Nitric oxide and septic vascular dysfunction

Multimodal strategy to counteract vasodilation in septic shock

Early initiation of a multimodal treatment strategy in the management of vasopressors during septic shock has been advocated to reduce delays in restoring adequate organ perfusion and to mitigate side effects associated with the administration of high-dose catecholamines. We provide a review that summarises the pathophysiology of vasodilation, the physiologic response to the vascular response, and the different drugs used in this situation, focusing on the need to combine early different vasopressors. Fluid loading being insufficient for counteracting vasoplegia, norepinephrine is usually the first-line vasopressor used to restore hemodynamics. Norepinephrine sparing is discussed in further detail through the concomitant use of adrenergic, vasopressinergic, and renin-angiotensin systems and the optimisation of endothelial reactivity with methylene blue. A blueprint for the construction of new studies is outlined to address the question of vasopressor selection and timing in septic shock.

The Biologically Relevant Coordination Chemistry of Iron and Nitric Oxide: Electronic Structure and Reactivity

Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological and pathological events in biology. Metal coordination chemistry, especially with iron, is at the heart of many biological transformations involving NO. A series of heme proteins, nitric oxide synthases (NOS), soluble guanylate cyclase (sGC), and nitrophorins, are responsible for the biosynthesis, sensing, and transport of NO. Alternatively, NO can be generated from nitrite by heme- and copper-containing nitrite reductases (NIRs). The NO-bearing small molecules such as nitrosothiols and dinitrosyl iron complexes (DNICs) can serve as an alternative vehicle for NO storage and transport. Once NO is formed, the rich reaction chemistry of NO leads to a wide variety of biological activities including reduction of NO by heme or non-heme iron-containing NO reductases and protein post-translational modifications by DNICs. Much of our understanding of the reactivity of metal sites in biology with NO and the mechanisms of these transformations has come from the elucidation of the geometric and electronic structures and chemical reactivity of synthetic model systems, in synergy with biochemical and biophysical studies on the relevant proteins themselves. This review focuses on recent advancements from studies on proteins and model complexes that not only have improved our understanding of the biological roles of NO but also have provided foundations for biomedical research and for bio-inspired catalyst design in energy science.

Clinical Outcomes of Peritoneal Dialysis in End-Stage Renal Disease Patients with Liver Cirrhosis: A Propensity Score Matching Study

Background

Clinical results of long-term peritoneal dialysis (PD) therapy in patients with liver cirrhosis (LC) and end-stage renal disease (ESRD) are controversial. This study evaluated the clinical outcomes of LC patients undergoing PD.

Methods

Clinical records were retrospectively collected from a single center between January 2007 and December 2014. An analysis of PD patients with LC and without liver disease was performed using propensity score matching. We further restricted matching by age, gender, and the presence of diabetes mellitus. Two cohorts of 33 patients each were selected. Early technical complications were defined as the presence of catheter-related complications, including malposition, leakage, omental wrapping, obstruction, and requiring a transfer to hemodialysis (HD) within 6 months of initiating PD.

Results

Mean PD duration was lower in LC patients (57.2 ± 46.1 months) than in controls (85.8 ± 64.2 months). Blood urea nitrogen, creatinine, and albumin levels were significantly lower in LC patients than in the control group. Cystatin C and cystatin C-based glomerular filtration rates were not significantly different in the LC group compared with those in the controls. We found that the risks for early technical complications, peritonitis, and long-term PD and patient survival were not higher in patients with LC than in those without LC. Ascites were easily controlled, and hepatic encephalopathy did not affect PD maintenance in LC patients.

Conclusions

The clinical outcomes, including technical complications, peritonitis, and patients’ survival, suggest that PD can be used as a renal replacement therapy in ESRD patients with LC.

Role of active nitrogen molecules in progression of septic shock

INTRODUCTION

Active nitrogen molecules are formed as a result of cell metabolism. They are essential for cell metabolism, but when produced in excess, they contribute to the pathogenesis of several disease processes. These nitrogen molecules play an important role in vascular instability of septic shock. This study was planned to detect the role of active nitrogen molecules in the progression of septic shock.

