Guinea pigs: a suitable animal model to study lipoprotein metabolism, atherosclerosis and inflammation

Obesity Arrhythmias: Role of IL-6 Trans-Signaling

Obesity is a chronic disease that is rapidly increasing in prevalence and affects more than 600 million adults worldwide, and this figure is estimated to increase by at least double by 2030. In the United States, more than one-third of the adult population is either overweight or obese. The global obesity epidemic is a major risk factor for the development of life-threatening arrhythmias occurring in patients with long QT, particularly in conditions where multiple heart-rate-corrected QT-interval-prolonging mechanisms are simultaneously present. In obesity, excess dietary fat in adipose tissue stimulates the release of immunomodulatory cytokines such as interleukin (IL)-6, leading to a state of chronic inflammation in patients. Over the last decade, increasing evidence has been found to support IL-6 signaling as a powerful predictor of the severity of heart diseases and increased risk for ventricular arrhythmias. IL-6's pro-inflammatory effects are mediated via trans-signaling and may represent a novel arrhythmogenic risk factor in obese hearts. The first selective inhibitor of IL-6 trans-signaling, olamkicept, has shown encouraging results in phase II clinical studies for inflammatory bowel disease. Nevertheless, the connection between IL-6 trans-signaling and obesity-linked ventricular arrhythmias remains unexplored. Therefore, understanding how IL-6 trans-signaling elicits a cellular pro-arrhythmic phenotype and its use as an anti-arrhythmic target in a model of obesity remain unmet clinical needs.

Theabrownin as a Potential Prebiotic Compound Regulates Lipid Metabolism via the Gut Microbiota, Microbiota-Derived Metabolites, and Hepatic FoxO/PPAR Signaling Pathways

The dysregulation of lipid metabolism poses a significant health threat, necessitating immediate dietary intervention. Our previous research unveiled the prebiotic-like properties of theabrownin. This study aimed to further investigate the theabrownin-gut microbiota interactions and their downstream effects on lipid metabolism using integrated physiological, genomic, metabolomic, and transcriptomic approaches. The results demonstrated that theabrownin significantly ameliorated dyslipidemia, hepatic steatosis, and systemic inflammation induced by a high-fat/high-cholesterol diet (HFD). Moreover, theabrownin significantly improved HFD-induced gut microbiota dysbiosis and induced significant alterations in microbiota-derived metabolites. Additionally, the detailed interplay between theabrownin and gut microbiota was revealed. Analysis of hepatic transcriptome indicated that FoxO and PPAR signaling pathways played pivotal roles in response to theabrownin-gut microbiota interactions, primarily through upregulating hepatic Foxo1, Prkaa1, Pck1, Cdkn1a, Bcl6, Klf2, Ppara, and Pparg, while downregulating Ccnb1, Ccnb2, Fabp3, and Plin1. These findings underscored the critical role of gut-liver axis in theabrownin-mediated improvements in lipid metabolism disorders and supported the potential of theabrownin as an effective prebiotic compound for targeted regulation of metabolic diseases.

A Comparison of Three Anesthetic Drug Combinations for Use in Inducing Surgical Anesthesia in Female Guinea Pigs (Cavia porcellus)

Guinea pigs are often used in translational research, but providing them with safe and effective anesthesia is a challenge. Common methods like inhalant anesthesia and injectable ketamine/xylazine induce surgical anesthesia but can negatively affect cardiovascular, respiratory, and thermoregulatory systems and complicate the interpretation of research outcomes. Several alternative anesthetic regimens have been investigated, but none have consistently achieved a surgical plane of anesthesia. Therefore, identifying an anesthetic regimen that achieves a stable state of the surgical plane of anesthesia while preserving cardiorespiratory function would be a valuable contribution. To address this issue, we compared the efficacy of 3 anesthetic combinations in female Dunkin-Hartley guinea pigs: 1) alfaxalone, dexmedetomidine, and fentanyl (ADF); 2) alfaxalone, midazolam, and fentanyl (AMF); and 3) alfaxalone, midazolam, fentanyl, and isoflurane (AMFIso). We monitored anesthetic depth, heart rate, oxygenation, respiratory rate, respiratory effort, blood pressure, and body temperature every 15 min from injection to recovery. We also recorded the time to loss of righting reflex, duration of anesthesia, and time to achieve a surgical plane. The results showed no statistically significant differences in induction and recovery times among the groups. In the AMFIso group, 100% of the animals achieved a surgical plane of anesthesia, whereas only 10% of the animals in the AMF group reached that level. None of the animals in ADF group reached a surgical plane of anesthesia. Respiratory rate was significantly lower in the AMFIso as compared with the ADF group (P < 0.001) but was not different between the AMF and ADF groups. Temperature was significantly lower in the AMFIso group as compared with both the ADF and AMF groups (P < 0.001). In conclusion, both combinations of solely injectable anesthetics assessed in this study can be used for short, nonpainful procedures without significant cardiorespiratory depression. However, for mildly to moderately painful surgical procedures, the addition of an inhalant anesthetic like isoflurane is necessary for female guinea pigs.

Mice, rats, and guinea pigs differ in FMOs expression and tissue concentration of TMAO, a gut bacteria-derived biomarker of cardiovascular and metabolic diseases

INTRODUCTION

Increased plasma trimethylamine oxide (TMAO) is observed in cardiovascular and metabolic diseases, originating from the gut microbiota product, trimethylamine (TMA), via flavin-containing monooxygenases (FMOs)-dependent oxidation. Numerous studies have investigated the association between plasma TMAO and various pathologies, yet limited knowledge exists regarding tissue concentrations of TMAO, TMAO precursors, and interspecies variability.

METHODS

Chromatography coupled with mass spectrometry was employed to evaluate tissue concentrations of TMAO and its precursors in adult male mice, rats, and guinea pigs. FMO mRNA and protein levels were assessed through PCR and Western blot, respectively.

RESULTS

Plasma TMAO levels were similar among the studied species. However, significant differences in tissue concentrations of TMAO were observed between mice, rats, and guinea pigs. The rat renal medulla exhibited the highest TMAO concentration, while the lowest was found in the mouse liver. Mice demonstrated significantly higher plasma TMA concentrations compared to rats and guinea pigs, with the highest TMA concentration found in the mouse renal medulla and the lowest in the rat lungs. FMO5 exhibited the highest expression in mouse liver, while FMO3 was highly expressed in rats. Guinea pigs displayed low expression of FMOs in this tissue.

CONCLUSION

Despite similar plasma TMAO levels, mice, rats, and guinea pigs exhibited significant differences in tissue concentrations of TMA, TMAO, and FMO expression. These interspecies variations should be considered in the design and interpretation of experimental studies. Furthermore, these findings may suggest a diverse importance of the TMAO pathway in the physiology of the evaluated species.

The Molecular Size of Bioengineered Oxygen Carriers Determines Tissue Oxygenation in a Hypercholesterolemia Guinea Pig Model of Hemorrhagic Shock and Resuscitation

Polymerized human hemoglobin (PolyhHb) has shown promise in preclinical hemorrhagic shock settings. Different synthetic and purification schemes can control the size of PolyhHbs, yet research is lacking on the impact of polymerized hemoglobin size on tissue oxygenation following hemorrhage and resuscitation in specialized animal models that challenge their resuscitative capabilities. Pre-existing conditions that compromise the vasculature and end organs, such as the liver, may limit the effectiveness of resuscitation and exacerbate the toxicity of these molecules, which is an important but minimally explored therapeutic dimension. In this study, we compared the effective oxygen delivery of intermediate molecular weight PolyhHb (PolyhHb-B3; 500-750 kDa) to high molecular weight PolyhHb (PolyhHb-B4; 750 kDa-0.2 μm) for resuscitative effectiveness in guinea pig models subjected to hemorrhagic shock. We evaluated how the size of PolyhHb impacts hemodynamics and tissue oxygenation in normal guinea pigs and guinea pigs on an atherogenic diet. We observed that while PolyhHb-B3 and -B4 equivalently restore hemodynamic parameters of normal-dieted guinea pigs, high-fat-dieted guinea pigs resuscitated with PolyhHb-B4 have lower mean arterial pressures, impaired tissue oxygenation, and higher plasma lactate levels than those receiving PolyhHb-B3. We characterized the plasma of these animals following resuscitation and found that despite similar oxygen delivery kinetics, circulating PolyhHb-B3 and -B4 demonstrated a size-dependent increase in the plasma viscosity, consistent with impaired perfusion in the PolyhHb-B4 transfusion group. We conclude that intermediate-sized PolyhHbs (such as -B3) are ideal for further research given the effective resuscitation of hemorrhagic shock based on tissue oxygenation in hypercholesterolemic guinea pigs.

