Atherosclerosis: Comparative Pathogenesis, Lipoprotein Metabolism, and Avian and Exotic Companion Mammal Models

Comparison of Lipoprotein Analysis Using Gel-Permeation High-Performance Liquid Chromatography and a Biochemistry Analyzer in Normolipidemic and Dyslipidemic Quaker Parrots (Myiopsitta monachus)

Lipid accumulation disorders are common in psittacine birds and can be associated with changes in plasma lipoproteins, most notably low-density lipoprotein (LDL) and high-density lipoprotein (HDL). However, lipoprotein analysis by standard laboratory analyzers or an indirect method, such as the Friedewald formula, has not been validated in parrots. A research colony of 12 Quaker parrots (Myiopsitta monachus) were used to compare plasma values from the Roche Cobas c501 biochemistry analyzer for total cholesterol, total triglycerides, LDL, and HDL to gel-permeation high-performance liquid chromatography (GP-HPLC). To increase sample size and broaden the analytical range to include dyslipidemic samples, 2 cross-over studies were performed on a 0.3% cholesterol diet and a 20% fat diet. Agreement between methods was assessed by linear mixed models and Bland and Altman plots. The LDL concentrations calculated by the Friedewald formula and alternative formulas, and the effects of triglycerides on the biases, were also evaluated. Forty-five plasma samples were used. The cholesterol diet induced a marked increase in cholesterol and all lipoproteins, whereas the fat diet did not lead to dyslipidemia. Direct and indirect LDL measurements obtained with the clinical analyzer were not in clinical agreement with GP-HPLC, whereas HDL had acceptable agreement for normotriglyceridemic samples. Hypertriglyceridemic plasma samples were found to interfere with lipoprotein measurements. This study found LDL measured by the Roche Cobas c501 biochemistry analyzer and indirect estimations cannot be recommended in the Quaker parrot, and non-HDL cholesterol should be used instead. Lipoprotein panels obtained from hypertriglyceridemic samples should be interpreted with care.

Blood Lipid Diagnostics in Psittacine Birds

Lipids are the main biomolecular constituents of plasma and occupy a central place in the pathophysiology of several common diseases of parrots. Dyslipidemias frequently occur in psittacine birds in relation to a variety of lipid accumulation disorders and female reproductive disorders. The five main lipid classes in the plasma are sterols, fatty acyls, glycerolipids, glycerophospholipids, and sphingolipids. Most lipids are transported in the blood within lipoproteins. Lipidologic diagnostic tests to characterize dyslipidemias and risk factors of lipid disorders include routine biochemical tests such as cholesterol and triglycerides, lipoprotein testing, and newer comprehensive techniques to assess whole lipid pathways using lipidomics.

The Diverse Roles of 17β-Estradiol in Non-Gonadal Tissues and Its Consequential Impact on Reproduction in Laying and Broiler Breeder Hens

Estradiol-17β (E2) has long been studied as the primary estrogen involved in sexual maturation of hens. Due to the oviparous nature of avian species, ovarian production of E2 has been indicated as the key steroid responsible for activating the formation of the eggshell and internal egg components in hens. This involves the integration and coordination between ovarian follicular development, liver metabolism and bone physiology to produce the follicle, yolk and albumen, and shell, respectively. However, the ability of E2 to be synthesized by non-gonadal tissues such as the skin, heart, muscle, liver, brain, adipose tissue, pancreas, and adrenal glands demonstrates the capability of this hormone to influence a variety of physiological processes. Thus, in this review, we intend to re-establish the role of E2 within these tissues and identify direct and indirect integration between the control of reproduction, metabolism, and bone physiology. Specifically, the sources of E2 and its activity in these tissues via the estrogen receptors (ERα, ERβ, GPR30) is described. This is followed by an update on the role of E2 during sexual differentiation of the embryo and maturation of the hen. We then also consider the implications of the recent discovery of additional E2 elevations during an extended laying cycle. Next, the specific roles of E2 in yolk formation and skeletal development are outlined. Finally, the consequences of altered E2 production in mature hens and the associated disorders are discussed. While these areas of study have been previously independently considered, this comprehensive review intends to highlight the critical roles played by E2 to alter and coordinate physiological processes in preparation for the laying cycle.

