Apigenin attenuates LPS-induced neurotoxicity and cognitive impairment in mice via promoting mitochondrial fusion/mitophagy: role of SIRT3/PINK1/Parkin pathway

Repositioning of baricitinib for management of memory impairment in ovariectomized/D-galactose treated rats: A potential role of JAK2/STAT3-PI3K/AKT/mTOR signaling pathway

AIMS

Neuroinflammation plays a pivotal role in amyloid β (Aβ) plaques formation which is among the hallmarks of Alzheimer's disease (AD). The present study investigated the potential therapeutic effects of baricitinib (BAR), a selective JAK2/ STAT3 inhibitor, in ovariectomized/ D-galactose (OVX/D-gal) treated rats as a model for AD.

MAIN METHODS

To induce AD, adult female rats (130-180 g) underwent bilateral ovariectomy and were injected daily with 150 mg/kg, i.p. D-gal for 8 consecutive weeks. BAR (10 and 50 mg/kg/day) was then given orally for 14 days.

KEY FINDINGS

BAR in a dose-dependent effect mitigated OVX/D-gal-induced aberrant activation of JAK2/STAT3 signaling pathway resulting in significant decreases in the expression of p-JAK 2, and p-STAT3 levels, along with deactivating AKT/PI3K/mTOR signaling as evidenced by deceased protein expression of p-AKT, p-PI3K, and p-mTOR. As a result, neuroinflammation was diminished as evidenced by decreased NF-κβ, TNF-α, and IL-6 levels. Moreover, oxidative stress biomarkers levels as iNOS, and MDA were reduced, whereas GSH was increased by BAR. BAR administration also succeeded in reverting histopathological alterations caused by OVX/D-gal, increased the number of intact neurons (detected by Nissl stain), and diminished astrocyte hyperactivity assessed as GFAP immunoreactivity. Finally, treatment with BAR diminished the levels of Aβ. These changes culminated in enhancing spatial learning and memory in Morris water maze, and novel object recognition test.

SIGNIFICANCE

BAR could be an effective therapy against neuroinflammation, astrogliosis and cognitive impairment induced by OVX/ D-gal where inhibiting JAK2/STAT3- AKT/PI3K/mTOR seems to play a crucial role in its beneficial effect.

Effectiveness of Flavonoid-Rich Diet in Alleviating Symptoms of Neurodegenerative Diseases

Over the past decades, there has been a significant increase in the burden of neurological diseases, including neurodegenerative disorders, on a global scale. This is linked to a widespread demographic trend in which developed societies are aging, leading to an increased proportion of elderly individuals and, concurrently, an increase in the number of those afflicted, posing one of the main public health challenges for the coming decades. The complex pathomechanisms of neurodegenerative diseases and resulting varied symptoms, which differ depending on the disease, environment, and lifestyle of the patients, make searching for therapies for this group of disorders a formidable challenge. Currently, most neurodegenerative diseases are considered incurable. An important aspect in the fight against and prevention of neurodegenerative diseases may be broadly understood lifestyle choices, and more specifically, what we will focus on in this review, a diet. One proposal that may help in the fight against the spread of neurodegenerative diseases is a diet rich in flavonoids. Flavonoids are compounds widely found in products considered healthy, such as fruits, vegetables, and herbs. Many studies indicated not only the neuroprotective effects of these compounds but also their ability to reverse changes occurring during the progression of diseases such as Alzheimer's, Parkinson's and amyotrophic lateral sclerosis. Here, we present the main groups of flavonoids, discussing their characteristics and mechanisms of action. The most widely described mechanisms point to neuroprotective functions due to strong antioxidant and anti-inflammatory effects, accompanied with their ability to penetrate the blood-brain barrier, as well as the ability to inhibit the formation of protein aggregates. The latter feature, together with promoting removal of the aggregates is especially important in neurodegenerative diseases. We discuss a therapeutic potential of selected flavonoids in the fight against neurodegenerative diseases, based on in vitro studies, and their impact when included in the diet of animals (laboratory research) and humans (population studies). Thus, this review summarizes flavonoids' actions and impacts on neurodegenerative diseases. Therapeutic use of these compounds in the future is potentially possible but depends on overcoming key challenges such as low bioavailability, determining the therapeutic dose, and defining what a flavonoid-rich diet is and determining its potential negative effects. This review also suggests further research directions to address these challenges.

