NLRP3 inflammasome in depression: A review

The present article provides a detailed concept of the role of NLRP3 inflammasome in the pathophysiology of depression-like chronic diseases where inflammation and release of various cytokines plays a pivotal role in exaggerating the condition. The various pathways involved in NLRP3 activation are the main target of NLRP3 inhibitors for the therapeutic management of depression as per the recent clinical and research studies conducted so far. Further various drug inhibitors for NLRP3 available in preclinical and clinical trials have been discussed in detail. Hence, blockage of the action of NLRP3 inflammasome is crucial to anticipate the inflammatory cytokine release from the mediators that contributes to cause depression.

Liquiritin Alleviates Depression-Like Behavior in CUMS Mice by Inhibiting Oxidative Stress and NLRP3 Inflammasome in Hippocampus

Objective

Central inflammation is generally accepted to be involved in the pathology of depression. We investigated whether liquiritin exerts antidepressant effects by inhibiting central NLRP3 inflammasomes.

Results

The behavioral despair model and chronic unpredictable mild stress (CUMS) model in mice were established to evaluate the antidepressant action of liquiritin. In the despair model study, liquiritin (40 mg/kg) administration reduced immobility time in tail suspension test (TST) and forced swimming test (FST) without affecting locomotion activity. In CUMS model study, liquiritin (40 mg/kg, once daily for 4 weeks) significantly increased sucrose consumption and body weight of CUMS mice. The behavioral experiment results showed that liquiritin reduced the immobile time of CUMS mice in TST and FST, respectively, and increased the time spent and open arm entries in the elevated plus-maze (EPM) test. Further, the hippocampal superoxide dismutase (SOD) activity was increased in liquiritin-treated group, while malonaldehyde (MDA) decreased. Additionally, the hippocampal cytokines interleukin-18 (IL-18) and interleukin-1 beta (IL-1β) contents were reduced in the liquiritin-treated group. Further, liquiritin downregulated the expression of NLRP3 in the hippocampus of CUMS mice rather than TLR4. Besides, NLRP3 inflammasome-associated proteins caspase-1 and ASC were also downregulated. However, liquiritin did not alter the thermal stability of NLRP3 in the cellular thermal shift assay (CETSA), suggesting that its inhibition of NLPR3 was not by direct targeting of NLRP3 protein.

Conclusions

Liquiritin attenuates depression-like behavior of CUMS mice and inhibited cytokines levels triggered by NLRP3 inflammasome, suggesting the antidepressant action is, at least partially, associated with antioxidant stress and inhibition of NLRP3 inflammasome activation.

Ginsenoside Rg1 attenuates chronic unpredictable mild stress-induced depressive-like effect via regulating NF-κB/NLRP3 pathway in rats

Ginsenoside (GS Rg1), which has neuroprotection and anti-inflammation activities, is the main active ingredient of Radix Ginseng. However, its antidepressant-like effect in rats remains unclear. Our study was conducted to investigate whether GS Rg1 confers an antidepressant effect in rats exposed to a chronic unpredictable mild stress model of depression and to explore its possible mechanisms. Our results revealed that GS Rg1 treatments for 3 weeks alleviated the depression-related behaviors of chronic unpredictable mild stress-exposed rats, as indicated by increasing sucrose preference, improving locomotor activity and shortening immobile time in both the forced swimming tests and tail suspension tests. And these ameliorative effects of GS Rg1 treatment were involved with regulating chronic unpredictable mild stress-induced pro-inflammatory cytokine interleukin beta (IL-1β) related neuro-inflammation. In addition, we further found that GS Rg1 reversed chronic unpredictable mild stress-induced IL-1β elevation, possibly by inhibiting nuclear factor kappa B pathway activation and regulating nucleotide binding and oligomerization domain-like receptor family pyrin domain-containing 3 inflammasome expression. In short, our results suggested that GS Rg1 exerted a potential antidepressant-like effect in chronic unpredictable mild stress rat model of depression, which may provide an insight into the potential of GS Rg1 in therapeutic implications for depression.

Antidepressant-like Effects Induced by Chronic Blockade of the Purinergic 2X7 Receptor through Inhibition of Non-like Receptor Protein 1 Inflammasome in Chronic Unpredictable Mild Stress Model of Depression in Rats

Objective

Purinergic 2X7 receptor (P2X7R) activation is known to be involved in pathogenesis of depression. Our aims were to investigate P2X7R-activated inflammasome pathways in parallel with induction of depression and to test the antidepressant-like effects of the selective P2X7R antagonist Brilliant Blue G (BBG) in a rat model of chronic unpredictable mild stress (CUMS).

