Aging research using the common marmoset: Focus on aging interventions

Comparative lifespan and healthspan of nonhuman primate species common to biomedical research

There is a critical need to generate age- and sex-specific survival curves to characterize chronological aging consistently across nonhuman primates (NHP) used in biomedical research. Accurate measures of chronological aging are essential for inferences into genetic, demographic, and physiological variables driving differences in NHP lifespan within and between species. Understanding NHP lifespans is relevant to public health because unraveling the demographic, molecular, and clinical bases of health across the life course in translationally relevant NHP species is fundamentally important to the study of human aging. Data from more than 110,000 captive individual NHP were contributed by 15 major research institutions to generate sex-specific Kaplan-Meier survival curves using uniform methods in 12 translational aging models: Callithrix jacchus (common marmoset), Chlorocebus aethiops sabaeus (vervet/African green), Macaca fascicularis (cynomolgus macaque), M. fuscata (Japanese macaque), M. mulatta (rhesus macaque), M. nemestrina (pigtail macaque), M. radiata (bonnet macaque), Pan troglodytes spp. (chimpanzee), Papio hamadryas spp. (baboon), Plecturocebus cupreus (coppery titi monkey), Saguinus oedipus (cotton-top tamarin), and Saimiri spp. (squirrel monkey). After employing strict inclusion criteria, primary analysis results are based on 12,269 NHP that survived to adulthood and died of natural/health-related causes. A secondary analysis was completed for 32,616 NHP that died of any cause. For the primary analyses, we report ages of 25th, 50th, 75th, and 85th percentiles of survival, maximum observed ages, rates of survivorship, and sex-based differences captured by quantile regression models and Kolmogorov-Smirnov tests. Our findings show a pattern of reduced male survival among catarrhines (African and Asian primates), especially macaques, but not platyrrhines (Central and South American primates). For many species, median lifespans were lower than previously reported. An important consideration is that these analyses may offer a better reflection of healthspan than lifespan. Captive NHP used in research are typically euthanized for humane welfare reasons before their natural end of life, often after diagnosis of their first major disease requiring long-term treatment with reduced quality of life (e.g., endometriosis, cancer, osteoarthritis). Supporting the idea that these data are capturing healthspan, for several species typical age at onset of chronic disease is similar to the median lifespan estimates. This data resource represents the most comprehensive characterization of sex-specific lifespan and age-at-death distributions for 12 biomedically relevant species, to date. The results clarify the relationships among NHP ages and will provide a valuable resource for the aging research community, improving human-NHP age equivalencies, informing investigators of the expected survival rates of NHP assigned to studies, providing a metric for comparisons in future studies, and contributing to our understanding of the factors that drive lifespan differences within and among species.

A pilot study evaluating dosing tolerability of 17α-estradiol in male common marmosets (Callithrix jacchus)

17α-estradiol extends healthspan and lifespan in male mice without significant feminization or deleterious effects on reproductive function, making it a candidate for human translation. However, studies in animal models that more accurately replicate human physiology are necessary to establish 17α-estradiol dosing standards for clinical trials. This study evaluated the tolerability of 17α-estradiol treatment in the common marmoset over a short treatment duration. We found that male marmosets tolerated two dosing regimens (0.37-0.47 or 0.62-0.72 mg/kg/day) as evidenced by the absence of gastrointestinal distress, changes in vital signs, or overall health conditions. 17α-estradiol treatment mildly decreased body mass, adiposity, and glycosylated hemoglobin, although these changes were not statistically significant in most instances. However, neither dose of 17α-estradiol elicited feminization in our study, thereby suggesting that optimized dosing regimens may provide health benefits without feminization in primates. Additional studies are needed to determine if longer duration treatments would also be nonfeminizing and elicit significant health benefits, which would aid in developing dosing regimens targeting healthy aging in humans.

