Nitric oxide production is intensely and persistently increased in tissue by thermal injury

Pathological changes in the brain after peripheral burns

Brain injuries are common complications in patients with thermal burns and are associated with unpleasant outcomes. In clinical settings, it was once believed that brain injuries were not major pathological processes after burn, at least in part due to the unavailability of specific clinical manifestations. Burn-related brain injuries have been studied for more than a century, but the underlying pathophysiology has not been completely clarified. This article reviews the pathological changes in the brain following peripheral burns at the anatomical, histological, cytological, molecular and cognitive levels. Therapeutic indications based on brain injury as well as future directions for research have been summarized and proposed.

Updates in the Management of Perioperative Vasoplegic Syndrome

Vasoplegic syndrome occurs relatively frequently in cardiac surgery, liver transplant, major noncardiac surgery, in post-return of spontaneous circulation situations, and in pateints with sepsis. It is paramount for the anesthesiologist to understand both the pathophysiology of vasoplegia and the different treatment strategies available for rescuing a patient from life-threatening hypotension.

Nitric oxide regulates intussusceptive-like angiogenesis in wound repair in chicken embryo and transgenic zebrafish models

Angiogenesis is the formation of new blood vessels that occurs by two distinct processes following sprouting angiogenesis (SA) and intussusceptive angiogenesis (IA). Nitric oxide (NO) is known for its pro-angiogenic functions. However, no clear mechanisms are delineated on its role in promoting angiogenesis in reparative wound healing. We propose that NO regulates SA to IA transition and vice versa in wound milieu. We have used three models which include a new chick embryo extra-vasculature (CEV) burn wound model, adult Tie2-GFP transgenic Zebrafish caudal fin regeneration model and Zebrafish skin wound model to study the mechanisms underlying behind the role of NO in wound healing. Wounds created in CEV were treated with NO donor (Spermine NONOate (SPNO)), NOS inhibitor (L-nitro-l-arginine-methyl ester (l-NAME)), NaNO₂, NaNO₃, and beetroot juice, a nitrite-rich juice respectively and the pattern of wound healing was assessed. Morphological and histological techniques tracked the wound healing at the cellular level, and the molecular changes were investigated by using real-time RT-PCR gene expression analysis. The result concludes that NO donor promotes wound healing by activating SA at an early phase of healing while NOS inhibitor induces wound healing via IA. At the later phase of wound healing NO donor followed IA while NOS inhibitor failed to promote wound repair. The current work underpinned a differential regulation of NO on angiogenesis in wound milieu and this study would provide new insights in designing therapeutics for promoting wound repair.

Combination of radiation and burn injury alters [¹⁸F] 2-fluoro-2-deoxy-D-glucose uptake in mice

Radiation exposure and burn injury have both been shown to alter glucose utilization in vivo. The present study was designed to study the effect of burn injury combined with radiation exposure on glucose metabolism in mice using [¹⁸F] 2-fluoro-2-deoxy-D-glucose (¹⁸FDG). Groups of male mice weighing approximately 30 g were studied. Group 1 was irradiated with a ¹³⁷Cs source (9 Gy). Group 2 received full thickness burn injury on 25% TBSA followed by resuscitation with saline (2 ml, IP). Group 3 received radiation followed 10 minutes later by burn injury. Group 4 were sham-treated controls. After treatment, the mice were fasted for 23 hours and then injected (IV) with 50 μCi of ¹⁸FDG. One hour postinjection, the mice were sacrificed, and biodistribution was measured. Positive blood cultures were observed in all groups of animals compared to the shams. Increased mortality was observed after 6 days in the burn plus radiated group as compared to the other groups. Radiation and burn treatments separately or in combination produced major changes in ¹⁸FDG uptake by many tissues. In the heart, brown adipose tissue, and spleen, radiation plus burn produced a much greater increase (P < .0001) in ¹⁸FDG accumulation than either treatment separately. All three treatments produced moderate decreases in ¹⁸FDG accumulation (P < .01) in the brain and gonads. Burn injury, but not irradiation, increased ¹⁸FDG accumulation in skeletal muscle; however, the combination of burn plus radiation decreased ¹⁸FDG accumulation in skeletal muscle. This model may be useful for understanding the effects of burns plus irradiation injury on glucose metabolism and in developing treatments for victims of injuries produced by the combination of burn plus irradiation.

