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

An Immunocompetent Mongolian Gerbil Model for Hepatitis E Virus Genotype 1 Infection

BACKGROUND & AIMS

Hepatitis E virus (HEV), primarily genotype 1 (HEV-1), causes approximately 20.1 million infections, 44,000 deaths, and 3000 stillbirths annually. Current evidence indicates that HEV-1 is only transmitted in humans. Here, we evaluated whether Mongolian gerbils can serve as animal models for HEV-1 infection.

METHODS

Mongolian gerbils were used for HEV-1 and hepatitis E virus genotype 3 infection experiments. HEV infection parameters, including detection of HEV RNA and HEV antigen, liver function assessment, and histopathology, were evaluated.

RESULTS

We adapted a clinical isolate of HEV-1 for Mongolian gerbils by serial passaging in feces of aged male gerbils. The gerbil-adapted strain obtained at passage 3 induced a robust, acute HEV infection, characterized by stable fecal virus shedding, elevated liver enzymes, histopathologic changes in the liver, and seroconversion to anti-HEV. An infectious complementary DNA clone of the adapted virus was generated. HEV-1-infected pregnant gerbils showed a high rate of maternal mortality and vertical transmission. HEV RNA or antigens were detected in the liver, kidney, intestine, placenta, testis, and fetus liver. Liver and placental transcriptomic analyses indicated activation of host immunity. Tacrolimus prolonged HEV-1 infection, whereas ribavirin cleared infection. The protective efficacy of a licensed HEV vaccine was validated using this model.

CONCLUSIONS

HEV-1 efficiently infected Mongolian gerbils. This HEV-1 infection model will be valuable for investigating hepatitis E immunopathogenesis and evaluating vaccines and antivirals against HEV.

Positive effect of a diggable substrate on the behaviour of a captive naked mole rat colony

Naked mole rats (Heterocephalus galber) are eusocial mammals from East Africa. Their extraordinary social organisation is accompanied by remarkable adaptations to an underground lifestyle, extreme longevity and resistance to many diseases, making naked mole rats a highly relevant model for biological research. However, their living conditions in controlled environments do not allow them to express fundamental behaviours: digging galleries and exploring. This gap probably constitutes a bias to any behavioural or even medical study, because it represents a potential obstacle to their well-being. In this article, we tested the effects of the introduction of a diggable substrate on the behaviour of a colony of naked mole rats at the Menagerie, le Zoo du Jardin des Plantes, Paris. We measured individual exploratory latencies, the number of entries per minute and the frequency with which naked mole rats gnawed tunnels during observation trials. We found that: (i) young individuals explore more quickly, (ii) the introduction of a diggable substrate encourages exploration and digging behaviour, and (iii) could therefore be a relevant element to introduce under human care. This new environmental design could improve the welfare of naked mole rats by creating opportunities for cognitive challenges such as exploration and environmental control.

Mammary and reproductive tract tumours and tumour-like lesions of 286 small pet mammals: a retrospective study

Small mammals are very popular companion animals, and the incidence of particular tumour types in these animals is the subject of extensive research. We carried out a retrospective and comparative analysis of the incidence of reproductive tract and mammary tumours and tumour-like lesions collected from 103 pet rabbits, 75 pet rats, 71 guinea pigs, 12 mice, 11 hamsters, eight African pygmy hedgehogs, four ferrets and two chinchillas. The results indicate that uterine tumours and tumour-like lesions are common in pet rabbits, guinea pigs and African pygmy hedgehogs. In pet rabbits, the most common uterine tumour was endometrial adenocarcinoma, while in guinea pigs benign lesions predominated (ie, leiomyoma, endometrial adenoma, cystic endometrial hyperplasia and deciduoma). Uterine tumours in African pygmy hedgehogs included adenosarcomas and endometrial polyps. Ovarian lesions were found only in guinea pigs (ovarian rete adenomas, rete cysts) and African pygmy hedgehogs (mostly granulosa cell tumours), while testicular tumours were diagnosed in pet rabbits, one pet rat and one guinea pig. Mammary tumours were common in pet rabbits, pet rats, guinea pigs, mice, hamsters and African pygmy hedgehogs. In pet rats, the most common mammary tumour was fibroadenoma, while in other animals carcinomas predominated. In guinea pigs and, to a lesser extent, in pet rats, a significant percentage of mammary tumours occurred in males. Guinea pigs seem to be predisposed to mammary tumours of ductal origin. This study describes for the first time uterine angioleiomyoma in the pet rabbit and mammary spindle cell carcinoma in the Djungarian hamster and chinchilla.

