The modulation of membrane structure and stability by dimethyl sulphoxide (review)

Modulation of bacterial membranes and cellular macromolecules by dimethyl sulfoxide: A dose-dependent study providing novel insights

Using Escherichia coli as a model, this manuscript delves into the intricate interactions between dimethyl sulfoxide (DMSO) and membranes, cellular macromolecules, and the effects on various aspects of bacterial physiology. Given DMSO's wide-ranging use as a solvent in microbiology, we investigate the impacts of both non-growth inhibitory (1.0 % and 2.5 % v/v) and slightly growth-inhibitory (5.0 % v/v) concentrations of DMSO. The results demonstrate that DMSO causes alterations in bacterial membrane potential, influences the electrochemical characteristics of the cell surface, and exerts substantial effects on the composition and structure of cellular biomolecules. Genome-wide gene expression data from DMSO-treated E. coli was used to further investigate and bolster the results. The findings of this study provide valuable insights into the complex relationship between DMSO and biological systems, with potential implications in drug delivery and cellular manipulation. However, it is essential to exercise caution when utilizing DMSO to enhance the solubility and delivery of bioactive compounds, as even at low concentrations, DMSO exerts non-inert effects on cellular macromolecules and processes.

Polyploidy in Xenopus lowers metabolic rate by decreasing total cell surface area

Although polyploidization is frequent in development, cancer, and evolution, impacts on animal metabolism are poorly understood. In Xenopus frogs, the number of genome copies (ploidy) varies across species and can be manipulated within a species. Here, we show that triploid tadpoles contain fewer, larger cells than diploids and consume oxygen at a lower rate. Drug treatments revealed that the major processes accounting for tadpole energy expenditure include cell proliferation, biosynthesis, and maintenance of plasma membrane potential. While inhibiting cell proliferation did not abolish the oxygen consumption difference between diploids and triploids, treatments that altered cellular biosynthesis or electrical potential did. Combining these results with a simple mathematical framework, we propose that the decrease in total cell surface area lowered production and activity of plasma membrane components including the Na+/K+ ATPase, reducing energy consumption in triploids. Comparison of Xenopus species that evolved through polyploidization revealed that metabolic differences emerged during development when cell size scaled with genome size. Thus, ploidy affects metabolism by altering the cell surface area to volume ratio in a multicellular organism.

Redefining the Molecular Interplay between Dimethyl Sulfoxide, Lipid Bilayers, and Dehydration

The potentially damaging action of dimethyl sulfoxide (DMSO) on phospholipid bilayers remains a matter of controversy. We have conducted a series of long-scale molecular dynamics simulations of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) bilayers at various levels of hydration in the presence of variable quantities of DMSO. These simulations provide evidence for a non-destructive dehydrating mechanism of action for DMSO on DOPC bilayers across a wide concentration range and levels of hydration. Specifically, under full- and low-hydration conditions, the bilayer underwent a minor lateral contraction, coinciding with surface dehydration in the presence of dilute DMSO solutions (X_DMSO < 0.3). At higher DMSO concentrations, this bilayer structure was retained despite a progressive deterioration of the hydration structure at the interface. A similar convergence of bilayer structural properties was observed under dehydration conditions for 0.3 < X_DMSO < 0.7. Destabilization occurred for dehydrated bilayers in the presence of X_DMSO ≥ 0.7, suggesting the existence of a DMSO concentration and/or dehydration threshold. However, such DMSO concentrations far exceed those established as toxic to other cellular components. Our findings represent a computational model for DMSO-DOPC interactions that is consistent with a range of experimental characterizations, offering new molecular insights into the cryoprotective mechanisms of action of DMSO.

Joint Reaction Coordinate for Computing the Free-Energy Landscape of Pore Nucleation and Pore Expansion in Lipid Membranes

Topological transitions of membranes, such as pore formation or membrane fusion, play key roles in biology, biotechnology, and in medical applications. Calculating the related free-energy landscapes has been complicated by the fact that such processes involve a sequence of transitions along highly distinct directions in conformational space, making it difficult to define good reaction coordinates (RCs) for the overall process. In this study, a new RC capable of driving both pore nucleation and pore expansion in lipid membranes is presented. The potential of mean force (PMF) along the RC computed with molecular dynamics simulations provides a comprehensive view on the free-energy landscape of pore formation, including a barrier for pore nucleation; the size, free energy, and metastability of the open pore; and the energetic cost for further pore expansion against the line tension of the pore rim. The RC is illustrated by quantifying the effects of (i) simulation system size and (ii) the addition of dimethyl sulfoxide on the free-energy landscape of pore formation. PMF calculations along the RC provide mechanistic and energetic understanding of pore formation, hence they will be useful to rationalize the effects of membrane-active peptides, electric fields, and membrane composition on transmembrane pores.

Cooperative Effects of an Antifungal Moiety and DMSO on Pore Formation over Lipid Membranes Revealed by Free Energy Calculations

Itraconazole is a triazole drug widely used in the treatment of fungal infections, and it is in clinical trials for treatment of several cancers. However, the drug suffers from poor solubility, while experiments have shown that itraconazole delivery in liposome nanocarriers improves both circulation half-life and tissue distribution. The drug release mechanism from the nanocarrier is still unknown, and it depends on several factors including membrane stability against defect formation. In this work, we used molecular dynamics simulations and potential of mean force (PMF) calculations to quantify the influence of itraconazole on pore formation over lipid membranes, and we compared the effect by itraconazole with a pore-stabilizing effect by the organic solvent dimethyl sulfoxide (DMSO). According to the PMFs, both itraconazole and DMSO greatly reduce the free energy of pore formation, by up to ∼20 kJ mol^-1. However, whereas large concentrations of itraconazole of 8 mol % (relative to lipid) were required, only small concentrations of a few mole % DMSO (relative to water) were sufficient to stabilize pores. In addition, itraconazole and DMSO facilitate pore formation by different mechanisms. Whereas itraconazole predominantly aids the formation of a partial defect with a locally thinned membrane, DMSO mainly stabilizes a transmembrane water needle by shielding it from the hydrophobic core. Notably, the two distinct mechanisms act cooperatively upon adding both itraconazole and DMSO to the membrane, as revealed by an additional reduction of the pore free energy. Overall, our simulations reveal molecular mechanisms and free energies of membrane pore formation by small molecules. We suggest that the stabilization of a locally thinned membrane as well as the shielding of a transmembrane water needle from the hydrophobic membrane core may be a general mechanism by which amphiphilic molecules facilitate pore formation over lipid membranes at sufficient concentrations.

