Hereditary Postprandial Hypertriglyceridemic Rabbit Exhibits Insulin Resistance and Central Obesity

Cholesterol dynamics in rabbit liver: High-fat diet, olive oil, and synergistic dietary effects

BACKGROUND & AIMS

Lipid metabolism disorders contribute to a range of human diseases, including liver-related pathologies. Rabbits, highly sensitive to dietary cholesterol, provide a model for understanding the development of liver disorders. Sterol regulatory element-binding protein isoform 2 (SREBP2) crucially regulates intracellular cholesterol pathways. Extra-virgin olive oil (EVOO) has shown reducing cholesterol levels and restoring liver parameters affected by HFD. The aim was to investigate the molecular impact of an HFD and supplemented with EVOO on rabbit liver cholesterol metabolism.

APPROACH & RESULTS

Male rabbits were assigned to dietary cohorts, including control, acute/chronic HFD, sequential HFD with EVOO, and EVOO. Parameters such as serum lipid profiles, hepatic enzymes, body weight, and molecular analyses. After 6 months of HFD, plasma and hepatic cholesterol increased with decreased SREBP2 and 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGCR) expression. Prolonged HFD increased cholesterol levels, upregulating SREBP2 mRNA and HMGCR protein. Combining this with EVOO lowered cholesterol, increased SREBP2 mRNA, and upregulated low-density lipoprotein receptor (LDLR) expression. HFD-induced metabolic dysfunction-associated fatty liver disease was mitigated by EVOO. In conclusion, the SREBP2 system responds to dietary changes.

CONCLUSIONS

In rabbits, the SREBP2 system responds to dietary changes. Acute HFD hinders cholesterol synthesis, while prolonged HFD disrupts regulation, causing SREBP2 upregulation. EVOO intake prompts LDLR upregulation, potentially enhancing cholesterol clearance and restoring hepatic alterations.

A Simple Telemetry Sensor System for Monitoring Body Temperature in Rabbits-A Brief Report

Continuous body temperature measurement is an important means of studying inflammation and metabolic changes using experimental animals. Although expensive telemetry equipment for collecting multiple parameters is available for small animals, readily used devices for mediate- or large-sized animals are rather limited. In this study, we developed a new telemetry sensor system that can continuously monitor rabbit body temperature. The telemetry sensor was easily implanted subcutaneously in rabbits housed in the animal facility while temperature changes were continuously recorded by a personal computer. Temperature data obtained by the telemetry was consistent with the rectal temperature measured by a digital device. Analysis of body temperature changes of unstrained rabbits, either under the normal condition or fever induced by endotoxin confirms the reliability and usefulness of this system.

Long-term changes in the diurnal temporal regulation and set points of metabolic parameters associated with chronic maternal overnutrition in rabbits

Metabolic syndrome (MS) and obesity have become a worldwide epidemic with an alarming prevalence in women of reproductive age. Maternal metabolic condition is considered a risk factor for adverse birth outcomes and long-term MS. In this study, we developed a rabbit model of maternal overnutrition via the chronic intake of a high-fat and carbohydrate diet (HFCD), and we determined the effects of this diet on maternal metabolism and offspring metabolic set points and temporal metabolic regulation in adult life. Before and during pregnancy, the female rabbits that consumed the HFCD exhibited significant changes in body weight, serum levels of analytes associated with carbohydrate and lipid metabolism, levels of liver and kidney damage markers, and liver histology. Our data suggest that rabbits are a valuable model for studying the development of MS associated with the chronic intake of unbalanced diets and fetal metabolic programming. Furthermore, the offspring of overnourished dams exhibited considerable changes in 24-h serum metabolite profiles in adulthood, with notable sexual dimorphism. These data suggest that maternal nutritional conditions due to the chronic intake of an HFCD adversely impact key elements related to the development of circadian rhythmicity in offspring.NEW & NOTEWORTHY Maternal overnutrition previous and during pregnancy leads to long-term changes in the 24-h regulation and setpoint of metabolic profiles of the offspring.

