Model Of Sickle Cell Disease Research Articles

Endothelin‐1 via ETA receptor activation promotes renal iron deposition in murine models of iron overload

Renal iron deposition correlates with elevated plasma ET‐1 in patients and mouse model of sickle cell disease (SCD). Additionally, excessive renal iron accumulation in sickle cell mice (HbSS) is ameliorated by ETA receptor antagonism. Thus, we hypothesized that ET‐1 via ETA receptor activity leads to dysfunctional renal iron trafficking, promoting iron accumulation in the kidney. We conducted time‐ and concentration‐dependent in vitro studies on mouse proximal tubule (PT) cells and observed that ET‐1/ ETA signaling promotes cellular iron uptake (by increasing transferrin receptor 1 expression) and inhibits cellular iron removal pathways (65% reduction of ferroportin‐1 (FPN‐1) and doubled hepcidin (Hamp) expression). In vivo studies demonstrated that altered expression of iron transporters in PT of male HbSS mice was consistent with iron accumulation phenotype. ETA receptor blockade attenuated expression of the cellular iron uptake mediator, DMT‐1, and also decreased renal iron accumulation (1.43±0.06 vs. 2.62±0.12; p=0.097) by preserving FPN‐1, reducing Hamp expression, and increasing urinary iron excretion (10.9±1.0 vs 6.4±1.2 μg/24h; p=0.010). To determine the long‐term effect of ET‐1 on chronic renal iron accumulation, we generated HbSS mice lacking ET‐1 in vascular endothelial cells mice (HbSS VEET KO; using Tie‐2 Cre). There were no differences in anemia status between 20 weeks old male HbSS VEET KO and flox mice. However, plasma iron concentration (117.3±4.3 vs. 103.9±4.3 μg/dl, p=0.04) and urinary iron excretion (10.4±1.9 vs. 7.4±1.1 μg/24h; p=0.059) were elevated and renal iron deposition attenuated (24.3±1.3 vs. 33.8±2.3; p=0.008) in HbSS VEET KO mice. To further elucidate ET‐1/ETA receptor‐mediated renal iron accumulation already observed with pharmacological and genetic approaches in HbSS mice, using PEPCK Cre we generated PT specific ETA receptor knockout (PT ETA KO) mice. At baseline, 16 weeks old male and female PT ETA KO mice presented with higher plasma iron concentration (1.0±0.2 vs. 0.5±0.1 μg/ml; p=0.03) and urinary iron excretion (4.5±0.7 vs. 1.7±0.5 μg/24h; p=0.002), whereas renal iron deposition remained unchanged (2.26±0.48 vs. 2.44±0.73 Kpix/ μm; p=0.85). To induce hemolysis with acute iron overload, mice were injected with phenylhydrazine (PhZ, 40 mg/kg, IP; 2 consecutive days) or saline. PhZ significantly reduced hemoglobin in both PT ETA KO and littermate controls when compared to saline injected mice. Moreover, PT ETA KO mice given PhZ had increased plasma iron concentration (4.4±0.3 vs. 3.0±0.5 μg/ml; p=0.03) and urinary iron excretion (5.6±0.7 vs. 3.4±0.7 μg/24h; p=0.05) and decreased renal iron accumulation (0.50±0.22 vs. 0.90±0.20; p=0.011) when compared with saline injected KO control mice. Together, these data demonstrate that ET‐1, via ETA receptor activity, contributes to renal iron accumulation in murine models of iron overload.

Evidence of protective effects of recombinant ADAMTS13 in a humanized model of sickle cell disease.

Sickle cell disease (SCD) is an inherited red blood cell disorder that occurs worldwide. Acute vaso-occlusive crisis is the main cause of hospitalization in patients with SCD. There is growing evidence that inflammatory vasculopathy plays a key role in both acute and chronic SCD-related clinical manifestations. In a humanized mouse model of SCD, we found an increase of von Willebrand factor activity and a reduction in the ratio of a disintegrin and metalloproteinase with thrombospondin type 1 motif, number 13 (ADAMTS13) to von Willebrand factor activity similar to that observed in the human counterpart. Recombinant ADAMTS13 was administered to humanized SCD mice before they were subjected to hypoxia/reoxygenation (H/R) stress as a model of vaso-occlusive crisis. In SCD mice, recombinant ADAMTS13 reduced H/R-induced hemolysis and systemic and local inflammation in lungs and kidneys. It also diminished H/R-induced worsening of inflammatory vasculopathy, reducing local nitric oxidase synthase expression. Collectively, our data provide for the firsttime evidence that pharmacological treatment with recombinant ADAMTS13 (TAK-755) diminished H/R-induced sickle cell-related organ damage. Thus, recombinant ADAMTS13 might be considered as a potential effective disease-modifying treatment option for sickle cell-related acute events.

Endothelin A receptor antagonist attenuated renal iron accumulation in iron overload heme oxygenase-1 knockout mice.

Progressive iron accumulation and renal impairment are prominent in both patients and mouse models of sickle cell disease (SCD). Endothelin A receptor (ETA) antagonism prevents this iron accumulation phenotype and reduces renal iron deposition in the proximal tubules of SCD mice. To better understand the mechanisms of iron metabolism in the kidney and the role of the ETA receptor in iron chelation and transport, we studied renal iron handling in a nonsickle cell iron overload model, heme oxygenase-1 (Hmox-1-/-) knockout mice. We found that Hmox-1-/- mice had elevated plasma endothelin-1 (ET-1), cortical ET-1 mRNA expression, and renal iron content compared with Hmox-1+/+ controls. The ETA receptor antagonist, ambrisentan, attenuated renal iron deposition, without any changes to anemia status in Hmox-1-/- mice. This was accompanied by reduced urinary iron excretion. Finally, ambrisentan had an important iron recycling effect by increasing the expression of the cellular iron exporter, ferroportin-1 (FPN-1), and circulating total iron levels in Hmox-1-/- mice. These findings suggest that the ET-1/ETA signaling pathway contributes to renal iron trafficking in a murine model of iron overload.

TGF-β1 Reduces Neutrophil Adhesion and Prevents Acute Vaso-Occlusive Processes in Sickle Cell Disease Mice.

