Nanoparticles reveal that human cervicovaginal mucus is riddled with pores larger than viruses.

The mechanisms by which mucus helps prevent viruses from infecting mucosal surfaces are not well understood. We engineered non-mucoadhesive nanoparticles of various sizes and used them as probes to determine the spacing between mucin fibers (pore sizes) in fresh undiluted human cervicovaginal mucus (CVM) obtained from volunteers with healthy vaginal microflora. We found that most pores in CVM have diameters significantly larger than human viruses (average pore size 340 +/- 70 nm; range approximately 50-1800 nm). This mesh structure is substantially more open than the 15-100-nm spacing expected assuming mucus consists primarily of a random array of individual mucin fibers. Addition of a nonionic detergent to CVM caused the average pore size to decrease to 130 +/- 50 nm. This suggests hydrophobic interactions between lipid-coated "naked" protein regions on mucins normally cause mucin fibers to self-condense and/or bundle with other fibers, creating mucin "cables" at least three times thicker than individual mucin fibers. Although the native mesh structure is not tight enough to trap most viruses, we found that herpes simplex virus (approximately 180 nm) was strongly trapped in CVM, moving at least 8,000-fold slower than non-mucoadhesive 200-nm nanoparticles. This work provides an accurate measurement of the pore structure of fresh, hydrated ex vivo CVM and demonstrates that mucoadhesion, rather than steric obstruction, may be a critical protective mechanism against a major sexually transmitted virus and perhaps other viruses.

Human immunodeficiency virus type 1 is trapped by acidic but not by neutralized human cervicovaginal mucus.

To reliably infect a primate model for human immunodeficiency virus (HIV), approximately 10,000-fold more virus must be delivered vaginally than intravenously. However, the vaginal mechanisms that help protect against HIV are poorly understood. Here, we report that human cervicovaginal mucus (CVM), obtained from donors with normal lactobacillus-dominated vaginal flora, efficiently traps HIV, causing it to diffuse more than 1,000-fold more slowly than it does in water. Lactobacilli acidify CVM to pH approximately 4 by continuously producing lactic acid. At this acidic pH, we found that lactic acid, but not HCl, abolished the negative surface charge on HIV without lysing the virus membrane. In contrast, in CVM neutralized to pH 6 to 7, as occurs when semen temporarily neutralizes the vagina, HIV maintained its native surface charge and diffused only 15-fold more slowly than it would in water. Thus, methods that can maintain both a high lactic acid content and acidity for CVM during coitus may contribute to both vaginal and penile protection by trapping HIV before it can reach target cells. Our results reveal that CVM likely plays an important but currently unappreciated role in decreasing the rate of HIV sexual transmission.

Sites in the AAV5 capsid tolerant to deletions and tandem duplications.

Gene therapy vectors based on adeno-associated virus (AAV) have shown much promise in clinical trials for the treatment of a variety of diseases. However, the ability to manipulate and engineer the viral surface for enhanced efficiency is necessary to overcome such barriers as pre-existing immunity and transduction of non-target cells that currently limit AAV applications. Although single amino acid changes and peptide insertions at select sites have been explored previously, the tolerance of AAV to small deletions and tandem duplications of sequence has not been globally addressed. Here, we have generated a large, diverse library of >10(5) members containing deletions and tandem duplications throughout the viral capsid of AAV5. Four unique mutants were identified that maintain the ability to form viral particles, with one showing improved transduction on both 293T and BEAS-2B cells. This approach may find potential use for the generation of novel variants with improved and altered properties or in the identification of sites that are tolerant to insertions of targeting ligands.

Evaluation of U.S. Food and Drug Administration Enteric Viruses Microarray for Detection of Hepatitis A Virus and Norovirus in Inoculated Tomatoes, Green Onions, and Celery.

ABSTRACT: Foodborne viral contamination of fresh produce has been associated with numerous outbreaks. Detection of such contaminated foods is important in protecting public health. Here, we demonstrate for the first time the capability of the U.S. Food and Drug Administration Enteric Viruses tiling microarray (FDA-EVIR) to perform rapid molecular identification of hepatitis A virus (HAV) and human norovirus extracted from artificially inoculated fresh produce. Two published viral extraction strategies, total RNA extraction or virus particle isolation, were used to prepare the viral targets. The total RNA extraction method was used on material eluted from tomatoes, using an alkaline Tris-glycine-beef extract (TGBE) buffer. Optimization procedures including DNase treatment and poly(A)-RNA enrichment were adopted to improve microarray sensitivity. For green onions or celery, material was eluted using either glycine buffer or TGBE buffer supplemented with pectinase, respectively, and then virus particles were concentrated by ultracentrifugation. We also assessed the amount of viral RNA extracted from celery using three commercially available kits and how well that RNA performed on FDA-EVIR. Our results confirm that FDA-EVIR can identify common enteric viruses isolated from fresh produce when present as either a single or mixed species of viruses. Using total RNA extraction from tomatoes yielded a limit of detection of 1.0 × 105 genome equivalents (ge) of HAV per array input. The limit of detection for viral RNA obtained using ultracentrifugation was 1.2 × 105 ge of HAV from green onions and 1.0 × 103 ge of norovirus from celery per array input. Extending microarray methods to other food matrices should provide important support to surveillance and outbreak investigations.

