Ileal mucosal oxygen consumption is decreased in endotoxemic rats but is restored toward normal by treatment with aminoguanidine

Pathophysiology, mechanisms, and managements of tissue hypoxia

Oxygen is needed to generate aerobic adenosine triphosphate and energy that is required to support vital cellular functions. Oxygen delivery (DO₂) to the tissues is determined by convective and diffusive processes. The ability of the body to adjust oxygen extraction (ERO₂) in response to changes in DO₂ is crucial to maintain constant tissue oxygen consumption (VO₂). The capability to increase ERO₂ is the result of the regulation of the circulation and the effects of the simultaneous activation of both central and local factors. The endothelium plays a crucial role in matching tissue oxygen supply to demand in situations of acute drop in tissue oxygenation. Tissue oxygenation is adequate when tissue oxygen demand is met. When DO₂ is severely compromised, a critical DO₂ value is reached below which VO₂ falls and becomes dependent on DO₂, resulting in tissue hypoxia. The different mechanisms of tissue hypoxia are circulatory, anaemic, and hypoxic, characterised by a diminished DO₂ but preserved capacity of increasing ERO₂. Cytopathic hypoxia is another mechanism of tissue hypoxia that is due to impairment in mitochondrial respiration that can be observed in septic conditions with normal overall DO₂. Sepsis induces microcirculatory alterations with decreased functional capillary density, increased number of stopped-flow capillaries, and marked heterogeneity between the areas with large intercapillary distance, resulting in impairment of the tissue to extract oxygen and to satisfy the increased tissue oxygen demand, leading to the development of tissue hypoxia. Different therapeutic approaches exist to increase DO₂ and improve microcirculation, such as fluid therapy, transfusion, vasopressors, inotropes, and vasodilators. However, the effects of these agents on microcirculation are quite variable.

Metabolic Resuscitation Strategies to Prevent Organ Dysfunction in Sepsis

Significance: Sepsis is the main cause of death among patients admitted to the intensive care unit. As current treatment is limited to antimicrobial therapy and supportive care, mortality remains high, which warrants efforts to find novel therapies. Recent Advances: Mitochondrial dysfunction is emerging as a key process in the induction of organ dysfunction during sepsis, and metabolic resuscitation might reveal to be a novel cornerstone in the treatment of sepsis. Critical Issues: Here, we review novel strategies to maintain organ function in sepsis by precluding mitochondrial dysfunction by lowering energetic demand to allow preservation of adenosine triphosphate-levels, while reducing free radical generation. As the most common strategy to suppress metabolism, that is, cooling, does not reveal unequivocal beneficial effects and may even increase mortality, caloric restriction or modulation of energy-sensing pathways (i.e., sirtuins and AMP-activated protein kinase) may offer safe alternatives. Similar effects may be offered when mimicking hibernation by hydrogen sulfide (H₂S). In addition H₂S may also confer beneficial effects through upregulation of antioxidant mechanisms, similar to the other gasotransmitters nitric oxide and carbon monoxide, which display antioxidant and anti-inflammatory effects in sepsis. In addition, oxidative stress may be averted by systemic or mitochondria-targeted antioxidants, of which a wide range are able to lower inflammation, as well as reduce organ dysfunction and mortality from sepsis. Future Directions: Mitochondrial dysfunction plays a key role in the pathophysiology of sepsis. As a consequence, metabolic resuscitation might reveal to be a novel cornerstone in the treatment of sepsis.

Time-related changes in hepatic and colonic mitochondrial oxygen consumption after abdominal infection in rats

Background

Evidence suggests that early adaptive responses of hepatic mitochondria occur in experimentally induced sepsis. Little is known about both colonic mitochondrial function during abdominal infection and long-term changes in mitochondrial function under inflammatory conditions. We hypothesize that hepatic and colonic mitochondrial oxygen consumption changes time-dependently after sterile laparotomy and in the course of abdominal infection. The aim of the present study was to investigate the hepatic and colonic mitochondrial respiration after sterile laparotomy and abdominal infection over up to 96 h.

Methods

After approval of the local Animal Care and Use Committee, 95 Wistar rats were randomized into 8 groups (n = 11–12): 1–4 sham (laparotomy only) and 5–8 colon ascendens stent peritonitis (CASP). Healthy, unoperated animals served as controls (n = 9). The mitochondrial respiration in colon and liver homogenates was assessed 24, 48, 72, and 96 h after surgery. Mitochondrial oxygen consumption was determined using a Clark-type electrode. State 2 (oxygen consumption in the presence of the substrates for complexes I and II) and state 3 respiration (ADP dependent) were assessed. The respiratory control ratio (RCR state 3/state 2) and ADP/O ratio (ADP added/oxygen consumed) were calculated for both complexes. Data are presented as means ± SD, two-way ANOVA followed by Tukey’s post hoc test.

Results

Hepatic RCR was initially (after 24 h) elevated in both operated groups; after 48 h only, the septic group was elevated compared to controls. In CASP groups, the hepatic ADP/O ratio for complex I was elevated after 24 h (vs. controls) and after 48 h (vs. sham) but declined after 72 h (vs. controls). The ADP/O ratio for complex II stayed unchanged over the time period until 96 h.

The colonic RCR and ADP/O did not change over time after sham or CASP operation.

Conclusion

Hepatic, but not colonic, mitochondrial respiration is increased in the initial phase (until 48 h) and normalizes in the longer course of time (until 96 h) of abdominal infection.

Electronic supplementary material

The online version of this article (10.1186/s40635-018-0219-9) contains supplementary material, which is available to authorized users.

Role of Oxidative Stress and Mitochondrial Dysfunction in Sepsis and Potential Therapies

Sepsis is one of the most important causes of death in intensive care units. Despite the fact that sepsis pathogenesis remains obscure, there is increasing evidence that oxidants and antioxidants play a key role. The imbalance of the abovementioned substances in favor of oxidants is called oxidative stress, and it contributes to sepsis process. The most important consequences are vascular permeability impairment, decreased cardiac performance, and mitochondrial malfunction leading to impaired respiration. Nitric oxide is perhaps the most important and well-studied oxidant. Selenium, vitamin C, and 3N-acetylcysteine among others are potential therapies for the restoration of redox balance in sepsis. Results from recent studies are promising, but there is a need for more human studies in a clinical setting for safety and efficiency evaluation.

