Hypothermia inhibits cytokine release of alveolar macrophage and activation of nuclear factor kappaB in endotoxemic lung

Mild Hypothermia via External Cooling Improves Lung Function and Alleviates Pulmonary Inflammatory Response and Damage in Two-Hit Rabbit Model of Acute Lung Injury

OBJECTIVES

Targeted temperature management (TTM) with therapeutic hypothermia (TH) has an organ-protective effect by mainly reducing inflammatory response. Here, our objective was to determine, for the first time, whether mild TH with external cooling, a simple and inexpensive method, could be safe or even beneficial in two-hit rabbit model of acute lung injury/acute respiratory distress syndrome (ALI/ARDS).

METHODS

Twenty-two New Zealand rabbits (6-month-old) were randomly divided into healthy control (HC) with conventional ventilation, but without injury, model group (ALI), and hypothermia group with external cooling (ALI-HT). After induction of ALI/ARDS through mild lung-lavages followed by non-protective ventilation, mild hypothermia was started in ALI-HT group (body temperature of 33-34 °C). All rabbits were conventionally ventilated for an additional 6-h by recording respiratory parameters. Finally, lung histopathology and inflammatory response were evaluated.

RESULTS

Hypothermia was associated with higher oxygen saturation, resulting in partial improvement in the P/F ratio (PaO2/FiO2), oxygenation index, mean airway pressure, and PaCO2, but did not affect lactate levels. The ALI-HT group had lower histopathological injury scores (hyperemia, edema, emphysema, atelectasis, and PMN infiltration). Further, tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6 and -8 levels in lung tissue and serum samples markedly reduced due to hypothermia.

CONCLUSION

Mild TH with external cooling reduced lung inflammation and damage, whereas it resulted in partial improvement in gas exchanges. Our findings highlight that body temperature control may be a potentially supportive therapeutic option for regulating cytokine production and respiratory parameters in ALI/ARDS.

Successful use of mild therapeutic hypothermia as compassionate treatment for severe refractory hypoxemia in COVID-19

BACKGROUND

COVID-19 is a disease associated with an intense systemic inflammation that could induce severe acute respiratory distress syndrome (ARDS), with life-threatening hypoxia and hypercapnia. We present a case where mild therapeutic hypothermia was associated with improved gas exchange, facing other therapies' unavailability due to the pandemic.

CASE REPORT

A healthy 38-year-old male admitted for COVID-19 pneumonia developed extreme hypoxia (PaO₂/FiO₂ ratio 42 mmHg), respiratory acidosis, and hyperthermia, refractory to usual treatment (mechanical ventilation, neuromuscular blockade, and prone position), and advanced therapies were not available. Mild therapeutic hypothermia management (target 33-34 °C) was maintained for five days, with progressive gas exchange improvement, which allowed his recovery over the following weeks. He was discharged home after 68 days without significant ICU associated morbidity.

CONCLUSIONS

Mild hypothermia is a widely available therapy, that given some specific characteristics of COVID-19, may be explored as adjunctive therapy for life-threatening ARDS, especially during a shortage of other rescue therapies.

Precision cut lung slices: a novel versatile tool to examine host-pathogen interaction in the chicken lung

The avian respiratory tract is a common entry route for many pathogens and an important delivery route for vaccination in the poultry industry. Immune responses in the avian lung have mostly been studied in vivo due to the lack of robust, relevant in vitro and ex vivo models mimicking the microenvironment. Precision-cut lung slices (PCLS) have the major advantages of maintaining the 3-dimensional architecture of the lung and includes heterogeneous cell populations. PCLS have been obtained from a number of mammalian species and from chicken embryos. However, as the embryonic lung is physiologically undifferentiated and immunologically immature, it is less suitable to examine complex host-pathogen interactions including antimicrobial responses. Here we prepared PCLS from immunologically mature chicken lungs, tested different culture conditions, and found that serum supplementation has a detrimental effect on the quality of PCLS. Viable cells in PCLS remained present for ≥ 40 days, as determined by viability assays and sustained motility of fluorescent mononuclear phagocytic cells. The PCLS were responsive to lipopolysaccharide stimulation, which induced the release of nitric oxide, IL-1β, type I interferons and IL-10. Mononuclear phagocytes within the tissue maintained phagocytic activity, with live cell imaging capturing interactions with latex beads and an avian pathogenic Escherichia coli strain. Finally, the PCLS were also shown to be permissive to infection with low pathogenic avian influenza viruses. Taken together, immunologically mature chicken PCLS provide a suitable model to simulate live organ responsiveness and cell dynamics, which can be readily exploited to examine host-pathogen interactions and inflammatory responses.

