A colorimetric assay for viral agents that produce cytopathic effects

Purification of a non-enveloped virus using sequential aqueous two-phase extraction

Virus-based vaccines and therapies require a purification method that is both cost-effective and easily scalable. An aqueous two-phase system (ATPS) consisting of polyethylene glycol (PEG) and citrate salt has been proven to deliver high virus recoveries along with high impurity removal. However, these systems often place the virus into a viscous PEG-rich phase or at the two-phase interface, leading to difficulties in subsequent downstream processes. This study explored a second ATPS to extract the virus product back into the citrate-rich phase by changing the chemical conditions, a required step for future application of ATPS in industrial processes. ATPS performance was tested as a function of phase component concentration, phase component volume ratios, PEG molecular weight, salt type, pH, and glycine addition to identify the most impactful parameters for the extraction of non-enveloped porcine parvovirus (PPV). By shifting the pH, lowering phase component concentrations, and increasing the volume ratio of the citrate-rich phase between the first and second ATPS steps, 66 % of infectious PPV was recovered with 2.0 logs of host cell protein removal and 1.0 logs of host cell DNA removal. Using a PEG molecular weight of 8 kDa enabled a pH shift between the first and second ATPS steps without precipitation. Glycine addition during the first step of ATPS and phosphate salt use during the second step of ATPS did not significantly increase the overall recovery. In future studies, the optimized process will be implemented for multiple viral vector types and continuously to demonstrate continuous and low-cost viral vector manufacturing.

Impact of Eco-Friendly Surfactant Structure and Class on Enveloped Virus Inactivation

BACKGROUND

Sustainable and effective strategies for virus inactivation are crucial for ensuring the safety and quality of biological products. The European Union's (EU) 2021 ban on Triton X-100 for viral inactivation in biomanufacturing has pushed the field to find sustainable alternatives with equal effectiveness. We aim to increase the sustainability of biopharmaceutical production by ensuring the effectiveness of eco-friendly surfactant-mediated virus inactivation by comparing the antiviral efficacy of Triton X-100 to glucosides and amine oxides.

RESULTS

Surfactants were evaluated for antiviral efficacy against herpes viruses, SuHV and HSV, and the retrovirus XMuLV. The surfactants demonstrated equivalent or superior inactivation efficacy compared to Triton X-100. Herpes viruses were inactivated similarly with all surfactants. For XMuLV, surfactants with longer alkyl chains achieved maximum log reduction values (LRV) at 1x CMC, outperforming Triton X-100, which required 2x CMC for comparable efficacy. Surfactants with bulky headgroups, such as LAPAO, showed lower efficacy against XMuLV. At a salt concentration of 2 M ionic strength, the antiviral efficacy of Triton X-100 and TDAO decreased for the herpes viruses. Variability in inactivation was observed among the surfactants at 0.5x CMC, indicating that surfactant characteristics influence their antiviral performance below CMC.

CONCLUSIONS

Adding salt enhanced the antiviral efficacy of surfactants by lowering their CMC while maintaining consistent virus inactivation. Among the surfactants tested, the glucoside with a longer tail, n-nonyl-β-D-glucoside (NG), emerged as the most robust and could function as an eco-friendly surfactant for virus inactivation in bioprocessing. For NG, virus inactivation was independent of all variables tested.

Utilizing Rapid Hydrogen Peroxide Generation from 6-Hydroxycatechol to Design Moisture-Activated, Self-Disinfecting Coating

A coating that can be activated by moisture found in respiratory droplets could be a convenient and effective way to control the spread of airborne pathogens and reduce fomite transmission. Here, the ability of a novel 6-hydroxycatechol-containing polymer to function as a self-disinfecting coating on the surface of polypropylene (PP) fabric was explored. Catechol is the main adhesive molecule found in mussel adhesive proteins. Molecular oxygen found in an aqueous solution can oxidize catechol and generate a known disinfectant, hydrogen peroxide (H2O2), as a byproduct. However, given the limited amount of moisture found in respiratory droplets, there is a need to enhance the rate of catechol autoxidation to generate antipathogenic levels of H2O2. 6-Hydroxycatechol contains an electron donating hydroxyl group on the 6-position of the benzene ring, which makes catechol more susceptible to autoxidation. 6-Hydroxycatechol-coated PP generated over 3000 μM of H2O2 within 1 h when hydrated with a small amount of aqueous solution (100 μL of PBS). The generated H2O2 was three orders of magnitude higher when compared to the amount generated by unmodified catechol. 6-Hydroxycatechol-containing coating demonstrated a more effective antimicrobial effect against both Gram-positive (Staphylococcus aureus and Staphylococcus epidermidis) and Gram-negative (Pseudomonas aeruginosa and Escherichia coli) bacteria when compared to unmodified catechol. Similarly, the self-disinfecting coating reduced the infectivity of both bovine viral diarrhea virus and human coronavirus 229E by as much as a 2.5 log reduction value (a 99.7% reduction in viral load). Coatings containing unmodified catechol did not generate sufficient H2O2 to demonstrate significant virucidal effects. 6-Hydroxycatechol-containing coating can potentially function as a self-disinfecting coating that can be activated by the moisture present in respiratory droplets to generate H2O2 for disinfecting a broad range of pathogens.

Design Rules for the Sequestration of Viruses into Polypeptide Complex Coacervates

Encapsulation is a strategy that has been used to facilitate the delivery and increase the stability of proteins and viruses. Here, we investigate the encapsulation of viruses via complex coacervation, which is a liquid-liquid phase separation resulting from the complexation of oppositely charged polymers. In particular, we utilized polypeptide-based coacervates and explored the effects of peptide chemistry, chain length, charge patterning, and hydrophobicity to better understand the effects of the coacervating polypeptides on virus incorporation. Our study utilized two nonenveloped viruses, porcine parvovirus (PPV) and human rhinovirus (HRV). PPV has a higher charge density than HRV, and they both appear to be relatively hydrophobic. These viruses were compared to characterize how the charge, hydrophobicity, and patterning of chemistry on the surface of the virus capsid affects encapsulation. Consistent with the electrostatic nature of complex coacervation, our results suggest that electrostatic effects associated with the net charge of both the virus and polypeptide dominated the potential for incorporating the virus into a coacervate, with clustering of charges also playing a significant role. Additionally, the hydrophobicity of a virus appears to determine the degree to which increasing the hydrophobicity of the coacervating peptides can enhance virus uptake. Nonintuitive trends in uptake were observed with regard to both charge patterning and polypeptide chain length, with these parameters having a significant effect on the range of coacervate compositions over which virus incorporation was observed. These results provide insights into biophysical mechanisms, where sequence effects can control the uptake of proteins or viruses into biological condensates and provide insights for use in formulation strategies.

