The relationship between Cd-induced autophagy and lysosomal activation in WRL-68 cells

Role of Autophagy in Cadmium-Induced Hepatotoxicity and Liver Diseases

Cadmium (Cd) is a toxic pollutant that is associated with several severe human diseases. Cd can be easily absorbed in significant quantities from air contamination/industrial pollution, cigarette smoke, food, and water and primarily affects the liver, kidney, and lungs. Toxic effects of Cd include hepatotoxicity, nephrotoxicity, pulmonary toxicity, and the development of various human cancers. Cd is also involved in the development and progression of fatty liver diseases and hepatocellular carcinoma. Cd affects liver function via modulation of cell survival/proliferation, differentiation, and apoptosis. Moreover, Cd dysregulates hepatic autophagy, an endogenous catabolic process that detoxifies damaged cell organelles or dysfunctional cytosolic proteins through vacuole-mediated sequestration and lysosomal degradation. In this article, we review recent developments and findings regarding the role of Cd in the modulation of hepatotoxicity, autophagic function, and liver diseases at the molecular level.

Dysregulation of autophagy acts as a pathogenic mechanism of non-alcoholic fatty liver disease (NAFLD) induced by common environmental pollutants

Non-alcoholic fatty liver disease (NAFLD) has been the most common chronic liver disease in the world, including the developing countries. NAFLD is metabolic disease with significant lipid deposition in the hepatocytes of the liver, which is usually associated with oxidative stress, inflammation and fibrogenesis, and insulin resistance. Progressive NAFLD can develop into non-alcoholic steatohepatitis (NASH) or hepatocellular carcinoma. The current evidence proposes that environmental pollutants promote development and progression of NAFLD, and autophagy plays a vital role but is multifactorial affected in NAFLD. In this review, we analyzed on the regulations of common environmental pollutants on autophagy in NAFLD. To clarify the involved roles of autophagy, we discussed the dysregulation of autophagy by environmental pollutants in adipose tissue and gut, and their interactions with liver, as well as epigenetic regulation on autophagy by environmental pollutants. Furthermore, protective roles of potential therapeutic treatments on the multiple-hits of autophagy in NAFLD were descripted.

Gap Junction Intercellular Communication Negatively Regulates Cadmium-Induced Autophagy and Inhibition of Autophagic Flux in Buffalo Rat Liver 3A Cells

Cadmium is an important environmental pollutant that poses a serious threat to the health of humans and animals. A large number of studies have shown that the liver is one of the important target organs of cadmium. Stimulation of cells can lead to rapid changes in gap junction intercellular communication (GJIC) and autophagy. Previous studies have shown that cadmium can inhibit GJIC and induce autophagy. In order to understand the dynamic changes of GJIC and autophagy in the process of cadmium-induced hepatotoxic injury and the effects of GJIC on autophagy, a time-gradient model of cadmium cytotoxicity was established. The results showed that within 24 h of cadmium exposure, 5 μmol/L cadmium inhibited GJIC by down regulating the expression levels of connexin 43 (Cx43) and disturbing the localization of Cx43 in Buffalo rat liver 3A (BRL 3A) cells. In addition, cadmium induced autophagy and then inhibited autophagic flux in the later stage. During this process, inhibiting of GJIC could exacerbate the cytotoxic damage of cadmium and induce autophagy, but further blocked autophagic flux, promoting GJIC in order to obtain the opposite results.

Cadmium-induced cytotoxicity in mouse liver cells is associated with the disruption of autophagic flux via inhibiting the fusion of autophagosomes and lysosomes

Cadmium (Cd) is an important environmental pollutant. Previous studies have shown that Cd can induce liver cell injury; however, the toxicity mechanisms of Cd have not been fully elucidated. This study aimed to further confirm the hepatotoxic effects of Cd in mouse liver cells by various methods both in vivo and in vitro. In addition, it found that Cd induced autophagy but also caused autophagy blockade, and autophagy blockade intensified Cd-induced injury in liver cells. Subsequently, the study investigated the effects of Cd on lysosomes and found that Cd induced lysosomal acidification, promoted the expression of lysosomal-associated membrane protein 2 and lysosomal hydrolase cathepsin B both in vivo and in vitro, and enhanced the lysosomal degradation capacity. It indicated that Cd triggered lysosomal activation. However, the fusion of autophagosomes with lysosomes was inhibited by Cd both in vivo and in vitro. Next, the expression of Rab7, a key protein that regulates autophagosome-lysosome fusion, was examined. Cd was found to inhibit Rab7 expression both in vivo and in vitro. In conclusion, the results indicated that Cd obstructed the autophagic flux by inhibiting the fusion of autophagosomes with lysosomes, thus exacerbating the Cd-induced hepatotoxicity. Moreover, the molecular mechanism of Cd-induced inhibition of autophagosome-lysosome fusion is probably related to the Cd-induced downregulation of Rab7.