Akt1-mediated CPR cooling protection targets regulators of metabolism, inflammation and contractile function in mouse cardiac arrest

Therapeutic hypothermia initiated during cardiopulmonary resuscitation (CPR) in pre-clinical studies appears to be highly protective against sudden cardiac arrest injury. Given the challenges to implementing CPR cooling clinically, insights into its critical mechanisms of protection could guide development of new CPR drugs that mimic hypothermia effects without the need for physical cooling. Here, we used Akt1-deficient mice that lose CPR hypothermia protection to identify hypothermia targets. Adult female C57BL/6 mice (Akt1^+/+ and Akt1^+/-) underwent 8 min of KCl-induced asystolic arrest and were randomized to receive hypothermia (30 ± 0.5°C) or normothermia. Hypothermia was initiated during CPR and extended for 1 h after resuscitation. Neurologically scored survival was measured at 72 h. Other outcomes included mean arterial pressure and target measures in heart and brain related to contractile function, glucose utilization and inflammation. Compared to northothermia, hypothermia improved both 2h mean arterial pressure and 72h neurologically intact survival in Akt1^+/+ mice but not in Akt1^+/- mice. In Akt1^+/+ mice, hypothermia increased Akt and GSK3β phosphorylation, pyruvate dehydrogenase activation, and NAD⁺ and ATP production while decreasing IκBα degradation and NF-κB activity in both heart and brain at 30 min after CPR. It also increased phospholamban phosphorylation in heart tissue. Further, hypothermia reduced metabolic and inflammatory blood markers lactate and Pre-B cell Colony Enhancing Factor. Despite hypothermia treatment, all these effects were reversed in Akt1^+/- mice. Taken together, drugs that target Akt1 and its effectors may have the potential to mimic hypothermia-like protection to improve sudden cardiac arrest survival when administered during CPR.

Mild hypothermia attenuate kidney injury in canines with oleic acid-induced acute respiratory distress syndrome

BACKGROUND

Hypothermia may attenuate ventilator induced-lung injury in acute respiratory distress syndrome (ARDS). However, the impact of hypothermia on extra-pulmonary organ injury in ARDS remains unclear. The purpose of this study was to investigate whether hypothermia affects extra-pulmonary organ injury in a canine ARDS model induced by oleic acid.

OBJECTIVES

Twelve anesthetized canines with oleic acid-induced ARDS were randomly divided (n=6 per group) into a hypothermia group (core temperature of 33±1°C, HT group) and a normothermia group (core temperature of 38±1°C, NT group) and treated for four hours. The liver, small intestine and kidney were assessed by evaluating biochemical parameters, plasma and tissue cytokine levels, and tissue histopathological injury scores.

RESULTS

The HT group showed a lower plateau pressure, lung elastance and pulmonary vascular resistance. Hypothermia was associated with lower oxygen consumption (138.4±55.0mlmin(-1)vs. 72.0±11.2mlmin(-1), P<0.05) and higher oxygen saturation of mixed venous blood (62.8%±8.0% vs. 77.5%±10.1%, P<0.05). Both groups had similar levels of tumour necrosis factor-α in the plasma and extra-pulmonary organ, however, plasma interleukin-10 (97.1±25.0pgml(-1)vs. 131.4±27.0pgml(-1), P<0.05) was higher in the HT group. Further, the animals in the HT group had a lower levels of plasma creatinine (54.6±19.1UL(-1)vs. 29.1±8.0UL(-1), P<0.05), and lower renal histopathological injury scores [4.0(3.5;7.0) vs. 1.5(0.8;3.0), P<0.05]. Hypothermia did not affect the histopathological injury of the liver and small intestine.

CONCLUSIONS

Short-term mild hypothermia can reduce lung elastance and pulmonary vascular resistance, increase the systemic anti-inflammatory response and attenuate kidney histopathological injury in a canine ARDS model induced by oleic acid.

Mild hypothermia increases pulmonary anti-inflammatory response during protective mechanical ventilation in a piglet model of acute lung injury

BACKGROUND

The effects of mild hypothermia (HT) on acute lung injury (ALI) are unknown in species with metabolic rate similar to that of humans, receiving protective mechanical ventilation (MV). We hypothesized that mild hypothermia would attenuate pulmonary and systemic inflammatory responses in piglets with ALI managed with a protective MV.

