Journal of Feline Medicine and Surgery (2009) 11, 82e90doi:10.1016/j.jfms.2008.05.005

Triglyceride response following an oral fat tolerancetest in Burmese cats, other pedigree catsand domestic crossbred cats

Elissa K Kluger BVSc1*, Chloe Hardman BVSc, FACVSc (Ophthalmology)

2,Merran Govendir BVSc, PhD, MACVSc, MEd (Higher Ed)

1,Randolph M Baral BVSc, MACVSc (Feline Medicine)

3, David R Sullivan MBBS, FRACP, FRCPA4,

David Snow DVSc, BSc (Vet), PhD5,

Richard Malik DVSc, DipVetAn, MVetClinStud, PhD, FACVSc (Feline Medicine), FASM1,6

1Faculty of Veterinary Science, TheUniversity of Sydney, NSW 2006,Australia2Animal Eye Care, 181 DarlingRoad, Malvern East, Victoria 3145,Australia3Paddington Cat Hospital, 183Glenmore Road, Paddington, NSW2021, Australia4Department of ClinicalBiochemistry, Royal Prince AlfredHospital, Camperdown, NSW 2050,Australia5Symbion Vetnostics, North Ryde,NSW 2113, Australia6Post Graduate Foundation inVeterinary Science, The Universityof Sydney, NSW 2006, Australia

*Corresponding author. Tel: þ61-ekluger@hotmail.com

1098-612X/08/020082+09 $34.00/0

Primary lipid disorders causing fasting triglyceridaemia have been documentedinfrequently in Burmese cats. Due to the known increased risk of diabetesmellitus and sporadic reports of lipid aqueous in this breed, the aim of this studywas to determine whether healthy Burmese cats displayed a more pronouncedpre- or post-prandial triglyceridaemia compared to other cats. Serumtriglyceride (TG) concentrations were determined at baseline and variably at 2, 4and 6 h after ingestion of a high-fat meal (ie, an oral fat tolerance test) ina representative sample of Burmese and non-Burmese cats. The median 4 and6 h serum TG concentrations were significantly higher in Burmese cats (4 h e2.8 mmol/l; 6 h e 8.2 mmol/l) than in other pedigree and domestic crossbredcats (4 h e 1.5 mmol/l; 6 h e 1.0 mmol/l). The non-Burmese group hadpost-prandial TG concentrations ranging from 0.6 to 3.9 mmol/l. Seven Burmesecats had post-prandial TG concentrations between 6.6 and 19.0 mmol/l, five hadconcentrations between 4.2 and 4.7 mmol/l, while the remaining 15 hadpost-prandial concentrations between 0.5 and 2.8 mmol/l. None of theseBurmese cats had fasting triglyceridaemia. Most Burmese cats with a 4 hTG > 6.0 mmol/l had elevated fasting very low density lipoprotein (VLDL)concentrations. This study demonstrates that a proportion of Burmese cats inAustralia have delayed TG clearance compared to other cats. The potentialrepercussions of this observation with reference to lipid aqueous, pancreatitisand diabetes mellitus in Burmese cats are discussed.

Date accepted: 12 May 2008 � 2008 ESFM and AAFP. Published by Elsevier Ltd. All rights reserved.

Lipaemia in cats is attributed to an increase intriglyceride (TG) concentrations in plasma.As chylomicrons (CM) and VLDL transport

the majority of exogenous and endogenous TGs,respectively, hypertriglyceridaemia results from anincrease in one or both of these lipoproteins in thecirculation. Lipoprotein lipase (LPL) is involved inreducing the circulating TG concentration byhydrolysing TG from CM and VLDL to producenon-esterified fatty acids and glycerol.1 This processis activated by the co-factor apolipoprotein C2(apoCII) and modulated by apolipoprotein E(apoE).2 Synthesis of LPL occurs mainly in adipose

2-9351-7094. E-mail :

� 2008 ESFM a

tissue, cardiac and skeletal muscle and it later attachesto the luminal surface of capillary endothelial cells viachains of heparin sulphate-proteoglycans.1 Heparinadministration is known to decrease LPL bindingfrom these sites, resulting in an increased circulatingLPL concentration which accelerates the rate ofplasma TG clearance.3

Over 60% of the variability in fasting serum lipidconcentrations in humans is due to the effects ofa variety of genes.4 Environmental factors such asdietary composition and obesity also influence fastinglipid concentrations.4 In humans, inherited primarydisorders resulting in hypertriglyceridaemia includedeficiencies in LPL, hepatic lipase and apoCII. Vary-ing degrees of fasting hypertriglyceridaemia and/orhypercholesterolaemia are associated with these

nd AAFP. Published by Elsevier Ltd. All rights reserved.

