Francisco J. Alonso

Intracellular redox status and oxidative stress: implications for cell proliferation, apoptosis, and carcinogenesis.

Oxidative stress can be defined as the imbalance between cellular oxidant species production and antioxidant capability. Reactive oxygen species (ROS) are involved in a variety of different cellular processes ranging from apoptosis and necrosis to cell proliferation and carcinogenesis. In fact, molecular events, such as induction of cell proliferation, decreased apoptosis, and oxidative DNA damage have been proposed to be critically involved in carcinogenesis. Carcinogenicity and aging are characterized by a set of complex endpoints, which appear as a series of molecular reactions. ROS can modify many intracellular signaling pathways including protein phosphatases, protein kinases, and transcription factors, suggesting that the majority of the effects of ROS are through their actions on signaling pathways rather than via non-specific damage of macromolecules; however, exact mechanisms by which redox status induces cells to proliferate or to die, and how oxidative stress can lead to processes evoking tumor formation are still under investigation.

Oxidative stress in apoptosis and cancer: an update

The oxygen paradox tells us that oxygen is both necessary for aerobic life and toxic to all life forms. Reactive oxygen species (ROS) touch every biological and medical discipline, especially those involving proliferative status, supporting the idea that active oxygen may be increased in tumor cells. In fact, metabolism of oxygen and the resulting toxic byproducts can cause cancer and death. Efforts to counteract the damage caused by ROS are gaining acceptance as a basis for novel therapeutic approaches, and the field of prevention of cancer is experiencing an upsurge of interest in medically useful antioxidants. Apoptosis is an important means of regulating cell numbers in the developing cell system, but it is so important that it must be controlled. Normal cell death in homeostasis of multicellular organisms is mediated through tightly regulated apoptotic pathways that involve oxidative stress regulation. Defective signaling through these pathways can contribute to both unbalance in apoptosis and development of cancer. Finally, in this review, we discuss new knowledge about recent tools that provide powerful antioxidant strategies, and designing methods to deliver to target cells, in the prevention and treatment of cancer.

Roles of dioxins and heavy metals in cancer and neurological diseases using ROS-mediated mechanisms

Oxidants have critical functions inside healthy and unhealthy cells. Deregulated cell cycle and apoptosis, both regulated by oxidative stress, have been described as hallmarks of mitotic (cancer) and postmitotic (neuronal) cells. This review provides an updated revision of the oxidant effects of some environmental contaminants such as dioxins and the heavy metals cadmium, cobalt, and copper. Dioxins exert their toxic actions by acting on phase I and phase II enzymes, such as cytochromes P450, superoxide dismutase, and glutathione peroxidase, promoting cell proliferation, growth arrest, and apoptosis, affecting cancer homeostasis and neuronal function. Heavy metals manifest cytotoxic effects in various cells and tissues, and tight regulation of metals is essential to the health of organisms. Cadmium modulates gene expression and signal transduction and reduces activities of proteins involved in antioxidant defense, interfering with DNA repair and modifying cancer development and brain function. Cobalt provokes generation of reactive oxygen species and DNA damage in cancer cells and brain tissues, altering proliferation and differentiation and causing apoptosis. Copper is a key metal in cell division processes in both normal and tumor cells. Copper also has been shown to have an important role in neurodegenerative diseases such as Alzheimer disease, Parkinson disease, and amyotrophic lateral sclerosis.

Glutamine homeostasis and mitochondrial dynamics

Glutamine is a multifaceted amino acid that plays key roles in many metabolic pathways and also fulfils essential signaling functions. Although classified as non-essential, recent evidence suggests that glutamine is a conditionally essential amino acid in several physiological situations. Glutamine homeostasis must therefore be exquisitely regulated and mitochondria represent a major site of glutamine metabolism in numerous cell types. Glutaminolysis is mostly a mitochondrial process with repercussions in organelle structure and dynamics suggesting a tight and mutual control between mitochondrial form and cell bioenergetics. In this review we describe an updated account focused on the critical involvement of glutamine in oxidative stress, mitochondrial dysfunction and tumour cell proliferation, with special emphasis in the initial steps of mitochondrial glutamine pathways: transport into the organelle and hydrolytic deamidation through glutaminase enzymes. Some controversial issues about glutamine catabolism within mitochondria are also reviewed.

Co-expression of glutaminase K and L isoenzymes in human tumour cells

The pattern of expression of glutaminase isoenzymes in tumour cells has been investigated to clarify its role in the malignant transformation and the prospect of its use as a clinically relevant factor. Using leukaemia cells from medullar blood of human patients and several established human cancer cell lines, we have developed a competitive RT (reverse transcriptase)-PCR assay to quantify simultaneously K-type (kidney-type) and L-type (liver-type) glutaminase mRNAs. Co-expression of both transcripts and higher amounts of L-type mRNA were always found in all cancer cell types analysed. However, mature lymphocytes from the medullar blood of a patient suffering aplasia did not express the K-type transcript and showed a 15-fold increase of L-type transcript. Co-expression was also confirmed at the protein level using isoform-specific antibodies; nevertheless, it did not correlate with the relative abundance of glutaminase transcripts and strong K-type protein signals were detected. On the other hand, marked differences were found with regard to glutamate inhibition and phosphate activation of tumour glutaminase activity. Taken together, the protein data suggest that K isoform would account for the majority of glutaminase activity in these human tumour cells. The results confirm that simultaneous expression of both isoenzymes in human cancer cells is a more frequent event than previously thought. Furthermore, the present work and other previous data suggest that K isoform is up-regulated with increased rates of proliferation, whereas prevalence of the L isoform seems to be related with resting or quiescent cell states.

