Effect of tumor necrosis factor-alpha on the reciprocal G-protein-induced regulation of norepinephrine release by the alpha2-adrenergic receptor

Pre-treatment plasma cytokine levels as potential predictors of short-term remission of depression

OBJECTIVES

The response to antidepressants varies significantly among individuals and is difficult to predict before treatment. In this randomised control trial, we explored cytokines that correlate with the therapeutic effect of mirtazapine (MIR) and selective serotonin reuptake inhibitors (SSRIs) and whether they could be predictors of remission for each antidepressant.

METHODS

Plasma cytokines, such as tumour necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-2, IL-4, IL-6, IL-8, and granulocyte-macrophage colony-stimulating factor (GM-CSF) were assayed in 95 participants before medication and assayed by the enzyme-linked immunosorbent assay. The Hamilton Rating Scale for Depression assessed depressive symptoms over 4 weeks.

RESULTS

In the SSRI group, the baseline GM-CSF level was significantly higher in the remission group than in the non-remission group (p = .022). In the MIR group, the baseline level of TNF-α was significantly higher (p = .039) and IL-2 was lower (p = .032) in the remission group than in the non-remission group. In patients prescribed with MIR, the cut-off values of TNF-α (10.035 pg/mL) and IL-2 (1.170 pg/mL) calculated from the receiver operating characteristic curve suggested that the remission rate, which corresponds to a positive predictive value, could be increased from 31.3% to 60.0% and 50.0%, respectively. For those prescribed with SSRIs, the remission rate was 37.0% and using the cut-off value of GM-CSF (0.205 pg/mL), the remission rate could be almost doubled to 70%.

CONCLUSIONS

Our study shows that pre-treatment plasma concentrations of TNF-α, IL-2, and GM-CSF may suggest the predictability of remission by SSRIs or MIR.

Understanding How Physical Exercise Improves Alzheimer’s Disease: Cholinergic and Monoaminergic Systems

Alzheimer’s disease (AD) is an age-related neurodegenerative disorder, characterized by the accumulation of proteinaceous aggregates and neurofibrillary lesions composed of β-amyloid (Aβ) peptide and hyperphosphorylated microtubule-associated protein tau, respectively. It has long been known that dysregulation of cholinergic and monoaminergic (i.e., dopaminergic, serotoninergic, and noradrenergic) systems is involved in the pathogenesis of AD. Abnormalities in neuronal activity, neurotransmitter signaling input, and receptor function exaggerate Aβ deposition and tau hyperphosphorylation. Maintenance of normal neurotransmission is essential to halt AD progression. Most neurotransmitters and neurotransmitter-related drugs modulate the pathology of AD and improve cognitive function through G protein-coupled receptors (GPCRs). Exercise therapies provide an important alternative or adjunctive intervention for AD. Cumulative evidence indicates that exercise can prevent multiple pathological features found in AD and improve cognitive function through delaying the degeneration of cholinergic and monoaminergic neurons; increasing levels of acetylcholine, norepinephrine, serotonin, and dopamine; and modulating the activity of certain neurotransmitter-related GPCRs. Emerging insights into the mechanistic links among exercise, the neurotransmitter system, and AD highlight the potential of this intervention as a therapeutic approach for AD.

Tumor Necrosis Factor (TNF) Is Required for Spatial Learning and Memory in Male Mice under Physiological, but Not Immune-Challenged Conditions

Increasing evidence demonstrates that inflammatory cytokines-such as tumor necrosis factor (TNF)-are produced at low levels in the brain under physiological conditions and may be crucial for synaptic plasticity, neurogenesis, learning and memory. Here, we examined the effects of developmental TNF deletion on spatial learning and memory using 11-13-month-old TNF knockout (KO) and C57BL6/J wild-type (WT) mice. The animals were tested in the Barnes maze (BM) arena under baseline conditions and 48 h following an injection of the endotoxin lipopolysaccharide (LPS), which was administered at a dose of 0.5 mg/kg. Vehicle-treated KO mice were impaired compared to WT mice during the acquisition and memory-probing phases of the BM test. No behavioral differences were observed between WT and TNF-KO mice after LPS treatment. Moreover, there were no differences in the hippocampal content of glutamate and noradrenaline between groups. The effects of TNF deletion on spatial learning and memory were observed in male, but not female mice, which were not different compared to WT mice under baseline conditions. These results indicate that TNF is required for spatial learning and memory in male mice under physiological, non-inflammatory conditions, however not following the administration of LPS. Inflammatory signalling can thereby modulate spatial cognition in male subjects, highlighting the importance of sex- and probably age-stratified analysis when examining the role of TNF in the brain.

