MRI measurement of liver fat content predicts the metabolic syndrome

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Availableonlineat

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Diabetes&Metabolism39(2013)314–321

Original article

MRI measurement of liver fat content predicts the metabolic syndrome

P.-H. Ducluzeau

^a,g,∗

, J. Boursier

^b,c

, S. Bertrais

^b,c

, S. Dubois

^a,g

, A. Gauthier

^a

, V. Rohmer

^a,g

, F. Gagnadoux

^d,g

, G. Leftheriotis

^e

, P. Cales

^b,c

, R. Andriantsitohaina

^g

, V. Roullier

^f

, C. Aubé

^f

aDepartmentofEndocrinology-Diabetology-Nutrition,LUNAMuniversité,universitéd’Angers,CHUd’Angers,49100Angers,France

bDepartmentofHepatology,LUNAMuniversité,universitéd’Angers,CHUd’Angers,49100Angers,France

cLaboratoryHIFIH,UPRES3859,LUNAMuniversité,universitéd’Angers,CHUd’Angers,49100Angers,France

dDepartmentofPneumology,LUNAMuniversité,universitéd’Angers,CHUd’Angers,49100Angers,France

eDepartmentofVascularExploration,LUNAMuniversité,universitéd’Angers,CHUd’Angers,49100Angers,France

fDepartmentofRadiology,LUNAMuniversité,universitéd’Angers,CHUd’Angers,49100Angers,France

gInserm,U1063,“oxidativestressandmetabolicdiseases”,LUNAMuniversité,universitéd’Angers,CHUd’Angers,49100Angers,France Received27September2012;receivedinrevisedform21January2013;accepted30January2013

Abstract

Backgroundandaims.–Theprevalenceofnon-alcoholicfattyliverdiseaseamongcardiometabolicpatientsisnotcompletelyknownbecause liverbiopsycannotberoutinelyperformed.However,asmagneticresonanceimaging(MRI)allowsaccurateandsafemeasurementofthehepatic fatfraction(HFF),theaimofthisstudywastoquantifyliverfatcontentinadysmetabolicadultpopulation.

Methods.–Atotalof156adultswereincludedinthiscross-sectionalstudy.LiverandvisceralfatwereassessedbyMRIinthesesubjects,who presentedwithzerotofivemetaboliccomponentsofthemetabolicsyndrome(MetS).Arterialstiffnesswasrecordedbyultrasonography,andthe maximumYoudenindexwasusedtosettheoptimalHFFcutoffvaluepredictiveofthepresenceoftheMetS.

Results.–Overall,72%ofparticipantsdisplayedthreeormoreMetScomponents.HFFrangedfrom0.3%to52%(mean13.4%).Age-and gender-adjustedHFFwaspositivelycorrelatedwithBMI(r=0.44),bloodpressure(r=0.19),triglyceridaemia(r=0.22)andglycaemia(r=0.31).

MRI-measuredvisceraladiposetissuedidnotinfluencetherelationshipofsteatosiswithglycaemia,HOMA–IRandcarotidstiffness,butthere wasadose–responserelationshipbetweenthenumberofMetScomponentsandmeanHFF.TheoptimalHFFforpredictingtheMetSwasfound tobe5.2%accordingtothemaximumYoudenindexpoint.

Conclusion.–Thisstudyhighlightedtheimpactofliversteatosisoncardiometabolicabnormalitieswithanoptimalcutoffvalueof5.2%for definingincreasedmetabolicrisk.

Keywords: Liversteatosis;Magneticresonanceimaging;Themetabolicsyndrome;Vascularstiffness Résumé

LedegrédestéatosehépatiquemesuréparIRMestunfacteurprédictifdelaprésenced’unsyndromemétabolique.

Contexteetobjectifs.–Laprévalencedestéatosehépatiquenonalcooliquechezlespatientsprésentantdescritèresdusyndromemétabolique estmalconnue,principalementdufaitquelabiopsiedufoienepeutpasêtrefaitesystématiquement.L’imagerieparrésonancemagnétique(IRM) permetunemesurepréciseetsûredufractionlipidiquehépatique(HFF).Lebutdecetteétudeétaitdequantifierlecontenulipidiquedufoiedans unepopulationadultedysmétabolique.

Méthodes.–Centcinquante-sixadultesontétéinclusdanscetteétudetransversale.Ledegrédestéatoseetlagraisseviscéraleontétéévaluéspar IRM.Lessujetsontétéclassésselonleurnombredecritèredusyndromemétabolique(MetS),dezéroàcinqcomposantes.Larigiditéartériellea étéenregistréeparl’échographie.L’indicemaximaldeYoudenaétéutilisépourétablirunevaleuroptimaledestéatoseprédicivedelaprésence d’unMetS.

Résultats.–Soixante-douzepourcentdesparticipantsprésentaientunMetS(soitplusdedeuxcritères).LaHFFvariaitde0,3à52%(moyenne 13,4%).Aprèsajustementsurl’âgeetlesexe,laHFFestpositivementcorréléeàl’IMC(r=0,44),lapressionartérielle(r=0,19),latriglycéridé

Abbreviations:HFF,hepaticfatfraction;MRI,magneticresonanceimaging;MRS,magneticresonancespectroscopy;MetS,metabolicsyndrome;NAFLD, non-alcoholicfattyliverdisease;PWV,Pulsewavevelocity;T2D,type2diabetes.

