Canine lipoproteins and atherosclerosis. II. Characterization of the plasma lipoproteins associated with atherogenic and nonatherogenic hyperlipidemia

Antimicrobial and Antiproliferative Coatings for Stents in Veterinary Medicine-State of the Art and Perspectives

Microbial colonization in veterinary stents poses a significant and concerning issue in veterinary medicine. Over time, these pathogens, particularly bacteria, can colonize the stent surfaces, leading to various complications. Two weeks following the stent insertion procedure, the colonization becomes observable, with the aggressiveness of bacterial growth directly correlating with the duration of stent placement. Such microbial colonization can result in infections and inflammations, compromising the stent's efficacy and, subsequently, the animal patient's overall well-being. Managing and mitigating the impact of these pathogens on veterinary stents is a crucial challenge that veterinarians and researchers are actively addressing to ensure the successful treatment and recovery of their animal patients. In addition, irritation of the tissue in the form of an inserted stent can lead to overgrowth of granulation tissue, leading to the closure of the stent lumen, as is most often the case in the trachea. Such serious complications after stent placement require improvements in the procedures used to date. In this review, antibacterial or antibiofilm strategies for several stents used in veterinary medicine have been discussed based on the current literature and the perspectives have been drawn. Various coating strategies such as coating with hydrogel, antibiotic, or other antimicrobial agents have been reviewed.

Spurious capillary zone electrophoresis pattern in hypercholesterolemic dogs

Capillary zone electrophoresis (CZE) is a relatively new serum protein electrophoresis method with higher resolution than other electrophoretic techniques. Hypercholesterolemic dogs exhibit a peculiar CZE pattern. Specifically, they have a shoulder or peak immediately next to the albumin peak. We investigated the prevalence of this spurious peak in hypercholesterolemic dogs and its correlation with the serum cholesterol concentration. Moreover, possible discrepancies between the CZE and spectrophotometric (bromocresol green [BCG] method) albumin concentrations in those animals were evaluated, as well as the accuracy in measuring albumin by a different CZE fractionation system. We retrospectively enrolled 500 hypercholesterolemic and normotriglyceridemic dogs. Each electrophoretic curve was inspected visually to identify a spurious peak (prevalence of 68.8%). We chose 120 dogs to further investigate the albumin concentration; CZE albumin was significantly higher than measured using the BCG method. A weak but significant correlation (r = 0.412; p <0.0001) was observed between the magnitude of the spurious peak and the serum cholesterol concentration. Finally, the significant difference between CZE and BCG albumin measurement disappeared (p = 0.92) when the spurious peak was considered as α1-globulins instead of albumin.

Dog models of human atherosclerotic cardiovascular diseases

Cardiovascular diseases (CVD) are one of the leading causes of death worldwide. Eighty-five percent of CVD-associated deaths are due to heart attacks and stroke. Atherosclerosis leads to heart attack and stroke through a slow progression of lesion formation and luminal narrowing of arteries. Dogs are similar to humans in terms of their cardiovascular physiology, size, and anatomy. Dog models have been developed to recapitulate the complex phenotype of human patients and understand the underlying mechanism of CVD. Different methods, including high-fat, high-cholesterol diet and genetic modification, have been used to generate dog models of human CVD. Remarkably, the location and severity of atherosclerotic lesions in the coronary arteries and branches of the carotid arteries of dog models closely resemble those of human CVD patients. Overt clinical manifestations such as stroke caused by plaque rupture and thrombosis were observed in dog models. Thus, dog models can help define the pathophysiological mechanisms of atherosclerosis and develop potential strategy for preventing and treating CVD. In this review, we summarize the progress in generating and characterizing canine models to investigate CVD and discuss the advantages and limitations of canine CVD models.

Roles of plant-based ingredients and phytonutrients in canine nutrition and health

Dogs possess the ability to obtain essential nutrients, established by the Association of American Feed Control Officials (AAFCO), from both animal‐ and plant‐based ingredients. There has been a recent increase in the popularity of diets that limit or completely exclude certain plant‐based ingredients. Examples of these diets include ‘ancestral’ or ‘evolutionary’ diets, raw meat‐based diets and grain‐free diets. As compared to animal sources, plant‐derived ingredients (including vegetables, fruits, grains, legumes, nuts and seeds) provide many non‐essential phytonutrients with some data suggesting they confer health benefits. This review aims to assess the strength of current evidence on the relationship between the consumption of plant‐based foods and phytonutrients (such as plant‐derived carotenoids, polyphenols and phytosterols) and biomarkers of health and diseases (such as body weight/condition, gastrointestinal health, immune health, cardiovascular health, visual function and cognitive function) from clinical trials and epidemiological studies. This review highlights the potential nutritional and health benefits of including plant‐based ingredients as a part of balanced canine diets. We also highlight current research gaps in existing studies and provide future research directions to inform the impact of incorporating plant‐based ingredients in commercial or home‐prepared diets.

Guidelines for animal exercise and training protocols for cardiovascular studies

Whole body exercise tolerance is the consummate example of integrative physiological function among the metabolic, neuromuscular, cardiovascular, and respiratory systems. Depending on the animal selected, the energetic demands and flux through the oxygen transport system can increase two orders of magnitude from rest to maximal exercise. Thus, animal models in health and disease present the scientist with flexible, powerful, and, in some instances, purpose-built tools to explore the mechanistic bases for physiological function and help unveil the causes for pathological or age-related exercise intolerance. Elegant experimental designs and analyses of kinetic parameters and steady-state responses permit acute and chronic exercise paradigms to identify therapeutic targets for drug development in disease and also present the opportunity to test the efficacy of pharmacological and behavioral countermeasures during aging, for example. However, for this promise to be fully realized, the correct or optimal animal model must be selected in conjunction with reproducible tests of physiological function (e.g., exercise capacity and maximal oxygen uptake) that can be compared equitably across laboratories, clinics, and other proving grounds. Rigorously controlled animal exercise and training studies constitute the foundation of translational research. This review presents the most commonly selected animal models with guidelines for their use and obtaining reproducible results and, crucially, translates state-of-the-art techniques and procedures developed on humans to those animal models.

