ß2-glycoprotein I promotes the clearance of circulating mitochondria.

ß2-glycoprotein I (ß2-Gp1) is a cardiolipin-binding plasma glycoprotein. It is evolutionarily conserved from invertebrates, and cardiolipin-bound ß2-Gp1 is a major target of antiphospholipid antibodies seen in autoimmune disorders. Cardiolipin is almost exclusively present in mitochondria, and mitochondria are present in circulating blood. We show that ß2-Gp1 binds to cell-free mitochondria (CFM) in the circulation and promotes its phagocytosis by macrophages at physiological plasma concentrations. Exogenous CFM had a short circulation time of less than 10 minutes in mice. Following infusion of CFM, ß2-Gp1-deficient mice had significantly higher levels of transfused mitochondria at 5 minutes (9.9 ± 6.4 pg/ml versus 4.0 ± 2.3 pg/ml in wildtype, p = 0.01) and at 10 minutes (3.0 ± 3.6 pg/ml versus 1.0 ± 0.06 pg/ml in wild-type, p = 0.033, n = 10). In addition, the splenic macrophages had less phagocytosed CFM in ß2-Gp1-deficient mice (24.4 ± 2.72% versus 35.6 ± 3.5 in wild-type, p = 0.001, n = 5). A patient with abnormal ß2-Gp1, unable to bind cardiolipin, has increased CFM in blood (5.09 pg/ml versus 1.26 ± 1.35 in normal) and his plasma induced less phagocytosis of CFM by macrophages (47.3 ± 1.6% versus 54.3 ± 1.3, p = 0.01) compared to normal plasma. These results show the evolutionarily conserved ß2-Gp1 is one of the mediators of the clearance of CFM in circulation.

Lisinopril-Induced Angioedema in a Patient with Plasma Prekallikrein Deficiency.

Angiotensin-converting enzyme (ACE) inhibitors are extensively prescribed to treat patients with hypertension, congestive heart failure, and diabetic nephropathy. A small fraction of these patients (approximately 0.7%) develop angioedema, manifested by swelling of the lips and oropharynx. Angioedema of oropharynx is a medical emergency that can lead to asphyxiation and death. The angioedema is due to bradykinin generated from high molecular weight kininogen by kallikrein, which is derived from plasma prekallikrein by action of the factor XIIa, factor Xia, or prolylcarboxypeptidase. Bradykinin induces vasodilation and increased vascular permeability. ACE is the major degrading enzyme of bradykinin in the intravascular department. ACE inhibitors inhibit the proteolytic inactivation of bradykinin. We report a patient with oropharyngeal angioedema associated with an ACE inhibitor with complete absence of plasma prekallikrein due to homozygous mutation (Ser97PhefsTer173).