Transport of tryptophan dipeptide derivatives and impact on inflammatory cytokines in monocyte/macrophage-like cells

Authors: Park, Jae; Peters, Renee

Submitted to: Heliyon
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2025
Publication Date: 2/27/2025
Citation: Park, J.B., Peters, R.C. 2025. Transport of tryptophan dipeptide derivatives and impact on inflammatory cytokines in monocyte/macrophage-like cells. Heliyon. 11(5):e43000. https://doi.org/10.1016/j.heliyon.2025.e43000.
DOI: https://doi.org/10.1016/j.heliyon.2025.e43000

Interpretive Summary: Tryptophan is an essential amino acid involved in many important biological processes in humans. Especially, tryptophan is believed to play significant roles in immune-related processes. In fact, macrophages are the most abundant myeloid cells found in most tissues, deeply involved in the development of several human diseases such as infection, diabetes, chronic liver disease, and inflammatory bowel disease (IBD). However, the absorption of tryptophan is relatively slow, compared to the absorption of tryptophan dipeptides in the cells including macrophages. Therefore, there are on-going efforts to find a way to increase tryptophan absorption using dipeptides and derivatives. Therefore, in this paper, four tryptophan dipeptide derivatives (tryptophanyl-tryptophan (WW), N-acetyl tryptophanyl-tryptophan (NWW), tryptophanyl-tryptophan methyl ester (WWM) and N-acetyl tryptophanyl-tryptophan methyl ester (NWWM)) were synthesized, and their uptakes and effects on inflammatory cytokines (TNF-alpha, IL-1beta, IL-6, and IL-8) were investigated in monocyte/macrophage-like cells (THP-1 and human peripheral blood mononuclear cells (PBMC)). This is the first report about the transport and anti-cytokine effects of tryptophan dipeptide derivatives (WW, NWW, WWM, NWWM) in monocytes/macrophage-like cells, especially suggesting that WWM may be used to increase tryptophan absorption and to modulate inflammatory cytokines in monocyte/macrophage-like cells.

Technical Abstract: Tryptophan is an essential amino acid with anti-inflammatory and immunomodulatory effects. However, the absorption of amino acids including tryptophan is relatively slowerthan the absorption of dipeptides. Therefore, we have two aims in this study: 1) to find a way to increase tryptophan absorption using tryptophan dipeptide derivatives. 2) to investigate their anti-cytokine effects in monocyte/macrophage-like cells. Methods: The uptakes of tryptophan dipeptide derivatives (tryptophanyl-tryptophan (WW), (Nacetyl tryptophanyl-tryptophan (NWW), tryptophanyl-tryptophan methyl ester (WWM) and Nacetyl tryptophanyl-tryptophan methyl ester (NWWM)) were investigated in THP-1 and human peripheral blood mononuclear cells (PBMCs) using HPLC. ELISA assays were performed to determine the levels of TNF-a, IL-1ß, IL-6 and IL-8. Results: In THP-1 cells, WWM and NWWM were transported better than WW and NWW (P <0.05), suggesting that the esterification may be requisite for the higher uptake. Also, WWM was found to be de-esterified and converted to tryptophan in THP-1 cells, meanwhile NWWM was deesterified, but not converted to tryptophan in the cells. Similarly, in PBMCs, WWM was transported, de-esterified and converted to tryptophan, but NWWM was not converted to tryptophan. Furthermore, WWM was found to inhibit inflammatory cytokines (TNF-a, IL-1ß, IL-6, and IL-8)better than WW in LPS-stimulated PBMCs (P < 0.05) suggesting that the transport may play a significant role in the inhibition. In summary, WWM can be transported, de esterified and converted to tryptophan and to inhibit inflammatory cytokines better than WW in monocytes/macrophage-like cells, suggesting that WWM may be a good candidate compound for not only nutritional but also clinical applications.