The Glyoxalase System and Methylglyoxal-Derived Carbonyl Stress in Sepsis: Glycotoxic Aspects of Sepsis Pathophysiology

Sepsis remains one of the leading causes of death in intensive care units. Although sepsis is caused by a viral, fungal or bacterial infection, it is the dysregulated generalized host response that ultimately leads to severe dysfunction of multiple organs and death. The concomitant profound metabolic changes are characterized by hyperglycemia, insulin resistance, and profound transformations of the intracellular energy supply in both peripheral and immune cells. A further hallmark of the early phases of sepsis is a massive formation of reactive oxygen (ROS; e.g., superoxide) as well as nitrogen (RNS; e.g., nitric oxide) species. Reactive carbonyl species (RCS) form a third crucial group of highly reactive metabolites, which until today have been not the focus of interest in sepsis. However, we previously showed in a prospective observational clinical trial that patients suffering from septic shock are characterized by significant methylglyoxal (MG)-derived carbonyl stress, with the glyoxalase system being downregulated in peripheral blood mononuclear cells. In this review, we give a detailed insight into the current state of research regarding the metabolic changes that entail an increased MG-production in septicemia. Thus, we point out the special role of the glyoxalase system in the context of sepsis.

Cytochrome C in Patients with Septic Shock

PURPOSE

Cytochrome c is an essential component of the electron transport chain, and circulating cytochrome c might be an indicator of mitochondrial injury. The objective of this study was to determine whether cytochrome c levels are elevated in septic patients, whether there is an association between cytochrome c levels and lactate/inflammatory markers, and whether elevated levels of cytochrome c are associated with poor outcomes.

METHODS

This was a single-center, prospective, observational, pilot study within a randomized, placebo-controlled trial. We enrolled adult patients in septic shock and with an elevated lactate (>3 mmol/L). Blood was collected at enrollment and at 12 and 24  h thereafter. Cytochrome c was measured in plasma using an electrochemiluminescence immunoassay.

RESULTS

We included 77 patients. Plasma cytochrome c levels were significantly higher in septic patients than in healthy controls (0.70  ng/mL [quartiles: 0.06, 1.99] vs. 0.19  ng/mL [quartiles: 0.03, 1.32], P = 0.008). Cytochrome c levels at enrollment were positively correlated with lactate levels (r(s) = 0.40, P < 0.001) but not with inflammatory markers. Patients who died before hospital discharge had significantly higher cytochrome c levels than survivors (0.99  ng/mL [quartiles: 0.36, 4.09] vs. 0.58  ng/mL [quartiles: 0.03, 1.64], P = 0.01). When analyzed over time, the difference between survivors and nonsurvivors remained significant (P < 0.001).

CONCLUSIONS

Cytochrome c levels are higher in septic patients than in controls. In unadjusted analysis, septic nonsurvivors had higher cytochrome c levels than survivors.

Critical Care Medicine: Major Changes in Dogma of the Past Decade

Critical care medicine is a young specialty that has experienced an expansion of research efforts in the last decade. Many physiologic and therapeutic principles or “dogmas” have been challenged, resulting in major “shifts” and minor “drifts” in thinking. This article reviews the available literature about some of these important and sometimes controversial changes, with emphasis on the practical implications of the concepts. Specific areas discussed include supply-dependent oxygen consumption in critical illness, manipulation of the cytokine cascade in sepsis, ventilation in the acute respiratory distress syndrome (ARDS), blood transfusion in the critically ill, the concept of the multiple organ dysfunction syndrome (MODS), the need for nutritional support in the critically ill, and others. Many of the changes discussed involve the recognition that the host response to a severe insult is exceedingly complex, and the understanding of this response and the effects of it at a tissue and cellular level are incomplete. As a result, the ability to impact the outcome of sepsis and MODS has thus far been disappointing, with the possible exception of “lung-protective” ventilation. The final challenge in critical care medicine is to gain information that will allow the practitioner to better understand, prevent, and treat the complex events that result in organ and cellular dysfunction. Future changes in dogma are welcome if they help achieve these goals.

Decreased glutamate, glutamine and citrulline concentrations in plasma and muscle in endotoxemia cannot be reversed by glutamate or glutamine supplementation: a primary intestinal defect?

Endotoxemia affects intestinal physiology. A decrease of circulating citrulline concentration is considered as a reflection of the intestinal function. Citrulline can be produced in enterocytes notably from glutamate and glutamine. The aim of this work was to determine if glutamate, glutamine and citrulline concentrations in blood, intestine and muscle are decreased by endotoxemia, and if supplementation with glutamate or glutamine can restore normal concentrations. We induced endotoxemia in rats by an intraperitoneal injection of 0.3 mg kg(-1) lipopolysaccharide (LPS). This led to a rapid anorexia, negative nitrogen balance and a transient increase of the circulating level of IL-6 and TNF-α. When compared with the values measured in pair fed (PF) animals, almost all circulating amino acids (AA) including citrulline decreased, suggesting a decrease of intestinal function. However, at D2 after LPS injection, most circulating AA concentrations were closed to the values recorded in the PF group. At that time, among AA, only glutamate, glutamine and citrulline were decreased in gastrocnemius muscle without change in intestinal mucosa. A supplementation with 4% monosodium glutamate (MSG) or an isomolar amount of glutamine failed to restore glutamate, glutamine and citrulline concentrations in plasma and muscle. However, MSG supplementation led to an accumulation of glutamate in the intestinal mucosa. In conclusion, endotoxemia rapidly but transiently decreased the circulating concentrations of almost all AA and more durably of glutamate, glutamine and citrulline in muscle. Supplementation with glutamate or glutamine failed to restore glutamate, glutamine and citrulline concentrations in plasma and muscles. The implication of a loss of the intestinal capacity for AA absorption and/or metabolism in endotoxemia (as judged from decreased citrulline plasma concentration) for explaining such results are discussed.

Bench-to-bedside review: sepsis - from the redox point of view

The pathogenesis of sepsis and its progression to multiple organ dysfunction syndrome and septic shock have been the subject of investigations for nearly half a century. Controversies still exist with regard to understanding the molecular pathophysiology of sepsis in relation to the complex roles played by reactive oxygen species, nitric oxide, complements and cytokines. In the present review we categorise the key turning points in sepsis development and outline the most probable sequence of events leading to cellular dysfunction and organ failure under septic conditions. We have applied an integrative approach in order to fuse current state-of-the-art knowledge about redox processes involving hydrogen peroxide, nitric oxide, superoxide, peroxynitrite and hydroxyl radical, which lead to mitochondrial respiratory dysfunction. Finally, from this point of view, the potential of redox therapy targeting sepsis is discussed.

