Stacey L. House

Cardiac-Specific Overexpression of Fibroblast Growth Factor-2 Protects Against Myocardial Dysfunction and Infarction in a Murine Model of Low-Flow Ischemia

Background—Preconditioning the heart before an ischemic insult has been shown to protect against contractile dysfunction, arrhythmias, and infarction. Pharmacological studies have suggested that fibroblast growth factor-2 (FGF2) is involved in cardioprotection. However, because of the number of FGFs expressed in the heart and the promiscuity of FGF ligand-receptor interactions, the specific role of FGF2 during ischemia-reperfusion injury remains unclear. Methods and Results—FGF2-deficient (Fgf2 knockout) mice and mice with a cardiac-specific overexpression of all 4 isoforms of human FGF2 (FGF2 transgenic [Tg]) were compared with wild-type mice to test whether endogenous FGF2 elicits cardioprotection. An ex vivo work-performing heart model of ischemia was developed in which murine hearts were subjected to 60 minutes of low-flow ischemia and 120 minutes of reperfusion. Preischemic contractile function was similar among the 3 groups. After ischemia-reperfusion, contractile function of Fgf2 knockout hearts recovered to 27% of its baseline value compared with a 63% recovery in wild-type hearts (P <0.05). In FGF2 Tg hearts, an 88% recovery of postischemic function occurred (P <0.05). Myocardial infarct size was also reduced in FGF2 Tg hearts compared with wild-type hearts (13% versus 30%, P <0.05). There was a 2-fold increase in FGF2 release from Tg hearts compared with wild-type hearts (P <0.05). No significant alterations in coronary flow or capillary density were detected in any of the groups, implying that the protective effect of FGF2 is not mediated by coronary perfusion changes. Conclusions—These results provide evidence that endogenous FGF2 plays a significant role in the cardioprotective effect against ischemia-reperfusion injury.

Albuterol Administration Is Commonly Associated With Increases in Serum Lactate in Patients With Asthma Treated for Acute Exacerbation of Asthma

BACKGROUND Controversy exists around the incidence and cause of hyperlactatemia during asthma exacerbations. We evaluated the incidence, potential causes, and adverse events of hyperlactatemia in patients with acute asthma exacerbation. METHODS This study was a subanalysis of subjects receiving placebo from a prospective, randomized trial evaluating an IV b -adrenergic agonist in acute asthma exacerbation. Plasma albuterol, serum lactate, and bicarbonate concentrations were measured at baseline and 1.25 h, and dyspnea score and spirometry were measured at baseline and hourly for 3 h. All subjects had a therapeutic trial comprising 5 to 15 mg nebulized albuterol, 0.5 to 1 mg nebulized ipratropium, and at least 50 mg oral prednisone or its equivalent prior to initiation of the study. Following randomization, subjects were treated with continued albuterol and IV magnesium at the discretion of their treating physician. Subjects were followed to hospital admission or discharge with follow-up at 24 h and 1 week. RESULTS One hundred seventy-fi ve subjects were enrolled in the parent trial, with 84 in the placebo group. Sixty-fi ve had complete data. Mean SD albuterol administration prior to baseline was 12.3 5.3 mg. Mean baseline lactate was 18.5 8.4 mg/dL vs 26.5 11.8 mg/dL at 1.25 h ( P , .001). Forty-fi ve subjects (69.2%) had hyperlactatemia. Mean baseline bicarbonate level was 22.6 2.9 mEq/L vs 21.9 4.0 mEq/L at 1.25 h ( P 5 .11). Plasma albuterol concentration correlated with lactate concentration ( b 5 0.45, P , .001) and maintained a significant association after adjusting for asthma severity ( b 5 0.41, P 5 .001). Hyperlactatemia did not increase the risk of hospitalization or relapse ( P 5 .26) or was associated with lower FEV 1 % predicted at 3 h ( P 5 .54). CONCLUSIONS Plasma albuterol was significantly correlated with serum lactate concentration after adjusting for asthma severity. Hyperlactatemia was not associated with poorer pulmonary function as measured by 3-h FEV 1 % predicted or increased hospitalization or relapse at 1 week.

