The plant ribosome inactivating proteins luffin and saporin are potent inhibitors of HIV-1 integrase

Phytochemistry and Biological Activities of Agrostemma Genus-A Review

The family Caryophyllaceae comprises more than 2600 species spread widely across all the continents. Their economic importance is mainly as ornamentals (carnation) and as weeds in agriculture. Some species have been used traditionally (and some are still) in herbal medicine or as emulsifiers in food processing. These applications are based on the high content of triterpenoid saponins. Typical for this family are also ribosome-inactivating proteins (RIPs), which are potentially highly toxic. Agrostemma githago L. (common corncockle) was historically considered a serious toxicological hazard owing to cereal grain contamination by its seeds. Notwithstanding, it was also recommended as a drug by various herbalists. In this review, the literature was searched in the PubMed, Google Scholar, and Scopus databases for papers focused on the chemical composition and bioactivity of the two accepted species of the Agrostemma genus. This systematic review adhered to the Preferred Reporting Items for Systematic Reviews and MetaAnalysis (PRISMA) guidelines. Current research reports the cytotoxicity against neoplastic cells; the protection against oxidative stress; the suppression of Leishmania major culture growth; the inhibition of protein synthesis; and the antiviral, anti-angiogenic, and antihypercholesterolemic activities of common corncockle. The future prospects of using A. githago saponins as adjuvants in drug formulations and enhancing the cytotoxicity of RIPs are also discussed.

A comprehensive overview on the role of phytocompounds in human immunodeficiency virus treatment

Acquired immune deficiency syndrome (AIDS) is a worldwide epidemic caused by human immunodeficiency virus (HIV) infection. Newer medicines for eliminating the viral reservoir and eradicating the virus are urgently needed. Attempts to locate relatively safe and non-toxic medications from natural resources are ongoing now. Natural-product-based antiviral candidates have been exploited to a limited extent. However, antiviral research is inadequate to counteract for the resistant patterns. Plant-derived bioactive compounds hold promise as powerful pharmacophore scaffolds, which have shown anti-HIV potential. This review focuses on a consideration of the virus, various possible HIV-controlling methods and the recent progress in alternative natural compounds with anti-HIV activity, with a particular emphasis on recent results from natural sources of anti-HIV agents. Please cite this article as: Mandhata CP, Sahoo CR, Padhy RN. A comprehensive overview on the role of phytocompounds in human immunodeficiency virus treatment. J Integr Med. 2023; Epub ahead of print.

Ethnomedicines for the treatment of scorpion stings: A perspective study

ETHNOPHARMACOLOGICAL RELEVANCE

Scorpion sting is a public health concern with limited clinical symptomatic treatment. The clinical treatment uses anti-scorpion antivenom and prazosin (α-adrenergic inhibitor), often in combination with insulin, to reduce scorpion venom-induced hyperglycemia and other complications. However, these therapies also possess some limitations, necessitating urgent exploration of ethnomedicines, mainly traditional medicinal plants, to treat scorpion stings. Unfortunately, several conventional treatments are not scientifically validated, thus raising questions about their quality and utility. Therefore, pharmacological re-assessment of such medicinal plants to alleviate scorpion stings' complications is essential.

AIM OF THE STUDY

The principal objectives of this study are to provide a brief overview of medically important scorpions of the world, outline the extant traditional practices, and comprehensively review plants used in conventional ethnic medicines to treat scorpion stings over time. Modern technological advances in identifying and characterizing plant bioactive molecules are also mentioned in this review.

MATERIALS AND METHODS

The traditionally used medicinal plants against scorpion stings were reviewed from the available literature in the database. The Plant List (http://www.theplantlist.org/) was used to validate the scientific names of the plants mentioned in this study. The search targeted literature on conventional treatments and crude plant extracts or their bioactive components with proven neutralization capacity against scorpion stings. Search words used were 'scorpion sting,' 'treatment for a scorpion sting,' 'antivenom and scorpion sting,' 'traditional treatment for scorpion stings, and 'natural compounds against scorpion stings'.

RESULTS

A list of more than 200 medicinal plants traditionally used in several countries for treating scorpion stings is presented in this review. Though some myth-based remedies are practiced to treat scorpion stings, no empirical evidence exists to validate this aspect of traditional knowledge. Only 38 traditional medicinal plant extracts have been tested under in-vivo and in-vitro conditions to determine their neutralization potency of scorpion envenomation. Although a few bioactive plant constituents showing scorpion venom neutralization potency have been characterized, they are not yet commercially available for clinical application.

CONCLUSIONS

There is tremendous potential locked in medicinal plants' traditional knowledge for scorpion envenomation treatment. Translating this knowledge into the clinical application will require pharmacological reassessment, in tandem with isolation and characterization of active compounds to prove their prophylactic prowess. Almost equally important would be the formulation of stringent strategies to conserve such medicinal plants from overexploitation.

MAP30 and luffin-α: Novel ribosome-inactivating proteins induce plant systemic resistance against plant viruses

Ribosome-inactivating proteins (RIPs) are toxic N-glycosylase that act on eukaryotic and prokaryotic rRNAs, resulting in arrest protein synthesis. RIPs are widely found in higher plant species and display strong antiviral activity. Previous studies have shown that PAP and α-MMC have antiviral activity against TMV. However, the localization of RIPs in plant cells and the mechanism by which RIPs activate plant defense against several plant viruses remain unclear. In this study, we obtained four RIPs (the C-terminal deletion mutant of pokeweed antiviral proteins (PAP-c), alpha-momorcharin (α-MMC), momordica anti-HIV protein of 30 kDa (MAP30) and luffin-α). The subcellular localization results indicated that these four RIPs were located on the plant cell membrane. Heterologous expression of RIPs (PAP-c, α-MMC, MAP30, luffin-α) enhanced tobacco mosaic virus (TMV) resistance in N. benthamiana. Compared with the control treatment, these RIPs significantly reduced the TMV content (149-357 fold) and altered the movement of TMV in the leaves of N. benthamiana. At the same time, heterologous expression of RIPs (MAP30 and luffin-α) could relieve TMV-induced oxidative damage, significantly inducing the expression of plant defense genes including PR1 and PR2. Furthermore, application of these RIPs could inhibit the infection of turnip mosaic virus (TuMV) and potato virus x (PVX). Therefore, this study demonstrated that MAP30 and luffin-α could be considered as new, effective RIPs for controlling plant viruses by activating plant systemic defense.