Nitric oxide activates intradomain disulfide bond formation in the kinase loop of Akt1/PKBα after burn injury

Severe burn injury is an acute inflammatory state with massive alterations in gene expression and levels of growth factors, cytokines and free radicals. During the catabolic processes, changes in insulin sensitivity and skeletal muscle wasting (unintended loss of 5–15% of lean body mass) are observed clinically. Here, we reveal a novel molecular mechanism of Akt1/protein kinase Bα (Akt1/PKBα) regulated via cross-talking between dephosphorylation of Thr³⁰⁸ and S-nitrosylation of Cys²⁹⁶ post severe burn injury, which were characterized using nano-LC interfaced with tandem quadrupole time-of-fight mass spectrometry (Q-TOF)^micro tandem mass spectrometry in both in vitro and in vivo studies. For the in vitro studies, Akt1/PKBα was S-nitrosylated with S-nitrosoglutathione and derivatized by three methods. The derivatives were isolated by SDS-PAGE, trypsinized and analyzed by the tandem MS. For the in vivo studies, Akt1/PKBα in muscle lysates from burned rats was immuno-precipitated, derivatized with HPDP-Biotin and analyzed as above. The studies demonstrated that the NO free radical reacts with the free thiol of Cys²⁹⁶ to produce a Cys²⁹⁶-SNO intermediate which accelerates interaction with Cys³¹⁰ to form Cys²⁹⁶-Cys³¹⁰ in the kinase loop. MS/MS sequence analysis indicated that the dipeptide, linked via Cys²⁹⁶-Cys³¹⁰, underwent dephosphorylation at Thr³⁰⁸. These effects were not observed in lysates from sham animals. As a result of this dual effect of burn injury, the loose conformation that is slightly stabilized by the Lys²⁹⁷-Thr³⁰⁸ salt bridge may be replaced by a more rigid structure which may block substrate access. Together with the findings of our previous report concerning mild IRS-1 integrity changes post burn, it is reasonable to conclude that the impaired Akt1/PKBα has a major impact on FOXO3 subcellular distribution and activities.

Previous burn injury predisposes mice to lipopolysaccharide-induced changes in glucose metabolism

In mice, it has been demonstrated that at 7 days after burn injury, injection of lipopolysaccharide (LPS) is more lethal than the same dose at 1 day after injury. In the present study, we examined the effect of LPS injection to mice burned 7 days previously on glucose metabolism ([(18)F] 2-fluoro-2-deoxy-D-glucose [(18)FDG] uptake) in vivo. CD-1 male mice (25-28 g, Charles River Breeding Laboratories, Wilmington, MA) were anesthetized, backs shaven, and subjected to dorsal full thickness burn on 25% TBSA. Sham-treated animals were used as controls. Six days after burn injury, all mice were fasted overnight. One half of the burned and sham controls were subsequently injected IP with LPS (10 mg/kg; Escherichia coli). The remaining animals were injected with saline IP. Two hours later, all mice were injected IV with 50 μCi of (18)F FDG. One hour later, the animals were euthanized, and biodistribution was measured. Tissues were weighed, and radioactivity was measured with a well-type γ counter. Results were expressed as %dose/g tissue, mean ± SEM. The combination of burn 7 days previously and LPS significantly increased mortality compared to animals with burn alone, LPS alone, or sham controls. Burn injury 7 days previously caused a significant decrease in (18)FDG uptake by the brain compared to sham controls. The combination of LPS and burn injury 7 days previously produced a significant increase in (18)FDG uptake by brown adipose tissue and heart compared with either treatment separately. LPS produced a significant increase in (18)FDG uptake by lung, spleen, and gastrointestinal tract of the sham animals, changes that were different in mice burned 7 days previously and injected with LPS. The present results suggest that burn injury 7 days previously predisposes mice to alterations in (18)FDG uptake produced by LPS. These changes may relate, in part, to the increased lethality of LPS injection in previously burned mice.

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.

Local delivery of nitric oxide: targeted delivery of therapeutics to bone and connective tissues

Non-invasive treatment of injuries and disorders affecting bone and connective tissue remains a significant challenge facing the medical community. A treatment route that has recently been proposed is nitric oxide (NO) therapy. Nitric oxide plays several important roles in physiology with many conditions lacking adequate levels of NO. As NO is a radical, localized delivery via NO donors is essential to promoting biological activity. Herein, we review current literature related to therapeutic NO delivery in the treatment of bone, skin and tendon repair.

SILAM for quantitative proteomics of liver Akt1/PKBα after burn injury

Akt1/protein kinase Bα (Akt1/PKBα) is a downstream mediator of the insulin signaling system. In this study we explored mechanism(s) for its role in burn injury. Akt1/PKBα in liver extracts from mice with burn injury fed with (²H₇)-L-Leu was immunoprecipitated and isolated with SDS-PAGE. Two tryptic peptides, one in the kinase loop and a control peptide just outside of the loop were sequenced via nano-LC interfaced with quadruple time-of-flight tandem mass spectrometry (Q-TOF tandem MS). Their relative isotopologue abundances were determined by stable isotope labeling by amino acids in mammalians (SILAM). Relative quantifications based on paired heavy/light peptides were obtained in 3 steps. The first step included homogenization of mixtures of equal amounts of tissue from burned and sham-treated animals (i.e., isotope dilution) and acquisition of uncorrected data based on parent monoisotopic MS ion ratios. The second step included determination of isotopic enrichment of the kinase from burned mice on Day 7 and the third step enrichment correction of partially labeled heavy and light monoisotopic MS ion ratios for relative quantification of bioactivity (loop peptide) and expression level (control peptide). Protein synthesis and enrichment after injury were found to be dependent on tissue and turnover of individual proteins. Three heavy and light monoisotopic ion ratios for albumin peptides from burned mice indicated ~55% enrichment and ~16.7-fold downregulation. In contract, serum amyloid P had ~66% enrichment and was significantly upregulated. Akt1/PKBα had ~56% enrichment and kinase level in response to the burn injury was upregulated compared with the control peptide. However, kinase bioactivity, represented by the Cys²⁹⁶ peptide, was significantly reduced. Overall, we demonstrated that i) quantitative proteomics can be performed without completely labeled mice; ii) measurement of enrichment of acyl-tRNAs is unnecessary and iii) Cys²⁹⁶ plays an important role in kinase activity after burn injury.