Mitochondrial function and dysfunction in sepsis

Mitochondria are the key source of cellular ATP and their structure and function are markedly affected by pathophysiologic processes associated with the host's response to invading pathogens. In particular, the highly reactive compound peroxynitrite, generated by the reaction of nitric oxide and superoxide anions, inhibits mitochondrial enzymes and damages lipids, proteins, and nucleic acids. Enhanced oxidative stress induces DNA strand breaks that are repaired by activation of poly(ADP-ribose)polymerase (PARP). This process consumes large amounts of nicotinamide adenine dinucleotide (NAD(+)) leading to cellular NAD(+) depletion that impairs flux of reducing equivalents into the respiratory chain and also further promotes inflammation. In experimental studies, novel therapeutic strategies that aim to ameliorate the host's pathogen response or to modulate intracellular signaling events related to oxidative stress protected mitochondrial function and preserved cellular respiration ultimately leading to improved organ function.

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

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

OPTICAL SPECTROSCOPY DEMONSTRATES ELEVATED INTRACELLULAR OXYGENATION IN AN ENDOTOXIC MODEL OF SEPSIS IN THE PERFUSED HEART

Recent clinical studies of patients with sepsis have shown that the delivery of adequate oxygen alone does not necessarily result in improved organ function or survival. This study was undertaken to determine if optical spectroscopy could detect higher intracellular oxygenations in isolated, perfused guinea pig hearts that have been treated with endotoxin (lipopolysaccharide [LPS]) than in controls. Four hours after intraperitoneal injection with LPS, adult guinea pigs were anesthetized, and hearts were excised and perfused in the Langendorff manner. Six control and eight LPS-exposed guinea pigs were studied. Myoglobin oxygen saturation was determined from analysis of optical reflectance spectra acquired from the left ventricular free wall. Myoglobin saturation was significantly higher at baseline with LPS than in controls (96.0% +/- 0.8% vs. 89.4% +/- 1.7%, P < 0.001). At the end of 30 s of ischemia, myoglobin saturation decreased to 15% +/- 1% in controls, but to only 60% +/- 7% in the LPS group. Myocardial performance was determined by measured left ventricular developed pressure, which was significantly depressed in the LPS-exposed hearts relative to controls (30 +/- 4 mmHg vs. 67 +/- 9 mmHg, P < 0.001). Myocardial oxygen consumption, calculated from measurements of arterial and venous PO2 and coronary flow, was lower in LPS hearts relative to controls (0.199 +/- 0.021 mL oxygen x min(-1) x g(-1) vs. 0.157 +/- 0.006 mL oxygen x min(-1) x g(-1)). In this model of sepsis in the perfused guinea pig heart, intracellular oxygenation was higher and oxygen consumption was lower than in controls. Cellular dysfunction seen in sepsis may be caused by compromised oxygen use rather than insufficient oxygen delivery. Optical spectroscopy has the potential to noninvasively monitor patients and their responses to therapy.

The effect of iNOS deletion on hepatic gluconeogenesis in hyperdynamic murine septic shock

OBJECTIVE

To investigate the role of the inducible nitric oxide synthase activation-induced excess nitric oxide formation on the rate of hepatic glucose production during fully resuscitated murine septic shock.

DESIGN

Prospective, controlled, randomized animal study.

SETTING

University animal research laboratory.

SUBJECTS

Male C57Bl/6 and B6.129P2-Nos2(tm1Lau)/J (iNOS-/-) mice.

INTERVENTIONS

Fifteen hours after cecal ligation and puncture, anesthetized, mechanically ventilated and instrumented mice (wild-type controls, n = 13; iNOS-/-, n = 12; wild-type mice receiving 5 mg.kg(-1) i.p. of the selective iNOS inhibitor GW274150 immediately after cecal ligation and puncture, n =8) received continuous i.v. hydroxyethylstarch and norepinephrine to achieve normotensive and hyperdynamic hemodynamics.

MEASUREMENTS AND RESULTS

Measurements were recorded 18, 21 and 24 h after cecal ligation and puncture. Liver microcirculatory perfusion and capillary hemoglobin O2 saturation (laser Doppler flowmetry and remission spectrophotometry) were well maintained in all groups. Despite significantly lower norepinephrine doses required to achieve the hemodynamic targets, the rate of hepatic glucose production (gas chromatography--mass spectrometry measurements of tissue isotope enrichment during continuous i.v. 1,2,3,4,5,6-13C6-glucose infusion) at 24 h after cecal ligation and puncture was significantly higher in both iNOS-/- and GW274150-treated mice, which was concomitant with a significantly higher hepatic phosphoenolpyruvate carboxykinase activity (spectrophotometry) in these animals.

CONCLUSIONS

In normotensive, hyperdynamic septic shock, both pharmacologic and genetic deletion of the inducible nitric oxide synthase allowed maintenance of hepatic glucose production, most likely due to maintained activity of the key regulatory enzyme of gluconeogenesis, phosphoenolpyruvate carboxykinase.

Prostacyclin in sepsis: A systematic review

According to current literature, infective processes greatly modify both vascular hemodynamics and anti-oxidant properties of affected tissues, causing a change in homeostasis that regulates the correct functioning of all cells responsible for the physiological and metabolic balance of various organs. As a consequence, the response to the infection that has caused the change is also likely to be weaker and, in the case of septic shock, ineffective. In this review, we will take into consideration these mechanisms and then focus on a group of vasodilator drugs (prostacyclin and its analogs) which, though have been used for over 20 years mainly to treat obstructive vascular diseases, have such hemodynamic and anti-inflammatory properties which prevent homeostatic changes. It is obvious that prostacyclin does not definitively have anti-infective characteristics; however, in association with anti-infective drugs (antibiotics, etc.), the effectiveness of the latter appears improved, at least in some circumstances. Similarly, the fact that prostacyclin and its analogs have a cytoprotective effect on the liver and reduce the ischemia-reperfusion damage following liver transplant is not a novelty and evidence that they improve hepatic hemodynamics suggests their use in those pathologies characterized by possible reduced perfusion or ascertained ischemia of the liver.

Bench-to-bedside review: potential strategies to protect or reverse mitochondrial dysfunction in sepsis-induced organ failure

The pathogenesis of sepsis-induced multiple organ failure may crucially depend on the development of mitochondrial dysfunction and consequent cellular energetic failure. According to this hypothesis, interventions aimed at preventing or reversing mitochondrial damage may have major clinical relevance, although the timing of such interventions will be critical to both ensuring benefit and avoiding harm. Early correction of tissue hypoxia, strict control of glycaemia, and modulation of oxidative and nitrosative stress may afford protection during the initial, acute systemic inflammatory response. The regulated induction of a hypometabolic state resembling hibernation may protect the cells from dying once energy failure has developed, allowing the possibility of functional recovery. Repair of damaged organelles through stimulation of mitochondrial biogenesis and reactivation of cellular metabolism may accelerate resolution of the multiple organ failure syndrome.