Global-scale GWAS associates a subset of SNPs with animal-adapted variants in M. tuberculosis complex

BACKGROUND

While Mycobacterium tuberculosis complex (MTBC) variants are clonal, variant tuberculosis is a human-adapted pathogen, and variant bovis infects many hosts. Despite nucleotide identity between MTBC variants exceeding 99.95%, it remains unclear what drives these differences. Markers of adaptation into variants were sought by bacterial genome-wide association study of single nucleotide polymorphisms extracted from 6,362 MTBC members from varied hosts and countries.

RESULTS

The search identified 120 genetic loci associated with MTBC variant classification and certain hosts. In many cases, these changes are uniformly fixed in certain variants while absent in others in this dataset, providing good discriminatory power in distinguishing variants by polymorphisms. Multiple changes were seen in genes for cholesterol and fatty acid metabolism, pathways previously proposed to be important for host adaptation, including Mce4F (part of the fundamental cholesterol intake Mce4 pathway), 4 FadD and FadE genes (playing roles in cholesterol and fatty acid utilization), and other targets like Rv3548c and PTPB, genes shown essential for growth on cholesterol by transposon studies.

CONCLUSIONS

These findings provide a robust set of genetic loci associated with the split of variant bovis and variant tuberculosis, and suggest that adaptation to new hosts could involve adjustments in uptake and catabolism of cholesterol and fatty acids, like the proposed specialization to different populations in MTB lineages by alterations to host lipid composition. Future studies are required to elucidate how the associations between cholesterol profiles and pathogen utilization differences between hosts and MTBC variants, as well as the investigation of uncharacterized genes discovered in this study. This information will likely provide an understanding on the diversification of MBO away from humans and specialization towards a broad host range.

Soluble Dietary Fibers as Antihyperlipidemic Agents: A Comprehensive Review to Maximize Their Health Benefits

The number of hypercholesterolemic people is increasing rapidly worldwide, with elevated lipid profiles representing a major risk factor of coronary heart diseases. Dietary intervention was shown to improve the lipid profile, thus enhancing the quality of life. Dietary fiber is a nondigestible form of carbohydrates, due to the lack of the digestive enzyme in humans required to digest fiber, and is classified according to its water solubility properties as either soluble (SDF) or insoluble dietary fiber (IDF). Consumption of SDF is associated with several health benefits such as reduced lipid levels, lower blood pressure, improved blood glucose control, improved immune function, and reduced inflammation. SDF has been shown to lower blood cholesterol by several action mechanisms including directly due to the gelling, mucilaginous, and viscous fiber nature, and indirectly due to its fermented products and modulation of the gut microbiome. This review aims to provide a holistic overview on how SDF impacts the lipid profile. We start by providing an overview of the chemical structure of the major SDFs including mucilage, gums (gum arabic and guar gum), pectin, and inulin.

Experimental models of fatty liver diseases: Status and appraisal

Fatty liver diseases, including alcohol-associated liver disease (ALD) and nonalcoholic fatty liver disease nonalcoholic fatty liver disease (NAFLD), affect a large number of people worldwide and become one of the major causes of end-stage liver disease, such as liver cirrhosis and hepatocellular carcinoma (HCC). Unfortunately, there are currently no approved pharmacological treatments for ALD or NAFLD. This situation highlights the urgent need to explore new intervention targets and discover effective therapeutics for ALD and NAFLD. The lack of properly validated preclinical disease models is a major obstacle to the development of clinical therapies. ALD and NAFLD models have been in the development for decades, but there are still no models that recapitulate the full spectrum of ALD and NAFLD. Throughout this review, we summarize the current in vitro and in vivo models used for research on fatty liver diseases and discuss the advantages and limitations of these models.

Brazilian green propolis extracts modulate cholesterol homeostasis in a preclinical guinea pig model: an in vitro and in vivo study

Green propolis produced by Apis melífera bees, having Baccharis dracunculifolia D.C. (Asteraceae) as the primary botanical source, has been used in traditional medicine to treat numerous disorders. However, studies evaluating propolis' potential in treating cardiovascular diseases via its effects on cholesterol metabolism are lacking. Therefore, this study investigated the effects of green propolis extracts on lipid metabolism in hypercholesterolemic guinea pigs. Chemical characterization of ethanolic extracts of green propolis samples was undertaken using HPLC. The in vitro characterization included an evaluation of the antioxidant capacity of the hydroalcoholic extract of green propolis (DPPH and FRAP assays) and its ability to act as an inhibitor of the HMG-CoA reductase enzyme. In vivo, we investigated the effect of the hydroalcoholic extract of green propolis on lipid metabolism in hypercholesterolemic guinea pigs. Results obtained validated previous reports of significant antioxidant activity. HPLC analysis confirmed that coumaric acid, artepillin C, and baccharin were the most common and abundant compounds in green propolis samples among the studied compounds. Furthermore, the compounds in these extracts acted as effective HMG-CoA reductase inhibitors in vitro. In vivo assays demonstrated that a hypercholesterolemic diet significantly reduced serum levels of the HDL cholesterol fraction. Simvastatin and propolis hydroalcoholic extracts promoted a significant increase in HDL cholesterol, suggesting that these extracts can improve the serum lipid profile of hypercholesterolemic guinea pigs. Results obtained in this study provide a perspective on the possible hypocholesterolemic effect of green propolis, suggesting that it can improve the serum lipid profile in hypercholesterolemic guinea pigs.

Vitamin C Deficiency Exacerbates Dysfunction of Atherosclerotic Coronary Arteries in Guinea Pigs Fed a High-Fat Diet

Vitamin C (vitC) deficiency has been associated with an increased risk of cardiovascular disease; while several putative mechanistic links have been proposed, functional evidence supporting a causal relationship is scarce. In this study, we investigated how vitC deficiency affects coronary artery vasomotor function and the development of coronary atherosclerotic plaques in guinea pigs subjected to chronic dyslipidemia by a high-fat diet regime. Female Hartley guinea pigs were fed either a control (low-fat diet and sufficient vitC) (N = 8) or a high-fat diet with either sufficient (N = 8) or deficient (N = 10) vitC for 32 weeks. Guinea pigs subjected to the high-fat diet developed significant atherosclerotic plaques in their coronary arteries, with no quantitative effect of vitC deficiency. In isolated coronary arteries, vasomotor responses to potassium, carbachol, nitric oxide, or bradykinin were studied in a wire myograph. Carbachol, bradykinin, and nitric oxide mediated relaxation in the coronary arteries of the control group. While vasorelaxation to carbachol and nitric oxide was preserved in the two high-fat diet groups, bradykinin-induced vasorelaxation was abolished. Interestingly, bradykinin induced a significant contraction in coronary arteries from vitC-deficient guinea pigs (p < 0.05). The bradykinin-induced contraction was unaffected by L-NAME but significantly inhibited by both indomethacin and vitC, suggesting that, during vitC deficiency, increased release of arachidonic acid metabolites and vascular oxidative stress are involved in the constrictor effects mediated by bradykinin. In conclusion, the present study shows supporting evidence that poor vitC status negatively affects coronary artery function.

Animal Models of Atherosclerosis-Supportive Notes and Tricks of the Trade

Atherosclerotic cardiovascular disease is a major cause of death among humans. Animal models have shown that cholesterol and inflammation are causatively involved in the disease process. Apolipoprotein B-containing lipoproteins elicit immune reactions and instigate inflammation in the vessel wall. Still, a treatment that is specific to vascular inflammation is lacking, which motivates continued in vivo investigations of the immune-vascular interactions that drive the disease. In this review, we distill old notions with emerging concepts into a contemporary understanding of vascular disease models. Pros and cons of different models are listed and the complex integrative interplay between cholesterol homeostasis, immune activation, and adaptations of the vascular system is discussed. Key limitations with atherosclerosis models are highlighted, and we suggest improvements that could accelerate progress in the field. However, excessively rigid experimental guidelines or limiting usage to certain animal models can be counterproductive. Continued work in improved models, as well as the development of new models, should be of great value in research and could aid the development of cardiovascular disease diagnostics and therapeutics of the future.