Sympathetic innervation, norepinephrine content, and norepinephrine turnover in orthotopic and spontaneous models of breast cancer

Activation of the sympathetic nervous system (SNS) drives breast cancer progression in preclinical breast cancer models, but it has yet to be established if neoplastic and stromal cells residing in the tumor are directly targeted by locally released norepinephrine (NE). In murine orthotopic and spontaneous mammary tumors, tyrosine hydroxylase (TH)+ sympathetic nerves were limited to the periphery of the tumor. No TH+ staining was detected deeper within these tumors, even in regions with a high density of blood vessels. NE concentration was much lower in tumors compared to the more densely innervated spleen, reflecting the relative paucity of tumor TH+ innervation. Tumor and spleen NE concentration decreased with increased tissue mass. In mice treated with the neurotoxin 6-hydroxydopamine (6-OHDA) to selectively destroy sympathetic nerves, tumor NE concentration was reduced approximately 50%, suggesting that the majority of tumor NE is derived from local sympathetic nerves. To evaluate NE utilization, NE turnover in orthotopic 4T1 mammary tumors was compared to spleen under baseline and stress conditions. In non-stressed mice, NE turnover was equivalent between tumor and spleen. In mice exposed to a stressor, tumor NE turnover was increased compared to spleen NE turnover, and compared to non-stressed tumor NE turnover. Together, these results demonstrate that NE in mammary tumors is derived from local sympathetic nerves that synthesize and metabolize NE. However, differences between spleen and tumor NE turnover with stressor exposure suggest that sympathetic NE release is regulated differently within the tumor microenvironment compared to the spleen. Local mammary tumor sympathetic innervation, despite its limited distribution, is responsive to stressor exposure and therefore can contribute to stress-induced tumor progression.

The hippocampus and TNF: Common links between chronic pain and depression

Major depression and chronic pain are significant health problems that seriously impact the quality of life of affected individuals. These diseases that individually are difficult to treat often co-exist, thereby compounding the patient's disability and impairment as well as the challenge of successful treatment. The development of efficacious treatments for these comorbid disorders requires a more comprehensive understanding of their linked associations through common neuromodulators, such as tumor necrosis factor-α (TNFα), and various neurotransmitters, as well as common neuroanatomical pathways and structures, including the hippocampal brain region. This review discusses the interaction between depression and chronic pain, emphasizing the fundamental role of the hippocampus in the development and maintenance of both disorders. The focus of this review addresses the hypothesis that hippocampal expressed TNFα serves as a therapeutic target for management of chronic pain and major depressive disorder (MDD).

Perispinal etanercept for post-stroke neurological and cognitive dysfunction: scientific rationale and current evidence

There is increasing recognition of the involvement of the immune signaling molecule, tumor necrosis factor (TNF), in the pathophysiology of stroke and chronic brain dysfunction. TNF plays an important role both in modulating synaptic function and in the pathogenesis of neuropathic pain. Etanercept is a recombinant therapeutic that neutralizes pathologic levels of TNF. Brain imaging has demonstrated chronic intracerebral microglial activation and neuroinflammation following stroke and other forms of acute brain injury. Activated microglia release TNF, which mediates neurotoxicity in the stroke penumbra. Recent observational studies have reported rapid and sustained improvement in chronic post-stroke neurological and cognitive dysfunction following perispinal administration of etanercept. The biological plausibility of these results is supported by independent evidence demonstrating reduction in cognitive dysfunction, neuropathic pain, and microglial activation following the use of etanercept, as well as multiple studies reporting improvement in stroke outcome and cognitive impairment following therapeutic strategies designed to inhibit TNF. The causal association between etanercept treatment and reduction in post-stroke disability satisfy all of the Bradford Hill Criteria: strength of the association; consistency; specificity; temporality; biological gradient; biological plausibility; coherence; experimental evidence; and analogy. Recognition that chronic microglial activation and pathologic TNF concentration are targets that may be therapeutically addressed for years following stroke and other forms of acute brain injury provides an exciting new direction for research and treatment.

