Alterations of rat liver mitochondrial oxidative phosphorylation and calcium uptake by benzo[a]pyrene

A New Quinone-Based Inhibitor of Mitochondrial Complex I in D-Conformation, Producing Invasion Reduction and Sensitization to Venetoclax in Breast Cancer Cells

Mitochondrial Complex I plays a crucial role in the proliferation, chemoresistance, and metastasis of breast cancer (BC) cells. This highlights it as an attractive target for anti-cancer drugs. Using submitochondrial particles, we identified FRV-1, an ortho-carbonyl quinone, which inhibits NADH:duroquinone activity in D-active conformation and reduces the 3ADP state respiration dependent on Complex I, causing mitochondrial depolarization, ATP drop, increased superoxide levels, and metabolic remodeling towards glycolysis in BC cells. Introducing methyl groups at FRV-1 structure produced analogs that acted as electron acceptors at the Complex I level or increased the inhibitory effect of FCCP-stimulated oxygen consumption rate, which correlated with their redox potential, but increased toxicity on RMF-621 human breast fibroblasts was observed. FRV-1 was inactive in the naphthoquinone oxidoreductase 1 (NOQ1)-positive BC cell line, MCF7, but the sensitivity was recovered by dicoumarol, a NOQ1 inhibitor, suggesting that FRV-1 is a NOQ1 substrate. Importantly, FRV-1 selectively inhibited the proliferation, migration, and invasion of NQO1 negative BC cell, MDA-MB-231, in an OXPHOS- and ROS-dependent manner and sensitized it to the BH3 mimetic drug venetoclax. Overall, FRV-1 is a novel Complex I inhibitor in D-active conformation, blocking possibly the re-activation to A-state, producing selective anti-cancer effects in NQO1-negative BC cell lines.

Apoptosis and blood-testis barrier disruption during male reproductive dysfunction induced by PAHs of different molecular weights

The association between polycyclic aromatic hydrocarbons (PAHs) and male reproductive dysfunction has attracted increasing attention. The purpose of this study was to compare the male reproductive toxicity of multiple PAHs and to investigate the underlying molecular mechanisms. TM4 cells (mouse testicular Sertoli cells, SCs) were treated with benzo(a)pyrene (BaP), pyrene (Py), fluoranthene (Fl) and phenanthrene (Phe) (0, 0.1, 1, 10, 50, or 100 μM) for varying time points (4, 12, 24, or 48 h), and male C57BL/6 mice were administered BaP and Py (0, 10, 50, or 100 mg/kg body weight) for 14 days based on the cell experimental results. Histopathological examination, western blotting, ELISA, biochemical assays, RT-PCR, flow cytometry, JC-1 staining and trans-epithelium electrical resistance (TEER) measurements were used to assess apoptosis, blood-testis barrier (BTB) integrity, intracellular calcium ([Ca²⁺]_i) concentrations and oxidative stress (OS). The results revealed that the mRNA levels and enzymatic activities of CYP450 and GST family members; levels of ROS, MDA, cleaved caspase 3 (c-caspase 3), caspase 9, Bax, and cytochrome C (CytC); and numbers of TUNEL-positive cells were significantly increased by BaP and Py, while levels of AhR, GSH, SOD, CAT, Bcl-2 and ΔΨm were decreased. Additionally, BaP and Py notably interfered with tight junctions (TJs) and adherens junctions (AJs) in the BTB. Intriguingly, BaP, but not Py, induced [Ca²⁺]_i overload and gap junction (GJ) destruction. There was no dramatic effect of Fl and/or Phe on any of the above parameters except that slight cytotoxicity was observed with higher doses of Fl. Collectively, these findings showed that BaP and Py elicited SC apoptosis and BTB disruption involving mitochondrial dysfunction and OS, but [Ca²⁺]_i fluctuation and GJ injury were only observed with BaP-induced reproductive toxicity. The male reproductive toxicity of the selected PAHs was ranked in the order of BaP > Py > Fl > Phe.

Filling the gap between chemical carcinogenesis and the hallmarks of cancer: A temporal perspective

BACKGROUND

Cancer is believed to arise through the perturbation of pathways and the order of pathway perturbation events can enhance understanding and evaluation of carcinogenicity. This order has not been examined so far, and this study aimed to fill this gap by attempting to gather evidence on the potential temporal sequence of events in carcinogenesis.

