Vascular damage by unstable hemoglobins: The role of heme-depleted globin

Antimalarial Quinoline Drugs Inhibit β-Hematin and Increase Free Hemin Catalyzing Peroxidative Reactions and Inhibition of Cysteine Proteases

Malaria caused by Plasmodium affects millions people worldwide. Plasmodium consumes hemoglobin during its intraerythrocytic stage leaving toxic heme. Parasite detoxifies free heme through formation of hemozoin (β-hematin) pigment. Proteolysis of hemoglobin and formation of hemozoin are two main targets for antimalarial drugs. Quinoline antimarial drugs and analogs (β-carbolines or nitroindazoles) were studied as inhibitors of β-hematin formation. The most potent inhibitors were quinacrine, chloroquine, and amodiaquine followed by quinidine, mefloquine and quinine whereas 8-hydroxyquinoline and β-carbolines had no effect. Compounds that inhibited β-hematin increased free hemin that promoted peroxidative reactions as determined with TMB and ABTS substrates. Hemin-catalyzed peroxidative reactions were potentiated in presence of proteins (i.e. globin or BSA) while antioxidants and peroxidase inhibitors decreased peroxidation. Free hemin increased by chloroquine action promoted oxidative reactions resulting in inhibition of proteolysis by three cysteine proteases: papain, ficin and cathepsin B. Glutathione reversed inhibition of proteolysis. These results show that active quinolines inhibit hemozoin and increase free hemin which in presence of H2O2 that abounds in parasite digestive vacuole catalyzes peroxidative reactions and inhibition of cysteine proteases. This work suggests a link between the action of quinoline drugs with biochemical processes of peroxidation and inhibition of proteolysis.

Safe coordinated trafficking of heme and iron with copper maintain cell homeostasis: modules from the hemopexin system

Studies with patients, animal models of human disease and hemopexin null mice have shown that the heme-binding protein hemopexin is vital for the protection of a variety of cell types and tissues against heme toxicity. The presence of hemopexin in all biological fluids examined to date indicates wide roles in abrogating heme toxicity in human tissues; and, thus, is clinically relevant. Heme-hemopexin endocytosis leads to coordinated trafficking of heme, iron and copper as heme traffics from endosomes to heme oxygenases (HOs) in the smooth endoplasmic reticulum and to the nucleus. This is safe redox-metal trafficking, without oxidative stress, as iron released from heme catabolism by HOs as well as copper taken up with heme-hemopexin move through the cell. To our knowledge, this coordinated metal trafficking has been described only for the hemopexin system and differs from the cell's response to non-protein bound heme, which can be toxic. We propose that defining how cells respond to heme-hemopexin endocytosis, a natural cytoprotective system, will aid our understanding of how cells adapt as they safely respond to increases in heme, Fe(II) and copper. This is relevant for many genetic hemolytic diseases and conditions, stroke and hemorrhage as well as neurodegeneration. Such analyses will help to define a pattern of events that can be utilized to characterize how dysfunctional redox and transition metal handling is linked to the development of pathology in disease states such as Alzheimer's disease when metal homeostasis is not restored; and potentially provide novel targets and approaches to improve therapies.

Hemoglobin levels during the first trimester of pregnancy are associated with the risk of gestational diabetes mellitus, pre-eclampsia and preterm birth in Chinese women: a retrospective study

BACKGROUND

Hemoglobin (Hb) measurement is a standard test among pregnant women during the first perinatal visit that is used to evaluate physical status and anemia. However, studies focusing on Hb levels and pregnancy outcomes are scarce. This study aimed to determine whether Hb levels in early pregnancy were associated with the risk of gestational diabetes mellitus (GDM), pre-eclampsia (PE) and preterm birth.

METHODS

A hospital-based retrospective study was conducted among 21,577 singleton, non-smoking pregnancies between June 2013 and January 2015. The demographic data and medical information of each participant were collected individually through questionnaires and patient medical records. Odds ratios were generated using a multivariate logistic regression analysis to evaluate the relative risk of GDM, PE and preterm birth continuously and across different hemoglobin ranges in the overall population and in women from different pre-pregnancy body mass index (BMI) categories, respectively. The level of statistical significance was set at 0.05.

