Ethanol-induced neurodegeneration is a growing concern in terms of chronic alcohol use which has been demonstrated to cause extensive damage to CNS. Alcohol use disorder remains a serious public health issue worldwide. Researchers have elucidated extensive mechanisms of alcohol-related neurodegeneration. From the generation of ROS to the activation of an inflammatory cascade in the CNS, alcohol acts to exert its neurotoxic effect on the body. Alcohol contributes to long-term cognitive deficits and neurodegenerative conditions such as alcohol-related dementias (Crews and Nixon, 2009). Various studies have examined the mechanisms behind alcohol-induced neurodegeneration, focusing on OS, apoptosis, and inflammation. Chronic ethanol consumption leads to significant neuronal loss and cognitive impairment, mediated by increased oxidative damage and neuroinflammation (Oscar-Berman and Marinkovic, 2003). Alcohol-induced neurodegeneration impacts various brain regions, leading to deficits in cognitive and motor functions (Crews et al., 2017). Literature has reported the negative impact of chronic ethanol use on memory and cognitive functions (Charlton and Perry, 2022). Findings of previous studies indicate that chronic ethanol consumption impairs various cognitive domains, including working memory, spatial navigation, and attention, due to neurochemical and structural brain changes (Stragier et al., 2015).
Our study demonstrates that chrysophanol protects the brain against alcohol-related neurodegenerations. The neuroprotective actions of chrysophanol are based on its ability to reduce oxidative stress and prevent the formation of ROS, hinder the activation of inflammatory pathways, and prevent apoptosis. Observations made on behavioral and tissue levels showed the positive effect of chrysophanol in mitigating alcohol-induced neurodegeneration. Our study investigates how chronic ethanol exposure leads to cognitive decline, focusing on memory impairments and executive dysfunction. Various mechanisms such as hippocampal damage, synaptic loss, and alterations in neurotransmitter systems, contribute to deficits in learning and memory. Key findings include deficits in memory consolidation and retrieval, along with impaired synaptic plasticity and neurodegeneration in the hippocampus. Long-term effects of chronic ethanol exposure on cognitive function, particularly memory, and learning have been established. Sustained alcohol use leads to remarkable cognitive impairments, including deficits in episodic memory and spatial learning, which are associated with structural and functional alterations in the brain. The behavioral results of this study including NOR Y-MAZE and MWZ tests analyzed cognitive deficit and memory impairment in mice. Results have shown remarkable recovery in chrysophanol-treated mice's cognitive decline and spatial memory. The formation of ROS is one of the major factors contributing to ethanol-induced neurodegeneration (Afzal et al., 2023). ROS plays a central role in ethanol-induced neurodegeneration. The research demonstrates that chronic ethanol exposure leads to elevated ROS levels, which contribute to neuronal damage through oxidative stress, inflammation, and apoptosis. Various mechanisms by which ROS mediate neurodegeneration and potential interventions to mitigate these effects. Key mechanisms include oxidative stress, activation of glial cells, and disruption of neurovascular integrity (Karoly et al., 2021). Chrysophanol has a remarkable impact in preventing damage related to ROS. Results of this study have shown that chrysophanol meticulously enhanced the antioxidant defense system and reduced the level of oxidant production. Results of our study show that chrysophanol significantly reduces ROS production and enhances antioxidant enzyme activity, suggesting its potential as a protective agent against oxidative damage. These findings follow the reports of Zhao and coworkers who explored the defensive effects of chrysophanol against oxidative stress, focusing on its role in reducing oxidant production (Zhao et al., 2018). The results show that chrysophanol reduces ROS production and modulates oxidative stress pathways, highlighting its capacity as an anti-inflammatory and antioxidant agent as supported by the previous findings.
Chrysophanol was also found to activate the Nrf2 pathway and increase the production of antioxidant enzymes such as GSH, GST, and CAT to strengthen the antioxidant defense system. Chrysophanol also decreases the production of oxidants such as MDA and NO to prevent further damage This study explores how chrysophanol activates the Nrf2 pathway, leading to enhanced cellular defense against oxidative stress. Our results show that chrysophanol induces Nrf2 translocation to the nucleus, increasing the expression of antioxidant enzymes and reducing oxidative damage in cellular models. Findings indicate that chrysophanol activates Nrf2, which in turn upregulates the expression of antioxidant and detoxifying enzymes, thereby mitigating oxidative stress and protecting neuronal cells from damage. The study provides evidence that chrysophanol enhances Nrf2 expression and its downstream targets, contributing to reduced cellular damage and improved antioxidant defense. These results are strengthened by the previously published studies by various researchers (Wen et al., 2021) (Ma et al., 2021).
