Reining in equine metabolic syndrome : a gluttony of challenges

We humans are complicated creatures. Despite remarkable intellect, a fearsome ability to push boundaries and superior survival mechanisms, we are at times our own worst enemy. Metabolic syndrome continues to be a premier health problem in developed, and now increasingly in undeveloped, nations. It is spreading across the planet like an infectious disease and is costing us millions. Metabolic disease remains an important focus both for medical research and for governments desperate to ease the burden on already over-taxed health systems. Unlike some previous worldwide health epidemics, obesity-related diseases will require more than a single, silver bullet. A simple vaccine or treatment cannot overcome a lack of education, awareness and in some cases sheer determination; the human element of these diseases. Undeniably, these ‘human elements’ also complicate our ability, as veterinarians, to effectively manage the growing incidence of equine obesity and metabolic disease...

Life and death in a civitas capital: metabolic disease and trauma in the children from late Roman Dorchester, Dorset

The impact that “Romanization” and the development of urban centers had on the health of the Romano-British population is little understood. A re-examination of the skeletal remains of 364 nonadults from the civitas capital at Roman Dorchester (Durnovaria) in Dorset was carried out to measure the health of the children living in this small urban area. The cemetery population was divided into two groups; the first buried their dead organized within an east–west alignment with possible Christian-style graves, and the second with more varied “pagan” graves, aligned north–south. A higher prevalence of malnutrition and trauma was evident in the children from Dorchester than in any other published Romano-British group, with levels similar to those seen in postmedieval industrial communities. Cribra orbitalia was present in 38.5% of the children, with rickets and/or scurvy at 11.2%. Twelve children displayed fractures of the ribs, with 50% of cases associated with rickets and/or scurvy, suggesting that rib fractures should be considered during the diagnosis of these conditions. The high prevalence of anemia, rickets, and scurvy in the Poundbury children, and especially the infants, indicates that this community may have adopted child-rearing practices that involved fasting the newborn, a poor quality weaning diet, and swaddling, leading to general malnutrition and inadequate exposure to sunlight. The Pagan group showed no evidence of scurvy or rib fractures, indicating difference in religious and child-rearing practices but that both burial groups were equally susceptible to rickets and anemia suggests a shared poor standard of living in this urban environment.

The gut microbiota in obesity and metabolic disease - a novel therapeutic target

Obesity is sweeping the westernized world at a rate which far outstrips human genomic evolution, highlighting the importance of the obesogenic environment. Diet is an important component of this obesogenic environment, with certain diets (high fat, high refined carbohydrates and sugar) predisposing to overweight. On the other hand, there are also foods shown to protect against obesity and the diseases of obesity, including whole plant foods, dairy products, dietary fibre and functional foods like probiotics, prebiotics and phytochemicals. Interestingly, many of these foods mediate their health-promoting activities through the gut microbiota. The human gut microbiota itself has recently been identified as a contributory factor in this obesogenic environment, with differences observed between lean and obese. Evidence from human studies indicates that important groups of fermentative bacteria differ in abundance between lean and obese. Recently it has been suggested that anomalous microbiota composition in infancy can predispose to overweight in later life, highlighting the important role of optimal microbiota successional development, and that – as observed in laboratory animals – the gut microbiota may contribute to the aetiology of obesity. In this review we will introduce the gut microbiota, describe its interactions with major dietary components and the host, and then go on to discuss evidence indicating that the gut microbiota may contribute to the obesogenic environment. Finally, we will explore possible strategies for modulating the composition and activity of the human gut microbiota which may impact on obesity or the metabolic diseases associated with obesity. (Nutritional Therapy & Metabolism 2009; 27: 113-33)

Intralesional bovine papillomavirus DNA loads reflect severity of equine sarcoid disease

