Abstract: BACKGROUND: The pathogenesis of congenital microtia is not clear. Current studies believe that microtia is related to the joint action of environmental and genetic factors, and drug teratogenesis is an important aspect of environmental factors.
OBJECTIVE: To observe the embryonic auricle development indexes of pregnant rats exposed to different concentrations of mycophenolate mofetil, in order to establish a drug-induced microtia model and provide a basis for further exploring the pathogenesis of microtia.
METHODS: Adult Sprague-Dawley rats were caged according to the ratio of male to female at 2:1, and the female rats were checked the next day. The presence of a vaginal plug was designated as gestational day 0. Thirty-two pregnant rats were randomized into four groups (n=8 per group): control group, 50, 100, and 200 mg/kg mycophenolate mofetil groups. Rats in the four groups were intragastrically given corn oil, and 50, 100, and 200 mg/kg mycophenolate mofetil corn oil respectively at 8 a.m. on gestational days 9 and 10. The pregnant rats in each group were decapitated under anesthesia on gestational day 20.5. The embryonic development and auricle development indexes were generally observed. The development of middle and inner ears was observed by micro-CT imaging. Auricle cartilage and soft tissue changes were histologically observed.
RESULTS AND CONCLUSION: (1) Compared with the control group, the numbers of dead fetuses and absorbed fetuses were increased and the number and rate of live fetuses decreased in different mycophenolate mofetil groups. There were significant differences in ear transverse length, ear longitudinal length, ear longitudinal length/ear transverse length, nasal occipital distance/biparietal diameter, eye distance, body length and body mass between different mycophenolate mofetil groups and control group (P < 0.05). The above-mentioned indexes were significantly different in the 50 mg/kg mycophenolate mofetil group from 100 and 200 mg/kg mycophenolate mofetil groups (P < 0.05). There were also significant differences in ear length, body length, body mass, and nasal occipital distance between 100 and 200 mg/kg mycophenolate mofetil groups (P < 0.05). (2) Compared with the control group, the main micro-CT changes in each mycophenolate mofetil group were dysplasia of the skull and incomplete development of auditory vesicle. (3) The results of hematoxylin-eosin staining, toluidine blue staining and type II collagen immunohistochemistry staining showed that mycophenolate mofetil affected the proliferation and differentiation of chondrocytes and the expression of type II collagen. (4) To conclude, mycophenolate mofetil can cause the dysplasia of rat embryonic auricle in a dose-dependent manner, because mycophenolate mofetil may inhibit the proliferation and differentiation of chondrocytes and the expression of type II collagen. Mycophenolate mofetil can be used to establish an animal model of microtia.

Key words: mycophenolate mofetil, rat, ear deformity, auricle development, chondrocyte, type II collagen