Nitric oxide production is increased in patients after burn injury

Intradermal methylene blue administration on the progression of burn injuries

OBJECTIVE

A burn injury has two defined areas: central necrosis and an adjacent area of ischaemia, which may or may not progress to necrosis. The concentration of nitric oxide (NO) increases after burn injury and may originate from potent oxidising agents. Methylene blue (MB) may act as an antioxidant and is supposed to reduce burn progression. This investigation was carried out to evaluate the effects of intradermal MB on necrosis progression in burns.

METHODS

Full-thickness burn injuries were performed by applying a heated metal comb on the shaved back of male Wistar rats. The animals were divided into three groups: Control (C, n=7); MB (2mg/kg) one hour after burn injury (MB1h, n=11); and MB (2mg/kg) six hours after burn injury (MB6h, n=8). After seven days the lesions were photographed for visual assessment of burn necrosis; full-thickness cuts of lesions were dyed with Masson and Giemsa for microscopic histopathology; and tissue fragments of unburned interspaces were processed for chemiluminescence with nitrite/nitrate (NOX) and malondialdehyde (MDA) as oxidative stress markers.

RESULTS

No statistically significant differences between groups were observed during visual analysis and NOX dosage. However, in microscopic analysis, the MB1h and MB6h groups showed smaller areas of necrosis, less inflammatory infiltration, and a more significant extension of interspaces. Furthermore, the dosage of MDA revealed that the MB1h group showed lower values when compared with the control group (p=0.001).

CONCLUSIONS

The study provided good evidence that MB intradermal injection can reduce necrosis progression in ischaemic perilesional areas and suggests an alternative to treating burns.

Nitric Oxide Therapy for Diabetic Wound Healing

Nitric oxide (NO) represents a potential wound therapeutic agent due to its ability to regulate inflammation and eradicate bacterial infections. Two broad strategies exist to utilize NO for wound healing; liberating NO from endogenous reservoirs, and supplementing NO from exogenous sources. This progress report examines the efficacy of a variety of NO-based methods to improve wound outcomes, with particular attention given to diabetes-associated chronic wounds.

Restoration of skin pigmentation after deep partial or full-thickness burn injury

Significant skin pigmentation changes occur when patients suffer deep burn injuries. These pigmentation disorders may cause not only cosmetic and psychological issues, but more importantly it increases the risk of skin cancer or photoaging. Severe burns significantly effect on the process of repigmentation as the pigmentation is tightly regulated by cell proliferation and differentiation of melanocytes and melanocyte stem cells which are housing in the epidermis and hair follicles of the skin. In the present review, we discuss the possible mechanisms to replenish the melanocytes from the healthy epidermis and hair follicles surrounding burn wounds. The molecular mechanisms of skin repigmentation following healing of burn injuries includes the differentiation of melanoblasts into melanocytes, the distribution and responses of melanocytes and melanocyte stem cells after burn injury, and the regulation of melanin production. We also reviewed advanced therapeutic strategies to treat pigmentation disorders, such as convectional surgery, laser, UV treatment and emerging concepts in skin tissue-engineering.

Polymerized human placenta haemoglobin attenuates myocardial injury and aortic endothelial dysfunction in a rat model of severe burns

This study was designed to investigate the effect of polymerized human placenta haemoglobin (PolyPHb) on cardiac dysfunction after severe burns. A total of 60 male Sprague-Dawley rats were randomly divided into 3 groups: Sham, Burn and Burn + PolyPHb groups. Rats were subjected to third-degree burns to 30% of total body surface area and the haemodynamics, cardiac enzyme release and aortic endothelium ultrastructure/function were measured. PolyPHb (0.5 gHb/kg) greatly improved mean arterial pressure, left ventricular developed pressure (LVDP), maximum LVDP increase and decrease rate and reduced left ventricular end-diastolic pressure as compared to the Burn group. The plasma levels of cardiac enzyme including CK-MB and troponin I were also significantly down-regulated in the Burn + PolyPHb group. In addition, PolyPHb treatment markedly restored the endothelium-dependent relaxation impaired by severe burns and pathological changes of endothelium in aorta. Therefore, our data suggest that PolyPHb can limit severe burn-induced myocardial injury, which is associated with protection of aortic endothelium.

Methylene blue reduces progression of burn and increases skin survival in an experimental rat model

Following burn, increased nitric oxide (NO) combine with superoxide anion forming peroxynitrite. Methylene blue (MB) has NO blocking and antioxidant effects. Male Wistar rats (250g) were burned bilaterally in dorsum with a comb metal plate heated inside boiling water and applied during 30s, creating four rectangular 10×20mm full-thickness burned areas separated by three 5×20mm unburned interspaces (stasis zone). 30 rats were randomized into three groups (n=10): treated groups received one dose of intraperitoneal (IP) MB injections (2mg/kg), one or six hours after injury, and control group received saline. Seven days after injury, wounds were visually analyzed for interspaces necrosis; full-thickness sections were evaluated with Masson staining; tissue fragments were processed for nitrite/nitrate (NOx) and malondialdehyde (MDA) dosages. Photographic analysis: interspaces progression to necrosis were higher in control (64.8%) than in one (44.7%) and six (13.3%) hours MB groups (P=0.0060). Histopathology showed lower necrosis percentage in one (34.85%) and six (41.62%) hours MB groups than control (77.03%) (P=0.0034) and higher normal skin percentage in one (25.33%) and six (26.85%) hours MB groups than control (8.32%) (P=0.0037). Re-epithelialization skin areas were higher in both MB groups (39.94% for one and 31.89% for six hours) than control (14.63%) (P=0.0210). Interspace's NOx increased in both MB groups (P=0.0130) with no difference in burned areas. No MDA difference was observed. IP MB injection one or six hours after injury reduced necrosis progression in stasis area in the rat comb burn model suggesting an antioxidant effect reducing oxidative stress.

Evaluation of plasma oxidative stress, with or without antioxidant supplementation, in superficial partial thickness burn patients: a pilot study

BACKGROUND

Oxidative stress is one of the main causes of pathophysiological alterations observed during burn injury. The present pilot study aimed to determine whether a specific oral antioxidant supplementation could in any way influence free radical blood values in patients affected by superficial partial thickness burns.

MATERIALS AND METHODS

Plasma oxidants and plasma antioxidant capacity were analysed in 20 superficial partial thickness burn patients for a 2-week period; patients were randomly divided into two groups, one of which was supported with a specifically designed oral antioxidant formula (Squalene 100 mg, Vitamin C 30 mg, Coenzyme Q10 10 mg, Zinc 5 mg, Beta Carotene 3.6 mg, Bioflavonoids 30 mg, Selenium 55 mcg) administered daily, starting from the day of admission, for the whole study period.

RESULTS

No significant differences were found in plasma oxidants and plasma antioxidant capacity between the two groups of patients.

CONCLUSIONS

These results did not reflect any significant benefits of an antioxidant oral supplementation at usual dosages when considering oxidative plasmatic values of superficial partial thickness burn patients.

Prevention of post-traumatic clinical capillary leak syndrome

Systemic capillary leak is an early feature of the inflammatory response to localized injury, and is proportional to the severity of the inflammatory insult. Loss of local control of inflammation leads to an exaggerated systemic inflammatory response known as systemic inflammatory response syndrome (SIRS). SIRS is associated with multiple organ failure and death when there is failure to maintain homeostasis.

Whilst the application of molecular biology and recombinant techniques have produced major advances in our understanding of the mediation of the inflammatory response, there is no agent currently available which will prevent SIRS and reduce the incidence of post-traumatic multiple organ failure. In the meantime, a more practical approach to the avoidance of SIRS and its attendant capillary leak syndrome is to attempt to reduce the deleterious effects of interstitial oedema by tailoring treatment to the rapid changes in capillary permeability.

