Microglia-dependent neuroprotective effects of 4-octyl itaconate against rotenone-and MPP+-induced neurotoxicity in Parkinson's disease

Protective effects of harpagoside on mitochondrial functions in rotenone‑induced cell models of Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease after Alzheimer's disease. Currently, no radical treatment is available for this disease. Harpagoside is a proposed neuroprotective iridoid active ingredient that can be derived from Scrophulariae buergeriana, Scrophularia striata and Harpagophytum procumbens. The present study aimed to investigate the effects of harpagoside on mitochondrial functions in rotenone-induced cell models of Parkinson's disease (PD). Neuro-2A (N2A) cells were treated with rotenone to establish in vitro cell models of PD. Cell viability and survival were measured using a Cell Counting Kit-8 assay. Biochemical assays with spectrophotometry were used to measure complex I activity, mitochondrial swelling and caspase 3 activity. The cell survival rate was first found to be significantly decreased by rotenone (20 nmol/l) treatment. However, intervention with harpagoside (10 µmol/l) was found to increase the cell survival rate of rotenone-induced N2A cell models differentiated with 1 mmol/l of dibutyryl-cAMP. At ≥0.1 µmol/l concentration, harpagoside significantly alleviated rotenone-induced mitochondrial swelling, whereas at 1 µmol/l it significantly counteracted the inhibitory effects of rotenone on complex I activity. At 10 µmol/l harpagoside significantly inhibited rotenone-induced caspase 3 activation. These results suggest that harpagoside has the potential to protect mitochondrial functions against rotenone-induced injury in N2A cell models of PD.

Severity of Repetitive Mild Traumatic Brain Injury Depends on Microglial Heme Oxygenase-1 and Carbon Monoxide

Traumatic brain injury is one of the most common cerebral incidences worldwide. Repetitive mild traumatic brain injuries occurring, for example, in athletes or victims of abuse, can cause chronic neurodegeneration due to neuroinflammation, in which the crosstalk between reactive astrocytes and activated microglia is crucial for modulating neuronal damage. The inducible enzyme heme oxygenase-1 and its product carbon monoxide are known to be ascribed neuroprotective and anti-inflammatory properties. We caused repetitive mild traumatic brain injuries in wild-type mice compared to mice without microglial heme oxygenase-1 expression. Additionally, mice were treated daily with either air or carbon monoxide exogenously. In wild-type mice, we observed enhanced microglia activation and astrogliosis as well as vasodilation after repetitive trauma. In heme oxygenase-1 knockout mice, we observed enhanced activation of microglia and astrocytes at baseline pretrauma with a lack of an adequate inflammatory response to repetitive injury. However, the knockout led to enhanced NF-κB and IFNγ expression in the post-trauma period. Carbon monoxide exerted neuroprotection, as suggested by reduced wake-up times in mice and by beneficially altering inflammation post-traumatic brain injury. This study further underlines the crucial role of the heme oxygenase-1/carbon monoxide system in the modulation of neuronal damage and the associated neuroinflammatory response after repetitive traumatic brain injury.

Multitarget Effects of Nrf2 Signalling in the Brain: Common and Specific Functions in Different Cell Types

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a crucial regulator of cellular defence mechanisms, essential for maintaining the brain's health. Nrf2 supports mitochondrial function and protects against oxidative damage, which is vital for meeting the brain's substantial energy and antioxidant demands. Furthermore, Nrf2 modulates glial inflammatory responses, playing a pivotal role in preventing neuroinflammation. This review explores these multifaceted functions of Nrf2 within the central nervous system, focusing on its activity across various brain cell types, including neurons, astrocytes, microglia, and oligodendrocytes. Due to the brain's vulnerability to oxidative stress and metabolic challenges, Nrf2 is emerging as a key therapeutic target to enhance resilience against oxidative stress, inflammation, mitochondrial dysfunction, and demyelination, which are central to many neurodegenerative diseases.