Swine Disease Models for Optimal Vascular Engineering

Swine disease models are essential for mimicry of human metabolic and vascular pathophysiology, thereby enabling high-fidelity translation to human medicine. The worldwide epidemic of obesity, metabolic disease, and diabetes has prompted the focus on these diseases in this review. We highlight the remarkable similarity between Ossabaw miniature swine and humans with metabolic syndrome and atherosclerosis. Although the evidence is strongest for swine models of coronary artery disease, findings are generally applicable to any vascular bed. We discuss the major strengths and weaknesses of swine models. The development of vascular imaging is an example of optimal vascular engineering in swine. Although challenges regarding infrastructure and training of engineers in the use of swine models exist, opportunities are ripe for gene editing, studies of molecular mechanisms, and use of swine in coronary artery imaging and testing of devices that can move quickly to human clinical studies.

Association of acute Babesia canis infection and serum lipid, lipoprotein, and apoprotein concentrations in dogs

BACKGROUND

Babesia canis infection induces a marked acute phase response (APR) that might be associated with alteration in lipid and lipoprotein metabolism and disease prognosis.

HYPOTHESIS

Dogs with B. canis-induced APR develop dyslipidemia with altered lipoprotein concentration and morphology.

ANIMALS

Twenty-nine client-owned dogs with acute B. canis infection and 10 clinically healthy control dogs.

METHODS

Observational cross-sectional study. Serum amyloid A (SAA) was measured using ELISA. Cholesterol, phospholipids, and triglycerides were determined biochemically. Lipoproteins were separated using agarose gel electrophoresis. Lipoprotein diameter was assessed by polyacrylamide gradient gel electrophoresis; correlation with ApoA-1 (radioimmunoassay) and SAA was determined.

RESULTS

Dogs with B. canis infection had a marked APR (median SAA, 168.3 μg/mL; range, 98.1-716.2 μg/mL) compared with controls (3.2 μg/mL, 2.0-4.2 μg/mL) (P < .001). Dogs with B. canis infection had significantly lower median cholesterol (4.79 mmol/L, 1.89-7.64 mmol/L versus 6.15 mmol/L, 4.2-7.4 mmol/L) (P = .02), phospholipid (4.64 mmol/L, 2.6-6.6 mmol/L versus 5.72 mmol/L, 4.68-7.0 mmol/L) (P = .02), and α-lipoproteins (77.5%, 27.7%-93.5% versus 89.2%, 75.1%-93.5%) (P = .04), and higher ApoA-1 (1.36 U, 0.8-2.56 U versus 0.95 U, 0.73-1.54 U) concentrations (P = .02). Serum amyloid A correlated with high-density lipoproteins (HDLs) diameter (rho = .43; P = .03) and ApoA-1 (rho = .63, P < .001).

CONCLUSIONS AND CLINICAL IMPORTANCE

Major changes associated with B. canis-induced APR in dogs are related to concentration, composition, and morphology of HDL particles pointing to an altered reverse cholesterol transport. Parallel ApoA-1 and SAA concentration increase is a unique still unexplained pathophysiological finding.

Evaluation of density gradient ultracentrifugation serum lipoprotein profiles in healthy dogs and dogs with exocrine pancreatic insufficiency

Changes in proportions of lipoprotein classes have been described in disease states in humans. In veterinary medicine, hyperlipidemia can cause complications, such as cutaneous xanthomas, liver disease, cholelithiasis, pancreatitis, glomerular disease, lipemia retinalis, or peripheral neuropathy, but there are few reports regarding lipoproteins in diseased animals. For canine serum, we partially validated continuous lipoprotein density profiling (CLPDP), a novel density gradient ultracentrifugation technique. We examined canine lipoproteins separated by CLPDP by transmission electron microscopy (TEM). We compared lipoprotein profiles between healthy control dogs ( n = 29) and dogs with exocrine pancreatic insufficiency (EPI; n = 28) using CLPDP. Dogs with EPI included those untreated (EPI-NT; n = 6) and those treated with enzyme supplementation (EPI-T; n = 22). Our preliminary assay validation showed that CLPDP was repeatable (CV = 11.2%) and reproducible (CV = 10.6%) in canine serum. The diameters of lipoproteins analyzed by TEM were similar to those reported previously. Dogs in the EPI-NT group had more severe dyslipidemia than dogs in the EPI-T group. Dogs in the EPI-T group had lipoprotein profiles similar to healthy control dogs. CLPDP might be a useful tool for evaluating dyslipidemia in dogs.

Apolipoprotein E: from cardiovascular disease to neurodegenerative disorders

Apolipoprotein (apo) E was initially described as a lipid transport protein and major ligand for low density lipoprotein (LDL) receptors with a role in cholesterol metabolism and cardiovascular disease. It has since emerged as a major risk factor (causative gene) for Alzheimer's disease and other neurodegenerative disorders. Detailed understanding of the structural features of the three isoforms (apoE2, apoE3, and apoE4), which differ by only a single amino acid interchange, has elucidated their unique functions. ApoE2 and apoE4 increase the risk for heart disease: apoE2 increases atherogenic lipoprotein levels (it binds poorly to LDL receptors), and apoE4 increases LDL levels (it binds preferentially to triglyceride-rich, very low density lipoproteins, leading to downregulation of LDL receptors). ApoE4 also increases the risk for neurodegenerative diseases, decreases their age of onset, or alters their progression. ApoE4 likely causes neurodegeneration secondary to its abnormal structure, caused by an interaction between its carboxyl- and amino-terminal domains, called domain interaction. When neurons are stressed or injured, they synthesize apoE to redistribute cholesterol for neuronal repair or remodeling. However, because of its altered structure, neuronal apoE4 undergoes neuron-specific proteolysis, generating neurotoxic fragments (12-29 kDa) that escape the secretory pathway and cause mitochondrial dysfunction and cytoskeletal alterations, including tau phosphorylation. ApoE4-associated pathology can be prevented by small-molecule structure correctors that block domain interaction by converting apoE4 to a molecule that resembles apoE3 both structurally and functionally. Structure correctors are a potential therapeutic approach to reduce apoE4 pathology in both cardiovascular and neurological disorders.

