Effects of cigarette smoke extracts on apoptosis and oxidative stress in two models of ovarian cancer in vitro

Proteomic analysis reveals that cigarette smoke exposure diminishes ovarian reserve in mice by disrupting the CREB1-mediated ovarian granulosa cell proliferation-apoptosis balance

Exposure to cigarette smoke (CS) adversely affects ovarian health and it is currently unknown how CS exposure causes ovarian injury. This study compared the differences in proteomics between CS exposure and healthy control groups using liquid chromatography-tandem mass spectrometry quantitative proteomics to further understand the molecular mechanism of ovarian cell injury in mice exposed to CS. Furthermore, western blotting and qPCR were carried out to validate the proteomic analysis outcomes. CREB1 was selected from the differentially expressed proteins, and then the down-regulation of CREB1 and phosphorylated CREB1(Ser133) expressions were confirmed in mice ovarian tissue and human ovarian granulosa cells (KGN cells) after CS exposure. In addition, the expressions of apoptosis-related proteins BCL-2 and BCL-XL were downregulated, and BAX expression was up-regulated. Moreover, the results of cellular immunofluorescence, flow cytometry, and transmission electron microscopy (TEM) showed that cigarette smoke extract (CSE) efficiently stimulated the production of reactive oxygen species, apoptosis, G1 phase arrest, mitochondrial membrane potential decreases, and ultrastructural changes in KGN cells. KG-501 (CREB inhibitor) aggravated CSE-induced mitochondrial dysfunction and apoptosis-proliferation imbalance in KGN cells mediated by down-regulated CREB1/BCL-2 axis. In addition, CREB1 over-expression partially restores mitochondrial dysfunction and apoptosis-proliferation imbalance of KGN cells induced by CSE. The results suggested that CSE diminished ovarian reserve in mice by disrupting the CREB1-mediated ovarian granulosa cell (GCs) proliferation-apoptosis balance and provided possible therapeutic targets for the clinical intervention of premature ovarian failure (POI) caused by CS exposure.

Role of the Nrf2 Signaling Pathway in Ovarian Aging: Potential Mechanism and Protective Strategies

The ovary holds a significant role as a reproductive endocrine organ in women, and its aging process bears implications such as menopause, decreased fertility, and long-term health risks including osteoporosis, cardiovascular disorders, and cognitive decline. The phenomenon of oxidative stress is tightly linked to the aging metabolic processes. More and more studies have demonstrated that oxidative stress impacts both physiologic and pathologic ovarian aging, and the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway plays a crucial role in regulating the antioxidant response. Furthermore, various therapeutic approaches have been identified to ameliorate ovarian aging by modulating the Nrf2 pathway. This review summarizes the important role of the Nrf2/ Kelch-like ECH-associated protein 1 (Keap1) signaling pathway in regulating oxidative stress and influencing ovarian aging. Additionally, it highlights the therapeutic strategies aimed at targeting the Nrf2/Keap1 pathway.

Establishment of a platform for measuring mitochondrial oxygen consumption rate for cardiac mitochondrial toxicity

The heart has an abundance of mitochondria since cardiac muscles require copious amounts of energy for providing continuous blood through the circulatory system, thereby implying that myocardial function is largely reliant on mitochondrial energy. Thus, cardiomyocytes are susceptible to mitochondrial dysfunction and are likely targets of mitochondrial toxic drugs. Various methods have been developed to evaluate mitochondrial toxicity by evaluating toxicological mechanisms, but an optimized and standardized assay for cardiomyocytes remains unmet. We have therefore attempted to standardize the evaluation system for determining cardiac mitochondrial toxicity, using AC16 human and H9C2 rat cardiomyocytes. Three clinically administered drugs (acetaminophen, amiodarone, and valproic acid) and two anticancer drugs (doxorubicin and tamoxifen) which are reported to have mitochondrial effects, were applied in this study. The oxygen consumption rate (OCR), which directly reflects mitochondrial function, and changes in mRNA levels of mitochondrial respiratory complex I to complex V, were analyzed. Our results reveal that exposure to all five drugs results in a concentration-dependent decrease in the basal and maximal levels of OCR in AC16 cells and H9C2 cells. In particular, marked reduction in the OCR was observed after treatment with doxorubicin. The reduction in OCR after exposure to mitochondrial toxic drugs was found to be associated with reduced mRNA expression in the mitochondrial respiratory complexes, suggesting that the cardiac mitochondrial toxicity of drugs is majorly due to dysfunction of mitochondrial respiration. Based on the results of this study, we established and standardized a protocol to measure OCR in cardiomyocytes. We expect that this standardized evaluation system for mitochondrial toxicity can be applied as basic data for establishing a screening platform to evaluate cardiac mitochondrial toxicity of drugs, during the developmental stage of new drug discovery.