Development of a noninvasive olfactory stimulation fMRI system in marmosets

Olfactory dysfunction is associated with aging and the earliest stages of neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases; it is thought to be an early biomarker of cognitive decline. In marmosets, a small non-human primate model used in brain research, olfactory pathway activity during olfactory stimulation has not been well studied because of the difficulty in clearly switching olfactory stimuli inside a narrow MRI. Here, we developed an olfactory-stimulated fMRI system using a small-aperture MRI machine. The olfactory presentation system consisted of two tubes, one for supply and one for suction of olfactory stimulants and a balloon valve. A balloon valve installed in the air supply tube controlled the presentation of the olfactory stimulant, which enabled sharp olfactory stimulation within MRI, such as 30 s of stimulation repeated five times at five-minute intervals. The olfactory stimulation system was validated in vivo and in a simulated system. fMRI analysis showed a rapid increase in signal values within 30 s of olfactory stimulation in eight regions related to the sense of smell. As these regions include those associated with Alzheimer's and Parkinson's diseases, olfactory stimulation fMRI may be useful in clarifying the relationship between olfactory dysfunction and dementia in non-human primates.

Genetic characterization of a captive marmoset (Callithrix jacchus) colony using genotype-by-sequencing

The marmoset is a fundamental nonhuman primate model for the study of aging, neurobiology, and many other topics. Genetic management of captive marmoset colonies is complicated by frequent chimerism in the blood and other tissues, a lack of tools to enable cost-effective, genome-wide interrogation of variation, and historic mergers and migrations of animals between colonies. We implemented genotype-by-sequencing (GBS) of hair follicle derived DNA (a minimally chimeric DNA source) of 82 marmosets housed at the Southwest National Primate Research Center (SNPRC). Our primary goals were the genetic characterization of our marmoset population for pedigree verification and colony management and to inform the scientific community of the functional genetic makeup of this valuable resource. We used the GBS data to reconstruct the genetic legacy of recent mergers between colonies, to identify genetically related animals whose relationships were previously unknown due to incomplete pedigree information, and to show that animals in the SNPRC colony appear to exhibit low levels of inbreeding. Of the >99,000 single-nucleotide variants (SNVs) that we characterized, >9800 are located within gene regions known to harbor pathogenic variants of clinical significance in humans. Overall, we show the combination of low-resolution (sparse) genotyping using hair follicle DNA is a powerful strategy for the genetic management of captive marmoset colonies and for identifying potential SNVs for the development of biomedical research models.

Changes in oral health during aging in a novel non-human primate model

Oral health plays a significant role in the quality of life and overall well-being of the aging population. However, age-related changes in oral health are not well understood due to challenges with current animal models. In this study, we analyzed the oral health and microbiota of a short-lived non-human primate (i.e., marmoset), as a step towards establishing a surrogate for studying the changes that occur in oral health during human aging. We investigated the oral health of marmosets using cadaveric tissues in three different cohorts: young (aged ≤6 years), middle-aged, and older (>10 years) and assessed the gingival bacterial community using analyses of the V3-V4 variable region of 16S rRNA gene. The oldest cohort had a significantly higher number of dental caries, increased dental attrition/erosion, and deeper periodontal pocket depth scores. Oral microbiome analyses showed that older marmosets had a significantly greater abundance of Escherichia-Shigella and Propionibacterium, and a lower abundance of Agrobacterium/Rhizobium at the genus level. Alpha diversity of the microbiome between the three groups showed no significant differences; however, principal coordinate analysis and non-metric multidimensional scaling analysis revealed that samples from middle-aged and older marmosets were more closely clustered than the youngest cohort. In addition, linear discriminant analysis effect size (LEFSe) identified a higher abundance of Esherichia-Shigella as a potential pathogenic biomarker in older animals. Our findings confirm that changes in the oral microbiome are associated with a decline in oral health in aging marmosets. The current study suggests that the marmoset model recapitulates some of the changes in oral health associated with human aging and may provide opportunities for developing new preventive strategies or interventions which target these disease conditions.

