Administration of tetrahydrobiopterin improves the microcirculation and outcome in an ovine model of septic shock

Microcirculation and Mitochondria: The Critical Unit

Critical illness is often accompanied by a hemodynamic imbalance between macrocirculation and microcirculation, as well as mitochondrial dysfunction. Microcirculatory disorders lead to abnormalities in the supply of oxygen to tissue cells, while mitochondrial dysfunction leads to abnormal energy metabolism and impaired tissue oxygen utilization, making these conditions important pathogenic factors of critical illness. At the same time, there is a close relationship between the microcirculation and mitochondria. We introduce here the concept of a "critical unit", with two core components: microcirculation, which mainly comprises the microvascular network and endothelial cells, especially the endothelial glycocalyx; and mitochondria, which are mainly involved in energy metabolism but perform other non-negligible functions. This review also introduces several techniques and devices that can be utilized for the real-time synchronous monitoring of the microcirculation and mitochondria, and thus critical unit monitoring. Finally, we put forward the concepts and strategies of critical unit-guided treatment.

Early ascorbic acid administration prevents vascular endothelial cell damage in septic mice

Oxidation of BH₄, a cofactor of nitric oxide synthase (NOS), produces reactive oxygen species (ROS) through uncoupling of NOS and affects vascular endothelial dysfunction. Ascorbic acid (AsA) inhibits the oxidation of BH₄ and reduces ROS. However, the kinetic changes of BH₄ in sepsis and its effect on the kinetic changes in AsA administration therapy, as well as the appropriate timing of AsA administration for AsA therapy to be effective, are unclear. Mice with sepsis, induced by cecal ligation and puncture (CLP), were examined for the effect of AsA administration (200 mg/kg) on vascular endothelial cell dysfunction at two administration timings: early group (AsA administered immediately after CLP) and late group (AsA administered 12 h after CLP). Survival rates were compared between the early and late administration groups, and vascular endothelial cell damage, indicated by the dihydrobiopterin/tetrahydrobiopterin ratio, serum syndecan-1, and endothelial nitric oxide synthase, as well as liver damage, were examined. The early group showed significantly improved survival compared to the non-treatment group (p < 0.05), while the late group showed no improved survival compared to the non-treatment group. Compared to the non-treated group, the early AsA group showed less oxidation of BH₄ in sepsis. Syndecan1, a marker of vascular endothelial cell damage, was less elevated and organ damage was reduced in the early AsA-treated group. In septic mice, early AsA administration immediately after CLP may protect vascular endothelial cells by inhibiting BH₄ oxidation, thereby reducing organ dysfunction and improving survival.

Endothelial dysfunction: a therapeutic target in bacterial sepsis?

INTRODUCTION

Endothelial cells maintain vascular integrity, tone, and patency and have important roles in hemostasis and inflammatory responses. Although some degree of endothelial dysfunction with increased vascular permeability may be necessary to control local infection, excessive dysfunction plays a central role in the pathogenesis of sepsis-related organ dysfunction and failure as it results in dysregulated inflammation, vascular leakage, and abnormal coagulation. The vascular endothelium has thus been proposed as a potential target for therapeutic intervention in patients with sepsis.

AREAS COVERED

Different mechanisms underlying sepsis-related dysfunction of the vascular endothelium are discussed, including glycocalyx shedding, nitrosative stress, and coagulation factors. Potential therapeutic implications of each mechanism are mentioned.

EXPERT OPINION

Multiple targets to protect or restore endothelial function have been suggested, but endothelium-driven treatments remain a future potential at present. As some endothelial dysfunction and permeability may be necessary to remove infection and repair damaged tissue, targeting the endothelium may be a particular challenge. Ideally, therapies should be guided by biomarkers related to that specific pathway to ensure they are given only to patients most likely to respond. This enrichment based on biological plausibility and theragnostics will increase the likelihood of a beneficial response in individual patients and enable more personalized treatment.

Targeting Oxidative Stress in Septic Acute Kidney Injury: From Theory to Practice

Sepsis is the leading cause of acute kidney injury (AKI) and leads to increased morbidity and mortality in intensive care units. Current treatments for septic AKI are largely supportive and are not targeted towards its pathophysiology. Sepsis is commonly characterized by systemic inflammation and increased production of reactive oxygen species (ROS), particularly superoxide. Concomitantly released nitric oxide (NO) then reacts with superoxide, leading to the formation of reactive nitrogen species (RNS), predominantly peroxynitrite. Sepsis-induced ROS and RNS can reduce the bioavailability of NO, mediating renal microcirculatory abnormalities, localized tissue hypoxia and mitochondrial dysfunction, thereby initiating a propagating cycle of cellular injury culminating in AKI. In this review, we discuss the various sources of ROS during sepsis and their pathophysiological interactions with the immune system, microcirculation and mitochondria that can lead to the development of AKI. We also discuss the therapeutic utility of N-acetylcysteine and potential reasons for its efficacy in animal models of sepsis, and its inefficacy in ameliorating oxidative stress-induced organ dysfunction in human sepsis. Finally, we review the pre-clinical studies examining the antioxidant and pleiotropic actions of vitamin C that may be of benefit for mitigating septic AKI, including future implications for clinical sepsis.