Comparison of 2 electrophoretic methods and a wet-chemistry method in the analysis of canine lipoproteins

BACKGROUND

The evaluation of lipoprotein metabolism in small animal medicine is hindered by the lack of a gold standard method and paucity of validation data to support the use of automated chemistry methods available in the typical veterinary clinical pathology laboratory. The physical and chemical differences between canine and human lipoproteins draw into question whether the transference of some of these human methodologies for the study of canine lipoproteins is valid. Validation of methodology must go hand in hand with exploratory studies into the diagnostic or prognostic utility of measuring specific lipoproteins in veterinary medicine.

OBJECTIVE

The goal of this study was to compare one commercially available wet-chemistry method to manual and automated lipoprotein electrophoresis in the analysis of canine lipoproteins.

METHODS

Canine lipoproteins from 50 dogs were prospectively analyzed by 2 electrophoretic methods, one automated and one manual method, and one wet-chemistry method.

RESULTS

Electrophoretic methods identified a higher proportion of low-density lipoproteins than the wet-chemistry method. Automated electrophoresis occasionally failed to identify very low-density lipoproteins.

CONCLUSIONS

Wet-chemistry methods designed for evaluation of human lipoproteins are insensitive to canine low-density lipoproteins and may not be applicable to the study of canine lipoproteins. Automated electrophoretic methods will likely require significant modifications if they are to be used in the analysis of canine lipoproteins. Studies aimed at determining the impact of a disease state on lipoproteins should thoroughly investigate the selected methodology prior to the onset of the study.

Preliminary Analysis of Modified Low-Density Lipoproteins in the Serum of Healthy and Obese Dogs and Cats

Oxidized low-density lipoprotein (LDL) is thought to play an important role in the inflammatory response associated with human obesity. The purpose of this preliminary study was to determine oxidized LDL concentrations in healthy dogs and cats, and to evaluate whether obesity affects oxidized LDL concentration, using 39 cats and 19 dogs that had visited two different veterinary clinics in Japan. We hypothesized that oxidized LDL concentrations measured against body condition score (BCS) may have a potential value in evaluating the qualities of accumulated or circulating lipids in obese dogs and cats that do not show signs of metabolic diseases. The mean oxidized LDL value in BCS3 dogs (2.4 ± 0.9 μg/dl) was very similar to that of BCS5 dogs (2.2 ± 0.3 μg/dl). The mean oxidized LDL value of BCS4 dogs was 7.2 ± 10.3 μg/dl and the highest among three groups. BCS4 dogs included two dogs whose oxidized LDL values were higher than the mean oxidized LDL value of healthy humans (11.2 ± 0.3 μg/dl). On the other hand, the mean oxidized LDL value of BCS3 cats was 2.5 ± 0.9 μg/dl, and those of BCS4 and 5 cats were higher than that of BCS3, but there was no significant difference. The BCS4 cat group included one cat with a higher oxidized LDL value, and the BCS5 group also included two cats with oxidized LDL values higher than the mean oxidized LDL value of healthy humans. Interestingly, the oxidized LDL values in two obese dogs and three obese cats were indeed higher than the mean oxidized LDL value of humans with coronary artery disease (20.1 ± 1.1 μg/dl). In conclusion, this preliminary study showed reference ranges of oxidized dogs and cats against BCS. Obesity alone does not appear to have any direct effect on serum oxidized LDL values in healthy dogs and cats.

Increased serum concentrations of adiponectin in canine hypothyroidism

Serum concentrations of adiponectin were compared between sex-matched hypothyroid (n = 18) and euthyroid (n = 18) client-owned dogs with comparable ages and body condition scores (BCS). Concentrations of adiponectin (mean; 95% confidence interval) were significantly (P < 0.01) higher in hypothyroid (17.2 µg/mL; 12.1-20.5 µg/mL) than healthy (8.0 µg/mL; 5.6-11.4 µg/mL) dogs following adjustment for potential confounders (BCS, age and sex). Serum concentrations of adiponectin were significantly negatively associated with concentrations of total thyroxine (P <0.05) and positively correlated with concentrations of cholesterol (r = 0.6, P <0.01) in hypothyroid dogs. In conclusion, this study demonstrated increased serum concentrations of adiponectin in dogs with hypothyroidism. Suggestive of the presence of resistance to adiponectin that could have contributed to development of hyperlipidemia and insulin resistance in these dogs or alternatively, could be a consequence of these metabolic alterations.

Serum lipoprotein changes in dogs with renal disease

Background

People with renal disease develop a dyslipidemia that contributes to progression of renal injury and development of cardiovascular disease. Lipoproteins in dogs with renal disease have not been investigated.

Hypothesis

Dogs with chronic kidney disease (CKD) have dyslipidemia characterized by increased lower density lipoproteins and decreased high‐density lipoproteins (HDLs). The degree of dyslipidemia is positively correlated with severity of disease, as reflected by serum creatinine concentration.

Animals

Prospective study of client‐owned dogs presented to the Cornell University Hospital for Animals: 29 dogs with confirmed CKD, 5 dogs with nephrotic syndrome (NS), and 12 healthy control dogs presented for routine vaccinations, dental cleaning, or owned by students.

Methods

Lipoprotein electrophoresis was used to quantify relative proportions of the 3 main classes of lipoproteins in canine serum: low‐density lipoproteins (LDL), very low‐density lipoproteins (VLDL), and HDL. Serum cholesterol and creatinine concentrations; urinalysis and urine protein‐to‐creatinine ratio were measured by standard methods.

