David D. Allen

Nanoparticle Surface Charges Alter Blood–Brain Barrier Integrity and Permeability

Purpose: The blood–brain barrier (BBB) presents both a physical and electrostatic barrier to limit brain permeation of therapeutics. Previous work has demonstrated that nanoparticles (NPs) overcome the physical barrier, but there is little known regarding the effect of NP surface charge on BBB function. Therefore, this work evaluated: (1) effect of neutral, anionic and cationic charged NPs on BBB integrity and (2) NP brain permeability. Methods: Emulsifying wax NPs were prepared from warm oil-in-water microemulsion precursors using neutral, anionic or cationic surfactants to provide the corresponding NP surface charge. NPs were characterized by particle size and zeta potential. BBB integrity and NP brain permeability were evaluated by in situ rat brain perfusion. Results: Neutral NPs and low concentrations of anionic NPs were found to have no effect on BBB integrity, whereas, high concentrations of anionic NPs and cationic NPs disrupted the BBB. The brain uptake rates of anionic NPs at lower concentrations were superior to neutral or cationic formulations at the same concentrations. Conclusions: (1) Neutral NPs and low concentration anionic NPs can be utilized as colloidal drug carriers to brain, (2) cationic NPs have an immediate toxic effect at the BBB and (3) NP surface charges must be considered for toxicity and brain distribution profiles.

Nanoparticle Technology for Drug Delivery Across the Blood-Brain Barrier

ABSTRACT Nanoparticles (NP) are solid colloidal particles ranging in size from 1 to 1000 nm that are utilized as drug delivery agents. The use of NPs to deliver drugs to the brain across the blood-brain barrier (BBB) may provide a significant advantage to current strategies. The primary advantage of NP carrier technology is that NPs mask the blood-brain barrier limiting characteristics of the therapeutic drug molecule. Furthermore, this system may slow drug release in the brain, decreasing peripheral toxicity. This review evaluates previous strategies of brain drug delivery, discusses NP transport across the BBB, and describes primary methods of NP preparation and characterization. Further, influencing manufacturing factors (type of polymers and surfactants, NP size, and the drug molecule) are detailed in relation to movement of the drug delivery agent across the BBB. Currently, reports evaluating NPs for brain delivery have studied anesthetic and chemotherapeutic agents. These studies are reviewed for efficacy and mechanisms of transport. Physiological factors such as phagocytic activity of the reticuloendothelial system and protein opsonization may limit the amount of brain delivered drug and methods to avoid these issues are also discussed. NP technology appears to have significant promise in delivering therapeutic molecules across the BBB.

Manganese distribution across the blood-brain barrier. I. Evidence for carrier-mediated influx of manganese citrate as well as manganese and manganese transferrin

Manganese (Mn) is an essential element and a neurotoxicant. Regulation of Mn movement across the blood-brain barrier (BBB) contributes to whether the brain Mn concentration is functional or toxic. In plasma, Mn associates with water, small molecular weight ligands and proteins. Mn speciation may influence the kinetics of its movement through the BBB. In the present work, the brain influx rates of 54Mn2+, 54Mn citrate and 54Mn transferrin (54Mn Tf) were determined using the in situ brain perfusion technique. The influx rates were compared to their predicted diffusion rates, which were determined from their octanol/aqueous partitioning coefficients and molecular weights. The in situ brain perfusion fluid contained 54Mn2+, 54Mn citrate or 54Mn Tf and a vascular volume/extracellular space marker, 14C-sucrose, which did not appreciably cross the BBB during these short experiments (15-180 s). The influx transfer coefficient (Kin) was determined from four perfusion durations for each Mn species in nine brain regions and the lateral ventricular choroid plexus. The brain Kin was (5-13) x 10(-5), (3-51) x 10(-5), and (2-13) x 10(-5) ml/s/g for 54Mn2+, 54Mn citrate, and 54Mn Tf, respectively. Brain Kin values for any one of the three Mn species generally did not significantly differ among the nine brain regions and the choroid plexus. However, the brain Kin for Mn citrate was greater than Mn2+ and Mn Tf Kin values in a number of brain regions. When compared to calculated diffusion rates, brain Kin values suggest carrier-mediated brain influx of 54Mn2+, 54Mn citrate and 54Mn Tf. 55Mn citrate inhibited 54Mn citrate uptake, and 55Mn2+ inhibited 54Mn2+ uptake, supporting the conclusion of carrier-mediated brain Mn influx. The greater Kin values for Mn citrate than Mn2+ and its presence as a major non-protein-bound Mn species in blood plasma suggest Mn citrate may be a major Mn species entering the brain.