Evolution of altered tubular metabolism and mitochondrial function in sepsis-associated acute kidney injury

Sepsis-associated acute kidney injury (s-AKI) has a staggering impact in patients and lacks any treatment. Incomplete understanding of the pathogenesis of s-AKI is a major barrier to the development of effective therapies. We address the gaps in knowledge regarding renal oxygenation, tubular metabolism, and mitochondrial function in the pathogenesis of s-AKI using the cecal ligation and puncture (CLP) model in mice. At 24 h after CLP, renal oxygen delivery was reduced; however, fractional oxygen extraction was unchanged, suggesting inefficient renal oxygen utilization despite decreased glomerular filtration rate and filtered load. To investigate the underlying mechanisms, we examined temporal changes in mitochondrial function and metabolism at 4 and 24 h after CLP. At 4 h after CLP, markers of mitochondrial content and biogenesis were increased in CLP kidneys, but mitochondrial oxygen consumption rates were suppressed in proximal tubules. Interestingly, at 24 h, proximal tubular mitochondria displayed high respiratory capacity, but with decreased mitochondrial content, biogenesis, fusion, and ATP levels in CLP kidneys, suggesting decreased ATP synthesis efficiency. We further investigated metabolic reprogramming after CLP and observed reduced expression of fatty acid oxidation enzymes but increased expression of glycolytic enzymes at 24 h. However, assessment of functional glycolysis revealed lower glycolytic capacity, glycolytic reserve, and compensatory glycolysis in CLP proximal tubules, which may explain their susceptibility to injury. In conclusion, we demonstrated significant alterations in renal oxygenation, tubular mitochondrial function, and metabolic reprogramming in s-AKI, which may play an important role in the progression of injury and recovery from AKI in sepsis.

Molecular mechanisms by which iNOS uncoupling can induce cardiovascular dysfunction during sepsis: Role of posttranslational modifications (PTMs)

Human sepsis is the result of a multifaceted pathological process causing marked dysregulation of cardiovascular responses. A more sophisticated understanding of the pathogenesis of sepsis is certainly prerequisite. Evidence from studies provide further insight into the role of inducible nitric oxide synthase (iNOS) isoform. Results on inhibition of iNOS in sepsis models remain inconclusive. Concern has been devoted to improving our knowledge and understanding of the role of iNOS. The aim of this review is to define the role of iNOS in redox homeostasis disturbance, the detailed mechanisms linking iNOS and posttranslational modifications (PTMs) to cardiovascular dysfunctions, and their future implications in sepsis settings. Many questions related to the iNOS and PTMs still remain open, and much more work is needed on this.

Bench to bedside review: therapeutic modulation of nitric oxide in sepsis-an update

Nitric oxide is a signalling molecule with an extensive range of functions in both health and disease. Discovered in the 1980s through work that earned the Nobel prize, nitric oxide is an essential factor in regulating cardiovascular, immune, neurological and haematological function in normal homeostasis and in response to infection. Early work implicated exaggerated nitric oxide synthesis as a potentially important driver of septic shock; however, attempts to modulate production through global inhibition of nitric oxide synthase were associated with increased mortality. Subsequent work has shown that regulation of nitric oxide production is determined by numerous factors including substrate and co-factor availability and expression of endogenous regulators. In sepsis, nitric oxide synthesis is dysregulated with exaggerated production leading to cardiovascular dysfunction, bioenergetic failure and cellular toxicity whilst at the same time impaired microvascular function may be driven in part by reduced nitric oxide synthesis by the endothelium. This bench to bedside review summarises our current understanding of the ways in which nitric oxide production is regulated on a tissue and cellular level before discussing progress in translating these observations into novel therapeutic strategies for patients with sepsis.

Minimizing catecholamines and optimizing perfusion

Catecholamines are used to increase cardiac output and blood pressure, aiming ultimately at restoring/improving tissue perfusion. While intuitive in its concept, this approach nevertheless implies to be effective that regional organ perfusion would increase in parallel to cardiac output or perfusion pressure and that the catecholamine does not have negative effects on the microcirculation. Inotropic agents may be considered in some conditions, but it requires prior optimization of cardiac preload. Alternative approaches would be either to minimize exposure to vasopressors, tolerating hypotension and trying to prioritize perfusion but this may be valid as long as perfusion of the organ is preserved, or to combine moderate doses of vasopressors to vasodilatory agents, especially if these are predominantly acting on the microcirculation. In this review, we will discuss the pros and cons of the use of catecholamines and alternative agents for improving tissue perfusion in septic shock.

Possible involvement of tetrahydrobiopterin in the disturbance of redox homeostasis in sepsis - Induced brain dysfunction

BACKGROUND AND AIM

Tetrahydrobiopterin (BH4) is an essential co-factor that regulates nitric oxide (NO) and reactive oxygen species (ROS) production by nitric oxide synthases (NOS). In this study, we evaluated the effects of sepsis on BH4 level and redox status in the brain by using the rat model of sepsis-induced by cecal ligation and puncture (CLP) and examined whether BH4 and/or acetyl-L-carnitine (ALC) could prevent the neuronal apoptosis and neurological changes induced by sepsis.

MATERIAL AND METHOD

Male albino rats were randomly and blindly divided into 8 groups: sham, sham + BH4, sham + ALC, sham +BH4+ ALC, CLP, CLP + BH4, CLP + ALC, and CLP+BH4+ ALC. We measured neurological indicators, brain levels of BH4, guanosine triphosphate cyclohydrolase (GTPCH), sepiapterin reductase (SR) and dihydropteridine reductase (DHPR) genes expression (Essential enzymes in BH4 biosynthesis and recycling pathways). We investigated also brain redox status and both endothelial and inducible NOS expressions.

RESULTS

Brain of septic rats demonstrated a reduced BH4 bioavailability, downregulation of BH4 synthetic enzymes, increased production of hydrogen peroxide and impaired antioxidant enzymes activities. Treatments with BH4 and/or ALC increased BH4 level, upregulated BH4 synthetic enzymes expressions, and attenuated oxidative-induced neuronal apoptosis.

