Nonhuman Primates and Teratological Research

The squirrel monkey model in clinical neuroscience

Clinical neuroscience research relying on animal models brought valuable translational insights into the function and pathologies of the human brain. The anatomical, physiological, and behavioural similarities between humans and mammals have prompted researchers to study cerebral mechanisms at different levels to develop and test new treatments. The vast majority of biomedical research uses rodent models, which are easily manipulable and have a broadly resembling organisation to the human nervous system but cannot satisfactorily mimic some disorders. For these disorders, macaque monkeys have been used as they have a more comparable central nervous system. Still, this research has been hampered by limitations, including high costs and reduced samples. This review argues that a squirrel monkey model might bridge the gap by complementing translational research from rodents, macaque, and humans. With the advent of promising new methods such as ultrasound imaging, tool miniaturisation, and a shift towards open science, the squirrel monkey model represents a window of opportunity that will potentially fuel new translational discoveries in the diagnosis and treatment of brain pathologies.

A Web-Based Atlas Combining MRI and Histology of the Squirrel Monkey Brain

The squirrel monkey (Saimiri sciureus) is a commonly-used surrogate for humans in biomedical research. In the neuroimaging community, MRI and histological atlases serve as valuable resources for anatomical, physiological, and functional studies of the brain; however, no digital MRI/histology atlas is currently available for the squirrel monkey. This paper describes the construction of a web-based multi-modal atlas of the squirrel monkey brain. The MRI-derived information includes anatomical MRI contrast (i.e., T2-weighted and proton-density-weighted) and diffusion MRI metrics (i.e., fractional anisotropy and mean diffusivity) from data acquired both in vivo and ex vivo on a 9.4 Tesla scanner. The histological images include Nissl and myelin stains, co-registered to the corresponding MRI, allowing identification of cyto- and myelo-architecture. In addition, a bidirectional neuronal tracer, biotinylated dextran amine (BDA) was injected into the primary motor cortex, enabling highly specific identification of regions connected to the injection location. The atlas integrates the results of common image analysis methods including diffusion tensor imaging glyphs, labels of 57 white-matter tracts identified using DTI-tractography, and 18 cortical regions of interest identified from Nissl-revealed cyto-architecture. All data are presented in a common space, and all image types are accessible through a web-based atlas viewer, which allows visualization and interaction of user-selectable contrasts and varying resolutions. By providing an easy to use reference system of anatomical information, our web-accessible multi-contrast atlas forms a rich and convenient resource for comparisons of brain findings across subjects or modalities. The atlas is called the Combined Histology-MRI Integrated Atlas of the Squirrel Monkey (CHIASM). All images are accessible through our web-based viewer ( https://chiasm.vuse.vanderbilt.edu /), and data are available for download at ( https://www.nitrc.org/projects/smatlas/ ).

A fiber coherence index for quality control of B-table orientation in diffusion MRI scans

PURPOSE

The diffusion MRI "b-vector" table describing the diffusion sensitization direction can be flipped and permuted in dimension due to different orientation conventions used in scanners and incorrect or improperly utilized file formats. This can lead to incorrect fiber orientation estimates and subsequent tractography failure. Here, we present an automated quality control procedure to detect when the b-table is flipped and/or permuted incorrectly.

METHODS

We define a "fiber coherence index" to describe how well fibers are connected to each other, and use it to automatically detect the correct configuration of b-vectors. We examined the performance on 3981 research subject scans (Baltimore Longitudinal Study of Aging), 1065 normal subject scans of high image quality (Human Connectome Project), and 202 patient scans (Vanderbilt University Medical Center), as well as 9 in-vivo and 9 ex-vivo animal data.

RESULTS

The coherence index resulted in a 99.9% (3979/3981) and 100% (1065/1065) success rate in normal subject scans, 98% (198/202) in patient scans, and 100% (18/18) in both in-vivo and ex-vivo animal data in detecting the correct gradient table in datasets without severe image artifacts. The four failing cases (4/202) in patient scans, and two failures in healthy subject scans (2/3981), all showed prominent motion or signal dropout artifacts.

CONCLUSIONS

The fiber coherence measure can be used as an automatic quality assurance check in any diffusion analysis pipeline. Additionally, the success of this fiber coherence measure suggests potential broader applications, including evaluating data quality, or even providing diagnostic value as a biomarker of white matter integrity.

