Characterization of obese phenotypes in a small nonhuman primate, the common marmoset (Callithrix jacchus)

In vitro matured oocytes have a higher developmental potential than in vivo matured oocytes after hormonal ovarian stimulation in Callithrix jacchus

BACKGROUND

The common marmoset, Callithrix jacchus, is an invaluable model in biomedical research. Its use includes genetic engineering applications, which require manipulations of oocytes and production of embryos in vitro. To maximize the recovery of oocytes suitable for embryo production and to fulfil the requirements of the 3R principles to the highest degree possible, optimization of ovarian stimulation protocols is crucial. Here, we compared the efficacy of two hormonal ovarian stimulation approaches: 1) stimulation of follicular growth with hFSH followed by triggering of oocyte maturation with hCG (FSH + hCG) and 2) stimulation with hFSH only (FSH-priming).

METHODS

In total, 14 female marmosets were used as oocyte donors in this study. Each animal underwent up to four surgical interventions, with the first three performed as ovum pick-up (OPU) procedures and the last one being an ovariohysterectomy (OvH). In total, 20 experiments were carried out with FSH + hCG stimulation and 18 with FSH-priming. Efficacy of each stimulation protocol was assessed through in vitro maturation (IVM), in vitro fertilization (IVF) and embryo production rates.

RESULTS

Each study group consisted of two subgroups: the in vivo matured oocytes and the oocytes that underwent IVM. Surprisingly, in the absence of hCG triggering some of the oocytes recovered were at the MII stage, moreover, their number was not significantly lower compared to FSH + hCG stimulation (2.8 vs. 3.9, respectively (ns)). While the IVM and IVF rates did not differ between the two stimulation groups, the IVF rates of in vivo matured oocytes were significantly lower compared to in vitro matured ones in both FSH-priming and FSH + hCG groups. In total, 1.7 eight-cell embryos/experiment (OPU) and 2.1 eight-cell embryos/experiment (OvH) were obtained after FSH + hCG stimulation vs. 1.8 eight-cell embryos/experiment (OPU) and 5.0 eight-cell embryos/experiment (OvH) following FSH-priming. These numbers include embryos obtained from both in vivo and in vitro matured oocytes.

CONCLUSION

A significantly lower developmental competence of the in vivo matured oocytes renders triggering of the in vivo maturation with hCG as a part of the currently used FSH-stimulation protocol unnecessary. In actual numbers, between 1 and 7 blastocysts were obtained following each FSH-priming. In the absence of further studies, FSH-priming appears superior to FSH + hCG stimulation in the common marmoset under current experimental settings.

Comparing different strategies to reduce hepatocellular damage in obese common marmosets (Callithrix jacchus)

BACKGROUND

Obesity in common marmosets (Callithrix jacchus) can lead to various liver pathologies. In other species, reduced caloric intake and weight loss improve prognosis, and, often, hepatoprotectants are used to halt or reverse hepatocellular damage from fat deposition in the liver. There are no published therapies for reducing hepatocellular damage in obese marmosets.

METHODS

Fifteen obese marmosets were used to evaluate the ability of caloric restriction and pharmacologic therapy (S-adenosylmethionine + milk thistle extract, or SMT), alone and combined, to reduce elevated liver enzymes. Body weight and serum chemistries were measured every 4 weeks for 6 months.

RESULTS

Across treatment groups, there was a significant reduction in liver enzymes ALT and AST over time. SMT alone significantly reduced liver enzymes ALT and AST at 6 months from baseline.

CONCLUSIONS

Caloric restriction and SMT, alone and combined, are effective at reducing liver enzyme levels in obese 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.

The common marmoset as a model of neurodegeneration

Human life expectancy has increased over the past few centuries, and the incidence of dementia in the older population is also projected to continue to rise. Neurodegenerative diseases are complex multifactorial conditions for which no effective treatments are currently available. Animal models are necessary to understand the causes and progression of neurodegeneration. Nonhuman primates (NHPs) offer significant advantages for the study of neurodegenerative disease. Among them, the common marmoset, Callithrix jacchus, stands out due to its easy handling, complex brain architecture, and occurrence of spontaneous beta-amyloid (Aβ) and phosphorylated tau aggregates with aging. Furthermore, marmosets present physiological adaptations and metabolic alterations associated with the increased risk of dementia in humans. In this review, we discuss the current literature on the use of marmosets as a model of aging and neurodegeneration. We highlight aspects of marmoset physiology associated with aging, such as metabolic alterations, which may help understand their vulnerability to developing a neurodegenerative phenotype that goes beyond normal aging.

Womb to womb: Maternal litter size and birth weight but not adult characteristics predict early neonatal death of offspring in the common marmoset monkey

A singular focus on maternal health at the time of a pregnancy leaves much about perinatal mortality unexplained, especially when there is growing evidence for maternal early life effects. Further, lumping stillbirth and early neonatal death into a single category of perinatal mortality may obscure different causes and thus different avenues of screening and prevention. The common marmoset monkey (Callithrix jacchus), a litter-bearing nonhuman primate, is an ideal species in which to study the independent effects of a mother's early life and adult phenotypes on pregnancy outcomes. We tested two hypotheses in 59 marmoset pregnancies at the Southwest National Primate Research Center and the Barshop Institute for Longevity and Aging Studies. We explored 1) whether pregnancy outcomes were predicted independently by maternal adult weight versus maternal litter size and birth weight, and 2) whether stillbirth and early neonatal death were differentially predicted by maternal variables. No maternal characteristics predicted stillbirth and no maternal adult characteristics predicted early neonatal death. In univariate Poisson models, triplet-born females had a significantly increased rate of early neonatal death (IRR[se] = 3.00[1.29], p = 0.011), while higher birth weight females had a decreased rate (IRR[se] = 0.89[0.05], p = 0.039). In multivariate Poisson models, maternal litter size remained an independent predictor, explaining 13% of the variance in early neonatal death. We found that the later in the first week those neonates died, the more weight they lost. Together these findings suggest that triplet-born and low birth weight females have distinct developmental trajectories underlying greater rates of infant loss, losses that we suggest may be attributable to developmental disruption of infant feeding and carrying. Our findings of early life contributions to adult pregnancy outcomes in the common marmoset disrupt mother-blaming narratives of pregnancy outcomes in humans. These narratives hold that the pregnant person is solely responsible for pregnancy outcomes and the health of their children, independent of socioecological factors, a moralistic framing that has shaped clinical pregnancy management. It is necessary to differentiate temporal trajectories and causes of perinatal loss and view them as embedded in external processes to develop screening, diagnostic, and treatment tools that consider the full arc of a mother's lived experience, from womb to womb and beyond.

