Effects of ATP-magnesium chloride on the cardiopulmonary manifestations of group B streptococcal sepsis in the piglet

Adenosine and ATPγS protect against bacterial pneumonia-induced acute lung injury

Lipopolysaccharide (LPS), a component of the outer membrane of gram-negative bacteria, disrupts the alveolar-capillary barrier, triggering pulmonary vascular leak thus inducing acute lung injury (ALI). Extracellular purines, adenosine and ATP, protected against ALI induced by purified LPS. In this study, we investigated whether these purines can impact vascular injury in more clinically-relevant E.coli (non-sterile LPS) murine ALI model. Mice were inoculated with live E. coli intratracheally (i.t.) with or without adenosine or a non-hydrolyzable ATP analog, adenosine 5'-(γ-thio)-triphosphate (ATPγS) added intravenously (i.v.). After 24 h of E. coli treatment, we found that injections of either adenosine or ATPγS 15 min prior or adenosine 3 h after E.coli insult significantly attenuated the E.coli-mediated increase in inflammatory responses. Furthermore, adenosine prevented weight loss, tachycardia, and compromised lung function in E. coli-exposed mice. Accordingly, treatment with adenosine or ATPγS increased oxygen saturation and reduced histopathological signs of lung injury in mice exposed to E. coli. Lastly, lung-targeting gene delivery of adenosine or ATPγS downstream effector, myosin phosphatase, significantly attenuated the E. coli-induced compromise of lung function. Collectively, our study has demonstrated that adenosine or ATPγS mitigates E. coli-induced ALI in mice and may be useful as an adjuvant therapy in future pre-clinical studies.

Current and future therapeutic options for persistent pulmonary hypertension in the newborn

Persistent pulmonary hypertension of the newborn (PPHN) is a potentially life-threatening condition that is characterized by supra-systemic pulmonary vascular resistance causing right-to-left shunting through the ductus arteriosus and/or foramen ovale, leading to a vicious cycle of hypoxemia, acidosis and further pulmonary vasoconstriction. Advances in neonatology including surfactant instillation, high-frequency ventilation, extracorporeal membrane oxygenation and, most importantly, inhaled nitric oxide (INO), have revolutionized the management of PPHN. However, given that INO does not improve oxygenation in a significant proportion (30-40%) of cases, there is an urgent need to consider other therapeutic options for PPHN. The issue is more important for developing nations with a higher PPHN-related health burden and limited resources. This article discusses the evidence about INO in term and preterm neonates in brief, and focuses mainly on the potential alternative drugs in the management of PPHN.

A systematic review of experimental treatments for mitochondrial dysfunction in sepsis and multiple organ dysfunction syndrome

Sepsis and multiple organ dysfunction syndrome (MODS) are major causes of morbidity and mortality in the intensive care unit. Recently mitochondrial dysfunction has been proposed as a key early cellular event in critical illness. A growing body of experimental evidence suggests that mitochondrial therapies are effective in sepsis and MODS. The aim of this article is to undertake a systematic review of the current experimental evidence for the use of therapies for mitochondrial dysfunction during sepsis and MODS and to classify these mitochondrial therapies. A search of the MEDLINE and PubMed databases (1950 to July 2009) and a manual review of reference lists were conducted to find experimental studies containing data on the efficacy of mitochondrial therapies in sepsis and sepsis-related MODS. Fifty-one studies were included in this review. Five categories of mitochondrial therapies were defined-substrate provision, cofactor provision, mitochondrial antioxidants, mitochondrial reactive oxygen species scavengers, and membrane stabilizers. Administration of mitochondrial therapies during sepsis was associated with improvements in mitochondrial electron transport system function, oxidative phosphorylation, and ATP production and a reduction in cellular markers of oxidative stress. Amelioration of proinflammatory cytokines, caspase activation, and prevention of the membrane permeability transition were reported. Restoration of mitochondrial bioenergetics was associated with improvements in hemodynamic parameters, organ function, and overall survival. A substantial body of evidence from experimental studies at both the cellular and the organ level suggests a beneficial role for the administration of mitochondrial therapies in sepsis and MODS. We expect that mitochondrial therapies will have an increasingly important role in the management of sepsis and MODS. Clinical trials are now required.

