Cardiovascular effects of centrally injected melittin in hemorrhaged hypotensive rats: the investigation of peripheral mechanisms

Integrated analysis of multi-omics data reveals T cell exhaustion in sepsis

Background

Sepsis is a heterogeneous disease, therefore the single-gene-based biomarker is not sufficient to fully understand the disease. Higher-level biomarkers need to be explored to identify important pathways related to sepsis and evaluate their clinical significance.

Methods

Gene Set Enrichment Analysis (GSEA) was used to analyze the sepsis transcriptome to obtain the pathway-level expression. Limma was used to identify differentially expressed pathways. Tumor IMmune Estimation Resource (TIMER) was applied to estimate immune cell abundance. The Spearman correlation coefficient was used to find the relationships between pathways and immune cell abundance. Methylation and single-cell transcriptome data were also employed to identify important pathway genes. Log-rank test was performed to test the prognostic significance of pathways for patient survival probability. DSigDB was used to mine candidate drugs based on pathways. PyMol was used for 3-D structure visualization. LigPlot was used to plot the 2-D pose view for receptor-ligand interaction.

Results

Eighty-four KEGG pathways were differentially expressed in sepsis patients compared to healthy controls. Of those, 10 pathways were associated with 28-day survival. Some pathways were significantly correlated with immune cell abundance and five pathways could be used to distinguish between systemic inflammatory response syndrome (SIRS), bacterial sepsis, and viral sepsis with Area Under the Curve (AUC) above 0.80. Seven related drugs were screened using survival-related pathways.

Conclusion

Sepsis-related pathways can be utilized for disease subtyping, diagnosis, prognosis, and drug screening.

The intermediary role of the central cyclooxygenase / lipoxygenase enzymes in intracerebroventricular injected nesfatin-1-evoked cardiovascular effects in rats

That nesfatin-1 is a neuromodulatory peptide for the cardiovascular system is well documented. Several central receptors have been shown to mediate the cardiovascular effects of nesfatin-1. Immunohistochemistry and Western blot studies showed that nesfatin-1 activated the expression of the central cyclooxygenase (COX) -1, -2 and lipoxygenase (LOX). In addition, microdialysis study showed that nesfatin-1 increased the release of total prostaglandins and leukotrienes from the hypothalamus. The present study investigated whether the central COX and LOX enzymes have a direct mediating role in the MAP and HR responses of nesfatin-1. Intracerebroventricularly administered nesfatin-1 produced dose-dependent pressor and phasic HR responses in normotensive conscious rats Sprague Dawley. Central pretreatment with a COX1/2 inhibitor, ibuprofen, completely blocked the nesfatin-1-induced responses. However, central pretreatment with a nonselective LOX inhibitor, nordihydroguaiaretic acid, partially attenuated the cardiovascular responses induced by nesfatin-1. The results suggest that centrally administered nesfatin-1 activates the central enzymes COX and LOX, which may be involved in the cardiovascular responses as a novel central mechanism for nesfatin-1.

The mediation of central cyclooxygenase and lipoxygenase pathways in orexin-induced cardiovascular effects

Previously it was reported that central orexin (OX) and arachidonic acid (AA) signaling pathways played an active role in the control of the cardiovascular system. It was also reported that they have exhibited their cardiovascular control role by using similar central or peripheral mechanisms. However, there has been no study demonstrating the interaction between OX and AA signaling pathways in terms of cardiovascular control. The current study was designed to investigate the possible mediation of the central cyclooxygenase (COX) and lipoxygenase (LOX) pathways in OX-induced cardiovascular effects in the rats. Intracerebroventricular injection of OX increased blood pressure and heart rate in a dose-dependent manner in normotensive male Sprague Dawley rats. Moreover, the microdialysis study revealed that intracerebroventricular injected OX caused a time-dependent increase in the extracellular total prostaglandin concentrations in the posterior hypothalamus. Interestingly, central pretreatment with a non-selective COX inhibitor, ibuprofen, or a non-selective LOX inhibitor, nordihydroguaiaretic acid, partially reversed pressor and tachycardic cardiovascular responses evoked by central administration of OX. In summary, our findings show that the central treatment with OX causes pressor and tachycardic cardiovascular responses along with an increase in posterior hypothalamic extracellular total prostaglandin concentrations. Furthermore, our results also demonstrate that central COX and LOX pathways mediate, at least in part, centrally administered OX-evoked pressor and tachycardic responses, as well.

