Mias Pretorius

Angiotensin-Converting Enzyme Inhibition Increases Human Vascular Tissue-Type Plasminogen Activator Release Through Endogenous Bradykinin

Background—Angiotensin-converting enzyme (ACE) inhibition potentiates the tissue-type plasminogen activator (t-PA) response to exogenous bradykinin. This study tested the hypothesis that ACE inhibition increases endothelial t-PA release through endogenous bradykinin. Methods and Results—We measured the effect of intra-arterial enalaprilat (5 &mgr;g/min) on forearm blood flow (FBF) and net t-PA release before and during intra-arterial infusion of bradykinin (25 to 400 ng/min) and methacholine (3.2 to 12.8 &mgr;g/min) in 24 smokers pretreated with bradykinin receptor antagonist HOE 140 (100 &mgr;g/kg intravenously) or vehicle. There was no specific effect of HOE 140 on FBF or forearm vascular resistance (FVR, 29.9±3.6 versus 29.7±3.6 mm Hg · mL−1 · min−1 · 100 mL−1 after vehicle and HOE 140, respectively, P =0.956 between groups). Resting FVR decreased during enalaprilat compared with vehicle or HOE 140, but not compared with baseline, and the effect was similar in the 2 groups (22.0±2.7 and 24.1±2.9 mm Hg · mL−1 · min−1 · 100 mL−1, respectively, P =0.610). In contrast, enalaprilat significantly increased resting net t-PA release (from 0.6±0.4 to 1.7±0.6 ng · min−1 · 100 mL−1, P =0.002); this effect was abolished by HOE 140 (0.1±0.3 ng · min−1 · 100 mL−1, P =0.036 versus enalaprilat alone). Enalaprilat increased the effect of exogenous bradykinin on FBF 60% (from 17.5±2.5 to 28.1±4.0 mL · min−1 · 100 mL−1 during 100 ng/min bradykinin, P =0.001) and on t-PA release 14-fold (from 21.2±7.9 to 317.4±118.9 ng · min−1 · 100 mL−1, P =0.024). Enalaprilat increased the t-PA response to bradykinin to a greater extent than the FBF response, shifting the relationship between net t-PA release and FBF (P =0.005). HOE 140 blocked these effects. There was no effect of enalaprilat or HOE 140 on the FBF or t-PA response to methacholine. Conclusion—ACE inhibition increases constitutive endothelial t-PA release through endogenous bradykinin.

Variation in the 4q25 Chromosomal Locus Predicts Atrial Fibrillation after Coronary Artery Bypass Graft Surgery

Background— Atrial fibrillation (AF) is the most common adverse event following coronary artery bypass graft surgery. A recent study identified chromosome 4q25 variants associated with AF in ambulatory populations. However, their role in postoperative AF is unknown. We hypothesized that genetic variants in the 4q25 chromosomal region are independently associated with postoperative AF after coronary artery bypass graft surgery. Methods and Results— Two prospectively collected cohorts of patients undergoing coronary artery bypass graft surgery, with or without concurrent valve surgery, at 3 US centers. From a discovery cohort of 959 patients, clinical and genomic multivariate predictors of postoperative AF were identified by genotyping 45 single-nucleotide polymorphisms (SNPs) encompassing the 4q25 locus. Three SNPs were then assessed in a separately collected validation cohort of 494 patients. After adjustment for clinical predictors of postoperative AF and multiple comparisons, rs2200733, rs13143308, and 5 other linked SNPs independently predicted postoperative AF in the discovery cohort. Additive odds ratios for the 7 associated 4q25 SNPs ranged between 1.57 and 2.17 (P=8.0×10−4 to 3.4×10−6). Association with postoperative AF were measured and replicated for rs2200733 and rs13143308 in the validation cohort. Conclusions— In 2 independently collected cardiac surgery cohorts, noncoding SNPs within the chromosome 4q25 region are independently associated with postoperative AF after coronary artery bypass graft surgery after adjusting for clinical covariates and multiple comparisons.

Postoperative acute kidney injury is associated with hemoglobinemia and an enhanced oxidative stress response

