Mechanisms and functional consequences of liver failure substantially differ between endotoxaemia and faecal peritonitis in rats

Increased peritoneal B1-like cells during acute phase of human septic peritonitis

Sepsis is a life-threatening condition caused by dysregulated host responses to infection. Myeloid cell accumulation and lymphocyte decline are widely recognized phenomena in septic patients. However, the fate of specific immune cells remains unclear. Here, we report the results of a human explorative study of patients with septic peritonitis and patients undergoing abdominal surgery without sepsis. We analyzed pairwise peritoneal fluid and peripheral blood taken 24 h after surgery to characterize immediate immune cell changes. Our results show that myeloid cell expansion and lymphocyte loss occur in all patients undergoing open abdominal surgery, indicating that these changes are not specific to sepsis. However, B1-like lymphocytes were specifically increased in the peritoneal fluid of septic patients, correlating positively with sequential organ failure assessment (SOFA) and acute physiology and chronic health evaluation II (APACHE-II) clinical severity scores. In support of this notion, we identified an accumulation of peritoneal B1b lymphocytes in septic mice.

Combination of Phycocyanin, Zinc, and Selenium Improves Survival Rate and Inflammation in the Lipopolysaccharide-Galactosamine Mouse Model

Sepsis is related to systemic inflammation and oxidative stress, the primary causes of death in intensive care units. Severe functional abnormalities in numerous organs can arise due to sepsis, with acute lung damage being the most common and significant morbidity. Spirulina, blue-green algae with high protein, vitamins, phycocyanin, and antioxidant content, shows anti-inflammatory properties by decreasing the release of cytokines. In addition, zinc (Zn) and selenium (Se) act as an antioxidant by inhibiting the oxidation of macromolecules, as well as the inhibition of the inflammatory response. The current study aimed to examine the combined properties of Zn, Se, and phycocyanin oligopeptides (ZnSePO) against lipopolysaccharide-D-galactosamine (LPS-GalN)-induced septic lung injury through survival rate, inflammatory, and histopathological changes in Balb/c mice. A total of 30 mice were allocated into three groups: normal control, LPS-GalN (100 ng of LPS plus 8 mg of D-galactosamine), LPS-GalN + ZnSePO (ZnPic, 52.5 µg/mL; SeMet, 0.02 µg/mL; and phycocyanin oligopeptide (PO), 2.00 mg/mL; at 1 h before the injection of LPS-GalN). Lung tissue from mice revealed noticeable inflammatory reactions and typical interstitial fibrosis after the LPS-GalN challenge. LPS-GalN-induced increased mortality rate and levels of IL-1, IL-6, IL-10, TGF-β, TNF-α, and NF-κB in lung tissue. Moreover, treatment of septic mice LPS-GalN + ZnSePO reduced mortality rates and inflammatory responses. ZnSePO considerably influenced tissue cytokine levels, contributing to its capacity to minimize acute lung injury (ALI) and pulmonary inflammation and prevent pulmonary edema formation in LPS-GalN-injected mice. In conclusion, ZnSePO treatment enhanced the survival rate of endotoxemia mice via improving inflammation and oxidative stress, indicating a possible therapeutic effect for patients with septic infections.

Evaluation of Hepatoprotective Effects of Piperlongumine Derivative PL 1-3-Loaded Albumin Nanoparticles on Lipopolysaccharide/d-Galactosamine-Induced Acute Liver Injury in Mice

In recent years, piperlongumine (PL) having specific cytotoxicity has attracted considerable attention for anticancer activity. Through structural modification, the active derivative PL 1-3 shows potential anti-inflammatory activity and low cytotoxicity, but its water solubility is low. Here, PL 1-3-loaded bovine serum albumin nanoparticles (1-3 NPs) were prepared and characterized, which can improve the dissolution. 1-3 NPs exhibited effective hepatoprotective effects on lipopolysaccharide/d-galactosamine-induced acute liver injury of mice, which was similar to liver injury in clinical settings. 1-3 NPs treatment can inhibit inflammation, oxidative stress, and apoptosis via the downregulation of NF-κB signaling pathways, the activation of Nrf2/HO-1 signaling pathways, and the inhibition of expression of Bax and caspase 3 proteins. The above results demonstrated that PL 1-3-loaded bovine serum albumin nanoparticles possessed potential value in intervention of inflammation-based liver injury.