Effects of burn injury on markers of hypermetabolism in rats

The basic metrics of hypermetabolism have not been thoroughly characterized in rat burn injury models. We examined three models expected to differ in sensitivity to burn injury to identify that which group(s) exhibited the most clinically relevant metabolic response. Six and 12 weeks old male CD (6 week mCD and 12 week mCD) rats, and 12 weeks old female Fischer (12 week fFI) rats received a 20% total body surface area burn, followed by saline resuscitation. Activity, core body temperature, heart rate (via implanted telemetry devices), body weight, food and water intake, and fecal output were measured daily for 1 week before and after burn. Rats lost weight initially postburn but resumed weight gain by 1 week, except for 12 week mCD rats. Core body temperature increased above normal 2 days postburn and returned to baseline by 1 week. Food intake, normalized to body weight, remained unchanged postburn for 12 week mCD rats, but decreased in 6 week mCD rats and increased in 12 week fFI rats. Heart rate in the 12 week mCD and 12 week fFI rats remained at 10 to 15% above baseline, whereas, in 6 week mCD, heart rates returned to baseline after 4 days. Activity levels were unchanged for 12 week fFI and 6 week mCD rats postburn, but decreased for 12 week mCD rats. Postburn hypermetabolism was most significant and sustained in 12 week mCD rats, of least consequence and brief in 6 week mCD rats, and intermediate in 12 week fFI rats. The disparate responses indicate that the choice of animal model should be carefully considered in hypermetabolism studies.

Basic properties and molecular mechanisms of exogenous chemical carcinogens

Exogenous chemical carcinogenesis is an extremely complex multifactorial process during which gene-environment interactions involving chronic exposure to exogenous chemical carcinogens (ECCs) and polymorphisms of cancer susceptibility genes add further complexity. We describe the properties and molecular mechanisms of ECCs that contribute to induce and generate cancer. A basic and specific property of many lipophilic organic ECCs including polycyclic aromatic hydrocarbons and polyhalogenated aromatic hydrocarbons is their ability to bioaccumulate in the adipose tissue from where they may be released in the blood circulation and target peripheral tissues for carcinogenesis. Many organic ECCs are procarcinogens and consequently need to be activated by the cytochrome P450 (CYP) system and/or other enzymes before they can adduct DNA and proteins. Because they contribute not only to the cocarcinogenic and promoting effects of many aromatic pollutants but also to their mutagenic effects, the aryl hydrocarbon receptor-activating and the inducible CYP systems are central to exogenous chemical carcinogenesis. Another basic property of ECCs is their ability to induce stable and bulky DNA adducts that cannot be simply repaired by the different repair systems. In addition, following ECC exposure, mutagenesis may also be caused indirectly by free-radical production and by epigenetic alterations. As a result of complex molecular interplays, direct and/or indirect mutagenesis may especially account for the carcinogenic effects of many exogenous metals and metalloids. Because of these molecular properties and action mechanisms, we conclude that ECCs could be major contributors to human cancer, with obviously great public health consequences.

Steric and electrostatic effects at the C2 atom substituent influence replication and miscoding of the DNA deamination product deoxyxanthosine and analogs by DNA polymerases

Deoxyinosine (dI) and deoxyxanthosine (dX) are both formed in DNA at appreciable levels in vivo by deamination of deoxyadenosine (dA) and deoxyguanosine (dG), respectively, and can miscode. Structure-activity relationships for dA pairing have been examined extensively using analogs but relatively few studies have probed the roles of the individual hydrogen-bonding atoms of dG in DNA replication. The replicative bacteriophage T7 DNA polymerase/exonuclease and the translesion DNA polymerase Sulfolobus solfataricus pol IV were used as models to discern the mechanisms of miscoding by DNA polymerases. Removal of the 2-amino group from the template dG (i.e., dI) had little impact on the catalytic efficiency of either polymerase, as judged by either steady-state or pre-steady-state kinetic analysis, although the misincorporation frequency was increased by an order of magnitude. dX was highly miscoding with both polymerases, and incorporation of several bases was observed. The addition of an electronegative fluorine atom at the 2-position of dI lowered the oligonucleotide T(m) and strongly inhibited incorporation of dCTP. The addition of bromine or oxygen (dX) at C2 lowered the T(m) further, strongly inhibited both polymerases, and increased the frequency of misincorporation. Linear activity models show the effects of oxygen (dX) and the halogens at C2 on both DNA polymerases as mainly due to a combination of both steric and electrostatic factors, producing a clash with the paired cytosine O2 atom, as opposed to either bulk or perturbation of purine ring electron density alone.

