Tissue hypoxanthine reflects gut vulnerability in porcine endotoxin shock

Metabolomic analysis for the protective effects of mangiferin on sepsis-induced lung injury in mice

This study aimed to investigate the efficacy of mangiferin, including its known antioxidant and anti-inflammatory effects on sepsis-induced lung injury induced by a classical cecal ligation and puncture (CLP) models in mouse using a metabolomics approach. A total of 24 mice were randomly divided into four groups: the sham group was given saline before sham operation. The CLP group received the CLP operation only. HMF and LMF groups were given mangiferin treatment of high dose and low dose of mangiferin, respectively, before the CLP operation. One week after treatment, the mice were sacrificed and their lungs were collected for metabolomics analysis. We developed ultra-performance liquid chromatography coupled with quadrupole-time-of-flight mass spectrometry to perform lung metabolic profiling analysis. With the methods of principal component analysis and partial least squares discriminant analysis, 58 potential metabolites associated with amino acid metabolism, purine metabolism, lipid metabolism and energy regulation were observed to be increased or reduced in HMF and LMF groups compared with the CLP group. Conclusively, our results suggest that mangiferin plays a protective role in the moderation of sepsis-induced lung injury through reducing oxidative stress, regulating lipid metabolism and energy biosynthesis.

HMGB1 redox during sepsis

During sepsis, the alarmin HMGB1 is released from tissues and promotes systemic inflammation that results in multi-organ damage, with the kidney particularly susceptible to injury. The severity of inflammation and pro-damage signaling mediated by HMGB1 appears to be dependent on the alarmin's redox state. Therefore, we examined HMGB1 redox in kidney cells during sepsis. Using intravital microscopy, CellROX labeling of kidneys in live mice indicated increased ROS generation in the kidney perivascular endothelium and tubules during lipopolysaccharide (LPS)-induced sepsis. Subsequent CellROX and MitoSOX labeling of LPS-stressed endothelial and kidney proximal tubule cells demonstrated increased ROS generation in these cells as sepsis worsens. Consequently, HMGB1 oxidation increased in the cytoplasm of kidney cells during its translocation from the nucleus to the circulation, with the degree of oxidation dependent on the severity of sepsis, as measured in in vivo mouse samples using a thiol assay and mass spectrometry (LC-MS/MS). The greater the oxidation of HMGB1, the greater the ability of the alarmin to stimulate pro-inflammatory cyto-/chemokine release (measured by Luminex Multiplex) and alter mitochondrial ATP generation (Luminescent ATP Detection Assay). Administration of glutathione and thioredoxin inhibitors to cell cultures enhanced HMGB1 oxidation during sepsis in endothelial and proximal tubule cells, respectively. In conclusion, as sepsis worsens, ROS generation and HMGB1 oxidation increases in kidney cells, which enhances HMGB1's pro-inflammatory signaling. Conversely, the glutathione and thioredoxin systems work to maintain the protein in its reduced state.

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Endotoxins (LPS) increase cellular oxidative stress during sepsis.

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During its translocation, HMGB1 gets oxidized in the cytoplasm.

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Thioredoxin and glutathione keep HMGB1 in a reduced redox state during sepsis.

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HMGB1 oxidation enhances its stimulation of inflammatory cyto-/chemokine release.

Intestinal injury in the rat model of 17α-ethynylestradiol-induced intrahepatic cholestasis

OBJECTIVE

Although the intimate relationship between liver and gut has been previously reported under physiological and pathological conditions, intestinal involvement in the process of intrahepatic cholestasis of pregnancy remains unclear. The aim of this study was to investigate intestinal changes in 17α-ethynylestradiol (EE)-induced cholestatic rat model.

METHODS

Liver injury was assessed by HE stain and serum biochemical parameters were measured. Intestinal transit was determined using ink marks. Neuronal protein expressions in the intestine were analyzed by Western blot.

RESULTS

EE treatment induced liver damage, including severe bile duct hyperplasia, portal edema, portal infiltration, a loss of hepatic structure in periportal areas and increased serum levels of aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase and total bilirubin. Large areas of inflammatory cell infiltration and increased myeloperoxidase activity were observed in the intestine of EE-induced cholestatic rats. The EE-treated group showed increased intestinal transit and malondialdehyde levels, while the glutathione content and superoxide dismutase activity were notably decreased, together with decreased protein gene product 9.5 and neuronal nitric oxide synthase expression in the ileum and colon. Furthermore, choline acetyltransferase expression was significantly decreased in the ileum, whereas no change was observed in the colon of EE-treated rats.