Economic simulation of batch and continuous aqueous two-phase purification for viral products

Vaccine manufacturing strategies that lower capital and production costs could improve vaccine access by reducing the cost per dose and encouraging localized manufacturing. Continuous processing is increasingly utilized to drive lower costs in biological manufacturing by requiring fewer capital and operating resources. Aqueous two-phase systems (ATPS) are a liquid-liquid extraction technique that enables continuous processing for viral vectors. To date, no economic comparison between viral vector purifications using traditional methods and ATPS has been published. In this work, economic simulations of traditional chromatography-based virus purification were compared to ATPS-based virus purification for the same product output in both batch and continuous modes. First, the modeling strategy was validated by re-creating a viral subunit manufacturing economic simulation. Then, ATPS capital and operating costs were compared to that of a traditional chromatography purification at multiple scales. At all scales, ATPS purification required less than 10% of the capital expenditure compared to chromatography-based purification. At an 11 kg per year production scale, the ATPS production costs were 50% less than purification with chromatography. Other chromatography configurations were explored, and may provide a production cost benefit to ATPS, but the purity and recovery were not experimentally verified. Batch and continuous ATPS were similar in capital and production costs. However, manual price adjustments suggest that continuous ATPS plant-building costs could be less than half that of batch ATPS at the 11 kg per year production scale. These simulations show the significant reduction in manufacturing costs that ATPS-based purification could deliver to the vaccine industry.

The Novel Porcine Parvoviruses: Current State of Knowledge and Their Possible Implications in Clinical Syndromes in Pigs

Parvoviruses (PVs) affect various animal species causing different diseases. To date, eight different porcine parvoviruses (PPV1 through PPV8) are recognized in the swine population, all of which are distributed among subfamilies and genera of the Parvoviridae family. PPV1 is the oldest and is recognized as the primary agent of SMEDI, while the rest of the PPVs (PPV2 through PPV8) are called novel PPVs (nPPVs). The pathogenesis of nPPVs is still undefined, and whether these viruses are putative disease agents is unknown. Structurally, the PPVs are very similar; the differences occur mainly at the level of their genomes (ssDNA), where there is variation in the number and location of the coding genes. Additionally, it is considered that the genome of PVs has mutation rates similar to those of ssRNA viruses, that is, in the order of 10-5-10-4 nucleotide/substitution/year. These mutations manifest mainly in the VP protein, constituting the viral capsid, affecting virulence, tropism, and viral antigenicity. For nPPVs, mutation rates have already been established that are similar to those already described; however, within this group of viruses, the highest mutation rate has been reported for PPV7. In addition to the mutations, recombinations are also reported, mainly in PPV2, PPV3, and PPV7; these have been found between strains of domestic pigs and wild boars and in a more significant proportion in VP sequences. Regarding affinity for cell types, nPPVs have been detected with variable prevalence in different types of organs and tissues; this has led to the suggestion that they have a broad tropism, although proportionally more have been found in lung and lymphoid tissue such as spleen, tonsils, and lymph nodes. Regarding their epidemiology, nPPVs are present on all continents (except PPV8, only in Asia), and within pig farms, the highest prevalences detecting viral genomes have been seen in the fattener and finishing groups. The relationship between nPPVs and clinical manifestations has been complicated to establish. However, there is already some evidence that establishes associations. One of them is PPV2 with porcine respiratory disease complex (PRDC), where causality tests (PCR, ISH, and histopathology) lead to proposing the PPV2 virus as a possible agent involved in this syndrome. With the other nPPVs, there is still no clear association with any pathology. These have been detected in different systems (respiratory, reproductive, gastrointestinal, urinary, and nervous), and there is still insufficient evidence to classify them as disease-causing agents. In this regard, nPPVs (except PPV8) have been found to cause porcine reproductive failure (PRF), with the most prevalent being PPV4, PPV6, and PPV7. In the case of PRDC, nPPVs have also been detected, with PPV2 having the highest viral loads in the lungs of affected pigs. Regarding coinfections, nPPVs have been detected in concurrence in healthy and sick pigs, with primary PRDC and PRF viruses such as PCV2, PCV3, and PRRSV. The effect of these coinfections is not apparent; it is unknown whether they favor the replication of the primary agents, the severity of the clinical manifestations, or have no effect. The most significant limitation in the study of nPPVs is that their isolation has been impossible; therefore, there are no studies on their pathogenesis both in vitro and in vivo. For all of the above, it is necessary to propose basic and applied research on nPPVs to establish if they are putative disease agents, establish their effect on coinfections, and measure their impact on swine production.

Multimodal peptide ligand extracts parvovirus from interface in affinity aqueous two-phase system

Aqueous two-phase systems (ATPS) have found various applications in bioseparations and microencapsulation. The primary goal of this technique is to partition target biomolecules in a preferred phase, rich in one of the phase-forming components. However, there is a lack of understanding of biomolecule behavior at the interface between the two phases. Biomolecule partitioning behavior is studied using tie-lines (TL), where each TL is a group of systems at thermodynamic equilibrium. Across a TL, a system can either have a bulk PEG-rich phase with citrate-rich droplets, or the opposite can occur. We found that porcine parvovirus (PPV) was recovered at a higher amount when PEG was the bulk phase and citrate was in droplets and that the salt and PEG concentrations are high. To improve the recovery, A PEG 10 kDa-peptide conjugate was formed using the multimodal WRW ligand. When WRW was present, less PPV was caught at the interface of the two-phase system, and more was recovered in the PEG-rich phase. While WRW did not significantly increase the PPV recovery in the high TL system, which was found earlier to be optimal for PPV recovery, the peptide did greatly enhance recovery at a lower TL. This lower TL has a lower viscosity and overall system PEG and citrate concentration. The results provide both a method to increase virus recovery in a lower viscosity system, as well as provide interesting thoughts into the interfacial phenomenon and how to recover virus in a phase and not at the interface.

