Localization and Differential Activity of P-glycoprotein in the Bovine Olfactory and Nasal Respiratory Mucosae

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.

Pharmacokinetics of intravenous, oral transmucosal, and intranasal buprenorphine in healthy male dogs

Effective management of pain in animals is of critical importance but options are limited for treating acute pain in dogs on an outpatient basis. The objective of this study was to compare the plasma concentrations and pharmacokinetics of a concentrated solution of buprenorphine, 1.8 mg/ml (Simbadol™) administered intravenously, intranasally, and via the oral transmucosal (OTM) route in healthy male dogs. Five healthy castrated adult male Beagle‐cross dogs were included in this randomized blocked crossover study. The dogs received 0.03 mg/kg body weight buprenorphine intravenously, intranasally, or via the OTM route, with a minimum 72‐h washout period between treatments. Blood samples were collected at multiple intervals up to 24 h post administration and buprenorphine plasma concentrations were determined by liquid chromatography tandem mass spectrometry. Non‐compartmental pharmacokinetic analysis revealed that the area under the curve of intravenous, intranasal, and OTM routes were 28.0 (15.1–41.3) h × ng/ml, 16.1 (3.4–28.7) h × ng/ml and 10.8 (8.8–11.8) h × ng/ml, respectively. The bioavailability of intranasal and OTM routes were 57.5 (22.7–93.7)% and 41.1 (25.5–69.4)%, respectively. Intranasal and OTM routes of administration of concentrated buprenorphine in dogs may allow for the provision of analgesic care at home.

Nanoparticles Based Intranasal Delivery of Drug to Treat Alzheimer's Disease: A Recent Update

Alzheimer Association Report (2019) stated that the 6th primary cause of death in the USA is Alzheimer's Disease (AD), which leads to behaviour and cognitive impairment. Nearly 5.8 million peoples of all ages in the USA have suffered from this disease, including 5.6 million elderly populations. The statistics of the progression of this disease is similar to the global scenario. Still, the treatment of AD is limited to a few conventional oral drugs, which often fail to deliver an adequate amount of the drug in the brain. The reduction in the therapeutic efficacy of an anti-AD drug is due to poor solubility, existence to the blood-brain barrier and low permeability. In this context, nasal drug delivery emerges as a promising route for the delivery of large and small molecular drugs for the treatment of AD. This promising pathway delivers the drug directly into the brain via an olfactory route, which leads to the low systemic side effect, enhanced bioavailability, and higher therapeutic efficacy. However, few setbacks, such as mucociliary clearance and poor drug mucosal permeation, limit its translation from the laboratory to the clinic. The above stated limitation could be overcome by the adaption of nanoparticle as a drug delivery carrier, which may lead to prolong delivery of drugs with better permeability and high efficacy. This review highlights the latest work on the development of promising Nanoparticles (NPs) via the intranasal route for the treatment of AD. Additionally, the current update in this article will draw the attention of the researcher working on these fields and facing challenges in practical applicability.

Different Culture Conditions Affect Drug Transporter Gene Expression, Ultrastructure, and Permeability of Primary Human Nasal Epithelial Cells

PURPOSE

This study aimed to characterize a commercially available primary human nasal epithelial cell culture and its gene expression of a wide range of drug transporters under different culture conditions.

METHODS

Human nasal cells were cultured in three different types of culture media at the air-liquid (A-L) or liquid-liquid (L-L) interfaces for 1 or 3 wks. The effects of the different cell culture conditions were evaluated using light and electron microscopy, transepithelial electrical resistance (TEER) measurements, permeation studies with dextran, and gene expression profiling of 84 drug transporters.

RESULTS

The type of culture medium affected cell ultrastructure, TEER, and dextran permeation across epithelia. The expression of 20 drug transporter genes depended on the culture interface and/or time in culture; the A-L interface and longer time in culture favored higher expression levels of five ABC and seven SLC transporters.

CONCLUSIONS

Culture conditions influence the morphology, barrier formation, permeation properties, and drug transporter expression of human nasal epithelial cells, and this must be taken into consideration during the establishment and validation of in vitro models. A thorough characterization of a nasal epithelial model and its permeability properties is necessary to obtain an appropriate standardized model for the design of aerosol therapeutics and drug transport studies.

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.

Intact soluble P-glycoprotein is secreted by sinonasal epithelial cells

BACKGROUND

P-glycoprotein (P-gp) is a 170 kDa transmembrane efflux pump, which is upregulated in chronic rhinosinusitis. Studies of leukemia demonstrated that P-gp may also be secreted in an intact soluble form. The purpose of this study was to explore whether sinonasal epithelial cells were capable of secreting soluble P-gp and whether P-gp has any functional role.

METHODS

Soluble and cytoplasmic P-gp were quantified in vehicle and lipopolysaccharide exposed cultures by enzyme-linked immunosorbent assay. The molecular weight of the soluble P-gp was determined by Western blot. Naive cultures were exposed to recombinant human P-gp at 0-2000 ng/mL. The degree of membranous interpolation was determined by quantitative fluorescent immunocytochemistry and function was determined by a calcein acetoxymethyl ester assay.