Cytokine signalling in rat pulp interstitial fluid and transcapillary fluid exchange during lipopolysaccharide-induced acute inflammation

The dental pulp consists of loose connective tissue encased in rigid dentinal walls. Because of its topography the tissue has low interstitial compliance and limited capacity to expand during fluid volume changes. Due to limitations regarding access to interstitial fluid, basic knowledge on transcapillary fluid transport parameters is lacking for this organ. The scope of this project was dual: first we aimed at establishing a method for isolation of pulp interstitial fluid (IF), and second we applied the method in rats subjected to lipopolysaccharide (LPS)-induced endotoxaemia. The aim was to measure colloid osmotic pressure (COP) and pro-inflammatory cytokines in the pulp IF during acute inflammation. Fluid volumes and pulpal blood flow (PBF) were measured to obtain more information about microcirculatory changes that take place in this pulpitis model. By centrifugation of incisor pulp at 239 g we were able to extract fluid representative for IF. Pulp IF had a relative high control COP (approximately 83% of plasma COP) and was similar to plasma COP 3 h after LPS challenge. The pulp exhibited a high content of IF (0.60 +/- 0.03 ml (g wet weight)(-1)) and a vascular volume of 0.03 +/- 0.01 ml (g w.w.)(-1) No differences were observed in the distribution of fluid volumes after 1.5 and 3 h LPS exposure. PBF and systemic blood pressure dropped significantly after LPS administration. PBF remained low whereas systemic blood pressure was re-established during the 3-h period, implying organ dysfunction. There was a differential pattern of cytokine expression in pulp IF and serum with cytokines such as IL-1alpha, IL-1beta and TNF-alpha locally produced, whereas others such as IFN-gamma and IL-6 were produced systemically and probably spilled over to the pulp IF after LPS exposure. Our findings show that pulp IF can be isolated by centrifugation and that this method is useful when studying fluid balance and extracellular signalling mechanisms in the dental pulp in normal and pathological conditions.

Tissue oxygen and hemodynamics in renal medulla, cortex, and corticomedullary junction during hemorrhage-reperfusion

Previous studies of intrarenal perfusion and tissue oxygenation have produced a wide range of results and have not matched tissue oxygen tension (tPo(2)) with concurrent changes in flow in three distinct regions. We thus used an anesthetized rat model of hemorrhage-reperfusion to address this question. Combined tpo(2)/laser-Doppler fiber-optic probes were simultaneously sited in cortical, corticomedullary (CMJ), and medullary regions of the left kidney. Total renal blood flow was measured in separate experiments. Recordings were made during exsanguination of 10 and 20% of estimated blood volume at 10-min intervals, followed by shed-blood resuscitation after a further 10 min. The decay in tpo(2) was then recorded following total cessation of blood flow, allowing estimation of local oxygen consumption. During exsanguination, tPo(2) was maintained in all intrarenal regions, despite significant falls in blood pressure and total renal blood flow. However, intrarenal flow was redistributed with reduced cortical, unchanged CMJ, and increased medullary blood flow. After resuscitation, significant rises above baseline were seen in blood pressure and in tpo(2) across all regions. Whereas cortical and medullary flows regained baseline values, CMJ flow fell. The ratio of tpo(2) to microvascular blood flow increased significantly in all regions during resuscitation, suggesting decreased oxygen consumption. On total cessation of blood flow, the cortex and CMJ showed significant increases in the oxygen decay half-life, consistent with decreased consumption. To our knowledge, this is the first quantitative demonstration of a markedly heterogeneous intrarenal cardiorespiratory response to a hemodynamic insult, with effects most marked at the corticomedullary junction.

Sublingual capnometry tracks microcirculatory changes in septic patients

OBJECTIVE

To test the hypothesis that microcirculatory blood flow is the main determinant of sublingual carbon dioxide pressure in patients with septic shock.

DESIGN

Prospective, open-label study.

SETTING

A 31-bed medico-surgical department of intensive care.

PATIENTS

Eighteen consecutive mechanically ventilated patients with septic shock.

INTERVENTIONS

A 5 microg/kg x min dobutamine infusion was used to increase blood flow.

METHODS

Sublingual carbon dioxide pressure was monitored using a microelectrode sensor, and sublingual microcirculation was assessed using orthogonal polarization spectral imaging. The sublingual carbon dioxide pressure gap was calculated as the difference between sublingual and arterial carbon dioxide pressures. In each patient, a nasogastric tonometry catheter was inserted for gastric mucosal carbon dioxide pressure measurement. The gastric carbon dioxide pressure gap was calculated as the difference between gastric mucosal and arterial carbon dioxide pressures.

MEASUREMENTS AND RESULTS

Dobutamine infusion was associated with increases cardiac index and mixed venous blood oxygen saturation. Dobutamine infusion resulted in decreases in sublingual carbon dioxide pressure gap from 40+/-15 to 17+/-8 mmHg (p<0.01). There was a significant correlation between sublingual and gastric mucosal carbon dioxide pressures (r 2=0.61, p<0.05). At baseline, sublingual carbon dioxide pressure gap correlated with the proportion of well-perfused capillaries (r 2=0.80). The decrease in sublingual carbon dioxide pressure gap paralleled the increase in the proportion of well-perfused capillaries in each patient.

CONCLUSIONS

Regional microcirculatory blood flow is the main determinant of sublingual carbon dioxide pressure. Sublingual capnometry could represent a simple, non-invasive method to monitor these microcirculatory alterations in septic patients.