Expanding role of ribosome-inactivating proteins: From toxins to therapeutics

Ribosome-inactivating proteins (RIPs) are toxic proteins with N-glycosidase activity. RIPs exert their action by removing a specific purine from 28S rRNA, thereby, irreversibly inhibiting the process of protein synthesis. RIPs can target both prokaryotic and eukaryotic cells. In bacteria, the production of RIPs aid in the process of pathogenesis whereas, in plants, the production of these toxins has been attributed to bolster defense against insects, viral, bacterial and fungal pathogens. In recent years, RIPs have been engineered to target a particular cell type, this has fueled various experiments testing the potential role of RIPs in many biomedical applications like anti-viral and anti-tumor therapies in animals as well as anti-pest agents in engineered plants. In this review, we present a comprehensive study of various RIPs, their mode of action, their significance in various fields involving plants and animals. Their potential as treatment options for plant infections and animal diseases is also discussed.

A ricin-based peptide BRIP from Hordeum vulgare inhibits Mpro of SARS-CoV-2

COVID-19 pandemic caused by SARS-CoV-2 led to the research aiming to find the inhibitors of this virus. Towards this world problem, an attempt was made to identify SARS-CoV-2 main protease (Mpro) inhibitory peptides from ricin domains. The ricin-based peptide from barley (BRIP) was able to inhibit Mpro in vitro with an IC50 of 0.52 nM. Its low and no cytotoxicity upto 50 µM suggested its therapeutic potential against SARS-CoV-2. The most favorable binding site on Mpro was identified by molecular docking and steered molecular dynamics (MD) simulations. The Mpro-BRIP interactions were further investigated by evaluating the trajectories for microsecond timescale MD simulations. The structural parameters of Mpro-BRIP complex were stable, and the presence of oppositely charged surfaces on the binding interface of BRIP and Mpro complex further contributed to the overall stability of the protein-peptide complex. Among the components of thermodynamic binding free energy, Van der Waals and electrostatic contributions were most favorable for complex formation. Our findings provide novel insight into the area of inhibitor development against COVID-19.

Lyophyllin, a Mushroom Protein from the Peptidase M35 Superfamily Is an RNA N-Glycosidase

Ribosome-inactivating proteins (RIPs) hydrolyze the N-glycosidic bond and depurinate a specific adenine residue (A-4324 in rat 28S ribosomal RNA, rRNA) in the conserved α-sarcin/ricin loop (α-SRL) of rRNA. In this study, we have purified and characterized lyophyllin, an unconventional RIP from Lyophyllum shimeji, an edible mushroom. The protein resembles peptidase M35 domain of peptidyl-Lys metalloendopeptidases. Nevertheless, protein either from the mushroom or in recombinant form possessed N-glycosidase and protein synthesis inhibitory activities. A homology model of lyophyllin was constructed. It was found that the zinc binding pocket of this protein resembles the catalytic cleft of a classical RIP, with key amino acids that interact with the adenine substrate in the appropriate positions. Mutational studies showed that E122 may play a role in stabilizing the positively charged oxocarbenium ion and H121 for protonating N-3 of adenine. The tyrosine residues Y137 and Y104 may be used for stacking the target adenine ring. This work first shows a protein in the peptidase M35 superfamily based on conserved domain search possessing N-glycosidase activity.

Expression and purification of a recombinant ELRL-MAP30 with dual-targeting anti-tumor bioactivity

MAP30 (Momordica antiviral protein 30kD) is a single-chain Ⅰ-type ribosome inactivating protein with a variety of biological activities, including anti-tumor ability. It was reported that MAP30 would serve as a novel and relatively safe agent for prophylaxis and treatment of liver cancer. To determine whether adding two tumor targeting peptides could improve the antitumor activities of MAP30, we genetically modified MAP30 with an RGD motif and a EGFRi motif, which is a ligand with high affinity for αvβ3 integrins and with high affinity for EGFR. The recombinant protein ELRL-MAP30 (rELRL-MAP30) containing a GST-tag was expressed in E. coli. The rELRL-MAP30 was highly expressed in the soluble fraction after induction with 0.15 mM IPTG for 20 h at 16 °C. The purified rELRL-MAP30 appeared as a band on SDS-PAGE. It was identified by western blotting. Cytotoxicity of recombinant protein to HepG2, MDA-MB-231, HUVEC and MCF-7 cells was detected by MTT analysis. Half maximal inhibitory concentration (IC₅₀) values were 54.64 μg/mL, 70.13 μg/mL, 146 μg/mL, 466.4 μg/mL, respectively. Proliferation inhibition assays indicated that rELRL-MAP30 could inhibit the growth of Human liver cancer cell HepG2 effectively. We found that rELRL-MAP30 significantly induced apoptosis in liver cancer cells, as evidenced by nuclear staining of DAPI. In addition, rELRL-MAP30 induced apoptosis in human liver cancer HepG2 cells by up-regulation of Bax as well as down-regulation of Bcl-2. Migration of cell line were markedly inhibited by rELRL-MAP30 in a dose-dependent manner compared to the recombinant MAP30 (rMAP30). In summary, the fusion protein displaying extremely potent cytotoxicity might be highly effective for tumor therapy.

Trichosanthin cooperates with Granzyme B to restrain tumor formation in tongue squamous cell carcinoma

BACKGROUND

Tongue squamous cell carcinoma (TSCC) is a common type of oral cancer, with a relatively poor prognosis and low post-treatment survival rate. Various strategies and novel drugs to treat TSCC are emerging and under investigation. Trichosanthin (TCS), extracted from the root tubers of Tian-Hua-Fen, has been found to have multiple biological and pharmacological functions, including inhibiting the growth of cancer cells. Granzyme B (GrzB) is a common toxic protein secreted by natural killer cells and cytotoxic T cells. Our group has reported that TCS combined with GrzB might be a superior approach to inhibit liver tumor progression, but data relating to the use of this combination to treat TSCC remain limited. The aim of this study was to examine the effectiveness of TCS on TSCC processes and underlying mechanisms.

