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© 2006 American Society for Nutrition J. Nutr. 136:2980-2986, December 2006

Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions

Adipose Fatty Acid Composition and Rate of Incorporation of {alpha}-Linolenic Acid Differ between Normal and Lipoprotein Lipase-Deficient Cats1,2

Brian C. Veltri3, Robert C. Backus5,*, Quinton R. Rogers4 and Edward J. DePeters3

3 Department of Animal Science and 4 Department of Molecular Biosciences, University of California, Davis, CA 95616 and 5 Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, MO 65211

* To whom correspondence should be addressed. E-mail: backusr{at}missouri.edu.


   ABSTRACT
TOP
 ABSTRACT
Introduction
 Materials and Methods
 Results
 Discussion
 LITERATURE CITED
 
Normal adiposity occurs in humans and mice deficient of adipose lipoprotein lipase (LPL) activity. Subnormal adiposity found in LPL-deficient cats is indicative of limited de novo synthesis of fatty acids (FAs). In 14 LPL-deficient (3.0 ± 0.1 kg) and 8 normal (3.7 ± 0.1 kg) queens, FAs in triacylglycerol (TAG), phospholipid (PL), and nonesterified FAs (NEFAs) of plasma and inguinal subcutaneous adipose were determined before and after (d 38, 61, 110, 117, and 251) dietary linseed oil supplementation (30 g/kg). By d 60, LPL-deficient queens gained body weight (+0.4 ± 0.1 kg), developed normal body fat mass (25 ± 2%), and were enriched in 18:3(n-3) in their plasma and adipose lipids. Adipose TAG 18:3(n-3) enrichment in LPL-deficient queens was subnormal at all sampling times and, as observed in normal queens, apparently not equilibrated by d 251. Adipose FA profiles in TAG but not PL were substantially different (P < 0.05) between LPL-deficient and normal queens; the 16:0 to 18:2(n-6) ratio was high in LPL-deficient (2.4–4.4) relative to normal queens (1.0–1.4). In LPL-deficient queens, fed-state plasma NEFA (n-6) and (n-3) enrichments were similar to those in adipose TAG, and plasma NEFA concentration was high (0.62 ± 0.05 mmol/L) and similar to that in normal queens after withholding diet for 16 h. These data indicate that LPL deficiency in cats reduces dietary FA storage efficiency, favors storage of saturated over unsaturated FAs, and stimulates de novo FA synthesis substantive enough to support normal adiposity.


   Introduction
TOP
 ABSTRACT
 Introduction
Materials and Methods
 Results
 Discussion
 LITERATURE CITED
 
Regulation of the size of body fat mass is not well understood, but it is assumed to be similar among animal models studied in obesity research. Modulation of activity of lipoprotein lipase (LPL)6 in adipose has long been considered a key regulatory site for size of adipose depots (1–3). A paradoxical finding about this role for LPL is the observation that adult humans with LPL-deficiency and LPL-knockout mice both achieve normal body fat mass (4,5). Alternative sources of substrate for adipose triacylglycerol (TAG) storage apparently occur in LPL-deficiency. Analyses of adipose composition indicate that de novo synthesis of fatty acids (FAs) increases in fat depots of LPL-deficient humans until normal body fat mass is achieved (6). Although liver is the primary site of FA synthesis in humans and rodents, adipose is recognized as a secondary site of synthesis (7). The mechanism compelling adipose to achieve normal size in LPL-deficiency is unknown. Individuals with LPL-deficiency appear to have normal adipocyte size and subcutaneous distribution of body fat (8).

