Pro-inflammatory and anti-inflammatory cytokine mRNA induction in the periphery and brain following intraperitoneal administration of bacterial lipopolysaccharide.

Gram-negative bacteria-derived lipopolysaccharide (LPS or endotoxin) is known to play an important role in immune and neurological manifestations during bacterial infections. LPS exerts its effects through cytokines, and peripheral or brain administration of LPS activates cytokine production in the brain. In this study, we investigated cytokine and neuropeptide mRNA profiles in specific brain regions and peripheral organs, as well as serum tumor necrosis factor (TNF)-alpha protein levels, in response to the intraperitoneal administration of LPS. For the first time, the simultaneous analysis of interleukin (IL)-1beta system components (ligand, signaling receptor, receptor accessory proteins, receptor antagonist), TNF-alpha, transforming growth factor (TGF)-beta1, glycoprotein 130 (IL-6 receptor signal transducer), OB protein (leptin) receptor, neuropeptide Y, and pro-opiomelanocortin (opioid peptide precursor) mRNAs was done in samples from specific brain regions in response to peripherally administered LPS. The same brain region/organ sample was assayed for all cytokine mRNA components. Peripherally administered LPS up-regulated pro-inflammatory cytokine (IL-1beta and/or TNF-alpha) mRNAs within the cerebral cortex, cerebellum, hippocampus, spleen, liver, and adipose tissue. LPS also increased plasma levels of TNF-alpha protein. LPS did not up-regulate inhibitory (anti-inflammatory) cytokine (IL-1 receptor antagonist and TGF-beta1) mRNAs in most brain regions (except for IL-1 receptor antagonist in the cerebral cortex and for TGF-beta1 in the hippocampus), while they were increased in the liver, and IL-1 receptor antagonist was up-regulated in the spleen and adipose tissue. Overall, peripherally administered LPS modulated the levels of IL-1beta system components within the brain and periphery, but did not affect the neuropeptide-related components studied. The data suggest specificity of transcriptional changes induced by LPS and that cytokine component up-regulation in specific brain regions is relevant to the neurological and neuropsychiatric manifestations associated with peripheral LPS challenge.

Neither acute nor chronic exposure to a naturalistic (predator) stressor influences the interleukin-1beta system, tumor necrosis factor-alpha, transforming growth factor-beta1, and neuropeptide mRNAs in specific brain regions.

Physical (neurogenic) stressors may influence immune functioning and interleukin-1beta (IL-1beta) mRNA levels within several brain regions. The present study assessed the effects of an acute or repeated naturalistic, psychogenic stressor (predator exposure) on brain cytokine and neuropeptide mRNAs. Acute predator (ferret) exposure induced stress-like behavioral effects, including elicitation of a startle response and reduced exploratory behaviors; these responses diminished after 30 sessions. Moreover, acute and repeated predator exposure, like acute restraint stress, increased plasma corticosterone levels measured 5 min later, but not 2 h after stressor exposure. In contrast, none of the stressors used influenced IL-1beta, IL-1 receptor antagonist, IL-1 receptor type I, IL-1 receptor accessory proteins I and II, or tumor necrosis factor-alpha mRNA levels in the prefrontal cortex, amygdala, hippocampus, or hypothalamus. Likewise, there were no stressor effects on transforming growth factor-beta1, neuropeptide Y, glycoprotein 130, or leptin receptor mRNAs in brain regions. Thus, the naturalistic/psychogenic stressor used does not affect any of the brain cytokine component mRNAs studied. It is suggested that this type of stressor activates homeostatic mechanisms (e.g., glucocorticoid release), which act to preclude brain cytokine alterations that would otherwise favor neuroinflammatory/neuroimmunological responses and the consequent increase of brain sensitivity to neurotoxic and neurodegenerative processes.

Cytokine-cytokine interactions and the brain.

Cytokine-cytokine interactions play a role in health and are crucial during immunological and inflammatory responses in disease. Cytokine interactions can result in additive, antagonist, or synergistic activities in maintaining physiological functions such as feeding, body temperature, and sleep, as well as in anorectic, pyrogenic, and somnogenic neurological manifestations of acute and chronic disease. These interactions involve signaling homology, convergence of signaling pathways, and/or positive or negative feedbacks within and among cytokine systems. The interplay of cytokines with neurotransmitters, peptides/neuropeptides, and hormones also influence cytokine action in the brain. Interactive chemical cascades involving cytokines are consistent with the homeostatic physiological mechanisms and with the multi-humoral, pleiotropic, and redundant processes that occur during acute and chronic disease.

Kindling modulates the IL-1beta system, TNF-alpha, TGF-beta1, and neuropeptide mRNAs in specific brain regions.