CONCLUSION

Our results suggest that BH4 and/or ALC might protect the brain against oxidative stress induced neuronal apoptosis by restoring bioavailability of BH4 and upregulating of BH4 synthetic enzymes in the brain during sepsis.

Vasodilators in Septic Shock Resuscitation: A Clinical Perspective

Microcirculatory abnormalities have been shown to be frequent in patients with septic shock despite "normalization" of systemic hemodynamics. Several studies have explored the impact of vasodilator therapy (prostacyclin, inhaled nitric oxide, topic acetylcholine, and nitroglycerin) on microcirculation and tissue perfusion, with contradictory findings.In this narrative review, we briefly present the pathophysiological aspects of microcirculatory dysfunction, and depict the evidence supporting the use of vasodilators and other therapeutic interventions (fluid administration, blood transfusion, vasopressors, and dobutamine) aiming to improve the microcirculatory flow in septic shock patients.

Detailing the cardiovascular profile in shock patients

Evaluation of the cardiovascular profile of critically ill patients is one of the most important actions performed in critically ill patients. It allows recognition that the patient is in shock and characterization of the type of circulatory failure. This step is crucial to initiate supportive interventions and to cure the cause responsible for the development of shock. Evaluation of tissue perfusion allows identification of the patient insufficiently resuscitated and also to trigger therapeutic interventions. Monitoring tissue perfusion can be achieved by lactate, venoarterial gradients in PCO₂, and central venous or mixed venous oxygen saturation. Ultimately, monitoring the microcirculation may help not only to identify alterations in tissue perfusion but also to identify the type of alterations: diffuse decrease in microvascular perfusion versus heterogeneity in the alterations, as in sepsis, with well perfused areas in close vicinity to poorly perfused areas. Regarding supportive therapy, a step-by-step approach is suggested, with fluid optimization followed by vasoactive support to preserve perfusion pressure and global and regional blood flows. The different variables should be integrated into decision and management pathways, and therapies adapted accordingly.

Seven unconfirmed ideas to improve future ICU practice

With imprecise definitions, inexact measurement tools, and flawed study execution, our clinical science often lags behind bedside experience and simply documents what appear to be the apparent faults or validity of ongoing practices. These impressions are later confirmed, modified, or overturned by the results of the next trial. On the other hand, insights that stem from the intuitions of experienced clinicians, scientists and educators-while often neglected-help place current thinking into proper perspective and occasionally point the way toward formulating novel hypotheses that direct future research. Both streams of information and opinion contribute to progress. In this paper we present a wide-ranging set of unproven 'out of the mainstream' ideas of our FCCM faculty, each with a defensible rationale and holding clear implications for altering bedside management. Each proposition was designed deliberately to be provocative so as to raise awareness, stimulate new thinking and initiate lively dialog.

Photonic monitoring of treatment during infection and sepsis: development of new detection strategies and potential clinical applications

Despite the strong decline in the infection-associated mortality since the development of the first antibiotics, infectious diseases are still a major cause of death in the world. With the rising number of antibiotic-resistant pathogens, the incidence of deaths caused by infections may increase strongly in the future. Survival rates in sepsis, which occurs when body response to infections becomes uncontrolled, are still very poor if an adequate therapy is not initiated immediately. Therefore, approaches to monitor the treatment efficacy are crucially needed to adapt therapeutic strategies according to the patient's response. An increasing number of photonic technologies are being considered for diagnostic purpose and monitoring of therapeutic response; however many of these strategies have not been introduced into clinical routine, yet. Here, we review photonic strategies to monitor response to treatment in patients with infectious disease, sepsis, and septic shock. We also include some selected approaches for the development of new drugs in animal models as well as new monitoring strategies which might be applicable to evaluate treatment response in humans in the future. Figure Label-free probing of blood properties using photonics.

Administration of Tetrahydrobiopterin (BH4) Protects the Renal Microcirculation From Ischemia and Reperfusion Injury

BACKGROUND

Abdominal aortic aneurysm surgery with suprarenal cross-clamping is often associated with renal injury. Although the mechanism underlying such injury is unclear, tissue ischemia and reperfusion, which induces endothelial dysfunction and decreases the availability of tetrahydrobiopterin (BH4), may play a role. We evaluated whether BH4 administration prevents renal ischemia/reperfusion injury in an animal model of aortic cross-clamping.

METHODS

Nineteen anesthetized, mechanically ventilated, and invasively monitored adult sheep were randomized into 3 groups: sham animals (n = 5) that underwent surgical preparation but no aortic clamping; an ischemia/reperfusion group (n = 7), where the aorta was clamped above the renal arteries for 1 hour, and a BH4 group (n = 7), in which animals received 20 mg/kg of BH4 followed by aortic cross-clamp for 1 hour. Animals were followed for a maximum of 6 hours after reperfusion. The renal microcirculation was evaluated at baseline (before clamping), and 1, 4, and 6 hours after reperfusion using side-stream dark field videomicroscopy. The renal lactate-to-pyruvate ratio was evaluated using microdialysis. The primary outcome was the change in proportion of small perfused vessels before and after injury. Secondary outcomes were renal tissue redox state and renal function.

RESULTS

Ischemia/reperfusion injury was associated with increases in heart rate and mean arterial pressure, which were blunted by BH4 administration. From the first to the sixth hour after reperfusion, the small vessel density (estimated mean difference [EMD], 1.03; 95% confidence interval [CI], 0.41-1.64; P = .003), perfused small vessel density (EMD, 0.84; 95% CI, 0.29-1.39; P = .005), and proportion of perfused small vessels (EMD, 8.60; 95% CI, 0.85-16.30; P = .031) were altered less in the BH4 than in the ischemia/reperfusion group. The renal lactate-to-pyruvate ratios were lower in the cortex in the BH4 than in the ischemia/reperfusion group from the first to the sixth hour after reperfusion (EMD, -19.16; 95% CI, -11.06 to 33.16; P = .002) and in the medulla from the first to the fourth hour (EMD, -26.62; 95% CI, -18.32 to 38.30; P = .020; and EMD, -8.68; 95% CI, -5.96 to 12.65; P = .019). At the sixth hour, serum creatinine was lower in the BH4 than in the ischemia/reperfusion group (EMD, -3.36; 95% CI, -0.29 to 1.39; P = .026).