CONCLUSION

EE-induced liver damage is associated with oxidative stress, inflammation and neural loss in the intestine, which may lead to altered intestinal motility.

Bombesin and neurotensin reduce endotoxemia, intestinal oxidative stress, and apoptosis in experimental obstructive jaundice

OBJECTIVE

To evaluate the effect of bombesin (BBS) and neurotensin (NT) on intestinal histopathology, intestinal oxidative stress, and endotoxemia in experimental obstructive jaundice.

SUMMARY BACKGROUND DATA

Obstructive jaundice compromises gut barrier function, resulting in endotoxemia. BBS and NT, exerting various biologic actions on gastrointestinal tissues, preserve gut mucosal integrity in cases of injury or atrophy.

METHODS

Seventy male Wistar rats were randomly divided into 5 groups: I = controls, II = sham operated, III = bile duct ligation (BDL), IV = BDL + BBS (30 microg/kg/d), V = BDL + NT (300 microg/kg/d). By the end of the experiment, on day 10, endotoxin was measured in portal and aortic blood. Tissue sections of the terminal ileum were examined histologically, and villus density, mucosal thickness, mitotic activity and apoptosis in crypts were assessed. In addition, ileal mucosa was analyzed for DNA and protein content. To estimate intestinal oxidant/antioxidant equilibrium, lipid peroxidation, protein oxidation, and thiol redox state (reduced glutathione [GSH], oxidized glutathione [GSSG], total nonprotein mixed disulfides [NPSSR], protein thiols [PSH], and protein disulfides [PSSP]) were determined on tissue homogenates from the terminal ileum.

RESULTS

BBS or NT administration significantly reduced portal and systemic endotoxemia observed in obstructive jaundice. Both factors reversed obstructive jaundice-induced morphologic features of intestinal atrophy, increasing villus density and mucosal thickness. This effect was accompanied by induction of mitoses and reduction of apoptosis in intestinal crypts. Mucosal DNA and protein content were reduced, although not to significant levels, in BDL animals and restored to control levels after BBS or NT treatment. Moreover, BBS or NT administration protected the intestine in jaundiced rats against oxidative stress, as demonstrated by reduction of intestinal lipid peroxidation, increase of the antioxidant GSH, and decrease of the oxidized forms GSSG and NPSSR, while BBS additionally reduced protein oxidation as well.

CONCLUSIONS

Administration of BBS or NT in bile duct-ligated rats exerts beneficial effects on intestinal oxidative stress, cell proliferation, apoptosis, and endotoxemia. This observation might be of potential value in patients with extrahepatic cholestasis.

SPLANCHNIC METABOLISM DURING GUT ISCHEMIA AND SHORT-TERM ENDOTOXIN AND HEMORRHAGIC SHOCK AS EVALUATED BY INTRAVASAL MICRODIALYSIS

The splanchnic area is of considerable interest in different types of shock. To characterize the metabolic changes in the splanchnic region in response to different types of shock we used a model where shock-induced metabolic changes in the splanchnic region were studied by the use of intravasal microdialysis. 23 anesthetized domestic pigs were randomized into four groups: Group I, serving as controls (n = 5); Group II, mesenteric ischemia for 180 followed by 120 min of reperfusion (n = 5); Group III, endotoxin shock for 5 h (n = 5); and Group IV, hemorrhagic shock for 180 min followed by re-transfusion of shed blood (n = 8). Microdialysis catheters were placed in the left femoral artery, portal vein and a small ileal mesenteric vein. Samples of the perfusate were continuously collected in micro-vials and analyzed for glucose, lactate, pyruvate and glycerol. In gut ischemia and endotoxin shock the outflow-pattern of lactate, lactate/pyruvate ratio and glucose in the mesenteric vein differed significantly from controls and hemorrhage whereas an increase in glycerol was only noted in the ischemic group. The most prominent differences were detected in lactate/pyruvate ratio, a marker of tissue ischemia with the most pronounced changes during mesenteric ischemia/reperfusion. During endotoxin shock increases in microdialysate metabolites were only noted in the splanchnic region suggesting a specific vulnerability in the region. Studying the lactate/pyruvate ratio may provide additional information when interpreting increased blood lactate levels. In addition glycerol may prove to be a useful marker of splanchnic ischemia. Intravasal microdialysis represents a potentially useful method for monitoring regional metabolic events.

