High critical temperature above T(g) may contribute to the stability of biological systems

Enantiospecific crystallisation behaviour of malic acid in mechanochemical reactions with vinpocetine

We report an intriguing example of enantioselectivity in the formation of new multicomponent crystalline solid containing vinpocetine and malic acid. Several experimental data sets confirmed that the multicomponent system presents a clear enantiospecific crystallisation behaviour both in the solid-state and in solution: only the system consisting of vinpocetine and L-malic acid produces a free-flowing solid consisting of a new crystalline form, while the experiments with D-malic acid produced an amorphous and often deliquescent material. The new vinpocetine-L-malic system crystallizes in the monoclinic space group of P21 and in a 1:1 molar ratio, where the two molecules are linked through intermolecular hydrogen bonds in the asymmetric unit. The vinpocetine-DL-malic system was partially crystalline (with also traces of unreacted vinpocetine) with diffraction peaks corresponding to those of vinpocetine-L-malic acid. Solid-state NMR experiments revealed strong ionic interactions in all the three systems. However, while vinpocetine-L-malic acid system was a pure and crystalline phase, the other two systems persistently showed the presence of unreacted vinpocetine. This resulted in a significant worsening of the dissolution profile with respect to the pure vinpocetine-L-malic crystalline salt, whose dissolution kinetics appeared superior.

Effect of Aerosol Size on Glass Transition Temperature

The amorphous phase state of suspended nanoparticles affects their atmospheric lifetimes and environmental impact. Influence of relative humidity and chemical composition on the glass-to-liquid transition is well-known. However, the influence of the particle size on the phase transition remains uncertain. Here we show experimental data that probe the amorphous phase transition of suspended sucrose particles as a function of particle size. The depression in glass-transition temperature follows the Gibbs-Thomson or Keesom-Laplace predicted proportionality of ΔTg ∝ D-1 for particles 100-700 nm in diameter, but the proportionality changes to ΔTg ∝ D-1/2 for smaller sizes. Literature data for glass-transition temperature depression in thin films and nanoconfined compounds show similar and strong deviations from the expected D-1 behavior. While the observed proportionalities remain incompletely understood, the results here provide evidence that the deviation from ΔTg ∝ D-1 is not attributable to substrate effects.

The dual effect of shellac on survival of spray-dried Lactobacillus rhamnosus GG microcapsules

Heat shock and hygroscopicity are two main factors that resulted in low viability of probiotics in spray-dried microcapsules during storage. Hydrophobic polyester shellac was combined with whey protein isolate (WPI) to solve this problem. The results suggested that although the survival rate after drying decreased from 20.63% to 0.01% with increased shellac to WPI ratio, the 1:1 shellac-WPI provided the best protection among all samples during storage. The consistence between moisture-adsorption-isotherm and bacterial inactivation constants confirmed the moisture barrier effect of shellac under moderate humidity. Single-droplet drying and differential scanning calorimeter revealed that shellac addition reduced the drying rate and glass transition temperature of microcapsules, which in turn decreased the membrane integrity and growth capability of the probiotics after drying. This study revealed the dual effect of hydrophobic material on instant and long-term survival of spray-dried probiotic microcapsules, which provided new sight to the design of composite wall materials.

Mixed Biopolymer Systems Based on Bovine and Caprine Caseins, Yeast β-Glucan, and Maltodextrin for Microencapsulating Lutein Dispersed in Emulsified Lipid Carriers

Lutein is an important antioxidant that quenches free radicals. The stability of lutein and hence compatibility for food fortification is a big challenge to the food industry. Encapsulation can be designed to protect lutein from the adverse environment (air, heat, light, pH). In this study, we determined the impact of mixed biopolymer systems based on bovine and caprine caseins, yeast β-glucan, and maltodextrin as wall systems for microencapsulating lutein dispersed in emulsified lipid carriers by spray drying. The performance of these wall systems at oil/water interfaces is a key factor affecting the encapsulation of lutein. The highest encapsulation efficiency (97.7%) was achieved from the lutein microcapsules prepared with the mixed biopolymer system of caprine αs1-II casein, yeast β-glucan, and maltodextrin. Casein type and storage time affected the stability of lutein. The stability of lutein was the highest (64.57%) in lutein microcapsules prepared with the mixed biopolymer system of caprine αs1-II casein, yeast β-glucan, and maltodextrin, whereas lutein microcapsules prepared with the biopolymer system of bovine casein, yeast β-glucan, and maltodextrin had the lowest (56.01%). The stability of lutein in the lutein microcapsules dramatically decreased during storage time. The antioxidant activity of lutein in the lutein microcapsules was closely associated with the lutein concentration.