Acute kidney injury (AKI) frequently afflicts patients undergoing cardiopulmonary bypass and independently predicts death. Both hemoglobinemia and myoglobinemia are independent predictors of postoperative AKI. Release of free hemeproteins into the circulation is known to cause oxidative injury to the kidneys. This study tested the hypothesis that postoperative AKI is associated with both enhanced intraoperative hemeprotein release and increased lipid peroxidation assessed by measuring F₂-isoprostanes and isofurans. In a case-control study nested within an ongoing randomized trial of perioperative statin treatment and AKI, we compared levels of F₂-isoprostanes and isofurans with plasma levels of free hemoglobin and myoglobin in 10 cardiac surgery AKI patients to those of 10 risk-matched controls. Peak plasma free hemoglobin concentrations were significantly higher in AKI subjects (289.0 ± 37.8 versus 104.4 ± 36.5mg/dl, P = 0.01), whereas plasma myoglobin concentrations were similar between groups. The change in plasma F₂-isoprostane and isofuran levels (repeated-measures ANOVA, P = 0.02 and P = 0.001, respectively) as well as the change in urine isofuran levels (P = 0.04) was significantly greater in AKI subjects. In addition, change in peak plasma isofuran levels correlated not only with peak free plasma hemoglobin concentrations (r² = 0.39, P = 0.001) but also with peak change in serum creatinine (r² = 0.20, P = 0.01). Postoperative AKI is associated with both enhanced intraoperative hemeprotein release and enhanced lipid peroxidation. The correlations among hemoglobinemia, lipid peroxidation, and AKI indicate a potential role for hemeprotein-induced oxidative damage in the pathogenesis of postoperative AKI.

Obesity and Oxidative Stress Predict AKI after Cardiac Surgery

Obesity increases oxidative stress, endothelial dysfunction, and inflammation, but the effect of obesity on postoperative AKI is not known. We examined the relationship between body mass index (BMI) and AKI in 445 patients undergoing cardiac surgery and whether oxidative stress (F(2)-isoprostanes), inflammation (IL-6), or antifibrinolysis (plasminogen activator inhibitor-1 [PAI-1]) contribute to any identified relationship. Overall, 112 (25%) of the 445 patients developed AKI. Higher BMI was independently associated with increased odds of AKI (26.5% increase per 5 kg/m(2) [95% confidence interval, 4.3%-53.4%]; P=0.02). Baseline F(2)-isoprostane (P=0.04), intraoperative F(2)-isoprostane (P=0.003), and intraoperative PAI-1 (P=0.04) concentrations also independently predicted AKI. BMI no longer predicted AKI after adjustment for the effect of F(2)-isoprostanes, suggesting that obesity may affect AKI via effects on oxidative stress. In contrast, adjustment for IL-6 or PAI-1 did not substantially alter the association between BMI and AKI. Further, deconstruction of the obesity-AKI relationship into direct (i.e., independent of candidate pathways) and indirect (i.e., effect of BMI on AKI via each candidate pathway) effects indicated that F(2)-isoprostanes, but not IL-6 or PAI-1, partially mediate the relationship between obesity and AKI (P=0.001). In conclusion, obesity independently predicts AKI after cardiac surgery, and oxidative stress may partially mediate this association.

Milrinone Use Is Associated With Postoperative Atrial Fibrillation After Cardiac Surgery

Background— Postoperative atrial fibrillation (AF), a frequent complication after cardiac surgery, causes morbidity and prolongs hospitalization. Inotropic drugs are commonly used perioperatively to support ventricular function. This study tested the hypothesis that the use of inotropic drugs is associated with postoperative AF. Methods and Results— We evaluated perioperative risk factors in 232 patients who underwent elective cardiac surgery. All patients were in sinus rhythm at surgery. Sixty-seven patients (28.9%) developed AF a mean of 2.9±2.1 days after surgery. Patients who developed AF stayed in the hospital longer (P<0.001) and were more likely to die (P=0.02). Milrinone use was associated with an increased risk of postoperative AF (58.2% versus 26.1% in nonusers; P<0.001). Older age (63.4±10.7 versus 56.7±12.3 years; P<0.001), hypertension (P=0.04), lower preoperative ejection fraction (P=0.03), mitral valve surgery (P=0.02), right ventricular dysfunction (P=0.03), and higher mean pulmonary artery pressure (27.1±9.3 versus 21.8±7.5 mm Hg; P=0.001) also were associated with postoperative AF. In multivariable logistic regression, age (P<0.001), ejection fraction (P=0.02), and milrinone use (odds ratio, 4.86; 95% confidence interval, 2.31 to 10.25; P<0.001) independently predicted postoperative AF. When only data from patients with pulmonary artery catheters were analyzed and pulmonary artery pressure was included in the model, age, milrinone use (odds ratio, 4.45; 95% confidence interval, 2.01 to 9.84; P<0.001), and higher pulmonary artery pressure (P=0.02) were associated with an increased risk of postoperative AF. Adding other potential confounders or stratifying analysis by mitral valve surgery did not change the association of milrinone use with postoperative AF. Conclusion— Milrinone use is an independent risk factor for postoperative AF after elective cardiac surgery.