Glutaminase isoenzymes as key regulators in metabolic and oxidative stress against cancer.

Cancer cells require a robust supply of reduced nitrogen to produce nucleotides, non-essential amino acids and a high cellular redox activity. Glutamine provides a major substrate for respiration as well as nitrogen for the production of proteins, hexosamines, and macromolecules. Therefore, glutamine is one of key molecules in cancer metabolism during cell proliferation. The notion of targeting glutamine metabolism in cancer, originally rationalized by the number of pathways fed by this nutrient, has been reinforced by more recent studies demonstrating that its metabolism is regulated by oncogenes. Glutamine can exert its effects by modulating redox homeostasis, bioenergetics, nitrogen balance or other functions, including by being a precursor of glutathione, the major nonenzymatic cellular antioxidant. Glutaminase (GA) is the first enzyme that converts glutamine to glutamate, which is in turn converted to alpha-ketoglutarate for further metabolism in the tricarboxylic acid cycle. Different GA isoforms in mammals are encoded by two genes, Gls and Gls2. As each enzymatic form of GA has distinct kinetic and molecular characteristics, it has been speculated that the differential regulation of GA isoforms may reflect distinct functions or requirements in different tissues or cell states. GA encoded by Gls gene (GLS) has been demonstrated to be regulated by oncogenes and to support tumor cell growth. GA encoded by Gls2 gene (GLS2) reduces cellular sensitivity to reactive oxygen species associated apoptosis possibly through glutathione-dependent antioxidant defense, and therefore to behave more like a tumor suppressor. Thus, modulation of GA function may be a new therapeutic target for cancer treatment.

Anticancer Antioxidant Regulatory Functions of Phytochemicals

Plant foods are not only a main source of nutrients, but they are also rich in physiologically bioactive bionutrients or phytochemicals. Consumption of fruit and vegetables is associated with a decreased risk of pathological status, including cancer. Reactive oxygen species play a key role in the genesis and development of cancer. Therefore, antioxidant functions of phytonutrients have been thoroughly investigated in the last years in relation to their crucial effect in the pathophysiology associated with neoplasia. This review discusses current knowledge on phytochemicals in relation to their potential as chemopreventive and/or chemotherapeutic molecule against human cancers. Finally, we will outline the use of bioactive phytochemicals on synergistic actions involved in the prevention and treatment of cancer as well as its future prospects.

Pathways from glutamine to apoptosis.

It is fascinating that a relatively simple amino acid like glutamine is involved in such large variety of cellular reactions. Glutamine is required for nitrogen-stimulated proliferation in many cells, but glutamine stimulates not only the growth of cells but also the expression of surface antigens, the formation of cytokines, the synthesis of heat shock proteins and many more vital events. Among all of them, apoptosis is a recent but outstanding incorporation to the whole of phenomena regulated by this peculiar amino acid. Apoptosis is an important process in a wide number of biologic systems. Apoptotic signalling mechanisms implicated in response to glutamine deprivation are cell type-specific. In any case, new findings indicate that glutamine availability is strongly related to the induction of apoptosis, working both as a nutrient and as a signalling molecule, acting directly or indirectly on the pathways leading to programmed cell death. Following, we will describe as glutamine and the related species glutamate, glutathione and glucosamine can play important roles in the pathways leading to apoptosis.

Natural Antioxidants: Therapeutic Prospects for Cancer and Neurological Diseases

An all out war is continuously occurring between oxidants and antioxidants inside the cells. This mini-review will provide an updated revision of the function of some natural compounds having main roles in antioxidant function. We will point on some phytochemicals working at two outstanding targets, tumour cells and neurons.

Glutaminase: a multifaceted protein not only involved in generating glutamate.

The protein glutaminase has been traditionally considered as a mitochondrial enzyme, playing a key role in the energy and nitrogen metabolism of mammalian cells. However, new experimental evidence in the last few years has challenged this simplified view. The recent discovery of novel extramitochondrial localizations, the identification of potential protein interacting partners, the existence of multiple transcripts for mammalian glutaminase genes, and the presence of signature sequences and protein motifs on its sequence support the notion of glutaminase being a multifaceted protein, which may be involved in other functions besides glutamate generation from glutamine. In this short review, we will briefly summarize recent works on glutaminase proteins in mammals, with particular emphasis in brain studies. This experimental evidence will then be used to highlight new potential roles for this classical metabolic enzyme.