Biological evaluation of both enantiomers of fluoro-thalidomide using human myeloma cell line H929 and others

Over the last few years, thalidomide has become one of the most important anti-tumour drugs for the treatment of relapsed-refractory multiple myeloma. However, besides its undesirable teratogenic side effect, its configurational instability critically limits any further therapeutic improvements of this drug. In 1999, we developed fluoro-thalidomide which is a bioisostere of thalidomide, but, in sharp contrast to the latter, it is configurationally stable and readily available in both enantiomeric forms. The biological activity of fluoro-thalidomide however, still remains virtually unstudied, with the exception that fluoro-thalidomide is not teratogenic. Herein, we report the first biological evaluation of fluoro-thalidomide in racemic and in both (R)- and (S)-enantiomerically pure forms against (in vitro) H929 cells of multiple myeloma (MM) using an annexin V assay. We demonstrate that all fluoro-thalidomides inhibited the growth of H929 MM cells without any in-vivo activation. Furthermore, we report that the enantiomeric forms of fluoro-thalidomide display different anti-tumour activities, with the (S)-enantiomer being noticeably more potent. The angiogenesis of fluoro-thalidomides is also investigated and compared to thalidomide. The data obtained in this study paves the way towards novel pharmaceutical research on fluoro-thalidomides.

Study of three non-syndromic cases of congenital thumb aplasia in captive rhesus monkeys

Although congenital thumb absence has been reported frequently in humans, their occurrence in macaques is rare. We observed three cases of spontaneous thumb defects in captive female rhesus monkeys. One animal exhibited bilateral absence and two other presented unilateral thumb absence, all with metacarpal integrity. This report presents the clinical, radiological, and genealogical details as well as possible etiologies in an attempt to draw a parallel with humans and other primate species.

Neotropical primate nursery in a squirrel monkey breeding unit in Brazil

Saimiri (squirrel monkey) is a neotropical primate of the Simian genus that has been bred in captivity for the development of research into human and animal health. They have been widely used in studies in ophthalmology, toxicology, pharmacology, psychiatry, neuroscience, vaccines and drug tests (such as malaria and measles agents), as well as effects on interactive behavior and cognition of Creutzfeldt-Jakob disease in man. The main concern of non-human primate (NHP) research centers is focused on the establishment of self-sustaining breeding colonies providing good quality research animals. Maternal rejection, dystocia and pneumonia are the main causes of newborn deaths in these species. Therefore, in order to ensure the survival of these valuable animals, the Laboratory Animals Breeding Center of the Oswaldo Cruz Foundation (CECAL)/Fiocruz, Rio de Janeiro, Brazil, has developed a protocol for the nursery rearing of these infants.

Nonhuman primates as animal models for toxicology research

There is a long history for the use of nonhuman primates in toxicological research. This unit reviews applications in reproductive toxicology and teratology, neural toxicology and neurobehavioral toxicology, immunotoxicology, respiratory (lung) toxicology, and chemical carcinogenesis.

Embryo fetal development studies in nonhuman primates

Embryo fetal development (EFD) studies in nonhuman primates are frequently conducted in macaques with Macaca fascicularis (cynomolgus monkey, long-tailed macaque, crab-eating macaque) being the most accepted model. EFD studies are also feasible in the marmoset. Due to recent guideline changes (ICH M3(R2) and S6(R1)), EFD studies are largely confined to conventional pharmaceutical compounds rather than biopharmaceuticals. This chapter describes basic study designs and provides working protocols for collecting, processing, and staining fetuses, including collection of amniotic fluid and umbilical cord blood. The chapter also covers the examination and terminology for external, visceral, and skeletal examinations of fetuses. The species covered in this chapter are cynomolgus monkey (long-tailed macaque) and marmoset monkey.

Simian herpesviruses and their risk to humans

A high level of genetic and physiological homology with humans has rendered non-human primates (NHP) an essential animal model for biomedical research. As such NHP offer a unique opportunity to study host-pathogen interactions in a species that closely mimics human biology but can yet be maintained under tight laboratory conditions. Indeed, studies using NHP have been critical to our understanding of pathogenesis as well as the development of vaccines and therapeutics. This further facilitated by the fact that NHPs are susceptible to a variety of pathogens that bear significant homology to human pathogens. Unfortunately, these same viruses pose a potential health issue to humans. In this review we discuss the simian herpesviruses and their potential to cause disease in researchers that come into close contact with them.

Characterization of rhesus cytomegalovirus genes associated with anti-viral susceptibility

Studies were initiated to determine whether rhesus cytomegalovirus (RhCMV)-infected macaques could serve as an animal model for evaluating anti-CMV compounds, as macaques have a naturally occurring CMV that is similar to human CMV (HCMV). Utilizing plaque reduction assays, RhCMV was tested to anti-viral susceptibility. By these assays. RhCMV displayed anti-viral susceptibility to ganciclovir at a 50% effective dose (ED50) of 0.8 microM, acyclovir at an ED50 of 15 microM, and foscarnet at an ED50 of 250 microM. By Southern blot analysis with HCMV-UL97 (phosphotransferase) and DNA polymerase (pol) genes as probes, we isolated viral DNA fragments that strongly hybridized. DNA sequence analysis of these DNA fragments revealed two open reading frames with homology to HCMV UL97 and DNA polymerase. Steady-state RNA analysis revealed that the RhCMV UL97 homologue and pol genes are transcribed as early late and early genes, respectively. Comparison against HCMV showed the RhCMV UL97 homologue exhibits 54.4% amino acid (aa) sequence identity to HCMV UL97 and the RhCMV DNA polymerase 59.2% aa sequence identity to HCMV DNA polymerase. Results from anti-viral assays and molecular characterization of these two viral genes suggest that RhCMV-infected rhesus macaques should serve as an excellent animal model for evaluating future anti-CMV compounds.

