Influence of age and sex on plasma lipid and lipoprotein concentrations and associated enzyme activities in cats

Sex specific differences in hepatic and plasma lipid profiles in healthy cats pre and post spaying and neutering: relationship with feline hepatic lipidosis

BACKGROUND

A link between lipid metabolism and disease has been recognized in cats. Since hepatic lipidosis is a frequent disorder in cats, the aim of the current study was to evaluate liver and plasma lipid dimorphism in healthy cats and the effects of gonadectomy on lipid profiling. From six female and six male cats plasma and liver lipid profiles before and after spaying/neutering were assessed and compared to five cats (three neutered male and two spayed female) diagnosed with hepatic lipidosis.

RESULTS

Intact female cats had a significantly lower level of plasma triacylglycerides (TAG) and a higher liver level of the long chain polyunsaturated fatty acid arachidonic acid (AA) compared to their neutered state. Both male and female cats with lipidosis had a higher liver, but not plasma TAG level and an increased level of plasma and liver sphingomyelin compared to the healthy cats.

CONCLUSION

Although lipid dimorphism in healthy cats resembles that of other species, intact female cats show differences in metabolic configuration that could predispose them to develop hepatic lipidosis. The increased sphingomyelin levels in cats with lipidosis could suggest a potential role in the pathogenesis of hepatic lipidosis in cats.

Metabolic Profiling Reveals Effects of Age, Sexual Development and Neutering in Plasma of Young Male Cats

Neutering is a significant risk factor for obesity in cats. The mechanisms that promote neuter-associated weight gain are not well understood but following neutering, acute changes in energy expenditure and energy consumption have been observed. Metabolic profiling (GC-MS and UHPLC-MS-MS) was used in a longitudinal study to identify changes associated with age, sexual development and neutering in male cats fed a nutritionally-complete dry diet to maintain an ideal body condition score. At eight time points, between 19 and 52 weeks of age, fasted blood samples were taken from kittens neutered at either 19 weeks of age (Early Neuter (EN), n = 8) or at 31 weeks of age (Conventional Neuter (CN), n = 7). Univariate and multivariate analyses were used to compare plasma metabolites (n = 370) from EN and CN cats. Age was the primary driver of variance in the plasma metabolome, including a developmental change independent of neuter group between 19 and 21 weeks in lysolipids and fatty acid amides. Changes associated with sexual development and its subsequent loss were also observed, with differences at some time points observed between EN and CN cats for 45 metabolites (FDR p<0.05). Pathway Enrichment Analysis also identified significant effects in 20 pathways, dominated by amino acid, sterol and fatty acid metabolism. Most changes were interpretable within the context of male sexual development, and changed following neutering in the CN group. Felinine metabolism in CN cats was the most significantly altered pathway, increasing during sexual development and decreasing acutely following neutering. Felinine is a testosterone-regulated, felid-specific glutathione derivative secreted in urine. Alterations in tryptophan, histidine and tocopherol metabolism observed in peripubertal cats may be to support physiological functions of glutathione following diversion of S-amino acids for urinary felinine secretion.

Lipoprotein cholesterol and triglyceride concentrations associated with dog body condition score; effect of recommended fasting duration on sample concentrations in Japanese private clinics

The objectives of this study were to survey clinics’ guidance about recommended fasting duration (FD) prior to lipoprotein analysis, and to characterize lipoprotein cholesterol and triglyceride concentrations in obese and overweight dogs categorized on the basis of the 5-point body condition score (BCS) scale. A dataset was created from lipoprotein analysis medical records of 1,538 dogs from 75 breeds in 354 clinics from 2012 to 2013. A phone survey was conducted to obtain the clinics’ FD. Two-level linear mixed-effects models were applied to the data. Over 50% of the clinics said they recommended fasting for 12 hr or more. Dogs in clinics with FD 12 hr or more had lower chylomicron triglyceride concentrations than those in clinics with FD less than 8 hr (P=0.05). Mean (± SEM) BCS at sampling was 3.7 ± 0.02. Obese and overweight dogs had higher very low density lipoprotein (VLDL) and high density lipoprotein (HDL) cholesterol and triglyceride concentrations than ideal dogs (P<0.05), but no such difference was found for low density lipoprotein cholesterol and triglyceride concentrations (P≥0.07). Across all BCS, as dog age rose from 0 to 8 years old, HDL cholesterol concentrations decreased by 13.5 mg/dl, whereas VLDL triglyceride concentrations increased by 81.7 mg/dl (P<0.05). In conclusion, FD of 8 hr or less may affect lipoprotein lipid concentrations. Obese and overweight dogs were characterized as having high VLDL and HDL cholesterol and triglyceride concentrations.