MATERIALS AND METHODS

Blood samples were collected from 118 critically ill patients admitted in ICU and from 95 healthy relatives accompanying the patients. Patients were categorized into three groups: systemic inflammatory response syndrome (n = 54), sepsis (n = 35) and septic shock (n = 29). Plasma total nitrite (nitrites and nitrates), cytokines like tumour necrosis factor-α (TNF-α) and plasma lactate were measured to assess inflammatory activity and severity of septic shock.

RESULTS

High plasma levels of nitrite and nitrate (No₂-/No₃-) were observed in critically ill patients (mean level 78.92 μmol/l in sepsis and 97.20 μmol/l in septic shock). Mean plasma TNF-α level in sepsis was 213.50 pg/ml and septic shock was 227.38 pg/ml.

CONCLUSION

Plasma No₂-/No₃- and TNF-α levels were high in patients with sepsis and septic shock, which increased with severity of sepsis.

Vasogenic shock physiology

Shock means inadequate tissue perfusion by oxygen-carrying blood. In vasogenic shock, this circulatory failure results from vasodilation and/or vasoplegia. There is vascular hyporeactivity with reduced vascular smooth muscle contraction in response to α1 adrenergic agonists. Considering vasogenic shock, one can understand its utmost importance, not only because of its association with sepsis but also because it can be the common final pathway for long-lasting, severe shock of any cause, even postresuscitation states. The effective management of any patient in shock requires the understanding of its underlying physiology and pathophysiology. Recent studies have provided new insights into vascular physiology by revealing the interaction of rather complicated and multifactorial mechanisms, which have not been fully elucidated yet. Some of these mechanisms, such as the induction of nitric oxide synthases, the activation of adenosine triphosphate-sensitive potassium channels, and vasopressin deficiency, have gained general acceptance and are considered to play an important role in the pathogenesis of vasodilatory shock. The purpose of this review is to provide an update on the pathogenesis of vasogenic shock.

LPS differentially affects vasoconstrictor responses: a potential role for RGS16?

The profound hypotension in septic shock patients is difficult to treat as it is accompanied by depressed constrictor responses to alpha1-adrenoceptor agonists. Bacterial lipopolysaccharide (LPS) is the main trigger for most of the cardiovascular alterations occurring in septic shock. In this study we investigated the effects of LPS exposure on vascular contractility in general and the role of Regulator of G protein Signalling (RGS) proteins in the LPS-induced vascular alterations. Exposure of rat aortic rings to various LPS concentrations (3, 10, 30 microg/ml) for 22 hours differentially affected agonist-induced contractile responses at four distinct G-protein coupled receptors (alpha1-adrenoceptors, angiotensin II, serotonin and endothelin-1 receptors). While the endothelin-1-induced contraction was unaffected by LPS pre-treatment, phenylephrine- and angiotensin II-induced contraction were significantly reduced whereas serotonin-induced contraction was significantly enhanced. Concomitantly, LPS treatment increased the RGS16 mRNA expression both in aortic rings and cultured vascular smooth muscle cells (VSMCs) but not that of RGS2, RGS3, RGS4 or RGS5. The significant increase in RGS16 mRNA expression in VSMCs by LPS was time- and concentration-dependent but independent of increased inducible NO synthase (iNOS) activity. The changes in RGS16 mRNA might contribute to the differential regulation of the contractile responses to vasoconstrictors upon LPS exposure.

Role of oxidative stress in experimental sepsis and multisystem organ dysfunction

Massive increase in radical species can lead to oxidative stress, promoting cell injury and death. This review focuses on experimental evidence of oxidative stress in critical illnesses, sepsis and multisystem organ dysfunction. Oxidative stress could negatively affect organ injury and thus overall survival of experimental models. Based on this experimental evidence, we could improve the rationale of supplementation of antioxidants alone or in combination with standard therapies aimed to reduce oxidative stress as novel adjunct treatment in critical care.

Induced nitric oxide impairs relaxation but not contraction in endotoxin-exposed rat pulmonary arteries

BACKGROUND

Many patients with severe acute lung injury do not respond to nitric oxide (NO) inhalational therapy with alleviation of pulmonary arterial hypertension and hypoxemia, so this treatment remains controversial. MATERIALS AND METHODS.: We investigated in endotoxin-exposed Wistar rat pulmonary arteries whether endogenous NO alters contractile and relaxing responses, by electrochemical NO and isometric force measurements.