Prospects of Inhaled Phage Therapy for Combatting Pulmonary Infections

With respiratory infections accounting for significant morbidity and mortality, the issue of antibiotic resistance has added to the gravity of the situation. Treatment of pulmonary infections (bacterial pneumonia, cystic fibrosis-associated bacterial infections, tuberculosis) is more challenging with the involvement of multi-drug resistant bacterial strains, which act as etiological agents. Furthermore, with the dearth of new antibiotics available and old antibiotics losing efficacy, it is prudent to switch to non-antibiotic approaches to fight this battle. Phage therapy represents one such approach that has proven effective against a range of bacterial pathogens including drug resistant strains. Inhaled phage therapy encompasses the use of stable phage preparations given via aerosol delivery. This therapy can be used as an adjunct treatment option in both prophylactic and therapeutic modes. In the present review, we first highlight the role and action of phages against pulmonary pathogens, followed by delineating the different methods of delivery of inhaled phage therapy with evidence of success. The review aims to focus on recent advances and developments in improving the final success and outcome of pulmonary phage therapy. It details the use of electrospray for targeted delivery, advances in nebulization techniques, individualized controlled inhalation with software control, and liposome-encapsulated nebulized phages to take pulmonary phage delivery to the next level. The review expands knowledge on the pulmonary delivery of phages and the advances that have been made for improved outcomes in the treatment of respiratory infections.

Impact of a Novel Nano-Protectant on the Viability of Probiotic Bacterium Lactobacillus casei K17

Probiotics are considered as desirable alternatives to antibiotics because of their beneficial effects on the safety and economy of farm animals. The protectant can ensure the viability of probiotics, which is the prerequisite of the beneficial effects. The objective of this study was to evaluate the effects of a novel nano-protectant containing trehalose, skim milk powder, phytoglycogen nanoparticles, and nano-phytoglycogen Pickering emulsions on the viability of Lactobacillus casei K17 under different conditions. The results indicated that the optimal concentration of the carbohydrate substrate was determined to be 10% skim milk powder (w/w) instead of trehalose. The combination of 10% skim milk powder (w/w), 1% phytoglycogen nanoparticles (w/w), and 10% Pickering emulsions (w/w) was selected as the optimal component of the protectant. Trilayer protectants with an optimal component had a more significant protective effect on the bacteria than that of the monolayer and bilayer protectants, or the control in feed storage, freeze-drying, and simulated gastrointestinal environment. A scanning electron microscope was used to monitor the morphological characteristics of the protectants for different layers on L. casei. In conclusion, the trilayer protectant exhibited a substantial effect on L. casei during storage and consumption, which could be used in the feed and functional food.

Desiccation-induced cell damage in bacteria and the relevance for inoculant production

Plant growth-promoting bacteria show great potential for use in agriculture although efficient application remains challenging to achieve. Cells often lose viability during inoculant production and application, jeopardizing the efficacy of the inoculant. Since desiccation has been documented to be the primary stress factor affecting the decrease in survival, obtaining xerotolerance in plant growth-promoting bacteria is appealing. The molecular damage that occurs by drying bacteria has been broadly investigated, although a complete view is still lacking due to the complex nature of the process. Mechanic, structural, and metabolic changes that occur as a result of water depletion may potentially afflict lethal damage to membranes, DNA, and proteins. Bacteria respond to these harsh conditions by increasing production of exopolysaccharides, changing composition of the membrane, improving the stability of proteins, reducing oxidative stress, and repairing DNA damage. This review provides insight into the complex nature of desiccation stress in bacteria in order to facilitate strategic choices to improve survival and shelf life of newly developed inoculants. KEY POINTS: Desiccation-induced damage affects most major macromolecules in bacteria. Most bacteria are not xerotolerant despite multiple endogenous adaption mechanisms. Sensitivity to drying severely hampers inoculant quality.

A new protectant medium preserving bacterial viability after freeze drying

Freeze-drying technology has been widely considered for decades as a suitable technique to preserve microorganisms. However, protective agents must be added prior to freeze drying to improve the survival and storage stability of the bacteria. The objective of our study was to evaluate the effect of a new protectant medium containing sucrose (10 %), trehalose (10 %), skimmed milk (10 %) and antioxidants on the viability of gut bacteria under different storage conditions. Two strains were tested, Escherichia coli and Akkermansia muciniphila, as examples of facultative aerobic and anaerobic bacteria, respectively. We studied the cell viability and bacterial morphology in 5 fecal samples in the presence and absence of this protectant medium using plating technique, flow cytometry and scanning electron microscopy. The results of bacterial viability assessed by plating method showed that the protectant medium yielded higher survival rates for both strains whatever the storage conditions (85-93 %) compared to normal saline solution (0.36-37.50 %). It also showed its effectiveness on fecal samples, where bacterial viability after freeze-drying was 89.47 ± 7.63 % and 84.01 ± 7.44 %, as evidenced by flow cytometry analysis and plating method. However unprotected samples showed the lowest cell viability at 19.01 ± 12.88 % and 13.23 ± 9.56 %, as measured by flow cytometry and plating method. In addition, bacterial size and shape were conserved in the protectant medium. In contrast, storage without protectant medium severely damaged bacterial morphology. In conclusion, our study is the first to use morphological features as well as culture-dependant and culture-independent tests to evaluate the effectiveness of a new protectant medium.

