Evidence of obesity-induced inflammatory changes in client-owned cats

Background and Aim

Insulin resistance and type 2 diabetes mellitus are common health issues in obese (OB) cats. In humans, obesity leads to alterations in adipokine and proinflammatory cytokine secretion, causing persistent inflammation. The inflammatory impact of obesity in cats remains unproven. This study investigated associations between obesity and inflammatory and metabolic changes in three groups of client-owned Brazilian domestic shorthair cats: naturally lean, overweight (OW), and OB.

Materials and Methods

Cats from the Veterinary Hospital of Professor Sylvio Barbosa e Cardoso (FAVET/UECE) were clinically evaluated. Blood samples were collected for hematological and biochemical profile measurements, and part of the serum was used for measuring adipokine and inflammatory cytokines using sandwich enzyme-linked immunosorbent assay.

Results

In both the OW and OB groups, serum cholesterol and insulin concentrations increased, while triglyceride concentrations were notably elevated in the OB group. In the OW and OB groups, serum adiponectin, tumor necrosis factor-α, and interleukin-1β levels were elevated, and leptin levels were significantly higher in the OB group.

Conclusion

This study is the first in Brazil to reveal increased serum levels of inflammatory markers in OW and OB client-owned felines. OW cats exhibited higher proinflammatory marker levels, implying obesity-induced inflammation.

Pathophysiology of Prediabetes, Diabetes, and Diabetic Remission in Cats

Diabetes mellitus (DM) has a heterogenous cause, and the exact pathogenesis differs between patients. Most diabetic cats have a cause similar to human type 2 DM but, in some, DM is associated with underlying conditions, such as hypersomatotropism, hyperadrenocorticism, or administration of diabetogenic drugs. Predisposing factors for feline DM include obesity, reduced physical activity, male sex, and increasing age. Gluco(lipo)toxicity and genetic predisposition also likely play roles in pathogenesis. Prediabetes cannot be accurately diagnosed in cats at the current time. Diabetic cats can enter remission, but relapses are common, as these cats might have ongoing, abnormal glucose homeostasis.

Feline comorbidities: Pathophysiology and management of the obese diabetic cat

PRACTICAL RELEVANCE

Up to 40% of the domestic feline population is overweight or obese. Obesity in cats leads to insulin resistance via multiple mechanisms, with each excess kilogram of body weight resulting in a 30% decline in insulin sensitivity. Obese, insulin-resistant cats with concurrent beta-cell dysfunction are at risk of progression to overt diabetes mellitus.

APPROACH TO MANAGEMENT

In cats that develop diabetes, appropriate treatment includes dietary modification to achieve ideal body condition (for reduction of insulin resistance), and optimization of diet composition and insulin therapy (for glycemic control and the chance of diabetic remission). Initially, as many obese cats that become diabetic will have lost a significant amount of weight and muscle mass by the time of presentation, some degree of diabetic control should be attempted with insulin before initiating any caloric restriction. Once body weight has stabilized, if further weight loss is needed, a diet with ≤ 12-15% carbohydrate metabolizable energy (ME) and >40% protein ME should be fed at 80% of resting energy requirement for ideal weight, with the goal of 0.5-1% weight loss per week. Other approaches may be necessary in some cats that need either substantial caloric restriction or do not find low carbohydrate diets palatable. Long-acting insulins are preferred as initial choices and oral antidiabetic drugs can be used in combination with diet if owners are unable or unwilling to give insulin injections. Glucagon-like peptide-1 (GLP-1) agonists have recently been investigated for use as adjunctive treatment in diabetic cats and sodium-glucose cotransporter-2 (SGLT2) inhibitors are currently being evaluated in clinical trials.

EVIDENCE BASE

The information in this review is drawn from: epidemiological studies on obesity prevalence; prospective longitudinal studies of development of insulin resistance with obesity; randomized controlled studies; and expert opinion regarding the effect of diet on diabetes management in cats.

Associations among echocardiography, cardiac biomarkers, insulin metabolism, morphology, and inflammation in cats with asymptomatic hypertrophic cardiomyopathy

Background

Insulin, insulin‐like growth factor‐1 (IGF‐1), and inflammation possibly are involved in cats with asymptomatic hypertrophic cardiomyopathy (aHCM).

Objectives

To evaluate echocardiography, morphology, cardiac and inflammatory markers, insulin and IGF‐1 in cats with aHCM.

Animals

Fifty‐one client‐owned cats with aHCM.

Methods

Observational descriptive study. Variables (body weight [BW], body condition score [BCS], echocardiography, and serum concentrations of N‐terminal pro‐B‐type natriuretic peptide [NT‐proBNP], ultra‐sensitive troponin‐I [c‐TnI], serum amyloid A [SAA], insulin, glucose and IGF‐1) were evaluated for significant increases above echocardiography cutoff values and laboratory reference ranges, associations and effect of left atrial (LA) remodeling and generalized hypertrophy.

