Celecoxib Encapsulation in β-Casein Micelles: Structure, Interactions, and Conformation

Abstract

β-Casein is a 24 kDa natural protein that has an open conformation and almost no folded or secondary structure, and thus is classified as an intrinsically unstructured protein. At neutral pH, β-casein has an amphiphilic character. Therefore, in contrast to most unstructured proteins that remain monomeric in solution, β-casein self-assembles into well-defined core-shell micelles. We recently developed these micelles as potential carriers for oral administration of poorly water-soluble pharmaceuticals, using celecoxib as a model drug. Herein we present deep and precise insight into the physicochemical characteristics of the protein-drug formulation, both in bulk solution and in dry form, emphasizing drug conformation, packing properties and aggregation state. In addition, the formulation is extensively studied in terms of structure and morphology, protein/drug interactions and physical stability. Particularly, NMR measurements indicated strong drug-protein interactions and noncrystalline drug conformation, which is expected to improve drug solubility and bioavailability. Small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM) were combined for nanostructural characterization, proving that drug-protein interactions lead to well-defined spheroidal micelles that become puffier and denser upon drug loading. Dynamice light scattering (DLS), turbidity measurements, and visual observations complemented the analysis for determining formulation structure, interactions, and stability. Additionally, it was shown that the loaded micelles retain their properties through freeze-drying and rehydration, providing long-term physical and chemical stability. Altogether, the formulation seems greatly promising for oral drug delivery.

Complex coacervate‐based materials for biomedicine

“…While reports on coacervation include variety of branched polymers, the majority of efforts have utilized naturally occurring polymers that are not well defined either chemically or physically. 19,158,[180][181][182][183] However, advances in polymer chemistry have enabled the synthesis of increasingly dense branched and brush polymer structures. These chemistries represent an intriguing opportunity to explore the steric limitations of electrostatic interactions.…”

Recent applications of light scattering measurement in the biological and biopharmaceutical sciences

“…The results are reported to be in good agreement with other estimates of size obtained from SAXS and cryo-TEM measurements. [38]. …”

Stimulus‐Responsive Hydrogel for Ophthalmic Drug Delivery

“…In the anterior segment of the eye, the corneal-aqueous humor barrier, physiological blinking, and tear drainage are dominant factors for rapid drug clearance after topical instillation. [17][18][19][20] Taking the most commonly used eye drops formulation as an example, once the eye drops are instilled topically to the ocular surface, the therapeutic agents are immediately diluted and washed away by tears, resulting in low ocular bioavailability (<5%). [21,22] This imparts the need for frequent administration regimens to maintain the therapeutic efficacy for anterior disorders.…”

“…Despite the distinct advantages of local therapies, a highly efficient ophthalmic drug delivery approach remains one of the most challenging tasks for pharmaceutical formulators and scientists because of various physiological barriers (Figure ) . In the anterior segment of the eye, the corneal‐aqueous humor barrier, physiological blinking, and tear drainage are dominant factors for rapid drug clearance after topical instillation . Taking the most commonly used eye drops formulation as an example, once the eye drops are instilled topically to the ocular surface, the therapeutic agents are immediately diluted and washed away by tears, resulting in low ocular bioavailability (<5%) .…”