83Triglyceride response following an OFTT in Burmese cats

genetic disorders, although heterozygous carrierswith a LPL deficiency may only show signs of diseasewhen secondary factors such as obesity are presentconcurrently.5

Primary lipid disorders are not commonly observedin cats. Lipid disorders secondary to diabetes mellitus,pancreatitis, hyperadrenocorticism and administra-tion of corticosteroids or progestagens are more likelyto account for fasting lipaemia in this species.6,7 Thebest characterised primary lipid disorder in cats is in-herited fasting hyperchylomicronaemia, an autosomalrecessive disorder resulting from reduced LPL activitydue to a point mutation in exon 8 of the LPL gene.8,9

Cats homozygous for this condition develop severefasting and post-prandial hypertriglyceridaemia,comprising a marked increase in CM and a mild tomoderate increase in VLDL. Heterozygous cats havenormal fasting TG concentrations but prolongedpost-prandial lipaemia after an oral fat challenge.10

Persistently elevated lipid concentrations in homozy-gous cats result in the development of one or moreof the following: lipaemia retinalis, peripheral neurop-athy, cutaneous xanthomatosis and, less commonly,anaemia.11e13 Abdominal pain and pancreatitis havenot been reported as features of hyperchylomicronae-mia in these cats, in contrast to similarly affectedcanine or human patients.14e16 These clinical manifes-tations can be successfully managed by feeding a lowfat diet.

Another manifestation of lipid disorders in cats islipid aqueous, a sporadic condition whereby lipid ac-cumulates in the aqueous humour of the eye. Thiscondition is thought to result from a transient break-down in the blood-aqueous barrier, possibly due toprimary anterior uveitis, in the setting of concurrentlyincreased plasma chylomicron and/or VLDL concen-trations.17 Large lipoproteins ‘leak’ across this barrier,causing a previously clear anterior chamber to becomehazy or even opaque,18 as illustrated in Fig 1. Inpreliminary reports, Hardman and collaborators ob-served a primary lipid disorder in otherwise healthyadolescent Burmese cats.19,20 These patients had

Fig 1. Appearance of two young Burmese cats with lipid aq(A) in the right eye of a lilac Burmese cat (photo courtesy of Dcat (reproduced with permission from Hardman and Stanley.1

initially presented with one or more episodes of lipidaqueous, with or without concurrent uveitis, and mildto moderately elevated fasting TG referable to in-creased VLDL lipoproteins. Although post-heparinLPL activity was not measured, plasma TG concentra-tions were unchanged after intravenous (IV) adminis-tration of heparin in three cats (Hardman,unpublished data). A similar condition has also beendescribed in young Burmese cats in the United King-dom (UK).17,21

In Australia and the UK, there is an over-represen-tation of diabetic Burmese cats,22e25 with affected catsoften having a greater requirement for exogenous in-sulin than domestic crossbred diabetic cats (DBChurch and R Malik unpublished observation). It ispossible that a defect in lipid metabolism may belinked to insulin resistance in this sub-group ofBurmese cats and that these cats may be at risk forthe development of lipid aqueous well before theydevelop diabetes.

On the basis of the existing knowledge on lipiddisorders in cats and other species, the hypothesisfor this study was that some Burmese cats have re-duced TG clearance from plasma which may explainthe aetiology of lipid aqueous. As measuring fastingTG concentrations has been demonstrated to be aninsensitive method for detecting subtle or incompletedefects in lipid metabolism,5 a modified oral fattolerance test (OFTT) was utilised in this study.

Methods

Cats

Healthy cats (Burmese, other pedigree and domesticcrossbred) were selected at random from three cat-teries (n¼ 25 cats) and four veterinary hospitals(n¼ 43 cats) in the Sydney metropolitan region. Onall but two occasions, it was possible to collect bloodspecimens from Burmese cats and non-Burmese catssharing a common diet, environment and likely

ueous; note the lipid accumulation in the anterior chamberr C Hardman) (B) and in the left eye of a brown Burmese

9

84 EK Kluger et al

having similar activity levels, ie, cats living in thesame household or cattery. Cats in both groupsdisplayed a wide range of ages, weights and bodycondition scores (BCSs) as might be expected fromthe broad inclusion criteria. BCS was determined us-ing a nine point scale (1e3¼ thin, 4e5¼ ideal, and6e9¼ overweight).26 Recent dietary history, in partic-ular diet composition, consistency (dry/canned/freshmeat) and frequency of feeding (once or twice daily, orad-libitum) were recorded. All cats were deemedhealthy based on prior medical history and routinephysical examination.

