The role of membrane transporters in the absorption of atrazine following nasal exposure.

OBJECTIVE: The purpose of these studies was to investigate the uptake of atrazine across the nasal mucosa to determine whether direct transport to the brain through the olfactory epithelium is likely to occur. These studies were undertaken to provide important new information about the potential for the enhanced neurotoxicity of herbicides following nasal inhalation. MATERIALS AND METHODS: Transport of atrazine from aqueous solution and from commercial atrazine-containing herbicide products was assessed using excised nasal mucosal tissues. The permeation rate and the role of membrane transporters in the uptake of atrazine across the nasal mucosa were also investigated. Histological examination of the nasal tissues was conducted to assess the effects of commercial atrazine-containing products on nasal tissue morphology. RESULTS: Atrazine showed high flux across both nasal respiratory and olfactory tissues, and efflux transporters were found to play an essential role in limiting its uptake at low exposure concentrations. Commercial atrazine-containing herbicide products showed remarkably high transfer across the nasal tissues, and histological evaluation showed significant changes in the morphology of the nasal epithelium following exposure to the herbicide products. DISCUSSION: Lipophilic herbicides such as atrazine can freely permeate across the nasal mucosa despite the activity of efflux transporters. The adjuvant compounds in commercial herbicide products disrupt the nasal mucosa's epithelial barrier, resulting in even greater atrazine permeation across the tissues. The properties of the herbicide itself and those of the formulated products play crucial roles in the potential for the enhanced neurotoxicity of herbicides following nasal inhalation.

Evaluation of bioadhesive gels for local action in the esophagus.

Direct drug administration to the esophagus faces several obstacles, including continuous salivary dilution and removal of the dosage form from the tissue surface due to esophageal peristalsis. These actions often result in short exposure times and reduced concentrations of drug at the esophageal surface, providing limited opportunities for drug absorption into or across the esophageal mucosa. A variety of bioadhesive polymers were investigated for their ability to resist removal by salivary washings using an ex vivo porcine esophageal tissue model. Hydroxypropylmethylcellulose and carboxymethylcellulose both have reported bioadhesive properties, but neither was able to withstand repeated exposure to saliva, and the gels formulated with these polymers were quickly removed from the esophageal surface. Two polyacrylic polymers, carbomer and polycarbophil, also showed limited esophageal surface retention when exposed to salivary washing, likely due to the ionic composition of saliva affecting the inter-polymer interactions necessary for these polymers to maintain their increased viscosities. In situ gel forming polysaccharide gels (ion-triggered), including xanthan gum, gellan gum, and sodium alginate, showed superior tissue surface retention, and formulations containing these bioadhesive polymers along with ciclesonide, an anti-inflammatory soft prodrug, were investigated as potential, locally-acting esophageal delivery systems. Exposure of a segment of esophagus to the ciclesonide-containing gels resulted in therapeutic concentrations of des-ciclesonide, the active drug metabolite, in the tissues within 30 min. Increasing des-CIC concentrations were also observed over a 3-hour exposure interval suggesting continued release and absorption of ciclesonide into the esophageal tissues. These results demonstrate the ability to achieve therapeutic drug concentrations in the esophageal tissues using in situ gel-forming bioadhesive polymer delivery systems, and these systems provide promising opportunities for the local treatment of esophageal disease.

Effect of Manufacturing Process on the Retention of Abuse-Deterrent Properties of PEO-Matrix Tablets.

Polyethylene oxide (PEO) is a widely used polymer in the development of abuse-deterrent oral formulations. Different manufacturing processes including direct compression (DC) followed by sintering, wet granulation (WG) followed by compression and sintering, and hot melt extrusion (HME) can be used to manufacture abuse-deterrent oral drug products. Three different manufacturing processes (DC, WG, HME) were evaluated to test the retention of their abuse-deterrent features following attempts to grind the tablets or extrudates. In vitro drug release studies were conducted on 10% and 32% drug-loaded tablets/extrudates prepared using these manufacturing methods, and the release profiles from all formulations showed good extended-release properties. Drug content analysis on the granules obtained from tablets prepared by direct compression showed non-uniform drug distribution where an unexpectedly high drug content was present in the smallest size (< 250 µm) granules, sizes which are likely to be inhaled by abusers. Granules from tablets prepared by wet granulation showed improved drug distribution across all granule sizes formed after grinding. Drug content testing on the granules obtained from extrudates prepared using hot melt extrusion showed excellent drug content uniformity along with sufficient strength to resist grinding into smaller particles. The retention of the abuse-deterrent properties of a dosage form following attempts to extract or abuse the drug is an important product characteristic, and the product design, formulation components, and manufacturing processes can all play critical roles in the retention of the desired abuse-deterrent properties.

