Inhaled fosamprenavir for laryngopharyngeal reflux: Toxicology and fluid dynamics modeling

Objectives

Approximately 25% of Americans suffer from laryngopharyngeal reflux (LPR), a disease for which no effective medical therapy exists. Pepsin is a predominant source of damage during LPR and a key therapeutic target. Fosamprenavir (FOS) inhibits pepsin and prevents damage in an LPR mouse model. Inhaled FOS protects at a lower dose than oral; however, the safety of inhaled FOS is unknown and there are no inhalers for laryngopharyngeal delivery. A pre-Good Lab Practice (GLP) study of inhaled FOS was performed to assess safety and computational fluid dynamics (CFD) modeling used to predict the optimal particle size for a laryngopharyngeal dry powder inhaler (DPI).

Methods

Aerosolized FOS, amprenavir (APR), or air (control) were provided 5 days/week for 4 weeks (n = 6) in an LPR mouse model. Organs (nasal cavity, larynx, esophagus, trachea, lung, liver, heart, and kidney) were assessed by a pathologist and bronchoalveolar lavage cytokines and plasma cardiotoxicity markers were assessed by Luminex assay. CFD simulations were conducted in a model of a healthy 49-year-old female.

Results

No significant increase was observed in histologic lesions, cytokines, or cardiotoxicity markers in FOS or APR groups relative to the control. CFD predicted that laryngopharyngeal deposition was maximized with aerodynamic diameters of 8.1-11.5 μm for inhalation rates of 30-60 L/min.

Conclusions

A 4-week pre-GLP study supports the safety of inhaled FOS. A formal GLP assessment is underway to support a phase I clinical trial of an FOS DPI for LPR.

Level of Evidence

NA.

Oral and Inhaled Fosamprenavir Reverses Pepsin-Induced Damage in a Laryngopharyngeal Reflux Mouse Model

OBJECTIVE

More than 20% of the US population suffers from laryngopharyngeal reflux. Although dietary/lifestyle modifications and alginates provide benefit to some, there is no gold standard medical therapy. Increasing evidence suggests that pepsin is partly, if not wholly, responsible for damage and inflammation caused by laryngopharyngeal reflux. A treatment specifically targeting pepsin would be amenable to local, inhaled delivery, and could prove effective for endoscopic signs and symptoms associated with nonacid reflux. The aim herein was to identify small molecule inhibitors of pepsin and test their efficacy to prevent pepsin-mediated laryngeal damage in vivo.

METHODS

Drug and pepsin binding and inhibition were screened by high-throughput assays and crystallography. A mouse model of laryngopharyngeal reflux (mechanical laryngeal injury once weekly for 2 weeks and pH 7 solvent/pepsin instillation 3 days/week for 4 weeks) was provided inhibitor by gavage or aerosol (fosamprenavir or darunavir; 5 days/week for 4 weeks; n = 3). Larynges were collected for histopathologic analysis.

RESULTS

HIV protease inhibitors amprenavir, ritonavir, saquinavir, and darunavir bound and inhibited pepsin with IC50 in the low micromolar range. Gavage and aerosol fosamprenavir prevented pepsin-mediated laryngeal damage (i.e., reactive epithelia, increased intraepithelial inflammatory cells, and cell apoptosis). Darunavir gavage elicited mild reactivity and no discernable protection; aerosol protected against apoptosis.

CONCLUSIONS

Fosamprenavir and darunavir, FDA-approved therapies for HIV/AIDS, bind and inhibit pepsin, abrogating pepsin-mediated laryngeal damage in a laryngopharyngeal reflux mouse model. These drugs target a foreign virus, making them ideal to repurpose. Reformulation for local inhaled delivery could further improve outcomes and limit side effects.

LEVEL OF EVIDENCE

NA. Laryngoscope, 133:S1-S11, 2023.

Acrolein Increases the Pulmonary Tumorigenic Activity of the Tobacco-Specific Nitrosamine 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)

Tobacco smoke is a complex mixture of more than 7000 chemicals, of which many are toxic and/or carcinogenic. Many hazard assessments of tobacco have focused on individual chemical exposures without consideration of how the chemicals may interact with one another. Two chemicals, the human carcinogen 4-methylnitrosamino-1-(3-pyridyl)-1-butanone (NNK) and a possible human carcinogen, acrolein, were hypothesized to interact with one another, possibly owing to the additive effects of DNA adduct formation or influence on the repair of mutagenic DNA adducts. To test our hypothesis that coexposure to NNK and acrolein is more carcinogenic than either chemical alone, A/J mice were exposed to NNK (i.p., 0, 2.5, or 7.5 μmol in saline) in the presence or absence of inhaled acrolein (15 ppmV). While the single 3 h exposure to acrolein alone did not induce lung adenomas, it significantly enhanced NNK's lung carcinogenicity. In addition, mice receiving both NNK and acrolein had more adenomas with dysplasia or progression than those receiving only NNK, suggesting that acrolein may also increase the severity of NNK-induced lung adenomas. To test the hypothesis that the interaction was due to effects on DNA adduct formation and repair, NNK- and acrolein pulmonary DNA adduct levels were assessed. There was no consistent effect of the coexposure on NNK-derived DNA adducts, and acrolein DNA adducts were not elevated above endogenous levels. This study supports the hypothesis that tobacco smoke chemicals combine to contribute to the carcinogenic potency of tobacco smoke, and the mechanism of interaction cannot be explained by alterations of DNA adduct levels.

Modulating insulin signaling and trafficking at the blood-brain barrier endothelium using lipid based nanoemulsions

The compositionally distinct lipid rafts present in the plasma membrane regulate the restrictive trafficking and signal transduction in the blood-brain barrier (BBB) endothelium. Several metabolic and neurodegenerative diseases are associated with lipid homeostasis disruption within the BBB endothelium. Here, we hypothesized that the delivery of lipid triglyceride based nanoemulsions containing unsaturated fatty acids (UFAs) provides a novel non-pharmacological approach to modulate lipid raft integrity and rectify the aberrant trafficking and signal transduction. The current study has shown that soybean oil nanoemulsions (SNEs) altered the morphology of lipid rafts that are stained by Alex Fluor 647 labelled cholera toxin (AF647-CTX) in polarized human cerebral microvascular endothelial (hCMEC/D3) cell monolayers. Moreover, western blot and flow cytometry analysis showed that SNEs containing polyunsaturated fatty acids (PUFAs) increased phospo-AKT (p-AKT) expression, a marker for the stimulation of metabolic arm of insulin signaling, and insulin uptake in hCMEC/D3 monolayers. However, olive oil nanoemulsions (ONEs) containing monounsaturated fatty acids (MUFAs) had no detectable impact on lipid raft integrity, AKT phosphorylation, or insulin uptake. These findings provided direct evidence that SNEs containing PUFAs can upregulate insulin-pAKT pathway, facilitate insulin trafficking at the BBB, and potentially address cerebrovascular dysfunction in metabolic and neurodegenerative diseases.

Coexposure to Inhaled Aldehydes or Carbon Dioxide Enhances the Carcinogenic Properties of the Tobacco-Specific Nitrosamine 4-Methylnitrosamino-1-(3-pyridyl)-1-butanone in the A/J Mouse Lung

Tobacco smoke is a complex mixture of chemicals, many of which are toxic and carcinogenic. Hazard assessments of tobacco smoke exposure have predominantly focused on either single chemical exposures or the more complex mixtures of tobacco smoke or its fractions. There are fewer studies exploring interactions between specific tobacco smoke chemicals. Aldehydes such as formaldehyde and acetaldehyde were hypothesized to enhance the carcinogenic properties of the human carcinogen, 4-methylnitrosamino-1-(3-pyridyl)-1-butanone (NNK) through a variety of mechanisms. This hypothesis was tested in the established NNK-induced A/J mouse lung tumor model. A/J mice were exposed to NNK (intraperitoneal injection, 0, 2.5, or 7.5 μmol in saline) in the presence or absence of acetaldehyde (0 or 360 ppmv) or formaldehyde (0 or 17 ppmv) for 3 h in a nose-only inhalation chamber, and lung tumors were counted 16 weeks later. Neither aldehyde by itself induced lung tumors. However, mice receiving both NNK and acetaldehyde or formaldehyde had more adenomas with dysplasia or progression than those receiving only NNK, suggesting that aldehydes may increase the severity of NNK-induced lung adenomas. The aldehyde coexposure did not affect the levels of NNK-derived DNA adduct levels. Similar studies tested the ability of a 3 h nose-only carbon dioxide (0, 5, 10, or 15%) coexposure to influence lung adenoma formation by NNK. While carbon dioxide alone was not carcinogenic, it significantly increased the number of NNK-derived lung adenomas without affecting NNK-derived DNA damage. These studies indicate that the chemicals in tobacco smoke work together to form a potent lung carcinogenic mixture.

