Adipose tissue plays an important role in energy homeostasis by serving as a storage organ and also through active secretion of adipokines, including adiponectin and leptin. Body fat content in cats is inversely associated with circulating concentrations of adiponectin and directly associated with concentrations of leptin, which is similar to findings in humans and other animals.1–4 Adiponectin, the most abundant adipokine, exerts a profound insulin-sensitizing effect by enhancing FA oxidation in skeletal muscle and the liver, thus reducing triglyceride content in these tissues. It also facilitates glucose uptake by skeletal muscle and inhibits glucose production by the liver, which leads to a decrease in blood glucose concentrations.5 Adiponectin also has anti-inflammatory and antiatherosclerotic effects.6,7 Leptin is an important regulator of adipose tissue mass and increases insulin sensitivity through multiple effects on satiety, energy expenditure, and neuroendocrine function. These effects are exerted predominantly through actions of leptin within the CNS and possibly by additional direct effects on insulin target tissues.8
Because adiponectin concentrations are decreased in obese subjects, low adiponectin concentrations are implicated in the pathogenesis of several metabolic alterations associated with obesity in humans, including insulin resistance and type 2 diabetes mellitus.7 Increased leptin concentrations also have been reported in association with insulin resistance and most likely indicate leptin resistance.8 Similarly in cats, low adiponectin and high leptin concentrations have been associated with obesity-related insulin resistance.4,9 In a preliminary report,a investigators indicated that diabetic status as well as body condition are predictors of low adiponectin concentrations in cats.
Authors of numerous studies10–22 have described beneficial effects of consumption of diets high in n-3 PUFAs on various disorders; many of those disorders are also associated with low concentrations of adiponectin. In an epidemiological study10 in humans, dietary intake of fish products, which are rich in long-chain n-3 PUFAs (EPA and DHA), was associated with a delay in the development of glucose intolerance. Obese cats consuming a diet high in n-3 PUFAs had improvement in long-term glucose control and decreases in plasma insulin concentrations, compared with results for cats consuming a diet rich in saturated FAs.22
Dietary FAs have also been associated with circulating concentrations of adiponectin and leptin. In healthy humans, serum adiponectin concentrations are directly associated with concentrations of n-3 PUFAs and inversely associated with n-6 PUFAs and saturated FAs.23 Increased leptin concentrations are associated with decreased n-3 PUFA concentrations in humans with acute myocardial infarction.17
Low adiponectin concentrations and high leptin concentrations in cats with insulin resistance and the reported improvement in insulin sensitivity as a result of dietary n-3 PUFAs suggest that the beneficial effects of these FAs may be mediated through an increase in adiponectin concentrations. Therefore, we hypothesized that circulating n-3 PUFA concentrations are directly associated with adiponectin concentrations in cats. The objective of the study reported here was to determine the associations between serum concentrations of n-3 PUFAs and concentrations of adiponectin, leptin, and insulin in healthy cats.
Materials and Methods
Animals—Fifty-six healthy adult (≥ 1 year old) client-owned cats admitted to the Veterinary Teaching Hospital at Michigan State University for routine examinations were included in the study. Cats were considered healthy on the basis of results of physical examination and routine biochemical analysis. Additional inclusion criteria reflected the medical and dietary history for a 3-month period preceding sample collection and included absence of any clinical signs indicative of illness, exclusive feeding of a commercially available nutritionally balanced and complete diet formulated for adult cats (based on Association of American Feed Control Officials minimums), and no administration of dietary nutritional products or medications. Cats with mild hyperglycemia (up to 9.0 mmol/L) were not excluded. This magnitude of increase in glucose concentration was considered to represent stress hyperglycemia consistent with a reported mean peak glucose concentration of 9.0 mmol/L in healthy cats that were subjected to an acute stressor but that had results for a glucose tolerance test within the anticipated reference limits.24 Informed consent was obtained from all owners. The study was performed in compliance with Michigan State University guidelines for research in animals.
Sample collection and serum analysis—Food was withheld from all cats for 12 hours before sample collection. Before sample collection, body condition of all cats was evaluated by a single investigator (PAS) and scored by use of a BCS system (scale, 1 to 9).25 A venous blood sample (2 mL) was collected from each cat. The sample was centrifuged (2,000 × g for 15 minutes at 4°C) immediately after clotting; serum was harvested and frozen at −20°C until analyzed.
