Lead toxicity induces autophagy to protect against cell death through mTORC1 pathway in cardiofibroblasts

Oyster (Crassostrea gigas) ferritin relieves lead-induced liver oxidative damage via regulating the mitophagy

Lead can induce oxidative stress and increase lipid peroxidation in biofilms, leading to liver damage and physiological dysfunction. This study aimed to investigate how oyster ferritin (GF1) attenuates lead-induced oxidative damage to the liver in vitro and in vivo. Animal experiments have confirmed that lead exposure can lead to oxidative damage and lipid peroxidation of the liver, and ferritin can regulate the activity of antioxidant enzymes and alleviate pathological changes in the liver. At the same time, oyster ferritin can regulate the expression of oxidative stress-related genes and reduce the expression of inflammasome-related genes. In addition, lead can induce apoptosis and mitophagy, leading to overproduction of reactive oxygen species and cell death, which can be effectively alleviated by oyster ferritin. Overall, this study provides a theoretical foundation for the use of oyster ferritin as a means of mitigating and preventing lead-induced damage.

Recent insights into autophagy and metals/nanoparticles exposure

Some anthropogenic pollutants, such as heavy metals and nanoparticles (NPs), are widely distributed and a major threat to environmental safety and public health. In particular, lead (Pb), cadmium (Cd), chromium (Cr), arsenic (As), and mercury (Hg) have systemic toxicity even at extremely low concentrations, so they are listed as priority metals in relation to their significant public health burden. Aluminum (Al) is also toxic to multiple organs and is linked to Alzheimer's disease. As the utilization of many metal nanoparticles (MNPs) gradually gain traction in industrial and medical applications, they are increasingly being investigated to address potential toxicity by impairing certain biological barriers. The dominant toxic mechanism of these metals and MNPs is the induction of oxidative stress, which subsequently triggers lipid peroxidation, protein modification, and DNA damage. Notably, a growing body of research has revealed the linkage between dysregulated autophagy and some diseases, including neurodegenerative diseases and cancers. Among them, some metals or metal mixtures can act as environmental stimuli and disturb basal autophagic activity, which has an underlying adverse health effect. Some studies also revealed that specific autophagy inhibitors or activators could modify the abnormal autophagic flux attributed to continuous exposure to metals. In this review, we have gathered recent data about the contribution of the autophagy/mitophagy mediated toxic effects and focused on the involvement of some key regulatory factors of autophagic signaling during exposure to selected metals, metal mixtures, as well as MNPs in the real world. Besides this, we summarized the potential significance of interactions between autophagy and excessive reactive oxygen species (ROS)-mediated oxidative damage in the regulation of cell survival response to metals/NPs. A critical view is given on the application of autophagy activators/inhibitors to modulate the systematic toxicity of various metals/MNPs.

Sodium Para-Aminosalicylic Acid Modulates Autophagy to Lessen Lead-Induced Neurodegeneration in Rat Cortex

Lead (Pb) is a common heavy metal contaminant in the environment, and it may perturb autophagy and cause neurodegeneration. Although sodium para-aminosalicylic (PAS-Na) has been shown to protect the brain from lead-induced toxicity, the mechanisms associated with its efficacy have yet to be fully understood. In this study, we evaluated the efficacy of PAS-Na in attenuating the neurotoxic effects of lead, as well as the specific mechanisms that mediate such protection. Lead exposure resulted in weight loss and injury to the liver and kidney, and PAS-Na had a protective effect against this damage. Both short-term and subchronic lead exposure impaired learning ability, and this effect was reversed by PAS-Na intervention. Lead exposure also perturbed autophagic processes through the modulation of autophagy-related factors. Short-term lead exposure downregulated LC3 and beclin1 and upregulated the expression of p62; subchronic lead exposure upregulated the expression of LC3, beclin1, and P62. It follows that PAS-Na had an antagonistic effect on the activation of the above autophagy-related factors. Overall, our novel findings suggest that PAS-Na can protect the rat cortex from lead-induced toxicity by regulating autophagic processes. (1) Short-term lead exposure inhibits autophagy, whereas subchronic lead exposure promotes autophagy. (2) PAS-NA ameliorated the abnormal process of lead-induced autophagy, which had a protective effect on the cerebral cortex.

