2.4　Insulin secretion assay

Insulin concentration in the supernatant which were collected after 48h cultivation was determined by ELISA using microplate reader(MB-530，Shenzhen Huisong technology development Co.，Ltd，Shenzhen，China).The measurement was conducted according to the instruction of Rat Insulin Elisa kit(R& D Systems，USA).(https://www.daowen.com)