Conjugated linoleic acid (CLA) is a mixture of positional and geometric isomers of linoleic acid, a fatty acid (or fat in plain English). CLAs have two conjugated (alternate) unsaturated double bonds at various carbon positions in the fatty acid chain. Each double bond can be a cis or trans, but those with one trans double bond are bioactive. CLAs are synthesized by the rumen microbes, primarily Butyrivibrio fibrisolvens, which is to say those present in the rumen of cows, sheep, goats, and buffaloes among the domestic animals. However, it can also be synthesized endogenously in the mammary gland from trans-11 C-18:1, also known as vaccenic acid, another fat of rumen origin, by an enzyme known as delta-9-desaturase.
Thanks to thousands of reports, principally based on in vitro, microbial, animal and of late clinical trials on humans, CLA is now linked to have beneficial effects in obesity, diabetes, cardiovascular disease, cancer, and atherosclerosis. While more than 28 isomers of CLA have been identified, there are two principal isomers that are of primary significance from both qualitative and quantitative perspective. Qualitative in the sense of human health and quantitative in the sense of availability. They are cis-9, trans-11 CLA and trans-10, cis-12 CLA. In this blog, I discuss the potential role of CLA as an antioxidant.
Some of the potential health benefits of CLA appear to be mediated through its antioxidant properties. When free radical scavenging properties against the stable radical, 2,2-diphenyl-1-picrylhydrazyl (DPPH) were investigated, both CLA isomers reacted and quenched DPPH at levels between 5 and 25 mM (Fagali and Catalá, 2008). Likewise, lipid peroxidation of triglycerides rich in C20:5 ώ-3 and C22:6 ώ-3 was inhibited by t-10, c-12 and c-9, t-11 isomers of CLA with the former being more effective than the latter (Fagali and Catalá, 2008). In another experiment, a mixture of CLA increased the activity of mitochondrial glutathione peroxidase, which may enhance antioxidant defenses (Moon et al., 2009). Yu et al. (2002) showed that both c-9, t-11 and t-10, c-12 isomers of CLA quench free radicals. It was also shown that the mixture of both isomers was more effective than either isomer alone. When the effect of CLA on paraoxygenase 1, one of the antioxidant proteins associated with high density lipoproteins, was studied in vitro, both c-9, t-11 and t-10, c-12 isomers of CLA showed 71 to 74% protection of paraoxygenase 1 (Su et al., 2003). Additionally the two isomers also protected paraoxygenase 1 from oxidative inactivation of H2O2 or cumene hydroperoxide (Su et al., 2003). The c-9, t-11 isomer of CLA scavenged more free radicals at steady state (Yu et al., 2002) and was more effective in protecting paraoxygenase 1 than t-10, c-12 isomer (Su et al., 2003). However, Leung and Liu (2000) reported a stronger oxyradical scavenging capacity for t-10, c-12 than c-9, t-11 isomer. In rat liver, CLA was more effective than vitamin A in protecting microsomes or mitochondria from peroxidative damage (Palacios et al., 2003).
Kim et al. (2004) investigated the antioxidant activities of arginine-CLA, a water-soluble salt. They found free radical scavenging capacity of arginine-CLA was double that of CLA with its antioxidant activity similar to vitamin E. Arginine-CLA, where an arginine moiety is attached to the CLA compound, may have further implications in expanding the scope of the application of CLA as a health-promoting agent because of its solubility in water, which is not the case with other CLAs.
In broiler chicks, increased total superoxide dismutase – an antioxidant enzyme – activities in the liver, serum and muscle were observed when diet had 10.0 g CLA/kg (Zhang et al., 2008). Dietary CLA at 10.0 g/kg also markedly elevated liver catalase – another antioxidant enzyme – whereas malondialdehyde, a marker of lipid peroxidation, decreased in the liver, serum and muscle in chicks given 5.0 and 10.0 g CLA/kg diet. In broiler chicks with repeated endotoxin exposure, CLA partially inhibited the increase of serum ceruloplasmin and malondialdehyde and notably suppressed the decrease of serum total superoxide dismutase activity that are usually associated with endotoxin exposure (Zhang et al., 2008) suggesting that CLA can ameliorate the antioxidant balance and improve the performance of chicks during oxidative stress. It has been suggested that the activation of detoxifying enzymes may be one of the mechanisms whereby dietary CLA down-regulates oxidative stress (Bergamo et al., 2007). The c9, t11-CLA mix (80% c-9, t-11) enhanced mitochondrial function and protection against oxidative stress by increasing the activities of cytochrome c oxidase, manganese-superoxide dismutase, glutathione peroxidase, and glutathione reductase and the level of GSH (Choi et al., 2007).
When the antioxidant efficacy of α-tocopherol, t-10, c-12 CLA and c-9, t-11 CLA (in graded concentrations) added to antioxidant-stripped corn oil was investigated, both CLA isomers displayed significant inhibition of corn oil lipid peroxidation induced by copper (Badr El-Din and Omaye, 2007). Inhibition of thiobarbituric acid reactive substances by CLA was concentration dependent for both isomers, with significant inhibition occurring at 0.1 and 1 ppm of CLA isomers or α-tocopherol, respectively (Badr El-Din and Omaye, 2007), suggesting that CLA compounds could serve as useful food antioxidants. These results indicate that both t-10, c-12 and c-9, t-11 isomers of CLA are effective antioxidants.
Overall, CLA appears to be a strong antioxidant. However, its effects and mechanism of action are not well understood. Therefore, it should not be construed as replacement for some other widely known and well established antioxidants or those prescribed by the physicians.
Contact the author regarding complete details about the references cited in the text or if you have any questions.
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