Food Lipids: Chemistry, Nutrition, and Biotechnology

inflammatory effects of CLA would be beneficial for the treatment of inflammatory
bone diseases.
In our laboratory, the dietary CLA effects on serum concentrations of IGF-I
and IGFBPs, and their subsequent impact on bone modeling, were examined in male
rats (74). The level of IGFBP in serum of rats was altered by n-6 and n-3 fatty acids,
but CLA had variable effects. Interestingly, CLA increased IGFBP level in rats given
a high dietary level of n-6 fatty acids but reduced it in those given a high level of
n-3 fatty acids. Rats given the n-3 fatty acids had the highest serum level of IGFBP-
3. This study also showed that CLA decreased the amount of IGF-I mRNA in liver
of rats given n-3 fatty acids. In liver of rats, the expression of IGF-I mRNA appeared
to be up-regulated by n-3 fatty acids and down-regulated by CLA. The lowering
effect of CLA on growth factors was associated with reduced mineral apposition rate
and bone formation rate in the tibia. These results showed that dietary PUFA type
(and level) and CLA modulate growth factors that regulate bone metabolism and
other aspects of health.
Different CLA isomers may also have their own unique mechanisms of action.
Although limited information is available on the biological activity of individual
CLA isomers, the data suggest that individual isomers exert different biological effects.
Currently, the c9,t11 isomer has been shown to be effective in reducing mammary
carcinogenesis and the t10,c12 isomer is more potent in inducing body compositional
change. de Deckere et al. (129) treated hamsters with CLA preparations
containing relatively pure c9,t11, t10,c12, or a mixture of both isomers and showed
that the t10,c12 isomer was the most active form of CLA in inducing biological
effects, such as increasing liver weight, decreasing fat deposition, and lowering LDL
cholesterol. The authors concluded that t10,c12 appeared to be the physiologically
active CLA isomer and the natural c9,t11 had little or no effect on lipid metabolism
in hamsters.
Studies performed on mouse and cell culture also indicate differences between
the two major CLA isomers in their clearance rate from the body. In skeletal muscle
of mice treated with dietary CLA supplements, the t10,c12 isomer was cleared significantly
faster than the c9,t12 isomer (94). Yotsumoto et al. (130) recently showed
that t10,c12, but not the c9,c11 isomer or LA inhibited cellular triacylglycerol synthesis
and reduced apolipoprotein B secretion in HepG2 cell cultures. In the same
study, the c9,c11 isomer inhibited cholesteryl ester synthesis but to a lesser extent
than the t10,c12 isomer (130). Information on the effects of individual CLA isomers
is inadequate at present because of the limited supply of pure CLA isomers. With
the advance in techniques for CLA preparation, individual CLA isomers will be
available for future research.
C. Immune Function Modulation
Though CLA appears to have an anti-inflammatory effect, Turnock et al. (131)
showed that feeding mice CLA for up to 4 weeks does not compromise their immune
function against Listeria monocytogenes, an intracellular pathogen.
In a study evaluating the effect of CLA on immune competence, early-weaned
pigs were given 0–2% of a dietary CLA supplement (132). On day 42, CLA induced
a linear increase in percentages of CD8� cytotoxic/suppressor T cells, indicating that
CLA could be effective in inhibiting disease-associated growth suppression in pigs.
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.