Bovine Colostrum Supplementation in Rabbit Diet Modulates Gene Expression of Cytokines, Gut-Vascular Barrier, and Red-Ox-Related Molecules in the Gut Wall

Rabbits, pivotal in the EU as livestock, pets, and experimental animals, face bacterial infection challenges, prompting a quest for alternatives to curb antibiotic resistance. Bovine colostrum (BC), rich in immunoregulatory compounds, antimicrobial peptides, and growth factors, is explored for disease treatment and prevention. This study assesses BC diet supplementation effects on rabbit intestines, examining gene expression. Thirty female New Zealand White rabbits at weaning (35 days) were divided into three experimental groups: control (commercial feed), 2.5% BC, and 5% BC. The diets were administered until slaughtering (81 days). BC-upregulated genes in the jejunum included IL-8, TGF-β, and CTNN-β1 at 5% BC, while PLVAP at 2.5% BC. Antioxidant-related genes (SOD1, GSR) were downregulated in the cecum and colon with 2.5% BC. BC 5% promoted IL-8 in the jejunum, fostering inflammation and immune cell migration. It also induced genes regulating inflammatory responses (TGF-β) and gastrointestinal permeability (CTNN-β1). BC 5% enhanced antioxidant activity in the cecum and colon, but no significant impact on anti-myxo antibody production was observed. These results suggest that BC has significant effects on the rabbit gastrointestinal tract's inflammatory and antioxidant response, but further research is required to fully understand its histological and physiological impact.

Advocating for Generalizability: Accepting Inherent Variability in Translation of Animal Research Outcomes

Advancing scientific discovery requires investigators to embrace research practices that increase transparency and disclosure about materials, methods, and outcomes. Several research advocacy and funding organizations have produced guidelines and recommended practices to enhance reproducibility through detailed and rigorous research approaches; however, confusion around vocabulary terms and a lack of adoption of suggested practices have stymied successful implementation. Although reproducibility of research findings cannot be guaranteed due to extensive inherent variables in attempts at experimental repetition, the scientific community can advocate for generalizability in the application of data outcomes to ensure a broad and effective impact on the comparison of animals to translation within human research. This report reviews suggestions, based upon work with National Institutes of Health advisory groups, for improving rigor and transparency in animal research through aspects of experimental design, statistical assessment, and reporting factors to advocate for generalizability in the application of comparative outcomes between animals and humans.

Unraveling the relationship among inflammatory responses, oxidative damage, and host susceptibility to Opisthorchis viverrini infection: A comparative analysis in animal models

Background and Aim

Opisthorchis viverrini infection-induced inflammation contributes to cholangiocarcinoma (CCA) development in humans and animals. Inflammation generates free radicals, such as reactive oxygen species and reactive nitrogen species (RNS), which damage the host's DNA. However, only 5% of O. viverrini-infected individuals develop malignancy, suggesting that variations in the inflammatory response of individuals to the parasite may influence susceptibility. Due to limitations in studying human susceptibility, we used an animal model to investigate the profiles of inflammatory reactions, oxidative burst, and irreversible DNA damage. This study aimed to explore the potential role of inflammation and RNS in causing DNA damage that may predispose susceptible hosts and non-susceptible animal models to cancer development in O. viverrini infection.

Materials and Methods

This experimental study was conducted on 30 Syrian golden hamsters (OV-H) and 30 BALB/c mice (OV-M) infected with O. viverrini, representing susceptible and non-susceptible models, respectively. Five animals per group were examined at six predetermined time points during the experiment. Biliary tract samples were systematically investigated using histopathological evaluation for inflammatory cell infiltration and immunohistochemical staining for RNS production and markers of DNA damage, including nitrotyrosine and 8-hydroxy-2'-deoxyguanosine. These features were quantified and compared among the experimental groups. Mann-Whitney U-test was used for statistical analysis, with p < 0.05 considered statistically significant.

Results

The comparison revealed that the OV-M group exhibited significantly earlier and higher rates of inflammatory cell infiltration during the acute phase, whereas the OV-H group exhibited chronic and more severe inflammation (p < 0.020). Intracellular RNS production and DNA damage were closely associated with the inflammatory response.

Conclusion

This study demonstrates differential responses in susceptible and non-susceptible models of O. viverrini infection regarding disease onset and duration, as well as intracellular RNS production and DNA damage caused by inflammation. Persistent inflammation generated oxidatively damaged DNA, which is a distinct pathological characteristic of susceptible hosts and may be critical for CCA development.