Modulation of arachidonic acid-evoked cardiorespiratory effects by the central lipoxygenase pathway

We previously reported that intracerebroventricularly (ICV) injected arachidonic acid (AA) could produce pressor and bradycardic responses on the cardiovascular system and hyperventilation effect on the respiratory system by activating cyclooxygenase (COX). We also demonstrated that centrally injected AA-induced cardiovascular and respiratory responses were mediated by COX-metabolites, such as thromboxane A₂ (TXA₂), prostaglandin (PG) D, PGE, and PGF_2α. Brain tissue is also able to express the lipoxygenase (LOX) enzyme and LOX-induced AA-metabolites. The current study was designed to investigate the possible mediation of the central LOX pathway in AA-induced cardiorespiratory effects in anesthetized rats. Central pretreatment with different doses of a non-selective LOX inhibitor, nordihydroguaiaretic acid (NDGA) (500 and 1000 μg; ICV) partially blocked the AA (0.5 μmol; ICV)-evoked pressor and bradycardic cardiovascular responses in male anesthetized Sprague Dawley rats. Pretreatment with different doses of NDGA (500 and 1000 μg; ICV) also reduced AA-induced hyperventilation responses, with an increase in tidal volume, respiratory rate and minute ventilation, in the rats. Moreover, AA-induced increasing pO₂ and decreasing pCO₂ responses were diminished by central NDGA pretreatment. In summary, our findings show that the central LOX pathway might mediate, at least in part, centrally administered AA-evoked cardiorespiratory and blood gases responses.

Intracerebroventricularly injected nesfatin-1 activates central cyclooxygenase and lipoxygenase pathways

Nesfatin-1 is a multifunctional neuropeptide having crucial autonomic roles. It is well known that nesfatin-1 collaborates with other central neuromodulatory systems, such as central corticotropin-releasing hormone, melanocortin, oxytocin, and cholinergic systems to show its autonomic effects. Central arachidonic acid cascade plays an important role to provide the homeostasis by exhibiting similar autonomic effects to nesfatin-1. Based on these similarities, the current study was designed to show the effects of intracerebroventricularly (ICV) injected nesfatin-1 on the hypothalamic arachidonic acid (AA) cascade. Immunochemistry and western blot approaches demonstrated that ICV administration of nesfatin-1 provokes an increase in the hypothalamic cyclooxygenase (COX) -1, -2 and lipoxygenase (LOX) protein expression. Moreover, the microdialysis study demonstrated that centrally injected nesfatin-1 increased the posterior hypothalamic extracellular AA products. In conclusion, these findings report that while nesfatin-1 is generating its autonomic effects, it also might be using central prostaglandins and leukotrienes by activating central COX and LOX pathways.

Centrally administered TNF increases arterial blood pressure independently of nitric oxide synthase

INTRODUCTION

Emerging evidence indicates that increased levels of TNF in the brain are associated with hypertension. Nitric oxide synthase (NOS) is involved in the central control of the cardiovascular system, exerting both pro- and antihypertensive effects. TNF induces hypothalamic synthesis of nitric oxide.

AIM

We checked if acutely administered TNF into the cerebral ventricles affects arterial blood pressure, heart rate and baroreflex sensitivity, and whether TNF actions are dependent on NOS in normotensive rats.

METHODS

We carried out hemodynamic measurements in 6 groups of freely moving, adult Sprague-Dawley male rats, intracerebroventricularly (ICV) infused with either: 1) saline (5μl/h); 2) TNF (200ng/5μl/h); 3) non-selective NO synthase inhibitor - l-NG-Nitroarginine Methyl Ester (l-NAME) (1mg/5μl/h); 4) TNF together with l-NAME (200ng and 1mg/5μl/h, respectively); 5) neuronal NO synthase inhibitor - 7-nitroindazole sodium salt (7-NI) (20μg/10μl/h); 6) or TNF together with 7-NI (200ng and 20μg/10μl/h, respectively). Mean arterial blood pressure (MABP), heart rate (HR) and spontaneous baroreflex sensitivity (sBRS) evaluated by the sequence method were analysed.

RESULTS

ICV infusion of TNF caused a significant increase in MABP accompanied by a transient increase in HR, and a decrease in sBRS. ICV infusion of l-NAME increased MABP, but it did not change HR, nor sBRS. ICV infusion of 7-NI did not affect MABP, nor HR, nor sBRS. TNF administered together with l-NAME increased MABP with a transient increase in HR without changes of sBRS. Similarly, ICV infusion of TNF with 7-NI increased MABP without changes in HR and sBRS.