Celecoxib enhances the effect of reboxetine and fluoxetine on cortical noradrenaline and serotonin output in the rat

A substantial number of patients with major depressive disorder (MDD) do not respond adequately to current antidepressant pharmacological treatments, which are all more or less based on a gradually increased enhancement of monoaminergic neurotransmission. Although a functional deficiency in monoaminergic neurotransmission may contribute to MDD, the etiology and pathophysiology are far from clarified. Recent studies suggest that inflammatory processes may contribute, since increased levels of pro-inflammatory cytokines and prostaglandin E(2) (PGE(2)) have repeatedly been observed in a subset of patients suffering from MDD. Interestingly, adjunct treatment with the anti-inflammatory drug celecoxib, a cyclo-oxygenase-2 (COX-2) inhibitor which blocks the PGE(2)-production, has shown to enhance the efficacy of both reboxetine, a selective noradrenaline reuptake inhibitor, as well as fluoxetine, a selective serotonin reuptake inhibitor, in treatment-resistant depression. To examine the neurobiological underpinnings to the clinical observations, we here studied the acute effects of a combined treatment with celecoxib and reboxetine on noradrenaline and dopamine output, as well as celecoxib and fluoxetine on 5-HT output in the medial prefrontal cortex, using in vivo microdialysis in awake freely moving rats. Celecoxib significantly potentiated the effects of reboxetine and fluoxetine on cortical noradrenaline and 5-HT output, respectively, but not the reboxetine-induced dopamine output. Moreover, celecoxib, when given alone, enhanced 5-HT output. These findings provide, in principle, novel experimental support for the clinical utility of combined treatment with antidepressant and anti-inflammatory drugs, such as COX-2 inhibitors, in MDD.

Adjuvant therapy with intrathecal clonidine improves postoperative pain in patients undergoing coronary artery bypass graft

BACKGROUND

Alpha2 adrenergic agonists have long been employed as analgesics and to sedate patients undergoing surgical procedures. In addition, their therapeutic response synergizes that elicited by opioids. Although this response is well known, the role of alpha2 agonists, such as clonidine, during various painful surgical procedures remains to be elucidated. The goal of our study was to evaluate the effects of the intrathecal administration of clonidine on postoperative pain control and time to extubation in patients undergoing coronary artery bypass grafting.

METHODS

Eighty-five patients undergoing coronary artery bypass grafting randomly received either an intrathecal injection of preservative free morphine 0.5 mg (MOR) or a combination of morphine 0.5 mg and clonidine 100 microg (CMC) before induction of anesthesia. Anesthesia was induced and maintained using a balanced anesthesia technique. Patients were transferred to the intensive care unit while intubated and weaned from mechanical ventilation following an established weaning protocol. Postoperative pain, opioid use within the first 24 hours, and time to extubation were used as primary outcome variables. Data were analyzed by a 2-tailed t test for continuous variables and Fisher exact test for nonparametric variables.

RESULTS

There were no demographic differences between the CMC and MOR groups. Postoperative pain, as assessed by a visual analog scale, was milder in the CMC group when compared with that of the MOR group (2.2+/-0.36 vs. 3.4+/-0.33, P<0.05). Similarly, patients in the CMC group required lower doses of morphine within 24 hours compared with the MOR group (2.02+/-0.36 vs. 6.47+/-0.49 mg, P<0.0001). Time to extubation was significantly shorter in patients receiving CMC than in those who received MOR (592+/-52 vs. 887+/-75 min, P<0.05). There was no mortality in either group. There was a trend for increased vasopressin use in the CMC group compared with the MOR group, although this was not statistically significant (P=0.07).

CONCLUSIONS

Addition of clonidine to neuraxial opioids improves the quality of analgesia postoperatively and expedites the process of weaning from mechanical ventilation. There were no serious adverse events in the cohort of the patients studied. However, the safety profile of this medication remains to be examined with a larger group of patients.