Electron Spin Resonance Evaluation of Buccal Membrane Fluidity Alterations by Sodium Caprylate and L-Menthol.

The ability of sodium caprylate and l-menthol to fluidize phospholipid bilayers composed of lipids simulating the buccal epithelium was investigated using electron spin resonance (ESR) to evaluate the action of these agents as permeation enhancers. 5-Doxyl stearic acid (5-DSA) and 16-doxyl stearic acid (16-DSA) were used as spin labels to identify alterations in membrane fluidity near the polar head groups or inner acyl regions of the lipid bilayer, respectively. The molecular motion of both 5-DSA and 16-DSA showed increased disorder near the polar and inner hydrophobic regions of the bilayer in the presence of sodium caprylate suggesting fluidization in both the regions, which contributes to its permeation enhancing effects. L-menthol decreased the order parameter for 16-DSA, showing membrane fluidization only in the inner acyl regions of the bilayer, which also corresponded to its weaker permeation enhancing effects. The rapid evaluation of changes in fluidity of the bilayer in the presence of potential permeation enhancers using ESR enables improved selection of effective permeation enhancers and enhancer combinations based on their effect on membrane fluidization.

Evaluation of Ribavirin-Poloxamer Microparticles for Improved Intranasal Absorption.

Ribavirin is a water-soluble antiviral compound which, owing to its inability to cross the blood-brain barrier, has limited effectiveness in treating viruses affecting the central nervous system. Direct nose-to-brain delivery was investigated for ribavirin in combination with poloxamer 188, an excipient known to enhance the absorption of drug compounds administered intranasally. Composite solid microparticles suitable for intranasal insufflation were prepared by suspending fine crystals of ribavirin in a matrix of poloxamer 188, which were cryogenically milled and characterized to ensure that ribavirin remained stable throughout preparation. In vitro diffusion of ribavirin across a semi-permeable regenerated cellulose membrane showed comparable cumulative drug release after 180 min from both fine solid particles (<20 µm) and 1:1 ribavirin:poloxamer microparticles (d50 = 20 µm); however, the initial release from polymer microparticles was slower, owing to gel formation on the membrane surface. When solid ribavirin was directly deposited on excised olfactory mucosa, either as fine drug particles or 1:1 ribavirin:poloxamer microparticles, permeation was significantly increased from microparticles containing poloxamer 188, suggesting additional interactions between the polymer and olfactory mucosa. These data indicate that for highly water-soluble drugs such as ribavirin or drugs subject to efflux by the nasal mucosa, a formulation of poloxmer-containing microparticles can enhance permeability across the olfactory epithelium and may improve direct nose-to-brain transport.

Endocytic Uptake of Solid Lipid Nanoparticles by the Nasal Mucosa.

Nanoparticles may provide unique therapeutic opportunities when administered via the nasal cavity, yet the primary uptake and transfer pathways for these particles within the nasal mucosa are not well understood. The endocytic pathways involved in the uptake of fluorescently labeled, (Nile Red) solid lipid nanoparticles (SLNs) of different sizes (~30, 60, and 150 nm) were studied using excised bovine olfactory and nasal respiratory tissues. Endocytic activity contributing to nanoparticle uptake was investigated using a variety of pharmacological inhibitors, but none of the inhibitors were able to completely eliminate the uptake of the SLNs. The continued uptake of nanoparticles following exposure to individual inhibitors suggests that a number of endocytic pathways work in combination to transfer nanoparticles into the nasal mucosa. Following exposure to the general metabolic inhibitors, 2,4-DNP and sodium azide, additional, non-energy-dependent pathways for nanoparticle uptake were also observed. While the smallest nanoparticles (30 nm) were the most resistant to the effects of pharmacologic inhibitors, the largest (150 nm) were still able to transfer significant amounts of the particles into the tissues. The rapid nanoparticle uptake observed demonstrates that these lipid particles are promising vehicles to accomplish both local and systemic drug delivery following nasal administration.