Serum adiponectin, leptin, and insulin concentrations were measured by use of commercially available assaysb–d previously used by others2,4 and validated in our laboratory for use in cats. Serum samples were diluted 1:1,111 in preparation for the adiponectin assay. For validation, serial dilutions of cat serum were prepared, and the observed curves were parallel to the standard curves for mouse adiponectin, human leptin, and human insulin standards. The dynamic range and minimum detection limit of the assays were 0.25 to 8 ng/mL and 15.6 pg/mL in diluted serum for adiponectin, 1 to 50 ng/mL and 1 ng/mL for leptin, and 36 to 2,153 pmol/L and 9 pmol/L for insulin, respectively. Intra-assay and interassay coefficients of variation were 5% and 7% for adiponectin, 6% and 10% for leptin, and 9% and 10% for insulin, respectively. Serum glucose concentrations were measured by use of an automated chemistry analyzer,e and concentrations of cholesterol and triglyceride were measured by use of a spectrophotometric method.f
Analysis of serum FA concentrations was performed by use of gas chromatography. Fatty acids in serum samples were methylated by incubation with 10% methanolic HCl at 75°C for 2 hours.26 Nonadecanoic acid was used as an internal standard. Samples (1 μL) of FA methyl esters in hexane were injected into the gas chromatograph.g A fused silica capillary column (100 m × 0.25 mm with a film thickness of 0.2 μm)h was used to resolve the FA methyl esters in each sample. Hydrogen was used as a carrier gas at a flow rate of 0.5 mL/min. The resolved components were detected by a flame ionization detector with an air flow of 400 mL/min and a hydrogen flow of 45 mL/min; the temperature of the detector was set at 255°C. Peaks were identified and validated by use of FA standards of known concentrations.i Serum FA concentrations were reported as percentages of total FAs.
Data analysis—Associations between serum concentrations of EPA, DHA, and ALA and serum concentrations of adiponectin, leptin, insulin, glucose, triglyceride, and cholesterol were evaluated by use of a general linear model that included EPA concentration, DHA concentration, ALA concentration, BCS, sex, and age as covariates. Lack of potential colinearity among serum concentrations of EPA, DHA, and ALA was confirmed. The additional covariates (ie, BCS, sex, and age) were included to control for potential confounding of the association between EPA, DHA, or ALA concentration and the outcome variables (adiponectin, leptin, insulin, glucose, triglyceride, or cholesterol concentration). The link function and the linear predictor for each of the variables were of the form E(y|x) = a + bx, where y is a natural logarithmic transformation of the measured values and has a normal distribution (as confirmed by examination of probability-probability plots) with a mean (a + bx) and constant variances. All interaction effects between EPA, DHA, or ALA concentrations and other variables in the models were assessed.
Post hoc categorization—Significant interaction effects between BCS and EPA concentration were detected in the analyses of the associations with adiponectin (P = 0.023), insulin (P = 0.025), and triglyceride (P = 0.006) concentrations. An interaction effect, which was not significant (P = 0.060), between BCS and DHA concentration was detected in the analysis of the associations with adiponectin concentration. Because of insufficient statistical power of the study to evaluate the effect of EPA concentration on the outcome variables in separate analyses of each BCS category with age and sex as additional covariates, cats were categorized into 2 groups (nonobese [BCS, 4 to 6] and obese [BCS, 7 to 8]) on the basis of the likelihood for a positive or negative association between EPA and adiponectin concentrations in the following separate analyses: exponentiated coefficients for the association between EPA and adiponectin concentrations in the analyses for BCS of 4, 5, 6, 7, and 8 were 0.11 (P > 0.10), 0.42 (P < 0.10), 0.87 (P > 0.10), 5.39 (P < 0.10), and 1.91 (P > 0.10), respectively. Associations between serum concentrations of EPA and DHA and serum concentrations of adiponectin, leptin, insulin, glucose, triglyceride, or cholesterol were evaluated separately for the non-obese and obese groups by use of a general linear model that included EPA concentration, DHA concentration, and sex as covariates in all models. Age was entered as an additional covariate in the models for all the outcome variables, except adiponectin concentration because its inclusion in the model decreased the model's adjusted R2. The ALA concentration was not included in the separate models because its inclusion decreased the model's adjusted R2.
Results were reported for all cats when no interaction effects were detected (associations of sex, age, DHA concentration, and ALA concentration with all outcome variables and associations of EPA concentration with leptin, glucose, and cholesterol concentrations) and separately for the nonobese and obese groups when significant interaction effects were detected (associations of EPA concentration with adiponectin, insulin, and triglyceride concentrations) as well as further evaluation of the associations between EPA concentration and leptin, glucose, and cholesterol concentrations or DHA concentration with all outcome variables. Data were analyzed by use of a commercially available statistical program.j A value of P < 0.05 was considered significant.
Results
One neutered female cat was excluded from the study because of hyperglycemia (serum glucose concentration, 14.8 mmol/L) in the serum sample obtained after food was withheld for 12 hours. The BCS of the remaining 55 cats was 4 (n = 5 cats), 5 (15), 6 (14), 7 (9), and 8 (12). Thus, 34 cats were categorized as nonobese and 21 were categorized as obese.
Median age of the nonobese cats was 3.0 years (interquartile range, 1.5 to 6.5 years), whereas that of the obese cats was 5.0 years (interquartile range, 3.5 to 7.0 years). Fourteen nonobese cats were neutered males and 20 were neutered females. Sixteen obese cats were neutered males and 5 were neutered females. The nonobese group comprised 26 domestic shorthair cats, 3 domestic longhair cats, 2 mixed-breed cats, 1 Siamese, 1 Birman, and 1 Bengal. The obese group comprised 14 domestic shorthair cats, 4 domestic longhair cats, 2 domestic medium-hair cats, and 1 mixed-breed cat. Median (interquartile range) serum concentrations of ALA, EPA, and DHA were 0.21 mg/100 mg of FAs (0 to 0.35 mg/100 mg of FAs), 0.34 mg/100 mg of FAs (0 to 0.48 mg/100 mg of FAs), and 1.75 mg/100 mg of FAs (1.37 to 2.82 mg/100 mg of FAs), respectively, in the nonobese group and 0.36 mg/100 mg of FAs (0.28 to 0.56 mg/100 mg of FAs), 0.21 mg/100 mg of FAs (0.06 to 0.44 mg/100 mg of FAs), and 2.15 mg/100 mg of FAs (1.29 to 2.66 mg/100 mg of FAs), respectively, in the obese group.
