Litchi Seed Flavonoids Suppress Cellular Senescence and Reverse Pulmonary Fibrosis
Total flavonoids from litchi seeds block the SASP via p65 suppression, reducing senescence markers and reversing bleomycin-induced lung fibrosis in mice.
Summary
Researchers at Guangxi Medical University found that total flavonoids of litchi seed (TFL) delay cellular aging by suppressing the senescence-associated secretory phenotype (SASP). In human lung fibroblasts, TFL reduced SA-β-galactosidase activity, lowered p21 and p16 protein levels, and decreased DNA damage markers after stress induction with bleomycin or etoposide. The key mechanism: TFL suppresses p65 (an NF-κB subunit), which in turn reduces IL-1α and IL-1β secretion. In a mouse model of idiopathic pulmonary fibrosis, TFL treatment for 14 days alleviated lung fibrosis and restored gut microbiome diversity disturbed by bleomycin. These findings position TFL as a candidate senomorphic agent with potential anti-aging and anti-fibrotic applications.
Detailed Summary
Idiopathic pulmonary fibrosis (IPF) is a fatal age-related lung disease with no effective cure. Cellular senescence and its hallmark secretory profile — the senescence-associated secretory phenotype (SASP) — drive IPF progression by releasing pro-inflammatory and pro-fibrotic cytokines. This study, published in Acta Biochimica et Biophysica Sinica, investigates whether total flavonoids of litchi seed (TFL), a natural extract rich in rutin and quercetin, can suppress cellular senescence and attenuate pulmonary fibrosis, building on prior evidence that TFL reduces liver fibrosis and modulates gut microbiota.
The study used MRC-5 human lung fibroblasts subjected to two senescence models: replicative senescence (serial passaging) and stress-induced senescence triggered by bleomycin (BLM, 10 µM) or etoposide (VP-16, 2 µM) for four days, with TFL treatment (low-dose 300 mg/L or high-dose 450 mg/L) continued for six days total. Senescence markers measured included SA-β-galactosidase (SA-β-Gal) activity, p21 and p16 protein levels via Western blot, and γH2AX foci by immunofluorescence as a DNA damage readout. RNA sequencing (transcriptome profiling) was performed on treated versus untreated senescent cells to identify pathway-level changes. In the animal arm, female C57BL/6 mice (n = 5 per group) received intraperitoneal BLM (2.5 mg/kg) to induce pulmonary fibrosis and were treated with oral TFL (450 mg/kg/day) by gavage for 14 days. Lung histology (H&E and Masson's trichrome staining), p21 immunohistochemistry, and 16S rRNA gut microbiome sequencing of fecal samples were performed.
TFL significantly reduced the percentage of SA-β-Gal-positive cells in both replicative and stress-induced senescence models. In BLM-treated fibroblasts, TFL-H reduced γH2AX foci, indicating attenuated DNA damage responses. Western blot analyses showed TFL dose-dependently decreased p21 and p16 protein levels in senescent cells. RNA-seq analysis revealed that TFL's most prominent transcriptomic effect was suppression of the SASP gene network, with NF-κB signaling identified as a central target. Specifically, TFL reduced p65 protein expression, and knockdown of p65 via siRNA phenocopied TFL's effects, while p65 overexpression via pcDNA3.1-HA-p65 transfection partially reversed TFL's senomorphic benefits. The downstream SASP components most affected were IL-1α and IL-1β, both critical drivers of fibrotic remodeling.
In the mouse IPF model, BLM-exposed lungs showed marked fibrotic thickening on Masson's trichrome staining and elevated p21 immunoreactivity. TFL treatment for 14 days substantially reduced collagen deposition and lung p21 expression compared to untreated BLM mice. Gut microbiome 16S rRNA profiling revealed that BLM exposure altered both alpha-diversity (Simpson index) and the relative abundance of specific bacterial taxa. TFL treatment reversed these compositional and functional shifts toward control-group profiles, suggesting a gut-lung axis contribution to TFL's anti-fibrotic effects.
These findings establish TFL as a senomorphic agent acting through p65-mediated SASP suppression, with translatable anti-fibrotic effects in vivo. The compound's natural origin, established safety profile, and dual action on cellular senescence and gut microbiota make it an attractive candidate for further clinical investigation. Limitations include the small animal group sizes (n = 5), a single dose and duration tested in vivo, and the absence of pharmacokinetic data confirming systemic TFL bioavailability. Human trials are needed before clinical recommendations can be made.
Key Findings
- TFL (300 and 450 mg/L) significantly reduced the percentage of SA-β-galactosidase-positive MRC-5 lung fibroblasts in both replicative and bleomycin-induced stress senescence models
- High-dose TFL (450 mg/L) decreased γH2AX nuclear foci in BLM-treated fibroblasts, indicating reduced DNA double-strand break signaling
- TFL dose-dependently downregulated p21 and p16 protein levels in senescent cells as measured by Western blot
- RNA-seq transcriptome profiling identified NF-κB signaling and SASP gene networks as the primary pathways suppressed by TFL treatment
- TFL reduced p65 protein expression; siRNA-mediated p65 knockdown replicated TFL's anti-senescence effects, while p65 overexpression partially reversed them, confirming p65 as the mechanistic target
- Oral TFL (450 mg/kg/day × 14 days) reduced collagen deposition on Masson's trichrome and lowered lung p21 immunoreactivity in BLM-induced pulmonary fibrosis mice (n = 5 per group)
- 16S rRNA gut microbiome analysis showed BLM exposure shifted bacterial taxa abundance and alpha-diversity (Simpson index), and TFL treatment restored these profiles toward control levels
Methodology
The study employed human MRC-5 lung fibroblasts in two senescence induction models (replicative passaging and chemical stress with BLM 10 µM or VP-16 2 µM), with TFL applied at 300 or 450 mg/L for six days. In vivo, female C57BL/6 mice (n = 5 per group) received BLM (2.5 mg/kg, intraperitoneal) and were gavaged with TFL (450 mg/kg/day) for 14 days, with control and BLM-only groups as comparators. Mechanistic validation used siRNA p65 knockdown and pcDNA3.1-HA-p65 overexpression. Transcriptome profiling via RNA-seq and gut microbiome analysis via 16S rRNA sequencing (Illumina MiSeq, OTU clustering at 97% similarity) provided systems-level data; statistical methods included standard parametric comparisons, though specific p-values for most endpoints were not comprehensively reported in the text.
Study Limitations
The mouse groups were small (n = 5 per group), limiting statistical power for the in vivo endpoints. Only a single TFL dose and treatment duration were tested in animals, and the study provides no pharmacokinetic data on TFL bioavailability or tissue distribution in vivo. The authors note the study is preclinical and that human clinical trials are required before any therapeutic recommendations can be made; no conflicts of interest were declared.
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