Dendrimer encapsulation enhances anti-inflammatory efficacy of silver nanoparticles

BACKGROUND

Our previous studies revealed that silver nanoparticles (AgNPs) promoted wound healing in part through their anti-inflammatory actions. As recent reports also suggested anti-inflammatory effects of dendrimers, we therefore undertook this study using dendrimer as the delivery system for AgNP to explore any potential synergistic anti-inflammatory efficacy.

METHODS

Lipopolysaccharide (LPS) was added to cultured RAW264.7 and J774.1 cells to mimic in vitro inflammation condition, followed by the addition of either silver dendrimer nanocomposite (Ag-DNC), AgNPs, or dendrimer. The levels of inflammatory markers TNF-alpha and interleukin-6 were assessed using ELISA assay. Furthermore, in vivo effects such of Ag-DNC, AgNPs, or dendrimer were studied in a burn wound model in mice.

RESULTS

Our results confirmed that both naked dendrimer and AgNPs had anti-inflammatory properties. In in vitro study, Ag-DNC was shown to have the best anti-inflammatory efficacy than AgNPs or dendrimer alone. In-vivo experiments also indicated that animals in the Ag-DNC group had the fastest healing time with the least inflammation.

CONCLUSION

Our study would suggest that dendrimer could provide additional anti-inflammatory benefits and might be an excellent delivery system for silver nanoparticles for future clinical application.

Falsely raised whole blood chloride caused by systemic absorption of cerium nitrate cream for burns

Whole blood, serum or plasma chloride is almost exclusively measured by potentiometry with an ion-selective chloride electrode which utilizes membrane selectivity to chloride ions. Other anions such as bromide, iodide and thiosulphate can interfere but usually are not present in high enough concentration to cause significant cross reactivity. A patient from our burns unit had serial chloride measurements on a Radiometer ABL800 blood gas analyser. The results were higher in contrast to plasma measurements on the Abbott Architect Ci8200, which were within reference intervals and in line with the patient's pathophysiological status. This indicated a likely interference with the blood gas analyser chloride estimation. The chloride results on the ABL800 for 3rd, 4th and 5th day after the burn accident were 170, 137 and 119 mmol/L. Corresponding plasma chloride results on the Ci8200 were all around 105 mmol/L. Nitrate was found to be markedly elevated in these samples, and the results were 6.7, 4.9 and 1.1 mmol/L, respectively (reference limit < 0.08 mmol/L). To further demonstrate nitrate was the causative agent, pooled plasma spiked with 7 mmol/L of sodium nitrate caused a rise in the ABL800 chloride from 105 to 202 mmol/L. Later we confirmed that the patient was topically medicated with cerium nitrate cream (Flammacerium®, Sinclair IS Pharma, UK) for his burns. In summary, the results clearly indicated nitrate was the interferent with the ABL800 chloride estimation and the source was the topical burns cerium nitrate cream.

Guanylate cyclase inhibition by methylene blue as an option in the treatment of vasoplegia after a severe burn. A medical hypothesis

Today it is known that severe burns can be accompanied by the phenomenon of vasoplegic syndrome (VS), which is manifested by persistent and diffuse vasodilation, hypotension and low vascular resistance, resulting in circulatory and respiratory failure. The decrease in systemic vascular resistance observed in VS is associated with excessive production of nitric oxide (NO). In the last 2 decades, studies have reported promising results from the administration of an NO competitor, methylene blue (MB), which is an inhibitor of the soluble guanylate cyclase (sGC), in the treatment of refractory cases of vasoplegia. This medical hypothesis rationale is focused on the tripod of burns/vasoplegia catecholamine resistant/methylene blue. This article has 3 main objectives: 1) to study the guanylate cyclase inhibition by MB in burns; 2) to suggest MB as a viable, safe and useful co-adjuvant therapeutic tool of fluid resuscitation, and; 3) to suggest MB as burns hypotensive vasoplegia amine-resistant treatment.

Estrogen treatment following severe burn injury reduces brain inflammation and apoptotic signaling

Background

Patients with severe burn injury experience a rapid elevation in multiple circulating pro-inflammatory cytokines, with the levels correlating with both injury severity and outcome. Accumulations of these cytokines in animal models have been observed in remote organs, however data are lacking regarding early brain cytokine levels following burn injury, and the effects of estradiol on these levels. Using an experimental animal model, we studied the acute effects of a full-thickness third degree burn on brain levels of TNF-α, IL-1β, and IL-6 and the protective effects of acute estrogen treatment on these levels. Additionally, the acute administration of estrogen on regulation of inflammatory and apoptotic events in the brain following severe burn injury were studied through measuring the levels of phospho-ERK, phospho-Akt, active caspase-3, and PARP cleavage in the placebo and estrogen treated groups.

Methods

In this study, 149 adult Sprague-Dawley male rats received 3rd degree 40% total body surface area (TBSA) burns. Fifteen minutes following burn injury, the animals received a subcutaneous injection of either placebo (n = 72) or 17 beta-estradiol (n = 72). Brains were harvested at 0.5, 1, 2, 4, 6, 8, 12, 18, and 24 hours after injury from the control (n = 5), placebo (n = 8/time point), and estrogen treated animals (n = 8/time point). The brain cytokine levels were measured using the ELISA method. In addition, we assessed the levels of phosphorylated-ERK, phosphorylated-Akt, active caspase-3, and the levels of cleaved PARP at the 24 hour time-point using Western blot analysis.

Results

In burned rats, 17 beta-estradiol significantly decreased the levels of brain tissue TNF-α (~25%), IL-1β (~60%), and IL-6 (~90%) when compared to the placebo group. In addition, we determined that in the estrogen-treated rats there was an increase in the levels of phospho-ERK (p < 0.01) and Akt (p < 0.05) at the 24 hour time-point, and that 17 beta-estradiol blocked the activation of caspase-3 (p < 0.01) and subsequent cleavage of PARP (p < 0.05).

Conclusion

Following severe burn injury, estrogens decrease both brain inflammation and the activation of apoptosis, represented by an increase in the levels of phospho-Akt and inhibition of caspase-3 activation and PARP cleavage. Results from these studies will help further our understanding of how estrogens protect the brain following burn injury, and may provide a novel, safe, and effective clinical treatment to combat remote secondary burn injury in the brain and to preserve cognition.

Bench-to-bedside review: Burn-induced cerebral inflammation--a neglected entity?

Severe burn injury remains a major burden on patients and healthcare systems. Following severe burns, the injured tissues mount a local inflammatory response aiming to restore homeostasis. With excessive burn load, the immune response becomes disproportionate and patients may develop an overshooting systemic inflammatory response, compromising multiple physiological barriers in the lung, kidney, liver, and brain. If the blood–brain barrier is breached, systemic inflammatory molecules and phagocytes readily enter the brain and activate sessile cells of the central nervous system. Copious amounts of reactive oxygen species, reactive nitrogen species, proteases, cytokines/chemokines, and complement proteins are being released by these inflammatory cells, resulting in additional neuronal damage and life-threatening cerebral edema. Despite the correlation between cerebral complications in severe burn victims with mortality, burn-induced neuroinflammation continues to fly under the radar as an underestimated entity in the critically ill burn patient. In this paper, we illustrate the molecular events leading to blood–brain barrier breakdown, with a focus on the subsequent neuroinflammatory changes leading to cerebral edema in patients with severe burns.