Fig 2. Appearance of t¼ 4 h serum after centrifugation.Serum on the left is from a domestic crossbred cat (TG1.5 mmol/l). Serum on the right is from an ‘affected’ Bur-mese cat (TG 9.3 mmol/l).

OFTT

Each cat was fasted for at least 15 h overnight prior toblood collection, at which time the baseline TGconcentration was determined (t¼ 0 h). For a smallnumber of cats (n¼ 4), a baseline sample was notcollected as this was not feasible due to the patients’non-compliance. Each cat received 1e1.5 g fat/kgbody weight using a standardised prescriptioncanned diet formulated for pets recovering frommajor surgery or illness (Hill’s Prescription Dietcanine/feline a/d). This diet consisted of 30.4% fat,44.2% protein and 15.4% carbohydrate on a dry-matter basis. This meal was selected in part becauseit is widely available worldwide and, therefore, suit-able for inclusion in a standardised test protocol.The test meal was either eaten voluntarily (33 cats)or gently force-fed (35 cats) over a 10e15 min period.Blood was collected for determination of TG concen-tration at 2, 4 and 6 h post-prandially. Due to a varietyof practical and technical limitations, not all cats hadblood collected at each time point.

Blood collection and handling

Blood was collected from the external jugular vein orcephalic vein using a 23 gauge needle and syringe ora 23 gauge butterfly needle and syringe, respectively.Blood was placed in plain serum and/or ethylene-diamine-tetra-acetic acid (EDTA) tubes. Followingcentrifugation for 10 min at 2500� g, serum or plasmawas inspected for the presence of lipaemia (Fig 2),separated and processed within 12 h of collection.Serum TG and cholesterol concentrations weredetermined and the remaining serum stored at 4�Covernight to determine the presence or absence ofCM. Fasting and 4 h post-prandial serum TG concen-trations were determined in 61 and 51 cats, respec-tively. Fasting serum cholesterol was determined in48 cats. Fasting and 4 h post-prandial serum glucoseconcentrations were determined in 30 cats; serumwas separated within 1 h of blood collection. Point-of-care devices to measure TG (Accutrend GCT, RocheDiagnostics, Auckland, New Zealand and PTS. Cardio-chek, Pursuit Performance, Adelaide, SA, Australia)27

and glucose concentrations in whole blood wereused concurrently. Lipoprotein electrophoresis was

performed on a number of representative fastingand 4 h post-prandial plasma or serum samplesfrom both Burmese (n¼ 12) and non-Burmese cats(n¼ 9).

Analytical methods

Serum TG and cholesterol concentrations were per-formed by a commercial NATA-accredited laboratory(Symbion Vetnostics Laboratory, North Ryde, NSW,Australia). The measurement of all serum analyteswas performed on an automated Hitachi-Rocheanalyser using standard methods. Serum TG andcholesterol concentrations were determined usingglycerol-phosphate oxidase and peroxidase (GPO-PAP) and cholesterol esterase, cholesterol oxidaseand peroxidase (CHOD-PAP) test kits, respectively(Boehringer Mannheim). Serum glucose concentra-tions were determined using a hexokinase methodwith a Gluco-quant enzyme kit (Roche Diagnostics/Hitachi). Both point-of-care devices used to measureTG used the GPO-PAP method and the blood glucosedevice utilised the hexokinase method incorporatedinto reagent strips.

Lipoprotein electrophoresis was performed by theProtein and Lipid Department, Royal Prince AlfredHospital, Sydney. Lipoproteins were separated usingthe CIBA Corning ACI Electrophoresis System usingstandard methods. Briefly, 5 ml of plasma or serumwas applied to a 0.6% agarose gel. Electrophoresiswas performed for 45 min in a Trisebarbital buffer

85Triglyceride response following an OFTT in Burmese cats

(pH 8.6) at 100 V. Gels were stained with fat red 7B(Helena Laboratories). Completed gels were ana-lysed quantitatively using a Beckman scanning den-sitometer, results of which were recorded asa percentage.