Goji Berry (Lycium barbarum) Supplementation during Pregnancy Influences Insulin Sensitivity in Rabbit Does but Not in Their Offspring

This study investigated the effects of Goji berry (Lycium barbarum) dietary supplementation during pregnancy on insulin sensitivity of rabbit does and their offspring. Starting from two months before the artificial insemination, 75 New Zealand White does were fed only commercial standard diet (C) or supplemented with 1% (G1) and 3% (G3) of Goji berries. Their offspring received a standard diet but kept the nomenclature of the mother’s group. Fasting and intravenous glucose tolerance test-derived indices were estimated at 21 days of pregnancy on rabbit does and at 90 days of age on the offspring. No difference was found in the fasting indices, while the diet modulated the response to glucose load of rabbit does. In particular, G3 group had the lowest glucose concentrations 5 min after the bolus administration (p < 0.05) and, as a result, differed in the parameters calculated during the elimination phase such as the elimination rate constant (Kel), the half-life of the exogenous glucose load (t1/2), and apparent volume of distribution (Vd; for all, p < 0.05). The high dose of Goji supplementation could thus enhance the first-phase glucose-induced insulin secretion. Findings on the offspring were inconsistent and therefore a long-term effect of Goji supplementation during pregnancy could not be demonstrated. Further study on the effect of Goji on the secretory pathway of insulin could clarify its hypoglycaemic action, while different protocols are needed to investigate its potential effects on foetal programming.

Comprehensive functional core microbiome comparison in genetically obese and lean hosts under the same environment

Our study provides an exhaustive comparison of the microbiome core functionalities (captured by 3,936 microbial gene abundances) between hosts with divergent genotypes for intramuscular lipid deposition. After 10 generations of divergent selection for intramuscular fat in rabbits and 4.14 phenotypic standard deviations (SD) of selection response, we applied a combination of compositional and multivariate statistical techniques to identify 122 cecum microbial genes with differential abundances between the lines (ranging from -0.75 to +0.73 SD). This work elucidates that microbial biosynthesis lipopolysaccharides, peptidoglycans, lipoproteins, mucin components, and NADH reductases, amongst others, are influenced by the host genetic determination for lipid accretion in muscle. We also differentiated between host-genetically influenced microbial mechanisms regulating lipid deposition in body or intramuscular reservoirs, with only 28 out of 122 MGs commonly contributing to both. Importantly, the results of this study are of relevant interest for the efficient development of strategies fighting obesity.

Genetically Modified Rabbits for Cardiovascular Research

Rabbits are one of the most used experimental animals for investigating the mechanisms of human cardiovascular disease and lipid metabolism because they are phylogenetically closer to human than rodents (mice and rats). Cholesterol-fed wild-type rabbits were first used to study human atherosclerosis more than 100 years ago and are still playing an important role in cardiovascular research. Furthermore, transgenic rabbits generated by pronuclear microinjection provided another means to investigate many gene functions associated with human disease. Because of the lack of both rabbit embryonic stem cells and the genome information, for a long time, it has been a dream for scientists to obtain knockout rabbits generated by homologous recombination-based genomic manipulation as in mice. This obstacle has greatly hampered using genetically modified rabbits to disclose the molecular mechanisms of many human diseases. The advent of genome editing technologies has dramatically extended the applications of experimental animals including rabbits. In this review, we will update genetically modified rabbits, including transgenic, knock-out, and knock-in rabbits during the past decades regarding their use in cardiovascular research and point out the perspectives in future.

Determining the glycaemic responses of foods: conventional and emerging approaches

A low-glycaemic diet is crucial for those with diabetes and cardiovascular diseases. Information on the glycaemic index (GI) of different ingredients can help in designing novel food products for such target groups. This is because of the intricate dependency of material source, composition, food structure and processing conditions, among other factors, on the glycaemic responses. Different approaches have been used to predict the GI of foods, and certain discrepancies exist because of factors such as inter-individual variation among human subjects. Besides other aspects, it is important to understand the mechanism of food digestion because an approach to predict GI must essentially mimic the complex processes in the human gastrointestinal tract. The focus of this work is to review the advances in various approaches for predicting the glycaemic responses to foods. This has been carried out by detailing conventional approaches, their merits and limitations, and the need to focus on emerging approaches. Given that no single approach can be generalised to all applications, the review emphasises the scope of deriving insights for improvements in methodologies. Reviewing the conventional and emerging approaches for the determination of GI in foods, this detailed work is intended to serve as a state-of-the-art resource for nutritionists who work on developing low-GI foods.