Results

Cats with aHCM had BCS ≥6/9 (P = .01) and insulin (P < .001), NT‐proBNP (P = .001) and cTn‐I (P < .001) above laboratory reference ranges. Associations were present between NT‐proBNP and maximum end‐diastolic interventricular septum thickness (IVSd; ρ = .32; P = .05), maximum end‐diastolic left ventricular free wall thickness;(ρ = .41; P = .01), LA/Aorta (ρ = .52; P = .001) and LA diameter (LA‐max; ρ = .32; P = .05); c‐TnI and LA/Aorta (ρ = .49; P = .003) and LA‐max (ρ = .28; P = .05); and SAA and number of IVSd regions ≥6 mm thickness (ρ = .28; P = .05). Body weight and BCS were associated with IGF‐1 (r = 0.44; P = .001), and insulin (ρ = .33; P = .02), glucose (ρ = .29; P = .04) and IGF‐1 (ρ = .32; P = .02), respectively. Concentrations of NT‐proBNP (P = .02) and c‐TnI (P = .01), and SAA (P = .02), were higher in cats with LA remodeling, and generalized hypertrophy, respectively.

Conclusions and clinical importance

Results suggest potential implications of insulin, IGF‐1, and inflammation in cats with aHCM, but it remains to be confirmed whether these findings represent a physiological process or a part of the pathogenesis and development of disease.

Association of circulating adipokine concentrations with indices of adiposity and sex in healthy, adult client owned cats

Background

Both diabetes mellitus (DM) and obesity are common in cats. The adipokines leptin, adiponectin, resistin and omentin are thought to have important roles in human obesity and glucose homeostasis; however, their functions in the pathophysiology of feline diabetes mellitus and obesity are poorly understood. We determined whether sexual dimorphism exists for circulating concentrations of these adipokines, whether they are associated with adiposity, and whether they correlate with basic indices of insulin sensitivity in cats. Healthy, client-owned male and female cats that were either ideal weight or obese were recruited into the study. Fasting blood glucose, fructosamine, cholesterol, triglycerides, insulin and plasma concentrations of adipokines were evaluated.

Results

Obese cats had greater serum concentrations of glucose and triglycerides than ideal weight cats, but fructosamine and cholesterol concentrations did not differ between groups. Body weight and body mass index were greater in male than female cats, but circulating metabolite cocentrations were similar between sexes of both the ideal weight and obese groups. Plasma concentrations of insulin and leptin were greater in obese than ideal weight cats, with reciprocal reduction in adiponectin concentrations in obese cats; there were no sex differences in these hormones. Interestingly, plasma omentin concentrations were greater in male than female cats but with no differences between obese and ideal weight states.

Conclusion

Together our findings suggest that rather than gender, body weight and adiposity are more important determinants of circulating concentrations of the adipokines leptin and adiponectin. On the contrary, the adipokine omentin is not affected by body weight or adiposity but instead exhibits sexual dimorphism in cats.

Risk of obesity in the neutered cat

Surgical neutering is one of the most common procedures performed on pets in the USA among other countries. There are known effects of neutering on the physiology and behavior of the cat that predispose to obesity, which is the most significant sequela from a nutritional perspective. Increased food intake is the most likely factor influencing weight gain in the neutered cat. Proactively addressing these changes with nutritional management strategies can help prevent weight gain and associated negative consequences.

Expression profiling feline peripheral blood monocytes identifies a transcriptional signature associated with type two diabetes mellitus

Diabetes mellitus is a common disease of cats and is similar to type 2 diabetes (T2D) in humans, especially with respect to the role of obesity-induced insulin resistance, glucose toxicity, decreased number of pancreatic β-cells and pancreatic amyloid deposition. Cats have thus been proposed as a valuable translational model of T2D. In humans, inflammation associated with adipose tissue is believed to be central to T2D development, and peripheral blood monocytes (PBM) are important in the inflammatory cascade which leads to insulin resistance and β-cell failure. PBM may thus provide a useful window to study the pathogenesis of diabetes mellitus in cats, however feline monocytes are poorly characterised. In this study, we used the Affymetrix Feline 1.0ST array to profile peripheral blood monocytes from 3 domestic cats with T2D and 3 cats with normal glucose tolerance. Feline monocytes were enriched for genes expressed in human monocytes, and, despite heterogeneous gene expression, we identified a T2D-associated expression signature associated with cell cycle perturbations, DNA repair and the unfolded protein response, oxidative phosphorylation and inflammatory responses. Our data provide novel insights into the feline monocyte transcriptome, and support the hypothesis that inflammatory monocytes contribute to T2D pathogenesis in cats as well as in humans.