Sickle cell disease (SCD) patients experience chronic inflammation and recurrent vaso-occlusive episodes during their entire lifetime. Inflammation in SCD occurs with the overexpression of several inflammatory mediators, including transforming growth factor beta-1 (TGF-β1), a major immune regulator. In this study, we aimed to investigate the role played by TGF-β1 in vascular inflammation and vaso-occlusion in an animal model of SCD. Using intravital microscopy, we found that a daily dose of recombinant TGF-β1 administration for three consecutive days significantly reduced TNFα-induced leukocyte rolling, adhesion, and extravasation in the microcirculation of SCD mice. In contrast, immunological neutralization of TGF-β, in the absence of inflammatory stimulus, considerably increased these parameters. Our results indicate, for the first time, that TGF-β1 may play a significant ameliorative role in vascular SCD pathophysiology, modulating inflammation and vaso-occlusion. The mechanisms by which TGF-β1 exerts its anti-inflammatory effects in SCD, however, remains unclear. Our in vitro adhesion assays with TNFα-stimulated human neutrophils suggest that TGF-β1 can reduce the adhesive properties of these cells; however, direct effects of TGF-β1 on the endothelium cannot be ruled out. Further investigation of the wide range of the complex biology of this cytokine in SCD pathophysiology and its potential therapeutical use is needed.

Abstract WP260: The Response Of Annexin A1 In Astrocyte Activation And White Matter Injury- A New Target For Stroke In Sickle Cell Disease

Introduction: Ischemic stroke is common in sickle cell disease (SCD). White matter injuries, incorporated into silent cerebral infarcts, are major risk factors of stroke in SCD. The pathogenesis of cerebral infarction in SCD is not known. Induced thrombogenesis may cause impaired astrocyte that stimulates demyelination leading to white matter injury. Annexin A1 (Anxa1) can regulate astrocyte function by inhibiting intracellular phospholipase A2 (PLA2). We hypothesized that astrocyte activation during thrombogenic events promotes white matter injury in SCD. We tested astrocyte dysfunction and white matter injury in a clinically relevant mouse model of SCD. Methods: Cerebral Infarctions induced by de novo thrombogenesis were identified by TTC staining in transgenic sickle (SS) and control (AA) mice with human sickle and normal hemoglobin respectively. Cerebral microvessels and astrocytes were isolated from SS and AA mice. Elisa assays were used to measure thrombin, PLA2 and Anxa1. Immunofluorescence staining was performed to determine astrocyte activation and demyelination. Results: Thrombogenesis within cerebral microvessels was elevated by ~2-fold (n=5, p<0.05), and cerebral infarction became prevalent in SS mice compared to AA mice (n=7, p<0.001). The infarcted brain tissue from SS mice showed neuronal cell death, whereas the brain tissue from the AA mice appeared normal. The SS mice had increased glial fibrillary acid protein positive (GFAP + ) activated astrocytes with significant increase in PLA2 accumulation. Relative abundance of non-phosphorylated neurofilament H (SMI32) and myelin basic protein (MBP) (SMI32/MBP), indicating white matter injury, was substantially induced in the SS compared to the AA. Expression of Anxa1 reduced significantly in plasma as well as within astrocytes’ end feet attached to the isolated cerebral microvessels of the SS mice. Recombinant Anxa1 prophylaxis to SS mice reduced the GFAP + astrocytes, PLA2 accumulation, demyelination and infarct score (n=6, p<0.01) compared to SS mice treated with vehicle. Conclusion: White matter injury in SS mice is associated with astrocyte dysfunction and lack of Anxa1, which may be developed as potential therapeutic targets to prevent and/or treat stroke in SCD.

Corrected cerebral blood flow and reduced cerebral inflammation in berk sickle mice with higher fetal hemoglobin

Fetal hemoglobin (HbF) is known to lessen the severity of sickle cell disease (SCD), through reductions in peripheral vaso-occlusive disease and reduced risk for cerebrovascular events. However, the influence of HbF on oxygen delivery to high metabolism tissues like the brain, or its influence on cerebral perfusion, metabolism, inflammation or function have not been widely studied. We employed a Berkley mouse model (BERK) of SCD with gamma transgenes q3 expressing exclusively human α- and βS-globins with varying levels of γ globin expression to investigate the effect of HbF expression on the brain using magnetic resonance imaging (MRI), MRI diffusion tensor imaging (DTI) and spectroscopy (MRS) and hematological parameters. Hematological parameters improved with increasing γlevel expression, as did markers for brain metabolism, perfusion and inflammation. Brain microstructure assessed by DTI fractional anisotropy improved, while myo-inositol levels increased, suggesting improved microstructural integrity and reduced cell loss. Our results suggest that increasing γ levels not only improves sickle peripheral disease, but also improves brain perfusion and oxygen delivery while reducing brain inflammation while protecting brain microstructural integrity.

Interleukin-1 receptor antagonism leads to improved anaemia in a murine model of sickle cell disease and is associated with reduced ex vivo platelet-mediated erythrocyte sickling.

Sickle cell disease (SCD) is associated with haemolytic anaemia and secondary activation of leucocytes and platelets, which in turn may further exacerbate haemolysis. As cytokine signalling pathways may participate in this cycle, the present study investigated whether pharmacological blockade of the interleukin-1 receptor (IL-1R) would mitigate anaemia in a murine model of SCD. Within 2 weeks of treatment, reduced markers of haemolysis were observed in anakinra-treated mice compared to vehicle-treated mice. After 4 weeks of anakinra treatment, mice showed increased numbers of erythrocytes, haemoglobin, and haematocrit, along with reduced reticulocytes. Blood from anakinra-treated mice was less susceptible to ex vivo erythrocyte sickling and was resistant to exogenous IL-1β-mediated sickling. Supernatant generated from IL-1β-treated platelets was sufficient to promote erythrocyte sickling, an effect not observed with platelet supernatant generated from IL-1R-/- mice. The sickling effect of IL-1β-treated platelet supernatant was inhibited by a transforming growth factor-β (TGF-β) neutralising antibody, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibition, and superoxide scavengers, but replicated by recombinant TGF-β. In conclusion, pharmacological IL-1R antagonism leads to improved anaemia in a murine SCD model. IL-1β stimulation of platelets promotes erythrocyte sickling. This effect may be mediated by platelet-derived TGF-β-induced reactive oxygen species generation though erythrocyte NADPH oxidase.