Domestic cats that are deficient of LPL activity as a result of a spontaneous mutation of the LPL gene (9) are reported to have a subnormal body fat mass (10). The lean state in LPL-deficient cats initially was attributed to a limitation of fat metabolism possibly unique to cats, a species considered a model for carnivores (11). Findings based on tissue culture led researchers to propose that de novo FA synthesis in cats is low relative to other species (7,12). Recently, it was demonstrated that LPL-deficient cats can be manipulated to gain body fat to the extent of being classified as obese (>30% of body weight as fat). Kanchuk et al. (13) reported that orchiectomy of LPL-deficient cats induces a 29% increase in body weight. The source of FA for adipose TAG in these cats is unknown. Increased de novo FA synthesis supports body fat development in LPL-deficient humans, but this mechanism appears inconsistent with previous findings in cats (12). Fatty acids released from circulating lipoproteins in the absence of LPL are sufficient for adipose TAG deposition in cats (13). Release of FA may be mediated by less active or remotely located lipases, such as either endothelial (14) or hepatic lipase (15).

Understanding the mechanisms controlling body fat mass in LPL-deficient cats may provide a novel perspective on control of FA deposition in adipose. In the present study, adipose FA composition in normal and LPL-deficient cats was compared among cats receiving the same diet. A marker FA [{alpha}-linolenic acid; 18:3(n-3)] was added to the diet to trace the relative rate of FA turnover in LPL-deficient and normal queens. The objective of the present study was to evaluate the contribution of dietary FA to the body fat of LPL-deficient cats.


   Materials and Methods
TOP
 ABSTRACT
 Introduction
 Materials and Methods
Results
 Discussion
 LITERATURE CITED
 
    Animals. Twenty-two adult (1–5 y), specific pathogen-free, domestic short-hair queens were studied. Eight were normal and 14 were LPL-deficient by virtue of being homozygous carriers of naturally occurring Gly412Arg mutation of the LPL gene (9). The cats were housed in 2 separate light (10–14 h light/10–14 h dark cycle) and temperature (18–24°C) controlled facilities at the University of California, Davis. The LPL-deficient queens were housed separately from the normal queens because of their origin from a facility in which feline rhinotracheitis virus had been identified 5 y previously. Water was continuously presented and body weight determined each week. Animal care and use was reviewed and approved by the Animal Care and Use Administrative Advisory Committee of the University of California at Davis.

    Diet. With the exception of brief periods when the cats were previously included in feeding trials, all weaned cats were fed a commercial, dry-type (extruded) diet that had passed growth and maintenance feeding-protocol testing (16). All diets used came from the same batch received from the manufacturer and were stored during the study within a temperature range of 16–27°C. After initial measurements, {alpha}-linolenic acid [18:3(n-3)] concentration was enriched in the diet by addition of 30 g of linseed oil [565 g of 18:3(n-3)/kg oil, Montana Specialty Mills] to each kg of the diet. The oil was mixed with d-{alpha}-tocopherol (1 mg/g oil) (Sigma-Aldrich) prior to the study and thereafter stored in aliquots at 7°C until added to portions of the diet as needed for 2 to 3-wk periods. The oil was dispersed in the diet by spraying and then combining for 5–10 min using a mixer (Hobart). The addition of oil increased diet energy density to an estimated 16.4 kJ/g with dietary fat accounting for a calculated 23% of metabolizable energy.

Ingredient and FA compositions of the diet are shown in Table 1. Proximate and FA analyses were conducted in triplicate on samples of the diet collected before and after the addition of oil, using established methods (17–20).


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  		TABLE 1 Commercial diet composition with and without added linseed oil12

 
    Experimental protocol. Prior to adding linseed oil to the diet, venous blood and subcutaneous adipose were obtained from each cat. Blood samples (3 mL) were collected by jugular venipuncture and transferred to anticoagulant-containing tubes (5.1 mg K3EDTA, Becton Dickinson Vacutainer Systems). Plasma of blood samples was promptly extracted by centrifugation (10 min at 456 x g). Adipose (~250 mg) was collected during intravenous anesthesia (10 mg/kg ketamine HCl + 0.5 mg/kg diazepam) from the inguinal fat pad after withholding the diet for 16 h. Plasma and adipose samples were sealed in a screw top vial purged with nitrogen gas, and stored at –80°C until later analyses.