METHODS

First, we screened the potential antitumor activity of TCS using two types of SCC cell lines. Subsequently, a subcutaneous squamous cell carcinoma xenograft model in nude mice was established. These model mice were randomly divided into four groups and treated as follows: control group, TCS treatment group, GrzB treatment group, and TCS/GrzB combination treatment group. Various tumorigenesis parameters, such as Ki67, PCNA, caspase-3, Bcl-2 and VEGFA, et al., were performed to determine the effects of these treatments on tumor development.

RESULTS

Screening confirmed that the SCC25 line exhibited greater sensitivity than the SCC15 line to TCS in vitro studies. TCS or GrzB treatment significantly inhibited tumor growth compared with the inhibition seen in the control group. The TCS/GrzB combination inhibited tumor growth more than either drug alone. TCS treatment inhibited tumor proliferation by downregulating Ki67 and Bcl2 protein expression while accelerating tumor apoptosis. In the TCS/GrzB-treated group, expression of Ki67 was further downregulated, while the level of activated caspase-3 was increased, compared with their expression in either of the single drug treatment groups.

CONCLUSION

These results suggest that the TCS/GrzB combination could represent an effective immunotherapy for TSCC.

Antiviral Activity of Ribosome-Inactivating Proteins

Ribosome-inactivating proteins (RIPs) are rRNA N-glycosylases from plants (EC 3.2.2.22) that inactivate ribosomes thus inhibiting protein synthesis. The antiviral properties of RIPs have been investigated for more than four decades. However, interest in these proteins is rising due to the emergence of infectious diseases caused by new viruses and the difficulty in treating viral infections. On the other hand, there is a growing need to control crop diseases without resorting to the use of phytosanitary products which are very harmful to the environment and in this respect, RIPs have been shown as a promising tool that can be used to obtain transgenic plants resistant to viruses. The way in which RIPs exert their antiviral effect continues to be the subject of intense research and several mechanisms of action have been proposed. The purpose of this review is to examine the research studies that deal with this matter, placing special emphasis on the most recent findings.

Structure-Activity-Relationship and Mechanistic Insights for Anti-HIV Natural Products

Acquired Immunodeficiency Syndrome (AIDS), which chiefly originatesfroma retrovirus named Human Immunodeficiency Virus (HIV), has impacted about 70 million people worldwide. Even though several advances have been made in the field of antiretroviral combination therapy, HIV is still responsible for a considerable number of deaths in Africa. The current antiretroviral therapies have achieved success in providing instant HIV suppression but with countless undesirable adverse effects. Presently, the biodiversity of the plant kingdom is being explored by several researchers for the discovery of potent anti-HIV drugs with different mechanisms of action. The primary challenge is to afford a treatment that is free from any sort of risk of drug resistance and serious side effects. Hence, there is a strong demand to evaluate drugs derived from plants as well as their derivatives. Several plants, such as Andrographis paniculata, Dioscorea bulbifera, Aegle marmelos, Wistaria floribunda, Lindera chunii, Xanthoceras sorbifolia and others have displayed significant anti-HIV activity. Here, weattempt to summarize the main results, which focus on the structures of most potent plant-based natural products having anti-HIV activity along with their mechanisms of action and IC50 values, structure-activity-relationships and important key findings.

Engineering of Ribosome-inactivating Proteins for Improving Pharmacological Properties

Ribosome-inactivating proteins (RIPs) are N-glycosidases, which depurinate a specific adenine residue in the conserved α-sarcin/ricin loop (α-SRL) of rRNA. This loop is important for anchoring elongation factor (EF-G for prokaryote or eEF2 for eukaryote) in mRNA translocation. Translation is inhibited after the attack. RIPs therefore may have been applied for anti-cancer, and anti-virus and other therapeutic applications. The main obstacles of treatment with RIPs include short plasma half-life, non-selective cytotoxicity and antigenicity. This review focuses on the strategies used to improve the pharmacological properties of RIPs on human immunodeficiency virus (HIV) and cancers. Coupling with polyethylene glycol (PEG) increases plasma time and reduces antigenicity. RIPs conjugated with antibodies to form immunotoxins increase the selective toxicity to target cells. The prospects for future development on the engineering of RIPs for improving their pharmacological properties are also discussed.

Ligand-Induced Conformational Changes near the Active Site Regulating Enzyme Activity of Momorcharins from Seeds of Bitter Gourd

It is reasonable to consider that Type I-ribosomal inactivation proteins (RIP) retain some specific affinity to harmful pathogens to complete the role as a bio-defense relating protein. In the present studies, it was shown that two Type I-RIPs, α- and β-momorcharins, maintained the abilities to bind with N-acetylglucosamine (NAG) to change the conformation around the active sites and to regulate their N-glycosidase activities. By the binding of NAG, the freedom of internal motion of Trp192 in α-momorcharin was increased 1.5 times near the active site and, on the other hand, the corresponding motion of Trp190 was limited 50% in β-momorcharin. The results in the fluorescence resonance excitation energy transfer experiments demonstrated that Trp-190 of β-momorcharin was kept away from Tyr-70 but Trp192 contrarily approached closer to the nearest neighboring Tyr residue consisting of the active center of α-momorcharin by the binding with NAG. These conformational changes near the active site close correlated with promotion and/or suppression of the N-glucosidase activities of β- and α-momorcharins.

