C-reactive protein as a potential biomarker in psychiatric practice: Are we there yet?

OBJECTIVES

Serum or plasma levels of C-reactive protein (CRP) and high-sensitivity CRP (hsCRP) are widely used clinical markers of inflammation in other branches of medicine, whereas its clinical use in psychiatry has been limited to research studies. We aimed to assess the possibility of using CRP/hsCRP in psychiatric practice. This is a review and evaluation of various lines of evidence supporting the concept of CRP as a biomarker for psychiatric disorders in certain conditions.

METHODS

We searched the literature for studies which assessed CRP/hsCRP levels in various psychiatric disorders.

RESULTS

The accumulating evidence from large studies and meta-analyses allows us to understand the role of CRP in major psychiatric disorders and increase our understanding of specific symptoms and subtypes of disorders. CRP may be considered a 'psychiatric biomarker' which can alert clinicians about neuroinflammation, adverse effects of medications, cardiometabolic status, co-morbidities, and may also predict clinical outcomes and guide optimal treatment.selection.

CONCLUSION

Although the underlying pathophysiological role of CRP and hsCRP is still elusive and the association between CRP and psychiatric disorders is inconsistent, CRP holds promise to become a psychiatric biomarker.

Suppression of TLR4/MyD88/TAK1/NF-κB/COX-2 Signaling Pathway in the Central Nervous System by Bexarotene, a Selective RXR Agonist, Prevents Hyperalgesia in the Lipopolysaccharide-Induced Pain Mouse Model

A selective RXR agonist, bexarotene, has been shown to have anti-inflammatory, anti-nociceptive, and neuroprotective effects in several models of numerous neurological diseases characterized by systemic inflammation. The mechanisms underlying these effects remains unknown. To elucidate these mechanisms, we investigated whether the TLR4/MyD88/TAK1/NF-κB/COX-2 signaling pathway in the CNS mediates the effect of bexarotene to prevent hyperalgesia in the LPS-induced inflammatory pain mouse model. The reaction time to thermal stimuli within 30 s was evaluated by the hot plate test in male mice treated with saline, LPS (10 mg/kg), DMSO, and/or bexarotene (0.1, 1, 3, or 10 mg/kg) after 6 h. The latency to the thermal stimulus (18.11 ± 1.36 s) in the LPS-treated mice was significantly decreased by 30% compared with saline-treated mice (25.84 ± 1.99 s). Treatment with bexarotene only at a dose of 10 mg/kg showed a significant increase in the latency by 22.49 ± 1.00 s compared with LPS-treated mice. Bexarotene also prevented the reduction in RXRα protein expression associated with a rise in the expression of TLR4, MyD88, phosphorylated TAK1, NF-κB p65, phosphorylated NF-κB p65, COX-2, and IL-1β proteins, in addition to COX-2 activity and levels of PGE2 and IL-1β in the brains and spinal cords of the LPS-treated animals. Likely, decreased activity of TLR4/MyD88/TAK1/NF-κB/COX-2 signaling pathway in addition to increased pro-inflammatory cytokine formation in the CNS of mice participates in the protective effect of bexarotene against hyperalgesia induced by LPS.

mTOR inhibition as a possible pharmacological target in the management of systemic inflammatory response and associated neuroinflammation by lipopolysaccharide challenge in rats