METHODS

Acute lung injury (ALI) was induced with surfactant deactivation in 38 piglets. The animals were then ventilated with low tidal volume, moderate positive end-expiratory pressure (PEEP), and permissive hypercapnia throughout the experiment. Subjects were randomized to HT (33.5°C) or normothermia (37°C) groups over 4 h. Plasma and tissue cytokines, tissue apoptosis, lung mechanics, pulmonary vascular permeability, hemodynamic, and coagulation were evaluated.

RESULTS

Lung interleukin-10 concentrations were higher in subjects that underwent HT after ALI induction than in those that maintained normothermia. No difference was found in other systemic and tissue cytokines. HT did not induce lung or kidney tissue apoptosis or influence lung mechanics or markers of pulmonary vascular permeability. Heart rate, cardiac output, oxygen uptake, and delivery were significantly lower in subjects that underwent HT, but no difference in arterial lactate, central venous oxygen saturation, and coagulation test was observed.

CONCLUSIONS

Mild hypothermia induced a local anti-inflammatory response in the lungs, without affecting lung function or coagulation, in this piglet model of ALI. The HT group had lower cardiac output without signs of global dysoxia, suggesting an adaptation to the decrease in oxygen uptake and delivery. Studies are needed to determine the therapeutic role of HT in ALI.

Hydrogen sulfide donor NaHS reduces organ injury in a rat model of pneumococcal pneumosepsis, associated with improved bio-energetic status

Sepsis is characterized by a generalized inflammatory response and organ failure, associated with mitochondrial dysfunction. Hydrogen sulfide donor NaHS has anti-inflammatory properties, is able to reduce metabolism and can preserve mitochondrial morphology and function. Rats were challenged with live Streptococcus pneumonia or saline and infused with NaHS (36 µmol/kg/h) or vehicle. Lung and kidney injury markers were measured as well as mitochondrial function, viability and biogenesis. Infusion of NaHS reduced heart rate and body temperature, indicative of a hypo-metabolic state. NaHS infusion reduced sepsis-related lung and kidney injury, while host defense remained intact, as reflected by unchanged bacterial outgrowth. The reduction in organ injury was associated with a reversal of a fall in active oxidative phosphorylation with a concomitant decrease in ATP levels and ATP/ADP ratio. Preservation of mitochondrial respiration was associated with increased mitochondrial expression of α-tubulin and protein kinase C-ε, which acts as regulators of respiration. Mitochondrial damage was decreased by NaHS, as suggested by a reduction in mitochondrial DNA leakage in the lung. Also, NaHS treatment was associated with upregulation of peroxisome proliferator-activated receptor-γ coactivator 1α, with a subsequent increase in transcription of mitochondrial respiratory subunits. These findings indicate that NaHS reduces organ injury in pneumosepsis, possibly via preservation of oxidative phosphorylation and thereby ATP synthesis as well as by promoting mitochondrial biogenesis. Further studies on the involvement of mitochondria in sepsis are required.

Induced hypothermia attenuates the acute lung injury in hemorrhagic shock

BACKGROUND

In previous animal studies, induction of therapeutic hypothermia (HT) in hemorrhagic shock (HS) had beneficial effects on the hemodynamic and metabolic parameters and on the survival. However, the effect of induced HT on acute lung injury (ALI) in HS has not been investigated. We sought to determine the effects of HT on ALI in HS.

METHODS

Male Sprague-Dawley rats (350-390 g; n = 8 per group) were randomized to the normothermia (NT; 36-37 degrees C) group or the moderate HT (27-30 degrees C) group and were subjected to volume-controlled (2 mL/100 g weight) HS (90 minutes) followed by 90 minutes of resuscitation. ALI score, lung malondialdehyde content, and myeloperoxidase activity were measured. The expression of glycogen synthase kinase 3beta (GSK-3beta), phosphorylated GSK-3beta, inducible nitric oxide synthase (iNOS), heat shock protein (HSP) 72, and nuclear factor-kappaB (NF-kappaB) in the lung were compared.

RESULTS

ALI score, lung malondialdehyde content, and myeloperoxidase were lower in the HT group. GSK-3beta and iNOS gene expressions in lung tissue were significantly decreased in the HT group (p < 0.05). On the contrary, the expression of phosphorylated GSK-3beta was increased in the HT group (p < 0.001). HSP 72 was expressed in the HT group but not in the NT group. The activated p65 NF-kappaB levels in lung nuclear extract were significantly lower in the NT group (p = 0.03).