After oil was added to the diet, adipose biopsies were repeated in all cats on d 110. On d 38 and 61, samples were collected from 4 cats randomly selected from each group, whereas on d 251, samples were collected from all queens retained for the study beyond d 130 (8 LPL-deficient and 3 normal queens). Blood sampling was also repeated at the times of the biopsies and on d 117 when blood was collected before and after withholding the diet for 16 h.

On d 109–111 and 251–252, body fat and lean mass of the cats were determined by modification (21) of the isotopic water dilution method (22).

    Biochemical analyses. Total lipid fractions were extracted from thawed samples of adipose and plasma using chloroform:methanol (2:1, v:v) containing 0.2% glacial acetic acid after the addition of internal standards (1,2-diundecanoyl-sn-glycero-3-phosphocholine and 1,2-dilauroyl-sn-glycero-3-phosphoethanolamine, Avanti Polar Lipids; trinonadecanoin and nonadecanoic acid, Nu Chek Prep)(23). Due to the high proportion of TAG in the adipose lipid extract, Sep-Pak Vac silica gel cartridges (500 mg, Waters) were used to separate neutral lipids from the more polar phospholipids (PL) (24). Extracted lipids were separated into TAG, nonesterified fatty acid (NEFA), and PL fractions using 200 µm layer thickness TLC plates (10 x 10 cm, HPK Silica Gel 60 Å, Whatman International), with a solvent system of hexane:diethyl ether:formic acid (80:20:2, v:v:v), and detection with fluorescent stain (2',7'-dichlorofluorescein solution under UV light) (25). Identified TAG, NEFA, and PL bands were scraped into individual glass tubes, sealed under nitrogen using a Teflon-coated cap, and stored at –80°C until FA analysis. TAG, NEFA, and PL fractions were isolated from plasma samples on d 117.

The FA composition of each isolated lipid fraction was determined using GC as described by DePeters et al. (26) with the following changes: methyl esters were formed by the addition of 100 µL of 1 mol/L sodium methylate in methanol. Due to the high concentration of TAG in adipose and plasma from LPL-deficient cats, all reagents were doubled in volume, and 300 µL of 1 mol/L sodium methylate in methanol was used to elicit a reaction for the TAG fractions. The column temperature program was 70°C for 10 min, 175°C for 29 min at 20°C/min, then 225°C for 10 min at 5°C/min. For analysis of FA from adipose, a split ratio of 1:125 was used, whereas for all other analyses, a ratio of 1:20 was used. Fatty acid analysis of the diet was conducted using the method described by Sukhija and Palmquist (27), except that hexane was substituted for benzene in the method.

Commercial kits were used to determine TAG and NEFA concentrations in plasma samples (TR22421, Thermo Electron Clinical Chemistry, and NEFA-C, Wako Pure Chemical Industries). Plasma from LPL-deficient cats had to be diluted in normal saline for TAG determinations.

    Statistical Analysis. Repeated-measure, general linear models ANOVA with least-squares post-hoc comparisons was used to determine significance of differences between LPL-deficient and normal queens in serially measured body weight and FA proportions in adipose TAG and PL. Paired t test was used to compare within-group differences between variables determined at 2 different times. Student's t test was used to compare variables between LPL-deficient and normal queens. Statistical analyses were conducted with commercial software (SAS, version 8.01, SAS Institute). Differences were considered significant when P ≤ 0.05. Variances reported with mean values are SEM, except for diet analyses, which are SD.


   Results
TOP
 ABSTRACT
 Introduction
 Materials and Methods
 Results
Discussion
 LITERATURE CITED
 
    Body composition. When linseed oil was first added to the diet (wk 1), body weight of normal queens were greater (P < 0.01) than those of LPL-deficient queens (Fig. 1). By wk 7, body weight of LPL-deficient queens increased to the extent that they did not differ from those of the normal queens. Body weight of normal queens during the same period did not differ from their weight during wk 1 of oil addition. On d 110, LPL-deficient cats, relative to normal queens, had less (P < 0.05) lean mass, but body fat mass and percentage body fat did not differ between the queen groups.


