黄嘌呤与缺血性脑卒中诱导的神经炎症：以神经胶质细胞为中心
翻译：研究生：张洮铭；科研秘书：刘虹；导师：陈晨
导语：缺血性卒中是全球严重的长期残疾和死亡的主要原因，也是我院神经内科收治最多的病种，这篇来自1区2024年最新文献提示，小胶质细胞、星形胶质细胞和浸润的免疫细胞参与了复杂的神经元炎症反应，在缺血性脑卒中的病理生理变化中发挥着复杂的作用。黄酮类化合物是植物特有的次生代谢产物，通过调节炎症反应对脑缺血损伤具有保护作用。
这是一篇很好的多学科交叉。涵盖了神内、中药学、转化医学等学科。高质量的文献和研究既提示我们学科融合、学科交叉的重要性，也给我们科学研究带来了新的思路。通读本文后，给我们研究者带来继续进行深入研究的思路和冲动。身处心血管病专科医院，上述病例和数据不难获得，要的就是十年如一日的科研坚持和随访。
下面我们就来阅读整篇文献。
ABSTRACT
Ischemic stroke is one of the most cases worldwide, with high rate of morbidity and mortality. In the pathological process of ischemic stroke, neuroinflammation is an essential process that defines the functional prognosis. After stroke onset, microglia, astrocytes and the infiltrating immune cells contribute to a complicated neuro
inflammation cascade and play the complicated roles in the pathophysiological variations of ischemic stroke. Both microglia and astrocytes undergo both morphological and functional changes, thereby deeply participate in the neuronal inflammation via releasing pro-inflammatory or anti-inflammatory factors. Flavonoids are plant-
specific secondary metabolites and can protect against cerebral ischemia injury via modulating the inflamma tory responses. For instances, quercetin can inhibit the expression and release of pro-inflammatory cytokines, such as tumor necrosis factor (TNF)-α, IL-6 and IL-1β, in the cerebral nervous system (CNS). Apigenin and rutin
can promote the polarization of microglia to anti-inflammatory genotype and then inhibit neuroinflammation. In this review, we focused on the dual roles of activated microglia and reactive astrocyte in the neuroinflammation
following ischemic stroke and discussed the anti-neuroinflammation of some flavonoids. Importantly, we aimed to reveal the new strategies for alleviating the cerebral ischemic stroke.
Introduction
Stroke is known as a leading cause of death worldwide, a half of stroke survivors are left with chronic disabilities. Ischemic stroke is
induced by cerebral vascular stenosis or occlusion and occupies approximately 80% of the stroke population. The acute phase of
ischemic stroke determines the dynamic changes and the evolution of the brain lesion and is closely associated with neuronal deficits. Until now, acute treatments of ischemic stroke include mechanical throm
bectomy and the thrombolytic therapy with recombinant tissue plas minogen activator (rt-PA). However, rt-PA treatment cannot be
performed on majority of patients for the limited therapeutic time windows and the secondary brain injury after reperfusion. Therefore, it is of great urgency to explore the therapeutic targets and find the possible drugs for ischemic stroke.
As reported in the literature, the neuronal death in the acute brain injury after ischemic stroke is directly caused by severe ischemia within minutes after stroke onset. In the pathological process of delayed brain injury, neuronal injury is mainly induced by neuroinflammation and the brain edema, which occurs several days following stroke onset. Thus,neuroinflammation is an essential process in ischemic stroke that defines the functional prognosis. After stroke onset, both astrocyte and microglia are activated and release the pro-inflammatory or
anti-inflammatory factors, thereby result in a complicated neuro inflammation cascade. Especially, microglia are rapidly activated by
ischemic insults and undergo both morphological and functional changes. Activated microglia produce the inflammatory factors, such as tumor necrosis factor alpha (TNF-α), interleukin (IL)−23, IL-1β and IL-12, or release the anti-inflammatory mediators, containing trans forming growth factor beta (TGF-β), IL-4 and IL-10. Similarly, as trocytes likewise undergo morphological and translational changes and then release the pro-inflammatory or anti-inflammatory factors. Therefore, both activated astrocytes and microglia have the double-edged sword effect on the neuroinflammation following the ischemic stroke.
Flavonoids, plant-specific secondary metabolites, have many phar macological effects against ischemic stroke, such as
anti-inflammation and antioxidation, and regulating the function of key cellular enzymes. Furthermore, flavonoids like nar
ingenin, (-)-epigallocatechin-3-gallate (EGCG), quercetin, rutin,apigenin and baicalein have been proven to counteract the neuro inflammatory responses following ischemic stroke. Accumulating study
has revealed the neuroprotective efficacy of these flavonoids against cerebral ischemic injury via anti-neuroinflammation. This review
aimed to discuss complicated roles of microglia and astrocytes on the ischemic stroke-induced neuroinflammation and revealed the thera peutic potential of flavonoids on ischemic brain injury.
