CLA Rumenic Acid

Fatty acids with trans or non-methylene-interrupted unsaturation occur naturally or are formed during processing for example, vaccenic acid (18 1 Hr) and the conjugated linoleic acid (CLA) rumenic acid (18 2 9tllc) are found in dairy fats. Hydroxy, epoxy, cyclopropane, cyclopropene acetylenic, and methyl branched fatty acids are known, but only ricinoleic acid (12(/f)-hydroxy-9Z-octadecenoic acid) (2) from castor oil is used for oleochemical production. OUs containing vernolic acid (12(5),13(/ )-epoxy-9Z-octadecenoic acid) (3) have potential for industrial use. 

The term conjugated linoleic add (CLA) refers to a mixture of positional and geometric isomers of linoleic add with a conjugated double bond system milk fat can contain over 20 different isomers of CLA. CLA isomers are produced as transient intermediates in the rumen biohydrogenation of unsaturated fatty acids consumed in the diet. However, cis-9, trans-11 CLA, known as rumenic acid (RA), is the predominant isomer (up to 90% of total) because it is produced mainly by endogenous synthesis from vaccenic acid (VA). VA is typically the major biohydrogenation intermediate produced in the rumen and it is converted to RA by A9-desaturase in the mammary gland and other tissues. 

Figure 3.2. Pathways for ruminal and endogenous synthesis of rumenic acid (cis-9, trans-11 CLA) in the lactating dairy cow. Pathways for biohydrogenation of linoleic and linolenic acids yielding vaccenic acid trans-11 18 1) are shown in the rumen box and endogenous synthesis by A9-desaturase is shown in the mammary gland box. Adapted from Bauman et at. (2003).

Figure 3.3. The A9-desaturase enzyme system showing the conversion of vaccenic acid (trans-11 18 1) to rumenic acid (cis-9, trans-11 CLA).

As the result of feeding cows encapsulated fat, desirable milk fat modification can be obtained so that the PEFA in fat are limited. A conjugated linoleic acid (CLA), also referred to as rumen acid cis-9, trans-11 -octadecadienoic acid), is a nutritionally important fat component. If present in the human diet, this acid prevents obesity,... 

The first discovered CLA precursor is linoleic acid cis-9,cis- 2 18 2). The double bond of linoleic acid present further for the carboxyl group can be translocated by cis- 2,trans- isomerase (Kepler Tove, 1967) and the resulting rumenic acid cis-9,trans- CLA) is then hydrogenated by the reductase of Butyrivibrio fibrisol-vens to vaccenic acid (frans-W 18 1) (Hughes, Hunter, Tove, 1982). These steps occur relatively fast, whereas the hydrogenation of vaccenic add to stearic acid is... 

CLA can also be synthesised in the human colon. Some bacterial strains normally present in the human large intestine (Lactobacillus, Propionibacterium and Bifidobacterium species and some Clostridium-like bacteria) have been found to metabohse linoleic acid and form CLA that is converted further to trans-1118 1 in vitro. Vaccenic acid may be also a precursor of rumenic acid (cis-9,trans-ll CLA) in human tissues (Devillard, McIntosh, Duncan, Wallace, 2007). 

The anti-diabetic effect of CLA may depend on both species and types of isomer. Rumenic acid seemed to be inactive (Martin Valeille, 2002), but the role of Irans-10,cis-12 isomer is controversial some studies verified decreasing glucose levels and increased insulin sensitivity with increased intake of lrans-10,cis-l2 CLA (see the review by Khanal, 2004), while others reported opposite effects - that is, the promotion of insnlin resistance (Khanal, 2004 Moloney, Yeow, Mullen, Nolan, Roche, 2004 Wang Jones, 2004). 