Sex-specific alterations in hepatic cholesterol metabolism in low birth weight adult guinea pigs

BACKGROUND

Intrauterine growth restriction and low birth weight (LBW) have been widely reported as an independent risk factor for adult hypercholesterolaemia and increased hepatic cholesterol in a sex-specific manner. However, the specific impact of uteroplacental insufficiency (UPI), a leading cause of LBW in developed world, on hepatic cholesterol metabolism in later life, is ill defined and is clinically relevant in understanding later life liver metabolic health trajectories.

METHODS

Hepatic cholesterol, transcriptome, cholesterol homoeostasis regulatory proteins, and antioxidant markers were studied in UPI-induced LBW and normal birth weight (NBW) male and female guinea pigs at 150 days.

RESULTS

Hepatic free and total cholesterol were increased in LBW versus NBW males. Transcriptome analysis of LBW versus NBW livers revealed that "cholesterol metabolism" was an enriched pathway in LBW males but not in females. Microsomal triglyceride transfer protein and cytochrome P450 7A1 protein, involved in hepatic cholesterol efflux and catabolism, respectively, and catalase activity were decreased in LBW male livers. Superoxide dismutase activity was reduced in LBW males but increased in LBW females.

CONCLUSIONS

UPI environment is associated with a later life programed hepatic cholesterol accumulation via impaired cholesterol elimination in a sex-specific manner. These programmed alterations could underlie later life cholesterol-induced hepatic lipotoxicity in LBW male offspring.

IMPACT

Low birth weight (LBW) is a risk factor for increased hepatic cholesterol. Uteroplacental insufficiency (UPI) resulting in LBW increased hepatic cholesterol content, altered hepatic expression of cholesterol metabolism-related genes in young adult guinea pigs. UPI-induced LBW was also associated with markers of a compromised hepatic cholesterol elimination process and failing antioxidant system in young adult guinea pigs. These changes, at the current age studied, were sex-specific, only being observed in LBW males and not in LBW females. These programmed alterations could lead to further hepatic damage and greater predisposition to liver diseases in UPI-induced LBW male offspring as they age.

Efficacy of Fibroblast Growth Factor 21 in non-alcoholic fatty liver disease in guinea pigs

Fibroblast Growth Factor 21 (FGF21) agonists have shown promising effects in preclinical models of non-alcoholic fatty liver disease (NAFLD) as well as in short-term clinical trials in patients with non-alcoholic steatohepatitis (NASH). Comparing drug formulation, dose, administration route and age, this exploratory study investigated effects of FGF21 on NAFLD-associated measures in a validated guinea pig model. In three separate studies, female guinea pigs received a high-fat diet prior to intervention with escalating doses of either recombinant native human FGF21 or a human FGF21 human recombinant analogue (FGF21/19 chimer) with an extended half-life. While no significant effects of native FGF21 on the investigated endpoints were observed, the long-acting FGF21/19 chimer significantly altered the levels of circulating lipids, increasing plasma concentrations of cholesterol (TC, LDLc and HDLc) in young guinea pigs (p<0.01 for all three parameters). Relative liver weights were reduced in FGF21/19-treated young animals (p<0.05) compared to mature animals, whereas FGF21/19 reduced body weights in both age groups (p<0.001). The FGF21/19 chimer effects on dyslipidemia, body and liver weights particularly in young animals, support an age-associated difference in the FGF21 response. The limited effects of the native human FGF21 highlights potential species-associated differences of this compound.

Research-Relevant Conditions and Pathology of Laboratory Mice, Rats, Gerbils, Guinea Pigs, Hamsters, Naked Mole Rats, and Rabbits

Animals are valuable resources in biomedical research in investigations of biological processes, disease pathogenesis, therapeutic interventions, safety, toxicity, and carcinogenicity. Interpretation of data from animals requires knowledge not only of the processes or diseases (pathophysiology) under study but also recognition of spontaneous conditions and background lesions (pathology) that can influence or confound the study results. Species, strain/stock, sex, age, anatomy, physiology, spontaneous diseases (noninfectious and infectious), and neoplasia impact experimental results and interpretation as well as animal welfare. This review and the references selected aim to provide a pathology resource for researchers, pathologists, and veterinary personnel who strive to achieve research rigor and validity and must understand the spectrum of "normal" and expected conditions to accurately identify research-relevant experimental phenotypes as well as unusual illness, pathology, or other conditions that can compromise studies involving laboratory mice, rats, gerbils, guinea pigs, hamsters, naked mole rats, and rabbits.

Considerations When Choosing High-Fat, High-Fructose, and High-Cholesterol Diets to Induce Experimental Nonalcoholic Fatty Liver Disease in Laboratory Animal Models

Nonalcoholic fatty liver disease (NAFLD) is intricately linked to metabolic disease (including obesity, glucose intolerance, and insulin resistance) and encompasses a spectrum of disorders including steatosis, nonalcoholic steatohepatitis (NASH), and fibrosis. Rodents consuming high-fat (HF; ∼40 kcal% fat including fats containing higher concentrations of saturated and trans fats), high-fructose (HFr), and high-cholesterol (HC) diets display many clinically relevant characteristics of NASH, along with other metabolic disorders. C57BL/6 mice are the most commonly used animal model because they can develop significant metabolic disorders including severe NASH with fibrosis after months of feeding, but other models also are susceptible. The significant number of diets that contain these different factors (i.e., HF, HFr, and HC), either alone or in combination, makes the choice of diet difficult. This methodology review describes the efficacy of these nutrient manipulations on the NAFLD phenotype in mice, rats, guinea pigs, hamsters, and nonhuman primates.

Temporal Development of Dyslipidemia and Nonalcoholic Fatty Liver Disease (NAFLD) in Syrian Hamsters Fed a High-Fat, High-Fructose, High-Cholesterol Diet

The use of translationally relevant animal models is essential, also within the field of nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). Compared to frequently used mouse and rat models, the hamster may provide a higher degree of physiological similarity to humans in terms of lipid profile and lipoprotein metabolism. However, the effects in hamsters after long-term exposure to a NASH diet are not known. Male Syrian hamsters were fed either a high-fat, high-fructose, high-cholesterol diet (NASH diet) or control diets for up to 12 months. Plasma parameters were assessed at two weeks, one, four, eight and 12 months and liver histopathology and biochemistry was characterized after four, eight and 12 months on the experimental diets. After two weeks, hamsters on NASH diet had developed marked dyslipidemia, which persisted for the remainder of the study. Hepatic steatosis was present in NASH-fed hamsters after four months, and hepatic stellate cell activation and fibrosis was observed within four to eight months, respectively, in agreement with progression towards NASH. In summary, we demonstrate that hamsters rapidly develop dyslipidemia when fed a high-fat, high-fructose, high-cholesterol diet. Moreover, within four to eight months, the NASH-diet induced hepatic changes with resemblance to human NAFLD.

Nitrous oxide improves cardiovascular, respiratory, and thermal stability during prolonged isoflurane anesthesia in juvenile guinea pigs

Anesthesia is frequently used to facilitate physiological monitoring during interventional animal studies. However, its use may induce cardiovascular (central and peripheral), respiratory, and thermoregulatory depression, confounding results in anesthetized animals. Despite the wide utility of guinea pigs as a translational platform, anesthetic protocols remain unstandardized for extended physiological studies in this species. Therefore, optimizing an anesthetic protocol that balances stable anesthesia with intact cardiorespiratory and metabolic function is crucial. To achieve this, 12 age and sex-matched juvenile Dunkin Hartley guinea pigs underwent extended anesthesia (≤150 min) with either (a) isoflurane (ISO: 1.5%), or (b) isoflurane + N2 O (ISO+ N2 O: 0.8% +70%), in this randomized cross-over designed study. Cardiovascular (HR, SBP, peripheral microvascular blood flow), respiratory (respiratory rate, SpO2 ), and thermal (Tre and Tsk ) measures were recorded continuously throughout anesthesia. Blood gas measures pre- and post- anesthesia were performed. Incorporation of 70% N2 O allowed for significant reductions in isoflurane (to 0.8%) while maintaining an effective anesthetic depth for prolonged noninvasive physiological examination in guinea pigs. ISO+N2 O maintained heart rate, peripheral blood flow, respiratory rate, and thermoregulatory function at levels closest to those of conscious animals, especially in females; however, it did not fully rescue anesthesia-induced hypotension. These results suggest that for studies requiring prolonged physiological examination (≤150 min) in guinea pigs, 0.8% isoflurane with a 70% N2 O adjuvant provides adequate anesthesia, while minimizing associated cardiorespiratory depression. The preservation of cardiorespiratory status is most marked throughout the first hour of anesthesia.

