A polysiloxane surfactant dissolves a poorly soluble drug (nystatin) in water

Reviving the interest in the versatile drug nystatin: A multitude of strategies to increase its potential as an effective and safe antifungal agent

Nystatin is an antifungal molecule with a remarkable yet squandered versatility. In this review, its mechanism of action is explored, along with its extensive action spectrum and toxicity. A multitude of methodologies to tackle the drug's physical and chemical hurdles are outlined along with some proven-effective strategies to increase its activity and/or decrease its toxicity. A separate detailed section focused on micro and nanotechnology solutions addresses new drug delivery systems made of polymeric, metallic or lipid materials. Although the topical route depicts greater representativeness amongst these formulations, the intravenous, dental, oral, vaginal and inhalation routes are also mentioned. The unsuccessful previous attempts at developing parenteral formulations of nystatin or even the withdrawal of a nystatin-loaded multilamellar liposome should not divert research away from this drug. In fact, the interest in nystatin ought to be reawakened with the ongoing clinical trials on the promising nystatin-like genetically engineered derivate BSG005.

From passive to emerging smart silicones

Amassing remarkable properties, silicones are practically indispensable in our everyday life. In most classic applications, they play a passive role in that they cover, seal, insulate, lubricate, water-proof, weather-proof etc. However, silicone science and engineering are highly innovative, seeking to develop new compounds and materials that meet market demands. Thus, the unusual properties of silicones, coupled with chemical group functionalization, has allowed silicones to gradually evolve from passive materials to active ones, meeting the concept of “smart materials”, which are able to respond to external stimuli. In such cases, the intrinsic properties of polysiloxanes are augmented by various chemical modifications aiming to attach reactive or functional groups, and/or by engineering through proper cross-linking pattern or loading with suitable fillers (ceramic, magnetic, highly dielectric or electrically conductive materials, biologically active, etc.), to add new capabilities and develop high value materials. The literature and own data reflecting the state-of-the art in the field of smart silicones, such as thermoplasticity, self-healing ability, surface activity, electromechanical activity and magnetostriction, thermo-, photo-, and piezoresponsivity are reviewed.

From Amorphous Silicones to Si-Containing Highly Ordered Polymers: Some Romanian Contributions in the Field

Polydimethylsiloxane (PDMS), in spite of its well-defined helical structure, is an amorphous fluid even at extremely high molecular weights. The cause of this behavior is the high flexibility of the siloxane backbone and the lack of intermolecular interactions attributed to the presence of methyl groups. These make PDMS incompatible with almost any organic or inorganic component leading to phase separation in siloxane-siloxane copolymers containing blocks with polar organic groups and in siloxane-organic copolymers, where dimethylsiloxane segments co-exist with organic ones. Self-assembly at the micro- or nanometric scale is common in certain mixed structures, including micelles, vesicles, et cetera, manifesting reversibly in response to an external stimulus. Polymers with a very high degree of ordering in the form of high-quality crystals were obtained when siloxane/silane segments co-exist with coordinated metal blocks in the polymer chain. While in the case of coordination of secondary building units (SBUs) with siloxane ligands 1D chains are formed; when coordination is achieved in the presence of a mixture of ligands, siloxane and organic, 2D structures are formed in most cases. The Romanian research group's results regarding these aspects are reviewed: from the synthesis of classic, amorphous silicone products, to their adaptation for use in emerging fields and to new self-assembled or highly ordered structures with properties that create perspectives for the use of silicones in hitherto unexpected areas.

Solubilization Behavior of Polyene Antibiotics in Nanomicellar System: Insights from Molecular Dynamics Simulation of the Amphotericin B and Nystatin Interactions with Polysorbate 80

Amphotericin B (AmB) and Nystatin (Nys) are the drugs of choice for treatment of systemic and superficial mycotic infections, respectively, with their full clinical potential unrealized due to the lack of high therapeutic index formulations for their solubilized delivery. In the present study, using a coarse-grained (CG) molecular dynamics (MD) simulation approach, we investigated the interaction of AmB and Nys with Polysorbate 80 (P80) to gain insight into the behavior of these polyene antibiotics (PAs) in nanomicellar solution and derive potential implications for their formulation development. While the encapsulation process was predominantly governed by hydrophobic forces, the dynamics, hydration, localization, orientation, and solvation of PAs in the micelle were largely controlled by hydrophilic interactions. Simulation results rationalized the experimentally observed capability of P80 in solubilizing PAs by indicating (i) the dominant kinetics of drugs encapsulation over self-association; (ii) significantly lower hydration of the drugs at encapsulated state compared with aggregated state; (iii) monomeric solubilization of the drugs; (iv) contribution of drug-micelle interactions to the solubilization; (v) suppressed diffusivity of the encapsulated drugs; (vi) high loading capacity of the micelle; and (vii) the structural robustness of the micelle against drug loading. Supported from the experimental data, our simulations determined the preferred location of PAs to be the core-shell interface at the relatively shallow depth of 75% of micelle radius. Deeper penetration of PAs was impeded by the synergistic effects of (i) limited diffusion of water; and (ii) perpendicular orientation of these drug molecules with respect to the micelle radius. PAs were solvated almost exclusively in the aqueous poly-oxyethylene (POE) medium due to the distance-related lack of interaction with the core, explaining the documented insensitivity of Nys solubilization to drug-core compatibility in detergent micelles. Based on the obtained results, the dearth of water at interior sites of micelle and the large lateral occupation space of PAs lead to shallow insertion, broad radial distribution, and lack of core interactions of the amphiphilic drugs. Hence, controlled promotion of micelle permeability and optimization of chain crowding in palisade layer may help to achieve more efficient solubilization of the PAs.

Surface Activity and Aggregation Behavior of Siloxane-Based Ionic Liquids in Aqueous Solution

Six novel siloxane-based surface-active ionic liquids (SAILs)--siloxane ammonium carboxylate [Si(n)N(2)-CA(1), (n = 3, 4)]--were designed and synthesized. Their melting points, surface activities, and self-aggregation behavior in aqueous solution were studied. The results showed that because of the bulky hydrophobic siloxane chains at the end of the tail, all six siloxane-based SAILs are room-temperature ionic liquids (RT-SAILs). The introduction of the siloxane group can reduce the melting point of ionic liquids to below room temperature and can promote the micellization and aggregation behavior more efficiently. These siloxane-based SAILs can greatly reduce the surface tension of water, as shown by the critical aggregation concentration (γCAC) values of 20 mN·m(-1); all six siloxane RT-SAILs can form a vesicle spontaneously in aqueous solution, indicating potential uses as model systems for biomembranes and vehicles for drug delivery.