PI3K/Akt Signaling Pathway Ameliorates Oxidative Stress-Induced Apoptosis upon Manganese Exposure in PC12 Cells

Advances of traditional Chinese medicine preclinical mechanisms and clinical studies on diabetic peripheral neuropathy

CONTEXT

Diabetic peripheral neuropathy (DPN) results in an enormous burden and reduces the quality of life for patients. Considering there is no specific drug for the management of DPN, traditional Chinese medicine (TCM) has increasingly drawn attention of clinicians and researchers around the world due to its characteristics of multiple targets, active components, and exemplary safety.

OBJECTIVE

To summarize the current status of TCM in the treatment of DPN and provide directions for novel drug development, the clinical effects and potential mechanisms of TCM used in treating DPN were comprehensively reviewed.

METHODS

Existing evidence on TCM interventions for DPN was screened from databases such as PubMed, the Cochrane Neuromuscular Disease Group Specialized Register (CENTRAL), and the Chinese National Knowledge Infrastructure Database (CNKI). The focus was on summarizing and analyzing representative preclinical and clinical TCM studies published before 2023.

RESULTS

This review identified the ameliorative effects of about 22 single herbal extracts, more than 30 herbal compound prescriptions, and four Chinese patent medicines on DPN in preclinical and clinical research. The latest advances in the mechanism highlight that TCM exerts its beneficial effects on DPN by inhibiting inflammation, oxidative stress and apoptosis, endoplasmic reticulum stress and improving mitochondrial function.

CONCLUSIONS

TCM has shown the power latent capacity in treating DPN. It is proposed that more large-scale and multi-center randomized controlled clinical trials and fundamental experiments should be conducted to further verify these findings.

Signal Transduction Associated with Mn-induced Neurological Dysfunction

Manganese (Mn) is a heavy metal that occurs widely in nature and has a vital physiological role in growth and development. However, excessive exposure to Mn can cause neurological damage, especially cognitive dysfunction, such as learning disability and memory loss. Numerous studies on the mechanisms of Mn-induced nervous system damage found that this metal targets a variety of metabolic pathways, for example, endoplasmic reticulum stress, apoptosis, neuroinflammation, cellular signaling pathway changes, and neurotransmitter metabolism interference. This article reviews the latest research progress on multiple signaling pathways related to Mn-induced neurological dysfunction.

Gene, Protein, and in Silico Analyses of FoxO, an Evolutionary Conserved Transcription Factor in the Sea Urchin Paracentrotus lividus

FoxO is a member of the evolutionary conserved family of transcription factors containing a Forkhead box, involved in many signaling pathways of physiological and pathological processes. In mammals, mutations or dysfunctions of the FoxO gene have been implicated in diverse diseases. FoxO homologs have been found in some invertebrates, including echinoderms. We have isolated the FoxO cDNA from the sea urchin Paracentrotus lividus (Pl-foxo) and characterized the corresponding gene and mRNA. In silico studies showed that secondary and tertiary structures of Pl-foxo protein corresponded to the vertebrate FoxO3 isoform, with highly conserved regions, especially in the DNA-binding domain. A phylogenetic analysis compared the Pl-foxo deduced protein with proteins from different animal species and confirmed its evolutionary conservation between vertebrates and invertebrates. The increased expression of Pl-foxo mRNA following the inhibition of the PI3K signaling pathway paralleled the upregulation of Pl-foxo target genes involved in apoptosis or cell-cycle arrest events (BI-1, Bax, MnSod). In silico studies comparing molecular data from sea urchins and other organisms predicted a network of Pl-foxo protein-protein interactions, as well as identified potential miRNAs involved in Pl-foxo gene regulation. Our data may provide new perspectives on the knowledge of the signaling pathways underlying sea urchin development.

