Interaction of 1,3,4-thiadiazolium mesoionic derivatives with mitochondrial membrane and scavenging activity: Involvement of their effects on mitochondrial energy-linked functions

The aim of this work was to assess the significance of the interaction of the 1,3,4-thiadiazolium derivatives MI-J, MI-4F and MI-2,4diF with mitochondrial membrane and their effects on energy-linked functions. Mitochondrial swelling in the absence of substrate was inhibited by all derivatives; however, the fluorine derivatives were most effective. MI-4F decreased swelling by ∼32% even at the lowest concentration (65nmolmg−1 protein), reaching ∼67% at the concentration of 130nmolmg−1 protein. Swelling of mitochondria in the presence of oxidizable substrates was also strongly decreased by all derivatives. This effect was more pronounced when using glutamate plus malate, and also fluorine derivatives, which promoted complete inhibition at all concentrations (6.5–130nmolmg−1 protein). Swelling occurred when succinate was the substrate in the presence of MI-J (6.5–65nmolmg−1 protein); however, the shrinkage rate was strongly decreased. MI-4F and MI-2,4diF also inhibited swelling, with total inhibition occurring at a concentration of 65nmolmg−1 protein. Lipid peroxidation induced by Fe3+–ADP/2-oxoglutarate in isolated mitochondria was inhibited time- and dose-dependently by the derivatives, reaching complete inhibition at the highest concentration (80nmolmg−1 protein). However, when lipid peroxidation was initiated by peroxyl radicals generated from AAPH, the inhibition was less intense, reaching ∼50%, ∼40% and ∼58% with MI-J, MI-4F and MI-2,4diF (80nmolmg−1 protein), respectively. The mesoionic compounds also showed superoxide radical scavenging ability of ∼22%, ∼32% and ∼40% (80nmolmg−1 protein), respectively. Fluorescence polarization experiments showed that the derivatives are able to enter the bilayer, decreasing its fluidity in the hydrophobic DMPC membrane region and ordering the fluid phase. Our results suggest that MI-J, MI-4F and MI-2,4diF interact significantly, albeit in different modes, with mitochondrial membrane, and that fluorine derivatives seem to alter the membrane's properties more markedly.