Effective inhibition of nitric oxide production by aminoguanidine does not reverse hypotension in endotoxaemic rats

GTS-21 attenuates loss of body mass, muscle mass, and function in rats having systemic inflammation with and without disuse atrophy

Muscle changes of critical illness are attributed to systemic inflammatory responses and disuse atrophy. GTS-21 (3-(2,4-dimethoxy-benzylidene)anabaseine), also known as DMBX-A) is a synthetic derivative of the natural product anabaseine that acts as an agonist at α7-acetylcholine receptors (α7nAChRs). Hypothesis tested was that modulation of inflammation by agonist GTS-21 (10 mg/kg b.i.d. intraperitoneally) will attenuate body weight (BW) and muscle changes. Systemic sham inflammation was produced in 125 rats by Cornyebacterium parvum (C.p.) or saline injection on days 0/4/8. Seventy-four rats had one immobilized-limb producing disuse atrophy. GTS-21 effects on BW, tibialis muscle mass (TMM), and function were assessed on day 12. Systemically, methemoglobin levels increased 26-fold with C.p. (p < 0.001) and decreased significantly (p < 0.033) with GTS-21. Control BW increased (+ 30 ± 9 g, mean ± SD) at day 12, but decreased with C.p. and superimposed disuse (p = 0.005). GTS-21 attenuated BW loss in C.p. (p = 0.005). Compared to controls, TMM decreased with C.p. (0.43 ± 0.06 g to 0.26 ± 0.03 g) and with superimposed disuse (0.18 ± 0.04 g); GTS-21 ameliorated TMM loss to 0.32 ± 0.04 (no disuse, p = 0.028) and to 0.22 ± 0.03 (with disuse, p = 0.004). Tetanic tensions decreased with C.p. or disuse and GTS-21 attenuated tension decrease in animals with disuse (p = 0.006) and in animals with C.p. and disuse (p = 0.029). C.p.-induced 11-fold increased muscle α7nAChR expression was decreased by > 60% with GTS-21 treatment. In conclusion, GTS-21 modulates systemic inflammation, evidenced by both decreased methemoglobin levels and decrease of α7nAChR expression, and mitigates inflammation-mediated loss of BW, TMM, fiber size, and function.

Neuromuscular Recovery Is Prolonged After Immobilization or Superimposition of Inflammation With Immobilization Compared to Inflammation Alone: Data From a Preclinical Model

OBJECTIVES

Recovery from ICU-acquired muscle weakness extends beyond hospital stay. We hypothesized that immobilization, more than inflammation, plays a prominent role in the delayed recovery from critical illness.

DESIGN

Prospective, randomized, controlled, experimental study.

SETTING

Animal laboratory, university hospital.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Animals were divided to have one hind limb immobilized (n = 129) or sham-immobilized (n = 129) on day -12. After surgery, rats were further assigned to two subgroups. To induce inflammation, rats received three IV injections of Corynebacterium parvum on days -12, -8, and -4. Controls received saline at the respective time-points. At day 0, the limbs were remobilized and recovery from inflammation and/or immobilization was followed for 36 days.

MEASUREMENTS AND MAIN RESULTS

At day 0 and after 4, 12, or 36 days of recovery, maximum tetanic tension and tetanic fade (functional parameters = primary outcome variables) as well as nicotinic acetylcholine receptor expression, muscle mass, and histologic changes (structural parameters = secondary outcome variables) were measured. Impaired maximum tetanic tension, decreased tibialis muscle mass, and fiber diameter due to inflammation alone recovered by day 4. Tetanic fade was not affected by inflammation. Immobilization-induced loss of tibialis muscle mass, decreased fiber diameter, and tetanic fade did not return to normal until day 36, while maximum tetanic tension had recovered at that time. In the presence of inflammation and immobilization, the decrease in tibialis muscle mass, fiber diameter, and maximum tetanic tension, as well as decreased tetanic fade persisted until day 36. Up-regulation of nicotinic acetylcholine receptors normalized before day 4 following inflammation, but persisted until day 4 following immobilization.

CONCLUSIONS

In our model, muscle function and structure recovered from inflammation within 4-12 days. Immobilization-induced neuromuscular changes, however, persisted even at day 36, especially if inflammation was concomitant.