Results

Dyslipidemia was consistently found in dogs with CKD and NS and was characterized by a decrease in HDL and variable increases in LDL and VLDL. Dogs with NS had a proportionately greater increase in the VLDL fraction, as compared with dogs with CKD.

Conclusion and Clinical Importance

Dyslipidemia similar to that documented in people with renal disease occurs in dogs with CKD, despite serum cholesterol concentrations often being within the reference interval. The contribution of altered lipoproteins to the pathogenesis of renal disease in dogs warrants additional study.

Animal models of atherosclerosis

In this mini-review several commonly used animal models of atherosclerosis have been discussed. Among them, emphasis has been made on mice, rabbits, pigs and non-human primates. Although these animal models have played a significant role in our understanding of induction of atherosclerotic lesions, we still lack a reliable animal model for regression of the disease. Researchers have reported several genetically modified and transgenic animal models that replicate human atherosclerosis, however each of current animal models have some limitations. Among these animal models, the apolipoprotein (apo) E-knockout (KO) mice have been used extensively because they develop spontaneous atherosclerosis. Furthermore, atherosclerotic lesions developed in this model depending on experimental design may resemble humans’ stable and unstable atherosclerotic lesions. This mouse model of hypercholesterolemia and atherosclerosis has been also used to investigate the impact of oxidative stress and inflammation on atherogenesis. Low density lipoprotein (LDL)-r-KO mice are a model of human familial hypercholesterolemia. However, unlike apo E-KO mice, the LDL-r-KO mice do not develop spontaneous atherosclerosis. Both apo E-KO and LDL-r-KO mice have been employed to generate other relevant mouse models of cardiovascular disease through breeding strategies. In addition to mice, rabbits have been used extensively particularly to understand the mechanisms of cholesterol-induced atherosclerosis. The present review paper details the characteristics of animal models that are used in atherosclerosis research.

Effect of dietary omega-3 fatty acids on red blood cell lipid composition and plasma metabolites in the cockatiel, Nymphicus hollandicus

Although dietary n-3 fatty acids have been extensively studied in poultry, they have not yet been prospectively investigated in psittacines, despite potential benefits for preventing and treating atherosclerosis, osteoarthritis, and other chronic disease processes. The objectives of this study were to investigate the incorporation of dietary n-3 fatty acids into red blood cells (RBC) and to determine the effects of supplementation of psittacine diets with fish or flax oil on plasma lipids and lipoproteins in the cockatiel. Adult cockatiels were fed a custom-formulated diet containing either 4% (wt/wt, as-fed) beef tallow (CON), 3% fish oil + 1% tallow (FSH), or 3.5% flax oil + 0.5% tallow (FLX; n = 20 per diet group). Baseline measurements were obtained for RBC fatty acid composition, triacylglycerides (TAG), and cholesterol. After 8 to 13 wk on the study diets, plasma chemistry profiles, lipoprotein density profiles, and RBC fatty acid composition were determined. At 8 wk, total plasma cholesterol was least in FSH birds (P < 0.05) and TAG concentrations were less in FSH birds than FLX birds (P < 0.05). Total n-3 fatty acids, docosahexaenoic acid, docosapentaenoic acid, and eicosapentaenoic acid were markedly greater in the RBC of FSH birds than FLX or CON birds (P < 0.05). Alpha linolenic acid was greatest in FLX (P < 0.05). Initial and final BW, and nonlipid plasma chemistry values did not differ among diet groups. No adverse effects of dietary supplementation of cockatiels with 3.5% flax oil or 3% fish oil were observed during the 13-wk feeding period. Although fish and flax oils provided similar total n-3 PUFA to the diets, fish oil caused greater reductions in cholesterol and TAG, and greater total RBC n-3 incorporation. Thus, dietary modification of psittacine diets with long chain n-3 PUFA from fish oil appears safe and may be beneficial to these long-lived companion birds.

Animal models of atherosclerosis

Cardiovascular disease is currently the predominant cause of mortality worldwide and its incidence is expected to increase significantly during the next decades owing to the unhealthy effects of modern lifestyle habits (e.g., obesity and lack of physical exercise). Cardiovascular death is frequently associated with acute myocardial infarction or stroke, which are generally the ultimate consequence of an underlying atherosclerotic process. Small and big animal models are valuable tools to understand the molecular mechanisms underlying atherosclerotic plaque formation and progression, as well as the occurrence of associated ischemic events. Moreover, animal models of atherosclerosis are pivotal for testing mechanistic hypothesis and for translational research, including the assessment of dietary and/or pharmacological interventions and the development of imaging technologies and interventional devices. In this chapter, we will describe the most widely used animal models that have permitted major advances in atherosclerosis research and significant improvements in the treatment and diagnosis of atherosclerotic disease.

Animal models for the atherosclerosis research: a review

Atherosclerosis is a leading cause of death worldwide, and its mechanisms are still unclear. However, various animal models have significantly advanced our understanding of the mechanisms involved in atherosclerosis and have allowed the evaluation of therapeutic options. The aim of this paper is to review those animal models (i.e., rabbits, mice, rats, guinea pigs, hamsters, avian, carnivores, swine, and, non-human primates) that have been used to study atherosclerosis. Though there is no single perfect animal model that completely replicates the stages of human atherosclerosis, cholesterol feeding and mechanical endothelial injury are two common features shared by most models of atherosclerosis. Further, with the development of genetically modified animals, these models are significantly broadening our understanding of the pathogenesis of atherosclerosis.

