Icariin Improves Cognitive Impairment after Traumatic Brain Injury by Enhancing Hippocampal Acetylation

Molecular mechanisms and therapeutic potential of icariin in the treatment of Alzheimer's disease

BACKGROUND

Icariin (ICA) is the main active component of Epimedium, a traditional Chinese medicine (TCM), known to enhance cognitive function in Alzheimer's disease (AD). This study aims to investigate and summarize the mechanisms through which ICA treats AD.

METHODS

The PubMed and CNKI databases were utilized to review the advancements in ICA's role in AD prevention and treatment by analyzing literature published between January 2005 and April 2023. To further illustrate ICA's impact on AD development, tables, and images are included to summarize the relationships between various mechanisms.

RESULTS

The study reveals that ICA ameliorates cognitive deficits in AD model mice by modulating Aβ via multiple pathways, including BACE-1, NO/cGMP, Wnt/Ca²⁺, and PI3K/Akt signaling. ICA exhibits neuroprotective properties by inhibiting neuronal apoptosis through the suppression of ER stress in AD mice, potentially linked to NF-κB, MAPK, ERK, and PERK/Eif2α signaling pathways. Moreover, ICA may safeguard neurons by attenuating mitochondrial oxidative stress injury. ICA can also enhance learning, memory, and cognition by improving synaptic structure via regulation of the PSD-95 protein. Furthermore, ICA can mitigate neuroinflammation by inactivating microglial activity through the upregulation of PPARγ, TAK1/IKK/NF-κB, and JNK/p38 MAPK signaling pathways.

CONCLUSION

This study indicates that ICA possesses multiple beneficial effects in AD treatment. Through the integration of pharmacological and molecular biological research, ICA may emerge as a promising candidate to expedite the advancement of TCM in the clinical management of AD.

Improvements of cognitive functions in mice heavily infected by Angiostrongylus cantonensis after treatment with albendazole, dexamethasone, or co-therapy

Angiostrongylus cantonensis, the causative agent of human eosinophilic meningitis and eosinophilic meningoencepalitis, has been reported to cause cognitive impairments in the host. To determine whether drug treatment improves the cognitive functions, BALB/c mice infected with 50 third-stage larvae were treated with albendazole, dexamethasone, or co-therapy since day 7 or 14 post-infection for one or two weeks. Abilities of spatial memory and learning of these animals were assessed with the Morris water maze. Our results showed that body weight was significant higher then infected group in the albendazole and combined therapy groups. Significantly lower worm recovery rates were found in mice treated with the same groups. The mice treated with dexamethasone since day 7 for 14 day had significant longer time in the remaining groups were found in forced swimming test. The animals treated with albendazole and combined therapy since day 7 for 14 days was demonstrated to have significantly shorter latencies to the platform in learning memory on day 3 and 4. Mice in these two groups were demonstrated to have significantly higher sores in spatial memory tests. These results indicate that treatment with albendazole or combined therapy may be more efficient in preventing brain damages and depression as well as preserving their capabilities in learning and memory. Therefore, administration of albendazole alone or combined with dexamethasone should have higher efficacies than dexamethasone alone in treatment of BALB/c mice infected with a heavy dose of 50 third-stage larvae of A. cantonensis.

Intradermal injection of icariin-HP-β-cyclodextrin improved traumatic brain injury via the trigeminal epineurium-brain dura pathway

The lower bioavailability after oral administration limited icariin applications in Central Nervous System. Icariin/HP-β-cyclodextrin (HP-β-CD) inclusion complex was prepared for acute severe opening traumatic brain injury (TBI) via facial intradermal(i.d.) in mystacial pad. After fluid percussion-induced TBI, icariin/HP-β-CD at 0.4 mg/kg i.d. preserved more neurons and oligodendrocytes than intranasal injection (i.n.) or intravenous injection via tail vein (i.v.) and decreased microglia and astrocyte activation. Icariin/HP-β-CD i.d. reduced apoptosis in cortical penumbra while i.n. and i.v. showed weak or no effects. Icariin/HP-β-CD i.d. reduced Evans blue leakage and altered CD34, ZO-1, Claudin-5 and beta-catenin expression after TBI. Moreover, icariin/HP-β-CD promoted human umbilical vein endothelial cells proliferation. Thus, Icariin/HP-β-CD i.d. improved TBI, including blood brain barrier opening. Fluorescein 5-isothiocyanate (FITC) and 3,3'-Dioctadecyloxacarbocyanine perchlorate (DiOC18(3)) mimic HP-β-CD and icariin respectively. FITC and DiOC18(3) were similarly delivered to trigeminal epineurium, perineurium and perivascular spaces or tissues, caudal dura mater and scattered in trigeminal fasciculus, indicating that icariin/HP-β-CD was delivered to brain via trigeminal nerve-dura mater-brain pathways. In sum, intradermal injection in mystacial pad might delivered icariin/HP-β-CD to brain and icariin/HP-β-CD improved acute severe opening TBI.