Figure 1
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  		Figure 1  Body weight of LPL-deficient (n = 14) and normal queens (n = 8) after dietary linseed oil supplementation (30 g/kg, d 0). Plotted values represent means ± SEM for 14 LPL-deficient and 8 normal queens. *Greater than wk 1 for LPL-deficient queens, P < 0.01. {dagger}Different from normal queens during the same wk, P < 0.05.

 
Eight LPL-deficient and 3 normal queens were retained for study from d 130 until d 308. Addition of dietary linseed oil was discontinued on d 252. On d 251, body weight, lean mass, and fat mass of the LPL-deficient cats were less (P < 0.05) than those of the normal cats (Table 2). Relative to findings on d 110, body weight (kg) and lean mass (kg) of the LPL-deficient cats decreased (P < 0.05), whereas body weight, lean mass, and fat mass of normal cats did not differ. Body weight of cats of both groups did not differ following withdrawal of the oil (data not shown).


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  		TABLE 2 Body composition of LPL-deficient and normal queens after consuming a diet supplemented with linseed oil for 110 and 251 d1

 
    Adipose lipids. The FA composition of adipose TAG in LPL-deficient queens was dramatically different from that of normal queens (Fig. 2). LPL-deficient queens had greater (P < 0.01) proportions of 10:0, 12:0, 14:0, 16:0, and 16:1 than normal queens. Relative to normal queens, LPL-deficient queens had lower (P < 0.01) proportions of 18 carbon FA including 18:0, 18:1, and 18:2(n-6). Fatty acids of chain length >18 were a low proportion of TAG FA (<0.3%) and the proportion did not differ between LPL-deficient and normal queens.


Figure 2
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  		Figure 2  Triacylglycerol fatty acid proportions in subcutaneous inguinal adipose of LPL-deficient (n = 14) and normal queens (n = 8) before and 110 d after addition of linseed oil (30g/kg) to diet. Plotted values represent means ± SEM. See Table 1 for definitions of FA abbreviations. *Different from normal queens at the same time, P < 0.05. {dagger}Different from d 0 for the same queen group, P < 0.05.

 
The proportion of 18:3(n-3) in adipose TAG on d 0 was low and did not differ between LPL-deficient and normal queens (Fig. 3). The proportion of 18:3(n-3) increased in both groups of queens following the addition of linseed oil, but at different rates. An increase (P < 0.01) in 18:3(n-3) was found on d 38 in normal queens but not until d 110 in LPL-deficient queens. Normal queens had greater (P < 0.01) 18:3(n-3) in adipose TAG than LPL-deficient queens on d 110 and 251. After the addition of linseed oil, proportions of FA other than 18:3(n-3) in adipose TAG did not differ (P < 0.05) (Fig. 2).


Figure 3
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  		Figure 3  Proportion of 18:3(n-3) in adipose phospholipid (PL, panel A) and triacylglycerol (TAG, panel B) in subcutaneous inguinal adipose of LPL-deficient (n = 14; on d 251, n = 8) and normal queens (n = 8; on d 251, n = 3) collected before and at d 38, 61, 110, and 251 after addition of linseed oil (30g/kg) to diet. Plotted values represent means ± SEM. *Different from d 0 for the same queen group, P < 0.05. {dagger}Different from normal queens at the same time, P < 0.05.

 
Differences in FA composition of adipose PL between LPL-deficient and normal queens were not as great as those in adipose TAG (Fig. 4). In LPL-deficient queens, PL proportion of 16:0 was greater and 18:2(n-6) and 20:5(n-3) were less than those in normal queens (P < 0.05). All other FA proportions did not differ between the groups of queens. The proportion of 18:3(n-3) increased (P < 0.01) after linseed oil addition in both groups and did not differ between the groups, except at d 110, when it was lower (P < 0.05) in LPL-deficient than in normal queens. Whereas 18:3(n-3) increased after the oil addition, the PL proportions of longer chain (n-3) FA, 20:5(n-3) and 22:6(n-3), did not increase.