Protective effects of exogenous fructose-1,6-biphosphate during small bowel transplantation in rats

BACKGROUND

We assessed the effect of adding exogenous fructose-1,6-biphosphate (F16BP) to the preservation solution (University of Wisconsin storage solution) used during an experimental procedure of small bowel transplantation in rats.

METHODS

We studied levels of the nucleotides hypoxanthine/xanthine and adenosine in tissue after cold ischemia, as well as histologic changes and associated deleterious processes such as bacterial translocation produced by the reperfusion associated with the transplantation.

RESULTS

The groups of rats treated with F16BP showed the lowest levels of hypoxanthine/xanthine and uric acid, the highest levels of adenosine, and the lowest levels of histologic damage and lactate dehydrogenase release to the bloodstream. Consumption of intestinal hypoxanthine during reperfusion was lowest in the groups treated with F16BP, as was the incidence of bacterial translocation.

CONCLUSIONS

This study shows a protective effect of exogenous F16BP added to University of Wisconsin solution during experimental intestinal transplantation in rats. This protective effect, reflected by decreased intestinal damage and bacterial translocation, was related to a decrease in adenosine triphosphate depletion during cold ischemia before intestinal transplantation, and to the reduced availability of xanthine oxidase substrates for free radical generation during reperfusion.

Regulation of kinase cascades and transcription factors by a poly(ADP-ribose) polymerase-1 inhibitor, 4-hydroxyquinazoline, in lipopolysaccharide-induced inflammation in mice

Activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP) is involved in numerous pathophysiological conditions. Because PARP-1 knockout mice are resistant to endotoxin-induced shock and inhibitors of the enzyme were reported to have similar beneficial properties, we investigated the effect of 4-hydroxyquinazoline (4-HQN), a potent PARP-1 inhibitor, on the modulation of kinase cascades and the regulation of transcription factors in a rodent septic shock model. T2-weighted magnetic resonance imaging showed the pattern of anatomical localization of the inflammatory response in bacterial lipopolysaccharide (LPS)-treated mice and the anti-inflammatory effect of the PARP-1 inhibitor. We have found that 4-HQN activated the phosphatidylinositol 3 (PI3)-kinase/Akt pathway in lung, liver, and spleen, and down-regulated two elements of the MAP kinase system. Namely, it dramatically attenuated the activation of the LPS-induced extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein (MAP) kinase in a tissue-specific manner. Furthermore, phosphorylation of p90RSK, a downstream target of ERK1/2, showed a similar pattern of down-regulation as did the phosphorylation of ERK1/2 and p38 after LPS and 4-HQN treatment. As a consequence of the aforementioned effects on the kinase pathways, 4-HQN decreased the activation of transcription factor nuclear factor-kappaB (NF-kappaB) and activator protein 1 (AP-1) in LPS-induced endotoxic shock. Our results provide evidence for the first time that the beneficial effects of PARP inhibition in endotoxic shock, such as attenuation of NF-kappaB- and AP-1 transcription factor activation, are mediated, at least partially, through the regulation of the PI3-kinase/Akt pathway and MAP kinase cascades.

Pancreatic enzymes sustain systemic inflammation after an initial endotoxin challenge

BACKGROUND

Sepsis is accompanied by severe inflammation whose mechanism remains uncertain. We recently demonstrated that pancreatic proteases in the ischemic intestine have the ability to generate powerful inflammatory mediators that can be detected in the portal vein and in the general circulation. This study was designed to examine several circulatory and inflammatory indices during experimental endotoxemia and intraintestinal pancreatic protease inhibition.

METHODS

Immediately after intravenous endotoxin administration, the small intestine was subjected to intraluminal lavage with and without gabexate mesilate, an inhibitor of pancreatic proteases. Shams and rats without lavage served as controls. Hemodynamics, leukocyte (neutrophil and monocyte), and endothelial cell activation, as well as organ injury in the intestine and the cremaster muscle, were examined.

