A study found that a crude thymus extract (Thymex‑L) can boost the effect of retinoic acid in turning a leukemia cell line into more mature cells, but the specific peptide thymosin‑alpha‑1 (the one many biohackers talk about) did not show any of this benefit. The active ingredient in the extract is a larger, heat‑stable molecule, not the small peptides usually used as supplements.

The human promyelocytic cell line HL-60 can be differentiated with retinoic acid (RA) along the granulocytic pathway. Numerous studies have identified many synergistic combinations of RA with cytostatics, cytokines and other inducers. A combination of RA with the crude thymus extract Thymex-L increased differentiation of HL-60 cells as confirmed by two functional assays and morphology, whereas the extract itself did not show any effect. The functional markers phagocytosis-associated chemiluminescence and nitroblue tetrazolium reduction were more enhanced (up to 4-fold with 1000 micrograms/ml Thymex-L) than morphology. The effect was found over a wide RA concentration range (10(-11) - 10(-6) M) and was dependent on extract concentration. The half-maximal induction of both functional markers was reached at 400 micrograms/ml. To achieve the same effect with the combination in comparison with RA alone, an RA dose reduction of about 100-fold was estimated. The effect was also seen when the cells were pretreated with the thymus extract for two days. The enhancement of RA action by Thymex-L was not correlated with an increase of extracellular or intracellular RA concentration. The active compound in Thymex-L is heat stable and bigger than 5 kDa as confirmed by gelfiltration. The defined thymus peptides thymosin alpha 1, prothymosin alpha 1 and thymopentin were unable to synergistically enhance HL-60 differentiation. These data suggest that the treatment with a thymus extract can increase the sensitivity of HL-60 cells for RA. This may have clinical implications.