Nitric oxide, antioxidant capacity, nitric oxide synthase and xanthine oxidase plasma levels in a cohort of burn patients

BACKGROUND

Nitric oxide (NO) is an important signal molecule in many types of cells and tissues. Efficiently balanced NO production was noted to play an important role in the healing of burns. However, the exact pathophysiological role of NO in burns and its potent relation with clinical and laboratory parameters has not been elucidated.

METHODS

A cohort of 23 burn patients followed for 5 days were enrolled. NO, antioxidant capacity (AC), NO synthase (NOS) activity and xanthine oxidase (XO) activity were indirectly determined by fluorophotometer. Multiple regression against total burn surface area (TBSA), age, weight, height, proximity of septic episode, hemoglobin, white blood cells, percent of neutrophils, platelets, glucose, urea, potassium, sodium and albumin was performed.

RESULTS

Elevation of NO, XO and AC levels is observed from day 2 (p<0.00001), day 4 (p=0.005) and day 6 (p=0.036), respectively. At the end of follow-up period (day 6), NO production was found to independently correlate with TBSA, glucose levels and percent of neutrophils (p=0.0004), AC with age, hemoglobin and glucose levels (p=0.012), and NOS with proximity of septic episode and glucose levels (p=0.027).

CONCLUSIONS

NO production exerts its prophylactic effect from the first 24h after burn, and is independently correlated with severe injury, enhanced neutrophil motivation and augmented glucose levels, thus possibly representing a response to stress. This need might trigger induction of XO and salvage of antioxidants, as suggested by their rise at a later stage. These data underline that an effort to compromise stress and to administer antioxidants could be a priority in the treatment of these patients.

Brain and cognitive impairments from burn injury in rats

Severe burn injuries affect not only the release of stress hormones but also the metabolism of nitric oxide (NO), a substance playing a large role in cognition. We investigated the effect of third-degree burns both on central NO-levels and on short-term memory in rats. Burns were administered under halothane-anesthesia by dipping 20% of the skin area in hot water. In a first experiment, NO-changes were estimated over hours by differential normal pulse voltammetry (DPNV) with a sensor implanted chronically in the frontal cortex. In a second experiment, cognitive abilities were tested over days by comparing the spontaneous time used to explore objects that the animals had, either never- or already-encountered before. Cerebral NO appeared steadily depleted for at least 12h after the injury, not after control anesthesia. During nine days following the burn, discrimination performance was lower compared to controls. Putting together the results of the two experiments, especially on the day of burn, NO changes are likely to account for the behavioral effect. A choice of neuro-pharmacological agents involved in NO-metabolism, together with a choice of proper anesthetics, should now be tested as means to alleviate cognitive impairments following third-degree burns.

Screening for the formation of reactive oxygen species and of NO in muscle tissue and remote organs upon mechanical trauma to the mouse hind limb

BACKGROUND

Until now, no systematic surveys exist in the literature on the early local and systemic generation of reactive oxygen species and of nitric oxide in response to muscle crush injury. Therefore, this study aims to evaluate the formation of reactive oxygen species and nitric oxide in different tissues (injured and contralateral muscle, liver, kidney, spleen and blood) that is induced by closed muscle trauma.

METHODS

5, 45 and 180 min after induction of blunt trauma to the mouse gastrocnemius muscle, animals were sacrificed, tissues harvested and homogenized, and analyzed for their content of glutathione, nitrate and thiobarbituric acid-reactive substances.

RESULTS

The local formation of reactive oxygen species in the injured muscle started immediately upon induction of the mechanical trauma as indicated by changes in the glutathione redox balance. Liver and kidney did not show any response to trauma; however, a marked and immediate increase in the splenic nitrate content was detected, thus suggesting a specific nitric oxide-dependent response of splenic cells to injury.

CONCLUSION

We conclude that immediately after the induction of trauma a formation of reactive oxygen species takes place at the site of crush injury. This might constitute the basis of further damage to the injured tissue by free radical-dependent mechanisms. The immediate formation of nitric oxide within the spleen upon muscle crush appears to represent a specific signalling mechanism of the body in response to distant organ injury.

The role of NO in macrophage dysfunction at early stage after burn injury

AIM

To explore the role of nitric oxide (NO) in macrophage dysfunction at early stage after burn injury.

METHOD

Peritoneal macrophages were isolated and cultured from early stage burnt mice. NO production and inducible NO synthase (iNOS) expression in the macrophages were checked by the Greiss method and real-time PCR (TaqMan), respectively. l-Arginine, the substrate of NO producing, or N-monomethyl-l-arginine (l-NMMA), a competing blocker of NOS was administered to the culture, the changes of NO, TNF-alpha and PGE2 productions were measured, additionally the changes of the iNOS, TNF-alpha and COX-2 expression were assayed by real-time PCR. After that, the effects of l-arginine and l-NMMA were determined on burnt macrophage influencing the proliferation of normal splenic lymphocytes.

RESULT

A large amount of NO was produced by macrophages from post burn hour 6 (6PBH) with a high level of iNOS expression. l-Arginine could increase NO production in a dosage-dependent manner, while l-NMMA attenuated NO production, but neither could affect iNOS expression. Moreover, l-arginine enhanced productions of both the latter produced TNF-alpha and PGE2 from burnt macrophages, and the expressions of TNF-alpha and COX-2 were improved significantly, while l-NMMA did reverse ways. It was found that macrophages from post burn hour 24 mice could inhibit Con A-stimulated normal splenic lymphocytes dramatically, l-NMMA could decrease this function significantly, but l-arginine could not influence the suppression.

CONCLUSION

Our experiment indicated NO derived from burnt macrophage played a vital role in macrophage producing excessive TNF-alpha and PGE2, and suppressing lymphocyte function at early stage after burn injury.

Skin nitric oxide and its metabolites are increased in nonburned skin after thermal injuries

Local and systemic inflammation can lead to progression of burn wounds, converting second- to third-degree wounds or extending the burn to adjacent areas. Previous studies have suggested that the skin is an important site of production of nitric oxide (NO), synthesized by inducible nitric oxide synthase (iNOS) activation after injury. NO increases in burned wounds, but its formation in noninjured skin has not been investigated. We hypothesized that after severe burns, NO and cytotoxic peroxynitrite would increase in noninjured skin. We also tested the hypothesis that BBS-2, a specific inhibitor of iNOS, would impair NO formation after burn. Thirteen female sheep were randomized into burn injury and smoke inhalation (n = 5, group 1), burn and smoke treated with BBS-2 (n = 3, group 2), and sham (saline treatment, no injury) (n = 5, group 3). All the animals, including the sham-injury group, were mechanically ventilated for 48 h. Samples of nonburned skin and plasma were collected from each animal, and levels of NO and its metabolites were evaluated using a NO chemiluminescent detector. Nitrotyrosine and iNOS expression were determined in the skin by Immunoperoxidase staining, and scoring of masked slides (epidermis, hair follicles, vessels, glands, and stroma) was performed. Skin NO and metabolites significantly increased in the burn and smoke injury group, and this was inhibited by BBS-2. Nitrotyrosine expression also increased significantly in the skin of burned animals. BBS-2 prevented the increase of NOx but not the increase of nitrotyrosine expression in skin. Plasma levels of NO increased in burned animals when compared with sham, but this increase was not significant. The increase of NO and its metabolites after burn in noninjured skin is followed by a significant increase in peroxynitrite, a potent cytotoxic mediator.