RESULTS

Soluble P-gp was secreted intact at 170 kDa. Mean (standard deviation) secretion was detected within vehicle wells at 55.43 ± 26.26 ng/mL, which significantly increased to 333.27 ± 305.98 ng/mL (p < 0.001) after lipopolysaccharide stimulation. Soluble P-gp strongly and significantly correlated with cytoplasmic P-gp (r = 0.57, p = 0.000001). Exposure to 2000 ng/mL of recombinant P-gp significantly increased corrected total cell fluorescence (1.34 ± 1.85) relative to vehicle control 0.29 ± 0.26 (p = 0.01) and significantly reduced calcein acetoxymethyl ester fluorescence (82.03 ± 43.69) relative to 100 ng/mL recombinant P-gp exposed cells (123.11 ± 42.16, p = 0.001).

CONCLUSION

Cultured sinonasal epithelial cells were able to both secrete intact P-gp and could functionally interpolate soluble P-gp into their cell membrane. These in vitro findings indicated that soluble P-gp may be present in nasal mucus as a biomarker and could participate in the maintenance of P-gp overexpression in chronic rhinosinusitis and associated inflammation.

Non-invasive intranasal delivery of quetiapine fumarate loaded microemulsion for brain targeting: Formulation, physicochemical and pharmacokinetic consideration

Systemic drug delivery in schizophrenia is a major challenge due to presence of obstacles like, blood-brain barrier and P-glycoprotein, which prohibit entry of drugs into the brain. Quetiapine fumarate (QF), a substrate to P-glycoprotein under goes extensive first pass metabolism leading to limited absorption thus necessitating frequent oral administration. The aim of this study was to develop QF based microemulsion (ME) with and without chitosan (CH) to investigate its potential use in improving the bioavailability and brain targeting efficiency following non-invasive intranasal administration. QF loaded ME and mucoadhesive ME (MME) showed globule size, pH and viscosity in the range of 29-47nm, 5.5-6.5 and 17-40cP respectively. CH-ME with spherical globules having mean size of 35.31±1.71nm, pH value of 5.61±0.16 showed highest ex-vivo nasal diffusion (78.26±3.29%) in 8h with no sign of structural damage upon histopathological examination. Circular plume with an ovality ratio closer to 1.3 for CH-ME depicted ideal spray pattern. Significantly higher brain/blood ratio of CH-ME in comparison to QF-ME and drug solution following intranasal administration revealed prolonged retention of QF at site of action suggesting superiority of CH as permeability enhancer. Following intranasal administration, 2.7 and 3.8 folds higher nasal bioavailability in brain with CH-ME compared to QF-ME and drug solution respectively is indicative of preferential nose to brain transport (80.51±6.46%) bypassing blood-brain barrier. Overall, the above finding shows promising results in the area of developing non-invasive intranasal route as an alternative to oral route for brain delivery.

Expression of P-glycoprotein in excised human nasal mucosa and optimized models of RPMI 2650 cells

To assess the transmucosal drug transport in the development of medications for intranasal administration, cellular in vitro models are preferred over the use of animal tissues due to inter-species variations and ethical concerns. With regard to the distribution of active agents and multidrug resistance, the ABC transporter P-glycoprotein plays a major role in several mammalian tissues. The present study compares the expression of this efflux pump in optimized in vitro models based on the human RPMI 2650 cell line with specimens of human turbinate mucosa. The presence of the ABCB1 gene was investigated at the mRNA and protein levels using RT-PCR and Western blot analysis in differently cultured RPMI 2650 cells and excised human nasal epithelium. Furthermore, the localization and activity of P-gp was examined by immunohistochemical staining and functionality assays using different substrates in both in vitro and ex vivo models. Both mRNA and protein expression of P-gp was found in all studied models. Furthermore, transporter functionality was detected in both RPMI 2650 cell culture models and excised human mucosa. The results demonstrated a highly promising comparability between RPMI 2650 models and explants of human nasal tissue concerning the influence of MDR1 on drug disposition. The RPMI 2650 cell line might become a useful tool in preclinical trials to improve reproducibility and achieve greater applicability to humans of experimental data regarding passive diffusion and active efflux of drug candidates.

Microarray Determination of the Expression of Drug Transporters in Humans and Animal Species Used for the Investigation of Nasal Absorption

Mice and rats are commonly used to investigate in vivo nasal drug absorption, yet their small nasal cavities limit their use for in vitro investigations. Bovine tissue explants have been used to investigate drug transport through the nasal respiratory and olfactory mucosae, yet limited information is available regarding the similarities and differences among these animal models compared to humans. The aim of this study was to compare the presence of a number of important drug transporters in the nasal mucosa of these species. DNA microarray results for nasal samples from humans, rats, and mice were obtained from GenBank, while DNA microarray and RT-PCR were performed on bovine nasal explants. The drug transporters of interest include multidrug resistance, cation, anion, peptide, and nucleoside transporters. Each of the species (mouse, rat, cattle, and human) shows similar patterns of expression for most of the important drug transporters. Several transporters were highly expressed in all the species, including MRP1, OCTN2, PEPT2, and y+LAT2. While some differences in transporter mRNA and protein expression were observed, the transporter expression patterns were quite similar among the species. The differences suggest that it is important to be aware of any specific differences in transporter expression for a given compound being investigated, yet the similarities support the continued use of these animal models during preclinical investigation of intranasally administered therapeutics.

