Feline Leptin: Immunogenic and Biological Activities of the Recombinant Protein, and Its Measurement by ELISA

Measures of insulin sensitivity, leptin, and adiponectin concentrations in cats in diabetic remission compared to healthy control cats

Objectives

Firstly, to compare differences in insulin, adiponectin, leptin, and measures of insulin sensitivity between diabetic cats in remission and healthy control cats, and determine whether these are predictors of diabetic relapse. Secondly, to determine if these hormones are associated with serum metabolites known to differ between groups. Thirdly, if any of the hormonal or identified metabolites are associated with measures of insulin sensitivity.

Animals

Twenty cats in diabetic remission for a median of 101 days, and 21 healthy matched control cats.

Methods

A casual blood glucose measured on admission to the clinic. Following a 24 h fast, a fasted blood glucose was measured, and blood sample taken for hormone (i.e., insulin, leptin, and adiponectin) and untargeted metabolomic (GC-MS and LC-MS) analysis. A simplified IVGGT (1 g glucose/kg) was performed 3 h later. Cats were monitored for diabetes relapse for at least 9 months (270 days).

Results

Cats in diabetic remission had significantly higher serum glucose and insulin concentrations, and decreased insulin sensitivity as indicated by an increase in HOMA and decrease in QUICKI and Bennett indices. Leptin was significantly increased, but there was no difference in adiponectin (or body condition score). Several significant correlations were found between insulin sensitivity indices, leptin, and serum metabolites identified as significantly different between remission and control cats. No metabolites were significantly correlated with adiponectin. No predictors of relapse were identified in this study.

Conclusion and clinical importance

Insulin resistance, an underlying factor in diabetic cats, persists in diabetic remission. Cats in remission should be managed to avoid further exacerbating insulin resistance.

Equal contributions of feline immunodeficiency virus and coinfections to morbidity in African lions

Feline immunodeficiency virus (FIV) is a pathogenic lentivirus related to human and simian immunodeficiency viruses that has been associated with AIDS-like pathologies in domestic and wild cats, as well as in hyenas. Despite known pathologies, progressive immunosuppression and ill health effects driven by these lentiviruses in association with other secondary infections remain understudied in free-ranging species. Here, the role of coinfections by gastrointestinal parasites and tick-borne hemoparasites for FIV disease progression was explored in 195 free-ranging African lions (Panthera leo) living in Kruger National Park (KNP), South Africa. Using statistical methodology, we evaluated the effects of FIV on a range of health indicators to explore how direct and indirect effects of FIV and associated coinfections align to determine lion health outcomes. Findings show direct negative effects of FIV on host immunity and nutritional status, and exacerbation of aggressive behaviors, conditions which may increase exposure/susceptibility to other secondary infections. When taken together, the contribution of coinfecting parasites to morbidity in lions is of similar magnitude as direct effects of FIV infection alone, suggesting that the particular coinfection assemblage may play a role in mediating disease progression within natural lion populations.

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Immunosuppression by FIV increases richness and abundance of secondary parasites.

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Infection by gastrointestinal parasites drives severe malnourishment in FIV hosts.

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Hemoparasite infection contributed to liver pathology and clinical wasting.

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Contributions of secondary infections to morbidity equal the direct effects of FIV.

Emerging Biomarkers and Targeted Therapies in Feline Mammary Carcinoma

Feline mammary carcinoma (FMC) is a common aggressive malignancy with a low survival rate that lacks viable therapeutic options beyond mastectomy. Recently, increasing efforts have been made to understand the molecular mechanisms underlying FMC development, using the knowledge gained from studies on human breast cancer to discover new diagnostic and prognostic biomarkers, thus reinforcing the utility of the cat as a cancer model. In this article, we review the current knowledge on FMC pathogenesis, biomarkers, and prognosis factors and offer new insights into novel therapeutic options for HER2-positive and triple-negative FMC subtypes.