But where do all the other isomers come from Desaturation should not occur in the reducing environment of the rumen and thus could not explain the array of isomers observed as desaturation of rra r-monoenes. On the other hand, hydrogenation is efficiently accomplished when rumen pH is appropriate for the organisms involved in the isomerization and hydrogenation of PUFA (16). Several of the organisms appear to have specific selectivity for certain structures of the PUFA on which they act. Different microbes could have different preferences for PUFA isomers, rumen pH, or nutrients but there is insufficient information at this time to clearly describe the rumen flora in a way that would explain the plethora of fatty acid isomers observed in the rumen and milk of dairy cows. The following discussion may provide insights into possible mechanisms to explain the presence of the myriad of trans, cis, and CLA fatty acids in rumen and milk fat. 

In food, CLA is found in milk fat, the tissue fat of ruminant animals, and products derived from them, although there are exceptions. About 90% of the CLA is represented by the cis-9, trani-11-isomer or rumenic acid (RA) (4). This isomer is produced in the rumen by the action of a linoleic acid isomerase on dietary linoleic acid as a first step in the biohydrogenation process. Further hydrogenation produces trans- - %. or vaccenic acid (VA), the predominant trans monounsaturat-ed fatty acid of milk and animal tissue fat. The major polyunsaturated fatty acids of pasture, a-and y-linolenic acid, cannot be converted to RA, but they do produce VA. A proportion of RA and VA escape further hydrogenation in the rumen and after absorption pass via the circulatory system to adipose tissue and the mammary gland where A -desaturases convert VA to RA. About 70% of RA in milk fat is produced by this pathway (5). 

An early diseovery in the biology of CLA in ruminants was the identification of cis-9, Irans-ll CLA in milk fat (8), and the common name of rumenic acid was proposed for this CLA isomer because of its unique relationship to ruminants (9). However, as analytical techniques improved, it became evident that ruminant... 

Interestingly, only the 10t,12c-18 2 increased the stearic acid content at the expense of 18 ln-9, which suggests an alteration in A9 desaturase activity. This observation was further confirmed by in vitro studies. Lee et al. (8) reported that CLA depressed the expression of stearoyl-CoA desaturase (SCD) mRNA. These effects were correlated with a decrease in the 16 1/16 0 and 18 1/18 0 ratios in mice liver, which are considered to be indices of A9 desaturation. Moreover, studies conducted with pure rumenic acid suggested that this effect on SCD was due mainly to other conjugated fatty acid isomers. Bretillon et al. (9) demonstrated that... 

Oxidative Metabolism. Because CLA are fatty acids, they are substrate for energy production through oxidative metabolism. However, few studies have been conducted to consider this metabolic pathway. One study was published on carbon dioxide production during 24 h after a bolus intragastric delivery of labeled CLA isomers compared with linoleic acid (16). It appeared (Fig. 15.2) that both CLA isomers studied were more oxidized than linoleic acid. In that study, 70% of the radioactivity was recovered as CO2, a value close to what was previouly observed with linolenic acid (17). However, when looking at the mechanisms involved in mitochondrial oxidation, Clouet et al. (18) showed that mitochondrial respiration with rumenic acid was lower than that with linoleic acid. These difference between both fatty acids may be due to a lower camitine-acylcamitine translocase activity. 

In a study conducted by Turpeinen et al. (30), it was shown that feeding 3 g/d of vaccenic acid induced an increase of CLA in serum TAG. The CLA content doubled within a few days and a steady state was achieved in 4-6 d. These data support the hypothesis that vaccenic acid may be desaturated into rumenic acid in humans as well as in rodents. On average, 19% of vaccenic acid was converted to CLA in healthy human subjects. 

In natural CLA, cB-9,fran -l 1-octadecadienoate (9c,llt-18 2, rumenic acid Figure 2.2) is always the major isomer, although a variety of other isomers can occur as minor components. Noteworthy are the lt,9c isomer, occurring at a level of about 10% of the major isomer, and the 10r,12cand Ilf, 13c isomers that can occur at significant levels under certain conditions (Lock and Bauman, 2004). In industrial preparations, the 9c,l If and 10f,12c isomers are the major components, but there are varying amounts of particularly the 8f,10c and 1 lc,13f isomers, and sometimes other positional isomers. Cis-cis and trans-trans isomers are also produced, usually as minor components. 

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