Statistical analysis

Serum TG and cholesterol concentrations werecompared at each time point using KruskalleWallisanalyses for four groups: (1) domestic crossbred cats,(2) other pedigree cats (3) Burmese cats and (4) pooledgroups 1 and 2. Independent effects of age, genderand diet on serum TG concentrations were deter-mined by analysis of co-variance. Correlations weredetermined using Spearman’s correlation coefficient.Significant associations between categorical variableswere determined using Fisher’s exact tests. Densitom-eter percentage readings were compared using a twosample t-test. Values are expressed as mean� stan-dard deviation (SD) and/or median and interquartilerange (IQR). P values of <0.05 were considered signif-icant. Reference intervals for fasting and 4 h serum TGconcentration were created using mean� 2SD fornon-Burmese cats. All data analyses were performedusing a statistical software package (Minitab 15.1.1,State College, PA, USA).

Table 1. Characteristics of Burmese, other pedigree(median [IQR] shown)

Domesticcrossbred (group 1)

Other(gro

Number 17 18Age (years) 3.5 (1.5e7.0) 5.0 (2.Gender 12 MN 10 M

5 FN 7 F (4

Weight (kg) 5.1 (4.5e6.5) 4.3 (3.Triglyceridey (mmol/l)

0 h# 0.4 (0.3e0.5) 0.4 (0.2 h 1.3 (0.4e2.0) 1.4 (0.4 h 1.6 (0.8e2.3) 1.4 (1.6 h 1.0 (0.7e1.3) 1.3 (0.

0 h cholesterolz (mmol/l)# 3.5 (2.8e4.6) 4.0 (3.0 h glucosex (mmol/l)# 4.4 (4.1e4.8) 5.1 (4.

*P< 0.05 (significantly different to all other groups); *ME¼male entire, MN¼male neutered, FE¼ female entiricantly different values (P< 0.05, P< 0.01, respectively) in#Reference ranges Symbion Vetnostics Laboratories: se2.4e5.2 mmol/l, serum glucose 3.9e8.3 mmol/l.yNot all cats were tested at each time point.z48 Cats tested.x30 Cats tested.kOne Tonkinese cat with marked post-prandial hypertrigfrom statistical analyses.

Results

Cats

Group 1A total of 17 crossbred cats were recruited, comprising14 domestic shorthair, two domestic medium-hair catsand one domestic longhair cat.

Group 2A total of 18 non-Burmese pedigree cats wererecruited, consisting of the following breeds: Tonki-nese (six cats e one of these cats was subsequentlyexcluded as an outlier), British Shorthair (two),Siamese (two), Oriental (two), Devon Rex (two),Snowshoe (one), Abyssinian (one), Burmilla (one)and Russian Blue (one).

Group 3Of the 33 Burmese cats, the distribution of coat colourwas as follows: brown (11), chocolate (six), lilac (four),red (four), lilac tortoiseshell (four), cream (two) andblue (two).

Age, weight and gender distributions for eachgroup are presented in Table 1. Although there weremore female cats in the Burmese group due to lownumbers of male cats at catteries, this was not

and domestic crossbred cats used in this study,

pedigreeup 2)k

Non-Burmese(groups 1 and 2 pooled)

Burmese(group 3)

35 330e7.0) 5.0 (1.8e7.0) 3.8 (1.0e8.6)(7 N, 3 E) 22 M (19 N, 3 E) 14 M (8 N, 6 E)N, 3 E) 12 F (9 N, 3 E) 19 F (13 N, 6 E)

7e5.6) 4.8 (4.0e5.6) 4.0 (3.6e4.8)

3e0.5) 0.4 (0.3e0.5) 0.4 (0.3e0.5)9e2.4) 1.3 (0.7e2.0) 1.9 (1.1e2.9)0e1.6) 1.5 (1.0e2.0) 2.8* (1.5e7.0)7e1.6) 1.0 (0.7e1.4) 8.2** (2.6e14.6)

0e5.0) 3.7 (2.9e4.8) 3.7 (2.9e4.0)5e5.8) 4.7 (4.2e5.6) 4.7 (4.1e5.0)

*P< 0.01 (significantly different to all other groups).e, FN¼ female neutered. Values in bold indicates signif-

Burmese compared to non-Burmese cats.rum triglyceride 0.1e0.8 mmol/l, serum cholesterol

lyceridaemia was considered an outlier and excluded

Fig 4. Serum TG concentrations at t¼ 4 h during an OFTTin Burmese (n¼ 25) and non-Burmese cats (n¼ 26). Y-axisreference line at 3.2 mmol/l demonstrates upper referenceinterval for 4 h post-prandial TG peak. Age groupings areadolescent (<1 year), adult (1e6 years) and senior (�7years).

