Hereditary methemoglobinemia in a cyanotic cat presented for ovariohysterectomy.

A 1-year-old, female, domestic shorthair cat with a history of cyanotic mucous membranes for several months was referred for ovariohysterectomy. Blood samples exhibited a noticeably brownish discoloration, while laboratory screening revealed mild-to-moderate erythrocytosis and near normal partial arterial oxygen pressure. Blood methemoglobin content was 41% of total hemoglobin concentration, and erythrocytic methemoglobin reductase activity was < 1% compared with control samples. A diagnosis of hereditary methemoglobinemia was established. After an intravenous injection of methylene blue, the cat's mucous membranes became transiently pink, and the ovariohysterectomy was uneventful. Methylene blue may have improved safety during anesthesia and surgery. Hereditary methemoglobinemia should be considered in persistently cyanotic cats with normal partial arterial oxygen pressure and lack of evidence of cardiopulmonary disease, anemia, or toxin exposure.

Méthémoglobinémie héréditaire chez une chatte cyanotique présentée pour une ovariohystérectomie. Une chatte domestique âgée de 1 an avec une anamnèse de muqueuses cyanotiques pendant plusieurs mois a été recommandée pour l'ovariohystérectomie. Des prélèvements sanguins présentaient une décoloration brune manifeste tandis que les tests de laboratoire ont révélé une érythrocytose de légère à modérée et une pression d'oxygène artérielle partielle presque normale. Le contenu de méthémoglobine sanguine était de 41 % de la concentration totale des hémoglobines et l'activité de la réductase de la méthémoglobine érythrocytaire était < 1 % comparativement aux prélèvements témoins. Un diagnostic de méthémoglobinémie héréditaire a été posé. Après une injection intraveineuse de bleu de méthylène, les muqueuses du chat sont devenues provisoirement roses et l'ovariohystérectomie a été réalisée sans complications. Le bleu de méthylène peut avoir amélioré l'innocuité durant l'anesthésie et la chirurgie.(Traduit par Isabelle Vallières).

Forced chromatin looping raises fetal hemoglobin in adult sickle cells to higher levels than pharmacologic inducers.

Overcoming the silencing of the fetal γ-globin gene has been a long-standing goal in the treatment of sickle cell disease (SCD). The major transcriptional enhancer of the ß-globin locus, called the locus control region (LCR), dynamically interacts with the developmental stage-appropriate ß-type globin genes via chromatin looping, a process requiring the protein Ldb1. In adult erythroid cells, the LCR can be redirected from the adult ß- to the fetal γ-globin promoter by tethering Ldb1 to the human γ-globin promoter with custom-designed zinc finger (ZF) proteins (ZF-Ldb1), leading to reactivation of γ-globin gene expression. To compare this approach to pharmacologic reactivation of fetal hemoglobin (HbF), hematopoietic cells from patients with SCD were treated with a lentivirus expressing the ZF-Ldb1 or with chemical HbF inducers. The HbF increase in cells treated with ZF-Ldb1 was more than double that observed with decitabine and pomalidomide; butyrate had an intermediate effect whereas tranylcypromine and hydroxyurea showed relatively low HbF reactivation. ZF-Ldb1 showed comparatively little toxicity, and reduced sickle hemoglobin (HbS) synthesis as well as sickling of SCD erythroid cells under hypoxic conditions. The efficacy and low cytotoxicity of lentiviral-mediated ZF-Ldb1 gene transfer compared with the drug regimens support its therapeutic potential for the treatment of SCD.

Elevated sphingosine-1-phosphate promotes sickling and sickle cell disease progression.

Sphingosine-1-phosphate (S1P) is a bioactive lipid that regulates multicellular functions through interactions with its receptors on cell surfaces. S1P is enriched and stored in erythrocytes; however, it is not clear whether alterations in S1P are involved in the prevalent and debilitating hemolytic disorder sickle cell disease (SCD). Here, using metabolomic screening, we found that S1P is highly elevated in the blood of mice and humans with SCD. In murine models of SCD, we demonstrated that elevated erythrocyte sphingosine kinase 1 (SPHK1) underlies sickling and disease progression by increasing S1P levels in the blood. Additionally, we observed elevated SPHK1 activity in erythrocytes and increased S1P in blood collected from patients with SCD and demonstrated a direct impact of elevated SPHK1-mediated production of S1P on sickling that was independent of S1P receptor activation in isolated erythrocytes. Together, our findings provide insights into erythrocyte pathophysiology, revealing that a SPHK1-mediated elevation of S1P contributes to sickling and promotes disease progression, and highlight potential therapeutic opportunities for SCD.