Therapeutic Potential of Luffa acutangula: A Review on Its Traditional Uses, Phytochemistry, Pharmacology and Toxicological Aspects

Luffa acutangula (Cucurbitaceae), a perennial plant grows mainly in India, Southeast Asia, China, Japan, Egypt, and other parts of Africa, it is widely used in the traditional Indian medicinal system to treat various health conditions. The plant has been used in jaundice, diabetes, hemorrhoids, dysentery, headache, ringworm infection, and leprosy. More than 50 chemical compounds have been isolated from a plant which mainly comprises flavonoids, anthraquinones, proteins, fatty acids, saponin triterpene, volatile components, and other phytoconstituents. Crude extract of plant and its isolated compounds possess broad pharmacological activities such as antidiabetic, hepatoprotective, antiulcer, anticancer, immunomodulatory, antihyperlipidemic, antioxidant, antimicrobial, CNS depressant, analgesic, and anti-inflammatory. The toxicological evaluation in preclinical studies reported safety of the plant for human consumption, but comprehensive evaluation in clinical studies is required. However, further investigation is necessary for transformation of experience based treatment of plant into evidence based information. Evaluation of pharmacological activity with indicative biomarkers will help to reveal the mechanism of action of chemical constituents of plant extract. The data from preclinical studies recommends clinical evaluation of safety and efficacy of the plant. The current paper summarizes up-to-date information about a review of the traditional uses, phytochemistry, pharmacological activities, and toxicology to highlight the future prospects of the plant.

Peptide Tk-PQ induces immunosuppression in skin allogeneic transplantation via increasing Foxp3+ Treg and impeding nuclear translocation of NF-κB

Solid organ transplantation is used as the last resort for patients with end-stage disease, but allograft rejection is an unsolved problem. Here, we showed that Tk-PQ, a peptide derived from trichosanthin, had an immune-suppressive effect without obvious cytotoxicity in vitro and in a mouse skin allo-transplantation model. In vitro, treatment of Tk-PQ administrated type 2 T helper cell (Th2)/regulatory T-cell (Treg) cytokines, and increased the ratio of CD4⁺CD25⁺Foxp3⁺ Treg by repressing the PI3K/mTOR pathway. In addition, Tk-PQ decreased NF-κB activation to downregulate pro-inflammatory cytokines. Tk-PQ treatment in the mouse skin transplantation model also caused the similar molecular and cellular phenotypes. Furthermore, Tk-PQ enhanced the suppressive function of Treg by increasing Foxp3 expression, and substantially improved allograft survival. These finding demonstrate that Tk-PQ has the potential to be used in clinical allogeneic transplantation.

Trichosanthin enhances the antitumor effect of gemcitabine in non-small cell lung cancer via inhibition of the PI3K/AKT pathway

Gemcitabine (GEMZ) is the first-line therapy used against non-small cell lung cancer (NSCLC), and studies have focused on investigating the potential effects of agents combined with GEMZ to enhance the anticancer efficacy in NSCLC. Previous studies have reported that trichosanthin (TCS) has various physiological and pharmacological effects, including anti-human influenza virus enzymes, inhibition of protein synthesis and antitumor activity. The purpose of the present study was to investigate if TCS enhanced the antitumor effects of GEMZ in NSCLC. MTT assay demonstrated that TCS significantly enhanced the cytotoxic effect of GEMZ (P>0.05). Furthermore, a propidium iodide/Αnnexin V staining assay revealed that TCS exerted its pharmacological effect by increasing the apoptotic population. In addition, western blot analysis demonstrated that the combination treatment of TCS with GEMZ further decreased the expression level of phosphoinositide 3-kinase (PI3K) and AKT via regulating the expression of insulin growth factor. The results of the present study demonstrated that TCS enhanced the cytotoxic and apoptotic effects of GEMZ in A549 cells via regulating the PI3K/AKT pathway. In conclusion, these observations may provide a potential rational basis for a combination strategy for chemotherapy treatment of NSCLC.

A Review of the Antiviral Properties of Black Elder (Sambucus nigra L.) Products

Black elder (Sambucus nigra L.) has a long ethnobotanical history across many disparate cultures as a treatment for viral infection and is currently one of the most-used medicinal plants worldwide. Until recently, however, substantial scientific research concerning its antiviral properties has been lacking. Here, we evaluate the state of current scientific research concerning the use of elderberry extract and related products as antivirals, particularly in the treatment of influenza, as well as their safety and health impacts as dietary supplements. While the extent of black elder's antiviral effects are not well known, antiviral and antimicrobial properties have been demonstrated in these extracts, and the safety of black elder is reflected by the United States Food and Drug Administration approval as generally recognized as safe. A deficit of studies comparing these S. nigra products and standard antiviral medications makes informed and detailed recommendations for use of S. nigra extracts in medical applications currently impractical. Copyright © 2017 John Wiley & Sons, Ltd.

Trichosanthin-induced autophagy in gastric cancer cell MKN-45 is dependent on reactive oxygen species (ROS) and NF-κB/p53 pathway

Trichosanthin (TCS), isolated from the root tuber of Trichosanthes kirilowii tubers in the Cucurbitaceae family, owns a great deal of biological and pharmacological activities including anti-virus and anti-tumor. TCS has been reported to induce cell apoptosis of a diversity of cancers, including cervical cancer, choriocarcinoma, and gastric cancer, etc. However, whether TCS would induce autophagy in gastric cancer cells was seldom investigated. In current study, human gastric cancer MKN-45 cell growth was significantly inhibited by TCS. The anti-proliferation effect of TCS was due to an increased autophagy, which was confirmed by monodansylcadervarine (MDC) staining, up-regulation of Autophagy protein 5 (Atg5), and conversion of LC3 I to LC3 II (autophagosome marker). In addition, TCS induced reactive oxygen species (ROS) in MKN-45 cells and ROS scavenger N-acetylcysteine (NAC) significantly reversed TCS-induced autophagy. Furthermore, NF-κB/p53 pathway was activated during the process of autophagy induced by TCS and the ROS generation was mediated by it in MKN-45 cells. In vivo results showed that TCS exerted significantly anti-tumor effect on MKN-45 bearing mice. Considering the clinical usage of TCS on other human diseases, these research progresses provided a new insight into cancer research and new therapeutic avenues for patients with gastric cancer.

Biological activities of ribosome-inactivating proteins and their possible applications as antimicrobial, anticancer, and anti-pest agents and in neuroscience research

Ribosome-inactivating proteins (RIPs) are enzymes which depurinate ribosomal RNA (rRNA), thus impeding the process of translation resulting in inhibition of protein synthesis. They are produced by various organisms including plants, fungi and bacteria. RIPs from plants are linked to plant defense due to their antiviral, antifungal, antibacterial, and insecticidal activities in which they can be applied in agriculture to combat microbial pathogens and pests. Their anticancer, antiviral, embryotoxic, and abortifacient properties may find medicinal applications. Besides, conjugation of RIPs with antibodies or other carriers to form immunotoxins has been found useful to research in neuroscience and anticancer therapy.

