Extrinsic Receptor-mediated Pathways Research Articles

Induction of intrinsic and extrinsic apoptosis through oxidative stress in drug-resistant cancer by a newly synthesized Schiff base copper chelate

Multidrug resistance (MDR) in cancer represents a variety of strategies employed by tumor cells to evade the beneficial cytotoxic effects of structurally different anticancer drugs and thus confers impediments to the successful treatment of cancers. Efflux of drugs by MDR protein-1, functional P-glycoprotein and elevated level of reduced glutathione confer resistance to cell death or apoptosis and thus provide a possible therapeutic target for overcoming MDR in cancer. Previously, we reported that a Schiff base ligand, potassium-N-(2-hydroxy 3-methoxy-benzaldehyde)-alaninate (PHMBA) overcomes MDR in both in vivo and in vitro by targeting intrinsic apoptotic/necrotic pathway through induction of reactive oxygen species (ROS). The present study describes the synthesis and spectroscopic characterization of a copper chelate of Schiff base, viz., copper (II)-N-(2-hydroxy-3-methoxy-benzaldehyde)-alaninate (CuPHMBA) and the underlying mechanism of cell death induced by CuPHMBA in vitro. CuPHMBA kills both the drug-resistant and sensitive cell types irrespective of their drug resistance phenotype. The cell death induced by CuPHMBA follows apoptotic pathway and moreover, the cell death is associated with intrinsic mitochondrial and extrinsic receptor-mediated pathways. Oxidative stress plays a pivotal role in the process as proved by the fact that antioxidant enzyme; polyethylene glycol conjugated-catalase completely blocked CuPHMBA-induced ROS generation and abrogated cell death. To summarize, the present work provides a compelling rationale for the future clinical use of CuPHMBA, a redox active copper chelate in the treatment of cancer patients, irrespective of their drug-resistance status.

Determinants of eosinophil survival and apoptotic cell death.

Eosinophils (Eos) are potent inflammatory cells and abundantly present in the sputum and lung of patients with allergic asthma. During both transit to and residence in the lung, Eos contact prosurvival cytokines, particularly IL-3, IL-5 and GM-CSF, that attenuate cell death. Cytokine signaling modulates the expression and function of a number of intracellular pro- and anti-apoptotic molecules. Both intrinsic mitochondrial and extrinsic receptor-mediated pathways are affected. This article discusses the fundamental role of the extracellular and intracellular molecules that initiate and control survival decisions by human Eos and highlights the role of the cis-trans isomerase, Pin1 in controlling these processes.

Mitochondria in the Center of Human Eosinophil Apoptosis and Survival

Eosinophils are abundantly present in most phenotypes of asthma and they contribute to the maintenance and exacerbations of the disease. Regulators of eosinophil longevity play critical roles in determining whether eosinophils accumulate into the airways of asthmatics. Several cytokines enhance eosinophil survival promoting eosinophilic airway inflammation while for example glucocorticoids, the most important anti-inflammatory drugs used to treat asthma, promote the intrinsic pathway of eosinophil apoptosis and by this mechanism contribute to the resolution of eosinophilic airway inflammation. Mitochondria seem to play central roles in both intrinsic mitochondrion-centered and extrinsic receptor-mediated pathways of apoptosis in eosinophils. Mitochondria may also be important for survival signalling. In addition to glucocorticoids, another important agent that regulates human eosinophil longevity via mitochondrial route is nitric oxide, which is present in increased amounts in the airways of asthmatics. Nitric oxide seems to be able to trigger both survival and apoptosis in eosinophils. This review discusses the current evidence of the mechanisms of induced eosinophil apoptosis and survival focusing on the role of mitochondria and clinically relevant stimulants, such as glucocorticoids and nitric oxide.