Effects of a single-bolus bupivacaine injection into the coccygeal spinal canal of rabbits

It has been reported that drugs intended for epidural administration through the lumbosacral junction are accidentally administered into the subarachnoid space frequently in rabbits. Therefore, we evaluated the epidural single-bolus injection technique for the administration of bupivacaine into the coccygeal spinal canal of rabbits. After epidural distribution was confirmed by the injection of iohexol into the coccygeal spinal canal, 0.3 ml/kg 0.5% bupivacaine or 0.3 ml/kg normal saline was injected via the same needle. After the first attempt of iohexol injection, although the contrast was found in the epidural space in all rabbits, the additional contrast was also found in blood vessel in 3 rabbits and in muscular layer in 1 rabbit. Subarachnoid distribution was not observed in any of the rabbits. The time taken to regain normal anal reflex, movement of the hind limbs during walking, conscious proprioception of the hind limbs, and pain sensation of the tail and left hind limb, following coccygeal spinal canal injection, were significantly longer in the bupivacaine group than in the normal saline group. These findings indicated that coccygeal epidural injection of bupivacaine in rabbits may provide anesthesia for the hind limbs, perineum, and tail, but inadvertent vascular entry of the epidural drug may occur.

Hyperlipidaemia and cardioprotection: Animal models for translational studies

Hyperlipidaemia is a well-established risk factor for cardiovascular diseases and therefore, many animal model have been developed to mimic the human abnormal elevation of blood lipid levels. In parallel, extensive research for the alleviation of ischaemia/reperfusion injury has revealed that hyperlipidaemia is a major co-morbidity that attenuates the cardioprotective effect of conditioning strategies (preconditioning, postconditioning and remote conditioning) and that of pharmacological interventions by interfering with cardioprotective signalling pathways. In the present review article, we summarize the existing data on animal models of hypercholesterolaemia (total, low density and HDL abnormalities) and hypertriglyceridaemia used in ischaemia/reperfusion injury and protection from it. We also provide recommendations on preclinical animal models to be used for translations of the cardioprotective strategies into clinical practice. LINKED ARTICLES: This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.23/issuetoc.

Hypertriglyceridemia and Atherosclerosis: Using Human Research to Guide Mechanistic Studies in Animal Models

Human studies support a strong association between hypertriglyceridemia and atherosclerotic cardiovascular disease (CVD). However, whether a causal relationship exists between hypertriglyceridemia and increased CVD risk is still unclear. One plausible explanation for the difficulty establishing a clear causal role for hypertriglyceridemia in CVD risk is that lipolysis products of triglyceride-rich lipoproteins (TRLs), rather than the TRLs themselves, are the likely mediators of increased CVD risk. This hypothesis is supported by studies of rare mutations in humans resulting in impaired clearance of such lipolysis products (remnant lipoprotein particles; RLPs). Several animal models of hypertriglyceridemia support this hypothesis and have provided additional mechanistic understanding. Mice deficient in lipoprotein lipase (LPL), the major vascular enzyme responsible for TRL lipolysis and generation of RLPs, or its endothelial anchor GPIHBP1, are severely hypertriglyceridemic but develop only minimal atherosclerosis as compared with animal models deficient in apolipoprotein (APO) E, which is required to clear TRLs and RLPs. Likewise, animal models convincingly show that increased clearance of TRLs and RLPs by LPL activation (achieved by inhibition of APOC3, ANGPTL3, or ANGPTL4 action, or increased APOA5) results in protection from atherosclerosis. Mechanistic studies suggest that RLPs are more atherogenic than large TRLs because they more readily enter the artery wall, and because they are enriched in cholesterol relative to triglycerides, which promotes pro-atherogenic effects in lesional cells. Other mechanistic studies show that hepatic receptors (LDLR and LRP1) and APOE are critical for RLP clearance. Thus, studies in animal models have provided additional mechanistic insight and generally agree with the hypothesis that RLPs derived from TRLs are highly atherogenic whereas hypertriglyceridemia due to accumulation of very large TRLs in plasma is not markedly atherogenic in the absence of TRL lipolysis products.

