Heather R. Cross

Male and female mice overexpressing the β2-adrenergic receptor exhibit differences in ischemia/reperfusion injury: role of nitric oxide

Objective: Cardiac overexpression of β2-adrenergic receptors (β2ARs) in male mice (MTG4) results in increased contractility and increased ischemic injury. Considering recent clinical data indicating that premenopausal women are protected from cardiovascular injury, we assessed the consequences of β2AR overexpression in females (FTG4). Since protection in females is mediated via estrogen, which activates endothelial and inducible nitric oxide synthases (eNOS and iNOS) we also examined the role of NOS in ischemia/reperfusion injury in male and female TG4 and wild-type (WT) mice. Methods: Hearts from MTG4, FTG4, MWT and FWT mice were isolated and perfused in the Langendorff mode. Hearts were pretreated with either 1 μmol/l of the nonspecific NOS inhibitor, l-NAME, or 100 nmol/l of the specific iNOS inhibitor, 1400W. Control hearts received no treatment. All hearts were subjected to 20 min ischemia and 40 min reperfusion while 31P-NMR spectra were acquired. Results: During ischemia, ATP and pH fell lower in MTG4 hearts than in FTG4 or WT hearts. Hearts from MTG4 mice exhibited increased ischemia/reperfusion injury as indicated by lower recoveries of postischemic contractile function, ATP and PCr than WT. Despite contractility being elevated in FTG4 hearts to the same level as MTG4 hearts, ischemia/reperfusion injury was not increased, as indicated by similar postischemic recoveries of contractile function, ATP and PCr in FTG4 hearts compared to WT. ATP and pH fell lower during ischemia in l-NAME-treated FTG4 hearts than in untreated FTG4 hearts, falling as low as untreated MTG4s. Recoveries of contractile function, ATP and PCr were as low in l-NAME-treated FTG4 hearts as in untreated MTG4 hearts and lower than untreated FTG4 hearts. In contrast, 1400W had no effect on FTG4 hearts. MTG4 hearts were unaffected by l-NAME or 1400W. Conclusions: β2AR overexpression increased ischemia/reperfusion injury in males but not females, thus females were protected from the detrimental effects of β2AR overexpression. Protection was abolished by treatment with l-NAME, but not 1400W, implying that protection was mediated by eNOS not iNOS.

Is Na/Ca exchange during ischemia and reperfusion beneficial or detrimental?

Abstract: Cytosolic calcium increases to approximately 3 μM after 15 min of global ischemia. Manipulations that attenuate this increase in cytosolic Ca2+ reduce myocyte death and dysfunction. The increase in cytosolic Ca2+ during ischemia is dependent on an increase in intracellular Na+, suggesting a role for Na/Ca exchange. Typical ischemic values for ionized intra‐ and extracellular Na+, Ca2+, and membrane potential are consistent with the Na/Ca exchanger operating near equilibrium during ischemia. Studies were undertaken using hearts from mice that overexpress the Na/Ca exchanger to determine if Na/Ca exchanger overexpression enhances or reduces ischemic injury. These studies suggest that overexpression of the Na/Ca exchanger enhances injury in males, but females are protected by a gender‐related mechanism.

Trimetazidine for stable angina pectoris

Stable angina pectoris, a symptom of coronary heart disease (CHD), manifests as stress-induced ischaemic episodes resulting in severe chest pain. Therapeutic aims are to improve quality of life by decreasing anginal attacks and to prevent myocardial infarction (MI) and death. Current anginal medications include β-blockers and calcium antagonists, which decrease ischaemic severity by reducing cardiac workload, and nitrates, which increase coronary blood flow. A new therapeutic approach is the use of metabolic agents, such as trimetazidine, which are cytoprotective during ischaemia. Results of several clinical trials demonstrated that trimetazidine, at the standard dose of 20 mg t.i.d., increased exercise capacity, decreased anginal incidence and decreased left-ventricular (LV) dysfunction compared to placebo. Trimetazidine was also as effective as propranolol (120 - 160 mg/day) and nifedipine (40 mg/day) in decreasing anginal episodes and improving exercise parameters. Trimetazidine improved anginal frequency and symptoms in patients in which treatment with diltiazem, nifedipine, propranolol, pindolol, oxprenolol or long-acting nitrates had failed. Trimetazidine was also more effective than isosorbide dinitrate (30 mg/day) as an adjunct to propranolol. Despite efficacy being equivalent to that of β-blockers and calcium antagonists, trimetazidine does not depress cardiac function and, correspondingly, is not contraindicated in any condition. Adverse effects of trimetazidine are mild and infrequent. In summary, clinical data indicate that trimetazidine is a safe, effective treatment for the symptoms of stable angina pectoris when used either as a monotherapy or an adjunctive therapy. Longer-term trials are necessary to determine whether trimetazidine will be effective in reducing rates of mortality and MI.