Protective effects of the imidazoline-like drug lnp599 in a marmoset model of obesity-induced metabolic disorders

BACKGROUND/OBJECTIVES

Overweight and obesity are undoubtable risk factors for type 2 diabetes and cardiovascular diseases and significantly contribute to the global morbi-mortality. We previoulsy reported that LNP599, a pharmacological imidazoline-like activator of hepatic AMPK/adiponectin signaling, protects against the development of adiposity and obesity and the associated cardio-metabolic disorders, suggesting that it may be a suitable drug candidate for a therapeutic approach targeting the development of obesity at very early stages. The objective of the present study was to evaluate the metabolic effects of LNP599 in a model of diet-induced overweight and metabolic disorders in a nonhuman primate, the common marmoset (Callithrix jacchus), and more particularly to establish the impact of the compound on cholesterol homeostasis, i.e., HDL and LDL/VLDL lipoproteins.

METHODS

Marmosets were fed normal (NC) or hypercaloric (HC) chow during 16 weeks. Diet-induced changes in body weight and metabolism were assessed. Effects of LNP599 were evaluated in a subset of HC animals (HC-LNP) receiving the compound at a daily dose of 10 mg/kg over the 16 weeks.

RESULTS

HC-feeding induced significant overweight associated with a marked dyslipidemia (hypertriglyceridemia, hypercholesterolemia, and reduced HDL over LDL/VLDL cholesterol ratio). LNP599 blunted the diet-induced body weight gain and largely protected against the development of hypertriglyceridemia. Total cholesterol was unchanged but the ratio of HDL over LDL/VLDL cholesterol was more than doubled.

CONCLUSIONS

The profile of metabolic troubles obtained upon enriched diet mimicked the disorders associated with spontaneous obesity in marmosets. HC marmosets represent an experimental model of high clinical relevance to study the pathophysiology of obesity and related dyslipidemia and to evaluate the effects of emerging therapies targeting these disorders. Our data confirm the preventing effects of LNP599 in a nonhuman primate model and demonstrate for the first time the high potency of this drug in promoting HDL-cholesterol.

Current practices in nutrition management and disease incidence of common marmosets (Callithrix jacchus)

BACKGROUND

A survey was developed to characterize disease incidence, common pathology lesions, environmental characteristics, and nutrition programs within captive research marmoset colonies.

METHODS

Seventeen research facilities completed the electronic survey.

RESULTS

Nutritional management programs varied amongst research institutions housing marmosets; eight primary base diets were reported. The most common clinical syndromes reported were gastrointestinal disease (i.e. inflammatory bowel disease like disease, chronic lymphocytic enteritis, chronic malabsorption, chronic diarrhea), metabolic bone disease or fracture, infectious diarrhea, and oral disease (tooth root abscesses, gingivitis, tooth root resorption). The five most common pathology morphologic diagnoses were colitis, nephropathy/nephritis, enteritis, chronic lymphoplasmacytic enteritis, and cholecystitis. Obesity was more common (average 20% of a reporting institution's population) than thin body condition (average 5%).

CONCLUSIONS

Through review of current practices, we aim to inspire development of evidence-based practices to standardize husbandry and nutrition practices for marmoset research colonies.

A Role of Glucose Overload in Diabetic Cardiomyopathy in Nonhuman Primates

Type 2 diabetes (T2D) plays a major role in the development of heart failure. Patients with T2D have an increased risk to develop HF than healthy subjects, and they always have very poor outcomes and survival rates. However, the underlying mechanisms for this are still unclear. To help develop new therapeutic interventions, well-characterized animal models for preclinical and translational investigations in T2D and HF are urgently needed. Although studies in rodents are more often used, the research findings in rodents have often failed to be translated into humans due to the significant metabolic differences between rodents and humans. Nonhuman primates (NHPs) serve as valuable translational models between basic studies in rodent models and clinical studies in humans. NHPs can recapitulate the natural progress of these diseases in humans and study the underlying mechanism due to their genetic similarity and comparable spontaneous T2D rates to humans. In this review, we discuss the importance of using NHPs models in understanding diabetic cardiomyopathy (DCM) in humans with aspects of correlations between hyperglycemia and cardiac dysfunction progression, glucose overload, and altered glucose metabolism promoting cardiac oxidative stress and mitochondria dysfunction, glucose, and its effect on cardiac resynchronization therapy with defibrillator (CRT-d), the currently available diabetic NHPs models and the limitations involved in the use of NHP models.

Marmosets: Welfare, Ethical Use, and IACUC/Regulatory Considerations

Use of marmosets in biomedical research has increased dramatically in recent years due, in large part, to their suitability for transgenic applications and utility as models for neuroscience investigations. This increased use includes the establishment of new colonies and involvement of people new to marmoset research. To facilitate the use of the marmoset as a research model, we provide an overview of issues surrounding the ethics and regulations associated with captive marmoset research, including discussion of the history of marmosets in research, current uses of marmosets, ethical considerations related to marmoset use, issues related to importation of animals, and recommendations for regulatory oversight of gene-edited marmosets. To understand the main concerns that oversight bodies have regarding captive biomedical research with marmosets, we developed a brief, 15-question survey that was then sent electronically to academic and biomedical research institutions worldwide that were believed to house colonies of marmosets intended for biomedical research. The survey included general questions regarding the individual respondent's colony, status of research use of the colony and institutional oversight of both the colony itself and the research use of the colony. We received completed surveys from a total of 18 institutions from North America, Europe, and Asia. Overall, there appeared to be no clear difference in regulatory oversight body concerns between countries/regions. One difference that we were able to appreciate was that while biomedical research with marmosets was noted to be either stable or decreasing in Europe, use was clearly increasing elsewhere.

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.

Utility of Common Marmoset (Callithrix jacchus) Embryonic Stem Cells in Liver Disease Modeling, Tissue Engineering and Drug Metabolism

The incidence of liver disease is increasing significantly worldwide and, as a result, there is a pressing need to develop new technologies and applications for end-stage liver diseases. For many of them, orthotopic liver transplantation is the only viable therapeutic option. Stem cells that are capable of differentiating into all liver cell types and could closely mimic human liver disease are extremely valuable for disease modeling, tissue regeneration and repair, and for drug metabolism studies to develop novel therapeutic treatments. Despite the extensive research efforts, positive results from rodent models have not translated meaningfully into realistic preclinical models and therapies. The common marmoset Callithrix jacchus has emerged as a viable non-human primate model to study various human diseases because of its distinct features and close physiologic, genetic and metabolic similarities to humans. C. jacchus embryonic stem cells (cjESC) and recently generated cjESC-derived hepatocyte-like cells (cjESC-HLCs) could fill the gaps in disease modeling, liver regeneration and metabolic studies. They are extremely useful for cell therapy to regenerate and repair damaged liver tissues in vivo as they could efficiently engraft into the liver parenchyma. For in vitro studies, they would be advantageous for drug design and metabolism in developing novel drugs and cell-based therapies. Specifically, they express both phase I and II metabolic enzymes that share similar substrate specificities, inhibition and induction characteristics, and drug metabolism as their human counterparts. In addition, cjESCs and cjESC-HLCs are advantageous for investigations on emerging research areas, including blastocyst complementation to generate entire livers, and bioengineering of discarded livers to regenerate whole livers for transplantation.

