Effects of conjugated linoleic acid isomers on lipid‐metabolizing enzymes in male rats

Abstract

Male weanling Wistar rats (n = 15), weighing 200-220 g, were allocated for 6 wk to diets containing 1% (by weight) of conjugated linoleic acid (CLA), either as the 9c,11 t-isomer, the 10t,12c-isomer, or as a mixture containing 45% of each of these isomers. The five rats of the control group received 1% of oleic acid instead. Selected enzyme activities were determined in different tissues after cellular subfractionation. None of the CLA-diet induced a hepatic peroxisome-proliferation response, as evidenced by a lack of change in the activity of some characteristic enzymes [i.e., acyl-CoA oxidase, CYP4A1, but also carnitine palmitoyltransferase-I (CPT-I)] or enzyme affected by peroxisome-proliferators (glutathione S-transferase). In addition to the liver, the activity of the rate-limiting beta-oxidation enzyme in mitochondria, CPT-I, did not change either in skeletal muscle or in heart. Conversely, its activity increased more than 30% in the control value in epididymal adipose tissue of the animals fed the CLA-diets containing the 10t,12c-isomer. Conversely, the activity of phosphatidate phosphohydrolase, a rate-limiting enzyme in glycerolipid neosynthesis, remained unchanged in adipose tissue. Kinetic studies conducted on hepatic CPT-I and peroxisomal acyl-CoA oxidase with CoA derivatives predicted a different channeling of CLA isomers through the mitochondrial or the peroxisomal oxidation pathways. In conclusion, the 10t,12c-CLA isomer seems to be more efficiently utilized by the cells than its 9c,11t homolog, though the Wistar rat species appeared to be poorly responsive to CLA diets for the effects measured.

Oxidized oils and dietary zinc and α-tocopheryl acetate supplementation: effects on rabbit plasma, liver and meat fatty acid composition and meat Zn, Cu, Fe and Se content

“…For instance, the higher content of c9,t11-CLA than other CLA isomers could be a consequence of the preferential use of t10,c12-CLA for b-oxidation (Martin et al, 2000) and for synthesizing longchain metabolites from it (Evans et al, 2002).…”

The effect of trans-10,cis-12 conjugated linoleic acid on lipogenesis is tissue dependent in hamsters

“…The reduction that we found in the mRNA expression of these transcriptional factors, induced by trans-10,cis-12, paralleled changes observed in ACC and FAS. Concerning the effects of CLA on liver, several studies in mice have shown that trans-10,cis-12 increased liver weight [8][9][10][11][12][13]. In some of these trials, hepatic triacylglycerol content was measured and it was concluded that hepatomegaly was due to lipid accumulation [5,[14][15][16].…”

“…In some of these trials, hepatic triacylglycerol content was measured and it was concluded that hepatomegaly was due to lipid accumulation [5,[14][15][16]. In contrast, the studies performed on rats reported no effects on liver weight induced by CLA [4,10,[17][18][19][20].…”

Os efeitos do ácido linoléico conjugado no metabolismo animal: avanço das pesquisas e perspectivas para o futuro

“…As evidências, em roedores, de que o CLA apresentava ação hipolipidemiante, por meio da indução da β-oxidação em diversos tecidos, mas especialmente no tecido adiposo, foram surgindo de forma mais constante. Aumento da produção de corpos cetônicos, da razão β-hidroxibutirato/acetoacetato, da atividade de enzimas envolvidas na β-oxidação de ácidos graxos, como a acil CoA oxidase e a carnitinapalmitoiltransferase-1, assim como o aumento de glutationa-S-transferase, enzima afetada por proliferador de peroxissoma, contribuíram para a conclusão de que o CLA aumenta a oxidação de ácidos graxos 83,84 . O trabalho de Sergiel et al 85 foi fundamental para comprovar essa hipótese.…”

“…A diminuição, particularmente pelo isômero trans-12, cis-12 CLA, da síntese de enzimas envolvidas na lipogênese (como a lipase lipoprotéica, acetil CoA carboxilase e ácido graxo sintase), responsáveis pela clivagem dos ácidos graxos das lipoproteínas circulantes para ressíntese de triacilglicerol (LPL) e pela síntese de novo dos lípides biológicos (ACC e FAS), tem sido reportada por muitos pesquisadores 88,97 . Por outro lado, como já discutido, o aumento da β-oxidação de ácidos graxos mitocondrial e peroxissomal induzido pelo CLA, também poderia ser responsável pela redução da síntese de triacilgliceróis e, dessa forma, contribuir para a não deposição dos mesmos no adipócito, reduzindo, assim, o seu tamanho 84,119,120 .…”