Metabolic Derangement of Essential Transition Metals and Potential Antioxidant Therapies

Essential transition metals have key roles in oxygen transport, neurotransmitter synthesis, nucleic acid repair, cellular structure maintenance and stability, oxidative phosphorylation, and metabolism. The balance between metal deficiency and excess is typically ensured by several extracellular and intracellular mechanisms involved in uptake, distribution, and excretion. However, provoked by either intrinsic or extrinsic factors, excess iron, zinc, copper, or manganese can lead to cellular damage upon chronic or acute exposure, frequently attributed to oxidative stress. Intracellularly, mitochondria are the organelles that require the tightest control concerning reactive oxygen species production, which inevitably leaves them to be one of the most vulnerable targets of metal toxicity. Current therapies to counteract metal overload are focused on chelators, which often cause secondary effects decreasing patients' quality of life. New therapeutic options based on synthetic or natural antioxidants have proven positive effects against metal intoxication. In this review, we briefly address the cellular metabolism of transition metals, consequences of their overload, and current therapies, followed by their potential role in inducing oxidative stress and remedies thereof.

Manganese overexposure results in ferroptosis through the HIF-1α/p53/SLC7A11 pathway in ICR mouse brain and PC12 cells

Manganese (Mn) overexposure has been associated with the development of neurological damage reminiscent of Parkinson's disease, while the underlying mechanisms have yet to be fully characterized. This study aimed to investigate the mechanisms leading to injury in dopaminergic neurons induced by Mn and identify novel treatment approaches. In the in vivo and in vitro models, ICR mice and dopaminergic neuron-like PC12 cells were exposed to Mn, respectively. We treated them with anti-ferroptotic agents ferrostatin-1 (Fer-1), deferoxamine (DFO), HIF-1α activator dimethyloxalylglycine (DMOG) and inhibitor LW6. We also used p53-siRNA to verify the mechanism underlying Mn-induced neurotoxicity. Fe and Mn concentrations increased in ICR mice brains overexposed to Mn. Additionally, Mn-exposed mice exhibited movement impairment and encephalic pathological changes, with decreased HIF-1α, SLC7A11, and GPX4 proteins and increased p53 protein levels. Fer-1 exhibited protective effects against Mn-induced both behavioral and biochemical changes. Consistently, in vitro, Mn exposure caused ferroptosis-related changes and decreased HIF-1α levels, all ameliorated by Fer-1. Upregulation of HIF-1α by DMOG alleviated the Mn-associated ferroptosis, while LW6 exacerbated Mn-induced neurotoxicity through downregulating HIF-1α. p53 knock-down also rescued Mn-induced ferroptosis without altering HIF-1α protein expression. Mn overexposure resulted in ferroptosis in dopaminergic neurons, mediated through the HIF-1α/p53/SLC7A11 pathway.

Flavonoid Compounds in Hippophae rhamnoides L. Protect Endothelial Cells from Oxidative Damage Through the PI3K/AKT-eNOS Pathway

Sea buckthorn, a traditional medicinal plant, has been used for several years in China for the prevention and treatment of various diseases, a practice closely associated with its significant antioxidant activity. The aim of this study was to investigate the protective effects of sea buckthorn flavonoids on vascular endothelial cells in an oxidative stress environment. We isolated and extracted active compounds from sea buckthorn and investigated their impact on endothelial nitric oxide synthase (eNOS) activity through the PI3K/AKT-eNOS signaling pathway through a combination of network pharmacology and cellular experiments, elucidating the regulatory effects of these compounds on endothelial cell functions. Three flavonoids, named Fr.4-2-1, Fr.4-2-2 and Fr.4-2-3, were obtained from sea buckthorn. The results of network pharmacology indicated that they might exert their effects by regulating the PI3K-AKT signaling pathway. In vitro results showed that all three flavonoids were effective in alleviating the degree of oxidative stress in cells, among which Fr.4-2-1 exerted its antioxidant effects by modulating the PI3K/AKT-eNOS pathway. Flavonoids in sea buckthorn can effectively inhibit oxidative stress-induced cellular damage, preserving the integrity and functionality of endothelial cells, which is crucial for maintaining vascular health and function.