The need for novel cryoprotectants and cryopreservation protocols: Insights into the importance of biophysical investigation and cell permeability

BACKGROUND

Cryopreservation is a key method of preservation of biological material for both medical treatments and conservation of endangered species. In order to avoid cellular damage, cryopreservation relies on the addition of a suitable cryoprotective agent (CPA). However, the toxicity of CPAs is a serious concern and often requires rapid removal on thawing which is time consuming and expensive.

SCOPE OF REVIEW

The principles of Cryopreservation are reviewed and recent advances in cryopreservation methods and new CPAs are described. The importance of understanding key biophysical properties to assess the cryoprotective potential of new non-toxic compounds is discussed.

MAJOR CONCLUSIONS

Knowing the biophysical properties of a particular cell type is crucial for developing new cryopreservation protocols. Similarly, understanding how potential CPAs interact with cells is key for optimising protocols. For example, cells with a large osmotically inactive volume may require slower addition of CPAs. Similarly, a cell with low permeability may require a longer incubation time with the CPA to allow adequate penetration. Measuring these properties allows efficient optimisation of cryopreservation protocols.

GENERAL SIGNIFICANCE

Understanding the interplay between cells and biophysical properties is important not just for developing new, and better optimised, cryopreservation protocols, but also for broader research into topics such as dehydration and desiccation tolerance, chilling and heat stress, as well as membrane structure and function.

Antimicrobial Susceptibility Testing of Antimicrobial Peptides to Better Predict Efficacy

During the development of antimicrobial peptides (AMP) as potential therapeutics, antimicrobial susceptibility testing (AST) stands as an essential part of the process in identification and optimisation of candidate AMP. Standard methods for AST, developed almost 60 years ago for testing conventional antibiotics, are not necessarily fit for purpose when it comes to determining the susceptibility of microorganisms to AMP. Without careful consideration of the parameters comprising AST there is a risk of failing to identify novel antimicrobials at a time when antimicrobial resistance (AMR) is leading the planet toward a post-antibiotic era. More physiologically/clinically relevant AST will allow better determination of the preclinical activity of drug candidates and allow the identification of lead compounds. An important consideration is the efficacy of AMP in biological matrices replicating sites of infection, e.g., blood/plasma/serum, lung bronchiolar lavage fluid/sputum, urine, biofilms, etc., as this will likely be more predictive of clinical efficacy. Additionally, specific AST for different target microorganisms may help to better predict efficacy of AMP in specific infections. In this manuscript, we describe what we believe are the key considerations for AST of AMP and hope that this information can better guide the preclinical development of AMP toward becoming a new generation of urgently needed antimicrobials.

Ultrafast Dynamics at the Lipid-Water Interface: DMSO Modulates H-Bond Lifetimes

Dimethyl sulfoxide (DMSO) is a common cosolvent and cryopreservation agent used to freeze cells and tissues. DMSO alters the H-bond structure of water, but its interactions with biomolecules and, specifically, with biological interfaces remain poorly understood. Here we investigate the effects of DMSO on the H-bond dynamics at the lipid-water interface using a combination of ultrafast two-dimensional infrared (2D IR) spectroscopy and molecular dynamics simulations. Ester carbonyl absorption spectra show that DMSO dehydrates the interface, and simulations show that the area per lipid is decreased. Ultrafast 2D IR spectra measure the time scales of frequency fluctuations at the ester carbonyl positions located precisely between the hydrophobic and hydrophilic regions of the membrane. 2D IR measurements show that low DMSO concentrations (<10 mol %) induce ∼40% faster H-bond dynamics compared with pure water, whereas increased concentrations (>10-20 mol %) once again slow down the dynamics. This slow-fast-slow trend is described in terms of two different solvation regimes. Below 10 mol %, DMSO weakens the interfacial H bond, leading to faster "bulk-like" dynamics, whereas above 10 mol %, water molecules become "relatively immobilized" as the H-bond networks becoming disrupted by the H-bond donor/acceptor imbalance at the interface. These studies are an important step toward characterizing the environments around lipid membranes, which are essential to numerous biological processes.

Intracellular Delivery by Membrane Disruption: Mechanisms, Strategies, and Concepts

Intracellular delivery is a key step in biological research and has enabled decades of biomedical discoveries. It is also becoming increasingly important in industrial and medical applications ranging from biomanufacture to cell-based therapies. Here, we review techniques for membrane disruption-based intracellular delivery from 1911 until the present. These methods achieve rapid, direct, and universal delivery of almost any cargo molecule or material that can be dispersed in solution. We start by covering the motivations for intracellular delivery and the challenges associated with the different cargo types-small molecules, proteins/peptides, nucleic acids, synthetic nanomaterials, and large cargo. The review then presents a broad comparison of delivery strategies followed by an analysis of membrane disruption mechanisms and the biology of the cell response. We cover mechanical, electrical, thermal, optical, and chemical strategies of membrane disruption with a particular emphasis on their applications and challenges to implementation. Throughout, we highlight specific mechanisms of membrane disruption and suggest areas in need of further experimentation. We hope the concepts discussed in our review inspire scientists and engineers with further ideas to improve intracellular delivery.