Nitric oxide synthase inhibition in sepsis? Lessons learned from large-animal studies

Nitric Oxide (NO) plays a controversial role in the pathophysiology of sepsis and septic shock. Its vasodilatory effects are well known, but it also has pro- and antiinflammatory properties, assumes crucial importance in antimicrobial host defense, may act as an oxidant as well as an antioxidant, and is said to be a "vital poison" for the immune and inflammatory network. Large amounts of NO and peroxynitrite are responsible for hypotension, vasoplegia, cellular suffocation, apoptosis, lactic acidosis, and ultimately multiorgan failure. Therefore, NO synthase (NOS) inhibitors were developed to reverse the deleterious effects of NO. Studies using these compounds have not met with uniform success however, and a trial using the nonselective NOS inhibitor N(G)-methyl-l-arginine hydrochloride was terminated prematurely because of increased mortality in the treatment arm despite improved shock resolution. Thus, the issue of NOS inhibition in sepsis remains a matter of debate. Several publications have emphasized the differences concerning clinical applicability of data obtained from unresuscitated, hypodynamic rodent models using a pretreatment approach versus resuscitated, hyperdynamic models in high-order species using posttreatment approaches. Therefore, the present review focuses on clinically relevant large-animal studies of endotoxin or living bacteria-induced, hyperdynamic models of sepsis that integrate standard day-to-day care resuscitative measures.

Inducible nitric oxide synthase inhibition improves intestinal microcirculatory oxygenation and CO2 balance during endotoxemia in pigs

OBJECTIVE

We examined whether selective inhibition of inducible nitric oxide synthase (iNOS) promotes intestinal microvascular oxygenation (microPO2) and CO2 off-load after endotoxic shock.

DESIGN AND SETTING

Prospective, controlled experimental study in a university animal research laboratory.

SUBJECTS

13 domestic pigs.

INTERVENTIONS

After baseline measurements shock was induced by 1 microg kg-1 h-1 endotoxin until mean arterial pressure fell below 60 mmHg. After 30 min in shock the animals were resuscitated with either fluid alone (control, n=6) or fluid and the iNOS inhibitor N-[3-(aminomethyl)benzyl]acetamidine hydrochloride (1400W, n=7). As final experimental intervention all animals received the nonselective NOS inhibitor L-NAME.

MEASUREMENTS AND RESULTS

Systemic and regional hemodynamic and oxygenation parameters were measured at baseline, during endotoxemia and shock, hourly for 3 h of 1400W therapy, and 30 min after the final L-NAME administration. microPO2 was assessed by the Pd-porphyrin phosphorescence technique, and the arterial to intestinal PCO2 gap was determined by air tonometry. Endotoxemia and shock resulted in a decrease in ileal mucosal and serosal microPO2 and a rise in PCO2 gap. The combination of 1400W and fluid resuscitation, but not fluid alone, normalized both the serosal microPO2 and the intestinal PCO2 gap. Administration of L-NAME decreased cardiac output and oxygen delivery and intestinal microPO2 and blood flow in both groups.

CONCLUSIONS

Partial blockade of NO production by 1400W increased serosal microvascular oxygenation and decreased the intestinal CO2 gap. This findings are consistent with the idea that 1400W corrects pathological flow distribution and regional dysoxia within the intestinal wall following endotoxic shock.

How monitoring of the microcirculation may help us at the bedside

PURPOSE OF REVIEW

Recent technologic developments have allowed the direct visualization of the microcirculation at the bedside. The present review explores how the monitoring of microcirculation can help in clinical practice.

RECENT FINDINGS

Using orthogonal polarization spectral (OPS) imaging techniques, various investigators have reported microcirculatory alterations in critically ill patients and especially in patients with severe sepsis and septic shock. These alterations include a decrease in vessel density and an increased proportion of nonperfused or intermittently perfused capillaries. The persistence of these alterations is associated with the development of organ failure and death. Several therapeutic interventions, including vasoactive agents, fluid resuscitation, and activated protein C, can affect the microcirculation. Vasoactive agents have variable effects but vasodilatory agents seem very promising. Unfortunately, although many animal studies have investigated the effects of many of these interventions, human data are limited.

SUMMARY

Microcirculation plays an important role in the pathogenesis of shock and organ dysfunction, especially in sepsis. Monitoring microcirculation at the bedside may be used to assess severity of the disease and to predict outcome, but in the absence of sufficient data regarding the effects of therapeutic interventions it cannot yet be used to guide therapy, even though this approach is promising.

EFFECTS OF DOPAMINE AND NOREPINEPHRINE ON SYSTEMIC AND HEPATOSPLANCHNIC HEMODYNAMICS, OXYGEN EXCHANGE, AND ENERGY BALANCE IN VASOPLEGIC SEPTIC PATIENTS

Dopamine is widely used to improve systemic and hepatosplanchnic hemodynamics and oxygenation during sepsis. However, some studies have suggest that norepinephrine may have beneficial effects on regional blood flow and metabolism, whereas dopamine might have deleterious effects related to redistribution of blood flow away from the intestinal mucosa or by decreasing directly the cell redox state. In 12 vasoplegic septic patients, we compared the effects of norepinephrine and dopamine on systemic and hepatosplanchnic hemodynamics, oxygenation, and energy metabolism. Catecholamines were administered in a crossover randomized order to maintain mean arterial pressure (MAP) at 80 mmHg. Hepatosplanchnic blood flow (Qspl) was determined using a continuous infusion of indocyanine green dye. Despite a similar MAP, the cardiac index was higher with dopamine than with norepinephrine (6.3 [5.3-7.3] vs. 4.3 [3.8-4.9] L.min.m) (P <0.001). Qspl was similar with both catecholamines, but the ratio of Qspl to cardiac output was significantly lower with dopamine (23.9% [17.5-33.5]) than with norepinephrine (33.5% [25.8-37]) (P <0.05). Although global O2 delivery and O2 consumption were higher with dopamine (782 [707-859] vs. 553 [512-629] mL.min.m, P <0.001 and 164 [134-192] vs. 128 [111-149] mL.min.m, P <0.001, respectively), hepatosplanchnic O2 delivery and consumption were not different. Hepatic lactate uptake was lower (0.47 [0.3-0.89] vs. 1.01 [0.69-1.34] mmol.min) (P <0.01), and hepatic venous lactate-to-pyruvate ratio was higher (15.3 [7.6-21.1] vs. 11.2 [6.6-15.1], P <0.05) with dopamine than with norepinephrine. In vasoplegic septic patients, maintaining mean arterial pressure, hepatosplanchnic hemodynamics, and oxygen exchange with dopamine requires a consequent increased cardiac output, which is responsible for an increased global oxygen demand when compared with norepinephrine. In addition, dopamine impairs the hepatic energy balance. Its position as a preferential treatment compared with norepinephrine in this context may therefore be questionable.