The recombinant maize ribosome-inactivating protein transiently reduces viral load in SHIV89.6 infected Chinese Rhesus Macaques

Ribosome inactivating proteins (RIPs) inhibit protein synthesis by depurinating the large ribosomal RNA and some are found to possess anti-human immunodeficiency virus (HIV) activity. Maize ribosome inactivating protein (RIP) has an internal inactivation loop which is proteolytically removed for full catalytic activity. Here, we showed that the recombinant active maize RIP protected chimeric simian-human immunodeficiency virus (SHIV) 89.6-infected macaque peripheral blood mononuclear cells from lysis ex vivo and transiently reduced plasma viral load in SHIV89.6-infected rhesus macaque model. No evidence of immune dysregulation and other obvious side-effects was found in the treated macaques. Our work demonstrates the potential development of maize RIP as an anti-HIV agent without impeding systemic immune functions.

Preparation and antitumor effect of a toxin-linked conjugate targeting vascular endothelial growth factor receptor and urokinase plasminogen activator

The aberrant signaling activation of vascular endothelial growth factor receptor (VEGFR) and urokinase plasminogen activator (uPA) is a common characteristic of many tumors, including lung cancer. Accordingly, VEGFR and uPA have emerged as attractive targets for tumor. KDR (Flk-1/VEGFR-2), a member of the VEGFR family, has been recognized as an important target for antiangiogenesis in tumor. In this study, a recombinant immunotoxin was produced to specifically target KDR-expressing tumor vascular endothelial cells and uPA-expressing tumor cells and mediate antitumor angiogenesis and antitumor effect. Based on its potent inhibitory effect on protein synthesis, Luffin-beta (Lβ) ribosome-inactivating protein was selected as part of a recombinant fusion protein, a single-chain variable fragment against KDR (KDRscFv)-uPA cleavage site (uPAcs)-Lβ-KDEL (named as KPLK). The KDRscFv-uPAcs-Lβ-KDEL (KPLK) contained a single-chain variable fragment (scFv) against KDR, uPAcs, Lβ, and the retention signal for endoplasmic reticulum proteins KDEL (Lys-Asp-Glu-Leu). The KPLK-expressing vector was expressed in Escherichia coli, and the KPLK protein was isolated with nickel affinity chromatography and gel filtration chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis test demonstrated KPLK was effectively expressed. Result of in vitro cell viability assay on non-small cell lung cancer (NSCLC) H460 cell line (uPA-positive cell) revealed that KPLK significantly inhibited cell proliferation, induced apoptosis, and accumulated cells in S and G2/M phases, but the normal cell line (human submandibular gland cell) was unaffected. These effects were enhanced when uPA was added to digest KPLK to release Lβ. For in vivo assay of KPLK, subcutaneous xenograft tumor model of nude mice were established with H460 cells. Growth of solid tumors was significantly inhibited in animals treated with KPLK up to 21 days, tumor weights were decreased, and the expression of angiogenesis marker CD31 was downregulated; meanwhile, the apoptosis-related protein casspase-3 was upregulated. These results suggested that the recombinant KPLK may have therapeutic applications on tumors, especially uPA-overexpressing ones.

Sugar binding effects on the enzymatic reaction and conformation near the active site of pokeweed antiviral protein revealed by fluorescence spectroscopy

In various trials for elucidating the physiological function of pokeweed antiviral protein (PAP), studies on the interaction with sugar are essential. The fluorescence titration curves showed that PAP retained the strong affinity against N-acetylglucosamine (NAG) and two sites in one PAP molecule co-operatively participated in the binding. In the complex of PAP with NAG, Trp208 located at the entrance lid site of substrate came closer to Tyr72 about 0.3 Å. Furthermore, the fluorescence anisotropy decay measurement demonstrated that the segmental rotation of Trp208 was enlarged by the binding of PAP with NAG. Such conformational changes around the active site closely correlate with the enzymatic activity of PAP. The N-glycosidase activity of PAP was enhanced more than two times in the presence of NAG. The obtained results consistently suggested the enzymatic activity of PAP would be regulated through the conformation change near the active site induced by the binding with NAG.

Inhibition of HIV-1 replication by balsamin, a ribosome inactivating protein of Momordica balsamina

Ribosome-inactivating proteins (RIPs) are endowed with several medicinal properties, including antiviral activity. We demonstrate here that the recently identified type I RIP from Momordica balsamina also possesses antiviral activity, as determined by viral growth curve assays and single-round infection experiments. Importantly, this activity is at play even as doses where the RIP has no cytotoxic effect. In addition, balsamin inhibits HIV-1 replication not only in T cell lines but also in human primary CD4⁺ T cells. This antiviral compound exerts its activity at a viral replicative step occurring later than reverse-transcription, most likely on viral protein translation, prior to viral budding and release. Finally, we demonstrate that balsamin antiviral activity is broad since it also impedes influenza virus replication. Altogether our results demonstrate that type I RIP can exert a potent anti-HIV-1 activity which paves the way for new therapeutic avenues for the treatment of viral infections.

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.

Structural characteristic of folding/unfolding intermediate of pokeweed anti-viral protein revealed by time-resolved fluorescence

The structural feature of unfolding intermediate of pokeweed anti-viral protein (PAP) was characterized using time-resolved fluorescence spectroscopic methods to elucidate protein folding/unfolding process. CD and fluorescence spectra consistently demonstrated that the unfolding of PAP completed at 4 M of guanidine hydrochloride (GuHCl). The fluorescence resonance energy transfer (FRET) and time-resolve fluorescence depolarization analysis of Trp208 and Trp237 located in the C-terminal domain of PAP suggested that peculiar unfolding intermediate populated before reaching to the unfolding state. The FRET distance of Trp237 to Tyr182 was extended to more than 28 Å with keeping the compact conformation in the unfolding intermediate state populated in the presence of 2 M GuHCl. On the other hand, Trp208 maintained the energy transfer pair with Tyr72 near the active site, although the rotational freedom was increased a little. There results suggest that the most distinguished structural feature of the unfolding intermediate of PAP is the separation of C-terminal domain from N-terminal domain. FRET and fluorescence depolarization studies also showed that C-terminal domain would be more separated to liberate the segmental motions of Trp208 and Trp237 distinctly at the unfolding state.