Roles of nitric oxide and prostaglandins in pathogenesis of delayed colonic transit after burn injury in rats

Burn injury has been shown to impair gut transit, but the exact mechanism remains unknown. The present study investigated whether nitric oxide synthase (NOS) and cyclooxygenase (COX) mediated changes in burn-induced colonic transit. After rats underwent 30% total body surface area burn injury, they were injected with S-methylisothiourea (SMT, selective inducible NOS inhibitor), 7-nitronidazole (7-NI, selective neuronal NOS inhibitor), and nimesulide (NIM, selective COX-2 inhibitor), respectively. The protein and mRNA of NOS and COX-2 were measured by Western blot analysis and real-time RT-RCR, and localization of NOS and COX-2 protein was determined by immunohistochemistry. Our results showed that colonic transit assessed by the geometric center was delayed from 3.47+/-0.28 in controls to 2.21+/-0.18 after burn (P<0.009). SMT and NIM significantly improved colonic transit in burned rats but had no effect in sham-operated rats. 7-NI failed to modify delayed transit in burned rats but significantly delayed colonic transit in sham-operated rats. Both protein and mRNA of inducible NOS and COX-2 increased significantly but not neuronal NOS in burned rats. Inducible NOS protein expression was noted not only in epithelial cells but also in neurons of the myenteric ganglia in burned rats. These findings suggest that nitric oxide (NO) produced by neuronal NOS plays an important role in mediating colonic transit under the physiological condition. NO produced by inducible NOS and prostaglandins synthesized by COX-2 are both involved in the pathogenesis of delayed colonic transit after burn injury. Inducible NOS expression in neurons of the myenteric ganglia may contribute to dysmotility with burn injury.

MAP kinases differentially regulate the expression of macrophage hyperactivity after thermal injury

Thermal injury increases the capacity of macrophages (Mphi) to produce various inflammatory mediators, (i.e., Mphi hyperactivity), which is believed to be involved in the development of subsequent immunosuppression, sepsis, and multiple organ failure. The signal transduction pathways involved in the expression of Mphi hyperactivity post-burn, however, remain to be clearly elucidated. To study this C57BL/6 female mice were subjected to a 25% TBSA burn and splenic Mphis were isolated 7 days later. LPS-stimulated inflammatory mediator production and MAPK expression (P38 ERK 1/2 and JNK) were determined. Burn injury increased LPS-induced P38 MAPK, suppressed JNK activation and ERK 1/2 activation was unaltered. These changes in MAPK activation were paralleled by the increased production of PGE(2), TNF-alpha, IL-1beta, IL-6, and IL-10. Differential sensitivity to the inhibition of the MAPK pathways was observed with regard to the mediator evaluated and the presence or absence of burn injury. In general cytokine production in the burn group was in part resistant to the inhibition of a single MAPK pathway as compared with shams. Thus, burn injury increases cross-talk between the MAPKs pathways, suggesting that alterations MAPK activation and signal transduction contribute to the development Mphi hyperactivity post-injury.

Nitric oxide, inflammation and acute burn injury

Nitric oxide (NOz.rad;) is a diatomic mediator liberated on oxidation of L-arginine by the nitric oxide synthase (NOS) family of enzymes. It has complex and wide ranging functions in vivo and has been implicated in the development of the profound inflammatory response that occurs as a result of cutaneous burn injury. In addition, dysregulation of NOS activity has been associated with multiple organ failure in human burn patients and may therefore represent a novel therapeutic target in such circumstances. This review focuses on the role of NOz.rad; in inflammation, with particular emphasis on the acute post-burn inflammatory response. Specific areas of discussion include the maintenance of microvascular haemostasis, leukocyte recruitment and remote organ dysfunction following thermal injury.

Effects of a thermal injury on brain and blood nitric oxide (NO) content in the rat

In the present study, the effects of a thermal injury on the nitric oxide (NO)-ergic system was investigated in freely moving rats. Using a voltammetric method allowing direct and in situ NO measurements, a significant decrease in cortical NO concentration was observed during the 24h following burning procedure. Since in the burning procedure halothane was employed, it was verified that this anaesthetic did not induce significant effect on cortical NO level. Experiments conducted in ex vivo conditions showed that blood NO and nitrites (NO(2)(-)) + nitrates (NO(3)(-)) concentrations increased strongly after burn injury while hypothalamic inducible NO-synthase (NOS(2)) mRNA level decreased significantly. A thermal injury was thus accompanied by a rapid impairment of the NO-ergic pathways, which might partly have been responsible for numerous changes occurring after burn injury.

Peroxynitrite is an important mediator in thermal injury-induced lung damage

OBJECTIVE

Intestinal ischemia and reperfusion injury was known to cause postinjury multiple organ failure by neutrophil and unclear nonneutrophil factors. Peroxynitrite formed by the rapid reaction between superoxide and nitric oxide, is a toxic substance that contributes to tissue injury in a number of biological systems. In this study, the role of nitric oxide and neutrophils on lung damage after burn was investigated.

DESIGN

Prospective, experimental study.

SETTING

Research laboratory at a university hospital.

SUBJECTS

Thermal injury models in the rat.

INTERVENTIONS

In experiment 1, specific pathogen-free Sprague-Dawley rats underwent 35% total body surface area burn. At 4, 8, 16, and 24 hrs after burn, intestinal mucosa and lung tissue were harvested for myeloperoxidase (MPO) assay, blood was collected for measurement of peroxynitrite-mediated oxidation of dihydrorhodamine 123, and pulmonary microvascular dysfunction was quantified by measuring the extravasation of Evans blue dye. In experiment 2, polymorphonuclear granulocyte antibody (0.12 mL/100 g administered intraperitoneally 16 hrs before burn), S-methylisothiourea (7.5 mg/kg, intraperitoneally, immediately after burn), a specific inducible nitric oxide synthase inhibitor, and sterile saline (15 mL/kg, intraperitoneally, immediately after burn) were given to different groups of thermally injured animals individually. The plasma dihydrorhodamine 123 oxidation level, intestinal and lung MPO activity, lung permeability, and lung histology were evaluated at 8 hrs after burn. The cellular localization of nitrotyrosine, a marker for peroxynitrite reactivity, was also examined by immunostaining. In experiment 3, 3-morpholinosydnonimine (10 mM, intraperitoneally), a peroxynitrite donor, was given to nonburned rats to examine the peroxynitrite effect on lung inducible nitric oxide synthase expression.

MEASUREMENTS AND MAIN RESULTS

The level of MPO activity in intestine and lung, blood dihydrorhodamine 123 oxidation, and lung permeability were increased up to 2-fold, 2.5-fold, 2-fold, and 2-fold of normal, respectively, at 8 hrs after burn. S-methylisothiourea injection significantly decreased (p <.05) 31% of the lung MPO activity, 41% of the blood peroxynitrite level, 54% of the lung permeability, and the lung peroxynitrite production in burned rats. Polymorphonuclear granulocyte antibody pretreatment significantly decreased 60% of the intestinal MPO, 92% of the blood peroxynitrite level, and 56% the lung MPO activity in burned rats, but the lung permeability was only slightly decreased by polymorphonuclear granulocyte antibody pretreatment. Furthermore, 3-morpholinosydnonimine increased the lung inducible nitric oxide synthase messenger RNA levels.

CONCLUSIONS

Thermal injury induces blood dihydrorhodamine 123 oxidation, intestinal and lung neutrophil deposition, lung nitrotyrosine production, and lung damage. Both specific inhibition of inducible nitric oxide synthase and polymorphonuclear granulocyte antibody pretreatment decrease blood dihydrorhodamine 123 oxidation and intestinal and lung neutrophil deposition, but only inducible nitric oxide synthase inhibition with S-methylisothiourea reduces lung peroxynitrite production and thermal injury-induced lung damage. Nitric oxide and the ensuing peroxynitrite production in lung play a more important role than neutrophil in contributing to thermal injury-induced lung damage.