Serum glucose concentration was higher than the reference range of 3.3 to 7.5 mmol/L in 5 nonobese and 2 obese cats. Serum triglyceride concentration was higher than the reference range of 21 to 155 mg/dL in 5 cats in the obese group and was within the reference range in all cats in the nonobese group. Serum concentration of cholesterol was within the reference range of 77 to 306 mg/dL in all cats.
Analysis of data for all cats revealed that the adjusted geometric mean serum concentration of adiponectin was 71% higher and the adjusted geometric mean serum glucose concentration was 15% lower in neutered females than in neutered males (Table 1). In addition, each 1-year increase in age was associated with a 2% increase in the adjusted geometric mean serum concentration of leptin (Table 2).
Effect of sex on adiponectin, leptin, insulin, glucose, triglyceride, and cholesterol concentrations in 55 healthy neutered cats.*
| Variable | Ratio (95% CI) | P value | Partial η2 |
|---|---|---|---|
| Adiponectin | 1.71 (1.10–2.66) | 0.019 | 0.12 |
| Leptin | 1.11 (0.95–1.29) | 0.187 | 0.04 |
| Insulin | 0.95 (0.74–1.22) | 0.689 | < 0.01 |
| Glucose | 0.85 (0.76–0.95) | 0.006 | 0.16 |
| Triglyceride | 0.91 (0.71–1.16) | 0.445 | 0.01 |
| Cholesterol | 1.02 (0.86–1.20) | 0.865 | < 0.01 |
Values reported are the ratio (95% CI) of adjusted geometric means of serum concentrations for female cats to serum concentrations for male cats for each variable.
Covariates in the general linear model include age, sex, BCS, and concentrations of EPA, DHA, and ALA.
Effect of age on adiponectin, leptin, insulin, glucose, triglyceride, and cholesterol concentrations in 55 healthy cats.*
| Variable | Fold increase (95% CI) | P value | Partial η2 |
|---|---|---|---|
| Adiponectin | 0.98 (0.93–1.04) | 0.492 | 0.01 |
| Leptin | 1.02 (1.00–1.04) | 0.048 | 0.08 |
| Insulin | 0.97 (0.94–1.00) | 0.057 | 0.08 |
| Glucose | 0.99 (0.98–1.00) | 0.224 | 0.04 |
| Triglyceride | 0.98 (0.95–1.01) | 0.224 | 0.03 |
| Cholesterol | 1.01 (0.99–1.03) | 0.257 | 0.03 |
Values represent the fold increase (95% CI) in adjusted geometric means of serum concentrations of each variable for each 1-year increase of age.
See Table 1 for remainder of key.
A significant association between serum concentrations of EPA and leptin was detected in the analysis for all cats; an increase in the serum concentration of EPA of 1 mg/100 mg of FAs was associated with a 314% increase in the adjusted geometric mean serum concentration of leptin (95% CI fold increase of adjusted geometric mean, 1.07 to 15.21; P = 0.039; partial η2 = 0.09). No significant associations between EPA concentration and glucose or cholesterol concentrations or between DHA or ALA concentrations and any of the outcome variables were detected in the analyses for all cats.
In the separate analyses for the nonobese group, an increase in the serum concentration of EPA of 1 mg/100 mg of FAs was associated with a 62% decrease in the adjusted geometric mean serum concentration of adiponectin and a 43% increase in the adjusted geometric mean serum concentration of leptin (Table 3). In the separate analyses for the obese group, an increase in the serum concentration of EPA of 1 mg/100 mg of FAs was associated with a 643% increase in the adjusted geometric mean serum concentration of adiponectin, a 70% decrease in the adjusted geometric mean serum concentration of insulin, and an 84% decrease in the adjusted geometric mean serum concentration of triglyceride (Table 4). Additionally, an increase in the serum concentration of DHA of 1 mg/100 mg of FAs was associated with a 54% increase in the adjusted geometric mean serum concentration of adiponectin in the separate analysis for the obese group (95% CI fold increase of adjusted geometric mean, 1.02 to 2.32; P = 0.041; partial η2 = 0.22). No significant associations were detected between serum concentrations of DHA and adiponectin in the separate analysis for the nonobese group or between serum concentration of DHA and concentrations of leptin, insulin, glucose, triglyceride, or glucose in the separate analyses for the nonobese or obese groups.
