THERMALLY OXIDIZED DIETARY-FAT AND COLON CARCINOGENESIS IN RODENTS

Thermally oxidized animal fat (beef tallow) was assessed for colon can cer-promoting and -initiating activity in F-344 rats and CF-I mice wit h the use of the aberrant crypt focus (ACF) assay. In two promotion st udies, extensively oxidized beef tallow (110 degrees C for 144-168 h, peroxide value approx 200 meq/kg, with >80% loss of allylic and olefin ic protons) had relatively little effects on the growth of ACF in F-34 4 rats. The multiplication constant for treatment/control of ACF size in aberrant crypts per A CF at 100 days was 1.07 (95% confidence inter val = 1.01-1.14) and 0.98 (95% confidence interval = 0.91-1.06). ACF s ize was not affected by less extensively oxidized beef tallow or by a 10-fold reduction of dietary alpha-tocopherol during the growth of the ACF. In initiation studies, extensively oxidized beef tallow administ ered by gavage increased the number of animals with ACF and the number of ACF per colon (II of 23 and 5 of 29 animals with ACF; 1.09 +/- 0.2 9 and 0.21 +/- 0.09 ACF/colon, respectively). Less severely oxidized b eef tallow was without effect. Further studies with CF-I mice confirme d that extensively oxidized beef tallow increased numbers of animals w ith ACF and average ACF per colon. The unsaturated aldehyde acrolein w as without effect in the ACF assay. These data suggest that highly the rmolyzed beef tallow contains an uncharacterized initiator or leads to conditions in which spontaneously initiated ACF are increased.