In Situ Blood–Brain Barrier Transport of Nanoparticles

AbstractPurpose. Two novel types of nanoparticles were evaluated as potential carriers for drugs across the blood–brain barrier (BBB). Methods. Nanoparticles were composed of biocompatible materials including emulsifying wax (E. Wax) or Brij 72. Brij 78 and Tween 80 were used as surfactants for E.Wax nanoparticles (E78 NPs) and Brij 72 nanoparticles (E72 NPs), respectively. Both nanoparticle formulations were prepared from warm microemulsion precursors using melted E. Wax or Brij 72 as the oil phase. Nanoparticles were radiolabeled by entrapment of [3H]cetyl alcohol, and entrapment efficiency and release of radiolabel were evaluated. The transport of E78 and E72 NPs across the BBB was measured by an in situ rat brain perfusion method. Results. Both formulations were successfully radiolabeled by entrapment of [3H]cetyl alcohol; ∼98% of radiolabel remained associated with nanoparticles at experimental conditions. The transfer rate (Kin) of E78 NPs from perfusion fluid into the brain was 4.1 ± 0.5 × 10-3 ml/s/g, and the permeability-surface area product (PA) was 4.3 ± 0.7 × 10-3 ml/s/g. The values for Kin and PA for E72 NPs were 5.7 ± 1.1 × 10-3 ml/s/g and 6.1 ± 1.4 × 10-3 ml/s/g, respectively. Conclusions. For both nanoparticle types, statistically significant uptake was observed compared to [14C]sucrose, suggesting central nervous system uptake of nanoparticles. The mechanism underlying the nanoparticle brain uptake has yet to be fully understood.

The transport of choline.

ABSTRACT Choline has many physiological functions throughout the body that are dependent on its available local supply. However, since choline is a charged hydrophilic cation, transport mechanisms are required for it to cross biological membranes. Choline transport is required for cellular membrane construction and is the rate-limiting step for acetylcholine production. Transport mechanisms include: (1) sodium-dependent high-affinity uptake mechanism in synaptosomes, (2) sodium-independent low-affinity mechanism on cellular membranes, and (3) unique choline uptake mechanisms (e.g., blood–brain barrier choline transport). A comprehensive overview of choline transport studies is provided. This review article examines landmark and current choline transport studies, molecular mapping, and molecular identification of these carriers. Information regarding the choline-binding site is presented by reviewing choline structural analog (hemicholinium-3 and 15, and other nitrogen/methyl-hydroxyl compounds) inhibition studies. Choline transport in Alzheimers disease, brain ischemic events, and aging is also discussed. Emphasis throughout the article is placed on targeting the choline transporter in disease and use of this carrier as a drug delivery vector.

Brain Iron Toxicity: Differential Responses of Astrocytes, Neurons, and Endothelial Cells

Iron accumulation or iron overload in brain is commonly associated with neurodegenerative disorders such as Parkinson’s and Alzheimer’s diseases, and also plays a role in cellular damage following hemorrhagic stroke and traumatic brain injury. Despite the brain’s highly regulated system for iron utilization and metabolism, these disorders often present following disruptions within iron metabolic pathways. Such dysregulation allows saturation of proteins involved in iron transport and storage, and may cause an increase in free ferrous iron within brain leading to oxidative damage. Not only do astrocytes, neurons, and brain endothelial cells serve unique purposes within the brain, but their individual cell types are equipped with distinct protective mechanisms against iron-induced injury. This review evaluates iron metabolism within the brain under homeostatic and pathological conditions and focuses on the mechanism(s) of brain cellular iron toxicity and differential responses of astrocytes, neurons, and brain vascular endothelial cells to excessive free iron.

In vivo and in vitro assessment of baseline blood-brain barrier parameters in the presence of novel nanoparticles.