A leptin sandwich ELISA kit unusable for domestic animals

An instance of hormone assay method flaw is reported. In this journal Chronobiology International, two papers appeared in which an ELISA method for human serum or plasma was utilized for blood serum of horse and sheep, respectively. From our testing, it is resulted that such method does not work at all for equine, sheep and other animal species. The use of commercial hormone assay kits for heterologous species always needs a careful validation procedure. First, the same hormone molecule by different species could not share enough homology to be regognized by and react with antibodies utilized in the method. Furthermore, even with a full overlap of the molecules, possible interferences by other components of the sample (matrix effect) have to be considered.

Serum and Tissue Expression Levels of Leptin and Leptin Receptor Are Putative Markers of Specific Feline Mammary Carcinoma Subtypes

Obesity is an established risk factor for breast cancer in post-menopausal women, being associated with elevated serum levels of leptin. Although overweight is a common condition in cat, the role of leptin and its receptor in feline mammary carcinoma remains unsettled. In this study, serum leptin and leptin receptor (ObR) levels were investigated in 58 cats with mammary carcinoma and compared with those of healthy animals, as were the expression levels of leptin and ObR in tumor tissues. The results showed that the Free Leptin Index is significantly decreased in cats with mammary carcinoma (p = 0.0006), particularly in those with luminal B and HER2-positive tumors, and that these animals also present significantly lower serum leptin levels (p < 0.0001 and p < 0.005, respectively). Interestingly, ulcerating tumors (p = 0.0005) and shorter disease-free survival (p = 0.0217) were associated to serum leptin levels above 4.17 pg/mL. In contrast, elevated serum ObR levels were found in all cats with mammary carcinoma (p < 0.0001), with levels above 16.89 ng/mL being associated with smaller tumors (p = 0.0118), estrogen receptor negative status (p = 0.0291) and increased serum levels of CTLA-4 (p = 0.0056), TNF-α (p = 0.0025), PD-1 (p = 0.0023), and PD-L1 (p = 0.0002). In tumor samples, leptin is overexpressed in luminal B and triple-negative carcinomas (p = 0.0046), whereas ObR is found to be overexpressed in luminal B tumors (p = 0.0425). Altogether, our results support the hypothesis that serum levels of leptin and ObR can be used as biomarkers of specific feline mammary carcinoma subtypes, and suggests the use of leptin antagonists as a therapeutic tool, reinforcing the utility of the cat as a cancer model.

Concentrations of leptin, adiponectin, and resistin in the serum of obese cats during weight loss

We monitored changes in serum leptin, adiponectin, and resistin concentrations in obese cats during weight loss. Six naturally developed obese cats were fed low-fat, high-fiber dry food during a 9-week experimental period. Serum leptin, adiponectin, and resistin concentrations were measured at week 0, 4, 8, and 9. Body weight became significantly lower week 4 onward than that at week 0 (P<0.05 or 0.01). At week 9, serum leptin concentrations were significantly lower than those at week 0 (P<0.05). Contrarily, serum adiponectin and resistin concentrations did not significantly differ within the 9 weeks. While serum leptin levels were strongly positively correlated with body weight (r=0.923, P<0.001), serum adiponectin levels were moderately negatively correlated with it (r=−0.529, P<0.01), with serum resistin having a no correlation with body weight. Serum leptin levels might be more closely related with pathogenesis of adiposity than serum adiponectin or resistin in cats.