86 EK Kluger et al

significantly different from the non-Burmese cohort(P¼ 0.1). There were no other obvious or statisticallysignificant differences in signalment between the threegroups.

OFTT

Groups 1 and 2Changes in TG concentrations in domestic crossbredand non-Burmese pedigree cats during an OFTTwere similar (Table 1). As differences between thegroups were not statistically significant, results forgroups 1 and 2 cats were pooled, as illustrated inTable 1 and Figs 3 and 4.

The TG concentration peaked at 4 h in all non-Burmese cats in which serial blood specimens werecollected at 0, 2, 4 and 6 h (n¼ 7 cats) and the mean,median and IQR for serum TG concentrations att¼ 4 h were 1.6, 1.5 and 1.0e2.0 mmol/l, respectively.Based on the mean� 2SD from cats in groups 1 and 2,the reference interval for 4 h post-prandial serum TGwas 0.1e3.2 mmol/l; therefore, TG concentrations inexcess of 3.2 mmol/l were considered to be elevated.Two Tonkinese and one domestic shorthair cat had4 h TG concentrations above this cut-off value (3.4,6.4 and 3.9 mmol/l, respectively). The Tonkinese catwith a post-prandial serum TG concentration of6.4 mmol/l was excluded as an outlier. Serum TGconcentrations returned to baseline or were reducedsubstantially 6 h after eating.

Group 3For 25 Burmese cats tested at 4 h the mean, medianand IQR for TG were 4.2, 2.8 and 1.5e7.0 mmol/l; sig-nificantly higher than non-Burmese cats (in groups 1and 2 combined; P¼ 0.05). Of these Burmese cats,12/25 (48%) had 4 h post-prandial TG concentrationsabove the reference interval of 3.2 mmol/l; seven ofthese 12 cats (28%) had markedly elevated TG concen-trations ranging from 6.6 to 11.5 mmol/l, while the

Fig 3. Serum TG concentrations in all cats, comparing Bur-mese and non-Burmese cats at 0, 2, 4 and 6 h post-oral fatchallenge.

remaining five (20%) had moderately elevated con-centrations of 4.2e4.7 mmol/l (Fig 3). In those catstested at 6 h (n¼ 5), in three the serum TGconcentrations were lower at 6 h (2.1, 3.0 and8.2 mmol/l) than 4 h post-prandially (4.3, 4.3 and9.5 mmol/l), while in the other two, serum TG washigher at 6 h (10.1 and 19.0 mmol/l) than at 4 h (8.2and 11.5 mmol/l).

The 12 cats with moderate (>4.0 mmol/l) andmarked (>6.0 mmol/l) 4 h post-prandial hypertrigly-ceridaemia were compared to the remaining 13 cats(‘non-affected’) in group 3. The mean� SD ages andweights of ‘affected’ cats (5.5� 3.5 years and4.5� 0.6 kg) were not significantly different comparedto ‘unaffected’ Burmese cats (4.2� 4.6 years and3.7� 0.8 kg). Two of the ‘affected’ Burmese cats were<1 year old, six were between 1 and 6 years-of-ageand four were older than 7 years. There was no signif-icant difference in post-prandial TG concentrationsbetween young and older cats, as illustrated in Fig 4.Eight of the 12 ‘affected’ cats had a BCS of 4 or 5,the remaining four cats were moderately overweight(BCS of 6 or 7). Only two of the 13 ‘non-affected’Burmese had a BCS of 6; the rest had a BCS of 4 or5. Differences in BCS between ‘affected’ and ‘non-affected’ Burmese were not significant (P¼ 0.4). Ofthe 12 ‘affected’ Burmese cats, males and femaleswere equally represented, but females accounted foreight of the 13 ‘non-affected’ Burmese cats.

Dietary comparisons between cats

Five of the seven Burmese cats with marked post-prandial hypertriglyceridaemia shared the sameenvironment and had been given the same diet as in-dividual cats included in the non-Burmese cats in

87Triglyceride response following an OFTT in Burmese cats

groups 1 and 2. An additional Burmese cat within thissub-group shared the same diet and environment asanother Burmese cat with a ‘normal’ OFTT response.

Of the 25 Burmese cats tested at t¼ 4 h, only 14 catsate the test diet willingly; interestingly nine of thesecats were ‘affected’ Burmese that developed moderateto marked post-prandial TG elevations. This relation-ship, however, was not statistically significant(P¼ 0.4).