Testing for Human Norovirus and Recovery of Process Control in Outbreak-Associated Produce Items.

The development of rapid and sensitive detection methods for human noroviruses (HuNoV) in produce items is critical, especially with the recent rise in outbreaks associated with this food commodity. In this study, 50-g portions of various produce items linked to a norovirus outbreak (celery, cucumber, lettuce, grapes, and radish) were artificially inoculated with murine norovirus (MNV-1) and concentrated either by ultracentrifugation or polyethylene glycol (PEG) precipitation after elution with an alkaline Tris-glycine-beef extract buffer supplemented with pectinase. As a viral concentration step following virus elution and clarification, ultracentrifugation yielded a faster method (<8 h, including reverse transcription quantitative PCR), with MNV-1 recoveries similar to or better, than those obtained with PEG precipitation. The addition of polyvinylpyrrolidone to the elution buffer, to remove polyphenolic inhibitors, improved MNV-1 recoveries by over two- and fivefold for cucumber and grapes, respectively. However, despite MNV-1 recoveries ranging from 10 to 38% as calculated with 10-fold diluted RNA, contaminating HuNoV was not detected in any of the outbreak-associated samples tested. For store-bought produce samples, the limit of detection for artificially seeded HuNoV GII.4 was determined to be 103 copies per 50 g, with reproducible detection achieved in grapes, radish, and celery. The results support the use of ultracentrifugation as an alternative approach to PEG precipitation to concentrate norovirus from a variety of produce items.

Directed evolution for drug and nucleic acid delivery.

Directed evolution is a term used to describe a variety of related techniques to rapidly evolve peptides and proteins into new forms that exhibit improved properties for specific applications. In this process, molecular biology techniques allow the creation of up to billions of mutants in a single experiment, which are then subjected to high-throughput screening to identify those with enhanced activity. Applications of directed evolution to drug and gene delivery have been recently described, including those that improve the effectiveness of therapeutic enzymes, targeting peptides and antibodies, and the effectiveness or tropism of viral vectors for use in gene therapy. This review first introduces fundamental concepts of directed evolution, and then discusses emerging applications in the field of drug and gene delivery.

Privileged delivery of polymer nanoparticles to the perinuclear region of live cells via a non-clathrin, non-degradative pathway.

The efficacy of many therapeutic molecules could be greatly enhanced by polymer-based nanoparticle systems capable of delivering them to the direct vicinity of the cell nucleus. However, degradation of the particles and encapsulated drugs within the enzyme-rich and low-pH environments of the endo/lysosomal pathway of cells has dramatically limited the efficacy of such systems. In this paper, we discovered that small polymeric particles (<25 nm) but not larger particles (>42 nm) enter live cells via a novel mechanism that leads to trafficking outside the endo/lysosomal pathway. Sub-25 nm particles rapidly transport to the perinuclear region of cells in vesicles that never acidify. The pathway is non-degradative, cholesterol independent, and non-clathrin and non-caveolae mediated. This privileged non-acidic pathway may be general since our results are surprisingly obtained with standard latex polymer beads without addition of ligands and may, therefore, provide a promising route for drug and gene delivery using biomaterial-based nanodevices.

Targeting glycosylation pathways and the cell cycle: sugar-dependent activity of butyrate-carbohydrate cancer prodrugs.

Short-chain fatty acid (SCFA)-carbohydrate hybrid molecules that target both histone deacetylation and glycosylation pathways to achieve sugar-dependent activity against cancer cells are described in this article. Specifically, n-butyrate esters of N-acetyl-D-mannosamine (But4ManNAc, 1) induced apoptosis, whereas corresponding N-acetyl-D-glucosamine (But4GlcNAc, 2), D-mannose (But5Man, 3), or glycerol (tributryin, 4) derivatives only provided transient cell cycle arrest. Western blots, reporter gene assays, and cell cycle analysis established that n-butyrate, when delivered to cells via any carbohydrate scaffold, functioned as a histone deacetylase inhibitor (HDACi), upregulated p21WAF1/Cip1 expression, and inhibited proliferation. However, only 1, a compound that primed sialic acid biosynthesis and modulated the expression of a different set of genes compared to 3, ultimately killed the cells. These results demonstrate that the biological activity of butyrate can be tuned by sugars to improve its anticancer properties.

