Irreversible methadone-induced GSTP1 downregulation in SH-SY5Y cells

Background: Methadone has been reported to downregulate the expression of glutathione S-transferase P1 (GSTP1) among nine antioxidant genes in SH-SY5Y cells after both short- and long-term treatment. GSTP1 plays a key role in the detoxification of many xenobiotics and is frequently associated with various diseases, especially tumors. The objective of this study is to determine whether this change is reversible. Methods: Two different treatment protocols were used. The first protocol evaluated the reversibility of the GSTP1 mRNA change, while the second protocol evaluated the methylation status of the GSTP1 promoter site. To investigate the reversibility of the GSTP1 mRNA change, SH-SY5Y cells were treated with methadone. The drug was then removed from the medium and the cells were cultured in methadone-free medium for a period of time. GSTP1 mRNA levels were expressed as cycle threshold (Ct) values using TATA box-binding protein as a calibrator gene. Methylation at the promoter site was detected by bisulfite treatment. Results: The analysis of variance revealed no significant change in GSTP1 mRNA levels in the cells after methadone was removed from the medium of methadone-treated cells. The study also examined the methylation status of a CpG island in the promoter of GSTP1 in the treated cells. The results demonstrate that although methadone downregulates the mRNA level of GSTP1 in treated cells, it does not induce methylation in the GSTP1 promoter region. Conclusions: The expression of the GSTP1 remains downregulated even after methadone removal from SH-SY5Y cell culture medium; however, methylation of the GSTP1 promoter site does not play a role in this process.