Frequency of spontaneous congenital defects in rhesus and cynomolgus macaques

This paper summarizes the spontaneous incidence of congenital defects in the rhesus and cynomolgus macaque colonies (Macaca mulatta and M. fascicularis) at the California Regional Primate Research Center. The computerized database used in this analysis included fetuses, term infants, juveniles, and adults that underwent a necropsy procedure over a 14-year period (1983-1996). The calculated malformation rates were 0.9% (40/4,390) and 0.3% (3/965) for the rhesus and cynomolgus monkey, respectively. Most of the observed malformations in both species affected the musculoskeletal and the cardiovascular systems, while a smaller number of defects were observed in the gastrointestinal, urogenital, endocrine, and central nervous systems. Inbreeding did not contribute to the spontaneous malformation incidence and there was no predilection for sex (male vs. female) or housing (indoors vs. outdoors) among the malformed cases. This spontaneous malformation database in our macaque colony aids in the interpretation of defects that occur in an experimental study as well as in the ongoing assessment of a healthy nonhuman primate breeding colony.

High levels of dietary arachidonic acid triglyceride exhibit no subchronic toxicity in rats

Arachidonic acid (AA), an n-6 long-chain polyunsaturated fatty acid (LC-PUFA), serves an important role in the body as a structural fatty acid of many tissues including neurological tissues. It is also a precursor of the n-6 class of eicosanoids and is the most abundant n-6 LC-PUFA found in human breast milk. We have optimized the production of a microfungal source of a triglyceride oil (ARASCO) which is enriched in AA to about 40% by weight. To establish the safety of this oil as a food, we evaluated the effect of ARASCO in Sprague-Dawley rats (20/sex/group) gavaged at dose levels of 1.0 and 2.5 g/kg/d for a period of 90 d, paying special attention to any potential neurotoxicity of the oil. Two groups of control animals received either untreated standard laboratory diet (untreated control) or the same diet and vehicle oil at the same dose volume administered to the treated animals (vehicle control). Physical observations, ophthalmoscopic examinations, body weight, food consumption, clinical chemistry, hematology parameters, neurobehavioral assessments, and macroscopic as well as microscopic postmortem evaluations were performed. Tissue fatty acid analyses indicated that the AA levels in the brain, heart, and liver of the high-dose ARASCO-fed animals increased by 8, 59, and 76%, respectively, indicating that the AA in the oil was readily incorporated into tissue lipids. In spite of this high elevation in tissue AA levels, no developmental, histopathological, or neuropathological differences were seen in the animals administered ARASCO compared with the vehicle control animals. Being highly enriched in AA, ARASCO offers the means to study the effect of this fatty acid in experimental settings and in human metabolic studies.

Infant mortality: The role of the macaque as a model for human disease

Factors which have been identified as the leading causes of infant mortality include birth defects, hemoglobinopathies, prematurity, and Sudden Infant Death Syndrome (SIDS). In order to further our understanding of the specific causes of infant mortality and the mechanisms by which they occur, suitable animal models will be required. Studies with nonhuman primates (specifically the macaque) have addressed malformation/functional deficit syndromes such as those associated with Fetal Alcohol Syndrome (FAS), nutritional deficiencies, and retinoid teratogenicity. These studies have provided critical information for further basic and preventive research. In addition, efforts to evaluate the safety of diagnostic ultrasound continue to aid in identifying safe methods for exposure. From a prenatal perspective, cellular transplantation has been shown to be a feasible method for treating individuals with inherited defects in utero, thereby avoiding postnatal transplantation and the associated risks. Longterm complications of prematurity have also been pursued with growth factors (i.e., epidermal growth factor) noted to play an important role in both pre- and postnatal development of the gastrointestinal tract and lung. As one of the most distressing causes of death in infancy, SIDS will require a concentrated effort to understand the basic mechanism(s) responsible for the characteristic respiratory complications. The nonhuman primate will continue to provide critical information as the model of choice for the human in determining the causes, mechanisms, and treatments for these significant causes of infant death. © 1994 Wiley-Liss, Inc.