REASONS FOR PERFORMING STUDY: Sarcoids are nonmetastasising, yet locally aggressive skin tumours that constitute the most frequent neoplasm in equids. Infection by bovine papillomaviruses types 1 and 2 (BPV-1, BPV-2) has been recognised as major causative factor in sarcoid pathogenesis, but a possible correlation of intralesional virus load with disease severity has not been established thus far. HYPOTHESIS: Given the pathogenic role of BPV-1 and BPV-2 in sarcoid disease, we suggest that intralesional viral DNA concentration may reflect the degree of affection. METHODS: Severity of disease was addressed by recording the tumour growth kinetics, lesion number and tumour type for 37 sarcoid-bearing horses and one donkey. Viral load was estimated via quantitative real-time PCR (qPCR) of the E2, E5, L1 and L2 genes from the BPV-1/-2 genome for one randomly selected lesion per horse and correlated with disease severity. RESULTS: Quantitative PCR against E2 identified viral DNA concentrations ranging from 0-556 copies/tumour cell. Of 16 horses affected by quiescent, slowly growing single tumours or multiple mild-type lesions, 15 showed a viral load up to 1.4 copies per cell. In stark contrast, all equids (22/22) bearing rapidly growing and/or multiple aggressive sarcoids had a viral load between 3 and 569 copies per cell. Consistent results were obtained with qPCR against E5, L1 and L2. CONCLUSIONS: While tumours of the same clinical type carried variable virus load, confirming that viral titre does not determine clinical appearance, we identified a highly significant correlation between intralesional viral load and disease severity. POTENTIAL RELEVANCE: The rapid determination of BPV viral load will give a reliable marker for disease severity and may also be considered when establishing a therapeutic strategy.

Maternal cholestasis during pregnancy programs metabolic disease in offspring

The intrauterine environment is a major contributor to increased rates of metabolic disease in adults. Intrahepatic cholestasis of pregnancy (ICP) is a liver disease of pregnancy that affects 0.5%-2% of pregnant women and is characterized by increased bile acid levels in the maternal serum. The influence of ICP on the metabolic health of offspring is unknown. We analyzed the Northern Finland birth cohort 1985-1986 database and found that 16-year-old children of mothers with ICP had altered lipid profiles. Males had increased BMI, and females exhibited increased waist and hip girth compared with the offspring of uncomplicated pregnancies. We further investigated the effect of maternal cholestasis on the metabolism of adult offspring in the mouse. Females from cholestatic mothers developed a severe obese, diabetic phenotype with hepatosteatosis following a Western diet, whereas matched mice not exposed to cholestasis in utero did not. Female littermates were susceptible to metabolic disease before dietary challenge. Human and mouse studies showed an accumulation of lipids in the fetoplacental unit and increased transplacental cholesterol transport in cholestatic pregnancy. We believe this is the first report showing that cholestatic pregnancy in the absence of altered maternal BMI or diabetes can program metabolic disease in the offspring.

Inheritance of equine sarcoid disease in Franches-Montagnes horses.

The mode of inheritance for susceptibility to equine sarcoid disease (ES) remains unknown. The objectives of this study were to analyse a large sample of the Franches-Montagnes (FM) horse population and investigate the heritability and mode of inheritance for susceptibility to ES. Horses were clinically examined for the presence of sarcoid tumours. A standardized examination protocol and client questionnaire were used and a pedigree- and subsequent segregation-analysis for the ES trait performed. To investigate the mode of inheritance, five models were evaluated and compared in a hierarchical way. The analyses reveal that variation in susceptibility to ES is best explained by a model incorporating polygenic variation. The possible effect of a major gene, such as specific equine leukocyte antigen alleles, is unlikely, but cannot be ruled-out entirely. The heritability of the phenotype on the observation scale for the trait 'affected with ES' was estimated to be 8%. A corrected value for the heritability on a liability scale was estimated at 21% and it is therefore possible to estimate breeding values for ES. The arguments against the practical implementation of an estimated breeding value in a multifactorial condition like ES are discussed.

Increased FOXP3 expression in tumour-associated tissues of horses affected with equine sarcoid disease.

Recent studies suggest that regulatory T cells (Tregs) are associated with disease severity and progression in papilloma virus induced neoplasia. Bovine papilloma virus (BPV) is recognised as the most important aetiological factor in equine sarcoid (ES) disease. The aim of this study was to compare expression levels of Treg markers and associated cytokines in tissue samples of ES-affected equids with skin samples of healthy control horses. Eleven ES-affected, and 12 healthy horses were included in the study. Expression levels of forkhead box protein 3 (FOXP3), interleukin 10 (IL10), interleukin 4 (IL4) and interferon gamma (IFNG) mRNA in lesional and tumour-distant samples from ES-affected horses, as well as in dermal samples of healthy control horses were measured using quantitative reverse transcription polymerase chain reaction (PCR). Expression levels were compared between lesional and tumour-distant as well as between tumour-distant and control samples. Furthermore, BPV-1 E5 DNA in samples of ES-affected horses was quantified using quantitative PCR, and possible associations of viral load, disease severity and gene expression levels were evaluated. Expression levels of FOXP3, IL10 and IFNG mRNA and BPV-1 E5 copy numbers were significantly increased in lesional compared to tumour-distant samples. There was no difference in FOXP3 and cytokine expression in tumour-distant samples from ES- compared with control horses. In tumour-distant samples viral load was positively correlated with IL10 expression and severity score. The increased expression of Treg markers in tumour-associated tissues of ES-affected equids indicates a local, Treg-induced immune suppression.