Neutrophil DREAM Promotes Neutrophil Recruitment in Vascular Inflammation Via Nuclear Factor Kappa B-Dependent and Independent Mechanisms

The interaction between neutrophils and endothelial cells (ECs) is critical for the pathogenesis of vascular inflammation. Neutrophil recruitment to inflamed tissues is initiated by rolling on activated ECs through the interactions between P-/E-selectins and their ligands. Subsequently, activated integrins (mainly αLβ2 and αMβ2) and chemokine receptors bind to their ligands on ECs and mediate slow-rolling, adhesion, crawling, and transmigration of neutrophils. Although many neutrophil adhesion receptors have been identified, the regulation of their ligand-binding function remains not fully understood. Using real-time intravital microscopy with mice lacking downstream regulatory element antagonist modulator (DREAM) and their bone marrow chimeric mice, we demonstrated that hematopoietic cell DREAM contributes to neutrophil recruitment to sites of vascular inflammation induced by TNF-α- but not a G protein-coupled receptor ligand, MIP-2 or fMLP. Our studies using adoptive neutrophil transfers and flow chamber assays revealed that neutrophil DREAM positively regulates the neutrophil recruitment processes under TNF-α-induced inflammatory conditions. Using RNA-seq and biochemical and cell biological studies, we found that neutrophil DREAM upregulates numerous pro-inflammatory molecules and down-regulates anti-inflammatory molecules after TNF-α treatment. In particular, neutrophil DREAM repressed expression of A20, a negative regulator of NF-κB signaling, and enhanced phosphorylation of IκB kinase (IKK) in response to TNF-α, suggesting the role of neutrophil DREAM in NF-κB activity. Furthermore, we observed that DREAM deletion and IKK inhibition significantly diminishes the ligand-binding activity of β2 integrins in neutrophils after short-term treatment with TNF-α and that deletion of neutrophil DREAM does not affect the expression of other neutrophil adhesion receptors, such as PSGL-1, L-selectin, CD44, CXCR2, and CXCR4. As assessed by flow cytometry using conformation-specific reporter antibodies, knockdown of DREAM in neutrophil-like HL-60 cells decreased TNF-α-induced activation of β2 integrins. Neutrophil DREAM promoted degranulation through IKK-mediated SNAP-23 phosphorylation after short-term treatment with TNF-α, implying the role of neutrophil DREAM-IKK signaling in NF-κB-independent signaling. Using intravital microscopy with Berkeley mice (a mouse model of sickle cell disease) deficient in hematopoietic or nonhematopoietic DREAM, we demonstrated that hematopoietic cell DREAM is crucial for inducing intravascular cell-cell aggregation and vaso-occlusive events in microvessels following the TNF-α challenge. Furthermore, infusion of DREAM KO neutrophils, compared with WT neutrophils, significantly reduced neutrophil recruitment and vaso-occlusive events in TNF-α-challenged SCD mice. These results demonstrate that neutrophil DREAM positively regulates β2 integrin function and promotes neutrophil recruitment during sterile inflammation via NF-κB-dependent and independent mechanisms. Our study provides evidence that targeting DREAM might be a novel therapeutic strategy to reduce excessive neutrophil recruitment in inflammatory diseases. DisclosuresNo relevant conflicts of interest to declare.

Ftx-6058 Induces Fetal Hemoglobin Production and Ameliorates Disease Pathology in Sickle Cell Mice

Sickle cell disease (SCD) is a genetic disorder of the red blood cells caused by a mutation in the HBB gene, which results in red blood cell sickling, hemolysis, vaso-occlusive crises (VOCs), and other complications. Increasing HbF has the potential to prevent or reduce disease-related pathophysiology, including the risk of recurring events such as hemolysis and VOCs. Individuals with SCD who also have hereditary persistence of fetal hemoglobin (HPFH) and exhibit HbF levels of 25 - 30% are often asymptomatic from their SCD, underscoring the protective effect of increased HbF in SCD. Preclinical results with FTX-6058 demonstrate robust target engagement and corresponding increases in HbF levels up to approximately 40% of total hemoglobin, demonstrating the potential to have a significant impact in people living with SCD.FTX-6058 is an investigational, potent, and selective oral small-molecule inhibitor of Embryonic Ectoderm Development (EED) that has been demonstrated to induce robust fetal hemoglobin (HbF) protein expression in cell and murine models of SCD. Here, we report the in vivo effects of EED modulation, and subsequent polycomb repressive complex 2 (PRC2) inhibition in the Townes mouse model of Sickle Cell Disease. Compared with untreated and hydroxyurea treated animals, FTX-6058 (QD, 5mg/kg) exhibits potent target engagement as evidenced by ~70% reduction in H3K27me3 levels, the key epigenetic mark catalyzed by PRC2. Consistent with the robust target engagement observed with FTX-6058, a 2 - 3 fold increase in F cells and HbF protein were observed after 13 and 21 days of FTX-6058 treatment, which was pharmacologically superior to the fetal hemoglobin induction observed with 100 mg/kg hydroxyurea (~25% relative increase in F cells and HbF protein). A linear correlation was also observed between F cells and HbF protein production with FTX-6058 treatment, further supporting the robust HbF induction observed. Consistent with SCD disease presentation, Townes model mice have high reticulocyte counts as a result of premature RBC destruction and hemolysis. Townes model mice treated for 21 days with FTX-6058 ameliorated hemolysis as evidenced by decreases in reticulocytes and increases in red blood cells and total hemoglobin levels. Furthermore, FTX-6058 demonstrated the ability to impact inflammatory drivers of disease as evidenced by decreases in neutrophils and white blood cells. FTX-6058 did not have effects on other hematopoietic lineages. FTX-6058 also impacted pathophysiologic symptoms (e.g., splenomegaly) associated with SCD, as evidenced by ~25% reduction in spleen weight. While some trends were detected, no statistically significant changes were observed in hematological parameters or pathophysiologic symptoms with hydroxyurea, the current standard of care in SCD. These results observed with hydroxyurea underscore the need for new, novel therapies in SCD and other hemoglobinopathies.Taken together, these studies further support the therapeutic rationale of PRC2 modulation in SCD. The fetal hemoglobin induction and effects on hematological parameters and pathophysiologic symptoms observed with FTX-6058 have the potential to translate to meaningful clinical benefits in SCD and other hemoglobinopathies. DisclosuresMatson: Fulcrum Therapeutics, Inc.: Current Employment. Xie: Fulcrum Therapeutics, Inc.: Current equity holder in publicly-traded company, Ended employment in the past 24 months. Roth: Fulcrum Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company. Stuart: Fulcrum Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company. Bruno: Fulcrum Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company. Efremov: Fulcrum Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company. Thompson: Fulcrum Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company. Silver: Fulcrum Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company. Moxham: Fulcrum Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company.