RESULTS

Receptor-independent contraction was similar in control and endotoxin-exposed arteries, while thromboxane analogue (TxA)-dependent contraction was less in the latter. Neither non-selective NO synthase (NOS) inhibition by N(G)-nitro-l-arginine (l-NA) or selective inducible-NOS2 inhibition by aminoguanidine (AG) improved TxA-induced contraction in endotoxin-exposed arteries. Acetylcholine-induced relaxation was impaired in endotoxin-exposed pulmonary arteries, despite a comparable acetylcholine-induced NO release in control arteries. Additionally, NO solution-induced relaxation of endotoxin-exposed arteries was impaired, but could be improved by l-NA or AG. Application of a phosphodiesterase-insensitive cyclic guanosine monophosphate analogue induced similar relaxation in both control and endotoxin-exposed arteries.

CONCLUSIONS

Endotoxin-associated NOS2-derived NO is thus associated with impaired NO-mediated relaxation, but does not underlie reduced receptor-mediated pulmonary contractile responses. An increased phosphodiesterase activity may underlie the former, so this route can be explored to replace or improve the effect of inhalational NO therapy in severe sepsis-induced acute lung injury in patients.

Endotoxin Releases a Substance from the Aorta that Dilates an Isolated Arteriole by Up-Regulating INOS

BACKGROUND

Loss of vascular tone in resistance arterioles has been implicated as the cause of hypotension in septic shock. It is believed that the overproduction of nitric oxide (NO) by the inducible isoform of nitric oxide synthase (iNOS) results in the vasodilatation seen in septic shock. However, we have shown that endotoxin has no effect on vascular tone of an isolated resistance vessel unless the endotoxin flows over a segment of aorta or vena cava upstream in the superfusion line. The aim of this study was to determine if the subsequent vasodilation was due to the release of a direct vasodilator or production of NO in the arteriole and if its source was iNOS by using its selective inhibitor, aminoguanidine.

MATERIALS AND METHODS

First-order rat cremaster arterioles (n = 36) were isolated and cannulated onto micropipettes, superfused with physiological buffer at 34 degrees C, pressurized to 70 mm Hg, and allowed to gain spontaneous tone over 90 min. A segment of abdominal aorta was then placed in series with the arteriole so that the superfusate passed over the aorta and then into the tissue bath containing the isolated arteriole. The vessels were allowed to equilibrate over 60 min. During this interval, the arteriole was exposed to l-NAME (100 mum), aminoguanidine (100 mum), or buffer. The aorta and arteriole were then superfused with endotoxin (Salmonella enteritidis 2.5 mug/ml). Internal diameters of cannulated arterioles were measured and recorded with videomicroscopy and videocalipers at a resolution of +/-1 mum every 15 min for 1 h. Six groups were created with n = 6 for each group: Group 1, endotoxin; Group 2, control; Group 3, l-NAME and endotoxin; Group 4, l-NAME; Group 5, aminoguanidine and endotoxin; and Group 6, aminoguanidine.

RESULTS

After the 60-min equilibration period, there was no significant difference in resting tone among the six groups. At t = 120, the percentage of tone in the control group was 42.7 +/- 0.4% (mean +/- SEM) and this was not changed by treatment with aminoguanidine (42.2 +/- 0.7%). However, exposure to l-NAME alone resulted in vasoconstriction with a gain in tone to 49.5 +/- 1.6% (P > 0.05). Endotoxin alone caused arteriolar tone to fall to 33.5 +/- 1.2% (P < 0.05). Arterioles treated with aminoguanidine did not lose tone (42.6 +/- 1.7%) when exposed to endotoxin and arterioles treated with l-NAME retained their elevated tone (46.0 +/- 2.2%) after treatment with endotoxin.

CONCLUSIONS

This study demonstrates that the aorta exposed to endotoxin releases a substance that vasodilates resistance arterioles through the up-regulation of iNOS. Aminoguanidine prevented the fall in tone following exposure to endotoxin, while use of the nonselective NOS inhibitor, l-NAME, not only blocked the fall due to endotoxin but increased basal tone by blocking the constitutively active eNOS.