Deficient DNA-ligase activity in the metabolic disease tyrosinemia type I

Hereditary tyrosinemia type I (HT1) is an autosomal recessive inborn error of metabolism caused by the deficiency of fumarylacetoacetate hydrolase, the last enzyme in the tyrosine catabolism pathway. This defect results in accumulation of succinylacetone (SA) that reacts with amino acids and proteins to form stable adducts via Schiff base formation, lysine being the most reactive amino acid. HT1 patients surviving beyond infancy are at considerable risk for the development of hepatocellular carcinoma, and a high level of chromosomal breakage is observed in HT1 cells, suggesting a defect in the processing of DNA. In this paper we show that the overall DNA-ligase activity is low in HT1 cells (about 20% of the normal value) and that Okazaki fragments are rejoined at a reduced rate compared with normal fibroblasts. No mutation was found by sequencing the ligase I cDNA from HT1 cells, and the level of expression of the ligase I mRNA was similar in normal and HT1 fibroblasts, suggesting the presence of a ligase inhibitor. SA was shown to inhibit in vitro the overall DNA-ligase activity present in normal cell extracts. The activity of purified T4 DNA-ligase, whose active site is also a lysine residue, was inhibited by SA in a dose-dependent manner. These results suggest that accumulation of SA reduces the overall ligase activity in HT1 cells and indicate that metabolism errors may play a role in regulating enzymatic activities involved in DNA replication and repair.

Skeletal muscle and nuclear hormone receptors: Implications for cardiovascular and metabolic disease

Skeletal muscle is a major mass peripheral tissue that accounts for similar to 40% of the total body mass and a major player in energy balance. It accounts for > 30% of energy expenditure, is the primary tissue of insulin stimulated glucose uptake, disposal, and storage. Furthermore, it influences metabolism via modulation of circulating and stored lipid (and cholesterol) flux. Lipid catabolism supplies up to 70% of the energy requirements for resting muscle. However, initial aerobic exercise utilizes stored muscle glycogen but as exercise continues, glucose and stored muscle triglycerides become important energy substrates. Endurance exercise increasingly depends on fatty acid oxidation (and lipid mobilization from other tissues). This underscores the importance of lipid and glucose utilization as an energy source in muscle. Consequently skeletal muscle has a significant role in insulin sensitivity, the blood lipid profile, and obesity. Moreover, caloric excess, obesity and physical inactivity lead to skeletal muscle insulin resistance, a risk factor for the development of type II diabetes. In this context skeletal muscle is an important therapeutic target in the battle against cardiovascular disease, the worlds most serious public health threat. Major risk factors for cardiovascular disease include dyslipidemia, hypertension, obesity, sedentary lifestyle, and diabetes. These risk factors are directly influenced by diet, metabolism and physical activity. Metabolism is largely regulated by nuclear hormone receptors which function as hormone regulated transcription factors that bind DNA and mediate the pathophysiological regulation of gene expression. Metabolism and activity, which directly influence cardiovascular disease risk factors, are primarily driven by skeletal muscle. Recently, many nuclear receptors expressed in skeletal muscle have been shown to improve glucose tolerance, insulin resistance, and dyslipidernia. Skeletal muscle and nuclear receptors are rapidly emerging as critical targets in the battle against cardiovascular disease risk factors. Understanding the function of nuclear receptors in skeletal muscle has enormous pharmacological utility for the treatment of cardiovascular disease. This review focuses on the molecular regulation of metabolism by nuclear receptors in skeletal muscle in the context of dyslipidemia and cardiovascular disease. (c) 2005 Published by Elsevier Ltd.