Safety and efficacy assessment of a GLP-1 mimetic: insulin glargine combination for treatment of feline diabetes mellitus

A commonly used therapeutic strategy for type 2 diabetes mellitus (DM) in humans involves the use of synthetic incretin hormone-based therapies including exenatide, a glucagon-like pepetide-1 hormone agonist. Glucagon-like pepetide-1 agonists can be used alone or as an ancillary therapy with other agents, including insulin and oral antihyperglycemics. Little is known about the role of these therapies for DM in cats. Therefore, the primary objective of this study was to evaluate the safety and efficacy of short-acting exenatide combined with insulin, as compared to placebo and insulin for the treatment of DM in cats. Treatment with exenatide was well tolerated; only 2 cats developed side effects requiring dose reduction. Two cats (25%) went into diabetic remission while receiving exenatide and insulin, whereas remission was not reported during placebo treatment. The average change in the daily exogenous insulin dose was significant (β = -0.56 U/kg, 95% confidence interval, -0.96 to -0.15, P = 0.007), and the dose of insulin administered was lower during exenatide treatment. The average weight loss experienced on exenatide was significantly higher than on placebo (β = 0.65 kg, 95% confidence interval, 0.09-1.21, P = 0.02). There was no significant difference in any of the hormone concentrations evaluated for cats on exenatide vs placebo treatments. Overall, the treatment of diabetic cats with insulin and a fixed dose of exenatide was found to be safe. The weight loss and decreased exogenous insulin requirement experienced with exenatide treatment could be a significant benefit for overweight diabetic cats and warrants further evaluation.

BRIDGING GAPS BETWEEN ZOO AND WILDLIFE MEDICINE: ESTABLISHING REFERENCE INTERVALS FOR FREE-RANGING AFRICAN LIONS (PANTHERA LEO)

The International Species Information System has set forth an extensive database of reference intervals for zoologic species, allowing veterinarians and game park officials to distinguish normal health parameters from underlying disease processes in captive wildlife. However, several recent studies comparing reference values from captive and free-ranging animals have found significant variation between populations, necessitating the development of separate reference intervals in free-ranging wildlife to aid in the interpretation of health data. Thus, this study characterizes reference intervals for six biochemical analytes, eleven hematologic or immune parameters, and three hormones using samples from 219 free-ranging African lions ( Panthera leo ) captured in Kruger National Park, South Africa. Using the original sample population, exclusion criteria based on physical examination were applied to yield a final reference population of 52 clinically normal lions. Reference intervals were then generated via 90% confidence intervals on log-transformed data using parametric bootstrapping techniques. In addition to the generation of reference intervals, linear mixed-effect models and generalized linear mixed-effect models were used to model associations of each focal parameter with the following independent variables: age, sex, and body condition score. Age and sex were statistically significant drivers for changes in hepatic enzymes, renal values, hematologic parameters, and leptin, a hormone related to body fat stores. Body condition was positively correlated with changes in monocyte counts. Given the large variation in reference values taken from captive versus free-ranging lions, it is our hope that this study will serve as a baseline for future clinical evaluations and biomedical research targeting free-ranging African lions.

Molecular cloning of feline resistin and the expression of resistin, leptin and adiponectin in the adipose tissue of normal and obese cats

Resistin, one of the adipokines that has a cycteine-rich C-terminus, is considered to relate to the development of insulin resistance in rats. However, in cats, there is little knowledge regarding resistin. In this study, we cloned the feline resistin cDNA from adipose tissue by RT-PCR. The feline resistin clone contained an entire open reading frame encoding 107 amino acids that had 72.8%, 75.4%, 50.9% and 51.8% homology with bovine, human, mouse and rat homologues, respectively. In both subcutaneous and visceral adipose tissues, the transcription levels of feline resistin mRNA were significantly higher in obese cats than normal cats, and those of feline adiponectin mRNA were significantly lower in obese cats than normal cats. However, there was no difference in the expression of feline leptin between normal and obese cats. On the other hand, in both normal and obese cats, there were no significant differences in resistin, leptin and adiponectin mRNA levels between subcutaneous and visceral adipose tissues. In cats, the altered expression of resistin and adiponectin mRNA with obesity may contribute to the pathogenesis of insulin resistance and subsequent diabetes mellitus. In addition to feline adiponectin, the feline resistin cDNA clone obtained in this study will be useful for further investigation of the pathogenesis of obesity in cats.