Translational value of animal models of obesity-Focus on dogs and cats

A prolonged imbalance between a relative increase in energy intake over a decrease in energy expenditure results in the development of obesity; extended periods of a positive energy balance eventually lead to the accumulation of abnormally high amounts of fat in adipose tissue but also in other organs. Obesity is considered a clinical state of impaired general heath in which the excessive increase in adipose tissue mass may be associated with metabolic disorders such as type 2 diabetes mellitus, hyperlipidemia, hypertension and cardiovascular diseases. This review discusses briefly the use of animal models for the study of obesity and its comorbidities. Generally, most studies are performed with rodents, such as diet induced obesity and genetic models. Here, we focus specifically on two different species, namely dogs and cats. Obese dogs and cats show many features of human obesity. Interestingly, however, dogs and cats differ from each other in certain aspects because even though obese dogs may become insulin resistant, this does not result in the development of diabetes mellitus. In fact, diabetes in dogs is typically not associated with obesity because dogs present a type 1 diabetes-like syndrome. On the other hand, obese cats often develop diabetes mellitus which shares many features with human type 2 diabetes; feline and human diabetes are similar in respect to their pathophysiology, underlying risk factors and treatment strategies. Our review discusses genetic and endocrine factors in obesity, discusses obesity induced changes in lipid metabolism and includes some recent findings on the role of gut microbiota in obesity. Compared to research in rodent models, the array of available techniques and tools is unfortunately still rather limited in dogs and cats. Hence, even though physiological and pathophysiological phenomena are well described in dogs and cats, the underlying mechanisms are often not known and studies investigating causality specifically are scarce.

A role for synaptic plasticity in the adolescent development of executive function

Adolescent brain maturation is characterized by the emergence of executive function mediated by the prefrontal cortex, e.g., goal planning, inhibition of impulsive behavior and set shifting. Synaptic pruning of excitatory contacts is the signature morphologic event of late brain maturation during adolescence. Mounting evidence suggests that glutamate receptor-mediated synaptic plasticity, in particular long-term depression (LTD), is important for elimination of synaptic contacts in brain development. This review examines the possibility (1) that LTD mechanisms are enhanced in the prefrontal cortex during adolescence due to ongoing synaptic pruning in this late developing cortex and (2) that enhanced synaptic plasticity in the prefrontal cortex represents a key molecular substrate underlying the critical period for maturation of executive function. Molecular sites of interaction between environmental factors, such as alcohol and stress, and glutamate receptor mediated plasticity are considered. The accentuated negative impact of these factors during adolescence may be due in part to interference with LTD mechanisms that refine prefrontal cortical circuitry and when disrupted derail normal maturation of executive function. Diminished prefrontal cortical control over risk-taking behavior could further exacerbate negative outcomes associated with these behaviors, as for example addiction and depression. Greater insight into the neurobiology of the adolescent brain is needed to fully understand the molecular basis for heightened vulnerability during adolescence to the injurious effects of substance abuse and stress.

Effects of increases in dietary fat intake on plasma lipid and lipoprotein cholesterol concentrations and associated enzyme activities in cats

OBJECTIVE

To determine the effects of increases in dietary intake of polyunsaturated and saturated fatty acids on plasma lipid and lipoprotein concentrations and activity of associated enzymes in healthy domestic cats.

ANIMALS

16 healthy adult sexually intact female cats.

PROCEDURES

A baseline diet (40% energy from fat) and 4 test diets, with increased amounts of fat (51% and 66% energy from fat) from the addition of polyunsaturated and saturated fatty acids, were fed for 6 weeks each. Plasma cholesterol, triglyceride, and lipoprotein cholesterol concentrations, along with activities of lipoprotein lipase, hepatic lipase, and lecithin-cholesterol acyl transferase, were measured at the end of each feeding period.

