Changes in plasma catecholamines during fever induced by bacterial endotoxin and interleukin-1 beta

Novel insights in the pathomechanism of Brugada syndrome and fever-related type 1 ECG changes in a preclinical study using human-induced pluripotent stem cell-derived cardiomyocytes

BACKGROUND

Brugada syndrome (BrS) is causing sudden cardiac death (SCD) mainly at young age. Studying the underlying mechanisms associated with BrS type I electrocardiogram (ECG) changes in the presence of fever and roles of autophagy for BrS remains lacking.

OBJECTIVES

We sought to study the pathogenic role of an SCN5A gene variant for BrS with fever-induced type 1 ECG phenotype. In addition, we studied the role of inflammation and autophagy in the pathomechanism of BrS.

METHODS

Human-induced pluripotent stem cell (hiPSC) lines from a BrS patient harboring a pathogenic variant (c.3148G>A/p. Ala1050Thr) in SCN5A and two healthy donors (non-BrS) and a CRISPR/Cas9 site-corrected cell line (BrS-corr) were differentiated into cardiomyocytes (hiPSC-CMs) for the study.

RESULTS

Reductions of Nav 1.5 expression, peak sodium channel current (INa ) and upstroke velocity (Vmax ) of action potentials with an increase in arrhythmic events were detected in BrS compared to non-BrS and BrS-corr cells. Increasing the cell culture temperature from 37 to 40°C (fever-like state) exacerbated the phenotypic changes in BrS cells. The fever-effects were enhanced by protein kinase A (PKA) inhibitor but reversed by PKA activator. Lipopolysaccharides (LPS) but not increased temperature up to 40°C enhanced the autophagy level in BrS-hiPSC-CMs by increasing reactive oxidative species and inhibiting PI3K/AKT signalling, and hence exacerbated the phenotypic changes. LPS enhanced high temperature-related effect on peak INa shown in BrS hiPSC-CMs. Effects of LPS and high temperature were not detected in non-BrS cells.

CONCLUSIONS

The study demonstrated that the SCN5A variant (c.3148G>A/p.Ala1050Thr) caused loss-of-function of sodium channels and increased the channel sensitivity to high temperature and LPS challenge in hiPSC-CMs from a BrS cell line with this variant but not in two non-BrS hiPSC-CM lines. The results suggest that LPS may exacerbate BrS phenotype via enhancing autophagy, whereas fever may exacerbate BrS phenotype via inhibiting PKA-signalling in BrS cardiomyocytes with but probably not limited to this variant.

Effects of peripheral administration of lipopolysaccharide on chronic sickness responses in TRPM8-deficient mice

Transient receptor potential melastatin 8 (TRPM8) is a cold-sensing thermoreceptor cation channel; however, its functional role in endotoxin-induced neuroinflammation remains unclear. In the present study, we investigated chronic sickness responses in TRPM8 knockout (KO) mice during lipopolysaccharide (LPS)-induced sepsis. The intraperitoneal administration of 5 mg/kg LPS generated longer-lasting hypothermia in TRPM8 KO mice than in wild-type (WT) mice. TRPM8 KO mice also exhibited longer-lasting declines in locomotor activity, body weight, and food and water intakes than WT mice upon LPS administration. In addition, LPS-induced decreases in the numbers of leucocytes and lymphocytes that persisted for a longer time in TRPM8 KO mice than in WT mice. The present results indicate TRPM8 attenuated chronic sickness responses in endotoxin-induced sepsis.

Infanticide vs. inherited cardiac arrhythmias

AIMS

In 2003, an Australian woman was convicted by a jury of smothering and killing her four children over a 10-year period. Each child died suddenly and unexpectedly during a sleep period, at ages ranging from 19 days to 18 months. In 2019 we were asked to investigate if a genetic cause could explain the children's deaths as part of an inquiry into the mother's convictions.

METHODS AND RESULTS

Whole genomes or exomes of the mother and her four children were sequenced. Functional analysis of a novel CALM2 variant was performed by measuring Ca2+-binding affinity, interaction with calcium channels and channel function. We found two children had a novel calmodulin variant (CALM2 G114R) that was inherited maternally. Three genes (CALM1-3) encode identical calmodulin proteins. A variant in the corresponding residue of CALM3 (G114W) was recently reported in a child who died suddenly at age 4 and a sibling who suffered a cardiac arrest at age 5. We show that CALM2 G114R impairs calmodulin's ability to bind calcium and regulate two pivotal calcium channels (CaV1.2 and RyR2) involved in cardiac excitation contraction coupling. The deleterious effects of G114R are similar to those produced by G114W and N98S, which are considered arrhythmogenic and cause sudden cardiac death in children.