∗Correspondingauthor.Departmentofnutrition,CHUd’Angers,4,rueLarrey,49033Angers,France.Tel.:+33241354497;fax:+33241355900.

E-mailaddress:phducluzeau@chu-angers.fr(P.-H.Ducluzeau).

http://dx.doi.org/10.1016/j.diabet.2013.01.007

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(r=0,22),etlaglycémie(r=0,31).Laquantitédetissuadipeuxviscéral,mesuréeparIRM,n’apasd’influencesurlarelationdelastéatoseavec laglycémie,leHOMA–IRetlarigiditécarotidienne.Ledegrédestéatosehépatiqueoptimalquipréditlemieuxlaprésenced’unMetSaétéétabli à5,2%.

Conclusion.–Cetteétudeamisenévidencel’impactdelastéatosehépatiquesurlesanomaliescardio-métaboliquescaractérisantleSMavec unevaleurseuiloptimalede5,2%pourladéfinitiond’unrisquemétaboliqueaccru.

Motsclés:Stéatosehépatique;Imagerieparrésonancemagnétique;Syndromemétabolique;Rigiditévasculaire

1. Introduction

Theprevalencesof bothtype2 diabetes(T2D) andcardio- vasculardisease areincreasing worldwide,andmoreeffortis neededtounderstandthepathophysiologyoftheseconditions.

Insulinresistanceisthecommonphysiologicalbasisofbothliver steatosisand the metabolic syndrome (MetS), andis present longbeforethe diagnosis of diabetes [1,2].Adipose tissueis commonlyassociatedwithinsulinresistancebut,morerecently, studieshaveshownthattheaccumulationoffatinthevisceral cavityandparticularly inthe liver,is moreclosely relatedto insulinresistancesyndromethanoveralladiposity[3–5].Itis now widelyaccepted that fatty liveris part of the MetS and thatnon-alcoholicfattyliverdisease(NAFLD)sharesthesame molecular characteristics as insulin resistance in hepatocytes [6–8].TheprevalenceofNAFLDhasincreasedtogreaterthan 70% of subjects who haveeither the MetS or T2D, butit is importanttonotethatthedegreeofsteatosiscanvaryovertime, witharound20to30%ofpatientsstudiedshowingaprogression tosteatohepatitisorfibrosis[9].Evidencehasalsonowaccumu- latedthatfattylivermeasuredbyultrasonographyorestimated bybloodtestscanpredicttheriskofT2DandtheMetS[10–14].

However, the impact of NAFLD on the progression of metabolicdiseaseshasyettobefullyelucidatedmainlybecause astandardandsafewaytomeasurethedegreeof steatosisis stilltobefound.Liverbiopsyisaninvasiveprocedurethatis notappropriate foreither theevaluationor follow-upofliver steatosisindysmetabolicpatients.Also,itsvalueishampered bysamplingbias,anditallowsonlysemi-quantitativescoring ofliversteatosis.Forthisreason,anaccessibleaswellasnon- invasivewayofquantifyingliverfatcontentwouldbeusefulfor largeclinicalstudies[15].Inthiscontext,thereferenceradiolog- icalmethodformeasurementoftriglyceride(TG)accumulation inlivertissueisprotonmagneticresonancespectroscopy(¹H- MRS)[16].Thetechnique,however,requiresspecificsoftware andstringentconditionstoensurethatsequenceacquisitionsare reliable.Overthelastcoupleofyears,ithasbeendemonstrated thatmagneticresonanceimaging(MRI)usingmulti-echogra- dientsequencesisverysimilarto¹H-MRSforquantifyingliver fatcontent.Nevertheless,relevantclinicalstudiesusingMRIin alargenumberofsubjectsarestillscarce[15–21].

In the present cross-sectional study, liver fat content was quantifiedusingavalidatedMRIprotocolinacohortofFrench adultswithvariousdegreesofmetabolicabnormalities.Thepur- poseofthestudywastoclarifytherelationshipofthehepatic fatfraction(HFF)witheachcomponentoftheMetSaswellas witheachpatient’sarterialstiffness.

2. Patientsandmethods 2.1. Studypopulation

Altogether,156 adultFrench subjectsaged30to75years, initiallyreferred to the departmentof nutrition for metabolic explorations, wereselectedforthestudy. Thesepatients were alsopartoftheNUMEVOXcohortandhadallundergoneMRI.

TheobjectiveoftheNUMEVOXcohort(Clinicaltrialsnumber NCT00997165)wastodescribetheimpactoffatdistributionon vascular andmetabolicevolution,andpatientswere recruited becausethepresenceoftheMetSwasacriterion.Patientswere classifiedintogroupsaccordingtothepresenceorabsenceofthe MetS(MetS+orMetS–)oroftype2diabetes(T2D).Presence oftheMetS wasdefinedaccordingtoCaucasianInternational DiabetesFederation(IDF)2005criteria[22].Informedconsent wasobtainedfromeachpatient,andthestudyprotocolhadthe approvalof the localinstitution’shumanresearchcommittee.