Quantitative Systems Pharmacology Model of Sickle Cell Disease and Response to Gene Editing Therapy to Support Clinical Development of SAR445136 (BIVV003)

Sickle cell disease (SCD) is caused by a mutation in the β-globin gene that produces abnormal hemoglobin (HbS), leading to clinical manifestations such as painful vaso-occlusive crises, anemia, and shortened lifespan due to organ damage. SAR445136 (BIVV003) is a zinc finger nuclease ex vivo gene editing therapy in Ph1/2 clinical development for treatment of SCD (PRECIZN-1; NCT03653247). SAR445136 targets the erythroid specific enhancer (ESE) region of the transcription factor BCL11A, which controls the switch from fetal hemoglobin (HbF) to adult forms (HbA in healthy subjects and HbS in SCD subjects). By expressing increased levels of HbF, SAR445136-edited cell progeny exhibit reduced HbS polymerization which is expected to ameliorate RBC sickling and the SCD phenotype.To better understand the dynamics and variability of clinical response to SAR445136, we developed a Quantitative Systems Pharmacology (QSP) model of SCD to describe both key elements of disease biology and the mechanism of action of SAR445136. The QSP approach provides a cohesive representation of the key disease processes in SCD by leveraging additional data sources (e.g. published and internal, clinical and preclinical) to complement data from ongoing clinical trials. The QSP model is applied to help assess mechanism-related questions, such as the observed inter-patient variability with respect to SAR445136 cellular dose, indels, and induced HbF and F cells.To explore the clinical factors that could influence the response to SAR445136, we centered the structure of the QSP model on a realistic representation of erythropoiesis that can describe hematopoietic stem and progenitor cells and erythroid progenitors in the bone marrow and the periphery, including regulation by cytokines EPO, IL-3, and stem cell factor (SCF) (Figure 1A). We first confirmed that the model recapitulates published bone marrow aspirate and blood cell sorting data from healthy individuals (Figure 1B). Next, we modified the model to describe stress erythropoiesis in SCD by incorporating published data on clinical, natural history, and in vitro assessments of SCD progenitor cells, and the resulting reticulocyte and erythrocyte levels (Figure 1B). The updated model describes key features of the SCD disease state, including reduced lifespan of HbS erythrocytes, elevated plasma reticulocytes (Steinberg MH, et al. Blood. 1997;89: 1078-1088), and altered levels of erythroid progenitors (Hoss SE, et al. Haematologica. 2020 Aug 27. doi: 10.3324/haematol.2020.265462) and cytokines, as well as the protective effects of endogenous HbF.Finally, we applied the SCD erythropoiesis model to describe the mechanism of action of SAR445136 by representing ablation followed by the introduction of CD34+ cells containing indels with enhanced HbF expression. The model captures the SAR445136 clinical data and simulates the therapeutic effects of increased total Hb and increased proportion of HbF due to the progeny of SAR445136 cells (Figure 1C). The model provides a quantitative framework for evaluating the effects of treatment parameters including cellular dose, mobilization and engraftment variability, indel quality (i.e., variable editing and HbF expression in erythroid progeny [Lessard S, et al. Blood. 2019;134(Supplement_1):97]) and assessing the pan-cellularity of the response. Due to its mechanistic structure, the model also enables exploration of inter-patient variability in terms of cytokine effects on erythropoiesis.In summary, the QSP model is a computational tool to provide mechanistic insight into emerging SAR445136 clinical data in the context of current understanding of SCD disease biology. The model is intended to provide both qualitative and quantitative support for the clinical development and competitive differentiation of SAR445136. For future development, the model can be expanded to include additional data representing the SCD bone marrow microenvironment to further explore patient heterogeneity. [Display omitted] DisclosuresKaddi: Sanofi: Current Employment. Holz: Sanofi: Current Employment. Tao: Sanofi: Current Employment. Galeon: Sanofi: Current Employment. Reiner: Sanofi: Current Employment. Rendo: Sanofi: Current Employment, Other: May hold shares and/or stock options . Zaph: Sanofi: Current Employment.

Monoacylglycerol Lipase Inhibition: A Strategy to Treat Chronic Pain in a Humanized Sickle Cell Mouse Model

Introduction: Sickle Cell Disease (SCD) is a major cause of morbidity and mortality worldwide, and affects more than 100,000 people in the US. Acute, vaso-occlusive pain crises are the hallmark of the disease and the primary cause of hospitalization. Recurrent, acute pain episodes compound and result in chronic pain for many patients, though the mechanisms of this transition are poorly understood. Although opioids remain the standard of care to treat SCD chronic pain, their myriad adverse side effects (e.g., constipation, respiratory depression, abuse liability, dependence) as well as the fact that SCD chronic pain requires prolonged opioid treatment that results in tolerance, severely limit their therapeutic utility. Thus, a pressing need exists to identify effective non-opioid analgesic strategies to reduce SCD chronic pain. Humanized mouse models of SCD, such as the Berkeley (BERK) model, provide a useful tool to investigate disease pathophysiology and evaluate novel therapeutic strategies. Dorsal Root Ganglion neurons are peripheral sensory neurons essential for pain preclinical investigations. DRG neurons from rodents in neuropathic pain models show hyperexcitability. Inhibitors of the major degradative enzyme of 2-arachidonoylglycerol, monoacylglycerol lipase (MAGL), reduce nociceptive behavior in neuropathic and inflammatory preclinical models of pain through cannabinoid receptor-dependent and -independent mechanisms. MAGL inhibitors have yet to be tested in BERK mice and we hypothesize that they will ameliorate pain-like behavior and neuronal hyperexcitability. Here we evaluate the effects of MJN110 in a series of pain-related behaviors in BERK mice.Methods: Male and female HbSS-BERK (sickle) and HbAA-BERK (control) mice were used as subjects for these experiments. Pain-like behaviors were assessed using the Von Frey, Hot Plate, and Grip Strength tests. Neuronal hyperexcitability was assessed using whole cell patch clamp electrophysiology of L4-S1 dorsal root ganglia (DRG) neurons. For the dose-response experiments, MJN-110 (1.25, 2.5, 5, and 10 mg/kg, i.p.) was administered one hour prior to testing. Data were analyzed as Student's t-test, one- and two-way ANOVAs followed by Tukey or Sidak post-hoc analysis when appropriate (p < 0.05 considered significant).Results: HbSS-BERK mice displayed profound mechanical allodynia, as well as thermal and deep tissues/musculoskeletal hyperalgesia. HbSS-BERK mice possess extremely hyperexcitable DRG neurons. MJN-110 dose-dependently reduced mechanical allodynia and thermal hyperalgesia in HbSS-BERK mice. Importantly, BERK mice given seven days of daily injections of MJN-110 (5 mg/kg) displayed sustained antinociception that did not undergo tolerance. Ongoing studies are aimed to determine whether MJN110 ameliorates the hyperexcitability of DRG neurons.Conclusion: These initial findings, not only validate that BERK mice show hypersensitive responses to mechanical and heat stimuli, but also demonstrate that neurons innervating the distal parts of BERK mice are hyperexcitable. Additionally, MJN110 reduces these hyper-nociceptive behaviors suggesting that MAGL inhibition represents a viable strategy to reduce chronic pain behaviors in the BERK mouse model. DisclosuresGupta: Tautona Group: Consultancy, Honoraria; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; 1910 Genetics: Other: Grantee; Grifols: Other: Grantee; SCDAA: Membership on an entity's Board of Directors or advisory committees; CSL Behring LLC: Honoraria; NIH: Other: Grantee; University of Minnestoa Foundation: Other: Philanthropic Funding; Southern California Institute for Research and Education Foundation: Other: Philanthropic Funding; Cyclerion: Research Funding; UCI Foundation: Other: Philanthropic Funding. Smith: Emmaus Pharmaceuticals: Consultancy; Global Blood Therapeutics: Consultancy, Honoraria, Research Funding, Speakers Bureau; Novartis Pharmaceuticsl: Consultancy, Honoraria; Novo-Nordisk: Other: DSMB; Pfizer: Consultancy, Research Funding; Imara: Research Funding; Forma Therapeutics: Consultancy, Research Funding; Agios: Research Funding.