Ribosome-inactivating proteins with an emphasis on bacterial RIPs and their potential medical applications

Ribosome-inactivating proteins (RIPs) are toxic due to their N-glycosidase activity catalyzing depurination at the universally conserved α-sarcin loop of the 60S ribosomal subunit. In addition, RIPs have been shown to also have other enzymatic activities, including polynucleotide:adenosine glycosidase activity. RIPs are mainly produced by different plant species, but are additionally found in a number of bacteria, fungi, algae and some mammalian tissues. This review describes the occurrence of RIPs, with special emphasis on bacterial RIPs, including the Shiga toxin and RIP in Streptomyces coelicolor recently identified in S. coelicolor. The properties of RIPs, such as enzymatic activity and targeting specificity, and how their unique biological activity could be potentially turned into medical or agricultural tools to combat tumors, viruses and fungi, are highlighted.

Enhanced cytotoxic activity of a bifunctional chimeric protein containing a type 1 ribosome-inactivating protein and a serine protease inhibitor

Both ribosome-inactivating proteins (RIPs) and plant proteinase inhibitors, belong to protein families known to regulate cellular homeostasis and likely involved in plant defense. Nevertheless the interest in these protein classes is due to their potential use for the treatment of several important human diseases such as cancer. Thus, in the present study, type 1 ribosome-inactivating protein and wheat subtilisin/chymotrypsin inhibitor, were engineered into a chimeric protein with cytotoxic action selective for murine tumor cells, while lacking any appreciable toxicity on murine normal cells. This chimeric protein selectively sensitizes to apoptotic death cells derived from Simian-virus-40-transformed mouse fibroblasts (SVT2 cells). The cytotoxicity of this new recombinant product has been detected also on three different human malignant cells. Therefore action on tumor cells of this protein could represent a potentially very attractive novel tool for anticancer drug design.

Immunoaffinity purification of α-momorcharin from bitter melon seeds (Momordica charantia)

α-Momorcharin (α-MMC), a type I ribosome-inactivating protein (RIP), has shown therapeutic potential such as anti-tumor and anti-viral agent. Traditional process of α-MMC purification from bitter melon seeds was time consuming and low efficient. To take this challenge, we made an affinity matrix by coupling the monoclonal antibody (McAb) with Sepharose 4B. Using this attractive strategy, 196 mg of α-MMC was obtained from 100 g of bitter melon seeds as the starting material. The yield of the protein was 2.7%. The homogeneity and properties of the protein were assessed by SDS-PAGE, acidic PAGE, RP-HPLC and N-terminal sequence as well as Western blot. Purified α-MMC showed remarkable inhibition to the melanoma cell line JAR and EMT-62058. In addition, it also displayed obvious inhibition on hepatitis B virus (HBV). This work provided a simple, rapid and efficient approach for α-MMC purification from Momordica charantia.

Effects of cathelicidin and its fragments on three key enzymes of HIV-1

Cathelicidins exhibit anti-HIV activity but it is not known if they reduce the activity of enzymes crucial to the life cycle of the retrovirus. It is shown in this investigation that human cathelicidin LL37 and its fragments LL13-37 and LL17-32 inhibited HIV-1 reverse transcriptase dose-dependently with an IC50 value of 15μM, 7μM, and 70μM, respectively. The three peptides inhibited HIV-1 protease with a weak potency, achieving 20-30% inhibition at 100μM. The mechanism of inhibition was protein-protein interaction as revealed by surface plasmon resonance. The peptides were devoid of the ability to inhibit translocation of HIV-1 integrase, which has been labeled with green fluorescent protein, into the nucleus. The peptides did not exert toxicity on human peripheral blood mononuclear cells.

Cloning and soluble expression of mature alpha-luffin from Luffa cylindrica and its antitumor activities in vitro

Luffin-a, a single-chain Type I ribosome-inactivating protein, which is known to be the most toxic of the luffin family and apparently possesses antitumor activity, was isolated from Luffa cylindrica seeds. In the present study, mature alpha-luffin was cloned from L. cylindrica and it was found that mature alpha-luffin shared 96% amino acid similarity with luffin-a. The recombinant mature alpha-luffin was successfully expressed in a partly soluble form in Escherichia coli after optimization of expression conditions. The effects of the recombinant protein on bacterial growth and its in vitro protein synthesis inhibition activity were tested. Then, its antitumor activities against different human cancer cell lines were evaluated by CCK-8 assay and flow cytometry. The results indicated that the recombinant alpha-luffin was slightly toxic to E. coli. It could inhibit protein synthesis in the rabbit reticulocyte lysate system. At the same time, it inhibited the growth of the tumor cell lines in a dose- and time-dependent manner. Additionally, recombinant alpha-luffin was able to induce cell death by apoptosis. The cytotoxicity of alpha-luffin towards tumor cells makes it a potential antitumor agent.