Early Postoperative Statin Therapy Is Associated With a Lower Incidence of Acute Kidney Injury After Cardiac Surgery

OBJECTIVE To test the hypothesis that perioperative statin use reduces acute kidney injury (AKI) after cardiac surgery. DESIGN A retrospective analysis of prospectively collected data from an ongoing clinical trial. SETTING A quaternary-care university hospital. PARTICIPANTS Three hundred twenty-four adult elective cardiac surgery patients. INTERVENTIONS None. MEASUREMENTS AND MAIN RESULTS The authors assessed the association of preoperative statin use, early postoperative statin use, and acute statin withdrawal with the incidence of AKI. Early postoperative statin use was defined as statin treatment within the first postoperative day. Statin withdrawal was defined as the discontinuation of preoperative statin treatment before surgery until at least postoperative day 2. Logistic regression and propensity score modeling were used to control for AKI risk factors. Sixty-eight of 324 patients (21.0%) developed AKI. AKI patients stayed in the hospital longer (p = 0.03) and were more likely to develop pneumonia (p = 0.002) or die (p = 0.001). A higher body mass index (p = 0.003), higher central venous pressure (p = 0.03), and statin withdrawal (27.4 v 14.7%, p = 0.046) were associated with a higher incidence of AKI, whereas early postoperative statin use was protective (12.5% v 23.8%, p = 0.03). Preoperative statin use did not affect the risk of AKI. In multivariate logistic regression, age (p = 0.03), male sex (p = 0.02), body mass index (p < 0.001), and early postoperative statin use (odds ratio = 0.32; 95% confidence interval, 0.14-0.72; p = 0.006) independently predicted AKI. Propensity score-adjusted risk assessment confirmed the association between early postoperative statin use and reduced AKI (odds ratio = 0.30; 95% confidence interval, 0.13-0.70; p = 0.005). CONCLUSIONS Early postoperative statin use is associated with a lower incidence of AKI among both chronic statin users and statin-naive cardiac surgery patients.

Relationship Between Carbamoyl-Phosphate Synthetase Genotype and Systemic Vascular Function

Abstract—Endothelial cells can convert l-citrulline to l-arginine, the precursor of nitric oxide. The present study tests the hypothesis that a C-to-A nucleotide transversion (T1405N) in the gene-encoding carbamoyl-phosphate synthetase 1, the enzyme catalyzing the rate-limiting step in l-citrulline formation, influences nitric oxide metabolite concentrations or nitric oxide-mediated vasodilation in humans. Bradykinin (100, 200, and 400 ng/min) was infused via brachial artery in 106 (CC:AC:AA=40:54:12) healthy subjects. Sodium nitroprusside (1.6, 3.2, and 6.4 &mgr;g/min) was also infused in 87 (CC:AC:AA=31:46:10) subjects. Forearm blood flow was measured by plethysmography and blood samples were collected for tissue-type plasminogen activator antigen, nitric oxide metabolites, and cyclic GMP. There was a significant relationship between carbamoyl-phosphate synthetase 1 genotype and nitric oxide metabolites, such that nitric oxide metabolite concentrations were highest in individuals homozygous for the C allele (mean±SD, 14.0±8.5 &mgr;mol/L), lowest in individuals homozygous for the A allele (9.1±3.1 &mgr;mol/L), and intermediate (11.8±6.6 &mgr;mol/L) in heterozygotes (P =0.036). There was a significant effect of carbamoyl-phosphate synthetase 1 genotype on forearm blood flow during bradykinin (P =0.028), such that the vasodilator response was greatest in C allele homozygotes (22.2±9.1 mL/min/100 mL at 400 ng/min), least in A allele homozygotes (13.6±6.2 mL/min/100 mL), and intermediate (19.4±10.7 mL/min/100 mL) in heterozygotes. Similarly, carbamoyl-phosphate synthetase 1 genotype influenced forearm blood flow during nitroprusside (maximal flow 19.2±8.3, 18.1±8.3, and 11.5±4.9 mL/min/100 mL in the CC:AC:AA groups, respectively; P =0.022). In contrast, there was no effect of carbamoyl-phosphate synthetase 1 genotype on the nitric oxide–independent tissue-type plasminogen activator response to bradykinin (P =0.943). These data indicate that a polymorphism in the gene encoding carbamoyl-phosphate synthetase 1 influences nitric oxide production as well as vascular smooth muscle reactivity.

Genetic Variation in Soluble Epoxide Hydrolase (EPHX2) Is Associated With Forearm Vasodilator Responses in Humans

