Prodotti di reazione di NO-donatori con molecole di interesse biologico e clinico: loro interazioni con i liposomi fosfolipidici e conseguenti cambiamenti delle caratteristiche chimico-fisiche di membrana

Abstract

The reaction of propofol with nitrosoglutathione lead to the formation of an active species which was identified, and then synthesised, as 2,6-diisopropyl-4-nitrosophenol (nitrosopropofol). We demonstrated the in vitro formation of nitrosopropofol, and discussed the interaction of propofol and nitrosopropofol with dimyristoyl-L-a-phosphatidylcholine multilamellar liposomes (DMPC) using differential scanning calorimetry and spin labelling techniques. The thermotropic profiles showed that these molecules affect the temperature and the cooperativity of the gel to fluid state transition of the liposomes differently: the effects of propofol on the lipid organisation are quite similar to phenol and coherently interpretable in terms of the disorder produced in the membrane by a bulky group; nitrosopropofol is a stronger perturbing agent, and ESR spectra indicate that this is due to a relative accumulation of the molecule into the interfacial region of the bilayer. Nitrosopropofol (2-6-diisopropyl-4-nitrosophenol) has also dramatic consequences for respiration, ATP synthesis and transmembrane potential of isolated rat liver mitochondria at concentrations at which propofol (2-6-diisopropylphenol) does not cause any apparent effects. These results correlate well with the above reported observation that nitrosopropofol is a stronger perturbing agent of phospholipid membranes. The results suggested the opportunity of extending the study to the possible biological activity of different phenols and nitrosophenols on mitochondrial respiration, and to their interactions with phospholipid liposomes, in order to get information about the drugs distribution and the modifications they impose on lipid bilayer. The results of the experiments performed on mitochondria and model membranes prove an interesting correlation between the effects of the molecules on both systems. Propofol, the substituted phenols and their nitroso derivatives, and some 4,4'-biphenyldioles have been compared for their scavenging ability towards DPPH and for their inhibitory action on lipid peroxidation. The results showed that the antioxidant properties of the various molecules depend on the steric and electronic effects of their substituents.