Exclusioncriteriawereabodymassindex(BMI)greaterthan 40kg/m²,HbA1cconcentrationgreaterthan9%,insulin-treated diabetes,severearterialhypertension(>180/120mmHg),severe hypertriglyceridaemia(TG>10g/L),severerenalfailure(cre- atinineclearance<30mL/min),viraloralcoholichepatitis,and anycontraindicationsforMRI.

2.2. Clinicalandbiologicalmeasurements

During hospitalization, weight, height and waist circum- ference were recorded as well as the 15-min brachial blood pressure, using an automatic bloodpressure cuff. The waist- to-hipratio(WHR)andBMIwere calculated.Bloodsamples were obtained after a 10-h fast and before any medications hadbeen taken.All biochemical measurements werecentral- ized. Leptin levels were measured using an enzyme-linked immunosorbentassay(ELISA,EMDMillipore,Billerica,MA, USA). Adiponectin was measured using an ELISA kit with intra- and inter-assay coefficients of variation of 7.25% and 6.32%, respectively (EMD Millipore). Insulin resistance was determinedbyhomoeostasismodelassessmentforinsulinresis- tance(HOMA–IR;fastingseruminsulinin␮U/mL×glucose levelinmmol/Ldividedby22.5).

2.3. MRIassessment

AnabdominalMRIwasperformedonall156patientsusing a1.5-T MR system(GeneralElectric MedicalSystems,Mil- waukee, IL,USA)withaphased-arraysurface coil.Areasof

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visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) were calculated on T1-weighted sequences using validated software [23]. HFF was quantified with a multi- echo gradient-echo (MFGRE) sequence using a previously validated method [24,25]. HFF calculation was based onthe signal intensities measured in two regions of interest in the anterior andposterior right lobe of the liveraway from liver vessels.

2.4. Vascularmeasurements

Eachpatientalsounderwentsupra-aortictrunkDopplerultra- sound with measurement of intima–media thickness (IMT) according torecommendations. Arterial stiffness was quantified by measuring the speed of the carotid pulse waveusing an echo-tracking system coupled with ultrasound equipment (eTRACKING,HitachiAlokaMedicalLtd,Tokyo,Japan)that allowed, after B-mode scanning, the simultaneous measurement of diameter variations and local pulse wave velocity (PWV) in the common carotid artery. A validated algo- rithm was used to calculate the local carotid PWV, which is directly proportional to carotid wall stiffness [26,27]. PWV was expressed as meters per second (m/s). The aortic PWV was measured using the samedevice bysequentially record- ing electrocardiogram-gated right carotid and femoral artery waveforms.

2.5. Statisticalanalysis

Statisticalanalysiswasperformedusingstandardprocedures foundinSASsoftware,version9.2(SASInstituteInc.,Cary, NC,USA).Allvariableswithaskeweddistributionwerelog- arithmically transformed, and presented as geometric means togetherwith95%confidenceintervals(CI).Categoricalvaria- bles were compared using chi-square tests, and analysis of variance (ANOVA)wasused for quantitativevariables;when theglobalFisher’stestwassignificant,theBonferronimethod wasappliedtoperformpairedcomparisonsformultiplecom- parisons.HFFinrelationtoeachparameterwasexpressedas gender- andage-adjustedSpearman’scorrelationcoefficients.

Inaddition,fourdifferentmultivariateregressionmodelswere constructedtoassesstheassociationofhepaticfatcontentwith the relevant metabolic andvascular parametersafter control- lingfor age,genderandanyadditionalpotentialconfounding factors,including BMI and/orVATandfastinginsulinlevels.

Also evaluatedwas theperformanceof hepatic fatcontentto identifypatientswhohadatleastthreecharacteristicabnormal- itiesoftheMetS.Thecutoffpointwasfixedatthemaximum valueoftheYoudenindex(sensitivity+specificity–1),andthe diagnosticperformanceatthisfixedcutofflevelwasmeasured interms of diagnostic accuracy, including proportion of true positivesandtrue negatives, sensitivity (Se),specificity (Sp), positivepredictive value (PPV)and negativepredictive value (NPV).

Forallanalyses,aPvalue<0.05wasconsideredsignificant, andalltestsweretwo-sided.

3. Results

3.1. Characteristicsofthestudypopulation

Atotalof156subjectswhohadavailableHFFassessedby MRIscanswereincludedinthepresentstudy.Allwereslightly younger than the 179 other participants in the NUMEVOX cohort (52.9±9.8 years vs 55.7±9.4 years, respectively;