Neuroinflammation following ischemic stroke
Neuroinflammation has been implicated in the initiation and pro gression of several CNS diseases, including ischemic stroke. Among
all of the damage factors involved in cerebral ischemia-induced brain injury, neuroinfl-ammation is critical one that defines the functional prognosis of both stoke patients and experimental stroke of animals. After stroke onset, microglia and astrocytes rapidly recognize and react to the ischemia stimuli and the neuronal damage. Activated
microglia and astrocytes participate in neuroinflammation via releasing the pro-inflammatory or anti-inflammatory factors. Pro-inflammatory factors amplify the neuronal damage and deteriorate the brain func
tion. In contrast, the anti-inflammatory factors can restrain the neuro inflammation and promote neuronal repair. Thus, microglia and
astrocytes are major players in the inflammation response following ischemic stroke. Exploration of the dual roles of microglia and astrocytes could have important implications for ischemic stroke treatment by informing the neuroinflammatory interventions.
Microglia in neuroinflammation (Fig. 1)
Microglia make up 4–11% of the CNS cell population and are in“resting stage” in a normal CNS environment. Microglia in “resting stage” can monitor their surrounding environment through extending and contracting their parapodium. This housekeeping function of microglia can clear the metabolic products and eliminate the deterio rated tissue components after brain injury. Importantly, microglia are the first response cells that are recruited to infarct lesions following ischemic stroke, and function in the occurrence and progression of
neuroinflammation. Afterwards, microglia are activated and polarize to two phenotypic subtypes, M1 and M2, M1 and M2
microglia respectively secrete pro-inflammatory cytokines, such as IL-1α, IL-1β, IL-6 and TNF-α, and anti-inflammatory cytokines, including IL-10 and IL-1R antagonist (IL-1Ra). These cytokines together form a complex signaling network in neuroinflammatory response after ischemic stroke.
Microglia-released TNF-α and neuroinf-lammation
TNF-αcontains a secreted form (solTNF) and a transmembrane form (tmTNF) and is the most studied cytokine in ischemic stroke. The signal of TNF-α is transferred via two TNF receptors (TNFRs): TNFR-1and TNFR-2 . The solTNF-TNFR-1 signal is mainly respon sible for pro-inflammatory effects. Conversely, TNFR-2 is only activated
by mtTNF, and mediates the beneficial effects, such as anti-inflammation and promoting the remyelination and improving the cell survival. Not surprisingly, removal of solTNF had been reported to alleviate the pathology and symptoms of cerebral ischemia inmice. Huang et al. likewise revealed the importantly regulatory roles of TNF-α-TNFR-1 signal in ischemic stroke-induced neuro inflammation. Therefore, removal of solTNF and retention of tmTNF can protect against brain injury in experimental stroke.
Microglia-released interleukins and neuroinflammation
The IL-1 family is closely involved in regulating immune cells and inflammatory processes during ischemic stroke. The roles of IL-1α, IL-1β, and IL-1 receptor antagonist (IL-1Rα) in IL-1 family members in ischemic stroke have been explored in plenty of studies. It has been reported in literature that IL-1α and IL-1β are dramatically elevated in the ischemic hemisphere. Depletion of IL-1α or IL-1β could reduce the ischemic stroke injury and restrain the BBB disruption in experimental stroke. Further study has revealed that IL-1α-mediated neurovascular inflammation and BBB injury could cause the infiltration of neutrophils to ischemic lesions , which played a major role in ischemic brain pathobiology. Besides, IL-1β likewise deteriorated neurons, glial cells and the vasculature after ischemic stroke. Furthermore, the deteriorated role of IL-1 family on stroke pathology was evidenced by decreased infarct volumes in experimental ischemic stroke in IL-1 (α/β) knockout (IL-1-/-) mice.
小胶质细胞释放的白细胞介素与神经炎症
IL-1家族与缺血性卒中期间免疫细胞和炎症过程的调节密切相关。大量研究探讨了IL-1家族成员中IL-1α、IL-1β和IL-1受体拮抗剂（IL-1 R α）在缺血性卒中中的作用。有研究发现，IL-1α或IL-1β耗竭可减轻缺血性脑卒中损伤，抑制实验性脑卒中中的血脑屏障（Blood-Brain Barrier, BBB）破坏。进一步的研究表明，IL-1α介导的神经血管炎症和BBB损伤可导致中性粒细胞向缺血性病变浸润，在缺血性脑病理生物学中起主要作用。此外，IL-1β在缺血性卒中后同样使神经元、神经胶质细胞和血管系统恶化]。IL-1（α/ β）基因敲除的小鼠实验性缺血性卒中的梗死量减少证明了这一点。
IL-6 also belongs to pro-inflammatory interleukins and is secreted by glial cells, monocytes and neurons. The IL-6 signaling pathway contains classic and trans-signaling mechanisms. In classic signaling, IL-6 stimulates target cells via membrane-bound IL-6 receptor (IL-6R), which upon ligand binding associates with the signaling re
ceptor protein gp130. Whereas trans-signaling requires prior binding of IL-6 to the soluble IL-6R (sIL-6R). In trans-signaling,
binding of IL-6 thesIL-6R activates effector cells via gp130 regardless of whether the cells express the IL-6R itself. The trans-signaling of IL-6is regarded to be accounted for the pro-inflammatory property of IL-6.