Role of NRF2 in Ovarian Cancer

Among gynaecologic malignancies, ovarian cancer is one of the most dangerous, with a high fatality rate and relapse due to the occurrence of chemoresistance. Many researchers demonstrated that oxidative stress is involved in tumour occurrence, growth and development. Nuclear factor erythroid 2-related factor 2 (NRF2) is an important transcription factor, playing an important role in protecting against oxidative damage. Increased levels of Reactive Oxygen Species (ROS) activate NRF2 signalling, inducing the expression of antioxidant enzymes, such as haem oxygenase (HO-1), catalase (CAT), glutathione peroxidase (GPx) and superoxide dismutase (SOD), that protect cells against oxidative stress. However, NRF2 activation in cancer cells is responsible for the development of chemoresistance, inactivating drug-mediated oxidative stress that normally leads to cancer cells’ death. In this review, we report evidence from the literature describing the effect of NRF2 on ovarian cancer, with a focus on its function in drug resistance, NRF2 natural and synthetic modulators and its protective function in normal ovarian preservation.

Cigarette Smoke Exposure Inhibits Osteoclast Apoptosis via the mtROS Pathway

It is widely known that smoking is a risk factor for bone loss and plays a key role in osteopenia. Despite this well-known association, the mechanisms by which smoking affects bone have not been definitively established. Since smoking increases bone loss and potentially affects bone resorption in response to mechanical force, we investigated the impact of cigarette smoke on osteoclast numbers and underlying mechanisms in a mouse model of orthodontic tooth movement (OTM). The experimental group was exposed to once-daily cigarette smoke while the control group was not, and tooth movement distance and osteoclast numbers were assessed. In addition, the effect of cigarette smoke extract (CSE) on osteoclast precursor proliferation and osteoclast apoptosis was assessed in vitro. We found that cigarette smoke exposure enhanced bone remodeling stimulated by mechanical force and increased osteoclast numbers in vivo. Also, CSE increased the number of osteoclasts by inhibiting osteoclast apoptosis via the mitochondrial reactive oxygen species/cytochrome C/caspase 3 pathway in vitro. Moreover, exposure of mice to cigarette smoke affected bone marrow cells, leading to increased formation of osteoclasts in vitro. This study identifies a previously unknown mechanism of how smoking has a detrimental impact on bone.

The Role of Oxidative Stress and Natural Antioxidants in Ovarian Aging

The ovarian system comprises vital organs in females and is of great significance for the maintenance of reproductive potential and endocrine stability. Although complex pathogenesis undoubtedly contributes to ovarian aging, increasing attention is being paid to the extensive influence of oxidative stress. However, the role of oxidative stress in ovarian aging is yet to be fully elucidated. Exploring oxidative stress-related processes might be a promising strategy against ovarian aging. In this review, compelling evidence is shown that oxidative stress plays a role in the etiology of ovarian aging and promotes the development of other ovarian aging-related etiologies, including telomere shortening, mitochondrial dysfunction, apoptosis, and inflammation. In addition, some natural antioxidants such as quercetin, resveratrol, and curcumin have a protective role in the ovaries through multiple mechanisms. These findings raise the prospect of oxidative stress modulator-natural antioxidants as therapeutic interventions for delaying ovarian aging.