Cytokines and neuropeptides may be involved in seizure-associated processes. Following amygdala kindling in rats, we determined alterations of IL-1beta, IL-1 receptor antagonist (IL-1Ra), IL-1 receptor type I (IL-1RI), IL-1 receptor accessory proteins (IL-1R AcPs) I and II, TNF-alpha, TGF-beta1, neuropeptide Y (NPY), glycoprotein 130 (gp 130) and pro-opiomelanocortin (POMC) mRNA levels in the parietal, prefrontal and piriform cortices, amygdala, hippocampus and hypothalamus. Messenger RNAs expression in all brain regions was determined 2 h or 3 weeks following the last generalized convulsive seizure triggered from the ipsilateral kindled amygdala. The same brain region sample was used to assay for changes of all mRNA components. The results show that the 2 h-kindled group exhibited a significant up-regulation of IL-1beta, IL-1RI, TNF-alpha and TGF-beta1 mRNAs in all three cortical brain regions, amygdala and hippocampus. The largest up-regulation occurred in the prefrontal cortex (about 30-fold induction for IL-1beta and TNF-alpha mRNAs). IL-1R AcP I and II mRNA levels were also up-regulated in the cortical regions. No changes in IL-1beta, IL-1RI or TNF-alpha mRNA levels occurred in the 3 week-kindled group. NPY mRNA levels increased in the hippocampus, prefrontal and piriform cortices in the 2 h-kindled group, while IL-1Ra, gp 130, or POMC mRNA levels did not change in any group. The overall profile of mRNA changes shows specificity of transcriptional modulation induced by amygdala kindling. The data support a role of cytokines and NPY in the adaptive mechanisms associated with generalized seizure activity, with implications for neuroprotection, neuronal dysfunction and vulnerability associated with epileptic activity.

Neuropeptide Y counteracts interferon-alpha-induced anorexia.

Interferon-alpha (IFN-alpha) immunotherapy is associated with significant adverse neurological effects, including anorexia, which can be a limiting factor in immunotherapy. Thus, it is important to develop strategies that could ameliorate IFN-alpha-induced neurological manifestations without significantly affecting its immunomodulating properties. In this study, we tested the hypothesis that an endogenous feeding-enhancing peptide, neuropeptide Y (NPY), could inhibit IFN-alpha-induced anorexia in rats. The results show that IFN-alpha induced significant anorexia when administered centrally into the third cerebral ventricle at an immunotherapeutically relevant dose (1,350 IU/rat). Heat-inactivated IFN-alpha had no effect. NPY (5.0 microg/rat) counteracted the IFN-alpha-induced anorexia when administered 3 or 10 h following IFN-alpha, or when it was concomitantly administered with IFN-alpha. The data suggest that NPY and its agonists could represent a potential novel intervention for IFN-alpha immunotherapy-associated anorexia.

Feeding response to neuropeptide Y-related compounds in rats treated with Y5 receptor antisense or sense phosphothio-oligodeoxynucleotide.

Neuropeptide Y (NPY), NPY 3-36 and pancreatic polypeptide (PP) increase short-term (2-h) food intake to varying degrees when given intracerebroventricularly (i.c.v.). Various Y receptor subtypes are proposed to participate in Y receptor ligand-induced stimulation of food intake. Here, we used an antisense phosphothio-oligodeoxynucleotide sequence (-5 relative to the initiating ATG) to the Y5 receptor subtype, which has been suggested to mediate NPY-induced feeding. Rats were treated with i.c.v. antisense or sense phosphothio-oligodeoxynucleotide for 3.5 days before NPY, NPY 3-36, or PP i.c.v. administration. The results show that antisense to the Y5 receptor had no effect on either spontaneous 2-h or NPY-, NPY 3-36-, or PP-stimulated 2-h food intake. However, there was a significant decrease relative to the sense control group in 10-h food intake following the initial 2-h feeding response to NPY (n = 10, p < 0.0001) or NPY 3-36 (n = 10, p < 0.05). The data suggest that the Y5 receptor has a modulatory role in the maintenance of feeding, but not as the critical receptor to confer for NPY and NPY 3-36 action on food intake.

Polyunsaturated Fatty Acids and Disease-associated and Cytokine-induced Neurological Manifestations.

Fish oil supplementation is suggested as possible mean to improve neurological manifestations of chronic diseases and cytokine immunotherapies. Preclinical and clinical studies show that fish oil supplementation seems able to reduce disease-associated anorexia and body weight loss. This improvement could be due to shifts in metabolism and changes in proinflammatory cytokine production and action. ω-3 Polyunsaturated fatty acids (PUFAs), especially eicosapentaenoic acid, are used as substrates for eicosanoid synthesis, competing for enzymes with arachidonic acid, which is a substrate for the synthesis of proinflammatory immunomodulators, such as prostaglandin E2. Fish oil supplementation is generally found to lower production of cytokines including interleukin-1 and tumor necrosis factor-α, thereby reducing various immune responses, including inflammation. However, conflicting results regarding the effects of fish oil interventions have been reported. The main factor that emerges from the contradictory reports is the variety of models, assays and methodologies that have been used. This brief review presents an overall perspective on the potential use of ω-3 PUFAs as a nutritional intervention to ameliorate disease-associated and cytokine-induced neurological manifestations. We conclude that substantial further research is required to understand the exact nature of n-3 PUFA-induced immunomodulation in health and disease.