Release of hepatic xanthine oxidase (XO) to the circulation is protective in intravascular hemolytic crisis
Heidi M. Schmidt,
Evan R. DeVallance,
Sara E. Lewis,
Katherine C. Wood,
Gowtham K. Annarapu,
Mara Carreño,
Scott A. Hahn,
Madison Seman,
Brooke A. Maxwell,
Emily A. Hileman,
Julia Z. Xu,
Murugesan Velayutham,
Werner J. Geldenhuys,
Dario A. Vitturi,
Sruti Shiva,
Eric E. Kelley,
Adam C. Straub
Affiliations
Heidi M. Schmidt
Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA, USA
Evan R. DeVallance
Center for Inhalation Toxicology, West Virginia University School of Medicine, Morgantown, WV, USA; Department of Physiology and Pharmacology, Health Sciences Center, West Virginia University, Morgantown, WV, USA
Sara E. Lewis
Department of Physiology and Pharmacology, Health Sciences Center, West Virginia University, Morgantown, WV, USA
Katherine C. Wood
Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, PA, USA
Gowtham K. Annarapu
Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, PA, USA
Mara Carreño
Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA, USA
Scott A. Hahn
Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, PA, USA
Madison Seman
Department of Physiology and Pharmacology, Health Sciences Center, West Virginia University, Morgantown, WV, USA
Brooke A. Maxwell
Department of Physiology and Pharmacology, Health Sciences Center, West Virginia University, Morgantown, WV, USA
Emily A. Hileman
Department of Physiology and Pharmacology, Health Sciences Center, West Virginia University, Morgantown, WV, USA
Julia Z. Xu
Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, PA, USA; Division of Hematology /Oncology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
Murugesan Velayutham
Department of Biochemistry, West Virginia University School of Medicine, USA
Werner J. Geldenhuys
Department of Pharmaceutical Sciences, School of Pharmacy, West Virginia University, Morgantown, WV, USA; Department of Neuroscience, School of Medicine, West Virginia University, Morgantown, WV, USA
Dario A. Vitturi
Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA, USA; Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, PA, USA
Sruti Shiva
Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA, USA; Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, PA, USA
Eric E. Kelley
Department of Physiology and Pharmacology, Health Sciences Center, West Virginia University, Morgantown, WV, USA; Corresponding author. West Virginia University School of Medicine, Department of Physiology and Pharmacology, 3074 Health Sciences Center North, 1 Medical Center Dr., Morgantown, WV, 15902, USA.
Adam C. Straub
Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA, USA; Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, PA, USA; Corresponding author. University of Pittsburgh School of Medicine, Department of Pharmacology and Chemical Biology, Heart, Lung, Blood and Vascular Medicine Institute, E1254 Biomedical Science Tower, 200 Lothrop St., Pittsburgh, PA, 15216, USA.
Xanthine oxidase (XO) catalyzes the catabolism of hypoxanthine to xanthine and xanthine to uric acid, generating oxidants as a byproduct. Importantly, XO activity is elevated in numerous hemolytic conditions including sickle cell disease (SCD); however, the role of XO in this context has not been elucidated. Whereas long-standing dogma suggests elevated levels of XO in the vascular compartment contribute to vascular pathology via increased oxidant production, herein, we demonstrate, for the first time, that XO has an unexpected protective role during hemolysis. Using an established hemolysis model, we found that intravascular hemin challenge (40 μmol/kg) resulted in a significant increase in hemolysis and an immense (20-fold) elevation in plasma XO activity in Townes sickle cell phenotype (SS) sickle mice compared to controls. Repeating the hemin challenge model in hepatocyte-specific XO knockout mice transplanted with SS bone marrow confirmed the liver as the source of enhanced circulating XO as these mice demonstrated 100% lethality compared to 40% survival in controls. In addition, studies in murine hepatocytes (AML12) revealed hemin mediates upregulation and release of XO to the medium in a toll like receptor 4 (TLR4)-dependent manner. Furthermore, we demonstrate that XO degrades oxyhemoglobin and releases free hemin and iron in a hydrogen peroxide-dependent manner. Additional biochemical studies revealed purified XO binds free hemin to diminish the potential for deleterious hemin-related redox reactions as well as prevents platelet aggregation. In the aggregate, data herein reveals that intravascular hemin challenge induces XO release by hepatocytes through hemin-TLR4 signaling, resulting in an immense elevation of circulating XO. This increased XO activity in the vascular compartment mediates protection from intravascular hemin crisis by binding and potentially degrading hemin at the apical surface of the endothelium where XO is known to be bound and sequestered by endothelial glycosaminoglycans (GAGs).
