The Lung, an Organ for Absorption?

A Breath of Fresh Air: Perspectives on Inhaled Nutrients and Bacteria to Improve Human Health

We propose that the human respiratory system and olfactory pathways sequester airborne nutrients (vitamins, fatty acids, and trace minerals) that are beneficial for health, which we term "aeronutrients." In addition, airborne bacteria, termed "aeromicrobes," have the potential for positive health effects by improving species diversity in the microbiotas of the respiratory and gastrointestinal tracts. These concepts have implications for people living in urban areas or those who have limited access to nature, such as astronauts exposed for long periods to highly filtered air that may be depleted of aeronutrients and aeromicrobes. The possibility that fresh air contributes to human nutrition and health may stimulate a re-evaluation of guidelines pertaining to nutrition and access to natural environments, and will open new avenues of scientific enquiry.

In vivo lung deposition and sub-acute inhalation toxicity studies of nano-sized alendronate sodium as an antidote for inhaled toxic substances in Sprague Dawley rats

INTRODUCTION

Alendronate sodium is a bisphosphonate agent used for the treatment of osteoporosis and other bone diseases. It has a strong chelating property to bind or, to some extent, counteract the effects of substances, such as magnesium, calcium citrate, ferrous fumarate, carbonyl iron, as well as the zinc gluconate, sulfate and acetate salts. The objective of the present study was to evaluate lung deposition and sub-acute inhalation toxicity of the alendronate sodium respiratory formulation.

METHODS

Particle dimension of aerosols of alendronate was measured using a particle size analyzer. Alendronate was radiolabeled using Technetium-99m for in vitro and in vivo biodistribution studies. Alendronate at doses, 0.5%, 1.0%, and 1.5% in ethanol-saline respiratory formulation was inhaled twice a day up to 5 weeks for inhalation toxicity investigations. Hematological, biochemical and lung toxicity biomarkers in bronchoalveolar lavage (BAL) fluid were determined at the end of the experiment. Histopathological analysis of lung tissues was carried out to observe any microscopic changes

RESULTS

Particle size analysis revealed the size within 300-500nm. Anderson cascade impactor results showed that the particles exhibited higher respirable fraction (55.52%) with MMAD of 4.66μm. Hematology, serum biochemistry and lung toxicity biomarkers in BAL fluid performed in the sub-acute toxicity studies indicated no adverse effects of alendronate sodium inhalation except for a significant increase in cholesterol levels and marginal increase in BAL fluid protein. At autopsy, no histopathological changes in major organs were observed.

CONCLUSIONS

The lung deposition and safety evaluation data observed from these studies suggested that aerosolized nanosized alendronate sodium by the inhalation route could be a new and promising route of administration as an antidote to radioactive substances through an increase in the bioavailability of the drug as well as a decrease in side effects on systemic delivery.

Organic cation transporters in the blood-air barrier: expression and implications for pulmonary drug delivery

Studies concerning the impact that hepatic, renal and intestinal transporters have on drug disposition have been frequently reported in the literature. Surprisingly, however, little is known regarding the distribution and function of drug-transporter proteins of the lung epithelium. Many drugs (delivered to the lung) have a net positive charge and, thus, are potential substrates of organic cation transporters; currently marketed compounds (e.g., bronchodilators), as well as novel drug candidates in development, are such substrates. It is the aim of this review to summarize the current state of organic cation-transporter expression analysis in the lung and in in vitro models of bronchial and alveolar barriers. Moreover, activity of selected transporters in lung epithelium in situ and in vitro will be highlighted, and their potential role in pulmonary drug disposition will be addressed. One example included here is the transporter-dependent absorption of beta2-agonists in respiratory epithelial cells.

Formulation and in vivo evaluation of sodium alendronate spray-dried microparticles intended for lung delivery

Spray-dried powders for lung delivery of sodium alendronate (SA) were prepared from hydroalcoholic solutions. Formulations display geometric particle size below to 12 μm and spherical shape associated to a hollow structure. The addition of leucine and ammonium bicarbonate leads to porous particles with rough surfaces. The tapped density ranges from 0.016 to 0.062 g/cm(3), decreasing with the increase of the leucine concentration. For all formulations, the calculated aerodynamic diameters are lower than 5 μm. The in vitro aerodynamic evaluation shows that all powders present a high emitted fraction of 100%, a fine particle fraction ranging from 34.4% to 62.0% and an alveolar fraction ranging from to 23.7% to 42.6%. An optimized sample was evaluated regarding sodium alendronate acute pulmonary toxicity and lung bioavailability. The bronchoalveolar lavage study shows that the intratracheal administration of sodium alendronate dry powder and sodium alendronate aqueous solution do not induce significant increases of lung toxicity indicators as compared with the positive control. Moreover, the intratracheal administration of sodium alendronate dry powder results in a 6.23 ± 0.83% bioavailability, a 3.5-fold increase as compared to oral bioavailability. Finally, these results suggest that sodium alendronate pulmonary delivery could be a new and promising administration route.