Macrophages and post-burn immune dysfunction

The activation of a pro-inflammatory cascade after burn injury appears to be important in the development of subsequent immune dysfunction, susceptibility to sepsis and multiple organ failure. Macrophages are major producers of pro-inflammatory mediators and their productive capacity for these mediators is markedly enhanced following thermal injury. Thus, macrophage hyperactivity (as defined by increased productive capacity for pro-inflammatory mediators) appears to be of critical importance in the development of post-burn immune dysfunction. This review will focus on the current state of knowledge with regards to the role of macrophages in the development of post-burn immune dysfunction. Particular areas of discussion include: nitric oxide synthase (NOS) and cyclooxygenase (COX) enzyme systems, macrophages and the T-helper (Th)-1/Th-2 cytokine responses, alterations in macrophages signal transduction and a potential role for gamma/delta T-cells in the development of macrophage hyperactivity following thermal injury. A more comprehensive understanding of the relationship between macrophage activity and post-burn immune dysfunction will hopefully provide the basis for improved therapeutic regimes in the treatment of burn patients.

Nitric oxide inhibits spleen cell proliferative response after burn injury by inducing cytostasis, apoptosis, and necrosis of activated T lymphocytes: role of the guanylate cyclase

We previously showed that an overproduction of nitric oxide (NO) by macrophages was responsible for the collapse of lymphoproliferative responses after burn injury in rats. First, we demonstrate here that 10 days post-burn, the inhibition of splenocyte response to concanavalin-A results from cytostatic, apoptotic, and necrotic effects of NO on activated T cells. This was evidenced by various criteria at the levels of DNA, mitochondria, and plasma membrane. Inhibition of NO synthase by S-methylisothiourea (10 microM) normalized all the parameters. Second, we show that two soluble guanylate cyclase (sGC) inhibitors, LY83583 and ODQ, restored the proliferative response in a concentration-dependent manner. LY83583 (0.5 microM) rescued T cells from apoptosis. Similar results were obtained with KT5823 (5 microM) a specific inhibitor of protein kinase G (PKG). In contrast, neither LY83583 nor KT5823 inhibited NO-induced necrosis. These results suggest that NO blocked T cells in the G1 phase and induced apoptosis through a sGC-PKG-dependent pathway and necrosis through an independent one.

Naltrexone attenuates plasma nitric oxide release following acute heat stress

Previous studies have shown that naltrexone attenuates morbidity and mortality in heat stress by inhibiting endogenous opioids. In this study, we hypothesized that naltrexone can decrease heat stress by attenuating nitric oxide release. Male Sprague-Dawley rats were pretreated with naltrexone or normal saline, and exposed to 45 degrees C for 25 min; controls were exposed to 25 degrees C. Colonic temperatures were recorded and plasma samples from an in-dwelling i.v. cannula were analyzed for nitrate/nitrite levels. Following heat stress, peak colonic temperature was significantly diminished (P < 0.05) in naltrexone-treated rats compared to saline-treated rats. Plasma nitrate/nitrite levels were significantly lower (P < 0.05) in naltrexone-treated rats compared to saline-treated rats. These findings suggest that naltrexone is able to attenuate the rise in plasma nitric oxide levels commonly observed after heat stress.

Clinical practice parameters for hemodynamic support of pediatric and neonatal patients in septic shock

BACKGROUND

The Institute of Medicine has called for the development of clinical guidelines and practice parameters to develop "best practice" and potentially improve patient outcome.

OBJECTIVE

To provide American College of Critical Care Medicine clinical guidelines for hemodynamic support of neonates and children with septic shock.

SETTING

Individual members of the Society of Critical Care Medicine with special interest in neonatal and pediatric septic shock were identified from literature review and general solicitation at Society of Critical Care Medicine Educational and Scientific Symposia (1998-2001).

METHODS

The MEDLINE literature database was searched with the following age-specific keywords: sepsis, septicemia, septic shock, endotoxemia, persistent pulmonary hypertension, nitric oxide, and extracorporeal membrane oxygenation. More than 30 experts graded literature and drafted specific recommendations by using a modified Delphi method. More than 30 more experts then reviewed the compiled recommendations. The task-force chairman modified the document until <10% of experts disagreed with the recommendations.

RESULTS

Only four randomized controlled trials in children with septic shock could be identified. None of these randomized trials led to a change in practice. Clinical practice has been based, for the most part, on physiologic experiments, case series, and cohort studies. Despite relatively low American College of Critical Care Medicine-graded evidence in the pediatric literature, outcomes in children have improved from 97% mortality in the 1960s to 60% in the 1980s and 9% mortality in 1999. U.S. hospital survival was three-fold better in children compared with adults (9% vs. 27% mortality) in 1999. Shock pathophysiology and response to therapies is age specific. For example, cardiac failure is a predominant cause of death in neonates and children, but vascular failure is a predominant cause of death in adults. Inotropes, vasodilators (children), inhaled nitric oxide (neonates), and extracorporeal membrane oxygenation can be more important contributors to survival in the pediatric populations, whereas vasopressors can be more important contributors to adult survival.

CONCLUSION

American College of Critical Care Medicine adult guidelines for hemodynamic support of septic shock have little application to the management of pediatric or neonatal septic shock. Studies are required to determine whether American College of Critical Care Medicine guidelines for hemodynamic support of pediatric and neonatal septic shock will be implemented and associated with improved outcome.

Nitric oxide-peroxynitrite-poly(ADP-ribose) polymerase pathway in the skin

In the last decade it has become well established that in the skin, nitric oxide (NO), a diffusable gas, mediates various physiologic functions ranging from the regulation of cutaneous blood flow to melanogenesis. If produced in excess, NO combines with superoxide anion to form peroxynitrite (ONOO-), a cytotoxic oxidant that has been made responsible for tissue injury during shock, inflammation and ischemia-reperfusion. The opposite effects of NO and ONOO- on various cellular processes may explain the 'double-edged sword' nature of NO depending on whether or not cellular conditions favour peroxynitrite formation. Peroxynitrite has been shown to activate the nuclear nick sensor enzyme, poly(ADP-ribose) polymerase (PARP). Overactivation of PARP depletes the cellular stores of NAD+, the substrate of PARP, and the ensuing 'cellular energetic catastrophy' results in necrotic cell death. Whereas the role of NO in numerous skin diseases including wound healing, burn injury, psoriasis, irritant and allergic contact dermatitis, ultraviolet (UV) light-induced sunburn erythema and the control of skin infections has been extensively documented, the intracutaneous role of peroxynitrite and PARP has not been fully explored. We have recently demonstrated peroxynitrite production, DNA breakage and PARP activation in a murine model of contact hypersensitivity, and propose that the peroxynitrite-PARP route represents a common pathway in the pathomechanism of inflammatory skin diseases. Here we briefly review the role of NO in skin pathology and focus on the possible roles played by peroxynitrite and PARP in various skin diseases.

[Inflammatory reaction and infection in severe burns]

Major burn injury is a lesion where the inflammatory reaction is exported to the whole body. After a short time of hemodynamic changes, this inflammation is kept by necrotic tissues, persistence of an opened wound, and by the pulmonary and gut reactions. When infection starts, it becomes difficult to distinguish its symptoms among the inflammatory signals. The main point of the care of burn patient consists in trying to control this reaction and the immuno-depression it leads to: early excision and grafts, early enteral nutrition, perfect nursing care. There is no specific medical treatment of this state. The antibiotic use must be well weighed up. Infection is often the trigger of the multiple organ dysfunction which is the way the burn patient dies but is not mandatory.

