Cell death pathology: perspective for human diseases

Apoptosis, a genetically regulated form of cell death with distinct biochemical and morphological features, plays a relevant physiological and pathological role in the organism, being pivotal in the maintenance of tissue development and homeostasis in the adult as well as in the regulation of immune responses. Deregulation of this process causes several human disorders including cancer, autoimmune and neurodegenerative diseases. Thus, modulation of the apoptotic process and of cell death in general, is a potential therapeutic approach for the treatment of several human pathologies.     

Erythropoietin for oncology supportive care

Recombinant human erythropoietin (rhEPO), the prototype erythropoiesis-stimulating agent developed in the 1980s, was among the first recombinant human proteins to be marketed for clinical use in the oncology setting. Anemia is a frequent concern in patients with cancer receiving myelosuppressive chemotherapy and the availability of rhEPO as an alternative to red blood cell transfusions to treat symptomatic anemia created excitement among clinicians, particularly during an era of mounting concern for transfusion-transmissible infections. Early studies of rhEPO for chemotherapy-induced anemia in patients with non-myeloid malignancies showed these agents improved hemoglobin levels and reduced transfusion rates. rhEPO therapy was reported to decrease fatigue and improve quality of life, although the magnitude and clinical meaningfulness of these effects have been debated. More recent clinical trials since 2003 linking rhEPO therapy to increased risk of tumor progression, thrombo-vascular events and mortality prompted implementation of use restrictions to minimize potential for harm. Scientific research to understand the basic mechanisms of the biologic effects of erythropoietin at the cellular receptor and signaling level has revealed pleiotropic cytokine effects extending beyond erythropoiesis regulation. The importance of erythropoietin receptor signaling in normal, non-erythroid tissues and in pre-clinical tumor models has been under intense investigation and scrutiny, as potential mechanisms of the adverse outcomes associated with rhEPO therapy have been debated. Further research will be required to clarify the complex interplay between the diverse hematopoietic and non-hematopoietic effects of erythropoietin in normal and malignant tissues and to optimize the clinical use of rhEPO in the supportive care of cancer patients.     

Trypanosoma cruzi: desferrioxamine decreases mortality and parasitemia in infected mice through a trypanostatic effect

Desferrioxamine (DFO) is a potent iron chelator that is also known to modulate inflammation and act as an efficient antioxidant under normal conditions and under oxidative stress. Many in vitro and in vivo studies have shown the efficacy of DFO in the treatment of viral, bacterial and protozoan infections. DFO is known to reduce the intensity of Trypanosoma cruzi infections in mice even during a course of therapy that is not effective in maintaining anaemia or low iron levels. To further clarify these findings, we investigated the action of DFO on mouse T. cruzi infection outcomes and the direct impact of DFO on parasites.Infected animals treated with DFO (5 mg/animal/day) for 35 days, beginning 14 days prior to infection, presented lower parasitemia and lower cumulative mortality rate. No significant effect was observed on iron metabolism markers, erythrograms, leukograms or lymphocyte subsets.In the rapid method for testing in vivo T. cruzi susceptibility, DFO also induced lower parasitemia.In regard to its direct impact on parasites, DFO slightly inhibited the growth of amastigotes and trypomastigotes in fibroblast culture. Trypan blue staining showed no effects of DFO on parasite viability, and only minor apoptosis in trypomastigotes was observed. Nevertheless, a clear decrease in parasite mobility was detected.In conclusion, the beneficial actions of DFO on mice T. cruzi infection seem to be independent of host iron metabolism and free of significant haematological side effects. Through direct action on the parasite, DFO has more effective trypanostatic than trypanocidal properties.     

A cyano-bridged FeRe(CN)2 cluster incorporating two high-magnetic anisotropy building units

The pentagonal bipyramidal high-spin iron(II) complex, [(TPA^2C(O)NHtBu)Fe(CF₃SO₃)]⁺, is shown to exhibit a high-anisotropy ground state, with fits to dc magnetization data providing an axial zero-field splitting parameter of D = − 7.9 cm⁻¹. The utility of this compound as a building unit is demonstrated, as its reaction with [ReCl₄(CN)₂]²⁻ affords the cyano-bridged dinuclear cluster (TPA^2C(O)NHtBu)FeReCl₄(CN)₂. dc magnetic susceptibility measurements reveal intracluster ferromagnetic exchange interactions between Fe^II and Re^IV centers, with J = +3.0 cm⁻¹, giving rise to a spin ground state of S = 7/2. Moreover, fits to dc magnetization data obtained for the FeRe cluster show the presence of strong axial anisotropy, with D = −2.3 cm⁻¹. Finally, variable-frequency ac susceptibility measurements reveal the onset of slow magnetic relaxation at low temperature, suggesting that the FeRe cluster is a single-molecule magnet.     

Liver iron overloading in captive muriquis (Brachyteles spp.)

Background Iron accumulation was investigated qualitatively and quantitatively in the liver of 15 captive Brachyteles spp. Methods Hepatic hemosiderosis index (HHI) was determined as the area percentage of the liver parenchyma occupied by hemosiderin and ferritin deposits, through computerized histomorphometric analysis of Prussian blue–stained histologic sections. Results All studied animals presented liver hemosiderosis, and HHI ranged from 0.2% to 41.7%. There were no significant differences in HHI between muriqui species or genders, and no correlations were detected among HHI and age, time in captivity or body mass. Iron deposits were accompanied by other hepatic disorders. Conclusions This is the first study addressing the occurrence and consequences of iron overloading in the liver of muriquis. We propose that hemosiderosis may act as a contribute factor for the development of hepatic injuries. Further studies are advised to clarify the role of diet in the pathogenesis of hemosiderosis in these atelids.     

