AMPK and metabolic disorders: The opposite roles of dietary bioactive components and food contaminants

Maduramicin ammonium impairs autophagic flux through activating AMPK-mediated eIF2α-ATF4 endoplasmic reticulum stress pathway in skeletal muscle

BACKGROUND

Maduramicin ammonium (MA), a widely used coccidiostat, has been reported to cause skeletal muscle degeneration in animals and even humans. In this study, we explore the underlying mechanism of its toxicity in skeletal muscle.

RESULTS

First, we observed that MA impaired autophagic flux which was evidenced by increased protein level of LC3-II and p62 in skeletal myoblast C2C12 and L6 cell lines and rectus femoris muscle tissues of rats and broilers. Then, we found that MA induced eIF2α phosphorylation and ATF4 expression in the cells and tissues. Co-treatment with ISRIB attenuated MA-induced LC3-II and p62 in C2C12 and L6 cells, suggesting that MA-induced eIF2α-ATF4 pathway contributed to impairment of autophagic flux in the cells. Lastly, we showed that MA activated AMPK signaling in skeletal muscle, since the phosphorylation of AMPK was increased by MA treatment in skeletal myoblast cell lines and muscle tissues. Furthermore, in AMPK downregulated C2C12 cells, MA-induced LC3-II, ATF4 and phosphorylation of eIF2α was reversed, supporting that AMPK was involved in the regulation of the eIF2α-ATF4 pathway and autophagic flux during MA exposure.

CONCLUSION

Our findings showed that MA impairs autophagic flux through activating the AMPK-induced eIF2α-ATF4 pathway in skeletal muscle. © 2024 Society of Chemical Industry.

Metformin attenuates diabetic osteoporosis by suppressing ferroptosis via the AMPK/Nrf2 pathway

Background

Ferroptosis is a critical factor in the impairment of osteoblast function in osteoporosis. Metformin (Met), a biguanide antidiabetic drug, has demonstrated anti-osteoporotic effects and has been confirmed to exert therapeutic benefits in diabetic osteoporosis (DOP). Nevertheless, the underlying mechanisms through which Met affects bone metabolism remain ambiguous.

Objective

This study seeks to elucidate the function of Met in DOP and to explore the potential mechanisms through which it mediates treatment effects.

Methods

In vitro, we utilized osteoblasts to explore the impact of Met on osteoblast differentiation and anti-ferroptosis in a high glucose and palmitic acid (HGHF) environment. In vivo, we developed a DOP model utilizing a high-fat diet along with streptozocin injections and evaluated the bone-protective effects of Met through micro-CT and histomorphological analyses.

Results

Met inhibits HGHF-induced ferroptosis in osteoblasts, as indicated by the elevation of ferroptosis-protective proteins (GPX4, FTH1, and SLAC7A11), along with decreased lipid peroxidation and ferrous ion levels. Furthermore, Met augmented the levels of osteogenic markers (RUNX2 and COL1A1) and enhanced alkaline phosphatase activity in osteoblasts under HGHF conditions. Mechanistic investigations revealed that Met activates the AMPK/Nrf2 pathway, effectively preventing ferroptosis progression. Additionally, in vivo results demonstrated Met alleviates bone loss and microstructural deterioration in DOP rats.

Conclusion

Met can activate the AMPK/Nrf2 pathway to prevent ferroptosis, thereby protecting against DOP.

Sulforaphane regulation autophagy-mediated pyroptosis in autoimmune hepatitis via AMPK/mTOR pathway