Effects of earthworm extract on the lipid profile and fatty liver induced by a high-fat diet in guinea pigs

Background

Non-alcoholic fatty liver disease (NAFLD), characterized by the accumulation of excess fat in the liver in people who consume little or no alcohol, is becoming increasingly common around the world, especially in developed countries. Extracts from earthworms have been used as alternative therapies for a variety of diseases but not in NAFLD. Therefore, the aim of this study was to investigate the effect of earthworm extract (EE) on diet-induced fatty liver disease in guinea pigs.

Methods

EE was extracted, and the effect of EE on the lipid levels and liver damage in guinea pigs fed a high-fat diet (HFD) was assessed. Thirty male guinea pigs at 3 weeks of age were allocated equally to five groups, namely, chow diet, HFD, and HFD with different dosages (0.3, 1.4 and 6.8 µg per kg bodyweight per day) of EE for 4 weeks, and their body weight was monitored throughout the experiment. Liver tissues were examined for gross morphology and histology. Serum levels of total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), alanine transaminase (ALT) and aspartate aminotransferase (AST) were determined using an autoanalyser.

Results

HFD induced NAFLD in guinea pigs. HFD-fed guinea pigs that received EE treatment showed milder increases in the serum levels of TC, TG and LDL-C, as well as in the body weight growth rate, compared to the HFD group without EE supplementation. EE intervention reduced the number of lipid-containing hepatocytes, hepatocellular ballooning and sinusoidal distortion in the liver in HFD-fed animals. ALT in serum was significantly elevated by HFD. No statistically significant difference in ALT levels was found between the chow diet group and the HFD group with EE treatment.

Conclusions

This study demonstrates that the administration of EE suppressed the induction of serum TC, TG and LDL-C in response to HFD. EE also reduced liver damage in HFD-fed guinea pigs. These findings suggest that EE has alleviating effects on dyslipidaemia and liver damage associated with NAFLD.

Testosterone deficiency accelerates early stage atherosclerosis in miniature pigs fed a high-fat and high-cholesterol diet: urine 1H NMR metabolomics targeted analysis

To gain insights into the role of testosterone in the development of atherosclerosis and its related metabolic pathways, we applied a proton nuclear magnetic resonance (¹H NMR)-based metabolomics approach to investigate urine metabolic profiles in miniature pigs fed a high-fat and high-cholesterol (HFC) diet among intact male pigs (IM), castrated male pigs (CM) and castrated male pigs with testosterone replacement (CMT). Our results showed that testosterone deficiency significantly increased atherosclerotic lesion areas, intima-media thickness, as well as serum lipid levels in the CM pigs. Moreover, seventeen significantly changed metabolites were identified in both IM vs. CM and CMT vs. CM groups. Among these, seven were shared between the two comparative groups and were all significantly reduced in the urine of the CM group but rescued in the CMT group. In addition, the correlation analysis demonstrated that several metabolites, including niacinamide, myo-inositol, choline and 3-hydroxyisovalerate, were negatively correlated with atherosclerotic lesion areas. Our study demonstrated that testosterone deficiency accelerated early AS formation in HFC diet-fed pigs, which involved several metabolites predominantly related to lipid metabolism, inflammation, oxidative stress and endothelial disorders. Our results reveal potential pathways in the pathogenesis of atherosclerosis caused by testosterone deficiency and HFC diet.

Management of Thermal Injuries in Donkeys: A Case Report

Simple Summary

Reports or descriptions of medical management of thermal injuries in donkeys is lacking. Four donkeys sustained burn injuries during the wildland–urban interface fire in Valparaiso, Chile, in 2014. The donkeys received first aid care at the scene of the fire, and then were hospitalized and treated for three months for thermal injuries, of various degrees of severity, in several body parts. The clinical findings and treatment of four of the donkeys are described in this paper. All donkeys recovered and were retired to an animal shelter.

Abstract

Burn injuries are uncommon in large animals and there are no reports of these injuries in donkeys. Burns cause local and systemic effects. Extensive thermal injuries can be challenging to manage and the extent of the burn surface affected will directly impact the severity of the illness and the prognosis. Burns are classified according to the depth of injury into four categories, from first-degree burns, and the least affect to fourth-degree burns, which are the more severely affected patients. This case report describes the medical management of four donkeys that sustained various degrees of external burn injuries during the wildland–urban interface fire in Valparaiso, Chile. The donkeys were treated topically for several weeks and closely monitor for inadequate nutritional intake. Water based topical medications are preferred in burn cases because they can be easily applied and removed without interfering with wound healing. Of note, the caloric demands of these cases can be achieved by increasing the amount of grain, adding fat (i.e., vegetable oil), and free-choice alfalfa hay. All donkeys recovered and were retired to an animal shelter.

Animal Models of Fibrosis in Nonalcoholic Steatohepatitis: Do They Reflect Human Disease?

Nonalcoholic steatohepatitis (NASH) is one of the most common chronic liver diseases in the world, yet no pharmacotherapies are available. The lack of translational animal models is a major barrier impeding elucidation of disease mechanisms and drug development. Multiple preclinical models of NASH have been proposed and can broadly be characterized as diet-induced, deficiency-induced, toxin-induced, genetically induced, or a combination of these. However, very few models develop advanced fibrosis while still reflecting human disease etiology or pathology, which is problematic since fibrosis stage is considered the best prognostic marker in patients and an important endpoint in clinical trials of NASH. While mice and rats predominate the NASH research, several other species have emerged as promising models. This review critically evaluates animal models of NASH, focusing on their ability to develop advanced fibrosis while maintaining their relevance to the human condition.

Fatty Acids of Microbial Origin in the Perirenal Fat of Rats (Rattus norvegicus domestica) and Guinea Pigs (Cavia porcellus) Fed Various Diets

Guinea pigs are assumed to practice caecotrophy to a higher degree than rats. Studies from leporids suggest that through the practice of caecotrophy, hindgut fermenting species could build up microbial fatty acids (FA) in body tissues. We hypothesized that microbial FA would be detectable in the body tissue of guinea pigs and rats, and this to a higher degree in guinea pigs. Twenty-four rats and guinea pigs were fed with four different pelleted diets (lucerne-, meat-, meat-bone-, insect-based) in groups of six animals for 8 weeks. Perirenal adipose tissue differed in FA composition between the species in spite of the common diets. FA typically associated with microbial activity (saturated FA (SFA; typically 18:0), monounsaturated FA (MUFA; typically trans-fatty acids TFA), and odd- and branched-chain FA (Iso-FA)), were all detected. Guinea pigs had higher SFA levels than rats except on the lucerne diet. Concentrations of 18:0 were higher for guinea pigs on the meat and bone diet. Iso-FA concentrations in guinea pigs exceeded those of rats on all diets. FA profiles with a microbial fingerprint appear-although in low proportions-in the body tissue of both species, and this seemingly to a higher extent in guinea pigs. With respect to whether consumption of rodent meat rich in microbial FA has particular effects on human health as shown for ruminant products, microbial FA concentrations are probably too low to cause any distinct effects.

Apolipoprotein M: new connections with diet, adipose tissue and metabolic syndrome

PURPOSE OF REVIEW

To focus on state-of-the-art knowledge on the apolipoprotein M (ApoM) physiology and physiopathology regarding metabolism.

RECENT FINDINGS

In humans, the ApoM was recently described as secreted by adipocytes. Obesity, metabolic syndrome and type 2 diabetes are associated with low circulating ApoM and adipose tissue APOM expression. Dieting-induced weight loss enhances adipose tissue expression and secretion, and exercise training increases plasma ApoM. The ApoM is a chaperone for the bioactive sphingolipid, sphingosine-1-phosphate (S1P), which has a specific role in inflammation. Its association with S1P in the inhibition of brown adipose tissue activity and subsequent insulin sensitivity was reported with the model of ApoM-deficient mouse.

SUMMARY

The adipose tissue is an endocrine organ responsible for obesity-related comorbidities. Obesity and dieting impact the adipose tissue secretory profile. The recent demonstration of ApoM being secreted by healthy adipocytes questions about the possible role of this adipose production in metabolic diseases. Low-circulating ApoM is associated with unhealthy metabolic phenotype. The lower circulating apoM during metabolic syndrome might be a cause of obesity-related comorbidities. Lifestyle interventions enhance ApoM production. Whether it acts in combination to S1P or other small lipidic molecules deserves further investigations.