Cytochrome P450-derived epoxyeicosatrienoic acids are potent vasodilators in preclinical models and are hydrolyzed by soluble epoxide hydrolase (EPHX2). Associations between the EPHX2 Lys55Arg and Arg287Gln polymorphisms and cardiovascular disease risk have been reported; however, their impact on vascular function in humans has not been investigated. In 265 volunteers (198 white, 67 black American), forearm blood flow was measured by strain-gauge venous occlusion plethysmography at baseline and in response to bradykinin, methacholine, and sodium nitroprusside. Forearm vascular resistance was calculated as mean arterial pressure/forearm blood flow. In white Americans, Lys55Arg genotype was associated with vasodilator response to bradykinin, such that forearm blood flow was significantly lower (P=0.043) and forearm vascular resistance was significantly higher (P=0.013) in Arg55 variant allele carriers compared to wild-type individuals. Significant associations were also observed with methacholine and sodium nitroprusside. In contrast, no relationship was observed in black Americans. In black Americans, Arg287Gln genotype was associated with vasodilator response to bradykinin. Although the difference in forearm blood flow did not reach statistical significance (P=0.058), forearm vascular resistance was significantly lower (P=0.037) in Gln287 variant allele carriers compared to wild-type individuals. Significant associations were also observed with methacholine and sodium nitroprusside. In white Americans, Gln287 variant allele carriers did not exhibit significantly higher forearm blood flow (P=0.128) or lower forearm vascular resistance (P=0.080). Genetic variation in EPHX2 is associated with forearm vasodilator responses in a bradykinin receptor- and endothelium-independent manner, suggesting an important role for soluble epoxide hydrolase in the regulation of vascular function in humans.

Plasminogen Activator Inhibitor-1 as a Predictor of Postoperative Atrial Fibrillation After Cardiopulmonary Bypass

Background— Postoperative atrial fibrillation (AF), leading to significant morbidity and prolongation of hospital stay, complicates 20% to 40% of surgical procedures requiring cardiopulmonary bypass (CPB). This study tests the hypothesis that biomarkers predict the development of postoperative AF. Methods and Results— We enrolled 253 adult patients undergoing elective cardiac surgery requiring CPB and who were in sinus rhythm at the time of surgery. Blood samples were obtained for measurement of 21 biomarkers immediately after separation from CPB and administration of protamine. Patients who developed postoperative AF (67 subjects, 26.5%) were significantly older (P<0.001), more likely to have a remote history of AF (P<0.001), and tended to be more likely to have had valve surgery (P=0.082). Plasminogen activator inhibitor-1 (P=0.014), interleukin (IL)-6 (P=0.019), and N-terminal prohormone brain natriuretic peptide (P=0.028) concentrations were significantly higher in the blood of patients who developed postoperative AF. Logistic regression identified age (P<0.001), remote history of AF (P=0.001), and postoperative PAI-1 (P=0.036) as independent predictors of postoperative AF. When preoperative PAI-1 antigen concentrations were included in the model age (P<0.001), remote history of AF (P<0.001) and preoperative PAI-1 (P=0.015) were identified as independent predictors of postoperative AF. The Chi-squared Automatic Interaction Detection (CHAID) model indicated that age was the primary determinant for the development of postoperative AF (17% in age ≤67.3 years versus 49% in age >67.3 years). Within younger patients (age ≤67.3 years) without remote history of AF, postoperative PAI-1 antigen concentration next determined risk of AF (13% if PAI-1≤28.5 ng/mL versus 46% if PAI-1>28.5 ng/mL). Conclusion— An elevated preoperative or postoperative PAI-1 antigen concentration is an independent predictor for development of AF after CPB. Studies are needed to determine whether drugs that reduce PAI-1 concentrations can also reduce the risk of postoperative AF.

Ethnicity Affects Vasodilation, but Not Endothelial Tissue Plasminogen Activator Release, in Response to Bradykinin

Previous studies indicate that the vasodilator response to bradykinin (BK) and other endothelium-dependent and -independent agonists is decreased in black Americans compared with white Americans. The purpose of the present study was to determine the effect of ethnicity on fibrinolytic function in humans. Graded doses of BK (100, 200, and 400 ng/min), acetylcholine (15, 30, and 60 &mgr;g/min; N=20), or methacholine (3.2, 6.4, 12.8 &mgr;g/min; N=20), and sodium nitroprusside (0.8, 1.6, and 3.2 &mgr;g/min) were infused via brachial artery in 19 white and 21 black age-matched normotensive subjects. Forearm blood flow (FBF) was measured by plethysmography, and venous and arterial samples were collected for tissue plasminogen activator (tPA) antigen. Compared with whites (increase in FBF from 3.7±0.5 to 23.9±2.5 mL · min−1 · 100 mL−1), blacks (increase in FBF from 2.8±0.3 to 15.2±1.9 mL · 100 mL−1 · min−1) exhibited a blunted FBF response to BK (P =0.035). Responses to sodium nitroprusside and methacholine or acetylcholine were similarly decreased. In contrast, there was no effect of ethnicity on net tPA antigen release in response to BK (increase from −0.2±0.4 to 67.3±15.2 ng · min−1 · 100 mL−1 in blacks; from 0.04±0.9 to 65.9±13.6 ng · min−1 · 100 mL−1 in whites). Thus, ethnicity significantly influenced the relationship between the flow and tPA release responses to BK (P =0.037). These data suggest that the BK-dependent alterations in vascular fibrinolytic function are preserved in black Americans compared with white Americans.