Effect of fish oil supplementation and restricted feeding on body fat distribution and blood lipid profile in a rabbit model of castration-induced obesity

This study investigates the effect of fish oil supplementation and restricted feeding on body fat distribution and blood lipid profile in experimentally induced obesity in rabbits. The trial was carried out with 30 male rabbits, divided into 5 groups of 6 animals each (NC - non-castrated, non-treated, full-diet fed; C100 - castrated, non-treated, full-diet fed; FO100 - castrated, treated with fish oil, full-diet fed; C50 - castrated, non-treated, 50% restricted fed; FO50 - castrated, treated with fish oil, 50% restricted fed). At the end of the experiment, plasma lipids measurement and quantification of fat distribution was performed. The results of this study indicate that fish oil supplementation reduces obesity-associated abnormalities in lipid profile (high-density lipoprotein cholesterol to low-density lipoprotein cholesterol ratio and non-esterified fatty acids) and in body fat distribution in full-diet fed rabbits. Restricted feeding (C50) alone and the combination of restricted feeding and fish oil supplementation (FO50) in particular, has a detrimental effect on the lipid profile despite the marked reduction in intra-abdominal fat.

An Experimental Model of Diet-Induced Metabolic Syndrome in Rabbit: Methodological Considerations, Development, and Assessment

In recent years, obesity and metabolic syndrome (MetS) have become a growing problem for public health and clinical practice, given their increased prevalence due to the rise of sedentary lifestyles and unhealthy eating habits. Thanks to animal models, basic research can investigate the mechanisms underlying pathological processes such as MetS. Here, we describe the methods used to develop an experimental rabbit model of diet-induced MetS and its assessment. After a period of acclimation, animals are fed a high-fat (10% hydrogenated coconut oil and 5% lard), high-sucrose (15% sucrose dissolved in water) diet for 28 weeks. During this period, several experimental procedures were performed to evaluate the different components of MetS: morphological and blood pressure measurements, glucose tolerance determination, and the analysis of several plasma markers. At the end of the experimental period, animals developed central obesity, mild hypertension, pre-diabetes, and dyslipidemia with low HDL, high LDL, and an increase of triglyceride (TG) levels, thus reproducing the main components of human MetS. This chronic model allows new perspectives for understanding the underlying mechanisms in the progression of the disease, the detection of preclinical and clinical markers that allow the identification of patients at risk, or even the testing of new therapeutic approaches for the treatment of this complex pathology.

Metabolic syndrome-associated sperm alterations in an experimental rabbit model: relation with metabolic profile, testis and epididymis gene expression and effect of tamoxifen treatment

The influence of metabolic syndrome (MetS) on sperm quality and function is debated. Using a well-established high fat diet (HFD) rabbit model resembling human MetS, including development of hypogonadism, we demonstrate that HFD decreased sperm motility, morphology and acrosome reaction in response to progesterone and increased sperm cholesterol content. All the above parameters were associated with most MetS features, its severity and plasma testosterone (T) at univariate analysis. After T adjustment, sperm morphology and motility retained a significant association, respectively, with mean arterial pressure and circulating cholesterol levels. MetS modified the expression of inflammatory and tissue remodelling genes in the testis and of aquaporins in the epididymis. In a multivariate analysis, sperm morphology resulted associated with testis expression of fibronectin and collagen type 1 genes, whereas motility with epididymis aquaporin 1 gene. Administration of tamoxifen, used in the treatment of idiopathic male infertility, to HFD rabbits partially restored motility, but further decreased morphology and increased spontaneous acrosome reaction, without restoring responsiveness to progesterone. Overall our results indicate that development of MetS produces detrimental effects on sperm quality and functionality by inducing metabolic disorders leading to alterations in testis and epididymis functions and evidence a role of hypertension as a new determinant of abnormal sperm morphology, in line with a previous human study from our group.

Effect of fish and krill oil supplementation on glucose tolerance in rabbits with experimentally induced obesity

PURPOSE

This study was conducted to investigate the effect of fish oil (FO) and krill oil (KO) supplementation on glucose tolerance in obese New Zealand white rabbits.

METHODS

The experiments were carried out with 24 male rabbits randomly divided into four groups: KO-castrated, treated with KO; FO-castrated, treated with FO; C-castrated, non-treated; NC-non-castrated, non-treated. At the end of treatment period (2 months), an intravenous glucose tolerance test (IVGTT) was performed in all rabbits.

RESULTS

Fasting blood glucose concentrations in FO and KO animals were significantly lower than in group C. The blood glucose concentrations in FO- and KO-treated animals returned to initial values after 30 and 60 min of IVGTT, respectively. In liver, carnitine palmitoyltransferase 2 (Cpt2) and 3-hydroxy-3-methyl-glutaryl-CoA synthase 2 (Hmgcs2) genes were significantly increased in FO-fed rabbits compared with the C group. Acetyl-CoA carboxylase alpha (Acaca) expression was significantly reduced in both KO- and FO-fed rabbits. In skeletal muscle, Hmgcs2 and Cd36 were significantly higher in KO-fed rabbits compared with the C group. Acaca expression was significantly lower in KO- and FO-fed rabbits compared with the C group.

