Chemical synthesis of 2'-O-alkylated siRNAs.

Chemical synthesis has been a major endeavor to create active siRNAs. The downregulation of mRNA by 21-mer double-stranded siRNAs can be improved by using modified nucleotides, especially 2'-O-alkylated ones. Besides the commercially available 2 cent-O-methyl ribosides, 2'-alkyl groups bearing positive charges are especially promising candidates. We have shown that in a proper formulation they are superior to unmodified siRNAs. This may be due to enhanced stability and most probably to a better uptake into the cells.

A large-scale chemical modification screen identifies design rules to generate siRNAs with high activity, high stability and low toxicity.

The use of chemically synthesized short interfering RNAs (siRNAs) is currently the method of choice to manipulate gene expression in mammalian cell culture, yet improvements of siRNA design is expectably required for successful application in vivo. Several studies have aimed at improving siRNA performance through the introduction of chemical modifications but a direct comparison of these results is difficult. We have directly compared the effect of 21 types of chemical modifications on siRNA activity and toxicity in a total of 2160 siRNA duplexes. We demonstrate that siRNA activity is primarily enhanced by favouring the incorporation of the intended antisense strand during RNA-induced silencing complex (RISC) loading by modulation of siRNA thermodynamic asymmetry and engineering of siRNA 3'-overhangs. Collectively, our results provide unique insights into the tolerance for chemical modifications and provide a simple guide to successful chemical modification of siRNAs with improved activity, stability and low toxicity.

A convenient approach towards 2'-O-modified RNA-oligonucleotides on solid support using universal nucleosides.

Here we report a novel synthetic pathway for an efficient modification of RNA-oligonucleotides on solid-support using universal nucleosides bearing a 2'-O-aminopropyl-tether.

RNAi activity of siRNAs modified with 2'-aminoalkyl-substituted fluorinated nucleobases.

We recently reported that a 1'-deoxy-1'-(4,6-difluoro-1H-benzimidazol-1-yl)-2'-(beta-aminoethyl)-beta-d-ribofuranose nucleoside appears to be a universal nucleoside which does not differentiate between the four natural nucleosides A, C, G, and U in duplexes. Moreover, ribozymes modified with this nucleoside analog showed a better or at least equal catalytic activity relative to Watson-Crick mismatches.[1] Due to these data, we investigated the ability of this compound to tolerate Watson-Crick mismatches in order to avoid HIV escape mutations in RNA interference. The influence of this nucleoside analog on siRNA efficiency was analyzed with a proven siRNA targeting GFP.

Emergency donor heart protection: application of the port access catheter technique using a pig heart transplantation model.

BACKGROUND: Organ shortage limits the number of transplantations, and donor deterioration may precede and often prevent conventional organ preservation. This study evaluates in situ perfusion as a bedside method for cardiac allograft procurement in a large animal model. METHODS: Thirty Landrace pigs (42 +/- 7 kg) were studied. The hearts in the conventional group underwent cardioplegic arrest with University of Wisconsin solution and sodium-hydrogen exchange inhibitor cariporide as an additive; they were explanted and stored on ice before transplantation. In the in situ group, one catheter was placed in the ascending aorta and another in the right atrium. After disconnection from the ventilator, hypoxia caused circulatory arrest. The aorta was endoclamped, and in situ perfusion of the aortic root was maintained with University of Wisconsin solution and cariporide. After explantation, hearts were stored on ice for 120 min. All hearts were implanted according to the Shumway technique. Ventricular pressure and cardiac output were monitored online, and troponin-I was measured intermittently. Two hours after weaning from extracorporal circulation, the animals were killed and histology was performed. RESULTS: Catheters were placed through introducers within 5 min. Functional recovery and histology were comparable between the two techniques. Troponin-I increased in both groups during reperfusion but at a faster rate in the in situ technique (P <0.01). CONCLUSION: In situ perfusion may be suitable for cardiac transplants when donor deterioration requires urgent organ preservation. Catheters can be placed at bedside and modified to achieve multi-organ protection through additional perfusion of the abdominal aorta.

Sodium-hydrogen inhibitor cariporide (HOE 642) improves in situ protection of hearts from non-heart-beating donors.

BACKGROUND: Reperfusion injury is a vital problem in non-heart-beating donor (NHBD) organs. The sodium-hydrogen inhibitor cariporide is thought to improve cellular integrity after ischemia and reperfusion. Recently, we demonstrated the possibility of preserving hearts with in situ perfusion after circulatory death. The purpose of this study was to determine whether cariporide improves in situ heart protection. METHODS: We studied 20 pigs (18 +/- 2 kg). Hearts in the conventional group (CON, n = 6) underwent cardioplegic arrest with University of Wisconsin solution and then were explanted and stored for 150 minutes on ice. In the other groups, a catheter was placed in each ascending aorta and right atrium. After disconnecting the ventilator, hypoxia caused circulatory arrest within 7 +/- 2 minutes. The aorta was endoclamped, and continuous in situ perfusion of the aortic root was maintained for 60 minutes with University of Wisconsin solution (UW, n = 7) or with UW solution and cariporide (CAR, n = 7). After explantation, the hearts were stored on ice for 90 minutes. In all groups, hearts were reperfused with homologous, whole pig blood in an isolated working heart model for 45 minutes. We monitored stroke-work index on-line, intermittently measured troponin I and malondialdehyde, and compared light microscopic examinations among the groups. RESULTS: Stroke-work index was higher in the CAR group compared with the UW group during the last 20 minutes of reperfusion (10(3)dynes x cm x beats(-1)x gm(-1), 6.6 +/- 1.4 vs 4.5 +/- 2.0, p < 0.05), troponin I was lower in the CAR group compared with the UW group (161 +/- 32 ng/ml vs 277 +/- 35 ng/ml, p < 0.05). Results of malondialdehyde and light microscopic examinations were slightly better in the CAR group, without reaching statistical significance. CONCLUSION: Cariporide as an additive to UW solution improves functional recovery and decreases myocardial damage in hearts from NHBDs protected with an in situ perfusion technique.

A non-heart-beating donor model to evaluate functional and morphologic outcomes in resuscitated pig hearts.

A non-heart-beating donor model was considered to examine whether pig hearts from the abattoir could be resuscitated by whole blood reperfusion. For preservation, machine perfusion using University of Wisconsin (UW) solution was compared with storage on ice. Nineteen hearts from abattoir pigs, harvested 25 +/- 3 min after exsanguination, were harvested and transported to the laboratory. Controls (n = 7) were immediately reperfused with homologous whole pig blood in an isolated heart model for 60 min with monitoring of left ventricular developed pressure (LVDP), contractility, and coronary flow. UW solution hearts (UW, n = 6) were perfused for 4 h with 10 degrees C cold UW solution before blood reperfusion. In the cold storage group (CS, n = 6), the organs were stored for an additional 4 h on ice before blood reperfusion. In all hearts, histology was performed after 60 min of blood reperfusion to evaluate myocardial reperfusion injury. All three groups showed significant increases in LVDP (p <.001), although this functional recovery was earliest in the control group and latest in the UW group. Significant declines were observed for both LVDP and contractility from the peak values in each group to the end of blood reperfusion. Coronary flow increased steadily over the time course for the UW group, whereas in the control and CS groups flow increased during the first 15 min of blood reperfusion and then decreased. In the UW and CS groups, there were significant positive correlations between coronary flow and LVDP (p <.001). Microscopic examination revealed no differences between the three groups. Thus, hearts from an abattoir with 25 min of warm ischemic time can be resuscitated. For storage of these organs, continuous machine perfusion with UW solution is superior to cold storage on ice.