Central Activation of Alpha7 Nicotinic Signaling Attenuates LPS-Induced Neuroinflammation and Sickness Behavior in Adult but Not in Aged Animals

Exposing the latent phenotype of Gulf War Illness: examination of the mechanistic mediators of cognitive dysfunction

Though it has been over 30 years since the 1990-1991 Gulf War (GW), the pathophysiology of Gulf War Illness (GWI), the complex, progressive illness affecting approximately 30% of GW Veterans, has not been fully characterized. While the symptomology of GWI is broad, many symptoms can be attributed to immune and endocrine dysfunction as these critical responses appear to be dysregulated in many GWI patients. Since such dysregulation emerges in response to immune threats or stressful situations, it is unsurprising that clinical studies suggest that GWI may present with a latent phenotype. This is most often observed in studies that include an exercise challenge during which many GWI patients experience an exacerbation of symptoms. Unfortunately, very few preclinical studies include such physiological stressors when assessing their experimental models of GWI, which creates variable results that hinder the elucidation of the mechanisms mediating GWI. Thus, the purpose of this review is to highlight the clinical and preclinical findings that investigate the inflammatory component of GWI and support the concept that GWI may be characterized as having a latent phenotype. We will mainly focus on studies assessing the progressive cognitive impairments associated with GWI and emphasize the need for physiological stressors in future work to create a more unified hypothesis that can identify potential therapeutics for this patient population.

Mitochondrial dysfunction precedes hippocampal IL-1β transcription and cognitive impairments after low-dose lipopolysaccharide injection in aged mice

Acute cognitive impairments termed delirium often occur after inflammatory insults in elderly patients. While previous preclinical studies suggest mitochondria as a target for reducing neuroinflammation and cognitive impairments after LPS injection, fewer studies have evaluated the effects of a low-grade systemic inflammation in the aged brain. Thus, to identify the significance of mitochondrial dysfunction after a clinically relevant systemic inflammatory stimulus, we injected old-aged mice (18-20 months) with low-dose lipopolysaccharide (LPS, 0.04 mg/kg). LPS injection reduced mitochondrial respiration in the hippocampus 24 h after injection (respiratory control ratio [RCR], state3u/state4o; control = 2.82 ± 0.19, LPS = 2.57 ± 0.08). However, gene expression of the pro-inflammatory cytokine IL-1β was increased (RT-PCR, control = 1.00 ± 0.30; LPS = 2.01 ± 0.67) at a more delayed time point, 48 h after LPS injection. Such changes were associated with cognitive impairments in the Barnes maze and fear chamber tests. Notably, young mice were unaffected by low-dose LPS, suggesting that mitochondrial dysfunction precedes neuroinflammation and cognitive decline in elderly patients following a low-grade systemic insult. Our findings highlight mitochondria as a potential therapeutic target for reducing delirium in elderly patients.

Emphasizing the Crosstalk Between Inflammatory and Neural Signaling in Post-traumatic Stress Disorder (PTSD)

Post-traumatic stress disorder (PTSD) is a chronic incapacitating condition with recurrent experience of trauma-related memories, negative mood, altered cognition, and hypervigilance. Agglomeration of preclinical and clinical evidence in recent years specified that alterations in neural networks favor certain characteristics of PTSD. Besides the disruption of hypothalamus-pituitary-axis (HPA) axis, intensified immune status with elevated pro-inflammatory cytokines and arachidonic metabolites of COX-2 such as PGE2 creates a putative scenario in worsening the neurobehavioral facet of PTSD. This review aims to link the Diagnostic and Statistical Manual of mental disorders (DSM-V) symptomology to major neural mechanisms that are supposed to underpin the transition from acute stress reactions to the development of PTSD. Also, to demonstrate how these intertwined processes can be applied to probable early intervention strategies followed by a description of the evidence supporting the proposed mechanisms. Hence in this review, several neural network mechanisms were postulated concerning the HPA axis, COX-2, PGE2, NLRP3, and sirtuins to unravel possible complex neuroinflammatory mechanisms that are obscured in PTSD condition.

