LPS-induced Tissue Damage Research Articles

Protective effects of nordalbergin against LPS-induced endotoxemia through inhibiting MAPK/NF-κB signaling pathway, NLRP3 inflammasome activation, and ROS production.

Nordalbergin is a coumarin extracted from Dalbergia sissoo DC. To date, the biological effects of nordalbergin have not been well investigated. To investigate the anti-inflammatory responses and the anti-oxidant abilities of nordalbergin using lipopolysaccharide (LPS)-activated macrophages and LPS-induced sepsis mouse model. Production of nitrite oxide (NO), prostaglandin E2 (PGE2), pro-inflammatory cytokines (tumor necrosis factor (TNF)-α, interleukin (IL)-6 and IL-1β), reactive oxygen species (ROS), tissue damage and serum inflammatory markers, and the activation of the NLRP3 inflammasome were examined. Our results indicated that nordalbergin reduced the production of NO and pro-inflammatory cytokines in vitro and ex vivo. Nordalbergin also suppressed iNOS and cyclooxygenase-2 expressions, decreased NF-κB activity, and attenuated MAPKs signaling pathway activation by decreasing JNK and p38 phosphorylation by LPS-activated J774A.1 macrophages. Notably, nordalbergin diminished NLRP3 inflammasome activation via repressing the maturation of IL-1β and caspase-1 and suppressing ROS production by LPS/ATP- and LPS/nigericin-activated J774A.1 macrophages. Furthermore, nordalbergin exhibited protective effects against the infiltration of inflammatory cells and also inhibited the levels of organ damage markers (AST, ALT, BUN) by LPS-challenged mice. Nordalbergin possesses anti-inflammatory effects in macrophage-mediated innate immune responses, alleviates ROS production, decreases NLRP3 activation, and exhibits protective effects against LPS-induced tissue damage in mice.

Heterozygous Apex1 deficiency exacerbates lipopolysaccharide-induced systemic inflammation in a murine model

The biological role of apurinic/apyrimidinic endonuclease 1/redox factor-1 (Apex1) in modulating systemic inflammation remains unclear. This study aimed to assess the impact of Apex1 deficiency on systemic inflammation triggered by lipopolysaccharide (LPS) in a murine model. The methods involved transcriptomic analysis and assessments of inflammatory responses in age-matched 8-week-old Apex1+/− and wild-type Apex1+/+ mice, generated using the CRISPR/Cas9 system. Apex1+/− mice displayed no overt changes in body weight, however, Apex1 protein expressions in tissues were significantly reduced compared to wild-type mice. Furthermore, in Apex1+/− mice transcriptomic analysis showed that genes associated with antioxidant pathways were downregulated, and levels of superoxide production, 8-hydroxy-2′-deoxyguanosine (8-OHdG), and malondialdehyde (MDA) were increased. Moreover, hematological analysis showed increased neutrophil levels and a twofold increase in the count of splenic lymphocyte antigen 6 family member G+ (Ly6G+) neutrophils in the Apex1+/− mice compared to those in Apex1+/+ mice. Furthermore, following LPS treatment, the levels of cytokines and chemokines, including interleukin-1β, interleukin-10, tumor necrosis factor-α, and monocyte chemoattractant protein 1, increased in the Apex1+/− mice. The Kaplan-Meier curve showed a significant reduction in the survival rates of Apex1+/− mice treated with LPS compared to those of Apex1+/+ mice. The hepatic and lung injury scores and Ly6G+ neutrophil infiltration levels also increased in Apex1+/− mice after LPS treatment. These results showed that Apex1 deficiency exacerbated the LPS-induced tissue damage in the lung and liver. These findings illustrate that in vivo Apex1 deficiency exacerbates LPS-induced systemic inflammation, tissue damage, and mortality in a murine model, highlighting the crucial role of Apex1 in mitigating inflammatory responses and maintaining a holistic physiological equilibrium.

Anti-cytokine Storm Activity of Fraxin, Quercetin, and their Combination on Lipopolysaccharide-Induced Cytokine Storm in Mice: Implications in COVID-19.

