Dietary conjugated linoleic acid reduces bone formation rate and alters biomarkers for bone metabolism in rats
Abstract
The impact of conjugated linoleic acid (CLA), along with the n-6, n-3 polyunsaturated fatty acids (PUFA), on prostaglandin E2 (PGE 2), insulin-like growth factor-I (IGF-I) and bone metabolism was investigated in the current study. Dietary lipid treatments modified the fatty acid composition in polar and neutral lipid fractions of all rat tissues analyzed. Generally, CLA was incorporated substantially more in neutral than in polar lipid and the distribution of its isomers may be tissue-specific. CLA tended to suppress monounsaturated fatty acids and n-6 PUFA, but increased n-3 PUFA in rat tissues. A variable effect of CLA on ex vivo PGE2 production in rat bone organ cultures was observed. CLA decreased PGE2 production in rats fed a high n-6 or high n-3 diet but had no effect in rats fed a beef fat supplemented diet. CLA effect on IGF-I also was dependent on dietary PUFA type. CLA tended to lower serum IGF-I levels, and upregulated IGF binding protein (IGFBP) in rats fed a high n-6 diet, but down-regulated IGFBP in those given high n-3 diet. Liver IGF-I mRNA also was affected by CLA, with decreased expression in rats fed a high n-3 diet and CLA. CLA's negative effect on bone metabolism was evidenced by a low bone formation rate in rats fed the CLA supplement and suppressed levels of serum osteocalcin and bone-specific alkaline phosphatase (BALP) activity. Though long chain n-3 PUFA also decreased tissue n-6 PUFA and suppressed PGE2 production, a positive effect on bone metabolism was noticed by a increased bone formation rate and increased serum BALP activity. CLA has been regarded as an effective natural chemoprotector against certain cancers and found to have other potential beneficial effects on human health. However, this study clearly showed that CLA may exert some undesirable actions on certain metabolic processes, for example in bone, and further research work is warranted to fully understand the mechanisms behind its action.
Degree
Ph.D.
Advisors
Watkins, Purdue University.
Subject Area
Nutrition|Animal sciences
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