Methods

Male Wistar albino rats were divided into control, CUMS, CUMS+BBG25 (25 mg/kg/day) and CUMS+BBG50 (50 mg/kg/day) groups (n=10 for each group). Various stressors were applied to rats for 6 weeks to establish the CUMS model and daily BBG treatment was started at the end of 3rd week. Sucrose preference test and forced swim test (FST) were performed to assess antidepressant-like effects. Brain samples were obtained for real-time polymerase chain reaction and immunohistochemistry analysis.

Results

In FST, duration of immobility was reduced in the CUMS+BBG50 group. Also, BBG treatment significantly enhanced sucrose preference. While NLRP3 gene expression levels were unchanged in rats exposed to the CUMS protocol, expression levels of other inflammasome pathway factors NLRP1, caspase-1, ASC, NF-κB, IL-1β, IL-6 and P2X7R were increased. BBG treatment reduced expression levels of these factors. Likewise, Iba-1 and GFAP immunoreactivities were enhanced by the CUMS protocol and this action was reversed by BBG treatment.

Conclusion

Chronic administration of BBG in CUMS model results in antidepressant-like activity in a dose dependent manner. Molecular and histological results show that these effects might be at least partially related to the suppression of inflammasome-related neuroinflammatory responses and suggest involvement of NLRP1 in depression.

Perilla aldehyde attenuates CUMS-induced depressive-like behaviors via regulating TXNIP/TRX/NLRP3 pathway in rats

BACKGROUND

Current evidence supports that inflammatory reaction in the hippocampus is a potential cause of major depressive disorder (MDD). Perilla aldehyde (PAH), a major constituent from Perilla frutescens, has been reported to have anti-inflammatory and anti-oxidant activity. The aim of this study is to explore the antidepressant-like effect and the underlying mechanism of PAH on the rats model induced by chronic unpredictable mild stress (CUMS).

METHODS

CUMS rats model was built to tested their depressive-like behaviors. The levels of pro-inflammatory cytokines were tested. Proteins were analyzed by Western blot and Immunohistochemistry.

RESULTS

We found that treatment with PAH (20, 40 mg/kg) and fluoxetine (FLU, 10 mg/kg) significantly improved the sucrose consumption, immobility time in forced swim test (FST), as well as locomotor activity in open-field test (OFT). The levels of pro-inflammatory cytokines in hippocampus were also suppressed effectively by PAH and FLU administration. Western blot analysis showed the up-regulated levels of TXNIP, NLRP3, Cleaved caspase-1 and p-NF-κB p65 in the hippocampus in rats exposed to CUMS paradigm, while different degrees of down-regulation in their expression were detected after PAH (20, 40 mg/kg) and FLU (10 mg/kg) treatment respectively. The results from histopathological examination further demonstrated that PAH (20, 40 mg/kg) and FLU (10 mg/kg) treatment reversed the alteration of TRX, NLRP3 and Cleaved caspase-1 induced by CUMS procedure.

CONCLUSIONS

Our results demonstrated that PAH exhibited antidepressant-like effect in CUMS-induced rats model of depression, which might be mediated by TXNIP/TRX/NLRP3 pathway.

Geraniol produces antidepressant-like effects in a chronic unpredictable mild stress mice model

Geraniol (GE), which has neuroprotection and anti-inflammation activities, is mostly abundant in the essential oils of rose, ginger, lemon, orange, lavender etc. However, its antidepressant-like effect has not been reported before. The present study was designed to investigate whether GE confers an antidepressant effect in mice exposed to a chronic unpredictable mild stress (CUMS) model of depression and to explore its possible mechanisms. The results showed that GE treatments for 3 weeks significantly alleviated the depression-related behaviors of CUMS-exposed mice, as indicated by restored decreased sucrose preference and shortened immobile time in both the forced swimming tests (FST) and tail suspension tests (TST). And these ameliorative effects of GE treatment were involved with regulating CUMS-induced pro-inflammatory cytokine interleukin-1 beta (IL-1β) related neuro-inflammation. We further found that GE treatment reversed CUMS-induced IL-1β elevation, possibly by inhibiting nuclear factor kappa B (NF-κB) pathway activation and regulating nucleotide binding and oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome expression. Taken together, our findings suggested that GE exerted a potential antidepressant-like effect in CUMS mice model of depression, which may provide an insight into the potential of GE in therapeutic implications for depression.