Influence of Composition and Spray-Drying Process Parameters on Carrier-Free DPI Properties and Behaviors in the Lung: A review

Although dry powder inhalers (DPIs) have attracted great interest compared to nebulizers and metered-dose inhalers (MDIs), drug deposition in the deep lung is still insufficient to enhance therapeutic activity. Indeed, it is estimated that only 10–15% of the drug reaches the deep lung while 20% of the drug is lost in the oropharyngeal sphere and 65% is not released from the carrier. The potentiality of the powders to disperse in the air during the patient’s inhalation, the aerosolization, should be optimized. To do so, new strategies, in addition to classical lactose-carrier, have emerged. The lung deposition of carrier-free particles, mainly produced by spray drying, is higher due to non-interparticulate forces between the carrier and drug, as well as better powder uniformity and aerosolization. Moreover, the association of two or three active ingredients within the same powder seems easier. This review is focused on a new type of carrier-free particles which are characterized by a sugar-based core encompassed by a corrugated shell layer produced by spray drying. All excipients used to produce such particles are dissected and their physico-chemical properties (Péclet number, glass transition temperature) are put in relation with the lung deposition ability of powders. The importance of spray-drying parameters on powders’ properties and behaviors is also evaluated. Special attention is given to the relation between the morphology (characterized by a corrugated surface) and lung deposition performance. The understanding of the closed relation between particle material composition and spray-drying process parameters, impacting the final powder properties, could help in the development of promising DPI systems suitable for local or systemic drug delivery.

Producing Powders Containing Active Dry Probiotics With the Aid of Spray Drying

Probiotics are microorganisms capable of conferring health benefits to humans and animals when ingested. Probiotic products that prevail in food market usually contain viable bacteria from Lactobacillus and Bifidobacterium genera. Bacterial strains in these genera often have complex nutrient requirements and tend to be fragile under environmental stresses. How to incorporate the cells into food matrix without causing undesired viability loss is a key issue for developing products of viable probiotics. Spray drying offers a rapid way to produce powders encapsulating probiotics in a matrix of protectant(s), which may extend the term of viability preservation and expand the application of probiotic products. In spray drying, feed solution that contains probiotic cells and dissolved or suspended protectant solids are atomized into droplets, which are quickly converted into particles by drying in a hot airflow. The harsh conditions and interplaying stresses make the maintenance of cell viability a challenging task. To enhance cell survival in dried powders, various approaches have been attempted, including the enhancement of the intrinsic stress tolerance of cells, adjustment of protectant composition, and optimization of the production process and dryer settings. This chapter discusses important factors influencing probiotic viability during spray drying from aspects of microbiology, food chemistry, and drying process. The mechanisms underlying the influences at the droplet and cellular levels and strategies taken to protect cell viability at the process level are discussed.

Ion-induced modification of the sucrose network and its impact on melting of freeze-dried liposomes. DSC and molecular dynamics study

Disaccharides play an important role in survival of anhydrobiotic organisms during extreme environmental conditions. A key protection feature is their capability to form the hydrogen bond (HB) network in a similar fashion as the one made by water. Since various ions also affect the HB network in completely hydrated systems, it is of a great interest to understand how they impact preservation when incorporated in a disaccharide network. To address this, we employ a combination of experimental and modeling techniques to study behavior of multilamellar 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes freeze-dried with sucrose in presence of NaCl or NaH₂PO₄·H₂O at various concentrations (0.01-1M). Differential scanning calorimetry (DSC) was employed in order to determine the cooperative unit size (CUS), the number of lipid molecules that constitute a domain of cooperative motion in the liposome, and the melting temperature (T_m). In the absence of salt CUS was estimated to be 122±12, whereas in the presence of NaCl CUS increases more (347±34 for c=1M) than for NaH₂PO₄·H₂O (193±26 for 1M). When it comes to T_m, the situation is reversed; NaCl induces increase by about 1K, while NaH₂PO₄·H₂O by about 10K. These findings clearly demonstrate how different interaction forces-hydrogen bonding, charge pairing, and van der Waals interactions between acyl chains-affect CUS and T_m. Their interplay and contribution of particular interaction was further analyzed with molecular dynamics (MD) simulations. This analysis demonstrated that the HB network of DMPC and sucrose is partially disrupted in the presence of NaCl ions, and even to a greater extent in the case of NaH₂PO₄·H₂O ions. Notably, H₂PO₄^- ions outcompete and replace the sucrose molecules at the DMPC surface, which in turn alters the nature of the DMPC-surrounding interactions, from a weaker HB-dominated to a stronger CP-dominated interaction network.