Abstract A19: Interactions between tobacco smoke chemicals in rodent tumor models

Tobacco is a complex chemical mixture, containing many toxicants and carcinogens. Most rodent risk assessment studies have focused on single chemicals or the complicated mixtures of tobacco smoke or its fractions. There are few studies evaluating how specific chemicals interact with one another to form the potent carcinogenic mixture of tobacco smoke. We hypothesized that tobacco smoke aldehydes like formaldehyde and acetaldehyde could enhance the carcinogenic properties of the tobacco-specific nitrosamines, N’-nitrosonornicotine (NNN) and 4-methylnitrosamine-1-(3-pyridyl)-1-butanone (NNK), through a variety of mechanisms. This hypothesis was tested in two established rodent tumor models, the NNN-induced rat esophageal tumor model and the NNK-induced A/J mouse lung tumor model. In the first model, rats were exposed to 0, 4, or 8 ppm NNN in the drinking water in the presence or absence of 3000 ppm acetaldehyde for up to 100 weeks. The number of esophageal papillomas per rat was doubled in animals receiving both acetaldehyde and 8 ppm NNN (0.5 versus 1.15 tumors/rat, respectively). Acetaldehyde alone did not cause esophageal tumors. DNA adduct levels were not affected by the combination of the two chemicals. In the second model, A/J mice were exposed to NNK (i.p, 0, 2.5, or 7.5 μmol in saline) in the presence or absence of acetaldehyde (0 or 360 ppmv) or formaldehyde (0 or 15 ppmv) for 3 hours in a nose-only inhalation chamber. Lung tumors were counted 16 weeks later. Neither aldehyde by itself induced lung tumors. However, mice receiving both NNK and acetaldehyde or formaldehyde had an increased number of adenomas with dysplasia or progression than those receiving only NNK, suggesting that aldehydes may increase dysplasia in tumors initiated by NNK. As in the rat study, DNA adduct levels were not affected by the coexposure. In a separate experiment, we tested the hypothesis that the elevated levels of carbon dioxide in tobacco smoke could affect the carcinogenic properties of NNK in the A/J mouse; tobacco smoke contains 12.5% carbon dioxide. Mice received a 3 h nose-only carbon dioxide (0, 5, 10, or 15%) coexposure of mice receiving NNK (i.p. in saline, 0, 2.5, or 7.5 μmol). The coexposure to carbon dioxide more than doubled the number of lung adenomas induced by 2.5 μmol NNK, with the maximal effect observed with 10% carbon dioxide (0%: 1.8 ± 1.9; 5%: 3.9 ± 2.8; 10%: 7.1 ± 3.5; 15%; 5.5 ± 2.9 lung adenomas/mouse). Lung adenomas were also significantly increased in mice receiving 7.5 μmol NNK, although to a lesser extent (0%: 11 ± 6.2; 5%: 13 ± 7.9; 10%: 18 ± 6.0; 15%; 12 ± 5.3 lung adenomas/mouse). This additive and synergistic effect of carbon dioxide was highly significant (p value = 1.0 × 10-14). The mechanism of this interaction is under investigation. Collectively, these studies support the hypothesis that the aldehydes and carbon dioxide present in the tobacco mixture interact to enhance the carcinogenic potency of the tobacco specific nitrosamines. (Funded by CA-184987.)

Citation Format: Lisa A. Peterson, Marissa K. Oram, Donna E. Seabloom, William E. Smith, Alessia Stornetta, Karin R. Vevang, Monica Flavin, Alexandru F. Tabaran, Ingrid Cornax, M. Gerard O’Sullivan, Pramod Upadhyaya, Lin Zhang, Stephen S. Hecht, Silvia Balbo, Timothy S. Wiedmann. Interactions between tobacco smoke chemicals in rodent tumor models [abstract]. In: Proceedings of the AACR Special Conference on Environmental Carcinogenesis: Potential Pathway to Cancer Prevention; 2019 Jun 22-24; Charlotte, NC. Philadelphia (PA): AACR; Can Prev Res 2020;13(7 Suppl): Abstract nr A19.

Drug Tissue Distribution of TUDCA From a Biodegradable Suprachoroidal Implant versus Intravitreal or Systemic Delivery in the Pig Model

Purpose

To determine local ocular tissue levels of the bile acid, tauroursodeoxycholic acid (TUDCA), in the pig model using oral, intravenous (IV), intravitreal injection (IVitI) and low- and high-dose suprachoroidal, sustained-release implants (SCI-L or SCI-H).

Methods

Forty-six pigs (92 globes) were included in the study. TUDCA was delivered orally in 5 pigs, IV in 4, IVitI in 6, SCI-L in 17, and SCI-H in 14. Testing timeframes varied from the same day (within minutes) for IV; 1 to 6 days, oral; and 1 to 4 weeks, IVitI and SCI. Enucleated globes were dissected, specimens from specific tissues were separated, and TUDCA was extracted and quantified using mass spectrometry.

Results

The highest TUDCA tissue levels occurred after IV delivery in the macula (252 ± 238 nM) and peripheral retina (196 ± 171 nM). Macular choroid and peripheral choroid levels were also high (1032 ± 1269 and 1219 ± 1486 nM, respectively). For IVitI delivery, macular levels at day 6 were low (0.5 ± 0.5 nM), whereas peripheral choroid was higher (15.3 ± 16.7 nM). Neither the SCI-L nor SCI-H implants delivered meaningful macular doses (≤1 nM); however, peripheral retina and choroid levels were significantly higher. Bile acid isoforms were found in the serum specimens.

Conclusions

The highest TUDCA tissue levels in the pig model were obtained using IV delivery. Oral delivery was associated with reasonable tissue levels. Local delivery (IVitI and SCI) was able to achieve measurable local ocular tissue levels.

Translational Relevance

Diffusional kinetics from the suprachoroidal space follow the choroidal blood flow, away from the macula and toward the periphery.

Inhaled Furan Selectively Damages Club Cells in Lungs of A/J Mice

Furan, a possible human carcinogen, is a product of incomplete combustion and is present in cigarette smoke, engine exhaust, and processed food. Oral administration induces liver toxicity and carcinogenesis in F344 rats and B6C3F1 mice. To assess possible adverse effects from inhalation, A/J mice were nose-only exposed for 3 hours to furan (0, 30, 75, 150, 300, or 600 ppmv) and euthanized after 24 hours, 48 hours, or 1 week. Histopathology evaluation revealed bronchiolar club cell necrosis (diffuse, marked) with airway denudation following exposure to 300 and 600 ppmv furan with evidence of club cell regeneration and partial repair after 1 week. Initial signs of hepatotoxicity were observed in the 150 ppmv furan-exposed group. Acute necrosis and mineralization were observed in livers at 24 and 48 hours with hepatocyte regeneration by 1-week postexposure in mice exposed to 300 and 600 ppmv furan; the 300 ppmv exposed group had multifocal mineralization that evoked a mild granulomatous response. Measurement of urinary furan metabolites confirmed that the mice metabolized furan to the toxic intermediate, cis-2-butene-1,4-dial. These observations indicate that inhaled furan is toxic to lungs with club cells as the target as well as liver.