Shengmai San, a Chinese Herbal Medicine Protects Against Rat Heat Stroke by Reducing Inflammatory Cytokines and Nitric Oxide Formation

The aim of the present study was to ascertain whether the possible occurrence of overproduction of inducible nitric oxide synthase (iNOS)-dependent nitric oxide (NO) in the brain and inflammatory cytokines in the peripheral blood exhibited during heat stroke can be reduced by prior administration of Shengmai San, a Chinese herbal medicine. Aminoguanidine, an iNOS inhibitor, was evaluated at the same time as a reference (positive control). Urethane-anesthetized rats were exposed to heat stress (ambient temperature of 43 degrees C) to induce heat stroke. Control rats were exposed to 24 degrees C. Mean arterial pressure and cerebral blood flow after the onset of heat stroke were all significantly lower than in control rats. However, cerebral iNOS immunoreactivity and NO levels were all greater after the onset of heat stroke. The serum levels of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha were all increased after the onset of heat stroke. Shengmai San (1.2 g/ml per rat) or aminoguanidine (30 micromol/ml per rat) was administered orally, daily, and consecutively for 7 days before the initiation of heat stress; and this significantly attenuated the heat stress-induced arterial hypotension, cerebral ischemia, and increased levels of brain iNOS-dependent NO production and serum cytokines formation. Shengmai San shared with the aminoguanidine almost the same efficacy in reducing iNOS-dependent NO and cytokines overproduction during heat stroke. These results suggest that Shengmai San or aminoguanidine protects against heat stroke-induced arterial hypotension and cerebral ischemia by inhibition of iNOS-dependent NO overproduction in the brain and excessive accumulation of several inflammatory cytokines in the peripheral blood stream.

Smooth muscle F-actin disassembly and RhoA/Rho-kinase signaling during endotoxin-induced alterations in pulmonary arterial compliance

Endotoxemia is associated with changed pulmonary vascular function with respect to vasoreactivity, endothelial permeability, and activation of inducible nitric oxide synthase II (NOSII). However, whether altered passive arterial wall mechanics contribute to this endotoxin-induced pulmonary vascular dysfunction is still unknown. Therefore, we investigated whether endotoxin affects the passive arterial mechanics and compliance of isolated rat pulmonary arteries. Pulmonary arteries of pentobarbital-anesthetized Wistar rats ( n = 55) were isolated and exposed to Escherichia coli endotoxin (50 μg/ml) for 20 h. Endotoxin increased pulmonary artery diameter and compliance (transmural pressure = 13 mmHg) in an endothelium-, Ca2+-, or NOSII-induced NO release-independent manner. Interestingly, the endotoxin-induced alterations in the passive arterial mechanics were accompanied by disassembly of the smooth muscle cell (SMC) F-actin cytoskeleton. Disassembly of F-actin by incubation of control arteries with the cytoskeleton-disrupting agent cytochalasin B or the Rho-kinase inhibitor Y-27632 induced a similar increase in passive arterial diameter and compliance. In contrast, RhoA activation by lysophosphatidic acid prevented the endotoxin-induced alterations in the pulmonary SMC F-actin cytoskeleton and passive mechanics. In conclusion, these findings indicate that disassembly of the SMC F-actin cytoskeleton and RhoA/Rho-kinase signaling act as mediators of endotoxin-induced changes in the pulmonary arterial mechanics. They imply the involvement of F-actin rearrangement and RhoA/Rho-kinase signaling in endotoxemia-induced vascular lung injury.

Prevention of perioperative acute renal failure: what works?

Perioperative acute renal failure (ARF) is associated with increased morbidity and mortality. Patients undergoing cardiac, vascular and major abdominal surgery and those with pre-operative renal insufficiency are at increased risk for developing post-operative ARF. The aetiologies of perioperative ARF are multi-factorial. However, pre-renal azotaemia and ischaemic acute tubular necrosis (ATN) are the predominant causes. Preventive strategies involve identifying patients at risk, optimizing intravascular volume as well as renal function with perioperative haemodynamic monitoring, and avoiding nephrotoxins. Various pharmacological agents have been used to optimize renal perfusion and tubular function. Unfortunately, none has been shown to be effective in randomized placebo-controlled trials. In this chapter, we discuss the prophylactic use of fluids, vasoactive drugs, diuretics and other agents, as well as modification of surgical techniques to reduce the incidence of perioperative ARF.