Uptake and Transport of Ultrafine Nanoparticles (Quantum Dots) in the Nasal Mucosa.

A wide variety of colloidal delivery systems, including polymeric nanoparticles, metal colloids, liposomes, and microemulsions have been reported to enhance the delivery of therapeutic agents across the nasal mucosa. The mechanisms involved in the uptake of these nanomaterials, especially ultrafine nanomaterials (diameters < 20 nm) through the nasal mucosa are not well understood. Fluorescent quantum dots (QDs) were used to investigate the uptake of ultrafine nanoparticles by bovine respiratory and olfactory mucosal tissues following in vitro exposure, and an inductively coupled plasma optical emission spectroscopy method was developed to quantify the amount of QDs localized within the tissues. QDs do not biodegrade or release their core materials and, as a result, this method allowed for the direct quantification of the nanoparticles themselves, rather than the measurement of a potentially dissociated drug or label. The results demonstrated that carboxylate-modified QDs (COOH-QDs) showed ∼2.5-fold greater accumulation in the epithelial and submucosal regions of olfactory tissues compared to that in respiratory tissues. Endocytic inhibitory studies showed that clathrin-dependent endocytosis, macropinocytosis, and caveolae-dependent endocytic process are all involved in the uptake of COOH-QDs into the respiratory tissues. In olfactory tissues, clathrin-dependent endocytosis is the major endocytic pathway involved in the uptake of COOH-QDs. Additional energy-independent pathways also appeared to allow the transfer of COOH-QDs within the olfactory mucosa. When polyethylene glycol-modified QDs known as PEGylated QDs (PEG-QDs) of similar size, ∼15 nm, were investigated, no nanoparticles were detected in the tissues suggesting that the PEG corona limits the interactions with endocytic and other uptake processes in the nasal epithelium. The capacity for nanoparticle uptake observed in the nasal mucosa, along with the ability of significant numbers of nanoparticles to enter the olfactory tissues using nonenergy-dependent pathways show that the pathways for ultrafine nanoparticle uptake in the nasal tissues have both drug delivery and toxicologic consequences. This places an increased importance on the careful selection of nanoparticle components and drugs intended for intranasal administration.

Use of Drug Release Testing to Evaluate the Retention of Abuse-Deterrent Properties of Polyethylene Oxide Matrix Tablets.

Abuse-deterrent formulations (ADFs) using physical/chemical barrier approaches limit abuse by providing resistance to dosage form manipulation to limit drug extraction or altered release. Standardizing in vitro testing methods to assess the resistance to manipulation presents a number of challenges, including the variation in particle sizes resulting from the use of various tools to alter the tablet matrix (e.g., grinding, chipping, crushing). A prototype, direct-compression ADF using a sintered polyethylene oxide (PEO) matrix containing dextromethorphan, an enantiomeric form of the opioid, levorphanol, was developed to evaluate testing methodologies for retention of abuse-deterrent properties following dosage form tampering. Sintered PEO tablets were manipulated by grinding, and drug content and release were evaluated for the recovered granules. Drug content analysis revealed that higher amounts of drug were contained in the smaller size granules (< 250 µm, 190% of the theoretical amount) compared with the larger particles (> 250 µm, 55-75% of theoretical amount). Release testing was performed on various size granule fractions (> 850 µm, 500-850 µm, 250-500 µm, and < 250 µm) using USP type I (basket), type II (paddle), and type IV (flow-through) apparatus. The USP type I and type II apparatus gave highly variable release results with poor discrimination among the release rates from different size granules. The observed sticking of the hydrated granules to the baskets and paddles, agglomeration of hydrated granules within the baskets/vessels, and ongoing PEO hydration with subsequent gel formation further altered the particle size and impacted the rate of drug release. The use of a flow-through apparatus (USP type IV) resulted in improved discrimination of drug release from different size granules with less variability due to better dispersion of granules (minimal sticking and aggregation). Drug release profiles from the USP type IV apparatus showed that the larger size granules (> 500 µm) offered continued resistance to drug release following tablet manipulation, but the smaller size granules (< 500 µm) provided rapid drug release that was unhindered by the hydrated granule matrix. Since < 500-µm size particles are preferred for nasal abuse, improved direct-compression ADF formulations should minimize the formation of these smaller-sized particles following tampering to maintain the product's abuse-deterrent features.