P<0.0067) and less frequently diabetic (23.1% vs 34.6%, respectively;P<0.020;datanotshown).Thestudyparticipants weredividedinthreegroups:68hadtheMetSwithoutdiabetes (the “MetS+”group);36 hadT2D (the“T2D”group)treated onlywithmetformin(n=25)ornotreatment(n=11);and52had neithertheMetSnorT2D(the“MetS–”group).Thecharacteris- ticsofallsubjectsaccordingtogroupareshowninTable1.The threegroupswerecomparableintermsofgenderandsmoking status.Asexpected,theMetS+patientshad,onaverage,higher hepaticfatcontentasmeasuredbyMRIthantheMetS–participants(15.0%vs9.4%,respectively),andT2Dpatientsdisplayed thesamemeanlevelofsteatosisastheMetS+subjects.Also,the percentageofVATwassignificantlylargerinT2Dpatientsthan inMetS+patients,whileglycaemiashowedsignificantincreases across allthreegroups.BothMetS+andT2Dgroupsshowed similarlevelsofinsulinresistancebasedonHOMA–IR.Leptin levelsweresignificantlyhigheronlyamongtheMetS+participants,therebysupportingtheobservationthatT2Dpatientshave lesssubcutaneousfatthanthosewhoareMetS+.Systolicblood pressure,aorticPWV,andcarotid IMTandPWVwerelower among theMetS– groupcomparedwith theT2D andMetS+

patients,withnodifferencesbetweenthelattertwogroups.

3.2. Correlationbetweenhepaticfatfractionand anthropometric,metabolic,vascularandliverparameters

Table2showstheassociationsbetweenHFFandclinicaland laboratorycriteriaoftheMetSafteradjustingforageandgen- der.TherewasasignificantcorrelationbetweenHFFandeach of thefollowingMetScriteria:waistcircumference (r=0.37);

WHR(r=0.27);systolicarterialbloodpressure(r=0.19);TG (r=0.22);andglycaemia(r=0.31).ThestrongestHFFrelation- shipswerefoundwithBMI(r=0.44)andtheMRI-basedVAT quantification (r=0.39), whereasabdominal SATwasrelated toalesserextenttoHFF.Althoughbothleptinandadiponectin werecorrelatedwithHFFinoursubjects,therewasbettercor- relationwithleptin(r=0.28)thanwithadiponectin(r=–0.17).

The HOMA–IR indexwas strongly andpositively associated with HFF for the whole of the study population (r=0.44), withnodifferencesacrossthethreegroups.Oftheliver-related biological parameters, serumalanine aminotransferase(ALT) displayedthestrongestrelationshipwithHFF(r=0.42),while gamma-glutamyltransferase(GGT)andferritinlevelswerealso relatedtoHFF.In addition,apositiverelationshipwasfound between HFF andlow-grade inflammationas assessed byC- reactiveprotein(CRP)levels.HFFwasalsopositivelyrelatedto vascularstiffness(withaorticvesselsmoresothanthecarotids).

Table3showstherelationshipsbetweenHFFandtherelevant metabolic andvascular componentsafter taking into account

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Table1

Characteristicsofthestudyparticipantsaccordingtotheirmetabolicsyndrome(MetS)anddiabetesstatus.

n MetS–

(n=52)

MetS+

(n=68)

Type2diabetics (n=36)

GlobalP Pairedcomparisons^d

Men,n(%) 156 37(71.1) 46(67.6) 29(80.6) 0.38 –

Smoker,n(%) 156 11(21.2) 14(20.6) 2(5.6) 0.10 –

Age(years) 156 50.5±9.9 52.2±10.2 57.6±7.5 0.0024 ^b,c

Weight(kg) 156 81.4±12.9 93.6±15.0 87.9±12.9 <0.0001 ^a

Height(m) 156 1.69±0.09 1.69±0.09 1.69±0.10 0.96 –

BMI(kg/m²) 156 28.5±4.8 33.0±5.4 31.0±4.2 <0.0001 ^a

Waistcircumference(cm) 156 97.4±10.4 108.5±12.2 105.0±10.0 <0.0001 ^a,b

Hipcircumference(cm) 156 103.6±9.4 111.1±11.0 106.2±9.2 0.0003 ^a

WHR 156 0.94±0.06 0.98±0.07 0.99±0.06 0.0015 ^a,b

Hepaticfatfraction(%) 156 9.4±10.3 15.0±13.4 16.8±14.0 0.0129 ^a,b

VAT(cm²) 156 132.5±72.4 204.8±88.7 217.7±87.5 <0.0001 ^a,b

SAT(cm²) 156 203.1±87.4 267.1±126 224.6±143.6 0.0145 ^a

VAT(%) 156 38.5±16.7 44.2±15.8 49.5±16.6 0.0086 ^b,c

SystolicBP(mmHg) 156 121.4±12.6 131.2±12.8 130.0±14.8 0.0003 ^a,b

DiastolicBP(mmHg) 156 75.4±8.6 78.3±9.8 76.9±10.9 0.28 –

Pulsepressure(mmHg) 156 46.0±9.5 52.9±9.4 53.1±11.3 0.0003 ^a,b

Heartrate(beats/min) 156 67.8±10.6 70.5±10.5 72.9±10.2 0.089 –

HbA1c(%) 155 5.64±0.35 5.86±0.42 6.73±0.59 <0.0001 ^a,b,c

Glucose(g/L) 156 0.95±0.09 1.08±0.13 1.32±0.23 <0.0001 ^a,b,c

Insulin(mU/L)^e 150 10.2

(8.7–11.9)

17.2 (15.0–19.6)

15.3 (12.7–18.5)

