Oral glucose leads to a differential response in glucose, insulin, and GLP-1 in lean versus obese cats

Laparoscopic vertical sleeve gastrectomy in felines: A cadaveric feasibility study and experimental case series in two cats

OBJECTIVE

To evaluate the feasibility of laparoscopic vertical sleeve gastrectomy (LVSG) in feline cadavers using endoscopic stapling equipment and report clinical outcomes in two live feline subjects.

STUDY DESIGN

Cadaveric study and experimental case series.

ANIMALS

Ten feline cadavers; two feline subjects.

METHODS

LVSG technique was refined on feline cadavers and included retraction of the liver, dissection of the stomach, assessment of proper location for gastrectomy via stapling, and leak testing. Appropriateness of gastrectomy, gastrectomy %, surgical times and complications were recorded. The procedure was performed on two live feline subjects, and they were followed for 4 months to report surgical complications.

RESULTS

LVSG was completed in 9/10 cadavers and both live patients. Stenosis at the incisura was recorded in 2/9 cadavers. No obvious leaks were seen in the 8 cadavers that were tested or either live patient. The mean surgical time for all cadaver procedures and live patients was 110.4 and 115 minutes, respectively. Mean weight of resected cadaver stomach was 10 g and the mean % of the total stomach weight resected was 27.6%. No intra- or postoperative surgical complications occurred in the live subjects.

CONCLUSION

LVSG technique appears feasible and safe for use in live patients.

CLINICAL RELEVANCE

This LVSG technique may be safely used for partial gastric resection in cats. Further studies are necessary to determine if it is effective at reversing the effects of obesity and diabetes in this population.

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.

The daytime feeding frequency affects appetite-regulating hormones, amino acids, physical activity, and respiratory quotient, but not energy expenditure, in adult cats fed regimens for 21 days

The effects of feeding frequency on postprandial response of circulating appetite-regulating hormones, insulin, glucose and amino acids, and on physical activity, energy expenditure, and respiratory quotient were studied in healthy adult cats. Two experiments were designed as a 2 x 3 replicated incomplete Latin square design. Eight cats, with an average body weight (BW) of 4.34 kg ± 0.04 and body condition score (BCS) of 5.4 ± 1.4 (9 point scale), were fed isocaloric amounts of a commercial adult maintenance canned cat food either once (0800 h) or four times daily (0800 h, 1130 h, 1500 h, 1830 h). Study 1 consisted of three 21-d periods. On day 14, two fasted and 11 postprandial blood samples were collected over 24 hours to measure plasma concentrations of ghrelin, GLP-1, GIP, leptin, PYY, insulin and amino acids, and whole blood glucose. Physical activity was monitored from day 15 to 21 of each period. In Study 2 indirect calorimetry was performed on the last day of each period. Body weight was measured weekly and feed intake recorded daily in both experiments. No effect of feeding regimen on BW was detected. Cats eating four times daily had lesser plasma concentrations of GIP and GLP-1 (P<0.05) and tended to have lesser plasma PYY concentrations (P<0.1). Plasma leptin and whole blood glucose concentrations did not differ between regimens (P>0.1). Cats fed once daily had a greater postprandial plasma amino acid response, and greater plasma ghrelin and insulin concentrations (P<0.05). Physical activity was greater in cats fed four times (P<0.05), though energy expenditure was similar between treatments at fasting and in postprandial phases. Finally, cats eating one meal had a lower fasting respiratory quotient (P<0.05). Overall, these data indicate that feeding once a day may be a beneficial feeding management strategy for indoor cats to promote satiation and lean body mass.