Multiorgan failure is an adaptive, endocrine-mediated, metabolic response to overwhelming systemic inflammation

Sepsis and other critical illnesses produce a biphasic inflammatory, immune, hormonal, and metabolic response. The acute phase is marked by an abrupt rise in the secretion of so-called stress hormones with an associated increase in mitochondrial and metabolic activity. The combination of severe inflammation and secondary changes in endocrine profile diminish energy production, metabolic rate, and normal cellular processes, leading to multiple organ dysfunction. This perceived failure of organs might instead be a potentially protective mechanism, because reduced cellular metabolism could increase the chances of survival of cells, and thus organs, in the face of an overwhelming insult. We propose that, first, multiple organ failure induced by critical illness is primarily a functional, rather than structural, abnormality. Indeed, it may not be failure as such, but a potentially protective, reactive mechanism. Second, the decline in organ function is triggered by a decrease in mitochondrial activity and oxidative phosphorylation, leading to reduced cellular metabolism. Third, this effect on mitochondria might be the consequence of acute-phase changes in hormones and inflammatory mediators.

Research: advances in cell biology relevant to critical illness

During the past decade, enormous advances have been made in cell biology. Major advances included the publication of the human genome sequence, the development of proteomics, and DNA microarray technologies and techniques to selectively "silence" genes using short strands of double-stranded RNA. Some areas of great progress that are particularly relevant to critical care medicine include huge improvements in our understanding of the signal transduction pathways involved in the innate immune response and adaptation to hypoxia. Other areas of important progress include improvements in our understanding of how inflammation causes derangements in epithelial structure and function and impairs cellular utilization of oxygen.

SELECTIVE INDUCIBLE NITRIC OXIDE SYNTHASE INHIBITION DURING LONG-TERM HYPERDYNAMIC PORCINE BACTEREMIA

We have recently demonstrated that selective inducible nitric oxide (NO) synthase (iNOS) inhibition with 1400W attenuated the hemodynamic and metabolic alterations affiliated with hyperdynamic porcine endotoxemia. In contrast to endotoxemia, limited evidence is available to document a relationship between NO and organ dysfunction in large animal bacteremic models. Therefore, using the same experimental setup, we investigated the role of selective iNOS blockade in porcine bacteremia induced and maintained for 24 h with a continuous infusion of live Pseudomonas aeruginosa. After 12 h of sepsis, animals received either vehicle (Control, n = 8) or continuous infusion of selective iNOS inhibitor, L-N6-(1-iminoethyl)-lysine (L-NIL; n = 8). Measurements were performed before, and 12, 18, and 24 h after P. aeruginosa infusion. L-NIL inhibited sepsis-induced increase in plasma nitrate/nitrite concentrations and prevented hypotension without affecting cardiac output. Despite comparable hepatosplanchnic macrocirculation, L-NIL blunted the progressive deterioration in ileal mucosal microcirculation and prevented mucosal acidosis. L-NIL largely attenuated mesenteric and hepatic venous acidosis, significantly improved P. aeruginosa-induced impairment of hepatosplanchnic redox state, and mitigated the decline in liver lactate clearance. Furthermore, the administration of L-NIL reduced the hepatocellular injury and prevented the development of renal dysfunction. Finally, treatment with L-NIL significantly attenuated the formation of 8-isoprostane concentrations, a direct marker of lipid peroxidation. Thus, selective iNOS inhibition with L-NIL prevented live bacteria from causing key features of metabolic derangements in porcine hyperdynamic sepsis. Underlying mechanisms probably include reduced oxidative stress with improved microcirculatory perfusion and restoration of cellular respiration.

Effect of combining nicotinamide as a PARS-inhibitor with selective iNOS blockade during porcine endotoxemia

OBJECTIVE

To investigate the effects of combined selective inducible nitric oxide synthase (iNOS) inhibition using 1400 W with nicotinamide (NAD) as a PARS-inhibitor on hepato-splanchnic hemodynamics, O(2) kinetics, and energy metabolism during hyperdynamic porcine endotoxemia.

DESIGN

Prospective, randomized, controlled, interventional experiment.

SETTING

Animal research laboratory.

SUBJECTS

Seventeen domestic pigs.

INTERVENTIONS

After 12 h of continuous i.v. endotoxin (LPS) infusion 17 pigs received either no drug (CON, n=9) or 1400 W, titrated to maintain mean arterial pressure (MAP) at pre-endotoxin level, plus 10 mg.kg.h NAD ( n=8;). Measurements were obtained before, 12 h, 18 h, and 24 h after starting LPS infusion.

MEASUREMENTS AND RESULTS

In addition to systemic and pulmonary hemodynamics and gas exchange, we measured hepatic arterial and portal venous blood flow, liver and portal venous drained viscera O(2) exchange, ileal mucosal-arterial PCO(2) gap, and portal as well as hepatic venous lactate/pyruvate ratios. Expired NO and plasma nitrate levels were assessed as a parameter of NO production. Without affecting cardiac output, therapy maintained MAP and blunted the LPS-induced rise in expired NO levels, attenuated the progressive fall in liver lactate clearance, and blunted the impairment of hepato-splanchnic redox state. The rise of ileal mucosal-arterial PCO(2) gap was not influenced.

CONCLUSIONS

Combining selective iNOS inhibition with NAD as a PARS blocker may prevent circulatory failure and attenuate the detrimental consequences of LPS in intestinal and hepatocellular energy metabolism. Given the potential hepatotoxicity of high-dose NAD treatment, more potent PARS blockers with higher selectivity might further enhance the benefit of this therapeutic approach.

Effects of dopamine, norepinephrine, and epinephrine on the splanchnic circulation in septic shock: which is best?

OBJECTIVE

To assess the effects of different doses of dopamine, norepinephrine, and epinephrine on the splanchnic circulation in patients with septic shock.

DESIGN

Prospective, randomized, open-label study.

SETTING

A 31-bed, medicosurgical intensive care unit of a university hospital.

PATIENTS

Convenience sample of 20 patients with septic shock, separated into two groups according to whether (moderate shock group, n = 10) or not (severe shock, n = 10) dopamine alone was able maintain mean arterial pressure >65 mm Hg.

INTERVENTIONS

Dopamine was progressively withdrawn and replaced successively by norepinephrine and then epinephrine (the order of the two agents was randomly determined) to maintain mean arterial pressure constant (moderate shock) or to increase mean arterial pressure above 65 mm Hg (severe shock).