CONCLUSIONS

In this sheep model of renal ischemia/reperfusion, BH4 pretreatment reduced renal microvascular injury and improved renal metabolism and function. Further work is needed to clarify the potential role of BH4 in ischemia/reperfusion injury.

Provision of physiological data and reference values in awake and anaesthetized female sheep aged 6-12 months

OBJECTIVE

To provide physiological data and reference values in awake and anaesthetized sheep aged 6-12 months.

STUDY DESIGN

Descriptive study.

ANIMALS

Data from 260 female sheep of the species Ovis orientalis aries aged 6-12 months were extracted from 10 experimental trials.

METHODS

Data from pulmonary arterial thermodilution in awake (cohort 1; n = 109) and anaesthetized animals (cohort 2; n = 81), and transpulmonary thermodilution in anaesthetized animals (cohort 3; n = 70) were analysed. General anaesthesia was induced by intramuscular injection of S-ketamine and midazolam and maintained by inhaled isoflurane. Standard laboratory variables (blood gas and clinical chemistry) were assessed.

RESULTS

A total of 7553 single data entries from 260 healthy sheep were included. Measurement errors or invalid data documentation meant that 313 data entries (4.1%) were excluded. A small confidence interval for median values was calculated for nearly all variables. The median body weight was 39.8 kg (2.5-97.5th percentile 30.6-48.1 kg). A set of reference values (2.5-97.5th percentiles) is provided for common cardiopulmonary and laboratory variables. Compared to awake animals, haemodynamic variables were markedly influenced by anaesthesia, as reflected by a considerably lower stroke volume index in anaesthetized sheep. There were also differences in stroke volume index between the cohorts of pulmonary artery and transpulmonary thermodilution.

CONCLUSIONS AND CLINICAL RELEVANCE

The present work presents a large and consistent database of a variety of physiological variables measured in healthy juvenile female sheep. The data appear to be robust and allow the establishment of standardized inclusion criteria for experimental studies and may help to better evaluate past, present and future research. Differences between pulmonary artery and transpulmonary thermodilution should be assessed in future studies.

Tetrahydrobiopterin improves microcirculation in experimental sepsis

BACKGROUND

Tetrahydrobiopterin (BH4), an endogenous nucleic acid derivative, acts as an important cofactor for several enzymes found within the vascular endothelium, which is deranged in sepsis.

OBJECTIVE

We hypothesized that BH4 would improve capillary density and decrease inflammation within the intestinal microcirculation of septic rats.

METHODS

We conducted a randomized, controlled trial using two previously validated models of sepsis in rats: 1) A fecal peritonitis model using a stent perforating the ascending colon, and 2) An endotoxemia model using lipopolysaccharide (LPS) toxin from E. coli. Experimental groups receiving BH4 (60 mg/kg) were compared to otherwise healthy controls and to untreated groups with sepsis-like physiology.

RESULTS

BH4 decreased leukocyte-endothelial adhesion by 55% and 58% (P < 0.05) in the peritonitis model and endotoxemia models, respectively. In the endotoxemia model but not the peritonitis model, BH4 improved functional capillary density in capillary beds within the intestine (141.3 vs. 106.7 mm/cm2, p < 0.05). Macrohemodynamic parameters were no different between placebo treatment and BH4-treated groups.

CONCLUSIONS

This study demonstrates that BH4 improves capillary density and inflammation in two separate models of sepsis. BH4 may represent a novel adjunct in the treatment of sepsis and septic shock in clinical practice. Further dose-finding studies and clinical trials are warranted.

THE ENDOTHELIUM IN SEPSIS

Sepsis affects practically all aspects of endothelial cell (EC) function and is thought to be the key factor in the progression from sepsis to organ failure. Endothelial functions affected by sepsis include vasoregulation, barrier function, inflammation, and hemostasis. These are among other mechanisms often mediated by glycocalyx shedding, such as abnormal nitric oxide metabolism, up-regulation of reactive oxygen species generation due to down-regulation of endothelial-associated antioxidant defenses, transcellular communication, proteases, exposure of adhesion molecules, and activation of tissue factor. This review covers current insight in EC-associated hemostatic responses to sepsis and the EC response to inflammation. The endothelial cell lining is highly heterogeneous between different organ systems and consequently also in its response to sepsis. In this context, we discuss the response of the endothelial cell lining to sepsis in the kidney, liver, and lung. Finally, we discuss evidence as to whether the EC response to sepsis is adaptive or maladaptive. This study is a result of an Acute Dialysis Quality Initiative XIV Sepsis Workgroup meeting held in Bogota, Columbia, between October 12 and 15, 2014.

Hemodynamic coherence in sepsis

Microvascular alterations are a hallmark of sepsis and play a crucial role in its pathophysiology. Such alterations are the result of overwhelming inflammation, which negatively affects all the components of the microcirculation. As the severity of microvascular alterations is associated with organ dysfunction and mortality, several strategies have been tested for improving microcirculation. Nevertheless, they are mainly based on the conventional manipulation of systemic hemodynamics to increase the total flow to the organs and tissues. Other therapeutic interventions are still being investigated. In this review, we discuss the pathophysiology of septic microcirculatory dysfunction and its implications for possible treatments.