SIRT1/mTOR pathway-mediated autophagy dysregulation promotes Pb-induced hepatic lipid accumulation in HepG2 cells

Lead (Pb) is a common and toxic metal pollutant in the ecological environment and has drawn significant attention due to its presence in various channels, including the use of lead-based paint, mineral extraction and smelting, exhaust gas from gasoline combustion. Autophagy is an essential catabolic pathway and blocked autophagy may result in abnormal lipid metabolism in liver. A body of evidence demonstrates that Pb exposure causes abnormal lipid droplet (LDs) accumulation in the liver, but the mechanism remains unknown. Here, we investigated whether Pb induced lipid accumulation by regulating autophagy in HepG2 cells. In this study, we found that Pb (50 μM) blocked the autophagy flux mainly by transcription factor EB (TFEB)-mediated impairment of lysosome formation and activity. Then we demonstrated that the dense lipid accumulation was observed upon Pb exposure, and induction of autophagy by the autophagy activator rapamycin (Rap) alleviated Pb-induced lipid accumulation, while suppression of autophagy by chloroquine (CQ) exacerbated Pb-induced lipid accumulation, suggested that Pb-induced autophagy blockage might be responsible for lipid accumulation. Moreover, we demonstrated that the SIRT1/mTOR pathway participated in Pb-induced autophagy dysregulation, leading to Pb-induced hepatic lipid accumulation. In summary, these results revealed a new insight into the relationship between Pb-caused autophagy dysregulation and lipid accumulation for the first time and highlight autophagy as a novel therapeutic target against Pb-induced hepatic lipid accumulation which supplying the theoretical basis and potential strategies for the intervention and treatment of Pb-related disease.

AMPK/PPAR-γ/NF-κB axis participates in ROS-mediated apoptosis and autophagy caused by cadmium in pig liver

The experiment was conducted to investigate the effects of Cadmium (Cd) on growth performance, blood biochemical parameters, oxidative stress, hepatocyte apoptosis and autophagy of weaned piglets. A total of 12 healthy weaned piglets were randomly assigned to the control and the Cd group, which were fed with a basal diet and the basal diet supplemented with 15 ± 0.242 mg/kg CdCl₂ for 30 d, respectively. Our results demonstrated that Cd significantly decreased final body weight, average daily feed intake (ADFI), average daily gain (ADG) and increased feed-to-gain (F/G) ratio (P < 0.05). For blood biochemical parameters, Cd treatment significantly decreased the red blood cell (RBC), hemoglobin (HGB), hematocrit (HCT), total protein, albumin, copper content and iron content (P < 0.05). In addition, liver injury was observed in the Cd-exposed group. Our results also demonstrated that Cd exposure contributed to the production of ROS, activated the AMPK/PPAR-γ/NF-κB pathway (increasing the expressions of P-AMPK/AMPK, NF-κB, I-κB-β, COX-2, and iNOS, decreasing the expressions of PPAR-γ and I-κB-α), finally induced autophagy (increasing the expressions of Beclin-1, the ratio of LC3-II/LC3-I and p62), and apoptosis (increasing the expressions of Bax, Bak, Caspase-9, and Caspase-3, decreasing the expression of Bcl-2). Overall, these findings revealed the vital role of AMPK/PPAR-γ/NF-κB pathway in Cd-induced liver apoptosis and autophagy, which provided deeper insights into a better understanding of Cd-induced hepatotoxicity.

