The new study, to be published in the October issues of The Journal of Nutritional Biochemistry , reports that the isomers of cis-9,trans-11 (c9,t11) and trans-10,cis-12 (t10,c12) were equally effective at inhibiting the spread (metastasis) of colon cancer cells in a mouse model.
If the results can be translated to humans, it may give us an important new weapon in the armoury against colon cancer, a disease responsible for about 492,000 deaths worldwide every year.
CLA are found predominantly in dairy products such as milk, cheese and meat, and are formed by bacteria in ruminants that take linoleic acids - fatty acids from plants - and convert them into conjugated linoleic acids, or CLA.
Knowledge surrounding the health benefits of the acids has been increasing, with studies indicating potential benefits for weight management, bone health and possibly even cancer.
For the new study, by researchers from Dankook and Hallym Universities, c9,t11 and t10,c12 isomers were tested for their ability to inhibit the metastasis of colon cancer cells in BALB/c mice.
"Because most deaths from cancer are related to metastasis, studies to determine the antimetastatic effects of various dietary components on colon cancer are very meaningful," explained lead researcher
So Mi Soela.
"However, the effects of the individual CLA isomers on metastasis have not been determined."
Four-week-old male BALB/c mice had colon cancer cells injected (CT-26) and were then divided into three diet groups - All diets were based on the AIN-93G diet and supplemented with no CLA (control), 0.1 per cent c9,t11 or t10,c12 CLA for four weeks.
Alone or together, these isomers are found in commercial CLA preparations.
The researchers report that both isomers were observed to significantly lower the number of so-called pulmonary nodules - small aggregations of cancer cells, compared to mice in the control group.
In vitro experiments using SW480 cells allowed the researchers to study the effects of the isomers on the activity of the MMP-9 enzyme, a key player in the degradation of the extracellular matrix (ECM) - degrading the cells around the tumour allows for easy spread of the cancer.
Despite similar results for the isomers from the in vivo study, the in vitro study showed that only c9,t11 CLA inhibited cell migration, while t10,c12 CLA had no effect.
In addition, neither isomer was found to affect MMP-9 levels.
"We have demonstrated that diets containing 0.1 per cent c9,t11 and t10,c12 CLA were equally effective in inhibiting colon cancer cell metastasis in vivo ," wrote Soela.
"However, in vitro , only c9,t11 but not t10,c12 inhibited colon cancer cell migration and MMP-9 activity."
The researchers stress that their results do not allow them to explain why the isomers acted differently during the in vitro and in vivo studies, suggesting merely that the t10,c12 isomer may have decreased the number of nodules via a mechanism unrelated to cell migration and MMP activity.
"In addition, previous results by other investigators have shown that t10,c12 CLA is more efficacious and potent in inhibiting colon cancer cell growth," they added.
More research is needed before these results can be translated to humans, but the results from the in vivo study appear promising for the ingredient most commonly linked to weight management and bone health.
Source: The Journal of Nutritional Biochemistry October 2007, Volume 18, Issue 10, Pages 650-657 "Influence of conjugated linoleic acid isomers on the metastasis of colon cancer cells in vitro and in vivo" Authors: So Mi Soela, Ok Sook Choia, Myung Hee Banga, Jung Han Yoon Parkb and Woo Kyoung Kima