[Initial shock from burns. Physiopathology: therapeutic principles]

Widespread destruction of the skin induces a large necrotic mass and a break of the skin barrier. It also leads to an intense inflammatory reaction. This activates keratinocytes, endothelial cells and neutrophils. Certain mediators (e.g. endothelin, histamine, bradykinin, serotonin, catecholamines, vasopressin, prostaglandins, cytokines and nitrogen monoxide) are thus released in large quantities and act both at the site of the burns and at a distance. The abnormally high level of albumin in the capillary wall and the increased capacity of absorption of the interstitial areas around the burns are the main abnormalities observed. This results in a hypovolemia associated with a hemoconcentration, hyponatremia, hypoalbuminemia, systemic vasoconstriction and myocardial malfunction, which is difficult to evidence. During the initial phase, the major risk is the appearance of hypovolemic shock, which is rapidly irreversible if early treatment is not administered. Vascular filling with iso- or hyper-osmolar sodium crystalloids, associated with buffer solutions, is the first line. There is still debate regarding the best moment at which to give albumin. A hyperkinetic shock may occur after several hours and despite the filling. The symptoms are tachycardia, increased heart rate and a dramatic decrease in systemic vascular resistance. This may lead to metabolic acidosis and multi-organ failure. Study of the hemodynamic profile of the patient allows the rational use of pressor amines and haemodialysis.

Humoral markers of severity and prognosis of critical illness

Despite the considerable advances made in understanding the pathophysiology of systemic inflammation during critical illness, clinical progress has been elusive as it remains a very deadly condition. Cortisol and thyroid hormone levels can be as predictive of outcome as the commonly used severity parameters (i.e. APACHE). Indeed, levels of endocrine humoral substances such as arachidonic acids, nitric oxide, endothelin, calcitonin precursors, leptin and adenosine correlate with the severity and outcome of critical illness. Furthermore, calcitonin precursors represent a potentially new hormokine paradigm, being transcriptionally activated in all cells in response to infection. The cytokines are immune markers that often correlate with severity and outcome, but their release is transient. In contrast, the so-called acute phase proteins, such as C-reactive protein and serum amyloid A, are highly sensitive to inflammatory activity and can be important markers of severity and outcome. Leukocyte esterase, adhesion molecules, platelet activating factor and activated protein C are additional humoral immune markers; the replacement of the latter has been shown to be a promising therapeutic option. Natriuretic peptides are neurocrine humoral markers that have important cardiovascular implications. The level of macrophage migrating inhibitory factor, released by the pituitary, is elevated in sepsis and counteracts glucocorticoid action. Cellular markers to severe stress include the enhanced expression of protective substances in the form of heat shock proteins. High mobility group-1 is a DNA-binding protein and a late mediator of the inflammatory response. Apoptotic markers such as the soluble fas ligand are also elevated in inflammation. In summary, during critical illness, the endocrine, immune and nervous systems elaborate a multitude of humoral markers, the roles of which merit further scrutiny in order to improve therapeutic outcome.

Effects of nitric oxide synthase inhibitors on vascular hyperpermeability with thermal injury in mice

The role of nitric oxide and related synthase in thermal injury was investigated by using models of experimental burn to evaluate severity from the aspect of vascular permeability. Thermal injuries were produced in the murine right ear by pinching with a pair of preheated tweezers. Immediately thereafter, Evans blue dye was intravenously administered, and the mice injured with burns were sacrificed at various times. The burned ears were collected and hydrolyzed, and the level of extracted dye was measured as an indicator of inflammation. Vascular hyperpermeability was suppressed by the administration of nitric oxide synthase inhibitors. LNAME not only suppressed vascular hyperpermeability in thermal injuries in a dose-dependent manner but was also effective with either prophylactic or therapeutic administration. Although aminoguanidine also suppressed the inflammatory response, it had no effect on the early inflammatory phase. Nitric oxide synthase is well known to have two types of isozymes. Aminoguanidine, an inhibitor specific to inducible nitric oxide synthase, suppressed the late phase 6 h after injury, suggesting that inducible nitric oxide synthase is involved in inflammatory responses of thermal injuries. These results also demonstrated that inducible nitric oxide synthase-like protein stained the burned region immunohistochemically. Therefore, both types of enzymes mediating nitric oxide affect inflammatory responses, i.e., vascular hyperpermeability, and their regulation may lead to the development of new therapy for thermal injuries.

Analysis of plasma nitrite/nitrate in human thermal injury

The aim of this study is to examine the characteristics of nitrite/nitrate (NOx), the final metabolite of nitric oxides, in plasma after burn injury. A total of 83 blood samples were collected from 19 patients on arrival, day 1, day 3, and day 5 after suffering burn injuries and from 7 non-burned volunteers. We measured the NOx levels in plasma using the Griess method, and analyzed the relationships among plasma the NOx levels, the burn-magnitude, and the blood examination data using a stepwise multivariate regression analysis. The plasma NOx levels at hospital-arrival after burns significantly exceeded those of non-burned volunteers, and the NOx levels in the plasma returned to normal range after day 1. Based on the findings of a multivariate analysis, the plasma NOx levels at admission to the hospital were not found to be related to the total burn surface area, the burn index or inhalation injury, but they were significantly related to age. Furthermore, these plasma NOx levels were also related to the platelet count, neutrophil count and blood urea nitrogen. The increase in the plasma NOx level may therefore play an important role in the pathophysiology of elderly burned patients, while the nitric oxide levels in the plasma might also play a role in inhibiting the constriction of microvascular smooth muscle in extensively burned patients.

[Systemic complications of extended burns]

Burns covering more than 10% of the total body surface area (TBSA) are responsible for systemic perturbations which, in very severe cases, can represent a vital risk and, in all cases, affect the wound evolution. Among these general perturbations, fluid volume and electrolyte changes, leading eventually to burn shock, have the most dramatic consequences. Burn shock is, still to day, a vital risk and can also, in case of inadequate early fluid resuscitation, results in secondary morbidity and mortality. Fluid replacement during the very first hours after injury represents certainly a key point of the management of severe burn cases. Estimation of resuscitation fluid needs during this period is frequently underestimated. For adult, we recommend, during the first hour, a minimum of one liter for all severe injuries and two liters if the injury exceeds 50% of TBSA. Pulmonary injuries due to smoke inhalation are frequent, about 25% of patients hospitalized in burn units, and responsible for numerous death at site of house fires. In burn units, about 25% of hospitalized patients have pulmonary injuries in relation with smoke inhalation. This population has a high mortality rate increasing with the area of the skin injury and with age. Patients with inhalation injury need more resuscitation fluids, are subject to pneumonia and necessitate frequently mechanical ventilation. Parameters of the mechanical ventilation have to be choice to avoid barotrauma. Severe burn patients are submitted to a very high metabolic level. This can leads to a deep nutritional deficit responsible for an immunological suppression. It is then of major importance to provide an adequate nutritional support. It is also necessary to fight against the stress and to put the patient in a warm environment. Finally, infection is the most frequent and the most severe complication of burn injuries. Everything have to be done to avoid bacteriological contamination including architecture, equipment's, care procedure, nutritional support, types of wound dressing and most importantly surgery. Surgical procedures have to be done as earliest as possible to excise necrosis and cover the wound.