Age-related changes in hematological biomarkers in common marmosets

Researchers and veterinarians often use hematology and clinical chemistry to evaluate animal health. These biomarkers are relatively easy to obtain, and understanding how they change across healthy aging is critical to clinical care and diagnostics for these animals. We aimed to evaluate how clinical biomarkers from a chemistry profile and complete blood count (CBC) change with age in common marmosets (Callithrix jacchus). We assessed blood samples collected during routine physical exams at the Southwest National Primate Research Center and the University of Texas Health San Antonio marmoset colonies from November 2020-November 2021. We found that chemistry and CBC profiles varied based on facility, sex, and age. Significant changes in albumin, phosphorus/creatinine ratio, albumin/globulin ratio, amylase, creatinine, lymphocyte percent, hematocrit, granulocytes percent, lymphocytes, hemoglobin, red cell distribution width, and platelet distribution width were all reported with advancing age. Aged individuals also demonstrated evidence for changes in liver, kidney, and immune system function compared with younger individuals. Our results suggest there may be regular changes associated with healthy aging in marmosets that are outside of the range typically considered as normal values for healthy young individuals, indicating the potential need for redefined healthy ranges for clinical biomarkers in aged animals. Identifying animals that exhibit values outside of this defined healthy aging reference will allow more accurate diagnostics and treatments for aging colonies.

Improving preclinical to clinical translation of cognitive function for aging-related disorders: the utility of comprehensive touchscreen testing batteries in common marmosets

Concerns about poor animal to human translation have come increasingly to the fore, in particular with regards to cognitive improvements in rodent models, which have failed to translate to meaningful clinical benefit in humans. This problem has been widely acknowledged, most recently in the field of Alzheimer's disease, although this issue pervades the spectrum of central nervous system (CNS) disorders, including neurodevelopmental, neuropsychiatric, and neurodegenerative diseases. Consequently, recent efforts have focused on improving preclinical to clinical translation by incorporating more clinically analogous outcome measures of cognition, such as touchscreen-based assays, which can be employed across species, and have great potential to minimize the translational gap. For aging-related research, it also is important to incorporate model systems that facilitate the study of the long prodromal phase in which cognitive decline begins to emerge and which is a major limitation of short-lived species, such as laboratory rodents. We posit that to improve translation of cognitive function and dysfunction, nonhuman primate models, which have conserved anatomical and functional organization of the primate brain, are necessary to move the field of translational research forward and to bridge the translational gaps. The present studies describe the establishment of a comprehensive battery of touchscreen-based tasks that capture a spectrum of domains sensitive to detecting aging-related cognitive decline, which will provide the greatest benefit through longitudinal evaluation throughout the prolonged lifespan of the marmoset.

Development and assessment of a stair ascension challenge as a measure of aging and physical function in nonhuman primates

Nonhuman primates (NHPs) are valuable models for studying healthspan, including frailty development. Frailty metrics in people centers on functional measures, including usual gait speed which can be predictive of all-cause mortality. This concept that physical competencies are able to prognosticate an individual's health trajectory over chronologic aging is well-accepted and has led to refinements in how physical function is evaluated, and include measures of strength and power along with walking speed. NHP studies of aging require evaluation of physical function, which can be difficult in field and research settings. We compared stair climb velocity to usual walking speed in 28 peri-geriatric to geriatric NHPs, as incorporating a climbing obstacle integrates multiple components of physical function: isolated leg and back strength, proprioception, balance, and range of motion. We find that stair climbing speed was reliable between observers, and whether timing was in-person take from video capture. The stair climb rates were 50% more associated with chronological age than walking speed (R = -0.68 vs. -0.45) and only stair climbing speeds were retained as predictive of age when walking speed and bodyweight were included in multivariate models (overall R2  = 0.44; p < 0.0001). When comparing young (10-16 years) versus geriatric (16-29 years) stair climbing speed was significantly different (p < 0.001), while walking speeds only tended to be slower (p = 0.12) suggesting that the additional challenge of a stair climb better unmasks subclinical frailty development that usual walking speed.

