Combination of Doxycycline with Metronidazole Protects against Pyroptosis in Rats with Endometritis through the Modulation of TLR4 / NF-κB Pathway.

BACKGROUND: Endometritis is a condition usually resulted from the bacterial infection of uterus, causing pelvic disease, sepsis, shock, uterine necrosis and even death if it is inappropriately treated. The aim of this study is to explore the pathogenesis of endometritis, and investigate whether the combination of doxycycline and metronidazole offers stronger protection against lipopolysaccharide (LPS)-induced endometritis, and decipher more about the mechanisms underlying endometritis-related pyroptosis.

METHODS: Sprague-Dawley (SD) rats were divided into five groups (n = 8 per group): control, model, metronidazole, doxycycline, and combination groups. In control group, the rats were injected with saline, while in other groups, lipopolysaccharide was injected into uterus of the rats to establish endometritis. Hematoxylin-eosin (H&E) staining was performed as part of the histopathological examination of endometrium. The integrity of chromatin and pyroptosis were evaluated by terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling (TUNEL) assay. Western blot and quantitative real-time reverse-transcription polymerase chain reaction (qRT-PCR) were performed to ascertain the activation of toll-like receptors ( TLR4 )/nuclear factor-kappa B ( NF-κB ) pathway by detecting protein levels of phosphorylated p50 (p-p50)/p50, phosphorylated nuclear factor-kappa B (p-NF-κB)/NF-κB, phosphorylated IkappaB (p-IκB), and TLR4 protein and mRNA. Development of pyroptosis was also detected by determining the levels of caspase-1 and caspase-5 through Western blot and qRT-PCR. Enzyme-linked immunosorbent assay (ELISA) was used to detect levels of interleukin (IL)-1β, IL-18, IL-2, IL-4, IL-6 and tumor necrosis factor alpha (TNF-α), and flow cytometry was adopted to determine T-helper (Th)1 and Th2 cell percentage to assess the extent of pyroptosis and Th1/Th2 imbalance.

RESULTS: The uterine of the model group exhibited pathological alterations and higher degree of cell apoptosis. Compared with the control rats, model group showed lower protein levels of p-p50/p50 ( p < 0.001), p-NF-κB/NF-κB ( p < 0.001), p-IκB ( p < 0.001), and TLR4 protein ( p < 0.001) and mRNA ( p < 0.001). Elevated levels of caspase-1 ( p < 0.001), caspase-5 ( p < 0.001), IL-1β ( p < 0.001), IL-18 ( p < 0.001), IL-2 ( p < 0.01), TNF-α ( p < 0.05) and Th1/Th2 ( p < 0.001) as well as reduced levels of IL-4 ( p < 0.05) and IL-6 ( p < 0.01) were observed in the model group, which could however be reversed by metronidazole ( p < 0.01) or doxycycline ( p < 0.01), with a more significant effect detected if a combination of the two drugs was administered ( p < 0.01).

CONCLUSIONS: The combination of doxycycline and metronidazole protects against rat endometritis by inhibiting TLR4 / NF-κB pathway-mediated inflammation and suppressing pyroptosis.