Inhibition of inducible nitric oxide synthase reduces an acute peripheral motor neuropathy produced by dermal burn injury in mice

The systemic inflammatory response produced by a full-thickness dermal burn injury is associated with a peripheral motor neuropathy. We previously reported that a 20% body surface area (BSA) full-thickness dermal burn in C57BL6 mice produced structural and functional deficits in motor axons at a distance from the burn site. The etiology of the neuropathy, however, is not well characterized. Burn injury leads to an increase in production of a number of proinflammatory mediators, including nitric oxide (NO). We tested the hypothesis that dermal burn-induced motor neuropathy is mediated by increased production of NO. NO synthase (NOS) activity was inhibited following a 20% BSA full-thickness burn by injection of non-specific NOS inhibitor, nitro-L-arginine methyl ester or inducible NOS (iNOS) inhibitors, L-N6-(1-iminoethyl) lysine, and aminoguanidine. NOS inhibitors also prevented the reduction in ventral roots mean axon caliber and the decrease in a motor nerve conduction velocity (MCV) following burn. iNOS knockout mice prevented MCV decrease in the first 3 days post-burn, but iNOS knockout MCV was significantly reduced at 7-14 days post-burn. These results suggest that an increase in NO production generated by systemic inflammatory response pathways after burn injury contributes to the development of structural and functional deficits in peripheral motor axons.

Nitrite to nitrate molar ratio is inversely proportional to oxidative cell damages and granulocytic apoptosis at the wound site following cutaneous injury in rats

Nitric oxide (NO) metabolism in response to the inflammatory cell infiltration and their apoptosis at the wound site, using a model of subcutaneously implanted sponges in Albino Oxford rats, were examined. The injured animals were sacrificed at days 1, 2 and 3 after the injury. Nitrites, nitrates (final products of NO metabolism), malondialdehyde (an indicator of oxidative cell damages), urea (product of arginase activity) and other parameters were measured both in plasma and wound fluid samples. Nitrite to nitrate molar ratio and sum of nitrites and nitrates (NO(x)) were calculated. The total cell numbers were at similar level throughout the examined period, but a gradual decrease of viable granulocytes, mainly due to the increased apoptosis, and the increase of monocyte-macrophage number occurred after the second day. A gradual increase of wound fluid nitrates, NO(x) and malondialdehyde suggested the increases of both NO and free oxygen radicals production. Interestingly, wound fluid nitrites peaked at the first day decreasing to the corresponding plasma levels thereafter. Wound fluid nitrite to nitrate molar ratio gradually decreased and negatively correlated both with the number of apoptotic cells (r= -0.752, p<0.05) and malondialdehyde (r= -0.694, p<0.05) levels. In conclusion, the inversely proportional relation between nitrite to nitrate molar ratio and both malondialdehyde and apoptotic cell number indicated a mutual relationship between NO metabolism, oxidative cell damages and cell apoptosis at the wound site early after the cutaneous wound. Moreover, the obtained findings suggest that measurement of both nitrites and nitrates contribute to better insight into overall wound NO metabolism.

Gene therapy via inducible nitric oxide synthase: a tool for the treatment of a diverse range of pathological conditions

Nitric oxide (NO(.)) is a reactive nitrogen radical produced by the NO synthase (NOS) enzymes; it affects a plethora of downstream physiological and pathological processes. The past two decades have seen an explosion in the understanding of the role of NO(.) biology, highlighting various protective and damaging modes of action. Much of the controversy surrounding the role of NO(.) relates to the differing concentrations generated by the three isoforms of NOS. Both calcium-dependent isoforms of the enzyme (endothelial and neuronal NOS) generate low-nanomolar/picomolar concentrations of NO(.). By contrast, the calcium-independent isoform (inducible NOS (iNOS)) generates high concentrations of NO(.), 2-3 orders of magnitude greater. This review summarizes the current literature in relation to iNOS gene therapy for the therapeutic benefit of various pathological conditions, including various states of vascular disease, wound healing, erectile dysfunction, renal dysfunction and oncology. The available data provide convincing evidence that manipulation of endogenous NO(.) using iNOS gene therapy can provide the basis for future clinical trials.

Substance P enhances wound closure in nitric oxide synthase knockout mice

INTRODUCTION

The neuropeptide, substance P (SP), up-regulates nitric oxide production (NO). The purpose of this study was to determine whether SP enhances response to cutaneous injury in nitric oxide synthase knockout (NOS null) mice.

METHODS

We studied mice with targeted deletions of the 3 NOS genes, neuronal NOS, inducible NOS, or endothelial NOS. Full thickness dorsal wounds were treated daily (d 0-6) with topical SP or normal saline (NaCl). Wounds were analyzed by flow cytometry for macrophage, leukocyte, endothelial, and dendritic cells. Healing time and wound epithelialization were compared using analysis of variance.

