Endocannabinoid modulation of hyperaemia evoked by physiologically relevant stimuli in the rat primary somatosensory cortex

BACKGROUND AND PURPOSE

In vitro studies demonstrate that cannabinoid CB(1) receptors subserve activity-dependent suppression of inhibition in the neocortex. To examine this mechanism in vivo, we assessed the effects of local changes in CB(1) receptor activity on somatosensory cortex neuronal activation by whisker movement in rats.

EXPERIMENTAL APPROACH

Laser Doppler flowmetry and c-Fos immunohistochemistry were used to measure changes in local blood flow and neuronal activation, respectively. All drugs were applied directly to the cranium above the whisker barrel fields of the primary somatosensory cortex.

KEY RESULTS

The CB(1) receptor agonist WIN55212-2 potentiated the hyperaemia induced by whisker movement and this potentiation was occluded by bicuculline. The CB(1) receptor antagonists, rimonabant and AM251, inhibited hyperaemic responses to whisker movement; indicating that activation of endogenous CB(1) receptors increased during whisker movement. Whisker movement-induced expression of c-Fos protein in neurons of the whisker barrel cortex was inhibited by rimonabant. Movement of the whiskers increased the 2-arachidonoylglycerol content in the contralateral, compared to the ipsilateral, sensory cortex.

CONCLUSIONS AND IMPLICATIONS

These results support the hypothesis that endocannabinoid signalling is recruited during physiologically relevant activation of the sensory cortex. These data support the hypothesis that the primary effect of CB(1) receptor activation within the activated whisker barrel cortex is to inhibit GABA release, resulting in disinhibition of neuronal activation. These studies provide physiological data involving endocannabinoid signalling in activity-dependent regulation of neuronal activation and provide a mechanistic basis for the effects of cannabis use on sensory processing in humans.

Substrate stiffness affects early differentiation events in embryonic stem cells

Embryonic stem cells (ESC) are both a potential source of cells for tissue replacement therapies and an accessible tool to model early embryonic development. Chemical factors such as soluble growth factors and insoluble components of the extracellular matrix are known to affect the differentiation of murine ESCs. However, there is also evidence to suggest that undifferentiated cells can both sense the mechanical properties of their environment and differentiate accordingly. By growing ESCs on flexible polydimethylsiloxane substrates with varying stiffness, we tested the hypothesis that substrate stiffness can influence ESC differentiation. While cell attachment was unaffected by the stiffness of the growth substrate, cell spreading and cell growth were all increased as a function of substrate stiffness. Similarly, several genes expressed in the primitive streak during gastrulation and implicated in early mesendoderm differentiation, such as Brachyury, Mixl1 and Eomes, were upregulated in cell cultures on stiffer compared to softer substrates. Finally, we demonstrated that osteogenic differentiation of ESCs was enhanced on stiff substrates compared to soft substrates, illustrating that the mechanical environment can play a role in both early and terminal ESC differentiation. Our results suggest a fundamental role for mechanosensing in mammalian development and illustrate that the mechanical environment should be taken into consideration when engineering implantable scaffolds or when producing therapeutically relevant cell populations in vitro.

Strabismus following endoscopic orbital decompression for thyroid eye disease

Endoscopic orbital decompression may be used to treat disfiguring proptosis or sight threatening optic nerve compression in patients with thyroid eye disease. Strabismus is common in thyroid eye disease and frequently follows decompression surgery. We retrospectively reviewed patients undergoing endoscopic decompression for thyroid eye disease, by a single surgeon, from 1994 to 2000. Twenty-three patients (21 female, 2 male) were identified with a mean age of 47.5 years. At presentation, 21 patients had proptosis, 8 optic nerve compression (2 without proptosis) and 11 strabismus (9 complained of diplopia) with a mean BSV score of 24.5 before decompression. Forty orbits were decompressed with a mean decrease in proptosis of 3.3 mm. Following decompression, the mean BSV score was 25, and 17 patients had manifest strabismus in primary gaze (3 at near only) of whom 10 had pre-existing strabismus. Five patients had new diplopia (22%). Eleven patients ultimately required strabismus surgery of whom 8 had manifest strabismus before decompression. Following strabismus surgery, the mean BSV score was 37. The final BSV score for those not requiring strabismus surgery was 29. Mean follow-up was 28 months. Endoscopic orbital decompression can effectively treat disfiguring proptosis. Diplopia is a common complication, but pre-existing diplopia may improve.