Sirtuins as Players in the Signal Transduction of Citrus Flavonoids

Sirtuins (SIRTs) belong to the family of nicotine adenine dinucleotide (NAD+)-dependent class III histone deacetylases, which come into play in the regulation of epigenetic processes through the deacetylation of histones and other substrates. The human genome encodes for seven homologs (SIRT1-7), which are localized into the nucleus, cytoplasm, and mitochondria, with different enzymatic activities and regulatory mechanisms. Indeed, SIRTs are involved in different physio-pathological processes responsible for the onset of several human illnesses, such as cardiovascular and neurodegenerative diseases, obesity and diabetes, age-related disorders, and cancer. Nowadays, it is well-known that Citrus fruits, typical of the Mediterranean diet, are an important source of bioactive compounds, such as polyphenols. Among these, flavonoids are recognized as potential agents endowed with a wide range of beneficial properties, including antioxidant, anti-inflammatory, hypolipidemic, and antitumoral ones. On these bases, we offer a comprehensive overview on biological effects exerted by Citrus flavonoids via targeting SIRTs, which acted as modulator of several signaling pathways. According to the reported studies, Citrus flavonoids appear to be promising SIRT modulators in many different pathologies, a role which might be potentially evaluated in future therapies, along with encouraging the study of those SIRT members which still lack proper evidence on their support.

Protective effects of apigenin on the brain transcriptome with aging

Brain aging is associated with reduced cognitive function that increases the risk for dementia. Apigenin is a bioactive plant compound that inhibits cellular aging processes and could protect against age-related cognitive dysfunction, but its mechanisms of action in the brain have not been comprehensively studied. We characterized brain transcriptome changes in young and old mice treated with apigenin in drinking water. We observed improved learning/memory in old treated mice, and our transcriptome analyses indicated that differentially expressed genes with aging and apigenin were primarily related to immune responses, inflammation, and cytokine regulation. Moreover, we found that genes/transcripts that were increased in old vs. young mice but downregulated with apigenin treatment in old animals were associated with immune activation/inflammation, whereas transcripts that were reduced with aging but increased with apigenin were related neuronal function and signaling. We also found that these transcriptome differences with aging and apigenin treatment were driven in part by glial cells. To follow up on these in vivo transcriptome findings, we studied aged astrocytes in vitro, and we found that apigenin reduced markers of inflammation and cellular senescence in these cells. Collectively, our data suggest that apigenin may protect against age-related cognitive dysfunction by suppressing neuro-inflammatory processes.

Targeting NAD Metabolism for the Therapy of Age-Related Neurodegenerative Diseases

As the aging population continues to grow rapidly, age-related diseases are becoming an increasing burden on the healthcare system and a major concern for the well-being of elderly individuals. While aging is an inevitable process for all humans, it can be slowed down and age-related diseases can be treated or alleviated. Nicotinamide adenine dinucleotide (NAD) is a critical coenzyme or cofactor that plays a central role in metabolism and is involved in various cellular processes including the maintenance of metabolic homeostasis, post-translational protein modifications, DNA repair, and immune responses. As individuals age, their NAD levels decline, and this decrease has been suggested to be a contributing factor to the development of numerous age-related diseases, such as cancer, diabetes, cardiovascular diseases, and neurodegenerative diseases. In pursuit of healthy aging, researchers have investigated approaches to boost or maintain NAD levels. Here, we provide an overview of NAD metabolism and the role of NAD in age-related diseases and summarize recent progress in the development of strategies that target NAD metabolism for the treatment of age-related diseases, particularly neurodegenerative diseases.

The Beneficial Role of Apigenin against Cognitive and Neurobehavioural Dysfunction: A Systematic Review of Preclinical Investigations

