title: In vitro evidence of the inhibitory capacity of chloroquine on arginase activity in sickle erythrocytes.
abstract: Increased levels of erythrocyte arginase activity are believed to play a key role in the pathogenesis of sickle cell disease (SCD). Because increased arginase activity has been implicated in the exacerbation of pulmonary hypertension in SCD, this enzyme is considered an important therapeutic target for identifying new drugs to treat and manage SCD and other inflammatory disorders. Although chloroquine (CQ) is prescribed as an anti-malarial and anti-rheumatoid drug, the mechanism of its anti-inflammatory activity is largely unknown. The present study found that CQ inhibited arginase in a dose-dependent manner, and also displayed a linear competitive inhibition on sickle erythrocyte arginase. The apparent K(M) values in the presence of inhibitor were considerably reduced at both physiological and slightly acidic pHs. Slope replots of the double reciprocal plots at pH 6.8 and 7.4 also indicated simple competitive inhibitory mechanism of CQ, and Ki values for CQ were within micromolar levels. To our knowledge, this is the first example of an anti-malarial and anti-inflammatory agent displaying competitive inhibition kinetics on arginase. The outcome of this study may provide a template for the rational design of specific agents either alone or in combination with CQ for the inhibition of arginase activity.
authors: Division of Hematology and Oncology, Children's Mercy Hospital, University of Missouri Medical Center, Kansas City, MO 64108, USA. eiyamu@cmh.edu
authors: Efemwonkiekie W
authors: EW
authors: Iyamu
authors: Syed
authors: S
authors: Jamal
authors: Chiazotam
authors: C
authors: Ekekezie
authors: Gerald M
authors: GM
authors: Woods
mesh_terms: D000293:Adolescent; D000755:Anemia, Sickle Cell / Q000097:blood / Q000201:enzymology*; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D000962:Antimalarials / Q000494:pharmacology*; D001119:Arginase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D002648:Child; D002738:Chloroquine / Q000494:pharmacology*; D002851:Chromatography, High Pressure Liquid; D004305:Dose-Response Relationship, Drug; D004912:Erythrocytes / Q000187:drug effects / Q000201:enzymology*; D006801:Humans; D016014:Linear Models; D008099:Liver / Q000201:enzymology; D013053:Spectrophotometry
chemical_list: D000893:Anti-Inflammatory Agents; D000962:Antimalarials; D002738:Chloroquine; D001119:Arginase