Swainsonine-induced vacuolar degeneration is regulated by mTOR-mediated autophagy in HT22 cells

Endoplasmic reticulum stress regulates swainsonine-induced the autophagy in renal tubular epithelial cells through UPR signaling pathway

Swainsonine (SW), the primary toxic component of locoweed, induces toxic response in grazing livestock. The swainsonine induced toxicity is characterized by symptoms including head tremors, ataxia, and limb paralysis. The mechanisms of the toxicity remained to be investigated. The unfolded protein response (UPR) plays a key role in alleviating endoplasmic reticulum stress (ERS) by reducing protein synthesis and promoting the degradation of misfolded proteins. ERS is closely associated with both the UPR and autophagy activation. However, the involvement of the UPR signaling pathway in SW-induced ERS and autophagy remains unclear. In this study, we demonstrate that SW up-regulates the expression of GRP78, XBP1s, LC3-II/I, and ATG5 in both in vitro and in vivo models, suggesting activation of ERS, UPR, and autophagy. To investigate the molecular mechanisms by which the UPR regulates autophagy under ERS in primary rat renal tubular epithelial cells (RTECs), we observed that inhibiting PERK led to increased levels of p62. Inhibition of ATF6 significantly reduced the up-regulation of LC3-II/I, p62, and ATG5. Furthermore, inhibiting IRE1α significantly decreased the expression of LC3-II/I and p62. These findings suggest that PERK and ATF6 regulate autophagy mainly by modulating the expression of autophagy-related genes, while IRE1α likely regulates these genes through the IRE1α-XBP1 pathway. Additionally, autophagy is directly regulated through the IRE1α-JNK signaling pathway.

Transcriptomic profiling provide insights into swainsonine-induced toxic responses and activation of the aryl hydrocarbon receptor pathway

Locoweed refers to poisonous plants in the genus Oxytropis and Astragalus and distributed widely throughout the World. Foraging livestock can be poisoned through ingestion of locoweed resulting in economic loss. Swainsonine is the main toxic component of locoweed and chemically belongs to indolizidine alkaloids. The mechanism of the swainsonine-induced toxic responses is not well understood. In this study, we performed comprehensive transcriptomic analysis examining the differential gene expression in primary renal tubular epithelial cells (RTECs) of rats treated with swainsonine. Our analysis uncovered differential expressions of ncRNA(DEncRNAs) and mRNAs(DEmRNAs) in response to swainsonine treatment. Significant pathways enriched by differential genes through transcriptome association analysis were xenobiotic metabolism-cytochrome P450, bile secretion, and steroid biosynthesis, etc. Notably, aryl hydrocarbon receptor (AhR)-regulated xenobiotic pathway is significantly activated as evidenced by the coordinated up-regulation of the classic AhR-regulated battery of genes Cyp1a1, Cyp1b1, AhRR, Nqo1, and phase II enzyme Gsta2, Gsta3, Gsta5. These results suggest that swainsonine is metabolically detoxified through the AhR regulated xenobiotic detoxification pathway and furthermore, our finding also suggest an intervention strategy to ameliorate to locoweed poisoning through activation of AhR-regulated deoxification pathway.

Increased intestinal permeability and lipopolysaccharide contribute to swainsonine-induced systemic inflammation

Long-term consumption of swainsonine could be poisonous to livestock, including facilitating apoptosis by impairing lysosomal function and inhibiting autophagic degradation, leading to liver inflammation and even death in livestock. However, the mechanism by swainsonine induced systemic inflammatory responses remained unclear, especially the effects of swainsonine on intestinal permeability, lipopolysaccharide (LPS) level and oxidative stress response were unknown. In this study, swainsonine increased intestinal permeability as evidenced by the significant down-regulation of colonic goblet cells, Akkermansia muciniphila and intestinal tight junction protein Occludin, Claudin 1 and ZO-1, and the significant up-regulation of mRNA expression level of the intestinal permeability indicator protein tyrosine phosphatase receptor type H (Ptprh) in the ileum of mice. Simultaneously, the elevated LPS biosynthetic genes in intestinal microbiota and increased intestinal permeability facilitated more bacterial endotoxin LPS to enter the blood. High concentration of free-form LPS induced high levels of proinflammatory cytokines and oxidative stress response, thereby causing the systemic inflammation. These findings provided a new perspective on swainsonine-induced systemic inflammation, suggesting that intestinal permeability and free-form LPS level may be the potential trigger factors.