Contrary to the role of pro-inflammatory cytokines in neuro inflammation, IL-10 is regarded as an anti-inflammatory cytokine, for it can reduce inflammation and limit the cellular apoptosis. In experimental ischemic stroke models of mice, upregulation of IL-10
using transgenic technology could reduce the brain infarct volume and inhibit the cellular apoptosis. Likewise, low-level of IL-10 is found to be correlated with poor outcome of experimental ischemic stroke, evidenced by significantly inflammatory reactions and worse neuro logical deficits. In a murine model of experimental stroke, Piepke
et al.confirmed the neuroprotective effects of IL-10 on the functional outcome post-ischemia, the researchers found that IL-10
deficient exhibit obviously increased infarct sizes and impaired neuro logical outcome and enlarged brain atrophy of mice following cerebral ischemia. Therefore, we proposed that the anti-inflammatory properties
of IL-10 can be used as a potential clue for the diagnosis and prognosis of ischemic stroke.
The phenotypic change of microglia and neuroinflammation
As aforementioned, microglia are the first responders in response to the ischemia insult and undergo both morphological and functional transformation during the pathological process of ischemic stroke,
which is known as activation of microglia. Activated microglia become a double sword, with phenotypic transformation to deleterious M1 and neuroprotective M2 types. M1 microglia can be identified by testing the expression of inducible nitric oxide synthase (iNOS), CD16, CD32, CD86, etc. Microglial polarization of the M1 subtype is charac
terized by high expression of IL-12 and IL-23 and low expression of IL-10. The polarization of M2 microglia is characterized by releasing
cytokine IL-10, TGF-β, IL-1R agonists, CD302, CD163, etc.
M1 microglia can damage the BBB integrity and further promote the neuronal injury via releasing pro-inflammatory mediators, such as IL-1α,IL-1β, IL-6,TNF-α and chemokine-chemokine ligand 2 (CCL2), and through deteriorating the neuroinflammation. The deteriorated
roles of IL-1α, IL-1β, IL-6, TNF-α on the neuroinflammation have been discussed previously. CCL2 and its corresponding receptor CCR2 have been found to up-regulate the inflammatory response in cerebral ischemia. Guo et al. have found that CCL2/CCR2 expression was positively related with infarct area and enlargement of lesion, upregu lation of CCL2 expression further aggravated the cerebral ischemia.
All these findings suggested that microglia -released CCL2 played a detrimental role in ischemic stroke.
Conversely, M2 microglia produce the anti-inflammatory factors, such as TGF-β, IL-10 and glucocorticoids to maintain BBB integrity, promote the proliferation and differentiation of neural cells and tissue repair. Importantly, anti-inflammatory effect of M2 microglia is found to be related with activating peroxisome proliferator-activated receptor-γ (PPARγ), which is known as a tran
scription factor with anti-inflammatory properties. These findings revealed that the dichotomous roles of activated microglia in inflam matory responses contribute to the phenotypic transformation. Without a doubt, attenuating M1 activation and enhancing M2 response of microglia represent promising therapeutic targets in ischemic stroke.
Astrocyte in neuroinflammation (Fig. 1)
Astrocytes provide the supportive roles in the CNS under physio logical condition through various ways, such as promoting BBB formation and participating in neuronal metabolic activity and structural supports. Besides, astrocytes participate in regulating cerebral blood flow and adjust the neurotransmitter release through “tripartite synapse”. The term ’tripartite synapse’ is a concept in synaptic physiology between astrocytes and neurons based on the demonstration of the existence of bidirectional communication, which is the classic’bipartite’ information flow between the pre- and postsynaptic neurons. Astrocytes likewise play vital roles in maintaining CNS homeo stasis and pruning synapses through phagocytosis and promoting the formation synapses.
Under the ischemia stimuli, astrocytes undergo morphological and functional changes, first as reactive astrocytes and then as scar-forming astrocytes. After that, reactive astrocytes form the astro cytic scars around the lesion epicenter and release the chondroitin sulfate proteoglycans (CSPGs), which can inhibit the remyelination and
axonal regeneration. Many studies have revealed two subtypes of reactive astrocyte, A1 and A2. The polarization of A1 (pro-in
flammatory) astrocytes are stimulated by neuroinflammatory mediators from activated microglia, containing IL-1α, C1q and TNF-α. A2 astro cytes are activated by ischemia stimuli. A1 astrocytes possess the neurotoxicity due to exacerbating the neuroinflammation through releasing TNF-α, IL-6 and IL-1β. Besides, A1 astrocytes phago cytize the surviving neurons and Furthermore, up-regulation of complement component 3 (C3) has been found in A1 astrocytes. C3 is harmful to both neurons and oligodendrocytes via activating C3 receptor.
