Mechanisms of haptoglobin protection against hemoglobin peroxidation triggered endothelial damage

Extracellular hemoglobin (Hb) has been recognized as a disease trigger in hemolytic conditions such as sickle cell disease, malaria, and blood transfusion. In vivo, many of the adverse effects of free Hb can be attenuated by the Hb scavenger acute-phase protein haptoglobin (Hp). The primary physiologic disturbances that can be caused by free Hb are found within the cardiovascular system and Hb-triggered oxidative toxicity toward the endothelium has been promoted as a potential mechanism. The molecular mechanisms of this toxicity as well as of the protective activities of Hp are not yet clear. Within this study, we systematically investigated the structural, biochemical, and cell biologic nature of Hb toxicity in an endothelial cell system under peroxidative stress. We identified two principal mechanisms of oxidative Hb toxicity that are mediated by globin degradation products and by modified lipoprotein species, respectively. The two damage pathways trigger diverse and discriminative inflammatory and cytotoxic responses. Hp provides structural stabilization of Hb and shields Hb's oxidative reactions with lipoproteins, providing dramatic protection against both pathways of toxicity. By these mechanisms, Hp shifts Hb's destructive pseudo-peroxidative reaction to a potential anti-oxidative function during peroxidative stress

Mitochondrial apoptosis is induced by Alkoxy phenyl-1-propanone derivatives through PP2A-mediated dephosphorylation of Bad and Foxo3A in CLL

Protein phosphatase 2 A (PP2A) is a tumour suppressor whose strong inhibition underlies the phosphorylation-dependent, anti-apoptotic mechanisms in Chronic Lymphocytic Leukemia (CLL). Inactivation of PP2A is due to the cooperative action of the phosphorylation of Y307 of its catalytic subunit by the aberrant cytosolic pool of the Src Family Kinase Lyn and the interaction with its protein inhibitor SET, which is overexpressed in CLL. In this study, we developed a library of compounds, the most potent being the one named CC11, which restores PP2A activity by disrupting the PP2A/SET complex, thereby triggering the mitochondrial pathway of apoptosis. This process involves the recruitment of the pro-apoptotic BH3-only proteins Bad and Bim to mitochondria, the former upon direct dephosphorylation and the latter being newly expressed upon dephosphorylation and activation of its transcription factor FoxO3a. These findings highlight that PP2A antagonizes the prosurvival pathways controlled by Akt, which phosphorylates and thereby suppresses a variety of pro-apoptotic factors and tumour suppressors including Bad and FoxO3a. Furthermore, the PP2A-mediated pro-apoptotic effect of CC11 is synergistically potentiated by the abrogation of Lyn's activity. Our results show that CC11 represents a promising lead compound for a new therapeutic rationale aimed at abrogating the aberrant oncogenic signals in CLL