Bruno Levy

Vascular hyporesponsiveness to vasopressors in septic shock: from bench to bedside

PurposeTo delineate some of the characteristics of septic vascular hypotension, to assess the most commonly cited and reported underlying mechanisms of vascular hyporesponsiveness to vasoconstrictors in sepsis, and to briefly outline current therapeutic strategies and possible future approaches.MethodsSource data were obtained from a PubMed search of the medical literature with the following MeSH terms: Muscle, smooth, vascular/physiopathology; hypotension/etiology; shock/physiopathology; vasodilation/physiology; shock/therapy; vasoconstrictor agents.ResultsNitric oxide (NO) and peroxynitrite are crucial components implicated in vasoplegia and vascular hyporeactivity. Vascular ATP-sensitive and calcium-activated potassium channels are activated during shock and participate in hypotension. In addition, shock state is characterized by inappropriately low plasma glucocorticoid and vasopressin concentrations, a dysfunction and desensitization of alpha-receptors, and an inactivation of catecholamines by oxidation. Numerous other mechanisms have been individualized in animal models, the great majority of which involve NO: MEK1/2–ERK1/2 pathway, H2S, hyperglycemia, and cytoskeleton dysregulation associated with decreased actin expression.ConclusionsMany therapeutic approaches have proven their efficiency in animal models, especially therapies directed against one particular compound, but have otherwise failed when used in human shock. Nevertheless, high doses of catecholamines, vasopressin and terlipressin, hydrocortisone, activated protein C, and non-specific shock treatment have demonstrated a partial efficiency in reversing sepsis-induced hypotension.

The relationship between CD4+CD25+CD127- regulatory T cells and inflammatory response and outcome during shock states.

IntroductionAlthough regulatory T lymphocytes (Tregs) have a pivotal role in preventing autoimmune diseases and limiting chronic inflammatory conditions, they may also block beneficial immune responses by preventing sterilizing immunity to certain pathogens.MethodsTo determine whether naturally occurring Treg cells have a role in inflammatory response and outcome during shock state we conducted an observational study in two adult ICUs from a university hospital. Within 12 hours of admission, peripheral whole blood was collected for the measurement of cytokines and determination of lymphocyte count. Sampling was repeated at day three, five and seven. Furthermore, an experimental septic shock was induced in adult Balb/c mice through caecal ligation and puncture.ResultsForty-three patients suffering from shock (26 septic, 17 non septic), and 7 healthy volunteers were included. The percentage of Tregs increased as early as 3 days after the onset of shock, while their absolute number remained lower than in healthy volunteers. A similar pattern of Tregs kinetics was found in infected and non infected patients. Though there was an inverse correlation between severity scores and Tregs percentage, the time course of Tregs was similar between survivors and non survivors. No relation between Tregs and cytokine concentration was found. In septic mice, although there was a rapid increase in Treg cells subset among splenocytes, antibody-induced depletion of Tregs before the onset of sepsis did not alter survival.ConclusionsThese data argue against a determinant role of Tregs in inflammatory response and outcome during shock states.

Soluble Trem-like Transcript-1 Regulates Leukocyte Activation and Controls Microbial Sepsis

The triggering receptor expressed on myeloid cells (TREM)-1 plays a crucial role during the onset of sepsis by amplifying the host immune response. The TREM-like transcript-1 (TLT-1) belongs to the TREM family, is selectively expressed on activated platelets, and is known to facilitate platelet aggregation through binding to fibrinogen. In this study, we show that a soluble form of TLT-1 is implicated in the regulation of inflammation during sepsis by dampening leukocyte activation and modulating platelet-neutrophil crosstalk. A 17-aa sequence of the TLT-1 extracellular domain (LR17) is responsible for this activity through competition with the TREM-1 ligand. Whereas early or late LR17 treatment of septic mice improves survival, treml-1−/− animals are highly susceptible to polymicrobial infection. The present findings identify platelet-derived soluble TLT-1 as a potent endogenous regulator of sepsis-associated inflammation and open new therapeutic perspectives. We anticipate soluble TLT-1 to be important in regulating leukocyte activation during other noninfectious inflammatory disorders.

GPU‐accelerated atom and dynamic bond visualization using hyperballs: A unified algorithm for balls, sticks, and hyperboloids

Ray casting on graphics processing units (GPUs) opens new possibilities for molecular visualization. We describe the implementation and calculation of diverse molecular representations such as licorice, ball‐and‐stick, space‐filling van der Waals spheres, and approximated solvent‐accessible surfaces using GPUs. We introduce HyperBalls, an improved ball‐and‐stick representation replacing tubes, linking the atom spheres by hyperboloids that can smoothly connect them. This type of depiction is particularly useful to represent dynamic phenomena, such as the evolution of noncovalent bonds. It is furthermore well suited to represent coarse‐grained models and spring networks. All these representations can be defined by a single general algebraic equation that is adapted for the ray‐casting technique and is well suited for execution on the GPU. Using GPU capabilities, this implementation can routinely, accurately, and interactively render molecules ranging from a few atoms up to huge macromolecular assemblies with more than 500,000 particles. In simple cases, based only on spheres, we have been able to display up to two million atoms smoothly.

MetaMol: high-quality visualization of molecular skin surface.

Modeling and visualizing molecular surfaces is an important and challenging task in bioinformatics. Such surfaces play an essential role in better understanding the chemical and physical properties of molecules. However, constructing and displaying molecular surfaces requires complex algorithms. In this article we introduce MetaMol, a new program that generates high-quality images in interactive time. In contrast with existing software that discretizes the surface with triangles or grids, our program is based on a GPU accelerated ray-casting algorithm that directly uses the piecewise-defined algebraic equation of the molecular skin surface. As a result, both better performances and higher quality are obtained.

