Citrulline alleviates oxidative stress-induced pyroptosis of nucleus pulposus cells via inhibiting the assembly of NLRP3 inflammasome.

Intervertebral disc degeneration (IVDD) is a significant contributor to low back pain and is associated with oxidative stress-induced pyroptosis of nucleus pulposus (NP) cell. Citrulline, a non-essential amino acid integral to the urea cycle and nitric oxide synthesis, plays an essential role in maintaining intracellular redox balance. This study aimed to investigate the protective effects of citrulline on oxidative stress-damaged human NP cells and its underlying molecular mechanism related to cellular pyroptosis. Primary human NP cells were isolated from non-degenerated intervertebral disc tissues of donors with lumbar fractures, and oxidative stress along with pyroptosis was induced using TBHP. TBHP exposure significantly induced oxidative stress and pyroptosis in NP cells, as evidenced by increased expression of NLRP3, ASC, cleaved caspase-1 and cleaved GSDMD, along with heightened ROS levels and augmented secretion of IL-1β and IL-18 in the supernatant. Notably, citrulline treatment effectively reversed these effects in a dose-dependent manner. Mechanistically, citrulline sustains intracellular redox homeostasis through the SLC7A2/eNOS signaling axis, a process correlated with suppressed NLRP3 inflammasome assembly in NP cells. Knockdown of either SLC7A2 or eNOS abolished the protective effects of citrulline. And upregulation of SLC7A2-eNOS axis enhanced the anti-oxidative and anti-pyroptotic effects of citrulline. Herein, Citrulline alleviates oxidative stress-induced pyroptosis in human NP cells by inhibiting the assembly of the NLRP3 inflammasome via the SLC7A2/eNOS signaling pathway, which suggests a novel potential therapeutic and nutritional intervention strategy for IVDD.