CONCLUSION

The present results indicate that FO and KO supplementation decreases fasting blood glucose and improves glucose tolerance in obese New Zealand white rabbits. This could be ascribed to the ameliorated insulin sensitivity and insulin secretion and modified gene expressions of some key enzymes involved in β-oxidation and lipogenesis in liver and skeletal muscle.

The role of hypertriglyceridemia in the development of atherosclerosis and endothelial dysfunction

A hereditary postprandial hypertriglyceridemic rabbit (PHT rabbit) is a new dyslipidemic model showing remarkably high plasma triglycerides with only limited elevation of plasma total cholesterol. In PHT rabbits, plasma triglyceride was markedly elevated postprandially compared with healthy Japanese white (JW) rabbits. In physiological experiments, the ring preparation of the thoracic aorta was suspended in an organ bath filled with modified Krebs-Henseleit solution, and the developed tension was recorded. Endothelial function was evaluated by acetylcholine-induced vasorelaxation in each preparation with intact endothelium. The acetylcholine-induced endothelium-dependent relaxation was diminished in PHT compared with JW rabbits, suggesting endothelial dysfunction in PHT rabbits. Histological examination was carried out in adipose tissue, liver and aorta. They were fixed in formaldehyde and embedded in paraffin. The tissues were sliced (4 μm) and stained using hematoxylin-eosin solution. In the adipose tissue, the visceral fat accumulated, and the size of adipose cells was enlarged in PHT rabbits. The liver of the PHT rabbit was fatty and degenerated. In aorta, increased intimal thickness was observed, suggesting the progression of atherosclerosis in the PHT rabbit. This study suggests the important role of postprandial hypertriglyceridemia in atherosclerosis. By using PHT rabbits, the effects of hypertriglyceridemia on health and diseases could be evaluated precisely.

Upregulation of fatty acid synthesis and the suppression of hepatic triglyceride lipase as a direct cause of hereditary postprandial hypertriglyceridemia in rabbits

Rabbits with hereditary postprandial hypertriglyceridemia exhibit central obesity and are regarded as a reliable model for metabolic syndrome. This study was performed to gain insight into the affected process of lipid metabolism and into the causative genes of the postprandial hypertriglyceridemia rabbits. Eleven genes that play key roles in lipid metabolism were selected, their mRNA levels were assessed by quantitative PCR, and their expressions were compared among postprandial hypertriglyceridemia rabbits using Japanese white rabbits as the control. Two genes appeared to be in causal connection with postprandial hypertriglyceridemia, and these were regarded as likely candidates for the pathogenesis. One was the fatty acid synthase gene, which had an expression constitutively higher in postprandial hypertriglyceridemia rabbits than in Japanese white rabbits during the fasting state and reached quite high levels after feeding. The other was the gene for hepatic triglyceride lipase with an expression that was approximately one order lower than that found in the Japanese white rabbits. The low plasma hepatic triglyceride lipase activities were consistent with the low levels of the transcript in the livers of the postprandial hypertriglyceridemia rabbits. Thus, elevated fatty acid synthesis and defected lipid hydrolysis together would cause the postprandial hypertriglyceridemia in postprandial hypertriglyceridemia rabbits.

Hypoglycemic and hypolipidemic potential of a high fiber diet in healthy versus diabetic rabbits

The aim of this study was to investigate potential hypoglycaemic and hypolipidemic effects of Plantago ovata husk included in the diet, in healthy and diabetic rabbits. We also examined the effects of this fiber in other biochemical parameters. Two groups of 18 rabbits were used. The first group was fed with standard chow and the second with chow supplemented with Plantago ovata husk (3.5 mg/kg/day). On day 14 diabetes mellitus was induced by the intravenous administration of alloxan (80 mg/kg). After an oral glucose load (3 g), glucose, insulin, and other biochemical parameters were determined on day 14 (healthy rabbits) and on day 28 (diabetic rabbits). In healthy rabbits, fiber did not modify glucose or insulin levels but decreased significantly total cholesterol, LDL-cholesterol, atherogenic index, and glycosylated hemoglobin. In diabetic rabbits, fiber was more beneficial in mild diabetics than in severe diabetics with significant decreases in glucose levels and increases in insulin concentrations. In these animals fiber caused an important reduction in cholesterol, indicating a beneficial effect of Plantago ovata husk in diabetic rabbits. Although further studies in patients are necessary, we think that Plantago ovata husk offers interesting perspectives to be administered to patients with diabetes mellitus.