CONCLUSIONS

HT attenuates HS-induced ALI in rats by the modulation of GSK, HSP 72, iNOS, and NF-kappaB.

Body temperature effects on lung injury in ventilated preterm lambs

AIMS

Mechanical ventilation causes lung injury in premature infants. Hypothermia may protect against and hyperthermia may augment lung injury. We tested the effects of hypo- and hyperthermia on ventilation induced acute lung injury in preterm lambs.

METHODS

Twin sheep fetuses at 128 d GA (term 150 d) were surgically delivered and randomized to unventilated control (UVC), normothermia (38-39 degrees C) without lung injury (NTNI), or to 1 of 3 injurious ventilation groups: hypothermic (33-34 degrees C, LT), normothermic (38-39 degrees C, NT) or hyperthermic (40-41 degrees C, HT). NT, LT and HT groups had 15 min of injurious ventilation (PEEP 0 cmH(2)O, V(T) escalation to 15 mL/kg) following delivery and prior to surfactant. The animals were then gently ventilated (PEEP 5cmH(2)O, V(T) 7.5 mL/kg) for 2h 45 min. NTNI lambs received surfactant at birth prior to gentle ventilation. The lambs were then euthanized, and bronchoalveolar lavage (BAL) fluid and lung tissue were used to evaluate lung injury, inflammatory cell counts, inflammatory markers and cytokine mRNA.

RESULTS

Target temperatures were achieved by 15 min of age and maintained for 3h. All ventilated groups had increased BAL protein, lung inflammation and increased cytokine mRNA. HT animals developed acidosis, premature death, pneumothoraces, impaired lung function and increased inflammatory mRNA expression. LT animals remained clinically stable without pneumothoraces or death, had improved ventilatory efficiency and trended toward lower inflammatory mRNA expression than NT animals.

CONCLUSION

Hyperthermia exacerbated ventilator induced lung injury, while hypothermia may protect against lung injury in the preterm lamb.

Penehyclidine prevents nuclear factor-kB activation in acute lung injury induced by lipopolysaccharide

Penehyclidine (PHCD) has been proposed to reduce lung and lethal toxicity. The present study was undertaken to investigate the mechanisms responsible for the protective effect of PHCD against acute lung injury (ALI) in rats. Tail-vein injection of lipopolysaccharide (LPS; 5 mgkg−1) was used to induce ALI in rats. Secondary increases in total protein, lactate dehydrogenase activity in bronchoalveolar lavage fluid and myeloperoxidase in lung tissue were used to evaluate the effects of PHCD on ALI in rats. Activated DNA binding activity and expression of nuclear factor kB (NF-kB) in lung tissue were measured using electrophoretic mobility shift assays assay and immunohistological staining. Levels and mRNA expression of tumour necrosis factor α (TNF-α) and interleukin 1β (IL-1β) were measured by enzyme-linked immunosorbent assay and reverse transcriptase-polymerase chain reaction. Pretreatment with PHCD (0.03 mgkg−1, 0.1 mgkg−1 and 0.3 mgkg−1 i.p.) significantly attenuated the LPS-induced changes in lung injury parameters and inhibited the activation and expression of NF-kB in lung tissue. Furthermore, PHCD also substantially reduced the LPS-induced TNF-α and IL-1β mRNA expression and production in lung tissue and suppressed neutrophil recruitment. The results suggest that PHCD attenuates LPS-induced acute lung responses through inhibition of NF-kB activation and LPS-induced TNF-α and IL-1β production and resulting neutrophil recruitment associated with acute lung inflammation and injury. PHCD may be a useful adjuvant to treatment strategies targeting clinical situations of acute inflammation.

Angiotensin-converting enzyme inhibitor captopril prevents oleic acid-induced severe acute lung injury in rats