The importance of social behavior in nonhuman primate studies of aging: A mini-review

Social behavior plays an important role in supporting both psychological and physical health across the lifespan. People's social lives change as they age, and the nature of these changes differ based on whether people are on healthy aging trajectories or are experiencing neurodegenerative diseases that cause dementia, such as Alzheimer's disease and Parkinson's disease. Nonhuman primate models of aging have provided a base of knowledge comparing aging trajectories in health and disease, but these studies rarely emphasize social behavior changes as a consequence of the aging process. What data exist hold particular value, as negative effects of disease and aging on social behavior are likely to have disproportionate impacts on quality of life. In this mini review, we examine the literature on nonhuman primate models of aging with a focus on social behavior, in the context of both health and disease. We propose that adopting a greater focus on social behavior outcomes in nonhuman primates will improve our understanding of the intersection of health, aging and sociality in humans.

Survival rates and mortality risks of Plecturocebus cupreus at the California National Primate Research Center

This article describes survivorship and explores factors affecting mortality risks in a captive colony of coppery titi monkeys (Plecturocebus cupreus) housed at the California National Primate Research Center (CNPRC), at UC Davis, in Davis, CA. We analyzed data collected on individuals since the colony's creation in the 1960s, with a sample of 600 animals with partially complete information (date of birth, age at death, body mass, parental lineage). We used three methods: (1) Kaplan-Meier regressions followed by a log-rank test to compare survival in male and female titi monkeys, (2) a breakpoint analysis to identify shifts in the survival curves, and (3) Cox regressions to test the effect of body mass change, parental pair tenure, and parental age on mortality risk. We found that males tend to have a longer median lifespan than females (14.9 and 11.4 years; p = 0.094) and that survival decreases earlier in males than in females during adulthood (9.8 and 16.2 years). A body mass loss of 10% from adulthood to the time of death led to a 26% higher risk of dying (p < 0.001) as compared to an individual with stable body mass. We found no evidence of sociobiological factors on mortality risks (parental age, parental pair tenure), but an exploratory analysis suggested that a higher rate of offspring conceptions increases mortality risks. This description of factors influencing survival and mortality in titi monkeys is a first step toward understanding aging in this species to consider titi monkeys as a primate model for socioemotional aging.

Review of Environmental and Health Factors Impacting Captive Common Marmoset Welfare in the Biomedical Research Setting

As a small-bodied neotropical nonhuman primate species, common marmosets have unique requirements for adequate husbandry and veterinary care to ensure proper maintenance and to promote good animal welfare in a biomedical research setting. Environmental conditions, as well as medical and research-related manipulations, can impact marmoset welfare. Research focus areas, including basic neuroscience, transgenics, and aging, involve additional implications for marmoset welfare. This manuscript provides a comprehensive review of factors that should be considered and mitigated as needed by clinical and research staff working with marmosets in biomedical research facilities to optimize the welfare of captive marmosets.

Functional Cardiovascular Characterization of the Common Marmoset (Callithrix jacchus)

Appropriate cardiovascular animal models are urgently needed to investigate genetic, molecular, and therapeutic approaches, yet the translation of results from the currently used species is difficult due to their genetic distance as well as their anatomical or physiological differences. Animal species that are closer to the human situation might help to bridge this translational gap. The common marmoset (Callithrix jacchus) is an interesting candidate to investigate certain heart diseases and cardiovascular comorbidities, yet a basic functional characterization of its hemodynamic system is still missing. Therefore, cardiac functional analyses were performed by utilizing the invasive intracardiac pressure-volume loops (PV loop) system in seven animals, magnetic resonance imaging (MRI) in six animals, and echocardiography in five young adult male common marmosets. For a direct comparison between the three methods, only data from animals for which all three datasets could be acquired were selected. All three modalities were suitable for characterizing cardiac function, though with some systemic variations. In addition, vena cava occlusions were performed to investigate the load-independent parameters collected with the PV loop system, which allowed for a deeper analysis of the cardiac function and for a more sensitive detection of the alterations in a disease state, such as heart failure or certain cardiovascular comorbidities.

