Plant Extracellular Vesicles and Nanovesicles: Focus on Secondary Metabolites, Proteins and Lipids with Perspectives on Their Potential and Sources.

While human extracellular vesicles (EVs) have attracted a big deal of interest and have been extensively characterized over the last years, plant-derived EVs and nanovesicles have earned less attention and have remained poorly investigated. Although a series of investigations already revealed promising beneficial health effects and drug delivery properties, adequate (pre)clinical studies are rare. This fact might be caused by a lack of sources with appropriate qualities. Our study introduces plant cell suspension culture as a new and well controllable source for plant EVs. Plant cells, cultured in vitro, release EVs into the growth medium which could be harvested for pharmaceutical applications. In this investigation we characterized EVs and nanovesicles from distinct sources. Our findings regarding secondary metabolites indicate that these might not be packaged into EVs in an active manner but enriched in the membrane when lipophilic enough, since apparently lipophilic compounds were associated with nanovesicles while more hydrophilic structures were not consistently found. In addition, protein identification revealed a possible explanation for the mechanism of EV cell wall passage in plants, since cell wall hydrolases like 1,3-ß-glucosidases, pectinesterases, polygalacturonases, ß-galactosidases and ß-xylosidase/α-L-arabinofuranosidase 2-like are present in plant EVs and nanovesicles which might facilitate cell wall transition. Further on, the identified proteins indicate that plant cells secrete EVs using similar mechanisms as animal cells to release exosomes and microvesicles.

Extracellular Vesicles from Fresh and Dried Plants-Simultaneous Purification and Visualization Using Gel Electrophoresis.

Although animal-derived extracellular vesicles (EVs) are moving increasingly into scientific focus, EVs from other kingdoms remain underestimated and our knowledge of them is still expandable, probably due to the lack of an easy and broadly executable isolation, purification and visualization method. Using differential centrifugation with subsequent agarose gel electrophoresis, we were able to simplify the terms of EV isolation. EVs from Nicotiana tabacum L., Vinca minor L., and Viscum album L. were purified, even though they did not migrate into the gel matrix. If 3,3- Dihexyloxacarbocyanine iodide (DiOC 6 ) is added to the specimen in excess, membranous components can already be detected by eye, or with higher sensitivity, using a UV transilluminator. The sample preparation can be adjusted to the EV species of interest. Moreover, EVs are separated from small charged contaminants and dye excess, because these impurities can pass the gel matrix, while EVs themselves are retained in the pocket. Significantly, we isolated EVs from dried plant material, which is-to our knowledge-the first proof that EVs are stable enough to overcome the drying process of plant material.

Extracellular Vesicles-Connecting Kingdoms.

It is known that extracellular vesicles (EVs) are shed from cells of almost every type of cell or organism, showing their ubiquity in all empires of life. EVs are defined as naturally released particles from cells, delimited by a lipid bilayer, and cannot replicate. These nano- to micrometer scaled spheres shuttle a set of bioactive molecules. EVs are of great interest as vehicles for drug targeting and in fundamental biological research, but in vitro culture of animal cells usually achieves only small yields. The exploration of other biological kingdoms promises comprehensive knowledge on EVs broadening the opportunities for basic understanding and therapeutic use. Thus, plants might be sustainable biofactories producing nontoxic and highly specific nanovectors, whereas bacterial and fungal EVs are promising vaccines for the prevention of infectious diseases. Importantly, EVs from different eukaryotic and prokaryotic kingdoms are involved in many processes including host-pathogen interactions, spreading of resistances, and plant diseases. More extensive knowledge of inter-species and interkingdom regulation could provide advantages for preventing and treating pests and pathogens. In this review, we present a comprehensive overview of EVs derived from eukaryota and prokaryota and we discuss how better understanding of their intercommunication role provides opportunities for both fundamental and applied biology.

Suicide nanoplasmids coding for ribosome-inactivating proteins.