Icariin improves brain function decline in aging rats by enhancing neuronal autophagy through the AMPK/mTOR/ULK1 pathway

CONTEXT

Icariin (ICA) is the main active ingredient of Epimedium brevicornu Maxim (Berberidaceae), which is used in the immune, reproductive, neuroendocrine systems, and anti-aging.

OBJECTIVE

To evaluate the effect of ICA on natural aging rat.

MATERIALS AND METHODS

16-month-old Sprague-Dawley (SD) rats were randomly divided into aging, low and high-dose ICA groups (n = 8); 6-month-old rats were taken as the adult control (n = 8). Rats were fed regular feed (aging and adult control) or feed containing ICA (ICA 2 and 6 mg/kg group) for 4 months. HE and Nissl staining were used to assess pathological changes. Western blot was used to test the expression of autophagy (LC3B, p62, Atg5, Beclin1) and p-AMPK, p-mTOR and p-ULK1 (ser 757). Immunofluorescence was used to detect the co-localization of LC3 and neurons.

RESULTS

ICA improved neuronal degeneration associated with aging and increased the staining of Nissl bodies. Western blot showed that ICA up-regulated autophagy-related proteins LC3B (595%), Beclin1 (73.5%), p-AMPK (464%) protein (p < 0.05 vs. 20 M) in the cortex and hippocampus of aging rats, down-regulated the expression of p62 (56.9%), p-mTOR (53%) and p-ULK1 (ser 757) (65.4%) protein (p < 0.05 vs. 20 M). Immunofluorescence showed that the fluorescence intensity of LC3 decreased in the aging rat brain, but increased and mainly co-localized with neurons after ICA intervention.

CONCLUSIONS

Further research needs to verify the expression changes of AMPK/mTOR/ULK1 and the improvement effect of ICA in elderly. These results will further accelerate the applications of ICA and the treatment for senescence.

Angiostrongylus cantonensis causes cognitive impairments in heavily infected BALB/c and C57BL/6 mice

Background

Parasitic infections may cause significant effects on behavior, learning, and memory of the host. In the brain of mice heavily infected with Angiostrongylus cantonensis, severe damage has been observed in the hippocampus. This component has been considered to have associations with spatial learning and memory in humans and vertebrates. This study was designed to determine the impairments in behavior, learning, and memory in BALB/c and C57BL/6 mice heavily infected with the parasite.

Methods

Each mouse was inoculated with 50 third-stage larvae of A. cantonensis. After infection, daily changes in weight and dietary consumption, worm recoveries and survival rates were determined. The forced swimming test, open field test, and Morris water maze test were employed to evaluate depression- and anxiety-like behavior as well as impairments in spatial learning and memory, respectively.

Results

The worm recovery rate in the BALB/c mice was significantly lower than that of C57BL/6 mice from day 14 post-infection. The survival rate in infected BALB/c mice decreased to 0% by day 25 whereas those with swim-training survived three more days. On day 42, the C57BL/6 mice had a survival rate of 85.7% in the swimming group and 70% in the non-swimming group. Significant differences were found in weight between infected and non-infected BALB/c and C57BL/6 mice from day 13 and day 12, respectively with corresponding changes in their dietary consumption. Depression-like behavior was found in the infected BALB/c mice but not in C57BL/6 mice. However, anxiety-like behavior was found to occur only in C57BL/6 mice. Impaired spatial learning and memory were also found in the two strains of mice which occurred from day 14 post-infection.

Conclusions

Results of this study indicate that A. cantonensis causes depression, anxiety, and impairments in spatial learning and memory in heavily infected mice. Moreover, significantly higher severity was observed in the Th-2 dominant BALB/c mice.

Icariin sustains the proliferation and differentiation of Aβ25-35-treated hippocampal neural stem cells via the BDNF-TrkB-ERK/Akt signaling pathway

OBJECTIVES

Icariin (ICA) can be potentially used to treat Alzheimer's disease (AD), but the mechanism was not clear. The current study explored the effects of ICA on hippocampal neural stem cells, aiming to provide a comprehensive basis for its clinical application.

METHODS

Hippocampal neural stem cells were isolated from newborn rats and their differentiation ability was evaluated by performing immunofluorescence staining. Next, Aβ cell model was constructed by treating the cells with Aβ_25-35, and then the model was further treated by ICA or shBDNF or the two in combination. The viability and differentiation of the cells were, respectively, analyzed by 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-Diphenyltetrazolium Bromide (MTT) and flow cytometry. The expression of BDNF-TrkB-ERK/Akt signaling pathway was assessed by quantitative real-time polymerase chain reaction (qRT-PCR) or Western blot (WB).

