Enhanced plasminogen activator inhibitor-1 expression in transgenic mice with hepatocyte-specific overexpression of superoxide dismutase or glutathione peroxidase

Insights on the mechanisms of action of ozone in the medical therapy against COVID-19

An increasing amount of reports in the literature is showing that medical ozone (O₃) is used, with encouraging results, in treating COVID-19 patients, optimizing pain and symptoms relief, respiratory parameters, inflammatory and coagulation markers and the overall health status, so reducing significantly how much time patients underwent hospitalization and intensive care. To date, aside from mechanisms taking into account the ability of O₃ to activate a rapid oxidative stress response, by up-regulating antioxidant and scavenging enzymes, no sound hypothesis was addressed to attempt a synopsis of how O₃ should act on COVID-19. The knowledge on how O₃ works on inflammation and thrombosis mechanisms is of the utmost importance to make physicians endowed with new guns against SARS-CoV2 pandemic. This review tries to address this issue, so to expand the debate in the scientific community.

Reactive Oxygen Species in Venous Thrombosis

Reactive oxygen species (ROS) have physiological roles as second messengers, but can also exert detrimental modifications on DNA, proteins and lipids if resulting from enhanced generation or reduced antioxidant defense (oxidative stress). Venous thrombus (DVT) formation and resolution are influenced by ROS through modulation of the coagulation, fibrinolysis, proteolysis and the complement system, as well as the regulation of effector cells such as platelets, endothelial cells, erythrocytes, neutrophils, mast cells, monocytes and fibroblasts. Many conditions that carry an elevated risk of venous thrombosis, such as the Antiphospholipid Syndrome, have alterations in their redox homeostasis. Dietary and pharmacological antioxidants can modulate several important processes involved in DVT formation, but their overall effect is unknown and there are no recommendations regarding their use. The development of novel antioxidant treatments that aim to abrogate the formation of DVT or promote its resolution will depend on the identification of targets that enable ROS modulation confined to their site of interest in order to prevent off-target effects on physiological redox mechanisms. Subgroups of patients with increased systemic oxidative stress might benefit from unspecific antioxidant treatment, but more clinical studies are needed to bring clarity to this issue.

Tissue-type plasminogen activator is not necessary for platelet-derived growth factor-c activation

Platelet-derived growth factors (PDGFs) are critical for development; their over-expression is associated with fibrogenesis. Full-length PDGF-C is secreted as an inactive dimer, requiring cleavage to allow receptor binding. Previous studies indicate that tissue-type plasminogen activator (tPA) is the specific protease that performs this cleavage; in vivo confirmation is lacking. We demonstrate that primary hepatocytes from tpa KO mice produce less cleaved active PDGF-CC than do wild type hepatocytes, suggesting that tPA is critical for in vitro activation of this growth factor. We developed mice that over-express full-length human PDGF-C in the liver; these mice develop progressive liver fibrosis. To test whether tPA is important for cleavage and activation of PDGF-C in vivo, we intercrossed PDGF-C transgenic (Tg) and tpa knock-out (KO) mice, anticipating that lack of tPA would result in decreased fibrosis due to lack of hPDGF-C cleavage. To measure levels of cleaved, dimerized PDGF-CC in sera, we developed an ELISA that specifically detects cleaved PDGF-CC. We report that the absence of tpa does not affect the phenotype of `PDGF-C Tg mice. PDGF-C Tg mice lacking tPA have high serum levels of cleaved growth factor, significant liver fibrosis, and gene expression alterations similar to those of PDGF-C Tg mice with intact tPA. Furthermore, urokinase plasminogen activator and plasminogen activator inhibitor-1 expression are increased in PDGF-C Tg; tpa KO mice. Our ELISA data suggest a difference between in vitro and in vivo activation of this growth factor, and our mouse model confirms that multiple proteases cleave and activate PDGF-C in vivo.

Sustained submicromolar H2O2 levels induce hepcidin via signal transducer and activator of transcription 3 (STAT3)

The peptide hormone hepcidin regulates mammalian iron homeostasis by blocking ferroportin-mediated iron export from macrophages and the duodenum. During inflammation, hepcidin is strongly induced by interleukin 6, eventually leading to the anemia of chronic disease. Here we show that hepatoma cells and primary hepatocytes strongly up-regulate hepcidin when exposed to low concentrations of H(2)O(2) (0.3-6 μM), concentrations that are comparable with levels of H(2)O(2) released by inflammatory cells. In contrast, bolus treatment of H(2)O(2) has no effect at low concentrations and even suppresses hepcidin at concentrations of >50 μM. H(2)O(2) treatment synergistically stimulates hepcidin promoter activity in combination with recombinant interleukin-6 or bone morphogenetic protein-6 and in a manner that requires a functional STAT3-responsive element. The H(2)O(2)-mediated hepcidin induction requires STAT3 phosphorylation and is effectively blocked by siRNA-mediated STAT3 silencing, overexpression of SOCS3 (suppressor of cytokine signaling 3), and antioxidants such as N-acetylcysteine. Glycoprotein 130 (gp130) is required for H(2)O(2) responsiveness, and Janus kinase 1 (JAK1) is required for adequate basal signaling, whereas Janus kinase 2 (JAK2) is dispensable upstream of STAT3. Importantly, hepcidin levels are also increased by intracellular H(2)O(2) released from the respiratory chain in the presence of rotenone or antimycin A. Our results suggest a novel mechanism of hepcidin regulation by nanomolar levels of sustained H(2)O(2). Thus, similar to cytokines, H(2)O(2) provides an important regulatory link between inflammation and iron metabolism.

Opposite expression of the antioxidant heme oxygenase-1 in primary cells and tumor cells: regulation by interaction of USF-2 and Fra-1

Heme oxygenase-1 is the rate-limiting enzyme for the degradation of the prooxidant heme. Previously, we showed that an E-box within the HO-1 promoter is crucial for the regulation of HO-1 expression in primary hepatocytes. Further to investigate the importance of this E-box, we determined the regulatory capacity of the E-box-binding factor USF-2 in primary cells in comparison with transformed cell lines. We found that HO-1 expression was inhibited by USF-2 in primary cells, whereas it was induced in tumor cell lines. Mutation of either the E-box or the AP-1 site within the HO-1 promoter only partially affected the USF-dependent regulation. However, this regulation was dramatically reduced in tumor cells and completely abolished in primary cells transfected with an HO-1 promoter construct containing mutations in both the E-box and the AP-1 site, suggesting that AP-1 factors and USF-2 may act in a cooperative manner. Indeed, protein-protein interaction studies revealed that USF proteins interacted with Fra-1. Further, the USF-dependent HO-1 promoter activity was not detectable with an USF-2 mutant lacking residues of the USF-specific region (USR) or the transactivation domain encoded by exon 4. Together, these data suggest that USF-2 has opposite regulatory roles for HO-1 gene expression in primary cells and tumor cell lines.

Redox regulation of the coagulation cascade

Enhanced coagulation and thrombosis are linked to a variety of cardiovascular and metabolic diseases, as well as to cancer. Many of these diseases are also associated with enhanced levels of reactive oxygen species (ROS). Indeed, ROS have been made responsible for promoting many of these diseases. They have been shown not only to be cytotoxic, but also to serve as signaling molecules in a variety of cells. Recently, evidence accumulated that ROS and the redox state are also important in the control of blood coagulation and thrombosis.