<0.0001 ^a,b

HOMA–IR^e 150 2.33

(1.97–2.70)

4.52 (3.91–5.22)

4.87 (3.98–5.99)

<0.0001 ^a,b

Totalcholesterol(g/L) 156 2.14±0.46 2.03±0.47 1.92±0.38 0.068 –

HDLcholesterol(g/L) 156 0.61±0.15 0.53±0.17 0.55±0.17 0.05 –

LDLcholesterol(g/L) 156 1.30±0.38 1.14±0.36 1.07±0.29 <0.0001 ^a,b,c

Triglycerides(g/L)^e 156 1.11

(0.97–1.28)

1.69 (1.50–1.90)

1.35 (1.15–1.60)

<0.0001 ^a

Leptin(␮g/L)^e 146 10.7

(8.4–13.6)

16.9 (13.7–20.8)

12.0 (9.1–15.9)

<0.0001 ^a

Adiponectin(mg/L) 145 7.75±3.55 7.30±3.28 7.10±3.73 0.67 –

CarotidIMT(mm) 140 0.60±0.08 0.64±0.08 0.66±0.08 0.0039 ^b

CarotidPWV(m/s) 142 6.32±0.87 6.79±1.26 7.04±1.49 0.0295 ^b

AorticPWV(m/s) 142 7.12±1.99 8.65±2.34 9.45±2.69 0.0034 ^a,b

BMI:bodymassindex;WHR:waist-to-hipratio;VAT:visceraladiposetissue;SAT:subcutaneousadiposetissue;BP:bloodpressure; HbA1c:glycosylated haemoglobin;HOMA–IR:homoeostasismodelassessmentforinsulinresistance;HDL/LDL:high-density/low-densitylipoprotein;IMT:intima–mediathickness;

PWV:pulsewavevelocity.

a P<0.05fordifferencebetweenMetS–andMetS+.

b P<0.05fordifferencebetweenMetS–anddiabetics.

c P<0.05fordifferencebetweenMetS+anddiabetics.

d ByBonferronittest.

e Skeweddistributionofvalues:statisticaltestswerecarriedoutonlogarithmicallytransformedvalues;valuesareexpressedasgeometricmeans(95%confidence interval).

otherpotentialconfounders,especiallyoveralladiposityandits visceraldistribution.In additiontoageandgender,themulti- variateregressionanalysisalsoincludedBMI,VATandinsulin levels (Table 4). Fasting serumglycaemia remainedstrongly andpositivelyassociatedwithHFFafteradjustingforBMIand VAT(P=0.003)andafterconsideringinsulinlevels(P=0.008).

Moreover,thesameresultsforHFFinrelationtoHbA1cwere foundevenafterexcludingT2Dpatientsfromtheanalysis(data not shown). The HFF–CRP relationship remainedsignificant afteradjustingforBMIandVAT,butwasnolongersignificant after furtheradjustmentfor insulinlevels andso was consis- tentwiththewell-knownroleofinsulinresistanceinlow-grade inflammation.TheHFF-to-systolicbloodpressurerelationship disappearedafteradjustingforVAT,butnotafteradjustingfor

BMI,whilethe relationshipbetweenaorticstiffness andHFF was lostafterentering eitherBMI orVAT intothe model.In contrast,thecarotidstiffnessandHFFrelationshipremainedsig- nificantafteradjustingforadiposityparameters,butdisappeared onlywheninsulinlevelswereincluded.

3.3. Hepaticfatfraction,numberofmetabolicsyndrome (MetS)componentsandcutoffvalueforMetSdiagnosis

Fig.1showsthedegreeofsteatosisinparticipantsgrouped accordingtothenumberofMetScomponentstheyhad(those witheitherzerooronecomponentwerepooled).HFFincreased gradually with the number of MetS components (P<0.0012 foralineartrend). AmongpatientswithfewerthantwoMetS

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Table2

Gender-andage-adjustedSpearman’scorrelationcoefficientsforhepaticfat fraction(HFF)andrelatedparameters.

r Pvalue

BMI(kg/m²) 0.441 <0.0001

Waistcircumference(cm) 0.374 <0.0001

WHR 0.275 0.0005

SystolicBP(mmHg) 0.191 0.0023

DiastolicBP(mmHg) 0.05 0.3852

Triglycerides(g/L) 0.219 0.0058

HDLcholesterol(g/L) –0.062 0.4434

LDLcholesterol(g/L) 0.021 0.8035

Glycaemia(g/L) 0.311 <0.0001

HbA1c(%) 0.263 0.0009

HOMA–IR 0.441 <0.0001

VATarea(cm²) 0.395 <0.0001

SATarea(cm²) 0.165 0.0458

Leptin(␮g/L) 0.281 0.0006

Adiponectin(mg/L) –0.169 0.0042

Microalbuminuria(mg/L) 0.124 0.1297

C-reactiveprotein(mg/L) 0.244 0.0029

GGT(IU/L) 0.201 0.0125

ALT(IU/L) 0.419 <0.0001

Ferritin(␮g/L) 0.203 0.0014

CarotidIMT(mm) 0.139 0.0937

CarotidPWV(m/s) 0.289 0.0005

AorticPWV(m/s) 0.401 0.0003

BMI: body mass index; WHR: waist-to-hip ratio; BP: blood pressure; HDL/LDL: high-density/low-densitylipoprotein; HbA1c: glycosylated haemoglobin;HOMA–IR:homoeostasismodelassessmentforinsulinresistance; VAT: visceral adipose tissue; SAT: subcutaneous adipose tissue;

