor growth and prolonged mouse survival more significantly in C57BL/6 immunocompetent mice than in nude mice. This reflected the fact that the host immune system was involved in tumor eradication. Using FACS analysis, we found that TCS increased the percentage of effector T cells, particularly Interferon-gamma (IFN-γ) producing CD4(+) and CD8(+) T cells from tumor-bearing mice. TCS also promoted the vigorous proliferation of antigen-specific effector T cells, markedly increased Th1 cytokine secretion and elicited more memory T cells in tumor-bearing mice, consequently enhancing the anti-tumor response and inducing immune protection. Furthermore, we found that TCS upregulated the expression of tumor suppressor in lung cancer 1 (TSLC1) in 3LL tumor cells and the expression of its ligand, class I-restricted T cell-associated molecule (CRTAM), in effector T cells. Blocking TSLC1 expression with small interfering RNA (siRNA) significantly eliminated the effects of TCS on the proliferation and cytokine secretion of effector T cells, suggesting that TCS enhances anti-tumor immune response at least partially by boosting the interaction between TSLC1 and CRTAM. Collectively, our data demonstrate that TCS not only affects tumor cells directly, but also enhances anti-tumor immunity via the interaction between TSLC1 and CRTAM. These findings may lead to the development of a novel approach for tumor regression.

Quantum dot ex vivo labeling of neuromuscular synapses

Nicotinic receptors (nAchRs) are responsible for fast excitatory signaling by the neurotransmitter acetylcholine (Ach). They are present on the postsynaptic membrane at neuromuscular junctions (NMJs) and also at brain synapses. Alpha-bungarotoxin (alpha-BTX), a high-affinity nAchR antagonist, inhibits Ach binding and neurotransmission. Here we demonstrate biotinylated alpha-BTX, bound to native mouse diaphragm nAchRs, can be quantified and visualized ex vivo using streptavidin-conjugated quantum dots. This approach provides a novel methodology for the direct assessment of the presence and mobility of neurotransmitter receptors in native tissue.

Effect of site-directed PEGylation of trichosanthin on its biological activity, immunogenicity, and pharmacokinetics

Trichosanthin (TCS) is a type I ribosome-inactivating protein (RIP) with multiple biological and pharmacological activities. It has been approved effective in the clinical treatment of AIDS and tumor, but its strong immunogenicity and short plasma half-life have limited the clinical administration. To reduce the immunogenicity and prolong the plasma half-life of this compound, three TCS muteins (M(1), M(2) and M(3)) and two PEGylated TCS muteins (PM(1) and PM(2)) were constructed by site-directed mutagenesis and PEGylation, respectively. Compared with the unmodified TCS, both PEGylated TCS showed a 3- to 4-fold decrease in immunogenicity, a 0.5- to 0.8-fold decrease in non-specific toxicity, and a 4.5- to 6-fold increase in plasma half-life. But there is a problem of activity reduction. The increased circulating half-life in vivo may compensate for the reduced activity. Together with the other benefits of PEGylation such as reduced immunogenicity and toxicity, it is worthwhile to further explore the potential application of the PEGylated TCS as a better therapeutic agent for AIDS and tumor.

Protective role of a novel erythrocyte-derived depressing factor on blood vessels of renovascular hypertensive rats

1. We have isolated a novel human erythrocyte-derived depressing factor (EDDF) that has a significant antihypertensive effect in various rat models of hypertension. The aim of the present study was to examine the mechanisms of action of EDDF on vascular function in two-kidney, one-clip (2K1C) renovascular hypertensive rats. 2. The EDDF was prepared from human erythrocytes. Experiments were performed in 18 male Wistar rats. The vascular ring perfusion assay and a two-photon laser scanning fluorescence microscope (TMP) were used to evaluate the vascular contractile response. The effects of EDDF on phenylephrine (PE)- and noradrenaline (NA)-induced vascular contraction were evaluated in 2K1C hypertensive rats. The proliferation and DNA synthesis in vascular smooth muscle cells (VSMC) were determined using the [3H]-TdR (thymidine) incorporation and 3-(4,5-dimethyl-2 thiazoyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assays. Flow cytometry, reverse transcription-polymerase chain reaction and western blots were used to measure cell cycle and apoptotic profiles, platelet-derived growth factor (PDGF)-A expression and the activity of extracellular signal-regulated kinase (ERK)-1/2, as well as the expression of cyclin D1 and cyclin-dependent kinase (CDK) 4. 3. At 10(-5) g/mL, EDDF significantly decreased the PE- and NA-induced hypertensive vascular contraction. In addition, EDDF inhibited DNA synthesis in primary VSMC from 2K1C rats. The mRNA expression of PDGF-A in VSMC was twofold higher in 2K1C rats compared with control rats, whereas EDDF significantly inhibited the increment in PDGF-A mRNA expression. In addition, EDDF inhibited the phosphorylation of ERK1/2 and decreased the expression of cyclin D1 and CDK4; p21 (Cip1) levels were increased after treatment with EDDF. 4. In conclusion, EDDF inhibits VSMC proliferation in 2K1C rats through G0/G1 cell cycle arrest. The effects may be mediated, in part, by enhanced expression of p21 (Cip1) and the inhibition of ERK1/2 phosphorylation and the expression of cyclin D1/CDK4 and PDGF-A.