The relationship between endoplasmic reticulum stress and autophagy in apoptosis of BEAS-2B cells induced by cigarette smoke condensate

Cigarette smoke (CS) is one of the severe risk factors for the development of the pulmonary disease. However, the underlying mechanisms, especially the CS-induced the human bronchial epithelial cells (BEAS-2B) apoptosis related to endoplasmic reticulum stress (ERS) and autophagy, remains to be studied. This study aims to investigate the relationship between ERS and autophagy in apoptosis induced by CS condensate (CSC). BEAS-2B cells were stimulated with 0.02, 0.04 and 0.08 mg/ml CSC for 24 h to detect the ERS, autophagy and apoptosis. Then, ERS and autophagy of BEAS-2B cells were inhibited, respectively, by using 4-PBA and 3-MA, and followed by CSC treatment. The results showed that CSC decreased cell viability, increased cell apoptosis, elevated cleaved-caspase 3/pro-caspase 3 ratio and Bax expressions, but decreased Bcl-2 expressions. The GRP78 and CHOP expressions and LC3-II/LC3-I ratio were dose-dependently increased. The structure of the endoplasmic reticulum was abnormal and the number of autolysosomes was increased in BEAS-2B cells after CSC stimulation. The LC3-II/LC3-I ratio was decreased after ERS inhibition with 4-PBA, but GRP78 and CHOP expressions were enhanced after autophagy inhibition with 3-MA. CSC-induced apoptosis was further increased, Bax expressions and cleaved-caspase 3/pro-caspase 3 ratio were improved, but Bcl-2 expressions were decreased after 3-MA or 4-PBA treatment. In conclusion, the study indicates that ERS may repress apoptosis of BEAS-2B cells induced by CSC via activating autophagy, but autophagy relieves ERS in a negative feedback. This study provides better understanding and experimental support on the underlying mechanisms of pulmonary disease stimulated by CS.

Nicotine inhibits MAPK signaling and spheroid invasion in ovarian cancer cells

Nicotine is the major addictive component of cigarette smoke and although it is not considered carcinogenic, it can enhance or inhibit cancer cell proliferation depending on the type of cancer. Nicotine mediates its effects through nicotinic acetylcholine receptors (nAChRs), which are expressed in many different neuronal and non-neuronal cell types. We observed that the nAChR α4, α5, α7 subunits were expressed in ovarian cancer (OC) cells. Nicotine inhibited the proliferation of SKOV3 and TOV112D OC cells, which have TP53 mutation and wild-type KRAS, but did not inhibit the proliferation of TOV21G or HEY OC cells, which have KRAS mutation and wild-type TP53. Exposure to nicotine for 96 h led to a significant reduction in the amounts of activated extracellular signal-regulated kinase (ERK) and activated p38 mitogen-activated protein kinases (MAPKs) in SKOV3 cells, and in activated ERK in TOV112D cells. In addition, SKOV3 and TOV112D invasion and spheroid formation were substantially inhibited by siRNA knockdown of mixed lineage kinase 3 (MLK3), or MEK inhibition. Nicotine treatment reduced SKOV3 and TOV112D spheroid invasion and compaction but did not significantly affect spheroid formation. Furthermore, SKOV3 spheroid invasion was blocked by p38 inhibition with SB202190, but not by MEK inhibition with U0126; whereas TOV112D spheroid invasion was reduced by MEK inhibition, but not by p38 inhibition. These results indicate that nicotine can suppress spheroid invasion and compaction as well as proliferation in SKOV3 and TOV112D OC cells; and p38 and ERK MAPK signaling pathways are important mediators of these responses.