Effect of EPA on adiponectin, leptin, insulin, glucose, triglyceride, and cholesterol concentrations in 34 nonobese (BCS, 4 to 6) cats.*
| Variable | Mean (95% CI)† | Fold increase (95% CI)‡ | P value | Partial η2 |
|---|---|---|---|---|
| Adiponectin (μg/mL) | 2.4 (1.8–3.1) | 0.38 (0.17–0.83) | 0.017 | 0.18 |
| Leptin (ng/mL) | 4.4 (4.1–4.8) | 1.43 (1.12–1.83) | 0.006 | 0.23 |
| Insulin (pmol/L) | 34 (29–39) | 0.95 (0.61–1.50) | 0.833 | < 0.01 |
| Glucose (mmol/L) | 5.7 (5.3–6.1) | 0.97 (0.78–1.20) | 0.772 | < 0.01 |
| Triglyceride (mg/dL) | 65 (58–72) | 0.84 (0.61–1.16) | 0.276 | 0.04 |
| Cholesterol (mg/dL) | 128 (117–140) | 0.87 (0.67–1.13) | 0.292 | 0.04 |
Covariates in the general linear model include sex, age, EPA, and DHA concentration (leptin, insulin, glucose, triglyceride, and cholesterol concentrations) or sex, EPA, and DHA concentration (adiponectin concentration).
Covariates in the models are evaluated at their mean values as follows: EPA = 0.31 mg/100 mg of FAs, DHA = 1.98 mg/100 mg of FAs, and age = 4.9 years.
Fold increases (95% CI) of adjusted geometric means of serum concentration of each variable represent the change with an increase in serum concentration of EPA of 1 mg/100 mg of FAs.
Effect of EPA concentration on adiponectin, leptin, insulin, glucose, triglyceride, and cholesterol concentrations in 21 obese (BCS, 7 or 8) cats.*
| Variable | Mean (95% CI)† | Fold increase (95% CI)‡ | P value | Partial η2 |
|---|---|---|---|---|
| Adiponectin (μg/mL) | 1.3 (0.8–2.0) | 7.43 (1.05–52.30) | 0.045 | 0.22 |
| Leptin (ng/mL) | 5.8 (4.8–7.1) | 0.84 (0.35–2.01) | 0.674 | 0.01 |
| Insulin (pmol/L) | 46 (36–60) | 0.30 (0.10–0.91) | 0.035 | 0.25 |
| Glucose (mmol/L) | 5.1 (4.6–5.7) | 0.98 (0.93–1.02) | 0.303 | 0.07 |
| Triglyceride (mg/dL) | 97 (71–134) | 0.16 (0.04–0.65) | 0.014 | 0.32 |
| Cholesterol (mg/dL) | 137 (116–161) | 0.96 (0.47–1.97) | 0.908 | < 0.01 |
Covariates in the models are evaluated at their mean values as follows: EPA = 0.24 mg/100 mg of FAs, DHA = 1.92 mg/100 mg of FAs, and age = 4.9 years.
See Table 3 for remainder of key.
Discussion
In the study reported here, it was found that circulating concentrations of adipokines (adiponectin and leptin), insulin, and triglyceride are associated with serum concentrations of long-chain n-3 PUFAs but not with concentrations of n-3 PUFAs of shorter chain lengths (ie, ALA) in healthy cats. These associations were detected primarily for EPA and differed between nonobese and obese cats. Specifically, concentrations of EPA were directly associated with concentrations of adiponectin and inversely associated with concentrations of insulin and triglyceride in obese cats. A direct association of serum concentrations of EPA with concentrations of leptin and an inverse association with concentrations of adiponectin were detected in the nonobese cats. The only significant finding for serum concentrations of DHA was a direct association with concentrations of adiponectin in obese cats, which was similar to the finding for EPA concentrations.
Although a cause-and-effect relationship cannot be determined from this cross-sectional study, a potential regulatory effect of long-chain n-3 PUFAs on adiponectin production and secretion in obese cats is suggested by the finding of direct associations of serum concentrations of adiponectin with concentrations of both EPA and DHA. The concentration of each of these FAs explained 22% of the variability in adiponectin concentration in the obese cats. These findings are in agreement with the reported direct association between circulating plasma adiponectin and n-3 PUFA concentrations in humans.23 In addition, other investigators27–32 have detected an increase in adiponectin concentration following dietary supplementation with n-3 PUFAs in rodents and humans, which supports a causal effect of these FAs on adiponectin secretion.
Long-chain n-3 PUFAs may have an effect that attenuates processes that occur in adipose tissue as it expands and result in reduced adiponectin production and secretion. One potential effect of these FAs is attenuation of the inflammation in adipose tissue of obese subjects.33 Tumor necrosis factor-α protein and mRNA concentrations were found to be higher in adipose tissue of obese cats,34,35 compared with results for lean cats, and increased TNF-α concentrations have been associated with downregulation of adiponectin production in cocultured adipocytes and macrophages.36 It has been suggested that in contrast to saturated FAs, n-3 PUFAs are unable to activate macrophages and may antagonize the proinflammatory effect of saturated FAs; the reduction of inflammation in adipose tissue then restores adiponectin production.30,37,38 A fish oil-enriched diet was associated with significant reductions in inflammatory cytokines and lymphocyte proliferation in dogs,12,13 but no significant differences in general immune function were found between cats fed diets rich in omega-3 PUFAs or saturated FAs.39 However, cytokine concentrations were not evaluated in that study in cats.39
Another potential mechanism by which n-3 PUFAs restore adiponectin concentrations in obese subjects is upregulation and activation of PPAR-γ. This nuclear receptor plays a key role in lipid and glucose homeostasis through effects on gene transcription, and its pharmacological activation can increase adiponectin concentrations.40 The PPAR-γ is expressed predominantly in adipose tissue, and its expression is decreased in obese cats.41 Eicosapentaenoic acid increases PPAR-γ expression in adipocytes,42 and DHA metabolites may act as ligands for PPAR-γ.28,43 It is possible that EPA and DHA decreased the inflammatory process and reversed the downregulation of PPAR-γ in the obese cats of the study reported here, which restored adiponectin concentrations.