Atherosclerosis and thrombosis: insights from large animal models

Atherosclerosis and its thrombotic complications are responsible for remarkably high numbers of deaths. The combination of in vitro, ex vivo, and in vivo experimental approaches has largely contributed to a better understanding of the mechanisms underlying the atherothrombotic process. Indeed, different animal models have been implemented in atherosclerosis and thrombosis research in order to provide new insights into the mechanisms that have already been outlined in isolated cells and protein studies. Yet, although no model completely mimics the human pathology, large animal models have demonstrated better suitability for translation to humans. Indeed, direct translation from mice to humans should be taken with caution because of the well-reported species-related differences. This paper provides an overview of the available atherothrombotic-like animal models, with a particular focus on large animal models of thrombosis and atherosclerosis, and examines their applicability for translational research purposes as well as highlights species-related differences with humans.

Influence of obesity on plasma lipid and lipoprotein concentrations in dogs

OBJECTIVE

To determine effects of obesity and diet in dogs on plasma lipid and lipoprotein concentrations by assaying plasma leptin and ghrelin concentrations and determining total plasma cholesterol and triglyceride concentrations as well as the concentrations of cholesterol and triglycerides in various lipoprotein classes (ie, very-low-density, low-density, and high-density lipoproteins).

ANIMALS

24 Beagles; 12 lean (mean [+/- SEM] body weight, 12.7 +/- 0.7 kg) and 12 chronically obese (21.9 +/- 0.8 kg) dogs of both sexes, between 1 and 9 years old.

PROCEDURES

Total plasma cholesterol and triglyceride concentrations; lipoprotein cholesterol and triglyceride concentrations; and plasma ghrelin, leptin, free fatty acids, insulin, and glucose concentrations were measured and compared between lean and obese dogs, both of which were fed a complete and balanced maintenance diet. Chronically obese dogs were subsequently fed a high-protein low-energy diet to evaluate effects of diet composition on plasma lipid and lipoprotein measurements.

RESULTS

Chronic obesity resulted in a significant decrease in plasma ghrelin concentration and a significant increase in plasma leptin, cholesterol, and triglyceride concentrations in dogs. High total plasma cholesterol and triglyceride concentrations resulted from increased cholesterol and triglyceride concentrations in all lipoprotein fractions. In obese dogs, modification of diet composition resulted in beneficial effects on plasma lipid and leptin concentrations, even before weight loss was observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Correlations exist between obesity and plasma measurements (ie, lipoproteins, leptin, insulin, and ghrelin) commonly associated with obesity. Modification of diet composition to control energy intake improves plasma lipid and leptin concentrations in obese dogs.

Hypercholesterolaemia in a family of rough collie dogs

A family of five privately owned rough collie dogs was referred for corneal lipidosis and also suffered from hypercholesterolaemia. The hypercholesterolaemia was characterised by an increase in the alpha-2 high density lipoprotein-1 band and was due to an increase in the cholesterol content of the very low density lipoprotein, low density lipoprotein and possibly the high density lipoprotein-1 fractions. A low-fat and energy-restricted diet did not reduce either total cholesterol or the corneal lipidosis. Corneal lipidosis regressed with short-chain fructo-oligosaccharide supplementation. However, the effects of short-chain fructo-oligosaccharides on total cholesterol were transient and variable.

Species-related variations in lipoprotein metabolism: The impact of FERHDL on susceptibility to atherogenesis

Several animal models have been used to investigate the mechanisms of atherogenesis. Each animal species has advantages and disadvantages with regard to similarity with human lipoprotein metabolism. In humans, fractional esterification rate in apolipoprotein B-depleted plasma (FER(HDL)) has been shown to correlate with the quality of high density lipoprotein particles. Increased values of FER(HDL) indicate an atherogenic lipoprotein profile. Such an association has not been defined in animal models. Thus, we have characterized plasma lipoprotein profile and FER(HDL) values in four animal species namely, cats, pigs, guinea pigs and rabbits. These animal species have been used in experimental dyslipidemia and atherosclerosis. Our data indicate a wide rage of variations among various animal species. High-density lipoprotein (HDL) particles contain approximately 40% of total plasma cholesterol concentrations in rabbits, pigs and cats <10% in guinea pigs. A negative association between FER(HDL) values and plasma HDL-cholesterol levels was observed in pigs, rabbits and guinea pigs. On the other hand, FER(HDL) values showed a positive association with plasma triglyceride levels in all animal species tested. These findings are in agreement with data reported in humans. More research is needed to identify the better animal models which closely resemble human lipoprotein metabolism.

Immunohistochemical detection of apolipoprotein A-I and B-100 in canine atherosclerotic lesions

We attempt to determine and compare the localization of apolipoproteins (apo) apoA-I and B-100 in atherosclerotic lesions of canine aortas, coronary arteries, and the peripheral arteries, using immunohistochemical techniques. Histopathologically, atherosclerotic lesions were characterized by deposition of lipids and infiltration of lipid-laden foamy cells in the tunica intima and tunica media, sometimes forming fibrofatty plaques containing abundant sudanophilic and mineralized material. Canine apoA (CapoA)-I and canine apoB (CapoB)-100 immunopositive signals were simultaneously observed in mild and severe atherosclerotic lesions of the aorta, coronary arteries, splenic arteries, and renal arteries in the double-immunolabeled sections. Both CapoA-I and CapoB-100 positive signals were seen in the cytoplasm of endothelial cells, smooth muscle cells, and macrophages. The subendothelial space and extracellular matrix in the tunica intima and media were also positive. Neither CapoA-I nor CapoB-100 positive signals were seen in normal arteries. These findings closely resemble those of the localization of apoA-I and apoB-100 in human atherosclerotic lesions.

Comparative lipid and lipoprotein metabolism

This review summarizes a number of recent reports in several areas of lipid and lipoprotein metabolism. Absorption of dietary lipids, cholesterol synthesis, and biliary cholesterol metabolism are mentioned only briefly to be complete. Comparative aspects of lipoprotein metabolism, however, are detailed in an effort to integrate the myriad metabolic events which characterize these important lipid transport particles. Where comparative information is known, those aspects of lipoprotein metabolism that may be protective against atherogenesis in certain mammalian species are also described. Efforts to understand atherogenic resistance comparatively in animals lends a better understanding of the metabolic events leading to coronary artery disease in humans. They also provide an important basis for understanding lipid metabolism in numerous veterinary species.