The possible role of ammonia toxicity on the exposure, deposition, retention, and the bioavailability of nicotine during smoking

A complete and rigorous review is presented of the possible effect(s) of ammonia on the exposure, deposition and retention of nicotine during smoking and the bioavailability of nicotine to the smoker. There are no toxicological data in humans regarding ammonia exposure within the context of tobacco smoke. Extrapolation from occupational exposure of ammonia to smoking in humans suggests minimal, non-toxicological effects, if any. No direct study has examined the effect of the ammonia on the total rate or amount of nicotine reaching the arterial bloodstream or brains of smokers. Machine-smoking methods have been reported which accurately quantify >99% of the nicotine in mainstream (MS) smoke for a wide variety of commercial and test cigarettes, including a series of experimental cigarettes having a range in MS smoke ammonia yields using the US Federal Trade Commission (FTC) protocol. However, the actual exposure of nicotine to smokers depends on their own smoking behavior. The nicotine ring system is relatively thermally stable. Protonated nicotine forms nicotine which evaporates before the nicotine ring system decomposes. The experimental data indicate that neither nicotine transfer from tobacco to MS smoke nor nicotine bioavailability to the smoker increases with an increase in any of the following properties: tobacco soluble ammonia, MS smoke ammonia, "tobacco pH" or "smoke pH" at levels found in commercial cigarettes. Gas phase nicotine deposits primarily in the mouth and upper respiratory tract. To the extent that ammonia increases the deposition of nicotine in the buccal cavity and upper respiratory tract during smoking, the total rate and amount of nicotine into the arterial bloodstream and to the central nervous system will decrease. Charged nicotine analogues are actively transported in a number of tissues. This active transport system appears to be insensitive to pH and the form of nicotine in the biological milieu, suggesting that protonated nicotine may be a substrate for active transport. Neither "smoke pH" of commercial cigarettes nor "smoke pHeff" nor the fraction of non-protonated nicotine in tobacco smoke particulate matter are useful, practical smoke parameters for providing understanding or predictability of nicotine bioavailability to smokers. Greater than 95% of both ammonia and nicotine are in the gas phase of environmental tobacco, and both are likely to deposit in the buccal cavity and upper respiratory tract following exposure.

P-glycoprotein (MDR1) functional activity in human alveolar epithelial cell monolayers

The distribution of the P-glycoprotein (P-gp/MDR1) efflux transporter at mucosal barriers has defined it as a functionally important element in limiting drug absorption into the systemic circulation. However, little is known about the distribution and functionality of P-gp/MDR1 in the human lung. Here, the presence of P-gp/MDR1 was investigated immunohistochemically in distal human lung tissue and at mRNA and protein levels in human alveolar epithelial cells (hAEpC) in primary culture. We studied the presence and activity of P-gp/MDR1 in hAEpC monolayers by Western blotting, by immunofluorescence microscopy and by conducting bi-directional transport studies employing a P-gp substrate (rhodamine 123) with and without a P-gp inhibitor (verapamil). The flux of fluorescein sodium was also examined as a paracellular transport marker. Alveolar tissue specimens showed P-gp localised at the luminal membranes of type I pneumocytes. Reverse transcription-polymerase chain reaction revealed the presence of mRNA encoding for P-gp/MDR1 in freshly isolated (i.e. type II) hAEpC and in monolayers of hAEpC cultured for 8 days (i.e. type I-like morphology). At the protein level, P-gp could be detected in hAEpC monolayers after 8 days in culture but not in freshly isolated type II pneumocytes. The flux of rhodamine 123 across hAEpC monolayers on day 8 in culture exhibited net secretion, which disappeared in the presence of verapamil. Fluorescein sodium fluxes showed no distinct directionality. Our findings indicate that P-gp is functionally active in the human alveolar airspace and that hAEpC monolayers might provide a suitable in vitro model for studying P-gp function mechanistically in the distal human lung.