RESULTS

Diet, amount of fat, or ratio of polyunsaturated to saturated fatty acids had no effect on plasma concentrations of cholesterol, triglycerides, and very-low-density or high-density lipoproteins or the activity of lecithin-cholesterol acyl transferase. Low-density lipoprotein concentrations were significantly lower in cats fed a high-fat diet containing polyunsaturated fatty acids. Lipoprotein concentration and hepatic lipase activity were significantly higher in cats fed the fat-supplemented diets, and this was unrelated to whether diets were enriched with polyunsaturated or saturated fatty acids.

CONCLUSIONS AND CLINICAL RELEVANCE

Diets containing up to 66% of energy from fat were tolerated well by healthy cats and did not affect plasma lipid concentrations. Therefore, high-fat diets probably will not contribute to hypercholesterolemia or hypertriglyceridemia in cats.

Fish oil supplementation maintains adequate plasma arachidonate in cats, but similar amounts of vegetable oils lead to dietary arachidonate deficiency from nutrient dilution

Because fatty acid (FA) metabolism of cats is unique, effects of dietary fish and vegetable oil supplementation on plasma lipids, lipoproteins, lecithin/cholesterol acyl transferase activities, and plasma phospholipid and esterified cholesterol (EC) FAs were investigated. Cats were fed a commercial diet supplemented with 8 g oil/100 g diet for 4 weeks using either high-oleic-acid sunflower oil (diet H), Menhaden fish oil (diet M), or safflower oil (diet S). When supplemented, diet M contained sufficient arachidonate (AA), but diets H and S were deficient. We hypothesized that diet M would modify plasma lipid metabolism, increase FA long-chain n-3 (LCn-3) FA content but not deplete AA levels. Also, diet S would show linoleic acid (LA) accumulation without conversion to AA, and both vegetable oil supplements would dilute dietary AA content when fed to meet cats' energy needs. Plasma samples on weeks 0, 2, and 4 showed no alterations in total cholesterol or nonesterified FA concentrations. Unesterified cholesterol decreased and EC increased in all groups, whereas lecithin/cholesterol acyl transferase activities were unchanged. Diet M showed significant triacylglycerol lowering and decreased pre-β-lipoprotein cholesterol. Plasma phospholipid FA profiles revealed significant enrichment of 18:1n-9 with diet H, LA and 20:2n-6 with diet S, and FA LCn-3FA with diet M. Depletion of AA was observed with diets H and S but not with diet M. Diet M EC FA profiles revealed specificities for LA and 20:5n-3 but not 22:5n-3 or 22:6n-3. Oversupplementation of some commercial diets with vegetable oils causes AA depletion in young cats due to dietary dilution. Findings are consistent with the current recommendations for at least 0.2 g AA/kg diet and that fish oil supplements provide both preformed LCn-3 polyunsaturated FA and AA.

Comparison of serum lipid compositions, lipid peroxide, alpha-tocopherol and lipoproteins in captive marine mammals (bottlenose dolphins, spotted seals and West Indian manatees) and terrestrial mammals

Concentrations of serum lipid components, lipid peroxide (LPO) and alpha-tocopherol and electrophoretic patterns of lipoproteins in serum samples obtained from captive marine mammals and terrestrial mammals were compared. Serum concentrations of total cholesterol, free fatty acid, and phospholipid in fish-eating animals were significantly higher than those in manatees and cows. Serum LPO and alpha-tocopherol concentrations in the fish-eating animals were also significantly higher than those in manatees, cows and dogs. Different patterns of densitometric scans of low density lipoprotein (LDL) and a significantly lower percentage of LDL were demonstrated in the dolphins compared with the seals, cow and dogs. The concentration of LPO was significantly correlated with triglyceride and phospholipid concentrations in serum from the dolphins. These results suggest that triglyceride and phospholipid are susceptible to oxidative reaction in fish-eating animals. Evaluation of serum lipids, LPO and alpha-tocopherol concentrations is needed for nutritional husbandry for fish-eating animals.