Effects of a skullcap root supplement on haematology, serum parameters and antioxidant enzymes in rabbits on a high-cholesterol diet

We studied the effects of Scutellaria baicalensis root on blood parameters and antioxidant enzyme activities in rabbits fed a high-cholesterol diet. Thirty-two New Zealand White rabbits were divided into four groups of eight animals each. They were fed a standard diet (C group), a diet with a 1% pure cholesterol supplement (CH group), a diet with a 1% pure cholesterol supplement and a 9% skullcap root supplement (CH+SR group), or a diet with a 9% skullcap root supplement (SR group). After 6 weeks, the rabbits fed the high-cholesterol diet had significantly decreased RBC and Hb levels and significantly increased MCV, MCH and Fe levels (p≤ 0.05). The skullcap root supplement had no adverse effects on the haematological parameters. The values for RBC, Hb, HCT, MCV, MCH and MCHC were similar in the skullcap root-treated and control rabbits. We also observed a remarkable elevation in the serum TC, LDL and TG levels at the end of the 6-week period. The rabbits fed the cholesterol diet showed decreased activity of the erythrocyte GSH-Px compared with the rabbits fed the basal diet. The GSH-Px activity was significantly higher in the rabbits fed the CH+SR diet than in those on the CH diet. The erythrocyte SOD activity was also significantly decreased in the rabbits on the CH diet. However, the CH+SR group rabbits showed significantly enhanced erythrocyte SOD activity. The SOD level in the CH+SR rabbits was 34.91 U/ml, which was a 23% increase (p≤ 0.05) in relation to the results for the CH group and only 15% diminished in relation to the control group. These results suggest that the dietary supplementation of skullcap root may improve rabbit antioxidant systems and protect against the risks from a high-cholesterol diet.

Contribution of animal models to the understanding of the metabolic syndrome: a systematic overview

The metabolic syndrome (MetS) is one of the most important challenges to public health and biomedical research. Animal models of MetS, such as leptin-deficient obese mice, obese spontaneously hypertensive rats, JCR: LA-cp rats and the Ossabaw and Göttingen minipigs, have contributed to our understanding of the pathophysiological basis and the development of novel therapies. For a complex disease syndrome, no animal model can be expected to serve all needs of research. Although each animal model has limitations and strengths, used together in a complementary fashion, they are essential for research on the MetS and for rapid progress in understanding the aetiology and pathogenesis towards a cure. The purpose of this review is to assess how current animal models contributed to our knowledge of the human MetS, and to systematically evaluate the strengths and weaknesses of the currently available 78 animal models from 11 species.

Hypercholesterolemia impaired sperm functionality in rabbits

Hypercholesterolemia represents a high risk factor for frequent diseases and it has also been associated with poor semen quality that may lead to male infertility. The aim of this study was to analyze semen and sperm function in diet-induced hypercholesterolemic rabbits. Twelve adult White New Zealand male rabbits were fed ad libitum a control diet or a diet supplemented with 0.05% cholesterol. Rabbits under cholesterol-enriched diet significantly increased total cholesterol level in the serum. Semen examination revealed a significant reduction in semen volume and sperm motility in hypercholesterolemic rabbits (HCR). Sperm cell morphology was seriously affected, displaying primarily a "folded head"-head fold along the major axe-, and the presence of cytoplasmic droplet on sperm flagellum. Cholesterol was particularly increased in acrosomal region when detected by filipin probe. The rise in cholesterol concentration in sperm cells was determined quantitatively by Gas chromatographic-mass spectrometric analyses. We also found a reduction of protein tyrosine phosphorylation in sperm incubated under capacitating conditions from HCR. Interestingly, the addition of Protein Kinase A pathway activators -dibutyryl-cyclic AMP and iso-butylmethylxanthine- to the medium restored sperm capacitation. Finally, it was also reported a significant decrease in the percentage of reacted sperm in the presence of progesterone. In conclusion, our data showed that diet-induced hypercholesterolemia adversely affects semen quality and sperm motility, capacitation and acrosomal reaction in rabbits; probably due to an increase in cellular cholesterol content that alters membrane related events.

