Drug Permeability: From the Blood-Brain Barrier to the Peripheral Nerve Barriers

Polyesters and Polyester Nano- and Microcarriers for Drug Delivery

Many therapies require the transport of therapeutic compounds or substances encapsulated in carriers that reduce or, if possible, eliminate their direct contact with healthy tissue and components of the immune system, which may react to them as something foreign and dangerous to the patient's body. To date, inorganic nanoparticles, solid lipids, micelles and micellar aggregates, liposomes, polymeric micelles, and other polymer assemblies were tested as drug carriers. Specifically, using polymers creates a variety of options to prepare nanocarriers tailored to the chosen needs. Among polymers, aliphatic polyesters are a particularly important group. The review discusses controlled synthesis of poly(β-butyrolactone)s, polylactides, polyglycolide, poly(ε-caprolactone), and copolymers containing polymacrolactone units with double bonds suitable for preparation of functionalized nanoparticles. Discussed are syntheses of aliphatic polymers with controlled molar masses ranging from a few thousand to 106 and, in the case of polyesters with chiral centers in the chains, with controlled microstructure. The review presents also a collection of methods useful for the preparation of the drug-loaded nanocarriers: classical, developed and mastered more recently (e.g., nanoprecipitation), and forgotten but still with great potential (by the direct synthesis of the drug-loaded nanoparticles in the process comprising monomer and drug). The article describes also in-vitro and model in-vivo studies for the brain-targeted drugs based on polyester-containing nanocarriers and presents a brief update on the clinical studies and the polyester nanocarrier formulation approved for application in the clinics in South Korea for the treatment of breast, lung, and ovarian cancers.

Advancing Central Nervous System Drug Delivery with Microtubule-Dependent Transcytosis of Novel Aqueous Compounds

The challenge of delivering therapeutics to the central nervous system due to the restrictive nature of the blood-brain barrier (BBB) is a substantial hurdle in neuropharmacology. Our research introduces a breakthrough approach using microtubule-dependent transcytosis facilitated by novel aqueous compounds. We synthesized a series of red-emitting pyran nitrile derivatives. The molecular structure of compounds, photophysical properties, and water solubility were characterized. BBB permeability of BN1 was assessed in an in vitro BBB model. The transmembrane transport mechanism was next analyzed. The derivative was injected in the wild-type mouse for evaluation of brain penetration and biodistribution in the brain. We further investigated the potential of BN1-functionalized BBB-nonpenetrated silica nanoparticles for brain targeting. This compound demonstrated an ability to form endosomes within the phospholipid layer, thus enabling efficient penetration of the BBB via microtubule-mediated transcytosis, as evidenced in vitro model. This was further confirmed by in vivo experiments that BN1 displays the excellent BBB penetration and retained in brain parenchyma. Furthermore, BBB-impermeable mesoporous silica nanoparticle codelivery system markedly enhanced the transport efficiency to the brain in vivo by BN1-functionalized. These findings indicate that our designed aqueous molecules not only are capable of traversing the BBB but also serve as a viable new strategy for central-nervous-system-targeted drug delivery.

Galacturonic acid-capsaicin prodrug for prolonged nociceptive-selective nerve blockade

There is an urgent clinical need to develop nerve-blocking agents capable of inducing long duration sensory block without muscle weakness or paralysis to treat post-operative and chronic pain conditions. Here, we report a galacturonic acid-capsaicin (GalA-CAP) prodrug as an effective nociceptive-selective axon blocking agent. Capsaicin selectively acts on nociceptive signaling without motor nerve blockade or disruption of proprioception and touch sensation, and the galacturonic acid moiety enhance prodrug permeability across the restrictive peripheral nerve barriers (PNBs) via carrier-mediated transport by the facilitative glucose transporters (GLUTs). In addition, following prodrug transport across PNBs, the inactive prodrug is converted to active capsaicin through linker hydrolysis, leading to sustained drug release. A single injection of GalA-CAP prodrug at the sciatic nerves of rats led to nociceptive-selective nerve blockade lasting for 234 ± 37 h, which is a sufficient duration to address the most intense period of postsurgical pain. Furthermore, the prodrug markedly mitigated capsaicin-associated side effects, leading to a notable decrease in systemic toxicity, benign local tissue reactions, and diminished burning and irritant effects.

Micro- and Nanostructured Fibrous Composites via Electro-Fluid Dynamics: Design and Applications for Brain

The brain consists of an interconnected network of neurons tightly packed in the extracellular matrix (ECM) to form complex and heterogeneous composite tissue. According to recent biomimicry approaches that consider biological features as active components of biomaterials, designing a highly reproducible microenvironment for brain cells can represent a key tool for tissue repair and regeneration. Indeed, this is crucial to support cell growth, mitigate inflammation phenomena and provide adequate structural properties needed to support the damaged tissue, corroborating the activity of the vascular network and ultimately the functionality of neurons. In this context, electro-fluid dynamic techniques (EFDTs), i.e., electrospinning, electrospraying and related techniques, offer the opportunity to engineer a wide variety of composite substrates by integrating fibers, particles, and hydrogels at different scales-from several hundred microns down to tens of nanometers-for the generation of countless patterns of physical and biochemical cues suitable for influencing the in vitro response of coexistent brain cell populations mediated by the surrounding microenvironment. In this review, an overview of the different technological approaches-based on EFDTs-for engineering fibrous and/or particle-loaded composite substrates will be proposed. The second section of this review will primarily focus on describing current and future approaches to the use of composites for brain applications, ranging from therapeutic to diagnostic/theranostic use and from repair to regeneration, with the ultimate goal of providing insightful information to guide future research efforts toward the development of more efficient and reliable solutions.