E ndothelial cells play a central role in maintaining vascular

Fraga-Silva et al    ACE2 Activation and Endothelial Function    1237

and tempol, reduces the vascular damage in response to Ang 

II.

12,13

 In contrast, it has been reported that Ang-(1–7) via Mas 

ameliorates endothelial dysfunction in animal models by 

decreasing the oxidative stress.

14–16

 In accordance with these 

findings, we showed that chronic treatment with XNT reduced 

the ROS content in aorta of diabetic rats to a similar level 

observed in nondiabetic animals. In addition, XNT treatment 

was also able to reduce the Ang II–induced ROS production 

in human aortic endothelial cells. No significant changes 

were observed in the aortic expression of catalase, superoxide 

dismutase, and NOX2 among any of the groups. Taking into 

account that these enzymes are critical ROS scavengers, our 

results suggest that the modulation of the expression of these 

enzymes is not a mechanism by which XNT reduces the ROS 

production in aorta. Moreover, it is pertinent to note that the 

effects of XNT on ROS generation must be evaluated under 

in vivo condition to further confirm the association between 

XNT treatment and oxidative stress reduction.

In attempting to explain the mechanisms by which XNT 

improves the endothelial function of diabetic rats, acute exper-

iments evaluating the role of the endothelium and Mas recep-

tor were run in rings extracted from normal animals. Thus, the 

translation of these data obtained in normal rats to diabetic and 

hypertensive animals must be done carefully. However, they 

are an evidence of the mechanisms involved in the beneficial 

endothelial actions of XNT in these pathological conditions. 

Also, the hypertensive model was less explored in our study 

and it was used with the intention of adding more generality 

to our data.

Perspectives

Our present study demonstrated that XNT improves the 

endothelial function of hypertensive and diabetic rats. These 

actions involved the Mas receptor and reduction of ROS pro-

duction. Thus, these results indicate that pharmacological 

ACE2 activation by XNT promotes beneficial effects on the 

endothelial function and that this compound is a lead mol-

ecule to develop potential therapeutic strategies and drugs to 

treat cardiovascular and metabolic diseases by improving the 

endothelial function.

Sources of Funding

This work was partially supported by Conselho Nacional de 

Desenvolvimento Científico e Tecnológico (CNPq-Brazil), Fundação 

de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG-

Brazil), and National Institutes of Health (NIH-USA).

Disclosures

None.

References

  1.  Loscalzo J, Welch G. Nitric oxide and its role in the cardiovascular sys-

tem. Prog Cardiovasc Dis. 1995;38:87–104.

 2. Vanhoutte PM. Endothelial dysfunction in hypertension. J Hypertens 

Suppl

. 1996;14:S83–S93.

  3.  Touyz RM. Reactive oxygen species and angiotensin II signaling in vas-

cular cells—implications in cardiovascular disease. Braz J Med Biol Res. 

2004;37:1263–1273.

  4.  Unger T. The role of the renin-angiotensin system in the development of 

cardiovascular disease. Am J Cardiol. 2002;89:3A–9A; discussion 10A.

  5. Ferreira AJ, Santos RAS. Cardiovascular actions of angiotensin-(1–7). 

Braz J Med Res

. 2005;38:499–507.

  6.  Ferreira AJ, Santos RA, Bradford CN, Mecca AP, Sumners C, Katovich 

MJ, Raizada MK. Therapeutic implications of the vasoprotective axis of 

the renin-angiotensin system in cardiovascular diseases. Hypertension. 

2010;55:207–213.

  7.  Touyz RM. Intracellular mechanisms involved in vascular remodelling of 

resistance arteries in hypertension: role of angiotensin II. Exp Physiol. 

2005;90:449–455.

  8.  Santos RAS, Simões e Silva AC, Maric C, et al. Angiotensin-(1–7) is an 

endogenous ligand for the G protein-coupled receptor Mas. Proc Natl 

Acad Sci U S A

. 2003;100:8258–8263.

  9.  Santos RA, Campagnole-Santos MJ, Andrade SP. Angiotensin-(1-7): an 

update. Regul Pept. 2000;91:45–62.

 10.  Zisman LS, Meixell GE, Bristow MR, Canver CC. Angiotensin-(1-7) for-

mation in the intact human heart: in vivo dependence on angiotensin II as 

substrate. Circulation. 2003;108:1679–1681.

 11.  Vickers C, Hales P, Kaushik V, Dick L, Gavin J, Tang J, Godbout K, 

Parsons T, Baronas E, Hsieh F, Acton S, Patane M, Nichols A, Tummino 

P. Hydrolysis of biological peptides by human angiotensin-converting 

enzyme-related carboxypeptidase. J Biol Chem. 2002;277:14838–14843.

 12.  Nishiyama A, Fukui T, Fujisawa Y, Rahman M, Tian RX, Kimura S, Abe Y. 

Systemic and regional hemodynamic responses to tempol in Angiotensin 

II-infused hypertensive rats. Hypertension. 2001;37:77–83.

 13. Wilson SK. Role of oxygen-derived free radicals in acute angiotensin 

II–induced hypertensive vascular disease in the rat. Circ Res. 

1990;66:722–734.

 

14. Rabelo LA, Alenina N, Bader M. ACE2-angiotensin-(1-7)-Mas 

axis and oxidative stress in cardiovascular disease. Hypertens Res. 

2011;34:154–160.

 15.  Faria-Silva R, Duarte FV, Santos RA. Short-term angiotensin(1-7) recep-

tor MAS stimulation improves endothelial function in normotensive rats. 

Hypertension

. 2005;46:948–952.

 16.  Xu P, Costa-Goncalves AC, Todiras M, Rabelo LA, Sampaio WO, Moura 

MM, Santos SS, Luft FC, Bader M, Gross V, Alenina N, Santos RA. 

Figure 3. 1-[[2-(Dimetilamino)etil]amino]-4-(hidroximetil)-7-[[(4-

metilfenil)sulfonil]oxi]-9H-xantona-9 (XNT) treatment reduces 

reactive oxygen species (ROS) content in aortic rings of 

diabetic rats. Representative photomicrographs of descending 

thoracic aorta sections showing the ROS production using DHE 

(dihydroethidium; 2 μmol/L) in nondiabetic rats (A), vehicle-treated 

diabetic rats (

B), and XNT-treated diabetic rats (C). Quantification 

of ROS content (

D). *P<0.05 (1-way ANOVA followed by the 

Bonferroni multiple comparison test). Each column represents the 

mean±SEM (n=6–8) of relative fluorescence in arbitrary unit (AU).

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