Ventilatory response to hypoxia during endotoxemia in young rats: role of nitric oxide

Administration of Escherichia coli endotoxin attenuates the ventilatory response to hypoxia (VRH) in newborn piglets, but the mechanisms responsible for this depression are not clearly understood. Nitric oxide (NO) production increases during sepsis and elevated NO levels can inhibit carotid body function. The role of endothelial NO on the VRH during endotoxemia was evaluated in 26 young rats. Minute ventilation (VE) and oxygen consumption (VO2) were measured in room air (RA) and during 30 min of hypoxia (10% O2) before and after E. coli endotoxin administration. During endotoxemia, animals received placebo (PL, n = 8); a nonselective nitric oxide synthase (NOS) inhibitor (NG-nitro-L-arginine methyl ester, L-NAME, n = 9), or a neuronal NOS (nNOS) inhibitor (7-nitroindazole, 7-NI, n = 9). During endotoxemia, a larger increase in VE was observed only during the first min of hypoxia in the L-NAME group when compared with PL or 7-NI (p < 0.001). VRH was similar in the PL and 7-NI groups. A larger decrease in VO2 at 30 min of hypoxia was observed in L-NAME and 7-NI groups when compared with PL (p < 0.03). These data demonstrate that the attenuation of the early VRH during endotoxemia is in part mediated by an inhibitory effect of endothelial NO on the respiratory control mechanisms.

Effects of infusion of adenosine triphosphate-magnesium chloride on cardiopulmonary and clinicopathologic variables, cytokine activity, and endothelin concentration in horses administered a low dose of endotoxin

OBJECTIVE

To evaluate systemic effects of i.v. infusion of ATP-MgCl2 subsequent to infusion of a low dose of endotoxin in horses.

ANIMALS

12 adult horses.

PROCEDURE

Horses were administered endotoxin (lipopolysaccharide [LPS]) or saline (0.9% NaCl) solution i.v., during a 30-minute period. Immediately thereafter, horses in each group were infused i.v. with ATP-MgCl2 or saline solution. Two weeks later, horses were administered the opposite solution (LPS or saline solution), but it was followed by the same infusion as 2 weeks previously (ie, ATP-MgCl2 or saline solution). Cardiopulmonary and clinicopathologic variables, cytokine activity, and endothelin (ET) concentrations were recorded.

RESULTS

IV infusion of ATP-MgCl2 after administration of a low dose of endotoxin failed to attenuate the cardiopulmonary, clinicopathologic, and cytokine alterations that develop secondary to endotoxin exposure. The combination of LPS and ATP-MgCl2 potentiated pulmonary hypertension, leukopenia, and neutropenia when compared with the combination of LPS and saline solution. The combination of LPS and ATP-MgCl2 resulted in thrombocytopenia. Endothelin concentration was increased in jugular venous and pulmonary arterial plasma in horses receiving LPS and ATP-MgCl2. Similar increases were not observed with LPS and saline solution.

CONCLUSIONS AND CLINICAL RELEVANCE

Administration of ATP-MgCl2 did not protect horses from systemic effects of experimentally induced endotoxemia. Furthermore, the use of ATP-MgCl2 during endotoxemia may worsen the cardiopulmonary and clinicopathologic status of affected horses. Because ATP and other adenine nucleotides are released from cells during shock, their potential role in the development of hemodynamic derangements, leukocyte adherence, and coagulopathies during endotoxemic episodes warrants further investigation.

The effect of Escherichia coli endotoxin infusion on the ventilatory response to hypoxia in unanesthetized newborn piglets