MEASUREMENTS AND MAIN RESULTS

Systemic circulation (pulmonary artery catheter) and splanchnic circulation (indocyanine green dilution and hepatic vein catheter) and gastric mucosal Pco(2) (gas tonometry) were measured during dopamine (moderate shock only), norepinephrine, and epinephrine administration (both groups). Data were analyzed with nonparametric tests and are presented as median [percentiles 25-75]. In moderate shock, cardiac index was similar to dopamine and norepinephrine (3.1 [2.7-3.8] vs. 2.9 [2.7-4.1] L/min.m2, p = nonsignificant) but greater with epinephrine (4.1 [3.5-4.4] p <.01 vs. dopamine and norepinephrine). Splanchnic blood flow was similar with the three agents (732 [413-1483] vs. 746 [470-1401] vs. 653 [476-1832] mL/min.m, p = nonsignificant). The gradient between mixed-venous and hepatic venous oxygen saturations was lower with dopamine than with norepinephrine and epinephrine, but the Pco(2) gap was similar with the three agents. In severe shock, cardiac index was higher, but splanchnic blood flow was lower, with epinephrine than with norepinephrine (4.6 [3.7-5.3] vs. 3.4 [3.0-4.1] L/min.m2, p <.01 and 860 [684-1334] vs. 977 [806-1802] mL/min.m2, p <.05, respectively). Epinephrine increased the mixed-venous and hepatic venous oxygen saturation gradient but did not alter Pco(2) gap.

CONCLUSIONS

Dopamine and norepinephrine have similar hemodynamic effects, but epinephrine can impair splanchnic circulation in severe septic shock.

Relationships of circulating nitrite/nitrate levels to severity and multiple organ dysfunction syndrome in systemic inflammatory response syndrome

Excessive nitric oxide (NO) production has been implicated to be responsible for the development of septic shock. To determine whether plasma nitrite/nitrate (NOx) levels are related to the severity of systemic inflammatory response syndrome (SIRS) and the degree of multiple organ dysfunction, we studied plasma NOx levels in 70 patients with SIRS consisting of noninfectious SIRS (n = 32), sepsis (n = 23), and septic shock (n = 15). Infection is a microbial phenomenon characterized by an inflammatory response to the presence of microorganism. Positive culture for microorganism is regarded as infectious SIRS (sepsis and septic shock) and negative culture is regarded as noninfectious SIRS. Plasma samples collected from each patient within 24 h from admission to the intensive care unit were subjected for measurement of NOx levels, the stable end products of NO, by the high performance liquid chromatography-Greiss system. Mean plasma NOx levels in patients with SIRS were 52.8 +/- 44 microM/L, ranging from 8.1 to 186.2 microM/L. Plasma NOx levels were positively correlated with Acute Physiology, Age, and Chronic Health Evaluation (APACHE) III score (r = 0.414, P < 0.01) and sequential organ failure assessment (SOFA) score (r = 0.433, P < 0.01). Plasma NOx levels in patients with sepsis (51.0 +/- 38.5 microM/L) and septic shock (94.5 +/- 53.7 microM/L) were significantly (P < 0.01) higher than those in patients with noninfectious SIRS (25.8 +/- 16.9 microM/L) and healthy subjects (29.6 +/- 8.9 microM/L). Our study shows that plasma NOx levels are increased in patients with infectious, but not noninfectious SIRS, which increase as the severity of SIRS and the development of multiple organ dysfunction syndrome, suggesting its possible pathogenic role in SIRS.

Impaired mitochondrial function induced by serum from septic shock patients is attenuated by inhibition of nitric oxide synthase and poly(ADP-ribose) synthase

OBJECTIVE

The purpose of this study was to determine the role of nitric oxide and poly(ADP-ribose) synthase on impaired mitochondrial function in septic shock.

DESIGN

Human umbilical vein endothelial cells were incubated with serum from ten healthy controls, 20 patients with septic shock, and seven critically ill patients who were not septic. The experiment was repeated after pretreatment with 3-aminobenzamide, a poly(ADP-ribose) synthase inhibitor, or N(G)-methyl-L-arginine, a nonspecific nitric oxide synthase inhibitor.

MEASUREMENTS

Mitochondrial respiration was measured using a modified MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide) assay.

SETTING

Research laboratory.

MAIN RESULT

Endothelial cell mitochondrial respiration was significantly depressed by septic serum and averaged 61% +/- 6% of control values (p <.05). Incubation with septic serum as compared with control serum also significantly decreased cellular adenosine triphosphate levels (6.7 +/- 1.2 nM vs. 13.5 +/- 1.9 nM, p<.01). The level of mitochondrial respiration in endothelial cells exposed to septic serum did not correlate with arterial lactate concentration but was correlated with both cardiac output (r(s) =.52, p<.05) and mixed venous oxygen saturation (r(s) =.61, p<.05). Pretreatment with N(G)-methyl-L-arginine significantly increased mitochondrial respiration in endothelial cells treated with septic serum from 63% +/- 6% of normal to 88% +/- 6% (p <.05) of normal values. Similarly, pretreatment with 3-aminobenzamide increased mitochondrial respiration in endothelial cells treated with septic serum from 64% +/- 6% to 100% +/- 4% (p <.01) of normal values. Endothelial cells incubated with serum from nonseptic critically ill patients did not demonstrate a significant decrease in mitochondrial respiration.

CONCLUSION

In vitro mitochondrial respiration was significantly depressed by septic serum. The addition of N(G)-methyl-L-arginine, a nitric oxide synthase inhibitor, and 3-aminobenzamide, a blocker of the poly(ADP-ribose) synthase pathway, significantly attenuated this suppression. These data suggest that nitric oxide and poly(ADP-ribose) synthase activation may play an important role in the inhibition of mitochondrial respiration in septic shock.

Bench-to-bedside review: microvascular dysfunction in sepsis--hemodynamics, oxygen transport, and nitric oxide

The microcirculation is a complex and integrated system that supplies and distributes oxygen throughout the tissues. The red blood cell (RBC) facilitates convective oxygen transport via co-operative binding with hemoglobin. In the microcirculation oxygen diffuses from the RBC into neighboring tissues, where it is consumed by mitochondria. Evidence suggests that the RBC acts as deliverer of oxygen and 'sensor' of local oxygen gradients. Within vascular beds RBCs are distributed actively by arteriolar tone and passively by rheologic factors, including vessel geometry and RBC deformability. Microvascular oxygen transport is determined by microvascular geometry, hemodynamics, and RBC hemoglobin oxygen saturation. Sepsis causes abnormal microvascular oxygen transport as significant numbers of capillaries stop flowing and the microcirculation fails to compensate for decreased functional capillary density. The resulting maldistribution of RBC flow results in a mismatch of oxygen delivery with oxygen demand that affects both critical oxygen delivery and oxygen extraction ratio. Nitric oxide (NO) maintains microvascular homeostasis by regulating arteriolar tone, RBC deformability, leukocyte and platelet adhesion to endothelial cells, and blood volume. NO also regulates mitochondrial respiration. During sepsis, NO over-production mediates systemic hypotension and microvascular reactivity, and is seemingly protective of microvascular blood flow.

