Enhancement of Nitric Oxide Production Is Responsible for Minimal Intimal Hyperplasia of Autogenous Rabbit Arterial Grafts

Effects of Hydroxytyrosol in Endothelial Functioning: A Comprehensive Review

Pharmacologists have been emphasizing and applying plant and herbal-based treatments in vascular diseases for decades now. Olives, for example, are a traditional symbol of the Mediterranean diet. Hydroxytyrosol is an olive-derived compound known for its antioxidant and cardioprotective effects. Acknowledging the merit of antioxidants in maintaining endothelial function warrants the application of hydroxytyrosol in endothelial dysfunction salvage and recovery. Endothelial dysfunction (ED) is an impairment of endothelial cells that adversely affects vascular homeostasis. Disturbance in endothelial functioning is a known precursor for atherosclerosis and, subsequently, coronary and peripheral artery disease. However, the effects of hydroxytyrosol on endothelial functioning were not extensively studied, limiting its value either as a nutraceutical supplement or in clinical trials. The action of hydroxytyrosol in endothelial functioning at a cellular and molecular level is gathered and summarized in this review. The favorable effects of hydroxytyrosol in the improvement of endothelial functioning from in vitro and in vivo studies were scrutinized. We conclude that hydroxytyrosol is capable to counteract oxidative stress, inflammation, vascular aging, and arterial stiffness; thus, it is beneficial to preserve endothelial function both in vitro and in vivo. Although not specifically for endothelial dysfunction, hydroxytyrosol safety and efficacy had been demonstrated via in vivo and clinical trials for cardiovascular-related studies.

Reduced Function of Endothelial Nitric Oxide and Hyperpolarization in Artery Grafts with Poor Runoff

BACKGROUND

The endothelium regulates vascular tonus by releasing nitric oxide (endothelium-derived nitric oxide, EDNO) and hyperpolarizing factor (endothelium-derived hyperpolarizing factor, EDHF). In vein grafts with poor runoff, lack of function of these factors causes severe intimal hyperplasia. This study evaluated how the functions of EDNO and EDHF are altered in artery grafts under poor runoff conditions.

MATERIALS AND METHODS

The right common carotid arteries of rabbits were excised and implanted in their original positions as autogenous grafts under normal runoff conditions ("nonoccluded grafts") or poor runoff conditions ("poor runoff grafts"). Histochemical changes, acetylcholine (ACh)-induced effects on endothelium-dependent relaxation and smooth muscle cell (SMC) hyperpolarization were examined.

RESULTS

Both artery graft types displayed negligible intimal hyperplasia. In the absence and presence of an EDNO synthase inhibitor, ACh-induced relaxation was lower in grafts with poor runoff than in nonoccluded grafts. Furthermore, ACh-induced but not nonreceptor agonist A23187-induced SMC hyperpolarization was lower in the poor runoff graft group than in the nonoccluded graft group.

CONCLUSIONS

Unlike in those in vein grafts, the functions of EDNO and EDHF in autogenous carotid artery grafts under poor runoff conditions were reduced but partly maintained. In such artery grafts, intimal hyperplasia caused by surgical operation was not present. These results may explain some of the mechanisms underlying the improved patency of artery grafts compared with vein grafts.

Exosomes derived from human umbilical cord mesenchymal stem cells inhibit vein graft intimal hyperplasia and accelerate reendothelialization by enhancing endothelial function

Background

In our previous research, we found that mesenchymal stem cell (MSC) transplantation therapy can inhibit intimal hyperplasia and enhance endothelial function in arterialized vein grafts in rats. However, whether MSC-derived exosomes (MSC-exosomes) can reduce neointimal formation and its possible mechanism is still unclear.

Methods

The primary human umbilical cord MSCs (hucMSCs) and human umbilical vein endothelial cells (HUVECs) were isolated and characterized by flow cytometry and immunofluorescence. The exosomes derived from hucMSCs (hucMSC-exosomes) were identified by transmission electron microscopy and western blots. hucMSC-exosomes were intravenously injected into a rat model of vein grafting, and its effect on vein grafts reendothelialization and intimal hyperplasia was assessed by physical, histological, immunohistochemistry, and immunofluorescence examinations. The effects of hucMSC-exosomes on endothelial cells were evaluated by integrated experiment, EdU staining, scratch assay, and Transwell assay. The expression levels of key gene and pathways associated with the biological activity of vascular endothelial cells were evaluated following the stimulation of hucMSC-exosomes.

Results

We successfully isolated and characterized primary hucMSCs and hucMSC-exosomes and primary HUVECs. We verified that the systemic administration of hucMSC-exosomes accelerates reendothelialization and decreases intimal hyperplasia of autologous vein graft in a rat model. We also identified that hucMSC-exosomes can be uptaken by endothelial cells to stimulate cell proliferative and migratory activity in vitro. Furthermore, we detected that vascular endothelial growth factor (VEGF) plays an important part in hucMSC-exosome-mediated proliferation and migration in HUVECs. In addition, we also provided evidence that the signalling pathways of PI3K/AKT and MAPK/ERK1/2 take part in hucMSC-exosome-induced VEGF regulation.

Conclusion

Our data suggest that hucMSC-exosomes exert a vasculoprotective role in the setting of vein graft disease, which may provide a new clue to protect against vein graft failure in the future.