Fig 5. Plasma lipoprotein electrophoretogram showinga t¼ 0 h and 4 h sample from a normal domestic crossbredcat (top two rows) and an ‘affected’ Burmese cat (bottomtwo rows). Note the difference in staining of the VLDLbands (arrows) at t¼ 0 h in both cats. Also note the markedtrailing due to excessive CM in the affected Burmese cat, asmarked with a star.

Fasting lipid and glucose concentrations

Fasting serum TG and cholesterol concentrations forgroups 1, 2 and 3 are illustrated in Table 1. Therewas no significant difference in median fasting TGconcentrations between Burmese, other pedigree anddomestic crossbred cats. The median fasting serumTG concentration was higher in ‘affected’ Burmesecats (0.5 mmol/l) than ‘non-affected’ Burmese cats(0.3 mmol/l) and non-Burmese cats (0.4 mmol/l), al-though this was not statistically significant (P¼ 0.5).Two cats, both domestic shorthairs, had fasting TGconcentrations above the reference interval(0.9 mmol/l), however, their 4 h TG concentrationswere below the 4 h reference cut-off of 3.2 mmol/l.All three groups had similar fasting serum cholesteroland glucose concentrations. Both Burmese and non-Burmese had similar or lower serum glucose concen-trations 4 h post-prandially compared to baseline. Nocorrelation was found between weight, age, gender ordiet and fasting serum TG or cholesterolconcentrations.

Lipid electrophoresis

Groups 1 and 2Lipoprotein electrophoresis using serum or plasmacollected at baseline and 4 h post-prandially was per-formed in nine ‘normal’ cats. Two cats had a faint chy-lomicron band despite a normal fasting TGconcentration. A 10-month-old, female neutered do-mestic shorthair cat had a more prominent fastingand VLDL band compared to the rest of those tested.This cat had a 4 h post-prandial TG concentration of3.9 mmol/l, the highest recorded TG concentrationin the non-Burmese group.

Group 3Lipoprotein electrophoresis was performed at 0 h (12cats) and 4 h post-prandially (13 cats). Of these, 10of the 12 ‘affected’ Burmese cats were included.None had chylomicron bands present at 0 h. Basedon densitometer readings, Burmese cats had moreprominent VLDL bands and less prominent high den-sity lipoprotein (HDL) bands compared to groups 1and 2 cats at 0 h (P¼ 0.04 and 0.06, respectively) butnot at 4 h (P¼ 0.6 and 0.3, respectively). Althoughlow density lipoprotein (LDL) bands were moreprominent in Burmese cats at both 0 and 4 h, the dif-ference was not significant (P¼ 0.5 and 0.1,

respectively). Post-prandial chylomicron band stain-ing reflected the degree of triglyceridaemia.

Six of the seven Burmese cats with marked post-prandial hypertriglyceridaemia (TG> 6.0 mmol/l)had 0 h plasma samples tested; four had prominentVLDL bands, one had a more prominent LDL bandand one cat had similar LDL and VLDL staining.These cats also had more prominent VLDL bandsand sometimes LDL bands at t¼ 4 h compared tonon-Burmese cats. An example, comparing an ‘af-fected’ Burmese to a normal domestic crossbred, is il-lustrated in Fig 5.

DiscussionThe most important findings of this study were thatseven of 25 Burmese and one Tonkinese cat hadmarked post-prandial hypertriglyceridaemia(6.6e19.0 mmol/l) 4e6 h after an oral fat challenge.A further five Burmese cats had moderately elevatedpost-prandial TG concentrations (4.2e4.7 mmol/l),compared to the remaining 13 Burmese cats(0.5e2.8 mmol/l). All other pedigree and domesticcrossbred cats had post-prandial TG concentrationsbetween 0.6 and 3.9 mmol/l. Of the 51 cats who hadblood collected 4 h post-prandially, 24 cats had a TGconcentration of �1.6 mmol/l (seven Burmese, 17non-Burmese), 15 cats had a TG concentration of1.7e4.0 mmol/l (six Burmese, nine non-Burmese)and 12 cats had a TG concentration >4.0 mmol/l (12Burmese). This shows that a sub-group of at least 12Burmese cats had a reduced ability to clear TGs fol-lowing a high-fat meal. This was thought to mostlikely reflect an inborn error of lipid metabolism, as

88 EK Kluger et al

unaffected cats of similar BCS and age, sharing thesame environment and lifestyle, had normal TG clear-ance. Most, but not all, Burmese cats with a markedpost-prandial TG response had more prominentVLDL bands in fasting serum samples compared to‘normal’ cats. Importantly, delayed TG clearance oc-curred mainly in adult Burmese cats over 3 years-of-age.