By contrast, A2 (anti-inflammatory) astrocytes are characterized as
neuroprotective subtype for producing neurotrophic factors. In addition, A2 astrocytes acquire the phagocytosis ability to clear the myelin debris, this action results in reduction of neuroinflammation. Moreover, A2 astrocytes can upregulate the expression of anti-inflammatory cytokine TGF-β, which has neuroprotective effect against cerebral ischemia injury via promoting the synapse formation.Therefore, the complicated (neuroprotective or neurotoxic) roles of
reactive astrocytes on the brain injury due to the phenotypic trans formation. Together, shifting A1 to A2 astrocytic transformation might be potential mechanisms of restraining the neuroinflammation and promoting the neuronal repair after ischemic stroke.
Peripheral immune cells in neuroinflammation (Fig. 2)
As aforementioned, neuronal inflammation is a key pathological process during ischemic stroke. The pro-inflammatory cytokines-
induced damages of endothelial cells and pericytes result in BBB disin tegration and BBB leakage, which can further lead to cerebral edema and increased expression of astrocytic aquaporin 4 (AQP4). The BBB breakdown and AQP4 facilitate the infiltration of peripheral immune cells into the CNS, containing macrophages and peripheral B
cells and T cells. The infiltration of peripheral immune cells further activates host immune cells, including microglia, and then de
teriorates the neuronal inflammation in CNS via releasing chemokines, cytokines and the other molecules. Furthermore, Kristian et al.
have revealed that infiltration of Blymphocytes induced the chronic inflammation and the delay cognitive dysfunction. Not only infiltrating macrophages but also activated microglia can induce further brain damage.
In addition, infiltration of T cells from blood into CNS likewise plays important and different roles in the neuronal inflammatory response. The T regulatory (Treg) cells are the famous peripheral cells and are
involved in the resolution of ischemic injury. For instance, Treg cells have been found to release anti-inflammatory cytokines IL-10 and
TGF-β, and protect against brain injury. In contrast, CD4+, CD8+ and gamma delta T (γδ) cells could deteriorate the brain injury via producing pro-inflammatory cytokines IFN-g and IL-17.
Moreover, peripheral lymphocytes in CNS likewise interact with oligodendrocytes and oligodendrocyte progenitor cells (OPCs). Briefly, the leakage of oligodendrocyte antigens, such as myelin basic protein
(MBP) and myelin oligodendrocyte glycoprotein (MOG), into the periphery through broken BBB can promote the infiltration of peripheral immune cells into CNS, this action is more significant in the corelesion than that in the peri-infarct lesion. Taken together, the infiltration of peripheral immune cells likewise has at least a dual role on inflammatory reaction following ischemic stroke.
Anti-neuroinflammation of flavonoids (Fig. 3)
Flavonoids have attracted more attention in recent years because of potential benefits in stroke treatment. The basic structure of flavonoids contains a skeleton of two phenyl (A and B) rings and a heterocyclic ring
(C ring, a chain of three carbon atoms). Flavonoids are classified into following subclasses, flavanones, flavanols, flavonols, flavones, antho cyanins, isoflavones, chalcones and dihydrochalcones, which can be found in the website, http://phenolexplorer.eu/compounds/ classification.
Accumulating studies have revealed that flavonoids could protect against cerebral ischemia injury via decreasing inflammatory responses. For instance, quercetin has been found to reduce the neuro inflammation through inhibiting the release of cytokines and che mokines, as well as decreasing leukocyte infiltration and cerebral edema. Besides, apigenin, rutin and the other flavonoids,have been found to possess the anti-neuroinflammatory effect via reducing the release of pro-inflammatory factors.
Flavanones and neuroinflammation
Naringenin is one of flavanones and widely distributed in oranges,grapefruits, citrus and tomatoes. Multiple therapeutic applications of
naringenin have been found in neurological disorders for its neuro protective roles via anti-inflammatory effec. For instance, nar
ingenin could inhibit the inflammatory signaling in glial cells and protect against neuroinflammation-mediated brain injury. Briefly, naringenin attenuated lipopolysaccharide (LPS)-induced inflammatory responses in vitro via regulating the NF-κB and MAPK signaling pathways
. Besides, the biological activities of naringenin have been proposed to reduce the expression of proinflammatory markers in microglia and astrocytes, containing iNOS and COX-2, through lowering the NF-κB
activity.