Maternal weight affects placental DNA methylation of genes involved in metabolic pathways in the common marmoset monkey (Callithrix jacchus)

Accumulating evidence suggests that dysregulation of placental DNA methylation (DNAm) is a mechanism linking maternal weight during pregnancy to metabolic programming outcomes. The common marmoset, Callithrix jaccus, is a platyrrhine primate species that has provided much insight into studies of the primate placenta, maternal condition, and metabolic programming, yet the relationships between maternal weight and placental DNAm are unknown. Here, we report genome‐wide DNAm from term marmoset placentas using reduced representation bisulfite sequencing. We identified 74 genes whose DNAm pattern is associated with maternal weight during gestation. These genes are predominantly involved in energy metabolism and homeostasis, including the regulation of glycolytic and lipid metabolic processes pathways.

The placental DNA methylation (DNAm) landscape of the marmoset placenta presents unique differences and similarities with human placental methylation patterns.

Maternal weight is associated with placental DNAm in genes that are predominantly involved in energy metabolism and homeostasis.

The impact of altered placental DNAm on placental function and development may also contribute to the potential role of placental DNAm in developmental programming in the marmoset monkey.

Aging research using the common marmoset: Focus on aging interventions

Traditional animal models have been used to make seminal discoveries in biomedical research including a better understanding of the biology of the aging process. However, translation of these findings from laboratory to clinical populations has likely been hindered due to fundamental biological and physiological differences between common laboratory animals and humans. Non-human primates (NHP) may serve as an effective bridge towards translation, and short-lived NHP like the common marmoset offer many advantages as models for aging research. Here, we address these advantages and discuss what is currently understood about the changes in physiology and pathology that occur with age in the marmoset. In addition, we discuss how aging research might best utilize this model resource, and outline an ongoing study to address whether pharmaceutical intervention can slow aging in the marmoset. With this manuscript, we clarify how common marmosets might assist researchers in geroscience as a potential model for pre-clinical translation.

Noninvasive cardiac psychophysiology as a tool for translational science with marmosets

The importance of marmosets for comparative and translational science has grown in recent years because of their relatively rapid development, birth cohorts of twins, family social structure, and genetic tractability. Despite this, they remain understudied in investigations of affective processes. In this methodological note, we establish the validity of using noninvasive commercially available equipment to record cardiac physiology and compute indices of autonomic nervous system activity-a major component of affective processes. Specifically, we recorded electrocardiogram and impedance cardiogram, from which we derived heart rate, respiration rate, measures of high-frequency heart rate variability (indices of parasympathetic autonomic nervous system activity), and ventricular contractility (an index of sympathetic autonomic nervous system activity). Our methods produced physiologically plausible data, and further, animals with increased heart rates during testing were also more reactive to isolation from their social partner and presentation of novel objects, though no relationship was observed between reactivity and specific indices of parasympathetic or sympathetic nervous system activity.

Diet, digestion and energy intake in captive common marmosets (Callithrix jacchus): research and management implications

Common marmosets (Callithrix jacchus) are susceptible to intestinal inflammation which leads to chronic diarrhea, weight loss, and vitamin D deficiency. We examined food intake and digestion in three mixed-sex groups of adult marmosets maintained on three commercial base diets. Animals underwent two consecutive 4-day digestion trials. Body mass stayed constant. Feces and diet were assayed for Mn, fat, and gross energy (GE). Apparent digestibility of dry matter (ADDM) was calculated by the total collection method and from dietary and fecal Mn; the methods produced correlated results (r = 0.658, p < 0.001). Apparent digestibility of energy (ADE) was calculated from ADDM and the GE of feces and diet; apparent digestibility of fat (ADfat) was calculated from ADDM and fecal fat. ADDM and ADE varied by diet (p < 0.001). We found poor digesters on all three diets. The concentration of fecal fat was inversely related to ADE (r = -0.729, p < 0.001). High fecal fat (>10%) was associated with ADfat of zero, consistent with lipid malabsorption. Mean digestible energy intake (DEI) was equal to 1.5 the estimated metabolic rate, but varied widely between individuals. The diet with the fewest animals with high fecal fat had the highest mean DEI and most animals above 450 g, suggesting it may be obesogenic.

Cross-sectional comparison of health-span phenotypes in young versus geriatric marmosets

The development of the marmoset as a translational model for healthspan and lifespan studies relies on the characterization of health parameters in young and geriatric marmosets. This cross-sectional study examined health phenotypes in marmosets for five domains of interest for human health and aging: mobility, cognition, metabolism, homeostasis, and immune function. Geriatric marmosets were found to have significant executive function impairment when compared to young animals. While geriatric animals did not show gross abnormalities in mobility and measures of locomotion, their types of movement were altered from young animals. Geriatric marmosets had alterations in cardiac function, with significantly increased mean arterial pressures; metabolism, with significantly lower VO2 ; and suppressed immune function. Further, this study sought to characterize and describe histopathology for both young and geriatric healthy marmosets. Overall this study provides a characterization of health parameters for young and geriatric marmosets which will greatly enhance future aging and interventional testing in marmosets.

[Usage of common marmoset to drug discovery research]

Rodent laboratory animals, such as mice and rats have been greatly contributing to biomedical research. Although its usefulness would not change in the future, nonhuman primates (NHPs) also offer excellent models for preclinical research to assess safety and efficacy of developing novel therapeutic approaches because of their similarities of genetics, metabolism and physiological characteristics to humans. Recent years, the gene modification technology in nonhuman primates has been developed. In fact, pre-clinical studies using nonhuman primates are increasing in the world, especially in the neuroscience research field. Among the NHPs, the common marmoset (Callithrix jacchus) is one of a suitable NHP laboratory animal for producing genetically modified models because they are fecund animal. This article outlines the common marmoset and that of the disease models.

Ovarian estradiol supports sexual behavior but not energy homeostasis in female marmoset monkeys

OBJECTIVE

In adult female rodents, ovarian estradiol (E₂) regulates body weight, adiposity, energy balance, physical activity, glucose-insulin homeodynamics, and lipid metabolism, while protecting against diet-induced obesity. The same E₂ actions are presumed to occur in primates, but confirmatory studies have been lacking.

METHODS

We investigated the consequences of ovariectomy (OVX) and E₂ replacement in female marmoset monkeys on major metabolic and morphometric endpoints. Sexual behavior and uterine diameters were assessed as positive controls for E₂ treatment efficacy. Metabolic parameters were measured 1 mo prior to OVX, and 3 and 6 mo thereafter. During OVX, animals received empty or E₂-containing silastic s.c. implants. To test the interaction between E₂ and diet, both treatment groups were assigned to either a higher fat diet (HFD) or a low-fat diet (LFD).

RESULTS

As anticipated, OVX animals exhibited diminished frequency (p = 0.04) of sexually receptive behavior and increased rejection behavior (p = 0.04) toward their male partners compared with E₂-treated OVX females. OVX also decreased (p = 0.01) uterine diameter. There were no treatment effects on total caloric intake. There were no significant effects of OVX, E₂ treatment, or diet on body weight, body composition, energy expenditure, physical activity, fasting glucose, or glucose tolerance. Regardless of E₂ treatment, serum triglycerides were higher (p = 0.05) in HFD than LFD females. Postmortem qPCR analysis of hypothalamic tissues revealed higher mRNA expression (p < 0.001) for PGR in E₂-treated monkeys versus OVX controls regardless of diet, but no differences between groups in other selected metabolic genes. In contrast, regardless of E₂ treatment, there was a decreased mRNA expression of PGC1α (PPARGC1A), HTR1A, and HTR5A in HFD compared with LFD females.

