Early natural history of regional left ventricular dysfunction after experimental myocardial infarction

Identification of a Toxin-Antitoxin System That Contributes to Persister Formation by Reducing NAD in Pseudomonas aeruginosa

Bacterial persisters are slow-growing or dormant cells that are highly tolerant to bactericidal antibiotics and contribute to recalcitrant and chronic infections. Toxin/antitoxin (TA) systems play important roles in controlling persister formation. Here, we examined the roles of seven predicted type II TA systems in the persister formation of a Pseudomonas aeruginosa wild-type strain PA14. Overexpression of a toxin gene PA14_51010 or deletion of the cognate antitoxin gene PA14_51020 increased the bacterial tolerance to antibiotics. Co-overexpression of PA14_51010 and PA14_51020 or simultaneous deletion of the two genes resulted in a wild-type level survival rate following antibiotic treatment. The two genes were located in the same operon that was repressed by PA14_51020. We further demonstrated the interaction between PA14_51010 and PA14_51020. Sequence analysis revealed that PA14_51010 contained a conserved RES domain. Overexpression of PA14_51010 reduced the intracellular level of nicotinamide adenine dinucleotide (NAD⁺). Mutation of the RES domain abolished the abilities of PA14_51010 in reducing NAD⁺ level and promoting persister formation. In addition, overproduction of NAD⁺ by mutation in an nrtR gene counteracted the effect of PA14_51010 overexpression in promoting persister formation. In combination, our results reveal a novel TA system that contributes to persister formation through reducing the intracellular NAD⁺ level in P. aeruginosa.

Left ventricular dilatation and failure post-myocardial infarction: pathophysiology and possible pharmacologic interventions

An important antecedent to the development of late congestive heart failure is left ventricular dilatation and remodeling following myocardial infarction, which occurs in 30-40% of acute anterior transmural infarcts. Dilatation and remodeling commence within the first 24 hours following myocardial infarction and may be steadily progressive over months to years. Both the infarcted and uninfarcted regions of the myocardium are equally involved in the process. The remodeling process comprises left ventricular wall thinning (mainly due to cell slippage), chamber dilatation, and compensatory hypertrophy of the uninfarcted segment of the myocardium. The hypertrophy may initially be physiologic but may ultimately become a pathologic process, and thereby contribute to pump dysfunction. The possible reasons why the ventricular hypertrophy may ultimately be dysfunctional include alterations in local architecture and their sequelae alone or in concert with local changes in the beta-adrenergic, alpha-adrenergic, or renin angiotensin systems. At the present time, there are encouraging data to suggest that nitroglycerin, or the angiotensin converting enzyme inhibitor captopril, may ameliorate this process.

The prevention of congestive heart failure: left ventricular dilation and its management

Left ventricular dilation and remodelling occur in 35-40% of anterior transmural myocardial infarcts and these events are important antecedents to the development of late congestive heart failure. This process commences within the first 24 hours following myocardial infarction and may be steadily progressive over months to years. Both the infarcted and the uninfarcted regions of myocardium are equally involved in the process. Thinning of the left ventricular wall occurs mainly as a result of cell slippage. In addition, compensatory hypertrophy occurs in the uninfarcted segment of the myocardium. While this hypertrophy may initially be physiological, it ultimately appears to become a pathological process and thereby contributes to pump dysfunction. At the present time there are encouraging data to suggest that nitroglycerin, administered in the setting of the acute infarction, or the angiotensin converting enzyme inhibitor captopril, may ameliorate this process. Whether a patent infarct related artery further limits dilation is uncertain and is currently under investigation.