Virucidal N95 Respirator Face Masks via Ultrathin Surface-Grafted Quaternary Ammonium Polymer Coatings

N95 respirator face masks serve as effective physical barriers against airborne virus transmission, especially in a hospital setting. However, conventional filtration materials, such as nonwoven polypropylene fibers, have no inherent virucidal activity, and thus, the risk of surface contamination increases with wear time. The ability of face masks to protect against infection can be likely improved by incorporating components that deactivate viruses on contact. We present a facile method for covalently attaching antiviral quaternary ammonium polymers to the fiber surfaces of nonwoven polypropylene fabrics that are commonly used as filtration materials in N95 respirators via ultraviolet (UV)-initiated grafting of biocidal agents. Here, C₁₂-quaternized benzophenone is simultaneously polymerized and grafted onto melt-blown or spunbond polypropylene fabric using 254 nm UV light. This grafting method generated ultrathin polymer coatings which imparted a permanent cationic charge without grossly changing fiber morphology or air resistance across the filter. For melt-blown polypropylene, which comprises the active filtration layer of N95 respirator masks, filtration efficiency was negatively impacted from 72.5 to 51.3% for uncoated and coated single-ply samples, respectively. Similarly, directly applying the antiviral polymer to full N95 masks decreased the filtration efficiency from 90.4 to 79.8%. This effect was due to the exposure of melt-blown polypropylene to organic solvents used in the coating process. However, N95-level filtration efficiency could be achieved by wearing coated spunbond polypropylene over an N95 mask or by fabricating N95 masks with coated spunbond as the exterior layer. Coated materials demonstrated broad-spectrum antimicrobial activity against several lipid-enveloped viruses, as well as Staphylococcus aureus and Escherichia coli bacteria. For example, a 4.3-log reduction in infectious MHV-A59 virus and a 3.3-log reduction in infectious SuHV-1 virus after contact with coated filters were observed, although the level of viral deactivation varied significantly depending on the virus strain and protocol for assaying infectivity.

Quantification of Infectious SARS-CoV-2 by the 50% Tissue Culture Infectious Dose Endpoint Dilution Assay

A number of viral quantification methods are used to measure the concentration of infectious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). While the traditional plaque-based assay allows for direct enumeration of replication competent lytic virions and remains the gold standard for the quantification of infectious virus, the 50% tissue culture infectious dose (TCID₅₀) endpoint dilution assay allows for a more rapid, large-scale analysis of experimental samples. In this chapter, we describe a well-established TCID₅₀ assay protocol to measure the SARS-CoV-2 infectious titer in viral stocks, in vitro cell or organoid models, and animal tissue. We also present alternative assays for scoring the cytopathic effect of SARS-CoV-2 in cell culture and comparable methods to calculate the 50% endpoint by serial dilution.

Rapid high-throughput compatible label-free virus particle quantification method based on time-resolved luminescence

Viruses play a major role in modern society and create risks from global pandemics and bioterrorism to challenges in agriculture. Virus infectivity assays and genome copy number determination methods are often used to obtain information on virus preparations used in diagnostics and vaccine development. However, these methods do not provide information on virus particle count. Current methods to measure the number of viral particles are often cumbersome and require highly purified virus preparations and expensive instrumentation. To tackle these problems, we developed a simple and cost-effective time-resolved luminescence-based method for virus particle quantification. This mix-and-measure technique is based on the recognition of the virus particles by an external Eu³⁺-peptide probe, providing results on virus count in minutes. The method enables the detection of non-enveloped and enveloped viruses, having over tenfold higher detectability for enveloped, dynamic range from 5E6 to 3E10 vp/mL, than non-enveloped viruses. Multiple non-enveloped and enveloped viruses were used to demonstrate the functionality and robustness of the Protein-Probe method.

Virus inactivation at moderately low pH varies with virus and buffer properties

BACKGROUND

Virus inactivation is a critical operation in therapeutic protein manufacturing. Low pH buffers are a widely used strategy to ensure robust enveloped virus clearance. However, the choice of model virus can give varying results in viral clearance studies. Pseudorabies virus (SuHV) or herpes simplex virus-1 (HSV-1) are frequently chosen as model viruses to demonstrate the inactivation for the herpes family.

RESULTS

In this study, SuHV, HSV-1, and equine arteritis virus (EAV) were used to compare the inactivation susceptibility at pH 4.0 and 4°C. SuHV and HSV-1 are from the same family, and EAV was chosen as a small, enveloped virus. Glycine, acetate, and citrate buffers at pH 4.0 and varying buffer strengths were studied. The inactivation susceptibility was found to be in the order of SuHV > HSV > EAV. The buffer effectiveness was found to be in the order of citrate > acetate > glycine. The smaller virus, EAV, remained stable and infectious in all the buffer types and compositions studied.

CONCLUSION

The variation in inactivation susceptibility of herpes viruses indicated that SuHV and HSV cannot be interchangeably used as a virus model for inactivation studies. Smaller viruses might remain adventitiously infective at moderately low pH.

Spectrophotometric microplate assay for titration and neutralization of avian nephritis virus based on the virus cytopathicity

INTRODUCTION

Plaque assay (PA) is a gold standard for virus titration and neutralization of various cytopathic viruses, including avian nephritis virus (ANV), the etiological agent associated with kidney disorders in chickens. In this study, as an alternative to the labor-intensive PA, we developed a spectrophotometric microplate assay (MA) for ANV titration and neutralization based on the virus cytopathicity to primary chicken kidney (CK) cells.

METHODS

CK cells were infected with ANV in the presence or absence of chicken serum in a 96-well microplate, and the virus-induced cytolysis was quantified by measurement of neutral red uptake using a spectrophotometer. The absorbance values obtained were subjected to a sigmoidal four-parameter logistic regression analysis for the virus titer determination and serum neutralization assessment. Accuracy and reliability of the serum neutralization MA in comparison to the standard PA was statistically evaluated.

RESULTS

The ANV-MA was capable of quantifying infectious virus titers based on a virus dose-dependent cytolysis of CK cells, and serum neutralization could be assessed as an inhibition of the virus-induced cytolysis accordingly. Statistical evaluation using a 2 × 2 contingency table and receiver-operating characteristic analyses showed 82 % sensitivity, 99 % specificity and 0.97 area under the curve, supporting an overall diagnostic accuracy of the neutralization MA.

CONCLUSION

The newly developed MA using simplified experimental procedures in the microplate format and direct spectophotometric data readout is readily applicable to general laboratories for high-throughput screening of serum neutralization of ANV.

Osmolyte enhanced aqueous two-phase system for virus purification

Due to the high variation in viral surface properties, a platform method for virus purification is still lacking. A potential alternative to the high-cost conventional methods is aqueous two-phase systems (ATPSs). However, optimizing virus purification in ATPS requires a large experimental design space, and the optimized systems are generally found to operate at high ATPS component concentrations. The high concentrations capitalize on hydrophobic and electrostatic interactions to obtain high viral particle yields. This study investigated using osmolytes as driving force enhancers to reduce the high concentration of ATPS components while maintaining high yields. The partitioning behavior of porcine parvovirus (PPV), a nonenveloped mammalian virus, and human immunodeficiency virus-like particle (HIV-VLP), a yeast-expressed enveloped VLP, were studied in a polyethylene glycol (PEG) 12 kDa-citrate system. The partitioning of the virus modalities was enhanced by osmoprotectants glycine and betaine, while trimethylamine N-oxide was ineffective for PPV. The increased partitioning to the PEG-rich phase pertained only to viruses, resulting in high virus purification. Recoveries were 100% for infectious PPV and 92% for the HIV-VLP, with high removal of the contaminant proteins and more than 60% DNA removal when glycine was added. The osmolyte-induced ATPS demonstrated a versatile method for virus purification, irrespective of the expression system.

