Interactions of oral permeation enhancers with lipid membranes in simulated intestinal environments

The oral bioavailability of therapeutic peptides is generally low. To increase peptide transport across the gastrointestinal barrier, permeation enhancers are often used. Despite their widespread use, mechanistic knowledge of permeation enhancers is limited. To address this, we here investigate the interactions of six commonly used permeation enhancers with lipid membranes in simulated intestinal environments. Specifically, we study the interactions of the permeation enhancers sodium caprate, dodecyl maltoside, sodium cholate, sodium dodecyl sulfate, melittin, and penetratin with epithelial cell-like model membranes. To mimic the molecular composition of the real intestinal environment, the experiments are performed with two peptide drugs, salmon calcitonin and desB30 insulin, in fasted-state simulated intestinal fluid. Besides providing a comparison of the membrane interactions of the studied permeation enhancers, our results demonstrate that peptide drugs as well as intestinal-fluid components may substantially change the membrane activity of permeation enhancers. This highlights the importance of testing permeation enhancement in realistic physiological environments and carefully choosing a permeation enhancer for each individual peptide drug.

Contrast-enhanced ultrasound imaging using capacitive micromachined ultrasonic transducers

Capacitive micromachined ultrasonic transducers (CMUTs) have a nonlinear relationship between the applied voltage and the emitted signal, which is detrimental to conventional contrast enhanced ultrasound (CEUS) techniques. Instead, a three-pulse amplitude modulation (AM) sequence has been proposed, which is not adversely affected by the nonlinearly emitted harmonics. In this paper, this is shown theoretically, and the performance of the sequence is verified using a 4.8 MHz linear capacitive micromachined ultrasonic transducer (CMUT) array, and a comparable lead zirconate titanate (PZT) array, across 6-60 V applied alternating current (AC) voltage. CEUS images of the contrast agent SonoVue flowing through a 3D printed hydrogel phantom showed an average enhancement in contrast-to-tissue ratio (CTR) between B-mode and CEUS images of 49.9 and 37.4 dB for the PZT array and CMUT, respectively. Furthermore, hydrophone recordings of the emitted signals showed that the nonlinear emissions from the CMUT did not significantly degrade the cancellation in the compounded AM signal, leaving an average of 2% of the emitted power between 26 and 60 V of AC. Thus, it is demonstrated that CMUTs are capable of CEUS imaging independent of the applied excitation voltage when using a three-pulse AM sequence.

Imaging therapeutic peptide transport across intestinal barriers

Oral delivery is a highly preferred method for drug administration due to high patient compliance. However, oral administration is intrinsically challenging for pharmacologically interesting drug classes, in particular pharmaceutical peptides, due to the biological barriers associated with the gastrointestinal tract. In this review, we start by summarizing the pharmacological performance of several clinically relevant orally administrated therapeutic peptides, highlighting their low bioavailabilities. Thus, there is a strong need to increase the transport of peptide drugs across the intestinal barrier to realize future treatment needs and further development in the field. Currently, progress is hampered by a lack of understanding of transport mechanisms that govern intestinal absorption and transport of peptide drugs, including the effects of the permeability enhancers commonly used to mediate uptake. We describe how, for the past decades, mechanistic insights have predominantly been gained using functional assays with end-point read-out capabilities, which only allow indirect study of peptide transport mechanisms. We then focus on fluorescence imaging that, on the other hand, provides opportunities to directly visualize and thus follow peptide transport at high spatiotemporal resolution. Consequently, it may provide new and detailed mechanistic understanding of the interplay between the physicochemical properties of peptides and cellular processes; an interplay that determines the efficiency of transport. We review current methodology and state of the art in the field of fluorescence imaging to study intestinal barrier transport of peptides, and provide a comprehensive overview of the imaging-compatible in vitro, ex vivo, and in vivo platforms that currently are being developed to accelerate this emerging field of research.