Membrane permeabilization of phosphatidylcholine liposomes induced by cryopreservation and vitrification solutions

Membranes are the primary site of freezing injury during cryopreservation or vitrification of cells. Addition of cryoprotective agents (CPAs) can reduce freezing damage, but can also disturb membrane integrity causing leakage of intracellular constituents. The aim of this study was to investigate lipid-CPA interactions in a liposome model system to obtain insights in mechanisms of cellular protection and toxicity during cryopreservation or vitrification processing. Various CPAs were studied including dimethyl sulfoxide (DMSO), glycerol (GLY), ethylene glycol (EG), dimethyl formamide (DMF), and propylene glycol (PG). Protection against leakage of phosphatidylcholine liposomes encapsulated with carboxyfluorescein (CF) was studied upon CPA addition as well as after freezing-and-thawing. Molecular interactions between CPAs and phospholipid acyl chains and headgroups as well as membrane phase behavior were studied using Fourier transform infrared spectroscopy. A clear difference was observed between the effects of DMSO on PC-liposomes compared to the other CPAs tested, both for measurements on CF-retention and membrane phase behavior. All CPAs were found to inhibit membrane leakiness during freezing. However, exposure to high CPA concentrations already caused leakage before freezing, increasing in the order DMSO, EG, DMF/PG, and GLY. With DMSO, liposomes were able to withstand up to 6M concentrations compared to only 1M for GLY. Cholesterol addition to PC-liposomes increased membrane stability towards leakiness. DMSO was found to dehydrate the phospholipid headgroups while raising the membrane phase transition temperature, whereas the other CPAs caused an increase in the hydration level of the lipid headgroups while decreasing the membrane phase transition temperature.

Single channel planar lipid bilayer recordings of the melittin variant MelP5

MelP5 is a 26 amino acid peptide derived from melittin, the main active constituent of bee venom, with five amino acid replacements. The pore-forming activity of MelP5 in lipid membranes is attracting attention because MelP5 forms larger pores and induces dye leakage through liposome membranes at a lower concentration than melittin. Studies of MelP5 have so far focused on ensemble measurements of membrane leakage and impedance; here we extend this characterization with an electrophysiological comparison between MelP5 and melittin using planar lipid bilayer recordings. These experiments reveal that MelP5 pores in lipid membranes composed of 3:1 phosphatidylcholine:cholesterol consist of an average of 10 to 12 monomers compared to an average of 3 to 9 monomers for melittin. Both peptides form transient pores with dynamically varying conductance values similar to previous findings for melittin, but MelP5 occasionally also forms stable, well-defined pores with single channel conductance values that vary greatly and range from 50 to 3000pS in an electrolyte solution containing 100mM KCl.

A screen of pharmaceutical drugs for their ability to cause short-term morbidity and mortality in the common bed bug, Cimex lectularius L

The common bed bug, Cimex lectularius L., is a hematophagous ectoparasite that preferentially feeds on humans. Pharmaceuticals present in a person's blood may adversely affect C. lectularius when it feeds. We fed >10,000 C. lectularius on blood samples containing more than 400 different drug doses and drug combinations using an in vitro feeding system to determine insect mortality. The majority of drug doses approximated the peak plasma concentration in humans taking those drugs. Twenty-one drugs were found to cause >17% 12-14-day mortality compared to 8.5% mortality in the control (p < 0.05), but postliminary testing of three of the drugs, famotidine, ethambutol, and primaquine, did not demonstrate an increase in C. lectularius mortality. We also tested 23 drugs for their effects on C. lectularius fecundity. The results may have implications for understanding C. lectularius population dynamics in an infestation.

Clobetasol propionate causes immunosuppression in zebrafish (Danio rerio) at environmentally relevant concentrations

Synthetic glucocorticoids (GCs) are potential endocrine disrupting compounds that have been detected in the aquatic environment around the world in the low ng/L (nanomolar) range. GCs are used as immunosuppressants in medicine. It is of high interest whether clobetasol propionate (CP), a highly potent GC, suppresses the inflammatory response in fish after exposure to environmentally relevant concentrations. Bacterial lipopolysaccharide (LPS) challenge was used to induce inflammation and thus mimic pathogen infection. Zebrafish embryos were exposed to ≤1000nM CP from ~1h post fertilization (hpf) to 96 hpf, and CP uptake, survival after LPS challenge, and expression of inflammation-related genes were examined. Our initial experiments were carried out using 0.001% DMSO as a solvent vehicle, but we observed that DMSO interfered with the LPS challenge assay, and thus masked the effects of CP. Therefore, DMSO was not used in the subsequent experiments. The internal CP concentration was quantifiable after exposure to ≥10nM CP for 96h. The bioconcentration factor (BCF) of CP was determined to be between 16 and 33 in zebrafish embryos. CP-exposed embryos showed a significantly higher survival rate in the LPS challenge assay after exposure to ≥0.1nM in a dose dependent manner. This effect is an indication of immunosuppression. Furthermore, the regulation pattern of several genes related to LPS challenge in mammals supported our results, providing evidence that LPS-mediated inflammatory pathways are conserved from mammals to teleost fish. Anxa1b, a GC-action related anti-inflammatory gene, was significantly down-regulated after exposure to ≥0.05nM CP. Our results show for the first time that synthetic GCs can suppress the innate immune system of fish at environmentally relevant concentrations. This may reduce the chances of fish to survive in the environment, as their defense against pathogens is weakened.

Controllable engineering of asymmetric phosphatidylserine-containing lipid vesicles using calcium cations

The presence of Ca²⁺ significantly increases the flip rate of DOPS lipid molecules due to the local membrane curvature.