X-ray diffraction measurement of cosolvent accessible volume in rhombohedral insulin crystals

X-ray crystallographic measurement of the number of solvent electrons in the unit cell of a protein crystal equilibrated with aqueous solutions of different densities provides information about preferential hydration in the crystalline state. Room temperature and cryo-cooled rhombohedral insulin crystals were equilibrated with 1.2M trehalose to study the effect of lowered water activity. The native and trehalose soaked crystals were isomorphous and had similar structures. Including all the low resolution data, the amplitudes of the structure factors were put on an absolute scale (in units of electrons per asymmetric unit) by constraining the integrated number of electrons inside the envelope of the calculated protein density map to equal the number deduced from the atomic model. This procedure defines the value of F(000), the amplitude at the origin of the Fourier transform, which is equal to the total number of electrons in the asymmetric unit (i.e. protein plus solvent). Comparison of the F(000) values for three isomorphous pairs of room temperature insulin crystals, three with trehalose and three without trehalose, indicates that 75±12 electrons per asymmetric unit were added to the crystal solvent when soaked in 1.2M trehalose. If all the water in the crystal were available as solvent for the trehalose, 304 electrons would have been added. Thus, the co-solvent accessible volume is one quarter of the total water in the crystal. Determination of the total number of electrons in a protein crystal is an essential first step for mapping the average density distribution of the disordered solvent.

Characterization of the temperature and humidity-dependent phase diagram of amorphous nanoscale organic aerosols

Atmospheric aerosols can exist in amorphous semi-solid or glassy phase states. These states are determined by the temperature (T) and relative humidity (RH). New measurements of viscosity for amorphous semi-solid nanometer size sucrose particles as a function of T and RH are reported. Viscosity is measured by inducing coagulation between two particles and probing the thermodynamic states that induce the particle to relax into a sphere. It is shown that the glass transition temperature can be obtained by extrapolation to 10¹² Pa s from the measured temperature-dependent viscosity in the 10⁶ to 10⁷ Pa s range. The experimental methodology was refined to allow isothermal probing of RH dependence and to increase the range of temperatures over which the dry temperature dependence can be studied. Several experiments where one monomer was sodium dodecyl sulfate (SDS), which remains solid at high RH, are also reported. These sucrose-SDS dimers were observed to relax into a sphere at T and RH similar to those observed in sucrose-sucrose dimers, suggesting that amorphous sucrose will flow over an insoluble particle at a viscosity similar to that characteristic of coalescence between two sucrose particles. Possible physical and analytical implications of this observation are considered. The data reported here suggest that semi-solid viscosity between 10⁴ and 10¹² Pa s can be modelled over a wide range of T and RH using an adapted Vogel-Fulcher-Tammann equation and the Gordon-Taylor mixing rule. Sensitivity of modelled viscosity to variations in dry glass transition temperature, Gordon-Taylor constant, and aerosol hygroscopicity are explored, along with implications for atmospheric processes such as ice nucleation of glassy organic aerosols in the upper free troposphere. The reported measurement and modelling framework provides a template for characterizing the phase diagram of other amorphous aerosol systems, including secondary organic aerosols.

Thermal Aggregation of Calcium-Fortified Skim Milk Enhances Probiotic Protection during Convective Droplet Drying

Probiotic bacteria have been reported to confer benefits on hosts when delivered in an adequate dose. Spray-drying is expected to produce dried and microencapsulated probiotic products due to its low production cost and high energy efficiency. The bottleneck in probiotic application addresses the thermal and dehydration-related inactivation of bacteria during process. A protective drying matrix was designed by modifying skim milk with the principle of calcium-induced protein thermal aggregation. The well-defined single-droplet drying technique was used to monitor the droplet-particle conversion and the protective effect of this modified Ca-aggregated milk on Lactobacillus rhamnosus GG. The Ca-aggregated milk exhibited a higher drying efficiency and superior protection on L. rhamnosus GG during thermal convective drying. The mechanism was explained by the aggregation in milk, causing the lower binding of water in the serum phase and, conversely, local concentrated milk aggregates involved in bacteria entrapment in the course of drying. This work may open new avenues for the development of probiotic products with high bacterial viability and calcium enrichment.

