CLA Isomer t10, c12 Induce Oxidation and Apoptosis in 3t3 Adipocyte Cells in a Similar Effect as Omega-3 Linolenic Acid and DHA

Background: Commercial conjugated linoleic acid (CLA) dietary supplements of contain an equal mixture of the C18:2 isomers, cis-9, trans-11 and trans-10, cis-12. CLA-c9t11 occurs naturally in meat and dairy products as the dominant CLA at 75%, whereas the CLAt10c12 occurs at less than 1%. CLA-c9t11 generally promotes lipid accumulation but CLA-t10c12 inhibits lipid accumulation and may promote inflammation. The omega-3 fatty acid α-linolenic acid (C18:3n-3) and docosahexaenoic acid (DHA) were also observed to inhibit growth of 3t3 adipose cells; therefore we examined the effects of the CLA vs. omega -3 fatty acids at the molecular level in vitro to determine if they are causing similar oxidative stresses. Methods: Purified CLA-c9t11 and CLA-t10c12 were added to 3T3 mature adipocyte cultures at 100uM concentrations and compared with 100uM C18:3(n-3) (α-linolenic acid) and 50uM docosahexaenoic acid (DHA) to study their effect on growth, gene transcription and general oxidation. The results of multiple separate trials were averaged and compared for significance at levels of p < 0.05, using one way ANOVA and Student's t-test. Results: C18:3(n-3), DHA and CLA-t10c12 were inhibitory to 3t3 adipose cell growth and caused significant lipid hydro peroxide activity. CLA-t10c12 and c9t11 increased AFABP, FAS and ACOX1 mRNA expression but DHA and C18:3(n-3) decreased the same mRNAs. CLA-c9t11 but not the t10c12 stimulated adipoQ expression even though; c9t11 had only a slightly greater affinity for PPARγ than CLA- t10c12. The expression of the xenobiotic metabolism genes, aldo-keto reductase 1c1 (akr1c1), superoxide dismutase (SOD) and inflammation chemokine secretions of eotaxin (CCL11), Rantes (CCL5), MIG (CCL9) and MCP-1 were increased by DHA, C18:3(n-3) and CLA-t10c12. This correlated with an increase in apoptosis factors, caspase 3, Bcl-2 and BAXs. Apoptosis factors were partially reduced by co-treatment with lipophilic anti-oxidant α-tocopherol. Conclusion: Based on this evidence, CLA-t10c12 promoted more reactive oxygen species (ROS) than CLA-c9t11, in a similar effect as omega 3 fatty acids, C18:3(n-3) and DHA. In response, cascades of genes are activated to deal with the potentially damaging effects of ROS through detoxification, inflammation or apoptosis.