Thermal adaptability and disease association in common carp (Cyprinus carpio communis) acclimated to different (four) temperatures

The present study was designed to investigate the effect of temperature (20 °C, 24 °C, 28 °C and 32 °C) on the heamato-biochemical and histological alterations of Cyprinus carpio communis. Increase in the temperature showed significant decrease in the serum protein, while a reduced level of blood glucose at high temperature of 32 °C was observed leading to hypoglycemic conditions in the experimental fishes. A significant correlation (P<0.01) was observed between cholesterol (Cho) and triglycerides (TG) for different temperature treatments. Elevated blood urea nitrogen (BUN) at high temperatures was a good indicator of gill osmoregulatory failure. A variation of 86.40% and 38.33%, respectively, was noticed in alanine aminotransferase (ALT) and aspartate aminotransferase (AST) at 32 °C over minimum experimental temperature of 20 °C. The increase in red blood cell (RBC) and Heamoglobin (Hb) concentration is associated with the decrease of mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC), could be the reason for observed poikilo-anisocytosis. Histological studies of different organs of experimental fishes showed accumulation of MMC's (melanomacrophagic centers) and atrophy of the interrenal tissue on exposure to various levels of temperature. These changes were related to severity of thermal stress, being most marked when high temperature was prolonged during acclimatization. Some fishes were found infested by protozoan parasite at elevated temperature of 32 °C. Increased levels of certain biochemical and haemotological parameters studied were strongly correlated with disease in the Cyprinus carpio communis species.     

Exploring the catalytic potential of the 3-His mononuclear nonheme Fe(II) center: discovery and characterization of an unprecedented maltol cleavage activity

Mononuclear nonheme iron enzymes (MNHEs) catalyze a range of very diverse reactions in O₂ metabolism, but they share a common principle active-site organization. To investigate a putative catalytic promiscuity of these enzymatic metal centers, we studied the reactivity of the 3-His ligated metal center of diketone cleaving enzyme (Dke1) toward non-native substrates, with a focus on alternative O₂ dependent reactions. From a screening approach, which aims at eliminating steric factors by including minimal substrate-substructures, three alternative, ‘non-β-dicarbonyl-cleavage’ reactions are identified, among them an unprecedented oxygenation of maltol. Maltol cleavage is characterized by steady state and fast kinetic measurements and shows an O₂ concentration dependent rate determining step k_cat/K_M(O₂) of 0.3 mM^− 1 s^− 1 and a strict coupling of O₂ reduction and substrate oxidation. Furthermore, the catalytic potential of the 3-His metal center for O₂ dependent catechol ring-cleavage and phenylpyruvate oxidation (PP) is demonstrated.     

Insights into modulation of calcium signaling by magnesium in calmodulin, troponin C and related EF-hand proteins

The Ca²⁺-binding helix-loop-helix structural motif called “EF-hand” is a common building block of a large family of proteins that function as intracellular Ca²⁺-receptors. These proteins respond specifically to micromolar concentrations of Ca²⁺ in the presence of ~1000-fold excess of the chemically similar divalent cation Mg²⁺. The intracellular free Mg²⁺ concentration is tightly controlled in a narrow range of 0.5-1.0 mM, which at the resting Ca²⁺ levels is sufficient to fully or partially saturate the Ca²⁺-binding sites of many EF-hand proteins. Thus, to convey Ca²⁺ signals, EF-hand proteins must respond differently to Ca²⁺ than to Mg²⁺. In this review the structural aspects of Mg²⁺ binding to EF-hand proteins are considered and interpreted in light of the recently proposed two-step Ca²⁺-binding mechanism (Grabarek, Z., J. Mol. Biol., 2005, 346, 1351). It is proposed that, due to stereochemical constraints imposed by the two-EF-hand domain structure, the smaller Mg²⁺ ion cannot engage the ligands of an EF-hand in the same way as Ca²⁺ and defaults to stabilizing the apo-like conformation of the EF-hand. It is proposed that Mg²⁺ plays an active role in the Ca²⁺-dependent regulation of cellular processes by stabilizing the “off state” of some EF-hand proteins, thereby facilitating switching off their respective target enzymes at the resting Ca²⁺ levels. Therefore, some pathological conditions attributed to Mg²⁺ deficiency might be related to excessive activation of underlying Ca²⁺-regulated cellular processes. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.     

HIV-1 Envelope Glycoprotein Biosynthesis, Trafficking, and Incorporation

The HIV-1 envelope (Env) glycoproteins play an essential role in the virus replication cycle by mediating the fusion between viral and cellular membranes during the entry process. The Env glycoproteins are synthesized as a polyprotein precursor (gp160) that is cleaved by cellular proteases to the mature surface glycoprotein gp120 and the transmembrane glycoprotein gp41. During virus assembly, the gp120/gp41 complex is incorporated as heterotrimeric spikes into the lipid bilayer of nascent virions. These gp120/gp41 complexes then initiate the infection process by binding receptor and coreceptor on the surface of target cells. Much is currently known about the HIV-1 Env glycoprotein trafficking pathway and the structure of gp120 and the extracellular domain of gp41. However, the mechanism by which the Env glycoprotein complex is incorporated into virus particles remains incompletely understood. Genetic data support a major role for the cytoplasmic tail of gp41 and the matrix domain of Gag in Env glycoprotein incorporation. Still to be defined are the identities of host cell factors that may promote Env incorporation and the role of specific membrane microdomains in this process. Here, we review our current understanding of HIV-1 Env glycoprotein trafficking and incorporation into virions.