RESULTS

(1) For women who were underweight, normal-weight, overweight and obese, early pregnancy Hb levels were 127.8 ± 10.1 g/L, 129.6 ± 9.7 g/L, 132.2 ± 9.5 g/L and 133.4 ± 9.4 g/L, respectively. (2) Women with GDM and PE had significantly increased Hb levels during early pregnancy compared with controls, whereas women with preterm birth processed significantly decreased Hb levels. (3) After adjusting for confounders, the risks for GDM and PE increased with high maternal Hb (OR: 1.27 for Hb 130-149; OR: 2.06 for Hb ≥ 150 g/L), and the risk for preterm birth decreased with high maternal Hb (OR: 1.30 for Hb 130-149; OR: 2.38 for Hb ≥ 150 g/L) and increased with low maternal Hb (OR: 1.41 for Hb <  110 g/L). Among women whose BMI was < 24 kg/m2, high GDM (OR: 1.27 for Hb 130-149; OR: 1.84 for Hb ≥ 150 g/L) and low preterm rates (OR: 0.77 for Hb 130-149; OR: 0.23 for Hb ≥ 150 g/L) were observed with high Hb, whereas in women whose BMI was ≥24 kg/m2, only high GDM rates were observed with Hb > 150 g/L (OR: 2.33).

CONCLUSION

These findings suggest that Hb levels during early pregnancy play a role in predicting the risk of GDM, PE and preterm birth.

Methemoglobin-induced signaling and chemokine responses in human alveolar epithelial cells

Diffuse alveolar hemorrhage is characterized by the presence of red blood cells and free hemoglobin in the alveoli and complicates a number of serious medical and surgical lung conditions including the pulmonary vasculitides and acute respiratory distress syndrome. In this study we investigated the hypothesis that exposure of human alveolar epithelial cells to hemoglobin and its breakdown products regulates chemokine release via iron- and oxidant-mediated activation of the transcription factor NF-κB. Methemoglobin alone stimulated the release of IL-8 and MCP-1 from A549 cells via activation of the NF-κB pathway; additionally, IL-8 required ERK activation and MCP-1 required JNK activation. Neither antioxidants nor iron chelators and knockdown of ferritin heavy and light chains affected these responses, indicating that iron and reactive oxygen species are not involved in the response of alveolar epithelial cells to methemoglobin. Incubation of primary cultures of human alveolar type 2 cells with methemoglobin resulted in a similar pattern of chemokine release and signaling pathway activation. In summary, we have shown for the first time that methemoglobin induced chemokine release from human lung epithelial cells independent of iron- and redox-mediated signaling involving the activation of the NF-κB and MAPK pathways. Decompartmentalization of hemoglobin may be a significant proinflammatory stimulus in a variety of lung diseases.

Pathological conditions involving extracellular hemoglobin: molecular mechanisms, clinical significance, and novel therapeutic opportunities for α(1)-microglobulin

Hemoglobin (Hb) is the major oxygen (O(2))-carrying system of the blood but has many potentially dangerous side effects due to oxidation and reduction reactions of the heme-bound iron and O(2). Extracellular Hb, resulting from hemolysis or exogenous infusion, is shown to be an important pathogenic factor in a growing number of diseases. This review briefly outlines the oxidative/reductive toxic reactions of Hb and its metabolites. It also describes physiological protection mechanisms that have evolved against extracellular Hb, with a focus on the most recently discovered: the heme- and radical-binding protein α(1)-microglobulin (A1M). This protein is found in all vertebrates, including man, and operates by rapidly clearing cytosols and extravascular fluids of heme groups and free radicals released from Hb. Five groups of pathological conditions with high concentrations of extracellular Hb are described: hemolytic anemias and transfusion reactions, the pregnancy complication pre-eclampsia, cerebral intraventricular hemorrhage of premature infants, chronic inflammatory leg ulcers, and infusion of Hb-based O(2) carriers as blood substitutes. Finally, possible treatments of these conditions are discussed, giving a special attention to the described protective effects of A1M.