CONCLUSIONS

Centrally administered TNF increases MABP and HR and blunts sBRS. The pressor effect of TNF appears to be independent of NOS activity in the brain. Inhibition of nNOS restores sBRS in TNF treated rats.

Activation of the central histaminergic system mediates arachidonic-acid-induced cardiovascular effects

The aim of this study was to explain the involvement of the central histaminergic system in arachidonic acid (AA)-induced cardiovascular effects in normotensive rats using hemodynamic, immunohistochemistry, and microdialysis studies. Intracerebroventricularly (i.c.v.) administered AA (0.25, 0.5, and 1.0 μmol) induced dose- and time-dependent increases in mean arterial pressure and decreased heart rate in conscious normotensive Sprague–Dawley rats. Central injection of AA (0.5 μmol) also increased posterior hypothalamic extracellular histamine levels and produced strong COX-1 but not COX-2 immunoreactivity in the posterior hypothalamus of rats. Moreover, the cardiovascular effects and COX-1 immunoreactivity in the posterior hypothalamus induced by AA (0.5 μmol; i.c.v.) were almost completely blocked by the H2 receptor antagonist ranitidine (50 and 100 nmol; i.c.v.) and partially blocked by the H1 receptor blocker chlorpheniramine (100 nmol; i.c.v.) and the H3–H4 receptor antagonist thioperamide (50 and 100 nmol; i.c.v.). In conclusion, these results indicate that centrally administered AA induces pressor and bradycardic responses in conscious rats. Moreover, we suggest that AA may activate histaminergic neurons and increase extracellular histamine levels, particularly in the posterior hypothalamus. Acting as a neurotransmitter, histamine is potentially involved in AA-induced cardiovascular effects under normotensive conditions.

Centrally administered CDP-choline induced cardiovascular responses are mediated by activation of the central phospholipase-prostaglandin signaling cascade

The present study was designed to determine the involvement of central prostaglandin synthesis on the pressor and bradycardic effect of cytidine 5'-diphosphocholine (CDP-choline). Intracerebroventricular (i.c.v.) administration of CDP-choline was made and blood pressure and heart rate were recorded in male Sprague Dawley rats throughout this study. Microdialysis and immunohistochemical studies were performed to measure extracellular total prostaglandin concentration and to show cyclooxygenase-1 and -2 (COX-1 and -2) immunoreactivities, respectively, in the posterior hypothalamic area. Moreover, rats were pretreated (i.c.v) with mepacrine [a phospholipase A2 (PLA2) inhibitor], ibuprofen [a nonselective COX inhibitor], neomycine [a phospholipase C (PLC) inhibitor] or furegrelate [a thromboxane A2 (TXA2) synthesis inhibitor] 5 min prior to the injection of CDP-choline to determine the effects of these inhibitors on cardiovascular responses to CDP-choline. Control rats were pretreated (i.c.v) with saline. CDP-choline caused a dose- and time-dependent increase in blood pressure and decrease in heart rate. Immunohistochemical studies showed that CDP-choline increased COX-1 and -2 immunoreactivities in the posterior hypothalamic area. CDP-choline also elevated hypothalamic extracellular total prostaglandin concentration by 62%, as shown in microdialysis studies. Mepacrine or ibuprofen pretreatments almost completely blocked the pressor and bradycardic responses to CDP-choline while neomycine or furegrelate partially attenuated the drug-induced cardiovascular effects. The results suggest that CDP-choline may stimulate prostaglandin synthesis through the activation of PLA2, cyclooxygenases (COX-1 and -2) and prostaglandins and at least TXA2, may mediate the drug׳s cardiovascular effects.

Effect of melittin on mice stomach

Melittin, the main bee venom component, has many positive biological effects and a relatively low toxicity in various cell types. However, there is no evidence of the effect of melittin on gastrointestinal cells. In the present study, we investigated the histological and immuonohistochemical effects of melittin on mice stomach. Adult male mice (Albino Swiss) were randomly divided into two groups (7 mice for each group): control group and melittin only treated group (10 and 40 μg/kg). These mice were sacrificed, then samples from the stomach were collected and prepared for histopathological studies by using alcian blue stain and immuonohistochemical studies by using smooth muscle actin (SMA) antibody. Treatment with melittin alone do not cause any harmful effect on the stomach tissue where the microscopic examination of Alcian blue stained section showed the normal distribution of the mucous secreting cells of the stomach tissues. On other hand, no changes were observed on smooth muscle cells. This study demonstrated the safety of using melittin on gastrointestinal tissues if used in definite dose and for suitable duration, which offers an opportunity for its use as a treatment for many diseases of the gastrointestinal tract.