Neuroinflammation plays a critical role during sepsis triggered by microglial activation. Mammalian target of rapamycin (mTOR) has gained attraction in neuroinflammation, however, the mechanism remains unclear. Our goal was to assess the effects of mTOR inhibition by rapamycin on inflammation, microglial activation, oxidative stress, and apoptosis associated with the changes in the inhibitor-κB (IκB)-α/nuclear factor-κB (NF-κB)/hypoxia-inducible factor-1α (HIF-1α) pathway activity following a systemic challenge with lipopolysaccharide (LPS). Rats received saline (10 mL/kg), LPS (10 mg/kg), and (or) rapamycin (1 mg/kg) intraperitoneally. Inhibition of mTOR by rapamycin blocked phosphorylated form of ribosomal protein S6, NF-κB p65 activity by increasing degradation of IκB-α in parallel with HIF-1α expression increased by LPS in the kidney, heart, lung, and brain tissues. Rapamycin attenuated the increment in the expression of tumor necrosis factor-α and interleukin-1β, the inducible nitric oxide synthase, gp91^phox, and p47^phox in addition to nitrite levels elicited by LPS in tissues or sera. Concomitantly, rapamycin treatment reduced microglial activation, brain expression of caspase-3, and Bcl-2-associated X protein while it increased expression of B cell lymphoma 2 induced by LPS. Overall, this study supports the hypothesis that mTOR contributes to the detrimental effect of LPS-induced systemic inflammatory response associated with neuroinflammation via IκB-α/NF-κB/HIF-1α signaling pathway.

Soluble epoxide hydrolase inhibitor trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl)urea prevents hyperalgesia through regulating NLRC4 inflammasome-related pro-inflammatory and anti-inflammatory signaling pathways in the lipopolysaccharide-induced pain mouse model

Epoxyeicosatrienoic acids (EETs) have anti-inflammatory effects and soluble epoxide hydrolase (sEH) inhibition might be a useful therapeutic approach to manage inflammatory disorders. The purpose of the study was to investigate whether nucleotide-binding and oligomerization domain-like receptor (NLR) C4 inflammasome-related pro-inflammatory and anti-inflammatory signaling pathways in the central nervous system (CNS) participates in the effect of trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl)urea (TPPU), a potent sEH inhibitor, to prevent hyperalgesia in the LPS-induced pain mouse model. The latency of pain within 30 s was measured by the hot plate test in male mice injected with saline, lipopolysaccharide (LPS) (10 mg/kg), and/or TPPU (0.3, 0.5, or 1 mg/kg) after 6 h. Hyperalgesia induced by LPS was associated with decreased 14,15-dihydroxyeicosatrienoic acid and interleukin (IL)-1β levels and enhanced expression of NLRC4, apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC), caspase-1 p20, IL-1β, and caspase-11 p20 in the brains and spinal cords of the animals. Besides the increased expression of nicotinamide adenine dinucleotide phosphate oxidase (NOX) subunits (gp91^phox and p47^phox ) and nitrotyrosine, a decrease in NLRC3, inducible nitric oxide synthase (iNOS), and neuronal NOS (nNOS) expression was also observed in the tissues of LPS-treated mice. TPPU at 0.5 mg/kg dose prevented the changes induced by LPS. Likely, decreased activity of pro-inflammatory NLRC4/ASC/pro-caspase-1 and caspase-11 inflammasomes and NOX in addition to enhanced levels of anti-inflammatory EETs and expression of NLRC3, iNOS, and nNOS in the CNS of mice participates in the protective effect of TPPU against LPS-induced hyperalgesia.

Pharmacological inhibition of soluble epoxide hydrolase attenuates chronic experimental autoimmune encephalomyelitis by modulating inflammatory and anti-inflammatory pathways in an inflammasome-dependent and -independent manner

