Novel coronavirus pneumonia, also known as coronavirus disease 2019 (COVID-19), is caused by a new coronavirus that infects the lungs. Although some patients with COVID-19 may be combined with neurological symptoms, there is no direct evidence that this new coronavirus can directly invade nerve system. A case of COVID-19 with tuberculous meningitis is reported to remind that when patients with COVID-19 present symptom of encephalitis or meningitis, a comprehensive pathogen examination is recommended.

Ferroptosis， a new form of programmed cell death different from apoptosis， necrosis， and autophagy， is closely associated with a variety of physiological and pathological processes. Iron-mediated accumulation of reactive oxygen species is the main inducement of ferroptosis， the mechanism of which is related to intracellular lipid metabolism， iron metabolism， and antioxidant defense pathways. Multiple signaling axes and regulators jointly regulate the occurrence and disruption of ferroptosis. Studies have demonstrated that ferroptosis regulates the growth and proliferation of tumor cells. Inducing ferroptosis in tumor cells can control the growth， metastasis， and multi-drug resistance of tumors. Therefore， the effect and mechanism of ferroptosis on tumor cells have become a hot topic in anti-cancer research. As the research advances， a variety of ferroptosis inducers has been used in the clinical chemotherapy for cancers and demonstrate significant efficacy. Accordingly， the development of ferroptosis-inducing anticancer drugs has become a new research direction for tumor treatment. Some active ingredients such as lycorine， oleanolic acid， dihydroartemisinin， pseudolaric acid B， and ophiopogonin B of Chinese medicines can induce ferroptosis in tumor cells via lipid metabolism， iron metabolism， system X_c^-， and GPX4/GSH to regulate the development of tumors， demonstrating a promising prospect in clinical treatment. Based on the theory of the mechanism of ferroptosis， this paper reviews the research progress in ferroptosis induced by active ingredients of Chinese medicines in tumor cells and describes the metabolic regulatory network of ferroptosis from signaling pathways and regulatory factors， providing new strategies for applying active ingredients of Chinese medicines in the treatment of tumors.

As a rare Chinese medicinal material， Paridis Rhizoma is mainly distributed in Yunnan， Guangxi， and Guizhou in southwestern China， with the effect of clearing heat and detoxifying， alleviating edema and relieving pain， cooling liver and tranquilizing mind. It is particularly effective for injuries from falls， fractures， contusions and strains， snake bites， cold wind-induced convulsion， and other diseases， which has been used for more than 2 000 years. According to modern research， polyphyllin Ⅱ， one of the main active components of Paridis Rhizoma， belongs to diosgenin in structure. It has the anti-tumor， anti-inflammatory， antiviral， antibacterial， immune-regulating， antioxidant， and multidrug resistance-reversing activities， showing good application prospect. Especially， the anti-tumor effect of polyphyllin Ⅱ has attracted wide attention， and the mechanism is inhibiting proliferation， migration， and invasion of tumor cells， inducing cell cycle arrest， apoptosis， and autophagy， suppressing angiogenesis， and modulating tumor microenvironment. However， the pharmacokinetic results show that polyphyllin Ⅱ has low bioavailability in vivo due to the low solubility， poor absorption， unsatisfactory distribution， and slow metabolism， which limit the clinical application. In recent years， there has been an explosion of research on the adverse reactions of polyphyllin Ⅱ， such as the strong hemolytic activity and obvious cytotoxicity to liver， kidney， myocardium and cardiovascular cells. Thus， papers were retrieved from "CNKI"， "VIP"， "Wanfang Data"， "PubMed"， "Web of Science"， and "Elsevier SD" with "Paris saponin Ⅱ"， "Polyphyllin Ⅱ" as the main keywords， and the pharmacological activities and mechanisms， pharmacokinetics， and adverse reactions were summarized. The findings are expected to serve as a reference for the in-depth research， development， and utilization of polyphyllin Ⅱ.