Intranasal application of vasopressin fails to elicit changes in brain immediate early gene expression, neural activity and behavioural performance of rats

Intranasal administration has been widely used to investigate the effects of the neuropeptides vasopressin and oxytocin on human behaviour and neurological disorders, although exactly what happens when these neuropeptides are administered intranasally is far from clear. In particular, it is not clear whether a physiological significant amount of peptide enters the brain to account for the observed effects. In the present study, we investigated whether the intranasal administration of vasopressin and oxytocin to rats induces the expression of the immediate-early gene product Fos in brain areas that are sensitive to centrally-administered peptide, whether it alters neuronal activity in the way that centrally-administered peptide does, and whether it affects behaviour in the ways that are expected from studies of centrally-administered peptide. We found that, whereas i.c.v. injection of very low doses of vasopressin or oxytocin increased Fos expression in several distinct brain regions, intranasal administration of large doses of the peptides had no significant effect. By contrast to the effects of vasopressin applied topically to the main olfactory bulb, we saw no changes in the electrical activity of olfactory bulb mitral cells after intranasal vasopressin administration. In addition, vasopressin given intranasally had no significant effects on social recognition or short-term recognition memory. Finally, intranasal infusions of vasopressin had no significant effects on the parameters monitored on the elevated plus maze, a rodent model of anxiety. Our data obtained in rats suggest that, after intranasal administration, significant amounts of vasopressin and oxytocin do not reach areas in the brain at levels sufficient to change immediate early gene expression, neural activity or behaviour in the ways described for central administration of the peptides.

P-glycoprotein functions as an immunomodulator in healthy human primary nasal epithelial cells

BACKGROUND

P-glycoprotein (P-gp) is an adenosine triphosphate (ATP)-dependent efflux pump that confers chemotherapeutic resistance in cancer cells. Recent studies suggest that P-gp may also function as an immunomodulator through regulation of cytokine transport. Sinonasal epithelial cells have been recognized as drivers of local innate and adaptive immunity and are known to overexpress P-gp in the setting of inflammation. The objective of this study is to therefore determine whether P-gp participates in the regulation of cytokine secretion in sinonasal epithelial cells.

METHODS

Primary nasal epithelial cell cultures (PNECCs) were cultivated from 5 healthy patients. Membranous P-gp was quantified through quantitative fluorescent immunohistochemistry (Q-FIHC) and confirmed by enzyme-linked immunosorbent assay (ELISA). Sensitivity to inhibition was determined using a rhodamine 123 accumulation assay. Baseline and lipopolysaccharide (LPS)-stimulated cytokine secretion of interleukin 6 (IL-6), IL-8, granulocyte macrophage colony stimulating factor (GM-CSF), and thymic stromal lymphopoietin (TSLP) were quantified by ELISA and compared to LPS stimulated secretion in the setting of P-gp-specific inhibition. Differences in P-gp expression and cytokine secretion were compared using 2-tailed Student t tests with post hoc testing using the Bonferroni procedure.

RESULTS

Membranous P-gp is detectable in PNECCs and upregulated following LPS exposure. P-gp is sensitive to inhibition by both PSC 833 and verapamil in a dose-dependent fashion. LPS stimulated secretion of normalized IL-6 (mean, 95% confidence interval [CI]) (79.67, 42.26-117.07), GM-CSF (39.92, 7.90-71.94), and TSLP (6.65, 5.35-7.96) was significantly reduced following P-gp inhibition (37.60, 11.54-63.65, p = 0.023; 7.64, 2.25-13.03, p = 0.044; and 5.13, 4.44-5.82, p = 0.038; respectively).

CONCLUSION

P-gp is functionally active in PNECCs. P-gp participates in modulation of epithelial secretion of LPS stimulated IL-6, GM-CSF, and TSLP.

Nasal-to-CNS drug delivery: where are we now and where are we heading? An industrial perspective

Delivery of drug therapeutics across the blood-brain barrier is a challenging task for pharmaceutical scientists. Nasal-to-CNS drug delivery has shown promising results in preclinical efficacy models and investigatory human clinical trials. The further development of this technology with respect to the establishment of valid, predictable preclinical species models, translatable pharmacokinetic-pharmacodynamic relationships and definition of toxicology impact will help attract additional pharmaceutical investment in this drug-delivery approach. Further discoveries in nasal nanotechnology, targeted delivery devices and diagnostic olfactory imaging will serve to fuel the advancements in this area of drug delivery.

Functional evidence of multidrug resistance transporters (MDR) in rodent olfactory epithelium

BACKGROUND

P-glycoprotein (Pgp) and multidrug resistance-associated protein (MRP1) are membrane transporter proteins which function as efflux pumps at cell membranes and are considered to exert a protective function against the entry of xenobiotics. While evidence for Pgp and MRP transporter activity is reported for olfactory tissue, their possible interaction and participation in the olfactory response has not been investigated.