Protective effect of green tea and epigallocatechin-3-gallate in a LPS-induced systemic inflammation model

Inflammation causes severe dysregulation of organ functions, via the development of oxidative stress and inflammation damage. Polyphenol compounds found in green tea (GTE), including the most important component epigallocatechin-3-gallate (EGCG), have a great therapeutic potential. Here, protective properties of GTE and EGCG against lipopolysaccharide (LPS)-induced inflammation are explored. To this end, the effects of GTE and EGCG were studied on LPS challenged macrophages. Mice received GTE (250 mg/kg/d/p.o) or EGCG (25 mg/kg/d/i.p.) for 7 d, before the inflammation shock was provoked with a single intraperitoneal injection of LPS. The frequencies of lymphocytes CD4⁺, CD8⁺, NK1-1⁺ and CD4⁺CD25^highFOXP3⁺ (Treg), macrophages CD11b⁺F480⁺, monocytes CD11b⁺Ly6C^low/high, neutrophils CD11b⁺Ly6G⁺, MDSCs CD11b⁺Gr-1^high, M2/N2-like phenotype CD206⁺ and M1-like phenotype CD86⁺ in spleen, bone marrow and peripheral blood were determined. In vitro studies revealed that GTE and EGCG significantly attenuated LPS-induced CD80 expression and increased the CD163 expression, showing a potential to reduce the macrophage inflammatory phenotype. In vivo, GTE and EGCG inhibited the inflammation, mainly by reducing M1-macrophages and increasing Treg cells in the bone marrow. In addition, GTE and EGCG increase M2-macrophages, N2-neutrophils and Tregs in the spleen and blood and block the migration of monocytes from the bone marrow to the peripheral blood. These findings indicate that EGCG and GTE prevent LPS-induced inflammatory damage contributing to restoring the immune system homeostasis.

Gingival-Derived Mesenchymal Stem Cells Protect Against Sepsis and Its Complications

Objective

In the present study, we separated and characterized mouse gingival-derived mesenchymal stem cells (GMSCs) and investigated whether GMSCs can improve lipopolysaccharide (LPS)-induced sepsis and its complications.

Methods

Ninety-six ICR mice were randomly divided into the following groups: the control (Sham), LPS, and LPS + MSC groups. Mice received 5 mg/kg LPS intraperitoneally to induce sepsis. Histopathological micrographs illustrated organ injury. We detected systemic inflammation, blood glucose levels, and serum levels of high-mobility group box 1 (HMGB1) and lactate. In addition, pulmonary inflammation, lung permeability, and oxidative stress-related indicators in lung tissue were measured.

Results

We successfully separated a novel population of MSCs from mouse gingiva. These cells had MSC-associated properties, such as a typical fibroblast-like morphology, multiple differentiation potential, and certain phenotypes. Cell-based therapy using GMSCs significantly improved the survival rate, systemic inflammation, hypoglycemia, multiple organ dysfunction syndrome (MODS), and aortic injury during sepsis. GMSCs administration reduced pulmonary inflammation, lung permeability, and oxidative stress injury. GMSCs administration reduced neutrophil infiltration partly because GMSCs inhibited neutrophil chemoattractants tumor necrosis factor (TNF-α), C-X-C motif chemokine ligand (CXCL-1), and Interleukin (IL-8). GMSCs impaired LPS-induced HMGB1 and lactate release during sepsis.

Conclusion

GMSCs administration is a novel therapeutic strategy targeting aerobic glycolysis for the treatment of sepsis because GMSCs impair LPS-induced HMGB1 and lactate release. GMSCs alleviate lung injury partly because GMSCs exert immune effects, inhibit neutrophilic inflammation, and reduce oxidative stress injury.