Effects of Different Crystalloid Solutions on Hemodynamics, Peripheral Perfusion, and the Microcirculation in Experimental Abdominal Sepsis

BACKGROUND

Crystalloid solutions are used to restore intravascular volume in septic patients, but each solution has limitations. The authors compared the effects of three crystalloid solutions on hemodynamics, organ function, microcirculation, and survival in a sepsis model.

METHODS

Peritonitis was induced by injection of autologous feces in 21 anesthetized, mechanically ventilated adult sheep. After baseline measurements, animals were randomized to lactated Ringer's (LR), normal saline (NS), or PlasmaLyte as resuscitation fluid. The sublingual microcirculation was assessed using sidestream dark field videomicroscopy and muscle tissue oxygen saturation with near-infrared spectroscopy.

RESULTS

NS administration was associated with hyperchloremic acidosis. NS-treated animals had lower cardiac index and left ventricular stroke work index than LR-treated animals from 8 h and lower mean arterial pressure than LR-treated animals from 12 h. NS-treated animals had a lower proportion of perfused vessels than LR-treated animals after 12 h (median, 82 [71 to 83] vs. 85 [82 to 89], P = 0.04) and greater heterogeneity of proportion of perfused vessels than PlasmaLyte or LR groups at 18 h. Muscle tissue oxygen saturation was lower at 16 h in the NS group than in the other groups. The survival time of NS-treated animals was shorter than that of the LR group (17 [14 to 20] vs. 26 [23 to 29] h, P < 0.01) but similar to that of the PlasmaLyte group (20 [12 to 28] h, P = 0.74).

CONCLUSIONS

In this abdominal sepsis model, resuscitation with NS was associated with hyperchloremic acidosis, greater hemodynamic instability, a more altered microcirculation, and more severe organ dysfunction than with balanced fluids. Survival time was shorter than in the LR group.

Renal perfusion in sepsis: from macro- to microcirculation

The pathogenesis of sepsis-associated acute kidney injury is complex and likely involves perfusion alterations, a dysregulated inflammatory response, and bioenergetic derangements. Although global renal hypoperfusion has been the main target of therapeutic interventions, its role in the development of renal dysfunction in sepsis is controversial. The implications of renal hypoperfusion during sepsis probably extend beyond a simple decrease in glomerular filtration pressure, and targeting microvascular perfusion deficits to maintain tubular epithelial integrity and function may be equally important. In this review, we provide an overview of macro- and microcirculatory dysfunction in experimental and clinical sepsis and discuss relationships with kidney oxygenation, metabolism, inflammation, and function.

Changes in kidney perfusion and renal cortex metabolism in septic shock: an experimental study

BACKGROUND

The etiology of renal dysfunction in sepsis is currently attributed to altered perfusion, microcirculatory abnormalities and cellular alterations. To clarify these mechanisms, we characterized the changes in renal perfusion and cortex metabolism in a large animal model of sepsis.

METHODS

We studied 12 adult female sheep randomized to peritonitis-induced sepsis (n = 8) or to sham procedure (n = 4). A flow probe was positioned around the renal artery to measure renal blood flow (RBF). Laser Doppler was used to measure regional flow in the kidney cortex and medulla. A microdialysis probe was inserted into the renal cortex to measure cortical glucose, lactate, and pyruvate. Fluid resuscitation was provided to keep pulmonary artery occlusion pressure at baseline levels. All animals were observed for 18 h.

RESULTS

Hypotension occurred after 9 h in the septic animals (P = 0.02 versus baseline). RBF and cortical flow were significantly lower than at baseline from 12 h in the septic animals (P = 0.01 and P = 0.03, respectively). Cortical lactate and pyruvate levels increased in the septic animals from 3 and from 6 h, respectively (both P = 0.02 versus baseline), and the L/P ratio from 15 h (P = 0.01). There was a correlation between cortical flow and cortical L/P ratio after shock onset (r = -0.60, P = 0.002) but not before.

CONCLUSIONS

In this peritonitis model, sepsis was associated with metabolic alterations that may reflect early induction of cortical glycolysis. Septic shock was associated with reduced renal perfusion and decreased cortical and medullary blood flow, followed by signs of anaerobic metabolism in the cortex when flow reductions became critical.

Microcirculatory dysfunction in sepsis: pathophysiology, clinical monitoring, and potential therapies

Abnormal microvascular perfusion, including decreased functional capillary density and increased blood flow heterogeneity, is observed in early stages of the systemic inflammatory response to infection and appears to have prognostic significance in human sepsis. It is known that improvements in systemic hemodynamics are weakly correlated with the correction of microcirculatory parameters, despite an appropriate treatment of macrohemodynamic abnormalities. Furthermore, conventional hemodynamic monitoring systems available in clinical practice fail to detect microcirculatory parameter changes and responses to treatments, as they do not evaluate intrinsic events that occur in the microcirculation. Fortunately, some bedside diagnostic methods and therapeutic options are specifically directed to the assessment and treatment of microcirculatory changes. In the present review we discuss fundamental aspects of septic microcirculatory abnormalities, including pathophysiology, clinical monitoring, and potential therapies.

Time courses of changes of para-, meta-, and ortho-tyrosine in septic patients: A pilot study

OBJECTIVES

Sepsis is associated with oxidative stress. Due to oxidative stress, three tyrosine isoforms, para-, meta-, and ortho-tyrosine (p-, m-, and o-Tyr), can be formed non-enzymatically in smaller amounts. p-Tyr is mainly formed physiologically in the kidneys through the activity of the phenylalanine hydroxylase enzyme. The three tyrosine isoforms may undergo different renal handling.