CONCLUSIONS

Our findings, overall, document a greatly diminished role for ovarian E₂ in the metabolic physiology of a female primate, and encourage consideration that primates, including humans, evolved metabolic control systems regulated by extra-ovarian E₂ or are generally less subject to E₂ regulation.

The common marmoset monkey: avenues for exploring the prenatal, placental, and postnatal mechanisms in developmental programming of pediatric obesity

Animal models have been critical in building evidence that the prenatal experience and intrauterine environment are capable of exerting profound and permanent effects on metabolic health through developmental programming of obesity. However, despite physiological and evolutionary similarities, nonhuman primate models are relatively rare. The common marmoset monkey ( Callithrix jacchus) is a New World monkey that has been used as a biomedical model for well more than 50 years and has recently been framed as an appropriate model for exploring early-life impacts on later health and disease. The spontaneous, multifactorial, and early-life development of obesity in the common marmoset make it a valuable research model for advancing our knowledge about the role of the prenatal and placental mechanisms involved in developmental programming of obesity. This paper provides a brief overview of obesity in the common marmoset, followed by a discussion of marmoset reproduction and placental characteristics. We then discuss the occurrence and utility of variable intrauterine environments in developmental programming in marmosets. Evidence of developmental programming of obesity will be given, and finally, we put forward future directions and innovations for including the placenta in developmental programming of obesity in the common marmoset.

Obesity, Metabolism, and Aging: A Multiscalar Approach

Obesity contributes to the aging process through the alteration of metabolic pathways evidenced biochemically in the relationship between caloric restriction and longevity. Humans have entered into an era of metabolism and aging entirely unprecedented in their evolution, with a diet that, for many, contains a majority of calories as sugar and yields an expected lifespan of over 80years in industrialized nations. Deeply embedded in the complex issue of obesity are questions of behavior, causality versus correlation, and appropriate models. For example, are primates a better reference than mice for studying metabolic connections between obesity and aging? We consider those issues from the standpoint of life-history theory, especially implications of the interplay of refined sugar and socioeconomic disparities for the future of human health.

Obesity and obesogenic growth are both highly heritable and modified by diet in a nonhuman primate model, the African green monkey (Chlorocebus aethiops sabaeus)

Objective:

In humans, the ontogeny of obesity throughout the life course and the genetics underlying it has been historically difficult to study. We compared, in a non-human primate model, the lifelong growth trajectories of obese and non-obese adults to assess the heritability of and map potential genomic regions implicated in growth and obesity.

Study population:

A total of 905 African green monkeys, or vervets (Chlorocebus aethiops sabaeus) (472 females, 433 males) from a pedigreed captive colony.

Methods:

We measured fasted body weight (BW), crown-to-rump length (CRL), body-mass index (BMI) and waist circumference (WC) from 2000 to 2015. We used a longitudinal clustering algorithm to detect obesogenic growth, and logistic growth curves implemented in nonlinear mixed effects models to estimate three growth parameters. We used maximum likelihood variance decomposition methods to estimate the genetic contributions to obesity-related traits and growth parameters, including a test for the effects of a calorie-restricted dietary intervention. We used multipoint linkage analysis to map implicated genomic regions.

Results:

All measurements were significantly influenced by sex, and with the exception of WC, also influenced by maternal and post-natal diet. Chronic obesity outcomes were significantly associated with a pattern of extended growth duration with slow growth rates for BW. After accounting for environmental influences, all measurements were found to have a significant genetic component to variability. Linkage analysis revealed several regions suggested to be linked to obesity-related traits that are also implicated in human obesity and metabolic disorders.

Conclusions:

As in humans, growth patterns in vervets have a significant impact on adult obesity and are largely under genetic control with some evidence for maternal and dietary programming. These results largely mirror findings from human research, but reflect shorter developmental periods, suggesting that the vervet offers a strong genetic model for elucidating the ontogeny of human obesity.

Assessment of behavioural deficits following ischaemic stroke in the marmoset

Stroke is a common and devastating disease worldwide. Over the last two decades, many therapeutic approaches to ameliorate ischaemic stroke have been promising in animal studies but failed when transferred to the clinical situation. One of the possible explanations for these failures is the widespread use of animal models of cerebral ischemia that do not mimic the pathology encountered in the clinic. Accordingly, many expert committees recommended the integration of higher order species such as non-human primates in pre-clinical stroke studies. The common marmoset (Callithrix jacchus), a small New World monkey, start to stand out in the neuroscience field as a good compromise between larger primates and rodents. In this review, we discuss the relevance of the use of the marmoset in stroke studies. We will focus on behavioural tests developed in this species to assess sensorimotor deficits and their recovery during acute and chronic stages of brain ischaemia. The aim of this appraisal is to provide a comprehensive overview of the existing approaches to induce stroke in the marmoset as well as the paradigms for behavioural testing in this species. The data summarized in this review should contribute to the improvement of future stoke studies in the marmoset and accordingly improve the translation of the results from bench to bed.

Non-human primates as a model for aging

There has been, and continues to be, a dramatic shift in the human population towards older ages necessitating biomedical research aimed at better understanding the basic biology of aging and age-related diseases and facilitating new and improved therapeutic options. As it is not practical to perform the breadth of this research in humans, animal models are necessary to recapitulate the complexity of the aging environment. The mouse model is most frequently chosen for these endeavors, however, they are frequently not the most appropriate model. Non-human primates, on the other hand, are more closely related to humans and recapitulate the human aging process and development of age-related diseases. Extensive aging research has been performed in the well-characterized rhesus macaque aging model. More recently, the common marmoset, a small non-human primate with a shorter lifespan, has been explored as a potential aging model. This model holds particular promise as an aging disease model in part due to the successful creation of transgenic marmosets. Limitations to the use of non-human primates in aging research exist but can be mitigated somewhat by the existence of available resources supported by the National Institutes of Health. This article is part of a Special Issue entitled: Animal models of aging - edited by "Houtkooper Riekelt".

Metabolic Dysregulation in Hepacivirus Infection of Common Marmosets (Callithrix jacchus)

Chronic hepatitis C has been associated with metabolic syndrome that includes insulin resistance, hepatic steatosis and obesity. These metabolic aberrations are risk factors for disease severity and treatment outcome in infected patients. Experimental infection of marmosets with GBV-B serves as a tangible, small animal model for human HCV infection, and while virology and pathology are well described, a full investigation of clinical disease and the metabolic milieu is lacking. In this study six marmosets were infected intravenously with GBV-B and changes in hematologic, serum biochemical and plasma metabolic measures were investigated over the duration of infection. Infected animals exhibited signs of lymphocytopenia, but platelet and RBC counts were generally stable or even increased. Although most animals showed a transient decline in blood glucose, infection resulted in several fold increases in plasma insulin, glucagon and glucagon-like peptide 1 (GLP-1). All infected animals experienced transient weight loss within the first 28 days of infection, but also became hypertriglyceridemic and had up to 10-fold increases in adipocytokines such as resistin and plasminogen activator inhibitor 1 (PAI-1). In liver, moderate to severe cytoplasmic changes associated with steatotic changes was observed microscopically at 168 days post infection. Collectively, these results suggest that GBV-B infection is accompanied by hematologic, biochemical and metabolic abnormalities that could lead to obesity, diabetes, thrombosis and atherosclerosis, even after virus has been cleared. Our findings mirror those found in HCV patients, suggesting that metabolic syndrome could be conserved among hepaciviruses, and both mechanistic and interventional studies for treating HCV-induced metabolic complications could be evaluated in this animal model.