Review: The plasma kallikrein/kinin and renin angiotensin systems in blood pressure regulation in sepsis

The hemodynamics of septic shock after endotoxinemiai s influenced by the plasma kallikrein/kinin and the renin angiotensin systems. In recent years, new information has improved understanding of the protein/biologically active peptide interactions between these two systems. The plasma kallikrein/kinin system, more commonly known as the contact system, has undergone a re-evaluation as to how it assembles on cell membranes for physiological and pathophysiological activation and as to its role in Gram-negative sepsis. It has been proposed that it counterbalances the plasma renin angiotensin system. Furthermore, more knowledge about the renin angiotensin system has become available on how it either opposes the actions of the kallikrein/kinin system or, in some cases, summates with it. Understanding the interactions between these two systems may lead to development of better pharmacological treatments for endotoxin-induced shock.

Optimization of filaggrin expression and processing in cultured rat keratinocytes

BACKGROUND

In normal mammalian epidermis, cell division occurs primarily in the basal layer where cells are attached to the basement membrane. Upon release from the basement membrane, these basal cells stop dividing and begin to differentiate and stratify producing cornified cells expressing differentiation markers, including the keratin bundling protein filaggrin, and cornified envelope proteins. Little is understood about the regulatory mechanisms of these processes. A rat epidermal keratinocyte cell line synthesizing and processing profilaggrin at confluence in a synchronous manner for 4-5 days provides a useful culture model for epidermal differentiation. Profilaggrin expression in this cell line however decreases with passaging, and its processing involves extensive nonspecific proteolysis.

OBJECTIVE

Our objective was to identify culture conditions that effect the decrease in profilaggrin expression with passaging and nonspecific proteolysis of profilaggrin in order to study epidermal differentiation more closely.

METHOD

The large amount of nonspecific proteolysis suggested autophagocytosis. To test this, cells were cultured in the presence of 3-methyladenine (3-MA). Two known gradients in epidermis are decreasing serum components and increasing calcium concentrations in the upper cell layers. To determine whether these gradients effected processing, cells were cultured in serum/DMEM or in serum-free KGM and under varying external calcium concentrations. Cells were also cultured in presence of aminoguanidine in an attempt to maintain profilaggrin expression with passaging.

RESULTS

Profilaggrin expression was enhanced in the presence of 3-MA, with optimum around 6mM. In the absence of aminoguanidine, profilaggrin expression decreased as a function of increasing passage number; in its presence, profilaggrin expression remained high in some, but not in all of the independently maintained cell lines. Thus, culturing in aminoguanidine was necessary, but not sufficient, for sustained ability to express profilaggrin at confluence. Production of filaggrin from profilaggrin was maximized in a serum-free medium with [Ca(2+)] at 5mM. Filaggrin associates with phospholipid vesicles in vitro forming aggregates similar to those seen in vivo, suggesting that filaggrin release induces vesicular aggregation and autophagocytosis.

CONCLUSION

We have used a keratinocyte cell line that synthesizes and processes profilaggrin after confluence as a culture model to study epidermal differentiation. In this system profilaggrin processing must be preceded by inhibition of autophagosome formation and/or modulation of vesicular trafficking, and these processes are regulated by epidermal calcium and serum factor gradients.

Systemic inflammatory response syndrome increases immobility-induced neuromuscular weakness

OBJECTIVE

Inflammation and immobility are comorbid etiological factors inducing muscle weakness in critically ill patients. This study establishes a rat model to examine the effect of inflammation and immobilization alone and in combination on muscle contraction, histology, and acetylcholine receptor regulation.

DESIGN

Prospective, randomized, experimental study.

SETTING

Animal laboratory of a university hospital.

SUBJECTS

Sprague-Dawley rats.

INTERVENTIONS

To produce systemic inflammation, rats (n = 34) received three consecutive intravenous injections of Corynebacterium parvum on days 0, 4, and 8. Control rats (n = 21) received saline. Both groups were further divided to have one hind limb either immobilized by pinning of knee and ankle joints or sham-immobilized (surgical leg). The contralateral nonsurgical leg of each animal served as control (nonsurgical leg).