To determine the effects of endotoxemia on the neonatal ventilatory response to hypoxia, 17 chronically instrumented and unanesthetized newborn piglets (</=7 d) were studied before and 30 min after the administration of Escherichia coli O55:B5 endotoxin (n = 8) or normal saline (n = 9). Minute ventilation, oxygen consumption, heart rate, arterial blood pressure, and blood gases were measured during normoxia and 10 min of hypoxia (fraction of inspired oxygen, 0.10). Basal ventilation was not modified by E. coli endotoxin infusion (mean +/- SE, 516 +/- 49 versus 539 +/- 56 mL/min/kg), but the ventilatory response to hypoxia was markedly attenuated at 1 min (955 +/- 57 versus 718 +/- 97 mL/min/kg, p < 0.002, saline versus endotoxin) and at 10 min (788 +/- 51 versus 624 +/- 66 mL/min/kg, p < 0.002). A larger decrease in oxygen consumption was observed during hypoxia and endotoxemia (6.3 +/- 2.8 versus 18.3 +/- 2.7%, p < 0.03, pre- versus post-endotoxin). A significant correlation was demonstrated between the changes in minute ventilation and oxygen consumption with hypoxia during endotoxemia (r = 0.9, p < 0.002). The ventilatory response to hypoxia was not modified by the saline infusion. These data show a significant attenuation in the ventilatory response to hypoxia during E. coli endotoxemia. This decrease in ventilation was associated with a significant decrease in the metabolic rate during hypoxia and endotoxemia.

Adenosine triphosphate-magnesium dichloride during hyperdynamic porcine endotoxemia: effects on hepatosplanchnic oxygen exchange and metabolism

OBJECTIVE

To assess the effects of adenosine triphosphate-magnesium dichloride (ATP-MgCl2) on systemic and hepatosplanchnic hemodynamics, oxygen exchange, and energy metabolism over 24 hrs of hyperdynamic normotensive porcine endotoxemia.

DESIGN

Prospective, randomized, controlled experimental study with repeated measures.

SETTING

Investigational animal laboratory.

SUBJECTS

Seventeen pigs were divided into two groups: eight animals receiving endotoxin served as a control group and nine animals received endotoxin (lipopolysaccharide) and ATP-MgCl2.

INTERVENTIONS

Pigs were anesthetized, mechanically ventilated, and instrumented. Endotoxemia was achieved by continuous intravenous infusion of Escherichia coli lipopolysaccharide. Animals were resuscitated by hetastarch targeted to maintain mean arterial pressure of >75 mm Hg. Twelve hours after the start of the endotoxin infusion, ATP-MgCl2, or its vehicle, were administered for 12 hrs.

MEASUREMENTS AND MAIN RESULTS

Mean arterial pressure was maintained in the control group because of a sustained increase in cardiac output achieved by fluid resuscitation, whereas ATP-MgCl2 significantly decreased mean arterial pressure because of further systemic vasodilatation. ATP-MgCl2 markedly increased portal venous flow. In contrast to the controls, hepatic arterial flow remained unchanged until the end of the experiment, despite the further increase in cardiac output. The ileal mucosal-arterial PCO2 gap (Delta PCO2) progressively increased (p <.05) in control animals, whereas it was restored to prelipopolysaccharide levels during ATP-MgCl2 infusion. Changes in Delta PCO2 correlated with those of portal vein blood flow in these animals (r = -.68, p <.05). Moreover, ATP-MgCl2 blunted the lipopolysaccharide-induced decrease in hepatic lactate balance but did not affect portal venous pH, hepatosplanchnic oxygen exchange, splanchnic lactate/pyruvate ratios, isoprostane, NO2- + NO3-, cytokine concentrations, or tissue nucleotide content.

CONCLUSION

During long-term hyperdynamic porcine endotoxemia, ATP-MgCl2 normalized the otherwise progressive rise of the ileal mucosal-arterial Delta PCO2. Furthermore, it allowed blunting of the continuous decrease in hepatic lactate clearance, thus preserving the metabolic coupling between lactate release from the intestine and lactate utilization by the liver.

Purinergic signalling: pathophysiological roles

In this review, after a summary of the history and current status of the receptors involved in purinergic signalling, we focus on the distribution and physiological roles of purines and pyrimidines in both short-term events such as neurotransmission, exocrine and endocrine secretion and regulation of immune cell function, and long-term events such as cell growth, differentiation and proliferation in development and regeneration. Finally, the protective roles of nucleosides and nucleotides in events such as cancer, ischemia, wound healing, drug toxicity, inflammation and pain are explored and some suggestions made for future developments in this rapidly expanding field, with particular emphasis on the involvement of selective agonists and antagonists for purinergic receptor subtypes in therapeutic strategies.