The mediation of the central histaminergic system in the pressor effect of intracerebroventricularly injected melittin, a phospholipase A2 activator, in normotensive rats

Melittin is a polypeptide component of bee venom that leads to an increase in arachidonic acid release and subsequently in prostaglandin synthesis by activating phospholipase A(2). Recently we demonstrated that centrally or peripherally administrated melittin caused pressor effect and central thromboxane A(2) (TXA(2)) and cholinergic system mediated these effects of melittin. Also centrally injected histamine leads to pressor and bradycardic response by activating central histamine receptors in normotensive rats and central cholinergic system involved the effects of histamine. The present study demonstrates an involvement of the central histaminergic system in melittin-induced cardiovascular effect in normotensive rats. Experiments were carried out in male Sprague Dawley rats. Intracerebroventricularly (i.c.v.) injected melittin (0.5, 1 and 2 nmol) caused dose- and time-dependent increases in mean arterial pressure (MAP) and decrease in heart rate (HR) as we reported previously. Moreover, H(2) receptor antagonist ranitidine (50 nmol; i.c.v.) almost completely and H(3)/H(4) receptor antagonist thioperamide (50 nmol; i.c.v.) partly blocked melittin-evoked cardiovascular effects, whereas H(1) receptor blocker chlorpheniramine (50 nmol; i.c.v.) had no effect. Also centrally injected melittin was accompanied by 28% increase in extracellular histamine concentration in the posterior hypothalamus, as shown in microdialysis studies. In conclusion, results show that centrally administered melittin causes pressor and bradycardic response in conscious rats. Moreover, according to our findings, there is an involvement of the central histaminergic system in melittin-induced cardiovascular effects.

The role of the central arachidonic acid-thromboxane A2 cascade in cardiovascular regulation during hemorrhagic shock in rats

The aim of the current study was to elucidate the underlying central mechanism(s) of the cardiovascular effects evoked by centrally injected melittin and arachidonic acid (AA) in hemorrhaged hypotensive condition, specifically, from central AA release from the cell membrane under the influence of phospholipase A(2) (PLA(2)) to central thromboxane A(2) (TXA(2)) signaling via the cyclooxygenase (COX) pathway. As the main control of the study, melittin (3 μg) or AA (150 μg) was injected intracerebroventricularly (i.c.v.) after the hemorrhage procedure, which was performed by withdrawing a total volume of 2.2 ml of blood/100g body weight over a period of 10 min. Both treatments generated a pressor response and abolished the hypotension-induced hemorrhage. Pretreatment with the PLA(2) inhibitor mepacrine (500 μg; i.c.v.) completely blocked the pressor response to melittin in the hemorrhagic hypotensive state. Pretreatments with the nonselective COX inhibitor indomethacin (200 μg; i.c.v.) or the TXA(2) synthesis inhibitor furegrelate (250 or 500 μg; i.c.v.) were made to test the role of central COX activity and, subsequently, the TXA(2) signaling pathway in the melittin- or AA-mediated reversal of hemorrhagic hypotension. Indomethacin completely prevented the pressor response to melittin and AA in the hemorrhaged, hypotensive state, but furegrelate did so only partially. In conclusion, these findings suggest that central COX activity and, subsequently, the central TXA(2) signaling pathway, are, at least in part, involved in the melittin- or AA-induced reversal effect during hemorrhagic shock.

Central mechanism underlying pressor and bradycardic effect of intracerebroventricularly injected arachidonic acid

The aim of the current study was to determine the central cyclooxygenase (COX) pathway and central thromboxane signaling in the cardiovascular effects evoked by arachidonic acid (AA). As a main control for the study, different doses of AA (75, 150, or 300 µg) were administered intracerebroventricularly (i.c.v.). Centrally injected AA dose- and time-dependently increased mean arterial pressure and decreased heart rate in conscious normotensive Sprague–Dawley rats. The maximal cardiovascular effects of AA were observed at min 10 of the injection and lasted almost 30 min. To investigate the central mechanism of the AA-induced cardiovascular effect in conscious normotensive animals, pretreatment with nonselective COX inhibitor indomethacin (200 µg; i.c.v.), thromboxane A2 (TXA2) synthesis inhibitor furegrelate (250 or 500 µg; i.c.v.), or TXA2 receptor antagonist SQ-29548 (8 or 16 µg; i.c.v.) was carried out 15 min before AA (150 µg; i.c.v.) injection. While indomethacin completely prevented the pressor and bradycardic responses to AA, furegrelate and SQ-29548 attenuated these effects in part in awake normotensive rats. In conclusion, these findings suggest that the pressor and bradycardic cardiovascular effects of centrally injected AA are dependent on COX activity being totally central and the TXA2 signaling pathway being subsequently central, at least in part.