Lack of specific and efficient therapy leads to the high mortality rate of acute lung injury (ALI) and acute respiratory distress (ARDS). Recent evidence implies that angiotensin-converting enzyme (ACE) plays an important role in the pathogenesis of ALI. Pharmaceutical inhibitors of ACE have been used clinically for hypertension but not for ALI/ARDS yet. The objective was to study the effects of ACE inhibition with captopril on severe lung injury induced by oleic acid (OA) in rats. Oleic acid was intravenously injected into Sprague Dawley rats, followed by i.p. administration of captopril or saline control. Lung injury, endothelium damage and related molecules, and disturbance of coagulation were examined in comparison between the treated and the nontreated groups. An OA-induced ALI was featured with thickening of the alveolar septa, alveolar hemorrhage, and infiltration of inflammatory cells. Comparing with the nontreated OA group, the administration of captopril prevented the rats from OA-induced severe lungs injury, with a significantly lower lung injury score, less albumin content and infiltrated cells in the alveoli, decreased wet/dry weight ratio of the lung tissues, and improved lung function (PaO2 per fraction of inspired oxygen). Captopril also dramatically reduced the expression of intercellular adhesion molecule-1 in the lung tissue and in the circulating endothelial cells in the blood, indicating a protective effect on endothelial cells activation/damage. Moreover, captopril treatment led to a blockage of nuclear factor kappaB activation in lung tissues and to the recovery of the fibrinolytic disturbance. Thus, our data suggest that the inhibition of ACE with its clinically used inhibitor offers protective effects on ALI/ARDS, implying the potential for therapeutic option.

Whole-body moderate hypothermia confers protection from wood smoke-induced acute lung injury in rats: The therapeutic window*

OBJECTIVE

Toxic smoke inhalation causes acute lung injury. We studied the efficacy and therapeutic window of whole-body hypothermia in rats with wood smoke-induced acute lung injury.

DESIGN

Randomized, controlled study.

SETTING

Research laboratory.

SUBJECTS

Anesthetized, paralyzed, and artificially ventilated rats (n = 100) were used.

INTERVENTIONS

Air or wood smoke (30 breaths) was delivered into the lung using a respirator. Immediately after challenge, the rat's colonic temperature was kept a) 37 degrees C (normothermia, NT) for 1 (NT-1-Air and NT-1-Smoke), 2.5 (NT-2.5-Air and NT-2.5-Smoke), or 5 hrs (NT-5-Air and NT-5-Smoke) in six groups; b) 30 degrees C (hypothermia, HT) for 2.5 (HT-2.5-Smoke) or 5 hrs (HT-5-Air and HT-5-Smoke) in three groups; c) 30 degrees C for the first 2.5 hrs followed by 37 degrees C for another 2.5 hrs (HT-NT-5-Smoke) in one group; or d) 37 degrees C for the first 2.5 hrs followed by 30 degrees C for another 2.5 hrs (NT-HT-5-Smoke) in on group.

MEASUREMENTS AND MAIN RESULTS

Various acute lung injury indexes were assessed at 1, 2.5, or 5 hrs after challenge. In the air group, whole-body hypothermia did not affect the level of lung lipid peroxidation and the amount of proteins, total and differential cell counts, and concentrations of tumor necrosis factor-alpha and interleukin-1beta in bronchoalveolar lavage fluid. In the smoke groups, these acute lung injury indexes were increased showing that NT-5-Smoke > NT-2.5-Smoke > NT-1-Smoke. Whole-body hypothermia prevented increases in these acute lung injury indexes in the HT-2.5-Smoke and HT-5-Smoke groups. The efficacy of whole-body hypothermia in the HT-NT-5-Smoke group was superior to that in the NT-HT-5-Smoke group and similar to that in the HT-5-Smoke group. Whole-body hypothermia also alleviated smoke-induced poor gas exchange, pulmonary edema, and pathohistologic injurious signs.

CONCLUSIONS

Whole-body hypothermia confers protection from wood smoke-induced acute lung injury in rats by suppressing oxidant bronchoalveolar damage and pulmonary inflammation. Early and short-period (2 hrs) application of whole-body hypothermia provides favorable therapeutic effects.

Moderate hypothermia therapy for acute liver failure in rats before liver transplantation

AIM: To observe the effect of moderate hypothermia on the donated livers in rats with acute liver failure (ALF) before liver transplantation.

METHODS: ALF rats model were established by hepatectomy and hepatic devascularization. In situ liver transplantations were carried out for hypothermia treated group (35.0ºC) and the control group (37.5ºC) 12 h after the transplantation. Blood and tissue samples were collected just before and 6 or 24 h after transplantation. The concentrations of TNF-α were compared before and after the transplantation. The content of malondialdehyde (MDA) and the apoptotic rate of hepatic cells after the transplantation were observed. The apoptotic rate and MDA contents in donated liver were also assayed. The morphological changes of liver tissues were observed under microscope.