RESULTS

Wound closure in the 3 NOS null mice was slower than the control mice (P < 0.05). SP treatment enhanced wound closure in NOS null mice (P < 0.02). NOS null wounds exhibited reduced inflammation. SP increased macrophage, leukocyte, and dendritic cell densities at d 3 and d 7 (P < 0.05) in all NOS null mice. SP increased endothelial cell number in neuronal NOS and inducible NOS null mice, but not in endothelial NOS null mice (P > 0.05).

CONCLUSIONS

SP ameliorated the impaired wound healing response observed in NOS null mice by enhancing wound closure kinetics and epithelialization. SP increased inflammatory cell density in the wounds supporting the essential role of inflammatory cells, especially macrophages, in wound repair.

Gene expression profiling of long-term changes in rat liver following burn injury

The inflammatory response initiated upon burn injury is also associated with extensive metabolic adjustments. While there is a significant body of literature on the characterization of these changes at the metabolite level, little is known on the mechanisms of induction, especially with respect to the role of gene expression. We have comprehensively analyzed changes in gene expression in rat livers during the first 7 d after 20% total body surface area burn injury using Affymetrix microarrays. A total of 740 genes were significantly altered in expression at 1, 2, 4, and 7 d after burn injury compared to sham-burn controls. Functional classification based on gene ontology terms indicated that metabolism, transport, signaling, and defense/inflammation response accounted for more than 70% of the significantly altered genes. Fisher least-significant difference post-hoc testing of the 740 differentially expressed genes indicated that over 60% of the genes demonstrated significant changes in expression either on d 1 or on d 7 postburn. The gene expression trends were corroborated by biochemical measurements of triglycerides and fatty acids 24 h postburn but not at later time points. This suggests that fatty acids are used, at least in part, in the liver as energy substrates for the first 4 d after injury. Our data also suggest that long-term regulation of energy substrate utilization in the liver following burn injury is primarily at the posttranscriptional level. Last, relevance networks of significantly expressed genes indicate the involvement of key small molecules in the hepatic response to 20% total body surface area burn injury.

Biological fate and clinical implications of arginine metabolism in tissue healing

Since its discovery in 1987, many biological roles (including wound healing) have been identified for nitric oxide (NO). The gas is produced by NO synthase using the dibasic amino acid L-arginine as a substrate. It has been established that a lack of dietary L-arginine delays experimental wound healing. Arginine can also be metabolized to urea and ornithine by arginase-1, a pathway that generates L-proline, a substrate for collagen synthesis, and polyamines, which stimulate cellular proliferation. Herein, we review subjects of interest in arginine metabolism, with emphasis on the biochemistry of wound NO production, relative NO synthase isoform activity in healing wounds, cellular contributions to NO production, and NO effects and mechanisms of action in wound healing.

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.

The immunological consequences of injury

Immediate and early trauma death rates are determined by "first hits" such as hypoxia, hypotension and organ injury, while late mortality correlates closely with "second hits" such as infection. An imbalance between the early systemic inflammatory response (SIRS), and the later compensatory counter-inflammatory response (CARS), is considered to be responsible for much post-traumatic morbidity and mortality. From a clinical perspective, this remains a significant healthcare problem, which has stimulated decades of experimental and clinical research aimed at understanding the functional effects of injury on the immune system. This review describes the impact of injury on the innate and adaptive immune systems. Though it is worth noting that the features of the immune response to injury overlap in many areas with immune dysregulation in sepsis, we attempt here to elucidate the mechanism by which injury predisposes to infection rather than to describe the alterations in host immunity consequent to established sepsis.

Nitrosoglutathione triggers collagen deposition in cutaneous wound repair

The presence of nitric oxide (NO) is associated with enhanced wound fibroblast collagen synthesis; previous observations have focused on the effect of NO on wound collagen content. This article emphasizes the effect of nitrosothiols on wound collagen deposition and matrix-metalloproteinase activity, which is the primary breakdown pathway of collagen. We examined the effects of S-nitrosoglutathione (GSNO) and glutathione (GSH) on rat scar tissue. Hydroxyproline content, matrix metalloproteinase activity, total glutathione, and total nitrite of scar tissue were measured 3, 5, 7, and 10 days after wounding. It was observed that, at Day 5 and Day 10, wound collagen content was 52.0 percent and 47.5 percent higher, respectively, after GSNO administration than in controls (p<0.05). GSH administration decreased wound collagen deposition 76.5 percent by Day 5 (p<0.05). GSH lowered the matrix metalloproteinase activity 67 percent at Day 5 and 50 percent (p<0.05) at Day 10. Nitrite and nitrate levels were 55 percent higher in the GSNO treated rats than in the control group (p<0.05) at Day 3, whereas the GSH-treated groups showed no changes. GSNO increased systemic nitrite 53 percent 3 hours after intraperitoneal injection. Our findings suggest that collagen deposition increases in cutaneous wound healing after the administration of GSNO and that this nitrosothiol does not interfere with the collagenolytic pathway, thus maintaining the physiological conditions necessary for wound healing.

