Airway relaxation mechanisms and structural basis of osthole for improving lung function in asthma.

Overuse of ß2-adrenoceptor agonist bronchodilators evokes receptor desensitization, decreased efficacy, and an increased risk of death in asthma patients. Bronchodilators that do not target ß2-adrenoceptors represent a critical unmet need for asthma management. Here, we characterize the utility of osthole, a coumarin derived from a traditional Chinese medicine, in preclinical models of asthma. In mouse precision-cut lung slices, osthole relaxed preconstricted airways, irrespective of ß2-adrenoceptor desensitization. Osthole administered in murine asthma models attenuated airway hyperresponsiveness, a hallmark of asthma. Osthole inhibited phosphodiesterase 4D (PDE4D) activity to amplify autocrine prostaglandin E2 signaling in airway smooth muscle cells that eventually triggered cAMP/PKA-dependent relaxation of airways. The crystal structure of the PDE4D complexed with osthole revealed that osthole bound to the catalytic site to prevent cAMP binding and hydrolysis. Together, our studies elucidate a specific molecular target and mechanism by which osthole induces airway relaxation. Identification of osthole binding sites on PDE4D will guide further development of bronchodilators that are not subject to tachyphylaxis and would thus avoid ß2-adrenoceptor agonist resistance.

Triplet Excitation Transfer between Carotenoids in the LH2 Complex from Photosynthetic Bacterium Rhodopseudomonas palustris.

We have studied, by means of sub-microsecond time-resolved absorption spectroscopy, the triplet-excited state dynamics of carotenoids (Cars) in the intermediate-light adapted LH2 complex (ML-LH2) from Rhodopseudomonas palustris containing Cars with different numbers of conjugated double bonds. Following pulsed photo-excitation at 590 nm at room temperature, rapid spectral equilibration was observed either as a red shift of the isosbestic wavelength on a time scale of 0.6-1.0 mus, or as a fast decay in the shorter-wavelength side of the T(n)<--T(1) absorption of Cars with a time constant of 0.5-0.8 mus. Two major spectral components assignable to Cars with 11 and 12 conjugated double bonds were identified. The equilibration was not observed in the ML-LH2 at 77 K, or in the LH2 complex from Rhodobacter sphaeroides G1C containing a single type of Car. The unique spectral equilibration was ascribed to temperature-dependent triplet excitation transfer among different Car compositions. The results suggest that Cars of 11 and 12 conjugated bonds, both in close proximity of BChls, may coexist in an alpha,beta-subunit of the ML-LH2 complex.

[Effects of lead and selenium on telomere binding protein Rap1p, telomerase and telomeric DNA in Saccharomyces cerevisiae].

The effects on S.cerevisiae telomere binding protein Rap1p, telomerase and telomeric DNA by the lead (Pb), the selenium (Se) and Pb + Se were tested respectively in this study. Compared with the control S.cerevisiae after 100 gene rations, the mean telomere length shortened, Rap1p concentration was significantly lower and the secondary structure of Rap1p was disturbed, the telomerase activity was reduced in Pb treated cells. In Se treated cells, telomere length was significantly longer, and telomerase activity expressed higher. The concentration and secondary structure of Rap1p were similar to that of the control. Further more, the viability of Pb treated cells were significantly reduced while cells undergone other three treatments were similar and normal. These results suggest that Pb could damage Rap1p, reduce telomerase activity, resulting in the telomer length shortening and cell death. On the other hand, Se could protect and repair the damage in Rap1p and telomere caused by Pb to some extent.