Panax notoginseng saponins inhibits oxidative stress- induced human nucleus pulposus cell apoptosis and delays disc degeneration in vivo and in vitro

Abstract

Ethnopharmacological relevance: Panax notoginseng (Burk) F. H. Chen has been a popular traditional Chinese medicine with a long history of treating low back pain. Its main active ingredient, Panax notoginseng saponins (PNS), can be found in several Chinese patent medicines that are frequently used to treat blood stasis type low back pain. Intervertebral disc degeneration (IDD) is the most common cause of back pain, and the injection of PNS has been used to relieve IDD-induced back pain in clinical practice. Despite its effectiveness, the exact mechanisms of action for PNS injections remain unclear.

Aim of the study: IDD as a consequence of aging involves apoptosis of nucleus pulposus (NP) cells and imbalanced degradation of extracellular matrix (ECM) induced by several factors including oxidative stress. We hypothesized that PNS may have a therapeutic effect on IDD via inhibiting apoptosis of NP cells and degradation of ECM under oxidative stress.

Materials and methods: In this study, network pharmacology was initially employed to predict the targets of PNS against IDD. Subsequently, commercial PNS was analyzed by high-performance liquid chromatography to confirm the ingredients for in vitro and in vivo experiments. In vitro experiments were conducted on human nucleus pulposus (HNP) cells, including CCK-8, RT-PCR, Western blot, immunofluorescence staining, autophagic flux detection, and TUNEL assay. In vivo experiments were also performed on rats with IDD of tail discs induced by annular fibrosus needle puncture, which involved MRI, HE staining, and immunohistochemistry.

Results: Our study demonstrated the theoretical targets of PNS against IDD, including Caspase 3, MMP13, Akt, and autophagy, based on network pharmacology. Subsequently, in vitro experiments revealed that PNS attenuated cellular apoptosis of NP by suppressing the expression of cleaved-caspase 3 and the ratio of Bax/Bcl-2 under H₂O₂ stimulation. Autophagy was also inhibited by PNS treatment, and the protective effect was abolished with rapamycin, an autophagy inducer, indicating that autophagy inhibition was involved in the protective effect of PNS on IDD. Furthermore, Akt/mTOR pathway activation was observed in HNP cells responding to H₂O₂ with PNS treatment, which played a role in autophagy downregulation. PNS was also shown to promote the expression of anabolic genes such as COL2A1 and ACAN while inhibiting the expression of catabolic gene MMP13 in HNP cells. In addition, the in vivo study revealed that PNS treatment could ameliorate IDD in a puncture-induced rat tail model. The development of IDD was significantly reduced, and there was decreased MMP13 expression, as well as increased COL2A1 protein expression in NP tissues.

Conclusion: Our study showed that PNS could protect HNP cells against apoptosis via autophagy inhibition and ameliorate disc degeneration in vivo, indicating its potential to be a therapeutic agent for IDD.

Keywords: Apoptosis; Autophagy; Intervertebral disc degeneration; Panax notoginseng saponins.