MEASUREMENTS AND MAIN RESULTS

After 12 days, body weight and muscle mass were significantly reduced in all C. parvum animals compared with saline-injected rats. Immobilization led to local muscle atrophy. Normalized to muscle mass, tetanic contraction was reduced in the surgical leg after immobilization (7.64 +/- 1.91 N/g) and after inflammation (8.71 +/- 2.0 N/g; both p < .05 vs. sham immobilization and saline injection, 11.03 +/- 2.26 N/g). Histology showed an increase in inflammatory cells in all C. parvum-injected animals. Immobilization in combination with C. parvum injection had an additive effect on inflammation. Acetylcholine receptors were increased in immobilized muscles and in all muscles of C. parvum-injected animals.

CONCLUSIONS

The muscle weakness in critically ill patients can be replicated in our novel rat model. Inflammation and immobilization independently lead to muscle weakness.

Deficiency of mitogen-activated protein kinase phosphatase-1 results in iNOS-mediated hypotension in response to low-dose endotoxin

Mitogen-activated protein kinase phosphatase-1 (MKP-1) is essential in limiting the proinflammatory response to lipopolysaccharide (LPS). We hypothesized that Mkp-1(-/-) mice would respond to low-dose LPS with a fall in blood pressure due to augmented expression of inducible nitric oxide (NO) synthase (iNOS). To test this hypothesis, Mkp-1(-/-) mice and their wild-type littermates were treated with 10 microg/kg iv LPS, and mean arterial blood pressure (MAP) and exhaled NO production (exNO) were measured. Tissues were harvested for an assessment of iNOS protein levels. Wild-type mice had no change in MAP or exNO during the experimental period, whereas Mkp-1(-/-) mice had a fall (P < 0.005) in MAP [79 +/- 5% of baseline (BL)] and an increase (P < 0.01) in exNO (266 +/- 50% of BL) after 150 min. The tissue levels of iNOS were greater in Mkp-1(-/-) than in wild-type mice. In additional experiments, 60 min after LPS treatment, Mkp-1(-/-) and wild-type mice were given N(omega)-nitro-l-arginine methyl ester (l-NAME) or aminoguanidine, and MAP and exNO were monitored for 90 min. Treatment with l-NAME prevented the LPS-induced increase in exNO and decrease in MAP but resulted in decreased exNO and elevated MAP in wild-type mice. Aminoguanidine prevented the increase in exNO and the fall in MAP caused by LPS in Mkp-1(-/-) mice, without significantly affecting MAP or exNO in wild-type mice. These results demonstrate that a deficiency of MKP-1 results in an exaggerated hypotensive response to LPS mediated by augmented iNOS expression. We speculate that defects in the Mkp-1 gene may increase susceptibility for the development of septic shock.

Nitric Oxide Does Not Cause Extravasation in Endotoxemic Rats

BACKGROUND

Nitric oxide (NO) formed from inducible NO synthase (iNOS) is assumed to promote vascular permeability in sepsis and endotoxemia.

METHODS

Thirty-seven anesthetized rats were examined for the effects of endotoxin. After randomization, 17 animals had lipopolysaccharide (LPS) administered and 20 rats served as controls and were given the corresponding volume of saline. The observation period was 5 hours after administration of endotoxin. Mean arterial blood pressure, heart rate, and hematocrit were recorded in all animals, and transcapillary exchange of albumin, tissue water content, immunohistochemistry for nitric oxide synthase, and blood gases were investigated in subsets of animals.

RESULTS

When anesthetized rats were studied for 5 hours after endotoxin (LPS), the sequestration of albumin decreased in the intestine (double-isotope method) and there was no increased water content (freeze-drying technique) when the elevated tissue plasma volume of the LPS-treated rats was corrected for. Immunohistochemical methods showed a similar distribution and intensity of staining for endothelial NOS and neuronal NOS in LPS and control groups. In the lung of the LPS-treated rats, there was a significantly larger number of infiltrating, inflammatory cells staining for iNOS. There was no iNOS demonstrated in vascular structures or heart.

CONCLUSION

At 5 hours after LPS, there was no increased loss of water or albumin from the circulation. This challenges the notion that NO causes vascular damage in endotoxemia and extravasation as an obligatory sequela to endotoxemia.