Songorine promotes cardiac mitochondrial biogenesis via Nrf2 induction during sepsis

Septic cardiomyopathy is characterized by impaired contractive function with mitochondrial dysregulation. Songorine is a typical active C₂₀-diterpene alkaloid from the lateral root of Aconitum carmichaelii, which has been used for the treatment of heart failure. This study investigated the protective role of songorine in septic heart injury from the aspect of mitochondrial biogenesis. Songorine (10, 50 mg/kg) protected cardiac contractive function against endotoxin insult in mice with Nrf2 induction. In cardiomyocytes, lipopolysaccharide (LPS) evoked mitochondrial reactive oxygen species (ROS) production and redistributed STIM1 to interact with Orai1 for the formation of calcium release-activated calcium (CRAC) channels, mediating calcium influx, which were prevented by songorine, likely due to ROS suppression. Songorine activated Nrf2 by promoting Keap1 degradation, having a contribution to enhancing antioxidant defenses. When LPS shifted metabolism away from mitochondrial oxidative phosphorylation (OXPHOS) in cardiomyocytes, songorine upregulated mitochondrial genes involved in fatty acid β-oxidation, tricarboxylic acid (TCA) cycle and electron transport chain in a manner dependent on Nrf2, resultantly protecting the capability of OXPHOS. Songorine increased luciferase report gene activities of nuclear respiratory factor-1 (Nrf1) and mitochondrial transcription factor A (Tfam) dependently on Nrf2, indicative of the regulation of Nrf2/ARE and NRF1 signaling cascades. Songorine promoted PGC-1α binding to Nrf2, and the cooperation was required for songorine to activate Nrf2/ARE and NRF1 for the control of mitochondrial quality and quantity. In support, the beneficial effects of songorine on cardioprotection and mitochondrial biogenesis were diminished by cardiac Nrf2 deficiency in mice subjected to LPS challenge. Taken together, these results showed that Nrf2 transcriptionally promoted mitochondrial biogenesis in cooperation with PGC-1α. Songorine activated Nrf2/ARE and NRF1 signaling cascades to rescue cardiomyocytes from endotoxin insult, suggesting that protection of mitochondrial biogenesis was a way for pharmacological intervention to prevent septic heart injury.

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Mitochondrial ROS increased calcium influx through CRAC channels.

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Nrf2 interacted with PGC-1α to regulate mitochondrial biogenesis.

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Songorine activated Nrf2 by promoting Keap1 degradation.

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Songorine regulated Nrf2/ARE and PGC-1α cascades to protect cardiac function.

Heme oxygenase-1 induction by hemin prevents oxidative stress-induced acute cholestasis in the rat

We previously demonstrated in in vitro and ex vivo models that physiological concentrations of unconjugated bilirubin (BR) prevent oxidative stress (OS)-induced hepatocanalicular dysfunction and cholestasis. Here, we aimed to ascertain, in the whole rat, whether a similar cholestatic OS injury can be counteracted by heme oxygenase-1 (HO-1) induction that consequently elevates endogenous BR levels. This was achieved through the administration of hemin, an inducer of HO-1, the rate-limiting step in BR generation. We found that BR peaked between 6 and 8 h after hemin administration. During this time period, HO-1 induction fully prevented the pro-oxidant tert-butylhydroperoxide (tBuOOH)-induced drop in bile flow, and in the biliary excretion of bile salts and glutathione, the two main driving forces of bile flow; this was associated with preservation of the membrane localization of their respective canalicular transporters, bile salt export pump (Bsep) and multidrug resistance-associated protein 2 (Mrp2), which are otherwise endocytosed by OS. HO-1 induction counteracted the oxidation of intracellular proteins and membrane lipids induced by tBuOOH, and fully prevented the increase in the oxidized-to-total glutathione (GSHt) ratio, a sensitive parameter of hepatocellular OS. Compensatory elevations of the activity of the antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) were also prevented. We conclude that in vivo HO-1 induction protects the liver from acute oxidative injury, thus preventing consequent cholestasis. This reveals an important role for the induction of HO-1 and the consequently elevated levels of BR in preserving biliary secretory function under OS conditions, thus representing a novel therapeutic tool to limit the cholestatic injury that bears an oxidative background.

