Oxidative/Nitrative Mechanism of Molsidomine Mitotoxicity Assayed by the Cytochrome c Reaction with SIN-1 in Models of Biological Membranes.

Molsidomine is currently used as a vasodilator drug for the treatment of myocardial ischemic syndrome and congestive heart failure, although still presenting some mitochondrial-targeted side effects in many human cells. As a model of molsidomine mitotoxicity, the reaction of cytochrome c with phosphatidylserine (PS)- and cardiolipin (CL)-containing liposomes was investigated in oxidative/nitrosative conditions imposed by SIN-1 decomposition, which renders peroxynitrite (ONOO-) as a main reactive product. In these conditions, the production of thiobarbituric acid-reactive substance (TBARs) and LOOH was affected by the lipid composition and the oxidative/nitrative conditions used. The oxidative/nitrative conditions were the exposure of lipids to SIN-1 decomposition, native cytochrome c after previous exposure to SIN-1, concomitantly to SIN-1 and native cytochrome c, native cytochrome c, and cytochrome c modified by SIN-1 that presents a less-rhombic heme iron (L-R cytc). TBARs and LOOH production by lipids and cytochrome c exposed concomitantly to SIN-1 differed from that obtained using L-R cytc and featured similar effects of SIN-1 alone. This result suggests that lipids rather than cytochrome c are the main targets for oxidation and nitration during SIN-1 decomposition. PS- and CL-containing liposomes challenged by SIN-1 were analyzed by Fourier transform infrared spectroscopy that revealed oxidation, trans-isomerization, and nitration. These products are consistent with reaction routes involving lipids and NOx formed via peroxynitrite or direct reaction of NO• with molecular oxygen that attacks LOOH and leads to the formation of substances that are not reactive with thiobarbituric acid.

Density-dependent patterns of thiamine and pigment production in the diatom Nitzschia microcephala.

In the present study we investigate how intraspecific (density-dependent) competition for nutrients by the diatom Nitzschia microcephala affects the level of oxidative stress in the algal cells as well as their production of pigments and thiamine. N. microcephala was grown in three different densities until the stationary growth phase was reached. Throughout the experiment, growth rate was negatively related to cell density. Superoxide dismutase activity, protein thiol, and diatoxanthin concentrations indicated increasing oxidative stress with increasing cell density, which was most probably caused by nutrient depletion of the medium. Pigment contents per cell (except for diatoxanthin) decreased with increasing cell density. N. microcephala was able to synthesize thiamine and its thiamine content per cell increased in concert with cell density. In comparison, the dinoflagellate Amphidinium carterae was unable to synthesize thiamine. These results suggest that cells of N. microcephala subjected to higher competition and lower growth rates have a lower carotenoid content and a higher thiamine content. If such responses would occur in nature as well, eutrophication (higher cell densities) may alter the quality of microalgae as food items for higher trophic levels not only by species shifts in the phytoplankton, but also by changes in the cellular nutritional value within species.