Kristen E. Bremmell

Tableting Lipid-Based Formulations for Oral Drug Delivery: A Case Study with Silica Nanoparticle–Lipid–Mannitol Hybrid Microparticles

Silica-lipid-mannitol hybrid (SLMH) microparticles have been developed that were compressible into high quality tablets suitable for oral dosing and delivery of poorly soluble drugs. SLMH tablets enable high lipid-loading levels (>40%) and retain the immediate release, enhanced lipase digestion and drug solubilisation performance. Specifically, we report formulation optimisation of SLMH microparticles and tablets using coumarin 102 (log P = 4.09) as a model Biopharmaceutics Classification System class II drug. SLMH tablets were acceptable according to standard British Pharmacopoeia friability, hardness and disintegration tests; this is not the case for conventional dry emulsions. Furthermore, in vitro dissolution and pancreatic-lipase-induced lipolysis studies under simulated intestinal conditions have demonstrated enzymatic-digestion-mediated drug solubilisation. SLMH microparticles and tablets are suitable as liquid lipid containing solid dosage forms for enhancing and controlling oral absorption of poorly soluble drugs.

Lyophilized Silica Lipid Hybrid (SLH) Carriers for Poorly Water‐Soluble Drugs: Physicochemical and In Vitro Pharmaceutical Investigations

Lyophilization was investigated to produce a powdery silica-lipid hybrid (SLH) carrier for oral delivery of poorly water-soluble drugs. The silica to lipid ratio, incorporation of cryoprotectant, and lipid loading level were investigated as performance indicators for lyophilized SLH carriers. Celecoxib, a nonsteroidal anti-inflammatory drug, was used as the model poorly soluble moiety to attain desirable physicochemical and in vitro drug solubilization properties. Scanning electron microscopy and confocal fluorescence imaging verified a nanoporous, homogenous internal matrix structures of the lyophilized SLH particles, prepared from submicron triglyceride emulsions and stabilized by porous silica nanoparticles (Aerosil 380), similar to spray-dried SLH. 20-50 wt % of silica in the formulation have shown to produce nonoily SLH agglomerates with complete lipid encapsulation. The incorporation of a cryoprotectant prevented irreversible aggregation of the silica-stabilized droplets during lyophilization, thereby readily redispersing in water to form micrometre-sized particles (<5 μm). The lyophilized SLH produced approximately 1.5-fold and fivefold increased drug solubilization than the pure drug under nondigesting and digesting conditions, respectively. The feasibility of lyophilization for producing nanostructured SLH formulations with desirable lipid loading and drug solubilization properties for enhanced oral delivery of poorly water-soluble therapeutics is confirmed.

In Situ ATR FTIR Spectroscopic Study of the Formation and Hydration of a Fucoidan/Chitosan Polyelectrolyte Multilayer

The formation of fucoidan/chitosan-based polyelectrolyte multilayers (PEMs) has been studied with in situ Fourier transform infrared (FTIR) spectroscopy. Attenuated total reflectance (ATR) FTIR spectroscopy has been used to follow the sequential build-up of the multilayer, with peaks characteristic of each polymer being seen to increase in intensity with each respective adsorption stage. In addition, spectral processing has allowed for the extraction of spectra from individual adsorbed layers, which have been used to provide unambiguous determination of the adsorbed mass of the PEM at each stage of formation. The PEM was seen to undergo a transition in growth regimes during build-up: from supra-linear to linear. In addition, the wettability of the PEM has been probed at each stage of the build-up, using the captive bubble contact angle technique. The contact angles were uniformly low, but showed variation in value depending on the nature of the outer polymer layer, and this variation correlated with the overall percentage hydration of the PEM (determined from FTIR and quartz crystal microbalance data). The nature of the hydration water within the polyelectrolyte multilayer has also been studied with FTIR spectroscopy, specifically in situ synchrotron ATR FTIR microscopy of the multilayer confined between two solid surfaces. The acquired spectra have enabled the hydrogen bonding environment of the PEM hydration water to be determined. The PEM hydration water is seen to have an environment in which it is subject to fewer hydrogen bonding interactions than in bulk electrolyte solution.