Ocular lipid deposition and hyperlipoproteinaemia

In all species there are potential ocular manifestations when circulating lipoproteins are raised and these may be transient or permanent Many factors, both systemic and local, influence lipid influx and accumulation (progression) and lipid mobilisation and efflux (regression). In both humans and animals some types of lipid deposition will regress if the local and systemic factors involved in pathogenesis can be modified. There are inescapable parallels with the same phenomena in other tissues.Three types of corneal lipid deposition have been linked with hyperlipoproteinaemia. In corneal arcus, lipid is deposited preferentially in the warmest part of the cornea initially and, in people, the lipid remains almost exclusively extracellular. In animals, corneal arcus is associated with initial extracellular lipid deposition followed by the appearance of intracellular lipid and vascularisation, so that established corneal arcus tends to become more typical of lipid keratopathy. In humans, hyperlipoproteinaemia may be an associated systemic factor and early onset corneal arcus is a recognised feature of certain primary hyperlipoproteinaemias and their secondary phenotypes. In dogs, corneal arcus is always associated with hyperlipoproteinaemia. Corneal vascularisation is a ubiquitous feature of lipid keratopathy in all species and both necrotic fibroblasts and foam cells are common in progressive lesions. The extent and position of lipid deposition and the evolution of lipid keratopathy can be related to local ocular disease and circulating lipids and lipoproteins. Many aspects of the pathogenesis of lipid keratopathy are similar to those of atherogenesis. Hyperlipoproteinaemia, especially hypercholesterolaemia is the commonest systemic abnormality. In crystalline stromal dystrophy (Schnyder's crystalline stromal dystrophy) of the cornea there is no inflammatory element and no vascularisation. The dystrophy is associated with accumulation of lipid within the corneal fibroblasts, but typical foam cells are absent, the crystalline opacity involves the coolest part of the cornea, correlates with local fibroblast death, and is always bilateral. Hyperlipoproteinaemia, may be present, but this is not universally so.The objective of this paper is to evaluate the factors that may influence ocular involvement in hyperlipoproteinaemia. A comparative approach, utilising information available from studies of both ocular and non-ocular tissues, aids elucidation of the complex pathogenesis.

Advances in experimental dyslipidemia and atherosclerosis

Among the models of dyslipidemia and atherosclerosis, a number of wild-type, naturally defective, and genetically modified animals (rabbits, mice, pigeons, dogs, pigs, and monkeys) have been characterized. In particular, their similarities to and differences from humans in respect to relevant biochemical, physiologic, and pathologic conditions have been evaluated. Features of atherosclerotic lesions and their specific relationship to plasma lipoprotein particles have been critically reviewed and summarized. All animal models studied have limitations: the most significant advantages and disadvantages of using a specific animal species are outlined here. New insights in lipid metabolism and genetic background with regard to variations in pathogenesis of dyslipidemia-associated atherogenesis have also been reviewed. Evidence suggests that among wild-type species, strains of White Carneau pigeons and Watanabe Heritable Hyperlipidemic and St. Thomas's Hospital rabbits are preferable to the cholesterol-fed wild-type animal species in dyslipidemia and atherosclerosis research. Evidence for the usefulness of both wild-type and transgenic animals in studying the involvement of inflammatory pathways and Chlamydia pneumoniae infection in pathogenesis of atherosclerosis has also been summarized. Transgenic mice and rabbits are excellent tools for studying specific gene-related disorders. However, despite these significant achievements in animal experimentation, there are no suitable animal models for several rare types of fatal dyslipidemia-associated disorders such as phytosterolemia and cerebrotendinous xanthomatosis. An excellent model of diabetic atherosclerosis is unavailable. The question of reversibility of atherosclerosis still remains unanswered. Further work is needed to overcome these deficiencies.

Hypercholesterolemia in Shetland sheepdogs

Plasma lipoprotein cholesterol in 64 clinically healthy Shetland sheepdogs was evaluated to assess whether the breed is more susceptible to hypercholesterolemia. The incidence of hypercholesterolemia was clearly higher in Shetland sheepdogs and mean plasma cholesterol level was significantly higher in Shetland sheepdogs than in control dogs. Blood biochemical examinations did not evidence the abnormalities, which imply the causative disorders, and thyroid hormone levels were not significantly different from the controls. These results suggest that the cholesterolemia is a primary disorder. Cholesterol fractionation by agarose gel electrophoresis and ultracentrifugation revealed that accumulation of alpha2-migrating lipoproteins was the common characteristic of dogs showing cholesterol level over 250 mg/dl in the breed. Increase in prebeta-beta-lipoproteins was also found in Shetland sheepdogs with marked hypercholesterolemia over 500 mg/dl. Therefore. Shetland sheepdogs may include more dogs with primary disorders in lipoprotein metabolism, which cause hypercholesterolemia. at least in Japan.

Enzyme-linked immunosorbent assays of canine apolipoproteins B-100 and A-I

An enzyme-linked immunosorbent assay (ELISA) for canine blood apolipoprotein (apo) B-100 and A-I was developed. The working range for the assay was 1.8 to 28.7 ng/well for apoB-100 and it was 50 to 410 ng/well for apoA-I. The intra- and inter-assay coefficients of variation for the assay for apoB-100 were 5.4 and 6.9%, respectively, and for apoA-I they were 5.8 and 10.6%, respectively. The average concentrations of apoB-100 and A-I in 25 beagles (males, aged 3-4 years) were 0.084 +/- 0.028 (mean +/- SD) mg/ ml and 6.29 +/- 1.55 mg/ml, respectively. The ratios of canine (C) apoB-100 to CapoA-I were 1.41 +/- 0.58%. The respective concentrations in one case of hyperlipidemia with systemic atherosclerosis were 0.454 mg/ml and 11.28 mg/ml (a ratio of 4.03%). These values were larger than those of the controls. These results suggest that the measurements of CapoB-100 and A-I concentrations by this newly developed ELISA are helpful for diagnosis of lipidosis.