RESULTS: In the hypothermia treated group, the concentrations of TNF-α before and after the transplantation were significantly lower than those in the control group (19.3±5.9 vs 43.4±9.0 µg/L, t= 5.008, P = 0.007; 6 h, 97.7±18.3 vs 137.1±23.3 µg/L, t = 9.471, P = 0.001); the MDA contents and apoptotic rate after transplantation were also significantly lower than those in the control group (407.1±49.4 vs 598.2±61.8 nmol/L, t = 34.46, P = 0.001; 18.3±3.9% vs 23.6±4.3%, t = 29.63, P = 0.001).

CONCLUSION: Moderate hypothermia can decrease TNF-α level and relieve the damages of the donated liver in rats with ALF.

Induced hypothermia as a new approach to lung rest for the acutely injured lung*

OBJECTIVE

To investigate whether low-frequency ventilation during hypothermia could attenuate lung injury associated with endotoxin and mechanical ventilation.

DESIGN

: Experimental animal study.

SETTING

University-affiliated animal laboratory.

SUBJECTS

Forty-eight Sprague-Dawley rats.

INTERVENTIONS

: Lipopolysaccharide was administered to rats intratracheally to induce acute lung injury. After 1 hr of this treatment, animals were assigned to normothermia-only (NO, rectal temperature 37 degrees C, ventilatory frequency 90/min), normothermia-lung rest (NR, 37 degrees C, 45/min), hypothermia-only (HO, 27 degrees C, 90/min), or hypothermia-lung rest (HR, 27 degrees C, 45/min). After 1 hr of injurious ventilation, the lungs of the rats were removed for bronchoalveolar lavage and histologic examination.

MEASUREMENTS AND MAIN RESULTS

Compared with the normothermia groups (NO, NR), the neutrophil counts (per milliliter) (NO, 7708 +/- 5704; NR, 10,479 +/- 11,152; HO, 1638 +/- 955; HR, 805 +/- 591) and interleukin-1beta levels (pg/mL) (1180 +/- 439, 1081 +/- 652, 620 +/- 426, 420 +/- 182, respectively) in the bronchoalveolar lavage fluid, the wet-to-dry lung weight ratios (6.0 +/- 0.4, 5.7 +/- 0.4, 5.6 +/- 0.2, 5.2 +/- 0.2, respectively), and histologic acute lung injury scores (8.3 +/- 2.7, 10.4 +/- 3.1, 3.5 +/- 2.1, 3.1 +/- 2.2, respectively) of the hypothermia groups (HO, HR) were lower (all p < .001). Compared with the HO group, the neutrophil counts and protein content (HO, 1367 +/- 490 mug/mL vs. HR, 831 +/- 369 mug/mL) in the bronchoalveolar lavage fluid, the serum lactate dehydrogenase levels (units/mL) (9.1 +/- 3.6 vs. 5.3 +/- 1.5), and the wet-to-dry lung weight ratios of the HR group were lower (all p < .05).

CONCLUSIONS

Reduction of ventilatory frequency in conjunction with hypothermia attenuated many variables of acute lung injury in rats. Use of hypothermia could be exploited as a new approach to lung rest for the ventilatory management of the acutely injured lung.

Solanum nigrum produces nitric oxide via nuclear factor-kappaB activation in mouse peritoneal macrophages

Nitric oxide (NO) is an antitumour molecule produced in activated macrophages and Solanum nigrum is a plant used in oriental medicine to treat tumours. In this study using mouse peritoneal macrophages, we have examined the mechanism by which Solanum nigrum regulates NO production. When Solanum nigrum was used in combination with 20 U/ml of recombinant interferon-gamma (rIFN-gamma), there was a marked cooperative induction of NO production. The increase in NO synthesis was reflected as an increased amount of inducible NO synthase (iNOS) protein. The production of NO from rIFN-gamma plus Solanum nigrum-stimulated peritoneal macrophages was decreased by treatment with N-monomethyl-L-arginine or N-tosyl-Phe chloromethyl ketone, an iNOS inhibitor. Additionally, the increased production of NO from rIFN-gamma plus Solanum nigrum-stimulated cells was almost completely inhibited by pretreatment with 100 micromol/l of pyrrolidine dithiocarbamate, an inhibitor of nuclear factor kappaB (NF-kappaB). Furthermore, Solanum nigrum increased activation of NF-kappaB. These findings suggest that Solanum nigrum increases the production of NO by rIFN-gamma-primed macrophages and NF-kappaB plays a critical role in mediating these effects.