Improved immune functions with administration of a low-fat diet in a burn animal model

The purpose of this study was to characterize the impact of a low-fat (LF; 1% fat) diet, a high-fat (HF; 25% fat) diet, and a standard (SD; 5% fat) diet on immune and oxidative parameters in a 20% body surface area burn animal model fed ad libitum for 10 days postinjury. Although the mechanisms are poorly understood, the amount of dietary lipid in nutritional support has been shown to have immunomodulatory effects after burn injury. Burned mice fed the LF diet showed a normal response in activated splenocyte proliferation compared to burned animals that received the SD or HF diet. Animals fed the SD and HF diets presented increased production of nitric oxide and prostaglandin E2 response after burn injury, which is associated with inhibited splenocyte proliferation. The total thiol concentration in spleen cells from burned animals kept on the HF diet was significantly higher than that in unburned animals, while no increase in these oxidative parameters was observed in LF-fed burned animals. Moreover, the LF diet significantly reduced hepatic lipid peroxidation, as measured by malonaldehyde concentration, compared to the other two diets. These results suggest that the administration of a LF diet in mice after a burn injury prevents inhibition of in vitro splenocyte proliferation and reduces the intensity of oxidative stress.

Are nitrite/nitrate (NOx) levels elevated by inhalation injury?

The relationship between airway burn and nitric oxide (NO) levels in the early burn stage was investigated by quantifying nitrite/nitrate (NOx), which are the final metabolites of NO, in 22 burn patients. Although total body surface area (TBSA) and burn index (BI) were significantly higher in patients with airway-burn than in patients without airway burn (P=0.0347 and 0.0422, respectively), no significant difference in NOx levels was observed between the two groups (P=0.6196). The NOx levels were found to correlate significantly with TBSA (r=0.4775, P=0.0246). A significant correlation was also noted between the NOx levels and BI (r=0.4391, P=0.0409). These results suggest that NO reflects the intensity of inflammation in the early burn stage, but that excessive NO formation is unlikely to be induced by stress, such as that caused by airway burn.

Effect of nitric oxide synthase inhibitor on experimentally induced burn wounds

BACKGROUND

Nitric oxide (NO) may have an important role in the healing of burn wounds. This study investigated the effect of NO on experimentally induced burn wounds by preventing NO synthesis.

METHODS

A total of 40 mice weighing 25 to 30 g were used in this study. The shaved skin on the back of the mice was immersed in 100 degrees C water for 10 seconds to achieve a partial-thickness scald burn. The mice were divided into two groups of 20. In group I (control group), 17.5 mg/kg of serum physiologic (placebo) was injected intraperitoneally two times a day for 15 days. In group II (study group), 17.5 mg/kg of aminoguanidine (NO synthase inhibitor) was injected intraperitoneally two times a day for 15 days. On day 15 of the burn, the animals were killed and the burn areas were investigated histologically. Histologic changes such as epithelial proliferation, abscess, collagen, and granulation tissue were evaluated.

RESULTS

Epithelial proliferation, formation of collagen, and granulation tissue with rich capillaries observed in the control group were statically significantly higher than those observed in the study group (z = -2.022, p < 0.05; z = -2.02, p < 0.05; and z = -2.022, p < 0.05; respectively).

CONCLUSION

We concluded that healing of the burn wound is delayed by preventing NO synthesis.

Nitric oxide indices in human septic shock

OBJECTIVES

To study the relation between nitrite, nitrate, nitrotyrosine, and nitrosothiols as NO indices in human septic shock.

DESIGN

A prospective clinical study.

SETTING

Intensive care units in a university hospital and a central county hospital.

PATIENTS

Sixteen patients admitted for septic shock. Nine healthy volunteers served as controls.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Patients with septic shock had a hyperdynamic circulatory response and required infusion of at least two vasopressors to maintain systemic blood pressure. Four episodes of recurrent shock occurred in two patients. Heparinized plasma was collected once daily for analysis of NO indices. Peak plasma concentrations of nitrite + nitrate (NOx) were elevated in first episodes of septic shock; 144+/-39 microM vs. controls, 20+/-3 microM (p < .05). Peak plasma NOx concentrations in recurrent shocks were; 160+/-19 microM. Peak plasma concentrations of 3-nitrotyrosine (NT) were elevated in primary septic shock 102+/-19 pmol x mL(-1) vs. controls 14+/-6 pmol x mL(-1) (p < .05). Peak NT concentrations were 117+/-37 pmol x mL(-1) in recurrent septic shock. Peak plasma NT concentrations did not coincide with peak NOx concentrations in half of the episodes of septic shock. Plasma NT was elevated (59+/-15 pmol x mL(-1) vs. controls 14+/-6 pmol x mL(-1), p < .05) in patients with normal plasma NOx concentrations throughout septic shock. Plasma concentrations of nitrosothiols did not change during septic shock.

CONCLUSIONS

Plasma concentrations of NOx and NT are elevated in primary episodes of septic shock and may also be elevated in secondary septic shock, but too few episodes of recurrent septic shock occurred to allow firm conclusions. Plasma concentrations of NT are elevated in patients with septic shock with normal plasma NOx concentrations, indicating that plasma concentrations of NOx may not always accurately reflect NO production. Reactive nitrogen species may be formed in septic shock, and measuring both NOx and NT may give a better indication of NO production in septic shock than NOx alone. Plasma levels of nitrosothiols did not change during septic shock.

Role of nitric oxide in wound healing

Nitric oxide is a short-lived free radical, that is capable of multiple effects at the molecular, cellular, and physiologic levels. Over the past several years, nitric oxide has been proved to play an important role in the healing of various types of wounds. The present review examines some of the recently defined roles of nitric oxide in normal and pathologic healing.

Generation of peroxynitrite in localised, moderate temperature burns

Simultaneous generation of nitric oxide (NO*) and superoxide (O2-) can lead to the formation of peroxynitrite (ONOO-), a potent oxidant that has been implicated in the pathogenesis of a number of disease states. This study was designed to investigate the possible generation of ONOO- in local cutaneous tissues following thermal injury. Male Wistar rats were anaesthetised in a nonrecovery procedure and subjected to a small (1 cm diameter), abdominal burn of moderate temperature (50 degrees C, 5-15 min). At either the 60 or 180 min time point postburn the animals were killed, and skin sites were removed and homogenised. An ELISA was used to quantify protein bound 3-nitrotyrosine (3NT), a biomarker for ONOO- in the rat skin. In separate experiments the accumulation of [125I]-albumin in thermally injured skin was used to calculate plasma extravasation. Thermal injury (50 degrees C, 10 min) to rat abdominal skin caused a significant increase in both 3NT (p < 0.05) and oedema formation (p < 0.001) when compared to unheated control sites at the 180 min time point postburn. This data is the first to show protein nitration in thermally injured, oedematous skin and strongly suggests that ONOO- is generated in thermally damaged cutaneous tissue.

Induction of nitric oxide production in infiltrating leukocytes following in vivo irradiation of tumor-bearing mice

Nitric oxide (NO) has been implicated both in regression and progression of tumors due to its production by both tumor cells and infiltrating leukocytes. Ionizing radiation causes the regression of tumors, and can augment the production of NO by macrophages in vitro. We examined the cellular and systemic production of NO in mice in which radiation-resistant RIF-1 fibrosarcoma cells were implanted subcutaneously and were then either irradiated or sham-treated at the tumor site. Ten days following implantation of the tumors, CD45- tumor cells and CD45+ leukocytes were derived from resected tumors immediately after irradiation with 60 Gy, a dose previously reported to reduce tumor growth. Leukocytes from tumors of irradiated hosts produced spontaneously up to four-fold more NO than did either leukocytes from unirradiated mice or CD45- tumor cells from either unirradiated or irradiated mice. Between days 10-14 following tumor implantation, serum NO2-/NO3- increased in both irradiated and unirradiated mice to an equal extent, culminating in levels higher than those of non-tumor-bearing mice. Though NO production is elevated in macrophages treated with 1-10 Gy of radiation in vitro, higher doses may be required by tumor-infiltrating macrophages in vivo and thus may indicate that tumor-infiltrating macrophages are deactivated.