New insights into crosstalk between pyroptosis and autophagy co-induced by molybdenum and cadmium in duck renal tubular epithelial cells

Pyroptosis and autophagy are two different biological processes that determine cell fates. Our previous studies revealed that pyroptosis and autophagy were involved in cytotoxicity co-induced by molybdenum (Mo) and cadmium (Cd) in duck renal tubular epithelial cells, but crosstalk between them is unclear. Hence, the cells were treated with 500.0 μM Mo, 4.0 μM Cd, 10.0 μM Z-YVAD-fluoromethylketone (YVAD), 2.5 μM 3-methyladenine (3-MA) and 10.0 μM chloroquine (CQ) alone or in combination for 12 h (CQ for the last 4 h). Under Mo and Cd co-stress, data evidenced that YVAD addition decreased the number of autophagosomes, LC3 puncta, and AMPKα-1, Atg5, Beclin-1, LC3A, LC3B mRNA levels and LC3-II/LC3-I, Beclin-1 protein levels, and increased p62 expression levels. Besides, both 3-MA and CQ addition increased NLRP3, Caspase-1, NEK7, ASC, GSDMA, GSDME, IL-1β, IL-18 mRNA levels, NLRP3, Caspase-1 p20, ASC, GSDMD protein and ROS levels, and NO, LDH, IL-1β, IL-18 releases. Collectively, our results revealed that pyroptosis and autophagy co-induced by Mo and Cd were interrelated in duck renal tubular epithelial cells, and inhibiting pyroptosis might attenuate Mo and Cd co-induced autophagy, but inhibiting autophagy might promote Mo and Cd co-induced pyroptosis.

Inhibition of autophagy aggravates molybdenum-induced mitochondrial dysfunction by aggravating oxidative stress in duck renal tubular epithelial cells

Excessive molybdenum (Mo) has adverse effects on animals. To elucidate the effects of autophagy on Mo-induced nephrotoxicity, the duck renal tubular epithelial cells were cultured in medium in absence and presence of (NH₄)₆Mo₇O₂₄.4H₂O (0, 480, 720, 960 μM Mo), 3-Methyladenine (3-MA) (2.5 μM), and the combination of Mo and 3-MA for 12 h. After 12 h exposure, the MDC staining, morphologic observation, LC3 puncta, cell viability, autophagy-related genes mRNA and proteins levels, lactate dehydrogenase (LDH) release, reactive oxygen species (ROS) level, antioxidant indices, mitochondrial membrane potential (MMP), mitochondrial mass, mitochondrial respiratory control ratio (RCR) and oxidative phosphorylation rate (OPR) were determined. The results showed that excessive Mo exposure significantly elevated the number of autophagosome and LC3 puncta, upregulated Beclin-1, Atg5, LC3A and LC3B mRNA levels, and LC3II/LC3I and Beclin-1 protein levels, decreased mTOR, p62 and Dynein mRNA levels and p62 protein level. Besides, co-treatment with Mo and 3-MA dramatically increased LDH release, ROS level, hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) contents as well as cell dam age, reduced cell viability, the activities of glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), catalase (CAT), MMP, mitochondrial mass, mitochondrial RCR and OPR compared to treatment with Mo alone. Taken together, these results suggest that excessive Mo exposure can induce autophagy in duck renal tubular epithelial cells, inhibition of autophagy aggravates Mo-induced mitochondrial dysfunction by regulating oxidative stress.

Ellagic acid restored lead-induced nephrotoxicity by anti-inflammatory, anti-apoptotic and free radical scavenging activities

Introduction

long-term environmental and occupational exposure to lead, which is a ubiquitous industrial pollutant, causes significant damage to tissues of kidney. This report aims to address this debilitating issue. A natural polyphenolic compound, Ellagic acid (EA) is having numerous potential medicinal properties. In this present study nephroprotective effects of EA has been evaluated in a rodent model with lead-induced toxicity.