Hepatoprotective Effect of Essential Oils from Hyptis crenata in Sepsis-Induced Liver Dysfunction

No specific therapeutics are available for the treatment of sepsis-induced liver dysfunction, a clinical complication strongly associated with the high mortality rate of septic patients. This study investigated the effect of the essential oil of Hyptis crenata (EOHc), a lamiaceae plant used to treat liver disturbances in Brazilian folk medicine, on liver function during early sepsis. Sepsis was induced by the cecal ligation and puncture (CLP) model. Rats were divided into four groups: Sham, Sham+EOHc, CLP, and CLP+EOHc. EOHc (300 mg/kg) was orally administered 12 and 24 h after surgery. The animals were sacrificed for blood collection and liver tissue samples 48 h after surgery. Hepatic function was evaluated by measuring serum bilirubin, alkaline phosphatase (ALP), aspartate aminotransferase, and alanine aminotransferase (ALT) levels. The levels of malondialdehyde and the activity of superoxide dismutase, catalase, and GSH peroxidase (GSH-Px) were measured for assessment of oxidative stress. Liver morphology was analyzed by hematoxylin and eosin staining. EOHc normalized serum ALP, ALT, and bilirubin levels and inhibited morphological changes. In addition, we observed that EOHc inhibited elevation in hepatic lipid peroxidation and reduction of the glutathione peroxidase activity induced by sepsis. Our data show that EOHc plays a protective effect against liver injury induced by sepsis.

Comprehensive comparison of three different animal models for systemic inflammation

Background

To mimic systemic inflammation in humans, different animal models have been developed. Since these models are still discussed controversially, we aimed to comparatively evaluate the most widely used models with respect to the systemic effects, the influence on organ functions and to the underlying pathophysiological processes.

Methods

Systemic inflammation was induced in C57BL/6N mice with lipopolysaccharide (LPS) treatment, peritoneal contamination and infection (PCI), or cecal ligation and puncture (CLP). Blood glucose and circulating cytokine levels were evaluated at 0, 2, 4, 6, 12, 24, 48, and 72 h after induction of inflammation. Additionally, oxidative stress in various organs and liver biotransformation capacity were determined. Markers for oxidative stress, apoptosis, infiltrating immune cells, as well as cytokine expression patterns, were assessed in liver and spleen tissue by immunohistochemistry.

Results

Treating mice with LPS and PCI induced a very similar course of inflammation; however, LPS treatment elicited a stronger response. In both models, serum pro-inflammatory cytokine levels rapidly increased whereas blood glucose decreased. Organs showed early signs of oxidative stress, and apoptosis was increased in splenic cells. In addition, liver biotransformation capacity was reduced and there was pronounced immune cell infiltration in both the liver and spleen. Mice exposed to either LPS or PCI recovered after 72 h. In contrast, CLP treatment induced comparatively fewer effects, but a more protracted course of inflammation.

Conclusions

The LPS model of systemic inflammation revealed to be most suitable when being interested in the impact of new therapies for acute inflammation. When using the CLP model to mimic human sepsis more closely, a longer time course should be employed, as the treatment induces delayed development of systemic inflammation.

Electronic supplementary material

The online version of this article (10.1186/s12929-017-0370-8) contains supplementary material, which is available to authorized users.

Low-Dose Lipopolysaccharide Causes Biliary Injury by Blood Biliary Barrier Impairment in a Rat Hepatic Ischemia/Reperfusion Model

This study explored whether bacterial endotoxins, in the form of lipopolysaccharides (LPS), could have an injurious effect on the biliary tract in conjunction with ischemia. A total of 64 rats were randomly assigned to 4 groups: sham operation (sham group), 1 mg/kg LPS intraperitoneal (LPS group), hepatic ischemia/reperfusion (IR; IR group), and IR combined with LPS (IR+LPS group). Following 1 or 6 hours of reperfusion, serum liver tests, bile duct histology, immunofluorescence microscopy (zonula occludens-1 [ZO-1]), bile composition (bile salts, phospholipids, lactate dehydrogenase), hepatic gene expression (bile salt transporters and inflammatory mediators), as well as serum and biliary cytokine concentrations were quantified and compared between the study groups. In addition, the integrity of the blood biliary barrier (BBB) was assayed in vivo using horseradish peroxidase (HRP). LPS administration induced severe small bile duct injury following 6 hours of reperfusion. Furthermore, total bile salts and bilirubin concentrations in serum were increased in the LPS groups compared with sham controls (LPS, + 3.3-fold and +1.9-fold; IR+LPS, + 3.8-fold and +1.7-fold, respectively). The BBB was impaired in the LPS groups as evidenced by elevated levels of HRP in bile (+4.9-fold), and decreased expression of claudin 1 (-6.7-fold) and claudin 3 (-3.6-fold). LPS was found to be a potent inducer of small bile duct injury following hepatic ischemia and 6 hours of reperfusion. This injury was associated with increased permeability of the BBB and impaired hepatic bile salt clearance. Liver Transplantation 23 194-206 2017 AASLD.