Efficient DNP NMR of membrane proteins: sample preparation protocols, sensitivity, and radical location

Although dynamic nuclear polarization (DNP) has dramatically enhanced solid-state NMR spectral sensitivities of many synthetic materials and some biological macromolecules, recent studies of membrane-protein DNP using exogenously doped paramagnetic radicals as polarizing agents have reported varied and sometimes surprisingly limited enhancement factors. This motivated us to carry out a systematic evaluation of sample preparation protocols for optimizing the sensitivity of DNP NMR spectra of membrane-bound peptides and proteins at cryogenic temperatures of ~110 K. We show that mixing the radical with the membrane by direct titration instead of centrifugation gives a significant boost to DNP enhancement. We quantify the relative sensitivity enhancement between AMUPol and TOTAPOL, two commonly used radicals, and between deuterated and protonated lipid membranes. AMUPol shows ~fourfold higher sensitivity enhancement than TOTAPOL, while deuterated lipid membrane does not give net higher sensitivity for the membrane peptides than protonated membrane. Overall, a ~100 fold enhancement between the microwave-on and microwave-off spectra can be achieved on lipid-rich membranes containing conformationally disordered peptides, and absolute sensitivity gains of 105-160 can be obtained between low-temperature DNP spectra and high-temperature non-DNP spectra. We also measured the paramagnetic relaxation enhancement of lipid signals by TOTAPOL and AMUPol, to determine the depths of these two radicals in the lipid bilayer. Our data indicate a bimodal distribution of both radicals, a surface-bound fraction and a membrane-bound fraction where the nitroxides lie at ~10 Å from the membrane surface. TOTAPOL appears to have a higher membrane-embedded fraction than AMUPol. These results should be useful for membrane-protein solid-state NMR studies under DNP conditions and provide insights into how biradicals interact with phospholipid membranes.

DMSO Enhances TGF-β Activity by Recruiting the Type II TGF-β Receptor From Intracellular Vesicles to the Plasma Membrane

Dimethyl sulfoxide (DMSO) is used to treat many diseases/symptoms. The molecular basis of the pharmacological actions of DMSO has been unclear. We hypothesized that DMSO exerts some of these actions by enhancing TGF-β activity. Here we show that DMSO enhances TGF-β activity by ∼3-4-fold in Mv1Lu and NMuMG cells expressing Smad-dependent luciferase reporters. In Mv1Lu cells, DMSO enhances TGF-β-stimulated expression of P-Smad2 and PAI-1. It increases cell-surface expression of TGF-β receptors (TβR-I and/or TβR-II) by ∼3-4-fold without altering their cellular levels as determined by (125) I-labeled TGF-β-cross-linking/Western blot analysis, suggesting the presence of large intracellular pools in these cells. Sucrose density gradient ultracentrifugation/Western blot analysis reveals that DMSO induces recruitment of TβR-II (but not TβR-I) from its intracellular pool to plasma-membrane microdomains. It induces more recruitment of TβR-II to non-lipid raft microdomains than to lipid rafts/caveolae. Mv1Lu cells transiently transfected with TβR-II-HA plasmid were treated with DMSO and analyzed by indirect immunofluoresence staining using anti-HA antibody. In these cells, TβR-II-HA is present as a vesicle-like network in the cytoplasm as well as in the plasma membrane. DMSO causes depletion of TβR-II-HA-containing vesicles from the cytoplasm and co-localization of TβR-II-HA and cveolin-1 at the plasma membrane. These results suggest that DMSO, a fusogenic substance, enhances TGF-β activity presumably by inducing fusion of cytoplasmic vesicles (containing TβR-II) and the plasma membrane, resulting in increased localization of TβR-II to non-lipid raft microdomains where canonical signaling occurs. Fusogenic activity of DMSO may play a pivotal role in its pharmacological actions involving membrane proteins with large cytoplasmic pools. J. Cell. Biochem. 117: 1568-1579, 2016. © 2015 Wiley Periodicals, Inc.

Novel properties of photofermentative biohydrogen production by purple bacteria Rhodobacter sphaeroides: effects of protonophores and inhibitors of responsible enzymes

Background

Biohydrogen (H₂) production by purple bacteria during photofermentation is a very promising way among biological H₂ production methods. The effects of protonophores, carbonyl cyanide m-chlorophenylhydrazone (CCCP), 2,4-dinitrophenol (DNP), and inhibitors of enzymes, involved in H₂ metabolism, metronidazole (Met), diphenyleneiodonium (DPI), and dimethylsulphoxide (DMSO) on H₂ production by Rhodobacter sphaeroides MDC6522 isolated from Jermuk mineral springs in Armenia have been investigated in both nitrogen-limited and nitrogen-excess conditions.

Results

With the increase of inhibitors concentrations H₂ yield gradually decreased. The complete inhibition of H₂ production was observed in the presence of DPI and CCCP. DPI’s solvent—DMSO in low concentration did not significantly affect H₂ yield. N,N′-dicyclohexylcarbodiimide (DCCD)-inhibited the F_OF₁-ATPase activity of bacterial membrane vesicles was analyzed in the presence of inhibitors. Low concentrations of DPI and DMSO did not affect ATPase activity, whereas Met and CCCP stimulated enzyme activity. The effect of DNP was similar to CCCP.

Conclusions and significance

The results have shown the low concentration or concentration dependent effects of protonophores and nitrogenase and hydrogenase inhibitors on photofermentative H₂ production by Rh. sphaeroides in nitrogen-limited and nitrogen-excess conditions. They would be significant to understand novel properties in relationship between nitrogenase, hydrogenase and the F_OF₁-ATPase in Rh. sphaeroides, and regulatory pathways of photofermentation. The inhibitors of nitrogenase and hydrogenase can be used in biotechnology for regulation of H₂ production in different technology conditions and development of scale-up applications, for biomass and energy production using purple bacterial cells.