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.

Bone Marrow and Peripheral Blood Cells Toxicity of a Single 2.0 Gy Cobalt60 Ionizing Radiation: An Animal Model

Background

Bone marrow is extremely vulnerable to damage caused by radiation therapy. Hence, bone marrow suppression is an important side effect of radiotherapy. Effective use of radiotherapy is therefore compromised by radiation-related injuries.

Material and Methods

Six Guinea-pigs were recruited for the study of which three were subjected to total body irradiation with Co⁶⁰ while the other three served as controls. Bone marrow and peripheral blood samples were collected before and at days 9, 14 and 21, post irradiation. Manual and automated counts were performed for bone marrow nucleated cells and peripheral blood cells respectively.

Results

Declining bone marrow cellularity was evident immediately post irradiation. Mean ± SD of marrow cell counted per mm³ were 121,924±281, 87,603±772, 121,367±375 and 122,750±1000 pre-irradiation and days 9, 14 and 21, postirradiation (p-values 0.10, 0.27 and 0.29 respectively). Significant drops in counts were noticed on day 9 post-irradiation for all red cell parameters (p-values <0.05), for Total White Blood Cell Count and Neutrophil count (p-values <0.05) and also on days 14 and 21 for Lymphocytes (p-values <0.05) and on day 21 for Eosinophil/Basophil/Monocytes (p-value <0.05). A significant drop in platelets counts was also noticed on day 9 (p-value <0.05) which significantly increased above pre-irradiation value on day 21.

Conclusion

Total body irrradiation with Co⁶⁰ significantly affects the bone marrow with maximum reductions in marrow nucleated cells and peripheral blood cells counts on day 9 post irradiation.

Guinea pig models for translation of the developmental origins of health and disease hypothesis into the clinic

Over 30 years ago Professor David Barker first proposed the theory that events in early life could explain an individual's risk of non-communicable disease in later life: the developmental origins of health and disease (DOHaD) hypothesis. During the 1990s the validity of the DOHaD hypothesis was extensively tested in a number of human populations and the mechanisms underpinning it characterised in a range of experimental animal models. Over the past decade, researchers have sought to use this mechanistic understanding of DOHaD to develop therapeutic interventions during pregnancy and early life to improve adult health. A variety of animal models have been used to develop and evaluate interventions, each with strengths and limitations. It is becoming apparent that effective translational research requires that the animal paradigm selected mirrors the tempo of human fetal growth and development as closely as possible so that the effect of a perinatal insult and/or therapeutic intervention can be fully assessed. The guinea pig is one such animal model that over the past two decades has demonstrated itself to be a very useful platform for these important reproductive studies. This review highlights similarities in the in utero development between humans and guinea pigs, the strengths and limitations of the guinea pig as an experimental model of DOHaD and the guinea pig's potential to enhance clinical therapeutic innovation to improve human health.

Cardioprotective Effects of Curcumin-Nisin Based Poly Lactic Acid Nanoparticle on Myocardial Infarction in Guinea Pigs

Myocardial infarction (MI) is the most prevalent cause of cardiovascular death. A possible way of preventing MI maybe by dietary supplements. The present study was thus designed to ascertain the cardio-protective effect of a formulated curcumin and nisin based poly lactic acid nanoparticle (CurNisNp) on isoproterenol (ISO) induced MI in guinea pigs. Animals were pretreated for 7 days as follows; Groups A and B animals were given 0.5 mL/kg of normal saline, group C metoprolol (2 mg/kg), groups D and E CurNisNp 10 and 21 mg/kg respectively (n = 5). MI was induced on the 7^th day in groups B-E animals. On the 9^th day electrocardiogram (ECG) was recorded, blood samples and tissue biopsies were collected for analyses. Toxicity studies on CurNisNp were carried out. MI induction caused atrial fibrillation which was prevented by pretreatment of metoprolol or CurNisNp. MI induction was also associated with increased expressions of cardiac troponin I (CTnI) and kidney injury molecule-1 (KIM-1) which were significantly reduced in guinea pig's pretreated with metoprolol or CurNisNp (P < 0.05). The LC₅₀ of CurNisNp was 3258.2 μg/mL. This study demonstrated that the formulated curcumin-nisin based nanoparticle confers a significant level of cardio-protection in the guinea pig and is nontoxic.

Capsaicin is beneficial to hyperlipidemia, oxidative stress, endothelial dysfunction, and atherosclerosis in Guinea pigs fed on a high-fat diet

Capsaicin has anti-inflammatory and antioxidant effects, as well as some benefits on the cardiovascular system. The exact effects of capsaicin on atherosclerosis are poorly understood. To investigate the effects of capsaicin on hyperlipidemia and atherosclerosis in guinea pigs fed on a high-fat diet, as well as its potential mechanisms. Guinea pigs (n = 48) were randomly divided into six groups (n = 8/group): normal diet (control); high fat diet (model); model + low-dose capsaicin (2.5 mg/kg); model + moderate-dose capsaicin (5 mg/kg); model + high-dose capsaicin (10 mg/kg), and model + simvastatin (1.5 mg/kg) (positive control). After 14 weeks, serum lipids, apolipoprotein B100, malondialdehyde (MDA), superoxide dismutase (SOD), nitric oxide (NO), and endothelin-1 were measured. Aortic atherosclerotic lesions were histologically examined. eNOS and iNOS were assessed by immunohistochemistry. The model group developed severe dyslipidemia and associated histologic changes and endothelial dysfunction. All doses of capsaicin decreased total cholesterol, triglycerides, low-density lipoprotein cholesterol, and apolipoprotein B-100, and increased high-density lipoprotein cholesterol (all P < 0.05). Capsaicin alleviated the plaque area (-17.9-70.5%), plaque area to intima ratio (-18.0-73.6%), and intima thickness (-20.5-83.6%) (all P < 0.05). Capsaicin decreased MDA (-45.5-76.1%), ET-1 (-19.6-51.6%), and average gray value (AGV) of eNOS (-10.9-48.8%), and increased SOD activity (+31.7-76.1%), NO (+11.2-36.8%), and AGV of iNOS (+6.8-+93.0%) (all P < 0.05). Similar changes were observed with simvastatin. Capsaicin is beneficial to hyperlipidemia and atherosclerosis in guinea pigs fed on a high-fat diet. Reduced oxidative stress and endothelial dysfunction were involved in these benefits. This could represent a novel approach to prevent cardiovascular diseases.

Liraglutide Decreases Hepatic Inflammation and Injury in Advanced Lean Non-Alcoholic Steatohepatitis

Although commonly associated with obesity, non-alcoholic fatty liver disease (NAFLD) is also present in the lean population representing a unique disease phenotype. Affecting 25% of the world's population, NAFLD is associated with increased mortality especially when progressed to non-alcoholic steatohepatitis (NASH). However, no approved pharmacological treatments exist. Current research focuses mainly on NASH associated with obesity, leaving the effectiveness of promising treatments in lean NASH virtually unknown. This study therefore aimed to evaluate the effect of liraglutide (glucagon-like peptide 1 analogue) and dietary intervention, alone and in combination, in guinea pigs with non-obese NASH. After 20 weeks of high-fat feeding (20% fat, 15% sucrose, 0.35% cholesterol), 40 female guinea pigs were block-randomized based on weight into four groups receiving one of four treatments for 4 weeks: continued high-fat diet (HF, control), high-fat diet and liraglutide treatment (HFL), chow diet (4% fat, 0% sucrose, 0% cholesterol; HFC) or chow diet and liraglutide treatment (HFCL). High-fat feeding induced NASH with severe fibrosis. Liraglutide decreased inflammation (p < 0.05) and hepatocyte ballooning (p < 0.05), while increasing hepatic α-tocopherol (p = 0.0154). Dietary intervention did not improve liver histopathology significantly, but decreased liver weight (p = 0.004), plasma total cholesterol (p = 0.0175), LDL-cholesterol (p = 0.0063), VLDL-cholesterol (p = 0.0034), hepatic cholesterol (p < 0.0001) and increased hepatic vitamin C (p = 0.0099). Combined liraglutide and dietary intervention induced a rapid weight loss, necessitating periodical liraglutide dose adjustment/discontinuation, limiting the strength of the findings from this group. Collectively, this pre-clinical study supports the beneficial effect of liraglutide on NASH and extends this notion to lean NASH.

