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Food Lipids: Chemistry, Nutrition, and Biotechnology

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(61,77,78) <strong>and</strong> in SCID (severe combined immunodeficiency) mice (59,79). Recent<br />

investigations with CLA failed to show a benefit on rodent models of colon carcinogenesis<br />

(80) <strong>and</strong> prostate metastasis (81).<br />

A. Cancer<br />

In dietary preparations, CLA provided a potent anticarcinogenic effect in a rat mammary<br />

cancer model. Ip et al. (55) found that administering weanling rats CLA at<br />

0.5–1.5% of the diet for 2 weeks before DMBA induction (oral intubation of 10 mg<br />

in 1 mL corn oil) <strong>and</strong> continuing for 36 weeks resulted in a significant reduction in<br />

tumor incidence. The effect of CLA was maximized at a dietary level of 1% in this<br />

study. In another experiment, much lower doses of dietary CLA (0.05–0.5%) were<br />

given to rats (53). The dietary treatments induced a dose-dependent inhibition in<br />

mammary tumor yield with a lower dose of 5 mg of DMBA. In the 5-week shortterm<br />

feeding experiment of 1% dietary CLA (53), rats were given CLA for 5 weeks<br />

<strong>and</strong> the carcinogens were introduced 1 week before the end of CLA treatment. Total<br />

tumor yield was reduced by 39% <strong>and</strong> 34% in the DMBA <strong>and</strong> methylnitrosourea<br />

(MNU) induction groups with CLA treatment, respectively, at the end of the experiment.<br />

The short-term feeding period corresponded to the maturation of the rat mammary<br />

gl<strong>and</strong> to adult stage morphology, <strong>and</strong> the supplement of CLA was stopped<br />

shortly after the induction with the carcinogens. Therefore, these results suggest that<br />

CLA may have a direct modulating effect on susceptibility of the target organ to<br />

neoplastic transformation.<br />

In a subsequent dietary study using the rat DMBA model, the inhibitory effect<br />

of CLA on induced mammary cancer was found to be independent of fat type (n-3<br />

fatty acids were investigated in the study) provided in the diet (56). When providing<br />

rats with a CLA supplement, the fatty acid isomers were incorporated into the mammary<br />

gl<strong>and</strong> lipids, <strong>and</strong> the amount in the neutral lipids greatly exceeded that in<br />

phospholipids (57,82). When CLA was removed from the diet after 4 <strong>and</strong> 8 weeks<br />

of feeding, neutral lipid- <strong>and</strong> phospholipid-CLA returned to basal values in about 4<br />

<strong>and</strong> 8 weeks, respectively. The author observed that the rate of CLA disappearance<br />

in neutral lipids subsequent to CLA withdrawal closely paralleled the occurrence of<br />

new tumors in the rat target tissue. It appears that the tissue accumulation of CLA<br />

is important to its antitumor effect <strong>and</strong> that the concentration of CLA in neutral lipid<br />

may be a more sensitive biomarker of tumor protection than the amount in phospholipid<br />

for this model. The effect of CLA on cancer was maximized at a dietary<br />

level of 1% as shown in several studies, <strong>and</strong> increasing the dietary level of CLA did<br />

not afford additional protection (55,82).<br />

The antitumor effect of naturally produced CLA was tested over a chemically<br />

prepared CLA mixture from LA which was used in previous studies (83). During<br />

the study, rats were given a diet with a high CLA content butter fat (equivalent to<br />

0.8% CLA in the diet) <strong>and</strong> a low-level CLA diet that served as the control group<br />

(equivalent to 0.1% CLA in the diet) for 1 month before tumor induction using MNU.<br />

After tumor induction, rats were changed to a regular diet without CLA for 24 weeks<br />

before the termination of the experiment. CLA in butter inhibited the tumor yield by<br />

53%. CLA was also shown to reduce the population of mammary terminal end bud<br />

(TEB) cells, the cells that are the primary target of attack by carcinogens, <strong>and</strong> the<br />

proliferation of TEB cells. Similar effects reported by Banni et al. (62) revealed that<br />

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

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