Metabolic consequences of long-term rapamycin exposure on common marmoset monkeys (Callithrix jacchus)

Rapamycin has been shown to extend lifespan in rodent models, but the effects on metabolic health and function have been widely debated in both clinical and translational trials. Prior to rapamycin being used as a treatment to extend both lifespan and healthspan in the human population, it is vital to assess the side effects of the treatment on metabolic pathways in animal model systems, including a closely related non-human primate model. In this study, we found that long-term treatment of marmoset monkeys with orally-administered encapsulated rapamycin resulted in no overall effects on body weight and only a small decrease in fat mass over the first few months of treatment. Rapamycin treated subjects showed no overall changes in daily activity counts, blood lipids, or significant changes in glucose metabolism including oral glucose tolerance. Adipose tissue displayed no differences in gene expression of metabolic markers following treatment, while liver tissue exhibited suppressed G6Pase activity with increased PCK and GPI activity. Overall, the marmosets revealed only minor metabolic consequences of chronic treatment with rapamycin and this adds to the growing body of literature that suggests that chronic and/or intermittent rapamycin treatment results in improved health span and metabolic functioning. The marmosets offer an interesting alternative animal model for future intervention testing and translational modeling.

Characterization of mammary epithelial stem/progenitor cells and their changes with aging in common marmosets

Age is the number one risk factor for breast cancer, yet the underlying mechanisms are unexplored. Age-associated mammary stem cell (MaSC) dysfunction is thought to play an important role in breast cancer carcinogenesis. Non-human primates with their close phylogenetic relationship to humans provide a powerful model system to study the effects of aging on human MaSC. In particular, the common marmoset monkey (Callithrix jacchus) with a relatively short life span is an ideal model for aging research. In the present study, we characterized for the first time the mammary epithelial stem/progenitor cells in the common marmoset. The MaSC-enriched cells formed four major types of morphologically distinct colonies when cultured on plates pre-seeded with irradiated NIH3T3 fibroblasts, and were also capable of forming mammospheres in suspension culture and subsequent formation of 3D organoids in Matrigel culture. Most importantly, these 3D organoids were found to contain stem/progenitor cells that can undergo self-renewal and multi-lineage differentiation both in vitro and in vivo. We also observed a significant decrease of luminal-restricted progenitors with age. Our findings demonstrate that common marmoset mammary stem/progenitor cells can be isolated and quantified with established in vitro and in vivo assays used for mouse and human studies.

Generation of transgenic cynomolgus monkeys that express green fluorescent protein throughout the whole body

Nonhuman primates are valuable for human disease modelling, because rodents poorly recapitulate some human diseases such as Parkinson’s disease and Alzheimer’s disease amongst others. Here, we report for the first time, the generation of green fluorescent protein (GFP) transgenic cynomolgus monkeys by lentivirus infection. Our data show that the use of a human cytomegalovirus immediate-early enhancer and chicken beta actin promoter (CAG) directed the ubiquitous expression of the transgene in cynomolgus monkeys. We also found that injection into mature oocytes before fertilization achieved homogenous expression of GFP in each tissue, including the amnion, and fibroblasts, whereas injection into fertilized oocytes generated a transgenic cynomolgus monkey with mosaic GFP expression. Thus, the injection timing was important to create transgenic cynomolgus monkeys that expressed GFP homogenously in each of the various tissues. The strategy established in this work will be useful for the generation of transgenic cynomolgus monkeys for transplantation studies as well as biomedical research.

Contributions of Nonhuman Primates to Research on Aging

Aging is the biological process of declining physiologic function associated with increasing mortality rate during advancing age. Humans and higher nonhuman primates exhibit unusually longer average life spans as compared with mammals of similar body mass. Furthermore, the population of humans worldwide is growing older as a result of improvements in public health, social services, and health care systems. Comparative studies among a wide range of organisms that include nonhuman primates contribute greatly to our understanding about the basic mechanisms of aging. Based on their genetic and physiologic relatedness to humans, nonhuman primates are especially important for better understanding processes of aging unique to primates, as well as for testing intervention strategies to improve healthy aging and to treat diseases and disabilities in older people. Rhesus and cynomolgus macaques are the predominant monkeys used in studies on aging, but research with lower nonhuman primate species is increasing. One of the priority topics of research about aging in nonhuman primates involves neurologic changes associated with cognitive decline and neurodegenerative diseases. Additional areas of research include osteoporosis, reproductive decline, caloric restriction, and their mimetics, as well as immune senescence and chronic inflammation that affect vaccine efficacy and resistance to infections and cancer. The purpose of this review is to highlight the findings from nonhuman primate research that contribute to our understanding about aging and health span in humans.

Plasma Metabolomics of Common Marmosets (Callithrix jacchus) to Evaluate Diet and Feeding Husbandry

Common marmosets (Callithrix jacchus) are an important NHP model for the study of human aging and age-related diseases. However, the full potential of marmosets as a research model has not been realized due to a lack of evidence-based, standardized procedures for their captive management, especially regarding diet and feeding husbandry. In the present study, we conducted a high-resolution metabolomics analysis of plasma from marmosets from a 3-mo dietary crossover study to determine whether significant metabolic differences occur with a semisynthetic chemically defined (purified) diet as needed for controlled nutrition research. Marmosets were fed a standard, diverse-ingredient diet, followed by a semisynthetic purified diet, and then were switched back to the standard diet. The standard diet used in this analysis was specific to the animal facility, but it is similar in content to the diets currently used for other marmoset colonies. High-resolution metabolomics of plasma with liquid chromatography-mass spectrometry and bioinformatics was used to measure metabolic differences. The concentration of the essential amino acids methionine, leucine/isoleucine, lysine, and threonine were higher when marmosets were fed the purified diet. In contrast, phenylalanine concentrations were higher during exposure to the standard diet. In addition, metabolic pathway enrichment and analysis revealed differences among metabolites associated with dopamine metabolism and the carnitine shuttle. These results show that diet-associated differences in metabolism occur in marmosets and suggest that additional nutritional studies with detailed physiologic characterization are needed to optimize standard and purified diets for common marmosets.