Figure 4
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  		Figure 4  Phospholipid fatty acid proportions in subcutaneous inguinal adipose of LPL-deficient (n = 14) and normal queens (n = 8) before and 110 d after addition of linseed oil (30g/kg) to diet. Plotted values represent means ± SEM. See Table 1 for definitions of FA abbreviations. *Different from normal queens at the same time, P < 0.05. {dagger}Different from d 0 for the same queen group, P < 0.05.

 
    Plasma lipids. As expected, plasma TAG concentrations in LPL-deficient queens were much greater (P < 0.01) than those in normal queens at all sampling times (Table 3). Plasma TAG concentrations did not significantly increase after linseed oil addition for either LPL-deficient or normal queens (data not shown). Plasma TAG concentrations in LPL-deficient queens decreased (P < 0.01) by ~50% upon withholding diet (Table 3). In contrast, plasma TAG concentrations in normal queens after withholding diet did not differ from concentrations before withholding the diet.


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  		TABLE 3 Fatty acid composition of plasma NEFA and TAG before (+) and after (–) 16 h of withholding diet in normal and LPL-deficient queens fed a diet supplemented with linseed oil for 117 d1

 
Fatty acid proportions in plasma TAG were similar in LPL-deficient and normal queens with a few exceptions (Supplemental Table 1). The most substantive difference was in 20:4(n-6) proportion, which was 50% lower (P < 0.01) in LPL-deficient than in normal queens. Other minor differences (P < 0.05) occurred with 14:0, 18:0 and 22:6(n-3) proportions.

Plasma PL FA proportions in LPL-deficient queens differed slightly (P < 0.05) from those in normal queens (Supplemental Table 1). Withholding the diet affected plasma PL FA proportions in LPL-deficient and normal queens similarly; proportional increases occurred in 18:0, 20:4(n-6), and 22:6(n-3), whereas decreases occurred in proportions of most of the other FAs.

Plasma NEFA concentration in normal queens increased (P < 0.05) with diet withholding (Table 3). An opposite response occurred in LPL-deficient queens. Plasma NEFA concentrations decreased (P < 0.05) with diet withholding in LPL-deficient queens. Plasma NEFA concentrations in LPL-deficient queens, when diet was continuously present, did not differ from plasma NEFA concentrations in normal queens when diet was withheld. With the exception of small differences in proportions of 12:0, 20:4(n-6), and 22:6(n-3), the FA proportions in NEFA did not differ between LPL-deficient and normal queens (Supplemental Table 1). Food withholding substantively altered FA proportions in plasma NEFA. Proportions of all PUFA decreased (P < 0.05) in the LPL-deficient and normal queens except for 22:6(n-3), which did not differ. The NEFA monounsaturated FA (MUFA; 16:1 and 18:1) proportions also decreased (P < 0.05) in LPL-deficient queens, but were unchanged in normal queens. All NEFA saturated FA (SFA; 12:0, 14:0, 16:0, and 18:0) proportions increased (P < 0.05) in LPL-deficient queens, whereas only 16:0 increased (P < 0.05) in normal queens.


   Discussion
TOP
 ABSTRACT
 Introduction
 Materials and Methods
 Results
 Discussion
LITERATURE CITED
 
Body weight gain in LPL-deficient queens, following the addition of dietary linseed oil to their diet, was not anticipated (Fig. 1). Slight variations in dietary fat content were not expected to affect body weight because of appropriate adjustments in food intake (28). The relative consistency of body weight observed in normal queens was in accord with insensitivity to minor variations in dietary fat concentration. The increase in body weight in LPL-deficient queens was probably a result of expanded fat mass. This conclusion is supported by the amount of weight gain observed in LPL-deficient queens (+ ~12%) and the near normal percentage of body fat (25 ± 2%) found in the cats after addition of linseed oil (d 110). Prior to adding the oil, LPL-deficient queens were assumed to be as lean as previously observed (~6% body fat) (10). The source of FA for the increased body fat was not evident. It also was not evident why body weight gain ceased while oil supplementation continued. Khokher and Dandona (29) observed that linolenic acid stimulates and potentiates insulin action on synthesis of FA and TAG in isolated rat adipocytes. Increased sensitivity of adipose to insulin might have led to normalization of body fat in the LPL-deficient queens. However, if this were the case, the lean state of LPL-deficient cats would stem from a reversible insulin resistance in adipose. Future evaluation of tissue-specific insulin sensitivity in LPL-deficient cats might be valuable toward understanding the mechanism that regulates body fat mass.