The effect of diet, adiposity, and weight loss on the secretion of incretin hormones in cats

Degree of adiposity and dietary macronutrient composition affect incretin hormone secretion in humans and mice, but little is known about their effect in cats. In this study, 7 overweight cats were fed a maintenance diet (MD) for at least 2 wk followed by a reduced calorie diet (RCD), which was lower in fat and higher in carbohydrates and fiber. Cats were fed ad libitum initially, and then, food was restricted to achieve 1%-2% loss of body weight weekly (11 wk). When lean, cats were fed MD for 2 wk. A standardized meal test (SMT) using a third diet was performed after at least 7 d on each diet, before and after weight loss (four SMT's total). Glucose, insulin, glucagon-like peptide-1 (GLP-1), and glucose-dependent insulinotropic peptide (GIP) concentrations were measured immediately before and over 6 h after feeding the SMT. Area under the curve (AUC) was compared for GLP-1, GIP, and insulin concentrations using 2-way analysis of variance. Leaner cats had increased GIP_AUC compared to obese cats (P = 0.025). There was a trend toward increased GIP_AUC on RCD compared to the MD (P = 0.085). There was a moderate negative correlation between body fat percentage and GLP-1_AUC (r = -0.45; P = 0.05). There was no effect of diet on GLP-1_AUC. In conclusion, degree of adiposity and dietary macronutrient content could be important in determining GIP responses not only acutely but also on a long-term basis. Further investigation of GIP responses in cats should take both diet and degree of adiposity into account.

Cats and Carbohydrates: The Carnivore Fantasy?

The domestic cat’s wild ancestors are obligate carnivores that consume prey containing only minimal amounts of carbohydrates. Evolutionary events adapted the cat’s metabolism and physiology to this diet strictly composed of animal tissues and led to unique digestive and metabolic peculiarities of carbohydrate metabolism. The domestic cat still closely resembles its wild ancestor. Although the carnivore connection of domestic cats is well recognised, little is known about the precise nutrient profile to which the digestive physiology and metabolism of the cat have adapted throughout evolution. Moreover, studies show that domestic cats balance macronutrient intake by selecting low-carbohydrate foods. The fact that cats evolved consuming low-carbohydrate prey has led to speculations that high-carbohydrate diets could be detrimental for a cat’s health. More specifically, it has been suggested that excess carbohydrates could lead to feline obesity and diabetes mellitus. Additionally, the chances for remission of diabetes mellitus are higher in cats that consume a low-carbohydrate diet. This literature review will summarise current carbohydrate knowledge pertaining to digestion, absorption and metabolism of carbohydrates, food selection and macronutrient balancing in healthy, obese and diabetic cats, as well as the role of carbohydrates in prevention and treatment of obesity and diabetes mellitus.

Gluconeogenesis during starvation and refeeding phase is affected by previous dietary carbohydrates levels and a glucose stimuli during early life in Siberian sturgeon (Acipenser baerii)

Gluconeogenesis responses was assessed during a short starvation period and subsequent refeeding in Siberian sturgeon (Acipenser baerii) previously fed different dietary carbohydrates levels and experienced to a glucose stimuli during early life. The sturgeon larvae were previously fed either a high glucose diet (G) or a low glucose diet (F) from the first feeding to yolk absorption (8 to 12 d post-hatching [dph]). Each group of fish was sub-divided into 2 treatments at 13 dph and was fed either a high-carbohydrate diet (H) or a low carbohydrate diet (L) until 20 wk. In the current study, the fish in 4 groups (GL, FL, GH and FH) were experienced to starvation for 21 d following by re-feeding of their corresponding diets for 21 d. Fish were sampled at postprandial 6 and 24 h before starvation (P6h and P24h), starvation 7, 14 and 21 d (S7, S14 and S21) and 1, 7, 14 and 21 d during refeeding (R1, R7, R14 and R21). Plasma samples during refeeding were taken at P6h at each time point. Glycaemia levels, liver and muscle glycogen contents, activities and mRNA levels of hepatic gluconeogenic enzymes were examined. We found that both dietary carbohydrate levels and early glucose stimuli significantly affected the metabolic responses to starvation and refeeding in Siberian sturgeon (P < 0.05). During prolonged starvation, Siberian sturgeon firstly mobilized the liver glycogen and then improved gluconeogenesis when the dietary carbohydrates were abundant, whereas preserved the liver glycogen stores at a stable level and more effectively promoted gluconeogenesis when the dietary carbohydrates are absent to maintain glucose homoeostasis. During refeeding, as most teleostean, Siberian sturgeon failed controlling the activities and mRNA levels of phosphoenolpyruvate carboxykinase cytosolic forms (PEPCK-C), fructose-1,6-bisphosphatase (FBPase), but particularly controlled phosphoenolpyruvate carboxykinase mitochondrial forms (PEPCK-M) activities and mRNA expression of glucose-6-phosphatase (G6Pase, except in GL group). Siberian sturgeon has a full compensatory ability on growth, but this ability would be obstructed by early glucose stimuli when refeeding the low carbohydrate diet after S21.