DESIGN

The methodology followed was to discuss first the temporal sequence of hallmarks of cancer from the point of view of pathological specimens of cancer (essentially branched mutations) and then to consider the hallmarks of cancer that one well-known carcinogen, benzo(a)pyrene, can modify.

RESULTS

Even though the sequential order of driving genetic alterations can vary between and within tumours, the main cancer pathways affected are almost ubiquitous and follow a generally common sequence: resisting cell death, insensitivity to antigrowth signals, sustained proliferation, deregulated energetics, replicative immortality and activation of invasion and metastasis. The first 3 hallmarks can be regarded as almost simultaneous while angiogenesis and avoiding immune destruction are perhaps the only hallmarks with a varying position in the above sequence.

CONCLUSIONS

Our review of hallmarks of cancer and their temporal sequence, based on mutational spectra in biopsies from different cancer sites, allowed us to propose a hypothetical temporal sequence of the hallmarks. This sequence can add molecular support to the evaluation of an agent as a carcinogen as it can be used as a conceptual framework for organising and evaluating the strength of existing evidence.

Mitochondria and mitochondrial DNA as relevant targets for environmental contaminants

The mitochondrial DNA (mtDNA) is a closed circular molecule that encodes, in humans, 13 polypeptides components of the oxidative phosphorylation complexes. Integrity of the mitochondrial genome is essential for mitochondrial function and cellular homeostasis, and mutations and deletions in the mtDNA lead to oxidative stress, mitochondrial dysfunction and cell death. In vitro and in situ studies suggest that when exposed to certain genotoxins, mtDNA accumulates more damage than nuclear DNA, likely owing to its organization and localization in the mitochondrial matrix, which tends to accumulate lipophilic, positively charged molecules. In that regard, several relevant environmental and occupational contaminants have physical-chemical characteristics that indicate that they might accumulate in mitochondria and target mtDNA. Nonetheless, very little is known so far about mtDNA damage and mitochondrial dysfunction due to environmental exposure, either in model organisms or in humans. In this article, we discuss some of the characteristics of mtDNA which render it a potentially relevant target for damage by environmental contaminants, as well as possible functional consequences of damage/mutation accumulation. In addition, we review the data available in the literature focusing on mitochondrial effects of the most common classes of environmental pollutants. From that, we conclude that several lines of experimental evidence support the idea that mitochondria and mtDNA are susceptible and biologically relevant targets for pollutants, and more studies, including mechanistic ones, are needed to shed more light into the contribution of mitochondrial dysfunction to the environmental and human health effects of chemical exposure.

Environmental carcinogenesis and pH homeostasis: Not only a matter of dysregulated metabolism

According to the World Health Organization, around 20% of all cancers would be due to environmental factors. Among these factors, several chemicals are indeed well recognized carcinogens. The widespread contaminant benzo[a]pyrene (B[a]P), an often used model carcinogen of the polycyclic aromatic hydrocarbons' family, has been suggested to target most, if not all, cancer hallmarks described by Hanahan and Weinberg. It is classified as a group I carcinogen by the International Agency for Research on Cancer; however, the precise intracellular mechanisms underlying its carcinogenic properties remain yet to be thoroughly defined. Recently, the pH homeostasis, a well known regulator of carcinogenic processes, was suggested to be a key actor in both cell death and Warburg-like metabolic reprogramming induced upon B[a]P exposure. The present review will highlight those data with the aim of favoring research on the role of H⁺ dynamics in environmental carcinogenesis.

The environmental carcinogen benzo[a]pyrene induces a Warburg-like metabolic reprogramming dependent on NHE1 and associated with cell survival

Cancer cells display alterations in many cellular processes. One core hallmark of cancer is the Warburg effect which is a glycolytic reprogramming that allows cells to survive and proliferate. Although the contributions of environmental contaminants to cancer development are widely accepted, the underlying mechanisms have to be clarified. Benzo[a]pyrene (B[a]P), the prototype of polycyclic aromatic hydrocarbons, exhibits genotoxic and carcinogenic effects, and it is a human carcinogen according to the International Agency for Research on Cancer. In addition to triggering apoptotic signals, B[a]P may induce survival signals, both of which are likely to be involved in cancer promotion. We previously suggested that B[a]P-induced mitochondrial dysfunctions, especially membrane hyperpolarization, might trigger cell survival signaling in rat hepatic epithelial F258 cells. Here, we further characterized these dysfunctions by focusing on energy metabolism. We found that B[a]P promoted a metabolic reprogramming. Cell respiration decreased and lactate production increased. These changes were associated with alterations in the tricarboxylic acid cycle which likely involve a dysfunction of the mitochondrial complex II. The glycolytic shift relied on activation of the Na⁺/H⁺ exchanger 1 (NHE1) and appeared to be a key feature in B[a]P-induced cell survival related to changes in cell phenotype (epithelial-to-mesenchymal transition and cell migration).