Dimethyl itaconate modulates neuroprotective effect on primary rat astrocytes under inflammatory condition by regulating the expression of neurotrophic factors and TrkA/B-P75 receptors

INTRODUCTION

Astrocytes, specialized glial cells, are essential for maintaining the central nervous system homeostasis. Inflammatory conditions can disrupt neurotrophic factors and receptor expression in astrocytes, leading to potential central nervous system damage. Itaconate, recently identified for its anti-inflammatory properties, was investigated in this study for its effects on neurotrophic factors in LPS-stimulated primary rat astrocytes.

METHODS

Primary rat astrocyte cells were isolated from one-day-old Wistar rats and exposed to 1 µg/ml lipopolysaccharide (LPS) for 6 h to stimulate inflammation. The effect of DMI (62.5, 125, and 250 µM for 18 h) on the cell viability of astrocyte cells exposed to LPS was evaluated by the MTT assay. The effects of DMI on the mRNA and protein levels of NGF, BDNF, and GDNF were evaluated using ELISA and qRT-PCR assays. Protein and mRNA levels of neurotrophic factor receptors (TrkA, TrkB, and P75) were evaluated using qRT-PCR and Western blot analyses.

RESULTS

The results showed that DMI suppressed astrocytes cell death induced by LPS in a dose-dependent manner. DMI dose-dependently restored the reduced mRNA and protein levels of NGF, BDNF, GDNF, and TrkA and TrkB receptors in LPS-treated astrocytes, but it significantly decreased the p75 expression in the same condition.

CONCLUSION

In conclusion, DMI may be able to support astrocyte survival and functions based on the restoration of neurotrophic factors and their receptors expression in LPS-stimulated astrocyte cells. This suggests that DMI could be a promising therapeutic option for neurodegenerative diseases characterized by inflammation-induced astrocyte dysfunction.

The anti-inflammatory effects of itaconate and its derivatives in neurological disorders

Almost 16 % of the global population is affected by neurological disorders, including neurodegenerative and cerebral neuroimmune diseases, triggered by acute or chronic inflammation. Neuroinflammation is recognized as a common pathogenic mechanism in a wide array of neurological conditions including Alzheimer's disease, Parkinson's disease, postoperative cognitive dysfunction, stroke, traumatic brain injury, and multiple sclerosis. Inflammatory process in the central nervous system (CNS) can lead to neuronal damage and neuronal apoptosis, consequently exacerbating these diseases. Itaconate, an immunomodulatory metabolite from the tricarboxylic acid cycle, suppresses neuroinflammation and modulates the CNS immune response. Emerging human studies suggest that itaconate levels in plasma and cerebrospinal fluid may serve as biomarkers associated with inflammatory responses in neurological disorders. Preclinical studies have shown that itaconate and its highly cell-permeable derivatives are promising candidates for preventing and treating neuroinflammation-related neurological disorders. The underlying mechanism may involve the regulation of immune cells in the CNS and neuroinflammation-related signaling pathways and molecules including Nrf2/KEAP1 signaling pathway, reactive oxygen species, and NLRP3 inflammasome. Here, we introduce the metabolism and function of itaconate and the synthesis and development of its derivatives. We summarize the potential impact and therapeutic potential of itaconate and its derivatives on brain immune cells and the associated signaling pathways and molecules, based on preclinical evidence via various neurological disorder models. We also discuss the challenges and potential solutions for clinical translation to promote further research on itaconate and its derivatives for neuroinflammation-related neurological disorders.

Itaconate alleviates anesthesia/surgery-induced cognitive impairment by activating a Nrf2-dependent anti-neuroinflammation and neurogenesis via gut-brain axis

BACKGROUND

Postoperative cognitive dysfunction (POCD) is a common neurological complication of anesthesia and surgery in aging individuals. Neuroinflammation has been identified as a hallmark of POCD. However, safe and effective treatments of POCD are still lacking. Itaconate is an immunoregulatory metabolite derived from the tricarboxylic acid cycle that exerts anti-inflammatory effects by activating the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway. In this study, we investigated the effects and underlying mechanism of 4-octyl itaconate (OI), a cell-permeable itaconate derivative, on POCD in aged mice.