Anaesthesia and changes in parameters that reflect glucose metabolism in pigs – a pilot study

Pigs are commonly used in diabetes research due to their many physiological similarities to humans. They are especially useful in imaging procedures because of their large size. However, to achieve imaging procedures the pig must lie completely still, and thus needs to be anaesthetized. Most anaesthetic drugs used in laboratory animals affect carbohydrate metabolism by the inhibition of insulin release. The aim of this pilot study was primarily to develop an anaesthetic protocol for pigs that did not have an effect on blood glucose levels throughout the 3 h of anaesthesia; and secondly, to evaluate the most promising protocol in combination with an oral glucose tolerance test (OGTT). Two anaesthetic protocols were used in four growing pigs. Intravenous propofol infusion caused hyperglycaemia in three out of four pigs within 5–10 min after induction and was therefore excluded. Intravenous infusion with tiletamine, zolazepam and butorphanol (TZB) for 3 h did not affect blood glucose levels. The pigs underwent OGTT twice, once without anaesthesia and once with TZB induction after glucose intake. Anaesthesia during OGTT resulted in a lower area under the curve (AUC) of glucose ( P < 0.05), higher AUC of glucagon ( P < 0.05) and an insulin response less than 10% of that during OGTT without anaesthesia. In conclusion, long-term infusion anaesthesia with TZB does not affect glucose homeostasis in pigs. However, the protocol is not effective when combined with OGTT, as glucose, insulin and glucagon levels are affected.

Dosing obese cats based on body weight spuriously affects some measures of glucose tolerance

The primary objective was to investigate whether dosing glucose by body weight results in spurious effects on measures of glucose tolerance in obese cats because volume of distribution does not increase linearly with body weight. Healthy research cats (n = 16; 6 castrated males, 10 spayed females) were used. A retrospective study was performed using glucose concentration data from glucose tolerance and insulin sensitivity tests before and after cats were fed ad libitum for 9 to 12 mo to promote weight gain. The higher dose of glucose (0.5 vs 0.3 g/kg body weight) in the glucose tolerance tests increased 2-min glucose concentrations (P < 0.001), and there was a positive correlation between 2-min and 2-h glucose (r = 0.65, P = 0.006). Two-min (P = 0.016 and 0.019, respectively), and 2-h (P = 0.057 and 0.003, respectively) glucose concentrations, and glucose half-life (T1/2; P = 0.034 and <0.001 respectively) were positively associated with body weight and body condition score. Glucose dose should be decreased by 0.05 g for every kg above ideal body weight. Alternatively, for every unit of body condition score above 5 on a 9-point scale, observed 2-h glucose concentration should be adjusted down by 0.1 mmol/L. Dosing glucose based on body weight spuriously increases glucose concentrations at 2 h in obese cats and could lead to cats being incorrectly classified as having impaired glucose tolerance. This has important implications for clinical studies assessing the effect of interventions on glucose tolerance when lean and obese cats are compared.

New Approaches to Feline Diabetes Mellitus: Glucagon-like peptide-1 analogs

CLINICAL RELEVANCE

Incretin-based therapies are revolutionizing the field of human diabetes mellitus (DM) by replacing insulin therapy with safer and more convenient long-acting drugs.

MECHANISM OF ACTION

Incretin hormones (glucagon-like peptide-1 [GLP-1] and glucose-dependent insulinotropic peptide [GIP]) are secreted from the intestinal tract in response to the presence of food in the intestinal lumen. GLP-1 delays gastric emptying and increases satiety. In the pancreas, GLP-1 augments insulin secretion and suppresses glucagon secretion during hyperglycemia in a glucose-dependent manner. It also protects beta cells from oxidative and toxic injury and promotes expansion of beta cell mass.