No survival benefit with empirical vancomycin therapy for coagulase-negative staphylococcal bloodstream infections in infants.

Background: Coagulase-negative Staphylococcus (CoNS) is the most common cause of bloodstream infections (BSI) in hospitalized infants. CoNS BSI is most reliably treated with vancomycin; however, concerns about side effects and promoting resistance often delay empirical vancomycin therapy until culture results become available. Methods: All infants with CoNS BSI discharged from 348 neonatal intensive care units managed by the Pediatrix Medical Group from 1997 to 2012 were identified. Empirical vancomycin therapy was defined as vancomycin exposure on the day of the first positive blood culture. Delayed vancomycin therapy was defined as vancomycin exposure 1–3 days after the first positive blood culture. We used multivariable logistic regression with random effects for site to evaluate the association between the use of empirical vancomycin therapy versus delayed vancomycin therapy and 30-day mortality, controlling for gestational age, small-for-gestational age status, postnatal age on the day of the first positive culture, oxygen requirement, ventilator support and inotropic support on the day the first positive culture was obtained. Results: A total of 4364 infants with CoNS BSI were identified; 2848 (65%) were treated with empirical vancomycin. The median postnatal age at first positive culture was 14 days (interquartile range: 9, 21). Unadjusted 30-day mortality was similar for infants treated with empirical vancomycin and infants treated with delayed vancomycin therapy [166/2848 (6%) vs. 69/1516 (4%); P = 0.08]. There was no significant difference in 30-day mortality on multivariable analysis [odds ratio: 1.14 (0.84, 1.56)]. The median duration of bacteremia was 1 day longer for infants with delayed vancomycin therapy [4 days (interquartile range: 2, 6) vs. 3 days (2, 5); P < 0.0001]. Conclusions: The median duration of bacteremia was 1 day longer in infants with CoNS BSI who received delayed vancomycin therapy. Despite this finding, empirical vancomycin therapy for CoNS BSI was not associated with improved mortality.

Antibacterial Resistance Leadership Group: Open for Business

Funded by the National Institute of Allergy and Infectious Diseases, the Antibacterial Resistance Leadership Group (ARLG) is tasked with developing a clinical research agenda and conducting clinical studies to address the growing public health threat of antibacterial resistance. The ARLG has identified 4 high-priority areas of research: infections caused by gram-negative bacteria, infections caused by gram-positive bacteria, antimicrobial stewardship and infection prevention, and diagnostics. The ARLG will be accepting proposals from the scientific community for clinical research that addresses 1 or more of these high-priority areas. These studies should have the potential to transform medical practice and be unlikely to occur without ARLG support. The purpose of this article is to make interested parties aware of clinical research opportunities made available by ARLG and to encourage submission of clinical research proposals that address the problem of antibacterial resistance.

Survival Benefit of Empirical Therapy for Staphylococcus aureus Bloodstream Infections in Infants.

Background: The impact of early adequate empirical antibiotic therapy on outcomes of infants in the neonatal intensive care unit (NICU) who develop Staphylococcus aureus bloodstream infections (BSI) is unknown. Methods: Infants with S. aureus BSI discharged in 1997–2012 from 348 NICUs managed by the Pediatrix Medical Group were identified. Early adequate empirical antibiotic therapy was defined as exposure to ≥1 antibiotic with anti-staphylococcal activity on the day the first positive blood culture was obtained. All other cases were defined as inadequate empirical antibiotic therapy. We evaluated the association between inadequate empirical antibiotic therapy on outcomes controlling for gestational age, small for gestational age status, gender, discharge year, mechanical ventilation, inotropic support and use of supplemental oxygen. The primary outcome was 30-day mortality. Secondary outcomes were 7-day mortality, death before hospital discharge and length of bacteremia. Results: Of the 3339 infants with S. aureus BSI, 2492 (75%) had methicillin-susceptible S. aureus (MSSA) BSI and 847 (25%) had methicillin-resistant S. aureus (MRSA) BSI. Inadequate empirical antibiotic therapy was administered in 725 (22%) cases. Inadequate empirical antibiotic therapy was associated with increased 30-day mortality (odds ratio: 2.03; 95% confidence interval: 1.08–3.82) among infants with MRSA BSI. Inadequate empirical antibiotic therapy was not associated with increases in mortality among infants with MSSA BSI. Conclusions: After controlling for confounders, inadequate empirical antibiotic therapy was associated with a modestly increased mortality at 30 days for infants with MRSA BSI.

Neonatal Escherichia coli Bloodstream Infections: Clinical Outcomes and Impact of Initial Antibiotic Therapy.