Isolation and characterization of ribosome-inactivating proteins from Cucurbitaceae

Due to their RNA-N-glycosidase activity, ribosome-inactivating proteins (RIPs) are attractive candidates as antitumor and antiviral agents in biomedical and agricultural research. We have isolated and characterized two such proteins, foetidissimin II and texanin, from two Cucurbitaceae species. Foetidissimin II, obtained from the roots of Cucurbita foetidissima, was identified as a type-2 RIP, with a molecular weight of 61 kDa, as estimated by gel electrophoresis. It is composed of two chains, a 29-kDa chain A, and a 32-kDa chain B. Texanin, isolated from the fruits of Cucurbita texana, is a type-I RIP, with a single chain of molecular weight 29.7 kDa, as estimated by MALDI-TOF-MS. Both proteins exhibit RNA-N-glycosidase activity, with aniline playing a critical role in rRNA cleavage. The IC50 value of foetidissimin II, determined by cell-free protein-synthesis inhibition, was 0.251 muM. In an in vitro cytotoxicity assay, foetidissimin II exhibited IC50 values of ca. 70 nM to both adenocarcinoma and erythroleukemia cells. Texanin exhibited a weaker anticancer activity against erythroleukemia cells, with an IC50 value of 95 microM, but no activity against adenocarcinoma cells. The N-terminal sequences of both proteins were compared with those of reported RIPs.

PKC inhibition is involved in trichosanthin-induced apoptosis in human chronic myeloid leukemia cell line K562

Trichosanthin (TCS), a type I ribosome-inactivating protein, induces cell death in various cell types including several tumor cell lines. However, the mechanism remains largely uncharacterized. In this study, we investigated the possible mechanism underlying its cytotoxicity by using human chronic myeloid leukemia cell line K562. We found that TCS induced apoptosis in K562 cells in a time- and concentration-dependent manner and can be blocked by caspase-3 inhibitors. Interestingly, TCS treatment induced a transient elevation in intracellular calcium concentration and a slow increase in reactive oxygen species production, while calcium chelators and antioxidants had no obvious effect on TCS-induced apoptosis, suggesting that calcium changes and reactive oxygen species may not be involved in TCS-mediated apoptosis in K562 cells. Instead we found that TCS partly inhibited PKC activity. Indeed, the PKC activator, PMA, inhibited while the PKC inhibitor, calphostin c, enhanced TCS-induced apoptosis. These PKC modulators had similar effects on TCS-induced cleavage of caspase-3, and caspase-3 inhibitors prevented calphostin c-enhanced apoptosis induced by TCS. In summary, we conclude that TCS induces apoptosis in K562 cells partly via PKC inhibition and caspase-3 activation.

Mapping the antigenic determinants and reducing the immunogenicity of trichosanthin by site-directed mutagenesis

Trichosanthin (TCS) is a type I ribosome-inactivating protein (RIP) possessing multiple pharmacological properties. One of its interesting properties is to inhibit human immunodeficiency virus (HIV) replication but its strong immunogenicity has limited the repeated clinical administration. To map the antigenic determinants and reduce the immunogenicity of TCS, two potential antigenic sites (YFF81-83 and KR173-174) were identified by computer modeling, and then three TCS mutants namely TCS(YFF81-83ACS), TCS(KR173-174CG), and TCS(YFF-KR) were constructed by site-directed mutagenesis. The RI activity and DNase-like activity of the three constructed TCS mutants were similar to natural TCS but with much lower immunogenicity. Results suggested that the two selected sites are all located at or near the antigenic determinants of TCS. In toxicity studies, the LD(50) of the three TCS mutants was not different from natural TCS. These findings would be useful in designing a better therapeutic agent for AIDS.

Cartap-induced cytotoxicity in mouse C2C12 myoblast cell line and the roles of calcium ion and oxidative stress on the toxic effects