CONCLUSION

A novel functional calmodulin variant (G114R) predicted to cause idiopathic ventricular fibrillation, catecholaminergic polymorphic ventricular tachycardia, or mild long QT syndrome was present in two children. A fatal arrhythmic event may have been triggered by their intercurrent infections. Thus, calmodulinopathy emerges as a reasonable explanation for a natural cause of their deaths.

Repeated Stress Exaggerates Lipopolysaccharide-Induced Inflammatory Response in the Rat Spleen

Spleen is an immune organ innervated with sympathetic nerves which together with adrenomedullary system control splenic immune functions. However, the mechanism by which prior stress exposure modulates the immune response induced by immunogenic challenge is not sufficiently clarified. Thus, the aim of this study was to investigate the effect of a single (2 h) and repeated (2 h daily for 7 days) immobilization stress (IMO) on the innate immune response in the spleen induced by lipopolysaccharide (LPS, 100 µg/kg). LPS elevated splenic levels of norepinephrine and epinephrine, while prior IMO prevented this response. LPS did not alter de novo production of catecholamines, however, prior IMO attenuated phenylethanolamine N-methyltransferase gene expression. Particularly repeated IMO exacerbated LPS-induced down-regulation of α1B- and β1-adrenergic receptors (ARs), while enhanced α2A- and β2-AR mRNAs. Elevated expression of inflammatory mediators (iNOS2, IL-1β, IL-6, TNF-α, IL-10) was observed following LPS and repeated IMO again potentiated this effect. These changes were associated with enhanced Ly6C gene expression, a monocyte marker, and elevated MCP-1, GM-CSF, and CXCL1 mRNAs suggesting an increased recruitment of monocytes and neutrophils into the spleen. Additionally, we observed increased Bax/Bcl-1 mRNA ratio together with reduced B cell numbers in rats exposed to repeated IMO and treated with LPS but not in acutely stressed rats. Altogether, these data indicate that repeated stress via changes in CA levels and specific α- and β-AR subtypes exaggerates the inflammatory response likely by recruiting peripheral monocytes and neutrophils to the spleen, resulting in the induction of apoptosis within this tissue, particularly in B cells. These changes may alter the splenic immune functions with potentially pathological consequences.

Sympathetic innervation of the spleen in male Brown Norway rats: a longitudinal aging study

Aging leads to reduced cellular immunity with consequent increased rates of infectious disease, cancer, and autoimmunity in the elderly. The sympathetic nervous system (SNS) modulates innate and adaptive immunity via innervation of lymphoid organs. In aged Fischer 344 (F344) rats, noradrenergic (NA) nerve density in secondary lymphoid organs declines, which may contribute to immunosenescence with aging. These studies suggest there is SNS involvement in age-induced immune dysregulation. The purpose of this study was to longitudinally characterize age-related change in sympathetic innervation of the spleen and sympathetic activity/tone in male Brown Norway (BN) rats, which live longer and have a strikingly different immune profile than F344 rats, the traditional animal model for aging research. Splenic sympathetic neurotransmission was evaluated between 8 and 32 months of age by assessing (1) NA nerve fiber density, (2) splenic norepinephrine (NE) concentration, and (3) circulating catecholamine levels after decapitation. We report a decline in NA nerve density in splenic white pulp (45%) at 15 months of age compared with 8-month-old (M) rats, which is followed by a much slower rate of decline between 24 and 32 months. Lower splenic NE concentrations between 15 and 32 months of age compared with 8M rats were consistent with morphometric findings. Circulating catecholamine levels after decapitation stress generally dropped with increasing age. These findings suggest there is a sympathetic-to-immune system dysregulation beginning at middle age. Given the unique T-helper-2 bias in BN rats, altered sympathetic-immune communication may be important for understanding the age-related rise in asthma and autoimmunity.

Metastatic-promoting effects of LPS: sexual dimorphism and mediation by catecholamines and prostaglandins

Inflammation is implicated in several medical conditions that are sexually dimorphic, including depression, cardiovascular diseases, autoimmunity, and presumably cancer progression. Here we studied the effects of the proinflammatory agent, LPS, on MADB106 lung tumor retention (LTR), and sought to elucidate underlying mechanisms and sexual dimorphism. F344 male and female rats were administered with LPS (0.001-1mg/kg i.v.) simultaneously with tumor cell inoculation, and treated with a beta-blocker (nadolol, 0.2-0.3mg/kg s.c.), a COX inhibitor (indomethacin, 4mg/kg s.c.) or both drugs. To study the role of NK cells, numbers and cytotoxicity of marginating-pulmonary NK cells were studied, and selective in vivo NK-depletion was employed. Serum levels of corticosterone, IL-6, and TNF-alpha were also assessed. The findings indicated that LPS increased LTR in both sexes, but 10-fold higher doses were needed in females to reach the increase evident in males. Additionally, nadolol and indomethacin reduced the effects of LPS, more so in males. In vivo NK-depletion and ex vivo NK activity studies suggested that LPS affected LTR through both NK-independent and NK-dependent mechanisms, the latter mediated through prostaglandin release in males. Corticosterone, IL-6, and TNF-alpha responses to LPS were sexually dimorphic, but were not associated with LPS or drugs' impacts on LTR. Overall, our findings demonstrate sexual dimorphism in LPS-induced elevated susceptibility to MADB106 experimental metastasis, and in potential humoral underlying mechanisms. Further studies are needed to elucidate additional immunological and non-immunological mediators of these dimorphisms, as well as to assess their involvement in other sexually dimorphic pathologies that are associated with inflammation.