Conventional eukaryotic expression plasmids contain a DNA backbone that is dispensable for the cellular expression of the transgene. In order to reduce the vector size, minicircle DNA technology was introduced. A drawback of the minicircle technology are considerable production costs. Nanoplasmids are a relatively new class of mini-DNA constructs that are of tremendous potential for pharmaceutical applications. In this study we have designed novel suicide nanoplasmid constructs coding for plant derived ribosome-inactivating proteins. The suicide-nanoplasmids were formulated with a targeted K16-lysine domain, analyzed for size, and characterized by electron microscopy. The anti-proliferative activity of the suicide-nanoplasmids was investigated in vitro by real time microscopy and the expression kinetic was determined using an enhanced green fluorescent protein nanoplasmid variant. In an aggressive in vivo neuroblastoma tumor model, treated mice showed a reduced tumor growth whereby the therapy was well tolerated.

Targeted suicide gene transfections reveal promising results in nu/nu mice with aggressive neuroblastoma.

Neuroblastoma represents the third most common malign neoplasm occurring in children and the most common in newborn. Although mortality in childhood cancer declined in the last decade, high-risk patients have poor prospects, due to the aggressiveness of the cancer. In the recent past, we underlined the potential of sapofectosid as novel and efficient transfection enhancer, demonstrating non-toxic gene delivery, but its value in tumor therapies has yet to be elucidated. A suicide gene, coding for saporin, a ribosome-inactivating protein type I, was incorporated into targeted, peptide-based nanoplexes. The nanoplexes were characterized for their size, zeta potential and appearance by electron microscopy. Gene delivery was observed via confocal imaging. In vitro transfections were conducted to monitor the real-time cell viability. After initial tolerability studies, NMRI nu/nu-mice bearing tumors from Neuro-2A-Luc-cells (murine neuroblastoma cells, transduced with a luciferase gene), were treated with targeted nanoplexes (30 µg saporin-DNA i.v./treatment) and sapofectosid (30 µg s.c. treatment). The treatment was compared to a vehicle (PBS) control and treatment without sapofectosid in terms of body weight, tumor growth and integrated density of tumor luminescence. The study revealed an anti-tumoral effect of the sapofectosid mediated gene therapy in the Neuro-2A-tumor model. The treatments were well tolerated by the animals indicating the applicability of this approach. With these results, we were able to proof the efficacy of a therapy, consisting of targeted suicide gene nanoplexes and sapofectosid, a novel and potent transfection enhancer. This study points out the enormous value for future targeted cancer and gene therapies.

Sapofectosid - Ensuring non-toxic and effective DNA and RNA delivery.

Different methods are being deployed for non-viral DNA/RNA delivery. However non-viral formulations for DNA/RNA-delivery are often accompanied by severe toxicity and thus low efficiency. Particular costly cell culture media are required as well. Here we introduce sapofection as a valuable enhancing method for non-viral DNA/RNA delivery. Sapofection is based on the application of DNA/RNA nanoplexes and sapofectosid, a plant derived natural transfection reagent. Sapofectosid was produced from plant raw material by chromatographic methods and characterized by tandem mass spectrometry and intensive one and two dimensional NMR-spectroscopy. Sapofectosid did enhance the transfection efficiency of different DNA- and RNA-nanoplexes formulated with liposomes, polyethylenimine (PEI) or targeted and non-targeted oligo-lysine peptides. All nanoplexes were characterized physicochemically and the influence of sapofectosid on the nanoplex integrity was determined by DNA complexation assays. The nanoplexes and sapofectosid were administered to a variety of cancer cell lines and the transfection efficiency was investigated by flow cytometry and confocal microscopy. Dependent on the cell line the transfection efficiencies varied from 6 to 76%. The saponin- and receptor-mediated endocytosis of nanoplexes was investigated by flow cytometry. As demonstrated by impedance based live cell imaging sapofection was non-toxic. The findings show the great potential of sapofection to be used as an effective and non-toxic transfection enhancing method.