engleski

Accumulation of porphyrin-based SOD mimics in mitochondria is proportional to their lipophilicity. S. cerevisiae study of ortho Mn(III) N-alkylpyridylporphyrins

Mitochondrial failure has been widely recognized as being critical in numerous diseases. Thus, strategies to target drugs to mitochondria have been aggressively explored. Compounds that bear both cationic and lipophilic character are likely to enter mitochondria, driven by the mitochondrial membrane potential. As mitochondria are considered to be the major source of superoxide, it is of interest to direct superoxide dismutase (SOD) mimics to that compartment. Mn(III) N-alkylpyridylporphyrins (MnPs) are among the most powerful SOD mimics and peroxynitrite scavengers. We have synthesized and tested three MnPs with ortho N-alkylpyridyl substituents of different lipophilicity: MnTM-2-PyP5+ (AEOL10112), MnTE-2-PyP5+ (AEOL10113) and MnTnHex-2-PyP5+. The compounds have methyl, ethyl and hexyl alkyl chains, respectively. All three have nearly identical (and high) SOD-like activity and peroxynitrite-scavenging ability in vitro, but differ in the length of the alkyl group. We hypothesized that the longer alkyl analogues might possess a combination of charge and the lipophilicity that would direct them preferentially to mitochondria. In order to determine the distribution of these compounds in the living cells, we grew yeast with 10 micromolar concentration of each MnP and prepared mitochondrial and cytosolic fractions. We then measured the concentration of MnP in each fraction using a newly developed LCMS/MS method that is advantageous over HPLC/fluorescence previously utilized. The method was optimized for each compound prior to analysis, and we were able to detect and quantitate the compounds in all fractions. We found that MnTM-2-PyP5+ was evenly distributed between mitochondria and cytosol, MnTE-2-PyP5+ was slightly higher in mitochondria than cytosol, and MnTnHex-2-PyP5+ was located mostly in the mitochondria (~ 90%). The mitochondrial distribution is roughly proportional to the number of carbon atoms in the N-alkylpyridyl chains, which is further proportional to the lipophilicity of MnPs. Our data may help explain variations in the biological activity of these compounds, for example, the remarkably high ability of MnTnHex-2-PyP5+ to suppress oxidative stress injuries in various animal models.

Mn porphyrin; SOD mimic; mitochondria; lipophilicity

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