Variability of the intestinal uptake of lipids is genetically determined in mice

The response of the plasma cholesterol concentration to changes in dietary lipids varies widely in humans and animals. There are variations in the in vivo absorption of cholesterol between different strains of mice. This study was undertaken in three strains of inbred mice to test the hypotheses that: (i) there are strain differences in the in vitro uptake of fatty acids and cholesterol and (ii) the adaptability of the intestine to respond to variations in dietary lipids is genetically determined. An in vitro intestinal ring technique was used to assess the uptake of medium- and long-chain fatty acids and cholesterol into jejunum and ileum of adult DBA/2, C57BL6, and C57L/J mice. The jejunal uptake of cholesterol was similar in C57L/J, DBA/2, or C57BL6 fed ad libitum a low-fat (5.7% fat, no cholesterol) chow diet. This is in contrast to a previous demonstration that in vivo cholesterol absorption was lower in C57L/J than in the other murine strains. The jejunal uptake of several long-chain fatty acids was greater in DBA/2 fed for 4 wk the high-fat (15.8% fat and 1.25% cholesterol) as compared with the low-fat diet. Furthermore, on the high-fat diet, the uptake of many long-chain fatty acids was higher in DBA/2 than in C57BL6 or C57L/J. The differences in cholesterol and fatty acid uptake were not explained by variations in food uptake, body weight gain, or the weight of the intestine. In summary: (i) there are strain differences in the in vitro intestinal uptake of fatty acids but not of cholesterol; (ii) a high-fat diet enhances the uptake of long-chain fatty acids in only one of the three strains examined in this study; and (iii) the pattern of strain- and diet-associated alterations in the in vivo absorption of cholesterol differs from the pattern of changes observed in vitro. We speculate that genetic differences in cholesterol and fatty acid uptake are explained by variations in the expression of protein-mediated components of lipid uptake.

Hyperlipemic-very low density lipoprotein, intermediate density lipoprotein and low density lipoprotein act synergistically with serotonin on vascular smooth muscle cell proliferation

BACKGROUND

Previous studies have shown that very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL) and low density lipoprotein (LDL) from hyperlipidemic plasma are more atherogenic than those from normal plasma. Since platelet aggregation at sites of atherosclerotic injury exposes the cells to high concentrations of serotonin (5HT), a known mitogen for vascular smooth muscle cells (VSMCs), it was examined whether VLDL, IDL or LDL from plasma of 1% cholesterol-fed rabbits can potentiate the mitogenic effect of 5HT on VSMC.

METHODS

Growth arrested primary aortic VSMC in 1st or 2nd passage were incubated with different concentrations of VLDL, IDL or LDL in the presence or absence of pertusis toxin (PTX) for 24 h followed by incubation with 5HT for 24 h. The amount of [3H]thymidine incorporated into the DNA as well as the increase in cell number was measured.

RESULTS

Either VLDL, IDL or LDL at a concentration of 60 microg/ml induced proliferation of VSMC by themselves (196, 137 or 122% increase in [3H]thymidine incorporation, or 122, 119 or 122% increase in cell number, respectively when compared to the control, P<0.05). This effect on DNA synthesis was markedly potentiated by 50 microM 5HT to 465, 714 and 1369%, respectively. PTX reversed the mitogenic effect of 5HT, but not that of VLDL, IDL or LDL.

CONCLUSION

These results suggest that even low concentration of VLDL, IDL or LDL from hypercholesterolemic plasma may significantly potentiate the mitogenic effect of 5HT, that is released by aggregating platelets at sites of vascular damage.

Atherosclerosis in a dog with diabetes mellitus

A seven-year-old male Pomeranian with unstable insulin-dependent diabetes mellitus developed atherosclerosis. Hyperlipidaemia, consisting of hypertriglyceridaemia and hypercholesterolaemia, was diagnosed concurrently with the onset of lipid-laden aqueous humour. Serum lipoprotein analysis was characterised by the presence of chylomicrons, an increase in the very low density lipoprotein fraction, with a broad very low density lipoprotein-low density lipoprotein band, and a reduced high density lipoprotein fraction. The dog developed ketoacidosis one year later and died. At postmortem examination, atherosclerotic plaques were observed in the terminal aorta and in medium-sized arteries, including the coronary arteries, renal and arcuate arteries, and arteries of the brain. Mineralised plaques or complicated plaques were not observed. The absence of clinical signs of organ ischaemia was thought to be associated with the absence of thrombosis and/or complete occlusion of all vessels examined. Signs of chronic organ hypoxia, although considered likely owing to the severe vessel lumen reduction, were restricted to only a low voltage QRS complex on the electrocardiogram.

Catabolism of HDL1 cholesteryl ester in the rat. Effect of ethinyl estradiol treatment

The present study was performed in control and ethinyl estradiol-treated rats in order to determine the mechanisms involved in the catabolism of HDL1 cholesteryl ester. Ligand blottings on liver membranes showed that purified HDL1, containing about 70% apolipoprotein E and 10% apolipoprotein AI, bind to the LDL receptor (130 kDa) and not to HB2 (100 kDa) or SR-BI (82 kDa), candidate HDL receptors. Immunoblots showed that the treatment increased the hepatic level of the LDL receptor five- to ten-fold, strongly decreased that of SRBI and did not change that of HB2. An in vivo kinetic study showed that the turnover of HDL1 cholesteryl ester is more rapid in treated than control rats. The liver participation (60%) in this clearance was not modified by the treatment. Therefore, it can be concluded that the catabolism of HDL1 cholesteryl ester, in control as in treated rats, is essentially ensured by the uptake of entire particles in the hepatocytes via LDL receptors.