An inverse association between EPA and adiponectin concentrations was found in the nonobese group, and the concentration of EPA explained 18% of the variability in adiponectin concentration in the nonobese cats. A potential explanation for this finding is not clearly apparent. Some clarification may be provided by the reported dose-dependent effect of EPA on PPAR-γ expression in isolated human adipocytes, which was characterized by an initial increase and a subsequent decrease of PPAR-γ expression at high EPA concentrations.42 Higher EPA concentrations could lead to suppression of the already high baseline PPAR-γ expression in relatively lean cats, which would result in lower circulating adiponectin concentrations.
A direct association of leptin concentration and EPA concentration was detected when data for all cats were analyzed, and further analysis of the subgroups revealed that this association was evident in nonobese cats but not in obese cats. This difference may have been related to the smaller number of obese cats than nonobese cats in the study. Alternatively, EPA may upregulate leptin production in nonobese cats but not in obese cats because of the high leptin concentrations resulting from leptin resistance in obese cats. The concentration of EPA explained 23% of the variability in leptin concentration in the nonobese cats in the present study. In other studies, there have been conflicting results regarding the effect of n-3 PUFAs on leptin concentrations. Some studies have indicated an increase,29,44,45 some have indicated a decrease,46,47 and others have indicated no change11,21 in leptin concentrations or mRNA expression following dietary supplementation with fish oil. The reason for these variable findings is unclear but could be related to study design or species differences.
An inverse association between serum concentrations of insulin and EPA was found in the obese cats but not in the nonobese cats. Concentration of EPA explained 25% of the variability in insulin concentration in the obese cats. These findings suggest a potential regulatory effect of EPA on insulin sensitivity and, consequently, insulin concentrations in obese cats. These findings agree with the reported beneficial effects of fish oil consumption on insulin sensitivity in humans and the decreased insulin concentrations in obese cats following feeding of a diet rich in n-3 PUFAs, compared with results after feeding a diet high in saturated FAs.22
The effect of n-3 PUFAs on insulin sensitivity may be mediated by increased adiponectin production and secretion because adiponectin has profound insulin-sensitizing properties. However, n-3 PUFAs may have additional insulin-sensitizing effects that are not directly related to increased adiponectin concentrations. Upregulation and activation of PPAR-γ by n-3 PUFAs in adipose tissue lead to transformation of small adipocytes that are more sensitive to insulin. Increased incorporation of n-3 PUFAs in cell membranes of insulin target tissues results in improved insulin activity. Omega-3 PUFAs may stimulate FA oxidation in the liver and skeletal muscle, which decreases tissue lipid accumulation and improves insulin action and may also improve glucose utilization by attenuation of obesity-induced downregulation of glucose transporter-4 in insulin target tissues.15,20,45 The effect of n-3 PUFAs to improve insulin sensitivity may also be mediated through reduction of adipose tissue TNF-α concentrations because TNF-α impairs insulin signaling by inhibiting tyrosine kinase activity of insulin receptors.48
Serum triglyceride concentrations were inversely associated with EPA concentrations in obese cats but not in nonobese cats. Concentration of EPA explained 32% of the variability in triglyceride concentration in the obese cats. Results of other studies support the lipid-lowering effect of EPA and fish oil in humans15,16 and dogs.49,50 The hypolipidemic effect of n-3 PUFAs is attributable to the suppression of transcription of genes encoding lipogenic enzymes and to increased FA oxidation in the liver.51 Additional beneficial effects on hyperlipidemia include stimulation of lipoprotein lipase activity, decrease in intestinal absorption of lipid and glucose, increase in cholesterol secretion into bile, and decrease in cholesterol absorption.14,18,19 The effect of n-3 PUFAs to decrease triglyceride concentrations may be partially mediated through suppression of TNF-α because TNF-α stimulates secretion of very–low-density lipoproteins from the liver and increases lipolysis in adipose tissue.52 Although studies22,53 in healthy cats have revealed no effect of dietary supplementation with n-3 PUFAs on triglyceride concentration, the findings of the study reported here warrant further investigation into the effect of EPA on triglyceride concentrations in hyperlipidemic cats.