Activation of 5-HT1A receptors in the medullary raphe reduces cardiovascular changes elicited by acute psychological and inflammatory stresses in rabbits

The present strategy for the prevention of excessive sympathetic neural traffic to the heart relies on the use of beta-blockers, drugs that act at the heart end of the brain-heart axis. In the present study, we attempted to suppress cardiac sympathetic nerve activity by affecting the relevant cardiomotoneurons in the brain using the selective serotonin-1A (5-HT(1A)) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). In conscious, unrestrained rabbits, instrumented for recordings of heart rate, arterial pressure, or cardiac output, we provoked increases in cardiac sympathetic activity by psychological (loud sound, pinprick, and air jet) or inflammatory (0.5 microg/kg iv lipopolysaccharide) stresses. Pinprick and air-jet stresses elicited transient increases in heart rate (+50 +/- 7 and +38 +/- 4 beats/min, respectively) and in mean arterial pressure (+16 +/- 2 and +15 +/- 3 mmHg, respectively). Lipopolysaccharide injection caused sustained increases in heart rate (from 210 +/- 3 to 268 +/- 10 beats/min) and in arterial pressure (from 74 +/- 3 to 92 +/- 4 mmHg). Systemically administered 8-OH-DPAT (0.004-0.1 mg/kg) substantially attenuated these responses in a dose-dependent manner. Drug effects were prevented by a selective 5-HT(1A) receptor antagonist, WAY-100635 (0.1 mg/kg iv). Similarly to systemic administration, microinjection of 8-OH-DPAT (500 nl of 10 mM solution) into the medullary raphe-parapyramidal region caused antitachycardic effects during stressful stimulation and during lipopolysaccharide-elicited tachycardia. This is the first demonstration that activation of 5-HT(1A) receptors in the medullary raphe-parapyramidal area causes suppression of neurally mediated cardiovascular changes during acute psychological and immune stresses.

Fever during anaesthesia

Fever occurs when pyrogenic stimulation activates thermal control centres. Fever is common during the perioperative period, but rare during anaesthesia. Although only a limited number of studies are available to explain how anaesthesia affects fever, general anaesthesia seems to inhibit fever by decreasing the thermoregulatory-response thresholds to cold. Opioids also inhibit fever; however, the effect is slightly less than that of general anaesthesia. In contrast, epidural anaesthesia does not affect fever. This suggests that hyperthermia, which is often associated with epidural infusions during labour or in the post-operative period, may be a true fever caused by inflammatory activation. Accordingly, this fever might be diminished in patients who receive opioids for pain treatment. Post-operative fever is a normal thermoregulatory response usually of non-infectious aetiology. Fever may be important in the host defence mechanisms and should not be routinely treated lest the associated risks exceed the benefits.

Role of Prostaglandin E2 and Indomethacin in the Febrile Response of Pigeons

Intravenous (i.v.) injection of 10 microg/kg Escherichia coli lipopolysaccharide (LPS), applied at 13:00, evoked in pigeons a biphasic rise of core temperature (T(core)), so that LPS induced with a latency of 30 min first a decrease of T(core), and 90 min after LPS, T(core) increased, obtaining maximum values from 18:00 to 20:00. Prostaglandins have been considered to be importantly involved in fevers in mammals. To investigate an involvement of prostaglandins in the cyclic variations of T(core) in birds, pigeons were injected i.v. with either 10 mg/kg indomethacin (INDO) or 100 mg/kg aspirin, or they were treated with intracerebroventricular (i.c.v.) injections of 100 microg/kg INDO at various times before or after LPS. When INDO or aspirin was i.v. injected 30 or 15 min before LPS, it diminished the initial decrease of T(core) by more than 50%, whereas the i.v. injection of these drugs 2 and 4 h after LPS did not affect the febrile rise of T(core). i.c.v. injections of INDO given either before or after LPS neither influenced the initial drop of T(core) nor the following febrile hyperthermia. Both the i.v. injection of 1 mg/kg prostaglandin E(2) (PGE(2)) and the i.c.v. injection of 1 microg/kg PGE(2) lowered T(core). Our observations suggest that prostaglandins are not involved in the febrile elevation of T(core) in pigeons, but appear to participate in the decrease of T(core), which shortly follows the i.v. injection of LPS. This initial drop of T(core) following LPS may be caused by a peripheral action of prostaglandins because it was not influenced by the i.c.v. injection of indomethacin.