Alcohol consumption has detrimental effects on the histology of both the hippocampus and cortex of the brain typically involved in cognitive and behavioral functions reported by researchers (Mira et al., 2020) (Moreira-Júnior et al., 2023). (Goldowitz et al., 2014). Alcohol consumption leads to neurotoxic effects in the hippocampus and cortex including shrinkage of the hippocampus and cortical thinning, contributing to cognitive deficits and impaired brain function. (Zahr and Pfefferbaum, 2017). (Geil et al., 2014).
Our result showed that chrysophanol protects the number of survival neurons in different regions of the brain (cortex and hippocampus). H&E staining of brain regions of ethanol treated group has shown extensive neuronal loss in the hippocampus, particularly in the CA1 and CA3 dentate gyrus and cortex. Chrysophanol treatment was successfully able to reverse this neuronal damage with reduced inflammation in these brain regions suggesting the amelioration of neuroinflammation.
Ethanol consumption activates the microglia in the hippocampus and causes the activation of the NFkB pathway by activating TLRs. Chronic ethanol exposure leads to microglial activation in the hippocampus, which in turn triggers the NF-κB, signaling through the activation of TLRs (Li et al., 2019).This activation leads to downstream activation of NF-κB and the production of pro-inflammatory cytokines contributing to neuroinflammation and neurodegeneration (Vetreno and Crews, 2015). Ethanol is also associated with reduced Nrf2 activity and contributes to neuronal stress. (Chen et al., 2013). The decreased Nrf2 activity leads to impaired antioxidant defenses, resulting in increased oxidative stress and neuronal damage(Shanmugam et al., 2019, Chen et al., 2013). Restoring Nrf2 activity through pharmacological intervention can reduce ethanol-induced neuronal stress and protect against cognitive decline. HO-1 is an enzyme regulated by NRF-2 that plays a role in the breakdown of heme into biliverdin, free iron, and carbon monoxide, which have antioxidant and anti-inflammatory properties (Young et al., 2003, Moon et al., 2013). Ethanol consumption also causes the activation of Caspase-3 leads to apoptotic cell death in neurons, contributing to the loss of neuronal populations in the hippocampus and cortex.
Our experimental Results of PCR for mRNA expression of TLR4, NFκB, IL-1β, TNF-α, Caspase-3 Nrf2 and HO-1 in the hippocampus and cortex have shown the effective role of chrysophanol in reducing the effects of these inflammatory and apoptotic gene expressions. COX-2 contributes to neuroinflammation through the formation of prostaglandins and ROS, while the NLRP3 inflammasome promotes the activation of pro-inflammatory cytokines like IL-1β. The interplay between these molecules amplifies the inflammatory response, leading to sustained neuroinflammation, oxidative stress, and ultimately, neuronal death. ELISA Results of Chrysophanol-treated groups have been shown to reduce the level of COX-2 and NLRP3 levels and mitigate inflammation.
Results of the comet assay showed that ethanol had increased tail length with increased percent of DNA in the tail. It may be caused by oxidative stress, impaired apoptotic process, and impaired DNA repair. Ethanol exposure leads to increased levels of inflammatory cytokines and markers of DNA damage in both the hippocampus and cortex, suggesting a link between inflammation and DNA damage. Moreover, the chrysophanol-treated group effectively managed to reduce tail length and was involved in the DNA repair process. Overall, this study demonstrates that chrysophanol has remarkable neuroprotective properties and is found effective in reversing ethanol-induced neurodegeneration. Chrysophanol has shown potential in mitigating DNA damage in the hippocampus through its antioxidant properties, enhancement of DNA repair mechanisms, and overall neuroprotective effects. These findings also follow previously reported data by (Crews and Nixon, 2009). This study highlights the ability of chrysophanol to reduce oxidative stress, improve DNA repair, and protect against neuronal damage, making it a promising candidate against ethanol-induced neurodegeneration.