Isoquercetin in Sickle Cell Anemia

Inclusion Criteria: * Eligible subjects require an established diagnosis of sickle cell disease/homozygous hemoglobin S (SCD-SS) or sickle cell disease hemoglobin β0-thalassemia (SCD-Sβ0-thal). * Patients on other therapy including hydroxyurea will be included. * Age 18-50 years. * Participants must have preserved organ and marrow function as defined below: * leukocytes ≥2,000/mcL * platelets ≥75,000/mcL * AST(SGOT)/ALT(SGPT) ≤2.5 × institutional upper limit of normal * Estimated creatinine clearance ≥45 mL/min/1.73 m2 for participants with creatinine levels above institutional normal. * Subjects with no evidence of worsening over the last 4 weeks (e.g. any acute complication of SCD including but not limited to VOC, acute chest syndrome and stroke, that required unscheduled medical attention or intervention) as determined by the investigator will be included. * Patients on anticoagulation therapy will be excluded. * The effects of isoquercetin on the developing human fetus are unknown. For this reason, women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation. Should a woman become pregnant or suspect she is pregnant while she or her partner is participating in this study, she should inform her treating physician immediately. Men treated or enrolled on this protocol must also agree to use adequate contraception prior to the study, for the duration of study participation, and 4 months after completion of isoquercetin administration. * Ability to understand and the willingness to sign a written informed consent document Exclusion Criteria: * Please ensure exclusion criteria are clearly worded to describe participants who will not be eligible. * Participants may not be concurrently receiving any other study agents. * Subjects with no evidence of worsening over the last 1 month (e.g. any acute complication of SCD including but not limited to VOC, acute chest syndrome and stroke, that required unscheduled medical attention or intervention) as determined by the investigator will be included. * Familial bleeding diathesis. * Known diagnosis of disseminated intravascular coagulation. * Currently receiving anticoagulant therapy. * Currently using daily use of aspirin (\>81mg daily), Clopidogrel (Plavix), cilostazol (Pletal), aspirin-dipyridamole (Aggrenox) (within 10 days) * History of allergic reactions attributed to compounds of similar chemical or biologic composition to isoquercetin. * Uncontrolled intercurrent illness including but not limited to ongoing or active infection, symptomatic congestive heart failure, unstable angina, cardiac arrhythmia, or psychiatric illness/social situations that would limit study compliance. * Pregnant women are excluded from this study because isoquercetin is a PDI inhibitor with the potential for teratogenic or abortifacient effects. Because there is an unknown but potential risk of adverse events in nursing infants secondary to treatment of the mother with isoquercetin, breastfeeding should be discontinued if the mother is treated with isoquercetin. These potential risks may also apply to other agents used in this study.