In vivo and in silico evaluation of a new nitric oxide donor, S,S'-dinitrosobucillamine

In a previous work, we have synthetized a new dinitrosothiol, i.e. S,S'-dinitrosobucillamine BUC(NO)₂ combining S-nitroso-N-acetylpenicillamine (SNAP) and S-nitroso-N-acetylcysteine (NACNO) in its structure. When exposed to isolated aorta, we observed a 1.5-fold increase of ^•NO content and a more potent vasorelaxation (1 log higher pD₂) compared to NACNO and SNAP alone or combined (Dahboul et al., 2014). In the present study, we analyzed the thermodynamics and kinetics for the release of ^•NO through computational modeling techniques and correlated it to plasma assays. Then BUC(NO)₂ was administered in vivo to rats, assuming it will induce higher and/or longer hypotensive effects than its two constitutive S-mononitrosothiols.

Free energies for the release of ^•NO entities have been computed at the density functional theory level assuming an implicit model for the aqueous environment. Degradation products of BUC(NO)₂ were evaluated in vitro under heating and oxidizing conditions using HPLC coupled with tandem mass spectrometry (MS/MS). Plasma from rats were spiked with RSNO and kinetics of RSNO degradation was measured using the classical Griess-Saville method. Blood pressure was measured in awake male Wistar rats using telemetry (n = 5, each as its own control, 48 h wash-out periods between subcutaneous injections under transient isoflurane anesthesia, random order: 7 mL/kg vehicle, 3.5, 7, 14 μmol/kg SNAP, NACNO, BUC(NO)₂ and an equimolar mixture of SNAP + NACNO in order to mimic the number of ^•NO contained in BUC(NO)₂). Variations of mean (ΔMAP, reflecting arterial dilation) and pulse arterial pressures (ΔPAP, indirectly reflecting venodilation, used to determine effect duration) vs. baseline were recorded for 4 h.

Computational modeling highlights the fact that the release of the first ^•NO radical in BUC(NO)₂ requires a free energy which is intermediate between the values obtained for SNAP and NACNO. However, the release of the second ^•NO radical is significantly favored by the concerted formation of an intramolecular disulfide bond. The corresponding oxidized compound was also characterized as related substance obtained under degradation conditions. The in vitro degradation rate of BUC(NO)₂ was significantly greater than for the other RSNO. For equivalent low and medium ^•NO-load, BUC(NO)₂ produced a hypotension identical to NACNO, SNAP and the equimolar mixture of SNAP + NACNO, but its effect was greater at higher doses (-62 ± 8 and -47 ± 14 mmHg, maximum ΔMAP for BUC(NO)₂ and SNAP + NACNO, respectively). Its duration of effect on PAP (-50%) lasted from 35 to 95 min, i.e. shorter than for the other RSNO (from 90 to 135 min for the mixture SNAP + NACNO).

A faster metabolism explains the abilities of BUC(NO)₂ to release higher amounts of ^•NO and to induce larger hypotension but shorter-lasting effects than those induced by the SNAP + NACNO mixture, despite an equivalent ^•NO-load.