Physiological and biochemical effects of conjugated linoleic acid and its use in aquaculture

R.Rosaetal.

repartitioningoffattolean(Duganetal.1997,2001;Parketal.1997,1999;Whighametal.2007),lowerbloodlipids(Evansetal.2002),tostimulateimmunefunction(Nugentetal.2005;Bhattacharyaetal.2006),andtoshowanti-angiogenic(Sikorskietal.2008),anticarcino-genic(Belury2002b;Kelleyetal.2007),antidiabetic,hypocholesterolaemicandanti-atherogenicproperties(Nicolosietal.1997;McLeodetal.2004).Inthepresentpaper,wediscusscurrentknowledgeoftheroleofCLAinanimalphysiologyandhealthandreviewadvancesinitsapplicationin shaquaculture.

Conjugatedlinoleicacid:de nitionandsynthesisConjugatedlinoleicacidisagenerictermforagroupofpolyunsaturatedfattyacidsthatexistaspositionalandstereoisomersoflinoleicacid(18:2cis-9,cis-12).Thedou-blebondsinCLAcanoccurinseveralpositionsalongthecarbonchain:atpositions7and9,8and10,9and11,10and12,11and13,or12and14.Themostprominentisomersinfoodsarecis-9,trans-11-CLA(abbreviatedc9t11-CLA,alsocalledrumenicacid),t7c9-CLA,t11c13-CLA,c8t10-CLA,t10c12-CLA.Although58differentisomershavebeenidenti edtodate,twoofthem(c9t11-CLAandt10c12-CLA)haveraisedspecialattentionasaresultoftheirbiologicalactivity(Fig.1)(Parizaetal.2000,2001).Mostexperimentalstudiescarriedoutinani-malshaveusedsyntheticmixturesofCLA(producedbyalkalineisomerizationoflinoleic-acid-richoils)contain-ingequimolarmixtureofc9t11-CLAandt10c12-CLA(Belury2002a).

BiologicalsynthesisofCLAoccursthroughmicrobialbiohydrogenation(bythebacteriumButyrvibrio brisolvens)ofdietarylinoleicacidinthedigestivetracts(rumen)ofruminantanimals(Fig.2)(Bessaetal.2000;Bauman&Griinari2001).AnotherbiologicalsourceofCLAisendogenoussynthesisviaD9-desaturaseoftrans-11C18:1,

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Linoleic acid (cis-9, cis-12 C18:2) Conjugated linoleic acid (cis-9, trans-11 CLA)

Trans-11 C18:1Stearic acid (C18:0)

Figure2Pathwaysofruminalbiohydrogenationoflinoleicacid.

thesecondintermediateoflinoleicacidbiohydrogenation(Griinarietal.2000;Corletal.2001).

ConjugatedlinoleicacidanditsbiologicaleffectsInterestinCLAisomershasgrownsubstantiallyoverthepastdecadebecauseofthesurprisingnumberofhealthbene tsthathavebeenattributedtoCLA,particularlytoitsmainisomers(c9t11andt10c12).Conjugatedlinoleicacidselicitspeci c,oftendifferent,metabolicandcell-signallingeffectsinavarietyoftissuesandcells,invivoandinvitro,whichcouldexplaintheirreportedhealthbene tsinanimals,includinghumans(Table1).MostresearchonCLAhasfocussedonitsanticarcinogenicproperties.Infact,theUSNationalResearchCouncilsta-tedin1996thatCLAistheonlyfattyacidshownunequiv-ocallytoinhibitcarcinogenesisinexperimentalanimals(NRC1996).Conjugatedlinoleicacidreportedlyhasanti-carcinogeniceffectsatvariousstagesofcancerdevelop-ment,includinginitiation,progressionandmetastasis(Belury2002b).ThebiochemicalmechanismwherebyCLAinhibitscarcinogenesiscouldresultfromthecombinedeffectsofanumberofCLAactivities,possiblyincludingdirecteffectsofoneormoreCLAisomers metabolitesoncelldifferentiation(Ipetal.1995;Thompsonetal.1997;Houseknechtetal.1998;Parketal.1999),andeffectsonthemetabolismoflinoleicacidandvitaminA(Bannietal.1999a,b).Moreover,CLAseemstosigni cantlyreduceprostaglandinE2synthesis,whichcouldinhibittumourformation(Kavanaughetal.1999).

Conjugatedlinoleicacidhasalsobeenshowntoreducebodyfatgaininmice,rats,hamsters,pigsanddogs(seereferencesinTable1),andinsomecasestoincreasetheleanbodymassingrowinganimals,inde-pendentlyofanychangesinfeedintake(DeLanyetal.1999;Keim2003).Studieshaveshownthatthemainindividualisomerscis-9,trans-11andtrans-10,cis-12havedistincteffectsonanimallipidmetabolismandevi-dencesuggeststhatthetrans-10,cis-12isomeristheonethataffectsbodycompositionandelicitedthegreatest

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