PRINCIPAL FINDINGS

Functional activity of putative MDR transporters was assessed by means of the fluorometric calcein acetoxymethyl ester (calcein-AM) accumulation assay on acute rat and mouse olfactory tissue slices. Calcein-AM uptake was measured as fluorescence intensity changes in the presence of Pgp or MRP specific inhibitors. Epifluorescence microscopy measured time course analysis in the olfactory epithelium revealed significant inhibitor-dependent calcein uptake in the presence of each of the selected inhibitors. Furthermore, intracellular calcein accumulation in olfactory receptor neurons was also significantly increased in the presence of either one of the Pgp or MRP inhibitors. The presence of Pgp or MRP1 encoding genes in the olfactory mucosa of rat and mouse was confirmed by RT-PCR with appropriate pairs of species-specific primers. Both transporters were expressed in both newborn and adult olfactory mucosa of both species. To assess a possible involvement of MDR transporters in the olfactory response, we examined the electrophysiological response to odorants in the presence of the selected MDR inhibitors by recording electroolfactograms (EOG). In both animal species, MRPs inhibitors induced a marked reduction of the EOG magnitude, while Pgp inhibitors had only a minor or no measurable effect.

CONCLUSIONS

The findings suggest that both Pgp and MRP transporters are functional in the olfactory mucosa and in olfactory receptor neurons. Pgp and MRPs may be cellular constituents of olfactory receptor neurons and represent potential mechanisms for modulation of the olfactory response.

Regional expression of epithelial MDR1/P-glycoprotein in chronic rhinosinusitis with and without nasal polyposis

BACKGROUND

P-glycoprotein (P-gp) is a 170-kDa transmembrane glycoprotein encoded by the MDR1 (ABCB1) gene and is constitutively expressed on lower airway epithelium. P-gp has been shown to function as an immunomodulator regulating efflux of T-helper 1/T-helper 2 (Th1/Th2) cytokines from its host cell; however, its association with sinonasal inflammation has not been described. The purpose of this study is to determine the pattern and degree of epithelial P-gp expression in chronic rhinosinusitis (CRS) with nasal polyposis (CRSwNP) or CRS without nasal polyposis (CRSsNP).

METHODS

Institutional Review Board (IRB)-approved study utilizing sinus, septal, and inferior turbinate mucosa in patients with no disease, CRS, and CRSwNP (n = 4 each). Quantitative fluorescent immunohistochemistry (Q-FIHC) was performed using an anti-P-gp antibody and a secondary fluorescein isothiocyanate (FITC)-conjugated Fc specific fragment. Protein expression was quantified by calculating the epithelial to nonspecific background intensity ratio (4 images/subsite). Scores less than 1 suggested negligible expression. Staining ratios between patient groups and subsites were compared using a 2-tailed Student t test.

RESULTS

Among the sinus mucosa, P-gp expression in CRSwNP (1.570 ± 0.354) was significantly greater than both CRS (1.224 ± 0.248) and control (0.762 ± 0.128) (p < 0.001, p = 0.002; respectively). CRS scores were significantly greater than control (p = 0.002). Among the septal mucosa, there was no significant difference between CRSwNP (0.914 ± 0.264), CRS (1.126 ± 0.476), or control (0.966 ± 0.327). Among the inferior turbinate mucosa, there was no significant difference between CRSwNP (1.047 ± 0.157), CRS (1.099 ± 0.362), or control (0.824 ± 0.181).

CONCLUSION

MDR1/P-gp is overexpressed in the epithelial layer of sinus mucosa in patients with both CRSwNP and CRS relative to other sinonasal subsites. Expression in healthy mucosa is negligible. Given its known immunomodulatory function this suggests that P-gp may play a role in the pathogenesis or maintenance of chronic sinonasal inflammation.

Expression and differential localization of xenobiotic transporters in the rat olfactory neuro-epithelium

Transporters, such as multidrug resistance P-glycoproteins (MDR), multidrug resistance-related proteins (MRP) and organic anion transporters (OATs), are involved in xenobiotic metabolism, particularly the cellular uptake or efflux of xenobiotics (and endobiotics) or their metabolites. The olfactory epithelium is exposed to both inhaled xenobiotics and those coming from systemic circulation. This tissue has been described as a pathway for xenobiotics to the brain via olfactory perineural space. Thereby, olfactory transporters and xenobiotic metabolizing enzymes, dedicated to the inactivation and the elimination of xenobiotics, have been involved in the toxicological protection of the brain, the olfactory epithelium itself and the whole body. These proteins could also have a role in the preservation of the olfactory sensitivity by inactivation and clearance of the excess of odorant molecules from the perireceptor space. The goal of the present study was to increase our understanding of the expression and the localization of transporters in this tissue. For most of the studied transporters, we observed an opposite mRNA expression pattern (RT-PCR) in the olfactory epithelium compared to the liver, which is considered to be the main metabolic organ. Olfactory epithelium mainly expressed efflux transporters (MRP, MDR). However, a similar pattern was observed between the olfactory epithelium and the olfactory bulb. We also demonstrate distinct cellular immunolocalization of the transporters in the olfactory epithelium. As previously reported, Mrp1 was mainly found in the supranuclear portions of supporting cells. In addition, Mrp3 and Mrp5 proteins, which were detected for the first time in olfactory epithelium, were localized to the olfactory neuron layer, while Mdr1 was localized to the capillary endothelium of lymphatic vessels in the subepithelial region. The pattern of expression and the distinct localization of the olfactory transporters showed in this work may highlight on their specific function in the whole olfactory epithelium.