Accuracy of Human and Veterinary Point-of-Care Glucometers for Use in Rhesus Macaques (Macaca mulatta), Sooty Mangabeys (Cercocebus atys), and Chimpanzees (Pan troglodytes)

Handheld, point-of-care glucometers are commonly used in NHP for clinical and research purposes, but whether these devices are appropriate for use in NHP is unknown. Other animal studies indicate that glucometers should be species-specific, given differences in glucose distribution between RBC and plasma; in addition, Hct and sampling site (venous compared with capillary) influence glucometer readings. Therefore, we compared the accuracy of 2 human and 2 veterinary glucometers at various Hct ranges in rhesus macaques (Macaca mulatta), sooty mangabeys (Cercocebus atys), and chimpanzees (Pan troglodytes) with that of standard laboratory glucose analysis. Subsequent analyses assessed the effect of hypoglycemia, hyperglycemia, and sampling site on glucometer accuracy. The veterinary glucometers overestimated blood glucose (BG) values in all species by 26 to 75 mg/dL. The mean difference between the human glucometers and the laboratory analyzer was 7 mg/dL or less in all species. The human glucometers overestimated BG in hypoglycemic mangabeys by 4 mg/dL and underestimated BG in hyperglycemic mangabeys by 11 mg/dL; similar patterns occurred in rhesus macaques. Hct did not affect glucometer accuracy, but all samples were within the range at which glucometers generally are accurate in humans. BG values were significantly lower in venous than capillary samples. The current findings show that veterinary glucometers intended for companion-animal species are inappropriate for use in the studied NHP species, whereas the human glucometers showed clinically acceptable accuracy in all 3 species. Finally, potential differences between venous and capillary BG values should be considered when comparing and evaluating results.

Metabolic Characterization of the Common Marmoset (Callithrix jacchus)

High-resolution metabolomics has created opportunity to integrate nutrition and metabolism into genetic studies to improve understanding of the diverse radiation of primate species. At present, however, there is very little information to help guide experimental design for study of wild populations. In a previous non-targeted metabolomics study of common marmosets (Callithrix jacchus), Rhesus macaques, humans, and four non-primate mammalian species, we found that essential amino acids (AA) and other central metabolites had interspecies variation similar to intraspecies variation while non-essential AA, environmental chemicals and catabolic waste products had greater interspecies variation. The present study was designed to test whether 55 plasma metabolites, including both nutritionally essential and non-essential metabolites and catabolic products, differ in concentration in common marmosets and humans. Significant differences were present for more than half of the metabolites analyzed and included AA, vitamins and central lipid metabolites, as well as for catabolic products of AA, nucleotides, energy metabolism and heme. Three environmental chemicals were present at low nanomolar concentrations but did not differ between species. Sex and age differences in marmosets were present for AA and nucleotide metabolism and warrant additional study. Overall, the results suggest that quantitative, targeted metabolomics can provide a useful complement to non-targeted metabolomics for studies of diet and environment interactions in primate evolution.

Isolation and characterization of a novel Helicobacter species, Helicobacter jaachi sp. nov., from common marmosets (Callithrix jaachus)

Purpose-bred common marmosets from domestic sources housed in a US research facility, and used in multiple drug discovery programmes, were noted to have a high incidence of spontaneous inflammatory bowel disease and sporadic cholecystitis and cholangiohepatitis. Inflammatory infiltrates increased in incidence and severity with age. Because Helicobacter spp. have been linked to gastrointestinal diseases, samples from the gastrointestinal tracts of 39 marmosets were screened for Helicobacter spp. by culture and PCR. Helicobacter spp. were frequently detected in marmosets; 28.2% of the marmosets were positive for a proposed novel species, Helicobacter jaachi sp. nov., by culture, and 48.7% were positive by Helicobacter genus-specific PCR. Seventeen strains of Helicobacter sp. from 11 marmosets were cultured from various gastrointestinal sites. Older animals (age 6-11 years) had a higher helicobacter prevalence rate (57.1%) compared with younger animals (age 3-5 years), which had a 27.2% prevalence rate. Cells of H. jaachi sp. nov. were catalase, urease and oxidase positive and had fusiform morphology, with periplasmic fibres and multiple bipolar, sheathed flagella. All isolates had similar 16S and 23S rRNA sequences, which clustered as representatives of a novel Helicobacter species closely related to 'Helicobacter sanguini' (97%), a species isolated from cotton-top tamarins and 'Helicobacter callitrichis' (96%) isolated previously from the faeces of common marmosets. The whole genome sequence of one of the liver isolates, H. jaachi sp. nov. MIT 09-6949(T), had a 1.9 Mb genome length with a 41 mol% DNA G+C content. The type strain of Helicobacter jaachi sp. nov., MIT 09-6949(T), has been deposited in the BCCM/LMG Bacteria Collection as LMG 28613(T). These findings add to the increasing number of animal species with gastrointestinal disease in which novel enterohepatic Helicobacter spp. have been isolated.

Testing efficacy of administration of the antiaging drug rapamycin in a nonhuman primate, the common marmoset

This report is the first description of dosing procedures, pharmacokinetics, biochemical action, and general tolerability of the antiaging drug rapamycin in the common marmoset, a small and short-lived monkey. Eudragit-encapsulated rapamycin was given orally to trained marmosets in a short-term (3 weeks) and a long-term (14 months) study. Circulating trough rapamycin levels (mean = 5.2 ng/mL; 1.93-10.73 ng/mL) achieved at roughly 1.0 mg/kg/day was comparable to those reported in studies of rodents and within the therapeutic range for humans. Long-term treated animals (6/8) indicated a reduction in mammalian target of rapamycin complex 1 signaling as noted by a decrease in the phospho rpS6 to total rpS6 ratio after 2 weeks of treatment. All long-term treated subjects had detectable concentrations of rapamycin in liver (4.7-19.9 pg/mg) and adipose tissue (2.2-32.8 pg/mg) with reduced mammalian target of rapamycin signaling in these tissues. There was no evidence of clinical anemia, fibrotic lung changes, or mouth ulcers. The observed death rate in the long-term study was as expected given the animals' ages. The ability to rapidly and reliably dose socially housed marmosets with an oral form of rapamycin that is well tolerated and that demonstrates a suppression of the mammalian target of rapamycin pathway leads us to conclude that this species offers a viable model for rapamycin testing to establish safety and efficacy for long-term antiaging intervention.

Metabolic consequences of the early onset of obesity in common marmoset monkeys

OBJECTIVE

The common marmoset as a model of early obesity was assessed. The hypotheses that juvenile marmosets with excess adipose tissue will display higher fasting glucose, decreased insulin sensitivity, and decreased ability to clear glucose from the blood stream were tested.

DESIGN AND METHODS

Normal and obese (body fat > 14%) common marmoset infants (N = 39) were followed up from birth until 1 year. Body fat was measured by quantitative magnetic resonance. Circulating glucose was measured by glucometer and insulin, adiponectin, and leptin by commercial assays. The quantitative insulin sensitivity check index (QUICKI; a measure of insulin sensitivity) was calculated for subjects with fasting glucose and insulin measures. Oral glucose tolerance tests (OGTTs) were conducted at 12 months on 35 subjects.