Moreover, Vafeiadou et al. have reported that naringenin could effectively reduce LPS/IFN-c-induced activation of microglia and as trocytes, and lower the related neuronal injury. Similarly, Raza et al. have revealed that the neuroprotective effect of naringenin against experimental stroke was related with inhibiting the NF-κB pathway, as
evidenced by the reduced nuclear translocation of the NF-κB subunit p65 in brain tissues of rats after cerebral ischemia/reperfusion.Furthermore, Zhang et
al.have revealed that anti-neuroinflammation of naringenin was related with promoting the
phenotypic transformation of microglia to the M2 subtype. The mech anism of naringenin-induced microglial polarization was dependent on inactivation of MAPK signaling, particularly relied on the inactivation of
c-Jun N-terminal kinase (JNK). Because the selective activator of JNK could inhibit the naringenin-mediated polarization of M2 microglia.
Flavanols and neuroinflammation
Flavanols belong to the Flavan-3-ols of flavonoid family because of the attachment of a hydroxyl group at position 3 on the C ring. Flavanols lack ketone group at position 4 of the C ring and a double bond between
C-2 and C-3. The main representatives of flavanols are epicatechins, (-) epigallocatechin (EGC), (-)-epicatechin-3-gallate (ECG), (-)-epicatechin (EC), (+)-catechin (C),(-)-epigallocatechin-3-gallate
(EGCG), (+)-gallocatechin-3-gallate (GCG), (+)-gallocatechin (GC), and
so on.
The anti-inflammatory properties of EGCG have been reported in previous studies. EGCG is the most abundant and biologically
active polyphenol in green tea. Lee et al. have found that EGCG could inhibit the inflammation through restraining the expressions of iNOS and COX-2 s, as well as through reducing the production of in
flammatory cytokines. These actions were found both in culture astro cytes and in the mice brain. Particularly, the researchers revealed that upregulated COX-2 and iNOS expressions were responsible for the
astrocyte activation . In addition, Wu et al. have confirmed the anti-neuroinflammatory effects of EGCG and EGCG enriched green tea extract in the rat cerebral ischemic stroke model. The authors revealed that the anti-inflammatory effects of EGCG in BV-2 microglia cells in vitro was related to inhibiting the iNOS/NO and COX-2.Moreover, the inhibitory effect of EGCG has been found in hypoxia-induced inflammation and oxidative stress in microglia, the mechanisms were via activating the Nrf-2/HO-1 pathway as well as abrogating the NF-κB pathway .
Furthermore, EGCG treatment could significantly increase the proliferation of neural progenitor cells (NPCs), which were isolated from ipsilateral subventricular zone (SVZ) of cerebral I/R mice. Strikingly,
EGCG could promote the phenotypic transformation of activated microglia to M2 subtype at 28d after mice cerebral ischemia, which were evidenced by lowering the expression of M1 markers, including CD32,
CD11b, CD16, iNOS and TNF-α, and increasing the expression of M2 markers, containing arginase-1 (Arg-1), YM1, IL-10 and TGF-β. Therefore, we declared that EGCG-mediated anti-inflammatory effect
might be related with promoting the phenotypic transformation of microglia to M2 subtype.
Flavonols and neuroprotection
Quercetin, a 3,3′,4′,5,7-pentahydroxyflavone, is the major represen
tative of flavonols and rich in fruits, tea, onion, leafy vegetables and herbs. The research about the pharmacokinetics of quercetin has revealed that quercetin administration at a dose of 1.5 g per day resulted in stable concentration of quercetin in humans plasma. The average terminal half-life of quercetin is 3.5 h in healthy humans. These findings suggested that quercetin may be a candidate drug for
clinical application.
黄酮醇与神经保护
槲皮素是一种3，3 ′，4 ′，5，7-五羟基黄酮，是黄酮醇类化合物的主要代表，在水果、茶叶、洋葱、叶菜和草药中含量丰富。关于槲皮素药代动力学的研究表明，以1.5 g/天的剂量给予槲皮素可使人血浆中的槲皮素浓度稳定。健康人体中槲皮素的平均终末半衰期为3.5小时。这些结果表明，槲皮素可能是一个候选药物的临床应用。
The anti-inflammatory effect of quercetin has been widely investi gated in animal model of cerebral I/R. Quercetin adminis
tration following cerebral I/R in rats significantly reduced the proinflammatory cytokines (IL-1β and IL-6) and increased the
anti-inflammatory cytokines (IL-4, IL-10 and TGFβ1). Further more, quercetin-induced reduction of IL-6 has been found to be related
with inhibiting the activation of astrocytes. A quercetin-enriched diet enhanced the neuronal activity in the medial prefrontal cortex and in the hippocampus after stress by inhibiting the activation of astrocytes
and microglia. Han et al. have also provided strong evidences that anti-inflammation of quercetin is through inhibiting the microglial in flammatory activation. Furthermore, Tsai et al. have revealed that quercetin significantly lowered the expressions of M1 microglia
markers, including IL-6, TNF-α and IL-1β, and increased the expression of M2 microglia marker IL-10. The researchers have reported that quercetin restrained M1 polarization-mediated neuroinflammatory responses, and enhanced the M2 microglial polarization [90]. Together, these findings provided valuable information that quercetin may act as a
potential drug for the treatment of ischemic stroke via anti-inflammatory effect.