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.

Relationships among changes of serum leptin concentration, leptin mRNA expression in white adipose tissue (WAT), and WAT fat-cell size in female Japanese black bears (Ursus thibetanus japonicus)

As a first step to study the relationship between fat accumulation and reproductive success in Japanese black bears ( Ursus thibetanus japonicus Schlegel, 1857) with the focus on leptin, we determined leptin cDNA sequences in the bears. Next, we studied the possibility of white adipose tissue (WAT) as a leptin secretion source by observing the changes of leptin mRNA expression in WAT by semiquantitative real-time reverse transcript – polymerase chain reaction, the index of WAT fat-cell size, and serum leptin concentration in pregnant bears. Then, based on our results, we discussed roles of leptin in those bears. The amino acid sequences of leptin from the bears were highly identical to that of other carnivores. The expression of leptin mRNA in WAT was detected from September to January, with a tendency to increase in late November and January; the relationship between changes in the index of WAT fat-cell size and those in serum leptin concentration was high (r = 0.55, P < 0.01), with an increase in both in mid-November. These results suggested that leptin was mainly secreted from WAT in bears and that serum leptin concentrations might reflect their nutritional condition. Moreover, leptin might serve as an indicator of their fat mass, which would affect their survival during hibernation and their reproductive success.

Inverse regulation of leptin mRNA expression by short- and long-chain fatty acids in cultured bovine adipocytes

Leptin is an adipose tissue-derived cytokine plays key roles in the regulation of food intake and energy expenditure. However, regulatory mechanisms of leptin gene expression are not fully elucidated in ruminants that utilize short-chain fatty acids (SCFA), known as volatile fatty acids, as principal energy sources. In this study, we determined effects of SCFA and long-chain fatty acids (LCFA) on leptin expression in bovine adipocytes. Bovine stromal vascular cells isolated from subcutaneous adipose tissue of Holstein cows were cultured to confluence and treated sequentially with dexamethasone and isobutylmethylxanthine for 2 days and insulin and troglitazone for 12 days to achieve full differentiation to adipocytes. The cells started to accumulate lipids 4 days after the onset of treatment, with increased mRNA expression of leptin, as well as aP2, adiponectin, and PPAR-gamma. Removal of fetal calf serum and reduction of glucose in the culture medium of differentiated adipocytes decreased leptin mRNA expression. Subsequent addition of acetate, butyrate, or propionate dose-dependently restored and rather increased leptin expression, while addition of LCFA suppressed it. The stimulatory effect of acetate was abolished by prior treatment of the cells with pertussis toxin and by addition of LCFA. Furthermore, cows fasted for 48h and fed thereafter, elaborate reduced and increased plasma leptin levels, respectively. Thus, these results suggest that plasma leptin levels in cows are inversely controlled at the transcription level by VFA and LCFA, and that the effects of SCFA possibly act through a G protein-coupled receptor for SCFA.

Gonadectomy and high dietary fat but not high dietary carbohydrate induce gains in body weight and fat of domestic cats

A high concentration of dietary carbohydrate is suggested to increase the risk of obesity and diabetes mellitus in domestic cats. To evaluate this, food intake, body weight, fat mass and circulating adiposity-related factors were determined in twenty-four sexually mature (9-12 months) cats assigned to four six-cat dietary groups balanced for body weight and sex. The effect of dietary fat in exchange for carbohydrate at 9, 25, 44 and 64 % of metabolisable energy (ME) in a purified diet of constant protein:ME ratio was studied 13 weeks before and 17 weeks after gonadectomy (GX). Body weight did not significantly change among the cats before GX except for an increase of 17 (sem 5) % in cats given the highest-fat diet. Following GX, all groups gained body weight, and body fat mass was positively correlated (r 0.50; P < 0.04) with dietary fat percentage. Post-GX weight gains were much greater for females (+39 (sem 5) %) than males (+10 (sem 4) %). Plasma ghrelin concentration negatively correlated (P < 0.02) with dietary fat percentage and, before GX, was greater (P < 0.05) in females than males. Plasma insulin concentration increased with weight gain induced by high dietary fat. Plasma glucose, TAG and leptin concentrations were not affected by dietary fat percentage, GX or weight gain. These data provide evidence that in cats, high dietary fat, but not carbohydrate, induces weight gain and a congruent increase in insulin, while GX increases sensitivity to weight gain induced by dietary fat.