A transgenic mouse model expressing exclusively human hemoglobin E: indications of a mild oxidative stress

Hemoglobin (Hb) E (β26 Glu→Lys) is the most common abnormal hemoglobin (Hb) variant in the world. Homozygotes for HbE are mildly thalassemic as a result of the alternate splice mutation and present with a benign clinical picture (microcytic and mildly anemic) with rare clinical symptoms. Given that the human red blood cell (RBC) contains both HbE and excess α-chains along with minor hemoglobins, the consequence of HbE alone on RBC pathophysiology has not been elucidated. This becomes critical for the highly morbid β(E)-thalassemia disease. We have generated transgenic mice exclusively expressing human HbE (HbEKO) that exhibit the known aberrant splicing of β(E) globin mRNA, but are essentially non-thalassemic as demonstrated by RBC α/β (human) globin chain synthesis. These mice exhibit hematological characteristics similar to presentations in human EE individuals: microcytic RBC with low MCV and MCH but normal MCHC; target RBC; mild anemia with low Hb, HCT and mildly elevated reticulocyte levels and decreased osmotic fragility, indicating altered RBC surface area to volume ratio. These alterations are correlated with a mild RBC oxidative stress indicated by enhanced membrane lipid peroxidation, elevated zinc protoporphyrin levels, and by small but significant changes in cardiac function. The C57 (background) mouse and full KO mouse models expressing HbE with the presence of HbS or HbA are used as controls. In select cases, the HbA full KO mouse model is compared but found to be limited due to its RBC thalassemic characteristics. Since the HbEKO mouse RBC lacks an abundance of excess α-chains that would approximate a mouse thalassemia (or a human thalassemia), the results indicate that the observed in vivo RBC mild oxidative stress arises, at least in part, from the molecular consequences of the HbE mutation.

An alternative view of the proposed alternative activities of hemopexin

Hemopexin is a plasma protein that plays a well-established biological role in sequestering heme that is released into the plasma from hemoglobin and myoglobin as the result of intravascular or extravascular hemolysis as well as from skeletal muscle trauma or neuromuscular disease. In recent years, a variety of additional biological activities have been attributed to hemopexin, for example, hyaluronidase activity, serine protease activity, pro-inflammatory and anti-inflammatory activity as well as suppression of lymphocyte necrosis, inhibition of cellular adhesion, and binding of divalent metal ions. This review examines the challenges involved in the purification of hemopexin from plasma and in the recombinant expression of hemopexin and evaluates the questions that these challenges and the characteristics of hemopexin raise concerning the validity of many of the new activities proposed for this protein. As well, an homology model of the three-dimensional structure of human hemopexin is used to reveal that the protein lacks the catalytic triad that is characteristic of many serine proteases but that hemopexin possesses two highly exposed Arg-Gly-Glu sequences that may promote interaction with cell surfaces.

Differential gene expression analysis of placentas with increased vascular resistance and pre-eclampsia using whole-genome microarrays

Pre-eclampsia is a pregnancy complication characterized by hypertension and proteinuria. There are several factors associated with an increased risk of developing pre-eclampsia, one of which is increased uterine artery resistance, referred to as “notching”. However, some women do not progress into pre-eclampsia whereas others may have a higher risk of doing so. The placenta, central in pre-eclampsia pathology, may express genes associated with either protection or progression into pre-eclampsia. In order to search for genes associated with protection or progression, whole-genome profiling was performed. Placental tissue from 15 controls, 10 pre-eclamptic, 5 pre-eclampsia with notching, and 5 with notching only were analyzed using microarray and antibody microarrays to study some of the same gene product and functionally related ones. The microarray showed 148 genes to be significantly altered between the four groups. In the preeclamptic group compared to notch only, there was increased expression of genes related to chemotaxis and the NF-kappa B pathway and decreased expression of genes related to antigen processing and presentation, such as human leukocyte antigen B. Our results indicate that progression of pre-eclampsia from notching may involve the development of inflammation. Increased expression of antigen-presenting genes, as seen in the notch-only placenta, may prevent this inflammatory response and, thereby, protect the patient from developing pre-eclampsia.

Perfusion of human placenta with hemoglobin introduces preeclampsia-like injuries that are prevented by α1-microglobulin

BACKGROUND

Preeclamptic women have increased plasma levels of free fetal hemoglobin (HbF), increased gene expression of placental HbF and accumulation of free HbF in the placental vascular lumen. Free hemoglobin (Hb) is pro-inflammatory, and causes oxidative stress and tissue damage.

METHODOLOGY

To show the impact of free Hb in PE, we used the dual ex vivo placental perfusion model. Placentas were perfused with Hb and investigated for physical parameters, Hb leakage, gene expression and morphology. The protective effects of α(1)-microglobulin (A1M), a heme- and radical-scavenger and antioxidant, was investigated.