Inhibition of Factor XII Attenuates Prothrombotic Complications in Sickle Cell Mice

Sickle Cell Disease (SCD) is the most common inherited hemoglobinopathy, affecting millions worldwide. Although characterized by chronic hemolytic anemia and recurrent vaso-occlusive episodes, SCD is increasingly recognized as a hypercoagulable state. Indeed, SCD patients have an 11-25% incidence of venous thromboembolism at a median age of 30 years, associated with a 3-fold increased risk of mortality. Moreover, ischemic stroke and silent cerebral infarctions occur in 7-13% of SCD patients. We have previously shown that tissue factor, an initiator of the extrinsic coagulation pathway, contributes to thrombo-inflammation and microvascular cerebral thrombosis in mouse models of SCD . Recently, the intrinsic coagulation pathway, including Factor XII (FXII), has received significant attention because targeting components of this pathway reduces thrombosis without affecting primary hemostasis. We have shown that FXII deficiency reduces plasma markers of thrombin generation and inflammation in sickle mice. However, the contribution of FXII to thrombosis and prothrombotic complications in SCD is not known. In this study we evaluated the effects of blocking FXII activity on venous thrombosis and ischemia/reperfusion (IR)-induced brain injury in SCD mice.First, Townes HbSS mice (SS) and non-sickle Townes HbAA controls (AA) (male and female, 16 weeks) received anti-FXII antibody or control IgGκ1 (10 mg/kg, IV) 30 minutes prior to subjecting them to venous thrombosis, initiated by applying positive current (3 volts, 90 sec) to the femoral vein. To visualize platelet and fibrin accumulation, mice were injected with rhodamine 6G and anti-fibrin antibody 59D8 labeled with Alexa Fluor 647, respectively. The femoral vein thrombi were imaged by intravital fluorescence microscopy using time-lapse capture every 10 seconds, to acquire images of fibrin and platelets over 60 min. The accumulation of platelets and fibrin was quantified for relative intensity of each fluorophore over the region of the observed thrombus. As previously shown, thrombi of SS/IgG mice showed an increased fibrin and platelet accumulation compared to AA/IgG group. Importantly, 15D10 treatment significantly attenuated both fibrin (p<0.001) and platelet (p<0.05) deposition over time in SS mice compared to SS/IgG group. The same effect of 15D10 treatment was observed in AA mice. At the end of experiment, clots were collected and stained with hematoxylin and eosin, and clot volume was assessed histomorphometrically (Nikon Ti-2, FIJI Software). Surprisingly, despite higher fibrin content, clots from SS/IgG mice had significantly smaller volume than clots from AA/IgG group (0.32 ± 0.04 versus 0.60 ± 0.11 mm 3, p<0.05). Importantly, administration of 15D10 significantly reduced clot volume in both SS (0.086 ± 0.01 mm 3, p<0.05) and AA mice (0.1 ± 0.02 mm 3, p<0.05).Next, AA and SS mice (male and female, 8-10 weeks) were subjected to brain IR injury induced by middle cerebral artery occlusion for 60 minutes followed by 24 hours of reperfusion (mouse model of ischemic stroke). 15D10 or control IgGκ1 (10 mg/kg, IV) were injected 30 minutes before occlusion and again at 6 hours into the reperfusion period to generate 3 experimental groups: AA/IgG, SS/IgG and SS/15D10. All analyzed parameters of brain IR injury were significantly worse in the SS/IgG group compared to the AA/IgG group. Compared to IgG, pre-treatment of SS mice with 15D10 significantly attenuated neuronal damage determined by volume of brain infarction (11.7 ± 3.7 vs 24.9 ± 2.4%, p<0.001) and improved behavioral deficit assessed by mean stroke score (9.0 ± 0.9 vs 14.6 ± 0.9, p<0.01). These changes were accompanied by a significant increase in leukocytes rolling (1978.0 ± 93.5 vs 1517.0 ± 180.3 rolling leukocytes/sec/mm 2, p<0.001), and significant reduction in the number of adherent leukocytes (367.2 ± 49.0 vs 723.4 ± 48.5, adherent leukocytes/mm 2, p<0.001) observed in the brain microvasculature of SS mice treated with 15D10 compared to SS/IgG group.Together, our data indicates that in the mouse model of SCD FXII contributes to the experimental venous thrombosis and ischemic stroke. Given that targeting the intrinsic pathway can reduce thrombosis without affecting hemostasis, our data suggest that targeting FXII might be a beneficial treatment in reducing inflammatory and thrombotic complications in SCD patients without a risk of bleeding. DisclosuresWallisch: Aronora Inc,: Current Employment. Key: Grifols: Research Funding; Takeda: Research Funding; BioMarin: Honoraria, Other: Participation as a clinical trial investigator; Sanofi: Consultancy; Uniqure: Consultancy, Other: Participation as a clinical trial investigator. Gruber: Aronora Inc.: Current Employment, Current equity holder in publicly-traded company; Oregon Health and Science University: Current Employment.

P-Selectin Deficiency Reduces Acute Vascular Complications but Not Chronic Organ Damage in Sickle Cell Mice