Methods

Rats were treated with EA doses of 50 mg/kg and 25 mg/kg and simultaneously co-administered with lead acetate (60 mg/kg) for 2 months through oral route. The extent to which EA treatment provides nephroprotective effect was estimated by measurement of serum biomarkers, tissue antioxidants, inflammatory mediators, apoptosis, autophagy pathway and histological examination.

Results

EA treatment caused significant restoration in the level of serum biomarkers, tissue antioxidants and histological architecture of renal tissue. Treatment with either of the doses of EA causes restoration of pro-inflammatory mediators to approximately pre-exposure concentration. This phenomena is caused by suppression of expression levels of inflammatory molecules like tumour necrosis factor-α (TNF-α), nuclear factor kappa B (NF-κB), interleukin-6 (IL-6), and interleukin-1β (IL-1β), as well as functional expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Moreover, it was also observed that EA suppressed apoptotic and autophagic pathway by reduction of expression of light chain 3B (LC3B) level which are the oxidative DNA damage markers of renal tissue.

Conclusion

It can be safely concluded that EA provides protection against lead-induced nephrotoxicity to a significant degree.

The antagonistic effect of selenium on lead-induced necroptosis via MAPK/NF-κB pathway and HSPs activation in the chicken spleen

Recent studies identified a novel programmed and regulated cell death that was characterized by a necrotic cell death morphology, termed necroptosis. Lead (Pb) is known as a persistent inorganic environmental pollutant that affects the health of humans and animals worldwide. However, there are no detailed reports of Pb-induced necroptosis of immune tissue. Selenium (Se) is a trace element that antagonizes the toxicity of heavy metals. Here, chickens were randomly divided into four groups, treated with Pb ((CH₃OO)₂Pb, 150 mg/kg) and/or Se (Na₂SeO₃, 2 mg/kg), aim to study the effect and mechanism of necroptosis in Pb-induced spleen injury and the antagonistic effects of Se on Pb toxicity. Our results showed that Pb exposure evidently increased the accumulation of Pb in spleen and caused necroptosis by upregulating the expression of RIP1, RIP3 and MLKL, and decreasing Caspase8 expression. Meanwhile, Pb treatment inhibited the activities of SOD, GPX, and CAT, caused the accumulation of NO and MDA, and induced oxidative stress, which promoted the expression of MAPK/NF-κB pathway genes (ERK, JNK, P38, NF-κB and TNF-α) and activated HSPs (HSP27, HSP40, HSP60, HSP70 and HSP90). However, the increased content of Pb in spleen and Pb-caused necroptosis were inhibited by Se cotreatment. Overall, we conclude that Se can prevent Pb-induced necroptosis by restoring antioxidant functions and blocking the MAPK/NF-κB pathway and HSPs activation in chicken spleen.

Arsenic induces dysfunctional autophagy via dual regulation of mTOR pathway and Beclin1-Vps34/PI3K complex in MLTC-1 cells

Arsenic poisoning and induced potential lesion is a global concern. However, the exact mechanisms underlying its toxicity especially in male reproductive system still remain unclear. Hence, this study aimed to explore the roles of mTOR and Beclin1-Vps34/PI3K complex during As-induced-toxicity using Rapamycin (mTOR inhibitor), Beclin1 siRNA and 3-methyladenine (3-MA, Vps34/PI3K inhibitor) in testicular stromal cells. For this, mouse testis Leydig Tumor Cell lines (MLTC-1) were challenged with As₂O₃ (0, 3, 6 and 9 μM) exposure for 24 hs. Lyso-Tracker Red and Monodansylcadaverine (MDC) staining results depicted a significant accumulation of autophagosomes in MLTC-1 cells exposed to arsenic. Meanwhile, arsenic treatment up-regulated autophagic markers including LC3, Atg7, Beclin1 and Vps34 expressions, mTOR downstream autophagy related genes and the Beclin1-Vps34/PI3K complex associated members. Furthermore, silencing of Beclin1, and inhibition of Vps34/PI3K and mTOR altered the arsenic-induced autophagosomes formation. However, p62, the substrate protein of autophagy, was also up-regulated by arsenic administration independent on Beclin1-Vps34/PI3K complex. Altogether, our results revealed that arsenic exposure induced autophagosomes formation via regulation of the Beclin1-Vps34/PI3K complex and mTOR pathway; the blockage of autophagosomes degradation maybe due to impaired function of lysosomes. Thus, this study provides a novel mechanistic approach with respect to As-induced male reproductive toxicity.