RESULTS

After endotoxin administration, control rats developed hypotension, tachycardia, hyperventilation, and leukopenia. The intestine and plasma contained mediators that activated leukocytes. The leukocyte-endothelial interaction within the cremaster muscle microcirculation was enhanced. Endotoxin administration resulted in elevated interleukin-6 plasma levels. Histologic evidence indicated liver and intestinal injury. In contrast, blockade of pancreatic proteases in the intestinal lumen significantly improved hemodynamic parameters and reduced all indices of inflammation in plasma and cell injury in skeletal muscle microcirculation.

CONCLUSIONS

Inflammatory mediators derived from the intestine by pancreatic proteases may be involved in the prolonged inflammatory response and sustain symptoms of sepsis after endotoxin challenge.

Intestinal ischaemia during cardiac arrest and resuscitation: comparative analysis of extracellular metabolites by microdialysis

Intestinal ischaemia is a major complication of shock syndromes causing translocation of bacteria and endotoxins and multiple organ failure in intensive care patients. The present study was designed to use microdialysis as a tool to monitor intestinal ischaemia after cardiac arrest and resuscitation in pigs. For this purpose, microdialysis probes were implanted in pig jejunal wall, peritoneum, skeletal muscle and brain, and interstitial fluid was obtained during circulatory arrest (induced by ventricular fibrillation) and after return of spontaneous circulation (ROSC). Cardiac arrest for 4 min caused a prolonged (60 min) reduction of blood flow in jejunal wall, muscle and brain as determined by the ethanol technique. This was accompanied by cellular damage in heart muscle and brain as indicated by increased levels of troponin-I and protein S-100, respectively. Plasma levels of glucose, lactate and choline were increased at 15-60 min following cardiac arrest. In contrast, cardiac arrest induced a rapid but variable decrease of interstitial glucose levels in all monitored organs; this decrease was followed by an increase over baseline during reperfusion. In the intestine, lactate, glutamate and choline levels were increased during ischaemia and reperfusion for 60-120 min; intestinal and peritoneal samples yielded parallel changes of lactate levels. Brain and muscle samples showed similar changes as in intestinum and peritoneum except for glutamate, which was increased in brain but not in muscle. We conclude that intestinal ischaemia occurs as a consequence of cardiac arrest and resuscitation and can be monitored by in vivo microdialysis. Comparative analysis by multi-site microdialysis reveals that the intestine is equally or even more sensitive to ischaemia than brain or muscle.

Decrease of the inflammatory response and induction of the Akt/protein kinase B pathway by poly-(ADP-ribose) polymerase 1 inhibitor in endotoxin-induced septic shock

The lack of efficacy of anti-inflammatory drugs, anti-coagulants, anti-oxidants, etc. in critically ill patients has shifted interest towards developing alternative treatments. Since inhibitors of the nuclear enzyme poly-(ADP-ribose) polymerase (PARP) were found to be beneficial in many pathophysiological conditions associated with oxidative stress and PARP-1 knock-out mice proved to be resistant to bacterial lipopolysaccharide (LPS)-induced septic shock, PARP inhibitors are candidates for such a role. In this study, the mechanism of the protective effect of a potent PARP-1 inhibitor, PJ34 was studied in LPS-induced (20mg/kg, i.p.) septic shock in mice. We demonstrated a significant inflammatory response by magnetic resonance imaging in the dorsal subcutaneous region, in the abdominal regions around the kidneys and in the inter-intestinal cavities. We have found necrotic and apoptotic histological changes as well as obstructed blood vessels in the liver and small intestine. Additionally, we have detected elevated tumor necrosis factor-alpha levels in the serum and nuclear factor kappa B activation in liver of LPS-treated mice. Pre-treating the animals with PJ34 (10mg/kg, i.p.), before the LPS challenge, besides rescuing the animals from LPS-induced death, attenuated all these changes presumably by activating the phosphatidylinositol 3-kinase-Akt/protein kinase B cytoprotective pathway.