Evaluation of the bioeffects of prenatal ultrasound exposure in the cynomolgus macaque (Macaca fascicularis): III. Developmental and hematologic studies

The multiple applications of diagnostic ultrasound in obstetrics have resulted in a continued rise in the prenatal population exposed each year. Although human epidemiologic and experimental studies with various animal models have not consistently documented any significant, reproducible findings related to clinically relevant exposures, technologic changes in scanning equipment and gaps in our knowledge regarding the interaction(s) of ultrasound with tissues emphasize the need to pursue safety issues. Studies with nonhuman primates have provided information on the potential for pre and postnatal effects on offspring exposed repeatedly during gestation (ATL MK 600, 7.5 MHz, ISPTA = 27 mW/cm2; ISPPA = 85 W/cm2; Estimated power = 12 mW--scanned for 10 min 5 times weekly gestational day [GD] 20-35; 3 times weekly GD 36-60; once weekly for 20 min GD 60-150). These studies have indicated transient effects on body weight, white blood cell counts (WBCs), and muscle tone postnatally. In an effort to confirm these findings and focus on hematologic changes, a second series of studies was initiated using the same exposure conditions (N = 22; 11 exposed, 11 sham controls). Data derived from both studies were combined and confirmed transient reductions in body weights for infants up through 4 months of age (P < or = 0.03); no statistically significant differences in muscle tone were noted. Similar to the original findings, WBCs were transiently reduced on days 3 (P < or = 0.02) and 21 (P < or = 0.05); prenatal sampling indicated a significant difference between the groups on GD 140 (P < or = 0.04). No direct effects were evident in bone marrow aspirates collected on postnatal days 3, 9, and 21 +/- 1. Although animals were able to compensate for these observed changes and remained unaffected by their occurrence, additional studies will be required to further our understanding of this phenomenon.

Teratogenicity of all-trans retinoic acid during early embryonic development in the cynomolgus monkey (Macaca fascicularis)

The embryotoxic and teratogenic potential of all-trans retinoic acid was assessed following exposure prior to and during early organogenesis in the cynomolgus monkey (Macaca fascicularis). Sixteen pregnant females were orally administered all-trans retinoic acid (Tretinoin, Hoffmann-La Roche) once daily from GD 10-20 and twice daily from GD 21-24 at three different dosages, 5 (n = 9), 10 (n = 6) and 20 mg/kg (n = 1). Adverse clinical signs resembling hypervitaminosis A were observed in one animal at 5 mg/kg, in three animals at 10 mg/kg, and in the animal treated with 20 mg/kg all-trans retinoic acid. Maternal weight loss was observed in the 10- and 20-mg/kg groups. A dose-dependent increase in embryolethality was observed, with 22% (2/9), 50% (3/6), and 100% (1/1) occurring at 5, 10, and 20 mg/kg, respectively. The majority of embryonic deaths occurred between GD 16 and 20; the incidence of these early losses was higher than in historical and concurrent controls. No malformations, but a single growth-retarded fetus, was observed in the 5-mg/kg group. Craniofacial malformations, consisting of external ear defects, mandibular hypoplasia, cleft palate, and temporal bone abnormalities, were seen in three viable fetuses in the 10-mg/kg group. Skeletal variations were common to the majority (70%, 7/10) of viable fetuses in both dose groups and were increased relative to historical controls (32%, 25/77). Unlike previous studies with 13-cis-retinoic acid during the pre- and early organogenic stages of development (Hummler et al., Teratology 42:263-272, 1990), no thymic hypo- or aplasia or heart anomalies were observed, which may be attributable to the slightly longer 13-cis retinoic acid treatment period, i.e., GD 10-27. However, external ear and temporal bone defects were common to both all-trans and 13-cis retinoic acid. The similarity observed in the malformation syndrome induced by both all-trans and 13-cis retinoic acid in the cynomolgus monkey and 13-cis retinoic acid embryopathy in humans supports this macaque species as a model for further developmental toxicity studies of vitamin A-related compounds.

The effect of dietary change on in vitro erythrocyte haemolysis, skin lesions and alopecia in common marmosets (Callithrix jacchus)

1. The effect of dietary change on common marmosets (Callithrix jacchus) exhibiting high in vitro erythrocyte haemolysis, skin lesions and alopecia was investigated. 2. The experimental diet was low in lipid, high in vitamin E and was devoid of n-3 long chain polyunsaturated fatty acids. 3. There were significant increases in the concentrations of plasma alpha-tocopherol (vitamin E) (P less than 0.05), all-trans retinol (vitamin A) (P less than 0.001) and total lipid (P less than 0.025), and a reduction in fibrinogen (P less than 0.02) concentration and neutrophil count (P less than 0.02). 4. Moreover, the mean in vitro erythrocyte haemolysis declined from an initial value of 64% to less than 2%, and there was a regression of skin lesions and alopecia with complete fur regrowth. 5. The amelioration of the conditions appear to be due to high circulating vitamin E which provided protection against oxidative stress, and the correction of membrane n-6:n-3 balance.