Mechanism of Babao Dan on fluorouracil-induced bone marrow suppression and T cell immune disorder through MAPK pathway

Babao Dan (BBD), a traditional Chinese herbal compound, has demonstrated significant antitumor effects and is clinically used as an adjunctive therapy for various gastrointestinal malignancies. However, its underlying mechanisms of action remain poorly understood. This study aimed to investigate the effects of BBD on 5-fluorouracil (5-FU)-induced myelosuppression and T-lymphocyte subpopulation alterations, and to explore its mechanism in ameliorating cellular immune dysfunction caused by myelosuppression via the MAPK signaling pathway. The major constituents of BBD are fatty acids, triterpenoids, flavonoids, and alkaloids, along with other compounds. BBD significantly improved survival, reduced body weight loss, and mitigated the decline in splenic index in mice following 5-FU-induced chemotherapy. Additionally, it alleviated the reduction of peripheral blood cells, including leukocytes, neutrophils, and reticulocytes, and attenuated 5-FU-induced bone marrow hematopoiesis suppression. Furthermore, BBD restored the imbalance in the proportions of Th1 and Th2 cells within the spleens of 5-FU-induced mice. It also reversed the inhibition of CD25⁺ and CD69⁺ expression, the reduction in lymphocyte division generation, and the decreased expression of Ki67 and PCNA, thereby enhancing T-cell activation and proliferation in splenic cells. Moreover, BBD alleviated the G1 phase blockage in the bone marrow cell cycle and upregulated the expression of key proteins, including CDK2, CDK4, CDK6, Cyclin D1, Cyclin E1, p-Rb, p-c-Fos, p-c-Jun, p-ERK, p-NF-κB p65, and p-p38, in bone marrow cells. BBD may promote the expression of G1/S checkpoint-related proteins in myeloid cells by regulating the MAPK signaling pathway, thereby upregulating the phosphorylation level of Rb and facilitating the transition from the G1 phase to the S phase. This orderly cell cycle progression enhances cell proliferation and improves the hematopoietic function of myeloid cells after 5-FU chemotherapy. Consequently, BBD restores the ratio of peripheral T-cell subsets, corrects the imbalance of Th-cell subsets, and enhances the activation and proliferation functions of CD4⁺T cells and CD8⁺T cells, ultimately rectifying the dysregulated immune homeostasis of the organism.