RESULTS

At 6 months, obese subjects already had significantly lower insulin sensitivity (mean QUICKI = 0.378 ± 0.029 vs. 0.525 ± 0.019, N = 11, P = 0.003). By 12 months, obese subjects also had higher fasting glucose (129.3 ± 9.1 mg/dL vs. 106.1 ± 6.5 mg/dL, P = 0.042), and circulating adiponectin tended to be lower (P = 0.057). Leptin was associated with percent body fat; however, birth weight also influenced circulating leptin. The OGTT results demonstrated that obese animals had a decreased ability to clear glucose.

CONCLUSIONS

Early-onset obesity in marmosets results in impaired glucose homeostasis by 1 year.

Relationships between body weight, fasting blood glucose concentration, sex and age in tree shrews (Tupaia belangeri chinensis)

The tree shrew (Tupaia belangeri chinensis) is a squirrel-like lower primate or a close relative of primates, commonly used as an animal model in biomedical research. Despite more than three decades of usage in research, the clear relationships between body weight, fasting blood glucose concentration, sex and age among tree shrews remain unclear. Based on an investigation of 992 tree shrews (454 males and 538 females) aged between 4 months and 4 years old, we found that male tree shrews have significantly higher body weight and fasting blood glucose concentration than female tree shrews (p < 0.001). The concentration of fasting blood glucose slightly increased with body weight in males (r = 0.152, p < 0.001). Meanwhile, in females, the body weight, concentration of fasting blood glucose and waist circumference positively increased with age (p < 0.001). Additionally, 17 tree shrews with Lee index [body weight (g)*0.33*1000/body length (cm)] above 290 had significantly higher body weight, waist circumference and glycated haemoglobin A1c (HbA1c) than non-obese tree shrews with a Lee index score below 290 (p < 0.001). Interestingly, 6 of 992 tree shrews (three males and three females, 2-4 years old) displayed impaired plasma triglycerides, HbA1c, low-density lipoprotein and oral glucose tolerance test, suggestive of the early symptoms of metabolic syndrome. This study provides the first clear relationships between body weight, fasting blood glucose concentration, sex and age in tree shrews, further improving our understanding of this relationship in metabolic syndrome (MetS). Given the similarity of tree shrews to humans and non-human primates, this finding supports their potential use as an animal model in the research of MetS.

Using snacks high in fat and protein to improve glucoregulatory function in adolescent male marmosets (Callithrix jacchus)

The common marmoset (Callithrix jacchus), a laboratory nonhuman primate, is a well-known model of several human diseases and conditions, but the nutritional needs of these animals are not fully understood. Here we describe a 4-mo controlled study in which we increased the dietary fat and protein of subadult male common marmosets by using healthy snacks. Six male marmosets received their normal diet (control), and an additional 6 were given their normal diet supplemented daily with a 14-kcal snack. Cashews and waxworms were used as the snack, given their high-fat content. Although body weight did not differ between the 2 groups, only control male marmosets showed increased chest circumferences over the course of the study. Glucoregulatory function remained consistent in the snack-fed marmosets, whereas control animals had progressed toward higher insulin. Other indices of glucoregulation indicated significant differences in adiponectin and the cortisol:cortisone ratio between the 2 groups, but no differences in lipid concentration were detected. Therefore, the most notable difference attributable to the snack feeding was improved glucoregulation. Because the snacks we used had a high proportion of unsaturated compared with saturated fat, we suggest that these healthy high-fat-high-protein snacks provide an important contribution to the nutrition of this laboratory species. This study also demonstrates the utility of marmosets as a model for understanding the implications of dietary fats in humans.

The development of obesity begins at an early age in captive common marmosets (Callithrix jacchus)

Animal models to study the causes and consequences of obesity during infancy in humans would be valuable. In this study, we examine the patterns of fat mass gain from birth to 12 months in common marmosets (Callithrix jacchus). Lean and fat mass was measured by quantitative magnetic resonance at 1, 2, 6, and 12 months for 31 marmosets, 15 considered Normal and 16 considered Fat (> 14% body fat) at 12 months. Animals were fed either the regular colony diet mix or a high-fat variation. Subjects classified as Fat at 12 months already had greater lean mass (198.4 +/- 6.2 g vs. 174.0 +/- 6.8 g, P = 0.013) and fat mass (45.5 +/- 5.0 g vs. 24.9 +/- 3.4 g, P = .002) by 6 months. Body mass did not differ between groups prior to 6 months, however, by 1 month, Fat infants had greater percent body fat. Percent body fat decreased between 1 and 12 months in Normal subjects; in Fat subjects, it increased. The high-fat diet was associated with body fat > 14% at 6 months (P = 0.049), but not at 12 months. This shift was due to three subjects on the normal diet changing from Normal to Fat between 6 and 12 months. Although maternal prepregnancy adiposity did not differ, overall, between Normal and Fat subjects, the subjects Normal at 6 and Fat at 12 months all had Fat mothers. Therefore, diet and maternal obesity appear to have potentially independent effects that may also vary with developmental age. Although birth weight did not differ between groups, it was associated with fat mass gain from 1 to 6 months in animals with > 14% body fat at 6 months of age (r = 0.612, P = 0.026); but not in 6-month-old animals with < 14% body fat (r = -0.012, P = 0.964). Excess adiposity in captive marmosets develops by 1 month. Birth weight is associated with adiposity in animals vulnerable to obesity.

Relation of food intake behaviors and obesity development in young common marmoset monkeys

OBJECTIVE

Increasing prevalence of childhood obesity and associated risks of adult type disease have led to worldwide concern. It remains unclear how genetic predisposition, environmental exposure to obesogenic food, and developmental programming interact to lead to overweight and obese children. The development of a nonhuman primate model of obesity, and particularly juvenile obesity, is an important step to elucidating the factors associated with obesity and evaluating intervention strategies.

DESIGN AND METHODS

Infant marmosets were followed from birth to 12 months of age. Feeding phenotypes were determined through the use of behavioral observation, solid food intake trials, and liquid feeding trials monitored via lickometer.

RESULTS

Marmosets found to be obese at 12 months of age (more than 14% body fat) start consuming solid food sooner and initiate more time off of care givers. These individuals developed stable feeding phenotypes that included being more efficient consumers during liquid intake trials, drinking more grams of diet per contact with the licksit.

CONCLUSIONS

The weaning process appears to be particularly important in the development of feeding phenotypes and the development of juvenile obesity for the marmosets, and thus this is the time that should be focused upon for intervention testing in both nonhuman primates and children.

Development of metabolic function biomarkers in the common marmoset, Callithrix jacchus

Metabolic assessment of a non-human primate model of metabolic syndrome and obesity requires the necessary biomarkers specific to the species. While the rhesus monkey has a number of specific assays for assessing metabolic syndrome, the marmoset does not. Furthermore, the common marmoset (Callithrix jacchus) has a small blood volume that necessitates using a single blood volume for multiple analyses. The common marmoset holds a great potential as an alternative primate model for the study of human disease but assay methods need to be developed and validated for the biomarkers of metabolic syndrome. Here we report on the adaptation, development, and validation of commercially available immunoassays for common marmoset samples in small volumes. We have performed biological validations for insulin, adiponectin, leptin, and ghrelin to demonstrate the use of these biomarkers in examining metabolic syndrome and other related diseases in the common marmoset.