Depletion of haptoglobin and hemopexin promote hemoglobin-mediated lipoprotein oxidation in sickle cell disease

Intravascular sickling and lysis of red blood cells, a hallmark feature of sickle cell disease (SCD), releases hemoglobin (Hb) into the circulation. Increased cell-free Hb has been linked to vasculopathy and in vitro lipid oxidation. Scavenger plasma proteins haptoglobin (Hp) and hemopexin (Hpx) can attenuate cell-free Hb and total plasma heme lipid-oxidative capacity but are depleted in SCD. Here, we isolated lipids from BERK-SS mice, guinea pigs (GP) infused with heme-albumin, and patients with SCD undergoing regular exchange transfusion therapy and evaluated the level of lipid oxidation. Malondialdehyde formation, an end product of lipid peroxidation, was increased in BERK-SS mice, purified lipid fractions of the heme-albumin infused GP, and patients with SCD compared with controls. In humans, the extent of lipid oxidation was associated with the absence of Hp as well as decreased Hpx in plasma samples. Postmortem pulmonary tissue obtained from patients with SCD demonstrated oxidized LDL deposition in the pulmonary artery. The relationship between no Hp and low Hpx levels with greater LDL and HDL oxidation demonstrates the loss of protection against cell-free Hb and total plasma heme-mediated lipid oxidation and tissue injury in SCD. Strategies to protect against plasma lipid oxidation by cell-free Hb and total plasma heme (e.g., therapeutic Hp and Hpx replacement) may diminish the deleterious effects of cell-free Hb and total plasma heme toward the vascular system in SCD.

Long-term Western diet fed apolipoprotein E-deficient rats exhibit only modest early atherosclerotic characteristics

In the apolipoprotein E–deficient mouse, the gut microbiota has an impact on the development of atherosclerosis, but whether such correlations are also present in rats requires investigation. Therefore, we studied female SD-Apoe^tm1sage (Apoe^−/−) rats fed either a Western diet or a low-fat control diet with or without gluten, which is known to promote gut microbiota changes, until 20 weeks of age. We hypothesized that the manifestation of atherosclerosis would be more severe in Apoe^−/− rats fed the Western high-fat diet, as compared with rats fed the low-fat diet, and that atherosclerosis would be accelerated by gluten. Both Western diet-feeding and gluten resulted in significant changes in gut microbiota, but the microbiota impact of gluten was transient. Compared with Apoe^−/− rats fed a low-fat diet, Western diet-fed Apoe^−/− rats were heavier and became glucose intolerant with increased levels of oxidative stress. They developed early fatty streak lesions in their aortic sinus, while there was no evidence of atherosclerosis in the thoracic aorta. No conclusions could be made on the impact of gluten on atherosclerosis. Although Western diet-fed Apoe^−/− rats exhibited a more human-like LDL dominated blood lipid profile, signs of obesity, type 2 diabetes and cardiovascular disease were modest.

Ischemia/reperfusion injury in male guinea pigs: An efficient model to investigate myocardial damage in cardiovascular complications

Myocardial ischemia/reperfusion (I/R) injury is the major problem that aggravates cardiac damage. Several established animal models fail to explain the similarity in disease mechanism and progression as seen in humans; whereas guinea pig shows high similarity in cardiovascular parameters. Hence, current study is aimed to develop an animal model using guinea pigs that may best correlate with disease mechanism of human myocardial I/R injury. Male guinea pigs were randomized into three groups: normal diet (ND), high fat diet (HFD) and sham; fed with respective diets for 90 days. Myocardial infarction (MI) was induced by ligating left anterior descending artery (LAD) for 30 min followed by 24 h and 7 days of reperfusion in ND and HFD groups. Electrocardiogram (ECG) showed the alterations in electrical conduction during myocardial I/R injury. Elevated levels of lactate dehydrogenase (LDH) and creatine kinase-MB ((CK-MB)) were higher in HFD compared to ND. Inflammatory markers such as tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) were up-regulated in I/R injury animals compared to sham. Fold change of these protein expression levels were higher in HFD compared to ND. Elevated lipid profile and increased aortic wall thickness in HFD animals depicts the risk of developing cardiovascular complications. ECG analysis strongly confirmed MI through changes in sinus rhythm that are reflected in infarcted tissue as verified through TTC staining. Thus the combination of HFD followed by I/R injury proved to be an efficient model to study pathophysiology of myocardial I/R injury with minimal tissue damage and surgical mortality.

Comparative studies of three cholesteryl ester transfer proteins and their interactions with known inhibitors

Cholesteryl ester transfer protein (CETP) is a plasma protein that mediates bidirectional transfers of cholesteryl esters and triglycerides between low-density lipoproteins and high-density lipoproteins (HDL). Because low levels of plasma CETP are associated with increased plasma HDL-cholesterol, therapeutic inhibition of CETP activity is considered an attractive strategy for elevating plasma HDL-cholesterol, thereby hoping to reduce the risk of cardiovascular disease. Interestingly, only a few laboratory animals, such as rabbits, guinea pigs, and hamsters, have plasma CETP activity, whereas mice and rats do not. It is not known whether all CETPs in these laboratory animals are functionally similar to human CETP. In the current study, we compared plasma CETP activity and characterized the plasma lipoprotein profiles of these animals. Furthermore, we studied the three CETP molecular structures, physicochemical characteristics, and binding properties with known CETP inhibitors in silico. Our results showed that rabbits exhibited higher CETP activity than guinea pigs and hamsters, while these animals had different lipoprotein profiles. CETP inhibitors can inhibit rabbit and hamster CETP activity in a similar manner to human CETP. Analysis of CETP molecules in silico revealed that rabbit and hamster CETP showed many features that are similar to human CETP. These results provide novel insights into understanding CETP functions and molecular properties.

Iron accelerates hemoglobin oxidation increasing mortality in vascular diseased guinea pigs following transfusion of stored blood

Non-transferrin-bound iron (NTBI) and free hemoglobin (Hb) accumulate in circulation following stored RBC transfusions. This study investigated transfusion, vascular disease, and mortality in guinea pigs after stored RBC transfusion alone and following cotransfusion with apo-transferrin (apo-Tf) and haptoglobin (Hp). The effects of RBC exchange transfusion dose (1, 3, and 9 units), storage period (14 days), and mortality were evaluated in guinea pigs with a vascular disease phenotype. Seven-day mortality and the interaction between iron and Hb as cocontributors to adverse outcome were studied. Concentrations of iron and free Hb were greatest after transfusion with 9 units of stored RBCs compared with fresh RBCs or stored RBCs at 1- and 3-unit volumes. Nine units of stored RBCs led to mortality in vascular diseased animals, but not normal animals. One and 3 units of stored RBCs did not cause a mortality effect, suggesting the concomitant relevance of NTBI and Hb on outcome. Cotransfusion with apo-Tf or Hp restored survival to 100% following 9-unit RBC transfusions in vascular diseased animals. Our data suggest that increases in plasma NTBI and Hb contribute to vascular disease-associated mortality through iron-enhanced Hb oxidation and enhanced tissue injury.

Use of the hyperinsulinemic euglycemic clamp to assess insulin sensitivity in guinea pigs: dose response, partitioned glucose metabolism, and species comparisons

The guinea pig is an alternate small animal model for the study of metabolism, including insulin sensitivity. However, only one study to date has reported the use of the hyperinsulinemic euglycemic clamp in anesthetized animals in this species, and the dose response has not been reported. We therefore characterized the dose-response curve for whole body glucose uptake using recombinant human insulin in the adult guinea pig. Interspecies comparisons with published data showed species differences in maximal whole body responses (guinea pig ≈ human < rat < mouse) and the insulin concentrations at which half-maximal insulin responses occurred (guinea pig > human ≈ rat > mouse). In subsequent studies, we used concomitant d-[3-³H]glucose infusion to characterize insulin sensitivities of whole body glucose uptake, utilization, production, storage, and glycolysis in young adult guinea pigs at human insulin doses that produced approximately half-maximal (7.5 mU·min^-1·kg^-1) and near-maximal whole body responses (30 mU·min^-1·kg^-1). Although human insulin infusion increased rates of glucose utilization (up to 68%) and storage and, at high concentrations, increased rates of glycolysis in females, glucose production was only partially suppressed (~23%), even at high insulin doses. Fasting glucose, metabolic clearance of insulin, and rates of glucose utilization, storage, and production during insulin stimulation were higher in female than in male guinea pigs (P < 0.05), but insulin sensitivity of these and whole body glucose uptake did not differ between sexes. This study establishes a method for measuring partitioned glucose metabolism in chronically catheterized conscious guinea pigs, allowing studies of regulation of insulin sensitivity in this species.

