ReviewThe biologically active isomers of conjugated linoleic acid
Introduction
Numerous fatty acids with conjugated double bonds occur naturally in edible fats derived from ruminant animals, for example milkfat and beef tallow [1], [2], [3]. Similar structures are generated when linoleic acid is heated in base [4]. The term conjugated linoleic acid and its acronym CLA refer generically to this class of positional and geometric conjugated dienoic isomers of linoleic acid, two of which (cis-9,trans-11 and trans-10,cis-12 CLA) are known to possess biological activity (Fig. 1) [5].
Prior to 1987 scientific interest in CLA was confined largely to rumen microbiologists who studied the cis-9,trans-11 CLA isomer as an intermediate in the biohydrogenation of linoleic acid [6], [7]. This changed when Ha et al. [8] reported that CLA produced by base-catalyzed isomerization of linoleic acid was an effective inhibitor of benzo(a)pyrene-initiated mouse epidermal neoplasia. Since then numerous biological and physiological effects of CLA have been reported [5], [9] (for a regularly updated listing of the scientific literature on CLA since 1987 see the Internet address http://www.wisc.edu/fri/clarefs.htm).
Recently we reviewed evidence for CLAs multi-functionality and its implications regarding possible biochemical mechanisms [5]. Emerging evidence indicates that the cis-9,trans-11 and trans-10,cis-12 CLA isomers produce different effects. Given the structural differences between these isomers it is most unlikely that a single biochemical mechanism underlies these effects. In fact, there is evidence indicating that more than one biochemical mechanism is involved in the specific effects of the trans-10,cis-12 CLA isomer [5].
Section snippets
Biosynthesis
Parodi [6] summarized the early literature describing the seasonal fluctuation of conjugated dienes (now recognized as CLA) in cow’s milk. The amounts in spring and summer (when cows were pastured) were substantially higher than in fall and winter (when cows were stall-fed). Parodi [10] established that cis-9,trans-11 CLA was the principal CLA isomer in milkfat, a finding that has been confirmed [1], [2], [3].
Dhiman et al. [11], [12], [13] studied the effect of diet on the CLA content of cow’s
Physiological effects
Numerous seemingly beneficial physiological effects have been attributed to CLA including inhibiting chemically induced carcinogenesis in several rodent models [8], [29], [30], [31], enhancing the immune response while reducing the catabolic effects of immune stimulation in rodents and chickens [32], [33], reducing atherosclerosis in rabbits [34] and hamsters [35], enhancing growth of rats [36] and pigs [37], reducing body fat gain in mice [27], [38], [39], [40], [41], [42], rats [43], [44],
Summary and conclusions
We have discussed many of the reported physiological effects of CLA with specific regard to the separate and/or synergistic actions of the two known biologically active isomers,cis-9,trans-11 and trans-10,cis-12 CLA. Previously published data were reviewed and new findings that relate to underlying biochemical mechanisms of action were presented.
Both the cis-9,trans-11 and trans-10,cis-12 CLA isomers occur naturally in food. The cis-9,trans-11 isomer is the principal dietary form of CLA, but
References (86)
- et al.
J Food Comp Anal
(1992) - et al.
J Biol Chem.
(1966) J Dairy Sci.
(1977)- et al.
J Dairy Sci.
(1999) - et al.
J Dairy Sci.
(1999) - et al.
J Dairy Sci.
(2000) - et al.
J Nutr
(1994) - et al.
J Nutr
(2000) - et al.
System Appl Microbiol
(1987) - et al.
Poultry Sci.
(1993)
Biochem Biophys Res Comm.
Conjugated linoleic acid and atherosclerosis in rabbits. Atherosclerosis
J Nutr
J Nutr
J Nutr
J Nutr
Biochem Biophys Res Commun.
J Nutr
Biochim Biophys Acta
J Nutr
Biochim Biophys Acta
J Nutr
Nutr Res.
Nutr Res.
Food Chem Toxicol
J Nutr
Lipids
Lipids
JAOCS
Proc Soc Exptl Biol Med.
Carcinogenesis
Appl Environ Microbiol
Prog Lipid Res.
Lipids
J Dairy Sci.
Lipids
Lipids
Agr Biol Chem.
Cited by (944)
Identification of potential antiviral compounds from Egyptian sea stars against seasonal influenza A/H1N1 virus
2024, Journal of Genetic Engineering and BiotechnologyYak milk and milk products: Functional, bioactive constituents and therapeutic potential
2023, International Dairy JournalEffect of dietary pomegranate by-product on lamb flavour
2023, Meat Science