Neuronal vulnerability to brain aging and neurodegeneration in cognitively impaired marmoset monkeys (Callithrix jacchus)

The investigation of neurobiological and neuropathological changes that affect synaptic integrity and function with aging is key to understanding why the aging brain is vulnerable to Alzheimer's disease. We investigated the cellular characteristics in the cerebral cortex of behaviorally characterized marmosets, based on their trajectories of cognitive learning as they transitioned to old age. We found increased astrogliosis, increased phagocytic activity of microglial cells and differences in resting and reactive microglial cell phenotypes in cognitively impaired compared to nonimpaired marmosets. Differences in amyloid beta deposition were not related to cognitive trajectory. However, we found age-related changes in density and morphology of dendritic spines in pyramidal neurons of layer 3 in the dorsolateral prefrontal cortex and the CA1 field of the hippocampus between cohorts. Overall, our data suggest that an accelerated aging process, accompanied by neurodegeneration, that takes place in cognitively impaired aged marmosets and affects the plasticity of dendritic spines in cortical areas involved in cognition and points to mechanisms of neuronal vulnerability to aging.

Co-registration of Imaging Modalities (MRI, CT and PET) to Perform Frameless Stereotaxic Robotic Injections in the Common Marmoset

The common marmoset has emerged as a popular model in neuroscience research, in part due to its reproductive efficiency, genetic and neuroanatomical similarities to humans and the successful generation of transgenic lines. Stereotaxic procedures in marmosets are guided by 2D stereotaxic atlases, which are constructed with a limited number of animals and fail to account for inter-individual variability in skull and brain size. Here, we developed a frameless imaging-guided stereotaxic system that improves upon traditional approaches by using subject-specific registration of computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET) data to identify a surgical target, namely the putamen, in two marmosets. The skull surface was laser-scanned to create a point cloud that was registered to the 3D reconstruction of the skull from CT. Reconstruction of the skull, as well as of the brain from MR images, was crucial for surgical planning. Localisation and injection into the putamen was done using a 6-axis robotic arm controlled by a surgical navigation software (Brainsight™). Integration of subject-specific registration and frameless stereotaxic navigation allowed target localisation specific to each animal. Injection of alpha-synuclein fibrils into the putamen triggered progressive neurodegeneration of the nigro-striatal system, a key feature of Parkinson's disease. Four months post-surgery, a PET scan found evidence of nigro-striatal denervation, supporting accurate targeting of the putamen during co-registration and subsequent surgery. Our results suggest that this approach, coupled with frameless stereotaxic neuronavigation, is accurate in localising surgical targets and can be used to assess endpoints for longitudinal studies.

Hallmarks of Testicular Aging: The Challenge of Anti-Inflammatory and Antioxidant Therapies Using Natural and/or Pharmacological Compounds to Improve the Physiopathological Status of the Aged Male Gonad

The evolutionary theory of aging supports a trade-off relationship between reproduction and aging. Aging of the male reproductive system primarily affects the testes, leading to a decrease in the levels of sexual hormones, alterations in sperm quality and production, and a decline in fertility that does not necessarily involve a complete cessation of spermatogenesis. Inflammation, oxidation, and apoptosis are events considered as predictors of pathogenesis and the development of age-related diseases that are frequently observed in aged testes. Although the molecular mechanisms are still poorly understood, accumulating evidence points toward pro-inflammatory molecules and reactive oxygen species as primary contributing factors for testicular aging. However, the real impact of aging-related testicular alterations on fertility, reproductive health, and life span is far from being fully revealed. This work discusses the current knowledge on the impact of aging in the testis, particularly of aging-related dysregulated inflammation and oxidative damage on the functioning of its different cell populations. More interestingly, this review covers the potential benefits of anti-aging interventions and therapies using either pharmacological compounds (such as non-selective non-steroidal anti-inflammatory medication) or more natural alternatives (such as various nutraceuticals or even probiotics) that exhibit anti-inflammatory, antioxidant, and anti-apoptotic properties. Some of these are currently being investigated or are already in clinical use to delay or prevent testicular aging.