RESULTS

The hippocampal neural stem cells can differentiate into neurons and astrocytes. ICA effectively promoted the viability and differentiation of Aβ cell models. The expression levels of BDNF and TrkB in Aβ cell models were obviously decreased, which were noticeably increased by ICA. Moreover, BDNF knockdown further inhibited the viability and differentiation of Aβ model cells, which could be reversed by ICA. BDNF knockdown not only suppressed the expressions of BDNF and TrkB in Aβ cell models but also effectively prevented the phosphorylation of ERK/Akt; however, these phenomena were significantly alleviated by ICA treatment.

DISCUSSION

ICA promoted the proliferation and differentiation of Aβ_25-35-treated hippocampal neural stem cells through BDNF-TrkB-ERK/Akt signaling pathway. The current findings might contribute to the treatment of AD.

An outline for the pharmacological effect of icariin in the nervous system

Icariin is a major active component of the traditional herb Epimedium, also known as Horny Goat Weed. It has been extensively studied throughout the past several years and is known to exert anti-oxidative, anti-neuroinflammatory, and anti-apoptotic effects. It is now being considered as a potential therapeutic agent for a wide variety of disorders, ranging from neoplasm to cardiovascular disease. More recent studies have shown that icariin exhibits potential preventive and/or therapeutic effects in the nervous system. For example, icariin can prevent the production of amyloid β (1-42) and inhibit the expression of amyloid precursor protein (APP) and β-site APP cleaving enzyme 1 (BACE-1) in animal models of Alzheimer's disease (AD). Icariin has been shown to mitigate pro-inflammatory responses of microglia in culture and in animal models of cerebral ischemia, depression, Parkinson's disease (PD), and multiple sclerosis (MS). Icariin also prevents the neurotoxicity induced by hydrogen peroxide (H₂O₂), endoplasmic reticulum (ER) stress, ibotenic acid, and homocysteine. In addition, icariin is implicated in facilitating learning and memory in both normal aging animals and disease models. To date, we still have no consolidated source of knowledge about the pharmacological effects of icariin in the nervous system, though its roles in other tissues have been reviewed in recent years. Here, we summarize the pharmacological development of icariin as well as its possible mechanisms in prevention and/or therapy of disorders afflicting the nervous system in hope of expanding the knowledge about the preventive and/or therapeutic effect of icariin in brain disorders.

The Regulatory Effects of Acetyl-CoA Distribution in the Healthy and Diseased Brain

Brain neurons, to support their neurotransmitter functions, require a several times higher supply of glucose than non-excitable cells. Pyruvate, the end product of glycolysis, through pyruvate dehydrogenase complex reaction, is a principal source of acetyl-CoA, which is a direct energy substrate in all brain cells. Several neurodegenerative conditions result in the inhibition of pyruvate dehydrogenase and decrease of acetyl-CoA synthesis in mitochondria. This attenuates metabolic flux through TCA in the mitochondria, yielding energy deficits and inhibition of diverse synthetic acetylation reactions in all neuronal sub-compartments. The acetyl-CoA concentrations in neuronal mitochondrial and cytoplasmic compartments are in the range of 10 and 7 μmol/L, respectively. They appear to be from 2 to 20 times lower than acetyl-CoA Km values for carnitine acetyltransferase, acetyl-CoA carboxylase, aspartate acetyltransferase, choline acetyltransferase, sphingosine kinase 1 acetyltransferase, acetyl-CoA hydrolase, and acetyl-CoA acetyltransferase, respectively. Therefore, alterations in acetyl-CoA levels alone may significantly change the rates of metabolic fluxes through multiple acetylation reactions in brain cells in different physiologic and pathologic conditions. Such substrate-dependent alterations in cytoplasmic, endoplasmic reticulum or nuclear acetylations may directly affect ACh synthesis, protein acetylations, and gene expression. Thereby, acetyl-CoA may regulate the functional and adaptative properties of neuronal and non-neuronal brain cells. The excitotoxicity-evoked intracellular zinc excess hits several intracellular targets, yielding the collapse of energy balance and impairment of the functional and structural integrity of postsynaptic cholinergic neurons. Acute disruption of brain energy homeostasis activates slow accumulation of amyloid-β_1-42 (Aβ). Extra and intracellular oligomeric deposits of Aβ affect diverse transporting and signaling pathways in neuronal cells. It may combine with multiple neurotoxic signals, aggravating their detrimental effects on neuronal cells. This review presents evidences that changes of intraneuronal levels and compartmentation of acetyl-CoA may contribute significantly to neurotoxic pathomechanisms of different neurodegenerative brain disorders.