Mechanism by which HDAC3 regulates manganese induced H3K27ac in SH-SY5Y cells and intervention by curcumin

Long-term excessive exposure to manganese can impair neuronal function in the brain, but the underlying pathological mechanism remains unclear. Oxidative stress plays a central role in manganese-induced neurotoxicity. Numerous studies have established a strong link between abnormal histone acetylation levels and the onset of various diseases. Histone deacetylase inhibitors and activators, such as TSA and ITSA-1, are often used to investigate the intricate mechanisms of histone acetylation in disease. In addition, recent experiments have provided substantial evidence demonstrating that curcumin (Cur) can act as an epigenetic regulator. Given these findings, this study aims to investigate the mechanisms underlying oxidative damage in SH-SY5Y cells exposed to MnCl2·4H2O, with a particular focus on histone acetylation, and to assess the potential therapeutic efficacy of Cur. In this study, SH-SY5Y cells were exposed to manganese for 24 h, were treated with TSA or ITSA-1, and were treated with or without Cur. The results suggested that manganese exposure, which leads to increased expression of HDAC3, induced H3K27 hypoacetylation, inhibited the transcription of antioxidant genes, decreased antioxidant enzyme activities, and induced oxidative damage in cells. Pretreatment with an HDAC3 inhibitor (TSA) increased the acetylation of H3K27 and the transcription of antioxidant genes and thus slowed manganese exposure-induced cellular oxidative damage. In contrast, an HDAC3 activator (ITSA-1) partially increased manganese-induced cellular oxidative damage, while Cur prevented manganese-induced oxidative damage. In summary, these findings suggest that inhibiting H3K27ac is a possible mechanism for ameliorating manganese-induced damage to dopaminergic neurons and that Cur exerts a certain protective effect against manganese-induced damage to dopaminergic neurons.

Ferroptosis at the crossroads of manganese-induced neurotoxicity: A retrospective study

Manganese is an essential trace element, but overexposure can cause neurotoxicity and subsequent neurodegenerative diseases. Ferroptosis is a form of cell death characterized by lipid peroxidation and iron overload inside cells, which is closely related to manganese neurotoxicity. Manganese can induce ferroptosis through multiple pathways: causing oxidative stress and increased cellular reactive oxygen species (ROS), resulting in lipid peroxidation; depleting glutathione (GSH) and weakening the antioxidant capacity of cells; disrupting iron metabolism and increasing iron-dependent lipid peroxidation; damaging mitochondrial function and disrupting the electron transport chain, leading to increased ROS production. Oxidative stress, iron metabolism disorders, lipid peroxidation, GSH depletion, and mitochondrial dysfunction, typical features of ferroptosis, have been observed in animal and cell models after manganese exposure. In summary, manganese can participate in the pathogenesis of neurodegenerative diseases by inducing events related to ferroptosis. This provides new insights into studying the mechanism of manganese neurotoxicity and developing therapeutic drugs.

Signaling Pathways Involved in Manganese-Induced Neurotoxicity

Manganese (Mn) is an essential trace element, but insufficient or excessive bodily amounts can induce neurotoxicity. Mn can directly increase neuronal insulin and activate insulin-like growth factor (IGF) receptors. As an important cofactor, Mn regulates signaling pathways involved in various enzymes. The IGF signaling pathway plays a protective role in the neurotoxicity of Mn, reducing apoptosis in neurons and motor deficits by regulating its downstream protein kinase B (Akt), mitogen-activated protein kinase (MAPK), and mammalian target of rapamycin (mTOR). In recent years, some new mechanisms related to neuroinflammation have been shown to also play an important role in Mn-induced neurotoxicity. For example, DNA-sensing receptor cyclic GMP-AMP synthase (cCAS) and its downstream signal efficient interferon gene stimulator (STING), NOD-like receptor family pyrin domain containing 3(NLRP3)-pro-caspase1, cleaves to the active form capase1 (CASP1), nuclear factor κB (NF-κB), sirtuin (SIRT), and Janus kinase (JAK) and signal transducers and activators of the transcription (STAT) signaling pathway. Moreover, autophagy, as an important downstream protein degradation pathway, determines the fate of neurons and is regulated by these upstream signals. Interestingly, the role of autophagy in Mn-induced neurotoxicity is bidirectional. This review summarizes the molecular signaling pathways of Mn-induced neurotoxicity, providing insight for further understanding of the mechanisms of Mn.