The effects of human burn injury on urinary nitrate excretion

Different studies have demonstrated both an increase and a decrease in the biosynthesis of nitric oxide (NO) during the first 2 days following experimental and human burn trauma. This study investigated changes in urinary nitrate excretion in humans following thermal injury in order to determine the temporal relationship between NO release and the initial injury. Urinary nitrate was measured in daily 24-h urine collections taken on days 1-7 following burn injury from 15 patients. The control group consisted of 11 healthy, age- and sex-matched patients who kept a nitrate-restricted diet for five days prior to collection of a single 24-h urine sample. The burns group had a mean age of 41.9 +/- 19.4 (mean +/- S.D.) years and a mean total burn surface area (TBSA) of 30.2 +/- 24.9% (mean +/- S.D.). In the burn injured patients, urinary nitrate levels peaked at day 4 and a 2-fold increase relative to day 1 was observed. Urinary nitrate levels were significantly higher in the burns group than the control group on days 4 and 5 only (p < 0.05 for both days). There was no correlation between TBSA and the measured urinary nitrate levels. This study confirms that the biosynthesis of NO is increased during the first week following burn trauma and establishes that the renal elimination of the by-products of NO metabolism is not increased during the first three days after injury. Notwithstanding the potential effects of burns on nitrate distribution, our findings may reflect a delay in the release of NO following the initial insult.

The effects of diaspirin cross-linked hemoglobin on hemodynamics, metabolic acidosis, and survival in burned rats

OBJECTIVE

Diaspirin cross-linked hemoglobin (DCLHb) is a vasoactive hemoglobin-based oxygen carrier or "blood substitute" that has been shown to improve base deficit in several experimental studies of hemorrhagic shock. Our objective was to determine if the addition of DCLHb to the resuscitation regimen would improve hemodynamic parameters, metabolic acidosis, and survival in our rat burn shock model compared with currently used resuscitation therapy.

METHODS

This was a randomized, controlled, experimental rat study. Male Wistar rats, weighing 200 to 250 g, were surgically prepared for an acute study. After placement of indwelling catheters, baseline hemodynamic values (mean arterial pressure, cardiac output, systemic vascular resistance, stroke volume, and base excess) were obtained. Thirty-two rats were used in the study, and they were either subjected to a 30% scald burn (experimental group) or sham burned (control group). The experimental animals were immediately intravenously resuscitated and followed for 6 hours. The resuscitation was based on the Parkland formula (4 mL/kg for each 1% of total body surface area [TBSA] burn), with 50% of the calculated fluid amount to be administered at a constant rate during the first 8 hours after burn. The animals were resuscitated for 6 hours and received between 9.00 and 11.25 mL of fluid depending on weight. The experimental animals were randomly assigned to one of three treatment groups: group I, lactated Ringer's solution; group II, lactated Ringer's solution-human serum albumin; group III, lactated Ringer's solution-DCLHb. Group I (n = 8) received 4 mL/kg lactated Ringer's solution for each 1% of TBSA burn. Group II (n = 8) received 2 mL/kg lactated Ringer's solution and 2 mL/kg human serum albumin for each 1% of TBSA burn. Group III (n = 8) received 2 mL/kg lactated Ringer's solution and 2 mL/kg DCLHb for each 1% of TBSA burn. The sham group (n = 8) was not burned and was not resuscitated. Animals that survived up to 6 six hours were killed.

RESULTS

We found that mean arterial pressure, cardiac output, stroke volume, and base excess were all improved in the DCLHb-lactated Ringer's solution-treated animals compared with the other experimental treatment groups. The 6-hour mortality rates were zero of eight (lactated Ringer's solution-DCLHb group), zero of eight (sham group), three of eight (lactated Ringer's solution-human serum albumin group), and six of eight (lactated Ringer's solution only group).

CONCLUSION

Early resuscitation with DCLHb is superior to non-oxygen-carrying resuscitative fluids in improving hemodynamics and survival in this model of burn shock. DCLHb might improve general tissue perfusion in the acute postburn period, and it could be useful in the early management of patients with severe burns.

Acetylcholine-induced and nitric oxide-mediated vasodilation in burns

Microvascular endothelial cells actively participate in local regulation of blood flow and blood-tissue exchange by producing various vasoactive substances including nitric oxide (NO). This study examined microcirculatory changes in the early stage of thermal injury and the NO-related mechanisms. Resistance arterioles of rat cremaster muscle were observed using intravital microscopy. Arteriolar diameter and flow velocity were measured and flow rate was calculated after administration of various vasoactive agonists in burns. In fluid-resuscitated rats with stable systemic blood pressure, microvascular caliber and blood flow were not significantly altered in the first hour following a 25% total body surface area full-thickness scald burn. Topical application of acetylcholine (ACh), an endothelium-dependent vasodilator, increased arteriolar diameter and flow rate in a dose-dependent fashion. The dose-responsive effects of ACh were significantly greater in burned rats than in sham-burned rats, and the augmentation was blocked by inhibition of NO production with NG-monomethyl-l-arginine (L-NMMA). Topical application of adenosine, an endothelium-independent vasodilator, and sodium nitroprusside, an exogenous NO donor, markedly increased arteriolar diameter and flow rate. The effects were not significantly different in burned and sham-burned animals, and the adenosine-induced vasodilation was not blocked by L-NMMA. These data suggest that endothelium-dependent and NO-mediated arteriolar dilation is enhanced in the early stage of thermal injury. This effect may play an important role in the pathophysiological events of microcirculation and blood-tissue exchange in burns.

The metabolic fate of long-term inhaled nitric oxide

PURPOSE

The fate of inhaled nitric oxide (NO) has not been precisely defined in critically ill patients. This study aimed at defining the effects of long-term NO inhalation on circulating NO byproduct levels.

MATERIAL AND METHODS

During NO therapy, plasma and urine from 13 critically ill patients were sampled daily for determination of the stable byproducts of NO (nitrite [NO2-] and nitrate [NO3-]. Routine monitoring data included inhaled NO concentration, hemodynamic parameters, arterial blood gases, creatinine clearance, and C-reactive protein.

RESULTS

For the first 24 hours of NO inhalation (6.3+/-1.1 ppm), NO3- plasma concentration increased (from 13.3+/-5.4 to 52.3+/-17.6 micromol/L), but NO2- plasma concentration was not affected. The NO3- plasma concentration was correlated with the C-reactive protein level, the inhaled NO concentration. Renal excretion of NO metabolites was unaltered by NO inhalation. The NO3 concentrations returned to baseline when NO therapy was discontinued.

CONCLUSION

Long-term NO inhalation was associated with a consistent increase in the NO3- plasma concentration. NO byproducts may be implicated in the systemic effects associated with this treatment.

The possible role of nitric oxide in the physiopathology of pain associated with temporomandibular joint disorders

Temporomandibular joint disorders (TMD) pose a significant challenge to the practice of oral and maxillofacial surgery. When painful, TMD are generally associated with hyperthermia of the overlying skin. It is hypothesized that this skin hyperthermia, caused by regional vasodilation, is induced by nitric oxide (NO) produced in the extravascular space of the joint. Extravascular NO can be produced by osteoblasts, chondrocytes and macrophages, or by stimulated neurons. It is suggested that this kind of pain is associated with NO-enhanced sensitivity of the peripheral nociceptors. Verification and clinical implications of the proposed mechanism are discussed.