Antinociception occurs with a reversal in alpha 2-adrenoceptor regulation of TNF production by peripheral monocytes/macrophages from pro- to anti-inflammatory

Tumor necrosis factor-alpha (TNF) plays a role in neuropathic pain. During neuropathic pain development in the chronic constriction injury model, elevated TNF levels in the brain occur in association with enhanced alpha 2-adrenoceptor inhibition of norepinephrine release. alpha 2-Adrenoceptors are also located on peripheral macrophage where they normally function as pro-inflammatory, since they increase the production of the cytokine TNF, a proximal mediator of inflammation. How the central increase in TNF affects peripheral alpha 2-adrenoceptor function was investigated. Male, Sprague-Dawley rats had four loose ligatures placed around the right sciatic nerve. Thermal hyperalgesia was determined by comparing hind paw withdrawal latencies between chronic constriction injury and sham-operated rats. Chronic constriction injury increased TNF immunoreactivity at the lesion and the hippocampus. Amitriptyline, an antidepressant that is used as an analgesic, was intraperitoneally administered (10 mg/kg) starting simultaneous with ligature placement (day-0) or at days-4 or -6 post-surgery. Amitriptyline treatment initiated at day-0 or day-4 post-ligature placement alleviated hyperalgesia. When initiated at day-0, amitriptyline prevented increased TNF immunoreactivity in the hippocampus and at the lesion. A peripheral inflammatory response, macrophage production of TNF, was also assessed in the current study. Lipopolysaccharide (LPS)-stimulated production of TNF by whole blood cells and peritoneal macrophages was determined following activation of the alpha 2-adrenoceptor in vitro. alpha 2-Adrenoceptor regulation of TNF production from peripheral immune-effector cells reversed from potentiation in controls to inhibition in chronic constriction injured rats. This effect is accelerated with amitriptyline treatment initiated at day-0 or day-4 post-ligature placement. Amitriptyline treatment initiated day-6 post-ligature placement did not alleviate hyperalgesia and prevented the switch from potentiation to inhibition in alpha 2-adrenoceptor regulation of TNF production. Recombinant rat TNF i.c.v. microinfusion reproduces the response of peripheral macrophages from rats with chronic constriction injury. A reversal in peripheral alpha 2-adrenoceptor regulation of TNF production from pro- to anti-inflammatory is associated with effective alleviation of thermal hyperalgesia. Thus, alpha 2-adrenoceptor regulation of peripheral TNF production may serve as a potential biomarker to evaluate therapeutic regimens.

Anticytokine therapy in neuropathic pain management

Cytokine activation or dysregulation is implied in a variety of painful disease states. Numerous experimental studies provide evidence that proinflammatory cytokines induce or facilitate neuropathic pain. Cytokine levels are rapidly and markedly upregulated in the peripheral nerves, dorsal root ganglia, spinal cord and in particular regions of the brain, after peripheral nerve injuries. Direct receptor-mediated actions on afferent nerve fibers as well as cytokine effects involving further mediators have been reported. Whereas direct application of exogenous proinflammatory cytokines induces pain, blockade of these cytokines or application of anti-inflammatory cytokines reduces pain behavior in most experimental paradigms. Cytokine measurements may identify patients at risk of developing chronic pain associated with their neuropathic conditions, as in the examples of peripheral neuropathies and postherpetic neuralgia. Anticytokine agents currently on the market are effective for the treatment of mostly inflammatory pain conditions, and are starting to be introduced for neuropathic pain states; however, their use is limited by potential life-threatening complications. Owing to the pleiotropy and redundancy of the cytokine system, the successful approach may not be inhibition of one particular cytokine but strategies shifting the balance between pro- and anti-inflammatory cytokines in properly selected patients. Agents that specifically target downstream signaling molecules may provide hope for safer and more specific therapies.

