Effect of treatment with cadmium on structure-function relationships in rat liver mitochondria: studies on oxidative energy metabolism and lipid/phospholipids profiles

Integrated metabolomic and transcriptomic analysis reveals perturbed glycerophospholipid metabolism in mouse neural stem cells exposed to cadmium

Cadmium (Cd) is a ubiquitous heavy metal with neurotoxicity. Our previous study reported that Cd could inhibit the proliferation of mouse neural stem cells (mNSCs). However, the underlying mechanisms are obscure. In recent years, the rapid growth of multi-omics techniques enables us to explore the cellular responses that occurred after toxicant exposure at the molecular level. In this study, we used a combination of metabolomics and transcriptomics approaches to investigate the effects of exposure to Cd on mNSCs. After treatment with Cd, the metabolites and transcripts in mNSCs changed significantly with 110 differentially expressed metabolites and 2135 differentially expressed genes identified, respectively. The altered metabolites were mainly involved in glycerophospholipid metabolism, arginine and proline metabolism, arginine biosynthesis, glyoxylate and dicarboxylate metabolism. Meanwhile, the transcriptomic data demonstrated perturbed membrane function and signal transduction. Furthermore, integrated analysis of metabolomic and transcriptomic data suggested that glycerophospholipid metabolism might be the major metabolic pathway affected by Cd in mNSCs. More interestingly, the supplementation of lysophosphatidylethanolamine (LPE) attenuated Cd-induced mitochondrial impairment and the inhibition of cell proliferation and differentiation in mNSCs, further supporting our analysis. Overall, the study provides new insights into the mechanisms of Cd-induced neurotoxicity.

Metabolomics analysis of the effects of quercetin on Cd-induced hepatotoxicityin rats

Cadmium(Cd) is known to cause damage to the liver. In this study, metabolomics technology was used to investigate the effect of quercetin(QE) on Cd-induced hepatotoxicity. A total of 60 male SD rats were randomly divided into the following 6 groups: control group (C), low and high dose QE group (Q1: 10 mg/kg·bw, Q2: 50 mg/kg·bw), Cd group (D), low and high dose QE and Cd combined intervention group (DQ1, DQ2). The rats were given Cd chloride (CdCl₂) at a concentration of 40 mg/L through free drinking water. After 12 weeks of treatment, liver samples of rats were collected for metabonomic analysis. A total of 12 metabolites were identified, the intensities of PC(18:0/14:1(9Z)) and Arachidonate acid were decreased in the Cd-treated group (p < 0.01), whereas the intensities of Chenodeoxyglycocholic acid, Cholic acid, Taurochenodesoxycholic acid, Glycocholic acid, Prostaglandin D2, 15-Deoxy-d-12,14-PGJ2, Oxidized glutathione, Cholesterol, Protoporphyrin IX, Bilirubinwere increased significantly in the Cd-treated group compared with group C(p < 0.01). When rats were given high doses of QE and Cd at the same time, the intensity of the above metabolites was significantly restored in group DQ2. Results suggest that The protective effect of QE on Cd-induced liver injury is associated with antioxidant activity of QE, as well as QE can regulates hepatic bile acid metabolism by affecting FXR and BSEP, and regulates AA metabolism by inhibiting Cd-induced activities of COX-2 and PLA2.

Cadmium-Induced Cytotoxicity: Effects on Mitochondrial Electron Transport Chain

Cadmium (Cd) is a well-known heavy metal and environmental toxicant and pollutant worldwide, being largely present in every kind of item such as plastic (toys), battery, paints, ceramics, contaminated water, air, soil, food, fertilizers, and cigarette smoke. Nowadays, it represents an important research area for the scientific community mainly for its effects on public health. Due to a half-life ranging between 15 and 30 years, Cd owns the ability to accumulate in organs and tissues, exerting deleterious effects. Thus, even at low doses, a Cd prolonged exposure may cause a multiorgan toxicity. Mitochondria are key intracellular targets for Cd-induced cytotoxicity, but the underlying mechanisms are not fully elucidated. The present review is aimed to clarify the effects of Cd on mitochondria and, particularly, on the mitochondrial electron transport chain.