Thermomechanical manipulation of aromatic peptide nanotubes

Self-assembling aromatic dipeptides are among the smallest known biological materials which readily form ordered nanostructures. The simplicity of nanotube formation makes them highly desirable for a range of bionanotechnology applications. Here, we investigate the application of the atomic force microscope as a thermomechanical lithographic tool for the machining of nanotubes formed by two self-assembling aromatic peptides; diphenylalanine and dinapthylalanine. Trenches and indentations of varying depth and width were patterned into the peptide tubes with nanometer precision highlighting the ability to thermally machine and manipulate these robust and versatile nanotubes.

A quantitative assessment of inhaled drug particle-pulmonary surfactant interaction by atomic force microscopy

To date limited consideration has been given to the physical interaction between inhaled drug particles and pulmonary surfactant (PS). This study combines atomic force microscopy (AFM) with a Langmuir-Blodgett (LB) approach to quantify the force of adhesion between micronised budesonide particles and simulated PS monolayers. A LB approach was used to prepare Survanta monolayers at pre-determined surface pressures and AFM was employed to facilitate their visualisation. Adhesion measurements between drug particles and PS monolayers were executed via AFM. Contact angle measurements were performed to probe material wetting characteristics, the data confirmed that budesonide is hydrophobic and Survanta films at increasing surface pressure exhibit a rising hydrophobic character. AFM revealed that PS properties were governed by applied surface pressure and that the degree of interaction of budesonide was greater at higher surface pressure, where packing of the lipid film was increased; consistent with the point of exhalation. This correlates well with the accepted inhaler technique. The increasing hydrophobicity of the PS film, on increased pressure, was believed to be the primary reason for increased interaction with the hydrophobic budesonide. Surface chemistries of the drug particles and PS interface are considered to be important for inhaled drug delivery.

An investigation into the rheology of pharmaceutical inter-granular material bridges at high shear rates

PURPOSE

This study was undertaken to investigate the rheological properties of inter-granular material bridges on the nano-scale when strained at high shear rates.

MATERIALS AND METHODS

Atomic force microscopy (AFM) was used as a rheometer to measure the viscoelasticity of inter-granular material bridges for lactose:PVP K29/32 and lactose:PVP K90 granules, produced by wet granulation.

RESULTS

The loss tangent (tan delta) and both the storage (G') and loss shear moduli (G'') of inter-granular material bridges were measured as a function of the probe-sample separation distance, oscillation frequency and relative humidity (RH). As the probe was withdrawn from the granule surface tan delta initially increased rapidly from zero to a plateau phase. G'' became increasingly dominant as the bridge was further extended and eventually exceeded G'. At high RH, capillary forces were foremost at bridge rupture, whereas at low RH elastic forces dominated. The effect of increasing frequency was to increase the effective elasticity of the bridge at high RH.

CONCLUSIONS

AFM has been employed as a rheometer to investigate the nano-scale rheology of inter-granular material bridges. This novel method may be used to obtain a fundamental understanding how different binders, granulated with different diluent fillers, behave at high shear rates.

Particulate drug interactions with polymeric and elastomeric valve components in suspension formulations for metered dose inhalers

PURPOSE

To characterise the adhesive interactions between three pulmonary active pharmaceutical ingredient (API) materials and the components of pressurised metered dose inhalers (pMDIs) obtained from two commercially available products (termed 'Prod-1' and 'Prod-2'). This is of potential interest, as a greater understanding of the interactions between specific APIs and surfaces may aid manufacturers in component selection during pMDI system development.

