Protective effect of Polygonatum sibiricum against cadmium-induced testicular injury in mice through inhibiting oxidative stress and mitochondria-mediated apoptosis

Polygonatum sibiricum (PS), the dried rhizome of the liliaceous plant including P. sibiricum Red., P. cyrtonema Hua. and P. kingianum Coll. et Hemsl., is a widely used Chinese herbal medicines. It was first published in "Special Records of Famous Doctors", in which is described to replenished Qi and nourish Yin, strengthening the spleen and nourishing the lungs and kidney. Based on the principle of kidney controlling the reproduction, kidney-tonifying therapy has traditionally been seen as most applicable to the treatment of infertility. The current investigation has focused on the protective effect of PS against cadmium-induced testicular injury in mice. To investigate the protective effect of PS against cadmium-induced testicular injury in mice via the TXNIP-NLRP3-Caspase-1 and CytC-Caspase-9-Caspase-3 pathways. PS was processed into Polygonatum sibiricum aqueous extract (PSAE). A mouse testicular injury model was established by a single intraperitoneal (i.p.) injection of cadmium chloride (CdCl2) (2.5 mg/kg b.w.), and the mice were treated intragastrically with PSAE (10 g/kg b.w.) once daily for 35 consecutive days. At the end of the experiment blood and testicular tissue samples were collected to analyze sperm survival rate and sperm deformity rate, serum testosterone T content, testicular oxidation related indicators levels (SOD, MDA, GSH, CAT) in testicular tissue, and histopathological changes of testicular tissues. The testicular cell cycle and reactive oxygen species (ROS) levels were measured by flow cytometry, the expression levels of thioredoxin-interacting protein (TXNIP), nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3), Caspase-1, interleukin (IL)-1β, Cyctochrome C (CytC), Caspase-3, and Caspase-9 mRNA in testicular tissue were detected by qRT-PCR and the protein expression levels of TXNIP, NLRP3, Caspase-1, CytC, Caspase-3, and Caspase-9 were detected by Western blot and immunohistochemical method. The results indicated that compared with the model group, PSAE brought testicular weight to a near-normal range, improved sperm survival rate and reduced sperm abnormality rate, elevated the level of testosterone, made the damaged testis tissue recover to near normal, reduced the level of ROS, and inhibited testicular cell apoptosis. Further study showed that PSAE significantly decreased the levels of relative genes and proteins in testicular cells, such as TXNIP, NLRP3, Caspase-1, IL-1β, CytC, Caspase-3, and Caspase-9, which suggested that PSAE could regulate oxidative stress through the TXNIP-NLRP3-Caspase-1 signaling pathway, and inhibit apoptosis in the mitochondrial pathway via CytC-Caspase-9-Caspase-3 pathway. In summary, we have confirmed that PSAE exerted a powerful protective effect on CdCl2-induced testicular injury in mice through inhibiting oxidative stress and mitochondria-mediated apoptosis.