Thermostabilization of viruses via complex coacervation

Widespread vaccine coverage for viral diseases could save the lives of millions of people each year. For viral vaccines to be effective, they must be transported and stored in a narrow temperature range of 2-8 °C. If temperatures are not maintained, the vaccine may lose its potency and would no longer be effective in fighting disease; this is called the cold storage problem. Finding a way to thermally stabilize a virus and end the need to transport and store vaccines at refrigeration temperatures will increase access to life-saving vaccines. We explore the use of polymer-rich complex coacervates to stabilize viruses. We have developed a method of encapsulating virus particles in liquid complex coacervates that relies on the electrostatic interaction of viruses with polypeptides. In particular, we tested the incorporation of two model viruses; a non-enveloped porcine parvovirus (PPV) and an enveloped bovine viral diarrhea virus (BVDV) into coacervates formed from poly(lysine) and poly(glutamate). We identified optimal conditions (i.e., the relative amount of the two polypeptides) for virus encapsulation, and trends in this composition matched differences in the isoelectric point of the two viruses. Furthermore, we were able to achieve a ∼103-104-fold concentration of virus into the coacervate phase, such that the level of virus remaining in the bulk solution approached our limit of detection. Lastly, we demonstrated a significant enhancement of the stability of non-enveloped PPV during an accelerated aging study at 60 °C over the course of a week. Our results suggest the potential for using coacervation to aid in the purification and formulation of both enveloped and non-enveloped viruses, and that coacervate-based formulations could help limit the need for cold storage throughout the transportation and storage of vaccines based on non-enveloped viruses.

Physiochemical properties of enveloped viruses and arginine dictate inactivation

BACKGROUND

Therapeutic protein manufacturing would benefit by having an arsenal of ways to inactivate viruses. There have been many publications on the virus inactivation ability of arginine at pH 4.0, but the mechanism of this inactivation is unknown. This study explored how virus structure and solution conditions enhance virus inactivation by arginine and leads to a better understanding of the mechanism of virus inactivation by arginine.

RESULTS

Large diameter viruses from the Herpesviridae family (SuHV-1, HSV-1) with loosely packed lipids were highly inactivated by arginine, whereas small diameter, enveloped viruses (equine arteritis virus (EAV) and bovine viral diarrhea virus (BVDV)) with tightly packed lipids were negligibly inactivated by arginine. To increase the inactivation of viruses resistant to arginine, arginine-derivatives and arginine peptides were tested. Derivates and peptides demonstrated that a greater capacity for clustering and added hydrophobicity enhanced virus inactivation. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) detected increases in virus size after arginine exposure, supporting the mechanism of lipid expansion.

CONCLUSIONS

Arginine most likely interacts with the lipid membrane to cause inactivation. This is shown by larger viruses being more sensitive to inactivation and expansion of the viral size. The enhancement of arginine inactivation when increased hydrophobic molecules are present or arginine is clustered demonstrates a potential mechanism of how arginine interacts with the lipid membrane.

Laboratory demonstration of the vertical transmission of Rift Valley fever virus by Culex tarsalis mosquitoes

Rift Valley fever virus (RVFV) is a mosquito-transmitted virus with proven ability to emerge into naïve geographic areas. Limited field evidence suggests that RVFV is transmitted vertically from parent mosquito to offspring, but until now this mechanism has not been confirmed in the laboratory. Furthermore, this transmission mechanism has allowed for the prediction of RVFV epizootics based on rainfall patterns collected from satellite information. However, in spite of the relevance to the initiation of epizootic events, laboratory confirmation of vertical transmission has remained an elusive research aim for thirty-five years. Herein we present preliminary evidence of the vertical transmission of RVFV by Culex tarsalis mosquitoes after oral exposure to RVFV. Progeny from three successive gonotrophic cycles were reared to adults, with infectious RVFV confirmed in each developmental stage. Virus was detected in ovarian tissues of parental mosquitoes 7 days after imbibing an infectious bloodmeal. Infection was confirmed in progeny as early as the first gonotrophic cycle, with infection rates ranging from 2.0–10.0%. Virus titers among progeny were low, which may indicate a host mechanism suppressing replication.

Rift Valley fever virus (RVFV) represents a significant threat in terms of its ability to emerge into naïve geographic areas. Furthermore, RVFV represents a global public health risk due to the ability of many mosquito species to transmit the virus and the ease with which the virus can be transported due to increased globalization. The vertical transmission of RVFV by mosquitoes has long been accepted by the research community due to limited field evidence. However, laboratory confirmation of vertical transmission has remained elusive for thirty-five years. We present the first laboratory evidence of vertical transmission of RVFV in the susceptible North American vector, Culex tarsalis. We present two studies that clearly show 1) the accumulation of RVFV antigen in the ovaries of infected mosquitoes and 2) the transmission of RVFV from parent to offspring immediately following an infectious blood meal.

Virus and chlorine adsorption onto guanidine modified cellulose nanofibers using covalent and hydrogen bonding

Unsafe drinking water leads to millions of human deaths each year, while contaminated wastewater discharges are a significant threat to aquatic life. To relieve the burden of unsafe water, we are in search of an inexpensive material that can adsorb pathogenic viruses from drinking water and adsorb toxic residual chlorine from wastewater. To impart virus and chlorine removal abilities to cellulosic materials, we modified the primary hydroxyl group with a positively charged guanidine group, to yield guanidine modified cellulose derivatives. Microcrystalline cellulose (MC) bearing covalently bonded guanidine hydrochloride (MC-GC) and hydrogen-bonded guanidine hydrochloride (MC-GH) were synthesized, and electrospun into nanofibers after blending with the non-ionogenic polyvinyl alcohol (PVA), to produce large pore sized, high surface area membranes. The MC-GC/PVA and MC-GH/PVA nanofibers were stabilized against water dissolution by crosslinking with glutaraldehyde vapor. The water-stable MC-GC/PVA mats were able to remove more than 4 logs of non-enveloped porcine parvovirus (PPV) and enveloped Sindbis virus and reached 58% of chlorine removal. The MC-GC/PVA nanofibers demonstrated better performance for pathogen removal and dechlorination than MC-GH/PVA nanofibers. This first study of MC-GC/PVA electrospun mats for virus removal shows they are highly effective and merit additional research for virus removal.