METHODS

The theoretical work of adhesion (DeltaG(132)) for each API-pMDI component interaction was calculated using the surface component analysis (SCA) approach. These results were correlated with corresponding API-pMDI component separation energy measurements determined using colloid probe AFM.

RESULTS

Strong correlations existed between separation energy and the DeltaG(132) parameters where the polar contribution was accounted for. This highlighted the adhesive influence of polar surface energy on each interaction in this study. Generally the largest adhesive interactions involved APIs and pMDI components which have a bipolar surface energy (i.e. both gamma(-) and gamma(+) >1 mJ m(-2)).

CONCLUSIONS

For each API-pMDI interaction in this study, the polar component of surface energy has the greater influence on adhesive events. The bipolar surface energetics of certain APIs and pMDI components were deemed responsible for the increased adhesive interactions observed with these materials. This study highlights that different materials can have different effects on the adhesive interactions with particulate APIs; information that could aid the manufacturer in producing more effective and efficient pMDI systems.

The surface characterisation and comparison of two potential sub-micron, sugar bulking excipients for use in low-dose, suspension formulations in metered dose inhalers

PURPOSE

This study compares the surface characteristics and surface energetics of two potential bulking excipients, anhydrous sub-micron alpha-lactose and sub-micron sucrose, for use with low-dose, suspension formulations in pressurised metered dose inhalers (pMDIs). Both sub-micron bulking excipients are processed from parent materials (alpha-lactose monohydrate/alpha-lactose monohydrate and silk grade sucrose, respectively) so the surface characteristics of each material were determined and compared. Additionally, the surface energetics and adhesive interactions between each sub-micron bulking excipient and some chosen active pharmaceutical ingredients (APIs) used in pMDI formulations were also determined. From this data, it was possible to predict the potential degree of interaction between the APIs and each sub-micron bulking excipient, thus determining suitable API-excipient combinations for pMDI formulation optimisation. Salmon calcitonin was also investigated as a potential API due to the current interest in, and the potential low-dose requirements for, the pulmonary delivery of proteins.

METHODS

The size and morphology of each sub-micron excipient (and parent materials) were determined using scanning electron microscopy (SEM) and the crystalline nature of each sub-micron excipient and parent material was assessed using X-ray diffraction (XRD). The surface chemistry of each sub-micron excipient was analysed using X-ray photoelectron spectroscopy (XPS). The surface energies of each sub-micron excipient, along with their respective parent materials and any intermediates, were determined using two techniques. The surface energies of these materials were determined via (a) single particle adhesive interactions using atomic force microscopy (AFM) and (b) 'bulk' material surface interactions using contact angle measurements (CA). From the CA data, it was possible to calculate the theoretical work of adhesion values for each API-excipient interaction using the surface component analysis (SCA). The Young's modulus for each sub-micron excipient and parent material was also determined using AFM. Finally, the adhesive interactions were determined between each sub-micron bulking excipient and five APIs (formoterol fumarate, salmeterol xinafoate, salbutamol sulphate, mometasone furoate and salmon calcitonin).

RESULTS

Both sub-micron sucrose and anhydrous sub-micron alpha-lactose exhibited a lower surface free energy than their respective parent materials/intermediates. In addition, both AFM and CA surface energy measurements also showed that sub-micron sucrose has a higher surface energy than anhydrous sub-micron alpha-lactose. Theoretical work of adhesion values between anhydrous sub-micron alpha-lactose and each API are considerably lower than those observed between micronised alpha-lactose monohydrate and each API. Corresponding theoretical work of adhesion values between sub-micron sucrose and each API were almost identical to those observed between silk grade sucrose and each API. Young's modulus determination revealed that sub-micron sucrose has a greater crystal hardness/elasticity ratio than anhydrous sub-micron alpha-lactose. With the exception of salmon calcitonin, sub-micron sucrose showed larger adhesive interactions to the selected APIs than anhydrous sub-micron alpha-lactose.