HYPERLIPIDEMIA AND XANTHOMATOSIS IN YELLOW-FOOTED ROCK WALLABIES (PETROGALE XANTHOPUS) UNDER MANAGED CARE

Xanthomas are localized lipid deposits in organs with associated granulomatous inflammation. Xanthomatosis is a rare condition in both human and veterinary medicine and is often linked to inherited or acquired dyslipidemias. Three female yellow-footed rock wallabies (Petrogale xanthopus) at a single institution were diagnosed via biopsy with cutaneous xanthomas secondary to hypertriglyceridemia and hypercholesterolemia, and an additional two female yellow-footed rock wallabies were diagnosed with xanthomas at a second institution. All cases presented with cutaneous masses at the haired skin and paw pad junctions of the extremities, and/or mucocutaneous junctions of the face or urogenital tract. The clinically affected individuals were overconditioned or obese, had lipemic serum, and had elevations in blood cholesterol and triglyceride levels. When full lipid panels were performed, inverse high- and low-density lipoprotein fractions were observed. Six other individuals at the first institution had identical husbandry but were of more appropriate body condition, were normolipidemic, and had no xanthomas. One of the affected animals was also concurrently diagnosed with hepatic lipidosis via liver biopsy. Pedigree review and evaluation for underlying endocrine diseases such as hypothyroidism were performed. Because all affected animals were found to be related, a genetic predisposition is possible but requires further investigation. Consideration for the predisposition of some individuals for obesity, hyperlipidemia, and subsequent xanthoma formation should be factored in the husbandry and medical management of this species.

Cardiovascular Diseases in Pet Birds: Therapeutic Options and Challenges

Cardiovascular disease, including congestive heart failure, pericardial disease, and atherosclerosis, is becoming increasingly better recognized in companion birds. A wide range of medications is available to treat these conditions, including diuretics, vasodilators, positive and negative inotropes, antiarrhythmic agents, and pentoxifylline. This review systematically discusses each of these drug classes and their potential applications in avian species. Although treatment approaches remain largely empirical and extrapolated from small animal and human medicine, the management strategies presented here have the potential to both maintain quality of life and extend survival time for the avian cardiac patient.

A Spectral Computed Tomography Contrast Study: Demonstration of the Avian Cardiovascular Anatomy and Function

As part of the cardiovascular examination, all birds underwent clinical and echocardiographic examinations. Radiographs and blood samples were taken. Each bird was premedicated with midazolam and medetomidin and anesthetized with inhalation anesthesia using isoflurane. We performed computed tomographic angiography (CTA) after intravenous injection of 1 to 2 mL contrast agent per kg followed by a 1 mL saline solution flush. We were been able to identify the arteries that previous studies revealed to be most likely affected by atherosclerotic lesions: the aorta, both pulmonary arteries, and both brachiocephalic trunks. CTA was safe and is of potential diagnostic value in birds.

Impact of Dietary Fructose on the Lipid Profile in Six Macaws

Atherosclerosis is frequently diagnosed in captive parrots. Recent studies have highlighted the potential role of high fructose intake in the development of human cardiovascular disease. The objective of this study was to investigate the effects of dietary fructose on the lipid profile in psittacine birds. Six macaws, composed of 3 green-winged macaws (Ara chloropterus, 2 females, 1 male), and 3 blue-and-gold macaws (Ara ararauna, 1 female, 2 males), ranging from 15 to 26 years of age, were used as subject animals for this dietary investigation. Initially, fruits were removed from the diet and replaced with vegetables lower in fructose for a month. Then, with a crossover study design, each bird was randomly selected to receive either 34 kcal of a fructose solution daily for 5 days then an equivalent volume of water for 5 days, or water in the first 5 days followed by the 34 kcal fructose solution. Lipid profiles were repeatedly performed over the course of the study at specific intervals. Serum cholesterol (3.01-5.55 mmol/L), triglycerides (0.27-2.70 mmol/L), high-density lipoprotein-cholesterol (1.43-4.79 mmol/L), low-density lipoprotein-cholesterol (0.02-0.85 mmol/L), and very low density lipoprotein-cholesterol (0.12-1.22 mmol/L) levels were not statistically significantly different over time and treatment. Although no significant effect could be demonstrated in this study, further studies are needed to investigate the effect of a high fructose intake in psittacine birds, because it could have a deleterious influence on their cardiovascular health if proven to be linked with dyslipidemia as reported in humans. Higher amounts of fructose and longer periods of administration should be considered for future studies.

The plasma lipidome of the Quaker parrot (Myiopsitta monachus)

Dyslipidemias and lipid-accumulation disorders are common in captive parrots, in particular in Quaker parrots. Currently available diagnostic tests only measure a fraction of blood lipids and have overall problematic cross-species applicability. Comprehensively analyzing lipids in the plasma of parrots is the first step to better understand their lipid metabolism in health and disease, as well as to explore new lipid biomarkers. The plasma lipidome of 12 Quaker parrots was investigated using UHPLC-MS/MS with both targeted and untargeted methods. Targeted methods on 6 replicates measured 432 lipids comprised of sterol, cholesterol ester, bile acid, fatty acid, acylcarnitine, glycerolipid, glycerophospholipid, and sphingolipid panels. For untargeted lipidomics, precursor ion mass-to-charge ratios were matched to corresponding lipids using the LIPIDMAPS structure database and LipidBlast at the sum composition or acyl species level of information. Sterol lipids and glycerophospholipids constituted the majority of plasma lipids on a molar basis. The most common lipids detected with the targeted methods included free cholesterol, CE(18:2), CE(20:4) for sterol lipids; PC(36:2), PC(34:2), PC(34:1) for glycerophospholipids; TG(52:3), TG(54:4), TG(54:5), TG(52:2) for glycerolipids; SM(d18:1/16:0) for sphingolipids; and palmitic acid for fatty acyls. Over a thousand different lipid species were detected by untargeted lipidomics. Sex differences in the plasma lipidome were observed using heatmaps, principal component analysis, and discriminant analysis. This report presents the first comprehensive database of plasma lipid species in psittacine birds and paves the way for further research into blood lipid diagnostics and the impact of diet, diseases, and drugs on the parrot plasma lipidome.