The Fas/Fas Ligand Apoptotic Pathway Is Involved in Abrin-Induced Apoptosis

Abrin is a plant glycoprotein toxin from the seeds of Abrus precatorius, sharing similarity in structure and properties with ricin. Abrin is highly toxic, with an estimated human fatal dose of 0.1-1 µg/kg, causing death after accidental or intentional poisoning. It is a potent biological toxin warfare agent. There is no chemical antidote available against the abrin. The elucidation of molecular mechanism of abrin-induced cell death is important for development of therapy. Intrinsic pathway-mediated apoptosis has been well established in abrin-induced cell death. However, the detailed mechanism especially extrinsic receptor-mediated pathway remains uncharacterized. To assess whether some of the apoptosis known to occur after abrin exposure might be mediated by Fas/Fas ligand (Fas L) interactions, we analyzed effect of abrin on Fas pathway in Jurkat cells. Here, we report that activation of the Fas pathway is involved in abrin-induced apoptosis. Following treatment of abrin, Fas L was induced, which stimulated the Fas pathway by cross-linking Fas receptor (Fas R). Apoptosis was mediated by cleavage of the Fas R proximal caspase-8 and the downstream caspase-3, resulting in activation of the prototype caspase substrate poly-(ADP-ribose) polymerase and caspase-activated DNase. Blocking Fas L/Fas R interaction by using Fas inhibitor reduced abrin-induced apoptosis, further confirms involvement of Fas pathway. Activation of components of Fas pathway and caspases upon abrin treatment was also found in splenocytes in mice. Our findings offer new perspective for understanding the fundamental mechanism in abrin-induced apoptotic mechanism and may have implication in developing novel therapeutic strategies in the management for abrin-induced complications.

Cadmium inhibits both intrinsic and extrinsic apoptotic pathways in renal mesangial cells

Cadmium is a potent nephrotoxin that has been shown to induce apoptosis in some cells but also to prevent it under certain circumstances. In several clinical situations and experimental models of injury to the renal glomerulus, pathological proliferation of mesangial cells is followed by resolution involving mesangial cell apoptosis. We investigated the effects of Cd(2+) on rat mesangial cells induced to undergo apoptosis through either the extrinsic receptor-mediated pathway or the intrinsic mitochondrial-dependent pathway. Camptothecin initiated the intrinsic pathway with activation of caspase-9 and caspase-dependent cleavage of procaspase-3. Tumor necrosis factor-alpha (TNF-alpha) initiated caspase-8 activity and cleavage of pro-caspase-3 at the convergence point of the two pathways. However, pro-caspase-8 levels were low, and caspase-9 was also activated in response to TNF-alpha, characteristic of what have been termed type II cells. With both TNF-alpha and camptothecin, concurrent exposure to 10 microM CdCl(2) suppressed DNA laddering, nuclear condensation, and pro-caspase-3 cleavage. It also decreased activity of both caspase-8 and caspase-9, prevented caspase-8-dependent cleavage of the proapoptotic factor Bid, and suppressed release of cytochrome c from mitochondria. At this 10-microM concentration, Cd(2+) was unique among a number of metal ions in preventing DNA fragmentation. We conclude that Cd(2+) is anti-apoptotic in rat mesangial cells, acting by a mechanism that may involve general caspase inhibition. This may have consequences for the resolution of nephritis in situations of mesangial cell hyperproliferation.

脳卒中における急性期脳保護療法―現在と将来―

Neuroprotective therapy is crucial to salvage the penumbra surrounding the core of ischemia in the acute phase of ischemic stroke. Cumulative evidence suggests that apoptosis plays a pivotal role in neuronal cell death after cerebral ischemia in various experimental animal models. The time-dependent molecular and biochemical sequelae that lead to apoptotic cell death after the interruption of cerebral blood flow have been established. Therefore, various kinds of neuroprotective agents have been developed.In this symposium we introduced the ischemic cell death pathway, especially intrinsic mitochondriadependent and extrinsic receptor-mediated pathway of apoptosis after ischemia, and also introduced our experimental studies on several kinds of brand-new neuroprotective compounds after focal ischemia. Moreover, extra-mild hypothermic therapy (35°C) enhanced that neuroprotective effect and prolonged that therapeutic time window, was introduced.°CThese present data show that these newly developed neuroprotective agents and the combination treatment with extra-mild hypothermia (35°C) are effective for neuroprotection in acute cerebral ischemia. These studies provide an impetus for novel therapeutic targets in neuroprotective strategies in acute ischemic stroke. These combined therapy may be useful in clinical medical care for acute ischemic stroke in human.