We aimed to determine the effect of soluble epoxide hydrolase (sEH) inhibition on chronic experimental autoimmune encephalomyelitis (EAE), a murine model of multiple sclerosis (MS), associated with changes in inflammasome-dependent and -independent inflammatory and anti-inflammatory pathways in the CNS of mice. C57BL/6 mice were used to induce chronic EAE by using an injection of MOG_35-55 peptide/PT. Animals were observed daily and scored for EAE signs for 25 days after immunization. Following the induction of EAE, the scores were increased after 9 days and reached peak value as determined by ≥ 2 or ≤ 3 with 8% mortality rate on day 17. On day 17, mice were administered daily PBS, DMSO, or TPPU (a potent sEH inhibitor) (1, 3, or 10 mg/kg) until the end of the study. TPPU only at 3 mg/kg dose decreased the AUC values calculated from EAE scores obtained during the disease compared to EAE and vehicle control groups. On day 25, TPPU also caused an increase in the PPARα/β/γ and NLRC3 proteins and a decrease in the proteins of TLR4, MyD88, NF-κB p65, p-NF-κB p65, iNOS/nNOS, COX-2, NLRC4, ASC, caspase-1 p20, IL-1β, caspase-11 p20, NOX subunits (gp91^phox and p47^phox), and nitrotyrosine in addition to 14,15-DHET and IL-1β levels compared to EAE and vehicle control groups. Our findings suggest that pharmacological inhibition of sEH attenuates chronic EAE likely because of enhanced levels of anti-inflammatory EETs in addition to PPARα/β/γ and NLRC3 expression associated with suppressed inflammatory TLR4/MyD88/NF-κB signalling pathway, NLRC4/ASC/pro-caspase-1 inflammasome, caspase-11 inflammasome, and NOX activity that are responsible for inflammatory mediator formation in the CNS of mice.

Modulation of oxidative–nitrosative stress and inflammatory response by rapamycin in target and distant organs in rats exposed to hindlimb ischemia–reperfusion: the role of mammalian target of rapamycin

Mammalian target of rapamycin (mTOR) has been recognized with potential immunomodulatory properties playing an important role in various physiopathological processes including ischemia–reperfusion (I/R) injury. I/R injury stimulate reactive oxygen and nitrogen species by activating nicotinamide adenine dinucleotide phosphate oxidase and inducible nitric oxide synthase, respectively. Controversial results have been obtained in different I/R models following localized I/R; however, the precise role of the mTOR signaling pathway remains undefined. The objective of the current study was to evaluate the role of the mTOR in oxidative–nitrosative stress and inflammation in hindlimb I/R-induced injury in target and remote organ injuries. In rats subjected to I/R, an increased expression of ribosomal protein S6 (rpS6), inhibitor κB (IκB)-α, nuclear factor-κB (NF-κB) p65, inducible nitric oxide synthase, cyclooxygenase 2, gp91phox, and levels of tumor necrosis factor α, nitrite, nitrotyrosine, malondialdehyde and the activities of myeloperoxidase and catalase in the tissues and (or) sera were detected. Treatment with rapamycin, a selective inhibitor of mTOR, reversed all the I/R-induced changes as manifested by its anti-inflammatory and antioxidant effects in kidney and gastrocnemius muscle of rats. Collectively, these findings suggest that rapamycin protects against I/R-induced oxidative–nitrosative stress and inflammation leading to organ injuries via suppression of mTOR/IκB-α/NF-κB signaling pathway.

Eicosanoids derived from cytochrome P450 pathway of arachidonic acid and inflammatory shock

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. Septic shock, the most common form of vasodilatory shock, is a subset of sepsis in which circulatory and cellular/metabolic abnormalities are severe enough to increase mortality. Inflammatory shock constitutes the hallmark of sepsis, but also a final common pathway of any form of severe long-term tissue hypoperfusion. The pathogenesis of inflammatory shock seems to be due to circulating substances released by pathogens (e.g., bacterial endotoxins) and host immuno-inflammatory responses (e.g., changes in the production of histamine, bradykinin, serotonin, nitric oxide [NO], reactive nitrogen and oxygen species, and arachidonic acid [AA]-derived eicosanoids mainly through NO synthase, cyclooxygenase, and cytochrome P450 [CYP] pathways, and proinflammatory cytokine formation). Therefore, refractory hypotension to vasoconstrictors with end-organ hypoperfusion is a life threatening feature of inflammatory shock. This review summarizes the current knowledge regarding the role of eicosanoids derived from CYP pathway of AA in animal models of inflammatory shock syndromes with an emphasis on septic shock in addition to potential therapeutic strategies targeting specific CYP isoforms responsible for proinflammatory/anti-inflammatory mediator production.