RESULTS

Hb-addition into the fetal circulation led to a significant increase of the perfusion pressure and the feto-maternal leakage of free Hb. Morphological damages similar to the PE placentas were observed. Gene array showed up-regulation of genes related to immune response, apoptosis, and oxidative stress. Simultaneous addition of A1M to the maternal circulation inhibited the Hb leakage, morphological damage and gene up-regulation. Furthermore, perfusion with Hb and A1M induced a significant up-regulation of extracellular matrix genes.

SIGNIFICANCE

The ex vivo Hb-perfusion of human placenta resulted in physiological and morphological changes and a gene expression profile similar to what is observed in PE placentas. These results underline the potentially important role of free Hb in PE etiology. The damaging effects were counteracted by A1M, suggesting a role of this protein as a new potential PE therapeutic agent.

Differential cellular responses to protein adducts of naphthoquinone and monocrotaline pyrrole

Protein-xenobiotic adducts are byproducts of xenobiotic metabolism. While there is a correlation between protein adduction and target organ toxicity, a cause and effect relationship is not often clear. Naphthoquinone (NQ) and monocrotaline pyrrole (MCTP) are two pneumotoxic electrophiles that form covalent adducts with a similar select group of proteins rich in reactive thiols. In this study, we treated human pulmonary artery endothelial cells (HPAEC) with NQ, MCTP, or preformed NQ or MCTP adducts to the protein galectin-1 (gal-1) and examined indicators of reactive oxygen species (ROS) oxidative injury, markers of apoptosis (caspase-3 and annexin V), and gene responses of cellular stress. ROS production was assayed fluorescently using CM-H(2)DCFDA. NQ adducts to gal-1 (NQ-gal) produced 183% more intracellular ROS than gal-1 alone (p < 0.0001). Caspase-3 activity and annexin V staining of phosphatidylserine were used to assess apoptotic activity in treated cells. HPAEC exposed to MCTP-gal had increases in both caspase-3 activation and membrane translocation of annexin V relative to gal-1 alone (p < 0.0001). Direct application of NQ produced significantly more ROS and induced significant caspase-3 activation, whereas MCTP did not. Human bronchial epithelial cells were also exposed to MCTP-gal and found to have significant increases in both caspase-3 activation and annexin V staining in comparison to that of gal-1 (p < 0.05). Western blot analysis showed that both NQ and MCTP significantly induced the Nrf2 mediated stress response pathway despite differences in ROS generation. ER stress was not induced by either adducts or parent compounds as seen by quantitative RT-PCR, but HOX-1 expression was significantly induced by NQ-gal and MCTP alone. Electrophile adduction to gal-1 produces different cytotoxic effects specific to each reactive intermediate.

Hemoglobin induces the expression of indoleamine 2,3-dioxygenase in dendritic cells through the activation of PI3K, PKC, and NF-kappaB and the generation of reactive oxygen species

Indoleamine 2,3-dioxygenase (IDO) is the rate-limiting enzyme in the kynurenine (Kyn) pathway of tryptophan (Trp) metabolism. IDO is immunosuppressive and is induced by inflammation in macrophages and dendritic cells (DCs). Previous studies have shown the serum Kyn/Trp levels in patients with hemolytic anemia to be notably high. In the present study, we demonstrated that hemoglobin (Hb), but not hemin or heme-free globin (Apo Hb), induced IDO expression in bone marrow-derived myeloid DCs (BMDCs). Hb induced the phosphorylation and degradation of I kappaB alpha. Hb-induced IDO expression was inhibited by inhibitors of PI3-kinase (PI3K), PKC and nuclear factor (NF)-kappaB. Hb translocated both RelA and p52 from the cytosol to the nucleus and induced the intracellular generation of reactive oxygen species (ROS). Hb-induced IDO expression was inhibited by anti-oxidant N-acetyl-L-cysteine (NAC) or mixtures of SOD and catalase, however, IDO expression was enhanced by 3-amino-1,2,4-triazole, an inhibitor of catalase, suggesting that the generation of ROS such as O(2) (-), H(2)O(2), and hydroxyl radical is required for the induction of IDO expression. The generation of ROS was inhibited by a PKC inhibitor, and this action was further enhanced by addition of a PI3K inhibitor. Hb induced Akt phosphorylation, which was inhibited by a PI3K inhibitor and enhanced by a PKC inhibitor. These results suggest that the activation of NF-kappaB through the PI3K-PKC-ROS and PI3K-Akt pathways is required for the Hb-induced IDO expression in BMDCs.