Lipoprotein characterization in Quaker parrots (Myiopsitta monachus) using gel-permeation high-performance liquid chromatography

BACKGROUND

Lipid accumulation disorders, such as atherosclerosis and hepatic lipidosis, are common in psittacine birds and associated with various dyslipidemias. Gel-permeation high-performance liquid chromatography (GP-HPLC) is a reference method for advanced lipoprotein profiling based on particle size separation, followed by an analysis of lipid contents.

OBJECTIVES

The objectives were to (a) characterize Quaker parrot lipoproteins using a commercial GP-HPLC method (Liposearch panel), and (b) obtain preliminary information on the reliability of the Friedewald formula for low-density lipoprotein-cholesterol (LDL-C) measurements.

METHODS

Plasma samples were collected from 12 fasted healthy Quaker parrots. Cholesterol concentrations, triglyceride concentrations, particle sizes, and particle numbers were determined by GP-HPLC for four classes and 20 sub-fractions of lipoproteins. The LDL-C concentrations obtained using the Friedewald formula and direct measurements were compared with Bland-Altman plots. Alternate formulas were determined using multiple linear regression.

RESULTS

High-density lipoprotein (HDL) was the predominant lipoprotein in Quaker parrots, and most particles were of medium-to-small sizes belonging to two sub-fractions (average size, 10.6 nm). LDL was the second most common lipoprotein and included large-to-small particles belonging to three sub-fractions (average size, 24.9 nm). Very-low-density lipoproteins (VLDL) and portomicrons were present in low concentrations. The Friedewald formula underestimated LDL-C concentrations with a significant bias of 0.44 mmol/L. An alternate formula was proposed: LDL-C = 0.75*Non-HDL-C.

CONCLUSIONS

GP-HPLC allowed unprecedented characterization of plasma lipoproteins in Quaker parrots. Characterizing psittacine lipoprotein is useful for validation and interpretation of routine clinical tests as well as for use in epidemiologic and experimental research on psittacine lipid accumulation disorders.

Unravelling fatty liver haemorrhagic syndrome: 1. Oestrogen and inflammation

Previous studies have implicated oestrogen as a factor in the induction of fatty liver haemorrhagic syndrome (FLHS). In this study, a refined laying hen model was employed to permit further investigations. Intramuscular (i.m.) injections of exogenous oestrogen as β-estradiol-17-dipropionate (E₂) (5 mg/kg BW) were given every 4 days for 20 days to 30-week-old hens fed either ad libitum or with restricted feed intake. Elevated (P < 0.01) plasma oestrogen concentrations produced significant macroscopic and microscopic hepatic alterations. Hens in the E₂-treated ad libitum fed (EAL) group experienced a higher incidence of FLHS than hens in the E₂-treated restricted feed intake group, showing that birds with a higher feed intake are more at risk of developing FLHS. Histological examination of livers revealed that hens in the E₂-treated ad libitum fed group had consistent and severe fat infiltration in the liver, and fat vacuolization within hepatocytes. Fat accumulation and fat droplets were found not only in the cytoplasm of hepatocytes but also in liver sinusoids. White blood cell counts and fibrinogen concentrations were altered (P < 0.01) in hens treated with E₂ when compared with controls. Plasma fibrinogen concentrations were altered over time, and correlated with white blood cell counts (Pearson's correlation r = 0.96; P = 0.001). Hens treated with E₂ had increased (P < 0.01) levels of cholesterol and triglycerides, confirming that E₂ induced hypercholesterolaemia and hypertriglyceridaemia. It was concluded that E₂ successfully induced FLHS in hens, with typical systemic and hepatic events resulting from a disturbance in lipid metabolism and chronic low-grade inflammation.