Design, Development, and Characterization of Imiquimod-Loaded Chitosan Films for Topical Delivery

Aldara™ (5% w/w imiquimod) topical cream is approved by the US FDA for the treatment of superficial basal cell carcinoma. However, the cream formulation suffers from dose variability, low drug availability due to the incomplete release, and poor patient compliance. To achieve sustained and complete release of imiquimod, chitosan films were prepared by casting using propylene glycol as a plasticizer. Chitosan films had appropriate physicochemical characteristics for wound dressing and excellent content uniformity and maintained the original physical form of imiquimod. Films were capable of releasing a defined dose of imiquimod over a period of 7 days. The bioactivity of imiquimod was not affected by its entrapment in chitosan matrix as indicated by the results of in vitro growth inhibition assay. In addition, the film formulation showed significantly (p ˂ 0.05) higher drug accumulation in the skin when compared to commercial cream formulation.

Enhancing therapeutic efficacy through designed aggregation of nanoparticles

Particle size is a key determinant of biological performance of sub-micron size delivery systems. Previous studies investigating the effect of particle size have primarily focused on well-dispersed nanoparticles. However, inorganic nanoparticles are prone to aggregation in biological environments. In our studies, we examined the consequence of aggregation on superparamagnetic iron oxide (SPIO) nanoparticle-induced magnetic hyperthermia. Here we show that the extent and mechanism of hyperthermia-induced cell kill is highly dependent on the aggregation state of SPIO nanoparticles. Well-dispersed nanoparticles induced apoptosis, similar to that observed with conventional hyperthermia. Sub-micron size aggregates, on the other hand, induced temperature-dependent autophagy through generation of oxidative stress. Micron size aggregates caused rapid membrane damage, resulting in acute cell kill. Overall, this work highlights the potential for developing highly effective anticancer therapeutics through designed aggregation of nano delivery systems.

Inhalable magnetic nanoparticles for targeted hyperthermia in lung cancer therapy

Lung cancer (specifically, non-small cell lung cancer; NSCLC) is the leading cause of cancer-related deaths in the United States. Poor response rates and survival with current treatments clearly indicate the urgent need for developing an effective means to treat NSCLC. Magnetic hyperthermia is a non-invasive approach for tumor ablation, and is based on heat generation by magnetic materials, such as superparamagnetic iron oxide (SPIO) nanoparticles, when subjected to an alternating magnetic field. However, inadequate delivery of magnetic nanoparticles to tumor cells can result in sub-lethal temperature change and induce resistance while non-targeted delivery of these particles to the healthy tissues can result in toxicity. In our studies, we evaluated the effectiveness of tumor-targeted SPIO nanoparticles for magnetic hyperthermia of lung cancer. EGFR-targeted, inhalable SPIO nanoparticles were synthesized and characterized for targeting lung tumor cells as well as for magnetic hyperthermia-mediated antitumor efficacy in a mouse orthotopic model of NSCLC. Our results show that EGFR targeting enhances tumor retention of SPIO nanoparticles. Further, magnetic hyperthermia treatment using targeted SPIO nanoparticles resulted in significant inhibition of in vivo lung tumor growth. Overall, this work demonstrates the potential for developing an effective anticancer treatment modality for the treatment of NSCLC based on targeted magnetic hyperthermia.

A combination antioxidant therapy prevents age-related hearing loss in C57BL/6 mice

OBJECTIVE

Age-related hearing loss (ARHL) is characterized by gradual, progressive sensorineural hearing loss, which impairs communication, lending to clinical depression and social withdrawal. There are currently no effective treatments for ARHL. The purpose of this study is to evaluate the potential of a combination antioxidant therapy in preventing ARHL.

STUDY DESIGN

Randomized controlled trial.

SETTING

Animal study.

SUBJECTS AND METHODS

C57BL/6 mice, a recognized animal model of ARHL, were assigned to one of three groups: early treatment (n = 12), late treatment (n = 9), or control group (n = 9). Treatment groups of mice were fed with a combination agent comprising six antioxidant agents that target four sites within the oxidative pathway: L-cysteine-glutathione mixed disulfide, ribose-cysteine, NW-nitro-L-arginine methyl ester, vitamin B12, folate, and ascorbic acid. Auditory brainstem response (ABR) thresholds were recorded at baseline and every three months following initiation of treatment.

RESULTS

Threshold shifts from baseline were decreased in the treatment groups when compared to the control group at all tested frequencies (P < 0.001). The ABR threshold shift at 12 months of age for the control group was 34.7 dB with a 95% confidence interval (CI) of +/-1.6. The mean threshold shifts for the early and late treatment groups were 7.5 dB (+/-0.87, 95% CI) and 9.2 dB (+/-1.6, 95% CI).

CONCLUSION

Combination antioxidant therapy effectively decreased threshold shifts on ABR within an animal model of ARHL. Combination antioxidant therapy, with further research and investigation, may provide a safe and cost-effective method of preventing presbycusis in the growing elderly population.

Effect of dietary green tea extract and aerosolized difluoromethylornithine during lung tumor progression in A/J strain mice

Chemoprevention strategies to prevent the development of lung cancer in at-risk individuals are a key component in disease management. In addition to being highly effective, an ideal chemopreventive agent will require low toxicity as patients are likely to require treatment for several years before their risk of cancer is lowered to background levels. In principle, a combination of safe agents that work through distinct mechanisms will improve efficacy while simultaneously maintaining a favorable safety profile. Here, we describe the use of the decaffeinated green tea extract Polyphenon E (Poly E) (1% in diet) and aerosolized difluoromethylornithine (DFMO) (20 mg/kg/day, 5 days/week) in a mouse lung cancer chemoprevention study using a progression protocol. Female A/J mice were injected with benzo[a]pyrene (B[a]P) at 8 weeks of age and precancerous lesions allowed to form over a period of 21 weeks before chemoprevention treatment for an additional 25 weeks. Poly E treatment did not significantly inhibit average tumor multiplicity but reduced per animal tumor load. Analysis of tumor pathology revealed a specific inhibition of carcinomas, with the largest carcinomas significantly decreased in Poly E-treated animals. Aerosolized DFMO did not have a significant effect on lung tumor progression. Magnetic resonance imaging of B[a]P-induced lung tumors confirmed the presence of a subset of large, rapidly growing tumors in untreated mice. Our results suggest a potential role for green tea extracts in preventing the progression of large, aggressive lung adenocarcinomas.

Disease guided optimization of the respiratory delivery of microparticulate formulations

BACKGROUND

Inhalation of microparticulate dosage forms can be effectively used in the treatment of respiratory and systemic diseases.

OBJECTIVE

Disease states investigated for treatment by inhalation of microparticles were reviewed along with the drugs' pharmacological, pharmacokinetic and physical chemical properties to identify the advantages of microparticulate inhalation formulations and to identify areas for further improvement.

METHODS

Microbial infections of the lung, asthma, diabetes, lung transplantation and lung cancer were examined, with a focus on those systems intended to provide a sustained release.

CONCLUSION

In developing microparticulate formulations for inhalation in the lung, there is a need to understand the pharmacology of the drug as the key to revealing the optimal concentration time profile, the disease state, and the pharmacokinetic properties of the pure drug as determined by IV administration and inhalation. Finally, in vitro release studies will allow better identification of the best dosing strategy to be used in efficacy and safety studies.

Deposition of aerosolized particles in the maxillary sinuses before and after endoscopic sinus surgery

BACKGROUND

Recent studies suggest that topical therapy is beneficial in many conditions underlying chronic sinusitis. Current literature has documented low aerosolized particle deposition efficiency into the paranasal sinuses. Mathematical modeling suggests that three factors influence the deposition efficiency: particle size, pressure gradient, and size of the sinus ostium. Ostium size is the most dominant factor. Therefore, we sought to determine if maxillary antrostomy and ethmoidectomy would increase the deposition efficiency.

METHODS

Five cadavers underwent pre- and postoperative scintigraphy after administration of aerosolized Tc-99M. Images were obtained with a gamma-camera and regions of interest (ROIs) were drawn around the maxillary sinuses. Counts per minute in the pre- and postoperative ROIs were then compared using the paired t-test.

RESULTS

Results indicated a significant increase in deposition of radioactivity in the maxillary sinuses in the postoperative state (p < 0.01).