METHODS

Twenty septic patients were involved in the study and 25 healthy individuals served as controls. Blood and urine levels of p-, m-, and o-Tyr were measured on admission and four consecutive days.

RESULTS

Serum m-Tyr levels were higher in septic patients than in controls on days 2 (P = 0.031) and 3 (P = 0.035). Serum p-Tyr levels were lower in the cases than in controls on days 1 (P = 0.005) and 2 (P = 0.040), and subsequently normalized due to a day-by-day elevation (P = 0.002). The tendency of urinary m-Tyr concentration was decreasing (P = 0.041), while that of urinary p-Tyr concentration was increasing (P = 0.001). Fractional excretion of m-Tyr (FEm-Tyr) showed a decreasing tendency (P = 0.009), and was, on all days, higher than FEp-Tyr, which remained near-normal, less than 4%. Procalcitonin showed significant correlation with FEm-Tyr (r = 0.454; P < 0.001).

DISCUSSION

Our data suggest that the oxidative stress marker m-Tyr and physiologic p-Tyr may be handled differently in septic patients. The excretion of m-Tyr correlates with inflammation. m-Tyr may be actively secreted or produced in the kidney in some patients, whereas the decreased serum level of p-Tyr is a consequence of diminished renal production and not of renal loss.

Could Biomarkers Direct Therapy for the Septic Patient?

Sepsis is a serious medical condition caused by a severe systemic inflammatory response to a bacterial, fungal, or viral infection that most commonly affects neonates and the elderly. Advances in understanding the pathophysiology of sepsis have resulted in guidelines for care that have helped reduce the risk of dying from sepsis for both children and older adults. Still, over the past three decades, a large number of clinical trials have been undertaken to evaluate pharmacological agents for sepsis. Unfortunately, all of these trials have failed, with the use of some agents even shown to be harmful. One key issue in these trials was the heterogeneity of the patient population that participated. What has emerged is the need to target therapeutic interventions to the specific patient's underlying pathophysiological processes, rather than looking for a universal therapy that would be effective in a "typical" septic patient, who does not exist. This review supports the concept that identification of the right biomarkers that can direct therapy and provide timely feedback on its effectiveness will enable critical care physicians to decrease mortality of patients with sepsis and improve the quality of life of survivors.

Endothelial cell tetrahydrobiopterin deficiency attenuates LPS-induced vascular dysfunction and hypotension

Overproduction of nitric oxide (NO) is thought to be a key mediator of the vascular dysfunction and severe hypotension in patients with endotoxaemia and septic shock. The contribution of NO produced directly in the vasculature by endothelial cells to the hypotension seen in these conditions, vs. the broader systemic increase in NO, is unclear. To determine the specific role of endothelium derived NO in lipopolysaccharide (LPS)-induced vascular dysfunction we administered LPS to mice deficient in endothelial cell tetrahydrobiopterin (BH4), the essential co-factor for NO production by NOS enzymes. Mice deficient in endothelial BH4 production, through loss of the essential biosynthesis enzyme Gch1 (Gch1(fl/fl)Tie2cre mice) received a 24hour challenge with LPS or saline control. In vivo LPS treatment increased vascular GTP cyclohydrolase and BH4 levels in aortas, lungs and hearts, but this increase was significantly attenuated in Gch1(fl/fl)Tie2cre mice, which were also partially protected from the LPS-induced hypotension. In isometric tension studies, in vivo LPS treatment reduced the vasoconstriction response and impaired endothelium-dependent and independent vasodilatations in mesenteric arteries from wild-type mice, but not in Gch1(fl/fl)Tie2cre mesenteric arteries. Ex vivo LPS treatment decreased vasoconstriction response to phenylephrine in aortic rings from wild-type and not in Gch1(fl/fl)Tie2cre mice, even in the context of significant eNOS and iNOS upregulation. These data provide direct evidence that endothelial cell NO has a significant contribution to LPS-induced vascular dysfunction and hypotension and may provide a novel therapeutic target for the treatment of systemic inflammation and patients with septic shock.

A Selective V(1A) Receptor Agonist, Selepressin, Is Superior to Arginine Vasopressin and to Norepinephrine in Ovine Septic Shock

OBJECTIVE

Selective vasopressin V(1A) receptor agonists may have advantages over arginine vasopressin in the treatment of septic shock. We compared the effects of selepressin, a selective V(1A) receptor agonist, arginine vasopressin, and norepinephrine on hemodynamics, organ function, and survival in an ovine septic shock model.

DESIGN

Randomized animal study.

SETTING

University hospital animal research laboratory.

SUBJECTS

Forty-six adult female sheep.

INTERVENTIONS

Fecal peritonitis was induced in the anesthetized, mechanically ventilated, fluid-resuscitated sheep, and they were randomized in two successive phases. Three late-intervention groups (each n = 6) received IV selepressin (1 pmol/kg/min), arginine vasopressin (0.25 pmol [0.1 mU]/kg/min), or norepinephrine (3 nmol [0.5 μg]/kg/min) when mean arterial pressure remained less than 70 mm Hg despite fluid challenge; study drugs were thereafter titrated to keep mean arterial pressure at 70-80 mm Hg. Three early-intervention groups (each n = 7) received selepressin, arginine vasopressin, or norepinephrine at the same initial infusion rates as for the late intervention, but already when mean arterial pressure had decreased by 10% from baseline; doses were then titrated as for the late intervention. A control group (n = 7) received saline. All animals were observed until death or for a maximum of 30 hours.

