Effects of methapyrilene measured in mitochondria isolated from naive and methapyrilene-treated rat and mouse hepatocytes.
Methapyrilene (MP) is a rat-specific liver carcinogen that alters mitochondrial number and morphology both in vivo and in vitro. This biological phenomenon may be due to the effects of MP on mitochondrial function. To test this hypothesis, studies were conducted to examine the effects of MP on DNA and protein synthesis and respiration in isolated mitochondria. DNA and protein synthesis activities were measured using [3H]thymidine and [3H]leucine incorporation. Mouse liver mitochondria were also examined for comparison since no tumor formation or alterations in mitochondrial morphology have been associated with MP treatment in mice. A significant decrease in basal DNA and protein synthesis levels was observed in mitochondria isolated from rats and mice following in vivo MP treatment. This effect could not be reproduced when mitochondria were exposed to 0 or 100 microM MP following isolation, despite the presence of an S9 activation system. Electron microscopic examinations were performed on isolated rat mitochondria and revealed morphologic differences between mitochondria from naive and MP-treated rats. Although significant differences in State 3 and State 4 respiratory rates were noted, the respiratory control ratio, ADP/O ratio, and uncoupler-stimulated respiratory rates were unaffected. Results demonstrate that: (1) MP irreversibly depresses DNA and protein synthesis in a majority of mitochondria, despite only localized morphologic changes; (2) these changes are not reflected by a decrease in respiratory function; and (3) depression of DNA and protein synthesis does not correlate with carcinogenic susceptibility.
Copple
D M
DM
Toxicology Research Laboratories, Division of Eli Lilly and Company, Greenfield, Indiana 46140.
Rush
G F
GF
Richardson
F C
FC
D000818:Animals; D002250:Carbon Radioisotopes; D002855:Chromatography, Thin Layer; D004247:DNA / Q000096:biosynthesis; D066298:In Vitro Techniques; D008297:Male; D008701:Methapyrilene / Q000378:metabolism / Q000494:pharmacology*; D051379:Mice; D008815:Mice, Inbred Strains; D008854:Microscopy, Electron; D008930:Mitochondria, Liver / Q000187:drug effects* / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects; D014176:Protein Biosynthesis; D051381:Rats; D011916:Rats, Inbred F344
D002250:Carbon Radioisotopes; D004247:DNA; D008701:Methapyrilene