Marc Niehoff

Physiology and Endocrinology of the Ovarian Cycle in Macaques

Macaques provide excellent models for preclinical testing and safety assessment of female reproductive toxicants. Currently, cynomolgus monkeys are the predominant species for (reproductive) toxicity testing. Marmosets and rhesus monkeys are being used occasionally. The authors provide a brief review on physiology and endocrinology of the cynomolgus monkey ovarian cycle, practical guidance on assessment and monitoring of ovarian cyclicity, and new data on effects of social housing on ovarian cyclicity in toxicological studies. In macaques, cycle monitoring is achieved using daily vaginal smears for menstruation combined with cycle-timed frequent sampling for steroid and peptide hormone analysis. Owing to requirements of frequent and timed blood sampling, it is not recommended to incorporate these special evaluations into a general toxicity study design. Marmosets lack external signs of ovarian cyclicity, and cycle monitoring is done by regular determinations of progesterone. Cynomolgus and marmoset monkeys do not exhibit seasonal variations in ovarian activity, whereas such annual rhythm is pronounced in rhesus monkeys. Studies on pair- and group-housed cynomolgus monkeys revealed transient alterations in the duration and endocrinology of the ovarian cycle followed by return to normal cyclicity after approximately six months. This effect is avoided if the animals had contact with each other prior to mingling. These experiments also demonstrated that synchronization of ovarian cycles did not occur. Competing Interests: This article was sponsored by Covance Inc. and Schering-Plough. Gerhard F. Weinbauer, Marc Niehofg, Michael Niehaus, Shiela Srivasav, and Antje Fuchs are employed by Covance Inc. Eric Van Esch is employed by Schering-Plough. No other competing interests were declared.

High Definition Oscillometry: a novel technique for non-invasive blood pressure monitoring in the cynomolgus monkey (Macaca fascicularis)

Background  Current approaches for accurate blood pressure determination rely predominantly on invasive techniques. High Definition Oscillometry (HDO) was evaluated as a potential non‐invasive approach for accurate blood pressure recordings in cynomolgus monkeys.

Effects of social housing of sexually mature male cynomolgus monkeys during general and reproductive toxicity evaluation

We investigated the effects of social housing on reproductive parameters and body weight in mature cynomolgus monkeys, the predominant nonhuman primate model in (reproductive) toxicology. Group housing (n=7) delayed body weight gain compared to single housing. Testicular volumes decreased to approx. 45% of baseline within 13 weeks in low ranking animals followed by return to baseline during weeks 21-26. Interestingly, ejaculate and endocrine parameters did not exhibit corresponding changes. Following separation of this group into a high rank group (n=4) and low rank group (n=3), testicular volumes varied within background variation (+/-15%). Re-allocation of new animals with prior contact/group housing experience into groups of 3 animals also prevented body weight and testicular effects. In conclusion, group formation markedly, albeit transiently, altered body weights and testicular size, and these effects could largely be avoided by previous social interaction for at least 26 weeks. These findings should be considered during social housing of mature animals in toxicity studies.

Measurement of hyper- and hypotension during repeated dose toxicity studies in either freely moving or physically restrained cynomolgus monkeys

INTRODUCTION The measurement of cardiovascular endpoints in standard toxicology studies remains a challenge as the routinely used non-invasive methods require physical restraint, causing an increase of sympathetic neural activity, leading to excitement and potentially hypertension in the experimental animals. In this study, a miniature telemetry blood pressure transmitter was used to evaluate if the acute hyper- and hypotension could be detected in free moving cynomolgus monkeys as well as physically restrained animals using positive control drugs. Furthermore, as a comparator, routine high definition oscillometry (HDO) was performed in restrained animals. METHODS Hemodynamic parameters were monitored continuously from conscious, freely moving animals following oral administration of vehicle (water) or 1 and 10mg/kg of etilefrine, and 1 and 4mg/kg of dihydralazine as positive control articles. A second dose session was performed to confirm the reproducibility of results and a third dose session combined with physical restraint procedures for blood collection and HDO measurements. RESULTS There was a dose-dependent, statistically significant increase in the systolic blood pressure following oral doses of etilefrine at all 3 dose sessions. This effect was less apparent during session 3, probably due to the physical restraint applied for the blood sampling and HDO measurement. No differences in the blood pressure were measured using HDO. On all three dose sessions following oral doses of dihydralazine the expected statistically significant decrease in the diastolic pressure could be clearly measured even when the telemetric data recordings were combined with physical restraint. DISCUSSION Due to the advantages of the minimally invasive telemetry technique compared to HDO and the possibility of prolonged measurement periods, it is an invaluable tool for blood pressure measurement in freely moving animals in toxicology studies.

Differential responses to JNJ‐37822681, a specific and fast dissociating dopamine D2 receptor antagonist, in cynomolgus monkey and Sprague–Dawley rat general toxicology studies: clinical observations, prolactin levels, mammary histopathology findings and toxicokinetics

JNJ‐37822681 is a potent, specific and fast dissociating dopamine D2 receptor antagonist intended for the treatment of schizophrenia. Its nonclinical toxicological profile was investigated in a series of general repeat dose toxicity studies in cynomolgus monkeys and Sprague–Dawley rats. The maximum duration of treatment was 9 and 6 months, respectively. Interspecies differences were noted in the response to JNJ‐37822681 in terms of extrapyramidal (EPS)‐like clinical signs and prolactin‐mediated tissue changes in the mammary gland. Monkeys showed severe EPS‐like clinical signs such as abnormal posture, abnormal eye movements and hallucination‐like behavior at relatively low exposures compared to those associated with EPS in patients with schizophrenia. The high sensitivity of the monkey to JNJ‐37822681‐induced EPS‐like signs was unexpected based on the fast dissociating properties of the compound. Rats, however, were not prone to EPS. Elevated serum prolactin levels were found in rats and monkeys. While rats showed slight to moderate prolactin‐related tissue changes upon histopathological examination in all studies, which among others affected the mammary gland, only minor mammary gland tissue changes were noted in monkeys. Prolactin levels were only slightly increased in patients with schizophrenia receiving relatively high dose levels of JNJ‐37822681. The monkey toxicology studies did not provide an exposure‐based safety margin, while in rats adverse effects were only noted at exposures considerably higher than those achieved at efficacious plasma concentrations in the clinic. Overall, the available data suggest that the cynomolgus monkey showed better predictivity towards the nature of JNJ‐37822681‐associated adverse events in humans than the Sprague–Dawley rat. Copyright