A rhenium tris-carbonyl derivative as a model molecule for incorporation into phospholipid assemblies for skin applications

A rhenium tris-carbonyl derivative (fac-[Re(CO)3Cl(2-(1-dodecyl-1H-1,2,3,triazol-4-yl)-pyridine)]) was incorporated into phospholipid assemblies, called bicosomes, and the penetration of this molecule into skin was monitored using Fourier-transform infrared microspectroscopy (FTIR). To evaluate the capacity of bicosomes to promote the penetration of this derivative, the skin penetration of the Re(CO)3 derivative dissolved in dimethyl sulfoxide (DMSO), a typical enhancer, was also studied. Dynamic light scattering results (DLS) showed an increase in the size of the bicosomes with the incorporation of the Re(CO)3 derivative, and the FTIR microspectroscopy showed that the Re(CO)3 derivative incorporated in bicosomes penetrated deeper into the skin than when dissolved in DMSO. When this molecule was applied on the skin using the bicosomes, 60% of the Re(CO)3 derivative was retained in the stratum corneum (SC) and 40% reached the epidermis (Epi). Otherwise, the application of this molecule via DMSO resulted in 95% of the Re(CO)3 derivative being in the SC and only 5% reaching the Epi. Using a Re(CO)3 derivative with a dodecyl-chain as a model molecule, it was possible to determine the distribution of molecules with similar physicochemical characteristics in the skin using bicosomes. This fact makes these nanostructures promising vehicles for the application of lipophilic molecules inside the skin.

The effects of organic solvents on the membrane-induced fibrillation of human islet amyloid polypeptide and on the inhibition of the fibrillation

The organic solvent dimethylsulphoxide (DMSO) and 1,1,1,3,3,3-hexafluoro-2-isopropanol (HFIP) have been widely used as a pre-treating agent of amyloid peptides and as a vehicle for water-insoluble inhibitors. These solvents are left in many cases as a trace quantity in bulk and membrane environments with treated amyloid peptides or inhibitors. In the present work, we studied the effects of the two organic solvents on the aggregation behaviors of human islet amyloid polypeptide (hIAPP) and the performances of an all-D-amino-acid inhibitor D-NFGAIL in preventing hIAPP fibrillation both in bulk solution and at phospholipid membrane. We showed that the presence of 1% v/v DMSO or HFIP decreases the rate of fibril formation of hIAPP at the lipid membrane rather than accelerates the fibril formation as what happened in bulk solution. We also showed that the presence of 1% v/v DMSO or HFIP impairs the activity of the inhibitor at the lipid membrane surface dramatically, while it affects the efficiency of the inhibitor in bulk solution slightly. We found that the inhibitor inserts into the lipid membrane more deeply or with more proportion in the presence of the organic solvents than it does in the absence of the organic solvents, which may hinder the binding of the inhibitor to hIAPP at the lipid membrane. Our results suggest that the organic solvents should be used with caution in studying membrane-induced fibrillogenesis of amyloid peptides and in testing amyloid inhibitors under membrane environments to avoid incorrect evaluation to the fibrillation process of amyloid peptides and the activity of inhibitors.

Cryoprotection of lipid membranes for high-resolution solid-state NMR studies of membrane peptides and proteins at low temperature

Solid-state NMR spectra of membrane proteins often show significant line broadening at cryogenic temperatures. Here we investigate the effects of several cryoprotectants to preserve the spectral resolution of lipid membranes and membrane peptides at temperatures down to ~200 K. Trehalose, glycerol, dimethylsulfoxide (DMSO), dimethylformamide (DMF), and polyethylene glycol (PEG), were chosen. These compounds are commonly used in protein crystallography and cryobiology. 13C and 1H magic-angle-spinning spectra of several types of lipid membranes show that DMSO provides the best resolution enhancement over unprotected membranes and also best retards ice formation at low temperature. DMF and PEG-400 show slightly weaker cryoprotection, while glycerol and trehalose neither prevent membrane line broadening nor prevent ice formation under the conditions of our study. Neutral saturated-chain phospholipids are the most amenable to cryoprotection, whereas negatively charged and unsaturated lipids attenuate cryoprotection. 13C-1H dipolar couplings and 31P chemical shift anisotropies indicate that high spectral resolution at low temperature is correlated with stronger immobilization of the lipids at high temperature, indicating that line narrowing results from reduction of the conformational space sampled by the lipid molecules at high temperature. DMSO selectively narrowed the linewidths of the most disordered residues in the influenza M2 transmembrane peptide, while residues that exhibit narrow linewidths in the unprotected membrane are less impacted. A relatively rigid β-hairpin antimicrobial peptide, PG-1, showed a linewidth increase of ~0.5 ppm over a ~70 K temperature drop both with and without cryoprotection. Finally, a short-chain saturated lipid, DLPE, exhibits excellent linewidths, suggesting that it may be a good medium for membrane protein structure determination. The three best cryoprotectants found in this work-DMSO, PEG, and DMF-should be useful for low-temperature membrane-protein structural studies by SSNMR without compromising spectral resolution.