Fibroblast Growth Factor Receptor 1 Signaling in Adult Cardiomyocytes Increases Contractility and Results in a Hypertrophic Cardiomyopathy

Fibroblast growth factors (FGFs) and their receptors are highly conserved signaling molecules that have been implicated in postnatal cardiac remodeling. However, it is not known whether cardiomyocyte-expressed FGF receptors are necessary or sufficient for ventricular remodeling in the adult heart. To determine whether cardiomyocytes were competent to respond to an activated FGF receptor, and to determine if this signal would result in the development of hypertrophy, we engineered a doxycycline (DOX)-inducible, cardiomyocyte-specific, constitutively active FGF receptor mouse model (αMHC-rtTA, TRE-caFgfr1-myc). Echocardiographic and hemodynamic analysis indicated that acute expression of caFGFR1 rapidly and directly increased cardiac contractility, while chronic expression resulted in significant hypertrophy with preservation of systolic function. Subsequent histologic analysis showed increased cardiomyocyte cross-sectional area and regions of myocyte disarray and fibrosis, classic features of hypertrophic cardiomyopathy (HCM). Analysis of downstream pathways revealed a lack of clear activation of classical FGF-mediated signaling pathways, but did demonstrate a reduction in Serca2 expression and troponin I phosphorylation. Isolated ventricular myocytes showed enhanced contractility and reduced relaxation, an effect that was partially reversed by inhibition of actin-myosin interactions. We conclude that adult cardiomyocytes are competent to transduce FGF signaling and that FGF signaling is sufficient to promote increased cardiomyocyte contractility in vitro and in vivo through enhanced intrinsic actin-myosin interactions. Long-term, FGFR overexpression results in HCM with a dynamic outflow tract obstruction, and may serve as a unique model of HCM.

Endothelial fibroblast growth factor receptor signaling is required for vascular remodeling following cardiac ischemia-reperfusion injury.

Fibroblast growth factor (FGF) signaling is cardioprotective in various models of myocardial infarction. FGF receptors (FGFRs) are expressed in multiple cell types in the adult heart, but the cell type-specific FGFR signaling that mediates different cardioprotective endpoints is not known. To determine the requirement for FGFR signaling in endothelium in cardiac ischemia-reperfusion injury, we conditionally inactivated the Fgfr1 and Fgfr2 genes in endothelial cells with Tie2-Cre (Tie2-Cre, Fgfr1(f/f), Fgfr2(f/f) DCKO mice). Tie2-Cre, Fgfr1(f/f), Fgfr2(f/f) DCKO mice had normal baseline cardiac morphometry, function, and vessel density. When subjected to closed-chest, regional cardiac ischemia-reperfusion injury, Tie2-Cre, Fgfr1(f/f), Fgfr2(f/f) DCKO mice showed a significantly increased hypokinetic area at 7 days, but not 1 day, after reperfusion. Tie2-Cre, Fgfr1(f/f), Fgfr2(f/f) DCKO mice also showed significantly worsened cardiac function compared with controls at 7 days but not 1 day after reperfusion. Pathophysiological analysis showed significantly decreased vessel density, increased endothelial cell apoptosis, and worsened tissue hypoxia in the peri-infarct area at 7 days following reperfusion. Notably, Tie2-Cre, Fgfr1(f/f), Fgfr2(f/f) DCKO mice showed no impairment in the cardiac hypertrophic response. These data demonstrate an essential role for FGFR1 and FGFR2 in endothelial cells for cardiac functional recovery and vascular remodeling following in vivo cardiac ischemia-reperfusion injury, without affecting the cardiac hypertrophic response. This study suggests the potential for therapeutic benefit from activation of endothelial FGFR pathways following ischemic injury to the heart.