CONCLUSION

Topical therapy for chronic sinusitis may be more feasible in the postoperative population.

Chemopreventive effect of aerosolized polyphenon E on lung tumorigenesis in A/J mice

Effective chemoprevention of lung cancer in high-risk patients through the administration of pharmacologic or nutritional agents is urgently needed. Aerosol inhalation can deliver chemopreventive agents directly to the respiratory tract to inhibit the tumorigenic process. In this study, polyphenon E (PolyE) and (-)-epigallocatechin-3-gallate (EGCG) were administered by aerosol delivery to A/J mice beginning 2 weeks after carcinogen treatment and continuing daily by inhalation throughout the remainder of the study (20 weeks). PolyE decreased tumor load by approximately 59%. However, EGCG, both at the same dose and at a higher dose, failed to inhibit lung carcinogenesis. These results indicate that aerosol delivery of PolyE, but not EGCG, may be a useful chemopreventive protocol in subjects at high risk for lung cancer.

Formation of Cholesterol Crystals at a Mucin Coated Substrate

PURPOSE

High-resolution, tapping-mode atomic force microscopy (AFM) was used to monitor the early stage of the formation of cholesterol crystals under simulated conditions of the gallbladder environment.

METHODS

AFM images of phosphatidylcholine/cholesterol vesicles were obtained using a mucin-coated mica substrate.

RESULTS

The vesicles appeared flattened with diameters from 100 to 300 nm and heights that varied from 10 to 100 nm. Phosphatidylcholine/cholesterol vesicles were mixed with bile salt solutions to yield supersaturated (with respect to cholesterol) dispersions, which were then placed onto mica, silanized mica, and mucin-covered mica substrates. After equilibration, sub-micron sized, plate-like structures were observed at the mica and mucin covered surface, but none were seen at the silanized surface. The morphology was characterized as it pertains to the relative growth rates of the crystal faces.

CONCLUSION

The comparison of these results with literature reports of cholesterol crystals grown in solution suggests that the physical chemical properties of the surface have an important influence in determining the nucleation and subsequent crystal growth of cholesterol.

Pharmacokinetics of 5-fluorouracil in the hamster following inhalation delivery of lipid-coated nanoparticles

The inhalation delivery of 5-fluorouracil (5-FU) in lipid-coated nanoparticles (LNPs) to hamsters was evaluated to determine the feasibility for use in lung cancer chemotherapy. The inhaled dose, 30 mg LNPs/kg body weight (1.5 mg/kg 5-FU), was delivered over an 8-min interval. Fluorescein isothiocyanate dextran (FITC-dextran) was included within the LNPs to provide an estimate of the particle concentration. The concentration of FITC-dextran and total 5-FU (released and LNP-associated) was determined as a function of time in the lung, trachea, larynx, esophagus, and serum. Concentrations of 5-FU and FITC-dextran were initially high in the trachea, larynx, and esophagus, and lower in the lung. Within 24 h, greater than 99% of the LNPs were cleared from the respiratory tract and total 5-FU concentrations mirrored the LNP concentration. An eight-compartment pharmacokinetic model was used to describe the observed trends in concentrations of LNPs and total 5-FU and to estimate the released 5-FU concentration in the above tissues. From this analysis, effective local targeting as well as sustained efficacious concentrations of 5-FU in the expected tumor sites were demonstrated.

Development of a respirable, sustained release microcarrier for 5-fluorouracil I: In vitro assessment of liposomes, microspheres, and lipid coated nanoparticles

The release rate of 5-fluorouracil (5-FU) from liposomes, microspheres, and lipid-coated nanoparticles (LNPs) was determined by microdialysis to investigate their use as a respirable delivery system for adjuvant (postsurgery) therapy of lung cancer. 5-FU was incorporated into liposomes using thin film hydration and into microspheres and LNPs by spray drying. Primary particle size distributions were measured by dynamic light scattering. Liposomes released 5-FU in 4-10 h (k(1) = 0.44-2.31/h, first-order release model). Extruded vesicles with diameters less than one micron released 5-FU more quickly than nonextruded vesicles. With poly-(lactide) (PLA) and Poly-(lactide-co-glycolide) (PLGA) microspheres, slower release rates were observed (k(1) = 0.067-0.202/h). Increasing the lactide:glycolide ratio (50:50-100:0) resulted in a progressive decrease in the release rate of 5-FU. poly-(lactide-co-caprolactone) (PLCL) microspheres released 5-FU more rapidly compared to PLGA systems (k(1) = 0.254-0.259/h). LNPs formulated with polymeric core excipients had lower release rates compared to monomeric excipients (k(1) = 0.043-0.105/h vs. k(1) = 0.192-0.345/h). Changing the lipid chain length of the shell lipid components had a relatively minor effect (k(1) = 0.043-0.129/h). Overall, these systems yielded a wide range of delivery durations that may be suitable for use as an inhalation delivery system for adjuvant therapy of lung cancer.

Development of a Respirable, Sustained Release Microcarrier for 5-Fluorouracil II: In Vitro and In Vivo Optimization of Lipid Coated Nanoparticles

The release rate of 5-fluorouracil (5-FU) from lipid-coated nanoparticles (LNPs) was determined to develop a respirable delivery system for use as adjuvant (postsurgery) therapy for lung cancer. LNPs were prepared by spray drying, and the in vitro release was measured by microdialysis. The composition of the core and shell affected the release rate. Increasing the core diameter at constant shell thickness and increasing shell thickness at constant core diameter reduced the release rate, suggesting that the lipid shell is the rate limiting step for the release of 5-FU. A model consisting of a sequential zero-order/first-order dependence on time from polydispersed cores within polydispersed shells was developed to describe the release. Based on studies of the effect of geometry of the layered particles, the optimal formulation was identified as a 600-nm diameter 5-FU/poly-(glutamic acid) core with a 200-nm thick tripalmitin/cetyl alcohol shell. This system is readily aerosolized by ultrasonic atomization, which did not change the release properties. Preliminary instillation and inhalation delivery studies to the hamster resulted in lung levels of the particles and 5-FU that were near the desired values. Through this effort, a sustained-release, respirable delivery system for adjuvant therapy of lung cancer in humans may ultimately be realized.

Measurement of drug release from microcarriers by microdialysis

The purpose of this study was to examine the feasibility of the microdialysis sampling technique as a method to precisely and conveniently measure drug release from microcarrier systems such as liposomes and microspheres. Release of 5-fluorouracil (5-FU) from liposomes and microspheres was evaluated in vitro using microdialysis. Retrodialysis calibration using 5-chlorouracil (5-CU) was performed in conjunction with on-line HPLC analysis. At a microdialysis perfusate flow rate of 0.5 muL/min, concurrent 5-FU gain and 5-CU loss ranged from 72% to 75%, while concurrent 5-FU loss and 5-CU ranged from 69% to 71%. After calibration, simultaneous 5-FU release profiles were obtained by continuous microdialysis and discrete equilibrium dialysis sampling using a side-by-side diffusion apparatus. Release rates were characterized by a first-order release model. The release rate constants for a representative liposomal formulation were 0.30 and 1.85/h by microdialysis in the acceptor and donor compartments, respectively, and 0.39/h by equilibrium dialysis in the acceptor compartment. The calculated release rate constant determined by equilibrium dialysis in the donor compartment (1.98/h) agrees with that determined by microdialysis (1.85/h) when the resistance of the equilibrium dialysis membrane with associated first-order rate constant of transfer of 0.42/h is taken into account. Release profiles of 5-FU from a number of different liposome and microsphere formulations were determined. The results indicate that a convenient and reproducible characterization of drug release from various liposome and microsphere formulations is readily obtainable by microdialysis.

Solubilization of cationic drugs in lung surfactant

PURPOSE

The association of hydrophobic, cationic drugs with lung surfactant was determined to assess the pharmacokinetic implications on drug disposition and retention in the lung.

