A functional XPNPEP2 promoter haplotype leads to reduced plasma aminopeptidase P and increased risk of ACE inhibitor-induced angioedema.

Angiotensin I-converting enzyme inhibitors (ACEi) are widely used antihypertensive agents that are associated with a potentially life-threatening reaction, ACEi-angioedema. Impaired metabolism of bradykinin and des-Arg(9) -bradykinin by aminopeptidase P (APP) is a key contributor to ACEi-angioedema. This study aimed to characterize the genetic regulation of the XPNPEP2 gene and identify the genetic factors contributing to variance in plasma APP activity and ACEi-angioedema. Additive genetic factors accounted for 47.3% of variance in plasma APP activity in healthy individuals. Nested deletion analysis identified the minimal promoter (-338 bp to -147 bp) and an enhancer region (-2,502 bp to -2,238 bp). Three polymorphisms (c.-2399C>A, c.-1612G>T, and c.-393G>A) were significantly associated with plasma APP activity. Haplotype ATG was significantly associated with reduced reporter gene activity and with reduced plasma APP activity. The c.-2399C>A polymorphism was located in an enhancer region and was predicted to differentially bind hepatic nuclear factor 4 (HNF4). Over expression of HNF4 increased the activation of haplotype ATG compared with haplotype CGG. In a case control study of subjects with a history of ACEi-angioedema, haplotype ATG was significantly associated with ACEi-angioedema (OR 4.87 [1.78-13.35] P = 0.002). The ATG haplotype is functional and contributes to ACEi-angioedema through a reduction in APP.

Role of fibrin structure in thrombosis and vascular disease.

Fibrin clot formation is a key event in the development of thrombotic disease and is the final step in a multifactor coagulation cascade. Fibrinogen is a large glycoprotein that forms the basis of a fibrin clot. Each fibrinogen molecule is comprised of two sets of Aα, Bß, and γ polypeptide chains that form a protein containing two distal D regions connected to a central E region by a coiled-coil segment. Fibrin is produced upon cleavage of the fibrinopeptides by thrombin, which can then form double-stranded half staggered oligomers that lengthen into protofibrils. The protofibrils then aggregate and branch, yielding a three-dimensional clot network. Factor XIII, a transglutaminase, cross-links the fibrin stabilizing the clot protecting it from mechanical stress and proteolytic attack. The mechanical properties of the fibrin clot are essential for its function as it must prevent bleeding but still allow the penetration of cells. This viscoelastic property is generated at the level of each individual fiber up to the complete clot. Fibrinolysis is the mechanism of clot removal, and involves a cascade of interacting zymogens and enzymes that act in concert with clot formation to maintain blood flow. Clots vary significantly in structure between individuals due to both genetic and environmental factors and this has an effect on clot stability and susceptibility to lysis. There is increasing evidence that clot structure is a determinant for the development of disease and this review will discuss the determinants for clot structure and the association with thrombosis and vascular disease.

The bradykinin-degrading aminopeptidase P is increased in women taking the oral contraceptive pill.

INTRODUCTION: The renin-angiotensin and kininogen-kinin hormonal systems are critically involved in regulating blood pressure and are candidates in contributing to oral contraceptive pill (OCP)-induced hypertension. Angiotensin-converting enzyme (ACE) and aminopeptidase P (AP-P) are key enzymes in these systems and are both involved in the degradation of the vasodilator bradykinin. METHODS: Circulating ACE and AP-P levels were measured by activity assay using selective fluorogenic peptide substrates in plasma samples from the Leeds Family Study. In addition, the effect of progesterone on the expression of AP-P and ACE was examined in cells. RESULTS: Women on the OCP had higher age-adjusted plasma AP-P (mean [95% confidence interval]) (0.27 [0.23-0.32] nmol/min/ml (n = 53)) compared with women not on the OCP (0.17 [0.16-0.19] nmol/min/ml (n = 133), p < 0.001) or males (0.19 [0.17-0.20] nmol/min/ml (n = 209), p<0.001). There were no differences in the age-adjusted plasma ACE levels among the three groups. In HepG2 cells, progesterone treatment increased the AP-P protein and mRNA expression, whereas no effect of progesterone treatment was observed for ACE. CONCLUSION: Increased AP-P may result in increased breakdown of bradykinin. These data suggest that progesterone-induced increases in AP-P may contribute to the development of OCP-induced hypertension in susceptible Women.