ADVANTAGES

Clinical data have revealed that GLP-1 analog drugs are as effective as insulin in improving glycemic control while reducing body weight in people suffering from type 2 DM. Furthermore, the incidence of hypoglycemia is low with these drugs because of their glucose-dependent mechanism of action. Another significant advantage of these drugs is their duration of action. While insulin injections are administered at least once daily, long-acting GLP-1 analogs have been developed as once-a-week injections and could potentially be administered even less frequently than that in diabetic cats.

OUTLINE

This article reviews the physiology of incretin hormones, and the pharmacology and use of GLP-1 analogs, with emphasis on recent research in cats. Further therapies that are based on incretin hormones, such as DPP-4 inhibitors, are also briefly discussed, as are some other treatment modalities that are currently under investigation.

What's in a Name? Classification of Diabetes Mellitus in Veterinary Medicine and Why It Matters

Diabetes Mellitus (DM) is a syndrome caused by various etiologies. The clinical manifestations of DM are not indicative of the cause of the disease, but might be indicative of the stage and severity of the disease process. Accurately diagnosing and classifying diabetic dogs and cats by the underlying disease process is essential for current and future studies on early detection, prevention, and treatment of underlying disease. Here, we review the current etiology-based classification of DM and definitions of DM types in human medicine and discuss key points on the pathogenesis of each DM type and prediabetes. We then review current evidence for application of this etiology-based classification scheme in dogs and cats. In dogs, we emphasize the lack of consistent evidence for autoimmune DM (Type 1) and the possible importance of other DM types such as DM associated with exocrine pancreatic disease. While most dogs are first examined because of DM in an insulin-dependent state, early and accurate diagnosis of the underlying disease process could change the long-term outcome and allow some degree of insulin independence. In cats, we review the appropriateness of using the umbrella term of Type 2 DM and differentiating it from DM secondary to other endocrine disease like hypersomatotropism. This differentiation could have crucial implications on treatment and prognosis. We also discuss the challenges in defining and diagnosing prediabetes in cats.

Effect of Acarbose, Sitagliptin and combination therapy on blood glucose, insulin, and incretin hormone concentrations in experimentally induced postprandial hyperglycemia of healthy cats

Acarbose (AC) and Sitagliptin (STGP) are oral hypoglycemic agents currently used either alone or in conjunction with human diabetic (Type 2) patients. AC has been used with diabetic cats, but not STGP thus far. Therefore, the objective of this study was to determine the potential use of AC or STGP alone and in combination for diabetic cats, by observing their effect on short-term post-prandial serum glucose, insulin, and incretin hormone (active glucagon-like peptide-1 (GLP-1) and total glucose dependent insulinotropic polypeptide (GIP)) concentrations in five healthy cats, following ingestion of a meal with maltose. All treatments tended (p<0.10; 5-7.5% reduction) to reduce postprandial glucose area under the curve (AUC), with an accompanying significant reduction (p<0.05, 35-45%) in postprandial insulin AUC as compared to no treatment. Meanwhile, a significant increase (p<0.05) in postprandial active GLP-1 AUC was observed with STGP (100% higher) and combined treatment (130% greater), as compared to either AC or no treatment. Lastly, a significant reduction (p<0.05) in postprandial total GIP AUC was observed with STGP (21% reduction) and combined treatment (7% reduction) as compared to control. Overall, AC, STGP, or combined treatment can significantly induce positive post-prandial changes to insulin and incretin hormone levels of healthy cats. Increasing active GLP-1 and reducing postprandial hyperglycemia appear to be the principal mechanisms of combined treatment. Considering the different, but complementary mechanisms of action by which AC and STGP induce lower glucose and insulin levels, combination therapy with both these agents offers great potential for treating diabetic cats in the future.

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.

Effect of the Glucagon-like Peptide-1 Analogue Exenatide Extended Release in Cats with Newly Diagnosed Diabetes Mellitus

Background

Exenatide extended release (ER) is a glucagon‐like peptide‐1 analogue that increases insulin secretion, inhibits glucagon secretion and induces satiation in humans with type 2 diabetes mellitus. The use of exenatide ER is safe and stimulates insulin secretion in healthy cats.

Objectives

The objective of this study is to assess the safety of exenatide ER and its effect on body weight, remission and metabolic control in newly diagnosed diabetic cats receiving insulin and a low‐carbohydrate diet.

Animals

Thirty client‐owned cats.