Low Temperature Thermal Dependent Filgrastim Adsorption Behavior Detected with ToF-SIMS

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) detected changes in Filgrastim (granulocyte colony stimulating growth factor, G-CSF) adsorption behavior at a solid interface when exposed to temperatures as low as 35 °C, i.e., before thermal denaturation, was detected by circular dichroism (CD) or dynamic light scattering (DLS). Biopharmaceuticals rely on maintaining sufficient conformation to impart correct biological function in vivo. Stability of such molecules is critical during synthesis, storage, transport, and administration. CD analysis indicated loss of structure at temperatures greater than ~60 °C, while DLS detected aggregation at ~42 °C. Furthermore, we demonstrate the nature of G-CSF interaction with a surface was altered rapidly and at relatively low temperatures. Specifically, after 10 min thermal treatment, changes in adsorption behavior occurred at 35 °C indicated by principal component analysis of spectra as primarily due to increasing yields of methionine fragments. This was likely to be due to either altering the preferential protein orientation upon adsorption or greater denaturation exposing the hydrophobic core. This investigation demonstrates the sensitivity of ToF-SIMS in studying biopharmaceutical adsorption and conformational change and can assist with studies into promoting their stability.

Synergistic role of solid lipid and porous silica in improving the oral delivery of weakly basic poorly water soluble drugs

&NA; Oral absorption of weakly basic drugs (e.g. cinnarizine (CIN)) is limited by their pH dependent precipitation in intestinal conditions. To overcome this challenge, a novel drug delivery system composed of solid lipid and porous silica, namely silica encapsulated solid lipid (SESL) particles, was developed via hot homogenization of melted lipid dispersion, followed by ultra‐sonication of the silica stabilized homogenized melted lipid dispersion. Scanning electron microscope (SEM) images of the SESL formulation revealed non‐spherical and aggregated hybrid particles, with rough exterior and structured nanoparticles visible on the surface. A 1.5, 2.2 and 7‐fold improvement in the dissolution of CIN was observed for the SESL particles, under simulated intestinal non‐digesting conditions, in comparison to the drug loaded in solid lipid (CIN‐SL) matrix, drug loaded in porous silica (CIN‐PS) and pure drug powder. Under simulated intestinal digestive condition, significant improvement in the drug solubilization was reported for the SESL formulation in compared to the individual drug loaded systems i.e. CIN‐PS and CIN‐SL. Thereby, silica encapsulated solid lipid system provides a promising oral delivery approach for poorly water soluble weakly basic drugs. Graphical abstract Figure. No caption available.

Porous Silica-Supported Solid Lipid Particles for Enhanced Solubilization of Poorly Soluble Drugs

ABSTRACTLow dissolution of drugs in the intestinal fluid can limit their effectiveness in oral therapies. Here, a novel porous silica-supported solid lipid system was developed to optimize the oral delivery of drugs with limited aqueous solubility. Using lovastatin (LOV) as the model poorly water-soluble drug, two porous silica-supported solid lipid systems (SSL-A and SSL-S) were fabricated from solid lipid (glyceryl monostearate, GMS) and nanoporous silica particles Aerosil 380 (silica-A) and Syloid 244FP (silica-S) via immersion/solvent evaporation. SSL particles demonstrated significantly higher rate and extent of lipolysis in comparison with the pure solid lipid, depending on the lipid loading levels and the morphology. The highest lipid digestion was observed when silica-S was loaded with 34% (w/w) solid lipid, and differential scanning calorimeter (DSC) analysis confirmed the encapsulation of up to 2% (w/w) non-crystalline LOV in this optimal SSL-S formulation. Drug dissolution under non-digesting intestinal conditions revealed a three- to sixfold increase in dissolution efficiencies when compared to the unformulated drug and a LOV-lipid suspension. Furthermore, the SSL-S provided superior drug solubilization under simulated intestinal digesting condition in comparison with the drug-lipid suspension and drug-loaded silica. Therefore, solid lipid and nanoporous silica provides a synergistic effect on optimizing the solubilization of poorly water-soluble compound and the solid lipid-based porous carrier system provides a promising delivery approach to overcome the oral delivery challenges of poorly water-soluble drugs.