Background: Escherichia coli is a common cause of bloodstream infections (BSIs) in infants and is associated with high mortality and morbidity among survivors. The clinical significance of antibiotic resistance and timing of appropriate antimicrobial therapy in this population is poorly understood. Methods: We identified all infants with E. coli BSIs discharged from 77 neonatal intensive care units managed by the Pediatrix Medical Group in 2012. We used multivariable logistic regression to evaluate the association between 30-day mortality and ampicillin-resistant E. coli BSI, as well as the number of active empiric antimicrobial agents administered, controlling for gestational age, small-for-gestational age status, early-onset versus late-onset BSI, oxygen requirement, ventilator support and inotropic support on the day of the first positive blood culture. Results: We identified 258 episodes of E. coli BSI, including 123 (48%) ampicillin-resistant isolates. Unadjusted 30-day mortality did not significantly differ between infants with ampicillin-resistant versus ampicillin-susceptible E. coli BSI [11 of 123 (9%) vs. 7 of 135 (5%); P = 0.33; adjusted odds ratio = 1.37 (95% confidence interval: 0.39, 4.77)]. Among ampicillin-resistant E. coli BSIs, 30-day mortality was not significantly lower for infants treated with at least one empiric antimicrobial active against ampicillin-resistant E. coli versus infants receiving no active empiric agent [adjusted odds ratio = 1.50 (0.07, 33.6)]. Conclusions: In this population of infants with E. coli BSI, ampicillin resistance was not associated with significantly increased mortality. Among the subset of infants with ampicillin-resistant E. coli, appropriate empirical antibiotic therapy was not associated with lower mortality.

Trimetazidine: a novel protective role via maintenance of Na+/K+-ATPase activity?

See article by El Banani et al. [31] (pages 688–696) in this issue. Trimetazidine (1-[2,3,4-trimethoxybenzyl]-piperazine; TMZ) is a piperazine compound that has been demonstrated to protect against ischaemic injury in a variety of tissues [1–4]. As a cardiovascular therapeutic agent, TMZ is protective during coronary artery bypass graft surgery [5] and catheter angioplasty [6], has been effective in the treatment of angina [7,8] and reduces infarct size when given before thrombolysis in patients with anterior myocardial infarction [9]. There have been insights into some of the molecular mechanisms of action of TMZ, however, new mechanisms continue to be discovered [10–12]. The best known action of TMZ is inhibition of the β-oxidation pathway of fatty acid metabolism [13]. Inhibition of the β-oxidation pathway during ischaemia and reperfusion concomitantly increases glucose oxidation [13]. Protection from ischaemic injury by TMZ is hypothesized to be due to the increase in glucose oxidation leading to lower rates of glycolysis and less H+ production [14–17]. Increased fatty acid oxidation and glycolysis do result in greater H+ production [18,19] and ischaemic intracellular pH changes have been observed in TMZ-treated hearts [14]. The detrimental effect of glycolytic H+ production in the ischaemic myocardium is thought to be due to increased Na+/H+ exchange activity [20–22]. H+ activate the Na+/H+ exchanger … * Tel.: +1-919-541-5411; fax: +1-919-541-3385 laszlo.deszi{at}richter.hu

Effect of p38 MAP kinases on contractility and ischemic injury in intact heart

The p38 MAP kinases are stress-activated MAP kinases whose induction is often associated with the onset of heart failure. This study investigated the role of p38 MAP kinase isoforms in the regulation of myocardial contractility and ischemia/reperfusion injury using mice with cardiac-specific expression of kinase dead (dominant negative) mutants of p38alpha (p38alphadn) or p38beta (p38betadn). Hearts were subjected to 20 min ischemia and 40 min reperfusion. Immunofluorescence staining for p38alphadn and p38betadn protein was performed on neonatal cardiomyocytes infected with adenovirus expressing flag-tagged p38alphadn and p38betadn protein. Basal contractile function was increased in both p38alphadn and p38betadn hearts compared to WT. Ischemic injury was increased in p38betadn vs. WT hearts, as indicated by lower posti-schemic recoveries of contractile function and ATP. However, despite a similar increase in contractility, ischemic injury was not increased in p38alphadn vs. WT hearts. Immunohistological analysis of cardiomyocytes with comparable levels of protein overexpression show that p38alphadn and p38betadn proteins were co-localized with sarcomeric alpha-actinin, however, p38alphadn was detected in the nucleus while p38betadn was exclusively detected in the cytosol. In summary, attenuated p38 activity led to increased myocardial contractility; specific isoforms of p38 and their sub-cellular localization may have different roles in modulating ischemic injury.

Transforming Concepts Into Clinical Trials and Creating a Multisite Network: The Leadership and Operations Center of the Antibacterial Resistance Leadership Group

The Leadership and Operations Center (LOC) is responsible for facilitating, coordinating, and implementing the Antibacterial Resistance Leadership Group (ARLG) scientific agenda by engaging thought leaders; soliciting research proposals; and developing the processes, tools, and infrastructure required to operationalize studies and create and sustain the ARLG network. These efforts are ongoing as new projects are developed and the network expands and grows to address the ever-changing priorities in antibacterial resistance. This article describes the innovations, accomplishments, and opportunities of the LOC since the inception of the ARLG in 2013.