Methods

Prospective placebo‐controlled clinical trial. Cats were treated with exenatide ER or 0.9% saline, administered SC, once weekly. Both groups received insulin glargine and a low‐carbohydrate diet. Exenatide ER was administered for 16 weeks, or in cats that achieved remission it was given for 4 weeks after discontinuing insulin treatment. Nonparametric tests were used for statistical analysis.

Results

Cats in the exenatide ER and placebo groups had transient adverse signs including decreased appetite (60% vs. 20%, respectively, P = .06) and vomiting (53% vs. 40%, respectively, P = .715). Body weight increased significantly in the placebo group (P = .002), but not in cats receiving exenatide ER. Cats on exenatide ER achieved remission or good metabolic control in 40% or 89%, respectively, whereas in control cats percentages were 20% or 58% (P = .427 and P = .178, respectively).

Conclusion and clinical importance

Exenatide ER is safe in diabetic cats and does not result in weight gain. Our pilot study suggests that, should there be an additional clinically relevant beneficial effect of exenatide ER in insulin‐treated cats on rate of remission and good metabolic control, it would likely approximate 20% and 30%, respectively.

Pharmacokinetics and pharmacodynamics of the glucagon-like peptide-1 analog liraglutide in healthy cats

Glucagon-like peptide-1 (GLP-1) is an intestinal hormone that induces glucose-dependent stimulation of insulin secretion while suppressing glucagon secretion. Glucagon-like peptide-1 also increases beta cell mass and satiation while decelerating gastric emptying. Liraglutide is a fatty-acid derivative of GLP-1 with a protracted pharmacokinetic profile that is used in people for treatment of type II diabetes mellitus and obesity. The aim of this study was to determine the pharmacokinetics and pharmacodynamics of liraglutide in healthy cats. Hyperglycemic clamps were performed on days 0 (HGC) and 14 (LgHGC) in 7 healthy cats. Liraglutide was administered subcutaneously (0.6 mg/cat) once daily on days 8 through 14. Compared with the HGC (mean ± standard deviation; 455.5 ± 115.8 ng/L), insulin concentrations during LgHGC were increased (760.8 ± 350.7 ng/L; P = 0.0022), glucagon concentrations decreased (0.66 ± 0.4 pmol/L during HGC vs 0.5 ± 0.4 pmol/L during LgHGC; P = 0.0089), and there was a trend toward an increased total glucose infused (median [range] = 1.61 (1.11-2.54) g/kg and 2.25 (1.64-3.10) g/kg, respectively; P = 0.087). Appetite reduction and decreased body weight (9% ± 3%; P = 0.006) were observed in all cats. Liraglutide has similar effects and pharmacokinetics profile in cats to those reported in people. With a half-life of approximately 12 h, once daily dosing might be feasible; however, significant effects on appetite and weight loss may necessitate dosage or dosing frequency reductions. Further investigation of liraglutide in diabetic cats and overweight cats is warranted.

Effects of the glucagon-like peptide-1 (GLP-1) analogues exenatide, exenatide extended-release, and of the dipeptidylpeptidase-4 (DPP-4) inhibitor sitagliptin on glucose metabolism in healthy cats

Incretin analogues and inhibitors of the breakdown of endogenous incretins are antidiabetic drugs that increase β-cell proliferation and glucose-stimulated insulin secretion in rodents and humans. Objectives were to test whether exenatide, exenatide extended-release, and sitagliptin can be safely used in cats, to identify the most effective drug, and to test the effects of prolonged exenatide extended-release administration. Three cats each were given exenatide (0.2-2 µg/kg, q12h, subcutaneously, 5 days), exenatide extended-release (40-400 µg/kg, subcutaneously, once), and sitagliptin (1-10 mg/kg, q24h, orally, 5 days). Before and after treatment, glucose, insulin and glucagon areas under the curve (AUC) were assessed by meal response tests (MRT). Exenatide increased insulin AUC by 224%, 258%, 331% and 93%, exenatide extended-release by 127%, 169%, 178% and 95%, and sitagliptin by 32%, 69%, 62%, and 43%, respectively. The tested drugs are safe to use in cats and enhance insulin secretion. Incretin-based therapy may be beneficial in cats with diabetes mellitus.