AbstractPurpose. Nanoparticles have advantage as CNS drug delivery vehicles given they disguise drug permeation limiting characteristics. Conflicting toxicological data, however, is published with regard to blood-brain barrier integrity and gross mortality. Methods. To address this issue two novel nanoparticle types: “emulsifying wax/Brij 78”and Brij 72/Tween 80 nanoparticles were evaluated in vivo for effect on cerebral perfusion flow, barrier integrity, and permeability using the in situ brain perfusion technique. Additional evaluation was completed in vitro using bovine brain microvessel endothelial cells for effect on integrity, permeability, cationic transport interactions, and tight junction protein expression. Results. In the presence of either nanoparticle formulation, no overall significant differences were observed for cerebral perfusion flow in vivo. Furthermore, observed in vitro and in vivo data showed no statistical changes in barrier integrity, membrane permeability, or facilitated choline transport. Western blot analyses of occludin and claudin-1 confirmed no protein expression changes with incubation of either nanoparticle. Conclusions. The nanoparticle formulations appear to have no effect on primary BBB parameters in established in vitro and in vivo blood-brain barrier models.

Prepharmacy predictors of success in pharmacy school: grade point averages, pharmacy college admissions test, communication abilities, and critical thinking skills.

Good admissions decisions are essential for identifying successful students and good practitioners. Various parameters have been shown to have predictive power for academic success. Previous academic performance, the Pharmacy College Admissions Test (PCAT), and specific prepharmacy courses have been suggested as academic performance indicators. However, critical thinking abilities have not been evaluated. We evaluated the connection between academic success and each of the following predictive parameters: the California Critical Thinking Skills Test (CCTST) score, PCAT score, interview score, overall academic performance prior to admission at a pharmacy school, and performance in specific prepharmacy courses. We confirmed previous reports but demonstrated intriguing results in predicting practice‐based skills. Critical thinking skills predict practice‐based course success. Also, the CCTST and PCAT scores (Pearson correlation [pc]=0.448, p<0.001) were closely related in our students. The strongest predictors of practice‐related courses and clerkship success were PCAT (pc=0.237, p<0.001) and CCTST (pc=0.201, p<0.001). These findings and other analyses suggest that PCAT may predict critical thinking skills in pharmacy practice courses and clerkships. Further study is needed to confirm this finding and determine which PCAT components predict critical thinking abilities.

Characterization of the blood-brain barrier choline transporter using the in situ rat brain perfusion technique: Blood-brain barrier choline transport

Choline enters brain by saturable transport at the blood–brain barrier (BBB). In separate studies, both sodium‐dependent and passive choline transport systems of differing affinity have been reported at brain capillary endothelial cells. In the present study, we re‐examined brain choline uptake using the in situ rat brain perfusion technique. Saturable brain choline uptake from perfusion fluid was best described by a model with a single transporter (Vmax= 2.4–3.1 nmol/min/g; Km = 39–42 µm) with an apparent affinity (1/Km) for choline five to ten‐fold greater than previously reported in vivo, but less than neuronal ‘high‐affinity’ brain choline transport (Km = 1–5 µm). BBB choline uptake from a sodium‐free perfusion fluid using sucrose for osmotic balance was 50% greater than in the presence of sodium suggesting that sodium is not required for transport. Hemicholinium‐3 inhibited brain choline uptake with a Ki (57 ± 11 µm) greater than that at the neuronal choline system. In summary, BBB choline transport occurs with greater affinity than previously reported, but does not match the properties of the neuronal choline transporter. The Vmax of this system is appreciable and may provide a mechanism for delivering cationic drugs to brain.

Cell Lines as In Vitro Models for Drug Screening and Toxicity Studies

ABSTRACT Cell culture is highly desirable, as it provides systems for ready, direct access and evaluation of tissues. The use of tissue culture is a valuable tool to study problems of clinical relevance, especially those related to diseases, screening, and studies of cell toxicity mechanisms. Ready access to the cells provides the possibility for easy studies of cellular mechanisms that may suggest new potential drug targets and, in the case of pathological-derived tissue, it has an interesting application in the evaluation of therapeutic agents that potentially may treat the dysfunction. However, special considerations must be addressed to establish stable in vitro function. In primary culture, these factors are primarily linked to greater demands of tissue to adequately survive and develop differentiated conditions in vitro. Additional requirements include the use of special substrates (collagen, laminin, extracellular matrix preparations, etc.), growth factors and soluble media supplements, some of which can be quite complex in their composition. These demands, along with difficulties in obtaining adequate tissue amounts, have prompted interest in developing immortalized cell lines which can provide unlimited tissue amounts. However, cell lines tend to exhibit problems in stability and/or viability, though they serve as a feasible alternative, especially regarding new potential applications in cell transplant therapy. In this regard, stem cells may also be a source for the generation of various cell types in vitro. This review will address aspects of cell culture system application, with focus on immortalized cell lines, in studying cell function and dysfunction with the primary aim being to identify cell targets for drug screening.