In the present study, associations were detected between concentrations of adipokines, insulin, and triglyceride with concentrations of long-chain n-3 PUFAs (primarily EPA) but not with n-3 PUFAs of shorter chain length (ie, ALA). If the potential biological effect of n-3 PUFAs is exerted via the long-chain n-3 PUFAs, then the lack of effect of the shorter-length n-3 PUFAs may be explained by the greatly limited conversion of ALA to the longer-chain derivatives (ie, EPA and DHA) because of low Δ-6 desaturase activity in cats.54
Sex accounted for 12% of the variability in serum concentrations of adiponectin. Higher concentrations were found in female cats than in male cats, which is similar to the sex effect on adiponectin concentrations reported in humans.55,56 A direct effect of testosterone to decrease adiponectin secretion has been proposed as the primary factor for this sex difference in humans and rodents,55 but it cannot explain the finding in the population of neutered cats in the present study. A study56 in a group of male and female human subjects of similar age and body condition revealed an inverse association of concentrations of adiponectin and nonesterified FAs in men but not in women, which suggests that additional factors may be involved in the effect of sex on adiponectin concentrations. Further evaluation of potential sex differences (other than those attributable to sex hormones) that may affect adiponectin production in neutered cats is warranted. The small increase in leptin concentration with age in the cats in the present study is of questionable clinical importance. Age-related increases in leptin concentrations in rodents is thought to result from decreased leptin signaling in the hypothalamus and development of leptin resistance.57
For the study reported here, we concluded that circulating concentrations of EPA in obese cats are directly associated with adiponectin concentrations and inversely associated with insulin and triglycerides concentrations. These findings suggest beneficial effects of EPA in obese cats, and further investigation into the regulatory effect of fish oil and individual n-3 PUFAs on adiponectin and leptin secretion, insulin sensitivity, and lipid metabolism is warranted to determine the potential role of n-3 PUFAs in the prevention and treatment of disorders associated with obesity in cats.
ABBREVIATIONS
| ALA | α-Linolenic acid |
| BCS | Body condition score |
| CI | Confidence interval |
| DHA | Docosahexaenoic acid |
| EPA | Eicosapentaenoic acid |
| FA | Fatty acid |
| PPAR | Peroxisome proliferator-activated receptor |
| PUFA | Polyunsaturated fatty acid |
| TNF | Tumor necrosis factor |
Brömel C, Nelson RW, Fascetti AJ, et al. Determination of adiponectin, a novel adipocyte hormone, in healthy and diabetic normal weight and obese cats (abstr). J Vet Intern Med 2004;18:403.
Mouse/rat adiponectin ELISA kit, B-Bridge, Mountain View, Calif.
Multispecies leptin RIA kit, Millipore, St Charles, Mo.
Human insulin RIA kit, Diagnostic Systems Laboratories, Webster, Tex.
AU640 chemistry-immuno analyzer, Olympus America, Center Valley, Pa.
Kodak Ektachem DT60 II, Eastman Kodak Co, Rochester, NY.
Clarus 500 gas chromatograph, Perkin Elmer, Shelton, Conn.
SP2560 fused-silica capillary column, Supelco, Bellefonte, Pa.
Nu-check Prep, Elysian, Minn.
SPSS, version 15.0 for Windows, SPSS Inc, Chicago, Ill.
References
- 1.
Appleton DJ, Rand JS, Sunvold GD. Plasma leptin concentrations in cats: reference range, effect of weight gain and relationship with adiposity as measured by dual energy x-ray absorptiometry. J Feline Med Surg 2000; 2: 191–199.
- 2.↑
Backus RC, Havel PJ, Gingerich RL, et al. Relationship between serum leptin immunoreactivity and body fat mass as estimated by use of a novel gas-phase Fourier transform infrared spectroscopy deuterium dilution method in cats. Am J Vet Res 2000; 61: 796–801.
- 3.
Ishioka K, Omachi A, Sasaki N, et al. Feline adiponectin: molecular structures and plasma concentrations in obese cats. J Vet Med Sci 2009; 71: 189–194.
- 4.
Hoenig M, Thomaseth K, Waldron M, et al. Insulin sensitivity, fat distribution, and adipocytokine response to different diets in lean and obese cats before and after weight loss. Am J Physiol Regul Integr Comp Physiol 2007; 292: R227–R234.
- 5.↑
Karbowska J, Kochan Z. Role of adiponectin in the regulation of carbohydrate and lipid metabolism. J Physiol Pharmacol 2006; 57 (suppl 6): 103–113.
- 6.
Ouchi N, Kihara S, Arita Y, et al. Adiponectin, an adipocyte-derived plasma protein, inhibits endothelial NF-kappaB signaling through a cAMP-dependent pathway. Circulation 2000; 102: 1296–1301.
- 9.
Appleton DJ, Rand JS, Sunvold GD. Plasma leptin concentrations are independently associated with insulin sensitivity in lean and overweight cats. J Feline Med Surg 2002; 4: 83–93.
- 10.↑
Feskens EJ, Bowles CH, Kromhout D. Inverse association between fish intake and risk of glucose intolerance in normoglycemic elderly men and women. Diabetes Care 1991; 14: 935–941.
- 11.
Lara JJ, Economou M, Wallace AM, et al. Benefits of salmon eating on traditional and novel vascular risk factors in young, non-obese healthy subjects. Atherosclerosis 2007; 193: 213–221.
- 12.
LeBlanc CJ, Dietrich MA, Horohov DW, et al. Effects of dietary fish oil and vitamin E supplementation on canine lymphocyte proliferation evaluated using a flow cytometric technique. Vet Immunol Immunopathol 2007; 119: 180–188.
- 13.