Apigenin is a flavone widely present in different fruits and vegetables and has been suggested to possess neuroprotective effects against some neurological disorders. In this study, we systematically reviewed preclinical studies that investigated the effects of apigenin on learning and memory, locomotion activity, anxiety-like behaviour, depressive-like behaviour and sensorimotor and motor coordination in rats and mice with impaired memory and behaviour. We searched SCOPUS, Web of Science, PubMed and Google Scholar for relevant articles. A total of 34 studies were included in this review. The included studies revealed that apigenin enhanced learning and memory and locomotion activity, exhibited anxiolytic effects, attenuated depressive-like behaviour and improved sensorimotor and motor coordination in animals with cognitive impairment and neurobehavioural deficit. Some of the molecular and biochemical mechanisms of apigenin include activation of the ERK/CREB/BDNF signalling pathway; modulation of neurotransmitter levels and monoaminergic, cholinergic, dopaminergic and serotonergic systems; inhibition of pro-inflammatory cytokine production; and attenuation of oxidative neuronal damage. These results revealed the necessity for further research using established doses and short or long durations to ascertain effective and safe doses of apigenin. These results also point to the need for a clinical experiment to ascertain the therapeutic effect of apigenin.

Stabilization of mitochondrial function by chlorogenic acid protects against kainic acid-induced seizures and neuronal cell death in rats

The current study investigated the effect of chlorogenic acid, a polyphenolic compound found in numerous plant products, on a kainic acid-induced seizure rat model and its potential mechanism. Rats were administered chlorogenic acid (10 and 50 mg/kg) intraperitoneally for 30 min before kainic acid (15 mg/kg) intraperitoneal administration. Pretreatment with chlorogenic acid decreased the seizure score, increased the latency to onset of the first seizure, and decreased the mortality rate. Chlorogenic acid pretreatment also resulted in a significant reduction in glutamate elevation and neuronal death in the hippocampus of kainic acid-treated rats. In addition, electron microscopy revealed that kainic acid-induced changes in hippocampal mitochondrial structure were prevented by chlorogenic acid pretreatment. Additionally, the levels of mitochondrial function-related proteins, including sirtuin 3, Complex I, glutamate dehydrogenase 1 and ATP synthase, were increased, and the level of the mitochondrial damage marker cytochrome C was decreased in the hippocampus of chlorogenic acid/kainic acid rats. Furthermore, the expression of mitochondrial biogenesis-related proteins [AMP-activated protein kinase (AMPK), sirtuin1, and peroxisome proliferator-activated receptor γ-coactivator-1α (PGC-1α)] and mitophagy-related proteins [phosphatase and tensin homolog (PTEN)-induced putative kinase 1 (PINK1), Parkin, and microtubule-associated protein 1 light chain 3 (LC3)] was decreased in the hippocampus of kainic acid-treated rats, which was reversed by chlorogenic acid pretreatment. These observations reveal the marked neuroprotective potential of chlorogenic acid against kainic acid-induced neurotoxicity and seizures through prevention of glutamate increase and preservation of AMPK/sirtuin 1/PGC-1α-mediated mitochondrial biogenesis and PINK1/Parkin-induced mitophagy to maintain adequate mitochondrial homeostasis and function.

Targeting mitophagy for neurological disorders treatment: advances in drugs and non-drug approaches

Mitochondria serve as a vital energy source for nerve cells. The mitochondrial network also acts as a defense mechanism against external stressors that can threaten the stability of the nervous system. However, excessive accumulation of damaged mitochondria can lead to neuronal death. Mitophagy is an essential pathway in the mitochondrial quality control system and can protect neurons by selectively removing damaged mitochondria. In most neurological disorders, dysfunctional mitochondria are a common feature, and drugs that target mitophagy can improve symptoms. Here, we reviewed the role of mitophagy in Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, stroke, and traumatic brain injuries. We also summarized drug and non-drug approaches to promote mitophagy and described their therapeutic role in neurological disorders in order to provide valuable insight into the potential therapeutic agents available for neurological disease treatment. However, most studies on mitophagy regulation are based on preclinical research using cell and animal models, which may not accurately reflect the effects in humans. This poses a challenge to the clinical application of drugs targeting mitophagy. Additionally, these drugs may carry the risk of intolerable side effects and toxicity. Future research should focus on the development of safer and more targeted drugs for mitophagy.