A protective role of autophagy in Pb-induced developmental neurotoxicity in zebrafish

Lead (Pb) is one of the most toxic heavy metals and has aroused widespread concern as it can cause severe impairments in the developing nervous system. Autophagy has been proposed as an injury factor in Pb-induced neurotoxicity. In this study, we used zebrafish embryo as a model, measured the general toxic effects of Pb, and investigated the effect of Pb exposure on autophagy, and its role in Pb-induced developmental neurotoxicity. Zebrafish embryos were exposed to Pb at concentrations of 0, 0.1, 1 or 10 μM until 4 days post-fertilization. Our data showed that exposure to 10 μM Pb significantly reduced survival rates and impaired locomotor activity. Uptake of Pb was enhanced as the concentration and duration of exposure increased. Inhibition of lysosomal degradation with bafilomycin A1 treatment abolished the suppression of Lc3-II protein expression by Pb. Furthermore, autophagosome formation was inhibited by Pb in the brain. In addition, mRNA expression of beclin1, one of the critical genes in autophagy, were decreased in Pb exposure groups at 72 h post-fertilization. Whole-mount in situ hybridization assay showed that beclin1 gene expression in the brain was reduced by Pb. Rapamycin, an autophagy inducer, partly resolved developmental neurotoxicity induced by Pb exposure. Our results suggest that autophagy plays a protective role in the developmental neurotoxicity of Pb in zebrafish embryos and larvae.

Pb disrupts autophagic flux through inhibiting the formation and activity of lysosomes in neural cells

Lead (Pb) has long been known as a metallic toxin to exert detrimental effects on human health, particularly on the central nervous system (CNS). Misregulated autophagy was regularly associated with multiple cellular dysfunctions and human diseases. However, the role of autophagy underlying Pb-induced neurotoxicity remains to be elucidated. In this study, we demonstrated that Pb promoted the accumulation of autophagosomes in PC12 cells, and subsequent findings revealed that this autophagosome accumulation was primarily caused by the inhibition of autophagic flux. Moreover, the results showed that Pb affected autophagy course through increasing Beclin 1 and ATG5 expression levels. Specifically, by double labeling with LC3-II (a marker of autophagosome) and LAMP-1 (a marker of lysosome), Pb impaired fusion between autophagosomes and lysosomes. Additionally, Pb exposure significantly reduced the number or size of lysosomes via decreasing the level of LAMP1, which is confirmed by the LysoTracker Red staining. Furthermore, the impairment of lysosomal activity was also signaled by the altered pH value of this acidic organelle. Overall, Pb exposure led to injuries of autophagy of neural cells through inhibiting the genesis and activity of lysosomes. The data provides insight with the neurotoxicity of Pb in a novel perspective, autophagy.

Antagonistic effects of selenium on lead-induced autophagy by influencing mitochondrial dynamics in the spleen of chickens