Effect of Potassium Channel and Cytochrome P450 Inhibition on Transient Hypotension and Survival during Lipopolysaccharide-Induced Endotoxic Shock in the Rat

The purpose of this study was to determine whether inhibition of potassium channels or cytochrome P450 attenuates the transient phase of hypotension during endotoxic shock in vivo, and to determine whether these interventions improve the rate of survival. Male Sprague-Dawley rats were pretreated with saline (0.2 ml, i.v.), tetraethylammonium chloride (TEA 30 mg/kg; 0.2 ml, i.v.), proadifen (SKF-525 A; 50 mg/kg, i.p.) or ketoconazole (50 mg/kg, i.p.) and challenged with lipopolysaccharide (LPS; 20 mg/kg, i.p.). Changes in heart rate, mean (MAP), systolic (SP) and diastolic (DP) arterial pressures as well as survival rate were then monitored for 45 min. Potassium channel inhibition with TEA had no effect on LPS-induced hypotension at any time point compared with saline (maximal fall in MAP of 79 +/- 18 and 80 +/- 13 mm Hg, respectively). Pretreatment with proadifen or ketoconazole, inhibitors of cytochrome P450, significantly attenuated LPS-induced hypotension compared with saline (maximal fall in MAP of 34, 26 and 63% below baseline, respectively). This effect was evident in all arterial pressures measured, MAP, SP and DP. At 45 min, the survival rate in the saline group was 66%. Pretreatment with TEA significantly reduced survival rate to 50% and pretreatment with proadifen or ketoconazole improved survival to 100% (p < 0.05). These results suggest that an arachidonic acid metabolite produced by a cytochrome P450-catalyzed reaction may contribute to the transient phase of LPS-induced hypotension. However, these effects do not appear to be mediated through potassium channel activation.

Sensitization of mesenteric afferents to chemical and mechanical stimuli following systemic bacterial lipopolysaccharide

BACKGROUNDS AND AIMS

The mechanisms underlying endotoxin-induced hyperalgesia remain unknown. We aimed to study the mechanisms underlying the sensitizing action of lipopolysaccharide (LPS) on intestinal afferent responses to mechanical and chemical stimuli.

METHODS

Extracellular recordings of jejunal afferent nerve discharge were obtained from pentobarbitone-anaesthetized rats.

RESULTS

Lipopolysaccharide (6 mg kg(-1), i.v.) stimulated a short-term, transient (<30 min) increase in chemosensitivity to systemic 5-HT (6 microg kg(-1)) and responses to mechanical distension and a delayed but maintained (>30 min) increase in spontaneous afferent discharge. Naproxen (10 mg kg(-1)) and the prostaglandin receptor antagonist AH6809 (1 mg kg(-1)) significantly attenuated both the short-term sensitization to mechanical distension and 5-HT and the long-term increase in baseline afferent firing following LPS. In contrast, the iNOS inhibitor aminoguanidine (15 mg kg(-1)) and the L-type calcium channel antagonist nifedipine (1 mg kg(-1)) both prolonged the period of afferent sensitization to distension and 5-HT without influencing the augmented baseline-firing rate. omega-Conotoxin GVIA attenuated the increase in afferent discharge to LPS, without any change in mechano- and chemosensitivity.

CONCLUSIONS

The long-term (>30 min) increase in afferent firing following systemic LPS involves neurogenic release of prostanoids. The short-term (<30 min) sensitization also appears to depend on prostanoid release, while nitric oxide production may serve to down-regulate LPS-induced afferent hypersensitivity.

Stress-restress evokes sustained iNOS activity and altered GABA levels and NMDA receptors in rat hippocampus

RATIONALE

Stress-related glucocorticoid and glutamate release have been implicated in hippocampal atrophy evident in patients with post-traumatic stress disorder (PTSD). Glutamatergic mechanisms activate nitric oxide synthase (NOS), while gamma-amino-butyric acid (GABA) may inhibit both glutamatergic and nitrergic transmission. Animal studies support a role for NOS in stress.

OBJECTIVES

We have studied the role of NOS and glucocorticoids, as well as inhibitory and excitatory transmitters, in a putative animal model of PTSD that emphasizes repeated trauma.

METHODS

Hippocampal NOS activity, N-methyl-D-aspartate (NMDA) receptor binding characteristics and GABA levels were studied in Sprague-Dawley rats 21 days after exposure to a stress-restress paradigm, using radiometric analysis, radioligand studies and high-performance liquid chromatography (HPLC) analysis with electrochemical detection, respectively. The NOS isoform involved, and the role of stress-mediated corticosterone release in NOS activation, was verified with the administration of selective iNOS and nNOS inhibitors, aminoguanidine (50 mg/kg/day i.p.) and 7-nitroindazole (12.5 mg/kg/day i.p.), and the steroid synthesis inhibitor, ketoconazole (24 mg/kg/day i.p.), administered for 21 days prior to and during the stress procedure.