Screening of an FDA-approved compound library identifies apigenin for the treatment of myocardial injury

Apigenin is the active ingredient in Ludangshen. Although previous studies reported the cardioprotective actions of apigenin against doxorubicin (Dox)-induced cardiomyopathy, the underlying mechanisms remain incompletely understood. Since apigenin beneficially regulates various aspects of mitochondrial function and dynamics, we asked whether apigenin improves heart function in mice with Dox-induced cardiomyopathy by regulating the mitochondrial unfolded protein response (UPRmt). Co-administration of apigenin significantly restored heart function, reduced myocardial swelling, inhibited cardiac inflammation, increased cardiac transcription of UPRmt-related genes, and promoted cardiomyocyte survival in Dox-treated mice. In turn, blockade of UPRmt abolished the mito- and cytoprotective effects of apigenin, evidenced by decreased ATP production, suppressed mitochondrial antioxidant capacity, and increased apoptosis, in Dox-treated, cultured HL-1 cardiomyocytes. Furthermore, apigenin treatment prevented Dox-induced downregulation of Sirt1 and Atf5 expression, and the beneficial effects of apigenin were completely nullified in Sirt1 knockout (KO) mice or after siRNA-mediated Sirt1 knockdown in vitro. We thus provide novel evidence for a promotive effect of apigenin on UPRmt via regulation of the Sirt1/Atf5 pathway. Our findings uncover that apigenin seems to be an effective therapeutic agent to alleviate Dox-mediated cardiotoxicity.

Synergism Antiproliferative Effects of Apigenin and Naringenin in NSCLC Cells

Non-small cell lung cancer (NSCLC) is one of the leading cancer killers. Apigenin (Api) and Naringenin (Nar) are natural bioactive substances obtained in various vegetables and fruits, possessing anti-tumor effects across multiple studies. This study investigated the latent synergistic antiproliferative functions of Api and Nar in A549 and H1299 NSCLC cells. Cell viability was determined after incubating with different concentrations of Api, Nar, or the combination of Api and Nar (CoAN) for 24 h. Analysis using the CompuSyn software revealed that the CI value of each combined dose was < 1, depicting that the two drugs had a synergistic inhibitory effect. The CoAN (A:N = 3:2) group with the lowest CI value was selected for subsequent experiments. The IC₅₀ of CoAN (A:N = 3:2) was used to determine the cell cycle, the expression ratio of Bax to Bcl2, Caspase 3 activity, and mitochondrial function to assess oxidative stress and apoptosis. The results established that CoAN treatment caused significant cytotoxicity with cell cycle arrest at G2/M phases. Furthermore, CoAN significantly enhanced mitochondria dysfunction, elevated oxidative stress, and activated the apoptotic pathway versus Api or Nar alone groups. Thus, the CoAN chemotherapy approach is promising and deserves further research.

NLRP3 inflammasome inhibition and M1-to-M2 microglial polarization shifting via scoparone-inhibited TLR4 axis in ovariectomy/D-galactose Alzheimer's disease rat model

Neuroinflammation mediated by microglia activation is a critical contributor to Alzheimer's disease (AD) pathogenesis. Dysregulated microglia polarization in terms of M1 overactivation with M2 inhibition is involved in AD pathological damage. Scoparone (SCO), a coumarin derivative, displays several beneficial pharmacological effects including anti-inflammatory and anti-apoptotic properties, however, its neurological effect in AD is still elusive. This study investigated the neuroprotective potential of SCO in AD animal model focusing on determining its effect on M1/M2 microglia polarization and exploring the plausible mechanism involved via investigating its modulatory role on TLR4/MyD88/NF-κB and NLRP3 inflammasome. Sixty female Wistar rats were randomly allocated into four groups. Two groups were sham-operated and treated or untreated with SCO, and the other two groups were subjected to bilateral ovariectomy (OVX) and received D-galactose (D-Gal; 150 mg/kg/day, i.p) alone or with SCO (12.5 mg/kg/day, i.p) for 6 weeks. SCO improved memory functions of OVX/D-Gal rats in the Morris water maze and novel object recognition tests. It also reduced the hippocampal burden of amyloid-β₄₂ and p-Tau, additionally, the hippocampal histopathological architecture was prominently preserved. SCO inhibited the gene expression of TLR4, MyD88, TRAF-6, and TAK-1, additionally, p-JNK and NF-κBp65 levels were significantly curbed. This was associated with repression of NLRP3 inflammasome along with M1-to-M2 microglia polarization shifting as exemplified by mitigating pro-inflammatory M1 marker (CD86) and elevating M2 neuroprotective marker (CD163). Therefore, SCO could promote microglia transition towards M2 through switching off TLR4/MyD88/TRAF-6/TAK-1/NF-κB axis and inhibiting NLRP3 pathway, with consequent mitigation of neuroinflammation and neurodegeneration in OVX/D-Gal AD model.