Before and after the addition of linseed oil to the diet, clear differences in adipose FA composition occurred between LPL-deficient and normal queens. Most notably, the proportion of 16:0 was higher, and 18:2(n-6) was lower, in adipose TAG of LPL-deficient cats than in normal queens (Fig. 2). A similar pattern was found in LPL-deficient humans and mice (5,6). The deviation in FA composition of LPL-deficiency compared with normal LPL might indicate poor entry of dietary FA into adipose tissue and a compensatory increase in FA synthesis to maintain adipose TAG stores. This explanation was deduced from observations that the principal product of de novo FA synthesis is 16:0 (30) and that 18:2(n-6) must be acquired from diet (31). Hence, it would appear that FA synthesis is substantial in cats lacking LPL, despite previous reports of low rates of FA synthesis in slices of adipose and liver tissue from cats (12). As in humans with functional LPL (30), normal cats may readily synthesize FA when dietary fat is low enough. To the authors' knowledge, the effect of dietary fat concentration on FA synthesis has not been previously evaluated in cats.

Proportions of 10:0, 12:0, 14:0, and 16:1 in adipose TAG were also increased in LPL-deficient queens. For 16:1, but not the other FA, a similar high proportion is found in LPL-deficient humans and mice. Elevation in 16:1 probably indicates increased desaturation of 16:0, which is enriched in LPL-deficient animals. Greater proportions of 10:0, 12:0, and 14:0 in LPL-deficient than in normal queens might indicate that cats, relative to humans and mice, are less proficient in elongating FA to 16:0. Alternatively, because 16:0 is highly enriched in adipose of LPL-deficient queens, the relatively high enrichments of 10:0, 12:0, and 14:0 may only reflect partial ß-oxidation of 16:0 in the queens.

Despite a lack of LPL catalytic activity in LPL-deficient cats (9), substantive amounts of dietary (n-6) and (n-3) FA were found in adipose of LPL-deficient queens (Figs. 2 and 3). Clearly, one or more alternative mechanisms must deliver FA to adipose in the absence of LPL. Fatty acids may be acquired by receptor-mediated endocytosis of lipoproteins, but this process appears limited in adipose (32,33). Activity of intravascular lipases structurally similar to LPL might be responsible. Hepatic lipase hydrolyzes TAG and PL in plasma lipoproteins (15) and occurs in extrahepatic vascular sites where the lipase may free FA for uptake and storage (8). Endothelial lipase may also release FA from plasma lipoproteins, although its activity is directed toward only PL. Endothelial lipase may be especially relevant in LPL-deficiency because its expression is upregulated when adipose lacks LPL (14).

High plasma NEFA concentration was found in LPL-deficient queens while the diet was continuously present (Table 3). A similar NEFA concentration was observed in normal queens when diet was withheld. The NEFA elevation might reflect activity of lipases other than LPL on plasma lipoproteins in extraordinary abundance. The very high plasma TAG concentration in LPL-deficient queens is consistent with the characteristic intravascular accumulation of chylomicrons and VLDL that is observed in LPL-deficiency (34). While the diet was present, the proportions of (n-6) and (n-3) NEFA in plasma were slightly greater (P < 0.05) than (n-6) and (n-3) FA proportions in adipose TAG (Table 3). This indicates that the acquisition of NEFA released from plasma lipoproteins is a plausible way for dietary FA to enter adipose in LPL-deficient cats. Utilization of plasma NEFA by adipose lacking LPL would probably be greatest in the absorptive state, when the hormonal signaling and abundance of substrate favors anabolism.