Impact of dispersed fuel oil on cardiac mitochondrial function in polar cod Boreogadus saida

In this study, impact of dispersed oil on cardiac mitochondrial function was assessed in a key species of Arctic marine ecosystem, the polar cod Boreogadus saida. Mature polar cod were exposed during 48 h to dispersed oil (mechanically and chemically) and dispersants alone. The increase observed in ethoxyresorufin-O-deethylase activity and polycyclic aromatic hydrocarbon metabolites in bile indicated no difference in contamination level between fish exposed to chemical or mechanical dispersion of oil. Oil induced alterations of O2 consumption of permeabilised cardiac fibres showing inhibitions of complexes I and IV of the respiratory chain. Oil did not induce any modification of mitochondrial proton leak. Dispersants did not induce alteration of mitochondrial activity and did not increase oil toxicity. These data suggest that oil exposure may limit the fitness of polar cod and consequently could lead to major disruption in the energy flow of polar ecosystem.

Influence of dihydropyridine calcium antagonist nitrendipine on benzo(a)pyrene-induced oxidative stress

The aim of this study was to investigate the influence of nitrendipine (NIT), a dihydropyridine derived calcium channel antagonist, on polycyclic aromatic hydrocarbon benzo(a)pyrene (BAP)-induced oxidative stress. Male Sprague Dawley rats (155-220 g) were divided into four groups: Control (corn oil, i.p.); BAP (200 mg/kg, i.p.), BAP + NIT (200 mg/kg, i.p. + 50 mg/kg, i.p.), and NIT (50 mg/kg, i.p.) groups. Twenty-four hours after the injection of BAP, the rats were sacrificed and blood samples, liver, lung, and brain tissues were removed to determine serum alanine transaminase (ALT), aspartate transferase (AST), and gamma-glutamyltransferase (GGT) activities and tissue thiobarbituric acid reactive substances (TBARS), glutathione (GSH), and superoxide dismutase (SOD) levels. BAP significantly elevated serum ALT and TBARS levels in all tissues. However, NIT pre-treatment protected against increasing TBARS levels in lung and brain tissues. In addition, NIT pre-treatment significantly increased SOD levels in lung and liver tissues, as well as GSH levels in the lungs, compared to the BAP group. Thus, in conclusion, further studies are required to confirm the protective effects of calcium channel blockers, especially in liver tissue.

Nuclear respiratory factor-1 is involved in mitochondrial dysfunction induced by benzo(a)pyrene in human bronchial epithelial cells

In this study, we investigated the role of nuclear respiratory factor-1(NRF-1) in benzo(a)pyrene (BaP)-induced mitochondrial events in human bronchial epithelial cells (16HBE). Cytotoxicity was determined with MTT assay, and apoptosis was measured by flow cytometry. The results showed that BaP inhibited cell proliferation in a dose-dependent manner and induced apoptosis in 16HBE cells. Time-dependent reactive oxygen species (ROS) generation induced by BaP was observed in 16HBE cells. The loss of mitochondrial membrane permeability transition (MPT) was obtained by a laser scanning confocal microscope, and the decreasing ATP level was detected by a Cell-Titer-Glo(®) Luminescent Cell Viability Assay. Results of western blotting assay revealed that both NRF-1 and mitochondrial transcription factor A (mtTFA) decreased in 12-μM BaP-treated cells at both 12 and 24 hr. The results of RT-PCR indicate that NRF-1 and mtTFA mRNA in 16HBE cells were not changed after BaP treatment 12 or 24 hr. Down-regulation of NRF-1 by shRNA further reduced the loss of MPT and increased ROS generation in response to BaP treatment. Therefore, our results demonstrate that NRF-1 is responsible for BaP-induced mitochondrial dysfunction in 16HBE cells and associated with the level of mtTFA protein, loss of MPT and ROS overproduction.