Protection by mTOR Inhibition on Zymosan-Induced Systemic Inflammatory Response and Oxidative/Nitrosative Stress: Contribution of mTOR/MEK1/ERK1/2/IKKβ/IκB-α/NF-κB Signalling Pathway

Mammalian target of rapamycin (mTOR), a serine/threonine kinase regulate variety of cellular functions including cell growth, differentiation, cell survival, metabolism, and stress response, is now appreciated to be a central regulator of immune responses. Because mTOR inhibitors enhanced the anti-inflammatory activities of regulatory T cells and decreased the production of proinflammatory cytokines by macrophages, mTOR has been a pharmacological target for inflammatory diseases. In this study, we examined the role of mTOR in the production of proinflammatory and vasodilator mediators in zymosan-induced non-septic shock model in rats. To elucidate the mechanism by which mTOR contributes to non-septic shock, we have examined the activity of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase system caused by mTOR/mitogen-activated protein kinase kinase (MEK1)/extracellular signal-regulated kinase (ERK1/2)/inhibitor κB kinase (IKKβ)/inhibitor of κB (IκB-α)/nuclear factor-κB (NF-κB) signalling pathway activation. After 1 h of zymosan (500 mg/kg, i.p.) administration to rats, mean arterial blood pressure (MAP) was decreased and heart rate (HR) was increased. These changes were associated with increased expression and/or activities of ribosomal protein S6, MEK1, ERK1/2, IKKβ, IκB-α and NF-κB p65, and NADPH oxidase system activity in cardiovascular and renal tissues. Rapamycin (1 mg/kg, i.p.), a selective mTOR inhibitor, reversed these zymosan-induced changes in these tissues. These observations suggest that activation of mTOR/MEK1/ERK1/2/IKKβ/IκB-α/NF-κB signalling pathway with proinflammatory and vasodilator mediator formation and NADPH oxidase system activity contributes to systemic inflammation in zymosan-induced non-septic shock. Thus, mTOR may be an optimal target for the treatment of the diseases characterized by the severe systemic inflammatory response.

Activation of mTOR/IκB-α/NF-κB pathway contributes to LPS-induced hypotension and inflammation in rats

Mammalian target of rapamycin (mTOR), a serine/threonine kinase plays an important role in various pathophysiological processes including cancer, metabolic diseases, and inflammation. Although mTOR participates in Toll-like receptor 4 signalling in different cell types, the role of this enzyme in sepsis pathogenesis and its effects on hypotension and inflammation in endotoxemic rats remains unclear. In this study we investigated the effects of mTOR inhibition on lipopolysaccharide (LPS)-induced changes on expressions and/or activities of ribosomal protein S6 (rpS6), an mTOR substrate, nuclear factor-κB (NF-κB) p65, inhibitor κB (IκB)-α, inducible nitric oxide synthase (iNOS), cyclooxygenase (COX)-2 with production of nitric oxide, peroxynitrite, prostacyclin, and tumor necrosis factor (TNF)-α and activity of myeloperoxidase (MPO), which results in hypotension and inflammation. Injection of LPS (10mg/kg, i.p.) to male Wistar rats decreased blood pressure and increased heart rate that were associated with elevated nitrotyrosine, 6-keto-PGF_1α, and TNF-α levels and MPO activity, and increased expressions and/or activities of rpS6, NF-κB p65, iNOS, and COX-2 and decreased expression of IκB-α in renal, cardiac, and vascular tissues. LPS also increased serum and tissue nitrite levels. Rapamycin (1mg/kg, i.p.) given one h after injection of LPS reversed these effects of LPS. These data suggest that the activation of mTOR/IκB-α/NF-κB pathway associated with vasodilator and proinflammatory mediator formation contributes to LPS-induced hypotension and inflammation.