Crispin17 briefly mentioned a presumptive familialhypertriglyceridaemia in Burmese cats, in whichplasma TG concentrations were twice that of age-matched controls. Although this was attributed to anelevation in both CM and VLDL concentrations, meth-odological details were lacking. In Hardman’s studies,Burmese cats that developed lipid aqueous with con-current fasting hypertriglyceridaemia had elevatedfasting VLDL concentrations with no CM on electro-phoresis.20 Apart from ocular signs, these cats wereclinically healthy with unremarkable biochemical ana-lytes. Furthermore, their clinical signs were transient,often resolving spontaneously or following topicaltreatment for uveitis, with or without institutinga low fat diet. As all these patients were ‘adolescent’cats and some cats had common ancestry, an inheritedfamilial disorder was thought most likely (C Hard-man, unpublished data).

On average, serum TG concentrations peak 3e4 hafter a meal, usually returning to baseline within 8 hin healthy feline, human and canine patients.10,28e30

In this study, a proportion of Burmese cats developedpost-prandial hypertriglyceridaemia with their peakTG concentration delayed for up to 6 h or longer.Two Burmese cats with lipid aqueous and twomatched normal Burmese cats in Hardman’s studydisplayed a moderate post-prandial TG response at2 h compared to domestic crossbred cats, suggestingthis lipid disorder can also occur in Burmese catswithout a history of lipid aqueous (C Hardman un-published data), a finding expanded upon by thepresent work. No Burmese cat with moderate ormarked post-prandial hypertriglyceridaemia in thecurrent study had a history of lipid aqueous, althoughthis may merely reflect an absence of an episode ofuveitis required to ‘unmask’ any underlying lipid me-tabolism defect.

The Burmese condition identified in this study ap-pears to be quite different to the fasting hypertrigly-ceridaemia of cats described by Jones et al,8 wheremild elevations in VLDL were accompanied bymarked elevations of CM in fasting plasma. Markedpost-prandial hypertriglyceridaemia has also beendescribed in cats with the same inherited LPL defi-ciency.10 Fasting TG concentrations in normal catsand those heterozygous for the LPL gene defect are in-distinguishable, although oral fat loading revealsa higher, delayed TG peak (mean 2.35 mmol/l) 5 h af-ter feeding in heterozygous cats, compared toa 1.1 mmol/l peak 3 h post-prandially in normalcats.10 Cats homozygous for the defective LPL allelehad elevated fasting TG concentrations (2.38 mmol/l)

which increased fourfold post-prandially to9.36 mmol/l, 7 h after feeding a high-fat meal. Peoplewho are heterozygous carriers for this condition donot invariably develop clinical signs, however, theymay or may not develop fasting hypertriglyceridae-mia depending on additional factors such as diabetesmellitus, obesity or hyperinsulinaemia.31,32 An OFTTis mandatory to distinguish these carriers from nor-mal patients, describing the inability to clear post-prandial TGs as ‘impaired TG tolerance’.5

The present study has uncovered a five- to 10-foldpost-prandial elevation, and subsequent delayedclearance of serum TG from normal fasting concentra-tions, in a substantial proportion of apparently normalBurmese cats. It is possible that a proportion of Bur-mese cats in Australia are heterozygous for a defectiveLPL allele, whereby normal fasting TG concentrationsare accompanied by an impaired TG tolerance after anoral fat challenge.

Lipid metabolism in cats is influenced by prior die-tary history, ie, proportion of fat, protein and carbohy-drate in the diet, as well as their adiposity andreproductive status.33 Prior to testing, all cats werefed varying types of commercial dry food and mostwere also given commercial canned food or freshmeat. As the cats in the current study did not consumea standardised diet for the period immediately priorto testing, it is possible that the observed TG responsemay in part be a reflection of their recent dietary his-tory. However, five of the seven Burmese cats withmarked post-prandial hypertriglyceridaemia werehoused with non-Burmese cats, while an additional‘affected’ Burmese cat was housed with an ‘unaf-fected’ Burmese cat; this provided a convenient andcogent ‘control’ for each affected Burmese as each‘pair’ shared the same environment and consumedthe same diet. Because of the effect of diet and otherconfounding variables, it is important to emphasisethat the percentage of Burmese cats with impairedTG clearance may be an underestimate, as feedinga higher fat meal for a longer period prior to testingmay help unmask this phenotype. Differences inpost-prandial TG concentrations between studiesmay in part also reflect the composition of the testmeal. An increase in fat and carbohydrate load duringan OFTT in humans has been shown to accentuatepost-prandial lipaemia,34 which may explain, in part,why non-affected cats in the current study had four-fold elevations in TG concentrations on average afterfeeding compared to previous studies demonstratingtwo-fold elevations in serum TG.10,28