LeBlanc CJ, Horohov DW, Bauer JE, et al. Effects of dietary supplementation with fish oil on in vivo production of inflammatory mediators in clinically normal dogs. Am J Vet Res 2008; 69: 486–493.
- 14.
Levy E, Thibault L, Turgeon J, et al. Beneficial effects of fish-oil supplements on lipids, lipoproteins, and lipoprotein lipase in patients with glycogen storage disease type I. Am J Clin Nutr 1993; 57: 922–929.
- 15.
Lombardo YB, Chicco AG. Effects of dietary polyunsaturated n-3 fatty acids on dyslipidemia and insulin resistance in rodents and humans. A review. J Nutr Biochem 2006; 17: 1–13.
- 16.
McKenney JM, Sica D. Role of prescription omega-3 fatty acids in the treatment of hypertriglyceridemia. Pharmacotherapy 2007; 27: 715–728.
- 17.↑
Oda E, Hatada K, Katoh K, et al. A case-control pilot study on n-3 polyunsaturated fatty acid as a negative risk factor for myocardial infarction. Int Heart J 2005; 46: 583–591.
- 18.
Smit MJ, Temmerman AM, Wolters H, et al. Dietary fish oil-induced changes in intrahepatic cholesterol transport and bile acid synthesis in rats. J Clin Invest 1991; 88: 943–951.
- 19.
Thomson AB, Keelan M, Lam T, et al. Fish oil modifies effect of high cholesterol diet on intestinal absorption in diabetic rats. Diabetes Res 1993; 22: 171–183.
- 20.
Ukropec J, Reseland JE, Gasperikova D, et al. The hypotriglyc-eridemic effect of dietary n-3 FA is associated with increased beta-oxidation and reduced leptin expression. Lipids 2003; 38: 1023–1029.
- 21.
Wang S, Ma AQ, Song SW, et al. Fish oil supplementation improves large arterial elasticity in overweight hypertensive patients. Eur J Clin Nutr 2008; 62: 1426–1431.
- 22.↑
Wilkins C, Long RC Jr, Waldron M, et al. Assessment of the influence of fatty acids on indices of insulin sensitivity and myocellular lipid content by use of magnetic resonance spectroscopy in cats. Am J Vet Res 2004; 65: 1090–1099.
- 23.↑
Fernandez-Real JM, Vendrell J, Ricart W. Circulating adiponectin and plasma fatty acid profile. Clin Chem 2005; 51: 603–609.
- 24.↑
Rand JS, Kinnaird E, Baglioni A, et al. Acute stress hyperglycemia in cats is associated with struggling and increased concentrations of lactate and norepinephrine. J Vet Intern Med 2002; 16: 123–132.
- 25.↑
Laflamme DP. Development and validation of a body condition score system for cats: a clinical tool. Feline Pract 1997; 25 (5–6): 13–18.
- 26.↑
Sukhija PS, Palmquist DL. Rapid method for determination of fatty acid content and composition of feedstuffs and feces. J Agric Food Chem 1988; 36: 1202–1206.
- 27.
Flachs P, Mohamed-Ali V, Horakova O, et al. Polyunsaturated fatty acids of marine origin induce adiponectin in mice fed a high-fat diet. Diabetologia 2006; 49: 394–397.
- 28.
Neschen S, Morino K, Rossbacher JC, et al. Fish oil regulates adiponectin secretion by a peroxisome proliferator-activated receptor-gamma-dependent mechanism in mice. Diabetes 2006; 55: 924–928.
- 29.
Rossi AS, Lombardo YB, Lacorte JM, et al. Dietary fish oil positively regulates plasma leptin and adiponectin levels in sucrose-fed, insulin-resistant rats. Am J Physiol Regul Integr Comp Physiol 2005; 289: R486–R494.
- 30.
Itoh M, Suganami T, Satoh N, et al. Increased adiponectin secretion by highly purified eicosapentaenoic acid in rodent models of obesity and human obese subjects. Arterioscler Thromb Vasc Biol 2007; 27: 1918–1925.
- 31.
Higuchi T, Shirai N, Saito M, et al. Levels of plasma insulin, leptin and adiponectin, and activities of key enzymes in carbohydrate metabolism in skeletal muscle and liver in fasted ICR mice fed dietary n-3 polyunsaturated fatty acids. J Nutr Biochem 2008; 19: 577–586.
- 32.
Duda MK, O'Shea KM, Lei B, et al. Dietary supplementation with omega-3 PUFA increases adiponectin and attenuates ventricular remodeling and dysfunction with pressure overload. Cardiovasc Res 2007; 76: 303–310.
- 33.↑
Tilg H, Moschen AR. Adipocytokines: mediators linking adipose tissue, inflammation and immunity. Nat Rev Immunol 2006; 6: 772–783.
- 34.
Miller C, Bartges J, Cornelius L, et al. Tumor necrosis factor-alpha levels in adipose tissue of lean and obese cats. J Nutr 1998; 128 (suppl 12): 2751S–2752S.
- 35.
Hoenig M, McGoldrick JB, de Beer M, et al. Activity and tissue-specific expression of lipases and tumor-necrosis factor alpha in lean and obese cats. Domest Anim Endocrinol 2006; 30: 333–344.