Modulation of dipalmitoylphosphatidylcholine monolayers by dimethyl sulfoxide

The action of the penetration-enhancing agent, dimethyl sulfoxide (DMSO), on phospholipid monolayers was investigated at the air-water interface using a combination of experimental techniques and molecular dynamics simulations. Brewster angle microscopy revealed that DPPC monolayers remained laterally homogeneous at subphase concentrations up to a mole fraction of 0.1 DMSO. Neutron reflectometry of the monolayers in combination with isotopic substitution enabled the determination of solvent profiles as a function of distance perpendicular to the interface for the different DMSO subphase concentrations. These experimental results were compared to those obtained from molecular dynamic (MD) simulations of the corresponding monolayer systems. There was excellent agreement found between the MD-derived reflectivity curves and the measured data for all of the H/D contrast variations investigated. The MD provide a detailed description of the distribution of water and DMSO molecules around the phosphatidylcholine headgroup, and how this distribution changes with increasing DMSO concentrations. Significantly, the measurements and simulations that are reported here support the hypothesis that DMSO acts by dehydrating the phosphatidylcholine headgroup, and as such provide the first direct evidence that it does so primarily by displacing water molecules bound to the choline group.

Mechanisms of neuronal membrane sealing following mechanical trauma

Membrane integrity is crucial for maintaining the intricate signaling and chemically-isolated intracellular environment of neurons; disruption risks deleterious effects, such as unregulated ionic flux, neuronal apoptosis, and oxidative radical damage as observed in spinal cord injury and traumatic brain injury. This paper, in addition to a discussion of the current understanding of cellular tactics to seal membranes, describes two major factors involved in membrane repair. These are line tension, the hydrophobic attractive force between two lipid free-edges, and membrane tension, the rigidity of the lipid bilayer with respect to the tethered cortical cytoskeleton. Ca(2+), a major mechanistic trigger for repair processes, increases following flux through a membrane injury site, and activates phospholipase enzymes, calpain-mediated cortical cytoskeletal proteolysis, protein kinase cascades, and lipid bilayer microdomain modification. The membrane tension appears to be largely modulated through vesicle dynamics, cytoskeletal organization, membrane curvature, and phospholipase manipulation. Dehydration of the phospholipid gap edge and modification of membrane packaging, as in temperature variation, experimentally impact line tension. Due to the time-sensitive nature of axonal sealing, increasing the efficacy of axolemmal sealing through therapeutic modification would be of great clinical value, to deter secondary neurodegenerative effects. Better therapeutic enhancement of membrane sealing requires a complete understanding of its intricate underlying neuronal mechanism.

Low concentrations of the solvent dimethyl sulphoxide alter intrinsic excitability properties of cortical and hippocampal pyramidal cells

Dimethylsulfoxide (DMSO) is a widely used solvent in biology. It has many applications perhaps the most common of which is in aiding the preparation of drug solutions from hydrophobic chemical entities. Recent studies have suggested that this molecule may be able to induce apoptosis in neural tissues urging caution regarding its introduction into humans, for example as part of stem cell transplants. Here we have used in vitro electrophysiological methods applied to murine brain slices to examine whether a few hours treatment with 0.05% DMSO (a concentration regarded by many as innocuous) alters intrinsic excitability properties of neurones. We investigated pyramidal neurones in two distinct brain regions, namely area CA1 of the hippocampus and layer 2 of perirhinal cortex. In the former there was no effect on resting potential but input resistance was decreased by DMSO pre-treatment. In line with this action potential count for any level of depolarizing current stimulus was reduced by ∼25% following DMSO treatment. I_h-mediated “sag” was also increased in CA1 pyramids and action potential waveform analysis demonstrated that DMSO treatment moved action potential threshold towards resting potential. In perirhinal cortex a decreased action potential output for various depolarizing current stimuli was also seen. In these cells action potential threshold was unaltered by DMSO but a significant increase in action potential width was apparent. These data indicate that pre-treatment with this widely employed solvent can elicit multifaceted neurophysiological changes in mammalian neurones at concentrations below those frequently encountered in the published literature.

N-linked glycolipids by Staudinger coupling of glycosylated alkyl diazides with fatty acids

Aiming for new glycolipids with enhanced chemical stability and close structural similarity to natural cell membrane lipids for the development of a drug delivery system, we have synthesized double amide analogs of glyco-glycerolipids. The synthesis applied a Staudinger reaction based coupling of a 1,3-diazide with fatty acid chlorides. While the concept furnished the desired glucosides in reasonable yields, the corresponding lactosides formed a tetrahydropyrimidine based 1:1 coupling product instead. This unexpected coupling result likely originates from steric hindrance at the iminophosphorane intermediate and provides an interesting core structure for potentially bioactive surfactants. The assembly behavior of both glycolipid types was investigated by optical polarizing microscopy, DSC and surface tension studies.

Structures, properties and nature of DMSO-XY (XY=ClF and BrF) complexes: redshift and blueshift of S=O stretch

The DMSO-XY (XY=ClF and BrF) complexes have been investigated with quantum chemical calculations. In general, two minima complexes were found, one with an O···X halogen bond and the other one with a S···X halogen bond. The former is more stable than the latter. Additionally, one first order saddle point complex was also observed. The interaction energies in the S complexes suffer a prominent influence from the calculation methods. At the CCSD(T)/aug-cc-pVDZ level, the interaction energies are calculated to be -9.19 and -12.73 kcal/mol for the Cl and Br global minima, respectively. Both complexes have also been evidenced to be stable at room temperature. The SO stretch vibration exhibits a red shift at the global minimum but a blue shift at the local minimum, whereas the CSC and CH stretch vibrations move to high frequency in both cases. The energy decomposition analyses indicate that the electrostatic interaction plays a dominant role in stabilizing these halogen-bonded complexes.

Influence of vehicles used for oral dosing of test molecules on the progression of Mycobacterium tuberculosis infection in mice

Preclinical evaluation of drug-like molecules requires their oral administration to experimental animals using suitable vehicles. We studied the effect of oral dosing with corn oil, carboxymethyl cellulose, dimethyl sulfoxide, and polysorbate-80 on the progression of Mycobacterium tuberculosis infection in mice. Infection was monitored by physical (survival time and body weight) and bacteriological (viable counts in lungs) parameters. Compared with water, corn oil significantly improved both sets of parameters, whereas the other vehicles affected only physical parameters.

