The Difficulty Of Dexamethasone Administration Causes Murine Palatoschisis By Inducing Palatal Mesenchymal Ceil Apoptosis And Local Down-regulation Of BMP-2

Palatoschisis is one of the most common craniofacial deformity possibly resulted byenvironmental factors and maternal gene alterations. Its incidence is about1in every500to2500infants. The deformity often burdens the patients with difficulties in daily activities andnegatively affects the patients’ psychological development. During the last20years,numerous reports have confirmed the embryo teratogenicity of dexamethasone(DEX)including its risk in inducing infant palatoschisis. However, whether the effect is dosedependent or frequency dependent remains unclear. Studies have shown the effect of DEXrepressing embryo palatal mesenchymal(EPM) cell growth in palate process development,while the association between EPM apoptosis and palatoschisis awaits determination.Therefore, we constructed the animal model of palatoschisis and studied the dose andfrequency dependency of DEX teratogenicity and the association between EPM apoptosisand the development of palatoschisis.Methods:Inbred mice from the same environments were randomly selected with male to femaleration of2:1and reared in the same cage at18:00. Female mice were checked for vaginalplug at7:30the next day, and were marked0GD and weighted if the vaginal plug waspresent, and weighted again on10GD at7:30with weight gain higher than2gram as theindication of pregnancy.45pregnant mice were randomly selected and evenly divided intoLD group (6mg DEX, consecutive intraperitoneal injection on11.5d,12.5d and13.5d), HDgroup(50mg DEX, single intraperitoneal injection on11.5d) and control group. All groupsare sacrificed on14.5d.. After being sacrificed the mice were placed on ice and for fetusretrieval. The mandibles of the fetus were observed and processed for HE staining,immune-staining, TEM.Results:Incidence of palatoschisis is41.14%(72/175) in LD group, and middleweight is0.31gram.61.17%(63/103) in HD group and middleweight is0.43gram.5.04%(7/139) incontrol group and middleweight is0.54gram. The incidence of palatoschisis in HD group issignificantly higher than LD group. HE staining showed longitudinal cleft with irregularmargins in the mandibles of the fetus with palatoschisis. TUNEL staining showed large amount to apoptotic cells in the palate process of fetus with palatoschisis. TEM observedmarked difference of EPM morphology and EPM cell organ structures between fetus withpalatoschisis and fetus from control group. The local protein level of BMP-2is lower in fetuswith palatoschisis, compared with control, and cleaved caspase-3is elevated which is alsosignificantly higher in HD group than LD group.Conclusion:1. High dose single administration of DEX induces higher risk of palatoschisiscompared to low dose multiple administration of DEX.2. Palatoschisis is associated with EPM apoptosis.3.Local BMP-2expression if affected by palatoschisis development.4. Alteration of BMP-2level is not dependent to DEX dose.