Metabolic changes detected by microdialysis during endotoxin shock and after endotoxin preconditioning

OBJECTIVE

Preconditioning with low doses of endotoxin has been shown to induce endotoxin hyporesponsiveness. The present study was designed to assess the metabolic response of various tissues during endotoxemia and after pretreatment with endotoxin.

DESIGN

Controlled experimental animal study.

SETTING

Research laboratory of a university hospital.

MEASUREMENTS AND RESULTS

Ten pigs were randomly assigned to a control ( n = 5) or a treatment group ( n = 5), the latter receiving incremental doses of endotoxin 5-2 days prior the experiments. Apart from hemodynamics and oxygen transport variables, lactate, glucose, and glycerol were measured in muscle, subcutaneous fat, and hepatic tissue using microdialysis. Endotoxin was infused (1 micro g.kg.h) until the animals died. A significant increase in tissue lactate (eightfold) and glycerol (fivefold) was observed in the control animals. This effect was almost completely abolished in the endotoxin pretreated group. Endotoxin pretreatment had no significant effects on mean arterial pressure [56 (range 34-89) mmHg vs 70 (47-88) mmHg, n.s.] or cardiac output [4.8 (3.0-5.9) l/min vs 3.2 (2.1-4.2) l/min, n.s.], but significantly improved arterial pO(2) and pH ( P<0.05). Increase of oxygen extraction was higher in control animals [from 34% (range 24-47%) to 72% (range 61-79%)] compared to the pretreatment group [from 30% (range 22-42%) to 44% (range 34-50%), P<0.05]. Endotoxin pretreatment increased survival time from 5.3 h (5.0-5.8) to 8.0 h (7.0-8.5) ( P<0.05), respectively.

CONCLUSIONS

Microdialysis monitoring revealed that endotoxin preconditioning ameliorates the increase in tissue metabolism during endotoxemia, accompanied by decreased systemic oxygen demand despite unchanged global hemodynamics.

Biochemical tissue monitoring during hypoxia and reoxygenation

Oxygen deficiency during critical illness may cause profound changes in cellular metabolism and subsequent tissue and organ dysfunction. Clinical treatment in these cases targets rapid reoxygenation to avoid a prolonged impaired synthesis of cellular high-energy phosphates (ATP). However, the effect of this therapeutic intervention on tissue metabolism has not been determined yet. Thus the present study was designed to determine the effects of hypoxia and reoxygenation with either room air or 100% oxygen on variables of interstitial metabolism in different tissues using in vivo microdialysis. Twenty-seven adult, male CD-rats (407-487 g; Ivanovas, Kisslegg, Germany) were studied during general anesthesia. Following preparation and randomization, rats were normoventilated for 45 min (FiO(2) 0.21), followed by induction of hypoxia (FiO(2) 0.1, 40 min) and reoxygenated for 50 min either with FiO(2) 1.0 (group 1, n=10) or FiO(2) 0.21 (group 2, n=10). Control animals (n=7) were ventilated with 21% oxygen during the observation period. Additional to invasive haemodynamic parameters, biochemical tissue monitoring was performed using CMA 20 microdialysis probes, inserted into muscle, subcutaneous space, liver, and the peritoneal cavity allowing analyses of lactate and pyruvate at short intervals. Hypoxia induced a significant reduction in mean arterial pressure (MAP) in group 1 and 2 compared with the control group (P<0.05) without any significant differences between both treatment groups. This was accompanied by a significant increase in blood lactate (10.5+/-3.1 mM (group 1) and 12.3+/-4.1 mM (group 2) vs. 1.5+/-0.3 mM (control); P<0.05) and severe metabolic acidosis (base excess (BE): -18.3+/-5 mM (1) and -17.3+/-7 mM (2) vs. -2.6+/-1.8 mM (control), P<0.05). During hypoxia, the interstitial lacate/pyruvate ratio in groups 1 and 2 increased to 455+/-199% (muscle), 468+/-148% (intraperitoneal), 770+/-218% (hepatic) and 855+/-432% (subcutaneous) (P<0.05 vs. control, respectively). No significant inter-organ or inter-group differences in interstitial dialysates were observed in the treatment groups, neither during hypoxia nor during reoxygenation. Our data suggest, that hypoxia induces comparable metabolic alterations in various tissues and that reoxygenation with 100% oxygen is not superior to 21% oxygen in restoring tissue metabolism after critical hypoxia.