A model of type 2 diabetes in the guinea pig using sequential diet-induced glucose intolerance and streptozotocin treatment

Type 2 diabetes is a leading cause of morbidity and mortality among noncommunicable diseases, and additional animal models that more closely replicate the pathogenesis of human type 2 diabetes are needed. The goal of this study was to develop a model of type 2 diabetes in guinea pigs, in which diet-induced glucose intolerance precedes β-cell cytotoxicity, two processes that are crucial to the development of human type 2 diabetes. Guinea pigs developed impaired glucose tolerance after 8 weeks of feeding on a high-fat, high-carbohydrate diet, as determined by oral glucose challenge. Diet-induced glucose intolerance was accompanied by β-cell hyperplasia, compensatory hyperinsulinemia, and dyslipidemia with hepatocellular steatosis. Streptozotocin (STZ) treatment alone was ineffective at inducing diabetic hyperglycemia in guinea pigs, which failed to develop sustained glucose intolerance or fasting hyperglycemia and returned to euglycemia within 21 days after treatment. However, when high-fat, high-carbohydrate diet-fed guinea pigs were treated with STZ, glucose intolerance and fasting hyperglycemia persisted beyond 21 days post-STZ treatment. Guinea pigs with diet-induced glucose intolerance subsequently treated with STZ demonstrated an insulin-secretory capacity consistent with insulin-independent diabetes. This insulin-independent state was confirmed by response to oral antihyperglycemic drugs, metformin and glipizide, which resolved glucose intolerance and extended survival compared with guinea pigs with uncontrolled diabetes. In this study, we have developed a model of sequential glucose intolerance and β-cell loss, through high-fat, high-carbohydrate diet and extensive optimization of STZ treatment in the guinea pig, which closely resembles human type 2 diabetes. This model will prove useful in the study of insulin-independent diabetes pathogenesis with or without comorbidities, where the guinea pig serves as a relevant model species.

Impact of birth weight and postnatal diet on the gut microbiota of young adult guinea pigs

Background

The gastrointestinal tract (GIT) microbiota is essential to metabolic health, and the prevalence of the Western diet (WD) high in fat and sugar is increasing, with evidence highlighting a negative interaction between the GIT and WD, resulting in liver dysfunction. Additionally, an adverse in utero environment such as placental insufficiency resulting in low birth weight (LBW) offspring, contributes to an increased risk of metabolic diseases such as fatty liver infiltration and liver dysfunction in later life. We sought to understand the potential interactive effects of exposure to a WD upon growing LBW offspring. We postulated that LBW offspring when challenged with a poor postnatal diet, would display an altered microbiota and more severe liver metabolic dysfunction.

Methods

The fecal microbiota of normal birth weight (NBW) and LBW young guinea pig offspring, weaned onto either a control diet (CD) or WD was determined with 16S rRNA gene next generation sequencing at young adulthood following the early rapid growth phase after weaning. A liver blood chemistry profile was also performed.

Results

The life-long consumption of WD following weaning into young adulthood resulted in increased total cholesterol, triglycerides and alanine aminotransferase levels in association with an altered GIT microbiota when compared to offspring consuming CD. Neither birth weight nor sex were associated with any significant changes in microbiota alpha diversity, by measuring the Shannon’s diversity index. One hundred forty-eight operational taxonomic units were statistically distinct between the diet groups, independent of birth weight. In the WD group, significant decreases were detected in Barnesiella, Methanobrevibacter smithii and relatives of Oscillospira guillermondii, while Butyricimonas and Bacteroides spp. were increased.

Discussion

These results describe the GIT microbiota in a guinea pig model of LBW and WD associated metabolic syndrome and highlight several WD specific GIT alterations associated with human metabolic disease.

Adjuvant-Induced Arthritis in Guinea Pigs

We propose a model of rheumatoid arthritis (RA) induced in outbred guinea pigs using a single subcutaneous injection of complete Freund's adjuvant to the hind paw. Histological examination of this model shows fibrin deposition on the surface of the synovial membrane, leukocyte infiltration of the synovial membrane and adjacent tissues, proliferation of the granulation tissue, and emergence of angioid areas, characteristic of RA. The cell response appears as an increase in the plasma cell count and development of follicle-like lymphoid infiltrates; erosion of the articular surface of the cartilage, frequently with deep cartilage destruction over large areas; and epiphysiopathy. The high reproducibility of arthritis induction in this RA model has been demonstrated. The proposed model is promising for the assessment of anti-arthritis preparations and dosage regimens.

High-fat but not sucrose intake is essential for induction of dyslipidemia and non-alcoholic steatohepatitis in guinea pigs

Background

Non-alcoholic fatty liver disease (NAFLD) and dyslipidemia are closely related. Diet plays an important role in the progression of these diseases, but the role of specific dietary components is not completely understood. Therefore, we investigated the role of dietary sucrose and fat/cholesterol on the development of dyslipidemia and NAFLD.

Methods

Seventy female guinea pigs were block-randomized (based on weight) into five groups and fed a normal chow diet (control: 4 % fat), a very high-sucrose diet (vHS: 4 % fat, 25 % sucrose), a high-fat diet (HF: 20 % fat, 0.35 % cholesterol), a high-fat/high-sucrose diet (HFHS: 20 % fat, 15 % sucrose, 0.35 % cholesterol) or a high-fat/very high-sucrose diet (HFvHS: 20 % fat, 25 % sucrose, 0.35 % cholesterol) for 16 and 25 weeks.

Results

All three high-fat diets induced dyslipidemia with increased concentrations of plasma cholesterol (p < 0.0001), LDL-C (p < 0.0001) and VLDL-C (p < 0.05) compared to control and vHS. Contrary to this, plasma triglycerides were increased in control and vHS compared to high-fat fed animals (p < 0.01), while circulating levels of free fatty acids were even between groups. Histological evaluation of liver sections revealed non-alcoholic steatohepatitis (NASH) with progressive inflammation and bridging fibrosis in high-fat fed animals. Accordingly, hepatic triglycerides (p < 0.05) and cholesterol (p < 0.0001) was increased alongside elevated levels of alanine and aspartate aminotransferase (p < 0.01) compared to control and vHS.

Conclusion

Collectively, our results suggest that intake of fat and cholesterol, but not sucrose, are the main factors driving the development and progression of dyslipidemia and NAFLD/NASH.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-016-0110-1) contains supplementary material, which is available to authorized users.

High-fat diet-dependent modulation of the delayed rectifier K(+) current in adult guinea pig atrial myocytes

Obesity is associated with hyperlipidemia, electrical remodeling of the heart, and increased risk of supraventricular arrhythmias in both male and female patients. The delayed rectifier K(+) current (IK), is an important regulator of atrial repolarization. There is a paucity of studies on the functional role of IK in response to obesity. Here, we assessed the obesity-mediated functional modulation of IK in low-fat diet (LFD), and high-fat diet (HFD) fed adult guinea pigs. Guinea pigs were randomly divided into control and obese groups fed, ad libitum, with a LFD (10 kcal% fat) or a HFD (45 kcal% fat) respectively. Action potential duration (APD), and IK were studied in atrial myocytes and IKr and IKs in HEK293 cells using whole-cell patch clamp electrophysiology. HFD guinea pigs displayed a significant increase in body weight, total cholesterol and total triglycerides within 50 days. Atrial APD at 30% (APD30) and 90% (APD90) repolarization were shorter, while atrial IK density was significantly increased in HFD guinea pigs. Exposure to palmitic acid (PA) increased heterologously expressed IKr and IKs densities, while oleic acid (OA), severely reduced IKr and had no effect on IKs. The data are first to show that in obese guinea pigs abbreviated APD is due to increased IK density likely through elevations of PA. Our findings may have crucial implications for targeted treatment options for obesity-related arrhythmias.