CONCLUSIONS

Anhydrous sub-micron alpha-lactose has been found to have lower adhesive interactions with a range of chosen, low-dose APIs compared to sub-micron sucrose. This could be related to the lower surface energy for anhydrous sub-micron alpha-lactose. Knowledge of the surface free energy and mechanical properties of potential sub-micron bulking excipients and API materials could provide useful information regarding the selection of suitable API-submicron bulking excipient combinations during the development and optimisation stages of suspension pMDI formulations.

Characterization of Ternary Solid Dispersions of Itraconazole, PEG 6000, and HPMC 2910 E5

In order to reduce the crystallinity of PEG 6000, blends were prepared by spray drying and extrusion with the following polymers; PVP K25, PVPVA 64, and HPMC 2910 E5. The maximal reduction of crystallinity in PEG 6000 was obtained by co-spray drying with HPMC 2910 E5. In the next step the model drug Itraconazole was added to the blend and the resulting ternary solid dispersions were characterized. The results of this study show that the addition of PEG 6000 to the Itraconazole/HPMC 2910 E5 system leads to phase separation that in most cases gives rise to recrystallization of either PEG 6000 or Itraconazole. For all ternary dispersions containing 20% of Itraconazole the drug was highly amorphous and the dissolution was improved compared to the binary 20/80 w/w Itraconazole/HPMC 2910 E5 solid dispersion. For all ternary dispersions containing 40% of Itraconazole, the drug was partially crystalline and the dissolution was lower than the dissolution of the binary 40/60 w/w Itraconazole/HPMC 2910 E5 dispersion. These results show that provided Itraconazole is highly amorphous the addition of PEG 6000 to HPMC 2910 E5 leads to an increase in drug release.

Implications of shortening the time spent in hospital

The decision to shorten the time spent in most areas of hospital care is extremely complex and hinges on the balance of numerous resulting credits and debits, which are largely unknown. The length of stay in hospital can be stabilized for many categories of medical care but the likely benefits may be disappointingly small in the face of unchanged demand for health care. Furthermore, a sustained reduction in length of stay could bring with it logistic contractual and personal problems, the costs of which could outweigh the benefits of stabilization. The best delivery of health care in a closed financial system seems to depend on a joint consideration of output per unit time and a provision of a service that comes near to satisfying the true need for that service. The appropriate level of service will be decided from a study of the true prevalence of the need and the ability of the service to satisfy it. The enthusiastic pursuit of traditional efficiency without adequate information may be counterproductive--by increasing demand, by demoralizing the health personnel and by diverting some of the demand into private practice. Our first priority is the rationalization of demand; this will need the combined efforts and goodwill of the consumer and the supplier. Only when demand has been rationalized may we expect a net benefit from shortening length of stay.

The application of ToF-SIMS to the analysis of herbicide formulation penetration into and through leaf cuticles

Understanding the movement of the active ingredient in relation to the other formulation components following application is crucial to an overall understanding of herbicide performance. We describe the novel use of time-of-flight secondary ion mass spectrometry (ToF-SIMS) as a tool for following the movement of herbicide formulation components into and across plant cuticles. This technique provides new insights since it provides both high (sub-micron) spatial resolution combined with the chemical specificity associated with organic mass spectrometry. The components studied include the oligomeric ethoxylate surfactants Synperonic A7 and A20 and active ingredient Sulfosate (trimesium glyphosate). The movement of these molecules, both separately and when combined in a simple formulation, into the surface of Prunus laurocerasus leaves and across the isolated plant cuticle was investigated and clear differences in penetration/diffusion behaviour were identified. ToF-SIMS was uniquely able to (simultaneously) spatially resolve all the species involved, including the anion and cation components of the active ingredient. Also, using spectral reconstructions from the imaging raw data streams, the behaviour of individual oligomers within the surfactant distributions, could be assessed. The observations are discussed with reference to the action of surfactants identified in parallel micro-structural studies and the current understanding of herbicide uptake.