Effects of localized hydrophilic mannitol and hydrophobic nelfinavir administration targeted to olfactory epithelium on brain distribution

Many nasally applied compounds gain access to the brain and the central nervous system (CNS) with varying degree. Direct nose-to-brain access is believed to be achieved through nervous connections which travel from the CNS across the cribriform plate into the olfactory region of the nasal cavity. However, current delivery strategies are not targeted to preferentially deposit drugs to the olfactory at cribriform. Therefore, we have developed a pressurized olfactory delivery (POD) device which consistently and non-invasively deposited a majority of drug to the olfactory region of the nasal cavity in rats. Using both a hydrophobic drug, mannitol (log P = -3.1), and a hydrophobic drug, nelfinavir (log P = 6.0), and POD device, we compared brain and blood levels after nasal deposition primarily on the olfactory region with POD or nose drops which deposited primarily on the respiratory region in rats. POD administration of mannitol in rats provided a 3.6-fold (p < 0.05) increase in cortex-to-blood ratio, compared to respiratory epithelium deposition with nose drop. Administration of nelfinavir provided a 13.6-fold (p < 0.05) advantage in cortex-to-blood ratio with POD administration, compared to nose drops. These results suggest that increasing the fraction of drug deposited on the olfactory region of the nasal cavity will result in increased direct nose-to-brain transport.

Nasal delivery of P-gp substrates to the brain through the nose-brain pathway

The objective of this study was to evaluate in rats the potential utility of the nasal route to enhance central nervous system (CNS) delivery of drugs recognized by P-glycoprotein (P-gp). Well-known P-gp substrates verapamil and talinolol were perfused nasally or infused intravenously, and when plasma concentrations following intravenous infusion and nasal perfusion showed similar profiles. The concentration of verapamil in the brain after nasal perfusion was twice that after intravenous infusion. Although talinolol in the brain and the cerebrospinal fluid after i.v. infusion were below the detection limit, it was detected after nasal perfusion. When rats were treated with cyclosporin A, brain concentrations of verapamil after both administration modes were increased significantly, while those of talinolol were not significantly changed. Since the permeability of talinolol is low, talinolol in the brain which was transported directly from the nasal cavity has little chance of transport by P-gp localized in the apical membrane of cerebral microvessel endothelial cells. The potential for drug delivery utilizing the nose-CNS route was confirmed for P-gp substrates. The advantage of nasal delivery over i.v. delivery of talinolol to the brain was more significant than that of verapamil, suggesting that nasal administration is more useful strategy for the brain delivery of low-permeability P-gp substrates than the use of P-gp inhibitors.

Lipophilic derivatives of leu-enkephalinamide: in vitro permeability, stability and in vivo nasal delivery

Leu-enkephalin is an endogenous pain modulating opioid pentapeptide. Its development as a potential pharmaceutic has been hampered by poor membrane permeability and susceptibility to enzymatic degradation. The addition of an unnatural amino acid containing a lipidic side chain at the N-terminus and the modification of the C-terminus to a carboxyamide was performed to enhance the nasal delivery of the peptide. Two lipidic derivatives with varying side chain lengths (C(8)-Enk-NH(2) (1), C(12)-Enk-NH(2) (2)) and their acetylated analogues were successfully synthesised. Caco-2 cell monolayer permeability and Caco-2 cell homogenate stability assays were performed. C(8)-Enk-NH(2) (1) and its acetylated analogue Ac-C8-Enk-NH(2) (3) exhibited apparent permeabilities (mean±SD) of 2.51±0.75×10(-6)cm/s and 1.06±0.62×10(-6), respectively. C12-Enk-NH(2) (2) exhibited an apparent permeability of 2.43±1.26×10(-6) cm/s while Ac-C12-Enk-NH(2) (4) was not permeable through the Caco-2 monolayers due to its poor solubility. All analogues exhibited improved Caco-2 homogenate stability compared to Leu-Enk-NH(2) with t(½) values of: C8-Enk-NH(2) (1): 31.7 min, C(12)-Enk-NH(2) (2): 14.7 min, Ac-C8-Enk-NH(2) (3): 83 min, Ac-C(12)-Enk-NH(2) (4): 27 min. However, plasma stability assays revealed that the diastereoisomers of C8-Enk-NH(2) (1) did not degrade at the same rate, with the l isomer (t(1/2)=8.9 min) degrading into Leu-enkephalinamide and then des-Tyr-Leu-Enk-NH(2), whereas the d isomer was stable (t(1/2)=120 min). In vivo nasal administration of C(8)-Enk-NH(2) to male rats resulted in concentrations of 5.9±1.84×10(-2) μM in the olfactory bulbs, 1.35±1.01×10(-2) μM in the brain and 6.53±1.87×10(-3) μM in the blood 10 min after administration.