Cardiovascular effect of peripheral injected melittin in normotensive conscious rats: Mediation of the central cholinergic system

Recently we demonstrated that centrally administrated melittin, a phospholipase A(2) (PLA(2)) activator, caused the pressor effect in normotensive, conscious rats. In the present study, we aimed to determine the cardiovascular effect of peripherally injected melittin and the involvement of the central cholinergic system on these effects in the normotensive conscious rats. For this reason, 250, 500 or 1000microg/kg doses of melittin were injected intraperitoneally to normotensive male Sprague Dawley rats. Melittin produced dose- and time-dependent increases in mean arterial pressure (MAP) and heart rate (HR). Both peripheral (5mg/kg; i.p.) and central (500microg; i.c.v.) pretreatment with indomethacin, nonselective inhibitor of cyclooxygenase (COX) 1 and 2, totally abolished cardiovascular effect of melittin. Intraperitoneal (i.p.) pretreatment with propranolol, a nonselective beta-adrenergic receptor blocker, completely abolished the tachycardic response to melittin. Also, the pressor effect of melittin was partially attenuated in these rats. In order to test the mediation of the central cholinergic system on the pressor and tachycardic effects of melittin, the rats were pretreated with atropine sulfate (10microg; i.c.v.), a cholinergic nonselective muscarinic receptor antagonist, mecamylamine (50microg; i.c.v.), a cholinergic nonselective nicotinic receptor antagonist, methyllycaconitine (10microg; i.c.v.) or alpha-bungarotoxin (10microg; i.c.v.), selective antagonists of alpha7 subtype nicotinic acetylcholine receptors (alpha7nAChRs) 15min prior to melittin (500microg/kg; i.p.) injection. Pretreatment with mecamylamine, methyllycaconitine or alpha-bungarotoxin partially diminished the pressor and tachycardic response to melittin in the normotensive conscious rats whereas pretreatment with atropine sulfate had no effect. In conclusion, our data demonstrate that peripherally administered melittin exerts a clear pressor and tachycardic effect by activating COX pathway. The activation of central cholinergic nicotinic receptors, predominantly alpha7nAChRs, appears to be involved in the pressor and tachycardic effects of the drug.

Peripheral mechanisms involved in the pressor and bradycardic effects of centrally administered arachidonic acid

In the current study, we aimed to determine the cardiovascular effects of arachidonic acid and peripheral mechanisms mediated these effects in normotensive conscious rats. Studies were performed in male Sprague Dawley rats. Arachidonic acid was injected intracerebroventricularly (i.c.v.) at the doses of 75, 150 or 300 microg and it caused dose- and time-dependent increase in mean arterial pressure and decrease in heart rate in normal conditions. Maximal effects were observed 10 min after 150 and 300 microg dose of arachidonic acid and lasted within 30 min. In order to evaluate the role of main peripheral hormonal mechanisms in those cardiovascular effects, plasma adrenaline, noradrenaline, vasopressin levels and renin activity were measured after arachidonic acid (150 microg; i.c.v.) injection. Centrally injected arachidonic acid increased plasma levels of all these hormones and renin activity. Intravenous pretreatments with prazosin (0.5 mg/kg), an alpha1 adrenoceptor antagonist, [beta-mercapto-beta,beta-cyclopentamethylenepropionyl1, O-Me-Tyr2-Arg8]-vasopressin (10 microg/kg), a vasopressin V1 receptor antagonist, or saralasin (250 microg/kg), an angiotensin II receptor antagonist, partially blocked the pressor response to arachidonic acid (150 microg; i.c.v.) while combined administration of these three antagonists completely abolished the effect. Moreover, both individual and combined antagonist pretreatments fully blocked the bradycardic effect of arachidonic acid. In conclusion, our findings show that centrally administered arachidonic acid increases mean arterial pressure and decreases heart rate in normotensive conscious rats and the increases in plasma adrenaline, noradrenaline, vasopressin levels and renin activity appear to mediate the cardiovascular effects of the drug.