The effects of pyrene exposure on exercise performance, muscle contraction, and mitochondrial O(2) consumption in the leopard frog (Rana pipiens)

The present study exposed frogs to the PAH pyrene and measured exercise performance, muscle contractile ability, mitochondrial O(2) consumption, and membrane potential. Leopard frogs, Rana pipiens, were exposed for seven days in control or pyrene saturated water aquaria. Frogs were randomly placed into one of four groups: (i) pyrene-exposed exercised, (ii) control, exercised, (iii) pyrene-exposed, non-exercised, and (iv) control, non-exercised. Following the acute exposure, exercise duration, muscle contractile ability, blood gases and pH, glycogen levels, crossbridge formation and contractile length, and mitochondrial respiration were measured. The data revealed that pyrene exposure produced many adverse effects in Leopard frogs including significant reductions in exercise performance, muscle contractile ability, and alterations to muscle mitochondrial O(2) consumption and membrane potential. These data suggest that PAH exposure may limit survival for frogs in the wild by limiting foraging, mating, and predator avoidance behaviors.

Multiple apoptotic pathways induced by p53-dependent acidification in benzo[a]pyrene-exposed hepatic F258 cells

Polycyclic aromatic hydrocarbons (PAH), such as benzo[a]pyrene (B[a]P), are ubiquitous genotoxic environmental pollutants. Their DNA-damaging effects lead to apoptosis induction, through similar pathways to those identified after exposure to other DNA-damaging stimuli with activation of p53-related genes and the involvement of the intrinsic apoptotic pathway. However, at a low concentration of B[a]P (50 nM), our previous results pointed to the involvement of intracellular pH (pHi) variations during B[a]P-induced apoptosis in a rat liver epithelial cell line (F258). In the present work, we identified the mitochondrial F0F1-ATPase activity reversal as possibly responsible for pHi decrease. This acidification not only promoted executive caspase activation, but also activated leucocyte elastase inhibitor/leucocyte-derived DNase II (LEI/L-DNase II) pathway. p53 appeared to regulate mitochondria homeostasis, by initiating F0F1-ATPase reversal and endonuclease G (Endo G) release. In conclusion, a low dose of B[a]P induced apoptosis by recruiting a large panel of executioners apparently depending on p53 phosphorylation and, for some of them, on acidification.

Effects of shark hepatic stimulator substance on the function and antioxidant capacity of liver mitochondria in an animal model of acute liver injury

This study was carried out to investigate whether shark hepatic stimulator substance (HSS) can prevent acute liver injury and affect mitochondrial function and antioxidant defenses in a rat model of thioacetamide (TAA)-induced liver injury. The acute liver injury was induced by two intraperitoneal injections of TAA (400 mg/kg) in a 24 h interval. In the TAA plus shark HSS group, rats were treated with shark HSS (80 mg/kg) 1 h prior to each TAA injection. In this group, serum liver enzyme activities were significantly lower than those in the TAA group. The mitochondrial respiratory control ratio was improved, and the mitochondrial respiratory enzyme activities were increased in the TAA plus shark HSS group. The mitochondrial antioxidant enzyme activities and glutathione level were higher in the TAA plus shark HSS group than in the TAA group. These results suggest that the protective effect of shark HSS against TAA-induced acute liver injury may be a result of the restoration of the mitochondrial respiratory function and antioxidant defenses and decreased oxygen stress.

Differential display of hepatic mRNA from killifish (Fundulus heteroclitus) inhabiting a Superfund estuary

Fundulus heteroclitus (Atlantic killifish, mummichog) from a highly contaminated site on the Elizabeth River (VA, USA) are resistant to the toxicity of sediment from the site. However, the mechanistic changes that confer resistance to the toxicity are not yet well understood. We utilized differential display to identify mRNAs that are differentially expressed in hepatic tissue of male and female killifish from the Elizabeth River environment, compared to killifish from a non-contaminated reference site, King's Creek (VA, USA). Seventy-four differentially expressed mRNAs were initially identified (including sex and population-specific differences), and 65 of these were isolated and sequenced. A reverse northern blot array constructed of these cDNAs (plus an additional 15 previously sequenced mRNAs of interest) was used to confirm and quantify expression differences. High interindividual variability was observed in mRNA expression, but multiple differentially expressed mRNAs were identified, including 11 population-specific differences occurring in both sexes, 24 population-specific differences occurring in only one sex, and 22 sex-specific differences. Many of these differentially expressed mRNAs were novel, or not previously hypothesized to play a role in response to contaminant exposure. In addition, the results indicate that the effect of contaminated sediment exposure on the expression of a large proportion of the differentially expressed mRNAs was dependent on the sex of the fish.