Preparation and evaluation of fexofenadine microemulsion for intranasal delivery

To enhance the solubility and bioavailability of poorly absorbable fexofenadine, microemulsion system composed of oil, surfactant and co-surfactant was developed for intranasal delivery. Phase behavior, particle size, viscosity and solubilization capacity of the microemulsion system were characterized. Histopathology and in vivo nasal absorption of the optimized microemulsion formulations were also investigated in rats. A single isotropic region was found in the pseudo-ternary phase diagrams developed at various ratios with Lauroglycol 90 as oil, Labrasol as surfactant and Plurol oleiqueCC49 or its mixture with PEG-400 (1:1) as cosurfactant. An increase in the microemulsion region in pseudo-ternary phase systems was observed with increased surfactant concentration. The optimized microemulsion formulations showed higher solubulization of fexofenadine, i.e., F1 (22.64mg/mL) and F2 (22.98mg/mL), compared to its intrinsic water solubility (1.51mg/mL). Nasal absorption of fexofenadine from these microemulsions was found to be fairly rapid. T(max) was observed within 5min after intranasal administration at 1.0mg/kg dose, and the absolute bioavailability (0-4h) was about 68% compared to the intravenous administration in rats. Our results suggested that these microemulsion formulations could be used as an effective intranasal dosage form for the rapid-onset delivery of fexofenadine.

Intranasal delivery to the central nervous system: mechanisms and experimental considerations

The blood-brain barrier (BBB) limits the distribution of systemically administered therapeutics to the central nervous system (CNS), posing a significant challenge to drug development efforts to treat neurological and psychiatric diseases and disorders. Intranasal delivery is a noninvasive and convenient method that rapidly targets therapeutics to the CNS, bypassing the BBB and minimizing systemic exposure. This review focuses on the current understanding of the mechanisms underlying intranasal delivery to the CNS, with a discussion of pathways from the nasal cavity to the CNS involving the olfactory and trigeminal nerves, the vasculature, the cerebrospinal fluid, and the lymphatic system. In addition to the properties of the therapeutic, deposition of the drug formulation within the nasal passages and composition of the formulation can influence the pathway a therapeutic follows into the CNS after intranasal administration. Experimental factors, such as head position, volume, and method of administration, and formulation parameters, such as pH, osmolarity, or inclusion of permeation enhancers or mucoadhesives, can influence formulation deposition within the nasal passages and pathways followed into the CNS. Significant research will be required to develop and improve current intranasal treatments and careful consideration should be given to the factors discussed in this review.

An improved primary human nasal cell culture for the simultaneous determination of transepithelial transport and ciliary beat frequency

Objectives

The aim was to establish a preclinical in-vitro system of the nasal mucosa for the simultaneous evaluation of nasal absorption and effects on ciliary activity.

Methods

Human nasal epithelial cells were grown in collagen-coated transport inserts with transparent polyethylene terephthalate membranes (3 μm). Transepithelial transport and ciliary beat frequency values were measured every 15 min for 1 h.

Key findings

The apparent permeability coefficients (Papp) for atenolol (mainly paracellular transport) and propranolol (transcellular transport) amounted to 0.1 ± 0.1 and 23.7 ± 0.6 × 10−6 cm/s, respectively, illustrating that the system can be used to discriminate between high permeability and low permeability compounds. Transport of talinolol (substrate for the P-glycoprotein efflux carrier) did not reveal polarity (0.3 ± 0.2 and 0.2 ± 0.1 × 10−6 cm/s for absorptive and secretory transport, respectively) and was not affected by verapamil (10 μm), suggesting the absence of P-glycoprotein in the nasal cell culture. No significant effects of atenolol, propranolol and talinolol on ciliary beat frequency were observed (98 ± 20% of the control condition after 60 min). Chlorocresol significantly decreased the ciliary activity but this decrease was not accompanied by effects on the transepithelial transport of atenolol, propranolol and talinolol.

Conclusions

A new system was developed which offers possibilities as a fast screening tool for studying the potential of compounds for nasal drug administration, since permeability and a possible cilio-toxic effect can be assessed simultaneously.

A new minimal-stress freely-moving rat model for preclinical studies on intranasal administration of CNS drugs

Purpose

To develop a new minimal-stress model for intranasal administration in freely moving rats and to evaluate in this model the brain distribution of acetaminophen following intranasal versus intravenous administration.

Methods

Male Wistar rats received one intranasal cannula, an intra-cerebral microdialysis probe, and two blood cannulas for drug administration and serial blood sampling respectively. To evaluate this novel model, the following experiments were conducted. 1) Evans Blue was administered to verify the selectivity of intranasal exposure. 2) During a 1 min infusion 10, 20, or 40 μl saline was administered intranasally or 250 µl intravenously. Corticosterone plasma concentrations over time were compared as biomarkers for stress. 3) 200 µg of the model drug acetaminophen was given in identical setup and plasma, and brain pharmacokinetics were determined.