Location and temporal memory of objects declines in aged marmosets (Callithrix jacchus)

Episodic memory decline is an early marker of cognitive aging in human. Although controversial in animals and called “episodic-like memory”, several models have been successfully developed, however they rarely focused on ageing. While marmoset is an emerging primate model in aging science, episodic-like memory has never been tested in this species and importantly in aged marmosets. Here, we examined if the recall of the what-when and what-where building blocks of episodic-like memory declines in ageing marmosets. We developed a naturalistic approach using spontaneous exploration of real objects by young and old marmosets in the home cage. We implemented a three-trial task with 1 week inter-trial interval. Two different sets of identical objects were presented in sample trials 1 and 2, respectively. For the test trial, two objects from each set were presented in a former position and two in a new one. We quantified the exploratory behaviour and calculated discrimination indices in a cohort of 20 marmosets. Young animals presented a preserved memory for combined what-where, and what-when components of the experiment, which declined with aging. These findings lead one to expect episodic-like memory deficits in aged marmosets.

Primary neuron and astrocyte cultures from postnatal Callithrix jacchus: a non-human primate in vitro model for research in neuroscience, nervous system aging, and neurological diseases of aging

The ability to generate in vitro cultures of neuronal cells has been instrumental in advancing our understanding of the nervous system. Rodent models have been the principal source of brain cells used in primary cultures for over a century, providing insights that are widely applicable to human diseases. However, therapeutic agents that showed benefit in rodent models, particularly those pertaining to aging and age-associated dementias, have frequently failed in clinical trials. This discrepancy established a potential "translational gap" between human and rodent studies that may at least partially be explained by the phylogenetic distance between rodent and primate species. Several non-human primate (NHP) species, including the common marmoset (Callithrix jacchus), have been used extensively in neuroscience research, but in contrast to rodent models, practical approaches to the generation of primary cell culture systems amenable to molecular studies that can inform in vivo studies are lacking. Marmosets are a powerful model in biomedical research and particularly in studies of aging and age-associated diseases because they exhibit an aging phenotype similar to humans. Here, we report a practical method to culture primary marmoset neurons and astrocytes from brains of medically euthanized postnatal day 0 (P0) marmoset newborns that yield highly pure primary neuron and astrocyte cultures. Primary marmoset neuron and astrocyte cultures can be generated reliably to provide a powerful NHP in vitro model in neuroscience research that may enable mechanistic studies of nervous system aging and of age-related neurodegenerative disorders. Because neuron and astrocyte cultures can be used in combination with in vivo approaches in marmosets, primary marmoset neuron and astrocyte cultures may help bridge the current translational gap between basic and clinical studies in nervous system aging and age-associated neurological diseases.

The Importance of Complementary Collaboration of Researchers, Veterinarians, and Husbandry Staff in the Successful Training of Marmoset Behavioral Assays

Interest in marmosets as research models has seen exponential growth over the last decade, especially given that the research community is eager to improve on gaps with historical animal models for behavioral and cognitive disorders. The spectrum of human disease traits that present naturally in marmosets, as well as the range of analogous human behaviors that can be assessed in marmosets, makes them ideally suited as translational models for behavioral and cognitive disorders. Regardless of the specific research aims of any project, without close collaboration between researchers, veterinarians, and animal care staff, it would be impossible to meet these goals. Behavior is inherently variable, as are marmosets that are genetically and phenotypically diverse. Thus, to ensure rigor, reliability, and reproducibility in results, it is important that in the research environment, the animal's daily husbandry and veterinary needs are being met and align with the research goals while keeping the welfare of the animal the most critical and highest priority. Much of the information described herein provides details on key components for successful behavioral testing, based on a compendium of methods from peer-reviewed publications and our own experiences. Specific areas highlighted include habituation procedures, selection of appropriate rewards, optimization of testing environments, and ways to integrate regular veterinary and husbandry procedures into the research program with minimal disruptions to the behavioral testing plan. This article aims to provide a broad foundation for researchers new to establishing behavioral and cognitive testing paradigms in marmosets and especially for the veterinary and husbandry colleagues who are indispensable collaborators of these research projects.