Although body fat mass expanded in LPL-deficient queens with linseed oil added to the diet, the rate of 18:3(n-3) incorporated into adipose TAG lagged well behind that in normal queens (Fig. 3). This response, in conjunction with the observed 16:0 to 18:2(n-6) proportions in LPL-deficient queens, indicates a much slower incorporation of dietary FA in adipose of LPL-deficient relative to normal cats. Hence, LPL appears to be important but not essential for dietary FA to enter into the adipose of cats. Also, LPL does not appear to be necessary for sustaining a normal adipose mass in cats. Similar findings in LPL-deficient humans prompted Fielding and Frayn (35) to suggest that control of FA deposition in adipose is regulated distally to LPL, probably involving regulation of hormone-sensitive lipase and FA esterification into TAG. Presumably, even without LPL, body adipose mass enlarges until feedback inhibition prevents further expansion.

Even after d 250, 18:3(n-3) concentration in adipose TAG of normal queens continued to increase. Similar long equilibration periods (>5 mo) for dietary FA incorporation into adipose are suggested to occur in cats (36) and are observed in other species (37,38). However, relative to 18:3(n-3), other dietary FA might equilibrate more rapidly in adipose TAG. Summers et al. (39) report that the net rate of adipose FA uptake in humans varies with FA species, ranking in an order of (n-3) FA < SFA < (n-6) FA < MUFA.

In adipose PL, FA compositional changes with the addition of linseed oil were different and more rapid than those in adipose TAG. 18:3(n-3) and other FA proportional changes in adipose PL of LPL-deficient were similar but not identical to those in normal queens (Fig. 3). The ratio of SFA to PUFA in PL in LPL-deficient queens was slightly greater (P < 0.05) than that of normal queens (Fig. 4). The 18:3(n-3) observations indicated FA composition of membrane PL depends little on LPL activity and was influenced only slightly by the abundance of de novo synthesized FA in adipose.

In conclusion, analysis of FA composition of subcutaneous adipose TAG of LPL-deficient cats indicates that substantial de novo FA synthesis occurs in domestic cats, and that synthesized FA contributes greatly to body fat stores of LPL-deficient cats. Use of 18:3(n-3) as a dietary FA marker shows that loading of adipose with 18:3(n-3) occurs slowly in cats, and that LPL-deficiency probably impairs adipose acquisition of all dietary FA. The NEFA in plasma during the absorptive state is a plausible source of FA found in adipose of LPL-deficient cats. Supplementing the diet with linseed oil appears to induce body weight gain and normalize body fat in LPL-deficient cats. The cause for this is unknown. Our observations are consistent with previous findings in other species, indicating that LPL is not required for the maintenance of normal adiposity, and that without LPL, FA composition of body fat is substantially altered and results in the storage of saturated over unsaturated FA.


   ACKNOWLEDGMENTS
 
The authors thank S. Taylor for assistance with fatty acid analyses and M. Afraz, K. Opp, N. La, K. Kovach, C. Heeb, N. Moulin, and D. Bee for assistance with experimental procedures and husbandry of the cats.


   FOOTNOTES
 
1 Supported by the Center for Companion Animal Health, School of Veterinary Medicine, University of California, Davis. Fatty acid analyses were supported by a grant from the California Dairy Research Foundation (Davis, CA) through the Dairy Milk Components Laboratory in the Department of Animal Science at UC Davis. Back

2 Supplemental Table 1 is available with the online posting of this paper at jn.nutrition.org. Back

6 Abbreviations used: FA, fatty acids; LPL, lipoprotein lipase; MUFA, monounsaturated FA; NEFA, nonesterified fatty acid; PL, phospholipid; SFA, saturated fatty acid; TAG, triacylglycerol. Back

Manuscript received 25 July 2006. Initial review completed 28 August 2006. Revision accepted 20 September 2006.


   LITERATURE CITED
TOP
 ABSTRACT
 Introduction
 Materials and Methods
 Results
 Discussion
 LITERATURE CITED
 

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