The influence of organic solvents on estimates of genotoxicity and antigenotoxicity in the SOS chromotest

In this work, the toxicity and genotoxicity of organic solvents (acetone, carbon tetrachloride, dichloromethane, dimethylsulfoxide, ethanol, ether and methanol) were studied using the SOS chromotest. The influence of these solvents on the direct genotoxicity induced by the mutagens mitomycin C (MMC) and 4-nitroquinoline-1-oxide (4-NQO) were also investigated. None of the solvents were genotoxic in Escherichia coli PQ37. However, based on the inhibition of protein synthesis assessed by constitutive alkaline phosphatase activity, some solvents (carbon tetrachloride, dimethylsulfoxide, ethanol and ether) were toxic and incompatible with the SOS chromotest. Solvents that were neither toxic nor genotoxic to E. coli (acetone, dichloromethane and methanol) significantly reduced the genotoxicity of MMC and 4-NQO. When these solvents were used to dissolve vitamin E they increased the antigenotoxic activity of this compound, possibly through additive or synergistic effects. The relevance of these results is discussed in relation to antigenotoxic studies. These data indicate the need for careful selection of an appropriate diluent for the SOS chromotest since some solvents can modulate genotoxicity and antigenotoxicity.

Relationship of proton motive force and the F(0)F (1)-ATPase with bio-hydrogen production activity of Rhodobacter sphaeroides: effects of diphenylene iodonium, hydrogenase inhibitor, and its solvent dimethylsulphoxide

Rhodobacter sphaeroides MDC 6521 was able to produce bio-hydrogen (H(2)) in anaerobic conditions under illumination. In this study the effects of the hydrogenase inhibitor-diphenylene iodonium (Ph(2)I) and its solvent dimethylsulphoxide (DMSO) on growth characteristics and H(2) production by R. sphaeroides were investigated. The results point out the concentration dependent DMSO effect: in the presence of 10 mM DMSO H(2) yield was ~6 fold lower than that of the control. The bacterium was unable to produce H(2) in the presence of Ph(2)I. In order to examine the mediatory role of proton motive force (∆p) or the F(0)F(1)-ATPase in H(2) production by R. sphaeroides, the effects of Ph(2)I and DMSO on ∆p and its components (membrane potential (∆ψ) and transmembrane pH gradient), and ATPase activity were determined. In these conditions ∆ψ was of -98 mV and the reversed ∆pH was +30 mV, resulting in ∆p of -68 mV. Ph(2)I decreased ∆ψ in concentrations of 20 μM and higher; lower concentrations of Ph(2)I as DMSO had no valuable effect on ∆ψ. The R. sphaeroides membrane vesicles demonstrated significant ATPase activity sensitive to N,N'-dicyclohexylcarbodiimide. The 10-20 μM Ph(2)I did not affect the ATPase activity, whereas 40 μM Ph(2)I caused a marked inhibition (~2 fold) in ATPase activity. The obtained results provide novel evidence on the involvement of hydrogenase and the F(0)F(1)-ATPase in H(2) production by R. sphaeroides. Moreover, these data indicate the role of hydrogenase and the F(0)F(1)-ATPase in ∆p generation. In addition, DMSO might increase an interaction of nitrogenase with CO(2), decreasing nitrogenase activity and affecting H(2) production.

Activation of the dormant secondary metabolite production by introducing gentamicin-resistance in a marine-derived Penicillium purpurogenum G59

A new approach to activate silent gene clusters for dormant secondary metabolite production has been developed by introducing gentamicin-resistance to an originally inactive, marine-derived fungal strain Penicillium purpurogenum G59. Upon treatment of the G59 spores with a high concentration of gentamicin in aqueous DMSO, a total of 181 mutants were obtained by single colony isolation. In contrast to the strain G59, the EtOAc extracts of nine mutant cultures showed inhibitory effects on K562 cells, indicating that the nine mutants had acquired capability to produce antitumor metabolites. This was evidenced by TLC and HPLC analysis of EtOAc extracts of G59 and the nine mutants. Further isolation and characterization demonstrated that four antitumor secondary metabolites, janthinone (1), fructigenine A (2), aspterric acid methyl ester (3) and citrinin (4), were newly produced by mutant 5-1-4 compared to the parent strain G59, and which were also not found in the secondary metabolites of other Penicillium purpurogenum strains. However, Compounds 1–4 inhibited the proliferation of K562 cells with inhibition rates of 34.6% (1), 60.8% (2), 31.7% (3) and 67.1% (4) at 100 μg/mL, respectively. The present study demonstrated the effectiveness of a simple, yet practical approach to activate the production of dormant fungal secondary metabolites by introducing acquired resistance to aminoglycoside antibiotics, which could be applied to the studies for eliciting dormant metabolic potential of fungi to obtain cryptic secondary metabolites.

The potential of nanoscale combinations of self-assembling peptides and amino acids of the Src tyrosine kinase inhibitor in acute lung injury therapy

Many newly discovered therapeutic agents require a delivery platform in order to translate them into clinical applications. For this purpose, a nanoscale formulation strategy was developed for the Src tyrosine kinase inhibitor PP2. The formulation utilizes the combination of the self-assembling peptides (EAK16-II) and amino acids to minimize the use of the toxic organic solvent DMSO; hence, the biocompatibility of the PP2 nanoformulations was significantly improved. They were found to be non-hemolytic and safe for intravenous and intratracheal administration; the formulations did not alter PP2 activity in Src inhibition on cultured cells. The PP2 nanoformulation was further evaluated on a lipopolysaccharide (LPS)-induced acute lung injury mouse model. Results revealed that the pretreatment of PP2 nanoformulation could decrease the inflammatory cell infiltration and the pro-inflammatory cytokine TNF-α production in the bronchoalveolar lavage fluid after LPS stimulation. The promising therapeutic efficacy and the formulation strategy developed in this work may help further translate PP2 and other hydrophobic therapeutic agents into clinical applications.

