Evaluation of Macaca mulatta as a model for genotoxicity studies

We have investigated the use of peripheral blood from the nonhuman primate (NHP) rhesus monkey (Macaca mulatta) as a model system for mutation detection. The rhesus monkey is metabolically closer to humans than most common laboratory animals, and therefore may be a relevant model for hazard identification and human risk assessment. To validate the model, conditions were determined for in vitro selection and expansion of 6-thioguanine-resistant (6-TGr) HPRT mutant and proaerolysin-resistant (ProAERr) PIG-A mutant lymphocytes from peripheral blood obtained by routine venipuncture. Also, flow cytometric methods were developed for the rapid detection of PIG-A mutant erythrocytes. The flow cytometric analysis of PIG-A mutant erythrocytes was based on enumerating cells deficient in surface markers attached to the cellular membrane via glycosylphosphatidyl inositol (GPI) anchors. Mutant cells were enumerated over an extended period of time in peripheral blood of male monkeys receiving daily doses of the electrolyte replenisher Prang™ (a common carrier for oral delivery of drugs in NHPs), and in the blood of one male monkey treated with a single i.p. dose of 50 mg/kg of N-ethyl-N-nitrosourea at ∼2 years of age and another similar injection at approximately 3.5 years of age. The spontaneous PIG-A and HPRT T-cell mutant frequency (MF) was low in animals receiving Prang (0–8 × 10−6), and treatment with ENU resulted in a clearly detectable increase in the frequency of ProAERr and 6-TGr lymphocytes (up to ∼28 × 10−6 and ∼30 × 10−6, respectively). Also, the ENU-treated animal had higher frequency of GPI-deficient erythrocytes (46.5 × 10−6 in the treated animal vs. 7.8 ± 4.2 × 10−6 in control animals). Our results indicate that the rhesus monkey can be a valuable model for the identification of agents that may impact upon human health as mutagens and that the PIG-A gene can be a useful target for detection of mutation in both white and red blood cells.