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FEATURE ARTICLE Angiogenesis Opens A Way for Chinese Medicine to Treat Stroke YANG A-li (杨阿莉)1,2,3△, LIANG Qing-hua (梁清华)1,3△, Cui Han-jin (崔寒尽)1,3, ZHOU Hua-jun (周华军)4, LUO Jie-kun (罗杰坤)1,3, and TANG Tao (唐 涛)1,3 ABSTRACT Based on the pathophysiology of the brain, advance in angiogenesis induced by stroke, and evidences of Chinese-medicine-mediated angiogenesis, the possibility to study the stroke-treating mechanism of Chinese medicine in angiogenesis was discussed. And regarding our previous work on angiogenesis modulated by qi-tonifying and stasis-eliminating therapy following intracerebral hemorrhage, we proposed some questions, which should be taken into account in the further work. KEYWORDS stroke, Chinese medicine, angiogenesis Dr. TANG Tao
Stroke is one of the major causes of morbidity and mortality worldwide. And along with the highspeed economic development and the population aging in China, stroke is becoming an innegligible threat to the health of Chinese people, which incurred a heavy burden on the victims' families and the society.(1) There is a long-history on the practice of Chinese medicine (CM) in stroke treatment, and most Chinese patients at the chronic or sequela stage are more willing to resort to CM nowadays.(2) In the past decades, clinical study on CM-treated stroke has been of the great interest, in which the multi-center, doubleblind and random controlled protocols were adopted in order to explore the efficacy evaluation methods to reflect the CM clinical characteristics. (3,4) As to the CM mechanisms in stroke treatment, besides many studies devoted to inhibiting neuron apoptosis, accumlative evidences were found that CM can enhance proliferation, migration and differentiation of neural stem cells, which contributes to brain self-repair after the stroke insult.(5,6)
Microvasculature and Brain Self-repair Recent studies have proved that there is widespread and dramatical reactions of inflammation and oxidative stress, in either ischemic or hemorrhage stroke. Besides neurons, microvasculature is also among the primary targets to these injuries. (7,8) It is well-known that the brain is a highly blooddependent organ, and blood is the only source of
glucose and oxygen for cerebral neurons. Thence, microvasculature is the basic way for substance exchange of neurons. In addition, blood-brain barrier is essential for the microevironment stability of neurons, in which cerebral endothelial cells (ECs) and astrocytes are the fundamental elements. Thus, the integrity of microvasculature can be the structural basis of function of the neuron, even of the brain.(9,10) Although proliferation of ECs ceases in the adult brains, the process can restart under many pathophysiological conditions. (11) The results of our peers and ours revealed that there is cerebral angiogenesis after stroke, accompanied by increase in local blood flow and expression of numerous angiogenesis-related factors.(12-15) And there is a close correlation between the cerebral vessel density and ©The Chinese Journal of Integrated Traditional and Western Medicine Press and Springer-Verlag Berlin Heidelberg 2013 Supported by National Natural Science Foundation of China (No. 30400581, 30873221, 81173175 and 81202625), Project for New Century Excellent Talents (No. NCET-11-0522), Hunan Provincial Natural Science Foundation (Grant No. 10JJ2023 ) and the Key-discipline Construct Programs of Hunan Province and State Administration of Traditional Chinese Medicien 1. Institute of Integrative Medicine, Xiangya Hospital, Central South University, Changsha (410008), China; 2. Institute of Neurology, Xiangya Hospital, Central South University, Changsha (410008), China; 3. Key Labatory of Chinese Gan of State Administration of Traditional Chinese Medicien, Changsha (410008), China; 4. Department of Neurology, Yichang Central Hospital, Yichang (443003), Hubei Province, China △ Those authors contribute to the work equally Correspondence to: Prof. TANG Tao, Tel: 86-731-84327122, Fax: 86-731-84327332, E-mail:
[email protected] DOI: 10.1007/s11655-013-1342-1
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the prognosis of stroke survivors.(16) Therefore, to enhance the repair of brain tissue via therapeutical angiogenesis may be a promising way for CM to treat stroke.
