Airway inflammation in subjects with gastro-oesophageal reflux and gastro-oesophageal reflux-related asthma

STUDY OBJECTIVES

Asthma and gastro-oesophageal reflux (GER) are both characterized by airway inflammation.

DESIGN

The purposes of this work were (i) to study airway inflammation in patients troubled by gastro-oesophageal reflux (GER) and GER associated with asthma, (ii) to ascertain whether GER can aggravate asthma by exacerbating the pre-existing airway inflammation and oxidative stress and (iii) to establish the validity of analysing breath condensate and induced sputum when studying the airways of subjects affected by GER. PATIENT S AND METHODS: We enrolled 14 patients affected by mild asthma associated with GER (40 +/-12 years), nine with mild but persistent asthma (39 +/- 13 years), eight with GER (35 +/- 11 years) and 17 healthy subjects (37 +/- 9 years). Sputum cell counts and concentrations of interleukin-4 (IL-4), IL-6 and 8-isoprostane were measured in breath condensate and supernatant.

MEASUREMENTS AND RESULTS

GER-related asthma is characterized by an eosinophilic inflammation, as determined by elevated concentrations of IL-4 in breath condensate and sputum supernatant, and by sputum cell analysis. GER alone presents a neutrophilic pattern of inflammation when determined by elevated concentrations of IL-6 in sputum cell analysis. A concomitant increase has been found in 8-isoprostane in GER associated (or not associated) with asthma.

CONCLUSIONS

We conclude that GER is characterized by a neutrophilic airway inflammation and by increased oxidative stress. GER does not however aggravate pre-existing airway inflammation in asthma patients. Determinations of inflammatory and oxidant markers in the breath condensate of subjects with GER reflect these measured in the induced sputum.

Beta-secretase processing of the beta-amyloid precursor protein in transgenic mice is efficient in neurons but inefficient in astrocytes

Alzheimer's disease is characterized by the extracellular deposition of beta-amyloid peptide (Abeta) in cerebral plaques and evidence is accumulating that amyloid is neurotoxic. Abeta is derived from the beta-amyloid precursor protein (APP). Proteolytic processing of APP by the enzyme, beta-secretase, produces the N terminus of Abeta, and releases a secreted ectodomain of APP (beta-s-APP). To develop animal models for measuring beta-secretase activity in specific brain cells in vivo, we have targeted the expression of the full-length human APP to either neurons or astrocytes in transgenic mice using the neuron- specific enolase (NSE) promoter or a modified glial fibrillary acidic protein (GFAP) gene, respectively. The APP cDNAs expressed were mutated (KM to NL at 670/671) to encode amino acid substitutions that enhance amyloidogenic processing in vitro. Western analyses revealed abundant production of beta-s-APP in the brains of NSE-APP mice and enzyme-linked immunosorbent assay analyses showed production of Abeta in fetal primary mixed brain cultures and brain homogenates from these transgenic animals. Because the NSE promoter drives expression primarily in neurons, this provides in vivo evidence that the beta-secretase cleavage necessary for generation of beta-s-APP and Abeta is efficiently performed in neurons. In contrast, only little beta-s-APP was detected in brain homogenates of GFAP-APP mice, indicating that astrocytes show very little beta-secretase activity in vivo. This provides strong in vivo evidence that the major source of Abeta in brain is from neurons and not from astrocytes.

Increased amyloid-beta42(43) in brains of mice expressing mutant presenilin 1

Mutations in the genes encoding amyloid-beta precursor protein (APP), presenilin 1 (PS1) and presenilin 2 (PS2) are known to cause early-onset, autosomal dominant Alzheimer's disease. Studies of plasma and fibroblasts from subjects with these mutations have established that they all alter amyloid beta-protein (beta APP) processing, which normally leads to the secretion of amyloid-beta protein (relative molecular mass 4,000; M(r) 4K; approximately 90% A beta1-40, approximately 10% A beta1-42(43)), so that the extracellular concentration of A beta42(43) is increased. This increase in A beta42(43) is believed to be the critical change that initiates Alzheimer's disease pathogenesis because A beta42(43) is deposited early and selectively in the senile plaques that are observed in the brains of patients with all forms of the disease. To establish that the presenilin mutations increase the amount of A beta42(43) in the brain and to test whether presenilin mutations act as true (gain of function) dominants, we have now constructed mice expressing wild-type and mutant presenilin genes. Analysis of these mice showed that overexpression of mutant, but not wild-type, PS1 selectively increases brain A beta42(43). These results indicate that the presenilin mutations probably cause Alzheimer's disease through a gain of deleterious function that increases the amount of A beta42(43) in the brain.

Heat-shock induces abnormalities in the cellular distribution of amyloid precursor protein (APP) and APP fusion proteins

The heat shock or stress response may play a role in the pathogenesis of Alzheimer's disease. We conducted experiments to visualize microscopically the distribution of wild type amyloid precursor protein (APP) and the behavior of an APP deletion mutant under stress. This was achieved by heat-shock treatment of cells expressing fusion recombinant APP proteins tagged with secreted placental alkaline phosphatase (SEAP). The fusion proteins were cleaved and secreted in a manner similar to wild type APP in unstressed control cells. SEAP activity was detected by cytochemical methods within the cytoplasm in less than 10% of transfected unstressed cells. Heat shocked cells showed a striking difference from the control cells in that over 90% of the stressed cells displayed strong intracytoplasmic SEAP activity occurring with Golgi-like pattern and/or membranous distribution. The effects of heat shock were not due to a peculiar behavior of the clones and depended on the APP portion of the constructs. This study shows miscompartmentalization of APP under stress. Such cellular changes may bear important implications in the processing of APP.