Autoimmune hepatitis (AIH) is a liver disease marked by inflammation of unknown origin. If untreated, it can progress to cirrhosis or liver failure, posing a significant health risk. Currently, effective drug therapies are lacking in clinical practice. Sulforaphane (SFN), a natural anti-inflammatory and antioxidant compound found in various cruciferous vegetables, alleviate pyroptosis and improve impaired autophagic flux, both of which contribute to AIH progression. However, whether SFN modulates autophagic flux and pyroptosis in S100-induced EAH through the AMPK/mTOR pathway remains unclear. Therefore, this study aims to investigate whether SFN can regulate AIH and elucidate its potential mechanisms of action. In this study, experimental AIH (EAH) was induced in male C57BL/6 J mice through intraperitoneal (i.p.) injection of S100. SFN was administered intraperitoneally every other day. After 28 days, the mice were euthanized, and their livers and serum were collected for histological and biochemical analyses. AML12 cells were used for the in vitro studies. The results showed that SFN mitigated pyroptosis by inhibiting the NLRP3 inflammasome and improving autophagic flux, which alleviates S100-induced EAH. Conversely, the autophagy inhibitor 3-MA negated the protective effects of SFN against inflammasome-mediated pyroptosis. Furthermore, SFN activated the AMPK/mTOR signaling pathway, offering protection against S100-induced EAH. Selective inhibition of AMPK suppressed the improvement in autophagic flux and protected against SFN-induced pyroptosis. Overall, SFN significantly ameliorates S100-induced EAH by enhancing autophagic flux and mitigating pyroptosis through activation of the AMPK/mTOR signaling pathway.

Topical rhubarb charcoal-crosslinked chitosan/silk fibroin sponge scaffold for the repair of diabetic ulcers improves hepatic lipid deposition in db/db mice via the AMPK signalling pathway

BACKGROUND

Type 2 diabetes mellitus (T2DM) is closely linked to metabolic syndrome, characterised by insulin resistance, hyperglycaemia, abnormal lipid metabolism, and chronic inflammation. Diabetic ulcers (DUs) comprise consequential complications that arise as a result of T2DM. To investigate, db/db mice were used for the disease model. The findings demonstrated that a scaffold made from a combination of rhubarb charcoal-crosslinked chitosan and silk fibroin, designated as RCS/SF, was able to improve the healing process of diabetic wounds in db/db mice. However, previous studies have primarily concentrated on investigating the impacts of the RSC/SF scaffold on wound healing only, while its influence on the entire body has not been fully elucidated.

MATERIAL AND METHODS

The silk fibroin/chitosan sponge scaffold containing rhubarb charcoal was fabricated in the present study using a freeze-drying approach. Subsequently, an incision with a diameter of 8 mm was made on the dorsal skin of the mice, and the RCS/SF scaffold was applied directly to the wound for 14 days. Subsequently, the impact of RCS/SF scaffold therapy on hepatic lipid metabolism was assessed through analysis of serum and liver biochemistry, histopathology, quantitative real-time PCR (qRT-PCR), immunohistochemistry, and Western blotting.

RESULTS

The use of the RCS/SF scaffold led to an enhancement in the conditions associated with serum glucolipid metabolism in db/db mice. An assessment of hepatic histopathology further confirmed this enhancement. Additionally, the qRT-PCR analysis revealed that treatment with RCS/SF scaffold resulted in the downregulation of genes associated with fatty acid synthesis, fatty acid uptake, triglyceride (TG) synthesis, gluconeogenesis, and inflammatory factors. Moreover, the beneficial effect of the RCS/SF scaffold on oxidative stress was shown by assessing antioxidant enzymes and lipid peroxidation. Additionally, the network pharmacology analysis verified that the adenosine monophosphate-activated protein kinase (AMPK) signalling pathway had a vital function in mitigating non-alcoholic fatty liver disease (NAFLD) by utilizing R. officinale. The measurement of AMPK, sterol regulatory element binding protein 1 (SREBP1), fatty acid synthase (FASN), and acetyl CoA carboxylase (ACC) gene and protein expression provided support for this discovery. Furthermore, the molecular docking investigations revealed a robust affinity between the active components of rhubarb and the downstream targets of AMPK (SREBP1 and FASN).

CONCLUSION

By regulating the AMPK signalling pathway, the RCS/SF scaffold applied topically effectively mitigated hepatic lipid accumulation, decreased inflammation, and attenuated oxidative stress. The present study, therefore, emphasises the crucial role of the topical RCS/SF scaffold in regulating hepatic lipid metabolism, thereby confirming the concept of "external and internal reshaping".