Sodium nitroprusside encapsulated in Silica nanoparticles as a strategy for safer nitric oxide delivery

Sodium nitroprusside (SNP) has been used as a nitric oxide (NO) donor in medicine for several decades, even before any knowledge of the biological role of NO. This medicine is used in cases of emergency of hypertension due to its fast release of NO causing fast drop in blood pressure. Unfortunately, this compound also releases cyanide (CN‐) as a side product. Nanoencapsulated nitroprusside was synthesized by using silica nanoparticles functionalized with primary amine (MPSi‐NH2) (the final compound was named APTES). The compound was bioassayed using vascular tissues from Wistar rats, albine guinea‐pigs and New Zealand rabbits. All the protocols were approved by the Ethic committee of the Ceará State University under the protocol # 2897836/15. The thoracic aorta, pulmonary artery or corpora cavernosa were carefully removed and mounted in a 5 mL organ bath containing Krebs–Henseleit solution at 37°C, gassed with 95% O 2 : 5% CO 2 , attached to isometric transducers coupled to a powerlab data acquisition system. After equilibration, the tissues were precontracted with phenylephrine (PE, 10 −6 –10 −5 M) and after a plateau was achieved increasing concentrations of SNP or APTES (10 −10 to 10 −5 M) were cumulatively added in intervals of 5 minutes. The relaxant effect was measured as percentage of the maximal contraction induced by phenylephrine. In addition, we also measured the level of phosphorylation of Ser239 of VASP, a useful marker for monitoring cGMP‐dependent protein kinase activation and signaling. SNP APTEs relaxed rat aortic rings with similar potency than non‐modified SNP with a concentration necessary to induce 50% vasodilation (CE 50 ) of 26 nM [95% confidence interval=20–33 nM] compared to 14 nM [95% confidence interval=7,9–21 nM] for non‐modified SNP. However, the maximal vasodilation induced by SNP APTEs (177.4±7.1%) was higher than the maximal relaxation induced by nonmodified SNP (143.8±9.6%). When comparing different vascular beds, i.e., guinea pig thoracic aorta vs. pulmonary arteries vs. rabbit corpora cavernosa, SNP APTEs was shown to have similar potency and efficacy (119.6±5.7% and 130nM vs. 108±6.3% and 275nM vs. 116±4.5% and 98 nM, respectively). Interestingly, SNP increase VASP phosphorylation by 3.8‐fold and APTES increased by 4.13‐fold (P<0.05 vs. control). Our synthetic strategy to make functionalized silica nanoparticles showed quite efficient to incorporate sodium nitroprusside, where we succeeded to have up to 320 umol g −1 . Remarkably, we noticed a minor release of cyanide or even NP, despite full effect of NO was observed during a series of biological assays. Indeed, EC50 and maximal response for relaxation in aorta, pulmonary arteries and Rabbit corpora cavernosa were quite similar. Support or Funding Information CAPES, CNPq and FUNCAPVasorelaxant Effect of Sodium nitroprusside encapsulated in Silica nanoparticles Original tracings depicting the strong and potent vascular relaxant effect of SNP APTES (panel A). Effect of SNP APTES on the phenylephrine precontracted aortic rings compared with non‐modified sodium nitroprusside (Panel B). Panel C depicts the Effect of 1 μM SNP or SNP APTES compared with the addition of vehicle only in the level of phosphorylation of the residues Serine 239 of the protein Vasodilator‐stimulated phosphoprotein (VASP) a substrate of activated cGMP‐activated protein kinase (PKG) *p<0.05 vs SNP at the same concentrationThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .