Sickle cell disease (SCD), a recessive inherited disorder caused by a point mutation in the hemoglobin chain of red blood cells (RBCs). Microvascular dysfunction is central to the pathobiology of SCD, leading to life- threatening consequences. A major consequence is occlusion of activated microvasculature with sickle RBCs leading to unpredictable and frequent episodes of acute pain called vaso-occlusive crises (VOC), frequent hospitalization and poor quality of life. Many individuals with SCD suffer chronic pain that may start during infancy and continue to increase throughout life. Opioids are the mainstay for treatment but their side-effects and fear of addiction remain a major concern. Hence, a major unmet need is to prevent and/or treat pain more effectively. VOC is associated with increased hemolysis that releases free heme. Our preliminary data reveal that administration of free heme causes hyperalgesia (pain) in transgenic sickle mice expressing human sickle hemoglobin (Hb) and in control mice expressing normal human HbA. Our preliminary data shows that heme stimulates mast-cell extracellular traps (ETs) by releasing nuclear DNA and citrullinated histones. Mast- cell activation promotes hyperalgesia in sickle mice. We hypothesize that heme-induced mast-cell activation leads to release of citrullinated histones and noxious substances and contributes to inflammation, vascular dysfunction and axonal injury leading to vasoocclusion and hyperalgesia in SCD (Schema I). Mast cells may play a causal role in VOC and chronic pain in SCD. Targeting mast cells will ameliorate VOC and pain at its source. We will test our hypothesis using a translational approach with four specific aims to establish whether, heme contributes to chronic and/or acute hyperalgesia (Aim1), heme contributes to chronic/acute pain via mast-cell activation (Aim2), and heme-induced hyperalgesia is driven by novel mast cell?dependent mechanisms leading to axonal and vascular injury (Aim3), including, release of inflammatory cytokines, proteases, ETs with DNA and citrullinated histones from mast cells that cause axonal injury in the periphery and DRG neurons, and endothelial activation via endoplasmic reticulum stress.
Aim4 will entail determining whether targeting the mechanisms of heme-induced mast- cell activation attenuates hyperalgesia and vaso-occlusion. We will use genetic and pharmacological approaches, namely [i] humanized transgenic HbSS-BERK sickle mice exclusively expressing human sickle Hb, [ii] HbAA-BERK control mice expressing normal human HbA, [iii] sickle mice deleted for, [a] mast cells or [b] TLR4 and their congenic controls; and mechanism-specific pharmacological inhibitors to prevent vaso- occlusion and pain. Mouse models and biologicals are available in our laboratories. By using multiple strategies in vivo and in vitro, involving mast cell?mediated hyperalgesia and their targeting with novel and/or FDA-approved drugs, we expect that our observations will lead to translationally relevant functional outcomes?reduction of VOC and acute as well as chronic pain in SCD.

Public Health Relevance

Sickle cell disease (SCD), an inherited disorder of red blood cell defect, afflicts millions of people. Consequences of SCD are life threatening, including debilitating pain. In SCD, pain is unique because of recurrent and unpredictable episodes of severe acute pain requiring hospitalization and opioids. Many patients suffer lifelong chronic pain. Opioids remain a sub-optimal approach due to side effects and fear of addiction. Therefore, we propose to develop strategies to target the mechanisms that lead to SCD-related pain to prevent pain from being evoked and prevent opioid use.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
7R01HL147562-02
Application #
9995185
Study Section
Hypertension and Microcirculation Study Section (HM)
Program Officer
Bai, C Brian
Project Start
2019-04-04
Project End
2023-03-31
Budget Start
2019-12-05
Budget End
2020-03-31
Support Year
2
Fiscal Year
2019
Total Cost
Indirect Cost
Name
University of California Irvine
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
046705849
City
Irvine
State
CA
Country
United States
Zip Code
92617