Peroxynitrite Decreases Dopamine???s Vasoconstrictive Activity

Peroxynitrite (ONOO(-1)) reacts with dopamine to form an oxidized derivative. To investigate the vasoconstrictive activity of this derivative, we performed functional examinations with dopamine treated with ONOO(-1) or 3-morpholinosydonimine-N-ethyl-carbamine (SIN-1; an ONOO(-1) producer) on isolated strips of rat thoracic aorta. To exclude the direct effect of ONOO(-1), the strips were pretreated with methylene blue, a guanylyl cyclase inhibitor. Dopamine induced concentration-dependent contraction, but dopamine pretreated with ONOO(-1) decreased the contraction in an ONOO(-1)-concentration-dependent manner. Both maximum contractions and 50% effective concentration values for dopamine-induced vasocontraction were significantly decreased by pretreatment with ONOO(-1). Dopamine incubated with SIN-1 also decreased the contraction, the decrease being dependent on the incubation time. ONOO(-1) formation is a favored reaction and occurs easily when cellular production of both nitric oxide and superoxide increases, as in septic shock. These results may, at least in part, account for dopamine's limitation as a vasoconstrictor in septic shock.

IMPLICATIONS

Peroxynitrite (ONOO(-1)) reacts with dopamine to form an oxidized derivative. We investigated the vasoconstrictive activity of this derivative with functional examinations using rat thoracic aorta and found the activity decreased. As ONOO(-1) formation increases in septic shock, our results may account for dopamine's limitation as a vasoconstrictor in septic shock.

Approach to intradialytic hypotension in intensive care unit patients with acute renal failure

The increasing prevalence of acute renal failure (ARF) patients with hemodynamic intolerance of intermittent hemodialysis (HD), generally because of septic vasoparesis or severe cardiac dysfunction, has led to the development of several strategies to improve the delivery of renal replacement therapy (RRT) in ARF patients. Intradialytic hypotension (IDH) is caused by the interaction of dialysis-dependent and dialysis-independent factors. Dialysis-dependent factors include the prescriptions for fluid removal, solute removal, and dialysate components such as sodium, buffer, and calcium. Dialysis-independent factors include hemodynamic compromise caused by hypovolemic, cardiogenic, vasodilatory, and mixed mechanisms. We propose an approach to the prevention and management of IDH in critically ill ARF patients, which minimizes hypovolemic, cardiogenic, and vasodilatory insults by optimizing fluid removal, cardiac function, and vascular contractility.

Nuclear factor-kappa B and mitogen-activated protein kinases mediate nitric oxide-enhanced transcriptional expression of interferon-beta

Mitogen-activated protein (MAP) kinase and nuclear factor-kappaB (NF-kappaB) activation are critical for initiating the transcriptional expression of cytokines, cell adhesion molecules, and other factors in the macrophage immune response. Nitric oxide (NO), an endogenous free radical, is a product of macrophages that mediates inflammatory and cytotoxic processes in the immune system. Here we report the effects of NO on MAP kinase signaling and NF-kappaB activation in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages and correlate these effects to the induction target genes, including interferon-beta (IFN-beta) and IkappaB-alpha. LPS alone induced a rapid phosphorylation of the stress-activated MAP kinases: c-Jun N-terminal kinase (JNK) and p38. Simultaneous treatment with LPS and the NO donor, diethylamine NONOate (DEA/NO), enhanced and prolonged JNK and p38 phosphorylation. Similarly, DEA/NO prolonged the LPS-induced degradation of the NF-kappaB inhibitory subunit, IkappaB-alpha, despite an increase in IkappaB-alpha mRNA levels. Whereas DEA/NO alone was sufficient to induce JNK and p38 phosphorylation, it was not sufficient to cause IkappaB-alpha degradation. The enhancement of IkappaB-alpha degradation by DEA/NO correlated with an increase in the nuclear levels of the p50 and p65 subunits and DNA-binding activity determined by electrophoretic mobility shift assay. DEA/NO and an additional NO donor, MAHMA/NO, are further demonstrated to enhance the transcriptional expression of the IFN-beta gene. The results suggest a role for NO in enhancing and propagating inflammatory conditions and the immune response.