Our previous study has demonstrated that instead of neuromuscular blockage cartap, an organonitrogen insecticide, could cause a marked irreversible Ca2+-dependent contracture in both isolated mouse and rabbit phrenic nerve-diaphragms. We further examined the potential of direct myocytotoxicity of cartap and the possible roles of calcium ion and oxidative stress on cartap-induced muscle cell injury using the mouse myoblast cell line, C2C12. Cartap exerted a dose- and time-dependent cytotoxic effect in C2C12 cells measured by MTT colorimetric assay and trypan blue dye exclusion. The extracellular activities of both creatine kinase (CK) and lactate dehydrogenase (LDH) were elevated in the cartap-treated groups at or greater than 100 microM. The isoenzymatic profiles showed that the elevations were mainly due to CK-3, LDH-3, and LDH-4. Following the addition of 0.5-2.5mM EGTA, a Ca2+ chelator, or 30-100 microM verapamil, an L-type Ca2+ channel blocker, the cartap-induced reduction in MTT metabolic rate of C2C12 cells was significantly restored in a dose-dependent manner in both EGTA and verapamil-treated cells. Furthermore, EGTA could significantly reduce the cartap-induced elevation in the levels of total extracellular CK and LDH activities. Additionally, cartap significantly increased the level of endogenous reactive oxygen species (ROS) in C2C12 cells in a dose- and time-dependent manner. The cartap-induced ROS generation could be significantly inhibited by antioxidants, including Vitamins C and E, catalase, and superoxide dismutase, with catalase the most effective. EGTA could significantly inhibit cartap-induced ROS generation in a dose-dependent manner. The results suggested that cartap could induce ROS generation in C2C12 cells via a Ca2+-dependent mechanism resulting in subsequent cytotoxicity, at least partially, to C2C12 cells. It is speculated that both Ca2+ and Ca2+-induced ROS may also play the central role on the myogenic contracture and myofiber injury of the diaphragm leading to respiratory failure and subsequent death in rabbits exposed ocularly to cartap.

Recent advances in trichosanthin, a ribosome-inactivating protein with multiple pharmacological properties

Trichosanthin (TCS), a ribosome-inactivating protein extracted from the root tuber of Chinese medicinal herb Trichosanthes kirilowii Maximowicz, has multiple pharmacological properties including abortifacient, anti-tumor and anti-HIV. It is traditionally used to induce abortion but its antigenicity and short plasma half-life have limited the repeated clinical administration. In this review, work to locating antigenic sites and prolonging plasma half-life are discussed. Studies on structure-function relationship and mechanism of cell entry are also covered. Recently, TCS has been found to induce apoptosis, enhance the action of chemokines and inhibit HIV-1 integrase. These findings give new insights on the pharmacological properties of TCS and other members of ribosome-inactivating proteins.

Both calcium and ROS as common signals mediate Na(2)SeO(3)-induced apoptosis in SW480 human colonic carcinoma cells

Recent studies have shown that reactive oxygen species (ROS) play a crucial role in Se-induced cell apoptosis. A number of studies have demonstrated that perturbed cellular calcium homeostasis has been implicated in apoptosis. The main objective of this study was to evaluate the role of Ca(2+) in Na(2)SeO(3)-induced apoptosis and the relationship between Ca(2+) and ROS in human colonic carcinoma cells SW480. When SW480 cells were exposed to 25-100 microM Na(2)SeO(3), both cell apoptosis and growth inhibition were observed by flow cytometric analysis and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. Na(2)SeO(3) was able to induce increase of [Ca(2+)](i) and ROS production and disrupt mitochondrial membrane potential (Delta Psi m) in SW480 cells monitored by using a confocal laser scanning microscope. Ca(2+) channel inhibitor CoCl(2) and an intracellular Ca(2+) chelator o-phtalaldehyde, 1,2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetra-acetic acid acetoxymethyl ester (BAPTA) completely inhibited [Ca(2+)](i) increase, but catalase had no effect on Na(2)SeO(3)-induced increase of [Ca(2+)](i). BAPTA-AM, CoCl(2), and mitochondrial Ca(2+) uptake inhibitor ruthenium red blocked Delta Psi m dissipation. The increase of ROS was also suppressed by CoCl(2), BAPTA, ruthenium red, N-acetylcysteine and catalase, respectively. The mitochondrial uncoupler carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone (FCCP) completely inhibited Na(2)SeO(3)-induced ROS increase. This showed that ROS increase is due to mitochondrial Ca(2+) overload. The Na(2)SeO(3)-induced apoptosis of SW480 cells was also inhibited by CoCl(2), BAPTA, ruthenium red, N-acetylcysteine, and catalase, respectively. The results mentioned above imply that both calcium and Ca(2+)-dependent ROS as a signal molecule mediate apoptosis induced by Na(2)SeO(3) in SW480 cells.

RIBOSOME-INACTIVATING PROTEINS: A Plant Perspective

Ribosome-inactivating proteins (RIPs) are toxic N-glycosidases that depurinate the universally conserved alpha-sarcin loop of large rRNAs. This depurination inactivates the ribosome, thereby blocking its further participation in protein synthesis. RIPs are widely distributed among different plant genera and within a variety of different tissues. Recent work has shown that enzymatic activity of at least some RIPs is not limited to site-specific action on the large rRNAs of ribosomes but extends to depurination and even nucleic acid scission of other targets. Characterization of the physiological effects of RIPs on mammalian cells has implicated apoptotic pathways. For plants, RIPs have been linked to defense by antiviral, antifungal, and insecticidal properties demonstrated in vitro and in transgenic plants. How these effects are brought about, however, remains unresolved. At the least, these results, together with others summarized here, point to a complex biological role. With genetic, genomic, molecular, and structural tools now available for integrating different experimental approaches, we should further our understanding of these multifunctional proteins and their physiological functions in plants.