Colloid-probe AFM studies of the surface functionality and adsorbed proteins on binary colloidal crystal layers

Colloid-probe-AFM has been widely used to measure the forces of interaction between two surfaces such as particles of different size and functionality or a flat surface and a particle in aqueous environments. However, the applicability of colloid-probe AFM to detect different surface chemistries on chemical or protein patterned surfaces has not been demonstrated. We show that the technique can be used to distinguish the regions of different surface chemistries or biomolecules located within a patterned surface in buffer solution. Our previously developed method, based on evaporation induced self-assembly, was used to generate binary colloidal crystal (bCC) layers of different chemical and/or protein patterns. Particles of different size and functionality, with or without adsorbed protein(s), were used to decorate solid supports with the bCCs. The results from the force measurements on the patterned surfaces revealed that the probe experiences both strong or weak repulsive interactions and attractive interactions depending on the net surface charge present on the particles within the bCC patterns. Measurements on bCC patterns where one particle is coated with a single protein demonstrate that the technique can also be used to probe surface diffusion of adsorbed proteins. Therefore, we are able to detect whether a protein remains adsorbed or diffuses to a region on the bCC containing no proteins. Furthermore, the applicability of this technique was extended to detect the presence of two different biomolecules (i.e., lysozyme and bovine serum albumin adsorbed on both the large and small particles) within the protein patterned bCC surface by their different interaction forces. The study demonstrates that colloid-probe AFM can be used to discriminate between the surface properties of binary colloid crystal patterned surfaces where the binary patterns are comprised of particles of either different surface chemistry or particles with different adsorbed proteins.

Interfacial analysis of siRNA complexes with poly-ethylenimine (PEI) or PAMAM dendrimers in gene delivery

Solution and interfacial analysis has been employed to gain insight into the complexation of siRNA using either G4 PAMAM dendrimers or 25kDa branched poly-ethylenimine (bPEI). The size, charge and shape/structure of the complexing agents were probed using atomic force microscopy (AFM), circular dichroism spectrometry (CD), dynamic light scattering (DLS), and gel electrophoresis (GE). The binding capability of these cationic polymers to the siRNA molecule, subsequently controls the surface/adsorption behaviour of the complexes to a negatively charged surface. G4 PAMAM dendrimers bind to the major groove of the siRNA structure, while bPEI binds to both major and minor groove. PAMAM-siRNA complexes form a thin uniform surface film with adsorption of monomeric particles, whilst bPEI-siRNA complexes adsorb as particles in random orientations at low bPEI concentration and form network structures across the surface at high charge ratio. This is due to their ability to bind to both regions within siRNA. This new understanding of the interfacial behaviour of siRNA complexes correlates with observations of cellular transfection and can be used in the design of optimal transfection agents.

Impact of PEGylation and non-ionic surfactants on the physical stability of the therapeutic protein filgrastim (G-CSF)

Improvement in the in vitro and in vivo stability of biotherapeutic proteins has been approached via a number of strategies, including protein PEGylation or formulation with non-ionic surfactants. Here we report on interaction and stability studies for the biotherapeutic protein filgrastim (granulocyte stimulating factor (G-CSF)) and its PEGylated analogue (PEG-GCSF), with polysorbate 20, using isothermal calorimetry, circular dichroism, surface tension and dynamic light scattering measurements. PEGylation of G-CSF did not alter temperature-induced conformational changes detected with circular dichroism, however did increase the amphiphilic nature of G-CSF, lowering the surface tension to a greater extent. G-CSF and PEG-GCSF both aggregated at temperatures below that of denaturation. G-CSF had an inverse relationship between concentration and the temperature at which aggregation was initiated, with aggregates continually increasing in size to greater than 2 μm. Importantly, PEG-GCSF was shown to have improved resistance to heat-induced aggregation; the presence of PEG attached to the protein minimised the aggregate size to below 120 nm. Interaction between polysorbate 20 and the proteins was weak and determined to result from a hydrophobic mechanism. A two-site binding model was found to best describe the interaction of polysorbate 20 with G-CSF, irrespective of PEGylation. Presence of polysorbate 20 did not minimise the thermal-induced instability for G-CSF or PEG-GCSF. These findings provide new insight into the mechanism of therapeutic protein stabilization using PEG and non-ionic surfactants.