Glutathione (GSH) plays an important role in a multitude of cellular processes, including cell differentiation, proliferation, and apoptosis, and disturbances in GSH homeostasis are involved in the etiology and progression of many human diseases including cancer. While GSH deficiency, or a decrease in the GSH/glutathione disulphide (GSSG) ratio, leads to an increased susceptibility to oxidative stress implicated in the progression of cancer, elevated GSH levels increase the antioxidant capacity and the resistance to oxidative stress as observed in many cancer cells. The present review highlights the role of GSH and related cytoprotective effects in the susceptibility to carcinogenesis and in the sensitivity of tumors to the cytotoxic effects of anticancer agents.

The transcription factor, nuclear factor erythroid 2 p45-related factor 2 (Nrf2), acts as a sensor of oxidative or electrophilic stresses and plays a pivotal role in redox homeostasis. Oxidative or electrophilic agents cause a conformational change in the Nrf2 inhibitory protein Keap1 inducing the nuclear translocation of the transcription factor which, through its binding to the antioxidant/electrophilic response element (ARE/EpRE), regulates the expression of antioxidant and detoxifying genes such as heme oxygenase 1 (HO-1). Nrf2 and HO-1 are frequently upregulated in different types of tumours and correlate with tumour progression, aggressiveness, resistance to therapy, and poor prognosis. This review focuses on the Nrf2/HO-1 stress response mechanism as a promising target for anticancer treatment which is able to overcome resistance to therapies.

Reactive oxygen species (ROS) and their products are components of cell signaling pathways and play important roles in cellular physiology and pathophysiology. Under physiological conditions, cells control ROS levels by the use of scavenging systems such as superoxide dismutases, peroxiredoxins, and glutathione that balance ROS generation and elimination. Under oxidative stress conditions, excessive ROS can damage cellular proteins, lipids, and DNA, leading to cell damage that may contribute to carcinogenesis. Several studies have shown that cancer cells display an adaptive response to oxidative stress by increasing expression of antioxidant enzymes and molecules. As a double-edged sword, ROS influence signaling pathways determining beneficial or detrimental outcomes in cancer therapy. In this review, we address the role of redox homeostasis in cancer growth and therapy and examine the current literature regarding the redox regulatory systems that become upregulated in cancer and their role in promoting tumor progression and resistance to chemotherapy.

BACKGROUND AND PURPOSEStrategies designed to enhance cerebral cAMP have been proposed as symptomatic treatments to counteract cognitive deficits. However, pharmacological therapies aimed at reducing PDE4, the main class of cAMP catabolizing enzymes in the brain, produce severe emetic side effects. We have recently synthesized a 3-cyclopentyloxy-4-methoxybenzaldehyde derivative, structurally related to rolipram, and endowed with selective PDE4D inhibitory activity. The aim of the present study was to investigate the effect of the new drug, namely GEBR-7b, on memory performance, nausea, hippocampal cAMP and amyloid-b (Ab) levels. EXPERIMENTAL APPROACHTo measure memory performance, we performed object recognition tests on rats and mice treated with GEBR-7b or rolipram. The emetic potential of the drug, again compared with rolipram, was evaluated in rats using the taste reactivity test and in mice using the xylazine/ketamine anaesthesia test. Extracellular hippocampal cAMP was evaluated by intracerebral microdialysis in freely moving rats. Levels of soluble Ab peptides were measured in hippocampal tissues and cultured N2a cells by ELISA. KEY RESULTSGEBR-7b increased hippocampal cAMP, did not influence Ab levels and improved spatial, as well as object memory performance in the object recognition tests. The effect of GEBR-7b on memory was 3 to 10 times more potent than that of rolipram, and its effective doses had no effect on surrogate measures of emesis in rodents. CONCLUSION AND IMPLICATIONSOur results demonstrate that GEBR-7b enhances memory functions at doses that do not cause emesis-like behaviour in rodents, thus offering a promising pharmacological perspective for the treatment of memory impairment.

Ischemic preconditioning improves liver resistance to hypoxia and reduces reperfusion injury following transplantation. However, the intracellular signals that mediate the development of liver hypoxic preconditioning are largely unknown. We have investigated the signal pathway leading to preconditioning in freshly isolated rat hepatocytes. Hepatocytes were preconditioned by 10-minute incubation under hypoxic conditions followed by 10 minutes of reoxygenation and subsequently exposed to 90 minutes of hypoxia. Preconditioning reduced hepatocyte killing by hypoxia by about 35%. A similar protection was also obtained by preincubation with chloro-adenosine or with A 2A -adenosine receptor agonist CGS21680, whereas A 1 -adenosine receptor agonist N-phenyl-isopropyladenosine (R-PIA) was inactive. Conversely, the development of preconditioning was blocked by A 2 -receptor antagonist 3,7-dimethyl-1-propargylxanthine (DMPX), but not by A 1 -receptor antagonist 8-cyclopenthyl-1,3-dipropylxanthine (DPCPX). In either preconditioned or CGS21680-treated hepatocytes a selective activation of ␦ and protein kinase C (PKC) isoforms was also evident. Inhibition of heterotrimeric G i protein or of phospholypase C by, respectively, pertussis toxin or U73122, prevented PKC activation as well as the development of preconditioning. MEK inhibitor PD98509 did not interfere with preconditioning that was instead blocked by p38 MAP kinase inhibitor SB203580. The direct activation of p38 MAPK by anisomycin A mimicked the protection against hypoxic injury given by preconditioning. Consistently, an increased phosphorylation of p38 MAPK was observed in preconditioned or CGS21680-treated hepatocytes, and this effect was abolished by PKC-blocker, chelerythrine. We propose that a signal pathway involving A 2A -adenosine receptors, G i -proteins, phospholypase C, ␦-and -PKCs, and p38 MAPK, is responsible for the deve- The term ischemic preconditioning refers to the resistance to ischemic injury acquired by tissue following one or more brief periods of ischemia followed by reperfusion. 1,2 Ischemic preconditioning was first described in the myocardium, 1 but has been shown in several other organs, including the brain, the skeletal muscles, and the small intestine. 3 In the heart, ischemic preconditioning occurs in 2 phases: an early phase (early preconditioning) that immediately follows the transient hypoxia and lasts 2 to 3 hours and a late phase (late preconditioning), which begins 12 to 24 hours from the transient ischemia and lasts for about 3 to 4 days. 3 Recent studies have shown that the same phenomenon could also be observed in the liver. [4][5][6][7][8][9][10] In particular, 10-minute interruption of liver blood supply in anesthetized rats followed by 10 minutes of reperfusion reduces transaminases released during a subsequent 90-minute period of ischemia and 90-minute reoxygenation. 5 A similar effect has also been observed in steatosic livers following heat shock preconditioning. 7 Furthermore, ischemic preconditioning before cold preserva...