Cr(VI) induced hepatocyte apoptosis through the CTH/H2S/Drp1 signaling pathway

Hexavalent chromium [Cr(VI)] is a highly hazardous heavy metal with multiple toxic effects. Occupational studies indicate that its accumulation in humans can lead to liver damage. However, the exact mechanism underlying Cr(VI)-induced hepatotoxicity remains unknown. In this study, we explored the role of CTH/H2S/Drp1 pathway in Cr(VI)-induced oxidative stress, mitochondrial dysfunction, apoptosis, and liver injury. Our data showed that Cr(VI) triggered apoptosis, accompanied by H2S reduction, reactive oxygen species (ROS) accumulation, and mitochondrial dysfunction in both AML12 cells and mouse livers. Moreover, Cr(VI) reduced cystathionine γ-lyase (CTH) and dynamin related protein 1 (Drp1) S-sulfhydration levels, and elevated Drp1 phosphorylation levels at Serine 616, which promoted Drp1 mitochondrial translocation and Drp1-voltage-dependent anion channel 1 (VDAC1) interactions, ultimately leading to mitochondria-dependent apoptosis. Elevated hydrogen sulfide (H2S) levels eliminated Drp1 phosphorylation at Serine 616 by increasing Drp1 S-sulfhydration, thereby preventing Cr(VI)-induced Drp1-VDAC1 interaction and hepatotoxicity. These findings indicated that Cr(VI) induced mitochondrial apoptosis and hepatotoxicity by inhibiting CTH/H2S/Drp1 pathway and that targeting either CTH/H2S pathway or Drp1 S-sulfhydration could serve as a potential therapy for Cr(VI)-induced liver injury.

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.

Mitochondrial calcium uniporter involved in foodborne mycotoxin-induced hepatotoxicity

Foodborne mycotoxins are toxic metabolites that are produced by fungi. The widespread contamination of food and its by-products by mycotoxins is a global food safety problem that potentially threatens public health and other exposed animals. Most foodborne mycotoxins induce hepatotoxicity. However, only few studies have investigated the regulatory mechanisms of mitochondrial calcium transport monomers in mycotoxin-induced hepatotoxicity. Therefore, according to relevant studies and reports, this review suggests that intracellular Ca(2 +) homeostasis and mitochondrial Ca(2 +) uniporter are involved in the regulation of mycotoxin-induced hepatotoxicity. This review provides some ideas for future research involving mitochondrial Ca(2 +) uniporter in the molecular targets of mycotoxin-induced hepatotoxicity, as well as a reference for the research and development of related drugs and the treatment of related diseases.

Regulation of Cr(VI)-Induced Premature Senescence in L02 Hepatocytes by ROS-Ca2+-NF-κB Signaling

Stress-induced premature senescence may be involved in the pathogeneses of acute liver injury. Hexavalent chromium [Cr(VI)], a common environmental pollutant related to liver injury, likely leads to premature senescence in L02 hepatocytes. However, the underlying mechanisms regarding hepatocyte premature senility in Cr(VI) exposure remain poorly understood. In this study, we found that chronic exposure of L02 hepatocytes to Cr(VI) led to premature senescence characterized by increased β-galactosidase activity, senescence-associated heterochromatin foci, G1 phase arrest, and decreased cell proliferation. Additionally, Cr(VI)-induced senescent L02 hepatocytes showed upregulated inflammation-related factors, such as IL-6 and fibroblast growth factor 23 (FGF23), which also exhibited reactive oxygen species (ROS) accumulation derived from mitochondria accompanied with increased concentration of intracellular calcium ions (Ca²⁺) and activity of nuclear factor kappa B (NF-κB). Of note is that ROS inhibition by N-acetyl-Lcysteine pretreatment not only alleviated Cr(VI)-induced premature senescence but also reduced the elevated intracellular Ca²⁺, activated NF-κB, and secretion of IL-6/FGF23. Intriguingly, the toxic effect of Cr(VI) upon premature senescence of L02 hepatocytes and increased levels of IL-6/FGF23 could be partially reversed by the intracellular Ca²⁺ chelator BAPTA-AM pretreatment. Furthermore, by utilizing the NF-κB inhibitor pyrrolidine dithiocarbamate (PDTC), we confirmed that NF-κB mediated IL-6/FGF23 to regulate the Cr(VI)-induced L02 hepatocyte premature senescence, whilst the concentration of intracellular Ca²⁺ was not influenced by PDTC. To the best of our knowledge, our data reports for the first time the role of ROS-Ca²⁺-NF-κB signaling pathway in Cr(VI)-induced premature senescence. Our results collectively shed light on further exploration of innovative intervention strategies and treatment targeting Cr(VI)-induced chronic liver damage related to premature senescence.