Effects of sitagliptin on plasma incretin concentrations after glucose administration through an esophagostomy tube or feeding in healthy cats

We investigated the effect of sitagliptin, a dipeptidyl peptidase 4 inhibitor, on plasma incretin concentrations after glucose administration through an esophagostomy tube or feeding in healthy cats. Six cats were used for the glucose administration experiment and 5 cats were used for the feeding experiment. Glucose administration through an esophagostomy tube increased plasma glucagon-like peptide 1 (GLP-1) concentrations by 6-fold, whereas plasma glucose-dependent insulinotropic polypeptide (GIP) concentrations did not change. Feeding increased both plasma GLP-1 concentrations by 1.5-fold and GIP concentrations by 4.6-fold. Sitagliptin was administered through an esophagostomy tube (25 and 50 mg per cat) in the glucose administration experiment and orally (25 mg per cat) in the feeding experiment. Sitagliptin treatment potentiated the GLP-1 response to glucose by 1.5-fold (P < 0.05). In addition, postprandial plasma GLP-1 concentration was higher by 2-fold when sitagliptin was administered (P < 0.05). In contrast, administration of sitagliptin did not affect plasma GIP concentrations after glucose administration or feeding. Sitagliptin enhanced insulin secretion following glucose administration by 1.5-fold (P < 0.05); however, it did not influence the plasma glucose concentration. Furthermore, sitagliptin had no effect on the postprandial plasma glucose and insulin concentrations. In conclusion, this study provides no evidence that sitagliptin is beneficial for management of feline diabetes mellitus.

Effects of dietary macronutrient composition and feeding frequency on fasting and postprandial hormone response in domestic cats

The objective was to evaluate the effects of dietary macronutrients and feeding frequency on blood glucose, insulin, total ghrelin and leptin. A total of twelve adult lean neutered male cats were used in three tests, all cross-over studies composed of a 15 d adaptation and blood sampling on day 16. In trial 1, differences between two- and four-meal feeding were tested. On day 16, blood samples were collected every 2 h for 24 h. In trial 2, macronutrient boluses were tested. Instead of the control diet, the morning meal on day 16 was replaced with an isoenergetic bolus of carbohydrate (maltodextrin), protein (chicken meat), fat or water. Fasted and ten postprandial blood samples were collected. In trial 3, diets high in fat (HF), protein (HP), carbohydrate (HC) or a control diet were tested. On day 16, fasted and ten postprandial blood samples were collected. Data were analysed to identify baseline and AUC changes. Cats fed four meals daily had greater (P = 0·03) leptin incremental AUC_0–24 h compared with cats fed twice daily. The carbohydrate bolus increased glucose (P < 0·001) and insulin (P < 0·001) incremental AUC_0–6 h and tended to increase (P = 0·09) leptin net AUC_0–6 h. Cats fed the control and HC diets had greater (P = 0·03) glucose incremental AUC compared with the HF and HP conditions. Circulating hormone data were highly variable and indicated changes due to dietary macronutrients and feeding frequency, but further study is needed to identify impacts on appetite and contributing mechanisms.

Distribution of K and L cells in the feline intestinal tract

Glucose-dependent insulinotropic peptide (GIP), glucagon-like peptide (GLP)-1 and GLP-2 are hormones secreted from specialized K cells (GIP) and L cells (GLP-1, GLP-2) in the intestinal mucosa. These hormones play major roles in health and disease by modulating insulin secretion, satiety, and multiple intestinal functions. The aim of this study was to describe the distribution of K cells and L cells in the intestines of healthy cats. Samples of duodenum, mid-jejunum, ileum, cecum, and colon were collected from 5 cats that were euthanized for reasons unrelated to this study and had no gross or histologic evidence of gastrointestinal disease. Samples stained with rabbit-anti-porcine GIP, mouse-anti-(all mammals) GLP-1, or rabbit-anti-(all mammals) GLP-2 antibodies were used to determine the number of cells in 15 randomly selected 400× microscopic fields. In contrast to other mammals (eg, dogs) in which K cells are not present in the ileum and aborally, GIP-expressing cells are abundant throughout the intestines in cats (>6/high-power field in the ileum). Cells expressing GLP-1 or GLP-2 were most abundant in the ileum (>9/high-power field) as in other mammals, but, although GLP-1-expressing cells were abundant throughout the intestines, GLP-2-expressing cells were rarely found in the duodenum. In conclusion, the distribution of GIP-secreting K cells in cats is different from the distribution of K cells that is described in other mammals. The difference in distribution of GLP-2- and GLP-1-expressing cells suggests that more than 1 distinct population of L cells is present in cats.