Sepsis: in search of cure

INTRODUCTION

Sepsis is a complex inflammatory disorder believed to originate from an infection by any types of microbes and/or their products. It is the leading cause of death in intensive care units (ICUs) throughout the globe. The mortality rates depend both on the severity of infection and the host's response to infection.

METHODS

Literature survey on pathobiology of sepsis in general and failure of more than hundred clinical trials conducted so far in search of a possible cure for sepsis resulted in the preparation of this manuscript.

FINDINGS

Sepsis lacks a suitable animal model that mimics human sepsis. However, based on the results obtained in animal models of sepsis, clinical trials conducted so far have been disappointing. Although involvement of multiple mediators and pathways in sepsis has been recognized, only few components are being targeted and this could be the major reason behind the failure of clinical trials.

CONCLUSION

Inability to recognize a single critical mediator of sepsis may be the underlying cause for the poor therapeutic intervention of sepsis. Therefore, sepsis is still considered as a disease-in search of cure.

Immunosuppression after sepsis: systemic inflammation and sepsis induce a loss of naïve T-cells but no enduring cell-autonomous defects in T-cell function

Sepsis describes the life-threatening systemic inflammatory response (SIRS) of an organism to an infection and is the leading cause of mortality on intensive care units (ICU) worldwide. An acute episode of sepsis is characterized by the extensive release of cytokines and other mediators resulting in a dysregulated immune response leading to organ damage and/or death. This initial pro-inflammatory burst often transits into a state of immune suppression characterised by loss of immune cells and T-cell dysfunction at later disease stages in sepsis survivors. However, despite these appreciations, the precise nature of the evoked defect in T-cell immunity in post-acute phases of SIRS remains unknown. Here we present an in-depth functional analysis of T-cell function in post-acute SIRS/sepsis. We document that T-cell function is not compromised on a per cell basis in experimental rodent models of infection-free SIRS (LPS or CpG) or septic peritonitis. Transgenic antigen-specific T-cells feature an unaltered cytokine response if challenged in vivo and ex vivo with cognate antigens. Isolated CD4(+)/CD8(+) T-cells from post-acute septic animals do not exhibit defects in T-cell receptor-mediated activation at the the level of receptor-proximal signalling, activation marker upregulation or expansion. However, SIRS/sepsis induced transient lymphopenia and gave rise to an environment of immune attenuation at post acute disease stages. Thus, systemic inflammation has an acute impact on T-cell numbers and adaptive immunity, but does not cause major cell-autonomous enduring functional defects in T-cells.

Prognoses of patients with acute-on-chronic hepatitis B liver failure are closely associated with altered SOCS1 mRNA expression and cytokine production following glucocorticoid treatment

Suppressor of cytokine signaling (SOCS) 1 plays a crucial role in the immune response and might contribute to the prognoses of liver failure treated with glucocorticoid. We recruited 47 acute-on-chronic hepatitis B liver failure (ACHBLF) patients receiving glucocorticoid treatment and 30 healthy controls to determine the potential effects of glucocorticoid on the transcriptional level of SOCS1 in peripheral blood mononuclear cells. On the third and twenty-eighth days of glucocorticoid treatment, SOCS1 expression was negatively correlated with model for end-stage liver disease (MELD) score. Interleukin-6 (IL-6) and tumor-necrosis factor-α (TNF-α) levels were statistically lower, while the SOCS1 transcription level was higher in survivors than non-survivors both in pre- and post-treatment ACHBLF patients. The methylation rate of the SOCS1 promoter in ACHBLF patients was higher than in healthy control patients as determined by methylation-specific polymerase chain reaction. The mRNA level of SOCS1 in methylated promoters was significantly lower than from patients with unmethylated SOCS1 promoters. interferon (IFN)-γ-responsive and STAT1-dependent gene expression was higher in survivors and was dramatically decreased with rising expression of SOCS1 after glucocorticoid treatment. Mortality rates were significantly higher in methylated patients than for those without methylation at the end of a 90-day follow-up. Furthermore, we found that five in six surviving patients displayed demethylated SOCS1 on the twenty-eighth day after treatment, while that number was 3 in 10 in the non-survivors. These findings suggested that ACHBLF patients without SOCS1 methylation may have a favorable response to corticosteroid treatment.

