Re-Use of Caco-2 Monolayers in Permeability Assays-Validation Regarding Cell Monolayer Integrity.

Caco-2 monolayers are a common in vitro model used to evaluate human intestinal absorption. The reference protocol requires 21 days post-seeding to establish a stable and confluent cell monolayer, which is used in a single permeability assay during the period of monolayer stability (up to day 30). In this work, we characterize variations in the tightness of the cell monolayer over the stable time interval and evaluate the conditions required for their re-use in permeability assays. The monolayer integrity was assessed through TEER measurements and permeability of the paracellular marker Lucifer Yellow (LY), complemented with nuclei and ZO-1 staining for morphological studies and the presence of tight junctions. Over 150 permeability assays were performed, which showed that manipulation of the cell monolayer in the permeability assay may contribute significantly to the flux of LY, leading to Papp values that are dependent on the sampling duration. The assay also leads to a small decrease in the cell monolayer TEER, which is fully recovered when cell monolayers are incubated with culture media for two full days. When this procedure is followed, the cell monolayers may be used for permeability assays on days 22, 25, and 28, triplicating the throughput of this important assay.

Derivation of Brain Capillary-like Endothelial Cells from Human Pluripotent Stem Cell-Derived Endothelial Progenitor Cells.

The derivation of human brain capillary endothelial cells is of utmost importance for drug discovery programs focusing on diseases of the central nervous system. Here, we describe a two-step differentiation protocol to derive brain capillary-like endothelial cells from human pluripotent stem cells. The cells were initially differentiated into endothelial progenitor cells followed by specification into a brain capillary-like endothelial cell phenotype using a protocol that combined the induction, in a time-dependent manner, of VEGF, Wnt3a, and retinoic acid signaling pathways and the use of fibronectin as the extracellular matrix. The brain capillary-like endothelial cells displayed a permeability to lucifer yellow of 1 × 10-3 cm/min, a transendothelial electrical resistance value of 60 Ω cm2 and were able to generate a continuous monolayer of cells expressing ZO-1 and CLAUDIN-5 but moderate expression of P-glycoprotein. Further maturation of these cells required coculture with pericytes. The study presented here opens a new approach for the study of soluble and non-soluble factors in the specification of endothelial progenitor cells into brain capillary-like endothelial cells.

A nanoformulation for the preferential accumulation in adult neurogenic niches.

Stimulation of adult neurogenesis by targeting the endogenous neural stem cells (NSCs), located in hippocampus and subventricular zone (SVZ), with nanoformulations has been proposed for brain repair in cases of neurodegenerative diseases. Unfortunately, it is relatively unknown the nanoformulation properties to facilitate their accumulation in the neurogenic niches after intravenous injection. Here, we have screened different gold-based formulations having variable morphology, surface chemistry and responsiveness to light for their capacity to cross the blood brain barrier (BBB) and accumulate preferentially in the neurogenic niches. Results obtained in a human in vitro BBB model showed that gold nanoparticles (Au NPs) and gold nanorods (Au NRs) conjugated with medium density of transferrin (Tf) peptides (i.e. between 169 and 230 peptides per NP) crossed more efficiently the BBB than the remaining formulations. This is due to a relatively lower avidity of these formulations to Tf receptor (TfR) and lower accumulation in the lysosomes, as compared to the other formulations. We further show that the near infrared light (NIR) irradiation of Au NRs, under a certain concentration and at specific cell culture time, lead to the opening of the BBB. Finally, we demonstrate that Au NRs conjugated with Tf administered intravenously in mice and activated by NIR had the highest accumulation in the neurogenic niches. Our results open the possibility of targeting more effectively the neurogenic niches by controlling the properties of the nanoformulations.

Nanoparticle-mediated brain drug delivery: Overcoming blood-brain barrier to treat neurodegenerative diseases.

The blood-brain barrier (BBB) is a vital boundary between neural tissue and circulating blood. The BBB's unique and protective features control brain homeostasis as well as ion and molecule movement. Failure in maintaining any of these components results in the breakdown of this specialized multicellular structure and consequently promotes neuroinflammation and neurodegeneration. In several high incidence pathologies such as stroke, Alzheimer's (AD) and Parkinson's disease (PD) the BBB is impaired. However, even a damaged and more permeable BBB can pose serious challenges to drug delivery into the brain. The use of nanoparticle (NP) formulations able to encapsulate molecules with therapeutic value, while targeting specific transport processes in the brain vasculature, may enhance drug transport through the BBB in neurodegenerative/ischemic disorders and target relevant regions in the brain for regenerative processes. In this review, we will discuss BBB composition and characteristics and how these features are altered in pathology, namely in stroke, AD and PD. Additionally, factors influencing an efficient intravenous delivery of polymeric and inorganic NPs into the brain as well as NP-related delivery systems with the most promising functional outcomes will also be discussed.