Application of next generation sequencing toward sensitive detection of enteric viruses isolated from celery samples as an example of produce.

Next generation sequencing (NGS) holds promise as a single application for both detection and sequence identification of foodborne viruses; however, technical challenges remain due to anticipated low quantities of virus in contaminated food. In this study, with a focus on data analysis using several bioinformatics tools, we applied NGS toward amplification-independent detection and identification of norovirus at low copy (<103 copies) or within multiple strains from produce. Celery samples were inoculated with human norovirus (stool suspension) either as a single norovirus strain, a mixture of strains (GII.4 and GII.6), or a mixture of different species (hepatitis A virus and norovirus). Viral RNA isolation and recovery was confirmed by RT-qPCR, and optimized for library generation and sequencing without amplification using the Illumina MiSeq platform. Extracts containing either a single virus or a two-virus mixture were analyzed using two different analytic approaches to achieve virus detection and identification. First an overall assessment of viral genome coverage for samples varying in copy numbers (1.1×103 to 1.7×107) and genomic content (single or multiple strains in various ratios) was completed by reference-guided mapping. Not unexpectedly, this targeted approach to identification was successful in correctly mapping reads, thus identifying each virus contained in the inoculums even at low copy (estimated at 12 copies). For the second (metagenomic) approach, samples were treated as "unknowns" for data analyses using (i) a sequence-based alignment with a local database, (ii) an "in-house" k-mer tool, (iii) a commercially available metagenomics bioinformatic analysis platform cosmosID, and (iv) an open-source program Kraken. Of the four metagenomics tools applied in this study, only the local database alignment and in-house k-mer tool were successful in detecting norovirus (as well as HAV) at low copy (down to <103 copies) and within a mixture of virus strains or species. The results of this investigation provide support for continued investigation into the development and integration of these analytical tools for identification and detection of foodborne viruses.

Optimizing a custom tiling microarray for low input detection and identification of unamplified virus targets.

Viruses are major pathogens causing foodborne illnesses and are often present at low levels in foods, thus requiring sensitive techniques for their detection in contaminated foods. The lack of efficient culture methods for many foodborne viruses and the potential for multi-species viral contamination have driven investigation toward non-amplification based methods for virus detection and identification. A custom DNA microarray (FDA_EVIR) was assessed for its sensitivity in the detection and identification of low-input virus targets, human hepatitis A virus, norovirus, and coxsackievirus, individually and in combination. Modifications to sample processing were made to accommodate low input levels of unamplified virus targets, which included addition of carrier cDNA, RNase treatment, and optimization of DNase I-mediated target fragmentation. Amplification-free detection and identification of foodborne viruses were achieved in the range of 250-500 copies of virus RNA. Alternative data analysis methods were employed to distinguish the genotypes of the viruses particularly at lower levels of target input and the single probe-based analysis approach made it possible to identify a minority species in a multi-virus complex. The oligonucleotide array is shown to be a promising platform to detect foodborne viruses at low levels close to what are anticipated in food or environmental samples.

Development of a rapid total nucleic acid extraction method for the isolation of hepatitis A virus from fresh produce.

Recently, there have been increasing reports of foodborne illnesses associated with the consumption of fresh produce. Among these, hepatitis A virus (HAV) remains epidemiologically important and has been continually implicated in several outbreaks. We describe a rapid method (<8h) for the isolation and subsequent detection with real-time quantitative PCR (RT-qPCR) of the HAV HM-175 cytopathic strain seeded onto baby spinach and sliced tomatoes using a total RNA extraction method, utilizing a high concentration (4M) guanidine thiocyanate buffer. Consistent detection of HAV genome from both produce items was achieved at an inoculation level of 3×10³ PFU/25 g of food, with less consistent detection achieved at 3×10² PFU/25g. Initial studies revealed that a final precipitation of recovered RNA with potassium acetate to reduce carryover of polysaccharides and the addition of polyvinylpyrrolidone to remove polyphenolics in spinach were essential. For tomatoes, virus isolation was achieved with the incorporation of either an elution step with a high pH Tris-glycine-beef extract (TGBE) buffer or with an enzymatic digestion with pectinase. We also describe the development of a protocol for the detection of HAV from tomatoes utilizing a Luminex® microbead-based suspension array. The results correlated well with the RT-qPCR assay suggesting the feasibility of the Bioplex® as a detection platform for viruses isolated from foods.

