PROD-activities and responsiveness to 1 mM PB in sequentially (+/-1 μM TSA) or cocktail (+/-1 μM TSA)-exposed hMSC. PB was added daily, starting on day 18. The graph is representative for 5 separate experiments, each, performed in duplicate. PB, phenobarbital. *: PROD-activity of sequentially TSA- and cocktail TSA-exposed hMSC is significantly higher than of sequentially- and cocktail-exposed hMSC with p < 0.05 (Student's t-test). $,$$: PB significantly induced PROD-activity of sequentially TSA- and cocktail TSA-exposed hMSC with p < 0.05 and p < 0.01, respectively (Student's t-test).