GPU-powered tools boost molecular visualization

Recent advances in experimental structure determination provide a wealth of structural data on huge macromolecular assemblies such as the ribosome or viral capsids, available in public databases. Further structural models arise from reconstructions using symmetry orders or fitting crystal structures into low-resolution maps obtained by electron-microscopy or small angle X-ray scattering experiments. Visual inspection of these huge structures remains an important way of unravelling some of their secrets. However, such visualization cannot conveniently be carried out using conventional rendering approaches, either due to performance limitations or due to lack of realism. Recent developments, in particular drawing benefit from the capabilities of Graphics Processing Units (GPUs), herald the next generation of molecular visualization solutions addressing these issues. In this article, we present advances in computer science and visualization that help biologists visualize, understand and manipulate large and complex molecular systems, introducing concepts that remain little-known in the bioinformatics field. Furthermore, we compile currently available software and methods enhancing the shape perception of such macromolecular assemblies, for example based on surface simplification or lighting ameliorations.

Increased muscle-to-serum lactate gradient predicts progression towards septic shock in septic patients

PurposeDuring septic shock, muscle produces lactate and pyruvate by way of an exaggerated Na+, K+-ATPase-stimulated aerobic glycolysis associated with epinephrine stimulation. We hypothesized that patients with sepsis without shock and increased epinephrine levels or an increased muscle-to-serum lactate gradient are likely to evolve towards septic shock. Thus, in sepsis patients, we investigated (1) whether muscle produces lactate and pyruvate, and (2) whether muscle lactate production is linked to epinephrine levels and the severity of the patients condition.MethodsWe studied 40 ventilated patients with sepsis without shock or hyperlactatemia and a control group of 10 ICU patients without infection. A microdialysis probe was inserted into the quadriceps muscle. Plasma lactate and pyruvate concentrations were measured in both the dialysate fluid and arterial blood samples every 6xa0h.ResultsThere was no gradient between muscle and arterial levels for lactate and pyruvate in the control group. In the sepsis group, muscle lactate and pyruvate concentrations were consistently higher than the arterial levels (Pxa0<xa00.01). Plasma epinephrine concentrations were also elevated (Pxa0<xa00.05). A total of 15/40 patients further developed septic shock, and on admission these patients had significantly higher musculo-arterial gradients of lactate (2.9xa0±xa00.3 vs. 0.7xa0±xa00.2xa0mmol/l) (Pxa0<xa00.05) and pyruvate (740xa0±xa060 vs. 200xa0±xa020xa0μmol/l) (Pxa0<xa00.05), and higher levels of epinephrine concentrations (6.2xa0±xa00.7 vs. 2.5xa0±xa00.24xa0nmol/l) (Pxa0<xa00.05). Both the lactate gradient and epinephrine concentrations measured on admission were good predictors of the evolution towards septic shock.ConclusionsMuscle produces lactate and pyruvate during sepsis, and this production is highly correlated with plasma epinephrine secretion and severity of illness.

Comparative effects of recombinant human activated protein C and dexamethasone in experimental septic shock.

PurposeTo compare the effects of recombinant human activated protein C (APC) and glucocorticoids alone and in combination in non-anesthetized resuscitated septic shock induced by cecal ligation and puncture (CLP) on (a) survival, (b) hemodynamics, and (c) vascular reactivity. The effects of treatments on major cellular pathways likely implicated were also studied.MethodsFour hours after CLP, rats were continuously infused with either saline (10xa0ml/kg/h), salinexa0+xa0APC, salinexa0+xa0dexamethasone (Dexa), or salinexa0+xa0APCxa0+xa0Dexa. Eighteen hours after CLP, arterial pressure, cardiac output, nitrite/nitrate ratio, and lactate concentrations were measured. Aortic rings and mesenteric arteries were isolated and mounted in a myograph, after which arterial contractility and endothelium-dependent relaxation were measured in the presence or absence of nitric oxide synthase (NOS) or cyclooxygenase (COX) inhibitors. Protein expression was assessed by Western blotting. Aorta NO and superoxide anion content were measured by electron paramagnetic resonance.ResultsAll treatments improved hemodynamic parameters and vascular reactivity and decreased lactate and nitrite/nitrate levels.In treated aorta and mesenteric arteries, contractility and endothelial dysfunction were improved. This effect was associated with an increase in the phosphorylated form of protein kinase B as well as an increase in COX vasodilatory pathways and a decrease in iNOS expression suggesting that these pathways are implicated in the vascular effect of the treatments. CLP was associated with a marked increase in aortic NO and superoxide anion content (pxa0<xa00.05), which were decreased by APC and Dexa and totally abolished by APCxa0+xa0Dexa (pxa0<xa00.01). Survival length was significantly increased by the APC–Dexa combination.ConclusionsBoth APC and Dexa improve arterial contractility and endothelial dysfunction resulting from septic shock in rats. Moreover, their combination increased the length of survival. These findings provide important insights into the mechanisms underlying APC- and/or Dexa-induced improvements of arterial dysfunction during septic shock.

Cardiovascular and metabolic responses to catecholamine and sepsis prognosis: a ubiquitous phenomenon?

Many parameters have been associated with sepsis prognosis. In the present issue of Critical Care, Kumar and colleagues demonstrate that a preserved cardiac answer to dobutamine evaluated by radionucleotide measurements was associated with a better prognosis during septic shock. In this context, it is interesting to note that not only is the cardiac response to catecholamine stimulation associated with prognosis, but also the vascular and metabolic responses are associated. The ability of exogenous catecholamine to increase the arterial pressure (dopamine test) or to increase the lactate level is also related to prognosis. According to the ubiquitous character of catecholamine sensitivity, therefore, we should think in terms of cellular ability to respond to catecholamines in defining the concept of physiological reserve.