Triglyceride response following an oral fat tolerance test in Burmese cats, other pedigree cats and domestic crossbred cats

Primary lipid disorders causing fasting triglyceridaemia have been documented infrequently in Burmese cats. Due to the known increased risk of diabetes mellitus and sporadic reports of lipid aqueous in this breed, the aim of this study was to determine whether healthy Burmese cats displayed a more pronounced pre- or post-prandial triglyceridaemia compared to other cats. Serum triglyceride (TG) concentrations were determined at baseline and variably at 2, 4 and 6h after ingestion of a high-fat meal (ie, an oral fat tolerance test) in a representative sample of Burmese and non-Burmese cats. The median 4 and 6h serum TG concentrations were significantly higher in Burmese cats (4h - 2.8mmol/l; 6h - 8.2mmol/l) than in other pedigree and domestic crossbred cats (4h - 1.5mmol/l; 6h - 1.0mmol/l). The non-Burmese group had post-prandial TG concentrations ranging from 0.6 to 3.9mmol/l. Seven Burmese cats had post-prandial TG concentrations between 6.6 and 19.0mmol/l, five had concentrations between 4.2 and 4.7mmol/l, while the remaining 15 had post-prandial concentrations between 0.5 and 2.8mmol/l. None of these Burmese cats had fasting triglyceridaemia. Most Burmese cats with a 4 h TG > 6.0 mmol/l had elevated fasting very low density lipoprotein (VLDL) concentrations. This study demonstrates that a proportion of Burmese cats in Australia have delayed TG clearance compared to other cats. The potential repercussions of this observation with reference to lipid aqueous, pancreatitis and diabetes mellitus in Burmese cats are discussed.

Dietary fatty acids alter plasma lipids and lipoprotein distributions in dogs during gestation, lactation, and the perinatal period

Alterations of plasma lipids and lipoproteins occur during mammalian pregnancy and reproduction. This study investigated the effects of dietary fatty acids on plasma lipid and lipoprotein alterations during canine gestation, lactation, and the neonatal period. Four diets containing varying amounts of alpha-linolenic acid relative to marine-based (n-3) long-chain fatty acids were studied and fed to dogs from the time of estrus, and throughout pregnancy and lactation. In addition, puppies born to these dams suckled and were weaned using the same diets their mothers had been fed. Plasma cholesterol (total, free, and esterified fractions) and triglycerides were determined at selected time points and lipoprotein fractions were characterized in both mothers and offspring. During gestation, plasma total cholesterol concentrations were depressed early on, then increased in the later stages independently of diet. Both beta- and alpha2-migrating lipoproteins also increased during these times. Lactation was also characterized by lower lipid and lipoprotein amounts compared with the nonpregnant state. In puppies, total plasma and beta-lipoprotein cholesterol were elevated at 4 and 10 d of age. Diet effects included cholesterol, triglyceride, and lipoprotein lowering with increased amounts of marine (n-3) fatty acids in all life stages investigated. The increase in beta-lipoprotein cholesterol in puppies during wk 1 of life is consistent with an earlier report of increased canine apoprotein B,E receptor activities in immature dogs compared with undetectable activities in mature animals in which the HDL fractions become even more predominant in this species.

Effects of obesity on lipid profiles in neutered male and female cats

OBJECTIVE

To examine whether obese cats, compared with lean cats, have alterations in lipoprotein metabolism that might lead to a decrease in glucose metabolism and insulin secretion.

ANIMALS

10 lean and 10 obese adults cats (5 neutered males and 5 neutered females each).

PROCEDURE

Intravenous glucose tolerance tests with measurements of serum glucose, insulin, and nonesterified fatty acid (NEFA) concentrations were performed. Lipoprotein fractions were examined in serum by isopycnic density gradient ultracentrifugation.

RESULTS

Obese cats had insulin resistance. Plasma triglyceride and cholesterol concentrations were significantly increased in obese cats, compared with lean cats. Very low density lipoprotein (VLDL) concentrations were increased in obese cats, compared with lean cats; however, the composition of various fractions remained unchanged between obese and lean cats, indicating greater synthesis and catabolism of VLDL in obese cats. Serum high density lipoprotein (HDL) cholesterol concentrations were increased in obese cats, compared with lean cats. Serum NEFA concentrations were only significantly different between obese and lean cats when separated by sex; obese male cats had higher baseline serum NEFA concentrations and greater NEFA suppression in response to insulin, compared with lean male cats.

CONCLUSIONS AND CLINICAL RELEVANCE

Lipid metabolism changes in obese cats, compared with lean cats. The increase in VLDL turnover in obese cats might contribute to insulin resistance of glucose metabolism, whereas the increase in serum HDL cholesterol concentration might reflect a protective effect against atherosclerosis in obese cats.