Diurnal variations of serum leptin in dogs: effects of fasting and re-feeding

Leptin is a protein synthesized and secreted primarily by adipocytes, and plays a key role in the regulation of energy balance. We have reported that serum leptin is elevated in obese dogs. In the present study, we examined diurnal variations of serum leptin in the dog, with special references to feeding and fasting cycles. Four male beagles were accustomed to feed once a day at 10:00 h, and blood samples were taken every 3 h for 24-36 h. Serum leptin concentration showed clear diurnal variations, being lowest before food intake (2.3+/-0.5 ng/mL) at 09:00 h, and highest (10.5+/-2.4 ng/mL) at 18:00 h. Such diurnal variations disappeared when the dogs were fasted. Serum insulin also showed diurnal variation with higher levels at 12:00-15:00 h. When insulin or glucose was injected in the fasted dogs to mimic the post-prandial insulin rise, serum leptin concentration was significantly increased in 4-8 h, but in both cases to a lesser extents than those after food intake. The results indicate that serum leptin concentrations change diurnally in association with feeding-fasting cycles in the dog, partially due to changes in insulin secretion.

Seasonal changes in serum leptin of the feral raccoon (Procyon lotor) determined by canine-leptin-specific ELISA

Several reports have been published on blood leptin concentrations in feral animals, including members of the Carnivora, using a commercially available multi-species radioimmunoassay (RIA) kit with anti-human leptin antibody. However, we observed weak immunoreactivity between recombinant canine leptin and anti-human leptin antibody, suggesting a limitation in the applicability of the RIA kit for leptin assays in Carnivora species. We tested the applicability of RIA and sandwich enzyme-linked immunosorbent assay (ELISA) with anti-canine leptin antibody to assay blood leptin in the dog (Canis familiaris) and the raccoon (Procyon lotor). When RIA was used for recombinant canine leptin and dog sera, values were much lower than those determined by ELISA at higher concentrations (>10 ng/ml), while rather higher at lower concentrations (<2 ng/ml). A similar discrepancy between the two methods was found for serum leptin concentrations in raccoons. Clear seasonal variations were observed by ELISA, but not by RIA, with high values in autumn (3.46+/-0.45 ng/ml) and low values in spring and summer (0.71+/-0.07 ng/ml). Serum leptin concentrations in raccoons correlated positively with their body weight (r=0.753) and body mass index (r=0.755), corroborating our previous findings of a strong positive correlation between serum leptin concentrations and body fat content in dogs. Thus, the canine leptin ELISA is useful for assays of dog and raccoon leptin, and blood leptin is a good marker of nutritional condition in the species of Carnivora assayed in this study.

Catalytic Signal Amplification Using a Heck Reaction. An Example in the Fluorescence Sensing of Cu(II)

Catalytic signal enhancement using an organometallic reaction is demonstrated. The reactivity of a Heck cross-coupling reaction that creates a fluorophore is modulated by the addition of a polyazacyclam inhibitor. The inhibitor will complex with Cu(II), which restores the activity of the Pd(II). The addition of Cu(II) therefore leads to the generation of fluorescence, thereby creating a very sensitive assay for Cu(II). The rate of the Heck reaction is followed by monitoring emission as a function of time. The rate is proportional to the Cu(II) concentration and correlates to the affinity of the inhibitor to various metals. This strategy represents a general technique that can be exploited with other catalytic organometallic reactions.