Tacrolimus (FK506) is a chemotherapeutic agent, which uses calcineurin pathway via inhibiting the stimulation of T cells to prevent the formation of immune response in the recipient individual in organ transplants. FK506 is mainly metabolized in the liver by cytochrome P450 enzyme system and is known that it has high toxic effects on different cells. Mesenchymal stem cells (MSCs) have recently gained importance since their potential to be used in cellular therapy and tissue regeneration. In some clinical cases, MSCs are transferred into the patient after the organ transplantations in order to support the treatment. Because of their immunomodulatory actions and assistance to the regeneration, popularity of MSCs have been increasing recently. However, since immunosuppressive agents have a potential cytotoxic and apoptotic effect on MSCs, researches have attempted to use it as a combination with an agent that alleviates these effects. Oxytocin (OT) is primarily acting as a neuromodulator in humans and is a peptide hormone secreted by the pituitary gland of the neurohypophysis. OT has such effects on cells as to confer resistance against oxidative stress on cells and to increase the proliferation and help regeneration. Studies on the active substance of FK506 were aimed to investigate the cytotoxic effects on human adipose tissue derived MSCs.

The purpose of this study was to determine the cytotoxic, apoptotic and morphological effects of FK506, an immunosuppressive agent, on adipose tissue − derived MSC (ADMSC) which has the potential to be used for immune suppression. In addition, it was aimed to determine whether the agent could reduce the cytotoxic, apoptotic, and morphological effects on ADMSCs when used in combination with OT.

For this purpose, the cytotoxic effects of the FK506 and OT on ADMSCs were determined by time and dose dependent manner by the WST-1 test. Isobologram analysis was evaluated using the WST-1 test according to IC₅₀ values of FK506 and OT. The apoptotic effects of the agents on the ADMSCs were determined by the Annexin V method. Immunofluorescence staining was performed to determine morphological changes. Changes in the levels of oxidative stress markers were measured by colorimetric and flourometric methods using lipid peroxidation, superoxide dismutase activity, catalase activity and glutathione peroxidase assays.

The IC₅₀ values of FK506 and OT on ADMSCs were calculated as 17.44μM and 13.43μM, respectively.FK506 and OT were found to have antagonistic activity on ADMSCs (CI value of the combination was 1.24). The effects of the agents individually and in combination on the levels of apoptosis and oxidative stress markers have been evaluated.

When the results obtained from the study are evaluated, the adipose- tissue derived mesenchymal stem cells used with takrolimus and oxytocin combination have a potential for novel treatment approaches.