Abstract
Dear Dr. Foster,
We very much appreciate the opportunity to respond to Drs. Nyska and Gruebbel’s comments regarding our recent manuscript entitled “Spontaneous Findings in the Heart of Mauritian-origin Cynomolgus Macaques (Macaca fascicularis).” We understand the sensitive nature of the matter and the potential impact on their clients, Bioculture (Mauritius) Ltd. We discussed this issue at length last year with both Dr. Nyska and representatives of Bioculture (Mauritius) Ltd. and addressed many of these concerns at that time, but we are happy to provide additional information for the readership of Toxicologic Pathology and the general scientific community.
We are pleased that Drs. Nyska and Gruebbel agree “with the descriptions and reported incidences of the various cardiovascular findings reported in this paper”; the concern that these results “include the lack of consistency with other data about cardiac pathology in macaques” is the very reason we felt this information was worthy of publication and of interest to the readership of Toxicologic Pathology. We first observed this spectrum of cardiac findings in 2005, shortly after completing a review of the background findings in dogs and cynomolgus macaques (Keenan and Vidal 2006). The striking difference between the recently completed review and the newly observed findings led us to a lengthy investigation that included a review of breeders, vendors, shipping practices, quarantine practices, handling procedures, caging and housing, technical staff involved, euthanasia procedures, and necropsy practices. We critically compared vehicles and routes of administration, but the spectrum of findings was observed regularly with routine vehicles, including oral administration of 1% methylcellulose and 0.5% hydroxypropylmethylcellulose/ 0.1% Tween 80, and was present with all routes of administration. The presence of potentially catecholamine-mediated cardiac findings led us to carefully re-evaluate our programs of animal care in our facility. Our facility is AAALAC International accredited and registered with the USDA as a research facility, and was during the time the data was acquired. The programs for animal husbandry and housing for both the Indonesian-origin and Mauritian-origin cynomolgus macaques at our facility were identical during the period of this review. The only change that was identified was a shift in the source of animals used at our laboratory. In 2005, we began using an increasing number of Mauritian-origin macaques in our nonclinical safety testing program, and from 2005-2007 our colony contained a mixture of Indonesian- and Mauritian-sourced macaques. The presence of macaques from both sources afforded us the opportunity to compare the impact of genetic source, given that these animals were housed and handled in the same manner by the same individuals in the same facility. The described spectrum of cardiac findings observed occurred only in Mauritian-sourced animals and was not observed in any of the concurrent Indonesian-sourced macaques (n = 19). We elected to focus on the review of the Mauritian-origin animals in this manuscript, as the findings in concurrent Indonesian animals were consistent with published observations, as described in our prior publication. Although we cannot account for differences in handling and shipping practices prior to arrival at our facility, the macaques used in this review were from two different vendors who sourced animals from two distinct Mauritian breeders. When we compared the two different vendors/breeders, there was no difference observed for myocardial necrosis or subendocardial hemorrhage, and we presented the pooled data for publication.
We understand and recognize the limitations pointed out by Drs. Nyska and Gruebbel regarding the lack of “appropriate controls.” In an ideal scientific world, we would have included a direct comparison of naïve Indonesian and Mauritian macaques in a prospective manner, but the ethical and animal welfare concerns inherent to nonhuman primate work prevailed and we elected to make the best use of the available resources to limit the number of animals used in our laboratory. In fact, the “recently published surveys of background pathology in control cynomolgus monkeys, including those of Mauritian origin,” cited by Drs. Nyska and Gruebbel as evidence of a lack of findings in Mauritian animals, suffer from all of the same scientific criticism they raise about our review (Drevon-Gaillot et al. 2006; Chamanza et al. 2006). In 2008, Chamanza et al. presented a poster at the annual STP meeting describing results from 488 cynomolgus macaques; these results differ from those of their own prior publication cited by Drs. Nyska and Gruebbel and include the statements, “An enigmatic idiopathic myocardial degeneration was recorded in a few studies but with a moderately high incidence in those studies in which it occurred” and “Acute haemorrhagic necrosis and fibrosis at the papillary muscle, resembling ischemic lesions seen with β-agonist and other cardioactive drugs were also encountered in occasional animals.” The authors also state: “Since the majority of our animals were from Mauritius no attempt was made to analyze the results based on the geographical origin of the animals” and that “differences could have been due to differences in the source and genetic background of animals.” These findings are similar to those described in our Mauritian-origin animals and, like the findings from Chamanza et al., are clearly different from past experience. Although poster presentations are not typically cited as references in manuscripts, these novel differences are critical for toxicologic pathologists to be aware of, and we appreciate the effort of Chamanza et al. for presenting an outstanding review despite the lack of concordance with previous data.
In the discussion section, we state: “Myocardial degeneration/necrosis and subendocardial hemorrhage are commonly reported findings in a variety of species and associated with elevations in catecholamines” and that “The findings observed in this review are consistent with those reported secondary to elevations in catecholamines and document the higher incidence of these findings in macaques of Mauritian origin than that observed in a published review from our facility using primarily Indonesian-source macaques.” This statement was meant only to highlight these points and bring them to the attention of other toxicologic pathologists. We agree with Drs. Nyska and Gruebbel that there are potential limitations and other factors that can contribute to the incidence of these findings and that not all facilities will see this spectrum of findings in all settings. Drs. Nyska and Gruebbel describe unpublished observations from an ongoing investigation at their client’s facility in Mauritius. Although we have not had the opportunity to see the results or details of this small pilot study, one would expect to see differences in the incidences of potentially catecholamine-driven lesions between animals in their native habitat and those animals that have undergone extensive shipping, handling, and use in acute toxicity testing. Catecholamine-driven cardiac effects are complicated and difficult to interpret, with many different environmental and experimental variables at play. The absence of findings in an unstressed setting does not rule out the possibility of seeing these lesions under a different set of experimental conditions, nor does the presence of these findings in our laboratory mean that all users of Mauritian animals will see these findings.
In our manuscript, we state: “the defined genetic status and Herpes B–, SIV-, and SRV-virus-free status of Mauritian origin animals are attractive characteristics for a variety of experimental studies,” and in our laboratory, noncardiac histopathologic background findings in Mauritian-origin animals are remarkably low (Vidal, unpublished observations). As with any strain of rat or breed of dog, it is important to understand both the desirable characteristics of the model as well as the potential complicating factors. In nonclinical safety testing, it is in the best interests of human safety to ensure that we thoroughly understand our model systems so we can appropriately identify hazards that are truly test-article–related and perform the most robust risk assessment possible. Our intent was only to document our observations for other toxicologic pathologists in as unbiased a manner as can be done with a retrospective review. We stand behind the data and interpretation of our manuscript as published. We hope that the scientific community will continue with this discussion and in time build the necessary weight of evidence to better understand the presentation and pathogenesis of this complicated finding.
Thank you again for the opportunity to discuss this matter and to provide additional information to the readership of Toxicologic Pathology.