Scanning probe microscopy in the field of drug delivery

The scanning probe microscopes (SPMs) are a group of powerful surface sensitive instruments which when used complimentarily with traditional analytical techniques can provide invaluable, definitive information aiding our understanding and development of drug delivery systems. In this review, the main use of the SPMs (particularly the atomic force microscopy (AFM)) and their successes in forwarding drug delivery are highlighted and categorised into two interlinked sections namely, preformulation and formulation. SPM in preformulation concentrates on applications in pharmaceutical processes including, crystal morphology and modification, discriminating polymorphs, drug dissolution and release, solid state stability and interaction. The ability of the AFM to detect forces between different surfaces and at the same time to operate in liquids or controlled humidity and defined temperatures has also been particularly useful in the study of drug delivery. In formulation, the use of SPMs in different drug delivery systems is discussed in light of different host entry routes.

Directional loading and stimulation of PcrA helicase by the replication initiator protein RepD

The replication initiator protein RepD recruits the Bacillus PcrA helicase directly onto the (-) strand of the plasmid replication origin oriD. The 5'-phosphate group at the nick is essential for loading, suggesting that it is the RepD covalently linked to the 5'-phosphate group at the nick that loads the helicase onto the oriD. The products of the unwinding reaction were visualised by atomic force microscopy (AFM) and monitored in real time by fluorescence spectroscopy. RepD remains associated with PcrA and stimulates processive directional unwinding of the plasmid at approximately 60 bp s(-1). In the absence of RepD, PcrA retains the ability to bind to a pre-nicked oriD, but engages the 3' end of the nick and translocates 3'-5' along the (+) strand in a poorly processive fashion. Our data provide a unique insight into the recruitment of PcrA-like helicases to DNA-nick sites and the processive translocation of the PcrA motor as a component of the plasmid replication apparatus.

Attachment of carbon nanotubes to atomic force microscope probes

In atomic force microscopy (AFM) the accuracy of data is often limited by the tip geometry and the effect on this geometry of wear. One way to improve the tip geometry is to attach carbon nanotubes (CNT) to AFM tips. CNTs are ideal because they have a small diameter (typically between 1 and 20nm), high aspect ratio, high strength, good conductivity, and almost no wear. A number of methods for CNT attachment have been proposed and explored including chemical vapour deposition (CVD), dielectrophoresis, arc discharge and mechanical attachment. In this work we will use CVD to deposit nanotubes onto a silicon surface and then investigate improved methods to pick-up and attach CNTs to tapping mode probes. Conventional pick-up methods involve using standard tapping mode or non-contact mode so as to attach only those CNTs that are aligned vertically on the surface. We have developed improved methods to attach CNTs using contact mode and reduced set-point tapping mode imaging. Using these techniques the AFM tip is in contact with a greater number of CNTs and the rate and stability of CNT pick-up is improved. The presence of CNTs on the modified AFM tips was confirmed by high-resolution AFM imaging, analysis of the tips dynamic force curves and scanning electron microscopy (SEM).

Nucleation and growth of insulin fibrils in bulk solution and at hydrophobic polystyrene surfaces

A technique was developed for studying the nucleation and growth of fibrillar protein aggregates. Fourier transform infrared and attenuated total reflection spectroscopy were used to measure changes in the intermolecular beta-sheet content of bovine pancreatic insulin in bulk solution and on model polystyrene (PS) surfaces at pH 1. The kinetics of beta-sheet formation were shown to evolve in two stages. Combined Fourier transform infrared, dynamic light scattering, atomic force microscopy, and thioflavin-T fluorescence measurements confirmed that the first stage in the kinetics was related to the formation of nonfibrillar aggregates that have a radius of 13 +/- 1 nm. The second stage was found to be associated with the growth of insulin fibrils. The beta-sheet kinetics in this second stage were used to determine the nucleation and growth rates of fibrils over a range of temperatures between 60 degrees C and 80 degrees C. The nucleation and growth rates were shown to display Arrhenius kinetics, and the associated energy barriers were extracted for fibrils formed in bulk solution and at PS surfaces. These experiments showed that fibrils are nucleated more quickly in the presence of hydrophobic PS surfaces but that the corresponding fibril growth rates decrease. These observations are interpreted in terms of the differences in the attempt frequencies and energy barriers associated with the nucleation and growth of fibrils. They are also discussed in the context of differences in protein concentration, mobility, and conformational and colloidal stability that exist between insulin molecules in bulk solution and those that are localized at hydrophobic PS interfaces.