MEASUREMENTS AND MAIN RESULTS

In addition to hemodynamic and organ function assessment, plasma interleukin-6 and nitrite/nitrate levels were measured. In the late-intervention groups, selepressin delayed the decrease in mean arterial pressure and was associated with lower lung wet/dry weight ratios than in the other two groups. In the early-intervention groups, selepressin maintained mean arterial pressure and cardiac index better than arginine vasopressin or norepinephrine, slowed the increase in blood lactate levels, and was associated with less lung edema, lower cumulative fluid balance, and lower interleukin-6 and nitrite/nitrate levels. Selepressin-treated animals survived longer than the other animals.

CONCLUSIONS

In this clinically relevant model, selepressin, a selective V(1A) receptor agonist, was superior to arginine vasopressin and to norepinephrine in the treatment of septic shock, especially when administered early.

Novel relationships between oxidative stress and angiogenesis-related factors in sepsis: New biomarkers and therapies

Sepsis is a systemic uncontrolled inflammatory response in the presence of an infection. It remains a major cause of morbidity and mortality in hospitalized patients. According to its severity, sepsis can progress to three different states: severe sepsis, septic shock, and multiple organ dysfunction syndrome, related to organ dysfunction and/or tissue hypoperfusion. Different processes underlie its pathophysiology; among them are oxidative stress, endothelial and mitochondrial dysfunction, and angiogenesis-related factors. However, no studies have integrated these elements in sepsis. The main difficulty in sepsis is its diagnosis. Currently, the potential of inflammatory biomarkers in septic patients remains weak. In this context, the research into new biomarkers is essential to aid with sepsis diagnosis and prognostication. Furthermore, even though the current management of severe forms of sepsis has been effective, morbimortality remains elevated. Therefore, it is essential to explore alternative approaches to therapy development. The aim of this review is to present an update of evidence supporting the role of oxidative stress and angiogenesis-related factors in the pathophysiology of the different forms of sepsis. It proposes a novel convergence between both elements in their role in the disease, and it will cover their utility as new diagnostic tools, predictors of outcome, and as novel therapeutic targets.

Randomized controlled trial of inhaled nitric oxide for the treatment of microcirculatory dysfunction in patients with sepsis*

OBJECTIVES

Sepsis treatment guidelines recommend macrocirculatory hemodynamic optimization; however, microcirculatory dysfunction is integral to sepsis pathogenesis. We aimed to test the hypothesis that following macrocirculatory optimization, inhaled nitric oxide would improve microcirculation in patients with sepsis and that improved microcirculation would improve lactate clearance and multiple organ dysfunction.

DESIGN

Randomized, sham-controlled clinical trial.

SETTING

Single urban academic medical center.

PATIENTS

Adult patients with severe sepsis and systolic blood pressure less than 90 mm Hg despite intravascular volume expansion and/or serum lactate greater than or equal to 4.0 mmol/L.

INTERVENTIONS

After achievement of macrocirculatory resuscitation goals, we randomized patients to 6 hours of inhaled nitric oxide (40 ppm) or sham inhaled nitric oxide administration. We administered study drug via a specialized delivery device that concealed treatment allocation so that investigators and clinical staff remained blinded.

MEASUREMENTS AND MAIN RESULTS

We performed sidestream dark-field videomicroscopy of the sublingual microcirculation prior to and 2 hours after study drug initiation. The primary outcome measure was the change in microcirculatory flow index. Secondary outcomes were lactate clearance and change in Sequential Organ Failure Assessment score. We enrolled 50 patients (28 of 50 [56%] requiring vasopressor agents; 15 of 50 [30%] died). Although inhaled nitric oxide significantly raised plasma nitrite levels, it did not improve microcirculatory flow, lactate clearance, or organ dysfunction. In contrast to previous studies conducted during the earliest phase of resuscitation, we found no association between changes in microcirculatory flow and lactate clearance or organ dysfunction.

CONCLUSIONS

Following macrocirculatory optimization, inhaled nitric oxide at 40 ppm did not augment microcirculatory perfusion in patients with sepsis. Further, we found no association between microcirculatory perfusion and multiple organ dysfunction after initial resuscitation.

Monitoring the microcirculation in critically ill patients

Alterations in microvascular perfusion have been identified in critically ill patients, especially in sepsis but also in cardiogenic shock, after cardiac arrest, and in high-risk surgery patients. These alterations seem to be implicated in the development of organ dysfunction and are associated with outcome. Even though microvascular perfusion can sometimes be homogenously decreased as in acute hemorrhage or in non-resuscitated cardiogenic shock, heterogeneity of perfusion is observed in sepsis and in resuscitated hemorrhagic/cardiogenic shock. Heterogeneity of perfusion has major implications for monitoring, as many techniques cannot detect microcirculatory alterations when heterogeneity of flow is present in significant amount. Indeed, devices such as laser Doppler or O2 electrodes and near-infrared spectroscopy have a relatively large sampling volume and measurements are affected by the highest values in the field. Using these techniques during a vascular occlusion test may help to characterize microvascular reactivity; however, microvascular reactivity sometimes fails to represent actual microvascular perfusion. Videomicroscopic techniques can nowadays be applied at bedside but are still restricted to some selected patients (quiet or sedated patients). Tissue PCO2 is an elegant alternative but is not yet broadly used. In this manuscript, we discuss the main advantages and limitations of the techniques available for bedside evaluation of the microcirculation in critically ill patients.