Effects of Water on Structure and Dynamics of Trehalose Glasses at Low Water Contents and its Relationship to Preservation Outcomes

Dry preservation of biologics in sugar glasses is regarded as a promising alternative to conventional cryopreservation. Evidence from various studies has suggested that there is a critical range of water content beyond which the viability of preserved biologics can be greatly compromised. In this study the viability of T-cells was determined as a function of end water content after microwave-assisted drying in trehalose solutions. Hydrogen-bonding and clustering phenomena in trehalose solutions of the same moisture content were also evaluated using molecular dynamics simulation. Post-rehydration viability decreased dramatically within the range of 0.1-1 gH2O/gdw. Molecular modeling revealed that as the water content approached 0.1 gH2O/gdw the matrix formed a large interconnected trehalose skeleton with a minimal number of bound water molecules scattered in the bulk. The diffusion coefficients of trehalose oxygen atoms most distant from the glycosidic linkage fluctuated around 7.5 × 10(-14) m(2)/s within the range of 0.02-0.1 gH2O/gdw and increased again to ~1.13 × 10(-13) m(2)/s at 0.01 gH2O/gdw and below due to the loss of water in the free volume between trehalose molecules. These insights can guide the optimal selection of final moisture contents to advance dry preservation methods.

Fungal spores for dispersion in space and time

Spores are an integral part of the life cycle of the gross majority of fungi. Their morphology and the mode of formation are both highly variable among the fungi, as is their resistance to stressors. The main aim for spores is to be dispersed, both in space, by various mechanisms or in time, by an extended period of dormancy. Some fungal ascospores belong to the most stress-resistant eukaryotic cells described to date. Stabilization is a process in which biomolecules and complexes thereof are protected by different types of molecules against heat, drought, or other molecules. This review discusses the most important compounds that are known to protect fungal spores and also addresses the biophysics of cell protection. It further covers the phenomena of dormancy, breaking of dormancy, and early germination. Germination is the transition from a dormant cell toward a vegetative cell and includes a number of specific changes. Finally, the applied aspects of spore biology are discussed.

Stabilization of proteins in solid form

Immunogenicity of aggregated or otherwise degraded protein delivered from depots or other biopharmaceutical products is an increasing concern, and the ability to deliver stable, active protein is of central importance. We review characterization approaches for solid protein dosage forms with respect to metrics that are intended to be predictive of protein stability against aggregation and other degradation processes. Each of these approaches is ultimately motivated by hypothetical connections between protein stability and the material property being measured. We critically evaluate correlations between these properties and stability outcomes, and use these evaluations to revise the currently standing hypotheses. Based on this we provide simple physical principles that are necessary (and possibly sufficient) for generating solid delivery vehicles with stable protein loads. Essentially, proteins should be strongly coupled (typically through H-bonds) to the bulk regions of a phase-homogeneous matrix with suppressed β relaxation. We also provide a framework for reliable characterization of solid protein forms with respect to stability.

Applications of Infrared and Raman Spectroscopies to Probiotic Investigation

In this review, we overview the most important contributions of vibrational spectroscopy based techniques in the study of probiotics and lactic acid bacteria. First, we briefly introduce the fundamentals of these techniques, together with the main multivariate analytical tools used for spectral interpretation. Then, four main groups of applications are reported: (a) bacterial taxonomy (Subsection 4.1); (b) bacterial preservation (Subsection 4.2); (c) monitoring processes involving lactic acid bacteria and probiotics (Subsection 4.3); (d) imaging-based applications (Subsection 4.4). A final conclusion, underlying the potentialities of these techniques, is presented.

A method of lyophilizing vaccines containing aluminum salts into a dry powder without causing particle aggregation or decreasing the immunogenicity following reconstitution

Many currently licensed and commercially available human vaccines contain aluminum salts as vaccine adjuvants. A major limitation with these vaccines is that they must not be exposed to freezing temperatures during transport or storage such that the liquid vaccine freezes, because freezing causes irreversible coagulation that damages the vaccines (e.g., loss of efficacy). Therefore, vaccines that contain aluminum salts as adjuvants are formulated as liquid suspensions and are required to be kept in cold chain (2-8°C) during transport and storage. Formulating vaccines adjuvanted with aluminum salts into dry powder that can be readily reconstituted before injection may address this limitation. Spray freeze-drying of vaccines with low concentrations of aluminum salts and high concentrations of trehalose alone, or a mixture of sugars and amino acids, as excipients can convert vaccines containing aluminum salts into dry powder, but fails to preserve the particle size and/or immunogenicity of the vaccines. In the present study, using ovalbumin as a model antigen adsorbed onto aluminum hydroxide or aluminum phosphate, a commercially available tetanus toxoid vaccine adjuvanted with potassium alum, a human hepatitis B vaccine adjuvanted with aluminum hydroxide, and a human papillomavirus vaccine adjuvanted with aluminum hydroxyphosphate sulfate, it was shown that vaccines containing a relatively high concentration of aluminum salts (i.e., up to ~1%, w/v, of aluminum hydroxide) can be converted into a dry powder by thin-film freezing followed by removal of the frozen solvent by lyophilization while using low levels of trehalose (i.e., as low as 2% w/v) as an excipient. Importantly, the thin-film freeze-drying process did not cause particle aggregation, nor decreased the immunogenicity of the vaccines. Moreover, repeated freezing-and-thawing of the dry vaccine powder did not cause aggregation. Thin-film freeze-drying is a viable platform technology to produce dry powders of vaccines that contain aluminum salts.