Angiogenesis and the Molecular Events New vessel growth occurs in 3 forms: vasculogenesis, angiogenesis and arteriogensis. Vasculogenesis is a process whereby angioblasts differentiate from the mesoderm into ECs to form a de novo primitive vascular network. While during angiogenesis, new vessels are formed from preexisting ones by sprouting and nonsprouting mechanisms. On the other hand, arteriogenesis is the remodeling of preexisting arteriolar collateral networks into large collateral arteries.(17) Although stroke can induce vasculogenesis,(18) angiogenesis is the primary form in adult mammalian brains.(19) Angiogenesis is a finely-tuned process mediated by the balance of a large variety of angiogenic factors and interaction between the newborn ECs and extracellular matrix (ECM). To form the functional microvasculature, angiogenesis consists of 3 steps: (1) the initial phase: many insults, including trauma, local inflammation, hypoxia and certain cytokines, increase the secretion of pro-angiogenic factors. The factors can induce angiogenesis after local accumulation; (2) the proliferative and invasive phase: by protein enzyme-like matrix m e ta l l o p r o te inases (MMPs), which de g ra d e s ECM and releases ECs from ECM, ECs begin to proliferate, migrate and extend their way into the surrounding tissues; (3) the mature phase: by lumen formation, ECs differentiation and vascular structure pruning, the mature microvasculature comes to meet the needs of the tissue (Figure 1).(20)
Figure1.
Among pro-angiogenic molecules, vascular endothelial growth factor (VEGF) is the only confirmed specific mitogen for ECs. By binding to its receptors (VEGF receptor, VEGFR) on ECs, it can trigger the first step of angiogenesis-sprouting, forming the immature vessels. Activation of VEGFR-1 (fms-like tyrosine receptor, Flt) can govern the cells to moderately proliferate and organizedly assembly(21) and activation of VEGFR-2 fetal liver kinase/kinase insert domain receptor (EIK/KDR) can start cell proliferation. (22) Angiopoietin (Ang) is another proangiogenic factor, which can mediate stabilization, mature and remodeling of a new-born vessel, by binding to its receptor, Tie-2.(23) Thrombospondins (TSPs), the angiogenesis inhibitors, can bind its cellular surface receptor, CD36, to stop their mitosis, migration and induce apoptosis.(24) ECM, creating the microenvironment for angiogenesis, is critical for EC shape, structure, survival and proliferation, together with EC growth factor expression and interactions with blood vessels. To allow new vessel outgrowth, ECM remodelled by MMPs is needed for removal of the physical barrier and preparation of the substrate that may stimulate ECs migration. Integrins are noncovalently linked heterodimer receptors that recognize specific ECM proteins. Functionally, integrins can regulate ECs behavior by: (1) forming a transmembrane link between the matrix and the cell cytoskeleton; (2) transducing extracellular stimuli to intracellular signals; and (3) generating increased receptor specificity by cellular activation. And the integrin-mediated recognition is crucial for the ECs biology and the lumen formation.