GGT: gamma-glutamyl transferase; ALT: alanine aminotransferase; IMT:

intima–mediathickness;PWV:pulsewavevelocity.

criteria,HFF showedamedianof4.4%andameanof 6.7%, whereas the medians with two, three and four criteria were 5.12%,7.7%and17.9%,respectively.PatientswithallfiveMetS criteriahadameanHFFof19.2%.Amongnon-diabeticsubjects, therelationshipbetweenMetScriteriaandHFFwasthesame

Fig.1.Unadjustedmeanlevelsofhepaticfatcontentaccordingtothenumber offulfilledcriteriaforthemetabolicsyndrome.

asthatfoundforthewholepopulation,indicatingthatdiabetic statushadnoinfluenceonthisassociation(resultsnotshown).

TheYoudenindexwasusedtoidentifyanHFFcutoffvalue forhavingatleastthreeormoreMetScriteria.Accordingtothe index, theoptimalHFF cutoff valuetoidentify subjectswith theMetSwas5.2%.Usingthisvalue,thediagnosticaccuracy, Se,Sp,PPVandNPVwere69.2%,76.8%,56.1%,75.2%and 58.2%, respectively. Table 4 shows the characteristics of the studypopulationaccordingtothosewithHFFslessthan5.2%

andthosewithHFFsgreaterthanorequalto5.2%.Thosewitha lowdegreeofsteatosis(<5.2%)had,onaverage,lowersystolic bloodpressure(123mmHgvs130mmHg;P=0.007)andlower levelsofVAT(141cm²vs206cm²;P<0.0001).Theyalsohad alowermeaninsulinlevelincomparisontothosewithanHFF greater than5.2%(10.9mIU/Lvs16mIU/L).Inaddition,the groupwithgreaterthan5.2%ofliverfathadameanserumALT level at45IU/Lwhiletheothergrouphadameanlevelof30 IU/L.

4. Discussion

The MetS isafrequently encounteredcondition thatasso- ciatesinsulinresistance,centralobesity(malefatdistribution), glucoseandlipidprofileanomalies,andhypertension,thereby increasing cardiovascular risk. Several studies have found a link between hepatic fat content as measured by magnetic resonancespectroscopy(MRS)andtheMetSinvariouspopu- lations [15,28,29]. In the present study, a validated MFGRE T1-weighted MRI protocol was used to quantify liver fat content and showed that HFF increases in proportion to the number of metabolic traits. Moreover, a cutoff point of 5.2% for HFF was used to identify the presence of the MetS.

1H-MRS hasbeen the referencestandardfor non-invasive steatosisquantificationforseveralyears.UsingMRS,Szczepa- niaketal.[16]demonstratedathresholdvalueof5.5%ofliverfat content,representingthe95thpercentileofhepaticTGcontent inarepresentativesampleofhealthyAmericanadults.Accuracy oftheHFFasmeasuredbymulti-echoMRIhasbeencompared with that of proton MRSinseveral previous studies[17,19].

Insurgicalpatients,vanWervenetal.[18]comparedthediag- nosticperformanceofultrasonography,computedtomography, T1-weighted dual-echo MRIandproton MRSfor the assess- mentofsteatosisusingliverresectionasthegoldstandard.That studyshowedsimilarandhighdiagnosticaccuracyinquantify- inghepaticsteatosisforbothMRIandMRSvshistopathological results, whileMRI was showntobe notinferiorto MRSfor liverfatquantification.Recently,MRIwascomparedwithliver biopsybyKuhnetal.[30],whichresultedinanexcellentcor- relationindependentofthepresenceofhepaticironorfibrosis as assessedby biopsy.Others, including the present authors, have already demonstrated the good reliability of MRI over liverbiopsyforquantifyingsteatosis[25,31,32].Thus,primar- ilybecause MRIisnon-invasiveandabletoassessthe whole liver,itrepresentsareliableandsafemethodformeasuringthe percentageoffatinhumanliver.Also,incomparisontoMRS, MRIusingmulti-echosequencesiseasilyperformedwithoutthe

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Table3

Multivariateregressionmodelsevaluatingtheassociationbetweenhepaticfatfractionandtherelevantmetabolicandvascularcomponents.

