Regulation of PAI-1 concentration in platelets by systemic administration of antisense oligonucleotides to rats

In this report we tested the effect of oligodeoxyribonucleotides antisense to PAI-1 mRNA administered into rats on PAI-1 concentration in platelets. Low doses of the antisense oligonucleotide (MPO-16R) reduced PAI-1 activity, both in rat blood plasma and platelet lysates by 20.5% and 28.7%, respectively. There was no change in platelet count after treatment with MPO-16R but treated platelets showed lower aggregability as compared with controls (37 +/- 13% and 54 +/- 12%, respectively). In an experimental model of rat arterial thrombosis, low doses of MPO-16R caused a significant delay in the occlusion time (31.8%). These data further support for the role of PAI-1 as a major determinant of arterial thrombolysis resistance and for the first time demonstrate the possibility of reduction of platelet PAI-1 concentration by antisense approach.

Structural study of a DNA.RNA hybrid duplex with a chiral phosphorothioate moiety by NMR: extraction of distance and torsion angle constraints and imino proton exchange rates

The solution structure of the thiophosphate-modified DNA.RNA hybrid duplex d(GCTATAApsTGG).r(CCAUUAUAGC) has been studied by NMR. Two samples with pure stereochemistry in the modified phosphate have been investigated. Two-dimensional NMR (2D NMR) methods have been applied to assign nearly all the resonances in both duplexes. Scalar coupling constants have been determined by comparing quantitative simulations with experimental double-quantum filtered COSY (DQF-COSY) cross-peaks. More than 300 distance constraints have been obtained from two-dimensional nuclear Overhauser spectroscopy (2D NOE) spectra recorded in D2O and H2O by using a complete relaxation matrix analysis as implemented in the program MARDIGRAS. This hybrid duplex presents a heteronomous structure. Riboses in the RNA strand are found in a N-type conformation typical of the A-form family as shown by the lack of H1'-H2' cross-peaks in DQF-COSY spectra and confirmed by the measured interproton distances. In contrast, the DNA strand adopts a different conformation with sugar puckers partially in the S-type domain, which is not in agreement with the A-family of structures. Coupling constants in deoxyriboses are not consistent with any single sugar conformation. Therefore, sugar pucker pseudorotation parameters are calculated according to a two-state dynamic equilibrium between N- and S-type conformers. In general, the population of major S conformer is lower than in double-stranded DNA duplexes, indicating that hybrid duplexes may be more flexible than pure DNA or RNA. The only differences observed in the spectra between the two stereoisomers studied originate from resonances of protons located near the modified phosphate. No significant differences in interproton distance have been detected, and only a slight difference of sugar pucker in the 5' neighbor has been found. The sulfur atom appears to be well-accommodated without further changes in the structure of the hybrid.