MicroRNA-216b-3p inhibits lung adenocarcinoma cell growth via regulating PDZ binding kinase/T-LAK-cell-originated protein kinase

Numerous studies have reported that microRNA (miR)-216b, as a tumor suppressor, is downregulated in a variety of cancer types. PDZ binding kinase (PBK)/T-LAK-cell-originated protein kinase (TOPK) is highly expressed in various types of human cancer, including lung cancer. The expression of miR-216b-3p and its potential roles in lung adenocarcinoma are still unclear and no research has been conducted into the association between miR-216b-3p and PBK/TOPK. Thus, the present study aimed to investigate the expression and role of miR-216b-3p in lung adenocarcinoma and to explore whether PBK/TOPK is involved in the underlying mechanisms of lung adenocarcinoma. The expression of miR-216b-3p in lung adenocarcinoma cell lines was detected. PBK/TOPK protein expression levels were also determined within lung adenocarcinoma cell lines. To investigate the association between miR-216b-3p and PBK/TOPK, TargetScan analysis was performed; PBK was predicted to be a potential target gene of miR-216b-3p, and a dual luciferase reporter assay was applied to confirm this prediction. To investigate the role of miR-216b-3p in lung adenocarcinoma, a lung adenocarcinoma cell line (GLC-82) was transfected with miR-216b-3p mimic or its negative control. An MTT assay was applied to detect cell proliferation, and cell apoptosis was analyzed by flow cytometry. Western blot analysis was performed to determine the protein expression levels of associated proteins. The results of the present study suggested that miR-216b-3p was downregulated in lung adenocarcinoma cell lines and PBK/TOPK was highly expressed in lung adenocarcinoma cells. miR-216b-3p directly targets PBK and negatively regulates its expression. miR-216b-3p overexpression may inhibit GLC-82 cell proliferation and induce cell apoptosis. In addition, miR-216b-3p overexpression may increase p53 and p21 expression, and prevent p38 MAPK activation. These effects on GLC-82 cells caused by miR-216b-3p overexpression may be eliminated by PBK/TOPK overexpression. In conclusion, miR-216b-3p was downregulated in lung adenocarcinoma and may function as a tumor suppressor by inhibiting cell growth via regulating PBK/TOPK expression.

Effects of elevated CO2 levels on subcellular distribution of trace metals (Cd and Cu) in marine bivalves

Hypercapnia (elevated CO₂ levels) and pollution with trace metals such as Cu and Cd are common stressors in estuarine habitats that can negatively affect physiology and health of marine organisms. Hypercapnia can modulate toxicity of trace metals including Cu and Cd; however, the physiological and cellular mechanisms of the metal-CO₂ interactions are not well understood. We investigated the effects of elevated P_CO2 (∼800 and 2000μatm) and metal exposure (50μgl^-1 of Cu or Cd) on subcellular distribution of metals in two common species of marine bivalves, Eastern oysters Crassostrea virginica and hard shell clams Mercenaria mercenaria. Oysters accumulated higher burdens of Cu and Cd in the gill tissues compared to clams. In both studied species, Cu was predominantly associated with the metabolically active cell compartments (mitochondria, lysosomes, microsomes and cytosolic enzymes), with a modest fraction sequestered by metallothioneins (∼30%) and the insoluble metal-containing granules (MCG) (∼15-20%). Unlike Cu, Cd was largely sequestered by metallothioneins (∼60-70%), with a relatively small fraction associated with the organelles and the cytosolic enzymes. Mitochondria were the main intracellular target for trace metals accumulating higher concentrations of Cd (and in the case of oysters - of Cu) than other organelles or cytosolic enzymes. Cu accumulation in the metabolically active cellular compartments was independent of the CO₂ levels, while Cd content of the organelles and cytosolic enzymes increased at elevated P_CO2 in both studied species indicating that hypercapnia may enhance cellular toxicity of Cd in bivalves. Hypercapnia suppressed the sequestration capacity of metallothioneins for Cu and Cd in oysters but increased Cu and Cd load in clam metallothioneins. Thus, metal-induced metabolic injury in oysters may be exaggerated by hypercapnia which enhances metal accumulation in the potentially sensitive intracellular fractions and suppresses the metal detoxification capacity. In contrast, clams appear to be more resistant to the combined effects of hypercapnia and metal exposure reflecting more efficient and robust detoxification mechanisms of this species.