Adipokines have a role to play in the treatment of metabolic disease

Editorial

The interaction between metabolic disease and ageing

Two of the greatest crises that civilisation faces in the 21st century are the predicted rapid increases in the ageing population and levels of metabolic disorders such as obesity and type 2 diabetes. A growing amount of evidence now supports the notion that energy balance is a key determinant not only in metabolism but also in the process of cellular ageing. Much of genetic evidence for a metabolic activity-driven ageing process has come from model organisms such as worms and flies where inactivation of the insulin receptor signalling cascade prolongs lifespan. At its most simplistic, this poses a conundrum for ageing in humans – can reduced insulin receptor signalling really promote lifespan and does this relate to insulin resistance seen in ageing? In higher animals, caloric restriction studies have confirmed a longer lifespan when daily calorie intake is reduced to 60% of normal energy requirement. This suggests that for humans, it is energy excess which is a likely driver of metabolic ageing. Interventions that interfere with the metabolic fate of nutrients offer a potentially important target for delaying biological ageing.

Metabolic dysfunction and laminitis

Objective: This review focuses on laminitis that develops as a result of metabolic dysfunction and aims to provide a concise assessment of the current state of knowledge on this form of the disease. Outline: The most prevalent form of laminitis is associated with metabolic or endocrinopathic diseases, such as Equine Metabolic Syndrome and pituitary pars intermedia dysfunction, and the feeding of high-energy diets, particularly those rich in non-structural carbohydrates. Insulin dysregulation is the key hormonal imbalance implicated in causing this form of laminitis and hyperinsulinaemia is an important risk factor for the disease. Hyperinsulinaemia can occur in association with insulin resistance, obesity, regionalised adiposity, dysregulated cortisol metabolism and may also be related to other factors, such as breed and genetic predisposition. Recognition of hyperinsulinaemia is best achieved by using a dynamic oral glucose test that can be performed relatively easily under field conditions. Insulin produces a unique pathological lesion in the lamellae and the features of this lesion have informed investigations on the pathogenesis of the disease. Research into the mechanism of disease is continuing so that more targeted therapies than are currently available can be developed. However, dietary restriction and exercise remain effective management strategies for metabolic disease. Conclusions: Although the pathogenic mechanism/s of metabolic and endocrinopathic forms of laminitis remain the subject of intense research, ample data on risk factors for the disease are available. Efforts focussed on preventing the disease should aim to identify metabolic disease and reduce obesity and insulin resistance in at-risk individuals.

The impact of prolonged hyperinsulinaemia on glucose transport in equine skeletal muscle and digital lamellae

REASONS FOR PERFORMING STUDY An increased incidence of metabolic disease in horses has led to heightened recognition of the pathological consequences of insulin resistance (IR). Laminitis, failure of the weight-bearing digital lamellae, is an important consequence. Altered trafficking of specialised glucose transporters (GLUTs) responsible for glucose uptake, are central to the dysregulation of glucose metabolism and may play a role in laminitis pathophysiology. OBJECTIVES We hypothesised that prolonged hyperinsulinaemia alters the regulation of glucose transport in insulin-sensitive tissue and digital lamellae. Our objectives were to compare the relative protein expression of major GLUT isoforms in striated muscle and digital lamellae in healthy horses and during hyperinsulinaemia. STUDY DESIGN Randomised, controlled study. METHODS Prolonged hyperinsulinaemia and lamellar damage were induced by a prolonged-euglycaemic hyperinsulinaemic clamp (p-EHC) or a prolonged-glucose infusion (p-GI) and results were compared to electrolyte-treated controls. GLUT protein expression was examined with immunoblotting. RESULTS Lamellar tissue contained more GLUT1 protein than skeletal muscle (p = 0.002) and less GLUT4 than the heart (p = 0.037). During marked hyperinsulinaemia and acute laminitis (induced by the p-EHC), GLUT1 protein expression was decreased in skeletal muscle (p = 0.029) but unchanged in the lamellae, while novel GLUTs (8; 12) were increased in the lamellae (p = 0.03), but not skeletal muscle. However, moderate hyperinsulinaemia and subclinical laminitis (induced by the p-GI) did not cause differential GLUT protein expression in the lamellae vs. control horses. CONCLUSIONS The results suggest that lamellar tissue functions independently of insulin and that IR may not be an essential component of laminitis aetiology. Marked differences in GLUT expression exist between insulin-sensitive and insulin-independent tissues during metabolic dysfunction in horses. The different expression profiles of novel GLUTs during acute and subclinical laminitis may be important to disease pathophysiology and require further investigation.