Promotion of aberrant crypt foci and cancer in rat colon by thermolyzed protein.
BACKGROUND
We have previously shown that thermolyzed protein (casein) cooked with fat in the diet of the rat promotes the growth of aberrant crypt foci (putative precursors of colon cancer) assessed at 100 days.


OBJECTIVE
To determine how thermolysis affects this promotion, we examined thermolysis conditions, quantity of thermolyzed protein in the diet, and duration of thermolysis. To determine whether the previous finding of promotion of aberrant crypt foci corresponds to promotion of cancers assessed much later, we carried out promotion studies until colon cancers appeared.


METHODS
F344 rats were given an initiating dose of azoxymethane and were then randomly allocated to groups receiving diets differing in their quantity and quality of casein. The groups were examined for aberrant crypt foci and tumors in the colon.


RESULTS
Aberrant crypt foci were promoted by diets containing thermolyzed casein (180 degrees C, 2 hours). Promotion increased with increasing level of thermolyzed casein in the diet (to 20%) and with increasing thermolysis time (to 4 hours). The number of animals with polyps and cancers was higher in the animals receiving thermolyzed protein (2 hours), 16/23 versus 9/26 (P less than .05) and 10/26 versus 3/27 (P less than .05), respectively. The number of aberrant crypts per focus and the number of large aberrant crypt foci were higher in the tumor-bearing animals.


CONCLUSIONS
Thermolyzed casein promotes early colonic precursor lesions in a dose-dependent and thermolysis time-dependent manner; thermolyzed casein also promotes colon cancer.


CONCLUSIONS
The promoter formed on thermolysis could be involved in colon cancers associated with diets cooked at elevated temperatures, such as can occur with high-fat diets.
Zhang
X M
XM
Department of Medical Biophysics, University of Toronto, Ontario Cancer Institute, Canada.
Stamp
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Minkin
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Medline
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Corpet
D E
DE
Bruce
W R
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Archer
M C
MC
D000818:Animals; D002364:Caseins / Q000008:administration & dosage / Q000633:toxicity*; D003110:Colonic Neoplasms / Q000139:chemically induced*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006358:Hot Temperature; D008297:Male; D011897:Random Allocation; D051381:Rats; D011916:Rats, Inbred F344; D013997:Time Factors
D002364:Caseins