Effects of castration-induced visceral obesity and antioxidant treatment on lipid profile and insulin sensitivity in New Zealand white rabbits

Molecular mechanisms, responsible for the impaired insulin-sensitivity state due to the obesity are not fully understood in both humans and animals. The purpose of this study was to investigate the effects of castration-induced visceral obesity and the influence of two antioxidants on constituents of blood lipid profile and insulin sensitivity in New Zealand white rabbits. Twenty-six clinically healthy male New Zealand white rabbits were used in the experiment and were divided into 3 groups: first group (CI, n=7) - castrated-obese and treated with antioxidants "Immunoprotect" for 2months; second group (CO, n=7) - castrated-obese; third group (NC, n=12) - control group (non-castrated, non-obese). At the end of the follow-up period of 2months after castration an intravenous glucose tolerance test (IVGTT) was performed after a 12-h fasting period as the blood samples for determination of glucose and insulin and their kinetic parameters were obtained at 5 and 0min before and at 5, 10, 30, 60 and 120min after the infusion of the glucose. The constituents of lipid profile, triglycerides (TG), total cholesterol (TC) and HDL-cholesterol (HDL-C) were also assessed in the overnight fasting blood samples. The body weight (BW), body mass index (BMI), amount of the visceral fat (VF) and VF/BW ratio were both measured and calculated before the IVGTT and at the end of the experimental period. All measured markers of obesity (BW, BMI, VF, VF/BW) were significantly higher in both groups of castrated rabbits than in the control group. Apart HDL-C, the plasma concentrations of all constituents of lipid profile (TG, TC, HDL-C) were the highest in CO group. There were generally no differences between CI and NC groups for the same traits. After glucose injection blood glucose concentrations and glucose and insulin kinetic parameters were considerably higher (except of glucose elimination rate) in CO rabbits than in NC ones. Castrated rabbits treated with "Immunoprotect" showed lower fasting plasma insulin and improved glucose kinetics dynamics than CO rabbits, but commensurable values of glucose and insulin kinetics parameters than NC group. The results of the current study clearly indicated that castration-induced visceral obesity affected negatively the lipid profile and insulin sensitivity and/or responsiveness. Treatment with antioxidant supplementation, consisted of d-limonene and vitamin E, improved blood lipid profile, fatty liver, glucose homeostasis and insulin sensitivity in obese rabbits. In addition, based on our results we may suggest that castrated male New Zealand white rabbits might be considered as an appropriate animal model to study various metabolic abnormalities related to visceral obesity, such as dyslipidemia and impaired insulin sensitivity.

Kinetic analysis of apolipoproteins in postprandial hypertriglyceridaemia rabbits

The postprandial hypertriglyceridaemia (PHT) rabbit, developed as a new animal model of metabolic syndrome, is characterized by PHT, central obesity and glucose intolerance. For detailed investigation of lipid metabolism characteristics in PHT rabbit, the plasma levels of apolipoproteins A-I, B, C-II, C-III and E were measured. Movements of apolipoproteins B100 and B48 were investigated using sodium dodecyl sulphate-polyacrylamide gel electrophoresis to determine whether postprandially increased triglyceride is exogenous or endogenous. The level of apolipoproteins A-I, B, C-II and E were increased in PHT rabbit after feeding. Apolipoproteins B100 and B48 were detected in the plasma fraction of d < 1.006 g/mL of the PHT rabbit. The postprandial increase in apolipoprotein B in the PHT rabbit reflects a numerical increase in lipoprotein particles in the blood; the increase in apolipoproteins C-II and E suggests some disturbance in lipoprotein catabolism. Apolipoprotein B48 was detected postprandially in PHT rabbits. These results suggest that delayed catabolism of exogenous lipids caused the retention of chylomicron remnants in the blood. Results also suggest that activities of the lipolytic enzyme lipoprotein lipase and hepatic triglyceride lipase were deficient and that the hepatic uptake of exogenous lipoproteins was delayed in the PHT rabbit. Especially, for examining remnant hyperlipoproteinaemia in humans, PHT rabbit is an excellent animal model for hypertriglyceridaemia research.