Hydroxyl Radical Generation Through the Fenton-Like Reaction of Hematin- and Catechol-Functionalized Microgels

Hydroxyl radical (^•OH) is a potent reactive oxygen species with the ability to degrade hazardous organic compounds, kill bacteria, and inactivate viruses. However, an off-the-shelf, portable, and easily activated biomaterial for generating ^•OH does not exist. Here, microgels were functionalized with catechol, an adhesive moiety found in mussel adhesive proteins, and hematin (HEM), a hydroxylated Fe³⁺ ion-containing porphyrin derivative. When the microgel was hydrated in an aqueous solution with physiological pH, molecular oxygen in the solution oxidized catechol to generate H₂O₂, which was further converted to ^•OH by HEM. The generated ^•OH was able to degrade organic dyes, including orange II and malachite green. Additionally, the generated ^•OH was antimicrobial against both gram-negative (Escherichia coli) and gram-positive (Staphylococcus epidermidis) bacteria with the initial concentration of 10⁶-10⁷ CFU/mL. These microgels also reduced the infectivity of a non-enveloped porcine parvovirus and an enveloped bovine viral diarrhea virus by 3.5 and 4.5 log reduction values, respectively (99.97-99.997% reduction in infectivity). These microgels were also functionalized with positively charged [2-(methacryloyloxy)ethyl] trimethylammonium chloride (METAC), which significantly enhanced the antibacterial and antiviral activities through electrostatic interaction between the negatively charged pathogens and the microgel. These microgels can potentially serve as a lightweight and portable source of disinfectant, for an on-demand generation of ^•OH with a wide range of applications.

Changes in Membrane Dielectric Properties of Porcine Kidney Cells Provide Insight into the Antiviral Activity of Glycine

The ability to monitor the status and progression of viral infections is important for development and screening of new antiviral drugs. Previous research illustrated that the osmolyte glycine (Gly) reduced porcine parvovirus (PPV) infection in porcine kidney (PK-13) cells by stabilizing the capsid protein and preventing virus capsid assembly into viable virus particles. Dielectrophoresis (DEP) was examined herein as a noninvasive, electric field- and frequency-dependent tool for real-time monitoring of PK-13 cell responses to obtain information about membrane barrier functionality and polarization. DEP responses of PK-13 cells were compared to those of PPV-infected cells in the absence and presence of the osmolyte glycine. With infection progression, PK-13 DEP spectra shifted toward lower frequencies, reducing crossover frequencies (f_CO). The spherical single-shell model was used to extract PK-13 cell dielectric properties. Upon PPV infection, specific membrane capacitance increased over the time progression of virus attachment, penetration, and capsid protein production and assembly. Following glycine treatment, the DEP spectra displayed attenuated f_CO and specific membrane capacitance values shifted back toward uninfected PK-13 cell values. These results suggest that DEP can be used to noninvasively monitor the viral infection cycle and screen antiviral compounds. DEP can augment traditional tools by elucidating membrane polarization changes related to drug mechanisms that interrupt the virus infection cycle.

Virus Isoelectric Point Determination Using Single-Particle Chemical Force Microscopy

Virus colloidal behavior is governed by the interaction of the viral surface and the surrounding environment. One method to characterize the virus surface charge is the isoelectric point (pI). Traditional determination of virus pI has focused on the bulk characterization of a viral solution. However, virus capsids are extremely heterogeneous, and a single-particle method may give more information on the range of surface charge observed across a population. One method to measure the virus pI is chemical force microscopy (CFM). CFM is a single-particle technique that measures the adhesion force of a functionalized atomic force microscope (AFM) probe and, in this case, a virus covalently bound to a surface. Non-enveloped porcine parvovirus (PPV) and enveloped bovine viral diarrhea virus (BVDV) were used to demonstrate the use of CFM for viral particles with different surface properties. We have validated the CFM to determine the pI of PPV to be 4.8-5.1, which has a known pI value of 5.0 in the literature, and to predict the unknown pI of BVDV to be 4.3-4.5. Bulk measurements, ζ-potential, and aqueous two-phase system (ATPS) cross-partitioning methods were also used to validate the new CFM method for the virus pI. Most methods were in good agreement. CFM can detect the surface charge of viral capsids at a single-particle level and enable the comparison of surface charge between different types of viruses.

Sequence and phylogenetic analysis of novel porcine parvovirus 7 isolates from pigs in Guangxi, China

Parvoviruses are a diverse group of viruses that infect a wide range of animals and humans. In recent years, advances in molecular techniques have resulted in the identification of several novel parvoviruses in swine. In this study, porcine parvovirus 7 (PPV7) isolates from clinical samples collected in Guangxi, China, were examined to understand their molecular epidemiology and co-infection with porcine circovirus type 2 (PCV2). In this study, among the 385 pig serum samples, 105 were positive for PPV7, representing a 27.3% positive detection rate. The co-infection rate of PPV7 and PCV2 was 17.4% (67/385). Compared with the reference strains, we noted 93.9%-97.9% similarity in the NS1 gene and 87.4%-95.0% similarity in the cap gene. Interestingly, compared with the reference strains, sixteen of the PPV7 strains in this study contained an additional 3 to 15 nucleotides in the middle of the cap gene. Therefore, the Cap protein of fourteen strains encoded 474 amino acids, and the Cap protein of the other two strains encoded 470 amino acids. However, the Cap protein of the reference strain PPV7 isolate 42 encodes 469 amino acids. This is the first report of sequence variation within the cap gene, confirming an increase in the number of amino acids in the Cap protein of PPV7. Our findings provide new insight into the prevalence of PPV7 in swine in Guangxi, China, as well as sequence data and phylogenetic analysis of these novel PPV7 isolates.