Cr (VI) induces abnormalities in glucose and lipid metabolism through ROS/Nrf2 signaling

The hexavalent form of chromium, Cr (VI), has been associated with various diseases in humans. In this study, we examined the mechanisms underlying the effect of Cr (VI) on glucose and lipid metabolism in vivo and in vitro. We found that Cr (VI) induced abnormal liver function, increased fasting blood glucose (FBG), as well as glucose and insulin intolerance in mice. Furthermore, Cr (VI) decreased glucose-6-phosphate (G6P) level and glucose transporter-2 (GLUT2) expression, increased the levels of triglyceride (TG), low-density lipoprotein-cholesterol (LDL-C), reduced high-density lipoprotein-cholesterol (HDL-C), and increased sterol regulatory element-binding proteins 1 (SREBP1) and fat synthase (FAS) in vitro and in vivo. Moreover, Cr (VI) promoted intracellular ROS production in vitro, and induced reduction of antioxidant enzyme level and Nrf2/HO-1 expression in vitro and in vivo. Also, N-acetyl cysteine (NAC, effective antioxidant and free radical scavenger) pretreatment inhibited the production of intracellular ROS, significantly suppressed Cr (VI)-induced oxidative stress, lipid accumulation, decreased G6P and GLUT2, and improved impaired glucose tolerance and glucose and insulin intolerance caused by Cr (VI) in mice. Dh404 activated expression of Nrf2 decreased ROS level, increased HO-1 expression, ameliorated activity of the antioxidant enzyme, inhibited Cr (VI) increase of SREBP1, FAS level, and reduction of G6P and GLUT2. To sum up, these data suggest that dysregulation of ROS/Nrf2/HO-1 has an important role in Cr (VI)-induced glucose/lipid metabolic disorder.

Sulforaphane attenuates hexavalent chromium-induced cardiotoxicity via the activation of the Sesn2/AMPK/Nrf2 signaling pathway

Hexavalent chromium (Cr(vi)), the most toxic valence state of chromium, is widely present in industrial effluents and wastes. Sulforaphane (SFN), rich in Brassica genus plants, bears multiple biological activity. Wistar rats were used to explore the protective role of SFN against the cardiotoxicity of chronic potassium dichromate (K2Cr2O7) exposure and reveal the potential molecular mechanism. The data showed that SFN alleviated hematological variations, oxidative stress, heart dysfunction and structure disorder, and cardiomyocyte apoptosis induced by K2Cr2O7. Moreover, SFN reduced p53, cleaved caspase-3, Bcl2-associated X protein, nuclear factor kappa-B, and interleukin-1β levels, and increased Sesn2, nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1, NAD(P)H quinone oxidoreductase-1, and phosphorylated adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) levels. This study demonstrates that SFN ameliorates Cr(vi)-induced cardiotoxicity via activation of the Sesn2/AMPK/Nrf2 signaling pathway. SFN may be a protector against Cr(vi)-induced heart injury and a novel therapy for chronic Cr(vi) exposure.

Blockage of ROS-ERK-DLP1 signaling and mitochondrial fission alleviates Cr(VI)-induced mitochondrial dysfunction in L02 hepatocytes