RESULTS

Stress evoked a sustained increase in NOS activity, but reduced NMDA receptor density and total GABA levels. Aminoguanidine or ketoconazole, but not 7-nitroindazole or saline, blocked stress-induced NOS activation.

CONCLUSIONS

Stress-restress-mediated glucocorticoid release activates iNOS, followed by a reactive downregulation of hippocampal NMDA receptors and dysregulation of inhibitory GABA pathways. The role of NO in neuronal toxicity, and its regulation by glutamate and GABA has important implications in stress-related hippocampal degeneration.

A selective inducible NOS dimerization inhibitor prevents systemic, cardiac, and pulmonary hemodynamic dysfunction in endotoxemic mice

Increased nitric oxide (NO) production by inducible NO synthase (NOS2), an obligate homodimer, is implicated in the cardiovascular sequelae of sepsis. We tested the ability of a highly selective NOS2 dimerization inhibitor (BBS-2) to prevent endotoxin-induced systemic hypotension, myocardial dysfunction, and impaired hypoxic pulmonary vasoconstriction (HPV) in mice. Mice were challenged with Escherichia coli endotoxin before treatment with BBS-2 or vehicle. Systemic blood pressure was measured before and 4 and 7 h after endotoxin challenge, and echocardiographic parameters of myocardial function were measured before and 7 h after endotoxin challenge. The pulmonary vasoconstrictor response to left mainstem bronchus occlusion, which is a measure of HPV, was studied 22 h after endotoxin challenge. BBS-2 treatment alone did not alter baseline hemodynamics. BBS-2 treatment blocked NOS2 dimerization and completely inhibited the endotoxin-induced increase of plasma nitrate and nitrite levels. Treatment with BBS-2 after endotoxin administration prevented systemic hypotension and attenuated myocardial dysfunction. BBS-2 also prevented endotoxin-induced impairment of HPV. In contrast, treatment with NG-nitro-l-arginine methyl ester, which is an inhibitor of all three NOS isoforms, prevented the systemic hypotension but further aggravated the myocardial dysfunction associated with endotoxin challenge. Treatment with BBS-2 prevented endotoxin from causing key features of cardiovascular dysfunction in endotoxemic mice. Selective inhibition of NOS2 dimerization with BBS-2, while sparing the activities of other NOS isoforms, may prove to be a useful treatment strategy in sepsis.

Beneficial effect of hyperbaric oxygen pretreatment on lipopolysaccharide-induced shock in rats

1. We investigated the effect of hyperbaric oxygenation (HBO2) pretreatment on the production of exhaled nitric oxide (ENO) and the expression of lung inducible nitric oxide synthase (iNOS) by Escherichia coli lipopolysaccharide (LPS)-induced shock in an experimental rat model. 2. Rats were randomized into four groups, anaesthetized, mechanically ventilated with room air and infused with normal saline (2 mL/h) through the jugular vein for 5 h. Group 1 (NS) received only normal saline. Group 2 (HBO2-NS) was pretreated with HBO2 at 2.8 absolute atmospheres for 2 h and then received normal saline. Group 3 (LPS) received LPS, 20 mg/kg, i.v., bolus. Group 4 (HBO2-LPS) was pretreated with HBO2 for 2 h, followed by LPS. 3. Arterial blood gases, blood pressure, blood pH and ENO production were measured every 30 min. Plasma nitrite/nitrate (NOx) concentrations were assessed at the beginning (baseline) and at the end of the study. Lung myeloperoxidase (MPO) activity, iNOS expression and histological scores were measured for the evaluation of lung injury. 4. Administration of LPS was associated with decreased blood pressure and pH, increased ENO production, plasma NOx concentrations, lung iNOS expression and MPO activity. 5. Pretreatment with HBO2 significantly alleviated the LPS-induced hypotension, acidosis and decreased ENO production, plasma NOx concentrations, lung MPO activity and expression of iNOS. Hyperbaric O2 had no effect on control rats. 6. Our data show that HBO2 pretreatment has beneficial haemodynamic effects in rats with endotoxin shock. The beneficial effects of HBO2 may be partially mediated by decreased ENO production via reduced LPS-induced lung iNOS expression.