Effects of dehydroepiandrosterone administration on rat hepatic metabolism following thermal injury

BACKGROUND

Severe burns cause dramatic alterations in liver and whole-body metabolism. Recently, there has been interest in using dehydroepiandrosterone (DHEA) as a treatment for trauma patients, and enhanced survival and immune function have been reported using DHEA in animal trauma models. The specific effects of DHEA on hepatic metabolism following burn injury have not been explored.

MATERIALS AND METHODS

Male rats received either (1) a burn covering approximately 20% of the total body surface area or a sham burn or (2) burn injury followed by two intraperitoneal injections of DHEA or vehicle. After 4 days, the livers were isolated and perfused in vitro, and 28 metabolite fluxes were measured. Metabolic flux analysis was used to obtain the intracellular metabolic flux distribution and provide an overview of the metabolic state of the livers in each experimental group.

RESULTS

Burn injury decreased the uptake of lactate and the production of beta-hydroxybutyrate and increased the deamination of glutamine to glutamate and asparagine to aspartate. DHEA, compared to vehicle treatment, decreased pentose phosphate pathway (PPP) fluxes and the uptake of several amino acids in burned rats. Furthermore, DHEA treatment restored liver metabolism in burned rats to a state that was very similar to that of the sham control group.

CONCLUSIONS

DHEA administration appears to normalize hepatocellular metabolism in burned rats but also decreases the PPP flux, which may impair the liver's ability to recycle endogenous antioxidants. DHEA treatment combined with exogenous antioxidants should receive further consideration in the management of burn and trauma patients.

Caffeic Acid Phenethyl Ester Improves Oxidative Erythrocyte Damage in a Rat Model of Thermal Injury

Oxygen-derived free radicals impair cell membrane functions and induce circulatory disturbances, and free radicals, such as superoxide anion, hydrogen peroxide, hydroxyl radicals, and peroxynitrite, have been suggested to play important roles in the pathogenesis of major burn injuries. The present study investigated the effects of thermal injury on erythrocyte lipid peroxidation and antioxidant status and investigated the effects of caffeic acid phenethyl ester (CAPE), a new antioxidant and anti-inflammatory agent, in rats subjected to thermal injury. Burn injury caused a remarkable increase in erythrocyte lipid peroxidation, levels of nitric oxide (NO), and activities of antioxidant enzymes and xanthine oxidase (XO). The treatment with CAPE decreased both activity of burn-induced XO activity and levels of NO in the erythrocytes. In conclusion, CAPE treatment resulted in decreased erythrocyte lipid peroxidation in thermal injury and helped to prevent oxidative damage by decreasing activity of XO and levels of NO.

Nitric oxide and wound healing

Nitric oxide is a short-lived free radical that acts at the molecular, cellular, and physiologic level. Since its discovery almost 20 years ago it has proven itself as an important element in wound healing. This review highlights many of the important aspects of nitric oxide in wound healing, including a review of the basic biology of nitric oxide, its role as part of the cytokine cascade and as a promoter of angiogenesis, as well as its more recently elucidated role in apoptosis.

Role of Thymus Oil in Burn Wound Healing

Thymus oil and its components are becoming increasingly popular as naturally occurring antimicrobial and antioxidant agents. The real importance of thymus on nitric oxide (NO) is unknown. NO is an important mediator in numerous physiologic and pathophysiologic events. Stasis and thrombosis in burn wound can progress as a result of the release of local mediators. The implication of NO in burn injury is not well studied. In this study, we tried to determine the role of burn-induced NO and whether thymus oil plays a protective role after a thermal injury. Rats were divided into five groups. We topically applied thymus oil, olive oil, and silverdin and sulfadiazine on the rats, respectively, during a period of 21 days after they were burned while under anesthesia. The burned control group and nonburned control group did not receive any treatment. The results of this study show that NO was overproduced by thermal injury and decreased during the days after burn injury. The decrease in rats treated with thymus and sulfadiazine was higher than the others. These data indicate that thymus oil may serve as a protective agent to the damaged tissues by decreasing the NO level. Histologic examination results show that the formation of new tissue in rats receiving thymus oil was more than other burned groups, and this finding supports our hypothesis.

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.

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 and wound repair: role of cytokines?

Wound healing involves platelets, inflammatory cells, fibroblasts, and epithelial cells. All of these cell types are capable of producing nitric oxide (NO), either constitutively or in response to inflammatory cytokines, through the activity of nitric oxide synthases (NOSs): eNOS (NOS3; endothelial NOS) and iNOS (NOS2; inducible NOS), respectively. Indeed, pharmacological inhibition or gene deletion of these enzymes impairs wound healing. The wound healing mechanisms that are triggered by NO appear to be diverse, involving inflammation, angiogenesis, and cell proliferation. All of these processes are controlled by defined cytokine cascades; in many cases, NO appears to modulate these cytokines. In this review, we summarize the history and present state of research on the role of NO in wound healing within the framework of modulation of cytokines.