Biomimetic recyclable microgels for on-demand generation of hydrogen peroxide and antipathogenic application

Microgels that can generate antipathogenic levels of hydrogen peroxide (H₂O₂) through simple rehydration in solutions with physiological pH are described herein. H₂O₂ is a widely used disinfectant but the oxidant is hazardous to store and transport. Catechol, an adhesive moiety found in mussel adhesive proteins, was incorporated into microgels, which generated 1-5 mM of H₂O₂ for up to four days as catechol autoxidized. The sustained release of low concentrations of H₂O₂ was antimicrobial against both gram-positive (Staphylococcus epidermidis) and gram-negative (Escherichia coli) bacteria and antiviral against both non-enveloped porcine parvovirus (PPV) and enveloped bovine viral diarrhea virus (BVDV). The amount of released H₂O₂ is several orders of magnitude lower than H₂O₂ concentration previously reported for antipathogenic activity. Most notably, these microgels reduced the infectivity of the more biocide resistant non-envelope virus by 3 log reduction value (99.9% reduction in infectivity). By controlling the oxidation state of catechol, microgels can be repeatedly activated and deactivated for H₂O₂ generation. These microgels do not contain a reservoir for storing the reactive H₂O₂ and can potentially function as a lightweight and portable dried powder source for the disinfectant for a wide range of applications. STATEMENT OF SIGNIFICANCE: Researchers have designed bioadhesives and coatings using the adhesive moiety catechol to mimic the strong adhesion capability of mussel adhesive proteins. During catechol autoxidation, hydrogen peroxide (H₂O₂) is generated as a byproduct. Here, catechol was incorporated into microgels, which can generate millimolar levels of H₂O₂ by simply hydrating the microgels in a solution with physiological pH. The sustained release of H₂O₂ was both antimicrobial and antiviral, inactivating even the more biocide resistant non-enveloped virus. These microgels can be repeatedly activated and deactivated for H₂O₂ generation by incubating them in solutions with different pH. This simplicity and recyclability will enable this biomaterial to function as a lightweight and portable source for the disinfectant for a wide range of applications.

Contemporary Zika Virus Isolates Induce More dsRNA and Produce More Negative-Strand Intermediate in Human Astrocytoma Cells

The recent emergence and rapid geographic expansion of Zika virus (ZIKV) poses a significant challenge for public health. Although historically causing only mild febrile illness, recent ZIKV outbreaks have been associated with more severe neurological complications, such as Guillain-Barré syndrome and fetal microcephaly. Here we demonstrate that two contemporary (2015) ZIKV isolates from Puerto Rico and Brazil may have increased replicative fitness in human astrocytoma cells. Over a single infectious cycle, the Brazilian isolate replicates to higher titers and induces more severe cytopathic effects in human astrocytoma cells than the historical African reference strain or an early Asian lineage isolate. In addition, both contemporary isolates induce significantly more double-stranded RNA in infected astrocytoma cells, despite similar numbers of infected cells across isolates. Moreover, when we quantified positive- and negative-strand viral RNA, we found that the Asian lineage isolates displayed substantially more negative-strand replicative intermediates than the African lineage isolate in human astrocytoma cells. However, over multiple rounds of infection, the contemporary ZIKV isolates appear to be impaired in cell spread, infecting a lower proportion of cells at a low MOI despite replicating to similar or higher titers. Taken together, our data suggests that contemporary ZIKV isolates may have evolved mechanisms that allow them to replicate with increased efficiency in certain cell types, thereby highlighting the importance of cell-intrinsic factors in studies of viral replicative fitness.

A convenient colorimetric assay for the quantification of porcine epidemic diarrhea virus and neutralizing antibodies

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PEDV is an economically important, enteric coronavirus of swine.

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Visual reading of 96 well plates for virus neutralization (V/N) or TCID₅₀ assays is time consuming.

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The newly developed colorimetric PEDV V/N and TCID₅₀ assays are reliable and convenient.

Neonatal enteritis caused by the porcine epidemic diarrhea virus (PEDV) is an important cause of high mortality and economic losses to the swine industry. Virus neutralization (V/N) assays are commonly requested in diagnostic laboratories for the assessment of protective antibodies. However, the visual assessment of viral cytopathic effects by operators to determine antibody titers or for viral quantification is a tedious, subjective and time-consuming process, especially when high volume testing is involved. To improve the ease of testing, a colorimetric virus neutralization and TCID₅₀ assays were developed and validated in this study using (3-(4,5-dimethylthiazol-2-yl) Tr-2,5-diphenyltetrazolium- bromide) (MTT), a colorimetric agent which measures cell viability. The respective conventional assays were used as the gold standards. An OD cut off value of ≤0.53, selected by receiver operating characteristics analysis, could distinguish between wells with and without CPE accurately. Performance and reproducibility parameters of the colorimetric assays were comparable to the conventional assays. The described methods can reduce testing time in diagnostic laboratories, while significantly improving current protocols.

Biology of Porcine Parvovirus (Ungulate parvovirus 1)

Porcine parvovirus (PPV) is among the most important infectious agents causing infertility in pigs. Until recently, it was thought that the virus had low genetic variance, and that prevention of its harmful effect on pig fertility could be well-controlled by vaccination. However, at the beginning of the third millennium, field observations raised concerns about the effectiveness of the available vaccines against newly emerging strains. Subsequent investigations radically changed our view on the evolution and immunology of PPV, revealing that the virus is much more diverse than it was earlier anticipated, and that some of the “new” highly virulent isolates cannot be neutralized effectively by antisera raised against “old” PPV vaccine strains. These findings revitalized PPV research that led to significant advancements in the understanding of early and late viral processes during PPV infection. Our review summarizes the recent results of PPV research and aims to give a comprehensive update on the present understanding of PPV biology.

Generation and Characterization of Eptesicus fuscus (Big brown bat) kidney cell lines immortalized using the Myotis polyomavirus large T-antigen

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Eptesicus fuscus kidney cells immortalized using Myotis polyomavirus T-antigen.

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E. fuscus interferon competent kidney cell line supports the growth of vesicular stomatitis virus, porcine epidemic diarrhea virus, herpes simplex virus and Middle-East respiratory syndrome coronavirus.

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All cell lines exhibit a marker for fibroblasts (vimentin), some also exhibit an epithelial marker (cytokeratin).

It is speculated that bats are important reservoir hosts for numerous viruses, with 27 viral families reportedly detected in bats. Majority of these viruses have not been isolated and there is little information regarding their biology in bats. Establishing a well-characterized bat cell line supporting the replication of bat-borne viruses would facilitate the analysis of virus-host interactions in an in vitro model. Currently, few bat cell lines have been developed and only Tb1-Lu, derived from Tadarida brasiliensis is commercially available. Here we describe a method to establish and immortalize big brown bat (Eptesicus fuscus) kidney (Efk3) cells using the Myotis polyomavirus T-antigen. Subclones of this cell line expressed both epithelial and fibroblast markers to varying extents. Cell clones expressed interferon beta in response to poly(I:C) stimulation and supported the replication of four different viruses, namely, vesicular stomatitis virus (VSV), porcine epidemic diarrhea coronavirus (PED-CoV), Middle-East respiratory syndrome coronavirus (MERS-CoV) and herpes simplex virus (HSV). To our knowledge, this is the first bat cell line from a northern latitude insectivorous bat developed using a novel technology. The cell line has the potential to be used for isolation of bat viruses and for studying virus-bat interactions in culture.