New incretin hormonal therapies in humans relevant to diabetic cats

Incretins (gastric inhibitory polypeptide and glucagon-like peptide 1 [GLP-1]) are hormones released from the gastrointestinal tract during food intake that potentiate insulin secretion. Native GLP-1 is quickly degraded by the enzyme dipeptidylpeptidase-4 (DPP-4), which has led to the development of GLP-1 agonists with resistance to degradation and to inhibitors of DPP-4 activity as therapeutic agents in humans with type 2 diabetes. In healthy cats, GLP-1 agonists and DPP-4 inhibitors have produced a substantial increase in insulin secretion. Although results of clinical studies are not yet available, incretin-based therapy promises to become an important new research area in feline diabetes.

Exendin-4 improves resistance to Listeria monocytogenes infection in diabetic db/db mice

The incidence of diabetes mellitus is increasing among companion animals. This disease has similar characteristics in both humans and animals. Diabetes is frequently identified as an independent risk factor for infections associated with increased mortality. In the present study, homozygous diabetic (db/db) mice were infected with Listeria (L.) monocytogenes and then treated with the anti-diabetic drug exendin-4, a glucagon-like peptide 1 analogue. In aged db/db mice, decreased CD11b(+) macrophage populations with higher lipid content and lower phagocytic activity were observed. Exendin-4 lowered high lipid levels and enhanced phagocytosis in macrophages from db/db mice infected with L. monocytogenes. Exendin-4 also ameliorated obesity and hyperglycemia, and improved ex vivo bacteria clearance by macrophages in the animals. Liver histology examined during L. monocytogenes infection indicated that abscess formation was much milder in exendin-4-treated db/db mice than in the control animals. Moreover, mechanistic studies demonstrated that expression of ATP binding cassette transporter 1, a sterol transporter, was higher in macrophages isolated from the exendin-4-treated db/db mice. Overall, our results suggest that exendin-4 decreases the risk of infection in diabetic animals by modifying the interaction between intracellular lipids and phagocytic macrophages.

The cat as a model for human obesity and diabetes

Obesity is the most common nutritional disorder of cats and is a risk factor for diabetes. Similar to developments in obese people, obese cats show peripheral tissue insulin resistance and may demonstrate glucose intolerance when challenged with pharmacological amounts of glucose. However, they compensate well for the insulin resistance and do not show elevated glucose concentrations when monitored during their regular daily routine, including postprandial periods. This is possible because obese cats in the fasted and postprandial state are able to maintain hepatic insulin sensitivity and decrease endogenous glucose production, which allows them to maintain normoglycemia. Also dissimilar to what is seen in many obese humans, cats do not develop atherosclerosis and clinical hypertension. The time course for progression to overt diabetes of obese cats is unknown. One might speculate that diabetes develops when the liver finally becomes insulin resistant and/or insulin secretion becomes too low to overcome increased glucose production. In addition, amyloid, demonstrated to be deposited in islet of chronically obese cats, may contribute to a reduction in insulin secretion by reducing functional β-cell mass.

Glucose metabolism in fish: a review

Teleost fishes represent a highly diverse group consisting of more than 20,000 species living across all aquatic environments. This group has significant economical, societal and environmental impacts, yet research efforts have concentrated primarily on salmonid and cyprinid species. This review examines carbohydrate/glucose metabolism and its regulation in these model species including the role of hormones and diet. Over the past decade, molecular tools have been used to address some of the downstream components of these processes and these are incorporated to better understand the roles played by carbohydrates and their regulatory paths. Glucose metabolism remains a contentious area as many fish species are traditionally considered glucose intolerant and, therefore, one might expect that the use and storage of glucose would be considered of minor importance. However, the actual picture is not so clear since the apparent intolerance of fish to carbohydrates is not evident in herbivorous and omnivorous species and even in carnivorous species, glucose is important for specific tissues and/or for specific activities. Thus, our aim is to up-date carbohydrate metabolism in fish, placing it to the context of these new experimental tools and its relationship to dietary intake. Finally, we suggest that new research directions ultimately will lead to a better understanding of these processes.