在脑I/R动物模型中广泛研究了槲皮素的抗炎作用。大鼠脑I/R后槲皮素给药显著降低了促炎细胞因子（IL-1β和IL-6），增加了抗炎细胞因子（IL-4、IL-10和TGFβ1）。此外，已发现槲皮素诱导的IL-6减少与抑制星形胶质细胞的活化有关。富含槲皮素的饮食是通过抑制星形胶质细胞和小胶质细胞的激活来增强应激后内侧前额叶皮层和海马的神经元活性。Han等人发现槲皮素的抗炎作用是通过抑制小胶质细胞的炎症激活。此外，Tsai等人揭示了槲皮素显著降低了M1小胶质细胞标志物（包括IL-6、TNF-α和IL-1β）的表达，并增加了M2小胶质细胞标志物IL-10的表达。研究人员报告说，槲皮素抑制M1极化介导的神经炎症反应，并增强M2小胶质细胞极化。总之，这些发现提供了有价值的信息，槲皮素可能作为一种潜在的药物，通过抗炎作用治疗缺血性卒中。
Rutin, another representative of flavonols, is also known as quercetin 3-O-rutinoside. Rutin can be extracted from many medicinal plants. Similar to the action of quercetin, rutin likewise has the neuro protective effect against cerebral I/R injury. For instance, rutin
administration can attenuate the expression and activity of metalloproteinase-9 (MMP-9) and promotes the BBB function in focal
cerebral ischemia rats. Further research has showed that rutin obviously improved the spatial memory of cerebral ischemia animals
and inhibited the repeated cerebral ischemia-induced neuronal death in the hippocampal CA1 area.
酮醇的另一个代表是芦丁，也被称为槲皮素3-O-芸香糖苷。可以从许多药用植物中提取。与槲皮素的作用类似，芦丁同样具有神经元保护作用，可防止脑I/R损伤。例如，给予芦丁可减弱金属蛋白酶-9（MMP-9）的表达和活性，并促进局灶性脑缺血大鼠的BBB功能。进一步研究表明，芦丁明显改善脑缺血动物的空间记忆，抑制反复脑缺血诱导的海马CA 1区神经元死亡。
Importantly, rutin has been found to increase the expression of phagocytic receptors of microglia and enhance the clearance capability of microglia. In addition, rutin facilitated the phenotypic transformation of microglia to an M2 subtype and inhibited M1 microglia-mediated neuroinflammation via restraining NO-dependent mechanism. Similarly, Lang et al. have confirmed that rutin
could promote the transformation of microglia from M1 to M2 state and might be a potential candidate for treating the neurological disorders. In addition, the authors found that rutin-mediated M2 microglial polari
zation was via inhibiting the TLR4/NF-κB signaling pathway. Therefore, rutin targeting microglial cells could be a promising strategy
to prevent inflammatory factors-mediated cerebral ischemia injury and promote outcome for ischemic stroke treatment.
重要的是，已发现芦丁可增加小胶质细胞吞噬受体的表达，并增强小胶质细胞的清除能力。此外，芦丁促进小胶质细胞向M2亚型的表型转化，并通过抑制NO依赖性机制抑制M1小胶质细胞介导的神经炎症。同样，Lang等证实芦丁可以促进小胶质细胞从M1状态向M2状态转化，可能是治疗神经系统疾病的潜在候选药物。此外，作者发现芦丁介导的M2小胶质细胞极化是通过抑制TLR 4/NF-κB信号通路。因此，芦丁可能是一个很有前途的治疗手段，以防止炎症因子介导的脑缺血损伤，促进缺血性卒中的治疗结果。
Flavones and neuroinflammation
Apigenin, 4’,5,7-trihydroxyflavone, represents one of flavones and can be obtained from vegetables and fruits. The potential biological effects of apigenin, including anti-inflammatory, antioxidative stress and anti-apoptotic activities, have been found in previous study. Besides, the preventive and therapeutic effects of
apigenin have been found in ischemic stroke, and the ability of apigenin across the BBB has been confirmed. Importantly, it has been found that apigenin could increase the proportion of M2 microglia and then
inhibit inflammation. Moreover, apigenin could decrease the release of proinflammatory cytokines, containing IL-6 and TNF-α. Further studies have confirmed that apigenin promoted the trans
formation of activated microglia to M2 subtype and inhibited the activation of M1 microglia. Jiang et al. have reported that
apigenin increased the release of anti-inflammatory cytokine IL-10 and reduced the inflammatory response via promoting the expression of PPARγ.