Myeloperoxidase, a leukocyte-derived vascular NO oxidase

Myeloperoxidase (MPO) is an abundant mammalian phagocyte hemoprotein thought to primarily mediate host defense reactions. Although its microbicidal functions are well established in vitro, humans deficient in MPO are not at unusual risk of infection. MPO was observed herein to modulate the vascular signaling and vasodilatory functions of nitric oxide (NO) during acute inflammation. After leukocyte degranulation, MPO localized in and around vascular endothelial cells in a rodent model of acute endotoxemia and impaired endothelium-dependent relaxant responses, to which MPO-deficient mice were resistant. Altered vascular responsiveness was due to catalytic consumption of NO by substrate radicals generated by MPO. Thus MPO can directly modulate vascular inflammatory responses by regulating NO bioavailability.

Management of the septic patient in the operating room

Sepsis, severe sepsis, and septic shock represent the spectrum of physiological response to a variety of infecting pathogens. Multiple-organ dysfunction may result from widespread activation of inflammatory and antiinflammatory mechanisms. Intensive multiorgan support, effective antibiotic therapy, and eradication of the inciting source remain the cornerstones in the care of septic patients. Perioperative planning and management need to ensure the continuation of such care in addition to providing for the requirements of the given surgical procedure.

Nitric oxide does not contribute to the hypotension of heatstroke

The purpose of this study was to determine whether nitric oxide (NO) contributes to the hypotensive state induced by prolonged environmental heat (EH) stress. Ketamine-anesthetized rats were instrumented for the measurement of arterial blood pressure, electrocardiogram, and temperature at four sites. Rats were exposed to EH (ambient temperature, 40 +/- 1 degrees C) until mean arterial blood pressure (MAP) decreased to 75 mmHg, which was arbitrarily defined as the induction of heatstroke. In addition to cardiovascular and temperature measurements, the time required to reach this MAP end point and the subsequent survival time were measured. In three separate experimental series, the competitive NO synthesis inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) was administered (0, 10, or 100 mg/kg) either before, during (30 min after initiation of EH), or immediately after EH. L-NAME administered at any of these times transiently increased MAP. L-NAME infusion either before or during EH did not alter the EH time required to decrease MAP to 75 mmHg, but L-NAME pretreatment did decrease the colonic temperature at which this MAP end point was reached. L-NAME infusion before or after EH did not affect subsequent survival time, but L-NAME administered during EH significantly decreased survival time. The administration of L-NAME at any time point, therefore, did not prove beneficial in either preventing or reversing heatstroke. Taken together, these data suggest that NO does not mediate the hypotension associated with heatstroke.

Effects of isoflurane, enflurane, and halothane on skeletal muscle microcirculation in the endotoxemic rat

PURPOSE

The cardiovascular effects of volatile anesthetics during sepsis sets patients at high risk for hemodynamic deterioration. We compared the microcirculatory alterations in skeletal muscle under anesthesia with isoflurane, enflurane, and halothane in an endotoxemic rat preparation.

MATERIALS AND METHODS

Twenty-one Sprague-Dawley rats under continuous hemodynamic monitoring and intravital microscopy of the spinotrapezius muscle were studied during two level lipopolysaccharide (0.2 mg/kg and 2 mg/kg) induced sepsis. The effects of equianesthetic concentrations (1.5 minimum alveolar concentration [MAC]) of either isoflurane [n:7], enflurane [n:7], or halothane [n:7] on microcirculatory vasoregulation were measured and histopathologic changes were evaluated.

RESULTS

During low-dose endotoxemia, arteriolar vasodilation under isoflurane was nearly abolished (P < .05). At high-dose endotoxemia, this lack of vasodilatory effect was similar (P < .05). Animals receiving 1.5 MAC of enflurane during low-dose endotoxin presented a significant decrease in arteriolar diameter by -11.3 (+/-2.9%), this response was less during high-dose endotoxemia (-7.0, +/-2.9%). Halothane caused pronounced vasoconstriction by -20 (+/-3.7%) during low-dose endotoxemia and moderate but significant constriction during high-dose endotoxemia (-7.9, +/-2.6%).

CONCLUSIONS

Isoflurane, enflurane, and halothane exert significantly different effects on vasoregulation of skeletal muscle arterioles in the endotoxemic rat.