The Okinawan diet: health implications of a low-calorie, nutrient-dense, antioxidant-rich dietary pattern low in glycemic load

Residents of Okinawa, the southernmost prefecture of Japan, are known for their long average life expectancy, high numbers of centenarians, and accompanying low risk of age-associated diseases. Much of the longevity advantage in Okinawa is thought to be related to a healthy lifestyle, particularly the traditional diet, which is low in calories yet nutritionally dense, especially with regard to phytonutrients in the form of antioxidants and flavonoids. Research suggests that diets associated with a reduced risk of chronic diseases are similar to the traditional Okinawan diet, that is, vegetable and fruit heavy (therefore phytonutrient and antioxidant rich) but reduced in meat, refined grains, saturated fat, sugar, salt, and full-fat dairy products. Many of the characteristics of the diet in Okinawa are shared with other healthy dietary patterns, such as the traditional Mediterranean diet or the modern DASH (Dietary Approaches to Stop Hypertension) diet. Features such as the low levels of saturated fat, high antioxidant intake, and low glycemic load in these diets are likely contributing to a decreased risk for cardiovascular disease, some cancers, and other chronic diseases through multiple mechanisms, including reduced oxidative stress. A comparison of the nutrient profiles of the three dietary patterns shows that the traditional Okinawan diet is the lowest in fat intake, particularly in terms of saturated fat, and highest in carbohydrate intake, in keeping with the very high intake of antioxidant-rich yet calorie-poor orange-yellow root vegetables, such as sweet potatoes, and green leafy vegetables. Deeper analyses of the individual components of the Okinawan diet reveal that many of the traditional foods, herbs, or spices consumed on a regular basis could be labeled "functional foods" and, indeed, are currently being explored for their potential health-enhancing properties.

Brassiparin, an antifungal peptide from Brassica parachinensis seeds

Aims:  To isolate and characterize an antifungal peptide from the seeds of Brassica parachinensis L.H.Bailey.

Methods and Results:  An antifungal peptide designated as brassiparin was isolated. It exhibited a molecular mass of 5716 Da. It potently inhibited mycelial growth in a number of fungal species including Fusarium oxysporum, Helminthosporium maydis, Mycosphaerella arachidicola and Valsa mali. The antifungal activity of brassiparin toward M. arachidicola exhibited pronounced thermostability and pH stability. It inhibited proliferation of hepatoma (HepG2) and breast cancer (MCF7) cells and the activity of HIV‐1 reverse transcriptase. Its N‐terminal sequence differed from those of antifungal proteins which have been reported to date.

Conclusions:  Brassiparin can be purified by using a protocol involving ion exchange chromatography, affinity chromatography and gel filtration. It manifests potent, thermostable and pH‐stable antifungal activity. It demonstrates antiproliferative activity toward tumour cells, and inhibitory activity toward HIV‐1 reverse transcriptase. Thus, brassiparin is a defense protein.

Significance and Impact of the Study:  Brassiparin represents one of the few antifungal proteins reported to date from Brassica species. Its antifungal activity has pronounced pH stability and thermostability. Brassiparin exhibits other exploitable activities such as antiproliferative activity toward hepatoma and breast cancer cells and inhibitory activity toward HIV‐reverse transcriptase.

The anti-viral protein of trichosanthin penetrates into human immunodeficiency virus type 1

Trichosanthin (TCS) is a type I ribosome-inactivating protein with potent inhibitory activity against human immunodeficiency virus type 1, and has been clinically applied in acquired immunodeficiency syndrome (AIDS) therapy. Previous studies revealed that TCS recognized human immunodeficiency virus type 1 (HIV-1) particles. Here, we investigated the physical relationship between TCS and HIV-1 particles, and demonstrated that TCS penetrates into viral particles, where it is protected from various protease digestion. The penetration of TCS exerts no obvious effect on viral integrity. FYY140-142, D176, and K177 were identified as key amino acid residues for the membranetranslocation process. Moreover, TCS penetrated into HIV-1 virions showed potent anti-viral activity. Overall, the observations suggest that the penetration of TCS into HIV-1 particles may be important for eliminating the virus.

Trichosanthin inhibits integration of human immunodeficiency virus type 1 through depurinating the long-terminal repeats

Trichosanthin (TCS) is a type I ribosome-inactivating protein with potent inhibitory activity against human immunodeficiency virus type 1. However, the anti-viral mechanism remains elusive. By a well-accepted HIV-1 integration assay, we demonstrated that TCS prevents HIV-1 DNA integration in a dose dependent manner in cell culture. At the same condition, TCS fails to induce obvious cytotoxicity and is also unable to interference viral early events such as viral entry, uncoating or reverse transcription. The HIV-1 integrase can integrate HIV-1 long-terminal repeats into cellular chromosome. The interaction of TCS with these viral integration components was also examined, indicating that TCS does not interact with HIV-1 integrase by the GST-pull down assay, but binds to the long terminal repeats in a transient manner. We further revealed that TCS can efficiently depurinate HIV-1 long-terminal repeats, which may be responsible for the inhibitory activity on HIV-1 integration. In conclusion, we elucidated that TCS specifically inhibits HIV-1 integration by depurinating the long-terminal repeats.

Preparation and biological properties of a melibiose binding lectin from Bauhinia variegata seeds

A dimeric 64-kDa melibiose-binding lectin was isolated from the seeds of Bauhinia variegata. The isolation procedure comprised affinity chromatography on Affi-gel blue gel, ion exchange chromatography on Mono Q, and gel filtration on Superdex 75. The lectin was adsorbed on the first two chromatographic media. Its hemagglutinating activity was stable after 30-min exposure to temperatures up to 70 degrees C. Since lectins may demonstrate biological activities such as antiproliferative, immunomodulatory, antifungal, antiviral, and HIV-1 reverse transcriptase inhibitory activities, the isolated lectin was tested for these activities. It was found that the lectin inhibited proliferation in hepatoma HepG2 cells and breast cancer MCF7 cells with an IC(50) of 1.4 microM and 0.18 microM, respectively. HIV-1 reverse transcriptase activity was inhibited with an IC(50) of 1.02 microM. The lectin and concanavalin A (Con A) evoked maximal mitogenic response from mouse splenocytes at similar concentrations, but the maximal response to B. variegata lectin was only 1/5 of that induced by Con A in magnitude. B. variegata lectin was devoid of antifungal activity.

A stable trypsin inhibitor from Chinese dull black soybeans with potentially exploitable activities

A dimeric 40-kDa Kunitz-type trypsin inhibitor was isolated from seeds of the Chinese black soybean Glycine max cv. ‘Dull Black’. The purification protocol comprised ion exchange chromatography on Q-Sepharose, SP-Sepharose, and Mono Q, and gel filtration on Superdex 75. The trypsin inhibitor inhibited chymotrypsin, albeit to a lesser extent than it inhibited trypsin. Its trypsin-inhibitory activity was unaffected after exposure to pH 1–14, or to temperatures up to 80 °C. The trypsin inhibitor was inhibited by dithiothreitol in a dose-dependent (from 2.5 to 50 mM) and a time-dependent (from 5 to 120 min) manner. Besides inhibiting serine proteases, the trypsin inhibitor demonstrated additional biological activities including stimulation of nitric oxide production by macrophages. It inhibited HIV-1 reverse transcriptase, cell-free translation and proliferation of liver cancer cells and breast cancer cells, with an IC₅₀ value 9.4, 14, 39 and 70 μM, respectively. However, it did not exhibit antifungal, antibacterial or mitogenic activity.

