Saikosaponin A restores the IDO1-driven gut-testis kynurenine axis to alleviate oligozoospermia

  • Phytomedicine. 2026 Aug:158:158414. doi: 10.1016/j.phymed.2026.158414.
Yaqiu Li  1 ,  Boqi Zhang  2 ,  Guitian He  2 ,  Caomeihui Shen  2 ,  Fuqiang Chang  2 ,  Junjun Yang  2 ,  Sihui Wang  2 ,  Yueying Wang  2 ,  Jinxin Zong  2 ,  Yuxin Luo  2 ,  Nan Wang  2 ,  Yanan Sun  2 ,  Yue Sui  2 ,  Mengting Wu  2 ,  Dongjin Lu  3 ,  Chunjin Li  4 ,  Xu Zhou  5
Affiliations
  • 1. College of Animal Sciences, Jilin University,Changchun, 130000, China; College of Basic Medical Sciences, Jilin Medical University, Jilin 132013, China.
  • 2. College of Animal Sciences, Jilin University,Changchun, 130000, China.
  • 3. Animal Husbandry General Station of Jilin City, Jilin 132013, China.
  • 4. College of Animal Sciences, Jilin University,Changchun, 130000, China. Electronic address: [email protected].
  • 5. College of Animal Sciences, Jilin University,Changchun, 130000, China. Electronic address: [email protected].
PMID: 42287814 DOI: 10.1016/j.phymed.2026.158414
Abstract

Background: Busulfan (Bus)-induced oligozoospermia still lacks a disease-modifying therapy, and its pathogenesis has been largely attributed to germ-cell DNA damage. Emerging evidence indicates that microbiota-derived metabolites are key determinants of spermatogenic failure. Saikosaponin A (SSA), a major triterpenoid from Bupleurum, has never been evaluated in male infertility. Consequently, its regulatory role in the gut microbiota-metabolite axis and causal efficacy remain completely undefined.

Purpose: To determine whether SSA rescues Bus-induced oligozoospermia via the gut microbiota-metabolite axis, and to uncover a novel pathogenic mechanism of Bus, beyond the known germ-cell DNA damage pathway, revealing a gut microbiota-metabolite-mediated regulatory axis.

Methods: Bus-induced oligozoospermia was established in male C57BL/6 J mice and followed by SSA treatment. Sperm count, testis index, and histology were assessed; spermatogenic proteins were quantified by Western blot. Microbiota and metabolites were profiled via 16S rDNA sequencing; serum metabolomics; and fecal microbiota transplantation (FMT) from SSA donors. Testicular transcriptome Sequencing identified differentially expressed pathways. Indole-3-carboxaldehyde (ICA) administration and Kynurenine (Kyn) supplementation were performed in parallel. Indoleamine 2,3-dioxygenase 1 (IDO1) protein level and activity were measured by Western blot and ELISA. ICA-IDO1 interaction was verified by molecular docking and surface plasmon resonance (SPR). The l-tryptophan/L-kynurenine ratio was determined by targeted liquid chromatography-mass spectrometry (LC-MS/MS).

Results: SSA restored sperm count, testis index, and tubular architecture while increasing DDX4, DAZL, and SYCP1/3. It reversed Bus-induced Lactobacillus expansion, decreased colonic ICA, relieved ICA-mediated IDO1 inhibition, thereby restoring colonic IDO1 activity, and elevated Kyn. FMT from SSA donors reproduced these protective effects. Transcriptomics showed up-regulation of AKT-mediated targets: pro-growth (CCND1), antioxidant (NRF2), and anti-apoptotic (Bcl-2), with down-regulation of pro-apoptotic genes. Mechanistically, SSA reshaped the gut microbiota, lowered colonic ICA, relieved ICA-mediated IDO1 inhibition, and restored Kyn-dependent testicular antioxidant and anti-apoptotic signaling.

Conclusion: By reshaping the gut microbiota, reducing colonic ICA and relieving ICA-mediated IDO1 inhibition, SSA restored Kyn-driven testicular antioxidant and anti-apoptotic signaling. This suggests a microbiota-directed, non-hormonal candidate preclinical approach for Bus-induced oligozoospermia; the gut microbiota-ICA-IDO1-Kyn axis offers a framework awaiting human validation.

Keywords
Busulfan; Gut microbiota; Indoleamine 2,3-dioxygenase 1 (IDO1); Oligozoospermia; Saikosaponin A (SSA); Tryptophan metabolite.
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