The influence of stabilizers and rates of freezing on preserving of structurally different animal viruses during lyophilization and subsequent storage

Aims

To make a comparative evaluation of the effects of different stabilizers and freezing rates on structurally different viruses during lyophilization and storage.

Methods and Results

Two virus strains from each of six animal virus families, including both enveloped and nonenveloped viruses, were lyophilized in (i) culture medium, (ii) with the addition of gelatine–sucrose and (iii) skim milk–sodium glutamate. All the virus suspensions were frozen (i) at −80°C or (ii) in liquid nitrogen before lyophilization. Virus titre assay after lyophilization and after 8 months storage at 4°C revealed that the efficacy of stabilizers depended on virus structure. Generally, the best protective quality for enveloped viruses was achieved with gelatine–sucrose, which best maintained their infectivity and envelope morphology. Even additive‐free culture medium proved adequate for nonenveloped viruses. Differences in stabilizer efficacy were also found between virus families and were expressed immediately after lyophilization; the activity of stabilizers in the course of storage was very similar. Freezing in liquid nitrogen proved beneficial for picornaviruses.

Conclusions

The choice of an appropriate stabilizer with respect to virus type is crucial for effective lyophilization.

Significance and Impact of the Study

This study contributes to the establishment of general guidelines for animal virus lyophilization, with particular respect to differences in virus structure.

Cytoplasmic transport: bacteria turn to glass unless kicked

Bacteria lack the cytoskeleton and motors of eukaryotic cells, and their cytoplasm has been considered to be purely fluid. New data show that bacterial cytoplasm can solidify to resemble a soft glass, unless enzymatic activity creates motions to fluidize it.

Long-term dry storage of an enzyme-based reagent system for ELISA in point-of-care devices

Lateral flow devices are commonly used for many point-of-care (POC) applications in low-resource settings. However, they lack the sensitivity needed for many analytes relevant in the diagnosis of diseases. One approach to achieve higher sensitivity is signal amplification, which is commonly used in laboratory assays, but uses reagents that require refrigeration and inherently requires multiple assay steps not normally compatible with POC settings. Enzyme-based signal amplification, such as the one used in ELISA, could greatly improve the limit of detection if it were translated to a format compatible with POC requirements. A signal-amplified POC device not only requires the reagents to be stored in a stable form, but also requires automation of the multiple sequential steps of signal amplification protocols. Here, we describe a method for the long-term dry storage of ELISA reagents: horseradish peroxidase (HRP) conjugated antibody label and its colorimetric substrate diaminobenzidine (DAB). The HRP conjugate retained ∼80% enzymatic activity after dry storage at 45 °C for over 5 months. The DAB substrate was also stable at 45 °C and exhibited no detectable loss of activity over 3 months. These reagents were incorporated into a two-dimensional paper network (2DPN) device that automated the steps of ELISA for the detection of a malarial biomarker. These results demonstrate the potential of enzyme-based signal amplification for enhanced sensitivity in POC devices for low resource settings.

Dehydrin accumulation and extreme low-temperature tolerance in Siberian spruce (Picea obovata)