黄酮类化合物与神经炎症
芹菜素，4 '，5，7-三羟基黄酮，是黄酮类化合物之一，可从蔬菜和水果中获得。在先前的研究中已经发现芹菜素的潜在生物学作用，包括抗炎、抗氧化应激和抗凋亡活性。此外，芹菜素在缺血性中风中的预防和治疗作用已被发现，其穿过BBB的能力已被证实。芹菜素还可以增加M2小胶质细胞的比例，抑制炎症。此外，芹菜素还能减少促炎细胞因子IL-6和TNF-α的释放。有研究表示芹菜素促进活化的小胶质细胞向M2亚型转化，抑制M1小胶质细胞的活化。Jiang等报道芹菜素通过促进PPARγ的表达增加抗炎细胞因子IL-10的释放并降低炎症反应。
Baicalein, another flavone, has been found to ameliorate the neurological deficit of cerebral I/R rats, as well as reduce the infarct
sizes and inhibit the brain edema. Liang et al. have confirmed that baicalein could be used to treat the cerebral I/R injury when adminis
tered in the acute phase of ischemic stroke. Rats treated with baicalein after cerebral I/R showed the decreased brain infarct volume
and reduced neurobehavioral deficits. Moreover, the researchers have revealed that baicalein could inhibit cerebral ischemia-induced neuroinflammation via promoting the M2 transformation and inhibiting M1 transformation, and suggested that baicalein exerted neuro protective effects by reducing neuroinflammation, apoptosis and autophagy. Thus, baicalein possesses the potential for development of therapies for the cerebral ischemia-induced neuroinflammation
and the neuronal injury.
黄芩素是另一种黄酮，已发现可改善脑I/R大鼠的神经功能缺损，以及减少梗死面积和抑制脑水肿。Liang等已证实，在缺血性卒中急性期给药时，黄芩素可用于治疗脑I/R损伤。脑I/R后用黄芩素治疗的大鼠显示脑梗死体积减少，神经行为缺陷减少。此外，研究人员发现黄芩素可通过促进M2转化和抑制M1转化抑制脑缺血诱导的神经炎症，并提示黄芩素通过减少神经炎症、细胞凋亡和自噬而发挥神经保护作用。因此，黄芩素具有开发脑缺血性神经炎症和神经元损伤治疗药物的潜力。
Anthocyanins and neuroinflammation
Anthocyanins (pentunidin-3-O-rutinoside
(p-coumaroyl)−5-O-glucoside) likewise possess the ability to reduce the damage to neuro vascular unit in middle cerebral artery occlusion (MCAO) rats. Shin et al. have found that anthocyanins reduced the focal cerebral ischemia-induced neuronal damage through blocking the JNK and p53 signaling pathway. In addition, anthocyanins prevented the infiltration of peripheral immune cells in the hippocampus following cerebral ischemia, reduced the release of proinflammatory cytokines and decreased the activity of myeloperoxidase in cortex and hippo
campus. These actions suggested the anti-inflammation of anthocyanins.Importantly, anthocyanins could strikingly reduce the activation of microglia and astrocyte in brain of mice exposed to LPS.
花青素与神经炎症
花青素（戊酮-3-O-芸香糖苷（对香豆酰）-5-O-葡萄糖苷）同样具有减少大脑中动脉闭塞（MCAO）大鼠神经血管单位损伤的能力。Shin等人发现花青素通过阻断JNK和p53信号通路减少局灶性脑缺血诱导的神经元损伤。此外，花青素还能抑制脑缺血后海马区外周免疫细胞的浸润，减少促炎细胞因子的释放，降低皮层和海马区髓过氧化物酶的活性。这些作用提示花青素具有抗炎作用。花青素还可以显著降低暴露于LPS的小鼠脑中小胶质细胞和星形胶质细胞的活化。
Furthermore, the effect of anthocyanins on the microglial M1/M2 phenotypes has also been demonstrated in the previous reports by using cyanidin‑3–O‑Glucoside (C3G), an anthocyanin. C3G could enhance the
expressions of CD206 and CD16, which are known as M2-specifcmarkers. The anti-inflammatory effect of C3G has been found in
LPS-stimulated BV2 microglia activation. The authors found that pretreatment with C3G significantly inhibited the activation of NF-κB and p38 MAPK signaling pathways in LPS-activated BV2 cells, and then reduced the production of pro-inflammatory cytokines IL-1β and IL-6. Moreover, Meireles et al. have explored the role of anthocyanins on the change of microglial phenotype by using N9 microglia cell line. They revealed that cyanidin, C3G and the amethylated form of C3G inhibited the polarization of M1 microglia after LPS/IL-4 stimulation. These findings suggested that the consumption of anthocyanins has the possibility of anti-neuroinflammation and against neuronal
injury following brain ischemia.