Bench-to-bedside review: Cytopathic hypoxia

The rate of oxygen consumption by certain tissues is impaired when mice or rats are injected with lipopolysaccharide. A similar change in the rate of oxygen consumption is observed when Caco-2 human enterocyte-like cells are incubated in vitro with cytomix, a cocktail of cytokines containing tumor necrosis factor, IL-1beta, and IFN-gamma. The decrease in the rate of oxygen consumption is not due to a change in oxygen delivery (e.g. on the basis of diminished microvascular perfusion), but rather to an acquired intrinsic defect in cellular respiration, a phenomenon that we have termed 'cytopathic hypoxia'. A number of different biochemical mechanisms have been postulated to account for cytopathic hypoxia in sepsis, including reversible inhibition of cytochrome a,a3 by nitric oxide, and irreversible inhibition of one or more mitochondrial respiratory complexes by peroxynitrite. Recently, however, our laboratory has obtained data to suggest that the most important mechanism underlying the development of cytopathic hypoxia is depletion of cellular stores of nicotinamide adenine dinucleotide (NAD+/NADH) as a result of activation of the enzyme, poly(ADP-ribose) polymerase-1. If cytopathic hypoxia is important in the pathophysiology of established sepsis and multiorgan dysfunction syndrome, then efforts in the future will need to focus on pharmacological interventions designed to preserve normal mitochondrial function and energy production in sepsis.

Microvascular blood flow is altered in patients with sepsis

Microvascular blood flow alterations are frequent in animal models of sepsis and may impair tissue oxygenation. We hypothesized that alterations of the microcirculation are present in patients with sepsis. We used an orthogonal polarization spectral imaging technique to investigate the sublingual microcirculation in 10 healthy volunteers, 16 patients before cardiac surgery, 10 acutely ill patients without sepsis (intensive care unit control subjects), and 50 patients with severe sepsis. The effects of topical application of acetylcholine (10(-2) M) were tested in 11 patients with sepsis. In each subject, five to seven sublingual areas were recorded and analyzed semiquantitatively. Data were analyzed with nonparametric tests and are presented as medians (25th-75th percentiles). No significant difference in microvascular blood flow was observed between healthy volunteers and patients before cardiac surgery or intensive care unit control subjects. The density of all vessels was significantly reduced in patients with severe sepsis (4.5 [4.2-5.2] versus 5.4 [5.4-6.3]/mm in volunteers, p < 0.01). The proportion of perfused small (< 20 microm) vessels was reduced in patients with sepsis (48 [33-61] versus 90 [89-92]% in volunteers, p < 0.001). These alterations were more severe in nonsurvivors. The topical application of acetylcholine totally reversed these alterations. In conclusion, microvascular blood flow alterations are frequent in patients with sepsis and are more severe in patients with a worse outcome.

Liposomal NAD(+) prevents diminished O(2) consumption by immunostimulated Caco-2 cells

Accumulating data support the view that sepsis is associated with an acquired intrinsic derangement in the ability of cells to consume O(2), a phenomenon that has been termed "cytopathic hypoxia." We sought to use an in vitro "reductionist" model system using cultured cells stimulated with proinflammatory cytokines to test the hypothesis that cytopathic hypoxia is mediated, at least in part, by depletion of intracellular levels of NAD(+)/NADH secondary to activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP). We measured O(2) consumption by Caco-2 enterocytes growing on microcarrier beads after cells were incubated for 24 h under control conditions or with cytomix, a mixture of tumor necrosis factor-alpha, interleukin-1beta, and interferon-gamma. Immunostimulated cells consumed O(2) at about one-half the rate of control cells, but this effect was largely prevented if any one of the following pharmacological agents was present during the period of incubation with cytomix: 4,5-dihydroxy-1,3-benzene disulfonic acid, a superoxide radical anion scavenger; 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, a nitric oxide scavenger; 5,10,15,20- tetrakis-[4-sulfonatophenyl]-porphyrinato-iron[III], a peroxynitrite (ONOO(-)) decomposition catalyst; urate, an ONOO(-) scavenger; 3-aminobenzamide, a PARP inhibitor; or N-(6-oxo-5,6-dihydrophenanthridin-2-yl)-N,N-dimethylacetamide HCl, a chemically dissimilar and more potent PARP inhibitor. The decrease in O(2) uptake induced by cytomix was associated with decreased cellular levels of NAD(+)/NADH. The decrease in cellular NAD(+)/NADH content and the decrease in O(2) uptake induced by cytomix were completely abrogated if liposome-encapsulated NAD(+) was added to the cultures during immunostimulation. Empty liposomes also increased O(2) uptake by immunostimulated Caco-2 cells, but much less effectively than liposomes containing NAD(+). These data are consistent with the view that enterocytes exposed to proinflammatory cytokines consume less O(2) due to NAD(+)/NADH depletion secondary to activation of PARP by ONOO(-) or other oxidants.

Cytopathic hypoxia. Is oxygen use impaired in sepsis as a result of an acquired intrinsic derangement in cellular respiration?

Several lines of evidence indicate that cellular energetics are deranged in sepsis, not by inadequate tissue perfusion but rather by impaired mitochondrial respiration; that is, organ dysfunction in sepsis may result from cytopathic hypoxia. If this concept is correct, the therapeutic implications are enormous. Efforts to improve outcome in septic patients by monitoring and manipulating cardiac output, systemic oxygen (DO2), and regional blood flow are doomed to failure. Instead, the focus should be on developing pharmacologic strategies (e.g., isoform-selective iNOS or PARP inhibitors) to restore normal mitochondrial function and cellular energetics.

Cytopathic hypoxia. Mitochondrial dysfunction as mechanism contributing to organ dysfunction in sepsis

Several lines of evidence support the notion that cellular energetics are deranged in sepsis, not on the basis of inadequate tissue perfusion, but rather on the basis of impaired mitochondrial respiration and/or coupling; that is, organ dysfunction in sepsis may occur on the basis of cytopathic hypoxia. If this concept is correct, then the therapeutic implications are enormous. Efforts to improve outcome in patients with sepsis by monitoring and manipulating cardiac output, systemic Do2, and regional blood flow are doomed to failure. Instead, the focus should be on developing pharmacologic strategies to restore normal mitochondrial function and cellular energetics.