Discovery of low mucus adhesion surfaces

Surface design of nanocarriers: Key to more efficient oral drug delivery systems

As nanocarriers (NCs) can improve the solubility of drugs, prevent their degradation by gastrointestinal (GI) enzymes and promote their transport across the mucus gel layer and absorption membrane, the oral bioavailability of these drugs can be substantially enhanced. All these properties of NCs including self-emulsifying drug delivery systems (SEDDS), solid lipid nanoparticles (SLNs), nanostructured lipid carriers (NLCs), liposomes, polymeric nanoparticles, inorganic nanoparticles and polymeric micelles depend mainly on their surface chemistry. In particular, interaction with food, digestive enzymes, bile salts and electrolytes, diffusion behaviour across the mucus gel layer and fate on the absorption membrane are determined by their surface. Bioinert surfaces limiting interactions with gastrointestinal fluid and content as well as with mucus, adhesive surfaces providing an intimate contact with the GI mucosa and absorption enhancing surfaces can be designed. Furthermore, charge converting surfaces shifting their zeta potential from negative to positive directly at the absorption membrane and surfaces providing a targeted drug release are advantageous. In addition to these passive surfaces, even active surfaces cleaving mucus glycoproteins on their way through the mucus gel layer can be created. Within this review, we provide an overview on these different surfaces and discuss their impact on the performance of NCs in the GI tract.

Probing mucin interaction behavior of magnetic nanoparticles

In this study, we developed iron oxide based magnetic nanoparticles (MNPs) by precipitation of iron salts in the presence of ammonia and created four different formulations: without functionality (plain MNPs, no coating), with β-cyclodextrin (MNPs+β-CD) or pluronic 127 polymer (MNPs+F-127), and both β-cyclodextrin and pluronic 127 polymer (MNPs+β-CD-F-127) functionality for its efficient use in mucosal delivery. We studied the interaction and/or binding behavior of these MNPs formulations with porcine stomach mucin using steady-state fluorescence spectroscopy, and then quantified the bound mucin from absorption studies. Toxicity of these MNPs against cervical cancer cells and red blood cells was evaluated. Ex-vivo studies were performed using freshly collected gastrointestinal, ovarian, pancreas and colon organ tissues of pig to evaluate binding and uptake phenomenon of MNPs. Transport studies of these MNPs in mucin was evaluated using Boyden's chamber assay. All these studies together suggest that the MNPs+β-CD-F-127 formulation was strongly interacted with mucin and interestingly transported through mucin compared to other MNPs formulations. Hence, MNPs+β-CD-F-127 formulation could be a good candidate for the mucoadhesive biopharmaceuticals and drug delivery system.

Mechanism of Four de Novo Designed Antimicrobial Peptides

As pathogenic bacteria become resistant to traditional antibiotics, alternate approaches such as designing and testing new potent selective antimicrobial peptides (AMP) are increasingly attractive. However, whereas much is known regarding the relationship between the AMP sequence and potency, less research has focused on developing links between AMP properties, such as design and structure, with mechanisms. Here we use four natural AMPs of varying known secondary structures and mechanisms of lipid bilayer disruption as controls to determine the mechanisms of four rationally designed AMPs with similar secondary structures and rearranged amino acid sequences. Using a Quartz Crystal Microbalance with Dissipation, we were able to differentiate between molecular models of AMP actions such as barrel-stave pore formation, toroidal pore formation, and peptide insertion mechanisms by quantifying differential frequencies throughout an oscillating supported lipid bilayer. Barrel-stave pores were identified by uniform frequency modulation, whereas toroidal pores possessed characteristic changes in oscillation frequency throughout the bilayer. The resulting modes of action demonstrate that rearrangement of an amino acid sequence of the AMP resulted in identical overall mechanisms, and that a given secondary structure did not necessarily predict mechanism. Also, increased mass addition to Gram-positive mimetic membranes from AMP disruption corresponded with lower minimum inhibitory concentrations against the Gram-positive Staphylococcus aureus.

Enzymatically active biomimetic micropropellers for the penetration of mucin gels

In the body, mucus provides an important defense mechanism by limiting the penetration of pathogens. It is therefore also a major obstacle for the efficient delivery of particle-based drug carriers. The acidic stomach lining in particular is difficult to overcome because mucin glycoproteins form viscoelastic gels under acidic conditions. The bacterium Helicobacter pylori has developed a strategy to overcome the mucus barrier by producing the enzyme urease, which locally raises the pH and consequently liquefies the mucus. This allows the bacteria to swim through mucus and to reach the epithelial surface. We present an artificial system of reactive magnetic micropropellers that mimic this strategy to move through gastric mucin gels by making use of surface-immobilized urease. The results demonstrate the validity of this biomimetic approach to penetrate biological gels, and show that externally propelled microstructures can actively and reversibly manipulate the physical state of their surroundings, suggesting that such particles could potentially penetrate native mucus.