Cigarette smoke triggers inflammation mediated by autophagy in BEAS-2B cells

Cigarette smoking, as an individual consumption habit, is associated with a variety of related diseases. Exposure of cigarette smoke was reported to induce autophagy and inflammation in experimental animals and humans. However, the toxicity mechanism of cigarette smoke in organisms has not been entirely investigated. In this present study, we studied the role of autophagy played in the inflammation caused by cigarette smoke in human bronchial epithelial cells (BEAS-2B), as well as the role of the phosphatidylinositol 3-kinase (PI3K) signaling pathway and the mitogen-activated protein kinase (MAPK) signaling pathways underlying autophagy and inflammation. We found that cigarette smoke induced autophagy and inflammation in BEAS-2B, and the blockage of autophagy significantly reduced the release levels of IL-1β, IL-6 and IL-8 in BEAS-2B exposed to cigarette smoke for 24 h. Cigarette smoke downregulated the activity of PI3K/Akt/mTOR pathway and elevated the activity of MAPK pathways. Pretreatment of autophagic inhibitor could inhibit autophagy and the activity of JNK and p38 pathways. These results suggested that cigarette smoke-induced autophagy triggered inflammation through the activation of JNK and p38 pathways, which might contribute to understanding the adverse outcome pathways induced by cigarette smoke exposure and provide the information about the risk assessment of tobacco products.

Cinnamon-flavored electronic cigarette liquids and aerosols induce oxidative stress in human osteoblast-like MG-63 cells

As noncombustible nicotine delivery devices, electronic cigarettes (e-cigarettes) are the most popular tobacco product among youth. The widespread popularity of e-cigarettes combined with possible health consequences suggest a need to further research health hazards associated with e-cigarette use. Since conventional tobacco use is a risk factor for osteoporosis, this study investigates the impact of nicotine-free, cinnamon-flavored e-cigarette liquid (e-liquid) on bone-forming osteoblasts compared to flavorless e-liquid. Human tumor-derived osteoblast-like MG-63 cells were exposed for 24 h or 48 h to 0.0.4 %, 0.04 %, 0.4 % or 1 % of unvaped e-liquid or 0.0025 %, 0.025 %, 0.25 %, 1 % or 2.5 % of aerosol condensate in addition to a culture medium only control. Changes in cell viability were assessed by MTT assay, and the expression of a key bone protein, collagen type I, was analyzed by immunofluorescence. Production of reactive oxygen species (ROS) was detected by fluorometry to assess oxidative stress. Cell viability decreased in a dose-dependent manner, and ROS production increased, which was most pronounced with cinnamon-flavored e-liquids. There were no detectable changes in collagen type I protein following exposure to any of the aerosol condensates. This study demonstrates osteoblast-like cells are sensitive to both e-liquids and aerosol condensates and suggests the cytotoxicity of cinnamon-flavored e-liquids might be associated with oxidative stress rather than changes in collagen type I protein expression. This in vitro study provides insight into the potential impacts of e-cigarette use on bone cells.

Apoptotic effects of cigarette smoke extracts on mouse embryonic stem cells via oxidative stress

Previous studies have reported that cigarette smoke and cigarette smoke extract (CSE) have negative effects on embryonic development. However, no studies have investigated the mechanism through which CSE affects the cellular signaling pathway leading to apoptosis and oxidative stress in embryonic cells, or how the two pathways are cross-linked. Thus, we studied the effects of CSE on apoptosis and oxidative stress in mouse embryonic stem cells (mESCs). Specifically, we measured changes in cell viability in response to CSEs (3R4F and two domestic cigarettes CSE 1 and 2) using a water soluble tetrazolium (WST) assay and a neutral red uptake (NRU) assay, which revealed that cell viability decreased in a concentration-dependent manner. Western blot analysis revealed that the expression of cyclin D1 and cyclin E1 was decreased and that of p21 and p27 was increased by CSE. Additionally, the number of terminal deoxynucleotidyl transferase (TUNEL)-stained cells was increased by CSE, while the levels of Bax and Caspase-3 increased and Bcl-2 decreased. Moreover, a 2',7'-dichlorofluorescin diacetate (DCF-DA) assay and reactive oxygen species (ROS)-Glo H2 O2 assay confirmed that ROS were generated in response to CSE and that they were associated with up-regulated Keaf-1 and CHOP. Overall, the results revealed that cigarette smoke extract (CSE) inhibited cell proliferation by regulating cell cycle-related protein expression and increased oxidative stress by regulating the expression of Kelch-like ECH-associated protein 1 (Keap-1) and CCAAT/enhancer-binding protein homologous protein (CHOP), resulting in apoptosis in mESCs.