Evaluation of a gel-permeation high-performance liquid chromatography for determining triglyceride levels in serum major lipoproteins, compared with the ultracentrifugation/precipitation method

OBJECTIVES

To evaluate the gel permeation high-performance liquid chromatography (GP-HPLC) method for determination of triglyceride (TG) levels in low-density lipoprotein (LDL) and high-density lipoprotein (HDL).

DESIGN AND METHODS

The GP-HPLC and the ultracentrifugation (UC)/precipitation methods were used and compared.

RESULTS

There was no significant difference in measured levels of LDL-triglyceride between the two methods, but the HDL-triglyceride levels measured by the GP-HPLC technique were significantly higher than the UC/precipitation one (145+/-47 mg/L and 121+/-45 mg/L respectively, n=38, p<0.0001).

CONCLUSIONS

A GP-HPLC technique provides LDL-TG levels comparable to those obtained by the UC/precipitation method.

The effects of rosiglitazone on aortic atherosclerosis of cholesterol-fed rabbits

INTRODUCTION

Thiazolidinedione (TZD) is widely used a drug for the treatment of type 2 diabetes and protects against cardiovascular events in human. However, it is not clear whether TZD can directly inhibit the progression of atherosclerosis. To test the hypothesis whether administration of TZD could reduce the development of atherosclerosis, we studied the effects of rosiglitazone on aortic atherosclerosis of rabbits fed a cholesterol diet.

MATERIALS AND METHODS

Male Japanese White rabbits were fed a diet containing either 0.3% cholesterol diet (control group, n=10) or 0.3% cholesterol with rosiglitazone (TZD-treated group, n=12) for 16 weeks. We compared the plasma lipids and the extent of aortic atherosclerosis between two groups.

RESULTS AND CONCLUSIONS

TZD treatment significantly resulted in the reduction of aortic atherosclerosis by 21% in the aortic arch (p<0.01), 20% in the thoracic aorta (p=0.14), and 28% in the abdominal aorta (p=0.25), without affecting the plasma levels of triglycerides, total cholesterol, high-density lipoprotein cholesterol, glucose and insulin. Immunohistochemical staining showed that the cellular components (macrophages and smooth muscle cells) of the lesions of TZD-treated rabbits were unchanged compared to those of control rabbits. In addition, TZD treatment also led to dramatic improvement of fatty liver in cholesterol-fed rabbits. Our results suggest that the activation of PPARgamma can be beneficial for the treatment of atherosclerosis and fatty liver independent upon the improvement of plasma lipids and glucose metabolism.

Diet-induced central obesity and insulin resistance in rabbits

The present study was designed to examine whether rabbits fed a diet containing high fat and sucrose could develop obesity and insulin resistance (IR), the major pathophysiological features of metabolic syndrome. Male Japanese white rabbits were fed either a normal chow diet (control) or high fat and sucrose diet (HFSD) for 36 weeks. Plasma levels of triglycerides (TG), total cholesterol (TC), glucose and insulin were measured. To evaluate glucose metabolism, we performed an intravenous glucose tolerance test. In addition, we compared adipose tissue accumulation in HFSD-fed rabbits with that in normal rabbits. HFSD constantly and significantly led to an increase in body weight of HFSD-fed rabbits, caused by significantly higher visceral adipose tissue accumulation. Although there were no differences in plasma TG, TC, glucose, insulin levels and blood pressure between the two groups, HFSD-fed rabbits showed impaired glucose clearance associated with higher levels of insulin secretion compared to control rabbits. Our results showed that HFSD induced IR and increased adipose accumulation in rabbits, suggesting that HFSD-fed rabbits may become a model for research on human IR and obesity.

Drug discovery in the metabolic syndrome: context and some recent developments

The metabolic syndrome, encompassing the clinically distinct but related areas of dyslipidaemia, insulin resistance, obesity and vascular disease, offers a wide arena for drug discovery. There is substantial and growing unmet medical need, particularly as the worldwide epidemic of obesity continues to develop. There are also many targets and biological mechanisms that can be exploited. However, the context for clinical development is challenging because of the many ways in which the syndrome can be approached. As with most therapeutic areas, preclinical data provide only limited confidence in the potential of a novel target in humans. In this review, the author outlines the context for drug discovery in the metabolic syndrome, the clinical and biological scope and recent developments in preclinical models. Finally, existing examples of drug targets for a range of biological mechanisms are considered, outlining their biology and points relevant to lead identification and optimisation and clinical development.