Ultra-resolution imaging of a self-assembling biomolecular system using robust carbon nanotube AFM probes

Nanoscale structural features of a novel self-assembling DNA based nanostructure have been resolved. Image data is of sufficient resolution to allow molecular orientation and the effect of surface adsorption to be characterized. This has been achieved using AFM with probes employing carbon nanotubes attached via a thin film of plasma polymerized hexane. This presents the nanotube with a highly hydrophobic coating to which it can adsorb, increasing production success and probe robustness.

Direct Observation of Single Particle Electrostatic Charging by Atomic Force Microscopy

PURPOSE

To show that atomic force microscopy (AFM) can be used to directly study the electrostatic charging and dissipation of single pharmaceutical particles.

MATERIALS AND METHODS

Particles of lactose attached to AFM cantilevers were charged on a glass surface at a relative humidity (RH) of 0.1%. By recording force-distance curves, we use a measurement of the long range electrostatic interaction to compare the generation of charge by contact charging and tribocharging and to study the effect of RH on charge dissipation.

RESULTS

As expected, tribocharging by scanning the particle across the glass surface generates considerably more charge than repeated local contacts. Increasing the RH from 0.1 to 5% over a period of 37 min dissipates the tribo-generated electrostatic charge.

CONCLUSIONS

Using a combination of the abilities of AFM to scan in contact mode and record force-distance curves, we have shown a novel method to study electrostatic charging of particles. By measuring the length of the long range electrostatic interaction, we are able to compare different mechanisms of generating charge and to study the effect of RH on charge dissipation.

Elastic modulus measurements from individual lactose particles using atomic force microscopy

The elastic modulus of pharmaceutical materials affects a number of pharmaceutical processes and subsequently formulation performance and is currently assessed by bulk methods, such as beam bending of compacts. Here we demonstrate the accurate measurement of the elastic modulus of alpha monohydrate lactose from the dominant (011) face of single crystals using atomic force microscopy (AFM) as 3.45+/-0.90GPa. The criteria to ensure this data is recorded within the elastic limit and can be modelled using Hertzian theory are established. We compare and contrast this AFM method to a permanent indentation technique based upon a much larger Berkovich pyramidal indenter on a lactose compact and the wider literature. Finally the AFM was utilized to study the elastic response of amorphous lactose, demonstrating that the physical state of the amorphous material changes under repeated loading and behaves in a more crystalline manner under repeated force measurements, suggesting a pressure induced phase transition. The AFM based approach demonstrated has the significant advantages of requiring minimal sample, no need for producing a compact, being non-destructive in that no permanent indent is required and providing a technique capable of detecting variations in material properties across a single particle or a number of particles.

Quantifying the dimensions of nanoscale organic surface layers in natural waters

Nanoscale surface films are known to develop on surfaces exposed to natural waters and have potential impacts on many environmental processes. A new method using atomic force microscopy is presented which physically removes the developed film in a defined area and then quantifies the difference in height between the film and the area where the film has been removed. The difference gives the absolute thickness of the surface film, which has not previously been measured. Suwannee River humic acid was exposed to substrates, and the surface film thickness as a function of pH and exposure time was measured. Discrete and very small colloids in the range 1-5 nm were observed as expected, and these sat on a coherent surface film, notthe original mica substrate. Low pH values of 2 gave rise to relatively thick surface films of about3 nm, although these films were not continuous at higher pH values. At pH 4.8, the film thickness increased with exposure time up to about 5 h and did not subsequently increase. The maximum film thickness measured was about 1 nm at that pH. The method is applicable to the measurement of many environmental surfaces, although resolution will depend on the substrate and film roughness.