Serum from patients with hepatitis E virus-related acute liver failure induces human liver cell apoptosis

The pathogenesis of acute liver failure has not been fully elucidated. The present study investigated the effects of the serum from patients with hepatitis E virus (HEV)-related acute liver failure on human liver cell survival and apoptosis, and evaluated the protective effects of anti-lipopolysaccharide(LPS) antibody recognizing core polysaccharide against acute liver failure serum-induced apoptosis. Serum was collected from patients with HEV-related acute liver failure. The levels of endotoxin (LPS) in the serum were measured using a quantitative tachypleus amebocyte lysate endotoxin detection kit with a chromogenic endpoint. Serum with a mean concentration of LPS was incubated with L02 human liver cells and the rate of apoptosis was detected by flow cytometry. The apoptotic rate was also evaluated in liver cells incubated with antibody and the HEV-related acute liver failure serum. The results indicated that the concentration of LPS in the serum of patients with HEV-related acute liver failure was 0.26±0.02 EU/ml, which was significantly higher than that of the control group (P<0.05). The rate of apoptosis in the human liver cells induced by acute liver failure serum was 5.83±0.42%, which was significantly increased compared with that in the cells treated with the serum of healthy individuals (P<0.05). The apoptotic rate of the cells incubated with antibody and the acute liver failure serum was 5.53±0.51%, which was lower than that of the cells incubated with acute liver failure serum alone (P>0.05). These results indicate that the serum of patients with HEV-related acute liver failure induces the apoptosis of human liver cells. LPS may be directly involved in the apoptosis of human liver cells. Moreover, the presence of the antibody did not significantly reduce the level of apoptosis of liver cells exposed to HEV-related acute liver failure serum.

The liver in sepsis: patterns of response and injury

PURPOSE OF REVIEW

Sepsis elicits profound changes in the concentrations of plasma proteins synthesized by liver parenchymal cells referred to as acute-phase proteins. Mechanisms controlling this orchestrated response include release of cytokines that induce acute-phase proteins, while other 'house-keeping' genes are downregulated.

RECENT FINDINGS

Although some acute-phase proteins help to control damage, functions of many other acute-phase reactants remain obscure. Changes in acute-phase gene expression are primarily subject to transcriptional regulation and can be comprehensively monitored by array techniques. Emerging evidence from such strategies implies that in addition to a 'common host response' also highly specific pathways are induced in specific disease contexts. Applying a systems biology approach to the integrated response of the hepatocyte to infection would suggest that the reprogramming of metabolic functions occurs in parallel with a severity-dependent disruption of phase I and II biotransformation and canalicular transport, that is, excretory failure. Although traditionally bilirubin serves to monitor excretion, emerging evidence suggests that bile acids indicate liver dysfunction with higher sensitivity and specificity.

SUMMARY

Sepsis induces reprogramming of the hepatic transcriptome. This includes induction of adaptive acute-phase proteins but also repression of phase I, II metabolism and transport with important implications for monitoring and pharmacotherapy.

Hyperresponsiveness of mice deficient in plasma-secreted sphingomyelinase reveals its pivotal role in early phase of host response

Plasma secretion of acid sphingomyelinase is a hallmark of cellular stress response resulting in the formation of membrane embedded ceramide-enriched lipid rafts and the reorganization of receptor complexes. Consistently, decompartmentalization of ceramide formation from inert sphingomyelin has been associated with signaling events and regulation of the cellular phenotype. Herein, we addressed the question of whether the secretion of acid sphingomyelinase is involved in host response during sepsis. We found an exaggerated clinical course in mice genetically deficient in acid sphingomyelinase characterized by an increased bacterial burden, an increased phagocytotic activity, and a more pronounced cytokine storm. Moreover, on a functional level, leukocyte-endothelial interaction was found diminished in sphingomyelinase-deficient animals corresponding to a distinct leukocytes’ phenotype with respect to rolling and sticking as well as expression of cellular surface proteins. We conclude that hydrolysis of membrane-embedded sphingomyelin, triggered by circulating sphingomyelinase, plays a pivotal role in the first line of defense against invading microorganisms. This function might be essential during the early phase of infection leading to an adaptive response of remote cells and tissues.