In healthy individuals, post-prandial hepatic VLDLproduction is suppressed by high insulin concentra-tions, allowing LPL to hydrolyse chylomicron-TG. In-sulin also acts directly on LPL, with a relative insulindeficiency contributing to reduced clearance of CMand VLDL from the circulation. Overweight, glucoseintolerant or diabetic human patients with normalfasting serum TG concentrations may display pro-longed post-prandial lipaemia due to a reduced

89Triglyceride response following an OFTT in Burmese cats

insulin effect on LPL activity.30 Obesity in cats alsoproduces insulin resistance and a subsequent increasein VLDL production.35 Although this may explain thepost-prandial lipaemia demonstrated in some of theoverweight cats in this study, eight ‘affected’ Burmesecats were of healthy BCS. A previous study has showna trend towards Burmese cats over 6 years-of-age hav-ing glucose intolerance and higher insulin concentra-tions compared to age-matched non-Burmese cats.36

It is conceivable that Burmese cats in this study hadglucose intolerance or higher fasting insulin concen-trations. However, of the cats tested, fasting andpost-prandial glucose concentrations were within thenormal range and no significant difference was foundbetween Burmese and non-Burmese cats. Age appearsto have had no effect on fasting serum TG concentra-tions despite senior cats (over 7 years) having lowerplasma LPL and hepatic lipase activities.37 A loweredenzyme activity with maturity does not explain whyonly four of the 12 ‘affected’ Burmese cats were over7 years old.

Most cases of post-prandial hypertriglyceridaemiain people are multifactorial, as numerous factors influ-ence TG clearance such as insulin concentration, LPLactivity and apoE concentration.38 In the currentstudy, 28% of healthy Burmese cats were found to de-velop marked (>6.0 mmol/l) post-prandial hypertri-glyceridaemia after a high-fat meal. The significanceof this finding currently remains unknown. It is possi-ble that these cats have a lipid disorder that is similarto the group of cats with lipid aqueous. In the absenceof uveitis, which results in increased permeability ofthe blood-aqueous barrier and, therefore, exposesthe phenotype, the condition was only detected withprovocative testing. Alternatively, lipid aqueous inyoung Burmese cats may be due in part to a transientsuppression of LPL activity, a known effect of viral orprotozoal infections in humans.39 This seems lesslikely, however, as many young non-Burmese cats de-velop infectious uveitis without the presence of lipidaqueous. As younger animals have greater permeabil-ity of iris micro-vasculature,17 this may also help toexplain why lipid aqueous occurred transiently insome Burmese cats with hypertriglyceridaemia with-out the presence of concurrent uveitis.

Further studies, such as pre- and post-heparin LPLactivity, apoCII activity, LPL and apoE genotyping inboth ‘affected’ and ‘non-affected’ age and diet-matched Burmese cats, will be required to determinewhether the underlying lipid metabolism defect hasa genetic basis, which seems likely. As a Tonkinesecat (Burmese/Siamese cross) was found to be ‘af-fected’, breeds originating from Burmese blood lines(eg, the Australian Mist) should be investigated also.Longitudinal studies of affected individuals will be re-quired to ascertain whether these cats are at greaterrisk for developing diseases such as pancreatitis or di-abetes mellitus. The use of an oral fat challenge mayaid in detecting ‘at-risk’ cats at a younger age, well be-fore adverse sequelae develop.

AcknowledgementsThis study was financially supported by the WalthamFoundation, UK. Thanks to Bajimbi, Sabrahn, Sarboo-bie and Ahnyo Kyaung catteries for their participa-tion. Thanks to the staff at Paddington Cat Hospital,Dr Sally Pegrum of Double Bay Veterinary Hospital,Dr Miriam Meek and Ms Angela Causley of RoseBay Veterinary Clinic and all clients and cats involvedfor their time and patience. Thanks to Professor Ro-land Stocker and Dr Cacang Suarna at the VascularResearch Laboratory for their advice. Richard Malikis supported by the Valentine Charlton Bequest ofthe Post Graduate Foundation in Veterinary Scienceat the University of Sydney.

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