此外，先前的报告中通过使用花青素-3-O-葡萄糖苷（C3 G），证明了花青素对小胶质细胞M1/M2表型的影响。C3 G可以增强CD 206和CD 16的表达，这两种标记物被称为M2特异性标记物。C3 G的抗炎作用已在LPS刺激的BV 2小胶质细胞活化中发现。C3 G预处理可显著抑制LPS激活的BV 2细胞中NF-κB和p38 MAPK信号通路的激活，进而减少促炎细胞因子IL-1β和IL-6的产生。此外，Meireles等通过使用N9小胶质细胞系探索了花青素对小胶质细胞表型变化的作用。他们发现矢车菊素、C3 G和C3 G的甲基化形式抑制LPS/IL-4刺激后M1小胶质细胞的极化。这些结果表明，食用花青素具有抗神经炎症和脑缺血后神经元损伤的可能性。
Isoflavones and the other flavonoids
Genistein (4’,5,7-trihydroxyisofavone) is a natural isoflavone compound, with neuroprotective activity, and the antioxidant and anti-inflammatory effects. Studies have revealed that genistein could protect against the chronic or acute brain damage via inhibiting the inflammatory responses. Moreover, genistein has been found
to suppress the polarization of M1 microglia and promote the trans formation of activated microglia to M2 subtype in rat hippocampus after stimulation with isoflurane. Besides, genistein could inhibit the expressions of TNF-α, IL-1β, IL-6 and IL-8 at mRNA level in
isoflurane-treated BV2 cells. Importantly, genistein promoted the transformation of microglia to M2 subtype. These data suggested that genistein-mediated anti-neuroinflammation might be related with
promoting the phenotypic transformation of microglia to M2 subtype.
异黄酮和其他类黄酮
染料木黄酮（4 '，5，7-三羟基异黄酮）是一种天然的植物化合磅，具有神经保护活性，以及抗氧化和抗炎作用。研究表明，染料木黄酮可以通过抑制炎症反应来保护慢性或急性脑损伤。此外，染料木黄酮还能抑制异氟醚刺激后大鼠海马M1小胶质细胞的极化，并促进激活的小胶质细胞向M2亚型转化。此外，染料木黄酮还能在mRNA水平上抑制异氟烷诱导的BV 2细胞TNF-α、IL-1β、IL-6和IL-8的表达。重要的是，染料木黄酮促进小胶质细胞转化为M2亚型。这些结果提示染料木黄酮介导的抗神经炎症作用可能与促进小胶质细胞向M2亚型转化有关。
Furthermore, chalcones and dihydrochalcones likewise have the
ability to modulate the neuroinflammation. The chalcone (2,20,50-trihydroxychalcone) has been reported to modulate neuroinflammatory activation in BV2 microglial cells and promote a shift from an M1 phenotype to a downregulated microglial profile. The 2’-hydroxy-4,3’,4’,6’-tetramethoxychalcone has also been found to inhibit the inflammatory responses in BV2 microglial cells induced by LPS.
查耳酮和二氢查耳酮同样具有调节神经炎症的能力。据报道，查耳酮（2，20，50-三羟基查耳酮）可调节BV 2小胶质细胞中的神经炎性激活，并促进从M1表型向下调的小胶质细胞特征转变。还发现2 '-羟基-4，3'，4 '，6'-四甲氧基查耳酮抑制LPS诱导的BV 2小胶质细胞中的炎症反应。
Conclusion
After stroke onset, the glial cells and the infiltrating immune cells contribute to a complicated neuroinflammation cascade, thereby underpin the ischemic stroke injury. Flavonoids are rich in our daily diet (e.
g., vegetables and fruits) and possess the respectable therapeutic effects on cerebral ischemia injury via inhibiting the neuroinflammation. For instance, naringenin, EGCG, quercetin, rutin, apigenin, baicalein, an thocyanins and the other flavonoids, have been found to inhibit and limit neuroinflammation following ischemic stroke via affecting the activation of microglia and/or astrocytes. These flavonoids might be
potential candidates for treating the ischemic stroke.
结论
脑卒中后，胶质细胞和浸润的免疫细胞参与了复杂的神经炎症级联反应，从而解除了缺血性脑卒中的损伤。我们的日常饮食中含有丰富的调味品（例如蔬菜和水果），通过抑制神经炎症对脑缺血损伤具有良好的治疗作用。例如，已经发现柚皮素、EGCG、槲皮素、芦丁、芹菜素、黄芩素、花青素和其他类黄酮通过影响小胶质细胞和/或星形胶质细胞的活化来抑制和限制缺血性中风后的神经炎症。这些黄酮类化合物有可能成为治疗缺血性脑卒中的潜在药物。
结束语：
神经内科3病区全体，预祝大家万事如意、心想事成！