3D printed calibration micro-phantoms for super-resolution ultrasound imaging validation

This study evaluates the use of 3D printed phantoms for 3D super-resolution ultrasound imaging (SRI) algorithm calibration. The main benefit of the presented method is the ability to do absolute 3D micro-positioning of sub-wavelength sized ultrasound scatterers in a material having a speed of sound comparable to that of tissue. Stereolithography is used for 3D printing soft material calibration micro-phantoms containing eight randomly placed scatterers of nominal size 205 μm × 205 μm × 200 μm. The backscattered pressure spatial distribution is evaluated to show similar distributions from micro-bubbles as the 3D printed scatterers. The printed structures are found through optical validation to expand linearly in all three dimensions by 2.6% after printing. SRI algorithm calibration is demonstrated by imaging a phantom using a λ/2 pitch 3 MHz 62+62 row-column addressed (RCA) ultrasound probe. The printed scatterers will act as point targets, as their dimensions are below the diffraction limit of the ultrasound system used. Two sets of 640 volumes containing the phantom features are imaged, with an intervolume uni-axial movement of the phantom of 12.5 μm, to emulate a flow velocity of 2 mm/s at a frame rate of 160 Hz. The ultrasound signal is passed to a super-resolution pipeline to localise the positions of the scatterers and track them across the 640 volumes. After compensating for the phantom expansion, a scaling of 0.989 is found between the distance between the eight scatterers calculated from the ultrasound data and the designed distances. The standard deviation of the variation in the scatterer positions along each track is used as an estimate of the precision of the super-resolution algorithm, and is expected to be between the two limiting estimates of (σ̃_x,σ̃_y,σ̃_z) = (22.7 μm, 27.6 μm, 9.7 μm) and (σ̃_x,σ̃_y,σ̃_z) = (18.7 μm, 19.3 μm, 8.9 μm). In conclusion, this study demonstrates the use of 3D printed phantoms for determining the accuracy and precision of volumetric super-resolution algorithms.

On-Demand Reversible UV-Triggered Interpenetrating Polymer Network-Based Drug Delivery System Using the Spiropyran-Merocyanine Hydrophobicity Switch

A reversible switchable on-demand UV-triggered drug delivery system (DDS) based on interpenetrating polymer networks (IPNs) with silicone as the host polymer and spiropyran (SP)-functionalized guest polymer is designed and demonstrated. The photo-responsive IPNs provide a new triggered drug delivery concept as they exploit the change in intermolecular interactions (work of adhesion) among the drug, matrix, and solvent when the incorporated hydrophobic SP moieties transform into the hydrophilic merocyanine form upon light irradiation without degradation and disruption of the DDS. The change in how the copolymer composition (hydrophilicity and content) and the lipophilicity of the drug (log P) affect the release profile was investigated. A thermodynamic model, based on Hansen solubility parameters, was developed to design and optimize the polymer composition of the IPNs to obtain the most efficient light-triggered drug release and suppression of the premature release. The developed IPNs showed excellent result for dopamine, l-dopa, and prednisone with around 90-95% light-triggered release. The model was applied to study the release behavior of drugs with different log P and to estimate if the light-induced hydrophobic-to-hydrophilic switch can overcome the work of adhesion between polymers and drugs and hence the desorption and release of the drugs. To the best of our knowledge, this is the first time that work of adhesion is used for this aim. Comparing the result obtained from the model and experiment shows that the model is useful for evaluating and estimating the release behavior of specific drugs merocyanine, IPN, DDS, and spiropyran.

Detection and Localization of Ultrasound Scatterers Using Convolutional Neural Networks

Delay-and-sum (DAS) beamforming is unable to identify individual scatterers when their density is so high that their point spread functions overlap. This paper proposes a convolutional neural network (CNN)-based method to detect and localize high-density scatterers, some of which are closer than the resolution limit of delay-and-sum (DAS) beamforming. A CNN was designed to take radio frequency channel data and return non-overlapping Gaussian confidence maps. The scatterer positions were estimated from the confidence maps by identifying local maxima. On simulated test sets, the CNN method with three plane waves achieved a precision of 1.00 and a recall of 0.91. Localization uncertainties after excluding outliers were ±46 [Formula: see text] (outlier ratio: 4%) laterally and ±26 [Formula: see text] (outlier ratio: 1%) axially. To evaluate the proposed method on measured data, two phantoms containing cavities were 3-D printed and imaged. For the phantom study, the training data were modified according to the physical properties of the phantoms and a new CNN was trained. On an uniformly spaced scatterer phantom, a precision of 0.98 and a recall of 1.00 were achieved with the localization uncertainties of ±101 [Formula: see text] (outlier ratio: 1%) laterally and ±37 [Formula: see text] (outlier ratio: 1%) axially. On a randomly spaced scatterer phantom, a precision of 0.59 and a recall of 0.63 were achieved. The localization uncertainties were ±132 [Formula: see text] (outlier ratio: 0%) laterally and ±44 [Formula: see text] with a bias of 22 [Formula: see text] (outlier ratio: 0%) axially. This method can potentially be extended to detect highly concentrated microbubbles in order to shorten data acquisition times of super-resolution ultrasound imaging.