Model1 Model2 Model3 Model4

␤±SE Pvalue

SystolicBP(mmHg) 0.13±0.07

P=0.05

0.11±0.07 P=0.12

0.10±0.07 P=0.14

0.07±0.07 P=0.33 Log-triglycerides(g/L) 1.00±1.93

P=0.60

0.75±1.96 P=0.70

–0.03±1.96 P=0.99

–1.62±2.00 P=0.42

HbA1c(%) 3.95±1.64

P=0.0175

4.45±1.66 P=0.0083

4.00±1.65 P=0.0170

3.49±1.63 P=0.034

Glucose(g/L) 15.87±4.99

P=0.0018

16.54±4.98 P=0.0011

14.99±4.99 P=0.0032

13.64±5.12 P=0.008

Log-insulin(mU/L) 6.72±1.83

P=0.0004

6.36±1.76 P=0.0004

5.88±1.88 P=0.0022

–

Log-HOMA–IR 6.91±1.62

P<0.0001

6.49±1.54 P<0.0001

6.22±1.66 P=0.0003

–

Adiponectin(mg/L) –0.68±0.32

P=0.0368

–0.59±0.33 P=0.074

–0.60±0.32 P=0.069

–0.27±0.34 P=0.42 C-reactiveprotein(mg/L) 1.02±0.43

P=0.0197

1.08±0.43 P=0.0130

0.94±0.42 P=0.0288

0.70±0.43 P=0.11

CarotidPWV(m/s) 2.31±1.01

P=0.0235

2.03±1.04 P=0.043

1.83±1.03 P=0.081

1.42±1.04 P=0.18

AorticPWV(m/s) 0.41±0.61

P=0.51

0.84±0.67 P=0.21

0.45±0.64 P=0.48

1.05±0.62 P=0.10 Model1:adjustedforage,genderandbodymassindex(BMI);Model2:adjustedforage,genderandvisceraladiposetissue(VAT);Model3:adjustedforage, gender,BMIandVAT;Model4:adjustedforage,gender,BMI,VATandfastinginsulinlevels;␤±SE:parameterestimate±standarderror;BP:bloodpressure;

HOMA–IR:homoeostasismodelassessmentforinsulinresistance;PWV:pulsewavevelocity.

needforspecializedequipment,makingitwidelyavailablefor clinicalresearchonliversteatosisanditsassociatedpathological conditions.

InourpresentstudyusingMRIforliverfatquantification,it wasshownthatT2Dpatientsdisplaythesamedegreeofsteatosis asMetS+subjects(HFFs16.8%and15%,respectively).Hepatic glucoseproduction is an energy-consumption process that is increasedinsteatosisandclosely relatedtoinsulinresistance [7,8,33–35].Thus,ourstudydemonstratesthatHFFcorrelates withfastingglycaemia,glycosylatedhaemoglobin(HbA1c)and insulinresistance(HOMA–IR) independentof the amountof VATandlevelofinsulin.Thisarguesforadirectroleofliver fatcontentinthewidespreadimpairedglucosetoleranceseen inadultsindependentlyofVAT[5,34].Despiteglycaemia,HFF correlateswithTGandsystolicbloodpressure,althoughthese relationshipsdisappearafteradjustingforBMIandvisceralfat mass,indicating that thesetwo components of the MetS are morecloselyrelatedtoadiposefatmassthansteatosisperse.As expected,ALT,ferritinandCRPwererelatedtoHFF,although therelationshipwithferritinwasweakerthanwithALT.Some authorshaverecentlyreportedthatserumferritinmaybemore predictiveoffibrosisthansimplesteatosis[36].

Regardingvascularfunctions,someauthorshavedescribed an association between carotid IMT and liver histology in NAFLDpatients[37].Otherauthors,includingthepresentones, couldfindnorelationshipbetweencarotidwallthicknessand

HFFasquantifiedbyMRS[38,39].Anothervasculartestthat is closelyrelated tothe MetSis the echocardiographic PWV test, whichreflectsarterialstiffness [40].Ourstudy described forthefirsttimealinearrelationshipbetweenHFFandarterial stiffnessattheleveloftheaortaandcarotidarteries.Moreover, theHFF–carotidstiffnessassociationwasindependentofBMI andvisceral fat, whereastheHFF–aortic stiffnessassociation appearstobemoredependentoncentralobesity.

The recognitionthatNAFLD isanindependentrisk factor for CVD is a major public-health concern, but one that has yettobefullydemonstratedmainlybecauseoftheabsenceof reliable liverquantification inpreviouscohorts. Whileawait- ingalongitudinalprospectivestudy,Hoenigetal.[28]recently reportedonacross-sectionalstudyofasmallgroupofadultswho allpresentedwithhighcardiovascularrisklevelsandsteatosis asmeasuredbyspectrometry.Theyalsoshowedarelationship betweenHFF andMetS components, butdid notadjusttheir results for other confounding factors because of their small samplesize.

In the present study, our aim was to describefor the first timeinalargercohorttherelationshipbetweenHFFas mea- suredbyMRIandthemetaboliccomponentsofMetSinawide range ofadultswhoexhibitedzerotofiveMetS components.

Ourfindingshaverevealedthatthedegreeofsteatosisincreases progressivelywiththenumberofMetScomponentspresent.The optimalMRI-basedHFFthatbestpredictedthepresenceofat

(7)

Table4

Comparisonofcharacteristicsaccordingtohepaticfatfraction(HFF)status.

