Characterization of cGMP-specific phosphodiesterases (PDE) in erythroid cells and effects PDE inhibitors on the production of fetal hemoglobin

Author(s)

Camila Bononi de Almeida

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Ciências Médicas
• Defense date: 2006-11-14

Examining board members

Nicola Amanda Conran Zorzetto; Alessandra Gambero; Vagner de Castro

• Advisor: Nicola Amanda Conran Zorzetto

Abstract

Sickle cell disease (SCD) is a systemic disease with a multifaceted pathophysiology; the polymerisation of the sickle haemoglobin molecule (HbS), when deoxygenated, has many consequences that include haemolysis, inflammation, dysregulated nitric oxide (NO) homeostasis and oxidative abnormalities. Agents, such as hydroxyurea (HU), that increase levels of fetal hemoglobin (HbF), with consequent inhibition of HbS polymerization, and that may counteract other aspects of the disease's pathophysiology characterize important therapies for the disorder. Whilst HU therapy successfully augments HbF levels in many patients, not all patients respond to treatment. Studies demonstrate that HU, when degraded, produces nitric oxide (NO), in turn activating the enzyme, soluble guanylate cyclase (GC) in erythroid lineage cells. GC converts GTP to cGMP, which acts as a second messenger for NO, possibly activating the transcription of the ?-globin gene and, consequently, increasing the concentration of HbF. Due to evidence that NO bioavailability may be decreased in SCD individuals, recent research into SCD has focused on the role of NO in the disease, particularly since this gas is an important vasodilator. The objective of this study was to investigate which family(ies) of phosphodiesterases (PDE) may mediate the degradation of cGMP in erythroid lineage cells and whether drugs that inhibit these PDEs are capable of augmenting the production of ?-globin and, consequently, HbF in erythroid cells in culture. For this, cultures of K562 erythroleukemic cells were treated with different PDE inhibitors; vinpocetine, sildenafil citrate, dipyridamole and zaprinast. In addition, cultures were also treated with the guanylate cyclase stimulator, BAY41-2272. Increased levels of cGMP were observed principally in cells treated with 10µg/ml dipyridamole and at some time-points in the presence of 10 and 50µM vinpocetine. No changes in cGMP levels were observed in cells treated with sildenafil nor with zaprinast. However, cells treated with BAY 41-2272 demonstrated augmented cGMP levels at all concentrations used. With regard to relative ?-globin gene expression, dipyridamole, vinpocetine, sildenafil and zaprinast did not increase ?-globin gene expression; in contrast, BAY 41-2272 (60 and 300nM) stimulated increased ?-globin expression after 48h of culture. The gene expressions of PDEs 1, 5 and 9 were also studied in different hematopoietic cell types and other tissues. PDE9 is expressed, at significantly higher levels, in K562 cells (erythroleukemic cells), reticulocytes and neutrophils than in numerous other cell types tested (T98G, colon, mammary, ovary, testicle, liver, skin, spleen, uterus, limphonode). Furthermore, the expression of this PDE was even higher in the reticulocytes and neutrophils of patients with SCD. In patients on HU therapy, the expression of PDE9 in reticulocytes was reversed back to levels similar to those seen in controls. In contrast, PDE9 expression in neutrophils was similar in patients on or of HU therapy. Thus, since the increase in intracellular levels of cGMP may be important for the production of HbF in erythroid cells and also to inhibit leukocyte adhesion, the inhibition of the action of PDE9 may represent a novel drug target for cell-specific treatment of SCD (AU)