3D Printed Hydrogel Multiassay Platforms for Robust Generation of Engineered Contractile Tissues

We present a method for reproducible manufacture of multiassay platforms with tunable mechanical properties for muscle tissue strip analysis. The platforms result from stereolithographic 3D printing of low protein-binding poly(ethylene glycol) diacrylate (PEGDA) hydrogels. Contractile microtissues have previously been engineered by immobilizing suspended cells in a confined hydrogel matrix with embedded anchoring cantilevers to facilitate muscle tissue strip formation. The 3D shape and mechanical properties of the confinement and the embedded cantilevers are critical for the tissue robustness. High-resolution 3D printing of PEGDA hydrogels offers full design freedom to engineer cantilever stiffness, while minimizing unwanted cell attachment. We demonstrate the applicability by generating suspended muscle tissue strips from C2C12 mouse myoblasts in a compliant fibrin-based hydrogel matrix. The full design freedom allows for new platform geometries that reduce local stress in the matrix and tissue, thus, reducing the risk of tissue fracture.

Tomato thymidine kinase is subject to inefficient TTP feedback regulation

A promising suicide gene therapy system to treat gliomas has been reported: the thymidine kinase 1 from tomato (toTK1) combined with the nucleoside analog pro-drug zidovudine (azidothymidine, AZT), which is known to penetrate the blood-brain barrier. Transduction with toTK1 has been found to efficiently increase the sensitivity of human glioblastoma cells to AZT, and nude rats with intracranial glioblastoma grafts have shown significantly improved survival when treated with the toTK1/AZT system. We show in our paper that the strong suicidal effect of AZT together with toTK1 may be explained by reduced TTP-mediated feedback inhibition of the AZT phosphorylation.

Designing CAF-adjuvanted dry powder vaccines: spray drying preserves the adjuvant activity of CAF01

Dry powder vaccine formulations are highly attractive due to improved storage stability and the possibility for particle engineering, as compared to liquid formulations. However, a prerequisite for formulating vaccines into dry formulations is that their physicochemical and adjuvant properties remain unchanged upon rehydration. Thus, we have identified and optimized the parameters of importance for the design of a spray dried powder formulation of the cationic liposomal adjuvant formulation 01 (CAF01) composed of dimethyldioctadecylammonium (DDA) bromide and trehalose 6,6'-dibehenate (TDB) via spray drying. The optimal excipient to stabilize CAF01 during spray drying and for the design of nanocomposite microparticles was identified among mannitol, lactose and trehalose. Trehalose and lactose were promising stabilizers with respect to preserving liposome size, as compared to mannitol. Trehalose and lactose were in the glassy state upon co-spray drying with the liposomes, whereas mannitol appeared crystalline, suggesting that the ability of the stabilizer to form a glassy matrix around the liposomes is one of the prerequisites for stabilization. Systematic studies on the effect of process parameters suggested that a fast drying rate is essential to avoid phase separation and lipid accumulation at the surface of the microparticles during spray drying. Finally, immunization studies in mice with CAF01 in combination with the tuberculosis antigen Ag85B-ESAT6-Rv2660c (H56) demonstrated that spray drying of CAF01 with trehalose under optimal processing conditions resulted in the preservation of the adjuvant activity in vivo. These data demonstrate the importance of liposome stabilization via optimization of formulation and processing conditions in the engineering of dry powder liposome formulations.

Deep-probe metal-clad waveguide biosensors

Two types of metal-clad waveguide biosensors, so-called dip-type and peak-type, are analyzed and tested. Their performances are benchmarked against the well-known surface-plasmon resonance biosensor, showing improved probe characteristics for adlayer thicknesses above 150-200 nm. The dip-type metal-clad waveguide sensor is shown to be the best all-round alternative to the surface-plasmon resonance biosensor. Both metal-clad waveguides are tested experimentally for cell detection, showing a detection limit of 8-9 cells/mm2.

