Potential Usefulness of Leukotriene B4 (LTB4) on Mobilization of Hematopoietic Progenitor Cells (HPC).

The mechanisms on HPC mobilization seem to be multifactorial processes. Many cell adhesion molecules (VLA-4, ICAM-1, VCAM-1 etc), SDF-1/CXCR4, and proteases (ie, MMP-9) may be important players for this mobilization processes. However, finding more mechanisms on HPC mobilization is under intense scrutiny. So far, G-CSF is the best known cytokine for this purpose. Meanwhile, its limitation on using G-CSF is to take 4–6 days for the optimal mobilization at clinic and its side effects (ie; bone pain, high WBC counts) are not negligible. LTB4 is lipid mediator during the process of inflammation, having many roles (ie; inducer of chemotaxis, the production of nitric oxide, transepithelial migration of neutrophil). In present study, we focused on the roles of LTB4 on HPC mobilization and its feasibility on mobilization in vivo.

Samples were collected from the peripheral blood via heart puncture and the bone marrow on time dependent manner (1hr, 4hr, 6hr, 12hr, 24hr, 48hr) after LTB4 injection which was given via intravenously and the dose dependent manner of LTB4 (0.5μg, 1μg, 2μg, 3μg). These data were compared with two other groups after G-CSF injection and normal saline injection. Collected total nucleated cells were analyzed for Sca-1+/Lin- using flow cytometry and CFU studies. There were definite increase of Sca-1+/Lin- cells after 1μg of LTB4 injection group (TNC: 29.55(±0.92)×10⁵/ml and HPC: 3.72(±0.09) %). Its control group showed as follows: TNC: 14.55(±0.21)×10⁵/ml, HPC: 0.41(±0.04) %, (p<0.05). Mobilization was optimal only after 4hours of LTB4 injection (TNC: 36.25(±2.90)×10⁵/ml & HPC: 3.50(±0.37) %). After 4hours of LTB4 injection, there was a obvious down pattern. In terms of quantity, more than 20 fold of HPC mobilization after one LTB4 injection was observed. There were no immediate toxicity in the cohort, though long term potential side effects are under investigations. In conclusion, we showed the rapid mobilization of HPC with LTB4 at only 4 hours post-injection. This finding with LTB4 could be significant in terms of shortening the optimal period of mobilization comparing to that by G-CSF, which takes at least 4–6 days by repetitive injection to reach the optimal timing for collection. The possible synergistic effects of G-CSF with LTB4 for larger quantity of HPC and the cellular and molecular mechanism(s) of mobilization by LTB4 are being investigated in our lab.