Exogenous Tβ4 can function like a hormone on cells in terms of its ability to modulate their biological behavior. Since one of the primary roles of Tβ4 in cells is the sequestration of actin monomers, and the protein is not secreted, previously indicated that it was unlikely that Tβ4 could have a hormonal function [42]. However, other studies have shown that the intracellular level of Tβ4 or its mRNA can be significantly and rapidly altered by external stimuli and that change in the level of Tβ4 often are correlated with cell differentiation [18, 43]. In the present study, exogenous Tβ4 peptide activate intracellular Tβ4, which results suggested that exogenous Tβ4 spontaneously enter the cytoplasm through rapid internalization, and acts their functions same as endogenous one [8, 18].
Established immortalized human PDLCs [22] that maintain the characteristics of primary PDLCs by transfecting human telomerase reverse transcriptase (hTERT) were used. These cell line were kindly provided by Professor Takashi Takata (Hiroshima University, Japan). Cells were cultured in α-MEM supplemented with 10% FBS, 100 U/mL penicillin, and 100 μg/mL streptomycin in a humidified atmosphere of 5% CO2 at 37°C. For the experiments, the cells were seeded into culture dishes and then cultured in α-MEM containing 10% FBS for 2 days until 70% confluent, and, then, the media was replaced by serum-free medium in order to minimize any serum-induced effects on PDLCs. Subsequently, the cells were exposed to H2O2 and human Tβ4 peptide (RegeneRx Biopharmaceuticals Inc., Rockville, MD). All treatments were performed in triplicate and approved by the local ethics committee.
5-HTP is sold over the counter in the United States, Canada, the Netherlands, and the United Kingdom as a dietary supplement for use as an antidepressant, appetite suppressant, and sleep aid. It is also marketed in many European countries for the indication of major depression under the trade names Cincofarm, Levothym, Levotonine, Oxyfan, Telesol, Tript-OH, and Triptum.[1]