Metabolic Effects of Obesity and Its Interaction with Endocrine Diseases

Obesity in pet dogs and cats is a significant problem in developed countries, and seems to be increasing in prevalence. Excess body fat has adverse metabolic consequences, including insulin resistance, altered adipokine secretion, changes in metabolic rate, abnormal lipid metabolism, and fat accumulation in visceral organs. Obese cats are predisposed to endocrine and metabolic disorders such as diabetes and hepatic lipidosis. A connection likely also exists between obesity and diabetes mellitus in dogs. No system has been developed to identify obese pets at greatest risk for development of obesity-associated metabolic diseases, and further study in this area is needed.

Circulating concentrations of glucagon-like peptide 1, glucose-dependent insulinotropic peptide, peptide YY, and insulin in client-owned lean, overweight, and diabetic cats

Our objectives were to measure plasma concentrations of glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), and peptide YY (PYY) in client-owned newly diagnosed diabetic cats and nondiabetic lean or overweight cats and to determine whether circulating concentrations of these hormones differed between study groups and if they increased postprandially as seen in other species. A total of 31 cats were recruited and placed into 1 of 3 study groups: lean (body condition score 4-5 on a scale of 1-9; n = 10), overweight (body condition score 6-8; n = 11), or diabetic (n = 10). Diabetics were newly diagnosed and had not had prior insulin therapy. Preprandial (fasting) and postprandial (60 min after meal) plasma hormone and glucose concentrations were measured at baseline and 2 and 4 wk. All cats were exclusively fed a commercially available high-protein and low-carbohydrate diet commonly prescribed to feline diabetic patients for 2 wk before the 2-wk assessment and continued through the 4-wk assessment. Results showed that plasma concentrations of GLP-1, GIP, PYY, and insulin increased in general after a meal in all study groups. Plasma PYY concentrations did not differ (P > 0.10) between study groups. Diabetics had greater plasma concentrations of GLP-1 and GIP compared with the other study groups at baseline (P < 0.05), and greater preprandial and postprandial GLP-1 concentrations than lean cats at 2 and 4 wk (P < 0.05). Preprandial plasma GIP concentrations were greater in diabetics than obese and lean (P < 0.05) cats at week 4. Postprandial plasma GIP concentrations in diabetics were greater than lean (P < 0.05) at week 2 and obese and lean cats (P < 0.05) at week 4. Together, our findings suggest that diabetic status is an important determinant of circulating concentrations of GLP-1 and GIP, but not PYY, in cats. The role of GLP-1, GIP, and PYY in the pathophysiology of feline obesity and diabetes remains to be determined.

Animal Models of Diabetic Retinopathy

Diabetic retinopathy (DR) is one of today's main causes of blindness in numerous developed countries worldwide. The underlying pathogenesis of DR is complex and not well understood, thus impeding development of specific, effective treatment modalities. Consequently, the use of animal models of DR is of critical importance for investigating the pathogenesis of and treatment for DR. While rats and mice are the most commonly used animal models of DR, the zebrafish now appears to be a promising model. Nonhuman primates and humans have similar eye structures, and both can develop spontaneous diabetes mellitus (DM). Although various traditionally used animal models of DR undergo a number of pathological changes similar to those of human DR, several human variations, e.g. retinal neovascularization, cannot yet be fully mimicked in any existing animal model of DM. Since both the animal models and the methods chosen for inducing DR have great influence on experimental results, a clear understanding of available animal models is vital for planning an experimental design. In this review, we summarize the mechanisms, methodologies and pros and cons of the most commonly used animal models of DR.

Management of obesity in cats

Obesity is a common nutritional disorder in cats, especially when they are neutered and middle-aged. Obesity predisposes cats to several metabolic and clinical disorders, including insulin resistance, diabetes mellitus, lameness, and skin disease. Prevention and treatment of obesity is therefore of great importance in veterinary practice. Correct assessment of body composition is important for recognizing early states of obesity and for monitoring success of weight-loss programs. Various methods for assessing body composition have been proposed, of which a 9-point body-condition score has been validated in cats, and is possibly the most simple to use in the clinic; however, for extremely obese individuals, it is less useful. When calculating the appropriate daily caloric intake for a weight-loss plan, the aim is to maintain a safe weight-loss rate, increasing the chance of preserving lean body mass and decreasing the risk of developing hepatic lipidosis, while also producing a sufficient weight-loss rate to keep owners motivated. A weight-loss rate of 0.5%–2% per week is recommended, which for a cat that needs to lose 3 kg body weight results in an anticipated time for reaching the target weight of 24–60 weeks. There are several purpose-made weight-loss diets available. The optimal composition of a weight-loss diet for cats is unknown, but most of the available products have lower caloric density, an increased nutrient:energy ratio, and higher protein and fiber content. Regular follow-up visits allow the caloric intake to be adjusted based on progress, and possibly increase the chance of success. This review discusses the risk factors for and consequences of obesity, and gives directions for formulating a weight-loss plan, including daily caloric intake, choice of diet, and common problems based on the current literature. This review further provides a nutritional comparison of the current composition of selected commercial veterinary-specific weight-loss diets.