A BSTRACT : Recently, glucose deprivation-induced oxidative stress has been shown to cause cytotoxicity, activation of signal transduction (i.e., ERK1, ERK2, JNK, and Lyn kinase), and increased expression of genes associated with malignancy (i.e., bFGF and c-Myc) in MCF-7/ADR human breast cancer cells. These results have led to the proposal that intracellular oxidation/ reduction reactions involving hydroperoxides and thiols may provide a mechanistic link between metabolism, signal transduction, and gene expression in these human tumor cells. The current study shows that several other transformed human cell types appear to be more susceptible to glucose deprivationinduced cytotoxicity and oxidative stress than untransformed human cell types. In a matched pair of normal and SV40-transformed human fibroblasts the cytotoxic process is shown to be dependent upon ambient O 2 concentration. A theoretical model to explain the results is presented and implications to unifying modern theories of cancer are discussed.

A series of experiments were designed to examine the potential cytotoxicity of nitric oxide (NO), or reactive species derived from NO, in HA1 fibroblasts and H202-resistant variants of this cell line, designated OC14 cells. A 1-h exposure at 37OC to a 1.7 mM bolus dose of NO, prepared in N2-gassed medium, significantly reduced clonogenic survival in the HA1 fibroblasts line to 60% of control cells treated with N2-gassed medium alone. The OC14 cells were found to be completely resistant (100% survival) to NO-mediated injury in comparable experiments. A second set of experiments was designed to determine the role of the intracellular antioxidant, glutathione, in protection against NO-mediated injury. Depletion of total glutathione resulted in a significant reduction in HA1 and OC14 clonogenic survival to 8% and 50% when compared with respective control cells. The effect of total glutathione depletion on NO-initiated toxicity in HA1 cells was dose-and cell-density dependent and was observed to occur within 5 min of exposure to NO. Further evidence of cytotoxicity was demonstrated by loss of trypan blue dye exclusion properties in glutathione-depleted HA1 cells after NO is a free radical molecule endogenously produced by a variety of cell types. NO has been demonstrated to participate in physiologic reactions involving regulation of vasomotor tone, neurotransmission, immune system function, and platelet aggregation (1-4). Recent clinical trials have demonstrated some efficacy for inhaled NO in treatment of neonatal pulmonary hypertension and adult respiratory distress syndrome (5-7). Paradoxically, elevated concentrations of atmospheric NO are known to be harmful in many animal models, and lethal exposures at high concentrations have been reported in both animals and humans (8-10). This same paradoxical beneficial and/or toxic effect of NO has been observed in vitro. Several Received August 10, 1993; accepted July 8, 1994. Correspondence: Dr. M. Whit Walker, Department of Neonatology, Greenville Hospital Systems, 701 Grove Road, Greenville, SC 29605.Supported by National Institutes of Health Grants HL42057, HL08841, HL51469, CA.51116, HD28810, GM08260, and DK38924.NO exposure. Other experiments demonstrated that nitrate and nitrite exposure produced no cytotoxicity in glutathione-depleted HA1 cells and that coincubation of NO-saturated medium with oxyhemoglobin inhibited NO-induced cytotoxicity in glutathione-depleted HA1 cells. These results demonstrate that 1 ) nitric oxide, or an NO-derived reactive nitrogen species other than nitrites or nitrates, is responsible for reduction in clonogenic survival and trypan blue dye exclusion capabilities in vitro; 2) biochemical pathways associated with cellular resistance to oxidative stress also confer resistance to NO-mediated injury in this cell model; and 3) total glutathione content determines a significant portion of cell sensitivity to NO-mediated cytotoxicity.

Background Precisely how silver nanoparticles (AgNPs) kill mammalian cells still is not fully understood. It is not clear if AgNP-induced damage differs from silver cation (Ag+), nor is it known how AgNP damage is transmitted from cell membranes, including endosomes, to other organelles. Cells can differ in relative sensitivity to AgNPs or Ag+, which adds another layer of complexity to identifying specific mechanisms of action. Therefore, we determined if there were specific effects of AgNPs that differed from Ag+ in cells with high or low sensitivity to either toxicant. Methods Cells were exposed to intact AgNPs, Ag+, or defined mixtures of AgNPs with Ag+, and viability was assessed. The level of dissolved Ag+ in AgNP suspensions was determined using inductively coupled plasma mass spectrometry. Changes in reactive oxygen species following AgNP or Ag+ exposure were quantified, and treatment with catalase, an enzyme that catalyzes the decomposition of H2O2 to water and oxygen, was used to determine selectively the contribution of H2O2 to AgNP and Ag+ induced cell death. Lipid peroxides, formation of 4-hydroxynonenol protein adducts, protein thiol oxidation, protein aggregation, and activation of the integrated stress response after AgNP or Ag+ exposure were quantified. Lastly, cell membrane integrity and indications of apoptosis or necrosis in AgNP and Ag+ treated cells were examined by flow cytometry. Results We identified AgNPs with negligible Ag+ contamination. We found that SUM159 cells, which are a triple-negative breast cancer cell line, were more sensitive to AgNP exposure less sensitive to Ag+ compared to iMECs, an immortalized, breast epithelial cell line. This indicates that high sensitivity to AgNPs was not predictive of similar sensitivity to Ag+. Exposure to AgNPs increased protein thiol oxidation, misfolded proteins, and activation of the integrated stress response in AgNP sensitive SUM159 cells but not in iMEC cells. In contrast, Ag+ cause similar damage in Ag+ sensitive iMEC cells but not in SUM159 cells. Both Ag+ and AgNP exposure increased H2O2 levels; however, treatment with catalase rescued cells from Ag+ cytotoxicity but not from AgNPs. Instead, our data support a mechanism by which damage from AgNP exposure propagates through cells by generation of lipid peroxides, subsequent lipid peroxide mediated oxidation of proteins, and via generation of 4-hydroxynonenal (4-HNE) protein adducts. Conclusions There are distinct differences in the responses of cells to AgNPs and Ag+. Specifically, AgNPs drive cell death through lipid peroxidation leading to proteotoxicity and necrotic cell death, whereas Ag+ increases H2O2, which drives oxidative stress and apoptotic cell death. This work identifies a previously unknown mechanism by which AgNPs kill mammalian cells that is not dependent upon the contribution of Ag+ released in extracellular media. Understanding precisely which factors drive the toxicity of AgNPs is essential for biomedical applications such as cancer therapy, and of importance to identifying consequences of unintended exposures.

Cardiovascular disease (CVD) is the most common cause of death in patients with native and post-transplant chronic kidney disease (CKD). To identify new biomarkers of vascular injury and inflammation, we analyzed the proteome of plasma and circulating extracellular vesicles (EVs) in native and post-transplant CKD patients utilizing an aptamer-based assay. Proteins of angiogenesis were significantly higher in native and post-transplant CKD patients versus healthy controls. Ingenuity pathway analysis (IPA) indicated Ephrin receptor signaling, serine biosynthesis, and transforming growth factor-β as the top pathways activated in both CKD groups. Pro-inflammatory proteins were significantly higher only in the EVs of native CKD patients. IPA indicated acute phase response signaling, insulin-like growth factor-1, tumor necrosis factor-α, and interleukin-6 pathway activation. These data indicate that pathways of angiogenesis and inflammation are activated in CKD patients’ plasma and EVs, respectively. The pathways common in both native and post-transplant CKD may signal similar mechanisms of CVD.