Herpes murine model as a biological assay to test dialyzable leukocyte extracts activity

Human dialyzable leukocyte extracts (DLEs) are heterogeneous mixtures of low-molecular-weight peptides that are released on disruption of peripheral blood leukocytes from healthy donors. DLEs improve clinical responses in infections, allergies, cancer, and immunodeficiencies. Transferon is a human DLE that has been registered as a hemoderivate by Mexican health authorities and commercialized nationally. To develop an animal model that could be used routinely as a quality control assay for Transferon, we standardized and validated a murine model of cutaneous HSV-1 infection. Using this model, we evaluated the activity of 27 Transferon batches. All batches improved the survival of HSV-1-infected mice, wherein average survival rose from 20.9% in control mice to 59.6% in Transferon-treated mice. The activity of Transferon correlated with increased serum levels of IFN-γ and reduced IL-6 and TNF-α concentrations. Our results demonstrate that (i) this mouse model of cutaneous herpes can be used to examine the activity of DLEs, such as Transferon; (ii) the assay can be used as a routine test for batch release; (iii) Transferon is produced with high homogeneity between batches; (iv) Transferon does not have direct virucidal, cytoprotective, or antireplicative effects; and (v) the protective effect of Transferon in vivo correlates with changes in serum cytokines.

Resveratrol inhibits enterovirus 71 replication and pro-inflammatory cytokine secretion in rhabdosarcoma cells through blocking IKKs/NF-κB signaling pathway

Polydatin and resveratrol, as major active components in Polygonum cuspidatum, have anti-inflammatory, antioxidant and antitumor functions. However, the effect and mechanism of polydatin and resveratrol on enterovirus 71 (EV71) have not been reported. In this study, resveratrol revealed strong antiviral activity on EV71, while polydatin had weak effect. Neither polydatin nor resveratrol exhibited influence on viral attachment. Resveratrol could effectively inhibit the synthesis of EV71/VP1 and the phosphorylation of IKKα, IKKβ, IKKγ, IKBα, NF-κB p50 and NF-κB p65, respectively. Meanwhile, the remarkably increased secretion of IL-6 and TNF-α in EV71-infected rhabdosarcoma (RD) cells could be blocked by resveratrol. These results demonstrated that resveratrol inhibited EV71 replication and cytokine secretion in EV71-infected RD cells through blocking IKKs/NF-κB signaling pathway. Thus, resveratrol may have potent antiviral effect on EV71 infection.

Detecting Virus-Like Particles from the Umgeni River, South Africa

It is important to consider viruses in water quality because of their incidence as causal agents for diarrhoeal disease, and due to their characteristics, which allow them to survive in changing environmental conditions indefinitely. This study assessed the viral quality of the Umgeni River in South Africa seasonally. A two-step tangential flow filtration process was setup to remove the bacteria and to concentrate the virus populations from large volume water samples. The concentrated water samples contained up to 659 and 550 pfu/mL of somatic and F-RNA coliphages, respectively. Several virus families including Adenoviridae, Herpesviridae, Orthomyxoviridae, Picornaviridae, Poxviridae and Reoviridae were found in the river based on the morphologies examined under transmission electron microscopy. All concentrated water samples produced substantial cytopathic effects on the Vero, HEK 293, Hela and A549 cell lines. These results indicate the potential of viruses in the water samples especially from the lower catchment areas of the Umgeni River to infect human hosts throughout the year. The present study highlights the importance of routine environmental surveillance of human enteric viruses in water sources. This can contribute to a better understanding of the actual burden of disease on those who might be using the water directly without treatment.

Virus adsorption of water-stable quaternized chitosan nanofibers

The burden of unsafe drinking water is responsible for millions of deaths each year. To relieve this burden, we are in search of an inexpensive material that can adsorb pathogens from drinking water. In this pursuit, we have studied the natural carbohydrate, chitosan. To impart virus removal features, chitosan has been functionalized with a quaternary amine to form quaternized chitosan N-[(2-hydroxyl-3-trimethylammonium) propyl] chitosan (HTCC). HTCC can be electrospun into nanofibers with the non-ionogenic polyvinyl alcohol (PVA), creating a high surface area mat. High surface area is a major requirement for effective adsorption processes. HTCC is antiviral and antimicrobial, making it a good material for water purification. However, HTCC dissolves in water. We have explored the parameters to crosslink the nanofibers with glutaraldehyde. We have imparted water stability so there is a maximum of 30% swelling of the fibers after 6h in water. The water stable fibers retain their ability to adsorb virus, as shown for an enveloped and nonenveloped virus. HTCC now has the potential to be incorporated into a microfiltration membrane that can remove viruses. This could create an inexpensive, low pressure filtration membrane for drinking water purification.

Reversible cyclic peptide libraries for the discovery of affinity ligands

A novel strategy is presented for the identification of cyclic peptide ligands from combinatorial libraries of reversible cyclic depsipeptides. A method for the solid-phase synthesis of individual cyclic depsipeptides and combinatorial libraries of these compounds is proposed, which employs lactic acid (Lact) and the dipeptide ester (Nα-Ac)-Ser(Ala)- as linkers for dilactonization. Upon alkaline treatment of the beads selected by screening a model library, the cyclic depsipeptides are linearized and released from the solid support to the liquid phase, to be sequenced via single-step tandem mass spectrometry (MS/MS). The protocol presented for library synthesis provides for wide structural diversity. Two model sequences, VVWVVK and AAWAAR, were chosen to present different structural examples for depsipeptide libraries and demonstrate the process of sequence determination by mass spectrometry. Further, a case study using the IgG binding cyclic depsipeptide cyclo[(Nα-Ac)-S(A)-RWHYFK-Lact-E] is presented to demonstrate the process of library screening and sequence determination on the selected beads. Finally, a method is shown for synthesis of the irreversible cyclic peptide corresponding to the proposed depsipeptide structure, to make the ligand stable to the aqueous acid and alkaline conditions encountered in affinity chromatographic applications. The cyclic peptide ligand was synthesized on a poly(methacrylate) resin and used for chromatographic binding of the target IgG.

The use of RT-PCR for determination of separate end-points for the strains IB H120 and IB D274 in titration of the combination vaccine Poulvac IB® primer

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Reading of live virus titrations by PCR.

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Determination of endpoints for different viruses in one titration by PCR.

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Similarity of titration results of reading by visual examination and reading by PCR.