The genus Oxytropis DC: application, phytochemistry, pharmacology, and toxicity

OBJECTIVES

Oxytropis DC is a perennial plant of Fabaceae family, which is widely distributed in the northern temperate zone. It is known as "locoweed" because of its toxic component swainsonine. However, it is widely used in Tibetan medicine and Mongolian medicine, mainly for the treatment of heat-clearing and detoxifying, pain-relieving, anti-inflammatory, hemostasis, and other diseases. To provide a basis for the further development and utilization of Oxytropis DC, the pieces of literature about the application, phytochemistry, pharmacological action, and toxicity of Oxytropis DC were reviewed and analyzed.

KEY FINDINGS

A total of 373 chemical constituents were found from Oxytropis DC, including flavonoids, alkaloids, steroids, terpenoids, and others. Pharmacological actions mainly include antitumor, antioxidation, anti-inflammatory, analgesic, antibacterial, antifibrosis, and other pharmacological actions, among them, the antitumor effect is particularly prominent.

SUMMARY

At present, studies on its pharmacological effects are mainly concentrated on the extracts, some flavonoids, and alkaloids. In the follow-up studies, research on the pharmacological activities of the other chemical constituents in Oxytropis should be strengthened. It has the potential to pave the way for research and development of novel Oxytropis medicines.

Autophagic-lysosomal damage induced by swainsonine is protected by trehalose through activation of TFEB-regulated pathway in renal tubular epithelial cells

Swainsonine (SW) is the main toxic component of locoweed. Previous studies have shown that kidney damage is an early pathologic change in locoweed poisoning in animals. Trehalose induces autophagy and alleviates lysosomal damage, while its protective effect and mechanism against the toxic injury induced by SW is not clear. Based on the published literature, we hypothesize that transcription factor EB(TFEB) -regulated is targeted by SW and activating TFEB by trehalose would reverse the toxic effects. In this study, we investigate the mechanism of protective effects of trehalose using renal tubular epithelial cells. The results showed that SW induced an increase in the expression level of microtubule-associated protein light chain 3-II and p62 proteins and a decrease in the expression level of ATPase H+ transporting V1 Subunit A, Cathepsin B, Cathepsin D, lysosome-associated membrane protein 2 and TFEB proteins in renal tubular epithelial cells in a time and dose-dependent manner suggesting TFEB-regulated lysosomal pathway is adversely affected by SW. Conversely, treatment with trehalose, a known activator of TFEB promote TFEB nuclear translocation suggesting that TFEB plays an important role in protection against SW toxicity. We demonstrated in lysosome staining that SW reduced the number of lysosomes and increased the luminal pH, while trehalose could counteract these SW-induced effects. In summary, our results demonstrated for the first time that trehalose could alleviate the autophagy degradation disorder and lysosomal damage induced by SW. Our results provide an interesting method for reversion of SW-induced toxicity in farm animals and furthermore, activation of TFEB by trehalose suggesting novel mechanism of treating lysosomal storage diseases.

Ipomoea carnea alkaloid extract vs swainsonine: A comparative study on cytotoxic activity against glial cells

The consumption of Ipomoea carnea produces a neurological syndrome in animals. The toxic principles of I. carnea are the alkaloids swainsonine (SW) and calystegines B1, B2, B3 and C1. In this study, we investigated the cytotoxicity of an alkaloid extract of Ipomoea carnea (AEE) and natural swainsonine (SW) isolated from Astragalus lentiginosus (25-1000 μM of SW) for 48 h in a glioma cell line. Although the natural SW did not induce any changes in cell viability, the AEE exhibited a dose dependent cytotoxic effect and release of lactate dehydrogenase (LDH) indicative of cytolysis. In order to evaluate the morphological changes involved, cells were examined using phase contrast and fluorescence microscopy with acridine orange-ethidium bromide staining. The AEE caused a cell death compatible with necrosis, whereas exposure to 1000 μM of SW resulted in cytoplasmic vacuolation. Immunocytochemical studies revealed that astrocytes treated with 150 μM of AEE from I. carnea or 1000 μM of SW exhibited morphological characteristics of cell activation. These findings suggest that swainsonine would not be the only component present in the AEE of I. carnea responsible for in vitro cytotoxicity. Calystegines might also play a role in acting synergistically and triggering cell death through necrosis.