Bigger or Smaller? Size and Loading Effects on Nanoparticle Uptake Efficiency in the Nasal Mucosa.

PLGA nanoparticles hold great promise for nasal administration, but only with careful design will efficient, effective, and safe delivery systems be developed. To better understand the size dependence of nasal epithelial uptake, PLGA nanoparticles (60 nm or 125 nm) loaded with Nile Red were prepared, and their uptake into excised sections of bovine nasal respiratory or olfactory mucosa was measured for 30 or 60 min. The epithelial layer and the submucosal tissues were separated, and the amount of Nile Red was used to calculate the number of nanoparticles in each tissue region. Both particle sizes were able to be internalized into the nasal tissues in as little as 30 min, but their total uptake represented less than 5% of the nanoparticles available. Nanoparticles were present both in the epithelial cells and in the submucosal tissues, and greater numbers of the 60-nm particles were present in the submucosa than the epithelium, while greater numbers of the 125-nm particles remained in the epithelial cell layer. The amount of Nile Red recovered from the mucosal tissues after exposure to 125-nm nanoparticles was at least 2-fold greater than from the 60-nm nanoparticles, however, due to the higher (~ 9-fold) loading capacity of the larger particles. The greater mass transfer of the Nile Red from the larger particles suggests that it may not be necessary to develop small nanoparticulate delivery systems for efficient drug delivery via the nasal mucosa. Well-designed nanoparticles with diameters > 100 nm show good uptake into the nasal epithelium and are capable of transfer to the submucosal tissues, near the location of significant populations of blood and lymphatic vessels. Graphical abstract.

Polyethylene Oxide (PEO) Molecular Weight Effects on Abuse-Deterrent Properties of Matrix Tablets.

While polyethylene oxide (PEO)-based matrix tablets are frequently used as abuse-deterrent dosage forms, there is limited information available regarding how the selection of formulation components and manufacturing processes affect the resulting abuse-deterrent properties. The objective of the current study was to evaluate the effects of formulation and process variables on the abuse-deterrent features of PEO-containing tablets. Directly compressed tablets were prepared using three different PEO molecular weights (100,000; 900,000; and 5,000,000). As anticipated, sintering/thermal treatment above the melting point of PEO was crucial to impart crush-resistant features (tablet hardness > 500 N). In addition to the sintering temperature, the weight fraction of PEO in the tablets affected their mechanical strength, and at least 50% w/w PEO was required to impart the desired crush-resistant features. In addition, the formulation and process variables also impacted syringeability and injectability of the PEO gels formed when the tablets were hydrated to simulate attempted drug extraction. High molecular weight PEO (900,000 and 5,000,000) produced gels more resistant to syringeability and injectability compared to low molecular weight PEO (100,000). Sintering above the polymer melting point decreased PEO crystallinity after cooling, and longer sintering times resulted in PEO degradation producing lower viscosity gels with reduced resistance to syringeability and injectability. Although sintering above the melting point of PEO imparts optimal mechanical strength to the tablets, prolonged sintering durations negatively impact polymer stability and alter the resulting abuse-deterrent features of the PEO-based tablet formulations.

Effects of Drug-Polymer Interactions on Tablet Properties During the Development of Abuse-Deterrent Dosage Forms.

The objective of the present study is to understand the effects of drug-PEO interactions during the thermal treatment of polyethylene oxide (PEO)-based, directly compressed, abuse-deterrent formulations (ADFs). The drugs studied were dextromethorphan HBr monohydrate, ketoprofen, promethazine HCl, and anhydrous theophylline. Thermal treatment above the melting point of PEO resulted in tablets with higher crushing strength (> 500 N). It was observed that drug-PEO interactions during thermal treatment (80°C) led to solubilization of the incorporated drug. Drugs with higher solubility in the molten PEO, when added at higher weight fractions, interfered with the process of tablet densification which led to an increase in tablet dimensions and created defects in the fused matrix. These changes resulted in the formation of a more porous matrix. Thermal treatment led to a decrease in PEO crystallinity. The decreased crystallinity led to differences in the hydration and dissolution properties of the PEO. The change in dissolution properties of PEO accompanied with the dimensional and microstructural changes resulted in a greater drug release for some of the studied drugs. In conclusion, although thermal treatment above the melting point of PEO is an efficient manufacturing process in imparting crush-resistant features, drug-PEO interactions during the thermal treatment and the impact of thermal treatment on the properties of formulation components may impact tablet properties and lead to potential performance differences.