Effect of IL-1alpha on the release of norepinephrine in rat hypothalamus

The increased release of norepinephrine (NE) in the brain as part of the 'acute phase response' has been postulated to result from a direct action of IL-1 on the hypothalamus. To test whether the effects of IL-1alpha were direct, we carried out in vivo experiments using microdialysis and measured NE release in the hypothalamus using high pressure liquid chromatography (HPLC). Two groups of male Sprague Dawley rats were either injected intraperitoneally with 1 ml of IL-1alpha (2 microg/ml) or had IL-1alpha 2 microl (100 ng/ml) infused directly into the medial hypothalamus. A significant increase in extracellular hypothalamic NE was observed in the animal group treated with IL-1alpha intraperitoneally and not in the controls or the group treated with IL-1alpha intracerebrally. One-way ANOVA showed a significant effect of drug and route of administration with the ip IL-1alpha treated group, differing from all other groups (vehicle ip, IL-1alpha ic, and vehicle ic). Therefore these findings suggest that some aspects of IL-1alpha actions on the HPA may be indirect requiring other intermediate steps or mediators outside the central nervous system.

KAT45 human pheochromocytoma cell line. A new model for the in vitro study of neuro-immuno-hormonal interactions

Normal rodent adrenal chromaffin cells and the PC12 rat pheochromocytoma cell line produce IL-1 cytokines. The role, if any, of these cytokines is currently unknown. In PC12 cells, they induce the expression of the L-AA decarboxylase mRNA, a major step in the biosynthesis of catecholamines. Very little if any of these cytokines are detectable in normal human adrenal medulla, being confined mainly in the 17 alpha-hydroxylase-positive steroid cells of the zona reticularis. The aim of the present work was to find out if human pheochromocytomas produce IL-1 cytokines, in vitro, and to examine what local role they may exert. As a model, we have used the new KAT45 cell line, which emerged spontaneously from a primary human pheochromocytoma cell culture. We have found that the KAT45 cells secrete IL-1 beta at 47.8 +/- 9 pg/mg total cellular protein (n = 7, at 24 hours). IL-1 beta increased the concentration of norepinephrine in the KAT45 culture medium from 24.2 +/- 3.5 micrograms/mg protein (n = 6 controls, at 24 hours), to 33.2 +/- 3.5 (IL-1 beta 10 mg/ml) or to 42.9 +/- 8 (IL-1 beta 30 mg/ml). This effect was blocked by IL-1ra. The KAT45 cells also produce CRH and ACTH. IL-1 beta stimulated the secretion of CRH from 19.2 +/- 4 pg/mg protein (n = 5 at 36 hours) to 38.7 +/- 4, an effect blocked by IL-1ra in excess. IL-1 beta had no effect on ACTH secretion.

Bacterial products and the control of ingestive behavior: clinical implications

Bacterial products such as lipopolysaccharides (LPS) and muramyl peptides are delivered in the course of infections. They trigger the host's acute phase responses to bacterial infections and are probably involved in the accompanying hypophagia because LPS and muramyl dipeptide (MDP, the minimal immunologically active muramyl peptide) reduce food intake after parenteral administration in animals. LPS and MDP inhibit feeding synergistically through separate but interacting mechanisms. The hypophagic effects of LPS and MDP are presumably mediated by the combined actions of interleukin-1, tumor necrosis factor, and other cytokines. More work is required to understand the interactions between these cytokines, and between bacterial products and cytokines, before cytokine antagonists can be used for treatment of the hypophagia during bacterial infections. As the hypophagia seems to be an early mechanism of host defense, a treatment should be carefully considered. If an intervention is indicated because of a patient's poor condition, inhibitors of eicosanoid synthesis and glucocorticoids may hold more promise for therapy because such substances block LPS and MDP hypophagia. Although LPS can reduce food intake by direct action on the brain, presently available evidence indicates that systemic LPS acts primarily in the periphery to generate a neural signal that is transmitted to the brain and inhibits feeding through the vagus. The exact site where LPS acts on peripheral nerves remains to be identified. LPS hypophagia is conditionable, but conditioning cannot solely account for LPS hypophagia under most test conditions. Whether MDP hypophagia is also conditionable and mediated by vagal afferents is not yet known. All in all, the putative mediators and mechanisms of LPS and MDP hypophagia suggest some options for a treatment of the hypophagia during bacterial infection, but present knowledge about the mechanisms and interactions of the involved substances is still fragmentary and requires further investigation.