Hexavalent chromium [Cr(VI)] is a common heavy metal pollutant widely used in various industrial fields. It is well known that mitochondria are the most vulnerable targets of heavy metals, but the key molecule/event that directly mediated mitochondrial dysfunction after Cr(VI) exposure is still unclear. The present study was aimed to explore whether Cr(VI) exposure could affect the mitochondrial fission/fusion process, and whether the related abnormal mitochondrial dynamics have been implicated in Cr(VI)-induced mitochondrial dysfunction. We found that the mitochondrial dysfunction caused by Cr(VI) exposure was characterized by decreased mitochondrial respiratory chain complex (MRCC) I/II activities and levels, collapsed mitochondrial membrane potential (MMP), depleted ATP, and increased reactive oxygen species (ROS) level. Cr(VI) induced abnormal mitochondrial fission/fusion events, the antioxidant Nacetyl-L-cysteine (NAC) restored the abnormal mitochondrial function as well as the fission/fusion dynamics. ROS was the up-stream regulator of extracellular regulated protein kinases (ERK) signaling, and the application of a specific ERK1/2 inhibitor PD98059 confirmed that activation of ERK1/2 signaling was associated with the abnormal mitochondrial fission/fusion and mitochondrial dysfunction. We also demonstrated that treatment with dynamic-like protein 1 (DLP1)-siRNA rescued mitochondrial dysfunction in Cr(VI)-exposed L02 hepatocytes. We reached the conclusion that blockage of ROS-ERK-DLP1 signaling and mitochondrial fission alleviates Cr(VI)-induced mitochondrial dysfunction in L02 hepatocytes, which may provide the new avenue for developing effective strategies to protect against Cr(VI)-induced hepatotoxicity.

Role of mitochondrial damage in Cr(VI)‑induced endoplasmic reticulum stress in L‑02 hepatocytes

Although it is well reported that mitochondrial damage and endoplasmic reticulum (ER) stress (ERS) are involved in heavy metal‑induced cytotoxicity, the role of mitochondrial damage in hexavalent chromium [Cr(VI)]‑induced ERS and the correlation between the two have not been described and remain to be elucidated. The present study evaluated the ability of Cr(VI) to induce ERS in L‑02 hepatocytes, and subsequently examined the role of reactive oxygen species (ROS)‑mediated mitochondrial damage in Cr(VI)‑induced ERS. The findings demonstrated that Cr(VI) induced ERS, which was characterized by the upregulation of ERS‑associated genes and the substantial release of Ca2+ from the ER. The Cr(VI)‑induced mitochondrial production of ROS, by disturbing mitochondrial respiratory chain complexes I and II, may damage mitochondria directly by inducing mitochondrial permeability transition pore opening and mitochondrial membrane potential collapse. The results additionally demonstrated that Cr(VI) induced Ca2+ release from the ER through ROS/caveolin‑1/protein kinase B/inositol 1,4,5‑trisphosphate receptor signaling. The application of the ROS scavenger N‑acetyl‑cysteine confirmed the role of ROS in Cr(VI)‑mediated mitochondrial damage, ERS and apoptotic cell death. The data obtained demonstrated the role of mitochondrial damage in Cr(VI)‑induced ERS and provide novel insight into the elucidation of Cr(VI)‑induced cytotoxicity.

Cr(VI) induces cytotoxicity in vitro through activation of ROS-mediated endoplasmic reticulum stress and mitochondrial dysfunction via the PI3K/Akt signaling pathway

The occupational and environmental toxicant hexavalent chromium [Cr(VI)] can cause severe damage to the liver; however, the exact mechanisms associated with its toxicity have not been thoroughly demonstrated. In the present study, the underlying mechanisms of Cr(VI)-induced hepatotoxicity were investigated. Our results showed that Cr(VI) inhibited the growth and proliferation of L-02 hepatocytes. Further study revealed that Cr(VI) significantly induced S-phase cell cycle arrest and apoptosis accompanying with the overproduction of reactive oxygen species (ROS). Cr(VI)-induced apoptosis could be prevented by inhibiting ROS with N-acetyl-l-cysteine (NAC). Additionally, our data showed that Cr(VI)-induced endoplasmic reticulum (ER) stress and mitochondrial dysfunction were concentration- and time-dependent. Moreover, inhibition of C/EBA homologous protein (CHOP) expression by siRNA partially prevented Cr(VI)-induced cell apoptosis, mitochondrial dysfunction and ROS generation. We also found that Cr(VI) treatment inhibited the PI3K/Akt pathway in a concentration- and time-dependent manner. After using IGF-1 (50ng/mL), the specific agonist of the PI3K/AKT signaling pathway, the facilitating effects of Cr(VI) were depressed. This finding demonstrated the relationship between the PI3K/Akt pathway, ER stress and mitochondrial dysfunction. Collectively, these findings indicated that Cr(VI) increased ROS production. Increased ROS production may account for inhibition of the PI3K/Akt pathway and lead to ER stress and mitochondrial dysfunction, which consequently induces apoptosis in L-02 hepatocytes. This study provides novel insights into the molecular mechanisms of Cr(VI)-induced cytotoxicity.