P-selectin (Psel) is an adhesion molecule expressed on platelets and endothelial cells, which interacts with its ligand PSGL-1 on leukocytes and a PSGL-1-like molecule on sickle red blood cells (RBCs). Psel mediates the formation of the multicellular aggregates that promote vaso-occlusive crisis (VOC) and acute painful episodes in sickle cell disease (SCD). Crizanlizumab, a monoclonal antibody blocking Psel, reduces the frequency of VOC in SCD patients. In SCD mice, Psel contributes to heme-induced microvascular stasis, and thrombus and platelet-neutrophil aggregate formation in the lung and liver. Unexpectedly, Psel deficiency promotes liver senescence in a mouse model of SCD, suggesting a possible detrimental effect of Psel inhibition. In this study, we further investigated the long-term effects of Psel deficiency on thromboinflammation and end-organ damage in murine SCD.We used Townes wild type (AA) and sickle (SS) mice (n=12-27) that either express Psel (Psel +/+) or lack Psel (Psel -/-) at 11-12 months of age. Kidney damage was evaluated by histology and urine analysis. Heart function was determined using echocardiography. Complete blood counts and plasma biomarkers of thrombin generation (thrombin anti-thrombin [TAT] complexes) and inflammation (interleukin [IL]-6) were also analyzed. In addition, in a pilot experiment, we analyzed the effect of Psel deficiency on experimental venous thrombosis in SS mice.SS Psel +/+ mice exhibited renal damage, urinary concentrating defect, and reduced creatinine clearance, which was not improved in SS Psel -/- mice. Psel deficiency attenuated glomerular (GLM) congestion (0.17±0.05 vs 0.39±0.06, p<0.05) but failed to prevent GLM injury, as evidenced by similar extent of GLM sclerosis, hypertrophy and podocyte loss in SS mice. Interestingly, only SS P-sel -/- mice presented withdistinct differences in GLM structure, demonstrated by extensive hypercellularity, mesangial expansion and mesangiolysis. We also observed tubular injury concomitant with brush border loss and interstitial fibrosis in SS mice, regardless of Psel expression. Additionally, there was a significant reduction in CD3 + T cells (5.0±1.2 vs 9.5±1.6 cells/field; p<0.05) and macrophages (1.0±0.1 vs 1.6±0.2 % of area; p<0.05) infiltration in the kidney cortex of SS Psel -/- compared to SS Psel +/+ mice. This corresponded to a greater renal iron accumulation in SS Psel -/- mice (59.9±4.2 vs 48.2±3.2 Mpix/μm; p<0.05).We observed cardiac hypertrophy (elevated heart weight to tibia length ratio) in SS mice, regardless of Psel expression. Echocardiography of left ventricle (LV) revealed that SS mice had increased LV mass and LV internal diameter with no change in ejection fraction or fractional shortening compared to AA mice. None of these parameters were affected by Psel expression. Furthermore, hypertrophy observed in other organs (kidney, liver, lung and spleen) of SS Psel +/+ mice was also not affected by Psel deficiency.Consistent with previous studies, SS Psel +/+ mice had elevated plasma levels of TAT and IL-6 compared to AA Psel +/+ mice. Psel deficiency significantly reduced IL-6 (47±15 vs 20±10 ng/mL, P<0.05), but had no effect on elevated plasma TAT levels in SS mice. Despite the lack of effect of Psel deficiency on systemic thrombin generation in SS mice, femoral vein thrombi formed after electrolytic injury exhibited a strong trend in reduced fibrin and platelet content compared to SS Psel+/+ mice (n=5 per group).As expected, SS Psel +/+ mice exhibited anemia as shown by reduced RBC number, hemoglobin (Hb) and hematocrit (Hct) compared to AA Psel +/+ animals. Interestingly, these parameters were further decreased in SS Psel -/- mice (p<0.01 for all); RBC (5.6±0.2 vs 4.4±0.4 x 10 6/mL), Hg (6.7±0.2 vs 5.7±0.2 g/dL) and Hct (25.1±1.1 vs 19.7±1.1%). This was accompanied by a significant increase in mean corpuscular Hb concentration (26.9±0.5 vs 29.2±0.5 g/dL p< 0.01) but no changes in RBC mean corpuscular volume in SS Psel -/-mice compared to SS Psel +/+ mice.Our data suggest that despite improving acute vascular pathologies, including VOC and thromboinflammation, long term deficiency of Psel does not prevent end-organ damage. If fact, it may contribute to organ dysfunction and enhanced anemia. More mechanistic studies are needed to better understand the long-term effects of anti-Psel treatment in SCD patients. DisclosuresReeves: Incyte Corporation: Honoraria; Takeda: Honoraria; Bristol-Myers Squibb: Speakers Bureau; Pharma Essentia: Consultancy, Honoraria. Sundd: CSL Behring Inc: Research Funding; Bayer: Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding.

Trpv1 and Trpa1 are not essential for Psickle-like activity in red cells of the SAD mouse model of sickle cell disease

The molecular identity of Psickle, the deoxygenation-activated cation conductance of the human sickle erythrocyte, remains unknown. We observed in human sickle red cells that inhibitors of TRPA1 and TRPV1 inhibited Psickle, whereas a TRPV1 agonist activated a Psickle-like cation current. These observations prompted us to test the roles of TRPV1 and TRPA1 in Psickle in red cells of the SAD mouse model of sickle cell disease. We generated SAD mice genetically deficient in either TRPV1 or TRPA1. SAD;Trpv1−/− and SAD;Trpa1−/− mice were indistinguishable in appearance, hematological indices, and osmotic fragility from SAD mice. We found that deoxygenation-activated cation currents remained robust in SAD;Trpa1−/− and SAD;Trpv1−/− mice. In addition, 45Ca2+ influx into SAD mouse red cells during prolonged deoxygenation was not reduced in red cells from SAD;Trpa1−/− and SAD;Trpv1−/− mice. We conclude that the nonspecific cation channels TRPA1 and TRPV1 are not required for deoxygenation to stimulate Psickle-like activity in red cells of the SAD mouse model of sickle cell disease.(159)

RASAL3 Is a Putative RasGAP Modulating Inflammatory Response by Neutrophils.

As first responder cells in host defense, neutrophils must be carefully regulated to prevent collateral tissue injury. However, the intracellular events that titrate the neutrophil’s response to inflammatory stimuli remain poorly understood. As a molecular switch, Ras activity is tightly regulated by Ras GTPase activating proteins (RasGAP) to maintain cellular active-inactive states. Here, we show that RASAL3, a RasGAP, is highly expressed in neutrophils and that its expression is upregulated by exogenous stimuli in neutrophils. RASAL3 deficiency triggers augmented neutrophil responses and enhanced immune activation in acute inflammatory conditions. Consequently, mice lacking RASAL3 (RASAL3-KO) demonstrate accelerated mortality in a septic shock model via induction of severe organ damage and hyperinflammatory response. The excessive neutrophilic hyperinflammation and increased mortality were recapitulated in a mouse model of sickle cell disease, which we found to have low neutrophil RASAL3 expression upon LPS activation. Thus, RASAL3 functions as a RasGAP that negatively regulates the cellular activity of neutrophils to modulate the inflammatory response. These results demonstrate that RASAL3 could serve as a therapeutic target to regulate excessive inflammation in sepsis and many inflammatory disease states.

Murine models of sickle cell disease and beta-thalassemia demonstrate pulmonary hypertension with distinctive features.