Alterations in lipoprotein profiles in dogs with lymphoma

After a 12-hour fast, blood samples were obtained from 31 dogs with previously untreated lymphoma. Blood samples were also collected from 16 of these dogs after up to 5 treatments with doxorubicin (30 mg/m2 intravenously every 3 weeks). All 16 dogs underwent complete remission. Five dogs were re-evaluated after relapse and after overt signs of cancer cachexia had become clinically apparent. Samples were assayed for 8 quantitative parameters: total cholesterol (T-CH) and total triglyceride (T-TG) concentrations, and the concentration of cholesterol and triglyceride in each of the three major lipoprotein fractions, very-low-density lipoprotein (LDL-CH and LDL-TG), and high-density lipoprotein (HDL-CH and HDL-TG). The results were compared with those from 20 healthy control dogs of similar weight and age before and 3 weeks after being given one dose of doxorubicin (30 mg/m2 intravenously). The administration of doxorubicin to control dogs resulted in a significant (P < .05) decrease in T-CH, LDL-CH, and HDL-CH, as well as a significant increase in VLDL-TG and HDL-TG. When compared with untreated controls, untreated dogs with lymphoma had significantly higher concentrations of VLDL-CH, T-TG, VLDL-TG, LDL-TG, and HDL-TG, and significantly lower concentrations of HDL-CH. HDL-TG and VLDL-TG concentrations from dogs with lymphoma were significantly increased above pretreatment values after relapse and development of overt signs of cancer cachexia.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and secretion of apo B containing lipoproteins by primary cultures of hepatocytes isolated from rats fed atherogenic diet

The effect of experimentally induced atherosclerosis on the synthesis and secretion of lipoproteins in the density range of very low density lipoproteins (VLDL) and low density lipoproteins (LDL) have been studied using primary cultures of rat hepatocytes. Rats fed atherogenic diet showed higher levels of lipids associated with serum VLDL and LDL fraction, aorta and liver when compared with animals fed normal diet. Incorporation of [3H]leucine into apo B associated with the cell layer and secreted by hepatocytes from rats fed atherogenic diet was significantly more when compared with normal hepatocytes. [14C]Acetate incorporation studies showed that the synthesis of cholesterol was lower in hepatocytes from atherogenic diet fed rats, but more of the newly synthesised cholesterol was found in the secreted VLDL; secretion of lipids, particularly triglycerides, unesterified cholesterol and cholesterol in the lipoproteins in the density range of VLDL and LDL was significantly more in these hepatocytes. The relative distribution of [3H]-radioactivity in the LDL density range was 57% in hepatocytes from atherogenic diet fed animals as compared with 28% in controls, suggesting a relatively higher production of lipoproteins in the LDL density range than VLDL by these cells. These results indicate that the hypercholesterolemia in atherogenic diet fed animals may among other factors be caused by increased synthesis of apo B by liver cells and resultant increase in the secretion of apo B containing lipoproteins.

Hypercholesterolaemia in briards in the United Kingdom

Elevated fasting plasma cholesterol concentrations were identified in clinically healthy briards. Biochemical investigations revealed no other major abnormalities. Plasma lipoprotein electrophoresis demonstrated a marked increase in the intensity of the alpha 2 band (compared with control dogs) which was reduced by dextran sulphate-magnesium chloride or sodium phosphotungstate-magnesium chloride precipitation of apo B and apo E containing lipoproteins in the plasma. The study has identified a hyperlipidaemia in briards characterised by increased cholesterol but normal triglyceride concentrations. The absence of obvious metabolic changes associated with secondary hypercholesterolaemia, suggests the breed may have a primary abnormality in cholesterol metabolism. The increased density of the precipitable lipoprotein which migrates to the alpha 2 band suggests that the hypercholesterolaemia may be due to an abnormal accumulation of high density lipoprotein (HDL) possibly HDLc. The possibility that abnormality in lipid metabolism might play a role in the development of retinal pigment epithelial dystrophy in briards is currently being investigated.

Characterization of dietary-induced hypercholesterolemia in the chicken

The effect of 2% dietary cholesterol on the distribution of cholesterol among the plasma lipoproteins was studied in 2-week old male chickens. Very-low-, intermediate-, low- and high-density lipoproteins (VLDL, IDL, LDL and HDL) were separated from plasma by density gradient ultracentrifugation in order to determine their concentration and chemical composition. VLDL were furthermore characterized as concerned their size, mobility and protein content. The lipoprotein profile was quantitatively and qualitatively normal in the control group (n = 6) fed the diet without cholesterol, HDL representing the major lipoprotein class (5.06 +/- 0.36 g/l) and the main carrier of cholesterol. Birds fed the cholesterol containing diets for 5 weeks (n = 6) exhibited a dramatic hypercholesterolemia (1.60 +/- 0.89 g/l free cholesterol and 6.70 +/- 3.22 g/l cholesteryl esters) and a shift in their lipoprotein pattern, with an accumulation of beta-VLDL (6.08 +/- 4.21 g/l) and a marked decrease in HDL level (3.53 +/- 0.91 g/l). The decrease or absence of LDL was balanced by a considerable amount of beta-VLDL remnants (namely IDL), so that the concentration of IDL + LDL considered as a whole was not modified significantly (2.10 +/- 0.95 g/l compared to 1.66 +/- 1.13 g/l in controls). Chicken beta-VLDL, smaller in size (31.0 nm) than control VLDL (33.5 nm), were typically enriched in cholesterol (67%) but they lacked apoE. About 60% of plasma cholesterol was associated with beta-VLDL which therefore represented the main atherogenic lipoprotein class and were probably responsible for the greater amount of cholesterol found in the aorta in these chickens (2.44 +/- 0.99 mg/g aorta vs. 1.32 +/- 0.57 in controls). Since LDL were very reduced or absent, the cholesterol-fed chicken provides a suitable model in which to study the role of beta-VLDL in atherogenesis.