METHODS

The distribution coefficients, K, were determined at 25 and 37 degrees in normal saline solution buffered at pH 7.4 for a series of structurally related, cationic drugs. Drugs were dispersed into lung surfactant, equilibrated, and then centrifuged to separate the aqueous phase from the surfactant pellet. Drug concentrations in the supernatant and pellet were determined following dilution using spectrophotometric assays. In addition, the apparent acid dissociation constant of quinacrine in the presence and absence of surfactant was determined by measuring the pH-dependent absorption spectra. The effect of stereochemistry on the distribution of drugs into surfactant was examined with (R)- and (S)-propranolol.

RESULTS

The mole fraction distribution coefficients for amitriptyline, promethazine, promazine, ethopropazine, imipramine, R-propranolol, and S-propranolol at 25 degrees C were 6,560 +/- 500, 28,400 +/- 1,500, 12,100 +/- 840, 5,480 +/- 330, 4,490 +/- 250, 8,680 +/- 260, 8,190 +/- 530, respectively. At 37 degrees C, the distribution coefficients were generally smaller indicating a significant exothermic heat of transfer for these solutes from aqueous solution to the lung surfactant. The pKa of quinacrine was 7.43 +/- 0.04 in aqueous solution and was shifted to 7.62 +/- 0.06 in the presence of lung surfactant. From this shift, the double layer potential for quinacrine-lung surfactant was estimated to be -0.012 V assuming a dielectric constant equivalent to that of water.

CONCLUSIONS

Cationic drugs have very favorable distributions from an aqueous solution to the lipid phase of lung surfactant. The transfer process generally has both a large entropic and enthalpic contribution. The latter thermodynamic aspect may be related to the charge interaction between the solute and the negatively charged surfactant. Finally, no significant effect of stereochemistry was evident with the distribution of (R)- and (S)-propranolol.

Chemoprevention of cancer of the upper respiratory tract of the Syrian golden hamster by aerosol administration of difluoromethylornithine and 5-fluorouracil

Research aimed at identifying effective chemopreventive compounds active against carcinogenesis of the upper respiratory tract (URT) has been largely unsuccessful. We are addressing this problem by efforts at agent identification and by using aerosol delivery. Two compounds, difluoromethylornithine (DFMO) and 5-fluorouracil (5-FU) were investigated. DFMO is an irreversible inhibitor of ornithine decarboxylase, an enzyme important in cell proliferation. It has been used widely by oral administration for chemoprevention. 5-FU is a pyrimidine analog used extensively as a chemotherapeutic agent. It is generally administered i.v. and can cause considerable toxicity. However, aerosol administration for therapy of lung cancer in humans has been reported to be without adverse effects (Tatsumura et al., Br J Cancer 1993;68:1146-9). The experimental model used herein entailed six intratracheal administrations of methylnitrosourea (MNU) to hamsters. Each of the test agents was started about 1 week after MNU and was continued for 29 weeks with DFMO. Infiltrating squamous cell carcinomas of the URT occurred in 92% of the controls and were reduced by 50% in animals receiving DFMO (P = 0.0001). The experiment with 5-FU was of shorter duration being terminated 20 weeks after MNU. Thirty percent of the controls had infiltrating carcinomas and were reduced by 60% in animals receiving 5-FU (P = 0.0274). Both compounds resulted in a significant increase in the percent of cancer-free animals. These two agents may have selected use in subjects at high risk of cancer of the URT.

Effect of chemopreventive agents on separate stages of progression of benzo[ ]pyrene induced lung tumors in A/J mice

The effects of aerosol budesonide and dietary myo-inositol on progression of benzo[alpha]pyrene (B[alpha]P) induced carcinogenesis were studied in A/J mouse lung. First, we determined when to intervene in the carcinogenesis process by exposing several animals to B[alpha]P at 100 and 150 mg/kg of body wt. Groups of these animals were necropsied from 1 to 36 weeks post-carcinogen. The presence of different categories of lung tumors was noted over the 36 week time period. Hyperplasia first appeared approximately 6 weeks post-carcinogen followed by adenoma at 9 weeks, then by carcinoma at 26 weeks. From this temporal sequence we determined we could test for effects of preventive agents on progression to hyperplasia by intervening at 3 weeks, for effects on progression to adenoma by intervening at 6 weeks and for effects on progression to carcinoma by intervention at 12 weeks. Intervention at 3 weeks post-carcinogen with aerosolized budesonide delayed both hyperplasia and adenoma formation. Once hyperplasia appeared in budesonide treated animals, however, it increased at the same rate as in control animals, indicating a delay in progression. Progression from adenoma to carcinoma was reduced when budesonide was given 12 weeks post-carcinogen. Dietary myo-inositol failed to suppress progression from adenoma to carcinoma when started 12 weeks post-carcinogen. In summary, budesonide is a chemopreventive agent that has inhibitory effects on B[alpha]P induced carcinogenesis of the lung in A/J mice at all stages of progression from hyperplasia formation to cancer.

Distribution and diffusion of sodium taurocholate and egg phosphatidylcholine aggregates in rat intestinal mucin

PURPOSE

The permeability of rat intestinal mucin (RIM) to sodium taurocholate/egg phosphatidylcholine (TC/PC)-mixed micelles has been investigated.

METHODS

The time dependence for the equilibration of TC/PC-mixed lipid micelles with isolated RIM was determined. Thereafter the distribution of TC/PC-mixed lipid micelles was assessed at low and high PC and intermicellar concentrations (IMC) and with different RIM concentrations. The equilibrium distribution of PC and TC was determined by analysis for phosphorus and by high-performance liquid chromatography, respectively, as well as by nuclear magnetic resonance spectroscopy. In addition, the diffusion coefficients of water, PC, and TC were measured by pulsed field gradient nuclear magnetic resonance spectroscopy. Two model solutes, phenylmethyltrimethylsilane (PTMS) and tetramethylsilyl-tetradeutero-proprionic acid (TSP), were added to the high PC, low IMC samples, and the diffusion coefficients were determined.

RESULTS

The time to reach equilibrium was 2 days for a system with a high intermicellar concentration of sodium taurocholate. At low PC concentrations, RIM had slightly higher PC concentrations relative to the control. In contrast, at high PC concentrations, RIM samples had lower PC concentrations. The concentration of TC was largely independent of mucin concentration. The water diffusivity was reduced proportionately to the concentration of RIM, and analysis indicated that about 150 g of water moved as a kinetic unit with each gram of mucin. The diffusion coefficients of PC were also reduced with increasing RIM concentration. The magnetization decay of TC did not always follow a monoexponential decay, reflecting the simultaneous diffusion and exchange among sites imparting different relaxation behavior on the TC. Magnetization decay curves were simulated and the diffusivity of TC in mucin was estimated. The diffusion coefficient of TSP was 10 times larger than that of PTMS in the presence of micelles and mucin.

CONCLUSIONS

RIM is highly hydrated, and dilute solutions have a minor exclusive effect on the high concentration of PC/TC micelles. At low concentrations of PC, there appears to be preferential association of the PC with the RIM. The permeability of mucin to solutes in the presence of bile salt mixed micelles critically depends on the degree of association of the solute with the micelle.

Analysis of the diffusion of bile salt/phospholipid micelles in rat intestinal mucin

The interaction of sodium taurocholate/egg phosphatidylcholine (TC/PC) micelles with mucin was determined to investigate the exclusion of lipids by mucus in the absorption process. The distribution of TC/PC was assessed at two intermicellar and three phospholipid concentrations with isolated, rat intestinal mucin (RIM) by dialysis. The diffusion coefficients were measured by NMR spectroscopy. At high [PC], RIM had lower [PC] relative to the control, while the concentration of TC was largely independent of mucin concentration. The PC diffusion coefficients were reduced in the presence of RIM. The magnetization decay of TC was compared with simulations to provide estimates of the monomeric diffusivity and exchange rate constant. The rate constants increased with increasing micelle concentration, and the free TC diffusion coefficient was reduced in the presence of mucin. Mucin has an exclusive effect on TC/PC mixed micelles that has been quantitatively determined through the use of diffusion measurements of dialyzed samples.

