Angiotensin 1-7 reduces mortality and rupture of intracranial aneurysms in mice

Abstract

Angiotensin II (Ang II) stimulates vascular inflammation, oxidative stress, and formation and rupture of intracranial aneurysms in mice. Because Ang 1-7 acts on Mas receptors and generally counteracts deleterious effects of Ang II, we tested the hypothesis that Ang 1-7 attenuates formation and rupture of intracranial aneurysms. Intracranial aneurysms were induced in wild-type and Mas receptor-deficient mice using a combination of Ang II-induced hypertension and intracranial injection of elastase in the basal cistern. Mice received elastase+Ang II alone or a combination of elastase+Ang II+Ang 1-7. Aneurysm formation, prevalence of subarachnoid hemorrhage, mortality, and expression of molecules involved in vascular injury were assessed. Systolic blood pressure was similar in mice receiving elastase+Ang II (mean±SE, 148±5 mm Hg) or elastase+Ang II+Ang 1-7 (144±5 mm Hg). Aneurysm formation was also similar in mice receiving elastase+Ang II (89%) or elastase+Ang II+Ang 1-7 (84%). However, mice that received elastase+Ang II+Ang 1-7 had reduced mortality (from 64% to 36%; P<0.05) and prevalence of subarachnoid hemorrhage (from 75% to 48%; P<0.05). In cerebral arteries, expression of the inflammatory markers, Nox2 and catalase increased similarly in elastase+Ang II or elastase+Ang II+Ang 1-7 groups. Ang 1-7 increased the expression of cyclooxygenase-2 and decreased the expression of matrix metalloproteinase-9 induced by elastase+Ang II (P<0.05). In Mas receptor-deficient mice, systolic blood pressure, mortality, and prevalence of subarachnoid hemorrhage were similar (P>0.05) in groups treated with elastase+Ang II or elastase+Ang II+Ang 1-7. The expression of Mas receptor was detected by immunohistochemistry in samples of human intracranial arteries and aneurysms. In conclusion, without attenuating Ang II-induced hypertension, Ang 1-7 decreased mortality and rupture of intracranial aneurysms in mice through a Mas receptor-dependent pathway.

Keywords: angiotein (1–7); angiotensin (1–7) receptor Mas, human; hypertension; intracranial aneurysm; subarachnoid hemorrhage.

Figure 1

Ang-1-7 does not attenuate Ang-II induced hypertension (A) in WT mice. (B) Ang-1-7 decreases mortality (*P<0.05) but does not attenuate aneurysm formation (C). Ang-1-7 decreased prevalence of subarachnoid hemorrhage (P<0.05). n= 28 WT mice treated with elastase+Ang-II and 25 WT mice treated with elastase+Ang-II+ Ang-1-7.

Figure 2

(A) Cerebral blood vessels in a control mouse (scale bar=1mm) (left). Section of anterior communicating artery (right). (B) Cerebral arteries in situ (left) and after excision (center) from a mouse with several intracranial aneurysms and acute subarachnoid hemorrhage, and histological sections of intracranial aneurysms (right). Sections were stained with Masson’s trichrome (Art: artery; An: Aneurysms. Scale bar= 100µm).

Figure 3

Ang-1-7 does not attenuate Ang-II induced hypertension (A) in Mas-KO mice. Ang-1-7 does not decrease mortality (B) aneurysm formation (C) or prevalence of subarachnoid hemorrhage in Mas KO mice (P>0.05). n= to 19 Mas-KO mice treated with elastase+Ang-II and 15 Mas-KO mice treated with elastase+Ang-II+Ang-1-7.

Figure 4

Gene expression in cerebral arteries in WT control mice (sham), and mice in which intracranial aneurysms were induced (mice received elastase+Ang-II or elastase+Ang-II + Ang-1-7). *P<0.05 vs control, †=P<0.05 vs Ang-II. n=8 WT shams, n=8–15 WT mice with aneurysms treated with elastase+Ang-II and 8–12 WT mice with aneurysms treated with elastase+AngII+Ang-1-7.

Figure 5

Gene expression in cerebral arteries from Mas receptor KO mice. Values are from mice treated withelastase+Ang-II or elastase+Ang-II+Ang-1-7, after induction of intracranial aneurysms (results were normalized to WT controls). No significant differences were found. n=7–8 Mas-KO mice with aneurysms treated with elastase+Ang-II and 8–9 Mas-KO mice with aneurysms treated with elastase+Ang-II+Ang-1-7.

Figure 6

Expression of Mas receptors in human intracranial aneurysms. Positive immunostaining for Mas was seen in samples from meningeal arteries, and in unruptured and ruptured intracranial aneurysms. Negative control immunostaining excluded the primary antibody for Mas. Images shown are representative of 5 meningeal or superficial temporal arteries and 5 unruptured and 3 ruptured aneurysms. L=Lumen; M=Media; A; Adventitia. Scale bar=50µm.