Results

In 96% of the rats, only the targeted nasal cavity was deeply colored. Corticosterone plasma concentrations were not influenced, neither by route nor volume of administration. Pharmacokinetics of acetaminophen were identical after intravenous and intranasal administration, although the Cmax in microdialysates was reached a little earlier following intravenous administration.

Conclusion

A new minimal-stress model for intranasal administration in freely moving rats has been successfully developed and allows direct comparison with intravenous administration.

Intranasal delivery: physicochemical and therapeutic aspects

Interest in intranasal (IN) administration as a non-invasive route for drug delivery continues to grow rapidly. The nasal mucosa offers numerous benefits as a target issue for drug delivery, such as a large surface area for delivery, rapid drug onset, potential for central nervous system delivery, and no first-pass metabolism. A wide variety of therapeutic compounds can be delivered IN, including relatively large molecules such as peptides and proteins, particularly in the presence of permeation enhancers. The current review provides an in-depth discussion of therapeutic aspects of IN delivery including consideration of the intended indication, regimen, and patient population, as well as physicochemical properties of the drug itself. Case examples are provided to illustrate the utility of IN dosing. It is anticipated that the present review will prove useful for formulation scientists considering IN delivery as a delivery route.

Distribution and clearance of bioadhesive formulations from the olfactory region in man: Effect of polymer type and nasal delivery device

There is an increasing need to identify novel approaches by which to improve the efficiency of drug transport from the nasal cavity (olfactory region) to the CNS, especially for treatment of central nervous system disorders. It is suggested, that one approach is the combination of active targeting of a bioadhesive formulation, that will retain the drug at the absorption site, potentially in combination with, an absorption enhancer. Two low methylated pectins, LM-5 and LM-12 were selected for evaluation as drug delivery systems, due to their ability to gel in the nasal cavity and their bioadhesive characteristics, together with chitosan G210, which acts both as a bioadhesive material and as an efficient absorption enhancer. It was found that all of the bioadhesive formulations were able to reach the olfactory region in the nasal cavity of human volunteers when delivered using a simple nasal drop device. Furthermore, the formulations displayed a significantly increased residence time on the epithelial surface. This was in contrast to a non-bioadhesive control delivered with the same device. In contrast, a pectin formulation administered with a nasal spray system did not show an increase in residence time in the olfactory region. It was further shown that the reproducibility of olfactory delivery of a polymer formulation was significantly better intra-subject than inter-subject.

Strategies for intranasal delivery of therapeutics for the prevention and treatment of neuroAIDS

Intranasal drug administration is a noninvasive method of bypassing the blood-brain barrier (BBB) to deliver neurotrophins and other therapeutic agents to the brain and spinal cord. This method allows drugs that do not cross the BBB to be delivered to the central nervous system (CNS) and eliminates the need for systemic delivery, thereby reducing unwanted systemic side effects. Delivery from the nose to the CNS occurs within minutes along both the olfactory and trigeminal neural pathways. Intranasal delivery occurs by an extracellular route and does not require that drugs bind to any receptor or undergo axonal transport. Intranasal delivery also targets the nasal associated lymphatic tissues (NALT) and deep cervical lymph nodes. In addition, intranasally administered therapeutics are observed at high levels in the blood vessel walls and perivascular spaces of the cerebrovasculature. Using this intranasal method in animal models, researchers have successfully reduced stroke damage, reversed Alzheimer's neurodegeneration, reduced anxiety, improved memory, stimulated cerebral neurogenesis, and treated brain tumors. In humans, intranasal insulin has been shown to improve memory in normal adults and patients with Alzheimer's disease. Intranasal delivery strategies that can be employed to treat and prevent NeuroAIDS include: (1) target antiretrovirals to reach HIV that harbors in the CNS; (2) target therapeutics to protect neurons in the CNS; (3) modulate the neuroimmune function of moncyte/macrophages by targeting the lymphatics, perivascular spaces of the cerebrovasculature, and the CNS; and (4) improve memory and cognitive function by targeting therapeutics to the CNS.

Transport of hydroxyzine and triprolidine across bovine olfactory mucosa: role of passive diffusion in the direct nose-to-brain uptake of small molecules

Hydroxyzine and triprolidine have both been reported to reach the CNS following nasal administration. The objective of this study was to investigate their in vitro permeation across bovine olfactory mucosa in order to further characterize the biological and physicochemical parameters that influence direct nose-to-brain transport. In vitro experiments were conducted using Sweetana-Grass (Navicyte) vertical diffusion cells to evaluate the effect of directionality, donor concentration and pH on the permeation of hydroxyzine and triprolidine across excised bovine olfactory mucosa. These studies demonstrated that the Jm-s (mucosal-submucosal flux) and Js-m (submucosal-mucosal flux) of hydroxyzine and triprolidine across the olfactory mucosa were linearly dependent upon the donor concentration without any evidence of saturable transport. Hydroxyzine inhibited the efflux of P-gp substrates like etoposide and chlorpheniramine across the olfactory mucosa. Both hydroxyzine and triprolidine reduced the net flux (Js-m-Jm-s) of etoposide with IC50 values of 39.2 and 130.6 microM, respectively. The lipophilicty of these compounds, coupled with their ability to inhibit P-gp, enable them to freely permeate across the olfactory mucosa. Despite the presence of a number of protective barriers such as efflux transporters and metabolizing enzymes in the olfactory system, lipophilic compounds such as hydroxyzine and triprolidine can access the CNS primarily by passive diffusion when administered via the nasal cavity.