ObjectiveTo explore the role of cucurbitacin B （CuB） in inducing ferroptosis in 4T1 cells and its mechanism. MethodsThe effects of CuB（0.2， 0.4， 0.8 μmol·L^-1）on the proliferation ability of 4T1 cells in vitro were detected using the methyl thiazolyl tetrazolium （MTT） assay. The clonogenic ability of 4T1 cells was detected by the plate cloning assay， and the levels of lactate dehydrogenase （LDH） in 4T1 cells were detected by the use of a kit. The mitochondrial membrane potential and reactive oxygen species （ROS） levels in 4T1 cells were detected by flow cytometry， and the mitochondrial ultrastructure of 4T1 cells was observed by transmission electron microscopy. The western blot was used to detect the expression of ferroptosis-related protein p53 in 4T1 cells， solute carrier family 7 member 11 （SCL7A11）， glutathione peroxidase 4 （GPX4）， long-chain acyl-CoA synthetase 4 （ACSL4）， transferrin receptor protein 1 （TFR1）， and ferritin heavy chain 1 （FTH1）. ResultsCompared with that in the blank group， the survival rate of 4T1 cells in CuB groups was significantly decreased （P<0.05）， and the number of cell clones in CuB groups was significantly reduced （P<0.01）. In addition， compared with that in the blank group， the leakage of LDH in cells in CuB groups was significantly increased （P<0.01）， and the mitochondrial membrane potential of cells in CuB groups decreased significantly （P<0.01）. Cellular ROS levels were significantly elevated in CuB groups （P<0.01）. The mitochondria of cells in CuB groups were obviously wrinkled， and the mitochondrial cristae were reduced or even disappeared. Compared with that in the blank group， the protein expression of p53， ACSL4， and TFR1 were significantly up-regulated in CuB groups （P<0.05）， and that of SLC7A11， GPX4， and FTH1 were significantly down-regulated （P<0.05）. ConclusionCuB may inhibit SLC7A11 and GPX4 expression by up-regulating the expression of p53， which in turn regulates the p53/SLC7A11/GPX4 signaling pathway axis and accelerates the generation of lipid peroxidation substrate by up-regulating the expression of ACSL4. It up-regulates TFR1 expression to promote cellular uptake of Fe³⁺ and down-regulates the expression of FTH1 to reduce the ability of iron storage， resulting in an elevated free Fe²⁺ level. It catalyzes the Fenton reaction， generates excess ROS， imbalances the antioxidant system and iron metabolism， and then induces ferroptosis in 4T1 cells.

ObjectiveTo explore the role of cucurbitacin B （CuB） in inducing ferroptosis in 4T1 cells and its mechanism. MethodsThe effects of CuB（0.2， 0.4， 0.8 μmol·L^-1）on the proliferation ability of 4T1 cells in vitro were detected using the methyl thiazolyl tetrazolium （MTT） assay. The clonogenic ability of 4T1 cells was detected by the plate cloning assay， and the levels of lactate dehydrogenase （LDH） in 4T1 cells were detected by the use of a kit. The mitochondrial membrane potential and reactive oxygen species （ROS） levels in 4T1 cells were detected by flow cytometry， and the mitochondrial ultrastructure of 4T1 cells was observed by transmission electron microscopy. The western blot was used to detect the expression of ferroptosis-related protein p53 in 4T1 cells， solute carrier family 7 member 11 （SCL7A11）， glutathione peroxidase 4 （GPX4）， long-chain acyl-CoA synthetase 4 （ACSL4）， transferrin receptor protein 1 （TFR1）， and ferritin heavy chain 1 （FTH1）. ResultsCompared with that in the blank group， the survival rate of 4T1 cells in CuB groups was significantly decreased （P<0.05）， and the number of cell clones in CuB groups was significantly reduced （P<0.01）. In addition， compared with that in the blank group， the leakage of LDH in cells in CuB groups was significantly increased （P<0.01）， and the mitochondrial membrane potential of cells in CuB groups decreased significantly （P<0.01）. Cellular ROS levels were significantly elevated in CuB groups （P<0.01）. The mitochondria of cells in CuB groups were obviously wrinkled， and the mitochondrial cristae were reduced or even disappeared. Compared with that in the blank group， the protein expression of p53， ACSL4， and TFR1 were significantly up-regulated in CuB groups （P<0.05）， and that of SLC7A11， GPX4， and FTH1 were significantly down-regulated （P<0.05）. ConclusionCuB may inhibit SLC7A11 and GPX4 expression by up-regulating the expression of p53， which in turn regulates the p53/SLC7A11/GPX4 signaling pathway axis and accelerates the generation of lipid peroxidation substrate by up-regulating the expression of ACSL4. It up-regulates TFR1 expression to promote cellular uptake of Fe³⁺ and down-regulates the expression of FTH1 to reduce the ability of iron storage， resulting in an elevated free Fe²⁺ level. It catalyzes the Fenton reaction， generates excess ROS， imbalances the antioxidant system and iron metabolism， and then induces ferroptosis in 4T1 cells.