Evaluation of cannabinoid receptor 2 and metabotropic glutamate receptor 1 functional responses using a cell impedance-based technology

Recently, new technologies based on biosensors and called label free have been developed. These technologies eliminate the need for using markers and dyes. The authors applied one of these technologies, based on measurement of cell impedance variation, to study the pharmacological profiles of ligands for the cannabinoid receptor 2 (CB2), a Gi-coupled receptor, and for the metabopotropic glutamate receptor 1 (mGluR1), a Gq-coupled receptor. Reference agonists and antagonists/inverse agonists for the 2 receptors were applied to recombinant cell lines and impedance monitored over time. Agonists (JWH133 and CP55940 for CB2; quisqualate, glutamate, 1S-3R-ACPD, and S-3,5-DHPG for mGluR1) triggered a variation of impedance consistent in both potency and efficacy with data obtained using classical assays measuring cAMP or Ca(2+) levels. This effect was not present in the parental nontransfected cell line, confirming specific receptor-mediated response. Application of antagonists (AM630 for CB2; YM298198, SCH1014222, J&J16259685, and CPCCOEt for mGluR1) reduced agonist-induced impedance changes. The only exception was the mGluR1 antagonist BAY367620 that, while active in the Ca(2+) assay, was inactive in the impedance assay. Overall, these results confirm the possibility of using cell impedance-based technology to study the pharmacological profile of ligands acting at G-protein-coupled receptors coupled to different downstream signaling pathways.

Synthesis and properties of fluorescence probe for detection of peroxides in mitochondria

In this study, a new type of fluorescence probe, diphenylpyrenylphosphine-conjugated alkyltriphenylphosphonium iodide which was accumulated in mitochondria, has been synthesized. This probe was detected peroxide in living cell. Comparison of the reactivity toward several peroxide indicated that the probe was existed in mitochondrial membrane. Using this probe, generation of peroxide in mitochondria of living cell was successfully visualized.

Interactions of dimethylsulfoxide with a dipalmitoylphosphatidylcholine monolayer studied by vibrational sum frequency generation

The interactions between phospholipid monolayers and dimethylsulfoxide (DMSO) molecules were investigated by vibrational sum frequency generation (VSFG) spectroscopy in a Langmuir trough system. Both the head and the tail groups of dipalmitoylphosphatidylcholine (DPPC) as well as DMSO were probed to provide a comprehensive understanding of the interactions between DPPC and DMSO molecules. A condensing effect is observed for the DPPC monolayer on a concentrated DMSO subphase (>20 mol %). This effect results in a well-ordered conformation for the DPPC alkyl chains at very large mean molecular areas. Interactions between DMSO and DPPC headgroups were also studied. DMSO-induced dehydration of the DPPC phosphate group is revealed at DMSO concentration above 10 mol %. The average orientation of DMSO with DPPC versus dipalmitoylphosphate sodium salt (DPPA) monolayers was compared. The comparison revealed that DMSO molecules are perturbed and reorient because of the interfacial electric field created by the charged lipid headgroups. The orientation of the DPPC alkyl chains remains nearly unchanged in the liquid condensed phase with the addition of DMSO. This suggests that DMSO molecules are expelled from the condensed monolayer. In addition, implications for the DMSO-induced permeability enhancement of biological membranes from this work are discussed.

A novel, nongenomic mechanism underlies retinoic acid-induced growth cone turning

The vitamin A metabolite, retinoic acid (RA), is well known for its roles in neural development and regeneration. We have previously shown that RA can induce positive growth cone turning in regenerating neurons in vitro. In this study, we address the subcellular mechanisms underlying this chemo-attractive response, using identified central neurons from the adult mollusc, Lymnaea stagnalis. We show that the RA-induced positive growth cone turning was maintained in the presence of the transcriptional inhibitor, actinomycin D. We also physically transected the neurites from the cell body and showed that isolated growth cones retain the capacity to turn toward a gradient of RA. Moreover, this attractive turning is dependent on de novo local protein synthesis and Ca(2+) influx. Most of RA's actions during neurite outgrowth and regeneration require gene transcription, although these data show for the first time in any species, that the chemotropic action of RA in guiding neurite outgrowth, involves a novel, nongenomic mechanism.

Nonsynchronous change in the head and tail of dioctadecyldimethylammonium bromide molecules during the liquid crystalline to coagel phase transformation process

Dioctadecyldimethylammonium bromide (DODAB) is known to self-assemble into several lamellar structures in water, existing as either liquid crystalline, gel, or coagel phases. In this work, by using differential scanning calorimetry, Fourier transform infrared spectroscopy, and X-ray diffraction techniques, we have characterized the details of the phase transition mechanisms of the DODAB aqueous dispersions. It was found that the liquid crystalline converts to the coagel phase via a two-step mechanism: first to the gel phase upon cooling and then to the stable coagel phase. Although significant conformational changes in the hydrocarbon tails were observed in both steps, changes in the headgroups of DODAB were only detected in the second step. More interestingly, we found that the lipid tails change prior to the headgroups during the overall liquid crystalline to coagel phase transformation process. This is regarded as a nonsynchronicity phenomenon, which reflects the regional (head/tail) imbalance in molecular interactions. Such a nonsynchronicity phenomenon in the self-assembled aggregates composed of the medium-sized DODAB molecules will shed light on our understanding of the polymorphism and reversibility of amphiphiles including both surfactants and biomembrane phospholipids.