METHODS

A POCD animal model was established by performing aseptic laparotomy in 18-month-old male C57BL/6 mice under isoflurane anesthesia while maintaining spontaneous ventilation. OI was intraperitoneally injected into the mice after surgery. Primary microglia and neurons were isolated and treated to lipopolysaccharide (LPS), isoflurane, and OI. Cognitive function, neuroinflammatory responses, as well as levels of gut microbiota and their metabolites were evaluated. To determine the mechanisms underlying the therapeutic effects of OI in POCD, ML385, an antagonist of Nrf2, was administered intraperitoneally. Cognitive function, neuroinflammatory responses, endogenous neurogenesis, neuronal apoptosis, and Nrf2/extracellular signal-related kinases (ERK) signaling pathway were evaluated.

RESULTS

Our findings revealed that OI treatment significantly alleviated anesthesia/surgery-induced cognitive impairment, concomitant with reduced levels of the neuroinflammatory cytokines IL-1β and IL-6, as well as suppressed activation of microglia and astrocytes in the hippocampus. Similarly, OI treatment inhibited the expression of IL-1β and IL-6 in LPS and isoflurane-induced primary microglia in vitro. Intraperitoneal administration of OI led to alterations in the gut microbiota and promoted the production of microbiota-derived metabolites associated with neurogenesis. We further confirmed that OI promoted endogenous neurogenesis and inhibited neuronal apoptosis in the hippocampal dentate gyrus of aged mice. Mechanistically, we observed a decrease in Nrf2 expression in hippocampal neurons both in vitro and in vivo, which was reversed by OI treatment. We found that Nrf2 was required for OI treatment to inhibit neuroinflammation in POCD. The enhanced POCD recovery and promotion of neurogenesis triggered by OI exposure were, at least partially, mediated by the activation of the Nrf2/ERK signaling pathway.

CONCLUSIONS

Our findings demonstrate that OI can attenuate anesthesia/surgery-induced cognitive impairment by stabilizing the gut microbiota and activating Nrf2 signaling to restrict neuroinflammation and promote neurogenesis. Boosting endogenous itaconate or supplementation with exogenous itaconate derivatives may represent novel strategies for the treatment of POCD.

Fluoxetine attenuates stress-induced depression-like behavior due to decrease in pro-inflammatory cytokines in male rats

Background: Pro-inflammatory cytokines are implicated in depression caused by both environmental- and alcohol-induced stress. The purpose of the study was to investigate the cytokine levels in serum and hippocampus following induction of depression-like behaviors (DLB) by either forced swimming test (FST) or ethanol-induced DLB (EID). We also investigated the effect of prior administration of antidepressant drug fluoxetine on cytokines in animals exposed to both models of DLB. Methods: Animals were pretreated with fluoxetine before inducing DLB, while DLB was induced in some animals using FST and ethanol in different groups of rats without fluoxetine pretreatment. The ELISA was used to detect changes in cytokine (IL-1β, IL-6, and TNF-α) levels in serum and hippocampus. Results: The mean levels of IL-1β and IL-6 measured in serum and hippocampus were significantly higher in FST and EID models when compared to the control group. The serum concentrations of IL-1β and IL-6 were significantly reduced in animals pre-treated with 5 mg/kg and 10 mg/kg of fluoxetine in both FST and EID models when compared to the untreated FST and EID groups respectively. Conclusions: In conclusion, both environment and alcohol can induce stress and DLB in rats with similar intensity, and their mechanisms of DLB induction involve activation of pro-inflammatory cytokines. Moreover, fluoxetine can prevent stress-induced inflammation in models of DLB.