Poulvac IB^® Primer is a lyophilized vaccine containing two attenuated infectious bronchitis strains in one vial, IB H120 and IB D274. For quantification of the viral content of the vaccine, dilution series of the final product are inoculated in embryonated chicken eggs. After the incubation period of seven days standard practice is for the embryos to be taken from each egg and examined visually for IB specific lesions; these readings are used to determine an end-point in viral titrations. The result is a titre value to which both strains contribute. However, it is not clear what the live virus titre is for strain IB H120 and for strain IB D274. In order to determine end-points in the titration for each of the two strains, we collected the allantoic fluids from each egg after the incubation period and tested these for the presence of IB H120 and IB D274 by a strain specific reverse phase PCR. Based on the data obtained by PCR we were able to determine an end-point for each of the two strains. For a given commercial batch of Poulvac IB primer we determined titres of 10^6.31 EID₅₀ per vial for IB H120 and 10^6.59 EID₅₀ for IB D274 using PCR for end-point determination. These end-points matched well with the end-point determined for both strains cumulatively after visual examination, i.e. 10^6.67 EID₅₀ per vial. It is concluded that PCR is a suitable means to determine end-points in titrations of live viruses.

Development of a new cell culture-based method and optimized protocol for the detection of enteric viruses

The development of rapid and effective methods to detect water- and food-borne enteric viruses is important for the prevention and control of mass infection. This study represents an attempt to develop a reliable cell culture-based detection system and optimize an effective and rapid protocol for the assaying of environmental samples for the presence of infectious enteric viruses. Six enteric viruses were used in this study: poliovirus, Coxsackie virus A9, Coxsackie virus B5, human rotavirus G1, hepatitis A virus, and adenovirus type 41. Among the cell lines from humans (A549, HeLa, HEK293, and HFF) and other primates (Vero, BS-C-1, FRhK-4, BGMK, and MA104), a cytopathic effect (CPE) analysis indicated that the MA104 cell line was the most optimal for use in the detection of infectious enteric viruses. Both the sensitivity and specificity of virus detection in MA104 cells were similar to or higher than those in standard BGMK cells. Next, a method was developed for the determination of the infectiousness of enteric viruses using the colorimetric thiazolyl blue (MTT) assay. This assay utilizes 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide to yield % values based on colorimetric results. These results were compared with those from a conventional CPE-based TCID(50) assay, revealing no statistically significant difference between the two methods. The MTT% values in MA104 cells were comparable to those in BGMK cells. This MA104 cell-based MTT assay could substitute for the classical BGMK cell-based CPE assay for infectious enteric viruses.

A colorimetric-based accurate method for the determination of enterovirus 71 titer

The 50 % tissue culture infectious dose (TCID50) is still one of the most commonly used techniques for estimating virus titers. However, the traditional TCID50 assay is time consuming, susceptible to subjective errors and generates only quantal data. Here, we describe a colorimetric-based approach for the titration of Enterovirus 71 (EV71) using a modified method for making virus dilutions. In summary, the titration of EV71 using MTT or MTS staining with a modified virus dilution method decreased the time of the assay and eliminated the subjectivity of observational results, improving accuracy, reproducibility and reliability of virus titration, in comparison with the conventional TCID50 approach (p < 0.01). In addition, the results provided evidence that there was better correlation between a plaquing assay and our approach when compared to the traditional TCID50 approach. This increased accuracy also improved the ability to predict the number of virus plaque forming units present in a solution. These improvements could be of use for any virological experimentation, where a quick accurate titration of a virus capable of causing cell destruction is required or a sensible estimation of the number of viral plaques based on TCID50 of a virus is desired.

A practical validation approach for virus titer testing of avian infectious bursal disease live vaccine according to current regulatory guidelines

The method for virus titer determination of avian infectious bursal disease (IBD) live vaccine, developed long before regulatory validation guidelines is a cell culture based biological assay intended for use in vaccine release testing. The aim of our study was to perform a validation, based on fit-for-purpose principle, of an old 50% tissue culture infectious dose (TCID(50)) method according to Guidelines of the International Cooperation on Harmonization of Technical Requirements for Registration of Veterinary Medicinal Products (VICH). This paper addresses challenges and discusses some key aspects that should be considered when validating biological methods. A different statistical approach and non-parametric statistics was introduced in validation protocol in order to derive useful information from experimental data. This approach is applicable for a wide range of methods. In conclusion, the previous virus titration method had showed to be precise, accurate, linear, robust and in accordance with current regulatory standards, which indicates that there is no need for additional re-development or upgrades of the method for its suitability for intended use.

Isolating toxic insulin amyloid reactive species that lack β-sheets and have wide pH stability

Amyloid diseases, including Alzheimer's disease, are characterized by aggregation of normally functioning proteins or peptides into ordered, β-sheet rich fibrils. Most of the theories on amyloid toxicity focus on the nuclei or oligomers in the fibril formation process. The nuclei and oligomers are transient species, making their full characterization difficult. We have isolated toxic protein species that act like an oligomer and may provide the first evidence of a stable reactive species created by disaggregation of amyloid fibrils. This reactive species was isolated by dissolving amyloid fibrils at high pH and it has a mass >100 kDa and a diameter of 48 ± 15 nm. It seeds the formation of fibrils in a dose dependent manner, but using circular dichroism and deep ultraviolet resonance Raman spectroscopy, the reactive species was found to not have a β-sheet rich structure. We hypothesize that the reactive species does not decompose at high pH and maintains its structure in solution. The remaining disaggregated insulin, excluding the toxic reactive species that elongated the fibrils, returned to native structured insulin. This is the first time, to our knowledge, that a stable reactive species of an amyloid reaction has been separated and characterized by disaggregation of amyloid fibrils.

Porcine parvovirus removal using trimer and biased hexamer peptides

Assuring the microbiological safety of biological therapeutics remains an important concern. Our group has recently reported small trimeric peptides that have the ability to bind and remove a model nonenveloped virus, porcine parvovirus (PPV), from complex solutions containing human blood plasma. In an effort to improve the removal efficiency of these small peptides, we created a biased library of hexamer peptides that contains two previously reported trimeric peptides designated WRW and KYY. This library was screened and several hexamer peptides were discovered that also removed PPV from solution, but there was no marked improvement in removal efficiency when compared to the trimeric peptides. Based on simulated docking experiments, it appeared that hexamer peptide binding is dictated more by secondary structure, whereas the binding of trimeric peptides is dominated by charge and hydrophobicity. This study demonstrates that trimeric and hexameric peptides may have different, matrix-specific roles to play in virus removal applications. In general, the hexamer ligand may perform better for binding of specific viruses, whereas the trimer ligand may have more broadly reactive virus-binding properties.