Cytokine release syndrome (CRS) is the leading cause of mortality in advanced stages of coronavirus patients. This study examined the prophylactic effects of fraxin, quercetin, and a combination of fraxin+quercetin (FQ) on lipopolysaccharide-induced mice. Sixty mice were divided into six groups (n=10) as follows: control, LPS only, fraxin (120 mg/Kg), quercetin (100 mg/Kg), dexamethasone (5 mg/Kg), and FQ. All treatments were administered intraperitoneally (IP) one hour before induction by LPS (5 mg/Kg) IP injection. Twenty-four hours later, the mice were euthanized. Interleukin one beta (IL-1β), interleukin 6 (IL-6), and tumor necrosis factor-alpha (TNF-α) were quantified using an enzyme-linked immunosorbent assay (ELISA), and lung and kidney tissues were examined for histopathological alterations. This study was conducted at Al-Nahrain University, Baghdad, Iraq, in 2022. FQ reduced IL-1β (P<0.001). All treatments significantly suppressed IL-6, fraxin, quercetin, dexamethasone, and FQ, all with P<0.001. The TNF-α level was reduced more with dexamethasone (P<0.001) and quercetin (P<0.001). Histopathological scores were significantly reduced mainly by quercetin and FQ in the lungs with scores of 12.30±0.20 (P=0.093), and 15.70±0.20 (P=0.531), respectively. The scores were 13±0.26 (P=0.074) and 15±0.26 (P=0.222) for quercetin and FQ in the kidneys, respectively. All used treatments reduced proinflammatory cytokine levels and protected against LPS-induced tissue damage.

Meta-Analysis illustrates possible role of lipopolysaccharide (LPS)-induced tissue injury in nasopharyngeal carcinoma (NPC) pathogenesis.

Nasopharyngeal carcinoma (NPC) is a cancer of epithelial origin with a high incidence in certain populations. While NPC has a high remission rate with concomitant chemoradiation, recurrences are frequent, and the downstream morbidity of treatment is significant. Thus, it is imperative to find alternative therapies. We employed a Search Tag Analyze Resource (STARGEO) platform to conduct a meta-analysis using the National Center for Biotechnology's (NCBI) Gene Expression Omnibus (GEO) to define NPC pathogenesis. We identified 111 tumor samples and 43 healthy nasopharyngeal epithelium samples from NPC public patient data. We analyzed associated signatures in Ingenuity Pathway Analysis (IPA), restricting genes that showed statistical significance (p<0.05) and an absolute experimental log ratio greater than 0.15 between disease and control samples. Our meta-analysis identified activation of lipopolysaccharide (LPS)-induced tissue injury in NPC tissue. Additionally, interleukin-1 (IL-1) and SB203580 were the top upstream regulators. Tumorigenesis-related genes such as homeobox A10 (HOXA10) and prostaglandin-endoperoxide synthase 2 (PTGS2 or COX-2) as well as those associated with extracellular matrix degradation, such as matrix metalloproteinases 1 and 3 (MMP-1, MMP-3) were also upregulated. Decreased expression of genes that encode proteins associated with maintaining healthy nasal respiratory epithelium structural integrity, including sentan-cilia apical structure protein (SNTN) and lactotransferrin (LTF) was documented. Importantly, we found that etanercept inhibits targets upregulated in NPC and LPS induction, such as MMP-1, PTGS2, and possibly MMP-3. Our analysis illustrates that nasal epithelial barrier dysregulation and maladaptive immune responses are key components of NPC pathogenesis along with LPS-induced tissue damage.

Protective Effect of Piplartine against LPS-Induced Sepsis through Attenuating the MAPKs/NF-κB Signaling Pathway and NLRP3 Inflammasome Activation.

Piplartine (or Piperlongumine) is a natural alkaloid isolated from Piper longum L., which has been proposed to exhibit various biological properties such as anti-inflammatory effects; however, the effect of piplartine on sepsis has not been examined. This study was performed to examine the anti-inflammatory activities of piplartine in vitro, ex vivo and in vivo using murine J774A.1 macrophage cell line, peritoneal macrophages, bone marrow-derived macrophages and an animal sepsis model. The results demonstrated that piplartine suppresses iNOS and COX-2 expression, reduces PGE2, TNF-α and IL-6 production, decreases the phosphorylation of MAPKs and NF-κB and attenuates NF-κB activity by LPS-activated macrophages. Piplartine also inhibits IL-1β production and suppresses NLRP3 inflammasome activation by LPS/ATP- and LPS/nigericin-activated macrophages. Moreover, piplartine reduces the production of nitric oxide (NO) and TNF-α, IL-6 and IL-1β, decreases LPS-induced tissue damage, attenuates infiltration of inflammatory cells and enhances the survival rate. Collectively, these results demonstrate piplartine exhibits anti-inflammatory activities in LPS-induced inflammation and sepsis and suggest that piplartine might have benefits for sepsis treatment.