Cell organelles as targets of mammalian cadmium toxicity

Ever increasing environmental presence of cadmium as a consequence of industrial activities is considered a health hazard and is closely linked to deteriorating global health status. General animal and human cadmium exposure ranges from ingestion of foodstuffs sourced from heavily polluted hotspots and cigarette smoke to widespread contamination of air and water, including cadmium-containing microplastics found in household water. Cadmium is promiscuous in its effects and exerts numerous cellular perturbations based on direct interactions with macromolecules and its capacity to mimic or displace essential physiological ions, such as iron and zinc. Cell organelles use lipid membranes to form complex tightly-regulated, compartmentalized networks with specialized functions, which are fundamental to life. Interorganellar communication is crucial for orchestrating correct cell behavior, such as adaptive stress responses, and can be mediated by the release of signaling molecules, exchange of organelle contents, mechanical force generated through organelle shape changes or direct membrane contact sites. In this review, cadmium effects on organellar structure and function will be critically discussed with particular consideration to disruption of organelle physiology in vertebrates.

Respiratory complex II in mitochondrial dysfunction-mediated cytotoxicity: Insight from cadmium

In the present work we studied action of several inhibitors of respiratory complex II (CII) of mitochondrial electron transport chain, namely malonate and thenoyltrifluoroacetone (TTFA) on Cd²⁺-induced toxicity and cell mortality, using two rat cell lines, pheochromocytoma PC12 and ascites hepatoma AS-30D and isolated rat liver mitochondria (RLM). It was shown that malonate, an endogenous competitive inhibitor of dicarboxylate-binding site of CII, restored in part RLM respiratory function disturbed by Cd²⁺. In particular, malonate increased both phosphorylating and maximally uncoupled respiration rates in KCl medium in the presence of CI substrates as well as palliated changes in basal and resting state respiration rates produced by the heavy metal on the mitochondria energized by CI or CII substrates. Notably, malonate enhanced Cd²⁺-induced swelling of the mitochondria energized by CI substrates in KCl and, in a much lesser extent and at higher [Cd²⁺], in sucrose media but did not influence on the Cd²⁺ effects in NaCl medium. Besides, malonate did not affect swelling in sucrose media of RLM energized by CIV substrates under using of Cd²⁺ or Ca²⁺ whereas it strongly increased the mitochondrial swelling produced by selenite. In addition, malonate produced some protection against Cd²⁺-promoted necrotic death of AS-30D and PC12 cells and reduced intracellular reactive oxygen species (ROS) formation evoked by Cd²⁺ in PC12 cells. Importantly, TTFA, an irreversible competitive inhibitor of Q-binding site of CII, per se induced apoptosis of AS-30D cells which was inhibited by co-treatment with Cd²⁺ as well as decreased the Cd²⁺-enhanced intracellular ROS formation. In turn, decylubiquinone (dUb) at low μM concentrations did not protect AS-30D cells against the Cd²⁺-induced necrosis and enhanced the Cd²⁺-induced apoptosis of the cells. High μM concentrations of dUb were highly toxic for the cells. As consequence, the findings give new evidence indicative of critical involvement of CII in mechanism(s) of Cd²⁺-produced cytotoxicity and support the notion on CII as a perspective pharmacological target in mitochondria dysfunction-mediated conditions and diseases.

Integrated redox proteomics and metabolomics of mitochondria to identify mechanisms of cd toxicity

Cadmium (Cd) exposure contributes to human diseases affecting liver, kidney, lung, and other organ systems, but mechanisms underlying the pleotropic nature of these toxicities are poorly understood. Cd accumulates in humans from dietary, environmental (including cigarette smoke), and occupational sources, and has a twenty-year biologic half-life. Our previous mouse and cell studies showed that environmental low-dose Cd exposure altered protein redox states resulting in stimulation of inflammatory signaling and disruption of the actin cytoskeleton system, suggesting that Cd could impact multiple mechanisms of disease. In the current study, we investigated the effects of acute Cd exposure on the redox proteome and metabolome of mouse liver mitochondria to gain insight into associated toxicological mechanisms and functions. We analyzed redox states of liver mitochondrial proteins by redox proteomics using isotope coded affinity tag (ICAT) combined mass spectrometry. Redox ICAT identified 2687 cysteine-containing peptides (peptidyl Cys) of which 1667 peptidyl Cys (657 proteins) were detected in both control and Cd-exposed samples. Of these, 46% (1247 peptidyl Cys, 547 proteins) were oxidized by Cd more than 1.5-fold relative to controls. Bioinformatics analysis using MetaCore software showed that Cd affected 86 pathways, including 24 Cys in proteins functioning in branched chain amino acid (BCAA) and 14 Cys in proteins functioning in fatty acid (acylcarnitine/carnitine) metabolism. Consistently, high-resolution metabolomics data showed that Cd treatment altered levels of BCAA and carnitine metabolites. Together, these results show that mitochondrial protein redox and metabolites are targets in Cd-induced hepatotoxicity. The results further indicate that redox proteomics and metabolomics can be used in an integrated systems approach to investigate complex disease mechanisms.