Role of dopamine transporter (DAT) in dopamine transport across the nasal mucosa

Dopamine is a catecholamine neurotransmitter necessary for motor functions. Its deficiency has been observed in several neurological disorders, but replacement of endogenous dopamine via oral or parenteral delivery is limited by poor absorption, rapid metabolism and the inability of dopamine to cross the blood-brain barrier. The intranasal administration of dopamine, however, has resulted in improved central nervous system (CNS) bioavailability compared to that obtained following intravenous delivery. Portions of the nasal mucosa are innervated by olfactory neurons expressing dopamine transporter (DAT) which is responsible for the uptake of dopamine within the central nervous system. The objective of these studies was to study the role of DAT in dopamine transport across the bovine olfactory and nasal respiratory mucosa. Western blotting studies demonstrated the expression of DAT and immunohistochemistry revealed its epithelial and submucosal localization within the nasal mucosa. Bidirectional transport studies over a 0.1-1 mM dopamine concentration range were carried out in the mucosal-submucosal and submucosal-mucosal directions to quantify DAT activity, and additional transport studies investigating the ability of GBR 12909, a DAT inhibitor, to decrease dopamine transport were conducted. Dopamine transport in the mucosal-submucosal direction was saturable and was decreased in the presence of GBR 12909. These studies demonstrate the activity of DAT in the nasal mucosa and provide evidence that DAT-mediated dopamine uptake plays a role in the absorption and distribution of dopamine following intranasal administration.

Transport of estrone sulfate by the novel organic anion transporter Oat6 (Slc22a20)

Recently, a novel Slc22 gene family member expressed in murine olfactory mucosa was identified and based on sequence homology proposed to be an organic anion transporter [Oat6 (Slc22a20); J. C. Monte, M. A. Nagle, S. A. Eraly, and S. K. Nigam. Biochem Biophys Res Commun 323: 429-436, 2004]. However, no functional data for Oat6 was reported. In the present study, we demonstrate that murine Oat6 mediates the inhibitable transport of estrone sulfate using both Xenopus oocyte expression assay and Chinese hamster ovary (CHO) cells stably transfected with mOat6 (CHO-mOat6). Uptake was virtually eliminated by probenecid and the anionic herbicide 2,4-dichlorophenoxyacetate. The organic anions ochratoxin A, salicylate, penicillin G, p-aminohippurate, and urate inhibited mOat6-mediated accumulation to varying degrees. Transport of estrone sulfate by mOat6 was demonstrated to be saturable, and K(m) estimates of 109.8 +/- 22.6 microM in oocytes and 44.8 +/- 7.3 microM in CHO-mOat6 cells were obtained. Inhibitory constants for 2,4-dichlorophenoxyacetate (15.7 +/- 2.0 microM), salicylate (49.0 +/- 4.4 microM), probenecid (8.3 +/- 2.5 microM), and penicillin G (1,450 +/- 480 microM) were also determined. Accumulation of estrone sulfate mediated by mOat6 was significantly trans-stimulated by glutarate, indicating that mOat6 functions as an organic anion/dicarboxylate exchanger. These data demonstrate for the first time that the novel murine gene Oat6 (Slc22a20) encodes a functional organic anion transporter and mOat6 is indeed the newest member of the OAT gene family.

Comparison of Human Tracheal/Bronchial Epithelial Cell Culture and Bovine Nasal Respiratory Explants for Nasal Drug Transport Studies

Ten drug compounds with varying physicochemical properties and transporter substrate specificities were investigated to compare their in vitro permeabilities across bovine nasal respiratory explants and the EpiAirway system, both established models for the assessment of nasal drug absorption. Permeability across the bovine explants and EpiAirway correlated well with the partitioning behavior of compounds whose clogDC values were greater than 0. The permeabilities of all ten compounds were well-correlated between the two tissue models, with the permeability values through the EpiAirway tissues being approximately 10-fold higher than through the bovine explants due to the thickness differences between the models. For more lipophilic compounds, the in vitro permeabilities measured with both tissue systems were also predictive of the reported in vivo nasal bioavailabilities. Deviations from these correlations were observed for compounds reported to be substrates of p-glycoprotein or OCT transporters, and differences were also seen between the permeabilities measured in the tissue models for these compounds. Both models can be used to estimate the systemic bioavailability of moderately lipophilic compounds administered intranasally, while each may have particular advantages or disadvantages in estimating the bioavailability of drug compounds that are subject to local mucosal metabolism or to carrier-mediated uptake or efflux.