Lead (Pb) may damage the immune function in human and animal. Selenium (Se) has antagonistic effects on Pb. In our study, brown layer chickens were randomly allocated to control group, Se group (1 mg/kg Se), Se+Pb group (1 mg/kg Se and 350 mg/kg Pb), and Pb group (350 mg/kg Pb). The chickens were sacrificed on the 90^th day; spleen tissues were subjected to observation of ultrastructure and detection of spleen-related indexes. The results revealed that in the Pb group, expression levels of the cytokines IL-1 and TNF-α significantly increased, and expression levels of IL-2 and INF-γ significantly decreased; activities of antioxidant enzyme GPX, SOD and CAT significantly decreased, and expression level of malondialdehyde (MDA) significantly increased; expression levels of mitochondrial fission-related genes (Mff and Drp1) significantly increased, and expression levels of mitochondrial fusion-related genes (Opa1, Mfn1 and Mfn2) significantly decreased; expression of autophagy-related genes (Beclin 1, Dynein, Atg 5, LC3-I and LC-II) was upregulated, while expression of mammalian target of rapamycin (mTOR) was downregulated. The results of transmission electron microscopy indicated that Pb induced mitochondrial fragmentation, and triggered autophagy in the spleen of chickens. The Se and Pb co-treatment remarkably alleviated these injuries induced by Pb in the spleen of chickens. In conclusion, Pb can induce the oxidative stress to influence the mitochondrial dynamics balance and lead to autophagy, which triggers the immune dysfunction in the spleen of chickens; the Se exhibits the antagonistic effects on lead-induced autophagy by influencing mitochondrial dynamics in the spleen of chickens.

Autophagy blockade and lysosomal membrane permeabilization contribute to lead-induced nephrotoxicity in primary rat proximal tubular cells

Lead (Pb) is a known nephrotoxicant that causes damage to proximal tubular cells. Autophagy has an important protective role in various renal injuries, but the role of autophagy in Pb-elicited nephrotoxicity remains largely unknown. In this study, Pb promoted the accumulation of autophagosomes in primary rat proximal tubular (rPT) cells, and subsequent findings revealed that this autophagosome accumulation was caused by the inhibition of autophagic flux. Moreover, Pb exposure did not affect the autophagosome-lysosome fusion in rPT cells. Next, we found that Pb caused lysosomal alkalinization, may be through suppression of two V-ATPase subunits. Simultaneously, Pb inhibited lysosomal degradation capacity by affecting the maturation of cathepsin B (CTSB) and cathepsin D (CTSD). Furthermore, translocation of CTSB and CTSD from lysosome to cytoplasm was observed in this study, suggesting that lysosomal membrane permeabilization (LMP) occurred in Pb-exposed rPT cells. Meanwhile, Pb-induced caspase-3 activation and apoptosis were significantly but not completely inhibited by CTSB inhibitor (CA 074) and CTSD inhibitor (pepstatin A), respectively, demonstrating that LMP-induced lysosomal enzyme release was involved in Pb-induced apoptosis in rPT cells. In conclusion, Pb-mediated autophagy blockade in rPT cells is attributed to the impairment of lysosomal function. Both inhibition of autophagic flux and LMP-mediated apoptosis contribute to Pb-induced nephrotoxicity in rPT cells.

Autophagy in Neurodegenerative Diseases and Metal Neurotoxicity

Autophagy generally refers to cell catabolic and recycling process in which cytoplasmic components are delivered to lysosomes for degradation. During the last two decades, autophagy research has experienced a recent boom because of a newfound connection between this process and many human diseases. Autophagy plays a significant role in maintaining cellular homeostasis and protects cells from varying insults, including misfolded and aggregated proteins and damaged organelles, which is particularly crucial in neuronal survival. Mounting evidence has implicated autophagic dysfunction in the pathogenesis of several major neurodegenerative disorders, such as Parkinson's disease, Alzheimer's disease and Huntington's disease, where deficient elimination of abnormal and toxic protein aggregates promotes cellular stress, failure and death. In addition, autophagy has also been found to affect neurotoxicity induced by exposure to essential metals, such as manganese, copper, and iron, and other heavy metals, such as cadmium, lead, and methylmercury. This review examines current literature on the role of autophagy in the mechanisms of disease pathogenesis amongst common neurodegenerative disorders and of metal-induced neurotoxicity.