Background: Endothelial cells (ECs), when exposed to diabetic milieu (high glucose concentrations), become dysfunctional and acquire new phenotypes, characterized by dysregulated angiogenesis, upregulation of inflammatory molecules and overproduction of reactive oxygen species (ROS). Considering that endothelial dysfunction is an early and reversible risk factor for the development of cardiovascular events, formulating effective strategies to prevent or reverse this phenomenon is crucial. In this context, the incretin hormone Glucagon-like peptide-1 (GLP-1), which exerts protective effects on the endothelium, has gained increasing attention. Methods: Human umbilical vein ECs (HUVECs) were cultured under normal (NG) or high glucose (HG) conditions for 7 days. Then, they were stimulated with a pro-inflammatory cytokine mix (IL-1b 40 ng/ml, TNFa 50 ng/ml, IL-6 50 ng/ml) for 24h, before or after 1 h treatment with GLP-1 (50 nM). The effect on gene and protein expression was assessed using qPCR and Western blot analysis. Results: In NG, pretreatment with GLP-1 prevents the increase in mRNA and protein expression of CLIC4, a cytokine-induced protein that activates the NLRP3 inflammasome, promotes endothelial angiogenesis and sensitizes β-cells to apoptosis. In HG, pretreatment with GLP-1 prevents the overexpression of α-smooth muscle actin (α-SMA), a marker of endothelial-to-mesenchymal transformation (EndMT). Pre- and post-treatment with GLP-1 reduces levels of YAP1, a critical mediator of inflammation and EndMT, while pretreatment reduces upregulation of its target CDC42 in HG. Moreover, GLP-1 reverts the HG-induced upregulation of IL12b, which contributes to phagocytic cell activation and inflammation. Furthermore, GLP-1 demonstrates a protective role towards mitochondrial function and against ROS overproduction as it increases transcription of KRIT1, SOD-1, Hsp27, COX2 and decreases GCN5 levels under both conditions, as well as it enhances NDUFA7 in NG and MNF1 and MFN2 in HG. Conclusions: GLP-1 can exerts beneficial effects on endothelial model grown under normal or chronic high glucose conditions by 1) downregulating inflammatory genes and 2) mitigating mitochondrial dysfunction. It demonstrates an attractive potential for alleviating endothelial inflammation and reducing oxidative stress generation.