Role of reciprocal interaction between autophagy and endoplasmic reticulum stress in apoptosis of human bronchial epithelial cells induced by cigarette smoke extract

Endoplasmic reticulum stress (ERS)-induced apoptosis of airway epithelial cells plays an important role in the pathogenesis of chronic obstructive pulmonary disease (COPD). Furthermore, autophagy is closely related to ERS under apoptosis. Here, this study aimed to investigate the role of the reciprocal interaction between autophagy and ERS in the cigarette smoke extract (CSE)-induced apoptosis of human bronchial epithelial (HBE) cells. Cell apoptosis was detected by flow cytometry analysis. Protein expression was examined by Western blot. The mRNA expression was detected using real-time quantitative reverse transcription PCR (qRT-PCR). The results showed that CSE treatment induced apoptosis, autophagy, and expression of ERS-related proteins in HBE cells. Furthermore, autophagy inhibition by 3-MA significantly decreased protein expression of GRP78, p-PERK, and p-eIF2α and increased CHOP, ATF4, and caspase-4, whereas ERS inhibition by 4-PBA led to autophagy suppression. Moreover, the CSE-induced autophagy was diminished by knockdown of GRP78, PERK, or eIF2α but enhanced by knockdown of ATF4 or CHOP; however, the CSE-induced HBE apoptosis was enhanced by knockdown of GRP78, PERK, or eIF2α but was attenuated by knockdown of ATF4 or CHOP. Additionally, both sodium hydrosulfide (NaHS) and melatonin attenuated the CSE-induced apoptosis, enhanced the CSE-induced autophagy, increased GRP78, p-PERK, and p-eIF2α, and decreased CHOP, ATF4, and caspase-4, via SIRT1/ORP150 pathway. Collectively, this study provided evidence about the role of the reciprocal interaction between autophagy and ERS in CSE-induced apoptosis of HBE cells. © 2018 IUBMB Life, 71(1):66-80, 2019.

Interaction of ERα and NRF2 Impacts Survival in Ovarian Cancer Patients

Nuclear factor erythroid 2-related factor 2 (NRF2) regulates cytoprotective antioxidant processes. In this study, the prognostic potential of NRF2 and its interactions with the estrogen receptor α (ERα) in ovarian cancer cells was investigated. NRF2 and ERα protein expression in ovarian cancer tissue was analyzed as well as mRNA expression of NRF2 (NFE2L2) and ERα (ESR1) in four ovarian cancer and one benign cell line. NFE2L2 silencing was carried out to evaluate a potential interplay between NRF2 and ERα. Cytoplasmic NRF2 expression as inactive form had significantly higher expression in patients with low-grade histology (p = 0.03). In the serous cancer subtype, high cytoplasmic NRF2 expression (overall survival (OS), median 50.6 vs. 29.3 months; p = 0.04) and high ERα expression (OS, median 74.5 vs. 27.1 months; p = 0.002) was associated with longer overall survival as well as combined expression of both inactive cytoplasmic NRF2 and ERα in the whole cohort (median 74.5 vs. 37.7 months; p = 0.04). Cytoplasmic NRF2 expression showed a positive correlation with ERα expression (p = 0.004). NFE2L2 was found to be highly expressed in the ovarian cancer cell lines OVCAR3, UWB1.289, and TOV112D. Compared with the benign cell line HOSEpiC, ESR1 expression was reduced in all ovary cancer cell lines (all p < 0.001). Silencing of NFE2L2 induced a higher mRNA expression of ESR1 in the NFE2L2 downregulated cancer cell lines OVCAR3 (p = 0.003) and ES2 (p < 0.001), confirming genetic interactions of NRF2 and ERα. In this study, both inactive cytoplasmic NRF2 and high ERα expression were demonstrated to be associated with improved survival in ovarian cancer patients. Further understanding of interactions within the estradiol⁻ERα⁻NRF2 pathway could better predict the impact of endocrine therapy in ovarian cancer.