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In Vivo Imaging and Quantitation of the Host Angiogenic Response in Zebrafish Tumor Xenografts
Published on: August 14, 2019
Expression of adenosine receptors and vegf during angiogenesis and its inhibition by pentoxifylline-A study using
Jhansi Rani Nathan1, Ganesh Lakshmanan2, Felicia Mary Michael2
1Department of Genetics, Dr. ALM PG IBMS, Universityof Madras, Taramani, Chennai-600113, Tamilnadu, India.
Abstract:
Angiogenesis, formation of new blood vessels is an important process involved in neovascular diseases and tumor progression. Understanding and defining novel therapeutic targets of neovascular diseases like retinopathy of prematurity, diabetic retinopathy and age-related macular degeneration have been hindered by a lack of appropriate animal models. Zebrafish provides an excellent vertebrate model to study above disorders since its circulatory system and retinal layers are similar to mammals. Adenosine is a known mediator of angiogenesis in hypoxic condition and adenosine receptor antagonists such as theophylline, theobromine are known to exert antiangiogenic properties. We evaluated the anti-angiogenic potential of a methylxanthine pentoxifylline (PTX) with various concentrations (0.1-1mM) at 50% epiboly stage (5.2 hpf) of zebrafish embryos and studied the mRNA expression of major angiogenic factors like vegfaa and its receptors under normal conditions and when treated with an adenosine analog NECA (5'-N-ethylcarboxamidoadenosine). Upregulation of adenosine receptors, hif-1α and vegfaa by NECA could possibly mimic hypoxic condition, but PTX downregulated vegfaa and other growth factors at 1mM concentration. Vegfa protein expression was also downregulated by PTX in the retina and the compound did not damage the retinal cells. Embryos treated with PTX generated abnormal phenotypic variants with poor vasculature, tail bending and developmental delay at 1mM. Survival rates, heart rate and hatching rates were also significantly lower. Targeting the vegf signaling pathway with small molecules inhibiting adenosine receptors in addition to antagonizing vegf might be a promising approach to treat neovascular diseases of the retina and also tumors.
Insights
Pentoxifylline (PTX) shows anti-angiogenic potential by downregulating vascular endothelial growth factor A (Vegfa) in zebrafish embryos. This suggests PTX may be a promising therapeutic for neovascular diseases and tumors.
Area of Science:
- Developmental biology
- Pharmacology
- Ophthalmology
Background:
- Angiogenesis is crucial for neovascular diseases and tumor growth.
- Zebrafish are a suitable vertebrate model for studying these conditions due to physiological similarities with mammals.
- Adenosine and its receptor antagonists influence angiogenesis, with methylxanthines like pentoxifylline (PTX) being potential anti-angiogenic agents.
Purpose of the Study:
- To evaluate the anti-angiogenic potential of pentoxifylline (PTX) in zebrafish embryos.
- To investigate the effects of PTX on the expression of key angiogenic factors, including vascular endothelial growth factor A (Vegfa).
- To assess the therapeutic implications of targeting adenosine receptors and Vegf signaling for neovascular diseases.
Main Methods:
- Zebrafish embryos were treated with varying concentrations of PTX (0.1-1mM) at the 50% epiboly stage.
- mRNA expression of angiogenic factors (vegfaa) and receptors was analyzed under normal and adenosine analog (NECA) treated conditions.
- Vegfa protein expression in the retina was assessed, along with phenotypic analysis of treated embryos.
Main Results:
- Pentoxifylline (PTX) at 1mM concentration downregulated vegfaa mRNA and Vegfa protein expression.
- NECA (adenosine analog) upregulated adenosine receptors, hif-1α, and vegfaa, mimicking hypoxic conditions.
- High concentration PTX treatment resulted in developmental abnormalities, including poor vasculature, tail bending, developmental delay, and reduced survival rates, without causing retinal cell damage.
Conclusions:
- Pentoxifylline exhibits anti-angiogenic properties by inhibiting the Vegf signaling pathway in zebrafish embryos.
- Targeting adenosine receptors and Vegf concurrently may offer a novel therapeutic strategy for treating retinal neovascular diseases and tumors.
- Zebrafish embryos serve as a valuable model for evaluating anti-angiogenic compounds and understanding neovascularization processes.
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