Psorinum 6 × triggers apoptosis signals in human lung cancer cells

OBJECTIVE

To provide in vitro evidence of Psorinum treatment against cancer cells in a controlled study.

METHODS

Effects of homeopathic Psorinum 6× on cell viability were initially determined in several cancer cell lines, including A549, HepG2 and MCF-7, using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and an ethanol 6× control. The cell line that exhibited highest inhibition was selected and used in the following experiments. A range of Psorinum 6× doses was used to explore treatment effects on cell cycle arrest, cell death (apoptosis), generation of reactive oxygen species (ROS) and change in mitochondrial membrane potential (MMP) using flow cytometry and fluorescence microscopy, respectively. Expression of several signal proteins related to apoptosis and cell survival were quantified with Western blotting and confocal microscopy. Further, circular dichroism (CD) spectroscopy was used to determine possible drug-DNA interactions, as well as the induction of conformational changes.

RESULTS

Treatment of cancer cell lines with Psorinum showed greater anticancer effects in A549 cells than in others. In A549 cells Psorinum treatment inhibited cell proliferation at 24 h after treatment, and arrested cell cycle at sub-G1 stage. It also induced ROS generation, MMP depolarization, morphological changes and DNA damage, as well as externalization of phosphatidyl serine. Further, increases in p53 expression, Bax expression, cytochrome c release, along with reduction of Bcl-2 level and caspase-3 activation were observed after Psorinum 6× treatment, which eventually drove A549 cells towards the mitochondria-mediated caspase-3-dependent pathway. CD spectroscopy revealed direct interaction of Psorinum with DNA, using calf thymus-DNA as target.

CONCLUSION

Psorinum 6× triggered apoptosis in A549 cells via both up- and down-regulations of relevant signal proteins, including p53, caspase-3, Bax and Bcl-2.

Palmitoyl-ceramide accumulation with necrotic cell death in A549 cells, followed by a steep increase in sphinganine content

Ceramides (Cers) have recently been identified as key signaling molecules that mediate biological functions such as cell growth, differentiation, senescence, apoptosis, and autophagy. However, the functions of Cer accumulation in necrotic cell death remain unknown. The aim of this study was to clarify the relationship between Cer accumulation with inhibition of the conversion pathway of Cer and concomitant necrotic cell death. In order to minimize the effect of apoptosis against necrotic cell death, A549 cells having the inhibiting effect of caspase 9 by survivin were used in this study. Consequently, Cer accumulation in A549 cells would likely be associated with a pathway other than the mitochondrial caspase-dependent pathway of apoptosis. Here, we showed that the dual addition of a glucosyl-Cer synthase inhibitor and a ceramidase inhibitor to A549 cell culture induced palmitoyl-Cer accumulation with Cer synthase 5 expression and necrotic cell death with lysosomal rupture together with leakage of cathepsin B/alkalization after 2–3 h, although it is unknown in this study whether the necrotic cell death was caused by the lysosomal rupture. This Cer accumulation was followed by a steep increase in sphinganine base levels via the activation of serine palmitoyltransferase activity brought about by the increase in palmitoyl-coenzyme A concentration as a substrate after 5–6 h. The increase in palmitoyl-coenzyme A concentration was achieved by activation of the fatty acid synthetic pathway from acetyl coenzyme A.

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Palmitoylceramide accumulation with necrosis is studied.

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The accumulation is with ceramide synthase 5 expression.

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The accumulation is followed by high sphinganine levels.