Sickle cell anemia and β-thalassemia intermedia are very different genetically determined hemoglobinopathies predisposing to pulmonary hypertension. The etiologies responsible for the associated development of pulmonary hypertension in both diseases are multi-factorial with extensive mechanistic contributors described. Both sickle cell anemia and β-thalassemia intermedia present with intra and extravascular hemolysis. And because sickle cell anemia and β-thalassemia intermedia share features of extravascular hemolysis, macrophage iron excess and anemia we sought to characterize the common features of the pulmonary hypertension phenotype, cardiac mechanics, and function as well as lung and right ventricular metabolism. Within the concept of iron, we have defined a unique pulmonary vascular iron accumulation in lungs of sickle cell anemia pulmonary hypertension patients at autopsy. This observation is unlike findings in idiopathic or other forms of pulmonary arterial hypertension. In this study, we hypothesized that a common pathophysiology would characterize the pulmonary hypertension phenotype in sickle cell anemia and β-thalassemia intermedia murine models. However, unlike sickle cell anemia, β-thalassemia is also a disease of dyserythropoiesis, with increased iron absorption and cellular iron extrusion. This process is mediated by high erythroferrone and low hepcidin levels as well as dysregulated iron transport due transferrin saturation, so there may be differences as well. Herein we describe common and divergent features of pulmonary hypertension in aged Berk-ss (sickle cell anemia) and Hbbth/3+ (intermediate β-thalassemia) mice and suggest translational utility as proof-of-concept models to study pulmonary hypertension therapeutics specific to genetic anemias.

Mitochondrial reactive oxygen species scavenging attenuates thrombus formation in a murine model of sickle cell disease

BackgroundSickle cell disease (SCD) is characterized by hemolysis‐associated platelet dysfunction that leads to increased risk of thrombosis and plays a role in the high morbidity and mortality of the disease. The mechanisms by which hemolysis induces platelet activation remain unclear. We recently demonstrated that patients with SCD showed increased platelet mitochondrial reactive oxygen species (mtROS) production that correlates with markers of hemolysis and platelet activation. Experiments in isolated platelets demonstrated that mtROS stimulated platelet activation. However, the role of hemolysis‐induced mtROS in thrombus formation in vivo remains unclear. ObjectivesHere, we hypothesize that scavenging of mtROS attenuates the propensity for thrombosis in mouse models of hemolysis. MethodsWe used models of hemolysate infusion into wildtype mice as well as the Berkley transgenic mouse model ofSCD, a chronic mode of hemolysis, to test the effect of hemolysis on platelet mtROS production and thrombosis. ResultsWe show that infusion of hemolysate in wildtype mice induces platelet mtROS production and decreases time to vessel occlusion in a model of ferric chloride‐induced carotid artery thrombosis. Increased mtROS and propensity for thrombosis was also observed in the Berkley transgenic mouse model of SCD. Notably, treatment with mtROS scavengers decreased platelet mtROS levels and attenuated the propensity for thrombus formation in both models. ConclusionsThese data demonstrate that mtROS significantly contribute to the mechanism of hemolysis‐induced thrombosis in vivo and suggest a potential role for mitochondrially targeted antioxidant therapy in hemolysis and SCD‐related thrombosis.

Hemopexin dosing improves cardiopulmonary dysfunction in murine sickle cell disease

Hemopexin (Hpx) is a crucial defense protein against heme liberated from degraded hemoglobin during hemolysis. High heme stress creates an imbalance in Hpx bioavailability, favoring heme accumulation and downstream pathophysiological responses leading to cardiopulmonary disease progression in sickle cell disease (SCD) patients. Here, we evaluated a model of murine SCD, which was designed to accelerate red blood cell sickling, pulmonary hypertension, right ventricular dysfunction, and exercise intolerance by exposure of the mice to moderate hypobaric hypoxia. The sequence of pathophysiology in this model tracks with circulatory heme accumulation, lipid oxidation, extensive remodeling of the pulmonary vasculature, and fibrosis. We hypothesized that Hpx replacement for an extended period would improve exercise tolerance measured by critical speed as a clinically meaningful therapeutic endpoint. Further, we sought to define the effects of Hpx on upstream cardiopulmonary function, histopathology, and tissue oxidation. Our data shows that tri-weekly administrations of Hpx for three months dose-dependently reduced heme exposure and pulmonary hypertension while improving cardiac pressure-volume relationships and exercise tolerance. Furthermore, Hpx administration dose-dependently attenuated pulmonary fibrosis and oxidative modifications in the lung and myocardium of the right ventricle. Observations in our SCD murine model are consistent with pulmonary vascular and right ventricular pathology at autopsy in SCD patients having suffered from severe pulmonary hypertension, right ventricular dysfunction, and sudden cardiac death. This study provides a translational evaluation supported by a rigorous outcome analysis demonstrating therapeutic proof-of-concept for Hpx replacement in SCD.

Cerebral Metabolic Alterations in Transgenic and Hemizygous Murine Models of Sickle Cell Disease