Quantification of grafted poly(ethylene glycol)-silanes on silicon by time-of-flight secondary ion mass spectrometry

Silicon grafted monodisperse poly(ethylene glycol) (PEG) silanes with various PEG chain lengths and mixtures of these were systematically analyzed with static time-of-flight secondary ion mass spectrometry (TOF-SIMS). The mass spectra show differences in the various relative signal intensities, an observation that was used to elucidate important aspects of the grafting process. The relationship between PEG-silane fragment ion abundances and Si(+) ion abundances were used to (i) qualitatively describe layer thicknesses of grafted mixtures of PEG-silanes on silicon, (ii) construct a calibration curve from which PEG chain length (or molecular mass) can be determined and (iii) quantitatively determine surface mixture compositions of grafted monodisperse PEG-silanes of different chain lengths (3, 7 and 11 PEG units). The results suggest that discrimination does take place in the adsorption process. The PEG-silane with the shorter PEG chain is discriminated for mixtures containing PEG3-silane, whereas the PEG-silane with the longer PEG chain is discriminated in PEG7/PEG11-silane mixtures. The origin of this difference in adsorption behavior is not well understood. Aspects of the grafting process and the TOF-SIMS analyses are discussed.

Histamine immunoreactive axons in the macaque retina

PURPOSE

The goal of these experiments was to identify the neurotransmitter in centrifugal axons of the macaque retina.

METHODS

Macaca mulatta retinas and optic nerves were fixed overnight in carbodiimide and labeled with an antiserum to histamine with the use of an immunofluorescence technique.

RESULTS

Several large histamine-immunoreactive axons ran from the optic nerve head to the peripheral retina, where they branched extensively and terminated in the inner plexiform layer, occasionally alongside retinal blood vessels. Other axons that emerged from the optic nerve head ran in the optic fiber layer to the central retina, circled the fovea, and then returned to the optic disc. These may be the source of histamine-immunoreactive axons that have been observed in central visual areas. No labeled cell bodies were present in the retina. Because perikarya in the posterior hypothalamus are the only known source of histamine in the primate central nervous system and because neurons there can be retrogradely labeled from the cut optic nerve, the histamine-immunoreactive axons must have originated there.

CONCLUSIONS

Centrifugal axons in the macaque retina are part of the system of axons containing histamine that originate in the hypothalamus and project throughout the brain. Because the activity of these neurons is highest during the morning, histamine might play a role in preparing the retina to operate in daylight. The contacts of histamine-immunoreactive axons with blood vessels suggest that histamine may also play a role in regulating the retinal microvasculature.

Mice transgenic for simian immunodeficiency virus nef are immunologically compromised

An intact nef gene is essential for rapid development of immunodeficiency in human immunodeficiency virus and simian immunodeficiency virus infections. To assess the role of nef in the immune response, mice transgenic for SIV nef were constructed and the humoral and cellular immune response to herpes simplex virus type-1 (HSV-1), measured. Mice transgenic for SIVmac239 nef exhibited a significantly increased mortality rate when challenged with HSV-1 and also showed unusual antibody kinetics in response to viral challenge. During a 32-week period following exposure to HSV, it was noted that IgG subclass titers continued to rise in the nef+ animals, while titers of nef- animals decreased. Additionally, following secondary challenge with HSV, nef- mice had a significantly greater rise in HSV-neutralizing antibody titers than nef+ mice. A decreased proliferative response to the T cell mitogen, PHA, was noted in the nef+ animals. These results suggest that the presence of nef+ is sufficient to induce immune dysfunction.

Structure and dynamics of lipid monolayers: implications for enzyme catalysed lipolysis

We have investigated the role of the substrate on the interfacial activation of lipases by an interdisciplinary study of the structure and dynamics of 1,2-sn dipalmitoylglycerol monolayers at distinct surface pressures. The diglyceride Langmuir film undergoes two phase transitions occurring at 38.3 and 39.8 A2 per molecule. The first transition is unique for diglyceride molecules and is driven by a reorganization of the headgroups causing a change in the hydrophobicity of the oil-water interface. X-ray diffraction studies of different mesophases shows that in the two highest pressure phases, the alkyl chains pack in an hexagonal structure relaxing to a distorted-hexagonal lattice in the lowest pressure phase with the alkyl chains tilted by approximately 14 degrees in a direction close to a nearest neighbour direction.

Langmuir-Blodgett Films of a Functionalized Molecule with Cross-Sectional Mismatch Between Head and Tail

A functionalized surfactant has been investigated as floating monolayers by synchrotron x-ray diffraction and as bilayers transferred to solid supports by the Langmuir-Blodgett technique through atomic force microscopy. The transfer process is accompanied by an increase of the unit cell area (about 17 percent) and by an increase of the average domain diameter of nanometer-scale domains (about three times). The unit cell area of the floating monolayer corresponds to close packing of the head groups and a noncharacteristic packing of the tifted alkyl chains. The larger unit cell area of the bilayer film is consistent with a particular ordered packing of the alkyl chains, leaving free space for the head groups.