Subcutaneous microdialysis for metabolic monitoring in abdominal aortic surgery

Microdialysis, that is the sampling of interstitial fluid via semi-permeable tubes, has been shown to be suitable for detecting ischemic changes e.g. in brain and heart tissue. The purpose of the present study was to investigate the possibility of monitoring with subcutaneous microdialysis peri-operative metabolic sequelac of elective abdominal aortic surgery. In 22 patients microdialysis catheters were inserted subcutaneously in the lower leg as well as the shoulder serving as a reference topographic region. Lactate, pyruvate and glycerol, which indicate ischemia or reperfusion, were measured. We observed severe metabolic changes within the interstitial fluid of the lower extremity during ischemia followed by normalization during reperfusion. Despite high interstitial concentrations of lactate and glycerol indicating severe ischemia during clamping of the abdominal aorta these parameters returned to pre-operative values within 2 hrs after declamping and all patients recovered completely.

OBJECTIVE

Information about the metabolic state of the lower extremity during and after infrarenal aortic aneurysm repair should modify peri-operative treatment. The aim of the study was to evaluate whether microdialysis of the subcutaneous tissue reflects metabolic changes during ischemia and reperfusion. Lactate, pyruvate and glycerol concentrations were measured in the subcutaneous tissue of the lower extremity and compared to the microdialysis measurements from shoulder subcutaneous tissue.

METHOD

In 22 patients microdialysis catheters were inserted preoperatively in the subcutaneous space of the left shoulder and the left calf. Samples were taken at timed intervals before, during and after clamping of the abdominal aorta.

RESULTS

The subcutaneous glycerol concentration of the calf was increased during the clamping period from initially 68 +/- 11 microM up to 182 +/- 27 microM (p < 0.05); the lactate/pyruvate (L/P) ratio was increased eightfold. After declamping these values normalized to baseline. Microdialysis measurements of the shoulder showed no prominent changes during the entire course of observation.

CONCLUSIONS

Subcutaneous microdialysis was able to detect metabolic changes due to ischemia during clamping of the abdominal aorta as well as reperfusion there after. It is a suitable technique to monitor the peri-operative course of the dependent tissue after abdominal aortic vascular surgery.

Microdialysis in the intensive care unit: a novel tool for clinical investigation or monitoring?

Microdialysis is a minimally invasive tool that allows us to gain insight into metabolism at the tissue level. In human investigations, it can be safely performed in the brain (neurosurgical patients), skeletal muscle and adipose tissue. Basically, the technique allows interstitial concentrations of small solutes to be evaluated. Several limitations of the method and possible ways to circumvent them are indicated. Recent technical developments are reviewed. At present, this method is rarely used in metabolic monitoring of critically ill patients, but its potential applications are highlighted.

[Chronic experimental bacteremia in Yucatan micropigs]

The Yucatan micropig has been used to develop an experimental model of chronic bacteremia. This animal exhibits clinical and biological characteristics that are close to those in humans, and the pharmacokinetic behaviours of many classes of drugs in this model are similar to those in man. Six adult female were intravenously inoculated with a mean Escherichia coli inoculum of 5.1 x 10(9) bacteria. During five days of spontaneous evolution, the medical follow-up includes biological, clinical and bacteriological parameters. A systemic inflammatory syndrome, a sepsis, an organ insufficiency and positive blood cultures mimic the human disease. In all animals there is an adynamia, a lack of motor coordination, an anorexia, a tachypnea, a fever, a leuconeutropenia followed by an hyperleucocytosis, an anemia, a thrombopenia, an acute tubulonephritis and an elevated sedimentation rate. In some cases, there is an increase of the C reactive protein, in others, an increase of IL-6 and IL-8. At day five, all animals are alive, and five micropigs have positive blood cultures. This chronic, reproducible model is thus suitable for further antibacterial treatments evaluations.