Conjugated linoleic acid mitigates testosterone-related changes in body composition in male guinea pigs

We hypothesize that conjugated linoleic acid (CLA) may be effective in preventing the changes in total and regional body composition and increases in interleukin (IL) 6 that occur as a result of hypogonadism. Male guinea pigs (n = 40, 70- to 72-week retired breeders) were block randomized by weight into 4 groups: (1) sham surgery (SHAM)/control (CTRL) diet, (2) SHAM/conjugated linoleic acid (CLA) diet (1%), (3) orchidectomy (ORX)/CTRL diet, and (4) ORX/CLA diet. Dual-energy x-ray absorptiometry scans were performed at baseline and week 16 to assess body composition. Serum IL-6 was analyzed using an enzyme-linked immune sorbent assay. Fatty acids (FAs) from visceral and subcutaneous adipose tissue were analyzed using gas chromatography. In ORX/CTRL guinea pigs, percent total body fat increased by 6.1%, and percent lean mass decreased by 6.7% over the 16-week treatment period, whereas no changes were observed for either parameter in ORX/CLA guinea pigs. Guinea pigs fed the CLA diet gained less percent total, upper, and lower body fat than those fed the CTRL diet regardless of surgical treatment. Regional adipose tissue FA composition was reflective of dietary FAs. Serum IL-6 concentrations were not different among groups. In this study, we observed that, in male guinea pigs, hypogonadism resulted in increased fat mass and decreased lean mass. In addition, CLA was effective in reducing gains in body fat and maintaining lean mass in both hypogonadal and intact guinea pigs.

Normal weight dyslipidemia: Is it all about the liver?

OBJECTIVE

The liver coordinates lipid metabolism and may play a vital role in the development of dyslipidemia, even in the absence of obesity. Normal weight dyslipidemia (NWD) and patients with nonalcoholic fatty liver disease (NAFLD) who do not have obesity constitute a unique subset of individuals characterized by dyslipidemia and metabolic deterioration. This review examined the available literature on the role of the liver in dyslipidemia and the metabolic characteristics of patients with NAFLD who do not have obesity.

METHODS

PubMed was searched using the following keywords: nonobese, dyslipidemia, NAFLD, NWD, liver, and metabolically obese/unhealthy normal weight. Additionally, article bibliographies were screened, and relevant citations were retrieved. Studies were excluded if they had not measured relevant biomarkers of dyslipidemia.

RESULTS

NWD and NAFLD without obesity share a similar abnormal metabolic profile. When compared with patients with NAFLD who have obesity, the metabolic abnormalities of NAFLD without obesity are similar or less severe. Furthermore, hepatic lesions develop independent of obesity, and the extent of dyslipidemia seems comparable.

CONCLUSIONS

NAFLD may impair hepatic lipid handling, causing faulty lipid homeostasis, and serves as a likely starting point for initiation and propagation of dyslipidemia along with associated comorbidities in patients without obesity.

Diet-induced dyslipidemia leads to nonalcoholic fatty liver disease and oxidative stress in guinea pigs

Chronic dyslipidemia imposed by a high-fat and high-caloric dietary regime leads to debilitating disorders such as obesity, nonalcoholic fatty liver disease (NAFLD), and insulin resistance. As disease rates surge, so does the need for high validity animal models to effectively study the causal relationship between diet and disease progression. The dyslipidemic guinea pig displays a high similarity with the human lipoprotein profile and may in this aspect be superior to other rodent models. This study investigated the effects of 2 long-term Westernized diets (0.35% cholesterol, 18.5% vegetable oil and either 15% or 20% sucrose) compared with isocaloric standard chow in adult guinea pigs. Biochemical markers confirmed dyslipidemia in agreement with dietary regimens; however, both high-fat groups displayed a decreased tissue fat percentage compared with controls. Macroscopic appearance, histopathologic evaluation, and plasma markers of liver function confirmed NAFLD in high-fat groups, supported by liver redox imbalance and markers suggesting hepatic endothelial dysfunction. Plasma markers indicated endothelial dysfunction in response to a high-fat diet, although atherosclerotic lesions were not evident. Evaluation of glucose tolerance showed no indication of insulin resistance. The 5% increase in sucrose between the 2 high-fat diets did not lead to significant differences between groups. In conclusion, we find the dyslipidemic guinea pig to be a valid model of diet imposed dyslipidemia, particularly with regards to hepatic steatosis and endothelial dysfunction. Furthermore, the absence of obesity supports the present study setup as targeting NAFLD in nonobese individuals.

Non-invasive cortisol measurements as indicators of physiological stress responses in guinea pigs

Non-invasive measurements of glucocorticoid (GC) concentrations, including cortisol and corticosterone, serve as reliable indicators of adrenocortical activities and physiological stress loads in a variety of species. As an alternative to invasive analyses based on plasma, GC concentrations in saliva still represent single-point-of-time measurements, suitable for studying short-term or acute stress responses, whereas fecal GC metabolites (FGMs) reflect overall stress loads and stress responses after a species-specific time frame in the long-term. In our study species, the domestic guinea pig, GC measurements are commonly used to indicate stress responses to different environmental conditions, but the biological relevance of non-invasive measurements is widely unknown. We therefore established an experimental protocol based on the animals' natural stress responses to different environmental conditions and compared GC levels in plasma, saliva, and fecal samples during non-stressful social isolations and stressful two-hour social confrontations with unfamiliar individuals. Plasma and saliva cortisol concentrations were significantly increased directly after the social confrontations, and plasma and saliva cortisol levels were strongly correlated. This demonstrates a high biological relevance of GC measurements in saliva. FGM levels measured 20 h afterwards, representing the reported mean gut passage time based on physiological validations, revealed that the overall stress load was not affected by the confrontations, but also no relations to plasma cortisol levels were detected. We therefore measured FGMs in two-hour intervals for 24 h after another social confrontation and detected significantly increased levels after four to twelve hours, reaching peak concentrations already after six hours. Our findings confirm that non-invasive GC measurements in guinea pigs are highly biologically relevant in indicating physiological stress responses compared to circulating levels in plasma in the short- and long-term. Our approach also underlines the importance of detailed investigations on how to use and interpret non-invasive measurements, including the determination of appropriate time points for sample collections.

Hypolipidemic activity of a hydroalcoholic extract of Cyperus scariosus Linn. root in guinea pigs fed with a high cholesterol diet

Lipid-lowering and antioxidant activities of a hydroalcoholic extract of Cyperus scariosus Linn. root (HCS) were evaluated in guinea pigs fed with a high cholesterol diet. Serum lipid profile (total cholesterol, triglycerides, LDL-C, VLDL-C, and HDL-C), atherogenic indices and serum enzymes (ALT, AST, ALP, LDH, and CK-MB) were performed in each group at 0 days and at the end of 60 days. Histological study of liver and kidney was done in groups 1, 2, 5, 6 and 7. The total phenolic and flavonoid content in HCS and its antioxidant activity were evaluated by the DPPH assay. Both doses of HCS decreased serum lipid profile and atherogenic indices (P < 0.05). HCS has lipid lowering, immunosuppressive and antioxidant properties, and mays have value in atherosclerosis prevention. The higher dose of HCS also reduced serum AST, ALP, and LDH levels and rosuvastatin increased AST and ALP levels (P < 0.05). Histology of the liver showed decreased lipid accumulation and improvement in hepatocytes in HCS-treated animals. The antioxidant activity of HCS may be responsible for its lipid lowering and cytoprotective action. HCS had significant lipid lowering and antioxidant activity, which; may be due to the phenolic compounds. HCS may be a safe and cost effective alternative to current statin therapy for patients with dyslipidaemia.

Animal models to evaluate anti-atherosclerotic drugs

Atherosclerosis is a multifactorial condition characterized by endothelial injury, fatty streak deposition, and stiffening of the blood vessels. The pathogenesis is complex and mediated by adhesion molecules, inflammatory cells, and smooth muscle cells. Statins have been the major drugs in treating hypercholesterolemia for the past two decades despite little efficacy. There is an urgent need for new drugs that can replace statins or combined with statins. The preclinical studies evaluating atherosclerosis require an ideal animal model which resembles the disease condition, but there is no single animal model which mimics the disease. The animal models used are rabbits, rats, mice, hamsters, mini pigs, etc. Each animal model has its own advantages and disadvantages. The method of induction of atherosclerosis includes diet, chemical induction, mechanically induced injuries, and genetically manipulated animal models. This review mainly focuses on the various animal models, method of induction, the advantages, disadvantages, and the current perspectives with regard to preclinical studies on atherosclerosis.

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.