Overview of intranasally delivered peptides: key considerations for pharmaceutical development.

INTRODUCTION: Intranasal (IN) delivery for peptides provides unique advantages compared to other invasive systemic delivery routes. However, there still lacks a clear understanding on how to evaluate the potential of the peptides for nasal delivery and key considerations for the nasal formulation development. AREAS COVERED: A retrospective analysis of intranasally delivered peptides was conducted. The goals of this undertaking were 1) to build a database of the key physicochemical and pharmacokinetic properties of peptides delivered by the nasal route, 2) to evaluate formulation attributes applied to IN peptide delivery systems, and 3) to provide key considerations for IN delivery of peptides. EXPERT OPINION/COMMENTARY: Extensive data mining showed that peptides with molecular weights up to 6000 Da have been delivered intranasally. The high solubility of some peptides highlighted the possibility of delivering sufficient amounts of peptide in the limited volume available for nasal sprays. Permeation enhancers and mucoadhesives have shown promise in improving the IN bioavailability of peptides. Other formulation considerations, such as the type of formulation, pH, osmolality, as well as drug deposition, are reviewed herein. Based on this retrospective analysis, key considerations for nasal peptides formulations were proposed to guide drug discovery and development for IN delivery of peptides.

A Simplified Geometric Model to Predict Nasal Spray Deposition in Children and Adults.

A mathematical approach was developed to estimate spray deposition patterns in the nasal cavity based on the geometric relationships between the emitted spray plume and the anatomical dimensions of the nasal valve region of the nasal cavity. Spray plumes were assumed to be spherical cones and the nasal valve region was approximated as an ellipse. The effect of spray plume angle (15-85°) on the fraction of the spray able to pass through the nasal valve (deposition fraction) was tested for a variety of nasal valve (ellipse) shapes and cross-sectional areas based on measured dimensions from pediatric and adult nasal cavities. The effect of the distances between the tip of the nasal spray device and the nasal valve (0.2-1.9 cm) on the deposition fraction was also tested. Simulation results show that (1) decreasing spray plume angles resulted in higher deposition fractions, (2) deposition fraction was inversely proportional to the spray distance and the nasal valve (ellipse) major/minor axis ratio, and (3) for fixed major/minor axis ratios, improved deposition occurred with larger nasal valve cross-sectional areas. For a typical adult nasal valve, plume angles of less than 40° emitted from a distance of 1 cm resulted depositions greater than 90% within the main nasal cavity, whereas for a 12-year-old child, only the most narrow plume angles (< 20°) administered resulted in significant deposition beyond the nasal valve.

In Vitro Assessment of Spray Deposition Patterns in a Pediatric (12 Year-Old) Nasal Cavity Model.

PURPOSE: Nasal sprays available for the treatment of cold and allergy symptoms currently use identical formulations and devices for adults as well as for children. Due to the obvious differences between the nasal airway dimensions of a child and those of an adult, the performance of nasal sprays in children was evaluated. METHODS: Deposition patterns of nasal sprays administered to children were tested using a nasal cast based on MRI images obtained from a 12 year old child's nasal cavity. Test formulations emitting a range of spray patterns were investigated by actuating the device into the pediatric nasal cast under controlled conditions. RESULTS: The results showed that the nasal sprays impacted in the anterior region of the 12 year old child's nasal cavity, and only limited spray entered the turbinate region - the effect site for most topical drugs and the primary absorptive region for systemically absorbed drugs. CONCLUSION: Differences in deposition patterns following the administration of nasal sprays to adults and children may lead to differences in efficacy between these populations. Greater anterior deposition in children may result in decreased effectiveness, greater anterior dosage form loss, and the increased potential for patient non-compliance.

Mandatory Change From Surgical Skull Caps to Bouffant Caps Among Operating Room Personnel Does Not Reduce Surgical Site Infections in Class I Surgical Cases: A Single-Center Experience With More Than 15 000 Patients.