Tetrahydrobiopterin in cardiovascular health and disease

Tetrahydrobiopterin (BH4) functions as a cofactor for several important enzyme systems, and considerable evidence implicates BH4 as a key regulator of endothelial nitric oxide synthase (eNOS) in the setting of cardiovascular health and disease. BH4 bioavailability is determined by a balance of enzymatic de novo synthesis and recycling, versus degradation in the setting of oxidative stress. Augmenting vascular BH4 levels by pharmacological supplementation has been shown in experimental studies to enhance NO bioavailability. However, it has become more apparent that the role of BH4 in other enzymatic pathways, including other NOS isoforms and the aromatic amino acid hydroxylases, may have a bearing on important aspects of vascular homeostasis, inflammation, and cardiac function. This article reviews the role of BH4 in cardiovascular development and homeostasis, as well as in pathophysiological processes such as endothelial and vascular dysfunction, atherosclerosis, inflammation, and cardiac hypertrophy. We discuss the therapeutic potential of BH4 in cardiovascular disease states and attempt to address how this modulator of intracellular NO-redox balance may ultimately provide a powerful new treatment for many cardiovascular diseases.

Nitroglycerin reverts clinical manifestations of poor peripheral perfusion in patients with circulatory shock

INTRODUCTION

Recent clinical studies have shown a relationship between abnormalities in peripheral perfusion and unfavorable outcome in patients with circulatory shock. Nitroglycerin is effective in restoring alterations in microcirculatory blood flow. The aim of this study was to investigate whether nitroglycerin could correct the parameters of abnormal peripheral circulation in resuscitated circulatory shock patients.

METHODS

This interventional study recruited patients who had circulatory shock and who persisted with abnormal peripheral perfusion despite normalization of global hemodynamic parameters. Nitroglycerin started at 2 mg/hour and doubled stepwise (4, 8, and 16 mg/hour) each 15 minutes until an improvement in peripheral perfusion was observed. Peripheral circulation parameters included capillary refill time (CRT), skin-temperature gradient (Tskin-diff), perfusion index (PI), and tissue oxygen saturation (StO2) during a reactive hyperemia test (RincStO2). Measurements were performed before, at the maximum dose, and after cessation of nitroglycerin infusion. Data were analyzed by using linear model for repeated measurements and are presented as mean (standard error).

RESULTS

Of the 15 patients included, four patients (27%) responded with an initial nitroglycerin dose of 2 mg/hour. In all patients, nitroglycerin infusion resulted in significant changes in CRT, Tskin-diff, and PI toward normal at the maximum dose of nitroglycerin: from 9.4 (0.6) seconds to 4.8 (0.3) seconds (P < 0.05), from 3.3 °C (0.7 °C) to 0.7 °C (0.6 °C) (P < 0.05), and from [log] -0.5% (0.2%) to 0.7% (0.1%) (P < 0.05), respectively. Similar changes in StO2 and RincStO2 were observed: from 75% (3.4%) to 84% (2.7%) (P < 0.05) and 1.9%/second (0.08%/second) to 2.8%/second (0.05%/second) (P < 0.05), respectively. The magnitude of changes in StO2 was more pronounced for StO2 of less than 75%: 11% versus 4%, respectively (P < 0.05).

CONCLUSIONS

Dose-dependent infusion of nitroglycerin reverted abnormal peripheral perfusion and poor tissue oxygenation in patients following circulatory shock resuscitation. Individual requirements of nitroglycerin dose to improve peripheral circulation vary between patients. A simple and fast physical examination of peripheral circulation at the bedside can be used to titrate nitroglycerin infusion.

Vasoplegia in septic shock: do we really fight the right enemy?

Vasoplegia is a key factor for the death of patients with septic shock in intensive care unit owing to persistent and irreversible hypotension. Impairment of vascular reactivity has been attributed to a combination of endothelial injury, arginine-vasopressin system dysfunction, release of other vasodilatory inflammatory mediators, and muscle hyperpolarizaton. Nitric oxide induced by a Ca(+2) independent isoform of nitric oxide synthase has been suggested to play an important role in sepsis-induced vasoplegia. However, inhibition of nitric oxide synthase only partially restores the endotoxin-induced vascular hyporeactivity. The aim of this review is to discuss in detail the recent suggested alternative mechanisms of vasoplegia and to briefly outline the current therapeutic strategies and the novel therapeutic options based on those mechanisms.

Pathophysiology of microcirculatory dysfunction and the pathogenesis of septic shock

Multiple experimental and human trials have shown that microcirculatory alterations are frequent in sepsis. In this review, we discuss the various mechanisms that are potentially involved in their development and the implications of these alterations. Endothelial dysfunction, impaired inter-cell communication, altered glycocalyx, adhesion and rolling of white blood cells and platelets, and altered red blood cell deformability are the main mechanisms involved in the development of these alterations. Microcirculatory alterations increase the diffusion distance for oxygen and, due to the heterogeneity of microcirculatory perfusion in sepsis, may promote development of areas of tissue hypoxia in close vicinity to well-oxygenated zones. The severity of microvascular alterations is associated with organ dysfunction and mortality. At this stage, therapies to specifically target the microcirculation are still being investigated.

The regulation of vascular tetrahydrobiopterin bioavailability

6R l-erythro-5,6,7,8-tetrahydrobiopterin (BH4) is an essential cofactor for several enzymes including phenylalanine hydroxylase and the nitric oxide synthases (NOS). Oral supplementation of BH4 has been successfully employed to treat subsets of patients with hyperphenylalaninaemia. More recently, research efforts have focussed on understanding whether BH4 supplementation may also be efficacious in cardiovascular disorders that are underpinned by reduced nitric oxide bioavailability. Whilst numerous preclinical and clinical studies have demonstrated a positive association between enhanced BH4 and vascular function, the efficacy of orally administered BH4 in human cardiovascular disease remains unclear. Furthermore, interventions that limit BH4 bioavailability may provide benefit in diseases where nitric oxide over production contributes to pathology. This review describes the pathways involved in BH4 bio-regulation and discusses other endogenous mechanisms that could be harnessed therapeutically to manipulate vascular BH4 levels.