Ultrasonic nebulization system for respiratory drug delivery

An ultrasonic spray system was tested for the production of aerosols for ultimate use in the respiratory delivery of drug to animals. A Sono-Tek ultrasonic spray system was mounted on top of a baffle to entrain aerosol particles within the carrier gas. Solvent was removed from the aerosol cloud by passing the droplets through drying columns composed of either charcoal or silica. The efficiency of removing ethanol and water were determined by measuring the outflow concentrations. Sodium fluorescein and sodium cromolyn dissolved in water were tested, and the effect of the liquid flow rate and drug concentration entering the atomizer on the output, and particle size distribution, were determined by the filter capture method, and by cascade impactor, respectively. Similar studies were conducted with budesonide and indomethacin dissolved in ethanol. The theoretical count median size distribution was calculated and compared with the experimental values calculated from the observed mass median aerodynamic diameter. The output rate expressed as the mass of aerosol collected in unit time increased nearly proportionately with the liquid flow rate (0.18-0.7 ml/min) and with the concentration of drug (0.19-12 mg/ml) entering the nebulizer. The mean particle size increased with solute concentration, but not by liquid flow rate. The calculated count median diameters were dependent on the type of solvent, but were independent of solute. At the high dose of cromolyn, there was very good agreement between the theoretical and observed. At lower doses, the observed size was larger than predicted, which was also true for the ethanol soluble solutes. The system has the potential of providing a wide range of dose levels for testing of drug delivery to animals including high doses with a controlled and relatively narrow particle size distribution.

The absorption of retinoic acids from the gastrointestinal tract is dependent upon chemical structure

PURPOSE

The gastrointestinal permeability of a number of retinoic acids was determined in order to evaluate whether the gastrointestinal membrane was able to distinguish between retinoids in which the polyene chain was present in several different isomeric forms. In addition, the structure of the six-membered ring was varied in order to determine which portion of the molecule was most important for its recognition by the membrane. The role of bile salt micelle composition in the intestinal absorption of retinoids was also evaluated.

METHODS

In situ perfused rat intestinal segment preparations (= 78) were used, and the retinoids were each perfused at a concentration of approximately 1 microg/ml in either simple micelles of sodium taurocholate (10 mM) or mixed micelles of sodium taurocholate/egg phosphatidylcholine (10 mM/10 mM). The flow rate of the perfusate was either 0.1 or 0.35 ml/min.

RESULTS

For each retinoid, the mixed micelles were associated with a higher degree of retinoid uptake into the jejunal cells than were the simple micelles. In addition, the permeability was higher when the perfusate flow was greater, indicating that the aqueous boundary layer of the intestine contributes to the resistance to the disappearance of the retinoid from the intestinal lumen. Retinoid structure was also found to have a significant effect on the permeability in the mixed micelle systems at both low and high flow rates, but not with simple micelles. The structure of the six-membered ring was not a major determinant of the permeability. However, the permeability of the retinoids with the polyene chain in the 13-cis position was significantly greater than when the chain was all-trans or in the 9-cis position.

CONCLUSIONS

The isomeric position of the polyene chain and the presence of phospholipid in the micellar vehicle have a significant influence on the membrane transport of the retinoic acids.

Note: dissolution of aerosol particles of budesonide in Survanta, a model lung surfactant

The effect of a pulmonary surfactant extract from bovine lung, Survanta, on the dissolution rate of aerosol particles of budesonide was determined. Aerosol particles of budesonide were generated from an ethanol solution, dried, and collected by a cascade impactor for characterization or by a liquid impinger for dissolution experiments. Powder x-ray diffraction, differential scanning calorimetry, differential thermal analysis, and scanning electron microscopy were used to characterize the aerosol particles and starting material. No change in phase was detected, although the aerosol particles appeared to contain residual solvent. The dissolution rate of the aerosol particles in saline was low and variable. Survanta increased the extent of dissolution of budesonide in proportion to the added concentration, which was also verified by equilibrium solubilization studies. Survanta also increased rate of dissolution, in a manner similar to sodium dodecyl sulfate. Analysis of the concentration of budesonide following ultracentrifugation indicated that there is rapid equilibration of budesonide between the Survanta and aqueous phase. These results show that lung surfactant has the potential of enhancing the rate and extent of dissolution of drugs administered to the lung.

Interaction of bile salt and phospholipids with bovine submaxillary mucin

PURPOSE

The purpose of this study was to determine the distribution and diffusion of sodium taurocholate-phospholipid micelles with mucin in order to provide the foundation for understanding the transport of ingested fat and poorly water-soluble drugs through the intestinal mucous layer.

METHODS

Sodium taurocholate (NaTC) was dispersed with egg phosphatidylcholines (PC) to yield mixed micelles of a specific size and concentration. A preliminary study was conducted to determine the time required for equilibration of PC/TC micellar solutions with mucin. PC/TC micellar solutions were dialyzed against fixed and variable concentrations of bovine submaxillary mucin after which the concentration of PC and NaTC was measured by an assay for total phosphorus and by HPLC, respectively. In addition, a quantitative assay of TC and PC by NMR was developed and used to estimate the mobile fraction of lipids in the samples. Finally, pulsed-field gradient spin echo NMR self-diffusion measurements were made of the water, TC, and PC in the samples obtained from dialysis.

RESULTS

TC/PC micellar solutions achieved equilibrium with mucin in 7 days. Mucin did not affect the equilibrium concentration of PC or TC, except at high concentrations of mucin (5%), and then the effect was small. NMR quantitation was valid for PC and TC systems containing small micelles, but deviated significantly with systems containing large micelles. Mucin decreased the diffusivity of water and the phospholipids, but the effect was relatively small. Mucin dramatically affected the mobility of TC, which prevented a straightforward interpretation of the calculated diffusion coefficients.

CONCLUSIONS

Mucin has a minor effect on the equilibrium distribution of phospholipids and bile salts. However, lipids are readily accommodated by mucus, which can significantly increase the permeability of the mucous layer, particularly for poorly water-soluble drugs.

Drug solubilization in lung surfactant

The relative affinity of glucocorticosteroids for lung surfactant was determined for the purpose of identifying chemopreventive agents with a high therapeutic index for lung cancer. The aqueous solubility and the extent of solubilization in Survanta, a native extract of bovine lung, of budesonide, triamcinolone acetonide, dexamethasone, and flunisolide were determined as a function of temperature by a dialysis technique. The aqueous solubilites at 37 degrees C were 19.6, 35.8, 104 and 120 microg/ml for the above listed compounds, respectively. The temperature dependence of the solubilities was modest consistent with the hydrophobic properties of the steroids. The amount of drug in solution was significantly enhanced in the presence of Survanta with solubilization ratios of 0. 019, 0.023, 0.014, and 0.02 microg drug dissolved per microg of Survanta phospholipid, respectively. In addition, the extent of solubilization also generally increased with temperature, although the phase transition of the surfactant lipid appeared to complicate the functional relation between temperature and solubilization. These results show that there is enhanced solubilization of glucocortosteroids by lung surfactant which is secreted by the cancer susceptible type II cells of the lung.

Chemoprevention of pulmonary carcinogenesis by brief exposures to aerosolized budesonide or beclomethasone dipropionate and by the combination of aerosolized budesonide and dietary myo-inositol

This investigation is part of an effort to develop chemoprevention for carcinogenesis of the lung. It focuses on the efficacy of low doses of synthetic glucocorticoids administered either as single agents or in combination with a second compound, myo-inositol. Glucocorticoids are potent inhibitors of carcinogenesis. The use of low doses is important to avoid potential side-effects. The synthetic glucocorticoid budesonide, administered by aerosol for 20 s three times a week, was studied to determine its effects on benzo[a]pyrene-induced pulmonary adenoma formation in female A/J mice. Two dose levels were employed, 10 and 25 microg/kg body wt. The lower dose produced a 34% reduction in lung tumor formation and the higher dose level a 60% reduction in lung tumors. In additional groups of mice, the effects of 0.3% myo-inositol added to the diet was found to reduce pulmonary tumor formation by 53%. The two agents given in combination resulted in a greater inhibition of lung tumor formation than either by itself. Budesonide at 10 microg/kg body wt plus 0.3% myo-inositol reduced the number of tumors by 60% and budesonide at 25 microg/kg body wt plus 0.3% myo-inositol reduced lung tumor formation by 79%. To determine whether a glucocorticoid other than budesonide would have inhibitory effects in this experimental model, beclomethasone dipropionate administered by aerosol for 20 s three times a week was studied as a single agent and showed almost identical inhibitory properties to budesonide. The doses of the glucocorticoids calculated on a daily basis are within the range of those used widely for control of chronic allergic respiratory diseases in the human. The capacity of low doses of inhaled glucocorticoids to prevent pulmonary neoplasia and the enhancement of this preventive effect by myo-inositol, an essentially non-toxic compound, are findings that should encourage further work to evaluate the applicability of these agents to the prevention of neoplasia of the lung in the human.