Angiogenesis in CM-treated Stroke Many recent reports have indicated that CM does have the effects on angiogenesis. (25) Both
Schema of Angiogenesis
Notes: Angiogenesis is a finely-tuned process mediated by the balance between pro-angiogenic factors and anti- angiogenic factors, interaction between the new-born ECs and ECM, which includes ECs proliferation, lumen formation and vasculature maturation
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the single herb (Radix Salviae miltiorrhizae ) and the composite formulae, such as Danggui Buxue Decoction (当归补血汤), Xuefu Zhuyu Decoction (血府逐瘀汤) and Xiongshao Capsule (芎芍胶囊), can enhance angiogenesis on chick embryo chorioallantoic membrane (CAM). (26) Shumai Decoction (舒脉汤) can promote VEGF and platelet-derived growth factor (PDGF)-BB-mediated angiogenesis and arteriogenesis through the PI3K/Akt signaling pathway after heart infart. (27) And Pien Tze Huang (片仔癀) inhibits angiogenesis in vivo in CAM model and in vitro on human umbilical vein endothelial cells (HUVECs) by depression of VEGF and basic fibroblast growth factor (bFGF).(28) By focal adhesion kinase activation, aqueous extract of the medicinal plant Patrinia villosa Juss enhances ECs proliferation, migration, and the lumen forming both in vitro and in vivo .(29) Leaded by academist CHEN Ke-ji, the therapy of activating blood circulation to remove stasis is the most fruitful field of integrative medicine. Ischemic stroke is one of the stereotypes of blood stasis syndrome, and there are many reports indicating that CM enhances angiogenesis following brain ischemia. Catalpol from Radix Rehmannia promotes infarctedbrain angiogenesis and ameliorates the brain edema by upregulating VEGF and erythropoietin coordinately.(30) Ginsenoside Rg1 facilitates angiogenesis after hypoxia ischemia in neonatal rat brains via hypoxia-inducible factor (HIF)-1α/VEGF signaling pathway. (31) Within 24 h post-ischemic stroke, administration of dl-3nbutylphthalide, a celery seed extract, contributes to rescuing brain tissue by VEGF and HIF-1α-associated angiogenesis.(32) Cornel iridoid glycoside promotes angiogenesis and improves neurological function after cerebral ischemia, by upregulation of VEGF and Flk.(33) Tongxinluo Capsule (通心络胶囊) significantly promoted the post-ischemic angiogenesis and the volume of blood perfusion, which plays a certain compensatory role in blood flow.(34) And Buyang Huanwu Decoction (补阳还五 汤), a classic formula, enhances the expression of VEGF and Flk in ischaemic brains, which facilitates motor function recovery and infarction volume reduction.(35) In addition, acupuncture, another CM method, also shows certain positive effects on stroke-induced angiogenesis.(36) Electroacupuncture (EA) at "Quze" (PC3) and "Neiguan" (PC6), along either large intestine meridian or pericardium meridian, can upregulate VEGF in serum and brain after ischemic
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stroke. (37) EA at Shuigou (GV26) increases ECs proliferation and regional cerebral blood flow in the ischemic boundary zone.(38) By the theory "Bleeding out of vessels forms blood stasis", our group conducted studies on the effects of qi-tonifying stasis-eliminating (QTSE) therapy on angiogenesis in hemorrhagic stroke. In the studies, the thoughts and the experiment design are guided by the CM concepts of dynamic balance and wholism, because the balance between proangiogenic and anti-angiogenic factors and the interaction of the ECs with its microenvironment, ECM, govern the sprouting vessels to become the mature microvasculature. And our work proved that hemorrhagic stroke induced angiogenesis by upregulation of VEGF, Ang1, TSPs and their own receptors. (14,39,40) Buyang Huanwu Decoction, the example of QTSE therapy, can facilitate the angiogenesis in the lesioned area, increase the expression of VEGF, Ang1 and the receptors, and change the profile of TSPs. (41-43) Moreover, the decoction can up-regulate the expression of type Ⅳ collagen, integrin αVβ3 and β3 subunit around the hemotoma,(44,45) and sustain MMP-2 increase in a long-term pattern.(46) And EA at Zusanli (ST36), along Stomach (Wei) meridian, which can both fortify qi and relieve blood stasis in CM theory, enhances cerebral angiogenesis after intracerebral hemorrhage.(47)
Prospective and Troubleshoots Although angiogenesis is a hot spot in brain repair now, the work on CM-regulated cerebral angiogenesis is still at the preliminary stage. The work on cardiovascular system and tumor is leading the frontier of angiogenesis, which has been providing many novel ideas and methods to the brain, besides the previous work in "blood circulation activation to remove stasis", which contributes to understanding the angiogenesis-related mechanisms of CM in treating stroke. And to our knowledge and experience in this field, there are some issues raised: (1) Although the multi-target pattern of CM composite formulae can explain that CM affects numerous angiogenic factors simultaneously, shall it be taken into account if there is a key factor like HIF-1αin the angiogenic upstream?(48) (2) Can we use a mathematical model to reflect the coordination of various angiogenic factors
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along the way to form the new microvasclature? (49) (3)There is significant overlap on angiogenesis and neurogenesis during tissue repair after stroke, is it still necessary to evaluate the significance of either process alone?(50)
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(Received March 1, 2013) Edited by WANG Wei-xia