Induction of calcium-independent nitric oxide synthase by allergen challenge in sensitized rat lung in vivo.

There is some evidence that nitric oxide synthase (NOS) is induced in the lungs of patients with allergic asthma, but the mechanism of this is not understood. The aim of the present study was to investigate whether the levels of NOS in rat lung could be altered by exposure of the animals to aerosols of allergen (ovalbumin). Brown-Norway rats were actively sensitized to ovalbumin, raising a mixed IgE/IgG antibody response. The levels of total and calcium-independent NOS in lung tissue homogenates were elevated at 6 h and 24 h after allergen exposure in sensitized rats but not in unsensitized rats. The induction was not due to contaminating lipopolysaccharide in the challenge solution. The allergen-induced increase in calcium-independent lung NOS was inhibited by pretreatment of the animals with the corticosteroid betamethasone (3 mg kg-1 i.p., 1 h prior to and 6 h after allergen). These results show that allergen challenge induces calcium-independent NOS in the lungs of sensitized rats, a process inhibited by an anti-inflammatory corticosteroid.     

Distribution of mutations in the PEX gene in families with X-linked hypophosphataemic rickets (HYP)

Mutations in the PEX gene at Xp22.1 (phosphate-regulating gene with homologies to endopeptidases, on the X-chromosome), are responsible for X-linked hypophosphataemic rickets (HYP). Homology of PEX to the M13 family of Zn2+ metallopeptidases which include neprilysin (NEP) as prototype, has raised important questions regarding PEX function at the molecular level. The aim of this study was to analyse 99 HYP families for PEX gene mutations, and to correlate predicted changes in the protein structure with Zn2+ metallopeptidase gene function. Primers flanking 22 characterised exons were used to amplify DNA by PCR, and SSCP was then used to screen for mutations. Deletions, insertions, nonsense mutations, stop codons and splice mutations occurred in 83% of families screened for in all 22 exons, and 51% of a separate set of families screened in 17 PEX gene exons. Missense mutations in four regions of the gene were informative regarding function, with one mutation in the Zn2+-binding site predicted to alter substrate enzyme interaction and catalysis. Computer analysis of the remaining mutations predicted changes in secondary structure, N-glycosylation, protein phosphorylation and catalytic site molecular structure. The wide range of mutations that align with regions required for protease activity in NEP suggests that PEX also functions as a protease, and may act by processing factor(s) involved in bone mineral metabolism.