Suppression of HIV replication using RNA interference against HIV-1 integrase

RNA interference (RNAi) has become one of the most powerful and popular approach on gene silencing in clinical research study especially in virology due to the gene-specific suppression property of small interfering RNA (siRNA). In this report, we demonstrate that expression of vector-mediated small hairpin RNA (shRNA) against human immunodeficiency virus type 1 (HIV-1) integrase (IN), one of the three important enzymes in HIV infection by controlling the integration of viral RNA to host DNA, could suppress the protein synthesis of EGFP-tagged IN in HeLa cell model efficiently. Furthermore, we show that IN shRNA can successfully reduce the HIV particles production in 293T cells at the level similar to the positive control of HIV-1 tat shRNA. These results provide the therapeutic possibility of HIV replication using RNAi against HIV-1 integrase.

X-ray sequence and crystal structure of luffaculin 1, a novel type 1 ribosome-inactivating protein

Background

Protein sequence can be obtained through Edman degradation, mass spectrometry, or cDNA sequencing. High resolution X-ray crystallography can also be used to derive protein sequence information, but faces the difficulty in distinguishing the Asp/Asn, Glu/Gln, and Val/Thr pairs. Luffaculin 1 is a new type 1 ribosome-inactivating protein (RIP) isolated from the seeds of Luffa acutangula. Besides rRNA N-glycosidase activity, luffaculin 1 also demonstrates activities including inhibiting tumor cells' proliferation and inducing tumor cells' differentiation.

Results

The crystal structure of luffaculin 1 was determined at 1.4 Å resolution. Its amino-acid sequence was derived from this high resolution structure using the following criteria: 1) high resolution electron density; 2) comparison of electron density between two molecules that exist in the same crystal; 3) evaluation of the chemical environment of residues to break down the sequence assignment ambiguity in residue pairs Glu/Gln, Asp/Asn, and Val/Thr; 4) comparison with sequences of the homologous proteins. Using the criteria 1 and 2, 66% of the residues can be assigned. By incorporating with criterion 3, 86% of the residues were assigned, suggesting the effectiveness of chemical environment evaluation in breaking down residue ambiguity. In total, 94% of the luffaculin 1 sequence was assigned with high confidence using this improved X-ray sequencing strategy. Two N-acetylglucosamine moieties, linked respectively to the residues Asn77 and Asn84, can be identified in the structure. Residues Tyr70, Tyr110, Glu159 and Arg162 define the active site of luffaculin 1 as an RNA N-glycosidase.

Conclusion

X-ray sequencing method can be effective to derive sequence information of proteins. The evaluation of the chemical environment of residues is a useful method to break down the assignment ambiguity in Glu/Gln, Asp/Asn, and Val/Thr pairs. The sequence and the crystal structure confirm that luffaculin 1 is a new type 1 RIP.

The non-toxic A subunit of Shiga toxin type 1 prevents replication of bovine immunodeficiency virus in infected cells

Shiga toxins are ribosome-inactivating proteins many of which are antiviral. Shiga toxin-producing Escherichia coli (STEC) may be pathogenic to humans, but are carried without ill effects by ruminants. We hypothesize that STEC have antiviral activity in ruminants, and showed previously that the non-toxic subunit A of Shiga toxin 1 (StxA1) acts selectively on cells infected with bovine leukemia virus, without harming normal cells, and that the numbers of intestinal STEC are inversely correlated with viral load in bovine leukemia virus-infected sheep. The purpose of the present study was to characterize StxA1 activity against a second bovine retrovirus, bovine immunodeficiency virus (BIV). Flow cytometry showed that StxA1 treatment induced apoptosis in BIV-infected cells but not in uninfected cells and immunoblot analysis showed that StxA1 curtailed synthesis of Gag p26 protein. A systematic electron microscopy description of BIV infection in fetal bovine lung fibroblasts showed an orderly sequence of changes in cell membrane, endoplasmic reticulum, Golgi, nucleus, and mitochondria, and suggested that the infected cells produce the virus within multivesicular bodies (MVBs). StxA1 interfered with all manifestations of BIV-induced transformation of infected cells into BIV-producing units. BIV-infected cells provided a suitable experimental system for investigation of the mechanism of Stx-antiviral activity.

Differential sensitivity of viruses to the antiviral activity of Shiga toxin 1 A subunit

The non-toxic enzymic A subunit of Shiga toxin 1 (StxA1) reduces expression and replication of the bovine retroviruses, bovine leukemia virus and bovine immunodeficiency virus (BIV). Here, the impact of StxA1 on representative positive and negative stranded RNA viruses was compared. BIV and equine infectious anemia virus were sensitive to picomolar concentrations of StxA1 while poliovirus, rhinovirus, and vesicular stomatitis virus were only marginally sensitive to nanomolar concentrations of toxin. Thus, the length of the reproductive cycle and/or other factors, but not viral encapsulation may play a role in determining sensitivity to StxA1. The effects of StxA1 at concentrations from 0.01 to 10 microg/ml on the most sensitive virus (BIV-infected cultures of fetal bovine lung cells) were analyzed by electron microscopy 48 h post challenge. Cells treated with 0.1 microg StxA1/ml or higher toxin concentrations were similar in appearance and showed progressively fewer viral factories with increasing toxin concentration. However, cells treated with 0.01 microg/ml StxA1 had a radically different appearance, exhibiting smooth cell membranes and high vacuolization. These results showed that complex retroviruses were more sensitive to StxA1 than single-stranded RNA viruses and that StxA1 interfered with retroviral replication in a concentration-dependent manner.