Marmoset Metabolism, Nutrition, and Obesity

The use of marmosets as nonhuman primate models of human disease has undergone rapid expansion in the United States in the last decade, with an emphasis in the field of neuroscience. With this expanding need, there has been an increase in the formation of small marmoset colonies. The standardization in care and husbandry techniques for marmosets has historically lagged behind other established nonhuman primate models, resulting in a great deal of variation in practices between colonies. There remains a lack of consensus and evidence-based recommendations regarding best standards for nutrition, enrichment, weight management, and diagnostics for clinical metabolic disease. Marmoset base diets vary broadly in their nutritional value, and therefore the physiological responses to these diets also vary broadly. In this review, we briefly outline what is known about nutrition for captive marmosets and highlight what is known regarding metabolic dysfunction and obesity.

Feasibility of fecal microbiota transplantation via oral gavage to safely alter gut microbiome composition in marmosets

Disruption of microbial communities within human hosts has been associated with infection, obesity, cognitive decline, cancer risk and frailty, suggesting that microbiome-targeted therapies may be an option for improving healthspan and lifespan. The objectives of this study were to determine the feasibility of delivering fecal microbiota transplants (FMTs) to marmosets via oral gavage and to evaluate if alteration of the gut microbiome post-FMT could be achieved. This was a prospective study of marmosets housed at the Barshop Institute for Longevity and Aging Studies in San Antonio, Texas. Eligible animals included healthy young adult males (age 2-5 years) with no recent medication use. Stool from two donors was combined and administered in 0.5 ml doses to five young recipients once weekly for 3 weeks. Safety outcomes and alterations in the gut microbiome composition via 16S ribosomal RNA sequencing were compared at baseline and monthly up to 6 months post-FMT. Overall, significant differences in the percent relative abundance was seen in FMT recipients at the phylum and family levels from baseline to 1 month and baseline to 6 months post-FMT. In permutational multivariate analysis of variance analyses, treatment status (donor vs. recipient) (p = .056) and time course (p = .019) predicted β diversity (p = .056). The FMT recipients did not experience any negative health outcomes over the course of the treatment. FMT via oral gavage was safe to administer to young adult marmosets. The marmoset microbiome may be altered by FMT; however, progressive changes in the microbiome are strongly driven by the host and its baseline microbiome composition.

Age-Related Alterations in Brain Perfusion, Venous Oxygenation, and Oxygen Metabolic Rate of Mice: A 17-Month Longitudinal MRI Study

Background: Characterization of physiological parameters of the aging brain, such as perfusion and brain metabolism, is important for understanding brain function and diseases. Aging studies on human brain have mostly been based on the cross-sectional design, while the few longitudinal studies used relatively short follow-up time compared to the lifespan. Objectives: To determine the longitudinal time courses of cerebral physiological parameters across the adult lifespan in mice. Methods: The present work examined longitudinal changes in cerebral blood flow (CBF), cerebral venous oxygenation (Yv), and cerebral metabolic rate of oxygen (CMRO2) using MRI in healthy C57BL/6 mice from 3 to 20 months of age. Each mouse received 16 imaging sessions at an ~1-month interval. Results: Significant increases with age were observed in CBF (p = 0.017) and CMRO2 (p < 0.001). Meanwhile, Yv revealed a significant decrease (p = 0.002) with a non-linear pattern (p = 0.013). The rate of change was 0.87, 2.26, and -0.24% per month for CBF, CMRO2, and Yv, respectively. On the other hand, systemic parameters such as heart rate did not show a significant age dependence (p = 0.47). No white-matter-hyperintensities (WMH) were observed on the T2-weighted image at any age of the mice. Conclusion: With age, the mouse brain revealed an increase in oxygen consumption. This observation is consistent with previous findings in humans using a cross-sectional design and suggests a degradation of the brain's energy production or utilization machinery. Cerebral perfusion remains relatively intact in aged mice, at least until 20 months of age, consistent with the absence of WMH in mice.