Antinociception mediated by alpha(2)-adrenergic activation involves increasing tumor necrosis factor alpha (TNFalpha) expression and restoring TNFalpha and alpha(2)-adrenergic inhibition of norepinephrine release

The central component that establishes chronic pain from peripheral nerve injury is associated with increased tumor necrosis factor-alpha (TNFalpha) production in the brain. This study examined TNFalpha and its reciprocally permissive role with alpha(2)-adrenergic activation during peak and progressive decline of thermal hyperalgesia in sciatic nerve chronic constriction injury (CCI). Accumulation of TNFalpha mRNA (in situ hybridization) increases in the hippocampus and locus coeruleus during the onset of neuropathic pain and persists as hyperalgesia abates. Activation of alpha(2)-adrenergic receptors in control rats decreases TNFalpha mRNA accumulation in these brain regions. In contrast, during hyperalgesia, alpha(2)-adrenergic activation enhances TNFalpha mRNA accumulation. Whether this enhanced TNFalpha production is associated with changes in the regulation of norepinephrine (NE) release was tested. Hippocampal slices were electrically depolarized to evaluate alpha(2)-adrenergic and TNFalpha regulation of NE release. While inhibition of NE release by TNFalpha is maximal during peak hyperalgesia, it subsequently transforms to facilitate NE release. In addition, alpha(2)-adrenergic receptor activation with clonidine (0.2mg/kg, i.p.) in CCI rats experiencing hyperalgesia restores TNFalpha and alpha(2)-adrenergic inhibition of NE release. While TNFalpha directs the development of hyperalgesia, it also directs its resolution. Transformed sensitivity to alpha(2)-adrenergic agonists during hyperalgesia demonstrates a mechanism for therapy.

Uncovering molecular elements of brain-body communication during development and treatment of neuropathic pain

Integral to neuropathic pain is a reciprocal interaction between tumor necrosis factor-alpha (TNF) production and the alpha(2)-adrenergic receptor response, offering an attractive therapeutic target. The effects of varying levels of brain TNF on alpha(2)-adrenergic regulation of cyclic AMP (cAMP) production in the hippocampus and sciatic nerve were investigated during the development and amitriptyline treatment of chronic pain. Increased levels of TNF during the development of chronic pain transform alpha(2)-adrenergic inhibition of cAMP production in the brain to potentiation. While alpha(2)-adrenergic receptors regulate TNF production, they also affect descending noradrenergic pathways. Increases in levels of TNF in the brain deeply impact peripheral inflammation through regulating alpha(2)-adrenergic receptors, offering insight into brain-body interactions during neuropathic pain. Amitriptyline as an analgesic inhibits pain-induced increases in brain-associated TNF and transforms peripheral alpha(2)-adrenergic receptors. The dynamic equilibrium between TNF levels and alpha(2)-adrenergic functioning is uniquely altered during development and treatment of neuropathic pain. Proper manipulations of this interaction offer efficacious treatment of neuropathic pain.

An antidepressant mechanism of desipramine is to decrease tumor necrosis factor-alpha production culminating in increases in noradrenergic neurotransmission

The monoamine theory of depression proposes decreased bioavailability of monoamines, such as norepinephrine (NE), as the underlying cause of depression. Thus, the antidepressant efficacy of NE-reuptake inhibitors such as desipramine is attributed to increases in synaptic concentrations of NE. The time difference between inhibition of reuptake and therapeutic efficacy, however, argues against this being the primary mechanism. If desipramine elicits its therapeutic efficacy by increasing NE release, in turn, increasing activation of the alpha(2)-adrenergic autoinhibitory receptor, then mimicking this increase with an exogenous agonist (clonidine) should support or even enhance the efficacy of the antidepressant. Intriguingly, simultaneous administration of clonidine with desipramine prevented the cellular and behavioral effects elicited by desipramine alone, in both acute and chronic administration paradigms. These results suggest the involvement of additional factor(s) in the mechanism of antidepressant action of this drug. Desipramine administration results in a virtual ablation of neuron-derived tumor necrosis factor-alpha (TNF), thus implicating an essential role of TNF in the therapeutic efficacy of this antidepressant. Additionally, following chronic administration of desipramine, TNF-regulation of NE release is transformed, from inhibition to facilitation. Here, we demonstrate that a transformation in TNF-regulation of NE release in the brain is a key element in the efficacy of this antidepressant. Interestingly, an increase in neurotransmission prior to the antidepressant's effect on TNF production prevents the efficacy of the antidepressant drug. Thus, the efficacy of desipramine is due to decreased levels of TNF in the brain induced by this drug, ultimately modifying noradrenergic neurotransmission.