Dipsacus and Scabiosa Species-The Source of Specialized Metabolites with High Biological Relevance: A Review

The genera Dipsacus L. and Scabiosa L. of the Caprifoliaceae family are widely distributed in Europe, Asia, and Africa. This work reviews the available literature on the phytochemical profiles, ethnomedicinal uses, and biological activities of the most popular species. These plants are rich sources of many valuable specialized metabolites with beneficial medicinal properties, such as triterpenoid derivatives, iridoids, phenolic acids, and flavonoids. They are also sources of essential oils. The genus Dipsacus has been used for centuries in Chinese and Korean folk medicines to treat bone (osteoporosis) and joint problems (rheumatic arthritis). The Korean Herbal Pharmacopoeia and Chinese Pharmacopoeia include Dipsaci radix, the dried roots of D. asperoides C.Y.Cheng & T.M.Ai. In addition, S. comosa Fisch. ex Roem & Schult. and S. tschiliiensis Grunning are used in traditional Mongolian medicine to treat liver diseases. The current scientific literature data indicate that these plants and their constituents have various biological properties, including inter alia antiarthritic, anti-neurodegenerative, anti-inflammatory, antioxidant, anticancer, and antimicrobial activities; they have also been found to strengthen tendon and bone tissue and protect the liver, heart, and kidney. The essential oils possess antibacterial, antifungal, and insecticidal properties. This paper reviews the key biological values of Dipsacus and Scabiosa species, as identified by in vitro and in vivo studies, and presents their potential pharmacological applications.

Role of SIRT3 in mitochondrial biology and its therapeutic implications in neurodegenerative disorders

Sirtuin 3 (SIRT3), a mitochondrial deacetylase expressed preferentially in high-metabolic-demand tissues including the brain, requires NAD⁺ as a cofactor for catalytic activity. It regulates various processes such as energy homeostasis, redox balance, mitochondrial quality control, mitochondrial unfolded protein response (UPRmt), biogenesis, dynamics and mitophagy by altering protein acetylation status. Reduced SIRT3 expression or activity causes hyperacetylation of hundreds of mitochondrial proteins, which has been linked with neurological abnormalities, neuro-excitotoxicity and neuronal cell death. A body of evidence has suggested, SIRT3 activation as a potential therapeutic modality for age-related brain abnormalities and neurodegenerative disorders.

Aqueous extract of Ceratonia siliqua L. leaves elicits antioxidant, anti-inflammatory, and AChE inhibiting effects in amyloid-β42-induced cognitive deficit mice: Role of α7-nAChR in modulating Jak2/PI3K/Akt/GSK-3β/β-catenin cascade

Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder attributed to several etiological factors including cholinergic dysregulation, neuroinflammation, oxidative stress, β-amyloidogenesis, and tauopathy. This demands the search for multitarget drugs, especially of natural sources owing to their pleiotropic activities and low adverse effects. The present study was conducted to investigate the cognitive-improving potential of Ceratonia siliqua L. (Cs) extract compared with donepezil, an acetylcholinesterase inhibitor, on AD-like pathological alterations induced by single intracerebroventricular amyloid-β42 (Aβ42) injection in mice. Aβ42-injected mice were treated with Cs (100 mg/kg/day, po) with or without methyllycaconitine (MLA; 1 mg/kg/day, ip), an α7-nAChR antagonist. Aβ42-injected animals demonstrated an elevation of hippocampal Aβ42, p-Tau, and acetylcholinesterase. They also showed a decline in phosphorylated levels of Jak2, PI3K, Akt, and GSK-3β, leading to induction of neuroinflammation and oxidative stress. Noteworthy, Cs improved the histopathological and behavioral variables in addition to mitigating AD hallmarks. It also exerted neuroprotection by reducing NF-κBp65 and TNF-α, while elevating Nrf2 and HO-1, along with stabilizing β-catenin under the impact of Jak2/PI3K/Akt/GSK-3β signaling. These beneficial effects of Cs were abrogated by MLA co-administration signifying the α7-nAChR involvement in Cs-mediated effects. Therefore, Cs can ameliorate Aβ42-induced neurodegeneration by modulating Jak2/PI3K/Akt/GSK-3β/β-catenin axis in an α7-nAChR-dependent manner.