Time- and Gender-Dependent Alterations in Mice during the Aging Process

Compared to young people and adults, there are differences in the ability of elderly people to resist diseases or injuries, with some noticeable features being gender-dependent. However, gender differences in age-related viscera alterations are not clear. To evaluate a potential possibility of gender differences during the natural aging process, we used three age groups to investigate the impact on spleens, kidneys, and adrenal glands. The immunofluorescence results showed that male-specific p21 proteins were concentrated in the renal tubule epithelial cells of the kidney. Histological staining revealed an increase in the frequencies of fat vacuoles located in the renal tubule epithelial cells of the cortex, under the renal capsule in the kidneys of male mice with age. In female mice, we found that the width of the globular zone in the adrenal gland cortex was unchanged with age. On the contrary, the male displayed a reduction in width. Compared to females, the content of epinephrine in adrenal gland tissue according to ELISA analysis was higher in adults, and a greater decline was observed in aged males particularly. These data confirmed the age-dependent differences between female and male mice; therefore, gender should be considered one of the major factors for personalized treatment in clinical diagnosis and treatment.

Standardization of Animal Models and Techniques for Platelet-Rich Fibrin Production: A Narrative Review and Guideline

Experimental research is critical for advancing medical knowledge and enhancing patient outcomes, including in vitro and in vivo preclinical assessments. Platelet-rich fibrin (PRF) is a blood by-product that has garnered attention in the medical and dental fields due to its potential for tissue regeneration and wound healing. Animal models, such as rabbits and rats, have been used to produce PRF and examine its properties and applications. PRF has demonstrated potential in the dental and medical fields for reducing inflammation, promoting tissue repair, and accelerating wound healing. This narrative review aims to compare existing evidence and provide guidelines for PRF animal research, emphasizing the importance of standardizing animal models, following ethical considerations, and maintaining transparency and accountability. The authors highlight the necessity to use the correct relative centrifugal force (RCF), standardize centrifugal calibration, and report detailed information about blood collection and centrifuge parameters for reproducible results. Standardizing animal models and techniques is crucial for narrowing the gap between laboratory research and clinical applications, ultimately enhancing the translation of findings from bench to bedside.

Comparison of Cardiovascular Pathology In Animal Models of SARS-CoV-2 Infection: Recommendations Regarding Standardization of Research Methods

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged as the viral pathogen that led to the global COVID-19 pandemic that began in late 2019. Because SARS-CoV-2 primarily causes a respiratory disease, much research conducted to date has focused on the respiratory system. However, SARS-CoV-2 infection also affects other organ systems, including the cardiovascular system. In this critical analysis of published data, we evaluate the evidence of cardiovascular pathology in human patients and animals. Overall, we find that the presence or absence of cardiovascular pathology is reported infrequently in both human autopsy studies and animal models of SARS-CoV-2 infection. Moreover, in those studies that have reported cardiovascular pathology, we identified issues in their design and execution that reduce confidence in the conclusions regarding SARS-CoV-2 infection as a cause of significant cardiovascular pathology. Throughout this overview, we expand on these limitations and provide recommendations to ensure a high level of scientific rigor and reproducibility.

Maternal exposure of rats to sodium saccharin during gestation and lactation on male offspring†

We investigated the effects of fetal programming in Sprague-Dawley rats through the maternal consumption of sodium saccharin on the testicular structure and function in male offspring. Feed intake and efficiency, organ and fat weight, quantification and expression of androgen receptor (AR), and proliferating cell nuclear antigen (PCNA) proteins, sperm count, and hormone levels were determined. Consumption alterations were found in the final weeks of the experiment. Decreases in AR and PCNA expression and quantification, tubular diameter, and luminal volume, and increases in epithelial and interstitial relative volumes were observed. Lower sperm count and transit, and lower estradiol concentration were also found. Sodium saccharin consumption by dams programmed male offspring by affecting the hypothalamic-pituitary-gonad axis with alterations in the Sertoli cell population, in spermatogonia proliferation, the expression and quantification of AR, and in sperm count. We hypothesized that these changes may be due to an estradiol reduction that caused the loosening of adhesion junctions of the blood-testis barrier, causing cell losses during spermatogenesis, also reflected by a decrease in tubular diameter with an increase in epithelial volume and consequent decrease in luminal volume. We conclude that maternal sodium saccharin consumption during pregnancy and lactation programmed alterations in the reproductive parameters of male offspring, thus influencing spermatogenesis.

Animal Study Translation: The Other Reproducibility Challenge

Animal research is currently an irreplaceable contributor to our efforts to protect and improve public health. Its relevance, importance, and contributions are represented in historical precedent, regulatory expectations, evidence of our rapidly developing understanding of human health and disease, as well as success in the development of novel therapeutics that are improving quality of life and extending human and animal life expectancy. The rapid and evolving success in responding to the current COVID pandemic significantly supported by animal studies is a clear example of the importance of animal research. But there is growing interest in reducing our dependence on animals and challenges to the effective translation of current animal studies to human applications. There are several potential contributors to gaps in the translatability of animal research to humans, including our approaches to choosing or rationalizing the relevance of a particular animal model, our understanding of their biological variability and how that applies to outcomes, the data we collect from animal studies, and even how we manage the animals. These important contributors to the success of animal research are explored in this issue of the ILAR Journal.