Body mass growth in common marmosets: toward a model of pediatric obesity

While much is known about adult obesity in nonhuman primates, very little is known regarding development of childhood adiposity. As small monkeys that are easy to handle and have a relatively fast life history, common marmoset monkeys (Callithrix jacchus) offer interesting opportunities to examine the question of fat versus lean mass growth in a nonhuman primate. This article provides an overview of our understanding of early life growth in mass in marmoset monkeys, based primarily upon our past 20 years of research, culminating in our recent findings on early life obesity in this species. Common marmosets display variance in early life growth patterns that is related to both pre- and postnatal factors and the marmoset uterine environment is exquisitely designed to reflect resources available for the gestation of multiple offspring, making them an interesting model of developmental programming. We have demonstrated that obesity can be generated in very early life in captive marmosets, with excess adiposity evident by one month of age, making this species a potentially valuable model in which to study pediatric obesity and its sequelae. Birth weight is associated with adiposity in animals vulnerable to obesity. Early life exposure to higher fat diets enhances the chances of postweaning obesity development. However, overall higher food consumption is also associated with obesity development at later ages. One unexpected finding in our studies has been the relatively high body fat percentage of neonatal (12-18%) marmosets suggesting that hypotheses regarding the uniqueness of high human neonatal adiposity merit further examination.

Establishing meal patterns by lickometry in the marmoset monkey (Callithrix jacchus): translational applications from the bench to the field and the clinic

The ability to measure and interpret variables associated with feeding behavior and food intake is essential to a variety of nonhuman primate study modalities. The development of a technique to accurately and efficiently measure food intake and meal patterning in captivity will enhance both the interpretation of foraging behavior in the wild as well as our ability to model clinically relevant human feeding pathologies. In this study, we successfully developed the use of a rodent lickometer system to monitor meal patterning in captive common marmosets. We describe the modifications necessary for this type of instrumentation to be used successfully with marmosets. We define variables of interest that relate to both previous rodent literature and human clinical measures. Finally, we relate our findings to potential translational value for both primate field research and biomedical applications.

Parameters of haematology, clinical chemistry and lipid metabolism in the common marmoset and alterations under stress conditions

Common marmosets are suitable non-human primate models for many human diseases. Standard values for blood parameters are required to evaluate physiological and pathological situations. Two studies were conducted: study I to determine standard values and study II to examine these under changed housing conditions. In study I, all parameters for clinical chemistry were similar in range for both genders with these specifics: male marmosets had significantly higher total and LDL cholesterol levels than females, whereas the mean corpuscular volume and the mean corpuscular haemoglobin were significantly lower than in females. In study II, glucose, lymphocytes and salivary cortisol were significantly lower, and faecal cortisol was increased during the change of housing conditions. In conclusion, standard values for haematology and clinical chemistry for the common marmoset were determined. Further on, parameters that are influenced by relocation stress and its importance for experimental results are described.

The marmoset monkey: a multi-purpose preclinical and translational model of human biology and disease

The development of biologic molecules (monoclonal antibodies, cytokines, soluble receptors) as specific therapeutics for human disease creates a need for animal models in which safety and efficacy can be tested. Models in lower animal species are precluded when the reagents fail to recognize their targets, which is often the case in rats and mice. In this Feature article we will highlight the common marmoset, a small-bodied nonhuman primate (NHP), as a useful model in biomedical and preclinical translational research.

Lactation and neonatal nutrition: defining and refining the critical questions

This paper resulted from a conference entitled "Lactation and Milk: Defining and refining the critical questions" held at the University of Colorado School of Medicine from January 18-20, 2012. The mission of the conference was to identify unresolved questions and set future goals for research into human milk composition, mammary development and lactation. We first outline the unanswered questions regarding the composition of human milk (Section I) and the mechanisms by which milk components affect neonatal development, growth and health and recommend models for future research. Emerging questions about how milk components affect cognitive development and behavioral phenotype of the offspring are presented in Section II. In Section III we outline the important unanswered questions about regulation of mammary gland development, the heritability of defects, the effects of maternal nutrition, disease, metabolic status, and therapeutic drugs upon the subsequent lactation. Questions surrounding breastfeeding practice are also highlighted. In Section IV we describe the specific nutritional challenges faced by three different populations, namely preterm infants, infants born to obese mothers who may or may not have gestational diabetes, and infants born to undernourished mothers. The recognition that multidisciplinary training is critical to advancing the field led us to formulate specific training recommendations in Section V. Our recommendations for research emphasis are summarized in Section VI. In sum, we present a roadmap for multidisciplinary research into all aspects of human lactation, milk and its role in infant nutrition for the next decade and beyond.

A peptidomimetic targeting white fat causes weight loss and improved insulin resistance in obese monkeys

Obesity, defined as body mass index greater than 30, is a leading cause of morbidity and mortality and a financial burden worldwide. Despite significant efforts in the past decade, very few drugs have been successfully developed for the treatment of obese patients. Biological differences between rodents and primates are a major hurdle for translation of anti-obesity strategies either discovered or developed in rodents into effective human therapeutics. Here, we evaluate the ligand-directed peptidomimetic CKGGRAKDC-GG-(D)(KLAKLAK)(2) (henceforth termed adipotide) in obese Old World monkeys. Treatment with adipotide induced targeted apoptosis within blood vessels of white adipose tissue and resulted in rapid weight loss and improved insulin resistance in obese monkeys. Magnetic resonance imaging and dual-energy x-ray absorptiometry confirmed a marked reduction in white adipose tissue. At experimentally determined optimal doses, monkeys from three different species displayed predictable and reversible changes in renal proximal tubule function. Together, these data in primates establish adipotide as a prototype in a new class of candidate drugs that may be useful for treating obesity in humans.

Nonhuman primates and other animal models in diabetes research

Animal models are important for determining the pathogenesis of and potential treatments for obesity and diabetes. Nonhuman primates (NHPs) are particularly useful for studying these disorders. As in humans, type 2 diabetes mellitus is the most common form of diabetes in NHPs and occurs more often in older obese animals, with a metabolic progression from insulin resistance (IR) and impaired glucose tolerance to overt diabetes. Histopathologic changes in pancreatic islets are also similar to those seen in humans with diabetes. Initially, there is islet hyperplasia with abundant insulin production to compensate for IR, followed by insufficient insulin production with replacement of islets with islet-associated amyloid. Diabetic NHPs also have adverse changes in plasma lipid and lipoprotein concentrations, biomarkers of obesity, inflammation, and oxidative stress, and protein glycation that contribute to the numerous complications of the disease. Furthermore, sex hormones, pregnancy, and environmental factors (e.g., diet and stress) affect IR and can also contribute to diabetes progression in NHPs. Additionally, due to their similar clinical and pathologic characteristics, NHPs have been used in many pharmacological studies to assess new therapeutic agents. For these reasons, NHPs are particularly valuable animal models of obesity and diabetes for studying disease pathogenesis, risk factors, comorbidities, and therapeutic interventions.