N-palmitoyl-D-glucosamine, a Natural Monosaccharide-Based Glycolipid, Inhibits TLR4 and Prevents LPS-Induced Inflammation and Neuropathic Pain in Mice.

Toll-like receptors (TLRs) are key receptors through which infectious and non-infectious challenges act with consequent activation of the inflammatory cascade that plays a critical function in various acute and chronic diseases, behaving as amplification and chronicization factors of the inflammatory response. Previous studies have shown that synthetic analogues of lipid A based on glucosamine with few chains of unsaturated and saturated fatty acids, bind MD-2 and inhibit TLR4 receptors. These synthetic compounds showed antagonistic activity against TLR4 activation in vitro by LPS, but little or no activity in vivo. This study aimed to show the potential use of N-palmitoyl-D-glucosamine (PGA), a bacterial molecule with structural similarity to the lipid A component of LPS, which could be useful for preventing LPS-induced tissue damage or even peripheral neuropathies. Molecular docking and molecular dynamics simulations showed that PGA stably binds MD-2 with a MD-2/(PGA)3 stoichiometry. Treatment with PGA resulted in the following effects: (i) it prevented the NF-kB activation in LPS stimulated RAW264.7 cells; (ii) it decreased LPS-induced keratitis and corneal pro-inflammatory cytokines, whilst increasing anti-inflammatory cytokines; (iii) it normalized LPS-induced miR-20a-5p and miR-106a-5p upregulation and increased miR-27a-3p levels in the inflamed corneas; (iv) it decreased allodynia in peripheral neuropathy induced by oxaliplatin or formalin, but not following spared nerve injury of the sciatic nerve (SNI); (v) it prevented the formalin- or oxaliplatin-induced myelino-axonal degeneration of sciatic nerve. SIGNIFICANCE STATEMENT We report that PGA acts as a TLR4 antagonist and this may be the basis of its potent anti-inflammatory activity. Being unique because of its potency and stability, as compared to other similar congeners, PGA can represent a tool for the optimization of new TLR4 modulating drugs directed against the cytokine storm and the chronization of inflammation.

The Impact of Prophylactic Lacosamide on LPS-Induced Neuroinflammation in Aged Rats.

Sepsis-induced central nervous system damage is called sepsis-associated encephalopathy (SAE). In addition to neuroinflammation, oxidative stress and apoptosis act in the development of SAE. In the current study, we evaluated the protective effects of lacosamide (LCM) on neuroinflammation induced by lipopolysaccharide (LPS). Twenty-four Wistar albino rats were divided into 3 groups as controls, LPS group (5mg/kg i.p.), and LPS plus LCM group (5mg/kg i.p and 40mg/kg i.p, respectively). In the rat brain, LPS-induced tissue damage was revealed histopathologically as hyperemia and microhemorrhages. LCM pretreatment ameliorated these histopathological changes. LPS decreased brain TAS levels and significantly increased MDA, CRP, HSP, IL-1β, and TNF-α expressions in the cortex, hippocampus, and cerebellum. Western analysis revealed increased brain tissue levels of TNF-α, NF-Kβ, and caspase-3 following LPS. Prophylactic LCM treatment reversed these parameters including oxidative stress, inflammation, and apoptosis in the cortex, hippocampus, and cerebellum.

Regulatory roles of PGE2 in LPS-induced tissue damage in bovine endometrial explants

Bovine endometritis is the most common uterine disease following parturition. The role of prostaglandin E2 (PGE2) in regulating normal physiological function in the bovine endometrium has been clearly established. Although PGE2 accumulation is observed in multiple inflammatory diseases, such as endometritis, its association with pathogen-induced inflammatory damage in the endometrium is unclear. To clarify the role of PGE2 in lipopolysaccharide (LPS)-induced endometritis in cultured bovine endometrial explants, the levels of PGE2 secretion, prostaglandin synthetases, pro-inflammatory factors, and damage-associated molecular patterns (DAMPs) were evaluated in the present study. Significant PGE2 accumulation in response to LPS stimulation, up-regulation of prostaglandin-endoperoxide synthase-2 (PTGS-2), microsomal prostaglandin E synthase-1 (mPGES-1), pro-inflammatory factors including interleukin-6 (IL-6), tumor necrosis factor (TNF-α), and induced nitric oxide synthase (iNOS)/nitric oxide (NO) and DAMPs including hyaluronan binding protein 1 (HABP1) and high mobility group box-1 (HMGB1), were observed compared to the control group. LPS induced distinct damage in the bovine endometrium, characterized by morphological changes and increases in HABP1 and HMGB1 expression. PTGS-2 inhibitors CAY10404 and NS398 effectively decreased the secretion of PGE2 and the expression of prostaglandin synthetases, pro-inflammatory factors and DAMPs, and alleviated LPS-induced tissue damage. These results indicate that PGE2 accumulates via PTGS-2 and mPGES-1 and induces tissue damage by upregulating pro-inflammatory factors and DAMPs in LPS-treated bovine endometrial explants. These findings provide a basis for the effect of PGE2 on LPS-treated bovine endometrium, and suggest a potential target for curing endometritis.

