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For toxicology testing of (agro)chemicals, different study types are being performed with general and/or reproductive toxicity endpoints (see Organisation for Economic Co-operation and Development guidelines). In most of these rat studies, vaginal cytology is performed on serial samples (collected by lavage) for evaluation of cycle regularity and evidence of mating, and/or on a single sample collected on the day of necropsy for information on the estrous cycle stage and allowing correlation with histopathology. In the latter case, the utility of vaginal cytology can be argued. In this article, estrous cycle stages based on vaginal cytology of samples taken on the day of necropsy and histopathology of ovaries, uterus, and vagina (gold standard for estrous cycle stage assessment) were compared. The agreement was generally low. Disagreement between the two methods could be explained by time differences between lavage and necropsy, by manipulation of vaginal epithelium during lavage which may impact epithelial morphology on histology, and by misinterpretation of vaginal cytology during or shortly after lactation. Based on the results of estrous staging within different study types, we strongly discourage vaginal cytology from samples collected on the day of necropsy since there is no added value, vaginal manipulation can be stressful and may complicate the histologic diagnosis. [ABSTRACT FROM AUTHOR]

AstraZeneca ran a bespoke study to generate age-matched clinical pathology and histopathology data from a cohort of Beagle dogs aged between 25 and 37 months to support the use of these older animals in routine preclinical toxicology studies. As the upper age range of Beagle dogs routinely used in toxicology studies does not normally exceed 24 months, there is an absence of appropriate age-matched historical control data. The generation of such data was crucial to understand whether age-related differences in spontaneous findings might confound the interpretation of toxicology study data. While the majority of the histopathology findings in all the older dogs occurred at a similar prevalence as those expected in young adult dogs (<24 months), a number of differences were observed in the thymus (involution), bone marrow (increased adiposity), testes (degenerative changes), and lung (fibrosis, pigment and alveolar hyperplasia) that could be misinterpreted as a test article effect. Minor differences in some clinical pathology values (hemoglobin, alkaline phosphatase, absolute reticulocytes) were of a small magnitude and considered unlikely to affect the interpretation of study data. [ABSTRACT FROM AUTHOR]

Cardiovascular safety signals in nonclinical studies remain among the main reasons for drug attrition during pharmaceutical research and development. Drug-induced changes can be functional and/or associated with morphological alterations in the normal heart histology. It is therefore crucial to understand the normal variations in histology to discriminate test article–related changes from background lesions. Rodent progressive cardiomyopathy is probably the most commonly encountered change in control animals of nonclinical toxicity studies. A multisite study mimicking standard short-term toxicity studies using young male Sprague-Dawley rats was performed to better characterize this finding. Using an enhanced sectioning method for this research study, it was observed that the incidence of background cardiomyopathy was 100%. The vast majority of the microscopic findings were inflammatory in nature, with associated necrotic changes (defined as necrosis/inflammatory cell infiltrate) and these changes were mainly located in the myocardium of the mid region of the ventricles (the left side being predominantly affected). The monitored environmental factors in this study (multiple facilities, study duration, handling) did not have an effect on the incidence or severity of the spontaneous cardiomyopathy. In addition, cardiac-specific serum troponin levels were measured and were within the published control range. [ABSTRACT FROM PUBLISHER]

Serum cardiac troponin-I has been validated as a biomarker for cardiotoxicity in numerous animal models; however, baseline reference ranges for cTnI concentration in a healthy population of laboratory rats, as well as an investigation of biological cTnI variability in rats with respect to time, handling, and placebo dosing methods, have not been reported. In this study, we used an ultrasensitive cTnI immunoassay to quantify hourly concentrations of cTnI in live rats handled under standard laboratory conditions using 15 µL of serum per determination. The baseline reference range (mean 4.94 pg/mL, range 1—15 pg/mL, 99% confidence interval [CI]) of cTnI concentration in rats was consistent with previously reported reference ranges for cTnI in humans (1—12 pg/mL) and with preliminary studies in dogs (1—4 pg/mL) and monkeys (4—5 pg/mL) using the same cTnI assay method. In addition, cTnI concentrations in individual rat serum samples show minimal biological variability over a twenty-four-hour interval when compared to a meaningful reference change value of 193% to 206%. Furthermore, measurements of cTnI concentration were consistent within the reference limits in individual rats over long periods and under three different standard laboratory handling conditions. Thus, using this new method, rats can be followed longitudinally at hourly intervals, and a doubling of cTnI concentration would be significant above biological variability. This is a new paradigm for preclinical testing, which allows transient changes in cTnI concentration to be accurately quantified. This understanding of baseline and biological variability in rats will be fundamental for designing and analyzing future studies that assess potential cardiotoxicity in drug development. [ABSTRACT FROM PUBLISHER]

The social, physical health and psychological benefits of housing primates in groups has been recommended for several years. However, in many U.S. facilities, primates have traditionally been housed singly for toxicology studies due to limited space, the need to keep experimental variables to a minimum, and for the ease of collecting data. In addition, doorway and hallway size at facilities generally make it difficult to use mobile cages of sufficient size to allow several monkeys to be housed as a group. Group housing of primates for toxicology studies has been successful in Europe; however, the cages used are often permanently installed into the rooms and are considerably larger than traditional mobile cages. Unfortunately, installing caging of that size in many U.S. laboratories is not practical. In order to gain the benefits known to occur with group housed primates and provide a mobile cage useful in most facilities; a custom built mobile housing unit was developed to allow group housing of up to four cynomolgus monkeys. This unit was designed as a bank of four cages, two on top and two on the bottom. Dividers open between all individual cages to allow movement of animals throughout the entire space. This group housing layout is maintained continuously once compatible groupings are achieved, but each primate can be singly housed if necessary. In our experience, additional time is required to achieve group compatibility within a housing unit, particularly with larger, more aggressive males. While it was not always possible to group-house four primates, in general cynomolgus monkeys group housed in these units showed less aggression, were easier to handle, and had fewer observations of fecal abnormalities indicating the animals were under less stress. Our results demonstrate the benefits of group housing cynomolgus monkeys in mobile cages that could be used in other toxicology laboratories. [ABSTRACT FROM AUTHOR]

Following the construction of a new toxicology facility, validation studies are routinely completed to demonstrate the successful ability to conduct animal studies. However, a literature search did not reveal a common approach or design for such studies. Therefore, 1-month studies in 4 common laboratory animal species (rat, mouse, dog, monkey), conducted in compliance with GLP regulations were designed and included many procedures commonly used in toxicology studies. Commonly used vehicles (HPMC, NaCl, ground diet), or loratadine, were administered daily via oral gavage or capsule, or twice weekly via intravenous or subcutaneous injection. Observations within the studies included clinical signs, body weights, food consumption, physical, ophthalmic, ECG, and neurological examinations, vital signs, blood pressure determinations, and clinical and anatomic pathology. Blood samples were also collected for bioanalytical analysis (all studies) and serology (rat study only). Dose formulations were accurately prepared, and dosing was successfully completed in all studies. Only minor clinical signs were observed, and no marked or adverse findings were seen in any of the other study parameters, although minor, procedure-related microscopic findings were found in the SC and/or IV groups of all species. Bioanalytical results in all studies demonstrated successful and expected exposure to loratadine. In the rat study, all serology results were negative. None of the dosing routes or study procedures had any effect on the health of the animals. Overall, the study designs were considered sufficiently inclusive and robust for the validation of new, or existing, toxicology facilities involved in conducting GLP studies. [ABSTRACT FROM AUTHOR]