BACKGROUND: Surgical site infections (SSIs) are noteworthy and costly complications. New recommendations from a national organization have urged the elimination of traditional surgeon's caps (surgical skull caps) and mandated the use of bouffant caps to prevent SSIs. OBJECTIVE: To report SSI rates for >15 000 class I (clean) surgical procedures 13 mo before and 13 mo after surgical skull caps were banned at a single site with 25 operating rooms. METHODS: SSI data were acquired from hospital infection control monthly summary reports from January 2014 to March 2016. Based on a change in hospital policy mandating obligatory use of bouffant caps since February 2015, data were categorized into nonbouffant and bouffant groups. Monthly and cumulative infection rates for 13 mo before (7513 patients) and 13 mo after (8446 patients) the policy implementation were collected and analyzed for the groups, respectively. RESULTS: An overall increase of 0.07% (0.77%-0.84%) in the cumulative rate of SSI in all class I operating room cases and of 0.03% (0.79%-0.82%) in the cumulative rate of SSI in all spinal procedures was noted. However, neither increase reached statistical significance (P > .05). The cumulative rate of SSI in neurosurgery craniotomy/craniectomy cases decreased from 0.95% to 0.75%; this was also not statistically significant (P = 1.00). CONCLUSION: National efforts at improving healthcare performance are laudable but need to be evidence based. Guidelines, especially when applied in a mandatory fashion, should be assessed for effectiveness. In this large, single-center series of patients undergoing class I surgical procedures, elimination of the traditional surgeon's cap did not reduce infection rates.

Relating Observed Psychoactive Effects to the Plasma Concentrations of Delta-9-Tetrahydrocannabinol and Its Active Metabolite: An Effect-Compartment Modeling Approach.

The medical use of marijuana is increasing, yet little is known about the exposure-response relationship for its psychoactive effects. It is well known that the plasma concentrations of the principal psychoactive component of marijuana, Δ9-tetrahydrocannabinol (THC), do not directly correlate to the observed psychoactive effects. The purpose of this research was to use an effect-compartment modeling approach to predict and relate the concentrations of the psychoactive components (THC and its active metabolite) in the "hypothetical" effect-site compartment to the observed psychoactive effects. A "hypothetical" effect-compartment model was developed using literature data to characterize the observed delay in peak "highness" ratings compared with plasma concentrations of the psychoactive agents following intravenous administration of THC. A direct relationship was established between the reported psychoactive effects ("highness" or intoxication) and the predicted effect-site concentrations of THC. The differences between estimated equilibration half-lives for THC and THC-OH in the effect-compartment model indicated the differential equilibration of parent drug and the active metabolite between plasma and the effect-site. These models contribute to the understanding of the pharmacokinetic-pharmacodynamic relationships associated with marijuana use and are important steps in the prediction of pharmacodynamic effects related to the psychoactive components in marijuana.

Pharmacoimaging of Blood-Brain Barrier Permeable (FDG) and Impermeable (FLT) Substrates After Intranasal (IN) Administration.

To illustrate the use of imaging to quantify the transfer of materials from the nasal cavity to other anatomical compartments, specifically, transfer to the brain using the thymidine analogue, [18F]fluorothymidine (FLT), and the glucose analogue, [18F]fluorodeoxyglucose (FDG). Anesthetized rats were administered FLT or FDG by intranasal instillation (IN) or tail-vein injection (IV). PET/CT imaging was performed for up to 60 min. Volumes-of-interest (VOIs) for the olfactory bulb (OB) and the remaining brain were created on the CT and transferred to the co-registered dynamic PET. Time-activity curves (TACs) were generated and compared. The disposition patterns were successfully visualized and quantified and differences in brain distribution patterns were observed. For FDG, the concentration was substantially higher in the OB than the brain only after IN administration. For FLT, the concentration was higher in the OB than the brain after both IN and IV and higher after IN than after IV administration at all times, whereas the concentration in the brain was higher after IN than after IV administration at early times only. Approximately 50 and 9% of the IN FDG and FLT doses, respectively, remained in the nasal cavity at 20 min post-administration. The initial phase of clearance was similar for both agents (t1/2 = 2.53 and 3.36 min) but the slow clearance phase was more rapid for FLT than FDG (t1/2 = 32.1 and 85.2 min, respectively). Pharmacoimaging techniques employing PET/CT can be successfully implemented to quantitatively investigate and compare the disposition of radiolabeled agents administered by a variety of routes.

Demonstration of Nucleoside Transporter Activity in the Nose-to-Brain Distribution of [18F]Fluorothymidine Using PET Imaging.