Biphasic Dose-Response of Mn-Induced Mitochondrial Damage, PINK1/Parkin Expression, and Mitophagy in SK-N-SH Cells

Excessive manganese (Mn) exposure produces neurotoxicity with mitochondrial damage. Mitophagy is a protective mechanism to eliminate damaged mitochondria to protect cells. The aim of this study was to determine the dose-response of Mn-induced mitochondria damage, the expression of mitophagy-mediated protein PINK1/Parkin and mitophagy in dopamine-producing SK-N-SH cells. Cells were exposed to 0, 300, 900, and 1500 μM Mn²⁺ for 24 h, and ROS production, mitochondrial damage and mitophagy were examined. The levels of dopamine were detected by ELISA and neurotoxicity and mitophagy-related proteins (α-synuclein, PINK1, Parkin, Optineurin, and LC3II/I) were detected by western blot. Mn increased intracellular ROS and apoptosis and decreased mitochondrial membrane potential in a concentration-dependent manner. However, at the low dose of 300 μM Mn, autophagosome was increased 11-fold, but at the high dose of 1500 μM, autophagosome was attenuated to 4-fold, together with decreased mitophagy-mediated protein PINK1/Parkin and LC3II/I ratio and increased Optineurin expression, resulting in increased α-synuclein accumulation and decreased dopamine production. Thus, Mn-induced mitophagy exhibited a novel biphasic regulation: at the low dose, mitophagy is activated to eliminate damaged mitochondria, however, at the high dose, cells gradually loss the adaptive machinery, the PINK1/Parkin-mediated mitophagy weakened, resulting in neurotoxicity.

Mechanisms of manganese-induced neurotoxicity and the pursuit of neurotherapeutic strategies

Chronic exposure to elevated levels of manganese via occupational or environmental settings causes a neurological disorder known as manganism, resembling the symptoms of Parkinson's disease, such as motor deficits and cognitive impairment. Numerous studies have been conducted to characterize manganese's neurotoxicity mechanisms in search of effective therapeutics, including natural and synthetic compounds to treat manganese toxicity. Several potential molecular targets of manganese toxicity at the epigenetic and transcriptional levels have been identified recently, which may contribute to develop more precise and effective gene therapies. This review updates findings on manganese-induced neurotoxicity mechanisms on intracellular insults such as oxidative stress, inflammation, excitotoxicity, and mitophagy, as well as transcriptional dysregulations involving Yin Yang 1, RE1-silencing transcription factor, transcription factor EB, and nuclear factor erythroid 2-related factor 2 that could be targets of manganese neurotoxicity therapies. This review also features intracellular proteins such as PTEN-inducible kinase 1, parkin, sirtuins, leucine-rich repeat kinase 2, and α-synuclein, which are associated with manganese-induced dysregulation of autophagy/mitophagy. In addition, newer therapeutic approaches to treat manganese's neurotoxicity including natural and synthetic compounds modulating excitotoxicity, autophagy, and mitophagy, were reviewed. Taken together, in-depth mechanistic knowledge accompanied by advances in gene and drug delivery strategies will make significant progress in the development of reliable therapeutic interventions against manganese-induced neurotoxicity.

Transcriptome and proteomics conjoint analysis reveal metastasis inhibitory effect of 6-shogaol as ferroptosis activator through the PI3K/AKT pathway in human endometrial carcinoma in vitro and in vivo

Endometrial cancer remains as one of the widespread female malignancies despite the existing treatment measures mainly surgery, radiotherapy, and chemotherapy. In recent times, studies have focused on medicinal plants such as ginger due to its multifaceted characteristics compared to conventional medicine. 6-Shogaol is regarded as the main active compound of ginger participating in pharmacological activities and combating various health disorders, especially cancer. In our study, we compared the effects of 6-gingerol, 6-paradol, and 6-shogaol on Ishikawa cells, and found 6-shogaol as a more effective ingredient against Ishikawa cell proliferation. Moreover, its promoted ferroptosis, as a result, triggered mitochondrial morphologic alternation, as well as changed iron concentration, GSH and MDA levels. Furthermore, 6-Shogaol inhibited cell metastasis by influencing cell invasion and migration. Finally, 6-shogaol could trigger PI3K/AKT signaling pathways in vitro and in vivo confirmed by western blotting assay and immunohistochemical evaluation. These findings suggest that 6-shogaol can be used as promising functional food component in health diet and in drug target methods for endometrial cancer therapy.