Effects of weight loss in obese cats on biochemical analytes related to inflammation and glucose homeostasis

The aim of the current study was to measure circulating metabolic and inflammation-related biochemical analytes in obese cats before and after weight loss. Thirty-seven overweight neutered cats were studied, median body weight 6.85 kg (range, 4.70 to 10.30 kg), representing a range of ages and both sexes. An individualized weight-loss program was devised for each cat and monitored until completion. Body fat mass was determined by dual-energy x-ray absorptiometry, whereas plasma concentrations of acute-phase proteins (APPs; eg, haptoglobin and serum amyloid A), hormones (eg, insulin, IGF-1, and adiponectin), and enzymes (eg, butyrylcholinesterase and paraoxonase type 1 [PON-1]) associated with inflammation and metabolic compounds (eg, glucose) were also measured. No significant changes were found in APPs after weight loss (P > 0.3), but significant increases in plasma adiponectin (P = 0.021) and IGF-1 (P = 0.036) were seen, whereas insulin (P < 0.001) and homeostasis model assessment (P = 0.005) decreased significantly. Plasma concentrations before weight loss of PON-1 (P = 0.004), adiponectin (P = 0.02), and IGF-1 (P = 0.048) were less in cats that failed to complete weight loss than cats that were successful, whereas glucose concentration was greater. Finally, multivariable linear regression analysis showed that lean tissue loss during weight management was associated with percentage weight loss (greater weight loss, greater lean tissue loss; R = 0.71, P < 0.001) and plasma adiponectin concentration before weight loss (lesser adiponectin, more lean tissue loss; R = -0.52, P = 0.023). In conclusion, various metabolic abnormalities occur in feline obesity, and these can be linked to outcomes of weight-loss programs. The changes that occur with weight loss suggest an improved metabolic status.

The GLP-1 mimetic exenatide potentiates insulin secretion in healthy cats

The glucagon-like peptide-1 mimetic exenatide has a glucose-dependent insulinotropic effect, and it is effective in controlling blood glucose (BG) with minimal side effects in people with type 2 diabetes. Exenatide also delays gastric emptying, increases satiety, and improves β-cell function. We studied the effect of exenatide on insulin secretion during euglycemia and hyperglycemia in cats. Nine young, healthy, neutered, purpose-bred cats were used in a randomized, cross-over design. BG concentrations during an oral glucose tolerance test were determined in these cats previously. Two isoglycemic glucose clamps (mimicking the BG concentration during the oral glucose tolerance test) were performed in each cat on separate days, one without prior treatment (IGC) and the second with exenatide (1 μg/kg) injected subcutaneously 2 h before (ExIGC). BG, insulin, and exenatide concentrations were measured, and glucose infusion rates were recorded and compared in paired tests between the two experiments. After exenatide injection, insulin serum concentrations increased significantly (2.4-fold; range 1.0- to 9.2-fold; P = 0.004) within 15 min. This was followed by a mild decrease in BG concentration and a return of insulin concentration to baseline despite a continuous increase in serum exenatide concentrations. Insulin area under the curve (AUC) during ExIGC was significantly higher than insulin AUC during IGC (AUC ratio, 2.0 ± 0.4; P = 0.03). Total glucose infused was not significantly different between IGC and ExIGC. Exenatide was detectable in plasma at 15 min after injection. The mean exenatide concentration peaked at 45 min and then returned to baseline by 75 min. Exenatide was still detectable in the serum of three of five cats 8 h after injection. No adverse reactions to exenatide were observed. In conclusion, exenatide affects insulin secretion in cats in a glucose-dependent manner, similar to its effect in other species. Although this effect was not accompanied by a greater ability to dispose of an intravenous glucose infusion, other potentially beneficial effects of exenatide on pancreatic β cells, mainly increasing their proliferation and survival, should be investigated in cats.