Feed processing effects on digestibility, palatability, excreta fermentation products and blood parameters in blue-fronted amazon parrots (Amazona aestiva)†

Captive parrots show a high incidence of obesity and other metabolic disorders due to the consumption of unbalanced diets. Therefore, this study evaluated the digestibility and metabolic effects of transitioning blue-fronted amazons from a high fat diet (sunflower seeds) to processed diets with three degrees of starch gelatinization (SG). The same feed formulation was processed to obtain pelletized feed (PEL) at 27.1% SG; low-cooked extruded feed (EXT_L ) at 81.6% SG; and high-cooked extruded feed (EXT_H ) at 98.5% SG. Thirty adult parrots were fed sunflower seeds for 90 days, then were distributed in a completely randomized design with 10 repetitions per treatment, and fed one of the three prepared diets for 160 days. Feed palatability, apparent digestibility, excreta concentrations of volatile fatty acids, lactate and ammonia, initial and final radiographic examinations, blood cell counts and glucose, triglycerides, cholesterol, total protein, albumin, aspartate aminotransferase (AST) and uric acid levels were evaluated. The data were analysed by an analysis of variance and compared by Tukey's test (p < 0.05). Sunflower seed was more digestible than processed feeds (p < 0.05). Diet processing interfered with fat and starch digestibility (p < 0.001), being higher in the PEL than in the EXT_H and EXT_L respectively. Transitioning from sunflower seeds to balanced diets reduced serum glucose, triglycerides, cholesterol and AST (p < 0.05) and increased red blood cell, haemoglobin, lymphocyte, monocyte and leucocyte counts (p < 0.01). Radiographs indicated a decreased hourglass (p = 0.015) and a reduced heart-liver ratio after ingesting the processed feeds (p < 0.05). Feed processing did not affect blood cell counts, serum biochemistry or radiographic examinations. In conclusion, parrots preferred the extruded diet and did not require an extensive SG to properly digest the feed. Consuming the processed diets improved the birds' metabolism and health.

Cardiovascular Drugs in Avian, Small Mammal, and Reptile Medicine

Cardiovascular disease, including congestive heart failure, pericardial disease, and atherosclerosis, is becoming increasingly better recognized in companion birds, small mammals, and reptiles. A wide range of medications is available to treat these conditions, including diuretics, vasodilators, positive and negative inotropes, antiarrhythmic agents, and pentoxifylline. This review systematically discusses each of these drug classes and their potential applications in exotic species. Although treatment approaches remain largely empirical and extrapolated from small animal and human medicine, the management strategies presented here have the potential to both maintain quality of life and extend survival time for the exotic cardiac patient.

Plasma Drug Concentrations of Orally Administered Rosuvastatin in Hispaniolan Amazon Parrots (Amazona ventralis)

Atherosclerotic diseases are common in pet psittacine birds, in particular Amazon parrots. While hypercholesterolemia and dyslipidemia have not definitely been associated with increased susceptibility to atherosclerosis in parrots, these are important and well-known risk factors in humans. Therefore statin drugs such as rosuvastatin constitute the mainstay of human treatment of dyslipidemia and the prevention of atherosclerosis. No pharmacologic studies have been performed in psittacine birds despite the high prevalence of atherosclerosis in captivity. Thirteen Hispaniolan Amazon parrots were used to test a single oral dose of 10 mg/kg of rosuvastatin with blood sampling performed according to a balanced incomplete block design over 36 hours. Because low plasma concentrations were produced in the first study, a subsequent pilot study using a dose of 25 mg/kg in 2 Amazon parrots was performed. Most plasma samples for the 10 mg/kg dose and all samples for the 25 mg/kg dose had rosuvastatin concentration below the limits of quantitation. For the 10 mg/kg study, the median peak plasma concentration and time to peak plasma concentration were 0.032 μg/mL and 2 hours, respectively. Our results indicate that rosuvastatin does not appear suitable in Amazon parrots as compounded and used at the dose in this study. Pharmacodynamic studies investigating lipid-lowering effects of statins rather than pharmacokinetic studies may be more practical and cost effective in future studies to screen for a statin with more ideal properties for potential use in psittacine dyslipidemia and atherosclerotic diseases.

Animal Models in Cardiovascular Research: Hypertension and Atherosclerosis

Hypertension and atherosclerosis are among the most common causes of mortality in both developed and developing countries. Experimental animal models of hypertension and atherosclerosis have become a valuable tool for providing information on etiology, pathophysiology, and complications of the disease and on the efficacy and mechanism of action of various drugs and compounds used in treatment. An animal model has been developed to study hypertension and atherosclerosis for several reasons. Compared to human models, an animal model is easily manageable, as compounding effects of dietary and environmental factors can be controlled. Blood vessels and cardiac tissue samples can be taken for detailed experimental and biomolecular examination. Choice of animal model is often determined by the research aim, as well as financial and technical factors. A thorough understanding of the animal models used and complete analysis must be validated so that the data can be extrapolated to humans. In conclusion, animal models for hypertension and atherosclerosis are invaluable in improving our understanding of cardiovascular disease and developing new pharmacological therapies.