Fibroblast growth factor-2-induced cardioprotection against myocardial infarction occurs via the interplay between nitric oxide, protein kinase signaling, and ATP-sensitive potassium channels

Fibroblast growth factor-2 (FGF2) protects the heart from ischemia–reperfusion (I-R) injury via a vast network of protein kinases. In the heart, downstream effectors of these FGF2-triggered signals have not yet been identified. It is hypothesized that nitric oxide (NO) signaling and ATP-sensitive potassium (KATP) channel activity are key effectors of protein kinases activated by FGF2-mediated cardioprotection. Hearts with a cardiac-specific overexpression of FGF2 (FGF2 Tg) were subjected to I-R injury in the absence or the presence of selective inhibitors of NO synthase (NOS) isoforms or sarcolemmal (sarcKATP) and mitochondrial (mitoKATP) KATP channels. Multiple NOS isoforms are necessary for FGF2-mediated cardioprotection, and nitrite levels are significantly reduced in FGF2 Tg hearts upon inhibition of protein kinase C or mitogen-activated protein kinases. Likewise, sarcKATP and mitoKATP channels are important for cardioprotection elicited by endogenous FGF2. These findings suggest that FGF2-induced cardioprotection occurs via protein kinase-NOS pathways as well as KATP channel activity.

Fibroblast growth factor 2 is an essential cardioprotective factor in a closed‐chest model of cardiac ischemia‐reperfusion injury

Fibroblast growth factor 2 (FGF2) is cardioprotective in in vivo models of myocardial infarction; however, whether FGF2 has a protective role in in vivo ischemia‐reperfusion (IR) injury, a model that more closely mimics acute myocardial infarction in humans, is not known. To assess the cardioprotective efficacy of endogenous FGF2, mice lacking a functional Fgf2 gene (Fgf2−/−) and wild‐type controls were subjected to closed‐chest regional cardiac IR injury (90 min ischemia, 7 days reperfusion). Fgf2−/− mice had significantly increased myocardial infarct size and significantly worsened cardiac function compared to wild‐type controls at both 1 and 7 days post‐IR injury. Pathophysiological analysis showed that at 1 day after IR injury Fgf2−/− mice have worsened cardiac strain patterns and increased myocardial cell death. Furthermore, at 7 days post‐IR injury, Fgf2−/− mice showed a significantly reduced cardiac hypertrophic response, decreased cardiac vessel density, and increased vessel diameter in the peri‐infarct area compared to wild‐type controls. These data reveal both acute cardioprotective and a longer term proangiogenic potential of endogenous FGF2 in a clinically relevant, in vivo, closed‐chest regional cardiac IR injury model that mimics acute myocardial infarction.

Efficacy of a new intravenous β2-adrenergic agonist (bedoradrine, MN-221) for patients with an acute exacerbation of asthma.

BACKGROUND Many patients with acute exacerbation of asthma are non-responders to inhaled β-adrenergic agonists. The goal of this study was to evaluate the safety and efficacy of intravenous bedoradrine (MN-221), a highly selective β2-adrenergic agonist, as adjunct to standard therapy in the management of patients with acute exacerbation of asthma who did not respond to standard therapy. METHODS Patients (N = 167) received standard therapy and were randomized to either bedoradrine (1200 μg) or placebo. Safety and efficacy parameters were monitored hourly for 3 h, followed by a 24-h follow-up visit and an 8-day follow-up phone call. Change in %FEV1 from baseline to Hour 3 was the primary outcome. Secondary outcome measures included change in %FEV1 at 1 and 2 h, change in dyspnea score at 1, 2, and 3 h, treatment failure rate, defined as a combination of hospitalization on the index visit or return to the emergency department within 1 week, and safety monitoring. RESULTS There was no significant difference in %FEV1 at 3 h between the 2 groups. The dyspnea scores were significantly improved for patients treated with bedoradrine compared to placebo (AUC0-2 hP < 0.005, AUC0-3 hP < 0.05). The safety profile for those treated with bedoradrine was consistent with the known mechanism of action of β-adrenergic agonists, and included both cardiovascular and metabolic effects. CONCLUSIONS Intravenous bedoradrine, in addition to standard therapy, did not significantly increase %FEV1 at 3 h, but it was associated with significantly improved dyspnea scores. TRIAL REGISTRATION Clinicaltrials.gov; study name: MN-221-CL-007, registration number: NCT00838591; www.clinical trials.gov.