Smallanthus sonchifolius leaf attenuates neuroinflammation

[Purpose]Yacon, Smallanthus sonchifolius, has anti-hypertensive, anti-inflammatory, and anti-cancer potential. However, its neuroprotective and anti-neuroinflammatory effects are unknown. Moreover, activation of microglia has been considered a mechanism in the development of Alzheimer’s disease. Therefore, the aim of this study was to determine the neuroprotective effects of an ethanolic yacon leaf extract (YLE) on lipopolysaccharide (LPS)-induced neuroinflammation in vitro and in vivo.[Methods]The viability of microglial BV2 cells was tested with 2,3-bis[2-methyloxy-4-nitro-5-sulfophenyl]-2H-tetrazolim-5-carboxanilide. The production of nitric oxide (NO) was determined by the Griess reagent. mRNA expression and protein levels of inflammatory mediators were evaluated by the real-time polymerase chain reaction and immunohistochemistry, respectively. In addition, we performed histological analysis in mice treated with an intraperitoneal injection of LPS (250 μg/kg).[Results]Our results showed that treatment with YLE significantly reduced NO production in LPS-stimulated BV2 cells. YLE also decreased mRNA levels of the inflammatory factors tumor necrosis factor alpha, inducible nitric oxide synthase, cyclooxygenase-2, and interleukin-1 beta. In vivo, YLE (40 mg/kg daily for seven days) significantly diminished LPS-induced tissue damage in the dentate gyrus and cornu amonis regions of the hippocampus by regulating the levels of inflammatory factors.[Conclusion]Our findings support the protective effects of YLE against the development of neurodegeneration.

Suppression of inflammation by tumor-derived exosomes: a kind of natural liposome packaged with multifunctional proteins

Exosomes are small-membrane vesicles secreted by hematopoietic and malignant epithelial cells as well as trophoblasts. The composition of cancerous exosomes has been proven to play pivotal roles in the maintenance of the microenvironment that is beneficial for the progression of cancer, such as Fas-ligand–triggered lymphocyte apoptosis. We supposed that the immunosuppressive effect of cancerous exosomes might be helpful in the treatment of diseases characterized by overactivation of the immune system and subsequent tissue injury. The aim of this study was to evaluate the protective effect of tumor-derived exosomes in the mice model of lipopolysaccharide (LPS)-induced inflammation. Tetrazolium (MTT) and DNA electrophoresis were used to measure the cytotoxicity of exosomes on lymphocytes. Pathologic observation of tissue sections, serologic analysis of aspartate aminotransferase/alanine aminotransferase (AST/ALT), and urinary analysis of protein were used to assess the protection effect of exosomes in LPS-induced multiorgan damage. In vitro outcomes of MTT and DNA electrophoresis showed the cytotoxicity of exosomes on lymphocytes. Together with the alleviation of organ damages evaluated by urine protein, serum AST/ALT, and pathologic analysis, we confirmed the possibility that pretreatment of mice with exosomes, produced by H22 hepatic tumor cells, resulted in protection against LPS-induced tissue damage, which is caused by overactivation of the immune system and inflammation response. This therapeutic strategy will raise an interesting way to search new therapeutics in pairs of diseases with complementarities in etiology and pathology, namely, a strategy of taking advantage of the mutual complementarities between diseases.