Role of nitric oxide in wound healing

Chronic wounds mainly affect elderly individuals and persons with comorbid diseases due to a compromised immune status. An age-related decline in immune function deters proper healing of wounds in an orderly and timely manner. Thus, older adults with 1 or more concomitant illnesses are more likely to experience and sufferfrom a nonhealing wound, which may drastically decrease their quality of life and financial resources. Novel therapies in wound care management rely heavily on our current knowledge of wound healing physiology. It is well established that normal wound healing occurs sequentially and is strictly regulated by pro-inflammatory cytokines and growth factors. A multitude of commercial products such as growth factors are available; however, their effectiveness in healing chronic wounds has yet to be proven. Recently, investigators have implicated nitric oxide (NO) in the exertion of regulatoryforces on various cellular activities of the inflammatory and proliferative phases of wound healing. Gene therapy in animal studies has shown promising results and is furthering our understanding of impaired wound healing. The purpose of this article is to review the literature on NO and its role in wound healing. A discussion of the physiology of normal healing and the pathophysiology of chronic wounds is provided.

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.

Role of nitric oxide in wound repair

After injury, wound healing is essential for recovery of the integrity of the body. It is a complex, sequential cascade of events. Nitric oxide (NO) is a small radical, formed from the amino acid L-arginine by three distinct isoforms of nitric oxide synthase. The inducible isoform (iNOS) is synthesized in the early phase of wound healing by inflammatory cells, mainly macrophages. However many cells participate in NO synthesis during the proliferative phase after wounding. NO released through iNOS regulates collagen formation, cell proliferation and wound contraction in distinct ways in animal models of wound healing. Although iNOS gene deletion delays, and arginine and NO administration improve healing, the exact mechanisms of action of NO on wound healing parameters are still unknown. The current review summarizes what is known about the role of NO in wound healing and points out path for further research.

Nitric oxide in the healing wound: a time-course study

INTRODUCTION

We studied the time course of nitric oxide expression in the healing wound and the cell populations responsible for its synthesis.

METHODS

Twenty four Lewis rats underwent subcutaneous implantation of polyvinyl alcohol sponges. Rats were sacrificed in groups of three on days 1, 3, 5, 7, 10, 14, and 35 after wounding. The conversion of 3H-labeled arginine to 3H-labeled citrulline, with or without N(G)-L-monomethyl-arginine (L-NMMA) in harvested sponges, was measured. Nitrate/nitrite (NOx) in plasma and wound fluid was quantified by Greiss reaction. Inducible nitric oxide synthase (iNOS) gene expression was determined by Northern analysis and reverse transcriptase-polymerase chain reaction (RT-PCR). Inducible NOS was identified in specific wound cell populations by dual-label flow cytometry.

RESULTS

Nitric oxide synthase (NOS) activity peaked at 24 h after wounding (37.7 +/- 0.9 micromol citrulline per milligram sponge), with a steady decline thereafter. Percentage inhibition of NOS activity by l-NMMA was highest on days 1-7 (70-80%). This declined to 50% by day 10 and to 25% by days 14-35. The iNOS gene expression paralleled NOS biochemical activity. RT-PCR confirmed low-level expression up to 10 days after wounding. Plasma NOx levels remained within a narrow range of 22.6 +/- 1.3 to 29.3 +/- 1.5 microM throughout the postwounding period, while corresponding levels in wound fluid (microM) increased steadily from 27 +/- 3.8 on day 1 to 107.2 +/- 10.0 on day 14. Inducible NOS expression was detectable by fluorescence-activated cell sorting in wound macrophages on days 1 and 3 after wounding.

CONCLUSIONS

Our findings suggest maximal NOS activity early in cutaneous wound healing, with sustained production up to 10 days after wounding. NOS biochemical activity was paralleled by iNOS gene expression. Plasma NOx remained constant, while wound fluid NOx increased steadily to peak at day 14. Wound macrophages appear to be a source of nitric oxide production in the early phase of wound healing.

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.

Arginine and ornithine kinetics in severely burned patients: increased rate of arginine disposal

Arginine serves multiple roles in the pathophysiological response to burn injury. Our previous studies in burn patients demonstrated a limited net rate of arginine de novo synthesis despite a significantly increased arginine turnover (flux), suggesting that this amino acid is a conditionally indispensable amino acid after major burns. This study used [15N2-guanidino-5,5-2H2]arginine and [5-13C]ornithine as tracers to assess the rate of arginine disposal via its conversion to and subsequent oxidation of ornithine; [5,5-2H2]proline and [5,5,5-2H3]leucine were also used to assess proline and protein kinetics. Nine severely burned patients were studied during a protein-free fast ("basal" or fast) and total parenteral nutrition (TPN) feedings. Compared with values from healthy volunteers, burn injury significantly increased 1) fluxes of arginine, ornithine, leucine, and proline; 2) arginine-to-ornithine conversion; 3) ornithine oxidation; and 4) arginine oxidation. TPN increased arginine-to-ornithine conversion and proportionally increased irreversible arginine oxidation. The elevated arginine oxidation, with limited net de novo synthesis from its immediate precursors, further implies that arginine is a conditionally indispensable amino acid in severely burned patients receiving TPN.

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.