Methylene blue reduces the serum levels of interleukin-6 and inhibits STAT3 activation in the brain and the skin of lipopolysaccharide-administered mice

It is valuable to search for novel and economical agents for inhibiting STAT3 activation and blocking increases in IL-6 levels, due to the important roles of STAT3 and IL-6 in inflammation. Since Methylene Blue (MB) has shown therapeutical potential for multiple diseases, it has become increasingly important to investigate the mechanisms underlying the effects of MB on inflammation. Using a mouse model of lipopolysaccharide (LPS)-induced inflammation, we investigated the mechanisms underlying the effects of MB on inflammation, obtaining the following findings: First, MB administration attenuated the LPS-induced increases in the serum levels of IL-6; second, MB administration attenuated LPS-induced STAT3 activation of the brain; and third, MB administration attenuated LPS-induced STAT3 activation of the skin. Collectively, our study has suggested that MB administration can decrease the levels of IL-6 and STAT3 activation - two important factors in inflammation. Since MB is a clinically used and relatively economical drug, our findings have suggested therapeutic potential of MB for multiple inflammation-associated diseases due to its effects on STAT3 activation and IL-6 levels.

Activation of α7nAChR by PNU282987 improves cognitive impairment through inhibiting oxidative stress and neuroinflammation in D-galactose induced aging via regulating α7nAChR/Nrf2/HO-1 signaling pathway

Aging is an important risk factor for neurodegenerative diseases. The activation of α7 nicotinic acetylcholine receptor (α7nAChR) is involved in inflammation and cognition, but the specific role it plays in aging remains unknown. This study aimed to investigate the anti-aging effect of the activation of α7nAChR on aging rats and BV2 cells induced by D-galactose, as well as its potential mechanism. D-galactose induced an increase in the SA-β-Gal positive cells, expression of p16 and p21 in vivo and in vitro. α7nAChR selective agonist PNU282987 decreased levels of pro-inflammatory factors, MDA, and Aβ, enhanced SOD activity and levels of anti-inflammatory factor (IL10) in vivo. PNU282987 enhanced the expression of Arg1, decreased the expression of iNOS, IL1β and TNFα in vitro. PNU282987 upregulated the levels of α7nAChR, Nrf2 and HO-1 in vivo and in vitro. The results of Morris water maze and novel object recognition tests showed that PNU282987 improved cognitive impairment in aging rats. Furthermore, α7nAChR selective inhibitor methyllycaconitine (MLA) results were opposite with PNU282987. PNU282987 improves cognitive impairment through inhibiting oxidative stress and neuroinflammation in D-galactose induced aging via regulating the α7nAChR/Nrf2/HO-1 signaling pathway. Therefore, targeting the α7nAChR may be a viable therapeutic approach for anti-inflammaging and neurodegenerative diseases.

Beneficial effects of QTC-4-MeOBnE in an LPS-induced mouse model of depression and cognitive impairments: The role of blood-brain barrier permeability, NF-κB signaling, and microglial activation

Clinical and preclinical investigations have suggested a possible biological link betweenmajor depressive disorder (MDD) and Alzheimer's disease (AD). Therefore, a pharmacologic approach to treating MDD could be envisioned as a preventative therapy for some AD cases. In line with this, 1-(7-chloroquinolin-4-yl)-N-(4-methoxybenzyl)-5-methyl-1H-1,2,3-triazole-4 carboxamide (QTC-4-MeOBnE) is characterized as an inhibitor of β-secretase, glycogen synthase kinase 3β, and acetylcholinesterase and has also shown secondary effects underlying the modulation of neurogenesis and synaptic plasticity pathways. Therefore, we investigated the effects of QTC-4-MeOBnE treatment (0.1 or 1 mg/kg) on depressive-like behavior and cognitive impairments elicited by repeated injections of lipopolysaccharide (LPS; 250 μg/kg) in mice. Injections of LPS for seven days led to memory impairments and depressive-like behavior, as evidenced in the Y-maze/object recognition test and forced swimming/splash tests, respectively. However, these impairments were prevented in mice that, after the last LPS injection, were also treated with QTC-4-MeOBnE (1 mg/kg). This effect was associated with restoring blood-brain barrier permeability, reducing oxidative/nitrosative biomarkers, and decreasing neuroinflammation mediated NF-κB signaling in the hippocampus and cortex of the mice. To further investigate the involvement with NF-κB signaling, we evaluated the effects of QTC-4-MeOBnE on microglial cell activation through canonical and non-canonical pathways and the modulation of the involved components. Together, our findings highlight the pharmacological benefits of QTC-4-MeOBnE in a mouse model of sickness behavior and memory impairments, supporting the novel concept that since this molecule produces anti-depressant activity, it could also be beneficial for preventing AD onset and related dementias in subjects suffering from MDD through inflammatory pathway modulation.