Modulation of lipopolysaccharide-induced oxidative stress by capsaicin

This study investigated the effect of capsaicin (the active principle of hot red pepper and a sensory excitotoxin) on oxidative stress after systemic administration of the endotoxin lipopolysaccharide (100μg/kg, i.p.) in rats. Capsaicin (15, 150 or 1,500μg/kg; 10, 100 or 400μg/mL) was given via intragastric (i.g.) or intraperitoneal (i.p.) routes at time of endotoxin administration. Rats were killed 4h later. Malondialdehyde (MDA) and reduced glutathione (GSH) were measured in brain, liver, and lungs. Alanine aminotransferase (ALT), aspartate aminotransferase, alkaline phosphatase (ALP), nitric oxide, and glucose were measured in serum. In addition, histopathological examination of liver tissue was performed. In LPS-treated rats, hepatic GSH increased significantly by 40.8% after i.p. capsaicin at 1,500μg/kg. Liver MDA increased significantly by 32.9% after the administration of i.g. capsaicin at 1,500μg/kg and by 27.8 and 37.6% after the administration of i.p. capsaicin at 150 and 1,500μg/kg, respectively. In lung tissue, both MDA and GSH were decreased by capsaicin administration. MDA decreased by 19-20.8% after i.g. capsaicin and by 17.5-23.2% after i.p. capsaicin (150-1,500μg/kg), respectively. GSH decreased by 39.3-64.3% and by 35.7-41.1% after i.g. or i.p. capsaicin (150-1,500μg/kg), respectively. Brain GSH increased significantly after the highest dose of i.g. or i.p. capsaicin (by 20.6 and 15.9%, respectively). The increase in serum ALT and ALP after endotoxin administration was decreased by oral or i.p. capsaicin. Serum nitric oxide showed marked increase after LPS injection, but was markedly decreased after capsaicin (1,500μg/kg, i.p.). Serum glucose increased markedly after the administration of LPS, and was normalized by capsaicin treatment. It is suggested that in the presence of mild systemic inflammation, acute capsaicin administration might alter oxidative status in some tissues and exert an anti-inflammatory effect. Capsaicin exerted protective effects in the liver and lung against the LPS-induced tissue damage.

Evaluation of the host response to endotoxemia of FVIII and FIX deficient mice

For several years, coagulation has been implicated in the pathogenesis of sepsis. However, results from clinical trials with natural anticoagulants, as well as studies with knock-out mice for specific coagulation factors yielded conflicting results on the role of coagulation in the pathogenesis of sepsis. The aim of this study was to evaluate the impact of severe The factor VIII:C (FVIII:C) and factor IX:C (FIX:C) deficiency on a lipopolysaccharide (LPS)-induced murine model of sepsis. FVIII:C and FIX:C deficient mice, and their haemostatic normal littermate controls were challenged with LPS, and several parameters of the host response were evaluated: seven-day survival experiments were performed using two dose levels of LPS; biochemical and histological markers of tissue damage, coagulation parameters, and pro-inflammatory cytokines were evaluated at baseline and after 3 h and 6 h after an injection of LPS. Severe FVIII and FIX deficiency were compatible with normal survival in experimental sepsis. In addition, LPS-induced tissue damage and coagulation activation were similar in FVIII or FIX deficient mice compared to their respective controls. A lower release of pro-inflammatory cytokines was observed in FIX but not in FVIII deficient mice. Severe FIX or FVIII deficiency does not protect mice from mortality or from tissue damage in the endotoxemia model, supporting the hypothesis that FVIII and FIX are not critical to the pathogenesis of experimental sepsis.

Endotoxin-induced HIF-1α stabilisation in equine endothelial cells: synergistic action with hypoxia

Hypoxia may enhance the deleterious effects of lipopolysaccharide (LPS) in the endotoxaemic horse. This study has examined some of the actions of LPS and hypoxia, alone and in combination, on cultured equine digital vein endothelial cells (EDVEC) and the signalling molecules involved. EDVEC were exposed to LPS, 5% O(2) and LPS then 5% O(2) for up to 24 h. HIF-1alpha stabilisation, neutrophil adhesion and EDVEC permeability were assessed by immunoblotting, measurement of myeloperoxidase and movement of FITC-dextran, respectively. Pharmacological inhibitors were used to assess the roles of p38 MAPK and HIF-1alpha. LPS and hypoxia significantly increased HIF-1alpha stabilisation, neutrophil adhesion and EDVEC permeability and the effects of the two stimuli in combination on HIF-1alpha stabilisation and neutrophil adhesion were more than additive. The effect of LPS, but not 5% O(2), on neutrophil adherence required activation of p38 MAPK, whereas EDVEC permeability in response to both stimuli was dependent on p38 MAPK and HIF-1alpha. Exposure of EDVEC to LPS prior to induction of hypoxia up-regulates responses that may enhance LPS-induced tissue damage in the endotoxaemic horse. Inhibitors of p38 MAPK or HIF-1alpha could reduce such unwanted effects.