To investigate the role of dehydrins (DHNs) in extreme low-temperature (LT) tolerance, we sampled needle tissue of Siberian spruce (Picea obovata Ledeb.) from trees growing in an arboretum in Trondheim, Norway from August 2006 to April 2007 and tracked changes in LT tolerance via relative electrolyte leakage. We used western blotting to estimate relative amounts of proteins binding a DHN K-segment antibody, measured relative amounts of nine transcripts for small (<25 kDa) DHNs by quantitative reverse transcription-polymerase chain reaction (PCR) using primers developed for DHN transcripts in a closely related species, Picea abies (L.) Karsten, and isolated and sequenced PCR products for five P. obovata DHNs. Three protein bands of 53, 35 and 33 kDa were detected on western blots of SDS-PAGE-separated protein extracts. The 53-kDa DHN was already present late in the growing season, but accumulated during acclimation, and levels decreased rapidly during deacclimation. The 33- and 35-kDa proteins, identified as Picg5 class DHNs by mass spectrometry, first appeared in detectable amounts late in the acclimation process and remained at detectable levels throughout the period of maximum LT tolerance. Levels of the 53-kDa DHN correlated with two LT tolerance parameters, while results for the 33- and 35-kDa proteins were equivocal due to limited sample size and variation in LT tolerance during the mid-winter period. Three additional bands of 30, 28 and 26 kDa were detected in extracts from needles collected in November 2010 using an immunity-purified antibody. Immunoblotting of two-dimensional gel electrophoresis gels loaded with proteins extracted from October and November samples corroborated the results obtained by SDS-PAGE western blots. One large spot in the 53 kDa range and two trains of spots in the same size range as the 33 and 35 kDa DHNs were detected using the K-segment antibody. Eight of the nine DHN transcripts closely tracked LT tolerance parameters, whereas the ninth DHN transcripts followed a reverse pattern, decreasing during winter and increasing again during deacclimation. Multiple regression models using principal components of the transcripts to predict two different LT tolerance parameters suggest separate but overlapping functions for different DHNs in establishing and maintaining extreme LT tolerance.

Characterization of dynamics in complex lyophilized formulations: II. Analysis of density variations in terms of glass dynamics and comparisons with global mobility, fast dynamics, and Positron Annihilation Lifetime Spectroscopy (PALS)

Amorphous HES/disaccharide (trehalose or sucrose) formulations, with and without added polyols (glycerol and sorbitol) and disaccharide formulations of human growth hormone (hGH), were prepared by freeze drying and characterized with particular interest in methodology for using high precision density measurements to evaluate free volume changes and a focus on comparisons between "free volume" changes obtained from analysis of density data, fast dynamics (local mobility), and PALS characterization of "free volume" hole size. Density measurements were performed using a helium gas pycnometer, and fast dynamics was characterized using incoherent neutron scattering spectrometer. Addition of sucrose and trehalose to hGH decreases free volume in the system with sucrose marginally more effective than trehalose, consistent with superior pharmaceutical stability of sucrose hGH formulations well below Tg relative to trehalose. We find that density data may be analyzed in terms of free volume changes by evaluation of volume changes on mixing and calculation of apparent specific volumes from the densities. Addition of sucrose to HES decreases free volume, but the effect of trehalose is not detectable above experimental error. Addition of sorbitol or glycerol to HES/trehalose base formulations appears to significantly decrease free volume, consistent with the positive impact of such additions on pharmaceutical stability (i.e., degradation) in the glassy state. Free volume changes, evaluated from density data, fast dynamics amplitude of local motion, and PALS hole size data generally are in qualitative agreement for the HES/disaccharide systems studied. All predict decreasing molecular mobility as disaccharides are added to HES. Global mobility as measured by enthalpy relaxation times, increases as disaccharides, particularly sucrose, are added to HES.

Expression of a GALACTINOL SYNTHASE gene is positively associated with desiccation tolerance of Brassica napus seeds during development

Desiccation tolerance of seeds is positively correlated with raffinose family oligosaccharides (RFOs). However, RFOs' role in desiccation tolerance is still a matter of controversy. The aim of this work was to monitor the accumulation of RFO during acquisition of desiccation tolerance in rapeseed (Brassica napus L.). Rapeseeds become desiccation tolerant at 21-24d after flowering (DAF), and the time was coincident with an accumulation of raffinose and stachyose. A gene encoding galactinol synthase (GolS; EC2.4.1.123), involved in RFO biosynthesis, was cloned and functionally characterized. Enzymatic properties of recombinant galactinol synthase were also determined. Accumulation of BnGOLS-1 mRNA in developing rapeseeds was concomitant with dry weight deposition and the acquisition of desiccation tolerance, and was concurrent with the formation of raffinose and stachyose. The physiological implications of BnGOLS-1 expression patterns in developing seeds are discussed in light of the hypothesized role of RFOs in seed desiccation tolerance.

Thermotropic phase behavior and headgroup interactions of the nonbilayer lipids phosphatidylethanolamine and monogalactosyldiacylglycerol in the dry state

BACKGROUND

Although biological membranes are organized as lipid bilayers, they contain a substantial fraction of lipids that have a strong tendency to adopt a nonlamellar, most often inverted hexagonal (HII) phase. The polymorphic phase behavior of such nonbilayer lipids has been studied previously with a variety of methods in the fully hydrated state or at different degrees of dehydration. Here, we present a study of the thermotropic phase behavior of the nonbilayer lipids egg phosphatidylethanolamine (EPE) and monogalactosyldiacylglycerol (MGDG) with a focus on interactions between the lipid molecules in the interfacial and headgroup regions.

