Abstract
Ischemia has been reported to be related to matrix metalloproteinase-9 (MMP-9) level upregulation. Neovascular glaucoma (NVG) (in proliferative diabetic retinopathy and central/branch retinal vein occlusion) and age-related macular degeneration are known vision-threatening retinal ischemic disorders. In this review, an extensive discussion has been made into how MMP-9 is related to retinal ischemia and what the underlying mechanisms of various traditional Chinese medicine (TCM) compounds and combinations are. High intraocular pressure-induced retinal ischemic changes were characterized by decreased electroretinogram (ERG) b-wave amplitudes, a loss of choline acetyltransferase (ChAT) immunopositive amacrine neurons/processes, increased Müller’s vimentin immunoreactivity, and profound retinal ganglion cell (RGC) death. It has also been observed hypoxia inducible factor-1α (HIF-1α), MMP-9 and vascular endothelium growth factor (VEGF) upregulation at the protein/mRNA levels. After ischemia, both the p38 mitogen-activated protein kinases (MAPKs)-stimulated MMP-9 upregulation and HIF-1α-triggered VEGF overexpression might result in neovascularization. Conclusively, baicalein seems to have neuroprotection via antioxidation, antiapoptosis, HO-1 upregulation and HIF-1α, VEGF, and/or MMP-9 downregulation. Furthermore, baicalein inhibition on retinal ischemia-induced MMP-9 upregulation seems to be “partly” associated with its antioxidation. Additionally, retinal ischemia, oxidative stress, and/or kainate excitotoxicity could be protected by resveratrol: “via MMP-9 and inducible nitric oxide synthetase (iNOS) downregulation, and heme oxygenase-1 (HO-1) upregulation,” S-allyl L-cysteine (SAC): “through iNOS, HIF-1α, VEGF inhibition and/or MMP-9 downregulation, and antiapoptosis,” Chi Ju Di Huang Wan: “by means of antiapoptosis, antioxidation, MMP-9 downregulation and p38 MAPK inhibition.”
Keywords
- matrix metalloproteinase-9
- retinal ischemia
- traditional Chinese medicine
- hypoxia inducible factor-1α
- vascular endothelium growth factor
- p38 mitogen-activated protein kinase
- baicalein
- resveratrol
- inducible nitric oxide synthetase
- heme oxygenase-1
- S-allyl L-cysteine
- Chi–Ju–Di–Huang–Wan
1. Introduction
Central retinal artery occlusion (CRAO) [16], primary open angle glaucoma (in urban areas) [24], diabetic retinopathy (type 2 diabetes) [21], and age-related macular degeneration (AMD; age ≥40 of years [17]) is related to retinal ischemia with the incidences of 0.0018, 4, 2.9, and 0.36%, respectively.
Central/branch retinal vein occlusion (CRVO/BRVO) are also associated with retinal ischemia. Retinal or choroidal ischemia can lead to angiogenesis, associated with subretinal fluid and bleeding. Fifteen percent of AMD patients experience profound central vision loss owing to choroidal neovascularization (CNV), namely neovascular AMD (nvAMD) [11]. This explains why nvAMD becomes a leading cause of blindness in the elderly. Vision deterioration further puts patients at a greater danger of falls and possibility of being in need of residential nursing care. There is an eminent necessity for new agents that trigger the self-protective mechanisms and avoid harmful neovascularization.
Oxidative stress in the human retinal pigment epithelium (hRPE) leads to the upregulation of matrix metalloproteinase-9 (MMP-9). Upregulation of MMP-9 can adversely degrade the extracellular matrix and induce irreversible retinal ganglion cell (RGC) death [9]. Brain ischemia has been reported to trigger MMP-9 upregulation [8]. In AMD, plasma MMP-2 and MMP-9 levels have been also indicated to be upregulated [6]. As a consequence, ischemia or oxidative stress may be related to MMP-9 level upregulation. In AMD, plasma MMP-9 concentrations promote neovascularization throughout the early phases of CNV [6]. Previous results have supported that increases in MMP-9, hypoxia inducible factor-1α (HIF-1
In our previous publications, there were active components of traditional Chinese medicine (TCM) that were proved to be antioxidants such as ferulic acid from Chuang Xiong [1, 2]. These include baicalein from Huángqín (
Resveratrol has shown to possess strong antioxidant properties. Resveratrol has also been confirmed to provide neuroprotective effects during cerebral ischemia plus reperfusion (I/R), [19], mice retinal I/R [12], and
Baicalein (5,6,7-trihydroxy-2-phenyl-4H-1-benzopyran-4-one) is a natural flavonoid from
Within macrophages and endotheliums, SAC, an organosulfur compound in aged garlic extracts, serves as an antioxidant [10]. It has been investigated whether and how SAC can protect against retinal ischemia. Changes in Thy-1, HIF-1
Traditional CJDHW includes
2. Body-research methods
A daily oral intake of 3 mL of water (vehicle; Group 2) or CJDHW (2.8 or 4.2 g/kg/day; CJDHW2.8 or CJDHW4.2; Group 3 or 4) was given for 7 consecutive days preischemia or postischemia. In Group 5, 4 μL of 0.5 mM SB203580 (p38 MAPK inhibitor) was intravitreously injected to the ischemic eye (15 min preischemia). The control rats received a sham procedure (Group 1).
3. Conclusion: key results
The role of MMP-9 in a TCM compound or the TCM combination: An invention of a new small-molecule medicine will run through considerable tedious and prolonged processes. These include the selection of a single compound, animal safety study, investigational new drug, preclinical trial, clinical trials, and new drug application. Launching a new medicine might take 10–15 years and cost billions of US dollars. The institutional review board would be somehow strict to the investigators or the pharmaceutical companies when they were involved in implementing their clinical trials.
Artemisinin, one effective compound against malaria, was first isolated from the TCM, Qinghao, and tested in the 1970s in China [22]. Thrillingly, the discovery of artemisinin that awarded Professor Youyou Tu, the first Chinese Nobel Winner of Medicine in 2016 has pushed the era of traditional medicine come around [23]. There are many intractable disorders, such as the ischemia-related vision-threatening eye diseases, namely nvAMD, branch retinal artery occlusion (BRAO)/BRVO, CRAO/CRVO, proliferative diabetic retinopathy (PDR), diabetic macular edema (DME), NVG, or choroidal melanoma as described previously. It is clear that the traditional medicine could be an alternative way, which might be able to be complementary to the modern medicine. With the evidence described above and discussion as follows ( Figure 1 ), we hopefully could find a way out to manage with the defined retinal ischemia-associated vision-threatening ocular disorders.
The HIOP-induced retinal ischemic changes were characterized by a decrease in ERG b-wave amplitudes, a loss of choline acetyltransferase immunopositive amacrine cell bodies/neuronal processes, and an increase in vimentin immunoreactivity, a Müller cell marker. It has also been observed the upregulation of MMP-9 at the protein/mRNA level.
A combination of single compounds or TCM combinations [20] might create synergistic pharmaceutical effects to the modern medicine owing to their various therapeutic mechanisms with less unwanted drug effects. Whether the traditional medicine is ready to be complementary to the modern medicine, it is will be clear if the era of Ethnopharmacology would be ready, is not it.
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