Analysis of a diffusion dryer for the respiratory delivery of poorly water soluble drugs

PURPOSE

The purpose of this study was to analyze a diffusion dryer as a means to remove organic solvents from aerosol particles of poorly water soluble drugs.

METHODS

Aerosols of methanol, ethanol, and ethyl acetate were generated with an ultrasonic nebulizer, and inflow to outflow concentration ratio of vapor in a annular charcoal column was determined as a function of time by gas chromotography at two to four different airflow rates. In addition, the particle transmission efficiency was determined with an ethanol solution of the test compound, budesonide. The results were analyzed with equations originally developed for assessing the loss of drug from intravenous tubing along with independent measures of the adsorption isotherm of the vapors onto charcoal.

RESULTS

Aerosol production was relatively constant with time, and the transmission of solid particles through the column occurred with efficiency nearing 100%. The inlet to outlet vapor concentration ratio was adequately described by a model of three resistances in series composed of the inner tube, the screen mesh, and the charcoal bed.

CONCLUSIONS

The diffusion dryer was found to be satisfactory for the removal of methanol, ethanol, and ethyl acetate and the efficiency may be assessed from the adsorption isotherms on charcoal and the geometry of the dryer.

Chemoprevention of pulmonary carcinogenesis by aerosolized budesonide in female A/J mice

This investigation is part of a continuing effort to develop effective chemoprevention for carcinogenesis of the lung. The present study explores the use of aerosol administrations for this purpose. The agent selected for initial study was the synthetic glucocorticoid budesonide. This selection was based on previous work in which budesonide added to the diet was found to inhibit pulmonary adenoma formation in female A/J mice. However, high dose levels were required, i.e., of the order of 300 microg/kg, of body weight [L. W. Wattenberg and R. D. Estensen, Carcinogenesis (Lond.), 18: 2015-2017, 1997]. For aerosol administration of budesonide, a nose-only technique has been developed that entails nebulization of the compound dissolved in ethanol and subsequent stripping off of the solvent (less than 3 microl ethanol/liter of air remaining at the site of inhalation). The budesonide particles produced by the apparatus had a mass median aerodynamic diameter of less than 1 microm. An experiment has been carried out in which the inhibitory effects of aerosolized budesonide, given for 1 min six times a week, were studied. Concentrations of budesonide of 26, 81, and 148 microg/liter of air (calculated doses of 23, 72, and 126 microg/kg of body weight) were used. The aerosols were started 1 week after three oral administrations of benzo(a)pyrene (2 mg/20 g of body weight) to female A/J mice. All three doses of budesonide resulted in more than 80% inhibition of pulmonary tumor formation compared to the aerosol control and 90% or greater compared to mice not exposed to aerosol. The difference in inhibition is due to the aerosol procedure itself, which produces a reduction in tumor formation. A decrease in splenic weight (evidence of a systemic effect) occurred at all doses of budesonide. To the best of our knowledge, this is the first published effort at the use of aerosol administration to prevent neoplasia of the respiratory tract. The results of the present study show that administration of a potential chemopreventive agent by aerosol at a low dose can inhibit the occurrence of pulmonary carcinogenesis in female A/J mice.

Ionization and solubilization of 4 alkyl benzoic acids and 4 alkyl anilines in sodium taurodeoxycholate solutions

PURPOSE

The aqueous solubility and the extent of solubilization and ionization constant in sodium taurodeoxycholate (NaTDC) solutions of a series of benzoic acid and aniline derivatives were measured as a basis to characterize and thereby help predict the nature of the interaction of drugs with bile aggregates.

METHODS

The aqueous solubility and the solubilization of two series of compounds, 4-alkyl benzoic acids and 4-alkyl anilines, was measured as a function of NaTDC in 0 and 150 mM NaCl. The ionization constants were determined in water and in 50 mM NaTDC at sodium chloride concentration of 0, 75 and 150 mM by spectrophotometric titration. The diffusion coefficients of NaTDC and the solutes were measured by pulsed-field gradient spin echo NMR spectroscopy.

RESULTS

The aqueous solubilities decreased with increasing alkyl chain length in both series, and the aniline derivatives had larger solubilities than the benzoic acid derivatives. The number of moles of solute solubilized per mole of bile salt ranged from 0.17 to 0.31 for the benzoic acid derivatives and from 1.3 to 3.0 for the aniline derivatives. The pKa values of the benzoic acid derivatives in the presence of NaTDC were higher relative to the controls, and the difference in the pKa (delta pKa,obs) increased with increasing chain length. With the aniline derivatives, the pKa values were also shifted to higher values in NaTDC relative to the control but only in the absence of salt. The presence of the solute caused a decrease in the diffusion coefficient of NaTDC, and the diffusion coefficients of the solutes decreased with increasing alkyl chain length. With the hexyl derivative, the diffusion coefficient of the solute was smaller than the diffusion coefficient of the bile salt. The chemical shift of the protons attached to carbon 18 and 19 of the salt were decreased to a greater extent in the presence of the solutes than the protons attached to carbon 26.

CONCLUSION

Both the solubilization and ionization behavior of solutes were affected by the presence of bile salt aggregates. The surface potential and effective polarity of NaTDC aggregates were found to be dependent on the alkyl chain length for these two homologous series of solutes. The solubilization ratio was largely independent of alkyl chain length, but the unitary partition coefficient was dependent on both alkyl chain length as well as ionization state. The derivatives reduced the diffusivity of the micelles suggesting the formation of larger size aggregates and the solutes (hexyl derivatives) appear to favor association with the larger sized aggregates. The phenyl ring of the solutes appears to be oriented parallel to the plane of the steroid frame with preferential positioning near the hydrophobic rings.

Analysis of the solubilization of steroids by bile salt micelles

Bile salt mixed micelles play an important role in the emulsification, solubilization, and absorption of cholesterol, fats, and lipid-soluble vitamins. Studies have also revealed the importance of wetting and solubilization of drugs by the bile salts; however, the capacity and specificity of bile salt simple and mixed micelles for solubilization are still undefined. Thus, in this study the aqueous solubility and the extent of solubilization in bile salt micellar solutions of a series of steroids were determined. The melting point and enthalpy of fusion were measured to determine the ideal mole fraction solubility of each steroid. From the ideal mole fraction solubility and the observed solubility of each steroid, the activity coefficient of each steroid in solution was calculated with respect to the supercooled pure liquid as the standard state. In aqueous solution, the activity coefficients decreased with increasing number of hydroxyl groups on the steroids. This trend also occurred in the bile salt solutions, although the values of the activity coefficients were smaller by about three orders of magnitude. The stereochemical position of the hydroxyl groups influenced the rank order of the activity coefficients in the aqueous and micellar solutions. Incorporation of a fluoro or methyl group resulted in an increase in the activity coefficient, whereas aromatization of the A ring of the steroid frame markedly decreased the activity coefficient. The results for the aqueous solubility are consistent with the expected interaction of the functional groups with the polar environment. The relatively small activity coefficients observed with the micellar solutions result from the nonpolar environment of the aggregates. However, the similarity of the relationship between the activity coefficient and the number of hydroxyl groups in the aqueous and micellar solutions indicates the importance of polar interactions for solubilization. These results may provide new insight into the solubilization of steroids by bile salt micellar solutions and may provide a basis for predicting solubilization of other compounds by bile salt aggregates.