Temperature and density dependent induction of a cytopathic effect following infection with non-cytopathic HAV strains.

Hepatitis A virus infection and growth in cultured cells is protracted, cell-type restricted, and generally not accompanied by the appearance of a cytopathic effect, with the exception of some culture-adapted strains. We demonstrate that the non-cytopathic HAV strain HM175/clone 1 can be induced to exhibit a cytopathic phenotype in both persistently or acutely infected cells under co-dependent conditions of lower incubation temperature (<34°C) and reduced cell density in both monkey (FRhK-4) and human (A549) cells. This phenotype is not virus-strain restricted, as it was also observed in cells infected with HAV strains, HAS-15 and LSH/S. Cytopathic effect was accompanied by rRNA cleavage, indicating activation of the RNase L pathway, viral negative strand synthesis, caspase-3 activation, and apoptosis. The results indicate that a cytopathic phenotype may be present in some HAV strains that can be induced under appropriate conditions, suggesting the potential for development of a plaque assay for this virus.

Transport of metal oxide nanoparticles and single-walled carbon nanotubes in human mucus.

Whether mucus layers lining entrance points into the body, including the lung airways, provide protection against the penetration of engineered nanoparticles remains poorly understood. We measured the diffusion coefficients of hundreds of individual nanoparticles of three different metal oxides (nMeOs) and two types of single-walled carbon nanotubes (SWCNTs) in undiluted human mucus. We found that the vast majority of these nanoparticles are efficiently trapped in human mucus and, further, that the mechanism of trapping is adhesive interactions as opposed to steric obstruction. However, a small fraction of zinc oxide (ZnO) nanoparticles moved at rates fast enough to penetrate airway mucus layers. We conclude that human mucus layers probably provide considerable protection for mucosal tissues from the penetration of most nMeOs and SWCNTs, and suggest that further investigation of the potential health risks of exposure to ZnO nanoparticles is warranted.

Common gene therapy viral vectors do not efficiently penetrate sputum from cystic fibrosis patients.

Norwalk virus and human papilloma virus, two viruses that infect humans at mucosal surfaces, have been found capable of rapidly penetrating human mucus secretions. Viral vectors for gene therapy of Cystic Fibrosis (CF) must similarly penetrate purulent lung airway mucus (sputum) to deliver DNA to airway epithelial cells. However, surprisingly little is known about the rates at which gene delivery vehicles penetrate sputum, including viral vectors used in clinical trials for CF gene therapy. We find that sputum spontaneously expectorated by CF patients efficiently traps two viral vectors commonly used in CF gene therapy trials, adenovirus (d∼80 nm) and adeno-associated virus (AAV serotype 5; d∼20 nm), leading to average effective diffusivities that are ∼3,000-fold and 12,000-fold slower than their theoretical speeds in water, respectively. Both viral vectors are slowed by adhesion, as engineered muco-inert nanoparticles with diameters as large as 200 nm penetrate the same sputum samples at rates only ∼40-fold reduced compared to in pure water. A limited fraction of AAV exhibit sufficiently fast mobility to penetrate physiologically thick sputum layers, likely because of the lower viscous drag and smaller surface area for adhesion to sputum constituents. Nevertheless, poor penetration of CF sputum is likely a major contributor to the ineffectiveness of viral vector based gene therapy in the lungs of CF patients observed to date.

Characterization of the intracellular dynamics of a non-degradative pathway accessed by polymer nanoparticles.

Recently, 24 nm polymer nanoparticles were found to access a privileged non-degradative intracellular pathway that leads to perinuclear accumulation. Here, we report the intracellular dynamics of vesicles containing polymer nanoparticles within this non-degradative pathway, characterized by clathrin- and caveolae-independent endocytosis, as compared to endosomes originating from classical clathrin-mediated endocytosis. Similar to transport of acidic endosomes and lysosomes, the dynamic movements of non-degradative vesicles exhibit substantial heterogeneity, including caged diffusion and pearls-on-a-string trajectories, a reflection of microtubule-dependent active transport that leads to rapid accumulation near the cell nucleus. However, the ensemble-averaged intracellular transport rate of vesicles in the non-degradative pathway is 4-fold slower than that of the acidic vesicles of late endosomes and lysosomes, highlighted by a 3-fold smaller fraction of actively transported vesicles. The distinct intracellular dynamics further confirms that small nanoparticles are capable of entering cells via a distinct privileged pathway that does not lead to lysosomal processing. This non-degradative pathway may prove beneficial for the delivery of therapeutics and nucleic acids to the nucleus or nearby organelles.