Purines inhibit poly(ADP-ribose) polymerase activation and modulate oxidant-induced cell death

Purines such as adenosine, inosine, and hypoxanthine are known to have potent antiinflammatory effects. These effects generally are believed to be mediated by cell surface adenosine receptors. Here we provide evidence that purines protect against oxidant-induced cell injury by inhibiting the activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP). Upon binding to broken DNA, PARP cleaves NAD+ into nicotinamide and ADP-ribose and polymerizes the latter on nuclear acceptor proteins such as histones and PARP itself. Overactivation of PARP depletes cellular NAD+ and ATP stores and causes necrotic cell death. We have identified some purines (hypoxanthine, inosine, and adenosine) as potential endogenous PARP inhibitors. We have found that purines (hypoxanthine > inosine > adenosine) dose-dependently inhibited PARP activation in peroxynitrite-treated macrophages and also inhibited the activity of the purified PARP enzyme. Consistently with their PARP inhibitory effects, the purines also protected interferon gamma + endotoxin (IFN/LPS) -stimulated RAW macrophages from the inhibition of mitochondrial respiration and inhibited nitrite production from IFN/LPS-stimulated macrophages. We have selected hypoxanthine as the most potent cytoprotective agent and PARP inhibitor among the three purine compounds, and investigated the mechanism of its cytoprotective effect. We have found that hypoxanthine protects thymocytes from death induced by the cytotoxic oxidant peroxynitrite. In line with the PARP inhibitory effect of purines, hypoxanthine has prevented necrotic cell death while increasing caspase activity and DNA fragmentation. As previously shown with other PARP inhibitors, hypoxanthine acted proximal to mitochondrial alterations as hypoxanthine inhibited the peroxynitrite-induced mitochondrial depolarization and secondary superoxide production. Our data imply that purines may serve as endogenous PARP inhibitors. We propose that, by affecting PARP activation, purines may modulate the pattern of cell death during shock, inflammation, and reperfusion injury.

Microdialysis in peripheral tissues

The objective of this review is to survey the recent literature regarding the applications of microdialysis in pharmacokinetic studies and facilitating many other studies in peripheral tissues such as muscle, subcutaneous adipose tissue, heart, lung, etc. It has been reported extensively that microdialysis is a useful technique for monitoring free concentrations of compounds in extracellular fluid (ECF), and it is gaining popularity in pharmacokinetic and pharmacodynamic studies, both in experimental animals and humans. The first part of this review discusses the use of microdialysis technique for ECF sampling in peripheral tissues in animal studies. The second part of the review describes the use of microdialysis for ECF sampling in peripheral tissues in human studies. Microdialysis has been applied extensively to measure both endogenous and exogenous compounds in ECF. Of particular benefit is the fact that microdialysis measures the unbound concentrations in the peripheral tissue fluid which have been shown to be responsible for the pharmacological effects. With the increasing number of applications of microdialysis, it is obvious that this method will have an important place in studying drug pharmacokinetics and pharmacodynamics.

Inactivation of catecholamines by superoxide gives new insights on the pathogenesis of septic shock

A major feature of septic shock is the development of a vascular crisis characterized by nonresponsiveness to sympathetic vasoconstrictor agents and the subsequent irreversible fall in blood pressure. In addition, sepsis, like other inflammatory conditions, results in a large increase in the production of free radicals, including superoxide anions (O(2)) within the body. Here we show that O(2) reacts with catecholamines deactivating them in vitro. Moreover, this deactivation would appear to account for the hyporeactivity to exogenous catecholamines observed in sepsis, because administration of a superoxide dismutase (SOD) mimetic to a rat model of septic shock to remove excess O(2) restored the vasopressor responses to norepinephrine. This treatment with the SOD mimetic also reversed the hypotension in these animals; suggesting that deactivation of endogenous norepinephrine by O(2) contributes significantly to this aspect of the vascular crisis. Indeed, the plasma concentrations of both norepinephrine and epinephrine in septic rats treated with the SOD mimetic were significantly higher than in untreated rats. Interestingly, the plasma concentrations for norepinephrine and epinephrine were inversely related to the plasma concentrations of adrenochromes, the product of the autoxidation of catecholamines initiated by O(2). We propose, therefore, that the use of a SOD mimetic represents a new paradigm for the treatment of septic shock. By removing O(2), exogenous and endogenous catecholamines are protected from autoxidation. As a result, both hyporeactivity and hypotension are reversed, generation of potentially toxic adrenochromes is reduced, and survival rate is improved.