Human stratum corneum lipids have a distorted orthorhombic packing at the surface of cohesive failure

The cohesive strength of the stratum corneum is determined by its unique molecular composition and structural architecture. Whereas the structure responsible for corneocyte cohesion has been visualized at the microscopic level, the structure of the intercellular domain has not been characterized at the molecular level. In this report, new insight into the molecular architecture of the stratum corneum has been provided by atomic force microscopy and x-ray photoelectron spectroscopy. The surface layer of human stratum corneum was stripped, yielding the characteristic polygonal corneocytes shown by scanning electron microscopy as well as low resolution atomic force microscopy. With atomic force microscopy, the resolution was increased to allow imaging of the molecular architecture of the stratum corneum. With the high resolution image, a repetitive pattern characteristic of lipids in an ordered state was visualized. The lattice appeared to be orthorhombic where the lattice distances were about 5.5 and 9 angstroms, and the lattice angle was close to 90 degrees. The atomic composition of the superficial layers was 82% carbon, 16.5% oxygen, and 1.4% nitrogen as determined by x-ray photoelectron spectroscopy. The high nitrogen content compared to the calculated stratum corneum lipid composition and measured model lipid composition suggests that proteins were detected. In summary, although proteins are present, the fracture plane of the stratum corneum is largely composed of lipids that appear to have a distorted orthorhombic packing.

Solubilization of retinoids by bile salt/phospholipid aggregates

PURPOSE

The capacity and specificity of bile salt (BS)/ phosphatidylcholine (PC) mixed lipid aggregated systems in solubilizing four structurally related retinoids, etretinate, motretinid, fenretinide and N-ethyl retinamide, were determined.

METHODS

Excess solid drug was dispersed into sodium taurocholate (NaTC)/egg PC systems at lipid ratios of 10:0, 10:2 and 10 mM:10 mM in isotonic HEPES buffer, pH 6.5. A sensitive HPLC method was used to quantify the amount solubilized. The melting point and associated enthalpy change as well as the aqueous solubilities were also measured.

RESULTS

The retinoids had aqueous solubilities of less than 25 nM. The predicted aqueous solubility was less than 0.01 nM. The amount of retinoid in 10 mM NaTC was increased from three to four orders of magnitude relative to the aqueous solubility. Further increases in the amount solubilized were observed in the 10:10 mixed micelle dispersion. Fenretinide and N-ethyl retinamide were particularly well solubilized by BS and BS/PC aggregated systems which may be related to the presence of a cyclohexenyl ring.

CONCLUSIONS

The discrepancy between the observed and predicted aqueous solubility may be due to self-association of the retinoids. Micellar/aqueous distribution ratios appear to be dominated by the hydrophobic effect, although specific interactions also are important. In considering intestinal absorption, the large increase in solubilization with BS/PC micelles would be capable of dramatically increasing the bioavailability in spite of the smaller effective diffusivity of the solubilized retinoid.

Diffusivity of bile salt/phospholipid aggregates in mucin

PURPOSE

The objective of this study is to evaluate the effect of the mucous layer on the transport of the drug-solubilizing bile salt/phosphatidylcholine (BS/PC) aggregates.

METHODS

The self-diffusion coefficient of BS/PC aggregates in bovine submaxillary mucin (BSM) was measured by Fourier-transform pulsed-field gradient spin-echo (FT-PGSE) 1H NMR spectroscopy.

RESULTS

In spite of the complexity of the mixture, the FT-PGSE technique allowed the unambiguous determination of the diffusivity of PC and 1H2HO (HDO, natural abundance in D2O). With a series of BS/PC total lipid concentrations ranging from 1 to 7 g/dl, a progressive decrease in the effective diffusivity of HDO was observed with an increase in the both the BSM and total lipid concentration. The effective diffusivity of PC decreased with increasing lipid concentrations in the presence of mucin, while in the controls it increased. After correcting the effective diffusivity of PC for the obstruction effect of mucin, the size of the BS/PC mixed micelle was assessed. It appears that PC associates with BSM resulting in a decrease in the available PC for micellization. This reduces the average size of the mixed micelle within the mucous layer.

CONCLUSIONS

The aggregation state of BS/PC micelle is altered by the presence of mucin which would have a direct impact on the transport of dietary lipid and solubilized drug through the aqueous boundary layer of the intestinal tract.

Retinoid absorption from simple and mixed micelles in the rat intestine

The absorption of three retinoid analogs etretinate (ET), acitretin (ETA), and motretinid (MOE) from two distinct micellar systems was studied in the rat intestine. Each of the three drugs was loaded into simple micelles consisting of 10 mM sodium taurocholate (NaTC) and mixed micelles consisting of 10 mM egg phosphatidylcholine (PC) and 10 mM NaTC. Following perfusion through the jejunum segments, both the fraction of drug disappearing from the segment and the permeability of the drug from the lumen into the gut wall (Peff) was greater with the mixed micelles as compared to the simple micelles. Perfusion flow rate had an influence on the Peff for ET and ETA. Similar trends as for the jejunum were seen in the ileum perfusions. The simultaneous uptake of PC and NaTC during the retinoid perfusions was monitored. There appeared to be a correlation between the Peff values for PC and that of the retinoids. The viability of the in-situ perfusion system was confirmed histologically. There is evidence to indicate that the permeability of the intestine is sensitive to subtle differences in the chemical structure of the retinoids.

Phase properties of mixtures of ceramides

Ceramides have been proposed to have a central role in the function of the stratum corneum. Ceramides also influence the phase properties of model skin lipid mixtures, but the relevance of this to the stratum corneum function is controversial. Because the stratum corneum contains several classes of ceramides, the type of ceramides used in model mixtures of stratum corneum lipid lamellae may be important. Thus, the properties of alpha-hydroxy fatty acid containing (HFAC) and nonhydroxy fatty acid containing (NFAC) ceramides and their mixtures have been investigated. Ceramides were obtained by the conversion of purified bovine brain cerebrosides. Isolated, anhydrous HFAC underwent an endothermic solid to liquid transition at 92 degrees C. With hydration, an endothermic transition at 71.8 degrees C was observed which was accompanied by a reduction in the birefringence. The enthalpy increased from 66 to 89 J/g with a 20-d storage time. These thermal properties are very similar to those observed with hydroxy fatty acid containing cerebrosides. In contrast, anhydrous nonhydroxy fatty acid containing ceramides underwent a broad endothermic transition over the temperature range of 50-90 degrees C. When hydrated, the initial endothermic transition was interrupted by an exothermic transition that was followed immediately by a second endothermic transition. During these thermal changes, there was a loss of birefringence, and with completion of the second endothermic transition, a nonbirefringent liquid was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Thermotropic phase properties of the hydroxyceramide/cholesterol system

The interaction of cholesterol with ceramides containing alpha-hydroxy fatty acyl chains (hydroxyceramides) has been studied as a foundation for characterizing the lipid bilayers of the stratum corneum. A relatively large quantity of cerebrosides was obtained from bovine brain and converted to ceramides through removal of the carbohydrate side chain. The ceramides were separated based on the absence or presence of hydroxy fatty acyl chains. The lyophilized hydroxyceramides showed a broad melting region at 92 degrees C. Hydroxyceramides dispersed in water produced a relatively narrow, thermotropic transition at 75 degrees C. The effect of cholesterol on this thermotropic phase transition of hydroxyceramides was determined by differential scanning calorimetry. With respect to the main transition, cholesterol caused a broadening of the phase transition at relatively low levels as well as a decrease in the peak transition temperature. The presence of cholesterol at levels in excess of 7 wt% gave rise to an additional low-temperature transition at 55 degrees C. Upon immediate rescanning, this transition was exothermic, but with increasing incubation time the area under the excess heat capacity curve as a function of temperature became smaller. After two days or more, the transition observed was endothermic. At cholesterol levels between 40 and 50 wt%, multiple peaks were observed. From comparisons with related systems, the cooperative thermal transitions of hydroxyceramides with cholesterol are suggested to result from changes in hydrogen bonding or be due to phase separation. The composition of isolated brain ceramides is being compared with that reported for the stratum corneum.