- 36.↑
Bruun JM, Lihn AS, Verdich C, et al. Regulation of adiponectin by adipose tissue-derived cytokines: in vivo and in vitro investigations in humans. Am J Physiol Endocrinol Metab 2003; 285: E527–E533.
- 37.
Todoric J, Loffler M, Huber J, et al. Adipose tissue inflammation induced by high-fat diet in obese diabetic mice is prevented by n-3 polyunsaturated fatty acids. Diabetologia 2006; 49: 2109–2119.
- 38.
Suganami T, Nishida J, Ogawa Y. A paracrine loop between adipocytes and macrophages aggravates inflammatory changes: role of free fatty acids and tumor necrosis factor alpha. Arterioscler Thromb Vasc Biol 2005; 25: 2062–2068.
- 39.↑
Jaso-Friedmann L, Leary JH III, Praveen K, et al. The effects of obesity and fatty acids on the feline immune system. Vet Immunol Immunopathol 2008; 122: 146–152.
- 40.↑
Bouskila M, Pajvani UB, Scherer PE. Adiponectin: a relevant player in PPARgamma-agonist-mediated improvements in hepatic insulin sensitivity? Int J Obes (Lond) 2005; 29 (suppl 1): S17–S23.
- 41.↑
Hoenig M, Caffall Z, Ferguson DC. Triiodothyronine differentially regulates key metabolic factors in lean and obese cats. Domest Anim Endocrinol 2008; 34: 229–237.
- 42.↑
Chambrier C, Bastard JP, Rieusset J, et al. Eicosapentaenoic acid induces mRNA expression of peroxisome proliferator-activated receptor gamma. Obes Res 2002; 10: 518–525.
- 43.
Yamamoto K, Itoh T, Abe D, et al. Identification of putative metabolites of docosahexaenoic acid as potent PPAR-gamma agonists and antidiabetic agents. Bioorg Med Chem Lett 2005; 15: 517–522.
- 44.
Hynes GR, Heshka J, Chadee K, et al. Effects of dietary fat type and energy restriction on adipose tissue fatty acid composition and leptin production in rats. J Lipid Res 2003; 44: 893–901.
- 45.
Peyron-Caso E, Taverna M, Guerre-Millo M, et al. Dietary (n-3) polyunsaturated fatty acids up-regulate plasma leptin in insulin-resistant rats. J Nutr 2002; 132: 2235–2240.
- 46.
Wang H, Storlien LH, Huang XF. Effects of dietary fat types on body fatness, leptin, and ARC leptin receptor, NPY, and AgRP mRNA expression. Am J Physiol Endocrinol Metab 2002; 282: E1352–E1359.
- 47.
Hun CS, Hasegawa K, Kawabata T, et al. Increased uncoupling protein2 mRNA in white adipose tissue, and decrease in leptin, visceral fat, blood glucose, and cholesterol in KK-Ay mice fed with eicosapentaenoic and docosahexaenoic acids in addition to linolenic acid. Biochem Biophys Res Commun 1999; 259: 85–90.
- 48.↑
Hotamisligil GS. Mechanisms of TNF-alpha-induced insulin resistance. Exp Clin Endocrinol Diabetes 1999; 107: 119–125.
- 49.
Schenck PA. Canine hyperlipidemia: causes and nutritional management. In: Pibot P, Biourge V, Elliott D, eds. Encyclopedia of canine clinical nutrition. Aimargues, France: Aniwa SAS, 2006; 222–245.
- 50.
LeBlanc CJ, Bauer JE, Hosgood G, et al. Effect of dietary fish oil and vitamin E supplementation on hematologic and serum biochemical analytes and oxidative status in young dogs. Vet Ther 2005; 6: 325–340.
- 51.↑
Lombardo YB, Chicco A, D'Alessandro ME, et al. Dietary fish oil normalize dyslipidemia and glucose intolerance with unchanged insulin levels in rats fed a high sucrose diet. Biochim Biophys Acta 1996; 1299: 175–182.
- 52.↑
Feingold KR, Grunfeld C. Role of cytokines in inducing hyperlipidemia. Diabetes 1992; 41 (suppl 2): 97–101.
- 53.
Plantinga EA, Beynen AC. The influence of dietary fish oil vs. sunflower oil on the fatty acid composition of plasma cholesterylesters in healthy, adult cats. J Anim Physiol Anim Nutr (Berl) 2003; 87: 373–379.
- 54.↑
Rivers JP, Sinclair AJ, Craqford MA. Inability of the cat to de-saturate essential fatty acids. Nature 1975; 258: 171–173.
- 55.↑
Nishizawa H, Shimomura I, Kishida K, et al. Androgens decrease plasma adiponectin, an insulin-sensitizing adipocyte-derived protein. Diabetes 2002; 51: 2734–2741.
- 56.↑
Plaisance EP, Grandjean PW, Judd RL, et al. The influence of sex, body composition, and nonesterified fatty acids on serum adipokine concentrations. Metabolism 2009; 58: 1557–1563.
- 57.↑
Carrascosa JM, Ros M, Andres A, et al. Changes in the neuroendocrine control of energy homeostasis by adiposity signals during aging. Exp Gerontol 2009; 44: 20–25.