BACKGROUND: In SCD, the mechanisms leading to the high incidence of acute stroke in both children and adults remain controversial, while the effects of chronic hypoxia, hyperemia and oxidative stress upon the sickle brain are poorly understood. In limited studies, elevation of brain N-acetyl-aspartate (NAA) has been observed in SCD inflicted children (Steen RG and Ogg RJ, AJNR, 2005). We recently presented evidence that NAA is elevated in one mild murine model (NY1DD) of SCD (Cui MH, NMR Biomed., 2017); we proposed that alterations in NAA are linked to neuronal metabolism and may be indicative of a compensatory increase in mitochondrial energy utilization. Here we present data obtained in additional animal models of SCD that further support these hypotheses.METHODS: Control animals (C57BL6) were compared to sickle animals; the BERK mouse expressing various levels of fetal hemoglobin (HbF, BERK-G) ; the BERK-TX mouse, based on C57BL6 mice irradiated to lethal levels and subsequently infused with nucleated cells from the bone-marrow of BERK mice; and the BERK-HEMI (Hemizygous sickle transgenic animals with murine a knockout, human HbS (aHbS) and a mouse b human S transgene (mb/hS). BERK-HEMI exhibit low O2 affinity hemoglobin (P50 ~ 57).Cerebral measurements were conducted using MRI/MRS methods at 9.4 Tesla. We measuredcerebral blood flow (CBF), cerebral oxygen extraction (using blood level oxygen dependent MRI during a short bolus of hyperoxia [BOLD-RHO]), brain microstructural integrity (from Diffusion Tensor Imaging [DTI] fractional isotropy [FA]) and tissue inflammation (from DTI mean diffusivity [MD]). Magnetic Resonance Spectroscopy (MRS) in the thalamus provided NAA, glutamate (Glu), myoinositial (Ins), and other metabolite measures.RESULTS: MRI and MRS findings exhibit increasing NAA, Glu and BOLD-RHO which seem to suggest a metabolic adjustment not just to anemia but to some other factor(s) (Figure 1); BERK-HEMI animals exhibit the most significant metabolic changes while the BERK-G animals (with low gamma) had the highest CBF and worst anemia, although NAA in the BERK-G appeared similar to WT levels. Evolving changes in the BERK-TX animal after transplant (Figures 2 and 3) suggest a phase of increasing NAA while HbSS and CBF peak. These changes inversely correlate with decreasing Ins. Oxygen extraction and brain inflamation appear to rise after NAA stabilizes or drops. Full BERK-like systemic pathology is established by 12 weeks post transplant but in brain > 12 weeks are required.CONCLUSIONS: NAA was not elevated where the anemia and CBF were the highest (BERK-G and advanced BERK-TX). Instead, NAA was highest in NY1DD and BERK-HEMI (both without significant anemia), in early BERK-TX, where CBF was mildly elevated. This suggests that something other than anemia was driving the NAA elevations. Possibilities include chronic mild hypoxia (from low Hb O2 affinity, reperfusion injury, or ROS). The changes evident in the early post-transplant BERK-TX brain suggest that CBF is driven by HbSS expression and not anemia, since hematocrit remains relatively stable (after an initial drop). This finding suggests likely candidates to be ROS activity, Hb O2 affinity, blood products or degredation in oxygen carrying capacity. The compensatory alterations in energy homeostasis (increased NAA and Glu, decreased Ins and other metabolite changes) may reflect a shift toward increased neuronal glycolysis or increased GSH production and recycling, both of which require increased mitochondrial energy utilization. Decreases in Ins may be related to altered astrocyte/neuronal homeostasis, or the increased cerebrovascular activity. In the advanced stages of the BERK-TX transition, NAA and glutamate levels drop, CBF plateaus, oxygen extraction is high, cerebral inflammation increases and neuronal structure is degraded, all of which are consistent with a system failure, which further predispose the brain to cerebrovascular injury and may explain why NAA increases have been observed only in children with SCD and not adults. If so, the decline of pediatric NAA levels to its “normalization” in adult patients may signal emergence of cerebral dysfunction and impaired cognition (Strouse JJ et al., Blood, 2006) and are consistent with elevations in oxygen extraction fraction and exhaustion of cerebrovascular reserves (Kosinski PD et al; Br. J Haematol., 2017). [Display omitted] DisclosuresAcharya:AIMA: Consultancy. Billett:Janssen Pharmaceutical: Research Funding.

Inhibition of Protein Disulfide Isomerase Ameliorates Vaso-Occlusion and Thrombosis in a Mouse Model of Sickle Cell Disease

IntroductionSickle cell disease (SCD) results from a single mutation in the β-globin gene. Altered erythrocyte physiology in SCD results in severe vascular complications, including vaso-occlusion (VOC) and painful crises along with various other manifestations, such as thrombosis and end organ damage. Extracellular protein disulfide isomerase (PDI) plays a critical role in the regulation of neutrophil recruitment, platelet activation and fibrin formation, processes implicated in the thrombo-inflammatory vasculopathy in SCD. We investigated the effect of a PDI inhibitor, isoquercetin, in combination with hydroxyurea, in TNFα-induced VOC and thrombosis in a mouse model of SCD. In addition, the effect of chronic PDI inhibition by isoquercetin on thrombo-inflammatory vasculopathy was also examined.MethodsHumanized TOWNES knock-in mice, containing human normal (βA/βA, control) or sickle (βS/βS, SCD) hemoglobin β chains, were used as a mouse model of SCD. PDI inhibition in the plasma was achieved by oral gavage or daily diet feeding of isoquercetin. Intravital microscopy was performed to determine vaso-occlusive events in the venules and thrombus formation in the arterioles in TNFα-stimulated mice. Plasma levels of PDI and parameters for coagulation and vascular inflammation were determined by ELISA. Neutrophil accumulation in the organs was determined as the myeloperoxidase (MPO) levels in tissue homogenates.ResultsCompared to control mice, SCD mice have elevated plasma PDI levels. Gavage of isoquercetin resulted in reduced PDI activity in the plasma of treated mice (38±10% inhibition, p <0.05). Isoquercetin ingestion increased leukocyte rolling flux fraction in TNFα-treated SCD mice as monitored using intravital microscopy, whereas the influence on leukocyte adhesion and shear rate was minimal. When a reversal agent for PDI inhibitor, b'x (the isolated substrate binding domain of PDI) was co-infused, the effect of isoquercetin on leukocyte rolling was reversed, suggesting this effect of isoquercetin is mediated by PDI inhibition. We also determined the effect of isoquercetin in combination with hydroxyurea, a treatment with established efficacy in SCD, on the vaso-occlusive events in our model. We confirmed that hydroxyurea treatment elevated the plasma nitric oxide level as determined by plasma nitrite/nitrate content (11.5±1.9 μM vs 5.0±1.9 μM, p <0.05). Consistent with previous studies, hydroxyurea decreased leukocyte adhesion while the rolling flux fraction was not changed. However, combined treatment with isoquercetin and hydroxyurea in SCD mice increased the rolling flux fraction (15±3% vs 6±1%, p <0.05), decreased leukocyte adhesion (158±13 mm-2 vs 289±24 mm-2, p <0.05), and increased vessel shear rate (302±18 s-1 vs 122±11 s-1, p <0.05). We investigated in vivo thrombus formation in the arterioles of TNFα-treated SCD mice using intravital microscopy following laser injury. Compared to the control mice, SCD mice have significantly enhanced fibrin generation but normal platelet accumulation. Both isoquercetin and hydroxyurea inhibited TNFα-induced platelet accumulation (62±36% AUC-Area Under the Curve with isoquercetin and 48±17% AUC with hydroxyurea of untreated SCD) and fibrin generation (30±6% AUC with isoquercetin and 44±9% AUC with hydroxyurea of untreated SCD). To study the effect of chronic isoquercetin treatment in SCD, control and SCD mice were fed isoquercetin for 4 weeks. Daily consumption of isoquercetin resulted in reduction of plasma PDI activity (18±5% inhibition, p <0.05). Consistent with the intravital microscopic data, chronic PDI inhibition reduced neutrophil migration and accumulation into the lung, as determined by the MPO level (481±85 ng/mg vs 829±140 ng/mg, p <0.05) in the tissue homogenate. Chronic treatment with isoquercetin also reduced plasma fibrinogen degradation products (FDP) (102±15 μg/ml vs 183±25 μg/ml, p <0.05) in SCD mice. In addition, a correlation (Pearson r=0.651) was observed between reducing plasma FDP and lung MPO levels.ConclusionsAcute and chronic PDI inhibition by isoquercetin may provide beneficial effect on vascular complications in a mouse model of SCD. PDI inhibition has the potential to ameliorate thrombo-inflammatory syndromes associated with SCD. These studies justify a longitudinal trial of PDI inhibitors in SCD. DisclosuresNo relevant conflicts of interest to declare.