Metabolic flux analysis of postburn hepatic hypermetabolism

The hepatic response to severe injury is characterized by a marked upregulation of glucose, fatty acid, and amino acid turnover, which, if persistent, predisposes the patient to progressive organ dysfunction. To study the effect of injury on liver intermediary metabolism, metabolic flux analysis was applied to isolated perfused livers of burned and sham-burned rats. Intracellular fluxes were calculated using metabolite measurements and a stoichiometric balance model. Significant flux increases were found for multiple pathways, including mitochondrial electron transport, the TCA and urea cycles, gluconeogenesis, and pentose phosphate pathway (PPP). The burn-induced increase in gluconeogenesis did not significantly increase glucose output. Instead, glucose-6-phosphate was diverted into the PPP. These changes were paralleled by increases in glucose-6-phosphate dehydrogenase (G6PDH) and glutathione reductase (GR) activities. Given that G6PDH and GR are the most significant NADPH producers and consumers in the liver, respectively, and that GR is responsible for recycling the free radical scavenger glutathione, these data are consistent with the notion that hepatic metabolic changes are in part due to the induction of liver antioxidant defenses.

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.

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.

Importance of nitric oxide in the regulation of burn oedema, proteinuria and urine output

Burn injuries trigger a pronounced inflammatory response in the burned skin, resulting in oedema formation and impaired circulation. This response involves activation of the nitric oxide (NO) synthetic pathway, which could play a key role in the complex hemodynamic and hemostatic changes occurring as a result of a burn trauma. The results presented in full-thickness skin burns of rats show that the NO-precursor, L-arginine (n = 10), inhibit burn-induced plasma extravasation as compared to saline-treated burned controls (n = 10) (p<0.001) to a level not significantly different from nonburned animals. Administration of the NO-synthase inhibitor. NG-nitro-L-arginine (L-NNA) (n = 10), did not significantly influence burn extravasation compared to burned controls. Accumulated urine volume 90 min post-burn increased ten-fold in burned animals treated with L-arginine compared to saline-treated burned controls (p<0.001) and nonburned animals (p<0.001), while L-NNA had no significant effect on diuresis. A significantly increased proteinuria occurred in L-arginine treated burned animals as compared to burned controls and nonburned controls (p<0.001), whereas L-NNA did not significantly influence the leakage of protein in the urine. Activation of NO synthesis significantly suppresses burn edema and strongly increases diuresis along with increased proteinuria.

Role of nitric oxide in the control of burn perfusion

Vascular changes following deep skin burns are characterised by vasoconstriction and progressive ischemia. Nitric oxide (NO) has been shown to be a potent regulator of vascular smooth muscle tone and tissue perfusion. We assessed the importance of NO on post-burn skin perfusion in rats using laser Doppler. The present results show that neither the NO-synthase inhibitor, NG-nitro-L-arginine (L-NNA) (n = 6) nor the NO precursor, L-arginine, significantly influenced skin perfusion in nonburned skin compared to saline-treated animals. In the area of full-thickness skin burn, neither L-arginine (n = 6) nor L-NNA (n = 6) had significant influence on post-burn perfusion compared to saline-treated controls (n = 6). Administration of L-NNA (n = 6) significantly impaired skin perfusion in the area adjacent to the contact burn representing a partial-thickness burn, while the NO precursor, L-arginine (n = 6) had no significant effect on burn perfusion as compared to saline-treated controls (n = 6). In conclusion, impairment of perfusion in a full thickness burn following administration of NO-synthase inhibitor suggests that nitric oxide is involved in the mechanisms responsible for maintaining adequate circulation post-burn. The lack of additional improvement of perfusion in response to L-arginine may suggest that NO synthesis in response to the thermal trauma is already at a peak.

Nitric oxide inhibits wounds collagen synthesis

Nitric oxide (NO) is a messenger molecule which regulates many physiological functions like immunity, vascular tone and serves as a neurotransmitter. Although it is known to participate in healing process, its role in collagen synthesis is not clear. Therefore, the present investigation was done to study the role of NO in wound collagen synthesis. Rats received full thickness, circular (8 mm), transdermal wounds which were treated with NO releaser, sodium nitroprusside (SNP, 0.001 100 microM) topically for 5 days. Wound collagen content estimated in terms of hydroxyproline (HP) and confirmed histochemically was decreased significantly by all SNP doses. L-Arginine, a substrate for nitric oxide synthase (NOS) when applied topically decreased collagen content of the wounded tissues. N-Nitro-L-arginine methyl ester (L-NAME), a competitive inhibitor of NOS, increased wound collagen content significantly as compared to untreated and SNP treated animal wounds when administered intraperitoneally at the doses 3, 10 and 30 mg/kg. Furthermore, histological findings also demonstrated laying down of thick collagen bundles and proliferation of fibroblasts together with prominent angiogenesis in L-NAME treated wound tissues as compared to untreated and SNP treated tissues. N-nitro-D-arginine methyl ester, an inactive isomer, was found to have no effect on wound collagen levels. When L-arginine was administered in L-NAME pretreated rats, it significantly elevated wound HP content. The results indicate that NO plays an important role in regulating the collagen biosynthesis in skin model of a healing wound.

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.

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.