Impaired perfusion and capillary dysfunction in prodromal Alzheimer's disease

INTRODUCTION

Cardiovascular disease increases the risk of developing Alzheimer's disease (AD), and growing evidence suggests an involvement of cerebrovascular pathology in AD. Capillary dysfunction, a condition in which capillary flow disturbances rather than arterial blood supply limit brain oxygen extraction, could represent an overlooked vascular contributor to neurodegeneration. We examined whether cortical capillary transit-time heterogeneity (CTH), an index of capillary dysfunction, is elevated in amyloid-positive patients with mild cognitive impairment (prodromal AD [pAD]).

METHODS

We performed structural and perfusion weighted MRI in 22 pAD patients and 21 healthy controls.

RESULTS

We found hypoperfusion, reduced blood volume, and elevated CTH in the parietal and frontal cortices of pAD-patients compared to controls, while only the precuneus showed focal cortical atrophy.

DISCUSSION

We propose that microvascular flow disturbances antedate cortical atrophy and may limit local tissue oxygenation in pAD. We speculate that capillary dysfunction contributes to the development of neurodegeneration in AD.

A review of the development of Respimat Soft Mist Inhaler

Respimat Soft Mist Inhaler (SMI) is a new generation inhaler from Boehringer Ingelheim developed for use with respiratory drugs. The device functions by forcing a metered dose of drug solution through a unique and precisely engineered nozzle (the uniblock), producing two fine jets of liquid that converge at a pre-set angle. The collision of these two jets generates the soft mist. The soft mist contains a high fine particle fraction of approximately 65 to 80%. This is higher than aerosol clouds from conventional portable inhaler devices, such as pressurised metered dose inhalers (pMDIs) and dry powder inhalers (DPIs). In addition, the relatively long generation time of the aerosol cloud (approximately 1.5s) facilitates co-ordination of inhalation and actuation--a major problem with pMDIs. These features, together with the slow velocity of the soft mist, result in larger amounts of the drug reaching the lungs and less being deposited in the oropharynx compared with either pMDIs or DPIs. Generation of the soft mist from Respimat SMI is purely mechanical, so propellants are not necessary. The innovative design of Respimat SMI, using water-based drug formulations, ensures patients receive consistent and reliable doses of the drug with each actuation. The device was initially tested in scintigraphic lung deposition studies and produced encouraging results when compared with the chlorofluorocarbon-based pMDI (CFC-MDI). Subsequent clinical studies have confirmed that Respimat SMI is effective and safe in delivering bronchodilators to patients with asthma or chronic obstructive pulmonary disease.

Inhaled ATP causes mucin release from goblet cells of intact rats

Secretion of mucins from airway epithelial cells has been studied almost exclusively using in vitro cell culture systems. Our understanding of in vivo secretion is greatly limited due to the unavailability of both suitable model systems and adequate assays. It has been reported that ATP induces mucin release from the cultured primary tracheal surface epithelial cell, but there is no clear demonstration of the effect of ATP on mucin release in vivo, which is important to understand the mechanism of mucin release in vivo and also to devise means for regulation of mucin release. The objective of this experiment was to see if inhaled ATP could stimulate airway mucin release in intact rats using both enzyme-linked immunosorbent assay (ELISA) and immunohistochemistry. The results were: (1) a new monoclonal antibody (mAbRT03) developed against purified rat mucins specifically recognized high-molecular-mass mucins; (2) ELISA results with conventional gel-filtration assay results are virtually superimposable; (3) inhalation of ATP in intact rats resulted in a dose-independent increase in the amount of mucins in the tracheal lavage fluid with a concomitant decrease in the number of mucin-positive cells in the trachea. We conclude that extracellular ATP can stimulate mucin release from the airway in vivo, and the present rat inhalation system combined with ELISA of the airway secretions should serve a useful model for studying the pharmacology of airway mucin secretion in vivo.