HFF<5.2% HFF≥5.2% Pvalue

n Mean±SD n Mean±SD

Men,n(%) 36 65.5% 76 75.2% 0.19

Age(years) 55 51.4±10.9 101 53.7±9.2 0.17

Bodymassindex(kg/m²) 55 28.2±4.7 101 32.6±5.0 <0.0001

Waistcircumference(cm) 55 97.4±10.6 101 107.6±11.4 <0.0001

Hipcircumference(cm) 55 103.6±9.6 101 109.6±10.6 0.0007

WHR 55 0.940±0.069 101 0.980±0.067 0.0003

SAT(cm²) 54 209.2±90.6 99 250.6±134.2 0.0249

VAT(cm²) 54 141.8±74.6 99 206.4±90.6 <0.0001

VAT(%) 54 39.3±16.1 99 45.8±16.7 0.0211

SystolicBP(mmHg) 55 123.7±13.4 101 129.8±13.8 0.0077

DiastolicBP(mmHg) 55 76.1±10.3 101 77.5±9.3 0.38

HbA1c(%) 54 5.82±0.59 101 6.07±0.60 0.0137

Glucose(g/L) 55 1.01±0.16 101 1.14±0.21 <0.0001

Insulin(mU/L)^a 50 10.9(9.3–12.8) 100 16.0(14.3–18.0) 0.0002

HOMA–IR^a 50 2.63(2.2–3.1) 100 4.39(3.8–4.9) <0.0001

Leptin(␮g/L)^a 50 11.0(8.7–13.9) 96 14.9(12–17.7) 0.0438

Adiponectin(mg/L) 49 7.87±3.57 96 7.17±3.41 0.25

HDLcholesterol(g/L) 55 0.57±0.20 101 0.55±0.15 0.53

LDLcholesterol(g/L) 55 1.18±0.41 101 1.18±0.33 0.95

Triglycerides(g/L)^a 55 1.25(1.09–1.44) 101 1.48(1.34–1.64) 0.061

C-reactiveprotein(mg/L)^a 52 3.08±1.51 96 4.32±2.64 0.0004

GGT(IU/L)^a 55 36.4(29.4–44.9) 100 55.5(47.4–64.9) 0.0020

ALT(IU/L) 55 30.1±21.4 100 45.0±26.0 0.0004

Ferritin(␮g/L)^a 53 169(135–211) 96 229(195–270) 0.0303

Carotidintima–mediathickness(mm) 51 6.36±1.28 91 6.89±1.18 0.0146

Aorticpulsewavevelocity(m/s) 34 7.27±2.13 45 9.17±2.42 0.0005

Plaquescore 55 2.22±2.03 101 2.55±1.89 0.30

WHR:waist-to-hipratio;SAT/VAT:subcutaneous/visceraladiposetissue;BP:bloodpressure;HOMA–IR:homoeostasismodelassessmentofinsulinresistance;

HDL/LDL:high-density/low-densitylipoprotein;GGT:gamma-glutamyltransferase;ALT:alanineaminotransferase.

aSkeweddistributionofvalues:statisticaltestswerecarriedoutonlogarithmicallytransformedvalues;reportedvaluesaregeometricmeans(95%confidence intervals);forcategoricalvariables,dataarefrequencies(%)andcharacteristicswerecomparedbetweenthetwogroupsusingchi-squaretests;forcontinuous variables,dataaremeans±SDunlessotherwisespecified;comparisonsbetweenthetwopatientgroupswerebyunpairedStudent’sttest.

leastthreeMetScomponentswas5.2%,usingtheYoudenindex (whichrepresentsthebestratioofSetoSp).Indeed,valuesof HFFbetween5%and10%displayedaYoudenindexcloserto thehighest one.It canthereforebespeculatedthat havingan HFFof5to10%confersthesameriskofhavingtheMetSand that,withanHFFgreaterthan10%,theprobabilityofhaving theMetSisveryhigh.Nevertheless,alarge-scalelongitudinal studyisstillneeded toconfirmthat HFFindeedincreasesthe riskofcardiovascularmorbidity.

Ourpresentresultsarelimitedbytherelativelysmallsizeof thepatientsubgroupsaswellasbythecross-sectionaldesign.

Theimpactofliverfatdepositiononcardiometabolicoutcomes needstobeconfirmedbylongitudinalstudiesincludingrecords ofcardiovasculareventsoverlongerdurationsoffollow-up[37].

Anotherlimitationofourstudyistherestrictedavailabilityof MRI for basicmedicine. However,it may bespeculated that thisimagingtechnology willbecomemoreandmoreaccessi- ble,andmoreaffordable,inthenearfutureandthereforebetter serve inastrategyof preventativemedicinefor dysmetabolic subjects.

In conclusion, our findings in French adults have shown that HFF is associated with several metabolic components of the MetS and also has relationships with glycaemia, insulinresistanceandcarotidstiffnessindependentofvisceral

adiposity. Using MRI quantification, it was calculated that a cutoffvalueof5.2%ofHFFcanidentifytheriskofhavingthe MetS.

Disclosureofinterest

The authors declare that theyhaveno conflictsof interest concerningthisarticle.

Financial support: National Clinical Research Hospital Project [Projet hospitalier de recherche clinique national (PHRC)2008]:“Diagnosisandquantificationofhepaticsteato- sis by MRI” (Diagnostic et quantiﬁcation de la stéatose hépatiqueparIRM).

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