The potential protective role of lysophospholipid mediators in nephrotoxicity induced by chronically exposed cadmium

Cadmium is a hazardous metal whose chronic exposure induces renal failure due to fibrosis, but the mechanisms are not well known. In this study we analyzed the molecular species of lysophosphatidic acid (LPA) and related phospholipids, together with their metabolic enzyme activity, in plasma from Wistar rats exposed up to 300ppm Cd(2+) in drinking water for 114days. Exposure of 300ppm Cd(2+) for 114days enhanced autotoxin (ATX)/lysophospholipase D activity, but significantly lowered the total levels of LPA and lysophosphatidylethanolamine. Interestingly, the total level of sphingosine-1-phosphate (S1P) was elevated dose-dependently by Cd(2+). Cultured rat kidney-derived interstitial fibroblast cells, NRK49F cells and proximal epithelial cells, NRK52E cells, were both responsive to the protective action of LPA or S1P against Cd(2+) toxicity. The former cell expresses ATX RNA. In conclusion, the elevation of LPA-producing enzyme activity and S1P concentrations in plasma after exposure of rats to Cd(2+) would protect from the renal toxicity of Cd(2+).

Zebrafish: a model animal for analyzing the impact of environmental pollutants on muscle and brain mitochondrial bioenergetics

Mercury, anthropogenic release of uranium (U), and nanoparticles constitute hazardous environmental pollutants able to accumulate along the aquatic food chain with severe risk for animal and human health. The impact of such pollutants on living organisms has been up to now approached by classical toxicology in which huge doses of toxic compounds, environmentally irrelevant, are displayed through routes that never occur in the lifespan of organisms (for instance injecting a bolus of mercury to an animal although the main route is through prey and fish eating). We wanted to address the effect of such pollutants on the muscle and brain mitochondrial bioenergetics under realistic conditions, at unprecedented low doses, using an aquatic model animal, the zebrafish Danio rerio. We developed an original method to measure brain mitochondrial respiration: a single brain was put in 1.5 mL conical tube containing a respiratory buffer. Brains were gently homogenized by 13 strokes with a conical plastic pestle, and the homogenates were immediately used for respiration measurements. Skinned muscle fibers were prepared by saponin permeabilization. Zebrafish were contaminated with food containing 13 μg of methylmercury (MeHg)/g, an environmentally relevant dose. In permeabilized muscle fibers, we observed a strong inhibition of both state 3 mitochondrial respiration and cytochrome c oxidase activity after 49 days of MeHg exposure. We measured a dramatic decrease in the rate of ATP release by skinned muscle fibers. Contrarily to muscles, brain mitochondrial respiration was not modified by MeHg exposure although brain accumulated twice as much MeHg than muscles. When zebrafish were exposed to 30 μg/L of waterborne U, the basal mitochondrial respiratory control ratio was decreased in muscles after 28 days of exposure. This was due to an increase of the inner mitochondrial membrane permeability. The impact of a daily ration of food containing gold nanoparticles of two sizes (12 and 50 nm) was investigated at a very low dose for 60 days (40 ng gold/fish/day). Mitochondrial dysfunctions appeared in brain and muscle for both tested sizes. In conclusion, at low environmental doses, dietary or waterborne heavy metals impinged on zebrafish tissue mitochondrial respiration. Due to its incredible simplicity avoiding tedious and time-consuming mitochondria isolation, our one-pot method allowing brain respiratory analysis should give colleagues the incentive to use zebrafish brain as a model in bioenergetics. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.