Nebulization and selective deposition of LTD4 in human lungs

In vitro and in vivo local tolerability of a synergistic anti-tuberculosis drug combination intended for pulmonary delivery

A drug combination, vancomycin (VAN) plus tetrahydrolipstatin (THL), has demonstrated an effective synergistic action in vitro against Mycobacterium tuberculosis (Mtb). The poor oral bioavailability of VAN and THL and the predominant tropism of Mtb infection to the lungs make their pulmonary administration very attractive. To evaluate their local tolerability, bronchial cells, alveolar cells and monocytes were exposed to concentrations around and above their minimal inhibitory concentration (MIC). The VAN had no inhibitory activity on the tested human cell lines, even at a concentration 125 times higher than its MIC, whereas the THL, alone or in combination with VAN, presented a cytostatic action. Monolayer epithelium showed no significant irreversible damage at concentrations up to 100 times the combination MIC. BALB/cAnNRj mice exposed to concentration of 50 times the combination MIC delivered endotracheally 3 times a week for 3 weeks showed no clinical signs or significant weight loss. The increase of proinflammatory biomarkers (i.e., IL-1, IL-6, TNF-α and proportion of inflammatory cells) and cytotoxicity in bronchoalveolar lavage fluid (BALF) were non-significant. Lung histopathology did not show significant tissue damage. The VAN/THL combination at doses up to 50 times the combination MIC is found to be thus well tolerated by pulmonary route. This study is a promising result and encouraging further investigations of pulmonary administration of VAN/THL combination as dry powder for anti-tuberculosis treatment.

Selective deposition of inhaled aerosols to mechanically ventilated rabbits

We have studied selective deposition of tracer aerosols to specific sites in airways and peripheral regions of the rabbit lung by varying droplet size and breathing pattern. The different breathing patterns were controlled by a Servo Ventilator 900C and different droplet sizes (polydisperse) were generated by an air jet nebulizer (MA2) using two types of impactor vessels (MMD 2.3 and 4.1 microns). Three tracer aerosols were evaluated; Evans blue dye, 99mTc-DTPA and monodisperse fluorescent polylatex spheres (PLS). When we combined large droplets with "rapid-shallow" breathing (central deposition mode, CDM), 30% of the aerosol was deposited in the central airways. When small droplets were combined with "deep-slow" breathing (peripheral deposition mode, PDM) 60% was deposited in the peripheral part of the lung. The different detection techniques showed similar results but gave complementary information. Since detection of the radiolabelled aerosol was more sensitive than the other methods, less aerosol could be given allowing a more precise evaluation of the deposition, both from the macro autoradiographic images as well as from the well counter measurements. In order to investigate how far into the lung periphery the aerosol could be detected, we used PSL microspheres. PLS could be detected in the alveolar region by a fluorescent light microscope. However, a complete selectivity can not be obtained by aerosol delivery. The different technique used to reach selective deposition, showed that it is only possible to deposit the aerosol either more to the central or more to the peripheral parts of the respiratory tract in small subjects.

Leukotrienes as a target in asthma therapy

Asthma is a chronic inflammatory condition characterised by bronchial hyper-responsiveness and reversible airways obstruction. Research has demonstrated that these effects are mediated by a wide range of compounds. In the last decade leukotrienes have been identified as products of arachidonic acid metabolism. Their effects mimic the pathological changes seen in asthma both in vitro and in vivo. Further research has demonstrated increased production of leukotrienes both during episodes of asthma and in patients with stable asthma. The demonstration that leukotrienes have proinflammatory biological properties relevant to the pathogenesis of asthma has stimulated the development of many potential therapeutic compounds to block these actions. Early studies in laboratory-induced asthma in human volunteers have shown the efficacy of some of these compounds. They have been shown to attenuate the bronchoconstriction caused by allergen challenge, exercise, aspirin and exposure to cold air. Most encouraging of all have been recent placebo-controlled studies in clinical asthma where significant improvements in terms of spirometry, symptoms and beta 2-agonist use have been demonstrated. Leukotriene receptor antagonists and synthesis inhibitors are the first mediator antagonists to have been shown to be effective in treating clinical asthma and as such represent one of the most interesting new classes of antiasthma drugs in development at present.