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Aims Liquorice is a widely used herbal medicine for treating various diseases native to southern Europe and parts of Asia. Isoliquiritin (ISL), a licorice root-derived flavonoid, has been reported to exhibit antioxidant, anti-inflammatory, anti-genotoxic activity and anti-depression activities. This study was aimed to explore the pro-angiogenic activity of ISL and explicate the underlying mechanism. Main methods In vitro, ISL-treated human umbilical vein endothelial cells (HUVECs) were analyzed for cell viability, cell migration and tube formation. In vivo, pro-angiogenic effects were evaluated for the intersegmental vessels (ISVs) formation in transgenic zebrafish embryos [Tg(fli-1: EGFP)]. Furthermore, a blocking assay with eight pathways-specific kinase inhibitors were also used to determine the potential pro-angiogenic mechanism of ISL. Key findings ISL counteracted tyrosine kinase inhibitor II (VRI)-induced endothelial cell apoptosis and promoted cell migration and tube formation in HUVECs. ISL markedly rescued ISVs loss induced by VRI in zebrafish embryos, probably by activating vascular endothelial growth factor receptor-2 (VEGFR-2), phosphoinositide 3-kinase (PI3K), Raf and mitogen-activated protein kinase (MEK)-dependent signaling pathways. Significance Our study first discovered and confirmed the pro-angiogenic activity of ISL both in HUVECs and zebrafish. Thus, ISL could be developed as a potential therapeutic agent by the role of pro-angiogenic activity for the treatment of cardiovascular diseases, cerebrovascular diseases and other vascular diseases.

Background Ischemic stroke is a multifactorial disease contributing to mortality and neurological dysfunction. Isoliquiritin (ISL) has been reported to possess a series of pharmacological activities including antioxidant, anti-inflammatory, antifungal, anti-depression, anti-neurotoxicity and pro-angiogenesis activities but whether it can be used for ischemic stroke treatment remains unknown. Purpose The goal of this study is to explore its therapeutic effect on ischemic stroke and demonstrated the potential mechanism of ISL in zebrafish model. Methods Using the photothrombotic-induced adult zebrafish model of ischemic stroke, we visualized the telencephalon (Tel) and optic tectum (OT) infarction injury at 24 h post-light exposure for 30 min by TTC and H&E staining. The effect of ISL on neurological deficits was analyzed during open tank swimming by video tracking. The antioxidant activity against ischemia injury was quantified by SOD, GSH-Px and MDA assay. Transcriptome analysis of zebrafish Tel revealed how ISL regulating gene expression to exert protective effect, which were also been validated by real-time quantitative PCR assays. Results We found for the first time that the Tel tissue was the first damaged site of the whole brain and it showed more sensitivity to the brain ischemic damage compared to the OT. ISL reduced the rate of Tel injury, ameliorated neurological deficits as well as counteracted oxidative damages by increasing SOD, GSH-Px and decreasing MDA activity. GO enrichment demonstrated that ISL protected membrane and membrane function as well as initiate immune regulation in the stress response after ischemia. KEGG pathway analysis pointed out that immune-related pathways, apoptosis as well as necroptosis pathways were more involved in the protective mechanism of ISL. Furthermore, the log2 fold change in expression pattern of 25 genes detected by qRT-PCR was consistent with that by RNA-seq. Conclusions Tel was highly sensitive to the brain ischemia injury in zebrafish model of ischemic stroke. ISL significantly exerted protective effect on Tel injury, neurological deficits and oxidative damages. ISL could regulate a variety of genes related to immune, apoptosis and necrosis pathways against complex cascade reaction after ischemia. These findings enriched the study of ISL, making it a novel multi-target agent for ischemic stroke treatment.

Ethnopharmacological relevance Tongnao Decoction (TND) is a Chinese decoction approved and used in Jiangsu Province Hospital for the treatment of ischemic stroke. It shows conclusive efficiency in the improvement of neurologic impairment and activities of daily living of the patients. Aim of the study Recently, angiogenesis has been recognized as a potential therapeutic strategy for treating cerebral ischemia. This study was aimed to provide comprehensive evidence for the pro-angiogenic effect of TND and characterize the underlying mechanism. Materials and methods We firstly established the chemical fingerprinting of TND. Then, the in vitro pro-angiogenic activities of TND were tested on human umbilical vein endothelial cells (HUVECs) through cell viability, wound healing and tube formation assays. The in vivo pro-angiogenic effects were evaluated on transgenic zebrafish embryos [Tg (fli-1: EGFP)] through the formation of intersegmental vessels (ISVs), subintestinal vessels (SIVs) and central arteries (CtAs). Lastly, the potential mechanisms of TND were analyzed by a blocking assay with eight pathways-specific kinase inhibitors. Results TND promoted the proliferation, migration and tube formation of HUVECs. TND also rescued the impairment of ISVs, SIVs and CtAs caused by VRI in a dose-dependent manner in zebrafish embryos. TND could activate vascular endothelial growth factor receptor-2 (VEGFR-2), phosphoinositide 3-kinase (PI3K) – protein kinase B (Akt) and Raf – mitogen-activated protein kinase1/2 (MEK1/2) – extracellular regulated kinase 1/2 (ERK1/2) signaling pathways. Conclusion Our study firstly demonstrated the pro-angiogenic activities of TND. Our work provided evidences for the clinical usage of TND in restoring neurovascular function through promoting angiogenesis in the ischemic cerebral microvascular.