To evaluate the role of nucleoside transporters in the nose-to-brain uptake of [18F]fluorothymidine (FLT), an equilibrative nucleoside transporter (ENT1,2) and concentrative nucleoside transporter (CNT1-3) substrate, using PET to measure local tissue concentrations. Anesthetized Sprague-Dawley rats were administered FLT by intranasal (IN) instillation or tail-vein injection (IV). NBMPR (nitrobenzylmercaptopurine riboside), an ENT1 inhibitor, was administered either IN or intraperitoneally (IP). Dynamic PET imaging was performed for up to 40 min. A CT was obtained for anatomical co-registration and attenuation correction. Time-activity curves (TACs) were generated for the olfactory bulb (OB) and remaining brain, and the area-under-the-curve (AUC) for each TAC was calculated to determine the total tissue exposure of FLT. FLT concentrations were higher in the OB than in the rest of the brain following IN administration. IP administration of NBMPR resulted in increased OB and brain FLT exposure following both IN and IV administration, suggesting that NBMPR decreases the clearance rate of FLT from the brain. When FLT and NBMPR were co-administered IN, there was a decrease in the OB AUC while an increase in the brain AUC was observed. The decrease in OB exposure was likely the result of inhibition of ENT1 uptake activity in the nose-to-brain transport pathway. FLT distribution patterns show that nucleoside transporters, including ENT1, play a key role in the distribution of transporter substrates between the nasal cavity and the brain via the OB.

Modulating nasal mucosal permeation using metabolic saturation and enzyme inhibition techniques.

OBJECTIVE: Presystemic elimination resulting from local enzymatic degradation can play a key role in limiting the bioavailability of intranasally administered drugs. The aim of this study was to evaluate the transfer of a metabolically susceptible drug across the nasal mucosa to illustrate the relative contributions of drug diffusivity and metabolic susceptibility on overall nasal mucosal permeation and to understand the effects of changes in enzymatic activity on the transfer across nasal epithelial and submucosal tissues. METHODS: The concentration-dependent permeation of melatonin, a CYP450 substrate, across excised bovine nasal olfactory and respiratory explants was studied along with quantifying the extent of melatonin 6-hydroxylation. Microsomal preparations were also used to determine the kinetic parameters for melatonin to 6-hydroxymelatonin biotransformation. KEY FINDINGS: Enzyme saturation at higher melatonin concentrations and inclusion of a CYP450 inhibitor both resulted in the significant increase in melatonin permeation across the nasal mucosa. CONCLUSIONS: Metabolic loss of melatonin during nasal permeation demonstrates CYP450 activity in the nasal epithelium and submucosal tissues. The extent of biotransformation of melatonin during its transport across the nasal mucosal explants suggests that, although the nasal route bypasses hepatic first-pass metabolism, nasal bioavailability can be significantly influenced by mucosal enzymatic activity.

The role of L-type amino acid transporters in the uptake of glyphosate across mammalian epithelial tissues.

Glyphosate is one of the most commonly used herbicides worldwide due to its broad spectrum of activity and reported low toxicity to humans. Glyphosate has an amino acid-like structure that is highly polar and shows low bioavailability following oral ingestion and low systemic toxicity following intravenous exposures. Spray applications of glyphosate in agricultural or residential settings can result in topical or inhalation exposures to the herbicide. Limited systemic exposure to glyphosate occurs following skin contact, and pulmonary exposure has also been reported to be low. The results of nasal inhalation exposures, however, have not been evaluated. To investigate the mechanisms of glyphosate absorption across epithelial tissues, the permeation of glyphosate across Caco-2 cells, a gastrointestinal epithelium model, was compared with permeation across nasal respiratory and olfactory tissues excised from cows. Saturable glyphosate uptake was seen in all three tissues, indicating the activity of epithelial transporters. The uptake was shown to be ATP and Na(+) independent, and glyphosate permeability could be significantly reduced by the inclusion of competitive amino acids or specific LAT1/LAT2 transporter inhibitors. The pattern of inhibition of glyphosate permeability across Caco-2 and nasal mucosal tissues suggests that LAT1/2 play major roles in the transport of this amino-acid-like herbicide. Enhanced uptake into the epithelial cells at barrier mucosae, including the respiratory and gastrointestinal tracts, may result in more significant local and systemic effects than predicted from glyphosate's passive permeability, and enhanced uptake by the olfactory mucosa may result in further CNS disposition, potentially increasing the risk for brain-related toxicities.