Colonic Protein Fermentation and Promotion of Colon Carcinogenesis by Thermolyzed Casein

Thermolyzed casein is known to promote the growth of aberrant crypt foci (ACF) and colon cancer when it is fed to rats that have been initiated with azoxymethane. We speculated that the promotion was a consequence of increased colonic protein fermentation (i.e., that the thermolysis of the casein decreases its digestibility, increases the amount of protein reaching the colon, and increases colonic protein fermentation and that the potentially toxic products of this fermentation promote colon carcinogenesis). We found that the thermolysis of casein reduces its digestibility and increases colonic protein fermentation, as assessed by fecal ammonium and urinary phenol, cresol, and indol-3-ol. Thermolysis of two other proteins, soy and egg white protein, also increases colonic protein fermentation with increased fecal ammonia and urinary phenols, and thermolysis of all three proteins increases the levels of ammonia and butyric, valeric, and i-valeric acids in the cecal contents. We found, however, that the increased protein fermentation observed with thermolysis is not associated with pro-motion of colon carcinogenesis. With casein, the kinetics of protein fermentation with increasing thermolysis time are clearly different from the kinetics of promotion of ACF growth. The formation of the fermentation products was highest when the protein was thermolyzed for one hour, whereas promotion was highest for protein that had been thermolyzed for two or more hours. With soy and egg white, thermolysis increased colonic protein fermentation but did not promote colon carcinogenesis. Thus, although thermolysis of dietary casein increases colonic protein fermentation, products of this fermentation do not appear to be responsible for the promotion of colon carcinogenesis. Indeed, the results suggest that protein fermentation products do not play an important role in colon cancer promotion

Folic acid supplementation promotes mammary tumor progression in a rat model.

Folic acid supplementation may prevent the development of cancer in normal tissues but may promote the progression of established (pre)neoplastic lesions. However, whether or not folic acid supplementation can promote the progression of established (pre)neoplastic mammary lesions is unknown. This is a critically important issue because breast cancer patients and survivors in North America are likely exposed to high levels of folic acid owing to folic acid fortification and widespread supplemental use after cancer diagnosis. We investigated whether folic acid supplementation can promote the progression of established mammary tumors. Female Sprague-Dawley rats were placed on a control diet and mammary tumors were initiated with 7,12-dimethylbenza[a]anthracene at puberty. When the sentinel tumor reached a predefined size, rats were randomized to receive a diet containing the control, 2.5x, 4x, or 5x supplemental levels of folic acid for up to 12 weeks. The sentinel mammary tumor growth was monitored weekly. At necropsy, the sentinel and all other mammary tumors were analyzed histologically. The effect of folic acid supplementation on the expression of proteins involved in proliferation, apoptosis, and mammary tumorigenesis was determined in representative sentinel adenocarcinomas. Although no clear dose-response relationship was observed, folic acid supplementation significantly promoted the progression of the sentinel mammary tumors and was associated with significantly higher sentinel mammary tumor weight and volume compared with the control diet. Furthermore, folic acid supplementation was associated with significantly higher weight and volume of all mammary tumors. The most significant and consistent mammary tumor-promoting effect was observed with the 2.5x supplemental level of folic acid. Folic acid supplementation was also associated with an increased expression of BAX, PARP, and HER2. Our data suggest that folic acid supplementation may promote the progression of established mammary tumors. The potential tumor-promoting effect of folic acid supplementation in breast cancer patients and survivors needs further clarification

Effects of insulin and analogues on carcinogen-induced mammary tumours in high-fat-fed rats

It is not fully clarified whether insulin glargine, an analogue with a high affinity for insulinlike growth factor-1 receptor (IGF-1R), increases the risk for cancers that abundantly express IGF-1R such as breast cancer or some types of breast cancer. To gain insight into this issue, female Sprague-Dawley rats fed a high-fat diet were given the carcinogen N-methyl-N-nitrosourea and randomly assigned to vehicle (control), NPH (unmodified human insulin), glargine or detemir (n=30 per treatment). Insulins were given subcutaneously (15U/kg/day) 5 days a week. Mammary tumours were counted twice weekly, and after 6 weeks of treatment, extracted for analysis. None of the insulin-treated groups had increased mammary tumour incidence at any time compared with control. At 6 weeks, tumour multiplicity was increased with NPH or glargine (P< 0.05) and tended to be increased with detemir (P=0.2); however, there was no difference among insulins (number of tumours per rat: control=0.8 +/- 0.1, NPH=1.8 +/- 0.3, glargine=1.5 +/- 0.4, detemir=1.4 +/- 0.4; number of tumours per tumour-bearing rat: control=1.3 +/- 0.1, NPH=2.2 +/- 0.4, glargine=2.7 +/- 0.5, detemir=2.3 +/- 0.5). IGF-1R expression in tumours was lower than that in Michigan Cancer Foundation-7 (MCF-7) cells, a cell line that shows greater proliferation with glargine than unmodified insulin. In rats, glargine was rapidly metabolised to M1 that does not have greater affinity for IGF-1R. In conclusion, in this model of oestrogen-dependent breast cancer in insulin-resistant rats, insulin and insulin analogues increased tumour multiplicity with no difference between insulin types

Summary of the effects of folic acid supplementation on all (sentinel+new) mammary tumors.

<p>The secondary objective of this study was to determine the effect of folic acid supplementation on the incidence and tumor burden variables of all mammary tumors including the sentinel and new mammary adenomas and adenocarcinomas at necropsy. Diet groups represent the amount of folic acid in mg per kg diet. Results are expressed as mean ± SEM. Within each row, means with different letters significantly differ at p<0.05. All analyses were adjusted for the effects of age at randomization and days on diet.</p

Summary of the effects of folic acid supplementation on main primary outcomes of the sentinel mammary tumors.

<p>Weanling female rats were placed on a control diet containing 2 mg kg folic acid/kg diet (basal dietary requirement for rats) until 7 weeks of age when the mammary carcinogen DMBA was administered. The animals continued to receive the control diet until a single mammary tumor between 0.7–0.9 cm (i.e., the sentinel tumor) developed. The animals were then randomized to receive different levels of folic acid (control, 5, 8, and 10 mg folic acid/kg diet) for 12 weeks. The primary objective of this study was to determine the effect of folic acid supplementation on the progression of the sentinel mammary tumors including both histologically confirmed adenocarcinomas and adenomas and on the sentinel tumor burden variables (weight, volume, and area). Diet groups represent the amount of folic acid in mg per kg diet. Results are expressed as mean ± SEM. Within each row, means with different letters significantly differ at p<0.05. All analyses were adjusted for the effects of age at randomization and days on diet.</p

Folate and homocysteine concentrations at necropsy.

<p>Diet groups represent the amount of folic acid in mg per kg diet. Results are expressed as mean ± SEM. Within each row, means with different letters significantly differ at p<0.05. All analyses were adjusted for the effects of age at randomization and days on diet.</p