RESULTS

Liposomes were investigated in the dry state by Fourier-transform Infrared (FTIR) spectroscopy and Differential Scanning Calorimetry (DSC). Dry EPE showed a gel to liquid-crystalline phase transition below 0°C and a liquid-crystalline to HII transition at 100°C. MGDG, on the other hand, was in the liquid-crystalline phase down to -30°C and showed a nonbilayer transition at about 85°C. Mixtures (1:1 by mass) with two different phosphatidylcholines (PC) formed bilayers with no evidence for nonbilayer transitions up to 120°C. FTIR spectroscopy revealed complex interactions between the nonbilayer lipids and PC. Strong H-bonding interactions occurred between the sugar headgroup of MGDG and the phosphate, carbonyl and choline groups of PC. Similarly, the ethanolamine moiety of EPE was H-bonded to the carbonyl and choline groups of PC and probably interacted through charge pairing with the phosphate group.

CONCLUSIONS

This study provides a comprehensive characterization of dry membranes containing the two most important nonbilayer lipids (PE and MGDG) in living cells. These data will be of particular relevance for the analysis of interactions between membranes and low molecular weight solutes or soluble proteins that are presumably involved in cellular protection during anhydrobiosis.

The descent into glass formation in polymer fluids

Glassy materials have been fundamental to technology since the dawn of civilization and remain so to this day: novel glassy systems are currently being developed for applications in energy storage, electronics, food, drugs, and more. Glass-forming fluids exhibit a universal set of transitions beginning at temperatures often in excess of twice the glass transition temperature T(g) and extending down to T(g), below which relaxation becomes so slow that systems no longer equilibrate on experimental time scales. Despite the technological importance of glasses, no prior theory explains this universal behavior nor describes the huge variations in the properties of glass-forming fluids that result from differences in molecular structure. Not surprisingly, the glass transition is currently regarded by many as the deepest unsolved problem in solid state theory. In this Account, we describe our recently developed theory of glass formation in polymer fluids. Our theory explains the origin of four universal characteristic temperatures of glass formation and their dependence on monomer-monomer van der Waals energies, conformational energies, and pressure and, perhaps most importantly, on molecular details, such as monomer structure, molecular weight, size of side groups, and so forth. The theory also provides a molecular explanation for fragility, a parameter that quantifies the rate of change with temperature of the viscosity and other dynamic mechanical properties at T(g). The fragility reflects the fluid's thermal sensitivity and determines the manner in which glass-formers can be processed, such as by extrusion, casting, or inkjet spotting. Specifically, the theory describes the change in thermodynamic properties and fragility of polymer glasses with variations in the monomer structure, the rigidity of the backbone and side groups, the cohesive energy, and so forth. The dependence of the structural relaxation time at lower temperatures emerges from the theory as the Vogel-Fulcher equation, whereas pressure and concentration analogs of the Vogel-Fulcher expression follow naturally from the theory with no additional assumptions. The computed dependence of T(g) and fragility on the length of the side group in poly(α-olefins) agrees quite well with observed trends, demonstrating that the theory can be utilized, for instance, to guide the tailoring of T(g) and the fragility of glass-forming polymer fluids in the fabrication of new materials. Our calculations also elucidate the molecular characteristics of small-molecule diluents that promote antiplasticization, a lowering of T(g) and a toughening of the material.

Development of desiccation tolerance and vitrification by preculture treatment in suspension-cultured cells of the liverwort Marchantia polymorpha

Some cultured plant cells are able to acquire tolerance to various stresses when they are cultured under suitably controlled conditions. Induction of a high level of desiccation tolerance in suspension-cultured cells of the liverwort Marchantia polymorpha was examined for studying the mechanisms of desiccation tolerance and vitrification at the cellular level. Desiccation tolerance level of cells was very low and the survival rate was less than 10% after exposure to drying below 0.1 g H(2)O g(-1) dry weight (DW). Preculture treatment in 0.5 M sucrose medium was the most effective method for inducing a high level of desiccation tolerance in cells and the survival rate was 87% even after being desiccated to below 0.1 g H(2)O g(-1) DW. Preculture treatment caused alteration of cell structures and accumulation of a large amount of sucrose and newly synthesized proteins in cells. Abundant sucrose and preculture-induced proteins were necessary for full development of desiccation tolerance in the cells. When water content decreased to below 0.1 g H(2)O g(-1) DW, desiccation-tolerant cells that had been precultured were vitrified above 0 degrees C and maintained stable viability. We have succeeded in the induction of desiccation tolerance that allows formation of intracellular glass with cell viability at ambient temperatures by controlling culture conditions, and our results suggest that suspension-cultured cells of M. polymorpha are useful for studying cellular mechanisms for the development of desiccation tolerance and the stabilization of vitrified cells.