Endocannabinoid System and Nitric Oxide are Involved in the Deleterious Effects of Lipopolysaccharide on Murine Decidua

Endocannabinoids are an important family of lipid-signaling molecules that are widely distributed in mammalian tissues and anandamide (AEA) was the first member identified. The uterus contains the highest concentrations of AEA yet discovered in mammalian tissues and this suggests that it might play a role in reproduction. Previous results from our laboratory have shown that AEA modulated NO synthesis in rat placenta. The production of small amounts of nitric oxide regulates various physiological reproductive processes such as implantation, decidualization and myometrial relaxation. But in an inflammatory setting such as sepsis, NO is produced in big amounts and has toxic effects as it is a free radical. The results presented in this study indicate that LPS-induced NO synthesis and tissue damage were mediated by AEA. Decidual LPS-induced NO production was abrogated either by co-incubation with CB1 (AM251) or CB2 (SR144528) antagonists which suggests that both receptors could be mediating this effect. On the other hand, LPS-induced tissue damage and this deleterious effect was partially abrogated by incubating tissue explants with LPS plus CB1 receptor antagonist. Our findings suggest that AEA, probably by increasing NO synthesis, participates in the deleterious effect of LPS in implantation sites. These effects could be involved in pathological reproductive events such as septic abortion.

Loss of SLP-76 Expression within Myeloid Cells Confers Resistance to Neutrophil-Mediated Tissue Damage while Maintaining Effective Bacterial Killing

The Src homology 2 domain-containing leukocyte phosphoprotein of 76 kDa (SLP-76) is an adaptor molecule critical for immunoreceptor and integrin signaling in multiple hemopoietic lineages. We showed previously that SLP-76 is required for neutrophil function in vitro, including integrin-induced adhesion and production of reactive oxygen intermediates, and to a lesser extent, FcgammaR-induced calcium flux and reactive oxygen intermediate production. It has been difficult to determine whether SLP-76 regulates neutrophil responses in vivo, because Slp-76(-/-) mice exhibit marked defects in thymocyte and vascular development, as well as platelet and mast cell function. To circumvent these issues, we generated mice with targeted loss of SLP-76 expression within myeloid cells. Neutrophils obtained from these animals failed to respond to integrin activation in vitro, similar to Slp-76(-/-) cells. Despite these abnormalities, SLP-76-deficient neutrophils migrated normally in vivo in response to Staphylococcus aureus infection and efficiently cleared micro-organisms. Interestingly, SLP-76-deficient neutrophils did not induce a robust inflammatory response in the localized Shwartzman reaction. Collectively, these data suggest that disruption of integrin signaling via loss of SLP-76 expression differentially impairs neutrophil functions in vivo, with preservation of migration and killing of S. aureus but reduction in LPS-induced tissue damage and vascular injury.

Chronic exercise and the pro-inflammatory response to endotoxin in the serum and heart

Purpose: To examine the effects of moderate intensity chronic exercise on tumor necrosis factor-alpha (TNFα) and inducible nitric oxide synthase (iNOS) responses to endotoxin in female Sprague-Dawley rats. Methods: Rats were divided into two groups, exercise ( n = 17) and sedentary ( n = 24). Exercise (Ex) rats completed 12 weeks of motorized treadmill running 3 days/week for 15–25 min at 22–25 m/min, while sedentary (Sed) rats remained in their cages. Twenty-four hrs after the last exercise session, animals were subdivided into three groups. One subgroup served as baseline controls. These rats received an injection of saline (s) and were killed immediately (Sed-s and Ex-s), while the other groups received an injection of lipopolysaccharide (LPS). LPS animals were killed 2 h (Sed-L2 and Ex-L2) or 4 h after the LPS injection (Sed-L4 and Ex-L4). Results: Serum TNFα was elevated 2 h after LPS injection in both Sed and Ex groups, but was significantly higher in the chronic exercise group (Ex-L2 versus. Sed-L2). Similarly, serum β glucuronidase activity, an indicator of tissue damage, was elevated 2 and 4 h after LPS injection, and was significantly higher in the exercise groups. Post-treatment left ventricular TNFα and iNOS activity, as well as stable nitric oxide derivatives in the serum (NO x ), were significantly higher in LPS-injected groups compared to saline groups, but no difference in LPS effect was observed between sedentary and exercise groups. Conclusions: Moderate intensity chronic exercise stress caused an exaggerated serum TNFα response to endotoxin and an elevation in a serum marker of LPS-induced tissue damage.